Modeling associated with the Sulfur Dioxide Data Requirements Rule.

1. www.all4inc.com | Philadelphia | Atlanta | Houston | Washington DC
Techniques for SO2
Designations
Mark Wenclawiak, CCM | mwenclawiak@all4inc.com | 678-460-0324
June 15, 2015
The Importance of Variable Emissions and
Ambient Air

2. 2 Your environmental compliance is clearly our business.
Agenda
 Key Distinctions from U.S. EPA SO2 Modeling TAD
to Regulatory Modeling Requirements
 Comparison of Model Results for Regulatory
Permitting Analysis Versus Designation Analysis
 Case Study Findings and Resulting Implications of
Upcoming Modeling and Regulatory Policies

3. Comparison of SO2
Modeling TAD to
Regulatory Modeling
Requirements

4. 4 Your environmental compliance is clearly our business.
SO2 Modeling TAD
 Actual emission rates
from past 3 years
 Characteristics can be
varied on an hourly basis
 Potential for 26,280 hours
of different emission
characteristics for each
emission source
 Use of current stack
heights
Stack Characteristics
Regulatory Modeling
 Potential to emit (PTE)
 Can vary emissions rates –
but typically not varied
hourly (and could result in
permit limits)
 Potential to model stack
heights as GEP, not
current stack height

5. 5 Your environmental compliance is clearly our business.
 Varied emissions data is intensive and time
consuming
 Intermittent sources (e.g., emergency
generators) only evaluated if operated enough
to contribute to 99th percentile
 Actual emissions can be an improvement over
allowable emissions
Considerations for TAD Modeled
Emission Rates

6. 6 Your environmental compliance is clearly our business.
SO2 Modeling TAD
 Distance between receptors
can vary depending on state
guidance
 Cartesian grid with dense
receptor spacing closer to the
Facility
 Remove receptors from areas
where ambient monitors
could not be installed (e.g.,
water, cliff, etc.)
Ambient Air Receptor Placement
Regulatory Modeling
 Distance between
receptors can vary
depending on state
guidance
 Receptors cover all area
surrounding a facility
regardless of terrain

7. 7 Your environmental compliance is clearly our business.
Traditional PSD Receptor Grid

8. 8 Your environmental compliance is clearly our business.
DRR Receptor Grid

9. Simplified Case Study
Comparison

10. 10 Your environmental compliance is clearly our business.
 Single stack for a coal fired boiler
• 230 foot stack height
• Typical mill building downwash (including a nearby
recovery furnace building)
• Standard receptor grid spacing – no terrain
• 140,000 acfm flowrate
• PTE Scenario: 565 lb/hr emission limit
• Actual emissions scenario: Varied coal firing rates,
0.6% sulfur content, fixed flowrate (varied flowrates
would impact results but not drastically since flow is
boiler loading and flow is fairly constant)
Case Study

11. 11 Your environmental compliance is clearly our business.
 Simple example to highlight:
• Differences due to actual versus allowable emission
rates
• Significant concentration gradients and differences
between fence line and exposure receptor impacts
 2 scenarios
• Constant PTE emission rate (NAAQS)
• Variable emission rate (actual rates from CEMS data)
Case Study

12. 12 Your environmental compliance is clearly our business.
 Use of actual emissions is an improvement over
allowable emissions
Emission Rate Considerations

13. 13 Your environmental compliance is clearly our business.
Case Study Results
 When using varying hourly emission rates
• 4th high concentrations are 33% lower than PTE
• 1-hour maximum is 21% lower than PTE

14. Implications of Upcoming
Policies

15. 15 Your environmental compliance is clearly our business.
 Constant maximum emission rate overly
conservative
• Compounded by combining with observed
monitoring concentrations as background
 Higher concentrations during periods of SSM
• May 22, 2015 SIP call rule
 Emission Variability Processor (EMVAP)
• Incorporate varying emissions with Monte Carlo
statistical technique
• 50th percentile monitored concentration as
background
Importance of Variable Emissions

16. 16 Your environmental compliance is clearly our business.
 What 1-hour background concentration do you
add to modeled concentration?
• Highest hourly concentration
• 3-year average of 99th percentile of maximum daily
(p=0.0001)
• EMVAP and 50th percentile background
concentration
 Probability of exceedance 0.005; equivalent to 99.5th
percentile, compared to 99th percentile form of the
standard
Selection of Ambient Air

17. 17 Your environmental compliance is clearly our business.
 Projected final DRR in September 2015
 Steps to take:
• Identify the applicability of your facility
• Conduct air dispersion modeling using the three year
actual emissions approach outlined in the TAD
• Evaluate options for compliance with dispersion
modeling
 The idea is to mirror the steps that the agency
and U.S. EPA will take
Planning Ahead

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Questions & Open Discussions