2010-08-30_REVISION - C1981008 (3)

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any pyrite (FeS2) oxidation gets neutralized by calcite (CaC03) present in the same spoil material. This results in the iron precipitating as iron oxides. The slightly higher than normal pH of the natural water means that there is sufficient acid-neutralizing ions such as hydroxyl (OH-) or bicarbonate (HC03-) in solution to absorb the acidic hydrogen (H+) ions produced by the pyrite oxidation. Soluble sulfate (S04_2) ions are also produced by the pyrite oxidation, and they are quickly taken up by the calcite to produce calcium sulfate or gypsum (CaSO4)1 which is not very soluble and also precipitates out of solution, especially when the pH of the solution is near normal. The (C03 -2) anion in the calcite goes in solution to replace the sulfate. Calcium stays as a solid in the new gypsum produced. Overall, the net change to the water quality is not significant as compared to overburden water, but some pyrite has been converted to other solid compounds: gypsum and iron oxides such as limonite. Strong support for this occurring is seen in the water quality comparison of underburden and overburden water to spoil water. Well GW-N40, which is southwest of the Phase 3 reclaimed area, best represents the spoil water. Well GW-N44, west of the New Horizon #2 Mine, shows the water quality of ground water in undisturbed overburden. Table 5 shows the comparative chemistry of the spoil ground water (GW-N40) and the overburden ground water (GW-N44). If the pyrite breakdown were occurring without any neutralization, the pH of the spoil water would be lower than overburden water. This has not occurred, and as can be seen in the following water data, the presence of all salts is lower in the spoil ground water. This is also reflected in the lower TDS of the spoil water. TABLE 5 Wa+nr nnali+?? rnmr?arienn - Unrlarhnrrlan Wa+Pr !f_W-Nddl ve Cnnil Water ((iW-N,10) Sample Date Average 2005 Average 2006 Average 2007 Average 2008 Annual Average Parameter GW- N44 GW- N40 GW- N44 GW- N40 GW- N44 GW- N40 GW- N44 GW- N40 GW- N44 GW- N40 Sulfate 2810 1875 2507.5 1880 2535 1842.5 2610 1812.5 2671 1845 Magnesium 404.8 164.5 364.3 167.5 358.5 199.8 379.5 183.8 382.2 147.7 Iron total 0.3 0.07 U 0.04 U A.08 U <0.04 0.1 <0.04 Bicarbonate 442.8 365 419.5 409.3 420.8 318.8 407.5 331.8 413.9 355.6 Calcium 427.8 578.5 439.3 573.5 426 530.3 428.5 517.8 432.1 465.3 TDS 4620 3210 4142.5 3162 4170 3112.5 4362 3045 4383 3073 pH 7.0 7.2 7.1 7.1 7.1 7.1 7.2 7.1 7.0 7.1 9 SL-12 DRAFT 20AUG10.wpd 41