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

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

The government says Minto is required to take action once the available storage capacity drops to below 300,000 cubic metres. The facility is now nearing that threshold, with storage capacity at 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 with the 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 as tailings management facilities, holding mine waste rock and contaminated water. The Yukon government is directing the 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 of Energy, 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 area to hold the contaminated water. He said any water stored in that pit would be treated before it's discharged into the environment.

"In our view ... the best, long term, risk-mitigation strategy for Minto Mine is to take proactive actions to protect the short term environmental risk caused by spring snow melt, while also protecting the integrity and viability of 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's water licence states that as of October 31 of each year, the mine must have a minimum excess storage capacity of at least one million cubic metres to handle spring freshet or flood flows. Government officials said Wednesday that the mine has been struggling in recent years to 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 government of Yukon and ultimately, taxpayers," Streicker said.