Effect of leachate on the hydraulic performance of Geosynthetic Clay Liners (GCLs) in landfill applications

Abstract

Geosynthetic Clay Liners (GCLs) are increasingly being adopted as hydraulic barrier components in landfill liner systems as alternatives to compacted clay liners (CCLs). While GCLs offer construction and material-consistency advantages, their hydraulic performance is sensitive to the chemistry of permeating liquids. This paper presents site-specific chemical compatibility testing of a needle-punched sodium bentonite GCL in accordance with ASTM D6766, using representative landfill leachate and construction water. Two hydration scenarios were evaluated: (i) direct hydration and permeation with leachate, and (ii) pre-hydration with construction water followed by leachate permeation. Although both scenarios produced hydraulic conductivity values below 1 × 10⁻⁹ m/s, significant differences in leakage performance were identified when evaluated using composite liner theory. A leachate-hydrated GCL exhibited leakage rates exceeding those of a conventional 600 mm-thick compacted clay liner, despite a lower intrinsic hydraulic conductivity. The results demonstrate that hydraulic conductivity alone is insufficient for regulatory equivalence assessments and that hydration history and chemical compatibility critically influence GCL performance. The findings emphasize the necessity for site-specific compatibility testing and controlled hydration conditions during construction when GCLs are used in landfill applications.