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Dike breach, sinkholes and leaked tailings among incidents
Dangerous occurrences at tailings storage facilities at mines in B.C. between 2000 and 2012 included a breach of a dike, the discovery of sinkholes and leaked tailings. The vast majority of the dangerous occurrences involved incidents with equipment, which crashed, sunk into tailings storage facilities or flipped over.
In several cases, workers were injured and two workers died. The B.C. Ministry of Energy and Mines provided details of 49 dangerous occurrences at tailings ponds at the request of The Vancouver Sun following Imperial Metals’ Mount Polley tailings dam collapse on Aug. 4.
The dam failure released millions of cubic metres of water and tailings containing potentially toxic metals into Quesnel Lake in central B.C., and has increased scrutiny at the province’s 98 tailings facilities, which store mine waste.
The chief inspector of mines’ annual reports provide an annual breakdown of the number of dangerous occurrences, but the mines ministry initially balked at providing details of the dangerous occurrences, requested 10 days ago.
Neither B.C. Mines Minister Bill Bennett nor chief inspector of mines Al Hoffman were available for comment Monday. “(The dike breach, the sinkholes and tailings leakage) were contained to the respective mine sites and posed no risk to the public,” mines ministry spokesman David Haslam said in a written statement. Mining Watch Canada program coordinator Ramsey Hart said the dangerous occurrence details should be part of routine disclosure.
“I think the public and even investors would welcome that,” said Hart, noting that information on corrective measures and effects is also needed to provide context. The incidents that involve tailings facility safety and potential environmental effects included the breach of a new tailings dike for 20 to 30 minutes at the Craigmont copper mine near Merritt on June 3, 2002 at 4 a.m.
Water passed over the dike into a trap and flooded the area before it could be contained. A machine operator constructed a temporary berm on top of the tailings dike to contain the flow, said the government records. The Craigmont copper mining operation was closed in 1982, but the mine has been operated since to produce magnetite for the coal industry. Companies are responsible for maintaining tailings facilities at closed mines.
On July 27, 2002, sinkholes were discovered at Northgate Gold’s Kemess South gold and copper mine in northern B.C., approximately 250 kilometres north of Smithers. The sinkholes were on the tailings beach, an important buffer between the dam’s embankment and water in the pond. The largest sinkhole was about 0.7 metres in diameter and the surface had dropped about 0.7 metres into the hole, according to the government information. The Kemess South mine closed in 2011.
Northgate Minerals was purchased three years ago by AuRico Gold, which has responsibility for the Kemess South 375-hectare tailings storage facility and one-kilometre-long, 140-metre-high dam. AuRico Gold chief operating officer Peter MacPhail said some changes in geotechnical design were made following the discovery of the sinkholes. There were no further incidents, he said. MacPhail noted the tailings facility (which is in reclamation mode) receives an annual inspection from geotechnical engineers and has a robust design.
“It gets a lot of monitoring. There is still staff up there,” he noted. On Sept. 1, 2004, at Barrick Gold’s Eskay Creek gold-silver mine, failure of a flow-measuring device on the tailings line caused about 12.5 tonnes of tailings to leak on the ground. The province said all the tailings were recovered. The mine, about 200 kilometres north of Terrace, closed in 2008.
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