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FIG. 1. — Construction of Peck's Run Sewer, Baltimore, Maryland.

Frontispiece.

FEW

SEWERAGE

AND

SEWAGE TREATMENT

HAROLD E. BABBITT, M.S.

Assistant Professor, Municipal and Sanitary Engineering,

University of Illinois; Associate Member

American Society of Civil Engineers

NEW YORK

JOHN WILEY & SONS, INC.

LONDON: CHAPMAN & HALL, LIMITED
1922

PRESS OF

BRAUNWOHTH ft CO.

BOOK MANUFACTURERS

BROOKLYN. N. V.

PREFACE

THIS book is a development of class-room and lecture notes
prepared by the author for use in his classes at the University
of Illinois. He has found such notes necessary, since among
the many books dealing with sewerage and sewage treatment
he has found none suitable as a text-book designed to cover the
entire subject. The need for a single book of the character
described has been expressed by engineers in practice, and by
students and teachers for use in the class-room. This book
has been prepared to meet both these needs. It is hoped that
the searching questions propounded by students in using the
original notes, and the suggestions and criticisms of engineers
and teachers who have read the manuscript, have resulted in a
text which can be readily understood.

The ground covered includes an exposition of the principles
and methods for the designing, construction and maintenance of
sewerage works, and also of the treatment of sewage. In covering
so wide a field the author has deemed it necessary to include some
chapters which might equally well appear in works on other
branches of engineering, such as the chapter on Pumps and
Pumping Stations. Special stress has been laid on che funda-
mentals of the subject rather than the details of practice, although
illustrations have been drawn freely from practical work. The
quotation of expert opinions which may be in controversy, or the
citation of examples of different methods of accomplishing the
same thing, has been avoided when possible in order to simplify
explanations and to avoid confusing the beginner.

The work is to some extent a compilation of notes and quota-
tions which have been collected by the author during years
of study and teaching the subject. Credit has been given
wherever due, and at the same time references have pointed out
the original sources whenever possible. These references, which

vi PREFACE

have been supplemented by brief bibliographies at the end of
certain chapters, will be useful to the student and engineer inter-
ested in further study. Occasionally the original reference has
been lost or the phraseology of a quotation has been so altered
by class-room use, as to make it impossible to trace the original
source, so that in some few instances full credit may be lacking.

The author is indebted to many of his friends for their criti-
cisms and suggestions in the preparation of the manuscript;
but he desires particularly to acknowledge the assistance of
Professor A. N. Talbot, Professor of Municipal and Sanitary
Engineering at the University of Illinois, and of Professor M. L.
Enger, Professor of Mechanics and Hydraulics at the University
of Illinois, in the entire work; also that of Mr. T. D. Pitts, Prin-
cipal Assistant Engineer of the Baltimore Sewerage Commis-
sion during the construction of the Baltimore sewers, for his
suggestions on the first half of the book; and to Mr. Paul Hansen,
consulting engineer, of Chicago, and to Mr. Langdon Pearse,
Sanitary Engineer of the Sanitary District of Chicago, for
their help on the section covering the treatment of sewage; and
to Professor Edward Bartow, Professor of Chemistry at the
University of Iowa, for his review of the chapter on Activated
Sludge; in general his thanks are due to all others who have
furnished suggestions, illustrations, or quotations, acknowledg-
ments of which have been included in the text.

H. E. B.
URBANA, ILLINOIS, 1922.

TABLE OF CONTENTS

CHAPTER I

INTRODUCTION

PAGES

1. Sewerage and the Sanitary Engineer. 2. Historical. 3. Methods
of Collection. 4. Methods of Disposal. 5. Methods of Treat-
ment. 6. Definitions. . 1-8

CHAPTER II
WORK PRKLIMINARY TO DESIGN

7. Division of Work. 8. Preliminary. 9. Estimate of cost. METH-
ODS OF FINANCING. 10. Bond Issues. 11. Special Assessment.
12. General Taxation. 13. Private Capital. PRELIMINARY
WORK. 14. Preparing for Design. 15. Underground Surveys.
16. Borings 9-23

CHAPTER III
QUANTITY OP SEWAGE

17. Dry Weather Flow. 18. Methods for Predicting Population.
19. Extent of Prediction. 20. Sources of Information on
Population. 21. Density of Population. 22. Changes in Area.
23. Relation between Population and Sewage Flow. 24. Char-
acter of District. 25. Fluctuations in Rate of Sewage Flow.
26. Effect of Ground Water. 27. Resume1 of Method for
Determination of Quantity of Dry-weather Sewage. QUANTITY
OF STORM WATER. 28. The Rational Method. 29. Rate of
Rainfall. 30. Time of Concentration. 31. Character of Sur-
face. 32. Empirical Formulas. 33. Extent and Intensity of

Storms 24-50

vii

viii CONTENTS

CHAPTER IV

HYDRAULICS OF SEWERS

PAGES

34. Principles. 35. Formulas. 36. Solution of Formulas. 37. Use
of Diagrams. 38. Flow in Circular Pipes Partly Full. 39. Sec-
tions Other than Circular. 40. Non-Uniform Flow 51-77

CHAPTER V
DESIGN OF SEWERAGE SYSTEMS

41. The Plan. 42. Preliminary Map. 43. Layout of the Separate
System. 44. Location and Numbering of Manholes. 45.
Drainage Areas. 46. Quantity of Sewage. 47. Surface Profile.
48. Slope and Diameter of Sewers. 49. The Sewer Profile.
DESIGN OF A STORM-WATER SEWER SYSTEM. 50. Planning the
System. 51. Location of Street Inlets. 52. Drainage Areas.
53. Computation of Flood Flow by McMath Formula. 54.
Computation of Flood Flow by Rational Method 78-98

CHAPTER VI

APPURTENANCES

55. General. 56. Manholes. 57. Lampholes. 58. Street Inlets.
59. Catch-basins. 60. Grease Traps. 61. Flush-tanks. 62.
Siphons. 63. Regulators. 64. Junctions. 65. Outlets. 66.
Foundations. 67. Underdrains 99-126

CHAPTER VII
PUMPS AND PUMPING STATIONS

68. Need. 69. Reliability. 70. Equipment. 71. The Building.
72. Capacity of Pumps. 73 Capacity of Receiving Well. 74.
Types of Pumping Machinery. 75. Sizes and Descriptions of
Pumps. 76. Definitions of Duties and Efficiency. 77. Details
of Centrifugal Pumps. 78. Centrifugal Pump Characteristics.
79. Setting of Centrifugal Pumps. 80. Steam Pumps and
Pumping Engines. 81. Steam Turbines. 82. Steam Boilers.
83. Air Ejectors. 84. Electric Motors. 85. Internal Com-

CONTENTS ix

PAGES

bustion Engines. 86. Selection of Pumping Machinery. 87.
Costs of Pumping Machinery. 88. Cost Comparisons of Dif-
ferent Designs. 89. Number and Capacity of Pumping Units. 127-163

CHAPTER VIII
MATERIALS FOR SEWERS

90. Materials. 91. Vitrified Clay Pipe. 92. Cement and Concrete
Pipe. 93. Proportioning of Concrete. 94. Waterproofing of
Concrete. 95. Mixing and Placing Concrete. 96. Sewer Brick.
97. Vitrified Clay Sewer Block. 98. Cast Iron, Steel, and Wood. 164-193

CHAPTER IX
DESIGN OF THE SEWER RING

99. Stresses in Buried Pipe. 100. Design of Steel Pipe. 101.
Design of Wood Stave Pipe. 102. External Loads on Buried
Pipe. 103. Stresses in Circular Ring. 104. Analysis of Sewer
Arches. 105. Reinforced Concrete Sewer Design 194-210

CHAPTER X

CONTRACTS AND SPECIFICATIONS

106. Importance of the Subject. 107. Scope of the Subject. 108.
Types of Contracts. 109. The Agreement. 110. The Advertise-
ment. 111. Information and Instructions for Bidders. 112.
Proposal. 113. General Specifications. 114. Technical Specifi-
cations. 115. Special Specifications. 116. The Contract.
117. The Bond. . . 211-232

CHAPTER XI
CONSTRUCTION

118. Elements. WORK OF THE ENGINEER. 119. Duties. 120.
Inspection. 121. Interpretation of Contract. 122. Unex-
pected Situations. 123. Cost Data and Estimates. 124.
Progress Reports. 125. Records. EXCAVATION. 126. Speci-
fications. 127. Hand Excavation. 128. Machine Excavation.

X CONTENTS

PAGES

129. Types of Machines. 130. Continuous Bucket Exca-
vators. 131. Cableway and Trestle Excavators. 132. Tower
Cableways. 133. Steam Shovels. 134. Drag Line and Bucket
Excavators. 135. Excavation in Quicksand. 136. Pumping
and Drainage. 137. Trench Pump. 138. Diaphragm Pump.
139. Jet Pump. 140. Steam Vacuum Pumps. 141. Centrif-
ugal and Reciprocating Pumps. 142. Well Points. 143. Rock
Excavation. 144. Power Drilling. 145. Steam or Air for Power.
146. Depth of Drill Hole. 147. Diameter of Drill Hole.

148. Spacing of Drill Holes. SHEETING AND BRACING.

149. Purposes and Types. 150. Stay Bracing. 151. Skeleton
Sheeting. 152. Poling Boards. 153. Box Sheeting. 154.
Vertical Sheeting. 155. Pulling Wood Sheeting. 156. Earth
Pressures. 157. Design of Sheeting and Bracing. 158. Steel
Sheet Piling. LINE AND GRADE. 159. Locating the Trench.
160. Final Line and Grade. 161. Transferring Grade and
Line to the Pipe. 162. Line and Grade in Tunnel. TUN-
NELLING. 163. Depth. 164. Shafts. 165. Timbering. 166.
Shields. '167. Tunnel Machines. 168. Rock Tunnels. 169.
Ventilation. 170. Compressed Air. EXPLOSIVES AND BLASTING.
171. Requirements. 172. Types of Explosives. 173. Per-
missible Explosives. 174. Strength. 175. Fuses and Deto-
nators. 176. Care in Handling. 177. Priming. Loading, and
Firing. 178. Quantity of Explosive. PIPE SEWERS. 179. The
Trench Bottom. 180. Laying Pipe. 181. Joints. 182. Labor
and Progress. BRICK AND BLOCK SEWERS. 183. The Invert.
184. The Arch. 185. Block Sewers. 186. Organization.
187. Rate of Progress. CONCRETE SEWERS. 188. Construction
in Open Cut. 189. Construction in Tunnels. 190. Materials
for Forms. 191. Design of Forms. 192. Wooden Forms. 193.
Steel-lined Wooden Forms. 194. Steel Forms. 195. Rein-
forcement. 196. Cost of Concrete Sewers. BACKFILLING. 197.
Method 233-331

CHAPTER XII

MAINTENANCE OF SEWERS

198. Work Involved. 199. Causes of Troubles. 200. Inspection.
201. Repairs. 202. Cleaning of Sewers. 203. Flushing Sewers.
204. Cleaning Catch-basins. 205. Protection of Sewers. 206.
Explosions in Sewers. 207. Valuation of Sewers 332-351

CHAPTER XIII
COMPOSITION AND PROPERTIES OF SEWAGE

208. Physical Characteristics. 209. Chemical Composition. 210.
Significance of Chemical Constituents. 211. Sewage Bacteria.

CONTENTS xi

PAGES

212. Organic Life in Sewage. 213. Decomposition of Sewage.
214. The Nitrogen Cycle. 215. Plankton and Macroscopic
Organisms. 216. Variations in the Quality of Sewage. 217.
Sewage Disposal. 218. Methods of Sewage Treatment 352-371

CHAPTER XIV
DISPOSAL BY DILUTION

219. Definition. 220. Conditions Required for Success. 221. Self-
purification of Running Streams. 222. Self-purification of
Lakes. 223. Dilution in Salt Water. 224. Quantity of Diluting
Water Needed. 225. Governmental Control. 226. Prelimi-
nary Treatment. 227, Preliminary Investigations 372-382

CHAPTER XV

SCREENING AND SEDIMENTATION

228. Purpose. 229. Types of Screens. 230. Sizes of Openings.
231. Design of Fixed and Movable Screens. PLAIN SEDIMEN-
TATION. 232. Theory of Sedimentation. 233. Types of Sedi-
mentation Basins. 234. Limiting Velocities. 235. Quantity
and Character of Grit. 236. Dimensions of Grit Chambers.
237. Existing Grit Chambers. 238. Number of Grit Chambers.
239. Quantity and Characteristics of Sludge from Plain Sedi-
mentation. 240. Dimensions of Sedimentation Basins. CHEM-
ICAL PRECIPITATION. 241. The Process. 242. Chemicals.
243. Preparation and Addition of Chemicals. 244. Results 383-409

CHAPTER XVI

SKITICIZATION

245. The Process. 246. The Septic Tank. 247. Results of Septic
Action. 248. Design of Septic Tanks. 249. Imhoff Tanks.
250. Design of Imhoff Tanks. 251. Imhoff Tank Results.
252. Status of Imhoff Tanks. 253. Operation of Imhoff Tanks.
254. Other Tanks 410-430

CHAPTER XVII

FILTRATION AND IRRIGATION

255. Theory. 256. The Contact Bed. 257. The Trickling Filter.
258. Intermittent Sand Filter. 259. Cost of Filtration. IRRI-
GATION. 260. The Process. 261. Status. 262. Preparation
and Operation. 263. Sanitary Aspects. 264. The Crop 431-464

xii CONTENTS

CHAPTER XVIII

ACTIVATED SLUDGE

PAGES

265. The Process. 266. Composition. 267. Advantages and
Disadvantages. 268. Historical. 269. Aeration Tank. 270.
Sedimentation Tank. 271. Reaeration Tank. 272. Air Dis-
tribution. 273. Obtaining Activated Sludge. 274. Cost 465-479

CHAPTER XIX

ACID PRECIPITATION, LIME AND ELECTRICITY, AND DISINFECTION

275. The Miles Acid Process. ELECTROLYTIC TREATMENT. 276.

The Process. DISINFECTION. 277. Disinfection of Sewage .... 482-493

CHAPTER XX

SLUDGE

278. Methods of Disposal. 279. Lagooning. 280. Dilution. 281. <

Burial. 282. Drying 495-505

CHAPTER XXI
AUTOMATIC DOSING DEVICES

283. Types."* 284. Operation. 285. Three Alternating Siphons.
286. Four or More Alternating Siphons. 287. Timed Siphons.
288. Multiple Alternating and Timed Siphons 506-512

SEWERAGE AND SEWAGE TREATMENT

CHAPTER I
INTRODUCTION

1. Sewerage and the Sanitary Engineer. — Present day concep-
tions of sanitation are based on the scientific discoveries which
have resulted so much in the increased comfort and safety of
human life during the past century, in the increase of our material
possessions, and the extent of our knowledge. The danger to
health in the accumulation of filth, the spreading of disease by
various agents, the germ theory of disease, and other important
principles of sanitation can be counted among the more recent
scientific discoveries and pronouncements. Experience has shown,
and continues to show, that the increase of population may be
inhibited by accumulations of human waste in populous districts.
The removal of these wastes is therefore essential to the existence
of our modern cities.

The greatest need of a modern city is its water supply. With-
out it city life would be impossible. The next most important
need is the removal of waste matters, particularly wastes con-
taining human excreta or the germs of disease. To exist without
street lights, pavements, street cars, telephones, and the many
other attributes of modem city life might be possible, although
uncomfortable. To exist in a large city without either water or
sewerage would be impossible. The service rendered by the sani-
tary engineer to the large municipality is indispensable. In
addition to the service necessary to the maintenance of life in
large cities, the sanitary engineer serves the smaller city, the
rural community, the isolated institution, and the private estate
with sanitary conveniences which make possible comfortable

2 INTRODUCTION

existence in them, and which are frequently considered as of
paramount necessity. Training for service in municipal sanita-
tion is training for a service which has a more direct beneficial
effect on humanity than any other engineering work, or any
other profession. W. P. Gerhard states:

A Sanitary Engineer is an engineer who carries out those
works of civil engineering which have for their object;

(a) The promotion of the public and individual health;

(6) The remedying of insanitary conditions;

A well-educated sanitary engineer should have a
thorough knowledge of general civil engineering, of archi-
tecture, and of sanitary science. The practice of the sani-
tary engineer embraces water supply, sewerage, and
sewage and garbage disposal for cities and for single build-
ings; the prevention of river pollution, the improvement
of polluted water supplies; street paving and street clean-
ing, municipal sanitation, city improvement plans, the
laying-out of cities, the preparation of sanitary surveys,
the regulation of noxious trades, disinfection, cremation,
and the sanitation of buildings.

The need of the work of the sanitary engineer in the provision
of sewers and drains is thrust upon us in our daily experience by
the clogging of sewers, the flooding of streets by heavy rains,
filthy conditions in unsewered districts, increased values of prop-
erty and improved conditions of living in sewered districts, and
in many other ways. The increasing demand for sewerage and
the amount of money expended on sewer construction is indicated
by the information given in Table I.

2. Historical. — An ordinance passed by the Roman Senate in
the name of the Emperor about A.D. 80, states:

I desire that nobody shall conduct away any excess
water without having received my permission or that of my
representatives ; for it is necessary that a part of the supply
flowing from the delivery tanks shall be utilized not only for
cleaning our city, but also for flushing the sewers.1

Neither the sewers mentioned nor the distributing pipes of
the public water supply were connected to individual residences.
The contributions to the sewers came from the ground and the
street surface. The streets were the receptacles of liquid and

1 Frontinus and the Water Supply of Rome, p. 81, by Clemens Herschel.

HISTORICAL

solid wastes and were often little more than open sewers. A
promenade after dark in an ancient, medieval, or early modern
city was accompanied not only by the underfoot dangers of an
uneven pavement or an encounter with a footpad, but with the
overhead danger from the emptying of slops into the streets from
the upper windows. Sewers were used for the collection of sur-
face water; the discharge of fecal matter into them was pro-
hibited. The problem of the collection of sewage remained
unsolved until the Nineteenth Century.

TABLE 1
POPULATION TRIBUTARY TO SEWERAOE SYSTEMS

1905*

1915f

1920 1

Population discharging raw sewage into
the sea or tidal estuaries

6500,000

8,500000

Population discharging raw sewage into
inland streams or lakes. ....

20,400,000

26,400,000

Population connected to systems where
sewage is treated in some way

1,100,000

6900000

Population connected with sewerage sys-
tems

28,000,000

41,800,000

46,300 000

* Estimated by G. W. Fuller. Trans. Am. Society of Civil Engineers, Vol. 44, 1906,
p. 148. The total population connected with sewerage systems was assumed to be the
total imputation in the United States in cities over 4000 in population.

t Estimated by Metcalf and Eddy, American Sewerage Practice, Vol. Ill, p. 240.

t Computed from report of the United States Census, 1920, on the same basis as
Fuller's estimate for 1905.

The development of the London sewers was commenced
early in the Nineteenth Century. The sewerage system of Ham-
burg, Germany, was laid out in 1842 by Lindley, an English
engineer who with other English engineers performed similar
work in other German cities because of their earlier experience
in English communities. Berlin's present system dates from 1860.
The construction of storm water drains in Paris dates from 1663. l
They were intended only as street drains but are now included in
the comprehensive system of the city. The first comprehensive
sewerage system in the United States was designed by E. S.
Chesbrough for the City of Chicago in 1855. Previous to this
1 Cosgrove, History of Sanitation.

4 INTRODUCTION

time sewers had been installed in an indifferent manner and with-
out definite plan. The installation of a comprehensive sewerage
system in Baltimore in 1915 marks the completion of installation
of sewerage systems in all large American cities.

In the early days of sewerage design it was considered unsafe
to discharge domestic wastes into the sewers as the concentration of
so much sewage was expected to create great nuisances and
dangers to health. That the fear that the concentration of large
quantities of sewage would create a nuisance was not ill founded
is proven by the conditions on the Thames at London in 1858-59.
Dr. Budd states: l

For the first time in the history of man, the sewage
of nearly three millions of people had been brought to
seethe and ferment under a burning sun in one vast open
cloaca lying in their midst.

The result we all know. Stench so foul we may well
believe had never before ascended to pollute this lower
air. Never before at least had a stink risen to the height
of an historic event. . . For months together the topic
almost monopolized the public prints . . . 'India is in
revolt and the Thames stinks' were the two great facts
coupled together by a distinguished foreign writer, to mark
the climax of a national humiliation.2

The problem of sewage disposal followed the more or less
successful solutions of the problem of sewage collection. In
England the British Royal Commission on Sewage Disposal was
appointed in 1857 and issued its first report in 1865. The first
studies in the United States were started in 1887 by the establish-
ment of an experiment station at Lawrence, Massachusetts, where
valuable work has been done. The station is under the State
Board of Health, which issued its first report containing the
results of the work at the station, in 1890.

Various methods of sewage treatment preparatory to disposal
have been devised from time to time. Some have fallen into
disuse, such as the A. B. C. (alum, blood and clay) process, and
others have taken a permanent place, such as the septic tank.
The unsolved problems of sewage collection, and the number of

1 Sedgwick: Sanitary Science and Public Health.

* No detrimental effect on the public health was noted as a result of this
condition however. It has never been conclusively proven that such nuisances
are detrimental to the public health.

METHODS OF COLLECTION 5

persons still unserved by sewerage and sewage disposal opens a
wide field to the study and construction of sewerage works.

3. Methods of Collection. — The method of collection which
involves the removal of night soil from a privy vault, the pail
system which involves the collection of buckets of human excreta
from closets and homes, indoor chemical closets, and other make-
shift methods of collection are of extreme importance where no
sewers exist, but they are not properly considered as sewerage
systems or sewerage works. These methods of collection are
generally confined to rural districts and to outlying parts of
urban communities. They require constant attention for their
proper conduct and little skill for their installation, the principal
requirements being to make the receptacles fly-proof.

The pneumatic system was introduced by Liernur, a Dutch
engineer.1 It is used in parts of a few cities in Europe, but it is
not capable of use on a large scale. It consists of a system of
air-tight pipes, connecting water closets, kitchen sinks, etc., with
a central pumping station at which an air-tight tank is provided
from which the air is partly exhausted. As little water as possible
is allowed to mix with the fecal matter and other wastes in order
not to overtax the system. Solid and liquid wastes are drawn
to the central station when the waste valve on the plumbing
fixture is opened.

The collection of sewage in a system of pipes through which it
is conducted by the buoyant effect and scouring velocity of water
is known as the water carriage system. This is the only method
of sewage collection in general use in urban communities. In
this system solid and liquid wastes are so highly diluted with
water as either to float or to be suspended therein. The mixture
resulting from this high dilution follows the laws of hydraulics as
applied to pure water, or water containing suspended matter.
It will flow freely through properly designed conduits and will
concentrate the sewage wastes at the point of ultimate disposal.

4. Methods of Disposal. — Sewage is disposed of by dilution in
water, by treatment on land, or occasionally by discharging it
into channels that contain no diluting water. Some forin-of treat-
ment to prepare sewage for ultimate disposal is frequently neces-
sary and will undoubtedly be required in a comparatively short
time for all sewage discharged into watercourses. The solid

1 Moore and Silcock, Sanitary Engineering. P- 67, 1909.

6 INTRODUCTION

matters removed by treatment may be buried, burned, dumped
into water, or used as a fertilizer.

If the volume of diluting water, or the area and character of
land used for disposal are not as they should be, a nuisance will
be created. The aim of all methods of sewage treatment has so
far been to produce an effluent which could be disposed of without
nuisance and in certain exceptional cases to protect public water
supplies from pollution. Financial returns have been sought
only as a secondary consideration. A few sewage farms and irri-
gation projects might be considered as exceptions to this as the
value of the water in the sewage as an irrigant has been the primary
incentive to the promotion of the farm.

It is to be remembered that since the aim of all sewage treat-
ment is to produce an effluent that can be disposed of without
causing a nuisance, the simplest process by which this result can
be attained under the conditions presented is the process to be
adopted. No attempt is made to purify sewage completely, or
on a practical scale to make drinking water.

5. Methods of Treatment. — Screening and sedimentation
are the primary methods for the treatment of sewage. By these
methods a portion of the floating and settleable solids are removed,
preventing the formation of unsightly scum and putrefying sludge
banks. Chemicals are sometimes added to the sewage to form a
heavy flocculent precipitate which hastens sedimentation of the
solid matters in the sewage. The process in these methods is
mechanical and the solid matters removed from the sewage must
be disposed of by other methods than dilution with the sewage
effluent. More complete methods of treatment are dependent on
biologic action. Under these methods of treatment complete
stabilization of the effluent is approached, and in the most com-
plete treatment an effluent is produced which is clear, sparkling,
non-odorous, non-putrescible, and sterile. Sterilization of sewage,
usually with chlorine or some of its compounds, has been used, not
to reduce the amount of diluting water necessary, but to reduce
the number of pathogenic germs and to minimize the danger of
the transmission of disease.

6. Definitions. — Sewage and sewerage are not synonymous
terms although frequently confused. Sewage is the spent water
supply of a community containing the waste from domestic,
industrial or commercial use, and such surface and ground water

DEFINITIONS 7

as may enter the sewer.1 Sewerage is the name of the system of
conduits and appurtenances designed to carry off the sewage.
It is also used to indicate anything pertaining to sewers.

A difference is made between sanitary sewage, storm sew-
age, and industrial wastes. Sanitary sewage, sometimes called
domestic sewage, is the liquid wastes discharged from residences
or institutions, and contains water closet, laundry and kitchen
wastes. Storm sewage is the surface run-off which reaches the
sewers during and immediately after a storm. Industrial wastes
are the liquid waste products discharged from industrial
plants.

A sewer is a conduit used for conveying sewage.

The names of the conduits through which sewage may flow
are:

Soil Stack. — A vertical pipe in a building through which waste
water containing fecal matter or urine is allowed to flow.

Waste Pipe. — A vertical pipe in a building through which
waste water containing no fecal matter is allowed to flow.

House Drain. — The approximately horizontal portion of a
house drainage system which conveys the drainage from the soil
stack or waste pipe to the point of discharge from the build-
ing.

House Sewer. — The pipe which leads from the outside wall of
the building to the sewer in the street.

Lateral Sewer. — The smallest branch in a sewerage system,
exclusive of the house sewers.

Sub-main or Branch Sewer. — A sewer from which the sewage
from two or more laterals is discharged.2

Main or Trunk Sewer. — A sewer into which the sewage from
two or more sub-main or branch sewers is discharged.3

Intercepting Sewer. — A sewer generally laid transversely to a
sewerage system to intercept some portion or all of the sewage
collected by the system.

Relief Sewer. — A sewer intended to carry a portion of the flow
from a district already provided with sewers of insufficient capacity
and thus preventing overtaxing the latter.4

1 Similar to the definition proposed by the Am. Public Health Assn.
1 Definition recommended by Am. Public Health Assn.
1 Ibid.
4 Ibid.

8 INTRODUCTION

Outfall Sewer. — That portion of a main or trunk sewer below
all branches.

Flushing Sewer. — A conduit through which water is conveyed
for flushing portions of a sewerage system.

Force Main. — A conduit through which sewage is pumped
under pressure.

CHAPTER II
WORK PRELIMINARY TO DESIGN

7. Division of Work. — Engineering work on sewerage can be
divided into four parts, namely: preliminary, design, construc-
tion and maintenance. An engineer may be engaged during
any one or all of these periods on the same sewerage system, and
should therefore be acquainted with his duties during each period.

8. Preliminary. — The demand for sewerage normally follows
the installation or extension of the public water supply. It may
be caused by: a lack of drainage on some otherwise desirable
tract of real estate; from a public realization of unpleasant or
unhealthful conditions in a built-up district; or through the
realization by the municipal administration of the necessity for
caring for the future. In whatever way the demand may be
created the engineer should take an active part in the promotion
of the work.

The engineer's duties during the preliminary period are: to
make a study of the possible methods by which the demand for
sewerage can be satisfied ; to present the results of this study in
the form of a report to the committee or organization responsible
for the promotion of the work; and so to familiarize himself with
the conditions affecting the installation of the proposed plans
as to be able to answer all inquiries concerning them. This work
will require the general qualities of character, judgment, efficiency
and the understanding of men in addressing interested persons
individually and collectively on the features of the proposed
plans, and the exercise of engineering technique in the survey
and the drawing of the plans. The engineer should assure him-
self that all legal requirements in the drawing of petitions, adver-
tising, permits, etc., have been complied with. This requires
some knowledge of national, state, and local laws. Although
none the less essential their description is not within the scope of
this book.

10 WORK PRELIMINARY TO DESIGN

The engineer's preliminary report should contain a section
devoted to the feasibility of one or more plans which may be
explained in more or less detail with a statement of the cost and
advantages of each. A conclusion should be reached as to the
most desirable plan and a recommendation made that this plan be
installed. Other sections of the report may be devoted to a history
of the growing demand, a description of the conditions necessitat-
ing sewerage, possible methods of financing, and such other sub-
jects as may be pertinent. The making of the preliminary plan
and the design of sewerage works are described in subsequent
chapters.

9. Estimate of Cost. — In making an estimate of cost the
information should be presented in a readable and easily compre-
hended manner. It is necessary that the items be clearly defined
and that all items be included. The method of determining the
costs of doubtful .items such as depreciation, interest charges,
labor, etc., and the probability of the fluctuation of the costs of
certain items should be explained.

The engineer's estimate may be divided somewhat as follows :

Labor.

Material.

Overhead. This may include construction plant,
office expense, supervision, bond, interest on borrowed
capital, insurance, transportation, etc. The amount of
the item is seldom less than 15 per cent and is usually
over 20 per cent of the contract price.

Contingencies. This allowance is usually 10 to 15 per
cent of the contract price.

Profit. This should be from 5 to 10 per cent of the
sum of the four preceding items.

The contract price is the sum of these items. To this may be
added :

Engineering. 2 to 5 per cent of the contract price.
Extra Work. Zero to 15 per cent of the contract price;
dependent on the character of the work, the completeness
of the preliminary information, the completeness of the
plans, etc.

Legal expense.

Purchase of land, rights of way, etc., etc.

The cost of the sewer may be stated as so much per linear
foot for different sizes of pipe, including all appurtenances

ESTIMATE OF COST 11

such as manholes, catch-basins, etc., or the items may be sep-
arated in great detail somewhat as follows:

Earth excavation, per cu. yd.

Rock excavation, per cu. yd.

Backfill, per cu. yd.

Brick manholes, 3 feet by 4 feet, per foot of depth.

Vitrified sewer pipe with cement joints, in place,

inches in diameter, 0 to 6 feet deep

6 to 8 feet deep
8 to 10 feet deep

Repaving, macadam per sq. yd.
asphalt per sq. yd.

Flush tanks, gal. capacity, per tank.

Service pipes to flush tanks, per linear foot., etc., etc.

These methods represent the two extremes of presenting cost
estimates. Each method, or modification thereof, may have its
use, dependent on circumstances.

Reliable cost data are difficult to obtain. Lists of prices of
materials and labor are published in certain engineering and trade
periodicals. The Handbook of Cost Data by H. P. Gillette
contains lists of the amount of material and labor used on certain
specific jobs and types of construction. The price of labor and
materials on the local market can be obtained from the local
Chamber of Commerce, contractors and other employers of labor,
and dealers in the desired commodities. Contract prices for
sewerage work published in the construction news sections of
engineering periodicals may be a guide to the judgment of the
probable cost of proposed work, but are generally dangerous to
rely upon as full details are lacking in the description of the work.
A wide experience in the collection and use of cost data is the
desirable qualification for making estimates of cost. It is pos-
sessed by few and is not an infallible aid to the judgment.

Having completed the design and summary of the bills of
material and labor necessary for each structure or portion of the
sewerage system, the product of the unit cost and the amount
of each item plus an allowance for overhead will equal the cost
of the item. The total cost will be the sum of the costs of each
item. The items should be so grouped that the cost of the differ-
ent portions of the system are separated in order that the effect
on the total cost resulting from different combinations of items
or the omission of any one item may be readily computed.

WORK PRELIMINARY TO DESIGN

A method for estimating the approximate cost of sewers,
devised by W. G. Kirchoffer1 depends upon the use of the diagram
shown in Fig. 2. The factors for local conditions are shown in
Table 2. For example, let it be required to find the cost of a
15-inch vitrified pipe sewer at a depth of 9 feet, if the unit costs

468

Diameter of Vitrified Pipe in Inches.
10 12 14 16 18 20 22 24 26 28 30 32 34 36

20 30 40 50 60 70 &0 90 ^

2 3456

'Cost of Sey/er in Dollars per Lineal Foot.

7 8 9 10 II n 14

FIG. 2. — Diagram for Estimating the Cost of Sewers.
Eng. News, Vol. 76, p. 781.

of labor and material and the conditions are the same as shown
in Table 3.

Solution

First: To find the factor depending on local condi-
tions, enter the diagram at the 10-inch diameter and
continue down until the intersection with the depth of
trench at 8.2 feet is found. Now go diagonally parallel
to lines running from left to right upwards to the inter-

!Eng. News, Vol. 76, 1916, p. 781. See also Eng. News-Record, Vol. 85,
1920, pp. 22, 1175.

ESTIMATE OF COST

section with the vertical line through a cost of 45 cents
per foot. The diagonal line running from left to right
downwards through this intersection corresponds to a
factor of about 11.

TABLE •*

FACTORS FOR COSTS OF SEWERS TO BE USED WITH FIGUBE 2

Character of Material

Factor

Character of Material

Factor

Clay, gravel and boulders,
Medford

Mostly sand, deep trenches
sheeted. Wages medium.
Richland Center

Sandy clay. Wages medium.
Labor conditions good at
Kiel

Sand. Sandy clay, some
water. Labor conditions
good. Pipe prices medium
at Manston

Gravelly clay, -n^h laid
concrete at Burlington . .

Sandy clay, some water, sheet-
ing at La Farge

Sand with water

Gravel and boulders. High
wages

Clay soil. Good digging. . . .

Sandy clay. Some water

22-26
21-22
15-20

14-20
13-22

17-23
20

26
17
23

Clay 2 miles inland. Laborers
boarded at sanitarium,
Wales

Clay, gravel and boulders at
Plymouth

Sand, clay and good digging
at Lake Mills

Red clay. Machine work at
North Milwaukee

Good digging. Wages me-
dium at West Salem

Sandy soil, bracing only re-
quired. No water. Wages
and pipe medium

Red sticky clay

Good digging in any soil
Work scarce

Red clay. No bracing

Work inland from railroad.
Boarding laborers and
other expenses

20-27

16-19

20-24

17-19

14
24

15
20

Second: To find the cost of 15-inch pipe at a depth of
9.0 feet, enter the diagram at a diameter of 15 inches
and continue down until the intersection with a depth of
trench at 9 feet is found. Now go diagonally parallel to
lines running from left to right upwards to the intersection
with the diagonal line running from left to right downwards
corresponding to the factor of 11 found above. The
vertical line passing through this point shows the cost to
be 67 cents per foot.

WORK PRELIMINARY TO DESIGN

TABLE 3

COST OF SEWER CONSTRUCTION AT ATLANTIC, IOWA
(From Gillette's Handbook of Cost Data)

Material: Clay, not difficult to spade and requiring little or no bracing and
practically no pumping. All hand work except backfill which was done by
team and scraper. Depth of trench averaged 8.2 feet; width 30 inches.
Diameter of pipe 10 inches.

Item

Wage,
Cents
per
Hour

Cost,
Cents
per
Foot.

Item

Wage,
Cents
per
Hour

Cost,
Cents
per
Foot.

Pipe

0.20
.003

.001
.006
.014
.014
.027

.130
.002
.002

Trenching. Bracing
men

17
17

17
10
30

.002
.010

.008

.005
.006
.022

Hauling team and
driver

30
17

Backfilling. Shovel .
Backfilling. Team
and scraper

Hauling. Man help-
ing . .

Cement and sand. . .

Backfilling. Man
and scraper

Pipe layers

22
17
17

17
17
17

Pipe layer's helper. .
Trenching. Top men
Trenching. Bottom
men

Water boy

Foreman

Total

.450

Trenching. Scaffold
men .

METHODS OF FINANCING

The construction of sewerage works may be paid for by the
issue of municipal bonds, by special assessment, by funds available
from the general taxes, or by private enterprise.

10. Bond Issues. — A municipal bond is a promise by the
municipality to pay the face value of the bond to the holder at a
certain specified time, with interest at a stipulated rate during
the interim. The security on the bond is the taxable property
in the municipality. The legal restrictions thrown around muni-
cipal bond issues, the value of the taxable property in the munici-
pality, all of which may be used as security for municipal bonds,
and the fact that a municipality can be sued in case of default,
make municipal bonds desirable and provide a good market for

SPECIAL ASSESSMENT 15

their sale. The funds available from a municipal bond issue are
limited by the amount that the legal limit is in excess of the out-
standing issues. The legal limit varies in different states from
about 5 to 15 per cent of the assessed value of the property in
the municipality. In some cases the amount available from
municipal bonds has been increased by forming a municipality
within a municipality such as a sanitary district, a park district,
a drainage district, etc., which comprises a large portion or all
of an existing municipal corporation. This case is well illustrated
in some parts of the City of Chicago where the municipal taxing
powers are shared by the City government, the Sanitary District,
and Park Commissioners. The right to create a new municipal
corporation must be granted by the state legislature. Knowledge
of fixed bonds, serial bonds, life of bonds, sinking funds, etc. is an
important part of an engineer's education.1

Bond issues must usually be presented to the voters for approval
at an election. If approved, and other legal procedure has been
followed, the bonds may be bought by some of the many bonding
houses, or by private individuals, and the money is immediately
available for construction. The bonds are redeemed by general
taxation spread over the period of the issue.

11. Special Assessment. — A special assessment is levied against
property benefited directly by the structure being paid for.
Special assessments are used for the payment for the construction
of lateral sewers which are a direct benefit to separate districts
but are without general benefit to the city. In case the construc-
tion of an outfall sewer or the erection of a treatment plant,
which may be of some general benefit, is necessary to care for a
separate district, a part of the expense may be borne by funds
available from general taxation. The legal procedure for the
raising of funds by special assessment and the purpose to which
the funds so raised may be applied are stipulated in great detail
in different states and their directions must be followed implicitly.
Illinois procedure, which is similar to that in some other states,
is as follows: a meeting of the interested property owners is called
by a committee or board of the municipal government, as the
result of a petition by interested persons or through the inde-
pendent action of the Board. At this preliminary meeting or

1 For a more extensive treatment of the subject see Principles and Methods
of Municipal Administration by W. B. Munro, 1916.

16 WORK PRELIMINARY TO DESIGN

public hearing arguments for and against the proposed improve-
ment are heard. The engineer is present at this meeting to
answer questions and to advise concerning the engineering
features of the plan. If approval is given by the Board the plan
and specifications are prepared complete in every detail and
incorporated in an ordinance which is presented to the legislative
branch of the city government for passage. If the project is
adopted it is taken to the county court. An assessment roll is
prepared by a commissioner appointed by the court. This roll
shows the amount to be assessed against each piece of property
benefited. A hearing is then held in the county court at which
the owner of any assessed property may voice objections to the
continuation of the project. The project may be thrown out of
court for many different reasons, such as the misspelling of a street
name, an error in an elevation, an error in the description of a
pavement, but most important of all is definite proof that the
benefit is not equal to the assessment. The many minor irregu-
larities which may nullify the procedure in a special assessment
differ in different states and in different courts in the same state,
but in general no court can approve an assessment greater than
the benefits given. After the project has passed through the
county court and the assessment roll has been approved, bonds
may be issued for the payment of the contractor. Special assess-
ment bonds are liens against the property assessed and have not
the same security as a general municipal bond. For this reason
a city which has reached its legal limit of municipal bond issues
can still pay for work by special assessment.

The funds available from special assessments are limited only
by the benefit to the property assessed. The amount of the
benefit is difficult to fix and may lead to much controversy. It
should not exceed the amount demanded for similar work in other
localities, unless unusual and well-understood reasons can be
given.

12. General Taxation. — In paying for public improvements
by general taxation the money is taken from the general municipal
funds which have been apportioned for that purpose by the
legislative department of the municipal government. This
method of raising funds for sewerage construction is seldom used
unless the political situation is unfavorable to the success of a
bond issue or special assessment and the need for the improvement

PREPARING FOR DESIGN 17

is great. It is usually difficult to appropriate sufficient funds for
new construction as the general tax is apportioned to support
only the operating expenses of the city, and statutory provisions
limit the amount of tax which can be levied.

13. Private Capital. — Private capital has been used for financ-
ing sewerage works in some cases because of the aversion of the
public in some cities to the payment of a tax for the negative
service performed by a sewer. Sewers are buried, unseen, and
frequently forgotten, but knowledge of their necessity has spread
and the number of privately owned sewerage works is diminishing
because of the better service which can be provided by the munici-
pality.

Franchises are granted to private companies for the construc-
tion of sewers only after the city has exhausted other methods for
the raising of capital. The return on the private capital invested
is received from a rental paid by the city, or paid directly by the
users of the system, an initial payment usually being demanded
for connection to the system. To be successful the enterprise
must be popular and must fill a great need. This method of
financing sewerage works is seldom employed as favorable con-
ditions are not common.

PRELIMINARY WORK

14. Preparing for Design. — Methods for the design of sewerage
systems are given in Chapter V. Before the design is made
certain information is essential. A survey must be made from
which the preliminary map can be prepared as described in Art.
42. Other necessary information which is the basis of subsequent
estimates of the quantity of sewage to be cared for must be obtained
by a study of rates- of water consumption and the density and
growth of population, the measurement of the discharge from
existing sewers, and the ' compilation of rainfall and run-off data.
If no rainfall data are available estimates must be made from
the nearest available data. Observations of rainfall or run-off
for periods of less than 10 to 20 years are likely to be misleading.
Methods for gathering and using this information are explained
in subsequent chapters.

Underground surveys are desirable along the lines of the
proposed sewers to learn of obstructions, difficult excavation

18 WORK PRELIMINARY TO DESIGN

and other conditions which may be met. All such data are seldom
gathered except for sewerage systems involving the expenditure
of a large amount of money. For construction in small towns
or small extensions to an existing system the funds are usually
insufficient for extensive preliminary investigation. The saving
in this respect is paid unknowingly to the contractor as com-
pensation for the risk in bidding without complete information.

15. Underground Surveys. — These may be more or less exten-
sive dependent on the character of the district in which construc-
tion is to take place. In built-up districts the survey should be
more thorough than in sparsely settled districts where only the
character of the excavated material is of interest and no obstruc-
tions are to be met.

Underground surveys furnish to the engineer and to prospect-
ive bidders on contract work information on which the design
and estimate of cost and the contractor's bid may be based and
without which no intelligent work can be done. By removing
much of the uncertainty of the conditions to be met in the con-
struction of the sewer, the design can be made more economical
and the contractor's bfd should be markedly lower, sufficiently
so to repay more than the expense of the survey. The information
to be obtained consists of the location of the ground-water level,
and the location and sizes of water, gas, and sewer pipes, tele-
phone and electric conduits, street-car tracks, steam pipes, and all
other structures which may in any way interfere with subsurface
construction. These structures should be located by reference
to some permanent point on the surface. The elevation of the
top of the pipes, except sewers, rather than the depth of cover
should be recorded, as the depth of cover is subject to change.
The elevation of sewers should be given to the invert rather than
to the top of the pipe.

A portion of the map of the subsurface conditions at Wash-
ington, D. C., is shown in Fig. 3. Many of the dimensions and
notations are not shown to avoid confusion on this small repro-
duction.1 Colors are generally used instead of different forms of
cross hatching to show the different classes of pipe and structures.
In addition to a record of the underground structures the char-
acter of the ground and the pavement should be recorded. A
comprehensive underground survey is seldom available nor does
1 Eng. Record, Vol. 74, 1916, p. 263.

UNDERGROUND SURVEYS

l-s

I-V

E §3
S-g.3

Q I

—A.

u a *

5 8.5

*• 2

2
£ ff

•o -•

assi!
2 e-f H

Inf

1*4,1*

& «^H s1

•«« rl!

^- 03

-p

8-s^
" 6g

>» fc; M

•IMP

£ -g £

Sal

«^^

«a|

•S S r

J«s o

i la

ll=.-

iijf

WORK PRELIMINARY TO DESIGN

time usually permit its being made preliminary to the design of a
sewerage system. The character of the material through which
the sewer is to pass should be determined in all cases.

Underground pipes and structures are located by excavations,
which may be quite extensive in some cases. Their position is
fixed by measurements referred to manholes and other under-
ground structures which are somewhat permanent
in position. A city engineer should grasp every
opportunity to record underground structures when
excavations are made in the streets. The character
of the material through which the sewer is to pass is
determined by borings.

16. Borings. — Methods used for the investigation
of subsurface conditions preliminary to sewer con-
struction are: punch drilling, boring with earth
auger, jet boring, wash boring, percussion drilling,
abrasive drilling, and hydraulic drilling. The last
three methods named are used only for unusually
deep borings or in rock.

Punch drills are of two sorts. The simplest punch
drill consists of an iron rod f of an inch to 1 inch in
diameter, in sections about 4 feet long. One section
is sharpened at one end and threaded at the other
so that the next section can be screwed into it with-
out increasing the diameter of the rod, as shown in
Fig. 4. The drill is driven by a sledge striking upon
a piece of wood held at the top of the drill to pre-
vent injury to the threads. The drill should be turned as it is
driven to prevent sticking. It is pulled out by a hook and lever as
shown in Fig. 5. It is useful in soft ground for soundings up to
8 to 12 feet in depth. Another form of punch drill described
by A. C. Veatch 1 consists of a cylinder of steel or iron, one
to two feet long split along one side and slightly spread. The
lower portion is very slightly expanded and tempered into a
cutting edge. In use it is attached to a rope or wooden poles
and lifted and dropped in the hole by means of a rope given a few
turns about a windlass or drum. By this process the material
is forced up into the bit, slightly springs it, and so is held. When
the bit is filled it is raised to the surface and emptied. Much
1 Professional paper No. 46, United States Geological Survey, 1906, p. 97.

FIG. 4.
Punch Drill.

BORINGS

;

FIG. 5. — Lever for Pulling Punch Drill.

deeper holes can be

made with this than

with the sharpened

solid rod.

Types of earth

augers about l£-

inches in diameter

are shown in Fig. 6.

They are screwed

on to the end of

a section of the

pipe or rod and as the hole is deepened successive lengths of pipe

or rod are added. The device is operated by two men. It is

pulled by straight lifting or with the assistance of a link and

lever similar to that shown
in Fig. 5. The device is
suitable for soft earth or
sand free from stones, and
can be used for holes 15
to 25 feet in depth. For
deeper holes a block and
tackle should be used for
lifting the auger from the
hole. It is not suitable
for holes deeper than about
35 feet.

In the jetting method
water is led into the hole
through a f-inch or 1-inch
pipe, and forced down-
ward through the drill bit
or nozzle against the bot-
tom of the hole. The
complete equipment is
shown in Fig. 7.1 It is
not always necessary to
case the hole as shown in
the figure as the muddy

PIG. 6.— Earth Augers. water and the vibration

; United States Geological Survey, Water Supply paper No. 257, 1911.

WORK PRELIMINARY TO DESIGN

Drive Weight—
Wooden Platform .
Clamped to
Casing

•Wooden Buffer
--Drive Head
Force Pump

-Drive Weight Pope
fo Hois-ring Drum or Spool

—Drill Rod Pope
fo Hoisting Drum

-- — RopeSupporting Drill Rods

,- Rubber Hote to Font

Pump

Clamp or Wrench
for Turn ing
Drill Pipe-—

/ Pipe Wrench for
' Turning Casing .

FIG. 7.— Jetting Outfit.

U. S. Geological Survey, Water Supply Paper, No. 257

1. Simple Jetting Outfit. 2. Jetting Process. 3. Common Jetting Drill.

4a and 46. Expansion Bit or Paddy. 5. Drive Shoe.

BORINGS 23

of the pipe puddle the sides so that they will stand alone. The
jet pipe may be churned in the hole by a rope passing over a block
and a revolving drum. In suitable soft materials such as clay,
sand, or gravel, holes can be bored to a depth of 100 feet and
samples collected of the material removed. An objection to the
method is the difficulty of obtaining sufficient water.

Methods of drilling in rock up to depths of 20 feet are described
in Chapter XI under Rock Drilling. For deeper holes percussion,
abrasive, or hydraulic methods as used for deep well drilling must
be employed.

CHAPTER III
QUANTITY OF SEWAGE

17. Dry-weather Flow.— Estimates of the quantity of dry-
weather sewage flow to be expected are ordinarily based on the
population, the character of the district, the rate of water con-
sumption, and the probable ground-water flow. Future condi-
tions are estimated and provided for, as the sewers should have
sufficient capacity to care for the sewage delivered to them during
their period of usefulness.

18. Methods for Predicting Population. — Methods for the
prediction of future population are given in the following para-
graphs.

The method of graphical extension. This is the quickest and
most simple of all. In this method a curve is plotted on rect-
angular coordinates to any convenient scale, with population as
ordinates and years as abscissas. The curve is extended into
the future by judgment of its general tendency. An example is
given of the determination of the population of Urbana, Illinois,
in 1950. Table 4 contains the population statistics which have
been plotted on line A in Fig. 8 and extended to 1950. The
probable population in 1950 is shown by this line to be about
21,000.

The method of geometrical progression. In this method the
rate of increase during the past few years or decades is assumed
to be constant and this rate is applied to the present population
to forecast the population in the future. For example the rate
of increase of population in Urbana for the past 7 decades has
varied widely, but indications are that for the next few decades
it will be about 20 per cent. Applying this rate from 1920 to
1950 the population in 1950 is shown to be about 17,800. It is
evident that this method may lead to serious error as insufficient
information is given in the table to make possible the selection of
the proper rate of increase.

METHODS FOR PREDICTING POPULATION

TABLE 4
POPULATION STUDIES

Urbana, Illinois

Population of

Abso-

Per

Year

Ann

Popu-
lation

lute
Increase
for Each

ent
Increase
forEach

Decatur

Dan-
ville

Cham-
paign

Kanka-
kee

Peoria

Bloom-
ington

Arbor,
Michi-

Decade

gan

1850

210

736

5,095

1,594

1860

2,038

1828

85.6

3,839

1,632

1,727

2,984

14,045

7,075

5,097

1870

2,277

239

10.5

7,161

4,751

4,625

5,189

22,849

14,590

7,368

1880

2,942

665

22.6

9,547

7,733

5,103

5,651

29,259

17,180

8,061

1890

3,511

569.

16.2

16,841

11,491

5,839

9,025

41,024

20,484

9,431

I'.mn

5,728

2217

38.7

20,754

16,354

9,098

13,595

56,100

23,286

14,509

1910

8,245

2517

30.5

31,140

27,871

12,421

13,986

66,950

25,786

14.817

1920

10,230

1985

19.4

43,818

33,750

15,873

16,721

76,121

28,638

19,516

Decades in Life of City of Urbana
1870 1680 1890 1900 1910 1920 1930 1940 1950

50,000

40,000

— 30,000_

20,000 r

10,000

60 50 40 30 20 10 0 10 20 30 40 50 60
Years Before and After which each City had a Population of 10,230

FIG. 8. — Diagram Showing Methods for Estimating Future Population.

26 QUANTITY OF SEWAGE

The method of utilizing a decreasing rate of increase. This
method attempts to correct the error in the assumption of a con-
stant rate of increase. After a certain period of growth, as the
age of a city increases its rate of increase diminishes. In applying
this knowledge to a prediction of the future population of a city
the population curve is plotted, as in the graphical method and a
straight line representing a constant rate or increase is drawn
tangent to the curve at its end. The curve is then extended at a
flatter rate in accordance with the rate of change of a similar
nearby larger city. This method has not been applied to any of
the cities included in Table 4, as none has reached that limiting
period where the rate of increase has begun to diminish.

The method of utilizing an arithmetical rate of increase. This
method allows for the error of the geometrical progression which
tends to give too large results for old and slow-growing cities.
This method generally gives results that are too low. The abso-
lute increase in the population during the past decade or other
period is assumed to continue throughout the period of prediction.
Applying this method to the same case, the increase in the popula-
tion during the past decade was 2,000. Adding three times this
amount to the population in 1920, the population of Urbana in
1950 will be about 16,000.

The method involving the graphical comparison with other
cities with similar characteristics. In this method population
curves of a number of cities larger than Urbana but having
similar characteristics, are plotted with years as abscissas and
population as ordinates, with the present population of Urbana
as the origin of coordinates. The population curve for Urbana
is first plotted. It will lie entirely in the third quadrant as shown
by the heavy full line in Fig. 8. The population curves of some
larger cities are then plotted in such a manner that each curve
passes through the Origin at the time their population was the
same as that of the present population of Urbana. These curves
lie in the first and third quadrants. The population curve of the
city in question is then extended to conform with the curves of
older cities in the most probable manner as dictated by judgment.
Such a series of plots has been made in Fig. 8. The results indi-
cate that the population of Urbana in 1950 will be about 25,500.

The last method described will give the most probable result
as it is the most rational. For quick approximations the geo-

EXTENT OF PREDICTION 27

metrical progression is used. The arithmetical progression is
useful only as an approximate estimate for old cities.

19. Extent of Prediction. — The period for which a sewerage
system should be designed is such that each generation bears its
share of the cost of the system. It is unfair to the present genera-
tion to build and pay for an extensive system that will not be
utilized for 25 years. It is likewise unfair to the next generation to
construct a system sufficient to comply with present needs only,
and to postpone the payment for it by a long term bond issue.
An ideal solution would be to plan a system which would satisfy
present and future needs and to construct only those portions
which would be useful during the period of the bond issue.
Unfortunately this solution is not practical, because, 1st, it is less
expensive to construct portions of the system such as the outfall,
the treatment plant, etc., to care for conditions in advance of
present needs, and 2nd, the life of practically all portions of a
sewerage system is greater than the legal or customary time limit
on bond issues.

A compromise between the practical and the ideal is reached
by the design of a complete system to fulfill all probable demands,
and the construction of such portions as are needed now in accord-
ance with this plan. The payment should be made by bond
issues with as long life as is financially or legally practical, but
which should not exceed the life of the improvement.

The prediction of the population should therefore be made
such that a comprehensive system can be designed with intelli-
gence. Practice has seldom called for predictions more than 50
years in the future.

20. Sources of Information on Population. — The United
States decennial census furnishes the most complete information
on population. Unfortunately it becomes somewhat old towards
the end of a decade. More recent information can be obtained
from local sources. Practically every community takes an annual
school census the accuracy of which is fairly reliable. The gen-
eral tendencies of the population to change can be learned by a
study of the post office records showing the amount of mail matter
handled at various periods. Local chambers of commerce and
newspapers attempt to keep records of population, but they are
often inaccurate. Another source of information is the gross
receipts of public service companies, such as street railways, water,

QUANTITY OF SEWAGE

gas, electricity, telephone, etc. The population can be assumed
to have increased almost directly as their receipts, with proper
allowance for change in rates, character of management, and other
factors.

21. Density of Population. — So far the study of population
has been confined to the entire city. It is frequently necessary
to predict the population of a district or small section of a city.
A direct census may be taken, or more frequently its population
is determined by estimating its density based on a comparison
with similar districts of known density, and multiplying this

FIG. 9. — Density, Area, and Population, Cincinnati, Ohio. 1850 to 1950.

density by the area of the district. In determining the density,
statistics of the population of the entire city will be helpful but
are insufficient for such a problem. A special census of the area
involved would be conclusive but is generally considered too expen-
sive. A count of the number of buildings in the district can be
made quickly, and the density determined by approximating the
number of persons per building. Statistics of the population of
various districts together with a description of the character of
the district are given in Table 5.

The density of population in Cincinnati from 1850 to 1913 with
predictions to 1950 is given in Fig. 9.1 This shows the densities
for the entire city and is illustrative of the manner in which future
1 From Eng. Cont., Vol. 41, 1914, p. 698.

DENSITY OF POPULATION

TABLE 5
DENSITIES OF POPULATION

City

Character of District

Area,
Acres

Density
per Acre

Philadelphia Thomas Run. Residential. Most'y pairs
of two and three-story houses. 1204 acres
settled 1,840 59

Pine Street. Residential. Mostly solid
four to six-story houses. 156 acres
settled 160 97

Shunk Street. Residential. Mostly pairs
of two and three-story houses. 539 acres
settled 539 119

Lombard Street. Tenements and hotels,
145 acres settled 147 113

York Street. Residential and manufactur-
ing. 354 acres settled 358 94

New York City Residential. Three-story dwellings with
18-foot frontage, and four-story flats with

20-foot frontage 100

Residential. Five-story flats 520-670

Residential. Six-story flats 800-1000

Residential. Six-story apartments. High
class 300

Chicago 1st Ward. Retail and commercial. The

"Loop" 1,440 20.5

2d Ward. Commercial and low-class resi-
dential solidly built up 800 53 . 5

3d Ward. Low-class residential 960 48. 1

5th Ward. Industrial. Some low-class

residences. Not solidly built up 2,240 25 . 51

6th Ward. Residential. Four and five-
story apartments. A few detached resi-
dences 1,600 47 . 0

7th Ward. Same as Ward 6. Not solidly

built up. Contains a large park 4,160 21 .7

8th Ward. Industrial. Sparsely settled .. 13,624 4.8
9th Ward. Industrial and low-class resi-
dential. Solidly built up 640 70.0

10th Ward. Same as Ward 9 640 80.8

13th Ward. Low-class residential. Solidly
built with three and four-story flats 6.100 36. 7

QUANTITY OF SEWAGE

TABLE 5 — Continued
DENSITIES OF POPULATION

Citv

Character of District

Area,
Acres

Density
per Acre

Chicago 16th Ward. Middle-class residential.

Some industries. Well built up 800 81 . 5

19th Ward. Industrial and commercial.

Some-low class residences 640 90. 7

20th Ward. Low-class residential. Some

industries. Entirely built up 800 77 . 1

21st Ward. Industrial. Entirely built up 960 49.9
23d Ward. Industrial and residential. . . . 800 55.4
24th Ward. Residential apartment houses

and middle-class residences 1,120 46.8

25th Ward. Residential. High-class
apartments. Wealthy homes. Contains

a large park 4,160 24.0

26th Ward. Residential. Middle-class
homes and apartments. Fairly well built

up 4,640 16.1

27th Ward. Residential. Sparsely settled . 20,480 5.5
29th Ward. Low -class residential. Two-
story frame houses. " Back of the Yards" 6,400 12 . 8

30th Ward. The Stock Yards 1,280 40 . 1

32d Ward. Scattered residences 8,480 8.3

33d Ward. Scattered residences 12,944 5 . 5

35th Ward. Scattered residences 4,960 12.0

General average The most crowded conditions with five-
story and higher, contiguous buildings in

poor class districts 750-1000

Five and six-story contiguous flat buildings 500- 750

Six-story high-class apartments 300- 500

Three and four-story dwellings, business
blocks and industrial establishments.

Closely built up 100- 300

Separate residences, 50 to 75-foot fronts,
commercial districts, moderately well

built up 50-100

Sparsely settled districts and scattered
frame dwellings for individual families 0- 50

CHANGES IN AREA 31

conditions were predicted for the design of an intercepting sewer.
The data given in Table 5 are of value in estimating the densities
of population in various districts. The Committee on City Plan
of the Board of Estimate and Apportionment of New York City
obtained some valuable information on this point, especially in
Manhattan. Three-story dwellings with 18-foot frontage, or four-
story flats with 20-foot frontage, presumably contiguous, were
found to hold 100 persons to the acre. Five-story flats held 520
to 670 persons per acre. Six-story flats held 800 to 1,000 persons
per acre, and high class six-story apartments held less than 300
per acre.

22. Changes in Area. — In order to determine the probable
extent of a proposed sewerage system it is important to estimate
the changes in the area of a city as well as the changes in the
population. With the same population and an increased area
the quantity of sewage will be increased because of the larger
amount of ground water which will enter the sewers. Predictions
of the area of a city are less accurate than predictions of popula-
tion because the factors affecting changes cannot be so easily
predicted. An area curve plotted against time would be helpful
in guiding the judgment, but its extension into the future based
on past occurrences would be futile. A knowledge of the city,
its political tendencies, possibilities of extension, and other factors
must be weighed and judged. The engineer, if he is ignorant of
the city for which he is making provision, is dependent upon the
testimony of real estate men, business men and others acquainted
with the local situation.

23. Relation between Population and Sewage Flow. — The
amount of sewage discharged into a sewerage system is generally
equal to the amount of water supplied to a community, exclusive
of ground water. The entire public water supply does not reach
the sewers, but the losses due to leakage, lawn sprinkling, manu-
facturing processes, etc., are made up by additions from private
water supplies, surface drainage, etc. The estimated quantity
of water used but which did not reach the sewers in Cincinnati
is shown in Table 6. The amount shown represents 38 per cent
of the total consumption. Unless direct observations have been
made on existing sewers or other factors are known which will
affect the relation between water supply and sewage, the average
sewage flow exclusive of ground water, should be taken as the

32 QUANTITY OF SEWAGE

average rate of water consumption. Experience has shown that
water consumption increases after the installation of sewers.

TABLE 6

ESTIMATED QUANTITY OF WATER USED BUT NOT DISCHARGED INTO THE
SEWERS IN CINCINNATI

Expressed in gallons per capita per day, and based on a total consumption
of 125 to 150 gallons per capita per day.

Steam railroads

6 to 7

Manufacturing and me-

Street sprinklers

6 to 7

chanical

6 to 7

Consumers not sewered . . .

9 to 10£

Lawn sprinklers

3 to3£

Leakage

18 to 21

The public water supply is generally installed before the sewer-
age system. By collecting statistics on the rate of supply of
water a fair prediction can be made of the quantity of sewage
which must be cared for. The rate of water supply varies widely
in different cities. It is controlled by many factors such as meters,
cost and availability of water, quality of water, climate, popula-
tion, etc. In American cities a rough average of consumption is
100 gallons per capita per day. Other factors being equal the
rate of consumption after meters have been installed will be
about one-half the rate before the meters were installed. Low
cost, good quantity and good quality will increase the rate of
consumption, and the rate will increase slowly with increasing
population. Statistics of rates of water consumption are given
in Table 7.

24. Character of District. — The various sections of a city are
classified as commercial, industrial, or residential. The residential
districts can be subdivided into sparsely populated, moderately
populated, crowded, wealthy, poor, etc. Commercial districts
may be either retail stores, office buildings, or wholesale houses.
Industrial districts may be either large factories, foundries, etc.,
or they may be made up of small industries housed in loft build-
ings.

In cities of less than 30,000 population the refinement of such
subdivisions is generally unnecessary in the study of sewage flow,
all districts being considered the same. The data given in Tables
8 and 9 indicate the difference to be found in different districts of

CHARACTER OF DISTRICT

large cities. The Milwaukee data are presented in a form avail-
able for estimates on different bases. These data are shown in
Table 10.

TABLE 7
RATES OF WATER CONSUMPTION

From Journals of American and New England Water Works Associations

Con-

Popu-

sump-

Popu-

sump-

lation

Per

tion,

lation

Per

tion,

City

Cent

Gal.

City

Cent

Gal.

Thou-

Metered

per

Thou-

Metered

per

sands

Capita

sands

Capita

per Day

Tacoma Wash . . .

100

11.6

460

Jefferson City, Mo

13.5

34.4

100

Buffalo N Y

450

4.9

310

Muncie Ind

23.8

Cheyenne, Wyo ....

270

4.5

Erie, Pa

3.0

198

Council Bluffs, la . .

75.5

Philadelphia, Pa

1611

4.6

180

San Diego, Cal ....

100

St. Catherines, Ont.

3.2

160

Monroe "Wis . . .

100

Port Arthur, Ont.. .

14.7

145

Yazoo City, Miss . .

84.1

Ogdensburg, N. Y . .

0.2

140

Oak Park, Illinois. .

100

Los Angeles, Cal. . . .

516

77.9

140

Portsmouth, Va. . . .

8.1

Wilmington, Del. . .

43.7

125

New Orleans, La. . .

360

99.7

Lancaster, Pa

34.6

120

Rockford, 111

93.0

Richmond, Va

120

75.2

115

Fort Dodge, la. ...

96.0

St. Louis, Mo

730

6.7

110

Manchester, Vt. . . .

1.5

69.0

Springfield, Mass. . .

100

94.4

110

Woonsocket, R. I. .

47.5

95.6

Keokuk, la

64.5

105

Attempts have been made to express the rate of sewage flow
in different units other than in gallons per capita per day. A unit
in terms of gallons per square foot of floor area tributary has been
suggested for commercial and industrial districts. It has not
been generally adopted. The rates of flow in New York City as
reported in this unit by W. S. McGrane are given in Table 1 1 .

The most successful way to predict the flow from commercial
or industrial districts is to study the character of the district's
activities and to base the prediction on the quantity of water
demanded by the commerce and industry of the district affected.

25. Fluctuations in Rate of Sewage Flow. — The rate of flow
of sewage from any district varies with the season of the year,
the day of the week, and the hour of the day. The maximum
and minimum rates of sewage flow are the controlling factors in
the design of sewers. The sewers must be of sufficient capacity

QUANTITY OF SEWAGE

to carry the maximum load which may be put upon them, and
they must be on such a grade that deposits will not occur during
periods of minimum flow. The maximum and minimum rates of
flow are usually expressed as percentages of the average rate of
flow.

TABLE 8
SEWAGE FLOW FROM DIFFERENT CLASSES OF DISTRICTS

Arranged from data by Kenneth Allen in Municipal Engineer's Journal,
Feb., 1918.

District

Gallons

per

Capita
per Day

Gallons

per

Acre
per Day

Buffalo, N. Y. From Report of International Joint Com-
mission on the Pollution of Boundary Waters:

Industrial: Metal and automobile plants. Maximum 13,000

Industrial: Meat packing, chemical and soap '. . . 16,000

Commercial: Hotels, stores and office buildings 60,000

Domestic: Average 80

Domestic : Apartment houses 147

Domestic: First-class dwellings 129

Domestic: Middle-class dwellings 81

Domestic: Lowest-class dwellings 35.5

Cincinnati, Ohio. 1913 Report on Sewerage Plan:

Industrial, in addition to residential and ground water 9,000

Commercial, in addition to residential and ground water .... 40,000
Domestic 135

Detroit, Mich.:

Domestic 228

Industrial, in addition to residential and ground water 12,000

Commercial, in addition to residential and ground water .... 50,000

Milwaukee, Wis. 1915 Report of Sewerage Commission:

Industrial, maximum 81 16,600

Industrial, average 31 8,300

Commercial, maximum 60,500

Commercial, average 37,400

Wholesale commercial, maximum 20,000

Wholesale commercial, average 9,650

CHARACTER OF DISTRICT

TABLE 9

OBSERVED WATER CONSUMPTION IN DIFFERENT CLASSES OF DISTRICTS IN

NEW YORK CITY

From data by Kenneth Allen in Municipal Engineers Journal, for 1918

Daily

Cons.

Hbtels

Gals, per
1000
Sq. Ft.

Tenements

Gals, per
1000
Sq. Ft.

Office and Loft
Buildings

Gals, per
1000
Sq. Ft.

Floor

Area

Building

Location

Building

Hotel Biltmor.'
Hotel McAlpin.

470

7 VI

094

78th-79th St. and
IV way

256

192

Mi-draw Bldg. . . .
N Y Telephone

309

200

Hotel Plaza

630

578

410 E 65th St. . . .

350

295

Bldg

194

Hotel Waldorf

30th St. and Madi-

Met. Life Bldg. .

256

618

482

son Ave

306

Iss

42d St Bldg

271

732

492

27 Lewis St

307

250

118

Hotel Vanderbilt . .

604

545

258 Delancey St . .

207

226

Equitable Bldg ....

366

268

634

526

Average

207

230

338

219

* Max. represents only the average maximum, not the greatest maximum.

TABLE 10

SEWAGE FLOW FROM DIFFERENT CLASSES OF DISTRICTS BASED ON 1915
REPORT OF MILWAUKEE SEWERAGE COMMISSION

Ratio of maximum to average rate for department store district ....

Ratio of maximum to average rate for hotel district

Ratio of maximum to average rate for office building district

Ratio of maximum to average rate for wholesale commercial district.

1.755
1.65
1.51
2.1

Average and maximum gallons per thousand square feet of

Avg.

Max

For department store district

232

407

For office building district

541

891

For wholesale commercial district ....

164

344

For all districts except wholesale commercial. .

381

618

Average and maximum gallons per day :
For all districts except wholesale commercial

17,700

29,800

For wholesale commercial district . .

9.650

20.000

QUANTITY OF SEWAGE

TABLE 11

RATES OF CONSUMPTION PREDICTED FOU DIFFERENT DISTRICTS IN NEW YORK

CITY

£o

-d '

13 -

• M

jj g

2ji

S ^

.S3

.S*'

•S£

o
O

.a 1.

Q".

^ 0

Q .

Q»

District

o! k. C

£-2-2

a c-

•A .

OCB

c
1

l-l

Xft

Q«

SL2

"^ Q) 01

<^ —

.( ;

*^"

»|§

"§2

•o

3J^

"8°.

•sJ

°~

3 t. fi

*z\

(M ^

tj ^

"E a g

3 g «

= g £

-g D.U

« 1

c^ <^ 2.

"I £<

1^4

i^-<

Hotel and midtown

24,800

634

526

500

.20

.29

.34

1.04

.146

Midtown and financial.

24,800

338

219

300

. 12

.18

.23

.078

.110

East and West of midtown. . . .

24,800

297

230

300

.074

.12

.15

.057

.097

Apartment, 59th to 155th Sts. .

20,400

230

300

.043

.06

.09

Manhattan north of 155th St. .

20,400

230

300

.031

.05

.08

Midtown district consists of department stores, large railroad terminals, industrial and
loft buildings, and sky-scraper office buildings.

It is difficult to set any definite figure for the percentage which
the maximum rate of flow is of the average. Fluctuations above
and below the average are greater the smaller the tributary
population. This relation can be expressed empirically as

= -
pn*

in which M represents the per cent which the maximum flow is
of the average, and P represents the tributary population in
thousands. The expression should not be used for populations
below 1,000 nor above 1,000,000. Having determined the expected
average flow of sewage by a study of the population, water con-
sumption, etc., the maximum quantity of sewage is determined
by multiplying the average flow by the per cent which the maxi-
mum is of the average. In this connection W. G. Harmon1 offers
the relation

,_>

4+Vp'

which was used in the design of the Ten Mile Creek intercepting

sewer at Toledo, Ohio. For rough estimates and for comparative

purposes the ratio of the average to the minimum flow can be

1 Eng. News-Record, Vol. 80, page 1233, 1918.

FLUCTUATIONS IN RATE OF SEWAGE FLOW

taken the same as the ratio of the maximum to the average flow,

unless direct gaugings or other information show it to be otherwise.

The fluctuations of flow in commercial and industrial districts

are so different from those in residential districts that the formulas

zoo

23456789 10 II
A.M.

23456789
P.M.

10 II

1. Toledo

2. Toledo

3. Toledo

4. Toledo

5. Toledo

FIG. 10. — Daily and Hourly Variations of Sewage Flow.

().; Manufacturing average.

O. ; Manufacturing, Monday.

<).; Manufacturing, Sunday.

O.; Residential, average.

O.; Residential, Monday.

6. Toledo, O.; Residential, Sunday.

7. Cincinnati, O., Industrial, average.

8. Cincinnati, O.; Residential, average.

9. Cincinnati, O. ; Commercial, average.
10. Average of 7 cities.

given should not be used in the design of sewers other than those
draining residential areas. It is reasonable to suppose that
fluctuations in rates of flow from industrial districts are dependent

38 QUANTITY OF SEWAGE

upon the character of the tributary industries. A study of these
industries will give valuable light on the maximum and minimum
rates at which sewage will be delivered to the sewers.

Hourly, daily, and seasonal fluctuations in rates of sewage
flow are of interest in the design of pumping stations to give
knowledge of the rates at which the pumps must operate at
various periods. The fluctuations in rates of sewage flow during
various hours and days in different cities and districts are shown
in Fig. 10. Fluctuations in rate of flow of sewage lag behind
fluctuations in rate of water consumption, the time being depend-
ent on the distance through which the wave of change must
travel in the sewer.

26. Effect of Ground Water. — Sewers are seldom laid with
water-tight joints. Since they usually lie below the ground
water level it is inevitable that a certain amount of ground water
will enter. Various units have been suggested for the expression
of the inflow of ground water in an attempt to include all of the
many factors. Some of these units are : gallons per acre drained
by the sewer per day, gallons per mile of pipe per day, gallons per
inch diameter per mile of pipe per day, etc. Since the ground
water enters pipe sewers at the joints, the longer the joints the
greater the probability of the entrance of ground water. The
last unit is therefore the most logical but the accuracy of the
result is scarcely worthy of such refinement and the unit usually
adopted is gallons per mile of pipe per day.

No definite figure can be given for the amount of ground
water to be expected in sewers since the character of the soil and
the ground water pressure must be considered. Relatively
normal infiltration may be found from 5,000 to 80,000 gallons per
mile of pipe per day. The minimum is seldom reached in wet
ground and the maximum is frequently exceeded. Table 12
shows the amount of ground water measured in various sewers
as given by Brooks.1

27. Resume of Method for Determination of Quantity of Dry-
weather Sewage. — The steps in the determination of the quantity
of sewage are: determine the period in the future for which the
sewers are to be designed; estimate the population and tributary
area at the end of this period ; estimate the rate of water consump-

1 Infiltration of Ground Water into Sewers. Transactions of the American
Society of Civil Engineers, Vol. 76, 1913, p. 1909.

EFFECT OF GROUND WATER

S <y

02 -a

8 w
2 I

* S

g o

•< >>

^>. "**

^* "3

s §4

Ho 8

M h 3)

« O §

2 * i

Hog
B H

tf -2

I -i

»— i ^

H »

DATA ON

QMOQQOQ<P7t!QeQQ<eeS ;?

^SooojigfiwgJgo^f?5**"

ob^riiJic^c^Tfli-irtth-i-iS

1-1

00 O b-Q OOOQO -OOCO -o

i—* ^ O O5 O <^ ^T O5 00 • O5 W 0s! Q

00 "5 dCO »^OiOOO^f • CO >~ ' >~l

o±; -I -3

p .5 « oo e«3 p i>-ri> t-. os 8

IN O O»O i-iT}ilNI>. • •£ 48

flj «4-l

i : 'So-

•s **

i '. : ;o -^

o d

O----00--IO-CC-*--- -O.

w ^

2S. I

§1 *

ft.
_ - *•

os ^>!;j>!;;;;j>''-^>~>!>-i.>^.i:-(;.c3c S>

CO •rf
CO . (N .

p - M oo -oo • 2^^^ 'co^^^-s g

1 i
1

* 'rv^Ko tc S *
•"laM pq

^ :::::::::::::::: |

•-s1^,

40 QUANTITY OF SEWAGE

tion and assume the sewage flow to equal the water consumption ;
determine the maximum and minimum rates of sewage flow;
and finally, estimate the maximum rate of ground water seepage
and add it to the maximum rate of sewage flow to give the total
quantity of sewage to be carried by the proposed sewers.

QUANTITY OF STORM WATER

28. The Rational Method. — The water which falls during a
storm must be removed rapidly in order to prevent the flooding
of streets and basements, and other damages. The quantity of
water to be cared for is dependent upon : the rate of rainfall, the
character and slope of the surface, and the area to be drained.
All methods for the determination of storm water run-off, whether
rational or empirical, depend upon these factors.

The so-called Rational Method can be expressed algebraically,
as,

Q = AIR,

in which Q = rate of run-off in cubic feet per second;

A =area to be drained expressed in acres;

7 = percentage imperviousness of the area;

R = maximum average rate of rainfall over the entire
drainage area, expressed in inches per hour, which
may occur during the time of concentration.

The area to be drained is determined by a survey. A discussion
of R and 7 follows in the next two sections. An example of the
use of the Rational Method is given on page 95.

29. Rate of Rainfall. — Rainfall observations have been made
over a long period of time by United States Weather Bureau
observers and others. Continuous records are available in a few
places in this country showing rainfall observations covering
more than a century. Such records have been the bases for a
number of empirical formulas for expressing the probable maximum
rate of rainfall in inches per hour, having given the duration of
the storm. Table 13 is a collection of these formulas with a
statement as to the conditions under which each formula is appli-
cable. The formula most suitable to the problem in hand should
be selected for its solution.1

1 A comprehensive discussion of rainfall formulas will be found in Vol. 54
of the Transactions Am. Society of Civil Engineers, 1905.

RATE OF RAINFALL

TABLE 13
RAINFALL FORMULAS

Name of
Originator

Conditions for which Formula is
Suitable

Formula

E. S. Dorr

150
'~*+30
360

A. N. Talbot. ...
A. N. Talbot

Maximum storms in Eastern United
States

<+30
105

Ordinary storms in Eastern United
States

Emil Kuichling. . .
L. J. Le Conte.. . .

Sherman

t+15

120
i= , etc.
<+20

<-7/f*

t = 25.12/*-687
» = 18/«K
i = 12/t°-6
105

Heavy rainfall near New York City. .

For San Francisco. See T. A. S. C. E.
v. 54,p. 198

Maximum for Boston, Mass

Sherman

Extraordinary for Boston, Mass

Webster .

Ordinary for Philadelphia, Pa

Hendrick

Ordinary storms for Baltimore. Eng.
& Cont., Aug. 9. 1911

J. de Bruyn-Kops.
C D Hill

t + 10
163

'~t+27
120

Ordinary storms for Savannah, Ga ....
For Chicago 111

Metcalf and Eddy
W. W. Homer. . . .

R. A Brackenbuj

Metcalf and Eddy
Metcalf and Eddy
Kenneth Allen . . .

Louisville, Ky. Am. Sew. Prac., Vol I.
St. Louis, Mo. Eng. News, Sept. 29,
1910

t+15
>-U/fH

t = 56/f<+5)'86
i 2392 10154

For Spokane, Wash. Eng. Record, Aug.
10, 1912

-<+2.15l(U5
i = 19/'^

"<-M

400 *

New Orleans

For Denver, Colo

Central Park, N. Y 51-Year Record.
Eng. News-Record, April 7, 1921,
p. 588..

2/+40

* Formula devised by H. E. Babbitt from Allen's 25-year curve.

30. Time of Concentration. — By the time of concentration is

meant the longest time without unreasonable delay that will be

required for a drop of water l to flow from the upper limit of a

drainage area to the outlet. Assuming a rainfall to start sud-

1 See Note under TaWe 14.

42 QUANTITY OF SEWAGE

denly and to continue at a constant rate and to be evenly dis-
tributed over a drainage area of 100 per cent imperviousness and
even slope towards one point, the rate of run-off would increase
constantly until the drop of water from the upper limit of the area
reached the outlet, after which the rate of run-off would remain
constant. In nature the rate of rainfall is not constant. The
shorter the duration of a storm the greater the intensity of rain-
fall. Therefore the maximum run-off during a storm will occur
at the moment when the upper limit of the area has commenced
to contribute. From that time on the rate of run-off will decrease.
The time of concentration can be measured fairly well by
observing the moment of the commencement of a rainfall, and the
time of maximum run-off from an area on which the rain is falling.
A prediction of the time of concentration is more or less guess
work. As the result of measurements some engineers assume the
time of concentration on a city block built up with impervious
roofs and walks, and on a moderate slope, is about 5 to 10 minutes.
This is used as a basis for the judgment of the time of concentra-
tion on other areas. For relatively large drainage areas such a
method cannot be used. The procedure is to measure the length
of flow through the drainage channels of the area, to assume the
velocity of the flood crest through these channels and thus to
determine the time of concentration. Table 14 shows the flood
crest velocities in various streams of the Ohio River Basin under
flood conditions. The velocity over the surface of the ground
may be approximated by the use of the formula1

V = 2,0007 VS,

in which V = the velocity of flow over the surface of the ground

in feet per minute;

7 = the percentage imperviousness of the ground;
$ = the slope of the ground.

For areas up to 100 acres where natural drainage channels are not
existent this formula will give more satisfactory results than guesses
based on the time of concentration of certain known areas.

Having determined the time of concentration, the rate of rain-
fall R to be used in the Rational Method is found by substitution
in some one of the rainfall formulas given in Table 13.
1 Sewerage by A. P. Folwell.

TIME OF CONCENTRATION

i-H

« a
«&

W02

> t.

5-2
<a

«
-i

• /

-5. a

H-i

0 03 te i

.
fl

C5 <»

§ § C

a 1.1 cj-

-S P-0.9

Sta

O Tj< rt* <N rt< F-H O Oi <N CO Tt< 00 iO CO «-H CO rt< —I CO O -

___._- _ ,_H .— 1 O5 T}< 1-1 I-H C^'-''— 1 I— I

O IM COCO t^-i-HOCKN O5COCO CO <N

C^GOrt<OiO'-iO5t^OOcOt~-r^(Na><N
O5 »O O CO I-H O • iO CO ^H I-H O5 <N (N CO CO CO <M •* •* iO N CO

CO CO •* Tj< CO t» GO O5

OiGOi^r-t^cocOcOiO-^cO'-i'

8(M(M
CCi-H

CO iO CO CO 00 CC O -^ O »H t^ CO id Tt< >O

QeO
O> OO

BJS

S-o

,3
I-

•58

4). a
-*
**'§

.-H

w ^
O«

the
Th

and are n
entration.

wav
f co

rest of the flo
ing the tim

ties
in

NOTE. — The velocities shown are the v
of the crest of the flood wave should be u
because of the storage in the river basin.

44 QUANTITY OF SEWAGE

31. Character of Surface. — The proportion of total rainfall
which will reach the sewers depends on the relative porosity, or
imperviousness, and the slope of the surface. Absolutely impervi-
ous surfaces such as asphalt pavements or roofs of buildings will
give nearly 100 per cent run-off regardless of the slope, after the
surfaces have become thoroughly wet. For unpaved streets,
lawns, and gardens the steeper the slope the greater the per cent
of run-off. When the ground is already water soaked or is frozen
the per cent of run-off is high, and in the event of a warm rain on
snow covered or frozen ground, the run-off may be greater than the
rainfall. The run-off during the flood of March, 191 3, at Columbus,
Ohio, was over 100 per cent of the rainfall. Table 15 l shows the
relative imperviousness of various types of surfaces when dry
and on low slopes. The estimates for relative impervious-
ness used in the design of the Cincinnati intercepter are given in
Table 16.

TABLE 15

VALUES OF RELATIVE IMPERVIOUSNESS

Roof surfaces assumed to be watertight 0 . 70-0 . 95

Asphalt pavements in good order 85- . 90

Stone, brick, and wood-block pavements with tightly cemented

joints 75- . 85

The same with open or uncemented joints 50- .70

Inferior block pavements with open joints 40- . 50

Macadamized roadways 25- . 60

Gravel roadways and walks 15- . 30

Unpaved surfaces, railroad yards, and vacant lots 10- . 30

Parks, gardens, lawns, and meadows, depending on surface slope

and character of subsoil 05- . 25

Wooded areas or forest land, depending on surface slope and char-
acter of subsoil 01- . 20

Most densely populated or built up portion of a city 70- . 90

C. E. Gregory2 states that I, in the expression Q = AIR is a
function of the time of concentration or the duration of the storm.
If t represents the time of concentration and T represents the
duration of the storm, then when T is less than t

7 = 0.175^,

1From an article by E. Kuichling in Transactions American Society of
Civil Engineers, Vol. 65, 1909, p. 399.

2 Trans. Am. Society Civil Engineers, Vol. 58, 1907, p. 483.

CHARACTER OF SURFACE

•

If.

5
5
g

46 QUANTITY OF SEWAGE

but when T is greater than t,

Gregory condenses Kuichling's rules with regard to the per cent
run-off, as follows:

1. The per cent of rainfall discharged from any given
drainage area is nearly constant for heavy rains lasting
equal periods of time.

2. This per cent varies directly with the area of imper-
vious surface.

3. This per cent increases rapidly and directly or uni-
formly with the duration of the maximum intensity of the
rainfall until a period is reached which is equal to the time
required for the concentration of the drainage waters from
the entire area at the point of observation, but if the rain-
fall continues at the same intensity for a longer period this
per cent will continue to increase at a much smaller rate.

4. This per cent becomes larger when a moderate rain
has immediately preceded a heavy shower on a partially
permeable territory.

Gregory's formulas have not been generally accepted and are
not widely used in practice. Marston stated: 1

All that engineers are at present, warranted in doing is
to make some deduction from 100 per cent run-off . . . the
deduction . . . being at present left to the engineer in
view of his general knowledge and his familiarity with local
conditions.

Burger states 2 in the same connection :

In its application there will usually be as many results
(differing widely from each other) as the number of men
using it.

In spite' of these objections the Rational Method is in more favor
with engineers than any other method.

32. Empirical Formulas. — The difficulty of determining run-
off with accuracy has led to the production by engineers of many
empirical formulas for their own use. Some of these formulas
have attracted wide attention and have been used extensively,

1 Trans. American Society of Civil Engineers, Vol. 58, 1907, p. 498.

2 Ibid.

EMPIRICAL FORMULAS 47

in some cases under conditions to which they are not applicable.
In general these formulas are expressions for the run-off in terms
of the area drained, the relative imperviousness, the slope of the
land, and' the rate of rainfall.

The Burkli-Ziegler formula, devised by a Swiss engineer for
Swiss conditions and introduced into the United States by Rudolph
Hering, was one of the earliest of the empirical formulas to attract
attention in this country. It has been used extensively in the
form

in which Q = the run-off in cubic feet per second;

i = the maximum rate of rainfall in inches per hour over
the entire area. This is determined only by ex-
perience in the particular locality, and is usually
taken at from 1 to 3 inches per hour;
S = the slope of the ground surface in feet per thousand,
A = the area in acres;

C — an expression for the character of the ground sur-
face, or relative imperviousness. In this form of
the expression C is recommended as 0.7.

The McMath formula was developed for St. Louis conditions
and was first published in Transactions of the American Society
of Civil Engineers, Vol. 16, 1887, p. 183. Using the same notation
as above, the formula is,

McMath recommended the use of C equal to 0.75, i as 2.75 inches
per hour, and S equal to 15. The formula has been extended
for use with all values of C, i, S, and A ordinarily met in sewerage
practice. Fig. 11 is presented as an aid to the rapid solution of
the formula.

Other formulas have been devised which are more applicable
to drainage areas of more than 1,000 acres.1 Such areas are met
in the design of sewers to enclose existing stream channels drain-
ing large areas. Kuichling's formulas, published in 1901 in the

1 The principles governing the run-off from large areas are explained in
Elements of Hydrology, by A. F. Meyer, 1917.

QUANTITY OF SEWAGE

3
-4

-S

-6

•8

:20

-30

-40
-£0
-60

-200

^300

•AW
•500
^600

1(800
1000

••2000

-j3000
-4000

-SOOO
j-6000

^8000
:.IO,000

Values of c
•0.1 0.2 03 04 OS 0.7 1.0

FIG. 11. — Diagram for the Solution of McMath's Formula,

<***

EMPIRICAL FORMULAS

report of the New York State Barge Canal, were devised for areas
greater than 100 square miles. The following modification of
these formulas for ordinary storms on smaller areas was published
for the first time in American Sewerage Practice, Volume I, by
Metcalf and Eddy :

25,000

30 40 50 60 70

Quantity in Cubic Feet per Second.

FIG. 12. — Comparison of Empirical Run-off Formulas.

It is to be noted that the only factor taken into consideration is
the area of the watershed. It is obvious that other factors such
as the rate of rainfall, slope, imperviousness, etc., will have a
marked effect on the run-off.

There are other run-off formulas devised for particular con-
ditions, some of which are of as general applicability as those
quoted. Two formulas which are frequently quoted are: Fan-
ning's, Q = 200Ms/i and Talbot's Q= 500M*, in which M is the area
of the watershed in square miles. A comprehensive treatment
of the subject is given in American Sewerage Practice, Vol. I,
by Metcalf and Eddy.

A comparison of the results obtained by the application of a
few formulas to the same conditions is shown graphically in Fig.
12. It is to be noted that the divergence between the smallest

50 QUANTITY OF SEWAGE

and largest results is over 100 per cent. As these formulas are
not all applicable to the same conditions, the differences shown are
due partially to an extension of some of them beyond the limits
for which they were prepared.

33. Extent and Intensity of Storms. — In the design of storm
sewers it is necessary to decide how heavy a storm must be pro-
vided for. The very heaviest storms occur infrequently. To
build a sewer capable of caring for all storms would involve a
prohibitive expense over the investment necessary to care for the
ordinary heavy storms encountered annually or once in a decade.
This extra investment would lie idle for a long period entailing a
considerable interest charge for which no return is easily seen.
The alternative is to construct only for such heavy storms as are
of ordinary occurrence and to allow the sewers to overflow on
exceptional occasions. The result will be a more frequent use of
the sewerage system to its capacity, a saving in the cost of the
system, and an occasional flooding of the district in excessive
storms. The amount of damage caused by inundations must be
balanced against the extra cost of a sewerage system to avoid the
damage. A municipality which does not provide adequate
storm drainage is liable, under certain circumstances, for damages
occasioned by this neglect. It is not liable if no drainage exists,
nor is it liable if the storm is of such unusual character as to be
classed legally as an act of God.

Kuichling's studies of the probabilities of the occurrence of
heavy storms are published in Transactions of the American
Society of Civil Engineers, Vol. 54, 1905, p. 192. Information
on the extent of rain storms is given by Francis in Vol. 7, 1878,
p. 224, of the same publication. Kuichling expresses the intensity
of storms which will occur,

. 105
once in 10 years as i =

120
once in 15 years as t =

in which i is the intensity of rainfall in inches per hour and t is
the duration of the storm in minutes.

CHAPTER IV
THE HYDRAULICS OF SEWERS

34. Principles. — The hydraulics of sewers deals with the
application of the laws of hydraulics to the flow of water through
conduits and open channels. • In so far as its hydraulic proper-
ties are concerned the characteristics of sewage are so similar to
those of water that the same physical laws are applicable to both.
In general it is assumed that the energy lost due to friction between
the liquid and the sides of the channel varies as some function of
the velocity, usually the square, and that the total energy passing
any section of the stream differs from the energy passing any
other section only by the loss of energy due to friction.

The general expression for the flow of sewage would then be,

h=(f)Vn,

in which h is the head or energy lost between any two sections,
and V is the average velocity of flow between these sections.
It is to be noted in this general expression that the quantity and
rate of flow past all sections is assumed to be constant. This
condition is known as steady flow. Problems are encountered
in sewerage design which involve conditions of unsteady flow,
and methods of solution of them have been developed based on
modifications of this general expression. The average velocity
of flow is computed by dividing the rate (quantity) of flow past
any section by the cross-sectional area of the stream at that
section. This does not represent the true velocity at any par-
ticular point in the stream, as the velocity near the center is faster
than that near the sides of the channel. The distribution of
velocities in a closed circular channel is somewhat in the form of
a paraboloid superimposed on a cylinder.

The laws of flow are expressed as formulas the constants of
which have been determined by experiment. It has been found
that these constants depend on the character of the material

52 THE HYDRAULICS OF SEWERS

forming the channel and the hydraulic radius. The hydraulic
iadius is defined as the ratio of the cross-sectional area of the
stream to the length of the wetted perimeter, or line of contact
between the liquid and the channel, exclusive of the horizontal
line between the air and the liquid.

35. Formulas. — The loss of head due to friction caused by
flow through circular pipes flowing full as expressed by Darcy is,

% flV2
h=fd2g>

in which h is the head lost due to friction in the distance I, V is
the velocity of flow, g is the acceleration due to gravity, and / is a
factor dependent on d and the material of which the pipe is made.
A formula for / expressed by Darcy as the result of experiments
on cast iron pipe is,

in which d is the diameter in feet. In using the formula with
this factor the units used must be feet and seconds.

Another form of the same expression is known as the Chezy
formula. It is an algebraic transformation of the Darcy formula,
but in the form shown here, by the use of the hydraulic radius,
it is made applicable to any shape of conduit either full or partly
full. The Chezy formula is,

in which R is the hydraulic radius, S the slope ratio of the hydraulic
gradient, and C a factor similar to / in the Darcy formula.

Kutter' s formula was derived by the Swiss engineers, Gan-
guillet and Kutter, as the result of a series of experimental observa-
tions. It was introduced into the United States by Rudolph
Bering and its derivation is given in Hering and Trautwine's
translation of " The Flow of Water in Open Channels by Gan-
guillet and Kutter." In English units it is,

V =

,7, .0028
•67H s —

VRS,

FORMULAS 53

in which n is a factor expressing the character of the surface of
the conduit and the other notation is as in the Chezy formula.
V is the velocity in feet per second, S is the slope ratio, and R the
hydraulic radius in feet. The values of n to be used in all cases
are not agreed upon, but in general the values shown below are
used in practice,

VALUES OF n IN KUTTER'S FORMULA

n CHARACTER OF THE MATERIALS

0.009 Well-planed timber.

0.010 Neat cement or very smooth pipe.

0.012 Unplaned timber. Best concrete.

0.013 Smooth masonry or brickwork, or concrete

sewers under ordinary conditions.

0.015 Vitrified pipe or ordinary brickwork.

0.017 Rubble masonry or rough brickwork.

0.020 1 0

0 QOK / Smooth earth

0.030
0.050

> Rough channels overgrown with grass.

Kutter's formula is of general application to all classes of material
and to all shapes of conduits. It is the most generally used for-
mula in sewerage design.

The cumbersomeness of Kutter's formula is caused somewhat
by the attempt to allow for the effect of the low slopes of the
Mississippi River experiments on the coefficients. The correct-
ness of these experiments has not been well established and the

0 0028

slopes are so flat that the omission of the term - - will have

no appreciable effect on the value of V ordinarily used in sewer
design. The difference between the value of V determined by
the omission of this term and the value of V found by including
it is less than 1 per cent for all slopes greater than 1 in 1,000
for 8 inch pipe (72 = 0.167 feet). As the diameter of the pipe or
the hydraulic radius of the channel increases up to a diameter of
13.02 feet (72 = 3.28 feet), the difference becomes less and at this
value of R there is no difference whether the slope is included or
not. For larger pipes the difference increases slowly. For a
16 foot pipe (R = 4 feet) on a slope of 1 in 1,000 the difference is
less than 0.2 per cent, and on a slope of 1 in 10,000 the difference
is approximately 1 per cent. Flatter slopes than these are

54 THE HYDRAULICS OF SEWERS

seldom used in sewer design, except for very large sewers where
careful determinations of the hydraulic slope are necessary. It
is therefore safe in sewer design to use Kutter's formula in the

0028
modified form shown below in which the term '- - has been

omitted.

Bazin's formula is

in which a and /3 are constants for different classes of material.
For cast-iron pipe a is 0.00007726 and ft is 0.00000647. This
formula is seldom used in sewerage design.

Exponential formulas have been developed as the result of
experiments which have demonstrated that V does not vary as
the one half power of R and S but that the relation should be
expressed as,

V=CRPS9,

in which p and q are constants and C is a factor dependent on
the character of the material. The various formulas coming
under this classification have been given the names of the experi-
menters proposing them. Examples of these formulas are:
Flamant's, in English units, for new cast iron pipe, which is,

7=232JR'715>S-572,

and Lampe's for the same material which is,
F=203.3#694S555.

These formulas are useful only for the material to which they
apply, but they can be used for conduits of any shape. A. V.
Saph and E. W. Schoder have shown l that the general formula
for all materials lies between the limits,

V= (93 to 50 to '5563 to "

1 Transactions of the American Society of Civil Engineers, Vol. 51, 1903,
p. 11.

SOLUTION OF FORMULAS 55

Hazen and Williams' formula is in the form,

in which C is a factor dependent on the character of the material
of the conduit. The values of C as given by Hazen and Williams
are,

C CHARACTER OP MATERIAL

95 Steel pipe under future conditions. (Riveted

steel.)
100 Cast iron under ordinary future conditions and

brick sewers in good condition.
110 New riveted steel, and cement pipe.
120 Smooth wood or masonry conduits under ordinary

conditions.
130 Masonry conduits after some time and for very

smooth pipes such as glass, brass, lead, etc.,

when old, and for new cast-iron pipe under

ordinary conditions.

This formula is of as general application as Kutter's formula and
is easier of solution, but being more recently in the field and
because of the ease of the solution of Kutter's formula by dia-
grams it is not in such general use. Exponential formulas are
used more in waterworks than in sewerage practice.
Manning's formula is in the form,

in which n is the same as for Kutter's formula. Charts for the
solution of Manning's formula are given in Eng. News-Record,
Vol. 85, 1920, p. 837.

36. Solution of Formulas. — The solution of even the simplest
of these formulas, such as Flamant's, is laborious because of the
exponents involved. Darcy's and Kutter's formulas are even
more cumbersome because of the character of the coefficient.
The labor involved in the solution of these formulas has resulted
in the development of a number of diagrams and other short cuts.
Since each formula involves three or more variables it cannot be
represented by a single straight line on rectangular coordinate
paper. The simplest form of diagram for the solution of throe
or more variables is the nomograph, an example of which is shown

THE HYDRAULICS OF SEWERS

72
-48 J

-36JE

24 o

0.00003

0.0001

-0.001

-0.01

O.I

1.5-

2 -

3 -

5 -

in Fig. 13 for the 'solution of Flamant's formula. A straight-edge

placed on any two points of
the scales of two different ver-
tical lines will cross the other
line at a point on the scale cor-
responding to its correct value
in the formula. Such a diagram
is in common use for the
solution of problems for the
flow of water in cast-iron
pipe.

Fig. 14 has been prepared
to simplify the solution of
Hazen and Williams' formu-
la. The scales of slope for
'OH different classes of material

FIG. 13.-Diagram for the Solution of are shown On Vertical Unes
Flamant's Formula for the Flow of to tne left of the slope line.
Water in Cast-iron Pipe. For use these scales must be

projected horizontally on the

slope line. The scales for other factors are shown on independent

reference lines.

For example let it be required to find the loss of head in
a 12 inch pipe carrying 1 cubic foot per second when the
coefficient of roughness is 100. A straight-edge placed
at 1.0 cubic feet per second on the quantity scale, and 12
inches on the diameter scale crosses the slope line at 0.00092
opposite the slope scale for c= 100. It crosses the velocity
line at 1.31 feet per second.

Kutter's formula is the most commonly used for sewer design
and has been generally accepted as a standard in spite of its
cumbersomeness. Fig. 15 is a graphical solution of Kutter's
formula for small pipes, and Fig. 16 for larger pipes. The dia-
grams are drawn on the nomographic principle and give solutions
for a wide range of materials, but they are specially prepared for
the solution of problems in which w=.015. In their preparation
the effect of the slope on the coefficient has been neglected. Fig.
17 is drawn on ordinary rectangular coordinate paper and can be
used only for the solution of problems in which n = .015. Both
diagrams are given for practice in the use of the different types.

SOLUTION OF FORMULAS

Values of C

-2

-0.9

0.7 S.

0.6?.

rO.4

-0.3'

-0.2

Mil

48'
42'

36-
33'
30'
27'

24'

22'
|?

20"

18-
15'

io-

9-
8'h

— 4
o

c ~

(f)

08-

0.9

1.0-

1.5-

Q- 3-

.E 3.5 -

4.5-

5.5

65
7

7.5

Fia. 14.— Diagram for the Solution of Hazen and Williams' Formula.

TIIF: rrvDHAi'Lifs m si:\vi.i;s

9
8
7

4
3

M
«

2 -

4-
0)

Values of n
5c> 5! c^^ cj

(ft

7C"

— . ? S

*x*

K.
-
s

33'

30'
28"
26"
24
IT

N \J.

Xx^^

•

, ^^

* v ^

^ s

X ^^

*) A."

Ift"

"* v

™ . s

" < h

u
C

I5"n

I2"u

fl'"

J
-R*

^V k,.

V /^

1.0 ,

0.9 o
<j

0.8$
0.7 g_

0.6 2

05*

3
u

0.4 =
|»

<§
Q2

1 1

s ^

r6 '
-4-

••

\ ^

S ^

_o .

tn :

-)000>

000?

0003

0004
0005
0006
0007
0008

001

002

003
004
005
006
.007
.008
.01

-.2

FIG. 15.— Diagram for the Solution of Kutter's Formula.

For values of n between 0.010 and 0.020. Specially arraiiKod for n = 0.015.
Q from G.I to 10 second-feet.

1.5-

2.0-

35-
4.0^

5-0:
5.5:

6.0:
6.5 ^
7.Q\

Values of

SOLUTION OF FORMULAS

Values of n

KLVlS^

qnn ^.^^^i

J k >

v " ^

19*

or\f\ •— ^ >* 5

' s s

!«'

oUU x ^ ^

> X ^ s,

17*

N^ S, /

^ ^ S

700 S 5,*

* X

Ih'

? S s S

1C*

"*Si s^ y

i . S

iOO r5^-

14*

s x

"V x

1 3*

cnn ^ „_ ^ /

s ^

"S. i. j

y*y* S,,

V .

[00 s ^^

^ ^ v

1 A'

*s. N

> ^

X ^

*- ^ s

s^ . v

, s

300 x ^j

X ^ s

^ s

90V

^s^ %^

"-V N

OA"

*\ «w J

' r x

o't

^v *v-

P s

78' -i

s^ ^ v a

v s

200 f!s *5

p ** ^

17' ~

V "V

S, N

. C ^ *

|> ^ ^

x, ^i

OD ,

o> S ^§

^ s

hir

<U ^

^*xT ^

T X

_ ..

x ^

O X. s

'• ^

-48'H

^ ^

100 ^«

a ^

-4^"

90^ *5i:

^ s

jO ^ ^ "

>. 1

•36

7fl 03 ^

<n "*\~

V "^ -

Tfim

tt, t V j

cn+- *.

-27'

50 « 2 K

x^^

S^ "Vs-

^ *•

o ^

^ .

• L*f

40 5

J \

Ol>

3 s -

••tl

7ft •>.

9 v

. Ifl*

•io

•C

3
a

20
10

•

UUUI
0002

0003

i
4--

0004

0005

0006
0007
0008

o-*
o

001

;

"(0

•

002

•

003

•o

004

•

o -

005

•

•£ ^

<0 -

tt -

006
007
008

L
Q>
Q-

o_-

£ :

10-

.02

II-

.03

12-

.04

13-

.05

14-

.06

.07

(5 —

.08

16-

17-

18-

19-

1.0

FIG. 16. — Diagram for the Solution of Kutter's Formula.

For values of n between 0.010 and 0.020. Specially arranged for n- 0.015. Values of
Q from 10 to 1,000 second-feet.

THE HYDRAULICS OF SEWERS

puooag_Jad

core?
oeo'o

080'0
OZO'O

000 O O
000 O O

ZOOO'O

§s§§ §

USE OF DIAGRAMS

FIG. 18. — Conversion Factors for
Kutter's Formula.

In Figs. 15 and 16 the diameter scales are varied for different
values of the roughness coefficient n. The velocity scale is shown
only for a value of n=.015.
The velocity for other values
of n can be determined by the
method given in the following
paragraphs.

37. Use of Diagrams. —
There are five factors in
Kutter's formula: n, Q, V, d
(or R), and S. If any three of
these are given the other two
can be determined, except when
the three given are Q, V, and d.
These three are related in the
form Q = AV, which is inde-
pendent of slope or the char-
acter of the material. There
are only nine different com-
binations possible with these
five factors, which will be met

in the solution of Kutter's formula. The solution of the
problems by means of the diagrams is simple when the data
given include n=.015. For other given values of n the solu-
tion is more complicated. Results of the solution of types of
each of the nine problems are given in Table 17 and the
explanatory text below.

// n is given and is equal to .015, the solution is simple.

For example in Table 17 case 1, example 1; to be solved
on Fig. 15. Place a straight-edge at 1.0 on the Q line and
at 6 inches on the diameter line for n= .015. The slope
and the velocity will be found at the intersection of the
straight-edge with these respective scales.

All problems in which n is given as .015 and the solution for which
falls within the limits of Fig. 15 or 16 should be solved by placing
a straight-edge on the two known scales and reading the two
unknown results at the intersection of the straight-edge and the
remaining scales.

For example in case 1, example 2 find the intersection
of the horizontal line representing Q= 100 with the sloping

THE HYDRAULICS OF SEWERS

diameter line representing d = 48 inches. The vertical
slope line passing through this point represents S= .0065
and the sloping velocity line passing through this point
represents 8.5 feet per second.

In general problems in which n=.015, can be solved on Fig. 17
by finding the intersection of the two lines representing the given
data, and reading the values of the remaining variables represented
by the other two lines passing through this point.

TABLE 17

SOLUTIONS OF PROBLEMS BY KUTTRR'S FORMULA

Case

Ex-
ample

Given

Found

1
1
1
1
2
2
3
3
4
4
5
6
7
7
8
9

1
2
3

4
1
2
1
2
1
2
1
1
1
2
1
1

0.015
.015
.020
.020
.015
.010
.015
.018
.015
.011
.015
.018

1.0
100.0
1.0
100.0
5.0
5.0

2.5

5 0

0.0575
.0065
.13
.0125

8.5

5.0

8 5

0.0003
.0003
.002
.0008

1.2
1.7
2 25

28
23.5

18
18

4 0

2.0

1 1

2.0
2.0

2.5
2.5
5.0
5.0

2.5
4.2

12
12

.00475
.0022
.0038

18
36

35 0

3.0
50.0
6.0

.001
.002
.005
.003
.00059

0.019
.012
.018
.011

185.0

1 7

7.0

100.0

// n is given and is not equal to .015 the solution is not so simple.
In Fig. 15 and 16 the diagram is so drawn that the position of
the diameter scales for all values of n is fixed on the vertical
" diameter " line. The scales of diameter change for each value
of n. These scales of diameter are shown for each value of n
from .010 to .020 on vertical lines to the left of the " diameter "
line. For use, the proper diameter scale for any given value of n
must be projected horizontally upon the vertical " diameter "
line. The velocity can be determined on Fig. 15 and 16, only

USE OF DIAGRAMS 63

when the diameter has been determined and then only when the
diameter scale for n equal .015 is used, since the only scale shown
for velocity is for n= .015.

For example, in Case 1, Example 3 there are given
n— .020, Q, and d. Find the intersection of the vertical
line for n = . 020 with the sloping diameter line for d = 6
inches. Project the intersection horizontally to the right
to the vertical "diameter" line. Place a straight-edge at
this point and at Q = 1 . 0 on the quantity scale. The
required value of S is read at the intersection of the straight-
edge and the slope scale and is equal to 0.13. The inter-
section of the straight-edge in this position with the velocity
scale is not the required value of the velocity since the
velocity scale is made out for n= .015 and not .020. It is
necessary to change the position of the straight-edge so that
it may lie on Q equal 1 . 0 and on d equal 6 inches for n
equal . 015. The value of V is shown in this position as 5
feet per second.

The reverse process for Fig. 15 and 16 is illustrated
by Case 4, Example 2 in which n= .011 and Q and V are also
given. When Q and V are given the value of d is fixed
independent of all other factors. Therefore the value of d
can be read from the scale with n= .015 and is found to be
12 inches. Now find the value of d= 12 inches on the scale
for n= .011 and project on to the "diameter" line. Place
the straight-edge at this point and at Q = 2. The required
slope is read as . 0022.

Fig. 17 is prepared for the solution of problems in which
n=.015 only. For problems in which n has some other value it
is necessary to transform the data to equivalent conditions in
which n=.015. This is done by means of the conversion factors
shown in Fig. 18. The given slope or velocity is multiplied by
the proper factor to convert from or to the value of n= .015.

For example in Case 1, Example 4 there are given
n = . 020, Q, and d. With Q and d given the value of V can
be read from Fig. 17 without conversion. The correspond-
ing value of S for n= .015 is .0065. It is now necessary to
use the transformation diagram Fig. 18. The hydraulic
radius of the given pipe is one foot. On Fig. 18 at the inter-
section of the slope line for R = 1 . 0 foot and n = . 020 the
value of the factor is read as 1 . 92. Since the given n is
for rougher material than that represented bv n= .015 the
required slope must be greater than for n= .015 to give the

64 THE HYDRAULICS OF SEWERS

same velocity. It is therefore necessary to multiply
. 0065 X 1 . 92 and the required slope is . 0125.

In Case 6, Example 1 there are given n— .018, d, and S,
The remaining factors are to be solved by Fig. 17. Solve
first as though n= .015 in order to find an approximate
value of d or R. In this case it is evident that d is greater
than 57 inches. The value of R is therefore about 1.25.
Referring to Fig. 18 the conversion factor for the slope for
n= .018 is about 1.52. Since the given slope for n= .018
is .001, for an equal velocity and for n=.015 the slope
should be less. Therefore in reading Fig. 17 it is necessary

001
to use a slope of j-^= .00066. The diameter is found to

1 . • i—

be about 80 inches. Since this is nearer to the correct
diameter the value of the conversion factor must be cor-
rected for this approximation. The hydraulic radius for an
80 inch pipe is 1 . 67 feet, and the conversion factor from
Fig. 18 is about 1.48. The slope for n=.015 should be

therefore ^—TQ— .000675 and from Fig. 17 the required

diameter and quantity are read as 80 inches and 185 second
feet, respectively.

If n is not given but must be solved for, the solution on Fig.
15 and 16 is relatively simple. The desired value of n is read at
the intersection of the sloping diameter line representing the
known diameter and the horizontal projection of the intersection
of the straight-edge with the vertical " diameter " line.

For example in Case 7, Example 1 there are given Q,
d, and S. Lay the straight-edge on the given values of
Q = 3 and S = . 002. At the point where the straight-edge
crosses the vertical "diameter" line project a horizontal
line to the sloping diameter line for d=18 inches. The
vertical line passing through this point represents a value of
n= .019. In order to find the value of V lay the straight-
edge on Q = 3 and d= 18 inches for n= .015. The value of
V is read as 1.7.

A slightly different condition is illustrated in the solu-
tion of Case 8, Example 1 in which Q, V and S are given.
Determine first the value of d as though n= .015. Then
proceed to determine n as in the preceding examples.

The solution for an unknown value of n on Fig. 17 is not so
simple. It must be determined by working backwards from the
conversion factor.

FLOW IN CIRCULAR PIPES PARTLY FULL 65

For example in Case 7, Example 2 there are given Q,
d, and S. The value of V is read directly as though n = .015
as 7 feet per second. The value of S read for n= .015 is
is .0075. But the given slope is .005. Since the given
slope is flatter than that for n= .015 the conversion factor

005
is less than unity and is therefore -^^. = 0 . 67. With this

value of the conversion factor and the value of R given as
0.75 the value of n is read from Fig. 18 as slightly greater
than .012.

38. Flow in Circular Pipes Partly Full. — The preceding
examples have involved the flow in circular pipes completely
filled. The same methods of solution can be used for pipes
flowing partly full except that the hydraulic radius of the wetted
section is used instead of the diameter of the pipe. Diagrams
are used to save labor in finding the hydraulic radius and the
other hydraulic elements of conduits flowing partly full.

The hydraulic elements of a conduit for any depth of flow are :
(a) The hydraulic radius, (6) the area, (c) the velocity of flow,
and (d) the quantity or rate of discharge. The velocity and
quantity when partly full as expressed in terms of the velocity
and quantity when full as calculated by Kutter's formula will
vary slightly with different diameters, slopes and coefficients of
roughness. The other elements are constant for all conditions
for the same type of cross-section. The hydraulic elements for
all depths of a circular section for two different diameters and
slopes are shown in Fig. 19. The differences between the
velocity and quantity under the different conditions are shown
to be slight, and in practice allowance is seldom made for this
discrepancy.

In the solution of a problem involving part full flow in a cir-
cular conduit the method followed is to solve the problem as
though it were for full flow conditions and then to convert to
partial flow conditions by means of Fig. 19, or to convert from
partial flow conditions to full flow conditions and solve as in the
preceding section.

For example let it be required to determine the quantity
of flow in a 12-inch diameter pipe with n= .015 when on a
slope of . 005 and the depth of flow is 3 inches. First find
the quantity for full flow. From Fig. 15 this is 2.0 cubic
feet per second. The depth of flow of 3 inches is one-fourth

THE HYDRAULICS OF SEWERS

or 0.25 of the full depth of 12 inches. From Fig. 19, run-
ning horizontally on the 0.25 depth line to meet the quantity
curve, the proportionate quantity at this depth is found to
be on the 0.13 vertical line, and the quantity of flow is
therefore 2 X0.13 = 0.26 cubic feet per second.

O.I 0.2 0.3 0.4 0.5 0.6 0.1 0.8 0.9 1.0 1.1 U
Hydraulic Elements in Terms of Hydraulic Elements for Full Section.

FIG. 19. — Hydraulic Elements of Circular Sections.

<i = 12'0" s = .0004 n = .015

d= I'O" s = .01 n = .013

Another problem, involving the reversal of this process is
illustrated by the following example :

Let it be required to determine the diameter and full
capacity of a vitrified pipe sewer on a grade of 0.002 if the
velocity of flow is 3.0 feet per second when the sewer is
discharging at 30 per cent of its full capacity, the depth of
flow being 12 inches. From Fig. 19 the depth of flow when
the sewer is carrying 30 per cent of its full capacity is 0 . 38
of its full depth. Since the partial depth is 12 inches

12
the full diameter is =31.6 inches. The velocity of

U . oo

flow at 38 per cent depth is 86 per cent of the full velocity.
Since the velocity given is 3.0 feet per second, the full

3 0
velocity is -^ = 3.5 feet per second. With a full ve-

.oO

locity of 3.5 feet per second and a diameter of 31.6 inches
from Fig. 16 the full capacity of the sewer is 18 cubic feet
. per second.

SECTIONS OTHER THAN CIRCULAR 67

39. Sections Other than Circular. — The ordinary shape used
for small sewers is circular. The difficulty of constructing large
sewers in a circular shape, special conditions of construction such
as small head room, soft foundations, etc., or widely fluctuating
conditions of flow have led to the development of other shapes.
For conduits flowing full at all times a circular section will carry
more water with the same loss of head than any other section
under the same conditions. In any section the smaller the flow
the slower the velocity, an undesirable condition. The ideal
section for fluctuating flows would be one that would give the
same velocity of flow for all quantities. Such a section is yet to
be developed. Sections have been developed that will give rela-
tively higher velocities for small quantities of flow than are given
by a circular section. The best known of these sections is the
egg shape, the proportions and hydraulic elements of which are
shown in Fig. 20. Other shapes that have the same property,
but which were not developed for the same purpose are the rect-
angular, the U-shape, and the section with a cunette. The egg-
shaped section has been more widely used than any other special
section. It is, however, more difficult and expensive to build
under certain conditions, and has a smaller capacity when full
than a circular sewer of the same area of cross-section. Various
sections are illustrated in Fig. 22 and 23.

The U-shaped section is suitable where the cover is small, or
close under obstructions where a flat top is desirable and the
fluctuations of flow are so great as to make advantageous a special
shape to increase the velocity of low flows. The proportions of a
U-shaped section are shown in Fig. 23 (6). Other sections used
for the same purpose are the semicircular and special forms of
the rectangular section.

The proportions and the hydraulic elements of the square-
shaped section are shown in Fig. 21. This is useful under low
heads where a flat roof is required to carry heavy loads, and the
fluctuations of flow are not large.

Sections with cunettes have not been standardized. A cunette
is a small channel in the bottom of a sewer to concentrate the low
flows, as shown in Fig. 22 (7). A cunette can be used in any
shape of sewer.

Sections developed mainly because of the greater ease of con-
struction under certain conditions are the basket handle, the gothic,

THE HYDRAULICS OF SEWERS

O.I

0 O.t 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 I.I 1.2
Hycfraulic Elements in Terms of Hydraulic Elements for Full Section

FIG. 20. — Hydraulic Elements of an Egg-shaped Section.
d = 6'y s = .00065 n = .015

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 I.I I.?
Hydraulic Elements in Terms of Hydraulic Elements fbrFull Section.

FIG. 21. — Hydraulic Elements of a Square Section.

s = .0004

n = .015

SECTIONS OTHER THAN CIRCULAR

the catenary, and the horse shoe. Some of these shapes are shown
in Fig. 22 and 23. They are suitable for large sewers on soft
foundations, where it is desirable to build the sewer in three
portions, such as, invert, side walls, and arch. They are also
suitable for construction in tunnels where the shape of the sewer
conforms to the shape of the timbering, or in open cut work where
the shape of the forms are easier to support.

Problems of flow in all sections can be solved by determining
the hydraulic radius involved, and substituting directly in the
desired formula, or by the use of one of the diagrams after con-
verting to the equivalent circular diameter. The determina-
tion of the hydraulic radius of these special sections is laborious,
and hence other less difficult methods are followed. Problems
are more commonly solved by converting the given data into an
equivalent circular sewer, solving for the elements of this cir-
cular sewer and then reconverting into the original terms, or by
working in the other direction. The hydraulic elements of vari-
ous sections when full are given in Table 18.

TABLE 18
HYDRAULIC ELEMENTS OF SEWER SECTIONS.

Vert.

Area

Dia. D

Hy-

in Terms

draulic

Terms

I v»u 1 nis in

Section

Vertical

terms of

Dia. d

Source

Diameter

Verticul

of Equiv-

Squared

DIA D

alent

j /iii . / ' .

Circular

Section

Circular

0.7854

0.250

1.000

Ear..

0.5150

. 1931

1.295

Eng. Record, Vol. 72: 608

Ovoid

0.5650

.2070

1.208

Eng. Record, Vol. 72: 608

Semi-elliptical

0.8176

.2487

1.041

Eng. News, Vol. 71 : 552

Catenary

0.6625

.2237

1.1175

Eng. Record, Vol. 72: 608

Horseshoe

0.8472

.2536

0.985

Eng. Record, Vol. 72: 608

Basket handle. .

0.8313

.2553

0.979

Eng. Record, Vol. 72 608

Rectangular

1.3125

2865

.7968

Hydraulic Dgins. and This.

Garrett

Square (3 sides wet) .

1.0000

.333

.7500

Eng. Record, Vol. 72: 608

Square (4 sides wet) .

1.0000

.250

1.0000

Eng Record, Vol. 72: 608

THE HYDRAULICS OF SEWERS

1. Standard Egg-shaped Section, North 2. Rectangular Section, Omaha, Nebraska,
Shore Intercepter, Chicago, Illinois. Eng. Contracting, Vol. 46, p. 49.

3. Trench in firm 4. Trench in

ground. Rock.

NOTE — Underdrains and Wedges to be
used only when Ordered by the
Engineer.

7. Brick and Concrete Sewer showing
cunette.

-IS',4 Rings fD
•— of Brick

Concrete

\ '-brave! or
Broken Stone/

5. Soft Founda-
tion.

6. Wet
ground.

t-3*K---i a—r\ i
13-10- — »J

8. Brick and Concrete Sewer, Evanston,
111., Eng. Contracting, Vol. 46, p. 227.

FlG. 22.

SECTIONS OTHER THAN CIRCULAR

PayLinefor

Excavation
and Concrete.

.. Pay Line for£xcoration , -

i^jt i (. Pay line -for
js-*".^-^ Concnte

1. Tunnel Sections. 2. Open Cut Sections.

Type A. Type B. Type C. Type D.

Where Rock is Where Rock is Where Rock is Where Rock 16' 6" Sewer. Where Rock
more than 16' more than 7' between drops below 25' Fill is above

above Spring- an less than Springing Line Springing Line Springing

ing Line. 16' above and 7' above on either Side. Line

Springing Line Springing Line
on both Sides, on both Sides.
Mill Creek Sewer, St. Louis, Eng. Record, Vol. 70, pp. 434, 435.

Limits of
Excavation

Soft Hard

Ground. Ground.

3. Circular Concrete Section in Soft and Hard
Ground, Eng. Record, Vol. 59, p. 570.

4. Semi-Elliptical Section, Louisville, Ky.,
Eng. News, Vol. 62, p. 416.

-36-3

v*T> M ir'

29 -o ->rk:

In Rock.

In Soft Ground.
5. Reinforced Concrete Sewer, Harlem Creek,
St. Louis, Eng. News, Vol. 60, p. 131.

FIG. 23.

-*-

-5 Vit. Bricks

6. U-Shaped Section, San Francisco,
Eng. News, Vol. 73, p. 310.

72 THE HYDRAULICS OF SEWERS

Equivalent sections are sections of the same capacity for the
same slope and coefficient of roughness. They have not neces-
sarily the same dimensions, shape, nor area. The diameter of
the equivalent circular section in terms of the diameter of each
special section shown is given in Table 18. The inside height of
a sewer is spoken of as its diameter.

For example let it be required to determine the rate of
flow in a 54-inch egg-shaped sewer on a slope of 0.001 when
n=.015. First convert to the equivalent circle. From

Table 18 the diameter of the equivalent circle is , nnp, times

1.295

the diameter of the egg-shaped sewer, which becomes in
this case 43 inches. From Fig. 16 the capacity of a circular
sewer of this diameter with S = 0.001 and n= .015 is 28
cubic feet per second, which by definition is the flow in the
egg-shaped sewer.

As an example of the reverse process let it be required
to find the velocity of flow in an egg-shaped sewer flowing
full and equivalent to a 48-inch circular sewer. Both sewers
are on a slope of 0 . 005 and have a roughness coefficient of
n= .015. It is first necessary to find the quantity of flow
in the circular sewer, which by definition is the quantity of
flow in the equivalent egg-shaped sewer. The velocity of
flow in the egg-shaped sewer is found by dividing this
quantity by the area of the egg-shaped section. As read
from the diagram the quanity of flow is 90 cubic feet per
second. From Table 18 the area of the egg-shaped sewer is
0 . 5 ID2 where D is the diameter of the egg-shaped sewer, and
D = 1 . 295d where d is the diameter of the equivalent cir-
cular sewer. Therefore the area equals (0 . 5 1 ) X ( 1 . 295 X 4)2

= 13.5 square feet and the velocity of flow is 10 _ =6.7

lo.o

feet per second. This is slightly less than the velocity
in the circular section.

Some lines for egg-shaped sewers have been shown on Fig. 17
by which solutions can be made directly. For other shapes, and
for sizes of egg-shaped sewers not found on Fig. 17 the preceding
method or the original formula must be used for solution. Prob-
lems in partial flow in special sections are solved similarly to
partial flow in circular sections, by converting first to the condi-
tions of full flow or by working in the opposite direction.

40. Non-uniform Flow. — In the preceding articles it is assumed
that .the mean velocity and the rate of flow past all sections are

NON-UNIFORM FLOW 73

constant. This condition is known as steady, uniform flow. In
this article it will be assumed that conditions of steady non-
uniform flow exist, that is, the rate of flow past all sections is
constant, but the velocity of flow past these sections is different
for different sections. Under such conditions the surface of the
stream is not parallel to the invert of the channel. If the velocity
of flow is increasing down stream the surface curve is known as
the drop-down curve. If the velocity of flow is decreasing down
stream the surface curve is known as the backwater curve. The
hydraulic jump represents a condition of non-uniform flow in
which the velocity of flow decreases down stream in such a manner
that the surface of the stream stands normal to the invert of the
channel at the point where the change in velocity occurs. Above
and below this point conditions of uniform flow may exist.

Conditions of non-uniform flow exist at the outlet of all sewers,
except under the unusual conditions where the depth of flow hi
the sewer under conditions of steady, uniform flow with the given
rate of discharge would raise the surface of water in the sewer, at
the point of discharge, to the same elevation as the surface of the
body of water into which discharge is taking place. By an appli-
cation of the principles of non-uniform flow to the design of out-
fall sewers, smaller sewers, steeper grades, greater depth of cover,
and other advantages can be obtained.

The backwater curve is caused by an obstruction in the sewer,
by a flattening of the slope of the invert, or by allowing the sewer
to discharge into a body of water whose surface elevation would
be above the surface of the water in the sewer, at the point of
discharge, under conditions of steady, uniform flow with the given
rate of discharge.

The drop-down curve is caused by a sudden steepening of the
slope of the invert; by allowing a free discharge; or by allowing a
discharge into a body of water whose surface elevation would be
below the surface of the water in the sewer, at the point of dis-
charge, under conditions of steady, uniform flow with the given
rate of discharge. The last described condition is common at
the outlet of many sewers, hence the common occurrence of the
drop-down curve.

The hydraulic jump is a phenomenon which is seldom consid-
ered in sewer design. If not guarded against it may cause trouble
at overflow weirs and at other control devices, in grit chambers,

74 THE HYDRAULICS OF SEWERS

and at unexpected places. The causes of the hydraulic jump
are sufficiently well understood to permit designs that will avoid
its occurrence, but if it is allowed to occur the exact place of the
occurrence of the jump and its height are difficult, if not impos-
sible, to determine under the present state of knowledge con-
cerning them. The hydraulic jump will occur when a high veloc-
ity of flow is interrupted by an obstruction in the channel, by a
change in grade of the invert, or the approach of the velocity to
the " critical " velocity. The " critical " velocity is equal to
V0S, where h is the depth of flow and g is the acceleration due to
gravity. The velocity in the channel above the jump must be
greater than Vghi, where hi is the depth of flow in the channel
above the jump. The velocity in the channel below the jump
must be greater than Vgrfo, where /i2 is the depth of flow below
the jump. The jump will not take place unless the slope of the

invert of the channel is greater than -^, in which C is the coeffi-

cient in the Chezy formula. With this information it is possible
to avoid the jump by slowing down the velocity by the installation
of drop manholes, flight sewers, or by other expedients.

The shape of the drop-down curve can be expressed, in some
cases, by mathematical formulas of more or less simplicity,
dependent on the shape of the conduit. The formula for a circu-
lar conduit is complicated. Due to the assumptions which must be
made in the deduction of these formulas, the results obtained by
their use are of no greater value than those obtained by approxi-
mate methods. A method for the determination of the drop-
down curve is given by C. D. Hill.1 In this method it is necessary
that the rate of flow past all sections shall be the same.; that the
depth of submergence at the outlet shall be known; and that the
depth of flow at some unknown distance up the stream shall be
assumed. The shape and material of construction of the sewer
and the slope of the invert should also be known. The problem is
then to determine the distance between cross-sections, one where
the depth of flow is known, and the other where the depth of flow
has been assumed. This distance can be expressed as follows:

T_(d2-d1)-(Hl-H2)_d'-H'
S-Si S' '

1 Municipal and County Engineering, Vol. 58, 1920, p. 164.

NON-UNIFORM FLOW

in which L = the distance between cross-sections;

d\ = the depth of flow at the lower section;

c?2 = the depth of flow at the upper section;
HI = the velocity head at the lower section;
#2 = the velocity head at the upper section;

*S = the hydraulic slope of the stream surface;

<Si = the slope of the invert of the sewer.

In order to solve such problems with a satisfactory degree of
accuracy the difference between d\ and cfe should be taken suffi-
ciently small to divide the entire length of the sewer to be investi-
gated into a large number of sections. The solution of the prob-
lem requires the determination of the wetted area, the hydraulic
radius, and other hydraulic elements at many sections. The
labor involved can be simplified by the use of diagrams, such as
Fig. 19, or by specially prepared diagrams such as those accom-
panying the original article by C. D. Hill. The solution of the
problem can be simplified by tabulating the computations as
follows:

DROP-DOWN CURVE COMPUTATION SHEET

Uniform discharge. Varying depth

Q- A. V=<>= *- L-*^-'
A 61

1.3

Depth

di-f/i

Elevation

</i

Sewer

W. L.

At the head of the computation sheet should be recorded the
diameter of the sewer in feet, the assumed volume of flow, the
area of the full cross-section of the sewer, the velocity of the
assumed volume flowing through the full bore of the sewer, and
the gradient or slope of the invert. In the 1st column enter the

76 THE HYDRAULICS OF SEWERS

assumed depth in decimal parts of the diameter for each cross-
section; in the 2nd column enter the same depth in feet; in the
3rd column enter the difference in feet between the successive
cross-sections; in the 4th column enter the hydraulic radius
corresponding to the depth at each cross-section ; in the 8th column
enter the velocity, equal to the volume divided by the wetted
area, for each cross-section; in the 5th column enter the cor-
responding velocity head; in the 6th column enter the difference
between the velocity heads at successive cross-sections; in the
7th column enter the difference between the quantities in the
third and in the sixth columns; in the 9th column enter the hydrau-
lic slope corresponding to the velocity and hydraulic radius of
each cross-section; in the 10th column enter the difference between
the hydraulic slope and the slope or gradient of the sewer; in the
llth column enter the computed distance between successive
cross-sections; in the 12th column enter the elevation of the
bottom of the sewer at each cross-section; and in the 13th column
enter the corresponding elevation of the surface of the water.

The table should be filled in until the distance to the required
section is determined, or if the distance is known, it should be
filled in until the depth of flow with the assumed rate of discharge
has been checked.

If only the depth of flow at some section is known and it is
required to know the maximum rate of flow with a free discharge,
or a discharge with a submergence at the outlet less than the
depth of flow with the maximum rate of discharge, it is necessary
to make a preliminary estimate of the maximum rate of flow in
order to fill in the quantity Q at the head of the table. The
procedure should be as follows;

1st. Assume a depth of flow at the outlet.

2nd. Compute the area (A) and the hydraulic radius (R)
at the known section and at the outlet.

3rd. Determine the area and the hydraulic radius half way
between these two sections as the mean of the areas
and the hydraulic radii of the two sections.

4th. Determine the rate of flow through the sewer from the
condition that the difference in head at the two
sections is the head lost due to friction caused by
the average velocity of flow between the sections

(IV2\ (

equals ^5 ) plus the gain in velocity head ( equals

NON-UNIFORM FLOW 77

— Vi2

j , which when combined and transposed

result in the expression :

/ 2Rgh

Q-AAlA2\2Al2A22gl+(A1-A2)(A2C2R)

in which Q = rate of flow;

A =the area determined in the 3rd step;

AI = the area at the upper cross-section;

_A2 = the area at the lower cross-section;

C =the coefficient in the Chezy formula;

g = the acceleration due to gravity;

h =the difference in elevation of the surface of the

stream at the two cross-sections;
I =the distance between the cross-sections;
R = the hydraulic radius determined in the third step.
5th. Continue this process by assuming different depths at
the outlet until the maximum rate of discharge has
been found by trial.

With this rate of discharge and depth of flow at the outlet, the
depth of flow at the known section can be checked. If appreci-
ably in error a correction should be made by the assumption of
a diiferent depth of flow at the outlet. The approximate character
of the method is scarcely worthy of the refinement in the results
which will be obtained by checking back for the depth of flow at
the known section. It will be sufficiently accurate to assume
the rate of flow obtained by trial from the preceding expression,
as the maximum rate of discharge from the sewer.

CHAPTER V
DESIGN OF SEWERAGE SYSTEMS

41. The Plan. — Good practice demands that a compre-
hensive plan for a sewerage system be provided for the needs of a
community for the entire extent of its probable future growth,
and that sewers be constructed as needed in accordance with
this plan.

Sewerage systems may be laid out on any one of three systems:
separate, storm, or combined. A separate system of sewers is
one in which only sanitary sewage or industrial wastes or both
are allowed to flow. Storm sewers carry only surface drainage,
exclusive of sanitary sewage. Combined sewers carry both
sanitary and storm sewage. The use of a combined or a separate
system of sewerage is a question of expediency. Portions of the
same system may be either separate, combined, or storm sewers.

Some conditions favorable to the adoption of the separate
system are where:

a. The sanitary sewage must be concentrated at one
outlet, such as at a treatment plant, and other outlets
are available for the storm drainage.

6. The topography is flat necessitating deep excavation,
and steeper grades for the larger combined sewers.

c. The sanitary sewers must be placed materially deeper
than the necessary depth for the storm water drains.

d. The sewers are to be laid in rock, necessitating more
difficult excavation for the larger combined sewers.

e. An existing sewerage system can be used to convey
the dry weather flow, but is not large enough for the storm
sewage.

/. The city finances are such that the greater cost of the
combined system cannot be met and sanitary drainage is
imperative.

g. The district to be sewered is an old residential section
where property values are not increasing and the assess-
ment must be kept down.

PRELIMINARY MAP

Some additional points given in a report by Alvord and Burdick
to the city of Billings, Montana, are:

The separate system of sewerage should be used, where:

1st. Storm water does not require extensive under-
ground removal, or where it can be concentrated in a few
shallow underground channels:

2nd. Drainage areas are short and steep facilitating
rapid flow of water over street surfaces to the natural water
courses.

3rd. The sanitary sewage must be pumped.

4th. Sewers are being built in advance of the city's
development to encourage its growth.

5th. The existing sewer is laid at grades unsuitable for
sanitary sewage, it can be used as a storm sewer.

A combined system must be relatively larger than a
separate storm sewer as the latter may overflow on ex-
ceptional occasions, but the former never.

A combined system of sewerage should be used where:
1st. It is evident that storm and sanitary sewerage
must be provided soon.

2nd. Both sanitary and storm sewage must be pumped.
3rd. The district is densely built up.

42. Preliminary Map. — The first step in the design of a sewer-
age system is the preparation of a map of the district to be served
within the limits of its probable growth. The map should be on
a scale of at least 200 feet to the inch in the built up sections or
other areas where it is anticipated that sewers may be built, and
where much detail is to be shown a scale as large as 40 feet to the
inch may have to be used. The adoption of so large a scale will
usually necessitate the division of the city or sewer district into
sections. A key map should be drawn to such a scale that the
various sections represented by separate drawings can all be
shown upon it. In preparing the enlarged portions of the map
it is not necessary to include these portions of the city in which
it is improbable that sewers will be constructed, such as parks and
cemeteries.

The contour interval should depend on the character of the
district and the slope of the land. In those sections drawn to a
scale of 200 feet to the inch for slopes over 5 per cent, the contour
interval need not be closer than 10 feet. For slopes between 1 and
5 per cent the contour interval should be 5 feet. For flatter

80 DESIGN OF SEWERAGE SYSTEMS

slopes the interval should not exceed 2 feet, and a one foot interval
is sometimes desirable. In general the horizontal distances
between contours should not exceed 400 feet and they should be
close enough to show important features of the natural drainage.
Elevations should also be given at street intersections, and at
abrupt changes in grade. For portions of the map on a smaller
scale the contours need be sufficiently close to show only the
drainage lines and the general slope of the land.

The following may be shown on the preliminary map: the
elevation of lots and cellars; the character of the built up districts,
whether cheap frame residences, flat-roof buildings, manufacturing
plants, etc.; property lines; width of streets between property
lines and between curb lines; the width and character of the
sidewalks and pavements; street car and railroad tracks; exist-
ing underground structures such as sewers, water pipes, telephone
conduits, etc.; the location of important structures which may
have a bearing on the design of the sewers such as bridges, rail-
road tunnels, deep cuts, culverts, etc.; and the location of possible
sewer outlets and the sites for sewage disposal plants.

Fig. 24 shows a preliminary map for a section of a city, on
which the necessary information has been entered. The map is
made from survey notes. All streets are paved with brick. The
alleys are unpaved. The entire section is built up with high-class
detached residences averaging one to each lot. The lots vary from
1 to 3 feet above the elevation of the street.

43. Layout of the Separate System. — Upon completion of the
preliminary map a tentative plan of the system is laid out. The
lines of the sewer pipe are drawn in pencil, usually along the center
line of the street or alley in such a manner that a sewer will be
provided within 50 feet or less of every lot. The location of the
sewers should be such as to give the most desirable combination
of low cost, short house connections, proper depth for cellar drain-
age, and avoidance of paved streets. Some dispute arises among
engineers as to the advisability of placing pipes in alleys, although
there is less opposition to so placing sewers than any other utility
conduit. The principal advantage in placing sewers in alleys is
to avoid disturbing the pavement of the street, but if both street
and alley are paved it is usually more economical to place the
sewer in the street as the house connections will be shorter. On
boulevards and other wide streets such as Meridian Avenue in

LOCATION AND NUMBERING OF MANHOLES 81

Fig. 24, the sewers are placed in the parking on each side of the
street, rather than to disturb the pavement and lay long house
connections to the center of the street.

All pipes should be made to slope, where possible, in the direc-
tion of the natural slope of the ground. The preliminary layout
of the system is shown in Fig. 24. The lowest point in the portion
of the system shown is in the alley between Alabama and Tennessee
Streets. The flow in all pipes is towards this point, and only
one pipe drains away from any junction, except that more than
one pipe may drain from a terminal manhole on a summit.

44. Location and Numbering of Manholes. — Manholes are
next located on the pipes of this tentative layout. Good practice
calls for the location of a manhole at every change in direction,
grade, elevation, or size of pipe, except in sewers 60 inches in diam-
eter or larger. The manholes should not be more than 300 to 500
feet apart, and preferably as close as 200 to 300 feet. In sewers
too small for a man to enter the distance is fixed by the length of
sewer rods which can be worked successfully. In the larger
sewers the distances are sometimes made greater but inadvisedly
so, since quick means of escape should be provided for workmen
from a sudden rise of water in the sewer, or the effect of an asphyx-
iating gas. In the preliminary layout the manholes are located
at pipe intersections, changes in direction, and not over 300 to
500 feet apart on long straight runs at convenient points such as
opposite street intersections where other sewers may enter.

No standard system of manhole numbering has been adopted.
A system which avoids confusion and is subject to unlimited
extension is to number the manholes consecutively upwards from
the outlet, beginning a new series of numbers prefixed by some
index number or letter for each branch or lateral. This system
has been followed with the manholes on Fig. 24.

45. Drainage Areas. — The quantity of dry weather sewage is
determined by the population rather than the topography. Lot
lines and street intersections or other artificial lines marking the
boundaries between districts are therefore taken as watershed
lines for sanitary sewers. The quantity of sewage to be carried
and the available slope are the determining factors in fixing the
diameter of the sewer. Since there may be no change in diameter
or slope between manholes the quantity of sewage delivered by a
sewer into any manhole will determine the diameter of the sewer

DESIGN OF SEWERAGE SYSTEMS

LAYOUT OF THE SEPARATE SYSTEM

84 DESIGN OF SEWERAGE SYSTEMS

between it and the next manhole above. In order to determine
the additional amount contributed between manholes a line is
drawn around the drainage area tributary to each manhole.
This line generally follows property lines and the center lines of
streets or alleys, its position being such that it includes all the
area draining into one manhole, and excludes all areas draining
elsewhere. An entire lot is usually assumed to lie within the
drainage area into which the building on the lot drains. In
laying out these areas it is best to commence at the upper end of a
lateral and work down to a junction. Then start again at the
upper end of another lateral entering this junction, and continue
thus until the map has been covered.

The areas are given the same numbers as the manholes into
which they drain. The dividing lines for the drainage areas on
Fig. 24 are shown as dot and dash lines, and the areas enclosed are
appropriately numbered. If more than one sewer drains into
the same manhole the area should be subdivided so that each
subdivision encloses only the area contributing through one
sewer. Such a condition is shown at manhole C2. The areas
are designated by subletters or symbols corresponding to the
symbol used for the sewer into which they drain. For example,
the two areas contributing to manhole C2 are lettered C2K and
C2z>. The sewer from manhole C3 to C2 receives no addition, it
being assumed that all the lots adjacent to it drain into the sewer
on the alley. There is therefore no area C2. Likewise there is
no area Alc.

46. Quantity of Sewage. — The remaining work in the compu-
tation of the quantity of sewage is best kept in order by a tabula-
tion. Table 19 shows the computations for the sewers discharging
from the east into manhole No. 142. The computation should
begin at the upper end of a lateral, continue to a junction, and then
start again at the upper end of another lateral entering this junc-
tion. Each line in the table should be filled in completely from
left to right before proceeding with the computations on the next
line. In the illustrative solution in Table 19, computations for
quantity have not been made between manholes where it was
apparent that there would be an insufficient additional quantity
to necessitate a change in the size of the pipe.

In making these computations the assumptions of quantity
and other factors given below indicate the sort of assumptions

QUANTITY OF SEWAGE 85

which must be made, based on such studies as are given in Chapter
III. The density of population was taken as 20 persons per acre,
the assumption being based on the census and the character of
the district. The average sanitary sewage flow was taken as
100 gallons per capita per day. The per cent which the maximum

500
dry weather flow is of the average was taken as M = p^-, in which

P is the population in thousands. The per cent is not to exceed
500 nor to be less than 150. The rate of infiltration of ground
water was assumed as 50,000 gallons per mile of pipe per day.

In the first line of Table 19, the entries in columns (1) to (6)
are self-explanatory. There are no entries in columns (7) to (10),
as no additional sewage is contributed between manholes 3.5 and
3.4. In column (11), 2250 persons are recorded as the number
tributary to manhole No. 3.5 in the district to the north and west.
These people contribute an average of 100 gallons per person per
day, or a total of 0.346 second foot. This quantity is entered in
column (13). The figure in column (14) is obtained from the

500
expression M = p^-. Column (15) is .01 of the product of columns

(13) and (14). Column (16) is the product of the length of pipe
between manholes 3.5 and 3.4, and the ground water unit reduced
to cubic feet per second. Column (17) is the sum of column (16),
and all of the ground water tributary to manhole 3.5, which i?
not recorded in the table. Column (18) is the pum of columns
(15) and (17).

No new principle is represented in the second and third lines.

In the fourth line the first 10 columns need no further explana-
tion. The (llth) column is the sum of the (10th) column, and the
(llth) column in the third line. It represents the total number
of persons tributary to manhole 3.4 on lateral No. 8. Column
(13) in the fourth line is the sum of column (13) in the third line
and the (12th) column in the fourth line, and the (15th) column
in the fourth line is the product of the 2 preceding columns in the
fourth line. Note that in no case is the figure in column (15)
the sum of any previous figures in column (15). With this intro-
duction the student should be able to check the remaining figures
in the table, and should compute the quantity of sewage entering
manhole No. 142 from the west, making reasonable assumptions
for the tributary quantities from beyond the limits of the map.

DESIGN OF SEWERAGE SYSTEMS

TABLE

COMPUTATIONS FOR QUANTITY OF SEWAGE

On Street

From Street

To Street

From
Man-
hole

To
Man-
hole

Length
Feet

Mark
of
Added
Areas

Nebraska St

Map margin

Alley S. Grant St. . .

3.5

3.4

338

Alley S of Grant St .

Railroad

E. of Missouri St

8 3

8 2

328

8 2

Alley S.of Grant St.
Alley S.of Grant St.

E. of Missouri St. . .
E. of Kansas St . . . .

E. of Kansas St. ...
Nebraska St

8.2
8 1

8.1
3 4

355
340

8.1
3 4s

Nebraska St

Alley S. of Grant St.

Alley S. of Meridian.

3.4

3.3

380

Nebraska St

7 2

3 3

800

7.1
3 3?

Nebraska St

Alley S. Meridian. . .

Alley S. of Smith Av.

3.3

3.2

304

Alley S.of Smith Ave.
Nebraska St

Railroad
Alley S. of Smith Ave.

Nebraska St
S. of Cordovez St. . .

6.2
3. '2

3.2
3.1

609
300

6.1
3.2,

S of Cordovez St

4 1

3 1

410

3 14

S of Cordovez St

5 1

3 1

380

3 U

Nebraska St

S of Cordovez St.

3 1

148

172

Long St

Map margin

Nebraska St

149

148

380

148

Long St

Nebraska St

N Carolina St

148

147

492

Long St

N Carolina St . .

147

146

430

Long St
Long St

Georgia St
Harris St

Harris St
Tennessee St

146
145

145
143

419
725

146
2.1

143-145

Column No. (1)

(2)

(3)

(4)

(5)

(6)

(7)

* Industrial waste.

TABLE

COMPUTATIONS FOR SLOPE AND DIAMETER OF

On Street

From Street

To Street

From
Man-
hole

Man-
hole

Length,
Feet

Nebraska St

Alley S. of Grant St. .

3 5

3 4

338

Alley S. of Grant St .

Railroad

East of Missouri St . .

8 3

8.2

328

Alley S. of Grant St .
Alley S of Grant St

East of Missouri St .

East of Kansas St. . . .
Nebraska St . .

8.2
8 1

8.1
3 4

355
340

Nebraska St. . . . . . .

Alley S. of Grant St.

Alley S. of Meridian. .

3.4

7 2

3.3

7 1

380
400

Alley S of Meridian

Nebraska St ...

7.1

3.3

400

Nebraska St . . .

Alley S. of Meridian.

Alley S. of Smith Ave.

3.3

3.2

304

AlleyS of Smith Ave

6 2

6.1

305

AlleyS of Smith Ave

Nebraska St

6.1

3.2

304

Nebraska St

Alley S. of Smith Ave.

Alley S. of Cordovez. .
Nebraska St

3.2
5.1

3.1

300
380

Alley S of Cordovez

Nebraska St

4.1

3.1

410

Nebraska St

Long St'

3 1

148

172

Long St

Nebraska St

149

148

380

Long St. . .
Long St

Nebraska St
North Carolina St . .

North Carolina St . . .
Georgia St

148

147

147
146

492
430

Long St

Georgia St

Harris St

146

145

419

Alley S of Janis St

2.2

2.1

350

Harris St.

Alley N of Janis St.

Long St

2.1

145

135

Long St
Long St
Tarbell Ave

Harris St
Kentucky St

Kentucky St
Tennessee St
Long St

145
144
1.1

144
143
143

258

282
417

Long St

Alley W. of Tenn. St..

143

142

185

Column No. (1)

(2)

(3)

(4)

(5)

(6)

QUANTITY OF SEWAGE

FOR A SEPARATE SEWERAGE SYSTEM

Cumu-

Per

Incre-

Area.
Acres

Popu-
lation
per
Acre

Num-
ber
of
Per-
sons

Total
Per-
sona
Tribu-
tary

£v*
Sani-
tary
Flow,
C.F.S.

lative
Avg.
Sani-
tary
Flow,

cent
Max.
Sani-
tary
is of

Total
Max.
Sani-
tary,
C.F.S.

ment
of
Ground
Water,
Cv <a

Cumu-
lative
Ground
Water,
C.F.S.

Total
Flow,
C.F.S.

Lino,
Num-
ber

C.F.S.

Average

.r .0.

2250

O.(MMM)

0.346

425

1.47

0.005

0.0187

1.66

2.7

'26

'54

.0084

500

0.041

.0048

0.046

3.41

122

.0106

.0190

500

0.095

.0052

.010

0.105

2.68

176

.0084

.0274

500

0.137

.0050

.015

0.152

2426

.0000

.373

423

1.58

.0056

.208

1.79

7.14

142

.0221

500

0.111

.0117

0.123

2568

.0000

.395

414

1.63

.0045

.224

1.85

3.82

.0119

500

0.060

.0089

0.069

2644

.0000

.407

414

1.68

.0044

.237

1.92

s.'io

"62

.0096

500

0.048

.006

0.054

2.69

.0084

.(K)S:1

500

0.042

.0056

0.048

2760

.0000

.425

409

1.74

.0025

.251

1.99

iiss

'20

"si

.0048

500

0.024

.0056

0.030

2791

.0000

.430

409

1.76

.0072

.264

2.02

2791

1 000*

.430

400

1.76

.0064

1.27

3.03

6!si

"ie

2807

.0025

.433

407

1.76

.0061

1.28

3.04

6.6

132

2936

.0205

.454

403

1 83

.024

1.30

3.13

(8)

(9)

(10)

(11)

(12)

(13)

(14)

(15)

(16)

(17)

(18)

Treated as ground water.

PIPES FOR A SEPARATE SEWERAGE SYSTEM

El. of Surface

Total
Flow,
C.F.S.

Slope

Dia.
of
Pipe,
Inches

Velocity
when
Full,
Ft. per
Second

Capacity
when
Full.
Second
Feet

El. of Invert

Line
Number

Upper
Man-
hole

Lower
Man-
hole

Upper
Manhole

Lower
Manhole

105.8
113.5
112.0
107.7
102.4
111.8
107.0
100.7
109.3
105.3
99.3
100.8
104.6
101.1
103.8
98.7
103.8
99.1
105.2
98.1
96.9
94.4
98.7
92.6

(7)

102.4
112.0
107.7
102.4
100.7
107.0
100.7
99.3
105.3
99.3
101.1
101.1
101.1
98.7
98.7
103.8
99.1
96.9
98.1
96.9
94.4
92.6
'.»•-' ti

IB. a

(8)

1.66
0.046
0.105
0.152
1.79

0.0108
.00575
.0110
.0156
.oo:<s.-,
.0120
.0157
.0042
.0131
.0197
.00213
.00574
.00854
.00213
.0134
.00213
.0016
.0016
.0203
.0088
.00353
00085
.0146
.0016

(10)

10
8
8
8
12
8
8
12
8
8
15
8
8
15
8
15
18
18
8
8
18
18
8
18

(11)

3.25
2.00
2.78
3.27
2.28
2.90
3.28
2.36
3.00
3.70
2.00
2.00
2.46
2.00
3.04
2.00
2.00
2.00
3.78
2.53
2.98
4.00
3.18
2.00

(12)

1.78
0.71
0.98
1.18
1.79
1.03
1.18
1.85
1.08
1.32
2.45
0.71
0.87
2.45
1.08
2.45
3.50
3.50
1.35
0.89
5.20
7.00
1.14
3.50

(13)

97.80
105.50
103.61
99.69
94.07
103 . 80
98.99
92.37
101.30
97.29
90.84

'.)!>., SO

96.60
90.04
95.80
BB.Sfl

NX. H'.l

87.99
97.20
90.09
87.31
86.39
90.70
83.77

(14)

94.40
103.62
99.70
94.40
92.61
99.00
92.70
91.09
97.30
91.30
90.20
90.62
93.10
89.87
90.70
88.94
88.00
87.32
90. 10

SS.(H)

86.40
84.60
84.60
83.47

(15)

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24

0.123
1.85

0.069
1.92

0.054
1.99
0.030
2.02
3.03
3.04

3.13
(9)

88 DESIGN OF SEWERAGE SYSTEMS

47. Surface Profile. — A profile of the surface of the .ground
along the proposed lines of the sewers should be drawn after the
completion of the computations for quantity. An example of a
profile is shown in Fig. 26 for the line between manholes No. 3.5
and No. 147. The vertical scale should be at least 10 times the
horizontal. A horizontal scale of 1 inch to 200 feet can be used
where not much detail is to be shown, but a scale of one 1 to
100 feet is more common and more satisfactory and even one inch
to 10 feet has been used. The information to be given and the
method of showing it are illustrated on Fig. 26. The profile
should show the character of the material to be passed through
and the location of underground obstacles which may be encoun-
tered. The method of obtaining this information is taken up in
Chapter II. The collection of the information should be com-
pleted as far as possible previous to design, and borings and other
investigations made as soon as the tentative routes for the sewers
have been selected.

48. Slope and Diameter of Sewers. — After the quantity of
sewage to be carried has been determined, and the profile of the
ground surface has been drawn, it is possible to determine the
slope and diameter of the sewer. A table such as No. 20 is made
up somewhat similar to No. 19, or which may be an extension of
Table 19 since the first 6 columns in both tables are the same.
The elevation of the surface at the upper and lower manholes is
read from the profile.

The depth of the sewer below the ground surface is first
determined. Sewers should be sufficiently deep to dram cellars
of ordinary depth. In residential districts cellars are seldom more
than 5 feet below the ground surface. To this depth must be
added the drop necessary for the grade of the house seweri Six-
inch pipe laid on a minimum grade of' 1.67 per cent is a common
size and slope restriction for house drains or sewers. An addi-
tional 12 inches should be allowed for the bends in the pipe and
the depth of the pipe under the cellar floor. Where the eleva-
tion of the street and lots is about the same, and the street is not
over 80 feet in width between property lines, a minimum depth
of 8 feet to the invert of sewers, 24 inches or less in diameter is
satisfactory. This is on the assumption that the axes of the
house drain and the sewer intersect. For larger pipes the depth
should be increased so that when the street sewer is flowing full,

SURFACE PROFILE

90 DESIGN OF SEWERAGE SYSTEMS

sewage will not back up into the cellars or for any great distance
into the tributary pipes.

The grade or slope at which a sewer shall lie may be fixed by :
the slope of the ground surface; the minimum permissible self-
cleansing velocity; a combination of diameter, velocity, and
quantity; or the maximum permissible velocity of flow. Sewers
are laid either parallel to the ground surface where the slope is
sufficient or where possible without coming too near the surface
they are laid on a flatter grade to avoid unnecessary excavation.
The minimum permissible slope is fixed by the minimum permis-
sible velocity.

The velocity of flow in a sewer should be sufficient to prevent
the sedimentation of sludge and light mineral matter. Such a
velocity is in the neighborhood of 1 foot per second. Since
sewers seldom flow full this velocity should be available under
ordinary conditions of dry weather flow. The minimum velocity
when full should therefore be about 2 feet per second. Under
this condition, the velocity of 1 foot per second is not reached
until the sewer is less than 18 per cent full. The velocity in small
sewers should be made somewhat faster than in large sewers
since the velocity of flow for small depths in small pipes is less
than for the same proportionate depth in large pipes. The
maximum permissible velocity of flow is fixed at about 10 feet
per second in order to avoid excessive erosion of the invert. If the
sewer is carefully laid this limit may be exceeded in sanitary sewers.

The method for determining the grade and diameter of sewers
is best explained through an illustrative problem which is worked
out in Table 20 for the profile shown on Fig. 26. The figures
are inserted in the table from left to right in each line, one line
being completed before the next one is commenced. The head-
ings in the first 6 columns are self-explanatory. The elevations
of the surface at the upper and lower manholes are read from the
profile. The total flow is read from column (18) in Table 19.
The slope of the ground surface is then computed, and with the
quantity, slope, and coefficient of roughness, the diameter of the
pipe and the velocity of flow are read from Fig. 15.

The following conditions may arise:

(1) The diameter required is less than 8 inches. Use a
diameter of 8 inches as experience has shown that the use of
smaller diameters is unsatisfactory.

SLOPE AND DIAMETER OF SEWERS 91

(2) The velocity of flow when the sewer is full is less than
2 feet per second. Increase the slope until the velocity
when full is 2 feet per second.

(3) The diameter of the pipe required is not one of the
commercial sizes shown in Fig. 15. Use the next largest
commercial size.

(4) The slope of the ground surface is steeper than
necessary to maintain the required minimum velocity
and the upper end of the sewer is deeper than the required
minimum depth. Place the sewer on the minimum per-
missible grade, or upon such a grade that its lower end
will be at the minimum permissible depth.

(5) The slope of the ground surface is so steep as to
make the velocity of flow greater than the maximum rate
permissible. Reduce the grade by deepening the sewer at
the upper manhole and using a drop manhole at this point.

It is not permissible to use a pipe larger than that called for
by the above conditions. This is attempted sometimes in order
to reduce the grade and thereby save excavation, under the rule
of a minimum velocity of 2 feet per second when full. It is
better to use the smaller pipe on the flat grade as the quantity of
sewage is insufficient to fill the larger sewer and the minimum
permissible velocity is more quickly reached.

Having determined the slope, the diameter, and the capacity
of the pipe to be used, these values are entered in the table.
The elevations of the invert of the pipe at the upper and lower
manholes are next computed and entered in the table. This
method is followed until all of the diameters, slopes, and eleva-
tions have been determined.

The slopes are computed from center to center of manholes,
but an extra allowance of 0.01 of a foot is allowed by some design-
ers for the increased loss in head in passing through the manhole.
When it becomes necessary to increase the diameter of the sewer
the top of the outgoing sewer is placed at the same elevation or
below the top of the lowest incoming sewer. No extra allow-
ance is made to compensate for loss in head in the manhole in this
case. This case is illustrated in columns (14) and (15) in lines
(16) and (17) of Table 20. All of the conditions listed above are
illustrated in Table 20, except the condition for a velocity greater
than 10 feet per second.

The first condition is met at the head of practically every
lateral, and is illustrated in the second line.

92 DESIGN OF SEWERAGE SYSTEMS

The second condition is also illustrated in the second line.
The slope of the ground surface is 0.0046, which gives a velocity
of only 1.8 feet per second in an 8-inch pipe. The slope is there-
fore increased to 0.00575, on which the full velocity is 2 feet per
second.

The third condition is met in the first line. The diameter
called for to carry 1.66 cubic feet per second on a slope of 0.0108
is slightly less than 10 inches. A 10-inch pipe is therefore used
and its full capacity and velocity are recorded.

The fourth condition is illustrated in the fourteenth line.
The cut at manhole No. 3.1 is 11.1 feet. The slope of the ground
is 0.014, much steeper than is necessary to maintain the minimum
velocity in a 15-inch pipe. The pipe is therefore placed on the
minimum permissible slope, and excavation is saved. The student
should check the figures in Table 20 and be sure that they are
understood before an attempt is made to make a design inde-
pendently.

49. The Sewer Profile. — The profile is next completed as
shown in Fig. 26, the pipe line being drawn in as the computa-
tions are made. The cut is recorded to the nearest -roth of a foot
at each manhole, or change in grade. It should not be given else-
where as it invites controversy with the contractor. The cut is
the difference of the elevation of the invert of the lowest pipe in
the trench at the point in question, and the surface of the ground.

The stationing should be shown to the nearest roth of a foot.
It should commence at 0+00 at the outlet and increase up the
sewer. The station of any point on the sewer may show the dis-
tance from it to the outlet, or a new system of stationing may be
commenced at important junctions or at each junction.

Elevations of the surface of the ground should be shown to
the nearest iVth of a foot, and the invert elevation to the nearest
Tiro-th of a foot.

Only the main line sewer is shown in profile in Fig. 26. The
profiles of the laterals computed in Table 20, have not been shown.
The approximate location of all house inlets are shown on the
profile and located exactly, and are made a matter of record
during construction.

PLANNING THE SYSTEM 93

DESIGN OF A STORM WATER SEWER SYSTEM

50. Planning the System. — Storm sewer systems are seldom
as extensive as separate or combined sewer systems, since storm
sewage can be discharged into the nearest suitable point in a
flowing stream or other drainage channel, whereas dry weather
or combined sewage must be conducted to some point where its
discharge will be inoffensive. The need of a comprehensive
general plan of a storm sewer system is quite as great, however,
as for a separate system. The haphazard construction of sewers
at the points most needed for the moment results in the duplica-
tion of forgotten drains, expense in increasing the capacity of
inadequate sewers, and difficult construction due to underground
structures thoughtlessly located. A comprehensive plan permits
the construction of sewers where they are needed as they are
required, and enables all probable future needs to be cared for at a
minimum of expense.

The same preliminary survey, map, and underground informa-
tion are necessary for the design of a storm sewer system as for a
separate sewer system. The map shown on Fig. 25 has been used
for the design of a storm-water sewer system.

The steps in the design of a storm- water sewer system are:
1st. Note the most advantageous points to locate the inlets
and lay out the system to drain these inlets. 2nd. Determine
the required capacity of the sewers by a study of the run-off from
the different drainage areas. 3rd. Draw the profile and compute
the diameter and slope of the pipes required.

51. Location of Street Inlets. — The location of storm sewers
is determined mainly by the desirable location of the street inlets.
The inlets must therefore be located before the system can be
planned. In general the inlets should be located so that no water
will flow across a street or sidewalk, in order to reach the sewer.
This requires that inlets be placed on the high corners at street
intersections, in depressions between street intersections, and at
sufficiently frequent intervals that the gutters may not be over-
loaded. City blocks are seldom so long as to necessitate the loca-
tion of inlets between crossings solely on account of inadequate
gutter capacity. The capacity of a gutter can be computed
approximately by the application of Kutter's formula. Inlet
capacities are discussed in Chapter VI. When the area drained

94 DESIGN OF SEWERAGE SYSTEMS

is sufficiently large to tax the capacity of the gutter or inlet, an
inlet should be installed regardless of the location of the street
intersections.

The street inlets are located on the map as shown in Fig. 25.
The sewer lines are then located so as to make the length of pipe
to pass near to all inlets a minimum. Storm sewers are seldom
placed near the center of a street because of the frequent crowded
condition on this line.

52. Drainage Areas. — The outline of a drainage area is drawn
so that all water falling within the area outlined will enter the
same inlet, and water falling on any point beyond the outline will
enter some other inlet. This requires that the outline follow
true drainage lines rather than the artificial land divisions used
in locating the drainage lines in the design of sanitary sewers.
The drainage lines are determined by pavement slopes, location
of downspouts, paved or unpaved yards, grading of lawns and
the many other features of the natural drainage which are altered
by the building up of a city. The location of the drainage lines
is fixed as the result of a study of local conditions.

The watershed or drainage lines are shown on Fig. 25 by means
of dot and dash lines. A drainage line passes down the middle of
each street because the crown of the street throws the water to either
side and directs it to different inlets. A watershed line is drawn
about 50 feet west of such streets as Kentucky St., Florida St., etc.,
because the downspouts from the houses on those streets discharge
or will discharge into the street on which they face. The location
of any watershed line within 20 feet more or less is, in most
cases, a matter of judgment rather than exactness. Each area
is given an identifying number or mark which is useful only in
design. It usually corresponds to the inlet number.

53. Computation of Flood Flow by McMath Formula. —
McMath's Formula is used as an example of the method pursued
when an empirical formula is adopted for the computation of
run-off, and because of its frequent use in practice. Other formu-
las may be mbre satisfactory under favorable conditions.

Computations should be kept in order by a tabulation such as
is shown in Table 21, in which the quantity of storm flow discharged
from the sewer at the foot of Tennessee St., on Fig. 25, has been
computed by means of the McMath Formula, using the constants
suggested for St. Louis conditions, 2 = 2.75, and c=0.75. The

FLOOD FLOW BY RATIONAL METHOD 95

solutions of the formula have been made by means of Fig. 11.
The column headings in the Table are explanatory of the figures
as recorded. The computation should begin at the upper end
of a lateral, proceed to the first junction and then return to the
head of another lateral tributary to this junction. They should
be continued in the same manner until all tributary areas have
been covered. Special computations will be necessary for the
determination of the maximum quantity of storm water entering
each inlet to avoid the flooding of an inlet or gutter. These
computations have not been shown as they are so easily made by
the application of McMath's Formula to each area concerned.

The determination of the average slope ratio is a matter of
judgment, based on the average natural slope of the surface of
the ground and an estimate of the probable future conditions.

54. Computation of Flood Flow by Rational Method. — The
rational method for the computation of storm water run-off is
described in Chapter III. An example of its application to storm
sewer design is given here for the district shown in Fig. 25.1
The computations are shown in Table 21. As in the preceding
designs the table has been filled in from left to right and line by
line. Computations have started at the upper end of laterals
tributary to each junction. The column headed / represents the
imperviousness factor in the expression Q = A IR. It is based on
judgment guided by the constants given in Chapter III concern-
ing imperviousness. The column headed " Equivalent 100 per
cent 7 acres " is the product of the two preceding columns. It
reduces all areas to the same terms so that they can be added for
entry in the column headed " Total 100 per cent 7 acres." It
may be necessary to record the values for this column on several
lines where the imperviousnesses of the tributary areas are differ-
ent. This condition is illustrated in the last line of the table,
for the length of sewer nearest the outlet. In the preceding lines
the imperviousness recorded represents an average for all the
tributary areas.

The time of concentration in minutes is assumed by judgment
for the first area. For all subsequent areas it is the sum of the
time of concentration for the area or areas tributary to the inlet
next above and the time of flow in the sewer from the inlet next

1 For diagrams for the Solution of the Rational Method, see Eng. News-
Record, Vol. 83, 1919, p. 868 and Vol. 85, 1920, p. 151.

DESIGN OF SEWERAGE SYSTEMS

TABLE
COMPUTATIONS FOE THE QUANTITY OF STORM SEWAGE

On Street

From Street

To Street

Identifying
Number of Areas

By McMath's Formula

£
c

fa
U

Drained

1*8

^"2

•5 'a

< £
— *

Slope of

State

N. Carolina

S. Carolina. .

91 and 92

2.35

0.005

5.5

State

S. Carolina

Georgia

88, 89 and 90

3.0

5.35

.005

10.8

State

Georgia

Florida

85, 86 and 87

3.0

8.35

.007

16.5

State

Florida

Kentucky. . .

81, 83 and 84

3.0

11.35

.009

22.0

State
State

Kentucky
Texas

Tennessee. . .
Louisiana. . . .

79, 80 and 82
76 and others
73, 74 and 75
70, 71 and 72
68, 69, 77 and 78
65, 66 and 67
64 and 64a

3.0
3.8

3.7
3.0
4.3
2.8
0.7

14.35
3.8
7.5
10.5
29.15
2.8
29.85

.010
.005
.007
.006
.15
.018
.15

28.0
8.3
15.0
19.0
52
8.4
55

State

Louisiana
Alabama . • .

Alabama. . . .
Tennessee. . .
Talon
Tennessee. . .
Burnside ....

State

Tennessee. .
Talon

State
Albemarle
Talon

Tennessee . .

Burnside. . .

N. Carolina

S. Carolina. .

57, 58 and 59

2.84

.008

7.2

Burnside . . .

S. Carolina

Georgia

54, 55 and 56

3.88

6.72

.010

14.9

Burnside. . .

Georgia

Florida

50, 52 and 53

3.88

10.60

.012

Burnside. . .

Florida

Kentucky. . .

47, 48 and 51

3.88

14.48

.013

Burnside. . .

Kentucky

Tennessee. . .

44, 45 and 46

3.88

18.36

.013

Tennessee. .

Burnside

Elm

42 and 43

2.84

51.05

.015

Elm

Above Chetwood .

Chetwood . . .

Included in next line below

Elm
Elm

Chetwood
Albemarle
Elm

Albemarle. . .
Tennessee. . .
Varennes. . . .

31, 32 and 33
27, 28, 29 and 30
25, 26 and 41

2.75
5.75
2.62

2.75

8.50
62.17

.007
.016
.017

7.0
20
100

Tennessee. .

Varennes. . .

S. Carolina

Georgia

17, 18 and 19

3.17

.010

8.3

Varennes. . .

Georgia

Florida

14, 15 and 16

3.17

6.34

.011

14.5

Varennes. . .

Florida

Kentucky. . .

11, 12 and 13

3.17

9.51

.013

Varennes. . .

Kentucky

Tennessee. . .

8, 9 and 10

3.17

12.68

.013

Tennessee. .

Varennes

Boulevard . . .

6 and 7

2.32

77.17

.017

120

Tennessee . .

Boulevard

Outlet

1, 2, 3, 4 and 5

4.72

81.89

.017

122

above to the inlet in question. For example, in line 2 the time
8.1 minutes is the sum of 7.0 minutes time of concentration to
the inlet at the corner of State and North Carolina St., and the
time of flow of 1.1 minute in the sewer on State St. from North
Carolina St. to South Carolina St. Where two sewers are con-
verging as at the corner of Varennes Road and Tennessee St. the
longest time is taken. For example, the tune of concentration

FLOOD FLOW BY RATIONAL METHOD

AT THE FOOT OF TENNESSEE STREET ON FIGURE 25

By Rational Method

Line Number

•3

Equivalent
100 Per Cent
/ Acres

•

u 4)
l\

Til

J°

Time of Con-
centration,
Minutes

Sewer Length,
Feet

Time in Sewer

2.35

0.50

1.17

7.0

4.8

5.6

0.011

4.6

300

1.1

3.00

.50

1.50

2.67

8.1

4.6

12.2

.010

5.5

300

0.9

3.00

.50

1.50

4.17

9.0

4.4

18.3

.012

5.8

300

0.9

3.00

.50

1.50

5.67

9.9

4.2

23.9

.009

6.0

300

0.8

3.00

.50

1.50

7.17

10.7

4.1

29.3

.009

6.2

300

0.8

3.80

.35

1.33

10.0

4.2

5.6

.009

3.2

370

1.9

3.70

.40

1.48

2.81

11.9

3.9

11.0

.011

5.2

300

1.0

3.00

.45

1.35

4.16

12.9

3.8

15.8

.002

3.2

300

1.6

4.30

.50

2.15

13.48

14.5

3.6

48.5

.019

9.8

450

0.8

2.80

.40

1.12

8.0

4.6

5.2

.004

3.0

210

1.2

0.70

.20

0.14

14.74

15.3

3.5

51.5

.006

5.0

120

0.4

2.84

.55

1.56

10.0

4.2

6.5

.008

4.5

300

1.1

3.88

.55

2.13

3.69

11.1

4.0

14.8

.007

4.7

300

1.1

3.88

.55

2.13

5.82

12.2

3.9

22.7

.011

5.8

300

0.9

3.88

.55

2.13

7.95

13.1

3.7

29.4

.016

7.5

300

0.7

3.88

.55

2.13

10.08

13.8

3.7

37.3

.019

9.2

300

0.5

2.84

.45

2.28

26.10

15.7

3.4

88.8

.015

10.2

280

0.5

2.75

.40

1.10

8.0

4.6

5.1

.020

5.3

480

1.5

5.75

.45

2.59

3.69

9.5

4.3

15.8

.012

6.1

410

1.1

2.62

.50

1.31

30.00

16.2

3.4

102

.012

10.2

180

0.3

3.17

.55

1.74

9.0

4.4

7.7

.012

5.2

270

0.9

3.17

.55

1.74

3.48

9.9

4.2

14.6

.010

5.7

300

0.9

3.17

.55

1.74

5.22

10.8

4.1

21.4

.017

7.7

300

0.6

3.17

.55

1.74

6.96

11.4

4.0

27.8

.015

7.8

300

0.6

2.32
0.18
1.38
2.80
0.36

.55
.80
.50
.55
.75

1.28
0.14
0.69
1.54
0.27

32.84
Area

Arc;l

Areas
35.48

16.5
No. 1
No. 2
No. 3
16.9

3.3

108

.012

10.2

230

0.4

26
27
28
29
30

and 4
3.3

117

Areas

No. 1-5 inclua

ive

down Varennes Road to Tennessee St. is shown in line 25 as
11.4+0.6= 12.0 minutes. The time to the same point down Ten-
nessee St. is shown in line 21 as 16.2+0.3 = 16.5 minutes. This
time is therefore used in line 26.

R, the rate of rainfall in inches per hour is determined by
Talbot's formula.

Q, is in cubic feet per second and is the product of the 8th

DESIGN OF SEWERAGE SYSTEMS

and 10th columns. Since the 8th column is the sum of the prod-
ucts of the 5th and the 6th columns for the lines representing
tributary areas, then the llth column is the product of A, I, and R.

S, is the slope on which it is assumed that the sewer will be
laid. It is usually assumed as parallel to . the ground surface
unless the velocity for this slope becomes less than 2 feet per sec-
ond. In such a case the slope is taken as one which will cause
this velocity.

V, the velocity in feet per second, is computed from diagrams
for the solution of Kutter's formula. The length in feet is scaled
from the map as the distance between inlets or groups of inlets,
and the time is the length in feet divided by the velocity in feet
per minute.

Having computed the quantity of flow to be carried in the
sewer, the design is completed by. drawing the profile and com-
puting the diameters and slopes by the same method as used in
the design of separate sewers.

CHAPTER VI
APPURTENANCES

55. General. — The appurtenances to a sewerage system are
those devices which, in addition to the pipes and conduits, are
essential to or are of assistance in the operation of the system.
Under this heading are included such structures and devices
as: manholes, lampholes, flush-tanks, catch-basins, street inlets,
regulators, siphons, junctions, outlets, grease traps, foundations
and underdrains.

56. Manholes. — A manhole is an opening constructed in a
sewer, of sufficient size to permit a man to gain access to the sewer.
Manholes are the most common appurtenances to sewerage sys-
tems and are used to permit inspection and the removal of obstruc-
tions from the pipes. The details of the Baltimore standard
manholes are shown in Fig. 27 and a manhole on a large sewer in
Omaha is shown in Fig. 28. The features of these designs which
should be noted are the size of the opening and working space,
and the strength of the structure. Manhole openings are seldom
made less than 20 inches in diameter and openings 24 inches in
diameter are preferable. A man can pass through any opening
that he can get his hips through provided he can bend his knees
and twist his shoulders immediately on passing the hole. For this
reason the manhole should widen out rapidly immediately below
the opening, as shown in Fig. 27 and 38.

The walls of the manhole may be built either of brick or of
concrete. Brick is more commonly used, as the forms necessary
for concrete make the work more expensive unless they can be
used a number of times. The walls of the manhole should be at
least 8 inches thick. Greater thicknesses are used in treacherous
soils and for deep manholes, or to exclude moisture. A rough
expression for the thickness of the walls of a brick manhole more

d
than 12 feet deep in ordinary firm material is ^ = ^+2, in which t

100

APPURTENANCES

is the thickness in inches and d is the depth in feet. The thick-
ness of brick walls may be changed every 5 to 10 feet or so. Con-
crete walls may be built thinner than brick walls.

The bottoms of brick manholes are frequently made of con-
crete as shown in Fig. 27. The floor slopes towards the center
and is constructed so that the sewage flows in a half round or
U-shaped channel of greater capacity than the tributary sewers.
The sides of the channel should be high enough to prevent the
overflow of sewage onto the sloping floor, which should have a

Straight Through
Manhole.

Manhole.

Junction Manhole.
FIG. 27. — Baltimore Standard Manhole Details.

pitch of about one vertical to 10. or 12 horizontal. In manholes
where two or more sewers join at approximately the same level
the channels in the bottom should join with smooth easy curves.
Where the inlet and outlet pipes are not of the same diameter
the tops of the pipes should ordinarily be placed at the same
elevation to prevent back flow in the smaller pipes when the
larger pipes are flowing full.

The dimensions of the manhole should not be less than 3 feet
wide by 4 feet long for a height of at least 4 feet, when built in
the form of an ellipse, or 4 feet in diameter when built circular.
No standard method for the reduction of the diameter of the man-
hole near the top is observed, the rate being more or less dependent

MANHOLES

101

on the depth of the manhole. The use of sloping sides above the
frost line is desirable as such a form is more resistant to heaving
by frost action.

For sewers up to 48 inches in diameter the manhole is usually
centered over the intersection of the pipes and has a special founda-
tion. For larger sewers the manhole walls spring from the walls
of the sewer as shown in Fig, 28.

In the case of a decided drop in the elevation of a sewer, or of
a tributary sewer appreciably higher than an outlet in any man-
hole, the sewage is allowed to drop vertically at the manhole,

Cross Section. Longitudinal Section.

Manhole at Omaha

Well Hole at St. Paul.

From Eng Record. Vol. 66. p.S7<V

FIG. 28.— Details of a Manhole and a Well Hole.

hence the name drop manhole. The Baltimore standard drop
manhole is shown in Fig. 27. A well hole is an unusually deep
drop manhole in which the force of the vertical drop of sewage
is broken by a series of baffle plates, or by a sump at the bottom
of the well hole. Fig. 28 shows a well hole at St. Paul, Minn.
The use of drop manholes can be avoided in large sewers by the
construction of a flight of steps or flight sewer as shown in Fig. 29,
which allows the use of a steep grade and serves to break the
velocity of the sewage.

The specifications of the Sanitary District of Chicago, cover-
ing the construction of manhole covers and frames are :

All castings shall be of tough, close grained, gray iron,
free from blow holes, shrinkage and cold shuts, and sound,
smooth, clean and free from blisters and all defects.

102 APPURTENANCES

All castings shall be made accurately to dimensions to
be furnished and shall be planed where marked or where
otherwise necessary to secure perfectly flat and true sur-
faces. Allowance shall be made in the patterns so that the
specified thickness shall not be reduced.

All castings shall be thoroughly cleaned and painted
before rusting begins and before leaving the shop with
two coats of high grade asphaltum or any other varnish
that the Engineer may direct. After the castings have
been placed in a satisfactory manner, all foreign adhering
substances shall be removed and the castings given one
additional coat of asphaltum. No castings shall be
accepted the weight of which shall be less than that due to
its dimensions by more than 5 per cent.

<- — 8-1"-- 4

»*"• *••'••-*&%

- 4 ?8-6- :*

FIG. 29.— Flight Sewer at Baltimore.

. Eng. Record, Vol. 59, p. 161.

The weights of frames and covers in use vary from 200 to 600
pounds, the, weight of the frame being about 5 times that of the
cover. The lightest weights are used where no traffic other than
an occasional pedestrian will pass over the manhole. Frames
and covers weighing about 400 pounds are commonly used on
residential streets, whereas 600 pound frames and covers are
desirable in streets on which the traffic is heavy. The frames
should be so designed that the pavement will rest firmly against
it and wear at the same rate as the surrounding street surface.
Experience has shown that vertical sides should be used for the
outside of the frame to approach this condition, and that the frame
should not be less than 8 inches high. The cover should be rough-
ened in some desirable pattern as shown in Fig. 30. Smooth
covers become dangerously slippery. Where the ventilation of

MANHOLES

103

^Corrugations
for Type C
Cover

the sewers is not satisfactory the manhole covers are sometimes
perforated. This is undesirable from other points of view as the
rising odors and vapors are
obnoxious at the surface and
the entering dirt and water are
detrimental to the operation
of the sewer. The stealing
and destruction of manhole
covers and the unauthorized
entering of sewers has occa-
sionally required the locking
of the covers to the frame when
in place. The locks commonly
used consist of a tumbler which
falls into place when the man-
hole is closed, and which can be
opened only by a special wrench

4>K

J^andCCovs&r Cover Cfobeused
, „ onallSidcwalh and

+ Crown e/senrhtre as dinchd.
" '-^ jframe and Coyer oiphalr.
~~— — -ed.Corrugo-

- J'-2"

FIG. 30. — Baltimore Standard Manhole

Frame and Cover.

or hook. Adjustable frames
are sometimes used where the
street grade is settling, or may
be raised in order that the

elevation of the top of the cover may be made to conform to that
of the street surface, without reconstructing the top of the man-
hole. One type of adjustable cover is shown in Fig. 31. Man-

FIG. 31. — Adjustable Manhole Frame and Cover.

hole covers should be so marked that the sanitary sewer can be
distinguished from the storm water sewer, and both from the
telephone conduit, etc.

Iron steps are set into the walls of the manhole about 15
inches apart vertically to allow entrance and exit to and from the
manhole. Galvanized iron is preferable to unprotected metal as
the action of rust is particularly rapid in the moist air of the sewer.

104

APPURTENANCES

One type of these manhole steps is shown in Fig. 27. The steps
should have a firm grip in the wall as a loose step is a source of
danger.

57. Lampholes. — A lamphole is an opening from the surface
of the ground into a sewer, large enough to permit the lowering
of a lantern into the sewer. Lampholes are used in the place of

manholes to permit the inspec-
tion or the flushing of sewers,
and to avoid the expense of a
manhole. They are located
from 300 to 400 feet from
the nearest manhole in such
a manner that a lamp lowered
in the lamp hole can be seen
from the two nearest man-
holes.

Lampholes should be con-
structed of 8- to 12-inch tile
or cast-iron pipe. The lower
section should be a cast iron
T on a firm foundation, but
if constructed of tile it should
be reinforced with concrete
to take up the weight of the
shaft. The details of the
Baltimore standard lamphole
are shown in Fig. 32.
Lampholes are not com-
monly used on sewerage sys-
tems on account of their
lack of real usefulness and
the troubles encountered by
breaking of the pipe below the shaft.

58. Street Inlets. — A street inlet is an opening in the gutter
through which storm water gains access to the sewer. The types
used in different cities vary widely. Details of an inlet in success-
ful use are shown in Fig. 33. The figure shows also a common
form of connection to the sewer. A water-seal trap is sometimes
used to prevent the escape of odors from the sewer. Care must
be taken in design that such traps do not freeze in winter nor dry

FIG. 32. — Baltimore Standard Lamphole.

STREET INLETS

105

<-— -

....

~2'-i

" * ~^i

~>r

L*0

17"

~~P

l"«C^

i •

p
V

fe=

.JJ

— n

!"*>

1 1

— u

~T|
J 1

-^.J

M^^MM

out in summer, although it is not always possible to prevent
these contingencies.

The important features to be observed in the design of a street
inlet are: height and length of opening, character of grating, and
location. The general location of inlets is discussed in Chapter V.
The clear height of opening commonly used is from 5 to 6 inches,
with a clear length of 24 to 30
inches or longer. Inlets of this
size have given satisfaction on
paved streets with moderate slopes,
where the drainage area is not
greater than 10,000 to 12,000
square feet of pavement. W. W.
Horner states:1

The St.Louis type of inlet
" old " style was a vertical
opening in the curb 8 inches
high and 4 feet in length
with a horizontal bar mak-
ing the net opening about
5 inches. It has a broad
sill extending under the
sidewalk. The " new " style
inlet is 4£ feet long with a
clear opening of 6 inches
and no bar. The sill is done
away with and the opening
drops down directly from
the curb. Tests were made
of the capacity of this inlet
on pavements on different
slopes with sumps of depths
varying from 0 to 6 inches
in front of the inlet, extend-
ing out 3 feet from the gutter,

and returning to the elevation of the gutter at a slope of 3
inches to the foot. The results of these tests are shown in
Table 22. The capacity of the inlet is expressed as the
amount of water entering just before some water begins to
lap past. If a large amount of water is allowed to flow past
much more water will enter the inlet thus furnishing a
factor of safety for large storms. It was noted that by
beginning the rise in the pavement about opposite the

1 Municipal and County Engineering, October, 1909.

k~ 26"-

FIG. 33. — Details of an Untrapped
Street Inlet, without Catch-Basin.

106

APPURTENANCES

middle of the inlet the capacity of the inlet was increased
from 20 to 50 per cent.

TABLE 22

CAPACITIES OF ST. Louis STREET INLETS
From tests by W. W. Horner. Cubic feet per second

Slope in Per Ct.

0.42

1.5

2.85

4.5

Depth of Sump,

0.0

4
1 27

0
0.03
0 03

2
0.25
0 ?8

4
0.78
0 87

6
1.49
1 62

0
0 02

2
0 15

4
0 45

i n

Capacity, old

Capacity, new

It 1

0 5

1 5

••> •",

0 08

0 4

1 1

? 1

Gratings with horizontal bars will admit more water than
gratings with vertical bars, but they will also admit more rubbish
such as sticks, papers, leaves, etc., which serve to clog the sewers.
Vertical barred gratings and gratings in the bottom of the gutter
clog more quickly than other types. In the selection of the type
of grating to be used a decision must be made as to whether it is
more desirable to clean the sewer or catch-basin, or to flood the
street as a result of clogged inlets. Where catch-basins are used
or the sewers are large, horizontal bars are more satisfactory.
The openings between bars should be small enough to prevent
the entrance of a horse's hoof or objects of sufficient size to clog
the sewer. Four inches in the clear for vertical openings and 6
inches for horizontal openings are reasonable sizes.

The location of the inlets at the intersection of the two curb
lines at a corner results in a lower first cost but on heavily traveled
streets this may result in a higher maintenance cost than for other
locations because of the concentration of traffic at street corners,
hammering the inlet 'casting out of shape or position. Vehicles
making short turns will tend to climb the curb and will intensify
the wear upon the inlet. These objections can be overcome by
the use of two inlets at each corner, set back far enough from the
curb intersection to avoid interference with the cross-walks.
This also makes it possible to raise the cross-walks without the
use of gutters under them.

The size of the pipe from the inlet to the catch-basin or sewer
should be large enough to care for all of the water which may enter

CATCH-BASINS

107

the inlet. As the capacity of the inlet is seldom known with accu-
racy and the capacity of the pipe is difficult of determination, it
has become customary to use a 10-inch or a 12-inch connecting
pipe for each ordinary independent inlet.

59. Catch-basins. — Catch-basins are used to interrupt the
velocity of sewage before entering the sewer, causing the deposi-
tion of suspended grit and sludge and the detention of floating
rubbish which might enter and clog the sewer. A separate catch-

FIG. 34. — CATCH-BASIN.

Outlets are not always trapped.

basin may be used for each inlet, or to save expense, the pipes from
several inlets may discharge into one catch-basin.

The types in successful use are extremely varied, but the dis-
tinguishing feature of all is an outlet located above the floor of
the basin. A common form of catch-basin is shown in Fig. 34.
It is constructed similar to a manhole with a diameter of about
4 or 4i feet and a depth of retained water from 3 to 4 feet. Catch-
basins of this size will care for the sewage from the inlets at the
four corners of a street intersection, each draining a city block.

108

APPURTENANCES

In unusual situations it may be necessary to install a larger basin,
but too large a catch-basin is less desirable than one which is too
small, as the former stinks and the latter is useless. Traps are
sometimes used to prevent the escape of odors from the sewer
into the street, but odors are often created in the catch-basins
themselves. Some engineers arrange the trap so that it can be
opened for observation down the sewer as in Fig. 34, thus com-
bining the advantages of a manhole with the catch-basin.

The use of catch-basins is objectionable because: they furnish
a breeding place for mosquitoes and other flying insects; the
septic action in them produces offensive odors; if on a combined
sewer they permit the escape of offensive odors in dry weather
when the water seal in the trap has evaporated; and the freezing
of the water seal in the trap prevents the entrance of water to
the sewer. The sole advantage lies in the prevention of the
clogging of the sewers, but this may be sufficient to overbalance
all of the disadvantages. In general catch-basins should be
provided on paved streets which are cleaned by flushing the
material into the sewers, or where the drainage is from an unim-
proved or macadamized street, sandy country, or into sewers in
which the velocity of flow is less than 2 feet per second.

60. Grease Traps. — The presence of grease in sewers results
in the formation of incrustations which are difficult to remove

and which cause a material loss in
the capacity of the sewer. The
presence of oil and gasoline has re-
sulted in violent and destructive ex-
plosions as is described in Chapter
XII. A type of grease trap used on
the drains' from hotels, restaurants,
or other large grease producing indus-

trieS. is sh°Wn in FiS' 35' .The traP
ig similar to a catch-basin except

that it is too small for a man to
enter, and the outlet is necessarily trapped in order to pre-
vent the escape of grease. The details of a gasoline and oil
separator approved by the New York City Fire Department are
shown in Fig. 36. *

1 "Cleaning and Flushing Sewers. " Journal of the Association of Engineer-
ing Societies, Vol. 33, 1904, p. 212.

FIG. 35.-Diagrammatic Sec-
tion through a Grease Trap.

FLUSH-TANKS

109

2"Kr/i/A«r4

FIG. 36. — Gasoline and Oil Separator.

61. Flush-Tanks. — These are devices to hold water used in
flushing sewers. They are. required only on sanitary and com-
bined sewers. Their use tends to prevent the clogging of sewers
laid on flat grades and permits
flatter grades in construction
than could otherwise be adopt-
ed. Flush-tanks may be oper-
ated either by hand or auto-
matically. Automatic operation
is more common than hand
operation. The hand-operated
tanks are similar to manholes
so arranged that the inlet and
outlet sewers can be plugged
while the manhole or tank is
being filled with water either
from a hose or a special service
connection. When sufficient
water has been accumulated
the outlet is opened and

the sewer is flushed by the rush of water. A sluice gate, flap
valve, or a specially fitted board is sufficient to fit over the mouth
of the inlet and outlet during the filling of the tank. Such an
arrangement has the advantage of being cheap, simple, and
satisfactory, though somewhat crude. In some ca,ses water is
run into the tank at the same rate that it is discharged through
the open outlet, maintaining a depth of 4 or 5 feet in the tank
until the water passing the manhole below runs clean. The
volume of water required by this method is large. Flushing
water under a relatively high head is sometimes obtained by the
use of tank wagons which are quickly emptied into the sewer
through a canvas pipe dropped down a manhole. In all such
cases if not well constructed the manhole is subject to caving due
to the rush of water around the outlet. Precautions should be
taken to minimize this danger by limiting the depth of water
which may be accumulated. This can be done by constructing
an overflow at a height of 4 or 5 feet above the bottom of the man-
hole, discharging into the sewer through an outside drain.

Automatic flush-tanks are constructed similar to a manhole,
but special care should be taken to make them water-tight. The

110

APPURTENANCES

Regula-

apparatus for providing the automatic discharge may operate
either with or without moving parts,- the latter being preferable
as they require less attention and are not so liable to get out of
order. An automatic flush-tank of the Miller type is shown in
Fig. 37. It is a patented device manufactured by the Pacific

Flush Tank Company. The
small pipe at the left is a
service connection to the water
main. Water is allowed to flow
continuously into the tank at
such a rate as to fill it in the
required interval between dis-
charges. The tanks are dis-
charged as nearly once a day
as it is practicable to regulate
them. The rate of flow into
the tank is determined by trial
and varies to some extent with
the water pressure. The regu-
lator shown in the figure is
desirable as the continuous flow
through the ordinary cock soon wears it away. Some waters
will cause deposits to form in the small passages of the cocks or
regulators, thus cutting off the flow.

The tank operates as follows: when the water rising in the
tank reaches the bottom of the bell, air is trapped in the bell and
prevented from escaping through the main trap by the water at A.
As the water continues to rise in the tank the air in the bell is
compressed, the water level at A is driven down and water trickles
from the siphon at C. The height of the water in the tank above
the level of the water in the bell is equal at all times to the height
of C above the lowering position of A. When A reaches the
position of B a small amount of air is released through the short
leg of the trap and a corresponding volume of water enters the
bell. The head of water above the bell then becomes greater
than the head of water in the short leg of the trap, which results
in the discharge of all of the air in the long leg of the trap and
the rapid discharge of the water in the tank through the siphon.
The discharge is continued until the siphonic action is broken by
the admission of air when the water level in the tank is lowered

FIG. 37. — Automatic Flush-Tank.

Pacific Flush Tank Co.

FLUSH-TANKS

111

to the bottom of the bell. The size of the siphons is fixed by the
diameter of the leg of the siphon. Table 23 shows the capacity
and size of sewers for which the different sizes of siphons are
recommended by the manufacturers.1

TABLE 23

SIZES OF SIPHONS TO BE USED WITH AUTOMATIC FLUSH-TANKS

Diameter
of

Diameter
of Tank

Total
Discharge

Average
Rate

Diameter
of

Height of
the

Siphon

at the
Discharge

for One

Flush

of
Discharge

Sewer

Discharge
Line above

in
Inches

Line
in Feet

in
Gallons

in
Sec.-ft.

in
Inches

the Edge of
the Bell

0.35

4 to 6

1 ft. 2 in.

100

0.73

6 to 8

1 ft. 11 in.

240

1.06

8 to 10

2 ft. 6 in.

280

2.12

12 to 15

2 ft. 11 in.

When flush-tanks are placed at the upper end of laterals
provision should be made for inspecting and cleaning the sewer
by the construction of a separate manhole, or by combining the
features of a manhole and a flush-tank in the same structure.
Such a combination is shown in Fig. 38 from a design by Alex-
ander Potter.

Except under unusual conditions flush-tanks are used only on
separate sewers. They should be placed at the upper end of
laterals in which the velocity of flow when full is less than 2 to
4 feet per second. The capacity of the tank or the volume of the
dose is dependent on the diameter and slope of the sewer. The
most effective flush is obtained by a volume of water traveling
at a high velocity and completely filling the sewer. A large
volume allowed to run slowly through the sewer will have but
little if any flushing action. Data on the quantity of flushing
water needed are given in Table 24. 2 As the result of a series of
experiments conducted by Prof. H. N. Ogden on the flushing of

1 Notes on the Design and Principles of Sewage Siphons, Eng. News-Record,
Vol.85, 1920, p. 1041.

2 From A. E. Phillips, Trans. Am. Society of Municipal Improvements,
1898, p. 70.

112

APPURTENANCES

Sectional
Plan.

FIG. 38. — Automatic Flush-Tank and Manhole.

Miller-Potter Design. Pacific Flush Tank Co.

TABLE 24
GALLONS OF WATER NEEDED FOR FLUSHING SEWERS

CI1

Diameter of Sewer in Inches

blope

0.005

100

.0075

.01

.02

.03

SIPHONS 113

sewers,1 the conclusion was reached that the effect of a flush of
about 300 gallons in an 8-inch sewer on a grade less than 1 per
cent would not be effective beyond 800 to 1,000 feet, but that on
steeper grades much smaller quantities of water would produce
equally good results.

Engineers do not agree upon the advisability of the use of
automatic flush-tanks, some believing that they are a needless
expense that can be avoided by hand flushing, and others feeling
that a flush-tank should be placed at the upper end of every lateral.
These diverse opinions are the result of different experiences in
different cities.

62. Siphons. — There are two forms of siphons used in sewerage
practice, a true siphon and an inverted siphon. A true siphon
is a bent tube through which liquid will flow at a pressure less
than atmospheric, first upwards and then downwards, entering
and leaving at atmospheric pressure. An inverted siphon is a bent
tube through which liquid will flow at a pressure greater than
atmospheric first downwards and then upwards, entering and
leaving at atmospheric pressure.

In sewerage practice the word siphon refers to an inverted
siphon unless otherwise qualified. Siphons, both true and
inverted, are used in sewerage systems to pass above or below
obstacles. True siphons are seldom used as they must be kept
constantly filled with liquid.2 Accumulated gas must be removed
in order to prevent the breaking of the siphon which results in the
cessation of flow. By the breaking of a true siphon is meant the
stoppage of siphonic action due to the accumulation of air or gas
at the peak of the siphon. Since the rate of flow of sewage fluc-
tuates widely it is extremely difficult to control the flow so that a
true siphon may be completely filled with liquid at all times.

In the design of inverted siphons care must be taken to pre-
vent sedimentation, and to permit inspection and cleaning.
Sedimentation is prevented by maintaining a velocity greater
than a fixed minimum, usually taken at about 2 feet per second.
This minimum is attained by providing a number of channels.
The smallest channel is designed to convey the least expected
flow at the minimum velocity. Each of the other channels is
made as small as possible, within the limits of economy and sim-

1 Trans. Am. Society of Civil Engineers, Vol. 15, 1886.

1 True Siphon at East Providence, Eng. News-Record, Vol. 85, 1920, p. 862.

114

APPURTENANCES

plicity, in order that the minimum velocity shall be exceeded
quickly after flow has commenced in them. The last channel or
channels to be filled are made somewhat larger, because the
sewage conveyed in them contains less settleable matter than is
contained in the more concentrated dry weather flow. The type
of siphon used in New York to pass under the subway is shown in
Fig. 39. Note should be taken of the clean-out manhole provided
on the 14-inch pipe. The other pipes are large enough for a man
to enter and clean.

Old

4-10x3-6"
Sewer
ci.---|

4-6'C/rcu/arffei'nf.Concrefe

'•/4 "C. /.(Dry WeathejPips
Sectional Plan

'-Gleanout Chamber
i Cle an out Manhole

WC.I.
Section A-A.

2,4'-6"(Storm) Pipes-'

Longitudi'nal Section.

Section B-B.

FIG. 39. — Sewer Siphon under New York Subway.

Eng. News Vol. 76, p. 443.

The computations involved in the design of a siphon are
illustrated in the following example, in which it is desired to con-
struct a siphon to pass under the railway cut shown in Fig. 40.
The first step is to determine the limiting diameter and slope of
the smallest pipe in the siphon. One-sixth of the capacity of the
6-foot approach sewer or 19 cubic feet per second will be assumed
as the minimum flow. The diameter of the pipe necessary to
carry 19 cubic feet per second at a velocity of 2 feet per second is
42 inches. The hydraulic gradient should have a slope of 0.0005
if the material used has a roughness coefficient of .015. This is
the minimum permissible slope of the siphon. The selection of a
steeper slope will necessitate the laying of the sewer at a greater
depth, and will permit the use of smaller pipes for the siphon.

SIPHONS

115

The selection of the exact slope must then be based on judgment
with the minimum limitation above placed. The slope will be
arbitrarily selected as 0.001, the same as that of the approach
sewer. The diameter of the dry weather pipe will therefore be
36 inches, with a capacity of 18 second-feet, which is approximately
the assumed dry-weather flow. The velocity of flow will be
2.5 feet per second. The length of flow along the siphon is 150 feet.
The next step should be the determination of the elevation at
the lower end of the 36-inch pipe. This is done by multiplying

40 1 0 ^j, 20-0"-

- El. 100.0

- 60 "6torm Sewer
,42"Storm Sewer

36 Dry
' Weather
Sewer

Vertical Cross Section

60 " Sewer

42. Sewer

36 " Sewer

Plan under Retaining Wall
FIG. 40. — Diagram for the Design of an Inverted Siphon.

the assumed grade by the equivalent length of straight pipe, and
subtracting the product from the elevation at the upper end.
The length of straight pipe which will give the same loss of head
as the siphon is called the equivalent pipe. It is determined as
follows:

First, determine the head loss at entrance. This will vary
between nothing and one velocity head, dependent on the arrange-
ment at the entrance.1 The length of straight pipe which will

1 "The Effect of Mouthpieces on The Flow of Water Through a Sub-
merged Short Pipe," by F. B. Seely. Bulletin No. 96, 1917, of the Eng'g.
Experiment Station of the University of Illinois.

116 APPURTENANCES

give this same loss can be computed from the expression 1=-^,

using for S the assumed slope of the hydraulic gradient.

Second, determine the head loss due to the bends. This is
determined from the expression

h-^V-
~d2g

in which /i = the head loss in the bend;
Z = the length of the bend;
d=the diameter of the pipe;
v = the average velocity of flow ;
</ = the acceleration due to gravity;
/=a factor dependent on the radius (R) of the bend
and d.

The relation between /, R, and d, for 90° bends is shown as

follows: 1

R/d 24 16 10 6 4 2.4

/ 0.036 0.037 0.047 0.060 0.062 0.072

After the head loss has been determined, the equivalent length of
straight pipe is determined as above.

Third. The equivalent length of pipe will be the sum of the
actual length of pipe and the equivalent lengths as found above.

In the problem in hand the head lost at the entrance will be
assumed as one-third of a velocity head, or 0.0324 foot. With
the assumed slope of 0.001 this is equivalent to 32 feet of pipe.
The radius of the bend is about 20 feet and the length for a 45°
central angle is about 16 feet. The head loss for this angle will
probably be a little more than one-half that for a 90° angle. The

expression will therefore be taken as about 0.2 ^— and for two

bends is equivalent to about 40 feet of pipe. The equivalent
length of pipe is therefore 150+32+40 = 222 feet. The elevation
at the lower end should therefore be: the elevation at the upper
end, 92.07 - 222 X. 001 = 91.85.

The diameters of the remaining pipes in the siphon are

determined so that the sewage in the approach sewer is backed

up as little as is consistent with good judgment before each pipe

comes into action. This is done satisfactorily by a method of

1 Trans. Am. Society of Civil Engineers, Vol. 49, 1902.

REGULATORS 117

cut and try. Let it be assumed that the siphon will be composed
of three pipes: the dry-weather pipe taking 18 second-feet, the
second pipe taking 28 second-feet, and the third pipe taking the
remaining 70 second-feet. The diameters of the two larger pipes
on the assumed slope of 0.001 will therefore be 42 inches and 60
inches respectively. Other combinations might be used which
would be equally satisfactory. There are many methods by which
the sewage can be diverted into the different channels of the
siphon. For example, the openings into the different pipes may
be placed at the same elevation, and the sewage allowed to enter
them in turn through automatically or hand-controlled gates, or
in another method of control the openings may be placed at such
elevations that when the capacity of one pipe has been exceeded
the sewage will flow into the next largest pipe as shown in Fig. 40.
The outlets from the different pipes are ordinarily placed at the
same elevation, thus leaving each pipe standing full of sewage.
Stop planks should be provided at the outlet in order that the
pipes may be pumped out for cleaning. The objection to this
arrangement is that the larger pipes may operate at a velocity
less than 2 feet per second, and they will be standing full of
sewage which might become septic. However, as they will take
nothing but the storm flow near the top of the sewer no difficulty
should be encountered from sedimentation in them, and all are
large enough for a man to enter for inspection or cleaning.

63. Regulators. — Regulators are commonly used to divert the
direction of flow of sewage in order to prevent the overcharging
of a sewer or to regulate the flow to a treatment plant. Sewer
regulators are of two types, those with moving parts and those
without moving parts. An example of the moving part type is
shown in Fig. 41. In this type as the sewage rises the float closes
the gate to the inlet sewer, thus preventing the entrance of sewage
under head from the larger sewer. There are many variations in
the details of float-controlled regulators, but the principle of opera-
tion is similar in all. These regulators can be adjusted to fix the
maximum rate of flow to a relief channel or sewage treatment
plant, or during times of storm to cut off the outlet to the dry
weather channel. Another form of the moving part type is shown
in Fig. 42.1 It has been used extensively by the Milwaukee

1 Described by W. L. Stevenson before the Boston Society of Civil Engi-
neers in 1916 .

118

APPURTENANCES

-•Storm Stwtr

Sewerage Commission. In its operation the dry-weather flow is
diverted by the dam into the intercepter. It passes under the
movable gate on its way to the treatment plant. As the flow

increases the dam is
overtopped and flood
waters are discharged
down the storm chan-
nel. The movable gate
is hung on a pivot
placed below center.
As the water rises in
the intercepter, the
.-Copper Float pressure against the
upper portion of the
gate becomes greater
than that against the
lower portion, and
the gate closes. An

opening is left at the bottom to allow an amount of sewage equal
to the dry-weather flow to escape beneath the gate to prevent
clogging or sedimentation in the intercepter channel.

Objections to all moving part regulators are their need of
attention and liability to become clogged.

FIG. 41. — Coffin Sewer Regulator.

Direction
of Flow

Regulator

Gate-,

- StormSewer-
Longitudinal Section

- Dry Weather- -Storm Flow-

Transverse Sections through Regulator.

FIG. 42. — Moving Part Regulator without Float.

The overflow weir and the leaping weir have no moving parts
and are used for the regulation of the flow in sewers. A leaping
weir is formed by a gap in the invert of a sewer through which
the dry-weather flow will fall and over which a portion or all of
the storm flow will leap. One form of leaping weir is shown in
Fig. 43. An overflow weir is formed by an opening in the side of
a sewer high enough to permit the discharge of excess flow into a
relief channel. A weir at San Francisco is shown in Fig. 44. A
series of tests were run on leaping weirs and overflow weirs in the
hydraulic laboratory of the University of Illinois. The type of

REGULATORS

119

leaping weir tested was formed by the smooth spigot end of a stand-
ard vitrified sewer pipe. The overflow weirs were formed by a

it-tiri'dr

.-Brick

Cast Iron
Orating

Concrete
•Iron
Casting

Section of Inlet.
Iron Casting to here

/JM Detail n

Plan of Inlet.
FIG. 43. — Leaping Weir at Danville, Illinois.

£ ""Long. Steel Ban &'--. Section throu'g

Reinforcement under Manhole.
Sectional Plan.

e'..i

Reinforct-

Section A-A. Section B-B. Section C~C.

FIG. 44. — Overflow Weir at San Francisco.

Eng. News, Vol. 73, p. 307.

steel knife edge in the side of the pipe parallel to its axis as shown
in Fig. 45. Tests were made in 18-inch and 24-inch pipes on various
slopes from 0.018 to 0.005, for both leaping weirs and overflow

120

APPURTENANCES

weirs. The overflow weirs were varied in length from 16 inches
to 42 inches and were placed at various heights from 25 per cent
to 50 per cent of the diameter above the invert of the sewer. As
the result of the observations the following formulas were
developed. For the leaping weir the expressions for the coordi-
nates of the curve of the surfaces of the falling stream, are :

For the outside surface z =
For the inside surface x = 0

FIG. 45. — Overflow Weir in Action.

Shadow of steel knife edge which forms the lip of the weir can be seen through the
falling sewage.

in which x and y are the coordinates. The origin is in the upper
surface of the stream vertically above the end of the invert of the
pipe. The ordinate y is measured vertically downwards. V is
the velocity of approach in feet per second. These expressions
are applicable to any diameter of sewer up to 10 or 15 feet. They
should not be used for depths of flow greater than about 14 inches;
nor for slopes of more than 25 per 1,000; nor for velocities less
than 1 foot per second nor more than 10 feet per second. The
expression for the ordinate of the inside curve is not good for less

JUNCTIONS 121

than 6 inches nor more than 5 feet. The expression for the ordi-
nate of the outside curve is limited to values between the origin
and 5 feet below it.

The expression for the length of an overflow weir of the type
shown in Fig. 45, necessary to discharge a given quantity, is in the
form,

in which I =the length of the weir in feet;

V =the velocity of approach in feet per second;
d =the diameter of the pipe in feet;
hi =the head of water on the upper end of the weir;
h,2 = the head of water on the lower end of the weir.

In the design of an overflow weir by this formula the height of the
weir above the invert of the sewer and the flow over the weir
should be determined arbitrarily. The height should be sub-
tracted from the computed depth of water above the weir to
determine the value of h\. The difference between the flow over
the weir and the flow above the weir will represent the rate of
flow in the sewer below the weir. The value of h? can then be
computed as the difference in the depth of flow below the weir
and the height of the weir above the invert. The value of V is
computed from Kutter's formula. The length of the weir is
determined by substituting these values in the formula.

64. Junctions. — At the junction of two or more sewers the
elevation of the inverts should be such that the normal flow lines
are at the same elevation in all sewers. The sewers should
approach the junction on a steep grade to prevent sewage backing
up in one when the other is flowing full. The velocity of flow at
the junction should not be decreased and turbulence should be
avoided in order to prevent sedimentation and loss of head.
The junction should be effected on smooth easy curves with radii
at least five times the diameter of the sewer where possible.
Curves with short radii cause backing up of sewage thus reducing
the capacity of the sewers.

The terms bellmouth or trumpet arch are sometimes applied
to the junction of sewers large enough to be entered by a man
In small sewers the Y branches and special junctions are manu-
factured so that the center lines of the pipes intersect, and the

122 APPURTENANCES

junctions of mains and laterals are made in manholes. In the
construction of a bellmouth the arch is carried over all the sewers.
A manhole should be constructed at these junctions as clogging
frequently occurs there, due to swirling and back eddies which
cannot be avoided.

65. Outlets. — The outlets to a sewerage system discharging
into a swiftly running stream must be protected against wash
and floating debris. In a stream or other body of water subject
to wide variations in elevation the backing up of the sewage during
high water should be avoided. Where tidal flats or low ground
about the outlet may be alternately submerged and uncovered
the discharge should always be into swiftly running water. In
quiescent bodies of water such as lakes and harbors, and in rivers
where the dilution is low, and in many other cases, the sewer
outlet should be submerged.

Outlets are protected against wash and the impact of debris
by the construction of deep foundations and heavy protecting
walls. Although the construction of an outlet in a slow current
or a back eddy would avoid danger from wash and debris, the
discharge of the sewage into the most rapid current possible aids
in the prevention of a local nuisance. A row of batter piles on
the upstream or exposed side of the sewer is desirable, or it may
be necessary to construct a break-water to prevent the wash of
the current from dislodging the pipe. These break-waters are

low dams of wood or broken
stone, more or less loosely
thrown together. The back-
ing up of water into the
sewer can be prevented by
constructing the sewer above
FIG. 46. — Tide Gate. the outlet on a steep grade.

Where this is not possible

the use of tide gates will be helpful. A tide gate, one form of
which is shown in Fig. 46, is a special form of check valve placed
on the end of the sewer.

Sewer outlets are sometimes constructed on long trestles in
order to reach deep or running water. Such a trestle is shown
in Fig. 47. In Boston the outlet sewers are submerged under the
harbor and discharge through outlets well out in the tidal currents.
The sewage is discharged under pressure and the pumps are

OUTLETS

123

operated at some of the stations only at such times as the tidal
currents will carry the sewage away from the harbor. It is not
always necessary in a combined sewerage system to carry the

if. 4-4L0- ^

Expanded ± ....32-6'—-

Metal-.
Portland

Concrete -\

I2"xl2"

FenderWalt-W^,

Half Cross Section.

Half Elevation.

6 Facing Port!. Concrete, A'g-'/g Granite Powdtr-^ --Porfl. Concrete, 1-24

Longitudinal Section.
FIG. 47. — Sewer Outlet on a Trestle.

Eng. News, Vol. 49, p. 9.

storm flow to a distant submerged outlet. A double outlet can
be constructed as shown in Fig. 48 in which the dry-weather flow
is carried to the channel in a submerged sewer and the storm

124

APPURTENANCES

flow is discharged on the bank.1 Cast-iron pipe should be used
for submerged outlets as the sewer is subject to disturbance by
the currents, anchors, ice, and other causes.

66. Foundations. — Sewers constructed in firm dry soil require

no special foundation to dis-
tribute the weight over the sup-
porting medium. In soft ma-
terials the lower half of the
sewer ring may be spread
as shown in Fig. 22, and in
rock the pressures on sewer
pipes are evenly distributed

Dry Weather Outlet •

by a

cushion of sand.

FIG. 48.-Dry Weather and Storm wet grOUnd Such. as

Sewer Outlet at Minneapolis, Min- sand> mud, swamp land, etc.,

nesota. a foundation must be con-

Eng. Record, Vol. es, p. 383. structed if the water cannot be

drained off.

The permissible intensities of pressure on foundations in
various classes of material allowed by the building codes in differ-
ent cities are given in Table 25. These figures are based on the
assumption that the material is restrained laterally, which is
generally the condition in sewer construction. In the softer
materials it becomes necessary to spread the foundations not
only to reduce the intensity of pressure, but also to care for the
thrust of the sewer arch. The arch thrust may be found by one
of the methods of arch analysis, and the haunches spread to care
for this, or the sewer invert may be transversally reinforced to
assist in caring for this action. Some sewer sections in hard and
soft material are shown in Fig. 22 and 23.

On soft foundations such as swamps or for outfalls on the muck
bottom of rivers the sewer may be carried on a platform. For
small sewers 2-inch planks, 2 to 4 feet longer than the diameter
of the pipe are laid across the trench, and the sewer rests directly
upon them. For large sewers imposing a heavy concentrated
load, a pile foundation should be constructed. The foundation
may consist of piles alone, pile bents, or a wooden platform sup-
ported on pile bents. The load which can be carried by a pile is

1 Multiple Outlet for Calumet Intercepting Sewer, by S. T. Smetters, Eng.
News:Record, Vol. 83, 1919, p. 728.

FOUNDATIONS

TABLE 25
ALLOWABLE BEARING VALUE ON SOILS IN VARIOUS CITIES

From Proc. Am. Soc. Civil Engre., Vol. 46, 1920, p. 906

125

Quicksand and alluvial soil

J to 1 ton per sq. ft. for Providence, R. I., } ton per
sq. ft. for 6 cities

Soft clay

1 ton per sq. ft. for 27 cities, 1 ton per sq. ft. for New
Orleans, 2 to 3 tons for Providence, R. I.

Moderately dry clay and fine sand,
clean and dry

2 tons for 7 cities, 1J to 2J for Chicago, 2} tons for
Louisville, 2 to 4 tons for Providence, 3 tons for
Grand Rapids and Los Angeles

Clay and sand in alternate layers

2 tons for 19 cities, 1} to 2J for Chicago, 3 to 5 tons
for Providence

Firm and dry loam or clay, or hard
dry clay or fine sand

3 tons for 24 cities, 2] tons for 2 cities, 2 to 3 tons for
Atlanta, 3J tons for Philadelphia, 4 tons for 6 cities

Compact coarse sand, stiff gravel or
natural earth

4 tons for 25 cities, 3} tons for Buffalo, 3 to 4 tons for
Atlanta, 4 to 5 tons for Cincinnati, 5 tons for
Denver, 4 to 6 tons for 3 cities, 6 tons for Rochester,

N. Y.

Coarse gravel, stratified stone and
clay, or rock inferior to best brick
masonry

6 tons for 3 cities, 5 tons for 2 cities, 8 tons for 1 city

Gravel and sand well cemented

8 tons for 5 cities, 6 tons for 2 cities, 8 to 10 tons for
1 city

Good hard pan or hard shale

10 tons for 4 cities, 6 tons for 2 cities, 8 tons for 1 city

Good hard pan or hard shale unex-
POSM! to air, frost or water

8 tons for 1 city, 10 to 15 tons for 1 city, 12 to 18
tons for 1 city

Very hard native bed rock

20 tons for 5 cities, 15 tons for 1 city, 10 tons for
1 city, 25 to 50 tons for 1 city

Rock under caisson

24 tons for Baltimore, 25 tons for Cleveland

determined with accuracy only by driving a test pile and placing
a load on it. Where piles do not penetrate to a firm stratum the
load they will support can be determined by any one of the various
formulas, either theoretical or empirical, which have been devised.
Probably the best known of these formulas are the so-called
Engineering News formulas one of which is:

2Wh .
P = •« TT for a pile driven by a drop hammer,

126 APPURTENANCES

in which P = the safe load on the pile in pounds. The factor

of safety is 6;

TF = the weight of the hammer in pounds;
7i = the fall of the hammer in feet;

$ = the penetration of the pile in inches at the last
driving blow. The blow is assumed to be driven
on sound wood without rebound of the hammer.

Reference should be made to engineering handbooks for other
forms of pile formulas. The accuracy of all of these formulas is
not of a high degree.

The piles are driven at about 2 to 4 feet centers, to a depth of
from 8 to 20 feet, unless hard bottom is struck at a lesser depth.
The butt diameter of the piles used for the smallest sewers is
about 6 to 8 inches. If bents are used, 2 or 3 piles are driven in a
row across the line of the sewer and are capped with a timber.
For brick, block, pipe, and some concrete sewers, a wooden plat-
form must be constructed between the pile bents for the support
of the sewer.

67, Underdrains. — The construction of special foundations
can sometimes be avoided by laying drains under the sewers,
thus removing the water held in the soil. The laying of the under-
drains facilitates the construction of the sewer and reduces the
amount of ground water entering the sewer. The underdrains
usually consist of 6- or 8-inch vitrified tile laid with open joints
from 1 to 2 feet below the bottom of the sewer as shown in Fig. 1.
If the sewers are large, parallel lines of drains may be laid beneath
them. An observation hole should be constructed from the bottom
of the manhole to each underdrain. This hole usually consists
of a 6- or 8-inch pipe, embedded in concrete, connected to the
drain and open at the top. It is too small to permit effective
cleaning of the underdrains, which are usually neglected after
construction, and which as a result clog and cease to function.
Since the principle period of usefulness of the drains is during
construction, their stoppage after the work is completed is not
serious. The hollow tile used in vitrified block sewers serve as
underdrains after construction, but are of little or no assistance
to the draining of the trench during construction,

CHAPTER VII
PUMPS AND PUMPING STATIONS

68. Need. — In the design of a sewerage system it is occasion-
ally necessary to concentrate the sewage of a low-lying district at
some convenient point from which it must be lifted by pumps.
In the construction of sewers in flat topography the grade
required to cause proper velocity of sewage flow necessitates deep
excavation. It is sometimes less expensive to raise the sewage
by pumping than to continue the construction of the sewers with
deep excavation.

In the operation of a sewage-treatment plant a certain amount
of head is necessary. If the sewage is delivered to the plant at a
depth too great to make possible the utilization of gravity for the
required head, pumps must be installed to lift the sewage. In
the construction of large office buildings, business blocks, etc.,
the sub-basements are frequently constructed below the sewer
level. The sewage and other drainage from the low portion of
the building must therefore be removed by pumping. Because
pumps are often an essential part of a sewerage system, their
details should be understood by the engineer who must write the
specifications under which they are purchased and installed.

69. Reliability. — If the only outlet from a sewerage system is
through a pumping station, the inability of the pumps to handle
all of the sewage delivered to them may so back up the sewage as
to flood streets and basements, endangering lives and health and
destroying property. Such an occurrence should be guarded
against by providing sufficient pumping capacity and machinery
of the greatest reliability.

70. Equipment. — The equipment of a sewage pumping station,
in addition to pumping machinery, may include a grit chamber, a
screen, and a receiving well. The grit chamber and screen are
necessary to protect the pumps from wear and clogging. Grit
chambers are not necessary in sewage devoid of gritty matter,

127

128

PUMPS AND PUMPING STATIONS

such as the average domestic sewage, unless reciprocating pumps
are used. Sufficient gritty matter is found in average domestic
sewage to have an undesirable effect on reciprocating pumps.
Receiving wells are used in small pumping stations where the
capacity of the pumps is greater than the average rate of sewage
flow. The pumps are then operated intermittently, the pumps
standing idle during the time that the receiving well is filling.

Except for a few types of pumps of which the valve openings
are unsuitable, any machine capable of pumping water is capable
of pumping sewage which has been properly screened. The
principles of sewage pumps are then similar to principles of water
pumps. The conditions under which these principles are applied
differ but slightly in the character of the liquid, and a smaller
range of discharge pressures. Pumps with large passages, dis-
charging under low heads are more commonly found among
sewage pumps.

71. The Building. — The pumping station should, if possible,
be of pleasing design and should be surrounded by attractive
grounds. The Calumet Sewage Pumping Station in Chicago is
shown in Fig. 49. Its architecture is pleasing particularly in

FIG. 49. — Calumet Sewage Pumping Station, Chicago, Illinois.

contrast with its location and immediate surroundings. Such
structures tend to remove the popular prejudice from sewerage
and to arouse interest in sewerage questions. Service to the

CAPACITY OF PUMPS 129

public is of value. It can be rendered more easily by arousing
public interest and co-operation by the erection of attractive
structures, than by feeding popular prejudice by the construction
of miserable eyesores.

72. Capacity of Pumps. — The capacity of the pumping equip-
ment should be sufficient to care for the maximum quantity of
sewage delivered to it, with the largest pumping unit shut down,
and the provision of such additional capacity as, in the opinion
of the designer, will provide the necessary factor of safety.

Pumps can usually be operated under more or less overload.
Power pumps and centrifugal pumps driven by constant speed
electric motors have no overload capacity. A power pump or a
centrifugal pump may be overloaded up to the maximum horse-
power of any variable speed motor or steam engine driving it,
provided the pump has been designed to permit it. Direct-acting
steam pumps which are designed for proper piston speed and
valve action at normal loads, can carry a 50 per cent overload for
short periods, although the strain on the pump is great. They
will carry a 20 to 25 per cent overload for about eight hours with less
vibration and strain. The use of pumps capable of working at
an appreciable overload is somewhat of an additional factor of
safety, but the overload factor should not be taken into considera-
tion in determining the capacity of the pumping equipment.

The load on a pumping station consists of the quantity of
sewage to be pumped and the height it must be lifted. Variations
in the quantity are discussed in Chapter III. The head against
which the pumps must operate fluctuates with the level in the
tributary sewer or pump well, and in the discharge conduit.
For a free discharge or discharge into a short force main the greater
the rate of sewage flow the smaller the lift, as the depth of flow
in the tributary sewer increases more rapidly than that in the
discharge conduit. If the discharge is into a large body of water
or under other conditions where the discharge head is approxi-
mately constant, the fluctuations in total head should not exceed
the diameter of the tributary sewer. Such fluctuations are of
minor importance in the operation of direct-acting steam pumps,
but may be of great importance in the operation of centrifugal
pumps, as is brought out in Art. 78.

73. Capacity of Receiving Well. — The use of receiving wells
is restricted to small installations which require, in addition to

130 PUMPS AND PUMPING STATIONS

the standby unit, only one pump, the capacity of which is equal
to the maximum rate of sewage flow. When the receiving well
has been pumped dry the pump stops, allowing the well to fill
again. Although the use of a large receiving well, or an equaliz-
ing reservoir, for a large pumping station would permit the opera-
tion of the pumps under more economical conditions, the storage
of sewage for the length of time required would not be feasible.
The sewage would probably become septic, creating odors and
corroding the pumps. The extra cost of the reservoir might not
compensate for the saving in the capacity and operation of the
pumps.

The capacity of the receiving well should be so designed that
the pump when operating will be working at its maximum capacity,
and the period of rest during conditions of average rate of flow
should be in the neighborhood of 15 to 20 minutes. For example,
assume an average rate of flow of 2 cubic feet per second, with a
maximum rate of double this amount. The pump should have a
capacity of 4 cubic feet per second, and if the receiving well is to
be filled in 15 minutes by the average rate of sewage flow its capac-
ity should be 15X5X60X7.5 or 14,000 gallons. Under these
circumstances the pump will operate 15 minutes and rest 15
minutes, during average conditions of flow.

74. Types of Pumping Machinery. — The two principal types
of pumping machines for lifting sewage are centrifugal pumps and
reciprocating pumps. A centrifugal pump is, in general, any
pump which raises a liquid by the centrifugal force created by a
wheel, called the impeller, revolving in a tight casing, as shown in
Fig. 50. A reciprocating pump is one in which there is a periodic
reversal of motion of the parts of the pump.

Centrifugal pumps are sometimes classified as volute pumps
and turbine pumps. A volute pump is a centrifugal pump with a
spiral casing into which the water is discharged from the impeller
with the same velocity at all points around the circumference, as
shown in Fig. 51. A turbine pump is a centrifugal pump in which
the water is discharged from the impeller through guide passages
into a collecting chamber, in such a manner as to prevent loss of
energy in changing from kinetic head to pressure head. A tur-
bine pump is shown in section in Fig. 51. Centrifugal pumps are
sometimes classified as single stage and multi-stage. A centrif-
ugal, pump from which the water is discharged at the pressure

TYPES OF PUMPING MACHINERY

131

created by a single impeller is called a single-stage pump. If the
water in the pump is discharged from one impeller into the suction
of another impeller the pump is known as a multi-stage pump.

Woodruff Keys

FIG. 50. — Section through de Laval Single-Stage, Double-Suction Centrifugal

Pump.

375 Lubricating ring. 554

380 Oil hole cap. 555

383 Oil drain tube. 555-1

404 Shaft sleeve lock nut. 556

440 Driving coupling. 560

441 Driven coupling. 563
443 Coupling check nut. 567R

450 Coupling bolt.

451 Coupling bolt nut. 567L

452 Coupling rubber.

453 Coupling rubber steel tube. 583
600 Pump case. 567 '

550 Bearing bracket cap. 583 /

551 Bearing. 600

552 Shaft. 692

553 Shaft sleeve, right hand thread 815
PW Impeller. 815-1

Shaft sleeve, left hand thread.

Shaft stop collar, inner.

Shaft stop collar, outer.

Guide ring.

Packing gland.

Bearing.

Impeller protecting ring, right hand

thread.
Impeller protecting ring, left hand

thread.
Pump case protecting ring.

Labyrinth packing.

Pump case cover.
Impeller key.
Bearing bracket, outer.
Bearing bracket, inner.

The number of impellers operating at different pressures deter-
mines the number of stages of the pump. A three-stage pump is
shown in Fig. 52.

132

PUMPS AND PUMPING STATIONS

Reciprocating pumps are generally driven by steam and are
either direct-acting, or of the crank-and-fly-wheel type. Power
pumps are reciprocating machines which may be driven by any
form of motor, to which they are connected by belt, chain or shaft.
A Deming triplex power pump is shown in Fig. 53. Power

-• Impeller

•Impeller Eye

-'Diffusion
Vanes

Volute Pump. TurbmePump, Circular Case.

FIG. 51. — Types of Centrifugal Pumps.

pumps can be used only where the character of the sewage will
not clog the valves nor corrode the pump. A direct-acting steam
pump is one in which the steam and water cylinders are in the
same straight line and the steam is used at full boiler pressure
throughout the full length of the stroke. The crank-and-fly-

FIG. 52. — Section of a Multi-Stage Centrifugal Pump.

Courtesy DeLaval Steam Turbine Co.

wheel type of pumping engine permits the use of steam expan-
sively during a part of the stroke, the energy stored in the fly-
wheel carrying the machine through the remainder of the stroke.
Reciprocating pumps are sometimes classified as plunger pumps
and piston pumps. In the action of a plunger pump the water is
expelled from the water cylinder, by the action of a plunger

133

53.— Triplex Power Pump.

Courtesy, The Deming Co.

which only partly fills the water cylinder, as shown in Figs. 54
and 55. In a piston pump the water is expelled from the water
cylinder by the action of a piston which completely fills the water
cylinder, as shown in Fig.
63, which illustrates a direct-
acting piston pump.

Plungers are better than
pistons for pumping sewage
as the wear between the pis-
tons and the inside face of
the cylinder soon reduces the
efficiency of the pump. Out-
side packed plungers are
better than the inside packed
type because the packing can
be taken up without stopping
the pump and the leakage

from the pump is visible at all times. Outside packed pumps
are more expensive in first cost, but are easier to maintain and
have a longer life than piston pumps.

In selecting a pump to perform certain work the size of the
water cylinder and the speed of the travel of the piston should be
_____________________________ investigated to insure proper

capacity. The average linear
travel of the piston for slow
speed pumps is estimated at
about 100 feet per minute,
dependent on the length of
stroke and the valve area.
For short strokes and small
valve areas the speed may
be as low as 40 feet per min-
ute, and for long stroke fire
pumps with large valves
the piston can be operated
at a speed of 200 feet per
minute.1 Vertical, triple-expansion, crank-and-fly- wheel, outside-
packed plunger pumps with flap valves can be operated at speeds
of 200 feet per minute when lifting sewage, and when equipped
1 " Direct Acting Steam Pumps," by F. R. Nickel, 1915.

FIG. 54. — Water End of Inside Center-
Packed Plunger Pump.

134

PUMPS AND PUMPING STATIONS

with mechanically operated valves and lifting water they can be
run at speeds of 400 to 500 feet per minute. The speed of travel
multiplied by the volume of piston or plunger displacement, with
proper allowance for slippage, will give the capacity of the pump.
The slippage allowance may be from 3 to 8 per cent for the best
pumps, and for pumps in poor conditions it may be a high as 30 to
40 per cent,

Channel Way
f * Pump

Main Suction Pipe

FlG. 55 — Water End of Outside Center-Packed Plunger Pump.

Courtesy Allis-Chalmers Co.

There are two types of ejector pumps used for lifting sewage.
One of these depends on the vacuum created by the velocity of a
stream of water or steam passing through a small nozzle. The
operation of this pump is described in Art. 139 and it is illustrated
in Fig. 97. The other type of ejector pump is known as the com-
pressed-air ejector. It is operated by means of compressed air
which is turned into a receptacle containing sewage. The details
of this type are explained in Art. 83 and are illustrated in Fig. 68.

SIZES AND DESCRIPTION OF PUMPS 135

75. Sizes and Description of Pumps. — The size of a centrif-
ugal pump is expressed as the diameter of the discharge pipe in
inches. It has nothing to do with the head for which the pump
is suited. On the assumption of a velocity of flow of 10 feet per
second through the discharge pipe the capacity of the pump can be
approximated.

The size of a reciprocating pump involves the expression of the
diameters of the steam cylinders, the water cylinder, and the length
of the stroke in inches, in the order named, beginning with the
steam cylinder with the highest pressure. A complete descrip-
tion of a steam pumping engine might be; compound, duplex,
horizontal, condensing, crank-and-fly-wheel, outside-center-
packed, 12"X24"X18"X24" pump. The word compound
means that there are a high-pressure and a low-pressure steam
cylinder; the word duplex means that there are two of each of
these cylinders; the word horizontal means that the axes of these
cylinders are in a horizontal plane; the word condensing means
that the steam is discharged from the low-pressure cylinders into a
condenser; the name crank-and-fly-wheel is self-explanatory;
the name outside-center-packed means that the water cylinder is
divided into two portions between which the plunger is exposed
to the atmosphere, and that the packing rings are on the outside
of the two portions of the cylinder as shown in Fig. 55 ; the figures
shown mean that the high-pressure steam cylinder is 12 inches in
diameter, the low-pressure 24 inches in diameter, the water cylin-
der is 18 inches in diameter, and the stroke of the pump is 24
inches.

76. Definitions of Duty and Efficiency. — The duty of a pump
is the number of foot pounds of work done by the pump per
million B.T.U., per thousand pounds of steam, or per hundred
pounds of coal, consumed in performing the work. These units
are only approximately equal as 100 pounds of coal or 1,000 pounds
of steam do not always contain the same number of B.T.U. and
may only approximately equal 1,000,000 B.T.U.

Since 1,000,000 B.T.U. are equal to 778,000,000 foot-pounds
of work, a pump with a duty of 778,000,000 will have an effi-
ciency of 100 per cent. The efficiency of a pump is therefore its
duty based on B.T.U. divided by 778,000,000. The efficiencies
or duties of various types of pumps are given in Table 26.1
1 From Heat Engines, by Allen and Bursley.

136 PUMPS AND PUMPING STATIONS

TABLE 26
APPROXIMATE DUTIES OF STEAM PUMPS

Small duplex, non-condensing 10,000,000

Large duplex, non -condensing 25,000,000

Small simple, flywheel, condensing 50,000,000

Large simple, flywheel, condensing 65,000,000

Small compound, flywheel, condensing 65,000,000

Large compound, flywheel, condensing 120,000,000

Small triple, flywheel, condensing 150,000,000

Large triple, flywheel, condensing 165,000,000

77. Details of Centrifugal Pumps. — A section of a centrifugal
pump with the names of the parts marked thereon is shown in
Fig. 50. Among the important parts which require the attention
of the purchaser are: the impeller (PW), the impeller packing
rings (567 R & L), the bearings (551, 563), the thrust bearings
(555-1), the shaft (552), and the shaft coupling (440).

The impeller should be of bronze, gun metal, or other alloy,
because there is no rusting or roughening of the surface, and the
efficiency does not fall with age. Normal fresh sewage is not
corrosive, but septic sewage and sludge are usually so corrosive
that iron parts cannot be used with success in contact with them.
The impeller should be machined and polished to reduce the fric-
tion with the liquid. Impellers are made either closed or open,
i.e., either with or without plates on the sides connecting the
blades to avoid the friction of the liquid against the side of the
casing. The closed type of impeller is shown in Fig. 50. Closed
impellers are slightly more expensive, but generally give better
service and higher efficiencies than the open type. Single impeller
pumps should have an inlet on each side of the impeller to aid in
balancing the machine, unless the plane of the impeller is to be
horizontal when operating. Multi-impeller pumps usually have
single inlet openings for each impeller. Vibration in the pump is
sometimes caused by an unbalanced impeller. The moving parts
may be balanced at one speed and unbalanced at another. To
determine if the moving parts are balanced the pump should be
run free at different speeds and the amount of vibration observed.
If the impeller is removed from the pump its balance when at
rest can be studied by resting it on horizontal knife edges. If
there is a tendency to rotate in any direction from any position
the impeller is not perfectly balanced.

DETAILS OF CENTRIFUGAL PUMPS

137

Packing rings are used to prevent the escape of water from
the discharge chamber back into the suction chamber. These
rings should be made of the same material as the impeller.
Labyrinth type rings, as shown in Fig. 50, are sometimes used as
the long tortuous passages are efficient in preventing leakage.

The bearings must be carefully made because of the high speed
of the pump. They are usually made of cast iron with babbitt
lining. They should be placed on the ends of the shaft on the
outside of the pump casing, as shown in Fig. 50, and should be
split horizontally so as to be easily renewed. Exterior bearings
are oil lubricated by means of ring or chain oilers with deep oil
wells. Where interior bearings are necessary, because of the length
of the shaft, they should be made of hard brass and should be
water lubricated.

Thrust bearings or thrust balancing devices are used to take
up the end thrust which occurs in even the best designed pumps.
To overcome this pumps are designed with double suction,
opposed impellers, or two pumps with their impellers opposed
may be placed on the same shaft. Due to inequalities in wear,
workmanship or other conditions, end thrust will occur and must
be cared for. Various types of thrust bearings are in successful
use, such as: the piston, ball, roller or marine types. The marine
type thrust bearing is shown in Fig. 56. The piston type of

FIG. 56. — Marine Type Thrust Bearing.
Courtesy, DeLaval Steam Turbine Co.

hydraulic balancing device is shown in Fig. 57. In the figure A
represents the impeller, and B a piston fixed to the shaft and
revolving with it. There is a passage for water through the open-
ings (1), (2), and (3) leading from the impeller chamber to the
atmosphere or to the suction of the pump. If the impeller tends
to move to the right opening (1) is closed resulting in pressure on

138 PUMPS AND PUMPING STATIONS

the right of the impeller forcing it to the left. If the impeller
moves to the left (1) is opened thus transmitting pressure to the
piston B forcing the impeller to the right. The flange C is not
essential, but is advantageous in pumps handling gritty matter.
As the channel (2) wears larger the pressure against the piston
decreases allowing it to move to the left. This partially closes
(3) building up the pressure again.

Flexible shaft couplings should be used if the shaft of the
driving motor and the pump are in the same line, as direct align-
ment is difficult to obtain or to
maintain. Where connected to steam
turbines, reduction gearing and rigid

couplings are usually used on sewage

& pumps to obtain slow speed and per-

'l 2'' H mit large passages. Flexible coup-

FIG. 57.— Piston Type of Thrust lingsare of various types, oneof which
Balancing Device. is shown in Fig. 50. A rigid coup-

ling would be formed by bolting

the flanges firmly together. Shaft couplings are usually not
necessary where the pump is driven by belt connection to the
engine or motor, or where the pump and pulley rest on only two
bearings.

The stuffing box shown in Fig. 50 is packed loosely with two
layers of hemp between which is a lantern gland, in order to permit
a small amount of leakage. A drip box is placed below this gland
to catch the leakage and return it to the pump. The leakage is
permitted as it aids in lubrication and the tightening of the gland
will cause binding of the shaft. The gland on the suction side of
the pump should be connected by a small pipe to the discharge
chamber in order to keep a constant supply of water for lubrica-
tion and to prevent the entrance of air to the suction end of the
pump.

78. Centrifugal Pump Characteristics. — The capacity of a
centrifugal pump is fixed by the size and type of its impeller and
by the speed of revolution. Roughly, the capacity of a pump,
for maximum efficiency, varies directly as the speed of revolution,
the discharge pressure varies as the square of the speed, and the
power varies as the cube of the speed. These relations are found
not to hold exactly in tests because of internal hydraulic friction
in. the pump.

CENTRIFUGAL PUMP CHARACTERISTICS

139

The characteristic curves for a centrifugal pump, or the so-
called pump characteristics, are represented graphically by the
relation between quantity and efficiency, quantity and power
necessary to drive, and quantity and head, all at the same speed.
The quantities are plotted as abscissas in every case. The curve
whose ordinates are head and whose abscissas are quantities is
known as " the characteristic." The curve showing the relation
between quantities and speeds is sometimes included among the
characteristics. Characteristics of pumps with different styles
of impellers are shown in Fig. 58. Fig. 59 shows the character-
istics of a pump run at different speeds, the efficiencies at these

Type 1.

0 10 20 30 40 50 60 70 80
Capacity in Gallons per Minute

FIG. 58. — Characteristics of Centrifugal Pumps with Different Styles of
Impellers at Constant Speed.

speeds when pumping at different rates, and the maximum effi-
ciency at different speeds. It is to be noted that the informa-
tion given in this figure is more extensive than that in Fig. 58.
The operating conditions under any head, rate of discharge, and
speed are given. The curves of constant speed are parallel, and
their distances apart vary as the square of the speed. The
line of maximum efficiency is approximately a parabola.

A study of the characteristics of any particular pump should be
made with a view to its selection for the load and conditions under
which it is to be used. Among the important things to be con-
sidered in the selection of a centrifugal pump for the expected
conditions of load are: the capacity required, the maximum and
minimum total head to be pumped against, the maximum varia-
tions in suction and discharge heads, and the nature of the drive.
For example, the pump, whose characteristics are shown in Fig.

140

PUMPS AND PUMPING STATIONS

59, should be operated at about 800 revolutions per minute.
Under total heads between 40 and 50 feet, the discharge for the

0 100 200 300 400 500 .600 700 800 900 1000 1100 1200 1300
Capacity in Gallons perJMfnute

FIG. 59. — Efficiency and Characteristic Curves of a Centrifugal Pump at

Different Speeds.

best efficiency will vary between 600 and 670 gallons per

minute.

The efficiencies of centrifugal pumps increase with their
capacities as is shown approximately
in Fig. 60.

79. Setting of Centrifugal Pumps.
—In setting a centrifugal pump, care
should be taken to provide a firm
foundation to hold the shafts of the
pump and the electric motor or the
reduction gearing in good alignment,
or to prevent the pump from being
displaced by the pull of a belt. It is
desirable that the foundation be level.
Centrifugal pumps should be set sub-
merged for small pumping stations

automatically controlled. Sludge pumps must be set submerged

as otherwise they will not prime successfully. Provision should be

•0

Jeo

50
40

•**

0 10 20 30 40 50

Size of Pumps in Inches

FIG. 60. — Efficiencies of Cen-
trifugal Pumps.

SETTING OF CENTRIFUGAL PUMPS

141

made by which the pump can be lifted from the sewage, or sludge,
for inspection and repair. In many cases the pump can be made
self-priming by setting it in a dry. water-tight vault below the low
level of sewage flow. Where possible it is desirable not to set the
pump submerged as it will receive better care when easily acces-
sible.

The suction pipe should be free from vertical bends where air
might collect and should be straight for at least 18 to 24 inches
from the pump casing. An elbow on the suction pipe, attached
directly to the casing of the pump gives a lower efficiency than a
suction pipe with a short straight run. Centrifugal pumps will
operate with as high a suction lift as reciprocating pumps, but at
the start they must be primed and some provision must be made
for priming them. The suction pipe should be equipped with
foot valves to hold the priming, or some method may be provided
for exhausting the air from the suction pipe. The foot valves
should be so installed as to form no appreciable obstruction to the
flow of water. They should have an area of opening at least 50
per cent greater than the cross-section of the suction pipe. A
strainer on the suction pipe is un-
desirable as it becomes clogged
and is usually in an inaccessible
position for cleaning. A screen
should be placed at the en-
trance to the suction well to
prevent the entrance of objects
that are likely to clog the pump.
A gate-valve and a check-valve
should be provided on the dis-
charge pipe, the former to assist
in controlling the rate of dis-
charge and the latter to prevent
back flow into the pump when
it is not operating.

Centrifugal pumps are well
adapted to service in either large
or small units. An installation
in a manhole at Park Point,

Duluth, is shown in Fig. 61. This station is controlled by an
automatic electric device which is operated by a float in the suc-

24"M.H.
Cover,

Overflo

Float-

61.— Centrifugal Pump in Man-

hole at Duluth, Minn.
Eng. Contracting, vol. 43. 1915, p. 310.

142

PUMPS AND PUMPING STATIONS

tion pit. Such automatic control is an added advantage of the
use of electrically driven centrifugal pumps. The Calumet
Pumping Station in Chicago, shown in Fig. 49, has a capacity of
approximately 1,000 cubic feet per second. The simplicity of the
layout of this station is shown in Fig. 62.

Suction Basin Gages

Dry Weaf her Discharge Basin Gag*
~''-6"-\~&.— -24'-

- ifn ~

'Storm Water
Discharge
Basin Oages \,/

-34-3- >k

FIG. 62. — Interior Arrangement of the Calumet Sewage Pumping Station,

Chicago.

Eng. News-Record, Vol. 85, 1920, p. 872.

80. Steam Pumps and Pumping Engines. — The direct-acting
steam pump, one type of which is shown in Fig. 63, is adapted to
pumping sewage the character of which will not corrode or clog
the valves. In this form of pump it is necessary to utilize the
steam at full pressure throughout the entire length of the stroke,
which results in high steam consumption. A fly-wheel permits
the use of steam expansively during a part of the stroke, thus
increasing the economy of operation. Other devices used for the
same purpose are known as compensators. They are not in
general use.

Steam engines are classified in many different ways, for
example ; according to the type of valve gear, as, plain slide valve,
Corliss, Lentz, etc.; or according to the number of steam expan-

STEAM PUMPS AND PUMPING ENGINES

143

sions, as, simple, compound, triple expansion, etc.; or according
to the efficiency of the uoachine as low duty or high duty; or as

FIG. 63. — Section of Duplex Piston Steam Pump.

Courtesy, The John H. McGowan Co.

STEAM END

2 Steam cylinder and housing combined.
8 Steam piston head.
0 Steam piston follower.

10 Steam piston inside ring.

11 Steam piston outside ring (2).

12 Steam cylinder head.
14 Steam chest.

16 Steam chest cover.

17 Steam slide valve.

18 Steam valve rod.

20 Steam valve rod, pin and nut.

22 Steam valve rod, collar and set screw.

23 Steam valve rod, stuffing box.

24 Steam valve rod, stuffing box, nut and

gland.
38 Piston rod.

47 Piston rod stuffing box.

48 Piston rod, stuffing box, nut and gland.
40 Valve gear stand.

51 Long valve crank and shaft.

52 Short valve crank and shaft.

PUMP END
115 Pump body.
127 Brass liner.

129 Water piston head.

130 Water piston follower.
137 Cylinder head.

139 Valve plate.

140 Cap

152 Suction flange.

161 Discharge flange.

162 Valve seat, suction or discharge.

163 Valve, suction or discharge.

164 Suction valve spring.

167 Discharge valve spring.

168 Valve plate, suction or discharge.

169 Valve stem, suction or discharge.

STEAM END

55 Crank pin.

56 Valve rod link.

61 Long rocker arm.

62 Short rocker arm.

63 Rocker arm wiper.
69 Cross head.

condensing or non-condensing, etc. Throttling engines or auto-
matic engines refer to the method of control of the steam by the
governor. In throttling engines the governor controls the amount

144

PUMPS AND PUMPING STATIONS

of opening of the throttle valve, in automatic engines the governor
controls the position of the cut-off.

The simple slide-valve, low-duty, non-condensing, throttling
engine, is the lowest in first cost and the most expensive in the
consumption of fuel. The triple-expansion Corliss, or the non-
releasing Corliss, high-duty pumping engine is the most expensive
in first cost but consumes less steam for the power delivered than
any other form of reciprocating engine. For pumps of very small
capacity the cost of fuel is not so important an item as the first
cost of the machine. For this reason and because of the lower

9x6 ' Non Condensing, Jhrottlincf
High Speed , Single Valve

125 K. W. Non Condensing, Automatic,
High Speed. Single Valve

den sing, Rotary 4 Valve, Mediumope

125 K,W. Compound Condensing,
Automatic, Highspeed, SingleValve--

•-450H.P. De Laval Turbine

400 K.W. Compound

Condensing, Medium Speed, Popped Valve

40 60 80

Per Cent of Rated Load

120

20
10(

1 1
»s^ ^Condensing

,Me4

H=J
ines

ium S

Deed,

Rotary

'41/al

i 1 —

,.Ct

mpour

id Con

densin

j, Medi

jmSpe

ed, Pof.

pettVa

Ive

) 200 400 600 600 1000 1200 140
Horse Power

FIG. 64. — Diagram Showing Rates of Steam Consumption for Different Size
Units under Different Loads.

cost of attendance low-duty pumps are more frequently found in
small pumping stations.

The steam consumption per indicated horse-power, better
known as the water rate of the engine, for various types of engines
at full and at part load is shown in Fig. 64. The steam consump-
tion of other types at full load is shown in Table 27. The indi-
cated horse-power (I.H.P.) of a steam engine is the product of
the mean effective pressure (M.E.P.), the area of the steam

STEAM PUMPS AND PUMPING ENGINES

145

Type of Engine

Power,
K.W.

Per Cent of Full Load

Boiler
Press,
Lbs.

100

125

Single cylinder, high speed, non-condensing

25
250

27
37.5

M.I

27.0
34.0

27.5
34.0

100 to
150

Automatic, flat four valve, high speed

150
250

32
33

30
31

26.5
28

29.0
30.0

100 to
125

Tandem compound condensing, high speed

125

19
20

17
19.5

18
21

100 to
150

Cross compound, condensing, high speed

23.5

125

Cross compound, non-condensing, highspeed

27.5

125

Single cylinder Corliss, condensing

120
500

23.7
26.3

20.4
22.8

19
21.3

18.5
20.8

19.0
21.3

100
125

Compound Corliss, condensing

16.5
22.2

14
19

12.5

17.0

12.1
16.5

12.5
17.0

100
150

Single cylinder, rotary four valve, non-con-
densing

75
400

26.2
35.0

22.3
27.2

21.3
26.4

21.6
26.0

22.8
26.8

100
180

Rotary four valve, tandem compound non-
condensing

125
600

32.0
40.0

22.0
28.3

20
23.2

18.25
22.5

18.5
22.7

100
150

Cross compound, non-condensing rotary
four valve

125
600

25
39.4

19.1
22.3

18.5
20.6

19.0

20.7

100
150

Single cylinder, poppett valve, non-con-
densing

120
600

22.7
28.5

20.5
26.0

19.7
25.0

19.1
24.3

20.1
25.5

100
150

Single cylinder, poppett valve, condensing

120

600

18.5
24.6

16.7
22.3

16.1
21.4

15.6
20.8

16.4
21.9

100
150

Compound condensing, poppett valve

200

1200

14.2
18.4

13.0
16.9

12.5
16.3

12.2
15.9

12.9
16.8

100
150

Uniflow

125
600

14.6
15.0

13.7
14.3

13.4
13.7

13.4

13.5

13.3
14.0

150

Steam turbines, condensing, Allia-Chalmers

300
2000

24
31.9

17
26.3

160
23.8

16.5
23.0

125
175

Steam turbines, condensing, Westinghouse

300

2000

13.7
18.2

12.8
16.9

12.2
16.2

12.6
16.8

125
175

Steam turbines, high pressure, non-con., 12*
to 36" wheel, 1000 to 3600 R.P.M.

4 to 8
stages

28.5
116.5

Ditto. Condensing, 26-inch

17.3
112.0

146 PUMPS AND PUMPING STATIONS

pistons, the length of the stroke, and the number of strokes per
unit of time. A common form of this expression is,

PLAN

33,000 '

in which P=the M.E.P. in pounds per square inch;
L = the length of the stroke in inches;
A = the sum of the areas of the pistons in square inches;
N = the number of revolutions per minute.

The I.H.P. multiplied by the mechanical efficiency of the machine
will give the brake or water horse-power, that is, the horse-power
delivered by the machine. The product of the M.E.P., the sum
of the areas of the steam pistons and the mechanical efficiency of
the machine, should equal the product of the total head of water
pumped against expressed in pounds per square inch and the sum
of the areas of the water pistons or plungers. The M.E.P. is
determined from indicator cards taken from the steam cylinders
during operation. These cards show the steam pressure on the
head and crank ends of each cylinder at all points during the stroke.
81. Steam Turbines. — Among the advantages in the use of
steam turbines as compared with reciprocating steam engines for
driving centrifugal pumps are their simplicity of operation, the
small floor space needed, their freedom from vibration requiring a
relatively light foundation, and their ability to operate success-
fully and economically either condensing or non-condensing
under varying steam pressure. They can be operated with steam
at atmospheric or low pressure, thus taking the exhaust from
other engines. The greatest economy of operation for the tur-
bine alone will be obtained by operating with high pressure, super-
heated steam and with a vacuum of 28 inches. In large units
the economy of operation of steam turbines is equal to that of the
best type of reciprocating engines. In order to develop the high-
est economy turbines are operated at speeds from about 3,600 to
10,000 r.p.m. or greater, the smaller turbines operating at the
higher speeds. As these speeds are usually too great for the
operation of centrifugal pumps for lifting sewage, reduction gears
must be introduced between the turbine and the pump. Although
the best form of spiral-cut reduction gears may obtain efficiencies
of 95, to 98 per cent, or even higher, their use, particularly in small

STEAM PUMPS AND PUMPING ENGINES

147

units, is an undesirable feature of the steam turbine for driving
pumps.

The steam consumption of DeLaval turbines of different
powers, and the steam consumption of a 450 horse-power DeLaval
turbine at different loads are shown in Fig. 64. Some steam con-
sumptions of other turbines are recorded in Table 27. It is to be
noted that the steam consumption of the 450 horse-power turbine
at part loads is not markedly greater than that at full loads.
This is an advantage of steam turbines as compared with recipro-
cating engines. The steam consumption of any turbine is depend-
ent on the conditions of operation and is lower the higher the
vacuum into which the exhaust takes place.

There are two types of turbines in general use, the single stage
or impulse machines, and the compound or reaction type. The
DeLaval is a well-known make
of the single stage or impulse type.
The principle of its operation is
indicated in Fig. 65, which is the
trade mark of the DeLaval Steam
Turbine Co. The energy of the
steam is transmitted to the wheel
due to the high velocity of the
steam impinging against the
vanes. In the compound or re-
action type of machine the steam
expands from one stage to the
next imparting its energy to the
wheel by virtue of its expansion
in the passages of the turbine.
For this'i reason the single-stage

or impulse type is operated at higher speeds than the compound
or reaction machines.

82. Steam Boilers. — Among the important points to be con-
sidered in the selection of a steam boiler for a sewage pumping
station are: the necessary power; the quality of the feed water;
the available floor space; the steam pressure to be carried; and
the quality and character of the fuel. Tubular boilers of the
type shown in Fig. 66, are lower in first cost than other types of
boilers. They are not ordinarily built in units larger than 250 to
300 horse-power and where more power is desired a number of

FIG. 65.— The DeLaval Trade
Mark, Illustrating the Principle
of the DeLaval Steam Turbine.

Courtesy, DeLaval Steam Turbine Co.

148

PUMPS AND PUMPING STATIONS

FIG, 66. — Horizontal Fire-tube Boiler.

units must be used. They are objectionable because of the

relatively large floor space
required, and because of their
relatively poor economy of
operation. The efficiencies
of water-tube boilers of dif-
ferent types are given in
Table 28. Large power units
of the water-tube type, as
shown in Fig. 67, although
more expensive in first cost,
require less floor space. Al-
most any desired steam
pressure can be obtained
from either type but water-
tube boilers are more com-
monly used for high pres-
sures. The grate or stoker

can be arranged to burn almost any kind of fuel under either
water-tube or fire-tube boilers. The use of poor quality of water
in water-tube boilers is un-
desirable as the tubes are
more likely to become clogged
than the larger passages of
the fire-tube boilers. If nec-
essary, a feed-water puri-
fication plant should be
installed, as it is usually
cheaper to take the inpurities
out of the water than to take
the scale out of the boiler.

Not less than two boiler
units should be used in any
power station, regardless of
the demands for power, and
if the feed water is bad, three pIG 67.— Babcock and Wilcox Water-
or even four units should tube Boiler,

be provided, as two units
may be down at any time.

An appreciable factor of safety is

provided by the ability of a boiler to be operated at 30 to 50 per

STEAM BOILERS

149

cent overload, if sufficient draft is available, but with resulting
reduction in the economy of operation. The number of units
provided should be such that the maximum load on the pumping
station can be carried with at least one in every 6 units or less,
out of service for repairs or other cause.

TABLE 28

EFFICIENCIES OF STEAM BOILERS
From Marks' Mechanical Engineer's Handbook

Per

Evap.

Com-

Cent

B.T.U.

from and

bined

Sq. Ft.

per

at 212°

Effi-

Type

Furnace

Grate

Rated

Lb.

per

ciency

Area

Capac-

Dry

Lb.

of Boiler

ity

Coal

Dry

and

D'vTd

Coal

Furnace

Babcock <fc Wilcox

300

118 7

11 912

8 81

71 8

Babcock & Wilcox

640

Hand-fired

118

121 5

14,602

10 83

72 0

1128

B. & W. chain grate .

187

198.3

12,130

9.51

76 1

Rust

335

Hand-fired

210 5

13,202

9 42

68 9

400

Green chain grate. . .

83.5

123.8

11,608

8.79

73 5

Maximum efficient

y recor

led

The steam delivered by a boiler is the basis of the measurement
of its capacity or power. A boiler horse-power is the delivery of
33,320 B.T.U. per hour. It is approximately equal to the raising
of 30 pounds of water per hour from a temperature of 100°
Fahrenheit, to steam at a pressure of 70 pounds per square inch,
or to 34 pounds of water per hour changed to steam from and at
212° Fahrenheit, at atmospheric pressure. The horse-power of a
boiler is sometimes approximated by the area of its grate or heat-
ing surface. Such a method of measuring has a low degree of
accuracy on account of the variations in the quality of the fuel,
and the rate of combustion. For example, the rate of combustion
under a locomotive boiler is high and there is less than ^th of a
square foot of grate area and about 4.5 square feet of heating
surface per boiler horse-power. The Scotch Marine type of boiler
used on steam ships, has slightly more grate area and slightly less
heating surface than the locomotive type of boiler, because the
rate of combustion is lower. Stationary water-tube boilers may
have 2 to 3 times as much grate area and heating surface per

150

PUMPS AND PUMPING STATIONS

horse-power as is found in locomotive boilers. If a poor type of
fuel is to be used the area of the grate should be increased about
inversely as the heat content of the fuel. The approximate heat
content of various types of fuels is shown in Table 29.

TABLE 29
APPROXIMATE HEAT VALUE OF FUELS

Fuel

B.T.U.
per
Pound

Pounds of Water
Evaporated from
and at 212° F.
All heat utilized

Anthracite

13,500

14 0

Semi-bituminous, Pennsylvania

15,000

15 5

Semi-bituminous, best, West Virginia

15,000

15 8

Bituminous, best, Pennsylvania

14,450

15 0

Bituminous, poor, Illinois

10,500

10 9

Lignite, best, Utah

11,000

11 4

Lignite, poor, Oregon

8,500

8 8

Wood, best oak

9,300

9 6

Wood, poor ash

8,500

8 8

83. Air Ejectors. — The Ansonia compressed-air sewage ejector
is shown in Fig. 68. In its operation, sewage enters the reservoir
through the inlet pipe at the right, the air displaced being expelled
slowly through the air valve marked B. The rising sewage lifts
the float which actuates the balanced piston valve in the pipe
above the reservoir when the reservoir fills. The lifting of the
valve admits compressed air to the reservoir. The air pressure
closes valve A and the inlet valve at the right, and ejects the
sewage through the discharge pipe at the left. As the float drops
with the descending sewage it shuts off the air supply and opens
the air exhaust through the small pipe at the top center. Sewage
is prevented from flowing back into the reservoir by the check
valve in the discharge pipe. Other ejectors operating on a similar
principle are the Ellis, the Pacific, the Priestmann and the Shone.

84. Electric Motors. — The most common form of alternating
current electric motor used for driving sewage pumps where con-
tinuous operation and steady loads are met is the squirrel-cage
polyphase induction motor. These motors operate at a nearly

ELECTRIC MOTORS

151

constant speed which should be selected to develop the maximum
efficiency of the pump and motor set. While Fig. 59 shows the
best efficiency under varying heads to be obtained with variable
speed, the advantages of cost, attention, and availability make
the use of a constant speed motor common.1 This type of motor
is undesirable where stopping and starting are frequent because
it has a relatively small starting torque and it requires a large

FIG. 68. — Ansonia Compressed-Air Sewage Ejector.

starting current. Such motors can be constructed in small sizes
for high starting torques by increasing the resistance of the rotor,
but at the expense of the efficiency of operation.

Alternating current motors are more generally used than direct-
current motors because of the greater economy of transmission of
alternating current, but where direct current is available constant
speed shunt wound motors should be adopted.

1 " The Economy Resulting from the Use of Variable Speed Induction
Motors for Driving Centrifugal Pumps " by M. L. Enger and W. J. Putnam.
Journal Am. Water Works Ass'n., 1920, Vol. 7, p. 536.

152 PUMPS AND PUMPING STATIONS

In the selection of a motor to drive a centrifugal pump it is
important that the motor have not only the requisite power, but
that its speed will develop the maximum efficiency from the pump
and motor combined. If the pump and motor operate on the
same shaft the speed of the two machines must be the same. If
the two are belt connected, the size of the pulleys may be selected
so as to give the required speed. If the motor is to be connected
to a power pump an adequate automatic pressure relief valve
should be provided on the discharge pipe from the pump, to pre-
vent the overloading of the motor or bursting of the pump in case
of a sudden stoppage in the pipe. The motor must be selected to
suit the conditions of voltage, cycle, and phase on the line. Trans-
formers are available to step the voltage up or down to practically
any value. Rotary converters are used to change direct to alter-
nating current or vice versa.

85. Internal Combustion Engines. — Internal combustion
engines are used for driving pumps. Units are available in size
from fractions of 1 horse-power to 2,000 horse-power or more,
although the use of the larger sizes is exceptional. These engines
are not commonly used for sewage pumping but when used they
are ordinarily belt connected to a centrifugal pump, or to an
electric generator which in turn drives electric motors which
operate centrifugal pumps. This type of engine is more com-
monly adapted to small loads, although not entirely confined to
this field, as they serve admirably as emergency units to supple-
ment an electrically equipped pumping station. The fuel effi-
ciency of internal combustion engines is higher than for steam
engines as is indicated in Table 30, but the fuel is more expensive.

The four-cycle gas engine shown in Fig. 69 is the type most
commonly used. Its horse-power is the product of: the mean
effective pressure, the length of the stroke, the area of the piston,
and the number of explosions per second divided by 550. The
M.E.P. is dependent on the character of the fuel used and the
compression of the gas before ignition. Producer gas will furnish
mean effective pressures between 60 and 70 pounds per square
inch, natural gas and gasoline, 85 to 90 pounds per square inch,
and alcohol from 95 to 110 pounds per square inch.

The Diesel Engine is the most efficient of internal combustion
engines. The original aim of the inventor, Dr. Rudolph Diesel,
was to avoid the explosive effect of the ordinary internal com-

INTERNAL COMBUSTION ENGINES

TABLE 30
COMPARATIVE FUEL COSTS FOR PRIME MOVERS

Type of Engine

Quantity of Fuel
per H.P. Hour

Cost of Fuel
in Cents per
Horse-power
Hour

Reciprocating steam engines, simple, non-
condensing, 25 to 200 H.P

21 to 8 Ib. coal

4.2to 1.6

Triple condensing, 2000 to 10,000 H.P. .

2. 3 to 1.91b. coal

0.46 to 0.37

Steam turbines, high pressure, non-con-
densing,
200 to 500 K.W

6. 5 to 4. 2 Ib. coal

1.3 to 0.86

500 to 3000 K.W

2. 6 to 1.9 Ib. coal

0.52 to 0.37

Condensing 5000 to 20,000 K.W. . .

1 8 to 1 43 Ib coal

0 36 to 0.28

Gas engines
Natural gas, 50 to 200 H.P

19 to 11 cu. ft.

Producer gas, 50 to 200 H P

2 to 1 5 cu ft

Illuminating gas, 10 to 75 H P .

26 to 19 cu. ft

2.1to 1.5

Gasoline, 10 to 75 H P

1 5 to 0 8 pints

5.6to 3.0

Oil engines, 100 to 500 H.P

1 . 1 to 0 75 Ib oil

NOTE. — Coal assumed at $4.00 per ton, illuminating gas at 80 cents per thousand
cubic feet, and gasoline at 30 cents per gallon.

FIG. 69. — Bessemer Oil Engine.
Twin Cylinder, Valve Side.

154 PUMPS AND PUMPING STATIONS

bustion engine by injecting a fuel into air so highly compressed
that its- heat would ignite the fuel, causing slow combustion of
the fuel thus utilizing its energy to a greater extent. The fuel
and air were to be so proportioned as to require no cooling.
Although the ideal condition has not been attained, the heat
efficiency of Diesel engines is high. They will consume from
0.3 to 0.5 of a pound of oil (containing 18,000 B.T.U. per pound)
per brake horse-power hour, giving an effective heat efficiency of
25 to 30 per cent. Although not now in extensive use in the
United States it is probable that this engine will be more generally
adopted for conditions suitable for internal combustion engines.

86. Selection of Pumping Machinery. — Centrifugal pumps
are particularly adapted to the lifting of sewage because of their
large passages, and their lack of valves. The low lifts, nearly
constant head, and the possibility of equalizing the load by
means of reservoirs are particularly suited to efficient operation
of centrifugal pumps. They require less floor space than recipro-
cating pumps of the same capacity, and because of their freedom
from vibration they do not demand so heavy a foundation. The
discharge from the pump is continuous thus relieving the piping
from vibration. In case of emergency the discharge valve can
be shut off without shutting down the pump, an important point
in " fool proof " operation.

Volute pumps are better adapted to pumping sewage as their
passages are more free and they are better suited to the low lifts
met. Gritty and solid matter will cause wear on the diffusion
vanes of turbine pumps in spite of the most careful design.
Although turbine pumps can possibly be built with higher effi-
ciency than volute pumps, their efficiency at part load falls rapidly
and the fluctuations of sewage flow are sufficient to affect the
economy of operation. Turbine pumps are more expensive and
heavier than volute pumps on account of the increased size neces-
sitated by the diffusion vanes.

Multi-stage pumps are used for high lifts and are seldom if
ever required in sewage pumping. As ordinarily manufactured,
each stage is good for an additional 40 to 100 pounds pressure,
but wide variations in the limiting pressures between stages are
to be found.

Reciprocating plunger pumps are sometimes used for sewage
pumping where the character of the sewage is such that the

SELECTION OF PUMPING MACHINERY 155

valves will not be clogged nor parts of the pump corroded. These
pumps are seldom used in small installations or for low lifts.
They are not adapted to automatic or long distance control as
are electrically driven centrifugal pumps. The use of recipro-
cating pumps for sewage pumping is practically restricted to very
large pumping stations with capacities in the neighborhood of
50,000,000 gallons per day or more. Steam-driven pumps are
the most common of the reciprocating type, but power pumps are
sometimes used in special cases for small installations and may be
driven by either a steam or gas engine or an electric motor.

Compressed air ejectors, as described in Art. 83 are used for
lifting sewage and other drainage from the basement of buildings
below the sewer level.

Centrifugal pumps electrically driven are, as a rule, the most
satisfactory for sewage pumping. Electric drive lends itself to
control by automatic devices, which are particularly convenient
in small pumping stations. The control can be arranged so that
the pump is operated only at full load and high efficiency, and
when not operating no power is being consumed, as is not the
case with a steam pump where steam pressure must be maintained
at all times. The electric driven pump is thrown into operation
by a float controlled switch which is closed when the reservoir
fills, and opens when the pump has emptied the reservoir. The
choice between steam and electric power for large pumping stations
is a matter of relative reliability and economy.

The selection of the proper type of pump, whether recipro-
cating or otherwise, requires some experience in the consideration
of the factors involved. Fig. 70 is of some assistance. In dis-
cussing this figure, Chester states:

" Fig. 70 attempts to represent graphically, the writer's
ideas under general conditions, of the machines that should
be selected for certain capacities for both principal engine
and alternate and the station duty they may be expected
to produce, but you must realize that this intends the
principal engine doing at least 90 per cent of the work and
that the head, the cost of coal, the load factor, the cost
of real estate . . . the boiler pressure, and the space avail-
able, and finally .'. . the funds available, are factors which
may shift both the horizontal and curved lines. In the
field of low service pumps of 10,000,000 capacity or over,
the centrifugal pump reigns supreme, and for constant

156 PUMPS AND PUMPING STATIONS

low heads of 20,000,000 capacity or over the turbine driven
centrifugal usurps the field."

A reciprocating pump of any type would have to be specially
built for pumping sewage not carefully screened or otherwise
treated, as the valves, ordinarily used in such pumps for lifting
water, would clog. The vertical triple-expansion pumping
engine with special valves and for large installations, and the
centrifugal pump for large or small installations are the only suit-

+Direct-Actinq Triple Expansion./.

'////A.-/ 't///*?-, I,1/ *///£/ sv /,///.

o 10

0 1 2 3 456 7 8 9 10 11 ft 13 R 15 16 17 18 19 20
Capacity in MiHions of Gallons per Day.

FIG. 70. — Expectancy Curves for Pumping Engines Working against a Pres-
sure of 100 Pounds per Square Inch.

J. N. Chester, Journal Am. Water Works Ass'n, Vol. 3, 1916, p. 493.

able types for pumping sewage. With steam turbine or electric
drive the centrifugal has the field to itself.

87. Costs of Pumping Machinery. — The cost of pumping
machinery can not be stated accurately as the many factors
involved vary with the fluctuations in the prices of raw materials,
transportation, labor, etc. The actual purchase price of machinery
can be found accurately only from the seller. The costs given in
this chapter are useful principally for comparative purposes and
for exercise in the making of estimates. The costs of complete
pumping stations are shown in Table 3 1.1 These figures repre-
sent costs in 1911.

1 C. A. Hague in Trans. Am. Society of Civil Engineers, Vol. 74, 1911,
p. 20.

COST COMPARISONS OF DIFFERENT DESIGNS

157

TABLE 31

COSTS OF COMPLETE PUMPING STATIONS

These costs include the best type of triple expansion engines, high-pressure
boilers, brick or inexpensive stone building with slate roof, chimney and intake.
Cost of land is not included.

O U

- c

•- s
§.-2

fei

ft*

u *

00 0)

b *

£^

00 a)

£*

« 0)

oS oT^

•§ 3 w

iii

t. Dolla
orse-po

<aO

o! ^^^
"S 3 C1

t, Dolla
orse-po

jgC3

S v*~

la"?

5. c &

sll

41
Si

«^ o

S^o,

•H

o"*

~- •' —

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o*'

.« See

SMM

; ~

562

6,750

277

7,750

110

200

8,750

438

7,000

250

8,000

120

187

9,000

362

7,250

229

8,250

130

192

10,000

312

7,500

100

213

8,500

88. Cost Comparisons of Different Designs. — In the design of
a pumping station and its equipment the relative costs of different
designs should be compared, and the least expensive design
selected, due consideration being given to serviceability, reliability,
and other factors without definite financial value. In comparing
the costs of different types of machinery, all items in connection
with the pumping station should be considered. For example,
the cost of an electrically driven centrifugal pump and equipment
may be less than the total cost of a steam driven reciprocating
pump and equipment because of the saving in the cost of boilers,
boiler house, etc., but a comparison of the capitalized cost of the
two might show in favor of the reciprocating steam pump because
of the lower cost of operation.

The total cost of a plant, or any portion thereof, may be
considered as made up of three parts: (1) The first cost, (2) opera-
tion and maintenance and, (3) renewal. The total cost *S can be
expressed as

hi which

C = the first cost;

0 = the annual expenditure for operation and mainte-

nance;

R = the amount set aside to cover renewal ;
r = the rate of interest.

158 PUMPS AND PUMPING STATIONS

S is called the capitalized cost of a plant. The annual payment
necessary to perpetuate a plant is

The value of R is useful when expressed in terms of the life of the
plant or machine and the current rate of interest. It is sometimes
called the depreciation factor or capitalized depreciation. If it
is borne in mind that R is the amount to be set aside at compound
interest for the life of the plant, at the end of which time the
accrued interest should be sufficient to renew the plant, it is evi-
dent that

in which n is the period of usefulness, or life of the plant, expressed
in years, no allowance being made for scrap value.

A comparison of the annual expense of three different plants is
shown in Table 32. It is evident from this comparison that the
machinery with the least first cost is not always the least expen-
sive when all items are considered.

A sinking fund is a sum of money to which additions are made
annually for the purpose of renewing a plant at the expiration of
its period of usefulness. The annual payment into the sinking
fund is equivalent to the term Rr in the expression for annual
cost, or in terms of C, r, and n, the annual payment is

Cr
(l+r)n-r

It is the same as the capitalized depreciation multiplied by the

rate of interest. The expression ,.._, \n_i ig sometimes called

the rate of depreciation.

The present worth of a machine is the difference between its
first cost and the present value of the sinking fund. If m repre-
sents the present age of a plant in years, then the present worth is

Where straight-line depreciation is spoken of it is assumed that
the worth of a machine depreciates an equal part of its first cost

COST COMPARISONS OF DIFFERENT DESIGNS

159

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160

PUMPS AND PUMPING STATIONS

each year. For example, if the life of a plant is assumed to be
20 years, straight-line depreciation will assume that the plant
loses ^ of its original value annually. The present worth of a
plant under this assumption would be the product of its first cost
and the ratio between its remaining life and its total life. This
method of estimating depreciation and worth is frequently used,
particularly for short-lived plants and for simplicity in book-
keeping, but it is less logical than the method given above.

89. Number and Capacity of Pumping Units. — In order to
select the number and capacity of pumping units for the best
economy, a comparison of the costs of different combinations of
units should be made and the most economical combination
determined by trial. The principles outlined in the preceding
articles should be observed in making these comparisons. In a
steam pumping station, when the number of units operating is
less than the average daily maximum for the period, steam must
nevertheless be kept on a sufficient number of boilers to operate
the maximum number of pumps. This, and corresponding
standby losses must not be overlooked, as they may show that a
smaller number of larger units is ultimately more economical.

TABLE 33

SUMMARY OF FLUCTUATIONS OF SEWAGE FLOW AT A PROPOSED
PUMPING STATION

•o

•a

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Qgg
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293

6.0

450

13.4

173

15.0

ill

163

8.6

354

13.5

169

15.6

119

10.0

300

13.8

158

16.0

106

10.6

284

13.9

154

16.5

11.2

249

14.2

143

16.8

12.2

211

14.4

137

6.5

18.0

12.4

204

14.6

129

Total horse-power days for one year, 102,000.
Average load in horse-power, 280.

For example, the sewage flow expected at a proposed pumping
station is shown in Table 33. The steps involved in the selection

NUMBER AND CAPACITY OF PUMPING UNITS

161

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NUMBER AND CAPACITY OF PUMPING UNITS 163

of the number and capacity of pumping units to care for these
quantities are as follows: (1) Determine the rated capacity of
the equipment to be provided. In this case the capacity will be
taken as 450 horse-power, which is the maximum load to be placed
on the pumps. (2) Select any number of units of such different
types and capacities as are available for comparison, and arrange
them in different combinations so that each unit will operate as
nearly as possible at its rated capacity. The work involved in
such a study for 5 units is shown in Table 34. The weight of
steam consumed per indicated horse-power hour corresponding
to the per cent of the rated capacity at which the unit is operating
is read from Fig. 64 or other data. (3) Repeat this step for other
numbers and types of units. (4) Prepare a table showing the
annual costs of combinations of different numbers and types of
units as shown for this example in Table 35. The figures in Table
35 show that the least expensive of the combinations of the units
studied is one 200 horse-power unit, and one 250 horse-power
unit, with a 250 horse-power unit in reserve. It is to be noted
that a reserve unit has been provided in each combination, the
capacity of which is equal to that of the largest unit of the com-
bination.

CHAPTER VIII
MATERIALS FOR SEWERS

90. Materials. — The materials most commonly used for the
manufacture of sewer pipe are vitrified clay and concrete. Cast
iron, steel, and wood are also used, but only under special condi-
tions. For pipes built in the trench, concrete, concrete blocks,
brick, and vitrified clay blocks are used. Concrete is being used
to-day more than bricks or blocks because it is cheaper. A decade
or more ago all large sewers were built of bricks. Vitrified clay
and concrete are used for manufactured pipe 42 inches and less in
diameter. Concrete is used almost exclusively for larger sizes of
pipe, particularly for pipe constructed in place, although a brick
invert lining is advisable when high velocities of flow are expected.

The character of the external load, the velocity of flow and the
quality of sewage are important factors in determining the material
to be used in the construction of sewers. Reinforced concrete
should be used for large sewers near the surface subjected to
heavy moving loads. A high velocity of flow with erosive sus-
pended matter demand a brick wearing surface on the invert.
Many engineers consider concrete less suitable than vitrified clay
or brick for conveying septic sewage or acid industrial wastes, as
concrete deteriorates more rapidly under such conditions. Con-
crete should be used on soft yielding foundations, whereas a hard
compact earth, which can be cut to the form of the sewer, is suit-
able to the use of brick or concrete.

Cast-iron pipe with lead joints is used for sewers flowing under
pressure, or where movements of the soil are to be expected. If
the sewage is not flowing under pressure, cement joints are some-
times used in the cast-iron pipe. Movements of the soil are to
be expected on side hills, under railroad tracks, etc. Steel pipe
is used on long outfalls or under other conditions where external
loads are light and the cost is less than for other materials.
Because of the thin plates used and the liability to corrosion steel
is not frequently used, It should never be deeply buried nor

164

VITRIFIED CLAY PIPE

165

externally loaded because of its weakness in resisting such forces.
Like wood pipe, its lightness is favorable to use on bridges, but the
greater heat conductivity of steel than wood necessitates protection
against freezing in exposed positions. Wood is preferable only where
the economy of its use is pronounced and the pipe is running full
at all times. It is desirable that the wood pipe should be always
submerged as the life of alternately wet and dry wood is short.

Corrugated galvanized iron and unglazed tile have been used for
sewers, but usually only in emergencies or as a make-shift. Corru-
gated iron is not suitable on account of its roughness and liability
to corrosion, and unglazed tile because of its lack of strength.

91. Vitrified Clay Pipe. — In general the physical and chemical
qualities of clays before burning are not sufficient to cause their
condemnation or approval by
the engineer, as their behavior in
the furnace is quite individual
and depends greatly on the man-
ner in which they are fired. The
engineer is interested in the re-
sult and writes his specifications
accordingly.

In the manufacture of clay
pipe,the clay as excavated is taken
to a mill and ground while dry, to
as fine a condition as possible. It
is then sent to storage bins from
which it is taken for wet grind-
ing and tempering. In this proc-
ess the clay is mixed with water
to the proper degree of plasti-
ity. A variation of 1 to 1$ per
cent in the moisture content will
mean failure. Too wet a mix-
ture will not have sufficient
strength to maintain its shape

in the kiln. Too dry a mixture
.... ... . FIG. 71. — Diagrammatic Section

will show laminations as it is through Clay-pipe Press,

pressed through the discs.

A press used in the manufacture of clay pipe is shown in
cross-section in Fig. 71. With the piston heads in the steam and

166

MATERIALS FOR SEWERS

mud cylinders at their extreme upward positions, the mud cylinder
is filled with clay of the proper consistency. Steam is then turned
into the steam cylinder under pressure and the clay is squeezed
into the space between the inner and outer shells of the die and
mandrel to form the hub of the pipe. The pressure on the clay
may be from 250 to 600 pounds per square inch. When clay
appears at the holes, marked hh at the bottom of the mud cylinder,

FIG. 72. — Clay-pipe Press.

Courtesy, Blackmer and Post Manufacturing Co.

the bottom plate and the center portion of the die are removed
and the remainder of straight portion of the pipe is formed by
squeezing the clay between the mandrel and the outer wall of the
die. A completely formed pipe can be seen issuing from the press
in Fig. 72. Any sized pipe that is desired can be formed from the
same press by changing the size of the dies and mandrel.

Curved pipes are made in two ways — by bending directly as
they issue from the press, or by shaping by hand in plaster of
paris molds. Junctions are made by cutting the branch pipe to
the shape of the outside of the main pipe, fastening the branch

VITRIFIED CLAY PIPE 167

in place with soft clay and then cutting out the wall of the main
pipe the size of the branch. Special fittings are usually made by
hand in plaster molds.

After being pressed into shape the pipes are taken to a steam-
heated drying-room where a constant temperature is maintained
in order to prevent cracking of the pipes. They remain in the
drying room from 3 to 10 days until diy, when they are taken to
the kilns. If taken to the kilns when moist blisters will be pro-
duced.

The dried pipes are piled carefully in the kiln so that heat and
weight may be as evenly distributed as possible, and the fire is
then started in the kiln. The process of burning can be roughly
divided into five stages:

1st. Water smoking, which lasts about 72 hours during which
the temperature is raised gradually to 350 degrees Fahrenheit.

2nd. Heating, during which the temperature is raised to 800
degrees Fahrenheit in 24 hours.

3rd. Oxidation, during which the temperature is raised to
1,400 degrees Fahrenheit in 84 hours.

4th. Vitrification, in which the temperature is raised to 2,100
degrees Fahrenheit in 48 hours, and finally,

5th. Glazing, during which the temperature is unchanged but
salt (NaCl) is thrown in and allowed to burn.

Oxidation must be complete before vitrification is started as
otherwise blisters will be raised due to imprisoned carbon dioxide.
The important points in vitrification are to make the required
temperature within a reasonable time and to maintain a uniform
distribution of heat throughout the kiln. When vitrification is
complete as shown by a glassy fracture of a broken sample taken
from the kiln, glazing is accomplished by throwing a shovelful of
salt on the hottest part of the fire. About five to six applications
of salt from two to three hours apart may be needed. The kiln
is then allowed to cool and the manufacture of the pipe is com-
plete. The completeness of vitrification is indicated by the
amount of water that the finished pipe will absorb. Completely
vitrified pipe will absorb no moisture. Soft-burned pipe may
absorb as much as 15 per cent moisture.

Vitrified clay blocks are made of the same material and in the
same manner as vitrified clay pipe.

The following data on vitrified pipe have been abstracted from

168 MATERIALS FOR SEWERS

the specifications for vitrified pipe adopted by the American
Society for Testing Materials.

Pipes shall be subject to rejection on account of the following:

(a) Variation in any dimension exceeding the per-
missible variations given in Table 36.

(6) Fracture or cracks passing through the shell or
hub, except that a single crack at either end of a pipe not
exceeding 2 inches in length or a single fracture in the hub
not exceeding 3 inches in width nor 2 inches in length will
not be deemed cause for rejection unless these defects
exist in more than 5 per cent of -the entire shipment or
delivery.

(c) Blisters or where the glazing is broken or which
exceed 3 inches in diameter, or which project more than
| inch above the surface.

(d) Laminations which indicate extended voids in the
pipe material.

(e) Fire cracks or hair cracks sufficient to impair the
strength, durability or serviceability of the pipe.

(/) Variations of more than £ inch per linear foot in
alignment of a pipe intended to be straight.

(0) Glaze which does not fully cover and protect all
parts of the shell and ends except those exempted in Sect.
31. Also glaze which is not equal to best salt glaze.

(h) Failure to give a clear ringing sound when placed
on end and dry tapped with a light hammer.

(1) Insecure attachment of branches or spurs.

Workmanship and Finish

(29) Pipes shall be substantially free from fractures,
large or deep cracks and blisters, laminations and surface
roughness.

(31) The glaze shall consist of a continuous layer of
bright or semi-bright glass substantially free from coarse
blisters and pimples. . . . Not more than 10 per cent
of the inner' surface of any pipe barrel shall be bare of
glaze except the hub, where it may be entirely absent.
Glazing will not be required on the outer surface of the
barrel at the spigot end for a distance from the end equal
to | the specified depth of the socket for the corresponding
size of pipe. Where glazing is required there shall be
absence of any well defined network of crazing lines or
hair cracks.

(32) The ends of the pipe shall be square with their
longitudinal axis.

(33) Special shapes shall have a plain spigot end and

VITRIFIED CLAY PIPE

169

S OF CLAY S
ons of the Am

PROPER
Specific

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170

MATERIALS FOR SEWERS

a hub end corresponding in all respects with the dimensions
specified for pipes of the corresponding internal diameter.

(a) Slants shall have their spigot ends cut at "an angle
of approximately 45 degrees with the longitudinal axis.

Decreaser 1-8 Curve Increaser

Double T Branch Running Trap with-
out Hand Hole

Breeches

Straight Pipe

Running Trap with Double Y Branch
. Side Hand Hoie

FIG. 73. — Standard Clay Pipe Specials.

Courtesy, Blaekmer and Post Manufacturing Co.

(6) Curves shall be at angles of 90, 45, 22fc and 11J
degrees as required. They shall conform substantially to
the curvature specified.

In Fig. 73 are shown the various forms of vitrified pipe and
specials which are ordinarily available on the market.

VITRIFIED CLAY PIPE

171

The life of vitrified clay sewers and some observations on the
results of the inspection of the sewers in Manhattan are discussed
in Chapter XII. The strength of vitrified sewer pipes is shown
in Table 37.

TABLE 37
STRENGTH OF SEWER PIPE

Strength in pounds per linear foot to carry loads from ditch filling material
such as ordinary sand and thoroughly wet clay, with the under side of the
pipe bedded 60° to 90° by ordinary good methods. From Proc. Am. Society
for Testing Materials, Vol. 20, 1920, page 604.

Breadth of the Ditch a Little Below the Top of the Pipe

Height

of Fill

1 Foot

2 Feet

3 Feet

4 Feet

5 Feet

Above

Top of
Pipe,

Ditch Filling Material

Feet

sand

clay

sand

clay

sand

clay

sand

clay

sand

clay

265

280

615

635

970

990

1330

1,350

1,690

1,710

400

450

1055

1125

1745

1825

2455

2,535

3,165

3,250

470

545

1370

1500

2370

2525

3405

3,575

4,460

4,740

505

605

1600

1790

2875

3115

4215

4,495

5,595

5,890

525

640

1765

2015

3275

3610

4900

5,295

6,590

7,020

535

660

1880

2185

3600

4030

5485

6,000

7,460

8,035

540

675

1965

2320

3855

4380

5975

6,620

8,225

8,950

545

680

2025

2425

4065

4675

6395

7,165

8,890

9,775

545

685

2070

2505

4230

4920

6750

7,630

9,480

10,520

545

690

2100

2565

4365

5130

7050

8,060

9,995

11,190

545

690

2125

2610

4470

5305

7305

8,425

10,445

11,795

545

690

2140

2645

4560

5445

7525

8,750

10,840

12,340

545

690

2150

2675

4630

5575

7705

9,035

11,185

12,830

545

690

2160

2695

4685

5680

7860

9,280

11,490

13,270

545

690

2165

2715

4725

5765

7990

9,500

11,755

13,670

Very great

545

690

2180

2770

4910

6230

8725

11,075

13,635

17,305

92. Cement and Concrete Pipe. — Although there is no general
recognition of a difference between cement and concrete pipe,
there is a tendency to term manufactured pipe of small diameter
cement pipe, and large pipes or pipes constructed in place, con-
crete pipe. Cement, unlike clay, is used in the manufacture of

172 MATERIALS FOR SEWERS

pipe in the field or by more or less unskilled operators in " one
man " plants. Great care should be used in the selection of
cement, aggregate, and reinforcement for precast cement pipe
since the shocks to which it is subjected in transit are more liable
to rupture it than the heavier but steadier loads imposed on it in
the trench.

The United States Government, various scientific and engi-
neering societies, and other interested organizations have col-
laborated in the preparation of specifications for cement and
cement tests. These specifications can be found in Trans. Am.
Soc. Civil Engineers, Vol. 82, 1918, p. 166, and in other publica-
tions.

The following abstracts have been taken from the proposed
tentative specifications for Concrete Aggregates, of the Am.
Society for Testing Materials, issued June 21, 1921:

1. Fine aggregate shall consist of sand, stone screen-
ings, or other inert materials with similar characteristics,
or a combination thereof, having clean, hard, strong,
durable uncoated grains, free from injurious amounts of
dust, lumps, soft or flaky particles, shale, alkali, organic
matter, loam or other deleterious substances.

2. Fine aggregates shall preferably be graded from
fine to coarse, with the coarser particles predominating,
within the following limits:

Passing No. 4 sieve 100 per cent

Passing No. 50 sieve, not more than 50 per cent

Weight removed by elutrition test, not more

than 3 per cent

Sieves shall conform to the U. S. Bureau of Standards
specifications for sieves.

3. The fine aggregate shall be tested in combination
with the coarse aggregate and the cement with which it
is to be used and in the proportions, including water, in
which they are to be used on the work, in accordance with
the requirements specified in Section 6. ...

7. Coarse aggregate shall consist of crushed stone,
gravel or other approved inert materials with similar
characteristics, or a combination thereof, having clean,
hard, strong, durable, uncoated pieces free from injurious
amounts of soft, friable, thin, elongated or laminated pieces,
alkali, organic or other deleterious matter.

The following Table indicates desirable gradings, in per-
centages, for coarse aggregate for certain maximum sizes.

CEMENT AND CONCRETE PIPE
OF COARSE AGGREGATES

173

Maximum
Size of
Aggregate
Inches

Circular Openings, Inches

Passing Screen Hav-
ing Circular Open-
ings J Inch in diam-
eter, not more than

3
2*
2
U

100

40-75

15 per cent
15 per cent
15 per cent
15 per cent
15 per cent
15 per cent
15 per cent

100

40-75

100

40-75

100

40-75

100

35-70
40-75

100

The manufaeture of small size cement pipe requires relatively
more skill than equipment. As a result great care must be
observed in the inspection of cement pipe and in the enforcement
of specifications. For large size concrete pipe and reinforced
concrete pipe the difficulty of holding the pipe together during
transportation and lowering into the trench aid in insuring a good
product.

Cement pipe is made by ramming a mixture of cement, sand,
and water into a cylindrical mold and allowing it to stand until set.
The mold is then removed and the pipe stands for a further period
of time to become cured. The selection and proportion of
materials, the amount of water, the method of ramming, the
period of setting, the length of time of curing, and the control of
moisture and temperature during this period are of great impor-
tance in the resulting product. E. S. Hanson l states that the
most conservative engineers recommend a mixture of one sack of
cement to 1\ cubic feet of aggregate measured as loosely thrown
into the measuring box. In making up the aggregate, clean gravel
or broken stone up to \ inch in size is used. The American Con-
crete Institute recommends that 100 per cent pass a ^-inch screen,
70 per cent a j-inch screen, 50 per cent a No. 10, 40 per cent a
No. 20, 30 per cent a No. 30, and 20 per cent a No. 40. The
materials should be carefully graded by experiment and not
guessed at, as the behavior of all aggregates is not the same.
Too coarse an aggregate is difficult to handle in manufacturing.
1 Proceedings Illinois Society of Engineers, 1916, page 81.

174

MATERIALS FOR SEWERS

It causes loss of pipe when the jacket or mold is removed and
results in rough pipe, stone pockets, and pin holes through which
water spurts when pressure tests are applied. Too fine an aggre-
gate causes loss of strength and with ordinary mixtures tends to
produce a pipe which will show seepage under internal pressure
tests. The amount of water in the mixture will vary, from 15 to
20 per cent. The mixture should appear dry but should ball in
the hand under some pressure.

The mixture can be rammed into the molds by hand or machine.
A machine-made pipe is preferable as it produces a more even and
stronger product. There are two types of machines for this
purpose. One type consists of a number of tamping feet which
deliver about 200 blows to the minute with a pressure of about
800 pounds per square inch of area exposed. In the other type a
revolving core is drawn through the pipe, packing and polishing
the concrete as it is pulled through, with special provision for

packing the bell of the pipe.
The tamping machines can
make 1,500 feet of small size
pipe to 300 feet of 24-inch
pipe in a day. Machines of
the second type can make 750
feet of 8-inch to 200 feet of
30-inch pipe in 30-inch lengths
in 9 hours. The inside and
outside forms for a 24-inch
pipe are shown in Fig. 74 as
used with the tamping ma-
chines. The forms are swab-
bed with oil before being filled

m in order to facilitate their

Elevation. removal. In making a Y-

branch or other special, a
hole is cut in the pipe or

Bottom view. Bottom view. mold the size of the joining

FIG. 74.— Details of 24-Inch Concrete pipe which is then set in place
Pipe Form. and the joint wiped smooth

with cement.

After the removal of the mold the pipe may be cured by the
water or the steam process. Hanson states:

Inside
Form

Top View.
.- -3-4- -»|

TTT1

<— 2^-_>

Outside

«0

Form.

=.-_-_^=.-=.-= S

H -f 11 ». i

II fl! li II) ! !.

CEMENT AND CONCRETE PIPE

175

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176 MATERIALS FOR SEWERS

By the former the pipe are simply set on the floor of
the plant and as soon as they are sufficiently strong so
that they can be sprinkled with water without falling
down; sprinkling is commenced and continued at such
intervals for 6 or 7 days that the pipe will be moist at all
times. This is a slower process than steam curing. It is
also less uniform and less subject to control than where
the product is cured by steam.

In the steam process the pipe is exposed to low-pressure steam
with plenty of moisture in a closed receptacle for 24 hours, or
until hardened. It has been found by tests that pipes sprinkled
for 28 days are as strong as steam-cured pipes.

The dimensions of cement concrete sewer pipe as recommended
by the Am. Society for Testing Materials are shown in Table 38.

The following has been abstracted from the description of the
manufacture of one form of concrete pipe by G. C. Bartram.1
All pipe are manufactured in 4-foot lengths near the site at which
they are to be installed because of their great weight, for example,
36-inch pipe weighs one ton. The plant for the manufacture of
the pipe consists of cast-iron bottom and top rings for each size
to be used on the job, and inside and outside steel casings.
There are three bases for each steel casing as the pipes stand on
the bases for 72 hours and the steel casing remains on for only
24 hours after the concrete has been poured. The pipes are then
lifted off the bases and stored for aging. The pipes are cast with
the spigot end up.

The concrete is ordinarily mixed in the proportions of 1 : 2 : 4.
The materials are placed in the mixer in the following order:
first, the stone, then the sand, then the cement, and finally the
water. Sufficient water is added to make the concrete flow freely.
In cold weather or for a hurry-up job the molds are covered with
canvas and are steamed for 2 or 3 hours immediately after the
concrete is poured. The molds are then removed but the pipe
should be steamed before use. Otherwise they are allowed to
stand 72 hours, as explained above. In cold weather the steam is
used to prevent freezing and not to hasten the completion of the
pipe.

One layer or ring of reinforcement is used for sizes from 24 to
48 inches and two layers or rings for larger pipe. A type of rein-

1 Municipal Engineers' Journal for April, 1918.

CKMFAT AND CONCRKTK PIPK

177

forcement sometimes used is the American Steel and Wire Com-
pany's Triangular Mesh, an illustration of which is shown in
Fig. 75. The wire mesh is cut to fit and is placed in a slot in the
cast-iron base. The slot is then filled with sand so that the con-

t'AMesft /i* 7~8~

Style *ZZ-
Section B-B Section A-A.

FIG. 75. — Triangle Mesh Reinforced Concrete Pipe.

As made by the Am. Concrete Pipe and Pile Co., Chicago.

w— v_— —

/Mortar

Tongue and Groove
Joint

Lock Joint,
Patented

Hub and Spigot Joint.

A Three Types of Joints Commonly Used m Reinforced Concrete Pipe
Sewer Construction

Single Line Double Line Elliptical

Reinforcing Reinforcing Reinforcing.

B Three Methods of Reinforcing Concrete Pipe

FIG. 76. — Methods of Joining and Reinforcing Concrete Pipe.

Crete cannot enter, thus leaving a portion of the reinforcement
exposed. The inside reinforcement extends through and out of
the spigot of the completed pipe. In the trench the two rein-
forcements overlap in the key-shaped space left on the inside of

178

MATERIALS FOR SEWERS

the pipe by the design of the bell and spigot. This space is shown
in Fig. 76 A. When the pipe is placed in the trench the key-shaped
space is plastered with mortar and a piece is knocked out of the
bell to receive the grout with which the joint is closed. A spring
steel band is then put on the outside of the joint and grout poured
into the hole at the top. The band is removed as soon as the
joint materials have set.

The rules for the reinforcement of concrete pipe recommended
in Volume XV, 1919, of the Transactions of the Concrete Insti-
tute are as follows:

No reinforcement is approved for pipe between 30 and
60 inches in diameter or in rock or hard soils. For pipe
36 inches in diameter or less the minimum thickness of
shell shall be 5 inches. For 60-inch pipe the minimum
thickness shall be 7 inches with intermediate sizes in pro-
portion. Reinforcement for circular pipe shall consist of
one or two rings of circular wire fabric or rods of the areas
shown in Table 39. All sewers near the surface and sub-
ject to vibration should be reinforced. For sewers 6 feet
or less in diameter the reinforcement should consist of
at least \ of 1 per cent of the area of the concrete. It
should be placed near the inside at the crown and near

TABLE 39

REINFORCEMENT FOR CIRCULAR CONCRETE SEWER PIPE
(See Vol. XV, Proceedings Am. Concrete Institute)

Mini-

Cross

Mini-

Cross

Diam-
eter

mum
Thick-

Number

Sec-
tional

Diam-
eter

mum
Thick-

Number

Sec-
tional

in
Inches

ness
of Shell

of Rings

Area of
Each

in
Inches

ness
of Shell

of Rings

Area of
Each

in
Inches

Ring

in
Inches

Ring

.058

48 '

.107

.068

.123

.080

.146

.107

.168

.146

.180

.146

.208

.153

96 V

.245

PROPORTIONING OF CONCRETE 179

the outside at the haunches. If large horizontal pressures
are expected the pipe should be reinforced for these reverse
stresses, which involves placing the reinforcement near
the outside at the crown and near the inside at the
haunches. The minimum thickness of the walls of sewers
greater than 6 feet in diameter with flat bottom and arch,
with or without side walls, should be 8 inches.

Three methods for the reinforcement of concrete sewers are shown
in Fig. 76 B.

93. Proportioning of Concrete. — In the proportioning of con-
crete questions of strength, of permeability, and of workability 1
may need consideration. All of these qualities are affected by
the amount of cement, the nature and gradation and relative
proportions of the fine and the coarse aggregate, and the amount
of mixing water used.

Other things being equal the strength varies with the amount
of cement put into the concrete. For the same amount of cement
and the same consistency of the mixture, the strength increases
with increased density of concrete (that is, with decreased voids),
and the effort should be made so to proportion the fine and coarse
aggregates as to produce the densest concrete (least voids) with
the aggregates available. For the same consistency, the strength
then will vary with the ratio of the amount of cement to the
amount of the voids.

So far as the mixing water is concerned, the greatest strength
in the concrete will be attained at a rather dry mix; that which
produces the least volume of concrete. The addition of more
water results in a concrete of less strength; 40 per cent more
water may give a concrete of less than half the normal strength.
The reduction in strength is then very marked for the wetter
mixes, and the water content used is a feature of considerable
importance in the design of concrete mixtures.

Permeability is affected by the same elements as strength,
but the size and discontinuity of the pores have a greater influence.

Workability is an important quality; in some respects it will
have to be obtained at the expense of strength. Increasing the
amount of mixing water increases the workability of the mixtures,
with a resulting decrease in strength which may have to be
accepted or else overcome by increasing the cement in the mix.

1 Workability involves ease in placing and smoothness of working.

180 MATERIALS FOR SEWERS

An excess of water is often used unnecessarily through ignorance
of the injurious results. A high- proportion of coarse aggregate,
up to a certain limit, will give concrete of high strength, but the
mixture will be harsh-working and not easy to place. Lower
proportions of coarse aggregate will give greater workability and
better uniformity of product, the latter being an important
matter. It is apparent that the degree of workability of the mix-
ture needed will depend upon the nature of the construction — for
a pavement where the concrete will receive substantial tamping
or working the water content may be much less than that which
may need to be used in placing concrete around reinforcement in
narrow members, or where little tamping or spading can be done.
The nature of the work will affect the standard of consistency to be
specified.

The proportioning of the concrete should then be dependent
upon the needs of the structure and the manner of placing the
concrete. The proportions selected should be carefully adhered
to and especially should care be taken to see that the right quan-
tity of mixing water is used.

The materials are commonly measured volumetrically (by
bulk). Because of the variations which are introduced by volu-
metric measurement of the materials by the presence of varying
degrees of moisture, measurements by weight would be more
accurate, but these would also be affected by differences in the
specific gravity of the materials. The methods of measuring,
the allowance for moisture, as well as the proportions of the
materials, should be specified.

The methods for proportioning concrete are:

(1) Arbitrarily selected proportions.

(2) Proportions based on minimum voids.

(3) Proportions based on trial mixtures.

(4) Proportions based on a sieve analysis curve.

(5) Proportions based on the surface area of the aggre-
gates.

(6) Proportions based on the water-cement ratio and
the fineness modulus.

(7) Proportions based on mortar-voids and cement-
voids ratio.

Arbitrarily selected proportions are in quite general use;
they are intended to apply to the materials most commonly used

PROPORTIONING OF CONCRETE 181

in the vicinity of the work. The most common practice is to
use twice as great a volume of coarse aggregate as fine aggregate,
as for instance 1 part cement, 2 parts fine aggregate, and 4 parts
coarse aggregate. Decreasing the ratio of coarse aggregate to
fine aggregate may give a more easily worked mix or require
relatively less water for a given workability, and in some cases it
will be proper to increase tnis ratio and thus secure an increase of
strength. Judgment and experience with given materials may
warrant changes from a stated ratio. The proportions are now
frequently given as one part cement to a certain number of parts
of the mixed aggregate, leaving the proportions of the fine to
coarse to be determined otherwise, since small variations in the
relation of these will not greatly affect the strength. Proportions
in common use are:1

Mortar for

Laying brick and stone masonry from 1:0 to 1 : 3

Filling joints in sewer pipe 1:0 to 1 : 2

Surfaces, floors, sidewalks, pavements . . 1 : 0 to 1 : 2

Waterproof linings 1:0 tol:2

Cement, bricks, and blocks 1 : 2£ to 1 : 4

Concrete for

Gravity retaining walls, heavy founda-
tions, structures needing mass more

than strength from 1:3:6 to 1 : 4 : 8

Retaining walls, piers, sewers, pave-
ments, foundations, and work requir-
ing strength. (Compressive strength
in 28 days, 1,500 to 2,000 pounds per

square inch) from 1:2:^ to 1 : 3 : 6

Floors, beams, pavements, reinforced
concrete, arch bridges, low-pressure
tanks. (Compressive strength in 28
days, 2,000 to 3,000 pounds per square

inch) from 1 : 1£ : 3 to 1 : 2£ : 4£

Reinforced concrete columns, conduit
pipe, impervious concrete. (Com-
pressive strength in 28 days, 3,000 to
4,000 pounds per square inch) . . .from 1:1:2 to 1 : 1£ : 3

The usual method of proportioning based on minimum voids

is to assume that the particles of fine aggregate should fill the

voids in the coarse aggregate and that the particles of the cement

will fill the voids in the fine aggregate. About 5 to 10 per cent

1 Johnson's Materials of Construction, 5th Edition, 1918, p. 432.

182

MATERIALS FOR SEWERS

additional fine aggregate is generally added to push the particles
of the coarse aggregate apart and thus give a more easily worked
concrete and one freer from void spaces. This method is inaccu-
rate, principally because of the effect of the moisture on the volume
of the voids, and because the effect on the volume by the addi-
tion of water is unknown.

Trial mixtures may be made by carefully weighing each of the
ingredients and then combining them to give a workable concrete.
Using a given amount of cement, the proportion of ingredients, of
the same total weight, which will give the least volume and there-
fore the densest concrete is adopted. When making the compari-
son the consistency of the mixes must be maintained constant.

Proportioning may be based on an ideal sieve analysis curve
of the mixed cement and aggregates. The sieve analysis of the
aggregates is made by screening a predetermined weight of the
sample through a series of 5 to 8 sieves graded in size from slightly
below the size of the largest particle to slightly above the smallest
particle of the aggregate. The analysis is then expressed in the
form of a curve. The ideal curve, according to Fuller,1 is shown
in Fig. 77.
100

0.25 0.50 0.75 1.00 1.25 1.50

Diameter of Particle in Inches.

FIG. 77. — Gravel Analysis.

The dotted line indicates the ideal combination of the coarse and fine portions. The heavy
full line indicates the combination attained.

1 Trans. Am. Society of Civil Engineers, Vol. 59, 1907, p. 146.

WATERPROOFING CONCRETE 183

The method of proportioning concrete by surface areas is
based on the theory that the strength of a concrete depends on the
amount of cement used in proportion to the surface area of the
aggregates.1

The proportioning of concrete on the basis of a water-cement
ratio and a fineness modulus was introduced by Prof. D. A.
Abrams.2 It is based on the theory that with fixed conditions
of aggi'egate, moisture, etc., the ratio of water to cement deter-
mines the strength of the concrete.

A method of proportioning concrete by determining experi-
mentally the voids in mortars made up with a given amount of
sand and definite proportions of cement, and then calculating
the voids in the concrete made up by adding a definite amount
of coarse aggregate to the mixture, has been developed.3 Ibc
method is based on the theory that the strength of the concrete
is a known function of the ratio of the volume of cement to the
volume of the voids in the concrete. The effect of varying the
proportion of the ingredients, including an increase in the amount
of mixing water beyond that required to give the densest mixture,
may be found by the method, and a comparison may be made of
results obtainable with different classes of fine and coarse aggre-
gates.

Arbitrarily selected proportions, proportions based on voids,
and proportions based on trial mixtures are usually satisfactory
for small jobs where the amount of materials involved is not large.
Where the saving in materials will permit, more accurate methods
should be used. The methods can be studied more fully by
reference to the original articles quoted in the footnotes, or to the
following texts:

Materials of Construction, Johnson, 5th Edition, 1918.
Materials of Engineering, H. F. Moore, 2d Edition, 1920.
Masonry Construction, I. O. Baker, 10th Edition, 1912.
Concrete Engineer's Handbook, Hool and Johnson, 1918.
Concrete, Plain and Reinforced, Taylor and Thompson, 1916.

1 L. N. Edwards, Trans. Am. Society Testing Materials, 1918, and R. B.
Young, Eng. News-Record, Vol. 82, 1919, p. 33.

1 Bulletin No. 1, Structural Materials Research Laboratory, Lewis Insti-
tute, Chicago, Illinois.

3 Proportioning Concrete by Voids in the Mortar, A. N. Talbot, read
before Am. Society Testing Materials, June 22, 1921. Abstract in Eng.
News-Record, Vol. 87, 1921, p. 147.

184 MATERIALS FOR SEWERS

94. Waterproofing Concrete. — The waterproofing of concrete'
is most satisfactorily done by making dense mixtures. In practice
such substances as hydrated lime, clay, alum and soap, and pro-
prietary compounds such as Ceresit, Medusa, etc., are frequently
mixed with the concrete under the theory that these very fine
substances will fill any remaining voids and render the concrete
impervious. The specifications of the Joint Committee issued on
June 4, 1921, are much briefer and contain less detailed instruc-
tion than those issued earlier.1 The earlier instructions follow.

Many expedients have been resorted to for making
concrete impervious to water. Experience shows, however,
that when mortar or concrete is proportioned to obtain
the greatest practicable density and is mixed to the proper
consistency, the resulting mortar or concrete is impervious
under moderate pressure.

On the other hand concrete of dry consistency is more
or less pervious to water, and, though compounds of vari-
ous kinds have been mixed with the concrete or applied
as a wash to the surface, in an effort to offset this defect,
these expedients have generally been disappointing, for
the reason that many of these compounds have at best
but temporary value, and in time lose their power of impart-
ing impermeability to the concrete.

In the case of subways, long retaining walls, and reser-
voirs, provided the concrete itself is impervious, cracks
may be so reduced, by horizontal and vertical reinforcement
properly proportioned and located, that they will be too
minute to permit leakage, or will be closed by infiltration
of silt.

Asphaltic or coal tar preparations applied either as a
mastic or as a coating on felt cloth or fabric, are used for
waterproofing, and should be proof against injury by liquids
or gases.

For retaining and similar walls in direct contact with
the earth, the application of one or two coatings of hot
coal tar pitch, following a painting with a thin wash of
coal tar dissolved in benzol, to the thoroughly dried sur-
face of concrete is an efficient method of preventing the
penetration of moisture from the earth.

Tar paper and asphaltic compounds are not often used in
sewer work as absolute imperviousness is seldom necessary.

95. Mixing and Placing Concrete. — Careful workmanship is
desirable in the mixing and placing of concrete in sewers since

1 Trans. Am. Society of Civil Engineers, Vol. 81, 1917, p. 1122.

MIXING AND PLACING CONCRETE 185

water-tight construction is desired. Because of the difficulty of
inspecting concrete in wet, dark and crowded excavations, and
the careless habits of workmen experienced in concrete Sewer
construction, the highest class of concrete work cannot be expected.
The situation is met by designing thick walls as shown in the
sections illustrated in Fig. 22 and 23.

In the report of the Joint Committee on Concrete and Rein-
forced Concrete in Transactions of the American Society of
Civil Engineers for 1917, on page 1101 the recommendation
is made concerning the mixing and placing of concrete as
follows:1

The mixing of concrete should be thorough and should
continue until the mass is uniform in color and is homo-
geneous. As the maximum density and greatest strength
of a given mixture depends largely on thorough and com-
plete mixing, it is essential that this part of the work
should receive special attention and care.

Inasmuch as it is difficult to determine by visual
inspection whether the concrete is uniformly mixed, especi-
ally where aggregates having the color of cement are used,
it is essential that the mixing should occupy a definite
period of time. The minimum time will depend on whether
the mixing is done by machine or hand.

(a) Measuring Ingredients: Methods of measurement
of the various ingredients should be used which will secure
at all times separate and uniform measurements of cement,
fine aggregate, coarse aggregate and water.

(6) Machine Mixing: The mixing should be done hi
a batch machine mixer of a type which will insure the
uniform distribution of the materials throughout the mass,
and should continue for the minimum time of 1^ minutes
after all the ingredients are assembled in the mixer. For
mixers of 2 or more cubic yards capacity, the minimum
time of mixing should be 2 minutes. Since the strength
of the concrete is dependent on thorough mixing, a longer
tune than this minimum is preferable. It is desirable
to have the mixer equipped with an attachment for auto-
matically locking the discharging device so as to prevent
the emptying of the mixer until all the materials have been
mixed together for the minimum time required after they
are assembled in the mixer. Means should be provided

1 See also Tentative Specifications for Concrete and Reinforced Concrete
submitted by the Joint Committee to its Constituent Organizations, June
4, 1921.

186 MATERIALS FOR SEWERS

to prevent aggregates being added after the mixing has
commenced. The mixer should also be equipped with
water storage, and an automatic measuring device which
can be locked if desired. It is also desirable to equip
the mixer with a device recording the revolutions of the
drum. The number of revolutions should be so regulated
as to give at the periphery of the drum a uniform speed.
About 200 feet per minute seems to be the best speed in
the present state of the art.

(c) Hand Mixing: Hand mixing should be done on
a watertight platform and especial precautions taken
after the water has been added, to turn all the ingredients
together at least 6 times, and until the mass is homo-
geneous in appearance and color.

(d) Consistency: The materials should be mixed wet
enough to produce a concrete of such a consistency as will
flow sluggishly into the forms and about the metal reinforce-
ment when used, and which at the same time can be con-
veyed from the mixer to the forms without separation
of the coarse aggregate from the mortar. The quantity
of water is of the greatest importance in securing concrete
of maximum strength and density; too much water is as
objectionable as too little.

(e) Retempering : The remixing of concrete and mortar
that has partly reset should not be permitted.

Placing Concrete

(a) Methods: Concrete after the completion of the
mixing should be conveyed rapidly to the place of final
deposit; under no circumstances should concrete be used
that has partly set.

Concrete should be deposited in such a manner as will
permit the most thorough compacting such as can be
obtained by working with a straight shovel or slicing tool
kept moving up and down until all the ingredients are in
their proper place. Special care should be exercised to
prevent the formation of laitance; where laitance has
formed it should be removed, since it lacks strength and
prevents a proper bond in the concrete.

Care should be taken that the forms are substantial
and thoroughly wetted (except in freezing weather) or
oiled, and that the space to be occupied by the concrete
is free from all debris. When the placing of concrete
is suspended, all necessary grooves for joining future work
should be made before the concrete has set.

When work is resumed concrete previously placed
should be roughened, cleansed of foreign material and

MIXING AND PLACING CONCRETE 187

laitance, thoroughly wetted and then slushed with a mortar
consisting of one part Portland cement and not more than
2 parts of fine aggregate.

The surfaces of concrete exposed to premature drying
should be kept covered and wet for at least 7 days.

Where concrete is conveyed by spouting, the plant
should be of such a size and design as to insure a practically
continuous stream in the spout. The angle of the spout
with the horizontal should be such as to allow the concrete
to flow without separation of the ingredients; in general
an angle of about 27 degrees or 1 vertical to 2 horizontal
is good practice. The spout should be thoroughly flushed
with water before and after each run. The delivery from the
spout should be as close as possible from the point of deposit.
Where the discharge must be intermittent, a hopper should
be provided at the bottom. Spouting through a vertical
pipe is satisfactory when the flow is continuous; when it
is checked and discontinuous it is highly objectionable unless
the flow is checked by baffle plates.

(6) Freezing Weather: Concrete should not be mixed
or deposited at a freezing temperature, unless special
precautions are taken to prevent the use of materials
covered with ice cystals or containing frost, and to prevent
the concrete from freezing before it has set and sufficiently
hardened.

As the coarse aggregate forms the greater portion of
the concrete, it is particularly important that this material
be warmed to well above the freezing point.

The enclosing of a structure and the warming of a space
inside the enclosure is recommended, but the use of salt
to lower the freezing point is not recommended.

(c) Rubble Concrete: Where the concrete is to be
deposited in massive work, its value may be improved
and its cost materially reduced by the use of clean stones
saturated with water, thoroughly embedded in and com-
pletely surrounded by concrete.

(d) Under Water: In placing concrete under water, it is
essential to maintain still water at the place of deposit.
With careful inspection the use of tremies, properly designed
and operated, is a satisfactory method of placing concrete
through water. The concrete should be mixed very wet
(more so than is ordinarily permissible) so that it will flow
readily through the tremie and into place with practically
a level surface.

The coarse aggregate should be smaller than ordinarily
used and never more than one inch in diameter. The
use of gravel facilitates the mixing and assists the flow.
The mouth of the tremie should be buried in the concrete

188 MATERIALS FOR SEWERS

so that it is at all times entirely sealed and the surrounding
water prevented from forcing itself into the tremie. The
concrete will then discharge without coming in contact
with the water. The tremie should be suspended so that
it can be lowered quickly when it is necessary either to
choke off or to prevent too rapid flow. The lateral flow
preferably should not be over 15 feet.

The flow should be continuous in order to produce a
monolithic mass and to prevent the formation of laitance
in the interior.

In case the flow is interrupted it is important that all
laitance be removed before proceeding with the work.

In large structures it may be necessary to divide the
mass of concrete into several small compartments or units
to permit the continuous filling of each one. With proper
care it is possible in this manner to obtain as good results
under water as in the air.

A less desirable method is the use of the drop bottom
bucket. Where this method is used the bottom of the
bucket should be released when in contact with the surface
of the place of deposit.

Concrete sewers should be constructed in longitudinal sections
in a continuous operation without interruption for the entire
invert, side walls, or arch. In pouring the concrete it should be
kept level in the forms and should rise evenly on each side of the
sewer. All rough places in the concrete should be finished smooth
by brushing with a grout of neat cement and water and honey-
combs should be filled with neat cement or a one-to-one mortar.

96. Sewer Brick. — The quality of brick used in sewers is
seldom specified with the minute care that is taken in the speci-
fications for concrete, iron, and certain other materials of con-
struction, as inferior materials in brick are more easily detected.
The specifications of the Baltimore Sewerage Commission for
sewer brick are:

Sewer brick shall be whole, new bricks of the best
quality, of uniform standard size, with straight and parallel
edges and square corners; they shall be of compact texture,
burned hard and entirely through, free from injurious
cracks and flaws, tough and strong, and shall have a clear
ring when struck together. The sides, ends and faces of
all bricks shall be plane surfaces at right angles and parallel
to each other. Bricks of any one make shall not vary
more than y^th of an inch in thickness, nor more than

VITRIFIED SEWER BLOCK 189

|th of an inch in width or length, from the average of the
samples submitted for approval.

The truest bricks shall be used in the face of the masonry
and the exposed surfaces shall be true and smooth planes.

All bricks delivered for use shall be culled by the Con-
tractor when required. No brick thrown out in the culling
shall be used in any work done under any contract of the
Sewerage Commission, except that the best of the culls
may "be used in manholes, above the level of the top of
the sewer, if permitted by the Engineer.

The average amount of water absorbed by the bricks,
after being thoroughly dried and then immersed for 24
hours, shall not exceed 6 per cent. All bricks shall be
uniform in quality and percentage of absorption.

Whenever vitrified bricks are required in the invert
of the sewer, they shall be smooth, hard, tough, and of
such durability as will fit them for this use. They shall
be of standard size, well and uniformly burned, thoroughly
vitrified throughout, and free from warps, cracks, and
other defects. The surfaces and edges shall be true and
straight and the corners sharp and square. They shall
be in every respect satisfactory to the Engineer, and in all
respects equal to the sample in the office of the Engineer.

The remaining paragraphs of the specifications deal with the
manner in which samples shall be submitted and the necessity for
conformity between the samples submitted and the bricks used.

A cotnmon size of brick in use for sewers is 2jX4X8j inches,
but the variations in size are many. The bricks in use on any
one job should be as near the same size as possible as the extra
mortar filling necessary to make up for small brick detracts from
the strength of the sewer. Small brick are undesirable as the
cost of laying small and large bricks is the same, but the thickness
of the finished sewer is less. Sewer brick should not absorb
more than 10 to 20 per cent moisture by volume, in 24 hours;
except the special paving brick used to prevent erosion at the
invert which should absorb less than 5 per cent moisture.

97. Vitrified Sewer Block. — Blocks and bricks are manu-
factured in a manner similar to the manufacture of vitrified sewer
pipe described in Art. 91. J. M. Egan describes two types of
sewer blocks1 as follows:

There are on the market two designs of blocks, one
being a single-ring block and the other a double-ring block.
1 Journal Illinois Society of Engineers for 1916, p. 75.

190 MATERIALS FOR SEWERS

The former has a ship-lap joint on the ends and a tongue-
and-groove joint on the sides. In the double block the laps
and joints are made in the construction of the sewer and
the blocks are placed one on top of the other as in a two-
ring brick sewer. The blocks are hollow longitudinally
with web braces. They are made for sewers from 30 inches
to 108 inches in diameter and weigh from 40 to 120 pounds.
They are 18 inches to 24 inches long, 9 to 15 inches wide,
and 5 to 10 inches thick. Short lengths are made for
convejoience in construction and for use on sharp curves.
Special blocks are made for connections and junctions.

A special block is also made for inverts, which has occasionally
been used with brick sewers to avoid the difficulty of constructing
with brick at this point. Such blocks are objectionable, as they
leave a line of weakness along the longitudinal joint so formed.
They are not used frequently in present-day practice.

Vitrified blocks are generally cheaper than bricks, but they
do not make so strong a structure. In some cases it is possible to
lay vitrified block without the expense of high-priced bricklayers,
thus saving on the cost of the sewer and obtaining a conduit with
a smoother interior finish.

98. Cast Iron, Steel; and Wood. — Cast iron, steel, and wood
pipe belong more to the field of waterworks than of sewerage, as
they are not extensively used in the construction of sewers.
There are, however, some special conditions under which these
materials may be serviceable.

The iron used in cast-iron pipe for sewers, and in castings for
manhole covers, inlet frames, etc., is seldom carefully or definitely
specified. The standard specifications of the American Water
Works Association with regard to the quality of iron for water
pipe are:

All pipe and special castings shall be made of cast iron
of good quality and of such character as shall make the
metal of the castings strong, tough, and of even grain and
soft enough to satisfactorily admit of drilling and cutting.
The metal shall be made without the admixture of cinder
iron or other inferior metal, and shall be remelted in a
cupola or air furnace.

The specifications of the Sanitary District of Chicago for the
quality of iron to be used in manhole covers, etc., are given on
page 101.

CAST IRON, STEEL, AND WOOD 191

Although sewer pipes are not ordinarily subjected to internal
pressure, cast-iron pipe for sewers should be as heavy or heavier
than water pipe to resist the corrosive action of the sewage and
the external stresses that are to be imposed upon it. The sizes
and details of standard cast-iron pipe used for both water works
and sewerage can be found in specification of the American and
New England Water Works Associations.

The quality of steel used for reinforcing concrete should be
carefully specified because of the possibility of the substitution of
inferior material. The specifications for " Billet Steel Concrete
Reinforcement Bars," of the American Society for Testing
Materials1 are the standard for engineering practice, or the fol-
lowing specifications may be used :

All reinforcement shall be free from excessive rust,
scale, paint, or coatings of any character which will tend
to destroy the bond. The bars shall be rolled from new
billets. No rerolled material will be accepted. All rein-
forcement bars shall develop an ultimate tensile strength
of not less than 70,000 pounds per square inch. The test
specimen shall bend cold around a pin, whose diameter
is two times the thickness of the bar, 180 degrees without
cracking on the outside portion. The reinforcing bars
shall in all respects fulfill the requirements of the standard
specifications of the American Society for Testing Materials
for Billet Steel Concrete Reinforcing Bars serial designa-
tion A 15-14.

The steel used in pipe should be a soft, open-hearth steel with
an ultimate tensile strength of 60,000 pounds per square inch, an
elastic limit of 30,000 pounds per square inch, an elongation in
8 inches before fracture between 22 and 25 per cent, and a reduc-
tion in area before fracture of 50 per cent. The working strength
of the steel is taken at 16,000 to 20,000 pounds per square inch in
tension, 10,000 to 12,000 pounds per square inch in shear, and
20,000 to 24,000 pounds per square inch in bearing. A liberal
allu\vance should be made for corrosion. The standard specifi-
cations for Open Hearth Boiler Plate and Rivet Steel of the Ameri-
can Society for Testing Materials, Aug. 16, 1919, include " flange
steel," which is suitable for the manufacture of plates, and extra
soft steel which is suitable for rivets.

Steel pipe should be coated both inside and out to protect it
1 See A. S. T. M. Standards for 1918, p. 148.

192 MATERIALS FOR SEWERS

against corrosion. The various proprietary coatings are mainly
coal-tar pitches, or mixtures of coal-tar pitch and asphalt. A
coal-tar pitch is a distillate of coal tar from which the naphtha has
been removed and to which about one per cent of heavy linseed oil
has been added. The coating is applied to the pipe at a tempera-
ture of about 300 degrees Fahrenheit, by dipping hot pipe in the
heated coating material. The pipe should be carefully cleaned
and all rust and scale removed before it is dipped. In some
cases the steel is pickled before dipping. This consists in rolling
the cold plates to a short radius to loosen the scale, heating them
to about 125 degrees, and dipping them in a warm 5 per cent acid
solution for about 3 minutes, and finally rinsing in a weakly basic
wash water.

The woods commonly used for the manufacture of wood pipe
are spruce, Oregon fir, Douglas fir, and California redwood.
Wood pipe lines have been constructed of other kinds of lumber
but only in more or less unusual conditions. The following has
been abstracted from the specifications for California redwood
given by J. F. Partridge.1

The staves shall be of clear, air-dried, California red-
wood, seasoned at least one year in the open air, and shall
be free from knots (except small knots appearing on one
face only), sap, dry rot, wind shakes, pitch, pitch seams,
pitch pockets, or other defects which would materially
impair their strength or durability. The sides of the
staves shall be milled to conform to the inside and outside
radii of the pipe; and the edges shall be beveled to true
radial planes. The staves shall be milled from stock sizes
of lumber, the net finished thickness of the stave, for the
various diameters of pipe, shall be as given in Table 40.
The ends shall be cut square and slotted to receive the
metallic tongues which form the butt joints. The slots
shall appear in the same position on each stave, and shall
be cut to make a tight fit with the tongues in all directions.
The staves shall have an average length of at least 15 ft.
6 in. and not more than one per cent shall have a length
of less than 9 ft. 6 in. Staves shorter than 8 ft. will not
be accepted.

The bands shall be spaced on the pipe with a factor of
safety of at least four, and shall consist of round, mild
steel rods, connected with malleable iron shoes. Either

1 Trans. Am. Society Civil Engrs., Vol. 82, 1918, p. 459.

CAST IRON, STEEL, AND WOOD

193

open-hearth or Bessemer steel may be used. . . . The ulti-
mate strength shall be from 55,000 to 65,000 Ib. per sq. in.

The original reference should be consulted for complete details
and for specifications for various kinds of wood and classes of
pipe. The discussion following the specifications is of value.

Machine-made wood pipe is superior to stave pipe put together
in the field. It is seldom manufactured in sizes large enough for
use in sewers, which results in the almost exclusive use of field
constructed stave pipe. The steel bands used to hold the staves
together should be coated similarly to steel plates. All lumber,
except California redwood should receive a preservative coating
of creosote 1 or other material. One of the best methods of pre-
serving the wood is to keep it submerged and to maintain the
pipe under internal pressure.

TABLE 40

DETAILS OF DESIGN FOR CONTINUOUS STAVE WOOD PIPE

CLASSES A, B, AND C
(B*y J. F. Partridge, Trans. A. S. C. E., Vol. 82, page 461)

Stave

Stock

Size

Top Width

Spacing of

Diameter,
Inches

Thickness,
Standard,

Size of
Lumber,

of Band,

Inches

of Staves,
Standard,

Bands for
100 Feet

Inches

Head

2X4

3.56

6.38

2X4

3.66

5.76

2X4

3.70

4.34

2X6

5.48

4.53

2X6

5.62

3.77

2X6

5.51

3.23

2X6

iorf

5.60

2.84or4.41

3X6

5.56

3.54

4X6

for*

5.69

2. 95 or 4. 24

4X6

5.65

3.63

120

4X6

5.68

2.54

144

4X6

iorj

5.64

2. 12 or 2. 89

1 See Trans. Am. Society Civil Eng., Vol. 82, 1918, p. 482.

CHAPTER IX
DESIGN OF THE SEWER RING

99. Stresses in Buried Pipe. — The stresses which sewer pipe
should be designed to resist are: internal bursting pressure, for
sewers flowing under pressure; stresses due to handling, for
precast pipe; temperature stresses; and external loads. The
latter is by far the most important and frequently is the only
stress considered in design.

The thickness of a pipe to resist internal stress should be

PR
ft'

in which P=the intensity of internal pressure;

R = the radius of the inside of the pipe, and
ft = the unit-strength of the material in tension

The derivation of this expression is simple. The stresses due
to handling cannot be computed and are cared for by a thickness
of material dictated by experience. These thicknesses are given
for vitrified clay and cement pipe in the specifications in the pre-
ceding chapter. Temperature stresses are not allowed for in the
design of the pipe ring, but allowance must be made for them in
long rigid pipe lines exposed to wide variations in temperature.
Such a condition seldom exists in sewerage works.

The external forces are ordinarily the controlling features in
the design of sewer rings. The simplest problems arise in the
design of a circular pipe. If the external loading is uniform about
the circumference of the pipe the internal stresses will all be com-
pression. Almost all other forms of loading will cause bending
moments resulting in tension and compression in different parts
of the pipe. The maximum bending is caused by two concen-
trated loads diametrically opposed. As such a condition is
extreme it is not cared for in ordinary design, but a loading between

194

DESIGN OF STEEL PIPE 195

this condition and perfect distribution is assumed, as explained
in Art. 103.

100. Design of Steel Pipe. — The stresses which may occur in
steel sewer pipes are commonly caused by the internal or bursting
pressure of the contained liquid. Occasionally a steel pipe may
be used as a bridge or as a stressed member of a bridge, but steel
pipes should not be used to withstand compression normal to the
axis. In order to avoid such stresses the bursting tensile stresses
should exceed the external compressive stresses. Such a condi-
tion in design requires that buried pipes shall never be emptied, a
condition that cannot always be fulfilled. Precaution should be
taken, by the installation of proper valves, to prevent the empty-
ing of the pipe at so rapid a rate that a vacuum is created result-
ing in the collapse of the pipe.

Steel pipes are ordinarily made of plates curved to the proper
diameter, the edges being held together by rivets. The design of
the pipe consists in the determination of the thickness of the plate
and the design of the riveted joint. The longitudinal joint and
the thickness of the plate are first designed. The design of the
joint consists in determining the diameter and pitch of the rivets
and the thickness of the plate so that the full strength of the uncut
metal shall be developed as nearly as possible under bearing,
tearing, and shearing. This is done by making the efficiency of
the joint the same under all stresses. The efficiency of the joint
is the ratio of the strength of the joint under any kind of stress to
the strength in tension of the unpunched plate. Properties of
riveted joints are given hi Table 41.

The diameter of the rivet holes should be computed as ^ of
an inch larger than the diameter of the rivets. Rivets and plates
should be designed for the nearest or next largest commercial
size, and a generous allowance for corrosion should be made in
determining the thickness of the plate. The distance from the
edge of the plate to the side of the rivet should not be less than
lj times the diameter of the rivet. The unit-strengths of the
metal are given in the preceding chapter.

The transverse joint must be designed empirically as the
stresses in it are indeterminate. The common form of joint for
pipes less than 48 inches in diameter is a single-riveted lap joint,
and for larger pipes or for pipes exposed to unusual stresses, a
double-riveted lap joint is used. The same size rivets are used as

196

DESIGN OF THE SEWER RING

in the longitudinal joint. The maximum permissible distance
between rivets should be used in the transverse ioint.

TABLE 41

PROPERTIES OF RIVETED JOINTS
(Chicago Bridge and Iron Works)

Effi-

Type of Joint

Thickness
Plate,
Inch

Diameter
of
Rivet,
Inch

Pitch,
Inches

ciency
of
Joint,
Per Cent

Thickness
Butt
Plate,
Inches

Single riveted lap

1.88

2.25

2.63

Double riveted lap

2.50

3.00

3.40

Triple riveted lap

2.39

2.96

3.53

4.09

Quadruple riveted lap .

3.20

3.90

Double riveted butt.. .

3.62

4.12

3.82

3.48

Triple rnjeted butt.. . .

4.94

5.62

5.16

4.66

Quadruple riveted butt

7.13

•

6.51

5.84

DESIGN OF WOOD STAVE PIPE 197

Pipes used as compression members of a bridge are stiffened
by riveting standard rolled steel sections longitudinally on the
pipe.

Lock Bar Pipe is a steel pipe with a special form of joint made
by the East Jersey Pipe Corporation. It is arranged as shown
in Fig. 78 and has the ad-
vantage of developing the
full strength of the plate.
It is equivalent to a joint
with 100 per cent efficien-
cy, which permits the use
of thinner plates.

101. Design of Wood
Stave Pipe. — In the de-
sign of wood stave pipe1
the entire bursting pres- Fro. 78.— Lock Bar Pipe.

sure is taken up by steel

bands wrapped around the outside of wood staves which make
up the shell of the pipe. The pipe is not designed to resist external
loads except those which may be overcome by the internal pressure
in the pipe. The thickness of the staves is fixed by experience.
The sizes of staves and bands recommended by J. F. Partridge 2
are given in Table 40. The size of the steel bands can be deter-
mined from the expression;

in which S = the total stress in the band;

R = the radius of the inside of the pipe;
2 = the thickness of the stave;

r=the area of bearing per unit length of the band on
the wood. For circular bands it is assumed as
the radius of the band;

C=the crushing strength of wood, usually taken at
650 pounds per sq. in.

The preceding expression can be derived easily by the
application of the laws • of mechanics, and from it the

1 See Trans. Am. Society Civil Engr., Vol. 41, 1899, p. 76, and Vol. 82,
1918, p. 433, Eng. News, Vol. 74, 1915, p. 400, and Vol. 75, 1916, p. 911.
* Trans. Am. Soc. Civil Engra., Vol. 82, 1918, p. 433.

198

DESIGN OF THE SEWER RING

expression for the distance between bands follows logically.
It is,

S
p~PR+kt

in which S = the strength of the band;

p = the distance between bands;
P = the intensity of bursting pressure in the pipe;
72 = the radius of the inside of the pipe;
t = the thickness of the staves;

/c = the swelling strength of wood, usually taken at
100 pounds per sq. in.

Transverse joints between staves are closed by inserting

metal strips between them, or by shaping the edges irregularly

so that they fit closely together
with an irregular joint. Trans-
verse joints between all staves
at any one point are avoided by
splitting the joints between staves.
Longitudinal j oints between
staves are usually made smooth

FIG. 79.— Shoe for Wood Stave Pipe. and are closed by steel bands

which are drawn tight about the

pipe by inserting the ends in coupling shoes as shown in Fig. 79.
102. External Loads on Buried Pipe. — Prof. Anston Marston

and H. C. Anderson published 1 the results of a series of experiments

on the loads on buried pipes which are

of extreme value in the design of sewer

pipe. The load on the pipe is given by

the empirical expression W=CwB2, in

which w is the weight of the backfilling

material in pounds per cubic foot, B is

the width of the trench in feet at the

elevation of the end of a radius making

an angle of 45 degrees upwards with the

horizontal diameter of the pipe as illus-
trated in Fig. 80, and C is a coefficient

dependent on the character of the backfill and the ratio of the

1 Bulletin No. 31 of the Engineering Experiment Station of the Iowa
State College of Agriculture.

FIG. 80.— B in Formula
W = CwB2.

EXTERNAL LOADS ON BURIED PIPE

199

width to the depth of the trench. Values of C are given in
Table 42. The weights of various classes of backfilling are given
in Table 43.

TABLE 42
APPROXIMATE SAFE WORKING VALUES OP C IN THE EXPRESSION

From Bulletin No. 31 of the Engineering Experiment Station, Iowa State
College of Agriculture.

Approximate Values of C

Ratio
of
Depth
to
Width

Damp
Top Soil
and Dry
and Wet
Sand

Satu-
rated
Top
Soil

Damp
Yrilow
Clay

Satu-
rated
Yellow
Clay

Ratio
of
Depth
to
Width

Damp
Top Soil
and Dry
and Wet
Sand

Satu-
rated
Top
Soil

Damp
Yellow
Clay

Satu-
rated
Yellow
Clay

0.5

0.46

0.47

0.48

7.0

2.73

2.95

3.19

3.55

1.0

0.85

0.86

0.88

0.90

7.5

2.78

3.01

3.27

3.65

1.5

1.18

1.21

1.25

1.27

8.0

2.82

3.06

3.33

3.74

2.0

1.47

1.51

1.56

1.62

8.5

2.85

3.10

3.39

3.82

2.5

1.70

1.77

1.83

1.91

9.0

2.88

3.14

3.44

3.89

3.0

1.90

1.99

2.08

2.19

9.5

2.90

3.18

3.48

3.96

3.5

2.08

2.18

2.28

2.43

10.0

2.92

3.20

3.52

4.01

4.0

2.22

2.35

2.47

2.65

11.0

2.95

3.25

3.58

4.11

4.5

2.34

2.49

2.63

2.85

12.0

2.97

3.28

3.63

4.19

5.0

2.45

2.61

2.78

3.02

13.0

2.99

3.31

3.67

4.25

5.5

2.54

2.72

2.90

3.18

14.0

3.00

3.33

3.70

4.30

6.0

2.61

2.81

3.01

3.32

15.0

3.01

3.34

3.72

4.34

6.5

2.68

2.89

3.11

3.44

3.03

3.38

3.79

4.50

TABLE 43

APPROXIMATE WEIGHTS OF DITCH FILLING MATERIAL TO BE USED IN THE
EXPRESSION W = CwB2*

Ditch Filling

Pounds per Cubic Foot

Partly compacted top soil (damp) . .

Saturated top soil

Partly compacted damp yellow clay .

Saturated yellow clay

Dry sand

Wet sand . .

90
110
100
130
100
120

* From bulletin No. 31, Engineering Experiment Station, Iowa State College of Aftri-
culture.

200

DESIGN OF THE SEWER RING

Where surface loads are to be carried on the sewer trench the
proper proportion of the load to be carried by the sewer is deter-
mined by the expression LP = CL, in which Lp is the equivalent
backfill load per unit length of the trench, L i \ the surface load
per unit length of the trench, and C is a coefficient in which allow-
ance is made for the character of the backfilling, the ratio of depth
to width o' trench, and the character of the load, whether long or
short. A long load 's a load extending along the length of the
trench such as a pile of building material. A short load is one
extend ng across the trench and for only a short distance along it,
such as that caused by a street car or road roller crossing the trench.
Values of C are given in Table 44 for long loads, and in Table 45
for short loads. Values of long and short loads occasionally met
in practice are given in Tables 46 and 47 respectively,

TABLE 44
RATIO OP LOAD ON PIPE TO LONG LOAD ON TRENCH *

Ratio
of
Depth
to
Width

Sand
and
Damp
Top
Soil

Satu-
rated
Top
Soil

Damp
Yellow
Clay

Satu-
rated
Yellow
Clay

Ratio
of
Depth
to
Width

Sand
and
Damp
Top
Soil

Satu-
rated
Top
Soil

Damp
Yellow
Clay

Satu-
rated
Yellow
Clay

0.0

1.00

3.0

0.37

0.41

0.45

0.51

0.5

0.85

0.86

0.88

0.89

4.0

0.27

0.31

0.35

0.41

1.0

0.72

0.75

0.77

0.80

5.0

0.19

0.23

0.27

0.33

1.5

0.61

0.64

0.67

0.72

6.0

0.14

0.17

0.20

0.26

2.0

0.52

0.55

0.59

0.64

8.0

0.07

0.09

0.12

0.17

2.5

0.44

0.48

0.52

0.57

10.0

0.04

0.05

0.07

0.11

* From Bulletin No. 31, Engineering Experiment Station, Iowa State College of Agri-
culture.

For example, let it be desired to determine the load
on a 72-inch concrete sewer with a 9-inch shell under the
following conditions: depth of backfill over the top of
the pipe, 15 feet; character of backfill, saturated yellow
clay; superimposed load, pile of building brick 6 feet
high. The ratio of the depth of backfill to the width of
the trench is 15-:- 9 or 1.67. The coefficient in the expression
CwB2 is 1.39, from Table 42. The weight of saturated
yellow clay is 130 pounds per cubic foot, from Table 43.
Therefore the load per foot length of the sewer due to the
backfill is:

W = CwB2 = 1 .39 X 130 X 81 = 14,600 pounds.

EXTERNAL LOADS ON BURIED PIPE

201

TABLE 45
RATIO OF LOAD ON PIPE TO SHORT LOAD ON TRENCH *

Ratio
of
Height
to
Width
of

Sand and Damp
Top Soil

Saturated
Top Soil

Damp Saturated
Yellow Clay Yellow Clay

Length of Load Equal to

Width

&
Width

Width

Trench

0.0

1.00

0.5

0.77

0.12

0.78

0.13

0.79

0.13

0.81

0.13

1.0
1.5
2.0
2.5
3.0
4.0
5.0
6.0
8.0
10.0

0.59
0.46
0.35
0.27
0.21
0.12
0.07
0.04
0.02
0.01

0.02

0.61
0.48

0.02

0.63
0.51

0.02

0.66
0.54

0.02

0.38

0.40

0.44

0.29

0.32

0.35

0.23

0.25

0 29

0.12

0.16

0 19

0.09

0.10

0 13

0.05

0.06

0 08

0.02

0.03

0 04

0.01

0.02

* From Bulletin No. 31, Engineering Experiment Station, Iowa State College of Agri-
culture.

TABLE 46

WEIGHTS OF COMMON BUILDING MATERIAL WHEN PILED FOR STORAGE.
POUNDS PER CUBIC FOOT

Brick 120

Cement 90

Sand 90

Broken stone . . . 150

Lumber 35

Granite paving 160

Coal 50

Pig iron 400

The pressure of the pile of brick per square foot of trench
area is, from Table 46, 120X6 = 720 pounds per square
foot. The value of C from Table 44, is about 0.70. There-
fore Lp is 0.7X9X720=4536 pounds. The equivalent
depth of backfill weighing 130 pounds per cubic foot is

4536

= 3.88 foot. The total equivalent depth of back

202

DESIGN OF THE SEWER RING

fill is therefore 3.88+15 = 18.88 feet. The ratio of depth

18 88
to width is — ^- =2.98. The coefficient C in the expression

W = CwB2 is 2.17. The total load per foot length of
sewer is therefore TF = 2. 17X130X81 = 22,800 pounds.

TABLE 47

WEIGHTS OF SHORT LOADS ON SEWER TRENCHES
(Adapted from Specifications of the American Bridge Company for Bridges)

Street railways, heavy

Street railways, light

For city streets, heavy traffic

For city streets, moderate traffic ....

For city streets, light traffic or coun-
try roads

Road rollers .

A load of 24 tons on 2 axles on 10 foot

centers.
A load of 18 tons on 2 axles on 10 foot

centers.
A load of 24 tons on 2 axles 10 feet

apart and 5 foot gage.
A load of 12 tons on 2 axles 10 feet

apart and 5 foot gage.
A load of 6 tons on 2 axles 10 feet

apart and 5 foot gage.

Total weight 30,000 pounds. Weight
on front wheel, 12,000 pounds, and
on each of two rear wheels, 9,000
pounds. Width of front wheel,
4 feet and of each of two rear wheels
20 inches. Distance between front
and rear axles 11 feet. Gage of
rear wheels, 5 feet, c. to c.

103. Stresses in Circular Ring — In Fig. 8 la the loads shown
indicate the distribution ordinarily assumed in sewer design, the
forces being uniformly distributed across the diameter. To find
the bending moment in the pipe caused by this loading, let ah in
Fig. 816 represent a section of a pipe loaded with equally dis-
tributed horizontal and vertical forces. Then the vertical com-
ponent on a strip of differential length ds is wds cos 6 and the
horizontal component is wds sin 0 and resolving, the resultant
«normal to the surface is wds, in which w is the intensity per unit
length of the horizontal and vertical forces and 9 is the angle
which the tangent to ds makes with the horizontal. Thus the load-
ing of the nature shown in Fig. 81& is equivalent to a loading of
equally distributed normal forces which give no moment in the ring.

STRESSES IN CIRCULAR RING

20:5

Considering a ring subjected to vertical forces only, the
moments will be as shown in Fig. 81c and if loaded with horizontal
forces only, the moments will be as shown in Fig. 81d. Because
of the symmetry of the figure, moment (1) equals moment (4)
but is opposite in direction and moment (2) equals moment (3)
but is opposite in direction. When the horizontal and vertical
forces are combined on the same ring as in Fig. 816 these moments
cancel each other as has been proven. Therefore moment (1)
equals moment (2) and moment (3) equals moment (4). Then
in Fig. 81e, Ma = Mb. Now 2Af = 0 for conditions of equilibrium,

(W \ id\ Wd

~o~)(l)=^ and solving Ma = -r^-. This
& / \4/ lo

moment occurs at the ends of the horizontal and vertical diameters
and causes tension on the inside of the pipe at the top and on the

-b-

-c-

-d-

-e-

FIG. 81. — Distribution of Stresses on Buried Pipe.

outside at the ends of the horizontal diameter. There will also
be compression at each end of the horizontal diameter equal to
one-half of the total load on the pipe. If the material of the
pipe is homogeneous, the maximum fiber stress / can be found

My P
through the expression /=-y-±-j in which M is the bending

moment, y is the distance from the neutral axis to the extreme
fiber of a cross-section of the shell of the pipe of unit length, / is the
moment of inertia of this cross-section about its neutral axis, P is
one-half the total load on the pipe, and A is the area of the cross-
section. For reinforced concrete, the standard formulas should
be used with this expression for M. The stresses in a circular
ring subjected to other distributions of loads are shown in Table
48. An exhaustive study of the stresses in circular rings was
published by Prof. A. N. Talbot in Bulletin No. 22 of the Engi-
neering Experiment Station at the University of Illinois, 1908.

204

DESIGN OF THE SEWER RING

Symmetrical
Vertical Loadings

Moment
at Crown
of Sewer

Moment
at End of
Horizontal
Diameter

Com-
pressive
Thrust
at
Crown

Com-
pressive
Thrust
at End of
Horizontal
Diameter

Shear
at
Crown

Shear
at End of
Horizontal
Diameter

Character

Width

Concentrated.
Uniform

0°
60°
90°
180°

W
+ . 318ft —
12

+ . 207ft—
12

W
+ . 169 R —
12

W
+ . 125ft—

W
- . 182ft —
12

W
- . 168ft —
12

W
- . 154ft —
12

W
- . 125ft —
12

0.000
0.000
0.000
0.000

W
+ .500 —
12

+-50V

W
+ .500-

W
+ .500 —
12

W
0.500 —
12

o.ooo—

W
0.000 —
12

W
0.000^-

0.000
0.000
0.000
0.000

Uniform

ft = the radius of the pipe, W = total weight of ditch filling and superimposed load plus
| of the weight of the pipe itself (usually neglected), expressed in pounds per foot length of
pipe. Moments are inch-pounds per inch length of pipe. Shears and thrusts are in pounds
per inch length of pipe.

104. Analysis of Sewer Arches. — The preceding method for
the determination of the stresses in a sewer ring has referred only
to a circular pipe uniformly loaded. Other methods must be
used if the pipe is not circular or the load is not uniformly dis-
tributed. The simplest method, is the static or so-called vouis-
soir method. In this method the arch is assumed to be fixed at
both ends, presumably at the springing line or line of intersection
between the inside face of the arch and the abutment, and it is so
designed that the resultant of all the forces acting on any section
shall lie within the middle third of that section.

To design an unreinforced sewer arch by the vouissoir method,
a desired arch is drawn to scale in apparently good proportions
for the loadings anticipated. The arch is then divided into any
number of sections of equal or approximately equal length called
vouissoirs, and the line of action of the resultant load, including
the weight of the vouissoir is drawn above each vouissoir as shown
in Fig. 82. The forces are assumed to act as shown in the figure.
In symmetrically loaded sewer arches there is no vertical reaction
at the crown. The resultant R is assumed to act at the lower
middle third of the skewback, which is the inclined joint between
the arch and the abutment. The upper horizontal force H is
assumed to ac^. at the upper middle third of the middle or crown

ANALYSIS OF SEWER ARCHES

205

section. The magnitude of H is computed by equating the sum
of the moments of all forces about the point of application of R
at the skewback to zero, and solving. The force polygon is then
drawn as shown in Fig. 83, and the equilibrium polygon is com-
pleted in Fig. 82 with its rays parallel to the corresponding strings
drawn from the end of H as origin in Fig. 83. If the equilibrium
polygon line, called the resistance line, lies wholly within the
middle third of each vouissoir, the arch is satisfactory to support
the assumed load without reinforcement. If any portion of the
resistance line lies outside of the middle third, an attempt should
be made to find a resistance line which lies wholly within the
middle third. The true resistance line is that which deviates the

R v
FIG. 82. — Voussoir Arch Analysis.

FIG. 83. — Force Polygon for
Voussoir Arch Analysis'.

least from the neutral axis of the arch. To approximate more
nearly the true resistance line find two points at which the resist-
ance line already drawn deviates the most from the neutral axis
of the arch. Select points M and N on these joints, M being
nearer the crown than N. Then let T^i and W% be the sum of all
the loads between the crown and M and N respectively, y repre-
sent the vertical distance from the crown to N, and y' represent
the vertical distance between M and N, and x\ and x% represent
the horizontal distance from W\ and Wz to M and N respectively.
Then the horizontal thrust H, and a, the distance from the crown
to the point of application of H, are,

1 From Vouissoir Arches by Cain.

206

DESIGN OF THE SEWER RING

A resistance line should be drawn with this new horizontal thrust.
If no resistance line can be found lying wholly within the middle
third, new sections should be designed until a resistance line can be
drawn lying wholly within the middle third — unless the arch is to
be reinforced. A number of satisfactory arches should be designed
and the easiest one to build should be selected. This method is
limited in its application to sewer arches with rigid side walls and
it cannot be extended to include the invert. Although an approxi-
mate method it is accurate within less than 10 per cent of the true
stresses and is usually quite close.

The elastic method for the design of arches locates the true
line of resistance without approximations and is more accurate
though not so simple to apply as the static or vouissoir method.
In this method a desired form of arch is drawn as in the static--
method and subdivided into vouissoirs so that the distance S
along the neutral axis between joints is such that the ratio I/S
shall be the same for all vouissoirs. I is the average of the
moments of inertia of the surfaces of the two limiting joints about
the neutral axis. If the thickness of the arch is constant the
distance between joints will be the same. The method for divid-
ing the arch into sections such that the ratio I/S shall be a con-
stant l is as follows: divide the half arch axis into any number of

FIG. 84. — Method for Dividing Arch into Proportion I/S.

equal parts; measure the radial depth at each point of division;
lay off the length of the arch axis to scale on a straight line;
divide this line into the same number of equal parts as the half
arch, as shown in Fig. 84; at each point erect a perpendicular
1 Baker's Masonry, 10th Edition, p. 676.

ANALYSIS OK SK\VKR AHCHKS

207

equal in length by scale to the moment of inertia at the correspond-
ing point on the arch section; draw a smooth curve through the
tops of these lines; draw a line ab at any slope from the center of
the original straight line to the curve, and then a line be back to
the straight line to form an isosceles triangle abc; continue forming
these triangles in a similar manner thus dividing the original
straight line in the required ratio. The distance between joints
is represented by the bases of the triangles. By construction the
altitude of the triangle represents the average moment of inertia
between the two limiting joints. The base of each isosceles
triangle is S, and I/S = $ tan a in which a is the base angle of all
the isosceles triangles.

FIG. 85. — Elastic Arch Analysis.

The following steps in the procedure are taken from the second
edition of the American Civil Engineers Pocket Book, p. 634 :

In Fig. 85 let the middle points of the joints be marked
1, 2, 3, etc. and the coordinates x and y from the crown
be found for each by computation or measurement. For
a load W placed at one of these points, let z denote the
distance from it, toward the nearest skewback, to another
middle point. Let 'Lzx be the sum of the products of all
the values of z by the corresponding x, and 2zy be the sum
of all the products of z by the corresponding y; that is,
each z in the last two summations is multiplied by the x
or y of the point back of W which corresponds to z.

For a single load W on the left semi-arch of Fig. 85
the following formulas are deduced from the elastic theory,

208 DESIGN OF THE SEWER RING

n being the number of parts into which the semi-arch is
divided.

/TF\n2zi/-2

yz* m

V 9 / n Ti/2 (
\& / fl'^y \

%W2z-HZy

2?/)2 ' ' W

f9ft

Shp^r at, CJrown Vr\~

n
%WZzx

. . . \£i)

(3)

2x2 ' '

For symmetrical loading such as W on the left and W on
the right the horizontal thrust and crown moment due
to both loads are double those found by the above formulas,
while the crown shear Fo is zero. For several loads unsym-
metrically placed the formulas are to be applied to each
in succession and the results added algebraically, the
value of FO being taken as negative for the left semi-arch
and positive for the right semi-arch.

For any joint whose middle point is at a distance x
from the crown

M = M0+Hy+Vox- 2Wz,
F=F0-ZTF,

where 2TF is the sum of all the loads between the joint
and the crown and 2Wz is the sum of the moments of
those loads with respect to the middle of the joint. The
components of the resultant thrust normal and parallel
to the joints are,

N = H cosd— V sin 8,

in which 6 is the angle which the plane of the joint makes
with the vertical.

The distances from the neutral axis to the resistance
line are,

at the crown, eo = -~t
li

at the joint, e=j^-

The resistance line should be located as in the vouissoir
method and if not within the middle third a new design should be
studied.

REINFORCED CONCRETE SEWER DESIGN 209

105. Reinforced Concrete Sewer Design. — The method to be
followed in the design of reinforced concrete arches is similar
except that the moment of inertia should include both the con-
crete and the steel, that is,

I = lc+nlt,

in which 7 is the moment of inertia to be employed, Ie is the
moment of inertia of the concrete, /, is the moment of inertia of
the steel, and n is the ratio of their moduli of elasticity, generally
taken as 15. All of the moments of inertia are referred to the
neutral axis of the beam. The reinforcement called for in pre-
cast circular pipes is given in Table 39. Sewers cast in place are
ordinarily designed to avoid reinforcement, except where the
depth of cover is small and the sewer may be subjected to super-
imposed loads.

Concrete sewers are sometimes reinforced longitudinally, with
expansion joints from 30 to 50 feet apart. This reinforcement is
to reduce the size of expansion and contraction cracks by dis-
tributing them over the length of a section. The pipe is divided
into sections to concentrate motion due to expansion or contrac-
tion at definite points where it can be cared for.

The amount of longitudinal reinforcement to be used is a
matter of judgment. It varies in practice from 0.1 to 0.4 per
cent of the area of the section. Since the coefficients of expan-
sion of concrete and of steel are nearly the same, movements of
the structure are as important as the stresses due to changes in
temperature.

Because of the uncertain and difficult conditions under which
concrete sewers are frequently constructed it is advisable to
specify the best grade of concrete and not to stress the concrete
over 450 pounds per square inch hi compression, with no allowable
stress hi tension. The concrete covering of reinforcing steel
should be thicker than is ordinarily used for concrete building
design, because of the possibility of poor concrete allowing the
sewage to gain access fco the steel, resulting in more rapid deteriora-
tion than would be caused by exposure to the atmosphere. A
minimum covering of about 2 inches is advisable, except in very
thin sections not in contact with the sewage. A minimum thick-
ness of concrete of about 9 inches is frequently used in design,
although crown thicknesses of 4$ inches have been used with

210 DESIGN OF THE SEWER RING

success. Greater thicknesses should be used near the surface,
particularly in locations subjected to heavy or moving loads.

Brick linings are often provided for the invert where moder-
ately high velocities of about 10 feet per second when flowing full
are to be expected. For velocities in the neighborhood of 20 feet
per second the invert should be lined with the best quality vitri-
fied brick. Although concrete may erode no faster than brick
under the same conditions, brick linings are more easily replaced
and at a smaller expense.

CHAPTER X
CONTRACTS AND SPECIFICATIONS

106. Importance of the Subject. — Sewers may be constructed
by day labor or by contract. Under the day labor plan a city
official or commission is charged with the purchase of material,
the hiring and firing of employees, and the management of the
work. Under the contract system a private individual or com-
pany contracts to supply all the material and labor necessary for
the completion of the work.

Under the day labor plan all persons engaged are " working
for the City." There is not the same sense of individual responsi-
bility, the same incentive to economize, the same feeling of loyalty
that is inspired by work under the personality of a contractor.
Under either the day labor or contract plan unscrupulous politics
are likely to enter into the relations of the employees of the city
and the city officials or between the contractor and the city
officials. Neither the day labor nor the contract plan offer a sure
cure for unscrupulous political misdealings. Under the contract
plan the contractor is led to keep his bid as low as possible, realiz-
ing the competition of other bidders, and during construction he
will obtain greater efficiency from his labor because of their
realization of the different conditions under which they are work-
ing. In some states and cities it is illegal for the municipality to
do sewer construction except under the contract method.

The contract method is therefore used in the majority of
cases, and it is to the interest of the engineer that he be acquainted
with the essentials of contracts and specifications necessary for
the proper prosecution of sewer construction.

107. Scope of Subject. — The making of a contract is one of
the most common episodes of every day life. The contract may
be an informal verbal agreement to meet at a certain place at a
certain time, or it may be a formal document hedged about by
confusing legal phraseology and bearing varieties of penalties and

211

212 CONTRACTS AND SPECIFICATIONS

dire consequences in the event of its breach. The purpose of this
chapter is to explain only those general features of an engineering
contract which have particular bearing upon sewerage construc-
tion. Only the most essential points can be touched in the limited
space available to this subject, it being presumed that the engi-
neer is previously grounded in the principles of business law.1

108. Types of Contracts. — Contracts are known as lump sum,
cost-plus, unit-price, and by other titles indicating the method of
payment.

A lump sum contract is one in which a stated amount is fixed
upon, before the execution of the contract, to be paid for all the
work to be done and materials to be furnished under the contract.
Such an arrangement is not advisable for a sewer contract, as the
cautious contractor will bid high enough to protect himself in the
event of a-ny probable emergency. The principal must therefore
pay whether the emergency or unforeseen difficulty is met or not.
The advantage of this type of payment is that the principal
knows exactly the cost of the work to him before construction is
commenced.

Cost-plus contracts are those in which the cost of the work to
the contractor is to be paid by the principal, plus, (a) a fixed sum
of money, (6) a percentage of the cost of the work, (c) a per-
centage of the cost of the work but with a fixed limit, (d) a per-
centage of the difference between the cost of the work and some
fixed sum, or other variations of this principle. Such contracts
have the advantage that the principal assumes all the risk in con-
struction and therefore pays for only those contingencies which
actually arise. Except for the last named form, they have the
disadvantage that there is little or no incentive for the contractor
to keep the cost of the work down. They are most successful
where the contractor can be selected by the principal, but where

1 Business Law for Engineers, C. Frank Allen, McGraw-Hill, 1917; En-
gineering Contracts and Specifications, J. B. Johnson, McGraw-Hill, 1904;
Contracts in Engineering, J. I. Tucker, McGraw-Hill, 1910; The Law Affect-
ing Engineers, W. V. Ball, Archibald Constable, 1909; Law and Business
of Engineering and Contracting. C. E. Fowler, McGraw-Hill, 1909; The
Economics of Contracting, D. J. Hauer, E. H. Baumgartner, 1915; The
Elements of Specification Writing, R. S. Kirby, John Wiley & Son, 1913;
Contracts, Specifications and Engineering Relations, D. W. Mead, McGraw-
Hill, 1916; Engineering and Architectural Jurisprudence, J. C. Wait, John
Wiley, 1912.

THE AGREEMENT 213

it is necessary to let contracts to the lowest bidder, the " cost-
plus *' contract is not easily managed. In most states a munici-
pality cannot make a cost-plus contract.

A unit-price contract is one in which the amount to be paid is
fixed in proportion to the amount of work done or materials sup-
plied. This type of contract is the most suitable for sewer con-
struction for a municipality where the contract must be let to the
lowest bidder. The contractor is protected in the event of many
unforeseen emergencies and the principal is protected against a
raise in bids to cover such emergencies and against increase in the
cost of the work in order to increase the profits under a " cost-
plus " contract.

It is sometimes desirable for the principal to furnish a portion
of the materials, the bidders being notified beforehand that this
material will be furnished. In this manner the quality of material
is assured, contractors with the necessary skill but small capital
may be attracted to bid, and uncertainties in the procuring of
materials is eliminated.

109. The Agreement. — A contract is an agreement between
two or more interested parties to do a certain thing. A contract
for the construction of a sewer is an agreement between a muni-
cipality or individual desiring sewerage facilities and a company or
individual engaged in the construction of sewers. The latter
promises to construct a sewer in return for which the former
promises to pay a certain amount of money.

The various portions of the agreement which are bound
together as the complete contract are: I. The Advertisement,
II. Information and Instructions for Bidders, III. Proposal,
IV. General Specifications, V. Technical Specifications, VI.
Special Specifications, VII. Contract, VIII. Bond, and IX.
Contract Drawings. These should be fastened together in pamph-
let form and constitute the complete instrument called the con-
tract. No binding contract and specifications can be drawn upon
logical deductions alone as legal precedent and tried methods
must be followed to insure success. To draw up an original con-
tract requires the combined knowledge of an engineer and a
lawyer. The engineer of to-day writes his specifications by copy-
ing copiously from specifications used on work which has been
completed successfully. In order that selections may be made
with judgment and discrimination some examples have

214 CONTRACTS AND SPECIFICATIONS

been selected from existing published specifications and con-
tracts.

110. The Advertisement. — This should contain: (1) A head-
ing indicating the type of work, (2) A statement as to when,
where and how bids will be received and opened, (3) A brief
description of the character and amount of work to be done, (4)
The method of payment, (5) The conditions under which further
information can be obtained, (6) A statement as to the amount
of money which must be deposited with the bid, and (7) Any
other pertinent facts concerning the work.1 An example of an
advertisement follows;

Sewer Construction
Construction Turkey Creek Sewer

Kansas City, Missouri.

Bids for the construction of the Turkey Creek Sewer, two sewage
pumping stations to be used in connection therewith, and certain
laterals and extensions of existing sewers thereto, for Kansas City,
Missouri, will be received up to 2 p. m. August 19, 1919, at the office
of the Board of Public Works, City Hall, Kansas City, Missouri.

The main sewer will be about one and one-fifth miles long, and the
laterals and extensions about three and one-half miles: the main
sewer will be constructed of reinforced concrete, the laterals and
extensions will consist of concrete, segment blocks, and clay pipe.

This work is estimated to cost from $1,500,000 to $1,760.000.
Payment for the work will be made in four year special tax bills,
bearing 7 per cent interest, payable one-fourth each year. Time
600 working days, barring strikes, bad weather, etc.

Bidders are required to deposit $15,000 in cash or a certified check
with bid, to insure signing of contract when let. Same to be returned
on execution of the contract or rejection of bid.

Complete plans and specifications for the work may be had and
all information obtained by seeing or writing to A. D. Ludlow,
Engineer of Sewers, City Hall, Kansas City, Missouri. Twenty-five
($25.00) Dollars will be required to be deposited for a set of the plans,
but $20.00 thereof will be refunded upon return of the plans in good
condition.

BOARD OF PUBLIC WORKS,

Kansas City, Missouri,

by F. E. McCabe, Secretary.

There are usually legal restrictions which require that the
advertisement be inserted a certain number of times in specified
newspapers or other advertising mediums before the opening of
bids. If the contract is of sufficient size to attract outside con-

1 See article by E. W. Bush in Eng. News-Record, Vol. 85, 1920, p. 122.

INFORMATION AND INSTRUCTIONS FOR BIDDERS 215

tractors, the advertisement should be inserted in engineering and
contracting journals of wide circulation. Although the adver-
tisement appears separately from the other portions of the con-
tract, a copy is usually bound in as the first page of the pamphlet
containing the contract and specifications and is made an integral
part thereof.

111. Information and Instructions for Bidders. — This is some-
what on the order of an introduction to the pamphlet in which the
specifications, contract, and contract drawings are published.
As examples of the type of information and instructions given to
prospective bidders the abstracts below have been taken from the
" Contract, Specifications, Bond, and Proposal for the North
Shore Sanitary Intercepting Sewer " by the Sanitary District of
Chicago. The information 'and instructions to bidders can be
divided into the following sections: 1st. Examination of Site,
2nd. Character and Quantity of Work, 3rd. Qualification for
Bidding, 4th. Instructions for Making out Proposal, 5th. Certified
Check, and 6th. Rejection of Bids,

REQUIREMENTS FOR BIDDING AND INSTRUCTIONS TO BIDDERS

Bidders are required to submit their bids upon the following
express conditions:

Bidders must carefully examine the entire sites of the
work and the adjacent premises, and the various means
of approach to the sites, and shall make all necessary
investigations to inform themselves thoroughly as to the
facilities for delivering and handling materials at the sites
and to inform themselves thoroughly as to all the difficulties
that may be involved in the complete execution of all work
under the attached contract in accordance with the speci-
fications hereto attached.

Bidders are also required to examine all maps, plans,
and data mentioned in the specifications, contract or pro-
posal as being on file in the office of the Chief Engineer,
for examination by bidders. No plea of ignorance of
conditions that exist or that may hereafter exist or of
conditions or difficulties that may be encountered in the
execution of the work under this contract, as the result
of a failure to make the necessary examinations and investi-
gations, will be accepted as an excuse for any failure or
omission on the part of the Contractor to fulfill in every
detail all of the requirements of said contract, specifica-

216 CONTRACTS AND SPECIFICATIONS

tions and plans, or will be accepted as a basis for any
claims whatsoever for extra compensation. Upon applica-
tion all information in the possession of the Chief Engineer
will be shown to bidders, but the correctness of such
information will not be guaranteed by the Sanitary District.
The following schedule of quantities, although stated
with as much accuracy as :s possible in advance, is approxi-
mate only, and is assumed solely for the purpose of com-
paring bids.

Then follows an itemized schedule of the quantity of work to be
done after which comes the following:

Bidders must determine for themselves the quantities
of work that will be required, by such means as they may
prefer, and shall assume all risks as to variations in the
quantities of the different classes of work actually furnished
under the contract. Bidders shall not at any time after
the submission of this proposal, dispute or complain of
the aforesaid schedules of quantities or assert that there
was any misunderstanding in regard to the amount or the
character of the work to be done, and shall not make any
claims for damages or for loss of profits because of a dif-
ference between the quantities of the various classes of
work assumed for comparison of bids and the quantities
of work actually performed.

Proposals that contain any omissions, erasures, or
alterations, conditions or items not called for in the con-
tract and plans attached hereto, or that contain irregu-
larities of any kind, will be rejected as informal.

Bids manifestly unbalanced will not be considered in
awarding the contract.1

No bid will be accepted unless the party making it
shall furn'sh evidence satisfactory to the Board of Trustees
of the Sanitary District of Chicago of his experience and
familiarity with work of the character specified and of
his financial ability to successfully and properly prosecute
the proposed work to completion within the specified time.

Each bid shall be accompanied by a certified check,
or cash, to the amount of ten (10) per cent of the total
amount of said bid figured on the quantities given here-

1 An unbalanced proposal is one in which the bids on some of the items
are obviously low and on other items are obviously or suspiciously high.
The purpose of submitting unbalanced bids is to keep secret the true or
supposed cost of the work to the contractor or to obtain more money by bid-
ding high on those items which are believed to have been underestimated
by the Engineer. A low bid is made on other items in order to keep down
the total amount of the bid.

PROPOSAL 217

with, the lowest alternative total being allowed. Said
amounts deposited with bids, shall be held until all of the
bids have been canvassed and the contract awarded and
signed. The return of said check or cash to the bidder to
whom the contract for said work is awarded will be con-
ditioned upon his appearing and executing a contract for
the work so awarded and giving bond satisfactory to said
Board of Trustees, for the fulfillment of each contract in
the amount of fifty (50) per cent of the amount of each
contract.

The said Board of Trustees reserves the right to re-
ject any or all bids.

Accompanying the contract form are plans which,
together with the specifications, show the work on which
said tenders are to be made.

The proposal must not be detached herefrom or from
the contract by any bidder when submitting a bid.

112. Proposal. — The proposal is a blank printed form on
which the bidder is required to enter the prices for which he
proposes to do the work. The proposal blank is necessary in
order that the bids may be sufficiently uniform for proper com-
parison. Sewers are often paid for, particularly for small sizes,
per foot of completed sewer as measured along the center line of
the pipe parallel to the surface of the ground with the exterior
length of manholes and other structures deducted. Sometimes,
under other conditions, a different rate is allowed for each addi-
tional two feet of depth of sewer, and special structures, such as
manholes, catch-basins, flush-tanks, etc., are paid for at a unit
price according to the depth. Water connections to flush-tanks
are paid for per foot of length of service pipe laid. In especially
large or difficult work, materials are paid for at a unit price, for
example, per cubic yard of excavation, per cubic yard of concrete,
per thousand feet board measure of lumber, etc.

The following example is taken from the contract for the
North Shore Intercepting Sewer previously quoted, to indicate
the type of Proposal used:

218 CONTRACTS AND SPECIFICATIONS

PROPOSAL

FOR THE CONSTRUCTION OF THE NORTH SHORE
INTERCEPTING SEWER

To the Honorable, the President and the Board of Trustees
of the Sanitary District of Chicago:

Gentlemen: — The undersigned hereby certi

that ha examined the specifications and form

of contract and the accompanying plans for the construc-
tion of the North Shore Intercepting sewer, and ha

also examined the premises at and adjacent to the sites
of the proposed work, as herein described, and the means
of approach to the said sites.

The undersigned ha also examined the fore-
going " Requirements for Bidding and Instructions to
Bidders " and propose. ... to do all the work called for in
said specifications and contract, and shown on said plans,
and to furnish all materials, tools, labor and all appliances
and appurtenances necessary to the full completion of
said work at the rates and prices for said work as follows,
to-wit:

(la) For six (6) by nme (9) foot concrete sewer, com-
plete in place, as specified, the sum of

Dollars and

cents ($ ) per linear foot.

(6a) For manholes, concrete, complete in place, as
specified the sum of

Dollars

and cents ($ ) each

The following plans showing the work to be performed
in accordance with the attached specifications, have been
examined by the undersigned in preparing the foregoing
proposal, to-wit:

In accordance with the requirements set forth in the
attached Information and Instructions for Bidders, there

is deposited herewith the sum of

Dollars and

cents (S ) which

under the terms therein mentioned entitle . .

to bid on said work, the said sum to be refunded to.

upon the faithful performance of all conditions set forth
in the Information and Instructions for Bidders.

Name

Address . .

GENERAL SPECIFICATIONS 219

Blanks are provided for each item. No place is left at the
end for a summary. The proposal ends with an acknowledgment
that the contract has been examined completely and all prelimi-
nary directions therein have been complied with. A blank is
prepared for inserting the amount of the required certified check,
and finally for the signature of the bidders.

113. General Specifications. — The specifications, both general
and technical, are occasionally incorporated in the contract form,
but more frequently they are printed separately and are bound in
the pamphlet preceding the contract. The general specifications
relate to the conditions under which all work must be performed
and are as applicable to the construction of a pumping station as
to the smallest lateral, unless otherwise specified. It is not pos-
sible to include a complete set of General Specifications in the
limited space of this text, but the more important specifications
will be emphasized by examples taken from specifications in use.1

The subjects covered in General Specifications are:

(1) Definitions of doubtful terms.

(2) The Engineer to settle disputes.

(3) Duties of the Engineer.

(4) Duties of the Contractor.

(5) Hours and days of work.

(6) No work to be done in the absence of an inspector.

(7) Contractor to be represented at all times.

(8) Time of commencing and completing the work.

(9) Liquidated damages for delay in completion.

(10) The City may change the plans.

(11) The City may increase the amount of the work.

(12) Inspection and its conduct.

(13) The Contractor to be acquainted with laws relat-

ing to the work.

(14) Contractor responsible for damages to persons or

property.

(15) City to be protected against patent claims.

(16) Abandonment of contract and its remedy.

(17) Estimates of work done and moneys due.

(18) Payments for extra work.

(19) Character of workmen to be employed.

(20) City may reserve a sum for repairs during stipu-

lated term after completion.

1 Taken mainly from specifications of the Sanitary District of Chicago
and the Baltimore Sewerage Commission, with miscellaneous selections
from other sources.

220 CONTRACTS AND SPECIFICATIONS

(21) City may use money due Contractor to pay claims

for labor or materials used on the work and not
paid for by the Contractor.

(22) The Contractor shall have no claim for damages

on account of delay or unforeseen difficulties.

(23) The Contractor may not assign nor sublet the

contract without the City's consent.

(24) Cleaning up after completion.

(25) The Contractor's relations to other contractors.

(26) The portions composing the contract.

The following examples cover the subjects named in the pre-
ceding titles:

1. Definitions. The word Engineer whenever not
qualified shall mean the Chief Engineer of the Commission,
acting either directly or through his properly authorized
agents, such agents acting severally within the scope of
the particular duties entrusted to them.

This article may include words that may be in dispute or ambigu-
ous such as: Board of Trustees, Elevation, City, Contractor,
Rock, Earth, etc., etc.

2. Disputes. To prevent disputes and litigations, the
Engineer shall in all cases determine the amount, quality,
and acceptability of the work which is to be paid for under
the contract; shall decide all questions in relation to said
work and the performance thereof, and shall in all cases
decide every question which may arise relative to the ful-
fillment of the contract on the part of the Contractor.
His determination, decision and estimate shall be final
and conclusive, and in case any question shall arise between
the parties touching the contract, such determination,
decision, and estimate shall be a condition precedent to
the right of the Contractor to receive any moneys under
the contract.

3. Duties of the Engineer. The Engineer shall make
all necessary explanations as to the meaning and intentions
of the specifications and shall give all orders and directions,
either contemplated therein or thereby, or in every case
in which a difficulty or unforeseen condition shall arise in
the performance of the work. Should there be any dis-
crepancies in or between, or should any misunderstanding
arise as to the import of anything contained in the plans
and specifications, the decision of the Engineer shall be
final and binding. Any errors or omissions in plans and spe-
cifications may be corrected by the Engineer, when such
corrections are necessary for the proper fulfillment of their

, intentions as construed by him.

GENERAL SPECIFICATIONS 221

4. Duties of the Contractor. The Contractor shall
do all the work and furnish all the labor, materials, tools
and appliances necessary or proper for performing and com-
pleting the work required by the contract, in the manner
called for by the specifications, and within the contract
time. He shall complete the entire work at the prices
agreed upon and fixed therefor to the satisfaction of the
Commission and its Chief Engineer and in accordance
with the specifications, the drawings, and such detailed
drawings as may be furnished from time to time, together
with such extra work as may be required for the perform-
ance of which written orders may be given and received
as hereinafter provided.

The Contractor shall place sufficient lights on or near
the work and keep them burning from twilight to sunrise;
shall erect suitable railings, fences or other protections
about all open trenches, and provide all watchmen on the
work, by day or night, that may be necessary for the public
safety. The Contractor shall, upon notice from the Engi-
neer that he has not satisfactorily complied with the fore-
going requirements, immediately take such methods and
provide such means and labor to comply therewith as the
Engineer may direct, but the Contractor shall not be
relieved of this obligation under the contract by any such
notice or directions given by the Engineer, or by neglect,
failure, or refusal on the part of the Engineer to give such
notice and directions.

The Contractor shall furnish such stakes and the neces-
sary labor for driving them as may be required by the
Engineer. He shall maintain the stakes when set, with
reasonable diligence, and stakes misplaced due to the careless-
ness of the Contractor or his workmen shall be reset under
the direction of the Engineer, at the Contractor's expense.

5. Night, Sunday, and Holiday Work:1 No night,
Sunday, nor holiday work requiring the presence of an
engineer or inspector will be permitted except in case of
emergency, and then only to such an extent as is absolutely
necessary and with the written permission of the Engineer;
provided that this clause shall not operate in the case of
a gang organized for regular and continuous night, Sunday,
or holiday work.

6. Absence of Engineer or Inspector. Any work done
without lines, levels, and instructions having been given
by the Engineer or without the supervision of an assistant

1 Restrictions are placed on work done outside of ordinary working hours
in order that the Contractor may not perform work in the absence of an
engineer or inspector.

222 CONTRACTS AND SPECIFICATIONS

or inspector, will not be estimated or paid for except when
such work is authorized by the Engineer in writing. Work
so done may be ordered removed and replaced at the
Contractor's sole cost and expense.

7. Absence of Contractor. During the absence of the
Contractor he shall at all times have a duly authorized
representative on the work. The Contractor shall give
written notice to the Commission of the name and address
of said representative and shall state where and how such
representative can be reached, at any and all hours, whether
by day or night.

Whenever the Contractor or his representative is not
present at any place on the work where it may be necessary
to give orders or directions, such orders or directions will
be given by the Engineer and they shall be received and
promptly obeyed by the superintendent or foreman who
may have immediate charge of the particular work in rela-
tion to which the order may be given.

8. Commencing Work. The Contractor agrees to

begin the work covered by this contract within

days of the execution of the contract and to prosecute the
same with all due diligence and to entirely complete the
work within days.

It is understood and agreed that time is of the essence
of this contract, and that a failure on the part of the Con-
tractor to complete the work herein specified within the
time specified will result in great loss and damage to said
Sanitary District and that on account of the peculiar
nature of such loss it is difficult, if not impossible, to accu-
rately ascertain and definitely determine the amount
thereof.

9. Liquidated Damages. It is therefore covenanted
and agreed that in case the said Contractor shall fail or
neglect to complete the work herein specified on or before
the date hereinbefore fixed for completion, the said Con-
tractor shall and will pay the said Sanitary District the
sum of Dollars for each and every day the Con-
tractor shall be in default in the time of completion of
this contract.

Said sum of Dollars per day is hereby agreed

upon, fixed and determined by the parties hereto as the
liquidated damages which said Sanitary District will
suffer by reason of such defaults, and not by way of a
penalty.

10. Changes in Plans. The Board reserves the right
to change the alignment, grade, form, length, dimensions
or materials of the sewers or any of their appurtenances,

> whenever any condition or obstructions are met that

GENERAL SPECIFICATIONS 223

render such changes desirable or necessary. In case the
alterations thus ordered make the work less expensive to
the Contractor a proper deduction shall be made from
the contract prices and the Contractor shall have no claim
on this account for damages or for anticipated profits on
the work that may be dispensed with. In case such
alterations make the work more expensive, a proper addi-
tion shall be made to the contract prices. Any deduction
or addition as aforesaid shall be determined and fixed by
the Engineer.

11. Extensions and Additions. In the event that any
material alterations or additions are made as herein speci-
fied which in the opinion of the Engineer will require
additional time for execution of all the work under this
contract, then, in that case the time of completion of the
work shall be extended by such a period or periods of time
as may be fixed by said Engineer and his decision shall be
final and binding upon both parties hereto, provided that
in such case the Contractor, within four (4) days after
being notified in writing of such alterations and additions,
shall request in writing an extension of time, but the
provisions of this paragraph shall not otherwise alter the
provisions of this contract with reference to liquidated
damages, and the said Contractor shall not be entitled to
any damages or compensation from the said Sanitary
District on account of such additional time required for
the execution of the work.

12. Inspection. All materials of whatsoever kind to
be used in the work shall be subject to the inspection and
approval of the Engineer and shall be subject to constant
inspection before acceptance. Any imperfect work that
may be discovered before its final acceptance shall be cor-
rected immediately, and any unsatisfactory materials used
in the work or delivered at the site shall be rejected and
removed on the requirement of the Engineer. The inspec-
tion of any work shall not relieve the Contractor of any
of his obligations to perform proper and satisfactory work
as herein specified, and all work which, during the progress
and before the final acceptance, may become damaged
from any cause, shall be removed and replaced by good
and satisfactory work without extra charge therefor. The
Engineer and his assistants shall have at all times free
access to every part of the work and to all points where
material to be used in the work is manufactured, procured
or stored and shall be allowed to examine any material
furnished for use in the work under this contract.

All inspection of any and all material furnished for use
in work to be performed under this contract shall be made

224 CONTRACTS AND SPECIFICATIONS

at the site of the work after the delivery of the material,
provided, that, if requested by the Contractor the Engi-
neer may at his option perform, or have performed, inspec-
tion of materials at points other than the site of the work.
In any such case the Contractor shall pay the Sanitary Dis-
trict the extra cost of such inspection, including the neces-
sary expenses of the inspector for the extra time expended
in performing any such inspection at said other points.

13. Legal Requirements. The Contractor shall keep
hinself fully informed of all existing and future national
and state laws and local ordinances and regulations in
any manner affecting those engaged or employed in the
work, or the materials used in the work, or of all such
orders and degrees of bodies or tribunals having any juris-
diction or authority over the same, and shall protect and
indemnify the party of the first part against any claim
or liability arising from or based on the violation of such
law, ordinance, regulation, order or decree, whether by
himself or his employees.

14. Damages. If any damage shah be done by the
Contractor or by any person or persons in his employ to
the owner or occupants of any land or to any real or per-
sonal property adjoining, or in the vicinity of the work
herein contracted to be done or to the property of a neigh-
boring contractor the Engineer shall have the right to esti-
mate the amount of said damage arid to cause the Sanitary
District to pay the same to the said owner, occupant, or
contractor, and the amount so paid shall be deducted
from the money due said Contractor under this contract.
Said Contractor covenants and agrees to pay all damages
for any personal injury sustained by any person growing
out of any act or doing of himself or his employees that
is in the nature of a legal liability, and he hereby agrees
to indemnify and save the Sanitary District harmless
against all suits or actions of every name and description
brought against said Sanitary District, for or on account
of any such injuries, or such damages received or sustained
by any person or persons; and the said Contractor further
agrees that so much of the money due to him under this
contract, as shall be considered necessary by the Board of
Trustees of said Sanitary District, may be retained by the
Sanitary District until such suit or claim for damages
shall have been settled, and evidence to that effect shall
have been furnished to the satisfaction of said Board of
Trustees.

15. Patents. It is further agreed that the Contractor
shall indemnify, keep and save harmless said Sanitary
District from all liabilities, judgments, costs, damages and

GENERAL SPECIFICATIONS 225

expenses which may in any wise come against said Sanitary
District, or which may be the result of an infringement
of any patent by reason of the use of any materials, machin-
ery, devices, apparatus, or process furnished or used in
the performance of this contract, or by reason of the use
of designs furnished by the Contractor and accepted by
the Sanitary District, and in the event of any claim or
suit or action at law or in equity of any kind whatsoever
being made or brought against said Sanitary District, then
the Sanitary District shall have the right to retain a suffi-
cient amount of money in the same manner and upon the
conditions as hereinafter specified.

16. Abandonment of Contract. If the work to be done
under the contract shall be abandoned by the Contractor,
or if at any time the Engineer shall be of the opinion, and
shall so certify, in writing, to the Commission, that the
performance of the contract is unnecessarily or unreason-
ably delayed, or that the Contractor is willfully violating
any of the conditions of the specifications, or is executing
the same in bad faith, or not in accordance with the terms
thereof, or if the work be not fully completed within the
time named in the contract for its completion, the Com-
mission may notify the Contractor to discontinue all
work thereunder, or any part thereof, by a written notice
served upon the Contractor, as herein provided; and
thereupon the Contractor shall discontinue the work, or
such part thereof, and the Commission shall thereupon
have the power to contract for the completion of said work
in the manner prescribed by law, or to procure and furnish
all necessary materials, animals, machinery, tools and
appliances, and to place such and so many persons as it
may deem advisable to work at and complete the work
described in the specifications, or such part thereof, and
to charge the entire cost and expense thereof to the Con-
tractor. And for such completion of the work or any part
thereof, the Commission may for itself or its contractors,
take possession of and use or cause to be used any or all
such materials, animals, machinery, tools and implements
of every description as may be found on the line of the said
work. The cost and expense so charged shall be deducted
from, and paid by the City out of such moneys as may be
due or may become due to the Contractor, under and by
virtue of the contract. In case such expense shall exceed
the amount which would have been payable under the con-
tract, if the same had been completed by the Contractor,
he shall pay the amount of such excess to the City. When
any particular part of the work is being carried on by the
Commission, by contract or otherwise, under the provisions

226 CONTRACTS AND SPECIFICATIONS

of this clause of the contract, the Contractor shall continue
the remainder of the work in conformity with the terms
of his contract, and in such manner as in no wise to hinder
or interfere with the persons or workmen employed by the
Commission by contract or otherwise as above provided,
to do any part of the work or to complete the same under
the provisions hereof.

17. Estimates. The Engineer shall from time to time
as the work progresses, on or about the last day of each
month, make in writing an estimate, such as he shall believe
to be just and fair, of the amount and value of the work
done and the materials incorporated into the work by the
Contractor under the specifications, provided however that
no such estimate shall be required to be made when, in the
judgment of the Engineer the total value of the work done
and the materials incorporated into the work since the last

preceding estimate is less than dollars. Such

estimates shall not be required to be made by strict measure-
ments, but they may be approximate only.

The Contractor shall not be entitled to demand from
the Commission as a right, a detailed statement of the
measurements or quantities entering into the several items
of the monthly estimates, but he will be given such oppor-
tunities and facilities to verify the estimates as may be
deemed reasonable by the Commission.

When in the opinion of the Engineer, the Contractor
shall have completely performed the contract on his part,
the Engineer shall make a final estimate, based on actual
measurements, of the whole amount of the work under
and according to the terms of the contract, and shall certify
to the Commission in writing, the amount of the final
estimate at the completion of the work. After the com-
pletion of the work the City shall pay to the Contractor
the amount remaining after deducting from the total
amount or value of the work, as stated in the final estimate,
all such sums as have theretofore been paid to the Con-
tractor under any of the provisions of the contract, except
such sums as may have been paid for extra work,' and also
any sum or all sums of money which by the terms thereof
the City is or may be authorized to reserve or retain;
provided that nothing therein contained shall affect the
right of the City, hereby reserved, to reject the whole
or any portion of the aforesaid work, should the said
cert'ficate be found or known to be inconsistent with the
terms of the contract or otherwise improperly given. All
monthly estimates upon which partial payments have been
made, being merety estimates, shall be subject to cor-
, rection in the final estimate, which final estimate may be

GENERAL SPECIFICATIONS 227

made without notice thereof to the Contractor, or of the
measurements upon which it is based.

18. Extra Work. The Contractor shall do any work
not herein otherwise provided for, when and as ordered
in writing by the Engineer or his agents specially authorized
thereto in writing, and shall when requested by the Engi-
neer so to do, furnish itemized statements of the cost of
the work ordered and give the Engineer access to accounts,
bills, vouchers, etc. relating thereto. If the Contractor
claims compensation for extra work not ordered as aforesaid,
or for any damages sustained, he shall within one week
after the beginning of any such work or the sustaining
of any such damage, make a written statement of the
nature of the work performed or the damage sustained,
to the Engineer, and shall, on or before the fifteenth day
of the month succeeding that in which any such extra
work shall have been done or any such damage shall have
been sustained, file with the Engineer an itemized statement
of the details and amount of any such work or damage; and
unless such statement shall be made as so required, his claim
for compensation shall be forfeited and he shall not be en-
titled to payment on account of any such work or damage.

For all such extra work the Contractor shall receive
the reasonable cost of said work, plus fifteen (15) per cent
of said cost.

19. Competent Employees. The Contractor shall
employ only competent skillful men to do the work; and
whenever the Engineer shall notify the Contractor, in
writing, that any man employed on the work is, in his
opinion unsatisfactory, such man shall be discharged from
the work and shall not again be employed on it, except
with the consent of the Engineer.

20. Money Retained. Upon the completion of the
work and its acceptance by the City, the City shall reserve
and retain five (5) per cent of the total value of the work
done under the contract as shown by the final estimate,
over and above any and all other reservations which the
city by the terms thereof is entitled or required to retain
and shall hold the said five (5) per cent for a period of nine
(9) months from and after the date of completion and
acceptance, and the City shall be authorized to apply
such part of said five (5) per cent so retained to any and
all costs of repairs and renewals as may become necessary
during such period of nine (9) months, due to improper
work done or materials furnished by the Contractor, if
the Contractor shall fail to make such repairs or renewals
within twenty-four (24) hours after receiving notice from
the City so to do.

228 CONTRACTS AND SPECIFICATIONS

Upon the expiration of said nine (9) months from and
after the completion and acceptance of the work, the City
shall pay to the Contractor the said five (5) per cent hereby
retained, less such sums as may have been retained here-
under.

21. Unpaid Claims against Contractor. The Con-
tractor shall furnish the City with satisfactory evidence
that all persons who have done work or furnished materials
under the contract, and have given written notices to the
City, before and within ten (10) days after the final com-
pletion and acceptance of the whole work under the con-
tract, that any balance for such work or materials is due
and unpaid, have been fully paid or satisfactorily secured.
And in case such evidence is not furnished as aforesaid,
such amount as may be necessary to meet the claims of
the persons aforesaid shall be fully discharged or such
notices withdrawn.

22. Delays and Difficulties. The Contractor shall not
be entitled to any claims for damages on account of post-
ponement or delay in the work occasioned by forces beyond
the control of the City, nor for postponement or delay in
the work where ten (10) days written notice has been given
the Contractor of such postponement or delay, nor where
unforeseen difficulties are encountered in the prosecution
of the work. In the event of a postponement or delay
ordered in writing by the City the time of completion of
the contract shall be extended a number of days equal to
the number of days that the work has been postponed or
delayed.

23. Assignment of Contract. The Contractor shall not
assign by power of attorney or otherwise, nor sublet the
work or any part thereof, without the previous written
consent of the party of the first part, and shall not either
legally nor equitably assign any of the moneys payable
under this agreement or his claim thereto unless by and
with the consent of the party of the first part.

24. Cleaning Up. On or before the completion of the
work, the Contractor shall, without charge therefor, tear
down and remove all buildings and other structures built
by him, shall remove all rubbish of all kinds from any
grounds which he has occupied, and shall leave the line
of the work in a clean and neat condition.

25. Access to Work and Other Contractors. The Com-
mission and its engineers, agents and employees may at
any time and for any purpose enter upon the work and the
premises used by the Contractor, and the Contractor shall
provide proper and safe facilities therefor. Other con-
tractors of the Commission may also when so authorized

TECHNICAL SPECIFICATIONS 229

by the Engineer, enter upon the work and the premises
used by the Contractor for all the purposes which may
be required by their contracts. Any differences or con-
flicts which may arise between this Contractor and other
contractors of the Commission in regard to their work
shall be adjusted and determined by the Engineer.

26. The Contract. It is understood and agreed by
the City and the Contractor that the terms of this contract
are embodied and included in the Advertisement. Informa-
tion and Instructions to Bidders, Proposal, Specifications
of every nature, the Bond and the contract drawings
hereto attached.

These few articles have been given as examples of some of the
essential subjects to be treated in general specifications. It is to
be understood that these examples do not represent a complete
set of general specifications and items have been omitted the
absence of which in a complete contract might be injurious to
the successful completion of the work.

114. Technical Specifications. — These ordinarily follow the
general specifications and have to do with the quality of materials,
the manner of putting them together, and the method of doing
the work. The subject headings in the Technical Specifications
on the Baltimore Sewerage Commission are:

Excavation Cement

Tunneling Mortar

Rock Excavation Concrete

Sheeting Brick

Sheet Piling Masonry

Sheeting and Bracing Reinforced Concrete

Piles Vitrified Pipe

Blasting Concrete and Brick Sewers

Pumping and Drainage Vitrified Pipe Sewers and Drains

Foundations Manholes

Refilling Iron Castings

Repaving House Connections

Underdrains Obstructions

Buildings Fences

Inlets and Catch-Basins Flush-Tanks

Each of these subjects is treated in the appropriate section of
this book.

An important part of each section of the technical specifica-
tions is the clause providing for the method of payment for the
work specified. This is usually the last clause in the section.

230 CONTRACTS AND SPECIFICATIONS

For example, the last clause in the Baltimore Specifications
relating to Rock Excavation, is:

"Payment will be made for the number of cubic yards
of rock measured and allowed as above specified at the
price of four dollars and fifty cents ($4.50) per cu. yd., meas-
ured in place. Payment for rock excavation will be made
in addition to the prices bid for excavation."

115. Special Specifications. — These have to do with problems,
methods of construction, or materials peculiar to certain contracts
or certain portions of the work. It frequently occurs that the
construction of sewerage works will be let out under a number of
contracts, or bids will be called for on different alternatives to
which the entire Advertisement, Information and Instructions
for Bidders, Proposal, and General Specifications are applicable.
The special specifications will apply only to the contract in ques-
tion, e.g., in some work done under the direction of the author,
the sewer on one contract came within twelve inches of the surface
of a highway. The special specification relating to this piece of
construction, was:

" Where crossing under the Chicago Road the pipe sewer
shall be embedded in concrete as shown on the contract
drawings. The concrete for this purpose shall be mixed
in the proportions of one (1) part cement, three (3) parts
fine aggregate, and six (6) parts coarse aggregate. Pay-
ment for the concrete so used will be made at the unit
price stated in the accompanying Proposal."

In order to avoid confusion the special specifications are either
incorporated directly in the Contract form, or follow the Technical
Specifications and are grouped according to the contracts to which
they apply.

116. The Contract. — The contract is a brief instrument which
includes a simple statement of the obligations of each party
involved. The following is an example of a form in successful use:

CONTRACT

This agreement made and entered into this

day of in the year one thousand nine

hundred and by and between the City of

by its duly constituted or elected authorities herein acting

for the City of without personal liability

to themselves, party of the first part, hereinafter desig-

THE CONTRACT 231

nated as the City, and

party of the second part hereinafter designated as the
Contractor.

WITNESSETH, that the parties to these presents each
in consideration of the undertakings, promises and agree-
ments on the part of the other herein contained, have
undertaken, promised and agreed, and do hereby under-
take, promise and agree, the party of the first part for

itself, its successors and assigns, and the part of

the second part for and heirs, executors,

administrators and assigns as follows, to-wit:

Art. I. To be bounden by all the articles of the General,
Technical, and Special Specifications applicable, and by
the terms of the Advertisement, Information and Instruc-
tions for Bidders, Proposal and Contract Drawings hereto
attached, and which are understood and acknowledged
to be an integral part of this contract.

Art. II. The work to be completed under this con-
tract is

Art. III. The City shall pay and the Contractor shall
receive as full compensation for everything furnished and
done by the Contractor under this contract, including all
work required but not specifically mentioned in the follow-
ing items, and also for all loss or damage arising from the
nature of the work aforesaid, or from the action of the
elements, or from any unforeseen obstruction or difficulty
encountered in the prosecution of the work and for well
and faithfully completing the work as herein provided,
as follows:

Then follows a copy of the Proposal with the prices bid. The
contract closes with the final clause:

In witness whereof the said City of , party

of the first part have hereunto set their hands and seals,
and the Contractor has also hereunto set his hand and
seal and the party of the first part and the Contractor
have executed this agreement in duplicate, one part to
remain with the party of the first part and one to be deliv-
ered to the Contractor this day of

hi the year one thousand nine hundred and

City of

Contractor .

232 CONTRACTS AND SPECIFICATIONS

117. The Bond. — The bond called for in the Information and
Instructions for Bidders is bound in the pamphlet following the
Contract. No uniform practice is followed in the amount of the
bond required. It varies from 50 to 100 per cent of the contract
price and may be stated as a lump sum before the contract price
is known. There is a possibility that the Contractor may fail
before he has commenced work and the City may be unable to
procure another contractor to take up the work. The City should
then be protected by a 100 per cent bond. Such a contingency is
remote. The Contractor seldom fails until work is well under
way, and other contractors are usually available, although the
failure of one contractor tends to increase the bids of other con-
tractors for the same work. In fixing the amount of the bond
the judgment of the Engineer is called into play in order that the
amount may be as low as possible in fairness to the Contractor,
and high enough to protect the interests to the City. By reducing
the amount of the bond the expense to the City is also reduced
as the City ult-'mately must pay its cost.

Upon the acceptance of the bond and the execution of the
Contract, the Engineer's duties take him out of the designing
office and into the construction field.

CHAPTER XI
CONSTRUCTION

118. Elements. — The principal elements in construction are:
labor, materials, tools, and transportation. The lack of or
inadequateness of any one of these detracts from the effectiveness
of the others. The engineer should assure himself of the com-
pleteness of his plans or those of the contractor on each of these
points. The disposition of labor and the handling of materials
to obtain the largest amount of good with the least expenditure
of money and effort are problems which must be solved by the
engineer or the contractor during construction.

WORK OF THE ENGINEER

119. Duties. — The duties of the engineer during construction
consist in giving lines and grades; inspecting materials; inter-
preting the contract, specifications and drawings; making deci-
sions when unexpected conditions are encountered; making esti-
mates of work done; collecting cost data; making progress reports;
keeping records; and in guarding the interests of the City.

120. Inspection. — In the inspection of workmanship and
materials, the engineer is assisted by a corps of inspectors and
assistants who act under his direction. The duties of the inspector
are to be present at all times that work is in progress and to act
for the engineer in enforcing the terms of the contract, the
details of the drawings, and the tests applicable to the workman-
ship and materials that he is delegated to inspect. He should
have a copy of the contract, or that portion of it which pertains
to his work, available at all times. He should examine all
materials as they are delivered on the job and see that rejected
materials are removed at once. An ordinary recourse of some
foremen will be to place rejected material to one side until a brief
absence of the inspector will present the opportunity for the use

233

234 CONSTRUCTION

of the rejected material. The methods to be followed in the
inspection of materials and workmanship should be such as to
discover discrepancies between the specifications and the materials
delivered or the work done. Other duties of the inspector are:
to record the location of house connections or to drive a stake
over them for subsequent location by the engineer; to see that
plugs are put in the branches left for future house connections;
to inspect the workmanship in the making of joints in pipe sewers;
to protect the line and grade stakes from displacement; to check
the size, depth, and grade of sewers and elevations of special
structures, etc.

*Dishonest and unscrupulous workmen have many tricks to
get by the inspector. These tricks are best learned by experi-
ence as no academic list can impress them properly on the memory.
The position of the inspector is not always enviable. He must
hold the respect of the workmen, of the contractor, and of the
engineer. To do this he must not be unreasonable or arbitrary
in his decisions, but when a decision is once made he must be
firm in following up its enforcement. He must be careful not to
give directions whose fulfillment he cannot enforce, nor for which
he cannot give adequate reason to his superiors. His integrity
must never be questioned. He must not allow himself to become
under obligations to the contractor by the acceptance of favors
he cannot return except at the expense of his employer, yet at
the same time he must not appear priggish by the refusal of all
favors or social invitations. In brief he must be friendly without
being intimate, independent without being aloof, and firm without
being arbitrary.

The engineer must support his inspectors in their decisions or
discharge them if he cannot.

121. Interpretation of Contract. — In interpreting the contract,
specifications and drawings, the engineer is supposedly an
impartial arbiter between the interests of the city and the con-
tractor. His decisions, as to the meaning of the contract, must
be founded on his engineering judgment, and should aim to pro-
duce the best results without demanding more from the contractor
than, in his honest opinion, it is the intention of the contract to
demand. However conscientiously he may attempt to remain
impartial, and in spite of the honesty of the contractor, his posi-
tion, as an employee of the city will almost invariably cause him

UNEXPECTED SITUATIONS 235

to favor the city in his decisions on close points. The experi-
enced contractor knows this and fixes his bid accordingly, the
personality of the engineer sometimes acting as an important
factor in the amount of the bid. The situation arises through
the character of the contract, and not through a lack of moral
integrity on the part of anyone concerned.

122. Unexpected Situations. — When unexpected or uncertain
conditions are encountered in construction the engineer should
visit the spot at once and should advise or direct, according to the
terms of the contract, the procedure to be followed. Such condi-
tions may be the encountering of other pipes, quicksand, rock, etc.
Each case is a problem in itself. Water, gas, telephone and elec-
tric wire conduits can be moved above or below the sewer being
constructed with comparative ease. Other sewers, if smaller,
may be permitted to flow temporarily across the line of the sewer
under construction and finally discharge into the completed sewer,
or one sewer must be made to pass under the other, either as an
inverted siphon or by changing the grade of one of the sewers.
Rock, or other material for which a special rate of payment is
allowed, must be measured as soon as uncovered in order to avoid
delaying the work or losing the record of the amount removed.
When quicksand is met special precautions must be taken to
safeguard the sewer foundation and to insure that the sewer will
remain in place until after the backfilling is completed. These
precautions are described in Art. 135.

123. Cost Data and Estimates. — Cost account keeping and
the making of monthly or other estimates are closely connected.
Cost accounts are of value in estimating the amount of work done
to date, and in making preliminary estimates of the cost of similar
work. Although the engineer is not always required to keep such
accounts, they are usually of sufficient value to pay for the labor
of keeping them. Under some contracts the contractor's accounts
are open to examination by the engineer. Usually, however, he
must depend on reports from the inspectors for information con-
corning the man-hours required on different pieces of work, and
on his own measurements of materials used and his knowledge of
their unit costs, in order to make up an estimate of total cost.

The measurement of a completed structure and a summary of
the materials used in its construction may act as a check on the
use of proper materials as called for in the contract. For example,

236

CONSTRUCTION

if it is known that 2,000 bricks are required for the construction
of a manhole and if only 15,000 have been used in the construction
of ten manholes, it is probable that some or all of the manholes
have been skimped. Similar conditions may show in the pro-
portions of concrete, backfilling in tunnels, sheeting to be left in
place, etc.

The statement of a few principles of cost accounting, and the
illustration of a few blanks in use should be sufficiently suggestive
to lead a resourceful engineer in the right direction.1 Costs should
be divided into four general classifications: labor, materials,
equipment, and overhead. Labor should be subdivided under
its several different classifications arranged in accordance with
rates of pay. The number of laborers under each classification
and the amount of work done per day should be recorded. Fig. 86
is an example of a form which may be used for such a purpose.

FOREMAN'S DAILY PAY ROLL REPORT.
Loc&iion....l4tk Avenue. ...No, Z....96" Sewer -...Date August 7, 1907
Itemized Pay Roll. Work Done, Pay Roll Distributed.

Foreman / days at
Engineer - / '
Labor 1 '
S7.4'
" "•*!

Carts "T '
Teams £-10 '
Hoister 1 '
Water boy 1 '

Total day's pay
roll

3
1

00
60
00
75
60

47
17

00
50
00
05
70

General Night Watchman and Water Boy
Excavation completed to station 18.40 Cost
Sheeting 18.30
Foundation pl'nk" 18.00
Backfilling "' 18.90
Sheeting Pulled " 17.10

2
19
8

2
3
2

25
26
26
63
00
62

3
ff
g

00
00
00
76

1
2

00
20
00
76

Brick Invert

Concrete Sides \ " 17.48
Concrete Roof / '*

Steel Bars set '" 17.48
Forms set to station 17.48
Forms Pipe laid to station

S
7

60
26

Manholes built to-day

Other items Pump
Teams working Cement 17.48

Carts working Gravel 17.48
Total day's pay roll

3
183

63
SO

00
10

Signed L.—W. Foreman.

FIG. 86. — Foreman's Daily Payroll Report.

From Engineering and Contracting, 1907.

Materials may be recorded as they are delivered on the job, as
they are used, or in both cases. Measurements are usually easier
to make at the time of delivery, but records made at the time

1 Cost Keeping and Management, by Gillette and Dana. Practical Cost
Keeping for Contractors, by F. R. Walker. Cost Keeping in Sewer Work,
by K. O. Guthrie in Eng. Contracting, Vol. 28, p. 238, 1905. Sewer Con-
struction Records at Scarsdale, Eng. News-Record, Vol. 83, p. Ill, 1919.

COST DATA AND ESTIMATES

237

materials are used are more serviceable. For example, 100
barrels of cement may be delivered on a job in November, 50 of
them are used before the job freezes up and the other 50 are held
over until spring. It would be misleading to charge 100 barrels
used in November. Fig. 87 is a form in use for an inspector's

FOREMAN'S DAILY MATERIAL RE
Location.... 14th Avtnut No. £ 96* E

PORT.

ate, August 7, 1907

Pull cement bags on hand las
received to-<

Total ..

t night

lay

160

JS44.

Pull cement used to-day on c<
' b

" ; c<

' IT

' P

snc. invert

rick "

snc. sides \

. 166

11 roof J

anholcs

Dinting up, etc.*.

167

Balance on hand to-night

Empty cement bags on hand 1
Full bags used to-day

ast night

167

Empty bags sent in to-day

Total »

164

140

Empty bags balance on hand to-night..

*4.«.

Materials received.

From.

Amounts.
47— L 16 — 16-(t.. ..

1S-

-4 x 6—14
I' roof en

-I — IS ft.

-ft..

E N

usty

Stetl Bars.

Car No. P RR 7284

ISO—

iso — 1 — 19-ti

Sheeting and bracing left in
place

None

76— |— SO-ft.

L. W.

Foreman.

FIG. 87. — Foreman's Daily Material Report.

From Engineering and Contracting, 1907.

report on materials. The total cost must be made up in the
office from these records and a knowledge of unit costs.

Equipment consists of tools, animals, machinery, and appara-
tus used in construction. Only equipment that is actually used
should be charged to the job and a credit should be made at the
completion of the job for the fair value of the equipment remain-
ing after the completion of the work.

Overhead charges include the expense of the office force,
superintendence, and miscellaneous items such as insurance, rent,

238 CONSTRUCTION

transportation, etc., which cannot be charged to any particular
portion of the work but are equally applicable to all portions. It
happens frequently that many jobs are handled in the same main
office. The division of overhead becomes more difficult and is
frequently arranged on an arbitrary basis, e.g., each job may be
charged the proportion of overhead that its contract price bears
to the total contract prices being performed under that office.
This rule may be modified when it becomes evident that some job
is taking distinctly more than its share of the overhead.

Estimates of work done in any period can be made with the
above data in hand by subtracting the total costs of the work up
to the beginning of the period from the total costs up to the end
of the period. Fig. 88 shows a sample blank from the final esti-
mate sheets used at Scarsdale, N. Y.

124. Progress Reports.1 — These are kept by the engineer in
order that he may see that the work is progressing as called for in
the contract, and any portion which is lagging behind without
reason may be pushed. Such reports are most useful when the
information is expressed graphically, as the eye quickly catches
points where the work is falling behind schedule.

125. Records. — The contract drawings are supposed to show
exactly where and how construction is to be done. Due to
unexpected contingencies changes occur, of which a record should
be made and preserved. These records may be kept in a form
similar to the contract drawings, or if the changes are not exten-
sive, they can be recorded on the original contract drawings.
The location of house and other connections should be recorded
in a separate note book available for immediate consultation.
The engineer should keep a diary of the work in which are recorded
events of ordinary routine as well as those of special interest and
importance. This diary should be illustrated by photographs
showing the condition of the streets before and after construction,
methods of construction, accidents, etc. Such accounts are of
great value in defending subsequent litigation and their existence
sometimes prevents litigation. A contractor may wait a year or
so after the completion of a piece of work until the engineer and
other city officials have broken their connection with the city.
Suit is then brought against the city and unless good records are

1 See Planning and Progress on a Big Construction Job, by Chas Penrose,
Eng.> News-Record, Vol. 84, 1920, pp. 554 and 627.

COST DATA AND ESTIMATES

239

24." VIT. SEWER
.6 FT. TO 8 FT. PEEP, INCLUDING A FT.

1914 LOCATION SCHEDULE FEET PRICE AMOUNT

•Thi

s siqn indioates that the item has been inclu

A &
eftcf in the

to fa.03$ 406. U*
monthly estimate

Y-BRANCHES ON 24" PIPE
LOCATION SCHEDULE NUnBER PRICE AMOUNT

Ifrdt

S &&***. M.H*4-&MH.*S (OtC&i&u)

* "^
6 4.oo .

2.4-. o«*

«r MANHOLES 6FTTo8FT.

?*
1914 io LOCATION SCHEDULE

PRICE AMOUNT

£ZS

, ^^^^^

* *
svoo ,

so. oa*

„ . MANHOLE DEPTHS EXCEEDING 6 FT.

"*"i
1914 io LOCATION SCHEDULE FEET PRICE AMOUNT

?/ W^tiujbrtt.^ tfit&ty&fie.

K 4-.

3 ^.00\. ,

2. 109

ROCK
IN SEWER TRENCH
•191.4 LOCATION SCHEDULE CU.YDS. PRICE AMOUNT

*^85^&~&

c< &

4-1 ^/f , //

'4. f3*

z ° R 0 "C K

| g^ IN MANHOLE EXCAVATION
1914 fc i LOCATION SCHEDULE CU.YDS. WICE AMOUNT

•4* ^>*4*W*yfSFtt

F : /^

* /

01 £Vf .

JO. 21

|g CONTINGENT EXTRAS
°5<« STANDARD-A-SECTION
£*.£§ CONCRETE FOR SEWERS
.EN6THS^2X LOCATION . SCHEDULE CU. YDS KICE AMOUNT

t7J.3

3 ^w^w<*™<&

J/02

S.oo

•

EXTRA ORDER
NUMBER

CONTINGENT EXTRAS

SHEETING ft SHORING
LOCATION SCHEDULEBQWttFT.Kia AMOUNT

*»,,<,

/£^#&4xt2*^3~4£4

//40.

'35!$ 31.

ft*

FIG. 88. — Samples of Cost Record Forma.

From Engineering and Contracting, 1909.

240 CONSTRUCTION

available the administration may be forced to buy the claimant
off or may elect to enter court, only to be beaten.

EXCAVATION

126. Specifications. — The following abstracts have been taken
from the specifications on Excavation by the Baltimore Sewerage
Commission as illustrative of good practice. In conducting the
work the contractor shall:

. . . remove all paving, or grub and clear the surface
over the trench, whenever it may be necessary and shall
remove all surface materials of whatever nature or kind.
He shall properly classify the materials removed, separat-
ing them as required by the Engineer; and shall properly
store, guard, and preserve such as may be required for
future use in backfilling, surfacing, repaving or otherwise.
Ah1 macadam material removed shall be separated and
graded into such sizes as the Engineer may direct and
materials of different sizes shah1 be kept separate from each
other and from any and all other materials.

All the curb, gutter, and flag-stones and all paving
material which may be removed, together with all rock,
earth and sand taken from the trenches shah* be stored hi
such parts of the carriageway or such other suitable place,
and in such manner as the Engineer may approve. The
Contractor shah1 be responsible for the loss of or damage
to curb, gutter and flag-stones and to paving material
because of careless removal or wasteful storage, disposal,
or use of the same.

. . . When so directed by the* Engineer the bottom of
the trench shall be excavated to the exact form of the
lower half of the sewer or of the foundation under the
sewer.

The bottom width of the trench for a brick or concrete
sewer shall be ... not less in any case than the overall
width of the sewer, as shown on the plans. In case the
trench is sheeted this minimum width will be measured
between the interior faces of the sheeting as driven, but in
no case shah1 bracing, stringers, or waling strips be left
within any portion of the masonry of the sewer except by
permission of the Engineer; and such braces, stringers
and waling strips shall not, in any case, be allowed to
remain within the neat lines of the masonry as shown on
the plans. In case that the distance between faces of the
- sheeting is less than that called for by the width of the

SPECIFICATIONS 241

sewer to be laid in the trench, the Engineer may direct the
sheeting to be drawn and redriven, or otherwise changed
and altered; or he may direct that the sewer be reinforced
in such manner and to such an extent as he may deem
necessary without compensation to the Contractor, even
though such narrower trench was not caused by negli-
gence or other fault on the part of the Contractor.

Trenches for vitrified pipe shall be at all points at least
six inches wider in the clear on each side than the greatest
external width of the sewer, measured over the hubs of the
pipe . . . Bell holes shall be excavated in the bottoms of
trenches for vitrified pipe sewers wherever necessary.

Not more than three hundred feet of trench shall be
opened at any one time or place in advance of the com-
pleted building of the sewer, unless by written permission
of the Engineer and for a distance therein specified. . . .

The excavation of the trench shall be fully completed
at least twenty feet in advance of the construction of the
invert, unless otherwise ordered.

During the progress of construction the Contractor will
be required to preserve from obstruction all fire hydrants
and the carriageway on each side of the line of the work.

The streets, cross walks, and sidewalks shall be kept
clean, clear, and free for the passage of carts, wagons, car-
riages and street or steam railway cars, or pedestrians,
unless otherwise authorized by special permission in writ-
ing from the Engineer. In all cases a straight and con-
tinuous passageway on the sidewalks and over the cross
walks of not less than three feet in width shall be pre-
served free from all obstruction.

Where any cross walk is cut by the trench it shall be
temporarily replaced by a timber bridge at least three feet
wide, with side railings, at the Contractor's expense. The
placing of planks across the trench without proper means
of connection or fastenings, or pipe or other material, or
the using of any other makeshift in place of properly con-
structed bridges, will not be permitted.

This is equally applicable to certain wagon bridges to be fixed
upon by the Engineer, on the basis of traffic requirements.

In streets that are important thoroughfares or in narrow
streets the material excavated from the first one hundred
feet of any opening or from such additional length as may
be required, shall upon the order of the Engineer, be
removed by the Contractor, as soon as excavated. The
material subsequently excavated 'shall be used to refill the
trench where the sewer has been built.

242 CONSTRUCTION

The preceding specifications are applicable to open-trench
excavation. Rigid restrictions are placed about tunneling
because of the greater difficulty of doing good work, the greater
danger to life and property and the possibility of later surface
subsidence if the backfilling is done improperly. A common
clause in specifications is:

All excavations for sewers and their appurtenances
shall be made in open trenches unless written permission
to excavate in tunnel shall be given by the Engineer.

127. Hand Excavation.— Earth excavation by pick and shovel
is the simplest and most primitive mode of excavation. Only
small jobs are handled in this manner in order to save the invest-
ment necessary in machines or the expense of hiring and moving
one to the work. The tools used in the hand excavation of trenches
are: picks, pickaxes, long-handled and short-handled pointed
shovels, square-edged long- and short-handled shovels, scoop
shovels, axes, crowbars, rock drills, mauls, sledges, etc. The
excavating gangs are divided up into units of 20 to 50 men under
one foreman or straw boss, and among the men may be a few
higher priced laborers who set the pace for the others. Each
laborer on excavation should be provided with a shovel, the
style being dependent on the character of the material being
excavated and the depth of the trench. In stiff material and
deep trenches requiring the lifting of the material in the shovel,
long-handled pointed shovels should be used. In loose sandy
material loaded directly into buckets short-handled, square
pointed shovels are satisfactory. Picks are used in cemented
gravels or where hard obstructions prevent cutting down with
the edge of the shovel. Very stiff but not hard material can be
cut out in chunks with a pickaxe and thrown from the trench or
into a bucket with a scoop shovel. Scoop shovels are also useful
in wet running quicksand. The number of picks, axes, crowbars,
and other tools must be proportioned according to the material
being excavated. Under the worst conditions of excavation in a
hard cemented gravel it may be necessary to provide each man
with a pick as well as a shovel, whereas in sand only a shovel is
necessary. Two or three crowbars, axes, a length of chain, two
or three screw jacks, etc., are provided per gang in case of an
unexpected encounter with an obstruction in the trench, such as
a boulder, a tree stump, a length of pipe, etc.

HAND EXCAVATION

243

In laying out the work the foreman marks the outlines of the
trench on the ground by means of a scratch made with a pick,
chalk marks, tape, or other devices. These marks are measured
from offset or center stakes set by the engineer. Center stakes
are less conducive to error but are more likely to be disturbed
before use than are offset stakes, but careless foremen make more
errors with offset than with center stakes. The inspector should
assist or be present at the laying out of the trench. After the
trench has been laid out each laborer should be given a certain
specific portion of it to dig and this portion is marked out on the
ground. In this way a check can be kept upon the performance
of each laborer and the knowledge of this fact tends to a uni-
formly better performance. The amount of work that can be
performed by one man with a pick and shovel is as shown in
Table 49. Some men may exceed these rates, many will not
attain them. The allotted task must be gaged on the character
of the ground in order that the tasks may be equal and a spirit of
competition fostered. The hard worker will set the pace for the
lazy man. Some contractors have adopted the expedient of dis-
missing laborers for the day as soon as the allotted task is done.

TABLE 49

AMOUNT OF MATERIAL MOVED BY ONE MAN WITH A PICK AND SHOVEL
(From H. P. Gillette)

Material

Cubic Yard
per Hour

Material

Cubic Yard
per Hour

Harclpan

0 33

Sand

1 25

Common earth

0 8to 1 2

Sandy soil

0 8 to 1 2

Stiff clay

0 85

Clayey earth

1 3

Clay..

1.00

Sandy soil (frozen) . .

0 75

The opening of the trench may be facilitated by breaking
ground with a plow. In hard ground or on paved roads it may
be necessary to cut through the surface crust with a hammer and
drill, although in some cases a plow can be used successfully.
Frozen ground can lx> thawed by building fires along the line of
the trench, or greater economy may !>«' achieved by placing steam
pipes along the surface with perforations about every 18 inches

244 CONSTRUCTION

and either boxing them on the top and sides or burying them in
the frozen earth with a covering of sand. Another arrangement
is to blow steam into a line of bottomless boxes in which each box
is about 8 feet long. Holes are left in the top of the boxes into
which the pipe is shoved, and after its withdrawal the holes are
covered. Blasting of frozen earth is sometimes successful but
cannot be resorted to in built up districts where it is unsafe unless
properly controlled. Once the frost crust is broken through it
can be attacked from below and frequently broken down by
undermining.

A laborer cannot dig and raise the earth much more than to
the height of his head, and preferably not quite so high, without
tiring quickly. After the trench has passed a depth of 4 feet he
cannot throw the earth clear of the trench. An additional laborer
is needed then at the surface to throw the earth back. He should
shovel the earth from a board platform placed at the edge of the
trench as a protection to the bank. When the trench passes the
6-foot depth a staging is put in about 4 feet from the top on which
the lowest laborer piles his materials. It is then passed up to the
surface by a second laborer on the staging, and a third laborer on
the surface throws the material back clear of the trench. Stag-
ings are put in about every 5 or 6 feet for the full depth of the
trench.

When the trench has come within half the diameter of the
pipe of the final grade, if the material is sufficiently firm, the
remainder of the trench should be cut to conform to the shape of
the lower half of the outside of the pipe, with proper enlargements
for each bell.

128. Machine Excavation. — On work of moderately large
magnitude excavation by machine is cheaper than by pick and
shovel alone. In comparing the cost of excavation by the two
methods all items such as sheeting, pipe laying, backfilling, etc.,
should be included, since these items will be affected by the method
of excavation. The cost of setting up and reshipping the machine
must be included as this is frequently the item on which the use
of the machine depends. Because of the cost of setting up and
shipping, which must be distributed over the total number of
yards excavated, the cost per cubic yard of excavating by machine
varies with the number of cubic yards excavated. The point of
economy hi the use of a machine is reached when the cost by hand

MACHINE EXCAVATION 245

and by machine are equal. For all work of greater magnitude,
excavation by machine will prove cheaper.1 Items favoring the
use of machinery which may cause its adoption for small jobs are:
its greater speed, reliability, ease in handling, economy in sheet-
ing, economy in labor, and small amount of space needed making
it useful in crowded streets. Continuous bucket machines, drag
lines, and occasionally steam shovels are not adapted to conditions
where rocks, pipes and other underground obstacles are frequently
met.

The following problem is an example of the work necessary in
making a comparison of the relative economy of machine and
hand excavation:

It is assumed that a man can excavate 15 feet of trench
30 inches wide and 8 feet deep in 10 hours. He receives
55 cents per hour for his work. A machine costing $10,000
has a life of 6 years. It can be kept busy 150 days in the
year. When operating it costs $1.25 per hour for the
operator, fuel and repairs. It will excavate 800 linear feet
of 30 inch trench to a depth of 8 feet in 10 hours. It is
assumed that capital is worth 10 per cent on such a venture
and that the sinking fund will draw 10 per cent. If the
cost of moving and setting up the machine is $1,800, how
many cubic yards of excavation must there be to make
excavation by machine economical. Costs of sheeting,
pumping, etc., are assumed to be the same for machine or
hand work.

Solution. — For hand work the man excavated 1.11
cubic yard per hour at 55 cents. The relative cost of hand
excavation is then 50 cents per cubic yard.

The cost of machine work will be divided into: interest
on first cost; operation and repairs; and sinking fund for
renewal. The interest on the first cost of $10,000 at
10 per cent is $1,000 per year. The machine works 1,500
hours in the year. Therefore the cost per hour is $0.67.

The sinking fund payment, as found from sinking fund
tables or the accumulation of $10,000 in. 6 years, is $1,300
per year or per hour for 1,500 hours is $0.87.

The cost of operation per hour is given as $1.25.

The total cost per hour is therefore $2.79.

The machine excavated 59.3 cubic yards per hour W
which makes the cost, exclusive of moving, equal to $0.47 ]\

1 See also " Ownership and Operation of Trench Excavators by the
Water Department of Baltimore," by V. B. Seims, presented before Am.
Water Works Association, June 9, 1921.

246 CONSTRUCTION

per cubic yard. In order to equalize the cost of machine
and hand excavation the cost of moving the machine must
be divided among a sufficient number of cubic yards so that
the cost per cubic yard shall be 3 cents. The cost of moving
is given as $1,800. This amount divided among 60,000
cubic yards equals 3 cents per cubic yard. Therefore the
job must provide at least 60,000 cubic yards of excavation
in order that the use of the machine shall be justifiable
from the viewpoint of economy alone.

129. Types of Machines. — Machines particularly adapted to
the excavation of sewer and water pipe trenches are of four types :
(1) continuous bucket excavators; (2) overhead cable way or track
excavators; (3) steam shovels; and (4) boom and bucket excava-
tors. Other types of excavating machinery can be used for
sewer trenches under special conditions. Machines are ordinarily
limited to a minimum width of trench of 22 inches. Between
widths of 22 inches and 36 inches the limit of depth for the first
class of machines is about 25 feet. For other types of machines
there is no definite limit, though the economical depth for open
cut work seldom exceeds 40 feet.

130. Continuous Bucket Excavators. — Continuous bucket
excavators are of the types shown in Figs. 89 and 90. The
buckets which do the digging and raising of the earth may be
supported on a wheel as in Fig. 89 or on an endless chain as in
Fig. 90. The support of the wheel or endless chain can be raised
or lowered at the will of the operator so as to keep the trench as
close to grade as can be done by hand work. In some machines
the shape of the buckets can be made such as to cut the bottom of
the trench, in suitable material, to the shape of the sewer invert.
In operation, the buckets are at the rear of the machine and
revolve so that at the lowest point in their path they are traveling
forward. The excavated material is dropped on to a continuous
belt which throws it on the ground clear of the trench, into dump
wagons, or on to another continuous belt running parallel with the
trench to the backfiller, by means of which the excavated material
is thrown directly into the backfill without rehandling. The
body of the machine supporting the engine travels on wheels
ahead of the excavation and is kept in line by means of the pivoted
front axle. When obstacles are encountered the excavating
wheel or chain is raised to pass over the obstacle, and allowed to
dig • itself in on the other side.

CONTINUOUS BUCKET EXCAVATORS

247

FIG. 89. — Buckeye Wheel Excavator.

Courtesy, Buckeye Traction Ditcher Co.

FIG. 90.— Buckeye Endless-chain Excavator.
Courtesy, Buckeye Traction Ditcher Co.

248

CONSTRUCTION

Wheel excavators are not adapted to the excavation of sewer
trenches over 3 to 4 feet in width and 6 to 8 feet in depth. The
endless-chain excavators are suitable for depths of 25 feet with
widths from 22 to 72 inches, and due to the arrangement permit-
ting buckets to be moved sideways they will cut trenches of differ-
ent widths with the same size buckets.. This is an advantage
where there are to be irregularities in the width of the trench
such as for manholes or changes in size of pipe. With excavating

machines pipe can be laid
within 3 feet of the moving
buckets and the trench back-
filled immediately, thus mak-
ing an appreciable saving
in the amount of sheet-
ing. In the construction of
trenches for drain tile at
Garden Prairie, Illinois, the
sheeting was built in the
form of a box or shield,
fastened to the rear of the
machine and pulled along
it as is shown in

FIG. 91. — Movable Sheeting Fastened to

Traction Ditcher.
From Eng. News-Record, Vol. 82, 1919, p. 740.

after
Fig. 91.

The performance of this type of excavating machine under
suitable conditions is large. A remarkable record was made by
Ryan and Co. in Chicago,1 with an excavating machine. 1338
feet of 32-inch trench were excavated to an average depth of 8^
feet in 7 hours, or an average of 160 cubic yards per hour. More
could have been accomplished if it had not been for delays in
supplies. Another crew at Greeley, Colorado,2 with a Buckeye
endless-chain ditcher weighing 17 tons and costing $5200, averaged
232 cubic yards per day for 300 days, and the cost was 10.7 cents
per cubic yard. A 15-ton Austin excavator can be expected to
remove 300 to 500 cubic yards per day.

The cost of operation of the machines is made up of items
listed in Table 50. The figures given are merely suggestive.

In making a comparison of the cost of hand and machine

1 Eng. and Contracting, Vol. 48, 1917, p. 492.

2 Earth Excavation by A. B. McDaniel.

CONTINUOUS BUCKET EXCAVATORS

249

Per Day

Total

Labor:
1 Operator at $150 per month

$6 00

1 Assistant Operator at $120 per month . . .

4 00

4 Laborers at $4 . 00 per day

16 00

«•>(•, on

Fuel:

20 Gallons of gasoline at 28 cents

5 60

Miscellaneous:
Oil, waste, etc

1 20

Repairs and maintenance

10 00

Interest, 6 per cent on $10,000 for 150 days. . .

4 00

Depreciation, 200 working days per year and an
8 year life

11 11

26 31

Total cost per day :

s:>7 '.»!

TABLE 51

COMPARISON OF COST OF HAND EXCAVATION AND MACHINE EXCAVATION
WITH CONTINUOUS-BUCKET EXCAVATOR

Hand Work

Per Day,

Dollars

Machine Work

Per Day,
Dollars

Foreman

4.00
3.00
2.50
80.00

Engineer

4.00
2.50
5.00
4.00
4 00
3.00
2.50
8.00
4.00

10.00

Timberman.

Fireman. .

Helper

Coal

40 Laborers at $2.00

Team

Total

Foreman

Pipe layer

Helper

2 Teams backfilling

2 Helpers

Interest, depreciation and
repairs

Total

95.00

54.50

250

CONSTRUCTION

excavation the figures given in Table 51 are from " Excavating
Machinery " by McDaniel, who quotes the cost of machine exca-
vation from the manufacturers of the Parsons machine issued as
the result of several years' experience with their excavator. In
the comparison the hand crew is assumed to dig 315 linear feet
of trench 28 inches wide by 12 feet deep in a day of 10 hours.
This assumes that each man will excavate 7 cubic yards per day.
The machine is assumed to excavate 250 feet of the same trench.
The comparison indicates that an excavator will work at about
50 per cent of the cost of hand excavation, if the cost of moving
the machine is not included.

FIG. 92. — Carson Excavating Machine on Trench Excavation in South Mil-
waukee.

Courtesy, Mr. C. F. Henning.

131. Cableway and Trestle Excavators. — Cableway and
trestle excavators are most suitable for deep trenches and crowded
conditions. They should not be used for trenches much less than
8 feet in depth. They differ from the continuous-bucket excava-
tors in that the actual dislodgment of the material is done by pick
and shovel, the excavated material being thrown by hand into the
buckets of the machine. A machine of the Carson type is shown
in Fig. 92. The machine consists of a series of demountable
frames held together by cross braces and struts to form a semi-
rigid structure. An I beam or channel extending the length of

CABLEWAY AND TRESTLE EXCAVATORS 251

the machine is hung closely below the top of the struts. The
lower flange of this beam serves as a track for the carriages which
carry the buckets. All the carriages are attached to each other
and to an endless cable leading to a drum on the engine. This
cable serves to move the buckets along the trench. The buckets
are attached to another cable which is wound around another
drum on the engine and serves to lower or raise all t he buckets at
the same time. In operation there are always at least two buckets
for each carriage, one in the trench being filled and the other on
the machine being dumped. There should be a surplus of buckets
to replace those needing repairs.

The machines may be from 200 to 350 feet in length, and the
number of buckets which can be lifted at one time varies from
one to a dozen or more. On trenches over 5 to 6 feet in width a
double line of buckets is sometimes used. The entire machine
rests on rollers and straddles the trench. It is moved along the
trench by its own power, either by gearing or chains attached to
the wheels, or by a cable attached to a dead-man ahead.

The Potter trench machine differs from the Carson in that
only 2 buckets are used at a time and these are carried on a car
which travels on a track on top of the trestle. The movement of
the buckets and the car are controlled by 2 dump men who
ride on the car and who can raise or lower the buckets inde-
pendently.

The organization needed to operate these machines is: a
lockman who locks and unlocks the buckets on the cable, a
dumper, as many shovelers as there are buckets on the machine,
and an engineman who is usually his own fireman. From 50 to
400 cubic yards of material can be excavated in a day with one of
these machines, dependent on the character of the material and
the depth of the trench. H. P. Gillette in his Handbook of Cost
Data reports that about 190 cubic yards were excavated per day
with a Potter machine. The machine was 370 feet long. Six
f-yard buckets were used, 4 in the trench and 2 on the carrier.
The trench was 10j feet wide and 18 feet deep in wet sand and
soft blue clay. The organization consisted of an engineman, a
fireman, 2 dumpmen on the carrier, and from 17 to 21 excavating
laborers depending on the kind and the amount of the excavation.
In general the capacity of such machines is limited by the amount
of material which can be shoveled into them by hand.

252 CONSTRUCTION

132. Tower Cableways. — These are essentially of the same
class as the trestle cableway machines. They differ in that the
carriage supporting the buckets travels on a cable suspended
between 2 towers instead of on a track supported on a trestle.
As a rule only one bucket is handled in the machine at a time.
They are used in sewer work only in exceptional cases as the
towers must be taken down and re-erected each time that there
is an advance in the trench greater than the distance between the
towers.

133. Steam Shovels. — The use of steam shovels for the exca-
vation of sewer trenches is becoming more prevalent because of
their growing dependability and durability as compared with other
machines, their adaptability for small trenches, and the relatively
large number of widely different uses to which they can be put.
In excavating a trench the shovel straddles the trench and runs on
tractors, wheels, or rollers on either side of it. The shovel cuts
the trench ahead of it. As a result it is difficult to set sheeting
and bracing close to the end of the trench while the shovel is
operating. Steam shovels are therefore not suitable for excava-
tion in unstable material, unless the sheeting is driven ahead of
the excavation. It is only in the softest ground that ordinary
wood sheeting can be driven ahead of the excavation. Steel
sheet piling is more suitable for such use. Fig. 93 l shows a shovel
at work on a trench in Evanston, Illinois.

Shovels are equipped with extra long dipper handles to adapt
them to trench excavation. The dipper handle in the picture is
longer than the standard for this type of machine. The method
of supporting the shovel can be seen in the picture under the
machine and the method of bracing and of finishing the trench
by hand work are also shown. The excavated material is taken
out in the shovel and dropped on the bank or into wagons.

The limiting depth to which trenches can be excavated by
steam shovels is about 20 to 25 feet, where the trench is too nar-
row for the shovel to enter. Wider trenches are cut in steps of
about 15 feet, the shovel working in the trench for additional
depths. Shovels are now made to cut trenches as narrow as a
man can enter to lay pipe. The greatest width that can be cut
from one position of the shovel is from 15 to 40 feet, dependent on
the size of the shovel. Occasionally «, combination of a drag line
1 Courtesy, Sanitary District of Chicago.

STEAM SHOVELS

253

and a steam shovel can be used, as on the construction of the
Calumet sewer in Chicago. On this work the first step was cut
by a steam shovel. It was followed by a drag line resting on the
step thus prepared, and excavating the remaining distance to
grade. The depth of
the trench in this work
averaged about 25 to
30 feet.

Steam shovels are
rated according to
their tonnage and the
capacity of the dipper
in cubic yards. Both
are necessary as the
size of the dipper is
varied for the same
weight of machine,
dependent on the char-
acter of the material
being excavated. For
rock the dipper is
made smaller than
for sand. Gillette in
his Hand Book of
Cost Data gives the
coal and water con-
sumption of steam
shovels as shown in
Table 52. The per-

formance of steam FIG. 93 .-Steam Shovel at Work on Sewer Trench
shovels is recorded for North Shore Intercepting Sewer, Evanston,
in Table 53. The Illinois,
conditions of the

work have a marked effect on the output of the shovel. A
shovel in a thorough cut, i.e., in a trench just wide enough
for the shovel to turn 180 degrees but too narrow to run
cars or wagons along side of it, will perform less than one-
half of the work that it can perform in a side cut, i.e., where
the cars can be run along side the shovel which turns less than
90 degrees.

254

CONSTRUCTION

TABLE 52

COAL AND WATER CONSUMPTION BY STEAM SHOVELS
(From Handbook of Cost Data, by H. P. Gillette)

Weight in tons

Dipper, cubic yards

Coal, tons per 10 hour day . .

Water, gallons per 10 hour day. .

1500

2000

2500

3000

4000

4500

TABLE 53

PERFORMANCE BY STEAM SHOVELS

Cost in

Weight
in

Dipper
Cubic

Depth
of Cut,

Width
of Cut

10-Hour
Perform-

Cents,
per

Authority

Remarks

Tons

Yards

Feet

ance

Cubic

Yard

36 in.

22.6

R. T. Dana Eng. Rec.,

69:581

35 in.

23.5

do.

16 ft.

569

6.7

do.

15-18

60 in.

300

A B McDaniel Excavat-

ing Machinery

134 ft.

400

Eng. Cont'r, 8-25-09

f Very

16 yd. }

\ wide

cars /

296

H P Gillette's Cost Data

280

Greater
than

\ 700

30. 6 <

G. C. D. Lenth, Eng.
News-Record, 85:22

78 in.

Remarks:

1. One runner at $5.00, one fireman at $2.31, two laborers at $1.70 each, supplies at $4.50,

and interest and depreciation on 200 days per year, $4.00. Total per day, $19.21.
Material, clay and gravel.

2. Average of 11 jobs with the same shovel.

3. Cost per day, one runner at $5.00, one craneman at $3.60, one fireman at $2.00,

7 roller men at $1.50 each, supplies $9.00 and interest and depreciation on $9000
at 200 days per year $8.00. Total, 338.10.

4. Hard clay.

5. Stiff clay for the basement of a building in Chicago.

6. Stripping ore. This is a maximum record. The average was about three hundred

and twenty 16 cubic yard cars per day.

7. Blasted mica schist.

8. General average.

DRAG LINE AND BUCKET EXCAVATORS 255

134. Drag Line and Bucket Excavators. — A drag line exca-
vator is shown in Fig. 94. The back of the bucket is attached to
a drum on the engine by means of a cable passing over the wheel
in the end of the long boom. The front of the bucket is attached
by another cable directly to another drum on the engine. In
operation the bucket is raised by its rear end and dropped out to
the extremity of the boom. It is then dragged over the ground
towards the machine, digging itself in at the same time. When
filled the bucket is raised by tightening up on the two cables,
swung to one side by means of the movable boom, and dumped.

FIG. 94. — Drag Line at Work on Trench for Drain Tile.

Drag line excavators will perform as much work as steam
shovels under favorable conditions. They are less expensive in
first cost and operation, and are equally reliable but they are not
adapted to the more difficult situations where steam shovels can
be used to advantage. Drag lines are suitable only for relatively
wide trenches in material requiring no bracing, and in a locality
where relatively long stretches of trench can be opened at one
time.

The bucket excavator differs from the drag line in that the
bucket can be lifted vertically only and the types of buckets used
in the two types of machine are different. The bucket may be
self filling of the orange-peel or clam-shell type, or a cylindrical
container which must be filled by hand. A drag line can be

256 CONSTRUCTION

easily converted into a boom and bucket excavator. Boom and
bucket excavators are well adapted to use in deep, closely braced
trenches and shafts.

136. Excavation in Quicksand.1 — A sand or other granular
material in which there is sufficient upward flow of ground water
to lift it, is known as quicksand. Its most important property,
from the viewpoint of sewer construction, is its inability to sup-
port any weight unless the sand is so confined as to prevent flow-
ing of the sand, or unless the water is removed from the sand.

Excavation in quicksand is troublesome and expensive and is
frequently dangerous. The material will flow sluggishly as a
liquid, it cannot be pumped easily, and its excavation causes the
sides of the trench to fall in or the bottom to rise. The founda-
tions of nearby structures may be undermined, causing collapse
and serious damage. These conditions may arise even after the
backfilling has been placed unless proper care has been taken.
The greatest safeguard against such dangers is not only to exer-
cise care in the backfilling to see that it is compactly tamped and
placed, but to leave all sheeting in position after the completion of
the work.

The ordinary method of combating quicksand and in conduct-
ing work in wet trenches is to drive water-tight sheeting 2 or 3 feet
below the bottom of the trench, and to dewater the sand by pump-
ing. When dry it can be excavated relatively easily. A more
primitive but equally successful method is to throw straw, brick-
bats, ashes, or other filling material into the trench in order to
hold the excavation once made, or this may supplement the
attempts at pumping, or the wet sand may be bailed out in buckets.
Successful excavation in quicksand requires experience, resource-
fulness, and a careful watch for unexpected developments. The
well points described in Art. 142 are used for dewatering quick-
sand.

136. Pumping and Drainage. — Ground water is to be expected
in nearly all sewer construction and provision should be made for
its care. Where geological conditions are well known or where
previous excavations have been made and it is known that no
ground water exists it may be safe to make no provision for
encountering ground water. Where ground water is to be expected

1 See article by J. R. Gow, Journal New England Waterworks Ass'n,
Sept., 1920, also Public Works, Vol. 50, p. 98.

TRENCH PUMP

257

the amount must remain uncertain within certain rather wide
limits until actually encountered.

In order to avoid the necessity for pumping, or working in wet
trenches it is sometimes possible to build the sewer from the low
end upwards and to drain the trench into the new sewer. The
wettest trenches are the most difficult to drain in this manner as
the material is usually soft and the water so laden with sediment
as to threaten the clogging of the sewer. It is undesirable to run
water through the pipes until the cement in the joints has set.
This necessitates damming up the trench for a period which may
be so long as to flood the trench or delay the progress of the work.
If it is not possible to drain the trench through the sewer already
constructed the amount of water to be pumped can be reduced
by the use of tight sheeting.

Pumps for dewatering trenches must be proof against injury
by sand, mud, and other solids in the water. For this purpose
pumps with wide passages and without valves or
packed joints are desirable. The types of pumps
used are: simple flap valve pumps improvised on
the job, diaphragm pumps, jet pumps, steam
vacuum pumps, centrifugal pumps, and recipro-
cating pumps. All are of the simplest of then-
type and little attention is paid to the economy of
operation because of the temporary nature of their
service.

137. Trench Pump. — A simple pump which can
be improvised on the job is shown in section in
Fig. 95. Its capacity is about 20 gallons per
minute but its operation is backaching work. It is
inexpensive, quickly put together and may be a
help in an emergency. It is to be noted that the
passages are large and straight, that there are no FlQ ^
packed joints, and that the velocity of flow is so improvised
small that it is not liable to clogging by picking up Trench Pump,
small objects.

138. Diaphragm Pump. — The type of pump shown in Fig. 96
is the most common in use for draining small quantities of water
from excavations. It is known as the diaphragm pump from the
large rubber diaphragm on which the operation depends. The
pump is made of a short cast-iron cylinder, divided by the rubber

Canvas '
or
Leather

258

CONSTRUCTION

diaphragm or disk to the center of which the handle is connected.
The valve is shown at the center of the disk. As the diaphragm
is lifted the valve remains closed, creating a partial vacuum in the

suction pipe and at the
same time 'discharging
the water which passed
through the valve on the
previous down stroke.
When the valve is
lowered the foot valve
on the suction pipe
closes, holding the water
in place, and the valve
in the pump opens
allowing the water to
flow out on top of the
••^•••••BET^- disk *° be discharged
on the next up stroke.
Table 54 shows the
capacities of some dia-
phragm pumps as rated
by the manufacturers. The smaller sizes are the more frequently
used and are equipped with a 3-inch suction hose with strainer and
foot valve. They are not adapted to suction lifts over 10 to 12
feet. Where greater lifts are necessary one pump may discharge
into a tub in which the foot valve of a higher pump is submerged.

TABLE 54
CAPACITIES OF DIAPHRAGM PUMPS

FIG. 96. — Diaphragm Pump.
Courtesy, Edson Manufacturing Co.

Diameter of

Length of

Capacity per

Cylinder,

Suction,

Stroke in

Stroke,

Inches

Gallons

0.49

1.47

0.75

12**

1.25

12i*

Power driven by 1

horse-power engine

0.58f

* Diameter of diaphragm,
t Gallons per minute

JET PUMP

259

139. Jet Pump. — The simplicity of the parts of the jet pump
is shown in Fig. 97. It has a distinct advantage over pumps

containing valves and moving

parts in that there are no obstruc-
tions offered to the passage of
solids as well as liquids through
the pump. It is not economical
in the use of steam, however. It
operates by means of a steam jet
entering a pipe at high velocity
through a nozzle. This action
causes a vacuum which will lift
water from 6 to 10 feet. The
lower the suction lift, however,
the greater the efficiency of the
work. The sizes and capacities
of jet pumps as manufactured by
the J. H. McGowan Co. are shown
in Table 55.

FIG. 97. — McGowan Steam Jet

Pump.
Courtesy, The John H. McGowan Co.

TABLE 55

CAPACITIES OF JET PUMPS
(J. H. McGowan Co.)

Size of Pump

Capacity,

Approximate

and

Discharge Pipe,

Steam Pipe,

Gallons

Horse-power

Suction Pipe,

per

Required

Inches

Minute

2§

140. Steam Vacuum Pumps. — This type of pump depends on
the condensation of steam in a closed chamber to create a vacuum
which lifts water into the chamber previously occupied by the

260

CONSTRUCTION

steam and from which the water is ejected by the admission of
more steam. The best known pumps of this type are the Pulsom-
eter, manufactured by the Pulsometer Steam Pump Co., the
Emerson, manufactured by the Emerson Pump and Valve Co.;
and the Nye Pump, manufactured by the Nj^e Steam Pump and
Machinery Co.

A section of a Pulsometer is shown in Fig. 98. It consists of
two bottle-shaped chambers A and B with their necks communi-

K-2

K-I

Sect
Discharge

through
Chamber

FIG. 98 — Pulsometer Steam Vaccum Pump.

eating at the top and each opening into the outlet chamber 0
through a check valve. Steam is admitted at the top and enters
chamber A or B according to the position of the steam valve C
as shown. This steam valve is a ball which is free to roll either
to the right or left and forms a steam-tight joint with whichever
seat it rests upon. In normal operation chamber A would be
filled with water as the steam enters the cylinder. At the same
time a check valve at the top opens to admit a small quantity of
air which forms a cushion insulating the steam from the water,
reduces the condensation of the steam, and serves as a cushion

STEAM VACUUM PUMPS

261

for the incoming water on the opposite stroke. The pressure of
the steam depresses the surface of the water without agitation
and forces the water through the check valve F into the discharge
chamber 0. When the water falls to the level of the discharge
chamber the even surface is broken up and the intimate contact
of the steam and water condenses the former instantaneously.
This forms a vacuum in chamber A which, assisted by a slight
upward pressure in chamber B
caused by the incoming water,
immediately pulls the ball C
over to the other seat and
directs the steam into chamber
B. The vacuum in chamber A
now draws up a new charge of
water through the suction pipe
into the chamber.

A section of the Emerson
pump is shown in Fig. 99. The
pump consists of two vertical
cylinders B and C. Each
chamber has a suction valve
L at the bottom, opening up-
ward from a common chamber
from which the discharge pipe
U extends. On the top of
each chamber is a baffle plate
G which operates to distribute
the steam evenly to the two
chambers and to prevent it
from agitating the surface of
the water in the chambers.
A condenser nozzle F is con-
nected with the bottom of the opposite chamber by a pipe
into which a check valve opens upward. As the pressure in
the chamber alternates water will be injected through F into the
opposite chamber and condense the steam therein, promptly
forming a vacuum. An air valve P admits a small quantity of
air while the chamber is filling with water, the air acting as an
insulating cushion as in the Pulsometer. Valve 0, just above the
top connection S is used to regulate the amount of steam that

FIG. 99. — Emerson Steam Vaccum
Pump.

262 CONSTRUCTION

enters the pump. The top connection S has two ports, one leading
to each chamber. An oscillating valve enclosed in it admits the
steam through these ports to the two chambers alternately. This
valve is driven by a small three-cylinder engine, the crank shaft of
which extends into the top connection in the center of the bearing
on which the valve oscillates. A positive geared connection is
made between the valve and the engine and so arranged that the
engine will run faster than the valve.

The action of these pumps consists of alternately filling and
emptying the two chambers. They will continue operation with-
out attention or lubrication so long as the steam is turned on. In
view of the simplicity of their operation and make-up, their ability
to handle liquids heavily charged with solids, and their reasonable
steam consumption these pumps are widely used for pumping
water in construction work. They have an added advantage
that no foundation or setting is required for them as they can be
hung by a chain from any available support.

These pumps are manufactured in sizes varying from 25 to
2500 gallons per minute at a 25-foot head, and with a steam con-
sumption of about 150 pounds per horse-power hour. They
reduce about 4 per cent in capacity for each 10 feet of additional
lift. They will operate satisfactorily between heads of 5 to 150
feet, with a suction lift not to exceed 15 feet. Lower suction lifts
are desirable and the best operation is obtained when the pump is
partly submerged. The steam pressure should be balanced against
the total head. It varies from 50 to 75 pounds for lifts up to
50 feet, and increases proportionally for higher lifts. The dryer
the steam the lower the necessary boiler pressure.

141. Centrifugal and Reciprocating Pumps. — The details of
these pumps, their adaptability to various conditions, and their
capacities are given in Chapter VII. The centrifugal is better
adapted to trench pumping as it is not so affected by water con-
taining sand and grit, but for clear water, high suction lifts and
fairly permanent installations, reciprocating pumps can be used
with satisfaction.

142. Well Points. — In dewatering quicksand a method fre-
quently attended with success is to drive a number of well, points
into the sand and connect them all to a single pump. Figure 100
shows a well point system used on sewer work in Indiana. The
well points are 3 feet apart and are connected to a 2|-inch header

ROCK EXCAVATION 263

which in turn is connected to six Nye pumps, each with a capacity
of 200 gallons per minute for a lift of 50 feet. The number and
size of well points and pumps to use will depend on conditions as
met on the job. On a piece of work in Atlantic City 1 the equip-
ment consisted of two complete outfits each comprising one hundred
1^-inch by 36-inch No. 60 well points, one hundred 6-foot lengths
of rubber hose, about 600 feet of suction main, one hundred
valved T connections, and a 7 X 8-inch Gould Triplex Pump with
a capacity of 200 gallons per minute, belted to a 1\ horse-power
motor.

FIG. 100. — Well Points Pumped by Nye Steam Vacuum Pump.

143. Rock Excavation. — A common definition of rock used in
specifications is: whenever the word Rode is used as the name of
an excavated material it shall mean the ledge material removed
or to be removed properly by channeling, wedging, barring, or
blasting; boulders having a volume of 9 (this volume may be
varied) cubic feet or more, and any excavated masonry. No soft
disintegrated rock which can be removed with a pick, nor loose
shale, nor previously blasted material, nor material which may
have fallen into the trench will be measured or allowed as rock.

Channeling consists in cutting long narrow channels in the

rock to free the sides of large blocks of stone. The block is then

loosened by driving in wedges or it is pried loose with bars. It is

a method used more frequently in quarrying than in trench exca-

1 Eng. News, Vol. 75, 1916 p. 1050.

264

CONSTRUCTION

vation where it is not necessary to preserve the stone intact. In
blasting, a hole is drilled in the rock, and is loaded with an explosive
which when fired shatters the rock and loosens it from its position.
In drilling rock by hand the drill is manipulated by one man
who holds it and turns it in the hole with one hand while striking
it with a hammer weighing about 4 pounds held in the other hand,
or one man may hold and turn the drill while one or two others
strike it with heavier hammers. In churn drilling a heavy drill

is raised and dropped in the hole,
the force of the blow developing
from the weight of the falling
drill. Hand drills are steel bars
of a length suitable for the depth
of the hole, with the cutting edge
widened and sharpened to an
angle as sharp as can be used
without breaking. The drill bar
is usually about |th of an inch
smaller than the diameter of the
face of the drill.

Wedges used are called plugs
and feathers. They are shown
in Fig. 101 which shows also the
method of their use. The feathers
are wedges with one round and
one flat face on which the flat
faces of the plug slide.

144. Power Drilling. — In power drilling the drill is driven by a
reciprocating machine which either strikes and turns the drill in
the hole, or lifts and turns it as in churn drilling, or the drill may
be driven by a rotary machine which is revolved by compressed
air, steam, or electricity. There are many different types of
machines suitable for drilling in the different classes of material
encountered and for utilizing the various forms of power available.
A jack hammer drill is shown in Fig. 102. In its lightest
form the drill weighs about 20 pounds and is capable of drilling
f-inch holes to a depth of 4 feet. Heavier machines are available
for drilling larger and deeper holes. The same machine can be
adapted to the use of steam or compressed air. When in use the
point of the drill is placed against the rock and a pressure on the

FIG. 101. — Plug and Feathers for
Splitting Rock.

POWER DRILLING

265

handle opens a valve admitting air or steam. The piston is caused
to reciprocate in the cylinder, striking the head of the drill at
each stroke. The drill is revolved in the hole by hand or by a
mechanism in the machine. A hollow drill can be used by means
of which the operator admits air or steam to the hole, thus blow-
ing it out and keeping it clean. These machines have the advan-
tage of small size, portability and simplicity. They can be easily
and quickly set up and the drills can be changed rapidly. Their
undesirable features are the vibration transmitted to the operator
and the dust raised in the trench.

i St'd Drill
JhroHle-

FIG. 102. — Jack Hammer Rock Drill.

FIG. 103.— Tripod Drill.

A type of drill heavier and larger than the jack hammer drill
is shown in Fig. 103. It requires some form of support such as a
tripod, or in tunnel work it can be braced against the roof or sides.
Some data on steam and air drills are given in Table 56. The
effect of the length of the transmission pipe, temperature of the
outside air, pressure at the boiler or compressor, etc., will have a
marked effect on the amount of steam or air to be delivered to the
drill. Compressed air is affected more than steam by these out-
side factors, but it has an advantage in that as it loses in pressure
it increases in volume so that the loss of power is not so marked.
Gillette states:

266 CONSTRUCTION

We may assume that a cubic foot of steam will do
practically the same work in a drill as a cubic foot of com-
pressed air at the same pressure, because neither the steam
nor the air acts expansively to any great extent in a drill
cylinder, due to the late cut-off. This being so ... one
pound of steam is equivalent to nearly 30 cubic feet of
free air ... all at the same pressure of 75 pounds per
square inch. If a drill consumes at the rate of 100 cubic
feet of free air per minute ... it would therefore consume
240 pounds of steam (at 75 pounds pressure) per hour.
. . . Where not more than three or four drills are to be
operated, probably no power can equal compressed air
generated by gasoline. It will require 12 horse-power to
compress air for each drill, hence 1^ gallons of gasoline will
be required per hour per drill while actually drilling.

TABLE 56

DATA ON ROCK DRILLS
(From H. P. Gillette)

Diameter of cylinder in inches
Length of stroke in inches . .

2*
5

25-
6

2!
6i

3i
6f

Length of drill from end of crank to
end of piston

Depth of hole drilled without change
of bit, inches

Diameter of supply inlet. Standard

Approximate strokes per minute with

500

450

375

350

325

300

Depth of vertical hole each machine
will drill easily, feet

Diameter of holes drilled, inches
Diameter of octagon steel, inches. . . .
Best size of boiler to give plenty of
steam at high pressure, horse-power
Best size of supply pipe to carry
steam 100 to 200 feet, inches . . .

Itoi
0

I to 1
8
J

1 to 1J s

1 to 1J

8
J

s desired
U toll

lj to li
10
1

Utoll
12
\\

Weight of drill unmounted, with
wrenches and fittings, not boxed,

128

190

265

315

385

390

Weight of tripod, without weights,

160

210

275

Weight of holding down weights,

120

270

285

330

375

Cubic feet of free air per minute
required to run one drill at 100

104

126

146

154

160

For more than one drill, multiply the value in the above line by the following factors:
For 2 drills, 1.8; 5by4.1; 10by7.1; 15by9.5; 20 by 11. 7; 30 by 15.8; 40by21.4; 70 by
33.2.

POWER DRILLING 267

Since gasoline air-compressors are self regulating, when the
drill is not using air very little gasoline is burned by the
gasoline engine driving the compressor. A gasoline com-
pressor possesses other very important economic advan-
tages over a small steam-driven plant. First, there is the
saving in wages of firemen and second, there is the saving in
hauling and pumping of water and the hauling of fuel.
The cost of gasoline is often less than the cost of coal for
operating a small plant.

An electric drill1 operated on the principle of the solenoid
does away with motor, valves, pipes, vapor, freezing, and other
difficulties attendant on the use of steam or air.

The rates of drilling in different classes of rock are shown in
Table 57. Frequent changes of drills and relocation of tripods
will materially reduce the performance of a drill, for as much as
45 minutes may be lost in making a new set up. In this the jack
hammer drills show their advantage as no time is lost in a set up.

TABLE 57
RATES OF ROCK DRILLING

Rates in Feet per Ten-hour Shift. Vertical Holes 10-20 Feet Deep.
(From Gillette)

Hard Adirondack granite 48

Maine and Massachusetts granite 45-50

Mica-schist of New York City. Possible 60-70

Mica-schist of New York City. Average 40-50

Hard, Hudson River trap rock 40

Soft red sand stone of Northern New Jersey 90

Hard limestone near Rochester, N. Y 70

Limestone of Chicago Drainage Canal 70-80

Douglass, Indiana, syenite. Difficult set ups 36

Canadian granite on Grand Trunk R. R 30

Windmill point, Ontario limestone:

3f-inch drills 75

2j-inch drills 00

2}-inch drills 37

146. Steam or Air for Power. — The choice between steam or
air is dependent on the conditions of the work. Steam is unde-
sirable in tunnels on account of the heat produced. In open cut
1 Mun. Engineering, Vol. 53, p. 6.

268

CONSTRUCTION

work it is at a disadvantage because of the loss of power due to
radiation from the hose or pipe. The life of the hose is not so
long as when air is used, escaping steam causes clouds of vapor
which obscure the work, and serious burns may occur due to hot
water thrown from the exhaust. It is advantageous since leaks
may be easily discovered and remedied, it requires less machinery
than air, and it is sometimes less expensive. With compressed
air, gasoline or electric motors can be used for operating the com-
pressors.

TABLE 58
ROCK BLASTING
(From Gillette)

Depth

Distance

Character of Material

Powder Used per Hole

of
Hole,

Back of
Face,

Hole to
Hole,

Feet

Limestone of Chicago

Drainage Canal

40 per cent dynamite

Sandstone •s

200 pounds

1 20

black powder

Granite \

2 pounds

Il2

4£to 5

60 per cent dynamite

Pit Mining, Treadwell,

Mine, Alaska

146. Depth of Drill Hole.— The depth of the hole is dependent
on the character of the work. The deepest holes can be used in
open cut work where the shattered rock is to be removed by steam
shovel. The face can be made 10 to 15 feet high. The depth of
the hole in center cut tunnel facings are from 6 to 10 or even 12
feet. In the bench the depth is equal to the height of the bench.
In narrow trenches where the rock is to be removed by derrick or
thrown into a bucket by hand, the hole should be sufficiently deep
to shatter the rock to a depth of at least 6 inches below the
finished sewer. Frequently shooting to this depth at one shot
cannot be done due to the built up condition of the neighborhood
or other local factors. The depth of the hole in trench work
should not much exceed the distance between holes. Deep holes

SPACING OF DRILL HOLES 269

are usually desirable as a matter of economy in saving frequent
set ups, but the holes cannot be made much over 20 feet in depth
without increasing the friction on the drill to a prohibitive amount.

147. Diameter of Drill Hole. — The diameter of the hole should
be such as to take the desired size of explosive cartridge. The
common sizes of dynamite cartridges are from £ inch to 2 inches in
diameter. In drilling, the diameter of the hole is reduced about one-
eighth of an inch at a time as the drill begins to stick. This reduc-
tion should be allowed for, and experience is the best guide for the
size of the hole at the start. In general the softer or more faulty
or seamy the rock, the more frequent the necessary reductions in
size of bit.1 For hard homogeneous rock the holes can be drilled
10 feet or more without changing the size of the drill bit.

148. Spacing of Drill Holes. — The spacing of holes in open
cut excavation is commonly equal to the depth of the hole. The
character of the material being excavated has much to do with the
spacing of the holes. The spacing, diameter and depth of holes
used on some jobs is shown in Table 58. Gillette states:

It is obviously impossible to lay down any hard and
fast rule for drill holes. In stratified rock that is friable,
and in traps that are full of natural joints 'and seams, it is
often possible to space the holes a distance apart somewhat
greater than their depth, and still break the rock to com-
paratively small sizes upon blasting. In tough granite,
gneiss, syenite, and in trap where joints are few and far
between, the holes may have to be spaced 3 to 8 feet apart
regardless of their depth for with wider spacing the blocks
thrown down will be too large to handle with ordinary
appliances. Since in shallow excavations the holes can
seldom be much further apart than one to one and one-half
times their depth we see that the cost of drilling per cubic
yard increases very rapidly the shallower the excavation.
Furthermore the cost of drilling a foot of hole is much
increased where frequent shifting of the drill tripod is
necessary.

The common practice in placing drill holes is to put
down holes in pairs, one hole on each side of the proposed
trench; and if the trench is wide one or more holes are
drilled between these two side holes 2 but in narrow trench

1 For types of drill bits see article by T. H. Proske, Mining and Scientific
Press, March 5, 1910.

1 These intermediate holes are seldom more than 3 feet apart.

270 CONSTRUCTION

work, such as for a 12-inch pipe, one hole in the middle of
the trench will usually prove sufficient.

The holes are spaced about 3 feet apart longitudinally. After
the holes have been completed they should be plugged to keep
out dirt and water.

SHEETING AND BRACING

149. Purposes and Types. — Sheeting and bracing are used in
trenching to prevent caving of the banks and to prevent or retard
the entrance of ground water. The different methods of placing
wooden sheeting are called stay bracing, skeleton sheeting, poling
boards, box sheeting, and vertical sheeting. Steel sheeting is
usually driven to secure water tightness and if braced the bracing
is similar to the form used for vertical wooden sheeting.

150. Stay Bracing. — This consists of boards placed vertically
against the sides of the trench and held in position by cross
braces which are wedged in place. The purpose of the board
against the side of the trench is to prevent the cross brace from
sinking into the earth. The boards should be from 1^X4 inches
to 2X6 inches and 3 to 4 feet long. The cross braces should not
be less than 2X4 inches for the narrowest trenches and larger
sizes should be used for wider trenches. The spacing between the
cross braces is dependent on the character of the trench and the
judgment of the foreman. Stay bracing is used as a precautionary
measure in relatively shallow trenches with sides of stiff clay or
other cohesive material. It should not be used where a tendency
towards caving is pronounced. Stay bracing is dangerous in
trenches where sliding has commenced as it gives a false sense of
security. The boards and cross braces are placed in position
after the trench has been excavated.

151. Skeleton Sheeting. — This consists of rangers and braces
with a piece of vertical sheeting behind each brace. A section of
skeleton sheeting is shown in Fig. 104 with the names of the differ-
ent pieces marked on them. This form of sheeting is used in
uncertain soils which apparently require only slight support, but
may show a tendency to cave with but little warning. When the
warning is given vertical sheeting can be quickly driven behind
the rangers and additional braces placed if necessary. The sizes
of pieces, spacing and method of placing should be the same as

POLING BOARDS

271

for complete vertical sheeting in order that this may be placed if
necessary.

152. Poling Boards. — These are planks placed vertically
against the sides of the trench and held in place by rangers and
braces. They differ from vertical sheeting in that the poling
board is about 3 or 4 feet long. It is placed after the trench has
been excavated; not driven down with the excavation like vertical
sheeting. An arrangement of poling boards is shown in Fig. 105.
This type of support is used in material that will stand unsup-
ported for from 3 to 4 feet in height. Its advantages lie in that no
driving is necessary, thus saving the trench from jarring; no

FIG. 104.— Skeleton Sheeting.

FIG. 105.— Poling Boards.

Showing Different Types of Crosa Bracing.

sheeting is sticking above the sides of the trench to interfere with
the excavation; and only short planks are necessary.

The method of placing poling boards is as follows: Excavate
the trench as far as the cohesion of the bank will permit. Poling
boards, l£ inch to 2 inch planks, 6 inches or more in width, are
then stood on end at the desired intervals along each side of the
trench for the length of one ranger. The poling boards may be
held in place by one or two rangers. Two are safer than one but
may not always be necessary. If one ranger is to be used it is
placed at the center of the poling board. After the poling boards
are in position the rangers are laid in the trench and the cross

272

CONSTRUCTION

braces are cut to fit. If wedges are to be used for tightening the
cross braces, the cross braces are cut about 2 inches short. If
jacks are to be used the braces are cut short enough to accommo-
date the jacks when closed, or adjustable trench braces may be used
as shown in Fig. 106. The use of extension braces saves the labor
of fitting wooden braces. With everything in readiness in the
trench, the cross brace is pressed against the ranger which is thus
held in place. The wedge or jack is then tightened holding the
poling boards and cross brace in position.

153. Box Sheeting. — Box sheeting is composed of horizontal
planks held in position against the sides of the trench by vertical
pieces supported by braces extending across the trench. The

arrangement of planks and braces
for box sheeting is shown in Fig.
106. This type of sheeting is
used in material not sufficiently
cohesive to permit the use of
poling boards, and under such
conditions that it is inadvisable
to use vertical sheeting which
protrudes above the sides of the
trench while being driven. This
sheeting is put in position as the
trench is excavated. No more
of the excavation than the width
of three or four planks need be
unsupported at any one time. In

Showing Different Types of Cross Bracing, placing the sheeting the trench

is excavated for a depth of 12 to

24 inches. Three or four planks are then placed against the sides
of the trench and are caught in position by a vertical brace which
is in turn supported by a horizontal cross brace.

154. Vertical Sheeting. — This is the most complete and the
strongest of the methods for sheeting a trench. It consists of a
system of rangers and cross braces so arranged as to support a
solid wall of vertical planks against the sides of the trench. An
arrangement of complete vertical sheeting is shown in Fig. 107.
This type can be made nearly water tight by the use of matched
boards, Wakefield piling, steel piling, etc. Wakefield piling is
ma.de up of three planks of the same width and usually the same

FIG. 106. — Box Sheeting.

VERTICAL SHEETING

273

thickness. They are nailed together so that the two outside planks
protrude beyond the inside one on one side, and the inside one
protrudes beyond the two out-
side ones on the other side as
shown in Fig. 108. The pro-
truding inside plank forms a
tongue which fits into the groove
formed by the protruding out-
side planks of the adjacent pile.
In placing vertical sheeting
the trench is excavated as far
as it is safe below the surface.
Blocks of the same thickness
as the sheeting are then placed
against the bank at the middle
and at the ends of two rangers
on opposite sides of the trench. j^ 10?.— Vertical Sheeting.
The ranger rest against blocks,

and are held away from the sides of the trench by them. Cross
braces are next tightened into position opposite the blocks to

hold the tt10®1** in Place- Alier the
skeleton sheeting is in place the planks

forming the vertical sheeting are put in

FIG. lOS.-Wakefield Sheet P°sition ^ a chisel edSe cut on the
lower end of the plank, with the flat side

against the bank. The planks should be
driven with a maul, the edge of the plank following closely behind
the excavation. In relatively dry work the driving of the plank
is facilitated by excavating beneath the edge as
it is driven. The upper end of the sheeting should
be protected by a malleable steel or iron cap to
prevent brooming of the lumber. A cap is shown
in Fig. 109. A sledge hammer may be used for
driving when the lumber is protected. If the
sheeting is to start at the surface and is to be
Driven by hand, the first length should not exceed
4 feet unless a platform is erected for the driver.
Succeeding lengths may be longer, the driver stand-
ing on planks supported on the cross braces in the trench. Steam
hammers and pile drivers are sometimes used for driving sheeting.

FIG. 109.

Section through

Malleable Steel

Driving Cap.

274 CONSTRUCTION

The framework of the sheeting should be placed with a cross
brace for each end of each ranger and a cross brace for the middle
of each ranger. If the ends of two rangers rest on the same cross
brace an accident displacing one ranger will be passed on to the
next and might cause a progressive collapse of a length of trench,
whereas the movement of an independently supported ranger
should have no effect on another ranger. The cross braces
should have horizontal cleats nailed on top of them as shown in
Fig. 107 to prevent the braces from being knocked out of place by
falling objects. In driving vertical sheeting a vacant place will
be left behind each cross brace corresponding to the original block
placed to hold the ranger away from the bank. This is an unde-
sirable feature in the use of vertical sheeting. It is ordinarily
remedied by slipping in planks the width of the slot and wedging
or nailing them against the convenient cross bracing. In extremely
wet trenches, after all other pieces of vertical sheeting are in place,
the original cleat behind the cross brace can be knocked out and a
piece of sheeting slipped into this opening and driven. Care
must be taken in this event not to drive the rangers down when
driving the sheeting. If the bracing begins to drop, it should be
supported by vertical pieces between the rangers and resting on a
sill at the bottom of the trench.

155. Pulling Wood Sheeting. — Wood sheeting is pulled after
the completion of the trench by a device shown in Fig. 110. In
wet trenches where the removal of the sheeting
would permit a movement of the banks, result-
ing in danger to the sewer or other structures,
the sheeting should be left in place in the trench.
If sufficient saving can be made the sheeting is
cut off in the trench immediately above the danger
line, usually the ground water line. The cutting

, is done with an axe or by a power driven saw
FIG. 110. — Steel , . , , ,,
Clamp for Pull- devlsed for the purpose.

ing Wood Sheet- 156. Earth Pressures.1 — The various theories

ing. of earth pressure are so conflicting in their

conclusions as to be confusing. Rankine's

theory, the most frequently used, assumes that the pressure

increases with the depth, whereas Meem's theory 2 leads

1 Earth Pressures, Old Theories and New Test Results, Eng. News-Record,
VoL 85, 1920, p. 632.

2 Trans. Am. Society Civil Eng'rs, Vol. 60, 1908.

EARTH PRESSURES 275

to an opposite conclusion. The discussion following Meem's
article is very illuminating. It indicates that no matter how
good the theory, practical experience together with the use of
generous sizes and close spacing are the best guides for bracing
trenches and coffer dams. All are not possessed with the desired
practical experience and some basis on which to commence work
is essential. Another factor affecting computations of sizes
based on theory is the tendency in practice to use the same size
material for rangers and braces on any one job for all except very
deep trenches and other special cases. Occasionally where there
is an independent brace for each end of each ranger, the brace is
made thinner, but is of the same depth as the ranger.

The application of Rankine's theory of earth pressure to the
computation of the sizes of rangers and braces will be shown.
His formula for the active earth pressure against a retaining
wall is:

.cos 6— Vcos2 6— cos2 <f>
P=whcos6— — .

cos 0+vcos2 6— cos2 <f>

in which w = the weight of earth in pounds per cubic foot;

h = depth in feet at point at which pressure is to be

determined;
6 = the angle of surcharge, or the angle which the surface

makes with the horizontal;
0 = the angle of repose of the earth. Usually taken as

33°-41' = l£ horizontal to 1 vertical;
P = the intensity of pressure in pounds per square foot on

a vertical plane in a direction parallel to the surface

of the ground.

In studying the pressures for trenches the surface of the ground
will be assumed as horizontal and the formula reduces to

1 — sin <£ ,

.
1+sm <£

167. Design of Sheeting and Bracing. — The trench shown in
Fig. Ill is assumed to be constructed in moist sand weighing 110
pounds per cubic foot, with an angle of repose of 30 degrees. The
material used for sheeting and bracing is yellow pine. The steps

276

CONSTRUCTION

, F4"x6"\
K B-4 -H

4"*6"

6x8<.

^ E>

\< — -e'-8-—-\

« 8-0 — — ^

4'iS" **lol

} , „ p

k — 6-4— H

ifr

:«

taken in the design of the sheeting and bracing for this trench are
as follows:

1. Earth Pressure. — Substituting the units given in the data,
in Rankine's formula for earth pressures,

P = 36.7ft.

Because the earth has been freshly cut and will not be kept open
long enough to break up the cohesiveness of the banks it is cus-
tomary to reduce the assumed
pressure by dividing by 2, 3, or
4, according to the natural
cohesiveness of the material.
The cohesiveness of sand is not
great, therefore the pressure
will be assumed as one-half of
the amount given by the form-
ula, or

p = 18h.

2. Thickness of Sheeting and
Spacing of Rangers. — It is desir-
able to use the same thickness
of sheeting throughout the depth
of the trench. Computations
should therefore be commenced
at the bottom of the trench
where the pressures are the
greatest and the thickest
sheeting will be required. It
is necessary to determine by
trial a spacing for the rangers
and a thickness of sheeting
so that the sheeting is stressed
to its full working strength.

Having determined the thickness of the sheeting at the bottom,

the remainder of the computations consists in determining the

spacing of the rangers.

In the example the lower ranger will be assumed as 3 feet from

the bottom of the trench and the distance to the next ranger as

4,feet,

Diagram
of Pressures
on Sheeting. |

FIG. 111. — Diagram for the Design of
Wood Sheeting.

DESIGN OF SHEETING AND BRACING

277

The intensity of pressure at 22 feet 9 inches is 409.5

pounds per square foot.
The intensity of pressure at 26 feet 9 inches is 481.5

pounds per square fot.

The distribution of pressures is shown by the diagram on Fig. 111.
The maximum bending moment is slightly below the point mid-
way between the rangers and for a 12-inch strip is 10,500 inch
pounds.

Assuming 3 inch sheeting the maximum fiber stress is:

Me 10,400X1.5X12

12X27

: = 568 pounds per square inch.

The working strength of yellow pine as given in Table 59, is
1200 pounds per square inch. Thinner sheeting should therefore
be used.

TABLE 59
WORKING UNIT STRESSES FOR TIMBER

The most used value in the Building Codes of Baltimore, Boston, Cin-
cinnati, Chicago, District of Columbia, and New York City

Wood

Tension,
lb.sq.in.

Com-
pression
With
Grain,
Ib.sq. in.

Com-
pression
Across
Grain,
Ib.sq. in.

Trans-
verse
Bending,
Ib.sq. in.

Shear
With
Grain,
Ib.sq. in.

Shear
Across
Grain,
Ib.sq. in.

Yellow pine

1200

1000

600

1200

500

White pine

800

400

800

250

Spruce and Va. pine.
Oak

800
1000

800
900

400
800

800
1000

50
100

320
600

Hemlock

600

500

600

275

Chestnut

600

500

1000

800

150

Locust

1200

1000

1200

100

720

Aa published in American Civil Engineers Pocket Book.

Assuming 2-inch sheeting, the fiber stress is 1,300 pounds per
square inch. This stress is too large. By reducing the ranger
spacing slightly the stress can be brought within the required
limits.

Assuming a ranger spacing of 3 feet 9 inches the depth to the
upper ranger is changed to 23 feet and the maximum stress in the

278 CONSTRUCTION

2-inch sheeting becomes 1,140 pounds per square inch, a satis-
factory result. The results for the computations for the other
ranger spacings are shown in Table 60. The spacing of the
rangers at the sheeting junctions is controlled by convenience
and is not computed so long as it is obviously safe.

3. Size of Rangers. — The rangers will be assumed as 16 feet
long with two end cross braces and one intermediate cross brace
for each ranger. Starting as before at the bottom of the trench.

The area of the panel below the ranger and between
cross braces is 24 square feet.

The average intensity of pressure is 28.25X18 = 508.5
pounds per square inch.

The load transmitted to the ranger is 6,000 pounds.

Similarly the load transmitted to the ranger from the
panel above is 6,890 pounds.

The total distributed load on the ranger is 12,890 pounds.

If b is the vertical dimension of the ranger and d is the hori-
zontal dimension in inches, then from the beam theory, using / as

1,200 pounds per square inch, bd?=-—, in which M is expressed

in inch pounds. The maximum bending moment is

Wl 12,200X8X12

-5- = — - - Q - = 155,000 inch-pounds.

o o

Therefore, bd2 = 775.

An 8X10 inch beam will fulfill the conditions closely. Substi-
tuting these dimensions in the beam formula

Mc= 155,000X5X12
*~ I '' 8X1000

= 1,160 pounds per square inch tension in outer fiber. The results
of the computations for other rangers are shown in Table 60.

4. Size of Cross Braces. — The cross braces act as columns.
The dimensions of the cross braces are determined by trial in such
a manner that the vertical dimension of the brace is equal to the
vertical dimension of the ranger and the compressive stress in
pounds per square inch is computed from the expression,

Adopted by the Am. Ry. and Maintenance of Way Ass'n in 1907.

DESIGN OF SHEETING AND BRACING

279

TABLE 60

COMPUTATIONS FOR SHEETING AND BRACING FOR TRENCH SHOWN IN

FIG. Ill

Material is moist sand weighing 1 10 pounds per cubic foot, with an angle of repose of 30°.
Lumber is yellow pine, with working stresses as given in Table 59. Working stresses for

columns given as S I 1

Sheeting 2 Inches X 12 Inches

Cross Braces

Maxi-

Actual

Allow-

Maxi-

mum

In-

able

Depth

mum
Bending
Moment,

Fiber
Stress,
Pounds

Depth and
Description

Total
Ix>ad,
Pounds

Size.
Inches

tensity,
Pounds
per

In-
tensity,
Pounds

Inch-
Pounds

per

Square

Square
Inch

per

Square

Inch

23'-26.75'

9100

1140

end at 26' 9"

6,445

4X8

202

784

iy-23'

8800

1100

int. at 26' 9"

12,890

4X8

403

784

13'-17.5'

8550

1070

end at 23' 0"

6,393

4X8

200

784

8'- 13'

7160

900

int. at 23' 0"

12,785

4X8

400

784

<y-6'

3000

375

end at 19' 0"

3,930

4X8

123

784

int. at 197 0"

7,860

4X8

246

784

end at 17' 6"

3,566

4X8

112

684

int. at 17' 6"

7,132

4X8

224

684

end at 13' 0"

4,385

4X8

137

684

int. at 13' 0"

8,770

4X8

274

684

end at 8' 0"

2,270

4X6

687

int. at 8' 0"

4,540

4X6

189

667

end at 6' 0"

1,344

4X6

584

int. at 6' 0"

2,687

4X6

112

584

end at 0* 0"

432

4X6

584

int. at ff 0"

863

4X6

584

Rangers

Maxi-

Area

In-

mum

Maxi-

tensity

Load Transmitted to

Bending

mum

Depth

Panel
Below

of
Pressure,

Total
Load

the Ranger from the

Size.

Moment
in

Stress
Pounds

this

Pounds

Inches

Thou-

per

Depth,

per

Pounds

sand

Square

Panel

Both

Inch-

Inch

Feet

Inch

Below

Above

Panels

Pounds

26* 9"

508.5

12,200

6000

6890

12,890

8X10

155

1160

23' 0"

448

13,440

6545

6240

12,785 8X10

153

1150

19' 0"

378

12,100

5860

2000

7,860 1 8X10

94.3

708

17' 6"

328.5

3,942

1942

5190

7,132

8X10

85.6

636

13' 0"

274.5

9,880

4690

4080

8,770

8X10

105

790

8'0"

189

7,560

3480

1060

4,540

6X 8

54.4

850

6'0"

126

2,020

960

1727

2,687

6X 8

32.2

503

O'O"

2,590

863

6X 8

10.4

161

280 CONSTRUCTION

in which S — permissible crushing across the grain in a

column whose length is greater than 15 diam-
eters ;

Si =unit working compressive strength of wood;
Z = length of the column;
d = smallest dimension of the column;
I and d are in the same units.

The lower intermediate cross brace supports a length of 8 feet of
the lower ranger on which the load has been found to be 12,890
pounds. The load on the end cross brace for the same ranger is
one-half of this or 6,445 pounds. The length of each brace is
4 feet 4 inches. From Table 59, & is 1,000 pounds per square
inch. From the column formula, S is 784 pounds per square
inch.

A 4X8 inch cross brace is the smallest that is feasible. This
is stressed only 12,890 pounds or 403 pounds per square inch,
which is well within the permissible limits. The results of the
other computations for cross braces are shown in Table 60.

158. Steel Sheet Piling. — This is coming into more general
use with the increased cost of lumber and better acquaintance
with its superiority over wood under many conditions. Although
its first cost is higher than that of wood, the fact that with proper
care it can be used almost an indefinite number of tunes renders
it economical to contractors who may have an opportunity to
make repeated use of it. The life of good yellow pine sheeting
with the best of care may be as much as three or four seasons.
With no particular care it will be destroyed at the first using.
Fig. 112 shows various sections of steel piling used for trench
sheeting. These forms are practically water tight and aid mate-
rially in maintaining dry trenches. The piling can be made water
tight by slipping a piece of soft wood between the steel sections
when they are being driven, or by pouring in between the piles
some dry material which will swell when wet. The piling is gen-
erally driven by a steam hammer and is pulled by attaching a
ring through a bolt hole in the pile, or by grasping the pile with a
clutch that tightens its grasp as the pull increases. An inverted
steam hammer attached to the pile is sometimes used in pulling
it. The impulses of the hammer together with a steady pull on
the cable serve to drag out the most stubborn piece of piling.

LOCATING THE TRENCH

281

LINE AND GRADE

159. Locating the Trench. — In order to locate a trench a line
of stakes should be driven at about 50-foot intervals along the
center line of the proposed sewer before excavation is commenced.
Reference stakes or reference points to this line are located at
some fixed offset or easily described point, or the stakes marking

15" Arched- Wet Section (No.S.RH 15)

Section Modulus, Smalt • Il.tO 46.Slb. persa. ft of Wall 22702 kg. per sgmettr of Wall.

» » ,lnttrTocM'l4.ll S8.l2lt>.nlin.ft.ofBor. 86.49* - lin. n .. Bar.

l4"Arched-WebSecHon(No5.REI4)

Station Modului. Single - 7.6/ is Ik n*r *n ft of Wall 170.90 kg.ptrfg.mtttr of Wall.

i 60.76 ?,» tin. „ „ Bar.

I5x TC" Center- Flanqe Section.
' (No.S.RFlB)

Section Modulus, Single - 5.71 48 Ib. persq. ft. of Wall.

n n ,lnterloci«d*62S 60 Id.. • Ifn.ft. of Bar.

234. 34 kg. per so. mgttr of Waif.
89.29 S „ lin. „ ,. Bar.

•» - yr ' v1^*.^ >

X^--X l2|xl"Straight-Web Section. "

(No.S.PAIZ)

Section Modulus, Single « 4.12 40 /b'peno. ft. of Wall. 195. 32 kg. per so;, merer of Wall.

n » f Interlocked* 4.21 42. Sit. .. lin.fr. of Bar. 63.25 ?, „ l,n. a „ Bar.

FIG. 112. — Sections of Lackawanna Steel Sheet Piling.

the center line of the trench may be driven at some constant
offset distance one side of the trench, in order to avoid danger of
loss or disturbance of the stakes. Grade or cut is seldom marked
on the line of preliminary stakes, although the approximate cut
may be indicated.

For hand excavation the foreman lays out the trench from
these stakes. In machine work the operator guides the machine
so as to follow the line of the stakes.

282

CONSTRUCTION

160. Final Line and Grade. — After the excavation of the trench
has proceeded to within a foot or two of the final depth, the grade
and line are transferred to markers supported over the center of
the trench. The markers are horizontal boards spanning the
trench and held in position either by nails driven into stakes at
the side of the trench, by nails driven into the sheeting, or by
weights holding the boards on the ground. Two stakes driven in
the ground at the side of the trench as shown in Fig. 113 are the
common method of support. If the banks are too weak to stand
under the jarring of the driving of the stakes, or pavement or
other causes prevent their use the horizontal cross piece may be
weighted down by bricks or a bank of earth. The cross pieces
are located about every 25 feet along the trench and at any con-

CenhrLine-

Center', Line-

FIG. 113. — Methods for the Support of the Grade Line.

venient distance above the surface of the ground. The nearer
the ground the stronger the support but the greater the inter-
ference with work in the trench. The center line of the sewer is
marked on the cross pieces after they are set, and vertical struts
are nailed on them with one edge of the strut straight, vertical,
and on the center line as shown in Fig. 1. The corresponding
edge should be used on all struts in order to avoid confusion.
The edge is placed in a vertical position by means of a plumb
bob or carpenter's level.

The cut to the invert of the sewer is recorded to an even
number of feet where practicable by driving a nail in the upright
strut so that the top edge of the nail is at the desired elevation
above the sewer, or the upright is nailed with its top at the proper
number of feet above the sewer invert. The cut is marked on
the upright in feet, tenths, and hundredths from the recorded
point to the elevation of the invert.

The inspector should watch these grade markers with care by
sighting back along them to see that they are in line and have not

TRANSFERRING GRADE AND LINE TO THE PIPE 283

moved. In quicksand or caving material the marks may move
during the setting of the pipes and the levelman should be on the
job constantly.

When excavation is being done by machine the depth of the
excavation is controlled by the operator who maintains a sighting
rod on the machine in line with the grade marks on the uprights.

161. Transferring Grade and Line to the Pipe. — In transfer-
ring grade and line to the sewer a light strong string is stretched
tightly from nail to nail on the

uprights marking the line and
grade. A rod with a right angle
projection at the lower end, as
shown in Fig. 114, is marked
with chalk or a notch at such
a distance from the end that
when the mark is held on the
grade cord the lower portion of
the rod which projects into the
pipe will rest on the invert. The
pipe is placed in line by hang-
ing a plumb bob so that the
plumb bob string touches the
grade and center line cord. These
marks are taken only as fre-
quently as may be necessary to

keep the sewer in line. An experienced workman can maintain
the line by eye for considerable distances. Measurements should
never be taken to the top of the pipe in order to determine position
and grade as the variations in the diameter of the pipe may cause
appreciable errors.

The position and elevation of the forms for brick, concrete,
and unit block sewers are located by reference to the grade line,
or they may be placed under the immediate direction of the survey
party, or by specially located stakes. For large sewers requiring
deep and wide excavation the grade and line stakes are driven in
the bottom of the trench about a foot above the finished grade.
This requires the constant presence of an engineer who is usually
available on work of such magnitude.

162. Line and Grade in Tunnel. — In tunnels, line and grade
are given by nails driven in the roof, the progress of excavation or

FIG. 114. — Diagram Showing the Use
of the Grade Rod for Fixing the
Elevation of a Sewer.

284 CONSTRUCTION

the shield being followed by eye and the forms set by direct
measurement to the nails.

TUNNELING

163. Depth. — The depth at which it becomes economical to
tunnel depends mainly upon the character of the material to be
excavated and on the surface conditions. In soft dry material
with unobstructed working space at the surface, open cut may be
desirable to depths as great as 35 or 40 feet. Tunnels are cut in
rock at depths of 15 feet or less. In some very wet and running
quicksand encountered in the construction of sewers for the Sani-
tary District of Chicago it was found economical to tunnel at depths
of 20 feet and less. Crowded conditions on the surface, expensive
pavements, or extensive underground structures near the surface
may make it advantageous to tunnel at shallower depths than
would otherwise be economical. Winter is the best season for
tunneling as the workmen are protected from the elements and
labor is more plentiful.

164. Shafts.— In sinking a shaft in soft material, the excava-
tion is usually done by hand, the material being thrown into a
bucket which is hoisted to the surface and dumped. The size of
the shaft is independent of the size of the sewer and depends princi-
pally on the machinery which it is necessary to lower into the
tunnel. Ordinarily a shaft 6 feet in the clear is satisfactory. A
method of timbering a shaft is shown in Fig. 115. Because of
the timbering the shaft must be started sufficiently large at the
top to finish with the desired dimensions at the bottom. This
excess size is sometimes obviated by driving the sheeting at an
angle to maintain the same size of shaft from top to bottom.

In timbering a shaft as shown in Fig. 115 the upper frame is
staked securely in position at the surface of the ground. This
frame is composed of timbers fastened together in the form of a
square with the ends of the timbers extending about 12 inches on
all sides. The protruding ends are used to hold the frame in
position. Excavation is begun inside the frame, and sheeting is
driven around the outside of it as excavation progresses. Only
two or three men can work advantageously at one time in these
small shafts. The second frame is made up of the same size tim-
bers, but all are cut off flush with the outside of the square. The

SHAFTS

285

v 2 "Jingle Sheeting

outside dimensions of this frame are such as to allow sheeting to be
slipped in between it and the sheeting already driven. The frame
is lowered into position and supported from the upper frame by
vertical struts nailed to it. The lower end of the sheeting already
driven is held out from the lower frame by blocks of the thickness
of the next length of sheeting. These blocks are removed as the
next length of sheeting is placed
and driven. The driving of the
sheeting is facilitated by excavating
beneath it as it descends.

The sizes of sheeting and timber-
ing should be computed on the same
basis as that for trench sheeting
except that for depths greater than
30 to 35 feet Rankine's Theory is
not applicable and judgment must
be relied on for computing the sizes
for deep shafts. In stiff dry ma-
terial the pressures will change very
little as the depth increases. Sheet-
ing is needed in shaft excavation
in rock only to protect the work-
men from falling fragments, but in
sand, particularly in quicksand
and in wet ground, the pressures
increase directly with the depth and
the sheeting should be computed
accordingly. Care must be taken
to prevent the formation of cavities
behind the sheeting, to fill them if
formed, and to see that all pieces
of the sheeting and bracing have a

firm bearing. It is difficult to prevent the collapse of the shaft
once the movement of earth against the sheeting has commenced.

Shafts are also sunk in soft ground by constructing a concrete
or metal shell resting on a cutting shoe on the surface. The
material inside is dug out and the shell sinks of its own or added
weight. The first section of the shell may be from 5 to 10 feet
long. As this section sinks other sections are added. This is
called the caisson method. It is advantageous in wet ground and

Sectiorf'jS-j-'ip A-A.

FIG. 115.— Section of Shaft Tim-
bering.

Abbot, Journal Western Society of
Engineers, Vol. 22.

286 CONSTRUCTION

when the shafts are to be left as a permanent manhole. If a
permanent shaft is to be left in an excavation being braced with
wood, the permanent lining should follow within 20 to 30 feet of
the shaft excavation. This is done to avoid the difficulty of
maintaining a great length of temporary wood shaft with the
danger of collapse, or of blocks or other objects falling on the
workers below.

The distance between shafts is controlled by the depth and
size of the tunnel, surface conditions, and the character of the
material being tunneled. Except where surface conditions are
crowded the shallower the cover to the tunnel the more frequent
the shafts. The advantage of frequent shafts lies in the possi-
bility of removing excavated material from the tunnel promptly,
and in making ventilation of the tunnel easier. The saving made
by the construction of numerous shafts must be balanced against
the extra cost of the shafts. For the shallowest tunnels the
shafts are seldom placed closer than every 500 feet.

165. Timbering. — After the shaft has been excavated to the
proper grade the tunnel is struck out either by cutting through
the wooden sheeting or by removing portions of the caisson
lining. Practically all tunnels except those in solid rock must be
framed to some extent. Some of the types of frames used in
tunnel construction are shown in Fig. 116. Different combina-
tions of these may be used in different classes of materials. In
solid rock which remains firm on exposure no timbering is neces-
sary. Where the roof only need be supported and the sides are
strong enough to be used for support, a timber " hitch " or frame
supported on the sides of the tunnel may be used. This is suit-
able for loose rock roofs with solid rock sides. Timbering such as
is shown in the lower left-hand corner of Fig. 116 becomes neces-
sary in extremely soft, wet, or swelling material, where the bottom
and sides as well as the roof tend to push in. The remaining
frame in Fig. 116 shows a form frequently used and lying
between the two extremes indicated. In wet tunnels a channel
may be cut in the bottom below the sill for drainage purposes as
shown in this form. The needle beam method of timbering is
also shown in Fig. 116. This method of timbering is used mainly
near the heading because of the speed and ease with which it can
be installed, but it is undesirable because of the space occupied.

The distance between frames is dependent on the size of the

TIMBERING

287

tunnel and the character of the material. It is seldom greater
than 6 feet and the frames are sometimes placed touching each
other. The size of the timbering is a matter of experience and is
generally determined by the judgment of the responsible person
in charge of the construction as the result of observation during
the progress of the work.

The sheeting between frames is called poling boards, or spiling
or lagging according as it is sharpened and driven ahead of the
excavation or placed after the excavation has progressed. The

Needle

Beam

'/v'-v :-if-'-i:-:.'----~'^^'r' >ir4?ib,;-:
'•' ' •'•-:-,--'•';:--•.-; . '•' •".-. •' '--'•'•';" '

Longitudinal Section.

Longitudinal Section
Showing Poling Boards.

Types of Frames and Timbering
for Tunnels.

Transverse Section,

Tunnel Bracing Showing
Needle Beam Support- for Roof.

FIG. 116. — Types of Frames and Timbering for Tunnels.

horizontal strips placed between the frames to keep them apart
are called wales.

In cutting out from the shaft in soft materials requiring sup-
port, where the width of the tunnel is the same or smaller than
that of the shaft, a frame with a maximum width four thicknesses
of sheeting less than the width of the tunnel is set up against the
lining of the shaft. The vertical side pieces of the tunnel frame
rest on the bottom frame of the shaft as a sill and are securely
wedged into position. As the lining of the shaft at the top is cut
away the top poling boards of the tunnel are slipped in between the
cap of the first tunnel frame and the shaft frame immediately above

288

CONSTRUCTION

it. The poling boards are driven with an upward pitch so that
there may be room to slip the second length of boards between the
next tunnel frame and the first length of boards. The placing of
the side sheeting follows in a similar manner. Excavation is then
started and the poling boards driven to keep pace with it. The
next frame is placed in position and the previous sheeting or
boards wedged out a sufficient distance to allow the advance
lining to be slipped in when the wedges are removed. Waling
pieces are nailed firmly between the frames to hold them in posi-
tion. The various phases in the driving of a 12-foot sewer tunnel
in Seattle are shown in Fig. 117.

In soft or running material it may be necessary to protect the
face of the tunnel by horizontal boards, called breast boards,

Driving HeaaingTunnet , .-. A"x6"Po//nqs • .-4t 6 Walfnq .::«• ,,-... ,.;

^^a^^pii^iaia^^^ •&!&jt®m§aH»

'•/2'i/ZCrdwnBars'*-'''

Phase I. Phase 2

Phase
6.

FIG. 117. — Stages of Sewer Tunneling.

Eng. Record, Vol. 69, 1914, p. 195.

wedged back to the last frame placed. The excavation is per-
formed by removing one board at a time, excavating behind it
and then replacing it in the advance position. The advance is
made from the top downwards. This represents the method
pursued in the most difficult material where wooden sheeting
without a shield is used. The timbering during the advance may
be modified in any manner that the character of the material will
permit. The timbering may lag behind the excavation a dis-
tance of two or more frames, or it may be omitted altogether.
Heavier timbering may be necessary in soft, slipping or shattered
rock.

166. Shields. — Shields are used in tunneling in soft wet
material and are particularly suitable for work under air pressure.
They are used in rock tunnels where water is anticipated or air

SHIELDS

289

pressure is used. The shields often save the expense and diffi-
culty of timbering as the masonry of the sewer follows closely
behind the shield. Fig. 118 shows the arrangement for a shield
for tunneling in soft material in the construction of the Milwaukee
sewers. The shield has an exterior diameter of 9 feet 4 inches

/ Cast Iron Jack Sea t
.-BJntPI

Fio. 118. — Shield for Driving Milwaukee Sewer Tunnel.

Eng. News- Record, Vol. 80, 1918, p. 669.

and an overall length of 9 feet 8| inches. The cutting edge sec-
tion is 20 inches long. The shell is made of one inch plate to the
back of the jack chambers and one-half inch plate in the tail.
The shield is driven by ten 60-ton hydraulic jacks. The jacks

290 CONSTRUCTION

are shown in position in the figure. These jacks rest against the
finished tunnel lining and serve to consolidate it at the same time
that they push the shield into the material to be excavated. The
face of the tunnel is cut with a pick and shovel while the jacks
are removed one at a time and a new ring of lining is put in place.
The lining may be temporary timbering to receive the thrust of
the jacks, but it is usually desirable that the permanent lining
follow immediately behind the shield. Since the shield is larger
than the outside of the lining the space left by its passage should
be grouted immediately after it has passed.

FIG. 119. — Method of Drilling and Loading Rock Tunnel Face.

Courtesy, Aetna Power Co.

167. Tunnel Machines. — Tunnel machines have been used
successfully on sewer tunnels in soft materials, but not in rock.1
The machines are of different types, but in general consist of a
revolving cutting head, equipped with knives, and driven by an
electric motor. The bearing on which the shaft for the cutting
head rests is supported against the sides of the tunnel. The muck
is carried away by means of a conveyor and dumped into muck
cars without rehandling. Rapid progress can be made with these
machines in suitable conditions.

168. Rock Tunnels. — Tunnels in rock are advanced by drilling
into the face as shown in diagrammatic form in Fig. 119. The

1 Tunneling Machines Successful on Detroit Sewers, Eng. News-Record,
Vol. 84, 1920, p. 329.

VENTILATION 291

holes near the center are driven in at an angle towards the center
and to depths from 6 to 15 feet. The harder the rock the greater
the angle with the tunnel. This is called the center cut. Other
holes are driven near the outer edge of the tunnel and parallel to
its axis. When fired, the wedge of rock between the center cut
holes is thrown back into the tunnel and a delayed explosion
then throws the sides into the hole thus made. A final delay
thrusting shot throws the muck so formed away from the face of
the tunnel. For tunnels up to 6 or 8 feet in height the entire bore
is cut out in this fashion. For larger tunnels, the upper portion
called the heading, is taken out in this way, and the remainder,
called the bench, is taken out by drilling and blowing holes normal
to the axis of the tunnel. The amount of powder necessary in
the bench holes is much less than that required in the heading.

169. Ventilation. — No tunnel more than 50 feet long should
be built without ventilation. A fair amount of air for ordinary
conditions is 75 cubic feet of free air per minute per person in the
tunnel, and double this amount for each animal. Where explosive
gases are met, or under conditions where the tunnel is hot, five or
six times as much air may be needed in order to cool the tunnel or
to dilute the gases. In order that the air may be fresh and cool
at the face of the tunnel where work is going on it should be con-
ducted to the tunnel face in a pipe and blown out into the tunnel.
Immediately following a blast at the face the current should be
reversed so as to draw the poisonous gases out of the tunnel
through the duct. The high pressure air line leading to the drills
should be opened at the same time to create a current towards the
face in order to accelerate the clearing of the air at the heading.
The capacity of the air machines should be sufficient to exhaust
four times the volume of the gases created by the explosion, in 15
minutes. This will ordinarily call for a capacity of about 4,000
cubic feet of free air per minute. If the same blower is to be
used for exhausting the gases as for ventilation while work is going
on, it should have a high overload capacity to care for this situa-
tion. The air line should be arranged to allow for reversal of flow.

The diameter of the air pipe should be determined by a study
of the saving of the cost and operation of the air equipment com-
pared to the increased cost of a larger pipe line. Other factors
affecting the size of the pipe line to be used are: the available
space in the tunnel, the temporary character of the installation,

292 CONSTRUCTION

the use of the exhaust from high-pressure air machines for the
purpose of ventilation, etc. Cast-iron, spiral-riveted galvanized
sheet iron, and canvas pipes have been used for conducting low-
pressure ventilating air.

Ventilation in tunnels working under air pressure is supplied
from the compressors, and the air is delivered near the face of
the heading, except that being used in the locks. In tunnels
using air drills, the air for the drills is conducted through a sep-
arate pipe as it is not economical to compress the ventilating air
to the pressure necessary to operate the drills.

170. Compressed Air. — Compressed air is used in tunnel work
to prevent the entrance of water into the tunnel and to keep the
work dry. The pressure of air used is closely that of the pressure
of the ground water but in a large tunnel or a tunnel with a weak
roof the pressure may be somewhat lower on account of the danger
of blowing through the roof. It is evident that the water pres-
sure cannot be balanced at the top and the bottom of the tunnel.
To balance it at the bottom makes a blow out near the top more
probable. To balance the pressure at the top may leave the
bottom wet. Judgment and care must be exercised during con-
struction and if the pressure is balanced at or near the bottom the
roof must be carefully guarded by grouting and puddling with
clay, or the surface, particularly if under water, may be covered
with a clay bank. If the cavities in the tunnel lining are large,
sawdust can be mixed with the grout to advantage, the mixture
being pumped through holes in the roof by hand or power operated
force pumps. " Blows " must be carefully guarded against as
they endanger the lives of the workmen and threaten the loss of
the tunnel. The pressure and volume of air supplied for some
large subaqueous tunnels is shown in Table 61.

Labor under compressed air is arduous and dangerous with
the best of safeguards.1 Pressure more than about 43 pounds
per square inch cannot be used and at this high pressure men can-
not work more than four hours at a time. Little or no distress
is noted at pressures less than 15 pounds.

Entrance and exit to the tunnel are gained through air locks.
These are sheet-iron cylinders concreted into the lining of the
tunnel or shaft. Air-tight iron doors are provided at both ends,

1 Rules on Compressed-Air Work of N. Y. State Industrial Commission,
Eng. News-Record, Vol. 85, 1920, p. 1225.

COMPRESSED AIR

29:;

TABLE 61

VOLUME AND PRESSURE OF COMPRESSED AIR IN TUNNELS
(American Civil Engineers Pocket Book)

Maxi-

Average

mum
Distance

Mini-

mum
Air

Air

Tunnel

High
Water

mum
Cover

Pressure,
Pounds

Conditions and Cubic Feet of
Free Air per Minute

per

to
Invert,

Feet

per

Square

Feet

Inch

City and South

In water bearing-sand. 1660

London

cubic feet per minute per face.

When grouted 1000 to 1300

cubic feet per minute per face

Blackwall

10,000 cubic feet per minute per

face in open ballast for some

time

Baker St. and

In gravel, 3300 cubic feet of air

Waterloo

per minute per face. Parallel

tunnel 1650 cubic feet per min.

per face

Greenwich

Average 83.5 per man per minute.

Never less than 66.7

Battery, East

In sand. Two working faces.

Kivt-r. N Y.

Maximum 32,000

East River, N. Y..

Maximum for one face 25,000

Penn. R.R.

cubic feet per minute for 24

hours. Capacity of plant for

8 faces, 80,400 cubic feet per

minute

North River,

Maximum in gravel 10,000 cubic

N. Y., Penn.

feet per man per hour. Gener-

R.R.

ally ranged between 1500 and

5000

which open inwards towards the tunnel. On entering the lock
from the outside the door to the tunnel is found tightly closed.
The outside door is then closed by hand, the ah- valve is opened
and air is admitted to the lock until the pressure on the lock side
of the tunnel door equalizes that on the tunnel side and the tunnel
door is swung open by hand. When the lock is open to the
tunnel the pressure in the tunnel keeps the outside door closed.
In order to leave the tunnel the process is reversed. Materials

294 CONSTRUCTION

are passed through the lock by the lock tender or tenders who
pass through the lock with the material if the pressure is low, or
who manipulate the air outside of the lock if the pressure is high.
If pressures of 30 to 40 pounds are being used, two or even three
locks may be necessary.

EXPLOSIVES AND BLASTING1

171. Requirements. — The desirable features in an explosive
to be used in trenching and tunneling in rock are: (1) stability
in make up so as not to deteriorate in strength or to become
dangerous during storage, (2) imperviousness to ordinary varia-
tions in temperature and moisture, (3) insensibility to ordinary
shocks received in transportation and handling, (4) not too diffi-
cult of detonation, (5) convenient form for transportation and
loading and for making up charges of different weights, (6) the
non-formation of poisonous gases when fired, (7) imperviousness
to water and usefulness in wet holes, (8) power without bulk, etc.

172. Types of Explosives. — Explosives which fill some or all
these requirements can be divided into two classes, deflagrating
and detonating. A deflagration is an explosion transmitted
progressively from grain to grain. A detonation is a sudden dis-
ruption caused by synchronous vibrations of a wave-like char-
acter. The deflagrating explosives are represented by gun-
powders and contractors' powders. They must be carefully
tamped in the hole to develop their full power and they must be
ignited by a fuse or flame. They are valueless in water or moist
holes. These powders are used mainly for loosening frozen earth,
soft sandstone, cemented gravels and similar materials where a
thrusting action rather than a disruption is desired. The detonat-
ing explosives are most commonly represented by the dynamites.
These are exploded by a shock usually caused by another explosive
which has been ignited by a fuse or electric spark, and which is
known as the " detonator." Detonating explosives are more
powerful than deflagrating explosives and are used in all but the
softest materials.

1 Taken mainly from the Engineer Field Manual of the U. S. Army;
Safety Factors in the Use of Explosives by W. O. Snelling, Technical Paper
No. 18, U. S. Bureau of Mines; and an article in Eng'g and Contracting,
¥01.52,1919,?. 585.

TYPES OF EXPLOSIVES 295

Gunpowder. — This is a mechanical mixture of sulphur, char-
coal, and saltpeter generally in the proportions of 10 parts sulphur,
15 parts charcoal, and 75 parts saltpeter (sodium nitrate). It
weighs about 62^ pounds per cubic foot and produces about 280
times its own volume in gas at a pressure of 4.68 tons per square
inch at a temperature of 32 degrees F., which amounts to a pres-
sure of approximately 38 tons per square inch at the temperature
of explosion of 4,000 degrees F.

Blasting Powder. — This is a mixture of 19 parts sulphur, 15
parts charcoal, and 66 parts saltpeter. These powders are made
in different size angular polished grains, from the size of a pin
head to sizes just passing a f to \ inch hole. The larger the grains
the slower the action of the powder.

Nitro-Substitution Compounds. — These compounds are formed
by the action of nitric acid on hydro-carbons. Triton, T.N.T.,
or trinitrotoluene, made famous during the war, is an example of
these compounds. It is made by the successive nitration of
toluene, a coal tar derivative. It melts at 80 degrees C., is very
stable, and is of great explosive strength. It is manufactured in
a convenient form, being compressed into blocks about 2 inches
square by about 4 inches long with a specific gravity of about 1.5.
The blocks are usually copper plated to protect the T.N.T. from
moisture. The more dense it is the less its sensitiveness. It is
also put up in crystalline form hi cartridges like dynamite, in
which condition it is practically equal to 40 per cent dynamite.
It can be cut with a knife, pounded with a hammer, and will burn
freely and slowly in small quantities in the open air without
exploding. It is suitable for all but the hardest rocks. It creates
poisonous gases on detonation which are quickly dissipated in the
open air but which render it unsuitable for use in tunnel work.

Nitro-glycerine. — This is formed by the action of nitric and
sulphuric acids on animal compounds such as gelatine or glycerine.
Nitro-glycerine is a yellowish, oily, highly unstable explosive
liquid with a specific gravity of about 1.6. It will burn quietly
when ignited in the open air. It will freeze at 41 degrees F., and
will explode at 388 degrees F., or on concussion at a lower tempera-
ture. It develops about 1,500 times its volume in gas, which due
to the heat of combustion is increased to about 10,000 times its
volume. It is a very dangerous explosive to handle, and is unsuit-
able for use in the liquid form.

296 CONSTRUCTION

Blasting Gelatine. — This is made by soaking guncotton in
nitro-glycerine. Gelatine dynamite is a combination of blasting
gelatine and an absorbent. For cite is a gelatine dynamite in
which the blasting gelatine, forming 50 per cent of the compound,
contains 90 per cent nitro-glycerine and 2 per cent guncotton;
and the absorbent, forming the other 50 per cent of the compound,
contains 76 per cent of sodium nitrate, 3 per cent sulphur, 20 per
cent of wood tar, and 1 per cent of wood pulp.

Blasting gelatine is packed in a jelly-like mass in metal lined
wooden boxes. It is less sensitive than straight dynamite and is
one of the most powerful explosives known. It can be made up
to equal 100 per cent dynamite. It is suitable for use in the hard-
est rocks and for subaqueous work as it is not affected by moisture.
It is suitable for use in tunnels as the amount of carbon monoxide,
peroxide of nitrogen, hydrogen sulphide and other dangerous
gases is comparatively low when fully detonated. Gelatine
dynamite J is sold as 30 per cent to 70 per cent dynamite, the
actual percentage of nitro-glycerine being less than the nominal
quantity given.

Dynamite. — The dynamites are made by soaking nitro-glycerine
in some absorbent. If the absorbent is some neutral substance
such as infusorial earth the combination is known as a true dyna-
mite. The false or active dynamites are those in which the absorb-
ent is also an explosive compound. The false dynamites form the
best known contractors' explosives. Among the materials mixed
with the nitro-glycerine are: magnesium carbonate, sulphur,
wood meal, wood pulp, wood fiber, wood tar, nut galls, kieselguhr,
sawdust, resin, pitch, sugar, charcoal, and guncotton. The
strength of dynamites is noted by the per cent of nitro-glycerine
and nitro substitutes contained. Dualin and Hercules powder
both contain 40 per cent nitro-glycerine. Dualin contains 30
per cent sawdust and 30 per cent potassium nitrate, but the
Hercules powder, which is stronger, contains 16 per cent sugar,
3 per cent potassium chlorate, 31 per cent potassium nitrate, and
10 per cent magnesium carbonate.

Dynamite is the most common explosive used on construction

work. It is supplied in cylindrical sticks wrapped in paper, the

diameter of the sticks varying between f and 2 inches. They are

about 8 inches long. Forty per cent dynamite is the common

> 1 See paper by C. T. Hall before Am. Inst. Chemical Engineers.

PERMISSIBLE EXPLOSIVES 297

strength found on the market. It is suitable for ordinary work
in all but very hard rocks or very soft material. Direct contact
with water separates the nitro-glycerine from the base and is
dangerous when the explosive is used in wet places unless it is
fired immediately after the hole is loaded. It freezes at about 42
degrees F., or at even higher temperatures and in the frozen state
it is highly dangerous, requiring powerful detonators for firing,
but exploding spontaneously from a slight jar, or the breaking of
the stick. Special low-freezing dynamites are made that will not
freeze above 35 degrees F.

Ammonia Compounds. — Ammonia dynamite is a combination
of nitro-glycerine, ammonium nitrate and such other ingredients
as sodium nitrate, calcium carbonate and combustible material.
This form of explosive is advantageous for underground work
because, like gelatine dynamite, its explosion does not create large
quantities of poisonous gases. It has a low freezing point and is
relatively low in cost. It is seriously affected by moisture, however,
and can not be used in wet places. Ammonium nitrate explosives
which do not contain nitro-glycerine include 70 per cent to 95 per
cent ammonium nitrate and some combustible material. Ammo-
nal is a special type of 'this class formed by a mixture of ammo-
nium nitrate, aluminum, and triton. All of these explosives are
deliquescent, insensitive to shock, and are cheaper than the dyna-
mites.

173. Permissible Explosives. — As specified by the United
States Bureau of Mines explosives whose rapidity, detonation,
and temperature of explosion will not ignite explosive mixtures
of pit gases and air are known as permissible explosives. They
include nitrate explosives, ammonia dynamite, and others.

Gunpowder, triton, picric acid, blasting gelatine, dynamite,
guncotton, etc., are not classed as permissible explosives.

174. Strength. — The relative weights for equal strength of
various explosives are given in Table 62.

175. Fuses and Detonators. — The explosion of gunpowder and
other deflagrating explosives is caused by the direct application
of a flame led to the charge by a powder fuse, or they may be
fired by a blasting cap which is itself exploded by the heat from
a fuse or an electric spark. The powder fuse is a cord made up of
a train of powder securely wrapped in a number of thicknesses of
woven cotton or linen threads and usually made water-proof.

298

CONSTRUCTION

TABLE 62

RELATIVE WEIGHTS OF EXPLOSIVES WITH THE SAME STRENGTH AS A
UNIT WEIGHT OF 40 PER CENT DYNAMITE

Explosive

Relative
Weight

Explosive

Relative
Weight

Picric acid

0.86

Triton

0.86

Gun powder (well tamped) .

3.10"

Blasting gelatine

0.43

Straight dynamite, 15%. .. .

1.45

Gelatine dynamite, 30%. . .

1.28

Straight dynamite, 20 ....

1.33

Gelatine dynamite, 35 ...

1.21

Straight dynamite, 25 ....

1.28

Gelatine dynamite, 40

1.14

Straight dynamite, 30 ....

1.18

Gelatine dynamite, 50

1.04

Straight dynamite, 35 ....

1.07

Gelatine dynamite, 55 ...

0.97

Straight dynamite, 40 ....

1.00

Gelatine dynamite, 60

0.90

Straight dynamite, 45 ....

0.93

Gelatine dynamite, 70 ...

0.83

Straight dynamite, 50 ....

0.86

Straight dynamite, 55 ....

0.83

Ammonia dynamites are

Straight dynamite, 60 ....

0.78

the same as gelatine

dynamites.

Low-freezing dynamites are

Chlorates (sprengle)

the same as straight

Rack-a-rock

1.33

dynamites

Guncotton

0.72

Smokeless powder, well

tamped

0.74

Ordinary fuse burns at about 2 feet per minute but there may be
wide variations from this rate due to the quality of the fuse,
moisture, temperature, or pressure. Moisture tends to retard the
rate, pressure to increase it. Instantaneous fuse will burn at
about 120 feet per second. It is distinguished from the ordinary
safety fuse both by eye and touch due to the rough red braid with
which it is covered. It is used in firing a number of charges
simultaneously. Powder fuses are lighted by the application of a
flame or smoldering torch to the freshly cut or opened end expos-
ing the powder grains. Cordeau Bickford is lead tubing filled with
triton, in which the flame travels at about 17,000 feet per second.
This is also used for igniting charges simultaneously.

The detonation of an explosive is caused by the shock or heat
of the explosion of a more sensitive substance which has been
exploded by a powder fuse or electric spark. The common
method of detonating explosive charges is by the firing of a blast-

FUSES AND DETONATORS

ing cap. These caps are copper cylinders, closed at one end,
about 1% inches long and \ to | of an inch in diameter, or larger.
They contain a mixture of about 85 per cent fulminate of mercury
and 15 per cent potassium chlorate held in place by a wad of
shellac, collodion, or paper. The strength of detonators is based
on the weight of fulminate of mercury and is designated as shown
in Table 63.

TABLE 63
STRENGTH OF BLASTING CAPS

Blasting Cap,
Commercial Grade

Grains
Fulminate
of
Mercury

Electric Cap,
Commercial Grade

Grains
Fulminate
of
Mercury

3X or Triple

8.3

Single strength

12 3

4X or Quadruple

10 0

Double strength

15 4

5X or Quintiple ....

12 3

Triple strength

23 1

6X or Sextuple

15.4

Quadruple strength

30 9

7X or Number 20

23.1

8X or Number 30

30 9

The force of the explosion is markedly affected by the strength
of the caps, the effect being greater for low-grade powders. For
40 per cent dynamite the explosion caused by a 5X cap is 15 per
cent stronger than that caused by a 3X cap. For 60 per cent
dynamite the difference is only 6 per cent. The deterioration of
the caps will reduce the strength of an explosion noticeably.
With straight dynamite, 3X caps are generally used, but with
gelatine dynamite 6X or heavier caps must be used. Caps may
be tested by exploding thorn in a confined space and noting the
report and the effect on the shell. A full strength cap will tear
the shell into minute pieces, while a deteriorated cap will merely
tear it into three or four large pieces. An ordinary blasting cap is
shown in Fig. 120 together with other equipment for blasting.

Firing by electricity is generally safer and more satisfactory
than by the use of ordinary caps and powder fuses. The explosion
is more certain and its exact time is under the control of the opera-
tor. Fig. 121 shows a section through an electric blasting cap or

300

CONSTRUCTION

detonator, commonly called an electric fuse. Delayed-action
electric detonators are made by inserting a slow-burning sub-
stance between the platinum bridge and the detonating substance.
The time of delay is controlled by the depth of the slow -burning
substance. Delayed-action detonators are useful in tunnel work
where it is desired to explode the charge in three or four stages
in order that the debris from one charge may be out of the
way of the following, and that the forces of the explosions may
not serve to nullify each other.

176. Care in Handling. — Some of the don'ts in the handling

MAGNETO

DYNAMlie, CARTRIDGES
POWDEF

ELECTRI
CAPS

ELECTRIC:

FUSE

BLASTING
CAPS

CAP CRIMPERS

SAFETY RESISTANCE
FUSE ____ COIL ........

FIG. 120. — Blasting Supplies.

' Courtesy, Aetna Powder Co.

GALVANOMETER

of explosives recommended by the U. S. Army Engineer Field
Manual are : in the use of nitro-glycerine explosives of all kinds —

(a) Don't store detonators with explosives. Detonators
should be kept by themselves.

(6) Don't open packages of explosives in a store house.

(c) Don't open packages of explosives with a nail puller,
pick or chisel. Packages should be opened with a hard
wood wedge and mallet, outside of the magazine and at
some distance from it.

(d) Don't store explosives in a hot or damp place. All
explosives spoil rapidly if so stored.

(e) Don't store explosives containing nitro-glycerine so
that the cartridges stand on end. The nitro-glycerine is
more likely to leak from the cartridges when they stand on
end than it is when they lie on their sides.

CARE IN HANDLING

301

-Electric Lead*

i -Copper Shell
.-Sulphur Filling

•Sulphur Plug

(/) Don't use explosives that are frozen or partly
frozen. The charge may not explode completely and seri-
ous accidents may result. If the explosion is not complete
the full strength of the charge is not exerted and larger
quantities of harmful gases are given off.

(g) Don't thaw frozen explo-
sives in front of an open fire, nor in
a stove, nor over a lamp, nor near
a boiler, nor near steam pipes, nor
by placing cartridges in hot water.
Use a commercial or improvised
thawer.

(h) Don't put hot water or
steam pipes in a magazine for
thawing purposes.

(t) Don't carry detonators and
explosives in the same package.
Detonators are extremely sensitive
to heat, friction, or blows of any
kind.

(.7) Don't handle detonators or
explosives near an open flame.

(k) Don't expose detonators or
explosives to direct sunlight for
any length of time. Such exposure
may increase the danger in their
use.

(0 Don't open a package of explosives until ready to
use the explosive, then use it promptly.

(m) Don't handle explosives carelessly. They are all
sensitive to blows, friction, and fire.

(ri) Don't crimp a detonator (blasting cap) around a
fuse with the teeth. Use a cap crimper, which is supplied
for this purpose.

(o) Don't economize by using a short length of fuse.

(p) Don't return to a charge for at least one-half hour
after a miss fire. Hang fires are likely to happen.

(q) Don't attempt to draw nor to dig out the charge in
case of a miss fire.

Some of the positive rules in connection with the handling of
explosives are: build the magazine on an earth foundation remote
from any other structures, protect it with earth embankments
that will direct the force of the explosion upwards, and build it
of materials that will supply as few missiles as possible. Hollow
tile brick, double-walled galvanized iron filled with sand, and
similar constructions are satisfactory. The magazine may be

•-Platinum Bridge

•Guncotton orLoose
Mercury Fulminate

•Mercury Fulminaft
Packed

FIG. 121.— Electric Fuse.

Full size.

302

CONSTRUCTION

heated by steam or hot-water pipes so located that explosives can-
not come in contact with them, or by a cluster of incandescent
bulbs, but if the explosives become frozen they must not be thawed
out by turning on the steam or hot water. If powder or nitro-
glycerine is dropped on the floor the magazine should be emptied,
washed out with a hose and spots of nitro-glycerine scrubbed with
a brush and a mixture of ^ gallon of wood alcohol, \ gallon of
water and 2 pounds of sodium sulphide. Frozen explosives may
be thawed by spreading out on special shelves in a warm thaw
house — not in the magazine proper, by burying in a manure pile
so that the explosive may not become moistened, or more com-
monly by heating slowly in a water bath. This is a dry kettle in
which the explosives are placed and covered. The kettle is then
put in another containing water which is heated gently to about
120 degrees F. It should not be boiled.

In case of a miss fire, instead of digging out the old charge put
a new charge on top of the old and fire the two
simultaneously.

177. Priming, Loading, and Firing. — Priming is
the act of placing the cap or detonntor in the cart-
ridge of explosive. The primer is either the cap or
the cap and cartridge which are to be detonated by
the fuse. If a cap and safety fuse are to be used the
paper at the upper end of the cartridge is opened, a
hole is poked in the explosive with the finger or a
piece of wood, the cap and the attached fuse are
pushed into the hole and gently embedded in the
explosive so that the end of the cap is exposed
sufficiently to prevent the fuse from igniting the
dynamite directly. The paper is then folded up
and tied firmly around the fuse with a piece of
string. The result is shown in Fig. 122.

In placing the fuse in the cap the end of the
fuse is cut off square, and inserted in the open
end of the cap, care being taken not to spill the
Safety Fuse, l°ose grains of powder or to grind the fuse down
and Cap. on top of the cap. When the fuse is shoved
firmly into place the upper portion of the copper
cap is pressed or crimped with the cap crimpers shown in Fig. 120.
The number of primers to be used is dependent on the size

FIG. 122. —
Dynamite
Cartridge,

PRIMING, LOADING, AND FIRING 303

and location of the charge, but in practically all sewer work only
one primer is used to each hole. In bulky charges the primer
should be placed near the center of the charge and the fuse so
protected that it will not ignite the charge prematurely. In drill
holes the primer is put in last with the cap end down.

In loading a hole, it is first pumped and cleaned out. This
can be done satisfactorily with the end of a stick frayed out into a
broom. Cartridges which very nearly fill the hole are dropped in
one at a time and are pressed firmly together, with a light wooden
tamping bar. They should not be pounded. After the primer
is placed, a wad of clay or similar material is pressed gently into
the hole against it and the hole is then filled with well-tamped clay.
In tunnel work tamping is not so essential as an overcharge of
powder is usually used and the time of tamping, which is worth
more than two or three sticks of dynamite, is saved. In handling
bulk explosives, such as gunpowder, they are poured into the hole,
the fuse is set in the upper portion and the remainder of the hole
is tamped with clay as for dynamite cartridges.

If a large number of charges are to be fired simultaneously
with a safety fuse, the length of the fuse to each charge should be
made equal or a safety
fuse used to a common
center and approxi-
mately equal lengths
of instantaneous fuse f

n j TJ- i r J Vttuiiiiiiiiuiii.......

or Cordeau Bickford ^

used from there to RG. 123.— Methods for Cutting Safety Fuse for
the charge. In splic- Splicing,

ing the fuses for such

connections they are cut diagonally as shown in Fig. 123 and bound
together firmly with tape. Electric connections are particularly
advantageous under such conditions as they avoid the dangers
incidental to spliced fuses and are less expensive. In tunnel
work simultaneous electric detonation is not desirable as the holes
should be fired progressively: 1st, the cuts; 2nd, the relievers;
3rd, the backs; 4th, the sides; and 5th, the lifters. Different
lengths of safety fuse, or delayed action electric fuses can be used
for these delay shots.

In igniting a safety fuse an open flame such as that furnished
by a match or candle is the most satisfactory. For electric fuses

304 CONSTRUCTION

the current is generated by a magneto shown in Fig. 120.
Pressing vigorously down on the handle closes the circuit and
generates an electric current which heats the platinum bridges
and explodes the charges. For the small number of charges used
in ordinary construction they are connected in series so that if
there is a broken connection anywhere no charge will be exploded.
If many charges are to be fired and a line circuit is to be used, the
final connection should not be made until just before the charge
is to be fired in order to obviate the danger of stray currents firing
the charge prematurely. Care should be taken to see that all
connections are good and that there are no broken wires on the line.

178. Quantity of Explosive. — The quantity of explosive to
be used can be determined satisfactorily only by experience on
the job in question, as the factors affecting the necessary quantity
are so diverse. The figures in Table 64 indicate the relative
amounts needed under different conditions.

PIPE SEWERS

179. The Trench Bottom. — It is customary to dig the bottom
of the trench to conform to the shape of the lower 45 degrees
to 90 degrees of the sewer if the character of the material will
allow such construction. In soft material which will not hold
its shape the sewer may be encased in concrete or a concrete
cradle may be prepared for the pipe. In rock the trench is
excavated to about 6 inches below grade and refilled with well-
tamped earth so as to form a cradle giving bearing to 60 to 90
degrees of the pipe circumference. For large sewers to be con-
structed in the trench special foundations are sometimes built.

180. Laying Pipe. — Before the pipe is lowered into the trench
the sections which are to be adjacent should be fitted together
on the surface and the relative positions marked by chalk so that
the same position can be obtained in the trench.

Small pipes are lowered into the trench and swung into posi-
tion on a hook as shown in Fig. 124. Pipes up to 15 or 18 inches
in diameter can be handled by the pipe layer and helper in the
trench without assistance. Heavier pipes may be lowered into
the trench by passing ropes around each end of the pipe. One
end of the rope is fastened at the surface and the ropes are paid
out by the men at the surface as the pipe is lowered. If the pipes

QUANTITY OF EXPLOSIVE

305

Remarks

Grade of
Dynamite,
Per Cent

9
9

S3 5* 3

3(2 £

0000000000000008

OOQOOOOOlNiO

•ppt^ic

• i-KNO^-i

OQ -000000000000011000
O i-< • OO OO O 1-1 IH O i-H O O >-H O

d of R

111

306 CONSTRUCTION

have been fitted together and marked at the surface it is undesir-
able to use this method of lowering as the position in which the
pipes arrive in the bottom of the trench can not be easily pre-
dicted. A cradle may be used for shoving the pipe into position
as is shown in Fig. 125.

Pipes above 24 to 27 inches in diameter are too large to be
handled from the side of the trench. A hook as shown in Fig.
124 is placed in the pipe so that it will be in the proper position
when lowered. It is raised by a rope passing through a block
at the peak of a stiff-legged derrick which spans the trench, or
by a crane. If a derrick is used the rope passes to a windlass
on the opposite side of the trench from the pipe. Mechanical

FIG. 124. — Hook for Lowering and FIG. 125. — Cradle for Placing

Placing Sewer Pipe. Sewer Pipe.

power may be used for raising pipes too heavy to be raised by hand.
The pipe is then lowered and swung into position while sup-
ported from the derrick. Excessive swinging is prevented by
holding back on the guide rope as the pipe is raised and lowered.
Pipes are usually laid with the bell end up grade as it is easier
to fit the succeeding pipe into the bell so laid and to make the
joint, particularly on steep grades. The Baltimore specifica-
tions state:

The ends of the pipe shall abut against each other in
such a manner that there shall be no shoulder or unevenness
of any kind along the inside of- the bottom half of the
sewer or drain. Special care should be taken that the

pipe are well bedded on a solid foundation The

trenches where pipe laying is in progress shall be kept dry,
and no pipe shall be laid in water or upon a wet bed unless
especially allowed in writing by the Engineer. As the
pipe are laid throughout the work they must be thoroughly
cleaned and protected from dirt and water, no water being
allowed to flow in them in any case during the construction
except such as may be permitted in writing by the Engineer.
No length of pipe shall be laid until the preceding length
has been thoroughly embedded and secured in place, so as
to prevent any movement or disturbance of the finished
. joint.

JOINTS 307

The mouth of the pipe shall be provided with a board
or stopper, carefully fitted to the pipe, to prevent all earth
and any other substances from washing in.

181. Joints. — Pipes may be laid with open joints, mortar
joints, cement joints, or poured joints. Open joints are used for
storm sewers in dry ground close to the surface. Mortar and
cement joints are commonly used on all sewers except in special
cases. Cement joints are more carefully made than mortar
joints and result in a greater percentage of water-tight joints.
Poured joints are used in wet trenches where it is necessary to
exclude ground water from the sewer.

A specification used in some cities for open joints is:

Pipes laid with open joints are to be laid with their
inverts in the same straight line and shall be firmly bedded
throughout their length on the bottom of the trench. No
cement or mortar is to be used in the joints. Not more
than | inch shall be left between the spigot end of the pipe
and the shoulder of the hub of the pipe into which it fits.
The joints shall be surrounded with cheese cloth, burlap,
broken pipe, gravel or broken stone.

The purpose of the cheese cloth, etc., is to prevent fine earth
from sifting into the pipe until the cheese cloth or other material
has rotted away, by which time the earth has become arched over
the opening.

Mortar joints are specified by Metcalf and Eddy as follows:

Before a pipe is laid the lower part of the bell of the
preceding pipe shall be plastered on the inside with stiff
mortar of equal parts of Portland cement and sand, of
sufficient thickness to bring the inner bottoms of the
abutting pipe flush and even. After the pipe is laid the
remainder of the bell shall be thoroughly filled with similar
mortar and the joint wiped inside and finished to a smooth
bevel outside.

In some work a wood block or a stone is embedded in the mor-
tar at the bottom of the joint to bring the spigot in place concen-
tric with the next pipe.

Cement joints are specified in the Baltimore specifications as
follows:

Cement joints shall be made with a narrow gasket of
hemp or jute and cement mortar, and special care shall be
taken to secure tight joints. The gasket shall be soaked

308 CONSTRUCTION

in Portland cement grout and then carefully inserted
between the bell and the spigot, and well calked with
suitable hardwood or iron calking tools. It shall be hi
one continuous piece for each joint, an$ of such thickness
as to bring the inverts of the two pipes smooth and even.
The remainder of the joint shall be filled with cement mortar
all around, on the bottom, top and sides, applied by hand
with rubber mittens, well pressed into the annular space
and beveled off from the outer edge of the bell to a dis-
tance of two inches therefrom, or to an angle of 45 degrees.
The inside of each joint shall be thoroughly cleansed of all
surplus mortar that may squeeze out in making the joint;
and to accomplish this some suitable scraper or follower,
or form shall be provided and always used immediately
after each joint is finished.

Cement joints so made, form the most satisfactory joint
for ordinary conditions and are the most frequently used. They
are not always water-tight and can be penetrated by roots. Some
roots are able to penetrate holes of almost microscopic size and
to form growths in the sewer or to split the joints.

Poured joints are made by pouring some jointing compound,
while in a fluid state, into the joint in which it hardens, thus seal-
ing the joint. Water-tightness in sewer lines to exclude ground
water has also been attempted by using the ordinary cement joint
and surrounding the pipe with a layer of cement or concrete.
This has not always been successful as it is difficult to obtain the
proper class of workmanship in wet sewer trenches.

The requisite qualities of a poured jointing material are:

(1) It should make a joint proof against the entrance
of water and roots.

(2) It should be inexpensive.

(3) It should have a long life.

(4) It should not deteriorate in sewage which may be
either acid or alkaline.

(5) It should adhere to the surface of the pipe.

(6) It should run at a temperature below about 400° F.,
as too high temperatures will crack the pipe.

(7) It should neither melt nor soften at temperatures
below 250° F. in order to maintain the joint if hot liquids
are poured into the sewer.

(8) It should be elastic enough to permit slight move-
ments of the pipes.

(9) It should not require great skill in using as it must
be handled ordinarily by unskilled workers.

JOINTS 309

The materials used for poured joints are: cement grout;
sulphur and sand; and asphalt or some bituminous compound
made of vulcanized linseed oil, clay, and other substances the
resulting mixture having the appearance of vulcanized rubber
or coal tar. The bituminous materials most nearly approach
the ideal conditions.

Cement grout is made up of pure cement and water mixed
into a soupy consistency. Its main advantages are its cheapness
and ease in handling in wet trenches or difficult situations. The
result is no better than a well made cement joint. There is no
elasticity to the joint and a movement of the pipe will
break it.

Sulphur and sand are inexpensive, comparatively easy to
handle, and make an absolutely water-tight and rigid joint which
is stronger than the pipe itself. It frequently results in the crack-
ing of the pipe and is objected to by some engineers on that
account. In making the mixture, powdered sulphur and very
fine sand are mixed in equal proportions. It is essential that the
sand be fine so that it will mix well with the sulphur and not
precipitate out when the sulphur is melted. Ninety per cent
of the sand should pass a No. 100 sieve and 50 per cent should pass
a No. 200 sieve. The mixture melts at about 260° F. and dees
not soften at lower temperatures. For making a joint in an 8
inch pipe about \\ pounds of sulphur, \\ pounds of sand, \
pound of jute, and 0.4 pound of pitch are used. The pitch is
used to paint the surface of the joint while still hot in order to
close up any possible cracks.

Among the better known of the bituminous joint compounds
are: " G.K." Compound made by the Atlas Company, Mertz-
town, Pa., Jointite and Filtite, manufactured by the Pacific Flush
Tank Co., Chicago and New York, and some of the products of
the Warren Brothers Co., Boston. These compounds fill nearly
all of the ideal conditions except as to cost and ease in handling.
They are somewhat expensive and if overheated or heated too
long become carbonized and brittle. In cold weather they do
not stick to the pipe well unless the pipe is heated before the
joint is poured. On some work jbints have been poured under
water with these compounds, but success is doubtful without
skillful handling. An overheated compound will make steam
in the joint causing explosions which will blow the joint clean,

310

CONSTRUCTION

and an underheated compound will harden before the joint is
completed.

The materials should be heated in an. iron kettle over a gaso-
line furnace or other controllable fire, until they just commence
to bubble and are of the consistency of a thin sirup. Only a
sufficient quantity of material for immediate use should be pre-
pared and it should be used within 10 to 15 minutes after it has
become properly heated. The ladle used should be large enough
to pour the entire joint without refilling. There are other
important points to be considered in pouring joints which can be
learned best by experience.

The quantity of material necessary for making these joints,
as announced by the manufacturers, is shown in Table 65.

TABLE 65
QUANTITY OF COMPOUND NEEDED FOR POURED JOINTS

Quantity of Material in Pounds per Joint

Diameter

of Pipe,

Standard Socket

Deep and Wide Socket

in Inches

Jointite

Filtite

O.K.

Jointite

Filtite

O.K.

0.82

0.72

0.42

1.46

1.28

0.72

1.06

0.95

0.73

1.82

1.60

1.25

1.30

1.15

0.89

2.26

1.98

1.52

2.08

1.82

1.42

2.65

2.32

1.80

2.52

2.20

1.74

3.20

2.80

2.20

3.02

2.64

2.58

3.75

3.29

3.25

3.44

3.00

2.86

4.30

3.78

3.60

3.62

3.16

3.13

4.62

4.07

3.97

4.03

3.50

3.41

4.91

4.31

4.27

In making a poured joint the pipes are first lined up in posi-
tion. A hemp or oakum gasket is forced into the joint to fill a
space of about f of an inch. An asbestos or other non-combustible
gasket such as a rubber hose smeared with clay is forced about
% inch into the opening between the bell and the spigot and the
compound is poured down one side of the pipe through a hole
broken in the bell, until it appears on the other side, and the hole

THE INVERT 311

is filled. Occasionally the non-combustible gasket is wrapped
tightly around the spigot of the pipe and pressed or tied firmly
to the bell. In pouring cement grout joints a paper gasket
is used which is held to the bell and spigot by draw strings.
Greater speed in construction and economy in the use of materials
are obtained by joining two or three lengths of pipe on the bank
and lowering them into the trench as a unit. The pipes are set in
a vertical position on the bank with the bell end up, one length
resting in the other. The joint is calked with hemp and poured
without the use of the gasket. The joint should always be poured
immediately after being calked so that the hemp can not become
water soaked. The asbestos gasket should be removed as soon
as possible after the joint is poured in order to prevent sticking
with resultant danger of breaking of the joint when attempting
to pull the gasket free.

One man can pour about 33 eight-inch joints, and two men
can complete about 26 twelve-inch joints per hour on the bank
where conditions are more or less fixed.

182. Labor and Progress. — The labor required for the laying
of pipe sewers, exclusive of excavation, bracing and backfilling,
consists of pipe layers and helpers. For pipes 24 to 27 inches
in diameter or smaller one pipe layer and one or more helpers
are necessary, dependent on the size of the pipe and the depth
of the trench. For larger pipes two pipe layers can work econom-
ically each working on one-half of the pipe and making hah" of
the joint. The speed of pipe laying is ordinarily limited by the
speed of the excavation, but on a job in Topeka, Kan.,1 where
the average day's progress with a machine excavator was 200
to 500 feet of trench per day, the pace was limited by the speed
of the pipe laying gang. This gang consisted of two pipe layers
in the trench and two helpers on the surface. The sizes of pipes
handled were from 8 to 27 inches.

BRICK AND BLOCK SEWERS

183. The Invert. — In good firm ground the excavation is
cut to the shape of the sewer and the bricks are laid directly on
the ground, being embedded in a thick layer of mortar. After
the foundation has been prepared and before the bricks are laid,

1 Eng. News, Vol. 75, 1916, p. 592.

312 CONSTRUCTION

two wooden templates, called profiles, are prepared, similar to that
shown in Fig. 126, to conform to the shape of the inside and
outside of the sewer. Each course of bricks is represented by
a row of nails in the profile and each nail corresponds to a joint
in the row. The two profiles are set true to line and grade. A
cord is stretched tightly between the two lowest nails on opposite
templates and a row of bricks is laid. The bricks are laid
radially and on edge with their long dimension parallel to the
axis of the sewer and with one edge just touching the string.
As each one or two or three rows are completed the guide line is
moved up to the next nails. When the bricks are laid on the
ground all but large depressions are filled in with tamped sand or
mortar by the masons. Approximately the
same number of rows of bricks is kept com-
pleted on either side of the center line. The
FIG. 126. — Profile for succeeding courses follow within three to five

Brick Sewers. rows of each other, the only bond between
courses being the mortar joint. This is
called row lock bond and with few exceptions has been used on
all brick sewers in the United States. As the sides of the sewer
become higher during the construction, platforms must be built
for the masons. These platforms are built of wood and rest
directly on the green brickwork. They should be designed to
spread the load as much as possible. The brickwork of the invert
is continued up in this way to the springing line. As soon as
one section is completed one profile is moved 10 to 20 feet ahead
along the trench according to the standard length of sections,
and set in position. The line is then strung from it to nails
driven or pushed into the cement joints of the last completed
section. Between work done on separate days the bricks are
racked back in courses to provide a satisfactory bond.

In ground too soft to support the brickwork directly a cradle
is prepared by placing profiles in position in the sewer and nailing
2-inch planks to these profiles, first firmly tamping earth under
the planks. The bricks are laid in this cradle in a manner
similar to that explained for sewers with a firm foundation. In
still softer ground it may be necessary to construct a concrete
cra'dle to support the bricks.

184. The Arch. — The arch centering consists of a wooden
form made up of wooden ribs as shown in Fig. 127. The center

BLOCK SEWERS '313

conforms to the shape of the inside of the arch with allowance
for the thickness of the lagging. The lagging is nailed on the ribs
in straight strips parallel to the axis of the sewer. The center
is supported on triangular struts resting against the sides and on
the bottom of the sewer and is lifted into position by wedges
driven between it and the support. The centers may be placed
immediately after the completion of the invert, or a day or two
may be allowed to pass to give the invert an opportunity to set.
After the centers are fixed in place the arch brick are carried up
evenly on each side and are pounded firmly into place. The center
is usually, but not always
" struck " immediately, and
the arch brick are cleaned
and pointed up from the
inside. The outside is cov-
ered with a layer of £ to f
of an inch of cement mortar
and may be backfilled to the
top of the arch in order to
maintain the moisture of the FIG. 127. —Centering for Brick Sewer,
mortar during setting and to

press the bricks of the arch together firmly. The centers are some-
times made collapsible so that they can be carried or rolled through
the finished brickwork to the advanced position. In "striking"
the centers the wedges are removed and the wings folded in.

In tunneling, the invert of the sewer is constructed in the same
fashion as for open-cut work. The arch centering is made in
short sections and the bricks are put in position by reaching in
over the end of the centering. All of the timbering of the tunnel
is removed except the poling boards or lagging against which
the bricks or mortar are tightly pressed, the boards being bricked
in permanently.

185. Block Sewers. — Sewers made of unit blocks of concrete
or vitrified clay are constructed in a similar manner to brick
sewers. Fig. 128 shows the construction of a block sewer at
Clinton, Iowa. In this sewer there are two rings; an inside one of
solid blocks and an outside one of hollow blocks. Block sewers
do not demand the skill in construction that is demanded by
brick sewers, as the blocks are so cast that the joints are radial,
whereas only experienced masons can lay bricks radially.

314

CONSTRUCTION

186. Organization. — The number of men employed on a
brick or block sewer is proportioned according to the size of the
sewer and the working conditions. The number of men working
on different tasks usually bears the same ratio to the number
of masons employed, regardless of the size of the work. These

proportions are shown
for different jobs, in
Table 66.

187. Rate of Progress.
— In a general way it can
be assumed that the lay-
ing of 1,000 bricks will
require 3f hours of the
time of one mason, 10
man hours for helpers
and laborers, 2 barrels of
cement, 0.6 cubic yard of
sand, and about 10 feet
board measure of center-
ing. One thousand bricks
will make about 2 cubic
yards of brickwork. To
the costs, as estimated
on the basis of materials
and labor, must be added
about 15 per cent for
overhead and an addi-
tional amount for the

contractor's profit. The number of bricks required in various
size sewers is shown in Table 67. A mason can lay more bricks
per hour in a large sewer than in a small one as there is a smaller
percentage of face work, there is more room to work, and it is
easier to lay the bricks radially. The number of bricks laid and
the rate of progress on various jobs are shown in Table 68.

FIG. 128. — Segmental Block Sewer at Clinton,
Iowa,

CONCRETE SEWERS

188. Construction in Open Cut. — In the construction of sewer
pipe of cement and concrete one of two methods may be em-
ployed; 1st, to manufacture the pipe in a plant at some distance

CONSTRUCTION IN OPEN CUT

313

from the place of final use, or 2nd, to manufacture the pipe in
place. The methods of the manufacture of cement and concrete
pipe which are to be transported to the place of use are treated
in Chapter VIII. The process of constructing the pipes in place
is ordinarily used for pipes 48 inches or more in diameter. For
smaller sizes, brick, vitrified clay, and precast cement pipes are
usually more economical.

TABLE 66
ORGANIZATIONS FOR THE CONSTRUCTION OF BRICK AND BLOCK SEWERS

84- to

Type of Work

General
Ratio on
Basis of
Four Brick
Layers

15-foot,
5-ring
Brick,
Chicago

66-inch
Circular
Brick,
Gary

84-inch
Circular
Brick,
Gary

108-inch
Sewer
Brick in
Detroit
Tunnel

42-inch
Lock-
Joint
Tile
Block

Foreman

Brick layers ....

Helpers .

Scaffold men ....

Brick tossers ....

Brick carriers. . .

Cement mixers . .

Cement carriers .

Form setters ....

Laborers . .

Source of
Information 1

Municipal
Engineering,
Vol.54,p.228

H. P.

Gillette, Handbook of Cost Data

The preparation of the foundation of a concrete sewer is
similar to that for a brick sewer. If the ground is suitable the
trench is shaped to the outside form of the sewer and the con-
crete poured directly on it. In soft material which would give
poor support to a sewer with a rounded exterior, the bottom of
the trench is cut horizontal and a concrete cradle of poorer quality
than that in the finished sewer is poured on the soft ground, on a
board platform, on piles, or on cribbing supported on piles.

If the invert of the sewer is so flat that the concrete will
stand without an inside form the shape of the invert is obtained

316

CONSTRUCTION

by a screed or straight-edge which is passed over the surface of
the concrete and guided on two centers, or on one center and the
face of the finished work. The construction of a flat invert
sewer at Baltimore is shown in Fig. 1. The center for the con-
crete is shown in the foreground. When the concrete for the
next section is poured it will be smoothed to shape by a screed or
straight-edge resting on the face of the finished concrete and the
center. The center is shaped to conform to that of the finished
concrete. It is firmly staked in position and acts as a bulk-
head for the concrete as it is poured, as well as a guide for the
screed.

TABLE 67

BRICK MASONRY IN CIRCULAR SEWERS. CUBIC YARDS PER LINEAR FOOT
(From H. P. Gillette)

Diameter,
Feet and Inches

One Ring
(4£ Inches)

Two Ring
(9 Inches)

Three Ring
(13| Inches)

0.103

0.240

0.125

0.280

0.147

0.327

0.169

0.371

0.191

0.415

0.213

0.458

0.234

0.501

0.802

0.256

0.545

0.867

0.278

0.589

0.933

0.633

1.000

0.677

1.063

0.720

1.128

0.763

1.193

0.807

1.260

0.851

1.325

0.895

1.390

0.938

1.456

If inside forms are to be used they are made as units in lengths
of 12 or 16 feet for wooden forms, and 5 feet for steel forms.
The inside form is supported by precast concrete blocks placed
under it and which are concreted into the sewer. It is held in
position by cleats nailed to the outside form, to the sheeting, or

RATE OF PROGRESS

317

Remarks

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n

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C^O 00 OS cb«D OS OOtbtb O

318

CONSTRUCTION

wedged against the outside of the trench. In some cases,
particularly where steel forms are used, the inside form is hung
by chains from braces across the trench as is shown in Fig. 129.
The form is easily brought to proper grade by adjustment of the
turnbuckles and is then wedged into position to prevent move-
ment either sideways or upwards during the pouring of the
concrete. It may be necessary to weight the forms down to
prevent flotation. Cross bracing in the trench which interferes
with the placing of the form is removed and the braces are placed

FIG. 129. — Blaw Standard Half -Round Sewer Form, Suspended from Overhead

Support.
Courtesy, Blaw Steel Form Co.

against the form until the concrete is poured. They are removed
immediately in advance of the rising concrete.

The sewer section may be built as a monolith, in two parts, or
in three parts. In casting the sewer as a monolith the complete
full round inside form is fixed in place by concrete blocks and
wires. The full round outside form is completed as far as pos-
sible without interfering too much with the placing and tamping
of the concrete. The concrete is poured from the top, being
kept at the same height on each side of the form, and tamped
while being poured. The remaining panels of the outside form
are placed in position as the concrete rises to them. An open-
ing is, left at the top of the outside arch forms which is of such a

CONSTRUCTION IN OPEN CUT 319

width that the concrete will stand without support. The casting
of sewers as a monolith is difficult and is usually undesirable be-
cause of the uncertainty of the quality of the work. It has the
advantage, however, of eliminating longitudinal working joints
in the sewers which may allow the entrance of water or act as a
line of weakness.

If the sewer is to be cast in two sections the invert is poured
to the springing line or higher. A triangular or rectangular
timber is set in the top of the ,A.

wet concrete as shown in Fig. /~^~l — c^ — r i

130. When the concrete has set / / «— *- — i I ,J

the timber is removed and the ^V

groove thus left forms a work- FIG. 130.— Construction Joints for

ing joint with the arch. After Concrete Sewers.

the invert concrete has set, the

arch centering is placed and the arch is completed. This is the

most common method for the construction of medium-sized

circular sewers.

Large sewers with relatively flat bottoms are poured in two or
three sections. First the invert is poured without forms and is
shaped with a screed. About 6 inches of vertical wall is poured
at the same tune. This acts as a support for the side-wall forms.
The side walls reach to the springing line of the arch and are
poured after the invert has set. At the third pouring the arch
is completed. The sewer shown in Fig. 1 is being poured in two
steps, as the side walls are so low that they are poured at the
same time as the invert. A transverse working joint similar to
one of the types used in Fig. 130 is set between each day's work.

The length of the form used and the capacity of the plant
should be adjusted so that one complete unit of invert, side wall,
or arch can be poured in one operation. The forms are left in
place until the concrete has set. Invert and side wall-forms are
generally left in position for at least two days, and in cold weather
longer. The arch forms are left in place for double this time.
For example if 20 feet of invert and arch can be poured in a day,
60 feet of invert form and 100 feet of arch form will be required.
As the forms are released they must be moved forward through
those in place. For this reason collapsible or demountable
forms are necessary and steel forms are advantageous. Wooden
arch forms are sometimes dismantled and carried forward in

320

CONSTRUCTION

sections, but are preferably designed to collapse as shown in
Fig. 131, so that they can be pulled through on rollers or a carriage.
189. Construction in Tunnels. — In tunnels the invert and
side walls are constructed in the same manner as for open cut
work. The tunneling, which acts as the outside form, is
concreted permanently in place. The concreting of a tunnel
by hand is shown in Fig. 132. If the work is to be done by hand
the concrete is thrown in between the ribs of the arch centering
and behind the plates or lagging, which are set in advance of the
rising concrete, The lagging plates are 5 feet long which makes

.-I x3 Lagging
Covered with
Galvanized
Sheet Iron.

FIG. 131. — Section through a Collapsible Wood Form.

it possible to throw the concrete in place at the arch, and to tamp
it in place from the end. A bulkhead and a well-greased joint
timber are placed in position as the concrete rises.

Pneumatic transmission of concrete is also used for filling
the arch forms as well as the side walls and invert forms. In
using this method the mixer may be placed at the surface or at
the bottom of the shaft or other convenient permanent location
which may be some distance from the form. The mixture is
discharged into a pipe line through which it is blown by air to
the forms. The starting pressure of about 80 pounds per
square inch can be reduced after flow has commenced. In con-
structing the St. Louis Water Works tunnel the compressor
equipment for moving the concrete had a capacity of 1,600

MATERIALS FOR FORMS 321

cubic feet per minute at a pressure of 110 pounds. The tunnel
is horse-shoe shaped, 8 feet in height and with walls varying from
9 to 20 inches in thickness. The extreme travel of the concrete
was 1,100 feet in an 8 inch pipe. The amount of air consumed at
110 pounds varied from 1.2 to 1.7 cubic feet of free air per linear
foot of pipe. By the time the batch had been discharged the
pressure had reduced to 25 to 40 pounds, depending on the length
of the pipe. It is reported that a 6-inch pipe line would probably
have given better results.

FIG. 132. — Ogier's Run Intercepting Storm-Water Drain, Baltimore, Mary-
land.

Placing concrete in Arch. T..r steel lagging of the forms is carried up in sections as the
concrete is deposited. The drain is horse-shoe shaped, and is 12 feet 3 inches high and 12
feet 3 inches wide.

The end of the concrete conveying pipe is provided with a
flexible joint the simplest form of which can be made by slipping
a section of pipe of larger diameter over the end of the trans-
mission line. The concrete is deposited directly on the invert
or into the side-wall forms and can be blown into the arch forms
for 20 to 25 feet.

190. Materials for Forms. — The materials used in forms for
concrete sewers are: wood, wood with steel lining, and steel
alone. The first cost of wood forms is lower than that of steel
but their life is relatively short. If the forms are to be used
a number of times steel is more economical. With proper care

322 CONSTRUCTION

and repairs steel forms will outlast any other material. Because
of the increasing price of lumber and improvements in steel
forms, wood forms are not frequently used. A common type
of specification under which forms are used is:

The material of the forms shall be of sufficient thick-
ness and the frames holding the forms shall be of sufficient
strength so that the forms shall be unyielding during the
process of filling. The face of the form next to the concrete
shall be smooth. If wooden forms are used the planking
forming the lining shall invariably be fastened to the stud-
ding in horizontal lines, the ends of these planks shall be
neatly butted against each other, and the inner surface of
the form shall be as nearly as possible perfectly smooth,
without crevices or offsets between the ends of adjacent
planks. Where forms are used a second time, they shall
be freshly jointed so as to make a perfectly smooth finish
to the concrete. All forms shall be water-tight and shall
be wetted before using.

Any material in contact with wet concrete should be oiled or
greased beforehand in order to prevent adherence to the concrete.

191. Design of Forms. — The design of forms for reinforced
concrete work requires some knowledge of the strength of materials
and the theories of beams, columns, and arches. Forms can be
constructed without such knowledge but that they will be both
economical and adequate is an improbability. The ordinary
beam and column formulas are applicable to the design of forms.
The maximum bending moment for sheeting and ribs is taken as

wl2

x-, where w is the load per unit length, and I is the length between
o

supports. Sanford Thompson recommends that the deflection be

wl3
calculated as Fr> in which E is the modulus of elasticity of

' -

the material, and I is the moment of inertia of the cross-section
referred to the neutral axis. The horizontal pressure of the con-
crete against the forms has been expressed empirically by E. B.
Smith,1 as

1 Pressure of Concrete on Forms Measured in Tests, by E. B. Smith,
before Am. Concrete Institute, Feb. 15, 1920. Abstracted in Eng. News-
Recojd, Vol. 84, 1920, p. 665.

DESIGN OF FORMS

323

in which P = lateral pressure in pounds per square inch;
R = rate of filling forms in feet per hour;
H = head of fill. Ordinarily taken as %R, but in cold

weather or when continuously agitated it may be

as high as f/£;

C = ratio, by volume, of cement to aggregate;
S = consistency in inches of slump.

Earlier investigators have usually concluded that the pressures
were equal to those caused by a liquid weighing 144 pounds
per cubic foot, but the tests of the United States Bureau of
Public Roads, from which the above formula was devised, show
the pressures to be decidedly below this amount under certain
conditions.

With these units and formulas the design of the lagging becomes
a matter of substitution in, and the solution of, the equations
produced.1 The forces acting on the ribs are indeterminate.
No more satisfactory design can be made
for the ribs than to follow successful prac-
tice, or what is seldom done, to determine
the stresses in the forms by the application
of one of the theories for the solution of
arch stresses. The sizes of the lumber
used in the ribs varies from 1^X6 inches
to 2X10 inches, depending on the size
of the sewer. If vertical posts are used
at the ends to support the arch forms pIG 133 .—Centering for
they are computed as columns taking the Large Forms,

full weight of the arch. If the span is

so wide that radial supports are used as shown in Fig. 133
the load at the center is assumed as one-fourth of the weight of
the arch.

192. Wooden Forms. — Norway and Southern pine, spruce,
and fir are satisfactory for form construction. White pine is
satisfactory but is generally too expensive. The hard woods
are too difficult to work. The lumber should be only partly
dried as kiln-dried lumber swells too much when it is moistened,
warping the forms out of shape or crushing the lagging at the

1See, also, Concrete Form Design, by E. F. Rockwood, Eng. and Con-
tracting, Vol. 55, 1921, p. 528.

324

CONSTRUCTION

joints. Green lumber must be kept moist constantly to prevent
warping before use and when it is used it does not swell enough
to close the cracks. The lumber should be dressed on the face
next to the concrete and at the ends. Either beveled or matched
lumber may be used for lagging. The joint made by beveled

FIG. 134. FIG. 135. FIG. 136.

FIG. 134.— Beveled Joint for Wood Fords.

FIG. 135. — Collapsible Wooden Invert Form for Concrete Sewers.
FIG. 136. — Support for Arch Centering.

FIG. 137. — Wooden Forma Used in Tunnel, North Shore Sewer, Sanitary Dis-
trict of Chicago.
Journal Western Society of Engineers, Vol. 22, p. 385.

lumber shown in Fig. 134 is cheaper but less satisfactory than a
tongued and grooved joint.

Types of wooden forms are shown in Figs. 135 and 136 for
use in sewers to be built as monoliths or in two portions. Fig.
137 shows the details of a built-up wooden form used in tunnel
work for a 42| inch egg-shaped sewer.

STEEL FORMS

325

193. Steel-lined Wooden Forms. — Sheet metal linings are
sometimes used on wooden forms. They permit the use of
cheaper undressed lumber, demand less care in the joining of the
lagging, and when in good condition give a smooth surface to
the finished concrete. Their use has frequently been found
unsatisfactory and more expensive than well-constructed wooden
forms because of the difficulty of preventing warping and
crinkling of the metal lining and in keeping the ends fastened
down so that they will not curl. Sheet steel or iron of No. 18 or
20 gage (0.05 to 0.0375 of an inch) weighing 2 to 1| pounds
per square foot is ordinarily used for the lining .

FIG. 138. — Blaw Standard Full Round Telescopic Sewer Forms, Showing
Knocked-Down Sections Loaded on a Truck.
Courtesy, Blaw Steel Form Co.

194. Steel Forms. — These are simple, light, durable, and easy
to handle. The engineer is seldom called upon to design these
forms as the types most frequently used are manufactured by the
patentees and are furnished to the contractor at a fixed rental
per foot of form, exclusive of freight and hauling from the point
of manufacture. The forms can be made in any shape desired,
the ordinary stock shapes such as the circular forms being the
least expensive. The smaller circular forms are adjustable
within about 3 inches to different diameters so that the same
form can be used for two sizes of sewers. The same form can be
used for arch and invert in circular sewers. Fig. 138 shows the

326

CONSTRUCTION

collapsible circular forms and the manner in which they are
pulled through those still in position. Fig. 129 shows a half
round steel form swung in position by chains and turnbuckles
from the trench bracing, and Fig. 139 shows the free unobstructed
working space in the interior of some large steel forms.

195. Reinforcement. — It is essential that the reinforcement
be held firmly in place during the pouring of the concrete. A
section of reinforcement misplaced during construction may
serve no useful purpose and result in the collapse of the sewer.

FIG. 139. — Interior of .Steel Forms for Calumet Sewer, Chicago.
Sewer is 16 feet wide. Note absence of obstructions. Courtesy, Hydraulic Steelcraft Co.

In sewer constructipn a few longitudinal bars may be laid in
order that the transverse bars may be wired to them and held
in position by notches in the centering and in fastenings to bars
protruding from the finished work. This construction is shown
in Fig. 1. The network of reinforcement is held up from the
bottom of the trench by notched boards which are removed as
the concrete reaches them, or better by stones or concrete
blocks which are concreted in. Sometimes the reinforcement
is laid on top of the freshly poured portion of the concrete the
surface of which is at the proper distance from the finished face

COSTS OF CONCRETE SEWERS 327

of the work. This method has the advantage of not requiring
any special support for the reinforcement, but it is undesirable
because of the resulting irregularity in the reinforcement spacing
and position.

In the side walls the position of the reinforcement is fixed by
wires or metal strips which are fastened to the outside forms or
to stakes driven into the ground. Wires are then fastened to the
reinforcement bars and are drawn through holes in the forms
and twisted tight. When the forms are removed the wires or
strips are cut leaving a short portion protruding from the face
of the wall. The reinforcing steel from the invert should pro-
trude into the arch or the side walls for a distance of about 40
diameters in order to provide good bond between the sections.
The protruding ends are used as fastenings for the new reinforce-
ment. The arch steel may be supported above the forms by
specially designed metal supports, by small stones or concrete
blocks which are concreted into the finished work; or by notched
strips of wood which are removed as the concrete approaches
them. Strips of wood are not satisfactory because thay are
sometimes carelessly left in place in the concrete resulting in a
line of weakness in the structure. Metal chairs are the most
secure supports. They are fastened to the forms and the bars
are wired to the chairs. In some instances the entire rein-
forcement has been formed of one or two bars which are fastened
into position as a complete ring. This results in a better bond in
the reinforcement, requires less fastening and trouble in handling,
but is in the way during the pouring of the concrete and inter-
feres with the handling of the forms.

196. Costs of Concrete Sewers. — Under present day conditions
a general statement of the costs of an engineering structure can
not be given with accuracy. Only the items of labor, materials,
and transportation that go to make up the cost can be estimated
quantitively, and the total cost computed by multiplying the
amount of each item by its proper unit cost obtained from the
market quotations.

A summary of some of the items that go to make up the cost
of a concrete sewer and the relative amount of these items on
different jobs is given in Tables 69 and 70.

328 CONSTRUCTION

TABLE 69

DIVISION OF LABOR COSTS FOR THE CONSTRUCTION OP
96-INCH CIRCULAR CONCRETE SEWER

Classification of Labor

Classification of Work

Task or Title

Number
of
men

Total
dollars
per day

Type of Work

Dollars
per foot

1
1
1

2
10
2
1
2
2
2
3
16
3
1

6.00
3.50
2.00
3.30
16.50
3.30
3.00
3.30
3.30
3.30
5.25
26.40
5.25
1.00
5.00

Excavation

1.80

0.58
0.17
0.45
0.33

1.17
1.54
0.29

0.20

0.09
0.62
0.62

Hoister (engineman)

Making and placing invert ....

Carpenter on bracing

Laying brick in invert
Bending and placing steel in
arch

Bending and placing steel in
invert

Mixing and placing concrete.
On steel forms

Moving forms and centers. . . .
Watchmen, water boy, etc. . . .

Total ....

Total .

90.40

7.86

NOTES. — Trench was 12j feet wide and of various depths. At depth of 12 feet the
cost of excavation was $1.61 per foot. From Engineering and Contracting, Vol. 47, p. 157.

BACKFILLING

197. Methods. — Careful backfilling is necessary to prevent the
displacement of the newly laid pipe and to avoid subsequent
settlement at the surface resulting in uneven street surfaces and
dangers to foundations and other structures.

The backfilling should commence as soon as the cement in the
joints or in the sewer has obtained its initial set. Clay, sand,
rock dust, or other fine compactible material is then packed by
hand under and around the pipe and rammed with a shovel and
light tamper. This method of filling is continued up to the top
of the pipe. The backfill should rise evenly on both sides of the
pipe and tamping should be continuous during the placing of the
backfill. For the next 2 feet of depth the backfill should be placed
with a shovel so as not to disturb the pipe, and should be tamped
while being placed, but no tamping should be done within 6
inches of the crown of the sewer. The tamping should become

BACKFILLING METHODS

329

progressively heavier as the depth of the backfill increases.
Generally one man tamping is provided for each man shoveling.

TABLE 70

DIVISION OP COSTS FOR THE CONSTRUCTION OF CONCRETE SEWERS

Gillette's Handbook of Cost Data.

Item

Location

Fond
du Lac

South
Bend

Wilming-
ton

Richmond, Indiana

Diameter in inches
Shape

30
circular
plain
0.11
47
1.20

39.0*
1.5
12.4
0.9
0.7
0.0
23.0
2.0
12.5
8.0
8
1908

66
circular
rein.
0.594
24 to 36
4.40

33.5
11.5
15.5

11.5
20.0
8.0

10
1906

53
horseshoe
rein.
0.37

2.97
33.0
18.9

14.5
27.5

6.1

54 48
circular circular
rein. rein.
5" shell 5" shell

1.35 1.08
17.1
19.3

28.3
32.0T

0.3

Prewar conditions

42
circular
rein.
4" shell

0.91

Plain or reinforced

Cubic yards per foot. . . .

Cost per foot, dollars ....
Per cent of total coat:
Labor

Tools

Water

Cement

Frost prevention
Forms

Length of day, hours ....
Year of construction . . . .

* Includes 6 cents per foot for excavation. Labor for this was 58 per cent of the total
labor cost.

t Cement at $1.25 per barrel.

Above a point 2 feet above the top of the sewer the method
pursued and the care observed in backfilling will depend on the
character of the backfilling material and the location of the
sewer. If the sewer is in a paved street the backfill is spread in
layers 6 inches thick and tamped with rammers weighing about
40 pounds with a surface of about 30 square inches. One man
tamping for each man shoveling is frequently specified. If no
pavement is to be laid but it is required that the finished surface
shall be smooth, slightly less care need be taken and only one
man tamping is specified for each two men shoveling. On paved
streets a reinforced concrete slab with a bearing of at least 12
inches on the undisturbed sides of the trench may be designed

330 CONSTRUCTION

to support the pavement and its loads. This is of great help
in preventing the unsightly appearance and roughness due to
an improperly backfilled trench. On unpaved streets the
backfill is crowned over the trench to a depth of about 6 inches
and then rolled smooth by a road roller. In open fields, in side
ditches, or in locations where obstruction to traffic or unsight-
liness need not be considered, after the first 2 feet of backfill have
been placed with proper care, the remainder is scraped or thrown
into the trench by hand or machine, care being taken not to
drop the material so far as to disturb the sewer.

If the top of the sewer, manhole, or other structure comes
close to or above the surface of the ground, an earth embank-
ment should be built at least 3 feet thick over and around the
structure. The embankment should have side slopes of at least
1^ on 1 and should be tamped to a smooth and even finish.

If sheeting is to be withdrawn from the trench it should be
withdrawn immediately ahead of the backfilling, and in trenches
subject to caving it may be pulled as the backfilling rises.

Puddling is a process of backfilling in which the trench is
filled with water before the filling material is thrown in. It
avoids the necessity for tamping and can be used satisfactorily
with materials that will drain well and will not shrink on drying.
Sand and gravel are suitable materials for puddling, heavy
clay is unsatisfactory. Puddling should not be resorted to before
the first 2 feet of backfill has been carefully placed. More
compact work can be obtained by tamping than with puddling.

Frozen earth, rubbish, old lumber, and similar materials
should not be used where a permanent finished surface is desired
as these will decompose or soften resulting in settlement. Rocks
may be thrown in the backfill if not dropped too far and the
earth is carefully tamped around and over them. In rock
trenches fine materials such as loam, clay, sand, etc., must be
provided for the backfilling of the first portion of the trench for
2 feet over the top of the pipe. More clay can generally be packed
in an excavation than was taken out of it, but sand and gravel
occupy more space than originally even when carefully tamped.

Tamping machines have not come into general use. One
type of machine sometimes used consists of a gasoline engine
which raises and drops a weighted rod. The rod can be swung
back and forth across the trench while the apparatus is being

BACKFILLING METHODS 331

pushed along. It is claimed that two men operating the machine
can do the work of six to ten men tamping by hand. The machine
delivers 50 to 60 blows per minute, with a 2 foot drop of the 80
to 90 pound tamping head.

Backfilling in tunnels is usually difficult because of the small
space available in which to work. Ordinarily the timbering is
left in place and concrete is thrown in from the end of the pipe
between the outside of the pipe and the tunnel walls and roof.
If vitrified pipe is used in the tunnel, the backfilling is done with
selected clayey material which is packed into place around the
pipe by workmen with long tamping tools. The backfilling
should be done with care under the supervision of a vigilant
inspector in order that subsequent settlement of the surface may
be prevented.

CHAPTER XII
MAINTENANCE OF SEWERS

198. Work Involved. — The principal effort in maintaining
sewers is to keep them clean and unobstructed. A sewerage
system, although buried, cannot be forgotten as it will not care
for itself, but becoming clogged will force itself on the attention
of the community. Besides the cleaning and repairing of
sewers and the making of inspections for determining the neces-
sity for this work, ordinances should be prepared and enforced
for the purpose of protecting the sewers from abuse. Inspec-
tions to determine the amount of the depreciation of sewers
with a view towards possible renewal, or to determine the
capacity of a sewer in relation to the load imposed upon it are
sometimes necessary. The valuation of the sewerage system
as an item in the inventory of city property may be assigned to
the engineer in charge of sewer maintenance.

The work involved in the inspection and cleaning of sewers
in New York City for the year ending May, 1914, included the
removal of 22,687 cubic yards of material from catch basins,
and 14,826 catch-basin cleanings. This made an average of
two and one-half cleanings per catch-basin per year, or 1^ cubic
yards removed at each cleaning. The 6,432 catch-basins were
inspected 71,890 times. There were 4,112 cubic yards of material
removed from 517 miles of sewers, or about 8 cubic yards per
mile. Inspection of 194 miles of brick sewers were made, 4.4
miles were flushed, and 27 miles were cleaned. Inspections of 198
miles of pipe sewers were made, 80 miles were examined more
closely, 37 miles were flushed, and 91 miles were cleaned. The
field organization for this work consisted of 17 foremen, 8
assistant foremen, 29 laborers, 71 cleaners, 13 mechanics, 7
inspectors of construction, 3 inspectors of sewer connections,
13 horses and wagons, and 28 horses and carts.1
1 Mun. Journal, Vol. 36, 1914, p. 736.
332

CAUSES OF TROUBLES 333

199. Causes of Troubles. — The complaints most frequently
received about sewers are caused by clogging, breakage of pipes,
and bad odors. Sewers become clogged by the deposition of sand
and other detritus which results in the formation of pools in
which organic matter deposits, aggravating the clogged condi-
tion of the sewers and causing the odors complained of. Grease
is a prolific cause of trouble. It is discharged into the sewer
in hot wastes, and becoming cooled, deposits in thick layers
which may effectively block the sewer if not removed. It can
be prevented from entering the sewers by the installation of
grease traps as described in Chapter VI. The periodic cleaning
of these traps is as important as their installation.

Tree roots are troublesome, particularly in small pipe sewers
in residential districts. Roots of the North Carolina poplar,
silver leaf poplar, willow, elm, and other trees will enter the
sewer through minute holes and may fill the sewer barrel com-
pletely if not cut away in time. Fungus growths occasionally
cause trouble in sewers by forming a network of tendrils that
catches floating objects and builds a barricade across the sewer.
Difficulties from fungus growths are not common, but constant
attention must be given to the removal of grit, grease, and roots.
Tarry deposits from gas-manufacturing plants are occasionally
a cause of trouble, as they cement the detritus, already deposited
into a tough and gummy mass that clings tenaciously to the
sewer.

Broken sewers are caused by excessive superimposed loads,
undermining, and progressive deterioration. The changing char-
acter of a district may result in a change of street grade, an increase
in the weight of traffic, or in the construction of other structures
causing loads upon the sewer for which it was not designed.
The presence of corrosive acids or gases may cause the deteriora-
tion of the material of the sewer.

200. Inspection. — The maintenance of a sewerage system
is usually placed under the direction of a sewer department. In
the organization of the work of this department no regular
routine of inspection of all sewers need be followed ordinarily.
Attention should be given regularly to those sewers that are
known to give trouble, whereas the less troublesome sewers
need not be inspected more frequently than once a year, pref-
erably during the winter when labor is easier to obtain.

334

MAINTENANCE OF SEWERS

The routine inspection of sewers too small to enter is made by
an examination at the manhole. If the water is running as freely
at one manhole as at the next manhole above, it is assumed
that the sewer between the manholes is clean and no further
inspection need be given unless there is some other reason to
suspect clogging between manholes. If the sewage is backed
up in a manhole it indicates that there is an obstruction in the
sewer below. If the sewage in a manhole is flowing sluggishly
and is covered with scum it is an indication of clogging, slow
velocity and septic action in the sewer . Sludge banks on the slop-
ing bottom of the manhole or signs of sewage high upon the

-Mirror

FIG. 140. — Inspecting Sewers with Reflected Sunlight.

walls indicate an occasional flooding of the sewer due to inade-
quate capacity or clogging.

If any of the signs observed indicate that the sewer is clogged,
the manhole should be entered and the sewer more carefully
inspected. Such inspection may be made with the aid of mirrors
as shown in Fig. 140 or with a periscope device as shown in Fig.
141. Sunlight is more brilliant than the electric lamp shown
in Fig. 141, but the mirror in the manhole directs the sunlight
into the eyes of the observer, dazzling him and preventing a good
view of the sides of the sewer. The observers' eyes can be pro-
tected against the direct rays of the electric light, which can be
projected against the sides of the pipe by proper shades and
reflectors. It is possible with this device to locate house con-

INSPECTION

335

nection, stoppages, breaks of the pipe, and to determine fairly
accurately the condition of the sewer without discomfort to the
observers.

Sewers that are large enough to enter should be inspected by
walking through them where possible. The inspection should be
conducted by cleaning off the sewer surface in spots with a
small broom, and examining the brick wall for loose bricks, loose
cement or cement lost from the joints, open joints, broken bond,
eroded invert, and such other items as may cause trouble. An
inspection in storm sewers is sometimes of value in detecting the
presence of forbidden house connections.

FIG. 141. — Inspecting Sewers with Periscope and Electric Light. The G-K

System.

Certain precautions should be taken before entering sewers
or manholes. If a distinct odor of gasoline is evident the sewer
should be ventilated as well as possible by leaving a number of
manhole covers open along the line until the odor of gasoline
has disappeared. The strength of gasoline odor above which
it is unsafe to enter a sewer is a matter of experience possessed
by few. A slight odor of gasoline is evident in many sewers
and indicates no special danger. A discussion of the amount of
gasoline necessary to create explosive conditions is given in
Art. 206. In making observations of the odor it should also be
noted whether air is entering or leaving the manhole. The
presence of gasoline cannot be detected at a manhole into which
ah* is entering.

336 MAINTENANCE OF SEWERS

As soon as it is considered that the odors from a sewer indicate
the absence of an explosive mixture, a lighted lantern or other
open flame should be lowered into the manhole to test the
presence of oxygen. Carbon monoxide or other asphyxiating
gases may accumulate in the sewer, and if present will extinguish
the flame. If the flame burns brilliantly the sewer is probably
safe to enter, but if conditions are unknown or uncertain, the man
entering should wear a life belt attached to a rope and tended
by a man at the surface. Asphyxiating or explosive gases are
sometimes run into without warning due to their lack of odor,
or the presence of stronger odors in the sewer. Breathing masks
and electric lamps are precautions against these dangers, the
masks being ready for use only when actually needed. More
deaths have occurred in sewers due to asphyxiating gases than
by explosions, as the average sewer explosion is of insufficient
violence to do great damage, although on occasion, extremely
violent explosions have occurred. During inspections of sewers
there should always be at least one man at the surface to call
help in case of accident and the inspecting party should consist
of at least two men.

It must not be felt that entering sewers is fraught with great
danger, as it is perfectly safe to enter the average sewer. The
air is not unpleasant and no discomfort is felt, but conditions
are such that unexpected situations may arise for which the man
in the sewer should be prepared. It is therefore wise to take
certain precautions. These may indicate to the uninitiated, a
greater danger than actually exists.

The inspection of sewers should include the inspection of the
flush-tanks, control devices, grit chambers, and other appurte-
nances. A common difficulty found with flush-tanks is that the
tank is " drooling," that is to say the water is trickling
out of the siphon as fast as it is entering the tank, and the inter-
mittency of the discharge has ceased. If, when the tank is first
inspected the water is about at the level of the top of the bell it
is probable that the siphon is drooling. A mark should be made
at the elevation of the water surface and the tank inspected again
in the course of an hour or more. If the water level is unchanged
the siphon is drooling. This may be caused by the clogging of
the snif t hole or by a rag or other obstacle hanging over the siphon
which permits water to pass before the air has been exhausted,

CLEANING SEWERS 337

or a misplacement of the cap over the siphon, or other difficulty
which may be recognized when the principle on which the siphon
operates is understood. Occasionally it is discovered that an
over zealous water department has shut off the service.

Control devices, such as leaping or overflow weirs, automatic
valves, etc., may become clogged and cease to operate satis-
factorily. They should be inspected frequently, dependent upon
their importance and the frequency with which they have been
ound to be inoperative. An inspection will reveal the obstacle
which should be removed. Floats should be examined for loss
of buoyancy or leaks rendering them useless. Grit and screen
chambers should be examined for sludge deposits.

Catch-basins on storm sewers are a frequent cause of trouble
and need more or less frequent cleaning. Cleanings are more
important than inspections for catch-basins for if they are
operating properly they are usually in need of cleaning after every
storm of any magnitude, and a regular schedule of cleaning should
be maintained.

A record should be kept of all inspections made. It should
include an account of the inspection, its date, the conditions
found, by whom made and the remedies taken to effect repairs.

201. Repairs. — Common repairs to sewerage systems consist
in replacing street inlets or catch-basin covers broken by traffic;
raising or lowering catch-basin or manhole heads to compensate
for the sinking of the manhole or the wear of the pavement;
replacing of broken pipes, loosened bricks or mortar which has
dropped out; and other miscellaneous repairs as the necessity
may arise. Connections from private drains are a source of
trouble because either the sewer or the drain has broken due
to careless work or the settlement of the foundation or the
backfill.

202. Cleaning Sewers. — Sewers too small to enter are cleaned
by thrusting rods or by dragging through them some one of the
various instruments available. The common sewer rod shown
in Fig. 142 is a hickory stick, or light metal rod, 3 or 4 feet long,
on the end of which is a coupling which cannot come undone in
the sewer. Sections of the rod are joined in the manhole and
pushed down the sewer until the obstruction is reached and
dislodged. Occasionally pieces of pipe screwed together are
used with success. The end section may be fitted with a special

338

MAINTENANCE OF SEWERS

cutting shoe for dislodging obstructions. In extreme cases these
rods may be pushed 400 to 500 feet, but are more effective at
shorter distances. Obstructions may be dislodged by shoving a
fire hose, which is discharging water under high pressure through
a small nozzle, down the sewer toward the obstruction. The
water pressure stiffens the hose, which, together with the support
from the sides of the conduit, make it possible to push the hose
in for effective work 100 feet or more from the manhole. A
strip of flexible steel about £ inch thick and 1^ to 2 inches wide
is useful for " rodding " a short length of crooked sewer.

Sewers are seldom so clogged that no channel whatever remains.
As a sewer becomes more and more clogged, the passage becomes
smaller, thereby increasing the velocity of flow of the sewage

FIG. 142.— Sewer Rods

around the obstruction and maintaining a passageway by erosion.
This phenomenon has been taken advantage of in the cleaning of
sewers by " pills." These consist of a series of light hollow balls
varying in size. One of the smaller balls is put into the sewer
at a manhole. When the ball strikes an obstruction it is caught
and jammed against the roof of the sewer. The sewage is backed
up and seeks an outlet around the ball, thus clearing a channel
and washing the ball along with it. The ball is caught at the
next manhole below. A net should be placed for catching the ball
and a small dam to prevent the dislodged detritus from passing
down into the next length of pipe. The feeding of the balls into
the sewer is continued, using larger and larger sizes, until the sewer
is clean. This method is particularly useful for the removal of
sludge deposits, but it is not effective against roots and grease.

CLEANING SEWERS

339

The balls should be sufficiently light to float. Hollow ir.et.Ll
balls are better than heavier wooden ones.

Plows and other scraping instruments are dragged through
pipe sewers to loosen banks of sludge and detritus and to cut
roots or dislodge obstructions. One form of plow consists of
a scoop l similar to a grocer's sugar scoop, which is pushed or

FIG. 143. — Cable and Windlass Method of Cleaning Sewers.

The cable is held to the bottom of the sewer by bracing a 2x4 upright in the sewer, with a
snatch block attached. A trailer is attached to the scoop to prevent loss of material.

dragged up a sewer against the direction of flow. As fast as the
scoop is filled it is drawn back and emptied. The method of
dragging this through a sewer is indicated in Fig. 143. At
Atlantic City the crew operating the scoop comprises five men,
two are at work in each manhole and one on the surface to warn
traffic and wait on the men in the manholes. The outfit of

FIG. 144. — Sewer Cleaning Device.
Eng. News, Vol. 42, 1899, p. 328.

tools is contained in a hand-drawn tool box and includes sewer
rods, metal scoops for all sizes of sewers, picks, shovels, hatchets,
chisels, lanterns, grease and root cutters, etc., and two winches
with from 400 to 600 feet of f-inch wire cable.

Another form of plow or drag consists of a set of hooks or
teeth hinged to a central bar as shown in Fig. 144. A root cutter
1 Mun. Journal, Vol. 39, 1915, p. 911.

340

MAINTENANCE OF SEWERS

and grease scraper in the form of a spiral spring with sharpened
edges, and other tools for cleaning sewers are shown in Fig. 145.
A turbine sewer cleaner shown in Fig. 146 consists of a set of
cutting blades which are revolved by a hydraulic motor of about

FIG. 145. — Tools for Cleaning Sewers.

3 horse-power under an operating pressure of about 60 pounds
per square inch. The turbine is attached to a standard fire
hose and is pushed through the sewer by utilizing the stiffness
of the hose, or by rods attached to a pushing jack as shown in
the figure. This machine was invented and patented by W. A.

FIG. 146. — Turbine Sewer Machine Connected to Forcing Jack.

The forcing jack is used when windlass and cable cannot be used.
Courtesy, The Turbine Sewer Machine Co.

Stevenson in 1914. Its performance is excellent. The blades
revo>ve at about 600 R.P.M., cutting roots and grease. The
revolving blades and the escaping water also serve to loosen
and stir up the deposits and the forward helical motion imparted
to the water is useful in pushing the material ahead of the machine

FLUSHING SEWERS 341

and in scrubbing the walls of the sewer. In Milwaukee four men
with the machine cleaned 319 feet of 12-inch sewer in 16 hours,
and in Kansas City 7,801 feet of sewers were cleaned in 14 days.

Sewers large enough to enter may be cleaned by hand. The
materials to be removed are shoveled into buckets which are
carried or floated to manholes, raised to the surface and dumped.
In very large sewers temporary tracks have been laid and small
cars pushed to the manhole for the removal of the material.
Hydraulic sand ejectors may also be used for the removal of
deposits, similar to the steam ejector pump shown in Fig. 97.
The water enters the apparatus at high velocity, under a pressure
of about 60 pounds per square inch, leaps a gap in the machine
from a nozzle to a funnel-shaped guide leading to the discharge
pipe. The suction pipe of the machine leads to the chamber
in which the leap is made. In leaping this gap the water creates
a vacuum that is sufficient to remove the uncemented detritus
large enough to pass through the machine, and will lift small
stones to a height of 10 to 12 feet. Occasionally barricades of
logs, tree branches, rope, leaves, and other obstructions which have
piled up against some inward projecting portion of the sewer,
must be removed by hand either by cutting with an axe or by
pulling them out. Projections from the sides of sewers are
objectionable because of their tendency to catch obstacles and
form barricades.

Little authentic information on the cost of cleaning sewers
is available. A permanent sewer organization is maintained
by many cities. The division of their time between repairs,
cleaning, and other duties is seldom made a matter of record.
From data published in Public Works 1 it is probable that the
cost varies from $3 to $15 per cubic yard of material removed.
From the information in Vol. II of "American Sewerage Practice"
by Metcalf and Eddy the combined cost of cleaning and flushing
will vary between $10 and $40 per mile; the expense of
either flushing or cleaning alone being about one-half of this.

203. Flushing Sewers. — Sewers can sometimes be cleaned or
kept clean by flushing. Flushing may be automatic and frequent,
or hand flushing may be resorted to at intervals to remove
accumulated deposits. Automatic flush-tanks, flushing man-
holes, a fire hose, a connection to a water main, a temporary
1 Formerly the Municipal Journal.

342 MAINTENANCE OF SEWERS

fixed dam, a moving dam, and other methods are used in flushing
sewers. The design, operation, and results obtained from the
use of automatic flush-tanks and flushing manholes are discussed
in Chapter VI.

The method in use for cleaning a sewer by thrusting a fire
hose down it can also be used for flushing sewers. It is an
inexpensive and fairly satisfactory method. There is, however,
some danger of displacing the sewer pipe because of the high
velocity of the water. An easier and safer but less effective
method is to allow water to enter at the manhole and flow down
the sewer by gravity. Direct connections to the water mains
are sometimes opened for the same purpose.

Sewers are sometimes flushed by the construction of a tempo-
rary dam across the sewer, causing the sewage to back up. When
the sewer is half to three-quarters full the dam is suddenly removed
and the accumulated sewage allowed to rush down the sewer, thus
flushing it out. The dam may be made of sand bags, boards fitted
to the sewer, or a combination of boards and bags. The expense of
equipment for flushing by this method is less than that by any
other method, but the results obtained are not always desirable.
Below the dam the results compare favorably with those obtained
by other methods, but above the dam the stoppage of the flow
of the sewage may cause depositions of greater quantities of
material than have been flushed out below. A time should be
chosen for the application of this method when the sewage is
comparatively weak and free from suspended matter. The
most convenient place for the construction of a dam is at a man-
hole in order that the operator may be clear of the rush of sewage
when the dam is removed.

Movable dams or scrapers are useful in cleaning sewers of a
moderate size, but are of little value in small sewers. The
scraper fits loosely against the sides of the sewer and is pushed
forward by the pressure of the sewage accumulated behind it.
The iron-shod sides of the dam serve to scrape grease and
growths attached to the sewer and to stir up sand and sludge
deposited on the bottom. The high velocity of the sewage
escaping around the sides of the dam aids in cleaning and
scrubbing the sewer.

A natural watercourse may be diverted into the sewer if
topographical conditions permit, or where sewers discharge

CLEANING CATCH-BASINS 343

into the sea below high tide a gate may be closed during the
flood and held closed until the ebb. The rush of sewage on the
opening of the gate serves to flush the sewers and stir up the
sludge deposited during high tide. Other methods of flushing
sewers may be used dependent on the local conditions and the
ingenuity of the engineer or foreman in charge.

In some sewers it is not necessary to remove the clogging
material from the sewer. It is sufficient to flush and push it
along until it is picked up and carried away by higher velocities
caused by steeper grades or larger amounts of sewage.

204. Cleaning Catch-basins.1 — Catch-basins have no reason
for existence if they are not kept clean. Their purpose is to
catch undesirable settling solids and to prevent them from
entering the sewers, on the theory that it is cheaper to clean a
catch-basin than it is to clean a sewer. If the cleaning of storm
sewers below some inlet to which no catch-basin is attached
becomes burdensome, the engineer in charge of maintenance
should install an adequate catch-basin and keep it clean. Catch-
basins are cleaned by hand, suction pumps, and grab buckets.
In cleaning by hand the accumulated water and sludge are
removed by a bucket or dipper and dumped into a wagon from
which the surplus settled water is allowed to run back into the
sewer. The grit at the bottom of the catch-basin is removed
by shoveling it into buckets which are then hoisted to the
surface and emptied.

Suction pumps in use for cleaning catch-basins are of the
hydraulic eductor type. The eductor works on the principle of
the steam pump shown in Fig. 97, except that water is used
instead of steam. The material removed may be discharged
into settling basins constructed in the street, or may be dis-
charged directly into wagons.2 In Chicago a special motor-
driven apparatus is used. This consists of a 5-yard body on a
5-ton truck, and a centrifugal pump driven by the truck motor.
In use, the truck, about half filled with water, drives up to the
catch-basin, the eductor pipe is lowered and water pumped from
the truck into the eductor and back into the truck again, together
with the contents of the catch-basin. The surplus water drains

1 See Eng. Record, Vol. 75, 1917, p. 463.

1 Eng. Record, Vol. 73, 1916, p. 141, and Eng. News-Record, Vol. 79,
1917, p. 1019.

344 MAINTENANCE OF SEWERS

back into the sewer. The Chicago Bureau of Sewers reports
a truck so equipped to have cleaned 1013 catch-basins, removing
1763 cubic yards of material, and running 1380 miles, during the
months of August, September and October, 1917. The cost,
including all items of depreciation, wages, repairs, etc., was
$1,393.89. Orange-peel buckets, about 20 inches in diameter,
operated by hand or by the motor of a 3| to 5-ton truck with a
water-tight body, are used for cleaning catch-basins in some cities.

Catch-basins in unpaved streets and on steep sandy slopes
should be cleaned after every storm of consequence. Basins
which serve to catch only the grit from pavement washings
require cleaning about two or three times per year, and from one to
three cubic yards of material are removed at each cleaning. The
cost of cleaning ordinary catch-basins by hand may vary from $15
to $25, but with the use of eductors or orange-peel buckets the
cost is somewhat lower. In Seattle the cost of cleaning large
detritus basins by hand is said 1 to vary from $45 to $60. With
the use of eductors this cost has been reduced to one-third or
one-fifth the cost of cleaning by hand.

205. Protection of Sewers.2 — City ordinances should be
wisely drawn and strictly enforced for the protection of sew-
ers against abuse and destruction. The requirements of some
city ordinances are given in the following paragraphs.

Washington, D. C.,3 sewer ordinances provide that:

No person shall make or maintain any connection with
any public sewer or appurtenance thereof whereby there
may be conveyed into the same any hot, suffocating,
corrosive, inflammable or explosive liquid, gas, vapor,
substance or material of any kind . . . provided that
the provisions of this act shall not apply to water from
ordinary hot water boilers or residences.

The following extracts from the ordinances of Indianapolis
are typical of those from many cities:

2950. No connection shall be made with any public
sewer without the written permission of the Committee
on Sewers and the Sewerage Engineer.

1 Eng. Record, Vol. 72, 1915, p. 690.

2 Eng. Record, Vol. 71, 1915, p. 256.

3 Eng. and Contr., Vol. 41, 1914, p. 250.

PROTECTION OF SEWERS 345

2953. No person shall be authorized to do the work
of making connections until he has furnished a satisfactory
certificate that he is qualified for the duties. He shall
also file bond for not less than SI, 000 that he will indemnify
the City from all loss or damage that may result from his
work and that he will do the work in conformity to the
rules and regulations established by the City Council.

2955. It shall be unlawful for any person to allow
premises connected to the sewers or drains to remain
without good fixtures so attached as to allow a sufficiency
of water to be applied to keep the same unobstructed.

2956. No butcher's offal or garbage, or dead animals,
or obstructions of any kind shall be thrown in any receiving
basin or sewer in penalty not greater than $100. Any
person injuring, breaking, or removing any portion of
any receiving basin, manhole cover, etc., shall be fined
not more than $100.

2962. No person shall drain the contents of any cess-
pool or privy vault into any sewer without the permission
of the Common Council.

The Cleveland ordinances are similar and contain the
following in addition :

1251. Rule 4. All connections with the main or branch
sewers shall be made at the regular connections or junctions
built into the same, except by special permit.

Rule 16. No stean pipe, nor the exhaust, nor the blow
off from any steam engine shall be connected with any
sewer.

Evanston, Illinois, protects its sewers against the additions of
grease and other undesirable substances as follows:

1444. It is unlawful for any person to use any sewer
or appurtenance to the sewerage system in any manner
contrary to the orders of the Commissioner of Public Works.

1446. Wastes from any kitchen sinks, floor drains, or
other fixtures likely to contain greasy matter from hotels,
certain apartment houses, boarding houses, restaurants,
butcher shops, packing houses, lard rendering establish-
ments, bakeries, 'launderies, cleaning establishments, gar-
ages, stables, yard and floor drains, and drains from
gravel roofs shall be made through intervening receiving
basins constructed as prescribed in par. VIII of this code.

Receiving basins suitable for the work required in the code
are illustrated in Chapter VI.

346 MAINTENANCE OF SEWERS

206. Explosions in Sewers. — Disastrous explosions in sewers
were first recorded about 1886.1 Up to about 1905 explosions
were infrequent and were considered as unavoidable accidents
and so rare as to be unworthy of study. For a decade or more
after 1905 explosions occurred with increasing violence and
frequency causing destruction of property, but by some freakish
chance, but little loss of life. A violent and destructive explosion
occurred in Pittsburgh on Nov. 25, 1913,2 and another on March
12, 1916. The property damage amounted to $300,000 to
$500,000 on each occasion, but there was no loss of life. Two
miles of pavement were ripped up, gas, water, and other sewer
pipes were broken, buildings collapsed and the streets were
flooded. The streets were rendered unserviceable for long
periods during the expensive repairs that were necessary. In
recent years the number of explosions in sewers has been smaller,
due probably to the gain in knowledge of the causes and intelli-
gent methods of prevention.

The three principal causes of explosions in sewers are: gasoline
vapor, illuminating gas, and calcium carbide. It is probable
that gasoline vapor is by far the most troublesome. Explo-
sions caused by these gases are not so violent as those caused
by dynamite or other high explosives, as the volume of gas and
the temperature generated are much less. The violence of sewer
explosions may be increased somewhat by the sudden pressures
that are put upon them.

Gasoline finds its way into sewers from garages and cleaning
establishments. A mixture of 1| per cent gasoline vapor and
ah* may be explosive. It needs only the stray spark of an
electric current, a lighted match, or a cigar thrown into the sewer
to cause the explosion. As the result of a series of experiments
on 2,706 feet of 8-foot sewer, Burrell and Boyd conclude:3

One gallon of gasoline if entirely vaporized produces
about 32 cubic feet of vapor at ordinary temperature
and pressure. If \\ per cent be adopted as the low explo-
sive limit of mixtures of gasoline vapor and air, 55 gallons
or a barrel of gasoline would produce enough vapor to
render explosive the mixture in 1,900 feet of 9 foot sewer

1 H. J. Kellogg in Journal Connecticut Society of Civil Engineers, 1914,
and Technical Paper 117, U. S. Bureau of Mines.
2Eng. News, Vol. 70, 1913, p. 1157.
Technical Paper No. 117, U. S. Bureau of Mines.

EXPLOSIONS IN SEWERS 347

provided the gasoline and the air were perfectly mixed.
Many different factors, however, govern explosibility,
such as: size of the sewer, velocity of the sewage, tem-
perature of the sewer, volatility and rate of inflow of the
gasoline. Only under identical conditions of tests would
duplicate results be obtained. A large amount of gaso-
line poured in at one time is less dangerous than the same
amount allowed to run in slowly. With a velocity of
flow of about 6? feet per second it was evident that 55
gallons of gasoline poured ah1 at once into a manhole
rendered the air explosive only a few minutes (less than
10) at any particular point. With the same amount of
gasoline run in at the rate of 5 gallons per minute, an
explosive flame would have swept along the sewer if ignited
15 minutes after the gasoline had been dumped. With
a slow velocity of flow and a submerged outlet the gasoline
vapor being heavier than air accumulated at one point
and extremely explosive conditions could result from a
small amount of gasoline. Comparatively rich explosive
mixtures were found 5 hours after the gasoline had been
discharged. High-test gasoline is much more dangerous
than the naphtha used in cleaning establishments, yet
on account of the large quantity of waste naphtha the
sewage from cleaning establishments may be very dan-
gerous.

Illuminating gas is not so dangerous as gasoline vapor as it is
lighter than air and it is more likely to escape from the sewer
than to accumulate in it. It requires about one part of
illuminating gas to seven parts of air to produce an explosive
mixture.

Calcium carbide is dangerous because it is self igniting. The
heat of the generation of gas is sufficient to ignite the explosive
mixture. The gases are highly explosive and cause a relatively
powerful explosion. Fortunately large amounts of this material
seldom reach a sewer, the gas being generated in garage drains
or traps and escaping in the atmosphere.

A hydrocarbon oil used by railroads in preventing the freezing
of switches, if allowed to reach the sewers, may cause explosions
therein.1 The oil crystallizes and in this form it is soluble in
water. It will thus pass traps and on volatilization will pro-
duce explosive mixtures.

Methane, generated by the decomposition of organic matter,

1 Eng. News, Vol. 71, 1914, p. 84.

348 MAINTENANCE OF SEWERS

is a feebly explosive gas occasionally found in sewers. Its
presence may add to the strength of other explosive mixtures.

Sewer explosions may be prevented by the building of proper
forms of intercepting basins to prevent the entrance of gasoline
and calcium carbide gases, and by ventilation to dilute the
explosive mixtures which may be made up in the sewer. There
are no practical means to predict when an explosion is about' to
occur, and after an explosion has occurred it is difficult to deter-
mine the cause as all evidence is usually destroyed.

207. Valuation of Sewers. — The necessity for the valuation
of a sewerage system may arise from the legal provisions in some
states limiting the amount of outstanding bonds which may be
issued by a municipality to a certain percentage of the present
worth of municipal property. The investment in the sewerage
system is usually great and forms a large portion of the City's
tangible property. It may be desirable also to determine the
depreciation of the sewers with a view towards their renewal.

The most valuable work on the valuation of sewers has been
done in New York City l by the engineers of the Sewer Depart-
ment. The committee of engineers appointed to do the work
recommended: (1) that the original cost be made the basis of
valuation, and that (2), in fixing this cost the cost of pavement
should be omitted or at most the cost of a cheap (cobblestone)
pavement should be included. Trenches previously excavated
in rock were considered as undepreciated assets.

The present worth of sewers depends on many factors aside
from the effects of age, such as the care exercised in the original
construction, the material used, the kind and quantity of sewage
carried, the care taken in maintenance, and finally the injury
caused by the careless building of adjoining substructures. Dur-
ing the progress of the inspections the examination of brick sewers,
due to their accessibility, yielded better results than the examina-
tion of pipe sewers. The routine of the examination of the
brick sewers consisted in cleaning off the bricks with a short
broom, tapping the brick with a light hammer to determine
solidity, and testing the cement joints by scraping with a chisel.
In addition, measurements of height and width were taken every
30 feet. The bricks in the invert at and below the flow line
were examined for wear.

1 Eng. News, Vol. 71, 1914, p. 82.'

VALUATION OF SEWERS

349

A study of the reports of these examinations disclosed that the
following defects were noticeable:

1. Cement partly out at water line.

2. Cement partly out above water line.

3. Depressed arch and sewer slightly spread.

4. Large open joints.

5. Loose brick.

6. Bond of brick broken.

7. Distorted sides, uneven bottom, joints out of line.

Age in Years.

— fw Nt --O>

100
92
84

•M

L,-

150
140

-100

- 92

- 84

76
^68

<3>

J» 60

£
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t

I-

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1

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in Bottom: Joint
i i I 1 I i 1

120

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Date of Construction
a. 6.

FIG. 147. — Diagrams used in Estimating Depreciation of Brick Sewers Due to
Age, Manhattan Borough, New York City.

o. Proportionate deterioration from various causes.

b. Percentage of depreciation based on examination of sewers, use of deterioration curve
(Fig. a), and age of sewers examined.

Eng. News, Vol. 71, p. 84.

Inspection of pipe sewers from manholes, the pipe being illu-
minated by floating candle?, was found to be unsatisfactory.
Reliance was placed on the reports of men experienced in making
connections and repairs to the sewers. Early pipe sewers in New
York were laid directly on the bottom of the trench. Under these
circumstances a small leak at a joint was sufficient to wash the
earth away and to drop the pipe, causing serious conditions
along the line. No wear or deterioration of pipe sewers were
noted, the only defects being cracking of the pipes at the center
line due to poor foundation and to defects in the pipe itself.

350

MAINTENANCE OF SEWERS

The depreciation of brick sewers as studied in New York,
is shown graphically in Fig. 147. At zero the sewer is in good
condition and at 100 it is in such a state of dilapidation as to
require instant rebuilding. Repairs are not considered economical
in this condition. In the preparation of this diagram each
condition on the list above was given a certain number of points,

Age in Years.

. c

»^

I'd

c 28
o ,9

("V '

\^V'

•5 36

* /

g-..

o 48

&SR

*> CA

hi «

D '

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0 I

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D I

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t- i
- r

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n c

u -

r> t

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71 C

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" <

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5 S c

00 00 CO CO 00

Da+e of Construction

FIG. 148. — Diagram Showing Rate of Depreciation of Pipe Sewers.

Eng. News, Vol. 71, p. 86.

which when added together represented the state of depreciation
of the sewer. These sums were plotted as ordinates and the
corresponding ages of the sewer were plotted as abscissas. The
various points were taken cumulatively, and where the bond
of the brickwork was broken (given a value of 72) plus other
defects gave a total of 164 the sewer was considered as valueless
and not worth repair. The scale of 164 was later reduced to
a percentage basis as shown on the right of the figure. Fig.
148 shows a similar diagram for the depreciation of pipe sewers.

VALUATION OF SEWERS 351

It was concluded that the life of a brick sewer in New York
is 64 years. Some of the sewers examined were over 200 years
old. The total original cost of 483 miles of brick, pipe and wood
sewers was figured as $23,880,000 with a present worth of
$18,665,000 and an average annual depreciation cf 2.2 per cent.
In figuring these amounts no account was taken of obsolescence.
The deterioration of catch-basins proceeded at about the same
rate as for brick sewers.

CHAPTER XIII
COMPOSITION AND PROPERTIES OF SEWAGE

208. Physical Characteristics. — Sewage is the spent water
supply of a community containing the wastes from domestic,
industrial, or commercial use, and such surface and ground water
as may enter the sewer.1 Sewages are classed as: domestic
sewage, industrial waste, storm water, surface water, street
wash, and ground water. Domestic sewage is the liquid dis-
charged from residences or institutions and contains water
closet, laundry, and kitchen wastes. It is sometimes called sani-
tary sewage. Industrial sewage is the liquid waste resulting
from processes employed in industrial establishments. Storm
water is that part of the rainfall which runs over the surface of
the ground during a storm and for such a short period following
a storm as the flow exceeds the normal and ordinary run-off.
Surface water is that part of the rainfall which runs over the
surface of the ground some time after a storm. Street wash
is the liquid flowing on or from the street surface. Ground
water is water standing in or flowing through the ground below
its surface.

Ordinary fresh sewage is gray in color, somewhat of the appear-
ance of soapy dish water. It contains particles of suspended
matter which are visible to the naked eye. If the sewage is
fresh the character of some of the suspended matter can be dis-
tinguished as: matches, bits of paper, fecal matter, rags, etc.
The amount of suspended matter in sewage is small, so small as
to have no practical effect on the specific gravity of the liquid
nor to necessitate the modification of hydraulic formulas
developed for application to the flow of water. The total
suspended matter in a normal strong domestic sewage is about
500 parts per 1,000,000. It is represented graphically in Fig.
149. The quantity of organic or volatile suspended matter
1 Similar to definition proposed by the Am. Public Health Ass'n.

352

PHYSICAL CHARACTERISTICS

353

is about 200 parts per 1,000,000. It is shown graphically in the
smaller cube in Fig. 149.

The odor of fresh sewage is faint and not necessarily unpleasant.
It has a slightly pungent odor, somewhat like a damp unven-
tilated cellar. Occasionally the odor of gasoline, or some other
predominating waste matter may hide all other odors. Stale
sewage is black and gives off
nauseating odors of hydrogen
sulphide and other gases. If
the sewage is so stale as to
become septic, bubbles of gas
will be seen breaking the sur-
face and a black or gray scum
may be present. Before the
South Branch of the Chicago
River was cleaned up and
flushed this scum became so
thick in places, particularly in
that portion of the Stock Yards
where the river became known
as Bubbly Creek, that it is said
that weeds and small bushes
"sprouted in it, and chickens
and small animals ran across
its surface.

A physical analysis of sewage should include an observation
of its appearance, and a determination of its temperature, tur-
bidity, color, and odor, both hot and cold. The temperature is
useful in indicating certain of the antecedents of the sewage,
its effect on certain forms of bacterial life, and its effect on the
possible content of dissolved gases. Temperatures higher than
normal are indicative of the presence of trades wastes discharged
while hot into the sewers. A low temperature may indicate
the presence of ground water. If the temperature is much over
40° C. bacterial action will be inhibited and the content of dis-
solved gases will be reduced. Turbidity, color, and odor deter-
minations may be of value in the control of treatment devices,
or to indicate the presence of certain trades wastes, which give
typical reactions. Since all normal sewages are high in color
and turbidity, the relative amounts of these two constituents

149.— Graphical Representation
of Relative Volumes of Liquids and
Solids in Sewage.

354 COMPOSITION AND PROPERTIES OF SEWAGE

in two different sewages has little significance regarding the
relative strengths of the two sewages or the proper method of
treating them. A fresh domestic sewage should have no highly
offensive odor. The presence of certain trades wastes can be
detected sometimes in fresh sewages, and a stale sewage may
sometimes be recognized by its odor.

Sewage is a liability to the community producing it. Although
some substances of value can be obtained from sewage x the cost
of the processes usually exceed the value of the substances
obtained. Where it becomes necessary to treat sewage the value
of these substances may be helpful in defraying the cost of
treatment.

209. Chemical Composition. — Sewage is composed of mineral
and organic compounds which are either in solution or are sus-
pended in water. In making a standard chemical analysis of
sewage only those chemical radicals and elements are determined
which are indicative of certain important constituents. Neither
a complete qualitative nor quantitative analysis is made. A
sewage analysis will not show, therefore, the number of grams of
sodium chloride present or any other constituent. A complete
standard sanitary chemical analysis will report the constituents
as named in the first column of Table 71. The quantities of
these materials found in average strong, medium and weak
sewages are also shown in this table. These values are not
intended as fixed boundaries between sewages of different
strengths. They are presented merely as a guide to the inter-
pretation of sewage analyses.

The principal objects of a chemical analysis of sewage are to
determine its strength and its state of decomposition. The
influents and effluents of a sewage treatment device are analyzed
to aid in the control of the device and to gain information con-
cerning the effect of the treatment. Chemical and other analyses,
in connection with the desired conditions after disposal, will
indicate the extent of treatment which may be required. The
standard methods of water and sewage analysis adopted by the
American Public Health Association have been generally accepted
by sanitarians. These uniform methods make possible com-

1 Economic Values in Sewage and Sewage Sludge, by Raymond Wells,
Proceedings Am. Society Municipal Improvements, Nov. 12, 1919. Eng.
News-Record, Vol. 83, 1919, p. 948.

CHEMICAL COMPOSITION

355

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356 COMPOSITION AND PROPERTIES OF SEWAGE

parisons of the results obtained by laboratories working according
to these standards.

210. Significance of Chemical Constituents. — Organic nitro-
gen and free ammonia taken together are an index of the organic
matter in the sewage. Organic nitrogen includes all of the
nitrogen present with the exception of that in the form of ammonia,
nitrites, and nitrates. Free ammonia or ammonia nitrogen is
the result of bacterial decomposition of organic matter. A fresh
cold sewage should be relatively high in organic nitrogen and
low in free ammonia. A stale warm sewage should be relatively
high in free ammonia and low in organic nitrogen. The sum of
the two should be unchanged in the same sewage.

Nitrites (RNO2) and nitrates (RNOs) 1 are found in fresh
sewages only in concentrations of less than one part per million.
In well-oxidized effluents from treatment plants the concen-
tration will probably be much higher. Nitrates contain one more
atom of oxygen than nitrites. They represent the most stable
form of nitrogenous matter in sewage. Nitrites are not stable
and are reduced to ammonias or are oxidized to nitrates. Their
presence indicates a process of change. They are not found in
large quantities in raw sewage because their formation requires
oxygen which must be absorbed from some other source than
the sewage. In an ordinary sewer or sluggishly flowing open
stream this absorption cannot take place from the atmosphere
with sufficient rapidity to supply the necessary oxygen.

Oxygen consumed is an index of the amount of carbonaceous
matter readily oxidizable by potassium permanganate. It does
not indicate the total quantity of any particular constituent,
but it is the most useful index of carbonaceous matter. Car-
bonaceous matter is usually difficult of treatment and a high
oxygen consumed is indicative of a sewage difficult to care for.
The amount of oxygen consumed, as expressed in the analysis,
is dependent on the amount of oxidizable carbonaceous matter
present, the oxidizing agent used, and the time and temperature
of contact of the sewage and the oxidizing agent. It is essential
therefore that the test be conducted according to some standard
method, since the results are of value only as compared with
results obtained under similar conditions.

Total solids (residue on evaporation) are an index of the
1 R represents any chemical element such as K, Na, etc.

SIGNIFICANCE OF CHEMICAL CONSTITUENTS 357

strength of the sewage. They are made up of organic and
inorganic substances. The inorganic substances include sand,
clay, and oxides of iron and aluminum, which are usually insolu-
ble, and chlorides, carbonates, sulphates and phosphates, which
are usually soluble. The insoluble inorganic substances are
undesirable in sewage because of their sediment forming prop-
erties which result in the clogging of sewers, treatment plants,
pumps, and stream beds. The soluble inorganic substances are
generally harmless and cause no nuisance, except that the
presence of sulphur may permit the formation of hydrogen
sulphide, which has a highly offensive odor. The organic sub-
stances are: carbo-hydrates, fats, and soaps, which are car-
bonaceous and are difficult of removal by biological processes;
and the nitrogenous substances such as urea, proteins, amines,
and amino acids. The inorganic and organic substances may be
either in solution or suspension or in a colloidal condition.

Volatile solids are used as an index of the organic matter
present, as it is assumed that the organic matter is more easily
volatilized than the inorganic matter. The amount of volatile
inorganic matter present is usually so small as to be negligible.

Fixed solids are reported as the difference between the total
and volatile solids. They are therefore representative of the
amount of inorganic matter present.

Suspended matter is the undissolved portion of the total
solids.. High volatile suspended matter is an indication of
offensive qualities in the nature of putrefying organic matter,
whereas fixed suspended matter is indicative of inoffensive
inorganic matter. It is difficult to obtain a sample of sewage
which will represent the amount of suspended matter in the
sewage, since a sample taken from near the surface will contain
less inorganic matter and grit than a sample taken near the bottom.

Settling solids are indicative of the sludge forming properties
of the sewage and of the probable degree of success of treatment
by plain sedimentation. Volatile settling solids indicate the
property of the formation of offensive putrefying sludge banks.
There is no chemical test which will indicate the scum-forming
properties of sewage. Fixed settling solids indicate the presence
of inorganic matter, probably gritty material such as sand, clay,
iron oxide, etc.

Colloidal matter is material which is too finely divided to be

358 COMPOSITION AND PROPERTIES OF SEWAGE

removed by filtration or sedimentation, yet is not held in solu-
tion. It can sometimes be removed by violent agitation in the
presence of a flocculent precipitate, as in the treatment with
activated sludge, or by the flocculent precipitate alone, as in
chemical precipitation, or by the acidulation of the sewage so
as to precipitate the colloids. Colloidal matter is probably the
result of the constant abrasion of finely divided suspended matter
while flowing through the sewer or other channel. High colloidal
matter may therefore indicate a stale sewage, or the presence of a
particular trades waste. Colloids are difficult of removal. For
this reason, where sewage is to be treated, turbulence in the
tributary channels should be avoided.

Alkalinity may indicate the possibility of success of the
biologic treatment of sewage, since bacterial life flourishes better
in a slightly alkaline than in a slightly acid sewage. Within
the normal limits of the amount of alkalinity in sewage the exact
amount has little significance in sewage analyses. Sewages are
normally slightly alkaline. An abnormal alkalinity or acidity
may indicate the presence of certain trades wastes necessitating
special methods of treatment. A method of sewage treatment
may be successful without changing the amount of alkalinity
in the sewage since the amount of alkalinity is not inherently
an objection.

Chlorine, in the form of sodium chloride, is an inorganic sub-
stance found in the urine of man and animals. The amount of
chlorine above the normal chlorine content of pure waters in the
district is used as an index of the strength of the sewage. The
chlorine content may be affected by certain trades wastes such
as ice-cream factories, meat-salting plants, etc., which will increase
the amount of chlorine materially. Since chlorine is an inorganic
substance which is in solution it is not affected by biological
processes nor sedimentation. Its diminution in a treatment
plant or in a flowing stream is indicative of dilution and the
reduction of chlorine will be approximately proportional to the
amount of dilution.

Fats have a recoverable market value when present in
sufficient quantity to be skimmed off the surface of the sewage.
Ordinarily fats are an undesirable constituent of sewage as they
precipitate on and clog the interstices in filtering material, they
form objectionable scum in tanks and streams, and they are acted

SIGNIFICANCE OF CHEMICAL CONSTITUENTS

359

on very slowly by biological processes of sewage treatment.
Although fats are carbonaceous matter they are not indicated
by the oxygen consumed test because they are not easily oxidized.
They are therefore determined in another manner; by evapora-
tion of the liquid and extracting the fats from the residue by
dissolving them in ether.

Relative stability and bio-chemical oxygen demand are
the most important tests indicating the putrefying character-
istics of sewage. Since stability and putrescibility have opposite
meanings the relative stability test is sometimes called the
putrescibility test. The relative stability of a sewage is an
expression for the amount of oxygen present in terms of the
amount required for complete stability.

A relative stability of 75 signifies that the sample
examined contains a supply of available oxygen equal
to 75 per cent of the amount of oxygen which it requires
in order to become perfectly stable. The available
oxygen is approximately equivalent to the dissolved oxygen
plus the available oxygen of nitrate and nitrite.1

TABLE 72
RELATIVE STABILITY NUMBERS

Time Required for
Decolorization at
20° C.
Days

Relative
Stability
Number

Time Required
for Decoloriza-
tion at 20° C.
Days

Relative
Stability
Number

0.5

8.0

1.0

1.5

10.0

2.0

11.0

2.5

12.0

3.0

13.0

4.0*

14.0

5.0

16.0

6.0

18.0

7.0

20.0

* Routine testa are ordinarily incubated for this period only, and if not decolorised in
this time are recorded as stable.

1 Standard Methods of Water Analysis, American Public Health Asso-
ciation, 1920.

360 COMPOSITION AND PROPERTIES OF SEWAGE

The relative stability numbers, given in Table 72, are computed
from the expression, S = 100(1— 0.7940 in which S is the
stability number and t is the time in days that the sample has
been incubated at 20° C. The bio-chemical oxygen demand is
more directly an index of the consumption of available oxygen
by the biological and chemical changes which take place in the
decomposition of sewage or polluted water. As such it is a
more valuable, though less easily performed test than the test
of relative stability.

The methods for the determination of the relative stability
and the bio-chemical oxygen demand are given to show more
clearly what these tests represent. The procedure in the
relative stability test is to add 0.4 c.c. of a standard solution
of methylene blue to 150 c.c. of the sample. The mixture is then
allowed to stand in a completely filled and tightly stoppered bottle
at 20° C. for 20 days or until the blue fades out due to the ex-
haustion of the available oxygen. There are three methods
in use for the determination of the biochemical oxygen demand;1
the relative stability method, the excess nitrate method, and the
excess oxygen method In the relative stability method the
sample to be treated should have a relative stability of at least
50. If it is lower than this the sample should be diluted with
water containing oxygen until the relative stability has been
raised to or above this point. The oxygen demand in parts
per million is then expressed as

0' =

in which 0' is the oxygen demand, 0 is the initial oxygen in parts
per million (p. p.m.) in the diluting water or sewage, P is the
proportion of sewage in the mixture expressed as a ratio, and
R is the relative stability of the mixture expressed as a decimal.
For the effluents from sewage treatment plants, polluted waters,
and similar liquids, the total available oxygen expressed as the
sum of the dissolved oxygen, nitrites, and nitrates, divided by

1 Determination of the Biochemical Oxygen Demand of Sewage and
Industrial Wastes, by E. J. Theriault, Report of the U. S. Public Health
Service, Vol. 35, May 7, 1920, No. 19, p. 1087.

2 Standard Methods of Water Analysis, American Public Health Asso-
ciation, 1920.

SIGNIFICANCE OF CHEMICAL CONSTITUENTS 361

the relative stability expressed as a decimal will give the bio-
chemical oxygen demand. The excess nitrate method requires
the determination of the total oxygen available as dissolved
oxygen, nitrites, and nitrates and the addition of a sufficient
amount of oxygen in the form of sodium nitrate to prevent the
exhaustion of oxygen during a 10-day period of incubation. At
the end of the period the total available oxygen is again deter-
mined. The difference between the original and the final oxygen
content represents the bio-chemical oxygen demand. The
excess oxygen test requires the determination of the total avail-
able oxygen as before, and the addition of a sufficient amount of
oxygen, in the form of dissolved oxygen in the diluting water,
to prevent exhaustion of the oxygen in a 10-day period of incu-
bation. The difference between the original and final oxygen
content represents the bio-chemical oxygen demand. Theriault
concludes as a result of his tests, that the relative stability and
excess nitrate methods are open to objections but that the excess
oxygen method yields very accurate and consistent results with
as little or less labor than is required by other methods.

Dissolved oxygen represents what its name implies, the
amount of oxygen (0%) which is dissolved in the liquid. Normal
sewage contains no dissolved oxygen unless it is unusually fresh.
It is well, if possible, to treat a sewage before the original dis-
solved oxygen has been exhausted. Normal pure surface water
contains all of the oxygen which it is capable of dissolving, as
shown in Table 73. The presence of a smaller amount of oxygen
than is shown in this table indicates the presence of organic
matter in the process of oxidation, which may be in such quanti-
ties as ultimately to reduce the oxygen content to zero. Normal
pure ground waters may be deficient in dissolved oxygen because
of the absence of available oxygen for solution. The presence
of certain oxygen-producing organisms in polluted or otherwise
potable surface waters may cause a supersaturation with oxygen
however.

The dissolved-oxygen test for polluted water is probably the
most significant of all tests. If dissolved oxygen is found in a
polluted water it means that putrefactive odors will not occur,
since putrefaction cannot begin in the presence of oxygen. It
is possible for different strata in a body of water to have different
quantities of dissolved oxygen, and putrefaction may be proceeding

362

COMPOSITION AND PROPERTIES OF SEWAGE

in the lower strata before the oxygen is exhausted from the upper
strata. The oxygen content of a river water will indicate the
ability of the river to receive sewage without resulting in a
nuisance.

TABLE 73
SOLUBILITY OF OXYGEN IN WATER

Under an atmospheric pressure of 760 mm. of mercury, the atmosphere
containing 20.9 per cent of oxygen.

Temperature, degrees C

0.00

Oxygen in parts per million . . .

14.62

14.23

13.84

13.48

13.13

12.80

12.48

12.17

Temperature, degrees C

Oxygen in parts per million. . .

11.87

11.59

11.33

11.08

10.83

10.60

10.37

10.15

Temperature, degrees C

Oxygen in parts per million. . .

9.95

9.74

9.54

9.35

9.17

8.99

8.83

•8.68

Temperature, degrees C

Oxygen in parts per million. . .

8.53

8.38

8.22

8.07

7.92

7.77

7.63

211. Sewage Bacteria. — A slight knowledge of the nature
of bacteria is necessary in order that the biological changes
which occur in the treatment of sewage may be understood.
Bacteria are living organisms which are so small that it is difficult
or impossible to study them either with the eye alone or with
the aid of powerful microscopes. They are studied by means
of cultures, stains, and certain characteristic phenomena such
as the production of a gas, the production of a red colony on
litmus lactose agar, etc. Bacteria occur in three forms:
spherical, called coccus; cylindrical, called bacillus; and spiral,
called spirillum. In size they vary from the largest at about
1/10,000 of an inch to sizes so small as to be invisible under the
most powerful microscope. An ordinary size is 1/25,000 of an
inch. The cylindrical or rod bacteria are about four times as long
as they are wide. Some bacteria possess the power of motion
due to the presence of flagella or hairs which can be moved and

ORGANIC LIFE IN SEWAGE 363

cause the cell to progress at a rate as high as 18 cm. per hour,
but usually the rate is very much less than this. The compo-
sition of the bacterial cell has never been definitely determined.

Bacteria are unicellular plants. They possess no digestive
organs and apparently obtain their food by absorption from the
surrounding media. Reproduction is by the division of the cell
info two approximately equal portions. This reproduction may
occur as frequently as once every half hour and if unchecked
would quickly mount to unimaginable numbers. The natural
cause limiting the growth of bacteria is the generation by the
bacterium of certain substances such as the amino acids, which
are injurious to cell life. The exhaustion of the food supply is
not considered as an important cause of inhibition of multipli-
cation. The products of growth of one species of bacteria may be
helpful or harmful to other forms. Where the products are
helpful the effect is known as symbiosis, and where harmful the
effect is known as antibiosis. In sewage the presence of both
aerobic and anaerobic bacteria is usually mutually helpful and
the condition is an example of symbiosis. The aerobes, some-
times called obligatory aerobes, are bacteria which demand
available oxygen for their growth. The anaerobes, or obligatory
anaerobes, can grow only in the absence of oxygen. There are
other forms that are known as facultative anaerobes (or aerobes)
whose growth is independent of the presence or absence of
oxygen.

Spores are formed by some bacteria when they are subjected
to an unfavorable environment such as high temperatures, the
absence of food, the absence of moisture, etc. Spores are cells-
in which growth and animation are suspended but the life of
the cell is carried on through the unsuitable period, somewhat
similar to the condition ir a plant seed.

212. Organic Life in Sewage. — Living organisms, both plants
and animals, exist in sewage. Bacteria are the smallest of these
organisms. Others, which can be studied easily under the
microscope or can be seen with difficulty by the naked eye but
which do not require special cultures for their study, are classed
as microscopic organisms or plankton. Organisms which are
large enough to be studied without the aid of a microscope or
special cultures are classed as macroscopic. The part taken in
the biolysis of sewage by macroscopic organisms belonging to

364 COMPOSITION AND PROPERTIES OF SEWAGE

the animal kingdom, such as birds, fish, insects, rodents, etc.,
which feed upon substances in the sewage is so inconsequential
as to be of no importance. Both plants and animals are found
among the macroscopic organisms.

Organisms in sewage may be either harmful, harmless, or
beneficial. From the viewpoint of mankind the harmful organ-
isms are the pathogenic bacteria. Their condition of life in sewage
is not normal and in general their existence therein is of short
duration. It may be of sufficient length, however, to permit
the transmission of disease. The diseases which can be trans-
mitted by sewage are only those that are contracted through
the alimentary canal, such as typhoid fever, dysentery,
cholera, etc. Diseases are not commonly contracted by contact
of sewage with the skin nor by breathing the air of sewers. It
is safe to work in and around sewage so long as the sewage is
kept out of the mouth, and asphyxiating or toxic gases are
avoided.

The beneficial organisms in sewage are those on which
dependence is placed for the success of certain methods of treat-
ment. These organisms have not all been isolated or identified.

The total number of bacteria in a sample of sewage has little
or no significance. In a normal sewage the number may be
between 2,000,000 and 20,000,000 per c.c. and because of the
extreme rapidity of multiplication of bacteria a sample showing
a count of 1,000,000 per c.c. on the first analysis may show 4 to
5 times as many 3 or 4 hours later. A bacterial analysis of
sewage is ordinarily of little or no value, since pathogenic organ-
isms are practically certain to be present, there is no interest
in the harmless organisms, and the helpful nitrifying and aerobic
bacteria will not grow on ordinary laboratory media. Occa-
sionally the presence of certain bacteria may indicate the presence
of certain trades wastes. In general, the total bacterial count,
as sometimes reported, represents only the number of bacteria
which have grown under the conditions provided. It bears no
relation to the total number of bacteria in the sample.

The presence of bacteria in sewage is of great importance
however, as practically all methods of treatment depend on
bacterial action, and all sewages which do not contain deleterious
trades wastes, contain or will support the necessary bacteria
for their successful treatment, if properly developed.

DECOMPOSITION OF SEWAGE 365

213. Decomposition of Sewage. — If a glass container be filled
with sewage and allowed to stand, open to the air, a black sedi-
ment will appear after a short time, a greasy scum may rise to
the surface, and offensive odors will be given off. This con-
dition will persist for several weeks, after which the liquid will be-
come clear and odorless. The sewage has been decomposed and is
now in a stable condition. The decomposition of sewage is brought
about by bacterial action the exact nature of which is uncertain.

It1 is well established that many of the chemical
effects wrought by bacteria, as by other living cells, are
due, not to the direct action of the protoplasm, but to
the intervention of soluble ferments or enzymes.

Enzymes are soluble ferments produced by the growth of the
bacterial cell.

In 2 many cases the enzymes diffuse out from the
cell and exert their effort on the ambient substances . . .
in others the enzyme action occurs within the cell and
the products pass out, (for example) . . . the alcohol-
producing enzymes of the yeast cell act upon sugar within
the cell, the resulting alcohol and carbon dioxide being
ejected.

Other chemical effects may be brought about by the direct action
of the living cells, but this has never been well established.

Metabolism is the life process of living cells by which they
absorb their food and convert it into energy and other products.
It is the metabolism of bacterial growth that in itself or by the
production of enzymes hastens the putrefactive or oxidizing
stages of the organic cycles in sewage treatment. Bacteria can
assimilate only liquid food since they have no digestive tract
through which solid food can enter. The surrounding solids
are dissolved by the action of the enzymes, the resulting solution
diffusing through the chromatin or outer skin, and being digested
throughout the interior cytoplasm.

Bacteria are sometimes classified as parasites and saprophytes.
The parasites live only on the growing cells of other plant or
animal life. The saprophytes obtain their food only from the

1 Jordan, General Bacteriology, 1909, p. 91.
* Ibid.

366 COMPOSITION AND PROPERTIES OF SEWAGE

life products of living organisms and do not exist at the expense
of the organisms themselves. Facultative saprophytes (or
parasites) may exist on either living or dead tissue.

The decomposition of sewage may be divided into anaerobic
and aerobic stages. These conditions are usually, but not
always, distinctly separate. The growth of certain forms of
bacteria is concurrent, while the growth of other forms is dependent
on the results of the life processes of other bacteria in the early
stages of decomposition.

When sewage is very fresh it contains some oxygen. This
oxygen is quickly exhausted so that the first important step in
the decomposition of sewage is carried on under anaerobic condi-
tions. This is accompanied by the creation of foul odors of
organic substances, ammonia, hydrogen sulphide, etc.; other
odorless gases such as carbon dioxide, hydrogen, and marsh
gas, the latter being inflammable and explosive; and other com-
plicated compounds. An exception to the rule that putrefac-
tion takes place only in the absence of oxygen is the production
of other foul-smelling substances by the putrefactive activity
of obligatory and facultative aerobes. Hydrogen sulphide may
be produced apparently in the presence of oxygen the action
which takes place not being thoroughly understood.

The biolysis of sewage is the term applied to the changes
through which its organic constituents pass due to the metab-
olism of bacterial life. Organic matter is composed almost
exclusively of the four elements: carbon, oxygen, hydrogen,
and nitrogen (COHN) and sometimes in addition sulphur and
phosphorus. The organic constituents of sewage can be divided
into the proteins, carbohydrates, and fats. The proteins are
principally constituents of animal tissue, but they are also found
in the seeds of plants. The principal distinguishing character-
istic of the proteins is the possession of between 15 and 16 per cent
of nitrogen. To this group belong the albumens and casein.
The carbohydrates are organic compounds in which the ratio
of hydrogen to oxygen is the same as in water, and the number
of carbon atoms is 6 or a multiple of 6. To this group belong
the sugars, starches and celluloses. The fats are salts formed,
together with water, by the combination of the fatty acids with
the tri-acid base glycerol. The more common fats are stearin,
palmatin, olein, and butyrine. The soaps are mineral salts of the

THE NITROGEN CYCLE 367

fatty acids formed by replacing the weak base glycerol with some
of the stronger alkalies.

The first state in the biolysis of sewage is marked by the
rapid disappearance of the available oxygen present in the water
mixed with organic matter to form sewage. In this state the
urea, ammonia, and other products of digestive or putrefactive
decomposition are partially oxidized and in this oxidation the
available oxygen present is rapidly consumed, the conditions
in the sewage becoming anaerobic. The second state is putre-
faction in which the action is under anaerobic conditions. The
proteins are broken down to form urea, ammonia, the foul-
smelling mercaptans, hydrogen sulphide, etc., and fatty and
aromatic acids. The carbohydrates are broken down into their
original fatty acid, water, carbon dioxide, hydrogen, methane,
and other substances. Cellulose is also broken down but much
more slowly. The fats and soaps are affected somewhat similarly
to the hydrocarbons and are broken down to form the original
acids of their make up together with carbon dioxide, hydrogen,
methane, etc. The bacterial action on facts and soaps is much
slower than on the proteins, and the active biological agents
in the biolysis of the hydrocarbons, fats, and soaps are not so
closely confined to anaerobes as in the biolysis of the proteins.
The third state in the biolysis of sewage is the oxidation or
nitrification of the products of decomposition resulting from
the putrefactive state. The products of decomposition are
converted to nitrites and nitrates, which are in a stable condition
and are available for plant food. It must be understood that
the various states may be coexistent but that the conditions
of the different states predominate approximately in the order
stated. In the biolysis of sewage there is no destruction of matter.
The same elements exist in the same amount as at the start of the
biolytic action.

214. The Nitrogen Cycle. — Nitrogen is an element that is
found in all organic compounds. Its presence is necessary to all
plant and animal life. The nitrogenous compounds are most
readily attacked by bacterial action in sewage treatment. The
non-nitrogenous substances such as soaps and fats, and the inor-
ganic compounds are more slowly affected by bacterial action
alone. The element nitrogen passes through a course of events
from life to death and back to life again that is known as the

368 COMPOSITION AND PROPERTIES OF SEWAGE

Nitrogen Cycle. It is typical of the cycles through which all
of the organic elements pass.

Upon the death of a plant or animal, decomposition sets in
accompanied by the formation of urea which is broken down
into ammonia. This is known as the putrefactive stage of the
Nitrogen Cycle. The next state is nitrification in which the
compounds of ammonia are oxidized to nitrites and nitrates,
and are thus prepared for plant food. In the state of plant life
the nitrites and nitrates are denitrified so as to be available as a
plant or animal food. The highest state of the Nitrogen Cycle
is animal life, in which nitrogen is a part of the living animal
substance or is charged from protein to urea, ammonia, etc., by
the functions of life in the animal. Upon the death of this
animal organism the cycle is repeated. The Nitrogen Cycle,
like the cycle of Life and Death, is purely an ideal condition as
in nature there are many short circuits and back currents which
prevent the continuous progression of the cycle. The con-
ception of this cycle is an aid, however, in understanding the
processes of sewage treatment.

215. Plankton and Macroscopic Organisms. — In general
the part played by these organisms in the biolysis of sewage is
not sufficiently well understood to aid in the selection of methods
of sewage treatment involving their activities. The presence
in bodies of water receiving sewage, of certain plankton which
are known to exist only when putrefaction is not imminent,
indicates that the body of water into which the discharge of
sewage is occurring is not being overtaxed. The control of sewage
treatment plant effluents so as to avoid the poisoning of fish life
or the contamination of shell fish is likewise important. The
study of plankton and macroscopic life in the treatment of sewage
is an open field for research.

216. Variations in the Quality of Sewage. — The quality of
sewage varies with the hour of the day and the season of the
year. Some of the causes of these variations are: changes in the
amount of diluting water due to the inflow of storm water or
flushing of the streets or sewers; variations in domestic activities
such as the suspension of contributions of organic wastes during
the night, Monday's wash, etc.; characteristics of different
industries which discharge different kinds of wastes according
to the stage of the manufacturing process, etc. In general

VARIATIONS IN THE QUALITY OF SEWAGE

369

TABLE 74

SEWAGE ANALYSES SHOWING HOURLY, DAILY, AND SEASONAL VARIATIONS

IN QUALITY

Place

Time

Total
Nitro-
gen

Chlo-
rine

Sus-
pended
Matter

Remarks

Refer-
ence

Marion Ohio

Mid't-noon, 5-21-06.

190

Industrial

Noon-mid't 5-21-O6.

133

Domestic

Westerville, Ohio

Day

10.2

118

\ college

Night

2.6

\ town

Columbus, Ohio

1904-1905

Mid't to 2 a.m.

4.6

131

2 a.m. to 4 a.m.

3.0

4 a.m. to 6 a.m.

2.3

6 a.m. to 8 a.m.

2.7

8 a.m. to 10 a.m.

16.3

476

10 a.m. to noon

11.4

100

324

Noon to 2 p.m.

11.3

246

2 p.m. to 4 p.m.

12.3

246

4 p.m. to 6 p.m.

22.0

368

6 p.m. to 8 p.m.

8.2

209

8 p.m. to 10 p.m.

7.8

120

10 p.m. to mid't

6.2

117

Center Ave., Chicago .

Mid't to 3 a.m.

123

4 a.m. to 7 a.m.

316

8 a.m. to 11 a.m.

608

Noon to 3 p.m.

785

4 p.m. to 7 p.m.

717

8 p.m. to 11 p.m.

287

Columbus, Ohio

Sunday

6.7

858

Monday

9.1

1048

Tuesday

9.4

1024

Wednesday

9.6

1005

Thursday

9.2

990

Friday

9.2

1018

Saturday

9.3

1016

Baltimore, 1907-1908

Aug. 1 to Sept. 1

16.0

246

Sept. 4 to Oct. 3

19.0

190

Oct. 6 to Nov. 4

20.0

188

Nov. 15 to Nov. 29

20.0

164

Dec. 3 to Dec. 29

20.0

123

Jan. 6 to Jan. 21

19.0

127

Feb. 2 to Feb. 26

20.0

149

Feb. 29 to Mar. 24

28.0

274

Mar. 27 to April 29

25.0

165

April 30 to May 26

19.0

104

June 8 to July 1 1

15.0

July 13 to Aug. 8

9.5

124

References:

1. 1908 Report of the Ohio State Board of Health.

2. Report on Sewage Purification at Columbus, Ohio, by G. A. Johnson, 1905.

3. Report on Industrial Wastes from the Stock Yards and Packingtown in Chicago, by

the Sanitary District of Chicago. 1921.

4. Report of the Baltimore Sewerage Commission, 1911.

370 COMPOSITION AND PROPERTIEvS OF SEWAGE

night sewage is markedly weaker than day sewage in both domestic
and industrial wastes, but in specific cases the varying strength
depends entirely upon the characteristics of the district. Some
analyses are given in Table 74, which emphasize these
points.

217. Sewage Disposal. — Previous to the development of the
water-carriage method for removing human excreta and other
liquid wastes the solid matter was disposed of by burial and the
liquid wastes were allowed to seep into the ground or to run
away over its surface. Following the development of the water-
carriage system, which necessitated the development of sewers,
the problem of ultimate disposal was rendered more serious by
the concentration of human excreta together with a large volume
of water. The unthinking citizen believes the problem of sewage
disposal is solved when the toilet is flushed or the bath tub is
drained. The problem may more truly be said to commence
at this point.

It would appear that the simplest method of disposal of
sewage would be to discharge it into the nearest water course.
Unfortunately the nature of sewage is such that it may be either
highly offensive to the senses or dangerous to health or both,
when discharged in this manner. Only the most fortunate,
communities are favored with a body of water of sufficient size
to receive sewage without creating a nuisance.

The problems of sewage disposal are to prevent nuisances
causing offense to sight and smell; to prevent the clogging of
channels; to protect pumping machinery; to protect public
water supplies; to protect fish life; to prevent the contamination
of shell fish; to recover valuable constituents of the sewage;
to enrich and to irrigate the soil; to safeguard bathing and boat-
ing; for other minor purposes; and in some cases to comply with
the law. Sewage may be treated to attain one or more of these
objects by methods of treatment varying as widely as the objects
to be attained.

218. Methods of Sewage Treatment. — In studying the sub-
ject of sewage treatment it must be borne in mind that it is
impossible to destroy any of the elements present. They may be
removed from the mixture only by gasification, straining or
sedimentation. Their chemical combinations may be so changed,
however, as to result in different substances than those intro-

METHODS OF SEWAGE TREATMENT 371

duced to the treatment plant. It is with these chemical changes
that the student of sewage treatment is interested.

The methods of sewage treatment can be classified as mechan-
ical, chemical and biological. These classifications are not sepa-
rated by rigid lines but may overlap in certain treatment devices
or methods. Mechanical methods of treatment are exemplified
by sedimentation, and screening. Chemical precipitation and
sterilization are examples of chemical methods. The biological
methods, the most important of all, include dilution, septiciza-
tion, filtration, sewage farming, activated sludge, etc. If for
any reason it is desired to treat sewage by more than one of these
methods the procedure should follow as nearly as possible the
order of the occurrence of the phenomena in the natural biolysis
of sewage. For example, in one treatment plant the sewage
would first pass through a grit chamber where the coarse sediment
would be removed, then through a screen where the floating
matter and coarse suspended matter would be removed, then
to a sedimentation basin where some finer suspended matter
might settle out, then to a digestive tank where the solid matter
deposited would be worked upon by bacterial action and partially
liquefied. Simultaneous to the liquefaction of the deposited
solid matter the liquid effluent from the digestive tank might
proceed to an aerating device to expedite oxidation, then to an
aerobic filter, and finally to disposal by dilution.

CHAPTER XIV
DISPOSAL BY DILUTION

219. Definition. — Disposal of sewage by dilution is the dis-
charge of raw sewage or the effluent from a treatment plant into
a body of water of sufficient size to prevent offense to the senses
of sight and smell, and to avoid danger to the public health.

220. Conditions Required for Success. — Among the desired
conditions for successful disposal by dilution are: adequate
currents to prevent sedimentation and to carry the sewage
away from all habitations before putrefaction sets in, or sufficient
diluting water high in dissolved oxygen to prevent putrefaction;
a fresh or non-septic sewage; absence of floating or rapidly
settling solids, grease or oil; and absence of back eddies or
quiet pools favorable to sedimentation in the stream into which
disposal is taking place. The conditions which should be pre-
vented are: offensive odors due to sludge banks, the rise of septic
gases, and unsightly floating or suspended matter. In some
instances the pollution of the receiving body of water is undesirable
and the sewage must be freed from pathogenic organisms and the
danger of aftergrowths minimized before disposal. Such con-
ditions are typified at Baltimore, where the sewage is discharged
into Back Bay, an arm of Chesapeake Bay. One of the impor-
tant industries of the state of Maryland is the cultivation of oysters.
The pollution of the Bay was therefore so objectionable that care-
ful treatment of the Baltimore sewage has been a necessary
preliminary to final disposal by dilution. It is unwise to draw
public water supplies, without treatment, from a stream receiving
a sewage effluent, no matter how careful or thorough the treat-
ment of the sewage. The treatment of the sewage is a safe-
guard, and lightens the load on the water purification plant,
but under no considerations can it be depended upon to protect
the community consuming the diluted effluent.

372

SELF-PURIFICATION OF RUNNING STREAMS 373

The sewer outlet should be located well out in the current of
the stream, lake, or harbor. Deeply submerged outlets are
usually better than an outlet at the surface, as a better mixture
of the sewage and water is obtained. The discharge of sewage
into a body of water of which the surface level changes, alternately
covering and exposing large areas of the bottom is unwise, as the
ludge which is deposited during inundation will cause offensive
odors when uncovered. Such conditions must be carefully
guarded against when selecting a point of disposal in tidal
estuaries because of the frequent fluctuations in level.

221. Self-Purification of Running Streams. — The self -purifi-
cation of running streams is due to dilution, sedimentation, and
oxidation. The action is physical, chemical, and biological.
When putrescible organic matter is discharged into water the
offensive character of the organic matter is minimized by dilution.
If the dilution is sufficiently great, it alone may be sufficient to
prevent all nuisance. The oxidation of the organic matter
commences immediately on its discharge into the diluting water
due to the growth and activity of nitrifying and other oxidizing
organisms and to a slight degree to direct chemical reaction.
So long as there is sufficient oxygen present in the water septic
conditions will not exist and offensive odors will be absent.
When the organic matter is completely nitrified or oxidized
there will be no further demand on the oxygen content of the
stream and the stream will be said to have purified itself. At
the same time that this oxidation is going on some of the organic
matter will be settling due to the action of sedimentation. If
oxidation is completed before the matter has settled on the
bottom the result will be an inoffensive silting up of the river.
If oxidation is not complete, however, the result will be offensive
putrefying sludger banks which may send their stinks up through
the superimposed layers of clean water to pollute the surrounding
atmosphere.

The most important condition for the successful self-purifi-
cation of a stream is an initial quantity of dissolved oxygen to
oxidize all of the organic matter contributed to it, or the addition
of sufficient oxygen subsequent to the contribution of sewage to
complete the oxidation. Oxygen may be added through the dilu-
tion received from tributaries, through aeration over falls and
rapids, or by quiescent absorption from the atmosphere. The

374 DISPOSAL BY DILUTION

rapidity of self-purification is dependent on the character of the
organic matter, the presence of available oxygen, the rate of
reaeration, temperature, sedimentation, and the velocity of the
current. Sluggish streams are more likely to purify themselves
in a shorter distance and rapidly flowing turbulent streams
are more likely to purify themselves in a shorter time, other
conditions being equal. Although the absorption of oxygen by
a stream whose surface is broken is more rapid than through a
smooth unbroken surface, the growth of algse, biological activity,
the effect of sunlight, and sedimentation are more potent factors
and have a greater effect in sluggish streams than the slightly
more rapid absorption of oxygen in a turbulent stream. It is
frequently more advantageous to discharge sewage into a
swiftly moving stream, however, regardless of the conditions
of self-purification, as the undesirable conditions which may
result occur far from the point of disposal and may be offensive
to no one.

The sewage from a population of about 3,000,000 persons
residing in and about Chicago is discharged into the Chicago
Drainage Canal. It ultimately reaches tide water through
the Des Plaines, the Illinois, and the Mississippi Rivers. The
action occurring in these channels is one of the best illustrations
known of the self-purification of a stream. In Table 75 are
shown the results of analyses of samples taken at various points
below the mouth of the Chicago River where the diluting water
from Lake Michigan enters, to Grafton, Illinois, at the junction
of the Illinois and Mississippi Rivers about 40 miles above St.
Louis. The effect of the physical characteristics of the stream
on its chemical composition is well illustrated in this table.
The rise in the chlorine content between Lake Michigan and the
entrance to the Drainage Canal is a measure of the addition
of sewage. Since the chlorine is an inorganic substance which
is not affected by biologic action, its loss in concentration in the
lower reaches of the rivers is due to dilution by tributaries and
sedimentation, e.g., between the end of the canal at Lockport
and the sampling point at Joliet, the entrance of the Des Plaines
River reduces the concentration of chlorine from 124.5 to 41.5
parts per million. The entrance of the Kankakee River at
Dresden Heights further reduces the chlorine to 24.5 p. p.m.
The - increase of albuminoid and ammonia nitrogen accompanied

SELF-PURIFICATION OF RUNNING STREAMS

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376 DISPOSAL BY DILUTION

by a decrease in nitrites and nitrates, between the upper end
of the canal at Bridgeport and its lower end at Lockport indicates
the reducing action proceeding therein. The oxidizing action
over the various dams and the effect of dilution with water
containing oxygen is shown between miles 34 and 38, at mile 79,
and at mile 294. The excellent effect of quiescent sedimentation
and aeration in Peoria Lakes is shown between miles 145, 161 and
165.

222. Self-Purification of Lakes. — Sewage may be disposed of
into lakes with as great success as into running streams if condi-
tions exist which are favorable to self-purification. Lakes and
rivers purify themselves from the same causes; oxidation, sedi-
mentation, etc., but in the former the currents are much less
pronounced and may be entirely absent. In shallow lakes
(20 feet or less in depth) dependence must be placed on horizontal
currents and the stirring action of the wind to keep the water
in motion in order that the sewage and the diluting water may
be mixed. In deeper bodies of water, currents induced by the
wind are helpful but entire dependence need not be placed upon
them. Vertical currents, and the seasonal turnovers in the spring
and fall completely mix the waters of the lake above those layers
of water whose temperature never rises higher than 4° C.

In the early winter the cold air cools the surface waters of
a lake. The cooling increases the density of the surface water
causing it to sink, and allowing the warmer layers below to rise
and become cooled. After the temperature of the entire lake
has reached 4° C. the vertical currents induced by temperature
cease, as continued cooling decreases the density of the surface
water maintaining the same layer at the surface. In the spring
as the temperature of the surface water rises to 4° C. and above
it becomes heavier and drops through the colder water below
causing vertical currents. These phenomena are known as the
fall and spring turnovers. The former is more pronounced.
These turnovers are effective in assisting in the self-purification
of lakes.

223. Dilution in Salt Water. — The oxygen content in salt
water is about 20 per cent less than in fresh water at the same
temperature. The greater content of matter in solution in
salt- water reduces its capacity to absorb many sewage solids.
This, together with the chemical reaction between the constitu-

QUANTITY OF DILUTING WATER NEEDED 377

ents of the salt water and those of the sewage,, serve to precipitate
some of the sewage solids and to form offensive sludge banks.
The evidence of the action which takes place in the absorption
of oxygen from the atmosphere by salt water and its effect on
dissolved sewage solids is conflicting, but in general fresh water
is a better diluting medium than salt water.

Black and Phelps have made valuable studies of the relative
rates of absorption of oxygen from the air by fresh and salt water.
The results of their experiments are published in a Report to the
Board of Estimate and Apportionment of N. Y. City, made
March 23, 19 II.1 Concerning these rates they conclude:

Therefore there is no reason to believe that the
reaeration of salt water follows any other laws than
those we have determined mathematically and experi-
mentally for fresh water. In the absence of fuller infor-
mation on the effect of increased viscosity upon the
diffusion coefficient, it can only be stated that the rate
of reaeration of salt water is less than that of fresh water,
in proportion to the respective solubilities of oxygen in
the two waters, and still less, but to an unknown extent,
by reason of the greater viscosity and consequent small
value of the diffusion coefficient.

224. Quantity of Diluting Water Needed. — In a large majority
of the problems of disposal of sewage by dilution it is not neces-
sary to add sufficient diluting water to oxidize completely all
organic matter present. Ordinarily it is sufficient to prevent
putrefactive conditions until the flow of the stream, lake, or
tidal current, has reached some large body of diluting water
or where putrefaction is no longer a nuisance. It is never desirable
to allow the oxygen content of a stream to be exhausted as putres-
cible conditions will exist locally before exhaustion is complete.
The exact point to which oxygen can be reduced in safety is in
some dispute. Black and Phelps have assumed 70 per cent of
saturation as the allowable limit; Fuller has placed it at 30
per cent; Kinnicutt, Winslow, and Pratt have placed it at 50
per cent. Since the reaction between the oxygen and the organic
matter is quantitative, others have placed the limit in terms of
parts per million of oxygen. Wisner,2 has recommended a mini-

1 Reprinted in Vol. Ill of Contributions from the Sanitary Research
Laboratory of Massachusetts Institute of Technology.

1 Formerly Chief Engineer of the Sanitary District of Chicago.

378 DISPOSAL BY DILUTION

mum of 2.5 p. p.m. as the limit for the sustenance of fish life,
which is not far from Fuller's limit for hot-weather conditions.

Formulas of various types have been devised to express the
rate of absorption of oxygen with a given quantity of diluting
water which is mixed with a given quantity and quality of sewage.
The quantity of sewage is sometimes expressed in terms of the
tributary population or in other ways. Knowing the rate at
which oxygen is exhausted and the velocity of flow of the stream,
the point at which the oxygen will be reduced to the limit allowed
is easily determined. The accuracy of none of these formulas
has been proven, and their use, without an understanding of the
effect of local conditions, may lead to error. They may be used
as a check on the bio-chemical oxygen demand determinations,
which should be conclusive.

The following formula, based on the work of Black and
Phelps, is a guide to the amount of sewage which can be added
to a stream without causing a nuisance. It is:

logo~

r< — —

kt >

in which C =per cent of sewage allowed in the water;

O'=per cent of saturation or the p.p.m. of oxygen in

the mixture at the time of dilution;
0=per cent of saturation or the p.p.m. of oxygen in
the stream after period of flow to point beyond
which no nuisance can be expected;
J=time in hours required for the stream to flow to

this point;

k= constant determined by test determinations of
the factors in the following expression:

i °'i
log 7^-

, _

in which 0'\ = per cent of saturation or the p.p.m. of oxygen in

the diluting water before mixing with the sewage;

Oi=per cent of saturation or the p.p.m. of oxygen

in an artificial mixture made in the laboratory,

after t\ hours of incubation;

QUANTITY OF DILUTING WATER NEEDED 379

Ci =per cent of sewage in the mixture;
ti = number of hours of incubation of the mixture of

sewage and diluting water under laboratory

conditions.

In the solution of these formulas it is desired to determine
the permissible amount of sewage to discharge into a given
quantity of diluting water. This value is expressed by C in the
first equation. In solving this equation:

0' is determined by laboratory tests and should repre-
sent the conditions to be expected during
various seasons of the year;

0 is determined by judgment. It may be 30 per cent

or 50 per cent or more as previously explained;

t is determined by float tests or other measurements
of the stream flow;

k is determined by laboratory tests in which mix-
tures of various strengths are incubated for vari-
ous periods of time. Different values of k will
be obtained for different characteristics of the
sewage; but for the same sewage the value of k
should be unchanged for different periods of
incubation.

Rideal devised the formula: 1

XO = C(M-N)S

in which X = flow of the stream expressed in second feet;

0 = grams of free oxygen in one cubic foot of water;
S =rate of sewage discharge in second feet;
M = grams of oxygen required to consume the organic

matter in one cubic foot of diluted sewage as

determined by the permanganate test with 4

hours boiling;
N = grams of oxygen available in the nitrites and

nitrates in one cubic foot of diluted sewage;
C = ratio between the amount of oxygen in the stream

and that required to prevent putrefaction. Where

C is equal to or greater than one, satisfactory

conditions have been attained.

1 From " Sewage," by Samuel Rideal, 1900, p. 16.

380 DISPOSAL BY DILUTION

In using this formula it is necessary to make analyses of trial
mixtures of sewage and water until the correct mixture has been
found.

Hazen's formula is: 1

x 4m
D=S=~0~>

in which D = dilution ratio;

x = volume of water;

S= volume of sewage;

m= result of the oxygen consumed test expressed in

p.p.m. after 5 minutes, boiling with potassium

permanganate;
0 = amount of dissolved oxygen in the diluting water

expressed in p.p.m.

For comparison with RideaFs formula the factor of 7 should be
used instead of 4 to allow for the increased time of boiling.

Since the amount of oxygen needed is dependent on the amount
of organic matter in the sewage rather than the total volume of
the sewage, and since the amount of organic matter is closely
proportional to the population, the amount of diluting water has
sometimes been expressed in terms of the population. Hering's
recommendation for the quantity of diluting water necessary for
Chicago sewage was 3.3 cubic feet of water per second per
thousand population. Experience has proven this to be too small.
Between a minimum limit of 2 second-feet and a maximum of 8
second-feet of diluting water per thousand population the success
of dilution is uncertain. Above this limit success is practically
assured and below this limit failure can be expected.

Even with these carefully devised formulas and empirical
guides, the factors of reaeration, dilution, sedimentation, tem-
perature, etc., may have so great an effect as to vitiate the con-
clusions. As shown in Table 75 dilution in winter is far more
successful than in summer. The lower temperatures so reduce
the activity of the putrefying organisms that consumption of
oxygen is greatly retarded.

225. Governmental Control. — A comprehensive discussion
of the legal principles governing the pollution of inland waters

1 See Am. Civil Engineers' Pocket Book, Second Edition, p. 982.

PRELIMINARY TREATMENT 381

is contained in " A Review of the Laws Forbidding the Pollution
of Inland Waters," by E. B. Goodell, published by the United
States Geological Survey in 1905, as Water Supply Paper No. 152.
The disposal of sewage by dilution is subject to statutory
limitations in many states. The enforcement of these laws is
usually in the hands of the state board of health, which is fre-
quently given discretionary powers to recommend and some-
times to enforce measures for the abatement of an actual or
potential nuisance. Such recommendations usually take the
form of a specification of certain forms of treatment preliminary
to disposal by dilution. No project for the disposal of sewage
by dilution should be consummated until the local, state,
national, and in the case of boundary waters, international laws
have been complied with. The attitude of the courts in dif-
ferent states has not been uniform. Little guidance can be taken
from the personal feeling of the persons immediately interested.
The opinion of the riparian owner 5 miles down stream may differ
materially from the popular will of the voters of a city, and it is
likely to receive a more favorable hearing from the court.
Statutes and legal precedents are the safest guides.

226. Preliminary Treatment. — If the sewage to be disposed
of by dilution contains unsightly floating matter, oil, or grease,
no amount of oxygen in the diluting water will prevent a nuisance
to sight, or the formation of putrefying sludge banks. Under
such conditions it will be necessary to introduce screens or sedi-
mentation basins, or both, in order to remove the floating and the
settling solids. Biologic tanks, filtration, or other methods of
treatment may be necessary for the removal of other undesirable
constituents.

227. Preliminary Investigations. — Before adopting disposal
of sewage by dilution without preliminary treatment, or before
considering the proper form of treatment necessary to render
disposal by dilution successful, a study should be made of the
character of the body of water into which the sewage or effluent
is to be discharged. This study should include: measurements
of th"1 quantity of water available at all seasons of the year:
analyses of the diluting water to determine particularly the
available dissolved oxygen: observations of the velocity and
direction of currents, and the effect of winds thereon: a study
of the effect on public water supplies, bathing beaches, fish life,

382 DISPOSAL BY DILUTION

etc. Good judgment, aided by the proper interpretation of
such information should lead to the most desirable location for
the sewer outlet. If preliminary treatment is found to be neces-
sary tests should be made to determine the necessary extent and
thoroughness of the treatment.

CHAPTER XV
SCREENING AND SEDIMENTATION

228. Purpose. — The first step in the treatment of sewage
is usually that of coarse screening in order to remove the larger
particles of floating or suspended matter. Screens and sedi-
mentation basins are used to prevent the clogging of sewers,
channels, and treatment plants; to avoid clogging of and injuries
to machinery; to overcome the accumulation of putrefying
sludge banks; to minimize the absorption of oxygen in diluting
water; and to intercept unsightly floating matter.

By the plain sedimentation of sewage is meant the removal
of suspended matter by quiescent subsidence unaffected by
septic action or the addition of chemicals or other precipitants.
In order to prevent septic action plain sedimentation tanks must
be cleaned as frequently as once or twice a week in warm weather
but not quite so often in cold weather.

Fine screening may take the place of sedimentation where
insufficient space is available for sedimentation tanks, and it is
desired to remove only a small portion of the suspended matter.
Recent American practice has tended to restrict the field of fine
screening to treatment requiring less than 10 per cent removal
of suspended matter, thus eliminating screens from the field
covered by plain sedimentation tanks. The practice is well
expressed by Potter, who states: 1

Where a high degree of purification is sought, the use
of fine screens is of doubtful value. A modern settling
tank will give better results and at a less cost for a given
degree of purification. A settled liquid is also superior
to a screened liquid for subsequent biological treatment
in filters. . . . Again the storing of large quantities of
screenings must necessarily be more objectionable than
the storing of the digested sludge of a modern settling
tank.

1 Trans. Am. Society Civil Engineers, Vol. 58, 1907, p. 988.
383

384

SCREENING AND SEDIMENTATION

229. Types of Screens. — The definitions of some types of
screens as proposed by the American Public Health Association
follow: A bar screen is composed of parallel bars or rods. A
mesh screen is composed of a fabric, usually wire. A grating
consists of 2 sets of parallel bars in the same plane in sets inter-
secting at right angles. A band screen consists of an endless
perforated band or belt which passes over upper and lower
rollers. A perforated plate screen is made of an endless band
of perforated plates similar to a band screen. A wing screen
has radial vanes uniformly spaced which rotate on a horizontal
axis. A disc screen consists of a circular perforated disc with
or without a central truncated cone of similar material mounted

(.-Band Screen. 2.- Wing Screen.

3.- Shovel -Vane
Screen.

4.- Drum Screen.

5-Riensch-Wurl
Screen.

FIG. 150. — Types of Moving Screens.
Trans. Am. Society Civil Engineers, Vol. 78, 1915, p. 893.

in the center. The Reinsch Wurl screen is the best known type
of disc screen. A cage screen 1 consists of a rectangular box
made up of parallel bars with the upstream side of the box or cage
omitted. Allen2 gives the following definitions: A drum
screen is a cylinder or cone of perforated plates or wire mesh
which rotates on a horizontal axis. A shovel vane screen is
similar to a wing screen with semicircular wings and a different
method of removing the screenings. Examples of a band screen,
a wing screen, a shovel vane screen, a drum screen and a disc

1 Not defined by the American Public Health Association.

2 Trans. Am. Society Civil Engineers, Vol. 78, 1915, p. 892.

TYPES OF SCREENS

screen are shown in Fig. 150. A bar screen is shown in Fig.
151 and a cage screen is shown in Fig. 152.

Direction
of Flow

Side View.

Front View
Looking down Stream.

FIG. 151. — Sketch of a Bar Screen.

Screens can be classed as fixed, movable, or moving. Fixed
screens are permanently set in position and -must be cleaned
by rakes or teeth that are pulled between the bars. Movable
screens are stationary when in
operation, but are lifted from
the sewage for the purpose of
cleaning. Moving screens are
in continuous motion when in
operation and are cleaned while
in motion. Fixed bar screens
may be set either vertical, in-
clined, or horizontal.

Movable screens with a
cage or box at the bottom
are sometimes used. Ihe box
should be of solid material
to prevent the forcing of

FIG. 152.— Sketch of a Cage Screen.

screenings through it \vhcii

the screen is being raised for

cleaning. A mesh screen should be used only under special

circumstances because of the difficulty in cleaning. Screens

which must be raised from the sewage for cleaning should be

386 SCREENING AND SEDIMENTATION

arranged in pairs in order that one may be working when the
other is being cleaned. Movable screens are undesirable for
small plants because the labor involved in raising and lowering
is greater than in cleaning with a rake and the screens are more
likely to be neglected. In a large plant rakes operated by hand
are too small for cleaning the screens. A fixed screen is sometimes
used with moving teeth fastened to endless chains. The teeth
pass between the parallel bars and comb out the screenings. If
the screen chamber in a small plant is too deep for accessibility
a movable cage or box screen may be desirable.

Moving screens are generally of fine mesh or perforated plates.
They are kept moving in order to allow continuous cleaning.
They are cleaned by brushes or by jets of air, water, or steam.

230. Sizes of Openings. — The area or size of the opening of
a screen is dependent upon the character of the sewage to be
treated and upon the object to be attained.

Large screens, with openings between 1^ inches and 6 inches
are used to protect centrifugal pumps, tanks, automatic dosing
devices, conduits, and gate valves from large objects such as
pieces of timber, dead animals, etc., which are found in sewage.
The quantity of material removed is variable, and is usually
small.

Medium-size screens with openings from \ inch to 1^ inches
are used to prepare sewage for passage through reciprocating
pumps, complex dosing apparatus, contact beds, and sand filters.
The amount of material removed varies from 0.5 to 10 cubic
feet per million gallons of sewage treated, dependent on the
character of the sewage and the size of the screen. Screenings
before drying contain 75 to 90 per cent moisture and weigh
40 to 50 pounds per cubic foot. At times the amount removed
may vary widely from the limits stated. Schaetzle and Davis l
state :

Screenings differ greatly both in amount and character.
. . . The amount varies with the days of the week as
well as during the course of the day. It reaches its
maximum about noon or shortly before and commences
to disappear about midnight, reaching a mimimum about
4 or 5 A.M. The material is almost wholly organic and

1 Removal of Suspended Matter by Sewage Screens, Cornell Civil En-
gineer, 1914. Abstracted in Engineering and Contracting, Vol. 41, 1914,
p. 451.

SIZES OF OPENINGS 387

consists of scraps of vegetables or fruit, cloth, hair, wood,
paper and lumps of fecal matter. The amount varies so
widely that it is impossible to state just what to expect
any definite size screen to remove. The amount of
water contained is small compared with that in the
sludge in sedimentation basins and amounts to from 70
per cent to 80 per cent. On account of its organic origin
it is highly putrescible.

Medium-size screens are sometimes placed close together with
the bars of the one opposite the openings in the other, thus
approaching a fine screen.

Fine screens vary in size of opening from f- inch to 50 open-
ings per linear inch or 2,500 per square inch. They are used for
removing solids preparatory to disposal by dilution, to protect
sprinkling filters, complex dosing apparatus, sand filters, sewage
farms, and to prevent the formation of scum in subsequent
tank treatment. In general, fine screens will remove from 0.1
to 1 cubic yard of wet material per million gallons of sewage
treated. The wet screenings will contain about 75 per cent
moisture and will weigh about 60 pounds per cubic foot. The
dry weight of the screenings will therefore be about 10 to 400
pounds per million gallons of sewage treated. The effect of the
removal of this amount of material is usually not detectable by
methods of chemical analysis, the amount of suspended matter
before and after screening being found unchanged.

In his conclusions on the discussion of the results to be
expected from fine screens, Allen states:1

With openings not more than 0.1 inch in size, fine
screening should remove at least 30 per cent of the sus-
pended solids and 20 per cent of the suspended organic
solids from ordinary domestic sewage, or 0.1 cubic yard
of screenings, containing 75 per cent water per thousand
population daily.

The effect of the use of different size openings under the same
conditions is shown in Fig. 153.2 Some data covering the amount
of material removed by screening are given in Table 76. More

* " The Clarification of Sewage by Fine Screens," Trans. Am. Society
Civil Engineers, Vol. 78, 1915, p. 1000.

J Langdon Pearse, Trans. Am. Society Civil Engineers, Vol. 78, 1915,
p. 1000.

388

SCREENING AND SEDIMENTATION

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DESIGN OF FIXED AND MOVABLE SCREENS

389

extensive data are given in Volume III of "American Sewerage
Practice" by Metcalf and Eddy.

231. Design of Fixed and Movable Screens. — The determina-
tion of the size of the opening is the first step ,in the design of
a sewage screen. This is followed by the computation of the net
area of openings in the screen. The final steps are the deter-

0.20

Removal by Screening.
0 Individual Resu/fc on Stockyards Sewage.
+• Average Results o

Screen

No. 6 Screen

400 800 1200 1600 2000 2400
Dry Screenings in Pounds per Million Gallons.

— -No. 10 Screen

-No. 16 Screen
•No. 20 Screen
-No. 24 Screen

- No. 50 Screen

- No AO Screen

2800

FIG. 153. — Screenings Collected on Different Sized Opening.

1921 Report on Industrial Wastes Disposal, Union Stock Yards District, Chicago, Illinois,
to the Sanitary District of Chicago.

mination of the overall dimensions of the screen; the size of the
bar, wire, or support ; and the dimensions of the screen chamber.
The net area of openings is fixed by the permissible velocity of
flow through the screen and the quantity of sewage to be treated.
In determining the velocity of flow the general principle should
be followed that the velocity should not be reduced sufficiently

390 SCREENING AND SEDIMENTATION

to allow sedimentation in the screen chamber. The velocity
of grit bearing sewage in passing through coarse screens should
not be reduced below 2 or 3 feet per second. If the sewage con-
tains no grit, or the screen is placed below a grit chamber the
velocity through a medium or fine screen should be from \ to \\
feet per minute. The velocity through the screen in a direction
normal to the plane of the screen can be reduced without reducing
the horizontal velocity of the sewage by placing the screen in a
sloping position.

The final steps are the design of the screen bar and the deter-
mination of the dimensions of the screen and of the screen chamber.
The size of the bar in a bar screen, or as a support to a wire mesh,
is dependent on the unsupported length of the bar. The stresses
in the bars are the results of impact and bending, caused by clean-
ing, and of the load due to the backing up of the sewage when the
screen is clogged. Allowance should be made for a head of
2 or 3 feet of sewage against the screen. A generous allowance
should be made in addition for the indeterminate stresses due to
cleaning. The screen should be supported only at the top and
bottom, as intermediate supports in a bar screen are undesirable
unless they are so arranged as not to interfere with the teeth
of the cleaning devices.

Fixed screens should be placed at an angle between 30° and
60° with the horizontal, with the direction of slope such that the
screenings are caught on the upper portion of the screen. A
small slope is desirable in order to obtain a low velocity through
the screen. The slope is limited since the smaller the slope the
longer the bars of the screen and the greater the difficulty of hand
cleaning. Small slopes will tend to make the screens self cleaning.
As the screen clogs, the increasing head of sewage will push the
accumulated screenings up the screen. The use of flat screens
in a vertical position is not desirable because of the difficulty of
cleaning and the accumulation of material at inaccessible points.
If a flat screen is placed in a horizontal position with the flow of
sewage downward difficulties are encountered in cleaning and
solid matter is forced through the screen as clogging increases.
An upward flow through a horizontal screen is undesirable as the
material is caught in a position inaccessible for cleaning. Movable
screens are more easily handled when placed in a vertical position.

In the construction of small screens, round bars are sometimes

THEORY OF SEDIMENTATION 391

used where the unsupported length of the bar is less than 3 or
4 feet. They are not recommended, however, as the efficient
area and the amount of material removed by the screen are
diminished. Bars which produce openings with the larger
end upstream are undesirable, as particles become wedged in
the screen, and are either forced through or become difficult
to remove.1 Rectangular bars are easily obtained and give
satisfactory service except where they are of insufficient strength
laterally. For greater lateral thickness a pear-shaped bar is
sometimes used, with the thicker side upstream. Fine mesh
screens or perforated plates are supported on grids or parallel
bars of stronger material designed to take up the heavy stresses
on the screen.

The dimensions of the bar may be selected arbitrarily. The
length and width of the screen are fixed to give desirable dimen-
sions to the screen chamber and to give the necessary net opening
in the screen. The width of the screen chamber and the screen
should be the same. The screen chamber should be sufficiently
long to prevent swirling and eddying around the screen. If the
dimensions thus fixed permit an undesirable, velocity in the screen
chamber they should be changed. A sufficient length of screen
should be allowed to project above the sewage for the accumula-
of screenings. The bars may be carried up and bent over at
the top as shown in Fig. 151 to simplify the removal of screenings.

Coarse screens are usually placed above all other portions
of a treatment plant. They may be followed by grit chambers
or finer screens. Coarse screens are occasionally placed as a
protection above medium or fine screens. In sewage containing
grit the smaller screens are sometimes placed below the grit cham-
ber. It is desirable to provide some means of diverting the sewage
from a screen chamber to allow of repairs to the screen and the
cleaning of the chamber. Screen chambers are sometimes
designed in duplicate to allow for the cleaning of one while the
other is operating.

PLAIN SEDIMENTATION

232. Theory of Sedimentation. — Sedimentation takes place in
sewage because some particles of suspended matter have a
greater specific gravity than that of water. All particles do
1 See article by Henry Ryon in Cornell Civil Engineer, 1910.

392 SCREENING AND SEDIMENTATION

not settle at the same rate. Since the weights of particles vary
as the cubes of their diameters, whereas the surface areas (upon
which the action of the water takes place) vary only as the
squares of the diameters, the amount of the skin friction on
small particles is proportionally greater than that on large
particles, because of the relatively greater surface area compared
to their weight. As a result the smaller particles settle more
slowly. The velocity of sedimentation of large particles has
been found to vary about as the diameter and of small particles
as the square root of the diameter. The change takes place at
a size of about 0.01 mm.

Sedimentation is accomplished by so retarding the velocity
of flow of a liquid that the settling particles will be given the
opportunity to settle out. The slowing down of the velocity
is accomplished by passing the sewage through a chamber of
greater cross sectional area than the conduit from which it came.
The time that the sewage is in this chamber is called the period
of retention. Although the shape of a basin, the arrangement
of the baffles and other details have a marked effect on the
results of sedimentation, the controlling factors are the period
of retention and the velocity of flow. Another factor affecting
the efficiency of the process is the quality of the sewage. Usually
the greater the amount of sediment in the sewage the greater the
per cent of suspended matter removed. A method for the
determination of the proper period of sedimentation has been
developed by Hazen in Transactions of the American Society of
Civil Engineers, Volume 53, 1904, page 45. The results of
his studies are summarized in Fig. 154 which shows the per cent
of sediment remaining in a treated water after a certain period
of retention. This period of retention is expressed in terms of
the hydraulic coefficient 1 of the smallest size particle to be
removed. Table 77 shows the hydraulic coefficients of various
particles. In Fig. 154 a represents the period of retention and
t the time that it would take a particle to fall to the bottom of
the basin. The different lines of the diagram represent the
results to be expected by various arrangements of settling basins.
The meaning of these lines is given in Table 78.

1 The hydraulic coefficient is denned as the rate of settling in mm. per
second.

THEORY OF SEDIMENTATION

393

TABLE 77
HYDRAULIC VALUES OF SETTLING PARTICLES IN MILLIMETERS PER SECOND

Diam-

Diameter
in

Hy-

draulic

Diameter
in

Hy-

draulic

Diameter
in

Hy-

draulic

eter

Hydraulic

mm.

Value

mm.

Value

mm.

Value

mm.

1.00

100

0.15

0.02

0.62

0.003

0.0138

0.80

0.10

0.015

0.35

0.002

0.0062

0.60

0.08

0.010

0.154

0.0015

0.0035

0.50

0.06

3.8

0.008

0.098

0.001

0.00154

0.40

0.05

2.9

0.006

0.055

0.0001

0.0000154

0.30

0.04

2.1

0.005

0.0385

0.20

0.03

1.3

0.004

0.0247

An example will be given to illustrate the method of using the
diagram and tables to determine the size of a sedimentation
basin to perform certain required work.

Let it be required to determine the period of retention
in a continuously operated sedimentation basin with good
baffling, corresponding to two properly baffled sedimentation
basins in series. The basins are to remove 60 per cent of
the finest particles which are to have a size of 0.01 mm.
The quantity to be treated daily is 3,000,000 gallons.

1st. Entering Table 77, we find that the hydraulic
value of the finest particles is 0.154 mm. per second.

2d. Since we wish to remove 60 per cent of the finest
particles, 40 per cent will remain. Since Fig. 154 shows
the per cent remaining after the time alt we enter Fig.
154 at 40 per cent on the ordinates and run horizontally
until we encounter Line 4 corresponding to good baffling
in Table 78. We then run down vertically from this
intersection and find that the ratio of a/t is 1.0.

Then a equals t, which means that the period of reten-
tion should equal the time that it takes a particle 0.01 mm.
in diameter to drop from the top to the bottom of the
basin. Since this depends on the depth of the basin it
is necessary to determine the depth before the other
dimensions of the basin can be fixed.

Although this method is seldom used in practice for the final
design of a sedimentation basin, it is a guide to judgment and
can be used to supplement the data obtained from tests.

394

SCREENING AND SEDIMENTATION

0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

•^, or Time of Settling,in Terms of Time Required for One ParficletpSettlefrornToptoBottom.

FIG. 154. — Hazen's Diagram, Showing the Relation between the Time of Set-
tling and the Period of Retention in Various Types of Sedimentation
Basins.

Trans. Am. Society Civil Engineers, Vol. 53, 1904, p. 45.

TABLE 78

COMPARISON OF DIFFERENT ARRANGEMENTS OF SETTLING BASINS
(From Hazen)

Description of Basins

Line
in
Fig.
154

Values of a/t.

Per Cent of Matter
Removed

87.5

Theoretical maximum. Cannot be reached ....
Surface skimming. Rockner Roth system
Intermittent basins, reckoned on time of service
only

A
B

C
D

16
8
4
2
1.5
E
1

0.50
0.54

0.63
0.69
0.71
0.73
0.76
0.82
0.90
1.26
1.00

0.75
0.98

1.26
1.38
1.45
1.62
1.66
2.00
2.34
2.50
3.00

0.875
1.37

1.89
2.08
2.23
2.37
2.75
3.70
4.50
3.80
7.00

Continuous basin Theoretical limit ....

Close approximation to the above

Very well baffled basin

Good baffling

Two basins tandem

Ono long basin well controlled

Intermittent basin in service half time

One basin continuous

TYPES OF SEDIMENTATION BASINS 395

The design of sedimentation basins should be based on
experimental observations made upon the quantity of sediment
removed at certain rates of flow and periods of retention in
different types of basins. Hazen's mathematical analysis is service-
able in making preliminary estimates and in checking the results.
The shape of the tank, period of retention and rate of flow pro-
ducing the most desirable results should be duplicated with the
expectation of obtaining similar results or results but slightly
modified from those obtained in the tests. This is the most
satisfactory method of determining the proper period of retention.

233. Types of Sedimentation Basins. — A sedimentation basin
is a tank for the removal of suspended matter either by quiescent
settlement or by continuous flow at such a velocity and time of
retention as to allow deposition of suspended matter.1 The
difference between sedimentation tanks and other forms of tank
treatment is that no chemical or biological action is depended
on for the successful operation of the tank. Sedimentation
tanks may be divided into two classes, grit chambers and plain
sedimentation basins.

A grit chamber is a chamber or enlarged channel in which the
velocity of flow is so controlled that only heavy solids, such as
grit and sand, are deposited while the lighter organic solids are
carried forward in suspension. If the velocity of flow is more
than about one foot per second, the tank is a grit chamber and
below this velocity it is a plain sedimentation basin.

There are sixth general types of plain sedimentation
basins :

1st. Rectangular flat-bottom tanks operated on the
continuous-flow principle.

2nd. Rectangular flat-bottom tanks operated on the
fill and draw principle.

3rd. Rectangular or circular hopper-bottom tanks
operated on the continuous-flow principle, with hori-
zontal flow.

4th. Rectangular or circular hopper-bottom tanks
operated on the fill and draw principle, with horizontal
flow.

5th. Rectangular or circular hopper-bottom tanks
operated on the continuous-flow principle with vertical flow.

6th. Circular hopper-bottom tanks operated on the
continuous-flow principle with radial flow.

1 Definition suggested by the American Public Health Association.

396

SCREENING AND SEDIMENTATION

TABLE 79

CRITICAL VELOCITIES FOR THE TRANSPORTATION OP DEBRIS
Sedimentation will not Occur at Higher Velocities

Diameter
of Particle

Critical Velocity, Feet per Second.

Size of Screen
or Number of

Specific Gravity

in
Millimeters

1.5

2.0

3.0

5.0

Meshes per Inch

0.010

0.13

0.20

0.22

0.28

0.050

0.23

0.34

0.39

0.50

More than 200

0.100

0.30

0.42

0.50

0.65

More than 150

0.500

0.55

0.73

0.91

1.15

More than 28

1.0

0.71

0.92

1.18

1.50

More than 14

1.25

0.77

1.00

1.30

1.60

2.0

0.92

1.20

1.50

1.90

More than 10

5.0

1.30

1.70

2.20

2.60

More than 4

1.70

2.20

2.8

3.4

Diameter in Millimeters for a Velocity of 1 Foot per Second

2.5

1.25

0.65

0.32

234. Limiting Velocities. — Sand, clay, bits of metal and other
particles of mineral matter will commence to deposit in appreci-
able quantities when the velocity of flow falls below 3 feet per
second. The amount deposited will increase as the velocity
decreases. In Table 79 are given the approximate horizontal
velocities at which certain size particles of mineral matter will
deposit. At a velocity of about one foot per second organic
matter will commence to deposit. It will be noticed by inter-
polation in Table 79,1 that particles with the same specific
gravity as sand (2.6), larger than one mm. in diameter will
deposit at a velocity of about one foot per second or less, and
that smaller and lighter particles will not deposit at velocity
of one foot per second or greater. It will also be noticed that a

1 Computed from formula by Gilbert in " Transportation of Debris by
Running Water," U. S. Geological Survey, Professional Paper No. 86, 1914.
1.28 (velocity)2'7

Diameter in mm. = -

Sp. gv.-l

QUANTITY AND CHARACTER OF GRIT

397

velocity of one foot per minute is sufficiently slow to permit the
deposit of the smallest and lightest particles. For this reason
velocities of 1 or 2 or even 3 feet per second have been adopted
as the velocities in grit chambers and velocities less than 1 foot
per minute in plain sedimentation basins.

235. Quantity and Character of Grit. — The amount of
material deposited in grit chambers varies approximately between
0.10 and 0.50 cubic yard per million gallons. It is to be noted
that grit chambers are used only for combined and storm sewage
and for certain industrial wastes. They are unnecessary for
ordinary domestic sewage. The material Heposited in grit cham-
bers operating with a velocity greater than one foot per second
is nonputrescible, inorganic, and inoffensive. It can be used for
filling, for making paths and roadways, or as a filtering material
for sludge drying beds. An analysis of a typical grit chamber
sludge is shown in Table 80.

TABLE 80
ANALYSIS OF GRIT CHAMBER SLUDGE

Velocity
Feet per
Second

Specific
Gravity

Per Cent
Moisture

Calculated to Dry Weight. Per Cent

Nitrogen

Fixed Matter

Miscellaneous

1.0

1.5

236. Dimensions of Grit Chambers. — The quantity of sewage
to be treated and the amount and character of the settling solids
which it contains should be determined by measurement and
analysis, and the amount of settling solids to be removed should be
determined by a study of the desired conditions of disposal, in
order that a grit chamber that will accomplish the desired results
may be designed. The period of retention and the velocity of
flow are the controlling features in the successful operation of
any grit chamber. These should be determined by experiment
or as the result of experience. Where neither are available,
Hazen's method can be followed or a decision made based on a
study of other grit chambers. In general, the period of retention

398 SCREENING AND SEDIMENTATION

in grit chambers is from 30 to 90 seconds, and the velocity of flow
is about one foot per second.

After having determined the quantity of sewage to be treated,
the quantity of grit to be stored between cleanings, the period
of retention, the arrangement of the chambers, and the velocity
of flow to be used, the overall dimensions of the chambers are
computed. The capacity of the chamber is fixed as the sum of
the quantity of sewage to be treated during the period of reten-
tion and the required storage capacity for grit accumulated
between cleanings. The length of the chamber is fixed as the
product of the velocity! of flow and the period of retention. The
cross-sectional area of the portion of the chamber devoted to
sedimentation is fixed as the quotient of the quantity of flow of
sewage per unit time and the velocity of flow. Only the relation
between the width and depth of the portion devoted to sedi-
mentation and the portion devoted to the storage of grit remain
to be determined. These should be so designed as to give the
greatest economy of construction commensurate with the required
results. They will be affected by the local conditions such as
topography, available space, difficulties of excavation, etc. Com-
mon depths in use lie between 8 and 12 feet, although wide varia-
tions can be found. A study of the proportions of existing
grit chambers will be of assistance in the design of other
basins.

237. Existing Grit Chambers. — The details of some typical
grit chambers are shown in Figs. 155 and 156. The grit chamber
at the foot of 58th Street, in Cleveland, Ohio, is shown in Fig.
155. The special feature of this structure is the shape of the
sedimentation basin, the bottom of which is formed by sloping
steel plates forming a 6-inch longitudinal slot above the grit
storage chamber. Flows between 8,000,000 and 16,000,000
gallons per day are controlled by the outlet weir so that the
velocity of flow remains at one foot per second. This is accom-
plished by increasing the depth of flow in the same ratio as the
increase in the rate of flow. The bottoms of the two chambers
differ, one having a special hopper for grit and the other a flat
bottom. This is due to the method of cleaning the chambers,
it being necessary in the one with a flat bottom to shut off the
flow when removing the grit while in the one with the hopper
bottqm it is hoped to remove the grit by the use of sand ejectors

EXISTING GRIT CHAMBERS

--^-C--> 50'-0" -»| A

399

«. SO'-O" -

M W^fc — S-l) H H W V JTJ

IJ j-£ jjj! »j JJJJMHMJ i \&

FIG. 155. — Grit Chamber at Cleveland, Ohio.

En'g. Record, Vol. 73, 1916, p. 409.

Weir .-12'Steej C;30lbs.
Penstocks , Screen J^Contr_
•Sewer

Cross Section.
FIG. 156.— Grit Chamber at Hamilton, Ontario.

Eng. News, Vol. 73, 1915, p. 425.

400 SCREENING AND SEDIMENTATION

without stopping the sewage flow. The details of the chamber
at Hamilton, Ontario, are shown in Fig. 156. In studying these
drawings the following features should be noted : 1st, the smooth
curves in the channel to prevent eddies, undue deposition of
organic matter, and difficulties in cleaning; 2nd, the hopper in the
upper end of the grit storage chamber and the slope of the bot-
tom of at least 1 : 20 ; and 3rd, the simplicity of the inlet and out-
let devices which may be either stop planks or cast iron sluice
gates.

The drawings shown are merely representative of some sat-
isfactory types. The number and variety of grit chambers
in existence is great. In designing grit chambers consideration
must be given to the method of cleaning. «They are ordinarily
cleaned by such methods as have been described for the cleaning
of catch-basins in Chapter XII. Continuous bucket scrapers
similar to excavating machines are sometimes used for the clean-
ing of large grit chambers. The period between cleanings is
variable. The design should be such as not to require more
frequent cleanings than twice a month under the worst conditions.
The fluctuations in quality and quantity of grit will vary the period
between cleanings.

238. Number of Grit Chambers. — The period of retention
in grit chambers is so short and the velocity of flow so near the
maximum and minimum limitations that the wide fluctuations
in the rate of discharge in storm and combined sewers necessi-
tates the construction of a number of chambers which should
be operated in parallel in order to maintain the velocity between
th<? proper limits. Unless arrangements are made permitting
the cleaning of grit chambers during operation, more than one
grit chamber should be installed in order that when one is being
cleaned the others may be in operation. The number of grit
chambers must be determined by the desired conditions of
operation and the cost of construction. The larger the number
of basins the more nearly the flow in any one basin can be
maintained constant, but the more expensive the construction.
The increase in velocity of flow with increasing quantity is
dependent on the outlet arrangements. In a shallow chamber
with vertical sides and a standard sharp-crested rectangular
weir at the outlet the velocity will vary approximately as the cube
root of the rate of flow. Similarly if the outlet is a V notch the

QUANTITY AND CHARACTERISTICS OF SLUDGE 401

velocity will vary as the fifth root of the rate of flow. In all
cases the deeper the basin the more nearly the velocity varies
directly as the rate of flow. The outlet weir can be arranged
as at Cleveland, so that the velocity remains constant for all
rates of flow within certain limits. It is seldom that more than
three grit chambers are necessary to care for the fluctuations
in flow.

239. Quantity and Characteristics of Sludge from Plain
Sedimentation. — The sludge removed from plain sedimentation
basins is slimy, offensive, not easily dried, and is highly putres-
cible and odoriferous. It contains about 90 per cent moisture
and has a specific gravity from 1.01 to 1.05. The amount
removed varies between 2 and 5 cubic yards per million gallons
of sewage. The percentage of suspended matter removed
varies between 20 and 60. The total amount removed and the
percentage removal depend on the character of the sewage,
the type of basin, and the period of detention.

240. Dimensions of Sedimentation Basins. — The dimensions
of a sedimentation basin are determined by a method similar
to the one given for the determination of the dimensions of a
grit chamber in Art. 236. The capacity of the basin is first
fixed upon to give the required period of sedimentation and
sludge storage capacity. The length of the basin is the product
of the velocity and the period of retention. The length, width,
and depth of the basin are normally fixed by considerations of
economy and the limitations of the local conditions, such as
available area, topography, foundations, etc., and examples of
good practice. A study of basins in use shows the relation
between length and width to vary normally between 2:1 and 4:1.
Widths greater than 30 to 50 feet are undesirable because of the
danger of cross currents and back eddies which will reduce the
efficiency of the sedimentation. Depths used in practice vary
too widely to act as guides for any particular design. Theo-
retically the shallower the basin the better the result. Tanks
abroad have been built as shallow as 3 feet and some in this
country as deep as 16 feet. The economical dimensions can be
determined by trial or by calculus. They will serve as a guide
in the adoption of the final dimensions.

The method to be pursued in determining the economical
dimensions of any engineering structure are:

402

SCREENING AND SEDIMENTATION

I. Express the total cost of the structure in terms of
as few variables as possible.

II. Express all of the variables in terms of any one and
rewrite the expression for the total cost in terms of this
one variable.

III. Equate the first derivative of the expression with
regard to this variable to zero and solve for the variable.
The result will be the economical value of the variable.
The values of the other variables can be computed from the
relations already expressed.

For example, let it be desired to determine the dimen-
sions of two continuous-flow sedimentation basins as shown
in Fig. 157, in which the
period of retention in each
is to be 2 hours, the veloc-
ity of flow is not to ex-
ceed one foot per second,
and the sludge accumula- I
ted will be 3 cubic yards
per million gallons of sew- I
age treated. The quantity

-L

• b — -

of sewage to be treated

is 18,000,000 gallons per FlG- 157.— Diagram for the Compu-

day. The shortest time tation of Economical Basin Di-

between cleanings will be mensions.

2 weeks.

The capacity of each basin must be 2/24 of 18,000,000
gallons, or 200,000 cubic feet in order to allow a period
of retention of 2 hours. To this volume should be added
sufficient capacity to allow for the 2 "weeks of sludge stor-
age between cleanings. When a basin is being cleaned
the load must be put on the remaining basins. Then if
Q represents the rate of accumulation of sludge per day,
n represents the number of days between cleanings, ra
represents the number of basins, and s the sludge capacity
of one basin, then

m—1'

The sludge storage capacity for the example given
will be approximately 11,000 cubic feet.

In expressing the total cost of the basins let

h = the depth in feet.
I =the length in feet.
6 = the width in feet.

DIMENSIONS OF SEDIMENTATION BASINS 403

The cost of land, floor, etc., per square foot =p dollars.
The cost of wall per foot length =qh2 dollars.

The cost of pipes, valves and appurtenances = P dollars.

Then the total cost C = (3Z+46) qh2+2plb+ P.

It is now necessary to express the three variables b, I,
and h, in terms of one of them. From the relation Q =
2blh it is possible to rewrite the expression for the total c\
cost as:

C =

Q- **

Holding h constant and differentiating with regard to
b in the first expression and with regard to I in the second
expression, equating to zero and solving we get:

J3Q

The economical relation between 6 and I is therefore
6 =0.7 51

regardless of the value of h.

Substituting these values of I and 6 in the original
expression for the total cost, it becomes

^+4. ^ atf+^+P.

Differentiating with regard to h, equating to zero, and
solving

9 /

In the example given if q = 0 . 2 and p = 1 . 0 then

h = 11 . 6 feet, b = 120 feet and I = 160 feet.

Since these are reasonable dimensions and in accord with good
practice they should be used, unless other conditions are unsuit-
able or the velocity of flow is too great. A width of channel of
120 feet as compared to a length of 160 feet is conducive to a
poor distribution of velocity across the basin. A ratio of width
to length of about 1:4 is desirable. In this case, by the use
of three baffles parallel to the length of the basin, thus dividing
it into channels 40 feet wide and 11.6 feet deep, the ratio of
width to length is changed to 1 : 4 and the velocity will be

404

SCREENING AND SEDIMENTATION

increased only to 0.06 foot per second or 3.6 feet per minute,
which is a reasonable velocity. It could be reduced by increasing
the spacing of the baffles or the depth of the chamber.

Complicated baffling is undesirable. Two or three overflow
baffles may be used to permit quiescent sedimentation in the
space thus formed, and hanging baffles may be placed before
the inlet and outlet to break up surface currents, or to prevent
the movement of scum. The hanging baffles should not extend
more than 12 to 18 inches below the water surface. The inlet
and outlet are sometimes arranged to permit the reversal of flow,
and the connecting channels between basins to allow the opera-
tion of any number of basins in series or in parallel, although
such arrangements are more important in water purification.
Sewage should enter and leave at the top of the basin.

Cleaning is facilitated by the location of a central gutter in
the bottom of the basin with the slope of the bottom of the basin
towards the gutter from 1 : 25 to 1 : 80 or steeper. A pipe,
2 inches or larger in diameter, containing water under pres-
sure with connections for hose placed at frequent intervals is a
useful adjunct in flushing the sludge from the sedimentation
basins. For equal capacity, deer- vertical flow tanks are more

expensive and difficult to con-
struct than the shallower rect-
angular type. Deep tanks are
advantageous, however, in that
sludge can sometimes be re-
moved by gravity or by pump-
ing without stopping the opera-
tion of the tank. They will
also operate successfully with
shorter periods of detention
and higher velocities. The up-
ward velocity should not be
greater than the velocity of
sedimentation of the smallest
particle to be removed. The

efficiency of sedimentation in them will be increased by the
sedimentation of the larger particles which drag some of the
smaller particles down with them. The Dortmund tank shown
in Fig. 158 is an example of this type.

FIG. 158. — Section through a Dort-
mund Tank.
Depth 20 to 30 feet.

CHEMICALS 405

Ordinarily it is not necessary to roof sedimentation basins
as the odors created are not strong, and difficulties with ice are
seldom serious.

CHEMICAL PRECIPITATION

241. The Process. — Chemical precipitation consists in adding
to the sewage such chemicals as will, by reaction with each other
and the constituents of the sewage, produce a flocculent precipi-
tate and thus hasten sedimentation. The advantages of this
process over plain sedimentation are a more rapid and thorough
removal of suspended matter. Its disadvantages include the
accumulation of a large amount of sludge, the necessity for
skilled attendance, and the expense of chemicals. The process
is not in extensive use as the conditions under which the
advantages outweigh the disadvantages are unusual. Sewage
containing large quantities of substances which will react with a
small amount of an added chemical to produce the required
precipitate are the most favorable for this method of treatment.

Chemical precipitation accomplishes the same result as plain
sedimentation, although the effluent from the chemically pre-
cipitated sewage may be of better quality than that from a plain
sedimentation basin.

242. Chemicals. — Lime is practically the only chemical used
for the precipitation of the solid matter in sewage. Commercial
lime used for precipitation consists of calcium oxide (CaO),
with large quantities of impurities. It should be stored in a dry
place and protected from undue exposure to the air to prevent
the formation of calcium carbonate (CaCOs), the formation of
which is commonly known as air slacking. The active work
in the formation of the precipitate is performed by the lime (CaO)
or calcium hydroxide (Ca(OH)2). The lime should therefore
be purchased on the basis of available CaO, which may be as
low as 10 to 15 per cent in some commercial products. The
amount of lime necessary depends on the quality of the sewage,
the period of retention in the sedimentation basin, the method
of application, the required results, and other less easily measured
factors. Full scale tests for the amount of lime needed to
produce certain results are the most satisfactory. In practice
the amount of lime necessary when lime alone is used as a pre-

406 SCREENING AND SEDIMENTATION

cipitant has been found to be about 15 grains per gallon. This
may be markedly different, dependent on the quality of the
sewage. For acid sewages, lime alone is not suitable as a pre-
cipitant since it is necessary to add sufficient lime to neutralize
the sewage before the calcium carbonate will be precipitated.

The use of copperas (FeSO4) together with lime, leads to
economy in the use of chemicals as the flocculent precipitate of
ferrous hydroxide (Fe(OH)2) is more voluminous than the
precipitate of calcium carbonate. This is commonly known as
the lime and iron process. The presence of iron in certain trade
wastes may reduce the cost of chemical precipitation, as the
necessary amount of copperas is reduced.- Where 15 grains of
lime alone will be needed per gallon of sewage, the total amount
of chemicals used will be reduced to 8 to 10 grains per gallon
with the use of lime and iron. This combination is less expensive
than the use of lime alone, and is even cheaper where the iron is
already present in the sewage. Such a condition is well illus-
trated by the sewage at Worcester, Mass., where the oldest and
best known chemical precipitation plant in the United States is
located. The amount of lime used at this plant has varied between
6 and 10 grains per gallon of sewage, the normal amount being
about 7 grains. No iron is added because of the amount already
in solution.

The results of a series of experiments on the chemical precipi-
tation of sewage by Allen Hazen, are given in the 1890 Report
of the Massachusetts State Board of Health, on p. 737 of the
volume on the Purification of Water and Sewage. Hazen con-
cludes as the result of his experiments: concerning lime,

There is a certain definite amount of lime . . .
which gives as good or better results than either more or
less. This amount is that which exactly suffices to form
normal carbonates with all the carbonic acid of the
sewage. This amount can be determined in a few minutes
by simple titration.

Concerning lime and iron (copperas) he states:

Ordinary house sewage is not sufficiently alkaline

to precipitate copperas, and a small amount of lime must

be added to obtain good results. The quantity of lime

required depends both upon the composition of the sewage

, and the amount of copperas used, and can be calculated

PREPARATION AND ADDITION OF CHEMICALS 407

from titration of the sewage. Very imperfect results are
obtained from too little lime, and, when too much is
used, the excess is wasted, the result being the same as
with a smaller quantity.

In precipitation by ferric sulphate and crude alum,
the addition of lime was found unnecessary, as ordinary
sewage contains enough alkali to decompose these salts.
Within reasonable limits the more of these precipitants
used the better is the result, but with very large quanti-
ties the improvement does not compare with the increased
cost.

Using equal values of different precipitants, applied
under the most favorable conditions for each, upon the
same sewage, the best results were obtained from ferric
sulphate. Nearly as good results were obtained from
copperas and lime used together, while lime and alum
each gave somewhat inferior effluents. . . . When lime
is used there is always so much lime left in solution that
it is doubtful if its use would ever be found satisfactory
except in case of an acid sewage.

It is quite impossible to obtain effluents by chemical
precipitation which will compare in organic purity with
those obtained by intermittent filtration through sand.

It is possible to remove from one-half to two-thirds
of the organic matter by precipitation . . . and it seems
probable that ... a result may be obtained which will
effectually prevent a public nuisance.

243. Preparation and Addition of Chemicals. — Lime is not
readily soluble in water. Therefore, it is not best to add the lime
as a powder to the sewage, but to form a milk of lime, that is,
a supersaturated solution containing from 2,000 to 4,000 grains
per gallon, although dry slaked lime has sometimes been applied
directly. The solution is prepared in tanks in a quantity sufficient
for some part of the day's run, commonly sufficient to last through
one shift of 8 or 10 hours. The lime is prepared by placing the
amount necessary to fill one storage tank into a slaking tank
containing some cold water. Sufficient water is added to keep
the solution just at the boiling point, or steam may be added to
make it boil. After slaking, it is run into the milk-of-lime solu-
tion tank and sufficient water added to bring to the proper
strength. The milk of lime is added in measured quantities,
being controlled by a variable head on a fixed orifice or weir,
so that it may be varied with the amount of sewage flowing through
the plant. The amount of lime to be added is determined by

408

SCREENING AND SEDIMENTATION

titration with phenolphthalein, experience indicating the color
to be obtained when the proper amount of lime has been added.
The use of either copperas or alum has been so rare, for the
precipitation of sewage, that a description of the methods of
handling these chemicals as a sewage precipitant is not war-
ranted. An excellent description of the methods of handling
these chemicals in water purification will be found in " Water
Purification " by Ellms.

TABLE 81
RESULTS OP CHEMICAL PRECIPITATION AT WORCESTER, MASSACHUSETTS*

1900

1910

1920

Amount of sewage treated, million
gallons

4,781

5,317

8893

Amount of sewage chemically
treated, million gallons

3,650

3,574

7,300

Gallons of wet sludge per million
gallons of sewage treated . . .

4,450

4,185

Per cent of solids in sludge

4.42

8.20

4 64t

Tons of solids

7,294

4,182

6,43 It

Pounds of lime added per million
gallons of sewage pumped

999§

762 f

534

Per cent of organic matter removed :
By albuminoid ammonia:
Total

52. 7t

58.4

51 9

Suspended

90. OJ

88.7

83 6

By oxygen consumed:
Total

62. 8J

61.1

62 5

Suspended

86. 6 J

89.7

86 2

* Computed from Annual Report of the Superintendent of Sewers, Nov. 30, 1919,
and 1920.

t These figures are for 1919. J These figures are for 1902. § These figures are for 1905.

244. Results. — The results of Hazen's experiments indicate
that a greater amount of suspended matter can be removed in
the same time by chemical precipitation than by plain sedimen-
tation. The percentage of removal of suspended matter may be
as high as 80 to 90 per cent with a period of retention of 6 to 8
hours and the addition of a proper amount of chemical. That

RESULTS 409

the method is not always a success is shown by the results of
some tests at Canton, Ohio.1 The report states:

.... lime treatment removes about 50 per cent of
the suspended matter, and in the main about 50 per cent
of the organic matter. . . . These data are instructive
as indicating that the addition of lime to the Canton
sewage in quantities as previously stated does not materi-
ally improve the character of the resulting effluent over
and above that which could be produced by plain sedi-
mentation alone.

The plant at Worcester, Mass., is the largest in the United
States and information from it is of value. A summary of the
results at Worcester for 1900, 1910, and 1920 are shown in Table
81.

1 Report of the Ohio State Board of Health, 1908, page 425.

CHAPTER XVI
SEPTICIZATION

245. The Process. — Septic action is a biological process caused
by the activity of obligatory or facultative anaerobes as the result
of which certain organic compounds are reduced from higher to
lower conditions of oxidation, some of the solid organic substances
are rendered soluble, and a quantity of gas is given off. Among
these gases are: methane, hydrogen sulphide, and ammonia.
The biologic process in the septic tank represents the downward
portion of the cycle of life and death, in which complex organic
compounds are reduced to a more simple condition available
as food for low forms of plant life. The disposal of sewage by
septic action, when introduced, promised the solution of all
problems in sewage treatment. Septic action is now better
understood, and it is known that some of the early claims were
unfounded.

The principal advantage of septic action in sewage treatment
is the relatively small amount of sludge which must be cared
for compared to that produced by a plain sedimentation tank.
The sludge from a septic tank may be 25 to 30 per cent and in
some cases 40 per cent less in weight, and 75 to 80 per cent less
in volume than the sludge from a plain sedimentation tank.
The most important results of septic action and the greatest
septic activity occur in the deposited organic matter or sludge.
The biologic changes due to septic action which occur in the
liquid portion of the tank contents are of little or no importance.
The installation of a septic tank, although it may fail to prevent
the nuisance calling for abatement, has a remarkable psycho-
logical effect in stilling complaints. Among other advantages
are the comparative inexpensiveness of the tanks and the small
amount of attention and skilled attendance required. The
tanks need cleaning once in 6 months to a year. If properly
designed no other attention is necessary.

410

THE SEPTIC TANK 411

The septic tank has fallen into some disrepute because of the
better results obtainable by other methods, the occasional dis-
charge of effluents worse than the influent, the occasional dis-
charge of sludge in the effluent caused by too violent septic boiling,
and on account of patent litigation. This last difficulty has been
overcome as the Cameron patents expired in 1916. Occasionally
the odors given off by the septic process are highly objectionable
and are carried for a long distance. These odors can be controlled
to a large extent by housing the tanks. Over-septicization must
be guarded against as an over-septicized effluent is more difficult
of further treatment or of disposal than a comparatively fresh,
untreated sewage. An over-septicized or stale sewage is indi-
cated by the presence of large quantities of ammonias, either
free or albuminoid, frequently accompanied by hydrogen sul-
phide and other foul-smelling gases. The oxygen demand in
an over-septicized sewage is greater than that in a fresh or more
carefully treated sewage.

246. The Septic Tank. — A septic tank is a horizontal, continu-
ous-flow, one-story sedimentation tank through which sewage
is allowed to flow slowly to permit suspended matter to settle
to the bottom where it is retained until anaerobic decomposition
is established, resulting in the changing of some of the suspended
organic matter into liquid and gaseous substances, and a conse-
quent reduction in the quantity of sludge to be disposed of.1
It is to be noted that a continuous flow is essential to a septic tank.
Small tanks containing stagnant household sewage are called cess-
pools, although sometimes erroneously spoken of as septic tanks.

Septic and sedimentation tanks differ in their method of opera-
tion only in the period of storage and the frequency of cleaning.
The period of flow in a septic tank is longer and it is cleaned less
frequently. The results obtained by the two processes differ
widely. A septic tank can be converted into a sedimentation
tank, or vice versa, by changing the method of operation, no
constructional features requiring alteration. The purpose of
the tank is to store the sludge for such a period of time that
partial liquefaction of the sludge may take place, and thus
minimize the difficulty of sludge disposal. For this reason the
sludge storage capacity of a septic tank is sometimes greater
than would be necessary for a plain sedimentation tank.
1 Definition proposed by the Am. Public Health Assn.

412

SEPTICIZATION

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RESULTS OF SEPTIC ACTION 413

247. Results of Septic Action. — The results obtained from
the septic tanks at the Columbus Sewage Experiment Station
are given in Table 82. The effluent is higher than the influent
in free ammonia, but the reduction of other constituents, par-
ticularly suspended matter, is marked.

Septic action is sensitive to temperature changes, and to cer-
tain constituents of the incoming sewage. Cold weather or an
acid influent will inhibit septicization. In winter the liquefaction
of sludge may practically cease, whereas in summer liquefaction
may exceed deposition. The amount of gas generated is a
measure of the relative amount of septic action. The rapid
generation of gas in warrii weather disturbs the settled sludge
and may cause a deterioration of the quality of the effluent because
of the presence of decomposed sludge. The results in Table 82
show the effect of cold weather on the process. In warm weather
the violent ebullition of gas sometimes causes the discharge of
sludge in the effluent, resulting in a liquid more difficult of
disposal than the incoming sewage. Since septic action is
dependent on the presence of certain forms of bacteria, where
these are absent there will be no septic action. Sewage generally
contains the forms of bacteria necessary for this action but it
has occasionally been found necessary to seed new tanks in order
to start septic action.

The sludge from septic tanks is usually black, with a slight
odor, though in some cases this odor may be highly offensive.
The sludge will flow sluggishly. It can be pumped by centrif-
ugal pumps and it will flow through pipes and channels. It
has a moisture content of about 90 per cent and a specific gravity
of about 1.03. It is dried with difficulty on open-air drying beds,
and it is worthless as a fertilizer. The composition of some
septic sludges are shown in Table 83.

248. Design of Septic Tanks. — The sedimentation chambers
of a septic tank are designed on the same principles as the sedi-
mentation basins described in Art. 240. The velocity of flow
should not exceed one foot per minute. The channels should bo
straight and free from obstructions causing back eddies. The
ratio of length to width of channel should be between 2 : 1 to 4 : 1
with a width not exceeding 50 feet, and desirably narrower.
The depths used vary between 5 and 10 feet, exclusive of the
sludge storage capacity. Hanging baffles should be placed, one

414

SEPTICIZATION

before the inlet and the other in front of the outlet, so as to
distribute the incoming sewage over the tank, and to prevent
scum from passing into the outlet. The baffles should hang
about 12 inches below the surface of the sewage. Intermediate
baffles are sometimes desirable to prevent the movement of
sludge or scum towards the outlet. The placing of baffles must
be considered carefully as injudicious baffling may lessen the
effectiveness of a tank by so concentrating the currents as to pre-
vent sedimentation or the accumulation of sludge. Baffles
should be built of concrete or brick, as wood or metal in contact
with septic sewage deteriorates rapidly. In designing the sludge
storage chambers it may be assumed that one-half of the organic
matter and none of the mineral matter will be liquefied or gasi-
fied. The net storage volume allowed is about 2 to 3 cubic yards
per million gallons of sewage treated. Variations between 0.1
and 10.0 cubic yards have been recorded, however. If grit is
carried in the sewage to be treated, it should be removed by
the installation of a grit chamber before the sewage enters the
septic tank.

TABLE 83
ANALYSIS OF TANK SLUDGES

Per Cent in Terms

of Dry Matter

JjpS

D« 03

03
ft

1 .

•H°

Kind of

Place

= a

«.2

Sludge

Reference

.t2

3 ^

1908 Report,

Mansfield, O...

1.11

80.8

Septic

State Board of

[

Health

Chicago, 111. ...

1.03

1.9

7.0

1.0

200

Septic

1.5

300

Columbus, O. . .

1.09

83.3

4.4

16.7

0.25

0.94

Septic <

G. A. Johnson
1905 Report

Atlanta, Ga

1.02

87.1

39 1

60.9

1.25

6.11

Imhoff <

f
I

Eng. Rec., V. 72,
1915 p. 4

Baltimore, Md.

1.02

91.9

66.2

2.45

4 0?

Diges- '
tion
Tank ,

Eng. News-Rec.,
V. 87, 1921, p. 98

Baltimore, Md .

1.02

92.4

62.7

2.75

Imhoff

do.

Raw

Baltimore, Md.

79.2

73.8

2.64

9.00

Sludge

do.

Baltimore, Md.

92.4

58.0

3.19

Settling

do.

Basin

DESIGN OF SEPTIC TANKS 415

Two or more tanks should be constructed to allow for the shut
down of one for cleaning and to increase the elasticity of the
plant. The number of tanks to be used is dependent on the
total quantity of sewage and the fluctuations in rate of flow. An
average period of retention of about 9 to 10 hours with a mini-
mum period of 6 hours during maximum flow is a fair average
to be assumed for design. The period of retention should not
exceed about 24 hours, as the sewage may become over-septi-
cized. The sludge storage period should be from 6 to 12 months.

A cover is not necessary to the successful operation of a septic
tank. Covers are sometimes used with success, however, in
reducing the dissemination of odors from the tank. They are
also useful in retaining the heat of the sewage in cold weather
and thus aid in promoting bacterial activity. Types of covers
vary from a building erected over the tank to a flat slab set close
to the surface of the sewage. In the design of a cover, good
ventilation should be provided to permit the escape of the gases,
and easy access should be provided for cleaning. Tightly
covered tanks or tanks with too little ventilation have resulted
in serious explosions, as at Saratoga Springs in 1906 and at
Florenceville, N. C., in 1915.1

The sludge may be removed through drains in the bottom of
the tank as described for sedimentation basins, or where such
drains are not feasible the sludge and sewage are pumped out.
For this purpose a pump may be installed permanently at the
tank, or for small tanks portable pumps are sometimes used.
Septic tanks should be cleaned as infrequently as possible without
permitting the overflow of sludge into the effluent. The less
frequent the cleaning the less the amount of sludge removed
since digestion is continuous throughout the sludge. It is
necessary to clean when the tank becomes so filled with sludge,
that the period of retention is materially reduced, or sludge is
being carried over into the effluent.

The details of the septic tank at Champaign, Illinois, are
shown in Fig. 159. This tank was designed by Prof. A. N.
Talbot, and was put in service on Nov. 1, 1897. It was among
the first of such tanks to be installed in the United States. The
tank shown in Fig. 159 is an example of present day practice
in single-story septic tank design.

1 See Eng. News. Vol. 73, 1915, p. 410.

416

SEPTICIZATION

Vain
Cfiarrii

her

Plan, with Roof Removed
FIG. 159. — Septic Tank at Champaign, Illinois.

^•Sludge Outlet

1 1

1 II

-/—

• 3

\_J<- Sump

JO 0)

K— .-

8-0"- sJ

Plan

6"lnlet

Sludge Ou-Het-.— —

Section .

FIG. 160. — Design for a Residential Septic Tank for a Family of Ten. Illinois
» State Board of Health.

IMHOFF TANKS

417

Small septic tanks for rural homes of 5 to 15 persons, or on
a slightly larger scale for country schools and small institutions,
are little more than glorified cesspools. Nevertheless much
attention has been given to the construction of such tanks by
the National Government and by state boards of health.1 The
recommendations of some of these boards have been compiled
in Table 84. A typical method for the construction of such tanks,
as recommended by the Illinois State Board of Health, is shown
in Fig. 160. A subsurface filter, into which the effluent is dis-
charged, is an important adjunct where no adequate stream is
available to receive the discharge from the tank.

Rule Recommended by
State Board of Health

Number,
Persons

Capacity,
Gallons
per Person

Period of
Retention

Remarks

Wisconsin .

30
50

24 hours

Not less than 560 gallons
Not more than 5 feet deep

25 per cent additional
capacity for sludge .

Not less than 500 gallons

Ohio

4 to 10

Kentucky

24 to 48 hours
24 hours
24 hours
24 hours

Texas

Illinois

} -

25
1 20
25 to 30

U. S. Dept. Agriculture.
North Carolina

Large
Schools
20 pupils
Medium
School
Homes

North Carolina

249. Imhoff Tanks. — In the discussion of septic tanks it has
been brought out that one of the objections to their use is the
unloading of sludge into the effluent which occasionally causes
a greater amount of suspended matter in the effluent than in the
influent. The Imhoff tank is a form of septic tank so arranged
that this difficulty is overcome. It combines the advantages
of the septic and sedimentation tanks and overcomes some of their
disadvantages. An Imhoff tank is a device for the treatment
of sewage, consisting of a tank divided into 3 compartments.
The upper compartment is called the sedimentation chamber. In

1 Sewage Treatment from Single Houses and Small Communities, by L.
C. Frank. U. S. Public Health Service, Bulletin 101, 1920.

418

SEPTICIZATION

it the sedimentation of suspended solids causes them to drop
through a slot in the bottom of the chamber to the lower com-
partment called the digestion chamber. In this chamber the solid
matter is humified by an action similar to that in a plain septic
tank. The generated gases escape from the digestion chamber to
the surface through the third compartment called the transition or
scum chamber. Sections of Imhoff tanks are shown in Fig. 161.
It is essential to the construction of an ImhorT tank that the slot
in the bottom of the sedimentation chamber does not permit

Effect o-f
Design on
Sludge-Storage
Capacity.
(AandB)

Downward and Upward
FlowTank

FIG. 161. — Typical Sections through Imhoff Tanks.

Eng. News, Vol. 75, p. 15.

the return of gases through the sedimentation chamber, and
that there be no flow in the digestion chamber.

The Imhoff tank was invented by Dr. Karl ImhorT, director
of the Emscher Sewerage District in Germany. Its design is
patented in the United States, the control of the patent being
in the hands of the Pacific Flush Tank Co. of Chicago, which
collects the royalties which are payable when construction work
begins. The fee for a tank serving 100 persons is $10, for 1,000
persons is $80 and for 100,000 persons is $2550. The rate of
the royalty reduces in proportion as the number of persons served
increases.1 As designed by ImhorT and used in Germany the tanks
were of the radial flow type and quite deep. The depth, as
1 Eng. News Record, Vol. 78, 1917, p. 566.

DESIGN OF IMHOFF TANKS

419

explained by Imhoff, is one of the chief requirements for the
successful operation of the tank. As adapted to American
practice the tanks are generally of the longitudinal flow type
and are not made so deep. An isometric view of a radial flow
Imhoff tank is shown in Fig. 162. The sewage enters at the
center of the tank near the surface and flows radially outward
under the scum ring and over a weir placed near the circum-
ference of the tank. One type of longitudinal flow tank is shown
in isometric view in Fig. 163.

Sludge Bed
\jSedimenMion Compt.

tV^_
- Sludge Corfip't

~El.'JeJ'~
FIG. 162. — Sketch of Radial Flow Imhoff Tank at Baltimore, Maryland.

Eng. Record, Vol. 70, p. 5.

250. Design of Imhoff Tanks. — The velocity of flow, period
of retention, and the quantity of sewage to be treated determine
the dimensions of the sedimentation chamber as in other forms
of tanks. The velocity of flow should not exceed one foot per
minute, with a period of retention of 2 to 3 hours. A greater
velocity than one foot per minute results in less efficient sedi-
mentation. A longer period of retention than the approximate
limit set may result in a septic or stale effluent, and a shorter
period may result in loss of efficiency of sedimentation. The
bottom of the sedimentation chamber should slope not less
than \% vertical to 1 horizontal, in order that deposited material
will descend into the sludge digestion chamber. Provision
should be made for cleaning these sloping surfaces by placing
a walk on the top of the tank from which a squeegee can be
handled to push down accumulated deposits. It is desirable
to make the material of the sides and bottom of the sedimenta-

420

SEPTICIZATION

tion chamber as smooth as possible to assist in preventing the
retention of sludge in the sedimentation chamber. Wood, glass,
and concrete have been used. The latter is the more common
and has been found to be satisfactory. The length of the sedi-
mentation chamber is fixed by the velocity of flow and the
period of retention. Tanks are seldom built over 100 feet in

Stop Plank ^Outlet Channel for Reverse Flow f~~$fQn pjank

InletChannel,
Direct Flow or
Outlet Channel,
Reverse Flow--

„ General ' Arrangement

t 10-0"
C.toC.

AJv

>jj^' Reinforced
'\i Concrete
^ Walls and
Partitions.

Reducer
Iron Suppoi

FIG. 163. — Isometric View of Longitudinal Flow Imhoff Tank at Cleburne,

Texas.

Eng. News, Vol. 76, p. 1029.

length, however, because of the resulting unevenness in the accu-
mulation of sludge. Where longer flows are desired two or more
tanks may be operated in series. The width of the chamber
is fixed by considerations of economy and convenience. It
should not be made so great as to permit cross currents. In
general a narrow chamber is desirable. Satisfactory chambers
have been constructed at depths between 5 and 15 feet. The

DESIGN OF IMHOFF TANKS 421

depth of the sedimentation chamber and the depth of the diges-
tion chamber each equal about one-half of the total depth of the
tank. This should be made as deep as possible up to a limit
of 30 to 35 feet, with due consideration of the difficulties of
excavation. C. F. Mebus states:1

In 9 of the largest representative United States
installations, the depth from the flow line to the slot
varies from 10 feet 10 inches to 13 feet 6 inches.

Imhoff states, concerning the depth of tanks:

Deep tanks are to be preferred to shallow tanks
because in them the decomposition of the sludge is
improved. This is so because in the deeper tanks the
temperature is maintained more uniformly and because
the stirring action of the rising gas bubbles is more
intense.

The stirring action of the gas bubbles is desirable as it brings the
fresh sludge more quickly under the influence of the active bac-
terial agents. The greater pressure on the sludge in deep tanks
also reduces its moisture content.

Two or more sedimentation chambers are sometimes used over
one sludge digestion chamber in order to avoid the depths called
for by the sloping sides of a single sedimentation chamber. An
objection to multiple-flow chambers is the possibility of interchange
of liquid from one chamber to another through the common
digestion chamber.

The inlet and outlet devices should be so constructed that
the direction of flow in the tank can be reversed in order that the
accumulated sludge may be more evenly distributed in the hop-
pers of the digestion chamber. The sewage should leave the
sedimentation chamber over a broad crested weir in order to
minimize fluctuations in the level of sewage in the tank. The
gases in the digesting sludge are sensitive to slight changes in
pressure. A lowering of the level of sewage will release com-
pressed gas and will too violently disturb the sludge in the
digestion chamber. Hanging baffles, submerged 12 to 16 inches
and projecting 12 inches above the surface of the sewage, should
be placed in front of the inlet and outlet, and in long tanks inter-
mediate baffles should be placed to prevent the movement of
1 Municipal Engineering, Vol. 54, p. 149.

422 SEPTICIZATION

scum or its escape into the effluent. An Imhoff tank which is
operating properly should not have any scum on the surface of
the sewage in the sedimentation chamber.

The slot or opening at the bottom of the sedimentation
chamber should not be less than 6 inches wide between the lips.
Wider slots are preferable, but too wide a slot will involve too
much loss of volume in the digestion chamber. One lip of the
slot should project at least 3 inches horizontally under the other
so as to prevent the return of gases through the sedimentation
chamber. A triangular beam may be used as shown in Fig. 161 A.
This method of construction is advantageous in increasing the
available capacity for sludge storage.

The digestion chamber should be designed to store sludge from
6 to 12 months, the longer storage periods being used for smaller
installations. In warm climates a shorter period may be used
with success. The amount of sludge that will be accumulated
is as uncertain as in other forms of sewage treatment. A widely
quoted empirical formula, presented in " Sewage Sludge " by
Allen, states:

C = 10 . 5 P D f or combined sewage;
C = 5 . 25 P D for separate sewage,

in which C = the effective capacity of the digestion chamber

in cubic feet ;

P = the population served, expressed in thousands;
D = the number of days of storage of sludge.

The effective capacity of the chamber is measured as the entire
volume of the chamber approximately 18 inches below the
lower lip of the slot. The capacity as computed from the above
formula is assumed as satisfactory for a deep tank. Frank
and Fries l recommend the increase of the capacity for shallow
tanks to compensate for the decreased hydrostatic pressure.
In any event the formula can be no more than a guide to design.
No formula can be of equal value to data accumulated from
tests on the sewage to be treated. The Illinois State Board of
Health requires 3 cubic yards of sludge digestion space per
million gallons of sewage treated. Frank and Fries recommend
an allowance of 0.007 cubic foot of storage per inhabitant per day
for combined sewage and one-half that amount for separate

1 Eng. Record, Vol. 68, 1913, p. 452.

DESIGN OF IMHOFF TANKS 423

sewage. If this is based on 80 per cent moisture content, the
volume for other percentages of moisture can be easily com-
puted. An average figure used in the Emscher District is one
cubic foot capacity for each inhabitant for the combined system,
and three-fourths of this for the separate system. Metcalf
and Eddy 1 recommend the following method for the deter-
mination of the sludge storage capacity: (1) From analyses of
the sewage or study of the sources ascertain the amount of sus-
pended matter. (2) Assume, or determine by test, the amount
which will settle in the period of detention selected, say 60 per
cent in 3 hours. (3) Estimate the amount which will be digested
in the sludge chamber at about 25 per cent, leaving 75 per cent
to be stored. (4) Estimate the percentage moisture in the sludge
conservatively, say 85 per cent. The total volume of sludge
can then be computed. This method is more rational than
the use of empirical formulas, but because of the estimates
which must be made its results will probably be of no greater
accuracy than those obtained empirically.

The digestion chamber is made in the form of an inverted
cone or pyramid with side slopes at most about 2 horizontal to
1 vertical and preferably much steeper without necessitating too
great a depth of tank. The purpose of the steep slope is to con-
centrate the sludge at the bottom of the hopper thus formed.
Concrete is ordinarily used as the material of construction as
a smooth surface can be obtained by proper workmanship.
Where flat slopes have been used, a water pipe perforated at
intervals of 6 to 12 inches may be placed at the top of the slopes,
and water admitted for a short time to move the sludge when the
tank is being cleaned.

A cast-iron pipe, 6 to 8 inches in diameter, is supported in an
approximately vertical position with its open lower end supported
about 12 inches above the lowest point in the digestion chamber.
This is used for the removal of sludge. A straight pipe from the
bottom of the tank to a free opening in the atmosphere is desir-
able in order to allow the cleaning of the pipe or the loosening
of sludge at the start, and to prevent the accumulation of gas
pockets. The sludge is led off through an approximately hori-
zontal branch so located that from 4 to 6 feet of head are available
for the discharge of the sludge. A valve is placed on the hori-
1 Am. Sewerage Practice, Vol. Ill, p. 437.

424 SEPTICIZATION

zontal section of the pipe. A sludge pipe is shown in Fig. 162
and 163. Under such conditions, when the sludge valve is opened
the sludge should flow freely. The hydraulic slope to insure
proper sludge flow should not be less than 12 to 16 per cent.
Where it is not possible to remove the sludge by gravity an air
lift is the best method of raising it.

The volume of the transition or scum chamber should equal
about one-half that of the digestion chamber. The surface area
of the scum chamber exposed to the atmosphere should be 25
to 30 per cent of the horizontal projection of the top of the
digestion chamber. Some tanks have operated successfully
with only 10 per cent, but troubles from foaming can usually
be anticipated unless ample area for the escape of gases has
been provided.

All portions of the surface of the tank should be made
accessible in order that scum and floating objects can be broken
up or removed. The gas vents should be made large enough
so that access can be gained to the sludge chamber through
them when the tank is empty.

Precautions should be taken against the wrecking of the tank
by high ground water when the tank is emptied. With an empty
tank and high ground water there is a tendency for the tank to
float. The flotation of the tank may be prevented by building
the tank of massive concrete with a heavy concrete roof, by
underdraining the foundation, or by the installation of valves
which will open inwards when the ground water is higher than
the sewage in the tank. Dependence should not be placed on the
attendant to keep the tank full during periods of high ground
water.

Roofs are not essential to the successful operation of Imhoff
tanks. They are sometimes used, however, as for septic tanks,
to assist in controlling the dissemination of odors, to minimize
the tendency of the sewage to freeze, and to aid in bacterial
activity. In the construction of a roof, ventilation must be
provided as well as ready access to the tank for inspection,
cleaning, and repairs.

251. Imhoff Tank Results. — The Imhoff tank has the
advantage over the septic tank that it will not deliver sludge
in the effluent, except under unusual conditions. The Imhoff
tank serves to digest sludge better than a septic tank and it

STATUS OF IMHOFF TANKS 425

will deliver a fresher effluent than a plain sedimentation tank.
Imhoff sludge is more easily dried and disposed of than the
sludge from either a septic or a sedimentation tank. This is
because it has been more thoroughly humified and contains
only about 80 per cent of moisture. As it comes from the tank
it is almost black, flows freely and is filled with small bubbles
of gas which expand on the release of pressure from the bottom
of the tank, thus giving the sludge a porous, sponge-like consist-
ency which aids in drying. When dry it has a inoffensive odor
like garden soil, and it can be used for filling waste land, without
further putrefaction. It has not been used successfully as a
fertilizer.

Offensive odors are occasionally given off by Imhoff tanks,
even when properly operated. They also have a tendency to
" boil " or foam. The boiling may be quite violent, forcing scum
over the top of the transition chamber and sludge through the
slot in the sedimentation chamber, thus injuring the quality
of the effluent. The scum on the surface of the transition chamber
may become so thick or so solidly frozen as to prevent the escape
of gas with the result that sludge may be driven into the sedi-
mentation chamber.

Some chemical analyses of Imhoff tank influents and efflu-
ents are given in Table 86 and the analyses of some sludges from
Imhoff tanks are given in Table 83. It is to be noted that the
nitrites and nitrates are still present in the effluent, whereas
they are seldom present in the effluent from septic tanks. The
per cent of moisture in the Imhoff sludge is less than that in the
septic tank sludge, and its specific gravity is higher. It is heavier
and more compact because of the longer time and the greater
pressure it has been subjected to in the digestion chamber of the
Imhoff tank.

252. Status of Imhoff Tanks.— The introduction of the
Imhoff tank into the United States, like the introduction of the
Burkli-Ziegler Run-Off Formula, and Kutter's Formula, is to be
credited to Dr. Rudolph Bering. He advised Dr. Imhoff to
come to the United States to introduce his tank and gave him
material aid through recommendations and introductions to
engineers. Shortly after its introduction, in 1907, the tank
became very popular and installations were made in many
cities. This popularity was caused by a growing dissatisfaction

426 SEPTICIZATION

with the septic tank, the litigation then progressing over septic
patents, the production of inoffensive sludge, and the promising
results which had been obtained in Germany. As a result of the
extended experience obtained in the use of Imhoff tanks American
engineers have learned that, like all other sewage treatment
devices introduced up to the present time, the Imhoff tank
requires experienced attention for its successful operation. These
tanks are now being installed in the place of septic tanks, and
they are frequently used in conjunction with sprinkling filters.

253. Operation of Imhoff Tanks. — The important feature
in the successful operation of an Imhoff tank is the proper
control of the sludge and transition chambers. During the
ripening process, which may occupy 2 weeks to 3 months after
the start of the tank, offensive odors may be given off, the tank
may foam violently, and scum may boil over into the sedi-
mentation chamber. This is usually due to an acid condition
in the digestion chamber which may possibly be overcome by
the addition of lime. A very fresh influent will have a similar
effect. Too violent boiling is not likely to occur where the
area for the escape of gas has been made large and the gas is
not confined. Any accumulation of scum should be broken up
and pushed down into the digestion chamber, or removed from
the tank. The stream from a fire hose is useful in breaking up
scum. The side walls of the sedimentation chamber should be
squeegeed as frequently as is necessary to keep them free from
sludge, which may be as often as once or twice a week. Material
floating on the surface of the sedimentation chamber should be
removed from the tank or sunk into the digestion chamber
through the gas vents in the transition chamber.

No sludge should be removed, except for the taking of samples,
until the tank is well ripened. The ripening of the sludge can be
determined by examining a sample and observing its color and odor.
An odorless, black, granular, well humified sludge is indicative
of a ripened tank. After the tank has ripened, sludge should be
removed in small quantities at 2 to 3-week intervals, except in
cold or rainy weather. The sludge should be drawn off slowly
to insure the removal of the oldest sludge at the bottom of the
digestion chamber. After the drawing off of the sludge has
ceased the pipe should be flushed with fresh water to prevent
its clogging with dried sludge in the interim until the next

OTHER TANKS 427

removal. Under no circumstances should all the sludge in the
tank be removed at any time. The removal of some sludge
during foaming after ripening may reduce or stop the foaming.
The ripening of a tank can be hastened by adding some sludge
from a tank already ripened.

Sludge should not be allowed to accumulate within 18 inches
of the slot at the bottom of the digestion chamber. The elevation
of the surface of the sludge can be located by lowering into the
tank, a stoppered, wide-mouthed bottle on the end of a stick.
The stopper is pulled out by a string when the bottle is at some
known elevation. The bottle is then carefully raised and
observed for the presence of sludge. The process is repeated
with the bottle at different elevations until the surface of the
sludge has been discovered. Another method is to place the
suction pipe of a small hand pump at known points, successively
increasing in depth, and to pump in each position until one posi-
tion is found at which sludge appears in the pump. When the
sludge in one portion of the digestion chamber has risen higher
than in another portion, the direction of flow in the sedimentation
chamber should be reversed if possible. In the ordinary routine
of operation it is never necessary to shut down an Imhoff tank.
Sludge is removed while the tank is operating. The shut down
of a tank will be caused by accidents and breaks to the structure
or control devices.

254. Other Tanks. — The Travis Hydrolytic Tank represents
a step in the development from the septic tank to the Imhoff
tank. The Doten tank and the Alvord tank are recent develop-
ments, and are somewhat similar in operation to the Imhoff
tank.

The Travis Hydrolytic Tank when first designed differed
from the later design of the Imhoff tank in the slot between
the sedimentation chamber and the digestion chamber which
was not trapped against the escape of gas from the latter to the
former, and in operation a small quantity of fresh sewage was
allowed to flow through the digestion chamber. The tank is
called a hydrolytic tank because some solids are liquefied in it.
The tank is mainly of historic interest as designs similar to it are
rarely made to-day. Better results are obtained from the use
of the Imhoff tank. Recent developments have altered the
original design of the Travis tank so that it is hardly recognizable.

428

SEPTICIZATION

The Travis tank at Luton, Eng., is shown in Fig. 164. The
detailed description given in the Engineering News in connection
with this illustration shows that the governing object of the
design is to separate as quickly as possible the sludge deposited

HYDROLIZING
> CHAMBER-.
•ft -t-~

,'18 "Outlet- Carrier
to Filter Beds
,9"fnler

^. ,InM
flT^k Chamber

'•I5"CJ.

^•^f^^fy^f^

Section through
Inlet Chamber.

Cross
Section..

FIG. 164. — Plan and Section of Hydrolytic Tank at Luton, England.
Eng. News, Vol. 76, 1916, p. 194.

by the sewage without septic action being set up. To aid in the
collection and settlement of flocculent matter vertical wooden
grids or colloiders are used. The suspended matter strikes these
and forms a slimy deposit on them that in a short time slips off
in pieces large enough to settle readily.

OTHER TANKS

429

The Doten tank 1 is a single-storied, hopper-bottomed septic
tank, views of which are shown in Fig. 165. It was devised by
L. S. Doten for army cantonments during the War. Its chief
purpose was to avoid the foaming and frothing so common to
Imhoff tanks when overdosed with fresh sewage. The first
Alvord tank was constructed in Madison, Wis., in 1913.2 As
now constructed the tank consists of three deep, single-story com-
partments with hopper bottoms. These compartments are
arranged side by side in any one unit. Sewage enters at the sur-

IS'C.f. $

— Slope /.4% 8"C.I.SoilPipe,6ludgeDrain^ Outlet*. t* g.

^•10'Gate Valve '%< 8"6a/efo/V8S V ) ¥\ ^i"5"

" ^f^r i \m i "TUT *'s

-4-0*4-0 "Trap Doors

±L

Slope Gutter to End of Building

•IO"b.I.Soil'Pipe

Trap

, , r— ] Doors'**

— i — \-~97-9 \--\

-23-6- — )\'< 23-6-—

-8"6afe Valve Z,

Plan of Septic Tank

.-2"x6'Plate &&'

Section B-B

FIG. 165. — Doten Tank for Army Cantonment Sewage Disposal.

Eng. News-Record, Vol. 79, 1917, p. 931.

face of one of the compartments and is retained here during
one-half of the total period of retention. It leaves the first
compartment over a weir and passes in a channel over the top
of the intermediate compartment to the third or effluent com-
partment, where it is held for the remainder of the period of
detention. Accumulated scum and sludge are drawn off into the
intermediate compartment at the will of the operator, this

1 Trans. Am. Society Civil Engineers, Vol. 83, 1920, p. 337.
1 Eng. News Record, Vol. 83, 1919, p. 510.

430

SEPTICIZATION

compartment being used for sludge digestion only. Such tanks
as the Doten and the Alvord have been used for plants receiving
very fresh sewages such as is discharged from military canton-
ments, in order to assist in the prevention of the foaming to be
expected from an Imhoff tank receiving such a fresh influent.
The tanks are suitable for small installations, or where excavation
to the depth required for an Imhoff tank is not practicable. •

CHAPTER XVII
FILTRATION AND IRRIGATION

255. Theory. — The cycle through which the elements forming
organic matter pass from life to death and back to life again
has been described in Chapter XIII. It has been shown in
Chapter XVI that septic action occupies that portion of the
cycle in which the combinations of these elements are broken
down or reduced to simpler forms and the lower stages of the cycle
are reached. The action in the filtration of sewage builds up
the compounds again in a more stable form and almost complete
oxidation is attained, dependent on the thoroughness of the
filtration. In the filtration of sewage only the coarsest particles
of suspended matter are removed by mechanical straining. The
success of the filtration is dependent on biologic action. The
desirable form of life in a filter is the so-called nitrifying bacteria
which live in the interstices of the filter bed and feed upon the
organic matter in the sewage. Anything which injures the
growth of these bacteria injures the action of the filter. In a
properly constructed and operated filter, all matter which enters
in the influent, leaves with the effluent, but in a different molec-
ular form. A slight amount may be lost by evaporation and
gasification but this is more than made up by the nitrogen and
oxygen absorbed from the atmosphere. The nitrifying action
in sewage filtration is shown by the analysis of sewage passing
through a trickling filter, as given in Tables 86 and 87. It is
shown by the reduction of the content of organic nitrogen, free
ammonia, oxygen consumed, and the increase in nitrites, nitrates,
and dissolved oxygen. The reduction of suspended matter is
interrupted periodically when the filter " unloads." The sus-
pended matter in the effluent is then greater than in the influent.

The nitrifying organisms have been isolated and divided
into two groups — nitrosom&nas, the nitrite formers, and nitrobacter,
the nitrate formers. Experiments indicate that the growth of the

431

432 FILTRATION AND IRRIGATION

nitrobacter organisms is dependent on the presence of the
nitrosomonas organisms, which are in turn dependent on the
presence of the putrefactive compounds resulting from the action
of putrefying bacteria. The existence of these organisms is an
example of symbiotic action in bacterial growth. The organisms
have been found to grow best on rough porous material on which
their zocgleal jelly can be easily deposited and affixed. Sewage
filters were constructed to provide these ideal conditions before
the action of a filter was thoroughly understood.

The action in irrigation is similar to that in filtration.
Although more strictly a method of final disposal rather than
preliminary treatment, the similarity of the actions which take
place, and the grading of sand filtration into broad irrigation
with no distinct line of difference has resulted in the inclusion of the
discussion of irrigation in the same chapter with filtration.

256. The Contact Bed. — A contact bed is a water-tight basin
filled with coarse material, such as broken stone, with which
sewage and air are alternately placed in contact in such a manner
that oxidation of the sewage is effected. A contact bed has some
of the features of a sedimentation tank and an oxidizing filter.
As such it marks a transitory step from anaerobic to aerobic
treatment of sewage. A plan and a section of a contact bed are
shown in Fig. 166.

Because of its dependence on biologic action a contact bed
must be ripened before a good effluent can be obtained. The
ripening or maturing occurs progressively during the first few
weeks of operation, the earlier stages being more rapidly
developed. The time required to reach such a stage of maturity
that a good effluent will be developed will vary between one and
six or eight weeks, dependent on the weather and the character
of the influent. During the period of maturing the load on the
bed should be made light.

The use of contact beds has been extensive where a more
stable effluent than could be obtained from tank treatment has
been desired, yet the best quality of effluent was not required.
The sewage to undergo treatment in a contact bed should be given
a preliminary treatment to remove coarse suspended matter.
The efficiency of the contact treatment can be increased by
passing the sewage through two or three contact beds in series.
In dpuble contact treatment the primary beds are filled with

THE CONTACT BED

433

coarser material and operate at a more rapid rate than the
secondary beds. Double contact gives better results than
single contact, but triple-contact treatment, though showing
excellent results, is hardly worth the extra cost. An advantage
which contact treatment has over all other methods of sewage
filtration is that the bed can be so operated that the sewage is
never exposed to view. As a result the odors from well-operated
contact beds are slight or are entirely absent and there should be

Sand .Filters ; Contact Beds

151' *K- 148--

,Hor. Scale.
0 20' 40' 60'

•" • ..' . •TopofSond,Et.3l.23

Longitudinal Section.

FIG. 166. — Plan and Section of Treatment Plant at Marion, Ohio, Showing

Septic Tank, Contact Bed, and Sand Filter.

1908 Report Ohio State Board of Health.

no trouble from flying insects. Such a method of treatment is
favorable to plants located in populous districts and to the fancies
of a landscape architect. Another advantage of the contact
bed is the small amount of head required for its operation,
which may be as low as 4 to 5 feet. This low head consumption
by a sewage filter is equaled only by the intermittent sand
filter.

The quality of the effluent from some contact beds is shown
in Table 85. It is to be noted that nitrification has been carried
to a fair degree of completion, and that the reduction of oxygen
consumed has been marked. In comparison with the effluent

434

FILTRATION AND IRRIGATION

from filters, contact effluent contains a smaller amount of nitro-
gen as nitrites and nitrates, and suspended solids. Contact
effluent is usually clear and odorless, but it is not stable without
dilution. The absence of nitrites and nitrates is sometimes
advantageous as the effluent will not support vegetable growths
dependent on this form of nitrogen. The absence of suspended
solids obviates the use of secondary sedimentation basins which
are needed with trickling filters. The head of 5 to 8 feet
required for contact treatment is low in comparison to the 10
to 15 feet required for trickling filters, but is slightly higher than
the head required for intermittent sand filtration. The cost
of contact treatment is higher than the cost of trickling filters
but is lower than the cost of intermittent sand filtration, as
shown in Table 90.

TABLE 85

QUALITY OF EFFLUENTS FROM CONTACT BEDS
Report on Sewage Purification at Columbus, Ohio, by G. A. Johnson, 1905.

"R o+o

Nitrogen as

Suspended
Matter

a
i

Size of

rtate,
Million

•

Material

Gallons

in Inches

per Acre

J3
"ft

per Day

•a
B

'-S

_C8

Parts

per Million

0.25-1.00

0.953

3.5

8.7

0.20

1.6

832

737

0.3

0.25-2.00

1.514

4.0

8.4

0.15

1.4

831

746

0.1

0.25-1.50

1.222

3.5

10.8

0.11

0.6

826

734

0.8

0.50-1.50

1.405

3.3

9.5

0.13

0.9

810

717

0.9

Per Cent Removal of Constituer

its of Appli(

;d Sew

age

0.25-1.00

0.953

0.25-2.00

1.514

0.25-1.50

1.222

0.50-1.50

1.405

The depth of the contact bed is generally made from 4 to
6 feet. The deeper beds are less expensive per unit of volume,
to construct, as the cost of the underdrains and the distribution
system is reduced in relation to the capacity of the filter. The
increased depth reduces the aeration, and the periods of filling

THE CONTACT BED 435

and emptying are so increased as to limit the depths to the figures
stated. The other dimensions of the bed are controlled by
economy and local conditions, as the success of the contact
treatment is not affected by the shape of the bed. Contact
units are seldom constructed larger than one-half an acre in area,
as larger beds require too much time for rilling and emptying.
A large number of small units is also undesirable because of the
increased difficulty of control. In general it is well to build as
large units as are compatible with efficient operation, elasticity
of plant, and which can be filled within the time allowed at the
average rate of sewage flow, or from dosing tanks in which the
storage period is not so long as to produce septic conditions.

The interstices in a contact bed will gradually fill up, due to
the deposition of solid matter on the contact material, the dis-
integration of the material, and the presence of organic growths.
The period of rest allowed every five or six weeks tends to restore
partially some of this lost capacity through the drying of the
organic growths. It is occasionally necessary to remove the
material from the bed and wash it in order to restore the original
capacity. It may be necessary to do this three or four times a
year, in an overloaded plant, or as infrequently as once in five or
six years in a more lightly loaded bed. The period is also
dependent on the character of the contact material and the quality
of the influent. This loss of capacity may reduce the voids from an
original amount of 40 to 50 per cent of voids to 10 to 15 per
cent. If the bed is not overloaded the loss of capacity will not
increase beyond these figures.

The rate of filtration depends on the strength of the sewage,
the character of the contact material, and the required effluent.
It should be determined for any particular plant as the result
of a series of tests. For the purposes of estimation and com-
parison the approximate rate of filtration should be taken at
about 94 gallons per cubic yard of filtering material per day on
the basis of three complete fillings and emptyings of the tank.
This is equivalent to 150,000 gallons per acre foot of depth per
day, or for a bed 5 feet deep to a rate of 750,000 gallons per acre
per day. The net rate for double or triple filtration is less than
these figures, but on each filter the rates are higher.

The material of the contact bed should be hard, rough, and
angular. It should be as fine as possible without causing clogging

436 FILTRATION AND IRRIGATION

of the bed. Materials in successful use are: crushed trap rock
or other hard stone, broken bricks, slag, coal, etc. Soft crumbling
materials such as coke are not suitable as the weight of the
superimposed material and the movement of the sewage crushes
and breaks it into fine particles which accumulate in the lower
portion of the filter and clog it. Roughness, porosity, and small
size are desirable, as the greater the surface area the more rapid
the deposition of material. After a short time, however, the
advantages of roughness and porosity are lost, as the sediment
soon covers all unevenness alike. The minimum size of the
material is limited by the tendency towards clogging. The sizes
in successful use vary between \ and f of an inch, \ inch being
a common size. The same size of material is used throughout
the depth of the bed except that the upper 6 inches may be
composed of small white pebbles or other clean material, which
does not come in contact with the sewage and which will give
an attractive appearance to the plant. In double or triple con-
tact beds 3 or 4-inch material is sometimes used for the primary
beds, and j-inch material in the final bed.

Sewage may be applied at any point on or below the surface.
The sewage is withdrawn from the bottom of the bed. It is
undesirable to have too few inlet or outlet openings as the
velocity of flow about the openings will be so great as to disturb
the deposit on the contact material. The distribution system
and the underdrains for the bed at Marion, Ohio, are shown in
Fig. 166.

The cycle of operation of a contact bed is divided into four
periods. A representative cycle might be: tune of filling, one
hour; standing full, 2 hours; emptying, one hour; standing
empty, 4 hours. The length of these periods is the result of long
experience based on many tests and are an average of the conclu-
sions reached. Wide variations from them may be found in
different plants, and tests may show successful results with
different periods. The combination of these four periods is known
as the contact cycle.

The period of filling should be made as short as possible
without disturbing the material of the bed nor washing off the
accumulated deposits. The sewage should not rise more rapidly
than one vertical foot per minute. During the contact or stand-
ing full period sedimentation and adsorption of the colloids are

THE TRICKLING FILTER 437

occurring on the area of surface exposed to the sewage. This
period should be of such length that septic action does not become
pronounced, and long enough to permit of thorough sedimenta-
tion. The period of emptying should be made as short as possible
without disturbing the bed, on the same basis that the period
of filling is determined. During the period of standing empty,
air is in contact with the sediment deposited in thin layers on the
contact material, and the oxidizing activities of the filter are taking
place. The filter is given a rest period of one or two days
every five or six weeks, in order that it may increase its
capacity and it biologic activity.

The control of a contact bed may be either by hand or auto-
matic, the latter being the more common. Hand control requires
the constant attention of an operator and results in irregularity
of operation, whereas automatic control will require inspection
not more than once a day and insures regularity of operation.
A number of automatic devices have been invented which give
more or less satisfaction. The air-locked automatic siphons,
without moving parts, have proven satisfactory and are practi-
cally " fool-proof." The operation of these devices is explained
in Chapter XXI.

257. The Trickling Filter. — A trickling or sprinkling filter
is a bed of coarse, rough, hard material over which sewage is
sprayed or otherwise distributed and allowed to trickle slowly
through the filter in contact with the atmosphere. A general
view of a trickling filter in operation at Baltimore is shown in
Fig. 167. The action of the trickling filter is due to oxidation
by organisms attached to the material of the filter. The solid
organic matter of the sewage deposited on the surface of the
material, is worked over and oxidized by the aerobic bacteria,
and is discharged in the effluent in a more highly nitrified con-
dition. At times the discharge of suspended matter becomes
so great that the filter is said to be unloading. The action differs
from that in a contact bed in that there is no period of septic
or anaerobic action and the filter never stands full of sewage.

The effluent from a trickling filter is dark, odorless, and is
ordinarily non-putrescible. Analyses of typical effluents are
given in Tables 86 and 87. The unloading of the filter may occur
at any time, but is most likely to occur in the spring or in a
warm period following a period of low temperatures. It causes

438

FILTRATION AND IRRIGATION

higher suspended matter in the effluent than in the influent
and may render the effluent putrescible. The action is marked
by the discharge of solid matter which has sloughed off of the
filter material and which increases the turbidity of the effluent.
Where the diluting water is insufficient to care for the solids so
carried in the effluent, they can be removed by a 2-hour period
of sedimentation. The effluent may become septic during this
time, however. The nitrogen in the effluent is almost entirely
in the form of nitrates, and the percentage of saturation with
dissolved oxygen is high. The effluent is more highly nitrified
than that from a contact bed, and its relative stability is also
higher, thus demanding a smaller volume of diluting water.

FIG. 167. — Sprinkling Filter in Operation in Winter at Baltimore.

The principal advantage of a trickling filter over other methods
of treatment is its high rate which is from two to four times faster
than a contact bed, and about seventy times faster than an inter-
mittent sand filter. The greatest disadvantage is the head of 12 to
15 feet or more necessary for its operation. Sedimentation of the
effluent is usually necessary to remove the settleable solids.
During the period of secondary sedimentation the quality of the
filter effluent may deteriorate in relative stability. In winter the
formation of ice on the filter results in an effluent of inferior
quality, but as the diluting water can care for such an effluent
at this time the condition is not detrimental to the use of the
trickling filter. In summer the filters sometimes give off offen-
sive odors that can be noticed at a distance of half a mile, and
flying insects may breed in the filter in sufficient quantities to

THE TRICKLING FILTER

439

become a nuisance if preventive steps are not taken. The dis-
semination of odors is especially marked when treating a stale
or septic sewage. The treatment of a fresh sewage seldom results
in the creation of offensive odors.

TABLE 86

ANALYSIS OF CRUDE SEWAGE, IMHOFF TANK, AND SPRINKLING FILTER
EFFLUENTS AT ATLANTA, GEORGIA

(Engineering Record, Vol. 72, p. 4)

£ «.

-1
a •§

Parts per Million

turation,
Oxygen

Nitrogen as

Suspended Matter

i t

OQ *

a •§
£«•

Organic

Free Am
monia

Nitrites

Nitrates

x «o

"3
e
E-i

Volatile

Per Cent
Dissol

Relative

Crude Se-vage

1913
Maximum

77
61

15.6
10 4

21.8
16.5

0.1
0.1

3.0
1.4

100.0
78 3

371
222

154
98

163
112

47
11

12.8

18.8

0.1

2.2

90.6

285

126

138

1914 (7 months)

16.9

33.4

2.3

431

9.5

18.1

1.6

279

13.4

27.1

2.0

351

Imhoff Effluent

1913
Maximum

78
58

13.2
6.5

21.9
16.8

0.2
0 1

3.1
1 1

68.0
53 1

90
35

50
42

9 0

20 0

0 2

2 1

60 1

1914 (7 months)
Maximum
Minimum

77
59

10.3
4.1

30.3
18.0

2.0
1.5

73
49

48
34

7.7

25.9

1.8

Sprinkling Filter Effluent

1913

Maximum

5.6

14.2

0.8

11.3

32.1

Minimum

2.6

6.2

0.5

5.8

23.6

3.8

9.9

0.7

8.2

28 2

1914 (7 months)

Maximum

8.5

20.7

11.2

106

Minimum

4.4

8.8

3.6

5.7

15.2

7.2

440

FILTRATION AND IRRIGATION

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THE TRICKLING FILTER 441

Raw sewage cannot be treated successfully on a trickling
filter. Coarse solid particles should be screened and settled out,
in order that the distributing devices or the filter may not become
clogged. The effluent from an Imhoff tank has proven to be a
satisfactory influent for a trickling filter. A septic tank effluent
may be so stale as to be detrimental to the biologic action in the
filter.

In the operation of a trickling filter the sewage is sprayed
or otherwise distributed as evenly as possible in a fine spray or
stream, over the top of the filtering material. The sewage then
trickles slowly through the filter to the underdrains through
which it passes to the final outlet. The distribution of the
sewage on the bed is intermittent in order to allow air to enter
the filter with the sewage. The cycle of operation should be
completed in 5 to 15 minutes, with approximately equal periods
of rest and distribution. Cycles of too great length will expose
the filter to drying or freezing and will give poorer distribution
throughout the filter. Cycles which are too short will operate
successfully only with but slight variation in the rate of sewage
flow. In some plants it has been found advantageous to allow
the filters to rest for one day in 3 to 6 weeks or longer, dependent
on the quality of the effluent.

The rate of filtration may be as high as 2,000,000 gallons per
acre per day, which is equivalent to 200 gallons per cubic yard
of material per day in a bed 6 feet deep. This is more than
double the rate permissible in a contact bed. The exact rate
to be used for any particular plant should be determined by
tests. It is dependent on the quality of the sewage to be treated,
on the depth of the bed, the size of the filling material, the
weather, and other minor factors.

The filtering material is similar to that used in a contact bed.
It should consist of hard, rough, angular material, about 1 to
2 inches in size. Larger sizes will permit more rapid rates of
filtration, but will not produce so good an effluent. Smaller
sizes will clog too rapidly.

The depth of the filter is limited by the possibility of ventila-
tion and the strength of the filtering material to withstand crush-
ing. The deeper the bed the less the expense of the distribution
and collecting system for the same volume of material, and the
more rapid the permissible rate of filtration. The depths in

442 FILTRATION AND IRRIGATION

use vary between 6 and 10 feet, with 6 to 8 feet as a satisfactory
mean. From a biologic standpoint the action of the filter seems
to be proportional to the volume of the filtering material and
therefore proportional to the depth of the bed, being limited to
a minimum depth of about 5 feet, below which sewage may pass
through the filter without treatment. The shape and other
dimensions of the filter depend on the local conditions and the
economy of construction. The filters need not be broken up
into units by water-tight dividing walls. One filter can be
constructed sufficient for all needs and various portions of it can
be isolated as units by the manipulation of valves in the dis-
tribution system. Ventilation is provided by the air entrained
with the sewage as it falls upon the surface. If the sides of the
filter are built of open stone crib work the ventilation will be
greatly improved, but it will not be possible to flood the filters
to keep down flies, and in cold climates these openings must be
covered in winter to prevent freezing. Filters have been con-
structed without side walls, the filtering material being allowed
to assume its natural angle of repose. This has usually been
found to be more expensive than the construction of side retaining
walls, due to the unused filling material and the extra under-
drains required.

The distribution of sewage is ordinarily effected by a system
of pipes and spray nozzles as shown in Fig. 168 and 169. Other
methods of distribution have been used. At Springfield, Mo.,1
a moving trough from which the sewage flows continuously is
drawn back and forth across the bed by means of a cable. In
England circular beds have been constructed and the sewage
distributed on them through revolving perforated pipes. At
the Great Lakes Naval Training Station 2 the distributing pipes
in the plant, now abandoned, were supported above the surface
of the filter. The sewage fell from holes in the lower side of these
pipes on to brass splash plates 14 inches above the filter. It
was deflected horizontally from these plates over the filter sur-
face. Pipes and spray nozzles have been adopted almost univer-
sally in the United States. Splash plates, traveling distributors,
and other forms of distribution have been used only in excep-

1 See Eng. News, Vol. 70, 1913, p. 1112; Eng. Record, Vol. 68, 1913, p.
440, and Eng. News, Vol. 75, 1916, p. 1028.
*See Eng. Record, Vol. 67, 1913, p. 232.

THE TRICKLING FILTER

443

tional cases. In a distributing system consisting of pipes and
nozzles, a network of pipes is laid out somewhat as shown in
Fig. 168, in such a manner that the head loss to all points is
approximately equal. The number of valves required should
be reduced to a minimum. The pipes may be laid out with the
main feeders leading from a central point and branches at right
angles to them, somewhat on the order of a spider's web, or they
may be laid out on a rectangular or gridiron system. The
radial system is advantageous because of the central location

16'C.I. Pipe Distributors

'••'^Crushed Stone Filling I 'to 2

.-Port Hole
fel

tyW!'-"W/p,

^-Flushing

Gallery
Cross Section A-A.

Grade 0.00 ?5 '-,

21 "Side Drain

... ,

^f 12" C.I. Pipe

No:7-l -?'•'-

6"C.f.H'aferMa/n^ 6"Disch Pipe

•-V

Grade 0.0028-

A '-W'By-rtiss

Drain
Plan

FIG. 168. — Section through Sprinkling Filter at Fitchburg, Mass., Showing

Distribution System.
Eng. Record, Vol. 07, p. 634.

of the control house, but it does not always lend itself favorably
to the local conditions, and the piping and nozzle location are
not so simple. The gridiron system lends itself favorably to
the equalization of head losses. The pipes used should be larger
than would be demanded by considerations of economy alone,
both for the purpose of reduction of head loss and ease in cleaning.
No pipe less than 6 inches in diameter should be used, and the
average velocity of flow should not exceed one foot per second.
Cast iron, concrete, or vitrified clay pipe may be used, but cast

444 FILTRATION AND IRRIGATION

iron is the material commonly used. The system should be
arranged for easy flushing and cleaning and the pipes so sloped
that the entire system can be drained in case of a shut down
in cold weather.

The pipes are placed far enough below the surface of the
filling material so that the top of the spraying nozzle is 6 to
12 inches above the surface of the filter. If the pipes are placed
near the surface they are accessible for repairs, but are exposed
to temperature changes. If the pipes are large their presence
near the surface of the filter may seriously affect the distribution
of the sewage through the filter. If the distributing pipes are
placed near the bottom of the filter they are inaccessible for
repairs and the nozzles must be connected to them by means
of long riser pipes. The distributing pipes should be supported
by columns extending to the foundation of the filter bed, there
being a column at every pipe joint with such intermediate sup-
ports as may be required. In some plants the pipes have been
supported by the filtering material. Although slightly less
expensive in first cost the practice of so supporting the pipes is
poor, as settling of the material may break the pipe or cause
leaks, and if the bed becomes clogged, removal of the material
is made more difficult. Valves should be placed in the distribut-
ing system in such a manner that different sets of nozzles can
be cut out at will, thus resting those portions of the filter
and permitting repairs without shutting down the entire
filter.

The spacing of the nozzles is fixed by the type and size of the
nozzle, the available head, and the rate of filtration. Various
types of sprinkler nozzles are shown in Fig. 169 and the dis-
charge rates, head losses, and distances to which sewage is
thrown for the Taylor nozzles, are shown in Fig. 170. Nozzles
are available which will throw circular, square, or semicircular
sprays. In the use of circular sprays there is necessarily some
portion of the filter which is underdosed if the nozzles are placed
at the corners of squares with the sprays tangent, and there is
an overdosing of other portions if the sprays are allowed to
overlap so that no portion of the filter is left without a dose.
Rectangular sprays will apparently overcome these difficulties,
but studies have shown that circular sprays with some over-
lapping, and the nozzles placed at the apexes of equilateral tri-

THE TRICKLING FILTER

445

A'Dfamefer
of Orifice.
B* Diameter
ofSpindle
at Orifice.

Prieslman-Beddoes Weand, Atlantic Type
Round Nonle. Round Noiile. Worcester1 Round

FIG. 169.— Sprinkling Filter Nozzles.

Bulletin No. 3, Engineering Experiment Station, Purdue University.

30 28

Discharge, Gallons per Mirru+e
26 24 22 20 18 16

VL 14 16

Nozzle Spacing, Feet.,

FIG. 170. — Diagram Showing the Discharge and Spacing of Taylor Nozzles.

446

FILTRATION AND IRRIGATION

angles as shown in Fig. 172 will give as satisfactory distribution
as other forms.

The nozzles should be selected to give the best distribution,
to consume all of the head available, and to give the proper
cycle of operation. The entire head available should be consumed
in order that the fewest number of nozzles may be used. An
excellent study of the characteristics of various types of nozzles
has been published in Bulletin No. 3 of the Engineering Experi-
ment Station at Purdue University, 1920. As a result of the
tests on the nozzles shown in Fig. 169, it was determined for all
nozzles, except No. 8, that

Q=CaV2gh;

in which Q =the rate of discharge in cubic feet per second;
C = a coefficient shown in Table 88 ;
a=the net cross-sectional opening of the nozzle in

square feet;
h =the pressure on the nozzle in feet of water.

TABLE 88
COEFFICIENTS OF DISCHARGE FOR SPRINKLER NOZZLES SHOWN IN FIG. 169

Nozzle Number

Coefficient

648

.756

.696

.666

.675

.598

.569

It is evident that if the head on the nozzles is constant and the
nozzle throws a circular spray, the intensity of dosing at the
circumference will be greater than nearer the center. This
difficulty is overcome by so designing the dosing tank from which
the sewage is fed that the head on the nozzle and the quantity
thrown will vary in such a manner that the distribution over
the bed is equalized. Intermittent action is obtained by an
automatic siphon which commences to discharge when the tank
is full and empties the tank in the period allowed for dosing.
Under such conditions the tank should discharge for a longer
time at the higher heads than at the lower heads as there is
more territory to be covered at the higher heads. The design
of the tank to do this with exactness is difficult, and the con-
struction of the necessary curved surfaces is expensive. Where

THE TRICKLING FILTER

447

a dosing tank is used for such conditions it has been found satis-
factory to construct the tank with plane sides sloping at approxi-
mately 45 degrees from the vertical (or horizontal). A tank
with curved surfaces is shown in Fig. 171. The dosing siphon
is usually placed in the tank as shown in the figure. The head
and quantity of discharge through the nozzles can be varied
also by maintaining a constant depth in a dosing tank by means

FIG. 171. — Section of 12-inch Siphon and Dosing Tank, for King's Park, Long

Island.

of a float feed valve, and varying the head and quantity dis-
charged to the nozzles by a butterfly valve in the main feed line,
or by the use of a Taylor undulating valve designed for this
purpose. The butterfly valve is opened and closed by a cam
so designed and driven at such a rate that the required distribu-
tion is obtained. The Taylor undulating valve is opened and
closed at a constant rate, the shape of the valve giving the
required variations in head and discharge Other methods
of control have been attempted but have not been used exten-
sively.

An example of the design of the nozzle layout and dosing
tank for a sprinkling filter follows:

448

FILTRATION AND IRRIGATION

Let it be required to determine the nozzle layout
for one acre of sprinkling filters with 5 feet available head
on the nozzles.

The selection of the type of nozzle and the size of
opening is a matter of judgment and experience. Noz-
zles with large openings are less liable to clog and fewer
nozzles are needed than where small nozzles are used,
but the distribution of sewage is not so even as with the
use of small nozzles. In this example Taylor circular
spray nozzles will be selected. Fig. 170 shows that a
Taylor circular spray nozzle will discharge 22.3 g.p.m.
under a head of 5 feet, and that the economical nozzle
spacing will be 15.3 feet. The least number of nozzles
at this spacing required for a bed of one acre in area is
found as follows: In Fig. 172, let n equal the number of

FIG. 172. — Typical Sprinkler Nozzle Layout.

nozzles in a horizontal row, counting half-spray nozzles as |,
and let ra equal the number of rows counting rows of half-
spray nozzles as half rows.1 Then the number of nozzles,
N, equals ran, and 15.3raXl3.2n equals 43,560 or ran
equals 215.

The next step should be the design of the dosing tank and
siphon. It is possible to design a tank which will give equal
distribution over equal areas of filter surface. It has been

1 The use of half-spray nozzles is not always advocated as it is consid-
ered that their use does not markedly improve the distribution. Where hah"
nozzles are used, a margin of 18 inches to 2 feet should be allowed between
the edge of the filter and the nozzle, to prevent the blowing of raw sewage
from the filter.

THE TRICKLING FILTER 449

found, however, that the expense of this refinement is unwar-
ranted as there are a number of outside factors which tend to
overcome the theoretical design. The effect of wind, unequal
spacing, and irregularities in the elevation of the nozzles have a
tendency to offset refinements in the design of a dosing tank.
It is therefore the general practice to slope the sides of the tank
at an angle of about 45 degrees as previously stated. The
dosing tank is generally designed to have a capacity which will
give a complete cycle of operation once in 15 minutes. In the
ordinary design the factors given are the rate of inflow and the
given time of filling. In the following example the time of filling
will be taken as 10 minutes, the time of emptying as 5 minutes,
and the rate of flow as 1,000,000 gallons per day. The capacity

1 000 000
of the tank will therefore be ' ' =7,000 gallons. The

diameter of the siphon to be selected can be computed as follows :

Let Q =the capacity of the tank in cubic feet;

q\ = the rate of discharge of the siphon in cubic feet per second ;
Q2 = the rate of inflow to the tank in cubic feet per second ;
q = the rate of emptying the tank in cubic feet per second =

(91-92);
A =the cross-sectional area of the free surface of the water

in the tank at any instant, in square feet;
a =the cross-sectional area of the siphon in square feet;
6 =the small dimension of the base of the tank in feet;
h =the head of water, in feet, on the discharge siphon;
hi =the initial head of water, in feet, on the siphon;
/i2 = the final head of water in feet, on the siphon ;
t =the time, in seconds, required to empty the tank,

then
and

but

—Adh
therefore t=

but A =4fc2+46/i+&2,

rh*(b2
= I

Jh, Q

AU f +4bh+4h2)dh

therefore t

AaV2gh-q2

1 From paper by E. G. Bradbury in Proceedings of the Ohio Eng. Society,
1910, p. 79.

450

FILTRATION AND IRRIGATION

The integration of this expression is tedious. Its solution
for siphons between 6 inches and 12 inches operating under
heads commencing from 3 feet to 6 feet, with a time of emptying
of 5 minutes and time of filling of 10 minutes is given in Fig.
173. In the example given the rate of inflow is 1.55 sec. feet
and the head is 5 feet. Then from Fig. 173 the size of the siphon
to be used is 12 inches. Where a siphon of the size required

Rate of Inflow; Cubic Feet per Second
0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 .1.7

2000

7000

8000

3000 4000 5000 6000

Capacity of Tank in Gallons.

FIG. 173. — Diagram for the Determination of the Capacities of Dosing Tanks
for Trickling Filters.

Time of emptying, 5 minutes. Time of filling, 10 minutes. Shape of tank is a right pyramid
or a truncated right pyramid with all four sides making an angle of 45 degrees with the ver-
tical. All horizontal cross-sections are squares.

to empty the tank in the time fixed is not available, combinations
of available sizes can sometimes be used.

For example, if the given head is 6 feet, and the rate
of inflow is 1.4 sec. feet, it is evident from Fig. 173 that
a 6,300-gallon dosing tank and two 8-inch siphons will
give the required cycle.

The method used for the design of the setting of Taylor
nozzles by the Pacific Flush Tank Co., is less rational but more
simple and probably as satisfactory. In this method the steps
are as follows:

(1) Divide the maximum daily rate of sewage flow by
. 1,000 to get the maximum minute inflow.

THE TRICKLING FILTER 451

(2) The number of nozzles required is determined by
dividing the preceding figure by 6. Generally a Taylor
nozzle with an orifice of | of an inch will discharge about
20 g.p.m. at the high head and about 8 g.p.m. at the low
head, and as the nozzles must have a capacity which
will take care of the inflow at the low head, the divisor 6
is used as a factor of safety instead of using 8 as the
divisor.

(3) The type of nozzle to be used is selected from
experience or as a matter of judgment. Circular-spray
nozzles are more generally used.

(4) The spacings are determined from Fig. 170.

(5) The dosing tank of the shape described is then
designed. The capacity is such as to give a complete
cycle once every 15 minutes. The method of this design
is similar to that followed previously.

(6) The dosing siphons are designed so that they will
have a capacity at the minimum head of from 40 to 50
per cent in excess of the maximum minute inflow, and the
draining depth of the siphon will be limited to a maximum
of 5 to 5^ feet. The siphons are all made adjustable with
a variation of 6 inches or more on either side of the normal
discharge line so that the spraying area and cycle can be
varied to secure the best results.

The underdrainage of a trickling filter should consist of some
form of false bottom such as the types shown in Fig. 174. Where
possible the underdrains should be open at both ends for the
purpose of ventilation and flushing. It is desirable that the
drains be so arranged that a light can be seen through them in
order that clogging can be easily located. The drains should be
placed on a slope of approximately 2 in 100 towards a main
collector. The length of the drains is limited by their capacity
to carry the average dose from the area drained by them.
The main collecting conduits must be designed in accordance
with the hydraulic principles given in Chapter IV. No valves,
or other controlling apparatus, are placed on the underdrains
or outlets from the filter.

Covers have been provided in winter for some trickling
filters in cold climates. The Taylor sprinkling nozzle has been
found to work successfully in extremely cold weather, and it is
generally accepted that the covering of filters is unnecessary, if
the filter is not to be shut down for any length of time in cold
weather.

452

FILTRATION AND IRRIGATION

The operation of devices for automatically controlling the
operation of a trickling filter is explained in Chapter XXI.

258. Intermittent Sand Filter. — An intermittent sand filter
is a specially prepared bed of sand, or other fine grained material,
on the surface of which sewage is applied intermittently, and
from which the sewage is removed by a system of underdrains.
It differs from broad irrigation in the character of the material,
the care and preparation of the bed, and the thoroughness of the
underdrainage. A distinctive feature of the intermittent sand

Slotted
Vitrified
Half
Tile.

Type C. Type D7 Type C-Z.

FIG. 174.— Types of False Bottoms for Trickling Filters.
Eng. News, Vol. 74, p. 5.

filter is the quality of the effluent delivered by it. In a properly
designed and operated plant the effluent is clear, colorless, odor-
less, and sparkling. It is completely nitrified, is stable and con-
tains a high percentage of dissolved oxygen. It contains no
settleable solids except at widely separated periods when a small
quantity may appear in the effluent. The percentage removal
of bacteria may be from 98 to 99 per cent. Some analyses of
sand filter effluents are given in Table 89. The dissolved solids,
the remaining bacteria, and the antecedents of the effluent are
the only differences between it and potable water. An effluent
from an intermittent sand filter is the most highly purified

INTERMITTENT SAND FILTER

453

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454 FILTRATION AND IRRIGATION

effluent delivered by any form of sewage treatment. The
effluent can be disposed of without dilution, on account of its
high stability. The treatment of sewage to so high a degree is
seldom required, so that the use of intermittent filters is not
common. Other drawbacks to their use are the relatively large
area of land necessary and the difficulty of obtaining good filter
sand in all localities.

The action in an intermittent sand filter is more complete
than in other forms of filters because a greater surface is exposed
to the passage of sewage by the fine sand particles, and the
sewage is in contact with the filtering material a longer time
due to the lower rate of filtration and the slow velocity of flow
through the filter. It is essential that the sewage be applied
to the bed intermittently in order that air shall be entrained in
the filter. The period between doses should not be so long that
the filter becomes dry.

In the operation of an intermittent sand filter one dose per
day is considered an ordinary rate of application, although
some plants operate with as many as four doses per day per filter,
and others on one dose at long and irregular intervals. It is
not always necessary to rest the filter for any length of time unless
signs of overloading and clogging are shown. The intermittent
dosing action may be obtained by the action of an automatic
siphon as is described in Chapter XXI. The sewage is distributed
on the beds through a number of openings in the sides of distribut-
ing troughs resting on the surface of the filter. The sewage is
withdrawn from the bottom of the filter through a system of
underdrains, into which it enters after its passage through the
bed. There are no control devices on the outlet, as the rate of
filtration is controlled by the action of the dosing apparatus
and the rate at which sewage is delivered to it. The action
of the dosing apparatus should respond quickly to variations
in sewage flow. As the doses are applied to a sand filter, a mat
of organic matter or bacterial zooglea is formed on the surface
of the bed. The mat is held together by hair, paper, and the
tenacity of the materials. It may attain a thickness of j to \
an inch before it is necessary to remove it. So long as the filter
is draining with sufficient rapidity this mat need not be removed,
but if the bed shows signs of clogging, the only cleaning that
may be necessary will be the rolling up of this dried mat. It

INTERMITTENT SAND FILTER 455

is believed that the greater portion of the action in the filter
occurs in the upper 5 to 8 inches of the bed, but occasionally the
beds become so clogged that it is necessary to remove f of an
inch to 2 inches of sand in addition to the surface mat, or to
loosen up the surface by shallow plowing or harrowing. The
necessity for such treatment may indicate that the filter is being
overloaded as a result of which the rate of filtration should be
decreased or the preliminary treatment should be improved.
The plowing of clogging material into the bed should be avoided
as under these conditions the final condition of the bed will be
worse than its condition when trouble was first observed.

In winter the surface of the bed should be plowed up into
ridges and valleys. The freezing sewage forms a roof of ice
which rests on the ridges and the subsequent applications of
sewage find their way into the filter through the valleys under
the ice. In a properly operated bed the filtering material will
last indefinitely without change. If a filter is operated at too
high a rate, however, although the quality of the effluent may be
satisfactory, it will be necessary at some time to remove the sand
and restore the filter.

The rate of filtration depends on the character of the influent,
the desired quality of the effluent, and the depth and character
of the filtering material. Filters can be found operating at rates
of 50,000 gallons per acre per day and others at eight times this
rate. For sewage which has had some preliminary treatment, the
rate should not exceed 100,000 gallons per acre per day, whereas
the rate for raw sewage should be less than this. For rough
estimates made without tests of the sewage in question, the rate
should not be taken at more than 1,000 persons per acre. If the
preliminary treatment of the sewage has been thorough and the
material of the sand filter is coarser than ordinary the rate of
filtration can be high. For less careful preliminary treatment
and fine filtering material the rates must be reduced. The
sewage must undergo sufficient preliminary treatment to remove
large particles of solid matter which would otherwise clog the
dosing apparatus and the filter. This treatment should include
grit removal, screening, and some form of tank treatment.
Some plants have operated successfully with a stale sewage and
no preliminary treatment, as at Brockton, Mass. Septic tank
effluent can be treated successfully on an intermittent sand

456 FILTRATION AND IRRIGATION

filter, but not so satisfactorily as the effluent from a tank
delivering a fresh sewage.

The material of the filter should consist of clean, sharp,
quartz or silica sand with an effective size l of 0.2 to 0.4 mm.,
preferably about 0.25 to 0.35 mm., and a uniformity coefficient 2
of 2 to 4. Within the limits mentioned no careful attention
need be given to the size of the material. Natural sand found
in place has been underdrained and used successfully for sewage
treatment. The size of the sand is fixed by the rate of filtra-
tion rather than the bacteriological action of the filter. A
coarse sand will permit the sewage to pass through the bed too
rapidly, and a fine sand will hold it too long or will become
clogged. The same size of material should be used throughout
the bed, except that a layer of gravel from 6 to 12 inches thick,
graded from very small sizes to stones just passing a 2-inch
ring should be placed at the bottom to facilitate the drainage of
the bed.

The thickness of the sand layer should not be less than 30
inches to insure complete treatment of the sewage. In shallower
beds the sewage might trickle through without adequate treat-
ment. Beds are ordinarily made from 30 to 36 inches deep,
but when deeper layers of sand are found in place there is no set
limit to the depth which may be used. The shape and overall
dimensions of the bed should conform to the topography of the
site and the rate of filtration adopted. A plan and cross-section
of an intermittent sand filter showing the distribution and
underdrainage systems are given in Fig. 166 and 175.

The distribution system consists of a system of troughs on
the surface of the filter, laid out in a branching form, as shown
in the figure. The openings in the troughs should be so
located that the maximum distance from any point on the bed
to the nearest opening should not exceed 20 to 30 feet. If the
filters are small enough, troughs need not be used, the sewage
being distributed from one corner, or from mid-points on the
sides. Where troughs are used they should be supported from

1 The effective size of sand is the diameter in millimeters of the largest
grain in that 10 per cent, by weight, of the material which contains the
smallest grains.

2 The uniformity coefficient is the ratio of the diameter of the largest
particle of the smallest 60 per cent, by weight, to the effective size.

INTERMITTENT SAND FILTER

457

the bottom of the filter in order to prevent uneven settling due
to the washing of the sand. The openings in the troughs are made
adjustable by swinging gates as shown in Fig. 176, or by other
means so that after the filter is in operation the intensity of the
dose on any portion of the filter can be changed. The troughs
may be placed with their bottoms level with the surface of the
sand and with sides of sufficient height to give the required gra-
dient to the water surface, or they may be built up above the sur-

^:Sand Filter
Section on Line A-B.

FIG. 175.— Plan and Section of an Intermittent Sand Filter Showing Central
Location of Control House.

face of the filter and given the required slope so that the surface
of the flowing water is parallel to the bottom of the trough.
In either case a splash plate should be placed at each opening,
so that not less than 2 feet of the surface of the sand is protected
in all directions from the opening. A stone or concrete slab
2 to 4 inches thick makes a satisfactory splash plate. Either
wood or concrete may be used for the construction of the
troughs. The former is less durable, but also less expensive

458

FILTRATION AND IRRIGATION

in first cost. The capacity of the troughs may be computed
by Kutter's formula with the quantity to be carried equal to the
maximum rate of discharge of the feeding siphon, with a reduc-
tion in size below each branch or outlet proportional to the
amount which will be discharged above this point.

The operation of automatic devices for dosing the bed is
explained in Chapter XXI. The dosing tank should have a
capacity sufficient to cover the bed to a depth of about 1 to 3
inches at one dose, and the siphon should discharge at a rate of
about one second-foot for each 5,000 square feet of filter area.
A dose should disappear within 20 minutes to half an hour after
it is applied to the filter. With the rate stated and four appli-

FIG. 176. — Distributing Trough with Adjustable Openings.

cations per day to a depth of 1 inch at each dose, the rate per
acre per day will be 109,000 gallons.

The filtration of sewage through sand in a manner similar
to the rapid sand filtration of water is being attempted at the
Great Lakes Naval Training Station. No results of this treat-
ment have been published and the practical success of the method
has not been assured.

259. Cost of Filtration. — Only comparative figures can be
given in stating the costs of filtration, as most data available
are based on pre-war conditions, and are therefore unreliable
for present conditions. The variations from the figures given
may be very large but in general the relative costs have not
changed. The figures given in Table 90 are suggestive of the rela-
tive costs of the different forms of filtration.

THE PROCESS

459

TABLE 90

RELATIVE COSTS OF DIFFERENT MKTIIODS OF SEWAGE TREATMENT
Costs in Dollars per Million Gallons per Day

Form of Treatment

First Cost *

Operation
and
Maintenance

Total

Coarse screens

0.20

Fine screens

3.00

Plain sedimentation

7.00

3.00

10 00

Chemical precipitation

22.00f

Septic tank

7.00

1.00

8.00

Imhoff tank

10.00

1.00

11.00

Contact bed

8.00

2.00

10.00

Trickling filter

4 00

2 00

6 00

Intermittent sand filter

15 00

10 00

25 00

Activated sludge

6 50

8 50

15 OOJ

* Interest at 6 per cent,
the sale of sludge.

t Worcester figures. t This method may show a profit from

IRRIGATION

260. The Process. — Broad irrigation is the discharge of
sewage upon the surface of the ground, from which a part of
the sewage evaporates and through which the remainder perco-
lates, ultimately to escape in surface drainage channels. Sewage
farming is broad irrigation practiced with the object of raising
crops. Broad irrigation can be accomplished successfully with-
out the growing of crops, but it is seldom attempted as some
return and sometimes even a profit can be obtained from the
crops raised. Broad irrigation and sewage farming differ from
intermittent sand filtration in the intensity of the application
of the sewage, the method of preparing the area on which the
sewage is to be treated, and the care in operation. In broad
irrigation and intermittent sand filtration the paramount con-
sideration is successful disposal of the sewage. In sewage farming
the paramount consideration is the growing of crops. The
growing of crops may be combined with irrigation and filtration,
however, but the crop should be sacrificed to the successful
disposal of the sewage.

460 FILTRATION AND IRRIGATION

The change which occurs in the characteristics of the sewage
due to its filtration through the ground is the same as occurs in
aerobic filtration. The effect on the crops is mainly that of an
irrigant, as the manurial value of the sewage is small.

261. Status. — The disposal of sewage by broad irrigation was
practiced in England previous to the development of any of the
more intensive biologic methods of treatment. It was con-
sidered the only safe and sanitary method for the disposal of
sewage, and as a result, areas irrigated by sewage were common
throughout England. Crops were grown on these areas as a
minor consideration, and sewage farming gained some of its
popularity from the apparent success of these disposal areas.
The success of sewage farms is due more to generous irrigation
in dry years than to fertilization by sewage.

The sewage farms of Paris and Berlin are frequently cited
as examples of the successful and remunerative disposal of
sewage by farming in connection with broad irrigation. Kinni-
cutt, Winslow, and Pratt l state:

The Berlin Sewage farms offer examples of broad
irrigation under better conditions ... of 21,008 acres
receiving sewage, 16,657 acres were farmed by the city,
3,956 acres were leased to farmers, and only 395 acres
were unproductive. The contributing population at this
time was 2,064,000 and the average amount of sewage
treated was 77,000,000 gallons, giving a daily rate of
treatment of about 3,700 gallons per acre of prepared
land. The soil is sandy and of excellent quality. A quarter
of the area operated by the authorities is devoted to
pasturage, and about a third to the cultivation of cereals,
of which winter rye and oats are the most important.
Potatoes and beets are grown in considerable amounts
and a wide variety of other crops in smaller proportions.
. . . Even fish ponds are made to yield a part of the
revenue, and the drains on some of the farms have been
successfully stocked with breed trout.

The cost of the Berlin farms to March 31, 1910,
was $17,470,000, somewhat more than half being the
purchase price of the land. The expenses for this year
amounted to $1,300,385 for maintenance, and $741,818
for interest charges. The receipts were $1,240,773 and
there was an estimated increase of $122,593 in value
of live stock and other property.

1 Sewage Disposal, 1919, p. 223.

PREPARATION AND OPERATION 461

The conditions at Berlin are quoted at length to indicate the
success which can accompany broad irrigation, and as an
example of what is being done abroad, where the rainfall is light
and the soil is suitable.

In the United States success in sewage farming has not been
marked. This may be due partially to the relative weakness of
American sewages, to the cost of labor, to lack of satisfactory
irrigation areas, and to inattention to details. An attempt was
made to grow crops on the sand filters at Brockton, Mass., but
it was finally abandoned as the interests of the crops and the
successful treatment of the sewage could not both be satisfied.
At Pullman, Illinois,1 in 1880, there was commenced probably
the most extensive attempt at sewage farming in eastern
United States. The farm was a failure from the start, because
of the clay soil, and it was subsequently abandoned. Sewage
farming, mainly as a subsidiary consideration to the filtration
of sewage, is practiced in a few cities in the eastern portion of
the United States to-day. Among the cities mentioned by
Metcalf and Eddy 2 are Danbury, Conn., and Fostoria, Ohio.
In the western portion of the United States where water is
scarce and the ground is porous, sewage has been used as an irri-
gant with some success. Such use of sewage cannot be considered
as a method of treatment since the prime consideration is the
growing of crops. In this process all sewage not used as an
irrigant is discharged without treatment into water courses.
According to Metcalf and Eddy there were 35 cities in Cali-
fornia in 1914 that were operating sewage farms. Among
these are Pasadena, Fresno, and Pomona. Other farms, notably
the pioneer farm at Cheyenne, Wyo., have been abandoned
because of the local nuisance created and the lack of financial
success.

262. Preparation and Operation. — A porous sandy soil on
a good slope and with good underdrainage is most suitable for
broad irrigation. Impervious clay or gumbo soils are unsuitable
and should not be used. They become clogged at the surface,
forming pools of putrefying sewage, or in hot weather form cracks
which may permit untreated sewage to escape into the underdrains.

The sewage may be distributed to the irrigated area in any

1 See Eng. News, Vol. 9, 1883, p. 203, and Vol. 29, 1893, p. 27.
1 American Sewerage Practice, Vol. III.

462 FILTRATION AND IRRIGATION

one of five ways which are known as: flooding, surface irriga-
tion, ridge and furrow irrigation, filtration, and sub-surface
irrigation. In flooding, sewage is applied to a level area
surrounded by low dikes. The depth of the dose may be from
1 inch to 2 feet. In surface irrigation the sewage is allowed to
overflow from a ditch over the surface of the ground into which
it sinks or over which it flows into another ditch placed lower
down. This ditch conducts it to a point of disposal or to another
area requiring irrigation. Ridge and furrow irrigation consists
in plowing a field into ridges and furrows and filling the furrows
with sewage while crops are grown on or between the ridges.
In filtration the sewage is distributed in any desired fashion on
the surface and is collected by a system of underdrains after it
has filtered through the soil. In subsurface irrigation the sewage
is applied to the land through a system of open joint pipes laid
immediately below the surface, similarly to a system of under-
drains. Combinations of and modifications to these methods
are sometimes made. Underdrains may be used hi connection
with any of these forms of distribution.

The preparation of the ground consists in: the construction
of ditches or dikes to permit of any of the above described
methods of application, grading of the surface to prevent
pooling, the laying of underdrains, and the grubbing and clearing
of the land. The main carriers may be excavated in open earth
or earth lined with an impervious material. The distribution
of the sewage from the main carriers to groups of laterals may
be controlled by hand-operated stop planks. If the soil has a
tendency to become waterlogged it may be relieved by install-
ing underdrains at depths of 3 to 6 feet, and 40 to 100 feet
apart. The tile underdrains may discharge into open ditches
excavated for the purpose which serve also to drain the land.
Drains should be used where the ground water is within 4 feet
of the surface, and the open ditches should be cut below the
drains to keep the ground water out of them. Four or 6-inch
open-joint farm tile may be used for underdrains. The porosity
of the soil will be increased by cultivation. Where particular
care is taken in the cultivation of the soil so that sewage can
be applied at a high rate, broad irrigation merges into the more
intensive intermittent filtration through sand.

Before being turned on to the land, sewage should be screened

SANITARY ASPECTS 463

and heavy-settling particles should be removed. The rate of
application may be increased as the intensity of the preliminary
treatment is increased. The rate at which sewage may be
applied is dependent also on the character of the soil, and may
vary between 4,000 and 30,000 gallons per acre per day, although
higher rates have been used with the effluent from treatment
plants and on favorable soil. The sewage should be applied
intermittently in doses, the time between doses varying between
one day and two or three weeks or more, dependent on the
weather and the condition of the soil. The methods of dosing
vary as widely as the rates. The dose may be applied con-
tinuously for one or two weeks with correspondingly long rests,
or it may be applied with frequent intermittency alternated
with short rests, interspersed with long rest periods at longer
intervals of time. When applying the sewage to the land the
rate of application of the dose is about 10,000 to 150,000 gallons
per acre per day. The area under irrigation at any one time
may be as much as 10 to 15 acres. The rate of the application
of the sewage is also dependent on the weather and may vary
widely between seasons. It is obvious that a rain-soaked
pasture cannot receive a large dose of sewage without danger
of undue flooding. One of the principal difficulties with the
treatment or disposal of sewage by broad irrigation is that the
greatest load of sewage must be cared for in wet seasons when the
ground is least able to absorb the additional moisture.

263. Sanitary Aspects. — A well-operated sewage farm should
cause no offense to the eye or nose, and is not a danger to the
public health. In Berlin, a portion of the sewage farms are
laid out as city parks. The liquid in the drainage ditches or
underdrains may be clear, odorless, and colorless, high in nitrates
and non-putrescible. Where the farm has been improperly
managed or overdosed the condition may be serious from both
esthetic and health considerations. Sewage may be spread
out to pollute the atmosphere and to supply breeding places for
flying insects which will spread the filth for long distances sur-
rounding the farm. The character of the crop is also a sani-
tary consideration.

264. The Crop. — From a sanitary viewpoint no crops which
come in contact with the sewage should be cultivated on a
sewage farm. Such products as lettuce, strawberries, asparagus,

464

FILTRATION AND IRRIGATION

potatoes, radishes, etc., should not be grown. Grains, fruits,
and nuts are grown successfully and as they do not come in con-
tact with the sewage there is no sanitary objection to their
cultivation in this manner. Italian rye grass and other forms
of hay are grown with the best success as they will stand a
large amount of water without injury. The raising of stock
is also advisable for sewage farms where hay and grain are culti-
vated. The stock should be fed with the fodder raised on the
irrigated lands and should not be allowed to graze on the crops
during the time that they are being irrigated. This is due as
much to the danger of injury to the distributing ditches and
the formation of bogs by the trampling of the cattle, as to the
danger to the health of the cattle.

ACTIVATED SLUDGE

265. The Process. — In the treatment of sewage by the
activated sludge process the sewage enters an aeration tank after
it has been screened and grit has been removed. As it enters
the aeration tank it is mixed with about 30 per cent of its
volume of activated sludge. The sewage passes through the
aeration tank in about two to four hours during which time air
is blown through it in finely divided bubbles. The effluent
from the aeration tank passes to a sedimentation tank where it
remains for one-half an hour to an hour to allow the sedimen-
tation of the activated sludge. The supernatant liquid from the
sedimentation tank is passed to the point of final disposal. A
portion of the sludge removed from the tank is returned to the
influent of the aeration tank. The remainder may be sent to
any or all of the following: the sludge drying process, the reae'ra-
tion tanks, or to some point for final disposal. Sections of the
activated sludge plant at Houston, Texas, are shown in Fig. 177.

The biological changes in the process occur in the aeration
tank. These changes are dependent on the aerobic organisms
which are intensively cultivated in the activated sludge. When
placed in intimate contact with fresh sewage, brought about by
the agitation caused by the rising air, and in the presence of an
abundance of oxygen, the organic matter is partially oxidized.
The putrefactive stage of the organic cycle is avoided. Col-
loids and bacteria are partially removed probably by the agita-
tion effected in the presence of activated sludge but the exact
action which takes place is not well understood.

266. Composition. — Activated sludge is the material obtained
by agitating ordinary sewage with air until the sludge has assumed
a flocculent appearance, will settle quickly, and contain
aerobic and facultative bacteria in such numbers that similar
characteristics can be readily imparted to ordinary sewage

465

466

ACTIVATED SLUDGE

sludge when agitated with air in the presence of activated sludge.
Copeland described activated sludge as follows:1

The sludge embodied in sewage and consisting of
suspended organic solids, including those of a colloidal
nature, when agitated with air for a sufficient period
assumes a flocculent appearance very similar to small
pieces of sponge Aerobic and facultative bacteria gather
inr these flocculi in immense numbers — from 12 to 14

8"6luice
Gate-.

/Sludge Return Channel

l2"AirP/pe.

Part Plan of Outside Unit Aeration and Settling Tank.

• - -- '-'

58-6"—,Approx,Posif/onof Drain'

29-6 H ; Sludge Blankets. Lonqitudi-

^1 A*! if, V, J^IA| naigection

A-A.
4"W.[.Pipe

Half Section through Settling Tanks.

•58 '- 6 " fo r North Side PI a nk-
sg'-o" «> South » _•• •*

Half Section through Aeration Tanks

FIG. 177. — Activated Sludge Plant at Houston, Texas.
Eng. News, Vol. 77, p. 236.

million per c.c. — some having been strained from the
sewage and others developed by natural growth. Among
the latter are species that have the power to decompose
organic matter, especially of an albuminoid or nitrog-
enous nature, setting the nitrogen free; and others
absorbing the nitrogen convert it into nitrites and
nitrates. These biological processes require time, air,
and favorable environment such as suitable temperature,

Reference 11, at end of this chapter.

COMPOSITION

467

food supply and sufficient agitation to distribute them
throughout all parts of the sewage.

Ardern states that the sludge differs entirely from the usual
tank sludge. It is inoffensive and flocculent in character. The
percentage of moisture is from 95 to 99 per cent. American
experience has generally been that the sludge does not readily
separate from its moisture by treatment on fine-grain filters,
but the results in England and at Milwaukee, Wisconsin, are in
conflict with this general experience. Upon standing 24 hours
or more partially dried activated sludge may start to decompose
accompanied by the production of offensive odors.

Duckworth states :

The activated sludge at Salford contained three times
as much nitrogen, twice as much phosphoric acid and
one-half as much fa ,y matter as ordinary sludge.

TABLE 91
COMPOSITION OF SEWAGE, IMHOFP SLUDGE, AND ACTIVATED SLUDGE AND

EFFLUENT AT MILWAUKEE
(W. R. Copeland, Eng. News, Vol. 76, p. 665)

Parts per Million

Nitrogen as

•

Nitrogen Reported

Period of

Source of

as Ammonia on a

Test

Sample

'5
o

"3.2

'o «

a 2

Basis of Sludge
Dried to 10 Per

•3

O ~

Cent Moisture.

- -

Three samples of
Sludge

•J.

Aug., I'.ll").

Sewage ....

253

14.6

7.88

0.15

0.13

Imhoff effluent. .

105

16.2

6.10

0.19

0.13

2.87

3.82

Activated sludge

effluent

3.8

3.19

0.29

6.00

5.71

4.97

7.04

Sept., 1915.

Sewage . .

300

13.5

8.81

0.25

0.14

Imhoff effluent. .

116

15.4

7.10

0.12

0.09

3.88

Activated sludge

effluent.

5.7

2.22

0.24

5.01

8.69

9.00

These results have been roughly checked by American experi-
menters as shown in Table 91. ' In the recovery of nitrogen
from sewage the activated sludge process is the most promising
for satisfactory results. In all other processes of sewage treat-

1 Reference 15.

468

ACTIVATED SLUDGE

ment the sludge is digested to some extent and nitrogen lost in
the gases or in the soluble matter which passes off with the
effluent. In the activated sludge process a negligible amount
of gasification and liquefaction take place and only a small
amount of nitrogen passes off with the effluent as compared with
the loss from the Imhoff process as shown in Table 91. The
percentage of nitrogen in dried activated sludge is shown in
Table 92,

TABLE 92

NITROGEN CONTENT OF DRY ACTIVATED SLUDGE AND SLUDGE
FROM OTHER PROCESSES

(G. W. Fuller, Eng. News, Vol. 76, p. 667)

Source •

Per Cent
Nitrogen

Milwaukee (Copeland)

4.40

Manchester, England (Ardern)

4.60

Salford, England (MeUing)

3 75

Urbana, Illinois (Bartow)

3 5 to 6 4

Armour and Co. (Noble)

4.6

Approximate range of all other processes .

l.Oto 3.0

These figures are expressed in terms of nitrogen and not of ammonia. Nitrogen is only
82 per cent of the ammonia content.

Nitrifying bacteria and other species which have the power
of destroying organic matter have been isolated from the sludge.
An analysis of the dried sludge at Urbana 1 showed the following
results after the weight had been reduced 95.5 per cent by drying:
6.3 per cent nitrogen, 4.00 per cent fat, 1.44 per cent phosphorus,
and 75 per cent volatile matter or loss on ignition. Analyses
of other domestic sewages have not shown such high contents
of these desirable constituents.

The dewatering of activated sludge is a problem which offers
serious obstacles to the successful operation of the process. It
is its greatest disadvantage. Five to ten times the volume of
sludge may be produced by the activated sludge process as by
an Imhoff tank, and the activated sludge contains a greater
percentage of water. According to Copeland :

1 Reference 2.

ADVANTAGES AND DISADVANTAGES 469

The best information now available points to a
combination of settling and decantation as a preliminary
dewatering process. By this means the water will be
cut down from about 99 per cent to 96 per cent. On
passing the concentrated residue through a pressure
filter the moisture can be cut down to 75 per cent. The
press cake can be dewatered in a heat drier to 10 per cent
moisture or less.1

The quantity of sludge produced at Milwaukee 2 is about 15
cubic yards per million gallons of sewage, the sludge having
about 98 per cent moisture. On the basis of 10 per cent mois-
ture it produces \ ton of dry sludge per million gallons of sewage
treated. At Cleveland,3 20 cubic yards per million gallons
at 97.5 per cent moisture are produced. Methods of drying
sludge are discussed in Chapter XX.

Chemical analyses and biological tests indicate that the
fertilizing value of the sludge is appreciable. Professor C. B.
Lipman states, as the result of a series of tests in which a sludge
and a soil were incubated for one month, as follows :4

The amounts of nitrates produced in one month's
incubation from the soil's own nitrogen and from the
nitrogen from the sludge mixed with the soil in the ratio
of one part of sludge to 100 of soil is, in milligrams of
nitrate, as follows: Anaheim soil without sludge 6.0,
with sludge 10.0; Davis soil without sludge 4.2, with
sludge 14.0; Oakley soil without sludge 2.2, with sludge
4.0.

The effect of the sludge on plant growth is shown in Table 93. 5
The results represent the growth obtained after fifteen weeks
from the planting of 30 wheat seeds in each pot.

267. Advantages and Disadvantages. — Some of the advantages
of the process are : a clear, sparkling, and non-putrescible effluent
is obtained; the degree of nitrification is controllable within
certain limits; the character of the effluent can be varied to
accord with the quantity and character of the diluting water

1 For mechanical methods of drying sludge, see Reference 22, p. 1127,
and No. 33, p. 843.

2 Reference 10.
1 Reference 13.

4 University of California, Bulletin 251, 1915.
4 Reference 25.

470

ACTIVATED SLUDGE

available ; more than 90 per cent of the bacteria can be removed ;
the cost of installation is relatively low; and the sludge has some
commercial value.

TABLE 93

FEKTILIZING VALUE OP ACTIVATED SLUDGE
(E. Bartow, Journal Am. Water Works Ass'n, Vol. 3, p. 327)

Cultivating Medium

Grams Contained in Experimental Pot

White sand

19,820
60
6
3
0

0
0

19,820
60
6
3
0

0
8.61

19,820
60
6
3
20

0
0

19,820
60
6
3
0

20
0

Dolomite .

Bone meal

Potassium sulphate

Activated sludge

Activated sludge extracted
with Ligroin

Dried blood

Number of heads of wheat.
Number of seeds

14
85
2.38
6.20

19.40
2.25
0.18

15
189
5.29
13.6

23.0

8.25
0.68

22
491
13.748
35.9

35.4
26.75
2.23

23
518
14.504
38.7

37.1
26.21
2.18

Weight of seeds, grams ....
Bushels per acre, calculated.
Average length of stalk,
inches

Weight of straw, grams. . .
Tons per acre, calculated . . .

Among the disadvantages of the process can be included,
uncertainty due to the lack of information concerning the
results to be expected under all conditions, high cost of operation
under certain conditions, the necessity for constant and skilled
attendance, and the difficulty of dewatering the sludge.

268. Historical. — The most notable work in the aeration of
sewage within recent years was that performed by Black and
Phelps for the Metropolitan Sewerage Commission of New York,
in 19 10,1 and by Clark and Gage at the Lawrence, Massachusetts,
Sewage Experiment Station in 1912 and 1913.2 The results of

1 See Report by Black & Phelps of Metropolitan Sewerage Commission,
1911, reprinted as Vol. VII of Contributions from the Sanitary Research
Laboratory of the Massachusetts Institute of Technology.

2 See Reports, Mass. State Board of Health.

AERATION TANK 471

these investigations showed that the treatment of sewage by
forced aeration might give a satisfactory effluent, but that the
time and expense in connection thereto rendered the method
impractical.

It remained for Messrs. Ardern and Lockett of Manchester,
England, to introduce the process of the aeration of sewage in
the presence of activated sludge, as a result of their connection
with Dr. Fowler, who attributes his inspiration to his visit to
the Lawrence Experiment Station and observing the work of
Clark and Gage. Ardern and Lockett commenced their experi-
ments in 1913. Their results were published in the Journal
of the Society of Chemical Industry, May 30, 1914, Vol. 33, p. 523.
Shortly thereafter experiments were started at the University
of Illinois by Dr. Edw. Bartow and Mr. F. W. Mohlmann of the
Illinois State Water Survey. At about the same time an experi-
mental plant was started at Milwaukee, by T. C. Hatton, Chief
Engineer of the Milwaukee Sewerage Commission. The United
States Public Health Service became actively interested in
December, 1914, and on February 20, 1915, announced its
intention to co-operate with the Baltimore Sewerage Commission
in the conduct of experiments. In May, 1915, patent number
1,139,024 was granted to Leslie C. Frank, Sanitary Engineer
of the U. S. Public Health Service, covering certain features of
the process. Mr. Frank generously donated this patent to the
public for the use of municipalities.

The first full sized plant for the treatment of sewage by
this method was erected in Milwaukee in December, 1915. This
plant had a capacity of 1,600,000 gallons per day. It was used
for experimental purposes and is not now in use. The Champaign,
Illinois, septic tank, among the first of its kind in the country,
was converted into an activated sludge tank on April 13, 1916.
The changes, developments, and the results obtained from these
and other plants have been reported in the technical press from
time to time.

269. Aeration Tank. — The sewage on leaving the screen and
grit chamber enters the aeration tank, which is usually operated
on the continuous-flow principle, although in the early days of
experimentation the fill-and-draw method was practiced. This
tank should be rectangular with a depth of about 15 feet and a
width of channel not to exceed 6 to 8 feet. Such proportions

472 ACTIVATED SLUDGE

allow better air and current distribution than larger tanks.
The bottom should be level to insure an even distribution of
air. The velocity of flow of sewage through the tank is usually
in the neighborhood of 5 feet per minute, dependent on the
length of the tank and the period of retention. The period of
retention is in turn dependent on the desired quality of the
effluent. The process is flexible and the quality of the effluent
can be changed by changing the period of retention or by changing
the rate of application of the air, or both. The period of retention
in the aeration tank is usually about 4 hours.

The bottom of the aeration tank is usually made of concrete
arranged in ridges and valleys, or small shallow hoppers, at the
bottom of which the air-diffusing devices are located, as shown
in Fig. 177. The inlet and outlet devices are similar to those
in a plain sedimentation tank.

270. Sedimentation Tank. — It is evident that as no sedi-
mentation is permitted in the aeration tank, the settleable parti-
cles will be discharged in the effluent unless some provision is
made for their detention. The effluent from the aeration tank
is therefore run through a plain sedimentation tank, usually
with a hopper bottom, which has been arranged to permit fre-
quent and easy cleaning. An air lift or a centrifugal sludge
pump is satisfactory for this purpose. Another type of sedi-
mentation tank which has been used has a smooth bottom with
a slight slope towards the center. A revolving scraper collects
the sludge continuously, scraping it towards the center of the
tank. Although this arrangement gives better results than the
hopper-bottom tank, its expense has usually prevented its instal-
lation.1

The period of sedimentation in different plants varies from
30 minutes to one hour, although the longer periods usually give
the better results. Approximately 65 per cent of the sludge will
settle in the first 10 minutes, 80 per cent in the first 30 minutes,
and about 5 per cent more in the next half hour.

The effluent from the sedimentation tank is ready for final
disposal or if desired, for further treatment by some other
method. The sludge, or a portion of it, is pumped back into the
influent of the aeration tank, provided the sludge is in a satis-
factory state of nitrification. Otherwise it should be pumped

1 Reference 47.

THE REAERATION TANK 473

to the reaeration tanks. The remainder of the sludge which is
not to be used in the process is ready for drying and final
disposal.

271. Reaeration Tank. — The purpose of the reaeration or
sludge aeration tank is to reactivate the sludge which has gone
through the aeration tank. During the process of the aeration
of the sewage in the aeration tank the activated sludge may lose
some of its qualities because of the deficiency of oxygen to
maintain aerobic conditions. By blowing air through the sludge
in the reaeration tank these properties are returned and the sludge
made available to be pumped back into the aeration tank. The
reactivation of the sludge obviates the necessity for supplying
sufficient air to the entire mass of the sewage to maintain aerobic
conditions, and results in an economy in the use of air. The
use of mechanical agitators has also been attempted both in the
reaeration and the aeration tanks with the expectation of saving
in the use of air, but with indifferent success.

It is difficult to say, without experimentation, what the size
of the reaeration tank should be, as the necessary amount or
reactivation is uncertain. In the experimental plant at Mil-
waukee, there were eight units of aeration tanks, one sedimenta-
tion tank, and two reaeration tanks, all of the same capacity and
general design. This represents a ration of about one reaeration
tank to four aeration tanks.

272. Air Distribution. — Air is applied to the sewage at the
bottom of the aeration tank at a pressure in the neighborhood
of J>.5 to 6.0 pounds per square inch, dependent on the depth of
the sewage, the loss of head through the distributing pipes,
and the rate of application. In different experimental plants
the pressure has varied from 3 to 30 pounds per square inch.
Such pressures are on the line which divides the use of direct
blowers for low pressures from turbo and reciprocating pressure
machines for pressures above 10 pounds per square inch. Posi-
tive-pressure blowers or direct blowers operate on the principle
of a centrifugal pump and because of the lighter specific gravity
of air they rotate at a very high speed. The Nash Hytor Turbo
Blower consists of a rotor with a large number of long teeth
slightly bent in the direction of rotation. The rotor, which has
a circular circumference, revolves in an elliptical casing. At
the commencement of operation the rotor and casing are partially

474

ACTIVATED SLUDGE

filled with water. The revolution of the rotor throws the water
to the outside of the elliptical casing thus forming a partial
vacuum between any two teeth as the water is thrown from near
the center of the short diameter of the casing to the extremity
of the long diameter of the casing. Air is allowed to enter
through the inlet port to relieve the vacuum. As the teeth pass
from the long diameter to the short diameter of the ellipse, the
water again approaches the center of the rotor compressing the

air trapped between the
teeth and forcing ic out
under pressure into tne ex-
haust pipe. Among the ad-
vantages of this compressor
are the washing of the air,
cooling, and ease in opera-
tion. Reciprocating air com-
pressors operate similarly to
direct-acting steam pumps
or crank - and - fly - wheel
pumps but at much higher
speeds, and they require
more floor space than either
of the other types. Fig.

FIG. 178. — Economic Range of Air Com-
pressors.
From Eng. News, Vol. 74, p. 906.

5 ,10 15 20 Z5
Volum* of Frea Air in Thousands
Cu. Ft per Minu+e

178 shows the field of
serviceability of various
types of air compression
machinery.

For pressures up to about 10 pounds per square inch the posi-
tive blower seems most desirable. It has a low first cost and a
relatively high efficiency of about 75 to 80 per cent of the power
input. No oil or dirt is added to the air to clog the distributing
plates, as in the reciprocating machine. A disadvantage is the
difficulty of varying the pressure or quantity of the output of
the machine. As the required pressure and volume of air
increases the turbo blower becomes more and more desirable
within the limits of pressure which are ordinarily used in this
process. For small installations the best form of power is
probably the electric drive, but when the capacity becomes
such as to make turbo blowers advisable they should be driven
by directly connected steam turbines.

AIR DISTRIBUTION 475,

The quantity of air required varies between 0.5 to 6.0 cubic
feet per gallon of sewage, with from 3 to 6 hours of aeration.
The quantity of air depends on the degree of treatment required,
the strength of the sewage, the depth of the tank, and the period
of aeration. The deeper the tank the less the amount of air
needed because of the greater travel of the bubble in passing
through the sewage, but the higher the pressure at which the
air must be delivered. Shallow tanks usually require a longer
period of retention. The depth of the tank then has very little
to do with economy in the use of air. Hatton states:1

The purification of sewage obtained varies decidedly
with the volume of air applied. Small volumes applied
for 5 or 6 hours do as well as larger volumes applied for
3 or 4 hours, but the tune of aeration required to obtain
a like effluent does not vary directly with the volume of
air applied per unit of time. For instance air applied
at a rate of 2 cubic feet per minute purifies the sewage
in less time than one cubic foot of air per minute, but will
not accomplish an equal degree of purification in half the
time.

It has been found that although a low temperature has a dele-
terious effect on the process, by the use of an additional quantity
of air good results can be maintained. The effect of changing
the quantity of air and the period of aeration are shown in Table
94 taken from Hatton.

The velocity of the air in the pipes should be about 1,000
feet per minute. There should be relatively few sharp turns
in the line, and the distributing mains should be arranged with-
out dead ends. It is desirable to use as little piping as possible
and at the same time to make the travel of the sewage long in
order to maintain a non-settling velocity and intimate contact
with the air. The piping should be accessible and well provided
with valves. It should be non-corrodible, particularly on the
inside, as flakes of rust will quickly clog the air diffusers. It
should drain to one point in order that it can be emptied when
flooded, as occasionally happens.

It is desirable to diffuse the air in small bubbles as by this
means the greatest efficiency seems to be obtained from the
amount of air added. A diameter ^ to $ of an inch is approxi-

1 Reference 10.

476

ACTIVATED SLUDGE

w
*/:

Pi OH

W °W

t-3 So

^ H

S as

J H

s
^
§

fc
W

-O V

Nitrite

5^3 °|

^'-D 3

O Oi-i •* to CO

OOOT-KNdOOOOOOOOO

O CO O Ci *- O5

t^co eor>- M r~-

GO Ci C~. CZ

73,
HOOOOO

OOOOOiCOOO

AIR DISTRIBUTION

477

mately the maximum limit for the size of an effective bubble.
Monel metal cloth, porous wood blocks, open jets, paddles, and
other forms of diff users have been tried, but none have given
the satisfaction of the filtros plate. The relative value of dif-
ferent types of diffusers is shown in Table 95 taken from Hatton.1
The Filtros plates are a proprietary article manufactured by
the General Filtration Company of Rochester, N. Y. They
are made of a quartz sand firmly cemented together and can be

TABLE 95

COMPARATIVE RESULTS FROM THE AERATION OF SEWAGE IN THE PRESENCE
OF ACTIVATED SLUDGE WITH THE USE OF DIFFERENT DISTRIBUTING
MEDIA

(T. C. Hatton, Eng. Record, Vol. 73, p. 255)

Pounds

Air,

Per

Nitrates,

Stability

Diff users

Months in 1915

per
Square

Cubic
Feet per

Cent
Bacteria

Parts
per

Effluent
in

Inch

Gallon

Removed

Million

Hours

Filtros plate

June 1 to Aug. 15

4.3

2.06

3.4

3.5

1.94

2 2

Filtros plate

Nov. 18 to Dec. 7

4.6

1.71

0.3

113

Monel metal

Nov. 18 to Dec. 7

3.0

1.71

0.2

obtained with practically any degree of porosity, size of pore
opening or dimension of plate, but they are made in a standard
size 12 inches square by \\ inches thick. The frictional loss
through the plate is not very great for the amount of air ordi-
narily used. The plates are classified in accordance with the
volume of air which will pass through them, when dry, per
minute when under a pressure of 2 inches of water. These
classes run from \ to 12 cubic feet of air per minute. The type
usually specified passes about 2 cubic feet of air per minute.
The loss of head through these plates as tested at Milwaukee
showed an initial loss of f of a pound and an additional loss
of about \ of a pound for every cubic foot of air per minute per
square foot of surface. It is necessary to screen and wash the
air before blowing it through the filtros plate as ordinary air
is so filled with dirt as to clog the pores of the diffuser quite
rapidly.

1 Reference 10.

478 ACTIVATED SLUDGE

The area of filtros plates required in the bottom of the tank
is usually expressed in terms of the free surface of the tank or
as a ratio thereto. In the Urbana tests the best ratio was
found. to be less than 1 : 3 and more than 1:9. In Milwaukee 1
the ratio adopted is in the neighborhood of 1 : 4 or 1 : 5. At
Fort Worth the ratio will be about 1 : 7 and at Chicago it will
be 1 : 8. The exact ratio should be determined by experiment
and will depend on the construction of the tank and the char-
acter of the raw sewage and the desired effluent. It is essential
that the filtros plates be placed level and at the same elevation
as otherwise the distribution of air will be uneven.

273. Obtaining Activated Sludge. — After a plant is once
started activated sludge is generated during the process of treat-
ment and with careful management a stock of activated sludge
can be kept on hand. When a plant is new, or if shut down for
such a length of time that the sludge loses its activation, it is
necessary to activate some new sludge. This is done by blowing
air continuously through sewage either on the fill and draw
method with periodic decantations of the supernatant liquid,
or by the continuous-flow process, but more preferably by the
latter. Where activated sludge is to be obtained from fresh
sewage alone the time required is in the neighborhood of 10 to
14 days, and purification begins at the start. An estimate of
the quantity which will be obtained can not be made with
accuracy. After the initial quantity of sludge has been obtained
activated sludge can be maintained during the process of aeration
of the raw sewage, or by means of the reaeration tanks previously
described.

The volume of activated sludge present in the aeration tank
should be about 25 per cent of the volume of the tank. The
volume of the sludge is measured in a somewhat arbitrary manner
as the amount by volume which will settle in 30 minutes in an
ordinary test tube. It is found that this is almost 90 per cent
of the solids settling in 4 to 6 hours.

274. Cost. — The available information on the cost of the
activated sludge process is meager and unreliable. The factors
entering into the cost are: the price of fuel, the size of the plant,
the period of sedimentation, the amount of air per gallon of sewage,
the air pressure, and the percentage of sludge to be aerated in the

1 Reference 10.

COST

479

mixture. In Milwaukee l the cost of construction is estimated
at $44,000 per million gallons, and $4.75 per million gallons for
operation. At Houston, Texas, the cost is estimated at $24,000
per million gallons, exclusive of the sludge-drying plant, which
may cost $40,000 per million gallons. At Milwaukee, the cost
of pressing the sludge is $4.82 per dry ton and of drying is $3.93
per dry ton. The sludge may be sold at the normal rate of $2.50
per unit of nitrogen. Based on the normal value the evident
profit will be $3.75 per ton. The net cost of disposing of Mil-
waukee sewage is estimated at $9.64 per million gallons of which
$4.89 is chargeable to overhead and $4.75 to repairs, operation
and renewal. In a comparison of the costs of activated sludge
and Imhoff tanks with sprinkling filters,2 the information given
by Eddy has been summarized in Table 96. In comparing the

TABLE 96

COMPARATIVE COSTS OF ACTIVATED SLUDGE, AND OF IMHOFF TANKS
FOLLOWED BY SPRINKLING FILTERS

(H. P. Eddy, Eng. Record, Vol. 74, p. 557)

Total Annual Cost at

4 Per Cent with

Process

First
Cost per
Million

Operation
per
Million

Sinking Fund at
2.5 Per Cent per

Gallons,

Dollars

Million
Gallons,

Capita,
Dollars

Dollars

Activated sludge

57,100

20.00

29.85

1 09

Imhoff tank and sprinkling filter.

78,500

8.50

21.84

0.80

relative areas required for different methods of sewage treatment,
activated sludge should be allowed about 15 million gallons
per acre per day on the basis of aeration tanks 15 feet deep.
This figure represents approximately the gross area of the plants
at Milwaukee and at Cleveland.

1 Hatton, reference 33.

Reference 18.

480

ACTIVATED SLUDGE

REFERENCES AND BIBLIOGRAPHY ON ACTIVATED

SLUDGE

The following abbreviations will be used: A.S. for Activated Sludge,
E.G. for Engineering and Contracting, E.N. for Engineering News, E.R.
for Engineering Record, E.N.R. for Engineering News-Record, p. for page,
and V. for volume.

No.

1. Cooperation Sought in Conducting A.S. Experiments at Baltimore,

by Franks and Hendrick. E.R. V. 71, 1915, pp. 521, 724, and 784.
V. 72, 1915, pp. 23, and 640.

2. Sewage Treatment Experiments with Aeration and A.S., by Bartow

and Mohlman. E.N. V. 73, 1915, p. 647, and E.R. V. 71, 1915, p. 421.

3. A.S. Experiments at Milwaukee, Wisconsin, by Hatton. E.N. V. 74,

1915, p. 134.

4. A.S. in America, An Editorial Survey, by Baker. E.N. V. 74, 1915,

p. 164.

5. Choosing Air Compressors for A.S., by Nordell, E.N. V. 74, 1915, p. 904.

6. A Year of A.S. at Milwaukee, by Fuller. E.N. V. 74, 1915, p. 1146.

7. A.S. Experiments at Urbana. E.N. V. 74, 1915, p. 1097.

8. Experiments on the A.S. Process, by Bartow and Mohlman. E.G. V.

44, 1915, p. 433.

9. Milwaukee's A.S. Plant, the Pioneer Large Scale Installation, by Hat-

ton. E.R. V. 72, 1915, p. 481 and E.G. V. 44, 1915, p. 322.

10. A.S. Experiments at Milwaukee, by Hatton. Journal American Water-

works Association and Proceedings Illinois Society of Engineers, 1916.
Also E.R. V. 73, 1916, p. 255. E.G. V. 45, 1916, p. 104, and E.N.
V. 75, 1916, pp. 262 and 306.

11. A.S. Defined. E.N. V. 75, 1916, p. 503, and E.N.R. V. 80, 1918, p. 205.

12. Status of A.S. Sewage Treatment, by Hammond. E.N. V. 75, 1916,

p. 798.

13. Trial A.S. Unit at Cleveland, by Pratt. E.N. V. 75, 1916, p. 671.

14. Air Diffuser Experience with A.S. E.N. V. 76, 1916, p. 106.

15. Nitrogen from Sewage Sludge, Plain and Activated, by Copeland,

Journal American Chemical Society, Sept. 28, 1916. E.N. V. 76,

1916, p. 665. E.R. V. 74, 1916, p. 444.

16. Tests Show A.S. Process Adapted to Treatment of Stock Yards Wastes.

E.R. V. 74, 1916, p. 137.

17. Aeration Suggestions for Disposal of Sludge, by Hammond. Journal

American Chemical Society, Sept. 25, 1916. E.R. V. 74, 1916, p. 448.

18. Cost Comparison of Sewage Treatment. Imhoff Tank and Sprinkling

Filters vs. A.S., by Eddy. E.R. V. 74, 1916, p. 557.

19. Large A.S. Plant at Milwaukee. E.N. V. 76, 1916, p. 686.

20. A.S. Novelties at Hermosa Beach, Cal. E.N. V. 76, 1916, p. 890.

21. A.S. Experiments at University of Illinois, by Bartow, Mohlman, and

Schnellbach. E.N. V. 76, 1916, p. 972.

REFERENCES AND BIBLIOGRAPHY 481

No.

22. A.S. Results at Cleveland Reviewed, by Pratt and Gascoigne. E.N.

V. 76, 1916, pp. 1061 and 1124.

23. Sewage Treatment .by Aeration and Activation, by Hammond. Pro-

ceedings American Society Municipal Improvements, 1916.

24. A.S., by Bartow and Mohlman, Proceedings Illinois Society of Engineers,

1916.

25. The Latest Method of Sewage Treatment, by Bartow. Journal Ameri-

can Waterworks Association, V. 3, March, 1916, p. 327.

26. Winter Experiences with A.S., by Copeland. Journal American Society

of Chemical Engineers, April 21, 1916. E.G. V. 45, 1916, p. 386.

27. A.S. Process Firmly Established, by Hatton. E.R. V. 75, 1917, p. 16.

28. Operate Continuous Flow A.S. Plant, by Bartow, Mohlman, and

Schnellbach. E.R. V. 75, 1917, p. 380.

29. Chicago Stock Yards Sewage and A.S., by Lederer. Journal American

Society of Chemical Engineers, April 21, 1916. E.G. V. 45, 1916, p. 388.

30. The Patent Situation Concerning A.S. E.G. V. 45, 1916, p. 208.

31. " Sewage Disposal " by Kinnicutt, Winslow, and Pratt, published by

John Wiley & Sons. 2d Edition, Chapter 12.

32. A.S. Tests Made by California Cities. E.N.R. V. 79, 1917, p. 1009.

33. Conclusions on the A.S. Process at Milwaukee. Journal American

Public Health Association, 1917. E.N.R. V. 79, 1917, p. 840.

34. Dewatering A.S. at Urbana, by Bartow. Journal American Institute

of Chemical Engineers, 1917. E.N.R. V. 79, 1917, p. 269.

35. Milwaukee Air Diffusion Studies in A.S. E.N.R. V. 78, 1917, p. 628.

36. A.S. Bibliography (up to May 1, 1917) by J. E. Porter.

37. Air Diffusion in A.S. E.N.R. V. 78, 1917, p. 255.

38. A.S. Plant at Houston, Texas. E.N. V. 77, 1917, p. 236, E.N.R. 83,

1919, p. 1003, and V. 84, 1920, p. 75.

39. A.S. Power Costs, by Requardt. E.N. V. 77, 1917, p. 18.

40. A.S. at San Marcos, Texas, by Elrod. E.N. V. 77, 1917, p. 249.

41. Filtros Plates Made the Best Showing in Air Diffuser Tests. E.N.R.

V. 79, 1917, 269.

42. Results of Experiments on A.S., by Ardern and Lockett. Journal

Society for Chemical Research, V. 33, May 30, 1914, p. 523.

43. Final Plans at Milwaukee. E.N.R. V. 84, 1920, p. 990.

44. A.S. Bibliography, published by General Filtration Co., Rochester,

N. Y., 1921.

45. A.S. at Manchester, Eng. by Ardern. Journal Society Chemical Indus-

try, 1921. E.G. V. 55, 1921, p. 310.

46. The Des Plaines River A.S. Plant, by Pearse. E.N.R. V. 88, 1920,

p. 1134.

47. Sewage Treatment by the Dorr System, by Eagles. Proceedings,

Boston Society of Engineers, 1920. Public Works V. 50, 1920, P. 53.

CHAPTER XIX

ACID PRECIPITATION, LIME AND ELECTRICITY, AND
DISINFECTION

275. The Miles Acid Process. — The Miles Acid Process for
the treatment of sewage was devised and patented by G. W.
Miles. It was tried experimentally at the Calf Pasture sewage
pumping station, Boston, Mass., 1911 to 1914. In 1916 it was
tried experimentally at the Massachusetts Institute of Tech-
nology, and it has been tested subsequently at other places, nota-
bly at New Haven, Conn., in 1917 and 1918. It is one of the
most recent developments in sewage treatment and no extensive
experience has been had with it. The process consists in the
acidification of sewage with sulphuric or sulphurous acid, as the
result of which the suspended matter and grease are precipitated
and bacteria are removed. The equipment required for the
process consists of devices for the production of sulphur dioxide
(802), and for feeding niter cake or other forms of acid; sub-
siding basins; sludge-handling apparatus; sludge driers; grease
extractors; grease stills; and tankage driers and grinders.

The first step is the acidification of the sewage. The period
of contact with the acid is about 4 hours. Sulphurous acid
seems to give better results than sulphuric because of the ease
in which it can be manufactured on the spot. It seems also to
be more virulent in attacking bacteria than an equal strength
of sulphuric acid. In experimental plants the acidulation has
been accomplished in different ways such as: by the addition
of compressed sulphur dioxide from tanks; by the addition of
sulphur dioxide made from burning sulphur; or by the roasting
of iron pyrite (FeS2). The acidulation precipitates most of the
grease as well as the suspended matter and results in a sludge
which gives some promise of commercial value. In referring
to the process R. S. Weston states:1

1 Reference 1, at end of this chapter.
482

THE MILES ACID PROCESS 483

(1) It disinfects the sewage by reducing the numbers
of bacteria from millions to hundreds per c.c.

(2) If the drying of the sludge and the extraction of
the grease can be accomplished economically, it is possible
that a large part, if not all, of the cost of the acid treat-
ment may be met by the sale of the grease and fertilizer
recovered from the sewage.

(3) The use of so strong a deodorizer and disinfectant
as sulphur dioxide would prevent the usual nuisances of
treatment works.

(4) The addition of sulphur dioxide to the sewage
also avoids any fly nuisance, which is a handicap to the
operation of Imhoff tanks and trickling filters.

The amount of acid used varies with the quality of the
sewage and the desired character of the effluent. At Bradford,
England,1 5,500 pounds of sulphuric acid are used per million
gallons, producing about 2,340 pounds of grease or 0.43 pound of
grease per pound of sulphuric acid. At Boston only 0.215 pound
of grease were produced per pound of sulphuric acid. The dif-
ference is probably due to the great difference in the amount of
grease in the raw sewage. In the East Street sewer at New Haven,
Conn.,2 only 700 pounds of acid are used per million gallons of
sewage as the alkalinity is only 50 p. p.m. This amount of acid
secures an acidity of 50 p.p.m. whereas in the Boulevard sewer
1,130 pounds of acid had to be added to produce the same result.
The results obtained by the experiments conducted by the
Massachusetts State Board of Health in 1917 are shown in
Table 97. The character of the sludge from the same tests
is shown in Table 98. After acidification3 the sewage contains
bisulphites and some free sulphurous acid, with some lime and
magnesium soaps which are attacked by the acid liberating the
free fatty acids. Part of the bisulphites and sulphurous acid
are oxidized to bisulphates and sulphuric acid. It was found
as a result of the New Haven3 experiments that the presence
of sulphur dioxide in the effluent caused an abnormal oxygen
demand from the diluting water and that this difficulty could be
partly overcome by the aeration of the effluent after acidulation
and sedimentation, without prohibitory expense. The effluent
and sludge are both stable for appreciable periods of time and
are suitable for disposal by dilution. The character of the

1 Reference 2. * Reference 6. * Reference 5.

484 ACIDIFICATION, ELECTROLYSIS, DISINFECTION

sludge as determined by the New Haven tests l is shown in Table
99.

TABLE 97

(Eng. News-Record, Vol. 80, p. 319)

Sample

Parts per Million

Bacteria,
Millions

Ammonia

Kjeldahl
Nitrogen

Chlor-
ine

Oxy-
gen
Con-
sumed

Free

Albuminoid

Total

Diss.

Total

Diss.

20°

37°

Paddock's Island

14.0
12.2

20.9

3.3
1.6

5.2

1.8
1.1

3.9

6.8
3.5

10.0

3.6

2.2

7.5

134

23.1
15.4

1.86

units
94

4.15

units
91

Acidified and settled

Deer Island

23.3
21.1

20.9

8.2
5.6

5.2

4.8
3.9

3.9

16.8
10.7

10.0

8.9
7.3

7.5

3100

87.3
62.2

2.63

units
147

1.50

units
85

Settled sewage
Acidified and settled

Calf Pasture

18.0
19.1

17.8

4.5
2.3

2.4

2.0
1.4

1.6

9.7
4.9

4.9

4.1
3.3

3.3

3254

41.2
25.8

1.89

units
277

0.98

units
149

Acidified and settled

•

The success of the Miles Acid Process in comparison with other
processes is dependent on the commercial value of the sludge
produced. The New Haven experiments indicate that 16 to 21
per cent of the grease in the sludge is unsaponifiable and seri-
ously impairs the value of the process.

1 Reference 6.

THE MILES ACID PROCESS

TABLE 98

485

AVERAGE AMOUNT OF SLUDGE AND FATS OBTAINED FROM SEWAGE ENTER-
ING BOSTON HARBOR AFTER EIGHTEEN HOURS SEDIMENTATION
WITH AND WITHOUT ACIDIFICATION

(Eng. News-Record, Vol. 80, p. 319)

Paddock's Island

Deer Island

Calf Pasture

Sedimentation

Plain

Acidu-
lated

Plain

Acidu-
lated

Plain

Acidu-
lated

Pounds of SC>2 used per million

818
959
3.38
27.30

1513
1939
3.45
19.40

1189
1427
2.83
26.30

Dry sludge per million gallons. .
Per cent Nitrogen in sludge. . . .

762
3.10
27.30

1709
3.57
24.60

1208
3.18
24.30

TABLE 99

CHARACTER OF MILES ACID SLUDGE AT NEW HAVEN
(Eng. News-Record, Vol. 81, p. 1034)

East Street Sewer

Boule-
. vard
Sewer

Length of run in days

25
260

3750
1.067
86.6

503
23.7
119

47.2
1.6

24
239.4

4025
1.048

483
24.0
116

51.2
1.6

44
407.8

3200
1.054
86.3

439
29
127

57.3
2.4

70
602.2

2600
1.061

85.7

368
32.6
120

63.8
2.0

29
145.5
5375

Total sewage treated, thou-
sand gallons

Gallons wet sludge per mil-
lion gallons sewage . . .

Specific gravity

Per cent moisture

92.5
403
30.9
124

78.5
3.0

Pounds of dry sludge per
million gallons sewage
Ether extract, per cent dry
sludge ...

Ether extract, pounds per
million gallons

Volatile matter, per cent dry
sludge

Nitrogen, per cent dry sludge

486 ACIDIFICATION, ELECTROLYSIS, DISINFECTION

The conclusions reached as a result of the New Haven experi-
ments are:1

Our experience with New Haven sewage lends no
color to the hope that a net financial profit can be obtained
by the use of the Miles Acid Process, except with sewage
of exceptionally high grease content and low alkalinity.
They do, however, suggest that for communities where
clarification and disinfection are desirable — where screening
would be insufficient and nitrification unnecessary — the
process of acid treatment comes fairly into competition
with the other processes of tank treatment, and that it
is particularly suited to dealing with sewages that contain
industrial wastes, and to use in localities where local
nuisances must be avoided at all costs and where sludge
disposal could be provided for only with 'difficulty.

The conclusions reached as a result of the Chicago experi-
ments are:2

The results on hand indicate that treatment of this
sewage with acid results in a somewhat greater retention
of fat. An apparent reduction in the oxygen demand
over that resulting from plain sedimentation, while remark-
able, is probably not real, being simply due to a retarda-
tion of decomposition by the sterilization of the bacteria
present, the organic matter being left in solution. . . .
However, there appears the added cost of acid treatment
and the cost of recovery of the grease, as well as the
uncertainty of the price to be received for the grease
recovered.

The cost of the treatment is estimated by Dorr to be $18 per
million gallons, and the value of the sludge obtained from the
Boston sewage as $24 per million gallons, giving a net margin
of profit of $6 per million gallons. At New Haven, the total
return is estimated at $7.09 per million gallons. Based on the
production of sulphur dioxide by burning sulphur (assumed to
cost $36 per long ton) and on drying from 85 per cent to 10
per cent moisture with coal assumed to cost $7.50 per ton, it
appears that the acid treatment of sewage should be materially
cheaper than either the Imhoff treatment or fine screening under
the local conditions. A comparison of the cost of the treatment
of the East Street and the Boulevard sewage at New Haven

1 Reference 6. 2 Reference 8.

THE MILES ACID PROCESS

487

and the Calf Pasture sewage in Boston is given in Table 100.
The cost of construction was estimated by Dorr and Weston
in 1919 as greater than $15,000 per million gallons of sewage
per day capacity.

TABLE 100

ESTIMATED COST OP SEWAGE TREATMENT AT NEW HAVEN AND BOSTON
BY THREE DIFFERENT PROCESSES

Cost in Dollars per Million Gallons Treated
(Engineering and Contracting, Vol. 51, p. 510)

Miles Acid Process

Imhoff Tank and
Chlori nation

Fine Screens
and Chlorination

East
Street

Boule-
vard

Calf
Pasture

East
Street

Boule-
vard

Calf
Pasture

East
Street

Boule-
vard

Tanks and Buildings
Int and Dep ....

2.47
6.93
2.09
1.78
0.17
1.06

1.00

2.47
10.74
2.04
1.91
0.17
2.65

1.00

2.47
18.65
10.34
9.12
0.10
1.06

1.00

5.28

0.46
1.20

1.00
4.05
11.99

11.99

4.44

1.15
1.50

1.00
4.05
12.14

12.14

4.60

0.47
1.42

0.50
4.05
11.03

11.03

4.60

1.15
2.05

0.50
4.05
12.35

12.35

Drying sludge

Degreftsing sludge. . . .
Redrying tankage. . . .

Labor on tanks and

Disposal of sludge or

15.50
6.57
8.93

20.98
10.66
10.32

42.75
47.59
4.84

Revenue

Net cost

ELECTROLYTIC TREATMENT

276. The Process. — This process has been generally unsuc-
cessful in the treatment of sewage and has grown into disrepute.
In the words of the editor of the Engineering News-Record: l

Thirty years of experiments and demonstrations with
only a few small working plants built and most of them
abandoned — such in epitome is the record of the electro-
lytic process of sewage treatment.

It is probably true that the process has never received a thorough
and exhaustive test on a large scale, but the small-scale tests have

1 Reference 20.

488 ACIDIFICATION, ELECTROLYSIS, DISINFECTION

not been promising of good results. Among the most extensive
tests have been those at Elmhurst, Long Island,1 Decatur, 111.,2
and Easton, Pa.3

Whatever degree of popularity the method has possessed
has been due possibly to the mystery and romance of " elec-
tricity " and to the personality of its promoters. The process
should, nevertheless, be understood by the engineer in order
that it may be explained satisfactorily to the layman interested
in its adoption.

In this process, sometimes called the direct-oxidation process,
all grit is removed and the sewage is passed through fine screens
before entering the electrolytic tank. In the electrolytic tank
the sewage passes in thin sheets between electrodes and an
electric current is discharged through it. A recent develop-
ment has been the addition of lime to the sewage at some point
in its passage through the electrolytic tank. From the elec-
trolytic tank the sewage flows to a sedimentation tank, where
sludge is accumulated, and from which the liquid effluent is
finally disposed of.

It is claimed that the action of the electricity electrolyzes
the sewage, releasing chlorine, which acts as a powerful disin-
fectant. The constituents of the sewage are oxidized so that
the dissolved oxygen, nitrates, and relative stability are increased
and the sludge is rendered non-putrescible. It is said that the
addition of lime increases the efficiency of sedimentation and
enhances the effect of the electric current. The results obtained
by tests at Easton, Pa., are shown in Table 101. It will be
observed from this table that the combination of lime and
electricity does not have a more beneficial effect than either one
of them alone. The amount of sludge produced by the com-
bination is about the same as by chemical precipitation alone,
but the character of the sludge produced with electricity is less
putrescible. The cost of the treatment as estimated at Elm-
hurst is shown in Table 102.

As a result of the tests at Decatur, comparing lime alone
with lime and electricity together, Dr. Ed. Bartow stated :

The purification by treatment with lime alone was
greater than that obtained in several of the individual
samples treated with lime and electricity.

, l Reference 17. 2 Reference 19. 3 Reference 21.

DISINFECTION OF SEWAGE

489

TABLE 101

COMPARATIVE RESULTS OBTAINED FROM THE TREATMENT OP SEWAGE BY
LIME ALONE, ELECTRICITY ALONE, AND LIME AND ELECTRICITY COMBINED

(Creighton and Franklin, Journal of the Franklin Institute, August, 1919)

Lime and

Electricity

Lime Alone

Electricity Alone

Change,
Parts

Change,
Per

Change,
Parts

Change,
Per

Change,
Parts

Change,
Per

per
Million

Cent

per
Million

Cent

per
Million

Cent

Chlorine

+1.2

+ 1.9

+ 12.3

+ 18.2

+ 1.6

+2.2

Nitrites

+0.014

+58.3

-.005

-10.0

-0.01

-20.0

Nitrates

+0.13

+23.6

+ .005

+0.8

-0.15

-20.0

Ammonia

-3.3

-18.3

+0.2

+1.3

+0.9

+6.6

Albuminoid am-

monia

-3.6

-12.1

-0.4

-1.7

-0.5

-2.3

Oxygen demand. . .

-13.0

-20.5

-7.7

-8.9

-6.5

-10.0

Dissolved oxygen . .

+1.78

+40.9

-0.93

-19.1

+ 1.61

+40.1

Total bacteria at

37° (Thousands)

-343

-92.7

-373

-82.4

-165

-37.8

Total bacteria at

20° (Thousands)

-688

-92.2

-1074

-90.1

-635

-70.0

B. Coli (Thou-

sands)

-77.9

-99.85

-96.3

-92 3

-45

-81.8

Oxygen absorbed

in 5 days

-3.40

-81.6

-1.03

-21.

+ 1.24

+31

DISINFECTION

277. Disinfection of Sewage. — Sewage is disinfected in order
to protect public water supplies, shell fish, and bathing beaches;
to prevent the spread of disease; to keep down odors, and to
delay putrefaction. Disinfection is the treatment of sewage
by which the number of bacteria is greatly reduced. Steriliza-
tion is the destruction of all bacterial life, including spores.
Ordinarily even the most destructive agents do not accomplish
complete sterilization. Chlorine and its compounds are practi-
cally the only substances used for the disinfection of sewage.
The liine used in chemical precipitation, the acid used in the Miles

490 ACIDIFICATION, ELECTROLYSIS, DISINFECTION

Acid Process, the aeration in the activated sludge process, all
serve to disinfect sewage, but are not used primarily for that
purpose. Copper sulphate has been used as an algaecide but
never on a large scale as a bactericide.1 Heat has been suggested,
but its high cost has prevented its practical application to the
disinfection of sewage.

TABLE 102

COST OF ELECTROLYTIC TREATMENT, ELMHURST, LONG ISLAND, AND
EASTON, PENNSYLVANIA

Three

One Million Gallon

Million

Gallon

Item

unit at

Easton,

Elmhurst,

Dollars

Hydrated lime:

Elmhurst, 1300 pounds at $7.90 ton. 1
Easton, 3720 pounds at $6.75 ton. j

12.56

5.14

15.42

Electric power electrolysis:

Elmhurst, 85 kw-h. at 4 cents j
Easton, 185 . 5 kw-h. at 2 . 26 cents j

4.19

3.40

9.60

Electric power, light and agitation:

Elmhurst, 60 kw-h. at 4 cents |
Easton, 6 . 25 kw-h. at 8 . 05 cents J

0.50

2.40

7.20

Heating

1.25

Labor and supervision

15.00

12 50

15 00

Maintenance, repairs and supplies

1 50

1 00

3 00

Sludge pressing and removal

5 11

15 33

Total

35.00

29 55

65 55

Cost per million gallons <

35.00

29.55

21.86

The action which takes place on the addition to sewage of
chlorine or its compounds is not well understood. The idea that
the bacteria are burned up with " nascent " or freshly born
oxygen, has been exploded.2 Likewise the idea that the toxic
properties of chlorine have no effect has not been borne out by

1 Reference 24.
. 2 Inorganic Chemistry, by Alexander Smith.

DISINFECTION OF SEWAGE 491

experiments. It has been demonstrated, particularly by tests
on strong tannery wastes, that the action of chlorine gas is more
effective than the application of the same amount of chlorine
in the form of hypochlorite. All that we are certain of at present
is that the greater the amount of chlorine added under the same
conditions, the .greater the bactericidal effect.

Chlorine is applied either in the form of a bleaching powder
or a gas. In ordinary commercial bleach (calcium hypochlorite)
the available chlorine is about 35 to 40 per cent by weight. In
order to add one part per million of available chlorine to sewage
it is necessary to add about 25 pounds of bleaching powder or
85 pounds of liquid chlorine per million gallons of sewage. This
can be computed as follows:

The molecular weight of calcium hypochlorite is
127.0. This reacts to produce two atoms of available
chlorine with a molecular weight of 70.9. If the bleach-
ing powder were pure the available chlorine would there-
fore represent 70.9 -f- 127, or 56 per cent of its weight.
Then to obtain one pound of chlorine it would be neces-
sary to have 1.79 pounds of pure bleaching powder.
Since 1,000,000 gallons of water weigh approximately
8,300,000 pounds, in order to apply one part per million of
chlorine to 1,000,000 gallons of sewage it is necessary to
apply 1.79X8.3 or 14.9 pounds of pure bleaching powder.
Commercial bleaching powder is only about 60 per cent
calcium hypochlorite. It is therefore necessary to add
14.9 -j- 0.60 or about 25 pounds of commercial bleach.

Since liquid chlorine is very nearly pure, approxi-
mately 85 pounds of it applied to 1,000,000 gallons of
sewage are equivalent to a dose of one part per million.

Commercial bleaching powder is a dry white powder which
absorbs moisture slowly, and which loses its strength rapidly
when exposed to the air. It is packed in air-tight sheet iron
containers, which should be opened under water, or emptied
into water immediately on being opened. The strength of the
solution should be from \ to 1 per cent. The rate of the appli-
cation of the solution to the sewage may be controlled by auto-
matic feed devices, or by hand-controlled devices.

Commercial liquid chlorine is sold in heavy cast steel con-
tainers, which hold 100 to 140 pounds of liquid chlorine under a
pressure of 54 pounds per square inch at zero degrees C. or 121
pounds per square inch at 20 degrees.

492 ACIDIFICATION, ELECTROLYSIS, DISINFECTION

The amount of chlorine used is dependent on the character
of the sewage to be treated, the stage of decomposition of the
organic matter, the desired degree of disinfection, the period of
contact, and the temperature. The amount of chlorine is
expressed in parts per million of available chlorine, regardless of
the form in which the chlorine is applied. In general about 15
to 20 parts per million of available chlorine with 30 minutes'
contact at a temperature of about 15° C. will effect an apparent
removal of 99 per cent of the bacteria from the raw sewage.
The effect is only apparent because many of the bacteria encased
in the solid matter of the sewage escape the effect cf the chlo-
rine, or detection in the bacterial analysis. Stronger and older
sewages, higher temperatures, and shorter periods of contact
will demand more chlorine to produce the same results. A
septic effluent will require more chlorine than a raw sewage
because of the greater oxygen demand by the septic sewage.
The results of experiments on disinfection made at different
testing stations have shown such wide variations in the amount
of chlorine necessary, as to demonstrate the necessity for inde-
pendent studies of any particular sewage which is to be chlori-
nated. For instance, at Milwaukee approximately 13 p.p.m.
of available chlorine applied to an Imhoff tank effluent effected
a 99 per cent removal of bacteria, whereas the same result was
obtained at Lawrence, Mass., on crude sewage with only 6.6
p.p.m. and at Marion, Ohio, only 9 per cent removal of bacteria
was obtained by the addition of 4,815 p.p.m. to crude sewage.
The Ohio and Massachusetts reports show irrational variations
among themselves. For instance, 6.2 p.p.m. applied to a septic
effluent effected 88 per cent removal whereas in another case
7.6 p.p.m. effected only 36 per cent removal. At Lawrence in
one case it took 8.6 p.p.m. to remove 99 per cent from a sand
filter effluent, but only 6.3 p.p.m. to effect the same result in the
effluent from a septic tank. The most consistent results are
those found at Milwaukee which show a steadily increasing
percentage removal with increasing amounts of chlorine.

Some time after sewage has received its dose of chlorine the
number of bacteria may be greater than in the raw* sewage.
Such bacteria are called after-growths. Certain forms of bac-
teria, particularly the pathogenic or body temperature types,
are most susceptible to disinfecting agents. These are killed

REFERENCES 493

off and leave the sewage in a condition more favorable to the
growth of more resistant fonns of bacteria. As the latter are
non-pathogenic and are generally aerobic their presence is
usually more beneficial than detrimental, as they hasten the action
of self-purification.

REFERENCES

The following abbreviations will be used: E.G. for Engineering and
Contracting, E.N. for Engineering News, E.R. for Engineering Record,
E.N.R. for Engineering News-Record, M.J. for Municipal Journal, p. for
page, and V. for volume.

No.

1. Grease and Fertilizer Base for Boston Sewage, by Weston, E.N. V. 75,

1916, p. 913 and Journal American Public Health Association, April,
1916.

2. Getting Grease and Fertilizer from City Sewage, by Allen. E.N. V. 75,

1916, p. 1005.

3. New Haven Tests Five Processes of Sewage Treatment. E.N.R. V. 79,

1917, p. 829.

4. Recovery of Grease and Fertilizer from Sewage Comes to the Front.

E.N.R. V. 80, 1916, p. 319.

5. Miles Acid Process may Require Aeration of Effluent, by Mohlman.

E.N.R. V. 81, 1918, p. 235.

6. Promising Results with Miles Acid Process in New Haven Tests.

E.N.R. V. 81, 1918, p. 1034.

7. Baltimore Experiments on Grease from Sewage. E.N. V. 75, 1916,

p. 1155.

8. Report on Industrial Wastes from the Stock Yards and Packingtown

in Chicago to the Trustees of the Sanitary District of Chicago, 1914,
pp. 187-195.

9. The Separation of Grease from Sewage, by Daniels and Rosenfeld.

Cornell Civil Engineer. V. 24, p. 13.

10. The Separation of Grease from Sewage Sludge with Special Reference

to Plants and Methods Employed at Bradford and Oldham, England,
by Allen. E.G. V. 40, 1913, p. 611.

11. Acid Treatment of Sewage, by Dorr and Weston. Journal Boston

Society of Civil Engineers, April, 1919. E.G. V. 51, 1919, p.
510. M. J. V. 46, 1919, p. 365.

12. The Miles Acid Process for Sewage Disposal. Metallurgical and Chemical

Engineering, V. 18, p. 591.

13. Miles Acid Treatment of Sewage, by Winslow and Mohlman. Journal

American Society Municipal Improvements, Oct., 1918. M. J. V. 45,

1918, pp. 280, 297, and 321.

14. New Electrolytic Sewage Treatment. M.J. V. 37, 1914, p. 556.

494 ACIDIFICATION, ELECTROLYSIS DISINFECTION

No.

15. Electrolytic Sewage Treatment. M.J. V. 47, 1919, p. 131.

16. Electrolytic Treatment of Sewage at Durant, Oklahoma, by Benham.

E.N. V. 76, 1916, p. 547. Municipal Engineering, V. 49, 1916,
p. 141.

17. Electrolytic Treatment of Sewage at Elmhurst, Long Island, by Travis.

Report to the President of the Borough of Queens, Aug. 31, 1914.
E.R. V. 70, 1914, pp. 292, 315, and 429. M.J. V. 39, p. 551. Muni-
cipal Engineering, V. 47, p. 281.

18. Tests of the Electrolysis of Sewage at Toronto, by Nevitt. E.N. V. 71,

1914, p. 1076.

19. Electrolytic Treatment of Sewage Little Better than Lime Alone, by

Bartow. E.R. V. 74, 1916, p. 596.

20. Electrolytic Sewage Treatment Not Yet an Established Process.

E.N.R. V. 83, 1919, p. 541.

21. Tests of Electrolytic Sewage Treatment Process at Easton, Pa. Journal

of the Franklin Institute, Aug., 1919. E.N.R. V. 83, 1919, p. 569.

22. The Disinfection of Sewage. U. S. Geological Survey, Water Supply

Paper, No. 229.

23. Sewage Disinfection in Actual Practice, by Orchard. E.R. V. 70, 1914,

p. 164.

24. Water "and Sewage Purification in Ohio. Report of the Ohio State Board

of Health, 1908, pp. 738-762.

25. Water Purification, by Ellms. Published in 1917 by McGraw-Hill

Book Co.

26. Electrolytic Sewage Treatment, A Half Century of Invention and

Promotion. E.N.R. V. 86, 1921, p. 25.

CHAPTER XX
SLUDGE

278. Methods of Disposal. — Sludge is the deposited suspended
matter which accumulates as the result of the sedimentation
of sewage. The methods for the disposal of sludge as discussed
herein will include the disposal of scum. Scum is a floating
mass of sewage solids buoyed up in part by entrained gas or
grease, forming a greasy mat which remains on the surface of the
sewage.1 The sludges formed by different methods of sewage
treatment are described in the chapter devoted to the particular
method. The disposal of sludge is a problem common to all
methods of sewage treatment involving the use of sedimentation
tanks.

Sludge is disposed of by: dilution, burial, lagooning, burning,
filling land, and as a fertilizer or fertilizer base. Certain methods
of disposal, such as burning or as a fertilizer, demand that the
sludge be dried preparatory to disposal. Sludge is dried on dry-
ing beds, in a centrifuge, in a press, in a hot-air dryer, or by
acid precipitation.

279. Lagooning. — This is a method of sludge disposal in
which fresh sludge is run on to previously prepared beds to a
depth of 12 to 18 inches or more, and allowed to stand without
further attention. The preparation of the lagoons requires
leveling the ground, building of embankments, and, if the
ground is not porous, the placing of underdrains laid in sand
or gravel. At Reading, Pa.,2 approximately one acre was
required for 1,700 cubic yards of wet sludge. The results of
lagooning at Philadelphia are given in Table 103.2

1 American Public Health Association definition.
* Sewage Sludge by Allen.
495

496

SLUDGE

TABLE 103

RESULTS OF DRYING SLUDGE IN LAGOONS AT PHILADELPHIA
("Sewage Sludge" by Allen)

Treatment

Days

Depth,
Inches

Per Cent,
Moisture

Rainfall,
Inches

Cubic Yards
per Acre

Screened

12.20

82 8

1600

Screened

7 67

57 0

1000

Screened

3 50

51 6

0 43

470

Screened

13.50

90 1

1800

Screened

7 00

61 0

3 14

950

Crude

12 00

88 7

1600

Crude

4.70

62 8

2 59

640

During the period of standing in the lagoon the moisture
drains out and evaporates and the organic matter putrefies,
giving off gases and foul odors. In the course of three to six months,
biological action ceases and the sludge has become humified and
reduced to about 75 per cent moisture. In the utilization of
this method of disposal the lagoons must be removed from
settled districts and should occupy land of little value for other
purposes. The odors created at the lagoons may be intense
and offensive. The land so used is rendered unfit for other pur-
poses for many years.

The digestion of sludge in special tanks is a form of lagooning
in which an attempt is made to maintain septic action as a result
of which a portion of the sludge is gasified or liquefied, leaving
less to be cared for by some of the other methods of treatment
or disposal. The results obtained by digestion tanks has not
been entirely satisfactory. A partial drying and consolidation
of the sludge may be effected, however, by the process of decanta-
tion, in which the supernatant liquid is run off, followed by further
sedimentation, rendering the final product more compact.

280. Dilution. — In the disposal of sludge by dilution, as in
the disposal of sewage by dilution, there must be sufficient
oxygen available in the diluting water to prevent putrefaction,
and a swift current to prevent sedimentation. Such conditions
exist in localities along the sea coast, and in communities

DILUTION 497

situated near rivers, when the rivers are in flood. In some sea-
coast towns, for example at London and Glasgow, the sludge is
taken out to sea in boats, and dumped. Since it is not necessary
to discharge sludge continuously, it can be stored to advantage
in the digestion chamber of a tank, until the conditions in the
body of diluting water are suitable to receive it.

The amount of diluting water to receive sewage sludge has not
been sufficiently well determined to draw reliable general con-
clusions. A dilution of 1,500 to 2,000 volumes may be considered
sufficiently safe to avoid a nuisance provided there is a sufficient
velocity to prevent sedimentation. Johnson's Report on Sew-
age Purification at Columbus, Ohio (1905), states that a dilution
of 1 to 800 is sufficient to avoid a nuisance. The character
of the sludge has a marked effect on the proper ratio of dilution,
the sludge from septic and sedimentation tanks requiring a
greater dilution than that from Imhoff tanks.

281. Burial. — Sludge can be disposed of by burial in trenches
about 24 inches deep with at least 12 inches of earth cover,
without causing a nuisance. The ground used for this purpose
should be well drained. This method of disposal is generally
used as a makeshift and has not been practiced extensively
because of the large amount of land required. Insufficient infor-
mation is available to generalize on the amount of land required
or the time before the land can be used for further sludge burial,
or for other purposes. Indications are that the sludge may
remain moist and malodorous for years and that the land may be
rendered permanently unfit for further sludge burial. Under
some conditions the land may be used again for the same or
other purposes. For example, Kinnicutt, Winslow and Pratt *
state that 500 tons of wet sludge can be applied per acre and :

The same land, it is claimed, can be used again after
a period of a year and a half to two years, if in two months
or so after covering the sludge with earth, the ground is
broken up, planted, and, when the crop is removed, again
plowed and allowed to remain fallow for about a year.

282. Drying. — Before sludge can be disposed of to fill land,
by burning, or for use as a fertilizer filler it must be dried to a
suitable degree of moisture. The removal of moisture from the

1 Sewage Disposal by Kinnicutt, Winslow and Pratt.

498 SLUDGE

sludge decreases its volume and changes its characteristics so
that sludge containing 75 per cent moisture has lost all the char-
acteristics of a liquid. It can be moved with a shovel or fork,
and can be transported in non-watertight containers. A reduction
in moisture from 95 to 90 per cent will cut the volume in half.

The change in volume on the removal of moisture can be
represented as:

7(100- P)
(100- Pi)'

in which P = the original percentage of moisture;
PI = the final percentage of moisture;
7= the original volume;
7i = the final volume.

The drying of sludge on coarse sand filter beds is more
particularly suited to sludge from Imhoff tanks. This sludge
does not decompose during drying, and is sufficiently light and
porous in texture to permit of thorough draining. The sludge
from plain sedimentation or chemical precipitation tanks is
high in moisture, putrescible, and when placed on a filter bed
it settles into a heavy, compact, impervious mass which dries
slowly. In order to avoid this condition the sludge is run on to
the beds as quickly as possible, to a depth of not more than 6
to 10 inches. Lime is sometimes added to the sludge at this
time as it aids drying by assisting in the maintenance of the
porosity of the sludge, and it is advantageous in keeping down
odors and insects.

Sludge filter beds are made up of 12 to 24 inches of coarse
sand, well-screened cinders, or other gritty material, underlaid
by 6 inches of coarse gravel and 6 or 8-inch open-joint tile
underdrains, laid 4 to 10 feet apart on centers, dependent on the
porosity of the subsoil. The side walls of the filters are made of
planks or of low earth embankments. The sludge filters at
Hamilton, Ontario, are shown in Fig. 179.

The size of the bed is dependent mainly upon the character-
istics of the sludge. For Imhoff tank sludge which comes from
the tank with about 85 per cent moisture, the practice is to
allow about 350 1 square feet of filter surface per 1,000 popu-
1 Sewage Disposal by Fuller.

DRYING

409

lation contributing sludge. For other types of sludge the area
varies from 900 to 9,000 square foot per 1,000 population con-
tributing sludge, and only experiments with the sludge in hand
can determine the proper allowance. Imhoff recommends 1,080

^S"C.f.S/udga Pipe.

Part Plan,
Movable

Wooden Trough-,

l^'Screentdt

Concrete &&&

Part Cross Section A-B,'

FIG. 179. — Sludge-drying Beds at Hamilton, Ontario.
Eng. News, Vol. 73, p. 426.

square feet per 1,000 population for septic tank sludge, and
6,480 square feet for sludge from plain sedimentation tanks.1
Kinnicutt, Winslow, and Pratt in their book on Sewage Disposal
state:

With an average depth of 10 inches per dose of sludge
of 87 per cent water content, one square foot of covered
(glass) bed should dry to a spadable condition one cubic
yard of sludge per year.

Sewage Sludge by Allen.

500 SLUDGE

The sludge is run on the bed in small quantities at periods from
two weeks to a month apart. In favorable weather Imhoff
sludge will dry in two weeks or less to approximately 50 to 60
per cent moisture. It is then suitable for use as a filling material
on waste land, for burning, or for further drying by heat. Glass
roofs, similar to those used on green-houses, have been used to
speed the drying process by preventing the moistening of partly
dried sludge during rainy weather. In some instances sludge
has dried to 10 per cent moisture on such beds. Imhoff sludge
can be removed from the drying beds with a manure or hay
fork. It has an odor similar to well-fertilized garden soil. It
is stable, dark brownish-gray in color, is of light coarse material,
and is granular in texture.

Sludge presses are suitable for removing moisture from the
bulky wet sludge obtained from plain sedimentation, chemical
precipitation, and the activated sludge process. The details
of a typical sludge press are shown in Fig. 180. The press
shown is made up of a number of corrugated metal plates about
30 inches in diameter with a hole in the center about 8 inches
in diameter. The corrugations run vertically except for a distance
about 3 inches wide around the outer rim, which is smooth. To
this smooth portion is fastened, on each side of the plate, an
annular ring about an inch thick and 2 to 3 inches wide,
of the same outside diameter as the plate. A circular piece
of burlap, canvas, or other heavy cloth is fastened to this
ring, covering the plate completely. A hole is cut in the center
of the cloth slightly smaller in diameter than the center hole
in the plate, and the edges of the cloth on opposite sides of
the plate are sewed together. The plates are then pressed
tightly together by means of the screw motion at the left end
of the machine, thus making a water-tight joint at the outer
rim. Sludge is then forced under pressure into the space
between the plates, passing through the machine by means of
the central hole. The pressure ori the sludge may be from 50
to 100 pounds per square inch. This pressure forces the water
out of the sludge through the porous cloth from which it escapes
to the bottom of the press along the corrugations of the sepa-
rating plate. After a period of 10 to 30 minutes the pressure
is released, the cells are opened, and the moist sludge cake is

DRYING

501

removed. The liquid pressed from the sludge is highly putres-
cible and should be returned to the influent of the treatment
plant. The pressing of wet greasy sludges is facilitated by the
addition of from 8 to 10 pounds of lime per cubic yard of sludge.
The cake thus formed is more cohesive and easy to handle. The
output of the press depends so much on the character of the
sludge that a definite guarantee of capacity is seldom given by
the manufacturer.

The simplest form of centrifugal sludge dryer is a machine
which consists of a perforated metal bowl lined with porous
cloth in which the sludge is placed. Surrounding this bowl is

FIG. 180.— Filter Press.

a second water-tight metal bowl so arranged as to intercept the
water thrown from the sides of the inner bowl as it revolves.
The peripheral velocity of the inner bowl is about 6,000 feet per
minute, which makes the effective weight of each particle about
250 times its normal weight when at rest. Very few data are
available on the operation of such machines, and their use has
not been extensive because of the difficulty of starting and
stopping the machine at each filling, and the difficulty of removing
the partially dried sludge from the inner basket. The Besco-
ter-Meer centrifuge, manufactured by the Barth Engineering
and Sanitation Co., can be operated continuously and the diffi-
culties of removing the dried sludge from the machine have

502

SLUDGE

been overcome. According to the manufacturers the centri-
fuge has been operated very successfully in Germany on plain
septic tank sludge. A removal of 70 per cent of suspended solids
in the raw sludge and a production of 3,600 pounds of sludge
per hour, containing 60 to 70 per cent of moisture, can be obtained
at less than 900 r.p.m. with a consumption of 15 horse-power.
Extensive tests of the machine were made at Milwaukee
from October, 1920, to September, 1921, on activated sludge,

Besco-ter-Meer Sludge Drying Centrifuge at Milwaukee, Wisconsin
Courtesy, Barth Engineering and Sanitation Co.

but results of these tests are not as yet available. Indications
are that the centrifuge has acted as a classifier. The coarser
particles of sludge have been removed but the finer particles
have been continuously returned with the liquid to the
sedimentation tank, ultimately filling this tank with fine
particles of sludge. An illustration of the unit tested at Mil-
waukee is shown on this page.

DRYING

503

Experiments on the drying of sludge by acid flotation have
not progressed sufficiently to allow the installation of a working
unit. The method, which has been applied principally to
activated sludge, consists in adding a small amount of sulphuric
acid to the sludge as it leaves the storage tank. The sludge is
coagulated by this action, the coagulated material rising to the
surface as a scum containing about 86 per cent moisture. The
consistency is such that it can be removed with a shovel. The
liquid can be withdrawn continuously from below the scum.

The moisture content of sludge to be used in the manufacture
of fertilizer must be reduced to 10 per cent or less. None of

FIG. 181. — Direct-Indirect Sludge Dryer.

Courtesy, the Buckeye Dryer Co.

the methods of drying described so far can be relied upon for
such a product and it becomes necessary to use direct or indirect
heat dryers. There are various types of dryers on the market.
The details of a Buckeye dryer are shown in Fig. 181. In the
operation of this machine moist sludge is fed in at the left end
at the point marked " feed." The hot gases pass from the fire box
up and around the cylinder which revolves at about eight r.p.m.
The gases are drawn into the inner cylinder through the open-
ings marked A which revolve with the two cylinders. The gases
escape from the inner cylinder through the openings to the
right and flow towards the left in the outer cylinder, They come

504 SLUDGE

in contact with the sludge at this point. The gases then pass
off through the fan at the left. The sludge is lifted by the small
longitudinal baffles fastened to the outer cylinder, as the drying
cylinders revolve. The right end of the cylinder is placed lower
than the left so that the drying sludge is lifted and dropped
through the cylinder at the same time that it moves slowly
toward the right-hand end of the cylinder. These dryers
require about one pound of fuel for 10 pounds of water evaporated.
The odors from the dryer can be suppressed by passing the gases
through a dust chamber and washer.

A summary of the results from methods of sludge drying
at Milwaukee 1 follows :

Excess sludge produced, 12,100 gallons, having 97.5
per cent moisture, per million gallons of sewage treated.

Sludge cake produced (by presses), 10,083 pounds
having 80.3 per cent moisture, per million gallons of
sewage treated.

Dried sludge (from heat driers) produced, 2,521 pounds
having 10 per cent moisture, per million gallons of sewage
treated.

Press will produce 3 pounds of cake per square foot of
filter cloth in four and a half hours, or five operations per
twenty-four hours.

Dryers will reduce 6,700 pounds of sludge cake at
80 per cent moisture to 10 per cent moisture, and will
evaporate 8 pounds of water per pound of combustible.

Thickening devices known as Dorr thickeners, patented and
manufactured by the Dorr Co. and originally intended for
metallurgical purposes, have been adapted to the thickening
of sewage sludge. These thickeners are circular sedimentation
tanks, from 8 to 12 feet deep, more or less, and are made in any
diameter up to 200 feet or more. An arm, pivoted in the center
and extending to the circumference, is provided at the bottom
with a number of baffles or squeegees set at an angle with the
arm. The arm revolves at from one to fifteen revolutions per
hour, and the squeegees, in contact with the bottom of the tank,
scrape the deposited sludge towards a central sump, from which

1 From Eng. News-Record, Vol. 84, 1920, p. 995.

DRYING 505

it is removed by a pump or by gravity, without interrupting
the operation of the thickener. The sludge so thickened may be
reduced to 95 or 96 per cent moisture. These devices are ordi-
narily used only in the activated sludge process in which they
have been a pronounced success.

CHAPTER XXI
AUTOMATIC DOSING DEVICES

283. Types. — Automatic dosing devices are used to apply
sewage to contact beds, trickling filters, and intermittent sand
filters. These devices can be separated into two classes; those
with moving parts and those without moving parts. The latter
are better known as air-locked dosing devices. Simple devices
without moving parts are less liable to disorders and are nearer
" fool-proof " than any device depending on moving parts for
its operation.

No one type of moving part device has been used extensively
in different sewage treatment plants. Designing engineers have
exercised their ingenuity at different plants, resulting in the
production of different types.1 Among the best known forms
is the apparatus designed by J. W. Alvord for the intermittent
sand filters at Lake Forest, Illinois.2 In its operation. , , ,

A float in the dosing chamber lifts an iron ball in one
of a series of wooden columns, and at a certain height
the ball rolls through a trough from one column to the
next, in its passage striking a catch, which opens an air
valve attached to one of ten bell-siphons in the dosing
chamber. Each of the siphons discharges on one of the
ten sand beds, which are thus dosed in rotation.

Since air-locked dosing devices are in more general use their
operation will be explained in greater detail.

284. Operation.— The simplest form of these devices is the
automatic siphon used for flush-tanks, the operation of which
is described in Art. 61.

In the operation of sand filters, sprinkling filters, or other
forms of treatment where there are two or more units to be dosed

1 A Simple Mechanical Control for Dosing Sewage Beds, by P. Thompson,
Eng. News-Record, Vol. 84, 1920, p. 1018.

2 Sewage Disposal by Kinnicutt, Winslow and Pratt.

506

OPERATION

507

it is desirable that the dosing of the beds be done alternately.
A simple arrangement for two siphons operating alternately is
shown in Fig. 182. They operate as follows: with the dosing
tank empty at the start water will stand at W in siphon No. 2
and at aaf in siphon No. 1. As the water enters through the
inlet on the left the tank fills. When the water rises sufficiently,
air is trapped in the bells, and as the water continues to rise in
the tank, surfaces a and 6 are depressed an equal amount. When
b has been depressed to d, a has been depressed to c. Air is
released from siphon No. 2 through the short leg, and siphon

Plan.
.-Bell-.

: y i/

<• Dosing

rti

~ §1

J.L.S

Tank

= \

=. V

! -

[

^Sm'ft

Pipe

Section

A-A

k.2

Fio. 182. — Diagram Showing the Operation of Two Alternating Siphons.

No. 2 goes into operation. Surface c rises in siphon No. 1 as
the tank empties and when the action of Siphon No. 2 is broken
by the admission of air when the bottom of the bell is uncovered
the water in siphon No. 1 has assumed the position of 66' and that
in No. 2 is at aa'. The conditions of the two siphons are now
reversed from that at the beginning of the operation and as the
tank refills siphon No. 1 will go into operation. It is to be
noted that these siphons are made to alternate by weakening
the seal of the next one to discharge and by strengthening the
seal of the one which has just discharged.

AUTOMATIC DOSING DEVICES

285. Three Alternating Siphons. — This principle can be
extended to the operation of three alternating siphons as shown
in Fig. No. 183. These operate as follows: with the dosing
tank empty at the start and water at aar in siphons 1 and 2,
and at bbr in siphon No. 3, the dosing tank will be allowed to
fill. As the water rises in the tank air is trapped in all the bells
and surfaces a and 6 are depressed. When surface b has been
depressed to d, a has been depressed to c. Air is released from
siphon No. 3 and this siphon goes into action. Surface c rises

Plan

,.-1

Ie/Ar v

E' — ir

r~ii

r— if •

§
^

Section

A-A.

FIG. 183. — Diagram Showing the Operation of Three Alternating Siphons.

in siphons 1 and 2 to the position 6, as the dosing tank is emptied.
At the same time a small amount of water is passed from siphon
No. 3 to the short leg of siphon No. 1, through the small pipes
shown, thus filling this leg so that when siphon No. 3 ceases to
operate the water in siphons 1 and 3 stands at aa' and that in
No. 2 stands at 66'. Siphon No. 2, having the weaker seal,
will be the next to operate. During its operation it will fill
siphon No. 3, leaving No. 1 weak. When No. 1 operates it will
refill No. 2, leaving No. 3 weak, thus completing a cycle for the
three siphons. This principle has not been applied to the operation

FOUR OR MORE ALTERNATING SIPHONS

50!)

of more than three alternating siphons and is seldom used on recent
installations.

286. Four or More Alternating Siphons. — An arrangement
for the alternation of four or more siphons is illustrated in Fig. 184.
At the commencement of the cycle it will be assumed that all
starting wells are filled with water except well No. 1, and that all
main and all blow-off traps are filled with water. The following

FIG. 184. — Miller Plural Alternating Siphons.
Courtesy, Pacific Flush Tank Co.

Section.

description of the operation of the siphons is taken from the
catalog of the Pacific Flush Tank Company :

The liquid in the tank gradually rises and finally
overflows into the starting well No. 1 and the starting
bell being filled with air, pressure is developed which is
transm tted, as shown by the arrows, to the blow-off
trap connected with siphon No. 2. When the discharge
line is reached, sufficient head is obtained on the starting
bell to force the seal in blow-off trap No. 2, thus releasing
the air confined in siphon No. 2 and bringing it into full
operation.

510 AUTOMATIC DOSING DEVICES

During the time that siphon No. 2 i is operating,
siphonic action is developed in the draining siphon con-
nected with starting well No. 2 and as soon as the level
in the tank is below the top of the well it is drained down
to a point below the bottom of starting well No. 2. It
can now be seen that after the first discharge starting well
No. 2 is empty, whereas the other three are full. . . . There-
fore when the tank is filled the second time, pressure is
developed in starting bell No. 2, which forces the seal of
blow-off trap No 3, thus starting siphon No. 3. ...

This alternation can be continued for any number of siphons.
Other arrangements have been devised for the automatic con-
trol of alternating siphons, but these principles of the air-locked
devices are fundamental.

287. Timed Siphons. — In the operation of a number of
contact beds not only must the dosing of the tanks be alternated,
but some method is needed by which the beds shall be automat-
ically emptied after the proper period of standing full. To fulfill
this need the principle of the timed siphon must be employed
in conjunction with the alternating siphons. Fig. 185 illustrates
the operation of the Miller timed siphon. Its operation is as
follows: water is admitted to the contact bed and transmitted
to the main siphon chamber through the " opening into bed."
Water flows from the main siphon chamber into the timing
chamber at a rate determined by the timing valve. The con-
tact bed is held full during this period. As the tuning chamber
fills with water air is caught in the starting bell and the pressure
is increased until the seal in the main blow-off trap is blown and
the main siphon is put into operation. As the water level in the
main siphon chamber descends, water flows from the tuning
chamber into the main siphon through the draining siphon
and the timing chamber is emptied, ready to commence another
cycle.

288. Multiple Alternating and Timed Siphons.1 — The alter-
nating and timing of a number of beds is more complicated.
The arrangement necessary for this is shown in Fig. 186. It
will be assumed at the start that all beds are empty and that all
feeds are air locked as shown in Section AB except that to bed
No. 4 into which sewage is running. As bed No. 4 fills, sewage

1 Design of Siphon by G. H. Bayles, Eng. News-Record, Vol. 84, 1920,
p. 974.

MULTIPLE ALTERNATING AND TIMED SIPHONS 511

is transmitted .through the opening in the wall into the timed
siphon chamber No. 4. When the level of the water in the bed
and therefore in this chamber has reached the top of the with-
draw siphon leading to the compression dome chamber No. 4,
this latter chamber is quickly filled. The air pressure in starting
bell No. 4a is transmitted to blow-off trap No. la. The seal
of this trap is blown, releasing the air lock in feed No. 1 and the

^••-Opening intoBed

Air Vent is not necessary
where Siphon discharges
into an open Carrier, or
Outlet is not more than

FIG. 185.— Miller Timed Siphon.

Courtesy, Pacific Flush Tank Co.

flow into bed No. 1 is commenced. At the same time the air
pressure in compression dome No. 4 is transmitted to feed No. 4,
air locking this feed and stopping the flow into bed No. 4. The
alternation of the feed into the different beds is continued in this
manner.

Bed No. 4 is now standing full and No. 1 is filling. When
compression dome chamber No. 4 was filled, water started
flowing through timing siphon valve No. 4 into timing chamber

512

AUTOMATIC DOSING DEVICES

No. 4 at a rate determined by the amount of the opening of the
timing valve. As this chamber fills compression is transmitted
to blow-off trap 46 and when sufficiently great this trap is blown
and timed siphon No. 4 is put into operation. Bed No. 4 is
emptied by it, and compression dome chamber No. 4 is emptied

Blow-off TrapNo.la
Bed No. I

FIG. 186.— Plural Timed and Alternating Siphons for Contact Bed Control.
Courtesy, Pacific Flush Tank Co.

through the withdraw siphon at the same time. This com-
pletes a cycle for the filling and emptying of one bed and the
method of passing the dose on to another bed has been explained.
The principle can be extended to the operation of any number
of beds.

INDEX

A. B. C. process of sewage treat-
ment, 4

Abandonment of contract, 225
Access to work, 228, 229
Accident, contractor's responsibility,

221, 224

Acetylene, explosive, 347
Acid precipitation. See Miles Acid
Process.

of sludge, 503

Acids as disinfectants, 489, 490.
Activated sludge. Chapter XVIII,
465-179

advantages and disadvantages,
469, 470

aeration tank, 471, 472

air diffusion, 475, 477

air distribution, 473-478

air quantity, 475, 476

area of filtros plates, 478

colloid removal, 358

composition, 465-469

cost, 478, 479

definition, 466

dewatering, 468, 469, 497-505

fertilizing value, 469, 470

historical, 470, 471

how obtained, 478

nitrogen content, 468

patent, 471

process, 465

quantity, 469

reaeration tank, 473

results, 467, 468, 476

sedimentation tank, 472
Advertisement, 214

Aeration, effect on oxygen dissolved,
373-375

of sewage, 371, 376, 465-479
Aerobes, 363

Aerobic decomposition, 366, 367
Aftergrowths, 492
Aggregates, specifications, 172-174
Air, see also ventilation, activated
sludge, compressed air, etc.

ejectors, 150

lock dosing apparatus. Chap. XXI,
506-512

machinery for activated sludge,

473, 474
Algae, 363
Alkalinity, 358
Alleys, sewers in, 80
Alum, 407, 408
Alvord tank, 427, 429
Ammonia, 366, 367, 374, 375, 410

explosives, 297
Analyses, bacteriological, 364

chemical, 354, 355

mechanical of sand, 182

physical, 352-354

sewage, 352-364
Anerobes, 363, 365-367
Anaerobic, action, 410

bacteria, 363

conditions, 367

decomposition, 365-367
Ann Arbor, Michigan. Population,

14
Annual expense, method of financing,

157, 158
Ansonia air ejector, 150, 151

513

514

INDEX

Antibiosis, definition, 363
Appurtenances to sewers. Chap. VI,

99-115
Arch, analyses, 204-208

elastic method, 206-208
vouissoir analysis, 204-206
brick construction, 312, 313
centers for brick sewers, 313
concrete construction, 318-321
Ardern and Lockett, development of

activated sludge, 467, 468, 471
Area of cities, 31
Asphyxiation in sewer gas, 336
Assessments, special, 15, 16
Augers, earth, 21
Automatic, regulators, 117-121
siphons, flush tanks, 110
double alternating, 507
multiple alternating, 508-512
timed, 510
timed and multiple alternating,

510-512
triple alternating/ 508

Bacillus, definition and morphology,

362, 363

Backfilling, 328-331
Backfill, puddling, 330
weight of, 199, 201
Backwater curve, 73
Bacteria, definition and morphology,

362, 363

good and bad, 363, 364
nature of, 362, 363
nitrifying, 431, 432
sanitary significance of, 364
in sewage, 362, 363
total count, 364
Bacterial analyses, results in sewage,

364

Baffles, scum, 404, 413, 414, 421
in sedimentation tanks, 404
in septic tanks, 413, 414
in Imhoff tanks, 421
Balls, for cleaning sewers, 338
Band screen, 384
Barring, definition, 263
Bars for screens, 390

Basins, sedimentation, baffling, 404

bottoms, 404

cleaning arrangements, 404

depth, 401

economical dimensions, 401-403

inlets and outlets, 404

scum boards, 404

types, 395
Basket handle sewer section, 67,

Bathing beaches, pollution, 381
Bazin's formula, 54
Bearings, for centrifugal pumps, 131,
137, 138

thrust, 138
Bellmouth, 121, 122
Bends in pipe, loss of head in, 116
Berlin, sewage farm, 460, 461

sewers, date of, 3
Bids, proposal, 217-219
Bidder's duties, 215-217
Bio-chemical oxygen demand, 359—

361

Biolysis of sewage, 366, 367
Black and Phelps dilution formulas,

377-379
Blasting and explosives, 294-304

caps, 297, 299, 300

detonators, 294, 297-300

firing, 302-304

fuses and detonators, 297-300

fuses, delayed action, 291, 300

fuses, electric, 299, 300
splicing, 303

gelatine, 296

loading holes, 303

powder, 295

precautions, 300-302

priming and loading, 303

rock, 269

size of charge, 304, 305

tunneling, 290, 291
Bleach, characteristics of for dis-
infection, 491
Block sewer, construction, 311-314

hollow tile as underdrains, 126
Blocks, vitrified clay, 189, 190
Boilers, steam, 147-150

INDEX

515

Boilers, efficiencies, 149

horse-power, 149
Bond, contractor's, 213, 214, 232

issues, 14

Bonds, definition and types, 14-16
Boring underground, 20
Bottom, activated sludge aeration

tank, 472
Imhoff tanks, 423
sedimentation tanks, 404
trickling filter, 451, 452
Box sheeting, 272
Branch sewer, denned, 7
Breast boards, 288
Brick, arch construction, 312, 313
and block sewer construction, 311-

315

invert construction, 311, 312
sewer construction, 311-315
arch centers, 313
invert, 311-312
organization, 314, 315
progress, 314
row lock bond, 312
specifications, 188, 189
sewers, life of, 351
Bricks for sewers, 316
British Royal Commission on Sewage

Disposal, 4

Broad irrigation. See under Irriga-
tion.

Bucket excavators, 246, 255, 256
Building material, weight of, 201
Burkli-Ziegler formula, 47, 425
Butryn, 366

Cableway excavators, 246, 250-252
Cage screen, 384, 385
Caisson excavation, 285, 286
Calcium carbide, explosive, 347
Calumet pumping station, 128, 142
Cameron septic patent, 411
Capacity of sewers, diagrams, 57-60
Capital, private invested in sewers, 17
Capitalization, method of financing,

157-160

Caps, blasting. See blasting.
Carbohydrate, 366, 367

Carbon, analysis for, 356

dioxide, 366, 367
Carson Trench machine, 250, 251
Cast-iron pipe, 122, 164, 190, 191

joints, 164

quality, 101, 102, 190
Castings, iron, 101, 102
Catch-basins, 99, 107-108, 217

cleaning, 343, 344

inspection, 337
Catenary sewer section, 69
Cellars, depth of, 88
Cellulose, 367
Cement. See also Concrete.

pipe, specifications, manufacture
and sizes, 171-179

vs. concrete, 164
Centrifugal pumps. See pumps,

centrifugal.

Centrifuge for sludge drying, 501, 502
Cesspool, 411, 416, 417
Champaign, Illinois, septic tank, 415,

416

Changes in plan, 222, 223
Channeling, definition, 263
Character of surface, 44
Chemical analyses, 354-362
Chemical precipitation, 371, 405-409

chemicals used, 405-407

preparation of chemicals, 407,
408

results, 408, 409

at Worcester, 408
Chezy formula, 52, 53
Chicago. See also Sanitary District
of Chicago.

drainage canal, 374, 375

dilution requirement for sewage,
380

early sewers, 3

method of sewage disposal, 374

population and density, 29, 30

trench excavation in, 248
Chlorine. See also Disinfection.

disinfectant, 489-493

in sewage, 358, 374, 375
Chlorine liquid, application, 491, 492
Cholera, trans mi ttable disease, 364

516

INDEX

Chromatin, 365
Chutes for concrete, 187
Circular sewer section, hydraulic ele-
ments, 65, 66, 69

types, 70, 71
City, growth of area, 31

growth of population, 24-28

legal powers, 219
Clay, life of pipe, 349-351

manufacture of pipe, 165-167

specifications for pipe, 168-170

unglazed for pipe, 165

vitrified blocks, 167, 189, 190

vitrified pipe, 165-171
Cleaning, grit chambers, 398, 400

sedimentation basins, 404

sewers, cost, 341

in N. Y. City, 332

methods, 337-343

tools, 338-340

up after completion of work, 228
Coccus, 362

Coefficient of uniformity of sand, 456
Coffin sewer regulator, 117, 118
Colloid, nature of, 358

treatment for, 358
Color of sewage, 352, 353
Combined sewer system, 78, 79
Commercial districts, characteristics

of and sewage from, 32, 34, 35
Compensators for pumps, 142
Compressed air. See also ventilation,
tunneling, drilling, etc.

activated sludge, 473-475

for drilling, 264-268

in tunnels, 292-294

transporting concrete, 320, 321
Concentration, time of flood flow,

41-i3, 96, 97
Concrete, aggregates, 172-174

mixing and placing, 184-188

pipe, details, 175-179
manufacture, 171-179
reinforcement, 177, 178, 209,
210

pipe, steam process, 176
sizes, 175

pressure against forms, 232, 323

Concrete, proportioning, 179-183
qualities, 179, 180
reinforcement, placing, 178, 326,

327

reinforcing steel, quality, 191
sewer construction, 314-328

arch, 318-321

form length, 319

labor costs, 327, 328

in open cut, 314-320

in tunnel, 320, 321

invert, 315-320

organization for, 328

working joints, 319
sewer costs, 327-329
strength, 181
waterproofing, 184
Conduits, special sections, 67, 70, 71
Connections to sewers, ordinances,

344, 345

record of 92, 238
Construction of sewers, Chap. XI,

233-331
Construction, elements of, 233

organizations, 315, 328
Contact bed, 432-437, 506
advantages and disadvantages,

432-434

automatic control, 437, 506
cleaning, 435
clogging, 435
construction, 434-436
control, 437, 506
cycle, 436, 437
depth, 434
description, 432, 433
design, 434-436
dimensions, 434, 435
loss of capacity, 435
material, 435, 436
multiple, 433, 435
operating conditions, 432-437
rate, 435
results, 433, 434
ripening, 432
Continuous bucket excavators, 246-

250
Contour interval on maps, 79, 80

INDEX

517

Contracts, Chap. X, 211-232

abandonment of, 225

assignment, 228

completion of, 222, 228

bond, 213, 222

content, 213, 230, 231

cost-plus, 212, 213

disputes, 220

divisions of, 213

drawings, 213

engineer as an arbitrator, 220

the instrument, 230, 231

interpretation of, 220, 234,
235

lump sum, 212

nature of, 211, 212

sample, 230, 231

time allowed, 222

types, 212, 213

unit price, 213
Contractor, absence of, 222

bond, 232

claims against, 228

duties, 221

liability, 224

relations with otKer contractors,

228, 229

Contractor's powder, 294
Control devices, automatic, for sew-
ers, 117-121
for niters, 506-512

inspection of, 336, 337
Copper sulphate, disinfectant, 490
Copperas, precipitant, 406-408
Cordeau Bickford, 298, 303
Corrugated iron pipe, 165
Cost. See under item wanted.
Cost, annual. Method of financing,
157-160

capitalized. Method of financing,
157-160

classification of, 235-238

comparisons of. Methods for
making, 157-160

collection of data, 10-14, 235-238

estimate. Method of making,
10-14

overhead, 237, 238

Couplings, flexible for shafts, 138
Covers, Imhoff tanks, 424

septic tanks, 415

trickling filters, 451
Crops on sewage farms, 463,464
Cunette, 67, 70

Cut, depth of excavation, 88, 92.
Cycle, contact bed, 436

life and death, 367, 431

nitrogen, 367, 368

trickling filter, 441
Cylinders, stresses in, 194, 202-204
Cytoplasm, 365

Damages, liquidated, 222

material, 221, 224
Darcy's formula, 52
Day labor, 211

Decomposition of sewage, 365-367
Definitions. See word defined.
Deflagration, definition, 294
Delays in contract work, 228
Delayed action fuses, 291, 300
Densities. See population.
Depreciation, of sewers, 348-351

rate of, financial, 158
Depth of sewers, 88
Design conditions, 88-92

economical, mathematics of, 401-
403

preparations for, 17-23
Detention period, grit chamber,
397

Imhoff tank, 419

plain sedimentation, 392-395, 401

septic tank, 415
Detonation, definition, 294
Detonator. See blasting cap.
Diameter of sewers, 57-60, 72, 88-

Diaphragm pump, 257, 258
Diesel engine, 152, 154
Digestion chamber, Imhoff tank, 422,

423
Digestion of sludge in separate tank,

427-430, 497
Dilution, amount needed, 377-380

conditions for success, 372, 373

518

INDEX

Dilution, definition, 372

formulas for quantity, 378-380

governmental control, 380, 381

preliminary studies, 381, 382

in salt water, 376, 377

in streams, 372-376

of sewage, 370 and Chap. XIV,

372-382

Diseases, water-borne, 364
Disinfection, 489-493

action of, 489-491

bleaching powder, 491

chlorine, liquid, 491
amount of, 492

disinfectants, 489, 490

purpose, 489

selective action of disinfectants,

492, 493
Disk screen, 384

Disposal of sewage, See sewage treat-
ment.

Disputes, engineer to settle, 220
Dissolved oxygen. See Oxygen dis-
solved.
Distribution of sewage,

contact beds, 436

irrigation, 461, 462

nozzles, 442-449

sand filter, 450-458

traveling distributor, 442

trickling filters, 441-451
Districts, character of, 29, 30, 32-37

classification of, 34, 35
Domestic sewage, defined, 6, 7, 352
Dorr Thickeners, 472, 504
Dortmund tank, 404
Dosing devices, 506-512

alternating and timed siphons,
500-512

Alvord device at Lake Forest, 506

four or more alternating siphons,
509

operation of automatic siphon,
110

three alternating siphons, 508

timed siphons, 510

two alternating siphons, 507

- types, 506

Dosing tank design, for trickling

filter, 446-450
Doten tank, 429, 430
Drag line excavators, 255, 256
Drainage areas, 81, 84, 94
Drills, electric, 267

jack hammer, 264, 265

punch, 20

size of cylinder for, 266

tripod, 264, 265
Drilling, methods, 20-23, 264-270

depth, diameter and spacing of
holes, 268-270

power for, 267, 268

rate of, in rock, 267

steam and air, 267, 268
Drop manhole, 100, 101
Drop-down curve, 73, 77
Drum screen, 384
Dry-weather flow, 24, 38
Drying sludge. See sludge drying.
Dualin, 296
Duty of contractor. See Contractor,

duties
Duty of engineer. See Engineer,

duties.
Duty of inspector. See Inspector,

duties.

Duty of a pump, defined, 135
Dynamite, 296-298, 300-302, 304,
305

cartridge, 268, 296, 302

thawing, 301, 302
Dysentery, 365

Earth pressures, theories, 274, 275
Economical dimensions, mathematics

of, 401-403

Effective size of sand, defined, 456
Efficiency of a pump, defined, 135
Effluents, character of

activated sludge, 467, 468

chemical precipitation, 408

contact bed, 434

Imhoff tank, 414, 424, 425, 432

lime and electricity, 489

Miles acid process, 484, 485

sand filter, 453

INDEX

519

Effluents, sedimentation tank, 401

septic tank, 412-414
Egg-shaped section, 67, 68, 70
Ejectors, air, 150, 151
Elastic arch analysis, 206-208
Electric motors, 150-152
Electrolytic treatment, 487-489
Elevations, method of recording, 92
Emergencies, duties of engineer, 235
Emerson pump, 261
Engines, internal combustion, 152-

154

steam, types, 142-144.
Engineer, absence of, 221
defined, 220

disputes settled by, 220, 234
duties of, 9, 10, 220, 233, 234,

238
individuality and personality, 9,

234

qualifications, 9
sanitary, definition, 2
Engineering News pile formula, 125,

126
Entering sewers, precautions, 335,

336

Enzymes, 365

Equipment for construction, 237
Equivalent sections, defined, 72
solution of problems in, 67-72
Estimates, cost and work done, 10-14
when made, 226
data for, 235

Excavation, depth of open cut, 284
drainage, 252, 262
hand, 242-245, 249
economy, 245
laborer's ability, 243
lay out of tasks, 243
Excavation, hand, opening trench,

243

vs. machine, 245, 249
tools, 242
machine, 244-246
economy, 245
limitations, 246
vs. hand, 245, 249
specifications, 240, 241

Excavating machines, bucket, 246, 255

cableway and trestle, 246, 250-
252

Carson machine, 250, 251

continuous belt, 246
bucket, 246, 247

drag line, 255

Potter machine, 251

steam shovel, 252-254

tower cableway, 252

wheel excavators, 246-250
Excavation, machine, organization,
249

pumping and drainage, 256, 257

quicksand, 256

rock, 263 264
payment for, 230

specifications, 240, 241

trench bottom, 241, 304, 311
Explosions in sewers, 108, 336, 346-
348

causes of, 346

historical, 346

prevention, 108, 348
Explosives. See also Blasting.
Explosives, and blasting, 294—304

ammonia compounds, 297

blasting gelatine, 296

contractor's powder, 294

deflagrating, 294

detonating, 294

detonators, 294, 297-300

" Don'ts," 300, 301

dynamite, 296-298, 300-302, 304,
305

fuses and detonators, 297-300

gelatine dynamite, 296

gunpowder, 295

handling, 300-302

nitro-glycerine, 295

nitro - substitution compounds,
295

permissible, 297

quantity, 304, 305

requirements, 294

strength of, 297, 298

T.N.T., 295

types, 294-297

520

INDEX

Exponential formulas for flow of

water, 54, 55
Extra work, compensation, 227

Facultative bacteria, 363
Tanning's run-off formula, 49
Farms, septic tanks for, 416, 417
Farming with sewage. See irrigation.
Fats in sewage, 357-359, 366, 367

from Miles acid process, 485-487
Feathers, for splitting rock, 264
Ferrous sulphate, precipitant, 406-

408

Fertilizer from sludge, 470, 495, 497
Fertilizing value of, activated sludge,
470

sewage, 459, 460
Filter press for sludge, 500, 501
Filters. See under name of filter.
Filtration,of sewage,370, 371, 431-459

action in, theory of, 431

cost, 458, 459
Filtros plates, 477, 478
Finances, mathematics of, 157-160
Financing, methods of, 14-17
Flamant's formula, 54, 56
Flies on trickling niters, 438
Flight sewer, 101, 102
Flood, crest velocities, 42, 43

flow computations, 94-98
McMath formula, 94, 96, 97
Rational method, 95-98
Flow, laws of, 52

velocity of, 52, 90, 91
Fluctuations, in rate of sewage flow,
33-38

in quality of sewage, 368-370
Flush tanks, automatic, 109-113

capacity, 111

details, 110, 112

inspection of; 336, 337

payment for, 217

siphon sizes, 111
Flushing, 109-113, 341-343

amount of water needed, 112

methods, 341-343

manhole, 109

sewer, defined, 8

Foaming of Imhoff tanks, 425, 426
Foot valves, 141
Force main, defined, 8
Forms, design of, 322, 323

length of, 319

materials, 321, 322

oiling, 174, 186, 322

specifications, 322

steel, 325, 326

steel lined, 325

support for, 316, 318

time in place, 319

wooden, 323, 324

Formulas, hydraulic, methods for
solution, 55-61

for flow of water, 52-55

for rainfall. See Rainfall.

for run-off. See Run-off.
Foundations, 99, 124-126
Franchises for sewers, 17
Free ammonia, 366, 367, 374, 375,

410
Freezing, catch-basins, 108

concrete, 186, 187

dynamite, 301, 302
Fresh sewage, characteristics, 352-

354
Friction losses. See Head losses.

flow in pipe, 51, 52
Fuel, consumption by prime movers,
153

costs, 153

heat value, 150
Fungus growth in sewers, 333
Fuses. See blasting fuses.

Ganguillet and Kutter's formula, 52-

65
Gas, chamber in Imhoff tank. See

Scum chamber,
engines, 152-154
illuminating, explosive, 347
sewer, 335, 336
Gasoline, explosive, 108, 109, 335,

346, 347

engines, 152-154
and oil separator, 109
odors, significance, 335, 353

INDEX

521

Gearing, reduction for turbines, 140,

146

Gelatine dynamite, 296
Glycerol, 366
Gothic section, 67

Governmental control, stream pol-
lution, 380, 381
Grade, of sewers. See also Slope.

how given, 281-284

selection of, 90
Stakes, 221, 281-283
Gravel, specifications, 172
Grease, in sewers, 99, 108, 333, 345
cutter, 340

ordinance concerning, 345
traps, 99, 108
Gregory's imperviousness formulas,

44, 46

Grit, cloggs sewers, 333
chambers, 127, 397-401

description, 395, 398

design, 397, 398

dimensions, 397, 398

existing, 398-400

outlet arrangements, 400

results, 397

retention period, 397

sludge analyses, 397

units, number of, 400, 401

velocity of flow in, 396-398
quantity and character of, 397
Gooves in concrete, working joints,

319
Ground water in sewers, 38, 39, 85,

87, 256, 352
Gun cotton, 296
Gunpowder, 295

Hazen, theory of sedimentation, 392-
395

dilution formula, 380
Hazen and William's formula, 55, 57
Head loss, in bends, 116

entrance, 115

friction in straight pipe, 51, 52, 115
Hercules powder, 296
Bering, Rudolph, dilution recom-
mendations, 380

Hering, Rudolph, introduction of
Imhoff tank and hydraulic
formulas, 425
Historical r£sum6 of sewerage and

sewage treatment, 2-5
Hitch, tunnel frame, 286, 287
Holes, drill. See Drill holes.
Holidays, work on, 221
Hook for lifting pipe, 304, 306
Horse-power, boiler, 149, 150

of pumps, 144-146
Horse-shoe sewer section, 71
House, connections, record of, 92, 234

drains, 7, 88, 90

sewer, defined, 7
Hydraulic, elements, 65, 69

formulas, 52-55

jump, 73-74

principles, 51, 52, 72, 73

value of settling particles, 393
Hydraulics of , sewers, Chap. IV, 51-
77

circular pipes partly full, 65, 66

equivalent sections, 72

non-uniform flow, 72-77

sections other than circular, 67-72

use of diagrams, 61-65
Hydrocarbon, 367
Hydrogen sulphide, 353, 366, 410
Hydrolytic tank, 427, 428
" Hypo " as a disinfectant, 491
Hyto Turbo blower, 473, 474

Illinois River, self-purification, 374-

376

Imhoff tank, and chlorination, costs,
487

cover, 424

description, 417-419

design, 419-424

digestion chamber, 422

inlet and outlet, 421

operation, 426-427

patent, 418

results, 414, 424, 425, 439, 467

sedimentation chamber, 419-422

scum chamber, 424

slot, 422

522

INDEX

Imhoff tank, sludge, 414, 467
sludge pipe, 423, 424
status, 425, 426
and trickling filter, cost, 479
Impeller, for centrifugal pump, 131,136
Imperviousness, relative, 40, 42, 44-

46, 95-97

Industrial, districts, 32-37
wastes, defined, 7, 352

tannery, 491
Information and instructions for

bidders, 213, 215-217
Inlets, street, 93, 94, 99, 104-107
Inspection, contract stipulations,

221-224

during construction, 233, 234
for maintenance, 104, 333-337,

348, 349

Inspector, absence of, 221, 222
duties, 233-234
qualifications, 234
Institutional sewage treatment plants,

416, 417

Intercepting sewer, denned, 7
Intermittents and filter. See Sand

filter.

Internal combustion engines, 152-154
Inverted siphon, 113-116
Iron, ferrous sulphate, precipitant,

406-408

cast. See cast iron.
Irrigation. See also Farming and

Sewage farming,
area required, 463
Berlin sewage farm, 460, 461
crops, 463, 464
description, 459
fertilizing value of sewage, 460, 470,

495, 498
vs. farming, 459
operation, 461-463
preliminary treatment, 462, 463
preparation for, 461-463
process, 459, 460
sanitary aspects 463
status, 460, 461,
theory, 432
in the United States, 461

Jack hammer drill, 264, 265
Jetting method, 21-23
Jet pump, 259, 341, 343
Joints, bituminous, 309-311

in cast-iron pipe, 164

cement, 307, 308

inspection of, 234

lead, 164

mortar, 307

open, 307

poured, 309-311
cement, 309, 311

riveted steel, 195, 196

sulphur and sand, 309

types, for pipe, 307

working, in concrete, 319
Junctions, 99

Kuichling, run-off rules, 46, 47, 49

storm intensity formulas, 50
Kutter's formula, 52-65

Labor, day vs. contract, 211

costs on concrete sewer, 328, 329
Labyrinth packing rings, 136, 137
Lagging, tunnel frames, 287

for forms, 322
Lagooning sludge, 495-497
Laitance, 186, 188
Lakes, self-purification of, 376
Lampe's formula, 54
Lampholes, 99, 104
Lateral sewer, defined, 7
Lawrence Experiment Station, 4
Leaping wen-, 118-121, 337
Legal requirements, construction, 224

dilution, 380, 381

in design, 9
Liernur system, 5
Life, organic in sewage, 363, 364

of sewers, 348-351
Lime as a precipitant, 405-408

with electricity, 488, 489

with iron, 406, 407
Line and grade, 281-284

how given, 281-283
Liquefaction of sludge, 411-413, 496,
497

INDEX

523

Liquid chlorine. See also Chlorine,

491

Liquidated damages, 222
Loads on, pipe, 198-202

Mansion's method, 198-202
trench, 199-202
Lock bar pipe, 197
Lock joint pipe, 177
Long loads, 201

Machine excavation. See Excavation.
Macroscopic organisms, 363, 368
Main sewer) defined, 7
Maintenance of sewers, Chap. XII,
332-351

catch-basin cleaning, 343, 344

cleaning sewers, 337-343

complaints, 333

cost, 341

entering sewers, 335, 336

flushing, 109-113, 341-343 .

hand cleaning, 341

inspection, 333-337

organization, 332

protection of sewers, 344, 345

repairs, 337

tools, 338-341

troubles, 333

work involved, 332
Man, shoveling ability, 243
Manholes, 81, 99-104

bottom, 100

cover, 102-103

drop, 101

flushing, 109, 342

location and numbering, 81

payment methods, 217, 218

steps, 100, 103, 104
Manning's formula, 55
Map, preliminary, 17, 79, 80, 82, 83
Marsh gas, 347, 366, 367, 410, 415
Marston's methods for external loads

on buried pipe, 198-202
Materials, for sewers, Chap. VIII,

164-193

measurement of, 236, 237
record of, 237

unit weights, 201, 202

McMath's formula, 47, 48, 94, 95
Meem's theory of earth pressure, 274,

275

Mercaptan, 367
Metabolism, 365
Methane, 347, 366, 367, 410, 415
Methylene blue, 360
Microscopic organisms, 363, 364, 368
Miles acid process, costs, 487

amount of acid, 483

analyses of sludge, 485

description, 482

results, 483-487

sludge, 485

Mineral matter in sewage, 357
Mirror, inspecting device, 334
Money retained by city, 227
Mosquitoes in catch-basins, 108
Motors, electric, 150-152
Municipal, bond, 14, 15

corporations, 15

n, value of in Kutter's formula, 53
New York City, density of population,
29, 31

siphons under subway, 114

grease and gasoline trap, 108, 109

aeration of sewage, 377, 470
' cleaning sewers, 332

depreciation of sewers, 348-351
Needle beam, 286, 287
Night, soil, 5

work, 221
Nitrates, 355, 356
Nitrites, 355, 356
Nitrifying organisms, 431, 432
Nitrobacter, 431, 432
Nitro explosives, 295, 296
Nitrogen, cycle, 367, 368

organic, 355, 356
Nitre-glycerine, 295
Nitrosomonas, 431, 432
Nomograph, 55, 56
Non-uniform flow, 72-77
Nozzles. See also Trickling filters,

coefficients of discharge, 446

types, 445

524

INDEX

Numbering, drainage areas, 81, 94

manholes, 81
Nye steam pump, 260, 263

Obstructions to construction, 235

Odor of sewage, 353

Oil in sewage, 108, 344-348

Oiling forms, 174, 186, 322

Olein, 366

Ordinances, for protection of sewers,

344, 345
Organisms in sewage, 363, 364,

368

Organic matter, composition, 366
Organizations for construction, 315,

317, 328

Orders, to whom given, 222
Outfall sewer, denned, 8
Outlets, 99, 122-124, 373
Overflow weir, 118-121

inspection of, 337
Overhead, costs, division of, 10, 237,

238

-track excavators, 246, 250, 251
Oxidation in streams, 373-376
Oxygen, absorption of, 374-377
consumed, 355, 356
demand, 359-361
computation of, 360
bio-chemical, 359-361
Oxygen dissolved
exhaustion of, 366
in dilution, 381
solubility, 362
supersaturation, 361
concentration for successful dilu-
tion, 377-380
formulas for concentration, 378-

380
significance of in sewage, 359-

362
Oysters, contamination of, 372, 489

Packing rings, labyrinth type, 136,

137

Palmatin, 366
Parasites, 365
Paris sewage farm, 460

Patents. Protection of City by

contractor, 224, 225
Pathogenic bacteria, 364
Pavement, replacing, 329
Payment, final on contract, 228
Payments, methods of making, 217,

218

Periscope inspecting device, 334, 335
Permissible explosives, 297
Phenolphthalein indicator, 408
Photographic records, 238
Piles for foundations, 123-126
Pills for cleaning sewers, 338
Pipe, bedding, 230, 304, 328

cast-iron. See under cast iron
pipe.

design of ring, Chap. IX, 194-210

external loads on, 198-202

joints. See Joints.

sewer construction, 304-311

laying, line and grade, 282-284
organization, 311

method of laying, 304, 306, 307

steel, design, 195-197

stresses in, external forces, 194,
202-204

stresses due to internal pressure,
194

stresses in buried pipe, 198-204

stresses in circular ring, 202-204

wood design, 197, 198
Plankton, defined, 363

in sewage, 368

Plans, changes in contract, 222, 223
Plug and feathers for splitting rock,

264
Pneumatic, collection system, 5

concreting, 320, 321
Poling boards, in open cut, 271, 272

in tunnel, 287

Pollution, legal features, 380, 381
Population, density, 28-31

predictions, 24-27

served by sewers in the U. S., 3

sources of information, 27, 28

and quantity of sewage, 31, 32
Potter trench machine, 251
Powder. See Blasting.

INDEX

525

Power pump, 132, 133

Precautions in entering sewers, 335,

336

Precipitants, chemical, 405-407
Preliminary, map, 17, 79, 80, 82, 83

work, 9, 17-23
Present worth, 158, 160
Pressing sludge, 500, 501
Priming explosives, 302-304
Private, capital, 17

sewers, 17
Privy, 5

Profile, for brick sewers, 312
sewer, 92
surface, 88
Progress, rate of, 222

reports, 238

Promotion (inception of sewers), 9
Proportioning concrete. See Con-
crete proportioning.
Proposal (contract), 213, 217-219
Protection of sewers (ordinances),

344, 345
Protein, 366
Puddling, backfill, 330
Pulsometer pump, 260, 261
Pumping, in excavations, 256-263
selection of machinery, 154-156
equipment, cost comparison, 162
station, 128, 142
costs, 156-163
equipment, 127, 128
Pumps, air ejector, 150, 151
capacity, 129, 160-163
capacity of units, 160-163
centrifugal, details, 130, 131, 136-

138

automatic control, 141, 142
characteristics, 138-140
efficiency, 140
for excavation, 262
motors for driving, 150-152
performance, 138-140
protection of, by screens, 386
selection of, 154-156
setting, 140-142
turbine, 130-132, 154
types, 130, 131

Pumps, centrifugal, volute, 130-132,

154

character of load, 129
costs, 156, 157

description of types, 130-134
for construction work, 256-263
diaphragm, 257, 258
direct-acting, 133
duty of, 135, 136
efficiencies, 135, 136
ejector, 134, 150, 151, 259, 341,

343

jet, 259
need for, 127
number of units, 160-163
packing of, 133, 134 .
piston, 133

speed, 133, 134
plunger, 133
power, 132, 133

reciprocating, 130, 132-135, 154-
156

for excavation, 262
reliability, 127
sizes, 135
steam, 134, 135, 142-146

consumption, 144, 145

vacuum, 259, 262
improvised for trench work, 257
turbine, 130-132, 154
volute, 130-132, 154
Putrescibility, 359, 360

Quantity, of sewage, 24-50, 84-87

variations, 33-38

storm water, 40-50, 94-98
Quicksand, definition, 256

excavation in, 256

safeguards, 235
Quiescent water, self -purification, 374

Racks. See Screens.
Pvainfall, 17, 40, 41, 50, 96, 97

data, 17

rate, 96, 97

Ptangers, 270-274, 276-279
Piankine's theory of earth pressure,
275

526

INDEX

Rapid sand filtration of sewage, 458
Rational method of run-off determi-
nation, 40, 95-98
Reaeration tank in activated sludge,

473

Receiving well, capacity, 129, 130
Reciprocating pumps. See Pumps,

reciprocating.

Records, character of, on construc-
tion, 238-240

Rectangular sewer section, 67-69
Regulators, 99, 117-121, 337

inspection of, 337
Reinforced concrete sewer design,

209, 210
Reinforcing steel, specifications, 191

placing, 326, 327
Reinsch-Wurl screen, 384
Relative stability numbers, 359
Relief sewer, denned, 7
Repairs to sewers, 337
Report, engineer's preliminary, 10
Reservoir, collecting capacity, 129,

130

Residences, septic tanks for, 416, 417
Residential districts, characteristics,

32-37

Residue on evaporation, 356, 357
Rideal's dilution formula, 379
Ring, design. Chap. IX, 194-210

stresses in circular, 202-204
River pollution, legal features, 380,

381

Rivers, self-purification of, 373-376
Riveted joints, properties, 196
Rock, blasting, 268, 290, 291
definition, 263 J
drill, data on, 266, 267
drilling. See also Drilling,
by hand, 264
by power, 264-268
rates, 267
excavation. See also Excavation.

payment for, 230
measurement of, in place, 235
tunnels, 290, 291
Rods, sewer, 338
Roman ordinance relative to sewers, 2

Roofs. See Covers.

Root cutters, 340

Roots, 333, 340

Row lock bond for bricks, 312

Running water, self-purification, 373-

376
Run-off, computations, 17, 40, 46-50,

94-98

Safeguards during construction, 221,

241

Salt water, dilution in, 376, 377
Sand, effective size, 456
uniformity coefficient, 456
filters, 452^59
action in 431, 432, 452-454
control, 458, 506-510
description, 452
dimensions, 456
distribution systems, 433, 456-

458

dosing, 454-456
dosing devices, 506-510
materials, 456
operation, 454, 455
preliminary treatment, 455
rate, 455
results, 452, 453
size of sand for, 456
thickness, 456
in winter, 455

Sanitary District of Chicago,
dilution factor, 380
specifications,

for manhole covers, 101, 102
tunnel cover, 284
tunnel ventilation, 291
Sanitary engineering, 1, 2
Sanitary sewage, defined, 7, 352
Saph and Schoder's formula, 54
Saprophytes, 365
Screed, 316
Screens, 383-391

chlorination and fine screens,

costs, 487
coarse, 386, 391
data on fine, 388, 389
design of, 389-391

INDEX

527

Screens, fine, 381, 382, 387-389
fixed, 385, 390
medium, 386

movable, 385, 386, 389-391
moving, 384-386
openings, 386-389
protection to pumps, 127, 141
purpose, 383
results, 386-389
size and performance, 386-389
sizes, 386-391
types, 384-386

sewage treatment by, 371, 381
Screening, vs. sedimentation, 383

purpose, object, 383
Screenings, character of, 386-389
Scum, boards for, septic tanks, 413,

414

Imhoff tanks, 421
chamber in an Imhoff tank, 424
definition, 495
Sediment, velocity of transportation,

396, 397

Sedimentation, 383-405
definition, 383
Hazen's analysis, 392-395
hydraulic values, 393
a method of treatment, 370
object, 383
Peoria Lakes, 376
protection of siphons, 113, 114
results from plain sedimentation

401

theory of, 391-395
transportation of debris, 396
velocity of, 392, 393
vs. screening, 383
velocities, limiting, 396, 397
Sedimentation, basins, arrangement,

394

baffling, 404
cleaning, 404
dimensions, 401-403
inlet and outlet, 404
operation, 411
types, 395

chamber, Imhoff tank, 419-422
Self-purification of lakes, 376

Self-purification of streams, 373-376
Separate sewer systems, 78-80
Septic action, 353, 365-368, 371, 410,
411, 496, 497

results, 412, 413

vs. sedimentation, 411
Septic tank, 411

baffling, 413, 414

capacities of small tanks, 417

for country homes, 416, 417

covers for, 415

definition, 411

design, 413-417

explosions in, 415

results, 412, 413

seeding, 413

sludge storage, 414

small, 416, 417

units, 415

Septic sludge analysis, 414
Septicization. Chap. XVI, 410-430

a method of treatment, 371

the process, 410, 411

results, 412, 413
Settling solids, 357
Sewage and water supply, 32

aeration, 371, 376, 465-479

alkalinity of, 358

analyses, chemical, 355, 369, 467
interpretation of, 356-362
physical, 352-354

average, 352-355

bacteria, 362-365

biolysis of, 366, 367

changes in, rate of discharge of,

33-38
characteristics, 368-370

characteristics of, 352-354

chemical constituents, 354-356

classification of, 6, 7, 352

collection, 5

color, 352, 353

components and properties, 352—
356

decomposition of, 365-367

definition, 6, 7, 352

disposal. See also Sewage treat-
ment.

528

INDEX

Sewage, disposal, methods, 6, 370, 371

purposes, 370, 371
domestic, 7, 352
farming. See Irrigation,
fertilizing value, 459, 460
flow fluctuations, 33-38

ratio of maximum to average,

36, 37, 85
fresh, 352-354
gas, 335, 336, 353
industrial, denned, 7, 352
life in, 363-365, 368
odor, 353
physical, analyses, 352-354

characteristics, 352-354
quality variations, 368-370
quantity. Chap. Ill, 24-50, and
84, 87

and population, 31, 32

of sanitary. 24-40

variations, 33-38
sanitary, denned, 7, 352
septic, 353, 365-368, 371, 410,

411, 496, 497
stability, 359, 360
stale, 353

storm, defined, 7, 352
strong, 355
temperature, 353
turbidity, 353
treatment processes, 370, 371

A. B. C., 4

activated sludge, Chap. XVIII,
465-^79

biological, 371

chemical, 371

contact bed, 432-437, 506

costs, 459

dilution. Chap. XIV, 372-382

disinfection, 489-493

electrolytic, 487-489

filtration, 431-459

increase of, 3

irrigation, 431, 459-464

mechanical, 471

Miles acid process, 482-487

purpose of, 6, 370

resume, 6, 370, 371

Sewage, treatment processes, sand

filter, 452^58
screening, 383-391
sedimentation, 391^409, 411
septicization. Chap. XVI, 410-430
trickling filters, 437-452

weak, 355

and water supplies, 31, 32
Sewerage, definition, 7

demand for, 2

design, 78-98

growth of, 2-4

historical, 2-4
Sewers, ancient, 2, 3

capacity, diagrams, 56-60

cost, 10-14

definitions of various types, 7, 8

depth of, 88

diameter, 58-60, 88-92

flat grades, 73, 109

flight, 101, 102

inspection of, 333-337

life of, 348-351

location of, 80, 81, 94

materials. Chap. VIII, 164-193

medieval, 3

pipe, properties of concrete, 175
design. Chap. IX, 194-210
vitrified clay, properties, 169-171

profile, 89, 92

section of different types, 67-72

separate system, 78, 79, 82, 86, 87

slope, 88-92

storm-water system, 78, 79, 83,
93,94

stresses in, 194, 198-204
Shafts, for tunnels, 284-287
Sheeting, 270-280

alignment, 240, 241

backfilling, 330

box, 272

design, 275-280

driving, 273

length, 273

lumber, 277

moving, 248

poling boards, 271, 272, 287

pulling, 274

INDEX

529

Sheeting, skeleton, 270, 271
stay bracing, 270
steel, 252, 280, 281
thickness, 276-278
types, 270

vertical, 270, 272-274
Wakefield piling, 273
Shellfish contamination, 372, 489
Shields, tunnel, 288-290
Short loads on trenches, 202
Shovels, for hand excavation, 242

steam. See Steam shovels.
Shovel vane screen, 384
Shoveling by hand, height raised, 244

performance by one man, 243
Simbiosis, definition, 363

example, 432
Sinking fund, 158

Siphons, automatic. Chap. XXI,
506-512. See also under Dosing
devices.

in flush-tanks, 109-110
inspection, 337
operation, 109-110, 506-512
for trickling filter, 448-451
true and inverted, 113-117
Skeleton sheeting, 270, 271
Slope, of sewers, 88-92

of tank bottoms, Imhoff, 419, 423

sedimentation tank, 404
Skewback, 204
Sludge. Chap. XX, 495-505

activated. Chap. XVIII, 465-
479. See also under Activated
sludge.

analyses, 414, 467, 468, 485, 496
characteristics, 495
definition, 495

digestion tanks, 427-430, 497
disposal methods, 495
drying, 497-505
acid flotation, 503
beds, 498, 500
centrifuge, 501-502
heat, 502, 503
press, 500-501
thickeners, 504, 505
fertilizing value, 470, 495, 497

Sludge, filters, 498-500

lagooning, 495, 496

measurement, 427

press, 500, 501

sedimentation, 401

septic analysis, 434

treatment methods, 495
Soaps, 357
Soil, bearing value, 125

stack, definition, 7
Solids in sewage, 356-368
Special assessment, 15, 16
Specifications. Chap. X, 211-232

general, 219-229

special, 230

technical, 229, 230
Spiling. See Piles.
Spirillum, 362
Spores, 363
Springing line, 204
Sprinkling filter. See Trickling filter
Square sewer section, 68, 69
Stability, relative, 359-361
Stagnant water, 374
Stakes, contractor to provide, 221

where driven, 281, 282
Stationing, 92
Stay bracing, 270
Steam boilers, 147-150
Steam, consumption by, pumps, 144

145

turbines, 144, 147
engines, 144, 145

pumping engines, 142-146

pumps. See Pumps, steam.

shovels, 246, 252-254

turbines, 146, 147
Stearin, 366
Steel, forms. See Forms, steel.

pipe, 164, 191, 192
design, 195-197
specifications, 191

reinforcement for concrete, 191,
326-327

sheet piling, 252, 280, 281
Stench, historic in London, 4
Sterilization. See Disinfection.
Storm, sewage, definition, 7, 352

530

INDEX

Storm, sewer system design, 93-98

water, quantity, 40-50
Storms, extent and intensity, 50
Stream pollution, regulation, 380,

381

Streams, self-purification, 373-376
Street, inlet. See Inlets.

wash, definition, 352
Stresses, in buried pipe, 198-204

in circular ring, 194, 202-204
Sub-main, defined, 7
Subsurface surveys, 18-20
Suction for centrifugal pump, 141
Sulphur and sand joint compound,

309

Sunday work, 221
Surface, elevation, 92

of ground, character, 44-46

profile, 88

water, 7, 352

Surveys, underground, 18-20
Suspended matter, 357

Talbot's run-off formula, 49
Tamping, backfilling, 328-331
Tannery wastes, disinfection, 491
Taxation, general, 16, 17
Taylor nozzles, 444, 445
Temperature of sewage, 353
Templates, brick sewers, 312
Thawing dynamite, 301, 302
Tide gate, 122
Timbering tunnels, 286-288
Timber, strength of, 277
Time of concentration, 41-43, 95-

97
Tools, for cleaning sewers, 337-341

excavating, 242, 246
Tower cableways, 252
Trade wastes. See Industrial wastes
Traps, in catch-basins, 107

grease, gasoline, and oil, 108, 109

in street inlets, 104, 105
Travis tank, 427, 428
Tremie, 187, 188
Tree roots, 333, 340
Trench, backfilling, 328-331

blasting in, 244, 269

Trench, bottom, shape of,241, 304,311

breaking surface, 243, 244

drainage, 256-263

excavating, by hand, 242-245
machine, 244-256

guarding and lighting, 221

layout of tasks, 243

length of open, 241, 248

line and grade, 281-284

location, 243, 281

opening, 243, 244

pumps, 256-263

sheeting, 270-280

width, 240, 241, 246
Trestle excavators, 250, 251
Trickling filter, 437-452

advantages, 438, 439

covers for, 451

depth, 441, 442

description, 437, 438

dimensions, 442

distribution of sewage, 442-451

dosing siphon, 446-451

dosing tank, 446-451

head lost, 438

insects, 438

material, 441

nozzles, 442-451
layout, 447-451

odors, 438, 439

operation, 441

rate, 441

results, 439, 440

siphon size, 449-451

underdrainage, 451, 452

unloading, 431, 437
Tripod drill, 265
Triton, 295

Troubles with sewers, causes, 333
Trumpet arch, 121
Trunk sewer, defined, 7
Tunnels, 283-294

backfilling, 331

breast boards, 288

brick invert, 313

compressed air in, 292-294

concrete construction, 320, 321

depth of cover, 284

INDEX

531

Tunnels, line and grade in, 283

machines, 290

rock, 290-292

shafts, 284-286

shield, 288-290

timbering, 284-288

ventilation, 291, 292
Turbidity of sewage, 353
Turbine, for cleaning sewers, 340

pumps, 130, 132

steam, 146, 147
Typhoid fever, 364

U-shaped sewer section, 67, 69, 71
Underdrains for. sewers, 126

trickling filters, 451, 452
Underground surveys, 18-20
Unexpected situations, 235
Uniformity coefficient of sand, 456
Unloading of filters, 431, 437
Urea, 367

Valuation of sewers, 332, 348-351
Velocities, depositing, 395-397
distribution of, 51
flow in sewers, 90
over surface of ground, 42
limiting for sedimentation, 396,

397

limiting in sewers, 396, 397
principles of flow in sewers, 51
transporting, 396 ,
Ventilation, air pressures, 291
compressed air, 292-294
pipes, 291

Ventilation, of sewers, 102, 103,

335

tunnel, 291

Vertical sheeting, 270-274
Vitrified clay. See Clay vitrified.
Volatile matter in sewage, 357
Volute pumps, 130, 132, 154
Vouissoir arch analysis, 204

Wakefield piling, 273
Wales, 288

Waste pipe, defined, 7
Wastes. See Industrial wastes.
Water consumption, 31-33

flow of, 51-77

rate of steam engines, 144, 145

supply and sewage flow, 31-33
Watershed. See Drainage area.
Weight, of backfill, 199

of building material, 201

of moving loads, 200, 202
Well, hole, 101

points, 262, 263
Wheel excavator, 246-250
Wing screen, 384
Wood, forms. See Forms.

pipe, materials, 164, 165, 190, 192

193
design, 197, 198

working strength of, 277
Work, extra, 227

preliminary to design, 9

Sunday, night, and holiday, 221
Workmen, competent, 227

dishonesty, 233, 234

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University of Toronto
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Under Pat. "Rcf. Index File"
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