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ARCADIS <br />Recommendations: <br />• Provide printout results of RO model projections. <br />• Consider including sulfuric acid dosing for pH adjustment prior to the RO system. <br />• Include a contingency plan in the event that the dewatering rate is not effective in drawing down <br />the mine pool elevation to the required levels. <br />5.3 In -situ Mine Pool Treatment <br />Background Concentrations <br />Overview: Uranium concentrations in the mine pool appear to be declining as shown in Figure 19 of the <br />Reclamation Plan. A linear trend line was fit to these data and used to ascertain that it will take <br />approximately 11 years if left undisturbed to achieve uranium concentrations of 2 mg /L in the mine pool, <br />which was assumed to approximate original background concentrations. <br />Data Adequacy: During the EPP review process, it was noted that background uranium concentrations in <br />the Schwartzwalder trend and adjacent bedrock are not well defined and may not be as high as previously <br />believed (ARCADIS 2011a and 2011b). A linear reduction in dissolved uranium concentrations to 2 mg /L <br />assumes that sufficient reducing capacity is available within the mine pool and that other strongly <br />complexing ions, such as dissolved carbonate, will not prevent uranium from continuing to be reduced at <br />this rate. <br />Recommendations: Development of a more detailed conceptual model and associated geochemical <br />predictive model would help to obtain a more quantitative assessment of changes in the mine pool water <br />quality over time. <br />Radium Concentrations <br />Overview: Figure 7 of the Reclamation Plan presents changes in uranium, molybdenum, and radium <br />concentrations (mg /L) with depth. <br />Data Adequacy: The data quality appears to be acceptable, but the unit typographical error should be <br />corrected. <br />Recommendations: Revise Figure 7 to include radium in picocuries per liter (pCi /L). <br />Page <br />8/16 <br />