Lake near Giant Mine will never recover from contamination, new research shows

Arsenic trioxide spewed from Giant Mine has done irreversible damage to the ecosystem of a nearby lake and continues to seep from the soil into water systems, according to a new study.  

The research was published by scientists from the University of Ottawa and Queen's University.  

They looked at areas within a 15 kilometre radius of the mine's roaster stack, and specifically at Pocket Lake, which is one kilometre west of the stack.

"We consider this the ground zero of impact for the mine," says Jules Blais, who directed the research. "We selected [the lake] because it would have received a maximum impact of emissions from the roaster stack."

The N.W.T.'s Giant Mine operated between 1948 and 2004. When the gold mine closed, 237,000 tonnes of arsenic trioxide was left behind in underground chambers.

Blais and his team looked specifically at lake sediment deposits before the mine was built and while the mine was operating.   

"We could see how the contamination changed over time," he says.  

The team found that before the mine was built, the levels of arsenic trioxide were low, but increased by 1,700 per cent when emissions were at their peak in the late 1950s and early 1960s.

Crustacea wiped out

Blais says the contamination in the lake was so high it wiped out the crustaceans that lived there. Crustacea, like small shrimps and crabs, are a valuable part of an aquatic ecosystem, providing food for fish and other aquatic life.  

Despite contamination levels dropping in recent years, the lake's ecosystem has not recovered and the crustaceans have never returned.

"It's a striking result," says Blais. "Because we have done similar studies in other mining areas, and we did not see such dramatic effects to the aquatic ecosystems."   

Emission controls at the mine only happened after 1958. During the first 10 years the mine operated, the arsenic from the roaster stack was airborne and settled to the ground — 20,000 tonnes of it.  

"So here we are, about 50 years after the major contamination happened and that arsenic is still in soils, and it's slowly leaching from soil to water," says Blais.

"This is part of the reason why some of the lakes in the area are still showing noticeably higher levels of arsenic."

Water systems safe

Blais doesn't believe the arsenic is a hazard to people, though. He thinks drinking water from the tap is safe, and municipal water systems are safe.  

He admits there are some lakes he'd avoid drinking from, but he says they're small and isolated to the northwest of the roaster, where people don't typically go.

Blais says the research has revealed some important takeaways.    

"If we start mucking up the environment, over long-term, we will be faced with longer term costs," he says.

Blais says the territory could continue to see higher arsenic in lakes for many decades to come.