37_ 



differencing routines with the four bathymetric data sets, both total accumulations and 

 apparent losses of material can be identified. 



By comparing a scaled down version of SAIC's baseline survey in July 1994 to the 

 OSI precap bathymetry, a UDM deposit with a height of 2.75 m and a width of 380 m was 

 detected south of the CDA buoy positions (Figures 3-14, 3-15, and 3-16). The apex of the 

 UDM mound was located approximately 145 m south of the CDA #1 buoy position. 

 DAMOS disposal logs reported the deposition of approximately 129,900 m 3 of UDM at 

 CLIS between the dates of 30 November and 13 December 1994 (Appendix D: Table 1). 

 Volume difference calculations detected a total accumulation of 1 14,700 m 3 of new 

 material in the vicinity of the CDA buoy (Appendix A: Table 3-2). By utilizing the 

 bathymetric profile of the disposal mound at the precap stage of development, calculations 

 based on successive bathymetric surveys accounted for 88% of the barge log estimates 

 submitted by on-site inspectors. These findings represent extremely good agreement 

 between the two methods of volume estimates (barge volume vs. sequential bathymetric 

 survey). 



The first phase of capping over the CLIS 94 mound was performed from 16 January 

 1995 through 22 April 1995 (Appendix D: Table 2). During that time period an estimated 

 barge volume of 41,700 m 3 of CDM was released over the initial UDM deposit, isolating 

 the majority of the contaminated material from the sediment/water interface. An interim 

 cap bathymetric survey was performed on 23 April 1995 to document the progress of 

 capping operations. The depth difference calculations based on comparisons of the April 

 1995 interim cap and July 1994 baseline surveys show the total accumulation of material 

 over the CLIS 94 mound (Figures 3-17 and 3-18). A maximum height of 2.75 m was 

 detected over the CLIS 94 mound, and the deposition of CDM has caused the dredged 

 material apron to expand to the north, east, and south, increasing its diameter to 

 approximately 490 m. 



Further bathymetric analysis between the December 1994 and April 1995 

 bathymetric surveys revealed a large pocket of consolidation over the center of the disposal 

 mound. Depth difference plots indicate a net loss in mound height, up to 1.0 m relative to 

 the precap stage of development (Figure 3-19). The deposition of 41,700 m 3 of capping 

 material over the UDM deposit caused the formation of three peaks of CDM approximately 

 1.25 m thick over the north, southeast, and southwest regions of the mound. The majority 

 of the CDM was reportedly released over the fringes of the consolidation pocket during the 

 initial stages of capping operations (Figure 3-19). Volume calculations detected 38,664 m 3 

 of new material over the restricted analysis area, which is considered to make up the ring 

 of accumulation around the CLIS 94 mound. In addition, a negative volume of 26,500 m 3 



Monitoring Cruise at the Central Long Island Sound Disposal Site, September 1995 



