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Daniel Arnold, Esq. January 25, 2011 <br />Denver Water Page 19 of 21 <br />from the waste rock piles and from the mine pool, and the long -term effectives will be <br />limited. <br />Borehole Plugging and Abandonment Program <br />The EPP discusses a program consisting of a historic records review to locate angled <br />boreholes drilled into the mine from the valley floor. If open boreholes are identified and <br />can be located, they will be plugged. <br />The EPP has recognized possible discharge of mine pool water from open boreholes and <br />included this plugging program as a mitigation action. The necessity of this action is <br />heightened by the recent discovery of the flowing borehole. It is likely that several <br />boreholes were drilled below the present -day Steve and Pierce adits during early <br />exploration of the ore body that have not been plugged. These boreholes are now covered <br />with 1 Os of feet of fill. This fill would have to be removed to expose the original collars <br />of the boreholes in order to properly plug the boreholes. If the fill is not removed, it is <br />likely that open boreholes could discharge mine pool water into the fill and alluvium. The <br />implications of this discharge are wide - ranging and impact the long -term effectiveness of <br />each mitigation option being considered at the mine. <br />Isolation of the Creek <br />Isolating the creek from the alluvial aquifer was mentioned in the EPP, but not further <br />evaluated as a possible mitigation option. Given the strong hydraulic connection between <br />groundwater and the creek, a physical barrier (i.e., lining of creek) between the creek and <br />alluvial aquifer may be the only measure that can achieve the uranium MCL in the creek <br />in the near- and long -term in combination with groundwater treatment. <br />4.0 REVIEW OF DRMS' COMMENTS ON THE EPP <br />DRMS' review of the EPP identified several data deficiencies including defining all <br />toxic - forming materials at the site including the valley fill, mine pool, and the creek. <br />Release response activities to monitor and mitigate each of these media were requested <br />by DRMS. Cotter was requested to pump and treat mine pool to remove uranium or treat <br />it in situ to immobilize uranium. DRMS expressed concern about migration of the mine <br />pool to the bedrock, alluvium, and creek. They identified data deficiencies in bedrock <br />monitoring wells and required point of compliance monitoring well downgradient of <br />sources. Overall, most of DRMS' comments are similar in nature to those in our current <br />review. There are two areas, however, where the current review either differs or <br />identified issues not raised by DRMS, and each is described below. <br />Waste Rock Piles <br />DRMS' comments on the EPP do not identify the waste rock piles as a contributing <br />source of uranium that requires mitigation. The current review found sufficient evidence <br />that the waste rock piles are contributing significant amounts of uranium to the alluvial <br />aquifer that eventually discharges to the creek. This evidence is from comparison of <br />uranium concentrations between MW -00, which is upgradient of the rock piles and has <br />