Giant Mine Surface Design Decisions
Early in 2015, the Giant Mine Remediation Project Team initiated an engagement process related to plans for the surface of Giant Mine. More than 100 people from Yellowknife, Dettah, and Ndilo participated in the surface design engagement (SDE) process. This process allowed local people to have input to the remediation plan and to ensure the Project Team understands the perspectives and preferences of everyone. The SDE focused on the major problem areas on the Giant Mine surface: especially Baker Creek and the tailings ponds, open pits, and contaminated soils. The Project Team has made many of the big decisions about the surface of Giant Mine.
Baker Creek will remain on site. It will be put into a wider channel that can handle floods safely. The channel will be designed for the Probable Maximum Flood. Contaminated sediment will be removed from the bottom of the creek and will be replaced with clean fill. Baker Pond will be made into a large channel. Reaches of the creek that go over the underground will be designed to prevent water from going into the underground mine. The breakwater will remain in place, and contaminated material around the edge of the breakwater will be removed. The shoreline areas will be revegetated. Fish access to Baker Creek will not be restricted, but the type and size of fish habitat that will be constructed in Baker Creek will be decided later after the Project Team consults with the Yellowknives Dene, the Department of Fisheries and Oceans Canada, and other stakeholders.
The underground under the pits will be stabilized so they can be backfilled safely. Pits will be filled with either new quarried rock or waste rock (also called granular fill) from the mine. A2, the pit that is the farthest south, will be filled with new quarried rock. Moving north, A1 will be filled with waste rock. C1 and B2, the next pits to the north, will be filled with new quarried rock. B1 will be filled with new quarried rock and/or waste rock. Some waste rock that is contaminated with arsenic will be placed in the portion of B1 that is frozen.
Some of the tailings will be used to backfill the underground mine. South Pond tailings will be moved to the North and Central Ponds, which will reduce the total footprint of tailings on the surface. The South Pond dams will be removed. All of the remaining tailings on the surface will be covered with a geosynthetic liner and clean quarried rock. This cover will reduce the amount of water that will contact the tailings. The stability of all of the remaining dams on the site will be reviewed and will comply with Canadian Dam Association (CDA) guidelines.
Contaminated soils will be cleaned up from areas of the site that had already been disturbed by mining activities. These areas will meet the Government of Northwest Territories industrial guideline for arsenic. The Townsite and Marina and land along the shoreline will also be cleaned up, but will meet the lower residential guideline for arsenic. Areas that have been cleaned up will be contoured and covered with quarried rock or soil. Areas that had been forested or covered by wetlands will be covered with soil so vegetation will come back. The contaminated soil will be disposed of in the tailings areas or in A1 and B1 pits. The Core Industrial Area will be fenced off to prevent public access to ground freezing and water treatment facilities, and areas where soils remain contaminated.
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