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HomeMy WebLinkAboutWPO200700082 Calculations 2007-12-05 c: ., , i Short Version BMP Computation: Worksheets 2 - 6 Albemarle County Water Protection urainance: Modified Simple Method Plan: Ashcroft West Water Resources Area: Development Area Preparer: JD Date: 05-Dec-07 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) Pj small storm correction factor, 0.9 I percent imperviousness P annual precipitation, 43"in Albemarle A project area in acres in subject drainage area, A= 2.40 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'� � 0l �. 0 0 0, 0,.._ 0 ; 0 0 1 0 88261 Driveways Length Width no. subtotal Length Width no. subtotal 'and walks 0 0 0 0 60 _... 1 600 0 0 0 _ 0 0 0 .._ 0 0 0 0 600t Parking Lots 1 2 3 4 1 2 3 4 0 _. ., 0 �i 0 Gravel areas Area 0 i Area x 0.70= 0= �i_. ]x 0.70 1 0 Structures Area no. subtotal Area no. subtotal 0 0 0 1200 1 1200 0 0 0 0' 0 ._ 0 1 -____....0 0 0 0 0 l 1200 . 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 I 0 0 Impervious Cover 0% 1 ,,w.. 10% l(pre)M .......... [(post) Rv(post) V 0.14 16.4 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 3.39 2.08 -1.30 -63% Development Area 0.35 1.00 0% 0.05 0.37 1.04 0.67 65% Drinking Water Watersheds 0.40 1.00 1% 0.06 0.50 1.19 0.69 58% 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 3.39 2.08 -0.97 -46% Development Area 0.35 0.85 0% 0.05 'I 0.37 1.04 0.73 70% Drinking Water Watersheds 0.40 0.85 1% 0.06 0.50 1.19 0.77 65% Other Rural Land Interim Manual, Page 70 rev. 16 Feb 1999 GEB Short Version BMP Computation: Worksheets 2 - 6 Albemarle County Water Protection ordinance: Modified Simple Method Plan: Ashcroft West Water Resources Area: Development Area Preparers TM Date: 25-Sep O7wm 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= 3.07 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(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 .ost-development Area Roads Length Width subtotal rLength Width subtotal 0 0 0 0. _...... .. 0 0 0 0 0 01 0 __. 0 I f 0 0 0 0 0 0 0 12490 Driveways Length Width no. subtotal Len. h Width no. subtotal and walks 0 0 01 0 70 10 3 2100 0 0 0( 0 0 0 0 0 ..._ 0 0 �_. _. 0 2100 Parking Lots 1 2 3 4 1 2 3 4 1... 0 0 _.. 0 . 0i 1Gravel areas Area 0 Area i x 0.70= 0 x 0.70= 0 [Structures Area no. subtotal , Area no. subtotal i 0 0 0 1200 2.5 30001 0 0 0 0 0 0 0 0 0 0 �0 3000 Actively-grazed pasture& Area Area I yards and cultivated turf 0 x 0.08= 0 i 0 x 0.08= 0€ Active crop land Area Area I jx0.25= 0 [ x0.25= 01 Other Impervious Areas 0 0 Impervious Cover 0% 13% ..............._. l(Pre) l(post) Rv(post)` _ V 0.17 : 27.1 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 4.33 3.17 -1.16 -37% Development Area 0.35 1.00 0% 0.05 0.47 1.59 1.12 70% Drinking Water Watersheds 0.40 1.00 1% 0.06 0.64 1.81 1.18 65% 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 4.33 i 3.17 -0.73 -23% Development Area 0.35 0.85 0% 0.05 0.47 ' 1.59 1.19 75% Drinking Water Watersheds 0.40 0.85 1% 0.06 0.64 1 1.81 1.27 70% Other Rural Land Interim Manual, Page 70 rev. 16 Feb 1999 GEB Short Version BMP Computation: Worksheets 2 - 6 Albemarle County Water Protection ordinance: Modified Simple Method Plan: Ashcroft West Water Resources Area: Development Area Preparers JD Date: 05-Dec-07 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) Pj 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= 2.90 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(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 1 0 0 0 0 0 0 0 1 �,.t 0 0 0 23300 Driveways Length Width no. subtotal Length Width no. subtotal and walks 0; � 0 0 0 0' 0 0 0; 01 0 0 0 0 0 0 Parking Lots 1 2 3 4 1 2 3 4 0 0 0 0 0 Gravel areas Area 0 Area x0.70= 0 _20.70 0' Structures Area no. subtotal Area no. subtotal 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0[ 0 0 0 0 Actively-grazed pasture& Area Area ards and cultivated turf 0 x 0.08= i 0 0 x 0.08= 0 Active crop land Area Area 1 x0.25= 0 i x 0.25= 1 0! Other Impervious Areas J j lw P 0 O= Impervious Cover 0% 18%1 I(pre) l(post) Rv(post) V 1 0.22 __..._.._36.0_.. 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 4.04 3.85 -0.25 -6% Development Area 0.35 1.00 0% 0.05 0.45 7 1.921- 1.48 77% Drinking Water Watersheds 0.40 1.00 1% µ 0.06 0.60 2.20E 1.60 73% 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 4.09 3.85 0.16 4% Development Area 0.35 0.85 0% 0.05 0.45 1.92 M 1.54 80% Drinking Water Watersheds 0.40 0.85 1% 0.06 0.60 2.20 ' 1.69 77% Other Rural Land i Interim Manual, Page 70 rev. 16 Feb 1999 GEB