Panel Report

6.1 Introduction

The existing McArthur River underground workings were developed as part of the 1993-95 exploration program. They are accessible via a concrete-lined shaft, with an inside diameter of 5.5 metres, through which ventilating air, water, power and other supplies are introduced into the underground work sites. To accommodate full-scale mining, this shaft would be deepened to 645 metres and three production drifts would be developed at the 530-, 580- and 640-metre levels.

The production drifts would be interconnected by an underground ramp, developed between the 530- and 640-metre levels. Cameco plans to use the deepened original shaft as the main service shaft. A second shaft, 6.0 metres in diameter, would be sunk to provide additional fresh air to the mine, a path for exhausting contaminated air, and an emergency evacuation route for workers. A third shaft, also 6.0 metres in diameter, would be constructed as a ventilation shaft. The ventilation system and airflow distribution plans described in the EIS have been designed to provide sufficient ventilating capacity to handle any upset conditions that might occur.

The EIS provides a comprehensive assessment of rock strength and the pre- and post-mining ground stress conditions expected to be characteristic of the McArthur River mine site. Based on the data presented, stress conditions would not adversely affect mine safety during development and production activities.³²

The proposed mining methods have been designed to reduce water inflow, maximize rock support capabilities, and protect mine workers from direct exposure to the high-grade uranium ore body. The principal mining methods are boxhole boring, raise boring and remote boxhole stoping. Such methods would be supported by ground freezing and grouting to reduce water inflow. Because these proposed mining methods could be directed by remote control, workers would be protected from direct exposure to the ore. The variety of methods proposed gives the proponent flexibility in dealing with variable ore geometry and ground conditions.

. . . the proponents, throughout the underground exploration program, have demonstrated the priority placed on radiation pro tee tion measures in dealing with high grade ore and high radon-bearing groundwater.

Fred Ashley, AECB, Transcripts of McArthur River Public Hearings, Saskatoon, Saskatchewan, September 1 1, 1996, p. 73.

6.1.1 Ground Freezing and Grouting

Each of the three proposed mining methods would use ground freezing and/or grouting to reduce the flow of radon-laden water into active mining areas. Both grouting, which involves the pressurized filling of existing rock fractures with cement, and ground freezing would improve excavation stability by strengthening the rock mass from which the ore would be extracted.

Ground freezing, which has been successfully demonstrated at the Cigar Lake test mine, would be the method chosen at sites such as the Pelite Ore zone where extensive rock fracturing precludes effective grouting. Cameco would apply the technique either by establishing a curtain of frozen rock around the ore or by freezing the entire zone containing the ore. Sets of parallel freeze galleries would be developed below the ore body in nonmineralized basement rock. From this level, rows of parallel, vertical holes would be drilled upward through the ore zones. Chilled brine at -35°C would then be circulated up through concentric tubes in the vertical holes to freeze ore zones.

In more competent, less fractured rock, grouting would be used to prevent water inflow. Grouting operations would be conducted from access openings located in non-mineralized rock, above and/or beside the ore zones.

The presence of many exploration drill holes, and the expected addition of more as a result of further exploration and production activities, will require attention. To protect against the flow of water and/or air through the drill holes into occupied work sites, all bore holes that intersect underground excavations should be sealed expeditiously.

6.1.2 Boxhole Boring

When boxhole boring is deemed to be the most appropriate mining method, drilling would be upward from the production drift, through inert basement rock and into the ore zones above. Ore and waste rock extraction would be accomplished solely by the action of drilling, without the use of explosives to fracture the rock. As rock is drilled, it would fall through the excavated borehole into sealed chutes and containers, located within the production drift, and be transported by gravity to the primary crushing level below. After crushing and grinding, it would be mixed with water and pumped to surface as a slurry in a dedicated pipeline. The production drift would be located within non-mineralized basement rock where the water inflow rates are expected to be low and manageable.³³

A variable-diameter boring head, rather than the customary fixed-diameter bit, would be used. The variable-diameter boring head can be expanded once contact has been made with the ore zone overhead. Its successful use has been demonstrated in underground mining trials at the Cigar Lake test mine.

Studies at the Cigar Lake test mine showed that the boxhole extraction technique is effective for isolating drilled rock fragments and process water from the workers on the production and primary crushing levels. Thus, the boxhole boring method, combined with the segregated transport of ore to primary crushing levels, would limit exposure of workers to radiation. To provide additional protection against radiation, the air surrounding the chutes, pipes and crushing chambers would be vented directly via secondary ventilation networks. The operator would also maintain rock stability within the ore body by rapidly backfilling each excavated borehole with cement after ore extraction.

Based on the history of boxhole boring, and the successful testing of the variable-diameter boring head at Cigar Lake, it is concluded that this mining method should provide satisfactory mine stability and adequate radiation shielding for workers at McArthur River.

6.1.3 Raise Boring

ln circumstances where raise boring would be the most appropriate ore extraction method, pilot holes would be drilled from an upper chamber downward through the ore, to intersect a production level below the ore. A large diameter cutting head would then be attached to the drill and pulled upward to create larger diameter excavations. As with boxhole boring, ore and waste extraction would occur solely through the action of drilling, without requiring the use of explosives. Ore and waste rock cuttings produced by drilling would drop to the lower production drift where they would be crushed, mixed with water, and transported as a slurry to the surface through dedicated pipelines. Drilling and crushing sites as well as the production drift would be located within non-mineralized rock, remote from the ore.

I feel we have got to realize what we are talking about. We are talking about developing uranium with 20 to 30 percent ore grades.

Maisie Shiell, Transcript of McArthur River Public Hearings, Saskatoon, Saskatchewan, September 9, 1996, p. 27.

As with boxhole boring, radiation protection would be enhanced by full enclosure of ore in the extraction, crushing, and piping circuits and by the direct venting of air through a secondary ventilation system. Mine stability would be improved by the use of small excavation spans and the rapid backfilling of excavated boreholes.

When the area above ore zones is composed of structurally competent rock suitable for the development of upper chambers for drilling sites, raise boring would be an acceptable extraction technique for mining McArthur River ore.

6.1.4 Remote Boxhole Stoping

Remote boxhole stoping would combine boxhole boring, from production drifts in non-mineralized basement rock below ore zones, and blasthole mining. As with conventional boxhole boring, fixed-diameter boxholes would be drilled upward from a lower drilling level to the top of the ore zone. The boxhole drilling head would then be retracted downward and blast holes would be drilled from an upper level to intersect the boxholes at an angle. Portions of each blasthole would be loaded with explosives, which would be detonated to fragment the adjacent ore. The broken ore would fall into the boxholes and pass to a lower production level through sealed chutes and pipes where it would be crushed, mixed with water, and transported to surface as a slurry.

This mining method offers safety measures similar to those described for boxhole boring to enhance radiation protection and mine stability. However, the use of explosives to fragment the ore would increase the potential for endangering nearby mechanical equipment, and the stability of the surrounding rock. Consequently, the proponent does not plan to use remote boxhole stoping in ore zones requiring ground freezing where blasting might damage freeze pipes. Therefore, remote boxhole stoping would only be suitable in ore zones where grouting, rather than ground freezing, will be used to reduce water inflow.

6.2 Liquid Effluent

The process water necessary for mine operation would be obtained from shaft inflow sources, thereby reducing the demand on nearby Toby Lake.

Tests done during the exploration program demonstrated that grouting significantly reduced the quantities of water inflow around the shaft. Also, very low inflow rates were observed in basement rock excavation sites.³⁴ Should zones of high water inflow be encountered during the development of production drifts, the proponent anticipates that grouting would provide sufficient control. The maximum quantities of mine water expected to be pumped to surface for treatment would be approximately 4,800 m³/day. Mine water pumping capacity, estimated at 16,400 m³/day, would, therefore, be more than adequate to handle normal and overflow dewatering needs.³⁵

Underground pretreatment of mine water during mine trials involved the use of aeration and chlorination at the sump.³⁶ This pretreatment resulted in a reduction in radon and lead-21 0 contamination in collected water. Application of similar techniques during production mining would result in a reduction in the amount of treatment required to mitigate effluent water impacts on the surface.

The mine water treatment plant would be designed to process water at rates of approximately 17,280 m³/day, using accepted industry procedures.³⁷ Treated water would be held in three storage ponds for testing prior to release into the muskeg adjacent to Boomerang Lake, near its outlet.

Water and sediment quality data collected during the 1993-1995 exploration phase of the project generally reflect those predicted using the IMPACT model³⁸ in the original environmental impact statement. From this correlation it is reasonable to assume that treated mine water discharged would have a minor effect on surface water quality, with Saskatchewan Surface Water Quality Objectives (SSWQO) being met near the point of release. However, as noted by Environment Canada and others, the SSWQO were developed to address water quality conditions in southern prairie water, and may not be suitable for assessing northern water quality. The development of alternative standards that would be more appropriate for assessing northern site conditions is required. The panel agrees with Environment Canada that, “Site-specific water quality objectives should be proposed which are some rational combination of SSWQO, CWQG, baseline water quality conditions, and scientific requirements for protecting aquatic ecosystems.”³⁹

Hydrogeological modelling indicates a potential for a lowering of the water table by up to 8 m in the area of the mine, with a cone of depression extending to Toby Lake where the water level could drop by 1 m.⁴⁰ This cone of depression would not be fully developed for several years, well after all four production areas are active. Thus, the actual lowering of the water table could be monitored. The impact of lowered water levels on Toby Lake could be mitigated by discharging the treated mine water into that watershed instead of into the muskeg adjacent to Boomerang Lake. This proposal is acceptable, provided an alternative source of potable water is found, and provided the proposed site of effluent discharge is monitored to obtain baseline information. Treated effluent released into the Toby Lake watershed would flow directly into Boomerang Lake, with minimal change in the overall impact.

6.3 Waste Rock Disposal

The proponent predicts that 215,000 tonnes of mineralized waste and 900,000 tonnes of nonmineralized waste would be produced by the McArthur River Project. Waste would be characterized as mineralized waste if it contained between 0.03% and 0.14% U₃O₈, or if it contained less than 0.03% U₃O₈ but was potentially acid-generating. Cameco proposes to store mineralized waste on a lined pad designed to retain fluids for pumping to the water treatment facility. At the time of mine decommissioning, mineralized waste would be disposed of either underground or in the tailings management facility at Key Lake. Nonmineralized waste rock, defined as waste containing less than 0.03% U₃O₈ with no potential to generate acid, would be placed on an unlined pad and used to manufacture aggregate material for backfill or road construction. Any non-mineralized waste rock not so utilized would remain on surface and be decommissioned in place.

Concerns regarding waste rock disposal were expressed by members of the public, by Environment Canada,⁴¹ by the Atomic Energy Control Board,⁴² and by the Government of Saskatchewan.⁴³ Of principal concern is the practical difficulty of accurately identifying and segregating mineralized from non-mineralized waste, in a timely fashion, on the basis of chemical or radiological testing. The procedures described by the proponents for assessing and identifying the uranium ore grade and acid-generating characteristics of rock materials⁴⁴ may not be sufficiently rapid to prevent unintentional mixing of mineralized and non-mineralized waste in the stockpile. Should this happen, contaminated leachate might be released from the waste rock stored on unlined pads. If such releases occurred during the mining phase, facilities would still be present for water treatment; however, if the contaminated leachate is released following decommissioning, the water treatment plant would no longer be operative. For this reason, it is imperative that the proponent demonstrate a satisfactory method for differentiating between mineralized and non-mineralized waste rock before mining starts. If this cannot be done, all waste rock pads should be lined and provided with seepage controls.

The Department... continues to be concerned over the proposed surface disposal of waste rock at McArthur River, given the potential for perpetual contaminated seepage...

Dr. Dennis Lawson, Transcript of McArthur River Public Hearings, Regina, Saskatchewan, September 6, 1996, p. 38.

6.4 Conclusions and Recommendations

The mining procedures proposed for the McArthur River Project are well developed and likely achievable by current industry standards. The shielding of production galleries from the ore body by several metres of barren rock; the use of non-entry mining methods; the use of freezing and/or grouting methods to eliminate or reduce water inflow; the venting of potentially radon-laden air through secondary ventilation networks; and the use of sealed ore slurry transport methods to remove ore from the mine should provide adequate shielding for underground workers from exposure to radioactive ore and contaminated water or air.

The decision to release treated mine water into the muskeg adjacent to Boomerang Lake is an acceptable procedure.

The development of site-specific water quality objectives similar to those described by Environment Canada is recommended. These should combine elements of the Saskatchewan Surface Water Quality Objectives and other water quality standards to provide standards more appropriate to the protection of the aquatic ecosystems found in northern Saskatchewan.

We recommend that more rigorous rock screening procedures be developed to improve the accuracy and efficiency of separating mineralized from non-mineralized waste rock. If a fail-safe method for distinguishing between mineralized and non-mineralized waste cannot be demonstrated, non-mineralized waste pads should be lined to provide containment of contaminants that might result from the imprecise screening of waste rock, and the subsequent leachate.

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³² McArthur River Project Environmental Impact Statement, Addendum, Cameco Corporation, June, 1996, Section 2.2.

³³ McArthur River Project Environmental Impact Statement, Main Document, Cameco Corporation, 1995, p. 2.3.18.

³⁴ McArthur River Project Environmental Impact Statement, Main Document, Cameco Corporation, October, 1995, p. 2.3.18.

³⁵ Ibid, p. 2.3.31.

³⁶ Ibid, p. 2.3.32.

³⁷ Ibid, p.2.4.2.

³⁸ McArthur River Project Environmental Impact Statement, Addendum, Cameco Corporation, June, 1996, pp. 2.1.2 - 2.1.6.

³⁹ Environment Canada (Prairie and Northern Region), Submission to the McArthur River Uranium Project Public Hearings, Regina, Saskatchewan, September 6, 1996, p. 32.

⁴⁰ McArthur River Project Environmental Impact Statement, Addendum, Cameco Corporation, June 1996, Section 3.3.

⁴¹ Ibid, p. 46.

⁴² Atomic Energy Control Board, Submission to the McArthur River Uranium Project Public Hearings, La Ronge, Saskatchewan, October 1, 1996, p. 4.

⁴³ Government of Saskatchewan, Submission to the Cigar Lake and McArthur River Projects Public Hearings, La Ronge, Saskatchewan, October 1, 1996, p. 2.

⁴⁴ McArthur River Project Environmental Impact Statement, Main Document, Cameco Corporation, October, 1995, pp. 2.3.28-2.3.30.