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 6 of 21 Proposed Grading in Front of Building D The grading indicated on the Preliminary & Final site plans SP15 and SP16 indicate that the finished grading will conform closely to the existing grade to the rear of the proposed building. The finished grades in front of the building are shown on the drawing markup attached to this letter for reference. The proposed grade follows the centerline profile of “Road D”. The roadway grade at the southwest corner of Building D.2 is shown at elevation 585 feet which is approximately 5 feet below the existing grade at that location. The roadway climbs to approximately elevation 592 at the entrance to the upper parking deck at the entrance. The proposed grade is approximately 2 feet above the existing grade at that point. The grade at the northern end of the building is near elevation 608 which is about 2 feet below the existing grade. The existing grades at the front building lines are generally higher than the finished grade at the wall and the grades along Road D. Cuts of up to 10 feet are indicated near the south end of Building D.2 near to the high point of the ridge. Stormwater Management (SWM) and Infiltration Basins The proposed limits of site grading are shown on the Langan Investigation Plan and correspond to the limits indicated on the Preliminary & Final Site Plan. The mapping indicates that the limits of grading will be 5 to 20 feet from the rear building line. The limit is within the line defining the high point of the ridge indicating that site runoff from the landscaped zone would be directed towards the building and to a stormwater collection system of yard inlets along the rear of Building D.1. The plan indicates that the discharge from the rear yard drains will be directed through the building to Stormwater Infiltration Basin 11. We understand that all the building roof drainage and the yard drainage including Road D will be directed to Basins 10 and 11. We further understand that these basins have been designed to retain a volume of runoff determined in accordance with the current

e yard drainage including Road D will be directed to Basins 10 and 11. We further understand that these basins have been designed to retain a volume of runoff determined in accordance with the current regulations. Review of the designs is beyond the scope of this study. We have included this description for consideration of the potential impact of concentrated stormwater infiltration on slope stability. The following description is based on information provided on Preliminary & Final Site Plan Drawing SP56: 1. Basin No. 10: The location of the basin is shown on the attached markup of the Investigation Plan. The basin details on the Site Plan indicate that the basin will be an open detention basin with a rim near elevation 580 feet, an outlet structure with a grate near elevation 576, a low-level outlet near elevation 576.3 and an invert out near elevation 573.75 feet. The basin is shown to be approximately 220 feet long and 60 feet wide. The 10-year recurrence storage elevation is shown as elevation 577.06 feet. The 100-year recurrence storage elevation is shown as elevation 578.3 feet. Bedrock was reported at