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Daniel Arnold, Esq. April 6, 2011 <br />Denver Water Page 2 of 12 <br />The available data continue to indicate that there are multiple sources of uranium loading <br />to Ralston Creek at the site (waste rock piles, mine pool, and alluvial fill) that have not <br />been investigated to the degree needed to understand the nature and extent of <br />contamination. Additional investigation and data analysis are necessary before corrective <br />measures can be adequately evaluated and implemented, to ensure that human health and <br />the environment are protected in the short and long term. <br />It is beyond the capacity of this Addendum to respond to each of Cotter's comments; <br />therefore, responses are developed only for comments that either provide additional data, <br />provide new interpretations of the nature and extent of contamination, or involve data <br />adequacy. <br />COMMENTS BY COTTER (ATTACHMENT 1) <br />Waste Rock Piles <br />Cotter agrees that additional studies need to be conducted at the waste rock piles. <br />However, several circumstantial reasons why the waste rock piles do not generate <br />leachate and impact groundwater are presented. <br />1) The waste rock piles are in a semi -arid climate with little precipitation to <br />generate leachate. The soil cover is not a low- permeable cover and is unlikely to <br />impede precipitation from infiltrating into the pile. It does not take much <br />infiltration to generate leachate with high concentrations of soluble radioactive <br />elements that can migrate to groundwater. The results of the gamma survey of the <br />waste rock piles (Figure 2 -3 of the EPP) indicates that even with the soil cover in <br />place and mature vegetation, the waste rock piles contain elevated radioactive <br />elements. For example, the gamma radiation is greater than 200 micro rems per <br />hour in several areas of the South Waste Rock Pile, and the waste rock piles have <br />a much higher gamma signature than the alluvial fill along the central mine area. <br />2) If leachate is generated it would be realized in the creek. As explained at the <br />January 26, 2011 meeting with agreement by Cotter representatives, the segment <br />of Ralston Creek along the waste rock piles is losing and not connected with the <br />alluvial groundwater system. Therefore, leachate does not enter the creek until <br />along the piles, instead it migrates in the alluvial groundwater parallel to the creek <br />and discharges at the southern end of the mine where groundwater is forced <br />upward into the creek. The absence of uranium in the creek near the waste rock <br />piles is due to its losing nature in this area and does not preclude the piles from <br />being a source. <br />