Observation and Three‐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 were carried out in a coastal sandy aquifer at Georgetown, South Carolina. The evolution of three‐dimensional chloride plumes during two tracer experiments was observed. A three‐dimensional finite element model for flow and transport was used with extensive hydraulic conductivity data obtained from slug tests to assess our ability to predict solute transport in the aquifer. Results showed that our predictive ability is limited to the bulk behavior of the plumes, which is mainly controlled by some “significant” heterogeneities. In addition, hydraulic conductivity 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 illustrate the importance of temporal variability in boundary conditions in the prediction of solute transport in aquifers.