Theory of Solute Transport by Groundwater

The transport of solutes in groundwater flow has been studied with increas­ ing intensity in the last two decades as a result of growing concern about water quality and pollution. The intensification of groundwater exploi­ tation, on the one hand, and the increase in solute concentration in aquifers due to saltwater intrusion, leaking repositories, use of fertilizers, etc., on the other, have made this a subject of immediate and wide interest. The phenomenon of solute transport is quite complex, as it depends on several factors, such as the complicated geohydrological structures of aquifers, the nonuniformity and unsteadiness of flow, the physico-chemical interactions between solutes and matrix, and the mechanism of solute spreading. The field study of solute transport also faces serious difficulties. First, measurements must be carried out by drilling numerous observation wells and by monitoring the concentration, which is quite costly and time con­ suming. Second, the spreading of the solutes is a very slow process, and an experiment may last many years if one wishes to investigate the long­ range transport process. Under these circumstances, the theory plays an important role, being instrumental in interpreting field tests and in predicting the fate of solutes under new conditions. The aims of the theory are to identify the main factors that influence transport and to provide the mathematical tools that permit one to compute the spatial distribution and the time evolution of the solute concentration, given the flow conditions.