U.S. firm Parsons wins bid to complete Giant Mine clean up in NWT

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One of the richest gold mines in Canadian history, Giant Mine produced some seven million ounces of gold from 1948 to 2004, acting as a major economic driver for the region. But when the mine closed, some 237,000 tonnes of arsenic trioxide was left stored in 14 underground chambers. Photo Credit: Marke Clinger/Wikimedia Commons.

U.S.-based engineering services firm, Parsons Inc., has won the latest remediation contract surrounding the cleanup of arsenic trioxide waste at Yellowknife’s Giant Mine in the Northwest Territories.

This main construction manager contract is Parsons’ third with the Giant Mine site, following decontamination and deconstruction of 10 major structures at the mine’s roaster complex completed in January 2015. The company has overseen several major projects in Canada, including the $960 million Kicking Horse Canyon improvement project in B.C.

One of the richest gold mines in Canadian history, Giant Mine produced some seven million ounces of gold from 1948 to 2004, acting as a major economic driver for the region. But when the mine closed, some 237,000 tonnes of arsenic trioxide was left stored in 14 underground chambers.

Now, the entire cleanup project is expected to take up to 10 years, starting in the near future.

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“When the mine was still in operation, the original underground storage method relied on the area’s natural permafrost, which worked as a frozen barrier,” according to a report by the recently dissolved federal department of Indigenous and Northern Affairs Canada. “It was believed that when the time came to close Giant Mine, permafrost would re-form around the storage chambers and stopes, and seal in the arsenic trioxide.”

However, the department adds, continued mining activity in the region caused the permafrost to thaw, allowing water to seep out from the underground storage areas. All contaminated water from the mine is currently being collected and pumped to a water treatment facility above ground on site.

The project is expected to use the Frozen Block Method, described by the federal department as “using a combination of active and passive freezing systems. The active freeze systems circulate cooled liquid through a series of underground pipes to freeze the designated areas around and within each of the chambers and stopes. This system is very similar to what is used to freeze ice in indoor rinks.”

The federal department states that the Frozen Block Method is not the least expensive method to contain the arsenic, but it is the safest. Less expensive, it notes, would be to manage the arsenic trioxide waste by continuing to pump it out through groundwater to be treated at a water treatment plant.

“The health and safety of northerners and the sound environmental management of contaminants are a top priority for the Government of the Northwest Territories,” announced Robert McLeod, Northwest Territories Minister of Environment and Natural Resources. “I am pleased to see progress being made to remediate the Giant Mine site in Yellowknife and satisfied that the federal government has structured the contract to allow for the fullest economic participation of Indigenous and northern businesses in supporting the work of Parsons Canada,” added McLeod.

The cleanup and remediation of the site was inherited by the federal government. As the main construction manager, Parsons will provide construction management services to the Giant Mine Remediation Project team over two terms. Work completed in Term 1 will centre around responsibility for site care and maintenance and emerging risks on site, as well as supporting planning efforts for the full remediation in Term 2. This work will start immediately and will be undertaken until March 31, 2020, at a cost of up to $32 million. The cost estimate of Term 2 will be determined following design work undertaken in Term 1.

In Term 2, set to begin in 2020, Parsons will oversee the implementation of the overall remediation plan and associated activities.

The Giant Mine Remediation Project is funded through the Federal Contaminated Sites Action Plan.

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