10 



3.0 RESULTS 



3.1 Bathymetry 



The 1988 and 1990 bathymetric surveys mapped six disposal mounds: NL-RELIC, 

 NL-I, NL-H, NL-HI, NL-85, and NL-88 (Figures 3-1 and 3-2). The NL-88 mound was first 

 identified in the 1988 survey approximately 150 m west of NL-85. Since August 1988, an 

 estimated 21,200 m 3 of additional dredged material was released at NL-88 (based on reported 

 barge volumes). The 1990 bathymetric survey identified a new mound, NL-TR (Figure 3-2). 

 The NL-TR mound formed from material released at the 1989 and 1990 buoy locations 

 150 m northwest of the NL-II mound. This material was released between 25 January and 

 10 March 1989, and 15 February and 17 June 1990. 



A comparison of the bathymetry between the 1988 and 1990 surveys showed 

 considerable changes in bottom topography at the NL-TR mound and smaller depth changes 

 around the NL-88 mound. In the vicinity of the active disposal buoys (Buoy 89 and Buoy 

 90), NL-TR covered approximately 550 x 400 m, and had many small peaks ranging from 

 0.9 m to 1.9 m height (Figures 3-3 and 3-4). The NL-88 mound covered an area 175 x 

 125 m and had gained 1.2 m in mound height since the 1988 survey (Figures 3-3 and 3-5). 

 The mound heights at most of the inactive disposal mounds (NL-RELIC, NL-I, NL-II, and 

 NL-III) were unchanged since the 1988 survey. The NL-85 mound gained approximately 

 40 cm in height between 1988 and 1990 (Figure 3-5). 



Volume calculations based on the bathymetric survey indicated that 46,710 m 3 + 

 14,920 m 3 (95% C.I.) of sediment have accumulated at the NL-TR disposal mound between 

 the July-August 1988 survey and the present. During this same period, barge logs showed 

 an estimated deposition volume of 100,270 m 3 . Volume calculations from the vicinity of the 

 NL-88 mound (which included the NL-85 mound) indicated that 11,560 m 3 + 2,220 m 3 

 (95% C.I.) have accumulated in this area of the disposal site since the 1988 master survey. 

 Barge reports for the same region and time period showed that approximately 21,200 m 3 was 

 deposited at the mound. 



3.2 REMOTS® Sediment-Profile Photography 



Recently deposited dredged material was identified in the central region of the 

 REMOTS® survey over the NL-TR mound. This material typically consisted of poorly 

 sorted sand overlying fine-grained mud (Figure 3-6[A]). The boundaries of this deposit were 

 roughly 200 m west and north of the central station, and 300 m to the east. The southern 

 boundary of the dredged material deposit at NL-TR extended beyond the NL-TR REMOTS® 

 grid (Figure 3-7). The thickness of the surface sand layer at NL-TR stations varied across the 

 mound and even within station replicates. At Station CTR, replicate 



Monitoring Cruise at the New London Disposal Site, June- July 1990 



