DISSOLUTION AND BIORESTORATION OF NONAQUEOUS PHASE HYDROCARBONS - MODEL DEVELOPMENT AND LABORATORY EVALUATION

A one-dimensional numerical model is presented for simulating the enha nced biorestoration of aquifer material contaminated with residual non aqueous phase liquid (NAPL) hydrocarbon. The model simulates the simul taneous dissolution, transport, and biodegradation of individual hydro carbons under oxygen-limiting conditions. Partitioning between the NAP L and aqueous phase is modeled as a linear first-order process where t he NAPL is composed of two fractions, a fast oil fraction with a high mass transfer rate and a slow oil fraction with a much lower mass tran sfer rate. Microorganisms are assumed to be present attached to the so il grains and are assumed to be immobile. Biodegradation of the proble m compounds is simulated as a multistep process where the parent compo unds are first biotransformed to oxygenated intermediates. These inter mediates may then be mineralized to CO2 and H2O. Comparison of model s imulations with experimental results from soil columns containing resi dual hydrocarbon and an active microbial population indicate that the model is capable of simulating the extent of hydrocarbon biodegradatio n using reasonable model parameters. Model simulations indicate that i f benzene, toluene, and xylene are assumed to be completely mineralize d, the model will greatly underestimate the extent of biotransformatio n. The model overestimated the extent of hydrocarbon biotransformation at low substrate concentrations.