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Using Physical Modeling to Refine Downwash Inputs to AERMOD at a Food Processing Facility


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Demonstrating compliance with air quality standards using dispersion modeling is increasingly difficulty because of significant tightening National Ambient Air Quality Standards (NAAQS) that has occurred in the last decade. Compliance with these standards is usually demonstrated using AERMOD, EPA’s standard model for assessing air quality impacts from industrial sources. However, AERMOD often produces higher predictions of air quality impacts due to the inherent conservative (high) assumptions and simplifications in its formulation. A specific situation involves the calculations used to assess the impacts of air flow downwash around buildings. Although the theory used to estimate these effects was developed for a limited set of building types, these formulae are applied indiscriminately to all types of buildings in a conservative fashion, often leading to significant overpredictions of downwash effects.

This presentation covers the basics of wind tunnel modeling and how it can be used to correct downwash induced overpredictions to achieve compliance. The presentation will also describe the setup and execution of wind tunnel modeling at a food processing facility to develop improved downwash parameters and increase the accuracy of dispersion modeling results.

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Using Physical Modeling to Refine Downwash Inputs to AERMOD at a Food Processing Facility

  1. 1. Using a Wind Tunnel Study to Show Compliance with Particulate Standards 2017 Food & Beverage Environmental Conference, Isle of Palms, SC John S. Kirkpatrick; Basic American Foods Steve Nelson; Coal Creek Environmental Sergio A. Guerra, Ron Petersen, CPP March 29, 2017 COAL CREEK ENVIRONMENTAL ASSOCIATES
  2. 2. Basic American Foods (BAF) Overview • Family owned and operated since 1933 – Ongoing innovation (40+ patents) – Shelf-stable potatoes and beans • Food Service • Limited Retail – Hungry Jack • Facility Locations – Idaho • Blackfoot • Shelley • Rexburg – Washington • Moses Lake
  3. 3. BAF Customers
  4. 4. BAF Blackfoot Facility
  5. 5. BAF Blackfoot Facility
  6. 6. Project History 2002 - ? Year Event 2002 DEQ requires submittal of ambient impacts analysis for all three BAF facilities in SE Idaho 2003 BAF submits ambient impacts analysis with excess PM-10 impacts. 2004-2008 BAF development of PM-10 compliance plan 2007 EPA adopts AERMOD as the dispersion model. Large increases in estimated impacts. 2009 BAF submits permit application with proposed PM10 compliance plan.
  7. 7. Project History Year Event 2011 DEQ issues revised facility permit. Includes a 3-year time period to prepare an Alternate Compliance Plan 2012 BAF prepares alternate plan for DEQ review. DEQ requests that alternate plan consider impacts from adjacent dehydration facility (Regional Outlook – feel good exercise) . 2012 With the addition of the adjacent facility, to the model, overall combined PM-10 impacts are more than 4x the air quality standard 2013 BAF buys the adjacent facility creating a combined operation.
  8. 8. Project History Year Event 2013 - 2015 BAF refines Alternate Compliance Plan to demonstrate that air quality is better at all locations under the combined plan 2015 DEQ rejects Alternate Compliance Plan. BAF required to submit a plan that shows compliance with air quality standards. Next Option????
  9. 9. Permitting and Modeling Challenges • No clear path to show needed reductions in PM10 impact (need 80% reductions in impact) – Modeling options exhausted – No apparent treatment options (most of the PM10 is non-filterable materials) – Stack height increases unfeasible • Wind Tunnel analysis of downwash appeared promising
  10. 10. Downwash Screening – Stack CXX
  11. 11. Downwash Screening – Stack EU_15
  12. 12. AERMOD OVERVIEW • Required model to estimate air quality impacts from industrial sources • Model include source emission rates and stack parameters, and fenceline • Also uses input data for site meteorology and building downwash effects
  13. 13. Building Downwash Image from Lakes Environmental Software
  14. 14. AERMOD/PRIME Overestimates Downwash Reality AERMOD Building Downwash Height of Building Downwash Zone Overestimated in PRIME
  15. 15. Equivalent Building Dimension Method for Downwash
  16. 16. How to Use EBD for Regulatory Purposes? Step 1: Develop a protocol outlining the EBD study Step 2: Submit EBD protocol for approval to regulatory agency. Also need to involve Model Clearinghouse Step 3: Perform wind tunnel testing Step 4: Use building geometry from EBD study in AERMOD to show compliance Step 5: Submit final report for agency review and approval
  17. 17. Baseline Case (with BPIP values)
  18. 18. Model Design and Construction • Obtain source/site data • Specify test wind speeds and directions • Compute model operating conditions • Construct scale model
  19. 19. Phase 1 Testing: Flakers
  20. 20. Phase 2 Testing: Dehydrators
  21. 21. Measure Ground-level Concentrations Data taken until good fit and max obtained Automated Max GL Concentration Mapper
  22. 22. Identify Wind Tunnel Determined EBD that Match Dispersion with Site Structures Present
  23. 23. Sample Result Plot
  24. 24. EBD Results for EU11
  25. 25. Baseline Case (with BPIP values)
  26. 26. WT EBD values for EU 11,12,13,14 (Phase 1) & EU 24, 25, 26, 27, 31,32,33 & 34 (Phase 2) Max PM10 H6H = 89.3 ug/m3
  27. 27. What Happens Next • DEQ has enthusiastically responded to the information obtained • EPA has reviewed the study and indicated general approval • BAF is resubmitting Alternate Compliance Plan using the EBD study results • With Alternate Compliance Plan approved, BAF will have greater flexibility to make future changes at the facility.
  28. 28. Questions?