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The Resources Agency 


partment of Wa ter Resources 

BULLETIN No. 144-68 

FEB 1 1972 
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Annual Report for FY 1967-68 


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The Resources Agency 



State of Colifomia 



Department of Water Resources 

The Resources Agency 

Department of Wa ter Resources 
BULLETIN No. 144-68 


Annual Report for FY 1967-68 



Administrafor Governor Director 

The Resources Agency State of California Department of Water Resources 


This is the first report in the Bulletin No. 144 series. It covers 
activities of the Department of Water Resources' Radiological Applications 
program from its inception in 1958 through the 1967-68 fiscal year. Subse- 
quent reports will be published annually by the Department for the use of all 
interested agencies and the general public. 

The term "radiological" pertains to the study and use of atomic 
energy in the form of radioactive isotopes and X-ray apparatus. The radio- 
logical applications program of the Department was initiated in 19 58, pursuant 
to House Resolutions 88 and 234, 1957 California legislative session. H. R. 
234, among other provisions, directed appointment of a Subcommittee to 
ascertain, study, and analyze all facts relating to ". . . development in the 
general field of peaceful use of atomic energy as these may relate to California 
water problems;. ..." 

It was clearly the intent of the legislature that the Departnnent assume 
an active role in studying and developing nuclear energy applications -- primar- 
ily power for water project pumping, but in a broader sense all applications 
that might benefit water resources development. These include radiological 

The term "program" as used herein differs from the conventional 
meaning of the word in Department usage. The Radiological Applications pro- 
gram in itself is not productive of an end result such as a plan, a design, or 
a recomnaendation for development of a water resource. Rather, it applies 
to the application of nuclear phenomena as an aid in measurement, identifi- 
cation, tracing, or detection, and is thus a device to be used in Department 
investigative programs or construction projects. Typical among such programs 
or projects are vegetative water use, aqueduct design, subsurface exploration, 
and construction of Thernnalito Forebay-Afterbay dams. 

Included in this report are brief descriptions of studies, investiga- 
tions and tasks related to water resources in which radiological applications 
have played a part -- some successful, some unsuccessful. Plans for other 
related applications which are expected to be useful in future activities of 
the Department are outlined in a separate section of the report. 

It is intended that this report series will keep those concerned with 
planning and development of water resources and the operation of water proj- 
ects currently infornned on the state of the art in radiation- related activities 
and will provide information on new developments which may be potentially 
useful in such activities. 

William R. Gianelli, Director 
Department of Water Resources 
The Resources Agency 
iii State of California 

September 19, 1968 








Introduction 1 

History of Department Activities 2 


Soil Moisture and Density Gauges 5 

Description of Nuclear Method 5 

Basis for Use 7 

Applications 8 

Vegetative Water Use 8 

Lajid Subsidence 12 

Delta -Channel Depletion 13 

Compaction Control 16 

Snow Measurements 17 

Miscellaneous Applications 20 

Isotopes as Tracers 21 

Basis for Use 21 

Methods of Use 22 

Applications 22 

Flow Measurement 22 

Pump and Turbine Rating 23 

Subsurface Flow Measurement 24 

Watershed Management 24 

Analysis of Water Quality 26 

Age Dating 27 

Stable Isotopes as Tracers 28 

Littoral Transport Studies 29 

Underground Nuclear Explosives 31 

Potential Future Radioisotope Applications 33 



Introduction 37 

History 39 

Criteria for Conducting Field Radiotracer Experiments 39 

Future Plans , 40 


Appendix A: Principles of Soil Moisture and Density- 
Measuring Devices 

Appendix B: Principles of Flow Measurements 

With Radioisotopes 

Appendix C: Definitions 




Illustrations i 

1. Determining Vegetative Water Use With Neutron 

Moisture Meters 10 

2. Field Use of Neutron Moisture Meters , , . . IJ, 

3. Nuclear Moisture-Density Equipment Used for 

Shallow Subsidence Evaluation 14 

4. Nuclear Moisture-Density Gauges Used for Compaction 

Control 18 

5. Two-Probe Snow Density Gauge in Use 19 

6. Radioactive Tracer Application at Castaic Damsite .... 25 

7. Radioisotope Sand Tracer Experiment Near Point 

Conception, California 32 




Schematic Diagram of Probe Used for Measurement of 
Subsurface Moisture or Density 


Radioactive Materials for Which Department is Licensed 

State of California 

The Resources Agency 


RONALD REAGAN, Governor, State of California 
NORMAN B. LTVERMORE, JR. , Administrator, The Resources Agency 

WILLIAM R. GIANELLI, Director, Department of Water Resources 

ALFRED R. GOLZE', Deputy Director, Department of Water Resources 

JOHN R. TEERINK, Deputy Director, Department of Water Resources 

Power Office 

James K. Cummings Chief 

This report was prepared under the direction of 

Maurice B. Andrew Chief, Nuclear Unit 


Irving Goldberg Assoc. Soils Specialist (Radiologic) 

Radiological Operations Officer 


The assistance provided by public agencies in helping to further 
Department of Water Resources' radiological applications program has been 
very valuable. It has aided the Department in pursuing a more extensive i 
program of study and application than otherwise would have been possible. ^ 
the cooperation and counsel provided by the following agencies, the Departmf 
is particularly appreciative: 

State Coordinator of Atomic Energy Development and 
Radiation Protection 

California Department of Public Health, Bureau of 
Radiological Health 

California Department of Industrial Relations, Division 
of Industrial Safety 

California Division of Highways, Materials and Research 

University of California at Davis, Department of Water 
Science and Engineering 

University of California at San Diego, Scripps Institu- 
tion of Oceanography 

U. S. Forest Service, Pacific Southwest Forest and 
Range Experiment Station 

U. S. Department of Agriculture, Agricultural Research 

U. S. Department of Interior, Bureau of Reclamation 

U. S. Department of the Armiy, Corps of Engineers 

U. S. Atomic Energy Commission, E. O. Lawrence 
Radiation Laboratory 

In addition, the Department appreciates the cooperation of the ind^ 
viduals and private organizations who provided generously of their time for 
consulting services and from whose experience in this emerging science the j 
Department has benefited greatly. Unfortunately, the list of these nnany coori 
erators is too long to include here. 

Special recognition is given Mr. Gene A. Blanc, State Coordinatej 
of Atomic Energy Development and Radiation Protection, Professor Warren 
Kaufman, and others of the Departments of Engineering and Public Health at 
the University of California, Berkeley, for their continuing counsel and tech- 
nical advice. 


Radiological techniques have been applied to more than 25 investigative prog 
of the Department or of other agencies with which the Department has coopei^ 
These techniques range from the development of a device to measure soil co; 
paction in earthwork construction to determination of the age of ancient tree 
stumps; from making in-place measurements of the physical properties of a 
snowbank on a mountain top to following the offshore movements of drifting 
sands. / Several possible future projects connected with Departmental func« 
tions might benefit from radiological applications. Among these are large- 
scale excavation by nuclear explosives, measurements of biological produC' 
tivity of water by radioisotopes, and the use of power produced by isotopic 
generators. / Radiometric measurements of flow and the ratings of pumps 
and turbines have shown potential value and are worthy of continuing evaluat^ 
as alternatives to the conventional methods used in the Departmient's water 
operations. / Since the Department's radiation protection program was 
begun, about 10 years ago, thousands of man-hours have been spent in hand 
ling potentially hazardous radioactive materials without a single reported 
instance of personnel overexposure. 



A major byproduct of the Atomic Age has been the substantial 
increase in, and ready availability of, man-made radioactive 
isotopes of the conventional elements. These radioactive forms 
of elements, which number more than a thousand, offer unique 
advantages for many industrial and research applications. 

When incorporated in chemical, metallurgical or biochemical 
systems, radioactive isotopes usually behave in much the same 
way as do their corresponding stable cousins. But, because they 
emit ionizing radiation, even minute quantities of radioactive 
isotopes can be dete cted or monitored by tracer techniques. 

The development of low -level counting instrviment systems has 
kept pace with the broadening field of tracer applications. Detec- 
tion limits for "tagged" elements are generally substantially 
lower than those obtainable in ordinary chemical or microchemical 
analyses. Thus, radiotracers are valuable in applications where 
minimal interference with the normal operation of a system is 
desired, or where conditions for extremely high dilution are pres- 

These same isotopes can also become sources of penetrating, 
ionizing radiation which can be used for gauging the thickness or 
density of materials, or used in place of X-ray sources for inspec- 
tion of parts. Special fabrication techniques have made possible 
small, portable neutron sources. These miniature neutron gen- 
erators have proved to be extremely useful in nondestructive in- 
place deternnination of moisture content of granular materials. 

Another promising potential peaceful use of the atom stems 
directly from the nuclear devices testing program. For a nximber 
of years, studies and experiments have been conducted under the 
U. S. Atomic Energy Commission's "Plowshare" program to 
determine the feasibility of peaceful uses of nuclear explosives. 
Among the various potential applications of nuclear explosives 
studied under the program are two of interest to the Department -- 
the improvement of ground water resources and large scale excava- 
tion. Practical field applications have not yet been made, but the 
numerous studies and tests have been encouraging, giving rise to 
hope that applications beneficial to the Department may eventually 
be developed. 



The Department of Water Resources initiated a program of studies 
dealing with radiological applications in 19 58 with the recognition 
that this expanding field would prove potentially valuable in activi- 
ties related to water resources development. 

During the initial period of these studies, the objectives were to 
become thoroughly informed on current developments in isotope 
technology, and to recommend utilization of any promising isotope 
application techniques in the Department's water resources inves- 
tigative programs. 

Some of the principal activities during this early period included: 

1. coordination and dissemination of information on the 
radiological aspects of the water quality monitoring 

2. investigation of the feasibility of using radiotracers 
for determination of surface and ground water flow, 

3. consultation on the radiation safety aspects of utili- 
zation of sealed radiographic sources for nondestruc- 
tive inspection of materials in construction activities, 

4. design and fabrication of special gauging devices for 
determination of in-place moisture content and density 
of soils, 

5. development and implementation of appropriate pro- 
cedures and regulations required for administration 
of the radiological safety aspects of radioisotope use 
by the Department, and initiation of a training program 
for personnel involved in handling radioisotopes. 

As a result of the decision in 1959 to utilize Department personnel 
in handling radioisotopes, the Departnnent was licensed by the 
Atomic Energy Commission to possess certain quantities of radio- 
active materials for its program. Since that time, radioisotope 
utilization has developed into a virtually standard technique in many 
investigations and shows promise of conning into more widespread 
use in several others. 

In 1962, the State of California assumed responsibility for regula- 
tory authority over the radioactive materials in this State 
from the U. S. Atomic Energy Commission. Consequently, the 

Department's license was transferred to the cognizance of the 
State Department of Public Health. 

The radioactive materials which the Department is currently 
licensed to possess are listed in Table 1. The twenty-one sources, 
which contain almost 1, 800 nnillicuries of radioactivity, are 
currently being utilized in several departmental investigations. 




Hydrogen- 3 
Actinium- 227 
Plutonium- 23 9 


8 session Linnit 




















Two of the most effective uses in Department operations of the 
unique properties of radioisotopes are the determinations of soil 
moisture and density. Soil nnoisture information is mainly used 
in the continuing program of estimating water use of various 
crops. The nuclear technique for this determination has virtually 
replaced the former soil sampling procedures. Other important 
uses of moisture gauging devices have also been made. Nuclear 
soil density determinations are primarily used in control of place- 
ment of embankments, but have a few other interesting applications 
as well. 

Description of Nuclear Method 

The nuclear method for in-place moisture and density determina- 
tions entails the use of sealed radioactive sources. A schematic 
drawing of a typical device used for subsurface measurements is 
shown in Fig. 1. The principles of operation of the soil moisture 
and density measuring devices in which these sources are incor- 
porated are described as follows: 

Moisture Gauges . Certain radiation phenomena lend them- 
selves admirably to the rapid, nondestructive measurement 
of moisture content of granular materials, such as soil. 
When a source emitting high energy or "fast" neutrons is 
placed in the vicinity of an hydrogenous medium, the neutrons 
are moderated, or "slowed", almost exclusively by collisions 
with nearby hydrogen atoms. Other elements with which the 
neutrons may collide cause a relatively insignificant loss of 
energy. Consequently, the number of slow neutrons produced 
is proportional to the density of the hydrogen atoms in the 
surrounding medium and is essentially independent of other 
chemical or physical properties. In soils, water is the prin- 
cipal contributor of hydrogen atoms. 

The measuring device is called a "neutron probe". It consists 
of a detector, which is sensitive only to slow neutrons, placed 
close to a fast neutron source. These components are enclosed 
in a metal cylinder. The probe is suspended by an electrical 
cable which connects it to a counting device, or scaler. When 
the probe is lowered into a cased bore hole in the soil, pulses 
due to slow neutrons will register on the scaler during a fixed 
time interval (usually one minute). The neutron count rate 










Figure No. 1. Schematic Diagram of Probe Used for Measurement 
of Subsurface Moisture or Density. 


may then be related to soil moisture in the vicinity of the 
probe through a prior instrument calibration. 

Density Gauges. By the application of somewhat similar 
principles, the use of a source of gamnna radiation and a 
gannma detector in a density probe, the electron density of 
the atoms composing the soil surroxinding the probe may be 
deternnined. Count rates resulting fronn this measurement 
may then be related to the bulk density of the mediunn in 
which the device is placed. 

The theoretical considerations by which the moisture and density 
gauges operate are treated in more detail in Appendix A. 

Basis for Use 

Subsurface Measurements . In investigations of moisture move- 
ment in soils -- over a long period of time -- the problem exists 
of how to deternaine nnoisture content and density at specific points 
in the soil mass. The method of sannpling by borings is obviously 
undesirable for this purpose, because, once a sample is taken at 
a particular point, the soil at that point is disturbed, its properties 
are changed, and another nearby location nnust be chosen for the 
next sample. Thus, the soil's heterogeneity introduces a variable 
into the measurements. 

Other devices which have been used for the in-place deternnination 
of soil moisture and density have several inherent disadvantages. 
First, a relatively long time may be required before equilibrium 
between the soil and the measuring device can be attained; second, 
a separate calibration is usually required for each material encoun- 
tered; third, the device may be accurate over only a relatively 
short range of moisture contents or densities; fourth, the environ- 
nnent may be greatly altered in placing the measuring instrunnent; 
and finally, in many instances, measurements may be nnade only 
at rather shallow depths. 

Surface Measurements . In earthwork construction projects where 
continuous information is required if control over the moisture 
content and density of the soil layer being compacted is to be main- 
tained, a rapid and accurate method which will provide values for 
these soil properties is desirable. This information is usually 
obtained by a displacement procedure. In this nnethod, a shallow 
hole is dug in the soil surface, and the hole filled with sand or a 
fluid (such as water). By connparing the weight of the soil removed 
with the volume of the standard displacing material, the bulk density 


of the soil at that location may be calculated. The moisture 
content is determined by oven -drying a sample of the removed 

Although this procedure provides reasonably satisfactory results, 
it is tedious and time-consuming. Even under ideal conditions, 
the determinations are not completed for several hours. Fre- 
quently, when modern large earthmoving equipment is utilized 
on a project, the results are not available until after the soil 
layer of interest has been covered by several additional layers 
of fill. Therefore, a procedure which can deliver information 
more rapidly is highly desirable. 


The adaptation of nuclear methods to the nondestructive, in-place 
determination of soil properties has provided an opportunity for 
significant advancement in the reliability of results, while achiev- 
ing substantial reductions in time requirements for data collection. 
This section describes some of the applications in which nuclear 
gauges have proved useful. 

Vegetative Water Use . A thorough knowledge of the nnechanism 
of the consumptive use of water is essential in water development 
planning. One method whereby consumptive use (evapotranspira- 
tion) by an irrigated crop may be evaluated on a seasonal and 
monthly basis is by repetitive field measurements of the depletion 
of moisture from the soil. 

In determining water use by a selected crop, a neutron probe is 
lowered into the soil through cased bore holes in the field in which 
the crop is growing. Moisture readings are normally made at 1- 
foot intervals, to the meiximum depth of casing, which can be as 
much as 25 feet. These measurements are made periodically, 
between irrigation cycles, during the growing season. This pro- 
cedure makes it possible to determine water content changes in 
the root zone of the soil, and the quantity of water depletion for 
any time interval selected. 

The instrumentation requirements of this investigation necessi- 
tated extensive modification of commercially available equipment, 
or the design and fabrication of new apparatus. As specific prob- 
lems arose, some novel methods were developed for their solution. 


Some of these innovations have been described as Department 
publications or in technical journals. * 

Vegetative water use measurements have been made at several 
field stations throughout the State. Areas in which neutron probes 
have been used by the Department for evapotranspiration studies 
include; 1) Kern County near Bakersfield, 2) Western San Luis 
Obispo County, 3) the Sacramento-San Joaquin Delta area, 4) the 
foothill areas of Placer and Nevada Counties, 5) near the Feather 
River in Sutter and Yuba Counties, 6) Sierra Valley in Pliimas and 
Sierra Counties, and 7) Shasta and Lassen Counties. 

Joint investigations of vegetative water use utilizing neutron probes 
have been conducted with the U. S. Agricultural Research Service 
in Santa Barbara County near Lompoc, with the U. S. Forest Serv- 
ice in Yuba County near Challenge, with the University of California 
in Yolo County near Davis, and with the U. S. Bureau of Reclama- 
tion in Fresno County near Fresno. 

These investigations have been directed toward correlating evapora- 
tive demand of the atmosphere with evapotranspiration by a nunaber 
of crops (pasture, alfalfa, cotton, deciduous orchards, citrus and 
vineyard) in several climatic zones of the State. Photographs of 
the equipment used for these measurements are shown on Illustra- 
tions 1 and 2. Analysis and statistical evaluation of the vast amounts 
of data accumulated using this procedure require electronic data 
processing methods. Computer programs have been developed spe- 
cifically to assist in data analysis for the neutron moisture gauges. 

* "A Technique for Rapid and Precise Positioning of Neutron 
Depth Probes". N. A. MacGillivray and Irving Goldberg. Soil 
Science Society of America Proceedings, Vol. 30, No. 6, pp. 
803-804. 1966. 

"Effect of Neutron Source Type on Soil Moisture Measurements". 
Irving Goldberg, N. A. MacGillivray and R. R. Zienner. American 
Nuclear Society Transactions. Vol. 10, No. 1. pp. 20-21. 1967. 

"Vegetative Water Use Studies, 1954-1960". Department of Water 
Resources Bulletin No. 113. August 1963. 

"Vegetative Water Use Studies in the San Joaquin Valley". Depart- 
ment of Water Resources Office Report. March 1964. 

"Vegetative Water Use". Department of Water Resources Bulletin 
No. 113-2. August 1967. 

"Measuring Moisture Near Soil Surface". R. R. Ziemer, Irving 
Goldberg and N. A. MacGillivray. U. S. Forest Service Research 
Note. PSW-158. 1967. _q_ 

Illustration 1. 

Determining Vegetative Water Use 
with Neutron Moisture Meters 

Measuring soil moisture depletion 
in a Kern County alfalfa field. 
The portable platforna was devised 
to minimize crop disturbance 
during measurements. 

Measuring soil moisture depletioi 
in a Kern Coionty cotton field. Ma 
nnum portability of equipment is 
required for taller row crops. 

Measuring soil moisture depletion 
in a Kern County plum orchard. 
Disturbance of growing plants by 
equipnnent is less important with 
this type of crop. 


Illustration 2. Field Use of Neutron Moisture Meters. 

The neutron soil moisture meter is readily adaptable 

to varied geographical and climatic conditions. 
This enables collection of information on soil moisture 
depletion during the nongrowing season. 

A. Determining soil moisture 
depletion in a Shasta County- 
alfalfa field during the 

Same field during the 



Nuclear applications in the vegetative water use prograna have 
helped to explain why atmospheric dennand for moisture frequently 
differs from measured soil moisture depletion. They have 
increased understanding of the influence of plant, soil and climatic 
factors on the vegetative transpiration process through the elimin- 
ation of many of the physical limitations of soil moisture measure- 
ment which are imposed by soil sannpling and other methods. Use 
of the neutron probe has significantly increased the number of 
measurements which can be made in a given length of time. The 
extent of soil which it is possible to measure has been greatly 
expanded due to the practically unlimited sampling depth which is 
afforded. The greater number and extent of measurements which 
may be made result in a more representative sample of the crop's 
soil moisture regime, and thus permit greatly increased confidence 
in the reliability of the data. 

Specifically, valuable knowledge has been acquired concerning the 
effectiveness of irrigation water applications, the amount and extent 
of extraction of moisture from the soil by crops, and the effect of 
micro-climate, vegetative cover and soil texture on the process 
of evapotranspiration. Without the application of the neutron gauge 
in evapotranspiration investigations, the knowledge gained by the 
Department in the field of vegetative water use would have been 
much more limited. 

Land Subsidence 

The route of the California Aqueduct traverses extensive "shallow 
subsidence" areas along the west side of the arid San Joaquin Valley. 
This subsidence phenomenon is characterized by marked sinking 
of the ground surface following the application of water. Tests 
made in 1957 and 1958, using infiltration wells, revealed the forma- 
tion of characteristic circular "stairstep" subsidence patterns, with 
the well structure at the center dropping as much as 25 feet from 
its original elevation. 

Shallow subsidence could impair the operation of the concrete-lined 
aqueduct, which has a grade of about 3 inches per mile of length. 
Recognizing that some measures would be necessary to stabilize 
the soil prior to construction, the Department made a reconnais- 
sance survey of the aqueduct route, and delineated potential problem 
areas. A test site was established near Mendota, and a series of 
investigations undertaken to determine the most effective feasible 
preconsolidation method. 


Soil moisture and soil density probes were adapted to make 
measurements to depths of 200 feet. This equipment is shown on 
the photographs in Illustration 3. The instruments were used to 
evaluate the depth and extent of water penetration for each of the 
several water application techniques tried. 

The test site investigations led to the selection of an optimum 
preconsolidation nnethod. This method involved forming embank- 
ments along the aqueduct right-of-way with material scooped from 
the future location of the channel. Dikes were constructed across 
the alignment and water introduced, forming a ser.ies of shallow 
ponds. Continuous flooding for periods ranging fronn a few months 
to more than a year caused the soil to settle to a final stabilized 
elevation. All that remained to be done following this procedure 
was to allow the soil surface to dry for a period of time so that 
heavy earthmoving equipment might commence excavating and 
grading operations. 

For the preconsolidation method used, the precise knowledge of 
the relationship of the depth and extent of the wetting front to the 
estimated depth of subsidable soil proved to be extremely valuable. 
These data were provided by routine use of the nuclear moisture 
and density probes during the ponding process. The measurements 
also indicated the rate of advance of the percolating water. This 
information was put to use in scheduling delivery of the relatively 
scarce and costly water supply, and in providing more precise 
knowledge of progress at each reach of the aqueduct for use in 
advance planning of construction operations. 

For the purposes of this investigation, no method other than the 
use of moisture-density gauges could have provided the desired 
information as rapidly, accurately and inexpensively. To date, 
many thousands of nneasurements have been made, and utilization 
of these data has contributed materially to the design and construc- 
tion of the California Aqueduct. 

Delta Channel Depletion 

In 1963, the Department began an investigation which incorporated 
a unique application of subsurface moisture gauges. The overall 
objective of the project was to balance the hydrologic equation for 
Sacramento-San Joaquin River Delta flow. This required a degree 
of knowledge of all the factors which contribute to inflow and out- 
flow of water in the river system. One of these factors for which 
quantitative data were reqmred was the seasonal fluctuation in sub- 
surface water storage in the area. Accretion jind release of water 
from the soil contributes significantly to flow in the channels. Mere 


Illustration 3. Nuclear Moisture -- ] 

Operation of density and moistt 
gauges in infiltration wells, F 
County (photos A and B) 

Note the depth and extent of 


.ent Used for Subsidence Evaluation 

Operation of density and moisture gauges in preconsol- 
idation ponds along the alignment of the California 
Aqueduct. Subsurface data is being collected fronn rafts 
(photo C) and from slant-drilled access tubes (photo D). 


measurement of water table elevations would have supplied insxif- 
ficient information for accurate determination of the total quantity 
of water retained in the soil. This was because of the relatively 
large potential storage capacity in the vmsaturated surface zone of 
the highly organic soil. The intensively cultivated Delta area is 
suitable for growing a large variety of crops. The unique irriga- 
tion practices required for some of these crops prevent accurate 
estimation of soil naoisture storage for a large portion of the Delta. 
Thus, field measurement of the amotints of water contained in the 
soil above the water table was necessary to obtain precise estimates 
of the contribution of soil moisture storage to the hydrologic balance. 

Obtaining representative naeasurements of water contained in a 
ten-foot depth of more than a half million acres of highly produc- 
tive agricultural land seemed to be a formidable task. Only through 
the use of the rapid, nondestructive neutron moisture gauge tech- 
nique could such a vast quantity of information have been collected 
in the three-year period of this investigation. Approximately 500 
measurement sites were established throughout the area. Three 
moisture meters were required. Each of the sites was gauged at 
least monthly. 

Two problems had to be solved in order for this technique to be 
successful. The first was that of developing a calibration for the 
instruments which would apply to the highly organic soils found in 
nnost of this area, soils which are atypical of those in other areas 
of the state where calibration curves had been developed. A stan- 
dardization procedure was developed and adequate meter calibration 
obtained thereby. The second problem was how to analyze expedi- 
tiously the large number of individual readings (approximately 250 
per day) resulting from the measurements. For this purpose, a 
comprehensive computer program was developed to assist in 
tabulating and obtaining estimates of reliability for all the data. 

The successful completion of this investigation was due, in a large 
measure, to the data obtained from the neutron soil naoisture 
measuring devices. 

Connpaction Control 

Utilization of devices containing radioactive sources for moisture 
and density control of earthwork structures is playing an increas- 
ingly prominent role in departmental activities. Testing started 
in 1963, when the first gauging instruments were purchased by the 
Department's Soils Laboratory. However, close liaison in nuclear 
instrumentation had been maintained with the State Division of 
Highways for several years prior to that time. 


The difference between nuclear compaction control tests and most 
other determinations of soil properties by radiation gauging tech- 
niques is the necessity for obtaining precise data within a limited 
period of time. In most subsurface applications, differences in 
soil characteristics may be measured over some time interval -- 
days or weeks. The measuring site is accessible at any time, so 
that a questionable reading may be repeated. In earthwork con- 
struction, however, availability of the measuring site is frequently 
limited to a few hours. Since it is not easily subject to later 
verification, the test must be highly reliable the first time it is 

A large number of possible variations in technique can insure 
higher reliability of the measurements. These approaches can 
best be evaluated by statistical methods. A cooperative investi- 
gation was landertaken with the Division of Highways to provide 
such an evaluation, and was completed during the 1964-65 fiscal 
year. The study was primarily a laboratory exercise, although 
field experiments were conducted at Bethany Forebay, Whale Rock 
and Frenchman Dams, as well as at several Division of Highways' 
road projects. 

Results of this investigation led to development of preliminary 
standard techniques which would best suit the purposes of Depart- 
ment projects. During the 1966 construction year, these tech- 
niques were put into practice on the Thermalito Afterbay Dam - 
Oroville Project. Photographs of the equipment in use on this 
project are shown in Illustration 4. A number of additional refine- 
ments were devised as a result of this experience, and in 1967 
the improved procedures were incorporated in the measurements 
made on the Thermalito Forebay Dam. 

The investigations which have been completed to date indicate that 
under certain circunnstances the use of surface moisture and den- 
sity gauges provides a significant improvement over conventional 
measurennents of soil compaction. Certain future construction 
projects of the Department have been proposed wherein these 
devices will be utilized as a regular tool in the construction inspec- 
tion procedure. 

Snow Measurements 

In 1956, the Department and the U. S. Forest Service began a 
joint research program to find ways to manage the snowpack of 
the Sierra Nevada. The two major aims were to seek ways 1) to 
increase the total annount of water delivered from the mountains 
to the streams, and 2) to delay the delivery of water from the 
melting snowpack until as late in the sxinnmer as possible. 


Illustration 4. Nuclear Moisture -- Density 
Gauges Used for Compaction Control 

A. Surface moisture content b« 
determined by device in cei 
of photograph. 

B. Surface density meter (lower 
left) measuring compaction 
at Therm alito Afterbay 



Essential for the determination of water yield of mountains is a 
more complete understanding of the dynamics of snow ripening 
and melt. This information is necessary in order to enable 
formulation of predictive equations of stream flow. Development 
of the radioactive snow gauges enables measurement of changes 
that occur in the snowpack in response to causative stimuli. 

Detailed descriptions of the application of moisture and density 
gauges to the measurement of changes which occur in the snow- 
pack and in the soils beneath have been published in annual reports 
issued by the U. S. Forest Service. The Department has assisted 
in the development and improvement of these nneasuring instru- 
ments. The two-probe gamma- attenuation snow density gauge 
shown in Illustration 5 makes possible frequent non-destructive 
density profiles of the snow pack. 

Illustration 5, Two-Probe Snow Density Gauge in Use. 


Observations made with this equipment have led to clarification 
of the phenomenon of movennent of moisture through snow and 
have enabled the snow hydrologists to formulate predictive equa- 
tions which represent significant advances in the state of the art. 

Certainly, any method of comparable accuracy which allows more 
frequent sampling than the snow-coring procedure, which has been 
used for 60 years, should result in more accurate streamflow pre- 

Miscellaneous Applications 

There have been a number of other investigations in which soil 
moisture and density gauges have been utilized. Among these are: 

1. Consumptive use of water by native vegetation. Neutron 
moisture probes were adapted for a study of soil moisture 
accretion of rainfall and depletion by native vegetation in 
the Sierra foothill region of the Southern Sacramento Valley. 
Measurements were made for approximately one year 
(1961-62). Although the results were satisfactory, the 
entire study was terminated before a sufficient period of 
time had elapsed for meaningful trends to be established. 

2. Sacramento Valley seepage investigation . In 1963-64, 
neutron probes were employed during the Sacramento 
Valley seepage investigation to measure the degree and 
change of soil moisture above the saturated zone. Mea- 
surements were taken before, during and after seepage 
occurrences. The moisture content was found to be near 
field capacity before the October to March seepage period 
and did not change appreciably during or after seepage 
occurrences. Although the measurements did not provide 
all the information the Department had hoped to obtain, 
they did assist in providing a better understanding of seep- 
age phenomena, and in particular the reason for the rapid 
recurrence of seepage after its initial occurrence. 

3. Twitchell Island investigation . In 1960-61, neutron 
soil moisture probes were utilized in conjiinction with an 
intensive hydrologic investigation of Twitchell Island in 
the Sacramento-San Joaquin Delta area. The hydrology 
and soils of this area are typical of most of the islands of 
the Delta lowlands. As a result of the use of these instru- 
ments in this investigation, the feasibility was established 
for their more extensive application in the Delta Channel 
Depletion Study, which has been described previously in 
this report. 


4. Sierra Valley investigation. In 1963, measurements were 
made with the neutron moisture probe in several areas of 
Sierra Valley, as part of an investigation to determine base- 
line soil moisture conditions of agricultural lands prior to 
the comipletion of Frenchman Dam, which is upstream from 
the study area. Repeated measurennents of soil moisture 
were made over a growing season, and results obtained 

for soil nnoisture depletion were satisfactory for the limited 
purposes of the investigation. 

5. Del Valle pipeline . In 1964, an investigation was under- 
taken to determine the feasibility of adapting surface soil 
density gauges for the purpose of locating voids in backfill 
around large diameter pipes. Measurements made in the Del 
Valle pipeline indicated that under certain conditions of soil 
and pipe uniformity, the nuclear method would be useful for 
this purpose. 

6. Ground water recharge. In cooperation with the U. S. 
Department of Agriculture, Agricultural Research Service, 
studies of the recharge front movement and position of the 
water table in Western Fresno Coixnty were carried out in 
1960-64, Neutron soil moisture probes proved to be a valu- 
able tool in this research endeavor. 

7. Soil moisture repletion studies. In cooperation with the 
U. S. Bureau of Reclamation, Fresno Field Division, soil 
moisture measurements have been made since 1967 near 
Fresno, in a controlled environment. The neutron probe 
results are being used as primary standards to calibrate 
direct reading evapotranspirometers, and determine their 
feasibility as indirect indices of evapotranspiration of crops. 


Basis for Use 

One of the primary reasons for the usefulness of radioisotopes in 
tracer applications lies in the fact that infinite simally small quan- 
tities may be detected. For example, less than 1 trillionth of an 
ounce of such common elements as phosphorus, sodium, calciunn, 
cobalt, zinc, and silver may be detected with this analytical tool. 
With such sensitivity a very large number of phenomena can be 
investigated in any chemical or physical state. 


The development and refinement of scintillation counters within 
the last decade has revolutionized many radioactivity measure- 
nnents. Newer measurement techniques (e. g. pulse height analysis) 
have also permitted investigators to assay mixtures of radioactive 
materials to a degree which was not formerly considered possible. 
The development of low-counting-rate techniques will undoubtedly 
expand the number of possible analytical applications. 

Methods of Use 

Measurement of flow. Radioactive tracers have been used to mea- 
s ure surface water flow velocities, to determine the type of flow, 
i. e. whether viscous or turbulent, to locate leakage and deternnine 
its magnitude, and to provide information on the mixing taking 
place in flow systems. One of the most direct and useful of these 
applications in the field of hydrology is the measurement of flow 
rates. The three basic techniques for measuring liquid flow velo- 
cities are peak timing, dilution and total cotmt. Detailed descrip- 
tions of the principles of these techniques are presented in Appendix B. 

In addition, activation analysis methods have been developed, using 
both direct activation of the medium in the field, or laboratory 
activation of samples after they have been collected. 

Age Dating . An outstanding characteristic of radioisotopes is the 
extreme uniformity of their decay constants, which are independent 
of the chemical or physical state of the material, and can provide 
valuable information regarding the age of certain materials. Pro- 
cedures have been developed to determine the age of geological or 
archeological samples with reasonable precision. 


Flow Measurement 

Radioactive tracers enable accurate identification of flow paths 
and accurate calculation of flow velocities in water bodies. Two 
1958 experiments dennonstrated these points to the Departnnent of 
Water Resources. A radioisotope of gold, in a successful experi- 
ment by Dr. D. Hull of Chevron Research Corporation, helped 
measure flow in the American River. Tritium, in a second success- 
ful experiment, helped the U. S. Bureau of Reclamation in con- 
sultation with Professor Warren Kaufman, University of California, 
to determine the extent of seepage from the Madera Canal. 

As a result, the Department planned, in 1963-64, to use tritium to 
trace hydraulic flow in the Sacramiento-San Joaquin Delta. For 


reasons unconnected with the technical feasibility of the experiment, 
the plan was not executed. The Department did make two dye 
releases into the Sacranriento River near Freeport, however, and 
did measure the dye concentrations so as to delineate control areas 
and to determine the amovuit and dilution of tritium necessary. 

Despite its rigid controls, the Public Health Department always 
has cleared proposed Departnaent of Water Resources experiments. 
Nevertheless, unreasoning fear of the introduction of radioactivity 
into the environment does exist. Local officials sometinaes do 
oppose the use of radioactive tracers. Public reaction to such use 
is oversensitive and offers an obstacle which time alone can over- 
come. In time, the benefit provided by radiotracer investigations 
will be viewed more rationally. Newer, more sensitive counting 
eqmpment has reduced the concentrations of radiotracers required 
for satisfactory results to values only slightly above those of the 
natural environment. Meanwhile, the Department of Water Resources 
maintains liaison with those agencies which do conduct radiotracer 
studies and thus keeps itself informed upon new techniques. For 
examiple, the acoustic velocity meter being used in river channels, 
canal pump lines and penstocks requires a primary calibration 
stsuidard. Isotope flow measurement techniques nnay be a prom- 
ising method of providing this calibration. 

Pump and Turbine Rating 

In hydroelectric powerplants, the efficiency of the turbines is deter- 
mined by measuring or calculating the rate of water flow through 
the turbine for a particular head and rate of electrical power pro- 
duction. Accurate measurements of power production are relatively 
simple, but nmeasurements of the corresponding water flow rate to 
the same degree of accuracy are more complex. Because turbine 
ratings are used not only to determine turbine efficiency but also 
to schedule reservoir releases, and in some cases to indicate 
total streamflow, turbine flow must be measured accurately. 
Essentially the'same fxindamental principles as described above 
are involved in rating pumps. 

Some experimental work on the use of a radiotracer method for 
rating hydraulic machinery has been done, primarily by the Bureau 
of Reclamation. The flow measurement method involves introducing 
the tracer into the pump or turbine flow and observing the passage 
of the tracer at some downstream point. The nnethod of computation 
of flow fronn the data obtained in this manner is a comparatively 
simple operation. Whether it has clearcut advantages over other 
methods cannot be established at this time, but the technique 
warrants periodic consideration to evaluate any innprovennents 
that might be developed. 


Subsurface Flow Measurement 

During 1964-65, the Department investigated the use of radioisotope 
tracers to determine subsurface conditions. During foundation 
drilling at the left abutment of the Castaic Damsite, high water 
losses were occasionally experienced in certain of the drill holes. 
Explanation of those losses was considered to be a necessary phase 
of foundation exploration. 

Sodium- 24 was used as a tracer material to determine rate and 
direction of flow of waters between appropriately located drill holes. 
This radioisotope may be detected at relatively low concentrations 
and has a short (approximately 15 hour) half-life. These charac- 
teristics make it suitable for use as a field tracer with virtually 
no attendant health hazards if reasonably simple safety precautions 
are observed. 

Approximately 9 millicuries of sodium-24 diluted in 10, 500 gallons 
of water were introduced into a drill hole in five separate injections. 
Measurements in adjacent drill holes with a logging tool containing 
a radiation detector resulted in no indications of increased radio- 
activity above natural background in any of the holes. Photographs 
of the procedure are shown in Illustration 6. 

Although results of this experiment were inconclusive, information 
was obtained which will prove valuable in our future applications of 
subsurface tracers. On the basis of the results of measurements 
within the injection hole, calculations were made which would accovmt 
for the failure to detect activity in the other measuring sites. The 
principal cause was a combination of subsurface physical conditions 
which could not have been predicted in advance. The published 
report* summarized the knowledge gained from this experinnent. 
Several recommendations were made which, if followed, will lead 
to more conclusive results in future investigations of this type. 

Watershed Management 

A rather dramatic use of tritium as a tracer was demonstrated in 
1966 on the Department sponsored watershed management research 
project in Placer County as conducted by the University of California, 
Davis, through the Water Resources Center. In this experinaent 
water was tagged at the water table 70 feet below the ground surface. 
Within days, the tracer was detected in the leaves of the nearby oak 

♦ "Application of a Radioactive Tracer to Ground Water Flow - Left 
Abutment - Castaic Damsite". J. S. Bigelow and Irving Goldberg, 
Department of Water Resources Office Report, Division of Design 
and Construction. July 1965. 


Illustration 6. Radioactive Tracer Application at Castaic Damsite 

Withdrawing measured quantity of 
radioisotope from shielded con- 

B. Mixing tracer in carrier salt 
s olution. 

C. Injecting tracer in ground fronn 
tank truck. 

D. Logging observation well with 
scintillation detector. 


Tracers have been used in U. S. Forest Service Watershed Man- 
agement Research in the snowlands, cooperatively supported by 
the Department, to determine the direction and velocity of water 
movement in a tree from the root, through the trunk, and to the 
leaves. The path of water movement was found to be rigidly linear 
and unbranching. 

Tracers have also been used to follow the path of melting water 
through a snow pack. It was found that such water does not move 
vertically only. In denser layers of snow, nnovement was down- 
slope within the dense layer, and with some horizontal movennent 
sideways. In the less dense snow layers, the motion was vertical. 

Analysis of "Water Quality 

There are at least two types of applications in which radiological 
techniques are found to be of benefit to the Department's water 
quality investigation program. One is the measurement of radio- 
activity in waters as part of the water quality monitoring program. 
The other involves use of radioisotopes in specific water quality 

1) The Department's water quality data program has included 
reporting of radioactivity in raw water samples since the mid 
1950 's. The radiological applications program has provided 
consultation and recommendations concerning technical aspects, 
such as statistical significance, of low-level radioactivity 
deternninations. In recent years, radionuclide analyses made 
by the State Department of Public Health on treated waters 

on other itenns for human consumption have, to a large extent, 
replaced this activity. 

The Department's reports provide a valuable addition to the 
record of radioactivity in the State's waters for the period 
antedating the State Health Department's more extensive 
participation in this field. The Department's data program 
has revealed a few instances of inadvertent concentration and 
release of natural radioactivity into water supplies by chemical 
processing activities. As a result, radioactivity might have 
exceeded annual limits set by State and Federal Radiation Pro- 
tection Guidelines. These resvilts were brought to the attention 
of the appropriate authorities, and the operations contributing 
to the releases were terminated prior to the buildup of radio- 
activity to undesirable levels. 

2) There are two analytical determinations directly connected 
with DepaTtment water quality investigations in which radio- 
active materials are used. One is the use of tritium in 


analytical instruments for the identification of pesticides. 
These instruments have been operated by analytical chennists 
in the Technical Services Office of the Department for several 
years. The second is the carbon-14 bioassay technique for 
determining biological productivity of waters. This procedure 
enaploys direct measurement of the growth of microscopic 
plants under natural conditions of temperature and light as 
an index of the "fertility" of waters. 

The carbon-14 bioassay procedure has a potentially large 
application as one of the biological nnonitoring and control 
procedures which are to be maintained for the State Water 
Project. In addition, increased interest in the preservation 
of our natural water supplies from environmental contamina- 
tion may lead to a monitoring program in several lakes and 
streams throughout the State. 

Age Dating 

An important area of knowledge, on which very little positive infor- 
mation is available, is the field of paleoclimatology. Precise knowl- 
edge of the long-term climatic changes of western North America 
could assist in predicting future trends, and would thus be valuable 
for water development planning investigations. The Department 
has sought this type of infornaation in a n\imber of ways, one of the 
most significant of which has been the maintenance of close contacts 
with some of the foremost authorities in the field of age-dating of 
specimens containing carbon. 

As an example of such cooperative efforts, in 1962 samples of wood 
from tree stumps were submitted to the Scripps radiocarbon labo- 
ratory in San Diego for age deternnination. These samples had been 
collected on the western shore of Lake Tahoe when the lake level 
was at its lowest point in several decades. It was possible at that 
time to recover wood samples from stumps of trees which apparently 
were killed by a rise in the lake level during prehistoric times. The 
age of these trees could possibly provide valuable information con- 
cerning a major climatic change in that area. 

The radiocarbon dates determined by the laboratory* indicated 
that the trees grew to maturity and were subsequently preserved 

* "La JoUa Natural Radiocarbon Measurements". C. L. Hubbs, 
G. S. Bien and H. E. Suess. American Journal of Science, Radio- 
carbon. Vol. 5. p 262. 1963. 


in the lake waters for nearly 5, 000 years. This result was 
unexpected due to the remarkable state of preservation of the 
wood. From this information, and from supplementary geolo- 
gical data, the hypothesis was presented that no major climato- 
logical changes which would have lowered the level of Lake Tahoe 
from its present elevation for any significant period of time could 
have occurred in at least the last 5 nnillennia. It was concluded 
that the rise in lake level which killed the trees along the shore- 
line was nnore likely due to diastrophism than to increased 

Specimens of wood from Eagle Lake, and from archeological find- 
ings along the California Aqueduct construction sites, have been 
submitted to the radiocarbon laboratory for age determination. 
Results of these analyses* have been less drannatic, but they 
have assisted in confirming some previously postulated theories 
concerning the past climate and geology of those areas of the State. 

Radiocarbon dating is thus seen as an important aid to the deriva- 
tion of rational bases for water resources development planning. 

Stable Isotopes as Tracers 

Although the radiological applications progrann deals principally 
with investigations concerned with utilization of radioactive nnaterials, 
there are several important investigations associated with this pro- 
gram which stable rather than radioactive isotopes are used. 

1) Recent studies have indicated that considerable information 
regarding the source and history of surface and grotuid waters 
may be obtained by analyses for the stable isotopes of hydrogen 
and oxygen normally present in such waters. These isotopes 
include hydrogen-1 and hydrogen-2 (deuteriuna), and oxygen-l6, 
oxygen-17 and oxygen-18. Because of differences in volatility 
caused by the normal distribution of these isotopes in water, 
there is a tendency to enrich waters, which are subject to 
free evaporation, in the heavier of these isotopic species. 
Similar phenomena govern the condensation of water vapor 
which falls as precipitation. Thus, there is a natural fraction- 
ation of the stable isotopes of hydrogen and oxygen in the hydro- 
logic cycle. 

A knowledge of the proportion of each of these isotopes in a 
sample of water can be a valuable indication of the source of 
that water. Instrumentation is now available to perform rapid 

*• "La Jolla Natural Radiocarbon Measurements". C. A. Hubbs, 
G. S. Bien and H. E. Suess. Annerican Journal of Science, 
Radiocarbon. Vol. 4. p 231. 1962 and Vol. 6. pp 604-610. 1964. 


and relatively inexpensive oxygen isotope analyses of water. 
Studies devoted to refinement of this technique and investiga- 
tions of the source and history of water supplies have been 
conducted at the Scripps Institution of Oceanography. The 
Department of Water Resources is closely following these 
studies, which are of great value to the understanding of 
fundamental hydrologic processes. 

2) Activation analysis has the potential to prove valuable in 
water resources applications. This method involves: 

a) introducing of a stable tracer into a system; 

b) allowing the process which is being measured to 
take place; 

c) removing a sample from the system? 

d) making the stable tracer artificially radioactive 
by neutron bombardment; 

e) naaking a quantitative deternnination of the radio- 
active species by conventional counting techniques. 

This procedure combines all the advantages of the radioactive 
tracer technique with the additional benefit of minimal health 
hazards to operating personnel and to the general public. 
Although the principal commercial applications of activation 
analysis are in industrial and forensic microchemistry, its 
use in large scale field studies involving water movement may 
some day be common. The principal shortcoming of the method 
at this time is the relatively high cost of the analysis, which is 
only partially offset by the low cost of equipmient and materials 
in the actual conduct of the experinaent. Nevertheless, there 
are investigations in which activation analysis may be the only 
economically feasible way to obtain the desired results. 

3) The detection and measurement of tritium deposited as fall- 
out from nuclear weapons testing provides a means for tracing 
the flow of surface and subsurface water. Tritium is not a 
stable isotope, but decays radioactively with a half-life of 
approximately 11 years. The analysis of water for "bomb tri- 
tium" has proved to be a valuable method of determining the 
recent history of the water. Such nneasurements have been 
used to provide useful information on the rate and direction 

of subsurface water movement, and on the distribution of 
surface waters. 

Littoral Transport Studies 

The Department of Water Resources has been directly involved in 
a continmng series of tests using radioisotope-tagged sand to 


determine the mechanics of offshore movement of sediment, partic- 
ularly around headlands. This study, called RIST (Radioisotopic 
Sand Tracer) is under the combined sponsorship of five agencies: 
U. S. Army, Navy, Air Force, NASA, and the DWR. Additional 
funds have been provided through a grant from the Atomic Energy 

Very little direct field information is available about the complex 
mecheoiism of sediment transport phenomena in the vicinity of head- 
lands. These processes are particularly significant in their rela- 
tionship to the serious problem of beach erosion. 

The techniques oi removing, labelling, and replacing particles of 
sediment so that their offshore movement may be traced were devel- 
oped as the first phase of this study. In April, 1957, a field evalua- 
tion test was conducted at Cape Kennedy, Florida. This resulted 
in development of the following procedure, which was subsequently 
used in two field tests near Point Conception, California. 

Several hundred pounds of sand were collected from the test area, 
and shipped to Oak Ridge National Laboratory in Tennessee. There 
the sand was placed in a furnace and heated to 900 C in an atmos- 
phere of radioactive xenon-133. The gas combined with the sand 
crystal structure, resulting in a supply of sand tagged with a chem- 
ically inert substance that had an effective half-life of 2.7 days. 
The tagged sand was shipped back to the injection site by air. One 
reason for the selection of xenon-133 as a tracer was that it will 
not interfere with the ecology of the marine environment. 

The monitoring system incorporates a solid state detector, which 
was mounted inside a cylindrical "detector vehicle" which rolled 
along the ocean bottom as it was towed by an amphibious vehicle 
(LARC) borrowed from the U. S. Army Mobility Equipment Com- 
mand. The readings of the detector, including radiation, position, 
and time, were recorded on an 8- channel punched tape located in 
the LARC. The electronic system enables differentiation between 
vertical and horizontal dispersion and nnixing of the tracer sand. 

The first pilot test in California was nnade commencing June 13, 1967, 
at the mouth of the Santa Ynez River near Vaoidenberg AFB. Initi- 
ally a point drop of a small amount (approximately 100 liters con- 
taining 10 curies) of the tagged sand was made, primarily for pur- 
poses of instrument calibration, establishment of measuring grids, 
and refinement of handling techniques. At a later date, a linear 
source, nornaal to the beach, was injected from the high tide line 
to a 20-foot depth, and tracing operations were again carried out. 


A second field injection was made commencing on November 27, 
1967, in the vicinity of Government Point, east of Point Conception. 
Photographs of the equipment used in that test are shown in 
Illustration 7. 

The progress of the RIST study is considered successful to date, 
being marked by significant accomplishments in its first two 
years. Results of the field studies have indicated that the basic 
tools are now available with which to trace movement of material 
around a headland, and thereby study the mechanics of its trans- 
port. Much work remains to be done, however, to refine the 
analytical techniques, and to further quantify the results of the 

Underground Nuclear Explosives 

An application of nuclear energy of potential value to the State is 
that of underground nuclear explosives. Consideration of such 
applications is included in this program, though in a strict sense 
a nuclear explosive is not in the category of radiological applica- 
tions. The latter depend for their usefulness upon the radioactive 
properties of the atom rather than upon the release of energy as 
occurs in an explosion. 

An underground explosion might increase the available water 
supply by facilitating recharge of an aquifer. This might be done 
by increasing storage capacity or rock permeability, or by 
breaking through a barrier to interconnect adjacent aquifers. 
Nuclear explosives can also be used for large scale excavation, 
an application which has been experimentally demonstrated at 
the AEC Nevada Test Site. 

An underground explosion might also produce a great amount of 
recoverable heat at moderate cost. The heat could possibly be 
released at a controlled rate by use of a transfer agent, such as 
water or gas, and used for the production of power, or in the 
form of heat for the conversion of salt water to fresh water. 

Study and experimentation in the peaceful uses of nuclear ex- 
plosive devices were initiated in 1957 at the E. O. Lawrence 
Radiation Laboratory (operated by the University of California) 
at Livermore as part of the AEC Project Plowshare Program. 
In addition to the possible applications relating to ground water, 
other uses being investigated by the laboratory include (1) ex- 
cavation, (2) isotope production, (3) recovery of oil from shales 
and tar sands, (4) mining, and (5) applications to scientific 
studies in seismology, geology, and special chemical reactions. 


Illustration 7, Radioisotope Sand Tracer Experiment 
Near Point Conception, California 

LARC containing tagged sand and 
detector preparing to embark on 
a sand tracer run. 

B. Amphibious craft returning i 
beach after tracer rtin. 

LARC with ramp down, showing 
detector sled (left center) and 
drum containing tagged sand 
(just right of sled) . 


The Department has participated in discussion with members of 
the laboratory staff concerned in Project Plowshare studies in an 
attempt to evaluate effects and possible benefits of an undergro\ind 
nuclear explosion in an aquifer. Insufficient infornnation is avail- 
able, however, to assess the effects of such an explosion on either 
the geological formations in which ground water occurs or liie water 
itself, and further investigative work is not planned by the Depart- 
ment at this time. 

A study of a project of this type, which the Department will observe 
with interest, will be conducted jointly by AEC and the Department 
of the Interior for Arizona beginning in July 1968. This study, to 
last about a year, will cover the feasibility of nuclear explofcives 
for water management purposes, possible sites for such explosions, 
cost analyses, and recomnnended courses of action. Radioactivity 
and legal problems of water rights will be stressed in the study. 

The possibility of producing controlled power or heat from an under- 
ground explosion appears quite remote. Some preliminary studies 
of the technical feasibility and economics of a process for transfer 
of residual heat from an underground explosion to water have been 
made. These studies indicate the probable costs to be quite high. 

In 1961, the Department entered into an agreement with the Atomic 
Energy Comnnission to conduct a study of the application of nuclear 
explosives to the West Side Conveyance System, a feature of one of 
the alternative plans for development of water in Northern California. 
The study* indicated that (1) conveyance channels could be excavated 
by nuclear explosions, at a significant savings in overall cost of the 
System, and (2) by the projected date of construction (1985 or 1990), 
the nuclear devices could be detonated with confidence and safety. 

Potential Future Radioisotope Applications 

In addition to those c_x rent investigations described in this report, 
there are other areas of interest, some of which are extensions of 
present applications, in which the feasibility of radioisotope use 
will be studied in detail. These are summarized as follows: 

Soil Moisture and Density Studies. Nuclear gauging devices, which 
have proved to be useful and valuable tools for nondestructive test- 
ing, will undoubtedly find more extensive and varied applications 
in future Department activities. Sonne possibilities are: 


♦ "Excavation for Water Conveyance with Nuclear Explosives", 

J. W. Keysor and M. B. Andrew. Proceedings, Third Plowshare 

Symposium. TID-7695 pp. 363-370. April 1964* 


1) Use of subsurface moisture gauges in an investigation of 
salinity conditions in the Suisun marsh area, preliminary- 
plans for which are under way; 

2) Evapotranspiration measurements of additional crops of 
importance of California agriculture; 

3) The control of preconsolidation using subsurface moisture 
and density gauges in any additional areas of shallow subsi- 
dence along the route of the California Aqueduct or other 
features of the State Water Project; 

4) Nuclear compaction control equipment in embankments in 
those projects for which it is found most suitable. The most 
likely of these are thought to be the Clifton Court Forebay 
and possibly the Castaic Dam.. 

Surface and Ground Water Tracer Studies . Conventional naethods 
have been selected for rating the Department's punaps and turbines 
and for measuring flow in the Aqueduct. However, the results of 
a radioisotope testing program for such ratings, which is being 
carried out by the Bureau of Reclamation at Denver, have been 
encouraging. If the superiority of these methods is established, 
they may some day be adapted for use in future Department testing 
and measurement program. 

Underground flow experiments utilizing radiotracers have a broad 
potential in future Department activities. Among those projects 
which have been mentioned for possible future use are: 

1) Measurement of ground water flow at proposed damsites, 

2) Tracing of sewage effluents in artificial recharge plots, 

3) Measurement and tracing of seepage of drain waters 
from regulatory and emergency storage reservoirs. 

Several applications of neutron activation analysis have potential 
in Departnnent activities. In any instance (such as measurement 
of aqueduct water flow close to turnouts) where there may be public 
over sensitivity to direct radioisotope injection, this technique is 
both possible eind feasible, though probably more costly than the 
alternative. Activation analysis has also been proposed as a nnethod 
for delineating seawater intrusion areas. This kind of analysis may 
also have some direct application in those instances where contamin- 
ation of water supplies by snaall traces of pollutants is suspected. 


Water quality studies would certainly benefit from more extensive 
applications of the carbon-14 uptake technique. This method has 
been proposed for use in the continuous monitoring of biological 
productivity in reservoir and aqueduct waters. 

Age-dating by isotopic content should have considerably more value 
as the importance of the dependence of long-range water supply 
forecasts on past history becomes more widely recognized. 

Isotopic tracer techniques have been suggested for detection or 
tracing of leakage fronn pipelines embedded in levees. 

Isotopic Power Generators . The recent developcnent of radioisotope 
power systems is being followed with interest, since this applica- 
tion has potential for use in Departmental activities. The AEC- 
sponsored SNAP (Systems for Nuclear Auxiliary Power) program 
has as its objective the use of various radioisotopes for electric 
generators. SNAP generators with a power range of from 25 to 
100 watts have been developed and are being tested to evaluate 
their reliability. An AEC- sponsored engineering design study is 
presently being made to assess the needs for isotopic powerplants 
in the 1- to 10-kilowatt power range. Compact isotopic plants could 
possibly fulfill moderate power requirements in the nnore remote 
areas of the Department's operations; for example, in the flood 
forecasting and Aqueduct operation and naaintenance activities. 




In the United States the possession of radioactive material by any 
person or organization is prohibited unless authorized by a license 
granted either by the Atomic Energy Commission or by a State 
which has been granted regulatory control by the AEC. In 1962, 
the State of California, through its Department of Public Health, 
assumed authority to license and otherwise to exercise regulatory 
control over nnost kinds of radioactive material within the State's 
boundaries by agreement with the Commission. 

In seeking approval for a license to use radioactive material, an 
applicant must establish that "his specified personnel are qualified 
by reason of training and experience to use radioactive material. . . 
in such a manner as to provide reasonable and adequate assurance 
of protection to health, life, and property;"* and that "the appli- 
cant's equipment, facilities, proposed uses and procedures are 
such as to provide reasonable and adequate assurance of protection 
to health, life and property;. . . "* 

Thus, a necessary adjunct to initiating and conducting any investi- 
gation involving use of ionizing radiation is the acquisition of the 
specialized training necessary for the establishment of an adequate 
radiation protection program. 


In 1959 the Department of Water Resources applied for its first 
license to possess sources of radiation. Because of AEC's require- 
ment for internal control and management of radiation, the posi- 
tion of "Radiological Operations Officer" was established, and the 
authority to be exercised by the individual appointed to that position 
was delineated in the Department's Administrative Manual. 

As uses of radioisotopes increased, the responsibility for manage- 
ment of the Department's radiation protection program also broad- 
ened. In i960, the Department was authorized, by amendment to 
its license, to conduct its own radiological training program, and 
to designate those employees thus qualified to handle radioactive 

*Title 17, California Administrative Code, Chapter 5, Subchapter 4. 
California Radiation Control Regulations, Sec. 30194 (a) and (b). 


materials. Individuals authorized by the Department's internal 
training prograna have been incorporated by reference as "individ- 
ual users" in the Department's Radioactive Materials License. 

At present, the Radiological Operations Officer is responsible for: 

a) Furnishing technical assistance in the planning 
and execution of work which involves the use of 
radioactive materials. 

b) Qualifying and designating departnnental employees 
as radiological operators. 

c) General surveillance of all radiation activities 
to assure safe use of radioactive materials 
throughout the Department. 

d) Distributing and processing personnel monitoring 

e) Supervising and coordinating the medical exam- 
ination program for radiological operators. 

f) Storing, issuing, and disposing of and super- 
vising the shipping of radioactive materials. 

g) Reviewing requests for equipment containing 
radioactive sources. 

h) Establishing and supervising decontamination 

i) Providing assistance to the Training Officer in 
establishing and conducting training in depart- 
mental radiological operating procedures and 

j) Representing the Department in contacts with 
manufacturers of radiation materials and equip- 
ment and with regulating agencies. * 

In addition to the above duties, the Radiological Operations Officer 
serves in a Radiation Protection liaison function with other agencies 

* DAM, Section 3 843. 3 


or contractors in programs involving use of radioactive materials 
in which the Department is a cooperator or a sponsor. 

In the nine years during which the Department has been licensed 
to use radioactive materials, no case involving injury by or over- 
exposure to radioactive materials of Department personnel or con- 
tractors has occurred. The occasional conditions of potential 
radiation hazards have been corrected following recommendations 
of the Radiological Operations Officer. 

As of the end of fiscal year 1967-68, almost 40 Department employ- 
ees were required to participate in the personnel monitoring program, 
due to being engaged in work in which exposure to ionizing radiation 
was a possibility. 

The Department is continuing to maintain close working relations 
with state and federal regulatory authorities in the field of radia- 
tion protection. 


One of the questions frequently asked by managers of programs 
which could benefit from application of a field tracer experiment 
deals with the possible complexity of securing permission to con- 
duct such an experiment. On the basis of experience gained in 
securing such permission the general requirements for an experi- 
ment of this type are discussed and summarized below. 

The State Legislature has set up a number of criteria for approval 
of field projects involving use of isotopes in California*. The 
intent of these requirements is that any tracer study: 

1) provide information of substantial public interest, 

2) be performed by persons competent to handle and 
use the radioactive material safety and with due regard 
for potential effects on public health, 

3) has been planned so as to impose the least exposure 
to ionizing radiation consistent with achieving the study's 
desired objectives, and 

* Division 20, California Health and Safety Code. Chapter 7. 
Section 25608. 


4) will not likely expose any person to ionizing radiation 
in excess of guide levels published by the Federal Radia- 
tion Covmcil. 

The law also provides for the fvill and complete disclosure of details 
of the study to all appropriate local and state authorities, and the 
presence of a representative of the State Department of Public 
Health during the procedure. 

It is the policy of the Health Department to judge each proposal for 
such a study on its own merits, with particular emphasis on mini- 
mizing potential exposure. Assuming all the above listed require- 
ments are fulfilled, a license is issued for possession of only 
enough of the radioisotope to perform one study. Separate license 
applications must be made for each individual experiment. 

In the use of short-lived radionuclides for tracing surface water 
flow, the technology has advanced to the State where few obstacles 
should stand in the way of obtaining full approval of Public Health 
authorities, providing the previously cited criteria are met. 


Although the Departnaent's radiation protection program was de- 
veloped primarily for its employees who are directly involved 
in using sources of radiation, attention is also being given to 
those individuals who may be incidentally exposed to radiation 
during performance of duties unrelated to handling radioactivity. 
For example, Department inspectors may work at construction 
sites where industrial radiography is being perform.ed. Criteria 
for monitoring these individuals are being developed and re- 
comm.endations for use of personnel monitoring devices are being 

It is anticipated that the need for a radiation protection program of 
the type presently in effect will be required in essentially its present 
form as long as the Department is involved in investigations which 
employ radioactive materials. The cost of this prograna is estimated 
to be approximately $4, 000 per year. 







Theory of Neutron Scattering 

Unstable isotopes spontaneously disintegrate and release energy 
in the form of alpha or beta particles and/or gamma radiation, 
and these radioactive isotopes can be used as a source of one or 
more desired radiations. 

If an alpha- emitting isotope is intimately mixed with a finely 
divided light element, such as beryllium, the bombardment of the 
atoms of the light element by the alpha particles will result in the 
ejection of a neutron from the nucleus. This fast neutron has a 
mass approximately equal to that of a hydrogen atom, has an aver- 
age kinetic energy of 4 or 5 million electron volts (mev), and is 
electrically neutral. 

If a point source* of fast neutrons is placed within a homogeneous 
medium, the neutrons travel radially outward from the source 
vmtil they collide with atoms of the surrounding material. In these 
collisions the neutron may be absorbed by the nucleus of the atom, 
or it may be elastically or inelastically scattered. For the elements 
contained in soils, the cross section, or probability of collision, for 
elastic scattering is predominant. The elastic scattering collisions 
conform to the laws of Newtonian mechanics, and it can be shown 
that a fast-moving neutron will lose energy in a collision with a 
slower moving atom. 

In a nnass of soil, a fast neutron is slowed, or moderated primarily 
by a series of elastic collisions \intil its kinetic energy approaches 
the average kinetic energy of the naoderating atoms, as determined 
by the ambient temperature. When a neutron has the same energy 
as the surrounding atoms, it is called a slow or thermal neutron. 
In the thermal region a neutron may gain or lose energy with equal 
probability, so the thermal energy is a lower limit to the slowing 
process. Thermal neutrons do not have a definite velocity direction 
with respect to the source, but move in a random fashion through- 
out the medium. Their motion can be described by the principles 
of diffusion theory. 

* Actually, a source of small but finite dimensions is used instead 
of the mathematical point source postulated here. 


Hydrogen is more effective in slowing fast neutrons than any other 
element; therefore, if an instrument which can detect slow neutrons, 
but which is insensitive to fast neutrons, is placed near a source in 
a medium such as soil, the counting rate of the detector will pri- 
marily be due to the hydrogen content of the soil. Hydrogen is a 
good moderator because its cross section for elastic scattering is 
large, and because in a collision with a hydrogen atom a neutron 
may lose a large fraction of its kinetic energy. This latter phenom- 
enon occurs because the mass of a neutron is about the same as 
that of a hydrogen atona, and in a head-on collision with a stationary 
hydrogen atom, a neutron may transfer virtually all its energy and 
momentum to the hydrogen nucleus. 

Since neutron moderation by other elements in the soil is small, 
and since in normal soils most of the hydrogen present is contained 
in the soil moisture, the detector response can be calibrated in 
terms of moisture content. Although the mineralogical, or grain 
structure and aggregation of soils vary widely, the elemental 
composition of most soils is remarkably similar. As the neutron 
scattering properties of soils depend upon the elemental composition 
(diffraction effects due to variation in crystal structure being neg- 
lected) a single calibration curve will serve for most soils. 

The presence in a soil of significant large quantities of a strong 
neutron absorber such as boron, lithium, cadmium or chlorine 
may introduce errors in the moisture determination. Likewise, 
measurements of moisture in soils containing a high percentage of 
organic matter will contribute to the total count rate. The hydrogen 
contained in the crystal lattice of clay minerals will contribute in 
the sanne manner to the covint rate. In general, soils containing 
large amounts of organic matter or clay contain proportionally 
larger amounts of moisture in the field condition. For this reason, 
the effect of the hydrogen from sources other than water becomes 
relatively small in actual practice. 


Theory of Gamma Ray Scattering 

The mass density of soils or granular materials is measured by 
counting the gamma rays which are backscattered to a detector by 
collisions with atoms of the material. 

The scattering of gannma rays is somewhat analogous to the scatter- 
ing of neutrons in that gamma photons suffer a change of direction 
and a loss of energy in a collision. Unlike neutrons, which interact 


with atomic nuclei, gamma rays are scattered primarily by elec- 
trons of the atonas in their path. Although the detectors commonly 
employed in density probes are somewhat energy dependent, the 
difference in energy of the source radiation and the scattered radia- 
tion is not sufficiently great to allow the detector to distinguish 
between the two. For this reason, it is necessary to shield the 
the detector from the source, so that only gamma rays scattered 
around the shield by collisions with atoms of the medium being 
measured will enter the detector. 

If the source and shielded detector are placed in a vacuum, the 
gamma rays will travel radially outward from the source and not 
reach the detector. If the region around the source contains atoms 
of scattering nnaterial, some of the gamma rays will be scattered 
into the detector by single collisions and a definite count rate will 
be observed. 

As the numerical density (number of atoms per unit volume) is 
increased, the probability of scattering by single collisions increases, 
and the count rate increases. However, as an increase in numerical 
density interposes a greater number of atoms between the point of 
the first collision and the detector, there is an increase in proba- 
bility that the gamma rays will be scattered away from their path to 
the detector by secondary collisions. This secondary scattering also 
results in significant energy loss to the gamnna rays, and further 
decreases the probability of their ultimate detection. Thus, the 
count rate at first increases with density, reaches a maximum, 
and then decreases with increasing numerical density. The mass 
density of a homogeneous material is proportional to the numerical 
density, so the above-described scattering phenomenon can serve 
as a measure of mass density. 






Flow Measurement by Peak Timing 

In the peak- timing technique, in order to obtain sharply defined 
peaks, the radiotracer is injected quickly at a point close to 
the section in which the velocity is to be timed. The tracer is 
then observed in transit down the stream at two points spaced 
a known distance apart, and in a uniform channel, and the tinne 
of passage of the peak of the tracer wave is determined using two 
submerged detectors, connected usually to a ratemeter and a 
recorder. The measured time interval is divided by the distance 
between the observation points to calculate the linear flow rate. 
If the mean area of the channel between the two points can be esti- 
mated or calculated, the volunne flow rate nnay be determined. 

Accurate results can only be obtained with the peak timing tech- 
nique for highly turbulent flow with effectively a flat velocity pro- 

Flow By Dilution 

The dilution method utilizes the fact that the concentration of tracer 
in a stream resulting from the continuous bleeding at a known rate 
of a tracer into the stream will be inversely proportional to the 
relative flow rates of the streann and the bleeder, if the tracer 
uniformly mixes with the flowing liquid. The concentration of the 
tracer in the stream can be deternnined by meeisuring either the 
beta or gamma activity in samples taken from the stream or by 
using a detector submerged in the stream. 

The disadvantage of the dilution technique is that it requires uniform 
mixing, which involves injecting across the total surface area of the 
flowing fluid and usually mixing the fluid in a pump. 

Flow by Total Count 

The total count method is based on the measurement of the total 
number of counts from the tracer as it flows past a detector. 


The total count bears a simple inverse relation to the flow rate 
and this property makes it useful for measuring flow rates in any 
type of flowing system for which a calibration constant can be 

In the total count method, a measured quantity (A) of radiotracer 
is introduced into the flowing stream; a counter fixed in, or near, 
the stream some distance below the injection point accumulates a 
certain number of counts while the tracer is passing. This number 
of counts (N) is independent of the distribution of the tracer along 
the stream, although the tracer must be viniformly distributed 
through the cross section of the stream so that the final count can 
be converted to the flow rate by use of a determined constant. 

The value of N is inversely proportional to the flow rate, Q, since 
a slow-moving stream allows more time for covints to accumulate. 
In addition, the more tracer used, the more counts are recorded. 
Thus N is directly proportional to A, the amount of isotope. 


N = AF or Q = AF 

Q ^ N 

where the proportionality factor F is a constant which is character- 
istic of the isotope, the covmter, and its geometrical relationship 
to the stream. The numerical value of F can be determined in the 
laboratory by exposing a counter to tracer solution in the same 
geometrical arrangement as in the field test, to find the counting 
rate that corresponds to a certain concentration of tracer. Calibra- 
tion for large canals or streams is done in a large tank of known 
volume where the boundary walls are maintained at a distance of 
several feet from the detector. This simulates the infinite condi- 
tions existing in the large body of water. 

The basic flow formula in hydraulics is Q = AV; with isotope mea- 
surement this becomes Q = AF , where 


A = isotope or tracer quantity 

F =» calibration factor,- and 

N = the net total number of counts 

The calibration factor F » R counts/sec , where R = counting rate 

C mci/ft3 

and C ■ concentration of tracer. 


These units can be rearranged so that the dimensions of F are 
those required in the basic equation 

F counts . ft^ . A n:icl « Q ft^ 

mc sec N counts sec 

In determining leakage rates, the equation can be rewritten 

A -NQ_ 





Alpha particle: 

Beta particle: 


Decay (Radioactive ] 

Decay constant; 

The process of artificially inducing radio- 
activity in a stable element, usually by bom- 
barding with neutrons. 

A basic form of radioactivity consisting of 

2 protons and 2 neutrons, hence identical with 

the nucleus of the helium atom. 

A negatively charged elementary particle 
identical to the electron. A basic form of 

The quantity of a radioactive substance having 
a radiation emission equal to that of one gram 
of radium, symbol Ci. A millicurie (MCi) is 
one -thousandth of a curie. 

The process of nuclear disintegration, by which 
an atom seeks stability. It is characterized by 
emission of particles (e. g. alpha or beta) or 
electromagnetic radiation. 

An expression of the rate of radioactive decay 
of a substance. 


Evapotranspiration ; 

Gamma ray ; 

An elementary particle carrying one vuiit of 
negative electric charge and usually considered 
as orbiting around the atomic nucleus. Electrons 
determine the chemical behavior of the elements. 

The quantity of water transpired by plants, 
retained in plant tissue, evaporated from plant 
foliage fronn surrounding surfaces and from adja- 
cent soil, in a specified time period. Usually 
expressed in depth of water per unit area. As 
used here, evapotranspiration is synonymous 
with consumptive use. 

A penetrating fornn of radiation originating in 
the nucleus of some atoms during radioactive 
decay. Equivalent to high energy X-ray. 


Isotope ; 

Neutron ; 
Nucleus ; 

Proton : 


Radioisotope ; 
Scintillation counter; 


One of two or more forms of an element having ' 
the samie atomic number, identical in chemical 
behavior but differing in atomic weight. 

An uncharged elementary particle contained 
within the nucleus of all atoms except hydrogen-L 

The core of an atom around which the electrons 
revolve. It is composed of protons and neutrons 
and has a positive charge equal to the nxunber of 

An elementary particle in the atomic nucleus, 
carrying one unit of positive electric charge. 
Mass is approximately that of the neutron. 

The spontaneous disintegration of unstable atomic 
nuclei accompanied by the emission of radiation 
- alpha particles, beta particles, or gamma raya. 

Radioactive isotopes of chemical elements. 

An instrumient that detects and measures ion- 
izing radiation by means of light flashes induced 
in certain materials called phosphors. The 
flashes are converted to electrical inapulses 
which may be counted by a meter. 

An isotope of hydrogen having atomic mass 3. 





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