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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 <br />lower annual precipitation (12 inches at New Horizon versus 17 inches at <br />Seneca). The calculated 800 -year duration is not meant to be a precise prediction <br />of the duration of elevated dissolved solids, but indicates the elevated solids can <br />be 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 />impact to the quality of the receiving waters must be addressed. As described <br />earlier, a spoil spring will develop on the northwestern part of the New Horizon <br />92 mine area where the single lowest point occurs along the lowwall crest, which <br />can be seen on Map 2.04.7 -1 -A. This is shown as Spoil Spring 44. <br />The Spoil Spring monitoring locations and NPDES point 001 are shown on Map <br />2.04.7 -1A. See descriptions below. <br />Spoil Spring #1 is shown as SS #1 and is located approximately 2100 feet <br />northeast of the NW corner of the New Horizon #2 permit area. This spring has <br />been monitored since 1984 by Peabody and then later by WFC. When Phase 3 <br />bond release on the majority of the New Horizon #1 Mine area was done in 2001, <br />41 <br />