Responses to Significant First-Round Comments on the 

Draft Guidance Documents on the Implementation of the 

Exceptional Events Rule 

U.S. Environmental Protection Agency 

June 2012 
Draft for Public Notice and Comment 

Revision Date: June 2012 2 

Table of Contents 

List of Acronyms .......................................................................................................................................... 4 

List of First-Round Commenters .................................................................................................................. 5 

A. INTRODUCTION ................................................................................................................................ 6 

B. RESPONSES TO SIGNIFICANT FIRST-ROUND COMMENTS ON THE EPA’S DRAFT 

GUIDANCE DOCUMENTS ON THE IMPLEMENTATION OF THE EXCEPTIONAL EVENTS 

RULE ............................................................................................................................................................ 7 

1. Timing of EER Demonstration Package Submittal and Review ......................................................... 7 

1.1. Resource availability ................................................................................................................. 7 

1.2. Letter of intent ......................................................................................................................... 12 

1.3. Air agency submittal of demonstration package ..................................................................... 12 

1.4. EPA prioritization of submitted demonstration packages ....................................................... 13 

1.5. EPA review and response timeframes..................................................................................... 16

2. Exceptional Event Website ............................................................................................................. 19 

2.1. Templates for demonstration documents ................................................................................ 19 

3. Draft Guidance Documents Still under Development .................................................................... 20 

3.1. Exceptional event wildfire / ozone guidance .......................................................................... 20 

3.2. Fire Policy ............................................................................................................................... 22 

3.3. General .................................................................................................................................... 23 

4. General AQS Procedures ................................................................................................................ 23 

4.1. Data flagging schedules .......................................................................................................... 23 

4.2. Use of flags ............................................................................................................................. 24 

4.3. Exclusion of data that do not meet “but for” ........................................................................... 26 

5. Exceptional Event Data Flagging for Air Quality Concentrations that Could Contribute to an 

Exceedance or Violation of the National Ambient Air Quality Standards ............................................. 27 

6. General Exceptional Events Rule Applicability and Implementation Issues .................................. 28 

6.1. Guidance versus rule ............................................................................................................... 28 

6.2. Public availability of demonstrations and associated EPA decisions ..................................... 30 

6.3. Mitigation requirements of 40 CFR 51.930 ............................................................................ 33 

6.4. Reasonable controls for sources outside of state/local/tribal jurisdiction ............................... 33 

6.5. Other ....................................................................................................................................... 35 

7. Guidance Specific to High Wind Dust Events ................................................................................ 39 

7.1. Definition of “event” for high wind dust events ..................................................................... 39 

7.2. Conceptual model ................................................................................................................... 39 

7.3. High wind threshold ................................................................................................................ 40 
Draft for Public Notice and Comment 

Revision Date: June 2012 3 

7.4. Recurrence .............................................................................................................................. 50 

7.5. Reasonable controls ................................................................................................................ 55 

7.6. Historical fluctuations ............................................................................................................. 72 

7.7. High Wind Action Plan ........................................................................................................... 73 

7.8. Checklist for demonstration submission ................................................................................. 76 

7.9. Recommended framework for high wind dust exceptional event demonstration package ..... 76 

7.10. General ................................................................................................................................ 77 

8. Treatment of Technical Criteria for Exclusion of Data Affected by Events ................................... 80 

8.1. Not reasonably controllable or preventable ............................................................................ 80

8.2. Natural event ........................................................................................................................... 81 

8.3. Clear causal relationship ......................................................................................................... 81 

8.4. Historical fluctuations ............................................................................................................. 82 

8.5. But for ..................................................................................................................................... 83
Draft for Public Notice and Comment 

Revision Date: June 2012 4 

List of Acronyms 

 

AAQ Affects Air Quality 

ADEQ Arizona Department of Environmental Quality 

APCD Air Pollution Control District 

AQS Air Quality System 

BACM Best Available Control Measures 

BAM Beta Attenuation Monitor 

BMP Best Management Practices 

CAA Clean Air Act 

CAPCOA California Air Pollution Control Officers Association 

CARB California Air Resources Board 

CCR Clear Causal Relationship 

CFR Code of Federal Regulation 

CO Carbon Monoxide 

EE Exceptional Event 

EER Exceptional Events Rule 

EPA Environmental Protection Agency 

GRIC Gila River Indian Community 

HAURL Human Activity Unlikely to Recur at a particular Location 

HF Historical Fluctuations 

HWAP High Wind Action Plan 

HYSPLIT HYbrid Single-Particle Lagrangian Integrated Trajectory 

MAG Maricopa Association of Governments (Arizona) 

MM5 Pennsylvania State University / National Center for Atmospheric Research Mesoscale 

Model 

mph Miles Per Hour 

nRCP not Reasonably Controllable or Preventable 

NAAQS National Ambient Air Quality Standards 

NACAA National Association of Clean Air Agencies 

NAM North American Mesoscale Model 

NASA National Aeronautics and Space Administration 

NEAP Natural Events Action Plan 

NEBF No Exceedance But For the event 

NOAA National Oceanic and Atmospheric Administration 

NOx Nitrogen Oxides 

NWCG National Wildfire Coordinating Group 
Draft for Public Notice and Comment 

Revision Date: June 2012 5 

NWS National Weather Service 

OAQPS Office of Air Quality Planning and Standards (U.S. EPA) 

PM Particulate Matter 

Q&A Question and Answer 

QA/QC Quality Assurance/Quality Control 

RACM Reasonably Available Control Measures 

SIP State Implementation Plan 

UNLV University of Nevada, Las Vegas 

USDA United States Department of Agriculture 

USFS United States Forest Service 

VOC Volatile Organic Compounds 

WESTAR Western States Air Resources Council 

WOE Weight-of-evidence 

WRAP Western Regional Air Partnership 

WRF Weather Research and Forecasting Model 

List of First-Round Commenters 

1. Chattanooga-Hamilton County Air Pollution Control 

2. Torres Martinez Desert Cahuilla Indians 

3. City of Albuquerque 

4. California Air Pollution Control Officers Association 

5. Great Basin Unified Air Pollution Control District 

6. Pinal County (Arizona) Air Quality - comments from Mr. DiBiase 

7. Santa Barbara County Air Pollution Control District 

8. California Air Resources Board 

9. South Coast Air Quality Management District 

10. Gila River Indian Community 

11. San Joaquin Valley Air Pollution Control District 

12. Imperial County Air Pollution Control District 

13. WESTAR 

14. Clark County (Nevada) Department of Air Quality and Environmental Management 

15. Maricopa Association of Governments 

16. NACAA 

17. Sacramento Metropolitan Air Quality Management District 

18. State of Wyoming 

19. Placer County (California) Air Pollution Control District 

20. North Carolina Department of Environment and Natural Resources - Division of Air Quality 

21. BP America Production Company 

22. San Luis Obispo County Air Pollution Control District 

23. Arizona Department of Environmental Quality 

24. Georgia Air Protection Branch 

25. Pinal County (Arizona) Air Quality - comments from Mr. Gabrielson 

26. Washington Department of Ecology 

27. Intertribal Council of Arizona, Inc. 

28. Pete Lahm, USDA Forest Service 
Draft for Public Notice and Comment 

Revision Date: June 2012 6 

Responses to Significant First-Round Comments on the Draft Guidance 

Documents on the Implementation of the Exceptional Events Rule

A. INTRODUCTION 

On May 2, 2011, the U.S. Environmental Protection Agency (EPA) released draft guidance on the 

implementation of the Exceptional Events Rule (EER). The released draft guidance documents included 

the “Draft Guidance to Implement Requirements for the Treatment of Air Quality Monitoring Data 

Influenced by Exceptional Events” (the Overview document), the “Draft Exceptional Events Rule 

Frequently Asked Questions” (the draft Q&A document), the “Draft Guidance on the Preparation of 

Demonstrations in Support of Requests to Exclude Ambient Air Quality Data Affected by High Winds 

under the Exceptional Events Rule” (the draft High Winds Guidance document), and the “Request for 

Comments on the Draft Guidance Documents on the Implementation of the Exceptional Events Rule” (the 

Request for Comments document). Together, these draft documents were intended to clarify key 

provisions of the 2007 Exceptional Events Rule (EER) and respond to questions and issues that 

stakeholders have raised since the EPA promulgated the rule. The EPA provided the draft guidance, along 

with examples of approved demonstrations on the EPA’s website 

(http://www.epa.gov/ttn/analysis/exevents.htm), to state, local, and tribal agencies, etc. and to other 

parties as requested, to solicit comment and help ensure that the EPA’s final guidance provides an 

efficient and effective process to make determinations regarding air quality data affected by events. 

This document, together with the revised draft guidance documents identified above, presents the 

EPA’s response to the 28 commenters who submitted numerous comments on the draft guidance 

documents. The EPA has addressed all significant issues raised during the initial comment period ending 

on June 30, 2011. 

As reflected in the Table of Contents, the EPA organized the responses by the specific draft guidance 

document, where appropriate, or by general issues that transcend the three revised draft guidance 

documents. The EPA responses presented in this document explain the changes incorporated into the 

revised draft guidance documents or address comments that did not result in changes in the revised draft 

guidance documents. 

At this time, as indicated in previous communications with reviewers, the EPA intends to solicit 

comments on the revised draft guidance documents by publishing a Notice of Availability with a 60-day 

comment period in the Federal Register. Following this comment period, the EPA will determine whether 

to pursue issuing final guidance or final guidance as an interim step prior to revising the Exceptional 

Events Rule. 

The EPA intends to follow the revised draft guidance during the review and document finalization 

process because we believe it is consistent with the Exceptional Events Rule and the guidance already 

provided in the preamble to the rule. 
Draft for Public Notice and Comment 

Revision Date: June 2012 7 

B. RESPONSES TO SIGNIFICANT FIRST-ROUND COMMENTS ON THE EPA’S DRAFT 

GUIDANCE DOCUMENTS ON THE IMPLEMENTATION OF THE EXCEPTIONAL 

EVENTS RULE 

1. Timing of EER Demonstration Package Submittal and Review 

1.1. Resource availability 

1.1.1. Comment: “There is a discrepancy between what a large agency and a small agency are 

able to do for documentation for exceptional events. On some past events, large agencies 

in the southeast have put 4 to 7 people working full-time on an event package. A small 

agency usually has one person working part-time on the package. A small agency does 

not usually have a meteorologist on staff or modeling capability....In some ways it has 

become a competition between agencies, and small agencies do not have the personnel or 

the financial resources to provide the same amount/types of documentation as a large 

agency.” 

Specific reference to guidance text: none 

Submitter: Kathy Jones, Air Monitoring Manager, Chattanooga-Hamilton County Air 

Pollution Control, 423-643-5970, jones_kathy@mail.chattanooga.gov

Date: 5/18/2011 via e-mail to EEGuidanceComments@epa.gov 

Response: The EPA recognizes the challenges that air agencies1

 face in preparing 

exceptional event demonstration packages. The EPA also recognizes the limited 

resources of the agencies that prepare and submit exceptional event demonstration 

packages and of the EPA regional offices that review these demonstration packages. One 

of the EPA’s goals in developing exceptional event implementation guidance is to 

establish clear expectations to enable affected agencies to better manage resources as they 

prepare the documentation required under the EER. The EPA expects submitters to 

prepare and submit the appropriate level of supporting documentation, which will vary on 

a case-by-case basis using the weight-of-evidence approach. The EPA’s draft guidance 

documents and the exceptional events website 

(http://www.epa.gov/ttn/analysis/exevents.htm) present examples to illustrate specific 

points and are not necessarily required for all demonstrations. The EPA further expects 

the resources required to prepare (and review) packages to decrease as we continue to 

identify ways to streamline the process and continue to build our database of example 

demonstrations and analyses. In addition, the EPA acknowledges that certain extreme 

exceptional event cases may require more limited demonstration packages. 

1.1.2. Comment: “Given the limited staff resources at the state, local, and federal levels, EPA 

must establish guidance that streamlines and focuses exceptional event documentation on 

the factors necessary to make defensible determinations that comply with the Exceptional 

Events Rule. We recommend that EPA work closely with CAPCOA and other state/local 

agencies to closely review and develop documentation guidance that is reasonable and 

consistent with prior approved exceptional events and the Exceptional Events Rule.” 

Specific reference to guidance text: none 

Submitter: Ken Koyama (Exec Director) for Thomas J. Christofk (President), California 

Air Pollution Control Officers Association, kenk@capcoa.org 

Date: 6/14/2011 via e-mail to Gina McCarthy 

Response: The EPA will continue to work with state, local, and tribal air agencies as we 

finalize the guidance documents. As part of an upcoming public comment process, the 

                                                           

1

 References to “air agencies” are meant to include state, local, and tribal air agencies responsible for implementing 

the EER. 
Draft for Public Notice and Comment 

Revision Date: June 2012 8 

EPA will solicit feedback on a series of questions, some of which will seek specific, 

broadly applicable, streamlining mechanisms. 

1.1.3. Comment: ... in light of likely adoption of a more stringent federal ozone standard 

expected to drastically increase the number of non-attainment areas across the nation, 

EPA needs to give serious consideration to streamlining the guidance and the information 

required for demonstration submittals. It is equally important that EPA implement all 

necessary steps to assure EPA staff review submittals in a timely manner, especially 

those that affect attainment designations. In advance of the release of the wildfire 

exceptional events guidance, we also suggest EPA step back to reflect on how 

streamlining measures can be worked into that guidance. 

Specific reference to guidance text: none 

Submitter: Brian Shafritz, Santa Barbara County Air Pollution Control District, 

ShafritzB@sbcapcd.org

Date: 6/23/2011 via e-mail to EEGuidanceComments@epa.gov

Response: The EPA will continue to work with state, local, and tribal air agencies as we 

finalize the guidance documents. As part of an upcoming public comment process, the 

EPA will solicit feedback on a series of questions, some of which will seek specific, 

broadly applicable, streamlining mechanisms. The EPA has not adopted the more 

stringent ozone National Ambient Air Quality Standards (NAAQS) referred to in the 

comment, and intends to complete its reconsideration of the 2008 ozone NAAQS as part 

of the current five-year review. 

1.1.4. Comment: It appears that EPA assumes that governmental entities with a large number 

of technical staff and other sophisticated technical resources will implement the guidance. 

These resources support air quality programs that have been in place for forty years or 

more. Although the Gila River Indian community (GRIC) air quality program has as 

much, if not more, resources devoted to protection of air quality as any tribe, it cannot 

match the resources in states and political subdivisions of states. Unfortunately, what is 

assumed to be the minimum level of information and data necessary to make the 

demonstration required by the guidance is far too resource intensive for GRIC or any 

other tribal environmental program with very limited staff and limited finances....it 

assumes that there are mechanisms available to gather the required evidence. ...to devote 

the resources necessary to obtain the evidence would require shifting the Community air 

quality effort away from permits, permit compliance and ensuring regulatory compliance. 

We do not believe that such a shift would be consistent with the highest and best use of 

our limited resources....An example of why the assumption as to necessary resources is 

problematic is the level of effort necessary to demonstrate that an event was not 

reasonably controllable or preventable [GRIC’s letter identifies the example components 

in the High Winds Guidance document and then says it does not have the resources to 

prepare a conceptual model, technical information for all six elements, time series graphs, 

etc. GRIC says that the examples provided are “complex” and “extensive.”] 

Specific reference to guidance text: High Winds Guidance document 

Submitter: Leroy Williams (Environmental Engineer) for William Rhodes (Governor), 

Gila River Indian Community, williams@gilanet.net 

Date: 6/23/2011 via letter to Gina with cc e-mail to EEGuidanceComments@epa.gov

Response: The EPA’s guidance documents apply uniformly to state and local air quality 

agencies and to tribal agencies that have implemented air quality monitoring networks or 

have authority to implement air quality programs. We recognize that resources vary 

among agencies and we are developing exceptional event implementation guidance to 

establish clear expectations to enable affected agencies to better manage resources as they 

prepare the documentation required under the EER. The EPA’s draft guidance documents 

and the exceptional events website (http://www.epa.gov/ttn/analysis/exevents.htm) 
Draft for Public Notice and Comment 

Revision Date: June 2012 9 

present examples and tools to assist submitting agencies prepare demonstration packages. 

The EPA further expects the resources required to prepare (and review) packages to 

decrease as we continue to identify ways to streamline the process and continue to build 

our database of example demonstrations and analyses. 

1.1.5. Comment: Overall, the District is concerned that the draft guidance released by EPA will 

require significant additional, potentially unavailable resources to prepare documentation 

for exceptional events, and will subsequently require additional EPA resources for the 

review of this documentation. The District notes that EPA’s draft guidance documents 

include “requirements that appear to go beyond the EER...[and create] additional 

requirements [such as] a comprehensive control analysis that includes back trajectories 

indicating specific sources in the upwind area, an inventory of the contribution for the 

significant sources, and detailed descriptions of controls and their effective 

implementation and enforcement....” The District recommends that EPA undertake a 

comprehensive review of its draft guidance and prior exceptional event approvals to 

develop revised guidance that provides for reasonable, robust, and streamlined 

exceptional event documentation.”

Specific reference to guidance text: none 

Submitter: Samir Sheikh (Director of Strategies and Incentives), San Joaquin Valley Air 

Pollution Control District 

Date: 6/29/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: One of the required elements that air agencies must demonstrate under the 

Exceptional Events Rule for the EPA’s concurrence is whether the event was “not 

reasonably controllable or preventable.” Because neither the Clean Air Act nor the EER 

defines “reasonable,” the EPA provides example factors in the revised draft High Winds 

Guidance document that air agencies can consider when determining the reasonableness 

of controls. The EPA notes that the presented factors are examples to illustrate specific 

points and not requirements for all demonstrations. 

1.1.6. Comment: “The draft guidance, other background documents, and examples provided on 

EPA’s website imply a level of expertise and resources that is simply not available in 

some State and local agencies, underscoring the importance of differentiating the simple 

cases from the more complicated. In this regard, a means of dispute resolution can reduce 

repeated requests for additional information where little gain may be realized. In any 

event, clear communication between EPA and the State on what is needed to approve a 

particular request is essential so that States can make informed decisions about whether 

to commit the resources to the task.” 

Specific reference to guidance text: none 

Submitter: David Collier (President), WESTAR 

Date: 6/30/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: The EPA’s draft guidance documents and the exceptional events website 

(http://www.epa.gov/ttn/analysis/exevents.htm) present examples to illustrate specific 

points. The example analyses and level of rigor are not necessarily required for all 

demonstrations. The EPA encourages submitting agencies to use the review and 

prioritization process identified in the draft guidance documents and to communicate 

with the reviewing EPA regional office to determine the appropriate level of rigor needed 

for a complete demonstration package. As part of an upcoming public comment process, 

the EPA will solicit feedback on a series of questions, some of which will seek specific, 

broadly applicable streamlining mechanisms. 

1.1.7. Comment: “Various requirements in the draft guidance and related documents, as well 

as the examples EPA provides on its website, assume a level of expertise and resources 

that some states and localities do not have. Accordingly, it is extremely important for 
Draft for Public Notice and Comment 

Revision Date: June 2012 10 

EPA to distinguish between the more straight-forward cases and the more complex and to 

communicate clearly to states and localities what their exceptional events demonstration 

package must include in order for a particular request to be approved, thus allowing them 

to determine whether and how they will proceed.” 

Specific reference to guidance text: none 

Submitter: Tad Aburn (Co-Chair), NACAA Criteria Pollutants Committee 

Date: 6/30/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: The EPA’s draft guidance documents and the exceptional events website 

(http://www.epa.gov/ttn/analysis/exevents.htm) present examples to illustrate specific 

points. The example analyses and level of rigor are not necessarily required for all 

demonstrations. The preamble to the Exceptional Events Rule at 72 FR 13569 recognizes 

that the weight-of-evidence approach means that in straightforward cases agencies may 

submit less information/evidence whereas complex events will likely require more 

documentation. The EPA encourages submitting agencies to use the review and 

prioritization process identified in the draft guidance documents and to communicate 

with the reviewing EPA regional office to determine the appropriate level of rigor needed 

for a complete demonstration package. As part of an upcoming public comment process, 

the EPA will solicit feedback on a series of questions, some of which will seek specific, 

broadly applicable, streamlining mechanisms.

1.1.8. Comment: Given the limited staff resources at the state, local and federal levels, EPA 

must establish future rule revisions that streamlines and focuses exceptional event 

documentation on the factors necessary to make defensible determinations that comply 

with the Exceptional Events Rule. 

Specific reference to guidance text: none 

Submitter: Larry Allen (Air Pollution Control Officer), San Luis Obispo Air Pollution 

Control District 

Date: 6/30/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: As part of an upcoming public comment process, the EPA will solicit 

feedback on a series of questions, some of which will seek specific, broadly applicable, 

streamlining mechanisms.

1.1.9. Comment: Georgia states that EPA should strive for a more streamlined approach for 

state submittals. Georgia further notes that the EPA’s responses in the draft Q&A 

document do not reflect streamlining. Specifically, Question 24 says that states need to 

present information to support their claim that emissions from wildfires are “not 

reasonably controllable or preventable.” Georgia believes this requirement is ambiguous 

and puts the demonstration burden back on the state. Georgia believes that states should 

not have to provide information to support that wildfires are not controllable or 

preventable. 

Specific reference to guidance text: Q&A document #24 

Submitter: Jac Capp (Chief, Air Protection Branch), Georgia Environmental Protection 

Division 

Date: 7/1/2011 via e-mail to EEGuidanceComments@epa.gov

Response: The EPA recognizes that emissions from wildfires are generally not 

reasonable to prevent or control. The EPA uses “generally” in this statement because the 

current United States Forest Service (USFS) definitions of “wildfire” and “prescribed 

fire” define these events in terms of purpose and deliberateness of ignition. Based on the 

USFS definitions, a wildfire may have started from an unintentional ignition, but the land 

manager may have allowed the fire to continue to burn although it could have been 

extinguished. In such a case, some of the explanation of the reasonableness of this 

decision is needed. Similarly, a prescribed fire might be one that could have been 

prevented but would be unreasonable to not undertake. 
Draft for Public Notice and Comment 

Revision Date: June 2012 11 

The EPA’s expectation is that air agencies identify the origin and evolution of the 

wildfire in simple terms when documenting the “not reasonably controllable or 

preventable” criterion in their demonstration submittal. Fires started by lightning, 

volcanoes, unauthorized activity, or accidental human-caused actions are unplanned and 

unwanted fires and; therefore, despite efforts to prevent or control such fires2

 the 

emissions may not be reasonably controllable or preventable. In these cases, it is often 

sufficient for agencies to provide a statement such as the following to document the “not 

reasonably controllable or preventable” criterion: “Based on the documentation provided 

in [section X] of this submittal, [lightning] caused the unplanned, unwanted wildfire 

event. The responsible agencies did their reasonable best to control the extent of and 

extinguish the fire by taking the following actions [insert list or description of actions 

taken]. Therefore, emissions from this fire were ‘not reasonably controllable or 

preventable.’” Emissions from intentionally ignited fires and escaped prescribed fires that 

burners allow to burn require additional supporting documentation to demonstrate the 

“not reasonably controllable or preventable” criterion. In these cases, the submitting 

agency must explain how the fire escaped or why the land manager allowed the fire to 

burn. Although the EPA expects to discuss the issue of control/prevention of wildfires in 

future guidance, the EPA also addresses this question in the draft Q&A document. 

1.1.10. Comment: In the response to Question 24, the EPA should make it clear that a 

mitigation plan is not needed for wildfires. The EPA should also provide examples of 

information that states should submit to demonstrate that wildfire emissions are not 

reasonably controllable or preventable. 

Specific reference to guidance text: Q&A document #24 

Submitter: Sheila Holman (Director), NC Division of Air Quality 

Date: 6/30/2011 via e-mail to EEGuidanceComments@epa.gov

Response: The Exceptional Events Rule does not contain a requirement to submit a 

mitigation plan for any type of event, and the EPA is not creating such a requirement 

with this guidance. Air agencies must take mitigation actions, but no plan is required. In 

every event demonstration package, an air agency must demonstrate that the event was 

not reasonably controllable or preventable. See the response to comment 1.1.9. for 

additional information regarding demonstration examples for the “not reasonably 

controllable or preventable” criterion for wildfires. 

 

1.1.11. Comment: “[Studies] show that the stratospheric contribution to surface ozone is 

significant and can lead to exceedances of the ozone NAAQS for a large area.” EPA 

should allow states to work together on demonstration submittals to conserve resources. 

EPA requires separate demonstrations when the same pollutant and event result in 

exceedances of multiple NAAQS (e.g., different averaging periods). The averaging 

period should not matter. “Requiring multiple submittals for the same pollutant is only 

adding unnecessary work for the states and EPA.” 

Specific reference to guidance text: none 

Submitter: Karen St. John (Sr. Director, Regulatory Affairs), BP America, Inc. 

Date: 6/30/2011 via e-mail to EEGuidanceComments@epa.gov

Response: The EPA encourages states and air agencies to coordinate with each other in 

compiling demonstration package components, and these agencies may submit some of 

the same data and analyses when a single event affects multiple jurisdictions. Each 

NAAQS exceedance, however, will likely have some unique properties (e.g., unique 

monitoring locations, different surrounding and potentially contributing sources with 

                                                           

2

 Prevention/control efforts could include posting High Fire Danger signs to make people more careful and prevent 

accidental fires, or taking reasonable action to contain a fire once it has started. 
Draft for Public Notice and Comment 

Revision Date: June 2012 12 

varying levels of control, different historical concentration patterns, etc.). States/agencies 

need to address these unique characteristics in individual submittal packages. Similarly, 

where a single event results in exceedances of multiple NAAQS (e.g., annual and 24-hour 

PM), the submitting agency needs to address the unique features of each NAAQS 

exceedance or violation (e.g., potentially different monitoring locations, different 

historical concentration patterns). An air agency could submit a single demonstration 

package for a single event affecting multiple NAAQS provided the air agency clearly 

identifies the unique characteristics of each NAAQS. 

1.1.12. Comment: “Tribes do not have the level of technical staff that more developed state and 

county air quality programs have. Even the minimum demonstration expectations are too 

resource intensive for tribes to fulfill on their own. Tribes do not have the budgets to 

fulfill the required expectations for excluding exceptional events data. Tribes request that 

EPA work with them through the demonstration process; providing assistance in the form 

of expertise, direct technical assistance and funding.” 

Specific reference to guidance text: none 

Submitter: John R. Lewis (Executive Director), Inter Tribal Council of Arizona, Inc. 

Date: 7/15/2011 via e-mail to Beth Palma and Rhea Jones 

Response: The EPA’s guidance documents apply uniformly to state and local air quality 

agencies and to tribal agencies that have implemented air quality monitoring networks or 

have authority to implement air quality programs. We recognize that resources vary 

among agencies. In general, the EPA will not prepare analyses or additional arguments to 

be included as components in a submitted demonstration package. Rather, the EPA will 

recommend demonstration package improvements to the submitting agency. However, 

the EPA may either assist with or independently prepare supporting analyses that could 

become part of the submission package or an EPA-prepared technical support document 

if a demonstration package is associated with an imminent regulatory action and the 

EPA’s action will best serve the public interest. Analyses prepared by the EPA could 

support either approval or disapproval of an air agency’s request for concurrence on 

flagged data. 

1.2. Letter of intent 

1.2.1. Comment: “When agencies have submitted letters of intent, EPA in several regions has 

briefly evaluated the “dates” listed in the intent letter, denied the event, and never looked 

at the documentation that followed....There should be no denial of an event based on the 

“dates” submitted in the letter of intent.” 

Specific reference to guidance text: Overview document, page 4 

Submitter: Kathy Jones, Air Monitoring Manager, Chattanooga-Hamilton County Air 

Pollution Control, 423-643-5970, jones_kathy@mail.chattanooga.gov

Date: 5/13/2011 via e-mail to EEGuidanceComments@epa.gov

Response: A letter of intent is an option for an air agency to use in situations where it 

may help communication and prioritization. It is not a requirement, and may not be useful 

in every case. The EPA will generally give priority to exceptional event determinations 

that affect near-term regulatory decisions. Under the revised draft guidance, the EPA 

intends to respond to such a letter within 60 days, thus allowing an agency to prioritize 

resources for those packages that the EPA intends to review in the near-term. The EPA 

response will provide the regional office’s best assessment of the priority that can be 

given to the submission once received and any case-specific advice the EPA may have to 

offer for the preparation of the demonstration. 

 

1.3. Air agency submittal of demonstration package 

1.3.1. Comment: “...supplemental information must be provided back to EPA as required in 

the review letter "typically be 60 days from receipt of the letter from EPA." Depending 
Draft for Public Notice and Comment 

Revision Date: June 2012 13 

on the information request from EPA, the Agencies may need more time to obtain this 

data. The District is requesting that language be included to allow this time frame to be 

negotiated on a case-by-case basis depending on the type of information being requested 

by EPA.” 

Specific reference to guidance text: High Winds Guidance document, page 28 

Submitter: Samir Sheikh (Director of Strategies and Incentives), San Joaquin Valley Air 

Pollution Control District 

Date: 6/29/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: The EPA is willing to work with agencies on timeframes for supplying 

supplemental information. The mandatory timing of EPA actions may limit the response 

time the EPA allows. The revised draft guidance documents indicate this willingness. 

1.4. EPA prioritization of submitted demonstration packages 

1.4.1. Comment: “EPA acknowledges the resource intensive process surrounding the 

preparation and submittal of demonstration packages but the guidance fails to explain 

EPA’s process and intention on handling the thousands of submittals that have been 

submitted prior to this draft guidance being released that may have an impact on agency 

planning efforts. EPA only states that they will be prioritizing review on those submittals 

that have near term impacts on rule approvals or SIP submittals. How will those 

submittals that do not rise to this prioritization level be handled? Will there be an effort to 

establish an amnesty on those submittals? CAPCOA would like to see a clear explanation 

on how EPA will be handling those types of submittals and on what timeline.” 

Specific reference to guidance text: none 

Submitter: Ken Koyama (Exec Director) for Thomas J. Christofk (President), California 

Air Pollution Control Officers Association, kenk@capcoa.org 

Date: 6/14/2011 via e-mail to Gina McCarthy 

Response: The Exceptional Events Rule requires air agencies to notify the EPA that 

exceptional events have influenced data by July 1 of the calendar year following the year 

in which the event occurred. Air agencies complete this notification process by flagging 

the data in AQS and providing an initial event description. Although flagging an event 

provides an initial notification to the EPA of potential exceptional event demonstration 

submittals, the EPA does not act on an agency’s initial flags. The EPA acts on submitted 

demonstration packages and, if the EPA concurs with the submittal, the EPA indicates 

agreement in AQS by concurring with the flag (or flags) identified in the demonstration 

package. Not all agency-submitted flags in AQS have corresponding exceptional event 

demonstration submittals; therefore, it may appear that the EPA has not acted upon 

numerous flags. Once an air agency submits a demonstration package, the reviewing EPA 

regional office will prioritize the package. The EPA will generally give priority to 

exceptional event determinations that affect near-term regulatory decisions. Prioritization 

of in-process submittals may change as the EPA promulgates new rules and then makes 

decisions based on data that may be influenced by exceptional events (e.g., new or 

revised NAAQS, new attainment determinations). 

1.4.2. Comment: Will EPA accept exceptional events packages for 2007 and the first half of 

2008 events (past the 3-year submittal window) since it took so long for EPA to develop 

and release draft guidance? 

Specific reference to guidance text: none 

Submitter: Scott DiBiase, Pinal County Air Quality, scott.dibiase@pinalcountyaz.gov 

Date: 6/23/2011 via e-mail to EEGuidanceComments@epa.gov

Response: Yes, if the demonstration is associated with a near-term regulatory decision. 

See response to comment 1.4.1. As indicated in the final area designations for the 2008 

ozone NAAQS, the EPA based final area designations on air quality monitoring data 
Draft for Public Notice and Comment 

Revision Date: June 2012 14 

from 2008-2010 or 2009-2011, if states early certified these data (See 77 FR 30088 and 

77 FR 34221). 

1.4.3. Comment: During the June 9, 2011 EPA Region 9 sponsored exceptional events 

conference call, EPA staff stated that they will pick and choose which exceptional events 

packages they will review. According to them “If they don’t matter, we won’t act on 

them.” What is the purpose of having a rule and providing guidance on that rule if EPA 

does not plan to review some or all submitted packages? 

Specific reference to guidance text: none 

Submitter: Scott DiBiase, Pinal County Air Quality, scott.dibiase@pinalcountyaz.gov 

Date: 6/23/2011 via e-mail to EEGuidanceComments@epa.gov

Response: This comment is not in the draft guidance documents on which the EPA 

sought public comment. However, as indicated in the responses to previous comments in 

this section, not every requested exceptional event data exclusion has regulatory 

consequence. The EPA will place lower priority on demonstration submittals with no 

regulatory consequence. 

1.4.4. Comment: In offline discussions with EPA, EPA staff have stated that they will not 

review any exceptional events packages submitted by certain agencies since according to 

EPA, a nonattainment designation is a foregone conclusion. However, EPA fails to see 

the relationship between exceptional events and potential design values and/or episode 

days associated with planning purposes for State Implementation Plans (SIP). This EPA 

attitude and practice appears to be arbitrary and capricious. 

Specific reference to guidance text: none 

Submitter: Scott DiBiase, Pinal County Air Quality, scott.dibiase@pinalcountyaz.gov 

Date: 6/23/2011 via e-mail to EEGuidanceComments@epa.gov

Response: This comment is not in the draft guidance documents on which the EPA 

sought public comment. The EPA does, however, address the subject of this comment in 

Question 13 of the revised draft Q&A document. 

1.4.5. Comment: South Coast Air Quality Management District staff greatly appreciates the 

efforts to provide guidance that will assist in both the preparation and the timely review 

of exceptional event documentation. It is our position that Agencies should flag all data 

that qualifies for exclusion under the Exceptional Events Rule so that the data are treated 

appropriately in regulatory decisions, progress demonstrations and strategic planning for 

air quality improvement. As such, EPA should review all exceptional events 

documentation for concurrence regardless of whether a pending regulatory decision 

hinges on that data. Inaction by U.S. EPA currently lapses to a non-concurrence with 

time. The proper treatment of data during exceptional events affects public perception of 

air quality and trends, as well as the use proper use of the data by researchers and air 

quality planners, with ramifications to planning of future control strategies and design 

values used for attainment demonstrations. Such considerations can extend beyond a 

simple view of pending regulatory decisions. Streamlining the event documentation, 

along with clear guidance as to what U.S. EPA will consider to concur with an 

exceptional event, will help everyone involved.... No submitted events should lapse into 

nonconcurrence by inaction on U.S. EPA's part. No nonconcurrence decision should be 

made by U.S. EPA without ample opportunity for discussion with the affected agency 

and opportunities to provide additional evidence or clarification. Communication through 

the process is critical. 

Specific reference to guidance text: High Winds Guidance document 

Submitter: Barry Wallerstein, South Coast Air Quality Management District 

Date: 6/28/2011 via e-mail to Matt Lakin and EEGuidanceComments@epa.gov
Draft for Public Notice and Comment 

Revision Date: June 2012 15 

Response: The EPA developed the draft guidance documents to aid submitting agencies 

as they internally prioritize and prepare demonstration packages. The EPA encourages 

submitting agencies to communicate with the reviewing EPA regional office to determine 

the appropriate level of rigor needed for a complete demonstration package. The EPA 

hopes that the submittal preparation, submission, and review process becomes more 

streamlined and efficient as both submitters and the EPA begin adhering to the principles 

in the draft guidance documents. Initially, this iterative process will require prioritization 

with higher priority given to exceptional event determinations that affect near-term 

regulatory decisions. The EPA encourages submitters to use query functions within AQS 

to include/exclude all flagged data or only concurred data to conduct “what if” analyses 

for planning purposes. The AQS scenarios may aid the submitter’s and the EPA’s 

prioritization efforts. 

1.4.6. Comment: EPA has not reviewed or acted on a backlog of Exceptional Event 

documentation submittals. The District has expended significant resources in developing, 

compiling, composing, and submitting this documentation to EPA. The District is 

currently awaiting EPA review for the following exceptional events: July 4-5, 2007 

(PM2.5) Fireworks, October 9 and 30, 2008 (PM10) High Winds, and October 13 and 27, 

2009 (PM10) High Winds. The District is currently compiling documentation for an April 

11, 2010 (PM10) High Winds. The guidance document does not clearly state if and how 

EPA will act on past submittals. 

Specific reference to guidance text: none 

Submitter: Samir Sheikh (Director of Strategies and Incentives), San Joaquin Valley Air 

Pollution Control District 

Date: 6/29/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: The EPA will generally prioritize exceptional event determinations that affect 

near-term regulatory decisions. The EPA will follow-up with the commenter regarding 

the status of the identified submittals. 

1.4.7. Comment: “We are impressed with the extent of the existing backlog of unanswered 

demonstration packages. We would encourage EPA to go beyond acting only on events 

upon which regulatory actions may be pending. The flagged data, much of which we 

think would be concurred (and excluded from the regulatory database) distorts the air 

quality values that are used for ongoing planning and regulatory purposes. It also affects 

eligibility for Limited Maintenance Plans.” 

Specific reference to guidance text: none 

Submitter: David Collier (President), WESTAR 

Date: 6/30/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: The EPA considers eligibility for a Limited Maintenance Plan to be a 

regulatory concern and would prioritize the related demonstration package. Submitters 

should clearly identify the Limited Maintenance Plan regulatory implications in the 

demonstration submittal cover letter. 

1.4.8. Comment: “In San Luis Obispo County and elsewhere, exceedences caused by 

Exceptional Events can affect our nonattainment severity classification and pollutant 

design values that could result in unwarranted additional regulatory requirements that 

would cause negative economic impacts to industry. If such exceedances are not deemed 

exceptional by EPA, industry may be required to implement costly controls that will not 

solve the problem causing the exceedance. Thus, we believe it imperative that EPA 

Region 9 review and respond to all Exceptional Event submittals and request a definitive 

answer on whether or not EPA will be acting on San Luis Obispo County APCD 

submittals and on what timeline.” 

Specific reference to guidance text: none 
Draft for Public Notice and Comment 

Revision Date: June 2012 16 

Submitter: Larry Allen (Air Pollution Control Officer), San Luis Obispo Air Pollution 

Control District 

Date: 6/30/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: The EPA refers the commenter to Question 13 of the revised draft Q&A 

document. 

1.5. EPA review and response timeframes 

1.5.1. Comment: Perhaps EPA Region 9 can elaborate on the exact internal office flow of 

exceptional events review and concurrence/nonconcurrence. 

Specific reference to guidance text: none 

Submitter: Scott DiBiase, Pinal County Air Quality, scott.dibiase@pinalcountyaz.gov 

Date: 6/23/2011 via e-mail to EEGuidanceComments@epa.gov

Response: Demonstration package characteristics and prioritization dictate the precise 

review process and internal office flow. Typically, the EPA will prioritize review of the 

package based on whether it affects near-term regulatory decisions and any additional 

considerations raised by the submitting agency. In all cases, multiple regional staff and 

managers are involved in concurrence and nonconcurrence decisions. Depending on the 

nature of the event, the location, and the pollutant involved, the EPA review in Region 9 

may also include discussions with other EPA regional offices and the EPA headquarters’ 

staff. Other EPA regional offices follow a similar review and decision-making process 

for submitted demonstration packages. 

1.5.2. Comment: GRIC provides a solution to their general comment that, even with the 

exceptional event guidance, demonstrations still require more resources than what GRIC 

can dedicate. GRIC states that they will file a notice of intent when an exceedance based 

on QA/QC’d data is attributed to an exceptional event and the Arizona Department of 

Environmental Quality makes the qualitative judgment that the exceedance is attributed 

to an exceptional event. The EPA will then determine the need for a demonstration based 

on regulatory significance. If the EPA determines that the exceptional event will affect a 

regulatory determination, then “EPA will collaborate with and assist the Community in 

preparing the exceptional event demonstration. Otherwise, no demonstration will be 

prepared.” 

Specific reference to guidance text: High Winds Guidance document 

Submitter: Leroy Williams (Environmental Engineer) for William Rhodes (Governor), 

Gila River Indian Community, williams@gilanet.net 

Date: 6/23/2011 via letter to Gina with cc e-mail to EEGuidanceComments@epa.gov

Response: The EPA agrees that the commenter’s proposed prioritization process follows 

the prioritization process identified in the draft guidance documents. The EPA may 

choose to either assist with or independently prepare supporting analyses that could 

become part of the submission package or an EPA-prepared technical support document 

if a demonstration package is associated with an imminent regulatory action and the 

EPA’s action will best serve the public interest. Analyses prepared by the EPA could 

support either approval or disapproval of an air agency’s request for concurrence on 

flagged data. 

1.5.3. Comment: “EPA should accelerate the contemplated timeframes for review and 

decisions on [submitted exceptional event demonstrations] and not require up to 18 

months for Agency review of complete requests for treatment of data as an [exceptional 

event].” 

Specific reference to guidance text: varies (additional documentation to support 

recommendation is provided in comment attachment at Submitted Comments\Need 

OCR\MAG_063011-ocr.pdf) 
Draft for Public Notice and Comment 

Revision Date: June 2012 17 

Submitter: Thomas Schoaf (Mayor, City of Litchfield Park and MAG Chair), Maricopa 

Association of Governments 

Date: 6/30/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: The EPA will strive to review packages in less than 18 months, but the EPA’s 

review of some demonstrations may take a full 18 months. 

1.5.4. Comment: “Demonstration package submittal and review - We suggest that the guidance 

encourage 60 day response period for any EPA request for additional or supplemental 

information, and request that EPA acknowledge that they will work with state/locals on a 

case-by-case basis and provide additional time for requests, where appropriate...we 

suggest the following language change to ‘Requested within timeframe identified by EPA 

in the initial review letter (step 6). EPA will work with agencies on a case-by-case basis 

if additional time is needed to provide the requested supplemental information.’”

Specific reference to guidance text: High Winds Guidance document, Section 5.2, EE 

Demonstrations Action #7, Timing, page 28 

Submitter: Larry Greene (Executive Director), Sacramento Metropolitan Air Quality 

Management District 

Date: 6/30/2011 letter via e-mail to Matt Lakin and EEGuidanceComments@epa.gov

Response: The EPA agrees with the commenter and can work with agencies on the 

timeframes for supplying supplemental information, provided the timing of associated 

EPA actions allows for the extended timelines. The EPA has clarified this concept in the 

revised draft guidance documents. See also response to 1.3.1. 

1.5.5. Comment: Wyoming Air Quality Division supports the identified review timeframes. 

Specific reference to guidance text: none 

Submitter: Steven Dietrich (Administrator), Wyoming Air Quality Division 

Date: 6/30/2011 via e-mail to EEGuidanceComments@epa.gov

Response: The EPA acknowledges commenter’s support. 

1.5.6. Comment: The North Carolina Division of Air Quality believes that submitting a data 

exclusion package within 12 months of the event occurrence may not be possible in 

situations where the basis of the exclusion is violating an annual standard or a 3-year 

design value. For example, in the case of an annual standard, one needs all 12 months of 

data to know what the annual average is going to be. If the event occurred during first 

quarter of the year, the necessary data to calculate the annual average may not be 

available until the end of the first quarter of the following year. Thus, the state could not 

notify the EPA of its intent to submit a data exclusion package until possibly 15 months 

after the event occurrence. 

EPA also needs to provide guidance for the schedule for excluding exceptional event 

influenced data that result in violations of 3-year design values. The state may not know 

that data influenced by an exceptional event caused the design value exeeedance until 3 

years after the event occurrence. How should the states handle these types of situations? 

When should the letter of intent be submitted and when should the demonstration 

package be submitted in these types of cases? The EPA should provide more guidance in 

Attachment 1 Section C Exceptional Event Data Flagging Schedules on how states 

should go about flagging and excluding a data point that only meets the criteria to be 

excluded after the deadline of July 1 of the calendar year following the datum year. 

Specific reference to guidance text: Overview guidance document, page 4 

Submitter: Sheila Holman (Director), NC Division of Air Quality 

Date: 6/30/2011 via e-mail to EEGuidanceComments@epa.gov

Response: The EPA acknowledges the possible occurrence of the scenario identified in 

several parts of the comment. The Exceptional Events Rule and the draft guidance 
Draft for Public Notice and Comment 

Revision Date: June 2012 18 

documents provide timeframes for the separate and distinct tasks of initial event flagging 

and for demonstration submittals. The EPA will review data submitted outside of these 

timeframes where the air agency presents good reason for a “late” submittal. Adherence 

to timeframes is more critical with near-term, nondiscretionary regulatory action, such as 

an initial designation under a new or revised NAAQS.

1.5.7. Comment: 60 days to provide complicated supplemental information (e.g., modeling) is 

insufficient. San Luis Obispo County APCD recommends at least a 120-day timeframe 

for complicated analyses. 

Specific reference to guidance text: 

Submitter: Larry Allen (Air Pollution Control Officer), San Luis Obispo Air Pollution 

Control District 

Date: 6/30/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: The EPA agrees that in some limited instances a 60-day response time may be 

insufficient. The EPA is willing to work with agencies on timeframes for supplying 

supplemental information when the agencies present good reason to do so. The 

mandatory timing of EPA actions may limit the response time the EPA allows. The 

revised draft guidance documents indicate this willingness. 

1.5.8. Comment: Georgia states that EPA’s use of the word “intends” when referring to EPA’s 

anticipated review timeframes (120 days and 18 months) does not “reflect a strong 

commitment...to work towards a timely resolution.” 

Specific reference to guidance text: Q&A #27 

Submitter: Jac Capp (Chief, Air Protection Branch), Georgia Environmental Protection 

Division 

Date: 7/1/2011 via e-mail to EEGuidanceComments@epa.gov 

Response: The EPA and air agencies are working towards the timely resolution of 

prioritized exceptional event demonstration submittals. Limited resources and changing 

regulatory promulgation dates create a need for flexibility for both air agency information 

submittal timeframes and for the EPA response timeframes. The EPA believes the word 

“intends” appropriately characterizes our desire for an expedient process. 

1.5.9. Comment: Arizona Department of Environmental Quality (ADEQ) offers the following 

suggestions regarding the prioritization and response process identified in the draft 

guidance documents. ADEQ questions the value of the Letter of Intent given the 

requirement to provide initial descriptions by July 1. If EPA determines that a Letter of 

Intent is needed, ADEQ recommends that the letter be submitted annually, not after each 

event occurs so as to eliminate unnecessary work. 

“During a May 11, 2011, briefing EPA indicated that up to five people, including other 

regions would be responsible for reviewing each exceptional event demonstration. ADEQ 

contends that this amount of review will lead to unnecessary delay and recommends that 

the number of layers of review be reduced to three including: the assigned staffer, the 

staff supervisor, and a coordinating manager in each EPA regional office. Issuance of a 

guidance document to the Regions should be sufficient to ensure consistency between 

EPA regional offices in handling exceptional events.” 

“ADEQ also requests that the concept of regulatory action in draft Section 5 "if needed 

for regulatory action" include determinations of eligibility and continuing eligibility for 

Limited Maintenance Plans as well as Clean Data Findings.” 
Draft for Public Notice and Comment 

Revision Date: June 2012 19 

ADEQ questions EPA’s need for 18 months to make a decision on a submittal and 

suggests 6 months after completeness and decision deadlines. ADEQ also suggests that 

EPA add these deadlines to the EER regulatory text. 

Specific reference to guidance text: none 

Submitter: Eric Massey (Director), Arizona Air Quality Division 

Date: 6/30/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: As the commenter indicates, the Exceptional Events Rule requires air 

agencies to notify the EPA that exceptional events have influenced data by July 1 of the 

calendar year following the year in which the event occurred. Although flagging an event 

provides an initial notification to the EPA of potential exceptional event demonstration 

submittals, the EPA does not act on an air agency’s initial flags. The EPA acts on 

submitted demonstration packages that may follow the data flagging task by as much as 3 

years. It is the EPA’s experience that not all agency-submitted flags in AQS result in 

corresponding exceptional event demonstration submittals. An air agency may flag 

numerous data entries and submit demonstrations for significantly fewer entries. The 

letter of intent is an option for the air agency to use in situations where it may help 

communication and prioritization. Air agencies could consider submitting an annual letter 

of intent if annual submittal makes sense for resource planning or for historically 

seasonal events. The EPA has clarified this concept in the revised draft guidance 

documents. 

The commenter notes that the EPA has indicated that up to five people are responsible for 

reviewing each exceptional event demonstration and recommends reducing the layers of 

review. In most cases, demonstration review consists of the assigned staff, the staff 

supervisor, and a coordinating manager. Staff review, however, may consist of multiple, 

parallel reviewers. For example, the regional staff lead, a modeler, and a technical staffer 

from another EPA region with particular past wildfire event experience may all 

simultaneously review a submitted wildfire demonstration submittal. The intent of 

multiple reviewers is to expedite, rather than delay, the review process. 

The EPA considers determinations of eligibility and continuing eligibility for Limited 

Maintenance Plans and Clean Data Findings to be types of regulatory actions that would 

result in prioritized demonstration submittal packages. The EPA has clarified this in the 

revised draft guidance documents. The EPA is deferring a decision on whether to include 

additional air agency or EPA timeframes in regulatory text. 

1.5.10. Comment: EPA’s suggested timeframes for submitting data exclusion packages (within 

12 months of the event) and providing supplemental information (60 days) are 

insufficient. In addition, EPA’s giving itself 18 months to make a decision effectively 

reduces the allowable time for states. 

Specific reference to guidance text: none 

Submitter: Karen St. John (Sr. Director, Regulatory Affairs), BP America, Inc. 

Date: 6/30/2011 via e-mail to EEGuidanceComments@epa.gov 

Response: The EPA is willing to work with agencies on timeframes for supplying 

supplemental information. The mandatory timing of EPA actions may limit the response 

time the EPA allows. The revised draft guidance documents indicate this willingness. 

2. Exceptional Event Website 

2.1. Templates for demonstration documents 

2.1.1. Comment: NCDAQ believed that the EPA would provide a website with tools needed to 

perform the data exclusion analyses. For example, the existing Data Fed website provides 

all of the tools (satellite imagery, fire modeling tools, trajectory analysis, multiple 

datasets, and browser/editor) that the NCDAQ would like to see made available. The 
Draft for Public Notice and Comment 

Revision Date: June 2012 20 

NCDAQ would like to hear comments on the status of the functionality of this website or 

similar web sites where data exclusion analysis can be performed. The NCDAQ would 

also like to see a database established that provided the information needed on prescribed 

burns and wildfires for preparing exceptional event data exclusion packages. 

Specific reference to guidance text: 

Submitter: Sheila Holman (Director), NC Division of Air Quality 

Date: 6/30/2011 via e-mail to EEGuidanceComments@epa.gov

Response: The EPA has added links to publicly available tools on the EPA Exceptional 

Events web page at http://www.epa.gov/ttn/analysis/exevents.htm under the heading 

Publicly Available Support Information and Tools. The EPA will also continue to post 

examples of successful demonstrations. 

 

2.1.2. Comment: The EPA must develop quantitative criteria along with efficient protocols and 

analytical tools for evaluating exceptional events. There are no tools or protocols that 

have been developed by EPA to assist states in identifying and demonstrating exceptional 

events other than those developed by Rudy Husar for PM2.5/fires 

(http://wiki.esipfed.org/index.php/Evidence_for_Flagging_Exceptional_Events). The 

EPA should develop peer-reviewed tools and protocols. This would ease the resource 

burden, expedite the demonstration process, and reduce the subjectiveness of the EPA’s 

“weight-of-evidence” review. 

Specific reference to guidance text: none 

Submitter: Karen St. John (Sr. Director, Regulatory Affairs), BP America, Inc. 

Date: 6/30/2011 via e-mail to EEGuidanceComments@epa.gov

Response: The EPA believes that the variability of exceptional events prevents the 

development of a set of “one size fits all” tools (or quantitative protocols) to support 

exceptional event demonstrations. The EPA believes that our guidance in combination 

with existing community-based analytical tools, such as those identified on the EPA 

Exceptional Events web page at http://www.epa.gov/ttn/analysis/exevents.htm, provides 

air agencies with the flexibility needed to develop exceptional event demonstration 

materials. The EPA will update the Exceptional Events web page with additional 

appropriate community tools and examples of successful demonstrations as they become 

available. 

3. Draft Guidance Documents Still under Development 

3.1. Exceptional event wildfire / ozone guidance 

3.1.1. Comment: The wildfire event guidance document that the EPA is currently developing 

should address long-range smoke transport and documentation expectations. A satellite 

picture showing smoke over the location and a Calipso vertical profile showing mixing to 

the surface and/or a HYSPLIT showing mixing to the surface should be enough. The 

EPA has previously denied fairly well-documented long-range smoke transport events 

even though NOAA and NASA acknowledge them. 

Specific reference to guidance text: General comment re ozone/wildfire event 

methodology 

Submitter: Kathy Jones, Air Monitoring Manager, Chattanooga-Hamilton County Air 

Pollution Control, 423-643-5970, jones_kathy@mail.chattanooga.gov

Date: 5/13/2011 via e-mail to EEGuidanceComments@epa.gov

Response: The EPA’s future wildfire / ozone exceptional event guidance document 

intends to include example applications of satellite imagery and HYSPLIT trajectories. 

The commenter’s example evidence may satisfy one of the criteria, e.g., the Clear Causal 

Relationship criteria, in an exceptional events demonstration. This same evidence, 

however, may not be sufficient to meet other criteria such as the No Exceedance But For 

criteria. Without additional supporting information, satellite imagery with a Calipso 

profile and/or a HYSPLIT trajectory does not show that the measured concentration 
Draft for Public Notice and Comment 

Revision Date: June 2012 21 

would have been below the applicable NAAQS in the absence of the event. Providing an 

analysis of event and non-event contributions or a seasonal analysis of concentrations 

might be ways to demonstrate the “but for” prong. 

3.1.2. Comment: The EPA has indicated that concurrence on exceptional event demonstrations 

for ozone exceedances related to wildfires will be difficult due to several reasons. These 

include wildfire smoke reducing solar radiation that is necessary for ozone formation and 

the fact that wildfires generally occur during the same seasons that exhibit high ozone 

making it difficult to differentiate between anthropogenic and wildfire precursor 

emissions. While we agree that wildfires may occur under the same meteorological 

conditions that are conducive to higher ozone concentrations, we believe that evidence 

the EPA has required thus far for exceptional event demonstrations is particularly 

rigorous, burdensome, and resource intensive. We suggest that the EPA develop a 

simplified and streamlined approach that state and local agencies can utilize as part of the 

“but for” test in cases relating to potential wildfire impacts on ozone concentrations. A 

simplified analysis could include the combination of trajectory analyses, satellite imagery 

and local observations, photographs and news reports. These straightforward and readily 

available tools should provide adequate evidence regarding the influence of wildfire 

smoke on ozone concentrations. This more straightforward approach would enable the 

development of exceptional event demonstrations that are much less onerous than what is 

suggested by the EPA (modeling, regression analyses, chemical speciation, etc.) and that 

would expedite the preparation and review of exceptional event demonstrations related to 

wildfire impacts. 

Specific reference to guidance text: Q&A document #6 (page 8) 

Submitter: Brian Shafritz, Santa Barbara County Air Pollution Control District, 

ShafritzB@sbcapcd.org

Date: 6/23/2011 via e-mail to EEGuidanceComments@epa.gov

Response: The example evidence identified in this comment may satisfy one criterion of 

the EER, for example the Clear Causal Relationship criterion, in an exceptional events 

demonstration. This same evidence, however, may not be sufficient to satisfy another 

criterion and demonstrate the No Exceedance But For criteria. The “but for” criteria 

requires an analysis showing that the measured concentration would have been below the 

applicable NAAQS in the absence of the event. Providing an analysis of event and nonevent contributions is needed to demonstrate the “but for” prong. 

The EPA has not specified, and does not intend to specify, a particular analysis or 

approach for any of the required exceptional event demonstration criteria. The draft 

guidance documents and the demonstration submittals posted on the Exceptional Events 

website contain example analyses prepared to illustrate specific points that may not apply 

to all exceptional events. The EPA encourages submitting agencies to use the review and 

prioritization process identified in the draft guidance documents and to communicate 

with the reviewing EPA regional office to determine the appropriate level of rigor needed 

for a complete demonstration package. As part of an upcoming public comment process, 

the EPA will solicit feedback on a series of questions, some of which will seek specific, 

broadly applicable, streamlining mechanisms. 

3.1.3. Comment: The draft guidance document states that the EPA is developing an Interim 

Fire Policy and Fire Guidance document; the District requests the opportunity to actively 

participate in the development of this guidance. Ideally, this engagement would occur 

early in the drafting stages so the District can assist the EPA given our extensive 

experience in forest fire issues in the San Joaquin Valley Air Basin.

Specific reference to guidance text: 
Draft for Public Notice and Comment 

Revision Date: June 2012 22 

Submitter: Samir Sheikh (Director of Strategies and Incentives), San Joaquin Valley Air 

Pollution Control District 

Date: 6/29/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: The EPA intends to develop a draft wildfire / ozone exceptional events 

guidance document and expects using an open process for its development and the 

development of the document to replace the Interim Air Quality Policy on Wildland and 

Prescribed Fires. 

3.1.4. Comment: “We would also like to add a word about another issue of great importance to 

NACAA members, also related to exceptional events – that of fires. We anxiously await 

the opportunity to review and comment on draft guidance on exceptional events affected 

by fires and the fire policy itself, which is long overdue, and look forward to having the 

opportunity to work collaboratively with EPA on this very important issue. In addition, 

once the fire policy is issued, we request a chance to review again the draft Exceptional 

Events Rule Frequently Asked Questions relative to fire issues.” 

Specific reference to guidance text: 

Submitter: Tad Aburn (Co-Chair), NACAA Criteria Pollutants Committee 

Date: 6/30/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: The EPA expects using open processes for policy and guidance development. 

See response to comment 3.1.3. for additional detail.

3.1.5. Comment: Georgia requests the opportunity to review the ozone/wildfire guidance 

document once released. 

Specific reference to guidance text: 

Submitter: Jac Capp (Chief, Air Protection Branch), Georgia Environmental Protection 

Division 

Date: 7/1/2011 via e-mail to EEGuidanceComments@epa.gov

Response: The EPA expects using open processes for policy and guidance development. 

See response to comment 3.1.3. for additional detail.

3.1.6. Comment: Washington Department of Ecology requests the opportunity to review the 

ozone/wildfire guidance doc once released. 

Specific reference to guidance text: 

Submitter: Stuart Clark (Air Quality Program Manager), Washington Department of 

Ecology 

Date: 7/5/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: The EPA expects using open processes for policy and guidance development. 

See response to comment 3.1.3. for additional detail.

3.2. Fire Policy 

3.2.1. Comment: Georgia asks to be involved in the development of the Fire Policy 

Specific reference to guidance text: 

Submitter: Jac Capp (Chief, Air Protection Branch), Georgia Environmental Protection 

Division 

Date: 7/1/2011 via e-mail to EEGuidanceComments@epa.gov

Response: The EPA expects using open processes for policy and guidance development. 

See response to comment 3.1.3. for additional detail.

3.2.2. Comment: Washington Department of Ecology requests the opportunity to review the 

Fire Policy once released. 

Specific reference to guidance text: 

Submitter: Stuart Clark (Air Quality Program Manager), Washington Department of 

Ecology 
Draft for Public Notice and Comment 

Revision Date: June 2012 23 

Date: 7/5/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: The EPA expects using open processes for policy and guidance development. 

See response to comment 3.1.3. for additional detail. 

3.3. General 

3.3.1. Comment: Please clarify the relationship between wildfires and “areas burned by 

anthropogenic fires.” ADEQ recommends that the EPA recognize that emissions from 

large scale wildfires are beyond the agency’s control whether or not the initiating event 

was natural or human caused. The demonstration should not only consider the ignition 

event but also the other factors (wind conditions, humidity, fuel type, fuel moisture, etc.) 

that contributed to the extent and progression of the wildfire. 

Specific reference to guidance text: see also comment at 7.5.19 

Submitter: Eric Massey (Director), Arizona Air Quality Division 

Date: 6/30/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Propose Response: The EPA has revised the language in the revised draft High Winds 

Guidance document that refers to “areas burned by anthropogenic fires.” The EPA further 

recognizes that emissions from wildfires are generally not reasonable to control or 

prevent. See also the response to comment 1.1.9, which further discusses the EPA’s 

expectations regarding the “not reasonably controllable or preventable” criterion for 

wildfires. 

3.3.2. Comment: In the response to Question 24 of the Q&A document, please strike “ignited 

by natural sources” from the sentence that reads, “Similarly, emissions from wildfires 

ignited by natural sources are also generally not reasonable to control.” Wildfires are, by 

definition, ignited by natural sources, making the addition of this language redundant and 

confusing. 

Specific reference to guidance text: Q&A#24 

Submitter: Pete Lahm (Smoke Manager), USDA Forest Service 

Date: 7/14/2011 via phone conversation with Beth Palma 

Response: The EPA has rewritten the Q&A, which primarily relates to emissions from 

natural deserts.

4. General AQS Procedures 

4.1. Data flagging schedules 

4.1.1. Comment: The guidance is unclear regarding data processing requirements, which 

appear to conflict with data certification requirements due May 1. ''The placement of 

flags and the submittal of an initial event description should be done concurrently with 

the submission of data to the AQS database (within 90 days of the end of the quarterly 

reporting period) but must be done not later than July 1st of the calendar year following 

the year in which the flagged measurement occurred." Please provide clarification on 

how an agency should handle data certification. 

Specific reference to guidance text: High Winds Guidance document, page 7. 

Submitter: Samir Sheikh (Director of Strategies and Incentives), San Joaquin Valley Air 

Pollution Control District 

Date: 6/29/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: Unless the EPA establishes a new schedule for flagging certain data (e.g., as 

part of a rule), air agencies must submit data flags and an initial event description to AQS 

no later than July 1st of the calendar year following the year in which the flagged data 

occurred. While the EPA encourages flagging prior the May 1st deadline, flagging is not 

linked to the AQS data certification schedules. The EPA’s Final Rule on the Treatment of 

Data Influenced by Exceptional Events; Correction (72 FR 28612) amended 40 CFR 

50.14 (c)(2)(i) to make this clarification. The EPA has also revised the text of the 
Draft for Public Notice and Comment 

Revision Date: June 2012 24 

referenced bullet in the “Process Requirements per EER” section of the revised draft 

High Winds Guidance document to reflect this amendment. 

4.2. Use of flags 

4.2.1. Comment: Wildland Fire Use Fire - US (IU) flag. The draft guidance requires the use of 

the Wildland Fire Use Fire flag in AQS. The term 'Wildland Fire Use' is no longer used 

or accepted by Land Management Agencies and does not apply to their current practices. 

There are only two types of fire: Wildfires and Prescribed fires. The only difference 

between the two is how the fire is started: planned verses unplanned. Both types of fire 

are managed identically. The EPA should consider identifying an adequate flag to be 

used to characterize a fire in AQS. 

Specific reference to guidance text: 

Submitter: Samir Sheikh (Director of Strategies and Incentives), San Joaquin Valley Air 

Pollution Control District 

Date: 6/29/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: The NWCG (National Wildfire Coordinating Group) considers fires as either 

planned ignitions (prescribed fire) or unplanned ignitions (wildfire). However, NWCG 

recognizes that objectives may change regarding the fire’s management throughout the 

duration of either type of fire. A comprehensive demonstration would explain the details 

of the fire’s management, as well as its ignition, to address criteria “not reasonably 

controllable or preventable” and “clear causal relationship.”

To respond to the commenter and to be consistent with land management agencies, the 

EPA will eliminate from AQS the Wildland Fire Use Fire – US (“IU”) and (“RU”) flags 

and the Forest Fire (“E”) flag. The EPA will continue to use the following flags to 

describe fires: 

 IF – Fire – Canadian (Informational Only) 

 IG – Fire – Mexico/Central America (Informational Only) 

 IM – Prescribed Fire (Informational Only) 

 IP – Structural Fire (Informational Only) 

 IT – Wildfire – US (Informational Only) 

 RF – Fire – Canadian (Request Exclusion) 

 RG – Fire – Mexico/Central America (Request Exclusion) 

 RM – Prescribed Fire (Request Exclusion) 

 RP – Structural Fire (Request Exclusion) 

 RT – Wildfire – US (Request Exclusion) 

The EPA believes it is appropriate to retain the Fire – Canadian (“IF/RF”) and Fire – 

Mexico/Central America (“IG/RG”) flags because these flags indicate the jurisdictional 

origin of the fire (i.e., outside of the submitting state/outside of the US) rather than the 

ignition source. The EPA has added a related question on this topic to the revised draft 

Q&A document. 

4.2.2. Comment: The EPA often uses the term "flag." The EPA should make it clear that when 

they are using the term "flag" they are talking about adding "R" data validation codes to 

the data. The NCDAQ believes the guidance would be more helpful if it clearly stated 

earlier in the document than Question 10 that AQS has two types of data validation codes 

for exceptional events - "I" data validation codes and "R" data validation codes and then 

describe how each code should be used. The EPA should also state that when they use the 

term "flag" throughout this document they are referring to "R" data validation codes 

unless other types of data validation codes are explicitly mentioned. Alternatively, 

Question 10 could be moved to be before Question 8 and the entire section moved to the 
Draft for Public Notice and Comment 

Revision Date: June 2012 25 

beginning of the document. The EPA should also indicate when it is appropriate to turn 

an "I" data validation code into an "R" data validation code, and this also harkens back to 

the last comment which requests more guidance for the schedule for excluding 

exceptional event influenced data that result in violations of three-year design values. 

Contrary to what the EPA says in Question 8, the NCDAQ believes that states should flag 

any data influenced by an exceptional event with an "I" data validation code whether or 

not the state plans to request the data be excluded. Information about whether or not data 

are influenced by an exceptional event is necessary for doing the atypical analysis. If data 

have been influenced by an exceptional event and these influences have not been tracked 

and documented in some way, it may hinder the ability to get data excluded as being 

influenced by an exceptional event in the future because it will bias the data used for the 

historical fluctuations analysis. 

In Question 9 the EPA should make it clear that states can use a reference to a website as 

the initial description when the "R" data validation code is added to AQS. It would also 

be good if the EPA clarified that initial descriptions are not required for "I" data 

validation codes. The answer to Question 9 also begs the question of why the states 

should have to make the extra effort to submit a letter of intent to the EPA when the 

answer to Question 9 indicates that the initial description in AQS serves as the notice to 

the EPA of an intent by the state to submit a data exclusion package. 

Specific reference to guidance text: Q&A Q#8, 9, 10 

Submitter: Sheila Holman (Director), NC Division of Air Quality 

Date: 6/30/2011 via e-mail to EEGuidanceComments@epa.gov

Response: The EPA does not require initial descriptions for “I” series data flags, 

although AQS allows initial descriptions to be included with “I” series flags. Air agencies 

may initially flag data they believe to be influenced by an exceptional event with an “I” 

series flag with no associated initial description. Later, the air agency may change the 

flag to an “R” series flag and add the initial description, but the air agency must do so 

before July 1st of the year following the year the data occurred. 

An initial description provides a preliminary explanation of why the air agency believes 

the accompanying flagged data may be considered as affected by an exceptional event. 

The initial description is a required part of the data flagging process, and it is recorded in 

AQS with the flags and the data. A letter of intent, on the other hand, is optional and is 

not part of the AQS record. The air agency may choose to submit a letter of intent to 

ascertain the EPA’s timetable for reviewing any associated demonstration; this 

information may be valuable to the air agency in allocating resources. 

A reference to a website does satisfy the requirements of an initial description when an 

“R” series data flag is used. 

The EPA has clarified these points in the revised draft guidance documents. 

4.2.3. Comment: The responses to Q#10 and Q#12 in the Q&A document seem to conflict. In 

Q#12, the EPA says that a state does not have access rights to apply flags to data from 

monitors operated by the National Park Service or other federal agencies, but that states 

must work with the agency or seek assistance from the EPA regional office. The response 

to Q#10 says that states should flag data by July 1. “How are states to ensure that the data 

is flagged by July 1 or by other [applicable deadlines] if they are not allowed to flag the 

data themselves?” The EPA should allow States to flag the data for the monitors in their 

state for which they must prepare the demonstration pack and develop a SIP. 
Draft for Public Notice and Comment 

Revision Date: June 2012 26 

Specific reference to guidance text: Q&A #10 and 12 

Submitter: Karen St. John (Sr. Director, Regulatory Affairs), BP America, Inc. 

Date: 6/30/2011 via e-mail to EEGuidanceComments@epa.gov

Response: To maintain data integrity, AQS is generally designed so that only the agency 

operating a monitoring site may enter or alter data for that site. Under normal 

circumstances, an air agency will not have access rights to apply event flags to data from 

monitors operated by other entities, such as the National Park Service or other state, 

local, or tribal agencies. When an air agency believes that an exceptional event affected 

the concentration recorded by monitors operated by other agencies, the air agency should 

contact the agency operating the monitor and request that the operating agency flag the 

identified data range for exclusion. The affected air agency should also develop and 

forward to the operating agency an initial event description that the operating agency can 

enter in AQS. If an air agency is unsuccessful in requesting that another agency apply 

exceptional event flags to that agency’s data, the air agency should contact the EPA 

regional office. If the EPA regional office is aware of the request, and if the request was 

prior to July 1st of the year following the datum year, the EPA will generally still consider 

the affected air agency’s request. However, this may not always be the case. Air agencies 

should notify the EPA regional office of such an instance as soon as possible. (Note that 

the EPA has reordered some of the questions in the revised draft Q&A document in 

response to commenter suggestions. As a result, Question 10 is now Question 8.) 

 

4.3. Exclusion of data that do not meet “but for” 

4.3.1. Comment: The NCDAQ also requests that the guidance be clearer on how states and 

local programs should handle data impacted by exceptional events that were exceedances 

but would have also been exceedances without the exceptional event. For example, the 

exceptional event caused a value to be 45 but without the exceptional event it would have 

been 37. Even though this value cannot be excluded for the purposes of determining 

design values unless it can be shown that it causes the design value to exceed the 

standard, there should be some way for the states and local programs to be able to 

exclude these types of data from calculations of statistics made from data sets containing 

typical data required to demonstrate that the data inf1uenced by the exceptional event are 

atypical. 

Obviously, it should be no problem excluding data influenced by exceptional events 

where the state has requested the data to be excluded and the EPA concurred. However, 

there may be some days when the data are influenced by an exceptional event but the 

criteria to have the data excluded are not met because the hourly or daily value is not high 

enough to cause an exceedance or violation of the standard or the "But For" test is not 

met. The NCDAQ believes these data where values are clearly impacted but do not 

qualify to be excluded should be excluded from the historical database used in calculating 

typical fluctuations used to demonstrate the data meeting the exclusion criteria are 

atypical. What evidence does the state need to provide to demonstrate to the EPA that the 

above stated data are not typical data and should not be considered as typical in the 

historical fluctuations analysis? 

Specific reference to guidance text: 

Submitter: Sheila Holman (Director), NC Division of Air Quality 

Date: 6/30/2011 via e-mail to EEGuidanceComments@epa.gov

Response: An air agency may apply “informational” flags to a concentration it believes 

is influenced by exceptional events even if the air agency knows the concentration is not 

eligible for exclusion. 

The historical fluctuations analysis is relevant to the “but for” criterion since comparisons 

to non-event affected days can be a type of evidence for that criterion. Each situation may 
Draft for Public Notice and Comment 

Revision Date: June 2012 27 

be different, so the EPA cannot provide simple universal rules for how an air agency can 

show whether data were influenced by an event or not, and by how much. However, the 

types of evidence and techniques used to assess “clear causal relationship” and “but for” 

generally should be applicable to showing that an ineligible data point was affected and 

should not be taken to represent normal air quality. 

Since the EPA does not evaluate the historical fluctuations analysis against a threshold, 

including previously excluded data in the historical database is unlikely to have a 

negative effect. The preamble to the Exceptional Events Rule states, “The general 

statistical approach of using all measured data during the past several years is 

independent of historical flagging practices and allows States to accurately represent 

events not likely to recur by including all monitoring data in analyses.” 72 FR 13569 

(emphasis added). 

While air agencies should “use” all historical data points in their analyses, they can 

present the data as a concentration time series, relative to annual data, or relative to 

seasonal data (see additional discussion of historical fluctuation analyses in the draft 

Q&A document). The Exceptional Events web page 

www.epa.gov/ttn/analysis/exevents.htm contains examples of historical fluctuations 

analyses that included all measured data. In these examples, the submitting agencies 

identified and explained high concentration values that associated with other events as 

part of their analyses: 

Summer 2007 Wildfires: 

Plumas Demonstration (6/17/09), Fig. 10 

EPA Technical Support Document (3/11/10), Table 3, Fig. 6. 

July 2007 Wildfire: 

Lindon Demonstration (12/24/07), pp. 16-17 

5. Exceptional Event Data Flagging for Air Quality Concentrations that Could Contribute to an 

Exceedance or Violation of the National Ambient Air Quality Standards 

5.1. Comment: In footnote 6 on page 22 of Attachment 1, the EPA states that 5-minute sulfur 

dioxide data should not be flagged for exclusion because they are not used to compare against a 

standard. However, states should be allowed to flag 5-minute sulfur dioxide data with 

informational ("I") data validation codes if they choose to do so. States probably would not 

choose to do so because it would be too labor intensive, however, that option should exist and it 

should be clear that states have that option. 

For several pollutant situations in Table Q30-2, the EPA states, "it is possible for a specific 

hourly concentration that was not originally concurred to be concurred as part of the new 8-hour 

maximum period." How can this be? If the 1-hour concentration was in the original 8-hour block 

that met the criteria for exclusion, the 1-hour concentration would have been excluded if it too 

met the criteria for being excluded. If it did not meet the criteria to be excluded initially and it 

finds itself in the second 8-hour block being evaluated, even if the second 8-hour block meets 

the criteria exclusion, the 1-hour value still will not meet the criteria for 1-hour values if it did 

not meet the criteria initially. It seems what the EPA may really mean is that it is possible for 

additional hourly concentrations that were not included in the original 8-hour block to be 

excluded as part of a second 8-hour block. It might be helpful if the EPA actually provided an 

example of how this type of calculation is performed. 

Specific reference to guidance text: Q&A footnote 6, Table Q30-2 

Submitter: Sheila Holman (Director), NC Division of Air Quality 

Date: 6/30/2011 via e-mail to EEGuidanceComments@epa.gov
Draft for Public Notice and Comment 

Revision Date: June 2012 28 

Response: The EPA agrees with the commenter and has added clarifying language in the 

revised draft Q&A document to Table Q30-2 and footnote 15 (i.e., footnote 6 in the May 2, 2011 

draft Q&A document). 

6. General Exceptional Events Rule Applicability and Implementation Issues 

6.1. Guidance versus rule 

6.1.1. Comment: “To be clear, we agree on the necessity for clarity and streamlining efforts to 

ensure that the Exceptional Events Rule is applied consistently. These efforts also 

enhance the planning agencies’ understanding of the requirements in a submittal package 

for EPA concurrence. The Exceptional Events Rule is a useful and needed tool for air 

agencies in our planning efforts. We also feel that, while guidance can be helpful, the 

appropriate mechanism to address the shortcomings of the rule is to work through the 

formal rule revision process. We believe the rule revision path more effectively and 

efficiently establishes clear regulatory language so that actions taken based on the rule 

will face fewer challenges.” 

Specific reference to guidance text: none 

Submitter: Ken Koyama (Exec Director) for Thomas J. Christofk (President), California 

Air Pollution Control Officers Association, kenk@capcoa.org 

Date: 6/14/2011 via e-mail to Gina McCarthy 

Response: The EPA developed the revised draft exceptional events guidance documents 

to help air agencies comply with the Exceptional Events Rule by clarifying the rule 

requirements. Guidance documents do not change, increase, or decrease rule 

requirements; they assist by providing information and illustrations for better 

understanding of and compliance with the rule. The EPA is deferring a decision on 

whether to revise exceptional events regulatory text. 

6.1.2. Comment: “...the current draft guidance falls short of providing the necessary 

definitiveness, clarity, and streamlining that was at the crux of this review and subsequent 

guidance and/or rule revision. ...While guidance can be helpful, the Imperial County 

APCD feels the appropriate mechanism to address the issues surrounding the rule is to 

work through the formal rule revision process. We believe the rule revision path is more 

effective in establishing clear regulatory language.” 

Specific reference to guidance text: none 

Submitter: Brad Poiriez, Imperial County Air Pollution Control District, 

bradpoiriez@co.imerial.ca.us 

Date: 6/14/2011 via e-mail to Gina McCarthy 

Response: See response to comment 6.1.1. 

6.1.3. Comment: “NACAA is concerned that under the draft guidance, if specific actions are 

not taken or criteria are not met by states and localities, the request that data be excluded 

may be denied. Such mandatory requirements appear to cross the line between guidance 

and regulation. Where requirements are to be established, rulemaking and not guidance is 

the appropriate administrative process.” 

Specific reference to guidance text: 

Submitter: Tad Aburn (Co-Chair), NACAA Criteria Pollutants Committee 

Date: 6/30/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: See response to comment 6.1.1. The EPA’s draft guidance documents and the 

exceptional events website (http://www.epa.gov/ttn/analysis/exevents.htm) present 

examples to illustrate specific points rather than requirements that all submitters must 

follow in all demonstrations. 

6.1.4. Comment: “Guidance that has the effect of requiring specific actions or establishes 

criteria that, if not met, results in denial of a State’s request for data exclusion is not 
Draft for Public Notice and Comment 

Revision Date: June 2012 29 

guidance but is regulation through guidance. WESTAR reiterates its view that the 

appropriate mechanism to address several of the implementation issues addressed in the 

draft guidance is to revise the regulation.” 

Specific reference to guidance text: none 

Submitter: David Collier (President), WESTAR 

Date: 6/30/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: See response to comment 6.1.1. The EPA’s draft guidance documents and the 

exceptional events website (http://www.epa.gov/ttn/analysis/exevents.htm) present 

examples to illustrate specific points rather than requirements that all submitters must 

follow in all demonstrations. 

6.1.5. Comment: “The San Luis Obispo County Air Pollution Control District (SLOAPCD) 

believes the rule revision path would more effectively provide regulatory language so that 

EPA actions, based on the rule, will face fewer challenges.” SLOAPCD expresses 

specific concern that the guidance adds new requirements (e.g., comprehensive control 

analysis with back trajectory, slide 29 of R9 6/9/11 presentation that “requires” a 

quantitative “but for” demonstration that the event emissions caused the concentration to 

exceed the standard). 

Specific reference to guidance text: none 

Submitter: Larry Allen (Air Pollution Control Officer), San Luis Obispo Air Pollution 

Control District 

Date: 6/30/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: See response to comment 6.1.1. The EPA’s draft guidance documents and the 

exceptional events website (http://www.epa.gov/ttn/analysis/exevents.htm) present 

examples to illustrate specific points rather than requirements that all submitters must 

follow in all demonstrations. The EPA believes that a qualitative demonstration of “but 

for” may be appropriate for some demonstrations but also believes that available 

quantitative approaches provide more assurance regarding concurrence. 

6.1.6. Comment: Georgia states that the EPA should use the regulatory process which includes 

public notice and comment versus guidance as the regulatory approach provides the 

“most open and transparent process for developing new requirements and allowing input 

from co-regulators, regulated sources, and the public.” 

Specific reference to guidance text: 

Submitter: Jac Capp (Chief, Air Protection Branch), Georgia Environmental Protection 

Division 

Date: 7/1/2011 via e-mail to EEGuidanceComments@epa.gov

Response: The EPA is not introducing new requirements with the draft exceptional 

event guidance documents. Rather, the EPA’s draft guidance documents and the 

exceptional events website (http://www.epa.gov/ttn/analysis/exevents.htm) present 

examples to illustrate specific points. The level of rigor for demonstrations may vary 

from those in the example analyses depending on various factors such as the type of 

event, its location, and other factors. As we finalize the exceptional event guidance 

documents, the EPA intends to pursue a public notice and comment period to allow input 

from co-regulators, regulated sources, and the public. 

6.1.7. Comment: While the draft guidance represents much needed progress, it is ultimately 

limited in its usefulness, as guidance cannot carry the weight of rule. The process 

described in the guidance is useful for ensuring consistency amongst the EPA regional 

offices, but it provides little relief for States should the EPA miss a deadline or otherwise 

fail to follow the process outlined in the guidance. In addition, several of the approaches 

in the EPA's guidance, including proposed changes to the "But For" test and historical 
Draft for Public Notice and Comment 

Revision Date: June 2012 30 

fluctuations appear to require rule revisions before the guidance can be fully 

implemented. ADEQ maintains that additional rulemaking remains necessary. 

Specific reference to guidance text: 

Submitter: Eric Massey (Director), Arizona Air Quality Division 

Date: 6/30/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: The EPA is not introducing new requirements with the draft exceptional event 

guidance documents. Rather, the EPA’s draft guidance documents and the exceptional 

events website (http://www.epa.gov/ttn/analysis/exevents.htm) present examples to 

illustrate specific points and are intended to help air agencies comply with the 

Exceptional Events Rule. The EPA will consider each request to exclude data on its own 

merits. 

6.1.8. Comment: Pursue rule changes to see full extent of needed changes. Guidance is limited 

in usefulness. “The current regulatory framework for dealing with exceptional events is 

not sufficient to deal with the anticipated very large increase in the number of events that 

will need to be analyzed as a result of revising the ozone NAAQS into the range of or 

lower than background levels.... [if] EPA plans to use the EER to handle background 

caused ozone exceedances under a new NAAQS, the rule must be revised to include a 

provision which allows the exclusion of background.” 

Specific reference to guidance text: none 

Submitter: Karen St. John (Sr. Director, Regulatory Affairs), BP America, Inc. 

Date: 6/30/2011 via e-mail to EEGuidanceComments@epa.gov

Response: See response to comment 6.1.1. 

6.2. Public availability of demonstrations and associated EPA decisions 

6.2.1. Comment: Section 5.3 (page 29) of the High Wind document provides for the possibility 

of public comment. How will the EPA determine if public comment is required? Great 

Basin believes that all efforts to excuse monitored exceedances of National Ambient Air 

Quality Standards should include an opportunity for the public to comment. Excluding 

real health-threatening air pollution from the record, regardless of reason, is not an action 

that should be handled solely by bureaucrats behind closed doors. 

Specific reference to guidance text: page 29 of High Winds Guidance document 

 Submitter: Ted Schade, Great Basin Unified Air Pollution Control District, 

tschade@gbuapcd.org

Date: 6/15/2011 via e-mail to EEGuidanceComments@epa.gov

Response: As indicated in the “Public Comments” section of the draft High Winds 

Guidance document, an air agency may need to provide an additional opportunity for 

public comment if the EPA requests and/or if the air agency provides supplemental 

information not included in the original documentation made available for public 

comment. The EPA will make a case-by-case decision regarding supplemental 

opportunities for public comment during the demonstration preparation, submittal, and 

review process. As part of this decision, the EPA may consider potential impact and/or 

expressed public interest in the claimed event, data uncertainty, historical application of 

demonstration approach, etc. Additionally, certain regulatory actions that may rely on 

exceptional event data exclusions (e.g., proposed designation or redesignation 

classifications and attainment determinations) require the EPA to provide an opportunity 

for public comment prior to the EPA’s taking final agency action. The EPA added 

Question 14a to the revised draft Q&A document to clarify the issue of public comment. 

6.2.2. Comment: “The guidance documents do not indicate how agencies can challenge a 

determination by EPA on the non-concurrence of an Exceptional Event submittal. While 

we prefer to work through the submittal process with EPA to address any issue that may 

arise before submittal, both the air districts and the California Air Resources Board have 
Draft for Public Notice and Comment 

Revision Date: June 2012 31 

submitted what we thought was the required documentation to show an Exceptional 

Event only to see that EPA failed to agree. Currently, if EPA makes a finding of nonconcurrence on a submittal, the only recourse left to the planning agency is to wait until 

that finding affects a formal action taken by EPA on a rule or State Implementation Plan 

at which time the agency can proceed with a legal action. In an effort to avoid spending 

precious resources and time on costly litigation processes, we recommend that the 

guidance document include a mechanism to seek resolution of disagreement regarding 

non-concurrence on submittal packages for exclusions of data due to Exceptional 

Events.” 

Specific reference to guidance text: none 

Submitter: Ken Koyama (Exec Director) for Thomas J. Christofk (President), California 

Air Pollution Control Officers Association, kenk@capcoa.org

Date: 6/14/2011 via e-mail to Gina McCarthy 

Response: Several mechanisms currently exist that air agencies can use at various points 

in the exceptional events process: 

 Engage in early dialogue with the appropriate EPA regional office as issues arise. 

 Submit requests for reconsideration to the official who made the determination if 

a request identifies a clear error or if information submitted by the agency was 

overlooked. 

 Elevate the concern within the EPA’s chain of command. 

 Participate in the public notice and comment process (see response to comment 

6.2.1 and Question 14a in the draft Q&A document). 

 Challenge in an appropriate court the regulatory decision subsequently made that 

is based on the EPA’s exceptional event determination. 

In addition, for complex exceptional events claims or those with significant regulatory or 

other impacts (e.g., those claims that directly influence proposed designation or 

redesignation, classifications, and attainment determinations), EPA regional office staff 

will generally seek input from other EPA regional offices and/or the EPA headquarters 

staff. The EPA has also added Question 28a in the revised draft Q&A document to 

address this dispute resolution comment. 

6.2.3. Comment: An appeals process for disagreement on nonconcurrence decisions would be 

beneficial. 

Specific reference to guidance text: High Winds Guidance Document 

Submitter: Barry Wallerstein, South Coast Air Quality Management District 

Date: 6/28/2011 via e-mail to Matt Lakin and EEGuidanceComments@epa.gov

Response: See response to comment 6.2.2. 

6.2.4. Comment: The Exceptional Events Rule and the guidance documents do not have a 

mechanism to challenge an EPA non-concurrence determination on an agency submittal. 

The only recourse available when the EPA makes a finding of nonconcurrence is to wait 

until the finding impacts a formal action taken by the EPA on a rule or State 

Implementation Plan. At that time, legal action may be the only recourse available. The 

District recommends that the EPA provide a mechanism that allows for the appeal and 

additional review for determinations of nonconcurrence. 

Specific reference to guidance text: 

Submitter: Samir Sheikh (Director of Strategies and Incentives), San Joaquin Valley Air 

Pollution Control District 

Date: 6/29/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: See response to comment 6.2.2. 

6.2.5. Comment: “Currently in the draft guidance there is no mechanism by which agencies 

can challenge a determination by EPA on the non-concurrence of an Exceptional Event 
Draft for Public Notice and Comment 

Revision Date: June 2012 32 

submittal. Imperial County APCD would prefer to work through the submittal process 

with EPA to address any issues that may arise before submittal, however there are times 

when both the air district and CARB believe they have fully established the required 

documentation required to show an Exceptional Event and EPA ultimately fails to agree. 

As it stands now, if EPA makes a finding of non-concurrence on a submittal, the only 

recourse left to the air districts is to wait until that finding impacts a formal action taken 

by EPA on a rule or State Implementation Plan (SIP), at which time the district can 

proceed with a legal action; this is exactly the position that Imperial County APCD finds 

itself in right now. In an effort to avoid spending precious resources and time on costly 

litigation processes, it would be more beneficial to EPA and the air districts and state air 

agencies if there were a mechanism by which to seek resolution of disagreement 

regarding non-concurrence on submittal packages for exclusions of data due to 

Exceptional Events.” 

Specific reference to guidance text: 

Submitter: Brad Poiriez, Imperial County Air Pollution Control District, 

bradpoiriez@co.imperial.ca.us 

Date: 6/29/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: See response to comment 6.2.2. 

6.2.6. Comment: “WESTAR believes that the guidance should include a section on dispute 

resolution. While we acknowledge the importance of having EPA regional office 

personnel with an understanding of local conditions evaluate exceptional event requests, 

we remain concerned about inconsistencies between regions in their respective 

evaluations of substantially similar events. We believe state and local regulatory agencies 

should have the opportunity to challenge non-concurrence rather than waiting for EPA 

regulatory action based on event-caused high values. A decision of non-concurrence and 

a subsequent regulatory action, such as non-attainment designation could be separated by 

several years, resulting in significant duplicative resource expenditure challenging the 

non-attainment designation while developing a non-attainment SIP to meet the submittal 

timing requirements.” 

Specific reference to guidance text: High Winds Guidance document 

Submitter: David Collier (President), WESTAR 

Date: 6/30/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: See response to comment 6.2.2. 

6.2.7. Comment: “Recourse for inaction or denial of an exceptional event request - We suggest 

the guidance incorporate a conflict resolution process to address circumstances where 

there is no regulatory action associated with EPA's decision, where EPA has not taken 

action on a request, and to ensure consistency among EPA regional offices.” 

Specific reference to guidance text: 

Submitter: Larry Greene (Executive Director), Sacramento Metropolitan Air Quality 

Management District 

Date: 6/30/2011 letter via e-mail to Matt Lakin and EEGuidanceComments@epa.gov

Response: See response to comment 6.2.2. 

6.2.8. Comment: “We are concerned that there is no avenue available to states and localities 

that wish to challenge an EPA denial of an exceptional events request or a failure by EPA 

to respond to a request (which equates to a denial of a request for an exclusion in that, 

absent a decision by EPA, the data will remain in the data set). While we appreciate and 

value EPA regional office staff knowledge and understanding of local conditions, we are 

keenly aware of the potential for inconsistency between regions in how they evaluate and 

act upon similar events and circumstances. Therefore, we recommend that EPA establish 
Draft for Public Notice and Comment 

Revision Date: June 2012 33 

a process for dispute resolution and would welcome the opportunity to work with you to 

design such a process.” 

Specific reference to guidance text: 

Submitter: Tad Aburn (Co-Chair), NACAA Criteria Pollutants Committee 

Date: 6/30/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: See response to comment 6.2.2. 

6.2.9. Comment: San Luis Obispo County APCD recommends the Rule Revision include a 

structured mechanism to seek resolution of any disagreement regarding non-concurrence 

on submittal packages.

Specific reference to guidance text: 

Submitter: Larry Allen (Air Pollution Control Officer), San Luis Obispo Air Pollution 

Control District 

Date: 6/30/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: See response to comment 6.2.2. 

6.2.10. Comment: ADEQ recommends the Rule Revision include a structured mechanism to 

seek resolution of any disagreement regarding non-concurrence on submittal packages.

Specific reference to guidance text: 

Submitter: Eric Massey (Director), Arizona Air Quality Division 

Date: 6/30/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: See response to comment 6.2.2. 

6.3. Mitigation requirements of 40 CFR 51.930 

6.3.1. Comment: In the response to Question 22, the EPA encourages the submittal of a 

mitigation plan with the demonstration package. What does the EPA expect to see in this 

mitigation plan? The NCDAQ believes submitting a mitigation plan is not a reasonable 

requirement for an event that is not expected to reoccur. 

Specific reference to guidance text: Q&A #22 

Submitter: Sheila Holman (Director), NC Division of Air Quality 

Date: 6/30/2011 via e-mail to EEGuidanceComments@epa.gov

Response: Although the language at 40 CFR § 51.930 requires air agencies to take 

mitigation steps, the rule does not contain a requirement to submit a mitigation plan for 

any type of event. The EPA is not creating a submittal requirement with this guidance. 

We do, however, encourage agencies to submit a mitigation plan for those events 

expected to recur. If submitted, the EPA will consider the mitigation plan independent of 

the demonstration package. The EPA will not use the mitigation plan to determine 

concurrence or nonconcurrence for the submitted demonstration package. In every event 

demonstration package, an air agency must demonstrate that the event was not reasonably 

controllable or preventable. The EPA has clarified this point in Question 22 of the revised 

draft Q&A document. 

6.4. Reasonable controls for sources outside of state/local/tribal jurisdiction 

6.4.1. Comment: The draft guidance does not discuss how events that involve in-state transport 

from sources outside of one county or nonattainment area that cause exceedances at 

monitors within another should be handled. ADEQ is concerned that there is currently no 

EPA methodology or mechanism to deal with these situations and recommends that the 

EPA include specific guidance on how intra-state, interstate, and international transport 

of air pollution should be addressed. 

Specific reference to guidance text: 

Submitter: Eric Massey (Director), Arizona Air Quality Division 

Date: 6/30/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov
Draft for Public Notice and Comment 

Revision Date: June 2012 34 

Response: Under the Clean Air Act, the EPA generally considers a state (not including 

areas of Indian country) to be a single responsible actor. Accordingly, neither the EPA 

nor the Exceptional Events Rule provides special considerations for intrastate scenarios 

when an event in one county affects air quality in another county in the same state, 

assuming that the event occurs on land subject to state authority (versus tribal 

government authority). For cases involving intrastate transport, the state or local air 

agency must evaluate whether emissions from neighboring (or contributing) counties are 

not reasonably controllable or preventable. As discussed in greater detail in the draft 

guidance documents, the assessment of “not reasonably controllable or preventable” is 

based on existing level of required control, and, for high wind dust events, wind speed 

and other factors. States and tribes should consult with their EPA regional office early in 

the development of an exceptional event demonstration package if they believe that 

emissions from sources on federally-owned and managed land (e.g., national parks within 

the state) have been affected by an event in a way that raises issues of reasonable control. 

Interstate and international transport events are different than intrastate events. As 

indicated in the response to Question 23 in the draft Q&A document, the EPA believes it 

is not reasonable to expect the downwind state (i.e., the state submitting the 

demonstration) to have convinced the upwind country or state to have implemented 

controls on sources sufficient to limit event-related air concentrations in the downwind 

state. As with any demonstration submittal, the submitting (downwind) state should 

sufficiently identify all natural and anthropogenic contributing sources of emissions (both 

in-state and out-of-state) to show the causal connection between an event and the affected 

air concentration values. A submitting state may provide a less detailed characterization 

of sources in the upwind state or country than of sources within its jurisdiction. After 

completing the source characterization, the submitting state should assess whether 

emissions from sources within its jurisdiction (i.e., in-state sources) were not reasonably 

controllable or preventable. Although the submitting state should also provide available 

information on the status of control measures for emissions from out-of-state sources, the 

submitting state may determine based on available information that the implemented 

controls on out-of state sources constitute reasonable controls and that the “not 

reasonably controllable or preventable” criterion is satisfied. When assessing emissions 

transported from other states or countries, the submitting state can say that it 

characterized the out of state sources, determined that these sources contributed to the 

noted exceedance or violation, and determined, based on jurisdictional boundaries and 

other available information, that contributing emissions from the upwind state or country 

were not reasonably controllable or preventable. Submitting states are further required to 

submit evidence/statements supporting the other exceptional event criteria (i.e., clear 

causal relationship, but for, human activity unlikely to recur or a natural event, affects air 

quality, and historical fluctuations). 

The EPA recommends a similar approach to significant out-of-state anthropogenic 

sources in the case of a mixed natural/anthropogenic event that the submitting state 

wishes to consider a natural event of the grounds that all significant anthropogenic 

sources were reasonably controlled. 

As with all exceptional event demonstrations, the EPA will evaluate the information on a 

case-by-case basis based on the facts of a particular exceptional event including any 

information and arguments presented in public comments received by the state in its 

public comment process or by the EPA in a notice-and-comment regulatory action that 

depends on the data exclusion. This response is not intended to discourage states from 

working cooperatively to plan and apply controls on both sides of a state boundary for 

their mutual benefit. 
Draft for Public Notice and Comment 

Revision Date: June 2012 35 

In addition to the provisions in the EER, the Clean Air Act provides mechanisms in 

sections 110(a)(2)(D) and 126 to address interstate transport issues and mechanisms in 

section 179(b) to address international transport issues. 

6.5. Other 

6.5.1. Comment: A Concentration Effect on Design Value but not NAAQS - There are times 

when a District cannot meet the “but for” test for an event because the District would 

have exceeded an applicable NAAQS anyway. The EPA gives two examples that impact 

classification and attainment demonstration in the answer to Question 13 in the Q&A 

document. The EPA states that on a case-by case basis, the EPA may choose to exclude 

the data from determining design values or attainment classification. The District 

supports this position since including that event would artificially increase the design 

values, potentially requiring excess emission reductions or assigning an inappropriate 

classification. The District requests the EPA to develop a method that will exclude these 

days from standardized and official reports produced by AQS or other parts of the EPA.

Specific reference to guidance text: Q#13 in the Q&A document 

Submitter: Samir Sheikh (Director of Strategies and Incentives), San Joaquin Valley Air 

Pollution Control District 

Date: 6/29/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: The Exceptional Events data flagging, demonstration submittal, and review 

process provides a retrospective determination of whether emissions from an event 

contributed to a violation of a NAAQS. Under the Exceptional Events Rule, concurred 

upon event-affected data are excluded in their entirety from regulatory decisions. The 

Exceptional Events Rule does not address data handling associated with events that are 

not considered “exceptional” under the EER. The EPA suggests that air agencies use 

“informational only” (“I”) flags to identify event-related data not meeting the definition 

of an exceptional event. Air agencies can extract “I” flagged data in AQS reports. 

The EPA addresses this issue in Question 13 in the draft Q&A document and intends to 

further address this topic in the proposed 2008 ozone NAAQS implementation rule. Air 

agencies should consult with their EPA regional office if they face this situation. 

6.5.2. Comment: Need for clear definitions: “CAPCOA believes that the Exceptional Events 

Rule must have clear definitions throughout the document and any future guidance 

documents. For example, the guidance document uses the important term ‘reasonable’ 

without defining what is ‘reasonable.’ Much of the guidance seems general in nature 

leaving the assessment and implementation up to interpretation by EPA. The document 

needs to strike the balance of providing specific guidance to the agencies, while retaining 

the goal of providing EPA with the ability to evaluate each unique case. At this point, the 

guidance document fails to meet this goal.” 

Specific reference to guidance text: none 

Submitter: Ken Koyama (Exec Director) for Thomas J. Christofk (President), California 

Air Pollution Control Officers Association, kenk@capcoa.org 

Date: 6/14/2011 via e-mail to Gina McCarthy 

Response: The EPA agrees that assessing “reasonable” is not amenable to a prior 

generally applicable definition. The EPA believes, however, that as the EPA decides 

more exceptional events demonstrations, air agencies will be able to anticipate what the 

EPA considers to be “reasonable.” Because “reasonable” varies by location / attainment 

status, pollutant, contributing sources, and event type, the EPA encourages air agencies to 

consider developing a High Wind Action Plan or a prospective controls analysis for high 

wind dust events to reach mutual agreement on “reasonable” in advance of an event. 
Draft for Public Notice and Comment 

Revision Date: June 2012 36 

6.5.3. Comment: “Imperial County APCD is adamant that there needs to be clear definitions 

throughout the rule and any potential guidance. Case in point, the heavily relied upon 

term of "reasonable" is used throughout the guidance document but it is not defined 

which is counter-productive to providing clarity. Much of the guidance seems open ended 

in nature leaving the assessment and implementation up to interpretation by EPA.” 

Specific reference to guidance text: none 

Submitter: Brad Poiriez, Imperial County Air Pollution Control District, 

bradpoiriez@co.imerial.ca.us 

Date: 6/14/2011 via e-mail to Gina McCarthy 

Response: Where appropriate, the EPA has developed or incorporated definitions into 

the revised draft guidance documents. In some cases, generally applicable definitions are 

not appropriate (see the response to comment 6.5.2.). 

6.5.4. Comment: “The revised Exceptional Events Rule must have clear definitions. For 

example, the revised rule and guidance documents should not use the important term 

“reasonable” without defining what is “reasonable.”.” 

Specific reference to guidance text: 

Submitter: Larry Allen (Air Pollution Control Officer), San Luis Obispo Air Pollution 

Control District 

Date: 6/30/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: Where appropriate, the EPA has developed or incorporated definitions into 

the revised draft guidance documents. In some cases, generally applicable definitions are 

not appropriate (see the response to comment 6.5.2.). 

6.5.5. Comment: “The draft guidance includes significant new documentation requirements 

that appear to be unreasonable and unnecessary and should be reconsidered. For 

example, EPA's request that exceptional event documentation include a comprehensive 

control analysis that includes a back trajectory indicating specific sources in the upwind 

area, an inventory of the contribution for the significant sources, and detailed descriptions 

of controls and their implementation and enforcement effectiveness is an excessive 

requirement that will require extensive staff effort to not only prepare, but to ultimately 

review by EPA. Many of these new requirements exceed the Exceptional Events Rule, 

and add layers of supplemental, unnecessary work to precedent already established 

through prior EPA approvals of well-documented exceptional events.” 

Specific reference to guidance text: none 

Submitter: Ken Koyama (Exec Director) for Thomas J. Christofk (President), California 

Air Pollution Control Officers Association, kenk@capcoa.org 

Date: 6/14/2011 via e-mail to Gina McCarthy 

Response: The EPA’s draft guidance documents and the exceptional events website 

(http://www.epa.gov/ttn/analysis/exevents.htm) present examples to illustrate specific 

points. The example analyses and level of rigor are not necessarily required for all 

demonstrations. The draft High Winds Guidance document provides examples (e.g., 

comprehensive control analysis with back trajectory, significant source contribution 

inventory, and detailed control descriptions with evidence of implementation and 

enforcement) of effective evidence that air agencies can use to demonstrate “not 

reasonably controllable or preventable.” Air agencies can provide, and the EPA will 

consider, types of evidence other than those provided as examples in the draft High 

Winds Guidance document. The EPA encourages submitting agencies to use the review 

and prioritization process identified in the draft guidance documents and to communicate 

with the reviewing EPA regional office to determine the appropriate level of rigor needed 

for a complete demonstration package. 
Draft for Public Notice and Comment 

Revision Date: June 2012 37 

6.5.6. Comment: “In the Conclusion section of the Overview of the Draft Guidance 

Documents, EPA states ‘EPA expects to adhere to the draft guidance provided in this 

overview document and its attachments during the review and document finalization 

process....’ With so many areas of the guidance still causing concerns due to such things 

as lack of definitiveness and clarity, EPA should not move forward on implementing 

guidance until it has been fully reviewed, commented on, or even formally approved. For 

an air quality issue that is very technical and has the potential to have great consequences 

on both EPA staff and local and state air planning agencies, this does not seem to be the 

appropriate pathway to move forward in determining adequacy and eventual concurrence, 

or not, of the submittal.” 

Specific reference to guidance text: conclusion of Overview document 

Submitter: Ken Koyama (Exec Director) for Thomas J. Christofk (President), California 

Air Pollution Control Officers Association, kenk@capcoa.org 

Date: 6/14/2011 via e-mail to Gina McCarthy 

Response: The EPA believes that the revised draft guidance documents are consistent 

with the Exceptional Events Rule and the guidance already provided in the preamble to 

the rule. The EPA intends to follow the revised draft guidance as the EPA developed 

these documents to assist air agencies in submitting complete and effective demonstration 

packages. 

6.5.7. Comment: From the Overview of Draft Guidance Documents Conclusion section, "EPA 

expects to adhere to the draft guidance provided in this overview document and its 

attachments during the review and document finalization process ... " The current draft 

guidance contains a number of deficiencies and issues as discussed in this comment letter 

that need to be addressed prior to being considered operational and ready for 

implementation. 

Specific reference to guidance text: 

Submitter: Samir Sheikh (Director of Strategies and Incentives), San Joaquin Valley Air 

Pollution Control District 

Date: 6/29/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: See response to comment 6.5.6. 

6.5.8. Comment: We greatly appreciate the hard work being done by the U.S. EPA and, in 

particular, the recognition that certain impacted values could be removed in determining 

design values in cases where an exceptional event increased the level of an exceedance. 

This will allow states to assemble more realistic tools to attain and maintain the National 

Ambient Air Quality Standards. 

Specific reference to guidance text: none 

Submitter: Lynn Terry (Deputy Executive Officer) for James Goldstene (Executive 

Officer), California Air Resources Board, ksnyder@arb.ca.gov 

Date: 6/24/2011 letter to Gina via e-mail to EEGuidanceComments@epa.gov

Response: The EPA acknowledges commenter’s support and refers to the response 

provided in 6.5.1. and Question 13 of the draft Q&A document. 

6.5.9. Comment: “In assessing whether violations of the ambient standards for particulate 

matter deserve regulatory forbearance based on designations as a wind-related 

‘exceptional event,’ the EPA should give full consideration to the practical impacts of 

those events on public health and the public welfare. At least in areas where history 

shows acute, deadly and recurring threats to transportation and public health resulting 

from wind-blown dust events, the EPA should condition ‘exceptional event’ approval 

upon obligatory implementation of a program that provides meaningful highway-oriented 

mitigation of activities and surface conditions that would otherwise compound those 

threats.”
Draft for Public Notice and Comment 

Revision Date: June 2012 38 

Specific reference to guidance text: 

Submitter: Don Gabrielson (Director), Pinal County Air Quality Control District 

Date: 7/1/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: The EPA agrees with the commenter that the “reasonableness” of control 

measures depends on the nature and frequency of local events and the air quality 

problems, which they cause or to which they contribute. The EPA believes that the 

revised draft guidance documents express this concept. 

6.5.10. Comment: ADEQ recommends that the EPA's concurrence be based upon a 

"preponderance of the evidence" rather than “weight of the evidence” as WOE does not 

go far enough to protect the interests of the states and it is unclear as to what evidence 

holds “weight” with the EPA. 

Specific reference to guidance text: 

Submitter: Eric Massey (Director), Arizona Air Quality Division 

Date: 6/30/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: The EPA believes we should consider all relevant evidence and qualitatively 

“weigh” this evidence based on its relevance to the EER criterion being addressed, the 

degree of certainty, its persuasiveness, and other considerations appropriate to the 

individual pollutant and the nature and type of event. The EPA has clarified this position 

by adding Question 19a to the revised draft Q&A document. 

6.5.11. Comment: BP recommends that the EPA conduct a public meeting as part of the EER 

guidance document comment process to discuss implementation issues specifically 

regarding the ozone NAAQS implementation and EER guidance. Concern is that “but 

for” and “historical fluctuations” provisions of rule would specifically disallow the 

exclusion of some ozone EEs because policy relevant background is nearing or at the 

anticipated level of the new/reconsidered ozone NAAQS. 

Specific reference to guidance text: none 

Submitter: Karen St. John (Sr. Director, Regulatory Affairs), BP America, Inc. 

Date: 6/30/2011 via e-mail to EEGuidanceComments@epa.gov

Response: The EPA believes that a first-round written comment process, supplemented 

by clarifying phone calls (and one meeting in Region 9) with commenters as needed, was 

the most useful approach for obtaining public comment on the draft guidance materials. 

The EPA invites BP to clarify its comments during the second-round comment period. 

Regarding the commenters’ concern about “policy relevant background” ozone 

concentrations and exceptional events, the EPA notes that these concepts are related and 

partially overlap. The 2007 Staff Paper3

 defines policy relevant background ozone “as the 

distribution of [ozone] concentrations that would be observed in the U.S. in the absence 

of anthropogenic (man-made) emissions of precursor emissions (e.g., VOC, NOx, and 

CO) in the U.S., Canada, and Mexico.” An exceptional event is a natural event 

(excluding stagnations, inversions, high temperatures, or precipitation) or an 

anthropogenic event that is unlikely to recur in the same location. Both exceptional 

events and policy relevant background include emissions from natural events like forest 

wildfires or stratospheric ozone intrusions. However, exceedances due to natural 

emissions that occur every day and contribute to policy relevant background, such as 

biogenic emissions, do not meet the definition of an exceptional event and are thus not 

eligible for exclusion under the EER. Routine anthropogenic emissions outside of the 

                                                           

3

 Environmental Protection Agency (2007a) Review of the national ambient air quality standards for ozone: 

assessment of scientific and technical information. OAQPS staff paper. (Updated Final) July 2007. Research 

Triangle Park, NC: Office of Air Quality Planning and Standards; EPA report no. EPA-452/R-07-007. Available 

online at: http://epa.gov/ttn/naaqs/standards/ozone/s_o3_cr_sp.html. 
Draft for Public Notice and Comment 

Revision Date: June 2012 39 

U.S. contribute to policy relevant background, but are not exceptional events. 

State/local/tribal preparation of a demonstration package and the EPA’s subsequent 

review of the demonstration package is case-by-case based on a weight-of-evidence 

approach and does not explicitly consider whether the event type might contribute to 

policy relevant background. However, if a natural event that contributes to policy 

relevant background causes an observed concentration that meets the statutory definition 

of an exceptional event and fulfills all of the exceptional event criteria, the EPA would 

consider the event to be an exceptional event. 

The EPA has added Question 16a to the revised draft Q&A document to address this 

issue. 

7. Guidance Specific to High Wind Dust Events 

7.1. Definition of “event” for high wind dust events 

7.1.1. Comment: ADEQ agrees that definitions of natural and anthropogenic windblown 

emissions developed in the WRAP handbook are appropriate. ADEQ further supports the 

analysis and recommendations provided by MAG on aerodynamic entrainment. 

Specific reference to guidance text: 

Submitter: Eric Massey (Director), Arizona Air Quality Division 

Date: 6/30/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: The EPA acknowledges commenter’s support. 

7.2. Conceptual model 

7.2.1. Comment: Requirement for a Conceptual Model - The guidance requires exceptional 

events packages to contain a “conceptual model” (High Wind document, Section 6.2.1, 

page 32). All exceptional events packages should provide a narrative description of the 

event. However, characterizing the “story” as a model is not appropriate. Great Basin 

believes the packages should contain real models of the event using wind speeds, wind 

directions, monitor locations, and monitor values. “Stories” should not be substituted for 

science and science should be used to the extent possible to verify exceptional event 

claims. 

Specific reference to guidance text: page 32 of High Winds Guidance document 

 Submitter: Ted Schade, Great Basin Unified Air Pollution Control District, 

tschade@gbuapcd.org

Date: 6/15/2011 via e-mail to EEGuidanceComments@epa.gov 

Response: The EPA uses the term “conceptual model” to mean the “story” or “executive 

summary” of the event. The conceptual model should provide an overview of the 

technical information in the demonstration package and help identify relevant 

quantitative information critical in satisfying the EER criteria. 

7.2.2. Comment: Page 48, bullet #3 – Description of weather conditions that created high 

winds (as part of Clear Causal Relationship). Isn’t this duplicating the effort in the 

conceptual model section? 

Specific reference to guidance text:

Submitter: Scott DiBiase, Pinal County Air Quality, scott.dibiase@pinalcountyaz.gov

Date: 6/23/2011 via e-mail to EEGuidanceComments@epa.gov

Response: The conceptual model summarizes the “story” presented in the demonstration 

package and, as such, is likely to repeat some information appearing in more detail in 

other sections of the demonstration. The “conceptual model” approach is similar to 

abstract or executive summary repeating information contained in the body of a 

document. As the EPA receives demonstration packages that contain conceptual models, 

the EPA will post them on the exceptional events website. 
Draft for Public Notice and Comment 

Revision Date: June 2012 40 

7.2.3. Comment: “A conceptual model is not a required component of an exceptional event 

demonstration package, but we think a comprehensive narrative lays the groundwork for 

the technical demonstrations and assists with weight-of-evidence showings. As such, it 

can be a positive addition to the demonstration package. This would be particularly 

helpful in reducing the need for detailed explanations later in each package.” 

Specific reference to guidance text: High Winds Guidance document 

Submitter: David Collier (President), WESTAR 

Date: 6/30/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov 

Response: The EPA acknowledges commenter’s support. 

7.2.4. Comment: ADEQ agrees that a narrative summary at the beginning of a demonstration 

package which explains how the event unfolded will provide context for the data and 

analysis provided in the demonstration. 

Specific reference to guidance text: 

Submitter: Eric Massey (Director), Arizona Air Quality Division 

Date: 6/30/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: The EPA acknowledges commenter’s support. 

7.3. High wind threshold 

7.3.1. Comment: We request that the EPA clarify the definition of a High Wind Dust Event 

and in Section 3.1.4 Consideration of Recurrence. Questions: 1. Is it a high wind dust 

event only when the standard is exceeded? 2. Is it a high wind dust event when the winds 

exceed 25 MPH sustained and shows only elevated particulate (but does not exceed the 

standard)? 

Specific reference to guidance text: threshold 

Submitter: Dan Gates, City of Albuquerque EHD-AQD, dgates@cabq.gov

Date: 6/2/2011 via e-mail to Jim Afghani in EPA Region 6 

Response: The commenter asks whether a high wind dust event must exceed the 

NAAQS to be considered an exceptional event. In general, a PM concentration below the 

level of the NAAQS would not be an exceedance and would not affect compliance with 

the NAAQS. Therefore, the EPA will generally not exclude a concentration below the 

level of the PM NAAQS created by a high wind dust event. The EPA’s guidance does, 

however, note in Questions 19, 29, and 30 of the revised draft Q&A document, a few 

limited situations in which an air quality concentration for particulate matter and other 

pollutants could contribute to an exceedance or violation and be below the level of a 

given NAAQS (and, as a result, be considered an exceptional event). 

The commenter further asks whether a high wind dust event must exceed the high wind 

threshold of 25 mph and exceed the standard to be exceptional. The EPA has modified 

the high wind threshold concept and refers the commenter to the response to comment 

7.3.2. regarding high wind thresholds. As the EPA states in this document and in the 

revised draft High Winds Guidance document, the high wind threshold is intended to help 

inform the rigor with which the EPA will review the “not reasonably controllable or 

preventable” criterion rather than a level above which the EPA would automatically 

consider an event to be exceptional. The EPA expects that only in very rare cases would 

an event be both below the NAAQS and below a given high wind threshold and be 

“exceptional.” As with all exceptional event demonstrations, the EPA will review each 

case on its own merits. 

7.3.2. Comment: 25 Miles per Hour Default Threshold Wind Speed “By far, Great Basin’s 

greatest issue of concern is the proposed use of 25 miles per hour (MPH) as the assumed 

minimum threshold wind speed necessary to entrain particles from stable (natural and 

controlled anthropogenic) surfaces. Any default wind speed, especially a low one like 25 
Draft for Public Notice and Comment 

Revision Date: June 2012 41 

mph, provides an excuse for not controlling serious PM sources and may encourage 

facilities to refrain from implementing dust controls where and when they are needed 

most. It is very important that 25 mph not be set as the hard, bright line as to what 

constitutes high wind events for all arid areas. Depending on the many variable local 

circumstances and conditions, the actual wind speed required to produce emissions from 

undisturbed and reasonably controlled surfaces will vary greatly from the 25 mph set 

forth in the draft guidance. In addition, the District contends such a default threshold is 

not allowed by the EER. The proposed guidance refers to ‘empirical evidence’ and 

‘numerous studies’ (High Winds Guidance document, pages 3 and 14) as justification for 

using 25 mph. It is unfortunate that EPA used only three limited studies to derive a 

proposed threshold number. None of the studies were designed to be used to set national 

air pollution guidance. In fact, based on Great Basin’s decades of studying this issue, we 

contend that there are virtually no undisturbed natural surfaces in the arid west with PM10

emission thresholds as low as 25 mph. PM10 emissions that occur at 25 mph almost 

certainly come from disturbed uncontrolled or poorly controlled surfaces. Please refer to 

the attached information discussing the proposed 25 mph threshold wind speed in more 

technical detail. Another concern regarding the concept of a default threshold wind speed 

is that it does not appear to be allowed by the EER. On page 14 of the proposed High 

Winds Guidance document it states, “In the absence of local studies, EPA intends to use 

25 mph as the minimum sustained wind speed.” In contrast, Section VII.B.2. of the rule 

states: “In this rule, EPA is not identifying a specific wind speed which should be 

considered when making a determination concerning whether an event should qualify as 

exceptional. Instead, EPA is requiring that States submit appropriate documentation that 

demonstrates why a particular event should be considered exceptional for the affected 

area. The EPA will review the documentation submitted by States concerning high wind 

events and will make decisions concerning whether to exclude the data as being 

influenced by an exceptional event on a case-by-case basis.” This makes is clear that 

EPA cannot set a threshold wind speed, but must require the states to submit appropriate 

documentation to exclude data that may be influenced by exceptionally high winds that 

would overwhelm BACM and reasonable dust control measures. As required by the rule, 

it is important that a case-by-case analysis by done for each area since BACM regulations 

and compliance needs are different in all states and areas. EPA should follow the rule and 

require every area to submit an exceptional events analysis based on real, area specific 

evidence. A presumed default threshold wind speed applicable to all areas under all 

circumstances is in conflict with the EER and is not the appropriately conservative 

approach that protection of public health requires. Finally, a concerning consequence of 

setting a low default wind speed threshold will be the pressure on local agencies from air 

polluters to flag the PM10 data that occur any day the winds exceed 25 mph. It is certainly 

simpler (and less expensive) to claim an exceptional event than it is to deploy effective 

controls. 

Specific reference to guidance text: High Winds Guidance document, reasonable 

controls 

Submitter: Ted Schade, Great Basin Unified Air Pollution Control District, 

tschade@gbuapcd.org

Date: 6/15/2011 via e-mail to EEGuidanceComments@epa.gov

Response: In identifying a high wind threshold, the EPA does NOT intend to set a bright 

line as to what speed constitutes a high wind dust event or to categorically concur with all 

events with sustained winds above a given threshold. Both the nullified preamble 

language and current EPA interpretation require appropriate event-specific information 

that the EPA will review on a case-by-case basis. The high wind threshold is the 

minimum threshold wind speed capable of overwhelming reasonable controls on 

anthropogenic sources (i.e. significant emissions from controlled sources) or causing 

emissions from natural undisturbed areas. This threshold is intended to help inform the 
Draft for Public Notice and Comment 

Revision Date: June 2012 42 

rigor with which the EPA will review the “not reasonably controllable or preventable” 

criterion. Above this threshold wind speed, a lesser amount of information and data could 

show that the event was not reasonably controllable or preventable. Conversely, more 

information might be required when demonstrating the not reasonably controllable or 

preventable criterion when sustained winds are below the threshold speed. The EPA 

further agrees with the commenter that wind speed, area-specific regulations, and 

compliance needs determine “reasonableness.” The EPA expects all agencies submitting 

high wind dust event demonstrations to address not only wind speed but also required 

controls, regulations and compliance, and public health needs. 

In its guidance documents, the EPA identifies that air agencies may establish a different 

threshold based on local studies. Given numerous commenter concerns regarding the 

EPA’s use of a default threshold, the EPA has modified its revised draft guidance. The 

EPA now suggests that agencies develop a high wind threshold for each area 

experiencing high wind dust events. Appropriate area-specific thresholds would consider 

local conditions and the variation in control strategies and specify a speed above which 

these controls would be overwhelmed. This approach is consistent with the Natural 

Events Policy where the EPA required the air agencies to define the conditions in which 

BACM level controls were overwhelmed. If an agency is unable to develop an areaspecific wind threshold, the EPA will accept a threshold of 25 mph for areas in the West 

provided the agencies provide evidence of this as the level at which they expect stable 

surfaces (i.e., controlled anthropogenic and undisturbed natural surfaces) to be 

overwhelmed. And, provided the agencies are able to show that conditions in that area are 

similar to conditions in Clark County, NV where studies show that 25 mph winds 

overwhelmed reasonable controls.4

 The EPA provides additional rationale for the 

development and use of high wind thresholds in the revised draft High Winds Guidance 

document. 

Air agencies wishing to prepare and submit a high wind threshold analysis can do so at 

any of the following times: 

1. In advance of agency submittal and the EPA review of any specific demonstration 

submittal 

2. With a letter of intent 

3. With a demonstration package 

4. As a component in a prospective controls analysis or High Wind Action Plan. The 

response to comment 7.4.1. presents additional information on prospective controls 

analyses. 

As described in later responses to comments and in the revised draft High Winds 

Guidance document, the EPA has also revised the intended lifespan of High Wind Action 

Plans. Once the EPA has approved these plans and they have gone through the notice and 

comment process, they will be effective for a minimum of 3 years with some possibility 

to be reopened and reviewed. (See response to comment 7.4.1.) 

7.3.3. Comment: Sustained Wind –“In addition to contending that 25 mph is too low for a 

default threshold wind speed (and is, in fact, prohibited by the EER), the use of oneminute averages to determine an exceptional event is inappropriate and, for most 

monitoring agencies, impractical. The PM10 standard is a 24-hour standard. How can one 

minute of 25 mph wind in a 24-hour period be considered exceptional? If control 

                                                           

4

 EPA intends to evaluate whether an event was not reasonably controllable or preventable at the time of the event 

by taking into account the wind speed and the reasonable controls in place, which is dependent on an area’s 

attainment status, the frequency and severity of exceedances, benefits of the controls, and other factors. 
Draft for Public Notice and Comment 

Revision Date: June 2012 43 

measures are in place, it is extraordinarily unlikely that a one to five minutes high wind 

could have a meaningful impact on the 24-hour PM10 standard. Many arid areas of the 

west experience episodic wind events. At Owens and Mono Lakes, it is not uncommon to 

experience high winds, with attendant elevated PM10 levels, for short periods (1 to 2 

hours) within the monitoring day, while the remaining hours of the day have much lower 

winds and PM10 levels. The few high wind/high PM10 hours are cancelled out by the 

numerous low wind/low PM10 hours and there is no exceedance. These frequent 

occurrences should not be grounds for excluding air quality data. We would argue that 

the truly exceptional events are the rare events with sustained high winds occurring over 

many hours or extreme winds (much higher than 25 mph) with extreme PM10 levels that 

occur for brief periods of time. An exceptional event is certainly not any day with one 

minute of 25 mph winds. It is our understanding that, although many agencies collect 

one-minute (or more frequent) wind speeds, the archived frequency is typically one hour. 

Great Basin normally samples at two-second intervals (to determine highest hourly 

gusts), but logs only hourly averages and the highest 2-second gust for every hour. The 

EPA’s “Quality Assurance Handbook for Air Pollution Measurement Systems (Volume 

4: Meteorological Measurements Version 2.0)” [EPA-454/B-08-002, March 2008] 

requires non-Ncore stations to collect at least 1 minute raw data, but the minimum sample 

frequency is hourly (Table 0-5). It would be appropriate to match exceptional event data 

requirements with the EPA’s own meteorological monitoring requirements. Exceptional 

winds should be at least one-hour average winds.” 

Great Basin also provided supplemental information re the use of a 25 mph wind speed 

threshold (see Submitted Comments\Great Basin APCD comments on draft EER 

guidance.pdf) 

Specific reference to guidance text: High Winds Guidance document, reasonable 

controls 

Submitter: Ted Schade, Great Basin Unified Air Pollution Control District, 

tschade@gbuapcd.org

Date: 6/15/2011 via e-mail to EEGuidanceComments@epa.gov

Response: Commenters providing feedback regarding high wind threshold averaging 

times have generally made two points: (1) an area is unlikely to see PM emissions that 

are significant enough to cause violations of the NAAQS during a 1 to 5 minute period 

and (2) the availability of 5 minute data is limited and requiring this type of information 

adds a burden to the air agencies. Further, agencies who have conducted wind tunnel 

studies in areas of the Southwest have historically extrapolated the minute-level wind 

tunnel data to hourly high wind thresholds. On these bases, the EPA has revised the draft 

guidance to focus on hourly wind data for the high wind threshold and; therefore, define 

“sustained wind” as an hourly average (i.e., the default wind threshold of 25 mph will be 

based on an hourly average). 

The EPA notes that the National Climate Center has started archiving the 2-minute winds 

for every 2-minute period of each hour for all ASOS stations in the country. Almost all 

sites have data since March 2005, with most archiving data since 2000. The EPA has 

further developed a preprocessor to AERMOD, called AERMINUTE, that takes minute 

observations and calculates an hourly average wind that can be fed into AERMET, the 

AERMOD meteorological processor. The AERMINUTE output is user friendly. 

AERMET can also accept, process, and calculate hourly average wind speeds from subhourly data with a resolution equal or greater than 5-minutes from sources other than 

AERMINUTE. 

The EPA will consider shorter-term “snapshots” of wind data such as National Weather 

Service hourly summaries as part of the weight-of-evidence demonstration. The EPA 
Draft for Public Notice and Comment 

Revision Date: June 2012 44 

intends to allow air agencies to use wind data from a multitude of sources and with 

different averaging times, including model outputs (e.g., MM5, WRF) in the development 

of high wind thresholds. The EPA further intends to solicit feedback on the available 

sources of wind data and their use in the second round of comments on the revised draft 

guidance documents. 

7.3.4. Comment: “CAPCOA understands the rationale behind establishing a default high-wind 

threshold to assist EPA in determining the required level of review and documentation 

necessary to make exceptional event determinations. However, it is very important that 

25 miles per hour not be set as the hard, bright line for what constitutes high wind events 

for all arid areas. Depending on local circumstances and conditions, the actual wind 

speed required to cause emissions from undisturbed and reasonably controlled surfaces 

will vary greatly from the 25 miles per hour set forth in the draft guidance. Some areas of 

the arid west may be able to demonstrate that a lower threshold is justified for their area 

while others could prove that the threshold should be higher. Examples of existing data 

for some areas of California indicate the threshold could be as low as 16 miles per hour in 

the San Joaquin Valley to 45 miles per hour or more in the Owens Valley. EPA selected 

the 25 mile per hour default threshold after reviewing a limited number of studies not 

intended for such a determination. EPA has acknowledged that alternative thresholds 

could be considered for individual areas with appropriate justification, but the guidance 

fails to set forth exactly what and how much documentation would be required for EPA 

to approve an alternative threshold.” 

Specific reference to guidance text: High Winds Guidance document 

Submitter: Ken Koyama (Exec Director) for Thomas J. Christofk (President), California 

Air Pollution Control Officers Association, kenk@capcoa.org

Date: 6/14/2011 via e-mail to Gina McCarthy 

Response: As indicated in the response to comment 7.3.2., the high wind threshold is 

not intended to be a “bright line.” The EPA’s guidance indicates that the wind speed will 

help inform the rigor needed to satisfy the not reasonably controllable or preventable 

requirement of the EER. The EPA will review wind speed, along with the submitter’s 

analysis of implemented reasonable controls, using a weight-of-evidence approach. 

Therefore, events with wind speeds below the high wind threshold may qualify as high 

wind exceptional events. Though these events may qualify as “exceptional,” the EPA 

expects submitters to develop more rigorous and convincing supporting documentation to 

demonstrate that the events in question were, in fact, not reasonably controllable or 

preventable. 

Also, as indicated in the response to comment 7.3.2., local high wind thresholds should 

define the local conditions capable overwhelming reasonable controls or causing 

emissions from natural undisturbed areas and should be supported and justified by local 

research. If local research or studies are not available, agencies may use a threshold of 25 

mph or consider appropriate, relevant information from other areas that share similar 

characteristics including similar soil types, land uses, and meteorological conditions. 

Please see the revisions to the revised draft High Winds Guidance document for 

additional information regarding development of high wind thresholds. 

7.3.5. Comment: Why did the EPA not include wind gust/max. in its guidance? Wind 

gusts/max play a vital role in the formation of haboobs/dust storms (“The Impact of 

Exceptional Events ‘Unusual Winds’ on PM10 Concentrations in Arizona,” Arizona 

Department of Environmental Quality (ADEQ), 10/15/09, online at 

http://www.azdeq.gov/environ/air/plan/download/assessments_white/091015%20The%2
Draft for Public Notice and Comment 

Revision Date: June 2012 45 

0Impact%20of%20Exceptional%20Events%20'Unusual%20Winds'%20on%20PM10%2

0Concentrations%20in%20Arizona.pdf

Specific reference to guidance text: High Winds Guidance document 

Submitter: Scott DiBiase, Pinal County Air Quality, scott.dibiase@pinalcountyaz.gov 

Date: 6/23/2011 via e-mail to EEGuidanceComments@epa.gov 

Response: While this information may be useful in the overall weight-of-evidence, 

information concerning maximum wind gusts should not serve as the primary basis for 

determining whether the wind speeds associated with the event in question are capable of 

overwhelming reasonable controls or causing emissions from natural undisturbed areas. 

Maximum wind speeds or wind gusts are often measured on an instantaneous basis, 

ranging from less than one second to multiple seconds. It is unlikely that one second of 

high wind would be sufficient to entrain dust from stable surfaces or cause an exceedance 

of the 24-hour PM10 or PM2.5 NAAQS and; therefore, the EPA is using “sustained” wind 

speeds as the appropriate measure for exceptional event purposes. The EPA supports 

inclusion of available gust information as additional information. 

7.3.6. Comment: Would it be possible for the EPA to put together a summary table and/or 

bibliography of specific studies related to choosing an alternative high wind threshold? It 

makes more sense to have a list prior to submitting a package to the EPA rather than the 

EPA waiting until a package is submitted before providing the information to a state/local 

agency. 

Specific reference to guidance text: Page 14, section 3.1.3, bottom of paragraph 2, High 

Winds Guidance document 

Submitter: Scott DiBiase, Pinal County Air Quality, scott.dibiase@pinalcountyaz.gov 

Date: 6/23/2011 via e-mail to EEGuidanceComments@epa.gov

Response: Yes, the EPA will provide a list of available relevant literature on this subject 

in an Appendix to the revised draft High Winds Guidance document.

7.3.7. Comment: AQMD staff applauds the effort to develop a tiered approach where the 

stronger wind events (25 mph sustained threshold used in the guidance) may need less 

analysis and documentation than those that are not clear cut. The most obvious, 

extremely high wind events should require even less analysis and event documentation. 

Hopefully, this will also result in quicker concurrence with the obvious events. For the 

most obvious high wind cases, a checklist approach with key supporting data should be 

adequate. We hope to continue to work with you to streamline the process and the 

documentation. 

Specific reference to guidance text: High Winds Guidance document 

Submitter: Barry Wallerstein, South Coast Air Quality Management District 

Date: 6/28/2011 via e-mail to Matt Lakin and EEGuidanceComments@epa.gov

Response: The EPA acknowledges commenter’s support. 

7.3.8. Comment: First, the level of complexity of the demonstration decreases significantly if 

the event was caused by sustained winds exceeding 25 mph. The 25 mph threshold is met 

by most of the exceedance measured on the Community for which exceptional event 

status might be sought. Nevertheless, long experience shows that significant levels of 

dust can be entrained by winds at levels well below 25 mph. The guidance suggests that 

the EPA may find that the lower wind speeds may pass muster as being sufficient to 

cause exceptional events, but there is no description in the guidance as to how a 

demonstration can be made to have the lower wind levels accepted. Moreover, it is 

unclear whether, once a demonstration is made that wind conditions, topography, the 

aerodynamic characteristics of the soil, and other Community-specific conditions are 

such that a lower wind velocity threshold can be substituted for the 25 mph presumptive 

threshold that the demonstration will be required each time an exceptional events 
Draft for Public Notice and Comment 

Revision Date: June 2012 46 

demonstration is made. In addition, if the quantum of information necessary to lower the 

presumptive threshold will have to match that presented by Clark County (e.g., wind 

tunnel testing) to establish the 25 mph threshold in the first place, the Community's task 

will always be cost prohibitive. 

Specific reference to guidance text: High Winds Guidance document 

Submitter: Leroy Williams (Environmental Engineer) for William Rhodes (Governor), 

Gila River Indian Community, williams@gilanet.net 

Date: 6/23/2011 via letter to Gina with cc e-mail to EEGuidanceComments@epa.gov

Response: As indicated in the response to comment 7.3.2., agencies can develop local 

high wind thresholds that define the local conditions capable of overwhelming reasonable 

controls or causing emissions from natural undisturbed areas. These thresholds should be 

supported and justified by local research. If local research or studies are not available, 

agencies may consider appropriate, relevant information from other areas that share 

similar characteristics including similar soil types, land uses, and meteorological 

conditions or identify 25 mph as the level at which they expect stable surfaces (i.e., 

controlled anthropogenic and natural undisturbed areas) to be overwhelmed. 

7.3.9. Comment: The usage of 25 mph as a default high wind speed threshold is inappropriate 

for the San Joaquin Valley and many other regions as it was derived from studies 

conducted in the desert, arid environments of Nevada and Arizona. The desert soil types 

are not representative of soil types found in other regions. For example, in the San 

Joaquin Valley, soil types are heavily composed of clay, and the District has scientifically 

documented a wind entrainment threshold of 17.9 mph that has been included and 

approved in prior exceptional event submittals to the EPA. The draft guidance is unclear 

regarding what information would be needed to demonstrate an alternative wind speed 

entrainment threshold. Given the prior approval of exceptional events by the EPA, the 

District requests that EPA approve 17.9 mph as the wind speed entrainment threshold for 

the San Joaquin Valley Air Basin in the draft guidance or provide clear direction to 

obtain approval for the lower high wind speed threshold. 

Specific reference to guidance text: High Winds Guidance document 

Submitter: Samir Sheikh (Director of Strategies and Incentives), San Joaquin Valley Air 

Pollution Control District 

Date: 6/29/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: See responses to comments 7.3.2. and 7.3.8. 

7.3.10. Comment: The guidance document states "sustained wind speed data are typically 

available from sources such as local air monitoring stations and National Weather Service 

stations." Most high wind events in the San Joaquin Valley air basin occur in remote 

areas where wind speed information is generally unavailable. The installation of wind 

speed equipment is extremely labor intensive and cost ineffective in trying to fulfill 

EPA's wind data requirements. On page 34, sustained wind speeds are determined by 

averaging times of one to five minutes. The NWS data is a snap shot (2-minute average) 

of the data toward the end of the hour, and there is no way to capture wind speed 

information during other parts of the hour. The data available from NWS are unlikely to 

capture the event. Wind speed measurements of this resolution are not readily available. 

The District recommends using MM5 or any other model output (for example CANSAC 

or NAM) to provide wind speed information. The guidance document should allow for 

alternative sources of wind speed measurements. 

Specific reference to guidance text: High Winds Guidance document 

Submitter: Samir Sheikh (Director of Strategies and Incentives), San Joaquin Valley Air 

Pollution Control District 

Date: 6/29/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov
Draft for Public Notice and Comment 

Revision Date: June 2012 47 

Response: In response to comments and as described in 7.3.3., the EPA has modified 

our approach to high wind threshold averaging times to allow extrapolating minute level 

data to hourly high wind thresholds. Even with this modified approach, the EPA 

understands that dense meteorological networks are not always available. A high wind 

exceptional event demonstration should include all relevant meteorological data from any 

available source. Generally, the EPA recommends using NWS data or the National 

Climate Center. Where meteorological data are not available for a particular area and 

such data are critical for the demonstration, agencies may substitute modeled wind speed 

surface measurements for actual measured data. Models that agencies can use to develop 

estimates for actual measured wind speed surface measurements include MM5, WRF, 

and, possibly, NAM. 

7.3.11. Comment: “Imperial County APCD understands the rationale behind establishing a 

default 25 M.P.H. high wind threshold for determining the level of review and 

documentation necessary to make an exceptional event determination. However, it is very 

important that the 25 M.P.H not be the "bright" line as to what constitutes high wind 

events for all areas. Imperial County appreciates EPA's acknowledgement that alternative 

thresholds could be considered for individual areas with appropriate justification but the 

guidance does not establish what type and how much documentation would be required 

for EPA to approve an alternative threshold. Agreeing that this should be a case-by-case 

evaluation, appropriate guidance on how and what is required to establish a different 

threshold would save all agencies involved valuable time and resources if they 

understood what needed to be provided to EPA.” 

Specific reference to guidance text: none 

Submitter: Brad Poiriez, Imperial County Air Pollution Control District, 

bradpoiriez@co.imerial.ca.us 

Date: 6/14/2011 via e-mail to Gina McCarthy 

Response: See response to comment 7.3.2. 

7.3.12. Comment: “EPA should not specify a minimum wind speed for definition of an 

exceptional event ("EE") or create a regulatory presumption as to minimum wind speed.” 

Specific reference to guidance text: varies (additional documentation to support 

recommendation is provided in comment attachment at Submitted Comments\Need 

OCR\MAG_063011-ocr.pdf) 

Submitter: Thomas Schoaf (Mayor, City of Litchfield Park and MAG Chair), Maricopa 

Association of Governments 

Date: 6/30/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: See response to comment 7.3.2. 

7.3.13. Comment: “EPA should consider additional technical information with regard to wind 

speed and aerodynamic entrainment (such as that provided in the attached detailed 

comments) and correct errors in its analysis of these matters.” 

Specific reference to guidance text: varies (additional documentation re aerodynamic 

entrainment and soil disturbance provided in comment attachment at Submitted 

Comments\Need OCR\MAG_063011-ocr.pdf) 

Submitter: Thomas Schoaf (Mayor, City of Litchfield Park and MAG Chair), Maricopa 

Association of Governments 

Date: 6/30/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: The Maricopa Association of Governments (MAG) asserts that a 25 mph high 

wind threshold is not supportable and discusses a number of factors that may affect the 

level of wind speed associated with high wind dust events, which include surface 

roughness, soil disturbance, and aerodynamic entrainment. The EPA based the 25 mph 

threshold on extensive windblown dust emissions research performed by the University 
Draft for Public Notice and Comment 

Revision Date: June 2012 48 

of Nevada, Las Vegas (UNLV). During UNLV’s studies, researchers used a wind tunnel 

to quantify emissions from undisturbed areas meeting the stabilization requirements of 

Clark County’s (Nevada) BACM level fugitive dust regulations and mechanically 

disturbed open areas. The research performed by UNLV is one of the few field studies 

that clearly relates BACM level control of windblown dust from open areas and PM10

emissions. The EPA believes that for Clark County and areas similar to it, the study 

results clearly differentiate emissions from these two types of conditions and provide a 

reasonable baseline for establishing a high wind threshold for exceptional events 

purposes. 

While the information presented in MAG’s detailed comments provides useful 

information on the mechanics of windblown dust in some areas, the high wind threshold 

is intended to represent the conditions that are capable of overwhelming reasonable 

controls on anthropogenic sources (i.e., significant emissions from controlled sources) or 

causing emissions from natural undisturbed areas, not the wind speed at which any level 

of emissions could occur from any source. This approach is also consistent with the 

Natural Events Policy where the EPA required air agencies to define the conditions in 

which BACM level controls were overwhelmed. 

In its guidance documents, the EPA notes that air agencies may establish a different 

threshold based on local studies. Given numerous commenter concerns regarding the 

EPA’s use of a default threshold, the EPA has revised the draft guidance. The EPA now 

suggests that agencies develop a high wind threshold for each area experiencing high 

wind dust events. As indicated in the response to comment 7.3.2., local high wind 

thresholds should define the local conditions capable overwhelming reasonable controls 

on anthropogenic sources (i.e., significant emissions from controlled sources) or causing 

emissions from natural undisturbed areas and should be supported and justified by local 

research.

7.3.14. Comment: Clarify the timing for a state to submit a recommended alternative wind 

speed based on local studies. “A state may conduct a study after a high wind event occurs 

and submit that as part of the demonstration package.” Sacramento Metropolitan Air 

Quality Management District requests that the guidance allow all studies to be included 

in a demonstration package. 

Specific reference to guidance text: High Winds Guidance document 

Submitter: Larry Greene (Executive Director), Sacramento Metropolitan Air Quality 

Management District 

Date: 6/30/2011 letter via e-mail to Matt Lakin and EEGuidanceComments@epa.gov

Response: The EPA agrees that agencies can submit high wind threshold analyses as 

part of a demonstration package. Agencies may also submit these analyses as part of 

other submittals as identified in the response to comment 7.3.2. 

7.3.15. Comment: Wyoming Air Quality Division supports a high wind threshold and believes 

that 25 mph is appropriate based on their experience. Wyoming Air Quality Division is, 

however, concerned that the EPA has “already determined that exceedances which occur 

or recur when winds are regularly greater than 25 mph will require a more detailed 

control analysis and enhanced controls. The purpose of the Guidance is to deal with high 

wind events defined as greater than 25 mph. To further caveat and categorize high winds 

greater than 25 mph is unwarranted given the level of documentation already being 

requested.” 

Specific reference to guidance text: High Winds Guidance document, Section 3.1.4 

Submitter: Steven Dietrich (Administrator), Wyoming Air Quality Division 

Date: 6/30/2011 via e-mail to EEGuidanceComments@epa.gov
Draft for Public Notice and Comment 

Revision Date: June 2012 49 

Response: Both this document (in the response to comment 7.3.2.) and the revised draft 

High Winds Guidance document now contain language to clarify the development and 

application of high wind thresholds. 

7.3.16. Comment: ADEQ requests that the EPA identify in the guidance, the literature, methods, 

and analytical process that the EPA used to define the 25 mile per hour threshold. This 

type of baseline would help agencies that want to conduct relevant local studies to submit 

alternative high wind thresholds more appropriate for specific areas. ADEQ recommends 

that the EPA change the guidance such that it is clear that the 25 mile per hour or other 

negotiated threshold will be used only to assess the amount of documentation necessary 

to support an exceptional event demonstration rather the status of the event as being 

exceptional. 

Specific reference to guidance text: High Winds Guidance document 

Submitter: Eric Massey (Director), Arizona Air Quality Division 

Date: 6/30/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: Appendix A of the revised draft High Winds Guidance document contains the 

rationale for the 25 mph threshold. As discussed in response to comment 7.3.13, the EPA 

based the 25 mph threshold on extensive windblown dust emissions research performed 

by the University of Nevada, Las Vegas (UNLV). During UNLV’s studies, researchers 

used a wind tunnel to quantify emissions from undisturbed areas meeting the stabilization 

requirements of Clark County’s (Nevada) BACM level fugitive dust regulations and 

mechanically disturbed open areas. The EPA believes that for areas similar to Clark 

County the study results clearly differentiate emissions from these two types of sources 

and provide a reasonable baseline for establishing a high wind threshold for exceptional 

events purposes. 

As previously noted in this document, the EPA is modifying its approach to high wind 

thresholds as discussed in the response to comment 7.3.2. and will no longer specify 25 

mph as a broadly applicable default threshold. The EPA maintains, however, that 

UNLV’s approach and results are sufficient to support a 25 mph high wind threshold for 

the Clark County, Nevada area and other areas that share similar characteristics including 

similar soil types, land uses, and meteorological conditions. 

7.3.17. Comment: Requiring agencies to use sustained wind speed data on the order of 1-5 

minute averages adds burdens to monitoring programs. Most meteorological data 

collected by agencies is in the form of hourly averages. While adjusting data logger 

programs to capture 1-5 minute averages is possible, this will increase data storage, staff 

time, and complexity of data review and quality assurance. Should the EPA use 1-5 

minute averages as a measure of sustained winds, ADEQ recommends that the EPA 

provide a conversion calculation from hourly average to the selected averaging time 

interval. Otherwise, ADEQ recommends the use of a comparable hourly average high 

wind threshold. 

Specific reference to guidance text: High Winds Guidance document 

Submitter: Eric Massey (Director), Arizona Air Quality Division 

Date: 6/30/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: See response to comment 7.3.3. 

7.3.18. Comment: “...soils in the Columbia Plateau of eastern Washington are powdery and 

easily raised by high winds. Research indicates that a much lower wind speed is a more 

suitable default for the Columbia Plateau. This research is discussed in Ecology’s Natural 

Events Action Plan for the Columbia Plateau.” 

Specific reference to guidance text: High Winds Guidance document 
Draft for Public Notice and Comment 

Revision Date: June 2012 50 

Submitter: Stuart Clark (Air Quality Program Manager), Washington Department of 

Ecology 

Date: 7/5/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: See responses to comments 7.3.2. and 7.3.8. 

7.4. Recurrence 

7.4.1. Comment: Clarification is requested in the definition of a High Wind Dust Event and in 

Section 3.1.4 Consideration of Recurrence. Questions: 3. Is recurrence based only on the 

high wind dust event definition? 4. Is recurrence based on the particulate standard being 

exceeded? 5. Is recurrence based only on the data that has been flagged over the three 

years? 6. What role does wind direction play in the definition and the recurrence 

evaluation? 

Example 1: 

The agency has implemented RACM on industry. Due to this most events, where the 

winds exceed 25 MPH, are controlled and only show elevated particulate (dust). Are 

these controlled events considered part of the recurrence evaluation or are only those 

events that result in an exceedance of the standard considered for the recurrence 

evaluation? 

Example 2: 

In those events where the standard is exceeded wind direction plays an important role in 

determining where the dust originated. There can be situations where the high wind 

threshold has been exceeded but the wind direction is from an area that may not entrain 

sufficient dust (or is sufficiently controlled) to exceed a standard, or the wind speed and 

directions were from an unusual direction and is not a common seasonal occurrence. It 

would seem appropriate to consider wind direction as an important aspect in the 

recurrence evaluation. 

Specific reference to guidance text: High Winds Guidance document definition of 

recurrence 

Submitter: Dan Gates, City of Albuquerque EHD-AQD, dgates@cabq.gov

Date: 6/2/2011 via e-mail to Jim Afghani in R6 

Response: The draft guidance said that in assessing whether an event was not reasonably 

controllable, the EPA would take into account whether the high wind event type was 

recurring such that more effective, but costly, controls would be reasonable compared to 

the situation in which a high wind event had been a unique occurrence. In response to this 

and other comments, the EPA has reconsidered this approach and is de-emphasizing 

recurrence. Although rare exceptions may exist, the EPA does not expect to receive or 

review demonstrations for non-recurring high wind dust events because these nonrecurring events will generally not violate the NAAQS. As an example, everyday 

sampling allows for one exceedance of the standard per year without causing a violation 

of the 24 hour PM10 NAAQS, unless sampling completeness is inadequate. 

In response to comments received, in an effort to streamline the demonstration process, 

and based on the recurrence premise stated above, the EPA has modified the recurrence 

discussion in the revised draft High Winds Guidance document in the following ways: 

 De-emphasized recurrence frequency when assessing “not reasonably 

controllable or preventable” analysis 

 Made basic controls analysis slightly more robust (more like recurring above 25 

mph case) to reflect vast majority of cases that are recurring. 
Draft for Public Notice and Comment 

Revision Date: June 2012 51 

 Added a Prospective Controls Analysis. Described in greater detail in section 

3.7.1 of the revised draft High Winds Guidance document, a prospective controls 

analysis is a generic5

 review of an area’s current windblown dust controls and 

high wind threshold. In the prospective controls analysis, the air agency would 

provide information on attainment status, identify natural and anthropogenic 

windblown dust sources and emissions, provide the status of SIP submittals (if 

applicable), and identify the high wind threshold up to which the collective 

windblown dust controls are expected to be effective. Once the EPA approves the 

prospective controls analysis, an air agency’s subsequent high wind exceptional 

event packages could reference the approved set of controls in the prospective 

controls analysis and show that the wind speed for the event in question is at or 

above the high wind threshold established in the prospective controls analysis. 

Air agencies would also include in their demonstration some positive showing 

that control requirements were being met on the day in question. An EPAapproved prospective controls analysis would generally be effective for a 

minimum of three years. 

 Described the High Wind Action Plan (HWAP) more thoroughly in Section 3.7.2 

of the High Wind Guidance document. 

o Air agencies can develop HWAPs to document their plans to implement 

needed controls on newly-identified sources that could emit dust during 

subsequent high wind events (similar to the process used in a Natural 

Events Action Plan). 

o The HWAP is an optional mechanism to implement necessary controls 

more expeditiously than with the normal regulatory planning process. 

o Preparation of a HWAP and its approval by the EPA could promote a 

common understanding between the air agency and the EPA about 

whether subsequent high wind dust events are not reasonably 

controllable or preventable. 

o The HWAP could document current windblown dust controls and current 

and/or planned mitigation measures as part of §51.930. 

 The EPA review and approval of controls and an appropriate high wind threshold 

is typically effective for a minimum of three years 

o The EPA does not expect to reconsider the determination of reasonable 

controls and high wind threshold for at least three years. After the threeyear time period, the EPA will notify the agency if the EPA intends to rereview the controls and high wind threshold. In some limited cases, the 

EPA may re-review the controls and high wind threshold within the 

three-year timeframe, such as if information on sources, enforcement, 

etc. suggests that controls may be inadequate or not 

implemented/enforced. The EPA may also re-evaluate the controls when 

an area that does not typically have recurring high wind dust events 

experiences unexpected recurrent events. 

o If an agency submits a package for an event with a wind speed below a 

previously EPA-approved high wind threshold, the submitting agency 

should also submit a new prospective controls analysis documenting the 

appropriateness of the lower threshold. 

o If the EPA has approved a SIP containing wind-blown dust controls 

within the past three years, then the submitting agency has the option of 

using the SIP-approved controls in place of the prospective controls 

analysis. The submitting agency would, however, need to specify a high 

wind threshold to which the controls are expected to be effective. 

                                                           

5

 “Generic” means a general review rather than a review specific to an identified event. 
Draft for Public Notice and Comment 

Revision Date: June 2012 52 

Together, the SIP-approved controls and the high wind threshold would 

constitute the set of controls that would have been reasonable to 

implement. 

If the EPA’s review reveals inadequacies in currently implemented agency controls, then 

the EPA may pursue subsequent action, such as a SIP call, to secure controls as quickly 

and effectively as possible. In many cases, submitting agencies should pursue regulatory 

planning, but in some cases an area can make significant progress quickly by addressing 

the high wind dust issues using the HWAP. Once adopted by the state/local jurisdiction, 

these mechanisms would be mandatory. As part of the exceptional event process, the 

EPA intends to promote both the regulatory planning mechanism and the HWAP 

approach for attainment areas. 

7.4.2 . Comment: Frequency of Exceptional Events - The Overview document states (page 6 of 

8): “A natural event would not have to be infrequent to qualify as an exceptional event 

under the EER.” How can a frequent event be exceptional? If the event is frequent, then 

reasonable controls should be developed for that event. For example, winds over 25 mph 

are frequent in the Owens Valley. During the 26-year period between March 1985 and 

May 2011, there were 3,408 days with hourly average (as opposed to 1-minute average) 

wind speeds greater than 25 mph. This is an average of 130 days per year. Even if the 

threshold was raised to a 45 mph (hourly) average, the Owens Valley experienced almost 

5 days per year (4.8) that exceeded this increased threshold during the 26-year period. 

High wind days are not infrequent or exceptional in the Owens Valley and the arid 

west—we expect the deployment of measures that control anthropogenic emissions on 

these days. Protecting public health requires as much.

Specific reference to guidance text: Overview document, page 6 

Submitter: Ted Schade, Great Basin Unified Air Pollution Control District, 

tschade@gbuapcd.org 

Date: 6/15/2011 via e-mail to EEGuidanceComments@epa.gov

Response: The statutory definition of an exceptional event at Clean Air Act section 319 

recognizes that natural events can be both recurring and exceptional. However, the EPA 

also agrees with the commenter that “frequent” and “exceptional” are area and event 

specific and must consider public health. As stated previously in this document, 

exceeding a specific wind speed does not, on its own, make an event “exceptional.” 

Rather the high wind threshold informs the rigor of the documentation required to 

support an exceptional events claim and also the rigor with which the EPA will review 

the “not reasonably controllable or preventable” criterion. The EPA agrees with the 

commenter that agencies should deploy reasonable controls to control emissions. The 

EPA’s intention is that individual areas identify a high wind threshold that defines the 

local conditions capable overwhelming reasonable controls on anthropogenic sources 

(i.e., significant emissions from controlled sources) or causing emissions from natural 

undisturbed areas. The Owens Valley situation is unique or nearly unique, and requires 

careful application of these general concepts. The high wind threshold addresses one of 

the exceptional event criterion. A demonstration package would need to address all the 

other exceptional event criteria. 

7.4.3. Comment: Is recurrence frequency calculated for all flagged high wind events or by site? 

Specific reference to guidance text: High Winds Guidance document

Submitter: Scott DiBiase, Pinal County Air Quality, scott.dibiase@pinalcountyaz.gov 

Date: 6/23/2011 via e-mail to EEGuidanceComments@epa.gov 

Response: See response to comment 7.4.1 
Draft for Public Notice and Comment 

Revision Date: June 2012 53 

7.4.4. Comment: It should be made clear that reasonable controls are not required to be in 

place for the first high wind dust exceptional event in a PM10 attainment area. This is 

important since PM10 attainment areas will likely not have any SIP approved or local dust 

control rules in place for sources like agricultural operations, and thus it would be 

impossible to make the control findings. (Note: Santa Barbara County has historically 

been in attainment of the federal PM2.5 and PM10 standards, and has no PM dust control 

rules in place for agricultural sources. The northern half of the County has large stretches 

of contiguous agricultural lands that at times get wind whipped, producing visible 

emissions and above normal PM10 concentrations). 

Specific reference to guidance text: High Winds Guidance Document, Section 3.1.2 

Submitter: Brian Shafritz, Santa Barbara County Air Pollution Control District, 

ShafritzB@sbcapcd.org 

Date: 6/23/2011 via e-mail to EEGuidanceComments@epa.gov

Response: As directed by the comment, this response is specific to attainment areas. The 

EPA agrees that controls are not expected for the first high wind dust exceptional event in 

a PM10 attainment area. However, the EPA is unlikely to consider a first high wind dust 

event, because the first event is unlikely to result in a violation of the NAAQS. In 

response to comment, the EPA has added language to the revised draft High Winds 

Guidance document stating that the EPA does not expect PM controls in areas with no 

“history” of high wind dust exceedances. If an area is violating the standard because of 

more than one high wind dust event in a three-year period, then the EPA will consider the 

area to “have a history” of high wind dust events. If wind speeds exceed a predetermined 

wind threshold, then the EPA may not consider the implementation of controls at the time 

of the event to be a condition for a determination that the event was not reasonably 

controllable. The EPA will determine this during the review process. The EPA does not 

expect to simply concur on events where sources that were not controlled caused a 

violation just because the area was previously in attainment. The EPA expects to look 

closely exceedances that occurred with wind speeds below the wind threshold to 

overwhelm reasonable controls or cause emissions from natural undisturbed areas. If an 

attainment area has violations below the high wind threshold and the EPA determines 

that the concentrations are attributable to sources that could be reasonably controlled 

going forward, the EPA will do one of the following: 

1. Request that the submitting agency develop and implement an adequate HWAP and 

concur upon approval of the HWAP going forward if all other EER criteria have been 

met. 

2. Nonconcur. If the nonconcurrence results in an area’s designation as non-attainment, 

then this nonconcurrence would also trigger preparation of a SIP incorporating 

appropriate PM controls. 

7.4.5. Comment: We are also concerned that the U.S. EPA's proposal implies that if a high 

wind event occurs more than once, new control measures would be more feasible and 

cost effective. The frequency of unpreventable high wind events should not change the 

assessment of what constitutes reasonable controls for windblown dust. 

To address the U.S. EPA concerns that we believe underlie this proposal, ARB plans to 

develop a technical document which discusses the nature of sources for key regions, a 

conceptual model of the types of conditions under which high wind events occur, and an 

analysis of reasonable controls for that region. Subsequent requests for approval of 

specific events would then focus on documenting the technical aspects of that individual 

event rather than a re-analysis of reasonable controls each time. This provides for region 

specific considerations. For example, California State law provides unique authority for 
Draft for Public Notice and Comment 

Revision Date: June 2012 54 

the Great Basin Unified Air Pollution Control to establish mitigation requirements for the 

Owens dry lakebed, which does not apply elsewhere in the State. 

Specific reference to guidance text: none 

Submitter: Lynn Terry (Deputy Executive Officer) for James Goldstene (Executive 

Officer), California Air Resources Board, ksnyder@arb.ca.gov 

Date: 6/24/2011 letter to Gina via e-mail to EEGuidanceComments@epa.gov

Response: Based on CARB’s and other’s comments, the EPA has modified its approach 

to high wind thresholds and High Wind Action Plans and has added a prospective 

controls analysis, with elements similar to those proposed by CARB (see responses to 

comments 7.3.2. and 7.4.1.). The EPA still maintains that the reasonableness of controls 

can depend on the number of days per year on which they will have an air quality benefit. 

7.4.6. Comment: The methodology used to determine recurrence frequency applies to high 

wind events. Will this also be applied to other event types? 

Specific reference to guidance text: High Winds Guidance document, Section 6.2.2.3 

Submitter: Unnamed commenter 

Date: 6/29/2011 via e-mail to EEGuidanceComments@epa.gov

Response: The draft High Winds Guidance document raised the concept of recurrence as 

it pertains to the reasonableness of controls with the belief that a natural event that recurs 

merits more effort at control than a one-time or very infrequent type of event. The EPA 

still adheres to this general concept for high wind dust events. The EPA does not expect 

the recurrence/reasonable control issue to arise for other types of natural events, either 

because the event is expected to be highly infrequent (e.g., 2008 California wildfires) or 

because controls are unlikely to be applied and/or effective (e.g., volcanic eruptions). If 

the EPA discovers that the recurrence concept described above applies to other event 

types, the EPA would apply the principles in the revised draft High Winds Guidance 

document and note this added application in further guidance. 

7.4.7. Comment: The guidance does not provide much streamlining for ADEQ as most of their 

submittals would require the “most comprehensive evaluations” as described in the 

EPA’s sliding scales. ADEQ has provided alternative approaches to handling High Wind 

Action Plans and believes that these approaches would provide some resource relief as 

well as regulatory certainty.

Specific reference to guidance text: High Winds Guidance document 

Submitter: Eric Massey (Director), Arizona Air Quality Division 

Date: 6/30/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: The EPA has incorporated some of the commenters’ approaches into our 

revised draft guidance documents. Since receiving this comment, staff in the EPA Region 

9 office have been working with staff at Arizona Department of Environmental Quality, 

Maricopa County, and Maricopa Association of Governments (MAG) to develop a 

consolidated exceptional events demonstration package that addresses 29 exceedances of 

the PM10 standard in 2011 that can serve as a model for future events. The collaborative 

effort is nearing completion with slightly more effort than it has historically taken to 

address a single high wind exceptional event. Much of the information included in the 

current demonstration package could be transferable to the remaining exceedances that 

are flagged as exceptional events, which will further aid the streamlining process. See 

also our response to comment 7.4.1.

7.4.8. Comment: The draft guidance is unclear regarding the determination of recurrence for 

exceptional events. For example, establishing recurrence appears to rely heavily on 

commonly occurring "informational" flags, as opposed to more appropriate "request to 

exclude" flags. Additionally, consecutive day high wind events are not clearly addressed 

by the draft guidance, and should be considered as a single event, and not multiple 
Draft for Public Notice and Comment 

Revision Date: June 2012 55 

events. Furthermore, the draft guidance includes additional documentation requirements 

for events determined to be recurrent that can otherwise clearly be demonstrated to be 

exceptional, including natural events. The District recommends that the EPA closely reevaluate its consideration of recurrent events to ensure that documentation beyond that 

needed to demonstrate compliance with the EER are not added through the draft 

guidance. 

Specific reference to guidance text: High Winds Guidance document 

Submitter: Samir Sheikh (Director of Strategies and Incentives), San Joaquin Valley Air 

Pollution Control District 

Date: 6/29/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: The EPA has modified its approach with respect to recurrence. See response 

to comment 7.4.1. 

7.4.9. Comment: “EPA should not link the ‘recurrence’ criteria in the statutory EE definition to 

requirements for additional controls or to otherwise establish a "more than once a year" 

definition of recurrence.” 

Specific reference to guidance text: varies (additional documentation to support 

recommendation is provided in comment attachment at Submitted Comments\Need 

OCR\MAG_063011-ocr.pdf) 

Submitter: Thomas Schoaf (Mayor, City of Litchfield Park and MAG Chair), Maricopa 

Association of Governments 

Date: 6/30/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: See response to comment 7.4.1. 

7.4.10. Comment: ADEQ questions the value of the EPA’s requiring additional analysis of air 

pollution controls for events that occur more than 1 time per year. Agencies typically 

review (and flag) events when they occur. The EPA has indicated that they likely will not 

review information until there is a related regulatory decision. If there are fewer than 3 

exceedances, then there will not be a regulatory decision, so the EPA’s approach really 

does not streamline the process. ADEQ recommends that the EPA not use recurrence of 

high wind events as a threshold for determining the extent of documentation needed to 

make the demonstration. Streamlining should be based on the merits of each event. 

Specific reference to guidance text: High Winds Guidance document 

Submitter: Eric Massey (Director), Arizona Air Quality Division 

Date: 6/30/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: See response to comment 7.4.1. 

7.4.11. Comment: WA ECY does not believe that it is appropriate to treat recurring high wind 

events differently than “one-time” events, particularly for agricultural areas where the 

amount of dust raised by high winds at one time and not another does not reflect better 

and worse levels of control but the cycle of agricultural practices. “While the draft 

guidance specifies a 3-year period to determine recurrence, we suggest basing 

‘recurrence’ on a longer period of record such as 10-to-20 years or even more.” 

Specific reference to guidance text: High Winds Guidance document 

Submitter: Stuart Clark (Air Quality Program Manager), Washington Department of 

Ecology 

Date: 7/5/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: See response to comment 7.4.1. 

7.5. Reasonable controls 

7.5.1. Comment: It is noted within the guidance that “HWD EE packages must address 

whether reasonable controls were in place for anthropogenic sources contributing to the 

event.” In the subject of agricultural operations within rule 403, most of these operations 
Draft for Public Notice and Comment 

Revision Date: June 2012 56 

are exempt from stringent dust controls and are obligated under “best management 

practices” (BMP) compliance, which in most cases are voluntary. It seems a contradiction 

to demonstrate or demand that reasonable controls may or may not have been in place 

during the EE, when BMP, at the very best, are voluntary. Again, agricultural operations 

are basically exempt in the area of the Coachella Valley, California, from stringent dust 

control compliance. 

Specific reference to guidance text: High Winds Guidance document, reasonable 

controls 

Submitter: Jonathan Chapman, Torres Martinez Desert Cahuilla Indians, 760-397-0300 

ext 1224, jchapman@torresmartinez.org 

Date: 6/13/2011 via e-mail to EEGuidanceComments@epa.gov 

Response: The fact that a particular “best management practice” is not mandatory for a 

specific source in a given area does not mean that it would not have been reasonable for 

air agencies to make it mandatory. Similarly, in light of the historical frequency and 

nature of high wind events in the area, it may have been reasonable for air agencies to 

encourage agricultural sources to implement the voluntary BMP more broadly or 

effectively. The EPA will assess scenarios on a case-by-case basis. 

7.5.2. Comment: Use of USDA Best Management Practices 

The guidance suggests that U.S. Department of Agriculture best management practices 

(BMPs) could be a source of reasonable controls for exceptional events (High Wind 

document, pages 3 and 12). USDA BMPs are developed to prevent soil loss—they are 

not intended to protect public health. BMPs are not BACM and it is certainly not 

appropriate to use such measures as a surrogate for public health protection.

Specific reference to guidance text: High Winds Guidance document, pages 3 and 12 

Submitter: Ted Schade, Great Basin Unified Air Pollution Control District, 

tschade@gbuapcd.org 

Date: 6/15/2011 via e-mail to EEGuidanceComments@epa.gov

Response: While many of the U.S. Department of Agriculture’s best management 

practices focus on soil loss/erosion prevention approaches, other BMPs are designed to 

effectively reduce fugitive dust emissions and prevent loss of soil during high winds. (See 

http://www.nrcs.usda.gov/wps/portal/nrcs/main/) The EPA has clarified in the revised 

draft guidance documents that implemented BMPs that reduce air and dust emissions 

may be part of the menu of controls that the EPA would consider to be reasonable. 

7.5.3. Comment: Definition of “Reasonable”- The terms “reasonable,” “reasonably 

controllable” and “reasonably controlled” are used throughout the documents and are 

crucial in deciding whether monitored emissions are exceptional or are the result of 

inadequate (or nonexistent) controls. For serious nonattainment areas, like the Southern 

Owens Valley (Owens Lake) and Mono Basin (Mono Lake), Best Available Control 

Measures (BACM) must be required to be in place and fully operational on all 

anthropogenic sources that cause or contribute to PM standard exceedances. Reasonably 

Available Controls (RACM) or other lesser levels of control are not sufficient for serious 

nonattainment areas. It appears that this may be required by the current draft guidance; 

however, the requirement is a footnote (#16) on page 13 of the High Winds document. 

This requirement should be made very clear. Effective BACM developed specifically for 

the source areas to be controlled should be effective in controlling emissions in all but the 

very highest winds—this is, after all, the whole point of a Best Available Control 

Measure. In addition, agencies must prove that actual controls were in place and 

operational—not just that controls are required by rule or regulation and are presumed to 

be in place. Our guiding principle of protecting public health requires us to do our very 

best to control anthropogenic sources on high wind days, especially if the winds cause 

PM emissions from undisturbed areas. These are just the conditions that cause the 
Draft for Public Notice and Comment 

Revision Date: June 2012 57 

greatest threat to public health and are the conditions under which we should be making 

our best efforts at public protection. 

Specific reference to guidance text: High Winds Guidance document, reasonable 

controls 

Submitter: Ted Schade, Great Basin Unified Air Pollution Control District, 

tschade@gbuapcd.org 

Date: 6/15/2011 via e-mail to EEGuidanceComments@epa.gov

Response: The EPA agrees with the commenter and has clarified the revised draft High 

Winds Guidance document by moving the referenced footnote into the body of the 

document. 

7.5.4. Comment: Page 14 of the High Winds Guidance document says “In areas where events 

continue to recur, EPA may consider BACM, or greater levels of control, as the 

appropriate starting point, regardless of attainment status.” Where does the EPA attain 

the legal right to consider BACM or greater levels of control as the appropriate starting 

point regardless of attainment status for areas where events continue to recur? There is 

nowhere in the Clean Air Act that give the EPA that authority. General RACM is 

required for nonattainment plans (CAA Section 172(c)(1), CAA Section 182(a)(2)(A) – 

RACT for Marginal ozone nonattainment areas, CAA Section 182(b)(2) – RACT for 

Moderate ozone nonattainment areas, CAA Section 189(a)(1)(C) – RACT for moderate 

PM10 NAA, Section 190 – RACM and BACM guidance. Further, page 2 of the High 

Winds Guidance document “....states are expected to consider and implement further 

controls as events continue to recur.” How are areas that are designated attainment for 

PM10 (and PM2.5) at the time of the exceptional events supposed to implement further 

controls (i.e. more stringent controls) on sources that will not even voluntarily commit to 

emissions reductions controls? There is no legal requirement for them to do so. Most 

sources that contribute to PM10 exceedances will not commit to control measures until 

forced to (i.e. nonattainment designation/threat of loss of highway funds). 

Specific reference to guidance text: High Winds Guidance document, pages 2 and 14 

Submitter: Scott DiBiase, Pinal County Air Quality, scott.dibiase@pinalcountyaz.gov 

Date: 6/23/2011 via e-mail to EEGuidanceComments@epa.gov

Response: The NAAQS are established for pollutants considered harmful to public 

health and the environment. When the EPA concurs on an air agency’s request to exclude 

data attributed to an exceptional event, the EPA must ensure that the concurred upon 

events are, in fact, exceptional and meet both statutory and regulatory requirements. The 

Exceptional Events Rule allows air agencies to request the EPA to disregard certain 

exceedances which meet the requirements of the Clean Air Act and the EER, including 

the requirement to implement reasonable controls. Air agencies are not required to flag 

data, petition the EPA, or meet the requirements of the EER; these actions are voluntary. 

Air agencies not petitioning the EPA to exclude certain exceedances might be designated 

to nonattainment, with BACM requirements following. Before submitting an exceptional 

events request to the EPA, air agencies may have voluntarily chosen to pursue controls, 

including RACM, BACM, or other controls, to avert an eventual nonattainment 

designation. These measures should be viewed as voluntary proactive control strategies, 

not as EPA required actions, as the exceptional event identification, demonstration, and 

review process is voluntary for state, local and tribal agencies. 

By starting point, the EPA means that the final analysis of reasonable controls could 

include either fewer or more controls than identified in the reference list of RACM or 

BACM measures depending on the specifics of the case as they existed at the time of the 

event. The EPA has modified the language in the revised draft High Winds guidance 

document. The EPA also notes that while RACM or BACM may be appropriate to 

implement under the specific sections of the CAA identified by the commenter, the 
Draft for Public Notice and Comment 

Revision Date: June 2012 58 

exceptional event requirements under section 319 of the CAA are separate and distinct. 

To qualify as an exceptional event under section 319 of the CAA and the associated 

promulgated regulations, submitting agencies must meet the underlying requirements 

including identifying what constituted reasonable controls for a particular event. The lack 

of a formal area designation does not, in itself, mean that no controls would have been 

reasonable to have been in place. Rather, the physical facts related to the event determine 

what constitutes “reasonable controls.” See also the response to comment 7.4.4. 

7.5.5. Comment: It should be made clear that reasonable controls are not required to be in 

place for the first high wind dust exceptional event in a PM10 attainment area. This is 

important since PM10 attainment areas will likely not have any SIP approved or local dust 

control rules in place for sources like agricultural operations, and thus it would be 

impossible to make the control findings. (Note: Santa Barbara County has historically 

been in attainment of the federal PM2.5 and PM10 standards, and has no PM dust control 

rules in place for agricultural sources. The northern half of the County has large stretches 

of contiguous agricultural lands that at times get wind whipped, producing visible 

emissions and above normal PM10 concentrations).

Specific reference to guidance text: High Winds Guidance Document, Section 3.1.2 

Submitter: Brian Shafritz, Santa Barbara County Air Pollution Control District, 

ShafritzB@sbcapcd.org 

Date: 6/23/2011 via e-mail to EEGuidanceComments@epa.gov

Response: See response to comment 7.4.4. and 7.5.4. 

7.5.6. Comment: The U.S. EPA's first principle in developing the Draft Guidance states, 

"States should not be held accountable for exceedances due to events that were beyond 

their control at the time of the event." High wind events will recur in the naturally dry 

arid regions of the West. Although reasonable measures to help mitigate the impact of 

these events should be implemented, such exceedances are fundamentally not 

preventable. We are especially concerned that the Draft Guidance suggests that despite a 

state's documentation that an uncontrollable wind event occurred, the U.S. EPA could 

still disapprove the exceptional event based on the U.S. EPA’s staff’s concerns regarding 

the adequacy of PM10 control measures. The determination as to whether a state has 

reasonable control measures in place should be an independent analysis taking into 

account technical feasibility and cost-effectiveness. 

If the U.S. EPA were to implement the guidance as proposed, states could be required to 

develop an attainment demonstration based on a value that is the result of an 

uncontrollable wind event. Such a State Implementation Plan would not be approvable, 

since there is no attainment strategy that can prevent exceedances caused by high Wind 

events. This is precisely the situation the U.S. EPA's first principal is designed to prevent. 

Specific reference to guidance text: none 

Submitter: Lynn Terry (Deputy Executive Officer) for James Goldstene (Executive 

Officer), California Air Resources Board, ksnyder@arb.ca.gov 

Date: 6/24/2011 letter to Gina via e-mail to EEGuidanceComments@epa.gov

Response: As previously discussed, local high wind thresholds should define the 

conditions capable overwhelming reasonable controls on anthropogenic sources (i.e., 

significant emissions from controlled sources) or causing emissions from natural 

undisturbed areas. The EPA supports the approach of a priori determining whether 

controls are adequate for exceptional events purposes as long as an analysis of an 

applicable high wind threshold is included (or referenced). For example, we could 

prospectively agree that a reasonable set of high wind dust controls are effective only up 

to sustained winds of 25 mph. Subsequently, events with wind speeds at or above 25 mph 

where such controls are in place generally would be considered to be not reasonably 
Draft for Public Notice and Comment 

Revision Date: June 2012 59 

controllable or preventable. In this case, any exceedances resulting from events with wind 

speeds less than 25 mph wind would either not be submitted to the EPA for data 

exclusion approval or would need additional justification. See response to comment 

7.4.1. 

In response to the commenter’s second point regarding the development of an attainment 

demonstration based on a value that is the result of an uncontrollable wind event, the 

EPA refers to the commenter to response to comment 6.5.1. and Question 13 in the 

revised draft Q&A document. The EPA has also added language addressing this point in 

the revised draft High Winds Guidance document. 

7.5.7. Comment: Contrary to the U.S. EPA's interpretation, the Clean Air Act does not 

authorize the U.S. EPA to require that anthropogenic sources of emissions be "reasonably 

controlled" in order to exclude a high wind event. Section 319(b)(1)(A) of the Clean Air 

Act defines the term "exceptional event" and includes the requirement that the event "is 

not reasonably controllable or preventable." Under the statute, the relevant criterion is 

whether the event itself is reasonably controllable, not whether the effects of the event 

could have been limited or controlled. There are two types of exceptional events: those 

caused by human activity that is unlikely to recur, and those cause by "natural events." 

While the degree of control on anthropogenic sources may be relevant to an exceptional 

event caused by human activity (e.g. a chemical spill), by the plain language of the statute 

it is not relevant to whether a natural event "is not reasonably controllable or 

preventable." In short, an agency cannot do anything to "control or prevent” the wind. 

The U.S. EPA has attempted to address this concern by redefining the term "event" to 

include both the high wind and the resulting dust emissions. This definition is illogical 

and convoluted. There is a clear difference between an event (high winds) and the results 

of the event (dust emissions). With respect to "natural events," the relevant consideration 

under the statute is whether the event itself is controllable or preventable. The Clean Air 

Act may allow consideration of controls on anthropogenic sources in deciding whether an 

exceptional event due to human activity is controllable, but the wind event itself is not 

controllable. 

Whether reasonable controls are applied to anthropogenic sources may be relevant to a 

separate provision of the Clean Air Act, but under that provision, the U.S. EPA's 

Exceptional Events Rule has already expressly decided that a demonstration of the degree 

of control will not be required. Therefore, to the extent the proposed Guidance would 

require a state to demonstrate that it has applied "reasonable controls" before excluding 

an exceptional event it violates the Exceptional Events Rule. The U.S. EPA's Exceptional 

Events regulation is authorized to consider several principles, including "the principle 

that each state must take necessary measures to safeguard public health, regardless of the 

source of the pollution." CAA section 319(b)(3)(iv). Under this principle, the U.S. EPA 

has already decided that it will not require states to control anthropogenic sources. In 

implementing this principle, the Exceptional Events Rule says that mitigation measures a 

state may take "may or may not include the implementation of control measures on 

contributing anthropogenic sources related to an event." 72 Fed. Reg. 13560, 13576. 

(March 22, 2007). Thus, control of anthropogenic sources is not automatically required. 

Further, the U.S. EPA said that "the implementation of RACM or BACM is not required 

... " (id.) Finally, the U.S. EPA expressly ruled that it "will not be requiring States to 

submit documentation concerning the actions that it (sic) took to mitigate the impact of 

exceptional events, in order for U.S. EPA to exclude data from regulatory consideration." 

The U.S. EPA's Proposed Guidance thus violates its own Exceptional Events Rule as well 

as the express terms of the Clean Air Act. This issue is currently being litigated in 
Draft for Public Notice and Comment 

Revision Date: June 2012 60 

Imperial County Air Pollution Control District v. U.S. EPA, Ninth Circuit Court of 

Appeals No.10-72709. 

The term "reasonable" is used in terms of controls in relation to the "not reasonably 

controllable or preventable" discussion. As discussed above, the U.S. EPA's use of this 

phrase to require that the effects of the event, rather than the event itself, be reasonably 

controllable or preventable, is not authorized by the Clean Air Act or the U.S. EPA's 

Exceptional Events Rule. While we agree that effective controls should be in place to 

protect public health, which is our most important consideration, the cost versus benefit 

of controls plays role in determining what control measures are reasonable in a given area 

or situation. Additional clarification in the guidance and the language of the Exceptional 

Events Rule itself may help state and local agencies identify the wind-driven 

anthropogenic sources in the area and to assess what controls could be applied. 

If the U.S. EPA continues to take the position that anthropogenic sources must be 

reasonably controlled in order to exclude data, it must at least recognize that in some 

cases, even reasonable controls would not have prevented the exceedance. States must 

have the ability to make the case to the U.S. EPA that those sources were reasonably 

controlled at the time of the exceedance and that the exceedance occurred despite the 

implementation of those controls, or that if the controls were not in place, they would not 

have prevented the exceedance in any case. The discussion of reasonable controls 

(Section 3.1.2) seems to indicate that agencies may only know the U.S. EPA's assessment 

of our control strategy for future events based on notice from the U.S. EPA that the U.S. 

EPA "considers controls on particular uncontrolled sources to be reasonable (e.g., as part 

of a previous exceptional event review)." Table 2 of the guidance provides some good 

insight into the thought process that the U.S. EPA will use for determining the 

reasonableness of controls. The difficulty is in how to best assess the adequacy of 

controls for events without that history of the U.S. EPA concurrence. Furthermore, 

additional clarification is needed on how source contributions that cross jurisdictional 

boundaries should be treated. One such example is particulates entrained from 

thunderstorms outflows over the deserts of northern Mexico or Arizona that affect 

measurements in California where the winds remain low. It is not completely clear what 

level of analysis is needed for such a transport case and whether a controls analysis is 

needed when anthropogenic sources are out of the air agency's jurisdiction. 

While AQMD has one of the most comprehensive and highly effective control programs 

in the country, there is concern that a minor source that is not considered fully controlled 

in the U.S. EPA assessment could stall this process. Do all known anthropogenic sources 

in an area need to be controlled to the full extent possible for BACM to be considered to 

be in place? Additional discussion in the guidance will help submitting agencies 

determine if their controls should be adequate and will help provide consistency within 

the U.S. EPA among the reviewers of exceptional event documents. To illustrate this 

concern, the example of reasonable agricultural controls is used. Can agricultural sources 

be adequately controlled with existing soil management practices (such as those from the 

U.S. Department of Agriculture's Natural Resources Conservation Service) or could 

stabilization of plowed or otherwise disturbed farmland be required, similar to what is 

often required of construction sites? Many would argue that such agricultural controls 

would be neither appropriate nor reasonable, for both economic and ecological reasons. 

Would air agency rulemaking to require best soil management practices on agricultural 

lands be needed in order to be able to consider agricultural source contributions to be 

reasonably controlled, or is soil management guidance adequate? Therefore, if the U.S. 

EPA elects to incorporate "reasonable control" in spite of our comments, any use of the 

term "reasonable control" must be clearly defined. 
Draft for Public Notice and Comment 

Revision Date: June 2012 61 

Specific reference to guidance text: High Winds Guidance document 

Submitter: Barry Wallerstein, South Coast Air Quality Management District 

Date: 6/28/2011 via e-mail to Matt Lakin and EEGuidanceComments@epa.gov

Response: The EPA agrees with the commenter that in some cases, there are no feasible 

and reasonable cost controls that would have prevented the exceedance. This is the 

concept behind the development of the prospective controls analysis (described in 

additional detail in the response to comment 7.4.1.). In a prospective controls analysis, air 

agencies should first identify an appropriate high wind threshold for an area and identify 

and implement “reasonable” controls that are expected to be effective up to that threshold 

speed. Once the EPA agrees with the identified controls and high wind threshold for that 

area, then, events with wind speeds above the high wind threshold would generally be 

assumed to be not reasonably controllable or preventable since implemented controls 

would be overwhelmed above the high wind threshold. Further, the EPA would generally 

assume that PM emissions below the wind threshold have been reasonably controlled. 

See responses to comments 6.5.2. and 7.3.2. In addition, as noted in the response to 

comment 7.4.1., the prospective controls analysis can be prepared and submitted to the 

EPA in advance of any event as CARB suggests, with a letter of intent, or as a 

component of a demonstration package. The EPA encourages submitters to use 

prospective analyses as a means of communicating and reaching a common 

understanding in advance of an event. 

The EPA further agrees with the commenter that the mitigation requirements discussed at 

72 FR 13576 allow air agencies to make determinations regarding reasonable mitigation 

measures and that these reasonable measures “may or may not include the 

implementation of control measures on contributing anthropogenic sources related to an 

event...” The EPA notes, however, that mitigation plans address measures that an air 

agency takes after an event. These measures may or may not be “reasonable” when 

addressing the “not reasonably controllable or preventable” criterion within an event 

demonstration package. 

The EPA does not intend to determine the adequacy of any individual control measures 

or practices in this response to comments document or in the revised draft guidance 

documents. Rather, we will assess reasonable controls as part of a demonstration 

submittal or as part of a prospective controls analysis. The EPA is not taking any position 

in this document on what controls may or may not be reasonable for plowed or otherwise 

disturbed farmland. 

The commenter also requests clarification regarding cross-jurisdictional boundary issues. 

The EPA addresses both interstate and international transport in the response to comment 

6.4.1. and in Question 23 in the revised draft Q&A document. The EPA refers the 

commenter to these responses. 

7.5.8. Comment: The "reasonableness of existing controls" and the required controls analysis 

assumes a regulatory structure that does not exist on the Community. GRIC has two 

adopted RACT level regulations for the significant PM-10 point source categories. 

Ordinances also are in place for area sources such as earth moving, material handling 

unpaved parking lots, disturbed surface areas, etc. However, agriculture does not have a 

regulatory program, other than for the control of pesticide application, specifically 

applicable to it. Thus, if the phrase "control measures in place" means controls necessary 

to satisfy a regulatory requirement, GRIC does not meet the requirement. The reason is 

primarily cultural and traditional properties of the Community that are protected by both 

tribal and federal regulation. The central cultural concern for the Gila River Community 

is agriculture. The Akimel O'odham people are culturally and traditionally 
Draft for Public Notice and Comment 

Revision Date: June 2012 62 

"agriculturalists" as opposed to "hunters and gatherers." The Community's very existence 

is founded upon agriculture and farming activities with a relationship and respect for the 

land and water. Any attempt to regulate how farming is conducted will be immediately 

opposed by the Community's decision makers. Of course, regulation of activities that 

directly relate to the safety of workers or Community members is as stringent as 

elsewhere, but regulation of the methods of tillage or the nature of how crops are grown 

is an anathema to the Community. This being said, the Community appreciates the need 

to control and mitigate dust from farming activities and has led the local farming 

jurisdictions in their ability to respond to the mitigation of dust issues. While the 

Community has developed and voluntarily implemented significant Best Management 

Practices, they have not been imposed as regulations but rather are adopted as 

Community farming methods. It is important to note that this is a voluntary, not a 

regulatory program, and the controls analysis contemplated by this guidance appears to 

be based entirely on the effectiveness of regulation, not the effectiveness of the voluntary 

control measures being implemented. It would be unreasonable to assume that cultural 

and traditional practices would be regulated under this guidance and such regulation 

would be unnecessary. 

“...there is a requirement that if dust from undisturbed natural desert is cited as a 

contributing cause of an exceedance, which causal connection must have "appropriate 

supporting documentation." The Community is entirely rural in character with large tracts 

of land that are undisturbed desert. However, it is unclear what documentation EPA 

expects to verify this condition or the fact that dust can be entrained from these tracts of 

land.”

Specific reference to guidance text: High Winds Guidance document 

Submitter: Leroy Williams (Environmental Engineer) for William Rhodes (Governor), 

Gila River Indian Community, williams@gilanet.net 

Date: 6/23/2011 via letter to Gina with cc e-mail to EEGuidanceComments@epa.gov

Response: The EPA commends the Community for recognizing the need to control and 

mitigate dust from farming activities and for leading the local farming jurisdiction in their 

ability to respond to mitigation of dust issues. The commenter notes that the Community 

has developed and voluntarily implemented significant Best Management Practices. They 

have not been imposed as regulations but rather are adopted as Community farming 

methods. The EPA will consider currently implemented controls at the time the event 

occurred, including voluntarily developed and implemented Best Management Practices 

in reviewing the "not reasonably controllable or preventable" element when reviewing 

tribal exceptional event demonstration submittals. The EPA may consider such 

implemented controls to be "reasonable" depending on the event. Conversely, it may be 

unreasonable not to have had certain controls in place when the event occurred. Thus, the 

EPA's controls analysis is not restricted "entirely on the effectiveness of regulation, [but 

could also consider] the effectiveness of the voluntary control measures being 

implemented." 

Additionally, the commenter makes a second point regarding the need for "appropriate 

supporting material" where dust from undisturbed natural desert is cited as a contributing 

cause of an exceedance. While the EPA’s position is generally that impacts from windblown dust from undisturbed natural deserts are inherently not reasonable to control, the 

tribe (or state) would need to assert this and provide appropriate supporting 

documentation in its demonstration package. The supporting documentation should 

include descriptions of the geographic area (with maps or available visuals) and a 

discussion of the historical land use, including prior disturbances, water diversions and 

other historical practices which may have occurred on the land, even if the land seems or 

is considered to be “undisturbed” at present. Submitting agencies should also identify all 
Draft for Public Notice and Comment 

Revision Date: June 2012 63 

sources contributing to an event and identify appropriate control strategies for each 

anthropogenic source. 

7.5.9. Comment: “EPA's requests to provide a comprehensive controls analysis that has back 

trajectories indicating specific sources in the upwind area, an inventory of the 

contribution for the significant sources, and detailed descriptions of controls and their 

effective implementation and enforcement is an excessive and unreasonable requirement. 

EPA needs to be realistic in establishing requirements for determining that reasonable 

controls were in place for the exceptional event documentation process. As in past 

approvals, EPA should recognize and streamline the approval process for areas that have 

implemented comprehensive BACM controls, such as the San Joaquin Valley. Similarly, 

the draft guidance includes a requirement that analyses be performed to determine 

whether natural sources were reasonably controlled during exceptional events. In an 

example included in the draft guidance, EPA cites performing an analysis of whether 

windbreaks and other potential controls are feasible as part of establishing whether 

reasonable controls were in place. Given the large potential geographic areas that 

contribute to exceptional events, and the implementation of comprehensive BACM 

controls, this requirement seems onerous and unreasonable.” 

Specific reference to guidance text: High Winds Guidance document 

Submitter: Samir Sheikh (Director of Strategies and Incentives), San Joaquin Valley Air 

Pollution Control District 

Date: 6/29/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: In response to comments received, the EPA has developed the concept of a 

prospective controls analysis that includes information on attainment status, identification 

of natural and anthropogenic windblown dust sources and emissions, the status of SIP 

submittals (if applicable), and identification of the high wind threshold up to which the 

collective windblown dust controls are expected to be effective. (The EPA describes this 

concept in additional detail in the revised draft High Winds Guidance document and in 

the response to comment 7.4.1.) In addition, as indicated in the response to comment 

7.4.1., the submitting agency can use SIP-approved controls in place of the prospective 

controls analysis if the following conditions are met: 

 The EPA has approved the SIP within the past three years6

 The SIP contains controls specifically for high wind dust events. The EPA will 

only consider as relevant, BACM or RACM for high wind dust for serious or 

moderate non-attainment areas, respectively (i.e., the EPA would consider 

BACM for harvesting operations irrelevant). 

 The submitting agency has specified a high wind threshold up to which the 

controls are expected to be effective. 

Once the EPA determines that the currently implemented controls are reasonable and the 

high wind threshold is appropriate, then the submitting agency can reference the 

prospective controls analysis in the “not reasonably controllable or preventable” portion 

of submitted packages for events exceeding the high wind threshold rather than preparing 

new controls analyses and “not reasonably controllable or preventable” demonstrations. 

The EPA has clarified this position in the revised draft High Winds Guidance document. 

                                                           

6

 EPA has identified 3 years as the “approvable” timeframe for SIPs. EPA believes that 3 years is reasonable 

because it corresponds to the minimum time used to represent recurrence and historical fluctuations. EPA further 

believes that BACM measures in a SIP older than 3 years may not constitute all “reasonable” measures because 

physical conditions in the SIP area may have changed, new monitoring sites may show air quality impacts not 

previously realized, control technology may have advanced, and the resources available in the community to apply 

controls may have increased. 
Draft for Public Notice and Comment 

Revision Date: June 2012 64 

7.5.10. Comment: The draft policy requires that a determination be made that controls were 

properly enforced during an exceptional event, and suggests that the number of 

inspections and notices of violations in upwind areas be considered as evidence that all 

reasonable controls were implemented and functioning appropriately. This requirement is 

unreasonable and inappropriate for areas that have successfully implemented 

comprehensive BACM controls through mature permitting and enforcement programs, 

such as in the San Joaquin Valley. Additionally, Exceptional Events can occur during off 

hours with limited staffing or in remote areas and the requirement to enforce controls 

appears unreasonable in these situations. 

Specific reference to guidance text: High Winds Guidance document 

Submitter: Samir Sheikh (Director of Strategies and Incentives), San Joaquin Valley Air 

Pollution Control District 

Date: 6/29/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: The EPA has revised the draft High Winds Guidance document to state that 

agencies should submit available inspection reports and/or notices of violations (NOVs) 

in upwind areas as evidence regarding whether all reasonable controls were implemented 

and functioning properly at the time of the event. The EPA recognizes that agencies have 

varied methods of permitting and enforcement and does not expect all agencies to have 

these records for all events. The EPA does, however, expect agencies to make a general 

showing that controls are being enforced to a reasonable degree (not necessarily on the 

particular day of the event). The EPA does not expect detailed records for events with 

wind speeds above the high wind threshold. 

7.5.11. Comment: “Imperial County APCD is extremely concerned with EPA's direction, which 

is at variance with the state's planning process for high wind events. Air Districts and 

states have to plan years ahead and setup their strategies to protect the public during a 

high wind episode. The air districts and states have to develop, adopt, and approve 

RACM/BACM rules in efforts to meet state and national air quality standards and also do 

this in anticipation of high wind events. If EPA has concerns with RACM/BACM rules 

adopted and approved by the local air district board and which are further approved by 

the states, EPA should use the process of development of the rules to submit their 

potential deficiency comments to these rules. The manner in which EPA proposes to 

evaluate RACM/BACM for high wind episodes in this draft guidance is not appropriate, 

nor productive. In this proposed draft guidance, EPA is evaluating rules in retrospect 

during which time it is highly unlikely that the local agencies and states would be able to 

resolve the issue by rule making. Instead, Imperial County APCD feels that EPA should 

not use the process of high wind episodes to contest RACM/BACM rules and concentrate 

only on the actual enforceability of these rules during the time of the event. If EPA finds 

deficiencies with the rules and determines that those rules need to be updated, EPA 

should work with the air districts and states by mutually agreeing on process and revision 

context of the rules to prevent any potential future impacts to the public. Imperial County 

APCD strongly opposes EPA's proposed language that basically conditions approvability 

and concurrence, or not, of high wind or other exceptional events on EPA-perceived 

deficiencies with the RACM/BACM rules due, in part, to lack of EPA's timely action on 

reviewing and approving said rules.” 

Imperial County APCD also provided information re their review of the High Winds 

Guidance doc (see Submitted Comments\Need OCR\ICAPCD_Poiriez_062911-

OCR.pdf) 

Specific reference to guidance text: High Winds Guidance document 
Draft for Public Notice and Comment 

Revision Date: June 2012 65 

Submitter: Brad Poiriez, Imperial County Air Pollution Control District, 

bradpoiriez@co.imperial.ca.us 

Date: 6/29/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: The EPA does and will continue to use the rule process to comment on 

RACM/BACM. The EPA further proposes to address the commenter’s concerns by 

implementing a prospective review of controls/threshold – see also response to comment 

7.4.1. and 7.5.9. 

7.5.12. Comment: “As a condition for approval of an exceptional event request, the draft 

guidance requires a State to demonstrate, to the satisfaction of the EPA regional office, 

that any control measures that could “reasonably” have been in place at the time of the 

event must have been in place, including escalating control measures in areas subject to 

recurring dust events. WESTAR reiterates its view that if a specific set of controls is 

required that is not currently in the State Implementation Plan, it is EPA’s responsibility 

to notify the State of the SIP deficiency or to clearly articulate in the regulation what 

emission controls are required as a condition of an exceptional events approval.” 

Specific reference to guidance text: none 

Submitter: David Collier (President), WESTAR 

Date: 6/30/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: The EPA proposes to address this by de-emphasizing recurrence and by 

providing an opportunity for developing and implementing a prospective review of 

controls/threshold – see response to comment 7.4.1. and 7.5.9 

7.5.13. Comment: “The Clean Air Act § 110 provides a clear process that EPA must follow 

when requiring an increase in stringency of controls on significant sources of air 

pollution, including the requirement that EPA issue a SIP call, give public notice, provide 

the public an opportunity to comment, and respond to public comments. EPA’s intent to 

circumvent §110 of the Act under cover of the draft guidance is set forth in § 3.1.2 in 

footnote 16 on Page 13: Legally, EPA believes the event-relevant measures that have 

already been included in the approved SIP as RACM or BACM to be an essential part of 

the set of controls that need to be in place for an event to be considered “not reasonably 

controllable or preventable,” but they may not be sufficient by themselves particularly if 

the SIP has not been recently reviewed or revised. (emphasis added) Clark County 

believes that control measures in an approved SIP should always meet the “...reasonable 

and appropriate measures (72 Fed. Reg. 13560, 13566 (Mar. 22, 2007))” criteria of the 

EER. Clark County believes that any action by EPA to require revisions to a state’s SIP 

control measures without following the Clean Air Act § 110 processes exceeds EPA’s 

authority under the Act and falls outside the purview of the EER. Clark County therefore 

encourages EPA to revise the draft guidance to indicate that where states are not under 

the provisions of an attainment/maintenance SIP, RACM level controls on affected 

anthropogenic sources will comply with the reasonable and appropriate measures 

requirements of the EER. Where the state falls under the provisions of an attainment or 

maintenance SIP, the approved control measures in the SIP will meet the reasonable and 

appropriate measures requirements of the EER.” 

Specific reference to guidance text: High Winds Guidance document 

Submitter: Tina Gingras (Assistant Director), Clark County DAQEM 

Date: 6/30/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: The EER does not impose new control requirements on sources or areas; 

rather, it defines the conditions under which certain exceedances and violations of the 

NAAQS are excluded when determining attainment. Per Section 319 of the Clean Air 

Act, reasonable measures to control wind-blown dust are a precondition for the EPA 

concurrence. This does not, however, impose mandatory requirements on agencies or 

districts. Requesting exclusion of data under the EER is optional and voluntary. 
Draft for Public Notice and Comment 

Revision Date: June 2012 66 

To make the exceptional events process more efficient for those who choose to pursue it, 

the EPA proposes to make the determination of the adequacy of controls for exceptional 

events purposes in advance of reviewing a complete exceptional event demonstration 

package by implementing a prospective review of controls including a high wind 

threshold. We have revised the draft High Winds Guidance document to indicate that 

implementing windblown dust BACM that has been recently approved or reviewed 

(within the past three years) generally should be adequate to satisfy the “not reasonably 

controllable” element provided the high wind threshold is exceeded. Further, we have 

revised the BACM/RACM language in the revised draft High Winds Guidance document 

to clarify that we will only consider windblown dust BACM as relevant BACM measures 

to reasonably control windblown dust during high wind events. See also the response to 

comment 7.4.1. and 7.5.9. 

7.5.14. Comment: The second guiding principle of the draft guidance states that it is desirable to 

implement reasonable controls to protect public health (draft guidance, p 1, emphasis 

added) which suggests RACM for attainment, unclassifiable, or moderate nonattainment 

areas and BACM or Most Stringent Measures for serious nonattainment areas. “Section 

3.1 et. seq. of the draft guidance, which establishes criteria for when an event is not 

reasonably controllable or preventable, sets forth de facto requirements which 

significantly exceed those set forth in the EER and which supersede the § 110 planning 

provisions of the Clean Air Act. In § 3.1.2 of the draft guidance the EPA states: If a set of 

control measures could reasonably have been in place for contributing sources at the time 

of the event, then they must have been in place for the event to qualify as an exceptional 

event under the EER. (p 12) This is one of several provisions in the guidance which 

exceed the scope of the EER and effectively turns the draft guidance document into a 

regulation. In § 3.1.2 on Page 14 of the draft guidance, the EPA states “. . . it could be 

reasonable to require controls more stringent than BACM or RACM, particularly in areas 

with recurring exceedances.” The EPA’s expectation that states would need controls 

“more stringent than BACM” to establish that an event was “not reasonably controllable 

or preventable” is illogical and is not supported by the language in the regulation. This 

expectation would also place extreme financial burdens on both air regulatory agencies 

and stakeholders that likely cannot be supported in the current economy.” 

Specific reference to guidance text: High Winds Guidance document 

Submitter: Tina Gingras (Assistant Director), Clark County DAQEM 

Date: 6/30/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: Developing a prospective review of controls allows resolution in the 

planning/rules context before the exceptional event demonstration review process. We 

have revised the draft High Winds Guidance document to indicate that implementing 

windblown dust BACM that has been recently approved or reviewed (within the past 

three years) generally should be adequate to satisfy the “not reasonably controllable” 

element provided the high wind threshold is exceeded. Further, we have revised the 

BACM/RACM language in the revised draft High Winds Guidance document to clarify 

that we will only consider windblown dust BACM as relevant BACM measures to 

reasonably control windblown dust during high wind events. 

7.5.15. Comment: “EPA should provide that implementation of Reasonably Available Control 

Measures ("RACM") and Best Available Control Measures ("BACM") will be 

considered to meet EER requirements related to "reasonably controllable or preventable." 

Specific reference to guidance text: varies (additional documentation to support 

recommendation is provided in comment attachment at Submitted Comments\Need 

OCR\MAG_063011-ocr.pdf) 
Draft for Public Notice and Comment 

Revision Date: June 2012 67 

Submitter: Thomas Schoaf (Mayor, City of Litchfield Park and MAG Chair), Maricopa 

Association of Governments 

Date: 6/30/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: See responses to comments 7.4.1., 7.5.9., and 7.5.14. 

7.5.16. Comment: Not reasonably controllable or preventable – “The guidance incorrectly treats 

reasonable controls as a pre-requisite for concurring with an exceptional event 

demonstration, regardless of whether the reasonable controls would have prevented the 

exceedance.” 

EPA considers a source that is "reasonably controlled" to be one whose emissions were 

not reasonably controllable or preventable"; therefore, these terms are used 

interchangeably throughout this document for anthropogenic controls. 

Comment: We suggest deleting this sentence (High Winds Guidance document, Section 

3.1, page 13) 

EPA also generally considers that wind-generated dust from previously disturbed land ... 

is also not reasonably controllable or preventable, provided that there are no reasonable 

active measures that could be taken to control dust during the transition back to natural 

conditions.

Comment - This incorrectly omits consideration of whether the "reasonable active 

measures" would have prevented the exceedance. We suggest adding the following to the 

end of this sentence, "unless the reasonable active measures would not have prevented 

the exceedance." (High Winds Guidance document, Section 3.1.1, paragraph 2) 

"If reasonable controls on wind-driven anthropogenic sources were not in place, then the 

event would not be considered "not reasonably controllable or preventable" and would 

not satisfy the nRCP element of the definition of an exceptional event. That is, to meet the 

EER the state should identify wind-driven contributing anthropogenic sources and show 

that reasonable controls were in place." 

Comment - This incorrectly eliminates "preventable." We believe that concurrence with a 

demonstration in areas where "reasonable controls" were not in· place is required if the 

area can show that that winds were so high that even reasonable controls could not have 

prevented the exceedance. We suggest adding the following sentence; "However, in areas 

where reasonable controls were not in place, the NRCP element could be satisfied if the 

area can show that those "reasonable controls" would not have prevented the 

exceedance." (High Winds Guidance document, Section 3.1.1, paragraph 3) 

"Under the EER the event must be "not reasonably controllable or preventable" 

[emphasis added]; therefore, controls need not prevent the exceedance altogether to be 

reasonable." 

Comment - We agree that whether the controls prevent the exceedance has nothing to do 

with the reasonableness of the control. We also agree that it is appropriate to emphasize 

the word "or.” We believe the error occurs in next sentence of that paragraph. "If a set of 

control measures could reasonably have been in place for contributing sources at the 

time of the event, then they must have been in place for the event to qualify as an 

exceptional event under the EER." That sentence either ignores "preventable" or 

effectively replaces "or" with "and" by requiring that both conditions "reasonable 

controls" AND "preventable" to be satisfied. We suggest that the following clause be 

added to the third sentence in the paragraph, "unless the state/local can show that the 

reasonable controls would not have prevented the exceedance.” (High Winds Guidance 

document, Section 3.1.2, paragraph 1) 
Draft for Public Notice and Comment 

Revision Date: June 2012 68 

Specific reference to guidance text: varies – see notes 

Submitter: Larry Greene (Executive Director), Sacramento Metropolitan Air Quality 

Management District 

Date: 6/30/2011 letter via e-mail to Matt Lakin and EEGuidanceComments@epa.gov

Response: The EPA generally agrees with the commenter on these issues and believes 

that the revised draft guidance reflects the spirit of the above comment. The EPA’s 

revised draft guidance includes a prospective controls analysis (discussed in more detail 

in the response to comment 7.4.1.). The prospective controls analysis should identify the 

set of reasonable controls and the wind speed up to which the rules are expected to be 

effective. The EPA expects that when winds are above the established high wind 

threshold, the set of pre-approved reasonable controls for the identified sources could be 

overwhelmed, resulting in the event being not reasonably controllable or preventable. In 

determining whether the event is not reasonably controllable or preventable, the EPA will 

consider whether the collection of anthropogenic sources has been reasonably controlled. 

For the EPA to consider the event to have been not reasonably controllable or preventable 

requires, among other considerations, that reasonable controls were in place on 

contributing anthropogenic sources. Since each source contributes incrementally, it is 

unlikely that controls on any one source would prevent an exceedance. Therefore, the 

EPA’s approach is to consider the collection of controls in its assessment of whether the 

event was not reasonably controllable or preventable. See response to comment 7.4.4. for 

areas that are attaining the standard. 

7.5.17. Comment: “What constitutes ’reasonable control’ - We suggest that the guidance rely on 

or more closely follow the process used when states conduct control measure analysis 

procedures used in plan preparation (e.g. RACT demonstrations) and not expect more 

stringent controls than required by the areas nonattainment designation and classification 

status without adequate notice by EPA to the state/local.” Sacramento Metropolitan Air 

Quality Management District supports Table 2 in Section 3.1.2 but suggests revisions that 

more closely follow the state (RACT/RACM) analyses process.” 

Comment – “We suggest revising Table 2 to first identify ’reasonable controls,’ and IF a 

reasonable control is identified that was NOT in place, the state/local then conducts an 

analysis to show whether the reasonable control would have prevented the exceedance. 

Only if ’reasonable controls’ are identified that are not in place would you evaluate 

whether the exceedance is preventable. If multiple ‘missing’ reasonable controls are 

identified, then, similar to EPA's RACM guidance, the state must show that the collective 

benefit of all missing reasonable controls would not have prevented the exceedance. If 

they would not have prevented the exceedance, then we believe EPA should not object to 

the exceptional event request.” 

Comment – “We suggest reordering the discussions in Table 2. Items numbered 1, 2, 4, 5, 

and 6 relate to identifying what are the ‘reasonable controls’ and should be grouped 

together as the first part of the analysis. Items 3 and 8 would go next. Item number 3 

relates to whether the ‘preventable’ analysis is required. Item 8 appears to reflect 

consideration of whether ‘de minimis’ controls would have prevented the exceedance and 

are not required. Item 7 relates to whether the collection of all reasonable controls would 

have prevented the exceedance. We suggest that item 8 be a component of the analysis to 

determine whether control(s) would have ’prevented’ the exceedance. We suggest that 

item 7 be the last step in the analysis and add the following sentence. ‘Reasonable 

controls are not a required condition for an exceptional event determination, if the 

collective benefits of all reasonable controls would not have prevented the exceedance.’” 
Draft for Public Notice and Comment 

Revision Date: June 2012 69 

Comment –“If a state/local has recently submitted a plan containing a RACM or BACM 

analysis (as required for the area), that analysis should suffice to identify what is a 

‘reasonable control’ and the appropriate implementation timeframe for controls. If the 

state has implemented those RACM/BACM controls, then we believe the state/local has 

satisfied the ‘not reasonably controllable or preventable’ requirement unless EPA 

previously objected to the state's plan RACM/BACM analysis. If the state/local has not 

implemented a control, but is on schedule to implement the reasonable controls, then we 

believe the state/local has also satisfied the ‘not reasonably controllable or preventable’ 

requirement, absent a prior EPA objection to the schedule. We acknowledge the guidance 

suggests that the state could include justification for why the controls are not in place, but 

believe that EPA discretion should be more explicitly limited in these circumstances. We 

suggest that EPA's concurrence on the initial event should be accompanied by a 

notification to the state (e.g. SIP call) of the additional required control and to give 

reasonable opportunity for the state to avoid effects of a future nonconcurrence.” 

Specific reference to guidance text: High Winds Guidance document, Table 2 in 

Section 3.1.2 

Submitter: Larry Greene (Executive Director), Sacramento Metropolitan Air Quality 

Management District 

Date: 6/30/2011 letter via e-mail to Matt Lakin and EEGuidanceComments@epa.gov

Response: See also responses to comments 7.4.1., 7.4.4., and 7.5.9. If an area is 

implementing its EPA-approved SIP which includes dust control measures and has been 

approved within 3 years, has met any other applicable regulatory requirements, and has 

high wind dust events only when the wind speeds are above the established local high 

wind threshold, then the EPA would generally consider these events to be not reasonably 

controllable or preventable. The EPA does not expect additional controls to be put in 

place if the exceedances only occur when the wind speed is above the high wind 

threshold under conditions when sources have been reasonably controlled. The EPA 

encourages agencies to address this issue in the prospective controls analysis. 

7.5.18. Comment: “The WAQD has serious concerns regarding elements that are required for 

the comprehensive controls analysis. The tools that EPA has proposed will result in 

highly inaccurate results. In particular, an emissions inventory of a short-term fugitive 

dust event is unreasonable. Emission factors currently available for fugitive dust add a 

degree of uncertainty to emission estimates when taking into account the short-term 

nature and exacerbation of high wind on the source. To use an inventory with little or no 

confidence in the emission rates in source apportionment modeling is ineffective. 

Additionally, the tools that EPA has specified to perform a back-trajectory will require 

localized wind fields to be developed. This is not always possible in areas where 

networks are sparse with large distances (50-100 miles) between meteorological 

monitoring locations.” 

Specific reference to guidance text: High Winds Guidance document 

Submitter: Steven Dietrich (Administrator), Wyoming Air Quality Division 

Date: 6/30/2011 via e-mail to EEGuidanceComments@epa.gov

Response: The EPA’s approval of an agency’s prospective controls analysis (see 

response to comment 7.4.1.) should help agencies know if currently implemented 

controls are reasonable. Demonstration packages with wind speeds below the approved 

high wind threshold will require more rigorous analyses. The rigor of the analyses will 

depend on how much below the threshold the wind was and the weight-of-evidence from 

other analyses. The EPA intends to take comment on technical analyses that can be used 

to demonstrate that the wind exceeded the high wind threshold and that the exceedance 

was caused by emissions that were not reasonably controllable. The EPA cannot concur 
Draft for Public Notice and Comment 

Revision Date: June 2012 70 

on cases where no information on wind speed and reasonable controls is available or 

provided, regardless of the technical difficulties that this might impose. 

7.5.19. Comment: Are wildfires included when we say “areas burned by anthropogenic fires”? 

Reference is to windblown dust from surfaces that have been significantly disturbed or 

altered by humans and thus should be categorized as anthropogenic emissions. 

Specific reference to guidance text: High Winds Guidance document, page 11, Section 

3.1.1 

Submitter: Ann Hobbs (Air Quality Specialist), Placer County Air Pollution Control 

District 

Date: 6/30/2011 via e-mail to EEGuidanceComments@epa.gov

Response: The EPA has modified the language in the revised draft High Winds 

Guidance document that refers to “areas burned by anthropogenic fires.” 

7.5.20. Comment: “ADEQ is concerned that the draft guidance does not provide any certainty 

regarding what control measures qualify as reasonable control measures during an 

exceptional event. Instead, the guidance appears to indicate that the more often an event 

occurs, the less exceptional it becomes, even though the event is overwhelming the 

control measures that are in a SIP.” The SIP approval process is the appropriate process 

for determining the reasonableness of control measures based on the classification of the 

planning area. “ADEQ recognizes that the excessive recurrence of exceedances of the 

standard would be cause for reconsidering the control strategy in place. In order to offer 

States more certainty, it is recommended that EPA consider rule changes that would 

allow a State and EPA to agree (perhaps through a mechanism such as a High Wind 

Action Plan) that the selected control measures are reasonable for a period of three to five 

years. During that time, a State would not need to review the controls that were in place 

at the time of the event(s) in order to benefit from the use of the Exceptional Events Rule. 

After that time period, should exceedances persist or excessively recur, the State and 

EPA could review the control measures in the SIP. If additional controls are deemed to be 

necessary, EPA could use the provisions of Clean Air Act Section 11 0(k)(5) to call for 

an update to the SIP. If no additional controls appear reasonable or necessary at that time, 

EPA and the State could enter into an additional three to five year agreement that the 

controls in place are reasonable for that area thereby streamlining exceptional event 

analyses and providing longer-term certainty for air quality planning areas.” 

Specific reference to guidance text: High Winds Guidance document 

Submitter: Eric Massey (Director), Arizona Air Quality Division 

Date: 6/30/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: The EPA proposes to address this by providing air agencies an opportunity to 

engage in implementing a prospective review of controls including a high wind threshold. 

See response to comments 7.4.1., 7.5.9. and 7.5.13. 

7.5.21. Comment: Monitoring sites in rural areas may not collect as much data as those in urban 

areas. Has the EPA considered how a control analysis for rural sites for which direct 

inspection and enforcement data specific to before, during, and after the event are not 

available? ADEQ recommends that the EPA include a section in the proposed guidance 

along with comparable examples that represent EE demonstrations in an area with a 

single filter-based monitor and for which meteorological data within the direct vicinity 

are not available. 

Specific reference to guidance text: High Winds Guidance document 

Submitter: Eric Massey (Director), Arizona Air Quality Division 

Date: 6/30/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: At this time, the EPA does not have an example of an approvable exceptional 

event demonstration package for an area with no local meteorology and a single filter-
Draft for Public Notice and Comment 

Revision Date: June 2012 71 

based monitor. As demonstrations for unique situations, such as the one identified by the 

commenter, become available, the EPA will update the Exceptional Events website to 

include such examples. The EPA has, however, modified the language in the revised draft 

High Winds Guidance document to address the availability of inspection/enforcement 

records and local meteorology. The EPA refers the commenter to this document and to 

the responses to comments 7.5.10. and 7.3.10. In addition, during the public review of the 

revised draft guidance documents, the EPA intends to take comment on technical 

analyses that can be used to demonstrate that the wind exceeded the high wind threshold 

and also that the exceedance was caused by emissions that were not reasonably 

controllable. The EPA cannot concur on cases where no information on wind speed and 

reasonable controls is available or provided, regardless of the technical difficulties that 

this might impose. 

7.5.22. Comment: “The draft guidance appears to indicate that it is important for submitting 

agencies to indicate whether natural sources could have been reasonably controlled. 

ADEQ opposes any suggestion that natural, undisturbed, non-anthropogenic sources 

should require controls. Such controls on natural sources might inherently disturb those 

sources, rendering them anthropogenic sources in EPA's view. ADEQ recommends that 

EPA revise the draft guidance to make it clear that there is no requirement to investigate 

whether natural sources could have been controlled during an event.” 

Specific reference to guidance text: High Winds Guidance document 

Submitter: Eric Massey (Director), Arizona Air Quality Division 

Date: 6/30/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: The statutory definition of an exceptional event, including a natural event, 

requires that the event be one that is not reasonably controllable and preventable. For a 

high wind event implicating only natural, undisturbed and non-anthropogenic sources, 

not having controls on these sources may be reasonable and therefore considered to meet 

the not reasonably controllable or preventable requirement. Agencies can indicate this 

point in demonstration submittals with a few sentences. 

7.5.23. Comment: Washington Department of Ecology believes that the guidance docs describe 

an escalating series of controls that is outside of the statutory framework established by 

the Clean Air Act. “Should EPA wish to require controls that go beyond a state’s SIP and 

voluntary commitments under a Natural Events Action Plan or High Wind Action Plan, 

EPA should not be establishing requirements through guidance. Instead EPA should 

establish control requirements through notice-and-comment rulemaking.” 

Specific reference to guidance text: High Winds Guidance document 

Submitter: Stuart Clark (Air Quality Program Manager), Washington Department of 

Ecology 

Date: 7/5/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: The EPA’s draft guidance documents and the exceptional events website 

(http://www.epa.gov/ttn/analysis/exevents.htm) present examples to illustrate specific 

points and are not necessarily required for all demonstrations. See also the response to 

comment 7.5.13. 

7.5.24. Comment: “Regional v. Local events. There is another aspect to the requirement in the 

guidance that controls were implemented “at the time of an event.” This seems to be a 

reasonable requirement for an event that involves local sources. However, many events in 

Washington’s Columbia Plateau are regional in scope and involve distant sources and can 

extend for as much as a couple hundred miles.” 

Specific reference to guidance text: High Winds Guidance document 

Submitter: Stuart Clark (Air Quality Program Manager), Washington Department of 

Ecology 
Draft for Public Notice and Comment 

Revision Date: June 2012 72 

Date: 7/5/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: The EPA addresses intrastate, interstate, and international transport in the 

response to comment 6.4.1. and in Question 23 in the revised draft Q&A document. The 

EPA refers the commenter to these responses. 

7.5.25. Comment: “Relation to agriculture. Attendees at EPA Region 9’s June 9, 2011, 

workshop on the draft guidance were informed that the EPA had decided not to consider 

agriculture in developing the guidance. Yet, the draft guidance brings both a state and the 

EPA face-to-face with agricultural practices and controls... One set of recommended 

Best Management Practices to deal with “farming with the wind” is various crop 

rotations. These involve recurring cycles of greater and less vulnerability to wind erosion 

dust generation depending upon such factors such as the specific crops or fallow periods 

in the rotation, agricultural activity such as tilling and harvest, and the state of crop 

development and the protection that affords against wind erosion.” 

Specific reference to guidance text: High Winds Guidance document 

Submitter: Stuart Clark (Air Quality Program Manager), Washington Department of 

Ecology 

Date: 7/5/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: At the EPA Region 9 workshop on June 9, 2011, the EPA staff stated that we 

do not intend to address agriculture as a separate and distinct category with unique high 

winds exceptional events issues. Rather, we will treat agriculture as we treat all other 

sources of dust. 

7.5.26. Comment: The language in the first (partial) paragraph on page 11 needs to be clarified 

and made consistent with the Fire Policy/Forest Service language. The commenter 

recommends that the phrase “areas burned by anthropogenic fires” be removed from the 

text as emissions from surfaces disturbed by large-scale fires, whether or not the initiating 

event was natural or human caused, are beyond “reasonable” control and should not be 

considered as anthropogenic. In the last sentence in paragraph 1 on page 11, the EPA 

identifies “naturally-ignited fires” as a natural source. Change this to “wildfires” to be 

consistent with Fire Policy/Forest Service language. 

Specific reference to guidance text: High Winds Guidance document, page 11 

Submitter: Pete Lahm (Smoke Manager), USDA Forest Service 

Date: 7/14/2011 via phone conversation with Beth Palma 

Response: The EPA has modified the language in the revised draft High Winds 

Guidance document that refers to “areas burned by anthropogenic fires.” 

7.6. Historical fluctuations 

7.6.1. Comment: How can an agency address the wind parameters and historical exceptional 

events if their temporal wind data is collected differently than what is in the draft 

guidance? Will the EPA accept the agency’s current wind data in different format (i.e. 

different data collection and handling than the EPA’s defined in the draft guidance: 

maximum sustained 1-5 minute average)? Also, what if an agency’s current equipment is 

incapable of collecting and/or storing wind data in those intervals? Does that preclude the 

agency from any future exceptional events submittals? 

Specific reference to guidance text: High Winds Guidance document

Submitter: Scott DiBiase, Pinal County Air Quality, scott.dibiase@pinalcountyaz.gov 

Date: 6/23/2011 via e-mail to EEGuidanceComments@epa.gov

Response: The “in excess of historical fluctuations” requirement in the EER only applies 

to the exceedace of the standard, not to the level of wind speed associated with an event. 

Furthermore, based on comments, the EPA has revised the draft guidance to rely 

primarily on hourly average wind data since air monitoring stations now typically collect 

data in this form or in a form that allows this to be calculated. The EPA also refers the 
Draft for Public Notice and Comment 

Revision Date: June 2012 73 

commenter to responses to comments 7.3.3. and 7.3.10. for additional information 

regarding wind speed data availability and averaging times. 

7.6.2. Comment: “Clark County does not believe that an analysis of historical fluctuations adds 

value to exceptional event documentation and in fact may be misleading to reviewers and 

the public...Clark County recommends that EPA revise the draft guidance to reduce the 

time period and number of data points for which the analysis must cover. The standard 

period used to calculate the design value for an attainment SIP is three years, and Clark 

County believes that this is also the appropriate time period for an historical analysis.”

Specific reference to guidance text: High Winds Guidance document 

Submitter: Tina Gingras (Assistant Director), Clark County DAQEM 

Date: 6/30/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: The EPA agrees that generally three years is an appropriate period for the 

historical fluctuations analysis. The revised guidance will rely on three years but allow a 

longer timeframe if an agency chooses to provide it; for example, a longer timeframe 

may be useful to support the “but-for” criterion. 

7.7. High Wind Action Plan 

7.7.1. Comment: Please clarify how a High Wind Action Plan becomes enforceable without 

formal rulemaking. In addition, since it would take time to develop and implement a High 

Wind Action Plan, other high wind dust exceptional events that might occur subsequent 

to the first event but prior to implementation of the Plan should also be excused from the 

requirement to have reasonable controls in place. This is even more critical in light of the 

potential for the EPA to adopt more stringent PM10 ambient standards. Attainment areas 

with windy conditions but no historical exceedances of the current PM10 standard could 

now suddenly experience an uptick in high wind dust events that drive PM10

concentrations over a reduced standard without any lead time to get controls in 

place. EPA needs to make exceptions for the control demonstration under this 

circumstance, as the rulemaking process to get controls in place may take considerable 

time. 

Specific reference to guidance text: High Winds Guidance document, Section 3.1.6 

Submitter: Brian Shafritz, Santa Barbara County Air Pollution Control District, 

ShafritzB@sbcapcd.org 

Date: 6/23/2011 via e-mail to EEGuidanceComments@epa.gov

Response: Air agency or source implementation of measures in a High Wind Action 

Plan (HWAP) that are not in an approved SIP is not federally enforceable but the 

measures within it may still be enforceable (e.g., agencies may incorporate measures in 

the HWAP into state or local law). While the HWAP is not in itself federally enforceable, 

the EPA’s concurrences on exceptional events rely upon it so that if it is not implemented 

effectively then exceptional events may not be concurrable. An agency will have six 

months to submit an adequate HWAP and the EPA’s concurrence on the specific event(s) 

in question and those going forward are contingent upon the EPA’s approval of the 

HWAP (i.e., the newly-identified sources would not be considered to meet the nRCP 

criterion if the HWAP is violated). If the agency meets this timeframe, then the EPA will 

consider high wind exceptional events that occur within that timeframe to be not 

reasonable controllable or preventable, assuming any “on-the-books” controls were 

enforced. 

7.7.2. Comment: The idea of a High Wind Action Plan, that could identify a mutually 

agreeable set of reasonable controls for an area with recurring events, has merit. This 

would also help streamline the documentation for recurring events, since it could be used 

as a reference for background information. Unfortunately, this may not apply to initial or 

infrequent events or when new monitoring or unforeseen conditions change the types of 
Draft for Public Notice and Comment 

Revision Date: June 2012 74 

sources that could impact a monitor. AQMD staff will continue to work with the U.S. 

EPA to explore this option. 

Specific reference to guidance text: High Winds Guidance document 

Submitter: Barry Wallerstein, South Coast Air Quality Management District 

Date: 6/28/2011 via e-mail to Matt Lakin and EEGuidanceComments@epa.gov 

Response: The EPA agrees that the HWAP will be most useful to areas that have 

frequent high wind dust events. Areas with infrequent/non-recurring events are unlikely 

to violate the PM standards due to high wind events and, therefore, the EPA would not 

likely review demonstration packages associated with these events because they would 

not be associated with near-term regulatory decisions. The EPA encourages agencies to 

submit a letter of intent, the review of which may prevent agencies from preparing 

documents (e.g., HWAP) for events with no regulatory bearing that the EPA may give 

low priority. 

7.7.3. Comment: If potential sources are not identified to EPA's satisfaction through the 

submittal of an "optional" HWAP, EPA may potentially find that reasonable controls 

were not in place during subsequent events, even in areas such as the San Joaquin Valley 

that implement comprehensive, approved Best Available Control Measures (BACM). For 

recurring events, the EPA will need to re-approve the High Wind Action Plan regardless 

of whether it is revised or remains as-is. For recurring natural events above the wind 

entrainment threshold, this additional documentation and review by the EPA does not 

seem appropriate or necessary. Additionally, the District has a Natural Event Action Plan 

(NEAP) that has been approved by the EPA. Can the District use the NEAP in place of 

the High Wind Action Plan (HWAP)? If not, how much more information is necessary to 

make the NEAP approvable? The draft guidance does not address what new information 

is needed when a NEAP is already in place. 

Specific reference to guidance text: High Winds Guidance document 

Submitter: Samir Sheikh (Director of Strategies and Incentives), San Joaquin Valley Air 

Pollution Control District 

Date: 6/29/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov 

Response: The EPA is de-emphasizing consideration of recurrence and altering the 

HWAP concept to be more similar to a NEAP in some respects (see section 3.7.2.4 of the 

revised draft High Winds Guidance document). A NEAP provides a good framework for 

the HWAP and an existing NEAP may be acceptable as a HWAP in some cases. The 

EPA has also revised the draft guidance documents to include a prospective controls 

analysis that would prevent the issue raised by the commenter. See response to comment 

7.4.1. 

7.7.4. Comment: “We are very uncomfortable with EPA’s expectation that States implement 

successive High Wind Action Plans with escalating emission control programs, outside of 

the statutory framework of the Clean Air Act, as a precondition of concurrence of 

recurring exceptional events. We are very uncomfortable with BACM, or greater levels 

of control, as the appropriate starting point for consideration of reasonable control 

measures in attainment, maintenance, and moderate areas.” 

Specific reference to guidance text: High Winds Guidance document 

Submitter: David Collier (President), WESTAR 

Date: 6/30/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: The development of a HWAP is voluntary (see comment 7.4.4). Agencies 

also have two options: pursuing the regulatory process and accepting a non-concurrence 

or preparing and submitting demonstrations showing that reasonable controls are in place 

for each flagged exceedance. The regulatory process would follow the normal path of the 

SIP process to implement reasonable controls. 
Draft for Public Notice and Comment 

Revision Date: June 2012 75 

In response to the commenter’s next point regarding the EPA’s reference to “starting 

point,” the EPA uses the term “starting point” to mean a point of reference at which to 

begin the evaluation. “Starting point” is not intended to indicate the lowest level for 

consideration. We have clarified this point in the revised draft guidance documents. 

7.7.5. Comment: “In § 3.1.6, EPA suggests that states dealing with recurring high-wind events 

develop a high-wind action plan that would “...identify mutually agreed upon reasonable 

controls that a state could implement for subsequent high wind events.” Although not 

expressly stated, the implication of this section is that states having recurring high-wind 

events that do not submit and obtain approval of high-wind action plans would not 

receive EPA concurrence for exclusion of future high-wind events. As set forth on page 

19 of the draft guidance, EPA will evaluate the long-term adequacy of the high-wind 

action plan and the ‘reasonableness’ of the plan’s control measures as follows: ‘Once the 

state has begun implementation of the measures approved by EPA and EPA has formally 

recognized implementation of the High Wind Action Plan, EPA would consider the 

controls to be reasonable as long as events do not recur. (emphasis added).’ This 

criterion is apparently based on the flawed assumption that if states and regulated entities 

will invest enough financial resources and effort on controls, then uncontrollable highwind driven events can be controlled. EPA has not provided any documentation to 

support the concept of high-wind driven events controllability and it is the experience of 

Clark County that such events are not controllable with any measures that could be 

implemented.” 

Specific reference to guidance text: High Winds Guidance document 

Submitter: Tina Gingras (Assistant Director), Clark County DAQEM 

Date: 6/30/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: The EPA is de-emphasizing consideration of recurrence and adding a 

prospective controls analysis, which should address these concerns. See also responses to 

comment 7.4.1. and 7.5.9. 

7.7.6. Comment: “If EPA decides to allow for voluntary High Wind Action Plans, the Agency 

should not require continual revision and updating of the plans (e.g., upon recurrence of 

EEs).” MAG states that linking the High Wind Action Plan to recurrence provides no 

incentive for a state to develop a plan because there is little benefit to develop a publicly 

reviewed, “SIP-like” plan for one event per year. MAG suggests that an incentive for 

completing a plan should be that the state would have “some assurance ahead of time that 

EPA finds their existing controls and implementation measures adequate.” 

Specific reference to guidance text: varies (additional documentation to support 

recommendation is provided in comment attachment at Submitted Comments\Need 

OCR\MAG_063011-ocr.pdf) 

Submitter: Thomas Schoaf (Mayor, City of Litchfield Park and MAG Chair), Maricopa 

Association of Governments 

Date: 6/30/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: The EPA is de-emphasizing consideration of recurrence and adding a 

prospective controls analysis, which should address these concerns. See response to 

comment 7.4.1. and 7.5.9. 

7.7.7. Comment: Wyoming Air Quality Division asks that EPA develop a process to include 

Natural Events Action Plans (NEAP) into High Wind Action Plans as many places in the 

West continue to rely on these agreements between EPA, States, industry and the public 

and the plans include many of the elements identified to be part of HWAPs. 

Specific reference to guidance text: High Winds Guidance document 

Submitter: Steven Dietrich (Administrator), Wyoming Air Quality Division 

Date: 6/30/2011 via e-mail to EEGuidanceComments@epa.gov 
Draft for Public Notice and Comment 

Revision Date: June 2012 76 

Response: An existing NEAP can be the basis of a HWAP. The EPA has revised the 

draft High Winds Guidance document to clarify the relationship between a NEAP and the 

HWAP (see section 3.7.2.4 of the revised draft High Winds Guidance document). 

7.7.8. Comment: Washington Department of Ecology asks that EPA address using or 

incorporating previously developed and currently used Natural Events Action Plans in the 

High Wind Action Plan as NEAPs proved the “core” components of a HWAP as 

envisioned by the draft guidance. 

Specific reference to guidance text: High Winds Guidance document 

Submitter: Stuart Clark (Air Quality Program Manager), Washington Department of 

Ecology 

Date: 7/5/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: An existing NEAP can be the basis of a HWAP. The EPA has revised the 

draft High Winds Guidance document to clarify the relationship between a NEAP and the 

HWAP (see section 3.7.2.4 of the revised draft High Winds Guidance document). 

7.8. Checklist for demonstration submission 

7.8.1. Comment: The draft guidance appears to require the submittal of a fully completed 

checklist and associated documentation requirements found in Appendix B of the draft 

guidance. The requirement that all of these items be included in all exceptional event 

submittals to the EPA goes against the spirit of the EER that allows for a weight-ofevidence approach to demonstrating the occurrence of exceptional events. The District 

recommends that flexibility be allowed to provide the relevant documentation necessary 

to demonstrate exceptional events and not be prescriptive in completing the checklist. 

Specific reference to guidance text: High Winds Guidance document checklist 

Submitter: Samir Sheikh (Director of Strategies and Incentives), San Joaquin Valley Air 

Pollution Control District 

Date: 6/29/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: The EPA has revised the checklist. The EPA has also clarified which 

elements are relevant, factoring in the potential for a prospective controls analysis and 

HWAP. The EPA believes that the tools provided in the draft guidance materials support 

the weight-of-evidence approach intended by the Exceptional Events Rule (see also 

response to comment 6.5.10. for a discussion of “weight-of-evidence”). 

 7.8.2. Comment: Clark County states that the caveat on the checklist stating, “...This checklist 

represents the minimum information that must be included in a package and serves to 

identify packages that are incomplete rather than show that a package is complete...” 

suggests that if “all of the items in the checklist are not included in the demonstration 

package, EPA will not review the package, leading to an automatic non-concurrence. 

Clark County requests refinement of the checklist and revision of the prefacing statement 

to clarify that where elements on the checklist are not required due to very high winds or 

other factors, EPA will review the demonstration documentation.” 

Specific reference to guidance text: High Winds Guidance document, page 60 

Submitter: Tina Gingras (Assistant Director), Clark County DAQEM 

Date: 6/30/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: The EPA has modified the Completeness Checklist for High Wind Dust 

Exceptional Events. See also the response to comment 7.8.1. 

7.9. Recommended framework for high wind dust exceptional event demonstration package 

7.9.1. Comment: “We are very supportive of the process timeframes and action steps outlined 

in the proposed guidance. They represent steps forward to resolve a number of longstanding issues of uncertainty about timing of communications and reducing unnecessary 

delays in processing exceptional events requests. We are also supportive of the optional 
Draft for Public Notice and Comment 

Revision Date: June 2012 77 

process steps to prioritize actions in recognition of the very limited resources we all have. 

The guidance should encourage continuing communication and negotiation of issues 

between states and EPA to make the process work.... We also are supportive of the 

overall recommended methods of preparing each of the technical elements and 

recommended order of analyses to facilitate using the technical work developed in 

support of one showing to support more than one element.” 

Specific reference to guidance text: High Winds Guidance document 

Submitter: David Collier (President), WESTAR 

Date: 6/30/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: The EPA acknowledges commenter’s support. 

7.10. General 

7.10.1. Comment: The figures on page 50 (measurements from monitoring stations) are 

unreadable. 

Specific reference to guidance text: High Winds Guidance document, page 50 

Submitter: Scott DiBiase, Pinal County Air Quality, scott.dibiase@pinalcountyaz.gov

Date: 6/23/2011 via e-mail to EEGuidanceComments@epa.gov

Response: The EPA appreciates the feedback and incorporated figures with improved 

resolution. 

7.10.2. Comment: The EPA guidance documents provide for the use of chemical speciation as 

supporting evidence to assist in establishing a Clear Causal Relationship. Because of the 

size of the air basin, the District, in a strategic effort to streamline staff time spent 

changing filters, is shifting PM collection from filter-based to real time with TEOMS 

monitors. However, this action will cause the District to potentially not have filters for a 

mandatory chemical speciation analysis. The draft guidance should be not requiring the 

use of chemical speciation to establish a Clear Causal Relationship, but leave as optional 

criteria in a weight-of-evidence approach. 

Specific reference to guidance text: none 

Submitter: Samir Sheikh (Director of Strategies and Incentives), San Joaquin Valley Air 

Pollution Control District 

Date: 6/29/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: In the draft High Winds Guidance document, the EPA identified several 

types of analyses that agencies can use to show a “clear causal relationship.” These 

analyses, including the use of chemical speciation, are “possible” analyses versus 

“required” analyses. Agencies may need some, all, or other analyses to demonstrate the 

clear causal relationship criterion. The EPA will evaluate the clear causal relationship 

criterion on a weight-of-evidence approach based on available information for each case. 

The EPA encourages areas with recurring high wind dust events to consider what 

information will be useful in a high wind dust exceptional events demonstration package 

when designing their monitoring networks. The EPA also recognizes that, due to limited 

resources and the unpredictability of high wind dust events, agencies may not have all the 

information listed in the “clear causal relationship” table for every event. 

7.10.3. Comment: The District has experienced and is expected to continue experiencing high 

wind PM2.5 exceptional events. The guidance document does not address documentation 

requirements for PM2.5 exceptional events. Towards that end, the District recommends 

that PM10 and PM2.5 documentation be handled within the same submittal to the extent 

possible, and that the EPA develop a test method for analyzing Beta Attenuation Monitor 

tape to assist in preparing the support documentation.

Specific reference to guidance text: none 

Submitter: Samir Sheikh (Director of Strategies and Incentives), San Joaquin Valley Air 

Pollution Control District 
Draft for Public Notice and Comment 

Revision Date: June 2012 78 

Date: 6/29/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov 

Response: The revised draft High Winds Guidance document states in the opening 

paragraph that the document applies to both PM10 and PM2.5 high wind dust events. Many 

of the examples contained in the document, however, are for PM10 because PM10

exceptional events (and associated demonstration submittals) are more prevalent than 

PM2.5 high wind dust events. 

At this point, the EPA does not believe that there is a need to develop a test method for 

chemically analyzing the PM spot on the Beta Attenuation Monitor (BAM) tape. 

Agencies can obtain chemical speciation data by using the filter media from the existing 

filter based sampling technologies. While this approach may be limited in its ability to 

provide short-term event characterization, agencies can still use it to support an event 

demonstration package. Additionally, emerging commercially available technologies 

have the potential to support higher time resolution of chemical speciation. The PM 

Integrated Science Assessment at http://www.epa.gov/ncea/isa/pm.htm details such 

technologies as does the following presentation made at the 2011 National Air Quality 

Conference: Evaluation of Simultaneous PM10, PM2.5, and PM10-2.5 Measurements 

Conducted in Bakersfield, CA with the Teledyne-API Model 602 BetaPLUS Particle 

Measurement System available on the web at 

http://www.airnow.gov/index.cfm?action=naq_conf_2011.aq3. 

 

7.10.4. Comment: “Most of the examples throughout the guidance assume more extensive 

meteorological monitoring than exists in many areas of the west. Source wind data do not 

typically exist when events cover large distances, for example, when the source is the 

southwest desert. Meteorological data are sometimes available from local airports. We 

suggest allowing the use of available regional wind data as surrogate for source data as 

needed.” 

Specific reference to guidance text: High Winds Guidance document 

Submitter: David Collier (President), WESTAR 

Date: 6/30/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: The EPA recognizes the sometimes limited spatial coverage of wind data 

needed for high wind dust EE demonstrations and supports using all available 

meteorological networks and data sources (see responses to comments 7.3.3. and 7.3.10. 

for additional information). The EPA welcomes additional information on meteorological 

networks. 

7.10.5. Comment: “We generally support the proposed [mitigation] guidance as written, which 

interprets actions to protect public health through individual actions as mitigation of 

exposure to exceedances from any source of air pollution, as distinguished from measures 

that control or prevent emissions. Emission control measures are covered in section 3.1, 

Not Reasonably Controllable or Preventable (including High Wind Action Plans), about 

which we have strong concerns.” 

Specific reference to guidance text: High Winds Guidance document 

Submitter: David Collier (President), WESTAR 

Date: 6/30/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: The EPA appreciates the feedback on mitigation and seeks additional 

feedback regarding analyses to support the “not reasonably controllable or preventable” 

criterion. See response to comment 7.4.1. 

7.10.6. Comment: “In this [public comment] section of the proposed guidance, EPA asserts, 

“the state should submit the public comments along with the state’s responses, if any, to 

EPA within 10 days of the close of the comment period.” In many cases, response to 

public comments within 10 days will not be possible.” 
Draft for Public Notice and Comment 

Revision Date: June 2012 79 

Specific reference to guidance text: High Winds Guidance document 

Submitter: David Collier (President), WESTAR 

Date: 6/30/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: The EPA has revised the draft High Winds Guidance document to allow air 

agencies to submit public comments along with the air agency’s response within 30 days 

of the close of the comment period. 

7.10.7. Comment: Clark County DAQEM agrees with guiding principles, but suggests that a 4th

principle, “It is desirable to implement a reasonable and cost-effective process for the 

development and EPA review of state exceptional events” be added to “allow both states 

and EPA to efficiently use scarce resources during this period of economic austerity.” 

Specific reference to guidance text: High Winds Guidance document, Critical Elements 

on page 2 

Submitter: Tina Gingras (Assistant Director), Clark County DAQEM 

Date: 6/30/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: While the EPA agrees with the commenter, the EPA has not added the 

suggested language as a 4th guiding principle. One of the EPA’s goals in developing 

exceptional event implementation guidance is to establish clear expectations to enable 

affected agencies to better manage resources as they prepare the documentation required 

under the EER. As part of an upcoming public comment process, the EPA will solicit 

feedback on a series of questions, some of which will seek specific, broadly applicable, 

streamlining mechanisms. 

7.10.8. Comment: “EPA should recognize that EEs can and do occur at one monitor while other 

monitors in the same area may not violate an air quality standard.” 

Specific reference to guidance text: varies (additional documentation to support 

recommendation is provided in comment attachment at Submitted Comments\Need 

OCR\MAG_063011-ocr.pdf), comment refers to page 22 of HIGH WINDS GUIDANCE 

DOCUMENT doc that says “For example, a hypothesis that an exceedance was caused 

by a large-scale wind event is inconsistent with a situation where an isolated monitor 

exceeds while nearby monitors do not.” 

Submitter: Thomas Schoaf (Mayor, City of Litchfield Park and MAG Chair), Maricopa 

Association of Governments 

Date: 6/30/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: The EPA agrees that high wind dust events can affect one monitor and not 

others and has revised the draft High Winds Guidance document to more clearly reflect 

this point. Agencies believing this scenario occurred in their areas are encouraged to 

explain the spatial extent of the exceedance in the conceptual model of their 

demonstration. For example, if the agency describes the event as a regional dust storm, 

then the EPA would expect monitors within the same regional scale to be similarly 

affected by the dust storm. Note that if an exceedance is due to low wind speeds, or 

sources that should have been reasonably controlled (e.g., lack of implementation or 

enforcement of controls) then this event would not meet the “not reasonably controllable 

or preventable” requirement. 

7.10.9. Comment: “If the six elements must be met for qualifying under the Exceptional Events 

(EE), and if wind direction, wind speed and recurrence are separate from HF, but are 

clearly “vital” as to how there was an exceptional exceedance, why are they not a part of 

the Critical Elements? These same Critical Elements are called technical elements on 

page 11. It is confusing with two different terms.” 

Specific reference to guidance text: High Winds Guidance document, Critical Elements 

on page 2 
Draft for Public Notice and Comment 

Revision Date: June 2012 80 

Submitter: Ann Hobbs (Air Quality Specialist), Placer County Air Pollution Control 

District 

Date: 6/30/2011 via e-mail to EEGuidanceComments@epa.gov

Response: The Exceptional Events Rule at 40 CFR §50.14 identifies both technical and 

process requirements for exceptional event (including high wind dust event) 

demonstration packages. The EPA tried to distinguish these in the draft guidance 

documents. In addition to the specific requirements of the regulatory language, there are 

additional technical analyses that agencies need to include in any high wind dust 

exceptional event demonstration. The EPA does not consider these analyses “critical 

elements” because they are not specifically identified by regulation nor are they standalone criteria. Rather, these analyses inform and support those criteria specifically 

required by the rule. There are linkages among most of the technical elements, making it 

more challenging to treat each criterion as an independent element. The EPA has clarified 

this in the revised draft guidance documents. 

7.10.10. Comment: Wyoming Air Quality Division asks that the following terms be defined: 

Anthropogenic fires (p. 11), Severe exceptional events (p.12), Mild isolated exceedances 

(p.12), Frequent [exceptional events] (p.12), Rare [exceedances] (p .12), Stable surfaces 

(p.3)

Specific reference to guidance text: High Winds Guidance document, varies 

Submitter: Steven Dietrich (Administrator), Wyoming Air Quality Division 

Date: 6/30/2011 via e-mail to EEGuidanceComments@epa.gov

Response: The EPA has clarified or defined the following in footnotes in the revised 

draft guidance documents: 

 Anthropogenic fires –The EPA has revised the language in the revised draft High 

Winds Guidance document. 

 Severe exceptional events - e.g., 24-hour average PM10 >250μg/m3 

 Mild isolated exceedances - e.g., exceedance at one site close to the standard 

 Change rare to non-recurring - <1 high wind dust event per year 

 Frequent - enough exceedances from high wind dust events to cause a violation 

of the NAAQS. 

 Stable surfaces - defined in the “Consideration of Wind Speed” section of the 

draft High Winds Guidance document 

8. Treatment of Technical Criteria for Exclusion of Data Affected by Events 

8.1. Not reasonably controllable or preventable 

8.1.1. Comment: “State Implementation Plans define the measures states must take to attain 

and maintain compliance with NAAQS. Section 110 of the Clean Air Act requires each 

State’s SIP to include enforceable emission limits and other control measures to prevent 

NAAQS violations and holds EPA responsible for ensuring that these measures are 

sufficient. If not, EPA’s responsibility is to require the State to revise its SIP to address 

any identified deficiencies through a SIP call.” WESTAR believes that “EPA proposes to 

implement this provision in such a way that for recurring events, States must implement 

escalating emission control measures, beyond those required under Section 110 and Part 

D (for nonattainment areas) of the Act, to be eligible for exclusion of data under the 

Exceptional Events Rule.” 

Specific reference to guidance text: Additional information on comments at Submitted 

Comments\WESTAReerfinal063011.pdf

Submitter: David Collier (President), WESTAR 

Date: 6/30/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov 

Response: The EPA’s draft guidance documents and the exceptional events website 

(http://www.epa.gov/ttn/analysis/exevents.htm) present examples to illustrate specific 
Draft for Public Notice and Comment 

Revision Date: June 2012 81 

points. They do not establish any new requirements. The revised draft High Winds 

Guidance document does not require that air agencies implement escalating control 

measures beyond those required in their SIP. Rather, the document states that, in the 

interest of protecting public health, it may be appropriate to implement escalating 

controls for events that recur. The EPA further identifies in the revised draft High Winds 

Guidance document that RACM/BACM measures may be a reference point, but not the 

sole means, by which the EPA assesses the reasonableness of controls. In its revisions to 

the draft guidance documents, the EPA has introduced the concept of a prospective 

controls analysis that could incorporate SIP-approved controls. See response to 

comments 7.4.1. and 7.5.9. 

8.1.2. Comment: “WESTAR is also concerned about EPA’s expectation that States show 

reasonable controls were implemented “at the time of the event.” While this is a 

reasonable requirement for local sources and sources addressed in the State 

Implementation Plan, it is ambiguous for many sources in the West. For example: For 

dust raised from distant sources by high winds, documentation of specific control 

measures underway “at the time of the event” is unlikely to be available. For many states, 

high wind events are regional in scope and can extend for hundreds of miles rather than 

being localized events and thus difficult to characterize because of their scope. Crop 

rotations, which are Best Management Practices for preventing agricultural wind erosion, 

are multi-year practices that include recurring cycles of greater and less vulnerability to 

wind erosion depending upon such factors such as the specific crops or fallow periods, 

tilling, crop development, and harvest. In summary, if EPA intends to require emission 

control measures beyond those required under Section 110 and Part D requirements, 

those requirements should be included in an amendment to the regulation with 

appropriate citations to the authorizing provisions of the Act. Until such a rulemaking has 

been completed, we reiterate that the test of reasonable controls should be limited to an 

evaluation of whether or not the State implemented the applicable provisions of their 

State Implementation Plan and any applicable High Wind Action Plan.” 

Specific reference to guidance text: Additional information on comments at Submitted 

Comments\WESTAReerfinal063011.pdf

Submitter: David Collier (President), WESTAR 

Date: 6/30/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: See response to comment 7.4.1. and 7.5.9. 

8.2. Natural event 

8.2.1. Comment: ADEQ agrees that a natural event does not need to be infrequent to qualify as 

an EE. 

Specific reference to guidance text: none 

Submitter: Eric Massey (Director), Arizona Air Quality Division 

Date: 6/30/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: The EPA acknowledges commenter’s support. 

8.3. Clear causal relationship 

8.3.1. Comment: “We think the section on process provides a good framework for review and 

timelines including early consultations and notifications of additional needed 

information. Our concerns remain as to the ability of agencies to produce ’all’ 

information requested. For example, the Clear Causal guidance in Section 3.3, Table 4, 

nos. 2. and 4 suggests an analysis to demonstrate temporal relationships, ’Wind direction 

data showing that emissions from sources identified as part of nRCP demonstration were 

upwind of the monitor(s) in question, satellite imagery,’ and, ’24-hour time series 

showing PM concentration at the monitor in question in combination with sustained and 

maximum wind speed data at area where dust was entrained.’ Examples of analyses are 
Draft for Public Notice and Comment 

Revision Date: June 2012 82 

given, but these are in areas that are extensively monitored. There are numerous areas 

throughout the arid west where source-receptor relationships are regional in scope, and 

where dust sources are remote from ambient monitors that may detect the event. In most 

such areas meteorological information at the source would not exist, because there are no 

wind instruments deployed there. Satellite imagery can be a matter of luck, with cloud 

cover or other visibility obscuring conditions. We would expect EPA to take such factors 

into consideration as well as resource commitments when determining the information to 

be requested from the State and level of analyses needed to demonstrate Clear Causal 

relationship.” 

Specific reference to guidance text: High Winds Guidance document, section 3.3, Table 

4, nos. 2 and 4 

Submitter: David Collier (President), WESTAR 

Date: 6/30/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: In the draft High Winds Guidance document, the EPA identified several types 

of analyses that air agencies can use to show a “clear causal relationship.” These analyses 

are “possible” analyses versus “required” analyses. Agencies may need some, all, or 

other analyses to demonstrate the clear causal relationship criterion. The EPA will 

evaluate the clear causal relationship criterion on a weight-of-evidence approach based 

on available information for each case. The EPA also recognizes that, due to limited 

resources and the unpredictability of high wind dust events, agencies may not have all the 

information listed in the “clear causal relationship” table for every event. 

8.3.2. Comment: “The Wyoming Air Quality Division would like EPA to take into 

consideration the resources and requirements of states when evaluating elements in this 

section. Many of the types of information to support these analyses are not available in 

states with smaller populations and less required monitoring. For instance, the Wyoming 

Air Quality Division's network of visibility monitoring is sparse and is not located near 

the industrial areas where exceedances usually occur. Additionally, the Wyoming Air 

Quality Division is only required to have speciated particulate monitoring at one location 

in the State.” 

Specific reference to guidance text: none 

Submitter: Steven Dietrich (Administrator), Wyoming Air Quality Division 

Date: 6/30/2011 via e-mail to EEGuidanceComments@epa.gov

Response: See response to comment 8.3.1. 

8.4. Historical fluctuations 

8.4.1. Comment: “We support the approach in the proposed guidance to demonstrate historical 

fluctuation.”

Specific reference to guidance text: none 

Submitter: David Collier (President), WESTAR 

Date: 6/30/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: The EPA acknowledges commenter’s support. 

8.4.2. Comment: Presenting evidence that an event is “in excess of normal historical 

fluctuations including background” becomes increasingly difficult as NAAQS levels are 

set close to or below the level of the policy relevant background (ozone is particular 

issue). 

Specific reference to guidance text: none 

Submitter: Karen St. John (Sr. Director, Regulatory Affairs), BP America, Inc. 

Date: 6/30/2011 via e-mail to EEGuidanceComments@epa.gov 

Response: As described in the EPA’s revised draft Q&A document, the EPA will use a 

weight-of-evidence approach to assess each demonstration on a case-by-case basis. The 

air agency’s obligation in satisfying this element is to provide analyses and statistics. The 
Draft for Public Notice and Comment 

Revision Date: June 2012 83 

submittal of data showing how the event concentration compared with historical 

concentrations will help the EPA determine whether the “clear causal relationship,” “but 

for,” and “affects air quality” criteria have been satisfied. 

8.5. But for 

8.5.1. Comment: “EPA’s draft guidance retains the requirement for a State to show that there 

would not have been a NAAQS exceedance but for the event without a clear explanation 

of how such a showing can be made. In fact, in the preamble to the Exceptional Events 

Rule, EPA commits to publishing, in a notice of proposed rulemaking, the means by 

which a state could make this showing once the techniques for adjusting data are 

sufficiently well documented. Until this rulemaking is completed, WESTAR sees no 

alternative but for EPA to revise the Exceptional Events Rule to remove the ‘but for’ 

test.” 

Specific reference to guidance text: Q&A document #13 

Submitter: David Collier (President), WESTAR 

Date: 6/30/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: The preamble to the Exceptional Events Rule states at 72 FR 13572, “When 

we determine that techniques for adjustment of air quality data are sufficiently welldemonstrated for use in exceptional events determinations, we will publish a notice of 

proposed rulemaking to seek comment on the appropriateness and scope of such use and 

its impact on the requirements set forth in this rule for determining an exceptional event.” 

This language refers to the partial adjustment of a 24-hour value rather than the exclusion 

of the entire 24-hour value, which is how the EPA handles concurred upon exceptional 

event data. Air agencies can satisfy the “but for” criterion with reasonably supportable 

adjustments, and in some cases, a qualitative analysis. 

As indicated in the draft guidance documents, the EPA has retained the “but for” 

provision and continues to believe that this regulatory criterion in the Exceptional Events 

Rule implements the Clean Air Act language that specifies that “a clear causal 

relationship must exist between the measured exceedances of a national ambient air 

quality standard and the exceptional event to demonstrate that the exceptional event 

caused a specific air pollution concentration at a particular air quality monitoring 

location...”and that States can petition the EPA to “exclude air quality monitoring data 

that is directly due to exceptional events from use in determinations...with respect to 

exceedances or violations.”(emphasis added) 

8.5.2. Comment: Clark County DAQEM believes that a quantitative NEBF analysis exceeds 

the provisions of the EER and “conflicts with the EER preamble, which states in part: 

The EPA will consider such [quantitative] analyses as part of the weight-of-evidence to 

judge ‘but-for,’ but will not make quantitative adjustments to reported measured values 

because the EPA does not believe sufficient quantitative methods are available at this 

time. (emphasis added) (72 Fed. Reg. 13560, 13572 (Mar. 22, 2007))...Clark County 

encourages EPA to remove this de facto requirement from the draft guidance.” 

Specific reference to guidance text: none 

Submitter: Tina Gingras (Assistant Director), Clark County DAQEM 

Date: 6/30/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: See response to comment 8.5.1. 

8.5.3. Comment: “The requirement for [the but for] test is included in EPA’s EER along with 

a commitment by EPA, in the rule’s preamble, to publish a proposed rule that would 

establish the parameters for making a demonstration once the agency “determine[s] that 

techniques for adjustment of air quality data are sufficiently well demonstrated for use in 

exceptional events determinations.” That proposal has not yet materialized, nor has the 
Draft for Public Notice and Comment 

Revision Date: June 2012 84 

agency provided a clear explanation of how to make such a demonstration. Therefore, 

NACAA believes that until such time as EPA is able to identify and promulgate 

technically feasible techniques for “backing out” that portion of the monitored data 

determined to have resulted from the exceptional event, EPA should revise the EER to 

remove the ‘but for’ test.” 

Specific reference to guidance text: none 

Submitter: Tad Aburn (Co-Chair), NACAA Criteria Pollutants Committee 

Date: 6/30/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: See response to comment 8.5.1. 

8.5.4. Comment: “There are no examples of a quantitative analysis of NEBF included in this 

document. Without documented examples, the requirement of a quantitative NEBF 

should be removed from the Guidance.” 

Specific reference to guidance text: none 

Submitter: Steven Dietrich (Administrator), Wyoming Air Quality Division 

Date: 6/30/2011 via e-mail to EEGuidanceComments@epa.gov

Response: The EPA refers the commenter to the ozone/wildfire demonstration package 

on the exceptional events website at http://www.epa.gov/ttn/analysis/exevents.htm. This 

package uses regression and related additional statistical evaluation, surrogate day and 

rule of thumb analysis, and evaluation of the frequency of high ozone concentrations as 

part of a quantitative “but for” submission. See also the response to comment 8.5.1. 

8.5.5. Comment: The NCDAQ requests that the U.S. EPA provide more guidance on what the 

EPA is willing to accept for weight-of-evidence for values that are just barely over the 

standard. For example, if the daily standard is 35 and the value impacted by the 

exceptional event is 37, what types of evidence will the U.S. EPA accept as proof that the 

value would have been 34 or 35 "but for" the exceptional event? 

NCDAQ would also like the EPA to provide additional guidance on what the EPA is 

willing to accept for weight-of-evidence for values that are between the annual and daily 

standard, for example, if the annual standard is 15, the daily standard is 35 and the value 

measured is 27. What types of evidence should the NCDAQ provide to demonstrate to 

the USEPA that but for the exceptional event, the value would have been 14 or 15? 

The EPA only discusses the "But For" test for ozone. The NCDAQ recommends that the 

EPA also include similar discussions for "But For" tests for sulfur dioxide and perhaps 

nitrogen dioxide too. If data collected by a sulfur dioxide monitor are influenced by an 

exceptional event such as a volcano or an industrial mishap, how would a state go about 

demonstrating that the exceptional event caused the exceedance? What weight-ofevidence would be required? Similarly, if data collected by a near road nitrogen dioxide 

monitor were influenced by an exceptional event, what weight-of-evidence would the 

EPA be looking forward to demonstrate the "But For" test? 

Specific reference to guidance text: Q&A document #13 

Submitter: Sheila Holman (Director), NC Division of Air Quality 

Date: 6/30/2011 via e-mail to EEGuidanceComments@epa.gov

Response: See response to comment 8.5.4. 

8.5.6. Comment: “EPA should provide examples of analyses that will be accepted to 

demonstrate a quantitative ‘but for’ test and what analysis is acceptable to distinguish 

between an event contribution and a non-event contribution.” 

Specific reference to guidance text: none 

Submitter: Larry Allen (Air Pollution Control Officer), San Luis Obispo Air Pollution 

Control District 
Draft for Public Notice and Comment 

Revision Date: June 2012 85 

Date: 6/30/2011 via e-mail to Gina McCarthy and EEGuidanceComments@epa.gov

Response: See response to comment 8.5.4. 

8.5.7. Comment: It is very difficult to demonstrate “but for,” particularly for ozone-related 

events. Most air pollutant exceedance events consist of contributions from multiple 

sources. The EPA’s guidance seems to apply differently for PM vs. ozone events. The 

EER preamble and the high winds guidance acknowledge that a PM exceedance can be 

exceptional even with contributions from natural and anthropogenic sources, but the 

answer to Q&A #6 implies that if an ozone/wildfire event has a contribution from an 

anthropogenic source as well as the fire, the event cannot be excluded under the EER. 

Further, demonstrating “that a fire plume has passed over a monitor is extremely difficult. 

All the methods that EPA suggested for demonstrating that a fire plume passed a monitor 

are insufficient as discussed below...” BP provides examples of satellite, modeling, and 

monitoring limitations and then identifies that if complete, detailed analyses are 

performed, they would likely exceed the desired response time and monetary resource 

availability. 

Specific reference to guidance text: Q&A document #6 (see document for additional 

detail: Submitted Comments\BP_063011pdf.pdf ) 

Submitter: Karen St. John (Sr. Director, Regulatory Affairs), BP America, Inc. 

Date: 6/30/2011 via e-mail to EEGuidanceComments@epa.gov 

Response: The EPA disagrees with the commenter’s interpretation of Q&A 6 that an 

ozone/wildfire-related exceptional event with contributions from the fire and 

anthropogenic sources cannot be excluded under the EER. In the response to Q&A 6 in 

the revised draft Q&A document, the EPA states that because the effects of a fire on 

ozone are complex, the ensuing “but for” demonstration may be more complicated than a 

“but for” demonstration for another pollutant, like particulate matter. The EPA can, and 

has, concurred on ozone/wildfire related exceptional events and refers the commenter to 

the website: http://www.epa.gov/ttn/analysis/exevents.htm 

The EPA recognizes that some demonstration analyses are resource intensive, but given 

the importance of accurately evaluating exceptional events, the EPA expects submitters 

to prepare and submit the appropriate level of supporting documentation, which will vary 

on a case-by-case basis using the weight-of-evidence approach. The EPA further notes 

that the CAA does not give the EPA the authority to exclude data if the air agency has not 

met and demonstrated each criterion.