Monitoring cruise at the Boston Lighthouse disposal site, August 1994

PEMY NE PAMDS
Covet, te 112

Monitoring Cruise
at the Boston Lighthouse Disposal Site,
August 1994

Disposal Area
Monitoring System
DAMOS

Ta ea
DISPOSAL AREA MONITORING SYSTEM

Contribution 113
August 1996

US Army Corps
of Engineers
___ New England Division

Ge
| [SF
| Derg

| no. HZ

Form approved
REPORT DOCUMENTATION PAGE

Public reporting concern for the collection of information is estimated to average | hour per persons inculding the time for reviewing
instructions, searching exsisting data sources, gathering, and measuring data needed and correcting and reviewing the collection of
information. Send comments regarding this burden estimate or any other aspect of this collectikon of information includin
suggestions for redueiie this burden to Washington Headquaters Services, Directoriate for Information Observations and Records,
Pas Jefferson Davis Highway, Suite 1204, Arlington VA 22202-4302 and to the Office of Management and Support.

1. AGENCY USE ONLY (LEAVE BLANK) 2. REPORT DATE 3. REPORT TYPE AND DATES
August 1996 Final Report

4. TITLE AND SUBTITLE

MONITORING CRUISE AT THE BOSTON LIGHTSHIP DISPOSAL SITE, AUGUST 1994
6. AUTHORS

Ed DeAngelo

7. PERFROMING ORGANIZATION NAME(S) AND ADDRESS(ES) i8. PERFORMING

6. FUNDING NUMBERS

Science Applications Intenational Corporation ORGANIZATION REPORT
221 Thrid Street
Newport, RI 02840 SAIC No. 328

9. SPONSORING/MONITORING AGENCY NAMES(S) AND ADDRESS(ES)
US Anny Corps of Engineers-New England Division
424 Trapelo Road
Waltham, MA 02254-9149

10. SPONSORING/
MONITORING AGENCY

DAMOS Contribution
Number 113

11, SUPPLEMENTARY NOTES Avaiable trom :

424 Trapelo Road
Waltham, MA 02254-9149

12a. DISTRIBUTION/AVAIABILTY STATEMENT 12b. DISTRIBUTION CODE
Approved for public release; distribution unlimited

13. ABSTRACT

Science Applications International Corporation (SAIC) conducted a reconnaissance REMOTS® sediment-
profile and plan view photographic survey of the Boston Lightship Disposal Site (BLDS) from 9 to 11 August 1994. From the
1940’s to 1976, when disposal stopped at BLDS, a majority of the Boston area’s dredged material and other debris had been
released at this site. The last recorded disposal at this site was in 1976 when about 8,000m3 were disposed. The REMOTS®
sediment-profile and plan view photographic stations were located to examine possible historic dredged material that had been
identified in a 1991 side-scan sonar survey of the area. The 1994 surveys were conducted as part of a long-term effort to examine
historical disposal areas to determine whether remediation activity is recommended. The assessment of the REMOTS® and plan
view data, in conjunction with the 1991 side-scan results, determined that remediation at the site was not necessary.
Recolonization of old dredged material has been extensive. The benthos in the areas sampled was populated by a diverse
community composed of Stage II and Stage III organisms representing a healthy benthic habitat with OSI values *6. No difference
was observed between the historic dredged material and the ambient sediment. In light of the healthy benthic habitat, only
periodic monitoring is recommended. Sediment samples were collected at BLDS in 1994. They were archived and are available
for analysis.

The REMOTS® sediment-profile and plan view photographic surveys were also conducted to gather information
on the area's sedimentary environment. This information would determine if the BLDS was suitable to potentially receive dredged
material from the Boston Harbor Navigation Improvement Project and Berth Dredging Project. The 1991 side-scan sonar survey
had mapped areas of circular or track-like dredged material patterns at the site. The use of the area for dredged material disposal
was consistent with its characterization as depositional or nonerosive (Knebel 1993). By focusing on the areas of dredged material
disposal with the REMOTS® sediment-profile and plan view photographic survey, the reconnaissance effort produced no evidence
to preclude the future use of BLDS for dredged material disposal. The major modal grain size was the silt/clay size class (>4 phi)
with very fine sands found in the surface sediments. Evidence of sediment resuspension was limited primarily to winnowing of
silts/clays from surface sediments.

The assessment of BLDS was efficiently accomplished by basing the REMOTS® sediment-profile and plan
view photographic survey on the results of the previous side-scan survey. The combined data sources provided a broad picture of
the status of the historical dredged material which has been at the disposal site for more than 20 years. Based on the 1994 survey
results, remediation is not necessary for BLDS, and the depositional environment does not preclude its use as a disposal area.

14. SUBECT TERMS

. : : : : : 15.NUMBER OF PAGES
Boston Lightship Disposal Site (BLDS) , Boston Harbor Improvement Project , benthic habitat,

Remote Monitoring of the Seafloor (REMOTS) , dredged material, nonerosive or depositional 16. PRICE CODE

17. SECURITY CLASSIFICATION OF REPORT | 18. SECURITY CLASSIFICATION 19. SECURITY CLASSIFICATION — 20.LIMITATION OF
UNCLASSIFIED OF THIS PAGE OF ABSTRACT ABSTRACT

6

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MONITORING CRUISE AT THE
BOSTON LIGHTHOUSE DISPOSAL SITE
AUGUST 1994

CONTRIBUTION #113

August 1996

Report No.
SAIC No. 328

Submitted to:

Regulatory Division
New England Division
U.S. Army Corps of Engineers
424 Trapelo Road
Waltham, MA 02254-9149

Prepared by:
Ed DeAngelo

Submitted by:
Science Applications International Corporation
Admiral's Gate
221 Third Street
Newport, RI 02840
(401) 847-4210

US Army Corps
of Engineers
New England Division

PRO terion

z teh
aa
fea g. SANTO ees el

a

MONITORING CRUISE AT THE HISTORIC
BOSTON LIGHTSHIP DISPOSAL SITE
AUGUST 1994

24 July 1996

Contract No. DACW33-93-D-0002
Work Order 21, Task 2
SAIC Report No. 328

Submitted to:

New England Division
US Army Corps of Engineers
424 Trapelo Road
Waltham, MA 02254-9149

Prepared by:
Ed DeAngelo

Submitted by:
Science Applications International Corporation
Admiral's Gate
221 Third Street
Newport, RI 02840
(401) 847-4210

De

TABLE OF CONTENTS

Page

LASSE LO} cM Be 24 1S) SI Rn or er ea Nee nea iain in niele ROM Me aan MOT ar Ca ON id OAR Le Se ill

TES MO BIRIG WIRES seers a ics alot carcuee teeretirterS cs ote ten rita yer tote a RP ee iv

Fea CU TGTINIE SS WIV IRE ins oreo wrest Sc clo Grverte ees ia ocean cede ge me Vi

OPN RO DW GTO § ceciacot cad seeee cena arse ater care ene salts seat San ncaa Oe aN eR ee a 1

AOR VAST OD) Sis a0 or eee retina dal iesssstacas acta cea a farty ase ance a ee en van 5

2.1 REMOTS® Sediment-Profile and Plan View Photography ...............0..0.0ec0eeeee 5

DO SCGUMENU SALT IIM Oto rac sg anaes oe aateeoild MASA aS RE Oe RCE aE ee Te ee 5

PO WINAN IS ALL OM tice ie satis Petes Hcciome a ene Tee ye iatecice Vn Rea ns TRH eR 8

She(0) LRLGIS UI] bal CS esa se rotor Ie ace te irene SUM Mee eR A EA ahs te 9

SeUREMOTS='Sediment-Profile Photography, .3.¢.2.-.0...-.-.520- ee eee 9

SalmioPresence:of Dredged*Matenialie gece ca natenn at eene ete. toe ate ener 9

Srl eZ i Gran Sizes DIS (IDUL OM seen oe ec eeies eee eos eee ree 9

3.1.3 Apparent Redox Potential Discontinuity (RPD) Depth.......................... 9

Sled SUECESSIONAlT Stage en ee ceae ta sue re neat meee tc neers aaa ak ee 14

Salo Oreanism-Sediment IMdex eaweaaseeeum neces eens see asa ee yen ee 14

Seca lan VIE Ws NOLO Staph yrs. screen see avec etoae ce ae eae ok Sasa enna oe ntals ee ane 14

ARUP TS @USSIOIN 25 i200 0s alae, ge NU aii tet cater Scuniaat seit sina iyczta ct UO nO na ctaatan DEE 24

4eleihe Sedimentary EnvironmentOr BEDS ies. .cso yee ee sean eee 24

Ae) spresence Om Dredgeds Material awn ueasncnnaessasen casero nes ne een ee ee 26

AS ABenthiCyRECOlOMIZANMOMS sssacn. cece cans ce sce aca ee Toren eae ec eel one Eee ene ID

SR OREONGIEW SION Bee cuut aaa Seb uct wa tne Sete eaters re Mcrtutte emer crag a ears trerti a ee eP 29

ORO PRE BEIRIEIN © ES age 22a sti ne ten diesen Nee h ae deen enna eater eae Ro ac ater RT om Mare ota 30

INDEX

APPENDIX

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Table 2-1.

LIST OF TABLES

Station Target Locations for REMOTS® Sampling at BLDS

Ul

a
‘
a

Figure 1-1.

Figure 1-2.

Figure 2-1.

Figure 3-1.

Figure 3-2.

Figure 3-3.

Figure 3-4.
Figure 3-5.

Figure 3-6.

Figure 3-7.
Figure 3-8.
Figure 3-9.
Figure 3-10.

Figure 3-11.

LIST OF FIGURES

Page
Site location map of the Boston Lightship Disposal Site ........................ 2
The relative locations of dredged material located by side-scan
sonar; 1994 REMOTS® sampling transects; a depositional
sedimentary environment above the 50 m depth contour; and
asproposed ‘disposallocationic. ewene-ccae-ceen ce ene eee ects nie aes eee 4
REMOTS® samphingttransects hectare tsa eee eee ee 6
The number of stations per transect where dredged material was
observed in-the/REMOTS® images eine arse lated ee eee 10
Light gray, high reflectance Boston Blue Clay located at Stations
C3=10i(A)randiC227.\(B) aeseen eee acces ge eda Sicuy hansen 11
Layer of biogenically reworked sediments over dredged material
and large Stage III polychaete feeding in the dredged material layer......... 12
Transect average apparent redox potential discontinuity depths (cm) ........ 13
Example of a thick RPD (4 cm) observed at Station C3-1..................... 15
Surface sediments at BLDS colonized by Stage II
"stick-building" amphipods (Family Podocerdiae; A) and
Stagealll tube-dwelling polychaetes (B) ie... 2. ye eeteene tee renceeet onan ene 16
Water-filled feeding void below the RPD at Station C6-4 ..................... 17
Bioturbating caudate holothurian Molpadia oolitica at Station C2-10........ 18
Transect average Organism-Sediment Index values ...................eeeeeee eee 19
Summary of bottom features observed in plan view photographs............. 20

Possible construction debris—large, sharp-angled, silt-covered
rocks observed in plan view photographs from transects Cl (A)
TNC ACB) eee Sa SALT oak rene Ce ree et ne a es err UM tea ar Tae 22

Iv

LIST OF FIGURES (continued)

Figure 3-12. Heterogeneous distribution of surface polychaete tubes ranging
froma dense\carpet (A):to nearly absent (B) 2220. one oie ses teenct ssc s oneal 23

Figure 4-1. Location of depositional environments in Massachusetts Bay from the
shore*to the 50 my depth: Comtour . i272. eset cecenss dae cee see oe eee eeeee 25

EXECUTIVE SUMMARY

Science Applications International Corporation (SAIC) conducted a reconnaissance
REMOTS® sediment-profile and plan view photographic survey of the Boston Lightship
Disposal Site (BLDS) from 9 to 11 August 1994. From the 1940s to 1976, when disposal
stopped at BLDS, a majority of the Boston area's dredged material and other debris had
been released at the site. The last recorded disposal at the site was in 1976 when about
8,000 m° were disposed. The REMOTS® sediment-profile and plan view photographic
stations were located to examine possible historic dredged material that had been identified
in a 1991 side-scan sonar survey of the area. The 1994 surveys were conducted as part of
a long-term effort to examine historical disposal areas to determine whether remediation
activity is recommended. The assessment of the REMOTS® and plan view data, in
conjunction with the 1991 side-scan results, determined that remediation at the site was not
necessary. Recolonization of old dredged material has been extensive. The benthos in the
areas sampled was populated by a diverse community composed of Stage II and Stage III
organisms representing a healthy benthic habitat with OSI values 26. No difference was
observed between the historic dredged material and the ambient sediment. In light of the
healthy benthic habitat, only periodic monitoring is recommended. Sediment samples were
collected at BLDS in 1994. They were archived and are available for analysis.

The REMOTS® sediment-profile and plan view photographic surveys were also
conducted to gather information on the area's sedimentary environment. This information
would determine if the BLDS was suitable to potentially receive dredged material from the
Boston Harbor Navigation Improvement Project and Berth Dredging Project. The 1991
side-scan sonar survey had mapped areas of circular or track-like dredged material patterns
at the site. The use of the area for dredged material disposal was consistent with its
characterization as depositional or nonerosive (Knebel 1993). By focusing on the areas of
dredged material disposal with the REMOTS® sediment-profile and plan view photographic
survey, the reconnaissance effort produced no evidence to preclude the future use of BLDS
for dredged material disposal. The major modal grain size was the silt/clay size class
(>4 phi) with very fine sands found in the surface sediments. Evidence of sediment
resuspension was limited primarily to winnowing of silts/clays from surface sediments.

The assessment of BLDS was efficiently accomplished by basing the REMOTS®
sediment-profile and plan view photographic survey on the results of the previous side-scan
survey. The combined data sources provided a broad picture of the status of the historical
dredged material which has been at the disposal site for nearly 20 years. Based on the
1994 survey results, remediation is not necessary for BLDS, and the depositional
environment does not preclude its use as a disposal area.

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1.0 INTRODUCTION

The consideration of BLDS as an alternative site for future disposal operations
(Normandeau Associates 1994) and the existence of an extensive data set on observed
dredged material at the site (Schoenherr et al. 1992) provided impetus for the study
described here. A reconnaissance survey of the Boston Lightship Disposal Site (BLDS), a
currently inactive site located 16 nmi east of Boston (Figure 1-1), was conducted under the
Disposal Area Monitoring System (DAMOS) Program as part of a long-term effort to
investigate historical disposal areas. From the 1940s to 1976, when disposal stopped at
BLDS, a majority of the Boston area's dredged material and other debris had been released
at the site. During the late 1960s and early 1970s, BLDS received approximately
2.3 million m° of material dredged from Boston Harbor (Normandeau Associates 1994).
Disposal at the site was directed toward the Dumping Ground (DG) buoy. However, the
buoy location only served as a general guide for the barges and was not used for point
dumping. Although disposal activity was concentrated in an area surrounding the buoy,
material was apparently disposed throughout the site.

Prior to the early 1970s, the oversight of the nature and placement of disposed
materials was less stringent than at present. The US Army Corps of Engineers, New
England Division (NED), has initiated a cooperative effort to investigate historical disposal
sites, whenever possible, to determine existing environmental conditions. One potential
remediative activity might be to use present disposal activities to cover old deposits.

Science Applications International Corporation (SAIC) conducted short (9-11
August 1994) REMOTS® sediment-profile and plan view photographic surveys of small
areas within the disposal area. These areas were deemed likely to contain dredged material
based on a previous side-scan survey. The primary objective of the survey was to explore
the need for dredged material remediation. The relative health of the benthic environment
was determined by the recolonization status of relic dredged material compared to results
obtained from ambient sediment. The secondary objective was to determine if there was
any evidence to preclude future use of the site for dredged material disposal. Small scale
sediment characteristics in the REMOTS® and plan view photographs, in conjunction with
features identified in the side-scan records, were examined to determine if the sedimentary
environment was suitable for future dredged material disposal.

Until recently, little was known regarding the location and nature of the material
that had been disposed at BLDS. In 1991, the US Environmental Protection Agency
(EPA) sponsored a side-scan and Remotely Operated Vehicle (ROV) survey of BLDS.
SAIC supported efforts to locate, identify, and determine the condition of waste containers
in the area (Schoenherr et al. 1992). Interpretation of the side-scan records over a 16 nmi-

Monitoring Cruise at the Historic Boston Lightship Disposal Site, August 1994

GLOUCESTER

ry,

MANCHESTER oy «shore Station

2
[Shore Station NG ‘3 42°30' N
MARBLEHEAD | \@2>
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Figure 1-1. Site location map of the Boston Lightship Disposal Site. The Boston
Lightship Disposal Site is located approximately 16 nmi east of Boston, MA.

Monitoring Cruise at the Historic Boston Lightship Disposal Site, August 1994

area (Figure 1-2) located 469 dredged material targets in addition to 43 potential waste
barrel fields, and 136 debris fields. Dredged material targets generally appeared on the
side-scan records as circular or track-like patterns of sediment with a marked contrast to
the surrounding natural sediments. While the dredged material targets were scattered
throughout the disposal area, high concentrations were located in a ring around the former
DG buoy location and to the south of the buoy beyond the 50 m depth contour. In the
1994 reconnaissance survey, the REMOTS® and plan view photography station locations
corresponded to areas of dense dredged material targets. This sampling scheme supported
the primary objective of the survey by maximizing the probability of collecting data from
relic dredged material where the potential need for remediation would be the greatest.

A secondary objective of the present survey was to characterize the dominant
processes controlling the sedimentary environment and to determine the suitability of the
area for potential future disposal. The area greater than 50 m depth at BLDS has been
suggested as a potential site for future disposal, such as 0.9 million m° of silty maintenance
material from the proposed Boston Harbor Navigation Improvement Project and Berth
Dredging Project (Normandeau Associates 1994). This material would be capped with
approximately one meter of parent material that lies under the silts of Boston Harbor.
Approximately half of BLDS lies below the 50 m depth contour on the slope of Stellwagen
Basin. Based on the sedimentary fabric observed in the REMOTS® and plan view
photographs, it was determined that below the 50 m contour BLDS is primarily a
depositional environment and that there is no evidence to preclude its use for the deposition
of silty dredged material.

Monitoring Cruise at the Historic Boston Lightship Disposal Site, August 1994

EPA SIDE-SCAN SURVEY

42°25'

*

ante)

Dredged Material from
Side-scan Survey
Depositional Area
(Knebel 1993)

42°23.500'
70°38.233'

42°19.550°
70°43.700°

70°40'

42°20'

42°19.550'
70°38.233'

Approximate Proposed
Disposal Location

Figure 1-2.

42°15!

The relative locations of dredged material located by side-scan sonar

70°35'

(Schoenherr et al. 1992); 1994 REMOTS® sampling transects; a depositional
sedimentary environment above the 50 m depth contour (Knebel 1993); and a
proposed disposal location (Normandeau Associates 1994)

Monitoring Cruise at the Historic Boston Lightship Disposal Site, August 1994

2.0 METHODS
2.1 REMOTS® Sediment-Profile and Plan View Photography

The August 1994 REMOTS® sediment-profiling survey was conducted along six
transects labeled C1 through C6. Transects C1, C3, C4, and C5 surrounded the DG buoy,
and transect C2 was south of the buoy in an area of dense dredged material targets. This
allowed us to maximize the potential of encountering dredged material (Figures 1-2 and 2-
1) and to focus on depositional areas determined suitable for future disposal (Normandeau
Associates 1994). Transect C6 was situated in an area where side-scan records did not
contain any targets interpreted as dredged material in order to assess benthic recolonization
on ambient sediments located within BLDS. Two of the transects, Cl and C6, were
oriented north to south while the remainder were oriented east to west. Each transect was
500 m long and consisted of ten stations spaced 50 m apart (a total of 60 stations; Table 2-
1). Two replicate photographs were taken at each station.

Surficial sediments were photographed with a Photosea submersible plan view
camera to permit evaluation of surface features including benthic animals and
sedimentological features. The plan view camera was attached to the REMOTS® camera
frame and photographed the sediment surface prior to camera frame touch-down in order
to record an image of undisturbed sediments.

2.2 Sediment Grab Sampling

Sediment samples were collected with 0.1 m’ van Veen grab sampler at three of the
six transects (C2, C3, and C4) and at the reference area FG-23. Grab samples were
collected at Stations 1, 5, and 10 (Table 2-1) of each transect for a total of nine grabs.
Three replicate samples were collected at the reference area.

Once the grab was brought aboard, four to five subcores were collected for
chemical analysis, and the remaining sediment was saved for benthic community analysis.
The chemistry subsample was composited in a teflon container and subsampled again for
polycyclic aromatic hydrocarbons (PAHs), metals, and grain size/total organic carbon
(TOC) analysis. The PAHs and metal subsamples were each placed in pre-cleaned 110 ml
I-CHEM jars, and the grain size/TOC subsamples were stored in ziplock plastic bags.

The remaining sediment set aside for benthic community analysis was sieved
through a 500 micron screen. The residue was placed in one liter nalgene jars with both
internal and external labels. Each biological sample was fixed in 10% formalin and stained
with rose bengal, an organic stain. Following field collection, all sediment samples,

Monitoring Cruise at the Historic Boston Lightship Disposal Site, August 1994

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Monitoring Cruise at the Historic Boston Lightship Disposal Site, August 1994

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biological and chemical, with the proper chain of custody forms were delivered to the US
Army Corps of Engineers, New England Division (NED) laboratory where the samples
were archived.

2.3 Navigation

Navigation for the survey was provided by an SAIC Portable Integrated Survey
System (PINSS). The PINSS is a PC-based system that receives navigation data,
mathematically weights these signals based on signal strength (via a Kalman filter), and
calculates both the position of the ship and the position error. The PINSS was interfaced
to a Magnavox MX4200 Global Positioning System (GPS) with a Magnavox MX50R
Differential-GPS (DGPS) receiver for vessel positioning with an accuracy of +5 m.

Monitoring Cruise at the Historic Boston Lightship Disposal Site, August 1994

3.0 RESULTS
3.1 REMOTS® Sediment-Profile Photography
3.1.1 Presence of Dredged Material

Dredged material was observed at five of the six transects sampled (Figure 3-1;
Appendix). Dredged material in the REMOTS® photographs appeared in two forms: 1)
dark silty material typically found in dredged material throughout New England and 2)
Boston Blue Clay (Figure 3-2, A and B). Boston Blue Clay, formed from silt and clay
particles in glacial melt water, is a common constituent of material dredged from Boston
Harbor (Camp, Dresser, and McKee, Inc. 1991). In most cases dredged material appeared
as a horizon below a sandy mud layer of reworked sediments several centimeters thick and
extended below camera penetration (Figure 3-3). However, in two instances (Figure 3-2,
A and B) the sandy layer was very small or absent, and dredged material was near the
sediment-water interface.

Spatial distribution of dredged material was patchy. Dredged material was often
seen in only one replicate per station even though the replicates were only a few meters
apart. The two transects containing the greatest number of stations with dredged material
(six stations) were C3 and C6 (Figure 3-1). Transects C1, C2, and C5 contained two to
three stations with dredged material while none was observed at transect C4.

3.1.2 Grain Size Distribution

Sediment grain size distribution was uniform throughout the area sampled.
Sediments were predominantly silts and clays with a major mode size of >4 phi
(Appendix). With the exception of two stations, C4-2 and 4, grain sizes ranged from very
fine sands (3 phi) to silts and clays (>4 phi). Fine-grained sediments were overlain by a
surface layer of very fine sands in most of the photographs. Stations C4-2 and 3 contained
coarse-grained surface material as large as -1 phi.

3.1.3. Apparent Redox Potential Discontinuity (RPD) Depth

The apparent redox potential discontinuity describes the region in which sediments
change from a surface oxidizing environment to an underlying reducing environment. The
depth of the RPD is determined by the net rate of transport of dissolved oxygen (DO)
across the sediment-water interface, and the rate of consumption of DO in the sediment
column. Mean apparent RPD depths (Figure 3-4), averaged for each transect by station,
were between 1.5 cm and 2.0 cm below the sediment-water interface (Appendix). The

Monitoring Cruise at the Historic Boston Lightship Disposal Site, August 1994

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Monitoring Cruise at the Historic Boston Lightship Disposal Site, August 1994

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Monitoring Cruise at the Historic Boston Lightship Disposal Site, August 1994

Figure 3-3. Layer of biogenically reworked sediments over dredged material and large
Stage III polychaete feeding in the dredged material layer

Monitoring Cruise at the Historic Boston Lightship Disposal Site, August 1994

13

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Monitoring Cruise at the Historic Boston Lightship Disposal Site, August 1994

14

shallowest RPD depth measured was 0.73 cm, and the deepest was 4.76 cm (Figure 3-5).
Because of shallow camera penetration, the RPD was deeper than penetration and could
not be measured in 11 photographs. Of these eleven photographs, prism penetration
ranged from 0.5 to 2 cm in 4 photographs, 2 to 3 cm in 6 photographs, and greater than
8 cm in one photograph.

3.1.4 Successional Stage

Sediments at BLDS contained a relatively robust benthic community. Infaunal
communities were dominated by the Stage II-on-Stage III class. Surface sediments at all
stations were populated by stick-building amphipods (Family Podocerdiae; Figure 3-6, A).
Sedentary polychaete tubes extended above the sediment-water interface at varying
densities throughout the study area (Figure 3-6, B). Below the surface Stage II
community, evidence of an abundant Stage II] community was commonly observed as
burrowing polychaetes (Figures 3-3 and 3-2, B) and/or subsurface feeding voids (Figure 3-
7). Pelletized sediments, indicative of actively feeding infauna, were found near the
sediment-water interface as well as inside feeding voids. Infaunal species were not limited
to polychaetes; a bioturbating caudate holothurian Molpadia oolitica was photographed at
C2-10 (Figure 3-8). In addition to infaunal species, several epifaunal species were
observed including large mud anemones, hydroids, and bryozoans.

3.1.5 Organism-Sediment Index

The REMOTS® Organism-Sediment Index (OSI) is a multiparameter tool used to
evaluate the interaction of infauna and the sediment in which they live. OSI values can
range between -10 and +11 and are based on RPD depth, successional stage, and the
presence of methane associated with anoxic sediments. As there was no indication of low
oxygen conditions, OSI values from BLDS were a function of RPD depth and successional
stage. Values ranged from a minimum station mean of 5 to a maximum station mean of 10
(Appendix). Mean transect OSI values ranged from 6 to 9 (Figure 3-9). OSI values 26
are indicative of relatively healthy sediments. OSI values could not be calculated for
twelve photographs: eleven due to indeterminate RPD depths, and one (replicate C1-7a)
due to indeterminate successional stage. (The plan view photograph for replicate C1-7a
shows the camera frame resting on a rock, restricting penetration.)

3.2 Plan View Photography
The plan view photographs provided useful information about surface sediment

characteristics which were not always discernible from the REMOTS® photographs.
Surface sediments at BLDS were composed primarily of silts and sands (Figure 3-10).

Monitoring Cruise at the Historic Boston Lightship Disposal Site, August 1994

Figure 3-5. Example of a thick RPD (4 cm) observed at Station C3-1
Monitoring Cruise at the Historic Boston Lightship Disposal Site, August 1994

16

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Monitoring Cruise at the Historic Boston Lightship Disposal Site, August 1994

17

we
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Figure 3-7. Water-filled feeding void below the RPD at Station C6-4; note the halo of
oxygenated sediments surrounding the void

Monitoring Cruise at the Historic Boston Lightship Disposal Site, August 1994

Figure 3-8. Bioturbating caudate holothurian Molpadia oolitica at Station C2-10

Momitoring Cruise at the Historic Boston Lightship Disposal Site, August 1994

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Monitoring Cruise at the Historic Boston Lightship Disposal Site, August 1994

21

While the resolution of the plan view photographs did not allow differentiation between
fine sands and silts, sediments containing pebbles, cobble, and rocks were clearly evident.
The plan view photos revealed two rocky areas, one at transect C1 and the other at C4
(Figure 3-11, A and B). The larger rocks at both of these sites were covered with silt and
encrusting bryozoans. Many of the rocks observed had sharp angular edges and were
probably disposed construction debris.

Plan view photographs also provided information on the small scale horizontal
distribution of the benthic community. In the plan view photos, both sedentary infaunal
polychaete tubes and epibenthic species were observed. Infaunal tubes were present at all
six transects. Tube distribution was patchy and rauged from dense mats (Figure 3-12, A)
that carpeted the bottom to absence (Figure 3-12, B). Epifauna observed at BLDS
included mud anemones, seastars, hydroids, gastropods, and bryozoans.

Monitoring Cruise at the Historic Boston Lightship Disposal Site, August 1994

22

Monitoring Cruise at the Historic Boston Lightship Disposal Site, August 1994

(B)

(A)
Figure 3-11. Possible construction debris—large, sharp-angled, silt-covered rocks observed in plan view

photographs from transects C1 (A) and C4 (B)

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Monitoring Cruise at the Historic Boston Lightship Disposal Site, August 1994

24
4.0 DISCUSSION
4.1 The Sedimentary Environment of BLDS

An understanding of the sedimentary environment at BLDS is necessary to
determine if there is evidence to preclude its suitability for dredged material disposal. For
example, the preferred locations for silty dredged material, such Boston Harbor sediment,
have been in low-energy environments where sediment resuspension and transport is
minimal.

BLDS is located between the 40 m and 70 m depth contours on the western slope of
Stellwagen Basin in Massachusetts Bay. The seafloor of Massachusetts Bay can be divided
into three major sedimentary environments: 1) areas of erosion or nondeposition; 2) areas
of sediment reworking, a combination of erosion and deposition; and 3) areas of sediment
deposition (Knebel 1993). The distribution of these sedimentary environments reflects the
dominant processes in operation. Areas in the bay subjected to high-energy (erosional)
conditions tend to be characterized by coarse glacial drift and bedrock outcrops while areas
of lower energy (depositional) are characterized by fine-grained sandy muds (Knebel
1993). Through a compilation of sonographic, photographic, and direct sediment
sampling, Knebel mapped these three sedimentary environments from the Massachusetts
Bay coastline to the 50 m depth contour of the continental shelf. Knebel's maps indicated
that erosional and sediment reworking environments comprise the majority of the shelf
bottom in the Bay. Depositional environments are found primarily in Boston Harbor and
at the 50 m contour of the Basin slope. The transects used in the present survey are all just
beyond the area characterized by Knebel (1993).

Based on Knebel's (1993) sedimentary environment maps, the majority of the
Massachusetts Bay Inner Shelf region is composed of erosional and sediment reworking
environments. However, deeper depositional areas appear along the 50 m depth contour
(Figure 4-1). This depositional zone begins within the southern portion of BLDS (Figure
1-2), but was not mapped in the initial study of Massachusetts Bay. The REMOTS® and
plan view photographs provided some insight about the nature of the sedimentary
environment within BLDS and support the extension of the depositional regime mapped by
Knebel north and eastward into the disposal site.

Grain sizes at BLDS below the 50 m depth contour ranged from very fine sands (3 phi) to
silt plus clay (>4 phi) with a major modal size of silt plus clay. Sediments in depositional
environments of Massachusetts Bay are composed primarily of sandy muds and muddy
sands and have average concentrations of 0.5% gravel, 45.8% sand, and 53.7% silt plus

Monitoring Cruise at the Historic Boston Lightship Disposal Site, August 1994

25

CYayew ' Sar
7°00 70°50 o. - 70°30'W

DEPOSITION

42°30'N

+

‘Unmapped Area

42°10’

10 Kilometers

Location of depositional environments in Massachusetts Bay from the shore

Figure 4-1.
to the 50 m depth contour (from Knebel 1993)

Monitoring Cruise at the Historic Boston Lightship Disposal Site, August 1994

26

clay (Knebel 1993). Following this definition the areas sampled may be described as
depositional environments.

Defining an area as a depositional environment does not preclude the potential for
resuspension of fine-grained particles, but merely implies that the combined result of the
dominating dynamic processes is net sedimentation. The deficiency of silt/clay particles in
the upper centimeter compared to deeper sediments is at least in part due to episodic
resuspension. The smaller fine-grained particles are more easily entrained in bottom
currents and are winnowed from the surface sediments, leaving behind coarser grained
material. Although periodic resuspension may occur during the stormy winter months
(Knebel 1993), there is no evidence of extensive sediment movement that might limit the
future use of this site for dredged material disposal.

4.2 Presence of Dredged Material

The primary purpose for this survey was to examine a historic unconfined disposal
site and attempt to determine if any deleterious environmental conditions still persist nearly
twenty years after disposal activity had ceased. The combined use of side-scan sonar with
REMOTS® sediment-profile and plan view photography allowed the 1994 reconnaissance
effort to be focused on areas where dredged material, and the need for remediation, was
more likely.

Disposal of dredged material at BLDS was widespread with material deposited in
localized patches throughout the site. The highest concentrations of dredged material,
located by side-scan sonar, encompassed the former DG buoy location and extended south
below the 50 m depth contour (Figure 1-2). REMOTS® photographs collected from the
transects surrounding the DG buoy location and to the south confirmed that the side-scan
records were indicative of dredged material deposits (Figure 3-1). However, the presence
of relic dredged material at transect C6, where no dredged material was detected in the
side-scan survey, indicates that limitations exist in the use of side-scan sonar as the only
tool for locating relic dredged material. Side-scan sonar, by detecting changes in the
acoustic signature of the surface sediments, displays patterns that are characteristic of
dredged material disposal. When dredged material is spread over a wide area or buried
beneath the surface, side-scan sonar may not detect it. Dredged material in the regions
surrounding the DG buoy was light gray, high-reflectance, fine-grained Boston Blue Clay
(Figures 3-2 and 3-3). This material may be part of the 2.3 million m? of Boston Harbor
dredged material deposited in the 1960s and 1970s (Normandeau Associates 1994).

Even though fine-grained dredged material was not observed in the REMOTS®
images from transect C4, which was also located in an area of concentrated dredged

Monitoring Cruise at the Historic Boston Lightship Disposal Site, August 1994

Pui

material targets, the plan view photographs revealed areas of cobble and larger sharp-
edged rocks (Figure 3-11). The sharp angularity of the rocks, and their presence at a
known disposal site, suggest that they may be construction debris. More solid evidence
that transect C4 contained construction debris was found while sieving one of the grab
samples. A small rounded piece of concrete with two planar sides was found in the grab
sample from Station C4-5. This small piece probably was bored from a larger slab either
for blasting or attachment of lifting cables.

4.3. Benthic Recolonization

The identification of a dredged material signature on side-scan records, and the
further investigation of the dredged material by REMOTS® sediment-profile photography,
were necessary to determine if remediation was needed. The primary step in determining
if remediation was required at BLDS was to examine the status of benthic recolonization
and compare the dredged material with apparent ambient sediments within the disposal
area. There was no preexisting reference area for BLDS; however, the ambient sediment
at Station C6 should provide a good basis for comparing the effects of dredged material
disposal on the benthic habitat. Information derived from sediment structures was
compiled into the multiparameter REMOTS® Organism-Sediment Index. At BLDS the
OSI value was primarily a function of the successional stage of the populating infauna and
the depth of biogenically enhanced oxygen penetration (RPD).

The most striking evidence for a healthy benthic habitat at BLDS was the abundant
and diverse benthic community. The subsurface sediments were populated by burrowing
polychaetes both large and small as well as other Stage III genera including caudate
holothurians (Figures 3-2, B; 3-3; and 3-8). The surface sediments were dominated by
sedentary, tube-dwelling Stage III polychaetes and by Stage II stick-building amphipods
(Family Podoceridae) (Figure 3-6, A). The presence of Stage II organisms in the surface
sediments is probably from secondary colonization, and not indicative of a recovery from a
recent disturbance. Following disposal activity and the progression of recolonization to a
Stage III community, the Stage III organisms began to feed in deeper sediments. The
movement of the Stage III group out of the upper sediment cleared space for reoccupation
by surface-dwelling Stage II infauna.

In addition to the abundant benthic community, several pieces of information from
the sedimentary structure suggested a healthy benthic habitat has persisted for some time.
Numerous water-filled voids were observed in subsurface sediments (Figures 3-2 and 3-7).
These voids were created by the feeding activity of head-down deposit feeding Stage III
organisms. A halo of oxidized sediments, which surrounded the voids, suggested recent

Monitoring Cruise at the Historic Boston Lightship Disposal Site, August 1994

28

active feeding. In addition, several of the voids contained coarse-grained particles that
were presumably discarded during particle-selective feeding habits (Figure 3-7).

Despite the healthy benthic community at BLDS, the RPD values are relatively
shallow. Normally, the combined activity of the subsurface burrowing Stage III
organisms, the sedentary tube-dwelling polychaetes, and surface-dwelling Stage II infauna
served to transport oxygen into the sediments resulting in relatively deep RPD depths.

' While irrigating their tubes, sedentary tube-dwelling polychaetes pump high dissolved
oxygen concentration seawater out of the tube bottoms directly into the sediments, forcing
a unidirectional upward displacement of interstitial fluid. However, the net diffusion of
dissolved oxygen from seawater injection and subsequent advective porewater transport
will be less where there is high sediment oxygen demand (SOD). With high SOD, oxygen
that is transported across the sediment-water interface is rapidly consumed by microbial
respiration and oxidation reactions. The observed RPD depths of only a few centimeters at
BLDS, combined with a well-established infaunal deposit-feeding community (Figure 3-5),
suggest that BLDS sediments have relatively high SOD.

Monitoring Cruise at the Historic Boston Lightship Disposal Site, August 1994

29

5.0 CONCLUSION

The reconnaissance plan view and REMOTS® sediment-profile surveys identified
areas of historic dredged material at BLDS. The identification of dredged material by
these surveys was accomplished with a low level of effort by focusing on areas targeted for
the presence of dredged material in the side-scan sonar survey of BLDS. However,
dredged material was also found in an area devoid of side-scan sonar targets, and some
areas of side-scan sonar targets did not yield the expected fine-grained dredged material.
Side-scan sonar has a limited ability to locate relic dredged material. This technology is
unable to detect dredged material that does not present a distinct surface acoustic signature.
Even when a distinct surface feature is present, the disposal pattern may be due to rock or
construction debris which is impenetrable to REMOTS®. Based on the results of all
surveys, dredged material at the site was distributed in patches over both large (side-scan
sonar) and small (REMOTS®) horizontal spatial scales.

Sediments which can support the level of recolonization observed at BLDS
generally should not require remediation action, only periodic monitoring (Germano et al.
1994). Twenty years after the cessation of disposal activity, the benthos of BLDS has a
Stage II and Stage III benthic community. The presence of these communities and the
evidence for extensive biogenic reworking of dredged material suggest a healthy benthic
habitat. Chemical analysis of the archived sediment samples is not recommended at this
time for the purpose of evaluating remediation. If the site is designated for additional
disposal, these archived sediments might be analyzed for evaluating baseline conditions.

The depositional environment characterized at BLDS beyond the 50 m contour
shows no evidence to preclude its use for future dredged material disposal. Any
resuspension and transport that may occur is most likely episodic and does not occur
frequently.

Monitoring Cruise at the Historic Boston Lightship Disposal Site, August 1994

30
6.0 REFERENCES

Benoit, J. M.; Torgersen, T.; O'Donnell, J. 1991. An advection/diffusion model for Rn-
222 transport in near-shore sediments inhabited by sedentary polychaetes. Earth Planet.
Sci. Letts. 105:463-473.

Camp, Dresser, and McKee, Inc. 1991. Environmental consequences of utilizing Boston
Blue Clay in landfill closures (Subtask 8.2). (Index and Section 3). Central
Artery/Tunnel Project, Rowars Task Assignment #1 Materials Disposal, Massachusetts
Department of Public Works.

DeAngelo, E. 1993. Quantification of porewater transport rates during hypoxia in Long
Island Sound. University of Connecticut. Unpubl. MS thesis. 117 p.

Germano, J. D.; Rhoads, D. C.; Lunz, J. D. 1994. An integrated, tiered approach to
monitoring and management of dredged material disposal sites in the New England
region. DAMOS Contribution No. 87 (SAIC Report No. 234). US Army Corps of
Engineers, New England Division, Waltham, MA.

Knebel, H. J. 1993. Sedimentary environments within a glaciated estuarine-inner shelf
system: Boston Harbor and Massachusetts Bay. Mar. Geol. 110:7-30.

Martin, W. R.; Sayles, F. L. 1987. Seasonal cycles of particle and solute transport
processes in nearshore sediments: Rn-222/Ra-226 and Th-234/U-238 disequilibrium at
a site in Buzzard's Bay, MA. Geochim. Cosmochim. Acta. 51:927-943.

Normandeau Associates Inc.; US Army Corps of Engineers. 1994. Boston Harbor
navigation improvement dredging, Berth Dredging Project. Draft Environmental
Impact Report/Environmental Impact Statement v1 & 2. Submitted to Massachusetts
Port Authority, MA and US Army Corps of Engineers, Impact Analysis Division,
Waltham, MA.

Rhoads, D. C.; Germano, J. D. 1982. Characterization of organism-sediment relations
using sediment profile imaging: an efficient method of remote ecological monitoring of

the seafloor (REMOTS® system). Mar. Ecol. Prog. Ser. 8:115-128.

Rhoads, D. C.; Germano, J. D. 1986. Interpreting long-term changes in benthic
community structure: a new protocol. Hydrobiol. 142:291-308.

Monitoring Cruise at the Historic Boston Lightship Disposal Site, August 1994

3]

Schoenherr, J.; Cook, J.; Carey, D.; Tracey, G. 1992. Location survey and condition
inspection of waste containers at the Boston Lightship Disposal Ground and
surrounding area. Draft Final Cruise Report for Work Assignment 13, Task 4.
Submitted to US Environmental Protection Agency, Environmental Research
Laboratory-Narragansett, Narragansett, RI.

Monitoring Cruise at the Historic Boston Lightship Disposal Site, August 1994

oes
aie So

uni cit .
me he

7 aH
ee ieee
ml Bust) ba Die

INDEX

anoxia, 19
waste, 1, 6

barge, | winnowing, Vi
benthos, vi, 1, 7, 8, 19, 29

amphipod, 19

epi, 19, 29

polychaete, 17, 19, 29
bioturbation

feeding void, 19, 24
buoy, 1, 6, 7

deposition, vi, vii, 4, 6, 7
dissolved oxygen (DO), 13

feeding void, 19, 24
grain size, vi, 7, 12

habitat, vi
hydroids, 19, 29

methane, 19

organics
polyaromatic hydrocarbon (PAH), 7
total organic carbon, 7

recolonization, vi, 1, 7
reference area, 7
REMOTSS, vi, 1, 4, 6, 7, 12, 19, 20
Organism-Sediment Index (OSI), vi, 19
resuspension, Vi
RPD
REMOTSS®, redox potential discontinuity (RPD),
12, 19, 22, 24

sediment
clay, vi, 12
cobble, 29
resuspension, Vi
sand, vi, 12, 29

silt, vi, 12, 29
sediment sampling

grabs, 7
species

dominance, 6
successional stage, 19

trace metals, 7

pec lles
Elen 2
Sate

boy fetontls o
eaten

TiN aay ay
PVT
ie

APPENDIX

5

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III 2881§ NO II 98815
III 238§ NO II a3eS
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Ill 2381§ NO II 23%S
I] 2881S
III 2381§ NO II 93k
II 9381S
Ill 238§ NO II 9881
III 9881§ NO II 23e1¢
II 281
III 2381§ NO II 298
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III 2381§ NO II 93k
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III 2381$ NO II 2385 vs'l
a8e1S$ wd uoneloued ddu asuey apow/- Joly wd uonenouod ayeol[day uones JyOosuely
JeuOIssa00Nn¢g jelloje yy pospaq aselaAy aZI§ uleI£y 9ZI§ ule‘) aselIAY

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(panuyjuos) Beq ayorg-jaUNIpsg gS LOWAY

sun tyd = azig uleip
aeuluLIa}apu, = LACNI

III 9881§ NO II 98e1§ 907 p< OE v< evs
III 2381§ NO II 9381 9b p< PH p< 161
III 9381$ NO I] 2881S ILTG ES ONS p< 06°S
III 9381S NO I 9881S ; Iv'€ p< OE p< 19°8
Ill 2381§ NO II 9385 CsI p< OE p< 8's
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III 2381§ NO II 2381S ISt p< og v< 7O'L
III 2381§ NO II 3881S 0 PTE “P< OE p< ETL
III 238§ NO II a8eI¢ 0 LOE p< OE p< b6'S
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Ill 2381 NO II 93815 0 (G7 Sale p< 79'L
III 2381§ NO I] 2881S ) Pll p< O1€ p< 6¢$'9
III 2381§ NO II 938815 76'S 6LT p< OE p< 17s
III 2381§ NO II 98815 bO'L GEG Axs ONS p< 60°9
Ill 2381§ NO II 93e1$ 16 COiGaee F< Ole p< 78°8
III 9381$ NO II 9881S ELL rT p< OE p< SUL
Ill 2381§ NO II 9381$ 0 OFZ p< OE b< €v'L
III 2381§ NO If 93815 ai OOF H< OE v< 1€°6
Il] 2881§ NO II 9881S 0 66€ p< OE v< 966 £0
III 9881§ NO II 9881S 0 6b7 = p< “OLE p< €r'Ol I €)
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(panuijuod) ejeq aljo1g-jUIUMIPaS gS LOWAY

sun 1yd = azis ulein
syeuluajapuy = LHCNI

III 9581$ NO II 9981
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II 28e)¢
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III 238§ NO II 9381S
III 9881$ NO II 9381S
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III 9381§ NO II 28e1$

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III 2381§ NO II a8eI1¢
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III 2381§ NO II 38e1§

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(penuljuod) Bed atjo1g-JUIUNIpIg gS LOWAY

sjtun tyd = 921g uleID
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LAGNI LAGNI 0 LAGNI p< O1€ p< 7S'0 q Ol se)
LAGNI III 9881S NO II 93e1S 0 Ndd<ddu p< O¢ v< 9€°7 B Ol co
LT 8988S NO II a8eI1¢ 16°9 SIT p< O¢ v< C79 A) 6 59)
LT 9388S NO II 28R15 0 £60 p< O1¢€ p< 98°8 q 6 se)
8 «TI. 9381 NO II 2881S 0 cS'I p< O1€ p< 89°01 A) 8 <0)
L II 888g NO II e885 0 II p< O1€ p< 8r'8 e 8 se)
9 I] 23e1¢ 0 191 pa og p< 00°6 q L 7(§9)
L Il 8881S NO II 28815 0 pel p< O1€ p< Cr'6 e iL 58)
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9 I] 98815 0 19'T p< O1¢€ p< 6£°6 e 9 se)
6 =I 8981S NO II e88IS 0 €7 p< O¢ t< 00°01 q Ss se)
¢ I] 8881S 0 9€'°I p< O1€ p< 078 e ¢ 0)
9 II 2381S 0 cS p< O1€ p< £68 q v se)
6 III 9381§ NO II 2381S 0 6£°7 p< O1€ p< 678 eB v 0)
8 «I. 93%1§ NO I] 28815 0 79'I p< O1€ p< 0S°6 q € se)
8 «IN 8881S NO II 2381S C6'L ESET p< O1€ t< p9'L e € <0)
8 II 9381S NO I] 2381S 16°8 68°1 p< O1¢€ p< 19°8 q (6 se)
8 TI 9381 NO I] 23815 0 Ll p< O1€ t< 60°6 e (6 58)
8 111 93%1§ NO II 2885 0 98°1 p< O1€ t< a) q I is@)
L111 8881§ NO II 9385 0 8r'1 p< O1€ p< GGL B I se)
ISO as 1S (UID) Uoleloued ddu osuey dspoyy JOleAy (WD) uonelouedg ayeotjday woes yOosuel

[euoIssaoon ellajey] pespaq

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(panuljuod) Be atJo1g-jUsUNIPIg gS LOWAY

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III 2881$ NO II 98eIS
III 2381§ NO II 9881§
III 9381S NO II 9881¢
II 9381S
III 2381§ NO II 93e1¢
II 2381S
III 2881§ NO II 98e1S
III 2381§ NO II 9881
III 2381§ NO II 93e1S
III 9381S NO II 9881
II] 9381S
III 2381§ NO II 93815
I] 2381S
III 9381S NO II 9381S
III 9381S NO II 9881$
II <- ] 9381S
Ill 2381§ NO II 93815
III 2381§ NO II 9381S
III 2881S NO | 938815
III 93e15
38e1$

(panuIjUOd) Bed IJO1g-JUIWIPIS gS LOWAU

stun 1yd = azIs ureIn

aeUIMLS}Opuy = LAYCNI

SO SCO GTO GO tO tO STH T SH OHO VY

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Aa Gs ay
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Meter $ ks

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