Construction and Performance of Bioretention Cells

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Construction and Performanceof Bioretention
Cells

• G.O. Brown, R.A. Chavez, D.E. Storm, and M.D.
  Smolen

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Objectives
8 at Grove onGrand Lake2 at Stillwater,
including a control pair

• Demonstrate use of bioretention cells to improve
  water quality primarily P reduction.
• Develop simple to follow design procedures.
• Quantify cell hydrology.
• Long-term test of fly ash in filter media.

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General Design

• 3 to 5 of area.
• Sized for runoff
• ½ in pool
• ½ in filter
• 1 topsoil.
• Sand plug on 25 of surface for infiltration.
• Filter media a blend of sand and 5 fly ash.
• Overflow designed for 50 year, 1 hour storm.

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A high-tech hole in the ground
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Infiltration plugs minimizestanding water
plug

• Designed to onlypond water for 24 hr.
• Addition of sand plugson surface
  compensatefor lower conductivityof top soil.
• 25 of surface layer are sand plugs with a
  specification that none touch.
• Proved to be easy to construct and effective.

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Class C fly ash significantly reducesP and
metals in effluent

• Batch sorption for Kd
• Column experiments simulated leaching within the
  cell.
• BCTs were fitted to find transport parameters.
• Long-term effluent modeled with fitted
  parameters.

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Phosphorous adsorption
Kd, mL/g Retardation
Peat moss -5.8 1
Teller loam 0.41 3
Dougherty sand 2.1 11
Expanded shale (MO) 1.2 7
Limestone 12 60
Expanded shale (KS) 280 1,400
Class C Fly ash 2180 11,000
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Fly ash will provide long-termP reductions
Effluent P Concentration Exceeds Lifetime, yr Lifetime, yr
Effluent P Concentration Exceeds Pavement Lawn
0.037 mg/L 4 11
0.5 mg/L 12 35
0.95 mg/L 36 99

• Lifetime of filter calculated assuming 1 ppm P
  inflow
• Runoff volume from pavement will be higher than
  lawns.
• Assumes reversible adsorption.

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Fly ash significantly reduces K

• Adding fly ash decreased the hydraulic
  conductivity of the sand exponentially
• Maximum 5 fly ash in Dougherty

Hydraulic conductivity of sand fly ash mix.
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Plantings

• Wet and dry tolerant
• No nitrogen fixers
• No invasive species
• Low-maintenance requirements
• Offer a color variety
• Plants had to be easily attainable and
  replaceable
• Included some native species in the plant list.

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Lots of discussion about the plants
Plant Type Surface Area
Trees 8 to 10
Shrubs 15 to 20
Flowering Perennials 1 to 5
Ornamental Grasses 10 to 15
Rock Accents 1 to 5
Of course, you could just plant grass.
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Constructed Cells Land Use Drainage Area (acres) Volume (m3)
Elm Creek Plaza Paved 0.62 128
Lendonwood Gardens Turf 0.54 19
Grove High School Paved 0.65 161
Grand Lake Association Turf Paved 1.90 435
Cherokee Queen Riverboats Paved 0.45 108
Spicer Residence Turf 0.39 93
Clark Residence Turf 0.18 27
Early Childhood Center Turf 0.11 70
OSU Botanical Gardens, Cell A Paved 0.32 66
OSU Botanical Gardens, Cell B Paved 0.90 208
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Construction
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Construction costs
7,500 51 volume
1,600 47 volume
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Mixing fly ash proved difficult
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Wide distribution in fly ash
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Hydraulic testing
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30 reduction in peak flow
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Water Quality Data are Inconclusive

• Water quality data collected to date are
  generally inadequate to draw strong conclusions.
• Problems arise due to the long response time of
  these cells and the difficultly of measuring both
  inflows and outflows over extended periods.
• Long-term, we will take core samples of the cells
  and determine the species and quantity of
  pollutants trapped.
• A comparison between the fly ash and sand filter
  control is possible for the initial operation.

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Impact of fly ash on effluent
Parameter Cell N Mean St Dev
pH Control 8 7.58 0.450
pH Fly Ash 6 9.78 0.436
NO3-N (mg/l) Control 8 3.44 2.53
NO3-N (mg/l) Fly Ash 6 5.95 3.03
Ortho-P (mg/l) Control 8 0.115 0.0441
Ortho-P (mg/l) Fly Ash 6 0.063 0.0816
Fe (mg/l) Control 8 2.29 2.85
Fe (mg/l) Fly Ash 6 0.122 0.046
Cu (mg/l) Control 8 lt0.02 0.007
Cu (mg/l) Fly Ash 6 0.022 0.004
Pb (mg/l) Control 8 lt0.02 0.002
Pb (mg/l) Fly Ash 6 lt0.02 0.016
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Two-sample T-test (95)
Parameter T-Value P-Value DF Significant Difference?
pH -9.26 0.000 11 Yes (Higher)
NO3-N -1.64 0.135 9 No
Ortho-P 3.24 0.014 7 Yes (Lower)
Fe 2.15 0.069 7 No
Cu -3.05 0.011 11 Yes (Higher)
Pb -1.09 0.326 5 No
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Next steps

• Finish analysis of cell hydrology.
• Quantify impact of the spatial variability in
  conductivity.
• Perform more field tests.
• Model results.
• Relate to watershed hydrology.
• Sample cells to determine retention of
  pollutants.
• Explore filter additives that will reduce N.

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Acknowledgements

• Funding for this project was provided by the
  Oklahoma Conservation Commission as part of a
  U.S. EPA Region VI, 319h grant.
• Fly ashdonated byGrand RiverDamAuthority.
• Modelingby ReidChristianson

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