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What YOU Need to Know About the 1-hour NAAQS Implementation Process
1. What YOU Need to Know About
the 1-hour NAAQS
Implementation Process
Dan P. Dix
Colin T. McCall
November 17, 2011
An All4 Inc. Webinar
Brought to you by EnviroReviewTM
4. About ALL4
Environmental consulting firm
Founded 2002 – currently 30+ employees
Offices in Kimberton, PA and Columbus, GA
Specialize in air quality consulting:
• Complex air permitting and strategy development
• Air dispersion modeling
• Ambient air quality monitoring
Dispersion modeling as a company-wide initiative
www.all4inc.com
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6. NAAQS Background
“Backdrop” of the Clean Air Act
States design their SIPs and enforce and
implement their regulations to meet the
NAAQS
Air quality construction permit programs are
designed around NAAQS compliance
• PSD: Maintaining NAAQS attainment
• NNSR: Getting into NAAQS attainment
NAAQS reevaluated every 5 years
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8. Attainment/Nonattainment Designations
U.S. EPA philosophy on the SO2 NAAQS
implementation process:
• Proposed NAAQS – designations based on
ambient monitoring data
• Final NAAQS – designations based primarily
on air quality modeling data
Shift to reliance on air quality modeling
will become a critical issue for individual
facilities
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10. SO2 NAAQS Implementation
NAAQS Implementation Schedule:
• June 2011: Initial state nonattainment
recommendations to U.S. EPA (most counties were
“unclassifiable”)
• June 2012: EPA to finalize attainment status (most
states will still be “unclassifiable” or attainment)
• June 2013: Maintenance SIP submittals including
individual facility modeling to achieve compliance
with the NAAQS (including air quality modeling for
individual facilities)
• August 2017: Full NAAQS compliance in all areas
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12. Implementation Update
Guidance for states to evaluate designations
using AERMOD was released on September 22,
2011
Most states are currently reviewing the U.S. EPA
guidance and crafting their plans
States need to decide:
• Modeling now for nonattainment designations
• Model after June 2012 for the June 2013
maintenance SIP
States or facilities conducting modeling?
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13. SO2 Maintenance SIP Submittals
U.S. EPA: Revising PSD/NNSR programs to include
new NAAQS is not sufficient. Five components are
required:
• “Attainment Emission Inventory”
• Maintenance Demonstration
• Control Strategy
• Contingency Plan
• Verification of Continued Attainment
Maintenance SIP will list enforceable 1-hour emission
limits (August 2017)
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14. SO2 NAAQS Implementation
State SIPs will be based on AERMOD dispersion
modeling for the following individual facilities (by
order of priority):
• SO2 Actual Emissions > 100 tons per year
• SO2 PTE > 100 tons per year
• Smaller facilities “with a potential to cause or
contribute” to a NAAQS violation
States are considering other options based on
population
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15. SO2 NAAQS Implementation
Legal challenges ongoing:
• Science behind NAAQS levels
• Approach of using modeling
Under the current approach, if states don’t
perform modeling, U.S. EPA will
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17. AERMOD Process
Hourly Wind Speed
Hourly Wind Direction
Hourly Ambient
Temperature
Land Use Patterns Predicted Ground Level
Topography Ambient
Concentrations (µg/m3)
Building Dimensions for all averaging times
Stack Dimensions
Exhaust Velocity
Exhaust Temperature
Emission Rates
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18. Air Quality Modeling Steps
1. Emission Inventory
2. Meteorological Data
(AERMET/AERSURFACE)
3. Terrain Data (AERMAP)
4. Building Downwash (BPIPPRM)
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19. Emission Inventories
Short-term (1-hour) emission rates
Potential to be used as permit limits
Intermittent emission units (e.g., emergency
generators, intermittent emission scenarios such as
startup/shutdown operations or alternative fuels)
• Latest guidance indicates following form of
standard as guideline for what to include (i.e., 99th
percentile (4th highest))
Stack characteristics (height, temperature, velocity,
diameter, location)
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21. Meteorological Data
5 years of National Weather Service data
Minimum of 1 year of onsite data
Surface characteristics and topography
surrounding the facility should be similar to
(representative of) those surrounding the
meteorological station
If no representative meteorological data are
available, SO2 implementation guidance
suggests possibility of using AERSCREEN (with
agency approval)
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22. Terrain Data
“Ambient Air”
Public access must be
restricted in some way
(e.g., fence, security
guard) in order for
onsite receptors to be
disregarded in the
modeling analysis
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26. Full NAAQS Evaluation
Includes facility and other local facilities
Any modeled emission rates should be
acceptable as a 1-hour permit limit with
the appropriate margin for compliance
Considerations for accounting for
emissions during startup and shutdown
Emergency unit considerations
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27. Modeled Emission Rate Examples
Combination Boiler SO2 modeling:
• Bark: > 97% of the annual heat input to the boiler
• Boiler fires 3% sulfur residual oil as a backup fuel
• Annual NAAQS modeling: 0.025 lb/MMBtu x Annual
Heat Input
• 1-hour NAAQS modeling: 3.14 lb/MMBtu at the oil
firing capacity of the boiler
Do we have the appropriate exhaust
information (e.g., temperature, flowrate)
to model the oil firing scenario?
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28. Modeled Emission Rate Examples
Power Boiler SO2 Modeling:
• Fires fuel oil and natural gas
• Current emission limit: 24-hour limit; compliance
demonstrated using a CEMS
• Evaluate the impact of using the 24-hour
emission limit as a modeled 1-hour emission rate
• One year of CEMS data: rare hourly exceedances of
the 24-hour limit, but they do occur
• Operations need to be managed more tightly to
ensure compliance with a 1-hour limit, flexibility is
lost
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29. Modeled Emission Rate Examples
Low-Odor Recovery Furnace:
• Typical operations: < 5 ppm SO2 during black liquor
solids firing
• Startup scenario: 2% sulfur fuel oil
• Do we need to account for startup emissions and
exhaust characteristics of the recovery furnace?
• U.S. EPA has given states flexibility; decision will
depend on the state agency
• No bright line for the annual startup/shutdown
duration that is said to significantly contribute to the
distribution of 1-hour daily maximum concentrations
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30. Local Sources
NAAQS evaluation must include sources
that result in a “significant concentration
gradient” in the vicinity of the facility
Same emission rate considerations apply
for local sources (although permit limit
concerns wouldn’t apply)
State agency typically dictates which local
sources to include in evaluation
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31. NAAQS Modeling Strategy
Start with an evaluation of each individual
emission source
Each source will have different factors that
drive resulting ambient concentrations
The cumulative ambient concentration
from all sources (plus background) will be
evaluated against the NAAQS
Evaluate each source against the NAAQS
as a first step
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32. NAAQS Modeling Strategy
Big picture factors that will drive ambient
concentrations for individual sources:
• Elevated emission rates
• Stack velocity (orientation of release and
flowrate)
• Stack temperature (plume buoyancy)
• Stack height versus surrounding terrain
• Surrounding buildings and structures (i.e.,
building downwash)
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33. Hypothetical Modeling Example
Modeling of a hypothetical facility with the
following SO2 emission sources:
• Process SO2 source
• Fuel oil combustion SO2 source
• Backup engine source
NAAQS modeling evaluation is based on
SO2 potential-to-emit
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37. Process SO2 Source Impacts
Highest impacts in complex terrain far from
facility
Wind speed doesn’t match location of elevated
concentrations
Impacts occur during periods of atmospheric
stability and low mixing heights (typically early
morning, low wind speed conditions)
High concentrations due partially to the
limitations of the AERMOD dispersion model
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38. Combustion SO2 Source
SO2 Emission Rate: 20 lb/hr (AP-42)
Stack Height: 60 feet
Stack Diameter: 2 feet
Exhaust Temp: 225 °F
Exhaust Flow: 16,000 acfm
Buoyant source, short stack (shorter than
the tallest buildings at the facility)
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40. Combustion SO2 Source Impacts
Elevated concentrations are closer to the
facility
Building downwash effects have a
noticeable impact on ambient
concentrations
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43. Engine SO2 Source Impacts
Elevated ambient concentrations at the
facility fenceline for two reasons:
• Low stack height (10 feet)
• No plume buoyancy due to horizontal
discharge
Ambient air considerations become very
important (i.e., public access)
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44. Modeling Refinements
“Process” SO2 Emission Source:
• Stack height increase is technically and
economically infeasible
• Raw materials are fixed due to product
and consumer demand
• Upgrades to the scrubber could achieve
control: ~30% more control (~170 lb/hr)
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47. Modeling Refinements
Combustion SO2 Emission Source:
• Stack height increase is technically and
economically infeasible
• Fuel oil firing is desirable due to cost savings
considerations
• Raw materials to the source bring inherent
scrubbing capacity: 50 to 65% based on
previous studies
• 50% inherent scrubbing brings emission rate
to 10 lb/hr (justify through testing)
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50. Modeling Refinements
Engine SO2 Emission Source:
• Simplest fix is to change the stack
discharge orientation from horizontal to
vertical
• No changes to the vendor-guaranteed
emission rate of the engine
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53. Cumulative Concentrations
The facility must cumulatively comply with
the NAAQS
Addressing each individual source helps
as a first cut
This scenario still exceeds the 1-hour
NAAQS for SO2 when the sources are
taken cumulatively
Haven’t even considered ambient
background concentrations
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54. Modeling Strategies
Emissions Strategies
Actual Distribution of Emissions
• Evaluate adequacy of emission limits
• Evaluate emissions control options
• Evaluate alternate fuels and fuel specifications
Facility Fence Line Strategies
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57. Final Thoughts
States developing their modeling plans now
States will reach out to request information and/or
modeling
Be involved with the SIP process:
• Provide states with good information
• Conduct your own modeling (either for the state
or in parallel with the state)
Avoid surprises (new limits) at the end of the SIP
process
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58. Questions?
We will follow up with questions submitted
during the presentation that were not
answered
Please feel free to e-mail or call us with
additional questions and we will follow up
with you
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59. Questions?
Dan Dix Colin McCall
ddix@all4inc.com cmccall@all4inc.com
(610) 933-5246 x18 (706) 221-7688 x14
2393 Kimberton Road 5900 River Road
PO Box 299 Suite 500
Kimberton, PA 19442 Columbus, GA 31904
All4 Inc.
www.all4inc.com
www.enviroreview.com
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