Sisson mine review raises water treatment concerns

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.

"In order for the project to proceed and be successful and to have the minimum impact, we need to understand all of the risks associated with the project," said Curry.

The open-pit mine would be built on 12.5 sq. km of land near Napadogan, north of Fredericton

'That's inherently risky'

Water treatment through the curtain system wouldn't be a quick process. Instead, it would happen at the end of the spring melt over 10 years.

The engineering company said the gradual pace, known as semi-batch treatment, appears to be a new concept for this type of project.

If it hasn't been tried and true, they'd want to be careful about something like that.- Scott Dunbar, University of British Columbia professor

CBC News asked several mining engineering experts if they were familiar with the system being used in open pit mining, but none were.

"[The semi-batch system] is a new concept, so that's inherently risky," according to Scott Dunbar, an associate professor and head of the University of British Columbia mining engineering department.

"If it hasn't been tried and true, they'd want to be careful about something like that. That's a serious concern actually."

The Sisson Partnership, comprised of Northcliff Resources and Todd Minerals, didn't provide a specific response to the report's finding. The company said it hasn't received the report from the government.

Myke Clark, the vice president of public affairs, said in a statement that the company understands how the provincial government hired a third party to review certain aspects of the licence submission.

"Our mining licence application has been made in accordance with government requirements and a third party review is common," the statement said.

"The Sisson Partnership is confident we have drafted a professional, supportable mining licence application and we remain ready to discuss it with the appropriate government department as it makes its way through the permitting process."

In addition to Amec Foster Wheeler's report, CBC News obtained a letter from the government asking the Sisson Partnership to prove the viability of the system.

"The semi-batch treatment in the pit planned for the post-closure period appears to be a new concept. Please provide an example of a successful full-scale operation at another site in order to help prove the feasibility," said the letter to The Sisson Partnership from the Department of Energy and Mines and the Department of Environment.

Environment Minister Brian Kenny said in a statement that "the EIA process involves the review of many pieces of information including various reports."

The provincial government's public consultation period of its environmental review of the open-pit mine ends on Friday.

Amec Foster Wheeler also found the Sisson Partnership had underestimated the costs to build the water treatment plant and restore the site after the mine shuts down by millions of dollars.