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