2025 12 19 Stormwater Report Rev 1

storm event. (See attached Hydraflow Output for Existing Conditions Hydrographs, CN Values, and Time of Concentration Calculations.) Table 3 – Existing Peak Runoff Rates DA-1 Current Adjusted Rainfall Future Projected Rainfall Existing Site Existing Site Existing Site Existing Site Storm Event Peak Runoff Runoff Volume Peak Runoff Runoff Volume 2 Year 9.339 cfs 44,031 cf 11.28 cfs 53,349 cf 10 Year 15.35 cfs 73,038 cf 18.49 cfs 88,329 cf 100 Year 27.41 cfs 132,192 cf 34.83 cfs 169,002 cf DA-2 Current Adjusted Rainfall Future Projected Rainfall Existing Site Existing Site Existing Site Existing Site Storm Event Peak Runoff Runoff Volume Peak Runoff Runoff Volume 2 Year 0.271 cfs 1,209 cf 0.345 cfs 1,533 cf 10 Year 0.503 cfs 2,237 cf 0.627 cfs 2,796 cf 100 Year 0.978 cfs 4,428 cf 1.271 cfs 5,815 cf PROPOSED CONDITIONS The existing site has been modeled as two drainage areas totaling 4.86 acres. (See Fig.1 Existing Drainage Area Map.) The point of analysis for Drainage Area 1 is the Type Double “B” Inlet at the rear of the site, which connects to the municipal storm sewer system within Deerfield Drive. The point of analysis for Drainage Area 2 is the rear property line that bypasses. The drainage areas include all areas of disturbance, as well as any other areas that drain to the point of analyses. DRAINAGE AREA 1 (DA-1) Drainage Area 1 consists of 4.68 acres of both pervious and impervious surfaces. The impervious area, 3.32 acres, consists of the existing and proposed parking lot and associated improvements. The pervious area, 0.27 acres, is comprised of landscaped and lawn areas that are in good condition. Two times of concentration have been calculated for this drainage area, one based on the current adjusted rainfall total and one for the future projected rainfall total. The times of concentration are 12.6 and 11.7 minutes, respectively. DRAINAGE

ea, one based on the current adjusted rainfall total and one for the future projected rainfall total. The times of concentration are 12.6 and 11.7 minutes, respectively. DRAINAGE AREA 2 (DA-2) Drainage Area 2 consists of 0.18 acres of both pervious and impervious surfaces. The impervious area, 0.04 acres, consists of walkways. The pervious area, 0.14 acres, is comprised of landscaped and lawn areas that are in good condition. Two times of 6

concentration have been calculated for this drainage area, one based on the current adjusted rainfall total and one for the future projected rainfall total. The times of concentration are 11.8 and 10.9 minutes, respectively. CURVE NUMBERS The CN values used have been taken from the TR-55 Manual “Urban Hydrology for Small Watersheds,” Table 2-2a and Table 2-2c, based on land cover and hydrologic soil groups. Table 4 – Curve Number (Proposed Conditions) Description Hydrologic Group Curve Number Landscaped Islands D 80 (Open Space-Good Conditions) Impervious D 98 PEAK FLOWS Using the information described above, the peak flows during the 2-, 10-, and 100-year storm events where calculated. Table 4 below summarizes the peak flows during each storm event. (See attached Hydraflow Output for Proposed Conditions Hydrographs, CN Values, and Time of Concentration Calculations.) As shown in this table, the proposed runoff rates and volumes are reduced from the existing to proposed conditions. Since this regulation requires that we show reductions at each time interval, we have included Tables 7-10 in the appendix of this report which shows the minute-by-minute flows leaving the site for each storm event and compares existing and proposed conditions. Table 5 – Overall Peak Runoff Rates – Current Adjusted Rainfall DA-1 Existing Site Existing Site Proposed Site Proposed Site Storm Event Peak Runoff Runoff Volume Peak Runoff Runoff Volume 2 Year 9.339 cfs 44,031 cf 9.179 cfs 43,147 cf 10 Year 15.35 cfs 73,038 cf 15.19 cfs 71,995 cf 100 Year 27.41 cfs 132,192 cf 27.27 cfs 130,994 cf DA-2 Existing Site Existing Site Proposed Site Proposed Site Storm Event Peak Runoff Runoff Volume Peak Runoff Runoff Volume 2 Year 0.271 cfs 1,209 cf 0.271 cfs 1,209 cf 10 Year 0.503 cfs 2,237 cf 0.503 cfs 2,237 cf

lume Peak Runoff Runoff Volume 2 Year 0.271 cfs 1,209 cf 0.271 cfs 1,209 cf 10 Year 0.503 cfs 2,237 cf 0.503 cfs 2,237 cf 100 Year 0.978 cfs 4,428 cf 0.978 cfs 4,428 cf 7

Table 6 – Overall Peak Runoff Rates – Future Projected Rainfall DA-1 Existing Site Existing Site Proposed Site Proposed Site Storm Event Peak Runoff Runoff Volume Peak Runoff Runoff Volume 2 Year 11.28 cfs 53,349 cf 11.12 cfs 52,402 cf 10 Year 18.49 cfs 88,329 cf 18.33 cfs 87,232 cf 100 Year 34.83 cfs 169,002 cf 34.70 cfs 167,752 cf DA-2 Existing Site Existing Site Proposed Site Proposed Site Storm Event Peak Runoff Runoff Volume Peak Runoff Runoff Volume 2 Year 0.345 cfs 1,533 cf 0.345 cfs 1,533 cf 10 Year 0.627 cfs 2,796 cf 0.627 cfs 2,796 cf 100 Year 1.271 cfs 5,815 cf 1.271 cfs 5,815 cf WATER QUALITY Since the proposed development does not result in a net increase of ¼ of an acre or more of impervious surface, the water quality aspect of the Stormwater Management Rules is not required. GROUNDWATER RECHARGE The site is located within the Metropolitan Planning Area. No groundwater recharge is required for the site. A map from Geo Web showing the site within this planning area can be found in the appendix of this report. STORM SEWER COMPUTATIONS A storm sewer system has been designed to collect the runoff associated with the proposed parking areas, drive aisles, walkways, and lawn areas. The pipes are designed to carry the flows for the 25-year storm. The rational method was used to calculate runoff rates. Manning’s equation was used to determine the capacity of each system. Storm Sewer Computations are included in the appendix of this report. Also, Fig.-3 shows the drainage areas to each inlet. 8

The entire site is mapped with soils considered Hydrologic Group D (See attached Appendix for Soil Map). For this analysis, all the drainage areas were assumed to have 0.99 as a Runoff Coefficient (C value), which is the most conservative value. CONCLUSION The proposed improvements meet all of the stormwater management regulations for both the Township of West Orange as well as the NJDEP. The stormwater quantity is satisfied through the use of non-structural strategies, specifically the reduction in impervious surfaces. The proposed development calls for the reconstruction of the existing parking lot, increasing the amount of landscape area by approximately 0.16 acres. The decrease in impervious also means that water quality measures are not required. The site is located in the Metropolitan Planning Area, which means that stormwater recharge is not required. 9

EXISTING CONDITIONS CURRENT ADJUSTED HYDROGRAPHS

Hydraflow Table of Contents Existing - Current Adjusted.gpw Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2025 Tuesday, 12 / 23 / 2025 Watershed Model Schematic...................................................................................... 1 Hydrograph Return Period Recap............................................................................. 2 2 - Year Summary Report......................................................................................................................... 3 Hydrograph Reports................................................................................................................... 4 Hydrograph No. 1, SCS Runoff, DA-1 Pervious....................................................................... 4 Precipitation Report............................................................................................................. 5 Hydrograph No. 2, SCS Runoff, DA-1 Impervious................................................................... 6 Precipitation Report............................................................................................................. 7 Hydrograph No. 3, SCS Runoff, DA-2 Pervious....................................................................... 8 Precipitation Report............................................................................................................. 9 Hydrograph No. 4, SCS Runoff, DA-2 Impervious................................................................. 10 Precipitation Report........................................................................................................... 11 Hydrograph No. 5, Combine, DA-1 Combined....................................................................... 12 Hydrograph No. 6, Combine, DA-2 Combined....................................................................... 13 10 - Year Summary Report....................................................................................................................... 14 Hydrograph

.................... 13 10 - Year Summary Report....................................................................................................................... 14 Hydrograph Reports................................................................................................................. 15 Hydrograph No. 1, SCS Runoff, DA-1 Pervious..................................................................... 15 Precipitation Report........................................................................................................... 16 Hydrograph No. 2, SCS Runoff, DA-1 Impervious................................................................. 17 Precipitation Report........................................................................................................... 18 Hydrograph No. 3, SCS Runoff, DA-2 Pervious..................................................................... 19 Precipitation Report........................................................................................................... 20 Hydrograph No. 4, SCS Runoff, DA-2 Impervious................................................................. 21 Precipitation Report........................................................................................................... 22 Hydrograph No. 5, Combine, DA-1 Combined....................................................................... 23 Hydrograph No. 6, Combine, DA-2 Combined....................................................................... 24 100 - Year Summary Report....................................................................................................................... 25 Hydrograph Reports................................................................................................................. 26 Hydrograph No. 1, SCS Runoff, DA-1 Pervious..................................................................... 26 Precipitation Report........................................................................................................... 27 Hydrograph No. 2, SCS Runoff, DA-1 Impervious................................................................. 28 Precipitation

............................................... 27 Hydrograph No. 2, SCS Runoff, DA-1 Impervious................................................................. 28 Precipitation Report........................................................................................................... 29 Hydrograph No. 3, SCS Runoff, DA-2 Pervious..................................................................... 30 Precipitation Report........................................................................................................... 31 Hydrograph No. 4, SCS Runoff, DA-2 Impervious................................................................. 32 Precipitation Report........................................................................................................... 33 Hydrograph No. 5, Combine, DA-1 Combined....................................................................... 34 Hydrograph No. 6, Combine, DA-2 Combined....................................................................... 35 IDF Report.................................................................................................................. 36