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The Mount Polley tailings dam failure (Canada)

(last updated 1 Dec 2018)

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.

The Panel concluded that evidence indicates the breach was the result of failure in the foundation of the embankment, a failure that occurred in a glaciolacustrine (GLU) layer of the embankment's foundation.
According to the Panel's report: "The Panel concluded that the dominant contribution to the failure resides in the design. The design did not take into the account the complexity of the sub-glacial and pre-glacial geological environment associated with the perimeter embankment foundation. As a result, foundation investigations and associated site characterization failed to identify a continuous GLU layer in the vicinity of the breach and to recognize that it was susceptible to undrained failure when subject to the stresses associated with the embankment."

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

Province government stays charges in Mount Polley private prosecution: The B.C. Prosecution Service will not take on a private prosecution launched by a former First Nation chief to keep alive provincial charges in the catastrophic 2014 Mount Polley tailings dam collapse.
The three-year time limit to lay charges under B.C.'s Environmental Management Act expired on Aug. 4, 2017. At the 11th hour, with the support of several environmental groups - including Mining Watch Canada and West Coast Environmental Law - former Xat'sull First Nation chief Bev Sellars filed private charges in provincial court under B.C.'s Environmental Management Act and the Mining Act over the earth-and-rock dam failure at Imperial Metals' Mount Polley mine northeast of Williams Lake. Stellars had said she hoped the private charges could act as a "doorstopper," buying time for an investigation to be completed and the potential for the province to carry on with charges.
On Tuesday (Jan. 30), the prosecution service said it had stayed the private prosecution. (Vancouver Sun Jan. 30, 2018)

Mount Polley mine engineers face disciplinary hearing: The regulatory body that oversees British Columbia's engineers and geoscientists is alleging negligence and unprofessional conduct against three engineers in connection with the 2014 Mount Polley dam collapse that sent millions of cubic metres of tailings-pond water into B.C. waterways.
Engineers and Geoscientists BC announced the hearings, scheduled for next year, on Wednesday (Sep. 26) following an independent investigation into the breach.
The regulator's investigation committee alleges that the three individuals, who were involved in the design, construction and monitoring of the tailings-storage facility, demonstrated negligence and/or unprofessional conduct in the course of their professional activities. The allegations have not yet been heard by a disciplinary panel and are unproven. (The Globe and Mail Sep. 27, 2018)

Engineering firms Knight Piesold and Amec Foster Wheeler agree to pay CDN$108 million in damages to Imperial Metals Corp. for failure of Mount Polley mine dam: On Nov. 27, 2018, Imperial Metals Corp. reported that an action for damages arising out of the August 4, 2014 failure of the perimeter embankment at the Mount Polley mine has been settled among all parties to the action in consideration of net payments to the Company totaling approximately CDN$108 million. Upon receipt of the payments, a consent dismissal order will be filed. This settlement represents compromises of disputed claims and does not constitute an admission of liability on the part of any party to the action, the company said.