The co-effect of heterogeneity and solute concentration on representative elementary volume of DNAPL in groundwater

Abstract

In this study, a laboratory investigation was conducted to determine the co-effect of heterogeneity and solute concentration on dense nonaqueous phase liquids (DNAPLs) migration regularity and corresponding representative elementary volume (REV). Four experiments of perchloroethylene (PCE) migration were performed in bench scale two-dimensional (2D) sandboxes to investigate the REVs of PCE saturation (So), PCE-water interfacial area (AOW). Experimental results of migration regularity indicated heterogeneity hindered PCE infiltration, while higher solute concentration enhance PCE migration along horizontal and vertical directions. Moreover, heterogeneity and high solute concentration led to larger values of the second moments and Ganglia-to-pool ratio (GTP) of PCE plume in experiments. In comparison with solute concentration, REV estimation suggested the heterogeneity has a larger impact on the REVs of DNAPL plume. The heterogeneity of porous media has decreased the mean values of So-REV sizes more than 0.79 mm and 1.80 mm under conditions of low and high solute concentrations, respectively. AOW-REV sizes due to the heterogeneity of the porous medium were decreased by 46.0% and 51.9% of the average rates under conditions of low and high solute concentrations, respectively. On the other hand, high solute concentration led to a higher mean value of AOW-REV size, while solute concentration had different influences on So-REV under respective heterogeneous and homogeneous conditions. These phenomena indicated AOW-REV size has the largest value under conditions of homogeneity and high solute concentration. Confidence intervals of AOW-REV sizes for Experiment-III (homogeneity, low solute concentration) and Experiment-IV (homogeneity, high solute concentration) and confidence intervals for Experiment-I (heterogeneity, low solute concentration) and Experiment-II (heterogeneity, high solute concentration) had no overlapping part. These experimental results indicate the significant effect of heterogeneity and solute concentration on REVs of DNAPL plume in groundwater system, which is essential to understand the characteristics of scale effect and corresponding migration behaviors of DNAPL in a complex subsurface environment.