Treatment of Data Influenced by Exceptional Events

Federal RegisterNov 20, 2015

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 50

[EPA-HQ-OAR-2013-0572, EPA-HQ-OAR-2015-0229; FRL-9935-73-OAR]

RIN 2060-AS02

Treatment of Data Influenced by Exceptional Events

AGENCY:

Environmental Protection Agency (EPA).

ACTION:

Proposed rule; notice of availability of related draft guidance; notice of hearing.

SUMMARY:

The Environmental Protection Agency (EPA) is proposing revisions to certain sections within the regulations that govern the exclusion of event-affected air quality data from regulatory decisions. The EPA is also providing a notice of availability of a draft version of the non-binding guidance document titled

Draft Guidance on the Preparation of Exceptional Events Demonstrations for Wildfire Events that May Influence Ozone Concentrations.

DATES:

Comments.

Written comments on this proposal and draft guidance must be received by January 19, 2016.

Public hearing:

The EPA will hold a public hearing on this proposal on Tuesday, December 8, 2015, in Phoenix, Arizona. Please refer to

SUPPLEMENTARY INFORMATION

for additional information on the comment period and public hearing.

ADDRESSES:

Submit your comments on the EPA's proposed revisions to 40 CFR part 50, identified by Docket ID No. EPA-HQ-OAR-2013-0572, at

http://www.regulations.gov.

Follow the online instructions for submitting comments. Once submitted, comments cannot be edited or removed from Regulations.gov. The EPA may publish any comment received to its public docket. Do not submit electronically any information you consider to be Confidential Business Information (CBI) or other information whose disclosure is restricted by statute. Multimedia submissions (audio, video, etc.) must be accompanied by a written comment. The written comment is considered the official comment and should include discussion of all points you wish to make. The EPA will generally not consider comments or comment contents located outside of the primary submission (

i.e.,

on the Web, Cloud or other file sharing system). For additional submission methods, the full EPA public comment policy, information about CBI or multimedia submissions and general guidance on making effective comments, please visit

http://www2.epa.gov/dockets/commenting-epa-dockets.

Submit your comments on the EPA's

Draft Guidance on the Preparation of Exceptional Events Demonstrations for Wildfire Events that May Influence Ozone Concentrations,

identified by Docket ID No. EPA-HQ-OAR-2015-0229, at

http://www.regulations.gov.

Follow the online instructions for submitting comments. Once submitted, comments cannot be edited or removed from Regulations.gov. The EPA may publish any comment received to its public docket. Do not submit electronically any information you consider to be CBI or other information whose disclosure is restricted by statute. Multimedia submissions (audio, video, etc.) must be accompanied by a written comment. The written comment is considered the official comment and should include discussion of all points you wish to make. The EPA will generally not consider comments or comment contents located outside of the primary submission (

i.e.,

on the web, cloud or other file sharing system). For additional submission methods, the full EPA public comment policy, information about CBI or multimedia submissions and general guidance on making effective comments, please visit

http://www2.epa.gov/dockets/commenting-epa-dockets.

Public hearing:

A public hearing will be held on Tuesday, December 8, 2015, in room 3175 in the Arizona Department of Environmental Quality main office building located at 1110 W. Washington Street, Phoenix, Arizona 85007. The public hearing will convene at 10 a.m. and continue until the earlier of 6 p.m. or 1 hour after the last registered speaker has spoken. We have scheduled a lunch break from 12:30 p.m. until 2 p.m. People interested in presenting oral testimony should contact Ms. Pamela Long, Air Quality Planning Division, Office of Air Quality Planning and Standards (C504-01), U.S. Environmental Protection Agency, Research Triangle Park, NC 27711, telephone (919) 541-0641, fax number (919) 541-5509, email address

long.pam@epa.gov,

at least 2 days in advance of the public hearing (

see

DATES

). People interested in attending the public hearing should also call Ms. Long to verify the time, date and location of the hearing.

FOR FURTHER INFORMATION CONTACT:

For additional information regarding this proposed rule, please contact: Beth W. Palma, U.S. EPA, Office of Air Quality Planning and Standards, Air Quality Policy Division, Mail Code C539-04, Research Triangle Park, NC 27711, telephone (919) 541-5432, email at

palma.elizabeth@epa.gov.

For additional information regarding the

Draft Guidance on the Preparation of Exceptional Events Demonstrations for Wildfire Events that May Influence Ozone Concentrations,

please contact Melinda Beaver, U.S. EPA, Office of Air Quality Planning and Standards, Air Quality Policy Division, Mail Code C539-04, Research Triangle Park, NC 27711, telephone (919) 541-1062, email at

beaver.melinda@epa.gov.

For information on the public hearing or to register to speak at the hearing, contact Ms. Pamela Long, U.S. Environmental Protection Agency, Office of Air Quality Planning and Standards, Air Quality Planning Division, Mail Code C504-01, Research Triangle Park, NC 27711, telephone (919) 541-0641, fax number (919) 541-5509, email at

long.pam@epa.gov

(preferred method for registering).

SUPPLEMENTARY INFORMATION:

I. General Information

A. Does this action apply to me?

Entities potentially directly affected by this proposal and the draft guidance document include all state air agencies and any local air quality agency to whom a state has delegated relevant responsibilities for air quality management, including air quality monitoring and data analysis. Tribal air agencies operating ambient air quality monitors that produce regulatory data may also be directly affected. Entities potentially affected indirectly by this proposal and the draft guidance document include federal land managers (FLMs) of Class I areas, other federal agencies and other entities that operate ambient air quality monitors and submit collected data to the EPA's Air Quality System (AQS) database.

B. What should I consider as I prepare my comments for the EPA?

Docket.

The EPA has established one docket for the proposed revisions to the 2007 Exceptional Events Rule and another docket for the draft guidance document. All documents in these dockets are listed on the

http://www.regulations.gov

Web site in the respective docket. The rulemaking docket is Docket ID No. EPA-HQ-OAR-2013-0572. The separate docket established for the

Draft Guidance on the Preparation of Exceptional Events Demonstrations for Wildfire Events that May Influence Ozone Concentrations

is Docket No. EPA-HQ-OAR-2015-0229. The EPA will not respond to comments relating to the guidance document as

part of this rulemaking, but will consider these comments in the development of the final guidance document. If comments on the draft guidance document are submitted to the rulemaking docket, the EPA will respond only to the portion of such comments that are relevant to the rulemaking. The EPA also relies on the documents in Docket ID No. EPA-HQ-OAR-2011-0887, the docket established for the July 2012 notice of availability for the Draft Exceptional Events Implementation Guidance, and incorporates this docket into the record for this action. However, no new comments may be directed to Docket ID No. EPA-HQ-OAR-2011-0887 and the EPA will not respond to comments that have already been submitted to this docket unless they are resubmitted to Docket ID No. EPA-HQ-OAR-2013-0572. Although listed in the indices to the rulemaking docket and the guidance docket associated with this action (

i.e.,

Docket ID No. EPA-HQ-OAR-2013-0572 and Docket No. EPA-HQ-OAR-2015-0229), some information is not publicly available, (

e.g.,

CBI or other information whose disclosure is restricted by statute). Certain other material, such as copyrighted material, will not be placed on the Internet but may be viewed, with prior arrangement, at the EPA Docket Center. Publicly available docket materials are available either electronically in

www.regulations.gov

or in hard copy at the Air and Radiation Docket and Information Center, EPA/DC, EPA William Jefferson Clinton West Building, Room 3334, 1301 Constitution Avenue NW., Washington, DC. The Public Reading Room is open from 8:30 a.m. to 4:30 p.m., Monday through Friday, excluding legal holidays. The telephone number for the Public Reading Room is (202) 566-1744 and the telephone number for the Air and Radiation Docket and Information Center is (202) 566-1742. For additional information about the EPA's public docket, visit the EPA Docket Center homepage at:

http://www.epa.gov/epahome/dockets.htm.

Submitting CBI.

Do not submit this information to the EPA through

http://www.regulations.gov

or email. Clearly mark the part or all of the information that you claim to be CBI. For CBI information in a disk or CD-ROM that you mail to the EPA, mark the outside of the disk or CD-ROM as CBI and then identify electronically within the disk or CD-ROM the specific information that is claimed as CBI. In addition to one complete version of the comment that includes information claimed as CBI, a copy of the comment that does not contain the information claimed as CBI must be submitted for inclusion in the public docket. Information so marked will not be disclosed except in accordance with procedures set forth in 40 CFR part 2.

Tips for Preparing Your Comments.

When submitting comments, remember to:

• Identify the rulemaking and/or draft guidance document by docket number and other identifying information (subject heading,

Federal Register

date, page number and guidance document title, if applicable).

• Follow directions—The agency may ask you to respond to specific questions or organize comments by referencing a Code of Federal Regulations (CFR) part or section number in the guidance.

• Explain why you agree or disagree; suggest alternatives and substitute language for your requested changes.

• Describe any assumptions and provide any technical information and/or data that you used.

• If you estimate potential costs or burdens, explain how you arrived at your estimate in sufficient detail to allow for it to be reproduced.

• Provide specific examples to illustrate your concerns, and suggest alternatives.

• Explain your views as clearly as possible, avoiding the use of profanity or personal threats.

• Make sure to submit your comments by the identified comment period deadline.

C. Where can I get a copy of these documents and other related information?

In addition to being available in the docket, an electronic copy of this notice and the draft guidance will be posted at

http://www2.epa.gov/air-quality-analysis/treatment-data-influenced-exceptional-events.

D. What should I know about the public hearing?

The EPA intends to hold a public hearing on Tuesday, December 8, 2015, in room 3175 in the Arizona Department of Environmental Quality main office building located at 1110 W. Washington Street, Phoenix, Arizona 85007. If you would like to attend or speak at the public hearing, please contact Ms. Pamela Long, U.S. Environmental Protection Agency, Office of Air Quality Planning and Standards, Air Quality Planning Division, Mail Code C504-01, Research Triangle Park, NC 27711, telephone (919) 541-0641, fax number (919) 541-5509, email at

long.pam@epa.gov

(preferred method for registering) at least 2 days in advance of the public hearing (

see

DATES

). Interested parties may submit oral and/or written comments. Interested parties do not need to attend the public hearing to submit written comments. Additional details concerning any public hearing for this proposed rule will be posted on the EPA's Web site for this rulemaking at

http://www2.epa.gov/air-quality-analysis/treatment-data-influenced-exceptional-events.

The public hearing will provide interested parties the opportunity to present data, views or arguments concerning the proposed revisions to the 2007 Exceptional Events Rule. The EPA will make every effort to accommodate all speakers who arrive and register. Individuals planning to attend the hearing will be required to sign in, and may be required to show valid picture identification to the security staff to gain access to the meeting room. In addition, no weapons will be allowed in the facility. Any weapons brought to the site will be stored in a locker at the facility. No large signs will be allowed in the building, and cameras may only be used outside of the building. The EPA may ask clarifying questions during the oral presentations but will not respond to the presentations at that time. Written statements and supporting information submitted during the comment period will be considered with the same weight as oral comments and supporting information presented at the public hearing. Commenters must submit written comments on the proposed rule and/or draft guidance by January 19, 2016. Commenters should notify Ms. Long if they will need specific equipment, or if there are other special needs related to providing comments at the hearing. The EPA will provide equipment for commenters to show overhead slides or make computerized slide presentations if we receive special requests in advance. Oral testimony will be limited to 5 minutes for each commenter. The EPA encourages commenters to provide the EPA with a copy of their oral testimony electronically (via email or CD) or in hard copy form. The hearing schedule, including the list of speakers, will be posted on the EPA's Web site at

http://www2.epa.gov/air-quality-analysis/treatment-data-influenced-exceptional-events.

Verbatim transcripts of the hearing and written statements will be included in the docket for the rulemaking. The EPA will make every effort to follow the schedule as closely as possible on the day of the hearing; however, please plan for the hearing to

run either ahead of schedule or behind schedule.

E. How is this document organized?

The information presented in this document is organized as follows:

I. General Information

A. Does this action apply to me?

B. What should I consider as I prepare my comments for the EPA?

C. Where can I get a copy of these documents and other related information?

D. What should I know about the public hearing?

E. How is this document organized?

II. Glossary of Terms and Acronyms

III. Executive Summary

IV. Background for Proposal

A. Purpose of and Statutory Authority for This Regulatory Action

B. The 2007 Exceptional Events Rule

C. Early Experience in Implementing the 2007 Exceptional Events Rule

D. The EPA's Interim Exceptional Events Implementation Guidance

E. More Recent Implementation Experience Including EPA-Recommended Best Practices for the Development of Exceptional Events Demonstrations

V. Proposed Rule Revisions

A. To whom and to what pollutants does the Exceptional Events Rule apply?

1. Current Situation

2. Proposed Changes

B. What is an exceptional event?

1. Current Situation

2. Proposed Changes

C. What types of ambient concentration data and data uses may be affected by the Exceptional Events Rule?

1. Current Situation

2. Proposed Changes

D. What is a natural event?

1. Current Situation

2. Proposed Changes

E. Technical Criteria for the Exclusion of Data Affected by Events

1. Human Activity Unlikely To Recur at a Particular Location or a Natural Event

2. Not Reasonably Controllable or Preventable

3. Clear Causal Relationship Supported by a Comparison to Historical Concentration Data

F. Treatment of Certain Events Under the Exceptional Events Rule

1. Exceedances Due to Transported Pollution

2. Wildland Fires

3. Stratospheric Ozone Intrusions

4. High Wind Dust Events

G. Other Aspects of Flagging Exceptional Events-Influenced Data and Demonstration Submittal and Review

1. Who may submit a demonstration and request for data exclusion?

2. Aggregation of Events for NAAQS With Periods Longer Than 24 Hours and Demonstrations With Respect to Multiple NAAQS for the Same Pollutant

3. Exclusion of Entire 24-Hour Value Versus Partial Adjustment of the 24-Hour Value for Particulate Matter

4. Flagging of Data

5. Initial Notification of Potential Exceptional Event

6. Submission of Demonstrations

7. Timing of the EPA's Review of Submitted Demonstrations

8. Dispute Resolution Mechanisms

VI. Mitigation

A. Current Situation

B. Proposed Changes

1. Defining Historically Documented or Known Seasonal Events

2. Mitigation Plan Components

3. Options for Implementing Mitigation Plans

VII. Draft Guidance on the Preparation of Exceptional Events Demonstrations for Wildfire Events That May Influence Ozone Concentrations

A. What is this draft guidance about and why is it needed?

B. What scenarios are addressed in the draft guidance?

VIII. Environmental Justice Considerations

IX. Statutory and Executive Order Reviews

A. Executive Order 12866: Regulatory Planning and Review and Executive Order 13563: Improving Regulation and Regulatory Review

B. Paperwork Reduction Act

C. Regulatory Flexibility Act

D. Unfunded Mandates Reform Act

E. Executive Order 13132: Federalism

F. Executive Order 13175: Consultation and Coordination With Indian Tribal Governments

G. Executive Order 13045: Protection of Children From Environmental Health & Safety Risks

H. Executive Order 13211: Actions Concerning Regulations That Significantly Affect Energy Supply, Distribution or Use

I. National Technology Transfer and Advancement Act

J. Executive Order 12898: Federal Actions To Address Environmental Justice in Minority Populations and Low-Income Populations

X. Statutory Authority

II. Glossary of Terms and Acronyms

The following are abbreviations of terms used in the preamble.

AQCR Air Quality Control Region

AQS Air Quality System

Be Beryllium

BACM Best available control measures

BLM Bureau of Land Management

BMP Best management practice(s)

BSMP Basic smoke management practices

CAA Clean Air Act

CASTNET Clean Air Status and Trends Network

CBI Confidential business information

CFR Code of Federal Regulations

CO Carbon monoxide

EPA Environmental Protection Agency

FLM Federal land manager responsible for management of a federally owned area that has been designated a Class I area as codified in 40 CFR part 81, subpart D

FR Federal Register

IPV Isentropic potential vorticity

Lidar A remote sensing technology that measures distance by illuminating a target with a laser and analyzing the reflected light

μg/m

Micrograms per cubic meter

mph Miles per hour

NAAQS National ambient air quality standard or standards

NAM North American Mesoscale Forecast System

NASA National Aeronautics and Space Administration

NEPA National Environmental Policy Act

Nitrogen dioxide

NOAA National Oceanic and Atmospheric Administration

NOV Notice of violation

NOx Nitrogen oxides

NPS National Park Service

NSR New source review

NRCS Natural Resources Conservation Service

NRDC Natural Resources Defense Council

NWCG National Wildfire Coordinating Group

NWS National Weather Service

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

OMB Office of Management and Budget

Pb Lead

PM Particulate matter

Particulate matter with a nominal mean aerodynamic diameter less than or equal to 10 micrometers

2.5

Particulate matter with a nominal mean aerodynamic diameter less than or equal to 2.5 micrometers

ppb Parts per billion

PSD Prevention of significant deterioration

PT Potential temperature

RACM Reasonably available control measures

RAQMS Real-time Air Quality Modeling System

RUC Rapid Update Cycle

SIP State implementation plan

SMP Smoke management program

Sulfur dioxide

TAR Tribal Authority Rule

TIP Tribal implementation plan

UMRA Unfunded Mandates Reform Act

USDA U.S. Department of Agriculture

USFS U.S. Forest Service

VOC Volatile organic compound or compounds

III. Executive Summary

This section summarizes the purpose of this regulatory action, the major provisions of this action, and the development of associated guidance.

Purpose of This Regulatory Action

Recognizing that it may not be appropriate for the EPA to use certain monitoring data collected by the ambient air quality monitoring network and maintained in the air quality data system (AQS) in the EPA's regulatory determinations, in 2005 Congress provided the statutory authority for the exclusion of data in specific situations by adding section 319(b) to the Clean Air Act (CAA). The EPA promulgated the 2007 Exceptional Events Rule (March 22, 2007, 72 FR 13560) to

implement this 2005 amendment of the CAA. The purpose of this action is to propose revisions to the 2007 Exceptional Events Rule to address certain substantive issues raised by state, local and tribal co-regulators and other stakeholders since promulgation of the rule and to increase the administrative efficiency of the Exceptional Events Rule criteria and process. The EPA intends to promulgate these rule revisions in advance of the date by which states, and any tribes that wish to do so, are required to submit their initial designation recommendations for the revised 2015 ozone NAAQS (expected in October of 2016). In addition, the EPA intends to address a 2008 D.C. Circuit Court decision in which the court found that certain preamble language was “legally null” because there was no associated implementing rule language.

Interpreting and implementing the 2007 Exceptional Events Rule has been challenging in certain respects both for the air agencies developing exceptional events demonstrations and for the EPA Regional offices reviewing and acting on these demonstrations. Since 2007, air agencies have submitted exceptional event demonstrations for a variety of pollutant and event combinations ranging from volcanic activity influencing sulfur dioxide (SO

) and particulate matter (PM) concentrations to stratospheric ozone intrusions. Air agencies preparing demonstrations have expressed specific concerns and identified challenges associated with preparing analyses to satisfy the “but for” rule criterion, determining what controls constitute reasonable controls particularly for natural sources and for interstate and international transport and identifying how much documentation to include in a demonstration.

As a result of both our experiences and feedback related to implementing the 2007 Exceptional Events Rule received from state, local and tribal co-regulators and other stakeholders via letters and numerous conference calls and meetings, the EPA developed and released Interim Exceptional Events Implementation Guidance in May of 2013. This guidance has addressed some of the concerns and challenges raised by interested parties, has helped reduce the burden of preparing demonstrations and has reduced the time needed for review. However, the EPA acknowledged that additional changes could only be accomplished through a notice-and-comment rulemaking. Therefore, when the EPA released the Interim Exceptional Events Implementation Guidance in May of 2013, we simultaneously announced our intent to pursue revisions to the Exceptional Events Rule. These changes are reflected in this proposed action.

Concurrent with preparing this proposed action, the EPA held conference calls with some air agencies to discuss more recent implementation experiences and to better understand currently employed exceptional events implementation processes and practices. As a result of these discussions, the EPA developed a list of best practices for communication and collaboration between the EPA and air agencies. Agencies using these approaches have developed a common understanding of expectations, terminology and interpretation of the EPA's regulations and policy, which, in turn, helps focus efforts, optimize resources and save time during the demonstration development and review process.

Based on our experiences and the input we have received from our collaborations with interested parties (including state, local and tribal air agencies) following the promulgation of the 2007 Exceptional Events Rule and since the development of the Interim Exceptional Events Implementation Guidance and based on the previous legal challenge, we have determined those aspects of the 2007 Exceptional Events Rule that most need to be addressed in this proposed action.

Summary of Major Provisions

For the first time, the EPA proposes to interpret CAA section 319(b) as applying to only a specific set of regulatory actions (

e.g.,

designations) because we believe that the criteria and process steps specified in the CAA were not clearly intended by Congress to apply to all types of regulatory actions and in some cases certain of the criteria and steps are not appropriate. We address this concept in this document in general terms, but we also intend to develop a separate guidance document to provide guidance on when data can be excluded and when they cannot for other specific types of regulatory actions.

The EPA proposes to return to the core statutory elements and implicit concepts of CAA section 319(b): The event affected air quality in such a way that there exists a clear causal relationship between the specific event and the monitored exceedance or violation, the event was not reasonably controllable or preventable and the event was caused by human activity that is unlikely to recur at a particular location or was a natural event. Within each of these elements, we are proposing clarifications regarding the desired analyses to include in exceptional events demonstrations and we discuss the applicability of these clarifications to certain event types or categories. As part of this return to the core statutory elements, we are proposing to remove from the Exceptional Events Rule a paragraph containing what is commonly referred to as the “but for” criterion.

The EPA is proposing to incorporate the statutory “affects air quality” criterion and the regulatory “historical fluctuations” criterion within the “clear causal relationship” element. We believe that if an air agency demonstrates that an event has a clear causal relationship to an exceedance or violation of a NAAQS, then the event has certainly affected air quality and that a submitting air agency does not need to address “affects air quality” as a distinct component. As we indicated in the Interim Exceptional Events Implementation Guidance (see section IV.D), we believe that a comparison of the claimed event-influenced concentration(s) to concentrations at the same monitoring site at other times is extremely useful evidence in an exceptional events demonstration, particularly as part of showing a clear causal relationship, and we propose to continue requiring this type of comparison. This proposed action details the minimum set of statistical analyses that the EPA expects to see in demonstrations.

With respect to the “not reasonably controllable or preventable” criterion, many states have requested that the EPA automatically consider an event to be reasonably controlled if the EPA has approved a state implementation plan (SIP) that contains controls for anthropogenic sources that contribute to the event that are also specific to the pollutant of concern in the exceptional events demonstration. In response, the EPA proposes that enforceable control measures implemented in accordance with an attainment or maintenance SIP, approved by the EPA within 5 years of the date of a demonstration submittal, that address the event-related pollutant and all sources necessary to fulfill the requirements of the CAA for the SIP to be reasonable controls with respect to all anthropogenic sources that have or may have contributed to event-related emissions. Also for this criterion, the EPA clarifies that air agencies generally have no obligation to specifically address controls if the event was natural or if it was due to emissions originating outside their jurisdictional (

i.e.,

state or tribal) border(s).

With respect to the “human activity that is unlikely to recur at a particular

location or was a natural event” criterion, we propose a general approach to determining whether the recurrence frequency of an event is “unlikely to recur at a particular location” and an approach applicable to prescribed fire on wildland only. We also clarify that natural events can recur, sometimes frequently, and reiterate our belief that we generally consider human activity to have played little or no direct role in causing emissions if anthropogenic emission sources that contribute to the event emissions are reasonably controlled at the time of the event.

Air agencies must address all of the core statutory elements and implicit concepts of CAA section 319(b) within an exceptional events demonstration. In this proposed action, the EPA clarifies the content and organization of exceptional events submittals to include the core statutory elements, but we also propose that states be required to include a conceptual model, or narrative, describing the event(s) causing the exceedance or violation and a discussion of how emissions from the event(s) led to the exceedance at the affected monitor(s) and documentation that the air agency conducted a public comment process. We are proposing to require an initial notification by the state to the EPA of a potential exceptional event as a preliminary step before submitting a demonstration, to ensure the submitting air agency and the reviewing EPA Regional office share a common understanding regarding the potential event and are in communication regarding the timeline for the demonstration to be submitted and to be reviewed by the Regional office.

Because affected air agencies have provided feedback regarding the difficulty associated with meeting the current regulatory timelines associated with data flagging, initial event descriptions and demonstration submittals, the EPA proposes to remove the specific deadlines that apply in situations other than initial area designations following promulgation of a new or revised NAAQS. Also associated with demonstration timing, the EPA proposes to officially terminate review of demonstrations that, due to the passage of time, will have no further regulatory significance specifically for the five types of regulatory actions identified in section V.C. of this preamble.

Since promulgation of the 2007 Exceptional Events Rule, stakeholders have raised numerous questions about fire-related components that were discussed, but not fully defined or clarified in the preamble to the 2007 Exceptional Events Rule. This proposed action addresses fire-related definitions, provides more clarity regarding expectations for smoke management programs (SMPs) and basic smoke management practices (BSMP), and proposes limited scenarios under which FLMs and other federal agencies may prepare and submit exceptional events demonstrations and data exclusion requests directly to the EPA.

Associated Guidance Documents

In addition to proposing revisions to the 2007 Exceptional Events Rule, this proposed action simultaneously provides a notice of availability of a draft non-binding guidance document titled,

Draft Guidance on the Preparation of Exceptional Events Demonstrations for Wildfire Events that May Influence Ozone Concentrations,

which applies the proposed Exceptional Events Rule revisions to wildfire/ozone events. This guidance document is intended to further address specific stakeholder questions regarding the Exceptional Events Rule and further increase the efficiency of rule implementation. In addition, the EPA is currently developing a guidance document titled,

Draft Guidance for Excluding Some Ambient Pollutant Concentration Data from Certain Calculations and Analyses for Purposes Other than Retrospective Determinations of Attainment of the NAAQS,

which will apply to the exclusion of certain data for certain applications using a process and criteria outside of the Exceptional Events Rule. The EPA intends to make this guidance document available shortly after proposing revisions to the Exceptional Events Rule. The EPA expects to finalize these guidance documents concurrently with promulgating revisions to the Exceptional Events Rule.

IV. Background for Proposal

A. Purpose of and Statutory Authority for This Regulatory Action

Part of the EPA's mission is to preserve and improve, when needed, the quality of our nation's ambient air to protect human health and the environment. As part of accomplishing this, the EPA develops the national ambient air quality standards (NAAQS) for criteria pollutants and oversees the states' programs to improve air quality in areas where the current air quality is unacceptable and to prevent deterioration in areas where the air quality meets or exceeds the NAAQS. The EPA then evaluates the status of the ambient air as compared to these NAAQS by using data collected in the national ambient air quality monitoring network established under the authority of section 319(a) of the CAA.

Recognizing that it may not be appropriate for the EPA to use certain monitoring data collected by the ambient air quality monitoring network and maintained in AQS in our regulatory determinations, in 2005 Congress provided the statutory authority for the exclusion of data in specific situations by adding section 319(b) to the CAA in 2005. The EPA promulgated the 2007 Exceptional Events Rule (March 22, 2007, 72 FR 13560) to implement this 2005 amendment of the CAA. The purpose of this action is to propose revisions to the 2007 Exceptional Events Rule to address certain issues raised by stakeholders since promulgation of the rule and to increase the administrative efficiency of the Exceptional Events Rule criteria and process.

In addition to proposing revisions to the 2007 Exceptional Events Rule, we are simultaneously providing a notice of availability of a draft non-binding guidance document titled,

Draft Guidance on the Preparation of Exceptional Events Demonstrations for Wildfire Events that May Influence Ozone Concentrations,

which applies the proposed Exceptional Events Rule revisions to wildfire/ozone events. We seek comment on whether the concepts in this guidance document should be finalized as rule text. We are also currently developing a second guidance document titled,

Draft Guidance for Excluding Some Ambient Pollutant Concentration Data from Certain Calculations and Analyses for Purposes Other than Retrospective Determinations of Attainment of the NAAQS,

which will apply to the exclusion of certain data for certain applications using a process and criteria outside of the Exceptional Events Rule. Both of these draft guidance documents are intended to further address specific stakeholder concerns regarding the Exceptional Events Rule and further increase the efficiency of rule implementation.

B. The 2007 Exceptional Events Rule

The 2007 Exceptional Events Rule created a regulatory process codified at 40 CFR parts 50 and 51 (sections 50.1, 50.14 and 51.930). These regulatory sections contain definitions, procedural requirements, requirements for air agency demonstrations, criteria for the EPA's approval of the exclusion of event-affected air quality data from the data set used for regulatory decisions,

and requirements for air agencies

to take appropriate and reasonable actions to protect public health from exceedances or violations of the NAAQS.

The 2007 Exceptional Events Rule superseded the EPA's previous natural events guidance and those sections of an earlier guidance document that addressed the treatment of data affected by exceptional events.

References to “air agencies” are meant to include state, local and tribal air agencies responsible for implementing the Exceptional Events Rule. The regulatory text in the 2007 Exceptional Events Rule often uses “State” to apply to “air agencies.” In the context of flagging data and preparing and submitting demonstrations, the role of and options available to air agencies would also apply to federal land managers of Class I areas and other federal agencies managing federal land.

Per the definition at 40 CFR 50.1(l), an

exceedance with respect to a national ambient air quality standard

means one occurrence of a measured or modeled concentration that exceeds the specified concentration level of such standard for the averaging period specified by the standard. Violations of a standard are standard-specific and are determined by applying the standard-specific procedures for air quality data handling identified in the appendices to 40 CFR part 50. For example, per the requirements in 40 CFR part 50, appendix N, an exceedance of the 2006 24-hour PM

2.5

NAAQS of 35 μg/m

occurs when the 24-hour concentration is above 35 μg/m

on a single day. A violation of the 2006 24-hour PM

2.5

NAAQS occurs when the 3-year average of the annual 98th percentile 24-hour concentrations is above 35 μg/m

Previous guidance and policy documents that either implied or stated the need for special treatment of data affected by an exceptional event include:

Guideline for the Interpretation of Air Quality Standards,

U.S. EPA, OAQPS No. 1.2-008, Revised February 1977. Available at

http://nepis.epa.gov/Exe/ZyNET.exe/2000YFDB.TXT?ZyActionD=ZyDocument&Client=EPA&Index=1976+Thru+1980&Docs=&Query=&Time=&EndTime=&SearchMethod=1&TocRestrict=n&Toc=&TocEntry=&QField=&QFieldYear=&QFieldMonth=&QFieldDay=&IntQFieldOp=0&ExtQFieldOp=0&XmlQuery=&File=D%3A%5Czyfiles%5CIndex%20Data%5C76thru80%5CTxt%5C00000007%5C2000YFDB.txt&User=ANONYMOUS&Password=anonymous&SortMethod=h%7C-&MaximumDocuments=1&FuzzyDegree=0&ImageQuality=r75g8/r75g8/x150y150g16/i425&Display=p%7Cf&DefSeekPage=x&SearchBack=ZyActionL&Back=ZyActionS&BackDesc=Results%20page&MaximumPages=1&ZyEntry=1&SeekPage=x&ZyPURL.

ii)

Guideline on the Identification and Use of Air Quality Data Affected by Exceptional Events

(the Exceptional Events Policy), U.S. EPA, OAQPS, EPA-450/4-86-007, July 1986.

iii)

Areas Affected by PM-10 Natural Events

(the PM

Natural Events Policy), memorandum from Mary D. Nichols, Assistant Administrator for Air and Radiation, to EPA Regional Offices, May 30, 1996. Available at

http://www.epa.gov/ttn/caaa/t1/memoranda/nepol.pdf.

iv)

Interim Air Quality Policy on Wildland and Prescribed Fires.

U.S. EPA. April 23, 1998. Available at

http://www.epa.gov/ttn/oarpg/t1/memoranda/firefnl.pdf.

Guideline on Data Handling Conventions for the PM NAAQS.

U.S. EPA, OAQPS, EPA-454/R-98-017, December 1998.

In general, the exceptional events regulatory process consists of the following steps. First, an air agency identifies a potential event-related exceedance or violation. After noting these data in AQS, the air agency prepares a draft demonstration package to support the exclusion of the identified event-related data and provides an opportunity for public comment. The air agency submits the draft demonstration and any received public comments to its EPA Regional office, which then reviews the submittal and concurs, nonconcurs or defers a decision related to the air agency's request to exclude data that have been affected by exceptional events. If the EPA agrees with the air agency's request, the data are excluded. If the EPA does not agree with the air agency claim, or if the EPA decides to defer a decision on the submittal, the data are used in regulatory determinations.

The 2007 Exceptional Events Rule was challenged in 2008. In

NRDC

EPA,

559 F.3d 561 (D.C. Cir. 2009), the Natural Resources Defense Council (NRDC) brought a petition for review challenging the EPA's definition of a natural event and seeking to vacate several statements in the preamble to the final 2007 Exceptional Events Rule concerning the types of events that could qualify as being eligible for exclusion under the rule provisions. In particular, NRDC objected to treating “events in which human activities play `little' causal role” as natural events. Regarding the definition of a natural event, the D.C. Circuit Court determined that NRDC did not identify its objection during the rulemaking process and, therefore, did not have standing under CAA section 307 to challenge the definition.

NRDC also challenged the preamble language addressing high wind events. In its decision, the D.C. Circuit stated,

In one section of the preamble, EPA refers to its “final rule concerning high wind events,” which “states that ambient particulate concentrations due to dust being raised by unusually high winds will be treated as due to uncontrollable natural events” when certain conditions apply. . . . There is no such final rule. The final rule does not mention high wind events or anything about “ambient particulate matter concentrations.” EPA calls this a drafting error. In light of the error, the high wind events section of the preamble is a legal nullity.

The EPA believes it is clear that the “high wind events section of the preamble” to which the court referred is the entire section titled, “

B. High Wind Events”

beginning at 72 FR 13576. Accordingly, since 2007, the EPA has not relied solely on this section of the preamble when implementing the 2007 Exceptional Events Rule. The EPA maintains that certain of the preamble passages determined to be “legally null” are in fact appropriate interpretations of the Exceptional Events Rule and are consistent with the CAA. For clarity and regulatory certainty, the EPA is proposing in rule text form some of the interpretative positions originally stated in the High Wind Events section of the preamble to the 2007 Exceptional Events Rule.

Within each topical area of this notice, the EPA has provided more detailed background information on specific aspects of the 2007 Exceptional Events Rule and its implementation to allow readers to consider the proposed changes in the context of the current situation.

C. Early Experience in Implementing the 2007 Exceptional Events Rule

Interpreting and implementing the 2007 Exceptional Events Rule has been a challenging process both for the air agencies developing exceptional events demonstrations and for the EPA Regional offices reviewing and acting on these demonstrations. Shortly after the EPA promulgated the rule in 2007, air agencies asked the EPA to clarify key rule provisions and expectations for these demonstrations. Air agencies also asked for demonstration templates and/or examples of acceptable demonstrations for various event and pollutant combinations. Although the EPA provided some of this information via the exceptional events Web site at

http://www2.epa.gov/air-quality-analysis/treatment-data-influenced-exceptional-events,

air agencies noted that, in their view, the information provided was insufficient and sought additional guidance to facilitate consistency among the EPA Regional offices in interpreting and implementing the 2007 Exceptional Events Rule. In the years since rule promulgation, air agencies continued to express concern, through various mechanisms including formal letters, informal emails, interaction at various meetings and Congressional testimony, about the consistent application of the 2007 Exceptional Events Rule and the resources expended to prepare exceptional events demonstrations.

The EPA has also faced challenges in reviewing submitted demonstrations. Because exceptional events are fact-specific and thus unique and varied, providing templates or general guidance was, and still is, challenging. The EPA also acknowledges that the final rule and preamble language for the 2007 Exceptional Events Rule provided room for interpretation, making it difficult for air agencies and the EPA to determine

how much evidence or technical analysis for demonstrations is needed. We do, however, think that providing additional recommendations on appropriate documentation would be helpful. Throughout this proposal, for example in section V.E, Technical Criteria for the Exclusion of Data Affected by Events, and in section V.F, Treatment of Certain Events Under the Exceptional Events Rule, we provide recommendations for language and analyses to include in demonstration packages. Additional detail regarding specific recommendations is available in the EPA's guidance documents and on the EPA's exceptional events Web site, which the EPA will update to incorporate the finalized rule changes concurrently with or shortly after promulgating the final rule. The EPA will also continue to maintain and update the exceptional events submissions table on its Web site with examples of approved submissions. These examples may help air agencies develop demonstration packages; however, they may not contain the minimum level of data or case-specific analyses necessary for all exceptional events demonstrations of the same event type. In addition, commenters on this notice may wish to provide suggestions on the appropriate documentation for specific types of exceptional events demonstrations.

D. The EPA's Interim Exceptional Events Implementation Guidance

As a result of stakeholder-identified concerns and the EPA's own experience related to implementing the 2007 Exceptional Events Rule, in 2010 the EPA began developing additional implementation guidance. In May of 2011, the EPA released the Draft Exceptional Events Implementation Guidance: The

Draft Guidance to Implement Requirements for the Treatment of Air Quality Monitoring Data Influenced by Exceptional Events,

the

Draft Exceptional Events Rule Frequently Asked Questions

document and 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 EPA provided these draft guidance documents to interested air agencies, FLMs, other federal agencies and other parties upon request, for preliminary review to solicit comment and help ensure that the EPA's final guidance provided an efficient and effective process to make determinations regarding air quality data affected by exceptional events. The EPA also placed additional examples of approved demonstrations on the EPA's Web site.

The EPA incorporated the commenters' feedback, as appropriate, into revised draft guidance documents, which were made available for broad public review in a July 6, 2012,

Federal Register

Notice of Availability (77 FR 39959) and in the associated docket (Docket ID No. EPA-HQ-OAR-2011-0887).

This docket includes a summary of the comment and response process from the 2011 preliminary review of the draft guidance documents. In addition to identifying specific comments on the draft guidance documents, this summary clearly identifies that implementation challenges originated shortly after the EPA promulgated the 2007 Exceptional Events Rule.

In May 2013, after a round of review and comment by the general public, the EPA finalized the Interim Exceptional Events Implementation Guidance and made these documents publicly available on the exceptional events Web site at

http://www2.epa.gov/air-quality-analysis/treatment-data-influenced-exceptional-events.

The EPA established Docket ID No. EPA-HQ-OAR-2011-0887 for the July 2012 notice of availability for the Draft Exceptional Events Implementation Guidance and has incorporated this docket into the record for this action.

Responses to Significant First-Round Comments on the Draft Guidance Documents on the Implementation of the Exceptional Events Rule,

U.S. EPA, June 2012. Available in Docket No. EPA-HQ-OAR-2011-0887.

The Interim Exceptional Events Implementation Guidance includes: The

Interim Guidance to Implement Requirements for the Treatment of Air Quality Monitoring Data Influenced by Exceptional Events,

the

Interim Exceptional Events Rule Frequently Asked Questions

(the Interim Q&A document), and the

Interim 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 Interim High Winds Guidance document).

With the release of the Interim Exceptional Events Implementation Guidance, the EPA simultaneously acknowledged the need to consider additional changes that could only be accomplished through a notice-and-comment rulemaking to revise the 2007 Exceptional Events Rule. To inform the development of proposed rule revisions, the EPA hosted exceptional events listening sessions in August and November of 2013 for interested air agencies, FLMs, other federal agencies, regional planning organizations, non-governmental organizations and other members of the public. The EPA has considered feedback from these listening sessions and the previous public comments on the Interim Exceptional Events Implementation Guidance in the development of these proposed revisions to the 2007 Exceptional Events Rule.

E. More Recent Implementation Experience Including EPA-Recommended Best Practices for the Development of Exceptional Events Demonstrations

Because of the passage of time since the 2013 exceptional events listening sessions, the EPA's Office of Air Quality Planning and Standards (OAQPS) held conference calls with some air agencies and the EPA Regional offices between September 2014 and March 2015 to ask whether any new implementation concerns had arisen and to better understand currently employed exceptional events implementation processes and practices.

As a result of these discussions, the EPA developed a list of best practices for communication and collaboration between the EPA and air agencies. These best practices include having discussions before, during and after the development and submission of exceptional events demonstration packages. Specifically, these best practices recommend that the EPA Regional offices and their air agencies discuss, on a mutually agreed upon frequency, those demonstrations that the agencies have developed and submitted for the EPA's action. These regular discussions should focus on whether the demonstrations have regulatory significance (

e.g.,

significance for any of the five types of regulatory actions identified in section V.C.) and, if not, whether the EPA can provide general technical or policy feedback that the air agency can include in future demonstrations. Prior to an air agency's development of future demonstrations, the air agency and the EPA should identify the relevant days and monitors of focus, the regulatory significance of these monitor days, the analyses of particular interest for a specific event and pollutant combination and the anticipated timeframe for demonstration submission and response. Discussions should continue while the air agency is developing the demonstration and after the agency submits the demonstration and while the EPA is reviewing the demonstration, to ensure both the air agency and the EPA are aware of status, direction and progress. Finally, after the EPA has acted on the demonstration, the reviewing EPA Regional office and the air agency should discuss elements of the process that should continue and those that should be improved, should understand the information in the demonstration that was useful versus the information that was extraneous and should discuss the possibility of

developing a demonstration template(s) for future events of the same type(s).

Agencies using this communications approach have developed a common understanding of expectations, terminology and interpretation of the EPA's regulations and policy, which, in turn, helps focus efforts, optimize resources and save time during the demonstration development and review process. A summary of this “best practices” approach to implementation is available at

http://www2.epa.gov/air-quality-analysis/treatment-data-influenced-exceptional-events

V. Proposed Rule Revisions

A. To whom and to what pollutants does the Exceptional Events Rule apply?

1. Current Situation

Under the CAA, states are primarily responsible for the administration of air quality management programs within their borders, which includes monitoring and analyzing ambient air quality, submitting monitoring data to the EPA, which are then stored in the EPA's AQS database, and identifying measurements that may warrant special treatment under the Exceptional Events Rule. The 2007 Exceptional Events Rule applies to all state air agencies and to local air quality agencies to whom a state has delegated relevant responsibilities for air quality management, including air quality monitoring and data analysis.

Additionally, the 2007 Exceptional Events Rule applies to some tribal air quality agencies who have been granted treatment as a state for section 319 of the CAA. Section 301(d) of the CAA authorizes the EPA to recognize tribal authority, allowing eligible, federally-recognized tribal governments to implement provisions of the CAA. Pursuant to section 301(d)(2), the EPA promulgated regulations, known as the Tribal Authority Rule (TAR), on February 12, 1999 (63 FR 7254, codified at 40 CFR part 49). That rule specifies those provisions of the CAA for which it is appropriate to treat tribes in a similar manner as states. Under the TAR, tribes may choose to develop and implement their own CAA programs, but are not required to do so. The TAR also establishes procedures and criteria by which tribes may request from the EPA a determination of eligibility to implement the provisions of the CAA. In cases where a tribal air quality agency is eligible to implement CAA section 319 and has installed and operates an air quality monitoring network that produces regulatory data that is affected by emissions from exceptional events, the criteria and procedures identified in these proposed rule revisions may be used to exclude data for purposes of regulatory decisions. Some tribes may implement only portions of the relevant air quality monitoring program and may choose not to address all of the procedures and requirements associated with excluding data that have been influenced by exceptional events (

e.g.,

a particular tribe may operate a monitoring network for purposes of gathering and identifying data appropriate for informational or educational purposes, but may choose not to implement relevant programs for the purpose of mitigating the effects of exceptional events). Where a tribal air quality agency is not eligible to implement CAA section 319 but operates an air quality monitoring network that produces regulatory data that is affected by emissions from exceptional events, the tribal air quality agency should consult with the EPA Regional office prior to addressing the procedures and requirements associated with excluding data that have been influenced by exceptional events.

In all cases, the EPA will continue to work with tribes in implementing any promulgated rule revisions.

As of the signature date of this action, only one tribe is eligible to implement all portions of CAA section 319 under the TAR. Several other tribes, however, operate air quality monitoring networks that produce regulatory data that could be affected by emissions from exceptional events.

While air agencies are responsible for administering air quality management programs within their borders, FLMs of Class I areas, other federal agencies and/or other entities (

e.g.,

industrial facilities pursuant to permit conditions) may also operate ambient air quality monitors that meet all requirements of 40 CFR parts 50 and 58.

The FLMs, other federal agencies and other entities operating these regulatory monitors may submit collected data to the EPA's AQS database.

These concentration measurements can be affected by exceptional events. The AQS software allows only the entity operating a monitor (and the EPA data system manager) to apply exceptional events flags to data from that monitor. Although FLMs and other entities can apply exceptional events flags to data from monitors they operate, the Exceptional Events Rule at 40 CFR 50.14(b)(1) states that the EPA shall exclude data from use in determinations of exceedances and NAAQS violations where a state demonstrates to the EPA's satisfaction that an exceptional event caused a specific air pollution concentration in excess of one or more NAAQS. The language, “where a State demonstrates” has resulted in an interpretation that only states can initiate the exceptional events process and submit demonstrations. Some stakeholders have asked the EPA to identify the process that the state air agency should follow if the state air agency does not have AQS access rights to place exceptional events flags on event-affected data from monitoring stations located within the state but not operated by the state. The EPA addressed this issue generally in Question 23 of the Interim Q&A document by indicating that air agencies should consult with their EPA Regional office early in the development of an exceptional event demonstration package if they believe that monitors on federally-owned and managed land (

e.g.,

national parks within the state) have been affected by an event. In these instances, the EPA has assisted in facilitating cross-agency coordination regarding the flagging of data, where needed.

The Ambient Air Quality Surveillance provisions in 40 CFR part 58 include, among other elements, the requirements for monitoring data certification and data submittal and archive in AQS. 40 CFR 58.3 provides that these data reporting requirements specifically apply to state air pollution control agencies and any local air pollution control agency to which the state has delegated authority to operate a portion of the state's monitoring network.

For a description of one network of monitoring sites operated by federal agencies,

see

the 2014 CASTNET (Clean Air Status and Trends Network) Annual Network Plan, available at

http://epa.gov/castnet/javaweb/ozone/CASTNET_Plan_2014_Final.pdf,

which applies to National Park Service (NPS) and Bureau of Land Management (BLM) site managers operating CASTNET monitors.

The 2007 Exceptional Events Rule applies to all criteria pollutant NAAQS.

This is appropriate given the language in CAA section 319(b)(3)(B)(iv), which applies to exceedances or violations of “the national ambient air quality standards.” The EPA regulations for the interpretation of ambient data with respect to the NAAQS that were in place prior to the 2007 Exceptional Events Rule and that have not been revised do not contain provisions allowing for the special handling of air quality data affected by exceptional events or do so without explicit reference to the Exceptional Events Rule as governing such exclusion. One NAAQS without a specific provision for handling event-

affected data is 40 CFR part 50, appendix K for PM with a nominal mean aerodynamic diameter less than or equal to 10 micrometers (PM

). Nevertheless, the EPA has enabled in AQS the capability to flag all criteria pollutant data, including the option for the EPA's concurrence, as the EPA maintains that the monitored concentrations of all NAAQS pollutants have the potential to be elevated by one or more event types and the Exceptional Events Rule should govern the process of data exclusion for certain types of regulatory actions (see section V.C).

There are NAAQS for carbon monoxide (CO), lead (Pb), nitrogen dioxide (NO

), ozone, particle pollution and sulfur dioxide (SO

). This applicability includes the primary and secondary NAAQS. At present, most of the secondary NAAQS are identical to the primary NAAQS for the same pollutant, so there is no distinction in how the Exceptional Events Rule applies. To date, the EPA has not encountered an exceptional event situation with respect to a non-identical secondary NAAQS.

2. Proposed Changes

As noted above, because FLMs and other federal agencies may operate regulatory monitors and submit collected data to the EPA's AQS database and emissions from exceptional events could affect these same monitors, the EPA proposes to allow FLMs and other federal agencies to prepare and submit exceptional events demonstrations and data exclusion requests directly to the EPA. The EPA believes that the CAA language at section 319(b)(3)(B)(i), which states that “the occurrence of an exceptional event must be demonstrated by reliable, accurate data that is promptly produced and provided by Federal, State, or local government agencies” provides authority for FLMs to initiate and submit such demonstration packages and data exclusion requests. Further, the EPA believes this is appropriate because, in many cases, the lands managed and/or owned by federal entities are not entirely within the jurisdictional boundary of a single state or local government. Also, as we discuss in more detail in section V.F.2, federal entities may either initiate prescribed fires or fight wildfires on lands managed and/or owned by federal entities. The EPA could determine both of types of fires to be exceptional events. The EPA expects that allowing FLMs and other federal agencies to submit exclusion requests directly will expedite the exceptional events demonstration development and submittal process. The EPA solicits comment on this proposed addition to the rule text, which appears at the end of this document. Based on comments received, the EPA may retain, modify or not include this provision in the final promulgated rule. This provision would apply only to FLMs and other federal agencies that either operate a monitor that has been affected by an event or that manage land on which an exceptional event originates. The provision would allow such FLMs and other federal agencies to provide demonstrations directly to the EPA only after a discussion with the state in which the monitor is operated. Alternatively, this discussion might result in an agreement that the federal agency flag the data in AQS at the air agency's request and then provide a draft demonstration document to the appropriate state air agency for adoption and submission by the air agency to the EPA, as is currently allowed. Regardless of who ultimately submits the demonstration, the EPA encourages collaboration between the FLMs and other federal agencies and the appropriate state air agency during the event identification and demonstration development process. If the provision for direct submission to the EPA is included in the final action, demonstrations prepared by FLMs or other federal agencies would be required to meet all provisions in the Exceptional Events Rule, including the requirement for a public comment period on a prepared demonstration

and the requirements related to schedules and procedures for demonstration package submittal (

see

sections V.G.4, V.G.5 and V.G.6) that apply to state agencies that operate monitors.

A public comment opportunity is important prior to submission to the EPA because under the Exceptional Events Rule the EPA is not required to provide a public comment opportunity prior to concurring with an air agency's request to exclude data. The EPA generally provides a public comment opportunity before we use air quality data, with or without such exclusions, in a final regulatory action. States typically provide an opportunity for public comment by posting draft demonstrations on a Web site. Federal agencies could do the same.

B. What is an exceptional event?

1. Current Situation

The existing definition of an exceptional event at 40 CFR 50.1(j) repeats the CAA definition, which provides that an exceptional event is one that affects air quality, is not reasonably controllable or preventable, is caused by human activity that is unlikely to recur at a particular location or is a natural event, and is determined by the Administrator in accordance with 40 CFR 50.14 to be an exceptional event. Also, CAA section 319(b)(3)(B)(ii) requires that a clear causal relationship must exist between the measured exceedances of a NAAQS and the exceptional event to demonstrate that the exceptional event caused a specific air pollution concentration at a particular air quality monitoring location. In addition to these defining elements, the 2007 Exceptional Events Rule at 40 CFR 50.14(c)(3)(iv) requires that the demonstration provide evidence that “the event is associated with a measured concentration in excess of normal historical fluctuations, including background” and evidence that “there would have been no exceedance or violation but for the event.”

Both the statutory and regulatory definitions of an exceptional event include the provision that the event affected air quality. Many types of events affect air quality by causing emissions or increasing otherwise occurring emissions. Stratospheric ozone intrusions, one type of event, differ from most other event types in that they transport ozone already formed in the stratosphere to a surface monitor. High temperatures, air stagnations and meteorological inversions can increase the level of air pollution formed from a given amount of emissions. However, both the statutory and regulatory definitions of an exceptional event specifically exclude stagnation of air masses, meteorological inversions and meteorological events involving high temperatures or lack of precipitation, as well as air pollution relating to source noncompliance.

While the CAA definition of an exceptional event excludes “a meteorological event involving high temperatures or lack of precipitation,” high temperatures and drought conditions can contribute to exceedances and violations caused by other exceptional events such as high wind dust events. If an air agency submits evidence showing that a severe drought that resulted in arid conditions (

e.g.,

lower than typical soil moisture content, decreased vegetation) was combined with an event, such as a high wind event, that falls within the CAA definition of an exceptional event and has affected air quality data, these data could be considered eligible for exclusion under the provisions of the Exceptional Events Rule. Under this scenario, the EPA would consider the high wind event as the critical exceptional event. The high wind event would need to meet the provisions of the Exceptional Events Rule, including assessing whether the event is a natural event or an event due to human activity unlikely to recur at a particular location. As another example, if a wildfire exacerbated by drought conditions causes ozone exceedances, then the EPA can consider the ozone exceedances for exclusion under the Exceptional Events Rule because wildfires, unlike lack of precipitation itself, are not excluded from the CAA definition of an exceptional event. However, high temperatures alone that result in elevated ozone concentrations would not be eligible for exclusion under the

Exceptional Events Rule. Elevated temperatures and inversions can affect ambient air quality apart from any interactions with emissions, but such conditions alone are not exceptional events by the very clear provisions of the CAA. The EPA believes that Congress intended air agencies to compensate for the effects of high temperature and inversions on concentrations formed from anthropogenic emissions through the development of SIPs.

To summarize, the 2007 Exceptional Events Rule specifies six elements that air agencies must address when requesting that the EPA exclude event-related concentrations from regulatory determinations:

• The event affected air quality.

• The event was not reasonably controllable or preventable.

• The event was a human activity that is unlikely to recur at a particular location, or was a natural event.

• There exists a clear causal relationship between the specific event and the monitored exceedance.

• The event is associated with a measured concentration in excess of normal historical fluctuations including background.

• There would have been no exceedance or violation but for the event.

Section 50.14(b)(3) clearly makes the first three of these elements preconditions for the EPA to approve an air agency's request to exclude data. However, the last three of these elements are listed only in § 50.14(c)(iv), which provides that the state “shall provide evidence” that they are true. Since promulgation of the 2007 Exceptional Events Rule, the EPA has treated all six elements as conditions that air agencies must address in a demonstration prior to the EPA's concurring with an air agency's request to exclude data. In the Interim Exceptional Events Implementation Guidance, the EPA stated that for the fifth of these elements (

e.g.,

the “historical fluctuations” element), there is no bright line that defines when a concentration is “in excess of historical fluctuations.” With respect to the sixth element, referred to as the “but for” criterion, although the EPA has, in some cases, expected demonstrations to contain a quantitative estimate of the concentration increment caused by the event, more frequently the EPA has considered the “but for” criterion to be satisfied by a more qualitative showing that the measured concentration was much greater than the non-exceedance concentration that would have normally been expected on the day in question.

In addition to considering whether or not an event is “exceptional” under the Exceptional Events Rule, an air agency and the EPA must also decide whether an “event” has occurred. An event, or anomaly, is a deviation from normal or expected conditions that contributes to air pollution. In some cases, air agencies or other observers can clearly see this “deviation,” for example unusually high wind speeds transporting dust, fires generating PM or ozone precursors or volcanoes venting plumes of SO

, PM and PM precursors.

In other cases, such as with stratospheric ozone intrusions, the physical effects of the event may not be visible and the occurrence of an event can only be inferred from seeing the effect on monitored air quality of emissions associated with the event. As described in section V.E.3, comparing the ambient pollutant concentrations in question to the historical distribution of concentrations of the same pollutant can help an air agency determine whether a deviation from normal concentrations occurred. However, such comparisons must consider that multiple factors often contribute to high pollutant concentrations. Some events, such as stratospheric ozone intrusions and high wind dust events, may last only a few hours at any one location. Still other events, such as volcanic activity, may occur and affect pollutant concentrations for a sustained period of time (

e.g.,

multiple days). Some events may create pollutant-increasing conditions that persist after the original event process has ceased, for example high winds or volcanic eruptions that leave deposits of dust on roadways.

The EPA considers on-going emissions from volcanic activity to be “events” even if they occur every day over a long period. The EPA considers this approach to be consistent with Congressional intent, but that extending the same treatment to air pollution due to every day biological processes or lightning would not be consistent with that intent.

2. Proposed Changes

The EPA is proposing the following generally applicable changes to the 2007 Exceptional Events Rule with respect to clarifying what constitutes an exceptional event:

• Revising the definition of exceptional event by including the concept of considering the combined effects of an event and the resulting emissions.

• Removing the “but for” element.

• Moving the “clear causal relationship” element into the list of criteria that explicitly must be met for data to be excluded.

• Subsuming the “affects air quality” element into the “clear causal relationship” element.

• Removing the term “historical fluctuations” and replacing it with text referring to a comparison to historical concentrations, identifying the types of analyses that are necessary in a demonstration to address the comparison of the event-affected concentration to historical concentrations and clarifying that an air agency does not need to prove a specific “in excess of” fact.

Making these changes would result in returning to the following three core statutory elements of CAA section 319(b) that air agencies must meet when requesting that the EPA exclude event-related concentrations from regulatory determinations:

• The event affected air quality in such a way that there exists a clear causal relationship between the specific event and the monitored exceedance or violation.

• The event was not reasonably controllable or preventable.

• The event was a human activity that is unlikely to recur at a particular location or was a natural event.

The implicit intent of CAA section 319(b) is that when the above conditions are met, the data should be excluded from regulatory decisions so as not to drive SIPs to include unreasonable or additional measures to address the effects of certain events.

a. Definition of an Event

While an event may have a physical component that is purely natural in origin, for example high wind speeds, human activity either prior to or simultaneous with the event may influence air quality during the event. In implementing the 2007 Exceptional Events Rule, the EPA's approach in determining whether an exceptional event that affected a monitored concentration was natural or due to human activity (an important distinction, as discussed in section V.D) has been to consider both whether the initiating physical event was natural or the result of human activity and whether human activity had any role in strengthening the emissions generation process. In contrast, some parties have argued that only the naturalness of the initiating physical event should be considered. To clarify that an event is not a “natural event” merely because natural processes initiated the emissions generation process, the EPA proposes to revise the regulatory definition of exceptional event to say that both the naturally occurring physical event and its associated resulting emissions are to

be considered when applying the definitions and criteria for exclusion provided in the Exceptional Events Rule. For example, an exceptional event might consist of a high wind and the subsequently entrained PM that is transported to a monitoring site or a wildfire that generates ozone or ozone precursors, which are transported to a monitoring site. The EPA would not consider the physical event (

e.g.,

in the previous example, the high wind or the wildfire) to be an exceptional event unless the resulting emissions (

e.g.,

the PM or ozone) reached and elevated the concentration at a monitoring location or locations.

b. “But For” Element

The EPA proposes to rely more directly upon the statutory requirement at CAA section 319(b)(3)(B)(ii) by removing the regulatory requirement at 40 CFR 50.14(c)(3)(iv)(D) that “there would have been no exceedance or violation but for the event” (

i.e.,

the “but for” criterion). In promulgating the 2007 Exceptional Events Rule, the EPA derived the “but for” criterion from the language at section 319(b)(3)(B)(ii), which requires “a clear causal relationship. . . between the measured exceedances . . . and the exceptional event to demonstrate that the exceptional event caused a specific air pollution concentration at a particular air quality monitoring location.”

The EPA combined this language with the requirement that there be “criteria and procedures for the Governor of a State to petition the Administrator to exclude . . . data that is

directly due

to the exceptional events.”

Under the EPA's interpretation of CAA section 319(b) at the time, these words suggested that a “but for” causation standard for exceptional events was appropriate.

The EPA believes that the terminology “specific air pollution concentration” refers to the identified exceedance or violation rather than a specific increment in the measured concentration, which implies quantitative source attribution and a supporting quantitative analysis.

CAA section 319(b)(3)(B)(iv) (emphasis added).

Air agencies have expressed concern that the EPA has, in many cases, historically interpreted the “but for” criterion as implying the need for a strict quantitative analysis to show a single value, or at least an explicitly bounded plausible range,

of the estimated air quality impact from the event. While a single event can in some cases clearly be shown to be a “but for” cause of a NAAQS exceedance or violation in the sense that without the event, the exceedance or violation would not have occurred, it is more often the case that the impact of emissions from events and other sources cannot be separately quantified and distinguished, and the “but for” role of a single source or event is difficult to determine with certainty. Even when the effects of events are quantifiable with a sufficient degree of confidence, air agencies have reported expending significant resources to quantify them. The EPA was aware of these concerns in 2007 as a result of public comment on the proposed rule and attempted to alleviate them by stating in the preamble to the 2007 Exceptional Events Rule that an air agency's “but for” analysis does not necessarily need to be precise and that the EPA would use a holistic “weight of evidence” approach in analyzing submitted demonstration packages.

Without clear examples of what the EPA would accept as satisfying a weight of evidence approach, some air agencies began using burdensome approaches to provide quantitative “but for” analyses in their exceptional events demonstrations. The reviewing EPA Regional offices use similarly resource-intensive approaches to validate these quantitative analyses as they review demonstrations. In some cases, the detailed quantitative approaches have not produced results any better than what could have been achieved with less burdensome measures. Therefore, the EPA is proposing to remove the “but for” regulatory language and focus on the “clear causal relationship” statutory criterion applied to the specific case, using a weight of evidence approach.

The EPA stated in the preamble to the 2007 Exceptional Events Rule that a “weight of evidence demonstration can present a range of possible concentrations, which is not as technically demanding as justifying a specific adjustment to a measured value.” 72 FR 13570 (March 22, 2007).

72 FR 13570 (March 22, 2007).

The term “weight of evidence” means that the EPA will consider all relevant evidence and qualitatively “weigh” this evidence based on its relevance to the Exceptional Events Rule criterion being addressed, the degree of certainty, its persuasiveness, and other considerations appropriate to the individual pollutant and the nature and type of event.

In so doing, we propose that in their submittals, air agencies demonstrate by the weight of evidence in the record that the event caused the specific air pollution concentration at issue.

Depending on the event characteristics and the case-by-case nature of the evaluation, an air agency may or may not need to provide quantitative analyses or estimates to support the weight of evidence approach. The EPA will discuss with an air agency the appropriate approach for a given event demonstration during conversations preceding the submittal of a demonstration. For example, when a concentration during an event is higher than any concentration previously observed in the same area and time of year, the air agency will generally not need to quantify the event impact to reach the conclusion that the event “caused” the concentration at issue. However, in cases where the concentrations on non-event days during the same season come close to or exceed the applicable NAAQS, thus providing evidence that non-event pollution sources may produce exceedances of the NAAQS, the EPA would expect an air agency's clear causal relationship showing to include a quantitative estimate (or range of estimates) of the specific event's impact on air pollution concentrations, even if uncertain, as a part of a weight of evidence showing alongside other qualitative evidence. Section V.E.3 of this proposal clarifies the EPA's expectations regarding analyses associated with the “clear causal” criterion.

This approach is consistent with language in the preamble to the 2007 Exceptional Events Rule that states, “The final rule permits a case-by-case evaluation, without prescribed threshold criteria, to demonstrate that an event affected air quality.” 72 FR 13569 (March 22, 2007).

c. Clear Causal Relationship Element

The EPA is proposing to modify the regulatory language in section 50.14(c)(iv) to more clearly indicate, consistent with the CAA directive, the requirement to “demonstrate” versus to merely “provide evidence” that a clear causal relationship must exist between the specific event and the monitored exceedance. The EPA will evaluate this criterion on a weight of evidence basis.

d. Affects Air Quality Element

As explained above, the EPA has treated the “affects air quality” element as a distinct criterion that air agencies must meet for data to be excluded, and has expected exceptional events demonstrations to conclude that the “affects air quality” condition has been satisfied. However, after carefully considering Congress' intent and air agencies' and the EPA's experience in implementing the 2007 Exceptional Events Rule, we propose to integrate the phrase “affected air quality” into the clear causal relationship criterion. We believe that separately requiring an air agency to provide evidence to support a conclusion that an event “affects air quality” is unnecessary if we finalize this proposal to require a mandatory clear causal relationship showing. If an air agency demonstrates that an event has a clear causal relationship to an exceedance or violation of a NAAQS,

then the event has certainly affected air quality. This proposed approach will reduce the time required to prepare demonstrations, reduce their length, result in more understandable demonstrations for the public during the notice-and-comment process, and simplify and expedite the EPA's review process.

e. Historical Fluctuations Element

As we indicated in the Interim Exceptional Events Implementation Guidance, we believe that a comparison of the claimed event-influenced concentration(s) to concentrations at the same monitoring site at other times is extremely useful evidence in an exceptional events demonstration. The EPA considers these comparisons as part of the evidence available for determining whether an air agency has satisfied the statutory and regulatory “clear causal relationship” criterion. Because preparing this type of comparison is within the ability and resources of every air agency, the EPA proposes to continue to require this type of comparison in every demonstration. However, the EPA is proposing to re-word the requirement to prevent misinterpretation that this comparison must show that the concentration in question was “in excess of normal historical fluctuations, including background.” This phrase is not clear and has caused confusion and regulatory uncertainty. For example, “fluctuations in concentrations” can convey either day-to-day or hour-to-hour differences in monitored concentrations. These concentration differentials cannot usefully be compared to an absolute concentration (

i.e.,

monitored concentration at a given point in time) because many absolute concentrations will be larger than the differences between concentrations. The phrase “in excess” might be interpreted to mean that the concentration at issue must be higher than all historical concentrations, but the EPA maintains that Congress did not intend this, nor would such an interpretation be reasonable. Concentrations that are exceedances of a standard but are not higher than all concentrations recorded at a particular monitor may be causally connected to an event of the type that Congress clearly identified for treatment as an exceptional event. Finally, the language “including background” is confusing. In many cases, the monitor or monitors intended to represent “background” concentrations are separated from the event-influenced monitoring site by some distance such that the event-influenced monitor and the “background” monitor reflect a different mixture of emissions sources, which could lead to misinterpretation. Regardless, the EPA sees no clear reason why such “background” concentrations are relevant for analyses associated with provisions in the Exceptional Events Rule.

The change that the EPA is proposing to the text of the 2007 Exceptional Events Rule would require demonstrations to include a comparative analysis of the concentration data alleged to have been affected by an event and data at other times, and would specify certain aspects of the analysis. The change would also make clear that there is no specific “in excess of” relationship between the event-affected data and other data that must be proven, for example that the event-affected data be above a certain percentile point in the annual distribution of data. Section V.E.3 of this proposal contains additional detail regarding the minimum set of statistical analyses that the EPA expects to see in demonstrations.

C. What types of ambient concentration data and data uses may be affected by the Exceptional Events Rule?

The CAA language at section 319(b)(3)(B)(iv) requires the Administrator to promulgate regulations that provide that there are criteria and procedures for the governor of a state to petition the Administrator to exclude air quality monitoring data that is directly due to exceptional events from use in

determinations by the Administrator with respect to exceedances or violations of the national ambient air quality standards

. The implementing language in the 2007 Exceptional Events Rule states at 40 CFR 50.14(a)(1) that air agencies may request that the EPA exclude data showing exceedances or violations of the NAAQS that are directly due to an exceptional event from use in determinations without naming those determinations in that paragraph. The rule at 40 CFR 50.14(b)(1) states that the EPA shall exclude data from use in determinations of exceedances and NAAQS violations where an air agency demonstrates to the EPA's satisfaction that an exceptional event caused a specific air pollution concentration in excess of one or more NAAQS. Thus, both the statutory language and the 2007 Exceptional Events Rule use the phrase “in determinations of exceedances and NAAQS violations” with no further explanation.

In this section, we consider the specific types of determinations by the Administrator that should be governed by CAA section 319(b). This issue was not specifically addressed in the rulemaking that promulgated the 2007 Exceptional Events Rule and consequently has caused some confusion and regulatory uncertainty.

1. Current Situation

The EPA believes that Congress clearly intended the CAA language in section 319(b) to apply to exclusions of ambient data from determinations of whether a NAAQS exceedance or violation occurred at an ambient monitoring site at a particular time in the past. We characterize these exceedances or violations as occurring in the “past” because the process of determining whether an actual exceedance or violation occurred involves reviewing the ambient air monitoring data collected at monitoring sites over some historical timeframe. For example, on December 14, 2012, the EPA promulgated a revised primary annual PM

2.5

NAAQS of 12.0 μg/m

, which is attained when the 3-year average of the annual arithmetic means does not exceed 12.0 μg/m

The EPA Administrator made initial area designation decisions for the revised NAAQS in December 2014 based on air quality monitoring data for the most recent period 3-year period, which was 2011 through 2013.

Historical, or “past,” data were reviewed and assessed to determine whether an exceedance or violation had occurred that would influence a current or future regulatory determination. Determinations of “past” exceedances or violations are key to the EPA's actions to designate or redesignate an area, to initially classify an area for a NAAQS (where classifications apply), to determine if a nonattainment area has attained the NAAQS for which it has previously been designated nonattainment, to determine whether a nonattainment area is eligible for an attainment date extension (where applicable) and, in some cases, to find that a SIP is inadequate and to issue a SIP call. No affected stakeholders with whom the EPA has interacted since 2007 have disputed this interpretation or approach.

78 FR 3086 (January 15, 2013).

80 FR 2206 (January 15, 2015).

It is not as clear whether CAA section 319(b) also means that data should be excluded from determinations of whether a NAAQS exceedance or violation will or is likely to occur in the future. Predictions of future NAAQS violation(s) generally involve reviewing the historical ambient concentration data that are the evident focus of CAA section 319(b), estimating expected

future emissions, and then using both of these data sets as inputs to an air quality modeling tool or other analytical approach that extrapolates these data to predict a future outcome. While science supports and the EPA relies on predictions of future NAAQS violations in several parts of the clean air program, such as in the EPA's approval of attainment demonstrations in SIPs, in prevention of significant deterioration (PSD) air permitting programs and in actions to reclassify a moderate PM

or PM

2.5

nonattainment area to serious,

the fact that these predicted future values rely only in part on historical monitoring data implies that a different standard for data exclusion may be appropriate.

Projection of future NAAQS exceedances or violations do not necessarily play a role in reclassification of an ozone nonattainment area to a higher classification level.

Another interpretation question is whether and under what conditions event-affected data should be excluded from determinations that are based wholly or in part on monitoring data but formally are not determinations of exceedances or violations of the NAAQS. For example, under 40 CFR part 51, subpart H, Prevention of Air Pollution Emergency Episodes, the required content of a state's emergency plan depends on whether the state has experienced air pollution that exceeds a specified threshold level that is well above any NAAQS. Also, under the EPA's guidance, the eligibility of an area for a simplified maintenance plan for PM

depends on the difference between the better-than-the-NAAQS air quality in an area and the NAAQS.

To date, the EPA has not issued guidance that explicitly and comprehensively identifies the types of data exclusion that are authorized and required by CAA section 319(b) or that may be otherwise appropriate and permissible. In the 2013 Interim Q&A document, the EPA provided only limited clarification regarding the meaning of “exclude data.”

Question 14a of the Interim Q&A document notes that when the EPA concurs based on the weight of evidence that an air agency has successfully made the demonstrations referred to in 40 CFR 50.14(a)(2) and (b)(1), then the EPA generally excludes the affected data from the following types of calculations and activities:

Interim Exceptional Events Rule Frequently Asked Questions

. U.S. EPA. May 2013. Available at

http://www2.epa.gov/sites/production/files/2015-05/documents/eer_qa_doc_5-10-13_r3.pdf

• The EPA's AQS does not count these days as exceedances when generating user reports, and does not include them in design values estimates,

unless the AQS user specifically indicates that they should be included, which may be appropriate for non-regulatory applications of interest to the user.

The EPA uses design values in many regulatory decisions, including, but not limited to, when designating areas as attainment, nonattainment or unclassifiable for a NAAQS and when determining whether a nonattainment area has attained or is still violating a NAAQS. A design value is a statistic that describes the air quality status of a given location relative to the level of a particular NAAQS. Design values are computed according to the procedures defined in 40 CFR part 50 and published annually by EPA's Office of Air Quality Planning and Standards. Design values are available at

http://www.epa.gov/airtrends/values.html.

In some cases where the EPA has revised a NAAQS by strengthening it, the default AQS query will exclude data for the more recent, revised NAAQS, but may include concurred data for the historical NAAQS.

• The EPA accepts the exclusion of these data for the purposes of selecting appropriate background concentrations for PSD air quality analyses

and for transportation conformity hot spot analyses.

If the EPA is the permitting authority, the EPA will propose permits on this basis. If the EPA is commenting on another permitting authority's proposed action, the EPA's comments will be consistent with the determinations in this guidance document and any applicable New Source Review (NSR) permitting and/or modeling guidance.

Transportation conformity hot spot analysis is applicable only to PM

and PM

2.5

. “Transportation Conformity Guidance for Quantitative Hot-spot Analyses in PM

2.5

and PM

Nonattainment and Maintenance Areas,” EPA-420-B-10-040, U.S. EPA Office of Transportation and Air Quality, December 2010, page 98.

• The EPA accepts the exclusion of these data for the purposes of selecting appropriate ambient data for projecting future year concentrations as part of a modeled attainment demonstration.

• The data continue to be publicly available, but the EPA's publications and public information statements on the status of air quality in the affected area generally do not reflect these data in any summary statistic of potential regulatory application, unless such inclusion is specifically noted.

These data may be included in statistics intended to describe current status and trends in actual air quality in the area for public information purposes including reporting of the Air Quality Index.

Thus, the EPA has maintained that once data are excluded under the Exceptional Events Rule, these same data should be excluded from the above-identified calculations and activities. The EPA has not clearly addressed whether approval for exclusion under the Exceptional Events Rule means that the data may or must be excluded for the purpose of other types of actions that use monitoring data but are not included in the list above. The EPA has also not clearly addressed whether data that have

not

been approved for exclusion under the Exceptional Events Rule can nevertheless under some other principle or interpretation be excluded from any of the various types of calculations and activities.

The current situation is further complicated by the fact that the conditions for data exclusion in CAA section 319(b) and the Exceptional Events Rule, while logical when applied to determinations of NAAQS exceedances or violations occurring in the past, may not be logical when applied to predictions of future exceedances or violations. The EPA recognizes, and acknowledged in Question 13 of the Interim Q&A document, that an event may have made a past air concentration significantly higher than it would have been in the absence of the event contribution, and thus elevated an exceedance for a NAAQS pollutant to an even greater degree of exceedance. This same event-influenced concentration may not be eligible for exclusion under the 2007 Exceptional Events Rule because the “but for” criterion is not satisfied because either (1) there would have been a 3-year violation with or without the event or (2) there would not have been a violation either with or without the event. The 2007 Exceptional Events Rule does not explicitly authorize the exclusion of data associated with such an event because the event fails to meet the clear causal relationship criterion and “but for” criterion. Retaining the event-influenced data could, however, have regulatory implications that seem contrary to the purpose of CAA section 319(b). For example, retaining such data in the calculation of the historical design value for a nonattainment area can make it seem that the area needs more emissions reduction to attain the NAAQS than is actually the case, and could lead to the EPA's disapproval of an attainment demonstration that is in fact adequate, and thus require the state to adopt additional emission controls.

The attainment demonstration would be adequate in the sense that if a similar event does not occur during the period on which actual attainment will be based, there would be no monitored NAAQS violation, and if a similar event were to occur during that period the event-affected data could be excluded and thus there would be no “official” violation.

As another example, events can make past air concentrations higher without causing an actual NAAQS exceedance or violation. However, retaining such data in the calculation of background concentrations used in air quality analysis for a PSD permit may suggest that there will be a NAAQS violation after construction of a new source and

thus could prevent the permitting authority from issuing the permit.

If a similar event were to occur after completion of construction, the event-affected data could be excluded and thus there would be no “official” violation.

2. Proposed Changes

To remove the ambiguities described in the preceding section and to provide greater regulatory certainty, the EPA proposes in regulatory language to interpret the CAA section 319(b) phrase “determinations by the Administrator with respect to exceedances or violations of national ambient air quality standards” to encompass determinations of current

or historical NAAQS exceedances/violations or non-exceedances/non-violations and determinations of the air quality “design value” at particular receptor sites when made as part of the basis for any of the following five types of regulatory actions:

The term “current” denotes the determination at issue in the current analysis. In actual practice, such determinations are based on historical data and thus reflect a past actual condition.

• An action to designate or redesignate an area as attainment, unclassifiable/attainment, nonattainment or unclassifiable for a particular NAAQS. Such designations rely on a violation at a monitoring site in or near the area being designated.

• The assignment or re-assignment of a classification category (marginal, moderate, serious, etc.) to a nonattainment area to the extent this is based on a comparison of its “design value” to the established framework for such classifications.

• A determination regarding whether a nonattainment area has actually attained a NAAQS by its CAA deadline.

• A determination that an area has had only one exceedance in the year prior to its deadline and thus qualifies for a 1-year attainment date extension, if applicable.

• A finding of SIP inadequacy leading to a SIP call to the extent the finding hinges on a determination that the area is violating a NAAQS.

For these types of actions, the EPA proposes to interpret the CAA to require that data be excluded only if the requirements of section 319(b) and the Exceptional Events Rule are satisfied. In addition, we propose that when one of these determinations is based on a combination of monitoring data and air quality modeling, the criterion requiring that there be a clear causal relationship between the event and a NAAQS exceedance or violation will apply to the combined estimate of air pollution levels rather than directly to the monitored background air quality data. That is, the event would not be required to have caused an actual exceedance or violation at the background ambient monitoring site, but rather to have made the critical difference in the combined estimate of air pollution levels (background plus source impact) resulting in a NAAQS exceedance or violation, because the event increased the background levels that are added to the air quality modeling output.

When the EPA designates or redesignates areas as attainment or nonattainment for the NAAQS; initially classifies ozone nonattainment areas as marginal, moderate, serious, severe or extreme; grants a request for a 1-year NAAQS attainment date extension where applicable; or determines whether areas designated nonattainment for the NAAQS have attained the respective NAAQS by the applicable attainment date, it does so based on monitoring data (where available) or modeling of actual air quality, or a combination thereof, as the evidence of the occurrence or non-occurrence of a NAAQS exceedance or violation and, in the case of classification actions, the degree of violation.

In the case of reclassifying an ozone nonattainment area to a higher classification, the new classification is based on the design value either at the time of the determination of attainment by the attainment deadline under CAA section 181(b)(2), or at the time of the EPA's grant of a voluntary request for reclassification from a state under CAA section 181(b)(3).

This proposal, if finalized, would in effect apply the exceptional events process in the same way across these related types of determinations and across the NAAQS, which we believe is an appropriate interpretation of the CAA 319(b) phrase “determinations by the Administrator with respect to exceedances or violations of national ambient air quality standards.” For these types of determinations, the EPA proposes to exclude event-affected data only if an air agency satisfies the procedural (

e.g.,

event identification, opportunity for public comment, demonstration submission) and substantive (

i.e.,

clear causal relationship, not reasonably controllable or preventable, and human activity not likely to recur or natural event) requirements of the exceptional events process. As indicated previously, the EPA has maintained to this point that once data are excluded under the Exceptional Events Rule, these same data also should be excluded from (i) design value estimates and AQS user reports (unless the AQS user specifically indicates that they should be included), (ii) selecting appropriate background concentrations for PSD air quality analyses and transportation conformity hot spot analyses, and (iii) selecting appropriate ambient data for projecting future year concentrations as part of a modeled attainment demonstration. As described below, we intend that EPA approval for exclusion of data under the Exceptional Events Rule continue to mean that the same data may be excluded for the three applications listed in the previous sentence, but that there should be other pathways for exclusion for the second and third of these applications (and others) as well.

The EPA's initial area designations process also makes use of other information relevant to the CAA criteria for designations, such as pollution contributions between nearby areas.

Reclassification of PM

and PM

2.5

nonattainment areas, by contrast, do not exclusively rely on area design values (and thus, past monitored violations) but can also result from the Administrator's determination that an area cannot practicably attain a standard by the attainment date.

See

CAA section 188(b)(1).

This action proposes to require that data exclusion associated with the five actions in the above bulleted list (

i.e.,

initial area designations, classifications, attainment determinations, determinations regarding requests for attainment date extensions and findings of SIP inadequacy leading to a SIP call) must follow the provisions in the Exceptional Events Rule. It does not, however, mean that the EPA would never exclude or agree to exclude event-affected data from other types of regulatory determinations. For example, while the EPA would exclude concurred-upon event-affected data from the five types of regulatory actions discussed in V.C.1, the EPA would

not

exclude these same data when setting priority classifications for emergency plans under 40 CFR 51.150 as the EPA believes that implementing the CAA principle at section 319(b)(3)(A) that “protection of public health is the highest priority” may necessitate that an air agency address in its emergency plan the appropriate planned response for any elevated concentration known to be possible because it has already been observed, although the appropriate type of response may depend on the cause(s) of the elevated concentration. The concept that the EPA does not consider CAA section 319(b) and the revised Exceptional Events Rule to be the necessary or sole governing authorities for

all

data exclusions will be discussed further in upcoming, new draft guidance on excluding (or in some cases not excluding) data, independent of the Exceptional Events Rule, from several

types of determinations and regulatory actions. The EPA is currently developing a supplementary guidance document,

Draft Guidance for Excluding Some Ambient Pollutant Concentration Data from Certain Calculations and Analyses for Purposes Other than Retrospective Determinations of Attainment of the NAAQS,

which will describe the appropriate additional pathways that we intend to make available for data exclusion for some monitoring data applications (

e.g.,

predicting future attainment that is the basis for approval of an attainment demonstration in the SIP for a nonattainment area, preparing required air quality analyses in an application for a PSD permit or preparing required air quality analysis for the purposes of transportation conformity). The EPA intends to post the draft guidance on the exceptional events Web site at

http://www2.epa.gov/air-quality-analysis/treatment-data-influenced-exceptional-events

and expects to finalize the document when we finalize these rule revisions. We intend that this guidance will recommend exclusion of data for PSD, transportation conformity and certain other applications in any situation in which exclusion has already been approved under the Exceptional Events Rule, as well as in applications in which the facts would support exclusion under the criteria of the Exceptional Events Rule even if an EPA determination has not yet been made under the Exceptional Events Rule and in some other situations that we will describe in the guidance.

D. What is a natural event?

1. Current Situation

The CAA definition at section 319(b)(1)(iii) specifies that an exceptional event “is an event caused by human activity that is unlikely to recur at a particular location or a natural event.” Thus, the statute limits the expected occurrence frequency of an event caused by human activity as “unlikely to recur” but does not limit the occurrence frequency of a natural event. Natural events may recur, even frequently.

Air agencies can request, and the EPA can agree, to exclude data affected by a natural event if an air agency's demonstration meets the other requirements of the Exceptional Events Rule. Thus, considering whether an event was a natural event or was caused by human activity is important to the content within and to the approval of a demonstration.

See

as examples, Hawaii's exceptional events demonstration for volcanic activity affecting PM

2.5

concentrations in 2011-2012 and California Air Resources Board's demonstration for wildfire events affecting PM

2.5

concentrations in 2008, both available at

http://www2.epa.gov/air-quality-analysis/exceptional-events-submissions-table.

As previously discussed, to be considered an exceptional event, an event, whether natural or anthropogenic in origin, must affect air quality at the affected monitor. 40 CFR 50.1(k) defines a natural event as one in which human activity plays little or no direct causal role in the generation of emissions. In some cases, such as stratospheric ozone intrusions or volcanic eruptions, the EPA recognizes that human activity plays no role in the magnitude of emissions or level of air pollution that occurs. In other cases, past or current human activity does influence the magnitude of emissions and hence the level of air pollution. For example, in high wind dust events, the pollution from the event may originate from a mixture of natural lands (

e.g.,

undisturbed soil), soil that has been disturbed by human activity and has been made more prone to wind-generated dust emissions (

e.g.,

recent construction activity), and materials accumulated and stored by human activity (

e.g.,

sand and gravel facilities).

The EPA generally considers human activity to have played little or no

direct

role in causing emissions if anthropogenic emission sources that contribute to the event emissions are reasonably controlled at the time of the event, regardless of the magnitude of emissions generated by these reasonably controlled anthropogenic sources and regardless of the relative contribution of these emissions and emissions arising from natural sources in which human activity has no role.

34 35

Thus, the event could be considered a natural event. In such cases, the EPA applies the reasonable interpretation that the anthropogenic source had “little” direct causal role. If anthropogenic emission sources that contribute to the event emissions can be reasonably controllable but reasonable controls were not implemented at the time of the event, then the event would

not

be considered a natural event. The EPA explained this concept in the preamble to the 2007 Exceptional Events Rule.

However, the rule text did not reflect the identified concept. This has resulted in some regulatory uncertainty as to whether the EPA's interpretation of the CAA and the 2007 Exceptional Events Rule as described here is appropriate.

For example, if an area affected by a high wind dust event has adequate rules or ordinances for sources of windblown dust (

e.g.,

rules that establish restrictions for operating vehicles on unpaved property, rules that control windblown dust emissions associated with lands disturbed by construction, earthwork and land development) and the air agency can provide evidence of implementation and enforcement, then the EPA would generally consider human activity to have played little or no direct causal role in causing the event-related emissions.

The EPA considers wildfires to be natural events even though some wildfires are initiated by human actions and to some degree the frequency and scale of wildfires may be influenced by prior land management practices. The EPA believes this interpretation best implements the Congressional intent and is a more appropriate approach than expecting air agencies to determine the initial cause of each wildfire of interest and classifying it as natural or anthropogenic based on that cause. In addition, land owners and managers and government public safety agencies are strongly motivated to reduce the frequency and severity of human-caused wildfires and the EPA believes they can be presumed to make reasonable efforts to avoid them.

72 FR 13565-13566 (March 22, 2007).

2. Proposed Changes

Based on the discussion above, the EPA proposes to revise the definition of natural event to clarify that anthropogenic emission sources that contribute to the event emissions that are reasonably controlled do not play a “direct role” in causing emissions. Thus, an event with a mix of natural emissions and reasonably controlled human-affected emission sources may be considered a natural event. However, an event resulting from

only

reasonably controlled human affected emissions may not be considered a natural event. This proposal is consistent with statements made in the preamble to the 2007 Exceptional Events Rule, and including it in the rule text provides more regulatory certainty to all parties.

When addressing the not reasonably controllable or preventable criterion for this same event type consisting of a mix of natural emissions and human-affected emission sources (

e.g.,

a high wind event affecting both open desert areas and urbanized lands), air agencies must assess reasonable controls for both the contributing natural and anthropogenic sources. While air agencies must “assess” reasonable controls for most types of contributing natural sources because this statutory factor applies to all events, they do not necessarily need to implement controls for these same sources. Additionally, because the rule revisions propose a categorical presumption of not reasonably controllable for wildfires and large-scale, high-energy and/or sudden high wind dust events, “assessing” these events would involve referencing the appropriate regulatory citation. As we explain in more detail in section V.E.2, for natural sources, we do not think that air agencies need to have implemented any controls for windblown dust from never-disturbed,

large-scale natural landscapes. Therefore, lack of controls on natural sources that contribute to event-related emissions would not disqualify the event from being considered as an exceptional event. When assessing the contribution from anthropogenic sources, similar to the analyses involved in determining whether these same sources play a “direct role” in causing event-related emissions, the air agency should identify the contributing anthropogenic sources, explain why the controls specified in rules or ordinances are reasonable, and provide evidence of implementation and enforcement. Also as explained in section V.E.2, in our view an event is “not reasonably controllable” if an exceedance or violation occurs even when reasonable controls were actually in place and any further control would have been beyond what was reasonable. The EPA intends to consider these aspects when applying the concept of “reasonable controls” on anthropogenic sources to determine whether the event can be considered a natural event and to evaluate the not reasonably controllable or preventable criterion.

With respect to determining whether anthropogenic emission sources that contribute to the event emissions were reasonably controlled at the time of the event, the EPA also proposes to revise the definition of a natural event to indicate that the reasonableness of available controls should be assessed as of the date of the event. The EPA does not believe that information related to the cost and effectiveness of control measures, or related to the frequency of events, that became available to the air agency after the date of the event should affect the assessment of whether anthropogenic sources were reasonably controlled and thus the identification of an event as natural or caused by human activity.

When addressing this criterion as part of an exceptional events demonstration, the EPA recommends that the submitting air agency clearly identify whether the event is natural or was a human activity that is unlikely to recur at a particular location. If purely natural (

e.g.,

lightning-ignited wildfire, volcanic or seismic activity, stratospheric ozone intrusion), the EPA recommends that the submitting air agency identify the purely natural status in the “human activity/natural event” section of its demonstration; provide the type/source of event, the resulting emissions, and the documented frequency of the event; and affirmatively state that in characterizing the event, the submitting air agency has satisfied the human activity/natural event criterion.

E. Technical Criteria for the Exclusion of Data Affected by Events

As described in section V.B, the EPA proposes to return to the core statutory elements and implicit concepts of CAA section 319(b): That the event affected air quality in such a way that there exists a clear causal relationship between the specific event and the monitored exceedance or violation, the event was not reasonably controllable or preventable, and the event was caused by human activity that is unlikely to recur at a particular location or was a natural event. All exceptional events demonstrations, regardless of event type or relevant NAAQS, must address each of these technical criteria. This section describes the EPA's proposals for rule revisions and guidance regarding each of these technical criteria. Section V.G discusses additional process-related components of exceptional events demonstration packages.

1. Human Activity Unlikely To Recur at a Particular Location or a Natural Event

The concept of recurrence applies to human activity; the statements in this section are not relevant for natural events. Section V.D includes a detailed discussion of a “natural event.”

a. Current Situation

According to both the regulatory and statutory definitions, an exceptional event must be “an event caused by human activity that is unlikely to recur at a particular location

a natural event” (emphasis added). For clarity, in this section, the EPA focuses on the language “unlikely to recur at a particular location.”

The “unlikely to recur at a particular location” requirement of CAA section 319(b) does not define “unlikely to recur.” Thus, this language requires interpretation on a case-by-case or event type-by-event type basis. The term “unlikely” implies consideration of the expected future frequency of events similar to the event that has already happened, but does not convey any particular benchmark for what frequency should be low enough to be considered “unlikely.” Also, the term “at a particular location” requires interpretation, as it could refer to the exact area or only to the general area of the event, to the location of the ambient monitoring station or stations that were affected by the event or to the combination of both.

The EPA's 1986

Guideline on the Identification and Use of Air Quality Data Affected by Exceptional Events

stated that events can be considered exceptional if they are not expected to “recur routinely at a given location.”

This document did not further define or give specific examples of “routinely.”

Guideline on the Identification and Use of Air Quality Data Affected by Exceptional Events

(the Exceptional Events Policy), U.S. EPA, OAQPS, EPA-450/4-86-007, July 1986.

The preamble to the 2007 Exceptional Events Rule did not provide specific guidance on the unlikely to recur criterion, except to say that recurrence is event-specific and should be assessed on a case-by-case basis and that in the particular case of prescribed fires a comparison to the natural fire return interval is a relevant consideration for this criterion.

The CAA section 319(b) and the 2007 Exceptional Events Rule do not specifically address temporary, but multi-day or multi-year activities, such as construction projects. However, Question 16 in the Interim Q&A document noted that the 2007 Exceptional Events Rule does not explicitly place a limit on the duration of a single event and that a submitting agency could make a showing that a prolonged activity (

e.g.,

a multi-year road construction project) is a single event that is not likely to recur at the location in question. The Interim High Winds Guidance document addressed recurrence for high wind events, as summarized in section V.F.4 of this document. Other than this, the Interim Exceptional Events Implementation Guidance did not provide any specific guidance on the unlikely to recur criterion.

b. Proposed Changes

While we believe that it is appropriate to consider recurrence to be event-specific and for the unlikely to recur criterion to be assessed on a case-by-case basis, we also believe that this proposed action presents an opportunity to clarify certain points. This section provides general clarifications with respect to the meaning of “unlikely to recur.” Section V.F.2 addresses this criterion for wildland fires (specifically prescribed fires on wildland) and section V.F.4 specifically addresses this criterion for high wind dust events. Also, under CAA section 319(b) and the 2007 Exceptional Events Rule, air pollution related to source noncompliance is not an exceptional event regardless of its frequency.

The EPA proposes, as guidance, to recommend the following boundaries on the interpretation of the unlikely to recur criterion. If an event type has not previously occurred within a given air

quality control region (AQCR)

in the 3 years preceding the submittal of an exceptional events demonstration, the EPA will consider this to be a “first” event and will generally consider it to be unlikely to recur in the same location. Similarly, a “second” event within the 3 years preceding the submittal of an exceptional events demonstration would also generally be considered unlikely to recur in the same location. If there have been two prior events of a similar type within a 3-year period in an AQCR, that would generally indicate the third event, for which the demonstration is being prepared (or would be prepared), does not satisfy the “human activity that is unlikely to recur at a particular location” criterion and, thus, would not qualify as an exceptional event. The terms “first” and “second” events refer to events that affect the same AQCR, even if they have not affected the same monitor.

This proposed guidance is consistent with the approach taken to recurrence in our Interim High Winds Guidance document in which we identified non-recurring events as being less than one event per year in a given area.

In the Interim High Winds Guidance, we did not define area other than to differentiate areas by attainment status or jurisdiction (

i.e.,

intrastate versus interstate or international).

Air Quality Control Regions are defined in 40 CFR part 81, subpart B, Designation of Air Quality Control Regions.

The EPA will consider previously flagged exceedances within AQS with their associated descriptions to be “events” regardless of whether the EPA has received or acted on event demonstrations. The EPA also notes that a single event could influence concentrations on multiple days.

See

footnote 27 in table 2 of

Interim 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.

U.S. EPA. May 2013. Available at

http://www2.epa.gov/sites/production/files/2015-05/documents/exceptevents_highwinds_guide_130510.pdf.

The EPA solicits comment on this proposed guidance regarding recurrence at a particular location, specifically the use of an AQCR to define the bounds for an area subject to event recurrence given that some AQCRs may be quite large. The EPA also solicits comments on whether this benchmark of three events in 3 years should be incorporated into the rule text, rather than being provided only as guidance.

The EPA proposes, as guidance, that to satisfy the documentation requirements for the “human activity that is unlikely to recur at a particular location” criterion, the submitting air agency should document and discuss, in a distinct “human activity/natural event” section of the demonstration, the type/source of event (

e.g.,

a particular type of chemical spill or other industrial accident or a fire in a particular type of structure), the resulting emissions and the documented frequency of the event in the prior 3 years. The demonstration should affirmatively state that in characterizing the event, the submitting air agency has satisfied the “human activity unlikely to recur at a particular location or a natural event” criterion.

2. Not Reasonably Controllable or Preventable

The CAA section 319(b) does not restrict the not reasonably controllable or preventable criterion to apply only to events caused by human activity. It also applies to natural events. Accordingly, the Exceptional Events Rule applies this criterion to all types of events. This section discusses the criterion in general terms. We discuss the criterion's applicability to fire events on wildland in section V.F.2 and to high wind dust events in section V.F.4.

a. Current Situation

As noted in section V.B of this document, the definition of an exceptional event at 40 CFR 50.1(j) repeats the CAA definition and includes the requirement at section 319(b)(1)(A)(ii) that an exceptional event, whether natural or caused by human activity, is one that “is not reasonably controllable or preventable.” Neither the rule text of the 2007 Exceptional Events Rule nor the preamble to the final rule provided additional clarification regarding this statutory element. Rather, the preamble to the final rule stated, “[w]e are not finalizing more detailed requirements for determining when an event is `not reasonably controllable or preventable' because we believe that such determinations will necessarily be dependent on specific facts and circumstances that cannot be prescribed by rule.”

While we maintain that determining whether or not an event is not reasonably controllable or preventable is event-specific and necessarily requires judgment by the air agency and the EPA, we also believe that some concepts regarding this criterion are broadly applicable.

72 FR 13564 (March 22, 2007).

To begin, the statutory requirement that an exceptional event is one that “is not reasonably controllable or preventable” contains two factors: Prevention and control. Within the context of the Exceptional Events Rule, we intend that “prevent” means to stop or avert the event, and “control” means to reduce the magnitude and impact of event-related emissions. We interpret CAA section 319(b) to mean that to qualify as an exceptional event, the event cannot be reasonably preventable and cannot be reasonably controllable, rather than that only one of the two elements must be satisfied. It would be contrary to the emphasis of section 319(b) on protection of public health if there were no requirement for reasonable control for an event merely because the event could not be reasonably prevented from happening. It is possible for an event to not be reasonably preventable, but to be reasonably controllable.

In this case, if emissions were reasonably controlled, then the event could be considered for concurrence as an exceptional event. It is also possible that an event be neither preventable nor its air quality impacts to be controllable to any degree, such as potential increases in SO

concentrations associated with volcanic eruptions.

For example, in section V.F.2, we propose that under certain circumstances a prescribed fire may not be reasonably preventable because of the safety or ecosystem benefits that would be foregone, but emissions and air quality impacts from the fire may be reasonably controllable through the application of basic smoke management practices.

The EPA considers the statutory requirement that an exceptional event be “not reasonably preventable” to mean that if a set of prevention measures

should reasonably have been in place

for anthropogenically-influenced emission sources that contribute to the event emissions, then those measures

must

have been in place for the event to qualify as an exceptional event under the Exceptional Events Rule. Similarly, we consider the statutory requirement that an exceptional event be “not reasonably controllable” to mean that if a set of control measures

should reasonably have been in place

for emission sources that contribute to the event emissions, then those controls

must

have been in place for the event to qualify as an exceptional event under the Exceptional Events Rule. Satisfying the not reasonably controllable element necessitates a showing of reasonable controls. Whether a set of controls constitutes “reasonable controls” is event-, time-, and place-dependent, and involves judgment by the air agency when preparing the demonstration and by the EPA when reviewing the demonstration.

We stated in the

Interim Exceptional Events Implementation Guidance, and we reiterate in this action, that it may not be reasonable to apply any prevention or control efforts for some events.

The EPA has many resources to help states identify appropriate control technologies and includes links to some of these sources on the Control Strategies Web site available at

http://www3.epa.gov/airquality/aqmportal/management/control_strategies.htm.

In the course of implementing the 2007 Exceptional Events Rule, both the EPA and air agencies have expressed concern regarding the determination of “reasonable” prevention or control efforts for particular events. When an air agency prepares a demonstration, it attempts to show that whatever efforts were made were all that were reasonable to make. When the EPA reviews a demonstration, we are responsible for determining if the demonstration is credible and convincing. The EPA has been unable to make this determination regarding reasonableness for some demonstrations because the content regarding the use and implementation of control measures is insufficient. Given the elasticity of the concept of “reasonable,” it is not surprising that disagreements have arisen. We have in the past few years, particularly since issuing the Interim Exceptional Events Implementation Guidance, worked with states to reach mutual understandings of what efforts are reasonable and to have those efforts in place before events happen. However, situations will likely occur in the future, as they have in the past, in which an assessment of reasonableness must be made retrospectively, when it is too late for the air agency to have applied greater efforts. The EPA recognizes that our action on the air agency's demonstration may have important regulatory consequences for the area in question.

The EPA has stated that for all types of events, we consider reasonableness in light of the technical information available to the air agency at the time the event occurred. An air agency “caught by surprise” by an event of a given type (or by an unexpected number of such events in a period over which NAAQS compliance is evaluated, typically 3 years) should not be expected to have implemented the same controls prior to an event as an air agency that has been aware that events of a certain type occur with regularity and cause NAAQS exceedances or violations. The EPA anticipates that nonattainment (or maintenance) areas have technical information needed to understand those measures that constitute reasonable control of anthropogenic sources in their jurisdiction for recurring events of the type(s) that cause or contribute to nonattainment (or that did previously). In contrast, the EPA generally does not expect areas identified as attainment, unclassifiable/attainment or unclassifiable for a NAAQS to have the same understanding or to have adopted the same level of event-relevant controls as areas that are nonattainment (or maintenance) for the same NAAQS. Also, if an area has been recently designated to nonattainment but is still developing its SIP and has not yet reached a deadline to implement controls, the EPA expects the level of controls that is appropriate for that planning stage.

Regardless of attainment status or natural/anthropogenic source contribution, each demonstration package should address the question of reasonable controls within the not reasonably controllable or preventable portion of the demonstration.

The CAA provides different timeframes for developing and implementing SIPs depending on the NAAQS and the nonattainment area's classification (

e.g.,

severity of the nonattainment problem). The EPA recognizes that within the SIP development and implementation process, some measures may be implemented relatively quickly (

e.g.,

transportation conformity, new source review) whereas other programs, such as development or rules for particular source types, can take time and involve state legislative processes.

The not reasonably controllable or preventable criterion is a source of particular complexity when an event occurs outside the jurisdiction of the state that is requesting that data be excluded. The area outside a state's jurisdiction may be in an area of Indian country, in another state, or in a foreign country. For these cases, the air agency requesting data exclusion, and other government authorities in the state, generally do not have regulatory authority over those who might have been able to prevent or control the event. Therefore, the EPA believes that event-related emissions that originate outside of the boundaries of the state within which the concentration at issue was monitored are generally “not reasonably controllable or preventable” even if no party has made any effort to control or prevent them. To date, we have advised air agencies that an exceptional events demonstration for such a case must nevertheless explicitly address the question of reasonable efforts towards prevention and control. For these situations, we have suggested template language to the effect that satisfying the not reasonably controllable or preventable element could consist of an air agency stating that because the event occurred outside of its jurisdiction, the not reasonably controllable or preventable criterion is satisfied.

Because the reasonableness of controls for event-related emissions is case-specific, the EPA has not issued guidance that particular controls are reasonable or are not reasonable. The Interim High Winds Guidance document indicates sources of information that identify measures that an air agency and the EPA should consider. In that guidance, we said that if the EPA has approved a SIP revision to windblown dust controls within the past 3 years of the event, then an air agency can rely on the SIP-approved controls to satisfy a portion of a “prospective controls analysis.”

By this, we meant that we would agree with the air agency that for any high wind dust events in the next 3 years, implementation of the controls in the SIP would be sufficient to establish that those events are not reasonably controllable. In our discussions during the development of these proposed revisions of the Exceptional Events Rule, air agencies have urged us to give more deference to relevant controls in the EPA-approved SIPs. Some air agencies have recommended that we always accept that the controls in the approved SIP are all that should have reasonably been in place at the time of the event (and/or that we accept no controls if there are no controls in the approved SIP). We understand at least some of those recommending this approach to mean it to apply both to nonattainment and maintenance areas that have approved attainment or maintenance plans and to areas whose SIPs have been approved only with respect to less specific infrastructure SIP requirements.

Interim 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.

U.S. EPA. May 2013. Available at

http://www2.epa.gov/sites/production/files/2015-05/documents/exceptevents_highwinds_guide_130510.pdf.

b. Proposed Changes

The EPA generally plans to continue its past interpretations with respect to the “not reasonably controllable or preventable” criterion. We propose to codify in regulatory language key aspects of these past interpretations to reduce uncertainty for air agencies and other parties. Specifically, we are proposing changes to the text of the Exceptional Events Rule to indicate that:

• The not reasonably controllable or preventable criterion has two prongs, prevention and control. An air agency must demonstrate that an event was both not reasonably preventable and not reasonably controllable.

• An event is not reasonably preventable if reasonable measures to prevent the event were applied at the time of the event.

• An event is not reasonably controllable if reasonable measures to control the impact of the event on air quality were applied at the time of the event.

• The reasonableness of measures is case-specific and is to be evaluated in light of information available at the time of the event.

• No case-specific justification is needed to support the “not reasonably controllable or preventable” criterion for emissions-generating activity that occurs outside of the boundaries of the state (or tribal lands) within which the concentration at issue was monitored.

Under the CAA, the EPA generally considers a state (not including areas of Indian country) to be a single responsible actor. Accordingly, neither the EPA nor the 2007 Exceptional Events Rule provides special considerations for

intra

state 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). The EPA expects controls appropriate for the designation status of the county (or portion of the county) in which the emissions originate.

With regard to the last of these proposed rule text changes, the EPA maintains that it is not reasonable to expect the downwind air agency (

i.e.,

the state or tribe submitting the demonstration) to have required or persuaded the upwind foreign country, state or tribe to have implemented controls on sources sufficient to limit event-related air concentrations in the downwind state or tribal lands, nor does the EPA believe that Congress intended to deny the downwind state or tribe relief in the form of data exclusion within the context of the Exceptional Events Rule. Submitting (downwind) air agencies will, however, need to assess potential contribution from local and state-wide sources and submit evidence and statements supporting the other exceptional events criteria (

i.e.,

clear causal relationship and human activity unlikely to recur or a natural event).

In addition to proposing to codify the five current interpretations listed above, with regard to this criterion, we are proposing and requesting comments on changes from our current interpretations and changes in the rule text that are explained below in more detail.

Natural Events and Natural Sources.

The not reasonably controllable or preventable criterion applies to natural events, including natural sources and any contributing anthropogenic sources and activities.

The EPA proposes, as guidance, that to satisfy the not reasonably controllable or preventable criterion for natural events, air agencies should identify in their demonstration the origin and evolution of the natural event, describe any local efforts to prevent the event and explain how any efforts to limit the duration, intensity or extent (and thus the emissions) from the event were reasonable.

An event with a significant contribution from anthropogenically-influenced emissions sources that have not themselves been reasonably controlled cannot be considered a natural event subject to this provision.

Large-scale natural landscapes, such as deserts, are one type of natural source from which emissions can originate and contribute to event-related emissions. We propose, as guidance for these types of natural sources, that air agencies would not need to have implemented any controls for windblown dust from never-disturbed, large-scale natural landscapes. If such a landscape is the only source of wind-blown dust, the EPA would consider the event in this scenario to be not reasonably controllable or preventable regardless of the past frequency of similar events. Other such cases include volcanic releases of SO

and stratospheric ozone intrusions. In these cases, the air agency should affirmatively state that the not reasonably controllable or preventable criterion is satisfied by the fact that the natural event was of a character that could not have been prevented or controlled and that there were no contributions of event-related emissions from anthropogenic sources.

We also propose, as guidance, for events other than high wind dust events and wildfire on wildland (for which the proposed rule revisions take an equivalent approach), to consider the direct effects of remote, large-scale, high-energy and/or sudden natural events to generally be not reasonable to prevent or control.

This concept, as it relates specifically to proposed rule changes addressing high wind dust events, is discussed in more detail in section V.F.4. Section V.F.2.c discusses how the same concept relates to proposed rule changes addressing the “not reasonably controllable or preventable” criterion for wildfire on wildland.

By “remote” events, we mean events that occur in locations where the application of control measures is either cost-prohibitive or presents unreasonable risks to worker safety because of the distance of the source from logistical staging areas, or absence of roads and/or location on rough or steep terrain. By “large-scale” we mean a regional event that involves a significant expanse of land and/or affects all/most monitors in an area. “High-energy” means an event involving levels of kinetic energy that feasible human efforts cannot absorb or redirect. Example large-scale and/or high-energy events might include seismic events, hurricanes, tornadoes and “haboobs” in the southwest where sustained wind speeds can exceed 40 mph and generate walls of dust several miles wide and more than a mile high.

There may, however, be natural events or activities associated with the clean-up following a natural event where some type of control effort would be reasonable. For example, while an initial volcanic dust event may not be controllable or preventable, it may be reasonable to implement a street cleaning program to control the subsequent re-entrainment of dust deposited on roadways after the eruption. Also, air quality impacts during the active period of a weather disaster event generally cannot be prevented or controlled and it would be reasonable for no effort to have been made to do so. However, air agencies should apply reasonable controls, as applicable, in the recovery period after the event (

e.g.,

during the removal or incineration

of debris following a hurricane or tornado). There may also be smaller scale natural sources and events for which some control actions would be reasonable. We request comment on additional general and event-specific recommendations that would be consistent with the CAA and the revised Exceptional Events Rule regarding natural events and sources that the EPA could include in guidance to provide more certainty and allow air agencies to efficiently prepare demonstrations.

When addressing reasonable controls for the incineration of debris associated with the recovery period following a natural disaster, air agencies may want to consider, as appropriate, the basic smoke management practices discussed in more detail in section V.F.2.d of this proposal.

The Role of Past Occurrences.

When assessing the controls that

should reasonably have been in place

in light of information available at the time of the event, both the air agency and the EPA should consider the then-known frequency and severity of recurring events of the same type as both characteristics should affect decisions regarding those measures that constitute reasonable controls. A measure may not be reasonable when the event type and severity was known to occur infrequently, but such measures may be reasonable if that event type and severity occurs frequently, because there are greater (more frequent) benefits to balance against the cost of implementation. If the event was the area's first experienced event of this type, then the submitting air agency would note that fact. The air agency could then rely on measures in the SIP and other controls in place at the time of the event, if any, to satisfy the not reasonably controllable or preventable criterion because, at the time of the event, the air agency did not have a basis for understanding the possible need for better controls for this type of event. If, however, the area has

previously experienced events of the type that are the focus of the demonstration, then the air agency has a basis for understanding the possible need for better controls.

Because a state is considered a single responsible entity for purposes of SIP development and implementation, there may be state governmental authorities whose knowledge of the need for an availability of controls at the time of the event is also relevant, particularly for in-state sources outside the geographic area covered by the air agency's regulatory authority.

We note that this consideration of past recurrence when determining what controls would have been sufficient to satisfy the not reasonably controllable or preventable criterion is not the same as the consideration of the likelihood of future recurrence for the purposes of the unlikely to recur criterion. Past experiences are a general guide to future likelihood but the EPA recognizes that future recurrence may follow a different pattern and may necessitate new measures to prevent events of a given type.

The Role of the EPA-approved SIP as the Benchmark for Reasonable Measures—In General.

As already mentioned, some air agencies have urged us to defer to relevant controls in EPA-approved SIPs as always sufficient to satisfy the not reasonably controllable or preventable criterion. The EPA could conceivably give “deference” to several different types of SIPs. CAA section 110(a)(1) and 110(a)(2) requires every state to develop and submit to the EPA an “infrastructure SIP” for each NAAQS within 3 years of the promulgation of a new or revised NAAQS. Infrastructure SIPs address a number of CAA requirements, including the requirement to contain emission limits to ensure attainment and maintenance of a NAAQS. However, under the EPA's interpretation of these CAA sections, infrastructure SIPs are not required to include attainment or maintenance demonstrations and are not required to demonstrate that the controls on particular sources are “reasonable.” Thus, in general, EPA-approved infrastructure SIPs do not necessarily constitute a robust assessment of those controls that are reasonable to have in place to address air quality impacts from particular types of events that may become the focus of exceptional events demonstrations.

In contrast, states with areas designated as nonattainment for a NAAQS must prepare attainment plan SIPs, which must include an attainment demonstration and reasonably available control measures (RACM), among other requirements.

Attainment plans for serious PM

or PM

2.5

areas must also contain best available control measures (BACM). When a nonattainment area reaches attainment, it may be redesignated to maintenance area status if it has implemented all applicable nonattainment area requirements and obtains the EPA's approval for a maintenance plan for a 10-year period. Thus, in both maintenance and nonattainment areas with approved attainment plan SIPs, the air agency and the EPA will have considered what controls are necessary and reasonable to provide for attainment, based on information available at the time of plan development and approval.

Marginal ozone nonattainment areas are exceptions because they are not required to submit attainment demonstrations.

Taken to its furthest limit, the deference recommended by some air agencies would mean that the EPA would always approve a state air agency assertion that the control measures in a SIP that has received full approval by the EPA as meeting currently applicable requirements related to the event-relevant NAAQS constituted the reasonable set of controls for the event in question and thus the event was not reasonably controllable or preventable. We believe that this degree of deference could, in some cases, result in the approval for data exclusion contrary to CAA requirements. Deference to the measures in an EPA-approved SIP is not always appropriate because EPA approval at some time in the past does not necessarily mean that (1) the control measures in a current SIP address all event-relevant sources of current importance, (2) the control measures that were considered by the air agency and the EPA at the time the EPA last approved the SIP are the same measures that were known and available at the time of a more recent event, or (3) that conditions in the area have not changed in a way that would affect the approvability of the same SIP if it newly needed the EPA's approval. However, we believe that it may be consistent with the CAA to revise the Exceptional Events Rule to identify the conditions under which the EPA and air agencies can rely upon measures in an EPA-approved SIP to satisfy the not reasonably controllable or preventable criterion. To clarify these scenarios, the EPA is proposing, and discusses below, various combinations of rule provisions and guidance for areas of different designation status.

The best time for air agency and federal officials to exchange both technical information and views on the balance between costs and benefits related to the sufficiency of reasonable controls is before an event happens. To avoid the EPA's retrospective second guessing of an air agency's consideration of information available to it before an event occurs, we have identified and described below several proposals, which would apply when an affected air agency and the EPA have

not

reached a mutual understanding regarding reasonable controls prior to an event.

The Role of the EPA-approved SIP in Nonattainment and Maintenance Areas.

To satisfy the not reasonably controllable or preventable criterion for nonattainment or maintenance areas, the EPA proposes to establish by rule a non-rebuttable presumption that, during a 5-year window (or, alternatively another appropriate timeframe) following approval of an attainment plan or maintenance plan SIP during which no subsequent new obligation for the air agency to revise the SIP has arisen, the control measures included in the SIP that are specific to the relevant pollutant, sources and event type are sufficient for purposes of the not reasonably controllable or preventable criterion.

The EPA believes that 5 years is an appropriate timeframe upon which to rely for SIP deference for several reasons. As noted earlier, deference to the measures in an EPA-approved SIP is not always appropriate because EPA approval at some time in the past does not necessarily mean that (1) the control measures in a current SIP address all event-relevant sources of current importance, (2) the control measures that were considered by the air agency and the EPA at the time the EPA last approved the SIP are the same measures that were known and available at the time of a more recent event, or (3) that conditions in the area have not changed in a way that would affect the approvability of the same SIP if it newly needed the EPA's approval. A 5-year window provides a reasonable timeframe under which to evaluate the above-identified potential changes. Additionally, as we discuss in section V.E.3 of this proposal, we encourage the use of 5 years of data when developing analyses to support the clear causal relationship criterion because we believe that 5 years of ambient air data represent the range of “normal” air quality.

A request for data exclusion must also show that the event was not a result of noncompliance with any existing state or local laws or rules that have not been incorporated into the SIP.

The EPA would evaluate the not reasonably controllable or preventable

criterion on a case-by-case basis for those demonstrations involving an event affecting a nonattainment or maintenance area with a SIP last approved more than 5 years prior to the submittal of the subject demonstration. Because the issue of deference to a SIP is most often applicable for high wind events, section V.F.4 further illustrates this proposal.

The Role of the EPA-approved SIP in Attainment, Unclassifiable/Attainment or Unclassifiable Areas.

Attainment, unclassifiable/attainment and unclassifiable areas should have EPA-approved infrastructure SIPs in place that the EPA approved within a few years following the promulgation of a new or revised NAAQS. Infrastructure SIPs for the 1987 PM

NAAQS are likely to be many years old, while infrastructure SIPs for ozone, PM

2.5

, 1-hour SO

and 1-hour NO

have been approved more recently.

In addition to the EPA-approved infrastructure SIPs, these areas may have in place other relevant state or local laws and rules, a natural events action plan, an SMP and/or other programs based on voluntary participation.

The NAAQS not mentioned here have rarely presented exceptional events issues.

Because the development and the EPA's review of infrastructure SIPs typically do not involve a robust assessment of needed measures to prevent or control the effects of particular types of events and because even in the absence of a pending SIP call the SIP may not reasonably address events of importance, the EPA does not propose to establish in rule text or in guidance any form of general deference to the SIP in attainment, unclassifiable/attainment or unclassifiable areas. The EPA will review exceptional events demonstrations on a case-by-case basis, applying the Exceptional Events Rule and the EPA's guidance. A case-by-case review may conclude that the measures that were in place under the SIP, a natural events action plan, an SMP or other state or local programs were sufficient or insufficient to satisfy the not reasonably controllable or preventable criterion.

If the air agency has historically documented recurring events, then the EPA would expect the submitting air agency to identify any anthropogenic emission sources that contribute to the event emissions and specifically document the controls that were in place for these sources at the time of the event. It is possible that the air agency may not be able to make a sufficient showing for the not reasonably controllable or preventable criterion if it has not implemented reasonable controls for anthropogenic sources that contribute to recurring events. In this case, the EPA Regional office may not be able to concur with an air agency's request for data exclusion. If the air agency has no such control plans and has no history of recurring events, then the air agency would note this in the not reasonably controllable or preventable portion of its demonstration and would rely on the fact that at the time of the event, the air agency did not have a basis for understanding the possible need for better reasonable controls.

Note that in section V.G.7 of this proposed action, “Timing of the EPA's Review of Submitted Demonstrations,” the EPA proposes to work with air agencies to prioritize exceptional events determinations that affect near-term regulatory decisions. In an attainment, unclassifiable/attainment or unclassifiable areas, the only likely non-discretionary regulatory action would be an initial designation under a new or revised NAAQS. Possible discretionary actions include a redesignation under a long-standing NAAQS or a SIP call. Under its planned prioritization approach, the EPA would not expect to act on demonstrations for events in an attainment, unclassifiable/attainment or unclassifiable areas unless the area could become nonattainment under a new or revised NAAQS, the area is the subject of a planned EPA discretionary redesignation for a long-standing NAAQS where the approval of a demonstration affects the basis for the redesignation, or the area becomes the subject of another EPA discretionary action (

e.g.,

a SIP call at the initiative of the EPA or in response to a petition) that hinges on the approval of a demonstration.

The Role of Prior Communications with the EPA in Case-Specific Assessments for Not Reasonably Controllable or Preventable.

As already stated, the EPA believes that an air agency must include in its exceptional events demonstration a retrospective assessment of whether an event was not reasonably controllable or preventable. The air agency should base this assessment on information available to relevant authorities (

e.g.,

the air agency submitting the demonstration and potentially other government authorities in the state, for example an upwind air quality control district where the event occurred) that could have implemented measures to prevent or control the event and its effects prior to and during the event. We are proposing to adopt the following approach as guidance to air agencies submitting demonstrations that will be subject to a case-specific assessment (

i.e.,

in situations other than when deferring to a nonattainment or maintenance plan SIP).

To satisfy the not reasonably controllable or preventable criterion in a case-specific assessment, the EPA proposes to consider communications between the EPA and the air agency when assessing “reasonableness” as part of assessing the technical information available to the air agency at the time the event occurred and what

should reasonably have been in place

at the time of the event for anthropogenic emission sources that contribute to the event emissions. It is not the EPA's intent to retroactively apply its current judgments about the reasonableness of controls for past events. However, it would also be inappropriate for an air agency to fail to respond to the EPA's recommendations prior to an event and then claim later in an event demonstration that it was unaware of a reasonable control issue.

The EPA recognizes that regulations and an area's planning status are often evol

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