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

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 sub-surface 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.