240916_40 ERW Stormwater Report FULL

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.