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Construction and Performance of Bioretention Cells

Construction and Performance of Bioretention Cells

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Construction and Performance of Bioretention Cells

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  1. Construction and Performanceof Bioretention Cells G.O. Brown, R.A. Chavez, D.E. Storm, and M.D. Smolen EWRI - Kansas City - 2009

  2. 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. EWRI – Kansas City - 2009

  3. 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. EWRI – Kansas City - 2009

  4. A high-tech hole in the ground EWRI – Kansas City - 2009

  5. Infiltration plugs minimizestanding water plug • Designed to onlypond water for 24 hr. • Addition of sand “plugs”on 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. EWRI – Kansas City - 2009

  6. 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. EWRI – Kansas City - 2009

  7. Phosphorous adsorption EWRI – Kansas City - 2009

  8. Fly ash will provide long-termP reductions • Lifetime of filter calculated assuming 1 ppm P inflow • Runoff volume from pavement will be higher than lawns. • Assumes reversible adsorption. EWRI – Kansas City - 2009

  9. 5.0% fly ash Ks=3.6 cm/hr 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. EWRI – Kansas City - 2009

  10. 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. EWRI – Kansas City - 2009

  11. Heritage River Birch Lots of discussion about the plants… Of course, you could just plant grass. EWRI – Kansas City - 2009

  12. EWRI – Kansas City - 2009

  13. Construction EWRI – Kansas City - 2009

  14. Construction costs $7,500 + $51* volume $1,600 * $47 * volume EWRI – Kansas City - 2009

  15. Mixing fly ash proved difficult EWRI – Kansas City - 2009

  16. Wide distribution in fly ash EWRI – Kansas City - 2009

  17. Hydraulic testing EWRI – Kansas City - 2009

  18. 30 % reduction in peak flow EWRI – Kansas City - 2009

  19. 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. EWRI – Kansas City - 2009

  20. Impact of fly ash on effluent EWRI – Kansas City - 2009

  21. Two-sample T-test (95%) EWRI – Kansas City - 2009

  22. 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. EWRI – Kansas City - 2009

  23. 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 EWRI – Kansas City - 2009

  24. EWRI – Kansas City - 2009