3.0 RESULTS 



3.1 Bathymetry 



The July 1988 bathymetric results indicated that minimum water depths at 

 the "A", "B", and "C" mounds were 29.50, 29.75, and 28.00 m, respectively (Figure 3-1). 

 In the present 800 x 800 m survey, the heights of the "A" and "C" mounds remained 

 relatively unchanged (minimum water depths of 29.75 and 28.25 m, respectively) 

 while the height of the "B" mound decreased approximately 1 m (minimum water 

 depth of 30.75 m) (Figure 3-2). The depth difference plot shows that material 

 accumulated at the active disposal point, forming the WLIS "D" mound, had an 

 approximate height of 5.3 m (minimum water depth of 28.00 m) and a diameter of 

 approximately 225 m. 



Based on depth difference analysis comparing the July 1988 and July 1990 

 surveys, volume calculations indicated that an additional 101,350 m 3 of dredged 

 material (95% confidence limits of 98,410 and 104,280 m 3 ) had accumulated within 

 the 500 X 350 m area surrounding the WLIS "D" mound (Figure 3-3). This calculation 

 incorporates decreases in depth as observed at the WLIS "D" mound and apparent 

 increases in depth as observed at the WLIS "A" mound. Tabulation of the disposal 

 barge logs for this same period indicated that approximately 185,000 m 3 of dredged 

 material were deposited at or near the buoy (Figure 3-4). 



The 1990 bathymetric plot of the entire WLIS Disposal Site exhibited many 

 topographical features present in the original, 1982 survey which was conducted 

 using 200 m lane spacing (Figures 3-5 and 3-6). In addition to enhancing the detail 

 of the site, the 1990 survey plot delineated clearly the "A", "B", "C", and "D" mounds. 

 A 3-D bathymetric plot provided a spatial perspective of the entire site (Figure 3-7). 



32 REMOTS® Sediment-Profile Photography 



Within the areal distribution of dredged material, as determined by the 

 REMOTS® survey (Figure 3-8), recently-deposited dredged material exceeded the 

 depth of camera prism penetration at several stations adjacent to the disposal point. 

 At some of these stations (e.g., CTR, 100N, and 100E) a mottled, streaky oxidized 

 sediment layer characterized dredged material, while at other stations (e.g., 100NE, 

 100SW, and 100W) dredged material had a clearly-defined apparent Redox Potential 

 Discontinuity (RPD) boundary and high apparent sediment oxygen demand (SOD) at 

 depth (Figures 3-9 and 3-10, respectively). 



The majority of WLIS stations (WLIS "D" and "B" REMOTS® grids) exhibited a 

 grain size major mode of £4 phi, with no obvious grain size anomalies 

 differentiating the recently-deposited dredged material from ambient sediment 

 (Figure 3-11). Some stations exhibited a slightly larger grain size major mode (4-3 

 phi) which, in several cases, was not attributable to the 1988 - 1990 disposal 



Monitoring Cruise at the Western Long Island Sound Disposal Site 



