ABSTRACT
This chapter presents preliminary results of small-scale, natural-gradient tracer tests conducted in oxic and suboxic zones of a shallow, unconfined sand and gravel aquifer near Falmouth, Massachusetts. A more fundamental, mechanistic approach that uses the surface ionization and coordination concept in conjunction with aqueous speciation models is now widely accepted for modeling the interactions of metal ions with mineral surfaces. The physical processes that lead to macrodispersion and fluid mixing may affect aqueous speciation of metals via dilution of complexing ligands or the addition of new solutes from dissolving mineral phases, each of which may have direct or indirect effects on the sorption of metal ions. However, the application of these models to metal transport in groundwaters is still limited by inadequate consideration of adsorption-desorption reactions within the models and the availability of relevant kinetic and thermodynamic data to describe metal sorption processes in the groundwater environment.
