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that some pyrite is oxidizing but is being neutralized, as described below. <br />The analysis of geochemical controls on groundwater quality at the New Horizon #1 <br />Mine spoil suggests that the water chemistry and concentrations of most elements of <br />concern are controlled by mineral reactions that will resist changes in water chemistry. <br />It appears that any pyrite (FeS2) oxidation gets neutralized by calcite (CaC03) present <br />in the same spoil material. This results in the iron precipitating as iron oxides. The <br />slightly higher than normal pH of the natural water means that there is sufficient <br />acid-neutralizing ions such as hydroxyl (OH-) or bicarbonate (HC03-) in solution to <br />absorb the acidic hydrogen (H+) ions produced by the pyrite oxidation. Soluble sulfate <br />(SOa '2) ions are also produced by the pyrite oxidation, and they aze quickly taken up <br />by the calcite to produce calcium sulfate or gypsum (CaSOa) which is not very soluble <br />and also precipitates out of solution, especially when the pH of the solution is near <br />normal. The (C03 -z) anion in the calcite goes in solution to replace the sulfate. <br />Calcium stays as a solid in the new gypsum produced. Overall, the net change to the <br />water quality is not significant as compazed to overburden water, but some pyrite has <br />been converted to other solid compounds: gypsum and iron oxides such as limonite. <br />Strong support for this occurring is seen in the water quality comparison of <br />overburden water to spoil water. Well GW-N9 is north of the mined azeas of New <br />Horizon #1 and has been unaffected by the mine since the flow gradient is to the <br />southwest. This well is best to use in the comparison. Spoil Spring 1, which developed <br />neaz the southwestern end of the reclaimed mine best, represents the spoil water. <br />If pyrite breakdown were occurring without any neutralization, the pH of the spoil <br />water would be lower than overburden water. This has not occurred; however, the <br />replacement of sulfate ion by cazbonate ion from the calcite should be seen as an <br />increased cazbonate or bicazbonate in solution. This is exactly what is seen between <br />the overburden water and the spoil water for each sampling period except for the <br />August 1998 sample, which must have had outside influence of surface water flows <br />since its total dissolved solids is much less than any other sample. All other ions in <br />solution aze more or less proportional to the level of TDS in the sample. Bicazbonate, <br />on the other hand, has consistently increased by approximately 33%. <br />There is no significant trend in TDS differences from the overburden water to the <br />spoil water, although averaging the samples from 1995, 1996, 2000 and 2001 shows a <br />difference of 200 ppm or a 6.6% increase. Overall, water quality of the spoil water <br />may be only slightly higher in TDS than the undisturbed overburden water. The <br />quality of both waters is relatively poor. However, the spoil water quality is affected to <br />a significant degree by the time of yeaz when irrigation is occurring on the surface. <br />The monthly flows and TDS values from the 001 discharge show a direct correlation <br />between TDS and flow rate. It is appazent, as the flow rate lowers, the TDS value <br />becomes higher. <br />It is important to understand what is truly different from the pre-mine condition tc the <br />zs <br />