HomeMy WebLinkAboutWPO201300035 Calculations 2013-05-13 Noe w
Short Version BMP Computations
Albemarle County Water Protection Ordinance: Modified Simple Method
Plan: Hollymeade Substation Expansion Water Resources Area: Development Area
Preparer: Date:
Project Drainage Area Designation Hollymeade Substation Site
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= 1.91
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'
o 0 0! 0'.
Driveways Length Width no. subtotal Length Width no subtotal
and walks 0 0 0 0 0 0 0 0'.
0 0 0 0- 0 0 0 0-
Parking Lots 1 2 3 4 1 2 3 4
0 0 0' 0
Gravel areas Area Area
56628 x 0.70= 39639.6 60984 x 0.70= 42688.8
Structures Area no. subtotal Area no. subtotal
0 0 0 0 1 0
0
0 0' 0 0 0
0 0 0 0; 0', 0
Actively-grazed pasture& Area Area
yards and cultivated turf 26571.6x 0.08= 2125.73 22215.6.x 0.08= 1777.248
Active crop.land Area _... Area
0{x0.25= 0 x0.25= 0
Other Impervious Areas
0!: 0'
Impervious Cover 50% 53%
l(pre) I(„post)
Rv(post) V
0.53 68.6
New Development(For Development Areas,existing impervious cover<=20%)
C f I(pre)* Rv(pre) L(pre) L(post) RR %RR Area Type
07,0 v 20% 0.50 5.88 6.23 0.34 6% Development Area
'045t-7.-;,*-- 1,.00; .0% 0.50 2.94 3.11 0.17 6% Drinking Water Watersheds
'4)4107:',; I:00' 1% 0.50 3.36 3.56 0.20 6% 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
. 10� Data 20% 0.50 5.88 6.23 0.93 15% Development Area
1.1. 0. 0;5.5' 0.50 2.94 3.11 0.61 20%. Drinking Water Watersheds
0.405, 0.50 3.36 3.56 0.70 ' 20% Other Rural Land