Imperial Metals sues engineering companies over Mount Polley disaster

It was one of the worst environmental disasters in Canadian history, and now, the company behind the 2014 Mount Polley mine tailings breach is looking to make somebody pay.

Imperial Metals (TSX:III) has filed a lawsuit for damages in the Supreme Court of British Columbia alleging negligence and breach of contract by Knight Piesold and AMEC (now Amec Foster Wheeler), two engineering firms in its employ up to the time when the tailings dam at Mount Polley gold and copper mine collapsed. The suit alleges that Knight Piesold designed a flawed tailings dam and monitored it from the late 1980s to 2011, while AMEC took over the monitoring until the dam's failure in summer of 2014.

The allegations have not been proven in court and neither company has filed a statement of defense, the Canadian Press reported on Saturday.

“Each of the defendants failed to undertake necessary, proper and reasonable investigation of the subsurface conditions underlying the (tailings storage facility) prior to and during its phased construction and operation,” states the suit. “The conduct of each of the defendants was negligent, was in breach of the applicable contracts and caused the ultimate failure of the (facility).”

The tailings dam failure on Aug. 14, 2014, caused an estimated 24 million cubic metres of water and tailings waste to spill into Quesnel Lake and Quesnel River. The operation was closed for nearly a year, before being given a "restricted restart" in July 2015. The event caused the mining industry a black eye in British Columbia and the provincial government was criticized for a lack of oversight.

B.C.'s chief mines inspector said in December 2015 that no charges would be laid by the provincial government due to the failure of the Mount Polley tailings dam.

"The chief inspector found that the mine and its engineers employed weak practices on the mine site and many recommendations go to new standards and guidelines to improve these practices," said the Ministry of Energy and Mines in a news release.

Six weeks later, a government-appointed panel released its findings, which concluded that ". . . there was no evidence that the failure was due to human intervention or overtopping of the perimeter embankments and that piping and cracking, which is often the cause of the failure of earth dams, was not the cause of the breach."

Rather it was design failures that were the main cause:

The breach of the Perimeter Embankment on August 4, 2014 was caused by shear failure of dam foundation materials when the loading imposed by the dam exceeded the capacity of these materials to sustain it. The failure occurred rapidly and without precursors.

Deposited in a complex geologic environment, the weaker glaciolacustrine layer was localized to the breach area. It went undetected, in part because the subsurface investigations were not tailored to the degree of this complexity. But neither was it ever targeted for investigation because the nature of its strength behaviour was not appreciated.

Another contributor was the construction of the downstream rockfill zone at a steep slope. The report's authors said if the downstream slope had been flattened, failure would have been avoided.

According to Canadian Press, Imperial Metals has not specified the amount of damages it is seeking, but alleges it continues to suffer losses from the dam failure.