J_2024 05 09_West Orange Stormwater Management Plan

PSE&G West Orange Switching Station West Orange, NJ Stormwater Management Report 2. Analysis of Pre-Development Stormwater Runoff This section presents hydrologic data and information to demonstrate that peak stormwater runoff flows under post development conditions will not exceed those under pre-development conditions during the 2-year, 10-year, and 100-year, 24-hour rainfall events. The analysis was performed using the methodology described in Technical Release No. 55, Urban Hydrology for Small Watersheds, published by the United States Department of Agriculture, Soil Conservation Service, dated June 1986. Hydrologic modeling was performed using HydroCad stormwater software developed by HydroCAD Software Solutions LLC. Pre-development runoff rates were determined by subdividing the drainage area into nine smaller drainage areas by land use. Existing land uses are listed in Table III-1. The PreDevelopment Drainage Area Plan is included in Appendix B. Table III-l Pre Development Drainage Areas1,2,3 LAND USE Impervious (Foundations) Gravel Road Gravel Yard Stone Meadow Grass Brush NonContributory Total EXDA 1 (ft2) EXDA2 (ft2) EXDA3 (ft2) EXDA4 (ft2) EXDAS (ft2) EXDA6 (ft2) EXDA? (ft2) EXDAS (ft2) EXDA 9A (ft2) EXDA 9B (ft2) 11158 4190 3042 31370 17517 9501 805 15912 1344 24703 661 0 0 0 53293 14189 0 0 0 0 10038 3705 35019 29686 0 26372 30906 0 5072 12803 8134 0 21568 0 0 0 0 0 2694 0 8481 0 43082 0 57041 27592 2198 0 10157 0 86177 5402 0 0 29261 0 1535 0 0 0 20580 0 0 0 0 670 20336 0 0 0 0 0 1964 0 982 0 0 79301 17933 125025 78947 20211 147661 104739 47690 21924 45709 1) 2) 3) 0 0 0 See Appendix B - Pre-Development Drainage Area Plan The total area within the Limit of Disturbance is 10.3 acres or 448,819 ft2. The total area within the Drainage Area is 15.8 acres or 686,140 ft2. The existing transformer secondary containment basin was assumed to be non-contributory under pre-development conditions. Rainfall totals for each event were obtained from the National Oceanic and Atmospheric Administration (NOAA) Atlas 14 for West Orange, NJ and are summarized in Table III- 2. TRC Engineers, Inc. 10 March 2012