V4 11 Stormwater Report Rev 3 1 26 2023

DRAIN TIME As shown by the Hydraflow Hydrographs attached to this report, the detention time of the system is below 72 hours and is broken down as follows: Detention Basin #1A —27 hrs. Detention Basin #1B — 27 hrs. Detention Basin #2 —27 hrs. Detention Basin #3 — 27 hrs. WATER QUALITY Water quality is not required for the proposed development as there is a reduction in the total motor vehicle surface onsite from existing conditions. GROUNDWATER RECHARGE The subject property is located within the metropolitan planning area and has been previously developed. As such, the proposed development is not required to meet the groundwater recharge standards. STORM SEWER COMPUTATIONS A storm sewer system has been designed to collect the runoff associated with the proposed parking lot and roof. The system's primary purpose is to properly drain the proposed site and deliver the runoff to the proposed stormwater management system for water quantity. See attached Storm Sewer Computations in the appendix of this report. The pipes flowing into the systems were designed for a 25-year storm event. The rational method was used to calculate the runoff rates, and the Manning's equation was used to determine the capacity of each system. The majority of the site is mapped with soils considered Hydrologic Group A & C. For this analysis it was assumed the entire site was Hydrologic Group C. Runoff coefficients (C values) for hydrologic soil group C were 0.51 and 0.99 for woods - good condition and pavement respectively. In addition, all areas were assumed to have a time of concentration of 6 minutes for a conservative model. As shown, all pipes were designed with adequate capacity to handle the proposed flows. CONCLUSION To summarize, a stormwater management strategy has been incorporated to satisfy both the structural and non-structural water quality and water quantity requirements. This is in keeping with the design and performance standards set forth in the West Orange Stormwater Management Ordinance and New Jersey DEP Regulations. & “ :