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sludge with the overburden materials, effluent data from individual ash and over- <br />burden leaching columns were also collected and analyzed for leachate concentra- <br />tion. <br />In order to obtain a homogenous sample of overburden representing various depths <br />and locations, spoil/overburden subsamples were collected from highwalls and <br />spoil benches of both Pits A and D. These subsamples were then composited to <br />obtain a single composite sample for Pits A and D. Similarly, a separate compo- <br />site sample.representative of Pit E was also obtained. <br />Weathered overburden was artificially generated in the laboratory by exposing <br />unweathered overburden to 25 cycles of freezing -thawing and wetting -drying. <br />All the test materials were uniformly packed into the leaching columns specially <br />built for this project. The details of column configuration and operational pro- <br />cedures for various combinations of materials and placement are illustrated in <br />Figures 4.3-6 to 4.3-9. Components of each column set were about 7.5 inches, 15 <br />inches and 30 inches long with an inside diameter of about 3 inches. The columns <br />were constructed of polycarbonate plastic to avoid contamination of boron from <br />4-58 <br />The fly ash and bottom <br />ash were obtained during the test burn of run -of -mine <br />Trapper Mine coal at Hayden <br />Station. This is the best alternative for obtaining <br />representative ash short <br />of actual combustion products from the Craig Station. <br />i <br />• <br />Seven sets of columns were prepared under controlled laboratory conditions. Two <br />waste combinations, i.e. <br />ash disposed of separately and in combination with simu- <br />lated sludge (gypsum), <br />and three waste options, i.e. in D Pit in the spoils <br />trough, spoils bench and <br />pit bottom, were initially investigated. Later, the <br />effect of disposal in E <br />Pit was studied through the addition of another column <br />set simulating disposal <br />on the spoil bench. Two columns of each overburden were <br />leached individually to <br />evaluate the effects of weathering and to provide neces- <br />sary data for evaluating the interactions of the overburden and utility waste, <br />during leaching. These <br />column sets are summarized in Table 4.3-14 for refer- <br />ence. <br />All the test materials were uniformly packed into the leaching columns specially <br />built for this project. The details of column configuration and operational pro- <br />cedures for various combinations of materials and placement are illustrated in <br />Figures 4.3-6 to 4.3-9. Components of each column set were about 7.5 inches, 15 <br />inches and 30 inches long with an inside diameter of about 3 inches. The columns <br />were constructed of polycarbonate plastic to avoid contamination of boron from <br />4-58 <br />