Yellowknife (July 10/06) - Contractors for the federal government are working feverishly to prevent a potential disaster triggered by flooding underground at Giant Mine which could dump large amounts of arsenic into Yellowknife Bay.

Mark Liskowich, former head of environmental and technical services for the Giant Mine clean-up, points to the underground bulkhead leading to arsenic chamber C-212. The picture was taken last summer. - NNSL file photo

The plan calls for diverting a 400-meter stretch of Baker Creek, which flows through the mine site, around a troublesome area known as Mill Pond.

Right now water is leaking into the underground workings only 25 to 50 feet from the bottom of a mining pit called C-1.

An underground chamber close to the mining pit contains 16,946 tonnes of deadly arsenic trioxide - a by-product of years of smelting operations at the now defunct mine. There are 15 arsenic chambers containing a total of 237,000 tonnes of the substance.

The mining pit sits immediately adjacent to the Ingraham Trail. In it, five sinkholes - one of which is 100 feet deep - have formed over the last three years due to water leaching from Baker Creek through crushed rock fill under the road. A new, rapidly growing sinkhole was discovered just last winter.

Bill Mitchell, Giant Mine clean-up co-ordinator for the Department of Indian Affairs and Northern Development (DIAND), said if the rock gives way, the entire creek bed could rupture and pour directly into the mine.

"It would be a real disaster because we probably couldn't keep the mine pumped out," said Mitchell. "We'd had have to do some real quick emergency work on surface to try and keep the creek from going into the mine, but the mine pumps would not be able to handle the amount of flow."

The underground workings extend fairly deep - 2,000 feet, which is far beneath where the arsenic is stored - but if the flooding reaches the chamber the high soluble arsenic trioxide could escape, said Mitchell.

He said it's possible the arsenic could enter nearby Yellowknife Bay, even though contaminated water inside the mine is routed through a treatment plant that extracts most of the arsenic and dumps it into a settling pond.

He said if the mine floods, the pumps wouldn't be able to work fast enough to collect all the arsenic-contaminated water and pump it back to the treatment plant.

"Potentially we could have quite large releases of arsenic," said Mitchell.

Another worry is that if the creek does give way, it could happen so suddenly that a "mud rush" could occur, dropping tonnes of rock and muck on top of anyone who may happen to be working underground at the time.

Mitchell said crews of six or more are often underground, removing old mining equipment and checking the water pumps.

Berms have been erected underground to protect the workers against a mud rush, but Mitchell said it's still a concern particularly during spring when water flow is at its highest.

"Even with berms, the large amount of water that was in that sinkhole (in spring), if that let go there is the potential for the mud rush to get over that berm," said Mitchell.

The new creek bed will keep the stream on the west side of the road and re-connect with the old creek a safe distance away. Work crews can be seen right now carving out mine rock in order to reach uncontaminated clay on which the new bed will be built.

The excavation project is expected to cost between $1 million and $1.5 million.

Mitchell said his department hopes to have the new creek bed ready this year, but conceded that they may not have enough time before winter sets in to complete the job. By then it could be too late.

"The concern is, say next freshet in the spring, if we get very high water levels, then all of a sudden it pushes all the clay out, the rock itself then begins to collapse and the whole thing comes down," said Mitchell.

If all goes well, however, there could be good news for fish who travel up the creek to spawn during spring. The new creek bed will be built to allow numerous pools and riffles to form, which would create more spawning beds.

Ernie Watson, the area habitat biologist for the Department of Fisheries and Oceans, said it's not clear whether the fish, which include Arctic grayling, pike, and suckers, are successfully spawning in Baker Creek.

The Arctic grayling caused a stir a few years ago when they came back after a decades-long absence due to pollution from the mine.

Unlike salmon, which migrate to home streams because of their specific water chemistries, grayling and pike only require good water flow and gravel to spawn on.

There is still enough arsenic entering Baker Creek, that it may not be possible for young fish to survive, said Watson.

"A long-term monitoring program will be implemented to look at the success of spawning," said Watson, which would include netting of juvenile fish in the stream - if any.

The creek excavation is being carried out under the authority of the minister of DIAND, who can make emergency orders if immediate action is required.

The overall clean-up of Giant Mine itself will require the approval of the Mackenzie Valley Land and Water Board, which will likely take a year or more. DIAND took over responsibility for cleaning up Giant mine after its former owner Royal Oak went bankrupt in 1999. Mitchell said clean-up is expected to take 10-15 years.

The government plans to freeze the arsenic stored underground using thermosyphon devices on the surface and coolants pumped underground to freeze the rock surrounding the arsenic chambers.

The entire project is expected to cost upwards of $200 million.