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Ms. Katie Larsen <br />5/06/2021 <br />Page 2 <br />Nadeau Acres 2nd Addition Engineering Review <br /> <br /> <br />After the project is completed, the site will include approximately 8.8 acres of new impervious <br />surfaces including the streets, sidewalks, paths, parking lots, and rooftops. Due to poor soils <br />in the south portion of the site and a high groundwater table in the north portion of the site, <br />infiltration is not feasible. <br /> <br />Groundwater was encountered at depths ranging from 4 to 19 feet. Topsoil was encountered at <br />½ to 1 foot. Below the topsoil, soils consist of glacial outwash sands and native clayey glacial <br />till and are classified as hydrologic groups HSG D in the southern portion and HSG C in the <br />north. <br /> <br />The applicant used a HydroCAD model based on the Atlas 14, 24-hour storms to design <br />the storm sewer conveyance system and ponds. The site is designed to reduce site runoff <br />rates for the 2-, 10-, and 100- year rainfall events. <br /> <br />Pre- and Post- Development Discharge Rates (cfs) <br />Condition 2-Year 10-Year 100-Year <br />Pre- <br />Development 19.2 46.7 103.3 <br />Post- <br />Development 9.8 32.2 87.0 <br /> <br />Post-development stormwater discharge rates are less than the pre-development rates. <br />Comments: <br />1. No comments at this time <br /> <br />• Water Supply <br />There is existing 8-inch diameter DIP watermain on Heritage Avenue that was <br />installed with the first addition construction. A 16-inch diameter DIP watermain exists <br />along the south side of Birch Street (CSAH 34). <br />The applicant is proposing an 8-inch diameter DIP watermain to serve Heritage <br />Avenue, Norma Way, and William Lane. The watermain will extend from the William <br />Lane to the south through Outlot A and connect into the existing 16” DIP watermain <br />on Birch Street (CSAH 34). <br /> <br />Comments: <br />1. Hydrants shall be spaced no more than 400 ft apart. Applicant to adjust <br />location of hydrant on William Lane to meet this requirement. <br />2. Anoka County Right-of-Way permit required for the Birch Street (CSAH 34) <br />connection. Staff recommends applying as soon as possible in case Anoka County <br />requires changes to the plans. <br /> <br />• Sanitary Sewer <br /> <br />There is existing 8-inch diameter poly-vinyl chloride (PVC) sanitary sewer stub on Heritage <br />Avenue that was installed with the first addition construction. <br /> <br />The applicant is proposing to serve the second addition with 8-inch diameter PVC sanitary <br />sewer. The proposed sanitary sewer drains to the existing sanitary sewer stub on Heritage <br />Avenue.