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this issue, Cotter is planning to install a pair of nested deep bedrock monitoring wells <br />screened within the Schwartz Trend at a location between the mine workings and the creek. <br />Should these monitoring wells produce definitive hydraulic and chemical evidence of <br />migration, the long-term mitigation strategy would include grouting measures (if technically <br />feasible) and reduction of the concentrations at the source with in-situ treatment of the mine <br />pool. <br />• Item 1(B)(3): This item requires a mitigation plan in the event an excursion of contaminated <br />water occurs. Again, the best plan to address this issue would include grouting measures <br />where technically feasible and to address the source with in-situ mine pool treatment to <br />reduce contaminants to levels approaching those that likely existed prior to mining. This <br />latter measure would significantly reduce the potential for any migration that could result in <br />water quality impacts to Ralston Creek in excess of applicable standards. <br />• Item 3: This item cites an additional Hard Rock Mining Rule [6.4.21(6)] which again <br />reiterates the same requirements previously stated in Items 1(B)(1) and 1(B)(2), each of <br />which is addressed by this TR as summarized above. Technical details concerning the plan <br />for in-situ mine pool treatment are provided in the attached Technical Memorandum. <br />• Item 4 (A and B): This item cites an additional Rule [6.4.21(7)] that partially reiterates <br />requirements previously stated and addressed above with respect to the mine pool as a <br />potential source of impacts. In-situ treatment of the mine pool combined with the grouting <br />program to seal any conduits for migration will be implemented in conjunction with cleanup <br />of alluvial fill source terin materials identified under TR-14 to help ensure that the mine pool <br />will not represent a potential additional source of impacts after cleanup of the alluvial fill. <br />In-situ treatment of the mine pool, the grouting program, and cleanup of the alluvial fill <br />represent multiple measures and redundancies to prevent and mitigate any releases of toxic <br />materials from the mine pool as well as from the alluvial fill. <br />Proposed Technical Revision <br />Alexco Resource US Corp (Alexco) has provided Cotter with a technical basis and conceptual <br />plan to implement in-situ treatment of mine pool water to reduce concentrations of uranium and <br />other metals through in situ formation of sulfide minerals. The proposed treatment will also <br />form non-pyritic iron sulfide (FeS) within and throughout the mine pool workings to encapsulate <br />the precipitated mineral forms of uranium, inhibiting the potential for re-dissolution or release of <br />the uranium back into the mine pool. The attached Technical Memorandum from Alexco is <br />submitted for consideration as the technical basis and conceptual plan for Technical Revision 16 <br />to Mining Permit M-1977-300. <br />The Alexco in-situ treatment process is not expected to reduce concentrations of Ra-226 in the <br />mine pool. However, radium in solution forms a positively charged divalent cation, similar to <br />barium, calcium, and strontium. Radium concentrations in natural waters are influenced by <br />solubility and sorption reactions and solubility is typically controlled by co-precipitation within <br />sulfate minerals (e.g. barite and gypsum). Radium adsorption on iron-hydroxides is well- <br />documented in natural systems (Schott and Wiegand, 2003). Under oxidizing conditions, radium <br />3 <br />