71 



The survey data collected over SE-REF indicated fine-grained, ambient sediments 

 that tended to have a high sulfide content. The side-scan images show even, weak to 

 moderate backscatter for the area, similar to USGS side-scan results for the region. The 

 USGS characterized the area as a combination of reworking and sorting and fine-grained 

 sediment deposition environment (Knebel et al. 1998). The sediment grab samples all 

 appeared to be very similar in composition and indicated uniform ambient conditions 

 characteristic of fine-grained sediment deposition environments. Below the thin oxidized 

 surface layer, the sediments were dark and had a sulfidic odor. Overall, the grab samples 

 corresponded to REMOTS® photographs from the area. Grain size analysis showed that 

 silts and clays were predominant in all grab samples similar to observations of grain size in 

 REMOTS® photographs. REMOTS® results indicated deep RPDs, Stage III successional 

 status, and high OSI values such as seen in lOON D (Figure 3-13). However, the 

 sediments tended to be very dark with low reflectance values relative to typical conditions 

 at reference areas such as SOUTH and SW-REF. Although some replicates did show 

 lighter sediments that were less sulfidic, the dark sediments found throughout SE-REF 

 might be characteristic of the western Long Island Sound ambient sediments. 



The mean water depth at SE-REF was 19.5 m, which is shallower than the average 

 depth at WLIS. Water depths ranged from 27 m to 35 m in the latest bathymetric survey 

 over the disposal mounds in the southeast quadrant of WLIS. The survey data over the 

 area of SE-REF indicated that the area was free of distinct topographic feamres or steep 

 slopes, although both are present just south of SE-REF. Although the water depth was 

 shallower at SE-REF relative to WLIS, the relief appeared to be acceptable for a reference 

 area. 



Consistent concentrations of the tested metals and organics were measured in the 

 sediment grab samples. No pesticides or PCBs were detected. The PAHs were at or 

 below the mean historic reference area values for WLIS (Figure 3-14). The low but 

 slightly variable PAH levels had a patchy spatial distribution that did not correlate with 

 location. The metals values were higher than the standard reference area data for WLIS, 

 but were within one to two standard deviations of the mean values. Figure 3-15 shows 

 overlapping 95 % confidence levels for SE-REF and the WLIS Reference Area datasets and 

 no significant statistical difference. The fine-grained sediments, such as those at SE-REF, 

 have a large surface area that attracts and accumulates trace metals (Horowitz 1985). In 

 addition, the sediments have high reduced iron and sulfide concentrations indicated by the 

 dark appearance of the sediments. Both iron hydroxide and organic matter have large 

 surface areas that easily collect trace metals and are chemically reactive. Because Long 

 Island Sound is surrounded by intensely urbanized areas and has a large drainage basin, 

 contaminants from many point and non-point sources enter the waters of the Sound and 

 settle in the bottom sediments of depositional environments and may be characteristic of 



Monitoring, Cruise at the WLIS Disposal Site, September 1997 and March 1998 



