09-25-2013 Council Agenda - Laserfiche WebLink

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3.4 Storm Water Management Staff recommends installing new storm sewer throughout the neighborhood to correct existing drainage issues. Upgrading the existing storm sewer to current engineering standards is recommended as well. Best Management Practices (BMPs) such as bio - filtration basins, rainwater gardens, and underground filtration cells are proposed to improve the water quality, reduce volume and control the rate of storm water runoff in the area. These BMPs will be designed to meet Ramsey - Washington Metro Watershed District (RWMWD) requirements, as well as city treatment requirements. The proposed storm sewer layout, as depicted in Exhibit 14, utilizes underground infiltration cells, rain gardens, and bio - filtration basins at select locations to reduce runoff volume and improve water quality. The neighborhood project will offer residents the option of installing and planting individual boulevard rain water gardens to help homeowners participate in providing storm water treatment for the neighborhood as a whole. Sump manholes will be utilized prior to all outfalls in order to capture sediments prior to discharge. Energy dissipation and erosion protection measures will be provided at all outlets. The installation of underground infiltration cells, rain gardens, and bio - filtration basins as depicted in Exhibit 14, will meet or exceed the requirements of RWMWD based on preliminary calculations. The following is a brief summary of the proposed drainage in each of the existing drainage areas noted in section 2.53. 3.41 Drainage Area 2 — 33.43 Acres Drainage Area 2 covers the majority of Arkwright Street, Clark Street, Lark Avenue, Laurie Avenue, and McMenemy Street. Drainage Area 1 becomes a part of drainage area 2 under the proposed layout. The overall drainage pattern in this area will remain the same in the proposed layout, generally flowing northwest to the existing storm sewer system near McMenemy Street and Lark Avenue. The existing storm sewer system will continue to direct runoff into the MnDOT controlled ditch system along Highway 36. The following improvements are proposed within Drainage area 2. • Extend storm sewer piping and catch basins to the intersections of McMenemy Street at Laurie Road, Laurie Road at Arkwright Street, and Laurie Road at Clark Street to relieve existing drainage issues. • Remove the ditch system along the east side of McMenemy Street. The ditch system will no longer be necessary with the proposed storm sewer extension and concrete curb and gutter. The boulevard areas will be graded to drain to the street, relieving property owners of the burden of maintaining this ditch system. • Construct underground infiltration systems and boulevard rain gardens to reduce the amount of runoff and improve it's quality prior to discharge. 3.42 Drainage Area 3 — 0.69 Acres Drainage area 3 represents a small portion of Viking Drive and the surrounding boulevard area. Runoff from this area will continue to flow to the existing storm sewer system near 360 Viking Drive and discharge directly into the MnDOT ditch system along Highway 36. The addition of boulevard) raingardens in this area will aid in reducing the amount of runoff while improving it's quality. 16 26