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SOMBA K'E/YELLOWKNIFE
A sinkhole the size of a small bus in a gravel roadway at Giant Mine is being monitored by the mine's remediation team to make sure that the nearby Baker Creek doesn't flow through it.

Adrian Paradis, acting project manager of the Giant Mine remediation project, stands in front of the sinkhole on July 25, 2011. A large sinkhole has developed since May 2 between pit B1 and Baker Creek, near Giant Mine along the Ingraham trail. - Tim Edwards/NNSL photo

The worst-case scenario, according to acting project manager Adrian Paradis, would be that the creek might overflow, and flow into the sinkhole for three to four days - by which time the remediation team, comprised of staff from Aboriginal Affairs and Northern Development Canada, might not have the capacity to pump the water back out.

The water would then overflow into pit B1 - a large open pit and one of eight at the mine - and through it into the underground arsenic chambers, which the team is currently working to freeze.

In such a scenario, groundwater would be contaminated -- though Paradis also described that situation as very unlikely.

"It is a concern, but we've got it under control," he said, pointing out there is a fair amount of flat land and a large slope the creek would have to flow over before it would reach the sinkhole. The distance between the hole and the creek is currently about 17.5 metres.

Paradis said the hole was first noticed on May 2, after spring freshet - where water levels rise from heavy rain or spring thaw - at which point it was just about one-square-metre in size.

He said the team has been monitoring the sinkhole daily since then and is still looking into the cause. But the general conclusion is that the hole appeared during the melt when water sucked away some of the gravel and dirt from the road.

"Every time it rains, the process repeats itself," Paradis said.

The sinkhole is now six-square-metres in size.

In the short term, he said the team's engineers are working on a plan to make sure there isn't a chance the sinkhole could open a route between Baker Creek and the mine's underground.

And in the long term Paradis said the team plans on stabilizing the underground mining tunnels in the area and filling in pit B1 and other pits while continuing the process of freezing the arsenic chambers and cleaning up the mine site.

Yellowknives Dene Dettah Chief Ed Sangris has previously expressed concern about arsenic contamination of the area, especially after a tailings pond overflowed into in Baker Creek earlier this year.

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