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

Global Stability Study for Eastern Slope near Building D West Essex – Highlands Development West Orange, New Jersey Langan Project No.: 101049801 14 January 2025 Page 3 of 4 Global Stability of Slope Our analysis included an evaluation of slope stability under both static and seismic (dynamic) design conditions. Building D is far enough from the top of the slope that there is no surcharge load that would impact the slope stability. Although no indication of a seasonal variability in groundwater elevation was observed in the test pits, we performed a sensitivity analysis to determine if changes in groundwater level would impact the stability of the subject slope. Our base case static and seismic analyses used the base groundwater level encountered in our one test pit. The results of the static case indicate the lowest factors of safety exceed 1.5, indicating stable slopes. The potential slip plane surface that resulted in the lowest factor of safety was limited in length to roughly 100 feet and occurred near the middle of the Subject Slope as a shallow surficial slip surface (i.e., within the upper 2 feet of soil). Similarly, the results of the dynamic (seismic) case indicate the lowest factors of safety to be greater than 1.2, indicating stable slopes during a potential earthquake. Factors of safety greater than 3.29 and 2.23 were computed where software-generated potential slip planes extend from the top of the Subject Slope to the downslope neighboring properties for the static and seismic cases, respectively. In addition to the base cases described above, we analyzed groundwater midway in the soil profile and at a depth of 2 feet below grade. Only when groundwater was modeled at a depth of 2 feet below grade did the factor of safety decrease to 1.36 under the static case. This potential slip surface is within 2 feet of ground and does not pose a hazard to the site of neighboring properties. Factors of safety greater than 3.0 were computed where software-generated potential slip planes extend from the top of the Subject Slope to the downslope neighboring properties and include unrealistically high-water levels in the soil. Construction Related Blasting Impacts We understand up to 25 feet of rock is expected to be excavated from one localized area at the top of the Subject Slope in order to reach design grades for Building D. It is common for

lasting Impacts We understand up to 25 feet of rock is expected to be excavated from one localized area at the top of the Subject Slope in order to reach design grades for Building D. It is common for rock excavation to be achieved using controlled blasting techniques, which include but are not limited to line and/or channel drilling, limiting charge per delay, use of blasting mats, and performing vibration monitoring. Such methods thereby limit the amount of energy transmitted to the surrounding rock, generally limit the nuisance impacts of construction compared to conventional earth excavating methods (i.e., less time to excavate and haul off material), and limit the potential for impacts to neighboring properties. OPINIONS Based on our investigation and analysis, the Subject Slope is not at risk of failure under current conditions or from proper construction of Building D. Our analyses further indicate that there would be negligible impact on the global stability of the Subject Slope even if groundwater levels were to rise. However, direct precipitation and runoff can be expected to flow over the sloping