BACK TO NATURE
Some recent television adverts claim that “Eventually EVERYONE retires.” The same can be said of mines. Eventually they run out of ore, a lease, permits, favourable economics, or management’s patience … and have to close. It then becomes the owner’s responsibility to clean up the site.
Like retirement, reclamation is evolving, with the regulatory bar ever-rising. Knowing this, the more responsible companies go beyond today’s expectations. Long-running mines are progressively reclaimed, and plans are adjusted to meet the new requirements. Unfortunately, the least responsible owners walk away from unreclaimed properties in the cloak of bankruptcy, leaving the public (i.e., the government) to do the work and foot the bill. How would you want your mine to retire?
Four major reclamation projects ongoing in Canada right now–Kam Kotia and Hollinger in Ontario, Hope Brook in Newfoundland, and Britannia in British Columbia–are all being conducted by provincial governments because the owners went out of business. (At Hollinger and Britannia, the new owners are sharing costs with the government.) We describe what is being done to clean up Kam Kotia and Hope Brook. We also discuss two mines slated for closure soon, where the owner–Teck Cominco Ltd.–has carefully planned the reclamation.
Sullivan Mine winding down after almost a century
The Sullivan underground zinc-lead-silver mine in Kimberley, B.C., has operated since 1909, producing 8 million tonnes of zinc and 9 million tonnes of lead from a sedimentary exhalative massive sulphide deposit hosted in argillaceous wackes. Its ore reserves will be drawn down and the mine will close by the end of 2001.
Sullivan ore and mine wastes are acid-generating. For many decades, solid and liquid wastes from mining and milling were discharged in a way that damaged the environment. Mine drainage and tailing decant were directly discharged to local water courses; 14.5 million tonnes of waste rock as well as 100 million tonnes of tailings, phosphogypsum and iron calcine were placed on porous gravels over shallow aquifers, allowing contamination of waterways, groundwater and soil. More than 1,000 hectares of land was severely disturbed.
In the early 1970s, Teck Cominco’s predecessor, Cominco Ltd., began measures to reduce the environmental disturbances. Most of these measures will become part of the post-closure acid rock drainage (ARD) management system and reclamation plan.
A drainage water treatment plant (DWTP) was commissioned in 1979. The plant uses a high-density sludge process, using lime to neutralize the acid and precipitate the metals into a free-draining, non-leaching sludge; the effluent discharges into the St. Mary River. The plant and its process have proven effective and reliable for more than 22 years. During this time, the DWTP has produced only 117,000 tonnes of sludge. The 17-ha impoundment that holds the sludge has 50 years of storage capacity at projected treatment rates.
Over the years, diversions have been constructed to reduce the flow of uncontaminated surface water and groundwater into the tailing pond and underground mine workings. A system of ditches, sumps, pumps and pipelines has been installed to collect seepage from waste dumps and tailings and gypsum pond dikes as well as contaminated groundwater.
Soil cover systems have been developed that prevent 90% of precipitation from infiltrating into ARD sources. By the end of 2000, some 310 ha of tailing and gypsum pond surface had been protected with the soil cover system. Some ARD source material has already been excavated: waste rock in groundwater discharge zones has been returned to the open pit, and tailings and contaminated soil from Cow Creek has been removed to the tailings pond.
The plan is to reclaim all of the tailings deposits and waste dumps in the area in order to bring them back to a level of productivity that will sustain wildlife and natural use for the long-term future. The anticipated cost is $70 million.
Following closure, surface and groundwater will continue to enter the underground mine workings, where they will be exposed to ARD conditions. The mine will take 3.5 years to fill to the 3,650-foot level, 50 feet (15 m) below the lowest opening to surface (the 3,700 level portal). The mine reservoir will not be allowed to rise above this level, but will operate between the 3,550- and 3,650-foot elevations, with a storage capacity of about 625,000 m3. There will also be a surface reservoir at the site of the former cooling ponds, which will be expanded to provide an additional 612,500 m3 of storage capacity.
The ARD water stored underground and on surface will be treated by the DWTP, which will operate at 20,000 L/min during two campaigns per year, spring and autumn. For the first three years it will operate for an average of 53 days total per year. Once mine dewatering begins in year four, the treatment plant will operate for about 94 days per year.
The challenge will be to comply with new federal and provincial regulations after mine closure. The total suspended solids (TSS) limit will soon be decreasing to 15 mg/L from the current 50 mg/L. To get a handle on TSS, Kimberley Operations has installed a new, very sensitive turbidity meter that requires scant operator attention. The clarifier performance has been improved with installation of a Fitch-style feedwell. The improvement in feed distribution has resulted in reduced TSS in the effluent to the river, and may eliminate the need to use infiltration, settling ponds or sand filters.
Before closure, the Sullivan team will ensure that all equipment is in good working order. The instrumentation has been upgraded with new PLC software and remote monitoring equipment.
All maintenance work after closure will be contracted out. The seepage collection system and environmental monitoring will require one operator. Samples will be analyzed at a commercial laboratory. During the biannual campaigns, the DWTP will require one operator, with remote monitoring from Teck Cominco’s Trail site on the off-shift. This work will continue as long as needed.
The post-closure operating costs depend mostly on two variables: the volume of water to be treated (which could vary each year 25% depending on precipitation) and the rate of lime consumption. Long-term post-closure operating costs have been estimated at $1.28 million annually. The bonding level to support these costs over a 100-year period, is estimated between $10 and $20 million.
For more information contact Bruce Dawson, Teck Cominco’s superintendent, services & environment, Kimberley Operations, tel. 250-427-8421; [email protected]
Polaris plans to close
Teck Cominco’s Polaris underground zinc-lead mine on Little Cornwallis Island, Nunavut, has operated since October 1981, and is scheduled to close in about August 2002. The 21-million-tonne deposit was a high-grade Mississippi-Valley-type orebody. The facilities include a mine, concentrator, accommodations / recreation complex, Garrow Lake tailings repository, an airstrip and a seaport on Crozier Strait of the Arctic Ocean.
Mine manager John Knapp has been involved for several years in planning for mine site reclamation, and he outlined the situation at Polaris for CMJ.
The detailed closure plan has been drawn up but not yet approved by the regulators. “Our intent,” says Knapp, “is to leave the land chemically and usability-wise as we found it,” which was as barren gravels and beach rock. The land on which the mine is situated supports little flora and fauna, but there is abundant marine life in the nearby ocean.
“Our biggest problems surround the regulatory climate,” he says. “Cominco has no qualms about doing the right thing, but it’s hard to find out what the right thing is. This will be the first mine to close in the Nunavut Territory. There are many regulatory bodies–Indian and Inuit associations, territorial bodies, federal regulators–and we want to make sure we are not overlooking any of their requirements.”
The proposed reclamat
ion plan will include the demolition of all surface buildings and improvements, and the cleaning off of concrete. This material will be placed in a nearby quarry and covered with rock and soil. The hazardous material will be repacked and shipped south for sale or proper disposal. The airstrip will be left, but pipes, lights, etc. will be removed. The gravel roads will remain but the shoulders will be rounded off, the culverts pulled up and the land recontoured to allow for natural drainage. The port structures and earthwork will be removed, and the port site restored to beachfront.
The most contentious issue involves the tailings repository. Garrow Lake was originally a 46-m-deep brackish lake, a bit of ocean stranded when the island rose. Before Polaris was built, the lake was fed only by meltwater, and discharged to Garrow Creek, which flows about 1 km to the ocean. A dam was built at the discharge, and tailings have been deposited into the bottom of the lake. The lake is meromictic (chemically stratified), with highly saline water at the bottom containing natural hydrogen sulphides, and brackish fresh water in the top 11 m.
Polaris’s plan is to siphon off a small portion of the top water, dropping the surface 2.5 m to its original level. The dam at the discharge will be partially removed, after the stability of the lake is verified. The land around the dam will be recontoured and covered with rip-rap to resist erosion. The lake will once again feed Garrow Creek on a seasonal basis, as it did before Cominco’s arrival. The tailings in the lake will remain intact below the 26-m level; any metals that might dissolve will be reprecipitated by the hydrogen sulphide there.
One of the lessons the Polaris team has learned is that background studies into regional soil quality and biology have to be properly grounded in the first place. Initial background studies found very high lead and zinc content on the property, probably due to mineralized rock outcrops. “If they were done today, our baseline studies would have been more extensive, and done to facilitate our reclamation strategy,” says Knapp. Lacking that, Polaris hired the consultant Gartner Lee to conduct a two-year, two-phase site assessment campaign that included sampling the disturbed area for lead, zinc and hydrocarbons on a grid basis. There were a number of other environmental studies as well. The resulting information is being used to determine the depth and volume of material that will have to be removed and placed back in the underground mine, there to be encased in permafrost.
The other lesson is that planners should include the cost of reclamation in the project economics, before deciding whether to build a mine. The cost of reclamation at Polaris is not yet known, as the work is currently out to tender, but Knapp estimates it will be in the tens of millions of dollars, a significant amount compared with the $250 million capital cost. He says that Cominco considered reclamation when it was planning Polaris, “but probably not to the extent necessary, considering changing regulations. This will always be the case: if you have a long property life, the regulations and requirements will have changed by the time of closure.”
Knapp adds that his company consistently goes beyond the regulations, such as at Blue Bell and Pinchy Lake. These two mines were properly closed under the regulations of the day. But Cominco has gone back in, re-evaluated them, and is spending millions of dollars to bring them up to today’s standards.
“It makes good sense philosophically and economically to exceed the regulatory requirements,” says Knapp. “It would be undesirable and extremely expensive for Teck Cominco to have to return to the island. Therefore our strategy will be to exceed the regulatory requirements.”
For more information, contact John Knapp, mine manager of Polaris, at tel. 867-253-2241; [email protected]
A pragmatic approach at Kam Kotia
The Kam Kotia former copper/zinc mine near Timmins, Ont., operated as an open pit from 1943-44 on behalf of a federal government agency. It was owned by Kam Kotia Porcupine Mines Ltd., which was 82.5%-owned by Hollinger Consolidated Gold Mines Ltd.
The mine operated again from 1961-72, mainly as an underground mine. In 1966 it was transferred to Violamac Mines Ltd.-Kam Kotia Mines Ltd., and transferred again in 1975 to Robison Mines Ltd. The surface and mining rights were forfeited to the Crown in 1988.
The legacy of this mine included about 6 million tonnes of unmanaged acid-generating tailings covering more than 500 ha. The environmental impacts of this are locally significant, including acidic leachate, dusting, ugliness and physical hazards. The north and east seeps drain ultimately into Kamiskotia River, and the south seep drains into Little Kamiskotia River, which discharges into Kamiskotia Lake.
In 1999, the Ontario Ministry of Northern Development & Mines launched a four-year, $27-million Abandoned Mines Rehabilitation Program aimed at returning abandoned mine sites around the province to an acceptable environmental state, for environmental and economic benefit to future generations. The Kam Kotia property was targeted for a large part of this work.
SENES Consultants in joint venture with Lakefield Research, ESG International and Denison Environmental Services reviewed the property in 2000, looking into the site chemistry and hazards, previous reports and pre-MEND (Mine Environment Neutral Drainage program) rehabilitation proposals. Based on this work, and incorporating the results of MEND, the consultants recommended a $40-million program including the relocation of the south unimpounded tailings, collecting the seepage and sending it through a treatment plant (to be constructed), consolidating the north unimpounded tails, constructing a dry cover on the north impounded tailings, upgrading the dam, and rehabilitating the plant site area.
Prior to the consultant study, the Minister of Northern Development & Mines had agreed to a $3-million expenditure and set up the Kam Kotia Steering Committee, comprised of three provincial ministries as well as Northwatch, a non-governmental organization with environmental interests. The committee’s mandate was to find a financially manageable approach that would significantly reduce the release and consequences of the acid leachate. The committee agreed to focus initially on improving the quality of water leaving the site, which would result in an improvement to downstream receivers and restore aquatic life.
The Mines Minister agreed to increase the budget for the reclamation of Kam Kotia to $9 million. The current program, from 2001 to the first quarter of 2003, was designed to reduce the impacts at a manageable cost. It represents a compromise between improving the environmental effects and leaving Kam Kotia untouched.
The Kam Kotia work in 2001-02 includes construction of an interceptor ditch and lime treatment plant to collect and treat ground and surface drainage from the northwest tailings. As well, a dam will be constructed within the unconfined northeast tailings. The cost this year will be $6.8 million. Contracts awarded for the current work include North America Construction (1999) Ltd. for the treatment plant, M.J. Labelle Ltd. for the tailings dam and B.H. Martin Ltd. to oversee construction.
During 2002-03 the south unimpounded tailings will be relocated to the new impoundment for the north unimpounded tailings and some revegetation work begun. It is hoped that future funding will become available to complete the whole recommended rehabilitation project.
For more information, contact John Robertson at tel. 705-670-5798; [email protected]
Reclamation work underway at Hope Brook
The Hope Brook open pit and underground gold mine on the southwest coast of the island of Newfoundland was operated by a subsidiary of BP Canada Inc. from 1987 to 1991, and by Royal Oak Mines Inc. from 1992 to September 1997. Gold mine
ralization was hosted by a zone of pervasive silica, pyrite and pyrophyllite alteration. The Hope Brook zone contained massive finely granular quartz, 3% to 8% pyrite, minor chalcopyrite, trace molybdenite and an average of 4.5 grams of gold per tonne. Waste rock and tailings probably contain silica, pyrite, minor pyrophyllite and mafic material.
Royal Oak had prepared a closure plan, but the company went into receivership in April 1999 prior to implementing it. The site was maintained by the receiver, PriceWaterhouseCoopers, until December 1999 when it was transferred to the Government of Newfoundland and Labrador. The province now owns the assets and is responsible for the abandoned site. Since mine closure, the acidic mine drainage has been captured and treated to ensure that the effluent complies with regulatory requirements.
Hatch & Associates was hired in April 2000 to verify and update the closure plan and to provide an updated cost estimate for closure and rehabilitation.
In the final report, received in September 2000, Hatch estimated an 18-month decommissioning period, and another 12 months of effluent treatment following completion of decommissioning, for a total cost of over $13 million.
Hatch outlined two important general steps. One was to prevent formation of acid rock drainage from waste rock, spent ore and tailings by disposal of this material under water cover. The other was to remove all buildings, plant equipment and materials and otherwise safeguard the site, to prevent injuries to humans and animals and to make it aesthetically acceptable. The open pit will be fenced off.
The only ongoing work anticipated by the government will be to conduct periodic water sampling and fence and dam inspections.
Denison Environmental Services of Elliot Lake, Ont., and Innova Quest Inc. of St. John’s, Nfld., were the joint venture partners hired as project manager in September 2001, to oversee the decommissioning and rehabilitation of the Hope Brook mine site. They will oversee the following site work over an 18-month period:
recovering residual gold from the mill;
treating and monitoring effluent;
sale of assets from the site;
moving waste rock and heap leach material into the open pit to eliminate acid mine drainage from these sources;
raising tailings dams to ensure an adequate water cover is maintained over exposed tailings to minimize acid generation; and
demolishing buildings and structures and final site restoration activities.
A Phase I Environmental Site Assessment was completed by the end of October, and a tender call has been issued for the recovery of residual gold from the mill. The project manager has begun to review the issues surrounding the proposed remediation of acid mine drainage, and has started a civil engineering investigation into raising the tailings dams. A strategy has been developed for dewatering the open pit during infilling with waste rock and heap leach material, and a safe method proposed for the infilling. An asset inventory has been made.
The ultimate plan is to return the Hope Brook site to acceptable environmental standards consistent with the natural surrounding land. The site is remote, not accessible by road, and the nearest community is about 15 km away. It will probably be used for little other than occasional hunting, fishing and snowmobiling.
For more information contact Earl Dwyer, environmental project engineer, Mineral Development Division, Department of Mines and Energy, tel. 709-729-3360, [email protected]