USE OF A REACTIVE GAS-TRANSPORT MODEL TO DETERMINE RATES OF HYDROCARBON BIODEGRADATION IN UNSATURATED POROUS-MEDIA

A mathematical model is presented that simulates the transport and rea ction of any number of gaseous phase constituents (e.g. CO2, O-2, N-2, and hydrocarbons) in unsaturated porous media. The model was develope d as part of a method to determine rates of hydrocarbon biodegradation associated with natural cleansing at petroleum product spill sites. T he one-dimensional model can be applied to analyze data from column ex periments or from field sites where gas transport in the unsaturated z one is approximately vertical. A coupled, non-Fickian constitutive rel ation between fluxes and concentration gradients, together with the ca pability of incorporating heterogeneity with respect to model paramete rs, results in model applicability over a wide range of experimental a nd field conditions. When applied in a calibration mode, the model all ows for the determination of constituent production/consumption rates as a function of the spatial coordinate. Alternatively, the model can be applied in a predictive mode to obtain the distribution of constitu ent concentrations and fluxes on the basis of assumed values of model parameters and a biodegradation hypothesis. Data requirements for the model are illustrated by analyzing data from a column experiment desig ned to determine the aerobic degradation rate of toluene in sediments collected from a gasoline spill site in Galloway Township, New Jersey.