82 



decaying amphipod (Ampelisca) tube mats. Stage III organisms were present in 19 of the 42 

 replicates and represented at all stations except 300N and 200E. 



The median OSI values ranged from +2 to +11, with an overall average of +8.6 for 

 the entire NL-91 and D/S mound complex (Figure 3-27). The only station displaying a 

 median OSI value of < +6 (indicating continued disturbance) was Station 300N (OSI +2) 

 primarily due to the lack of Stage III organisms and shallow RPD depths. Conditions 

 indicative of low bottom water DO concentrations were observed in sediments at three 

 stations. One or more of the replicate images collected from stations 100E, 300E, and 300N 

 displayed shallow RPD depths and dark, sulfidic sediment located at or near the sediment- 

 water interface, suggesting a recent reduction in available oxygen. However, the presence 

 of Stage III individuals and moderate to deep RPD depths in other replicate images obtained 

 from stations 100E and 300E contributed to high OSI values, +10 and +8, respectively. 

 The highest OSI (+11) was calculated for Stations 100N, 100W, and 200S, reflecting a 

 Stage II on III successional stage and deep RPD depths in all three replicate images collected 

 for each station. 



3.1.2.4 July 1998 Survey 



REMOTS® results from the 1998 survey over the NL-91 and D/S mound complex 

 were used to document the placement of supplemental cap material during the 1997-1998 

 disposal season. In addition, REMOTS® sediment-profile photography was used to 

 evaluate the benthic recolonization over the center of the disposal mound and continue 

 assessment of the overall recovery of the dredged material deposit. The 13-station 

 sampling grid established in 1995 was reoccupied, and three replicate photographs were 

 collected at each station. 



Dredged material was detected in layers having a thickness which exceeded the 

 camera prism penetration depth at all stations, with minimum dredged material layer 

 thickness ranging from 6.4 cm to 14.6 cm (overall average of 1 1.9 cm). Apparent new 

 dredged material was observed over the northern and central areas of the original NL-91 

 deposit (Figure 3-29). The thickness of new material was measured in the REMOTS® 

 photographs, where fresh material over older deposits was clearly evident (Figure 3-30). 



The DAMOS Capping model was used to calculate the footprint of the 1997-98 

 sediment deposit on the NLDS seafloor and forecast where new material would 

 accumulate. Based on reported barge volumes and disposal positions, the model predicted 

 the footprint would consist of two overlapping deposits (represented as circles on Figure 3- 

 30) with diameters of 400 m (5,650 m 3 reported volume) and 300 m (1,200 m 3 reported 

 volume). The circles encompass the majority of the REMOTS® sediment-profile 



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



