Liner system reliability is of key importance for landfill risk mitigation. There are many design recommendations and standards from several environmental agencies around the world. Among them, single liners and composite liners designs are frequently used. In this article, leakage through single and composite liners was determined in order to evaluate environmental risk. A sensitivity analysis of the governing equation for flow through geomembrane holes was performed and a Monte Carlo simulation for single and composite liner leak was performed. Obtained results allowed confirming that quality control during construction and operation is of key importance for liners performance. Also these findings helped to statistically determinate the equivalency between different alternative liners for the containment of landfill leachate.