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Transcript of Bioretention Technology Presented by: The Low Impact Development Center, Inc. A non-profit water...
Bioretention Technology
Presented by:
The Low Impact Development Center, Inc. A non-profit water resources and sustainable design organizationwww.lowimpactdevelopment.org
Presented by:
The Low Impact Development Center, Inc. A non-profit water resources and sustainable design organizationwww.lowimpactdevelopment.org
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.
COPYRIGHT MATERIALS
This educational activity is protected by U.S. and International copyright laws. Reproduction, distribution, display, and use of the educational activity without written permission of the
presenter is prohibited.
© Low Impact Development Center, 2012
The purpose of this presentation is to provide detailed information on bioretention pollutant removal, design variations, and sizing methods
At the end of this presentation, you will be able to:• Describe how bioretention works physically and
chemically • Design bioretention systems
Purpose and Learning Objectives
Overview
• Performance research
• State-of-the-art in bioretention design
• Design tools
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
Pollutant Removal MechanismsPhysical / Chemical / Biological
ProcessesSedimentationFiltration AdsorptionAbsorptionCation Exchange Capacity Polar / Non-polar SorptionMicrobial Action (aerobic / anaerobic)
decomposition / nitrification / denitrificationPlant UptakeCycling Nutrients / Carbon / MetalsBiomass Retention (Microbes / Plant)Evaporation / Volatilization
System Components
Mulch
Course Sand
Pore Space
Surface Area
Complex Organics
Microbes
Biofilm
Plants
“Ecological Structure”
Plant-and-Microbe-Mediated Pollutant Removal
• Phytoremediation o Translocateo Accumulate o Metabolizeo Volatilizeo Detoxifyo Degrade
• Exudates
• Bioremediation• Soils
o Capture / Immobilize Pollutants
Nitrogen Removal
• Step 1: Nitrificationo Ammonia/urea → nitrateo Aerobic processo Nitrate is highly mobile, and tends to be exported
• Step 2: Denitrificationo Nitrate → nitrogen gaso Anaerobic processo May occur in gravel storage layer beneath underdrain
Phosphorus Removal
• Dependent on the amount of phosphorus present in the BSM • Measured by the p-index of the topsoil used to mix BSM• High p-index soils export phosphorus
Other Pollutants
• Heavy metals o Adsorb to clay and humus in BSMo May be taken up by plants
• Organics (oil and grease, pathogens, PAHs, etc)o Filtered by mulch and BSMo Digested by microbeso Taken up by plants
• TSS o Filtered by mulch and BSMo Bioturbation by earthworms may prevent clogging
Bioretention Pollutant RemovalUniversity of Maryland
Cumulative Depth
(ft) Copper Lead ZincPhos-
phorus TKN Ammonia Nitrate
1 90 93 87 0 37 54 -972 93 99 98 73 60 86 -1943 93 99 99 81 68 79 23
Field 97 96 95 65 52 92 16
Removal Efficiency (%)
Box Experiments
Dr. Allen Davis, University of Maryland
Pollutant Mass RemovalUniversity of Maryland
Pollutant Mass removal
TSS 57 %
TP 78 %
Cu 80 %
Pb 86 %
Zn 62 %
NO3-N 93 %
• Field experiments• Small events produced zero
effluent, so comparing inflow/outflow EMC underestimates removal
• Mass removal is a better metric, but produces misleadingly low removal rates for pollutants occurring at low concentrations (e.g. Cu, Pb, and Zn)
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 events
• 18% of storm events had no outflow
Louisburg BioretentionDr. Bill Hunt
North Carolina State Research
Load Reductions: Louisburg Removal vs. P-Index
Cell TN TP
L-1(unlined)
64% 66%
L-2(lined)
68% 22%
June 2004- February 2005
P-Index
1 to 2
85 to 100
Inflow vs. Outflow Rates
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.1
1/13/2005 12:00 1/14/2005 0:00 1/14/2005 12:00 1/15/2005 0:00 1/15/2005 12:00 1/16/2005 0:00
Dis
char
ge
(cfs
)
0
0.2
0.4
0.6
0.8
1
1.2
Dep
th (
in)
Inflow
Outflow
CumulativeRainfall
Design Considerations
• Design Objectives (Quality / Volume / Flow / Recharge) • Media Specifications / Consistency • Sizing • Offline / Flow–Through Systems• Pretreatment • Unique configurations / designs (costs)• Custom Application (Bacteria / Metals / Oil and Grease)
Bioretention Design Objectives
• Peak Discharge Control o 1-, 2-, 10-, 15-, 100-year stormso Bioretention may provide part or all of this control
• Water Quality Controlo ½”, 1” or 2” rainfall most frequently usedo Bioretention can provide 100% control
• Ground water rechargeo Many jurisdictions now require recharge
( e.g., MD, PA, NJ, VA)
2’
2” Mulch
Infiltration System
Highly Pervious Soils
Existing Ground
2’
2” Mulch
Drain Pipe
Combination Filtration / Infiltration
Gravel
Sandy Organic Soil
Existing Ground
Bioretention
Shallow Ponding - 4” to 6”
• Mulch 3”
• BSM Depth 2’ - 2.5’
• BSM• 50% Sand
• 30% Sandy Loam
• 20% Shredded Hardwood/ Compost
• Underdrain System
• Plants
X 2’
Under Drain
Bioretention Soil Medium Final proportion Component Properties
50% by volumeSand Conforms to ASTM C33 Fine
Aggregate
20% by volumeOrganic Material Compost or shredded
hardwood mulch
30% by volume
Topsoil Sand (2.0 – 0.050 mm) 50 – 85% by weight Silt (0.050 – 0.002 mm) 0 – 50% by weight Clay (less than 0.002 mm) 10 – 20% by weight * Organic Matter 1.5 – 10% by weight pH 5.5 – 7.5 (NOTE: pH can be
corrected with soil amendments if outside acceptable range)
Magnesium Minimum 32 ppm (NOTE: magnesium sulfate can be added to increase Mg)
Phosphorus (Phosphate - P2O5)
Not to exceed 69 ppm
P-index should be less than 25 Potassium (K2O) Minimum 78 ppm (NOTE:
potash can be added to increase K)
Soluble Salts Not to exceed 500 ppm* If the proposed topsoil is known to contain expansive clays, clay content should not exceed 10% by weight.
Other Media Considerations
• Homogenous Mixture• Peat / Clays / Silts slow flows • Test and standardize the media! • But performance varies with source! • Min 1.0’ depth of media • Max depth varies with vegetation.• Organic Component (Shredded Hardwood vs. Compost)
Underdrain System • Needed for subsoils with percolation rates less than ½” per
hour
• Filter fabric vs pea gravel diaphragm
• Minimum of 3" of gravel over pipes; not necessary underneath pipes
• Underdrain Piping ASTM D-1785 or AASHTO M-2786" rigid schedule 40 PVC 3/8" perf. @ 6" on center, 4 holes per row; or corrugated perforated HDPE
• Observation wells
Design Configuration Considerations
• Off line vs. Flow-through• Inlet • Surface Storage• Underdrain – Dewater media
Off-line
2005 Lake County, OH
Flow-through
2005 Lake County, OH
Plant Considerations
• Pollutant uptake • Evapotranspiration • Soil ecology / structure / function • Number & type of plantings may vary,
o Aestheticso Morphology (root structure trees, shrubs and herbaceous) o Native plants materialso Trees 2 in. caliper / shrubs 2 gal. size / herbaceous 1 gal size. o landscape plan will be required as part of the plan. o Sealed by a registered landscape architect.o Plants are an integral part no changes unless approved o Plant survival
• Irrigation – Typical / customary
Sizing
• Flow rate• Infiltration rate• Volume• Void space• Drainage area (Smaller the Better)
“Kerplunk” Method
• Bioretention 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)
“Kerplunk” Method
𝐴𝑟𝑒𝑎=𝑅𝑢𝑛𝑜𝑓𝑓 𝑣𝑜𝑙𝑢𝑚𝑒
𝐸𝑓𝑓𝑒𝑐𝑡𝑖𝑣𝑒𝑠𝑡𝑜𝑟𝑎𝑔𝑒 h𝑑𝑒𝑝𝑡
𝐸𝑓𝑓𝑒𝑐𝑡𝑖𝑣𝑒𝑠𝑡𝑜𝑟𝑎𝑔𝑒 h𝑑𝑒𝑝𝑡 =𝑝𝑜𝑛𝑑𝑖𝑛𝑔 h𝑑𝑒𝑝𝑡 +(𝐵𝑆𝑀 h𝑑𝑒𝑝𝑡 ∗𝐵𝑆𝑀 𝑝𝑜𝑟𝑜𝑠𝑖𝑡𝑦 )+(𝑔𝑟𝑎𝑣𝑒𝑙 h𝑑𝑒𝑝𝑡 ∗𝑔𝑟𝑎𝑣𝑒𝑙𝑝𝑜𝑟𝑜𝑠𝑖𝑡𝑦)BSM porosity ≈ 0.35Gravel porosity ≈ 0.4
RECARGA
• Developed by the University of Wisconsin-Madison Department of Civil Engineering
• Capable of single event or continuous simulation• Incorporates infiltration, evapotranspiration, overflow, and
underdrain flow
RECARGA
http://dnr.wi.gov/runoff/stormwater/technote.htm
Thank you for your time.
QUESTIONS?
Low Impact Development Center, Inc.www.lowimpactdevelopment.org
301.982.5559