Presentation on theme: "Bioretention Technology"— Presentation transcript:
1 Bioretention Technology Presented by:The Low Impact Development Center, Inc.A non-profit water resources and sustainable design organizationPresented by:The Low Impact Development Center, Inc.A non-profit water resources and sustainable design organization
2 The Low Impact Development Center, Inc The Low Impact Development Center, Inc. has met the standards and requirements of the Registered Continuing Education Program. Credit earned on completion of this program will be reported to RCEP at RCEP.net. A certificate of completion will be issued to each participant. As such, it does not include content that may be deemed or construed to be an approval or endorsement by RCEP.
4 Purpose and Learning Objectives The purpose of this presentation is to provide detailed information on bioretention pollutant removal, design variations, and sizing methodsAt the end of this presentation, you will be able to:Describe how bioretention works physically and chemicallyDesign bioretention systemsWhy is LID an Important tool for the Navy? Because LID Meets Policy and Regulatory Requirements, Helps the Installation get “points” for Sustainable Design AND Meets Regulator Guidance for implementing Better Site Design into Navy Stormwater Projects.UFC Manual was completed in October 2004, and is a complete guide to the inclusion of LID features in DoD construction and retrofit projects.“Getting Points”Following regulator guidance for using “Better Site Design” techniques will help Navy installations get “points” with regulators, can reduce regulatory requirements and allow precious Navy funding to be directed to other needed facility and environmental projects.Meeting Navy policy and EO requirements will help Navy installations get “points” with HQ Navy and DOD. This can help in situations where installations are being considered for BRAC. Good News stories from a Navy Installation that used innovative methods to reduce requirements is more likely to be considered for future funding and future missions.
5 Overview Performance research State-of-the-art in bioretention design Design tools
6 What is Bioretention?Filtering stormwater runoff through a terrestrial aerobic (upland) plant / soil / microbe complex to remove pollutants through a variety of physical, chemical and biological processes.The word “bioretention” was derived from the fact that the biomass of the plant / microbe (flora and fauna) complex retains or uptakes many of the pollutants of concern such as N, P and heavy metals.It is the optimization and combination of bioretention, biodegradation, physical and chemical that makes this system the most efficient of all BMP’s
9 Nitrogen Removal Step 1: Nitrification Step 2: Denitrification Ammonia/urea → nitrateAerobic processNitrate is highly mobile, and tends to be exportedStep 2: DenitrificationNitrate → nitrogen gasAnaerobic processMay occur in gravel storage layer beneath underdrain
10 Phosphorus RemovalDependent on the amount of phosphorus present in the BSMMeasured by the p-index of the topsoil used to mix BSMHigh p-index soils export phosphorus
11 Other Pollutants Heavy metals Adsorb to clay and humus in BSMMay be taken up by plantsOrganics (oil and grease, pathogens, PAHs, etc)Filtered by mulch and BSMDigested by microbesTaken up by plantsTSSBioturbation by earthworms may prevent clogging
12 Bioretention Pollutant Removal University of Maryland Dr. Allen Davis, University of Maryland
13 Pollutant Mass Removal University of Maryland Field experimentsSmall events produced zero effluent, so comparing inflow/outflow EMC underestimates removalMass removal is a better metric, but produces misleadingly low removal rates for pollutants occurring at low concentrations (e.g. Cu, Pb, and Zn)PollutantMass removalTSS57 %TP78 %Cu80 %Pb86 %Zn62 %NO3-N93 %
14 Volume Reduction University of Maryland Allen Davis at the University of Maryland has found that even lined bioretention cells with underdrains reduced runoff volume by at least 33% for 55-62% of events18% of storm events had no outflow
15 Louisburg Bioretention Dr. Bill Hunt North Carolina State Research
16 Load Reductions: Louisburg Removal vs. P-Index CellTNTPL-1(unlined)64%66%L-2(lined)68%22%P-Index1 to 285 to 100June February 2005
19 Bioretention Design Objectives Peak Discharge Control1-, 2-, 10-, 15-, 100-year stormsBioretention may provide part or all of this controlWater Quality Control½”, 1” or 2” rainfall most frequently usedBioretention can provide 100% controlGround water rechargeMany jurisdictions now require recharge( e.g., MD, PA, NJ, VA)
23 Bioretention Soil Medium Final proportionComponentProperties50% by volumeSandConforms to ASTM C33 Fine Aggregate20% by volumeOrganic MaterialCompost or shredded hardwood mulch30% by volumeTopsoilSand (2.0 – mm)50 – 85% by weightSilt (0.050 – mm)0 – 50% by weightClay (less than mm)10 – 20% by weight *Organic Matter1.5 – 10% by weightpH5.5 – 7.5 (NOTE: pH can be corrected with soil amendments if outside acceptable range)MagnesiumMinimum 32 ppm (NOTE: magnesium sulfate can be added to increase Mg)Phosphorus (Phosphate - P2O5)Not to exceed 69 ppmP-index should be less than 25Potassium (K2O)Minimum 78 ppm (NOTE: potash can be added to increase K)Soluble SaltsNot to exceed 500 ppm* If the proposed topsoil is known to contain expansive clays, clay content should not exceed 10% by weight.
24 Other Media Considerations Homogenous MixturePeat / Clays / Silts slow flowsTest and standardize the media!But performance varies with source!Min 1.0’ depth of mediaMax depth varies with vegetation.Organic Component (Shredded Hardwood vs. Compost)
25 Underdrain SystemNeeded for subsoils with percolation rates less than ½” per hourFilter fabric vs pea gravel diaphragmMinimum of 3" of gravel over pipes; not necessary underneath pipesUnderdrain Piping ASTM D-1785 or AASHTO M-2786" rigid schedule 40 PVC 3/8" 6" on center, 4 holes per row; or corrugated perforated HDPEObservation wells
26 Design Configuration Considerations Off line vs. Flow-throughInletSurface StorageUnderdrain – Dewater media
29 Plant Considerations Pollutant uptake Evapotranspiration Soil ecology / structure / functionNumber & type of plantings may vary,AestheticsMorphology (root structure trees, shrubs and herbaceous)Native plants materialsTrees 2 in. caliper / shrubs 2 gal. size / herbaceous 1 gal size.landscape plan will be required as part of the plan.Sealed by a registered landscape architect.Plants are an integral part no changes unless approvedPlant survivalIrrigation – Typical / customary
30 Sizing Flow rate Infiltration rate Volume Void space Drainage area (Smaller the Better)
31 “Kerplunk” MethodBioretention cell is sized to store a target runoff volume within the ponded area and soil/gravel pore space.This method makes several simplifying assumptions, but works reasonably well (see Reese, Stormwater Magazine, September 2011)
33 RECARGADeveloped by the University of Wisconsin-Madison Department of Civil EngineeringCapable of single event or continuous simulationIncorporates infiltration, evapotranspiration, overflow, and underdrain flow