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Some filters include [[additives]] such as zeolite or iron to enhance the contaminant removal process for target water quality variables by increasing chemical adsorption and/or precipitation.
Some filters include [[additives]] such as zeolite or iron to enhance the contaminant removal process for target water quality variables by increasing chemical adsorption and/or precipitation.
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+==Key system design parameters==
+When sizing filtration systems for specific sites using local historical rainfall records, several key system design parameters need to be considered. These are defined in the sizing section of the Filtration MTD page.
+Non-proprietary bioretention systems are sized as filters much more conservatively based on design storms, surface ponding depth and minimum media infiltration rates. The ratio of drainage area imperviousness to the surface area of bioretention facilities (referred to as the impervious-to-pervious ratio) is often many times lower than that for filtration MTDs. This ensures longer intervals for sediment maintenance and significant reductions in stormwater volumes through infiltration. See here for more information on sizing.
+Permeable pavements can also be considered to be a type of filter. In this case, runoff and rainwater is filtered through the surface pores or granular media between the pavers, as well as through the bedding and base layers. Most of the sediment directed onto the pavements is trapped near the surface where it can be more easily accessed for cleaning. Since permeable pavements need to maintain a high rate of infiltration to avoid ponding, the area of impervious surface draining on to them should be no larger than the area of the permeable pavement itself. See here for more information on permeable pavement sizing.