UPDATE 2-Canada investigation finds flawed design led to mine dam spill

Fri Jan 30, 2015 5:38pm EST
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(Adds quotes from panel, statement from province, closing share price)

By Julie Gordon and Susan Taylor

VANCOUVER/TORONTO Jan 30 (Reuters) - A massive spill from a dam containing mine waste in British Columbia last year was caused by a flawed design for the embankment, which did not account for the presence of a glacial lake deposit at the foundation, an independent panel said on Friday.

The probe found that the breach at Imperial Metal's Mount Polley mine, which sent billions of gallons of wastewater and sludge into waterways, happened because the dam's weight was too much for the foundation to bear.

"We concluded the dominant contribution to the failure resides in the design," the panel's chair, Norbert Morgenstern, said after the 5-1/2-month investigation.

"The design did not take into account the complexity of the sub-glacial and pre-glacial geological environment associated with the perimeter embankment foundation."

The panel, appointed by the provincial government with the backing of two Aboriginal bands from the Mount Polley area, also found the collapse was triggered by the construction of a downstream rockfill zone at an overly steep slope.

They concluded that had the slope been flattened, work that was under way when the accident happened, the failure could have been averted.

Morgenstern said design flaws created a "loaded gun" and the construction of the steep slope "pulled the trigger."   Continued...