Giant Mine Closure and Reclamation Plan

Information about the Closure and Reclamation Plan is being prepared 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 includes 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 order to provide an update in advance of the formal regulatory process. You can access these documents on the Board’s Public Registry.

Please contact the Project team by emailing aadnc.giantmine.aandc@canada.ca for more information. The public will also have opportunities to provide input directly to the Land and Water Board.

What is in the Closure and Reclamation Plan?

The Closure and Reclamation Plan identifies the activities the Project team is proposing 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. Components of the Plan are summarized below.

Site Infrastructure

Currently, the site has approximately 85 buildings, 25 debris stockpiles, and up to 30 kilometres of road network, utilities, and fencing. As part of remediation, the Project team plans to decommission, 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. This includes:

  • A fence around the central area of the site (the area that will contain the freeze infrastructure, new water treatment plant, and non-hazardous landfill)
  • 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
  • An office space and vehicle garage
  • A non-hazardous waste landfill
  • A closed portal for future underground mine access (if required)
  • Space to be managed by the Yellowknife Historical Society
  • A memorial

Underground

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. Temperatures will be monitored to ensure the areas remain frozen.

Open Pits

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 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

Contaminated Materials

The areas previously developed for mining (except the town site and marina lands) will be remediated to the GNWT industrial soil quality guidelines.

Contaminated soils in the former mine townsite, boat launch, and shoreline will be cleaned up to meet the GNWT residential guidelines for arsenic and fuel in soils. 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 developed by the mine 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 and 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 remain open to support the ongoing operation of the water treatment plant. Hazardous waste will be removed from site and disposed of in an approved facility.

Borrow and Quarry Areas

Rock quarry and fine-grained borrow areas will provide the material needed to fill the pits and construct covers on Tailings Containment Areas. Wherever possible, rock generated by other site activities will be used. For example, material will be produced by constructing a tailings spillway.

After remediation is complete, the borrow areas surface will be graded to match surrounding topography. This is to prevent erosion and impacts to surface water flows.

Water Management

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 being released into Yellowknife Bay, near the outlet of Baker Creek.

Baker Creek Surface Water

Baker Creek will stay in its current location, although some small sections will be realigned. The alignment will allow the passage of large amounts of water in case of a flooding event. As well, all contaminated sediment will be removed from Baker Creek. Fish access to Baker Creek will not be restricted. However, any fish habitat the Project team may construct in Baker Creek will be determined based on future consultation with Fisheries and Oceans Canada, the Yellowknives Dene First Nation, and other 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 mine water pool and treated prior to discharge. This will continue until monitoring confirms surface runoff from remediated areas is suitable for discharge to the environment.

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