Sorption and desorption of volatile alkyl halides in a desert soil

Abstract

A series of twelve laboratory column experiments were conducted to determine equilibrium partitioning coefficients (K ) and kinetic rate coefficients for sorption of four hydrophobic pollutants on a low organic carbon natural soil. K 's for trichloroethene (ICE), tetrachloroethene (PCE), 1,1,1-trichloroethane (TCA), and 1,1,2,2-tetrachloroethane (PCA), were 0.17, 0.44, 0.06, and 0.05, respectively; about as expected based on empirical carbon-based partitioning equations found in the literature. Tailing of the breakthrough curves could be accounted for with a two-site non-equilibrium solute transport model. Rates were fast compared to pore water velocities normally encountered in an alluvial aquifer, but kinetic effects were observed at pore water velocities likely to be encountered during pumping, such as for site cleanup. Desorption was faster than adsorption, with forward rates of about 10⁻⁴ to 10⁻⁵ s⁻¹ and reverse rates about 10⁻³ to 10⁻⁴ s⁻¹. The two-site model indicated that slower sites constituted roughly half the total number of sites.