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JD-6 Mine Report <br />Geoscience Services <br />dilution factor of 106--far exceeding the requirement of 50x required by the Colorado <br />Division of Mineral and Geology for groundwater. Since selenium is contained in the <br />upper portions of the Salt Wash and does not reach the groundwater, there is substantial <br />protection of the groundwater resources in the azea. <br />Comparing the extent of uranium and selenium migration shown in Figures 3 and <br />4, illustrates the effects of sorption, Selenium exhibits a Kd value for sandstone four <br />times higher than uranium resulting in greater sorption and the subsequent retardation of <br />the selenium plume. The other analytes such as aluminum, lead, and arsenic would <br />behave in a similar manner and pose no significant threat to the underlying groundwater <br />resources. This statement is based on the facts that uranium exhibits the highest degree <br />of mobility in the subsurface and a concentration an order a magnitude higher than any <br />values for waste rock or ore measured for aluminum, lead, or arsenic. Consequentiy, the <br />extent of migrations in the subsurface for these additional constituents of concern would <br />be significantly less than uranium. <br />6.0 Conclusions and Recommendations <br />Numerical modeling studies of the transport of constituents of concern ftom the <br />waste rock pile (or temporary ore storage piles) at the SM-18 mina and applied to the JD- <br />6 mine indicate that the pile poses no significant threat to underlying groundwater <br />resources. The flow and transport model incorporated several conservative assumptions <br />regarding the hydraulic and geochemical parameters. Most conservative was the <br />assumption that the pore-water in the waste pile contained contaminant concentrations <br />that reflected SPLP test conditions. Actual rainwater exhibits a higher pH value (less <br />acidic than SPLP leaching fluid) and would leach constituents of concern at lower <br />concentrations. In addition, for the 1000 year simulation, concentrations of constituents <br />of concern in the waste-rock pore water were maintained at initial concentrations. In <br />reality, as constituents of concern aze leached from the waste rock, concentrations would <br />steadily decline with time. The net result is a model that over predicted the amount and <br />availability of constituents of concern for transport. <br />12 <br />