Revised Stormwater Management Report

DocuSign Envelope ID: DB0533B0-B14B-449D-A0A8-3B9C3C0DF5D9 Porous Pavement system 9 Tc Computations System 9 collects stormwater from Road D from the clubhouse area past the Bridge crossing of the stream. The ratio of contributing areas to the Porous pavement area is 2.36 : 1 The system is above natural grade and backfill will be permeable soil meeting the permeability rate of 4 inches per hour with a factor of safety of 2. The proposed Tc for the area flowing to PP9 uses the following input Sheet flow 100 lf @ 10% over grass 7.2 minutes Shallow Concentrated Flow 40 lf @ 7.5% over grass .2 minutes Total Tc = 7.4 minutes The porous pavement system is considered green technology for both groundwater recharge and water quality. Small Scale Infiltration Basin 10 This stormwater system collects water from the roof of building D and the the roadway/ parking area in front of Building D and some adjacent grass areas. The total contributory area is 1.88 acres. The system will have soil replacement with a permeability of 4 in/hr with a factor of safety of 2. The proposed Tc for the area flowing to Basin 10 uses the following input Sheet flow 59 lf @2% over grass Tc= 9 minutes Shallow concentrated flow 210 lf over grass @ 4.8 % Tc = 1 minutes Pipe Flow 110 lf @ 2.5 fps .7 minutes Total Tc = 10.7 minutes Basin 10 is designed as a small scale basin with exfiltration at the rate of the replacement soil. Exfiltration is set at the replacement soil rate. Pre-treatment is achieved with MTD that is approved for 50% removal prior to discharge to the basin 9