O30 Princeton Hydro Report Dated 9 3 25

West Essex Highlands Review 4 West Orange, NJ Permit No. 722-04-0001.1 LUP230001 ‘April 2025 that the groundwater level found in a test pit can fluctuate based on recent precipitation. Using soil mottling to determine the SHWT is recommended because it estimates the highest (most conservative) elevation that does not vary with time. It is the position of Princeton Hydro that reliance on observed groundwater elevation has underestimated the elevation of the SHWT. The New Jersey BMP Manual requires that BMPs maintain a minimum vertical difference of two feet from the bottom of the BMP to the SHWT elevation for BMPs without underdrains. The BMPs in this project do not have underdrains. Although, BMPs 2, 6 and 7 appear to maintain that minimum separation, the method used to establish the SHWT is not compliant with the NJDEP BMP manual as discussed above. If the SHWT elevations are higher than what was recorded in this plan, then there is a risk these designs will not function as envisioned and will not fully comply with the New Jersey BMP Manual. 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 can provide. 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 both of those standards. It is also important to point out that the depth to the SHWT more offen than not follows a topographic gradient in which the SHWT is deeper in higher landscape positions and becomes increasingly shallower while moving downslope. For this Site this gradient typically ends in the wetlands present at the base of a slope and adjacent to a headwater stream. Based on the landscape position of the wetlands on the Site, in general at the base of slopes, the primary source of hydrology for the wetlands is related to groundwater and groundwater discharge. For an area to be defined as a wetland in New Jersey the SHWT in the wetland must be at a depth of twelve inches or less. A general understanding of this flow path from higher landscape positions to the wetlands is not just important as it relates to wetland impact but also to understanding groundwater on the Site and

s. A general understanding of this flow path from higher landscape positions to the wetlands is not just important as it relates to wetland impact but also to understanding groundwater on the Site and how well the proposed stormwater BMPs will function. There are at least two examples, Basin 2 and 7, where the proposed basin bottom will be excavated to an elevation below that of the closest wetland and stream. In these cases, the proposed BMP would result in the disruption of the current hydrologic gradient toward the wetland to one that redirects the hydrologic gradient toward the BMPs from the stream or wetland. This will not only impact the wetland but will add an additional source of water to the BMPs that has not been identified by the applicant. This will be discussed again in Section 2.5. 2.2 BMP DESIGN STANDARDS AND SHWT Princeton Hydro reviewed the SHWT elevations documented in the subsurface investigations against the proposed BMP designs to confirm that each of the proposed BMP's met the minimum two vertical feet of separate from the bottom of the basin to the SHWT. Despite the issue identified in the previous section with respect to the SHWT being underestimated by only observing seepage, Princeton Hydro found that the following BMP’s did not meet that minimum standard: © BMP 6 (Porous Pavement) Princeton Hydro, LLC Page | 6