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f' <br />t <br />K^; <br />PUllM/WIRK <br />Letter to Mr. Ron Quanbeck <br />Minnehaha Creek Watershed District <br />RE: Rick’s Super Valu - Navarre, Minnesota <br />Project #1006.13 <br />Novemcer 7, 1990 <br />Page 2 <br />These numbers are tabulated as follows: <br />On site to retention <br />So.Ft. Hard <br />83.320 <br />So.Ft. Grass <br />33,020 <br />Adjacent to retention 13,300 3,20C <br />Total Areas to Retention 97,120 Sq.Ft.36,220 Sq.Ft. <br />If we assign Imperviors factors of 0.9 for hard cover and 0.3 for grass, the <br />composite "c“ wIM be 3.74. A 20 minute, 100 year storm will produce <br />0.74 X 5.9 X 133,340 r 43,560 x 20 x 60 = 16,000 cu.ft. to the proposed <br />retention with a volume of 8,100 cu.ft. The outlet will need to be designed <br />for a rate of about 6.6 cfs. This does not allow for any retention In the <br />underground storage. If an allowance Is made for this storage and a lower <br />Intensity design storm is used, a low outlet rate is possible. <br />I would like an opportunity to discuss this plan with you. Please call me at <br />your convenience at 828-4510 <br />Sincerely, <br />PLANJf.RK <br />Bruce R. Kelley, P.E. <br />Enclo.«ures <br />cc:Lyle {. Super Valu <br />Polly SCUf., PLANMARK <br />Jean Mabusin, Orono <br />John Gerhardson, Orono <br />Jk/100613 <br />Miliiiil'iiiiiVi^li iiii