Giant Mine cleanup team opts for dry freeze of arsenic over wet

It's a busy time for the Giant Mine remediation project in Yellowknife.

To keep the public up to date about what's going on, staff at Indigenous and Northern Affairs Canada are holding an information session March 2 atthe Prince of Wales Northern Heritage Centre's Museum Cafe in Yellowknife, starting at 7 p.m.

CBC News attended a shortened version of that presentation made to Yellowknife city council on Monday.

Here are some highlights.

Better dust control

Two years ago, residents in Ndilo were concerned when a dust cloud hovered near the community. INAC confirmed the dust came from tailings on the surface of Giant Mine, though no traces of highly-toxic arsenic trioxide dust were detected.

INAC worked with the Yellowknives Dene First Nation to find a better dust suppressant for the site.

• No arsenic trioxide in Giant Mine's springtime dust clouds, new research suggests

"We came up with a new product that we're going to start using this year," said deputy project director Natalie Plato. "It's an environmentally-safe, polymer-based product that seals the tailings, seals the roads.

"It can be applied at lower temperatures, so it can be applied earlier in the season, and it lasts longer three to fiveyears as opposed to our old product."

Filling a Giant underground hole

Before the freezing of 237,000 tonnes of arsenic trioxide dust can begin, INAC needs to finish stabilizing other parts of the mine's vast underground workings.

"A lot of them are at risk for failure or for collapsing," said Plato.

That largest remaining underground chamber that needs stabilizing is the C5-09 Stope Complex.

"It's about as big as Somba Ke Park, wide, and as deep as three Precambrian Buildings," said Plato.

The chamber will be filled with a paste made of old tailings.

INAC hopes to start filling the chamber in the summer of 2018.

Wet vs. dry freezing of arsenic trioxide dust

INAC had already decided to go with a passive freezing system for containing the arsenic trioxide dust underground in more than a dozen underground chambers.

Now it's also decided not to wet the dust before freezing it, as it had originally envisioned.

"Wet would involve filling those chambers with water and then freezing them much like you would an ice cube," said Plato.

"Dry freezing would just freeze the rock around the chambers to prevent water from getting into the chambers. The goal of both of those would be to keep water out of arsenic chambers and obviously keep the arsenic in."

INAC has opted for the dry method, Plato said.

"That means that, should we need to reverse the freeze and let the chambers thaw for a better solution, we wouldn't have all that water to deal with."

Securing permanent funding for the cleanup

The total cost of the entire remediation project has been estimated at around $900 million.

But there isn't a permanent pot of money for the project; its budget currently only goes to 2020.

INAC hopes to change that.

"We were directed to find a source of funding indefinitely, so we've gone to the Treasury [Board of Canada]," said Plato.

"We want to get mainlined right into the budget."