A properly designed engineered landfill system is essential for the disposal of hazardous and non-hazardous wastes to avoid various geo-environmental issues. Even though leachate collection and detection systems are well designed in engineered landfills, migration of contaminants through landfill liners might not be completely avoided because of its transfer through diffusion. A detailed study is warranted to evaluate the efficacy of the landfill lining systems. In this study, contaminant transport due to diffusion through composite liners under unsaturated conditions was assessed numerically using commercially available finite element software. Geomembrane, geosynthetic clay liner, and/ or compacted clay liner were studied to examine their efficacy as landfill liners, focusing on CCL thickness, CCL desaturation coefficient, distribution coefficient, effective diffusion coefficient, and effect of the volumetric water content on the effective diffusion coefficient using different unsaturated diffusive model. The significance of each of the above-mentioned parameters in contributing to the efficiency of the composite liners was quantified from the simulation results.