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Orono Garage Condos – Orono, MN <br />September 18, 2024 <br />Page 2 <br /> <br /> <br />t 320.759.0764 | 219 6th Avenue East, Alexandria, MN 56308 | www.hagstromeng.com <br /> <br />INTRODUCTION <br /> <br />The purpose of this Preliminary Drainage Report is to determine the effects of the <br />proposed civil construction design of the Orono Garage Condos (site) within the <br />historic condition, as well as to design proper conveyance for the developed <br />stormwater runoff within the site in accordance with all applicable criteria. <br />I. GENERAL LOCATION AND DESCRIPTION <br /> <br />A. Site Location <br />The site analyzed for this report is located in Lot 1, Block 1, Crystal Bay Business <br />Center, Hennepin County, MN. The site falls within the City of Orono as well as the <br />Minnehaha Creek Watershed District (MCWD). The site is bound by Orono <br />Industrial Boulevard on the north, private property on the east, State Highway 12 <br />on the south, and Old Crystal Bay Road N on the west. See Appendix A for the <br />vicinity map. <br /> <br />B. Description of Property <br />The historic site analyzed in this report contains grassed areas and trees totaling <br />4.89 acres with 0 acres of impervious surfaces. With the proposed construction, <br />the total disturbed area of the site will be over 1 acre with 3.87 acres impervious <br />surfaces. <br /> <br />According to the Natural Resources Conservation Service, three soil types exist <br />within the site. The soil types are Cordova loam, 0 to 2 percent slopes, Le Sueur <br />loam, 1 to 3 percent slopes, and Hamel-Glencoe complex, 0 to 2 percent slopes <br />all belonging to Hydrologic Soil Group (HSG) C. Soils within HSG C are defined <br />as having a slow infiltration rate when thoroughly wet. Refer to Appendix A for <br />the soils report and map. <br /> <br />The historic site drains to three locations – south to an existing ditch, to the middle <br />of the site where an existing ditch draining south is located, and to the east as <br />sheet flow. All drainage ultimately reaches the ditch south of the site that runs <br />east. Slopes on site range from 1.5 percent to 45 percent. <br /> <br />The historic site is 0% impervious and was broken into three drainage basins, each <br />allowing runoff to flow to a different location. Under existing conditions, stormwater <br />runoff from the north is routed onto the site, contributing to the middle ditch running <br />south. Under proposed conditions, this contribution will be re-routed to an existing <br />storm sewer stub on the east side of the site, routing the runoff around the site. No <br />other offsite basins were analyzed as stormwater runoff from offsite is routed <br />around the site. <br />96