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 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.