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pH. The soil reaction (or pH) of the growth medium significantly <br /> affects the availability of essential nutrients in addition to the <br /> solubility of potentially toxic ions. The pH ranges from extremely acid <br /> (2.8) to moderately alkaline (8.2) . The extremely acidic pH values <br /> occur in the overburden and interburden when shallow coal is <br /> encountered. Core hole site 2C, located near Mine Areas 2 and 3 had the <br /> lowest pH values. Based upon the data presented in Tables 6-6 and 6-7 <br /> and Figure 6-4 (also see Figure 6-3) , pH values were determined on Phase <br /> II samples and will continue to be determined on all subsequent samples <br /> collected at Nucla Mine. <br /> Total Sulfur - Acid Base Potential . The sulfur content of overburden <br /> and interburden is determined to predict the acid - producing potential <br /> of this material . In conjunction with potential acidity, the <br /> neutralization potential from alkaline carbonates , exchangeable bases <br /> and weatherable silicates is measured. After the potential acidity and <br /> the neutralization potential are determined, an acid base balance is <br /> determined by subtracting the potential acidity from the neutralization <br /> potential . <br /> The sulfur content and acid-forming potential is greatest for the <br /> interburden and also the 5 to 15 feet of overburden immediately above <br /> the upper Dakota coal seam. Core hole site 2C located near Mine Areas 2 <br /> and 3, had the lowest acid base potential values (Figures 6-3 and 6-4) . <br /> These strata correlate well with the extremely acidic zones identified <br /> previously in the pH section. Potential acidity and neutralization <br /> potential were determined on all samples collected from Mine Areas 2 and <br /> 3. Sulfur fractionation (i .e. , pyritic, sulfate and organic) analyses <br /> were performed when potential acidity exceeded the neutralization <br /> potential and/or when the total sulfur content was greater than 0.5 <br /> percent. <br /> Ca, Mg, Na and SAR. The water soluble Ca, Mg and Na analyses reveal the <br /> type and concentration of salt that exists in solution. The ion <br /> concentration is directly proportional to the soil conductivity. The <br /> ratio of soluble Na to Ca plus Mg, referred to as SAR, is commonly used <br /> to predict both chemical and physical properties of a growth medium. <br /> 6-25 Revised 3/6/87 <br />