251203_42 ERW_Stormwater Report

Stormwater Management Report October 18, 2024 Last Revised: December 3, 2025 Proposed Residential Improvements Block 106, Lot 24.01 Town of West Orange, Essex County, New Jersey Prepared for: Prepared by: Waystone Realty, LLC 40 Eagle Ridge Way West Orange, NJ 07052 _______________________________ Jesse B. Cokeley, P.E. New Jersey Professional Engineer License No. GE54006 Colliers Engineering & Design 300 Tice Boulevard Suite 101 Woodcliff Lake, New Jersey 07677 Main: 877 627 3772 Colliersengineering.com Project No. 24006174A

Table of Contents Limitation .............................................................................................................................................. 1 Introduction........................................................................................................................................... 2 Purpose .................................................................................................................................................. 2 Method .................................................................................................................................................. 2 Stormwater Quantity ............................................................................................................................ 3 1.1 Stormwater Management ..................................................................................................................................... 3 1.2 Summary Table........................................................................................................................................................ 3 1.3 Stormwater Management Facility Operations and Maintenance ................................................................ 3 1.4 Conveyance System................................................................................................................................................ 3 1.5 Downstream Stability ............................................................................................................................................. 4 Stormwater Quality............................................................................................................................... 4 Groundwater Recharge (N.J.A.C. 7:8-5.4).............................................................................................. 4 Groundwater Recharge Summary ................................................................................................................................. 4 Conclusion ............................................................................................................................................. 5 Appendix A HydroCAD Output Appendix B Recharge Worksheet Appendix C Existing and Proposed Drainage Area Map Appendix D USGS Soil Survey Location Map Appendix E Geotechnical Data Report Appendix F Stormwater

ix A HydroCAD Output Appendix B Recharge Worksheet Appendix C Existing and Proposed Drainage Area Map Appendix D USGS Soil Survey Location Map Appendix E Geotechnical Data Report Appendix F Stormwater Conveyance System HydroCAD Output – Failure Condition Conduit Outlet Protection Calculations Stormwater Management Report | October 18, 2024 – Last Revised December 3, 2025

Limitation The sole purpose of this report and the associated services performed by Colliers Engineering & Design, Inc., is to undertake a hydrologic assessment for the proposed residential development in accordance with the scope of services set out in the contract between Colliers Engineering & Design and Waystone Realty, LLC. Colliers Engineering & Design derived the data in this report from a variety of sources. The sources are identified at the time or times outlined in this report. The passage of time, manifestation of latent conditions or impacts of future events may require further examination of the project and subsequent data analysis, and re-evaluation of the data, findings, observations, and conclusions expressed in this report. Colliers Engineering & Design has prepared this report in accordance with the usual care and thoroughness of the consulting profession, for the sole purpose of the project and by reference to applicable standards, procedures, and practices at the date of issue of this report. For the reasons outlined above, however, no other warranty or guarantee, whether expressed or implied, is made as to the data, observations and findings expressed in this report. This report should be read in full, and no excerpts are to be taken as representative of the findings. No responsibility is accepted by Colliers Engineering & Design for use of any part of this report in any other context. This report has been prepared on behalf of, and for the exclusive use of Waystone Realty, LLC and is subject to, and issued in connection with, the provisions of the agreement between Colliers Engineering & Design and Waystone Realty, LLC. Stormwater Management Report | October 18, 2024 – Last Revised December 3, 2025 Page 1

Introduction This Stormwater Management Report for the proposed project has been prepared by Colliers Engineering & Design for Waystone Realty, LLC. Colliers Engineering & Design performed a hydrological assessment for the property located at 42 Eagle Ridge Way, West Orange, New Jersey, also defined as Block 106, Lot 24.01. The site is currently ±3.09-acres in size and was previously occupied by a single-family home and associated driveways and site improvements. The house was recently demolished and the property was cleared, and is currently occupied by stockpiles of gravel and other materials. The proposed development consists of the construction of a single-family home and a barn and indoor arena for the keeping of horses. There will also be an outdoor arena, grass paddocks, and associated driveways and pathways. The proposed development results in a total disturbance of approximately 3.07 acres and a total impervious area of approximately 0.85 acres (0.53-acre increase) within the proposed development area. Purpose This report assesses the hydrologic aspects, and the stormwater drainage conditions as a result of the proposed construction, including the house, barn, arenas, paddocks, landscaping areas, stormwater management facilities, associated utilities, and related site improvements. The focus of the study is the identification of the existing drainage characteristics prior to the demolition of the house in comparison to post-development conditions. Calculations documenting the design of the stormwater management system are illustrated on the Site Plan drawing documents, prepared by Colliers Engineering & Design. Method Generally, stormwater runoff from the site flows overland from west to east and discharges to an existing drainage channel located at the northeastern corner of the site (Design Point 1). The remainder of the site drains overland to the south (Design Point 2). The area, curve number, and time of concentration for each existing watershed can be seen on the Existing Drainage Area Map included in the appendix. For the purposes of this analysis the existing conditions include the previously demolished house and site improvements. Under proposed conditions, the site will generally mimic the existing drainage pattern; however, the majority of the proposed development will be captured and routed through a subsurface infiltration basin to

oposed conditions, the site will generally mimic the existing drainage pattern; however, the majority of the proposed development will be captured and routed through a subsurface infiltration basin to attenuate peak flows. New inlets and pipes will be installed to convey the stormwater runoff from certain areas to the infiltration basins. Tributary areas to the infiltration basin are outlined on the Proposed Drainage Area Map and include the house, barn, arenas, and the majority of the proposed pathways and paddocks. The area, curve number, and time of concentration for each proposed watershed can be found on the Proposed Drainage Area Map and HydroCAD output included in the appendix. Stormwater Management Report | October 18, 2024 – Last Revised December 3, 2025 Page 2

Stormwater Quantity 1.1 Stormwater Management As mentioned above, a subsurface infiltration basin has been designed to provide water quantity mitigation for the runoff discharging to the existing drainage channel. Initial geotechnical investigations on the site found bedrock in the area of the proposed basin at an approximate elevation of 611.00, and infiltration rates of 2.2 in/hr and 30 in/hr. A design infiltration rate of 1.0 in/hr was used for the proposed infiltration basin sizing. The Geotechnical Data Report for 42 Eagle Ridge Way is included as an appendix to this report. Full HydroCAD output calculations are provided in the appendix. The results are summarized in the table below. 1.2 Summary Table Description A. Existing Conditions Design Point 1 Required Reductions (50%, 75%, 80%) Design Point 2 Required Reductions (50%, 75%, 80%) B. Proposed Conditions Design Point 1 Design Point 2 2 Year Storm 10 Year Storm 100 Year Storm 3.95 cfs 1.98 cfs 0.77 cfs 0.39 cfs 8.17 cfs 6.13 cfs 1.63 cfs 1.22 cfs 18.32 cfs 14.66 cfs 3.70 cfs 2.96 cfs 1.75 cfs 0.37 cfs 5.37 cfs 0.74 cfs 14.42 cfs 1.64 cfs According to §25-29.4.r of the Township of West Orange, stormwater management measures shall be designed so that the post-construction peak runoff rates for the 2-, 10-, and 100-year storm events are 50%, 75%, and 80%, respectively, of the preconstruction peak runoff rates. As can be seen in the Summary Table above, the post-construction peak runoff rates for the 2-, 10-, and 100-year storm events have been reduced below the required peak runoff rates. 1.3 Stormwater Management Facility Operations and Maintenance The long-term operations and maintenance of the proposed stormwater management facilities shall be performed in accordance with the Stormwater Management Facility Operations & Maintenance Manual, which will be prepared prior to construction. This Manual will explain how often maintenance should be performed and how long it should take for the proposed on-site stormwater management systems to drain to ensure proper operation. 1.4 Conveyance System Pipe sizing calculations are included in the appendix of this report. Pipe sizing calculations were be performed using the Rational Method and 25-year design storm for capacity verification. Stormwater Management Report | October 18, 2024 – Last Revised December 3, 2025 Page 3

1.5 Downstream Stability The 25-year frequency discharge from the proposed infiltration basin is 5.27 cfs under failure conditions. This corresponds to a velocity of 3.52 fps discharging from the 18” diameter outflow pipe. The existing soils on site are Yalesville loam, 0 to 8 percent slopes, extremely stony, which have an allowable velocity of 5.0 fps. A 7.5 ft by 9 ft scour hole with a d50 of 4 in is proposed at the outflow of the proposed basin to provide additional conduit outlet protection and point of discharge stability. Scour hole sizing calculations are included in the appendix of this report. In accordance with the Standard for Off-Site Stability, the proposed peak flows are reduced to 50% and 75% of the predeveloped peak rates for 2 and 10 year storms, providing downstream stability. Stormwater Quality As per NJDEP Regulations, stormwater management measures shall only be required for water quality control if an additional ¼ acre of regulated motor vehicle surface is being proposed on a development site. For this project, the existing motor vehicle surface area totals approximately 0.13 acres and the proposed motor vehicle surface area totals approximately 0.35 acres, which results in an increase of 0.22 acres. Therefore, as the proposed improvements result in less than ¼ acre of new regulated motor vehicle surfaces, water quality treatment is not required. Groundwater Recharge (N.J.A.C. 7:8-5.4) To meet Township and NJDEP requirements for groundwater recharge, the proposed development is designed to maintain 100 percent of the average annual pre-construction groundwater recharge volume for the site. As the entire subject property falls within one (1) HUC-14 sub-watershed, compliance with the groundwater recharge standard is met by analyzing the site as a whole. The site is within the Passaic River Lower (Nwk Bay to Saddle) HUC-14 drainage area. The New Jersey Groundwater Recharge Spreadsheet, Version 2.0, November 2003 is utilized to calculate the post-development annual recharge deficit for the project site and annual recharge volume for each proposed BMP. The following table provides a summary of the post-development deficit and proposed recharge volume. Full calculation spreadsheets and a summary of the proposed recharge volume for each BMP are provided in the Appendix. Groundwater Recharge Summary HUC-14

opment deficit and proposed recharge volume. Full calculation spreadsheets and a summary of the proposed recharge volume for each BMP are provided in the Appendix. Groundwater Recharge Summary HUC-14 Drainage Area Pre-Development Total Annual Recharge (cubic feet) Proposed Annual Recharge Volume (cubic feet) Percentage of Average Annual Pre-Construction Groundwater Recharge Volume Passaic River Lower (Nwk Bay to Saddle) 150,467 200,794 133.45% Stormwater Management Report | October 18, 2024 – Last Revised December 3, 2025 Page 4

As shown in the above table, the proposed development is designed to maintain 100 percent of the average annual pre-construction groundwater recharge volume for the site. Conclusion As discussed above, water quantity mitigation is provided for all watersheds for all storm events studied in accordance with NJDEP and Township of West Orange regulations. A subsurface infiltration basin was utilized to achieve the required reductions for all Design Points. Furthermore, water quality treatment is not required for this project site. As such, there should be no adverse impacts due to stormwater, on-site or off-site, as a result of the proposed development. Included in the appendix of this report is the HydroCAD output for back-up on both the existing and proposed conditions. Additionally, the aforementioned Existing and Proposed Drainage Area Maps, an Inlet Area Map, Pipe Capacity Report, and Scour Hole Sizing Calculations are provided in the appendix of this report. Stormwater Management Report | October 18, 2024 – Last Revised December 3, 2025 Page 5