Revised Stormwater Management Report

DocuSign Envelope ID: DB0533B0-B14B-449D-A0A8-3B9C3C0DF5D9 Introduction The West Essex Highlands property has been designated as the location for multifamily housing as part of a court approved settlement agreement which is part of the affordable housing requirements for the Township of West Orange. Part of the Settlement Agreement provides that disturbance on the 120-acre parcel is limited to 30 acres leaving the remainder as open space to be utilized as passive recreation in its natural condition. The initial submittal to NJDEP relied heavily on three stormwater basins in the southern area of the property where deeper soil and seasonal high ground water prevailed. Reviews of this submission and subsequent modifications to it found that the NJDEP preferred a design that managed stormwater more broadly over the entire site. Several video conferences were held with NJDEP to review in more detail the existing site soil conditions, the overall soil testing that had been performed to date and to develop a conceptual plan for the re-design of the stormwater management system with stormwater managed neared to it source. The concept plan required new soil testing within the approved soil testing window to establish the seasonal high-water table at each proposed stormwater system. The testing resulted in areas with high water tables, shallow bedrock and poor soil permeability in many of the tested areas. As a result, the site grading design was raised to achieve a greater distance to groundwater and bedrock and soil replacement was used to address permeability issues. A video conference was held with NJDEP to review the new concept and the consensus was to proceed to full design of the new concept. Previous soil testing results reviewed by the NJDEP have resulted in the designation of some areas of the project as type D soils. Thiessens Polygon Method has been utilized to determine the limits of the D soils. The plan showing this analysis is included in the Appendix. The project design includes a stormwater management design in accordance with the concept plan review with NJDEP. It meets state stormwater standards for water quality, groundwater recharge and discharge rate. The drainage design has a combination of small-scale infiltration basins, porous pavement systems and a large scale infiltration basin. The systems have been located throughout the disturbed area

ate. The drainage design has a combination of small-scale infiltration basins, porous pavement systems and a large scale infiltration basin. The systems have been located throughout the disturbed area to manage the stormwater near its source. The calculations utilize Hydrocad, version 9.10, NJDEP approved intensity curves, and the SCS TR20 methodology to calculate the pre-and post-development runoff. 2