Locating the critical cross-section and critical failure surface is the first step in the analysis of the static and seismic stability of landfill slopes. Locating the critical crosssection is usually accomplished by analyzing two-dimensional cross-sections through a particular slope. Only cross-sections that represent a realistic, or plausible, sliding direction should be selected. For example, a cross-section depicting the down canyon direction, or bedrock dipping away from the slope, should be selected. Figures 1 through 7 depict typical failure modes of landfill slopes. The two-dimensional cross-sections are usually analyzed using a limit equilibrium slope stability method to estimate the factor of safety. Each cross-section is searched to locate the critical failure surface, (i.e., the failure surface with the lowest factor of safety in that cross-section).