The Giant Mine remediation project team says thermosyphons are going to be installed at the underground chambers this summer. Currently, 237,000 tons of arsenic remain stored in the chambers on site. Crews are finishing internal work inside the new water treatment plant at Giant Mine. Commissioning activities are scheduled to start later this year and full operation of the new water is scheduled to begin in 2027.
Candace Ross, the Giant Mine Remediation project’s acting deputy director, reported that to date, remediation efforts achieved a number of milestones including underground stabilization, backfill, the deconstruction of the roaster as well as the demolition of the town site.
“We’re about to kick off a lot of big projects and things are going to get quite busy on site,” said Ross at the annual Giant Mine remediation update at the last Yellowknife city council meeting.
Geneva Irwin, project engagement manager, presented an overview of a perpetual care plan in development.
“The Perpetual care plan won’t start to come into effect until the project is in the post-closure phase. So we’re starting the project long in advance, over 10 years.”
Irwin said because there are “still a lot of unknowns” about the long term future of the site, a task force has begun planning to help identify “gaps, questions and recommendations.”
The first version of the plan is being developed by various stakeholders including the Yellowknives Dene First Nation, the North Slave Métis Alliance, Alternatives North, the city of Yellowknife, the territorial government and the Giant Mine Oversight Board.
Giant Mine is located on the traditional territories of the Yellowknives Dene First Nation. The mine began operations in 1948 and closed in 2004.
After the mine opened, Dene children and Elders died due to arsenic poisoning. Official records show that in 1951, Abel, a Dene child, died of arsenic poisoning and at least two more children died that same year, according to testimonies of Elders. At the time, an agent with Indian Affairs also reported widespread illness including hospitalizations.
When mine operations stopped, the federal government took over the site.
About 13 years ago, the Giant Mine Oversight Board (GMOB) was able to get the federal government to make that commitment through the Giant Mine Remediation Project team. In 2012, in response to calls from GMOB, the Mackenzie Valley Environmental Impact Assessment Review Board ruled that the remediation project team would need to treat mine water according to drinking water standards (containing no more than 0.01 mg/L) before the remediation project could begin.
The current water treatment plant on the mine’s site uses pumps to prevent uncontrolled flooding of the mine, which could potentially release contaminants into the bay. These were measures that the GMOB had advocated for.
The new water filtration system will pump water directly to the surface, pumping and treating the water, versus storing the water.
Underground access to Giant Mine was formally closed in November 2024. Temperature and water quality monitoring continues from the ground level.
“Once the stabilisation was complete, we put pace backfill into underground openings. We removed hazardous materials from the underground and disposed of them offsite.
Access portals have been and are being secured so that there’s no longer access to the underground,” said Ross.
“We’ve turned off the ventilation and heating to the underground. So things are starting to get colder down there. And we continue to monitor the underground from surface. So We look at temperature stability and water quality in the underground,” added Ross.
Ross said that to date remediation work at the site was focussed on mitigating the “highest risks” and this year a number of new “big” projects are scheduled to begin.
“Until now we’ve really focused on reducing the highest risks at site. We’ve completed projects like the roaster deconstruction the underground, the stabilisation is finished. We’ve closed the underground. We finish the paste backfill program. We’ve constructed our non-hazardous waste landfill and we’ve also demolished a lot of buildings on site. Most noticeably on the town site, houses are gone. Right now we’re in the process of building our new water treatment plant, a lot of work on contaminated, soils. And we are working on our core area building deconstruction.”
Ross said the mill on site is currently enclosed as crews work on decontaminating the building, which is scheduled to be deconstructed this year.
“We still have a lot of work to go. We’re still working on our designs, but we have our bigger creek remediation realignment. We’re gonna be doing a lot of in-more work within your short for sure.
“We’re filling our pits, building, our tailings covers, so lots of work to still come.”
Ross said the plant is scheduled to go online by next year. Work on the water treatment plant building began in 2025 with blasting and levelling the surface where the water treatment plan is built.
“We built the outfall, which is where the effluent from the water treatment plant will be discharged into Great Slave Lake. That in water work to build the outfall was finished last year. We also drilled, our water intake rails. So that’s where we’re going to pull water up from the underground, ring it to the plant. And we started internal work on the building. Which is really what we’re working on now is finishing that internal work and we expect to start commissioning activities, later this year with full operation in 2027.”
At a presentation last spring, Natalie Plato, then deputy director of the project, explained that the new water plant is designed to prevent uncontrolled flooding of the mine, which could potentially release contaminants into the bay. The new system will pump water directly to the surface, pumping and treating the water, versus storing the water.
In June, Plato gave a presentation on how the new water remediation plant will work.
Ross said that the team is working on procuring, the operator contract for the water treatment plant which will be a four and a half year contract.
Ross said to improve overall health and safety, crews are also upgrading access to the Giant Mine site along the Ingram Trail, including for the Effluent Treatment Plant Crossing.
“That’ll help us get our aggregate material from one side of the highway to the other. And also bring contaminated soils back across the highway. We are also going to be moving our main site, access from where it is right now by the Historical Society out to the other site [the Brock Gate.}”
The updates to the crossing are scheduled to come into effect in the summer.
Ross said thermosyphons have begun being installed including on one of the damns to help with stability.
“We’re going to start freezing, the underground chambers and that is supposed to start this summer.”
Thermosyphons are tubes filled with carbon dioxide that are designed to operate based on the ambient air temperature.
Ross said that contaminated soil remediation in and around the Sailing Club is scheduled to happen in 2029.
Irwin said a public engagement session is being planned for this spring.
