Victoria, B.C. – The Mount Polley Independent Expert Engineering Investigation and Review Panel recently delivered a Final Report on its investigation into the cause of the failure of the tailings storage facility at the Mount Polley Mine on August 4, 2014. The report was delivered 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). The report also contains recommendations on actions that can be taken to ensure a similar failure does not occur at other mine sites in B.C.
The Panel concluded that evidence indicates the breach was the result of a 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 released January 30, 2015: “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.”
The report also indicated that the failure was triggered by construction of the downstream rockfill zone at a steep slope. The Panel concluded that had the downstream slope been flattened failure would have been avoided. The slope was in the process of being flattened to meet its ultimate design criteria at the time of the accident.
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