2025 01 14 West Essex Highlands Development Building D Slope Stability Study

MEMO Global Slope Stability Study for Building D West Essex Highlands Project Langan Project No.: 101049801 14 January 2025- Page 10 of 11 We modeled the existing slope and the proposed building loads per the available topographic survey plan, boring and test pit data and the anticipated building and seismic loads as outlined in the “Modeling Parameters” section of this memorandum. Geologic Hazard Review Based on rock maps and our subsurface findings, igneous basalt rock is near the surface at the upper portion of the slope with a few visible rock outcrops. The lower portion of the slope is anticipated to consist of sedimentary rock as part of the Feltville Formation at depth greater than 50 ft from existing surface grade based on the subsurface investigation. The eastern slope does not appear to have significant amounts of exposed rock outcrops along the slope so rock fall hazard due to the toppling of exposed rock faces would be limited. Due to the relatively shallow slope and distance to adjacent properties, rock fall does not appear to be a high risk. Based on a review of New Jersey earthquake history provided by the New Jersey Department of Environmental Protection (NJDEP), the seismic risk of the site appears to be low. Stability for Gravity Loading Condition Our evaluation indicates that the factor of safety values for the gravity loading (static) condition for both the existing and proposed conditions is greater than the minimum required safety factor of 1.5, indicating stable slopes. The proposed construction of Building D will have a negligible impact on the global stability of the eastern slope as shown in Tables 2A and 2B. Stability for Seismic Loading Condition Our evaluation indicates that the factor of safety values for the seismic loading (dynamic) condition for both the existing and proposed conditions is greater than the minimum required safety factor of 1.15, indicating stable slopes. Additionally, the proposed construction of Building D will have a negligible impact on the global stability of the eastern slope as shown in Tables 3A and 3B. Groundwater Impacts Our sensitivity analysis associated with groundwater level indicates the factors of safety with respect to global stability generally decrease when the water level increases. Although highly unlikely, we modeled the groundwater immediately below the topsoil layer resulting in a

rs of safety with respect to global stability generally decrease when the water level increases. Although highly unlikely, we modeled the groundwater immediately below the topsoil layer resulting in a factor of safety of 1.36 for the critical potential failure surface. This potential slip surface is surficial and does not pose an impact on the downslope residences. The lowest factor of safety against sliding for gravity loads at varying groundwater levels was approximately 3.09 when the groundwater was modeled to be below the topsoil layer for the infinite slope analysis. This is above the minimum required safety factor of 1.5, indicating stable slopes. = = =