Abstract:

Mining in the Northwest Territories, Canada, is under the jurisdiction one of four Water Boards, which are co-managed regulatory bodies composed of both federal and First Nations members. The directive of these Water Board’s is to regulate the use of land and water, and the deposition of waste, in the sensitive environment of Canada’s North. As such, these Water Boards are responsible for the issuance and regulation of permits and authorizations in the region, including Water Licences.

A critical component of Water Licences in the region is seepage from above-ground waste rock storage areas (WRSAs). Seepage volumes are highly variable in this permafrost-driven terrain, and rarely does seepage report directly to a receiving environment such as freshwater lakes and streams. ERM Consultants Canada (ERM) developed an approach to set terrestrial quality objectives for evaluating seepage quality from WRSAs to supplement the traditional approach of using water quality guidelines for the protection of aquatic life. Terrestrial quality objectives are water quality criteria intended to support the overall intent of Water Licence guidance from the Water Boards and are designed to be protective of wildlife that might use seepage areas as a source of water. They are distinct from the freshwater aquatic life pathway that often restricts operational discharge criteria.

The process for establishing these terrestrial quality objectives will be discussed. The process starts with default guidelines from organizations including the Canadian Council of Ministers of the Environment (CCME), Environment and Climate Change Canada (ECCC), and relevant Canadian provincial and territorial governments (i.e., the Government of British Columbia). Hydrogeological information from the WRSA conceptual model is used to help identify potential areas for monitoring. Species-specific drinking water thresholds are then derived for substances that exceed the initial screening values using the available toxicological literature. As with any monitoring program, trend analyses plays an important role to identify priority seeps where more intensive monitoring may be warranted. The net result is a framework that increases the confidence that seepage water is not presenting an unacceptable hazard to wildlife resources, and ultimately, leads to a more robust risk-based closure process to help mines transition to post-closure land uses.

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Jessica Lowey