O30 Princeton Hydro Report Dated 9 3 25

West Essex Highlands Review West Orange, NJ Permit No. 722-04-0001.1 LUP230001 April 2025 measurement of the hydraulic conductivity of the soil at the elevation where infiltration is proposed. It is a crucial part of the design process. Typically, each BMP is required to have two test pits but more can be required based on the size of the proposed BMP. The SHWT can vary based on its location and it is important to take measurements at different locations to better understand that variation. If an insufficient number of soil tests are taken, the engineer runs the risk of not understanding the elevation of the SHWT across the BMP and could design a BMP that does not have the required separation from the SHWT. A good example of this is PP4 and PPé. If you choose to review only portions of the test pit data the BMP seems properly designed but when you review the data in its entirety, including the 2021 data, you can see how the SHWT varies by location and the design needs to be modified to accommodate the variation. Princeton Hydro compared the infiltration area of each BMP on the plan to what was entered into the stormwater calculations model. Table 1 is a comparison of the infiltration area found in the model calculations and the infiltration area shown on the plan. The infiltration area is the bottom of the basin, not the side slopes. Table 1 Comparison of Infiltration Areas shown in the Plan and Stormwater Calculations Model. BMP ID- BMP Type Model Infiltration Area Plan Infiltration Area Difference, Model — Plan (SF) (SF) (SF) 1 - Large Scale Infiltration 42,000 45,490 -3,490 Basin 2 - Small Scale Infiltration 26,023 25,830 193 Basin 3— Porous Pavement 5,227 5,558 -331 4— Porous Pavement 12,197 12,369 -172 5— Porous Pavement 14,810 14,611 199} 6— Porous Pavement 35,719 37,473 -1,754 7 - Small Scale Infiltration 14,375 13,405 970 Basin 8 — Porous Pavement 10,019 15,900 -5,881 9 — Porous Pavement 6,534 17,981 -11,447 10 — Small Scale Infiltration 9,583 9,467 116 Basin 11 = Porous Pavement 13,504 22,826 9,322 12 — Small Scale Infiltration 900 1,004 -104 Basin There are differences between what was modeled and what was shown on the plan. Many of these differences are not consequential but the differences at BMP 1, 8, 9 and 11 are especially significant and the model should match what is shown on the plan. Princeton Hydro, LLC Page | 11