37 



Loss or compaction of dredged material resulted in underestimated total unit 

 thicknesses above BBC. 



5.1.4 Subbottom 



In the southern area of the cell, a sharp seafloor reflector indicated a smooth 



surface with little topography to scatter sound; 



In the central and northern portions of the cell, the surface was highly irregular 



and very rough, coincident with the sand cap and sand wave area; 



Below the surface in the sand-capped area, a series of discontinuous internal 



reflectors indicated a more heterogeneous deposit, and most or all of the sound 



was lost in the upper portion of the deposit; 



The data suggested that delineating cap thickness using the subbottom method 



will not be effective if there is a mixed zone that is greater than the resolution of 



the acoustic system; 



New material from the cell wall appeared to have settled on top of the uncapped 



material, suggesting that the strength of the material has increased and is 



potentially in a state of consolidation sufficient to support even large sized cap 



materials with minimal mixing. 



5.1.5 Video 



• Video data confirmed the presence of thick sand waves in the central and 

 northern parts of the cells, and the transition from the sand cap to the uncapped 

 dredged material was apparent both in audio and video; 



• Further evidence of consolidation of the uncapped material was suggested by the 

 presence of sled tracks noted during the second pass of the sled; 



• The video captured images of ex situ material deposited on top of the 

 dredged/cap material deposit, including entrapped debris and BBC, indicating 

 that material had become entrapped below the ambient current above the cell; 



• The presence of tunicates on the sand cap indicated that the sand provided 

 sufficiently hard substrate, within a fairly quiescent envirormient; 



• The video data collected along the cell walls confirmed that the steep walls were 

 scalloped, primarily from the dredging process. 



5.2 Recommendations 



Results from all of the environmental monitoring surveys were discussed among the 

 project proponents and the BHNIP TAC. Recommendations to modify the requirements 

 for dredging and disposal operations, and potential alterations to the environmental 

 monitoring approach, were considered. The recommendations briefly described below 

 were summarized from the October monitoring survey report (Murray 1997), and 

 preliminary recommendations from the project proponents as summarized by the CZM 



MONITORING RESULTS FROM THE FIRST BHNIP CONFINED AQUATIC DISPOSAL CELL 



