By John Mackenzie, AECOM
The Tundra Mine site is located approximately 240 kilometres northeast of Yellowknife, NWT, on the east side of Matthews Lake, and ultimately discharges into the east arm of Great Slave Lake. The site is remote and lies within the Akaitcho Territory, the Wek’eeshii and Monwhi Goga De Nittaee areas of the Tlicho Land Claim Agreement and North Slave Métis traditional lands.
Tundra Mine, owned by Royal Gold, was operated as an underground gold mine from 1964 until 1968 and supported operations at the nearby Salmita Mine from 1983 to 1987. During its lifetime, Tundra Mine produced some 3,250 kg (104,480 troy ounces) of gold. In 1987, the mine was permanently closed, and in 1999, it reverted to the Crown when the mine’s owner went into receivership. Crown-Indigenous Relations and Northern Affairs Canada (CIRNAC) is currently the custodian of the site.
The Canadian government is responsible for numerous orphan mine sites across the Arctic. Historically, mining operations were started with no closure plan in place or funding set aside for site remediation and reclamation when mining stopped. As in many cases, as the profitability of the mines decreased, the owners declared bankruptcy and abandoned the mine, along with all the associated contamination, equipment, and buildings.
After the site became the responsibility of CIRNAC, it was assessed, and a plan was made for the cleanup. The initial phase of the cleanup was started over a decade ago, with tailings and hydrocarbon contamination remediation work completed in the initial phase. During this phase of the project, it was found that two tailings ponds on the site were reaching precariously high levels and the dams were at risk of failing. This failure would result in the release of millions of litres of arsenic-contaminated water, as well as tailings that could potentially contaminate the surrounding watershed for hundreds of kilometres.
This critical situation meant it was urgent to reduce the volume of arsenic-contaminated water in the tailings ponds to reduce the risk of dam failure to manageable and acceptable levels. At this point, 100,000 cubic metres of tailings water was treated so that the contaminant levels were reduced to well below acceptable background levels in the discharge streams. At the same time, this activity eliminated the risk of a dam failure and a discharge of contaminated water into the environment (See article titled “Tundra Mine Emergency Treatment Challenge” in the 2010 NTWWA Journal).
During this phase, work was also done on the tailings area, which originally included two tailings ponds. In total, over 10,000 cubic metres of hydrocarbon contaminated soils were collected from the two tailings ponds, in addition to debris and waste rock which could potentially acidify rain and snow melt water. These soils were moved into a central tailings area, which was covered with layers of geomembrane and covered with gravel and sand to protect the liner and control erosion. Placing all the tailings and other contaminated materials into the one tailings area will reduce the potential for surface water to become contaminated, thereby keeping “clean water clean”. Consolidating the materials into one place also limits the actual footprint where contaminated materials still exist on site. Later, the tailings ponds were covered with erosion protection material, and they continue to serve as drainage and flow-through areas for clean surface water.
An important part of the design of the new consolidated tailings area was the installation, through the cover material and tailings, of ground temperature sensors and instruments to measure the underground water pressure. These monitoring instruments were placed in several locations so the information collected from them would give a good representation of the conditions, in various places and at various depths, of the area holding the tailings. The data collected by these instruments can be recorded at daily or hourly intervals so the conditions of the ground, tailings, and ground water can be assessed throughout the seasons.
When the mine was established in the 1960s, the natural drainage path between Mill Pond and Hambone Lake was cut off. Restoring this drainage path, which was done during the latter part of the project, added tremendous value for the natural environment and First Nations’ stakeholders.
When the remedial work was completed in 2018, the Tundra Mine remediation project shifted to a management phase, during which monitoring, and assessments will determine whether the remediation works will withstand the environmental conditions at this site and are performing as expected. This determination will include assessment of both the remedial work done and the environment downstream from this area.
The accomplishments in each phase of this remediation project at the Tundra Mine site resulted in significant improvements to the site and the surrounding environment. Removing and disposing of hazardous materials off site, as well as the demolition and on-site landfilling of non-hazardous materials and derelict buildings, was a necessary and critical first task to ensure safe work conditions for the public and for following phases of the work.
With the completion of the Tundra Mine remediation project, the immediate risks to the public have been eliminated and the environment is protected in a manner consistent with the Water Licence and Land Use Permit. The design of the project deliberately considered the low maintenance of the entire site in the future, along with the appropriate level of monitoring for the low maintenance framework.
The Tundra Mine Remediation project was an award-winning submission to the Consulting Engineers of Alberta at the 2019 Showcase Awards.
Reprinted with permission from the NTWWA Journal, Ken Johnson, editor.
