T7_ 



the 1994 survey (CTR, 200N, 400S) showed improvement, although two replicates at CTR 

 had thin and patchy RPD and low OSI values of 2 and 3 (Figures 3-7 and 3-8). 

 Comparisons of the 1995 NHAV 93 REMOTS® results to the reference areas indicate the 

 oxygenation status at the sediment/water interface over the region may have been affected 

 by seasonal hypoxia. As a result, RPD and OSI values on the mound and in the reference 

 areas may have decreased in response to the reduction in available oxygen. 



3.1.3 Geotechnical Coring 



A total of eleven geotechnical cores were collected to provide a deep, cross- 

 sectional view of the multiple sediment layers that make up the NHAV 93 mound (Figure 

 3-9; Appendix A: Table 2-2). Seven cores with penetration depths varying from 131 cm 

 (GC-9) to 272 cm (GC-6) were split, visually described, and analyzed for the properties 

 listed in Section 2.4 of this document. These seven cores represent the end-member of a 

 five-core data set collected over the NHAV 93 mound at different stages of development 

 (baseline, precap, postcap, four months postcap, and eighteen months postcap; Appendix 

 C: Table 1). Graphics depicting the entire time-series data set are provided in Appendix 

 C. A report pertaining to the geotechnical analysis of cores GC-1 through GC-11 will be 

 included in a final report submitted by Armand J. Silva, P.E., of Geotechnical Consulting 

 Engineers. 



Core GC-5 was obtained over the southwest flank of the NHAV 93 mound 

 (41°08.996' N, 72°53.629' W) and penetrated 269 cm into the sediments (Figure 3-9). 

 The visual core description indicates the first 180 cm of material constitutes the New 

 Haven project CDM (Figure 3-10). The CDM layer is composed of several sediment 

 strata of soft, black and olive-gray sands, silts, and clays. A thin layer of New Haven 

 UDM, olive-grey clayey silt, was visible from 180 cm to 200 cm of penetration. A 10 cm 

 to 15 cm layer of dark silt is representative of the historic dredged material that makes up 

 the CLIS 88 and Norwalk mound aprons. The remaining 55 cm of sediment collected in 

 Core GC-5, olive-gray, clayey silt with shell fragments, is typical of ambient, basement 

 material at CLIS. 



Core GC-10 was taken approximately 75 m southwest of the NHAV 93 mound 

 center (41°09.075' N, 72°53.521' W; Figure 3-9). A total of 248 cm of CDM, UDM, and 

 historic dredged material was recovered in GC-10. The top 134 cm of sediment was 

 composed of soft, black, clayey silt with organics and shell fragments (Figure 3-10). No 

 distinct horizon was visually detected between New Haven cap and dredged material 

 layers; however, the UDM/CDM interface is estimated at approximately 100 cm of 

 penetration. From 100 cm to 218 cm of penetration this core is made up of the various 

 layers of silt, sand, and gravel. The division between New Haven dredged material and 



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



