Geochemical calculations and observations on salt water intrusions. II. Validation of a geochemical model with laboratory experiments

Column experiments with aquifer sediments have been performed. A description is given of procedures and equipment which can maintain the anaerobic status of the sediments from sampling in the field to subsequent experimentation in the laboratory. From two sediments native pore solutions were displaced with SrCl 2 solutions; another was percolated alternately with groundwater and once diluted seawater. The chromatographic pattern which develops when exchangeable cations are eluted, was modelled with the earlier presented geochemical (multicomponent) transport model. Proper description of the SrCl 2-elution required reformulation of the cation exchange reaction for one sediment; the other sediment showed proton buffering and calcite dissolution with slow kinetics. These elutions could be modelled with constant exchange coefficients, but during fresh/saltwater displacements the selectivity for Ca/Mg exchange was variable.