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

ATTACHMENT A SUPPORTING GLOBAL STABILITY STUDY MEMORANDUM BY LANGAN = = =

Memorandum 300 Kimball Drive To: Parsippany, NJ 07054 T: 973.560.4900 F: 973.560.4901 Mark Hoffman / Garden Homes From: Mark K. Seel / Langan Ronald D. Boyer / Langan Info: Adam Yoda / Langan John Cote / Langan Michael Vitello / Langan Date: 14 January 2025 Re: Global Slope Stability Study for Building D West Essex Highlands Project West Orange, New Jersey Langan Project No.: 101049801 Ronald D. Boyer, P.E. Professional Engineer NJ Lic. No. 24GE04200300 This memorandum summarizes the subsurface investigation and global slope stability evaluation performed by Langan Engineering and Environmental Services, LLC (Langan) for the eastern portion of the proposed West Essex Highlands development site located in West Orange, New Jersey. The following sections provide a description of existing site conditions, proposed development, subsurface investigation and conditions, our global slope stability analysis and our evaluation regarding slope stability with respect to the associated building construction. EXISTING CONDITIONS AND PROPOSED CONSTRUCTION The subject project site is located on Lot 32, Block 179, and is bounded by Avon Drive and Howell Drive and residential properties to the north, and residential developments to the south, east and west. The study area for the global slope stability analysis is the easternmost portion of the site bounded by Rosemont Terrace and Mayfair Drive to the east. The study area is heavily wooded and surface grades slope downward from west to east. There is a 25-foot-wide utility easement that bisects the subject area running in the north-south direction. Site surface grades generally range from approximately elevation (el) 616 to el 450. Typically, the slope in the subject area ranges from 2 Horizontal (H): 1 Vertical (V) or approximately 26 degrees from horizontal at its steepest to approximately 6H:1V or approximately 10 degrees from horizontal east of the utility easement. The proposed residential development will consist of the construction of new 4-story structures over structured parking. Based on available site drawings prepared by Anderson Consulting Services, LLC. (ACS), the closest building to the subject slope is proposed Building D, which is to be located at the top of the slope within the study area approximately 700 ft west of the eastern property line. We understand that no site improvements are proposed

s proposed Building D, which is to be located at the top of the slope within the study area approximately 700 ft west of the eastern property line. We understand that no site improvements are proposed in the wooded subject area located approximately 20 ft east of the proposed eastern building line of Building D.

Global Slope Stability Study for Building D West Essex Highlands Project Langan Project No.: 101049801 14 January 2025- Page 2 of 11 MEMO Based on the proposed grading plans, we understand the proposed construction of Building D will not include any grade changes from the existing conditions immediately east. The lowest proposed level will range from elevation (el) 607 to el 582 which will require cuts up to about 25 ft from existing surface grade in some isolated areas. The lower structured parking level for Building D will be nested into the eastern slope with adjacent grades east of the proposed building remaining unchanged. The building will be supported on shallow foundations bearing on natural soils or rock. A site location map showing the approximate limits of the study area and proposed Building D is provided below and as Figure 1. PROPOSED BUILDING D LOCATION N APPROXIMATE SUBJECT SLOPE AREA (WOODED) ROSEMONT TERRACE 700 FT +/EXISTING SEWER EASEMENT APPROXIMATE TOP OF SLOPE MAYFAIR DR APPROXIMATE BOTTOM OF SLOPE Proposed Site Map REGIONAL GEOLOGY According to the available geological maps we reviewed, the upper portion of the subject slope is underlain by the Preakness Basalt. The lower portion of the slope is mapped as the Feltville Formation, which consists of sandstone, siltstone or mudstone. A high-angle fault with no history of activity is mapped about 2,000 ft to the east of the site. An abandoned sandstone rock quarry is also identified about 1,000 ft southeast of the site. A copy of the geologic mapping is provided on Figure 2. SUBSURFACE INVESTIGATION A targeted subsurface investigation for the global slope stability study consisting of borings and test pits was completed between November and December 2024 under full-time supervision by = = =

MEMO Global Slope Stability Study for Building D West Essex Highlands Project Langan Project No.: 101049801 14 January 2025- Page 3 of 11 Langan. The borings and test pits were performed at accessible areas along two cross-sections running in the east-west direction through the subject area. The locations of the borings and test pits are shown on Figure 1. Logs of the borings and test pits are provided in Appendix A and Appendix B, respectively. Borings Four (4) borings, identified as LB-1 through LB-4, were drilled within the subject area by Craig Geotechnical Drilling Co. Inc. (Craig). The borings were performed using a track-mounted drill rig and mud-rotary drilling techniques. Borings extended approximately 19 ft to 50 ft below existing surface grades. Borings LB-1 and LB-3 were performed at the higher portion of the slope near the proposed Building D footprint area. Borings LB-2 and LB-4 were performed east of the existing sewer easement located at the lower portion of the slope. Soil samples were collected, and Standard Penetration Tests (SPT) were performed using a standard 2-inch outside-diameter split-spoon sampler driven by a 140-pound automatic hammer in accordance with ASTM D1586. Soil sampling and SPTs were typically performed continuously in the upper 12 ft and at 5 ft intervals thereafter. Recovered soil samples were visually examined and classified in the field in accordance with the Unified Soil Classification System (USCS). Where encountered, rock was cored for a minimum of 10 ft using an NQ-sized core barrel. Test Pits Eight (8) test pits were excavated by Frank Semeraro Construction using a John Deere 75G excavator. Test pits identified as TP-1 through TP-8 were performed throughout the subject area and extended approximately 3.5 ft to 13 ft below existing surface grades. Upon completion, the test pits were backfilled with excavated materials and the backfill was compacted with the excavator bucket. 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 C. SUBSURFACE CONDITIONS The generalized subsurface conditions consisted of

y to determine the unconfined compressive strength of the rock. The results of the laboratory tests are included in Appendix C. 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 = = =

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, = = =

MEMO Global Slope Stability Study for Building D West Essex Highlands Project Langan Project No.: 101049801 14 January 2025- Page 5 of 11 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 The groundwater level could not be inferred from the moisture content of the soil samples during drilling. Water seepage at approximately 11 ft below existing surface grade in the decomposed rock layer was observed in test pit TP-1. 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 subjected 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 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

urface 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 the proposed Building D footprint and down the subject area slope to the eastern residences for our slope stability analyses. Locations of Sections A and B 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. = = =