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Non-Tributary Support: Cash Mine Borehole AdrianBrown <br />been approximately the same or less than this value. Accordingly, the minimum saturated <br />thickness available for water supply in the mine location is 668 feet minus 30 feet, or 638 feet. <br />3. Specific yield of aquifer materials. The specific yield of the aquifer materials is considered to be <br />equal to the drainable porosity of the bedrock, which is estimated,in Section 2.6 above to be: <br />We Bedrock (50-100 feet thick): 5% <br />Unweathered Bedrock (below 50-100 feet depth): 1% <br />Using these. values, assuming a minimum of 20 feet of saturated weathered bedrock, the Recoverable <br />Volume of water can be computed: <br />Recoverable Volume [AFY] = [480 acres * 20 feet * 5%] + [480 acres * 618 feet * 1%] <br />= 3,446 acre feet <br />The inflow to the Cash Mine in any year is not expected to exceed 10 acre feet2l, or 0.29% of the total <br />recoverable volume. Thus, there is a demonstrated lack of material injury under the definition of Section <br />37-90-137(4) (b) (I), C.R.S. <br />4.5 Prevention of Material Injury <br />Section 37-90-137 (7) C.R.S. states in part that: <br />"(7) (b) ... The state engineer shall allow the rate of withdrawal stated by the applicant to be necessary <br />to dewater the mine; except that, if the state engineer finds that the proposed dewatering will cause <br />material iniurv to the vested water rights of others, the applicant may vrovose. and the hermit shall <br />contain, terms and conditions which will prevent such injury. The reduction of hydrostatic pressure <br />level or water level alone does not constitute material injury. "(emphasis added) <br />In the event that the State Engineer finds (notwithstanding the above) that the proposed dewatering will <br />cause material injury to the vested water rights of others; the applicant hereby proposes the following <br />terms and conditions which will prevent injury. <br />Two bases are considered to determine an extraction flow that will prevent material injury: <br />Prevention of Impact at Nearest Well. Injury cannot occur to a water supply well if drawdown <br />does not occur at their well". The extent of the drawdown cone is determined by the area <br />required to capture sufficient groundwater infiltration to satisfy the mine dewatering flow. Based <br />on the material presented in Section 4.4.1 above, extraction of 2.5 acre feet per year causes the <br />drawdown cone to extend an average of 756 feet from the Cash Mine Borehole. The nearest <br />water supply well is located a distance of 1974 feet from the Cash Mine Borehole, so <br />26 The distinction is made here between inflow to the mine from the bedrock, which results in an average flow rate of 1.56 gpm (2.5 acre <br />feet per year) and a peak flow rate of 6 gpm (10 acre feet per year), and flow from the dewatering pump to dewater the mine, which can <br />be achieved at any flow rate that the pump can deliver until the mine is fully dewatered. If the mine were completely dewatered from <br />full in a single year, the required flow in that year is computed to be 16.4 acre feet (Section 2.7 above). <br />27 It is noted that Section 37-90-137 (7) C.R.S. states in part that "(t)he reduction of hydrostatic pressure level or water level alone does <br />not constitute material injury". However, material injury of any other kind cannot occur if there is no drawdown. <br />1601A-20070125 15