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The New Horizon Mines are similar to the Seneca II Mine in terms of <br />depositional history and observed spoil leachate chemistry. These similarities <br />indicate the oxidation of pyrite can be assumed to be the main source of increased <br />TDS in spoil aquifer water at New Horizon, as at Seneca II Mine. <br />The pyritic sulfur content in New Horizon's spoil averaged 0.52% (by weight) in <br />the 72 overburden core samples whose analyses are reported in the permit <br />application. Pyrite is 53% sulfur (by weight); therefore, the 0.52% pyritic sulfur <br />content indicates that pyrite comprises roughly 0.98% of the mass of the subject <br />mine's spoil. Applying Williams and Clark's 1,600 year exhaustion time for 1.0% <br />pyrite, the subject mine's spoil can be expected to generate high sulfate <br />concentrations for at least 1,500 years. <br />The calculated 1,600 year duration is reduced to about 800 years when reductions <br />are taken into account for piping through the spoil (assumed to be 25%) and lower <br />annual precipitation (12 inches at New Horizon versus 17 inches at Seneca). The <br />calculated 800-year duration is not meant to be a precise prediction of the <br />duration of elevated dissolved solids, but indicates the elevated solids can be <br />expected to last, possibly, several centuries. <br />The New Horizon Mine has two significant differences to the results observed at <br />Seneca II. First, the calcite present in the spoil at New Horizon seems to react <br />with acid produced by the oxidation of pyrite and take a substantial amount of <br />sulfate from solution into solid calcium sulfate. This keeps the dissolved solids <br />content somewhat constant no matter how high or low the the inflow water <br />quality is with regard to TDS. Second, the Seneca II site is a dryland reclaimed <br />area where the only recharge into the spoil is a minor amount from precipitation <br />and seepage from the underburden aquifers. Total measured discharge from the <br />spoil was only 3" per year. The New Horizon Mine is principally irrigated with <br />water of very good quality over a large portion of the year. As described earlier, <br />this results in a total movement through the spoil of approximately 16" per year. <br />Since the amount of water moving through the New Horizon spoil is so much <br />greater, it should oxidize the pyrite much more rapidly and also flush other salts <br />which are contributing to the increase in TDS at a much higher rate. For this <br />reason, a ratio of the discharge at both sites could be used to predict the time <br />frame of slightly elevated spoil water quality. This ratio - 3"/16", as applied to <br />1500 years results in a time frame of 280 years until all the pyrite is oxidized. <br />When considering all the variables involved, this means that it could dissipate <br />within a range of 100 to 500 years. The TDS should begin to drop before this <br />time. Once the pyrite is fully oxidized and other salts are flushed out, the spoil <br />water quality should approach the irrigation water quality, possibly dropping to <br />300 ppm TDS. <br />Impacts To Receiving Waters <br />Since these spoil springs were never present in the pre-mine landscape, their <br />41