Northern Wood Preservers Alternative Remediation Concept (NOWPARC)

In the late nineties a major effort was put forward to clean the contaminated bottom of Lake Superior in the Port of Thunder Bay, ON. Pierre Gagne Contracting was awarded two contracts that were part of the clean-up activities. 

The scope of work for the first contract was the construction of a rockfill berm and a storage cell for sediment treatment. The berm was 850 meters long and 1.5 meters above Lake Superior water level. The final as-build rock fill material used  amounted to 147,709 cubic meters or 300,000 metric tonnes. The storage cell had an area of 1.5 hectares.

The second contract was for the dredging of the lake bottom in coordination with the berm construction. To deal with site specific conditions, such as the unconsolidated nature of the highly contaminated sediment, a variety of debris mixed in with the sediment, and the lack of space for dewatering a Cable Arm Environmental Clamshell was used with 5.5 m3 grab capacity. It was operated from a 100 ton crane mounted on a spudded barge with several refinements to minimize environmental impacts. The dredge depth below top of sediment was locally as much as 2.5 m but was more typically of the order of 1 m or less. Total volume of the dredged sediment was 2,000 cubic meters. Numerous and lengthy periods of downtime were experienced, mainly associated with handling a large quantity of subsurface debris (sawdust, logs, poles, wires and a few rail cars) located close to the pier wall which hindered the operations.