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<br />carbonate and sulfate minerals, and hence are controlled by the soT ubiiities of calcite <br />aM gypsum. EquSlibri um with calcite and gypsum is well-demonstrated. <br />Neutre/l zati on CaicuT ati ons. Acidic environnenta occur fn the lower Oakata coal, aM <br />may exist in the intarburdon between the upper and lower coals, On the other hand, <br />calcite is quite cov®on in surrounding materials. PHREEOE was used to investlgata the <br />neutralization of acidic Haters, and the mixing of acidic and neutral waters. <br />The sample with tfie lowest pH (GW-N20, July 12, 1906) was chosen to represent the acidic <br />wafer. The results of the geochemi cal modeling of saturation Tntllees is presented in <br />Table 17-10. A further seep In the analysis cansi ated of equilibrating this water with <br />calcite. The calculations indicated that 2.6x10 3 moles (0.26 gma) of calcite per liter <br />of water would be in the equilibration process, and the pH wou70 increase from 4.68 to <br />7.73. <br />Tha models nq of the mixing process was performed in three steps, and the resulting pH's <br />are gS van in Table 17 -11. In the analysi c, water from C.a-N20 (pH 4.68) was nixed with <br />water from CN-N21 (pH 7.77), a noni tors ng wall to the overDUrden. Fi rat, no mineral <br />• precipitation or di asolutian was modal ed. Next, .because the CM-N20 sample appears to be <br />at equSlfbrfuo with giDbslta, and the precipitation of gihbaita 7s a source of acfdtty, <br />its prectpi tali on was modeled. 7hirO, when the wafer waves into surrounding rocks, <br />calcite should di saol ve, gi bbalta and gypsum ahauld prncipitete. The third analysis <br />allowed these reacts ons W occur to equilibrium. Nixing proportions ware varied in steps <br />of 20 percent. <br />If no mineral reaeti ons occur, mixing of 20 percent G!/-N21 water with 80 percene Ot7-N20 <br />water increases the pN by over one pH unit and nautrali zation occurs rapidly, If gtbbatee <br />preoT pi totes, the pH increase fs not ea great at these proportions. But. if cal of to <br />dissolves, anO gypsum and gf Obaite precipitate. the pH inerea sea to above 7. The <br />neutralization is due to cal cf to di saoluti on rather than the mS xing process. The anal yais <br />indicates that at'greater proportions of Otl-N21 water, the pH is acCUally lower in the <br />third ease buC Ss caused by the Ow-N21 water not bas ng eonpl etely at equilibrium with <br />calcite and gypsum. <br />these calculations 1ndl cote that neutralization of acid should occur vary readily Sn the <br />geochemi gal aetti ng found at Nuela East, and that acid is waters should not typically <br />result from mt ning. <br />77-50 Revised 04/11/88 <br />• <br />REVISED MARCH 2006 Attachment 2.05.6(3}-2-59 <br />