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December 2015

Vol. 20, No. 52 Week of December 27, 2015

Northern Neighbors: B.C. inspector says weak practices, design led to Mt. Polley dam failure

The British Columbia Chief Inspector of Mines Dec. 17 released a report outlining the findings of his investigation into the causes of an August 2014 tailings dam breach at Imperial Metals Corp.’s Mount Polley Mine in western B.C. The report found, as did an earlier panel, that the dam failed because the strength and location of a layer of clay underneath the dam was not taken into account in the design or in subsequent dam raises. The chief inspector also found other factors including the slope of the perimeter embankment, inadequate water management, insufficient beaches and a sub-excavation at the outside toe of the dam exacerbated the collapse and the ensuing environmental damage. Chief Inspector of Mines Al Hoffman said, “Through our investigation, we determined that while the mine did not contravene any existing regulatory requirements, its management and operational practices failed in a number of areas such as water management and misplaced confidence in the TSF (tailings storage facility) design.” After consulting with B.C. Ministry of Justice, Hoffman did not find sufficient evidence that though mine engineers employed weak practices at Mount Polley, the mine operator – Mount Polley Mining Corp. – did not breach any existing regulatory requirements. As a result, the chief mine inspector will not be pursuing any legal actions. An ongoing investigation by the B.C. Conservation Officer Service, however may still find that the mine operator was out of compliance with environmental regulations. In his report, the chief mine operator made 19 recommendations in seven categories directed toward the mining operator, the mining industry, professional organizations and the government regulator to prevent such incidents in the future and build a safer, more sustainable industry. In response to the findings and recommendations, B.C. Energy and Mines Minister Bill Bennett said the province will introduce new regulations and requirements that will make British Columbia a national and international leader in safety standards for tailings storage facilities. “We’ve learned from this investigation that in the case of Mount Polley, the allowable margin of risk around the design, construction and management of the tailings storage facility was too narrow to allow for an unknown factor, the layer of unstable soils below the dam embankment. We’ve also learned that weak practices on the mine site increased the risk of dam failure and exacerbated environmental consequences from the breach. This is unacceptable,” said Bennett. The chief inspector of mines’ investigation team conducted roughly 100 interviews and reviewed more than 100,000 pages of documents going back to 1989. The B.C. government said it is the largest and most complex investigation and analysis ever carried out in the province.

- Shane Lasley






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