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I I I I I I I I I I I I I I I I I I I 2.11.02 Table 9 Capital and Maintenance Costs for BMP's . BMP Type Typical Cost' Notes Annual Maintenance Cost ($tcf) (% of Construction Cost) Retention and 0.55-1.11 Cost range reflects economies of scale 30/0 - 6% Detention Basins in designing this BMP. The lowest unit cost represents approx. 150,000 CF of storage, 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 lhan detention basins. infiltration Basin 1.44 Represents typical cost for a 0.25-acre 5%-10% infiltration basin. Sand Filter 3.32 - 6.65 Range in costs largely due to different 11%-13% designs. Of the three most common, perimeter sand filters are moderate cost while surface and underground sand filters are the most expensive. Bioretention 5.87 Bioretention is relatively constant in cost 5%-7% because it is usually designed as a constant fraction of the total drainage cost. Grass Swale 0.55 Based on cost per square foot, 5%-7% assuming 6 inches of storage in filter. FiiterStrip 0-1.44 Based on cost per square foot, $320/acre (maintained) assuming 6 inches of storage in the filter strip. The lowest cost assumes that the buffer uses existing vegetation, while highest cosl assumes that sod was used to establish the filter strip. . e TypICal capItal cost on a volume basIS: August 2001 While detention ponds have an initial high cost for construction, their annual operation and maintenance cost is among the lowest of alternatives. Table 10 illustrates the capital cost estimate for the proposed treatment ponds. Also provided in the table is the unit cost per cubic foot of pond storage. The USEP A cost is taken from the aforementioned document unit cost. . City ot Arden Hills, Minnesota Local Water Resource Management Plan A-ARDEN010l.00 Page 47