Big numbers: Remediation of Giant Mine a cleanup on a vast scale


YELLOWKNIFE — The scale of the cleanup required at the Giant Mine almost beggars belief.

Big numbers: Remediation of Giant Mine a cleanup on a vast scale© Provided by The Canadian Press

Eight open mine pits. Six tailings ponds. About 100 buildings, many laced with asbestos. Untold tonnes of rusting scrap. A 900-hectare surface site poisoned with 13.5 million tonnes of arsenic, with a creek flowing through it that drains into Great Slave Lake.

And the kicker — there are 237,000 tonnes of arsenic stored underground in 13 huge, poorly mapped subterranean chambers, sealed off behind crumbling concrete bulkheads and sitting uncovered in huge dunes of highly soluble poison adjacent to the lake.

Removing that arsenic, the preferred solution of many northerners, would require workers to go deep underground into poorly understood environments wearing hazmat suits with separate air supplies. Even if possible, it would be incredibly dangerous.

So the arsenic will be frozen in place with the use of so-called thermosiphons.

A total of 858 thermosiphons, essentially long tubes filled with pressurized carbon dioxide, will be sunk from levelled-off platforms built over the arsenic chambers. The tops of the thermosiphons, which work without a power supply, will be exposed to air and the bottoms will penetrate about 76 metres down.

As heat from the ground warms the carbon dioxide in the bottom of the siphon, the gas slowly rises to the top. Winter air will cool it, condensing it to a liquid. That liquid falls to the bottom of the siphon, where ground heat warms it again.

As its heat is slowly pumped up and dissipated, the ground at the bottom cools and eventually freezes, sealing off the arsenic behind a wall of ice. Arsenic from surface soils and contaminated buildings will also be frozen in place underground.

Thermosiphons are commonly used across the North to protect foundations of buildings that are sunk into permafrost, but they have never been used in quite this way before, said project director Brad Thompson.

"We have kilometres of drilling to do and it's all very precise drilling."

Although thermosiphons won't work in the summer, Yellowknife winters are expected to be long and cold enough for the process to work, even as the climate changes.

It will have to. The thermosiphons will have to work in perpetuity, or until a safe method is found to bring the arsenic to the surface.

A test of the system conducted in 2011 found that thermosiphons cooled one of the mine's smaller chambers to about -5 C within two years.

Nor are the thermosiphons the only part of the cleanup that will have to work long-term. Water from the mine's depths will have to be pumped to the surface and treated in perpetuity.

About 700,000 cubic metres of water a year are already being treated. A new plant is being built, which will treat water to drinking standards before it's released into Great Slave Lake.

Under the mine siteis a network of tunnels and chambers, many of which make the surface prone to sinking.

"There are a lot of voids," Thompson said. "We're filling those holes with cement backfill."

By the end of 2024, those holes will have absorbed about 400,000 cubic metres of backfill.

A landfill the size of a small city block is also being built on the site to take in non-hazardous waste.

The mine's remaining townsite, a few dozen company houses, will be demolished and the asbestos-contaminated materials shipped to a disposal facility.

Water from the tailings ponds will be drained and treated. Open pits will be filled in with clean waste rock.

Although the remediation plan dates to 2014, work couldn't begin until the project received a licence from northern regulators, which was granted in 2019. Work was again delayed by the COVID-19 pandemic and crews didn't get on the site until last summer.

The original timeline for the project has been extended to 2038 from 2031. Its original budget, set in 2014, was about $940 million.

This report by The Canadian Press was first published Sept. 28, 2022.

— Follow Bob Weber on Twitter at @row1960

Bob Weber, The Canadian Press

Gold, arsenic and murder: A look at the complex history of N.W.T.'s Giant Mine

YELLOWKNIFE — A team working to address environmental and health effects from a former gold mine outside Yellowknife has provided an update on the effort to clean up one of the most contaminated places in Canada.

Gold, arsenic and murder: A look at the complex history of N.W.T.'s Giant Mine© Provided by The Canadian Press

The Giant Mine Remediation Project, co-managed by the Canadian and Northwest Territories governments, is expected to take until 2038 to complete. Arsenic trioxide waste stored underground is anticipated to require perpetual maintenance.

Here is a look at the mine's history:

— Summer of 1935: C.J. (Johnny) Baker and H. Muir stake the original 21 "Giant" claims near Great Slave Lake's Back Bay while working for Burwash Yellowknife Mines Ltd.

— June 3, 1948: The mine, owned by Frobisher Explorations, pours its first gold brick. Ownership later changes hands several times.

— 1949-1951: Airborne arsenic emissions at the mine, where no pollution control has been installed, is estimated at 7,500 kilograms per day.

— 1951: There are reports of widespread sickness, including skin lesions, among residents on Latham Island, where the Yellowknives Dene use snowmelt for drinking water. Local newspaper ads warning about arsenic in water sources are published in English, which many of the Dene cannot read.

— April 1951: A two-year-old Dene child dies from acute arsenic poisoning after drinking water. Giant Yellowknife Gold Mines Ltd. gives the family $750 in compensation.

— October 1951: A Cottrell Electrostatic Precipitator is installed to capture and control emissions. Arsenic emissions drop to 5,500 kilograms per day. That same year, storage of arsenic trioxide dust in underground storage chambers begins.

— 1959: Emissions drop to 200 to 300 kilograms per day after the installation of a second electrostatic precipitator and a baghouse.

— 1969: Water intake for Yellowknife is relocated to avoid contamination.

— 1974: Three uncontrolled releases of tailings into Back Bay occur. Environmental studies later find contamination of Back Bay, Baker Creek and Yellowknife Bay.

— 1975: The federal government begins public health studies, including hair and urine sampling in Yellowknife, which find especially high arsenic levels in mine workers.

— 1977: The National Indian Brotherhood conducts an independent study with United Steelworkers and the University of Toronto's Institute for Environmental Studies, which finds high arsenic levels in mine workers and Indigenous children.

— 1990: Royal Oak Resources Ltd. gains control of the mine.

— April 1992: Local 4 of the Association of Smelter and Allied Workers and Royal Oak reach a tentative agreement, which a majority of union members vote down.

— May 22, 1992: The day before workers plan to go on strike, Royal Oak locks out union members and plans to use replacement workers.

— June 1992: A riot breaks out as a group of striking workers tears down a fence and storms the mine grounds, damaging property and injuring security guards. Later that month, a group of strikers, calling themselves "Cambodian Cowboys," break into the mine, steal explosives and write threatening graffiti on an underground tunnel. They later set off explosions that cause damage.

— Sept. 18, 1992: Nine mine workers in an underground railcar are killed by a bomb.

— November 1993: The Canada Labour Relations Board orders an end to the lockout.

— 1995: Roger Warren is convicted of nine counts of second-degree murder in the 1992 bombing.

— 1997: The federal and N.W.T. governments begin studying how to manage the arsenic trioxide waste.

— 1999: Royal Oak goes into receivership and rights to the mine are transferred to the federal government, which then sells the assets to Miramar Giant Mine Ltd. while severing environmental liabilities.

— 2004: The federal government announces plans to freeze the arsenic trioxide dust underground long-term.

— 2004: The N.W.T. workers' compensation board is awarded $10.7 million following a lawsuit against the territorial government, union, Royal Oak and private security firm Pinkerton that sought compensation for families of the workers who died in the bombing.

— 2005: The Giant Mine officially becomes an abandoned site.

— 2008: The decision on compensation for families of the workers killed in the bombing is overturned on appeal.

— 2012-2014: The roaster at the mine site is demolished.

— June 2015: The federal government signs an environmental agreement for remediation with the N.W.T. government, City of Yellowknife, Yellowknives Dene First Nation, Alternatives North and North Slave Métis Alliance.

— 2016: The N.W.T. issues a public health advisory warning residents to avoid drinking water, swimming, fishing and harvesting plants and berries in and around several lakes in the Yellowknife area due to high arsenic levels.

— 2019: Initial baseline results from urine and toenail samples from residents of Yellowknife, Dettah and N'dilo find arsenic exposure levels similar to the rest of Canada.

— August 2020: The Mackenzie Valley Land and Water Board approves the federal government's land-use permit to remediate the site and the Northern Affairs minister approves the project's water licence the following month.

— December 2020: The Yellowknives Dene call for a federal apology and compensation for the mine, as well as involvement in remediation.

— July 2021: Full remediation begins.

— Aug. 2021: Canada and the Yellowknives Dene sign three agreements, including a community benefits agreement that promises up to $20 million over 10 years to support the First Nation's participation in the remediation project.

— April 2022: The federal budget earmarks $2 million between 2022 and 2024 to support the Yellowknives Dene in their pursuit of an apology and compensation.

This report by The Canadian Press was first published Sept. 28, 2022.

Emily Blake, The Canadian Press