British Columbia Mine Reclamation Symposium

Capillary break cover design at Lorado mill tailings site Tong, Alvin; Miskolczi, Iozsef; Allen, Dianne; Wilson, Ian; Rykaart, Maritz 2014

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  CAPILLARY BREAK COVER DESIGN AT LORADO MILL TAILINGS SITE  Alvin Tong, PEng1  Iozsef Miskolczi, PEng1 Dianne Allen2 Ian Wilson2 Maritz Rykaart, PhD, PEng1  SRK Consulting (Canada) Inc.,Vancouver BC  Saskatoon Research Council Saskatoon, SK  ABSTRACT   The historical Lorado mill tailings site deposited uranium tailings within and adjacent to nearby Nero Lake. The remediation plans called for a capillary break tailings cover with in-lake water treatment to reduce radiation exposure from the tailings, limit tailings dust inhalation and acid generation, prevent efflorescent salts formation, and block tailings pore fluid uptake from vegetation. Detailed designs, including water and load balances were developed to establish appropriate in-lake water treatment design criteria and to set measurable load reduction targets for the cover efficiency. A borrow source investigation was carried out to confirm whether appropriate volumes of suitable cover materials were available for the proposed design. These studies showed original remediation plan assumptions were no longer valid. This paper will describe the engineering process that was followed to evaluate and ultimately adopt appropriate design criteria to ensure that realistic, site-wide closure objectives could be met. The authors will emphasize the importance of linking design criteria to measurable and achievable performance criteria that can be properly evaluated over the intended life of the design.  INTRODUCTION  The historical Lorado mill tailings site is located in Saskatchewan near Uranium City. The operation deposited uranium tailings within and adjacent to Nero Lake. As part of the overall site remediation plan, a capillary break cover for the tailings in conjunction with in-lake water treatment was identified to reduce the negative environmental effects of the site. The original objectives for the cover, as identified during the environmental assessment stage, were to reduce gamma and radon exposure, limiting inhalation of tailings dust, reduce tailings acid generation by preventing formation of efflorescent salts, and block uptake of tailings pore fluid into vegetation.  As part of the detailed engineering phase for the cover, a water and load balance was developed and a comprehensive borrow source investigation was carried out. The water and load balance was required to establish appropriate in-lake water treatment design criteria and to set measurable load reduction targets for the cover efficiency. The borrow source investigation was done to confirm whether appropriate volumes of suitable cover materials were available for the proposed design, specifically the coarse materials required for the capillary break. The outcomes of these studies concluded that  some of the original design assumptions that led to the proposed cover design and associated design criteria were no longer valid and more appropriate cover design criteria were warranted.   This paper describes the engineering assessment to develop quantifiable criteria for design. Each of the criteria is supported by detailed analyses, risk evaluation and reasoning. One of the main purposes of the   detailed assessment is to address and quantify identifiable variables by reducing the amount of assumptions and information gaps. The resulting parameters from the assessment would then become design criteria of the remediation design. The key engineering assessments included in this paper are water quality prediction, capillary break modeling, radiation attenuation, and water-cover assessment. There are other assessments completed for the cover design but are not described in this paper.   The authors will emphasize the importance of linking quantifiable design criteria to remediation objectives such that the success and performance of the cover can be properly measured over its intended design life.  BACKGROUND  In the 1950s uranium exploration and development boomed in the remote wilderness of northern Saskatchewan, resulting in the construction of three uranium mills and numerous uranium mines. The town of Uranium City, and a few other towns that no longer exist, developed in response to this activity. Interest in the area’s resources dropped off within a few years as the markets changed and richer deposits were found elsewhere. The mine and mill sites were abandoned with little or no decommissioning. It wasn’t until the 2000s that the provincial and federal governments took stock of the safety and environmental liabilities at these sites and made a commitment to deal with the risks they presented.   The historical Lorado uranium mill tailings site is one of these legacy sites. It is located 8 kilometers southwest of Uranium City, on the north shore of Lake Athabasca. The mill operated from 1957 to 1960, processing 305,000 tonnes of low-grade uranium ore and producing somewhere between 190,000 to 344,000 cubic meters of tailings deposited near the shore of and in the western part of Nero Lake. Originally tailings were deposited on land upstream of Nero Lake and over time the tailings have reached land capacity and spilled out into the western portion of the lake. A natural isthmus southeast of the Nero Lake was built up with an earth berm (also known as the land bridge) to artificially raise the lake level during mill operation. The land bridge now separates Nero Lake with approximately 3 m of head above Beaverlodge Lake.  Although not abandoned, the Lorado site was neglected as ownership changed hands, ending up as property of Conwest Exploration Company Ltd. This company oversaw the demolition of the mill buildings in 1990. When the parent company of Encana Corporation bought Conwest, the Lorado site was transferred as well. Encana contracted Golder Associates in 2004 to characterize the site. Some measures were taken at that time to reduce safety and environmental risks. In 2007, the property was transferred to the Saskatchewan Government along with funds for the site remediation.  The Saskatchewan Research Council (SRC) was contracted to manage the remediation of the former Lorado uranium mill site as well as the Gunnar uranium mine and mill site and 35 legacy uranium mine and exploration sites in northern Saskatchewan. SRC submitted a proposal to remediate the Lorado site to the Saskatchewan Ministry of Environment and Canadian Nuclear Safety Commission (CNSC) in 2009, where it was determined that an environmental assessment was required under both the Saskatchewan Environmental Assessment Act and the Canadian Environmental Assessment Act.   SRC managed the development of a Risk Reduction Plan (RRP) and an Environmental Impact Statement (EIS) for the site. The project endpoints were developed with input from community members of   Uranium City and government regulators. The overall risk management goal identified for the Lorado site was that “risk reduction at the site has achieved an acceptable level of residual risk to human health, and to terrestrial ecological populations, and to the aquatic population of Hanson Bay and Beaverlodge Lake”. The specific objectives for a tailings cover were to reduce gamma and radon exposure, while limiting inhalation of tailings dust, reduce tailings acid generation and prevent formation of efflorescent salts, and block uptake of tailings pore fluid into vegetation (Golder 2013).  SRC obtained a Waste Nuclear Substance License from the CNSC to manage the Lorado site in 2013. SRK Consulting (Canada) Inc. was contracted in 2013 to begin the detailed design for the remediation. The detailed design included a borrow investigation, water quality prediction and treatment, radiation attenuation analyses, and hydrologic and hydraulic evaluations (SRK 2014). The project to remediate the historical Lorado site was approved by the provincial government in February 2014.  TAILINGS COVER DESIGN  General  The Lorado Tailings Cover is approximately 14 ha in size with tailings upwards of 6 m deep. The cover is divided into upland and beach cover. The upland is defined as the cover portion that is above normal water level (NWL), and beach cover is the portion that covers the tailings below the NWL. The cover extends beyond the exposed tailings, tying into the natural terrain to prevent ponding and to facilitate runoff. A small section of provincial Highway 962 would be raised to match the cover and organic debris islands would be constructed at strategic locations to create microclimate and moisture traps to encourage natural vegetation growth. Figure 1 shows the site general arrangement of Lorado Tailings Cover.    Source: SRK, 2014 Figure 1: Lorado Tailings Cover General Arrangement.     Following the objectives described in of the RRP and EIS, the preferred option must be technically feasible, practically constructible, and sustainable. The chosen option is to cover the surface tailings in situ with an engineered cover system that incorporates a capillary break type soil cover, including tailings within the immediate beach area and the adjacent affected soil and vegetation. Within this context, the specific mitigation objectives for the cover were to limit, as much as practical, formation of efflorescent salts, potential for inhalation and intake of tailings dusts and salts, limit surface water infiltration into the tailings to not greater than the uncovered state, and reduce gamma and radon exposure to background levels.   To ensure these objectives were met over the life of the cover, a set of quantifiable and measureable criteria for long-term monitoring was adopted. The comparison between the monitoring data and the criteria determines if the cover is performing as intended and is meeting the remediation objectives. Hence, a set of practical and measurable criteria are crucial to the Lorado—and for that matter any—remediation project.   Design Criteria  Specific decommissioning and closure objectives for the remediation were not explicitly measureable as they were descriptions of desired achievements. The CNSC typically requires environmental effects to be predicted with a 10,000 year time frame. While it was recognized that the Lorado tailings cover will remain in place for a very long period, its performance could not be credibly and practically measured in geological time lines. A 100 year design criterion was adopted that was consistent with industry best practices and provided a realistic time frame to monitor the cover performance and effectiveness.   The original intention of the RRP was to prevent formation of efflorescent salts to reduce the acidity loading into Nero Lake and potential of inhalation (Golder 2013). Nonetheless, further analysis (SRK 2013) demonstrated that the acidity load from the salts will not significantly affect the water quality in Nero Lake. With this information, the cover criteria was to practically minimize formation of efflorescent salts on the cover to no more than 10% of the original tailings surface at any time to satisfy reduction in inhalations. Details of the water quality prediction are discussed in the following section.   As a spot reading, gamma radiation and radon gas exposure limit measured 1 m above cover must be no greater than 2.5 µSv/hr (micro Sievert per hour) above background and no higher than 1.0 µSv/hr above background as an average measure over 1 ha. A zero-reading is not a practical target as the Uranium City areas natural environment background is above 0 µSv/hr average.   The effect of differential settlement on the cover could have an effect on the cover surface drainage pattern and a secondary effect on infiltration regime that may influence vegetation diversity. None of these effects are detrimental to the stated objectives of the cover, resulting in the tolerance of up to 0.3 m in the upland cover and 0.6 m in the beach cover.   The RRP stipulates that any tailings in water less than 3 m deep within Nero Lake should be covered. The rational is that in case of a land bridge failure where the water level between Nero and Beaverlodge Lake equalized, the tailings would not be exposed. The risk of failure could be mitigated with a regular geotechnical inspection. It was recommended that the in-water tailings cover be designed based on best   practices for tailings water cover design theory that stipulates a water cover must be thick enough to prevent re-suspension of tailings resulting from wave action and ice scour. The resulting evaluation concluded conservatively that only tailings in water depth less than 1.3 m, as measured from the normal water level (NWL), needed to be covered.   Water Quality Prediction  Previous studies (Golder 2013) confirm that runoff from the tailings area dissolves the efflorescent salt precipitate containing metals, acidity, and total dissolved solids and dissolves them into Nero Lake. This surface flow contributes towards 80% of the mass loading to Nero Lake, and there is enough acid inventory remaining in the tailings deposit to contribute acidity and metal loadings to Nero Lake for the long-term. An additional 16% of the mass loading is from surface runoff carrying material from the upper, oxidized tailings and 4% is from seepage through the deeper unoxidized tailings and from diffusion from lakebed tailings. The oxidized tailings contain very high acidity and metals; however, these metals are not as concentrated as in the efflorescent salts. The unoxidized tailings are potentially acid-generating, and have low pH and elevated contaminant concentrations.  Further analysis (SRK 2013) demonstrated that once Nero Lake is neutralized through in-situ treatment, the acidity load contributed by the uncovered tailings would not be sufficient to result in re-acidification, due to excess natural alkaline inflows to the lake. A sensitivity analysis confirmed construction of a tailings cover that results in a load reduction of 50 to 95% would have no discernible effect on the long-term Nero Lake water quality. As a result, there was no real requirement to specify either an infiltration or load reduction criteria for the cover system to ensure suitable water quality in Nero Lake over the long-term.  Preventing the unoxidized tailings from oxidizing by limiting oxygen ingress will not make a discernible difference in the acidity of the pore water and therefore constructing an oxygen limiting cover was not warranted.  As demonstrated (SRK 2013), reduction of surficial efflorescent salts formed through evapo-concentration will not result in measurable water quality benefits to Nero Lake; however, it will provide environmental benefits including, but not limited to, improving visual impact, providing an improved substrate for re-establishment of vegetation, and limiting exposure to terrestrial animals, birds, and aquatic life.  Capillary Break Cover Design  The initial screening of the soil cover options (Golder 2013) established that store-and-release or infiltration-reducing type covers could be suitable for the site based on the climate analysis. However, the objective of reducing pore water from the tailings that wick to the surface and precipitate contaminant salts was best mitigated by a capillary break cover.   A capillary break cover consists of a relatively coarse material adjacent to a layer of relatively fine grained material. The contrast in hydraulic properties between the coarse and the fine layers ensures that, under average conditions, water is retained in the fine layer, thus reducing the transfer of water between layers. In the case of Lorado, the cover objective was to prevent tailings pore water from rising through   the cover. The coarse layer was in this case placed directly over the fine-grained tailings. In effect, this is an inverted capillary break cover where suction developing in the coarse layer above should remain low enough to prevent water from being wicked up from the tailings. A top layer of well-graded till was also included in the design to provide a suitable substrate for vegetation.   Numerical modelling was carried out by Golder to confirm the suitability of the capillary break. The hydraulic properties of the sand used in the model were, however, not based on laboratory testing of samples collected from the actual available borrow sources at Lorado, but through empirical estimations using particle size distribution data (Golder 2013).  In 2013, SRK carried out a comprehensive borrow investigation (SRK 2014) to determine the quantity and location of the cover materials available on site. This included laboratory characterization of the physical and hydraulic properties of the soils to be used to construct the capillary break cover.   Although the gradation of the sand used by Golder (2013) was similar to the gradation obtained by SRK (2014), the estimated soil water characteristic curve (SWCC) was more favorable in terms of capillary break effect than the SWCC measured in the laboratory. Following SRK’s review of the obtained data, it became clear that the soils available on site may not be ideally suited for a capillary break type cover.   As a result, a more comprehensive performance prediction of the proposed cover concept was then carried out by SRK (2014), with focus on estimating the capillary rise afforded by the sands. The idea was that although the capillary break effect was marginal, the water retaining properties of the available sands were such that capillary rise to the surface (hence wicking of tailings pore water) could be minimized by a sufficiently thick sand layer.  Two distinct methods (i.e. analytical and numerical) were used to estimate the magnitude of capillary rise for the sand materials considered for covers. The methods are vastly different in terms of the concepts used to estimate capillary rise, but they yielded comparable results.  Analytical Approach  The analytical method used relied on a theoretical formulation using the surface tension of pure water and clean glass tubes as an analogue for interconnected pores in a soil column (Holtz and Kovacs, 1981). The advantage of this method is its flexibility in studying changes in capillary rise by adjusting the effective particle size of the material corresponding to the D10 particle fraction.   The theoretical capillary rise of the coarse and medium sand were in the range of 0.65 to 0.75 m, whereas the fine sand exhibited a much higher capillary rise at 2.5 m. Increasing the effective grain size of the fine sand by applying a fines cutoff (D10) at 0.13 mm reduced the theoretical capillary rise to 1.15 m. This method is excessively conservative because it does not take into account the complexity of the internal soil structure.  Numerical Approach The numerical model makes use of the Richards equation to predict the capillary rise in a state of equilibrium with the suction forces present in the soil. The mechanics of the SVFlux model relied on a specified SWCC fitted to a smooth curve using one of the built-in fitting methods. This method utilized   hydraulic properties obtained from laboratory testing; thus it provided representative actual behavior of the soils in the area.   The capillary rise predicted by the numerical model was approximately 0.5, 0.85, and 1.4 m for the coarse, medium, and fine sand, respectively.   Correlation of Analytical and Numerical Results The theoretical capillary rise values using the analytical methods were compared with those predicted by the numerical model (Table 1).   The reasonably good correlation (R2 = 0.91) between the estimated and predicted values allowed the approximation of the capillary rise predicted by the numerical model (considered more accurate than the analytical method) as a response to changes in the D10 particle fraction applied in the analytical model. Based on this correlation, changing the fines cutoff in the sand materials to obtain a D10 of 0.13 mm would result in a theoretical capillary rise of approximately 1.15 m in the analytical model that would in turn correspond to a capillary rise of about 1 m as predicted by the numerical model.   Table 1 Comparison of Capillary Rise Values  Material Estimated Value (Holtz and Kovacs 1981) Predicted Value (SV Flux) Fine Sand (SRK, WP-64)1 2.50 m 1.40 m Medium Sand (SRK, BB-88)1 0.65 m 0.85 m Coarse Sand (SRK, B1-15)1 0.75 m 0.50 m Modified Fine Sand (D10 = 0.13 mm) 1.15 m 1.001 m 1. Predicted based on the correlation graph  Final Cover Design  As an outcome of the model results, the initial upland cover design proposed by Golder (2013) consisting of 0.5 m of sand (capillary break layer) overlain by 0.5 m till (infiltration reduction layer) was refined to include a 1 m thick sand layer (capillary break) overlain by 0.25 m of till (vegetation substrate). A capillary break sand layer is only required over the upland dry tailings. The extended cover that was outside of tailings did not require the sand for capillary break and consisted of 1.25 m of till. Figure 2 shows the typical configuration of the Lorado tailings upland cover. The beach covers for the submerged tailings under NWL would be saturated at all times. The beach covers would be built to 0.2 m above NWL from sand for its constructability in water. Figure 3 shows the typical configuration of the Lorado tailings beach cover.      Source: SRK, 2014 Figure 2: Typical Section of Lorado Tailings Upland Cover   Source: SRK, 2014 Figure 3 Typical Section of Lorado Beach Cover  Radon and Radiation Attenuation Design The radon attenuation calculation was completed using the empirical formulation developed in the RAECOM model (Rogers and Nielson 1984). The model utilized effective diffusion coefficient and physical properties of the cover material (e.g., porosity and gravimetric water content (GWC)). Sensitivity analyses were completed to determine the effect on radon attenuation due to variations in physical material properties.   The results of the attenuation model are illustrated in Figure 4 and Figure 5. At assumed natural moisture contents, a 0.25 m thick till cover attenuated 65% radon and 1.0 m of sand attenuated 52%. Using these material attenuations and the high average radiation source of 14.4 µSv/hr recorded on site as conservative approach, the sand attenuated 52% (7.28 µSv/hr) of the initial source and the till then   attenuated 65% of the remaining radon (4.4 µSv/hr) to release 2.35 µSv/hr of radon immediately above the cover. The combined 1.25 m thick soil cover attenuated 83% of source radon. This meets the criterion of less than 2.5 µSv/hr of single spot reading as described in Section 0.    Source: SRK, 2014 Figure 4 Radon attenuation through a 1.0 m thick Sand material at Lorado with a porosity of 0.4.   Source: SRK, 2014 Figure 5 Radon attenuation through a 0.25 m thick Till material at Lorado with a porosity of 0.3.     The gamma ray exposure at the site was a result of radium-226 decay. Gamma ray attenuation was estimated using the empirical formulation based on an exponential decay function presented by Inyang et al. (2005). Sensitivity analysis was done on various material properties to determine their effect on gamma ray attenuation as shown in Figure 6. The results indicated that while gamma ray attenuation was sensitive to material properties, the attenuation was raised very rapidly with an increase in cover thickness; hence, the thickness of the cover is the governing factor. At 0.6 m cover thickness, 100% attenuation was achieved irrespective of cover properties.   Source: SRK, 2014 Figure 6 Gamma ray reduction as a function of soil material thickness.   Water Cover Design  The current accepted best practice in water cover design is documented in MEND (1998). According to this guideline, there are five processes that affect waterbed stability: seiche, seasonal lake turnover, currents, wave action, ice entrainment and scouring. For small tailings impoundments with less than 500 ha water surface area and water depth less than 10 m, only wave action, and ice entrainment and scouring should be considered. Nero Lake falls into the small impoundment category, with surface area of approximately 160 ha and depth less than 9 m.   For tailings re-suspension due to wave action, the Lorado design compared the MEND (1998) and Lawrence et al. (1991) methods using the US Army Corps of Engineer, Coastal Engineering Research Center (CERC 1984) theory to substitute the minimum water cover requirements. The wave action evaluation methods took into account the wind speed and direction, water surface fetch length, water 60657075808590951000 10 20 30 40 50 60 70 80 90 100GRI (%)Soil Cover Depth (cm)Case 1Case 2Case 3Case 4Case 5Case 6Case 7Case 8Case 9Case 10Case 11Case 12Case 13Case 14Case 15Case 16Case 17Case 18Case 19Case 20Case 21Case 22Case 23Case 24  depth, median particle size of sediment (MEND 1998), and threshold velocity (Lawrence et al. 1991). The MEND (1998) and Lawrence et al. (1991) methods are valid in deep water waves (ratio of water depth over wave length is less than 0.5) that do not apply to shallow Nero Lake conditions. To overcome this, the design substituted the appropriate shallow wave theory (CERC 1984) results into MEND (1998) and Lawrence et al. (1991) formulations to suit shallow conditions at Nero Lake. The water cover thicknesses calculated using modified shallow wave action theory are shown in  Table 2. Since the two empirical methods used were considered equally valid, the average of water thickness was used and resulted in a design cover thickness of 1.3 m.   Table 2 Water cover thickness comparison using deep and shallow water wave theory. Method Water cover thickness using shallow water wave results  Lawrence et al. (1991) 1.5 m MEND (1998) 1.1 m Final Lorado Water Cover Design 1.3 m  Ice entrainment occurs when the ice layer is sufficiently thick that it freezes to the lake bed, also known as grounded ice. As the ice thaws, sediment entrained in the ice is released into the water column. Ice scouring occurs where the underwater velocities increase in the restricted flow area due to ice grounding. MEND (1998) recommends the minimum water cover should be the ice thickness plus a 1.1 factor of safety. Nero Lake has no record of ice thickness so an ice growth model (US Army Corps of Engineers 2005) was used to predict the ice thickness. The model used daily average air temperature, a calibrated empirical factor () using Environment Canada data from four nearby sites (Fort Reliance, Fort Chipewyan, Cree Lake and Brochet). Using the climatic data set and statistical analysis, a maximum ice thickness associated with the 100 year recurrence interval was determined to be 1.06 m and with a 1.1 factor of safety equated to a thickness of 1.17 m.  Since the wave action requirement was greater than the ice entrainment, the final design adopted the 1.3 m water cover.   Other Cover Design Components  As far as practical, ponding on the dry tailings surface was avoided since it would result in saturation of the capillary break layer rendering it ineffective. The tailings surface would be re-graded and landscaped to allow overland sheet to flow toward two drainage channels and then to flow into Nero Lake. The channels were integrated into the tailings surface with appropriate thicknesses of cover materials to be placed on top. The final channel configuration had a 6 m wide base and side slopes of 3H:1V (horizontal to vertical). The overall drainage grade was variable between 0.5 to 1%. The channels were designed to convey a 24-hour, 1-in-200 year precipitation event at 1.57 m3/s.   Organic debris islands were designed as landform features to create a micro-climate to promote vegetation growth over the cover. The islands provide windbreaks, retain moisture from precipitation, trap seeds, and offer nutrients through decomposition. The organic debris is expected to decompose over time so they are not considered permanent features. Natural, local vegetation is expected to grow in place over   the long-term. Organic debris (e.g., tree slashing, tree stumps, and topsoil from borrow developments) would be placed in strategic configurations. A total of twenty-five organic debris islands configured approximately 1.5 m high and 5 m by 5 m at the base would be placed on the completed cover.   CONCLUSION  A post-construction geotechnical monitoring program will be implemented to confirm that the Lorado tailings cover is performing in accordance to design criteria and meeting remediation objective. These inspections are expected to be done by qualified personnel annually for three years following construction completion and every five years thereafter. A set of inspection parameters are laid out to measure cover physical properties and water quality.   It is acknowledged that while the tailings cover is a permanent structure and has a 100 year design life, there will be some degree of damage over time that will have to be address through planned maintenance activities. While regularly scheduled maintenance is not likely required, it is unrealistic to expect an earthen structure that supports natural vegetation to be maintenance free for its design duration. Over time, nature will reclaim the land as the design intended. Until such time, appropriate maintenance, repair work, and monitoring schedule will be prepared and subsequently executed by the appropriate qualified professionals. Areas requiring maintenance and repair will be identified from the monitoring program.   Every project has its unique criteria that influence the project’s acceptable risks, allowable ongoing maintenance, and overall remediation costs. While many remediation ideologies desire an end product with low remediation project costs, little or no risks and little or no post-construction management, it is unrealistic to expect all projects to meet all such criteria. Furthermore, with a post-construction monitoring program and on-demand maintenance requirements, the design criteria becomes more important to be realistically defined and kept as record for the life of the structure. A set of realistic, measureable design criteria can turn often descriptive remediation objectives into specific achievable targets by defining the functional limits of the structure, identifying the monitoring parameters needed to measure ongoing performance, and establishing clear maintenance repair targets.   REFERENCE  Inyang H., Wachsmuth P. et al, 2005, Simplified Design of Georadiological Barriers for Contaminated Sites. Practice Periodical of Hazardous, Toxic, and Radioactive Waste Management. 9, pp 253-262  Golder Associates, 2013, Environmental Impact Statement – Risk Reduction Plan for the Inactive Lorado Uranium Tailings Site, prepared for the Saskatchewan Research Council.   Holtz, R.D., and Kovacs, W.D., 1981, An Introduction to Geotechnical Engineering, Prentice-Hall Civil Engineering and Engineering Mechanics Series, Inglewood Cliffs, NJ, 733 p.  Rogers V., and Nielson K, 1984, Radon Attenuation Handbook for Uranium Mill Tailings Cover Design. NUREG/CR-3533, U.S. Nuclear Regulatory Commission, Washington, DC., 75 p + Appendices.    SRK Consulting (Canada) Inc., 2013, Nero Lake Acidity and Alkalinity Load Balance – Draft. SRK Project Number 4CS008.003,  21p + Appendices  SRK Consulting (Canada) Inc, 2014, Detailed Cover Design Report for the Lorado Mill Site Tailings and Peripheral Areas. SRK Project Number 4CS008.003, 33p + Appendices.  Komar, P.D. and Miller, M.C. 1975. On the comparison between the threshold of sediment motion under waves and unidirectional currents with a discussion of the practical evaluation of the threshold. Journal of Sedimentary Petrology, Vol.45, pp. 362-367.  Lawrence, G.A., et al., 1991. Wind-Wave-Induced Suspension of Mine Tailings in Disposal Ponds – A Case Study. Canadian Journal of Civil Engineering, Vol. 18, pp.1047-1053.  MEND 1998. Design guide for the subaqueous disposal of reactive tailings in constructed impoundments. Project 2.11.9, 87 p + Appendices.  U.S. Army Corps of Engineers. 2005. Review of Ice Processes and Properties. In: U.A. Engineers, Engineering and Design: Ice Engineering, pp. 2-1, 2-17.  U.S. Army Corps of Engineer, Coastal Engineering Research Center. 1984. Shore Protection Manual, Volume 1. Department of the Army Waterways Experiment Station, Corps of Engineers, Vicksburg, Mississippi. 652 p.  


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