Partition constants and adsorption desorption hysteresis for volatile organic compounds on soil from a Louisiana superfund site

The adsorption of four volatile organic compounds (1,4-dichlorobenzene,1,2- dichloroethane, 1,2,2-trichloroethane and 1,1,2,2,-tetrachloroethane) on th ree soil types from a Superfund site (Petroprocessors Inc) in Baton Rouge, LA was studied with the purpose of obtaining an overall correlation for inc lusion in a groundwater transport model being developed for site remediatio n. The soil-water partition constant, K-d was determined using a standard A STM procedure (E-1195-87). Using the data for different soil types (fractio n organic carbon between 0.11% and 1.13%) and different mineral surface are as (7 to 45 m(2)/g), the organic carbon contribution (K-oc) and the mineral matter contribution (K-min) to the partition constant were determined. The soils obtained were either from the Pleistocene period or recent shallow d eposits at the site. Both log K-oc and log K-min were linearly correlated t o log K-ow, the octanol-water partition constant. This data provided the ba sis for obtaining a general correlation for K-d on different soil types at the site. The predicted values were in agreement with that for a composite soil from the same site. The desorption of compounds from the high clay soi l after the 24 hour adsorption period was observed to show a biphasic behav ior, namely, an easily desorbed fraction and a desorption resistant fractio n. The easily desorbed fraction was found to be satisfactorily predicted us ing the conventional K-d as obtained from the adsorption experiment. The sl owly desorbing fraction had a time constant of several weeks. The concentra tion in the desorption resistant compartment was found to be dependant on t he initial amount of contaminant available for adsorption. The aqueous phas e concentration in equilibrium with the desorption resistant fraction was f ound to be similar to 8 mu g/L for dichlorobenzene and similar to 12 mu g/L for dichloroethane.