25 10 28 Slope Stability Review

Chairman and Members of the West Orange Planning Board Application No. PB24-01, West Essex Highlands, LLC, Warner Road, Block 179, Lot 32 Review of Applicant’s Engineer’s Slope Stability Analysis Reports, the Objector’s Engineer’s Response Reports; and the Applicant’s Engineer’s Rebuttal Report October 28, 2025 Page 14 of 21 Mapping. The apparent density indicates that the materials were likely to have been deposited by the glacier and subject to heavy pressures from the overlying glacier. These soils extended to the decomposed rock layer in most of the borings directly underlain by the Basalt formation. Langan has assigned a strength envelope based on a cohesion of 0 psf and an angle of internal friction of 34 degrees. The bedrock formation, as described by Langan based on observations of the outcrops and descriptions and photographs of rock cores in their report, conformed, based on our understanding, to the following description: Decomposed Rock: This description, in our experience, describes the zone of deterioration of the parent bedrock material and, in at least one classification system, may be represented as rock with a standard penetration resistance less than 50 blows per inch. The area was glaciated, and it is apparent that the igneous rock had been worked by the action of the glacier. The decomposed layer appears to be a few feet thick. Langan has assigned a strength envelope based on a cohesion of 0 psf and an angle of internal friction of 38 degrees. Basalt Bedrock: The outcrops of basalt as mapped on the drawings are of low height. Langan reported a joint set dipping downward to the east on a slope of 17 degrees. A downward dip to the east is not, in our experience, a favorable inclination, which would be downward towards the west. Langan indicated a contact rock on rock friction angle of 35 degrees. Unconfined compressive strength test results were examined for 2 rock samples obtained from Boring LB-3, reportedly from 8.5 to 10.5 feet. We anticipate that the core samples were taken from the same segment of core since the depth of the sample is listed as the same range. We reviewed the core box photo (Exhibit C – Select Rock Core Photographs) in the Langan Rebuttal Report (Reference 1C) but were unable to identify the section of core from which the samples were taken. The laboratory report prepared by RSA Geolab of Union, New Jersey,

aphs) in the Langan Rebuttal Report (Reference 1C) but were unable to identify the section of core from which the samples were taken. The laboratory report prepared by RSA Geolab of Union, New Jersey, indicated an unconfined compressive strength of 515,719 pounds per square foot (psf) which is equivalent to 3,580 pounds per square inch (psi) for C1-A. The result for C1-B was 323,260 psf (2,200 psi). The results are a small fraction of the anticipated strength range for Basalt and roughly equivalent to that of a low to medium strength concrete. The wet density of the core was recorded to be 182.3 pounds per cubic foot (pcf) which we understand to be in the normal range. Langan, in their Rebuttal Report, attributed the unusually low strength to porosity, and crystalline grain size characteristics in the rock which would likely have been subjected to external cooling at the edge of the sill. Langan has used the Slope/W computer software which utilizes the Rock Mass Rating (RMR) and Geologic Strength Index (GSI) to model a representative strength for failure