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Imperial Metals’ estimate of the size of the spill from its Mount Polley mine tailings dam collapse is nearly 70 per cent greater than the initial estimate.
The B.C. government has estimated that 10 million cubic metres of water and 4.5 million cubic meters of finely ground rock containing potentially-toxic metals was released by the collapse of the dam on Aug. 4.
But Imperial Metals has estimated the size of the spill at 10.6 million cubic metres of water, 7.3 million cubic metres of tailings and 6.5 million cubic metres of “interstitial” water. That’s enough water and material to fill nearly 9,800 Olympic-sized swimming pools.
Interstitial water is the water suspended in the spaces between the finely ground rock of the tailings.
“It’s a bit disconcerting — its speaks to the crudeness of the initial estimate,” said Mining Watch Canada program director Ramsey Hart of the increased spill estimate.
Imperial Metals did not respond to a request Wednesday for comment. Hart said there will need to be a better accounting of the spill’s size, including the volume of tailings deposited in the lake and in the Hazeltine Creek watershed.
The early numbers were best estimates, later refined by Imperial Metals, said B.C. Mines Ministry spokesman Ryan Shotton in a written statement.
“The company is undertaking work to fully characterize the chemistry of the tailings and water that have been released. This work will include testing for a full suite of parameters, including metals,” the statement said.
University of B.C. mining engineering professor Scott Dunbar said he didn’t believe there would be a significant difference in the composition of the interstitial water and the water above the tailings in the storage facility. The company has said the water above the tailings was near drinking-water quality.
And Dunbar said while the tailings certainly have been physically damaging, the science suggests they will not be chemically damaging.
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