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n <br />U <br />Tha Ad's range from -25 {n a886E (Unit 4) to +20 in a1861E (Unit 3), The more actdfc <br />material is asaoci ated with high pyrite coneentr aei ons which are higheaC in 5886E (Unit 4, <br />1.5 percent), I882E (Unit 4, 1.38 percent), and.in a<887E (Unit 2, 3.8 parcmt). The zones <br />of highest pyrite content occur almost ~axeluai vely directly above either the upper or <br />lower Dakota coal seams. <br />Underburden Material. The undarburden (UniE 6) consists of the sandstone and <br />asaoci ated shale directly beneath the lower Oekota coal seam (Table 17-8). All core ho7 es <br />atop in ve ri oua parts of the sandstone ao undarburden thi ckneases cannot be accurately <br />defined or computstl. Trace elements found in low eencentrations and considered to ba <br />naturally occurring are B, Fe, Hn, Ca, Pb, Ln, Ni, Ca end Hg. Analyses of soil pH ahaw a <br />range frga 7,3 to 8,0 and AeP ealculati ons range from -12.4 in /BB1E to +67,6 in k870E. <br />The pyrite content ranges from .03 to .80 percent in 1861 E. <br />Controls on Cround Water puality. <br />lntroducti on, The chemistry and quality of ihs ground water is detarni ned by <br />chemical reactions (such as dissolution or pyrite, caT cf to and other minerals) and by <br />• dilution ni th irri getion mater. In the Nucla East arse, the water is marginal to poor <br />quality, and 1a not suitable for drtnki ng Hater. The total di aaolved solids content and <br />sal}ate concentrations are high, and drinking water atanderde far niCrata, cadmium and <br />sal ant ua are exceeded in some ereaa. 9aconda ry drinking water standards for from, sulfate <br />. and manganese are exceeded throughou! the area. <br />This section wi T1 address the controls on water charm stry by several approaches. The <br />geoehemf cal aped ati on code PHRE£OE (Parkhurst, et al ., 7980) will be used to analyze <br />mineral salability controls. Soars of the tools and interburdens contain high <br />wneentrat; ons of pyrite, and low paste pH's have been measured. The Smpact of acid <br />product; on and evidence of 1ta Impacts will be addreaeed. The effects of dl luti on by <br />irrigation will be investigated us trg data from faY-N9. Because of the potential for <br />mobil tzi~g' trace metals with the production of acfd through oxidation of pYri te, the <br />pote~ial far production of acid will bs addressed first. <br />Meehani sma for Production of Acid. She iron disulfide mi nerels pyri Ee and na roast to <br />are thermodynamically unstable under ox idizf ng environments. In coal-forming <br />environments, iron sulfide (mackinaws te) and disulfides (pyrite and marcasite) era formed <br />17-37 - Ravi sad 04/11/86 <br />• <br />REVISED MARCH 2006 Attachment 2.05.6(3}2-45 <br />