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 4 2.1 Soil Testing Requirements: “…It appears that the SHWT was only established using the elevation of the water found in the test pit or boring and no effort was made to document mottling. As noted in the NJDEP BMP Manual, there are instances where mottling can be absent from a soil profile, but it is highly unusual that mottling was not found in any of the soil test pits or borings provided by the applicant. Mottling is a natural and common process, thus it is fair to assume mottling should have been observed in some of the soil profiles. The concern is that the groundwater level found in a test pit can fluctuate on a daily basis based on the recent weather. Using the mottling to determine the SHWT is recommended because it estimates the highest (most conservative) elevation that does not vary with time. If one only uses the observed groundwater elevation, it is safe to assume that the SHWT elevation is probably underestimated.” As indicated above, the New Jersey Stormwater Best Management Practices Manual (NJ BMP Manual) notes that there are instances where mottling can be absent from a soil profile, therefore, observing mottling in a soil profile is not a requirement. Further, Chapter 12 of the NJ BMP Manual specifically outlines the methods for determining the seasonal high-water table (SHWT) when mottling is not observed in a soil profile. Therefore, based on our review, the Applicant’s Engineer’s method of determining the SHWT is consistent with the NJ BMP Manual. 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 BMPs met the minimum two vertical feet of separate from the bottom of the basin to the SHWT. Princeton Hydro found that the following BMPs did not meet that minimum standard: • • • BMP 6 (Porous Pavement) BMP 4 (Porous Pavement) BMP 9 (Aboveground basin)” The submitted soil testing includes Test Pit Logs that indicate approximate ground surface elevations which were determined by the Applicant’s geotechnical engineer interpolating between existing ground contours depicted on the site

des Test Pit Logs that indicate approximate ground surface elevations which were determined by the Applicant’s geotechnical engineer interpolating between existing ground contours depicted on the site plan that was provided to the Applicant’s geotechnical engineer prior to completing the soil testing. Therefore, the Test Pit Logs should be reviewed in conjunction with the site plan drawings and associated existing ground contours shown at the location of each soil profile/test pit to verify the existing ground surface elevations and corresponding seasonal high-water table (SHWT) elevation. Based on our review of the depth to SHWT shown on the Test Pit Logs and the existing ground surface elevations shown on the site plan drawings, the proposed BMPs S:\West Orange\Planning Board\VWRP0179.01 - West Essex Highlands, Inc\2025-08-15 - WEH - SWM Memo.docx