Introduction: Modeling groundwater flow and reactive transport in physically and chemically heterogeneous media

Abstract

The research community is actively studying subsurface fluid flow and reactive mass transport, where both the reactions and the transport are processes of primary importance. There are formidable challenges to overcome in advancing knowledge in this area. The subsurface has a challenging level of complexity in its physical and chemical properties. It is difficult to characterize this complexity because of many challenges presented in acquiring subsurface data. This difficulty in characterization creates, in turn, challenges in developing conceptual models for physical processes and biogeochemical reactions. The relevant length and time scales span a large range. There is nonlinear interplay between influences of heterogeneity in physical and chemical properties and the forces driving reactions between adjacent zones. Material properties may themselves be evolving with the chemical evolution of the system. Advances in our understanding of flow and reactive transport in physically and chemically heterogeneous media will likely come through a nexus of some of the following: (1) advancing the body of observational data from which processes can be characterized and modeled, including data on physical, chemical, and biological reactions and interactions; (2) combining information from experimentation at different scales: laboratory bench, mesoscale tanks, and in-situ at field sites; (3) advancing the body of observational data from which the heterogeneity of physical and chemical properties associated with these processes can be characterized and modeled; (4) developing upscaling methods to represent complexity at spatial scales below the model grid scale; (5) developing more efficient algorithms for solving large systems of coupled equations, and for estimating parameters; (6) using benefits of exponential growth in the speed of computational processing and digital storage when running simulations; and (7) using advances in visualization tools, which facilitate the interpretation of simulation results. To present the state of the science, a fullday session was organized for the 2004 Geological Society of America Annual Meeting, titled ‘‘Modeling Flow and Transport in Chemically and Physically Heterogeneous