Contaminant sources and sinks: summary of R & D 1985 to 2002, South Bay

Abstract

The South Bay Waste Management Area (SBWMA) is located in Northern Ontario, approximately 85 km north east of Ear Falls (51o 08N, 92o 40E). A zinc and copper mine was operated on the site from 1970 to 1981. The mine, the site of the former mill, a waste rock pile and the tailings are all located on a peninsula within the watershed of Confederation Lake, an important fishing lake with hunting lodges in the English River drainage basin. In fact, the former mine site is virtually surrounded by a chain of tributary lakes which feed Confederation – Boomerang Lake (1M m3) to the south which flows directly into Confederation, and Mud Lake (0.07M m3) and Lena Lake ( 0.7Mm3) to the north and northwest which flow to Confederation by way of Armanda Lake (1 M m 3). Boomerang Lake was contaminated during the life of the mine, and Mud Lake was contaminated in 1994 by a groundwater plume moving from the tailings. Both have been designated as part of the SBWMA and have been utilized in the clean-up effort. . Decommissioning activities, undertaken immediately after the closure of the mine, consisted of burying the portal and sealing the shaft, raises and caps. All buildings were destroyed - except for the concrete foundations that were left in place - and the contaminated building materials buried except for those materials subsequently used in the restoration. The tailings were covered in gravel to a depth of one foot and revegetated. These efforts had no effect on the generation of acidity and contaminants. A 1986 environmental study noted that acidic plumes were leaving the site and recommended that they be treated by the occasional liming of Boomerang Lake, a proposal that was not accepted. In 1986, Boojum Research Limited was invited to assess the potential applications of ecological engineering at the SBWMA and the site has thus become a demonstration site of this decommissioning approach. The SBWMA contains two distinct contaminant-generating areas; the Mine/Mill Site and the tailings basin. Measures taken at the SBWMA have substantially reduced the mobilization of contaminants on the site, and redirected all contaminants into two major contaminant sinks, Boomerang Lake and Mud Lake. Mass balances are presented below for the contaminants mobilized on-site and captured by the sinks. The noted retention of tons of contaminants provides a measure of the effectiveness of the effort to date.