COMPARISON OF LEACHATE FLOW-THROUGH COMPACTED CLAY LINERS AND GEOSYNTHETIC CLAY LINERS IN LANDFILL LINER SYSTEMS

The purpose of this paper is to provide an approach for comparing the effectiveness of geosynthetic clay liners (GCLs) and compacted clay li ners (CCLs) used in association with geomembranes to form composite li ners. Comparing the effectiveness of these two types of composite line rs is required in ''equivalency demonstrations'' intended to demonstra te that a geomembrane-GCL composite liner is equivalent to a conventio nal geomembrane-CCL liner prescribed by a regulation. In the first par t of the paper, the contribution of the geomembrane is ignored and the paper presents analytical evaluations of advective leachate flow thro ugh GCLs, low-permeability soil layers (such as CCLs), and two-layer s ystems including a GCL and a low-permeability soil layer. The analyses presented explain why some calculations typically performed for landf ill liner system design or for equivalency demonstrations lead to the paradoxical result that the advective flow of leachate is greater when a GCL is placed on a layer of low-permeability soil than when the GCL is placed on a layer of high-permeability soil. The second part of th e paper presents an analytical method for comparing the effectiveness of a composite liner including a GCL and a composite liner including a CCL. This analytical method enables design engineers to compare the e ffectiveness of various composite liners without neglecting the benefi cial effect of the geomembrane. A parametric study presented in the pa per shows that neglecting the geomembrane liner in equivalency demonst rations (which is frequently done in the current state of practice) pe nalizes composite liners that incorporate a GCL.