This report presents a three-dimensional finite-element numerical model designed to simulate chemical transport in subsurface systems with temperature effect taken into account. The three-dimensional model is developed to provide (1) a tool of application, with which one is able to deal with a variety of real-world problems, (2) a tool of education, with which one can study how a factor would affect the whole system, and (3) a substructure, which one could modify to handle specific problems. The hydrological environment to which the model can be applied is a heterogeneous, anisotropic, saturated-unsaturated subsurface medium under either transient-state or steady-state flow conditions. In addition, the temperature within the system of interest can be for both time- and location-dependent. The model employs chemical equilibrium to describe the relationship among chemicals. The chemical reactions included in the model are aqueous complexation, multi-site adsorption/desorption, multi-site ion-exchange, precipitation/dissolution, redox, and acid-base reactions. To extend its applicability to more real-world problems, two approaches are presented for the chemical transport module in this report. The first approach uses the pore velocity and dispersion coefficient to handle advection and dispersion, respectively, for aqueous components, whereas the second approach employs the retarded pore velocity and the retarded dispersion coefficient. The governing equations of subsurface flow, chemical transport, chemical equilibrium, and heat transfer are stated and/or derived. The governing equations of subsurface flow, chemical transport, chemical equilibrium, and heat transfer are stated and/or derived. The numerical approaches with the finite element method to solve the governing equations are described. Four application examples, including a three-dimensional subsurface flow example, a three-dimensional reactive chemical transport example, a three-dimensional heat transfer example, and a three-dimensional coupled flow-transport-transfer example, are presented to demonstrate the capability of the model. Data input guide and program description are stated in Appendix A and Appendix B, respectively. in Appendix C, parameter specification for array dimensions in 3DHYDROGEOCHEM is given.

"EPA 600-R-98-159." "July 1999." Cover title. Project Officer, Thomas E. Short, Subsurface Protection and Remediation Division, National Risk Management Research Lab, Ada, OK. Includes bibliographical references (pages 149-150).