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<br />SITE DRAINAGE NARRATIVE <br />PAGE 1 OF 4 <br />VILLAS OF LAKE GERVAIS <br />(Little Canada, Ramsey County) <br />Site Drainage Narrative & Storm Water Calculations <br />Date: July 25, 2022 <br />Revised: September 14, 2022 <br />Revised: September 21, 2022 <br />Revised: January 3, 2023 <br /> <br />This project proposes the subdivision of a 3.1-acre undeveloped property into single-family residential <br />lots. The site is located on the west side of Edgerton Street (CSAH 58), north of Little Canada Road. The <br />site falls within the Ramsey Washington Metro Watershed District. <br /> <br />Soils <br />A USDA NRCS web soil survey shows that site consists of 35% Zimmerman fine sands (north) and <br />65% Zimmerman complex sands (south.) The Zimmerman sands are generally very well-draining <br />granular soils. which are typically modeled as HSG “A” type soils. <br /> <br />Site specific borings show varying thicknesses of topsoil over poorly graded sand with silt (SP- <br />SM), silty sand (SM), sandy lean clay (CL), and sandy silt (ML). Boring #5, located in the proposed <br />BMP, shows clay at a depth of about 4 feet. But most of the soils immediately beneath the <br />topsoil are sandier, so HGS B soils will be assumed. <br /> <br />Storm Water Modeling <br />Modeling uses HydroCAD with Atlas 14 rainfall events and MSE Type 3 storm distribution. HSG <br />“B” type soils are assumed based on soils data noted above. The rainfall events are as follows: <br /> <br /> 2-year storm = 2.81” <br /> 10-year storm = 4.19” <br /> 100-year storm = 7.39” <br /> <br />The following curve numbers area assumed: <br /> <br /> Impervious & Gravel CN = 98 <br /> Open water CN = 98 <br /> Grass (>75%) CN = 61 <br /> Woods CN = 55 <br /> <br />Wetlands <br />The site was inspected for wetlands and none were found. <br /> <br />Existing Conditions <br />In existing conditions, the site is heavily wooded on the north side, with less tree coverage on <br />the south side. There is an existing concrete pad, presumably for a tennis court. There is no <br />other impervious on the site. The site primarily drains north to a low area, some run-off going <br />directly through the site, and the rest draining onto Edgerton and then to the low area. Field