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!! r <br />acidwneutralizing ions such as hydroxyl ?flH-} or bicarbonate (HCO?-) in solution to absorb the acidic <br />hydrogen (H+} ions produced by the pyrite oxidation. Soluble sulfate X504 -?) ions are also produced by <br />the pyrite oxidation, and they are quickly taken up by the calcite to produce calcium sulfate or gypsum <br />?CaSO?} which is not very soluble and also precipitates out of solution, especially when the pH of the <br />solution is near normal. The {C0? -?} anion in the calcite goes in solution to replace the sulfate. Calcium <br />stays as a solid in the new gypsum produced, Overall, the net change to the water quality is not significant <br />as compared to overburden water, but some pyrite has been converted to other solid compounds: gypsum <br />and iron oxides such as limonite, Strong support far this occurring is seen in the water quality comparison <br />of overburden water to spoil 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 well is best to use in the <br />comparison. Spoil Spring ?, which developed near the southwestern end of the reclaimed mine best, <br />represents the spoil water. <br />if pyrite breakdown were occurring without any neutralization, the pH of the spoil water would be lower <br />than overburden water. This has not occurred; however, the. replacement of sulfate ion by carbonate ion <br />from the calcite should be seen as an increased carbonate or bicarbonate in salutian. This is exactly what <br />is seen between the overburden water and the spoil water for each sampling period except for the August <br />1998 sample, which must have had outside influence of surface water flows since its total dissolved solids <br />is much less than any other sample. All other ions in solution are mare or less proportional to the level <br />of TDS in the sample. Bicarbonate, on the other hand, has consistently increased by approximately 33 ??. <br />There is na significant trend in TDS differences from the overburden water to the spoil water, although <br />averaging the samples from 1995, 199, 2000 and 2001 shows a difference of 200 ppm or a 6.6°1a <br />increase. Overall, water quality of the spoil water may be only slightly higher in TDS than the <br />undisturbed overburden water. The quality of both waters is relatively poor. However, the spoil water <br />quality is affected to a significant degree by the time of year when irrigation is occurring an the surface. <br />The monthly flows and TDS values from the OOi discharge show a direct correlation between TDS and <br />flow rate. ?t is apparent, as the flow rate lavers, the TDS value becomes higher. <br />It is important to understand what is truly different from the pre-mine condition to the spoil condition. <br />In the pre-mine condition, very good quality water from precipitation and from the irrigation ditches <br />infiltrates through the soil and through the mare permeable strata and picks up dissolved solids. The water <br />quality becomes pear tapprax. 3000 ppm TDS}, but this process takes a very long time since the water <br />manes very slowly through the tight strata with low hydraulic permeability values that range from .5 to <br />5.5 ftlday. <br />In the case of the spoil, the hydraulic permeability is increased to 40 ftlday and more irrigation water is <br />recharged rapidly through the permeable, broken spoil material. This good quality water picks up <br />dissolved solids as in the case of the overburden, but does so much mare rapidly. water infiltrating into <br />the spoil at the upper end of the New Horizon #f spoil may only spend ?5-45 days in the spoil before the <br />water is discharged at the spring. Yet, during this short time, it is approximately the same quality as the <br />overburden water. The average TDS of the irrigation ditch water is only 100 to 280 ppm. Due to the <br />increased porosity and higher level of oxygen in the rapidly infiltrating precipitation water and irrigation <br />water, the pyrite breaks down at a faster rate but is buffered by the calcite, as described above. Therefore, <br />the overall impacts to water quality are as follows: <br />A? In the pre-mine condition, a large portion. of the irrigation eater runs off the surface and picks up some <br />TDS in the fields and is gathered in return. ditches. in the post-mine condition, a large portion of the <br />irrigation water will infiltrate and recharge the spoil due to the increase in porosity. The TDS of the spoil <br />water at the New Horizon #i Mine will increase approximately ?% compared to that of the overburden <br />water immediately after reestablishment afirrigation. This is approximately 3300 ppm of TDS.