Once the Remediation Plan is implemented, the Giant Mine landscape will change drastically.
The Remediation Plan calls for all buildings and infrastructure that no longer serve a purpose or function to be disposed of according to industry best-practices. There are approximately 100 buildings on the site, including those at the Giant Mine Townsite.
Many of the buildings on the site contain hazardous materials that pose risks to site workers and the environment during building demolition. To protect human health and safety, as well as the environment, the buildings will be decontaminated prior to being torn down.
Any arsenic-contaminated materials will be removed and placed underground and frozen. Materials containing asbestos will also be removed and disposed of according to regulations.
Because of health and safety risks, some infrastructure work has already taken place. For instance, in spring 2012, the conveyor gallery was taken down. Also, the siding on the main headframe was also removed after it was no longer stable. Starting in the summer of 2013, the roaster complex will be taken down as it has deteriorated to the point where it poses unacceptable risks to the public and the environment.
What are tailings?
Tailings are milled and finely crushed rock leftover after the process of separating the gold from the ore-bearing rock.
There are four ponds containing approximately 16 million tonnes of tailings covering about 95 hectares (the equivalent of 300 football fields). There is also a section of historic tailings located on the shores of Great Slave Lake.
While the tailings on the shore of Great Slave Lake have already been contained, the cover will be reinforced to prevent any water erosion. The tailings contain moderate amounts of arsenic. They are subject to wind erosion when dry, and could also be directly taken up by animals looking for salt.
The remediation plan calls for the tailings and sludge areas to be covered with one layer of quarried rock and a second, top layer of fine-grained soil.
The objectives of the cover are to:
- prevent contact with the tailings by humans or animals;
- allow vegetation to establish;
- reduce water infiltration;
- allow for future recreational and/or traditional use; and
- eliminate airborne tailings fines on windy days.
There are eight open pits on the mine site, five of which are substantial in size. These will either be filled in or fenced off.
One of the pits sits on top of two of the chambers that contain arsenic trioxide waste. This pit will be partially filled to allow for the frozen block method to be implemented.
Contaminated material that is found on the surface will be placed in the pit and will be frozen along with the arsenic chambers. The pit will also be filled with waste rock, quarry rock or clean demolition debris. The entire backfilled area will then be covered and contoured with soil and re-vegetated.
There are also some quarries and borrow pits. These will be re-sloped for improved drainage and stability. This will reduce physical hazards and return the site to more natural conditions.
Contaminated soils and waste rock
Contaminated soils and waste rock around the mine will be removed. Contaminated soils are mainly found around the roaster and mill area, while there are approximately 12,000 tonnes of waste rock located around the site.
The contaminated soils and waste rock will be used to fill the pit that is above the arsenic trioxide chambers. This will facilitate the installation of the freezing system in that area.
The site will be cleaned up to at a minimum the Government of Northwest Territories industrial standard. That said, large sections of the site will meet higher standards and could be used for other purposes.
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