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Schoell Madson <br />Planning Engineering Surveying <br />June 2, 2006 <br />Ken Powell <br />Rice Creek Watershed District <br />4325 Pheasant Ridge Drive, Suite 611 <br />Blaine, MN 55449 <br />Re: Stormwater Management Plan <br />Walser Buick Pontiac GMC of Roseville <br />Dear Ken, <br />15050 23rd Ave�ue North <br />Plymouth, MN 55447 <br />T 163-746-1600 <br />F 163-746-1699 <br />www,schoellmadso�,com <br />On behalf of Phillips Architects, Schoell Madson is submitting this stormwater management plan <br />for the Walser Buick Pontiac GMC project located at 2775 Highway 35 North in Roseville. <br />Existing Conditions <br />The site is occupied by a automobile dealership facility that is nearly 100% impervious. The <br />entire site is directed via storm sewer and direct overland flow to a regional pond to the south of <br />the project. <br />Proposed Conditions <br />The proposed plan for the site calls for the demolition of the existing building and construction of <br />a new building, the total hardcover on the site will be reduced to approximately 95%. We have <br />been directed by the city to reduce the flow rate off the site by 25%. We are proposing to use an <br />underground detention/infiltration facility to meet this requirement for the site. This underground <br />facility will make use of the StormTech system, which consists of parabolic arch chambers with <br />open bases that are enveloped in angular stone and geotextile. Rate control is achieved by <br />utilizing the storage volume in a combination of the open spaces of the chambers and the voids in <br />the angular stone. The system will also provide improvements to water quality through infiltration, <br />as the water in the rock envelope will seep through the stone envelope and into the underlying <br />aggregate layer where it will be picked up by draintile. <br />