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Voisey's Bay Mine and Mill Environmental Assessment Panel Report
6 Tailings, Mine Rock and Site Water Management
The mineral resource at Voisey's Bay contains highly reactive sulphide minerals. Therefore controlling acid generation in the tailings and waste rock generated during mining and milling and requiring storage for perpetuity will be a critical issue. In addition, large volumes of process water would be needed to concentrate the ore through the milling process and to transport the tailings to the storage areas. While a significant portion of this water could be recycled, the exact amount is difficult to predict from pilot testing. The proposed production of two concentrates, the accumulation of process contaminants, and the requirement for fresh water to mix reagents and to cool pump seals would all affect the amount of water that could be recycled. Excess water would be treated and discharged to the marine environment; some participants were concerned about the effects of disposing of the resulting sludge. The source of the fresh water will reduce flow to Reid Brook.
6.1 Tailings and Mineralized Waste Rock Disposal
VBNC proposes to use a phased approach to dispose of mine wastes that could generate acid. It suggests disposing of these wastes underwater in two natural lake basins. Based on a proven ore resource of 150 million tonnes, VBNC would produce approximately 13.2 million m³ of tailings from the Ovoid operations and 5.5 million m³ of potentially reactive waste rock from both open pit and underground mining over the life of the mine. The company plans to dispose of these wastes in Headwater Pond. VBNC plans to begin placing up to 59.6 million m³ of tailings from underground mining in the North Tailings Basin once the Ovoid is exhausted; this disposal would continue until the end of the Project. Water treatment sludge would be co-disposed with tailings in both basins.
A pipeline system, approximately 8 km long, would transport slurry tailings from the mill for disposal in Headwater Pond. A 7-km extension would be required for the North Tailings Basin. Another pipe would carry reclaimed water from the basins back to the mill for use as recycled process water. The access roads to the basins would parallel the pipelines, and VBNC would use the road to Headwater Pond to haul mineralized waste from the Ovoid and the underground operations to the southeast section of the basin for disposal.
All participants consider the subaqueous disposal of acid-generating material to be the best option for managing wastes. The Province states that eliminating air by submerging the material underwater is the most accepted method of minimizing the oxidation of sulphides. Natural Resources Canada (NRCan) states that acid generation is very difficult to stop once it starts, but reactive tailings can have a very stable geochemistry underwater. Therefore, lake disposal would create a stable and secure environment that would minimize engineered structures and yield a low-cost closure and maintenance system with a very low risk of failure over the long term. An expert from the Labrador Inuit Association (LIA) said that the issues of concern were not insurmountable. LIA felt that the overall tailings and waste rock conceptual design, and the plans for underwater disposal, were reasonable.
6.1.1 Tailings Basin Designs
VBNC considered eight sites for disposal of mine tailings and mineralized waste rock before arriving at its preferred sites of Headwater Pond and the North Tailings Basin (see map on page 38 Waste Disposal Areas). It considered only candidate sites that were located outside of the Reid Brook watershed or could be permanently diverted out of it; that could provide permanent water cover; and that could accommodate the required volumes of mine wastes, based on a mineral resource of 150 million tonnes. The volume of waste that could be contained versus the volume of rock required for dam construction was an added consideration. Smaller dams require less rock (thus reducing the Project footprint), are safer and minimize seepage.
By applying further environmental and engineering criteria - such as minimal environmental effects, expansion capability, safety and ease of closure, topographic and hydrological containment, cost effectiveness, aesthetic acceptability, interference with the ore body and regulatory time frame - VBNC eliminated all but three candidate sites. Although the third candidate site, Option 5, met the criteria, VBNC did not select it as a preferred site because of its distance from the mill and its need for higher dams than the North Tailings Basin.
Depositing tailings and waste rock in Headwater Pond would require construction of two perimeter dams with heights of 13 m and 15 m. At the west end of the basin, Dam H2 would permanently cut off drainage to Otter Pond and the Reid Brook watershed. Seepage from the dam is estimated to be 0.2 L/s. A second dam, H1, would block drainage eastward into the Throat Bay watershed. Outward seepage from this dam is estimated to be 0.1 L/s. As the volume of the Ovoid tailings is less than the basin's natural capacity, all tailings would be deposited below the existing lake outlets.
For the North Tailings Basin, six dams would be required to increase the capacity of this three-lake system to accommodate an estimated 59.6 million m³ of tailings. Two of the dams, N4 and N5, would be diversion structures to prevent fresh water from entering the basin. Dam N1 would be a temporary control structure between the upper and lower lakes. Three perimeter dams - N2, N3 and N6 - would increase the capacity of the basin. Ranging in height from 13 m to 35 m, they would be developed in stages as the tailings were deposited. Outward seepage from the dams ranges up to 0.3 L/s into the Kangeklukuluk Bay watershed and up to 0.2 L/s into the Kangeklualuk Bay watershed.
VBNC stated that water cover in the basins is predicted to range between 2 m and 4 m and that this cover would be maintained during extreme drought conditions. Environment Canada expressed concern about the effectiveness of a shallow water cover to prevent oxidation and re-suspension of tailings, and LIA questioned whether ice and wind action would disturb the water cover. Whether provisions were adequate to minimize metal flux from the tailings into the water column was also an issue.
NRCan indicated that findings from the field verification of the Mine Environment Neutral Drainage program determined that the critical minimum depth of water cover needed to prezvent oxidation and avoid wave disturbance is 1.3 m to 1.4 m.
The Panel heard concerns about potential seepage and the need to detect, collect and treat seepage before it is released to the environment. VBNC proposes to grout bedrock foundations of the dams with a blanket and grout curtain to control seepage. For dams founded on overburden, seepage would be controlled using a slurry trench cut-off. Seepage from the tailing basins would be monitored using a combination of surface water sampling, both upstream and downstream of the dams, and groundwater wells installed near the dam toes. If adverse effects on water quality were detected, through either monitoring or visual dam inspections, VBNC would collect the water and pump it back into the basin. Then the company would assess the potential causes and consider measures to reduce seepage, such as additional grouting or other dam design modifications.
Some participants expressed concern that an apparent fault associated with the north end of both Headwater Pond dams could provide a conduit for groundwater seepage or lead to dam failure. VBNC stated that all structural features were incorporated into hydrogeologic modelling and that they are geologically stable. The company would grout bedrock foundations to reduce hydraulic conductivity and investigate them for seepage potential. There was similar concern that a landslide mapped north of Dam H2 could cause failure of the dam, but again VBNC described this area as being stable.
In the hearings, participants also discussed the need to monitor and maintain dam integrity and concerns about the effectiveness of bentonite dam cores under similar climatic conditions. VBNC stated that the dams proposed for both basins are conventional water-retaining dams.
Participants expressed concerns about potential ruptures of tailings pipelines. VBNC described the pipelines as one pipe inside another with insulation between the two. Pipes would be adjacent to travel routes and would be monitored. In addition, the rate of discharge flow would be monitored and any flow discrepancy in comparison to the input would trigger an alarm. There were also questions about the capacity of emergency dump pockets to contain the pipeline contents should emergency stoppage of flow occur when tailings were present in the line. VBNC stated that emergency pumps would normally empty slurry material from the line before it was shut down. As an example of how seldom the dumping option would be used, VBNC described the experience of the Louvicourt Mine in northern Quebec. At that mine, which uses similar technology for an extended tailings pipeline operated under similar climatic conditions, it has not been necessary to dump the line since the mine began operating approximately six years ago. Should it be necessary, however, VBNC stated that it would immediately contain or clean up material removed from the line.
6.1.2 Alternative Disposal Plans
Many participants told the Panel that VBNC should explore alternatives to the North Tailings Basin for disposing of underground mine tailings. Alternatives they suggested included submarine disposal, and backfilling of the open pit and underground workings. These alternatives could reduce the size of the dams needed for the North Tailings Basin. Depending on the size of the mined ore reserves, backfilling the mine workings, in conjunction with backfilling the open pit, might possibly even eliminate the need for a second disposal basin.
Submarine disposal of tailings has been practised internationally and at two locations in Canada, the Island Copper and Kitsault projects in British Columbia.
At Island Copper, both waste and tailings were discharged into the ocean during the entire life of a large tonnage copper mine. The Panel understands that there are varying opinions about the residual environmental effects at this site. The Panel also notes that the biological productivity of that marine disposal site is quite different from that of the Project area, so results may not be transferable.
An expert for LIA stated that submarine disposal, either confined or unconfined, reduces engineering requirements, provides greater chemical stability and reduces the footprint on land. However, LIA indicated that it was not necessarily recommending consideration of this option. NRCan submitted that, with changes in technology and knowledge of the behaviour of tailings in a marine environment, submarine disposal merits future consideration, possibly as an alternative to the North Tailings Basin for tailings disposal during the underground phase. Environment Canada stated that, under current regulations, VBNC would be required to demonstrate that submarine disposal was the only practical option or was the best option for the environment; such disposal would also require site-specific approval under subsection 36(5) of the Fisheries Act. The Province considers submarine disposal risky because of the inability to predict, control or rectify the spread of contaminants throughout the environment. It indicated that it would not likely grant approval at this time.
The Panel observes that Saskatchewan uranium mining operations routinely store tailings in mined-out pits. Those tailings contain metal concentrations in addition to residual radioactivity. These operations minimize the level of tailings contaminants entering groundwater by surrounding the tailings with a pervious envelope of waste rock or an impervious liner. The volume of those pits in relation to the tailings placed, however, is much higher than for the Ovoid.
VBNC indicated that several issues affect the potential use of backfilling. First, underground operations must be adequately isolated from the pit to ensure no danger of inflow exists. Second, since the pit is close to the Reid Brook watershed, ensuring acceptable water conditions or isolating the material from potential migration to Reid Brook is critical.
An expert speaking on behalf of the Innu Nation suggested that, instead of creating a deep pit lake once the Ovoid operations have finished, VBNC should backfill the pit with sulphide-bearing waste to the original sulphide horizon, place a cap of clean material on top, and then flood it. He suggested that, while the water in a pit lake would turn over seasonally, incorporating oxygen in the process, the water contained in the flooded waste would oxygenate much more slowly. This would reduce the migration of oxygenated water to the sulphide rock on the sides of the pit. This option would also ensure long-term submerging of the waste with no risk of containment failure.
In all underground mining methods suited to this deposit, backfilling would be a necessity. VBNC has committed to further investigating backfilling alternatives. It stated that the staged approach of using Headwater Pond for Ovoid tailings and mineralized mine rock before commissioning the North Tailings Basin gives the company an opportunity to assess other disposal options, particularly if underground ore reserves are less than predicted. VBNC said it needs operational experience to evaluate the viability of using the open pit as a containment facility for mine wastes. The company also stated that the first preference for backfill is waste rock and that it is impossible to determine whether tailings from the underground would be suitable as backfill without a bulk sample. The greatest potential problem would be high sulphur content in the backfill, which could cause combustion and produce dangerous gases.
The Panel is aware that the technology of backfill placement is advancing. Paste technology, for example, may eliminate restrictions on the use of tailings with high sulphur content. It is also understood that all the tailings cannot be placed in the mined-out areas. Typically, the density of tailings is roughly half that of in-situ ore and they occupy more than twice the original volume.
The Province stated that alternative disposal underground or in the open pit could be dealt with during the approval process, when the details of mining would be better understood.
As another alternative, the Innu Nation emphasized the need to minimize the number of mine waste disposal sites and suggested restricting them to a single watershed to reduce environmental effects. Due to the high ecological value of the Reid Brook watershed, it suggested reconsidering the use of Headwater Pond, placing all tailings in an expanded North Tailings Basin and using Option 3 for disposal of mineralized waste rock.
6.1.3 Tailings Basin Decommissioning
When closing the mine, VBNC proposes to construct permanent dam spillways to allow the basins to discharge while maintaining a 5.5-m freeboard to prevent overtopping of the dam. The slopes of the tailings dams would be flattened and additional erosion controls installed for long-term stability. For the North Tailings Basin, diversion dams would be removed and drainage would be redirected through the basin as before. The company would remove unneeded structures or facilities and replant vegetation on exposed areas. Decommissioning activities would be designed to ensure that the tailings and waste rock placed in the tailings basins remained permanently flooded to prevent acidification, in water deep enough to prevent re-suspension of tailings.
VBNC proposes to continue treating water from both tailings basins until it is clean enough to release directly into the environment. As a contingency measure, VBNC proposes to investigate the method of placing passive barriers on tailings to reduce contaminant flux. Once acceptable for release, effluent from Headwater Pond would be discharged eastward into the Throat Bay watershed, and effluent from the North Tailings Basin would be returned to its natural drainage into the brook below Dam N2, where it would discharge into Kangeklualuk Bay. There was some discussion of the possibility of returning all or a portion of the Headwater Pond discharge to the Reid Brook watershed. VBNC said that was feasible if water quality was acceptable at that time. The Panel notes that VBNC did not define acceptable standards. At minimum, these would have to be compatible with the Metal Mining Liquid Effluent Regulations (MMLER) but could be more stringent, depending on site-specific requirements.
Conclusions and Recommendations
The Panel concludes that VBNC's site selection process was adequate and did incorporate environmental factors. The Panel believes that VBNC chose the best available natural options. The storage-to-dam ratios are high, and the fact that the tailings in Headwater Pond would be placed below the natural outflow level is a significant safeguard to prevent an accidental tailings spill into the sensitive Reid Brook watershed.
Since the long-term security of the tailings facilities will depend on the integrity of the perimeter dams, the Panel believes that dam design and maintenance will be crucial. The Panel was not presented with any evidence suggesting that the proposed dam designs were inadequate or inappropriate, but nevertheless it believes it would be prudent for VBNC to learn from experiences elsewhere, particularly in similar climatic zones.
The Panel was assured that all dams would be designed for the worst case seismic event and that, on decommissioning, dam slopes would be stabilized and reduced. The Panel also believes that VBNC should incorporate provisions for seepage collection, should it prove necessary.
The Panel believes that the proposed design would allow VBNC to maintain water cover in both tailings facilities during dry years. During operations, Headwater Pond would have 0.26 million m³ of excess water in a normal year, while North Tailings Basin would have 2.68 million m³. During exceptionally dry years, VBNC would be able to take corrective action, which could include increasing the use of recycled water or, if necessary, reducing or stopping production.
The Panel recommends that VBNC
- ensure the final design of all dams includes provision for the worst possible seismic event;
- evaluate best environmental management practices in Canada and elsewhere for dam design and construction in order to identify provisions for seepage collection and treatment; and
- prepare and implement a dam safety inspection and maintenance program for all Project phases.
The Panel agrees with the staged use of Headwater Pond, with subsequent development of the North Tailings Basin depending on the final resource volume and the results of the ongoing evaluation of alternatives, as discussed above. The Panel believes that VBNC should vigorously investigate the possibility of disposing of tailings or waste rock both in the open pit and underground as a way to avoid developing the North Tailings Basin. This would diminish the Project's footprint, preventing the disturbance of another watershed and reducing the loss of harlequin duck habitat.
The Panel recommends that, before deciding to commission the North Tailings Basin, VBNC should evaluate the potential for using the mined-out Ovoid as a disposal site for either tailings or waste rock. It should also investigate, when adequate samples are available, the adequacy of both acid-generating waste rock and tailings as underground backfill material. During this environmental evaluation, the company should consider the best currently available technology for disposing of tailings and the results of the harlequin duck monitoring program (see Recommendation 65). This evaluation should be subject to review and recommendations by the proposed Environmental Advisory Board.
6.2 Non-Mineralized Waste Rock Management
VBNC proposes to dispose of approximately 22 million tonnes of waste rock, which will not generate acid, in two land storage sites adjacent to the open pit (see map on page 38, Waste Disposal Areas). Over 90 percent of all waste rock is non-reactive. The East Mine Rock Storage is designed to contain 18 million tonnes, while the North Rock Storage is designed for 4 million tonnes. In addition, approximately 9 million tonnes of overburden material would be placed in the South Overburden Storage.
VBNC conducted static and kinetic tests on mine rock types to identify potentially acid-generating materials and to determine associated rates of reactivity. Testing also showed sulphide content to be a good indicator of metal content; nickel is the main metal of concern in reactive mine rock leachate. VBNC proposes to use sulphur content to distinguish between reactive and non-reactive waste rock. Rock with less than 0.2 percent sulphur would be disposed of on land, and the remaining waste rock would be treated as reactive and disposed of underwater in Headwater Pond. This compares to the British Columbia guidelines, which recommend a 0.3-percent cut-off, and suggestions by an expert for the Innu Nation that waste rock above a 0.1-percent sulphur cut-off be managed as reactive. VBNC stated that there is very little material present in this critical range.
The troctolite was determined to be acid generating and VBNC proposes to dispose of it entirely underwater. For the open pit, the vast majority of gneiss was characterized as non-reactive, although small amounts of higher sulphur gneiss are associated with the troctolite contact zone. Troctolite and gneiss can be easily distinguished visually. Tests on overburden materials indicate they are not acid generating.
During operations, blasting could result in the mixing of rock types, although VBNC stated that if any ore became mixed with waste rock, the resultant material would be sent to the concentrator. To evaluate waste rock content, VBNC proposes to develop a protocol consisting of a regular sampling procedure that would analyze samples on site before rock pile characterization is determined. Testing would continue until rock could be sorted reliably using other techniques, such as visual differentiation. During Project construction, a temporary analytical facility would be set up to test rock from roads and borrow pits.
Environment Canada, LIA and Innu Nation expressed concerns that the waste rock disposal sites on land could release contaminants into the environment. Specifically, they were concerned that acid-generating material would end up in non-acid-generating waste dumps. The Panel was told that a conservative characterization of mine rock to distinguish between reactive and non-reactive waste rock, and an effective rock sorting process during mining, are both critically important to prevent disposal of reactive rock on land. These procedures must be verifiable and errorless under all operating conditions, including some anticipated severe weather conditions.
Participants also wanted VBNC to ensure that on-land storage piles performed to predicted standards and to establish measures to address any problems encountered.
VBNC proposes to continue testing to verify expected behaviour of mine rock over the long term. A system of drainage ditches would collect runoff from the mine rock storage areas and direct it to the South Sedimentation and Surge Pond. Capturing drainage would allow VBNC to treat any contaminated water before discharging it. In response to an Environment Canada recommendation, VBNC agreed to implement a verification and field monitoring program for waste rock and to develop a contingency plan to deal with reactive material found in the non-mineralized waste rock storage piles.
Participants also argued that VBNC should make maximum use of non-reactive mine rock as a construction aggregate, to minimize the need to develop additional quarry and borrow sites. VBNC has indicated that it would treat non-mineralized waste rock as a priority construction material but that such rock would not be available in the early years of mining development.
The Panel concludes that the operational sorting of acid-generating waste would require close attention. As described by VBNC, the Ovoid contains a large volume of waste rock that contains no sulphide minerals. Rock that does contain sulphides either looks different or is limited to zones close to the main sulphide-bearing areas. The Panel believes that good mine planning, combined with appropriate blasting procedures, could minimize the chances that reactive ore would be mixed with non-reactive waste rock. The volume of mixed material would therefore be sufficiently small that VBNC would be able to send it all to the mill as proposed.
There was little discussion of the way VBNC would sort acid-generating material in the underground operation. While it would probably be easier to identify acid-generating waste material underground, continued segregation of the material in the waste handling system could be more difficult. This could require VBNC to include additional waste handling flexibility at the mine design stage.
The Panel recommends that VBNC
- prepare and implement a program, which can be carried out throughout the life of the Project, to verify and monitor open pit and underground waste rock that is disposed of on the surface;
- develop procedures to segregate all waste that originates from potentially acid-generating zones but is sorted as non acid-generating, and to assign this waste to a specific dump site so that the company can take mitigative measures if monitoring reveals a problem;
- outline contingency plans for dealing with reactive material encountered in the non-mineralized piles, particularly for managing runoff; and
- ensure that the waste handling system designed for the underground operation allows separate handling and disposal of acid-generating material.
6.3 Water Quality Issues
The proposed milling operation is a complex water handling facility that, at its peak, would use some 11 million m³ of water annually to treat ore from the open pit. While much of that water would be recycled, 5.4 million m³ would be discharged into Edward's Cove annually during the operation of the open pit. This would be the only discharge of water into the environment. The main sources of this water would be
- 1.1 million m³ of fresh water from Camp Pond;
- a net of 2.32 million m³ from the Headwater Pond drainage area; and
- the remainder from site runoff and dewatering of the open pit.
During the underground operation, the discharge to Edward's Cove would increase to 7.5 million m³, with the extra supply coming from the North Tailings Basin. In addition, 2.68 million m³ would be released as excess from the North Tailings Basin to Kangeklualuk Bay.
VBNC predicts that the quality of the water that would be released to Edward's Cove would be well below discharge limits imposed by the MMLER or by the Newfoundland Department of Environment and Labour (NDOEL). For example, the most recent pilot plant test results predict that concentrations of nickel would be lower than 0.01 mg/L, as opposed to a monthly average of 0.5 mg/L, which is the MMLER requirement.
6.3.1 Water Balance
Maintaining the balance of water requires a complex water handling system. To reduce treatment requirements, an initial pumpdown of Headwater Pond would remove approximately 8 million m³ of water and lower the water level to 84 m above sea level. The water balance in Headwater Pond would be maintained by pumping an estimated 5.18 million m³ of recycled process water to the mill annually with an excess of 0.26 million m³ going to the treatment plant. The proposed initial pumpdown of the North Tailings Basin would remove 4 million m³ of water and decrease the water level to 124 m above sea level. Reclaimed water would also be collected from the North Tailings Basin for use in the milling process. Excess water would be treated at a dedicated water treatment plant located at the basin, if water quality required it, and piped to Kangeklualuk Bay for discharge through a diffuser.
Participants questioned the need for two water treatment plants and effluent discharge points. The treatment plant at the North Tailings Basin has been planned to treat the excess discharge during operation and all discharge on decommissioning. Since a return water line back to the main treatment plant would exist, the discharge could possibly be directed there. VBNC stated that this would require an expansion of the pumping and water treatment capacity of the main plant, and that the company would consider this option in future plans. This issue is discussed further in Chapter 9, Marine Environment: Land-Based Effects.
The Panel heard from both Innu Nation experts and Environment Canada that measures must be taken to maximize water recycling, since reduced water recycling would increase both freshwater withdrawals and the volume of water requiring treatment prior to release as effluent. The water treatment facilities must also be designed to handle the volumes of water needing treatment if the company recycles less water than expected. Environment Canada suggested that evidence does not support VBNC's claims that the company could manage increased volumes without significantly increasing loadings into Edward's Cove.
6.3.2 Water Quality
VBNC predicted that the tailings basin water and tailings pore water would contain small amounts of heavy metals, most prominently nickel, in concentrations lower than MMLER limits. It also predicted elevated levels of ammonia, introduced through the use of ammonium and nitrate fuel oil blasting agents. VBNC would mitigate any acidification of the basins by adding lime. The Panel notes that findings from ongoing pilot testing by VBNC have so far confirmed many of the predictions in the Environmental Impact Statement (EIS), with the exception of higher thiosalt and lower iron levels than predicted.
Environment Canada expressed concerns about the need to prevent or minimize impacts associated with acidification of the tailings ponds, particularly thiosalt generation. Thiosalts are formed in alkaline environments and are unstable intermediate oxidation products of sulphide minerals. Oxidation of thiosalts can acidify tailings ponds and release metals into the water column. In addition, thiosalts in recycled water can lower metallurgical recovery, reducing the amount of recycled water available to the mill and increasing freshwater withdrawals.
Environment Canada and NRCan stated that it is difficult to predict and to control thiosalt production, as thiosalts are resistant to conventional effluent treatments. They have low toxicity but they may be oxidized by bacteria to lower the pH. Their acidity can be seasonal. Currently, thiosalts are treated by natural degradation in ponds. However, the Canada Centre for Mineral and Energy Technology is coordinating a consortium to study approaches to managing thiosalts that will minimize environmental effects and maximize metal recovery.
VBNC claims thiosalts posed no problems to metallurgical recovery during pilot plant testing, even when the plant was running with 100-percent recycled water. Also, since thiosalts are a product of the milling process, they are introduced into tailings ponds during the operations stage only. They oxidize to sulphates in ponds over time. If the ponds do become acidified, VBNC calculates that it could neutralize the amount of acid released by adding only 300 tonnes of lime to the pond through the tailings line.
Environment Canada also expressed concerns to the Panel about impacts associated with releasing ammonia into the environment. Ammonia is toxic in its ionic form, which occurs in high pH environments. Environment Canada is concerned that high ammonia levels in a high pH effluent could be lethal to fish. VBNC predicts that the concentration of ammonia would fall below 0.180mg/L and claims that, although the pH of the tailings pond would be high during operations, the company would adjust the pH of all effluent to an acceptable level before discharge.
Environment Canada was also concerned about the settling characteristics and chemical stability of sludge co-disposed with tailings. Since metal fluxes from the sludge could affect metal concentrations in pond water and increase the need for make-up water, accurate predictions of sludge volume are important. Environment Canada was particularly interested in how VBNC would monitor sludge and how it would manage sludge during shutdowns and after decommissioning.
VBNC predicts that sludge production would range between 4000 and 6000 dry tonnes/year. Sludge would be composed primarily of iron hydroxide, but it would also contain small amounts of other heavy metals. VBNC states that, since hydroxides would probably be present in the tailings, it does not expect an incremental increase in hydroxide levels to affect pond water quality. It maintains that the tailings provide a geochemically stable environment for sludge storage over the long term, but it is committed to completing sludge stability tests. Settling tests completed in the pilot plant show that sludge settles rapidly and that, when co-disposed with tailings, it can improve solids settling. VBNC considers that the co-disposal scenario would also eliminate the need for an additional waste management facility.
Conclusions and Recommendations
The Panel concludes that the proposed milling operation could produce effluent concentrations that fall well within discharge standards. The Panel also realizes that pilot test results are indicators only and that VBNC would need to monitor and manage the process constantly to achieve similar results during the variable conditions under which this plant would operate. In addition, MMLER standards are currently under review and the Panel feels that this operation should perform, not to discharge standards, but to the best achievable levels.
The amount of water recycled and the build-up of contaminants in process water would significantly affect water quality. The Panel therefore makes the following recommendations.
The Panel recommends that VBNC further develop its water recycling plans, in consultation with Environment Canada, incorporating
- procedures to maximize the volume of recycled water of acceptable quality, taking into account factors that could limit the use of recycled water in the mill process; and
- contingency plans to deal with potential requirements for additional raw water withdrawals and wastewater treatment.
The Panel recommends that VBNC integrate into its environmental protection plan, in consultation with Environment Canada,
- pollution prevention procedures that apply the best management practices for minimizing thiosalt production;
- pollution prevention procedures that reconcile pH levels and ammonia concentrations in ponds and effluents, taking into account the potential accumulation of ammonia under ice; and
- a sludge management plan that takes into account alternative sludge disposal options, the long-term potential for metal dissolution from sludge co-disposed with tailings, and the implications of mill shutdowns and decommissioning.
6.4 Open Pit Water Issues
Once the Ovoid has been mined out, VBNC proposes to stabilize the sides of the pit and then allow it to flood. As discussed above, many participants suggested that the mined-out pit first be filled with acid-generating waste rock or tailings before final decommissioning. Many also mentioned issues that might delay the flooding of the pit. Regardless of the final decision, all participants stressed that, not only would the open pit lie in the Reid Brook watershed, but the potential exists for long-term groundwater migration towards Reid Brook. In addition, during scoping sessions, community members expressed concern about the interaction of wildlife, especially caribou, with the flooded pit.
6.4.1 Flooding of the Open Pit
VBNC has proposed that, after completing mining in the Ovoid, it would flood the pit to reduce acid generation. The company assumes it would take 6 years to flood the pit if diversions were directed into the pit and 16 years if they were not. Early flooding is considered essential for reasons of water quality control. LIA expressed concerns that more information is needed on the effects of flooding, on time needed to flood the pit and on acid generation by sulphide-bearing rock exposed at the pit wall before flooding. The provincial government stated that extreme care would be needed if flooding posed a risk to safety in the underground operation. The Province added that it would not permit VBNC to flood the pit if such a risk existed.
Although VBNC assumed that water quality in the flooded open pit would be similar to that in the tailings ponds, participants were concerned that this is an overly optimistic assumption. Both the Innu Nation and Environment Canada stated that the long exposure of pit walls to oxidation and the unknown chemical quality of groundwater could degrade water quality over time. In addition, sulphide material would be exposed on the pit wall toward Discovery Hill that would not be flooded; the company might need to use an alternative method to prevent oxidation there.
As necessary, VBNC plans to continue to pump water from the pit for treatment and discharge at Edward's Cove until pit water quality reaches discharge standards.
6.4.2 Open Pit Hydrology
Participants were concerned about the predicted time it would take for groundwater from the open pit to reach Reid Brook. The EIS stated 200 to 1000 years, but an Innu Nation expert's calculations suggested a few decades. VBNC provided calculations for clarification, which suggested that it would take 475 years for pit water to reach the wetlands at the base of Discovery Hill, assuming a 1-km pathway. The company said it would be unrealistic to expect a direct seepage pathway to Reid Brook to develop.
VBNC stated that groundwater contamination would not be an issue because the hydraulic gradient would run towards the pit during operations and while the pit is flooding. VBNC will then continue to pump in order to maintain this hydraulic gradient until the water in the pit is of acceptable quality to be released to both surface water and groundwater.
The Panel concludes that VBNC should consider backfilling the open pit. However, before beginning excavation, VBNC should put a reclamation plan in place to help it fill the pit rapidly, backfill the pit or maintain a dewatered pit, if underground safety requires that option. The ultimate goal is to achieve the best water quality as quickly as possible in order to return flows to Camp Brook and to create an aesthetically pleasing and ecologically functional landscape.
The Panel recommends that VBNC develop a long-term management and rehabilitation plan for the open pit. The plan should be subject to review and recommendations by the Environmental Advisory Board, and should include
- ongoing modelling and laboratory testing of evolving water quality in the flooded pit, of discharge rates and of the type and length of treatment required;
- a strategy to reduce the time that the open pit walls will be exposed before the pit is flooded, developed by evaluating best environmental management practices; and
- measures to reclaim the surrounding area to promote wildlife safety and the development of appropriate shoreline habitat.
The Panel also concludes that potential seepage pathways between the open pit and Reid Brook could and should be monitored, using strategically placed groundwater monitoring wells, which would give ample warning if contaminants were migrating through the bedrock. VBNC would then need to take corrective action, which would presumably include continuing to pump and treat the water in the pit.
The Panel recommends that VBNC establish monitoring wells between the open pit and Reid Brook, and develop suitable threshold levels for contaminants and a contingency plan to take corrective action if contaminants are found in groundwater flowing towards Reid Brook.
- 1 Introduction
- 2 The Project and Sustainable Development
- 3 Project Need and Resource Stewardship
- 4 Land Claims and Impact and Benefit Agreements
- 5 Air Quality
- 6 Tailings, Mine Rock and Site Water Management
- 7 Contaminants in the Environment
- 8 Freshwater Fish and Fish Habitat
- 9 Marine Environment: Land-Based Effects
- 10 Marine Environment: Shipping
- 11 Marine Mammals
- 12 Terrestrial Environment and Wildlife
- 13 Birds
- 14 Aboriginal Land Use and Historical Resources
- 15 Employment and Business
- 16 Family and Community Life, and Public Services
- 17 Environmental Management
- 18 Recommendations
- Appendix A: Panel Members
- Appendix B: List of Abbreviations and Acronyms
- Appendix C: Memorandum of Understanding
- Appendix D: Transcript of Proceedings
- Appendix E: Acknowledgements
- Date Modified: