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The Mount Polley tailings dam failure (Canada)

(last updated 18 Dec 2015)


The dam failure and its impacts

On Aug. 4, 2014, the tailings dam of Imperial Metals Corp.'s Mount Polley copper and gold mine near Likely, British Columbia, Canada, failed, releasing 7.3 million m3 of tailings, 10.6 million m3 of water, and 6.5 million m3 of interstitial water into the environment. The tailings flowed into adjacent Polley Lake and, through Hazeltine Creek, into Quesnel Lake (Mitchell Bay), snapping countless trees in its 50 m wide flowpath.

On June 18, 2015, Mount Polley Mining Corporation released the Mount Polley Post-Event Environmental Impact Assessment Report, prepared by Golder Associates.

"To date, the studies conducted and data analyzed as part of this Post-Event Environmental Impact Assessment indicate that the tailings dam failure has resulted in physical impact to Hazeltine Creek, the mouth of Edney Creek and the West Basin of Quesnel Lake. When the tailings mixed with eroded soil entered Quesnel Lake, most of the material settled on the lake bottom. Some finer particulates stayed in the water column and a turbidity plume formed near the lake bottom. The turbidity plume persisted in the deeper part of the lake until the fall turn-over happened. In addition, there were a few events following windy weather when some of the turbid water came to the surface. The main body of Quesnel Lake has now returned to normal, clear conditions and further turbid water events are not expected.
This short term assessment has found evidence for a physical impact on the Polley Lake, Hazeltine Creek and a portion of Quesnel Lake near Hazeltine Creek. A chemical change has also occurred, but the findings of the geochemical testing indicates that the tailings mixture is relatively inert. These findings indicate that although there are higher concentrations of copper in soil, sediment and water, they are not expected to result in adverse effects because release of metals from the tailings is unlikely. These findings of the geochemical impact assessment are supported by the findings to date of the biological impact assessment. The toxicity testing of sediment and water indicated that the copper in sediment and water was not toxic to aquatic life."
Submit your comments on the report until September 12, 2105.
> Download: Key Findings Report (main text) (73 p., 48.5MB PDF) · Appendices A-I (2261 p., 154MB PDF)
> View Mount Polley Mine Tailings Pond Breach Updates (Environment B.C.)


The causes of the dam failure

Following the breach of the tailings storage facility at the Mount Polley Mine, the Government of British Columbia, through the Ministry of Energy and Mines, together with the Williams Lake Indian Band and the Soda Creek Indian Band, established an independent expert investigation and review panel (the Panel) to investigate and report on that breach. The Panel presented its report on January 30, 2015. No charges under British Columbia's mining laws for failure of Mount Polley mine dam: No charges will be issued under the province's mining laws against Imperial Metals after the catastrophic failure of its Mount Polley gold and copper mine tailings dam. B.C.'s chief inspector of mines decided not to forward charges to Crown counsel involving the Aug. 4, 2014 incident. "Although there were poor practices, there were no non-compliances we could find," B.C. chief inspector of mines Al Hoffman said Thursday (Dec. 17) in releasing a report into the investigation, which took more than a year. The province said Hoffman had advice from the B.C. Ministry of Justice in making his decision. There will also be no fines issued because B.C.'s mining laws do not allow for administrative penalties, as do other natural resource ministries and agencies such as WorkSafeBC. (Vancouver Sun Dec. 17, 2015)
> Download: Chief Inspector of Mines' Investigation Report on Mount Polley , Nov. 30, 2015





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