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

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

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 13 of 13 roadway will have a negligible impact on the global stability of the eastern slope as shown in Tables 3A and 3D. Groundwater Impacts Our analysis assuming a continuous groundwater level develops in the future indicates stable slopes. As part of the proposed development, we understand that appropriate drainage conveyances will be provided to prevent site development stormwater from entering the eastern slope. As such, the proposed construction of Building D will not have an impact on increasing groundwater levels at the eastern slope. LIMITATIONS Our evaluation is based on the geotechnical subsurface data collected at the subject area (at accessible areas), the topographic survey data, currently existing site conditions and proposed building information made available to us. Any proposed changes in proposed structures (location, layout, loading, elevation) or existing slope conditions should be brought to our attention so that we can determine whether such changes affect our conclusions. CLOSURE This memorandum summarized our global slope stability analyses and results associated with the proposed eastern slope of the West Essex Highlands project site located in West Orange, New Jersey. \\langan.com\data\PAR\data8\101049801\Project Data\_Discipline\Geotechnical\Reports\Slope Stability\Additional Investigation\2025-06-18 - Attachment A - Slope Stability Analysis Memo Revised.docx

FIGURES Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Investigation Location Plan with Sections A, B, C and D Geological Map Outcrop Plan Landslide Susceptibility Map USGS Recorded Landslide Map = = =

SLAY HOWELL DRIVE HOWELL DRIVE RG EME ENC Y AC S CES ROAD 'D' ROSEMONT TERRACE FF:618.0 GF:607.0 ING ILD BU D.1 FF:618.0 GF:597.0 w A w w B C FF:600.1 BF:587.1 POOL 586.2 CLUBHOUSE LGF:582.0 DRI R I VE A F Y MA RO Langan Engineering and Environmental Services, Inc. 300 Kimball Drive Parsippany, NJ 07054 T: 973.560.4900 F: 973.560.4901 © 2023 Langan AD 'D' BUILDING D.2 FF:618.0 GF:594.0 www.langan.com NJ CERTIFICATE OF AUTHORIZATION NO. 24GA27996400 Date: 6/18/2025 Time: 12:20 User: rblocker Style Table: Langan.stb Layout: Layout1 Document Code: 101049801-0201-BL101-0101

N APPROXIMATE DEVELOPMENT BOUNDARY APPROXIMATE BUILDING D LOCATION APPROXIMATE SUBJECT SLOPE AREA LEGEND Preakness Basalt – Dark-greenish-gray to black, fine-grained, dense, hard basalt Feltville Formation – Reddish-brown or light-grayish-red, fine-to-coarse-grained sandstone, siltstone, shaly siltstone and silty mudstone. Source: Bedrock Geologic Map of The Caldwell Quadrangle, Essex and Morris Counties, New Jersey by Richard A. Volkert (2006) WEST ESSEX - HIGHLANDS GEOLOGIC MAP WEST ORANGE NEW JERSEY PROJECT NO. SCALE DATE FIGURE 1010498014 N.T.S. 6/18/2025 2 \\langan.com\data\PAR\data8\101049801\Project Data\_Discipline\Geotechnical\Reports\Slope Stability\Figures, Tables, Plans\Figure 2 - Geologic Map.docx

SLAY HOWELL DRIVE HOWELL DRIVE FACING SOUTH RG EME ENC Y AC S CES FACING WEST FACING SOUTH FACING NORTH FACING WEST FACING WEST FACING NORTH ING ILD BU D.1 FACING WEST ROSEMONT TERRACE ROAD 'D' FF:618.0 GF:607.0 FACING WEST FF:618.0 GF:597.0 FACING EAST w A w FACING EAST w B C FF:600.1 BF:587.1 POOL 586.2 FACING WEST CLUBHOUSE FACING WEST FACING NORTH BUILDING D.2 FF:618.0 GF:594.0 BOULDER A BOULDER C BOULDER B FACING NORTH DRI R I VE A F Y MA Langan Engineering and Environmental Services, Inc. 300 Kimball Drive Parsippany, NJ 07054 T: 973.560.4900 F: 973.560.4901 © 2023 Langan LGF:582.0 RO AD 'D' FACING WEST www.langan.com NJ CERTIFICATE OF AUTHORIZATION NO. 24GA27996400 Date: 6/17/2025 Time: 14:12 User: rblocker Style Table: Langan.stb Layout: Layout1 Document Code: 101049801-0201-BL101-0101

N APPROXIMATE BUILDING D LOCATION LEGEND Source: Landslide Susceptibility for Essex County, New Jersey by Scott D. Stanford, New Jersey Geological Survey (2001) WEST ESSEX - HIGHLANDS LANDSLIDE SUSCEPTIBILITY MAP WEST ORANGE NEW JERSEY PROJECT NO. SCALE DATE FIGURE 101049801 N.T.S. 6/18/2025 4 \\langan.com\data\PAR\data8\101049801\Project Data\_Discipline\Geotechnical\Reports\Slope Stability\Additional Investigation\Final PDF\Figure 4 -Hazus Map UPDATED.docx

N Source: APPROXIMATE BUILDING D LOCATION USGS Online Database WEST ESSEX - HIGHLANDS USGS LANDSLIDE MAP WEST ORANGE NEW JERSEY PROJECT NO. SCALE DATE FIGURE 101049801 N.T.S. 6/18/2025 5 \\langan.com\data\PAR\data8\101049801\Project Data\_Discipline\Geotechnical\Reports\Slope Stability\Figures, Tables, Plans\Figure 5 - USGS Landslide Map.docx