The objective of this paper is to examine the influence of correlation length and hydraulic conductivity distribution on the probability of failure of a clay liner system. To achieve this objective, a two-dimensional (in plan) clayey liner system is simulated with a probabilistic modeling program, mrflow2D. The correlation length, variance, and mean of hydraulic conductivity of the clayey liner are varied in the simulations. In this study, the worst case correlation length for probability of failure was found to be approximately equal to 10% - 20% of the liner size in any direction when the mean hydraulic conductivity of the soil liner is the same as the regulatory specified hydraulic conductivity used in the simulation. This implies that there is a worst-case correlation length with results in a maximum probability of failure which is ideally what one would use when modelling such a system.