1.0 INTRODUCTION 



The Cornfield Shoals Disposal Site (CSDS), a dredged material disposal site 

 managed by the US Army Corps of Engineers, New England Division, as part of the 

 Disposal Area Monitoring System (DAMOS) Program, has been used for the disposal of 

 dredged material since 1978. The site is located 6.12 km south of Cornfield Point in Old 

 Saybrook, CT (Figure 1-1). Because the site is exposed to strong tidal currents, dredged 

 material released at the site is expected to be dispersed following disposal (Bohlen et al. 

 1992). It is the only open water disposal site managed by NED as a dispersive disposal 

 site. Although it is not detrimental for material to remain on site, any dredged material 

 released there must have no adverse impact if it is to be transported away from the area. 

 All other DAMOS disposal sites are containment sites where it is desirable for the dredged 

 material to remain on site in a stable deposit. 



Evidence of active bed transport in a 1990 survey at CSDS prompted concern by the 

 National Marine Fisheries Service and the Connecticut Department of Environmental 

 Management about possible impacts of suspended sediment transport on shellfish beds 

 north of CSDS. In 1991 and 1992, the site was monitored during the disposal of sands 

 from the Connecticut River (50,800 m 3 ) and fine-grained material from North Cove 

 (105,479 m 3 ). This was the first time a taut-wire moored buoy was deployed at the site. 

 This study determined that, although the area had a high degree of active bed transport, 

 some of the fine-grained material formed a detectable deposit at the disposal location and 

 remained on site for a period of at least eight months (Wiley 1996a). These results 

 suggested that CSDS might require management information regarding the longer term fate 

 of sediments deposited at the site. 



The deposit of fine-grained material was documented in REMOTS® sediment- 

 profile photographs and in changes to the bathymetry. The REMOTS® photographs, in 

 addition to detecting the presence of the fine-grained dredged material, also documented a 

 layer of sand that had moved over the deposit since its deposition. Because the sand 

 limited the penetration depth of the REMOTS® camera, it was unclear how extensive the 

 fine-grained deposit beneath the sand layer was. At the conclusion of the study in August 

 1992, the deposit had been in place for four months, and the fate of the fine-grained 

 deposit over a longer time frame was unknown (Wiley 1996b). 



The disposal of fine-grained dredged material onto a sandy seafloor provides a 

 layering of different grain size and sediment densities that may allow for the detection of 

 the boundary between fine-grained dredged material and ambient sand by swept-frequency 

 subbottom seismic profiling. Subbottom seismic profiling determines changes in sediment 

 acoustic impedance (the product of the sediment's density and the speed of sound). The 



Bat hy metric and Subbottom Survey at the Cornfield Shoals Disposal Site, July 8, 1994 



