complete drainage report rev 9

Docusign Envelope ID: E802A2F1-2485-417E-948D-E0A4008C75BD Methodology The drainage for the development area of the property is calculated for the existing and proposed conditions for each of the three Points of Analysis. The proposed analysis is broken down into the overall un-detained in the analysis area and the flow to each of the stormwater management systems. The existing conditions for the site are considered wooded in good conditions per NJDEP guidance documents. Discharge rates for the existing conditions under the 2, 10 and 100-year storm events are calculated with The Hydrocad drainage program and the SCS TR-20 method. Hydrographs for the proposed conditions for areas detained and un-detained are developed. Allowable discharge rates for the detention system are calculated and the proposed hydrograph is routed through a proposed detention system until the desired discharge rate is achieved for each storm. Discussion Water Quality Each drainage basin uses green technology to achieve the required 80% suspended solid removal rate. Small-scale infiltration basins are paired with a pre-treatment separator to achieve 90% removal rate. Chapter 9.8 permits non-GI Approved MTD’s to be used as pre-treatment as noted on page 10. “Pretreatment may consist of a forebay or an BMPs found in chapter 9 or 11”. Porous pavement systems remove 80% per the BMP manual. Roof areas with roof leaders connecting directly to the porous pavement systems will have pre-treatment in the form of a cascade separator or leaf guard. The large-scale basin utilizes a green technology approved MTD (filterra) at its inlets to achieve the 80% water quality requirement. Water Quantity The stormwater system proposed has been designed to reduce the discharge from the site for the 2-, 10- and 100-year storms as required by the stormwater regulations. Each of the drainage/detention areas has been designed to control stormwater to below its current discharge rate. The results of the stormwater analysis for existing and proposed discharge are provided in the summary tables for each point of analysis. Detailed Hydrocad output is also included in the appendix of this report. Existing Conditions The analysis of the existing conditions was completed for the 3 points of analysis on the project. The 3 points are the Canoe Brook, The Canoe Brook Tributary and to the Howell Drive drainage system. Each

analysis of the existing conditions was completed for the 3 points of analysis on the project. The 3 points are the Canoe Brook, The Canoe Brook Tributary and to the Howell Drive drainage system. Each point of analysis assumes the surface condition of wood in good condition. The Tc for each POA drainage area is shown on the existing conditions drainage area map and utilizes type C soils except where a modification of the soil type has been verified by soil testing and reviewed by the NJDEP. In these instances, area of the site have been determined to be type D. The Theissens Polygon soil type map for the soil type determination is included in the appendix of this report. 3