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<br />6.233 STORMWATER INFILTRATION AND DETENTION <br />As a watershed beccnnes more developed, the amount of impervious surface increases, <br />causing a decrease in the rate at which stormwater runoff which can be absorbed into the <br />soil. This results in more stormwater flowing directly into streams and other water bodies. <br />Because this direct runoff has not been filtered through the soil, pollutants from the air and <br />land surface enter streams and increase the potential for pollution of drinking water <br />supplies. <br />The effects of stormwater pollution on drinking water supplies can be minimized by one of <br />two general approaches. First, the amount of stormwater runoff which reaches drinking <br />water supplies can be controlled by assuring that there is adequate ground area into which <br />water can be absorbed.. This type of non-structural control is achieved through limitations <br />on impervious surface. A second approach is to collect stormwater run-off in engineered <br />ponds so that pollutants may settle. The water is then slowly released and contains fewer <br />impurities when it reaches the water supply reservoir. The watershed protection standards <br />adopted by Orange County utilize a combination of these two approaches. <br />a) Non-Structural Stormwater Control <br />The first inch of stormwater run-off shall be controlled to the extent possible <br />through on-site infiltration and through the use of methods which rely on natural <br />soil properties for absorption and treatment. <br />In order to promote infiltration of stormwater runoff into the soil and minimize <br />direct and immediate runoff into streams and water supply impoundments, the <br />maximum percentage of the total lot area which may be covered with an impervious <br />surface shall be specified. This limit is referred to as the "impervious surface ratio". <br />lmpervious surface calculations for an individual development shall be cumulative <br />for original construction and any subsequent additions. One-half of the width of any <br />of any existing or proposed road adjacent to an individual lot shall be included as <br />impervious surface for that lot, except in the case where an existing road was <br />contained within a dedicated public right-of--way at the time that the watershed <br />a~ulations were first applied to the watershed within which the development is <br />1.. <br />Infiltration techniques not only remove both suspended and dissolved pollutants, but <br />they require less maintenance, reduce flooding, promote groundwater rechazge and <br />help maintain stream flow during dry periods. <br />Where on-site infiltration methods are utilized, areas for such purposes shall be <br />designated on the plat and shall remain undisturbed both during and after <br />construction. Undisturbed areas for infiltration of run-off shall also be located <br />downslope from impervious surfaces and shall not include areas characterized by <br />floodplains, highly erodible or impervious soils, steep slopes or previously disturbed <br />