HYDROCARBON DISSOLUTION AND TRANSPORT - A COMPARISON OF EQUILIBRIUM AND KINETIC-MODELS

The dissolution and transport of trapped nonaqueous phase liquid hydrocarbon (oil) was examined in a laboratory column study using aquifer material from a site contaminated with aviation gasoline. Two mathematical models were compared for simulating the dissolution of trapped oil. The first model assumes that mass transfer will be rapid relative to groundwater flow and that the concentrations in the aqueous and oil phases will be at equilibrium. The second model assumes that mass transfer between the aqueous and oil phases is best described by a linear resistance relationship. Both models assume that equilibrium concentrations in the oil and the aqueous phases can be estimated by equating activities in each phase. Numerical simulations using both models are generated and compared with column study results. Overall, the kinetic model appears to provide a somewhat better description of the dissolution process, although this model requires significantly greater computation times. A simple procedure is described to develop an order of magnitude estimate of the number of pore volumes of water required to flush individual hydrocarbons from the aquifer material.