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 4 of 13 Rock Outcrop and Boulder Mapping As part of the supplemental investigation, exposed rock outcrops and boulders along the subject slope were located using handheld survey equipment and evaluated from a slope stability perspective. Six (6) shallow test pits, identified as R-series test pits, were performed at exposed rock outcrop areas or boulders observed on the slope to gather further information for our evaluation. The approximate location of the rock outcrops and boulder and select photographs are provided on Figure 3. Logs of the R-series test pits are provided in Appendix C. A discussion of observations is presented in the following section and findings are presented in the “Geological Hazard Review” section of this memorandum. Geotechnical Laboratory Testing Soil and rock samples collected during the subsurface investigation were classified and examined in the field by a Langan geotechnical engineer. Representative rock samples were tested by a geotechnical laboratory to determine the unconfined compressive strength of the rock. The results of the laboratory tests are included in Appendix D. SUBSURFACE CONDITIONS The generalized subsurface conditions consisted of surficial materials (topsoil) underlain by natural sand and silt overlying a decomposed rock and rock strata. Detailed descriptions of the subsurface conditions are given below. Surficial Materials Surficial materials at the test locations generally consisted of topsoil. The thickness of the topsoil was observed to vary from 6 inches to 24 inches. Boulders and cobbles as well as rock outcrops were also visible at the surface throughout the subject area. It should be noted it was difficult to differentiate between deeply buried boulders and a rock outcrop during our evaluation. Rock Outcrops: Rock outcrops and boulders were identified on or near the subject eastern slope. Generally, the rock outcrops had exposed faces less than 15 ft high with the majority of the outcrops having exposed faces less than 2 ft high. In general, the larger exposed rock outcrops (Outcrop #1 and #4 identified in Figure 3) with two principal joint sets, one near vertical that is oriented perpendicular to the rock face and one dipping 10 degrees to 20

arger exposed rock outcrops (Outcrop #1 and #4 identified in Figure 3) with two principal joint sets, one near vertical that is oriented perpendicular to the rock face and one dipping 10 degrees to 20 degrees out of the face. The near vertical jointing pattern for these outcrops was generally observed to be spaced 1 inch to 12 inches apart with the horizontal jointing pattern typically spaced 2 ft to 4 ft apart. The exposed outcrop faces typically dip eastward (downslope) between 60 degrees and 85 degrees from horizontal. Separated rock pieces that originated from the parent rock outcrop were observed to be generally less than 6-inch-thick sheets and located immediately in front of the exposed face at Outcrop #4. The joint surfaces are typically rough and slightly irregular. Exposed Boulders: Boulders with varying sizes were observed along the subject slope. Larger boulders were observed on top of or in close proximity to Outcrop #1. The dimensions of a large