Panel Report

Cameco proposes to transport the McArthur River ore to Key Lake for milling and tailings disposal. The mill was built to handle the Key Lake ore with its average grade of 2% U₃O₈. The McArthur River ore, because it is much richer, averaging 15% U₃O₈, would be blended with special waste to produce an acceptable mill feed grade. It is expected that the mill will process approximately 200,000 tonnes of this blended ore annually over a period of about 15 years.

8.1 Ore Dilution

Cameco proposes annually to blend about 50,000 tonnes of McArthur River ore with approximately 150,000 tonnes of Key Lake special waste, to produce a mill feed with an average grade of 4% U₃O₈.⁴⁵ As a result of this blending, only minor modifications would be required to the existing mill, and the proponent predicts negligible changes in radiological doses for workers involved in the milling process.⁴⁶ The exposures currently recorded for workers at the Key Lake mill and tailings disposal facility are acceptably low when compared to the regulatory limits, confirming that the operator is exercising appropriate health and safety controls.

The proponent’s decision to mill McArthur River ore at Key Lake has environmental and economic benefits. The environmental damage associated with construction of a new mill site would be avoided; the inventory of contaminated waste on the surface at Key Lake would be decreased; and the operating life of the existing mill, and its attendant employment, would be extended.

8.2 The Deilmann Tailings Management Facility

The Deilmann Tailings Management Facility (DTMF) is located 4 km east of the Key Lake mill. It is a mined-out pit, 1300 m long, 600 m wide and 170 m deep. Cameco has received approval for the disposal of approximately 2 million cubic metres of Key Lake ore tailings and special waste within the DTMF.⁴⁷ The placement of Key Lake tailings began on December 31, 1995, using subaerial deposition within a pervious surround of crushed rock and sand. The system depends on in-pit dewatering, a side-drain, and on a ring of dewatering wells, placed about the pit perimeter. During operation of the DTMF, the water collected in the under-drain would be pumped to surface and treated to remove contaminants.

The facility would be modified to receive the tailings from the milling of McArthur River ore, when the milling of the Key Lake ore has been completed. At that time, it is estimated that about 30 metres of tailings would be in the bottom of the pit; i.e. the pit would be filled to a level 412 metres above sea level. Subaerial deposition would then cease, with the pervious surround sealed by tailings. Groundwater pumping would then be reduced to permit the pit to flood above the consolidated tailings.

The tailings potentially represent the greatest long term threat.

Steve Lawrence, Written Submission, Received September 19, 1997, p. 1.

The tailings obtained from milling the richer McArthur River ore would be thickened and deposited under the water cover on top of the Key Lake tailings. This subaqueous placement of tailings would be done from a barge, using a tremie pipe injection system, as shown in Figure 4. There would not be a pervious surround envelope in the portion of the pit used for subaqueous disposal. The water cover would provide protection for workers against gamma radiation, radon and radioactive dust. It would also protect the tailings from freezing.

After 15 years of milling McArthur River ore, consolidated tailings would occupy approximately 4.5 million cubic metres of the DTMF. The final elevation of the deposited tailings would reach approximately 448 metres above sea level, leaving an excess storage capacity of approximately 8.5 million cubic metres in the DTMF.

During disposal of the McArthur River tailings, pumping from the pit would be regulated to maintain a water cover above the rising tailings column. The water elevation in the flooded pit would be maintained at a minimum of 5 metres below the groundwater surface to ensure that groundwater flow would always be directed into the pit. Upon completion of tailings deposition, a cover of 2 metres of sand or till would be placed on top of the tailings mass. The cover layer would promote further tailings consolidation and act as a diffusion barrier against contaminant release. Treatment of the water in the pond above the tailings mass would continue until it was of acceptable quality. The pit would then be permitted to flood to a depth of approximately 60 metres above the tailings cover, matching the natural groundwater surface.

Following long-term consolidation, Cameco predicts that the tailings would be frost-free, with an average hydraulic conductivity of 10^-7 m/s or less.⁴⁸ The permeability of the consolidated tailings would then be approximately two orders of magnitude less than that of the surrounding Athabasca Basin sandstone. Such conditions would ensure the effective diversion of groundwater flow around, rather than through, the consolidated tailings.

These predictions are based on computer modelling. During the hearings, much of the experimental data used in modelling protocols was questioned and it is not possible to have a great deal of confidence in these predictions. For this reason, the DTMF will have to be carefully monitored to ensure that it is performing to specifications. Because it will eventually contain an enormous amount of waste that is both toxic and radioactive, this facility, if it is not managed carefully, could be very destructive to the northern environment. If seepage from the DTMF into the surrounding groundwater were to occur, extensive contamination of the now pristine northern rivers and lakes could develop. It is, therefore, important that monitoring be carefully done and that any malfunction be mitigated. These requirements are expanded upon in Chapters 10 and 12.

Despite the reservations mentioned above and in Chapters 10 and 12, subaqueous tailings placement in the DTMF does have some potential advantages, both with respect to protection of the environment in the long term and for concerns associated with the need to protect workers’ health during operations. These include:

• a reduction in the volume of water discharged from the DTMF to groundwater;
• the elimination of consolidation problems associated with frozen tailings;
• a decrease in worker exposure to radiation; and
• a reduction in the surface inventories of special waste which have accumulated at Key Lake since 1983.

The proposed tailings management program received support during the public review. The Province of Saskatchewan stated that:

The Key Lake hydrogeologic regime is better defined than any other uranium mine in Saskatchewan... The Department is confident that the technology exists and is constantly improving such that impacts associated with the DTMF can be quantified and mitigated throughout operations and during decommissioning.⁴⁹

The Atomic Energy Control Board voiced a similar opinion:

The staged sub-aerial and sub-aqueous deposition methods proposed are acceptable in concept... The under-drain system has functioned as designed during the sub-aerial Key Lake tailings deposition period to date...⁵⁰

However, the AECB also emphasized the need for monitoring to confirm that its confidence in the system had not been misplaced:

The on-going monitoring and evaluation of the operation of the system is an essential element for feedback control and facility adjustments to meet requirements.⁵¹

Environment Canada was even more clearly of the opinion that continuous monitoring, and redesign if necessary, was essential:

...the assumptions and engineering judgment used in the design and modelling of the proposed impacts must be validated through instrumentation, research and re-running of the impact models at regular intervals throughout the operational and decommissioning phases of the mine to ensure the environment is adequately protected.⁵²

It appears that the potential benefits of the DTMF could compensate adequately for the associated risks and the panel recommends that cautious approval of the facility be granted. We are, however, keenly aware that this is a new technology in an experimental stage of development and our recommendation should not be taken as a general endorsement of natural surround in-pit tailings disposal facilities. Another panel’s acceptance of the Rabbit Lake pervious surround tailings disposal facility was used to justify approval of a similar facility for the JEB pit.⁵³ Our recommendation for the DTMF is site-specific and should not be used in a similar way to justify another project.

It will be possible to evaluate the performance of the DTMF only after it has been in operation for many years. The technology cannot be considered to be fully proven until it has been shown, by actual measurements, that the tailings have consolidated to yield a material of low permeability, and that any migration of contaminants falls within acceptable levels.

It is apparent that rigorous performance monitoring will be required during all stages of development and operation of the DTMF. At a minimum, monitoring should include regular assessment of tailings consolidation characteristics and water quality conditions, as evaluated at both the peripheral dewatering wells and at the main pit over a long period of time. It is not likely that it will ever be possible to completely walk away from this pit once it has been filled with tailings.

As you know and have heard over and over, our greatest concern is our environment and the environment that we are going to leave behind for our future generations.

Pierre Robillard, Elder, Black Lake, Transcript of Public Hearings, La Ronge, Saskatchewan, October 1, 1996, p. 35.

8.3 Conclusions and Recommendations

Significant environmental benefits could result from the decision to mill the McArthur River ore at the Key Lake site. Past performance of the mill suggests that health and safety controls’are sufficient to protect the workers and that the environment can be protected from unacceptable contamination in the long term.

The proposed tailings management regime has the potential to offer significant benefits; however, because of the experimental nature of combining subaerial with subaqueous deposition within the same tailings management facility, careful monitoring will be essential. Deposition of tailings should be permitted to proceed only as long as all modelling predictions are met, or appropriate mitigation is implemented.

The panel recommends cautious approval of the Deilmann Tailings Management Facility as described in the EIS, with the understanding that rigorous performance monitoring will be undertaken during all stages of development, operation, decommissioning and postdecommissioning.

Figure 4: Deilmann Tailings Management Facility - Subaqueous Tailings Deposition

⁴⁵ McArthur River Projmt Environmental Impact Statement, Executive Summary, Cameco Corporation, October, 1995, pp. 3-7.

⁴⁶ McArthur River Project Environmental Impact Statement, Main Document, Cameco Corporation, October, 1995, pp. 2.7.1-2.7.4.

⁴⁷ Government of Saskatchewan, Submission to the McArthur River Public Hearings, Regina, Saskatchewan, September 5, 1996, p. 29.

⁴⁸ McArthur River Project Environmental Impact Statement, Main Document, Cameco Corporation, October, 1995, pp. 2.8.8-2.8.17.

⁴⁹ Government of Saskatchewan, Submission to the McArtur River Pubic Hearings, Saskatoon, Saskatchewan, September 17, 1996, p. 11.

⁵⁰ Atomic Energy Control Board, Submission to the McArthur River Public Hearings, Saskatoon, Saskatchewan, September 17, 1996, pp. 2-3.

⁵¹ Ibid, p. 6.

⁵² Saskatchewan Environment and Resource Management, Submission to the McArtur River Public Hearings, Saskatoon, Saskatchewan, September 17, 1996, p. 15.

⁵³ The Government’s Position on Proposed Uranium Mining Developments in Northern Saskatchewan, Government of Saskatchewan, December, 1993, p. 29.