OBSERVATION AND 3-DIMENSIONAL SIMULATION OF CHLORIDE PLUMES IN A SANDY AQUIFER UNDER FORCED-GRADIENT CONDITIONS

Two-well, forced-gradient tracer experiments over a distance of 5 m we re carried out in a coastal sandy aquifer at Georgetown, South Carolin a. The evolution of three-dimensional chloride plumes during two trace r experiments was observed. A three-dimensional finite element model f or flow and transport was used with extensive hydraulic conductivity d ata obtained from slug tests to assess our ability to predict solute t ransport in the aquifer. Results showed that our predictive ability is limited to the bulk behavior of the plumes, which is mainly controlle d by some ''significant'' heterogeneities. In addition, hydraulic cond uctivity values estimated by the Hvorslev method for analysis of slug tests best represented the hydraulic conductivity distribution of the sandy aquifer. Finally, the results of a long-term experiment illustra te the importance of temporal variability in boundary conditions in th e prediction of solute transport in aquifers.