18 ^^_ 



3.2.2 Grain Size Distribution 



The majority of disposal site stations (WLIS "E" and "D" REMOTS® grids) exliibited 

 a grain size major mode of 4-3 plii, with no obvious grain size anomalies differentiating 

 recently deposited dredged material from ambient sediments (Figure 3-7). At several stations 

 on the mound, surface sediments appeared to be coarser than underlying sediments. This can 

 result when the fine-grained component of surface sediments is washed away and transported 

 to nearby lower-lying stations. Some of this redistributed material may account for the 

 predominately silt/clay (>4 phi) sediments north and south of the disposal point. Surface 

 sand and shell lag deposits characterized several stations on the WLIS "D" mound which was 

 formed during the 1989-1990 disposal season (Figure 3-8). 



Sediments at the 2000W and WLJS-REF reference areas consisted of mixtures of 

 silt/clay and very fine sand. As noted during the 1990 survey, several stations within the 

 2000S reference area continued to exhibit poorly sorted sediments with layering of sand and 

 mud in addition to surface shell lags (Figure 3-9). 



3.2.3 Boundary Roughness 



The frequency distribution of mean boundary roughness values for the disposal site 

 stations had major modes in the 2 and 3 class intervals (ranging from 0.6 to 1.4 cm; Figure 

 3-10). Observed boundary roughness was attributed primarily to physical (as opposed to 

 biological) processes resulting from disposal operations and/or sediment surface ripples. The 

 mean boundary roughness of the pooled reference sites had similar major modes of 2 and 3 

 (Mann- Whitney U-Test, p = 0.884). As noted with the disposal site stations, boundary 

 roughness at the reference areas was attributed primarily to physical processes. 



3.2.4 Apparent RPD Depth 



The frequency distribution of apparent RPD depths for the WLIS "E" survey grid had 

 a major mode in the 2.0 - 2.5 cm depth range (Figure 3-11) and a mean of 2.16 cm. The 

 areal distribution of RPD depths showed no clear relationship between RPD depths and the 

 proximity of a station to the designated disposal point (Figure 3-12). Most stations within 

 100 m of the WLIS "E" mound center exhibited moderately developed RPD layers 

 (> 2.0 cm). Many of the western stations including the station nearest the "A" motmd 

 (E400W) exhibited relatively shallow RPD depths (< 2.0 cm). Dark subsurface sediments, 

 indicative of a high sulphide content and a high apparent sediment oxygen demand (SOD), 

 characterized many of the sediment profiles from these shallow RPD stations (Figure 3-13). 



RPD depths for the pooled 1991 reference areas had a major mode in the 1.0 - 

 1.5 cm depth range (mean of 2.03 cm) and were not significantly different from the WLIS 

 "E" REMOTS® stations (Mann-Whitney U-Test, p = 0.836). As noted during the 1990 



Monitoring Cruise at the Western Long Island Sound Disposal Site, June 1991 



