In 1985 Boojum Research Ltd. began work to decommission the 60-hectare site of the South Bay Mine, a former copper and zinc mine in north-western Ontario using Ecological Engineering. The work continued until the site was turned over to the provincial government in 2002.
The site was complex, the mine site and mill were contaminated allowing runoff from a mill pond to contaminate a nearby lake (Boomerang Lake), underground workings were producing leachate which was entering the lake, the tailings were releasing leachate underground, and other groundwater plumes were becoming contaminated and threatening to contaminate other nearby lakes. Boojum decided to use Boomerang Lake as a polishing pond, and route underground leachate into it. Groundwater was treated in situ.
Most of Boojum’s efforts were then concentrated in remediating Boomerang Lake. The overall project required the use of a number of Boojum’s technologies to slow and contain the AMD leachate which was threatening to contaminate a nearby trophy fishing lake. This was not easy, given that the site is a peninsula almost entirely surrounded by the fishing lake and its tributaries. Virtually every technique in Boojum’s ecological toolbox was deployed at South Bay. Many techniques developed there have since been applied at sites elsewhere.
Much of the site has been restored to a wilderness state, although the tailings basin and the flooded mine workings continue to generate acidity, and will do so for thousands of years.
During the mine’s lifetime (1971 to 1982) acidic effluent was directed into Boomerang Lake, one of the Confederation tributaries, where acidity was controlled by periodic applications of lime. The lime induced the precipitation of iron, zinc, copper and other metals which settled into the lake sediment, where they remained.
Boojum’s first contract at South Bay was to reduce the contaminants arriving in Boomerang Lake by way of a settling pond, Mill Pond, which intercepted contaminated run-off from the mine, mill, and a small waste rock pile. Although the mine was closed and the mill dismantled, considerable amounts of ore concentrates had been spilled in the area, while the gravel, used to level the ground beneath the structures, contained considerable amounts of pyritic minerals so the run-off reaching the pond was still acidic.
Boojum began the rehabilitation of Mill Pond in 1986 by adding several tonnes of sawdust and hay bales to the pond bottom to begin the formation of sediment within which ARUM could occur. Later, hay, fertilizer and Carbonaceous Phosphate Mining Waste (CPMW) were added (See CPMW). The outflow from the pond followed a long, narrow valley to Boomerang Lake. Boojum build dams in the valley to create ponds within which ARUM and Biological Polishing could take place.
In 1988, Boojum added 120 bales of hay to Decant Pond, a five-hectare impoundment located on the tailings deposit (SEE ARUM). The deposit itself, containing an estimated 785,000 tonnes of acid-generating tailings was located on the thin neck of the peninsula, separating Boomerang Lake and Mud Lake. Within a month, the pH of the pond had increased from 3.1 to 5.0, while the level of dissolved metals, most notably zinc and iron, dropped sharply. More organic matter in the form of 30 truckloads of forestry waste was added to the shallow waters off the tailings beach in 1992.
By 1992, an estimated 16 tons of sulphur per year was reaching Boomerang Lake, either in seepage directly from the tailings, or by way of drainage ditches which had been dug to divert contaminated surface and groundwater from directly reaching Confederation Lake. The contaminants had lowered the pH of the Boomerang Lake to 3.5, approaching the critical level of 2.5 below which iron precipitates. This would remobilize the previously contaminated lake sediments.
In the spring of 1992, 9 tonnes of Carbonaceous Phosphate Mining Waste were added to the Boomerang Lake to stimulate in situ vegetation and to raise the pH (see CPMW). This application was followed by placement of more than 20,000 brush cuttings to provide substrate for attached algal growth (See BIOLOGICAL POLISHING). More sediment and brush were added over the next few summers. Mass balance calculations determined that, from 1995 to 1999, the sediment captured 0.6 tonnes of copper, 407 tonnes of iron, 238 tonnes of sulphur and 57 tonnes of zinc. In 2003, 6 tonnes of magnesium scrap were suspended in the lake on an experimental basis to react with hydrogen in the water and counteract any further decrease in the pH. Subsequent analysis has confirmed that this, in fact, occurred.
Until 1993, the muskeg bog that separated Mud Lake from the tailings basin had protected it from acidity and contamination. However, in spring 1994 the lake’s pH abruptly dropped to below 2.5. Sixty tonnes of NPR were added to the lake, raising the pH to 3 where it remained until 2001 when it again began to fall (See CPMW). Hydrological studies determined that a contaminated plume of groundwater flowing through and beneath the tailings was following the floor of a deep bedrock canyon and had migrated beneath the muskeg and was welling up through the Mud Lake sediment. With support from the National Research Council, Boojum began to inject urea and sugar into the groundwater stream to stimulate the activity of ureolytic and sulfate reducing bacteria, to increase pH and precipitate metals before the plume arrived at the lake. To reduce the flow of AMD out of the tailings, in 1999 Boojum applied CPMW to the tailings surface (see CPMW), a further field trial of PHITO. Tests of both treatment applications are ongoing, as is the Mg test application to Boomerang Lake.
For a PDF, please send an email to: margarete.kalin@utoronto.ca
C92 Kalin, M., 2001 Closure with Ecological Engineering of a Remote Cu/Zn Concentrator: Overview of 10 years R & D Field Program. Proceedings of the Fourth International Symposium on Waste Processing and Recycling in Mineral and Metallurgical Industries, MET SOC 40th Annual Conference of Metallurgists of CIM, Waste Processing and Recycling in Mineral and Metallurgical Industries IV, Toronto, August 26-29, pp. 521-533.
B4 Kalin, M. 1998. Biological Polishing of Zinc in a Mine Waste Management Area in Acid Mining Lakes: Acid Mine Drainage, Limnology and Reclamation, W. Geller, H. Klapper and W. Salomons (Eds.), Springer-Verlag, Berlin, Germany, pp. 321-334.
P13 Lau, Peter C.K., H. Bergeron and M. Kalin, 1998. Identifying Culpable and Potentially Useful Bacteria in Acid Mine Groundwater Seepage Path. Proceedings of ‘Quebec 98’ Conference (AGC/GAC, AMC/MAC, APGGQ) Abstract Volume, Quebec City, Quebec, May 18-20, p. A-103.
P10 Kalin, M., M. Berezowsky and J. Pawlowski, 1997. Evaluating Remedial Measures on Plumes of Acid Mine Drainage in the Groundwater with Ground Geophysics. ICARD Conference, Vancouver, B.C., May 31-June 6, P-06.