Richard Gleeson
Northern News Services
Yellowknife (Jun 11/01) - Freezing it where it lies is the safest and cheapest way of dealing with the 265,000 tons of arsenic trioxide laced dust stored in Giant mine, concludes a report released today.
Prepared by SRK Consulting, the report looks at four methods of dealing with the dust, collected from the stack of the mine's gold roaster and blown into underground vaults during a half century of mine operation.
A public workshop at the Explorer Hotel today and tomorrow focuses on how best to deal with the underground arsenic. The workshop is hosted by the Department of Indian and Northern Affairs, which assumed responsibility for the problem when former Giant Mine owner Royal Oak Mines went into receivership two years ago.
Counting costs
Three of the four methods involve extracting the dust, composed of 60 per cent arsenic trioxide, from 15 vaults.
Removal would be done through remote control robotic equipment because of the toxicity of the compound -- officials have estimated two aspirin sized tablets are enough to kill a person if ingested.
The cost of removing the dust ranges from $143-409 million, the report estimates. Leaving the dust where it is and freezing it through the use of thermosyphons would cost $39-69 million.
Though the report states freezing the dust where it is stored poses the least risk to human and environmental health, city councillor and environmentalist Kevin O'Reilly said doing so would perpetuate the problem.
"I just don't think it's the responsible thing to do," O'Reilly said. "This generation made the mess and we should clean it up."
O'Reilly said perpetual care and monitoring would be required to ensure the freezing continues. He questioned how viable a method it would be if global warming trends continue.
An earlier report on the same technique noted a number of other difficulties with the technique:
- Thermosyphons would have to be replaced every 50-100 years, and it will be difficult to replace the syphons placed beneath the vaults
- Freezing the ground beneath Baker Creek, where one of the vaults is located, may be impractical
- Freezing would be also be impractical for three other vaults
The official overseeing the clean-up of Giant noted the report is far from the last word on the clean up.
Dave Nutter said the purpose of the workshop is to engage experts and the public in the process of settling on a final solution.
"The land and water board and the environmental impact review board will both be looking at public reaction," said Nutter. "It's in nobody's interests to force something through or be perceived to be forcing something through."
'Unmanaged base case'
The study also looked at what would happen if the pumps used to artificially lower the water table to keep ground water from coming into contact with the arsenic were shut off.
It is known that water has penetrated some of the vaults, but officials say the water is being captured in a sump beneath the mine and pumped to a tailings pond for treatment.
The report estimates 2,000-8,000 kg of arsenic trioxide would be flow from the vaults into the environment if the water table were left to rise to its natural level.
Up to 2,000 kg of arsenic could be released to the environment without any appreciable negative impact on the environment, SRK concluded.
Release of more than 4,000 kg annually could create health risks for people who consume "significant amounts" of fish and water from Back Bay.
A worst case release rate of 16,000 kg per year would spread the health risk to all of Yellowknife Bay.
