Mount Polley panel says design flaw led to dam failure

Energy and Mines critic Macdonald says government still bears some responsibility

Columbia River Revelstoke MLA Norm Macdonald

Columbia River Revelstoke MLA Norm Macdonald

The independent panel investigating the Mount Polley tailings storage facility failure returned its findings Friday, January 30.

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 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 panel determined that the strength and location of a layer of clay underneath the dam was not taken into account in its original design. As a result, this layer became overstressed, causing the portion of the dam on top of that layer to collapse.

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.

Minister of Energy Bill Bennett said the government will act immediately on key recommendations in the report and launch a code review to consider the other recommendations.

Immediate actions include the  Chief Inspector of Mines requiring all operating mines with TSF  dams to provide a letter by June 30, 2015, to confirm whether foundation materials similar to those at Mount Polley exist below any of their dams. This would not apply to closed facilities such as the Sullivan Mine tailings in Kimberley, which recently passed a government-ordered inspection. You can see the entire inspection reports at under Mineral Exploration and Mining, Dam Safety Inspections 2014.

All operating mines will also be required to establish independent tailings dam review boards.

“I am relieved to know the cause of the failure at Mount Polley and want to thank the panel for their important work. Now we can devote all of our energy to taking a leadership role in Canada and internationally to learn from this and ensure it never happens again.,” Bennett said.

Columbia River Revelstoke MLA Norm Macdonald, who is also the Energy and Mines critic, has several issues with the findings.

“The structure of the embankment at the Mount Polley tailings storage facility that failed uses the same basic elements found in every earth-filled dam or retaining wall,” he said.,

“BC Hydro has structures using this technology in use at Mica, parts of Revelstoke, and WAC Bennett to name a few. The failure of those structures would be so catastrophic that their integrity supersedes all other factors.

“At Mount Polley the tailings facility was allowed by the government to hold too much water which caused the massive damage but not the retaining wall failure according to the report. The report says the retaining wall was built up from the original design at too steep an angle. This design modification was allowed by the government, as the government had allowed increased mining that produced more water and tailings than the original design of the retaining facility could handle. The water problem was first identified in 2010 but another arm of the government did not allow release of water for those four years.

“Just prior to the collapse of the retaining wall this August there was a belated order that the steepness of the height enhanced retaining wall be reduced by putting more material to reduce the slope and by expanding a buttress to the base of the area of the place where the retaining wall failed.

“All other parts of the wall had been buttressed but I was told by workers in Likely that there were cost factors that had prevented the buttressing and slope reduction work from being done.

“This panel said essentially at mine sites cost or economic factors can *compromise* safety and that unlike BC Hydro dams the structures are not built with a zero chance of failure regime. The panel says safety of structures must come first and failure of structures must be completely unacceptable. There remains an incredible amount yet to know. The panel said visual inspections would not have helped here but it leaves a tremendous amount of the oversight of these facilities and the quality of compliance still to be understood. The government says they have two remaining investigations going on.

Both are the government investigating themselves and a major donor. I have seen enough of those in the past ten years to have little faith they will get to the bottom of things.  For Bill Bennett and the BC Liberals, limiting political damage trumps the more crucial environmental and safety considerations. If this government and this minister put the public interest first, Bennett would have stepped aside months ago.