We have added several new and significant capabilities to UTCHEM to make it into a general-purpose NAPL simulator. The simulator is now capable of modeling transient and steady-state three-dimensional flow and mass transport in the groundwater (saturated) and vadose (unsaturated) zones of aquifers. The model allows for: changes in fluid properties as a site is remediated; heterogeneous aquifer properties; the flow and transport of remedial fluids whose density, viscosity and temperature are variable, including surfactants, cosolvents and other enhancement agents; the dissolution and/or mobilization of NAPLs by nondilute remedial fluids; and chemical and microbiological transformations. Appropriate physical, chemical and biological process models important in describing the fate and transport of NAPLs in contaminated aquifers have been incorporated into the simulator, such as multiple organic NAPL phase, nonequilibrium interphase mass transfer, sorption, microbiological and geochemical reactions, and the temperature dependence of pertinent chemical and physical properties. The biodegradation model includes inhibition, sequential use of electron acceptors, and cometabolism and can be used to model a very general class of bioremediation processes. The model can be used to simulate the actual field operation of remediation activities such as surfactant remediation or bioremediation as well as laboratory experiments with large-scale aquifer models. A systematic evaluation was undertaken to assess the applicability and accuracy of all physical and chemical models of the various pertinent phenomena such as capillary pressure, relative permeability, adsorption, nonequilibrium mass transfer, dispersion, and phase behavior. The microbiological model suitable for very general bioremediation simulations was added to UTCHEM and tested with data from the literature with good agreement. Comparisons to analytical solutions were made and numerical dispersion control and accuracy
testing were performed. The model was tested against experimental and field data. The FORTRAN source code has been delivered to EPA along with sample input and output files. This report contains 12 sections. Section 1 gives an overview of the project objectives and accomplishments. Sections 2 through 12 describe the formulation of UTCHEM. Appendix A contains the users guide for UTCHEM, Appendix B contains the users guide for UTCHEM local grid refinement. Appendix C presents the discretized flow equations. This report was submitted in fulfillment of CR-821897 by The University of Texas at Austin under partial sponsorship of the U.S. Environmental Protection Agency. This report covers a period from September 1994 to September 1996 and work was completed as of September 1996.