(last updated 30 Jul 1996)
Radioactive Waste Management Associates
October 27, 1995
(reproduced here with permission)
526 W. 26th Street Rm.517, New York, NY 10001, USA
Tel. +1-212-620-0526, Fax: +1-212-620-0518, E-Mail: email@example.com
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Figure 3 shows a schematic diagram of the proposed operations. Both the Midwest and Cigar Lake mines will be underground, and ground water will tend to flow into them. This water will be pumped out, and much of it will be used for mining operations. Each site will have a water treatment plant for liquid wastes, and treated effluent will be discharged into local watersheds. The mines will also produce large volumes of waste rock, of which some will be replaced in the mines, and some will remain in above-ground piles or be dumped into a nearby lake. Ore will be prepared and trucked to the McClean Lake mill.
Following uranium extraction, mill tailings and other wastes are to be deposited into a pit, initially excavated to mine the JEB ore. Huge amounts of ground water will be pumped from perimeter wells to `dewater' the JEB pit, causing a cone of depression in the water table surrounding the pit. The pumped water will be discharged to nearby Sink Lake, which will also receive effluent from the JEB water treatment plant (associated with the JEB pit and McClean Lake mill) and another water treatment plant associated with the McClean Lake and Sue mines. To avoid problems with dust, radon, and ice lenses, a 10-meter-deep pond will be maintained above the tailings. Water will also be pumped from below the tailings, to promote consolidation of the tailings and capture the escaping porewater. The tailings are supposed to become so dense that they are less permeable than the surrounding rock, so that ground water will not flow through them and carry away contamination. After milling ceases, decommissioning of the pit will involve installing a cover consisting of sandy materials, waste rock and soil.
The Midwest and Cigar Lake mining operations will have a major effect on the area's environment. The mines, mill, and pit will produce large amounts of wastewater, and even after treatment this water will contaminate the lakes into which it is discharged. Waste rock will be a source of arsenic, radium and radon contamination, and radon will emanate from the mill and the tailings facility as well. Pumping associated with the JEB pit will lower the water table enough to dry up or lower several nearby lakes, and plants and animals in fragile wetlands will die. Finally, over the long term the pit will remain a source of ground water contamination. All of these problems add to the cumulative effects of the region's other uranium mining operations. In this report, we detail the environmental effects which must be weighed in considering whether to approve the proposed mining operations. We also identify a number of unresolved issues which Cogema and the Cigar Lake Mining Corporation should address.
Most of these issues involve the JEB pit. It is not clear that all of the material intended for the pit will fit inside, and contingency plans for enlarging the pit are of doubtful value. Also, assertions that the tailings will be effectively isolated from the ground water may prove overly optimistic. Although most of the porewater escaping from the tailings is supposed to be captured in the pit's underdrain pump, porewater could also escape sideways, contaminating the ground water and the water pumped from the perimeter wells, which would then have to be treated. In addition, if pumping from the underdrain is impaired, the amount of water pumped from the pond above the tailings may have to increase. These problems would require that the JEB water treatment plant be enlarged, but contingency plans do not estimate the volumes that would need to be treated.
Decommissioning plans for the pit are especially problematic. Plans for installing the cover are vague and apparently do not take into account the effect of settling due to tailings consolidation. The frequency of ground water monitoring after the pit's closure is unspecified, and contingency plans for remediation in case of excessive ground water contamination are unconvincing. Also, water treatment will continue after the pit is closed, but the disposal of resulting sludges has not been addressed. Finally, estimates of the amount of radium leaching from the tailings are not conservative. We are also concerned that radon emanation may have been underestimated, and that ice could interfere with water treatment and effluent discharge.
The wastewater from Cigar Lake mine operations will be treated, and 28.5 m3/hour will be discharged to a muskeg bog southwest of the site. From the muskeg, it will drain into Aline Lake, and thence into Aline Creek, Seru Bay and Waterbury Lake. The intent is to meet the SSWQ Objectives in the center of Seru Bay, a huge body of water which will have a diluting effect on the effluent. It is expected that the muskeg bog will not be able to meet the SSWQO's until 5 years after closure, and that the bog sediments will tend to concentrate heavy metals and radionuclides.
At Midwest, water will be used for such mining operations as drilling and jet boring, ore handling, ore stockpile and paste preparation, and in the freeze and backfill plants. Recycled ground water from mine inflow will be the main source of industrial water. As needed, water from South McMahon Lake will be used as another industrial water source (see Fig.5). To reduce the volumes requiring treatment, treated water will be recycled as much as possible, and the ore zone will be frozen. Potable water will be trucked in from the nearby Points North facility. Waste rock will be stockpiled, with some rock to be returned to the underground mine, some to be dumped in the Sue C pit at the McClean Project site (see Fig.6), and some to remain near Mink Arm of South McMahon Lake.
The liquid wastes from Midwest operations, along with site run- off water, will go to a wastewater treatment plant at Midwest. The plant is intended to remove most of the radium, arsenic, and other radionuclides and metals from the wastewater and will be able to handle 6,000 m3/day. A surge pond will hold water before treatment, and three monitoring ponds will hold the treated effluent for testing before it is released to Mink Arm. Almost 39 million m3 of total discharge to Mink Arm can be expected from 1998-2009. These projections apparently assume that flow occurs from January to December in most years, although the EIS states elsewhere that mining at Midwest will take place only from May to October.
The ore that will be mined at Midwest has a very high uranium grade and is also rich in arsenic, nickel, and sulphate. The monthly mean concentrations of arsenic, copper, lead, nickel, total suspended solids, uranium, zinc, lead-210, and radium-226 predicted for Mink Arm are at the Saskatchewan Recommended Wastewater Quality Criteria limits. One can assume that on certain days the levels would be even higher. It should be noted that since Mink Arm is very shallow and has the lowest flushing rate in the area, the influx of highly contaminated wastewater will have a significant effect on aquatic life.
The JEB open pit mining is scheduled to begin in late 1995. Once mined out, JEB will be converted into a tailings facility, which will accept wastes from the McClean Project mines (McClean and Sue A, B, and C), Midwest and Cigar Lake over the life of the projects. Tailings will be deposited in the pit for 40 years, from 1997 to 2037, and various other wastes will also end up in the pit. Cogema hopes to avoid dust, radon and ice lens problems by keeping the tailings under a `pond,' which will be formed by the ground water flowing into the pit. Pond water will be pumped to maintain a depth of at least 5 m, with a preferred level of 10 m. Tailings placement will take place from a mobile floating barge. A ring of 29 perimeter wells around the pit will pump the local ground water to maintain their hydraulic head ~2m above the pond, so that all surrounding ground water flows toward the pit.
The `pervious surround' concept which had been proposed in earlier tailings disposal plans has been altered slightly in the current plan. Instead of lining the JEB pit with a sand layer to promote ground water movement around rather than through the tailings, this plan counters that the host rock itself will act as a `pervious surround envelope,' because the dense paste tailings will be less permeable than the host rock. Tailings consolidation will further reduce their permeability, and will be promoted by active pumping from an underdrain. During tailings placement, a 5-meter differential head will be maintained between the top of the pond water and the water being drawn out at the bottom, by manipulating water levels in pumping wells. This is intended to create a downward gradient through the tailings and capture any escaping pore water before it enters the ground water. The water level in the underdrain will rise gradually, as the thickness of tailings increases. The water pumped from the pond and underdrain will be treated at the JEB treatment plant. The perimeter well water will not be treated, unless it exceeds background levels of contaminants.
Pumping and removal of the local ground water will have several impacts. The pumping will create a cone of depression of about 1 to 2.5 km radius surrounding the JEB pit. This means that over this area, ground water will tend to flow toward the pit. The water table will be lowered in adjacent areas, decreasing lake elevations and meaning that `several lakes may become completely dewatered.' These would most likely be Pat, Fox, Wallace and Johannes Lakes. Since Pat Lake is the source of fresh water for the facility, dewatering could jeopardize the drinking water supply. Furthermore, because dewatering for the JEB area will last 42 years, fragile wetland habitats will be destroyed as organic layers become dried out and species are displaced. Once dewatering ends, reclamation is expected to take a long time.
In order to mitigate the effects of this much additional water on downstream ecosystems, Cogema will dam Sink Lake and release its contents gradually. Sink Lake will become a reservoir. Averaging over the 40 year duration of the project, a volume of water 6 times the natural volume of Sink Lake will be discharged into it each year. Because of the dam, the reservoir will hold 5 million m3 of water, over 12 times the lake's natural volume.
Despite water treatment efforts, water quality in Sink Lake will be poor. Cogema's EIS predicts that maximum mean monthly concentrations of the following constituents will exceed Saskatchewan Surface Water Quality Objectives: ammonia, arsenic, cadmium, nickel, selenium, total dissolved solids, zinc, and uranium. Lead and radium-226 are predicted to exceed the standards at the 95th percentile values of contamination. There are no Water Quality Objectives for molybdenum, sulphate, vanadium, lead-210, or thorium-230, but these contaminants will exceed background levels. Downstream lakes will also be contaminated. Predicted maximum mean concentrations of arsenic, cadmium, copper and nickel in Sink Lake sediments in the 16th year of McClean Lake/JEB operations will exceed `severe effect' levels.
Cogema assumes that the water from the perimeter wells around the JEB pit will not require treatment at all. If it does, due to its being contaminated with tailings pore water, the JEB treatment plant would have to be expanded. The emergency plan to manage larger than expected volumes of water involves expanding the existing minewater sedimentation pond, and adding tanks and clarifiers to the treatment plant. Cogema does not present an estimate of the additional volumes that might have to be accommodated, so it is difficult to evaluate whether the contingency plans are adequate. In addition, contaminated water would probably be released before the expansion of the treatment plant could be completed. Plans call for the ground water to be monitored only monthly or semi-annually during operations, and presumably the contingency plans would take some time to implement. Even with the necessary additional treatment capacity on-line, contamination of the ground water from the perimeter wells would increase the contamination of the Sink Lake reservoir, since as demonstrated above, treatment is not completely efficient.
At JEB, Cogema relies on two factors to isolate the contaminants in the tailings from the surrounding ground water. First, porewater flowing out of the tailings as they consolidate is supposed to be captured by pumping from the underdrain, and this pumping is supposed to promote further consolidation. Second, as the tailings consolidate, their permeability will supposedly drop to the point that ground water will flow around them rather than through them. The permeability of the tailings is estimated at 10-8 m/sec, some 10 to 1,000 times less than the rock surrounding the JEB pit.
However, consolidation may not occur as planned. Cogema's estimates of tailings density at different depths shows that the density decreases markedly at the depth of the sandstone aquifer. This indicates that the altered sandstone will still be conducting ground water into the pit, despite the perimeter dewatering wells' efforts, inhibiting consolidation. In addition, consolidation itself may impair the underdrain pumping operations, since it will become increasingly difficult to draw porewater down through the tailings. The sand filter beneath the tailings could also become plugged, and remedial or repair work beneath the pit would be impossible. If underdrain pumping operations fail, the tailings will consolidate less, making them more likely to release contamination over the long term and raising the possibility that not all of the material intended for the pit will fit. Any escaping porewater would not be captured as planned, and the perimeter wells and surrounding ground water would become contaminated.
Even if the underdrain operates as planned, another concern is whether the perimeter wells could draw water laterally out of the pit, bypassing the underdrain material. Tensional fractures associated with the pit-bounding faults have millimetric to centimetric openings, and the permeability of faulted, fractured sandstone in the JEB pit is ~10-5 m/sec, compared to 10-6 to 10-7 for intact sandstone. This means that the contaminated porewater that leaves the consolidating tailings will move 10 to 100 times more readily through the fractured rock zones. Two local faults intersect directly under the pit, and the contaminant plumes as modeled by Cogema do indeed tend to travel outward along those fault zones, over time. Two zones of increased hydraulic conductivity, one 60 m wide, trending NW-SE and the other 30 m wide and trending SW-NE will later become directions of preferred ground water flow, according to Cogema's application of the MODFLOW program.
`Consolidation flows' (the highly-contaminated water coming out of the tailings paste) are estimated to be 1 million m3 over the operating period and another 1 million m3 in the following 20 years. Cogema's MODFLOW simulations of contaminant transport `predict increasing concentrations of all species in the pumped [perimeter well] water after 17 months of pumping.' Cogema postulates that `increased pumping rates or non-uniform pumping of perimeter wells during dewatering' could account for these contaminants escaping the JEB pit. It is clear that the escape of contaminants from the pit will take place to some degree, and that these will mix with uncontaminated regional ground water. A series of figures shows the development of plumes of sulphate, radium-226, arsenic and molybdenum in the sandstone and drift units. The plumes move outward horizontally along fault zones in the sandstone, and vertically upward through drift to Fox and Pat Lakes. It should be noted that fresh water will be pumped from Pat Lake for use at the mill and as potable water for the camp.
Over the long term, an estimated 20 m3/day of ground water will originate from the decommissioned tailings at JEB and enter the ground water system. This will include 2,580 MBq/yr of radium-226 and 86 kg/yr of arsenic. Since the JEB pit site is adjacent to a ground water divide, one can expect the JEB pit to be a long-term source of ground water contamination for anyone near the pit, and for more than one watershed area. Furthermore, because of the huge volume of effluent to be added to Sink Lake (whose normal average depth is only about 1.5 m), there could be some artificial recharge of ground water from Sink Lake. The increased lake recharge could have an influence on ground water flow patterns, pushing ground water toward the JEB pit and making it more difficult to avoid capturing regional ground water.
Estimated radium concentrations in pit leachate appear low, based on the radioactivity in the tailings. The Cigar Lake EIS estimates that the tailings paste will contain 850 Bq/g radium- 226, yet the tailings leachate is estimated to contain only 65- 190 Bq/L. That is, only 1 part in 10,000 in the tailings solid is assumed to enter liquid form. Compared to the EPA default value of 400 mL/g, the estimated amount of radium-226 that leaches off tailings into water is too low by a factor of 100- 300.
Tailings deposition will last for 40 years, beginning in 1997. By the end of tailings disposal, 3.26 million m3 of thickened paste tailings (before consolidation) will have been placed in the JEB pit, from the Midwest, Cigar Lake, and McClean Lake (JEB, Sue A, B and C, and McClean) ores combined. The radium-rich sludges from the Midwest, Cigar Lake, JEB, and Sue water treatment plants are to be sent to the JEB pit; however, they will be prepared at the mill and are apparently included in the estimated tailings volume. That leaves about 1.5 million m3 of volume for anything else to fit into the pit. Contaminated solid wastes, sewage, and residual contaminated materials from decommissioning will also be put into the pit. Huge volumes of waste rock are to be stored on the surface just east of the JEB pit. The southern end of this pile will include `special wastes' high in uranium, arsenic, nickel, and sulphur, that will generate acid and produce leachates with elevated metals and radionuclides. These special wastes, which weigh 565,000 tonnes, may also end up being put into the tailings pit.
The volumes of all these non-tailings materials are unspecified in the EIS. But since the 16.5 m underdrain thickness and a 20 m thick cover must also fit into the JEB pit, whether or not all these wastes will fit is cause for concern. Cigar Lake Corp. states that if, because of greater tonnages of ore or less tailings consolidation than planned, the pit needs to be bigger, its upper part would be enlarged to accommodate the additional volume. But in the years to come, as pit capacity is exceeded or if it starts to flood with greater-than-expected volumes of ground water, more excavation may be exceedingly difficult to accomplish without disrupting the pumping operations. We are concerned that the company's `contingency plans' may be scrapped in favor of dumping the JEB tailings into a nearby lake, such as Bizarre Lake, which will be used as a waste rock receptacle for the Cigar Lake mine.
Plans for the cover are quite unclear. The cover is supposed to be 20 m thick, but some sections of the EIS state only that the pit will be backfilled `to an elevation at or slightly above the existing ground surface.' The edges of the pit are at 448 m on one side and 460 m on the other. If in fact the top of the tailings reach elevation 447 m, the 3 m of drain material would not even fit into the lower side of the pit, and the cover would be considerably more than `slightly' elevated above ground, assuming it to be in fact 20 m thick. Furthermore, the effect of tailings consolidation on the elevation of the cover has not been considered. It is possible that the elevation of the top of the cover would drop below the water table, allowing a lake to form above the tailings. Among the disadvantages Cogema mentions about such a water cover are the potential for increased contaminant release into ponded water, the need for flood control to prevent release of this `unsuitable water,' the development of aquatic life in such water, and the potential for radon build-up under ice. Since the use of a water cover has been rejected for all of these reasons, the issue of cover settlement must be resolved.
Another issue of concern involves the treatment of the upper and lower drain water. During operations, radium-rich sludges from the water treatment plants are to be sent to the JEB pit after preparation at the mill. Once the pit is closed, sludges from continuing water treatment will have to be disposed of elsewhere. The disposal of these sludges has not been addressed.
While ground water monitoring plans are specified for the operations period, it is not clear what the sampling frequency will be after decommissioning. If after decommissioning higher-than-expected levels of contaminants are found in ground water downstream of the JEB pit, Cogema will undertake a `new hydrogeological assessment' to estimate if Saskatchewan surface water limits will be exceeded downstream. They have proposed the `hydraulic cage concept' to contain radioactive ground water. This would mean blasting a ring around the JEB pit, in which the `rubbled space' would create a zone of enhanced permeability to act as a conduit, diverting ground water around the tailings rather than through them. This plan is not convincing.
Cogema maintains that the ring of intact rock that would remain between the pit and the blasted, rubbled space would act as a low permeability `hydraulic cage' around the tailings. They project that the low permeability of this ring will reduce or eliminate the transport of contaminants from the tailings mass, and that instead ground water will flow along the rubbled zone and around the tailings rather than through them. But one should remember that the ring of rock around the pit does not have any such low permeability. In fact, Cogema's whole `pervious surround' notion relies on the rock surrounding the pit having a relatively higher hydraulic conductivity. Ground water in the rock surrounding the pit is conducted primarily through fractures. The explosive charges that will create the rubbled zone could open up some existing fractures even more, and increase ground water flow away from the tailings mass. Furthermore, the `hydraulic cage' blasting program is to be initiated when high levels of ground water contamination have already been able to escape from the pit and are detected downstream, i.e. when the `pervious surround envelope' has failed. If downstream contamination is detected soon after decommissioning, while water is still being pumped from the underdrain and overdrain materials at the JEB pit, the blasting itself could affect pumping and thus tailings consolidation. The EIS also does not describe subsequent ground water monitoring both near the pit and further downstream, to check the effectiveness of the `hydraulic cage.'
The operators of each of these sites rely on dilution downstream to dissipate the effects of their operations on surface water quality. The Cigar Lake EIS summarizes which water bodies will receive cumulative impact from mining properties as follows. Wollaston Lake receives input from the Key Lake, McClean and Rabbit Lake project sites. Hatchet Lake receives a portion of the outflow from Wollaston Lake as well as input from the Midwest project site. Finally, Black Lake receives the outflow from Hatchet Lake via the Fond du Lac River and inputs from the Cigar Lake and McArthur River sites. The Cigar Lake Mining Company finds that none of these downstream lakes will be significantly polluted. However, the assessment fails to account for the increasing risk of accidents or `excursions' as the overall level of mining activity increases. It also assumes that it is acceptable to continue to add to the number of small, upstream lakes that each exceed water quality standards.
Air emissions can also have a cumulative effect. Radon and the radioactive particles into which it decays are concentrated locally, but they do become distributed in the Northern Hemisphere atmosphere. There they add to the background dose of radiation affecting everyone's health. Ground water contamination can be viewed similarly. Residents of the area around Waterbury Lake and Wollaston Lake will be affected by environmental releases from several nearby mining sites, and the cumulative effects of ground water contamination will be of particular concern for them.
Uranium milling will release particulates into the air, and radon will emanate from the waste rock and tailings. Huge piles of waste rock will be left on the ground surface, and at the Cigar Lake site, waste rock will be bulldozed into Bizarre Lake and will eventually occupy much of the lake's volume. Because of heavy metals leaching out of this waste rock, arsenic levels will exceed regulatory limits just 20 years after operations begin. Several other lakes will be drained dry as ground water is pumped from around the JEB pit.
The uranium ores contain large amounts of radium-226, which will be concentrated throughout milling and disposal operations and will ultimately be sent to the JEB pit. Since radium-226 is especially mobile in surface water and ground water, the migration of radium-226 away from the tailings pit is of particular concern. Contamination from the tailings pit will eventually escape and enter the local ground water system. Cogema predicts that plumes of sulphate, radium-226, arsenic and molybdenum will develop around the pit. The plumes will move outward and eventually reach at least as far as Fox and Pat Lakes. With the operators of several proposed and operating sites each relying on downstream dilution to dissipate the effects of their particular operation on local surface water, ground water and air, the cumulative effect of regional mining activities is another important concern. All of these environmental impacts must be weighed in deciding whether to approve the Midwest and Cigar Lake proposals.
In addition, we have identified a number of unresolved issues, particularly with regard to plans for the JEB tailings pit. The following issues should be addressed before any decision is made to allow the proposed operations to begin.
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