Tailings pond dyke breached at Casa Berardi Mine
The breach of an internal tailings dyke at Aurizon’s Casa Berardi Mine 95 km north of La Sarre May 1 spilled up to 150,000 cubic metres of contaminated water into the James Bay watershed.
Aurizon says initial estimates were overstated, claiming that between 50,000 and 60,000 cubic metres of water and 2000 cubic metres of solid waste were released during the incident.
“We believe that most of the material spilled into another cell inside the tailings pond, but because of the surge when the dyke was breached, some water and suspended solids went over the dyke that surrounds the tailings pond and into the environment,” said Aurizon Vice President of Operations Martin Bergeron.
Although the Casa Berardi mine site is located just south of where Waskaganish Cree trap lines begin, Grand Council Mining Engineer Aurora Hernandez says spills in the region could easily affect game and fish North of the mine. However, the mine is outside of the boundary coinciding with the limits of the Cree trap lines outlined in section 22 of the James Bay and Northern Quebec Agreement. This means that Cree authorities have little to no involvement in assessing the environmental damage of any spill or accident. Despite the mine’s proximity to trap lines, an impact assessment is not performed on behalf of the Cree, although it is for mines that are further North.
The gold mine is in its seventh year of operation. According to the company, the site has four tailings containment ponds that are examined visually twice daily, and examined by engineers on a monthly basis.
The breach occurred during the night, and Quebec Environment Ministry officials were not on hand to analyze the spill’s environmental impact until the following morning.
“When the dyke broke there was a very high flow and the discharged water was rapidly received into the environment,” said Stephanie Lemieux, head of communications for the ministry. “Because of that and the fact that we only tested the next day, it’s very difficult to determine the environmental impact. We’ll never know.”
According to Bergeron, the impacted area outside of the pond was roughly 200 metres long and 150 metres wide. Tests were carried out in the vicinity of the spill in accordance with provincial Directive 019, which stipulates legal limits for the presence of several different heavy metals in the environment. Arsenic, cyanide, lead, iron, copper, zinc and nickel were all tested for at the Casa Berardi mine site, and none were found to be over the limit. However, suspended solids, the only tailings material that cannot immediately recede into the environment, were found to exceed allowable limits. Aurizon employees cleaned up the solids with rakes and shovels.
While Quebec mines regularly test their tailing ponds for the presence of the chemicals and minerals specified in 019, other hazardous chemicals that have been known to find their way into the environment through mining contamination, are not. Dangerous levels of chromium and cadmium were found to be present in Chibougamau and Dore Lakes in a 2002 environment ministry study that when exposed, revealed the dangerous impact mines in the area were having on the region. Aurizon does not test their ponds for these chemicals, nor any others that aren’t included in the directive.
Lemieux says that the ministry is investigating whether negligence was a cause of the event. Other potential causes could be related to high water volume in the pond’s spillway due to heavy rain and melting snow.
“It may have started with a crack or some erosion because we suspect that the water went over the top of the dyke on each side of the spillway,” said Bergeron. “It’s possible that the water was too much for the spillway to handle.”