By Bruno Herlin, P.Eng.
The former Kam Kotia Mine was in operation for several decades, rendering copper, zinc, and secondary silver and gold. The site is located in northeastern Ontario, within Robb Township, northwest of the city of Timmins.
This abandoned site had approximately 6 million metric tonnes (MT) of unmanaged acid-generating tailings covering more than 500 hectares (1,235 acres). Decades of environmental damage, since closure of the mine in the ’70s, were evident as the surrounding soil was burnt orange, the water red, and the area void of vegetation and wildlife. It is considered one of the worst environmental disasters in Ontario history.
The mine was originally developed in the 1940s under the federal government’s War Minerals Program. Subsequent to the ending of that program, the mine was operated as a commercial venture intermittently, finally ceasing operations in 1972. Since then, the mining and surface rights to most of the site have reverted to the Crown, leaving the responsibility of rehabilitation in the public realm.
In addition to physical hazards located on the site, there were about 6 million MT of high-sulfide tailings located within 3 distinct tailings areas, much of which was unimpounded and covered more than 500 hectares (1,235 acres).
Acid mine drainage (AMD), and leached heavy metals produced from all 3 of the tailings areas, had a severe impact on nearby land and water. The 3 tailings areas located on the Kam Kotia Mine site are referred to as: (a) the “North Unimpounded Tailings” or “NUT,” located in the northeast area of the site; (b) the “North Impounded Tailings” or “NIT,” located in the northwest area of the site; and (c) the “South Unimpounded Tailings” or “SUT,” located in the southern area of the site (Figure 1). For many years, the area to the south of the mine site was known as the “south kill zone.” This was an area where virtually all vegetation was destroyed by the site’s AMD. In addition, acidic drainage from the SUT area into the Little Kamiskotia River south of the site resulted in severe effects on the biota of that river, with its waters at a pH of 3 or lower. The areas to the north and northeast were similarly affected by contaminated drainage from the NUT area, as was the Kamiskotia River to the north of the mine site.
In response to rising concerns about the effects to the local environment from the contaminated drainage from the site, and the possibility of the contamination of groundwater in the area, MNDM contracted a consortium of firms, headed by SENES Consultants Ltd., in 2000. The SENES consortium developed a 5-phase plan to rehabilitate each of the environmental, health, and safety hazards on the site.
Projected rehabilitation costs for the entire site were originally estimated at approximately C$40 million, but that total was also projected to go up to achieve a complete cleanup.
The Kam Kotia Mine
Principle exploration: 1926-1928, exploration shaft
Mining 1943-1944: 169,000MT open pit (mining carried out on behalf of Wartime Metals Corp., a federal government agency)
Mining 1961-1972: 5.84 million MT, mainly underground
Total production: 6.0 million MT—1.1% copper, 1.17% zinc, 0.10oz/tonne silver
Patented 1932: Kam Kotia Porcupine Mines Limited (82.5% owned by Hollinger Consolidated Gold Mines Ltd.)
Transferred 1966: Violamac Mines Ltd./Kam Kotia Mines Ltd.
Transferred 1975: Robison Mines Ltd.
January 1988: land surface rights forfeited to Crown (Canadian government)
March 1988: mining rights forfeited to Crown
1961: 270,000 MT in unconfirmed area north of mill
1961: 170,000 MT in South Unimpounded Tailings (SUT) area
1961-67: 2.73 MT deposited in North Unimpounded Tailings (NUT) area
1967: Ontario Water Resources Commission (OWRC) required construction of dams to create the North Impounded Tailings (NIT) area
1967: 1.5 MT deposited in open pit
1968-1972: 1.4 MT deposited in NIT
North and east seeps, with a pH of 2-3, drain NUT, east half of NIT and north half of plant site to the Kamiskotia River in the north
South seep drains SUT, south half of NIT, and plant site to Little Kamiskotia River in the south, which has a pH of 3.5-4
5-phase remediation plan
During fiscal 2000-01, Senes Consulting developed a 5-phase conceptual rehabilitation plan for the Kam Kotia Mine site. Funding for Phases A and B came from the Abandoned Mines Rehabilitation Fund.
Phase A, 2001-2002, included construction of a lime addition treatment plant, as well as all of its required infrastructure, and the construction of a new NUT impoundment dam structure, including the stabilization and reinforcement of the existing “north-south” dam. This impounded area was designed to hold all of the remaining unimpounded tailings, which were physically relocated to within the dam area during the subsequent phases of rehabilitation, neutralized with lime, with the impounded area developed as a wetland.
Final cost: C$10.2 million.
Phase B, 2002-2003, dealt primarily with the relocation of the SUT tailings, estimated at 330,000m3, to within the new NUT impoundment area where they were mixed with lime and neutralized. The completion of this work meant that there would be little new impact to areas south and southwest of the mine site—the areas where there is human habitation.
Upon completion of the work, more than 340,000m3 of SUT tailings had been relocated and buffered withEnviroLime. Lime was also spread over the peat/soil surface in the SUT area to buffer residual acidity.
Final cost: C$3.6 million.
(A large cost saving was created by using an acid-neutralizing product, EnviroLime, to neutralize the relocated tailings, instead of the more common hydrated lime. Although a slightly greater amount of the EnviroLime was required to get the same results as the hydrated lime, the cost for the EnviroLime per unit volume was less than half that of hydrated lime. The EnviroLime was also an easier product to apply to the relocated tailings than hydrated lime, as it can be applied in a dry state and doesn’t tend to be as windblown due to its coarser, granular consistency. The constituents of EnviroLime are: CaO 63-75%, MgO 1-8%, SiO2 1-2%.)
Phase C involved the relocation and buffering of the unimpounded NUT tailings to within the new NUT impoundment area. However, due to the large “pond” of acidified, metal-bearing water that collected within the NUT impoundment area, the 611,000m3 of the NUT tailings that were relocated during the winter of 2003-04 were stacked around the perimeter of the impoundment area. Approximately 34,000m3 of tailings remained to be relocated from the farthest edge of the NUT area and from the various seeps and creeks. Estimated cost: C$8.2 million.
Once the contaminated water project was completed, and the remainder of the NUT area tailings relocated, Phase D involved the construction of the wet/moist NUT impoundment area cover. The Phase D work included dealing with the rehabilitation of the north and east seeps and creeks in the northeast area of the site. Estimated cost: C$3.4 million.
Finally, Phase E involved the construction of an engineered aggregate “dry” cover over the NIT area, and addressed the physical hazards on the mine site, including the thin crown pillar and the open pit. As Phases C and D could not be completed due to the contaminated NUT pond, the initial 2 layers of the Phase E NIT cover were built during the winter of 2004-05. The remainder of the Phase E work was completed during the winter of 2006-2007. Estimated cost: C$11.4 million.
Finalizing Phase E
Final construction of a composite cover soil system that includes a geosynthetic clay liner (GCL) at the former Kam Kotia Mine in Ontario started in November 2006, with an intial deployment of 10,000m2 on day 1 of the project. Eventually, more than 120,000m2 were used in the project in 2006.
Construction resumed in 2007, and when completed in the spring, there was an 800,000m2 soil cover system completed for the Ontario Ministry of Northern Development and Mines at the abandoned mine site southeastern Ontario.
The soil cover is designed to effectively impede the entry of water and oxygen into the high-sulfide tailings, substantially reducing acid generation and metal leaching effects from within the tailings.