Biogeochemical modeling of reactive transport applied to laboratory and field studies on jet-fuel contamination

Within the PHREEQC framework, a dual Monod kinetics formulation has been included, which allows rate dependencies of both substrates, terminal electron acceptors and inhibitors. In this way, PHREEQC will simulate the redox processes under concern both with regard to kinetics and thermodynamics. Furthermore, PHREEQC allows one-dimensional reactive transport to be simulated.

The biogeochemical processes involved in transport and biodegradation of dissolved jet-fuel were simulated for two cases by PHREEQC with this Monod kinetics scheme. The column studies of Knudsen (2003) exploring dissolved jet-fuel transport and biodegradation within initially pristine aquifer sediments dominated by pyrite oxidation and calcite dissolution. Pyrite oxidation will compete with aerobic biodegradation, thereby reducing the efficiency of aerobic bioremediation. The 1D column simulations gave reasonable agreement with measured biodegradation, mineralization and pyrite oxidation rate, and reproduced the overall microbial processes well, but they failed to mimic the observed ferrous iron. A dual porosity approach should be included.

The second case with a jet-fuel contaminated plume under monitoring was simulated with a 1D PHREEQC column from a plume cross section along the flow direction. The biogeochemical reactions themselves were described reasonably well, but dispersional/diffusional transport effects could not be simulated sufficiently with a 1D column of PHREEQC alone. Here truly coupled models of 3D flow and biogeochemical reactions must be applied.