Elevated levels of mercury and PCBs in sediment and fish contributed to Peninsula Harbour being designated as one of several Great Lakes “Areas of Concern.” Peninsula Harbour is the main harbour at Marathon, Ontario on Lake Superior. Mercury contamination resulted from historic discharges associated with the pulp and paper industry, specifically a chlor-alkali plant producing chlorine dioxide for use in bleaching paper.
A thin-layer “cap” was chosen as the preferred remedial option by government and the community. Construction in 2012 entailed placement of 15 to 20 cm of clean sand on top of the area of highest contamination in Peninsula Harbour. The project cost 7 million dollars with funding provided by the federal and provincial governments and former owners of the mill and associated facilities.
The intent of the thin-layer cap is not complete isolation of the underlying contaminated sediment, but rather enhancement of natural recovery due to cessation of the source of contamination and burial of existing sediments through natural deposition.
Provincial and federal government commitment to long-term monitoring is evidenced through the extensive suite of work to be completed during summer, 2017. The Ontario Ministry of the Environment and Climate Change and Environment and Climate Change Canada are cooperating to carry out this work. The Peninsula Harbour Community Liaison Committee, a cross-section of Marathon and Pic River area residents, also support long-term monitoring of the cap and Peninsula Harbour Area of Concern.
2017 long-term monitoring activities include:
- Performance monitoring to evaluate cap placement and to determine if the native sediment has been incorporated into the thin-layer cap;
- Remedial goal monitoring to evaluate cap effectiveness (i.e. determine if the average concentration of mercury on the cap is <3mg/kg); and,
- Ecological recovery monitoring to evaluate benthic and submerged aquatic vegetation re-colonization of the cap, and evaluate trends of mercury in fish tissue. Benthic organisms are organisms living on or in lake bottom sediment.
Scientists will also be looking at the sediment near the boat launch area and in other parts of the harbour.