77 



reflects both the presence of ambient bottom conditions (parts of the seafloor not yet covered 

 with dredged material) and fine-grained mud that represents disposed materials. Grain size 

 information from CLIS-88 and CLIS-89 surveys that overlaps the sixty-six-station grid has 

 been incorporated into the distribution of grain size in the area (Figure 3-5). 



3.2.1.2 Inactive Mounds and Reference Areas 



The grain size major mode for inactive mounds CS-1, MQR, FVP, and NHAV-74 was 

 mostly silt-clay (>4 phi). On mounds CLIS-88 and CLIS-89, the very fine sand and the fine 

 sand, respectively, may be the result of extensive dredged material disposal in the area over 

 time. The natural ambient bottom in the central Long Island Sound basin within and 

 surrounding CLIS consists of brown to grey silt-clay mud (>4 phi) (Figure 3-6). Silt-clay 

 was the dominant textural mode for CLIS-REF, 4500W-REF, and most of the 2500W-REF. 

 Five stations at the 2500W-REF had a major textural mode in the 4-3 phi range. The water 

 depth at this western reference area (13 m) is shallower than the CLIS-REF and the 4500E- 

 REF areas. This very fine sand mode probably reflects the proximity of the western reference 

 area to the mud-sand transition at approximately the 13 m depth contour in this part of the 

 Sound (see NOAA Chart 12354). 



3.2.2 Distribution of Dredged Material 



3.2.2.1 Active Mounds 



The CLIS-90 and CS-90-1 disposal locations at CLIS were in an area that received 

 spatially dispersed dredged material over the past few years (Germano et al. 1993). All 

 REMOTS® photographs in the CLIS survey area showed the presence of dredged material 

 (Figure 3-7). Within the main survey area, the sediment is either fresh or relic dredged 

 material based on sediment grain size, optical reflectance, and sediment fabric (SAIC 1990; 

 Figure 3-8). The fresh dredged material followed a NE -SW trend through the center of the 

 survey over the CLIS-90, CLIS-89, and part of the CS-90-1 mounds. Isolated patches of relic 

 and fresh material occurred at one or two stations near the edge of the survey area. 



3.2.2.2 Inactive Mounds and Reference Areas 



The REMOTS® survey at the three reference areas detected only ambient sediment. 

 Relic or more weathered dredged material was concentrated in the REMOTS® grids over 

 inactive mounds CS-1, NHAV-74, and FVP. Station 100E at FVP was classified as fresh 

 dredged material due to very dark reduced sediment at depth. At MQR, the REMOTS® 

 photographs showed silt-clay dredged material with layered or chaotic fabrics, the presence of 

 methane gas, and low reflectance of sediment below the RPD (resulting from high sulphide 

 content). These are all characteristics often attributed to recent or fresh dredged material, but 

 can also be indicative of retrograde conditions. Because there was no recent 



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



