Tailings pond spill: What happens to effluent over time
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.
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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."
This also presumes the tailings pond doesn't actually leak out into the groundwater, he said.
An Environment Canada study released in February found that mining waste water from oilsands tailing ponds was leaking into the Athabasca River. The study estimated that one dam was leaking 6.5 million litres of polluted water a day into groundwater.
The Mining Association of BC, which represents the province's coal, mineral and precious metal mining interests, estimates more than 1,000 tailings ponds are operating across Canada.
Stacking 'dry cake' tailings
Angela Waterman, the association's vice-president of environment and technical affairs, said that for the past 40 years in B.C., mining operators are required to carry out a reclamation program as part of their operating permits once mining activities cease.
The idea is to have former tailings sites "blend back into the background," she said. Reclaimed tailings impoundments have also been turned into grazing areas or became solar farms.
Tailings management consultants are increasingly looking to viable alternatives beyond conventional impoundment, which uses vast amounts of water.
[The tailings] wouldn't be extracted; it would be buried. The cover would be on top of it.- Angela Waterman, Mining Association of BC, vice-president of environment and technical affairs
Some mines in Chile and at least one in the Yukon have taken to producing dry-filtered tailings, said Dirk Van Zyl, chair of mining and the environment at the University of British Columbia.
"You either take a screen and press the tailings against them to push the water out, or you put a vacuum to it and suck the water out," she said.
These dewatered tailings, sometimes called "dry cake," could be stacked like soil and might help solve the problem of controlling seepage into aquifers.
At the moment, conventional tailings ponds appear to be the status quo in B.C.
"[The tailings] wouldn't be extracted; it would be buried. The cover would be on top of it," Waterman said.
A layer of soil mixed with synthetic materials would construct a "geo-membrane" that would be used as a liner, and could then be greened over, likely with whatever vegetation is indigenous to the area.
"You can stand on it, you can run on it, and you might never know it existed after it's dewatered, of course," Waterman said, adding that she believes B.C. still has among the most stringent guidelines on discharged water quality in Canada.
Use in construction material
Under increased scrutiny about the mining industry's role in environmental stewardship, some companies are examining the potential for recycling tailings or using them in construction.
In an email, Alan Fair, a tailings management expert with Canada's Oil Sands Innoviation Alliance, said the association is focusing on "new and improved" technologies that can turn wet tailings into materials that could be "successfully integrated into the final reclaimed mine-site."
The Phoenix-based copper mining firm Freeport-McMoRan Inc. developed a patent for packing residual tailings into building bricks.
Van Zyl has one of the brick prototypes sitting on his office desk at UBC.
"It's a very good product, but it's quite expensive to do," he says. He adds that another drawback is that many tailings ponds happen to be in remote areas where transportation costs of tailings-made building materials would not be economically feasible.
Regulation of tailings management is cross-jurisdictional, between provincial, federal and territorial governments.
Donahue said B.C. takes primary jurisdiction over mining regulations related to management, monitoring and assessment for tailings ponds under its Mines Act.
The federal government steps in when matters concern the environment or fish habitats, for example. In this case, federal Metal Mining Effluent Regulations would likely apply under the Fisheries Act, Donahue said, noting that the environmental disaster caused by the Mount Polley mine spill comes at a particularly crucial time.
"It's supposed to be a record spawning year, and unfortunately the spawning season is starting now," he said of the Quesnel waterways, major sockeye salmon tributaries and spawning grounds.
Waterman said the mining industry is committed to maintaining the trust of the public and protecting the environment, and she believes Canada's dam safety regulations are already among the most stringent in the world.
- B.C. Ministry of Environment
- Imperial Metals: Mount Polley Mine
- Cariboo Regional District Emergency Operations Centre
"But are things ever worth a review? Of course," she said.
A spokesperson with the B.C. Ministry Environment said the ministry issued five warnings to Imperial Metals — the latest was in May — related to the water level in the tailings ponds exceeding permitted limits relating to volume.
Yet the breach happened anyway.
"The mentality of a lot of these regulatory agencies is we're not interested in punishing anyone; we just want to make sure they comply, so what happens is companies when they don't comply, they don't really suffer any consequences," Donahue said.
"They need to be more punitive and heavy-headed, and the industry needs to start understanding this cannot happen. Tailings ponds cannot fail."