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3.0 RESULTS 



3.1 NHAV 93 Mound 



3.1.1 Bathymetry 



Seven bathymetric and three REMOTS® sediment-profiling surveys were conducted 

 over the NHAV 93 mound since September 1993 to monitor the progress of the CAD 

 mound construction and consolidation over time. The latest bathymetric survey (1600 m x 

 1600 m), eighteen months after capping operations were completed, displays a mound 

 complex approximately 820 m wide and composed of eight disposal mounds (CLIS 87, 

 COS 88, CLIS 89, CLIS 90, CLIS 91, SP, NORWALK, and NHAV 93) (Figures 3-1 and 

 3-2). Overall, little change in size or shape was detected in the mound complex relative to 

 previous surveys, indicating continued lateral stability. 



Depth difference calculations detected 0.25 m of consolidation over the majority of 

 the NHAV 93 mound in comparison to the postcap bathymetric survey of March 1994 

 (Figure 3-3). Smaller pockets of 0.50 m of consolidation were detected near the center of 

 the NHAV 93 mound. Comparisons with the September 1993 baseline survey calculated 

 the total accumulation of material within the 2.56 km 2 area over the past two years. The 

 depth difference contour plot displays the central NHAV 93 mound with a height of 

 2.25 m at the apex and a diameter of approximately 800 m (Figure 3-4). In addition the 

 CLIS 94 mound is clearly visible to the northeast. A ridge of dredged material up to 

 0.5 m thick connects the two mounds, forming a berm that could be useful in containing a 

 future UDM deposit. 



3.1.2 REMOTS® Sediment-Profile Photography 



The REMOTS® sediment-profile photographic survey over the NHAV 93 mound 

 was conducted to evaluate the recolonization status of the CAD mound in comparison to 

 the July 1994 survey, as well as to search for evidence of surface layer consolidation, 

 bedload transport, and oxidation within the surface sediment layers. Complete REMOTS® 

 results for the NHAV 93 disposal mound are available in Appendix B Table 1 . 



3.1.2.1 Sediment Grain Size and Stratigraphy 



Grain size and surface roughness data indicated no distinct pattern at the NHAV 93 

 disposal mound. The major modal grain size at every station was >4 phi, indicating no 

 significant coarsening of surface CDM due to bedload transport of fine-grained material. 

 Boundary roughness values ranged from 0.42 cm to 1.82 cm with the lowest surface 



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



