Approximations for solute transport through porous media with flow transverse to layering

Analytical approaches for the prediction of solute transport in layered porous media are investigated for the case of flow perpendicular to the direction of layering. One approach involves the use of averaging techniques to treat the profile as an equivalent homogeneous medium. The method is demonstrated on hypothetical and laboratory-measured data sets and a criterion for validity of the method is given. The second approach involves the use of time convolution to predict breakthrough curves for layered systems on the assumption that layer interactions have no significant effect on transport. Accuracy criteria are derived by comparing moments of the exact and approximate solutions and it is found that the convolution method has broader applicability than the equivalent single-layer analysis. An extension of the convolution method to include consideration of nonequilibrium transport due to the presence of mobile-immobile regions is presented and demonstrated by analysis of laboratory breakthrough data from a two-layer system exhibiting mobile-immobile regions.