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sludge with the overburden materials, effluent data Erom 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 [he laboratory by exposing <br />unweathered overburden to 25 cycles of freezing-thawing and wetting-drying. <br /> The fly ash and bottom ash were obtained during the test burn of run-of-mine <br /> Trapper Mine coal at Hay den S[a[ion. This is the best alternative for obtaining <br /> representative ash short of actual combustion products from [he Craig Station. <br />i <br />• <br /> Seven sets of columns were prepared under controlled laboratory conditions. Two <br /> waste combinations, i. e. ash disposed of separately and in combination with simu- <br /> lated sludge gypsum), and three waste options, i.e. in D Pit in the spoils <br /> trough, spoils bench an d pit bottom, were initially investigated. Later, the <br /> effect of disposal in E Pit was studied through the addition of another column <br /> set simulating disposal on the spoil bench. Two columns of each overburden were <br /> leached individually to 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 column sets are summarized in Table 4.3-14 for refer- <br /> ence. <br />All [he test materials were uniformly packed into [he leaching columns specially <br />built for this project. The details of column configuraCion and operational pro- <br />cedures for various combinations of materials and placement are illustrated in <br />Figures 4.3-6 [0 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 />