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 5 of 13 boulder resting directly on Outcrop #1 were approximately 8 ft long by 5 ft wide by 6 ft high. The contact surface of this boulder and the underlying rock outcrop was observed to be rough and had a generally flat slope of 15 degrees from horizontal sloping downward to the east. Other boulders, similar in size, were also observed in the area and appeared to be partially buried in the existing soil slope. Natural Overburden Soils Natural sandy and silty soils were encountered below the topsoil in all test pits and borings. The natural sand was typically described as brown to reddish brown fine to coarse silty sand or sandy silt with varying amounts of clay, gravel and roots. Boulders and cobbles were encountered in several test pits and borings at varying depths. The top of the natural soils was first encountered at depths ranging from the existing surface grade to approximately 2 ft, corresponding to elevation (el) 614 to el 522. The thickness of the natural soil varied typically between 7 ft and 12 ft in the borings located at the higher portion of the slope near the proposed building D footprint and proposed access road. At the lower portion of the slope, the thickness of the natural soil layer was approximately 43 ft in boring LB-2. Boring LB-4 was terminated in natural sand at approximately 45 ft below surface grade or at approximately el 503. The thickness of the natural soil layer was approximately 8 ft and 20 ft in borings NLB-1 and NLB-3, respectively. The recorded N-values in this stratum typically ranged from 11 bl/ft to split-spoon refusal values, indicative of medium dense to very dense materials and the presence of cobbles and boulders. The recorded N-values typically increased with depth. Decomposed Rock A decomposed rock stratum was encountered in borings LB-1, LB-2, LB-3 and test pits TP-1, NTP-1, NTP-2, R-3, R-4A and R-4B. The thickness of this decomposed rock layer ranged from 0.5 ft to 7 ft. This decomposed rock was in the form of a mixture of brown sand with silt, clay, gravel and rock fragments. All recorded SPT N-values in this decomposed zone were split-spoon sampler refusals. It should be noted that it is difficult to differentiate between the very dense soils and the

l and rock fragments. All recorded SPT N-values in this decomposed zone were split-spoon sampler refusals. It should be noted that it is difficult to differentiate between the very dense soils and the decomposed rock stratum with the limited split-spoon sample recovery. Bedrock Bedrock consisting of gray basalt was encountered in borings LB-1, LB-3, NLB-1, NLB-2, NLB-3 and NLB-4 below the overburden soils and decomposed rock stratum between approximately 10 ft and 25 ft below existing surface grade or between approximately el 605 and el 544. The top of rock was determined by rock coring in these borings. The recorded rock recovery (REC) values typically varied from 75% to 100% and the rock quality designation (RQD) values varied typically from 42% to 93%, indicative of fair to good quality rock. Low RQD values of 0% and 23% were

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 6 of 13 recorded in boring NLB-1. As previously stated, some basalt rock outcrops were visible at the subject eastern slope and within the proposed building footprint. Bedrock was not encountered at the termination depths of borings LB-2 and LB-4, which are located at the lower slope approximately 420 ft and 350 ft east of proposed Building D, respectively. Boring LB-2 was terminated at about 50 ft below existing surface grade or at approximately el 472. Boring LB-4 was terminated at about 45 ft below existing surface grade or at approximately el 503. The top of rock contours are expected to vary considerably between investigation locations. Therefore, it should be noted that the top of rock elevations given herein are approximate and the reported conditions refer to the conditions at the specific investigation locations. Variations in the top of rock elevations, rock quality and weathering should be expected across the site. Laboratory Testing: Unconfined compressive tests were performed on 2 rock core samples taken from boring LB-3 located at the upper portion of the slope. The tests suggest that the unconfined compressive strength of the basalt rock samples varied between approximately 2,200 pounds per square inch (psi) and 3,500 psi or approximately 316,800 pounds per square foot (psf) and 504,000 psf. Groundwater A site-wide static groundwater table was not encountered. Water seepage at approximately 11 ft below existing surface grade in the decomposed rock layer was observed in test pit TP-1. Limited water seepage was observed approximately 2 ft below existing surface grade on top of the rock surface exposed in test pit R-1B. Water seepage or indications of mottling were not observed in any other test pit. Surface water flowing over the sloping rock surface should be expected, especially during wet seasons. Groundwater levels are subject to seasonal fluctuations. GLOBAL SLOPE STABILITY ANALYSIS As requested, Langan performed a global stability analysis of the subject area slope. The purpose of such a study is to evaluate if the slope is stable, with an adequate factor of safety, in the existing condition and in the proposed building or roadway loading condition. The analysis consisted of

of such a study is to evaluate if the slope is stable, with an adequate factor of safety, in the existing condition and in the proposed building or roadway loading condition. The analysis consisted of performing two-dimensional Limit Equilibrium Method (LEM) analyses for representative slope cross-sections to evaluate the global slope stability. During our study and analyses, we performed the following key tasks: 1. We reviewed the available geotechnical subsurface information along with our targeted subsurface investigation results for the subject slope area. 2. We reviewed the soil and rock geometry in the cross-sections along with the proposed building gravity building loads. We chose two sections (section A and section B) across

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 7 of 13 the proposed Building D footprint and down the subject area slope to the eastern residences for our slope stability analyses. We also chose two additional sections (section C and section D) across the northeastern portion of the subject area and down the subject area slope near the northeastern residences on Howell Drive. The locations of the sections are shown on Figure 1. 3. We estimated strength parameters for the soil based on visual observation and the collected N-value results obtained during sampling. 4. We estimated strength parameters for the rock based on laboratory testing results and rock recovery and rock quality designation values obtained in the rock cores. 5. We analyzed the global slope stability using LEM for the estimated proposed Building D load and access road load and we calculated factors of safety with respect to global stability for the static condition. 6. We analyzed the slope stability using the LEM for the combined service and seismic loads and we calculated factors of safety with respect to global stability for the maximum considered earthquake. We used the computer software SLOPE/W for the LEM analyses. An overview of our analyses and a summary of our results are presented below. Model Parameters Model Geometry For our two-dimensional global stability analyses, we selected two representative cross-sections (section A and section B) across the proposed Building D footprint extending to the eastern property line in the subject area. The eastern property line is approximately 900 ft east of the proposed Building D footprint. We also selected two representative cross-sections (section C and section D) across the northern portion of the proposed Building D footprint and proposed access road north of the Howell Drive cul-de-sac extending to the northeastern property line. The northeastern property line is approximately 200 ft and 250 ft east of the proposed access road and proposed Building D footprint, respectively. The soil and rock elevations used in the model are based upon the results of available subsurface investigation information, which was collected from the accessible explored areas of the site. Material Properties The generalized subsurface conditions

based upon the results of available subsurface investigation information, which was collected from the accessible explored areas of the site. Material Properties The generalized subsurface conditions consisted of surficial materials (topsoil) underlain by natural sand and silt over decomposed rock and rock strata. No subsurface investigation was performed beyond the northeastern property line as part of the supplemental investigation.

Global Slope Stability Study for Building D West Essex Highlands Project Langan Project No.: 101049801 Revised 18 June 2025 Revised 18 June 2025 - Page 8 of 13 MEMO We estimated the material parameters including friction angle (ϕ’), of the surficial fill, natural soil and decomposed rock layers based on in-situ test data. The soil parameters utilized in our analyses are presented in Table 1 provided below. Table 1: Soil Strength Properties Soil/Rock Unit Weight (pcf) Friction Angle, ϕ' (deg.) Cohesion, c (psf) Topsoil 115 30 0 Medium Dense Sand 120 32 0 Dense Sand 125 34 0 Decomposed Rock/Very Dense Granular Soil 135 38 0 The rock encountered and cored during the investigation at the upper portion of the slope was classified as basalt. Rock properties were estimated using values recommended in the SLOPE/W manual and a Geologic Strength Index (GSI) of 65, an intact rock parameter (m i) of 17, a disturbance factor (D) of 1 and an unconfined compressive strength (UCS) of 316,800 psf (lowest laboratory value) were used in the analyses. Groundwater It should be noted that our original subsurface investigation was performed during a time of drought and not during the wet season. The supplemental investigation was performed at the end of the wet season as defined by the latest NJDEP stormwater best management practices manual and groundwater was not encountered in the test pits. Therefore, our primary analysis excludes groundwater, and our secondary analysis assumes a high groundwater level to be at the top of the decomposed rock / very dense granular soil layer. Proposed Building D Loading Proposed Building D will be 4-stories above structured parking. A total uniform service load of 1,000 psf was applied to the eastern slope to simulate the effect of the proposed building. This service load estimate was derived from live loads specified in the New Jersey UCC Building Subcode 2021 and an approximate estimation of the dead loads. A total uniform load of 250 psf was applied to the slope to simulate the effect of the proposed access road. LEM Analyses and Results (Service Loads) The LEM analyses were performed to represent the pre-construction condition and postconstruction condition after the construction of the structure. We used the Morgenstern-Price LEM for our analysis, which satisfies the equilibrium of forces and moments. To consider the

ition and postconstruction condition after the construction of the structure. We used the Morgenstern-Price LEM for our analysis, which satisfies the equilibrium of forces and moments. To consider the effect of the proposed construction on slope stability, the critical slip surfaces for

Global Slope Stability Study for Building D West Essex Highlands Project Langan Project No.: 101049801 Revised 18 June 2025 Revised 18 June 2025 - Page 9 of 13 MEMO the existing and proposed gravity (static) loading conditions for Sections A, B, C and D are provided in the tables below. LEM analysis results under gravity loading (static) condition satisfy a minimum acceptable factor of safety of 1.5, and are presented in Appendix E. Table 2A - LEM Factors of Safety against Sliding for Service Loads – Section A Condition Critical Slip Surface Critical Slip Surface That Reaches the Downslope Building Existing 2.20 3.29 Proposed 2.20 3.29 Table 2B - LEM Factors of Safety against Sliding for Service Loads – Section B Condition Critical Slip Surface Critical Slip Surface That Reaches the Downslope Building Existing 1.67 6.46 Proposed 1.67 6.45 Table 2C - LEM Factors of Safety against Sliding for Service Loads – Section C Condition Critical Slip Surface To Upper Tier Retaining Wall Existing 1.59 Proposed 1.59 Table 2D - LEM Factors of Safety against Sliding for Service Loads – Section D Condition Critical Slip Surface within Site Limits Existing 1.94 Proposed 1.94 Seismic Slope Stability Analyses Seismic slope stability analyses have traditionally been performed by using pseudo-static limit equilibrium analyses. These analyses consist of applying a lateral force to the slope equal to the product of a seismic coefficient (kh) and the weight of the slope. The seismic coefficient is based on the actual anticipated level of acceleration in the failure mass and corresponds to some

Global Slope Stability Study for Building D West Essex Highlands Project Langan Project No.: 101049801 Revised 18 June 2025 Revised 18 June 2025 - Page 10 of 13 MEMO fraction of the anticipated peak acceleration (amax). Hynes-Griffin and Franklin (1984)1 seismic coefficient equation kh=0.5amax/g is considered appropriate to use for most slopes (Kramer, 1996)2. For this site, we utilized the Hynes-Griffin and Franklin (1984) criteria that resulted in kh=0.0875. To consider the effect of the proposed construction on slope stability, the critical slip surfaces for the existing and proposed seismic loading conditions for Sections A, B, C and D are provided in the tables below. LEM analysis results under seismic conditions satisfy a minimum acceptable factor of safety of 1.15 and are presented in Appendix F. Table 3A: LEM Factors of Safety against Sliding for Seismic Loads – Section A Condition Critical Slip Surface Critical Slip Surface That Reaches the Downslope Building Existing 1.65 2.23 Proposed 1.65 2.23 Table 3B: LEM Factors of Safety against Sliding for Seismic Loads – Section B Condition Critical Slip Surface Critical Slip Surface That Reaches the Downslope Building Existing 1.29 4.59 Proposed 1.30 4.59 Table 3C: LEM Factors of Safety against Sliding for Seismic Loads – Section C Condition Critical Slip Surface To Upper Tier Retaining Wall Existing 1.26 Proposed 1.26 Table 3D: LEM Factors of Safety against Sliding for Seismic Loads – Section D 1 2 Condition Critical Slip Surface within Site Limits Existing 1.47 Proposed 1.47 Hynes-Griffin Mary E; Franklin Arley G (2007). “Rationalizing the Seismic Coefficient Method”. Department of the Army. Steven L Kramer. “Geotechnical Earthquake Engineering” 1996.