Canadian Consulting Engineer

Giant Mine toxic dust to be stored underground with artificial freezing

February 17, 2004
By Canadian Consulting Engineer

The Canadian Department of Indian and Northern Affairs has decided that the best way to treat 237,000 tonnes of tox...

The Canadian Department of Indian and Northern Affairs has decided that the best way to treat 237,000 tonnes of toxic dust in the Giant Mine near Yellowknife in Northwest Territories is to freeze it and store it in-situ underground.

The toxic dust is left over from 60 years of gold mining at the plant, which is still being mined but has had many troubles over the years, including the death of nine workers during a labour dispute in 1992.
Bill Mitchell, manager of the clean-up team for the Department of Indian Affairs explains that when the operations began at the mine in 1948 there were no requirements for reclaiming toxic waste and nowhere near the same environmental rules as we have today. “Things have changed,” he says, and explains that today mining operations have to put up substantial dollar amounts to ensure the public is not left responsible for remediating their sites after they have finished extracting.

Between 1951 to 1999 the Giant Mine collected the arsenic trioxide dust as a by-product of extracting gold from ore. The dust was stored in mined out cavities and underground chambers in the permafrost. However, by the end of the 1970s, the permafrost in the arsenic storage areas disappeared and groundwater movement increased. It is thought that the loss of permafrost may have been caused by activity and warm ventilation air in the mine. Currently a drainage and pumping system ensures virtually no contaminated water is released into the environment.

After the former owner of the mine, Royal Oak, went bankrupt in 1999, the land reverted to the Crown and the federal government began exploring options of what to do with the waste. The mine is still operated by its new owner Miramar Giant Mines, but Miramar is not responsible for cleaning up the existing contamination.

The government reviewed 56 possible technologies for dealing with the waste, says Mitchell, and a technical advisory group led by SRK Consulting whittled the choice down to 12 and then two in a final report in March 2003. Other experts on the technical team with SRK were Lakefield Research, Senes Consulting, HGE Engineering and Golder Associates.

One alternative was to remove the dust from the underground storage areas and encase it in cement. It would be stored permanently at the site on the surface. The other option — the one finally chosen — is to keep the dust in its current locations by artificially freezing the storage chambers and surrounding areas into frozen blocks.

After further public consultations and an independent peer review of the Technical Advisor’s report the government has now decided that the preferred option is the latter in-situ approach. According to a CBC report, the chosen option is not the most popular with Yellowknife’s Dene First Nation, who would have preferred to see the toxic byproduct removed.


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