Decommissioning of the South Bay Mine using ecological engineering : final report.

Abstract

The water quality data for Confederation Lake do not suggest a deterioration. Although the discharge from Boomerang Lake at station C1 was high during spring run-off in 1994, by the end of the year, the concentrations were similar to those reported for 1992. This reduction can be potentially accounted for by the phosphate rock application carried out in 1993 and 1994 in Boomerang Lake. Further applications of fine ground phosphate rock are planned for 1995 to counteract the slow, but steady, acidification of Boomerang Lake. The Backfill Raise Diversion Ditch has reduced the contaminant loading to Confederation Lake from the surface seepages significantly. The bottom water at station C8 shows higher concentrations of zinc than the surface water. Electromagnetic surveys have established that a seepage enters Confederation Lake at a depth of about 6 m at the Mill site. The effects of the diversion ditch, in terms of stopping the deep seepage discharge, are more difficult to quantify. A slower response by the groundwater flow regime to hydrogeological modifications can be anticipated, compared to more rapid surface water seepage responses. Monitoring will continue in 1995 and remedial actions will be developed. The hydrological reevaluation of the perched tailings area carried out in 1993 leads to the conclusion that, with changes in the geochemical and hydrological conditions in the tailings, permeability and flows leaving the tailings area can change correspondingly. It was suspected that Mud Lake water quality may be deteriorating. This indeed was the case, and the investigations carried out in 1994 have been documented in a separate report which has been submitted to the Ministry of Environment and Energy in December 1994. In the Mud Lake Report, detailed recommendations are made for a full hydrological assessment of the entire site in 1995. The deterioration of Decant Pond water quality, due to acid discharge from the tailings beach (noted in 1992), has been successfully counteracted through the installation of an ARUM (Acid Reduction Using Microbiology) berm along the beach. Treatment of the acid pool on the tailings with phosphate rock has reduced the iron and aluminum loadings to the pond. Zinc concentrations in the discharge from Decant Pond have been around 1 mglL in 1994, as compared to 9 mglL by the end of 1992. The biological polishing process, its capacity to remove zinc, along with detailed evaluations of iron cycling, sediment chemistry and the work carried out on the phosphate rock applications in Boomerang Lake, have been summarized in a report entitled: Biological Polishing Phase IV: Model Verification and Scale-up (CANMET Contract, July 1994). This report has also been submitted to the Ministry of Environment and Energy, and describes part of the ongoing research for the decommissioning of the South Bay mine site.