A SUMMARY OF SUBSURFACE HYDROLOGICAL AND HYDROCHEMICAL MODELS

Numerical simulation in space and time is an established method in fluid flow and solute transport studies. Similarly, the modeling of equilibrium chemistry of aqueous systems has been well developed. Coupling hydrologic transport models and aqueous chemical models is being actively pursued by a number of research groups. To provide a review for researchers as well as field practitioners who may need to select and use models of varying degrees of complexity, summaries of 56 major numerical codes are made in comparative tables with selected references for three broad classes of codes: hydrologic transport models, geochemical models, and hydrochemical models that combine the chemical and transport models. Criteria for code selection and explanations as to how their characteristics were compiled are described. The governing equations for hydrologic flow, solute transport, and chemical relations are briefly described and discussed in light of the assumptions made by the different codes that employ them. Limitations of current modeling conceptualization and practice and areas of present active research effort are noted. Some comments are also given on model validation, a topic of current concern for modeling. Experience in model applications for each code and available information regarding its verification and validation are given in the appendix.