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ions are, also produced by the pyrite oxidation, and they are quickly taken up <br />by the calcite to produce calcium sulfate or gypsum (CaS04) which is not very <br />soluble -and also precipitates out of solution, especially when the pH of the <br />solution is near normal. The (C03 -2) anion in the calcite goes in solution to <br />replace the sulfate. Calcium stays as a solid in the new gypsum produced. <br />Overall, the net change to the water quality is not significant as compared to <br />overburden water, but some pyrite has been converted to other solid <br />compounds: gypsum and iron oxides such as limonite. Strong support for this <br />occurring is seen in the water quality comparison of overburden water to spoil <br />water. Well GW-N9 is north of the mined areas of New Horizon #1 and has <br />been unaffected by the mine since the flow gradient is to the southwest. This <br />well is best to use in the comparison. Spoil Spring 1, which developed near <br />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 <br />spoil water would be lower than overburden water. This has not occurred; <br />however, the replacement of sulfate ion by carbonate ion from the calcite <br />should be seen as an increased carbonate or bicarbonate in solution. This is <br />exactly what is seen between the overburden water and the spoil water for <br />each sampling period except for the August 1998 sample, which must have <br />had outside influence of surface water flows since its total dissolved solids is <br />much less than any other sample. All other ions in solution are more or less <br />proportional to the level of TDS in the sample. Bicarbonate, on the other hand, <br />has consistently increased by approximately 33%. <br />There is no significant trend in TDS differences from the overburden water to <br />the spoil water, although averaging the samples from 1995, 1996, 2000 and <br />2001 shows a difference of 200 ppm or a 6.6% increase. Overall, water quality <br />of the spoil water may be only slightly higher in TDS than the undisturbed <br />overburden water. The quality of both waters is relatively poor. However, the <br />spoil water quality is affected to a significant degree by the time of year when <br />irrigation is occurring on the surface. <br />The monthly flows and TDS values from the 001 discharge show a direct <br />correlation between TDS and flow rate. It is apparent, as the flow rate lowers, <br />the TDS value becomes higher. <br />It is important to understand what is truly different from the pre-mine <br />condition to the spoil condition. In the pre-mine condition, very good quality <br />water from precipitation and from the irrigation ditches infiltrates through the <br />soil and, through the more permeable strata and picks up dissolved solids. The <br />water quality becomes poor (approx. 3000 ppm TDS), but this process takes a <br />very long time since the water moves very slowly through the tight strata with <br />low hydraulic permeability values that range from 3.5 to 5.5 ft/day. <br />In the case of the spoil, the hydraulic permeability is increased to 40 ft/day <br />31