2024 03 Drainage Statement

DRAINAGE STATEMENT Prepared For Aaron Friedman Proposed Single-Family Residential Dwelling Block 80.03, Lot 10 10 Ridge Road Township of West Orange Essex County, New Jersey Prepared by: 1904 Main Street Lake Como, NJ 07719 (732) 974-0198 Matthew J. Bersch, PE NJ Professional Engineer License #54522 March 2024 DEC # 5142-24-00053

TABLE OF CONTENTS Section Page I. Drainage Summary ..............................................................1 II. Design Methodology ............................................................2 III. Runoff Rate Reductions Performance ....................................3 IV. Conclusion ...........................................................................4 APPENDIX • USGS Map • NRCS Web Soil Survey • Hydrograph Summary Reports – 2- & 10-Year Storm Events • Stormwater Collection System Calculations (Pipe Sizing) • Outlet Control Structure Detail • Drainage Area Maps

I. Drainage Summary This Drainage Statement has been prepared to define and analyze the stormwater drainage conditions that would occur as a result of the development of Block 80.03, Lot 10 as shown on the Township of West Orange Tax Map Sheet No. 32, located in the Township of West Orange, Essex County, New Jersey. The subject site consists of 5.77 acres (251,368 SF) and is located at 10 Ridge Road. Under existing conditions, the site is undeveloped, consisting of overgrown wooded areas. The proposed project consists of the construction of a 2,900 SF footprint, two and a half story single-family residential dwelling. Additional site improvements will include a paved driveway, swimming pool, pickleball court, landscaping, grading, stormwater management, utilities and other associated site amenities as shown on the accompanying Site Plan drawings. The project also proposes a sanitary sewer main extension. The new development will result in 39,823 SF (0.91 AC) of disturbance on site and 2,418 SF (0.06 AC) disturbance within the right-of-way for a total disturbance of 42,241 SF (0.97 AC), along with a 10,113 SF (0.23 AC) increase in impervious coverage. Of the increase in impervious coverage, 3,916 SF (0.09 AC) is motor vehicle surface consisting of the proposed driveway. The project consists of less than one (1) acre of disturbance and will not increase the net impervious coverage on-site by ¼ acre or more, nor the motor vehicle surface. Therefore, the proposed project does not meet the definition of a ‘major development’ as defined by NJAC 7:8 and therefore is not subject to the NJDEP Stormwater Management Rules & Regulations (NJAC 7:8). As the proposed development proposes disturbance of greater than 5,000 SF with an increase of impervious area less than ¼ acre, the project is subject to New Jersey standards for Soil Erosion & Sediment Control runoff rate reductions for downstream stability required for the 2 & 10-year storms. The stormwater drainage for the proposed site has been designed to maintain existing runoff patterns to the maximum extent feasible. In existing conditions, stormwater runoff from the project area drains to two points of analysis. Stormwater runoff from the northern corner of the site flows via overland flow to the existing headwall located within the adjacent Lot 21. The remaining stormwater runoff within the project area flows via

water runoff from the northern corner of the site flows via overland flow to the existing headwall located within the adjacent Lot 21. The remaining stormwater runoff within the project area flows via overland to the existing concrete channel at the eastern corner of the site. Aaron Friedman DEC# 5142-24-00053 March 2024 1

II. Design Methodology The intention of the design of the proposed stormwater management facility for this project is to provide measures as required to address applicable aspects of the Standards for Soil Erosion and Sediment Control in New Jersey and the Township of West Orange Stormwater Management Control Ordinance. The stormwater runoff from the project area is ultimately tributary to two points of analysis as previously described. The stormwater drainage for the proposed project has been designed to maintain existing runoff patterns on-site to the maximum extent practicable. A grading plan has been developed for the proposed site improvements with consideration to the existing drainage patterns. The project proposes an underground detention system located to the north of the dwelling. A proposed roof leader system will collect stormwater runoff from the dwelling and discharge into the basin. Two (2) yard inlets are proposed onsite to collect stormwater runoff from the project area. The proposed basin is designed with an outlet control structure which will release stormwater runoff at a controlled rate to the existing stormwater conveyance pipe located to the east of the proposed dwelling, which is ultimately tributary to the existing concrete channel. A portion of stormwater runoff from the project area will continue to flow undetained via overland to the existing headwall within the adjacent Lot 21. The hydrology for the site was calculated using the NRCS Runoff Equation and Dimensionless Unit Hydrograph as noted in Part 630, Hydrology National Engineering Handbook. The following particular references were used: • Curve Numbers were established via Chapter 9 – Hydrologic Soil-Cover Complexes • Time of Concentrations were calculated in accordance with Chapter 15 • Rainfall Distributions are based on NOAA Type D rainfall distributions • The SCS Dimensionless Unit Hydrograph was utilized. Aaron Friedman DEC# 5142-24-00053 March 2024 2

III. Runoff Rate Reduction Performance As noted previously, a majority of stormwater runoff from the project area will be collected by the proposed stormwater conveyance system, detained in an on-site underground detention basin, and released at a controlled rate to the existing onsite stormwater infrastructure. A significant amount of stormwater runoff from the surrounding wooded areas flows through the project area, to be collected and detained in the proposed basin. As these areas remain undisturbed in existing and proposed conditions, peak flows from these areas were accounted for in the basin sizing and outlet control structure design, but were excluded in the peak flow reduction calculations. The undisturbed wooded areas which drain towards the existing headwall within the adjacent Lot 21 were also included in the peak flow calculations, but were excluded in determining the required peak flow reduction. As a result of the improvements associated with the proposed development, the peak flows discharging to each point of analysis decreases for the two (2) and ten (10) year design storms, modeled as 24-hour SCS Type III design storms, as compared to existing conditions. In addition, the proposed basin and outlet control structure have been designed to provide a fifty (50) percent reduction for the two (2) year and a twenty-five (25) percent reduction for the ten (10) year design storms for the project as a whole. Please refer to the appendix of this report for the hydrograph summary reports indicating same. Pre-Development and Post Development Peak Runoff Results Summary Point of Analysis A (Lot 21 Headwall) Pre-Development Design Undisturbed Areas Storm (CFS) 2 Year 0.33 10 Year 0.80 Pre-Development Disturbed Areas (CFS) 0.21 0.52 Point of Analysis B (Concrete Channel) Pre-Development Pre-Development Design Undisturbed Areas Disturbed Areas Storm (CFS) (CFS) 2 Year 1.17 0.36 10 Year 2.84 0.87 Aaron Friedman DEC# 5142-24-00053 Total Allowable Peak Flow Total Proposed Peak Flow (CFS) 0.54 1.32 0.37 0.87 Total Allowable Peak Flow Total Proposed Peak Flow (CFS) 1.53 3.71 1.23 3.48 March 2024 3

Total Site Design Storm Pre-Development Undisturbed Areas (CFS) Pre-Development Disturbed Areas (CFS) 2 Year 10 Year 1.34 3.25 0.47 1.14 IV. Reduction in Flow in Disturbed Areas (%) 50 25 Total Allowable Peak Flow Total Proposed Peak Flow (CFS) 1.58 4.11 1.57 4.11 Conclusion The proposed project has been designed to ensure safe and efficient control of stormwater runoff in a manner that will not adversely impact the existing drainage patterns, existing structures, or adjacent parcels. Furthermore, the project results in a decrease in peak stormwater runoff rates from the parcel, increasing downstream stability. As a result, it is anticipated that the proposed development will not adversely impact the existing drainage infrastructure located onsite or within the surrounding properties. Aaron Friedman DEC# 5142-24-00053 March 2024 4

APPENDIX

USGS MAP

Dynamic Engineering Consultants, PC 1904 Main Street Lake Como, NJ 07719 T. 732-974-0198 USGS MAP: CALDWELL QUADRANGLE (Not to scale) www.dynamicec.com Lake Como, NJ • Chester, NJ • Toms River, NJ • Newark, NJ • Marlton, NJ • Newtown, PA • Philadelphia, PA Bethlehem, PA • Allen, TX • Houston, TX • Austin, TX • Delray Beach, FL • Annapolis, MD