Revised Stormwater Management Report

DocuSign Envelope ID: DB0533B0-B14B-449D-A0A8-3B9C3C0DF5D9 Point of Analysis 2 This drainage area discharges to the Canoe Brook Tributary which exists at the site near the Warner Road entrance to the property. The stormwater management systems in this drainage area are small scale infiltration basins 2 , 7 & 10 and porous pavement systems 3,4, 8, &10. Each of these systems are considered green technology for quantity, quality and recharge. POA#2 Existing Conditions Tc Computations. This drainage area is in a forested cover with very light underbrush due to deer over browsing. The path of the existing conditions Tc is shown on the Existing Conditions Drainage Area Map. The Tc is calculated in the Hydrocad program with the factors shown on the map and is as follows. The Basin 2 contributing area is 850291 sf of Woods in good condition. The initial 100 LF is sheet flow with a slope of 4.5% in woods with light underbrush. Tc=14.9 min The next segment is shallow concentrated flow 1740 lf with a slope of 5.9% through woods with light underbrush. There is no discernable channel in the field along this path that would change the categorization of the flow type. Tc = 7.4 minutes. Total pre-development Tc= 22.3 minutes Small Scale Infiltration Basin 2 This stormwater system collects water from the parking lot and grass areas behind Building A. The total contributory area is 2.49 acres. The system will have soil replacement with a permeability of 4 inches per hour with a factor of safety of 2. The proposed Tc for the area flowing to Basin 2 uses the following input Sheet flow 93lf @5% over grass Tc= 9 minutes Shallow concentrated flow 370 lf over pavement @ 6.5% Tc = 1.5 minutes Total Tc = 10.5 minutes Basin 2 is designed as a small-scale basin with exfiltration at the rate of the replacement soil with a factor of safety of 2 as an outlet. Pre-treatment is achieved with MTD that is approved for 50% removal prior to discharge to the basin. 6