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• 19 <br />Two general features of acid development in the humidity cell effluents from the various <br />samples are evident in Figure 3. First, the difference between initial pH and current pH is <br />most marked in groups 3 and 4 while in groups 1,2, and 5 there has been little change in <br />pH over the time of the tests. Second, the relationship between pH and total sulfur is such <br />that there is a general increase in effluent acidity with increasing sulfur content from <br />groups 1 through 4 but group 5, with the highest sulfur content of all the samples, does <br />not show the greatest acidity or lowest pH. <br />The data in Figure 3 appear to be generally consistent with the explanation for <br />variations in pH offered by the authors or the reviewed report as these variations <br />relate to acid release and neutralization reactions in the various horizons or zones of <br />the Cresson materials. The fact that humidity cell tests span a varied lifetime in this <br />sample set may complicate this analysis but at this time there is no evidence that this <br />complication will invalidate the conclusions presented in the report. <br />The materials in groups 3 and 4, and possibly in group 5, are judged by the authors to be <br />the most likely materials to present a risk of substantial long term acid release when they <br />are contacted by air and water in the natural environment. These samples represent 50% <br />of the total number of samples reported for humidity cell tests and consist of materials <br />with total sulfur contents over about 0.32%. <br />Based upon the behavior of the 5 groups of materials in the humidity cell tests, the authors <br />of the report propose to divide the set of samples into two "types" which they designate <br />TYPE A and TYPE B. The TYPE A materials have a total sulfur content of 0.80% or <br />less while the TYPE B materials have total sulfur contents higher than 0.8%. Any plan to <br />separate materials on the basis of total sulfur content is operationally favored by the <br />relative simplicity of performing total sulfur analyses with the Leco analyzer and I believe <br />this is a more reliable analyzer for sulfur content than visual estimate of pyrite which has <br />been suggested as a field method in the past for material grading. <br />Given the apparent level of acid release in groups 3 and 4 materials and the high <br />sulfur (and probably reactive sulfide levels) in the group 5 materials, I think a case <br />can be made for considering groups 1 & 2 to be TYPE A material and the remaining <br />materials to be classed as TYPE B. This would have the effect of moving the total <br />sulfur content for the separation between TYPES A & B materials to about 0.5%, <br />significantly lower than the proposed 0.8%. This would, of course, mean that more <br />of the overburden materials would be classed as TYPE B and have to be managed as <br />amore acid generating waste. <br />OWII.R951DEH <br />