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• glass or [race metals from steel. The translucent nature of the column allows <br />visual observation of performance of the columns, e.g. detection of channeling. <br />The diameter and length of the column minimizes wall effects. The relative <br />lengths of the columns simulate mass ratios of waste and overburden anticipated <br />in [he field. Deionized water was percolated upgradient through [he columns to <br />avoid channeling and [o .provide the reproducibility necessary for comparison of <br />column sets. Depending on specific objectives of each column set, ash and gypsum <br />leacha[es were allowed [o flow continuously or periodically into the columns con- <br />taining the natural spoil material to study the trace element attenuation. <br />Results <br />Analytical results of these eight chemical parameters for each of the columns of <br />ash, ash-gypsum, and overburdens are presented in Tables 4.3-15 through 4.3-20. <br />In addition [o these parameters, pH, total dissolved solids, and conductivity are <br />referenced. The data are organized according to date the aliquot was taken and <br />_ the total volume of leachate collected. <br />Generally, concentrations of contaminants decrease with increasing volumes of <br />leachate passed through a given mass of material. This occurs as soluble mater- <br />ial is leached from the waste during the passage of [he first few aliquots of <br />water. This type of behavior was exhibited by barium, aluminum, boron, chromium, <br />molybdenum, and sulfate in [he leaching of the ash. The mixture of ash (80 <br />weight percent) and gypsum (20 weight percent) exhibited similar behavior with <br />[he exception of barium. This leaching behavior is graphically presented in <br />Figures 4.3-10 through 4.3-13. <br />The leaching characteristics of boron are very similar for both the ash column <br />and [he ash-gypsum column indicating [h a[ dissolved calcium sulfates from [he <br />gypsum have little effect on the leaching characteristics of boron (Figure <br />4.3-10). The concentration of boron is significant when compared to the irriga- <br />tion water limit of 0.75 mg/l. Even after the passage of 16,000 ml of leachate <br />through 1,000 grams of ash the concentation of boron in the ash leachage was <br />still exceeding 3 mg/1. These high concentrations would require significant <br />~. attenuation by [he overburden in order to protect [he ground water .if a leachate <br />occurred. <br />4-64 <br />