Unexpected Conditions, Unforeseen Complications and Unplanned Expenditures: Lessons Learned in the Dredging of PCB-Contaminated Sediment from the St. Lawrence River

In the spring of 2001, an ambitious dredging project was kicked off in Massena, New York. The objective: remove an estimated 77,000 yd³ of PCB-contaminated sediment from the St. Lawrence River opposite the former Reynolds Metals Company St. Lawrence Reduction Plant. A 3800-ft long sheet pile wall to isolate the remediation area from the river was installed, within which contaminated sediment were dredged using specialized clamshell buckets and hauled ashore for dewatering, processing and disposal. The project was exquisitely detailed and diagramed, from the expected percentage of analytical variability in sediment PCB analyses down to the timing, in minute and seconds, of each bucket cycle, for the work had to be accomplished in one season—the sheet pile wall had to be pulled and equipment demobilized before the river froze. A number of complications ensued, both onshore and on the water, requiring frequent departures from the expected flow of work and schedule. In the end, work was being driven as much by the Contingency Plan as it was by the Final Design and Work Plan. Many lessons were learned, which fall into several broad categories, including equipment and labor; pre-dredging bottom conditions and extent of contamination; and regulatory oversight.