The URL can be used to link to this page

Home My WebLink AboutWPO201000057 Calculations 2011-01-25 I/uTCA� 521 Progress Drive Suite H t'��.�;= gait t Linthicum,MD 21090 ` t Toll Free:866.740.3318 CONSTRUCTION PRODUCTS INC. Fax:866.376.8511 www.contech-cpi.com Graham Murray, PE January 25th,2011 Collins Engineering 800 E.Jefferson Street Charlottesville,VA 22902 RE: Review of Storm Filter Design for Avinity. The purpose of this letter is to document for Albemarle County and VA DCR our review of the plans and the proposed application of the StormFilter at Avinity as you have requested. CONTECH has reviewed the treatment train design for new construction at Avinity in Albemarle County. We believe the CDS, corrugated metal pipe(CMP)and Volume StormFilter combination is an appropriate water quality solution for this site.The StormFilter system has been approved for use by VA DCR for 50%Total Phosphorous(TP) removal. Hydrodynamic separators,such as CDS, are approved for 15-20%TP removal. The engineer of record reports a drainage area of 9.11 acres with impervious cover contributing 4.98 acres. The CDS hydrodynamic separator was designed to treat the flow rate(before internal bypass) associated with the first 0.50" of runoff over the impervious area, as required by VA DCR. This flow rate is calculated using the TR-20 hydrograph method with HydroCAD 2009. The Volume StormFilter system was designed to temporarily store and slowly release the water quality volume. The system was sized based on the 0.5"rainfall event for this site. To adequately treat the water quality volume of 9,030cf we (CONTECH) recommend an 8'x11'StormFilter with (25) 27" cartridges,with upstream CMP storage. All flows greater than the water quality storm (0.5") will be directed to the flow control weir plate in the 120" detention system. Each StormFilter cartridge contains a restrictor disk with a 0.443" orifice, which is designed to flow at 7.50gpm at 120"of head.Therefore, it will take at least 6 hours to treat the entire water quality volume. The configuration of the CDS and StormFilter pipes are acceptable.The systems appear to be constructible and are located in order to facilitate maintenance activities. Our systems require periodic maintenance to continue operating properly. Given typical street pollutant loading rates, CONTECH Construction Products recommends maintenance inspections on an annual basis. Based on the location of the system, we anticipate StormFilter cartridge replacement should be done every 2 years for the system to continue to remove pollutants. In summary, these systems are expected to operate in accordance with CONTECH Construction Products' design intent. Please feel free to contact me if you have any questions or concerns. Sincerely, Aaron M. Lowell Design Engineer—Stormwater Products CONTECH Construction Products Inc. lowella@contech-cpi.com www. contechstormwater. com eps "hr Slormv.dtir�.fan3gemn C Vortechs CMP DETENTION SYSTEMS �j CONp SPANS StormFilter PCOT :-V-I,CVal APT FiNcr ok vAAr.:_A \-)6:- (.01-tr."t•&, DIV :•• r t,ct -LI t 4....VC*se,.> , ,-,,, , , ,.., , A j'Al)..)& P$Ot Cel/K‘K`: STo0a)16 S.,-,fs07 V).ts-tA,kace, ç4,, Li-v,..Nw i (oval. k._N-1_ S'\f.• %0-..6c) 5NE Q 1; 5C L-vc roP. 5 1 vAA,a.g tr,-; L r LEPC'tA of' ‘)'. A: f\LE7 av&AI c " sc--re-,.:,p 'Pe4:-. 1),) 6PPok: ,p 4 _S>lz 5 = \019 _. • '-----."--' 5-.:. \ i't. ..\....., .,,, _7 s ..) -. _ (.. a _., CR Es:c CA\Jr- -- Gko3 -i4 \ A si a. kCno.'4 7,L0 S-: 46.'-ib C- 15 .... N A '------> 5 r Li E,,4 6 .----- --N cy,- \51 5164 a-. _____ _ N- ..--c,,, ,r 0,,i;;;,,,;if.-..: 7 5T-onlpG 5'16/-4-1: 'OA .1*.A 04 e IC ro*. \\541 -n-luc, Mpg0-16 Mrs Dr:l..- -Te_rwLi cot,c1-1,Ap.A. 16,i-o117-zoNAu...`t —14 I-kr/J-1)-0-M k Vfm-AAt- TcP• A ao orii ore:t. _Ts 9 FLA. CIZCV1 C UA v•CS. o ‘Y-Sl; 1 fiiks A k: vALts,c, t.t. 7,67 -11-Kis voga,Jc T('-x,-; Veira) (olAIZtaAjo.)T. i \---Ii- ikah t=". A Ocovik.N 570QQ0.16 .,.,,...1cf(-1- Dx5v4),e-c_ ON v-.1 Aix 1 Lt c.T. (51A \*1,.,) i 576 p 1 I L = a s _ LAG° , A ,- ..., ...... (-\* L :o.ssil ‹.. L J ---------- = \0.5-a. ,--1, L---- las •,.., [5 'N- ________ mo5N ReST,J2.10.V.IC 7 4 Zki Accoawkwc( ,r4 Tn Vl yi.,.\a4;$11- Tr-tE DE 5s61.1 0 510Q.:046. cOz sl A kiCE Tio,KJ T IV /1-10%"1/44M tAil PEO\i'VE:0 siven)16 ST6 RI- Dysi Apex( k 5), PrO 0 47 X0141 Lel 11-k E Oe 5.16NE't) K \JA,...v..v / 11-tFlA 1-146, Mvq...0•Aup v< \Auks HYDROLOGIC METHODS CHAPTER 4 TABLE 4 -6b Runoff Curve Numbers for Agricultural Areas' Adapted from TR-55 Table 2-2b--Runoff Curve Numbers for Other Agricultural Lands* Cover Description Curve Numbers for Hydrologic Soil Group: Cover Type Hydrologic A B C D Condition Pasture, grassland, or range - continuous forage for grazing 2 Good 39 61 74 80 Meadow- continuous grass, protected from grazing and generally mowed for hay ---- 30 58 71 78 Brush - brush-weed-grass mixture with brush Good 230 48 65 73 the major element2 Woods - grass combination (orchard or tree Good 32 72 79 farm)2 Good 230 55 70 77 go 7. wxv5 Woods 2 Farmsteads - buildings, lanes, driveways, ---- 59 74 82 86 and surrounding lots *Average runoff condition and'a= 0.2S 'Refer to TR-55 for additional cover types and general assumptions and limitations. 2For specific footnotes, see TR-55 Table 2-2b. RCN Determination Assumptions (TR-55): l. The urban curve numbers,for such land uses as residential, commercial, and industrial, are computed with the percentage of impervious area as shown. A composite curve number should be re-computed using the actual percentage of imperviousness if it differs from the value shown. 2. The impervious areas are directly connected to the drainage system. 3. Impervious areas have a runoff curve number of 98. 4-34 • 1 HYDROLOGIC METHODS CHAPTER 4 TABLE 4 - 6a Runoff Curve Numbers for Urban Areas Adapted from TR-55 Table 2-2a. —Runoff Curve Numbers for Urban Areas' Cover Description Curve Numbers for Hydrologic Soil Group: Cover Type and Hydrologic Condition Average percent A B C D impervious areal Fully developed urban areas (vegetation established) : Open space (lawns, parks, golf courses, cemeteries, etc.)2: Good condition (grass cover> 75%) 39 61 74 80 Impervious areas: Paved parking lots, roofs, driveways, etc. (excluding right-of-way) 98 98 98 98 0.tt sycA SIN of Streets and roads: uksT =�r Paved; curbs and storm sewers (excluding right-of-way) 98 98 98 98 =►n Paved; open ditches (including right-of-way) 83 89 92 93 <o.n[tkCAN'0 v4 Gravel (including right-of-way) 76 85 89 91 Dirt(including right-of-way) 72 82 87 89 54'06 Urban districts: Commercial and business 85 89 92 94 95 Industrial 72 81 88 91 93 Residential districts by average lot size: 1/8 acre or less (town houses) 65 77 85 90 92 1/4 acre 38 61 75 83 87 1/3 acre 30 57 72 81 86 '/z acre 25 54 70 80 85 1 acre 20 51 68 79 84 2 acres 12 46 65 77 82 Developing urban areas: Newly graded areas (pervious areas only, no vegetation) 77 86 91 94 ':„-‘,60�. Idle lands (CN's are determined using cover types similar to those in of a TR-55 Table 2-2c). ke.e6N) *Average runoff condition and to = 0.2S 'Refer to TR-55 for additional cover types and general assumptions and limitations. 2For specific footnotes, see TR-55 Table 2-2a. 4-33 J u v-L .. J --1! (1f7,c) °'2. ':‘4'.11, r Lt L c �. ik p4* ' ri' 1 • HYDROLOGIC MET ODS CHAPTER 4 Q = CCfIA Equation 4-2 Rational Formula Frequency Factor The Cf values are listed in Table 4-4. The product of Cf x C should not exceed 1.0. TABLE 4-3 Rational Equation Runoff Coefficients J Land use "C" Value Business,industrial and commercial 0.90 Apartments 0.75 Schools 0.60 Residential -lots of 10,000 sq.ft 0.50 -lots of 12,000 sq.ft. 0.45 -lots of 17,000 sq.ft. 0.45 -lots of acre or more 0.40 Parks, cemeteries anckluumproved areas 0.34 TQEvs'c Cw' 0.35 Paved and roof areas 0.90 v,IAS Boa Hzbti Cultivated areas 0.60 Pasture 0.45 Forest 0.30 Steep grass slopes(2:1) 0.70 Shoulder and ditch areas _ 0.50 -- Maize A 4.10,14.41 C (tivns ._ �� . E><2tt�` t-crk soot) Ck 5C4. 000 . Source:VDOT CAS r1oT c_NANNELLZr? TABLE 4-4 Rational Equation Frequency Factors Cr Storm Return Frequency 1.0 10 yr. or less 1.1 25 yr. 1.2 50 yr. 1.25 100 yr. Source:VDOT 4-20 1992 35 — z .7 30 — V Paved 9 - z- 2 5 — — 300 '0 .7 - - Bare 0- u' 2 0 0 Soil . .4 2 0 — H Poor - - \ Grass 6_.5 f_ _ NSurf ace < w - P"v� w - Average =- .a = 0.5 - — *A. Ml It+. w Grass c� w w �� o�1 Z 1 00 Surface - 1 .0 0 1 5� 2 <%As FLew J / .- - 9 0 > 2.0 u / Z a- 7._ g 0 Dense a — 7 0 Grass z N 5.0 ~� - i�� u' 60 \ Na / � I . 0 - tea' 0 5 0 ? .✓ w z F� - ,cc/<4 - i .� 20 D_ - V FLOW J — 40 \ z _ _ / I0 - o H — 30 \� 9 -- w Z - J g � z — 20 I- * uss C,0-- Q 3S -› tL�.ly .►.,--N - _ use Cw= 0.ao c \2 . 7 — — 1 0 6 -- OVERLAND FLOW TIME (Seelye Chart) Source: Data Book for Civil Engineers, E.E. Seelye Plate 5-1 V - 11