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Billions of liters of wastewater and tailings sediment ended up in river systems after a tailings dam breach at Imperial Metals' Mount Polley mine in British Columbia on Monday morning.
The Canadian mining company confirmed on Tuesday that the breach had been stabilized and said that it was working to mitigate the immediate impact.
The failure of the dam led to an estimated 10 billion liters of water and 4.5 million cubic meters of metals-laden fine sand flowing into Polley Lake, CBC News reported. The tailings are alkaline with an average ph of 8.5 and are not acid-generating.
While the company could not confirm the exact composition of the discharged wastewater, Brian Kynoch, president of Imperial Metals, said that it was "very close to drinking water quality." It contains no mercury and very low levels of arsenic and other metals.
Nevertheless, residents and visitors in the local area have been advised not to drink or bathe in the water of Polley Lake, Quesnel Lake, Hazeltine Creek, Cariboo Creek and the Quesnel and Cariboo river systems to Fraser River.
At the moment it is not clear what caused the breach. Imperial Metals stated that the dam is an independently engineered structure that operated within design limits and specifications. Monitoring instruments at the site gave no indication of an impending breach.
Kynoch said that the company accepts full responsibility for the incident and is working closely with provincial ministries, local agencies and emergency response officials.
The Mount Polley mine has been placed on care and maintenance and Imperial Metals has notified the company's business interruption and physical damage insurers. It is not yet known how long it will take to restore operations.