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.

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. 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. BAF Customers

4. BAF Blackfoot Facility

5. BAF Blackfoot Facility

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. 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. 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. 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. Downwash Screening – Stack CXX

11. Downwash Screening – Stack EU_15

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. Building Downwash
Image from Lakes Environmental Software

14. AERMOD/PRIME
Overestimates
Downwash
Reality
AERMOD Building Downwash
Height of Building Downwash Zone Overestimated in PRIME

15. Equivalent Building Dimension
Method for Downwash

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. Baseline Case (with BPIP values)

18. Model Design and Construction
• Obtain source/site data
• Specify test wind speeds and directions
• Compute model operating conditions
• Construct scale model

19. Phase 1 Testing: Flakers

20. Phase 2 Testing: Dehydrators

21. Measure Ground-level Concentrations
Data taken until good fit and max obtained Automated Max GL Concentration Mapper

22. Identify Wind Tunnel Determined
EBD that Match Dispersion with Site
Structures Present

23. Sample Result Plot

24. EBD Results for EU11

25. Baseline Case (with BPIP values)

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. 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. Questions?