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Seasonal Monitoring Cruise At The
Western Long Island Sound Disposal Site
August 1986



Disposal Area
Monitoring System
DAMOS




Contribution 61
March 1988



US Army Corps
of Engineers

New England Division



DOCUMENT
LIBRARY

Woeds Hole Oceanography
Institution




DOCUMENT v
LIBRARY

Woods Hole Oceanographic
institution





SEASONAL MONITORING CRUISE






AT THE WESTERN LONG ISLAND SOUND






DISPOSAL SITE






AUGUST 1986






CONTRIBUTION #61






11 JANUARY 1988






Report No.
SAIC - 87/7500&C61






Contract No. DACW-86-D-0004
Work Order No. 2






Submitted to:






Regulatory Branch

New England Division

U.S. Army Corps of Engineers

424 Trapelo Road

Waltham,MA 02254-9149




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Submitted by:




~i^= Lr)
I

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Science Applications International Corporation

Admiral's Gate

221 Third Street

Newport, RI 02840

(401) 847-4210






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JS Arm)


Corps



New England Division



TABLE OF CONTENTS

Page

1 . INTRODUCTION 1

2.0 METHODS 1

2 . 1 Bathymetry and Navigation 1

2.2 REMOTS® Sediment Profile Photography 2

2.3 Sediment Sampling and Analysis 3

2.4 Benthic Community Analysis 3

2 . 5 Body Burden Analysis 4

3 . RESULTS 5

3 . 1 Bathymetry 5

3.2 REMOTS® Sediment-Profile Photography 6

3.3 Sediment Characteristics 8

3.4 Benthic Community Analysis 9

3.5 Body Burden Analysis 10

4.0 DISCUSSION 11

4.1 Bathymetry 11

4.2 REMOTS® Sediment-Profiling 11

4.3 Sediment Characteristics 14

4 . 4 Benthic Community 15

4 . 5 Body Burden Analysis 16

5.0 CONCLUSIONS 17

6.0 RECOMMENDATIONS 19

7.0 REFERENCES 19

FIGURES
TABLES



LIST OF FIGURES



Figure 2-1. The Western Long Island Sound Disposal Site.

Figure 2-2. REMOTS® stations occupied during the 1986 survey
of the WLIS disposal area.

Figure 3-1. Contoured bathymetric chart of WLIS, August 1986.

Figure 3-2. Contoured bathymetric chart of WLIS, October 1985.

Figure 3-3. The distribution of grain-size major modes.

Figure 3-4. The distribution of sand and sand layers in the
survey area.

Figure 3-5. A REMOTS® image from station 4-G showing both
surface and subsurface sand layers.

Figure 3-6. The distribution of dredged material in the WLIS
area.

Figure 3-7. A REMOTS® image from station 5-E showing a low-
reflectance dredged material layer overlying a
high-reflectance pre-disposal interface.

Figure 3-8. A benthic process map showing features indicative
of bottom disturbances.

Figure 3-9. A REMOTS® image from station 5-F showing reduced
sediment patches at the interface.

Figure 3-10. A REMOTS® image from station 3-D showing a methane
gas pocket at depth in sediment.

Figure 3-11. Freguency distributions of boundary roughness
values at WLIS and WLIS reference.

Figure 3-12. Freguency distributions of mean RPD depths at WLIS
and WLIS reference.

Figure 3-13. The distribution of RPD depths.

Figure 3-14. The distribution of infaunal successional stages.

Figure 3-15. The freguency distribution and Organism-Sediment
Index values at WLIS and WLIS reference.

Figure 3-16. The distribution of Organism-Sediment Index
values.



List of Figures
(continued)

Figure 4-1. REMOTS® images from station 6-H showing recently
deposited dredged material and from station 3-D
and WLIS Reference showing relict dredged material
layers.



LIST OF TABLES



Table 2-1. Comparison of REMOTS® Grain-Size Major Mode
Estimates with Conventional Sediment Analyses

Table 2-2. The REMOTS® Organism-Sediment Index is Arrived at
by Summing the Subset Indices Below

Table 2-3. Instrument Operating Conditions and Detection
Limits for Metals Analyzed by Flame Atomic
Absorption Spectrometry

Table 2-4. Instrument Operating Conditions and Detection
Limits for Metals Analyzed by Graphite Furnace
Atomic Absorption Spectrophotometry

Table 2-5. Replicate Analysis of Pitar Samples and NRC
Lobster Hepatopancreas Tissue to Determine
Analytical Precision

Table 3-1. Chemical Analysis of Sediment Collected at WLIS
Disposal Site, August 1986

Table 3-2. Physical Characteristics of Sediment from the
Biological Samples, WLIS Disposal Site, August
1986

Table 3-3. Visual Descriptions of Biological Sediment Samples
Collected at WLIS, August 1986

Table 3-4. Benthic Community Analysis of Sediment Collected
at WLIS, August 1986

Table 3-5. Summary of Totals of Species and Individuals Among
Major Taxa Collected at Western Long Island Sound
Disposal Site, August 1986

Table 3-6. Trace Metals (Dry Weight) in Body Tissues of
Nephtys Collected at WLIS Disposal Site, August
1986

Table 3-7. Trace Metals (Wet Weight) in Body Tissues of
Nephty s Collected at WLIS Disposal Site, August
1986

Table 3-8. PCB Concentrations in Nephtys Collected at WLIS
Disposal Site, August 1986

Table 4-1. Comparison of REMOTS® Data from the August 1986
and October 1985 Surveys at WLIS



List of Tables
(continued)

Table 4-2 Comparison of Chemical Analysis of Sediment
Collected in Long Island Sound

Table 4-3 Comparison of Chemical Analysis of Nephtys
Collected in Long Island Sound



SEASONAL MONITORING CRUISE

AT THE WESTERN LONG ISLAND DISPOSAL SITE

AUGUST 1986



1.0 INTRODUCTION

During the period 7 August to 13 August 1986, field
operations were conducted at the Western Long Island Sound
Disposal Site to provide information related to the fates and
effects of past dredged material disposal operations. The field
operations included precision bathymetric surveys, sediment-
profile photography (REMOTS®) , and sediment sampling for
chemical, physical and benthic community analyses. The primary
objectives of this study were to:

■ Determine if management controls initiated by the New
England Division, Corps of Engineers have minimized
dispersion of the disposed material and environmental
impacts at the site;

■ Collect baseline data on body burden levels of selected
contaminants for the local benthic fauna within the
disposal site for comparison with future monitoring
studies.

The Western Long Island Sound (WLIS) disposal area is
located 2.5 nautical miles north of Lloyd Point, NY between two
previously used disposal sites designated as the Stamford and
Eatons Neck disposal grounds. Currents in the area are known to
flow generally in an east-west direction with maximum tidal
velocities on the order of 25 cm/sec. The wave climate at the
site is controlled primarily by the fetch distance, which is only
significant in an easterly direction. SAIC's baseline sampling
of the WLIS area (January 1982) found that the depth in the
center of the site was approximately 32 meters and that the
sediments consisted primarily of fine silts and clays. Disposal
operations have taken place at the WLIS disposal site since 1982
depositing an average of 153,000 m 3 (200,000 yd 3 ) of dredged
material annually.

2 . METHODS

2.1 Bathymetry and Navigation

The precise navigation reguired for all field
operations was provided by the SAIC Integrated Navigation and
Data Acguisition System (INDAS) . A detailed description of INDAS
and its operation can be found in Contribution #60 (SAIC, 1986a) .
Positions were determined to an accuracy of ±3 meters from ranges
provided by a Del Norte Trisponder System. Shore stations were



established over known benchmarks at Eatons Neck Light and the
Norwalk Harbor Power Plant.

The depth was determined to a resolution of 0.1 feet
(3.0 cm) using a Raytheon DE-719 Precision Survey Fathometer with
a 2 08 kHz transducer. The fathometer was calibrated with a bar
check at fixed depths below the transducer before the survey
began. A Raytheon SSD-100 Digitizer was used to transmit the
depth values to the SAIC computer system. Survey lanes were run
east and west at 25 meter lane spacing over an 800 by 800 meter
area centered around the WLIS "A" mound and including the "B" and
"C" mounds (Figure 2-1) . This lane spacing provides good
resolution for subsequent data analysis and the production of
detailed depth contour charts.

Analysis of the bathymetric data corrects the raw depth
values to Mean Low Water by adjusting for ship draft and for
tidal changes for the duration of the survey. All data points in
terms of depth and position are checked for unreasonable values
due to any malfunctions with the peripheral instrumentation
(navigation or bathymetry) so that the final contour plots will
not contain errors.

2 . 2 REMOTS® Sediment Profile Photography

The 198 6 WLIS REMOTS® survey was conducted to map the
distribution of dredged material and to evaluate benthic habitat
conditions and the process of recolonization in the survey area.
In 1985, REMOTS® surveys were conducted at WLIS in August (normal
survey area) and in October (a post-hurricane "Gloria" survey
limited to the vicinity of the three disposal mounds) .

REMOTS® images were taken with a Benthos Model 3731
Sediment-Profile Camera (Benthos, Inc. North Falmouth, MA) . The
REMOTS® camera is designed to obtain in-situ profile images of
the top 15-20 cm of sediment. A detailed description of REMOTS®
camera operation and image analysis is presented in DAMOS
Contribution #60 (SAIC, 1986a) .

The WLIS 1986 REMOTS® sampling grid consisted of a 63
station orthogonal grid (7x9) with stations equally spaced 100
meters apart (Figure 2-2) . Three replicate images were obtained
at each station. In addition, twenty REMOTS® images were
obtained at the WLIS Reference station (40°59.70N, 73°27.75W).
Of the three REMOTS® replicate images obtained at each station,
one was analyzed for this report and two were archived for
possible future analysis. Twenty replicate images from WLIS
Reference were analyzed for this report.



2.3 Sediment Sampling and Analysis

Triplicate sediment samples were collected at the WLIS
"A" disposal mound and the Reference station using a 0.1 m 2
Smith-Mclntyre Grab Sampler. Six polycarbonate plastic core
liners (6.5 cm ID) were pushed into the sediment grab sample and
extracted; the six cores were combined and placed into bags for
subsequent chemical and physical analysis by the NED laboratory.
The top 2 cm of the cores were bagged for separate analysis to
determine whether the surface sediment was relatively more or
less contaminated than the deeper sediment due to the desorption
of contaminants or the deposition of cleaner material. The
samples were kept cold and returned to the NED laboratory where
they were stored at 4°C until analyzed. Parameters measured
included grain size, trace metals, and several organic
constituents .

Sediment analyses were conducted using methods
described by the U.S. Environmental Protection Agency (Plumb,
1981) . Mercury analysis was performed using acid digestion and
cold vapor atomic absorption spectrophotometry; arsenic analysis
was accomplished using acid digestion and gaseous anhydride
atomic absorption spectrophotometry. The other trace metals (As,
Pb, Zn, Cr, Cu, Cd, and Ni) were analyzed using acid digestion
and flame atomic absorption spectrophotometry.

Carbon, hydrogen, and nitrogen analyses were conducted
with an autoanalyzer using a combustion technique. Oil and
grease measurements were made by extracting the sediment with
freon and then analyzing the freon by infrared spectrophotometry.
PCBs were extracted with hexane and also analyzed by electron
capture gas chromatography.

2.4 Benthic Community Analysis

Quantitative benthic samples were obtained with a
Smith-Mclntyre grab at the center of the WLIS "A" mound and the
Reference station. Five sediment samples were collected and
sieved onboard the research vessel through nested 2 and 0.5mm
mesh screens. The material retained on the sieves was preserved
with buffered formalin for later sorting and identification in
the laboratory. Only three of the samples from each of these
stations were analyzed while the remaining two were archived for
future reference if necessary. A small subsample of each grab
was collected for grain size analysis by the NED laboratory using
a 3.0 cm inner diameter core tube. A visual description of each
sediment grab was recorded prior to sieving. In the laboratory,
benthic samples were stained with 0.2% rose bengal and sieved on
1.0 and 0.1 mm screens immersed in water. All samples were
analyzed under the supervision of Mr. Sheldon Pratt at the
University of Rhode Island.



The samples collected at the center of the "A" mound
had a large volume of homogeneous organic detritus and a large
number of polychaetes and polychaete fragments in the fine
low-density fraction. Following a technique used with similar
samples from the EPA/COE Field Verification Program, this
fraction was divided with a plankton splitter and one-half
counted. Because of the large numbers of polychaetes recovered
and the homogeneity of the samples in terms of species
composition, one half was considered to give an adequate
representation of the assemblage present and is the basis of the
counts given here. The remaining half was sorted and counted to
provide a check on the technique for possible inclusion in future
WLIS monitoring plans.

Organisms were identified to species in most cases.
Individuals from all fractions were combined during counting.
All individuals were stored in 70% alcohol. Sieve residues were
described in laboratory notes and discarded. A combined
reference collection was made of all species found in 1986
Central and Western Long Island Sound disposal site samples and
is being maintained at the University of Rhode Island, Graduate
School of Oceanography.

2.5 Body Burden Analysis

The test organisms for body burden analysis were
collected at the Reference station and at the WLIS "A" mound with
the Smith-Mclntyre grab. Sediment was sieved through a 2mm mesh
and the deposit-feeding organisms (the polychaete Nephtys incisa)
were isolated and placed in seawater at ambient temperature.
Sufficient biomass was collected for triplicate analyses. The
animals were allowed to purge their gut contents for 2 4 hours
before they were frozen and transported to the laboratory for
chemical analysis. The polychaetes were analyzed for eight trace
metals and PCBs. These analyses were conducted by the SAIC
laboratory in La Jolla, California. A detailed description of
the methods used for the analysis of the polychaete tissue can be
found in DAMOS Contribution #60 (SAIC, 1986a) .

The PCB analyses were quality assured by measuring the
recovery of a surrogate compound (dibutylchlorendate) in each
sample. The recovery of this compound was 62% ±9 for the Western
Long Island Sound Disposal Site samples.



3 . RESULTS

3 . 1 Bathymetry

The minimum depths for the three disposal mounds "A" ,
"B", and "C" (Figure 3-1) are 29.25, 32.5, and 27.75 meters,
respectively. These minimum depths were found during the October
1985 survey (Figure 3-2) to be 29.25, 32.5, and 28.5 meters,
respectively. This change in bottom topography at mound "C" was
the result of disposal operations occurring there between 3
October 1985 and 8 August 1986. Tabulation of scow logs for this
period indicate that approximately 73,23 cubic meters (95,730
cubic yards) of dredged material were deposited at or near the
buoy location. The scow logs also indicate that individual scow
loads were dumped up to 2 00 meters from the buoy in all
directions although the average distance to the buoy was closer
to 50 meters. Comparison of Figures 3-1 and 3-2 reveals a
significant decrease in depth at mound "C" as well as the west
flank of "C" and the northeast flank of mound "A". These areas
are well within the scope of the recent disposal operations.

Volume difference calculations conducted for the
October 1985 and August 1986 surveys estimated the amount of
dredged material deposited to be approximately 35,700 cubic
meters. Much of the large difference in this volume estimate
from the scow log estimate (7 3,230 m 3 ) can be attributed to the
methods of estimation. The scow log estimates are derived from
the draft of the loaded scow. The scow typically holds a large
volume of water collected with the dredged material. This leads
to an overestimate of the total amount of material. The volume
difference calculations are based on acoustic measurements that
can reliably detect differences in depth of approximately 10-15
cm. The amount of material at the flanks of the mound in layers
less than this can be significant and therefore causes an
underestimate of dredged material deposited. This effect can be
more pronounced when environmental factors, such as weather,
reduce the positioning capabilities of the disposal scows. In
addition, the effects of the loss of interstitial water from the
dredged material during descent and compaction once on the bottom
will contribute to the difference in volume estimates (see
Section 4.1 for further discussion).

To determine the significance of this estimated deposit
of material, the statistical error of this estimate was
calculated for the WLIS survey area. A detailed description of
the calculations reguired to determine this error and the 95%
confidence limits around it can be found in DAMOS Contribution
#60 (SAIC, 1986a) . For the present volume difference
calculations of the 800 x 800 m survey area, the standard error
was determined to be 6720 m 3 . To insure the reliability of this
estimated volume difference, 95% confidence limits were
calculated and resulted in a range of 22,530 to 48,870 m 3 . This



calculation simply implies that the actual (and unknown) volume
difference will occur within these limits with a probability of
0.95.

3 . 2 REMOTS® Sediment-Profile Photography

As observed in previous REMOTS® surveys within the WLIS
disposal site, most of the survey area was dominated by silt-clay
(> 4 phi) sediments (Figure 3-3) . However, a cluster of 6
stations on and east of mound "C" consisted of very fine, fine,
and medium sands. Figure 3-4 shows the distribution of sandy
sediments across the survey area. Distinct sand layers, either
at the surface or buried, were evident throughout the northern
and eastern half of the region (Figure 3-5). Mounds "A" and "B",
composed predominately of silt-clay, also exhibited some near-
surface layers of sand. Based on this distribution, the sands
appear to represent dredged material deposited since the last
complete survey of this area in August 1985. This inference is
also supported by the lack of sand layers in images from the
western portion of the survey area and from the WLIS Reference
station. All replicates collected at the WLIS Reference station
exhibited a major mode of silt-clay (> 4 phi) .

Dredged material layers (Figure 3-6) deposited since
1985 were readily detected when dredged material thickness was
less than the prism penetration depth (20 cm) . This was because
the relatively high-reflectance, pre-disposal interface was
evident below the low-reflectance dredged material (Figure 3-7) .
This high-reflectance material could be either natural bottom or
previously deposited dredged material that had developed a deep
RPD layer. The pre-disposal interface was not evident in many of
the images from the region around disposal mound "C" indicating
that dredged material layers were at least 2 cm or greater
throughout this area. Overall, dredged material was widespread
in the area surveyed. Only the southern portion of the site
lacked readily discernible dredged material layers.

At the Reference station, thirty-five percent (7 of 20)
of the images showed subsurface low-reflectance layers overlying
high-reflectance sediments. These layers do not sharply contrast
with adjacent sediments and are generally discontinuous. They
are inferred to represent relict dredged material (i.e., material
disposed of a number of years ago) . Recently deposited dredged
material would be expected to contrast more sharply with the
buried pre-disposal interface. Similar dredged material layers
were observed at the Reference station in 1985 and 1984. At
those times, it was also concluded that this material represented
relict dredged material deposited in an historically-used
disposal site in that area (Eatons Neck) . REMOTS® images were
not obtained at the WLIS reference site prior to 1984.



A process map of the survey area shows the distribution
of features which are indicative of bottom disturbance (Figure 3-
8) . For example, many stations showed the presence of low
reflectance (black) sediment at, or near, the sediment surface.
This reduced sediment appears to have its origins from below the
high reflectance (ferric hydroxide) bioturbated zone as either a
layer or discrete mud clasts (Figures 3-7 and 3-9) . Oxidized mud
clasts were also present in many images. Surface patches of
reduced sediment (which were also observed in the August 1985
WLIS survey) were likely produced by predator excavation and/or
bottom scour. The depth of excavation or scour need not be great
to expose this reduced material to the interface because RPD
depths are shallow (< 2.0 cm) over much of the area. Methane gas
pockets were observed at depth in the sediment at station 3-D
(Figure 3-10) . The presence of methane is an indication of high
sediment oxygen demand (SOD) . Surface shell lag deposits,
produced by physical bottom scour, were observed in 5 images. In
general, evidence of small-scale physical and biogenic bottom
disturbance was widespread. This is similar to the pattern
observed during the post-"Gloria" REMOTS® survey in October 1985.
The relative frequency distributions of surface boundary
roughness values at the WLIS survey area and WLIS Reference are
shown in Figure 3-11. The major mode was 0.80 for both regions.
This represents an increase in small-scale surface roughness
since August 1985 when the major modal value was 0.4 cm. This
may reflect the impacts of Hurricane Gloria on the region.

The mean apparent Redox Potential Discontinuity (RPD)
frequency distribution for the survey area (Figure 3-12) is
bimodal with modes centered at 1.0 cm and 3.0 cm. The mean RPD
depth was 2.16 cm. The WLIS Reference RPD distribution is skewed
right with the major mode at 1.0 cm, and a mean value of 0.59 cm.
RPD depths at WLIS Reference were significantly shallower than
RPD depths at the survey area (Mann-Whitney U-test, p < 0.001).
This pattern is noteworthy and suggests that the "disturbance"
factors affecting the WLIS Reference station were more severe
than the effects of the dredged material disposal operations
occurring within the WLIS survey area. At the WLIS survey area,
RPD depths have shallowed significantly since August 1985 (ANOVA,
p = 0.004); suggesting an increase in oxygen depletion in the
region. The mapped distribution of mean RPD depths is shown in
Figure 3-13. The hatched areas exhibited RPD values greater than
3 cm. In general, these areas were restricted to the edge of the
survey area. Most of the region was represented by RPD values
between 3 and 1 cm. Based on past experience, values less than 1
cm represent highly stressed habitats. The largest highly-
stressed area extended N-S through the area occupied by mounds
"A" and "C" ; this likely reflects the influence of recent
disposal operations. Another area of low values existed adjacent
to mound "B".



The location of the three disposal mounds appears to
"straddle" regions of both Stage I and Stage I-III successional
seres (Figure 3-14) . Stage III seres occurred in three large
patches in the eastern, southern, and north-central portion of
the survey area. Comparison of Figures 3-14 and 3-13 reveals a
poor correspondence between Stage III seres and deep RPD's. This
pattern may indicate that a retrograde successional condition was
being caused by reduced rates of bioturbation (possibly due to
seasonal hypoxic conditions) . About half of the WLIS -survey area
stations and 70% of the WLIS Reference replicates exhibited a
Stage I assemblage. Again, this pattern suggests that, overall,
the WLIS Reference station was more highly stressed than the
active disposal area. In August 1985, the distribution of Stage
III seres was much less widespread in the eastern portion of the
region.

Based on the results of past REMOTS® surveys, Organism-
Sediment Index (OSI) values of +6 or less are considered to
indicate that the bottom is stressed or has experienced recent
disturbance (erosion, dredged material disposal, hypoxia, or
demersal predator foraging) . The polymodal OSI frequency
distribution of the WLIS survey area (Figure 3-15) indicates a
mosaic of past disturbances (the major mode at 6 and 7,
subordinate modes at 3 and 9) . The WLIS Reference site had a


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Online LibraryUnited States. Army. Corps of Engineers. New EnglaSeasonal monitoring cruise at the Western Long Island Sound Disposal Site, August 1986 → online text (page 1 of 4)