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27 <br /> reduce flooding,promote groundwater recharge and help maintain stream flow during dry <br /> 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 construction. <br /> Undisturbed areas for infiltration of run-off shall also be located downslope from <br /> impervious surfaces and shall not include areas characterized by floodplains, highly <br /> erodible or impervious soils,steep slopes or previously disturbed areas. Areas designated <br /> as suitable for septic tank nitrification fields may not be used for stormwater infiltration <br /> purposes. <br /> Run-off from roads, parking lots, and/or sidewalks shall be directed to undisturbed areas <br /> through use of berms, grassed diversion ditches or swales, or other acceptable means to <br /> reduce run-off velocity and filter out pollutants. <br /> b) Structural Measures <br /> Non-structural methods may not adequately control the first inch of stormwater runoff <br /> due to the amount of impervious surface proposed to be developed, and other factors <br /> such as soil type, slope, presence of floodplains and erodible soils, and/or lack of <br /> vegetative cover. In such cases, structural detention ponds, which capture stormwater <br /> for slow release through an outlet, are required. Where required, detention ponds shall <br /> be constructed in accordance with Appendix <br /> c) Impervious Surface and Detention Pond Requirements <br /> For all protected watersheds, there is a absolute limit on the percentage of lot area which <br /> can be covered with impervious surfaces. In some cases, detention ponds are required <br /> when the proposed impervious surface ratio exceeds a specified percentage, which is <br /> below the absolute limit. <br /> 1. Residential Development <br /> Impervious Surface/detention pond standards as shown in the following tables have <br /> been revised as follows: <br /> Development on existing and new residential lots in all protected watersheds <br /> classified as by DEM as WS-II(except UNIV-PW and UNIV-CA) or WS-HI are <br /> proposed to be subject a sliding-scale impervious surface limit. <br /> The upper limit for impervious surface within WS-IV watersheds is proposed <br /> to be changed from 50% to 70% to correspond with the limits allowed by the <br /> State mandate. In preparing the draft Ordinance, it was the intention of staff <br /> to apply the limits as allowed by the State mandate. The 50%limitation, which <br /> is required only within WS-IV critical areas, was an oversight. <br /> 4 <br />