A string of catastrophic failures has raised alarm about dams meant to contain muddy mine wastes.
The dam, a 40-meter wall of rocks and dirt, gave way without warning, unleashing a torrent of mud. Within a day, some 21 million cubic meters of gray goo and water—the tailings waste left behind by 16 years of copper and gold mining at the Mount Polley mine in western Canada—escaped from a holding pond behind the dam, buried a creek, and poured into Quesnel Lake, home to one-third of British Columbia’s legendary Fraser River sockeye salmon.
The 2014 Mount Polley disaster shocked mining engineers around the world. Many considered Canada a leader in developing rules aimed at preventing the failure of such tailings dams, and respected the mine’s owner, Imperial Metals.
“That wasn’t supposed to be able to happen,” Jim Kuipers, an engineer and former tailings dam manager who now consults for environmental groups, recalls a colleague telling him.
Since then, the sense of crisis has deepened. In 2015, a tailings dam in Brazil collapsed, unleashing a mammoth mud spill that killed 19 people, contaminated 668 kilometers of river, and reached the Atlantic Ocean.
In 2018, a dam failed at a major mine in Australia; luckily, a second barrier prevented disaster. Last year, a dam disintegrated at a decommissioned Brazilian iron mine, releasing a torrent that killed 270 people.
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