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 18 of 21 Princeton Hydro Analysis Cases Static Case with Groundwater Phreatic Surface at Top of Decomposed Rock Failure Surfaces in Soil Overburden: 1. The critical factor of safety on Section C was computed to be 1.589 for the proposed condition. 2. The critical factor of safety on Section D was computed to be 1.938 for the proposed condition. Static Case with Groundwater Phreatic Surface at Top of Decomposed Rock Failure Surfaces in Weak Zone of Rock with GSI = 20: 1. The critical factor of safety on Section C was computed to be 1.76 for the proposed condition. 2. The critical factor of safety on Section D was computed to be 1.65 for the proposed condition. The computed minimum factors of safety exceed 1.50 in the analysis cases presented by Princeton Hydro. There is a surface shown for analysis Section C with critical failure surface passing through the medium dense sands with factor of safety of 1.48 which is only slightly less than 1.50. Langan has questioned the assumed stratification on that section stating that it does not consider dense sands on that section, which were indicated by the borings. Langan Rebuttal Analysis Cases In Exhibit A of their rebuttal, Langan derives a lower-bound Rock Mass Rating and Geologic Strength Index of 50, which exceeds the value of 20 used by Princeton Hydro. They also performed analyses which indicate that the existing sanitary sewer trench would not significantly reduce the stability of the slope. The factors of safety exceed the values computed by Princeton Hydro, but the factors of safety using the GSI of 20 were, in our evaluation, satisfactory and do not indicate instability. The detailed results are contained in the Langan Rebuttal Case. CONCLUSION AND RECOMMENDATIONS TO THE BOARD General We have described our review of the project based on the submittals to the Planning Board. Our evaluation of the Memoranda from the Applicant’s and Objector’s Engineers is as follows: 1. The description of subsurface conditions conforms to the reported bedrock and surficial geology with the exception that Langan

Memoranda from the Applicant’s and Objector’s Engineers is as follows: 1. The description of subsurface conditions conforms to the reported bedrock and surficial geology with the exception that Langan did not consider the transition to the Feltsville