After 12-years of hard work, the Colomac Mine Remediation Project concluded in the fall of 2011. Located in the Northwest Territories, Colomac was one of the first major contaminated mine sites in the north to be remediated, and was a challenging project on many levels. The successful remediation of the Colomac site is largely due to the strong partnership between the Aboriginal people who hold a land claim in the area, called the Tlicho, and the federal government, as well as the application of traditional knowledge, good science and sound engineering throughout all phases of the project.
The Colomac Mine is a former gold mine located approximately 220 kilometres north of Yellowknife, NWT. The mine was commissioned in 1990 with sporadic production until late 1997, when the mine’s last owner, Royal Oak Mines Inc., placed the mine into care and maintenance. In April 1999, Royal Oak went into receivership and the site reverted to Aboriginal Affairs and Northern Development Canada (AANDC). Colomac’s relatively short mine life left a significant scar on the local landscape.
At abandonment, the site presented significant legacy issues including cyanide contaminated tailings water and solids, hydrocarbon impacted soil, bedrock and lake sediments, extensive inventories of waste petroleums, oils and lubes and hazardous chemicals, abandoned mine infrastructure, open pits, waste rock dumps, and quarries.
The most pressing issue was the management of contaminated tailings water which, by the end of 1998, was threatening to overtop the main water retention structure, Dam 1. Due to poor construction and absence of as-built drawings, the effective elevation of the dam was confirmed at mine closure to be one metre less than the freeboard limit specified in the Water Licence. This, coupled with the rapid rise in Tailings Lake water levels in 1998, made water management critical and emergency measures were invoked under the NWT Waters Act. The measures allowed for the transfer of millions of cubic metres of contaminated tailings from Tailings Lake to the Zone 2.0 Pit for storage and treatment.
Added to this was the fact that Dam 1 had been constructed on a major fault and seepage rates began to increase dramatically towards mine closure, to approximately 250 U.S. GPM. The seepage contained elevated concentrations of cyanide and ammonia which required continuous pump back to Tailings Lake to prevent adverse impacts to downstream environments. Following the successful water management effort, remedial efforts shifted to the treatment of the highly toxic tailings water in Tailings Lake and the Zone 2.0 Pit. Through the Enhanced Natural Removal process (simple addition of phosphorus via fertilizer), water treatment in Tailings Lake and Zone 2.0 Pit was completed by 2007.
With water management and treatment under control, the remedial focus shifted to other areas. Hydrocarbon remediation included demolition of the bulk tank farm, excavation and treatment of contaminated soils, construction of a bio-remediation facility and recovery of free product from bedrock. Other work included construction of a new dam, capping of exposed tailings and construction of an outlet channel for the treated water from Tailings Lake. Taking the advice of Tlicho Elders, a fence was constructed around the tailings to protect migrating caribou from the contaminants. The area was deemed safe for caribou in 2008, and the majority of the fence was dismantled later that year.
Final remediation of the site commenced in 2010, and included a major demolition and decontamination program for mine infrastructure and major civil works for the remediation of Steeves Lake shoreline and restoration of original drainage and fish passage.
The monitoring phase of the project began in 2012, and includes: an adaptive hydrocarbon management program, which will address residual hydrocarbons in the fractured bedrock; water quality, water levels in lakes, streams and pits; geotechnical stability of engineered structures (Dam 1B, tailings cap, spillway and discharge channel, and non-hazardous landfill); erosion and site drainage; re-vegetation success; and aquatic/terrestrial wildlife health. Monitoring will continue at the site until it can be determined that remediation has been effective and that site conditions have reached a steady state.
The airstrip will remain in place as an emergency airstrip and the large steel warehouse, known as “Big Blue,” will remain on-site and is being transferred to the Tlicho Government.
To celebrate the completion of the final remediation contract and to acknowledge the efforts of many people over the years, AANDC held an event in Behchoko, NWT in December 2011. Elders from the surrounding three Tlicho communities were flown into Behchoko to join in the festivities. The Tlicho Grand Chief and Community Chiefs were also in attendance as well as representatives from the Tlicho Government, Tlicho Investment Corporation, and Wek’èezhìi Land and Water Board.
The evening included a feast and the presentation of recognition plaques to over 60 individuals, companies and organizations, all of whom made significant contributions to the project.
In June 2012, a smaller event was held at the former mine site. This included a site blessing ceremony by Tlicho Elders and the unveiling of a commemorative monument that will tell visitors about the three phases of the site: traditional use of the area by the Tlicho people in the past, mine production, and socio-economic benefits and the remediation of the site. The monument is written in English, French, and Tlicho.
Regulatory and operational approaches to mining have changed since Colomac was in production. Legislation has been introduced to ensure that new mining operations do not leave a legacy of environmental and human health hazards, and to ensure that these operations are responsible for the costs of returning the environment to an acceptable state. The standard in the north today is for mining operations to plan for reclamation at the feasibility stage and then to clean up as they go.
The remediation of Colomac has set the standard for remediation projects in the north. A success on many levels, the conclusion of the remediation of the site marks the mitigation of ecological risks that had long been a concern of those who use the area for traditional and recreational activities. By building strong relationships with those users of the land, the project team was able to address concerns head on. The remediation of the Colomac Mine site is an excellent example of what can be achieved when many minds meet to solve a problem – scientific minds combined with traditional knowledge to develop well-rounded solutions that work.
Submitted by Aboriginal Affairs and Northern Development Canada
*Editor’s note: In December 2011, Nighthawk Gold Corp. announced an interest in exploring mineral claims around the Colomac Mine property. AANDC and Nighthawk, with support from the Tlicho Executive, have agreed that in return for the mineral claims and leases at the Colomac site, Nighthawk will remediate three smaller sites in the area: Diversified/Indigo Mine, Spider Lake Exploration Site and Chalco Lake Exploration Site.