2022 08 Drainage Report

Study Area Basin D: This area consists primarily of the stormwater runoff associated with the development of improvements associated with the proposed Lot 4 located at the north-west portion of the tract, which includes the proposed single-family residential house, driveway, a small portion of Ridge Road, and open grass/lawn cover. Stormwater runoff from this area will flow overland to the proposed bioretention basin located at the east side of the proposed lot. Stormwater runoff generated within this area is ultimately tributary to Mount Pleasant Avenue located at the east of the site. V. DESIGN METHODOLOGY The intention of the design of the proposed stormwater management facilities for this development is to provide measures as required to address the applicable aspects of the Township of West Orange Land Use Ordinance and NJAC 7:8. In order to prepare the stormwater management design for the subject site, extensive initial investigation of the property and topography was performed. On-site review of the tract was initially performed by Dynamic Engineering Consultants, PC to verify existing site conditions and land cover characteristics. Dynamic Survey, LLC was contracted to prepare the ALTA/NSPS Land Title Survey with topography to depict the existing site conditions. Furthermore, Dynamic Earth, LLC performed test pits within the site to establish the seasonal high-water table and soil permeability rates. Based on our review of the existing site conditions and survey, the Drainage Area Maps for the existing and proposed site conditions as defined within this report were established. A grading plan was developed for the proposed site improvements with consideration to the existing drainage patterns. The plan was designed to ensure runoff from the proposed development could be directed to stormwater management facilities in order to address the applicable sections of the Township of West Orange Land Development Ordinance and NJAC 7:8. The rainfall data utilized for the analysis of the existing and proposed drainage conditions is based upon the New Jersey 24 Hour Rainfall Frequency Data for Essex County as published by the USDA NRCS utilizing the NOAA Region D rainfall distribution. Under proposed conditions, the stormwater runoff from the subject site and surrounding areas is conveyed by overland flow for collection by the proposed aboveground

AA Region D rainfall distribution. Under proposed conditions, the stormwater runoff from the subject site and surrounding areas is conveyed by overland flow for collection by the proposed aboveground small-scale bioretention basins with underdrains. The proposed basins are designed to detain and infiltrate through the planted vegetation in the soil bed to the underdrains and be released at a controlled rate through outlet control structures in order to satisfy the runoff peak rate reductions (quantity requirement) set forth by the Township of West Orange and NJAC 7:8. The overall stormwater management design for the subject site has been evaluated by Dynamic Engineering Consultants to ensure that the overall development satisfies the standards set forth in the Township of West Orange Land Use Ordinance and NJAC 7:8. SHI Builders August 2022 DEC# 4266-99-001 -4-