55_ 



between the 1997 and 1998 bathymetric datasets displayed only isolated patches of 

 consolidation of approximately 0.25 m (Figure 4-4B; SAIC 2001). 



The objective of the August 2000 bathymetric survey at the Seawolf Mound was to 

 detect any changes in topography relative to the last survey of July 1998. The comparison 

 between the two surveys failed to detect any significant topographic changes in the mound, 

 over and above the artifacts or "noise" associated with the depth differencing procedure 

 (Figure 3-10). These results are consistent with those obtained in July 1998, in showing that 

 consolidation of the Seawolf Mound was greatest in the year following its creation but has 

 slowed significantly since September 1997. Past studies of dredged material mound 

 consolidation also serve to demonstrate that consolidation rates are highest immediately 

 following mound creation and then become significantly reduced with time (Poindexter- 

 Rollings 1990; Brandes et al. 1991; SAIC 1997, 1998). Therefore, the August 2000 depth 

 difference results showing no significant consolidation since July 1998 were within 

 expectations for a mound that was four years old at the time of the survey. 



The objective of the August 2000 sediment profile photography survey over the 

 Seawolf Mound was to determine its benthic recolonization status relative to previous 

 surveys and the nearby reference areas. Overall, the results indicate that overall benthic 

 habitat quality over the mound was slightly better than that on the ambient seafloor and had 

 improved somewhat fi:om that observed in September 1997 and July 1998. The average 

 median OSI value of +8.0 for the Seawolf Mound stations is indicative of relatively healthy 

 or undisturbed benthic habitat quality, and is roughly comparable to the average median OSI 

 value of +7.0 for the reference areas. The increase in the average OSI value fi-om +7.5 in 

 1997 and +6.1 in 1998 to +8.0 in August 2000 suggests an improvement in overall benthic 

 habitat quality at this mound over the two year period 1 998 to 2000 (Table 4-2). This is 

 mainly attributed to deeper RPD depths in August 2000 compared to July 1998, as well as an 

 increase in the number of replicate images showing more advance successional stages (i.e., 

 Stages II and EI). 



Similar to the NL-91 and D/S Mound Complex, it was predicted that the 

 recolonization status of the Seawolf Mound would be advanced, with a community 

 comprised of Stage II and Stage III organisms. The August 2000 results confirmed this 

 prediction, as both Stage II and III organisms were abimdant in the sediment profile images 

 across the mound (Figures 3-15 and 3-16). Stage II on III has been observed consistently at 

 this mound since September 1997 (Table 4-2), with the Stage II community comprised 

 predominantly of dense surface mats of the amphipod Ampelisca sp. Large tubes of the 

 Stage III polychaete Chaetopterus sp. observed at several stations across the mound (e.g.. 

 Figure 3-16A) provide fiirther evidence of the advanced stage of benthic recolonization at 

 this mound in August 2000. 



Monitoring Cruise at the New London Disposal Site, August 2000 



