Cleaning up the giant heaps of toxic ore created by the proposed Carmacks Copper Project could take longer than expected.
Experts hired to assess the proposal have found the cleanup could take twice as long and cost the company three times more than initial estimates.
The Yukon Environmental and Socio-economic Assessment board has asked Western Copper Corporation for more data.
“We want additional information around the heap detoxification and closure time and some clarifications on the cost estimates,” said the assessment board’s executive committee member Stephen Mills.
The sludge-water treatment system is also being scrutinized, as is the management of minerals in the water discharge during closure and a waste rock storage area cover.
Western Copper Corporation wants to build its open pit mine 38 kilometres northwest of Carmacks.
The corporation plans to extract the copper through acid heap leaching.
Crushed ore is piled onto rubber liners and doused with sulphuric acid, which dissolves the copper.
The process leaves behind millions of tons of acid-laced ore.
If untreated, these toxic piles could continue to leach copper and other heavy metals into groundwater for years.
Western Copper is proposing to neutralize the acid through a wash of water and an alkali treatment.
The assessment board believes this system will detoxify the heap.
However, there are discrepancies about how much time it will take.
Company-sponsored tests suggest 4.5 years.
Lorax Environmental Services, a consulting firm hired by the Yukon government has estimated the rinsing period will take about nine years.
Ron Nicholson of EcoMetrix, the assessment board’s consultant, estimates about 10 years.
The longer it takes, the more expensive the detoxification gets, said Mills.
“We’re estimating at least $15 million just for some of the treatment costs of the water, not including pumping and other costs,” he said.
“And the company has come up with less than a third of that cost.”
The assessment board wants an updated cost estimate.
Western Copper has been doing additional testing of the detox process.
The company had not submitted any additional results to the assessment board as of Thursday morning, said Mills.
The assessment may not be going deep enough, said Gerry Couture of the Yukon Conservation Society.
“I’m not certain that they’ve fully dealt with the concern we have about the term it will take to detoxify this heap or even of the fact that the heap may not be detoxifiable,” he said.
“I still have seen no evidence of one of these heaps being detoxified anywhere in the world.”
Usually such mines have been in arid areas where there is little risk of heavy metals entering the water supply.
The Carmacks Copper Project is located nine kilometres from the Yukon River.
According to the assessment act, Western Copper has up to 180 days to respond to the information request, said Mills.
The assessment board expects a response much sooner.