34 



material into ambient bottom (Figure 3-9). The top 70 cm of sediment in GC-6 is 

 composed of black, clayey silt with traces of sand and shell and is representative of New 

 Haven CDM (Figure 3-11). The second layer of sediment extends from 70 cm down to 

 122 cm and is similar to the cap material but displays a noticeable increase in water 

 content. As a result, the second stratum is likely to be a constituent of the New Haven 

 UDM. Two thin layers of sands and gravel also appear to be part of the heterogenous 

 UDM deposit. From 123 cm to 210 cm of penetration, several strata of clays, silts, and 

 sands make up a deposit of historic dredged material originating from disposal activity at 

 the CLIS 89 mound. 



3.2 CLIS 94 Mound 



3.2.1 Bathymetry 



The new CLIS 94 mound is evident in both the large 2.56 km 2 (1600 m x 1600 m) 

 and the smaller 1.0 km 2 (1000 m x 1000 m) survey areas. The mound is approximately 

 490 m wide at the center with a minimum depth of 15.75 m (Figure 3-12). The CLIS 94 

 mound is irregularly shaped with the apex of the mound 20 m northwest of the first 

 position of the 1994 "CDA" disposal buoy (CDA #1). The mound becomes broader and 

 less pronounced as it extends to the south. The new mound has completely incorporated 

 the historic CS 90-1 mound and encroaches on the northeast flank of the historic CLIS 90 

 mound. Depth difference plots indicate a mound height of 3.0 m at the apex (Figure 3- 

 13). 



Barge logs indicated that approximately 290,900 m 3 of dredged material was 

 released at the CDA 94 buoy positions. Volume calculations based on depth differences 

 between the July 1994 and September 1995 surveys indicate that 169,600 m 3 of sediment 

 accumulated in the vicinity of the disposal buoy (Appendix A: Table 3-2). A large 

 percentage of the 121,300 m 3 mass balance shortfall can be accounted for by restricting the 

 size of the analysis models and closely monitoring the development of the CLIS 94 mound. 

 The refocused analysis of the CLIS 94 bathymetric data has revealed a significant amount 

 of consolidation, mainly due to compression and de-watering of the UDM deposit at the 

 center of the mound during capping operations. 



Bathymetric survey data collected by Ocean Surveys, Inc. (OSI) of Old Saybrook, 

 Connecticut, at the precap (18 December 1994) and interim cap (23 April 1995) stages of 

 development, in conjunction with SAIC's baseline (July 1994) and postcap (September 

 1995) surveys, were used to document the development of the CLIS 94 mound as well as 

 detect significant amounts of central mound consolidation. By performing several depth 



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



