Velocity scaling of nonequilibrium solute transport in heterogeneous soils: Numerical and experimental results
Nonequilibrium transport of solute in porous media typically refers to any time-dependent process additional to the usual advection and dispersion transport mechanisms. Nonequilibrium solute transport is commonly observed in laboratory experiments carried out using either artificial media or natural soils. These experiments have shown that the rate parameter α changes with flow velocity. Flow variations within the porous medium contribute to the observed nonequilibrium effects. The mobile/immobile region concept, is a specialisation of this. However, continuous flow variations also yield nonequilibrium effects that can be simulated by two region model. Analysis of results from a series of laboratory experiments with a real soil and systematic numerical experiments suggest that α may be linearly related to flow velocity. The model parameters are determined by fitting, and are usually highly correlated, possibly resulting in non unique solutions. A technique is reported in which the effective hydraulic conductivity can be used to cross- check the appropriateness of the parameter values obtained from the fitting procedure.