250701_42 ERW_Stormwater Report

1.4 Conveyance System Pipe sizing calculations are included in the appendix of this report. Pipe sizing calculations were be performed using the Rational Method and 25-year design storm for capacity verification. 1.5 Downstream Stability A scour hole is proposed at the outflow of the proposed basin to provide conduit outlet protection and downstream stability. Scour hole sizing calculations are included in the appendix of this report. Stormwater Quality As per NJDEP Regulations, stormwater management measures shall only be required for water quality control if an additional ¼ acre of regulated motor vehicle surface is being proposed on a development site. For this project, the existing motor vehicle surface area totals approximately 0.19 acres and the proposed motor vehicle surface area totals approximately 0.40 acres, which results in an increase of 0.21 acres. Therefore, as the proposed improvements result in less than ¼ acre of new regulated motor vehicle surfaces, water quality treatment is not required. Groundwater Recharge (N.J.A.C. 7:8-5.4) To meet Township and NJDEP requirements for groundwater recharge, the proposed development is designed to maintain 100 percent of the average annual pre-construction groundwater recharge volume for the site. As the entire subject property falls within one (1) HUC-14 sub-watershed, compliance with the groundwater recharge standard is met by analyzing the site as a whole. The site is within the Passaic River Lower (Nwk Bay to Saddle) HUC-14 drainage area. The New Jersey Groundwater Recharge Spreadsheet, Version 2.0, November 2003 is utilized to calculate the post-development annual recharge deficit for the project site and annual recharge volume for each proposed BMP. The following table provides a summary of the post-development deficit and proposed recharge volume. Full calculation spreadsheets and a summary of the proposed recharge volume for each BMP are provided in the Appendix. Groundwater Recharge Summary HUC-14 Drainage Area Pre-Development Total Annual Recharge (cubic feet) Proposed Annual Recharge Volume (cubic feet) Percentage of Average Annual Pre-Construction Groundwater Recharge Volume Passaic River Lower (Nwk Bay to Saddle) 150,467 155,572 103.39% As shown in the above table, the proposed development is designed to maintain 100 percent of the average annual pre-construction groundwater

River Lower (Nwk Bay to Saddle) 150,467 155,572 103.39% As shown in the above table, the proposed development is designed to maintain 100 percent of the average annual pre-construction groundwater recharge volume for the site. Stormwater Management Report | October 18, 2024 – Revised July 1, 2025 Page 4