Inco Ltd. is currently in the process of decommissioning the Whistle Mine site located in northern Ontario, Canada. Closure of the mine site includes relocation of waste rock from two waste rock piles into an open pit, and construction of an engineered dry cover system over the potentially acid-generating waste material. The final contoured surface of the backfilled pit will have a 20% slope. Site-specific field information is required on the construction feasibility and potential performance of dry cover systems prior to finalizing the design of the full-scale cover system. Three experimental dry cover systems were constructed over acid-generating waste rock at Whistle Mine in the fall of 2000. Each test cover plot has a different barrier layer overlain by a protective layer of non-compacted soil. The three barrier layers being evaluated are a geosynthetic clay liner (GCL), a compacted sand-bentonite mixture, and a compacted local silt/trace clay material. A monitoring system was installed to evaluate field performance of the test covers, which includes continuous monitoring of climatic parameters, gaseous oxygen / carbon dioxide concentrations and moisture / temperature conditions within the cover and waste materials. The quantity of net percolation through each test cover is also being monitored. A waste rock platform with a 20% slope was constructed to support the test cover systems, as well as a seepage collection system to prevent contamination of the local groundwater system. This paper describes the construction of the test cover plots, the waste rock platform and seepage collection system, and installation of the field performance monitoring equipment.
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