12 2026 02 12 Crestmont CC Stormwater Management Report

formations. A geotechnical investigation is proposed in order to confirm the presence of any underlying karst formations within the portion of the property subject to development. 2.3 Flood Hazard Area Based on a review of the Federal Emergency Management Agency (FEMA) Flood Insurance Rate Map (FIRM) for Essex County, Map #34013C0084F, #34013C0091F, and #34013C0092F, dated effective June 4, 2007, the proposed area of redevelopment and improvements within the Eagle Rock Avenue right-of-way are not located within a flood hazard area; refer to Figure 2 – FEMA Flood Insurance Rate Map. According to NJDEP mapping, there are unnamed tributaries to Canoe Brook located on the subject property but south of the proposed redevelopment area. The proposed redevelopment is located outside of the watershed to the unnamed tributary and no improvements are proposed within the flood hazard area. 2.4 Proposed Development The proposed redevelopment at the project site will consist of the following improvements: • Installation of a new traffic signal at Eagle Rock Avenue & Oval Road intersection; • Widening along Eagle Rock Avenue to support the new lane geometry required at the new signal; • Re-alignment of the Crestmont egress driveway to connect into the new intersection; • Onsite improvements to both increase the number of parking spaces and re-design the parking around the new egress driveway. • Associated driveways, sidewalks, parking areas, stormwater and utility infrastructure, and landscaping; and, • A proposed stormwater management system consisting of the following: o A subsurface conveyance system consisting of inlets, manholes, and pipes to convey stormwater runoff from the 25-year design storm event; o 2 small-scale bioretention basins; and, o 1 porous asphalt pavement system. 3.0 STORMWATER MANAGEMENT The proposed redevelopment disturbs over 1 acre of land and generates more than one-quarter acre of new regulated motor vehicle surface; therefore, this project is considered a major development as defined by the NJDEP stormwater rules (NJAC 7:8). Projects that qualify as major developments are required to design stormwater management systems that address: • Stormwater quantity; • Stormwater quality; 4

• Groundwater recharge; and, • Nonstructural measures The following sections provided additional detail regarding each of the stormwater design regulations. 3.1 Stormwater Quantity Design 3.1.1 Design Criteria In accordance with N.J.A.C. 7:8-5.6.(b).3, stormwater management measures are to be designed so that the post-construction peak runoff rates for the 2-, 10-, and 100-year design storm events are 50, 75, and 80%, respectively, of the pre-construction runoff rates for the portion of the site on which the proposed development is to be constructed. The portions of the project site that are to remain undisturbed in the post-construction condition are not subject to rate control measures. Therefore, it shall be demonstrated in accordance with N.J.A.C. 7:8-5.6.(b).3 that the post- construction peak runoff rates for the 2-, 10-, and 100-year design storm events are 50, 75, and 80%, respectively, of the pre-construction runoff rates for the portion of the site on which the redevelopment is to take place and quantity control through the implementation of BMPs is required. In accordance with N.J.A.C. 7:8-5.7, the 2-, 10-, and 100-year design storm events must be analyzed for both the “current” and “future” rainfall events. 3.1.2 Design Methodology This study was prepared utilizing the Natural Resources Conservation Service (NRCS - formerly SCS) method to analyze the pre- and post-development stormwater runoff rates and volumes. This methodology meets the NJDEP stormwater calculation requirements presented in Section 7:8-5.7.(a).1 of the New Jersey Administrative Code (N.J.A.C.) recognizing existing conditions. Stormwater hydrographs were developed utilizing the NOAA Atlas 14 Region D 24-hour storm distribution, and precipitation depths are referenced from the NOAA Atlas 14, Volume 2, Version 3 Point Precipitation Frequency Estimates Table for West Orange, New Jersey, accessed on March 20, 2024, for the 2-, 10-, 25-, and 100-year return periods. The table below summarizes the rainfall event totals. 5

Table 2 – NOAA Atlas 14 Precipitation Summary for 24-Hour Storm Events 2-yr 10-yr 25-yr 100-yr (in) (in) (in) (in) 3.43 5.22 6.46 8.72 In accordance with N.J.A.C. 7:8-5.7.(c), the precipitation depths from NOAA Atlas 14 shall be modified for the “current” storm events using the following precipitation adjustment factors, which are based on the project site’s location within Essex County. Table 3 – Current Precipitation Adjustment Factors for Essex County 2-yr 10-yr 25-yr 100-yr 1.01 1.03 1.04 1.06 Note: The adjustment factor for the 25-year storm event was found using a weighted average of the 10-year and 100-year storm event adjustment factors. The purpose of determining the 25-year storm event adjustment factor is for inputting basin-routed discharge rates into the conveyance network design software, as the proposed conveyance networks are designed for the 25-year design storm event. Table 4 – Current Precipitation Summary for 24-Hour Storm Events 2-yr 10-yr 25-yr 100-yr (in) (in) (in) (in) 3.46 5.38 6.72 9.24 In accordance with N.J.A.C. 7:8-5.7.(d), the precipitation depths from NOAA Atlas 14 shall be modified for the “future” storm events using the following precipitation adjustment factors, which are based on the project site’s location within Essex County. Table 5 – Future Precipitation Adjustment Factors for Essex County 2-yr 10-yr 25-yr 100-yr 1.19 1.22 1.26 1.33 Note: The adjustment factor for the 25-year storm event was found using a weighted average of the 10-year and 100-year storm event adjustment

.19 1.22 1.26 1.33 Note: The adjustment factor for the 25-year storm event was found using a weighted average of the 10-year and 100-year storm event adjustment factors. The purpose of determining the 25-year storm event adjustment factor is for inputting basin-routed discharge rates into the conveyance network design software, as the proposed conveyance networks are designed for the 25-year design storm event. 6

Table 6 – Future Precipitation Summary for 24-Hour Storm Events 2-yr 10-yr 25-yr 100-yr (in) (in) (in) (in) 4.08 6.37 8.13 11.60 A time of concentration was calculated for each watershed. The time of concentration is defined as the time for runoff to travel from the hydraulically most remote point of the watershed to the point of interest. Values of the time of concentration were determined for existing and proposed conditions based on land cover and slope of the flow path using methods described in TR-55 and Chapter 5 of the New Jersey Best Management Practices (BMP) Manual. A time of concentration calculation was performed for both the pervious and impervious land coverage areas within each watershed in order to more accurately model peak runoff rates. For the post- construction time of concentration calculations, the McCuen-Spiess limitation is applied to the sheet flow travel time portion of the calculation. Due to technical limitations of the hydrologic software used to develop hydrographs, the minimum time of concentration is 2 minutes. A runoff curve number (CN) was selected based upon the land cover type and underlying soil hydrologic classification within each watershed. In accordance with Chapter 5 of the New Jersey BMP Manual, peak runoff rates are calculated for each individual land cover type within the watershed and then hydraulically added together to determine the peak runoff rate of the watershed, rather than using the weighted runoff curve number (CN) methodology. Runoff curve numbers are referenced from Tables 2-2a and 2-2c of TR-55: Urban Hydrology for Small Watersheds. 3.1.3 Points of Analysis All stormwater runoff generated from the area of redevelopment ultimately discharges to the existing conveyance networks located within the Eagle Rock Avenue right-of-way, but leaves the subject tract via the points of analysis described below: Point of Analysis 1 (POA-1) refers to an existing manhole within Eagle Rock Avenue, to the northwest of the subject property. Runoff from this point is ultimately conveyed to xx via the existing conveyance network. Point of Analysis 2 (POA-2) refers to an existing catch basin within Eagle Rock Avenue, to the northeast of the subject

om this point is ultimately conveyed to xx via the existing conveyance network. Point of Analysis 2 (POA-2) refers to an existing catch basin within Eagle Rock Avenue, to the northeast of the subject property. Runoff from this point is ultimately conveyed to xx via the existing conveyance network. 7

3.1.4 Existing Watersheds The existing watersheds are depicted on Figure 4 – Existing Watershed Map. Watershed EX-1-DISTURBED is approximately 1.52± acres and consists of predominantly wooded areas, open space areas, and portions of the existing parking lot that are proposed to be disturbed in the post-construction condition. This watershed is conveyed via overland flow to the existing conveyance network within Laurel Avenue and Eagle Rock Avenue. From there it is conveyed to the existing manhole in Eagle Rock Avenue, Point of Analysis 1 (POA-1). Watershed EX-1-UNDISTURBED is approximately 5.00± acres and consists of portions of the existing building, parking area, driveway, Laurel Avenue, Eagle Rock Avenue, and pervious grass and wooded areas that are proposed to remain undisturbed in the post-construction condition. This watershed is conveyed via overland flow and the existing onsite conveyance network to the existing conveyance network within Laurel Avenue and Eagle Rock Avenue. From there it is conveyed to the existing manhole in Eagle Rock Avenue, Point of Analysis 1 (POA-1). Watershed EX-2-DISTURBED is approximately 2.41± acres and consists of portions of the existing parking area, driveway, and pervious wooded and grass areas that are proposed to be disturbed in the post-construction condition. This watershed is conveyed via overland flow and the existing onsite conveyance network to the existing conveyance network within Eagle Rock Avenue. From there it is conveyed to the existing catch basin in Eagle Rock Avenue, Point of Analysis 2 (POA-2). Watershed EX-2-UNDISTURBED is approximately 2.92± acres and consists of prtions of the existing parking area, buildings, Eagle Rock Avenue, and pervious wooded and grass areas that are proposed to remain undisturbed in the post-construction condition. This watershed is conveyed via overland flow and the existing onsite conveyance network to the existing conveyance network within Eagle Rock Avenue. From there it is conveyed to the existing catch basin in Eagle Rock Avenue, Point of Analysis 2 (POA-2). Refer to Appendix A for weighted curve number (CN) calculation worksheets and supporting hydrologic calculations for the determination of peak runoff rates. 3.1.5 Allowable Peak Discharges The proposed development increases the amount of impervious coverage compared to the existing condition, causing

culations for the determination of peak runoff rates. 3.1.5 Allowable Peak Discharges The proposed development increases the amount of impervious coverage compared to the existing condition, causing post-construction peak runoff rates to exceed pre-construction peak runoff rates within the watersheds with the most concentrated areas of development. Therefore, it shall be demonstrated in accordance with N.J.A.C. 7:8-5.6.(b).3 that the post-construction peak 8

runoff rates for the 2-, 10-, and 100-year design storm events are 50, 75, and 80%, respectively, of the pre-construction runoff rates for the portions of the site on which the proposed development is to be constructed and quantity control BMPs are required to be implemented. Watersheds noted as being “disturbed” in the watershed descriptions in Section 3.1.4 of this report represent the areas on the project site that are to be disturbed as part of the proposed redevelopment and are therefore subject to post-construction peak rate reductions if post- construction peak runoff rates exceed pre-construction peak runoff rates and quantity control BMP’s are required to be implemented. Watersheds noted as being “undisturbed” in the watershed descriptions in Section 3.1.4 of this report represent the areas on the project site that are to remain undisturbed as part of the proposed redevelopment and are therefore not subject to peak rate reductions. The following section summarizes the quantity control criteria being established for each point of analysis, which watersheds are subject to peak rate reductions, and the allowable peak discharges for each point of analysis. • Point of Analysis 1 (POA-1): The proposed development within this watershed results in peak runoff rates increasing in the proposed condition, and quantity control BMPs are required to be implemented. Therefore, it shall be demonstrated in accordance with N.J.A.C. 7:8-5.6.(b).3 that the post-construction peak runoff rates for both the current and future 2-, 10-, and 100-year design storm events are 50, 75, and 80%, respectively, of the pre-construction runoff rates for the disturbed portions of the overall watershed. Table 7 – POA-1 Allowable Peak Discharges (Current) Design Storm Existing Peak Allowable Peak Event Discharge (CFS) Discharge (CFS) 2-Year 13.48 12.57 10-Year 23.47 22.52 100-Year 44.56 42.92 Note: Total Allowable Peak Discharges are calculated by hydraulically adding runoff hydrographs and may not reflect the

100-Year 44.56 42.92 Note: Total Allowable Peak Discharges are calculated by hydraulically adding runoff hydrographs and may not reflect the direct addition of peak discharge rates. Refer to the hydrograph report calculations in Appendix A. 9