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On the morning of August 4, 2014, the tailings storage facility (TSF) at the Mount Polley Mine (MPM) breached, spilling 17.1M m3 of supernatant and tailings pore water, and 7.9M m3 of tailings and earthen construction material. While it was subsequently determined by geotechnical experts that the TSF itself had not failed, that the breach was caused by the failure of an underlying clay layer (known as the glaciolacustrine or GLU layer), the breach nonetheless caused significant physical damage to the area adjacent to the TSF, including 8.5 km along Hazeltine Creek, about 500 metres of lower Edney Creek, and a few hundred metres along the shorelines of Polley Lake and Quesnel Lake. In addition, a significant amount of water, tailings and scoured creek material entered Polley Lake and Quesnel Lake.
In total, about 2.4 square kilometres of terrestrial area was impacted by the breach. Extensive studies were undertaken by MPM in support of their response and remediation planning, and to satisfy the Pollution Abatement Order (PAO) issued to the mine on August 5, 2014 by the Ministry of Environment and Climate Change (ENV). These studies included: two Post-Event Environmental Impact Assessments reports, issued June 2015 and June 2016, Human Health and Ecological Risk Assessments, issued in May 2017 and Dec 2017. A Remediation Plan for the site was prepared by MPM in March 2019, and accepted by ENV (a final requirement of the PAO). This order was lifted September 12, 2019.
The results of the expert studies concluded the impacts associated with the spill were primarily physical and not chemical. Risks to human health were determined to be low, and risks to the environment were low to moderate, with the moderate risk being related to physical impacts, not chemical. The risks of chemical contamination from the spill were determined to be low to very low in both the terrestrial and aquatic environments. In response to these findings, MPM has focused its remediation efforts on physical clean-up and remediation of the physical impacts of the spill.
Some of the major milestones of the mine’s environmental remediation efforts to-date include:
Community Update bulletins, technical memos and reports were prepared by MPM in response to community concerns and questions raised at community meetings and at meetings of the mine’s Public Liaison Committee. Refer to our Community Outreach page.