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I I ,. I I I I I I .. I I I I I I I , I 9,7.01 The term structural BMP refers to a physical facility designed and constructed to remove pollutants from storm water runoff, potentially reduce downstream erosion, provide flood control, and promote ground water recharge. Typical structural BMPs include: . Detention basins . Retention basins . Constructed wetlands . Infiltration practices . Filters . Biofilters (swales and filter strips) . Precast or cast-in-place treatment devices. The typical capital costs for BMPs were evaluated based upon a recent U.S. Environmental Protection Agency document entitled: Preliminary Data Summary of Urban Storm Water Best Management Practices, (Office of Water, Washington, D.C. August, 1999. EPA-82l-R-99-012). Table 9 has been adapted from the USEPA document (Table 6-1, page 6-3) to show typical capital construction costs. Table 9 Annual Operating Costs BM? Type Typical Cost' Notes Annual Maintenance Cost ($/cf) , (% of Construction Cost) Retention and 0.55-1.11 Cost range reflects economies of scale 3%-6% Detention Basins in designing this BMP. The lowest unit cost represents approx. 150,000 CF of Istorage, while the highest is approx. 15,000 CF. Constructed 0.66 - 1.38 Little data available to assess cost. It is < 1% Wetland assumed they are approx. 25% more expensive due to plant selection and sediment forebay requirements than detention basins. Infiltration Trench , 4.43 I ~epresents typical cost for a 100-foot 2% long trench. Infiltration Basin 1.44 I Represents typical cost for a 0.25-acre 5%-10% infmration basin. Sand Filter 3.32 - 6.65 Range in costs largely due to different 11%-13% designs, Of the three mosf common, perimeter sand filters are moderate cost while suliace and underground sand filters are the most expensive. City of Arden Hills, Minnesota Local Water Resource Management Plan A,ARDEN0101.00 Page 45