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3.6.3 September 1997 Survey 



A total of 13 randomly selected stations were surveyed with the REMOTS® 

 sediment-profile camera at NLON REF, NE REF and WEST REF reference areas as part 

 of the September 1997 field effort. Four stations were surveyed in NLON REF, four at 

 WEST REF, and five in the NE REF. These data were used as the basis for comparison in 

 assessing benthic habitat quality over the NL-94 mound and the NL-91 and D/S mound 

 complex. 



No dredged material was present in any of the replicate photographs obtained from 

 the three reference areas. Replicate averaged camera penetration depth ranged from 

 4.6 cm to 10.3 (Table 3-10). The shallow to moderate camera penetration documented 

 limited sand-over- mud layering at several stations within each reference area. All of the 

 reference areas showed some evidence of physical reworking or erosion of sediment as 

 shown by the following characteristics: poor sediment sorting, shell layers near the surface 

 (shell lag), hydroids, or ripped up 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 3 to 4 phi (very fine sand). Station 10 in the WEST REF was 

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

 (medium to fine sand; Table 3-10). 



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 3-10). 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 3-10). 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 3-10). The reference 

 area NLON REF showed primarily Stage II organisms progressing to Stage III (three of 

 four stations) and one station in which Stage I organisms were present at the sediment 

 surface over Stage III deposit feeders. The images from NLON REF and NE REF showed 

 dense amphipod tube mats (Stage II). The mats at NE REF were in the process of being 

 eroded during the survey, while those at NLON REF were largely intact. 



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



