The Snap Lake Mine (the Mine) is a former underground diamond mine operated by De Beers Canada (De Beers), located about 220 kilometres northeast of Yellowknife in the Northwest Territories. The Snap Lake Mine operated from 2008 to 2015, and entered a Care and Maintenance mode in December 2015. In February 2017, the Mine underground workings were decommissioned and allowed to flood, in December 2017, De Beers announced the intent to enter into final closure, and in March 2019, De Beers submitted the Final Closure and Reclamation Plan for the Mine. Water management has always been an important component at the Mine and was considered in development of the Final Closure Plan to achieve the overall goal of “returning the site and affected areas around the Mine to technically viable and, where practicable, self-sustaining ecosystems that are compatible with a healthy environment and with human activities”.

Water management at the Mine has changed significantly since diamond mining operations ceased. During diamond mining operations, a large volume of water was pumped from the underground to the surface for management and release to Snap Lake and the downstream environment. This mine water was relatively high in total dissolved solids and total suspended solids and therefore had to be treated prior to discharge. Now that the underground is flooded, there is no longer a need to pump mine water to the surface and water management has been greatly simplified. Since 2017, small volumes of runoff water from the North Pile (a surface disposal facility that was used for processed kimberlite, waste rock, and non-hazardous solid waste during operations) is collected for management and release to the underground and to Snap Lake. Water quality and aquatic ecosystem monitoring has been conducted yearly since pre-mining. Results of these programs have informed adaptive management at the site and informed plans for closure.

The focus of this presentation is on water management and monitoring, for the Mine to the receiving environment, covering the history of the Mine to present and into planning for closure.