An aerial view of the Mount Polley mine tailings pond shows the area where the earthen wall gave way early on the morning of August 4. Ministry of the Environment
Knight Piésold Consulting, whose engineers had designed the Mount Polley tailings pond containment system, says the Vancouver company had warned mine owners in 2011 that the containment pond was "getting large."
"The original engineering done by Knight Piésold Ltd. accommodated a significantly lower water volume than the tailings storage facility reportedly held at the time of the breach," the company said in a statement posted Friday to its website.
On August 4., a breach of the tailings pond's earthen wall sent billions of litres of potentially toxic waste water into local waterways and lakes.
At the time, Imperial Metals president Brian Kynoch said the dam was an independently engineered structure that operated within design limits and specifications, and there was no indication of an impending breach.
Knight Piésold informed mine owners in a February 2011 letter it would not continue as the engineers of the tailings pond system, but its statement gave no reason why it made that decision.
In the letter, it noted, "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."
It then opted out of the bidding to remain as engineers.
"It is essential that it be recognized, Knight Piésold will not have any responsibility for any aspects of the on-going operations, or of any modifications to the facilities that are undertaken from now onwards," wrote managing director Ken Brouwer.
Knight Piésold says it provided the Mount Polley mine with a formal design, construction and monitoring handover the following month.
While it was the engineer of record in 2006, Knight Piésold said an independent third party dam safety review by AMEC Earth and Environmental confirmed the three embankments it had built were well-designed and well-constructed from a dam safety perspective.
The company says significant engineering and design changes were made subsequent to its involvement, and it has no knowledge of and cannot comment on the current design.
Gerald MacBurney, a former foreman who worked on the tailings pond, says he had warned of a disaster in the making for two years. He said management kept building the dam higher but ignored his requests to shore up the dam with enough rock to make it safe.
On mobile? Click here for Knight Piésold's letter
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