Panel Report

The environmental concerns resulting from the production of mine waste rock vary significantly depending on its characterization, the volume produced and the method of its disposal. Some of the options for disposal of waste rock are: storage as a surface pile, burial in a water body, return to the excavation from which it came, or use as construction aggregate.

Normally, mine waste rock is classified as either clean waste or special waste, depending on its mineral content and its propensity to be acid-generating. The Cigar Lake Mining Corporation (CLMC) proposes a management strategy which would assume that all waste rock produced during mining operations, estimated at 2.6 million tonnes, would be designated and handled as special waste. Clean sandstone waste produced during shaft sinking would be used for road construction and other civil engineering requirements. [The Cigar Lake Environmental Impact Statement, Additional Information , Cigar Lake Mining Corporation, March 1996, p. 1-71.]

6.1 Disposal Options

Deposition of the special waste in a manner which protects the environment would require identification of an appropriate method and location for disposal.

The initial option in CLMC's management strategy is to retain as much waste rock as possible underground and use it to backfill the mined-out drifts and galleries. It is estimated that about 30 per cent of the waste could be handled in this way. [Ibid, p. 1-70.] This option is to be encouraged and maximized; however, it is evident that most of the waste rock would require disposal by other means.

A primary concern with surface storage is that contaminants associated with the rock might be mobilized either through surface runoff or by the infiltration of precipitation into the waste rock pile. If water enters the pile, it has the potential to produce a leachate by dissolving heavy metal contaminants within the rock. This leachate could then enter the groundwater or be discharged to the surface environment, causing significant environmental impacts.

There is a particular environmental concern with much of Cigar Lake's waste rock because it contains relatively high levels of sulphides along with significant amounts of arsenic and nickel. When exposed to precipitation and oxygen, sulphide minerals produce acid which increases the leaching of other contaminants from the waste rock. Acid generation occurs readily in mineralized waste piles because the sulphides within the rock are exposed to both oxygen and water when the rock is broken and brought to surface. Under certain conditions, sulphide oxidation is also enhanced by the presence of autotrophic bacteria. [L.M. Broughton, R.W. Chambers and A. Mac G. Robertson, Mine Rock Guidelines, Design and Control of Drainage Water Quality, Saskatchewan Environment and Public Safety, April 1992, Chapter 3.] If unmitigated, acid production would continue until all available sulphide minerals were depleted. Depending on the characteristics of the waste rock pile, acid generation and the associated dissolution of metals, such as arsenic and nickel, could threaten the receiving environment for many decades.

Methods to reduce or limit the potential for acid generation are well understood. The most effective method is to limit the amount of oxygen available for the production of acidic leachate. A proven technique to ensure that potentially acid-generating (PAG) waste rock is not exposed to oxygen for an extended length of time is to place it below a water cover. [Ibid, Chapter 6.] Similar results could be achieved with placement in a mined-out pit, under a cap of clean waste rock and till.

The diffusion coefficient for oxygen in water is nearly 100,000 times less than the diffusion coefficient for oxygen in air. For this reason, less than a metre of relatively stagnant, oxygen-depleted water will reduce the oxidation rate of submerged sulphide minerals to almost zero. Such a management strategy has been well researched and has received support from the regulatory agencies:

• The AECB supports the concept that, with appropriate controls, underwater or in-pit disposal of potentially acid generating waste rock is preferable to surface stockpiling. [S. Isanen, Atomic Energy Control Board, Transcript of the McArthur River and Cigar Lake Public Hearings, Saskatoon, September 18, 1996, p. 37.]
• Sub-aqueous disposal is accepted by the Department as a technique for dealing with PAG waste rock that would have potential impacts, if simply left on the surface. [R. Sentis, Saskatchewan Environment and Resource Management, Transcript of the McArthur River and Cigar Lake Public Hearings Regina, September 4, 1996, p. 54.]

However, for this strategy to be effective over time, the water cover must be permanent. If PAG waste rock is exposed at any time in the future, acid generation would begin and the associated negative environmental impacts caused by the contaminated leachate would occur.

The option for disposal initially proposed by CLMC in its EIS was subaqueous disposal of the PAG waste rock in Bizarre Lake, a small but relatively deep lake located approximately 3 kilometres northeast of the mine site. However, Bizarre Lake contains a fish population, including lake trout, that is duplicated by only one other lake in the region, Waterbury Lake. During the review of the Cigar Lake EIS, it was evident that some government agencies, departments and members of the public were concerned about the impact that subaqueous disposal of the waste rock would have on Bizarre Lake, particularly on its lake trout population:

• Cigar Lake Mining Corporation's proposal to treat Bizarre Lake as a waste management facility, is completely unacceptable. Bizarre Lake is a deep, reasonably ecologically diverse lake, with a good lake trout population. [P. Prebble, Saskatchewan Environmental Society, Transcript of the McArthur River and Cigar Lake Public Hearings, Saskatoon, Saskatchewan, September 16, 1996, p. 159.]
• With respect to its location, the size, the greater-than-average mean depth, and fish species assemblage in Bizarre Lake render it atypical when compared with similar sized lakes within this part of northern Saskatchewan. [B. Fallis, Department of Fisheries and Oceans, Transcript of the McArthur River and Cigar Lake Public Hearings, Saskatoon. Saskatchewan, September 18, 1996, p. 145.]

It is evident that CLMC has not justified the selection of Bizarre Lake as the most appropriate location for disposal of the waste rock generated from mining the Cigar Lake ore body. Destruction of the fish habitat of Bizarre Lake for the reasons given by the proponent is unacceptable. For these reasons, Cigar Lake has withdrawn its proposal to use Bizarre Lake for waste rock disposal.

Cigar Lake has heard the clear and firm positions expressed by both federal and provincial agencies...the selection of Bizarre Lake is unacceptable...Cigar Lake Mining Corporation are now prepared to respond to the agency's views and adopt Lake 497 as the mine rock disposal option.

G. Acott, Cigar Lake Mining Corporation Transcript of the McArthur River and Cigar Lake Public Hearings, Saskatoon, Saskatchewan, September 18, 1996, p. 13.

Two additional options for subaqueous disposal are identified and briefly discussed in the EIS: disposal in Lake 497, a smaller, less ecologically diverse lake in the vicinity of the mine; and disposal in the Sue C pit, located at the McClean Lake mine site, which is owned and operated by Cogema Resources Inc. Both the Sue C pit and Lake 497 may be viable options, but both must be subjected to a detailed examination before a decision that minimizes future uncertainties can be made.

Use of the Sue pits at McClean Lake for disposal of PAG waste rock provides an additional decommissioning option - that of covering the special waste with several metres of clean waste capped by a metre or two of till. Such an approach would return the area to approximately the same condition as existed prior to mine development and thereby provide compliance with one of the fundamental decommissioning objectives, as discussed in Chapter 10. If no other alternative presents a clear environmental advantage, this would be our preferred option.

Sufficient site-specific information to fully assess the appropriateness of these two options for the disposal of the Cigar Lake waste rock is currently not available. From a consideration of the limited information available with respect to their ability to provide environmental protection, it would seem that both options have advantages and disadvantages which would require intensive investigation. For example, selection of the Lake 497 option could not be considered without collection and analysis of more detailed baseline data for the lake and downstream water bodies. It must also be shown capable of maintaining a permanent water cover of sufficient depth over the deposited waste rock to ensure long-term environmental protection. The Sue C option, on the other hand, could not be selected without additional knowledge of the geology and hydrogeology of this yet to be constructed pit. The potential for contaminant migration in the ground water would also have to be carefully modelled before Sue C could be considered to be a viable option. If neither of these options proves to be acceptable, other solutions to the Cigar Lake waste rock disposal problem would have to be considered. Approval for the project should not be granted until a location that provides secure environmental protection has been found.

Both solutions, lake and pit disposal, contain future uncertainties that could result in environmental damage. It appears that waste rock disposal in Lake 497 would not cause an unacceptable loss of fish habitat; however, it is possible that future conditions, as yet unrecognized, could cause the water level to drop, exposing the wastes to atmospheric oxygen. On the other hand, the pits at McClean Lake have yet to be completely excavated and the hydrogeology there may make them unsuitable for waste rock deposition. Furthermore, it is expected that the Sue pits may not be fully excavated by the time Cigar Lake starts production, thereby requiring the storage of waste rock on surface in contact with atmospheric oxygen for several years before deposition could begin. By the time that deposition could begin, the acid-generating processes would be well established in the stockpile.

Before approval to operate can be granted for the Cigar Lake Project, CLMC should submit a detailed report to the provincial and federal regulators, giving a comprehensive evaluation of its waste rock disposal options and available locations. The report should indicate a preferred option, supported by a thorough justification. Two of the options evaluated should be the use of the Sue C pit, and the use of subaqueous disposal in a water body such as Lake 497.

We believe that if the Cigar Lake Mine development is to go ahead, the option of using the Sue C pit for waste rock disposal should be further examined.

A. Coxworth, Saskatchewan Environment Society, Transcript of McArthur River and Cigar Lake Public Hearings, Saskatoon, Saskatchewan, September 19, 1996, p. 69.

In selecting the preferred disposal option, the wishes of the traditional users of the land in the area should be respected. Before a disposal site is selected, CLMC and the regulators should consult the impact commu-nities and give them an opportunity to assess the potential benefits and liabilities associated with the options being considered. This consultation could take place through the Environmental Quality Committees. The wishes of the communities should be integrated into the final decision-making process, and documented as part of the justification for the preferred option.

Tables 6.1 and 6.2 provide a list of issues associated with lake and till-capped pit disposal that should be considered during site selection. The list is not intended to be exhaustive; the proponent, the regulatory agencies and the public may suggest additional issues judged to be significant and relevant. Economic considerations should not play a significant role in the decision with respect to the final disposal option. Any funds spent on transporting and disposing of the waste rock will be relatively insignificant when compared to the overall value of the project.

The president of Cigar Lake Mining commented--gave a figure of $10 million as a number to the cost to transport the waste rock to the Sue C pit and he looked at that as a loss to the company and the Saskatchewan government, but you have to ask yourself where would that $10 million be spent. It would be spent hiring northern trucking firms and northern people to do that job. So you would be paying northern people to protect the northern environment. And I think $10 million to save a lake from destruction is worth it.

N. Sinclair, Transcript of McArthur River and Cigar Lake Public Hearings, Saskatoon, Saskatchewan, September 18, 1996, p. 160.

After a detailed evaluation, if no other option presents a clear environmental advantage over the others, it is recommended that the proponent be required to dispose of the Cigar Lake mine waste rock in one of the Sue pits at McClean Lake. This recommendation is based on the principle that, where possible, waste rock should be disposed of in an area already disturbed by mining activity rather than in an undisturbed area. In addition, refilling of a mined-out pit has the added advantage of being a preferred option for the decommissioning of the Sue pits.

6.2 Conclusion and Recommendation

The proponent must submit to federal and provincial regulators a detailed comparative evaluation of various options for waste rock disposal, indicating the option which is the most advantageous for environmental protection. The options evaluated must include the Sue pits and Lake 497. Approval for the project should not be granted until a location that provides secure environmental protection has been found.

If no other option presents a clear environmental advantage, it is recommended that the proponents be required to dispose of Cigar Lake waste rock in one of the Sue pits at McClean Lake, and that the disposal site be decommissioned by filling the remainder of the pit with several metres of clean waste, capped by one or two metres of till.