| The objective of this work is the development of a numerical model which can simulate the complex combination of physical, chemical, and biological processes affecting contaminant fate and transport in porous media. The resulting computer program, HYDROBIOGEOCHEM, is a coupled model of hydrologic transport, geochemical and microbiological reactions in heterogeneous, anisotropic, variably saturated porous media. Chemical processes included are aqueous complexation, acid-base reactions, reduction-oxidation reactions, adsorption, ion-exchange and precipitation-dissolution, Microbiological reactions address growth of biomass and degradation of substrate by microbial metabolism of substrates, nutrients and electron acceptors. Chemical reactions controlled by equilibrium are solved using the law of mass action relating the thermodynamic equilibrium constant to the activities of the products and reactants. Kinetic chemical reactions are solved using reaction rate equations. Microbiologically mediated reactions for substrate removal and biomass growth are specified using modified Monod kinetics. HYDROBIOGEOCHEM iteratively solves the two-dimensional transport equations and the ordinary differential and algebraic equations of mixed geochemical and microbiologically mediated reactions. Input to the program includes the geometry of the system, the properties of the media, the relevant chemical and microbiological reactions, and initial and boundary conditions. Output includes the spatial distribution of chemical and biomass concentrations at desired times. The model provides a tool for evaluating the physical, chemical, and biological aspects of soil and groundwater contamination problems and for assessing remediation alternatives. |
