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Memo to Russ Means 2 March 9, 2010 <br />Engineering Review File No. M-2008-012 <br />3. Rip rap proposed for installation and described in the design details required under items 1 and 2 above <br />must be durable and non-slaking. It is unlikely the local rock from the Last Chance Mine vicinity will be <br />suitable. <br />4. The volume and peak flow of runoff from the ore stockpile area during a 100-year storm must be analyzed <br />and a demonstration provided that the runoff will be non-erosively passed to the mine portal. The permit <br />application describes the strata intersected by the mine workings as being essentially dry and states that the <br />Summerville Formation below the mine workings is a confining unit. Under the described circumstances, <br />collection of ore stockpile runoff into the mine workings will not result in an adverse impact to ground water <br />quality. As mining progresses and as characterization of local ground water conditions evolves, if the <br />circumstances described in the application are counter indicated, the DRMS may require alternative <br />management of runoff and potential seepage from the ore stockpile area to protect water quality. <br />The application states that any water collected in the underground workings, presumably including runoff <br />from the ore stockpile that is routed into the mine, will be used for drilling or washing operations. The <br />application states that water collected in the sediment traps will be evaporated, or used for drilling and dust <br />control. The Applicant must describe and provide documentation of the source of the legal right to use the <br />water. <br />cAacs files\My documents 4-19-06 thrulast chance review.docx