Bioretention “Rain Garden” Technical Seminar
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Transcript of Bioretention “Rain Garden” Technical Seminar
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Bioretention “Rain Garden” Technical Seminar
San Francisco Regional Water Quality Control BoardSan Francisco Regional Water Quality Control BoardSanta Clara Valley Urban Runoff Pollution Prevention ProgramSanta Clara Valley Urban Runoff Pollution Prevention Program
Larry S. Coffman, President Stormwater Services , LLLP
Phone: 301 580 6631email: lcoffman @ filterra.com
Prince George’s County, Maryland * Low Impact Development Center Filterra Division
A Growing Idea in Stormwater Treatment
Manufactured by:
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Overview
• Functions • Design Criteria • Construction • Maintenance • Inspection • Enforcement• Lessons • Applications
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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
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Pollutant Removal MechanismsPollutant Removal Mechanisms““Physical / Chemical / Biological”Physical / Chemical / Biological”
ProcessesSedimentationFiltration AdsorptionAbsorptionCation Exchange Capacity Polar / Non-polar SorptionMicrobial Action (aerobic / anaerobic)
decomposition / nitrification / denitrification
Plant 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”
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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
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Interesting Study Findings
• Mulch and Metals• Plants and Metals • P Uptake• Capacity / Longevity• Residence Time• Oil and Grease 95% Removal• 90% Bacteria Removal• Flow rate varies with moisture content
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Pollutant Removal - Plant Microbe
• Phytoremediation – Translocate– Accumulate – Metabolize– Volatilize– Detoxify– Degrade
• Exudates• Bioremediation• Soils Soils
– Capture / Immobilize PollutantsCapture / Immobilize Pollutants
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Phosphorus Cycle
Animals
ATP
Plants & Microbes
PO43-
Water
Kx,NaxHyPO4
Detergents
Na3PO4
Manure
Cax(OH)y(PO4)z
NaxHyPO4
KxHyPO4
Soil & Rock
Cax, Fex, Mgx, Alx
(OH)y(PO4)z
Fertilizer
NaxHyPO4
KxHyPO4
Land
Aquatic
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Louisburg BioretentionDr. Bill Hunt
North Carolina State Research
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Load Reductions: Louisburg Removal vs. PI
Cell TN TP
L-1
(unlined)64% 66%
L-2
(lined)68% 22%
June 2004- February 2005June 2004- February 2005
PI
1 to 2
85 to 100
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GSO: Load Reduction
G-1Inflow Load
Outflow Load
% reduction
H2O (1000 L) 2670 1170 56
TN (kg) 4.69 3.13 33
TP (kg) 0.53 0.48 9
G-2G-2
H2O (1000 L) 2670 1010 62
TN (kg) 4.36 2.5 43
TP (kg) .41 .57 -39-39
(July 03- Dec 04)(July 03- Dec 04)
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Inflow V. 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
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NC Shellfish Closures
• 100,000 acres of shellfish waters are permanently or temporarily closed to harvesting.
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Hal Marshall Bioretention: Fecal Coliform Concentrations
1
10
100
1,000
10,000
100,000 FC- InFC- Out
Con
cent
ratio
n in
C
once
ntra
tion
in
Col
/100
ml
Col
/100
ml
Min. DetectMin. Detect
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Bioretention Construction Costs
Excavation (assume no hauling)
$3 - $5 / cy
Fill Media $15 - $20 / cy
Vegetation/ Mulch $1.00 - $1.50 / sf
Underdrains /Gravel & Outlet
$0.50 - $1.50 / sf
Total $10 - $14 / sf
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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)
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Bioretention Design Objectives
• Peak Discharge Control – 1-, 2-, 10-, 15-, 100-year storms– Bioretention may provide part or all of this control
• Water Quality Control– ½”, 1” or 2” rainfall most frequently used– Bioretention can provide 100% control
• Ground water recharge– Many jurisdictions now require recharge
( e.g., MD, PA, NJ, VA)
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2’
2” Mulch2” Mulch
Infiltration System
Highly Pervious Soils
Existing Existing GroundGround
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2’
2” Mulch2” Mulch
Drain Pipe
Filtration System Filtration System
Existing Existing GroundGround
Highly Pervious Soils
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2’
2” Mulch2” Mulch
Drain Pipe
Combination Filtration / InfiltrationCombination Filtration / Infiltration
Moderately Pervious Soils
Gravel
Sandy Organic Soil
Existing Ground
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BioretentionBioretention Shallow Ponding - 4” to 6”
• Mulch 3”
• Soil Depth 2’ - 2.5’
• Sandy Top Soil
• 65% Sand
• 20% Sandy Loam
• 15% Compost
• Under Drain System
• Plants
X 2’
Under Drain
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Low Flow Media2 to 10 inches / hour
Peat / Sand / Aggregate Matrix - PSD
Peat 15 to 20% by volume
Clay <5% (<0.002 mm)
Silt <5% (0.002-0.05 mm)
Very Fine Sand 5-10% (0.05-0.15 mm)
Fine Sand 15-20% (0.15-0.25 mm)
Medium to Coarse Sand 60-70% (0.25-1.0 mm)
Coarse Sand 5-10% (1.0-2.0 mm)
Fine Gravel <5% (2.0-3.4 mm)
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High Flow Media10 to 50 inches / hour
Peat Sand / Aggregate Matrix - PSD
Peat 5 to 10% by volume
Clay <2% (<0.002 mm)
Silt <2% (0.002-0.05 mm)
Very Fine Sand 5% (0.05-0.15 mm)
Fine Sand 10% (0.15-0.25 mm)
Medium to Coarse Sand 70% (0.25-1.0 mm)
Coarse Sand 10-15% (1.0-2.0 mm)
Fine Gravel 5-10% (2.0-3.4 mm)
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City of Portland , ORCity of Portland , OR
Low Flow - 1” to 3” / Hour “Soaker”
Sand / Municipal Compost
Ocean City, MDOcean City, MD
High Flow - + 100” / Hour Filterra
Corse Sand / Peat
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Other Media Considerations
• Homogenous Mixture
• Peat / Clays / Silts slow flows
• Test and standardize the media!
• But performance varies with source!
• Min 1.0” of media
• Max varies with Veg.
• Organic Component (Peat vs. Compost)
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Media Components Properties
Sand Silt Loam Compost Peat
Permeability (cm/hr) 3.3 0.1-0.4 - 0.25-140
Water holding capacity (cm/cm) 0.14 .07-0.1 - .01-0.2
Bulk density (g/cm) 2.65 1.25 1-2 <0.1-0.3
pH - 5.7 7.8 3.6-6.0
Organic matter (%) <1 <20 30-70 80-98
Cation exchange capacity 1-3 12-18 66 183-265
Total phosphorus (%) 0 0.09 <0.1 <0.1
Total nitrogen (%) 0 0.15 <1.0 <2.5
Filtration efficiency after
18 in. (%) 93 94 16 47
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Louisburg Bioretention Cells
• Soil Media:Soil Media:– Nominally 0.75 m DeepNominally 0.75 m Deep– 60% Sand60% Sand– 40% “Ballfield Mix” 40% “Ballfield Mix”
• Low PI (1-2) fillLow PI (1-2) fill– 85% Sand– 10% Fines– 5% Organics
• Constructed Spring 2004
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Other Media Considerations
• Mulch – Hardwood / Pine bark
– Use as pretreatment
– Water retention
– Pollutant removal
– Maintenance
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Underdrain System
• Avoid Filter Fabric use bridging stone (pea gravel around pipe)
• 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;
• Observation wells
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Pretreatment – NOT NECESSARY! Little additional benefit
Additional Maintenance issues Requires additional space
Restricts use
New York Design Manual, Appendix C
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Design Configuration Considerations
• Off line vs. Flow-through
• Inlet
• Surface Storage
• Underdrain – Dewater media
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Off-line
2005 Lake County, OH
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Flow-through
2005 lake County, OH
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Plants Considerations
• Pollutant uptake • Evapotranspiration • Soil ecology / structure / function • Number & type of plantings may vary,
– Aesthetics– Morphology (root structure trees, shrubs and herbaceous) – Native plants materials– Trees 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 approved – Plant survival
• Irrigation – Typical / customary
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Bioretention: Site Analysis
• Map site soils by soil series, hydrologic soil type (A, B,C, D), textural classification and engineering properties
• If possible, avoid laying impervious surfaces (roads, parking lots, driveways) over HSG A and B soils
• Minimize cut and fill in A & B soils (site fingerprinting)
• Infiltration facilities in C & D soils require underdrains.
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Sizing
• Flow rate
• Infiltration rate
• Volume
• Intensity
• Void space
• Drainage area (Smaller the Better)
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Design MethodsInfiltration Design
Af = WQv / n(Df) + KsTf
Where:
Af = Surface area of bioretention bed (sq.ft.)
WQv = Water quality treatment volume (cu.ft.)
Df = Planting soil-bed (ft)
Ks = Final soil infiltration Rate (inches/ hour)
n = Planting soil bed porosity
Tf = Time allowed to dewater facility (hours)
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Design MethodsInfiltration Design Example 1
Calculate size of bioretention area required to control 1 inch of rainfall from a one acre parking lot (Rv=0.95)
WQv = PxRv = [1.0” x 0.95/12”/ft] X 43,560 cu.ft/ac = 3,449 cu.ft.
K = 0.5 in/hr Df = 2.5 ft (soil) + 1.0 ft (sand) = 3.5 ft. n = 0.30 Tf = 48 hrs
Af = 3,449 cu.ft. / [(0.30)(3.5) + (0.5/12)(48)] = 1131 sq. ft.
% of site area = 1131 sq.ft / 43560 sq.ft) = 2.6%
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Design MethodsInfiltration Design Notes
WQv = based on design storm (1/2 -1 in for water
quality); 2-3 inches for volume control
(2 yr-storm)
Df = 18 – 48 in.
Ks = 0.5 in/hr minimum
n = 0.35
Tf = 48 hours
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Design MethodsInfiltration Design Example 2
Calculate size of bioretention area required to control 3 inch of rainfall from a one acre parking lot (Rv=0.95)
WQv = PxRv = [3.0” x 0.95/12”/ft] X 43,560 cu.ft/ac = 10,347 cu.ft.
K = 0.5 in/hr Df = 2.5 ft (soil) + 1.0 ft (sand) = 3.5 ft. n = 0.30 Tf = 48 hrs
Af = 10,347 cu.ft. / [(0.30)(3.5) + (0.5/12)(48)] = 3,393 sq. ft.
% of site area = 3,393 sq.ft / 43560 sq.ft) = 7.79%
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Construction / InspectionConstruction / Inspection
• Preconstruction meeting” with the contractor / owner / architect / engineer
• Geotechnical Report• Ensure sediment control measures in place • Sub grade soils and preparation.• Presence of Ground water • Under drain and filter media installation.• Soil certifications for back fill. • Topsoil layers should be thoroughly wetted achieve settlement. • Plant placement / warrantee / type• Proper site grading • Site stabilization before planting.• U&O
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Inspection / Maintenance
• Require a long term maintenance plan• Non Erosive Designs Inlet / Outlet / Flow-
through• Sediment build-up• Annual inspection / plant care• Excessive ponding (Longer than 8 hours)• Use underdrains• Right Vegetation• Spills
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Maintenance Funding
• Poorly addressed and biggest failure!• Private systems • Private systems built to public standards
– Capitalize maintenance costs– Maintenance fee– General or dedicated funds
• Manufacturer's provide “long term” maintenance – Up front options to renew– Encourage competition
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Enforcement
• Site Inspectors – field adjustments• Site restoration or construction bonds• Site Inspection fees• Individual property owner agreement• Home Owner Association • Easements / Rights-of-way
– Enable local government actions – Fees / Fines / Penalties
• Administrative and Court actions
• Community standards• U&O
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Lessons Learned High Failure Rates Due to:
• Use of Old Design Standards - clay / organic / K factor
• Poor Drainage - Under drain design / Geo-fabrics / Saturated soils
• Media Variability - Reliable Sources
• Contractor Substitutes • Contamination
- P, N and Heavy Metals • Sizing / Space • Maintenance
- Can be high as system become larger
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AlhambraAlhambra
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Bioretention ApplicationsBioretention Applications
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Rain GardensRain Gardens
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Rain Garden in an office building project along the G.W. Parkway. (Looking East)
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Residential Rain Gardens
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Example Bioretention Areas
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Bioretention Types
Fieldstone weep garden design
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Weep Wall Weep Wall FilterFilter
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Rain Garden on a commercial project with turf grass near I-395 and Edsall Road.
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Rain Garden with turf grass treating the rooftop runoff (sheet-flows across lawn) of a hospital facility.
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The first Rain Garden in Virginia, located in a turning circle in front of St. Stephens School, Alexandria.
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St. Stephens Rain Garden- 5 years later.
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Rain Gardens used through-out the Alexandria Central Library to treat all impervious runoff
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New River MCAS
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All green space can be All green space can be designed to be hydrologically designed to be hydrologically functional and treat runoff.functional and treat runoff.
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Port Towns Shopping Center
Flow
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0.94 Acres @ $29,000$30,000 / Ac.
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Buckman Heights courtyard with infiltration garden
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Buckman Heights Apartments – Infiltration garden
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Division Street Planters
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Environmental Education and Outreach
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Maintenance
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