contrast in grain size and density between the sand and the mud should result in a change 

 in acoustic impedance and therefore a visible boundary or horizon on the subbottom 

 records. 



The current CSDS survey, conducted on July 8, 1994, employed swept- frequency 

 subbottom technology to map the extent of the fine-grained deposit. This survey was 

 extended 300 m west of the 1991/1992 survey boundaries to try to detect deposits caused 

 by the east-west transport documented in previous physical oceanographic studies of the 

 area (Bohlen et al. 1992, NUSC 1979). A bathymetric survey was run concurrent with the 

 subbottom survey. By comparing the 1994 results to previous surveys, the bathymetric 

 results documented areas of erosion and accumulation over the last two years. The 

 detection of an acoustic reflector under approximately one meter of material at the location 

 used for the disposal of fine-grained North Cove dredged material confirmed the 

 conclusion of previous REMOTS® and bathymetric surveys. Detection of a fine-grained 

 dredged material deposit at a taut-wire moored buoy so many months after disposal is 

 further evidence that the deposit is stable. 



Bathymetric and Subbottom Survey at the Cornfield Shoals Disposal Site, July 8, 1994 



