SIMULATING SOLUTE TRANSPORT USING LABORATORY-BASED SORPTION PARAMETERS

The experimental in situ aquifer biorestoration site at Moffett Field, California, is a small, confined, sand and gravel aquifer, interspersed with layers of silts and clays. Laboratory sorption and solids characterization studies were carried out on core material recovered from in and around the aquifer zone. Equilibrium (distribution coefficient K(d)) and nonequilibrium (effective pore-diffusion coefficient D(p)) sorption parameters, estimated from batch experiments, were used in one-dimensional simulations of the breakthrough of three halogenated organic compounds: trichloroethylene (TCE), carbon tetrachloride (CT), and vinyl chloride (VC). Three types of transport models were used: equilibrium partitioning, spherical diffusion, and equivalent first-order diffusion. The hydrodynamic parameters (dispersion coefficient and porc water velocity) were determined previously using field-scale tracer tests. Simulations reconfirmed the theory that while an accurate K(d) value is required for each compound. it is sufficient, for similar compounds, to measure the rate parameters for one compound. then calculate these parameters for the other compounds. Although the simulations were generally successful, difficulty in estimating the field particle size, and a lack of understanding of field-scale heterogeneities, limited the accuracy of the simulations and the potential for model verification.