James A. Davis has performed extensive research on geochemical processes occurring at mineral surfaces and their effects on water and sediment phase compositions in aquifers. The work has examined geochemical processes at multiple scales, from molecular-scale spectroscopic studies to large field-scale investigations. The field investigations include studies of uranium and other metal contaminant transport at various physical scales and in differing geochemical regimes, including detailed studies conducted at two uranium mill tailings (UMTRAP) sites (Naturita and Rifle, Colorado, USA), at two uranium (and other radionuclide) disposal legacy sites (Hanford 300 Area, Washington, USA and Savannah River F-area, South Carolina, USA), and a uranium tailings pit closure project (Ranger uranium mine, Australia). The work has focused on how the transport of uranium(VI), arsenic(V) and arsenic(III) are affected by coupled adsorption, redox reactions, and competitive sorption processes, and the incorporation of conceptual models for these processes into reactive transport simulations. An approach to modeling the influence of variable chemistry on uranium and metal ion adsorption and transport has been demonstrated at several field sites at the km scale. In addition, bioremediation and passive reactive barriers have been studied in detail as remediation techniques for uranium-contaminated sites at an UMTRAP site (Rifle) and a uranium ore upgrading site (Fry Canyon, Utah, USA). Current research is focused on the biogeochemistry of uranium and arsenic and their transport in engineered or natural groundwater systems.