Revised Stormwater Management Report

DocuSign Envelope ID: DB0533B0-B14B-449D-A0A8-3B9C3C0DF5D9 The Basin 1 contributing area is 414691 sf of Woods in good condition. The initial 100 lf (linear feet) is sheet flow with a slope of 5% in woods with light underbrush. Tc=14.3 min The next segment is shallow concentrated flow 1980 lf with a slope of 5.4% 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 = 8.8 min. Total pre-development Tc= 23.1 minutes Large Scale Infiltration Basin #1 This stormwater system collects water from Kusik Drive and the lawn areas adjacent. The total contributory area outside the basin itself is 2.5 acres but when the basin area is included the total drainage area is 3.49 Acres. The proposed Tc for the area flowing to Detention 1 uses the following input Sheet flow 59 lf @2% over grass Tc= 9 minutes Shallow concentrated flow 425 lf over pavement @ 6.5% Tc = 1.7 minutes Pipe flow 425 lf pipe , 2.5 fps Tc = 3.4 minutes Total Tc = 14.1 minutes Basin 1 is designed as a large scale basin without exfiltration as an outlet. The Basin details do include soil replacement with a permeable sand to allow infiltration to occur. Water quality is achieved with MTD’s at each inlet location. Porous Pavement system #5 Porous pavement #5 collects stormwater from the Building B parking lot, Building B roof and grass areas around the building. The total drainage area is 1.07 acres with the majority of that area the building roof or the porous pavement surface. The ratio of other contributing areas to the Porous pavement area is .4 : 1 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 PP5 uses the following input Sheet flow 40 lf @2% over pavement Tc= .6 minutes Pipe flow 182 lf pipe , 2.5 fps Tc = 1.2 minutes Total Tc = 1.8 minutes The porous pavement system is considered green technology for both groundwater recharge and water quality. 4