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TSF Breach

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.

“the breach was caused by the failure of an underlying clay layer”

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.

“impacts associated with the spill were primarily physical and not chemical”

The results of the expert studies (ref: key documents below) 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. The remediation conducted is based on the results of detailed site investigations, and the human health and ecological risk assessments. The goal of the environmental remediation work is to repair and rehabilitate the areas impacted by the tailings spill and provide a path to self-sustaining ecological processes that result in productive and connected habitats for aquatic and terrestrial species.

“risks of chemical contamination from the spill were determined to be low
to very low in both the terrestrial and aquatic environments”

Some of the major milestones of the mine’s environmental remediation efforts to-date include:

  • Repair of lower Edney Creek, re-establishment of link to Quesnel Lake and installation of new fish habitat for spawners from Quesnel Lake, completed in spring 2015, with evidence of successful spawning by Interior Coho, Kokanee and Sockeye Salmon.
  • Completion of construction of a new Hazeltine Creek channel in May 2015, to control erosion and provide base for remediation of the creek itself and the creek valley.
  • Ongoing planting of native trees and shrubs in the riparian and upland areas along the creek, now totally more than 600,000 trees and shrubs planted.
  • Installation of over 6 kilometres of new fish spawning and rearing habitat in upper to middle Hazeltine Creek. Evidence of successful 2018 and 2019 Rainbow trout spawning in upper Hazeltine Creek.
  • Clean-up and repair of 400 metres of Quesnel Lake shoreline, including placement of new fish spawning gravels.
  • Re-establishment of wetlands in the Polley Flats area adjacent to the repaired TSF.

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.

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KEY DOCUMENTS

Key Reports

Pollution Abatement Order

Technical Memos & Reports

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