A Retardation Factor Considering Solute Transfer Between Mobile and Immobile Water in Porous Media

In advective-dispersive simulations of aquifers, retardation factors using linear adsorption isotherms are commonly employed to represent the adsorption-desorption process for solutes in soil. In particular, the retardation factors that use entire pore space (total porosity) or effective pore space (effective porosity) are widely used. Although another retardation factor that describes solute transfer between mobile and immobile water in porous media has been developed, characteristics of the model have not been examined extensively. This retardation factor retains the ease of use and characteristics of the first two models; for example, its breakthrough curve is similar to those generated by models that employ total porosity for aquifers in which groundwater flow is fast and solute transport by advection and mechanical dispersion is predominant, as well as models that employ effective porosity for aquifers in which groundwater flow is slow, solute transport by molecular diffusion is predominant, and a large amount of adsorption-desorption occurs. It is therefore expected that when performing advective-dispersive simulations of aquifers with complex structures (e.g., aquifers in which sand and clay layers alternate), the reproducibility of the simulation results will be improved by using the retardation factor of this latter model, which considers solute transfer between mobile and immobile water.