Giant Mine Remediation Project

About the Giant Mine Remediation Project

The Giant Mine Remediation Project addresses the long-term containment and management of the arsenic trioxide waste, the demolition and removal of all buildings on the surface, and the remediation of surface areas including the tailings ponds at the former Giant Mine site in Yellowknife. It also includes water management and treatment options.

The Giant Mine Remediation Project submitted its application for a Type A Water Licence to the Mackenzie Valley Land and Water Board on April 1, 2019. The Mackenzie Valley Land and Water Board Public Registry is where the Project’s documents related to the Water Licence and Land Use Permit will be permanently posted for public access.

The main objectives of the Giant Mine Remediation project are to:

  • minimize public and worker health and safety risks
  • minimize the release of contaminants from the site to the surrounding environment
  • remediate the site in a manner that instills public confidence
  • implement an approach that is cost-effective and robust over the long term

The Giant Mine Remediation Project is co-managed by the Governments of Canada and the Northwest Territories. For more information on the Giant Mine Cooperation Agreement and how the two governments work together as co-proponents, refer to the Giant Mine Cooperation Agreement.

For regular updates on the Giant Mine Remediation Project, visit the project page.

Parsons, the Main Construction Manager for the Giant Mine Remediation Project is responsible for the majority of hiring and contracting associated with the Giant Mine Remediation Project. For more information, or if you seek employment, please visit their website at

Arsenic Trioxide Waste Storage

Between 1948 and 2004, Giant Mine was a major economic driver for Yellowknife and the Northwest Territories. When the mine stopped operating and the Government of Canada became the site custodian, attention focused on the environmental issues left behind. The most notable is the 237,000 tonnes of arsenic trioxide stored in underground chambers.

There are five stopes and 11 chambers at Giant Mine that contain arsenic trioxide dust. Between 2001-2003 extensive scientific and technical research, and community consultation took place to determine the safest way to manage arsenic trioxide underground. The Project team considered 56 options for managing the arsenic.

Freezing the arsenic trioxide in place was determined to be the best strategy for managing the arsenic for the long-term to protect people and the environment. However, this is not a permanent solution for managing arsenic trioxide. The Giant Mine Oversight Board is tasked with supporting research into technical approaches that could serve as a permanent solution. 

In order to release the gold found in minerals called arsenopyrite ore, Giant Mine and other legacy mining operations around Yellowknife had to roast the ore at extremely high temperatures. Unfortunately, this roasting process also released arsenic rich gas, a highly toxic byproduct. In the early days, much of that arsenic was released directly into the environment. As a result, some areas in the Yellowknife area contain increased levels of arsenic. For more information on the arsenic monitoring and research that takes place around Yellowknife, visit our page on Monitoring legacy arsenic in the Yellowknife area.

Perpetual Care Plan engagement

Giant Mine’s remediation is expected to take approximately ten years, but the project itself has a defined life of 100 years, with some components that will require operation and maintenance into perpetuity. It is important to ensure that, once active remediation is complete, there is a plan in place for how the site will be managed and how future generations will be informed about the site. This plan also needs to include considerations for how records are managed and how future risk scenarios are assessed that could impact perpetual care of Giant Mine.  As part of planning, the project team has begun engaging with the signatories to the Environmental Agreement and other interested parties. The project team held the first workshop to start building a common understanding of what a perpetual care plan should contain, as well as any next steps for the site, on October 31, 2019. 

From this workshop, the team established an advisory task force to provide recommendations to the Giant Mine Working Group about the Perpetual Care Plan. The project team will engage with this task force and the working group as they develop the plan in 2020.

Perpetual Care Plan - October 2019 Planning Workshop