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The water holding capacity of refuse material is low. Mixing <br />refuse material with prep plant slurry could possibly increase <br />this capacity. <br />2.4 Relative Acidi <br />Statistical tests indicated no significant differences in <br />acidity between new refuse material and topsoil; however, new <br />refuse with an average pH of 8.65 was significantly more basic <br />than old refuse pH (X=7.56). Linear regression analysis indicat- <br />ed a highly significant negative correlation between age of <br />refuse material and pH. Only one refuse pile sampled had pH <br />levels that could be considered toxic to plants. The pH of this <br />60 year old refuse pile was 2.96. However, pH exhibited varia- <br />tion even within data groups. For example, two 30 year old <br />refuse piles located in the same general area had pH's of 6.24 <br />and 8.46. This is probably due to the variation in geologic <br />strata from which the coal material was obtained. <br />The potential for acid formation results from the oxidation <br />of pyrite which is often associated with coal seams. In eastern <br />coal refuse, acid formation in the presence of certain types of <br />iron bacteria and high precipitation often proceeds at a rapid <br />rate. In the west, acid formation may take considerably longer <br />since precipitation regimes are low. Acid formation is also <br /> <br />2-9 <br />