2025 06 18 WEH Slope Stability Analysis Letter Report

MEMO Global Slope Stability Study for Building D West Essex Highlands Project Langan Project No.: 101049801 Revised 18 June 2025 Revised 18 June 2025 - Page 12 of 13 the Feltville Formation at depth greater than 50 ft from existing surface grade based on the subsurface investigation. Our mapping indicates the predominance of vertical jointing oriented approximately E-W, which is perpendicular to the direction of the eastern slope. The joint spacing varies from a few inches to several feet. The orientation and dip of the slab-like features formed by the joints are favorable with respect to stability. A secondary set of joints, oriented approximately orthogonal to the primary vertical set, typically dips to the east (out of the rockface) between 10 degrees and 20 degrees. The joint surfaces are typically rough and slightly irregular thereby effectively increasing the resistance to movement along the joint. A design rock-on-rock (joint) friction angle for a tightly jointed (low to no aperture) basalt is 35 degrees, excluding the irregularities (asperities) along the jointing. The blocks in the outcrops and boulders bearing on rock outcrop result in kinematically stable configurations, meaning the rock is stable. Based on a review of the New Jersey earthquake history provided by the New Jersey Department of Environmental Protection (NJDEP), the seismic risk of the site appears to be low. We reviewed the available Landslide Susceptibility Map for Essex County dated 2001 for the site vicinity. The map indicates that the subject eastern slope has a Landslide Class of B III – weakly cemented rock and soils with a slope angle of 10-15 degrees. Landslide susceptibility as defined by the author means “susceptible” to a landslide depending on many factors, which we have accounted for in our study. The classification was developed as a risk tool, not as a site-specific analysis of a particular condition. A copy of the map is provided as Figure 4. We also reviewed the USGS online database to identify any recordable landslides or rockfall incidents within the site vicinity. A recorded minor debris flow landslide incident was identified at a residence on Nestro Road located about 500 ft southeast of the site in 1998. The approximate location of the incident is shown as Figure 5. Stability for Gravity Loading Condition Our evaluation of global slope stability provided in

about 500 ft southeast of the site in 1998. The approximate location of the incident is shown as Figure 5. Stability for Gravity Loading Condition Our evaluation of global slope stability provided in the previous sections of this memorandum 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 and the associated roadway will have a negligible impact on the global stability of the eastern slope as shown in Tables 2A through 2D. Stability for Seismic Loading Condition Our evaluation of global slope stability provided in the previous sections of this memorandum 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 and the associated