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<br />Another indicator of the potentl al for producing acid is the pasta pH. This is measured <br />M forming a slurry of the solids in distilled water. Nhile Phis test is not quantitative <br />in terms of amount oP aefd that potentially could be produend, it reflects the presence or <br />aDSenee of reactive DYrite. <br />An important factor in the production of acid by oxidation of pyrite is the rate that <br />fer roue iron is oxidl zed to ferrte Iron. At neutral pH's and higher, the reaction occurs <br />quickly. At loner pH's, bacterial catalysis is requS red far the reactt on to proceed <br />rapidly. The bacteria heeaoa aeti va at pH's below approximately 4.5 to 5. NS[hin The <br />aDProximate pH range of 5 to 7 there is a ^kinetie valley" where the reach an proceeds <br />al owly, The nautralizati on tapeeity of the rock, primarily provided by calcite, keeps the <br />pH above the range where bacterial catalysis 1a effective. Tha calcite serves primarily <br />to prevent the acid tram being protluead, and secondarily to neutralize the acid that is <br />produced. <br />Nucla East Core Data. Paste pH's and ABP's were naasured on sampias of overburden <br />and intsrburden fray the Nucla East area, Figure 17-10 is a plot of ABP versus pacts pH <br />for dace from core holes 1n the Nupla East area. Note that not ail samples wt th A[iP's <br />• leas than zero produce pasta pH's leas than 7.0, rather many with negative ABP'a have pH's <br />greeter than 7.0. Ths presence of pyrtta, or a negative ABP, is not itself an ind icetor <br />Nat acid problems are likely. , <br />Tha re appear to be two separate groups or popul ationa in the plot. Croup A sampl ea Forn a <br />hurl zontal trend line where the pH does not saes to be a function of ABP. Tha pH 1n th4a <br />group is generally aDOVe 6.5 or 7.0. The second group (B) tonsi ate of sanples where Ma <br />pH does appear to be a funet/on of ABP. The overburden, upper interhurden, and lower <br />intarburdan cantatn samples in Croup B, though not excT usi voly. For example, Me <br />overburden samples tall into both groups. Based on Carucaio's work, the dinttnetS On <br />between the two groups nisy be the presence or absence of franhoidel pyrite. The fl gore <br />FurMer ill uatratan that only a few of the nampl ea had low pH's. <br />As previ ousfy discussed, acidic zones (pN 4.5) were Tound in the upper and lower <br />interburdens (Uni to 2 and 4) in Noles 3H72E, ,f886E, anO 1877 E. No aeitlie zones were found <br />in the underburden. A thin acidic horizon (0.7 fk) occurred to the overburden to Hole <br />fi1t12E. Of the 4q8 ft of core from rocks overlyt nq the lower Dakota coal in the Nucla Eact <br />area, 74 ft (3.1 percent) axhi bit paste pH •a lower than 0.5. <br />17-a0 Revt sad Oq/ll/BB <br />• REVISED MARCH 2006 Attachment 2.05.6(3)-2-48 <br />