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Are Detention Ponds Holding You Back? May 30 th, 2007 Brian Bates Don Alexander
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Stormwater Management in Greenville County May 30 th, 2007 Ground Rules True or False: “Detention ponds are a bad thing for water quality” FALSE
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Stormwater Management in Greenville County May 30 th, 2007 Attributes of Detention Peak discharge control Volume control Pollutant trapping −Sediment −Heavy metals −Floatables −Oil and grease −Nutrients −Bacteria …When Properly Designed, Constructed, and Maintained
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Stormwater Management in Greenville County May 30 th, 2007 Ground Rules Continued State Law – Regulation 72-300 −Post development peak discharge not exceed predevelopment rates for 2 and 10-yr. Storm −Permanent quality ponds with a permanent pool must store and release the first half inch of runoff for 24-hrs. −Permanent quality ponds without a permanent pool must store and release the first inch of runoff for 24-hrs. Greenville County is a delegated review authority under 72-300
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Stormwater Management in Greenville County May 30 th, 2007 Quantity and Quality Standards Good −Detention Peak flow comparison – 2, 10, 25, etc. −Water Quality 1-in. of runoff – dry detention ½-in. of runoff – wet detention
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Stormwater Management in Greenville County May 30 th, 2007 Quantity and Quality Standards Better −Detention Volume based comparison – 2, 10, 25, etc. −Water Quality Design storm runoff (e.g. 1-in. storm)
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Stormwater Management in Greenville County May 30 th, 2007 Quantity and Quality Standards Best −Detention Peak flow comparison and Volume based comparison −Water Quality Effluent standards
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Stormwater Management in Greenville County May 30 th, 2007 Key Words “Properly Designed, Constructed, and Maintained” −Historic Design Issues No small storm detention Short circuiting Pre-developed calculations (high CNs) Designed for built out conditions
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Stormwater Management in Greenville County May 30 th, 2007 Pelzer Pond Example
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Stormwater Management in Greenville County May 30 th, 2007 Key Words “Properly Designed, Constructed, and Maintained” −Historic Construction Issues Sledge hammer orifice No riser Incorrect invert elevations 24 hour first flush drainage controls
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Stormwater Management in Greenville County May 30 th, 2007 Pelzer Pond Example
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Stormwater Management in Greenville County May 30 th, 2007 Key Words “Properly Designed, Constructed, and Maintained” −Historic Maintenance Issues Sediment accumulation Vegetation Trash racks Damaged risers
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Stormwater Management in Greenville County May 30 th, 2007 County’s approach Review and inspect to assure compliance with current standards Encourage water quality BMPs in conjunction with detention −Vegetated filter strips −Bioretention −Engineered devices −LID Provide tools for design community −SUDS −IDEAL −Design manual Explore ordinance revisions
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BMP Retrofit Study
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Stormwater Management in Greenville County May 30 th, 2007 Problem Statement What is the best way to meet water quality standards in developed areas? How many BMPs are needed? At what scale are BMP benefits insignificant? Where is the best place to locate? How do we measure improvement? We assume that standards/TMDLs cannot be met without retrofits to developed areas.
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Stormwater Management in Greenville County May 30 th, 2007 Project Location No construction Basin size Monitoring constraints
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Stormwater Management in Greenville County May 30 th, 2007 Project Location
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Stormwater Management in Greenville County May 30 th, 2007 Runoff Analysis Three automatic samplers in parallel Grab samples taken at each site for fecal coliform analysis Sample analysis performed by Rogers & Calcott To Date: −3 storms, 12-24 samples taken and analyzed per storm for TSS, TN, TP −Fecal Coliforms - 3-6 samples per storm −H&H Model developed & trying to calibrate
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Stormwater Management in Greenville County May 30 th, 2007 Study Update To Date 3 Storms, with 12-24 samples taken and analyzed per storm Fecal Coliforms - 3-6 samples per storm H&H Model developed & trying to calibrate
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Stormwater Management in Greenville County May 30 th, 2007 Bioretention Retrofit at Our Lady of the Rosary Catholic Church has been successful May be the best BMP for combining quantity and quality control Can be modeled in IDEAL along with VFS, sand filters, ponds, and bioswales
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Stormwater Management in Greenville County May 30 th, 2007 Greenville County
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Stormwater Management in Greenville County May 30 th, 2007 Next Steps Model BMP scenarios −Pond outlet structures −Conversion to another type of BMP −Engineered devices −Focused public ed. Scenario selection based on B:C Implement best scenario Monitor post-retrofit runoff events and compare results
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IDEAL Post-construction Water quality BMP Model
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Stormwater Management in Greenville County May 30 th, 2007 IDEAL Integrated Design and Evaluation Assessment of Loadings Model
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Stormwater Management in Greenville County May 30 th, 2007 An OCRM Dilemma Compliance with Antidegradation & TMDLs Needed an explicit BMP model −Model Hydrology & Hydrualics and pollutant yield from urban areas. −Estimate BMP performance. −Base predictions on accepted predictive procedures. 20022003200420012000 1999
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Stormwater Management in Greenville County May 30 th, 2007 IDEAL Initiated Woolpert hired by OCRM Scope of Model Literature review Watershed Framework Post Construction BMP Design Aid Manual and IDEAL Spreadsheet 2001 20022003 20042005
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Stormwater Management in Greenville County May 30 th, 2007 IDEAL Development Primary Researchers Dr Bill Barfield – Oklahoma State University Dr. John Hayes – Clemson University
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Stormwater Management in Greenville County May 30 th, 2007 IDEAL OCRM version BMP Trapping Sedimentology and soil isotherms Hydrology Single storm and Total annual runoff 4 pollutants 3 BMPs Pond routing Single watershed Post-construction
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Stormwater Management in Greenville County May 30 th, 2007 Pervious Imp Pervious and Unconnected Impervious Impervious Directly Connected Impervious BMP Dry/Wet Detention Basin Outflow From Watershed Watershed Modeling Framework
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Stormwater Management in Greenville County May 30 th, 2007 Rainfall Statistics Growing Season P=0.664 AMC 1 P=0.797 AMC 2 P=0.104 AMC 3 P=0.100 Dormant Season P=0.336 AMC 1 P=0.543 AMC 2 P=0.231 AMC 3 P=0.226 12 Storms 0.25’’ to 10.5’’ Values for Greenville, SC Precip Amount Prob P
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Stormwater Management in Greenville County May 30 th, 2007 Loading Sediment −Pervious Areas - MUSLE − Impervious Areas - EMC Approach Nutrients and Bacteria - EMCs
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Stormwater Management in Greenville County May 30 th, 2007 BMP Trapping Predicts trapping of sediments in ponds through overflow rate calculations for 5 particle classes. Predicts nutrient trapping by settling of particulate matter and sorbed portion on trapped active clay content of the sediment by isotherms. Predicts bacteria trapping using isotherms and mortality
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Stormwater Management in Greenville County May 30 th, 2007 IDEAL OCRM Model Limitations Only for use on the SC coast Limited outlet configurations Numerous spreadsheet constraints Untested BMP algorithms No resuspension, denitrification, direct loading on BMP, or bacteria growth.
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Stormwater Management in Greenville County May 30 th, 2007 Woolpert hired by County Isotherms and Rainfall Analysis Continue to use spreadsheet Greenville County 2002 20012003 20042005
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Stormwater Management in Greenville County May 30 th, 2007 Greenville County 2003 20012002 20042005 Dry pond verification study
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Stormwater Management in Greenville County May 30 th, 2007 Greenville County 2004 20012002 20032005 VB GUI developed Bioretention cell research begun Multiple watersheds Literature review −Swales & Engr. Devices
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Stormwater Management in Greenville County May 30 th, 2007 Greenville County Sept 20012002 20032005 EPA BMP Design Manual EPA/600/R-04/121 2004
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Stormwater Management in Greenville County May 30 th, 2007 Greenville County 2005 2006 2002 20032004 Bioretention cell added and revised −Greenhouse study −Greenville Co. study FC loading function
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Stormwater Management in Greenville County May 30 th, 2007 Greenville County 2005 2006 2002 20032004 Bioretention cell added and revised −Greenhouse study −Greenville Co. study FC loading function
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Stormwater Management in Greenville County May 30 th, 2007 Greenville County
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Stormwater Management in Greenville County May 30 th, 2007 Greenville County 2006 2005 2002 20032004 Sand filter and bioswale added Conceptual algorithms developed for engr. devices Conveyance routing algorithms −Pipe, Channel, Simple translation Model presented to EPA Region 4 VB GUI revised to current layout −Distributed Jan 2007 to GC engineers
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Stormwater Management in Greenville County May 30 th, 2007 Greenville County Object oriented VB.net “Drag n Drop” version
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Stormwater Management in Greenville County May 30 th, 2007 Ongoing Improvements Technical Advisory Group −Barfield and Hayes −Dr. John Sansalone -Fla −Dr. Bob Pitt –Ala −Mike Borst – EPA-ORD −Mark Schlautman – Clemson −Khaled Gasem – Okla State Enhanced Bioswale research with EPA-ORD, Edison, NJ User’s Manual
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Stormwater Management in Greenville County May 30 th, 2007 Summary of versions OCRM Spreadsheet VB.Net PollutantsSediments, Nutrients, Bacteria Watersheds1200+ BMPsWet/Dry Ponds, VFS Wet/Dry Ponds, VFS, Bioretention cells, Sand filter ConveyancesNone Pipes, channels, and translation only Isotherms & Rainfall Analysis SC CoastGreenville Co.
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Stormwater Management in Greenville County May 30 th, 2007 Uses BMP design for small to large developments projects TMDL compliance Antidegradation restrictions Watershed master planning LID design
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Stormwater Management in Greenville County May 30 th, 2007 Future Steps Bacteria growth function Engineered device algorithms development Bioswale algorithm revision Conveyance design functionality GIS/CAD interface Optimization Large scale watershed considerations Performance enhancement and user support Continue to use best science available
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