2151002Princeton Hydro West Essex Stormwater Comments to Planning Board 20250310

Stormwater Management Review for Municipal Planning Board Approval West Highlands, Inc. Block No. 179, Lot No.32, West Orange Township, Essex County, New Jersey March 2025 Princeton Hydro, LLC: 2151.002 4 The NJDEP BMP Manual requires that BMPs maintain a minimum vertical difference of 2 feet from the bottom of the BMP to the SHWT elevation for BMPs without underdrains. The BMPs in this project do not have underdrains. BMPs 2, 6 and 7 maintain that minimum separation. If the SHWT elevations are higher than what was recorded in this plan, then there is a risk these designs are not compliant with the NJDEP BMP Manual. The manual requires these depths as a precaution to prevent groundwater from mounding into the storage area of the basins during rain storms. If the groundwater mounding encroaches on the storage area, it will increase the stormwater runoff from the BMP and decrease the amount of groundwater recharge the BMP provides. N.J.A.C. 7:8 5.4 (§25-29.4 P) sets the groundwater recharge requirements and 7:8 5.6 (§25-29.4 R) sets the minimum reductions in the peak flow rates for runoff exiting a site. If the SHWT is higher in BMPs 2, 6 or 7 that would impact the site’s compliance with those two standards. Figure 2: Example of Soil Profiles that use the Munsell Method to document SHWT and the Soil Profiles for this project