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SM-18 Mine Report <br />GeoScience Services <br />Uranium and selenium were chosen to show the impact of unsaturated flow and <br />sorption on the transport of contamination. Uranium exhibits the lowest Kd value for <br />sandstone of the analytes selected in the SPLP tests. Consequently, uranium will behave <br />more conservatively, or in other words, will be sorbed to the geologic material to a lesser <br />degree resulting in larger transport distances. As shown in Figure 2, uranium is predicted <br />to migrate approximately 200 feet vertically at a concentration of 10~ of the original <br />concentration in the pore water of the waste rock. The uranium plume is contained in the <br />Salt Wash Member of the Momson Formation. The plume does not enter the Entrada <br />Sandstone, the regional aquifer for the area. The Summerville Formation provides an <br />additional buffer zone restricting potential contamination from entering the groundwater. <br />Using the SPLP tests for ore of 2700 ug/L, uranium was only found at 2 ug/L in <br />the waste rock, the predicted concentration at 200 feet below the waste-rock pile would <br />be 0.0027 ug/L. To meet water quality values required by the Colorado Division of <br />Mineral and Geology (which is a comparison to surface water standards of the Lower <br />Dolores River Basin, CDPHE Regulation No. 35), a dilution factor of 9x for uranium is <br />necessary. The modeling simulation showed a dilution factor of a million times for pore <br />. water in the unsaturated zone-a factor of 105 higher than required by the Colorado <br />~ DMG. <br />Selenium migration is illustrated in Figure 3 and the predicted transport distance <br />for a period of 1000 yeazs is approximately 80 ft at a concentration of 1E-06 of the <br />original pore-water concentration in the waste rock. Using the SPLP test results that <br />indicated 86 ug/L of selenium for the waste rock, the resultant concentration at a depth of <br />80 feet below the pile would be 0.000086 ug/L. Once again, this represents a dilution <br />factor of 106--far exceeding the requirement of SOx stated by the Colorado DMG. Even <br />higher selenium values of 230 ug/L reported for ore piles would result in 0.000230 ug/L-- <br />still exceeding the SOx dilution requirement. Since selenium is contained in the upper <br />portions of the Salt Wash and does not reach the groundwater, there is substantial <br />protection of the groundwater resources in the area. <br />11 <br />