240916_40 ERW Stormwater Report FULL

Proposed Residential Improvements Block 106, Lot 20.03 Township of West Orange, Essex County, NJ Prepared for: The Waymaker LLC 40 Eagle Ridge Way West Orange, NJ 07052 Prepared by: _______________________________ Jesse B. Cokeley, P.E. NJ Licensed 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 Stormwater Management Report September 16, 2024

Stormwater Management Report | September 16, 2024 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 ................................................................ 4 1.4 Conveyance System ................................................................................................................................................ 4 Stormwater Quality .................................................................................................................................... 4 Groundwater Recharge (N.J.A.C. 7:8-5.4) .................................................................................................. 4 Groundwater Recharge Summary ................................................................................................................................. 4 Conclusion ................................................................................................................................................... 5

Stormwater Management Report | September 16, 2024 Page 1 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 The Waymaker, 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 The Waymaker, LLC and is subject to, and issued in connection with, the provisions of the agreement between Colliers Engineering & Design and The Waymaker, LLC.

Stormwater Management Report | September 16, 2024 Page 2 Introduction This Stormwater Management Report for the proposed project has been prepared by Colliers Engineering & Design for The Waymaker, LLC. Colliers Engineering & Design performed a hydrological assessment for the property located at 40 Eagle Ridge Way, West Orange, New Jersey, also defined as Block 106, Lot 20.03. The site is currently ±2.07-acres in size and consists of a single- family home and associated driveways and site improvements. The owner previously obtained permits for and constructed a pool and pool house as part of a minor development, however due to unforeseen site conditions the project disturbed greater than 1 acre and therefore became a major development. The current project consists of the construction of a stormwater management system to bring the site into compliance as a major development, as well as the reconstruction of the existing paved driveway with pervious pavers. For the purposes of this report, the completed construction of the pool and associated improvements are considered as part of the proposed project. The proposed development results in a total disturbance of approximately 1.88 acres and a total impervious area of approximately 0.46 acres (0.13-acre increase) within the proposed development area. Purpose This report assesses the hydrologic aspects, and the stormwater drainage conditions as a result of the pool construction, including the pool, pool house, 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 construction of the pool 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 from west to east and discharges to an existing drainage channel located at the southern end of the site. A drainage pipe is located at the southeastern corner of the site which conveys runoff from the portion of the existing drainage channel located onsite to the portion of the existing drainage channel located downstream. The western portion of the existing site drains overland and via an existing storm sewer system

ting drainage channel located onsite to the portion of the existing drainage channel located downstream. The western portion of the existing site drains overland and via an existing storm sewer system to the portion of the channel located upstream of the pipe. The central portion of the existing site drains overland to the portion of the channel located downstream of the pipe. The remainder of the site drains overland to the east. The existing site is analyzed at the top of pipe (Design Point 1), at the beginning of the downstream channel (Design Point 2), and for the overall site (Design Point 3). 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 in order to adequately account for the existing building’s roof runoff the existing drainage areas do not include the buildings impervious area which is accounted for under proposed conditions as if it were proposed to be constructed.

Stormwater Management Report | September 16, 2024 Page 3 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 attenuate peak flows. New inlets and pipes will be installed to convey the stormwater runoff from certain areas to the infiltration basin. Tributary areas to the infiltration basin are outlined on the Proposed Drainage Area Map and include the house, the pool house, and surrounding lawn area. The previously installed drywell system is also included within this model and has a tributary area including the surrounding impervious areas around the Pool house and pool area. 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 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. As the site is located in HSG ‘C’ soils, infiltration is anticipated to be the minimum allowable 1 in/hr. Soil testing, including groundwater elevation determination, will be performed prior to construction. Full HydroCAD output calculations are provided in the appendix. The results are summarized in the table below. 1.2 Summary Table Description 2 Year Storm 10 Year Storm 100 Year Storm A. Existing Conditions Design Point 1 1.41 cfs 2.64 cfs 5.22 cfs Required Reductions (50%, 75%, 80%) 0.70 cfs 2.23 cfs 4.10 cfs Design Point 2 2.08 cfs 4.38 cfs 9.04 cfs Required Reductions (50%, 75%, 80%) 1.04 cfs 3.28 cfs 7.23 cfs Design Point 3 2.47 cfs 5.16 cfs 10.82 cfs Required Reductions (50%, 75%, 80%) 1.23 cfs 3.87 cfs 8.65 cfs B. Proposed Conditions Design Point 1 0.65 cfs 1.37 cfs 2.88 cfs Design Point 2 0.99 cfs 1.97 cfs 4.04 cfs Design Point 3 1.23 cfs 2.53 cfs 5.44 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

ts 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.

Stormwater Management Report | September 16, 2024 Page 4 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 prepared by Colliers Engineering & Design (under separate cover). This Manual explains how often maintenance should be performed and how long it should take for the proposed on-site stormwater management systems (porous pavement) to drain to ensure proper operation. Tables showing the data to support the listed drain times are included in the appendix of this report. 1.4 Conveyance System Pipe sizing calculations have been performed using the Rational Method and 25-year design storm for capacity verification. Calculations supporting pipe sizing are attached in the appendix of this report. 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 0.22 acres and the proposed motor vehicle surface area totals approximately 0.21 acres, which results in a decrease of 0.01 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

posed 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 Drainage Area Pre-Development Total Annual Recharge (cubic feet) Proposed Annual Recharge Volume (cubic feet) Percentage of Average Annual Pre-Construction Groundwater Recharge Volume

Stormwater Management Report | September 16, 2024 Page 5 Passaic River Lower (Nwk Bay to Saddle) 97,738 126,642 129.57% 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 and a Pipe Capacity Report are provided in the appendix of this report.