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'/�'BOnCSi/00 <br /> Memo ��� <br /> Ergu�ea16 Archltecb <br /> Project Name: Hill School Client:City of Orono <br /> To:Tom Kellogg File No: 139-06-000 <br /> From: Lance Hoff Date:8-22-06 <br /> Re: Drainage Review <br /> Summary of Recommendations <br /> Based on our review of the Hill School Expansion, we offer the following comments: <br /> 1. A riprapped outlet should be provided for the proposed filtration basin. We estimate that a 2'-wide <br /> EOF at an elevation of 959 will help to control peak rates while maintaining the City's freeboard <br /> requirements. <br /> 2. Peak rates leaving the site have been modeled and are summarized below: <br /> Peak Flows(cfs) <br /> Location Existing Proposed* <br /> . 2-yr 10-yr 100-yr 2-yr 10-yr 100-yr <br /> NW 0.3 0.7 1.3 0.0 0.0 0.6 <br /> N E 0.4 0.7 1.2 0.8 1.2 1.8 <br /> Overall 0.7 1.4 2.5 0.8 1.2 1.9 <br /> "Includes an addition to the filtration basin of a 2'-wide riprapped <br /> emergency overflow at an elevation of 959. <br /> Existing peak rates to the NW have been adequately managed by utilizing the proposed filtration <br /> basin. Peak rates to the NE are shown to exceed existing conditions. While this would not typically <br /> meet City requirements, the additional flow the NE is likely manageable. The increase in peak rates <br /> is relatively small, largely due to the relatively small lot size (�0.6 acre). Routing of runoff from the <br /> east side of the site (parking lot) to the filtration basin would be difficult and unwanted due to <br /> existing drainage facilities located to the NW of the site. Just north of the site, a private draintile <br /> system conveys flows from a low area to the north. Our primary concern for this site is to ensure <br /> that any existing drainage problems in that area are not exacerbated. Modeling shows that peak <br /> rates and runoff volume will be decrease to the NW under proposed conditions. Overall existing <br /> peak flow rates have also largely been met for the site. Therefore, we do not recommend any <br /> modifications of the proposed site aside from Comment 1. <br /> Bonestroo, Rosene,Anderlik and Associates, Inc. <br /> 2335 West Highway 36+ St. Paul, MN 55113+ Phone: 651-636-4600+ Fax: 651-636-1311 <br />