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Home My WebLink AboutSUB199800025 Calculations Stormwater Management Plan 1998-07-13COUNTY OF ALBEMARLE Department of Engineering & Public Works 401 McIntire Road, Room 211 Charlottesville, Virginia 22902-4596 (804) 296-5861 July 13, 1998 Mr. Arthur F. Edwards B. Aubrey Huffman & Associates, Ltd. Post Office Box 6124 Charlottesville, Virginia 22906 RE: Porters Village — BMP Plan (SUB-98-025) Dear Mr. Edwards: This is a proactive letter concerning the Stormwater/BMP Plan for Porters Village. As you know, this plan is required by the Water Protection Ordinance, and the final road plan and erosion control plan cannot be approved until the Stormwater/BMP Plan is submitted and approved. I have attached the BMP calculation spreadsheet for the project and a sketch showing a grass Swale modified for water quality purposes. Please submit the spreadsheet and show the water quality swale on the final road plan in place of the V-ditch. Please also resubmit the erosion control plan showing the water quality swale and relabel the plan, "Erosion Control & Stormwater/BMP Plan.". When these items are addressed, the project will receive its final approval. Thank you for your cooperation, and please let me know if you have any questions Sincerely, David J. Hirschman Water Resources Manager DJH/ctj Attachment Copy: Jack Kelsey, Chief of Engineering Andre Williams, Senior Engineer Kenny Thacker, Erosion Control Officer File: hirschman/sub9825 FAX IR041 W9-40!15 �YpI AL 9TiCN v A l- f r Y SE (- T-CvrJ SWALE 1i(: I boa d -rrtT l7YrrlT"trmT"ITarrr+TT) �.� 0! 3, 1 or �E5S \ \.y�\ lPSS -1 P ci lA r (,,4J Tie o r aY:�e'c>" tc'c�''`, _� c_•. . '' < a YTfegMd Gx(, Che4 -Pam— 10 Minir.,u�� 2- I 1✓iio bUT)Am Q►(1 S r �-e s lvpt.s If 1 s �or(. t..;. Or, dowilk i fide i pd ►}l E ( _ 3, Tyre D efF vr,+ Scour • Sppd�� wr{) R"d iaraf yr KY- 31 « C�e�k daNs kvery Soa I&Yoj dI- -Ch . 1 s+vvie on dow" kd1 sides 4 t. )e,rk dams 6A.oL . 4,g soC 4+1S -4E, r � �hriaa COUNTY OF ALBEMARLE Department of Engineering & Public Works 401 McIntire Road, Room 211 Charlottesville, Virginia 22902-4596 (804) 296-5861 t}� July 13, 1998 Mr. Arthur F. Edwards J B. Aubrey Huffman & Associates, Ltd. Post Office Box 6124 Charlottesville, Virginia 22906 RE: Porters Village — BMP Plan (SUB-98-025) Dear Mr. Edwards: This is a proactive letter concerning the StormwaterBMP Plan for Porters Village. As you know, this plan is required by the Water Protection Ordinance, and the final road plan and erosion control plan cannot be approved until the Stormwater/BMP Plan is submitted and approved. I have attached the BMP calculation spreadsheet for the project and a sketch showing a grass swale modified for water quality purposes. Please submit the spreadsheet and show the water quality swale on the final road plan in place of the V-ditch. Please also resubmit the erosion control plan showing the water quality swale and relabel the plan, "Erosion Control & StormwaterBMP Plan.". When these items are addressed, the project will receive its final approval. Thank you for your cooperation, and please let me know if you have any questions. Sincerely, David J. Hirschman Water Resources Manager DJH/ctj Attachment Copy: Jack Kelsey, Chief of Engineering Andre Williams, Senior Engineer Kenny Thacker, Erosion Control Officer File: hirschman/sub9825 Short Version BMP Computations `, Worksheets 2 - 6 ..� Albemarle County Water Protection Ordinance: Modified Simple Method Plan: Porters Village Water Resources Area: Other Rural Land Preparer: David Hirschman Date: 7/9/98 Project Drainage Area Designation entire project L storm pollutant export in pounds, L = [P(Pj)Rv/12 ] [ C(A)2.72 ] Rv mean runoff coefficient, Rv = 0.05 + 0.009(I) 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 = 24.22 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) Roads Length Width subtotal 1 E Length Width subtotal I I 0: 01 01 8001 183 144001 j 0 01 01 0; 0 I _01 V -�� 0; 01 I i 0 01 ; 907' 1530T Driveways Length Width no. subtotal Length Width no. subtotal and walks 0! 0 01 01 1001 101 8i 8000 - i _ T 01 0 0 0! _ 0i �01 01 �0: 0! 01 1 0! 8000 Parking Lots 1 2 3 41 1 2 3 4' 0i ; 0! 0 ;Structures Area no. subtotal Area no. subtotal 0, 01 01 i 9001 8i 7200 j 01 0 Oi 01 0! 0 1 0i 01 __ 01 0''; 0' 7200' !Actively-grazed pasture & Area _�.._.__ .. __ �..__.. _. �.. _.....___.__.AreaV�- yards and cultivated turf Oix 0.08 = 0": 400001x 0.08 = 32001 Active crop land Area --�x0.25= Area 0 1x0.25= 0 !Other Impervious Areas 0! 01 Impervious Cover 06 ��3°/ I(pre) I(post) Rv(post) i n i 0.08 52.0 New Development (For Development Areas, existing impervious cover <= 20%) C i f 1 I (pre) * Rv(pre) L(pre) 1 L(post) RR % RR ` Area Type 0.23 34.20 11.71 -22.49 -119922%Development Area 0.05 ! 3.72 5.85E 2.14 7% Drinking Water Watersheds 0.06 j 5.01 6.69 1.681 25%I Other Rural Land ' min. values Redevelopment (For Development Areas, existing impervious cover > 20%) C f I I (pre) * Rv(pre) ; L(pre) I L(post) ! RR % RR Area Type 0.23 ; 34.20 11.71 -19.07 -163%° Development Area MINE0.05 ; 3.72 5.85 i 2.70 46%r Drinking Water Watersheds 0.06 ; 5.01 6.69 j 2.43 36%i Other Rural Land Interim Manual, Page 70 rev. 31 March 1998 GEB 0 E 31 If TypI:CAL y�TC++ SE(-Tsurj WATER QVALf TY SWALE 3:1 or less Y Rai (rodcl Tie ar TreaFpd 6X6 c�e�k DQm— keyed „n-jb bail',orn arld `#1 +0e s i k slo es ah dvwrl k i ll side • Li,,ed w4 EC - 3 , Type. A -b Qreve►,t scow( • S2 ea wi-� Reed Canary ar KY 31 Check darns lever% So' ales d4c, . k1 s4,,e ov, downk;11 sides 4 cke-cK dawns