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 10 of 21 glaciated indicates that the existing soils and rock have been subjected to relatively high surface loadings in the past. Langan derived a horizontal ground acceleration to compute seismic effects on the slope stability using a recognized seismic coefficient of 0.5 times the peak acceleration of the maximum considered earthquake. In general, descriptions of geologic conditions in the letters and reports prepared by the Applicant’s and Objector’s Engineers conform to the descriptions contained in the references reviewed by CME. There is disagreement principally in the determination of strength properties for the bedrock as discussed later in this letter. Topographic Conditions Topographic conditions are shown on the attached markup of the Langan submittal Investigation Plan, Drawing No. 1. The existing ridge line is shown on the Investigation drawing and is highlighted in Blue. The elevations along the ridge range from a high of elevation 614 feet near Langan Boring No. LB3, decreases to elevation 601 opposite the proposed building main entrance, and rises to approximately 610 at the north end of Building D.1. The eastern slope begins to steepen at distances of 40 to 120 feet of the ridge up to the northern end of the building where it reduces to approximately 15 feet. The ridge begins to trend further to the northwest to the north of the building. Outcrops of Basalt bedrock are primarily located along and below the line where the slope begins to steepen. For the purpose of this review, the upper slope is considered to run from the 500 feet elevation contour to the ridge line. We have computed local slope based on the spacing of 10 feet contours in several areas. This evaluation indicates that the slope varies locally from 21 degrees to 29 degrees. The residence at 15 Howell Drive (represented on Langan Analysis Section C-C) is built on a terraced lot between elevation 540 and 544. Terraced retaining walls provide a grade separation of about 12 feet. The residence on 13 Howell Drive has a level bench near elevation 518. A single

t on a terraced lot between elevation 540 and 544. Terraced retaining walls provide a grade separation of about 12 feet. The residence on 13 Howell Drive has a level bench near elevation 518. A single retaining wall on the rear yard provides a grade separation on the order of 12 feet high, as well. The lower slope below the 500 contour decreases to 7.5 degrees to 10 degrees. Locally the slope steepens to 23 degrees along the rear lot lines of the residences on Rosemont Terrace and Mayfair drive. It is anticipated that the reduction in the slope is associated with the underlying transition to the Feltville formation sandstone beginning near the 500 feet contour based on the bedrock geology mapping.