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Whetstone <br />Associates <br />Technical Memorandum <br />Water quality in the mine pool has shown a trend of decreasing uranium and molybdenum <br />concentrations over time. Although the uranium concentrations are still significantly above water <br />quality standards, the chemistry of the mine pool is expected to eventually return to an equilibrium <br />chemistry that resembles pre-mining background, as oxygen is consumed and redox conditions <br />become less oxidizing. <br />A pump and treat system would increase oxidation of the mine pool and wall rock in the shaft, as <br />water levels rise and fall during pump cycling. During the pilot feasibility study for pump and treat <br />of the mine pool, the pump was set at 27 ft below the Steve Level shaft opening and the pumping <br />rate was only 1.2 gpm. Significant drawdown would be induced during pumping, exposing wall <br />rock to additional oxidation. The low flow rates achieved during the pilot test feasibility study and <br />the trend of declining uranium concentrations indicate that uranium recovery from a pump and treat <br />system would not be economical. Also, since hydrologic calculations indicate that the water level in <br />the mine pool will not reach the Steve level, the pump and treat system is not considered to be <br />necessary. <br />Bench scale studies of in-situ treatment of the mine pool would be difficult to implement, since <br />representative wall rock samples are not available. The underground workings include 208,600 <br />cubic feet of void space, and are accessible only through a 64 square foot shaft opening. Mixing and <br />distribution of reductants throughout the workings would not be feasible, since the extensive <br />workings are accessible only through the Steve Level Shaft. Access to the Steve Level is limited and <br />dangerous. Supporting structures within the underground mine (i.e., timbers and backs) are <br />deteriorating rapidly, and the safety of personnel is a concern. <br />Based on the trend in water chemistry and the hydrogeologic conceptual model, the most effective <br />and practical method for treating water in the mine pool is to intercept and treat any seepage from <br />the mine pool water that reaches the alluvium. Flow rates are low, and the source may be diffuse. <br />However, the groundwater in the alluvium can be intercepted and treated using the mitigation <br />strategies presented in the revised EPP. <br />3) Because the underground workings are containing the contaminants in the mine pool water, <br />DRMS contends that the underground workings should be designated as an Environmental <br />Protection Facility and therefore subject to the provisions of Rule 64.20(7)(e). Operator must <br />describe any release response procedures, redundancies, and "backup" measures necessary, <br />appropriate, and economically reasonable, to control, prevent and mitigate releases of the toxic <br />forming materials from the containment facility (i.e., the underground workings) outside the permit <br />area. <br />The underground workings were included in Section 7 of the EPP submitted to DRMS in August <br />2009. Each section of the EPP corresponds to the sections in Rule 6.4.20 (EXHIBIT T - Designated <br />Mining Operation Environmental Protection Plan). Section 7 (Facilities Evaluation) corresponds to <br />Rule 6.4.20(7). Additional text has been added to the revised EPP referring to the monitoring <br />program in place, planned additional monitoring, natural hydrogeologic controls on releases, and <br />proposed mitigation of the mine pool via the alluvial groundwater pathway. <br />4109C.100416 3