2025 08 15 WEH SWM CME Memo

Chairman and Members of the West Orange Township Planning Board August 15, 2025 Re: West Essex Highlands, LLC (PB 24-01) Our File No. 115.WRP0179.V01 Response To Objector’s Stormwater Management System Review Page 7 the Department as necessary to provide designs specifications on additional best management practices and new information on already included practices reflecting the best available current information regarding the particular practice and the Department’s determination as to the ability of that best management practice to contribute to compliance with the standards contained in this chapter (N.J.A.C. 7:8). Alternative stormwater management measures, removal rates, or calculation methods may be utilized, subject to any limitations specified in this chapter, provided the design engineer demonstrates to the review agency, in accordance with N.J.A.C. 7:8-5.2(g), that the proposed measure and its design will contribute to achievement of the design and performance standards established by this chapter.” Chapter 12 of the NJ BMP Manual outlines the location and number of required soil explorations. Our office defers to NJDEP review regarding the number of required soil explorations for the proposed development. With that said, it is our understanding that the Applicant’s Engineer worked with the NJDEP to determine the number of required soil explorations for the development prior to completion. Finally, as indicated above, the Applicant received a NJDEP Permit which granted a Flood Hazard Area Individual Permit, Freshwater Wetlands General Permit 10B, Freshwater Wetlands General Permit 11, Freshwater Wetlands General Permit 17, and a Water Quality Certificate, dated November 15, 2024. 2.4 Groundwater Mounding Calculations: “…the groundwater mounding analysis for the 100-year storm has errors in it and upon further investigation, the groundwater mounding will reach into the storage volume for the following BMPs: • • • BMP 3 BMP 4 BMP 10” Chapter 13 of the NJ BMP Manual outlines the method(s) to complete groundwater mounding calculations for an infiltration BMP. Our office agrees that there appears to be some discrepancies with the groundwater mounding calculation methodology completed by the Applicant’s Engineer as compared to the methodology outlined in the BMP Manual. With that said, as indicated above, the BMP Manual provides guidance to address

calculation methodology completed by the Applicant’s Engineer as compared to the methodology outlined in the BMP Manual. With that said, as indicated above, the BMP Manual provides guidance to address the standards in the Stormwater Management Rules, N.J.A.C. 7:8 and alternative stormwater management calculation methods may be utilized provided the design engineer demonstrates to the review agency that the proposed measure and its design will S:\West Orange\Planning Board\VWRP0179.01 - West Essex Highlands, Inc\2025-08-15 - WEH - SWM Memo.docx

Chairman and Members of the West Orange Township Planning Board August 15, 2025 Re: West Essex Highlands, LLC (PB 24-01) Our File No. 115.WRP0179.V01 Response To Objector’s Stormwater Management System Review Page 8 contribute to achievement of the design and performance standards established by N.J.A.C. 7:8. Further, Special Condition #2 of the NJDEP Permit referenced above indicates that the Department has determined that this project meets the requirements of the Stormwater Management Rules at N.J.A.C. 7:8. 2.5 Impacts to Wetlands: The proposed stormwater system intends to route the stormwater runoff through a pipe network to down-gradient basins where all of the surface runoff will discharge much further downstream. The wetlands uphill of the discharge locations will therefore collect less stormwater runoff due to their reduced contributory drainage areas. Impacts to Freshwater Wetlands are under the jurisdiction of the New Jersey Department of Environmental Protection (NJDEP). As indicated above, the Applicant has received the necessary Freshwater Wetland permitting from NJDEP. 2.6 Peak Flow Calculations: “Based on our review of the existing conditions mapping and modeling, we believe the time of concentration computations were done incorrectly for this project.” “…It appears that the designer used an old method to determine the TC for drainage areas POA 1 and 2.” “…Princeton Hydro would note that the NJDEP ruling on this project means that the latest (2023) Stormwater Rule update does not apply. However, the TC calculation methodology referenced above was updated with the previous rule change in 2021.” Chapter 5 of the NJ BMP Manual outlines the method to complete time of concentration calculations. Our office agrees that there appears to be some discrepancies with the time of concentration calculation methodology completed by the Applicant’s Engineer as compared to the methodology outlined in the BMP Manual. With that said, as indicated above, the BMP Manual provides guidance to address the standards in the Stormwater Management Rules, N.J.A.C. 7:8 and alternative stormwater management calculation methods may be utilized provided the design engineer demonstrates to the review agency that the proposed measure and its design will contribute to achievement of the design and performance standards established by N.J.A.C. 7:8. S:\West Orange\Planning

demonstrates to the review agency that the proposed measure and its design will contribute to achievement of the design and performance standards established by N.J.A.C. 7:8. S:\West Orange\Planning Board\VWRP0179.01 - West Essex Highlands, Inc\2025-08-15 - WEH - SWM Memo.docx

Chairman and Members of the West Orange Township Planning Board August 15, 2025 Re: West Essex Highlands, LLC (PB 24-01) Our File No. 115.WRP0179.V01 Response To Objector’s Stormwater Management System Review Page 9 Further, Special Condition #2 of the NJDEP Permit referenced above indicates that the Department has determined that this project meets the requirements of the Stormwater Management Rules at N.J.A.C. 7:8. 2.7 Separation of Sanitary Infrastructure and BMP “The design has a sanitary pipe traveling through porous pavement system (Figure 11). While Princeton Hydro could not find a specific rule against a sanitary line traveling through a subsurface basin, there are rules dictating adequate separation between stormwater piping and sanitary piping.” Sanitary sewer piping will not be installed within any stormwater management system. The Applicant’s Engineer will be required to revise the plans to indicate the same prior to any construction. 3.0 Summary: Informational/Opinion. No comment needed. S:\West Orange\Planning Board\VWRP0179.01 - West Essex Highlands, Inc\2025-08-15 - WEH - SWM Memo.docx