Beneficial reuse of coal combustion byproducts requires an evaluation of metal leaching potential. Reuse of high carbon fly ash in highway embankment construction was evaluated using different soil-fly ash mixtures and three common leaching tests: the water leach test (WLT), the Toxicity Characteristic Leaching Procedure (TCLP), and the column leach test (CLT). The effect of test methodology and pH on Cu, As, and Cr leaching was examined. TCLP concentrations for Cu and As exceeded those from WLTs in the majority of mixtures due to lower pH conditions, while Cr was higher in the WLT for alkaline fly ash mixtures. Peak CLT concentrations were higher than TCLP and WLT concentrations for the majority of mixtures, but usually decreased rapidly, suggesting that leachate concentrations might exceed regulatory limits, but only for a short time. Based on these results, a combined WLT and CLT leaching protocol for testing fly ash mixtures is presented.