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