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

 + 10, with an overall average of +6.8 (Table 3-10). Once again, the reference areas in 1997 

 showed a small improvement in benthic habitat conditions relative to previous years (1995 

 and 1992). No low DO conditions or methane gas was detected in any replicate image. 



3.6.4 July 1998 Survey 



As part of the July 1998 survey over NLDS, 13 randomly selected stations were 

 surveyed with the REMOTS® sediment-profile camera at NLON REF, NE REF and 

 WEST REF reference areas. 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-91 and D/S mound complex. 



Camera penetration ranged from 5.6 cm to 11.7 cm, with an average of 7.8 cm, 

 which was comparable with 1997 results (Table 3-11). 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 

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

 replicates. 



Fine to very fine sands (3 to 4 phi) characterized most of the sediment at the 

 reference areas (Table 3-11). Two stations within NE REF were composed primarily of 

 fine-grained sediments ( > 4 phi) while WEST REF displayed several stations with a 

 significant fine sand component (2 to 3 phi). 



Boundary roughness values were generally low (< 1 cm), except at WEST REF 

 Station W13 (STA 08), which had a replicate average value of 1.7 cm. Disturbances 

 within the surface sediments at the reference areas were primarily attributed to physical 

 forces. However, evidence of biological activity causing the surface disturbance was 

 present in approximately 33% of the reference area photographs. 



The RPD depths ranged from 1.55 cm to 3.98 cm, with an overall average of 2.55 

 cm (Table 3-11). In general, the RPD depths at both NLON REF and WEST REF tended 

 to be deeper relative to NE REF. Redox rebound layers were apparent roughly 4 cm 

 below the sediment- water interface at two stations within NE REF (Stations 10 and 12). 



Tube mats were common at the reference areas; some of these mats appeared to be 

 disturbed at NE REF and WEST REF. Stage II was considered the dominant successional 



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



