V3 RESUBMISSION Stormwater Management Report Rev 2 Dated November 3 2022

CURVE NUMBERS Table 1 —- Curve Number (Existing Conditions) Description Hydrologic Curve Group Number Woods A 30 Woods (e 70 Woods D 71 Open Space 6: 74 Open Space D 80 Impervious A/B/C/D 98 PEAK FLOWS Using the information described above, the peak flows during the 2-, 10-, and 100-year storm events were calculated. Table 2 below summarizes the peak flows during each storm event. (See attached Hydraflow Output for Existing Conditions Hydrographs, CN Values, and Time of Concentration Calculations.) Table 2 — Existing Peak Runoff Rates Storm Event | Existing Site Runoff 2 Year 20.08 cfs 10 Year 45.76 cfs 100 Year 96.75 cfs POST-DEVELOPMENT RUNOFF TARGET Since the improvements on the site are considered a major development, proposed runoff rates shall meet the NJDEP Stormwater regulations and reductions for the 2, 10, and 100-year storm events. NJ standards require that the preconstruction runoff rates are to be reduced to at least 50, 75, and 80, respectively, for the areas which are to be disturbed or developed. The proposed reductions will only account for the areas of the site, which are being disturbed as a result of the proposed development. The equations below were used to determine the reductions based on the limit of disturbance, as shown on the Soil Erosion and Sediment Control Plan. 2 Year Reduction = 10.50(0.50) _ 0.260 ear Keduction = 20.16 =U. 10 Year Reduction = 10.50(0.25) = 0.130 ear Keduction = 20.16 =U. 100 Year Reduction = 10,50(0.20) _ 0.104 ear Keauc ons 20.16 Hv.

Table 3 — Target Runoff Rates Storm Existing | Percent Offsite Runoff Total Post- Event Runoff | Reduction | Reduction Development (Yr.) Rates (cfs) Target Runoff (cfs) (cfs) 2 Year 20.08 cfs 26.0% 20.08 (0.260) = 20.08 — 5.221 = 5.221 cfs 14.859 cfs 10 Year | 45.76 cfs 13.0% 45.76 (0.130) = 45.76 — 5.949 = 5.949 cfs 39.811 cfs 100 Year | 96.75 cfs 10.4% 96.75 (0.104) = 96.75 — 10.062 = 10.062 cfs 86.688 cfs PROPOSED CONDITIONS The same overall drainage area used in existing conditions was used for proposed conditions. This drainage area was modeled as 5 drainage areas totaling 20.16 acres. (See Fig.-2 Proposed Drainage Area Map.) DRAINAGE AREA 1A (DA-1A) Drainage Area 1A consists of the portion of the building to be constructed under phase I , 1.14 acres. This roofed area drains to proposed Basin #1A, a subsurface detention basin. See below for a detailed description of the basin. A time of concentration of 6 minutes was used for this drainage area, which is the minimum time that can be used. At this time, we have not taken any credit for green roofs in our calculations. As the final roof plans are developed, we may choose to recalculate the runoff and required detention volume for the system servicing the roof area. DRAINAGE AREA 1B (DA-1B) Drainage Area 1A consists of the portion of the building to be constructed under phase II, 1.75 acres. This roofed area drains to proposed Basin #1B, a subsurface detention basin. See below for a detailed description of the basin. A time of concentration of 6 minutes was used for this drainage area, which is the minimum time that can be used. At this time, we have not taken any credit for green roofs in our calculations. As the final roof plans are developed, we may choose to recalculate the runoff and required detention volume for the system servicing the roof area. DRAINAGE AREA 2 (DA-2 Drainage Area 2 consists of both pervious and impervious surfaces, which will bypass the proposed basins onsite and drain into the Pleasant Valley Way ROW. The pervious area, 3.19 acres, consists of mostly landscape and grass areas along with some existing wooded areas, which are to remain. The impervious area, 1.22 acres, consists of parking areas, ° 5

drive aisles, and sidewalks. A time of concentration of 10.14 minutes was calculated for this drainage area. DRAINAGE AREA 3 (DA-3) Drainage Area 3 consists of both pervious and impervious surfaces which drain to Basin #2. The pervious area, 5.56 acres, consist primarily of the wooded areas in the rear of the site along with some landscaped area around the proposed parking lot. The impervious area, 1.38 acres, is mainly comprised of the proposed parking lot. A time of concentration of 14.46 minutes was calculated for this drainage area. DRAINAGE AREA 4 (DA-4) Drainage Area 4 consists of both pervious and impervious surfaces which drain to Basin #3. The pervious area, 4.84 acres, consists primarily of the wooded area located to the rear of the site, along with some lawn and landscape areas around the proposed building and parking lot. The impervious area, 1.08 acres, is comprised of the portion of building to be constructed in phase III, as well as some proposed parking lots, drive aisles, sidewalks, and patios. A time of concentration of 14.30 minutes was calculated for this drainage area. CURVE NUMBERS Table 4 — Curve Number (Existing Conditions) Description Hydrologic Curve Group Number Woods A 30 Woods Cc 70 Woods D 71 Open Space A 39 Open Space € 74 Open Space D 80 Impervious A/B/C/D 98 WATER QUANTITY BASIN #1A — 3.230 CF Detention Basin #1A is a subsurface detention basin with 3,230 cubic feet of storage. The system is comprised of 3 rows of 48" diameter HDPE pipe, each 75 feet in length. The bottom of the basin is at elevation 418.00, along with 1 — 4" x 6.5" orifice. At elevation 420.50, 1 — 8” x 12" orifice will also be placed, followed by a 4' weir at an elevation of 421.30. ° 6

BASIN #1B — 4.474 CF Detention Basin #1B is a subsurface detention basin with 4,474 cubic feet of storage. The system is comprised of 5 rows of 48" diameter HDPE pipe, totaling 300 feet in length. The bottom of the basin is at elevation 404.00, along with 2 — 4" x 5" orifices. At elevation 406.35, 1 — 6” x 18" orifice will also be placed, followed by a 4' weir at an elevation of 407.25. BASIN #2 — 16,898 CF Detention Basin #2 is a surface basin with 16,898 cubic feet of storage. The bottom of the basin is set at elevation 414.00 along with 1 — 8" x 16" rectangular orifice. 2 — 13” x 22” orifices will be placed at elevation 416.00, and a 4' weir is placed at elevation 418.00. It should be noted that the 100-year storm event reaches an elevation of 417.97, just below the elevation of the weir. The top of the basin is set at 419, which allows for 1 foot of freeboard. BASIN #3 — 11,200 CF Detention Basin #3 is another surface basin with 11,200 cubic feet of storage. The bottom of the basin is set at elevation 416.00, where 1 — 4” x 10" orifice will also be placed. 2 — 6” x 10" orifices will be placed at elevation 417.00, and 2 — 8” x 10" orifices will be placed at an elevation of 418.00. Finally, a 4' weir will be placed at elevation 420.00. It should be noted that the 100-year storm event reaches an elevation of 419.98, just below the elevation of the weir. The top of the basin is set at 421.00, which allows for 1 foot of freeboard. POST-DEVELOPMENT RUNOFF Using the information described above, the peak flows during the 2-, 10-, and 100-year storm events were calculated. Table 5 below summarizes the peak flows during each storm event. (See attached Hydraflow Output for Proposed Conditions Hydrographs, CN Values, and Time of Concentration Calculation.) Table 5 — Proposed Peak Runoff Rates Target Storm Event Site Proposed Site Runoff Runoff 2 Year 14.859 cfs 14.78 cfs 10 Year 39.811 cfs 39.73 cfs 100 Year _| 86.688 cfs 86.57 cfs DRAIN TIME As shown by the Hydraflow Hydrographs attached to this report, the detention time of the system is below 72 hours and is broken down as follows: Detention Basin #1A — 27 hrs. Detention Basin #1B — 27 hrs. Detention Basin #2 —-27 hrs. Detention Basin #3 — 27 hrs.

WATER QUALITY Water quality is not required for the proposed development as there is a reduction in the total motor vehicle surface onsite from existing conditions. GROUNDWATER RECHARGE The subject property is located within the metropolitan planning area and has been previously developed. As such, the proposed development is not required to meet the groundwater recharge standards. STORM SEWER COMPUTATIONS A storm sewer system has been designed to collect the runoff associated with the proposed parking lot and roof. The system's primary purpose is to properly drain the proposed site and deliver the runoff to the proposed stormwater management system for water quantity. See attached Storm Sewer Computations in the appendix of this report. The pipes flowing into the systems were designed for a 25-year storm event. The rational method was used to calculate the runoff rates, and the Manning's equation was used to determine the capacity of each system. The majority of the site is mapped with soils considered Hydrologic Group A & C. For this analysis it was assumed the entire site was Hydrologic Group C. Runoff coefficients (C values) for hydrologic soil group C were 0.51 and 0.99 for woods - good condition and pavement respectively. In addition, all areas were assumed to have a time of concentration of 6 minutes for a conservative model. As shown, all pipes were designed with adequate capacity to handle the proposed flows. CONCLUSION To summarize, a stormwater management strategy has been incorporated to satisfy both the structural and non-structural water quality and water quantity requirements. This is in keeping with the design and performance standards set forth in the West Orange Stormwater Management Ordinance and New Jersey DEP Regulations.

EXISTING CONDITIONS HYDROGRAPHS

Hydraflow Table of Contents Existing Conditions.gpw Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2023 Wednesday, 11 / 2 / 2022 Watershed Model Schematic...................................................................................... 1 Hydrograph Return Period Recap............................................................................. 2 2 - Year Summary Report......................................................................................................................... 3 Hydrograph Reports................................................................................................................... 4 Hydrograph No. 1, SCS Runoff, DA-1A (Impervious)............................................................... 4 Precipitation Report............................................................................................................. 5 Hydrograph No. 2, SCS Runoff, DA-1A (Pervious).................................................................. 6 Precipitation Report............................................................................................................. 7 Hydrograph No. 3, Combine, DA-1A........................................................................................ 8 Hydrograph No. 4, SCS Runoff, DA-1B................................................................................... 9 Precipitation Report........................................................................................................... 10 Hydrograph No. 5, SCS Runoff, DA-2.................................................................................... 11 Precipitation Report........................................................................................................... 12 Hydrograph No. 6, SCS Runoff, DA-3 (Impervious)............................................................... 13 Precipitation Report........................................................................................................... 14 Hydrograph No. 7, SCS Runoff, DA-3

......... 13 Precipitation Report........................................................................................................... 14 Hydrograph No. 7, SCS Runoff, DA-3 (Pervious).................................................................. 15 Precipitation Report........................................................................................................... 16 Hydrograph No. 8, Combine, DA-3........................................................................................ 17 Hydrograph No. 9, SCS Runoff, DA-4 (Impervious)............................................................... 18 Precipitation Report........................................................................................................... 19 Hydrograph No. 10, SCS Runoff, DA-4 (Pervious)................................................................ 20 Precipitation Report........................................................................................................... 21 Hydrograph No. 11, Combine, DA-4....................................................................................... 22 Hydrograph No. 12, SCS Runoff, DA-5 (Impervious)............................................................. 23 Precipitation Report........................................................................................................... 24 Hydrograph No. 13, SCS Runoff, DA-5 (Pervious)................................................................ 25 Precipitation Report........................................................................................................... 26 Hydrograph No. 14, Combine, DA-5...................................................................................... 27 Hydrograph No. 15, SCS Runoff, DA-6.................................................................................. 28 Precipitation Report........................................................................................................... 29 Hydrograph No. 16, Combine, To Basin #1............................................................................ 30 Hydrograph No. 17, Reservoir, Basin

...................... 29 Hydrograph No. 16, Combine, To Basin #1............................................................................ 30 Hydrograph No. 17, Reservoir, Basin #1................................................................................ 31 Pond Report - Basin #1..................................................................................................... 32 Hydrograph No. 18, Combine, Combined - SS Southern Driveway....................................... 33 Hydrograph No. 19, Combine, Total Offsite............................................................................ 34 10 - Year Summary Report....................................................................................................................... 35 Hydrograph Reports................................................................................................................. 36 Hydrograph No. 1, SCS Runoff, DA-1A (Impervious)............................................................. 36 Precipitation Report........................................................................................................... 37 Hydrograph No. 2, SCS Runoff, DA-1A (Pervious)................................................................ 38 Precipitation Report........................................................................................................... 39 Hydrograph No. 3, Combine, DA-1A...................................................................................... 40 Hydrograph No. 4, SCS Runoff, DA-1B................................................................................. 41

Contents continued... Existing Conditions.gpw Precipitation Report........................................................................................................... 42 Hydrograph No. 5, SCS Runoff, DA-2.................................................................................... 43 Precipitation Report........................................................................................................... 44 Hydrograph No. 6, SCS Runoff, DA-3 (Impervious)............................................................... 45 Precipitation Report........................................................................................................... 46 Hydrograph No. 7, SCS Runoff, DA-3 (Pervious).................................................................. 47 Precipitation Report........................................................................................................... 48 Hydrograph No. 8, Combine, DA-3........................................................................................ 49 Hydrograph No. 9, SCS Runoff, DA-4 (Impervious)............................................................... 50 Precipitation Report........................................................................................................... 51 Hydrograph No. 10, SCS Runoff, DA-4 (Pervious)................................................................ 52 Precipitation Report........................................................................................................... 53 Hydrograph No. 11, Combine, DA-4....................................................................................... 54 Hydrograph No. 12, SCS Runoff, DA-5 (Impervious)............................................................. 55 Precipitation Report........................................................................................................... 56 Hydrograph No. 13, SCS Runoff, DA-5 (Pervious)................................................................ 57 Precipitation Report........................................................................................................... 58