Comparison of Solute Transport in Three Composite Liners

Three composite landfill liners were compared in this study based on leakage rate, mass flux, and sorptive capacity. One composite liner consisted of a geomembrane and a geosynthetic clay liner (GCL). The other two had a geomembrane and a thicker soil barrier (61 or 122 cm). The analyses employed one- and three-dimensional numerical models that were developed for analyzing contaminant transport through defects in the geomembrane component of composite liners and diffusion of volatile organic compounds through intact composite liners (i.e., composite liners without holes in the geomembrane). Cadmium was used to represent inorganic leachate constituents and toluene was used to represent organic leachate constituents. The composite liner, having a GCL had the lowest leakage rate of the three composite liners. For cadmium, the mass flow rate and sorptive capacity for the three composite liners varied within an order of magnitude. However, for toluene, the mass flux from the GCL composite liner was two to three orders of magnitude greater than that through composite liners having a thicker soil liner. Additionally, for leachate having similar concentrations of cadmium and toluene, the mass flux of toluene can be as much as seven orders of magnitude greater than that for cadmium. For toluene, the sorptive capacity of thicker liners was an order of magnitude greater than that for the GCL composite liner. Similar behavior is expected for other inorganic and organic solutes.