25 10 28 Slope Stability Review

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

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 7 of 21 Test Pit D2 in 2021 at 9 feet depth at the southern end of the basin location. This is estimated to be at approximate elevation 568 feet. Seepage was encountered at a depth of 6 feet which is anticipated to be near elevation 571 feet. Bedrock was not encountered in Test Pit D1 which extended to 16 feet depth which is estimated to be equivalent to below elevation 567 feet. Groundwater seepage was reported at a depth of 10 feet which is estimated to be equivalent to elevation 573 feet. 2. Basin No. 11: Basin No. 11 is a subsurface infiltration basin. The storage is shown to be approximately 325 feet long. The width is not indicated on the reference plan. The inflow is through a 12” porous HDPE pipe at 0 slope discharging into a gravel bed 2.42 feet in thickness, with base at elevation 590. The gravel bed is overlain by a select fill which is, in turn, overlain by a porous pavement. The storage elevation at the 10-year recurrence event is shown to be at elevation 591.27 feet and at the 100-year recurrence to be elevation 592.06. Rock was not encountered and is estimated to be below elevation 579 feet at Test Pit E-1 and to be below elevation 576 feet at Test Pit E-2. Seepage was encountered at estimated elevation 584 feet at Test Pit E-1 and at estimated elevation 581 at Test Pit E-2. The elevations of the recharge basins are equivalent to that of the middle of the upper slope. The Applicant’s Engineers should, in our opinion, review the results of mounding analyses at the basins near the ridge and confirm that concentrated infiltration will not affect the stability of the slopes by hydraulically surcharging rock joints that may increase seepage pressures on the slope below. Emergency Access Roadway The emergency access roadway is located to the north of Building D.1 and will connect the Road D Cul de Sac to the Howell Drive Cul de Sac. It will cross the top of the ridge near Langan Boring NLB1 and is at the top of the slope on Langan Analysis Section C-C. The centerline of the road is approximately 170 feet horizontally from the retaining

l cross the top of the ridge near Langan Boring NLB1 and is at the top of the slope on Langan Analysis Section C-C. The centerline of the road is approximately 170 feet horizontally from the retaining walls on the west edge of 15 Howell Drive. The grading of the road will direct runoff to the Howell Drive Cul de Sac. The original stormwater management investigation reports (References 3A and 3B) indicated that porous pavement and infiltration was being considered for this road, but the Preliminary & Final Site Plan does not indicate that this is included in the current plan. It would not be appropriate, in our opinion, to employ infiltration on the slope at this location which is above the residence at 15 Howell Drive. Langan has considered a live load of 250 psf which is, in our experience, equivalent to the highway live load surcharge recommended for earth retaining structures and is, in our opinion, conservative for a road with limited usage.

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 8 of 21 Construction Considerations Our review of the reference reports indicates that a principal concern for slope stability expressed by Princeton Hydro is that the construction, which involves excavations in rock to a depth of approximately 25 feet below the top of rock at the high point of the ridge, could lead to disturbance and weakening of the slope, particularly if blasting is used. We understand that Langan’s reply indicates that it is their opinion that it is too early in the planning stage to determine whether blasting needs to be employed, and, if it is required, the size of the blasting charge can be controlled to reduce vibration effects on the slope. For the purpose of our review, we recommend that the following construction-related conditions be addressed in the requirements that are set forth in this Planning Board Review and subsequent Municipal Reviews of the application for construction permits: 1. Clearing Site 2. Protection of the forestry on the slope 3. Soil Erosion and Sediment Control 4. Limitation of surcharges and equipment loads 5. General Excavation 6. Rock Excavation 7. Dewatering and control of runoff 8. Final Grading and Landscaping REVIEW OF EXISTING SITE CONDITIONS General This section covers a review of the existing topographic, geologic and subsurface conditions. Our review is based on both the descriptions contained in the Applicant’s and Objector’s Engineer’s reports and the references cited above. Geologic and Seismic Design Considerations The existing ridge is a segment of a prominent geological feature known as the Second Watchung Mountain. The bedrock Geology mapping was included on the map entitled “Bedrock Geologic Map of Caldwell Quadrangle” (Reference 6A). A section of this map is contained in the Langan Report dated June 18, 2025 as Figure No. 2. We have attached an extracted copy of Figure No. 2 for ease of reference by the Board. Our interpretation of the information is as described below: 1. The bedrock on the upper ridge is included in the unit described as the Preakness Basalt with map symbol

ease of reference by the Board. Our interpretation of the information is as described below: 1. The bedrock on the upper ridge is included in the unit described as the Preakness Basalt with map symbol Jp. The basic map description is given as Dark Greenish Gray to black fine-grained, dense and hard. Quarried basalt is usually high strength from deep within

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 9 of 21 the formation. Our Geotechnical Engineers observed the outcrop of the rock referenced as Outcrop No. 4. The height of the exposure was only 4 to 6 feet. The appearance of the rock indicated that it has been weathered and somewhat softer than fresh cuts exposed in outcrops or as was exposed in the highway cut for Route 280 to the southwest of the site. The principal jointing pattern indicated jointing with dip favorably downward into the slope and steep, nearly vertical joints. Some of the exposed rock showed a series of tight vertical cracks spaced as close as 1 or 2 inches. We anticipate that the outcrops represent the materials that were near the edge of the volcanic flow, and that the outcrops have been exposed and undergone substantial deterioration. 2. The reference map indicates that jointing in the igneous rocks (i.e., the basalt) consists of columnular joints that are rated due to cooling and joints due to faulting. A prominent fault is mapped approximately 2,000 feet from the site, as shown on the copy of Langan Figure No. 2. Tectonic jointing is reported to range from a few feet to many feet far from the mapped faults but become closely spaced near the faults. We note that several closely spaced faults were identified in the Route 280 cut into the Second Watchung Mountain. 3. The closest well to the site shown on the reference map is Well No. 53 and appears to have been drilled with a ground surface elevation near elevation 560 feet. The following results were indicated on the map for Well No. 53, assuming the surface elevation was near elevation 560 feet: Depth 0 to 35 feet 35 – 165 165 – 300 Driller Description Sand and Clay Trap Rock Red Sandstone Inferred Elevation Top of basalt near Elev. 525 feet Base of basalt near Elev. 395 feet Bottom of well near Elev. 260 feet 4. The surface contact between the Preakness Basalts and the Feltville formation red sandstones in the area near the site is mapped along the elevation 500 contour on the reference map. The mapping indicates that the bedding of the sandstones dip towards the

he Feltville formation red sandstones in the area near the site is mapped along the elevation 500 contour on the reference map. The mapping indicates that the bedding of the sandstones dip towards the west (into beneath the basalt sill on a slope of approximately 9 degrees from the horizontal. The surficial soils reported in the borings and in the test pits performed by the Applicant’s Engineers conformed to the description of Rahway Till Yellow Phase included on the surficial Geology Map. The description in the mapping indicates that the formation on the slopes contain concentrations of basalt cobbles and “flagstones” formed by both post-glacial mechanical weathering and glacial deformation of finely jointed basalt. This description agrees with the weathered appearance of the outcrops on the site. The confirmation that the site had been

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.

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 11 of 21 The ridge and slope area are wooded. We understand that the wooded area on the slope is protected by regulation. Effective maintenance of the health of the forested area is necessary to maintain the benefits of the forest towards the stability of the slope. West Orange Sanitary Sewer Easement The West Orange Sanitary Sewer easement traverses the upper slope from the top of the ridge (where it is to the south of the building) to its intersection on Howell Drive between the residences at 11 and 13 Howell Drive. The easement appears graded as a side hill bench. Langan has indicated the location and inferred depth in the analysis sections. The section results did not include sections going through the sewer. Slope Hazard Mapping The slope hazard mapping for Essex County that has been reproduced in the Langan Report identifies an area of risk on the slope. The risk is categorized as Landslide Case BIII, Weakly Cemented Rock and Soil (Hazus Number 3) Slope angle 10 to 15 degrees. The map legend indicates that the slope was determined by measuring spacing of 20 feet contours on the Caldwell Quadrangle Map. The slope angle on the upper slope, as determined by the spacing of contours created by aerial survey, is steeper than indicated by the contours and ranges from 17 to 29 degrees, which may require a re-evaluation of the Hazus Class by the Agency publishing the map. The range indicated by the spacing of the contours could put it into Class BV, Hazus No. 7. We were not able to obtain additional background information on the basis of the classification in time for this review. The analyses performed by both Langan and Princeton Hydro do not, in our opinion, indicate instability under the assumed conditions. SUBSURFACE INVESTIGATION REVIEW General Our review of the Slope Stability Investigations included review of reports and subsurface exploration logs and laboratory test result reports contained in the CME files for the Planning Board Application review. Langan performed explorations on the slope for the slope stability investigation being