Finding solutions to ARD

One of the most serious environmental challenges for the mining industry is acid rock drainage (ARD).

ARD occurs naturally through the physical and chemical weathering of rocks that contain metal-sulphide minerals. When sulphide minerals are exposed to air and water, they react in such a way as to produce acid, which can then dissolve the metals they contain. Runoff from these sites can contaminate water courses and harm aquatic life. The visual effects of naturally occurring ARD have been used by prospectors who look for potential mineral deposits around rust-coloured rocks or waters.

Activities such as building roads and developing mines can duplicate and accelerate the weathering process by exposing sulphide-bearing rocks to air and water. Some metal and coal deposits are relatively rich in sulphide minerals. Sources of ARD at mining operations can include runoff and seepage from waste-rock and tailings.

Until recently, the potential long-term impact of ARD on the environment was poorly understood. Over the past few decades, however, governments and industry have lent their financial support to research programs aimed at predicting, preventing and controlling this problem. ARD prediction plans must be submitted as part of an application for a permit to mine in British Columbia. Plans are updated every five years or whenever significant changes to the operation occur. Permits issued under Section 10 of the Mines Act contain conditions for ARD prediction and prevention, including conditions for excavation, waste deposition, waste characterization, reclamation and the provision of financial security to cover the costs of any outstanding reclamation liability. The principle behind these practices is to prevent ARD by limiting exposure of sulphide minerals to air and water. Reducing infiltration of water by laying a soil cover and then planting vegetation is one strategy that can limit ARD generation; another is to place sulphide-bearing rock wastes under water to restrict contact with air. In cases where ARD cannot be eliminated, integrated collection and water treatment systems are implemented. British Columbia’s Ministry of the Environment, Lands and Parks sets water quality standards to protect the aquatic environment. Compliance with water quality requirements is monitored through regular sampling, the results of which are reported to government and are a matter of public record.

— The preceding is an excerpt from Mining: Who Needs It? — an information bulletin published by the Mining Association of British Columbia.