2025 01 14 West Essex Highlands Development Building D Slope Stability Study

MEMO Global Slope Stability Study for Building D West Essex Highlands Project Langan Project No.: 101049801 14 January 2025- Page 4 of 11 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. Large boulders and cobbles as well as rock outcrops were also visible at the surface throughout the subject area. 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 at varying depths and several large boulders were encountered in boring LB-4 starting about 16 ft below existing surface grade. The top of the natural soils was first encountered at depths ranging from approximately 0.5 ft to 2 ft, corresponding to elevation (el) 614 to el 522. The thickness of the natural soil varied typically between 7 ft and 9 ft in the borings located at the higher portion of the slope near the proposed building D footprint. 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 recorded N-values in this stratum ranged from 21 bl/ft to split-spoon refusal values, indicative of dense to very dense materials and the presence of cobbles and boulders. The recorded Nvalues typically increased with depth. Decomposed Rock A decomposed rock stratum was encountered in all Langan borings, excluding boring LB-4. The thickness of this decomposed rock layer ranged from 2 ft to 5 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 decomposed rock stratum with the limited split-spoon sample recovery. Bedrock Bedrock consisting of gray basalt was encountered in borings LB-1 and LB-3 below the overburden soils and decomposed rock stratum at approximately 14 ft and 9 ft below existing surface grade or at approximately el 590 and

gray basalt was encountered in borings LB-1 and LB-3 below the overburden soils and decomposed rock stratum at approximately 14 ft and 9 ft below existing surface grade or at approximately el 590 and el 605, respectively. The top of rock was determined by rock coring in these borings. The recorded rock recovery (REC) values varied from 87% to 97% and the rock quality designation (RQD) values varied from 58% to 82%, indicative of fair to good quality rock. As previously stated, some basalt rock outcrops were visible typically at the upper portion of section A near the proposed Building D 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, = = =