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HomeMy WebLinkAboutSDP200700002 Calculations 2007-01-30Short Version BMP Computations For Worksheets 2 - 6 Albemarle County Water Protection Ordinance: Modified Simple Method Plan: The Meadows Expansion Water Resources Area: Development Area Preparer: Brian P. Smith, PE Date: 1/30/2007 Project Drainage Area Designation DA #1 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) Pi small storm correction factor, 0.9 1 percent imperviousness P annual precipitation, 43" in Albemarle A project area in acres in subject drainage area, A = 1.66 C pollutant concentration, mg /I or ppm target phosphorus f factor applied to RR V required treatment volume in cy, 0.5" over imperv. area = A(1)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 0 0 Driveways Length Width no. subtotal Length Width no. subtotal and walks 0 0 0 0 0 0 0 1644 0 0 0 0 0 0 0 1478 0 0 0 3122 Parking Lots 1 2 3 4 1 2 3 4 0 0 6184 0 6184 Structures Area no. subtotal Area no. subtotal 0 0 0 3025 2 6050 0 0 0 0 0 0 0 0 0 0 0 6050 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 x0.25=0 Other Impervious Areas 0 0 Impervious Cover 0%21% I(pre)post) Rv(post) V 0.24 23.7 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 2.34 2.46 0.11 5%Development Area 0.35 1.00 0% 0.05 0.25 1.23 0.97 79%Drinking Water Watersheds 0.40 1.00 1 % 0.06 0.34 1.40 1.06 76%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 2.34 2.46 0.35 14%Development Area 0.35 0.85 0% 0.05 0.25 1.23 1.01 82%Drinking Water Watersheds 0.40 0.85 1 % 0.06 0.34 1.40 1.11 79%Other Rural Land Interim Manual, Page 70 rev. 31 March 1998 GEB Short Version BMP Computations For Worksheets 2 - 6 Albemarle County Water Protection Ordinance: Modified Simple Method Plan: The Meadows Expansion Water Resources Area: Development Area Preparer: Brian P. Smith, PE Date: 1/30/2007 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) P] small storm correction factor, 0.9 1 percent imperviousness P annual precipitation, 43" in Albemarle A project area in acres in subject drainage area, A = 1.75 C pollutant concentration, mg /I or ppm target phosphorus f factor applied to RR V required treatment volume in cy, 0.5" over imperv. area = A(1)43560(0.5112)/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 0 0 Driveways Length Width no. subtotal Length Width no. subtotal and walks 0 0 0 0 0 0 0 5235 0 0 0 0 0 0 0 0 0 0 0 5235 Parking Lots 1 2 3 4 1 2 3 4 0 0 6184 4671 0 10855 Structures Area no. subtotal Area no. subtotal 0 0 0 3025 3 9075 0 0 0 0 0 0 0 0 0 0 0 9075 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 x0.25=0 Other Impervious Areas 0 0 Impervious Cover 0%33% I(pre)post) Rv(post) V 0.35 38.8 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 2.47 3.73 1.26 34%Development Area 0.35 1.00 0% 0.05 0.27 1.86 1.60 86%Drinking Water Watersheds 0.40 1.00 1% 0.06 0.36 2.13 1.77 83%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 2.47 3.73 1.51 40%Development Area 0.35 0.85 0% 0.05 0.27 1.86 1.64 88%Drinking Water Watersheds 0.40 0.85 1 % 0.06 0.36 2.13 1.82 86%Other Rural Land Interim Manual, Page 70 rev. 31 March 1998 GEB Short Version BMP Computations For Worksheets 2 - 6 Albemarle County Water Protection Ordinance: Modified Simple Method Plan: The Meadows Expansion Water Resources Area: Development Area Preparer: Brian P. Smith, PE Date: 1/30/2007 Project Drainage Area Designation DA #3 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) Pi small storm correction factor, 0.9 1 percent imperviousness P annual precipitation, 43" in Albemarle A project area in acres in subject drainage area, A = 2.34 C pollutant concentration, mg /I or ppm target phosphorus f factor applied to RR V required treatment volume in cy, 0.5" over imperv. area = A(1)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 11,071 0 0 11071 0 0 0 0 0 7104 0 0 0 556 0 11071 0 18731 Driveways Length Width no. subtotal Length Width no. subtotal and walks 0 0 0 1844 0 0 0 1844 0 0 0 0 0 0 0 4180 0 1844 0 6024 Parking Lots 1 2 3 4 1 2 3 4 0 0 0 0 Structures Area no. subtotal Area no. subtotal 0 0 6,053 6053 0 0 0 1512 3 4536 0 0 0 6053 3025 1 3025 13614 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 x0.25=0 Other Impervious Areas 0 0 Impervious Cover 19%38% l(pre)post) Rv(post) V 0.39 59.2 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 3.31 5.59 2.28 41%Development Area 0.35 1.00 0% 0.22 1.56 2.79 1.23 44%Drinking Water Watersheds 0.40 1.00 1% 0.22 1.79 3.19 1.41 44%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 3.31 5.59 2.61 47%Development Area 0.35 0.85 0% 0.22 1.56 2.79 1.46 52%Drinking Water Watersheds 0.40 0.85 1% 0.22 1.79 3.19 1.67 52%Other Rural Land Interim Manual, Page 70 rev. 31 March 1998 GEB