241220_42 ERW_Stormwater Report FULL

Stormwater Management Report | October 18, 2024 – Revised December 20, 2024 Page 4 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) 150,467 156,306 103.88% 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. Conclusion As discussed above, water quantity mitigation is provided for all watersheds for all storm events studied in accordance with NJDEP and Township of West Orange regulations. A subsurface infiltration basin was utilized to achieve the required reductions for all Design Points. Furthermore, water quality treatment is not required for

and Township of West Orange regulations. A subsurface infiltration basin was utilized to achieve the required reductions for all Design Points. Furthermore, water quality treatment is not required for this project site. As such, there should be no adverse impacts due to stormwater, on-site or off-site, as a result of the proposed development. Included in the appendix of this report is the HydroCAD output for back-up on both the existing and proposed conditions. Additionally, the aforementioned Existing and Proposed Drainage Area Maps, an Inlet Area Map and a Pipe Capacity Report are provided in the appendix of this report.