Researcher says it might be better to leave some old N.S. mine tailings undisturbed
The Montague Gold Mine on the outskirts of Dartmouth, N.S., is full of toxic waste from historical mining that ended in the 1940s.
The mine produced more than two tonnes of gold in its day, but high levels of mercury and arsenic were the result.
With growing environmental concern, Build Nova Scotia promised to start to clean up 60 historical mine sites next year, which will cost at least $148 million.
But one researcher says the best approach to remediation might be to leave some wetland tailings alone.
Montague was classified as high risk along with Goldenville Mine in Guysborough County due to its proximity to people and high levels of arsenic, which are well above the province’s soil quality guideline for human health.
Michael Parsons, a research geologist at Natural Resources Canada, said cleaning up these mine sites is more complicated that it might seem.
Do not disturb, study suggests
In a study, Parsons’s team collected different types of tailings and exposed them to rainwater and oxygen. They determined that while the two types of tailings in this particular mine have the potential to generate acid, the ones that had vegetation growing on them, such as horsetail and ferns, were mostly unreactive.
To Parsons, this means that wetland tailings are more stable under those conditions and should not be disturbed unless it is necessary.
“Mother Nature, over the last eight decades, has re-established that wetland on top of the tailings and the advantage of that is it actually has removed direct contact between the old mine waste and oxygen,” he said.
Linda Campbell, a professor of environmental science at Saint Mary’s University, said this does not mean the species there are thriving.
“If you look closely, you can actually look at the species variation and it’s very limited. It’s to just tolerant species,” she said, speaking through a sign language interpreter.
“And not only that, when they do grow, they’re very stunted in their growth compared to when they’re growing in a healthier area”
Hardpan tailings
Parsons said the other type of mining waste found at the site, known as hardpan tailing, contains high levels of arsenic and is dusty, allowing it to travel through the air when it gets windy.
But the wind is not the only thing blowing the toxic dust. Off-road vehicles using the Montague site as a race track are part of the problem.
Parsons said the hardpan tailings could be contained to avoid erosion but the province must then control access to the site to avoid human interference.
“There are a lot of excellent solutions to try and encapsulate waste and cover them with various engineered covers, but you also need to make sure that people are not actively running over those mine waste landforms with off-road vehicles and that,” he said.
Campbell said the dust can be bad for the health of local communities, calling mercury and arsenic a “double whammy” of toxins.
Beyond cleanups
Donnie Burke, the senior environmental director with Build Nova Scotia, said the in an email that it is aware of the study and plans a cleanup that is supported by research.
“The conclusions [of the study] align with how our geochemists anticipate treating the two bigger sites, Montague and Goldenville where we have thoroughly delineated and validated the wetland areas to limit disturbance of tailings,” he wrote.
The province will begin to clean up dozens of historical mine sites around the province next year. But a recent study shows the process is complicated. Giuliana Grillo reports.
