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 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 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) BMP 6 shows a SHWT of 598 ft using the 2024 soil testing data but 2021 shows a different story. TP 4 shows seepage at 608 ft, which is 10 feet higher than what the plans show. Based on this finding, the porous pavement design not compliant. The SHWT intersects the storage volume of the basin as shown in Figure 3. Figure 3: Cross Section of PP6, Proximity of TP-4 to PP6 and TP-4 Soil Profile Likewise, BMP 4 records the SHWT at 567 ft (Figure 4) on the plans but that is only using data from the soil tests taken in 2024 (TP 28). In 2021, soil tests were also taken and TP 10 (Figure 4) is very close to BMP 4. TP 10 shows a SHWT of 573 ft, 6 feet higher than TP 28 which would have the SHWT intersecting the storage bed of the BMP. Please note that there is an error on the TP-10 soil profile. On the right-hand side of the document, there is an entry for the water level found; it is left blank. Elsewhere on the document it states that seepage was found at 3