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Colowyo Response - PR3 adequacy No. 2 5 May 6, 2011 <br />Rule 2.04.7(3) Alternative Water Supply Information <br />I . The application is deficient with regard to any analysis or study to determine what, if any, <br />impact could occur to registered ground water users proximate to the mine dewatering <br />operations that will occur over the life of the mine. In particular, mining in the Collom Lite pit <br />will result in dewatering of the overburden to varying degrees from both pit dewatering and pit <br />development. Please provide permit text narrative discussing specific details regarding <br />dewatering and associated impacts, including estimates of the cone of depression, maps, cross- <br />sections and other information sufficient to reflect what impacts may occur to registered <br />owners of wells in the proposed permit and adjacent area. <br />The application remains inadequate. Revised information submitted on page 133 under the <br />heading "Potential Impacts to Groundwater Users due to Pit Dewatering and Development" <br />provides no specific information on wells, well ownership, well permit number, areal extent of <br />the cone of depression, or any other specific information or estimate of the extent that pit <br />dewatering and pit development could impact registered wells proximate to the pit. The <br />original question remains outstanding. Please provide permit text narrative discussing specific <br />details regarding dewatering and associated impacts, including estimates of the cone of <br />depression, maps, cross-sections and other information sufficient to reflect what impacts may <br />occur to registered owners of wells in the proposed permit and adjacent area. <br />Colowyo's Response: <br />As noted in the response under Hydrology Description, the land for the Collom permit <br />0 expansion area is predominantly owned and/or controlled by Rio Tinto Colowyo and/or its <br />subsidiaries. The rest of the land is owned by the Bureau of Land Management or the State of <br />Colorado. The wells within the Collom permit expansion area are thus controlled by Colowyo. <br />Thus, the only impact from any dewatering will be on Colowyo itself. <br />As previously noted, dewatering wells will be required to mine any coal below the estimated <br />piezometric surface/water table surface. Based on studies (predominantly the 2005 study by <br />WMC) in this area, this estimated piezometric surface/water table surface is at approximately <br />7150-+50 feet elevation in the Collom Lite mining area (below the F1 seam in the initial boxcut <br />area). <br />The dewatering wells will have to be placed close to and in the pit to have the maximum cone <br />of influence diameter for dewatering, without causing pumping problems during dewatering. <br />Based on a long term well test performed by WMC (2005) in the NW%, Section 35, T. 4 N., R. <br />94 W., the estimated dewatering well spacing is 1, 000 feet. This well spacing has been <br />determined based on the proposed depth of mining and the hydraulic characteristics of the <br />Williams Fork formation obtained during the test. This data are presented in the WMC (2005) <br />report, included as an appendix. <br />This spacing is required to allow for the closest placement of the dewatering wells to the pit <br />boundary to achieve the maximum cone of influence in the pit. Dewatering will not be needed <br />for the entire life of the mine. It is only needed for the approximate northern third of Collom <br />Lite. Once the mining moves south, dewatering efforts will cease since the seams to be mined <br />will be above the piezometric surface.