The role of aquatic ecological risk assessment to guide effluent management from mine waste Lower, N.; Quach, M.; Marsland, R.
Mine waste can pose a risk to the natural environment, especially if on-site closure conditions change. At remote locations in particular, such sites can be viewed as an unknown risk by regulators, and mining companies are often asked to monitor or treat an unknown risk or to develop management options to reduce them. This paper presents a case study for a historic mine site in northwest British Columbia. Discharges from the mine portals and waste dumps are entering the river, which flows into southeast Alaska. Aquatic risk assessment was used to evaluate the potential for contamination of aquatic biota due to changes in water quality. To complete the risk assessment, scientists studied water quality upstream and downstream from mine site discharges and completed a detailed review of historic data. The team identified cadmium, copper, lead and zinc as the contaminants of potential concern and assessed the discharges’ impact on a variety of fish species including coho salmon, sockeye salmon, Chinook salmon and bull trout. Although significant levels of copper and zinc were found downstream from the mine, the drainage was assessed to pose a low risk to fish in the river. The potential risks to fish were measured using a hazard quotient (HQ): if this is greater than one, it can indicate unacceptable risks to fish and other aquatic life. The study concluded that, regardless of whether a water treatment plant were to be operating or not, the HQs were less than one for the majority of the year, including during critical time periods for fish migration and spawning. The study identifies data gaps on the ecology of the river, for example, the use of the river by fish during the winter and spring thaw; if needed, additional data collection could be targeted to supplement the aquatic risk assessment. This case study showcases an approach to evaluating ecological risk at remote locations and guiding focused data collection and management options. This demonstrates the need to implement treatment and management strategies that are appropriate to reduce off-site impacts.
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