J_2024 05 09_West Orange Stormwater Management Plan

Stormwater Management Plan Revision 0 Site Conditions which are shown in Hydrologic Soil Group D on a USDA Soil Texture Triangle, in accordance with Chapter 12 of the BMP Manual. The soil map, soil descriptions and ratings can be found in Appendix F. 1.5 Floodplain As depicted on FEMA Map Number 34013C0092F (effective date June 4, 2007), the project site is located within a FEMA Zone X, area of minimal flood hazard. The Flood Insurance Rate Map (FIRM) can be found in Appendix F . Public Service Electric & Gas Company 1-3 Burns & McDonnell

Stormwater Management Plan Revision 0 Site Conditions Figure 1-1 General Vicinity Map Public Service Electric & Gas Company 1-4 Burns & McDonnell

Stormwater Management Plan Revision 0 2.0 2.1 Hydrology and Hydraulics HYDROLOGY AND HYDRAULICS Rainfall Data Rainfall Depths for Essex County were obtained from the NOAA National Weather Service Precipitation Frequency Data Server (See Appendix F). The SCS rainfall distribution for this project is NOAA 24-Hr Type D. See Table 2.1 for existing rainfall data. Table 2.1: Design Storm Frequency-Depth Return Frequency (yr) 24 Hour Depth (in) 2 3.42 10 5.20 25 6.44 100 8.71 Per the updated N.J.A.C. 7:8 regulations effective July 17, 2023, an adjustment factor for the respective county is applied for both the current precipitation (per N.J.A.C. 7:8, Table 5-5) and future precipitation (per N.J.A.C. 7:8, Table 5-6) for Essex County for the 2-, 10-, and 100-year return frequencies. The current and future adjusted 24-hour depths are used for stormwater modeling. The resulting design rainfall depths are shown below in Table 2.2. Table 2.2: Design Storm Frequency with Depth Precipitation Adjustment Factors (AF) Return Frequency (yr) Water Quality (WQ) 2 10 25 100 NOAA Atlas 14 (in) 1.25a 3.42 5.20 6.44 8.71 24 Hour Depth Current Current Future Adjusted AF AF (in) Future Adjusted (in) 1.01 1.03 N/A 1.06 4.07 6.36 N/A 11.58 3.45 5.37 N/A 9.23 1.19 1.22 N/A 1.33 a N.J.A.C. 7:8-5.5 requires the WQv storm to be 1.25 inches of rainfall in two hours. 2.2 Runoff Data HydroCAD-10 software was utilized to model the stormwater runoff at the site. The SCS TR-55 methodology was used for this model to calculate the pre- and post-developed runoff rates for storage design. Table 2.3 provides detailed information regarding curve numbers and land coverages for pre- and post-developed watersheds, respectively. Public Service Electric & Gas Company 2-1 Burns & McDonnell

Stormwater Management Plan Revision 0 Hydrology and Hydraulics Table 2.3: Land Coverages Land Coverage CN HSG Pre-Development Impervious, Pavement 98 D >75% Grass cover, Good 80 D Yard Stone/Gravel Pad 85 D Brush, Good 73 D Non-Contributory* 73-85 D Post-Development Impervious, Pavement 98 D >75% Grass cover, Good 80 D Yard Stone/Gravel Pad 85 D Brush, Good 73 D Non-Contributory* 73-85 D Area (acres) 1.735 1.752 2.011 1.271 1.456 2.054 1.665 2.332 2.024 0.150 *Non-Contributory refers to areas that do not contribute to bioretention or the existing Aquashield system. NonContributory areas include the grassed slope areas and the transformer pits. Public Service Electric & Gas Company 2-2 Burns & McDonnell

Stormwater Management Plan 2.3 Revision 0 Hydrology and Hydraulics Stormwater Management Facilities As previously stated in Section 1.3, this project is considered a major development, but is only required to treat quantity. A series of bioretention basins with underdrains is proposed to mitigate the effects of higher runoff rates from the proposed development. The bioretention basins consist of a topsoil layer of at least 18 inches in depth, a middle sand layer of at least 6 inches and a bottom gravel layer of at least 12 inches. Filter fabric will also be installed along the sides and bottom of each basin. Perforated underdrains, 4 inches in diameter, will be located throughout the basin. In accordance with the BMP manual, inverts will not be required to be at least 3 inches from the bottom because of the use of a concrete/non-earthen bottom. Pipe crowns will be required to be at least 3 inches from the top of the gravel layer. The bioretention basin systems are located to the east and south of the proposed station upgrades and are designed according to the New Jersey Stormwater Best Practices Manual, Chapter 9.7, Small-Scale Bioretention Systems. The bioretention basins are designed so that the post-construction peak runoff rates for the current and future 2-, 10- and 100-year storm events are less than 50%, 75% and 80%, respectively, of the preconstruction peak runoff rates as shown in Table 2.4. During storm events, the bioretention basins will capture stormwater runoff, which will filter through the basin’s media layers and drain out through a network of perforated underdrains at the bottom of each of the basins. Water will be released from the underdrain system into a stormwater conveyance system, ultimately connecting and discharging into the Township’s existing stormwater network, located within Mount Pleasant Avenue. Table 2.4: Bioretention Basins Discharge Return Frequency (yr) Inflow (cfs) Discharge (cfs) Stage Elevation (ft) Surface Area (sf) Max Available Storage (cf) Approx. SHWT Elevati on (ft) Bottom of Bioretention Basin Elevation (ft) 6,639 595.00 596.00 BR-1 WQ 0.44 0.12 596.68 2 (Current) 0.93 0.24 598.20 2 (Future) 1.21 0.30 599.34 10 (Current) 1.67 0.33 600.08 10 (Future) 2.13 0.42 600.58 100 (Current) 3.18 1.24 601.35 100 (Future) 4.23 1.65 602.16 Public Service Electric & Gas

0 2 (Future) 1.21 0.30 599.34 10 (Current) 1.67 0.33 600.08 10 (Future) 2.13 0.42 600.58 100 (Current) 3.18 1.24 601.35 100 (Future) 4.23 1.65 602.16 Public Service Electric & Gas Company 1,759 2-3 Burns & McDonnell

Stormwater Management Plan Return Frequency (yr) Inflow (cfs) Revision 0 Discharge (cfs) Stage Elevation (ft) Hydrology and Hydraulics Max Available Storage (cf) Approx. SHWT Elevati on (ft) Bottom of Bioretention Basin Elevation (ft) 1,578 2,187 597.00 598.00 2,175 5,822 593.00 594.00 2,894 4,782 593.70 594.70 1,575 3,203 592.80 593.80 Surface Area (sf) BR-2 WQ 0.37 0.11 598.55 2 (Current) 0.65 0.19 599.40 2 (Future) 0.84 0.23 600.04 10 (Current) 1.14 0.33 601.13 10 (Future) 1.44 0.74 601.23 100 (Current) 2.14 1.85 601.42 100 (Future) 2.83 2.78 601.47 BR-3 WQ 0.31 0.10 594.44 2 (Current) 0.59 0.17 595.19 2 (Future) 0.77 0.20 595.56 10 (Current) 1.05 0.26 596.66 10 (Future) 1.34 0.31 597.57 100 (Current) 1.97 0.34 598.43 100 (Future) 2.63 0.50 599.05 BR-4 WQ 0.50 0.08 595.04 2 (Current) 0.83 0.14 595.53 2 (Future) 1.05 0.16 595.75 10 (Current) 1.44 0.20 596.26 10 (Future) 1.79 0.23 596.69 100 (Current) 2.68 0.32 598.36 100 (Future) 3.49 0.44 598.73 BR-5 WQ 0.33 0.08 594.16 2 (Current) 0.59 0.15 594.69 2 (Future) 0.75 0.17 594.95 10 (Current) 1.04 0.21 595.55 10 (Future) 1.30 0.25 596.23 100 (Current) 1.96 0.32 597.66 100 (Future) 2.55 0.35 598.22 *Basin Information from Exhibit A - Pre-Developed Watershed Map. Public Service Electric & Gas Company 2-4 Burns & McDonnell

Stormwater Management Plan Revision 0 Hydrology and Hydraulics A series of trench drains are also included, adjacent to each bioretention basin. These trench drains are intended to prevent off-site drainage from flowing onto the station pad or into the bioretention basins. These areas have been labeled as Non-Contributory and were not taken into consideration when evaluating the bioretention basins. The trench drains adjacent to the basins will connect into a separate stormwater conveyance system, ultimately connecting and discharging into the Township’s existing stormwater network, located within Mount Pleasant Avenue, at outfall 0-1A. As shown in Table 2.7, these areas are considered non-contributory because they are to remain in their existing condition and are only captured at the watershed lowpoint to directly route runoff to the stormwater network in Mount Pleasant Avenue to prevent any impact to the station. Each Discharge Point was analyzed to regard only watersheds that contributed to that outfall and were analyzed differently as not all areas are being disturbed/impacted by these improvements. In Table 2.7, the pre-development outfalls comparison versus the post-development outfalls show less flow leaving the site in the post-development condition for each of the current and future projected design storm outfalls per the criteria described in N.J.A.C 7:8. Stormwater flow from three of the post developed watersheds, PO-DA-A, PO-DA-M and portions of PODA C, will mimic the pre-developed drainage patterns of PO-DA 6 and PO-DA 8, utilizing the existing stormwater conveyance system, routing to the existing Aquashield treatment device, ultimately discharging into the Township’s existing stormwater network located within Mount Pleasant Avenue. As shown in Table 2.7, post-development flows to O-Aquashield were significantly reduced from predevelopment flows, this was accomplished by routing runoff to other BMPs. By reducing the footprint of the watersheds routing to O-Aquashield, we were able to reduce the load to this device and add new capture and treatment via bioretention. Soil tests were conducted by GZA GeoEnvironmental, Inc. between May 31st, 2022 and January 6th, 2023 (See Appendix E). During the soil investigation, GZA excavated five test pits in the bioretention areas, TP-203, TP-204, TP-205, TP-103 and TP-102, from north to south. The test

and January 6th, 2023 (See Appendix E). During the soil investigation, GZA excavated five test pits in the bioretention areas, TP-203, TP-204, TP-205, TP-103 and TP-102, from north to south. The test pits extended to depths of approximately 6 to 10 feet below grade. Groundwater seepage was encountered at varying depths. Table 2.5 provides estimated Seasonal High Water Table (SHWT) elevations used for each basin. Based off the acquired groundwater locations, each bioretention basin was initially designed to allow for a minimum of 1’ of separation between the SHWT and the bottom of the bioretention basin (See Table 2.5). Design was modified to utilize a sealed bioretention basin with concrete on all sides and so therefore in accordance with the New Jersey Stormwater Best Practices Manual, Chapter 9.7, Small-Scale Bioretention Systems, the basins are not required to maintain a separation from the Seasonal High Water Table. Public Service Electric & Gas Company 2-5 Burns & McDonnell

Stormwater Management Plan Revision 0 Hydrology and Hydraulics Each bioretention basin will have its own outlet control structure (Refer to Table 2.6) that discharge into a subsurface pipe network that will ultimately drain to Outfall O-1B, located in Mount Pleasant Avenue. Table 2.5: Bioretention Basin Control Devices Outlet Control Structure Name CS-01 CS-02 CS-03 CS-04 CS-05 2.4 Control Device Outlets (1) – 2.5” circular orifice @ 596.00’ (1) – 12.0”W x 2.5”H rectangular orifice @ 600.50’ (1) – 48.0”W x 48.0”L overflow orifice @ 602.40’ (1) – 12” diameter RCP (SD-21) @ 591.57’ (1) – 2.5” circular orifice @ 598.00’ (1) – 36.0”W x 2.5”H rectangular orifice @ 601.10’ (1) – 48.0”W x 48.0”L overflow orifice @ 601.40 (1) – 12” diameter RCP (SD-22) @ 590.35’ (1) – 2.5” circular orifice @ 594.00’ (1) – 2.5”W x 2.5”H rectangular orifice @ 598.50’ (1) – 48.0”W x 48.0”L overflow orifice @ 601.15‘ (1) – 15” diameter RCP (SD-23) @ 588.19’ (1) – 2.5” circular orifice @ 594.70’ (1) – 2.5”W x 2.5”H rectangular orifice @ 598.30’ (1) – 48.0”W x 48.0”L overflow orifice @ 599.65‘ (1) – 15” diameter RCP (SD-24) @ 586.53’ (1) – 2.5” circular orifice @ 593.80’ (1) – 12.0”W x 2.5”H rectangular orifice @ 598.20’ (1) – 48.0”W x 48.0”L overflow orifice @ 599.65‘ (1) – 18” diameter RCP (SD-25) @ 584.63’ Results The post-developed watersheds PO-DA A and PO-DA M, which discharge into the existing onsite stormwater pipe network that drains to the AquaShield, will be a reduction in size from the pre-developed watersheds PO-DA 6 and PO-DA 8, thus providing no adverse impact to the original AquaShield design or outfall. As summarized in Section 2.3, a series of bioretention basins with underdrains will be constructed to address the water quantity for the peak discharge for the newly developed areas associated with the substation expansion, specifically post-developed watersheds PO-DA C, PO-DA E, PO-DA G, PO-DA I, and PO-DA J. Flow rate calculations were completed using HydroCAD software. Refer to Appendix B for the calculations. Public Service Electric & Gas Company 2-6 Burns & McDonnell