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Buffer Zones Based on Air Dispersion Modeling - An Effective Approach to Odor Mitigation

Buffer Zones Based on Air Dispersion Modeling - An Effective Approach to Odor Mitigation. Bill Tomerlin, Cliff Hoelscher, and Ray Kemp. Paul Bonnici and Perry Holland. Project Description.

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Buffer Zones Based on Air Dispersion Modeling - An Effective Approach to Odor Mitigation

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  1. Buffer Zones Based on Air Dispersion Modeling -An Effective Approach to Odor Mitigation Bill Tomerlin, Cliff Hoelscher, and Ray Kemp Paul Bonnici and Perry Holland

  2. Project Description • Study to define odor impact of City of Fort Collins Drake Water Reclamation Facility (DWRF) and Mulberry Water Reclamation Facility (MWRF) on surrounding community • Model DWRF odors using an air dispersion model to justify a 1000 foot buffer zone • Develop odor mitigation strategy based on model and treatment alternatives

  3. DWRF Description • Capacity = 23 mgd • Treatment includes primary treatment and two-stage biological treatment • Solids treatment facilities treat solids from both the DWRF and MWRF

  4. DWRF Schematic

  5. Drake Water Reclamation Facility

  6. Presentation Overview • Buffer Zones and Odor Mitigation • Air Dispersion Modeling • Sampling/Testing for Odors at the DWRF • Air Dispersion Model Output • Conclusions

  7. Buffer Zones • Zones intended to provide buffer between plant odor sources and developed areas • Buffer Zones prevent development immediately adjacent to wastewater treatment facilities • Buffer reduced the overall required odor mitigation measures at each facility

  8. Buffer Zone Regulations

  9. Buffer Zone Example • www.srcsd.com/buffer.html

  10. Air Dispersion Modeling • Uses topographical and meteorological data to estimate pollutant concentrations at downwind locations • Air Dispersion Model Software - ISCST3

  11. Basic Steps to Develop an Air Dispersion Model • Obtain meteorological data • Data came from NCDC and private weather station ~ 1 mile from the DWRF site • Looked at 5 years of data and chose the worst year

  12. Basic Steps to Develop an Air Dispersion Model • Obtain odor source and building parameters • Odor source: coordinates, release height, areas, exit velocity, air flow factor, temp., line or area source designation • Building parameters: includes physical dimensions of plant structures • Also included future anticipated structures and processes

  13. Basic Steps to Develop an Air Dispersion Model • Obtain land use and terrain data • Land use must be classified rural or urban • Terrain data was incorporated into the model using USGS DEM (digital elevation model) data

  14. Basic Steps to Develop an Air Dispersion Model • Build a receptor grid • DWRF receptor grid consists of 100-meter receptor spacing • The grid does not include receptors inside the fenceline but does include fenceline receptors

  15. Basic Steps to Develop an Air Dispersion Model • Build receptor grid

  16. Basic Steps to Develop an Air Dispersion Model • Develop an odor sampling plan • Continuous H2S • Sensory Analysis • Gas Chromatography Analysis • Liquid Sulfide Analysis • Ammonia Draeger Tubes

  17. Basic Steps to Develop an Air Dispersion Model

  18. Basic Steps to Develop an Air Dispersion Model • Continuous H2S Monitoring

  19. Basic Steps to Develop an Air Dispersion Model • Sampling equipment

  20. Basic Steps to Develop an Air Dispersion Model • Sample testing - Winter

  21. Basic Steps to Develop an Air Dispersion Model • Sample testing - Summer

  22. Develop emissions estimates for each odor source based on measured DT values 1) Area and Line Sources: Emission Rate ((DT/s)/m2) = Air Flow Factor (cfm/m2) / Conversion Factor (0.58) * DT 2) Point Sources: Emission Rate (DT/s) = Air Flow Rate From Stack (m3/s)* DT Where: Air Flow Factor = 3 cfm/m2 (turbulent surfaces), 1.37 cfm/m2 (quiescent surfaces) Conversion Factor = 35.3 ft3/m3 / 60 s/min = 0.58 DT = maximum sampling result Basic Steps to Develop an Air Dispersion Model

  23. Air Dispersion Model Output -Odor Impacts Extents by Year Legend 1993 1994 1995 1996 1997

  24. Air Dispersion Model Output -Cumulative Summary • CDPH&E regulations • Hog Farms= 2 DT • Other Sources = 7 DT • Odor impact is typically defined as 2 DT

  25. Air Dispersion Model Output -Culpability Summary Legend South Plant Aeration Basins North Plant Aeration Basins Master Plan Aeration Basins Primary Clarifier Weir Zone Thickening Building Fan Primary Clarifier Settling Zone Digested Sludge Odor Control Centrate Holding Tank __ = Buffer Zone

  26. Air Dispersion Model Output: Frequency of Odor Excursions Over 2 DT in hrs./yr.

  27. DWRF Odor Source Magnitude and Frequency

  28. DWRF Odor Source Rankings

  29. Conclusions • Air Dispersion Model results show significant odors outside 1,000 foot buffer zone; therefore, additional on-site odor mitigation will be required • Buffer Zone will help reduce the amount of on-site mitigation required • The air dispersion model will be used to model various odor mitigation technologies and their effectiveness

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