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Orono Garage Condos – Orono, MN <br />September 18, 2024 <br />Page 3 <br /> <br /> <br />t 320.759.0764 | 219 6th Avenue East, Alexandria, MN 56308 | www.hagstromeng.com <br /> <br /> <br />With the proposed design, runoff will generally follow historic drainage patterns by <br />ultimately discharging to the south. A regional drainage facility is located <br />approximately 0.18 miles to the east of the site, which will provide detention for all <br />storm frequency events. A water quality pond will be implemented on site to <br />account for the increased site impervious per Minnesota Pollution Control Agency <br />criteria. See below for detailed description of the proposed drainage system and <br />Appendix C for historic and proposed drainage maps. <br /> <br /> There are no waters within one mile of the site that have an EPA -approved <br />impairment, therefore no additional best management practices or plan review for <br />compliance with the NPDES/SDS construction permit is required. See Appendix A <br />for impaired waters map. There are no wetlands that exist on the site. There are <br />no other protected areas known to exist on the site. <br /> <br />C. Adjacent Areas <br />There are no existing access points to the site. An apron will be constructed under <br />proposed conditions creating an access from Orono Industrial Boulevard. <br />This site is located on FEMA FIRM Map Number 27053C0302F and is shown <br />within Zone X which indicates that there are no floodplains located on the site. <br />Refer to Appendix A for the FIRMette. <br /> <br />II. DRAINAGE BASIN <br /> <br />A. Major Drainage Basin <br />All stormwater runoff from impervious areas on site will be routed to the proposed <br />water quality control volume (WQCV) pond. For preliminary analysis, the following <br />calculation was completed to size the pond: <br /> <br />WQCV = 1” x New Impervious Area = 1” x 3.87 acres = 14,027 cubic feet <br /> <br />Larger storm events will be routed downstream where they will be treated by the <br />existing regional facility. Please see the appendices for the Proposed Drainage <br />Map. <br /> <br />III. DRAINAGE DESIGN CRITERIA <br /> <br />A. Regulations <br />This drainage report has been prepared in conformity with the City of Orono, the <br />Minnehaha Creek Watershed District, and the Construction Stormwater General <br />Permit for the State of Minnesota. <br /> <br /> <br />97