It’s too soon to determine the extent of damage and cost of repairs caused by the Aug. 4 Mount Polley Mine tailings pond failure, officials say. The blowout dumped about 2.6 million gallons of water and 5.9 million cu yd of sand and silt into two lakes and a creek in western Canada.

But a clue to the costs came as mine owner Imperial Metals Corp., Vancouver, British Columbia, announced Aug. 14 it would issue $100 million in bonds, in addition to insurance payments, to pay for remediation at the mine. British Columbia officials say Imperial is responsible for “all costs associated with the cleanup of the breach.” 

Investigators remain at the site trying to determine a cause for the 984-ft breach at the open-pit copper and gold mine that started operating in 1997. The mine is about 20 miles from Lively, British Columbia, and is about 377 miles north of Vancouver.

Residents in the area were banned from using water in the days immediately after the spill, but drinking water was declared safe in Quesnel River and Quesnel Lake by Aug. 9. Test results on samples at the area where Polley Lake enters Hazeltine Creek and on sediment samples at the breach were due by Aug. 18.

The ministry earlier ordered Imperial to halt any more mine tailings releases and to make a comprehensive environmental impact assessment and submit a detailed action plan by Aug. 15.

Imperial has suspended all mining operations at the site.

The company had a warning of possible trouble with the pond in 2011, from Knight Piesold Ltd., the Vancouver-based consulting engineering firm that had been engineer of record.

“The embankments and the overall tailings impoundment are getting large and it is extremely important that they be monitored, constructed and operated properly to prevent problems in the future,” Ken Brouwer, managing director, said in a letter.

Knight Piesold would not continue as engineer of record after February 2011 and, as a result, would “not have any responsibility for any aspects of the ongoing operations, or of any modifications to the facilities that are undertaken from now onwards,” the letter said, and added, “It must be understood that Knight Piesold will no longer have any responsibility for the performance of the tailings storage facility.”

In a statement issued Aug. 8, Knight Piesold said its engineering for the pond “accommodated a significantly lower water volume than the tailings storage facility reportedly held at the time of the breach. … Significant engineering and design changes were made subsequent to our involvement, such that the tailings storage facility can no longer be considered a Knight Piesold Ltd. design.”