Mount Polley mine disaster report prompts tighter rules in B.C.

The government of British Columbia is taking immediate action to implement new requirements for mine tailings pond operators following the release of the independent expert engineering panel on the environmental disaster at the Mount Polley Mine in B.C. last year.

The “Report on Mount Polley Tailings Storage Facility Breach,” was delivered on to the Ministry of Energy and Mines, the T’exelc First Nation (Williams Lake Indian Band) and the Xat’sull First Nation (Soda Creek Indian Band) on January 30.

The experts concluded that the dominant cause of the dam’s failure was in its design, and that inspections by the B.C. Ministry of Energy and Mines “would not have prevented failure.”

The breach from an open pit copper and gold mine occurred overnight on August 4, 2014 at the Mount Polley Mine located near Likely in the Cariboo region of northeast British Columbia. The breach sent an estimated 10 million cubic metres of water and 4.5 million cubic metres of slurry into Polley Lake and other waterways, causing the lake to rise by 1.5 metres.

Following the release of the expert report, B.C. Minister of Energy and Mines Bill Bennett said the Chief Inspector of Mines will require all operating mines with tailings dams to provide a letter by June 30 to confirm whether foundation materials similar to those at Mount Polley exist below any of their dams. If those materials are present, the letters must also confirm that testing shows that the dams were designed to account for the conditions. The Minister also said it will also be launching a code review, and that the province will require all operating mines with tailings facilities in the province to establish independent tailings dam review boards. These boards “will support improved engineering practices by providing third-party advice on the design, construction, operation and closure of TSFs.” Some mines in B.C. already have similar boards in place.

At the same time as the panel’s report was released, the province released the results of the third party inspections it ordered following the breach at Mount Polley. The reviews did not uncover any immediate safety problems.

The independent engineering panel that reviewed the Mount Polley breach had three experts: Dr. Norbert R. Morgenstern, P.Eng. (chair), Steven G. Vick, P.E., and Dr. Dirk Van Zyl, P.Eng.. They concluded that the breach of the dam was caused by the shear failure of the dam foundation materials.

Furthermore, they said: “The Panel concluded that the dominant contribution to the failure resides in the design. The design did not take into 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.”

Another factor they found was the steep slope of the downstream rockfill zone.  The slope was in the process of being flattened to meet its ultimate design criteria at the time of the accident.

The panel also looked at whether more attention from the Ministry of Energy and Mines might have prevented the failure, noting that no government inspections were done from 2009 to 2011. However, they concluded “this lack of inspection was immaterial to the failure because there were no precursors that could have been detected, even on the eve of the breach. By definition no amount of inspection can discover a hidden floor.”

For recommendations, the panel said best available technologies and best available practices should be introduced for existing, new and closing tailings ponds using a phased approach.

They said the Association of Professional Engineers and Geoscientists of British Columbia (APEGBC) should develop guidelines to improve the site characterization for tailings dams. The panel also noted that the current Canadian Dam Association Guidelines had limitations. They said improved guidelines should be developed that are tailored to the conditions in British Columbia and that emphasize protecting public safety.

The panel thanked Thurber Engineering for its “outstanding” technical contributions and mentioned the team members by name. The consulting engineers were retained by the panel for various tests and analyses, including site mapping and drilling.
See related story related to the breach of the mine.

To read the expert “Report on Mount Polley Tailings Storage Facility Breach,” of January 30, 2015 click here.

To read the APEGBC response, click here.

To read the release from the B.C. Government, click here.