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 16 of 21 Langan considered a seepage case in their analysis with the phreatic surface approximately following the top of the decomposed Rock. This approach is, in our opinion, reasonable provided there is no indication of spring activity or emerging seepage on the slope below the ridge under present conditions. STABILITY ANALYSES General Both the Applicant’s and the Objector’s Engineers (the “Engineers”) have utilized the Slope/W computer software program to perform the comparative analyses of the slope stability. This program is recognized as an effective analysis tool for complex slopes and is capable of performing searches to determine the critical failure surface that determines the stability of the slope. The Engineers disagree, as indicated in the Objector Report and the Langan Rebuttal, on the strength properties used for the strata and, in particular, for the bedrock, as determined by the Geological Strength Index. The presentation of the results in the report provides the geometry of the slope and sub-surface stratification model prepared by the user and the strength properties derived by the user and entered in the input file. The analyses have been performed using the Limiting Equilibrium Method which derives the safety factor as the limiting shearing resistance available on the assumed failure surface divided on the shearing resistance required on the surface to maintain equilibrium. The method of computation selected by Langan is the Morgenstern Price method which is considered the most rigorous method of analysis. In our opinion, the method of analyses selected by the Engineers are appropriate for evaluation of the stability of the slope. A detailed summary of the computation results is summarized in the individual Engineer’s reports and are not repeated in detail herein. Required Minimum Factors of Safety The Langan report references the Naval Facilities Command Manual DM7 standards for a recommended minimum factor of safety of 1.50 for static load cases and 1.15 for seismic load cases. This standard is, in our opinion, applicable

the Naval Facilities Command Manual DM7 standards for a recommended minimum factor of safety of 1.50 for static load cases and 1.15 for seismic load cases. This standard is, in our opinion, applicable as a standard for the slope in this case. The Army Corps of Engineers Engineering Manual EM1110-2-1902 is consistent with the recommendation of DM-7. Princeton Hydro has referenced Corps of Engineers Manual EM-1110-2-2908 Rock Foundations as requiring a minimum factor of safety of 2.00. This standard is not, in our opinion, applicable as a standard for the slope in this case.