110 



The replicate-averaged apparent RPD ranged from 1.8 to 6.2 cm (4.3 cm average), 

 with no apparent spatial pattern (Figure 3-46; Table 3-7). Six stations had a visible redox 

 rebound ranging from 4 to 9 cm, suggesting a recent reduction in RPD depth. 



Similar to the 1995 data, the successional status was advanced, showing healthy 

 Stage II or Stage II on III communities inhabiting the sediments of the NL-94 mound 

 (Figure 3-47). Some of the photographs were identified as Stage I to II due to the presence 

 of disturbed amphipod (Ampelisca) tube mats. Stage III organisms were present in half of 

 the replicate images and 11 of the 15 stations. 



The median OSI ranged from +7 to +11, with an overall average of +8.3 (Figure 

 3-46; Table 3-7). A replicate-averaged OSI of < +6 suggested a disturbed benthic habitat 

 at Station 50SE. A number of replicates had indeterminant OSI values due to camera 

 faceplate wiper smearing or artifacts on the sediment profile. The overall average OSI in 

 1997 was slightly higher than that observed during the survey conducted in 1995 (+7.4), 

 indicating a slight improvement in benthic conditions. 



3.4 Northern Region 



3.4.1 1997 Master Bathymetric Survey 



The 2100 x 2100 m precision bathymetric survey performed over the NLDS 

 provided a new DGPS baseline to aid in the development of a Geographic Information 

 System (GIS) database for the disposal site, as well as to facilitate comparisons with future 

 project-specific surveys. This survey yielded a bathymetric chart of the 4.41 km 2 area 

 with a minimum depth of 13.5 m over the NL- RELIC mound and a maximum depth of 

 24.75 m approximately 100 m south of the disposal site boundary (Figure 3-48). A total 

 of 1 1 dredged material disposal mounds were apparent within the confines of the disposal 

 site, although many of them overlapped to form one larger feature. A vertically 

 exaggerated, three-dimensional view of the NLDS displays the various dredged material 

 deposits in contrast to the natural topography, indicating the presence of a central "bowl" 

 surrounded by dredged material mounds (Figure 3-49). 



The overall topography of the NLDS slopes from a depth of less than 14 m in the 

 Northern Region towards the south and southwest. A northwest-southeast oriented trough 

 divides the area elevated by active dredged material disposal throughout the center of the 

 site and the elevated area in the southwest corner (Figures 3-48 and 3-49). This ridge is in 

 close proximity to the U.S. Coast Guard (USCG) special purposes buoy "NL." The data 

 collected as part of the July 1986 master bathymetry survey covered an area of the seafloor 



Monitoring Cruise at the New London Disposal Site, 1992 - 1998 



