A Practical Measurement Strategy to Estimate Nonlinear Chlorinated Solvent Sorption in Low f_oc Sediments

In this study, we tested a practical strategy useful for accurate chlorinated volatile organic compound (cVOC) sorption prediction. Corresponding to the feature of the superposition of adsorption due to thermally altered carbonaceous matter (TACM) with organic carbon-water partitioning, a nonlinear Freundlich sorption isotherm covering a wide range of aqueous concentrations was defined by equilibrium sorption measurement at one or a few low concentration points with extrapolation to the empirical organic carbon-water partition coefficient (K_oc,e) near compound solubility. We applied this approach to obtain perchloroethene equilibrium sorption isotherm parameters for TACM-containing glacial sand and gravel subsoil samples from a field site in New York. Sorption and associated K_oc,c applicable to low (5-500 μg/L) and high (>100,000 μg/L) aqueous concentrations were determined in batch experiments. (The K_oc,c is the organic carbon-normalized sorption partition coefficient corresponding to aqueous concentration C_w.) The K_oc,c measurements at low concentration (~5 μg/L) were 6 to 34 times greater than the K_oc,e. The importance of this type of data is illustrated through presentation of its substantial impact on the site remedy. In so doing, we provide an approach that is broadly applicable to cVOC field sites with similar circumstances (low carbon content glacial sand and gravel with TACM).