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June 25, 2010 6 of 15 <br />achieve the 40% reduction in the uranium concentrations described above. Pumping down the mine pool, <br />even for a short period of time, will expose wall rocks to oxygen, thus liberating uranium unnecessarily, <br />disturbing the favorable trend of decreasing concentrations, and potentially causing environmental harm. <br />80 <br />70 <br />60 <br />50 <br />o? <br />40 <br />E <br />30 <br />20 <br />10 <br />Dissolved Uranium in Schwartzwalder Mine Pool <br /> <br /> <br /> • <br /> • <br />• <br /> <br /> <br /> <br />A^ 5§' ?0 ? A? PQ?Sk 0, cso dF' Aso V X01 ADO cSA? Sp ?0 01 ?", <br />? <br />PQ PQ OP vs o-Y eO oy PQ vsoy t4 dy PQr' <br />Figure 3. Uranium Concentrations in Schwartzwalder Mine Pool <br />Mine flooding is a recognized remedial strategy for stabilizing groundwater chemistry. <br />Numerous scientific and technical articles have been published about intentionally flooding mines to <br />prevent oxidation. Mine flooding can be an effective preventive and corrective measure for controlling <br />water chemistry in inactive mine workings because it isolates wall rock from coming in direct contact with <br />air, thus retarding the oxidation process. Uranium is generally mobile in oxidizing conditions and <br />immobile under reducing conditions. <br />Geochemical conditions and hydrogeologic conditions determine which mines will benefit from flooding. <br />The Schwartzwalder Mine was hosted in rocks with a net neutralizing capacity, and pH has remained near <br />neutral in the mine pool. The decrease in oxidation that occurs as a mine floods is beneficial for lowering <br />concentrations in the mine pool at the Schwartzwalder and at specific mines worldwide. <br />Taylor and Waring, 2001, state that "the use of controlled flooding using carefully designed bulkheads <br />capable of holding substantial water pressures is essentially the only option available for improving water <br />quality from underground workings." <br />Mine flooding successfully lowered the concentrations of zinc, copper, cadmium, mercury, and lead at a <br />number of lead-zinc mines in the Iglesias district of Italy. Pumping ceased in 1997 and the underground <br />workings were allowed to flood. At the start of flooding, an increase in dissolved Zn, Cd, Pb, and Hg was