65_ 



The geotechnical cores collected over the NHAV 93 mound during the July 1994 

 monitoring cruise confirmed the subbottom profiler data set. The X-Star system detected 

 the differences in acoustical signamre based on a sharp increase in sediment pore water at 

 the CDM/UDM interface. The increase in water content corresponded to a sharp decrease 

 in sediment density, creating an acoustic reflector within the sediment deposit. Geotechnical 

 cores were originally obtained over NHAV 93 at several stages of mound development to 

 supplement the bathymetric data set as well as examine and quantify mound consolidation. 

 This suite of geotechnical cores provided a solid comparison for the bathymetric models and 

 exceptional ground truth data for the subbottom profiler data (Figures 3-29 and 3-30). 



Core U, collected over the center of the NHAV 93 mound, penetrated 180 cm into 

 the sediments. Bathymetry detected 2.0 m of UDM and an undetermined thickness of CDM 

 deposited in the area of Core U (Figure 3-29). The subbottom data indicated the presence of 

 2.0 m of UDM and 1 .0 m of CDM over the center of the mound (Figure 3-30). The 

 geotechnical analysis of Core U observed CDM at the sediment-water interface and 

 extending to 87 cm of penetration (Figure 3-31 A). The New Haven project UDM extended 

 down the core an additional 93 cm to the penetration limit. 



Core V penetrated 210 cm into the southwestern flank of the NHAV 93 mound, 

 outside the area of concentrated subbottom analysis. Both the bathymetric and subbottom 

 paper trace data reveal that the area around Core V received less than 0.25 m of UDM firom 

 the 1993-1994 New Haven Capping Project. However, approximately 1.5 m of capping 

 material was deposited over the southwest flank of the mound in February 1994 as part of 

 the final phase of CDM deposition (Figures 3-29 and 3-30). The core sampled 

 approximately 160 cm of CDM over a 15 cm thick layer of project UDM and a 25 cm layer 

 of historic dredged material originating from the Norwalk and CLIS 88 mounds (Figure 3- 

 31B). 



Core W was collected over the northeast margin of the NHAV 93 mound, penetrating 

 260 cm into the CLIS sediments. The bathymetric data indicated approximately 0.25 m of 

 CDM and less than 0.25 m of UDM in the vicinity of Core W (Figure 3-29). Subbottom 

 remms detected approximately 1.5 m of dredged material (project UDM and historic) 

 overlaid by 0.25 m to 0.5 m of NHAV 93 CDM (Figure 3-30). The core description 

 reported the presence of a CDM layer 40 cm thick overlaying a 15 cm to 20 cm layer of 

 project UDM. Historic dredged material from the CLIS 89 mound was visible to 200 cm of 

 penetration (Figure 3-32A). 



Monitoring Cruise at the Central Long Island Sound Disposal Site, July 1994 



