44 , 



of material was found and is considered to be the product of the central mound 

 consolidation (Appendix A: Table 3-2). 



These results suggest that the amount of consolidation was significant, concentrated 

 in the UDM deposit, and expedited by the placement of capping material. The area of 

 dredged material subsidence showed an overall reduction in height up to 1.0 m beyond the 

 thickness of the new cap material. This major dredged material consolidation within the 

 center of the mound is responsible for 22% of the 121,300 m 3 mass balance shortfall 

 experienced in the standard baseline to postcap volume difference calculations. 



From 24 April to 27 May 1995 the final 119,300 m 3 of capping was released over 

 the CLIS 94 mound (Appendix D: Table 2). The bottom feature was resurveyed in 

 September 1995, three months after capping operations were completed (Figure 3-20). 

 Comparisons between the September postcap and April interim cap surveys show the 

 additional capping material placed over the CLIS 94 mound (Figure 3-21). Major 

 accumulations of CDM were detected in the vicinity of the CD A buoy, as well as over the 

 northwest and southeast flanks of the mound. Volume calculations have determined an 

 additional of 51,000 m 3 (43%) of CDM detectable through the use of successive 

 bathymetric surveys had accumulated over the CLIS bottom (Appendix A: Table 3-2). 

 Larger disposal barges (4000 yd 3 ) were employed during the last phase of capping and 

 were fundamental in the placement of a large volume of capping material in a short period 

 of time (35 days). 



Further analysis of the postcap survey shows an apparent ring of CDM 

 approximately 375 m in diameter clearly visible as "Total Net CDM Accumulation" as 

 well as a central "Total Net Consolidation" feature (Figure 3-22). The majority of smaller 

 barge (700 yd 3 ) release points appear to be north-northwest of the CDA #2 buoy position, 

 adding to the small mound of capping material visible at the interim cap stage of 

 development. The northern CDM feature is 3.0 m high at the apex and 110 m wide and is 

 responsible for the irregular shape of the CLIS 94 mound. The remainder of the CDM 

 layer exhibits several other high spots south and southeast along the ring. The 4000 yd 3 

 capacity barges concentrated their efforts over the central area of the mound. As a result, 

 the pocket of consolidation discovered in the analysis of earlier surveys seems to have been 

 filled to a certain degree, as a total negative volume of 10,800 m 3 is the end result 

 (Appendix A: Table 3-2). 



By tracking the three stages of development for the CLIS 94 mound, the UDM 

 deposit appears to be successfully capped and laterally stable (Figure 3-23). The survey 

 artifact that is visible as an irregular projection of UDM in most of the depth difference 

 plots corresponds to the northeast apron of the CLIS 90 mound. Differences in lane 



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



