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<br />`Nucla East mining areas. Tha waters arm close to equilibrium with dolomite. Dolomite <br />typi tally does not exht bSt the same control that ealei to does; the larger vari att on in <br />dolomite's SI (compared to that of cal ci te)'indi eaten that at Nuc1a and Nuc]a East, <br />dolomite may affect, but probably does not ^control" the water chemistry. The presence of <br />dolomi to has not been eonfi reed. <br />An exception to the above statement about cslelta and gypsum solubility controls on <br />chemistry is GW-N20. The well is completed in a pyrite-rich coat. This discussion <br />addressee the water sample pith Che lancet pH from either the Nuc1a or Nucla East areas. <br />No a]kaltnity wan measured in this sample. Therefore, an SI for cal of to could not DB <br />calculated, and presumably eeleite aquilibrtun exerei ssd ttttle control on the Chemi atry <br />of this sample. Tha low pH suggest9 the absence of Carbonate minerals. The acid <br />was produced by oxidatf on of pyrite, producing sulfate and precipitating gypsum. The <br />aluminum concentration, probably resul tf ng from di saoluCion of clay mi nerais, to high, and <br />appears to be controlled by prnci pitaCi on of gt bbsite (or perhaps amorphous A1(OH)3). The <br />water is undersaturated with fluorite, because of an alwai num fluori da complex that makes <br />the fluoride unavailable for precipitation of fluorite. <br />• The geoChami cal analyses can he used to evaluate the behavior of irate, amtala. Where <br />Cadmium and lead are present in detectable quantities, they aDPear to be in equflibri usi <br />with their rsspeCti ve carbonate minerals. Thin sugges to that prectpt Cation of atavi to end <br />cerrusite limit the ConC6ntrationa of these metnla. Because these ara carbonate minerals, <br />their aolubt llty is pH sensitive. <br />Coneentratt ons of, for example, cadmium appears to be strongly controlled by the <br />soluDSltty of otavtte (CdC03). In order to invasti gate the sol ability of eatlmium as a <br />function of pH, the analyses of the October, 1978 sample from CVi-N15 »ere alloned (using <br />PHREEOE) to equilibrate with calcite, gypsum. cerrusS tam bar; te, and otavi te, after <br />netting the pH to several pH's in the range 4 to 10. Ths results ere shown in Figure <br />17-13. At pH about 7.5, the equilibrium cadmium co~antrati on is approximately constant <br />aC 5 to 6 ug/l, As pH Oecreaaea, the equilibrium eoneentratl on increases, aspeei ally <br />below pH fi. In this instance, the Drinking Water Standard »oultl be exceeded at pH•s lean <br />than approximately 6.2 or 6.3. haters with slightly different Chemistry might behave a <br />little di}farently. Lead is predicted to behave in a aims lar manner. Both lead and <br />cadmium form complexes with aulfata, so that their Conesntrati one wt 17 be a function of <br />Me su ifate concentration, which, in turn, is controlled by the solubility of gypsum. <br />77-47 Revi sad 04/11/86 <br />\J <br />REVISED MARCH 2006 Attachment 2.05.6(3)-2-56 <br />