Composite liners comprised of geomembranes and geosynthetic clay liners can be an effective means of minimizing fluid flow and associated groundwater contamination from municipal solid waste landfills. There remains uncertainty, however, regarding the long-term performance of such systems under conditions of elevated temperature that may occur at the base of landfills attributable to exothermic waste degradation processes. The heat generated by these processes may lead to the development of a thermal gradient through the lining system that creates a risk of desiccation within the uppermost portion of the subsoil and the geosynthetic clay liner itself. To investigate this issue, a series of small-scale laboratory experiments were developed in an effort to simulate the hydraulic and thermal conditions existing at the base of a landfill. This paper presents the results of investigations into the influence of various parameters on the behavior of a composite liner. The distribution of temperature and water content over time is discussed, as well as potential impacts on the performance of the geosynthetic clay liner.