2025 06 18 WEH Slope Stability Analysis Letter Report

Global Slope Stability Study for Building D West Essex Highlands Project Langan Project No.: 101049801 Revised 18 June 2025 Revised 18 June 2025 - Page 11 of 13 MEMO Analysis due to Groundwater We analyzed the impact of a continuous groundwater level on the slope stability for the static loading condition. The estimated resulting factors of safety are provided in Table 4A. Table 4A: LEM Factors of Safety against Sliding for Gravity Loads with Groundwater Groundwater Level Section A (Critical Slip Surface) Section B (Critical Slip Surface) Section C (Critical Slip Surface) Section D (Critical Slip Surface) Top of Decomposed Rock / Very Dense Granular Soil 2.20 1.67 1.59* 1.94 *This factor of safety is based on using dense sand below the topsoil layer in the analysis, which is the condition indicated by the borings. We also performed an infinite slope analysis for the high groundwater case. The estimated resulting factors of safety from this analysis are provided in Table 4B. In all cases the factor of safety is greater than 1.5. Table 4B: LEM Factors of Safety against Sliding for Gravity Loads with Groundwater (Infinite Slope Analysis) Groundwater Level/Critical Slip Surface Location Section A Section B Section C Section D Top of Decomposed Rock / Very Dense Granular Soil 3.94 3.87 1.81 2.23 EVALUATION We utilized the NAVFAC Design Manual 7.1 “Soil Mechanics” (NAVFAC 1986) reference in the evaluation of the factors of safety calculated in our global slope stability evaluation for the static and seismic design loading conditions. This manual indicates that a factor of safety of no less than 1.5 should be utilized for permanent or sustained (static) loading conditions of slopes, and a factor of safety of no less than 1.15 should be utilized for seismic loading conditions of slopes due to earthquakes. Geologic Hazard Review Based on rock maps and our subsurface findings, hard igneous basalt rock is near the surface at the upper portion of the slope with a few several rock outcrops identified in the upper portion of the slope. The lower portion of the slope is anticipated to consist of sedimentary rock as part of