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compared to the groundwater level beneath the mine's waste pile. Assuming a conservative <br />hydraulic gradient of 180 feet/mile, similar to the value used in the SM-18 analysis, this would <br />result in a water level under the mine's waste pile of 109 feet below the water table in the <br />alluvium iu the Paradox Valley. <br />To determine the depth to ground water under the waste pile at JD-6, one may properly <br />use the well elevation of 5704 feet and then subtract the depth to water, which calculation yields <br />a potentiometric surface of 5444 feet. Next, by subtracting the hydraulic gradient necessary for <br />water to flow from the alluvium to the bedrock, we see a resulting potentiometric surface of 5335 <br />feet. <br />Since the JD-6 mine's waste rock pile is located at an average elevation of 5850 feet, the <br />resulting depth to water is 515 feet over 100 feet lower than assumed in the earlier <br />analysis. <br />Referring to the attached geologic cross section, the potentiometric surface would be <br />approximately at the base of the Entrada Sandstone. The Cotter migration pathway computer <br />analysis showed that, after 1,000 years, concentrations at one millionth of the initial waste rock <br />leakage concentration would only reach the upper portion of the Entrada Sandstone. <br />Using the Division's reasonable assumption that hydraulic communication exists between <br />the alluvium and bedrock aquifers, the depth to water at the JD-6 mine can be reasonably <br />estimated to be significantly lower than the previous modeling analysis and, therefore, there is no <br />technical reason for installing a monitoring well. <br />JD-8 Mine <br />The analysis of fracture flow in unsaturated conditions which is attached was <br />submitted to the Division in response to questions raised about the JD-8 mine. This analysis <br />