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 



