What YOU Need to Know About the 1-hour NAAQS Implementation Process

Dan P. DixColin T. McCall

November 17, 2011

An All4 Inc. Webinar

Brought to you by EnviroReviewTM

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Agenda Summary of NAAQS NAAQS Implementation Updates Dispersion Modeling Basics and

Inputs NAAQS Modeling Demonstration

Approach

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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

National Ambient Air Quality

Standards (NAAQS)

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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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NAAQS SummaryPollutant Averaging Period

Historic NAAQS (µg/m3)

Revised NAAQS (µg/m3)

CO1-Hour 40,000 40,0008-Hour 10,000 10,000

Ozone 8-Hour 75 ppb WithdrawnPb 3-Month Rolling 1.5 0.15

PM10 24-Hour 150 150

PM2.5

24-Hour 65 35Annual 15 15

NO2

1-Hour N/A 188Annual 100 100

SO2

1-Hour N/A 1963-Hour 1,300 1,300

24-hour 365 Revoked

Annual 80 Revoked

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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

NAAQS Implementation

Updates

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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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SO2 NAAQS Monitoring Data

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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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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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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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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

Dispersion Modeling Basics

and Inputs

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AERMOD Process

Hourly Wind Speed

Hourly Wind Direction

Hourly Ambient Temperature

Land Use PatternsTopography

Building DimensionsStack DimensionsExhaust Velocity

Exhaust Temperature

Emission Rates

Predicted Ground Level Ambient Concentrations (µg/m3) for all

averaging times

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Air Quality Modeling Steps

1. Emission Inventory2. Meteorological Data

(AERMET/AERSURFACE)3. Terrain Data (AERMAP)4. Building Downwash (BPIPPRM)

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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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Meteorological Data

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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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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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Building Downwash

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Building Downwash

NAAQS Modeling Demonstration

Approach

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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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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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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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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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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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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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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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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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Hypothetical Facility Terrain

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“Process” SO2 Source SO2 Emission Rate: 240 lb/hr (CEMS) Stack Height: 290 feet Stack Diameter: 16.5 feet Exhaust Temp: 350 °F Exhaust Flow: 230,000 acfm Elevated emission rate, buoyant

source, tall stack (taller than the tallest buildings at the facility)

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Process SO2 Source Impacts

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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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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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Combustion SO2 Source Impacts

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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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Engine SO2 Source SO2 Emission Rate: 3 lb/hr (Vendor) Stack Height: 10 feet Stack Diameter: 1.3 feet Exhaust Temp: 935 °F Exhaust Flow: Horizontal Discharge Horizontal discharge, short stack

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Engine SO2 Source Impacts

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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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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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Process SO2 Source Impacts (Before)

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Process SO2 Source Impacts (After)

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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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Combustion SO2 Source Impacts (Before)

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Combustion SO2 Source Impacts (After)

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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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Engine SO2 Source Impacts (Before)

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Engine SO2 Source Impacts (After)

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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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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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Modeling Strategies Stack/Exhaust Strategies:

• Combined source exhausts• Co-located exhaust points to

increase buoyancy• Turn horizontal stacks vertical• Increase stack heights

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Modeling Strategies Temporal pairing approach Plume transport time Surrounding surface

characteristics Wind speed monitor thresholds Mechanical mixing height

considerations Alternative models (e.g.,

CALPUFF)

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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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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

Questions?

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Questions?

Dan Dixddix@all4inc.com(610) 933-5246 x182393 Kimberton RoadPO Box 299Kimberton, PA 19442

All4 Inc.www.all4inc.com

www.enviroreview.com

Colin McCall

cmccall@all4inc.com(706) 221-7688 x14

5900 River RoadSuite 500

Columbus, GA 31904