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Cresson Project Hvdrogeochemistry AdrianBrown <br />3. HYDROGEOCHEMICAL EVALUATION <br />This section of the report describes and quantifies the components of the hydrogeochemical system, and <br />the potential impact that MLE2 will have on ground water quality. <br />3.1 Hydrogeochemical System <br />Mined overburden materials from MLE2 will be placed in the SGOSA and ECOSA, and will be used as <br />mine backfill material in portions of the Main Cresson, East Cresson, and North Cresson Mines areas. <br />Infiltration of precipitation through these materials and through the remaining surface mines may <br />mobilize soluble products of oxidation of sulfides in the overburden and transport them into the <br />subsurface diatremal rock. The flow passes generally vertically through approximately 3,000 feet of <br />unsaturated rock and will contact neutralizing materials in the rock. The flow will migrate to the <br />regional ground water table and then pass laterally to the Carlton Tunnel through the saturated portion <br />of the Diatreme, contacting further neutralizing materials. Finally, the water flows through the Carlton <br />Tunnel into Fourmile Creek. This hydrogeochemical system is shown schematically in . <br />3.2 Potential Impact of Sulfide Oxidation <br />The mining activities associated with MLE2 have the potential to impact ground water quality as a result <br />of oxidation of sulfide minerals in the material mined, and of materials exposed in the mine walls that <br />remain after closure. Oxidation of sulfides generates acid and mobilizes metals, which have the potential <br />to impact water quality. <br />3.2.1 Method <br />Acid base accounting was conducted for the entire rockmass that will be mined in MLE2. The <br />methodology used was to identify for each 50' x 50' x 35' block of material that will be mined the <br />expected total sulfur and total carbon concentrations, based on a total of more than 30,000 LECO <br />furnace analyses. The sulfur and carbon concentrations were converted to Acid Generating Potential <br />( "AGP ") and Acid Neutralizing Potential ( "ANP ") respectively, and Acid Base Accounting ( "ABA ") <br />computations performed on the resulting totals by mine and by material type (ore or overburden) to <br />determine the release of constituents from the ore and overburden during and after mining The impact <br />of release is evaluated after passage through the District to the regional ground water regime as <br />intersected by the Carlton Tunnel <br />3.2.2 Acid Generating Potential <br />AGP is the potential for a material to generate acid by oxidation of sulfides. The AGP is related to the <br />total sulfur content of a rock material; the total sulfur measurement includes the sulfides that oxidize. <br />The maximum AGP for the rock is computed by assuming that the entire sulfur content of the sample is <br />in pyrite form (as the pyrite content is not generally measured in LECO analyses), and that the pyrite <br />form oxidizes as follows: <br />FeS + 15/4 0 + 7/2 H = Fe(OH) + 2 SO4 + 4 H <br />1385L.20120125 14 <br />