Published on January 15, 2013
The break in the dam, which once fully surrounded the waste at the former Gullbridge copper mine. Evaluations in the years leading up to the dam failure recommended action be taken to reinforce the dam, after detailed study of the abandoned mine structure. — Photo courtesy of Department of Environment and Conservation
Published on January 15, 2013
The site of the Gullbridge Mines dam break is shown above. — Submitted image
Government says response was standard; time needed for study
South Brook Mayor Paul Mills says it took two tractor-trailer loads of bottled water to get his town through an environmental crisis in the leadup to Christmas.
A non-consumption order was placed on the local water supply from Dec. 17-24. The advisory was in response to the failure of the dam holding back waste at the former Gullbridge copper mine, about 20 kilometres from the town’s water supply intake.
A spokeswoman for the Department of Environment and Conservation said there has been no concern over the water supply since it was first cleared and the advisory lifted.
And things are back to normal in the community now, Mills said.
The town is looking for the provincial government to cover the cost of the crisis.
“I was talking to the town clerk this morning and all our invoices and time sheets and related paperwork has all been submitted,” he said. “Before all this happened, personally I knew there had been a mine. I knew there had been a tailings pond, but I really hadn’t given it a second thought beyond that.”
The mayor was unaware the provincial government and its hired consultants were doing work at the site during the two years leading up to the dam’s failure.
In response to requests from The Telegram, the Department of Natural Resources provided copies of two reports on the structure, filed with government in 2011 and 2012 respectively, warning of the potential for just such a failure.
Timeline of response
The failure, on Dec. 17, 2012, was more than 2 1/2 years after staff with the Department of Natural Resources took photos of cracking on the wall of the dam.
The failure was more than a year and a half after a preliminary report on the structure was filed by Stantec with the provincial government, on March 2, 2011.
“Note that if the current physical condition of the dam is not improved, or at least maintained, the condition of the structure will continue to deteriorate due to weathering ... eventually progressing to failure of the structure,” the document warned.
However, the provincial government did act on concerns relating to the the dam, according to deputy minister of Natural Resources Charles Bown and other senior officials within the department, who took questions from The Telegram Monday.
While there were clear signs of problems with the structure as of the 2011 study, the department had no historical records on the dam — it did not know what it was made out of, or how it was made — and risked making structural problems worse without further study, they said.
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It was decided a more detailed report on the dam would be completed. That second study was filed with government Oct. 26, 2012.
Next, the province had to decide what would be done with the structure, and had to hire a contractor to do the work.
“It’s a process that you have to go through,” said Bown.
Risk to people low: consultant
It is worth noting the same reports warning of the potential for failure of the old tailings dam also stated a failure was unlikely to lead to deaths or environmental devastation, making it a “low-consequence structure” under national standards for tailings dams.
“Given the flat, boggy terrain, with some forested areas between the dam and South Brook, it is not anticipated that even a large scale dam failure would result in the movement of significant tailings materials to South Brook,” the 2011 Stantec report stated.
A priority in the reports was something had to be done about the stability of the structure.
The dam did not meet set standards on several points, including the slope of its walls, the 2012 study notes.
“The steeper the slope, the more likely it is to move,” said Alex Smith, director of mineral development with the Department of Natural Resources, trying to simplify the explanation.
There were also “beached” tailings, material not covered by water, within the holding area. When not covered by water, the copper mine tailings can oxidize, making the water covering the settled tailings more acidic over time.
“Ideally, a modern, well-designed tailings facility would keep everything covered by water,” said assistant deputy minister, Dave Liverman.
“When that happens, oxygen can’t get to it, which means that your sulfides stay as sulfides. They don’t get oxidized, which means that you don’t get as much acid generating.”
For now, the department has put a hold on any further work at the dam site until it can assess its options in dealing with the dam failure.
The province also has a hold on plans for work at other abandoned mine sites until it can be determined exactly what caused the failure at Gullbridge.