Soil heating for enhanced remediation of chlorinated solvents: A laboratory study on resistive heating and vapor extraction in a silty, low-permeable soil contaminated with trichloroethylene

Thermally enhanced remediation of trichloroethylene (TCE) from a 50 cm deep silty soil was demonstrated in a hive-dimensional laboratory tank. Volatilized TCE was captured by vapor extraction in an overlaying coarse sand layer. Soil vapor extraction was first tested alone at 23 degrees C, showing very little efficiency due to the low-permeable layer and an estimated cleanup time of more than 1 year. By injecting electric current, the temperature was increased to 85 and 100 degrees C in steps, and the fluxes of TCE increased by factors of 2.6 and 19, respectively. After 37 days of heating, the mass of TCE in the soil was reduced from 35 to 0.072 g, corresponding to 99.8% mass removal. Average soil TCE concentrations were reduced from 273 to 0.6 mg/kg. Steam production by boiling of pore water and a 9-fold increase in the Henry's law constant of TCE were identified as the major mechanisms for overcoming mass-transfer limitations. The silty soil did not dry out due to water addition at the current electrodes, which is promising for the use of thermal enhancements for remediation of water-saturated clay layers and in shallow groundwater. In-situ thermal cleanups can be done in a few months, at costs typically below $100/m(3), and with very high removal efficiency for volatile and semivolatile organics.