Tailings pond spill: What happens to effluent over time – by By Matt Kwong (CBC News British Columbia – August 08, 2014)


Toxic slurry from mining operations often buried, revegetated after mines close, experts say after B.C. breach

Tailings — the slurry of water, finely ground rock, ore and chemical byproducts washed away during the mining process — never quite go away. The same goes for the risk of failure for even the best-engineered “tailings impoundment” dams, environmental experts say.

A sobering reminder came in the form of an environmental catastrophe this week in B.C. when the tailings pond overseen by Imperial Metals breached, spilling five million cubic metres of effluent into the Quesnel-Cariboo river system.

Asked by CBC’s Chris Hall how long it might take to eventually restore affected areas to their natural state, Ramsey Hart of MiningWatch Canada gave a grim assessment.

“I don’t think it will ever entirely be cleaned up,” said Hart, who researches mining issues, including waste management, the impacts of mining on aquatic ecosystems, and mining and indigenous rights.

Manmade tailings ponds, or reservoirs that use natural geologic features such as valleys or lakes to contain the mine waste, store the tailings solids in water to prevent their exposure to oxygen.

In the mining industry, this is called “capping” and is meant to reduce the risk of a toxic outflow known as acid mine drainage, says Bill Donahue, director of policy and science with the Alberta-based environmental non-profit Water Matters.

Keep tailings away from oxygen

As long as the mine waste is capped or submerged in a tailings pond, he said, “all the sediments full of waste rock and heavy metals don’t get a lot of oxygen,” which in turn reduces acid production.

“Tailings ponds are not considered a stopgap; they’re considered a solution, I would say. And not really reasonably so,” Donahue said from Edmonton.

“Even just using a tailings pond presumes the dam is not going to fail. As a risk management solution, it’s certainly a risky one.”

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