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<br />SITE DRAINAGE NARRATIVE <br />PAGE 3 OF 4 <br />Total new impervious area to the IESF: <br /> 32,296 sf New impervious <br /> <br />This is approximately 80% of the new impervious (32,296 ÷ 40,229) x 100 = 80.0%. Additionally, <br />there is some existing impervious that is also to the basin; this area is included in the model but <br />not included when computing the required treatment volume (it is not disturbed.) <br /> <br />The maximum allowed credit in the IESF basin is: <br /> 32,296 sf x 1.1-in x 1/12 x 2.5-in = 7,401 cf <br />The basin meets this requirement. <br /> <br />To maximize run-off capture at the catch basins, high-capacity inlets are proposed; there is a city <br />standard detail for this (included in the plans.) These have been added to the HydroCAD model; <br />they have limited storage area but do have 6” for head build-up and two orifices: <br /> Horizontal Orifice (Neenah R-3067-VB) <br /> Square foot opening = 2.7 sf <br /> (Covert to 22.2-in diameter horizontal opening for modeling) <br /> Vertical Orifice (Neenah R-3067-VB) <br /> Modeled as 6-in high x 36-in tall vertical opening <br /> <br />Per the HydroCAD model, both sides of the road have 100% interception. <br /> <br /> <br /> <br /> <br /> <br />