Take a look inside Giant Mine’s new water treatment plant

Construction is under way on a new water treatment plant at the Giant Mine site, which could be operational by February 2027.

“Getting that plant finished, commissioned and operational will be the most significant milestone we meet in the next year to year and a half,” Natalie Plato, deputy director for the Giant Mine Remediation Project, told reporters during a tour of the site last Friday.

Remediation of the former Giant Mine site on the edge of Yellowknife, which is expected to cost $4.38 billion and take until at least 2038, officially began in 2021.

Work completed so far has included deconstruction of the old roaster – once one of Canada’s most contaminated buildings – and the former townsite, as well as the creation of a non-hazardous waste landfill and closure of the mine’s underground.

Plato told Yellowknife city councillors earlier this year that the new water treatment plant is “the big item on site right now.”

Patrick Schmidt, an engineer with the remediation project, explained that once operational, water from underground at Giant Mine will be pumped into the plant for treatment before being discharged into Great Slave Lake.

He said the water will be treated so the arsenic level meets drinking water quality guidelines before it goes into the lake.

Currently, water at the Giant Mine site is treated at an effluent treatment plant and discharged into Baker Creek, which flows into Great Slave Lake.

Plato said differences between the current plant and the new water treatment plant include that water will be treated to a higher standard, while water pumping and treatment will be continuous rather than seasonal.

The new treatment plant will also not require the use of a settling and polishing pond, she said. Instead, it will produce sludge that will be disposed of in a specially designed cell at Giant Mine’s landfill.

Another feature of the new water treatment plant is that it will be heated by biomass to reduce greenhouse gas emissions.

Schmidt said water at Giant Mine will need treatment until a permanent solution is found for the approximately 237,000 tonnes of arsenic trioxide dust stored in underground chambers at the site.

The remediation project’s current plan is to freeze the chambers using thermosyphons to prevent that dust from entering the surrounding environment.

The Giant Mine Oversight Board – a separate, independent body tasked with scrutinizing the federally led remediation project – continues to research possible permanent solutions including vitrification, or transforming the dust into glass.

Other changes at Giant Mine since reporters were last invited to tour the site in September 2022 include that the mill has been wrapped. Plato said that has been done to contain any hazardous materials, such as asbestos, when the building is torn down.

Last year, the remediation project awarded a $101.3-million, two-year contract to True North Environmental Ltd to demolish the big remaining structures at the Giant Mine site.

That includes the former mill, C-Dry and tailings reprocessing plant, which you can see from the Ingraham Trail, that are expected to come down next year.

Motorists may have also noticed a new gravel pad by the Ingraham Trail. Plato said trailers will be placed on the pad to serve as office space to replace the C-Dry building.

Work planned in the future includes burying more than 360 seacans containing contaminated material from the former roaster in an underground pit.

Other items on the project’s list include remediation in Baker Creek, soil remediation, decommissioning of the effluent treatment plant, and boat launch and nearshore cover.

While vegetation is often used to reclaim mine tailings, the remediation project team has committed to the Yellowknives Dene First Nation that this won’t be the case for Giant Mine, where tailings will be left rocky.

Plato said the First Nation wants “the site to remain grey and ugly so people would remember in future generations that there was a mine here, and that there is contamination probably still existing.”