Canadian Mining Journal


TAILINGS: Mines Inspector reports on Mount Polley dam failure

BRITISH COLOMBIA – The British Columbia Chief Mines Inspector has released his report on the Aug. 4, 2014, dam failure at the Mount Polley copper-gold mine belonging to Imperial Metals Corp. of Vancouver.

The report concluded that the primary cause of the failure was associated with engineering designs that did not properly characterize the strength of a clay unit in the soil 10 metres beneath the failed section of the dam.

A contributing factor was the high volume of water in the tailings storage facility. As the water continued to accumulate, Imperial applied for water discharge permit in 2006. When it was finally granted in 2012, the permit carried an amendment restricting the discharge to less than the amount for which the application was made.

The Mines Inspector further found no evidence that the mining company failed to comply with the requirements of the Mines Act, its regulations, the Mount Polley permit, or the health, safety and reclamation code of the province.

One improvement to come out of the report, according to Imperial, will be the establishment of independent engineering review pans as an industry standard. The idea is to strengthen the professional reliance model where geophysical engineers are contracted rather being on a company’s payroll. Imperial says it adopted this concept and established its own IERP in early 2015.

Imperial is a member of the Mining Association of Canada and as such is bound by the protocols of the Towards Sustainable Mining program. The company’s compliance with the Level A tailings management part of TSM was verified after the spill by an external auditor.

Imperial has spent $65 million to mitigate the release of tails and recently received a new treated water discharge permit for Mount Polley. Treated water is now discharged into Hazeltine Creek where it will collect in a settlement pond and then into twin pipelines that will discharge about 40 or 50 metres below the surface of Quesnel Lake.

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