125_ 



3 to 4 phi (very fine sand) and >4 (silt). Shell fragments and shell lag deposits were also 

 a major characteristic of the surface sediments at WEST REF. 



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

 boundary roughness values, ranging from 0.0 cm to 2.2 cm across all three areas 

 (Table 3-9). Boundary roughness determinations were classified as biogenic for the 

 majority of the photographs collected in August 1992. 



The replicate averaged RPD depths within the three areas ranged from 0.0 cm to 

 2.3 cm, the overall average RPD was 1.44 cm (Table 3-9). The WEST REF exhibited 

 slightly deeper RPD layers than those at NE REF and NLON REF. No redox rebound 

 layers were observed in any of the replicate images collected at the three reference areas. 



The NE and NLON reference areas exhibited Stage II populations (amphipod tube 

 mats) with several stations progressing to Stage III, while the reference area WEST REF 

 showed signs of recent benthic disturbance. Five of the 13 stations sampled at WEST REF 

 had exclusively Stage I populations (Table 3-9). Four stations had Stage I organisms 

 colonizing the sediment surface over Stage III deposit feeders at depth. The eastern-most 

 station displayed evidence of a healthy Stage III population. Stations 300 m north, 100 m 

 east, and 200 m east had indeterminate successional stages due to low camera penetration. 



The median OSI values at the reference areas in 1992 ranged from +2 to +8, with 

 an overall average of +5.4. The majority of stations had index values of +5 and +7 

 (Table 3-9). There were five indeterminate stations at the disposal site and three at the 

 WEST REF area, due to indeterminate RPD values or successional stages. Neither low 

 DO conditions nor sediment methane were noted at any of the 39 reference stations in 

 August 1992. 



3.6.2 August 1995 Survey 



The surficial sediments at the NLDS reference areas (NLON REF, NE REF, and 

 WEST REF) were examined with REMOTS® sediment-profile photography as part of the 

 August 1995 survey. These reference areas served as a baseline for determining the health 

 of the benthic community at the NL-94 and USCGA mounds, as well as the NL-91 and D/S 

 mound complex. In contrast to 1992, a total of 15 stations were surveyed in August 1995 

 (four at NLON REF, five at NE REF, and six at WEST REF). These stations were 

 randomly distributed within a 300-m radius of the center of each reference area 

 (Figure 2-8). 



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



