JMA02P003 262 270 Main Street Development Stormwater Management Report

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