Mount Polley mine workers began pumping water from Polley Lake down a discharge pipe to Quesnel Lake Sunday, after the water passed lab tests with no significant contamination.

The surge of water and mine tailings from the breach of the mine tailings pond Aug. 4 created an unstable plug of debris at the mouth of the smaller Polley Lake, raising its level even after the majority of the torrent scoured out Hazeltine Creek and poured down into Quesnel Lake.

Government and Cariboo Regional District officials approved the pumping in an effort to avoid another breach and uncontrolled release, to make the site safe for further water testing and reconstruction.

Water samples from the shore of Polley Lake Aug. 7 tested “very close to historical levels” where it was used for drinking water, the province said in a statement released Sunday afternoon. Water being pumped from the lake will continue to be tested daily.

Environment ministry water samples from six locations on the Quesnel River and Quesnel Lake also met federal and provincial drinking water guidelines for the third straight day. Water from portions of the river have been approved for drinking and bathing. The water use ban remains for Polley Lake as confirmation water testing continues, with results expected by Tuesday.

The CRD has established a restricted access order to the affected region as investigation continues to determine the cause of the dam breach.

Mount Polley Mine is an open-pit copper-gold mine that opened in 1997, owned by Imperial Metals. It had recently undergone expansion of the mine and tailings pond.

The mine ore body does not contain acid-producing minerals, so heavy metal and other contaminants in the ground rock of the mine tailings are not dissolved in water in high concentrations.

Imperial Metals president Brian Kynoch said the water in the tailings pond was routinely tested with rainbow trout and did not harm the fish.