This study was conducted to evaluate the potential for leaching of metals from fly ash stabilized subgrade soils used in highway construction. Four different tasks were undertaken: (1) water leach testing (WLT), (2) laboratory column testing, (3) field lysimeter testing, and (4) numerical modeling. Testing was conducted on soil-fly ash mixtures that were prepared with three locally available fly ashes and four subgrade soils representing a range of subgrade soil conditions that might be encountered in Wisconsin. The WLTS showed that concentrations of metals in the leachate from soil-fly ash mixtures tend to be lower (1.5 to 2.5 times) than those from fly ash alone. The concentration increases non-linearly with increasing fly ash content, and cannot be estimated from a simple dilution calculation. The partitioning of metals between the solid and liquid phases is non-linear because the pH of the leachate increases nonlinearly with increasing fly ash content. Column leaching tests conducted in the laboratory showed that the pH of the effluent and initial effluent concentration from soil-fly ash mixtures increases wit
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