Modeling chemically and microbiologically reactive contaminant transport in porous media

HYDROBIOGEOCHEM is a finite element model which couples simulation of microbiological and geochemical transformation with hydrological transport of contaminants in soil and groundwater. Microbiological reactions addressing growth of biomass and degradation of substrate by microbial metabolism of substrates, nutrients, and electron acceptors are simulated using modified Monod kinetics. Chemical processes in this code may be equilibrium or kinetic and include aqueous complexation, acid-base reactions, reduction/oxidation reactions, adsorption, ion-exchange and precipitation/dissolution. Simulation of hydrological transport is performed in two dimensions and includes the processes of advection, dispersion, and molecular diffusion. Two alternate numerical schemes are included. A fully implicit, iterative scheme provides a more accurate solution. An operator splitting scheme provides a more robust but less accurate solution for those problems in which convergent solutions are difficult to achieve. This paper summarizes the governing equations solved by HYDROBIOGEOCHEM and the numerical schemes used to achieve a solution to these equations and presents an example problem to demonstrate the application of this computer code.