Verification of Environmental Clamshell Dredging - St. Lawrence River Remediation Project

Abstract

Reynolds Metals Company, under Administrative Order by the United States Environmental Protection Agency and the New York Department of Environmental Conservation, conducted the remediation of contaminated sediment in the St. Lawrence River associated with its Massena Plant operations. Mobilization for this effort started in Spring 2001 and dredging operations were completed by mid-October 2001. Chemicals of concern included polychlorinated biphenyls (PCBs), polyaromatic hydrocarbons (PAHs), and dibenzofurans; with PCB concentrations ranging from below method-detection limits to greater than 2000 parts per million. Identified areas of contamination approximated 70,000 cubic yards of sediment along a half-mile stretch of the St. Lawrence River, with water depths ranging from 0 to 28 feet. Sediment was removed through use of a Cable Arm Environmental Clamshell bucket. The use of the Cable Arm buckets allowed for a level cut, and minimized turbidity/water collection. Each bucket was outfitted with depth sounders, pressure transducers and pressure switches that assisted in obtaining the location of the bucket in the water column, design depth determination, and removal verification. WinOPS dredge positioning software interfaced the bucket data with global positioning systems (located on both the crane boom tip and dredge barge), tide gauge, and bathymetric data in order to provide real-time monitoring and archival of these parameters in an electronic format.