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Remediation Updates





Summary: August 4, 2014 Tailings Storage Facility Breach at the Mount Polley Mine

A breach of the tailings storage facility (TSF) occurred at the Mount Polley mine on August 4, 2014 causing water and tailings to be released. Emergency protocol procedures were immediately enacted. The mill was shut down and placed on care and maintenance status.

The TSF breach caused physical impact to the downstream environment:

  • erosion of the embankment separating the TSF from Polley Lake, as well as along Hazeltine Creek
  • deposition of trees and woody debris in Polley Lake, along the sides of the erosion path associated with Hazeltine Creek, and into Quesnel Lake at the mouth of Hazeltine Creek
  • deposition of tailings and eroded earth in Polley Lake, Hazeltine Creek and Quesnel Lake

The estimated summary of materials released or displaced by the TSF breach:

  • supernatant water 10.6M m3
  • tailings slurry: tailings solids 7.3M m3; interstitial water 6.5M m3
  • construction materials 0.6M m3

Pollution Abatement Order No. 107461 (the Order) was issued to Mount Polley Mining Corporation (MPMC) by the Province of British Columbia on August 5, requiring MPMC to prepare and submit documentation describing its response, and provide communications to the Ministry of Environment (MOE) regarding response progress. A Conceptual Interim Erosion and Sediment Control Plan (the Plan) for mitigating ongoing erosion and sediment transport within impacted areas downstream of the breach was submitted by MPMC. Specific objectives of the Plan are summarized as:

  • provide water management structures to improve the quality of water flowing into Quesnel Lake
  • reduce potential for re-mobilization of tailings and sediments deposited or exposed by the TSF breach
  • minimize and control water flows from the TSF and re-direct these flows to the Springer pit

Three high priority areas were identified where in-stream controls were planned to mitigate potential future erosion and/or sediment transport:

  1. within and down-gradient of the TSF
  2. where the water pumped from Polley Lake was transferred into Hazeltine Creek
  3. up-stream of the mouth of Hazeltine Creek, prior to draining into Quesnel Lake

Rock berms were constructed upstream of the breach area to secure the remaining tailings in the TSF and to collect surface water. Repair of the breach to prevent any release of tailings with the spring runoff was completed in 2Q2015. The water level of Polly Lake rose 1.7 metres when a portion of the water from the breach became trapped by a plug of material at the outlet to the lake. The water was pumped out of Polley Lake and into Hazeltine Creek. The outlet of Polley Lake was subsequently restored to reconnect Polley Lake to Hazeltine Creek.

Best Management Practices were implemented over the remaining areas of impact to reduce potential for erosion of and sediment migration from Hazeltine Creek. The Plan was implemented in cooperation with the MOE, subject to completing ongoing designs and site inspections to confirm details and design standards.

Rehabilitation of Hazeltine Creek included reconstruction of the channel, and restoration of riparian habitat along the creek banks. A set of sedimentation ponds were constructed in the lower reaches of Hazeltine Creek to remove suspended solids from the water before entering into Quesnel Lake. An ongoing revegetation program will reestablish a productive ecosystem, and for water management in order to control sedimentation. The rehabilitation also includes the establishment of spawning and rearing habitat for fish.

The rehabilitation strategy summary is subject to change and is updated from time to time. MPMC provides the community and local First Nations with updates and information on the progress of our rehabilitation on an ongoing basis.

Overview of Area Affected by TSF Breach

Overview of affected area

Independent Expert Engineering Investigation and Review Panel

In August 2014 the Government of British Columbia, in conjunction with the Soda Creek Indian Band (Xats’ull First Nation) and Williams Lake Indian (T’exelcemc) Band, ordered an independent expert engineering investigation and review into the Mount Polley TSF breach to determine the root cause. The geotechnical work program in support of the review included mapping, geophysical surveys, drilling and test pitting. The Independent Expert Engineering Investigation and Review Panel issued their report (the Report) on January 30, 2015. The Report stated no evidence of failure was found due to human intervention, overtopping, or piping and/or cracking resulting in internal erosion. The water accumulation within the TSF was not a cause of failure but did contribute to the release of tailings. The Report concluded the perimeter embankment of the TSF failed because a glacio-lacustrine layer lying approximately 8 metres below the base of the dam in the area of the breach was not as strong as had been assumed in the design of the TSF. The Report noted the omissions associated with site characterizations remained undetected, notwithstanding the large number of experienced geotechnical engineers associated with the TSF over the years.

Rehabilitation Strategy

Rehabilitation plans normally take shape after sources and discharges are controlled, and after an assessment of impacts has been done. MPMC is providing the community and local First Nations with updates on the progress of our rehabilitation. The rehabilitation strategy summary is subject to change and will be updated from time to time.

Water Management Plan

The mine has a surplus water balance, which means the amount of water impacting the mine site as precipitation exceeds the amount of water consumed in processing (when mine is operating) or water that leaves the site by evaporation. Precipitation at the mine area averages 5.9 million cubic metres annually, and up to 9.3 million cubic metres during a 1-in-200 wet year weather event. This amount of water must be handled, treated, and discharged to maintain a neutral water balance. MPMC is working with the regulators and First Nations to develop an effective long term water management plan for the mine site to manage, treat, and dispose of mine water through to mine closure, to ensure the protection of human health and the environment. A short term water discharge permit was issued in November 2015, which included the construction of a water discharge plant.

Environmental Monitoring

Environmental monitoring and data collection includes water chemistry at sampling stations in Quesnel Lake, Polley Lake, Hazeltine Creek and the Quesnel River. The monitoring program also includes geochemical, physical limnology and biological testing. Water sampling has concluded affected areas were not toxic to aquatic life. Water quality information has been communicated to the local community and stakeholders on a regular basis.

Post Event Environmental Impact Assessment Report

Golder Associates completed a Post Event Environmental Impact Assessment—Key Findings Report for MPMC in June 2015. The report provided an assessment of the physical, chemical and biological impacts immediately following the TSF breach, and in the first 6-8 months following. The assessment of any long term impacts will continue, and results will be updated on a regular basis.

Modified Restart of Mine Operations

MPMC received permit amendments on July 9, 2015 from the Ministry of Energy and Mines and MOE which allowed for a modified operation plan to process a maximum of 4 million tonnes of ore over a period of up to one year. During the modified operation plan, ore is being mined from the Cariboo pit and the Boundary zone underground workings, and tailings are being stored in the Springer pit. An application was filed in March 2016 and is in the review process to permit the resumption of normal operations at Mount Polley, and for use of the TSF when the temporary permit expires in spring 2016. The Mount Polley mine is important to the regional economy as the mine and its employees play a substantial role in the economy and fabric of the surrounding communities. Throughout the rehabilitation, resumption of operations, and current permit application, MPMC management and staff have and will continue to work closely with the local communities and are appreciative of their ongoing support.

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Update Mar | 2016