ABSTRACT
Ion exchange is a very important process in determining the migration of a number of solutes, including pollutants, through aquifer systems. It affects the relative proportions of ions, and by doing so can induce other reactions to occur resulting in the loss or gain of solute to the groundwater and, often, a change in pH, for example, displacement of fresh, calcite-saturated groundwater by an Na-rich solution (e.g., landfill leachate or sea water) will usually result in the increase of Ca in solution and hence, possibly, the precipitation of calcite and a fall in pH. Such changes in chemistry will often have implications for migration of pollutants, for example, transition metals. Ion exchange is also directly involved with attenuating a number of pollutant species (e.g., transition metals and NH4 +).
