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Description: <br />Filtration devices, depending on the design, <br />can treat stormwater to reduce nutrients, <br />sediment, floatables, metals, oil, and/or organic <br />compounds. Different filtration media are <br />used depending on the type of pollutant to be <br />removed. Filter media may be a screen, fabric, <br />activated carbon, perlite, zeolite, or other <br />materials. Often a combination of filter media <br />can be used to target the specific pollutants of <br />interest. <br />These devices differ from the structural <br />stormwater filters described in Chapter 12 <br />in two aspects. First, these devices are <br />proprietary and are designed to fit as an insert <br />into the hydraulic infrastructure (eg. a catch <br />basin). Second, the media material may have <br />unique characteristics which are different from <br />the soil/sand media recommended for general <br />stormwater filtration. <br />Filtration devices have been developed <br />for use in locations such as underground <br />chambers, catch basins, trench drains, and <br />roof drains. The manufacturer specifications <br />should indicate key design parameters such <br />as size, allowable flow rate, allowable pollutant <br />concentrations, and removal efficiency. A <br />bypass should be part of the system to allow <br />high flows to circumvent the filtration device. <br />Performance data are often provided by <br />the manufacturer. Users should review this <br />information to ensure it was provided by an <br />independent source. <br />The MPCA Construction General Permit allows <br />limited use of proprietary devices or "alternative <br />methods." Use of the alternative device <br />as a stand alone BMP must be approved <br />by the MPCA prior to installation. Approval <br />is limited to those devices that achieve <br />approximately 80% removal of total suspended <br />solids. Additionally, the MPCA requires a <br />two-year monitoring plan to measure the <br />actual effectiveness of the method. If a device does <br />not meet this 80% total suspended solids removal <br />requirement, then these devices could be used as <br />pretreatment or supplemental to another stormwater <br />practice. <br />Selection: <br />When selecting or specifying a filtration device, <br />designers should research the following: <br />1. What are the minimum or maximum drainage <br />areas recommended for the device or method? <br />2. What flow rates or volumes can the device <br />accommodate? Will accessory structures <br />be necessary to divert high flow around the <br />filtration device? <br />3. What are the characteristics of the pollutants in <br />the water used for testing? What particle size <br />distribution was tested? Research protocols <br />used for testing. <br />4. Are pollutant removal tests verified by <br />independent organizations such as USEPA, <br />University of New Hampshire, University of <br />Minnesota, Wisconsin Department of Natural <br />Resources, or others? <br />5. Does the device contain a by-pass for high <br />flows? If so, then what is the percentage of <br />flow is prior to by-pass. <br />6. What are the construction costs? Does the cost <br />include all materials, installation, and delivery? <br />7. What are the maintenance requirements? What <br />are the costs of the required maintenance? Is <br />there a standard operation and maintenance <br />plan? What is the typical life of the filtration <br />unit? <br />8. Does the local regulatory authority approve the <br />use of filtration devices? <br />9. Will the manufacturer provide design <br />computations and CADD details? <br />Chapter 12 -FACT Volume 2 2005 Minnesota Stormwater Manual, Version 1.0 <br />