Geochemistry, Groundwater and Pollution: "Learning by Modeling"

Predicting the fate of chemicals that leach from waste deposits and deciphering their transport in the invisible subsoil must rely on 1) understanding the pattern of groundwater flowlines and travel times, 2) insight in the chemical reactions which retard the solutes, and 3) the quality of the database of the geochemical model. Inhomogeneities in an aquifer can be deduced from tritium/helium age profiles with depth, and otherwise from costly tracer experiments. The retardation of heavy metals is illustrated for a case of acid mine drainage from a former uranium mine. In addition to retardation by sorption, U(6) may disperse into confining layers where it reduces to U(3) and precipitates. Lastly, a model is presented for the release of arsenic in Bangladesh groundwater. With a recently defined carbonate surface complex in the database, carbonate appears important for displacing sorbed arsenic to poisonous aqueous concentrations.