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BMP Descriptions <br />In heavily urbanized settings stormwater is immediately intercepted along roadway catch basins and <br />conveyed rapidly via storm sewer pipes to its destination. Once stormwater is intercepted by catch <br />basins, it can be very difficult to supply treatment without large end -of -pipe projects such as regional <br />ponds. One of the possible solutions is the hydrodynamic device (Figure 7). These are installed in -line <br />with the existing storm sewer network and can provide treatment for up to 10-15 acres of upland <br />drainage. This practice applies some form of filtration, settling, or hydrodynamic separation to remove <br />coarse sediment, litter, oil, and grease. These devices are particularly useful in small but highly <br />urbanized drainage areas and can be used as pretreatment for other downstream stormwater BMPs. <br />Each device's pollutant removal <br />potential was estimated using <br />WinSLAMM. Devices were sized based <br />on upstream drainage area to ensure <br />peak flow does not exceed each device's <br />design guidelines. For this analysis, <br />Downstream Defender devices were <br />modeled based on available information <br />and to maintain continuity across other <br />SRAs. Devices were proposed along <br />particular storm sewer lines and often <br />just upstream of intersections with <br />another, larger line. Model results <br />assume the device is receiving input <br />from all nearby catch basins noted. <br />Pavement 1 <br />Surface <br />Oillfloatable <br />collection chamber <br />Treatment How Inlet <br />Path. Stormwater <br />eaters device, flaws <br />downward, then <br />travels alone devices <br />_w <br />periphery in a vortex <br />manner <br />Stormwater <br />treatment vortex <br />Cleanout access <br />In order to calculate cost -benefit, the <br />N <br />cost of each project had to be estimated.Chamber: <br />Sediment Collection. <br />Settleable <br />To fully estimate the cost of project <br />solids collect at base <br />device isolated <br />installation, labor costs for project <br />of <br />from the energy of <br />outreach, promotion, design, <br />the treatment flow <br />administration, and maintenance over <br />path preventing <br />a resusI� ension of <br />. <br />the anticipated life of the practice were <br />collected material <br />considered in addition to actual <br />construction costs. Load reduction Figure 7: Schematic of a typical hydrodynamic device <br />estimates for these projects are noted in the Catchment Profiles section. <br />21 <br />City of Ramsey Stormwater Retrofit Analysis <br />