36 



Little change in size or shape was detected in the mound complex, relative to 

 previous surveys. However, depth difference calculations found 0.25 m to 0.75 m of 

 consolidation over the majority of the mound in comparison to the postcap bathymetric 

 survey of March 1994 (Figures 3-16 and 3-17). The pockets of 0.5 m to 0.75 m of 

 consolidation detected near the center of the NHAV 93 mound in September 1995 appear 

 to be slightly enlarged in the 1996 survey (Morris 1997). 



The current shape of the capped mound is apparent in depth difference comparisons 

 with the September 1993 baseline bathymetry (Figure 3-18). As of July 1996, the NHAV 

 93 mound has a maximum mound height of 2.25 m and is connected to the CLIS 94 

 mound by a ridge of CDM approximately 0.5 m thick (Figure 3-19). Comparisons 

 between the detectable limits of NHAV 93 in July 1996 and September 1995 indicate slow 

 consolidation of the apron material evident in the narrowing of the detectable margins of 

 the disposal mound. 



3.3.2 REMOTS® Sediment-Profile Photography 



The REMOTS® survey over the NHAV 93 mound was conducted primarily to 

 evaluate the recolonization status of the center of this capped mound. Complete REMOTS® 

 results for the NHAV 93 disposal mound are available in Appendix D. Analysis of the 

 images provides additional information on the presence or absence of erosion of surface 

 sediments which can aid in interpretation of bathymetric results. 



3.3.2.1 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 dredged material (i.e., no loss of fine material). The 

 replicate-averaged mean camera penetration ranged from 14.97 cm to 16.74 cm (Appendix 

 A, Table 3-3). Boundary roughness values ranged from 0.49 cm to 0.75 cm. The primary 

 cause of boundary roughness was classified as physical dismrbance. However, several 

 replicates are showing signs of increased biogenic activity in the surficial sediment layers. 



Historic dredged material was detected and measured at all five REMOTS® camera 

 stations. As expected, dredged material thickness was greater than penetration in all 

 replicate photographs. Redox rebound intervals were noted at each station over the center 

 of the NHAV 93 mound. These results provide no indication of winnowing (coarsened 

 grain sizes) or scour (> 3.0 cm physical boundary roughness) which is consistent with a 

 conclusion of no erosion of the cap sediments during the study period. 



Monitoring Cruise ai the Central Long Island Sound Disposal Site, July 1996 



