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through bathymetric depth differencing (Figure 3-3).

3.1 .2 REMOTS® Sediment-Profile Photography

REMOTS® results from the NL-91 and D/S Mound Complex were used to delineate
the distribution of the CDM on the seafloor and to evaluate the status of the benthic

Monitoring Cruise at the New London Disposal Site, August 2000



16




72 04,200W



\_x 0.5 m contours
MIn : 22.1
Meters
Max: 14,8



New London Disposal Site

NL - 91 and D/S Mound Complex

August 2000 • Hillshaded Bathymety



200

_l



t



Projection: Lambert Conformal Conic

(CT State Piane)

Grid Size: 25m

Units: Meters

Datum: NAD83

Hillstiade Az. 045

Hillshade Alt. 055

Vertical Exaggeration: 5x



File: nlds ds hs.mxd



edits: K. Shufeldl. SAIC, 11/09/01



Figure 3-1. Hillshaded bathymetry of the 800 x 800 m NL-9 1 and D/S Mound Complex
survey area, August 2000



Monitoring Cruise at the New London Disposal Site, August 2000



n



72'04.600W 72°04.500'W 72*04.400W 72"04.300W 72'04.200W 72*04.100'W







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UDM deposit



72°04.700'W 72*04.600W 72'04.500'W 72'04.400'W 72°04.300'W 72*04.200'W 72'04.100W

New London Disposal Site

NL - 91 and D/S Mound Complex

August 2000 - September 1997 Depth Difference Grid

97-00 Depth Difference (m) 100 200

[1110.375 ' 1 1

^^_ MntRrR

1^0.376-0.500

M Disposal Buoy Locations

EZI 1991 UDM 0.25m contour



I



Pfojedlon: Lambert Conformal Conic
(CT Slate Plane)
Units: Meiers
Datum; NAD83



File: nlds_d3_dm.n



edits: K. Shuleldl, SAIC, 1 1/D9/01



Figure 3-2. Final depth difference results produced from comparisons between the August
2000 and September 1 997 bathymetry surveys



Monitoring Cruise at the New London Disposal Site, August 2000



18



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1997 - 199B Season

• GALES FERRY MARINA (3.097 CM)
Recommended Capping Points ^ SHENNECOSSETT YACHT CLUB (3,594 CM)



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A BREWERS DAUNTLESS SHIPYARD (3,211 CM) '^

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□ Shennecossett Yacht Club (1 ,376 CM) Da'"m: NAD83



alils: K. Sliufeiai, SAIC, 11/09/01



Figure 3-3. Plots of placement locations for Capping Dredged Material (CDM) from
several different dredging projects at the NL-91 and D/S Mound Complex,
1 997 to 2000. The placement locations are based on coordinates recorded in
the Disposal Scow Logs (See Appendix A)



Monitoring Cruise at the New London Disposal Site, August 2000



19

community. Thirteen sampling stations were occupied in August 2000; these are the same
stations sampled in three previous REMOTS® surveys over this bottom feature. At least
three replicate images were obtained and analyzed at each station, except station SOON (only
two replicates obtained/analyzed). A complete set of REMOTS® image analysis results is
provided in Appendix B 1 ; these results are summarized in Table 3 - 1 .

The images showed that sediments comprising the surface of the NL-91 and D/S
Mound Complex were predominantly silt/clay (grain size major mode of >4 phi). This
silt/clay appeared to contain a significant fraction of very fine to fine sand at each station,
such that surface sediments across the site are best described as "sandy mud." Sandy mud
was also the predominant sediment type at the three reference areas.

All of the sediment observed in the REMOTS® images at each of the thirteen stations
was identified as capping dredged material. This CDM generally extended fi-om the
sediment surface to below the imaging depth of the REMOTS® camera prism at each station
(see dredged material thickness measurement indicated with a "greater than" sign in Table 3-
1). The CDM observed in the images at the majority of stations in August 2000 appeared to
be placed recently (i.e., within the past year or two) and was therefore categorized as the
newer, supplemental CDM (Figures 3-4 and 3-5 A). At stations 200S, 300E, 400E, and 500E,
the CDM displayed characteristics similar to those observed in previous surveys (1995, 1997,
and 1998) and was therefore categorized as "old" CDM (Figure 3-5B). The contour line in
Figure 3-4 indicates that the distribution of supplemental CDM as detected in the REMOTS®
images correlates very well with the bathymetric depth difference results. The deposit of
supplemental CDM completely covers the original main deposit of UDM placed at the D/S
buoy in 1991.

The apparent RPD measured in each REMOTS® image provides an indication of the
degree of oxygen penetration into the sediment. A well-developed RPD depth (defined as
greater than 3 cm) generally indicates good or healthy sediment aeration as a result of active
bioturbation by benthic organisms. The replicate-averaged apparent RPD depths fi-om the
mound complex ranged fi-om 1.8 to 4.9 cm, with an overall average of 3.4 cm (Figure 3-6;
Table 3-1). This average value was greater than the average RPD depth of 2.6 cm measured
at the reference stations (Table 3-2) and is considered indicative of healthy aeration of the
surface sediments.

The successional status was advanced, with Stage II or Stage II on HI communities
inhabiting the surface sediments of the mound complex (Figure 3-7). Stage III organisms
were present at 12 of 13 stations. In addition, tubes of the amphipod Ampelisca sp. were
observed at the sediment- water interface at 12 of the 13 stations. At numerous stations, the
tubes appeared to be mature or in a state of decay (Figure 3-8 A). However, patches of



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A NL-91 and D/S REMOTS
□ 1991 UDM 0.25m contour
97-00 Depth Difference (m)
CD 0,375
■I 0.376 -0.500

_M Disposal Buoy Locations



New London Disposal Site

NL - 91 and D/S Mound Complex

Distribution of New CDM



100

I



Projection: Lamtiert Confoimal Conic
(CT State Plane)
Units: Meters
Datum: NAD83



B.D. Andrews, SAIC: edits: K. Shuteldl. 11;09/01



Figure 3-4. Contour line showing the distribution of recently placed supplemental CDM at
the NL-91 and D/S Mound Complex as detected in REMOTS® sediment
profile images



Monitoring Cruise at the New London Disposal Site, August 2000




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NL - 91 and D/S Mound Complex

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100 200

1 I I Projection: Lambert Conformal Conic
' ' ' (CT State Plane)



\



OSI Value



Meters



Units: Meters
Datum: NAD83



Flle:nlds REMOTS.mxd



edits: K. Shufeldt, SAIC, 11/09/01



Figure 3-6. Map of replicate-averaged RPD and median OSI values calculated for the
REMOTS® stations occupied over the NL-91 and D/S Mound Complex



Monitoring Cruise at the New London Disposal Site, August 2000



25



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NL - 91 and D/S Mound Complex

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A NL-91 and D/S REMOTS



t



100 200



Projection: Lambert Conformal Conic
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Datum: NAD83



Fit: DS_SSIag9 mud



tdils K Shufaklt. SAIC. 11/oa/OI



Figure 3-7. Map of succesional stage assemblages detected at the REMOTS® stations
occupied over the NL-91 and D/S Mound Complex



Monitoring Cruise at the New London Disposal Site, August 2000



27_

smaller amphipod tubes were noted, indicative of juvenile amphipod population development
(Figure 3-8B). Almost all of the images showed a depositional layer of organic detritus
present at the sediment surface at the time of the survey (i.e., "organic draping").

Replicate-averaged mean and median OSI values ranged from +6 to +10, with an
overall average of +8 (Figure 3-6; Table 3-1). This average is slightly higher than the overall
average OSI value of +7 for the reference areas (Table 3-2), suggesting that overall benthic
habitat quality over the NL-91 and D/S Mound Complex was comparable to that on the
siuTOunding ambient seafloor at the time of the survey in August 2000.

3.2 Seawolf Disposal Mound

3.2.1 Bathymetry

The August 2000 bathymetric survey of the Seawolf Mound showed depths ranging
from 1 3.4 m over the top of the NL-Relic Mound in the eastem portion of the survey area to
23.0 m in the deeper trough along the southwest comer of the area (Figure 3-9). Water
depths over the Seawolf Mound varied from about 15 to 19 m, which was relatively
consistent with the most recent survey of 1998. The Seawolf Mound continues to have two
small apex regions at depths of 15 to 16 m, and a broad, flat distribution of deposited
sediments (Figure 3-9).

The comparison of the August 2000 and July 1998 bathymetric surveys of the
Seawolf Mound resulted in the construction of a depth difference map (Figure 3-10). This
map shows only a few small, scattered locations where there was an apparent depth change
on the order of -0.5 m. These areas generally coincide with the more complex seafloor
features, where it is known that minor deviations in depth measurements can become
exaggerated when successive bathymetric surveys are compared. Because there has been no
dredged material placement activity over the Seawolf Mound area since 1996, the apparent
depth changes are considered to be normal artifacts of the depth differencing procedure. The
results suggest there have been no significant topographic changes at the Seawolf Mound
between the July 1998 and August 2000 bathymetric surveys.

3.2.2 REMOTS® Sediment-Profile Photography

Benthic recolonization of the Seawolf sediments was evaluated using REMOTS®
sediment-profile photography. A complete set of REMOTS® image analysis results for the
Seawolf Mound is presented in Appendix B2. The sediment observed in the REMOTS®
images at the majority of the Seawolf Mound stations was classified as dredged material
(Figures 3-1 1 and 3- 12 A). This material generally extended from the sediment- water



Monitoring Cruise at the New London Disposal Site, August 2000



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0.5 meter contours



Wew London Disposal Site
Seawolf Mound
August 2000 Hillshaded Battiymetry ^ . ^. , ^, , ^ , , ^

^ ' ' Projection: Lambert Conformal Conic

i{CT State Plane)
Units: Meters
Grid Size: 25m
Datum: NAD83
Hillstiade Az. 045
Hillsiiade Alt. 055
Vertical Exaggeration: 5x



File: NLOS SW HS.mxd



edits: K. Sliufeldl, SAIC. 11/09/01



Figure 3-9. Hillshaded bathymetry of the 1000 x 1000 m Seawolf Mound survey area,
August 2000



Monitoring Cruise at the New London Disposal Site, August 2000



30




72"04.760'W



New London Disposal Site

Depth Difference In Meters Seawolf Mound

^ -1 25 - -1 00 August 2000 - July 1998 Depth Difference



t



I- : I -0.99- -0.75
I I -0.74- -0.50
I I -0.49 - -0.25

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Projection: Lambert Con formal Conic

(CT State Plane)

Units: Meters

Datum: NAD83

Contour Interval: 1 m

Grid Cell Size:25 m



File: NLDS SW Diff25m.mxd



B.D.Andrsws,SAIC,23 May 01 : edits, K. ShufBldl, 11/09/01



Figure 3-10. Depth difference comparison between the August 2000 and July 1998
1000 X 1000 m bathymetric surveys of the Seawolf Mound



Monitoring Cruise at the New London Disposal Site, August 2000



31




Figure 3-11. Map showing the distribution of dredged material at the Seawolf Mound as
detected in the August 2000 REMOTS® survey

Monitoring Cruise at the New London Disposal Site, August 2000





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interface to below the imaging depth of the REMOTS® camera prism at each station
(dredged material thickness measurement indicated with a "greater than" sign in Table 3-3).
There was no dredged material observed in the images at stations 300E, 450N, and 450NE
located on the mound apron (Figures 3-1 1 and 3-12B). At these stations, the surface
sediment appeared to consist of ambient sandy mud.

The Seawolf Mound consisted predominantly of fine-grained silt/clay sediments
(grain size major mode of >4 phi) having a significant fine sand component. At most of the
stations on the mound, the dredged material comprising the surface sediments was described
as a "sandy mud" or "sandy gray clay." The gray clay (Gardiners Clay) is characteristic of
this mound and has been observed consistently in previous surveys (SAIC 2001b).

The boundary roughness at the Seawolf Mound ranged fi-om 0.7 to 4.0 cm, with an
average of 1 .5 cm, which was greater than the average value measured at the reference areas
(0.8 cm; Tables 3-2 and 3-3). There was no obvious spatial pattern of boundary roughness
values, which were attributed primarily to biological activity (tube construction). Similar to
the NL-91 and D/S Mound Complex, a depositional layer of organic detritus was observed
on the sediment surface at almost all of the stations.

Lag deposits of shells or pebbles were noted at the sediment-water interface at several
stations over the Seawolf Mound (Figure 3-1 3 A and B). These lag deposits are the result of
minor winnowing of fine-grained sediments and serve to armor the surface of the disposal
mound. By blocking the winnowing effects of near bottom water currents, these armoring
deposits actually prevent mobilization of the underlying fine-grained material and stabilize
the surface of the disposal mound.

The replicate-averaged apparent RPD depth for each station ranged fi-om 1 .76 to
4.35 cm (Figure 3-14; Table 3-3). The overall average for the Seawolf stations was 3 cm,
which was greater than the average RPD (2.66 cm) at the reference areas, suggesting healthy
aeration of the sediment surface on the Seawolf Mound. There was no evidence of low
dissolved oxygen (DO) conditions or redox rebounds observed in the Seawolf mound
sediment profile images.

The successional status was advanced, with Stage II or Stage II on III communities
inhabiting the sediments of the Seawolf Mound (Figure 3-15). Stage III organisms were
present at 23 of 29 stations. Large tubes of the polychaete Chaetopterus sp. were visible in
several of the replicate images, providing fiirther evidence of advanced recolonization over


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