Spring melt threatens to overwhelm tailings storage pits at Minto Mine, Yukon gov't says

The Yukon government is directing the owners of the Minto Mine to brace for a heavy spring melt, and to take some needed measures now to avoid a tailings pond spill into the environment.

The territoryis experiencing its fourthconsecutive year of above-average snow pack, and that's raised concerns about whether the melt might overwhelm the mine's water storage capacity. The minesite is about 40 kilometres from the community of Pelly Crossing, Yukon.

During a technical briefing held on Wednesday, Yukon government officials shared concerns ofpotential risks to the environment if the mine'sstorage issue isn't addressed.

The governmentsaysMintois required to take action once the available storage capacity drops to below300,000 cubic metres. The facilityis nownearing thatthreshold, with storage capacityat about 360,000 cubic metres.

Graphs shared at Wednesday's technical briefing showed that if nothing is done, storage capacity could be depleted by May withthe spring melt. That increases the risk of untreated water from tailings pits being spilled into nearby Minto Creek, and from there into the Yukon River, nine kilometres downstream.

There are two pits at the mine that serve astailings management facilities, holding mine waste rock and contaminated water. The Yukon government isdirectingthe mine owners to now use another pit.

"The company must divert contaminated water from the current water storage facilities to another on-site pit known as the Minto North pit to ensure safe storage prior to treatment," said John Streicker, minister ofEnergy, Mines and Resources, at Wednesday's briefing.

"At that time they've also been directed to temporarily cease depositing tailings during the spring snow melt to allow water storage levels to recover."

Streicker said the Minto North pit is not part of the mine's water licence but it is a stable areato hold the contaminated water. He said any water stored in that pit wouldbe treated before it's discharged into the environment.

"In our view ... the best, long term, risk-mitigation strategy for MintoMine is to take proactive actions to protect the short term environmental risk caused by spring snow melt, while also protecting the integrity and viabilityof the project in the long term," Streicker said.

Yearly comparison

Data was also shared on Wednesday showing how the mine's tailings-storage capacity has changed over time.

Since January of last year, capacity has decreased significantly. At that time, storage capacity was closer to 700,000 cubic metres. This past January, it was around 350,000 cubic metres.

The mine'swater licence states that as of October 31of each year, the minemust have a minimum excess storage capacity of at least one million cubic metresto handle spring freshet or flood flows. Government officials said Wednesday that the mine has been struggling in recent yearsto meet that requirement.

Streicker said his government is working with Minto Metals and the Selkirk First Nation in Pelly Crossing to deal with the situation.

"Our hope is that these actions will lessen the likelihood that the mine will become the direct responsibility of the governmentof Yukon and ultimately, taxpayers," Streicker said.