Panel Report

The primary technical challenge addressed in the Cigar Lake EIS is the development of mining methods which allow for the safe extraction of high-grade ore, without excessive environmental damage. During its test mining program, CLMC evaluated various remote-entry mining techniques that would permit safe and efficient mining. Because the ground surrounding the deposit is largely incompetent, creative approaches for improving ground stability were also evaluated. These innovative approaches have enhanced the technical capabilities of the industry to mine similar problematic ores.

This chapter provides a brief description of the mining methods that the CLMC proposes to use, and the environmental and safety concerns associated with them.

5.1 Mining Methods

The Cigar Lake ore body is located between 410 and 450 m below the surface in very incompetent ground at the unconformity between metamorphic basement rocks and the overlying sandstone rocks. Ground freezing, originating from drifts in basement rock below the ore body, would be used to enhance the competence of the rock associated with the ore, and to restrict water flow into and through the mine excavations. Mining by non-entry methods would be controlled from production drifts, also located below the ore body.

The underground facilities of the mine would be serviced by three shafts. The existing test mine shaft would provide access to the freeze and production drifts. Two additional shafts, through which ventilating air would be exhausted and emergency egress could occur, would be developed in the future.

The mining methods proposed by CLMC have been designed to reduce water inflow, preclude direct exposure of workers to the high-grade uranium ore body, and improve rock support capabilities. The EIS describes mining methods compatible with the variable geometry of the Cigar Lake ore deposit, and the methods that would be required to control water inflow.

The techniques proposed to mine the ore are boxhole boring and jet boring, both of which are remote, non-entry mining methods. Ore-handling processes, including transport of ore from the excavation sites, crushing of the ore on the production level, and pumping of ore slurry to surface, would take place in shielded conduits that protect workers from radiation at all times. The intent of the proposed mining and ore-handling techniques is to minimize worker exposure to the high-grade ore being recovered.

As mining progresses, ore and waste excavations would be backfilled using a high-strength concrete mix designed to cure under freezing conditions. This concrete fill material would provide structural support within the ore body and limit the flow of water through the mining horizon as ore extraction proceeds.

For drift development, the CLMC plans to use conventional drilling and blasting methods, as well as conventional ground support techniques, where the ground is competent. Where rock is less competent, CLMC proposes to use mechanized procedures, such as the New Austrian Tunnelling Method (NATM) and the Shielded Mine Development System (SMDS), for development.

5.1.1 The New Austrian Tunnelling Method and the Shielded Mine Development System

From information collected during underground test mining and diamond drilling from surface, CLMC has identified eight distinct geotechnical zones within and about the ore body. Three of these zones exhibit rock mass conditions that are characterized as being fair to extremely poor, and include significant zones of incompetent rock, squeezing clay, unconsolidated sand and friable sandstone. Poor rock mass conditions are typical within the altered basement rock below the Cigar Lake ore body where the proponent plans to develop the freeze and production drifts. Excavations created in these rock zones would require substantial support during and after excavation, and could not be developed effectively using traditional drilling and blasting techniques. [ The Cigar Lake Project, Response to Request for Additional Information, Cigar Lake Mining Corporation, March, 1996, pp. 2-5 to 2-7 and Figure 2.1.1.5.]

Due to the very poor ground conditions below the orebody, in which the conventional drill and blast method allowed limited success, it was necessary to introduce the New Austrian Tunnelling Method.

B. Schmitke, Cigar Lake Mining Corporation, Transcript of Cigar Lake Public Hearings, Saskatoon, Saskatchewan, September 10, 1996, p. 2.

Based on test mine experience, the proponent plans to use the NATM and SMDS techniques for excavation where the ground is not sufficiently competent to permit conventional mining operations. Both techniques employ the principles of mechanized rock excavation within shielded covers, including the pre-installation of partial support and the rapid deployment of long-term rock support after excavation. These techniques have been designed to increase worker safety during rock excavation, and to reduce the time necessary to place rock support following excavation. Although not technologically innovative in terms of rock excavation science, the proposed methods are considered state-of-the-art in their ability to provide safe and effective mine development and support. CLMC would use the NATM technique in approximately 10 per cent, the SMDS technique for about 60 per cent, and conventional techniques for the remaining 30 per cent of underground excavations.

All excavations would be lined with concrete or shotcrete for rock support. To reduce radiation exposure, the excavations would be sloped to convey seepage water and inadvertent ore slurry spills away from workers.

5.1.2 Ground Freezing

From test mine data, the ore body is known to exhibit poor to fair rock mass quality, low strength, high porosity and high water saturation characteristics. Groundwater sampling from drill holes in the sandstone and altered sandstone formations indicated the potential for groundwater inflows of 2700 m³/hr during mining. Within basement rocks, low hydraulic conductivities were found, yielding significantly lower water inflow rates. CLMC expressed several concerns for mining within the ore body, including:

• the support of the weak rock associated with the ore body;
• the potential for a large inrush of water while mining the ore; and
• the containment of the ore cuttings and any associated water to minimize the potential for radiation exposure. [ The Cigar Lake Project Environmental Impact Statement, Main Document, Cigar Lake Mining Corporation, July, 1995, p. 3-32.]

During test mining, CLMC evaluated the ability of various techniques to address these concerns. Conventional rock excavation and support techniques, including grouting, proved to be less effective than ground freezing for improving mine stability and limiting the inflow of radon-laden water. In contrast, rock preconditioning, using curtain grouting and ground freezing, reduced inflow rates to approximately 20 m³/hr during test mining. Based on these positive test mine results and the knowledge that ground freezing applications have been used as standard operating procedures in many mines, including potash operations in southern Saskatchewan, CLMC proposes to apply this technology during mine development.

Ground freezing would be achieved by circulating a cold brine solution through freeze pipes drilled upwards through the ore from horizontal galleries excavated below the ore body. It is anticipated that the ore body would be frozen over the entire width and height of the ore zone. In addition, rock zones lying between the freeze level and the ore body would be frozen and therefore structurally reinforced.

The containment of ore cuttings and associated water would be addressed by installation of a preventer on the jet boring machine. This preventer would divert broken ore and water away from workers and into a crusher. [B. Schmitke, Presentation to Public Hearings, Saskatoon, Saskatchewan, September 10, 1996, pp. 2 and 9.]

The presence of approximately 88,000 m of exploration drill holes, [The Cigar Lake Environmental Impact Statement, Main Document, Cigar Lake Mining corporation, July, 1995, p. 3-5.] and the possible addition of 70,000 m more (30,000 m required for the complete delineation of the ore body, [Ibid, p. 3-18.] and 40,000 m of geotechnical core and rotary drilling [Ibid, p. 3-24.] ) are cause for concern. A significant number of the completed and planned drill holes encroach upon the ore zones, providing pathways for radon-laden water or air into occupied excavations. Such flow could occur wherever ungrouted holes are intercepted or ground freezing is incomplete. To protect against the intrusion of water or air, all bore holes that intersect underground workings should be sealed systematically. The proponent should not rely only on ground freezing or area grouting to seal the bore holes.

5.1.3 Jet Boring

Based on test mining results, CLMC proposes to use jet boring as its primary mining method. Ore removal by jet boring involves insertion of a jetting head through a hole that has been drilled from the production drift to the top of the ore body. Water under high pressure is then pumped through the jet while the head is rotated, cutting the frozen ore and washing it down the hole. The jet is slowly lowered, eventually creating a cylindrical excavation in the ore about 2 m in diameter. The broken ore and water washing down the hole would be diverted to a crusher by use of a preventer. In this way, workers in the production drift are protected from direct contact with the highly radioactive ore. Test mine experience indicates that this process will recover about 95 per cent of the ore. [The Cigar Lake Project, Response to Request for Additional Information, Cigar Lake Mining Corporation, March, 1996, Table 2.3.1.1.]

After ore extraction, the bore holes would be filled with a high-strength concrete mixture to maintain the structural integrity of the frozen ore zone during mining. At the conclusion of mining, and after thawing of the rock, the competence of these zones is expected to be better than that of the originally intact ore. Replacement of weak, friable and saturated ore by high-strength concrete should reinforce the existing rock structure.

5.1.4 Boxhole Boring

The proposed boxhole boring technique, which would be used to extract about 5 per cent of the ore, requires dry excavation of holes 1.5 m in diameter. Drilled vertically upward from the production drifts, the holes would pass through inert basement rock and into the ore above. The extraction of ore and accompanying waste rock would occur solely through the action of drilling, without the use of explosives to fracture the rock. As the rock is drilled, it would fall through the excavated borehole into sealed chutes and containers, located within the production drifts.

The mining industry has safely used similar remotely-operated boxhole boring techniques for decades. At Cigar Lake, however, it would be necessary to modify boxhole boring by fully enclosing the extraction chutes, and to provide remote transport of slurried ore to surface. This approach is required to protect workers on the production levels from contact with the highly radioactive ore. Following ore extraction, the relatively small boxhole excavations would be rapidly backfilled with cement to maintain rock stability.

Although boxhole boring was successfully demonstrated during underground mining trials at the Cigar Lake test mine, it would be a secondary option for mining the ore body. It is less attractive than jet boring because of potential dust problems and excessive waste rock generation.

5.2 Liquid Effluent

5.2.1 Water Conservation

As noted in Section 5.1.2, the application of grouting and ground freezing is expected to substantially reduce the flow of water into the mine. Residual inflow is expected to occur at a rate of 30 m³/hr. To minimize the amount of mine water requiring treatment, CLMC plans to recirculate process water at the rate of approximately 20 m³/hr into the underground jet boring operations. This recirculated volume would account for approximately 40 per cent of the total average water volume necessary for jet boring and slurry preparation, and would reduce effluent treatment requirements accordingly.

5.2.2 Primary Treatment

Any process water which is not reused would be treated in the primary water treatment facility on surface. The primary treatment facility, which would process contaminated mine water, surface runoff and recycled water, is designed to handle water at an average rate of 100 m³/hr. However, under conditions of excessive inflow, this facility could be operated at a contingency rate of 700 m³/hr.

5.2.3 Secondary Treatment

A secondary water treatment facility would be used for final polishing of effluent from the primary treatment facility, as well as for surface runoff water, prior to release into the environment. Under mine operating conditions, approximately 39.5 m³/hr of primary treatment effluent would flow through the secondary treatment facility, which would have the capability to handle quantities up to 825 m³/hr. Final release of effluent to the environment is planned at the rate of approximately 28.5 m³/hr. Release would be into a muskeg area located upstream from Aline Lake. [ The Cigar Lake Project Environmental Impact Statement, Response to Request for Additional Information, Cigar Lake Mining Corporation, March, 1996, Figure 1.3.1.1.]

Following secondary treatment, it is predicted that the effluent will meet Saskatchewan Surface Water Quality Objectives.

5.2.4 Modelling of Environmental Loadings

The proponent reported the results of modelling exercises that it used to predict environmental loadings due to effluent release for average- and worst-case test mine conditions. For the worst-case scenario, modelling predicted that the contaminant concentrations in Aline Lake would not exceed Saskatchewan Surface Water Quality Objectives (SSWQO) during the proposed 41-year operating life of the Cigar Lake mine. [The Cigar Lake Project, Response to Request for Additional Information, Cigar Lake Mining Corporation, March, 1996, pp. 1-53 and 1-54.] SERM also reported modelling studies, using conservative arsenic effluent concentrations, which indicated that water quality conditions within Aline Lake would be at or below the limits of the SSWQO.

Should mine water concentrations of heavy metals, specifically arsenic and molybdenum, prove to be higher than predicted, CLMC has proposed contingency treatment plans. Such remediation would involve primary treatment to precipitate contaminants within settling ponds, prior to secondary water treatment.

CLMC should be required to monitor all toxic chemicals and heavy metal contaminants (not just arsenic and molybdenum), which might impact downstream water quality conditions. Site-specific water quality objectives should be developed for the Cigar Lake site and, if contaminant concentrations are found to be above those objectives, appropriate mitigative measures should be implemented.

5.2.5 The Need for Additional Research

The mine water treatment capabilities, as described in the EIS, appear to be adequate. We concur with the conclusions stated by Saskatchewan Environment and Resource Management:

Mine water treatment at the Cigar Lake site would be conducted using existing and proven treatment technologies. Treatment technologies are such that all metal contaminants and radionuclides can be removed to acceptable levels in the effluents. [Saskatchewan Environment and Resource Management, Submission to Cigar Lake Public Hearings, Regina, Saskatchewan, September 4, 1996, pp. 21-22.]

We also agree with SERM's conclusion that additional research is required into methods that could be used to further reduce the environmental impacts resulting from the release of effluent at the Cigar Lake mine site. The current practices of aeration and chlorination in underground sumps to disperse radon and reduce lead-210 dissolution are the minimal pretreatment processes which should occur. As improved treatment technologies become available, they should be incorporated expeditiously.

In addition, research should be done to identify appropriate site-specific water quality objectives. The SSWQO currently in use were developed primarily for the southern part of the province where the total dissolved solids in natural water systems are typically much higher than in northern Saskatchewan. Site-specific objectives should reflect this difference in existing natural conditions.

5.3 Conclusions and Recommendations

The panel is satisfied that the proponent has adequately addressed the technical challenges of mining the high-grade Cigar Lake ore. Non-entry mining methods would provide protection from radiation exposure in three ways: both jet boring and boxhole boring methods, controlled from production galleries separated from the ore body by about 15 m of rock, would shield workers from the highly radioactive ore body; the use of sealed conduits for transporting slurried ore within the mine and to surface would reduce the extent of radiation exposure from the mined ore; and, ground freezing, limiting the incursion of radioactive water flows into occupied mine excavations, would protect workers from contact with radon and radon progeny.

All exploration, development and production drill holes should be sealed to prevent inflow of potentially contaminated air or water into under-ground work sites.

Site-specific water quality objectives reflecting natural conditions in northern water bodies should be developed for the Cigar Lake mine. CLMC should develop monitoring and treatment contingencies for all chemical and heavy metal contaminants (not just arsenic and molybdenum) which may potentially impact downstream water quality conditions. If monitoring of effluent indicates concentrations above the site-specific water quality objectives, mitigative measures should be implemented.

Additional research is recommended for the development of methods to further reduce the environmental impacts resulting from effluent releases.