Experimental assessment of solute dispersion in stratified porous media

Abstract

The objective of this paper is to evaluate effects of stratified porous formation on solute dispersion using two-dimensional laboratory tracer tests. An image analysis technique was used to analyze the solute dispersion processes and quantify the dispersivity and behaviors of forward and backward tails of solute plumes. Longitudinal dispersivity estimates for the stratified porous media increased with travel distance and are in reasonable agreement with previous work. Moreover, in all of the stratified cases the transverse dispersivity exhibited a similar trend which decayed with travel distance. The summary of dispersivities estimated from this study and previous studies suggests that if both degree of heterogeneity and scale for stratified and randomly heterogeneous porous media are similar, the longitudinal dispersivity is larger in stratified media than in randomly heterogeneous media. In order to quantify behaviors of forward and backward tails, we defined the travel distances x₀₅ and x₉₅ corresponding to the 5th and 95th percentiles, respectively, of the cumulative concentrations in the longitudinal direction, and found that the distance between x₀₅ and x₉₅ spread out linearly in the stratified cases.