24 



(sand-over-mud layer, buried oxygenated layers, consolidated sediments, etc.) complicated 

 the mapping of the recently deposited sediments. Therefore, a combination of the 

 REMOTS® and bathymetric data was utilized to differentiate between relic and recently 

 deposited dredged material. 



Dredged material, both relic and recently deposited, appeared in REMOTS® 

 photographs at 18 of the 25 WLIS "F" stations. REMOTS® photographs from stations on 

 the "F" mound showed that the recently deposited material consisted of mixtures of silt/clay 

 and very fine sands (Figure 3-8). Some of the sediments were deposited as consolidated 

 clays. 



Due to the relatively small volume of material deposited during the 1991-1992 season 

 and the proximity of the WLIS "D" and "E" mounds to the "F" buoy, dredged materials 

 observed at stations F300N, F400N, and F400W were presumed to originate from the WLIS 

 "D" and "E" footprints or as a combination of new and old dredged materials. REMOTS® 

 photographs from stations F200S, F300S, F400S, and F200SE revealed thin surface layers of 

 cobble without evidence of dredged materials (Figure 3-9). Typically, cobble layers are 

 indicative of dredged sediments; however, these four stations were located on the flanks of 

 the ridge which extends into the survey area. This area may experience unique erosional and 

 depositional forces; therefore, ambient sediment characteristics along the ridge may differ 

 significantly from ambient sediment characteristics of the flat, level regions of western Long 

 Island Sound. This still does not preclude dredged material as a source for this cobble layer, 

 but the stations were classified as ambient. 



The homogeneous REMOTS® sediment profiles at stations F200E and F400E did not 

 indicate past dredged material disposal. One replicate photograph from Station F300E 

 revealed a band of dark subsurface sediment. This sediment layer is possibly the result of an 

 historical disposal event. 



3.2.2 Grain Size Distribution 



As noted in previous monitoring surveys of WLIS, grain size analyses did not 

 differentiate recently deposited dredged material from ambient sediments. Sediments within 

 the disposal site consisted of silt/clay (>4 phi) and very fine sand (3-4 phi) (Figure 3-10). 

 Several stations exhibiting silt/clay sediments were clustered on the WLIS "F" mound and 

 within 100 m of the mound. Additional silt/clay REMOTS® stations were north and west of 

 the WLIS "F" mound and adjacent to the WLIS "D" and "E" mounds. Sediments at these 

 stations (F400N, F400W, and D100W) likely resulted from disposal operations prior to 

 November 1991. 



The majority of the 1992 REMOTS® stations were very fine sand (3-4 phi). Sediment 

 profiles at these stations showed mixtures of sand throughout a predominantly silt/clay 



Monitoring Cruise at the Western Long Island Sound Disposal Site, July 1992 



