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120 <br /> 1 <br /> As the site consists of 80.33 Acres, 4.7k of the site will be <br /> impervious. This amount falls well below the allowed 12x maximum <br /> allowable impervious ratio for R-1 with public water/sewer <br /> unavailable,'1 (Pg.19, Table B of Subdivision Regulations <br /> Admendment). <br /> In addition to the relatively low ratio of impervious material . to <br /> vegetation on this site. it must be noted that the natural terrain <br /> .'of this site, along with swales, will allow all of the runoff to <br /> I' either pass through natural vegetation or to be retained in one of <br /> three the ponds. <br /> The stormwater runoff from the roads will be carried to different <br /> parts of the site by means of a grassed swale. The grass swale <br /> will slow the runoff down and allow some pollutants to settle <br /> within the swale. <br /> Along Windy Bill there will be several places where, the swales on <br /> the southern side will be allowed to discharge runoff into the - - <br /> ponds. It is estimated that no more than 1.2 acres or <br /> Based of the Rational Method for determining runoff (Qi-CIA) . <br /> Area e 1.2 Acres <br /> Runoff Coeff. = 0.9 <br /> 4 1 Intensity of rain = 7.5 in/hr . <br /> A = 8.1cfs <br /> an estimated flow of 8.1 cfs will be discharging toward the pond <br /> during a 10 year storm. This Is to be considered a moderate <br /> amount of runoff. Therefore, relatively little stormwater, with <br /> 5 the long overland distance it will travel in the swales, will <br /> combine to provide a very substantial infiltration and filtering <br /> system. <br /> 1 <br /> A relatively barge portion of the northern side of Windy Hill will <br /> appear to be on a fill section of material. Therefore, all runoff <br /> from the centerline on the road (if not superelevated) will flow <br /> perpendicular off the road and down' the grassed slope into natural <br /> vegation. This will allow infiltration to take place. <br /> The runoff from High Meadow will be discharged and controlled in <br /> the same manner as Windy Hill. However, one section of High <br /> Meadow will be discharging to the South through a 15"RCP with <br /> approximately; <br /> 0=CIA <br /> A = 0.5 Acres <br /> i 1 = 7.5 In/Hr <br /> II C - 0.9 <br /> n = 3.4 cfs <br /> t . <br /> ii <br /> i <br /> Windy Hill Farm 12/12/85 Page 2 <br /> i <br /> 1 \■= . <br />