Diffusion and sorption of hexachlorobenzene in sediments and saturated soils

In order to understand the transport and fate of hydrophobic organic chemic als (HOCs) in consolidated sediments and saturated soils, long-term (up to 512 d), one-dimensional, time-dependent diffusion experiments were done wit h a representative HOC, hexachlorobenzene (HCB), in three different sedimen ts and soils. In addition, long-term HCB partitioning experiments in suspen ded sediments at high concentrations and tritiated water diffusion experime nts in consolidated sediments were done in order to more accurately interpr et the HCB diffusion experiments. Numerical models were used to analyze the results. Good agreement between the experimental data and calculated resul ts was obtained. Despite the length of the experiments, the experimental re sults demonstrate that the HCB in the consolidated sediments was far from a steady-state chemical equilibrium. Experiments and theoretical results als o indicate that the assumption of local chemical equilibrium was not valid, and sorption rates must therefore be considered for a valid analysis of tr ansport.