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• Aluminum, like barium, was highly attenuated in each case. Concentrations typi- <br />cally were reduced from 100 mg/1 to less than 0.5 mg/1 with underlying overburden <br />and [o less than 5 mg/1 with overlying overburden when the waste is placed in the <br />pit. The attenuation capacity of the overburden for aluminum exceeds 400 mg/kg <br />as shown in Figure 4.3-15. <br />Boron, on [he other hand, is only slightly attenuated by [he overburden as demon- <br />strated in Figure 4.3-16. Concentrations in the ash leachate are initially <br />attenuated from in excess of 50 mg/L to less Chan 2 mg/1 with bench disposal and <br />0.84 mg/1 with trough disposal. Pit disposal was relatively ineffective at <br />reducing the concentrations. The irrigation water standard is 0.75 mg/1. The <br />attenuation capacity of the overburden was calculated a[ approximately 30 mg(l. <br />Chromium concentration in the ash leachate was successfully attenuated in each of <br />the three disposal options to a concentration approximately equal or less [h an <br />the primary drinking water limit of 0.05 mg/1. The attenuation capacity of the <br />overburden is estimated [o be .approximately 0.75 mg/kg as derived in Figure <br />4.3-17. <br />Molybdenum was attenuated by the overburden to [he tune of 0.5 mg/kg. Break- <br />through of molybdenum in S-2 is half of the volume required by S-1; consistent <br />with the mass ratios of the overburden. Prior to breakthrough, concentrations <br />were reduced to values below the analytical detection limit of 0.04 mg/1. The <br />spike displayed in Figure 4.3-18 for S-4 may be [he "chromatographic peak" of 5 <br />mg/1 concentration fo the firs[ aliquot of the ash leachate. <br />Sulfate and vanadium and manganese are not attenuated by [he overburden as shown <br />in Figures 4.3-19, 4.3-20 and 4.3-21. <br />A kilogram of overburden in either trough or bench disposal will attenuate 30 mg <br />of boron and 0.5 mg of molybdenum. Attenuation capacities for aluminum and bar- <br />ium are greater than 80 and 400 mg/kg, respectively, and represent a lower bound <br />as the overburden was no[ saturated with these species. The higher attenuation <br />capacity of the bench disposal for chromium may be [he result of analytical sen- <br />sitivity as [he effluent concentration approached the ICAP detection limit. <br />4-81 <br />