The movement of chemicals in soils and groundwater aquifers (solute transport) plays a central role in global biogeochemical cycling. Human activities have placed many new chemicals into the environment and greatly enhanced the local loading of wastes to the subsurface. Obvious applications of an understanding of solute transport in porous media include the efficacy and fate of agricultural chemicals (fertilizers and⧸or pesticides); the treatment and disposal of wastewaters and wastewater treatment products from human, animal, and industrial sources; and contamination resulting from landfills, mining operations, industrial activities, high-level radioactive waste disposal, etc. Given its great importance in the maintenance of safe water supplies, the nourishment of plants, regulation of the fate of soil-applied chemicals, and many other critical hydrologic processes, solute transport has long been the focus of intense research in soil science, groundwater hydrology, and chemical engineering. Nevertheless, our a priori capability to predict solute transport remains limited.
