Giant Mine Closure and Reclamation Plan
Information about the approved Closure and Reclamation Plan is for the Giant Mine Remediation Project.
Closure and reclamation Planning
The Giant Mine Remediation Project has resubmitted its application for a Type A Water Licence on April 1, 2019. This included submitting an updated Closure and Reclamation Plan and other supporting documents, such as management and monitoring plans, to the Mackenzie Valley Land and Water Board.
These documents were made available to the public in June 2018 in advance of the formal regulatory process. The public had opportunities to provide input directly to the board. The project was granted its water licence in September 2020.
Documents associated with the project’s regulatory process can be found the board’s Public Registry. For more information, email the Project team.
Information about the project’s surface design engagement work is also available.
Closure and Reclamation Plan
The Closure and Reclamation Plan identifies the activities the Project team proposes to remediate the site. It provides details for the on-going monitoring, management and reduction of environmental effects. It also describes how the Project team will meet the plan’s objectives. Below is a summary of the plan’s components.
The site consists of:
- 85 buildings
- 25 debris stockpiles
- up to 30 km of road network
As part of remediation, the Project team plans to decommission, decontaminate, demolish and remove the majority of existing infrastructure. The Project team will construct some new infrastructure that will stay on the site after remediation is complete, including:
- a fence around the central area of the site
- thermosyphons for the freeze program
- a transport network of the roads, culverts and bridge(s) to access the remaining infrastructure
- power and communications services
- an overland treated water pipeline and near shore outfall
- a non-hazardous waste landfill
- a closed portal that can be used for future underground mine access, if needed
- space that the Yellowknife Historical Society will manage
- a memorial
The remediation will include filling some underground areas with tailings and other materials based on stability assessments. All openings to the underground will be covered, capped or plugged to prevent public access.
Freezing of arsenic chambers and B1 pit
The remediation includes freezing the chambers and stopes that contain the arsenic trioxide dust. The project team will also freeze part of the B1 pit, as it will contain some arsenic-impacted materials. The frozen zone established around these areas will be maintained at -5°C or colder throughout the year. Temperatures will be monitored to make sure the areas remain frozen.
The remaining pits will be filled with a combination of new quarried rock and coarse waste rock from the mine site. Pits will be filled and covered to protect the underground from flooding and prevent unauthorized access.
Tailings and dams
The plan for the tailings areas and dams is to:
- use some tailings to make paste to fill underground areas
- cover the tailings containment areas with a rock cover and a liner
- relocate the south pond tailings into the north and central tailings ponds
- drain and cover the settling and polishing ponds with a cover similar to the tailings containment areas
- cover the foreshore tailings area with rock
- long-term monitoring and maintenance of dams in accordance with Canadian Dam Association guidelines
The areas previously developed for mining, except the townsite and marina lands, will be remediated to an arsenic concentration of 340 milligrams per kilogram. This was the Government of the Northwest Territories’ guideline for industrial soil quality when the project was submitted for its water licence in 2019.
Contaminated soils in the former mine townsite, boat launch and shoreline will be cleaned up to an arsenic concentration of 160 milligram per kilogram. This was the Government of the Northwest Territories’ guideline for residential soil quality when the project was submitted for its water licence in 2019.
Contaminated soils around the former mill and roaster building with the highest concentrations of arsenic will be disposed of in the freeze area. Contaminated soils located in other areas that were developed during mine operations will be disposed of in the pits or the tailings containment areas.
Landfill and other waste
A non-hazardous waste landfill will be constructed within the site’s central area of the site. This landfill will contain non-hazardous waste, such as:
- demolition debris
- double-bagged asbestos waste
Water treatment plant residuals, sludge and filter media will be disposed of in a separate cell of the landfill. This section of the landfill will stay open to support the ongoing operation of the water treatment plant. Hazardous waste will be taken away from the site and disposed of in an approved facility.
Borrow and quarry areas
Rock quarry and fine-grained borrow areas will provide the material the project needs to fill the pits and construct covers on tailing containment areas. Wherever possible, rock generated by other site activities will be used. For example, material will be produced when the project constructs a tailings spillway.
After remediation is complete, surface of the borrow areas will be graded to match surrounding topography. This is to prevent erosion and impacts to surface water flows.
A new water treatment plant will remove arsenic and other contaminants from the mine water before it is discharged into the environment. The existing effluent treatment plant will be removed after the new water treatment plant is in operation.
The new water treatment plant will be built in the central area of the site. It will be designed to produce a minewater discharge that:
- meets drinking water quality guidelines for arsenic
- meets water quality criteria to be set during the regulatory process
- is protective of human health and the environment
The plant will run year round. Treated mine water will be transported by overland pipe before to be released into Yellowknife Bay, near the outlet of Baker Creek.
Baker Creek surface water
Baker Creek will stay in its current location, although some sections will be realigned. The alignment will allow the passage of large amounts of water in case of a flooding event. All contaminated sediment will be removed from Baker Creek. Fish access to Baker Creek will not be restricted. However, the Project team may construct fish habitat in Baker Creek, as determined based on consultation with Fisheries and Oceans Canada, the Yellowknives Dene First Nation, the North Slave Métis Alliance and stakeholders.
Site-wide surface water
Runoff that contacts the tailings covers and other engineered covers will be collected in sumps. It will then be conveyed to the minewater pool and treated before discharge. This will continue until monitoring confirms surface runoff from remediated areas is suitable for discharge to the environment.