The test freezing project began late last month at the Giant Mine site, which produced more than seven million ounces of gold from 1948 until it closed in 1999. ((CBC))

A crew at the Giant Mine site near Yellowknife is freezing an underground vault where arsenic trioxide dust is being stored, as part a test run of the federal government's plan to freeze thousands of tonnes of the toxic dust at the defunct gold mine.

About 237,000 tonnes of arsenic trioxide dust resulted from decades of gold production at the mine, which produced more than seven million ounces of the precious metal from 1948 until 1999.

The federal Indian and Northern Affairs Department, which is responsible for cleaning up the leftover contamination at the mine site, wants to freeze the underground chambers that are storing the arsenic dust.

As part of the test run, which began at the end of March, a cooling brine is being injected into holes that have been drilled into the ground around the walls of one of the chambers.

'Massive ice cube'

The process is similar to freezing ice in indoor rinks, said Joel Cawthorn, a director with Calgary-based Startec Refrigeration Services Ltd., which is carrying out the work.

"The intent with that is to form that frozen wall. And then once they've got that, that becomes an impermeable barrier," Cawthorn told CBC News on Tuesday.

"Subsequent to that, they'll be reflooding the chamber and introducing more water until finally they'll top it up," he added. "So you can envision it being just a massive ice cube."

Cawthorn said it will take three or four months to freeze the wall, and about a year to freeze the entire chamber.

Officials with the Indian and Northern Affairs Department will review the results and decide how effective the arsenic freezing plan is, how long the process would take, and how much it would cost, he added.