Stormwater Report 1

Table 6 – Overall Peak Runoff Rates – Future Projected Rainfall 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 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. 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 7

proposed development calls for the reconstruction of the existing parking lot, increasing the amount of landscape area by approximately 0.09 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. 8

EXISTING CONDITIONS CURRENT ADJUSTED HYDROGRAPHS

Hydraflow Table of Contents Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2023 Existing - Current Adjusted.gpw Monday, 12 / 30 / 2024 Watershed Model Schematic...................................................................................... 1 Hydrograph Return Period Recap............................................................................. 2 2 - Year Summary Report......................................................................................................................... 3 Hydrograph Reports................................................................................................................... 4 Hydrograph No. 1, SCS Runoff, DA-EX Pervious.................................................................... 4 Precipitation Report............................................................................................................. 5 Hydrograph No. 2, SCS Runoff, DA-EX Impervious................................................................ 6 Precipitation Report............................................................................................................. 7 Hydrograph No. 3, Combine, <no description>........................................................................ 8 10 - Year Summary Report......................................................................................................................... 9 Hydrograph Reports................................................................................................................. 10 Hydrograph No. 1, SCS Runoff, DA-EX Pervious.................................................................. 10 Precipitation Report........................................................................................................... 11 Hydrograph No. 2, SCS Runoff, DA-EX Impervious.............................................................. 12 Precipitation Report........................................................................................................... 13 Hydrograph No. 3, Combine, <no description>...................................................................... 14 100 - Year Summary Report....................................................................................................................... 15 Hydrograph

..................................... 14 100 - Year Summary Report....................................................................................................................... 15 Hydrograph Reports................................................................................................................. 16 Hydrograph No. 1, SCS Runoff, DA-EX Pervious.................................................................. 16 Precipitation Report........................................................................................................... 17 Hydrograph No. 2, SCS Runoff, DA-EX Impervious.............................................................. 18 Precipitation Report........................................................................................................... 19 Hydrograph No. 3, Combine, <no description>...................................................................... 20 IDF Report.................................................................................................................. 21

1 Watershed Model Schematic Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2023 1 2 3 Legend Hyd. Origin Description 1 2 3 DA-EX Pervious DA-EX Impervious <no description> SCS Runoff SCS Runoff Combine Project: Existing - Current Adjusted.gpw Monday, 12 / 30 / 2024

2 Hydrograph Return Period Recap Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2023 Hyd. Hydrograph No. type (origin) Inflow hyd(s) Peak Outflow (cfs) 1-yr 2-yr 3-yr 5-yr 10-yr Hydrograph Description 25-yr 50-yr 100-yr 1 SCS Runoff ------ ------- 1.749 ------- ------- 3.502 ------- ------- 7.132 DA-EX Pervious 2 SCS Runoff ------ ------- 7.590 ------- ------- 11.85 ------- ------- 20.28 DA-EX Impervious 3 Combine 1, 2 ------- 9.339 ------- ------- 15.35 ------- ------- 27.41 <no description> Proj. file: Existing - Current Adjusted.gpw Monday, 12 / 30 / 2024

3 Hydrograph Summary Report Hyd. Hydrograph No. type (origin) Peak flow (cfs) Time Time to interval Peak (min) (min) Hyd. volume (cuft) Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2023 Inflow hyd(s) Maximum elevation (ft) Total strge used (cuft) Hydrograph Description 1 SCS Runoff 1.749 6 732 7,463 ------ ------ ------ DA-EX Pervious 2 SCS Runoff 7.590 6 732 36,568 ------ ------ ------ DA-EX Impervious 3 Combine 9.339 6 732 44,031 1, 2 ------ ------ <no description> Existing - Current Adjusted.gpw Return Period: 2 Year Monday, 12 / 30 / 2024

4 Hydrograph Report Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2023 Monday, 12 / 30 / 2024 Hyd. No. 1 DA-EX Pervious Hydrograph type Storm frequency Time interval Drainage area Basin Slope Tc method Total precip. Storm duration = SCS Runoff Peak discharge = 1.749 cfs = 2 yrs Time to peak = 12.20 hrs = 6 min Hyd. volume = 7,463 cuft = 1.360 ac Curve number = 80 = 0.0 % Hydraulic length = 0 ft = User Time of conc. (Tc) = 13.60 min = 3.47 in Distribution = Custom = S:\Petry Engineering Cad Projects\2024\24-170 Shape factor - Baginski = 484 - Manor - West Orange DA-EX Pervious Q (cfs) Q (cfs) Hyd. No. 1 -- 2 Year 2.00 2.00 1.00 1.00 0.00 0.00 0 2 4 Hyd No. 1 6 8 10 12 14 16 18 20 22 24 26 Time (hrs)

5 Precipitation Report Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2023 Monday, 12 / 30 / 2024 Hyd. No. 1 DA-EX Pervious Storm Frequency Total precip. Storm duration = 2 yrs Time interval = 6 min = 3.4700 in Distribution = Custom = S:\Petry Engineering Cad Projects\2024\24-170 - Baginski - Manor - West Orang Incremental Rainfall Precipitation Precip (in) Precip (in) Hyd. No. 1 : DA-EX Pervious - 2 Year 0.50 0.50 0.45 0.45 0.40 0.40 0.35 0.35 0.30 0.30 0.25 0.25 0.20 0.20 0.15 0.15 0.10 0.10 0.05 0.05 0.00 0.00 0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0 22.0 24.0 Time (hrs) Custom Design Storm -- S:\Petry Engineering Cad Projects\2024\24-170 - Baginski - Manor - West Orange\Civil\Curre