Mass transport of solutes in dual‐porosity media

In many aquifers, solute mass transport is controlled by molecular diffusion between mobile and static water. This is especially the case in fissured aquifers in which the rock matrix has a high porosity but low permeability. In order to model mass transport in such a dual‐porosity medium, an analytical solution for diffusion from a constant concentration boundary has been incorporated into a two‐dimensional mass transport model. The model uses Galerkin's method of weighted residuals and isoparametric finite elements to solve the flow and transport equations. The method has been successfully applied to a largescale pollution event. Historical data on the event were available over a long period of time and permitted calibration of the model. In situations in which such historical data are not available, calibration is very difficult, particularly the determination of dispersivities. This is because the molecular diffusion between mobile and static water so greatly retards the transport of solutes that field tests at the appropriate scale are essentially preempted.