70? 



some evidence of physical reworking or erosion/winnowing of sediment as shown by the 

 following characteristics: poor sediment sorting, shell layers near the surface (shell lag), 

 hydroids, or disturbed amphipod tube mats. WEST REF showed the most widespread 

 evidence of physical reworking, with shell lag at 4 out of 6 stations. 



All of the reference areas were similar in sediment grain size distributions with a 

 predominant major mode of 4 to 3 phi (very fine sand). Station 10 in the WEST REF was an 

 exception to this and exhibited a predominant grain size major mode of 3 to 2 phi (medium to 

 fine sand; Table 3-2). 



Each of the three reference areas showed relatively low intra- and inter-station mean 

 boundary roughness thickness values, ranging from 0.39 cm to 1.39 cm (Table 3-2). The 

 overall average boundary roughness was 0.73 cm, with the majority of replicates displaying 

 physical disturbances. 



The replicate averaged RPD ranged from 1.75 cm to 3.48 cm, with an overall mean of 

 2.35 cm within the three areas (Table 3-2). Redox rebound layers approximately 5 cm deep 

 were identified in two replicates obtained from NE REF. 



The NE REF and WEST REF reference areas exhibited primarily Stage II populations, 

 with several stations having Stage III present (Table 3-2). The reference area NLON REF 

 showed primarily Stage II organisms progressing to Stage HI (three of four stations) and one 

 station in which Stage I organisms were present at the sediment surface over Stage in deposit 

 feeders. The images from NLON REF and NE REF showed dense amphipod tube mats (Stage 

 II). The mats at NE REF appeared to be in the process of being eroded during the survey, 

 while those at NLON REF were largely intact. 



Median OSI values for the reference area REMOTS® stations ranged from +5 to +10, 

 with an overall average of +6.8 (Table 3-2). Once again, the reference areas in 1997 showed a 

 small improvement in benthic habitat conditions relative to previous years (1992 and 1995). 

 No low DO conditions or methane gas was detected in any replicate image. 



3.2.2 July 1998 Survey 



Camera penetration ranged from 5.6 cm to 1 1.7 cm, with an average of 7.8 cm, 

 which was comparable with 1997 results (Table 3-2). No evidence of dredged material was 

 apparent in any of the photographs. Sand or sandy silt over mud stratigraphy was observed 

 in many of the photographs. Sediments at NE REF and NLON REF were moderately sorted, 

 whereas WEST REF sediments were primarily poorly sorted. Organic detritus, surface 

 scour, and/or shell fragments were present at the surface in many of the replicates. 



Monitoring Cruise at the New London Disposal Site, Seawolf Mound 1995 - 1998 



