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ITASCK <br /> Denver, Inc. <br /> mineral dissolution it is approximately 0.4. Samples B5, PC3, and L2 had sulfate to acidity ratios <br /> near 1.0 from approximately week 25 through the end of testing. <br /> Figure 4-2 shows the HCT leachate pH versus acidity. The highest acidity values are related to the <br /> first flush of solutes from PC3. Samples with pH values as low as 4.0 had acidity concentrations <br /> at the detection limit. The acidity measured in leachate from samples B8 and B12 is low relative <br /> to samples with similar or higher pH. <br /> 4.3 COMPARISON TO ABA AND NAG RESULTS <br /> Figure 4-3 shows the Phase II sample NNP values from ABA testing versus their average HCT <br /> leachate pH. Samples B5, B7, B8, B12, L2, PC3, and PP6 were net acid-generating based on ABA <br /> testing and generated acidic HCT leachate (Figure 4-3). Each of these samples except for B8 also <br /> had NAG pH values less than 4.5. Sample B2 was mildly net acid-neutralizing based on its ABA <br /> test results, with an NNP value of 12.2 kg CaCO3/t (Figure 4-3). Sample B2 also generated <br /> circumneutral leachate in humidity-cell testing. This result is consistent with the net neutralizing <br /> result from the ABA test and the NAG pH value greater than 4.5. Samples AP7, B3, PP2, and PP4 <br /> had negative NNP values based on ABA testing but generated circumneutral leachate in humidity- <br /> cell testing (Figure 4-1g). Each of these samples except for B3 had NAG pH values greater than <br /> 4.5, indicating that the samples are not acid-generating based on the NAG test. Three of these <br /> samples had NNP values between -20 and 0 kg CaCO3/t, indicating that there is uncertainty in the <br /> samples' potential to generate acidity.The fourth sample,AP7, had an NNP value that was slightly <br /> less than-20 kg CaCO3/t(-23.1 kg CaCO3/t).Thus,the HCT results generally corroborated the ABA <br /> and NAG testing results for the Phase II samples. <br /> 4.4 PARTICLE-SIZE DISTRIBUTION <br /> Weathering reactions are typically especially sensitive to the reactive surface area of a mineral. In <br /> this study, the specific surface area (SSA) was estimated using the results of a particle-size <br /> distribution analysis.The SSA was calculated usingthe assumption that the sample grains are shaped <br /> 27 <br />