Laboratory assessment of BTEX soil flushing

Soil cores from the unsaturated zone of a waste site contaminated with benzene, toluene, ethylbenzene, and xylenes (BTEX) were flushed with water under conditions representative of those proposed for site remediation. With a laboratory column dispersivity of 1 cm, kinetic modeling of the breakthrough curves gave desorption rate constants of 0.01-0.1 h(-1). Desorption studies in batch tests gave similar rates after accounting for differences in the solid-to-water ratios. The presence of nonaqueous phase liquid (NAPL) in one soil column was deduced from the flushing behavior of the xylenes, which showed increasing effluent concentration with increasing time. The amount of NAPL was estimated to be 5 mg(NAPL)/g(soil) from the flushing of the most water-soluble constituent, benzene. This quantity of NAPL would increase the site's estimated flushing time by more than a factor of 5 over the case with only kinetically limited desorption of BTEX from soil particles.