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HomeMy WebLinkAboutWPO200800086 Stormwater Management Maintenance Agree. 2008-08-20 A -.\:\li% ►ITC'A1J1' s"'%0417'' `'"''' Sizing Summary STORMWATER , g ' 7 S—�O UL TIONS. Hollymead Towncenter Area Al Stormwater Treatment System /Design Summary Albemarle County, VA December 15, 2008 Information provided: • Total Area (A) = 8.94 Acres • C- factor = 0.84 • Presiding agency = Albemarle County Assumptions: • Flow -based sizing • WQ Design storm = Modified Rational method • Rainfall intensity (I) = 0.35in /hr (Accepted by the VDCR) • Media = Zeolite /Perlite /GAC • See additional sizing assumptions on attached calculations page Size estimates: The Stormwater Management StormFilter® is a passive, siphon- actuated, flow- through stormwater filtration system consisting of a structure that houses rechargeable, media - filled filter cartridges. The StormFilter works by passing stormwater through the media - filled cartridges, which trap particulates and adsorb pollutants such as dissolved metals, nutrients, and hydrocarbons. The StormFilter system is VDCR verified and as a result has received approval for 80% TSS and 50 -65% TP removal. This site utilized a flow -based sizing which requires calculation of the peak water quality flow rate associated with the design storm. The water quality flow rate was calculated using the Modified Rational Method assuming a rainfall intensity of 0.35 inches per hour. This flow rate is then divided by the per cartridge flow rate to determine the required number of filter cartridges (N) rounded up to the nearest whole cartridge number. The per cartridge flow rate is derived from the specific flow rate associated with each cartridge and the filter surface area of each cartridge See the sizing calculations below for further details. • The recommended StormFilter size for this system is an 8'x22' precast StormFilter vault with (53) 27" ZPG filter cartridges each. The system must be placed off -line. Please discuss with CONTECH Stormwater Solutions Stormwater Design Engineers the details of designing this bypass structure, typically designed as a weir structure or a high -low pipe configuration. ©2006 CONTECH Stormwater Solutions 521 Progress Drive, Suite H, Linthicum, MD 21090 TS -B025 contechstormwater.com Toll -free: 866.740.3318 Fax 866.376.8511 `'' - Sizing Summa STORMWA� ..,, SOLUTIONS_ Maintenance The StormFilter requires regular maintenance to operate effectively. The expected maintenance interval for systems in Virginia is 24 -30 months, but may vary depending on weather and site conditions. CONTECH Stormwater Solutions Inc. offers full maintenance services to all of our clients, as well as a cartridge exchange program to facilitate owner provided maintenance. Please contact CONTECH Stormwater Solutions or navigate to contechstormwater.com for more information in this regard. Thank you for the opportunity to present this to you and your client. System Specifications Cartridge Specific Flow Rate: 2 gpm /sf of filter surface area Cartridge filter surface area: 11.25 sf of filter surface area (27" cartridges) Cartridge Media: ZPG (Zeolite— Perlite— Granular Activated Carbon) Sizing C *I * Number of Cartridges (N) = (Qv* * Ac) / 449 s Where C = Weighted C factor / = Water Quality storm rainfall intensity (per VDCR) = 0.35 " /hr A = Contributing drainage area Q = Cartridge specific flow rate = 2 gpm /sf A = Cartridge filter surface area = 7.5 sf 449 is conversion factor (449 gpm per cfs) StormFilter System Drainage Area (A) = 8.94 acres Weighted C factor = 0.84 0.84 *0.35 *8.94 = 52.4553 N51 = (2 *11.25)/ 449 o 8'x22' precast StormFilter vault with (53) 27" ZPG filter cartridges ©2006 CONTECH Stormwater Solutions 521 Progress Drive, Suite H, Linthicum, MD 21090 TS-B025 contechstormwater.com Toll -free: 866.740.3318 Fax: 866.376.8511