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In summary, blending of the gypsum with [he ash will increase leachability of <br />vanadium from the ash. The blending of gypsum with [he ash will reduce the <br />leachability of barium and aluminum from [he ash. <br />Effect of Disposal Options <br />There are three basic options for disposal of the ash and scrubber sludge in the <br />mine: the bottom of [he pi[ (S-4), on [he spoils bench (S-2), and in [he spoils <br />trough (S-1 ). (Spoil depressions are considered to be the same as bottom of the <br />pit.) Each of these disposal options could have an impact on the quality of any <br />percolate from the mine if a percolate occurred. It should be noted again that a <br />percolate is not expected. <br />The hydrological impact of these waste placement options has been evaluated <br />through the use of three sets of columns representing the options and a column of <br />ash to establish the inlet concentration. Concentrations of eight key chemical <br />species (Ba, A1, A, Cr, Mo, 504, V and Mn) plus pH, conductivity, and TDS are <br />summarized in Tables 4.3-21, 4.3-22, and 4.3-23 for S-1, S-2, and S-4. <br />Both the graphical representation of attenuated concentration as a function of <br />volume of effluent and the mass normalized attenuation (mg of element attenuated <br />per kilogram of overburden) as a function of percolation (cumulative effluent <br />volume per unit area of the column) for each element will be presented together <br />for ease of reference. <br />Barium in the ash leachate was highly attenuated in each of the three disposal <br />options as can be seen in Figure 4.3-14. Concentrations were reduced from 90 <br />mg/1 to less than 0.4 mg/1. The primary drinking water limit is 1 mg/l. This <br />attenuation may be due in par[ to the limited solubility of barium sulfate. The <br />attenuation behavior of S-4 indicates [hat either [he coal is attenuating Ba or <br />the chemical characteristics of the overburden leachate preclude the leaching of <br />Ba. The normalized attenuation of the overburden is calculated [o be in excess <br />of 80 mg/kg as "breakthrough" of barium has no[ been observed. <br /> <br />4-76 <br />