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00082 <br /> shall be controlled through infiltration, retention or <br /> detention structures, and diversion devices. <br /> IV-B-9-C. -Infiltration Standards <br /> For all new subdivisions, the preliminary and/or final plat may not <br /> be approved unless provision has been made for controlling the <br /> first one-half (1/2) inch of stormwater runoff from impervious <br /> surfaces. Impervious surfaces are those areas which prevent <br /> infiltration of water into the soil and include parking areas, <br /> roads, sidewalks, and other similar facilities constructed of <br /> asphalt and/or concrete. <br /> Control of stormwater runoff shall be accomplished insofar as <br /> possible through on-site infiltration of the first one-half (1/2) <br /> inch of runoff and through the use of methods which rely on natural <br /> soil properties for absorption and treatment. Infiltration <br /> techniques not only remove both suspended and dissolved pollutants, <br /> but they require less maintenance, reduce flooding, promote <br /> groundwater recharge and help maintain stream flow during dry <br /> periods. <br /> Where, due to soil type, steep slopes, presence of flood plains, <br /> highly erodible soils, vegetative cover and/or previous land <br /> disturbances, infiltration is impractical, the following <br /> alternative measures may be permitted: <br /> 1) Flow attenuation methods, such as grass swales, to reduce <br /> runoff velocity and filter out pollutants. <br /> 2) Retention ponds which capture stormwater runoff allow <br /> suspended pollutants to settle out and release the runoff at <br /> reduced rates. <br /> 3) Retention ponds with no outlet structures which retain all <br /> runoff until it infiltrates or evaporates. <br /> Where on-site infiltration methods are utilized, areas for such <br /> purposes shall be designated on the plat and shall remain <br /> undisturbed both during and after construction. Undisturbed areas <br /> for infiltration of runoff shall also be located downslope from <br /> impervious surfaces and shall not include areas characterized by <br /> floodplains, highly erodible or impervious soils, steep slopes or <br /> previously disturbed areas. Areas designated as suitable for <br /> septic tank nitrification fields may not be used for stormwater <br /> infiltration purposes. Runoff from roads, parking lots and/or <br /> sidewalks shall be directed to undisturbed areas through the use of <br /> beams, grassed diversion ditches or swales, or other acceptable <br /> means. <br />