_76 



3.0 RESULTS 



Since 1982, all disposal activity at WLIS has been directed to the southwest 

 quadrant of the disposal site into the east- west trending bottom depression. The July 1996 

 bathymetric survey at WLIS detected a total of eight dredged material disposal mounds on 

 the WLIS seafloor (Figure 3-1). Mound C remains the largest disposal mound with an 

 approximate width of 250 m and a maximum height of 4 m. The water depth over the C 

 mound was 29.5 m at MLLW, with slightly deeper depths bemg recorded over mound D 

 (29.75 m) 240 m to the south. A maximum depth of 35.25 m was found at 40°59. 180' N, 

 73°29.350' W within the east-west trending trough. 



During the 1400 m x 1000 m bathymetric survey of WLIS, a minimum depth of 

 27.5 m was detected over a strongly sloping bottom feature along the southern edge of the 

 bathymetric survey area. The color contour plot displays the distinct, shoaling bottom 

 feamre, visible approximately 210 m north of the southern limit of the bathymetric survey 

 area. The strong slopes are representative of the northern margins of the terminal moraine 

 which forms Long Island, New York, produced by the advance of the southwest lobe of 

 the Wisconsian Ice Sheet approximately 18,000 years before present (Sugden and John 

 1976). Three-dimensional imagery of the WLIS seafloor displays the possible beneficial 

 uses (i.e., lateral containment) of this glacial feamre and the excellent depositional 

 environment it tends to produce (Figure 3-2). 



The three newest disposal moimds at WLIS were constructed around taut-wire 

 disposal buoys deployed in close proximity to the strongly sloping bottom feamre. To 

 provide valid comparisons with previous data sets, the 1996 bathymetric data was re- 

 gridded to a 1200 m x 1000 m area (Figure 3-3). Depth difference comparisons with the 

 July 1992 bathymetry data show the development of two new bottom feamres (G and H) as 

 well as the deposition of additional material over the F and D moimds (Figure 3-4). Due 

 to the relatively close placement, all three mounds are interconnected by a 0.25 m thick 

 layer of dredged material resulting from the overlapping aprons of the three independent 

 disposal moimds. 



Several survey artifacts that correspond to the margins of the terminal moraine are 

 visible to the south of the disposal mounds. Slight differences in the 1992 and 1996 survey 

 vessel tracks over the strong slopes tend to appear as accumulation of material although no 

 disposal activity occurred in this area. The apparent accumulation of 0.5 m of material 

 north of the G mound may be the result of acmal disposal activity during early March 

 1994, when the WDA 93 buoy was dragged more than 2,500 m off station. The buoy was 

 off-station for six days (1 March to 6 March 1994), during the deposition of 1,375 m^ of 

 material dredged from the Glen Cove and Charles Creeks. Without a DAMOS buoy to 



Monitoring Cruise at the Western Long Island Sound Disposal Site, July 1996 



