Trace Elements Leaching from Organic Soils Stabilized with High Carbon Fly Ash

Leaching of four trace elements [cadmium (Cd), chromium (Cr), selenium (Se), and silver (Ag)] from soft organic soils stabilized with high carbon fly ashes (HCFAs) was assessed using water leach tests (WLTs) and column leach tests (CLTs) on soil alone, fly ash alone, and soil-fly ash mixtures. Concentrations from the WLTs on soil-fly ash mixtures were lower than concentrations from the WLTs on fly ash alone, and were controlled more by the fly ash than the soil. However, dilution calculations based on tests on soil alone and fly ash alone were unreliable. Thus, leaching assessments should be conducted directly on soil-fly ash mixtures. Leaching patterns from the CLTs followed first-flush and lagged-response patterns with comparable frequency, although first-flush patterns were more common with fly ash with higher calcium oxide content. Cd and Cr exhibited first-flush leaching more frequently, Ag a lagged-response pattern more frequently, and Se exhibited first-flush or lagged-response patterns with similar frequency. The hydrogen ion concentration (pH) had a strong effect on leaching concentrations, with lower concentrations of Ag and Cd and higher concentrations of Cr at a higher pH. Peak concentrations of Ag and Cd for flow-through conditions can conservatively be estimated as 50 times the WLT concentration, whereas a factor of 100 should be applied for Cr and Se for organic soil-HCFA mixtures. DOI: 10.1061/(ASCE)GT.1943-5606.0000653. (C) 2012 American Society of Civil Engineers.