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HomeMy WebLinkAboutWPO200400093 Calculations 2004-08-26 STORMWATER BMP CALCULATIONS FOR ADVANCE MILLS FARM SUBDIVISION PHASE 1 July 6, 2002 REV: August 26, 2004 LOCATION: Tax Map 20 Parcel 6A1 Whitehall District, Albemarle County, Virginia OWNER: oN Advance Mills Land Trust, LLC �gpLTH P.O. Box 8147 f.,:e0 , Charlottesville, VA 22911 2 v '► T Y RAY MILLER DEVELOPER: • 0402030542 • C. W. Hurt • 195 Riverbend Road ‘12gio_t L6..0 ' / 41 Charlottesville, VA 22906 nvioNAL 04G` PREPARED BY: Rivanna Engineering & Surveying, PLC P. O. Box 7603 Charlottesville, VA 22906 434.984.1599 F: 434.984.8863 RESI@CSTONE.NET The Stormwater Quality BMP's for this subdivision shall be a 200' Riparian Buffer Easement along the North Fork Rivanna River. Short Version BMP Computations For Worksheets 2-6 Albemarle County Water Protection Ordinance: Modified Simple Method Plan: Advance Mills Farm-Phase II Water Resources Area: Preparer TRM Date: 25-Aug-04 Project Drainage Area Designation Rural Subdivision 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= 198,00 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 260018 46800 0 0 0 p 0 0 O 0 0 0 O 0 0 46800 Driveways Length Width no. subtotal Length Width no. subtotal and walks 1500 10 1 15000 20010 1 2000 O 0 0 0 0 0 0 0 O 15000 0 2000 Parking Lots 1 2 3 4 1.._, 2__ 3 4 O 0 16786 0 16786 Gravel areas Area Area x0.70= 0 x0.70= 0 Structures Area no. subtotal Area no. subtotal 800 1 800 800 1 800 0 0 0 1500 10 15000 0 0 0 800 0 15800 Actively-grazed pasture& Area Area yards and cultivated turf 8,609,080 x 0.08= 688726.4 8,543,494 x 0.08= 683479.52 Active crop land Area Area x0.25= 0 x0.25= 0 Other Impervious Areas 0 0 Impervious Cover 896 9% Rv(post) V I(pre) l(post) . ,. 0.13 1180.3 New Development(For Development Areas,existing impervious cover<=20%) C f I(pre)* Rv(pre) L(pre) L(post) RR % RR Area Type G.70 1.00 20% 0.23 279.57 157.79 -121.78 -77% Development Area 0.35 t.b0 0% 0.12 75.07 78.90 3.83 5% Drinking Water Watersheds o.4o, 1. ;_. 114 0.12 85.79 90.17 4.37 �`. 5% 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% 0.23 279.57 157.79 -93.82 -59% Development Area 0.3$ 0.85 0% 0.12 75.07 78.90 15.09 19% Drinking Water Watersheds 1% 0.12 85.79 90.17 17.24 0*" ���'�•� ' 19% Other Rural Land Interim Manual, Page 70 rev. 16 Feb 1998 GEB