System used to treat water from tailings after the mine closes is unreliable and untested: report
A Sisson mine cost review commissioned by the provincial government goes a step beyond looking at the numbers, pointing out that the system proposed to treat tailings water after the open-pit mine shuts down is “known to fail.”
Engineering firm Amec Foster Wheeler was hired by the Department of Energy and Mines to review the costs for water treatment and restoring the tungsten and molybdenum mine after it closes.
But the company’s report, which was obtained by CBC News through the Right to Information Act, also said “there are some concerns regarding design of the post-closure water treatment process.”
“Curtain systems in pit lakes have been known to fail, especially in freeze-thaw,” the report from April 2015 said. “Therefore the idea of a floating baffle curtain wall may not be feasible.”
After the proposed Sisson mine closes, the tailings pond would flow into the open pit over a 10-year period, creating a permanent lake.
The curtain system would be set up in the mining pit lake to separate filtered from unfiltered water.
A chemical used to remove arsenic and antimony from the water would settle at the bottom of the curtain for disposal and the treated water would eventually flow into the Sisson Brook.
“This kind of information just adds more uncertainly around the risk assessment that needs to be done on the project,” said Allen Curry, a professor of biology, forestry and environmental management at the University of New Brunswick.
Curry has thoroughly reviewed the environmental impact assessment report for the Sisson mine and made a presentation at a provincial public meeting on the project last month.
He said he doesn’t believe enough work has been done to understand the full risks of the project.
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