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HomeMy WebLinkAboutSDP200900016 Calculations 2009-04-22Short Version BMP Computations ror Worksheets 2 - 6 Albemarle County Water Protection Ordinance: Modified Simple Method Plan: NORTH FORK REGIONAL PUMP STATION Water Resources Area:Development Area Preparer:YLM Date: 22- Apr -09 Project Drainage Area Designation DA# 2 L storm pollutant export in pounds, L = [P(Pj)Rv /12 ] [ C(A)2.72 ] Rv mean runoff coefficient, Rv = 0.05 + 0.009(1) Pj small storm correction factor, 0.9 percent imperviousness P annual precipitation, 43" in Albemarle A project area in acres in subject drainage area,A =3.25 C pollutant concentration, mg /I or ppm target phosphorus f factor applied to RR required treatment volume in cy, 0.5" over imperv. area = A(I)43560(0.5/12)/27 RR required removal , L(post) - f x L(pre) RR removal efficiency , RR100 /L(post) Impervious Cover Computation (values in feet & square feet) Item pre - development Area post - development Area Roads Length Width subtotal Length Width subtotal 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 8465 8465 Driveways Length Width no.subtotal Length Width no.subtotal and walks 0 0 0 0 8 4 1 32 0 0 0 0 4 4 1 16 0 0 464.05 512.05 Parking Lots 1 2 3 4 1 2 3 4 0 0 0 0 0 Gravel areas Area Area x0.70=0 x0.70=0 Structures Area no.subtotal Area no.subtotal 0 0 0 600 1 600 0 0 0 212.5 1 212.5 0 0 0 0 36 1 36 848.5 Actively - grazed pasture &Area Area yards and cultivated turf 0 x 0.08 =0 0 x 0.08 =0 Active crop land Area Area x0.25=0 0x0.25=0 Other Impervious Areas 0 0 Impervious Cover 0%7% l(pre)post) Rv(post) V 0.11 15.2 New Development (For Development Areas, existing impervious cover <= 20 %) C f I (pre) * Rv(pre) L(pre) L(post) RR RR Area Type 0.70 1.00 20% 0.23 4.59 2.24 2.35 105% Development Area 0.35 1.00 0% 0.05 0.50 1.12 0.62 56% Drinking Water Watersheds 0.40 1.00 1% 0.06 0.67 1.28 0.61 48% Other Rural Land min. values Redevelopment (For Development Areas, existing impervious cover > 20 %) C f I (pre) * Rv(pre) L(pre) L(post) RR RR Area Type 0.70 0.90 20% 0.23 4.59 2.24 1.89 84% Development Area 0.35 0.85 0% 0.05 0.50 1.12 0.70 62% Drinking Water Watersheds 0.40 0.85 1% 0.06 0.67 1.28 0.71 55% Other Rural Land Interim Manual, Page 70 rev. 16 Feb 1998 GEB