JMA02P003 262 270 Main Street Development Stormwater Management Report

Hudson Engineering, LLC. Every Project Needs a Plan 25 W 8th Street, Ste B Bayonne, NJ, 07002 (201) 589-0906 info@hudsoneng.com Project: 262-270 Main St Development Project #: JMA02P003 Subject: Engineering Stormwater Narrative Date: May 26, 2026 Prepared by: Jordan Cecinini, PE License #: GE54968 Contents 1 Introduction..................................................................................................................................... 1 2 Methodology ................................................................................................................................... 1 3 Pre-Design Investigative Analysis .................................................................................................... 1 4 Pre-Developed Condition................................................................................................................. 1 5 Post-Developed Condition ............................................................................................................... 1 6 Groundwater Recharge .................................................................................................................... 2 7 Groundwater Mounding................................................................................................................... 3 8 Conclusion ...................................................................................................................................... 3 Appendix A: Precipitation Frequency Estimates ....................................................................................... 4 Appendix B: Soils Maps & Soil Data ....................................................................................................... 5 Appendix C: Pre-Development Analysis .................................................................................................. 6 Appendix D: Post-Development Analysis ................................................................................................ 7 Appendix E:

............................................... 6 Appendix D: Post-Development Analysis ................................................................................................ 7 Appendix E: Water Quality Analysis ....................................................................................................... 8 Appendix F: Groundwater Recharge ...................................................................................................... 10 1

Engineering Stormwater Narrative JMA02P003- May 26, 2026 262-270 Main St Development Appendix G: Groundwater Mounding .................................................................................................... 11 Appendix H: Low Impact Development Checklist.................................................................................. 12 2

Engineering Stormwater Narrative JMA02P003- May 26, 2026 262-270 Main St Development 1 Introduction Hudson Engineering, LLC (HE) was engaged by Jorge Mastropietro Architects to perform a Geotechnical Investigation for the new development at 262-270 Main St West Orange, NJ,07052 (Block: 114 Lot: 50 & 55) in Essex County, New Jersey (“Project Site”). The proposed development will consist of a new supermarket and parking lot. This Stormwater Management plan references the Best Management Practices (BMPs) to control stormwater and erosion during and upon the completion of the proposed supermarket at the Project Site. The design is in accordance with the New Jersey Department of Environmental Protection (NJDEP) stormwater regulations as the proposed work does disturb more than one acre of land. 2 Methodology The site was modeled for the Site Specific 24 hour storm event, as provided by the NOAA, using HydroCAD, the Soil Conservation Service (SCS) TR-20’s software to aid in the design of the stormwater system. The rainfall data for the 2-, 10-, & 100-year storm events was used, and the precipitation factors from NJAC 7:8 for both the current and future storms were used for the design storm. The “Complex Number” (CN) value was determined based on the soil type, surface conditions, and land use. The minimum “Time of Concentration” (Tc) was used per the BMP. 3 Pre-Design Investigative Analysis A pre-design investigative analysis was previously performed including deep hole test. Deep test holes were excavated for the existing project site and labeled [T1 & T2], as shown on the plans.  B1 was excavated to a depth of 30-feet and contained silty gravel to a depth of 18-feet and silty sand down to 30-feet to the bottom of the excavation. Ground water was not observed.  B2 was excavated to a depth of 9.5-feet and contained sand with silt to a depth of 9.5-feet down to the bottom of the excavation. Ground water was not observed. See Appendix E for the geotechnical report. 4 Pre-Developed Condition In the pre-developed condition, the project site can be characterized as moderately sloped from west to east. The soil classification, based upon Essex County Soil Mapping, is Urban land, Boonton

tion In the pre-developed condition, the project site can be characterized as moderately sloped from west to east. The soil classification, based upon Essex County Soil Mapping, is Urban land, Boonton substratum – Boonton complex, red sandstone lowland. The site is located on Main Street in between 262 and 270 Main Street. The site is mostly developed impervious. 5 Post-Developed Condition In the post-developed condition, the proposed impervious areas were modeled as two (2) watersheds which flow into two stormwater management systems, “Basin A” and “Porous Pavement B.” The watershed contains approximately 29,311 square feet of impervious coverage consisting of the proposed supermarket and asphalt driveways. Two (2) stormwater systems are proposed on the site. One (1) is an approximate 2,140 square foot underground Cultec system that collects all of the runoff from the roof of the supermarket. The system is designed to contain the full Water Quality Volume for the required storm event from the watershed and percolate the water into the soil, whilst discharging the Water Quantity storms into the storm system on Main Street. Since the roof runoff is not a surface where vehicles will travel, treatment is not required for this runoff. One (1) is an approximate 5,700 square feet porous pavement system that collects the runoff from the parking area. The system is designed to contain the full Water Quality Volume for the required storm event from the watershed and percolate the water into the soil, whilst discharging the Water Quantity storms into the storm system on Main Street. Since the parking area is subject to regular vehicular traffic, a TSS removal rate of 80% is required. A portion of the parking area discharges directly into the porous pavement system, which treats the runoff at a rate of 80%. 1

Engineering Stormwater Narrative JMA02P003- May 26, 2026 262-270 Main St Development The remaining runoff discharges into two (2) trench drain systems that flow into an Aqua-Ponic treatment unit. The Aqua-Ponic unit treats the runoff at a rate of 80% before discharging into the porous pavement system for quantity control. Therefore, the total treatment for the site meets the required 80% and complies with Water Quality requirements. As for Water Quantity requirements, the NJDEP requires a reduction of 50%, 75%, and 80% for the 2-, 10-, and 100-year storm events, respectively, from the existing flow rates to the proposed flow rates. These requirements apply for the quantity storm events with both the current and future reduction factors applied as listed in NJAC 7:8 tables 5-5 and 5-6. These requirements will be met by the underground Cultec system and the porous pavement system which both discharge from their respective outlet control structures into the existing storm system on Main Street. The tables below demonstrate how the project complies with the Quantity reduction requirements. STORMWATER ANALYSIS (CURRENT) STORM TYPE EXISTING PERCENTAGE MAXIMUM PROPOSED RUNOFF RUNOFF RATE OF REDUCTION ALLOWABLE RATE (CFS) (CFS) RUNOFF RATE (CFS) 2-YEAR 2.68 50% 1.34 0.06 10-YEAR 4.20 75% 3.15 0.39 100-YEAR 7.27 80% 5.82 3.15 STORMWATER ANALYSIS (FUTURE) STORM TYPE EXISTING PERCENTAGE MAXIMUM PROPOSED RUNOFF RUNOFF RATE OF REDUCTION ALLOWABLE RATE (CFS) (CFS) RUNOFF RATE

RUNOFF RATE OF REDUCTION ALLOWABLE RATE (CFS) (CFS) RUNOFF RATE (CFS) 2-YEAR 3.17 50% 1.59 0.11 10-YEAR 4.98 75% 3.74 1.34 100-YEAR 9.13 80% 7.30 4.05 6 Groundwater Recharge According to chapter 5.4 of NJAC 7:8, groundwater recharge is required for a major development project. The groundwater recharge was calculated using the GSR-32 spreadsheet taken from the New Jersey Best Management Practices (NJBMP) manual. The post-development annual recharge deficit was calculated to be -543 cubic feet. Since the deficit is negative, which indicates that more groundwater will be recharged into the soil for post- development conditions than pre-development conditions, the groundwater recharge requirements for this project have been met. 2

Engineering Stormwater Narrative JMA02P003- May 26, 2026 262-270 Main St Development 7 Groundwater Mounding GROUNDWATER MOUNDING BMP ESTIMATED BOTTOM OF BMP GROUNDWATER GROUNDWATER SHGWT ELEVATION MOUNDING HEIGHT MOUNDING ELEVATION Basin A 91.50 95.70 3.19 94.69 Porous Pavement B 91.50 97.00 4.00 95.50 As shown in the table above, the groundwater mounding does not exceed the bottom elevation of the stormwater management measures. Therefore, the groundwater mounding requirements have been met. 8 Conclusion The stormwater management plan proposed meets all the requirements set forth by the NJDEP. Design modification requirements that may occur during the approval process will be performed and submitted for review to the Township of West Orange. 3

Engineering Stormwater Narrative JMA02P003- May 26, 2026 262-270 Main St Development Appendix A: Precipitation Frequency Estimates 4

NOAA Atlas 14, Volume 2, Version 3 Location name: West Orange, New Jersey, USA* Latitude: 40.7866°, Longitude: -74.2324° Elevation: 196 ft* * source: ESRI Maps ** source: USGS POINT PRECIPITATION FREQUENCY ESTIMATES GM. Bonnin, D. Martin, B. Lin, T. Parzybok, M.Yekta, and D. Riley NOAA, National Weather Service, Silver Spring, Maryland PE tabular | PF_graphical | Maps_& aerials PF tabular PDS-based point precipitation frequency estimates with 90% confidence intervals (in inches)! Average recurrence interval (years) Duration| [1 [2 | 5s J] 1 | 2 | 50 || 100 | 200 || 500 || 1000 5-min 0.335, 0.400 0.473 0.528 0.593 0.639 0.685, 0.726 0.780 0.818 (0.306-0.368) | |(0.366-0.439)]|(0.432-0.519) |(0.480-0.579) |(0.538-0.650)]||(0.577-0.700) |(0.616-0.750)]|(0.648-0.795)]|(0.690-0.857) |(0.718-0.901) 40-min 0,534 0.638 0,755, 0,838 0,938 1,01 1,08 1.14 1.22 1.27 4 (0.488-0.586)||(0.583-0.699)]|(0.689-0.829) |(0.763-0.919)]| (0.852-1.03) || (0.913-1.11) || (0.971-1.18) |] (1.02-1.25) |] (1.08-1.34) || (1.12-1.40) 45-min 0.664 0.798 0.951 1.06 1.19 1.28 1.36 1.44 1.53 1.60 }(0.607-0.729)||(0.730-0.876)]| (0.868-1.04) | (0.962-1.16) || (1.08-1.30) || (1.15-1.40) || (1.23-1.49) |] (1.28-1.58) || (1.36-1.68) || (1.40-1.76) 30-min 0.907 1.10 1.34 1.52 1.75 1.91 2.07 2.22 242 2.56 (0.829-0.995)|| (1.00-1.20) |] (1.23-1.48) || (1.38-1.67) 1.59-1.91) || (1.72-2.09) || (1.86-2.27) || (1.98-2.43) || (2.14-2.66) || (2.25-2.82) 60-min 1.13 1.37 1.72 1.98 2.32 2.58 2.84 3.10 3.45 3.72 (1.03-1.24) || (1.26-1.51) || (1.57-1.89) | (1.80-2.17) || (2.10-2.54) |} (2.33-2.82) || (2.55-3.11) |} (2.77-3.40) || (3.05-3.79) || (3.26-4.10) 2-hr 1.38 1.68 2.13 2.48 2.97 3.37 3.78 4.20 4.80 5.28 (1.26-1.52) || (1.54-1.85) || (1.94-2.35) | (2.26-2.73) || (2.68-3.26) |] (3.02-3.69) || (3.36-4.14) |} (3.72-4.61) || (4.20-5.28) |] (4.57-5.81) 3-hr 1.54 1.88 2.38 2.78 3.32 3.77 4.23 4.71 5.38 5.91 (1.41-1.70) || (1.72-2.07) || (2.18-2.62) | (2.53-3.05) || (3.01-3.65) |] (3.39-4.13) || (3.78-4.63) || (4.17-5.16) || (4.71-5.90) || (5.13-6.49) 6-hr 1,99 2.42 3.06 3.58 4,33 4.95 5.61 6.31 7.33 8.17 " (1.83-2.19) || (2.22-2.66) || (2.80-3.35) | (3.26-3.91) || (3.91-4.71) |] (4.44-5.38) || (4.99-6.10) |} (5.56-6.87) || (6.36-7.98) || (7.01-8.91) 42-hr 2.48 3.01 3.82 4.51 5.52 6.38 7.31 8.34 9.86 11.2 ” (2.27-2.73) || (2.75-3.31) || (3494.20) | (4.10-4.94) || (4.97-6.01) |] (5.70-6.94) ||