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e <br /> . . � � <br /> City of Orono <br /> September 3, 2009 <br /> Page 2 . <br /> 4. Based on the tributary watershed having an area of 11,300 square feet, and the watershed <br /> having a runoff curve number of 72 (35%impervious), a 2 inch rainfall event will <br /> generate 0.29 inches of runoff from the watershed. This corresponds to 273 cubic feet of <br /> total runoff volume from the watershed. Given that 320 cubic feet of runoff will be stored <br /> in the infiltration azea,runoff will only leave this watershed during rainfall events that <br /> exceed 2 inches in 12 hours. This is significantly less than the runoff volume generated <br /> from a completely undeveloped area. <br /> Based on this analysis, the proposed improvements for this lot, coupled with the construction of <br /> the proposed filtration/infiltration system will eliminate runoff from over one-half of this lot <br /> including a laxge road right of way area for almost all rainfall events commonly occurring in a <br /> given year, and will more than offset the additional runoff volume generated by all the <br /> impervious surfaces that are present on the lot. <br /> Should you have any questions,please feel free to contact me at 763-287-7188. <br /> w:�PaeWN�MO-dryofamo-090709.dac � . <br />