[Federal Register Volume 80, Number 224 (Friday, November 20, 2015)]
[Proposed Rules]
[Pages 72839-72897]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2015-29350]



[[Page 72839]]

Vol. 80

Friday,

No. 224

November 20, 2015

Part III





Environmental Protection Agency





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40 CFR Part 50





Treatment of Data Influenced by Exceptional Events; Proposed Rule

Federal Register / Vol. 80 , No. 224 / Friday, November 20, 2015 / 
Proposed Rules

[[Page 72840]]


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ACTION: Proposed rule; notice of availability of related draft 
guidance; notice of hearing.

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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of the non-binding guidance document titled Draft Guidance on the 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 Written comments on this proposal and draft guidance 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 [email protected], 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 [email protected]. 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 [email protected]. 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 [email protected] (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?

    1. 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

[[Page 72841]]

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.
    2. 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.
    3. 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 
[email protected] (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

[[Page 72842]]

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
[mu]g/m\3\ 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
NO2 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
PM10 Particulate matter with a nominal mean aerodynamic 
diameter less than or equal to 10 micrometers
PM2.5 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
SO2 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

[[Page 72843]]

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 (SO2) 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

[[Page 72844]]

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,

[[Page 72845]]

and requirements for air agencies \1\ to take appropriate and 
reasonable actions to protect public health from exceedances or 
violations of the NAAQS.\2\ 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.\3\
---------------------------------------------------------------------------

    \1\ 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.
    \2\ 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 
PM2.5 NAAQS of 35 [mu]g/m\3\ occurs when the 24-hour 
concentration is above 35 [mu]g/m\3\ on a single day. A violation of 
the 2006 24-hour PM2.5 NAAQS occurs when the 3-year 
average of the annual 98th percentile 24-hour concentrations is 
above 35 [mu]g/m\3\.
    \3\ Previous guidance and policy documents that either implied 
or stated the need for special treatment of data affected by an 
exceptional event include:
    i) 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 PM10 
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.
    v) 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 v. 
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

[[Page 72846]]

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).\4\ 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.\5\ 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.\6\
---------------------------------------------------------------------------

    \4\ 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.
    \5\ 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.
    \6\ 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

[[Page 72847]]

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.\7\ 
In all cases, the EPA will continue to work with tribes in implementing 
any promulgated rule revisions.
---------------------------------------------------------------------------

    \7\ 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.\8\ The 
FLMs, other federal agencies and other entities operating these 
regulatory monitors may submit collected data to the EPA's AQS 
database.\9\ 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.
---------------------------------------------------------------------------

    \8\ 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.
    \9\ 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.\10\ 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-

[[Page 72848]]

affected data is 40 CFR part 50, appendix K for PM with a nominal mean 
aerodynamic diameter less than or equal to 10 micrometers 
(PM10). 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).
---------------------------------------------------------------------------

    \10\ There are NAAQS for carbon monoxide (CO), lead (Pb), 
nitrogen dioxide (NO2), ozone, particle pollution and 
sulfur dioxide (SO2). 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 
\11\ 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.
---------------------------------------------------------------------------

    \11\ 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

[[Page 72849]]

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 
Sec.  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 SO2, PM and PM 
precursors.\12\ 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.
---------------------------------------------------------------------------

    \12\ 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

[[Page 72850]]

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.'' \13\ 
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.'' \14\ 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.
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    \13\ 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.
    \14\ 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,\15\ 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.\16\ 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.\17\
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    \15\ 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).
    \16\ 72 FR 13570 (March 22, 2007).
    \17\ 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.
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    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.\18\ 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.
---------------------------------------------------------------------------

    \18\ 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,

[[Page 72851]]

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 PM2.5 NAAQS of 12.0 [mu]g/m\3\, which 
is attained when the 3-year average of the annual arithmetic means does 
not exceed 12.0 [mu]g/m\3\.\19\ 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.\20\ 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.
---------------------------------------------------------------------------

    \19\ 78 FR 3086 (January 15, 2013).
    \20\ 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

[[Page 72852]]

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 PM10 or PM2.5 
nonattainment area to serious,\21\ 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.
---------------------------------------------------------------------------

    \21\ 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 PM10 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.'' \22\ 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:
---------------------------------------------------------------------------

    \22\ 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,\23\ unless the AQS user specifically indicates that 
they should be included, which may be appropriate for non-regulatory 
applications of interest to the user.\24\
---------------------------------------------------------------------------

    \23\ 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.
    \24\ 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 \25\ and for transportation conformity hot spot 
analyses.\26\
---------------------------------------------------------------------------

    \25\ 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.
    \26\ Transportation conformity hot spot analysis is applicable 
only to PM10 and PM2.5. ``Transportation 
Conformity Guidance for Quantitative Hot-spot Analyses in 
PM2.5 and PM10 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.\27\
---------------------------------------------------------------------------

    \27\ 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.\28\
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    \28\ 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

[[Page 72853]]

thus could prevent the permitting authority from issuing the 
permit.\29\
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    \29\ 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 
\30\ 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:
---------------------------------------------------------------------------

    \30\ 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.\31\ 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).\32\ 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.
---------------------------------------------------------------------------

    \31\ 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.
    \32\ Reclassification of PM10 and PM2.5 
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

[[Page 72854]]

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.\33\ 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.
---------------------------------------------------------------------------

    \33\ See as examples, Hawaii's exceptional events demonstration 
for volcanic activity affecting PM2.5 concentrations in 
2011-2012 and California Air Resources Board's demonstration for 
wildfire events affecting PM2.5 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.\36\ 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.
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    \34\ 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.
    \35\ 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.
    \36\ 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,

[[Page 72855]]

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 or 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.'' \37\ This document did not further define or give 
specific examples of ``routinely.''
---------------------------------------------------------------------------

    \37\ 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

[[Page 72856]]

quality control region (AQCR) \38\ 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.\39\ 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.\40\ 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).
---------------------------------------------------------------------------

    \38\ Air Quality Control Regions are defined in 40 CFR part 81, 
subpart B, Designation of Air Quality Control Regions.
    \39\ 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.
    \40\ 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.'' \41\ 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.
---------------------------------------------------------------------------

    \41\ 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.\42\ 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 SO2 concentrations 
associated with volcanic eruptions.
---------------------------------------------------------------------------

    \42\ 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.\43\ We stated in the

[[Page 72857]]

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.
---------------------------------------------------------------------------

    \43\ 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.\44\ 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.
---------------------------------------------------------------------------

    \44\ 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.'' \45\ 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.
---------------------------------------------------------------------------

    \45\ 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.

[[Page 72858]]

     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.\46\
---------------------------------------------------------------------------

    \46\ 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 intrastate scenarios when an 
event in one county affects air quality in another county in the 
same state, assuming that the event occurs on land subject to state 
authority (versus tribal government authority). 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.\47\ 
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.
---------------------------------------------------------------------------

    \47\ 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 
SO2 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.\48\ 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.
---------------------------------------------------------------------------

    \48\ 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 \49\ 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.
---------------------------------------------------------------------------

    \49\ 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

[[Page 72859]]

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.\50\
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    \50\ 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.\51\ Attainment plans for serious 
PM10 or PM2.5 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.
---------------------------------------------------------------------------

    \51\ 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.\52\ 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.
---------------------------------------------------------------------------

    \52\ 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

[[Page 72860]]

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 PM10 NAAQS are likely to be many years 
old, while infrastructure SIPs for ozone, PM2.5, 1-hour 
SO2 and 1-hour NO2 have been approved more 
recently.\53\ 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.
---------------------------------------------------------------------------

    \53\ 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 evolving and changing. The EPA may have recently promulgated 
new or revised federal rules requiring controls on particular sources 
or promulgated a new or revised nationally applicable standard that 
will ultimately result in an air agency's adoption of new control 
measures. The planning process to implement these new standards (e.g., 
the SIP or maintenance plan approval process) can be lengthy, sometimes 
spanning several years and involving multiple rounds of formal and 
informal communications between the affected air agency and the EPA 
regarding the appropriateness and completeness of planning elements. In 
some cases, discussion of issues regarding appropriate controls, 
including what controls would constitute ``reasonable'' controls for 
exceptional events purposes, are part of this iterative communications 
process. The EPA solicits comment on what form of communication (short 
of a SIP call) would be most effective in conveying the EPA's views to 
the affected air agency and whether this approach would be most 
appropriately addressed through guidance or regulatory text.
    Prospective Agreement on Assessments of Not Reasonably Controllable 
or Preventable. In the Interim High Winds Guidance, the EPA suggested 
that an air agency could develop an assessment showing that the 
controls in place for a particular type of event, or a planned 
enhancement of those controls, were sufficient to meet the not 
reasonably controllable or preventable criterion, and then obtain the 
EPA's review and concurrence with

[[Page 72861]]

the assessment prior to more events of that type occurring. This 
prospective approach would reduce disagreements that might otherwise 
occur over later retrospective assessments. To date, most air agencies 
that face recurring event issues have not pursued this option, but the 
EPA will work with any air agency expressing an interest in pursuing 
this approach.
    Summary of Requests for Comments Regarding Not Reasonably 
Controllable or Preventable. The EPA solicits comment on the following 
clarifications to the ``not reasonably controllable or preventable'' 
criterion:
     The EPA solicits comment on recommending as guidance that 
when addressing the ``not reasonably controllable or preventable'' 
criterion within an exceptional events demonstration, air agencies 
should: (1) Identify the natural and anthropogenic sources of emissions 
causing and contributing to the event emissions, including the 
contribution from local sources, (2) identify the relevant SIP or other 
enforceable control measures in place for these sources and the 
implementation status of these controls, and (3) provide evidence of 
effective implementation and enforcement of reasonable controls, if 
applicable.\54\ In identifying natural and anthropogenic sources, the 
air agency should assess both potentially contributing local/in-state 
and upwind sources. We also request comment on whether we should revise 
the rule text to require these elements in a demonstration.
---------------------------------------------------------------------------

    \54\ The EPA generally expects evidence that the controls 
determined to be reasonable, if any, were effectively implemented 
and appropriately enforced. This assessment of local sources should 
include a review and description of any known nearby facility upsets 
or malfunctions that could have resulted in emissions of the 
relevant pollutant(s) that influenced the monitored measurements on 
the day(s) of the claimed events. In the case of a high wind dust 
event, for example, for the identified potentially contributing 
local and upwind sources, the analysis should explain how 
significant dust emissions occurred despite having reasonable 
controls in place (e.g., that controls were overwhelmed by high 
wind), if appropriate.
---------------------------------------------------------------------------

     The EPA proposes to codify rule language to specify that 
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.
     The EPA solicits comment on specific guidance or rule 
requirements regarding what constitutes reasonable control of 
particular natural events and sources.
     The EPA proposes to codify in rule language that, provided 
the air agency is not under an obligation to revise the SIP, the EPA 
would consider (i.e., give deference to) enforceable control measures 
implemented in accordance with a state implementation plan, 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.
     The EPA proposes to codify in rule language the time 
period for such deference to be 5 years from the date of the SIP 
approval measured to the date of an event at issue, but is taking 
comment on whether and what other timeframes might be appropriate. To 
the extent an alternative timeframe might be appropriate, comments 
should explain how it would address the criteria provided above in 
support of the 5-year timeframe.
     The EPA proposes to consider communications and planning 
status when assessing the status of reasonable controls and proposes to 
do this through guidance. The EPA solicits comment on methods to 
definitively identify the status of communications and planning efforts 
(e.g., formal correspondence or other documentation, timelines for 
responding) and whether this approach would be more appropriately 
addressed through rule language.
3. Clear Causal Relationship Supported by a Comparison to Historical 
Concentration Data
a. Current Situation
    The CAA at section 319(b)(3)(B)(ii) requires that ``a clear causal 
relationship must exist between the measured exceedances of a national 
ambient air quality standard and the exceptional event to demonstrate 
that the exceptional event caused a specific air pollution 
concentration at a particular air quality monitoring location.'' The 
clear causal relationship criterion establishes causality between the 
event and a measured exceedance or violation of a NAAQS. As stated in 
the preamble to the 2007 Exceptional Events Rule, given the directive 
in CAA section 319(b)(3)(B)(ii), it would be unreasonable to exclude 
data affected by an exceptional event simply because of a trivial 
contribution of an event to air quality.\55\ The EPA does, however, 
recognize that distinguishing trivial contributions from more 
significant contributions to an exceedance may be difficult. As with 
the other exceptional events criteria, the EPA has used a weight of 
evidence approach when reviewing analyses to support a causal 
relationship between an event and a monitored exceedance.
---------------------------------------------------------------------------

    \55\ 72 FR 13569 (March 22, 2007).
---------------------------------------------------------------------------

    Showing that an event and elevated pollutant concentrations 
occurred simultaneously may not establish causality. The clear causal 
relationship section of an exceptional events demonstration should 
include analyses showing that the event occurred and that emissions of 
the pollutant of interest resulting from the event were transported to 
the monitor(s) recording the elevated concentration measurement(s). The 
example analyses to support the clear causal relationship criterion, 
shown in Table 1 and first summarized in the EPA's Interim Exceptional 
Events Implementation Guidance, are generally appropriate analyses for 
most event types.\56\ The EPA does not expect air agencies to include 
all of the evidence and analyses identified in the table below, but 
rather to use available information to build a weight of evidence 
showing. The EPA may accept limited analyses (e.g., a comparison to 
historical concentrations in combination with one or two additional 
analyses from Table 1) for areas whose monitored ambient air 
concentrations are generally well below the NAAQS on non-event days. 
Additional analyses are beneficial if they establish a different facet 
of the event and/or if they are used in combination with other analyses 
with limited data. For example, the EPA expects that areas prone to 
frequent elevated ozone (or other pollutant) concentrations, such as 
nonattainment areas, to have more sophisticated air quality prediction 
tools. We would expect these areas could use these tools when 
supporting an exceptional events demonstration and developing analyses 
to support a clear causal relationship. Additionally, photochemical or

[[Page 72862]]

regression modeling analyses may be beneficial in situations where the 
causality between the event and a measured exceedance of a NAAQS is not 
clearly established with evidence and analyses identified in Table 1. 
For example, if a fire occurs during the normal high ozone season and 
the ozone level associated with the fire is in the range of otherwise-
occurring ozone levels and/or only slightly above the ozone NAAQS, the 
causal relationship between the fire and the exceedance or violation 
may not be clear. In such a situation, modeling may produce a specific 
estimate of the ozone contribution from the fire. Air agencies should 
discuss with their EPA Regional office those types of analyses that may 
be adequate to satisfy the weight of evidence requirement in individual 
exceptional events demonstrations.
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    \56\ For purposes of summarizing example clear causal 
relationship analyses in one place, the EPA has included an entry 
for the comparison to historical concentrations showing in Table 1. 
The EPA notes that although the Interim High Winds Guidance and the 
Interim Q&A document discussed the comparison to historical 
concentrations showing, neither of these guidance documents 
presented this showing as part of the clear causal relationship. See 
specifically 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 and 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.

    Table 1--Example Clear Causal Relationship Evidence and Analyses
------------------------------------------------------------------------
  Example of clear causal relationship    Types of analyses/information
                evidence                     to support the evidence
------------------------------------------------------------------------
Comparison to Historical Concentrations  Analyses and statistics showing
                                          how the observed event
                                          concentration compares to the
                                          distribution or time series of
                                          historical concentrations of
                                          the same pollutant.
Occurrence and geographic extent of the  Special weather statements,
 event.                                   advisories, news reports,
                                          nearby visibility readings,
                                          measurements from regulatory
                                          and non-regulatory (e.g.,
                                          special purpose, emergency)
                                          monitoring stations throughout
                                          the affected area, satellite
                                          imagery.
Transport of emissions related to the    Wind direction data showing
 event in the direction of the            that emissions from sources
 monitor(s) where the measurements were   identified as part of the
 recorded.                                ``not reasonably controllable
                                          or preventable'' demonstration
                                          were upwind of the monitor(s)
                                          in question, satellite
                                          imagery, monitoring data
                                          showing elevated
                                          concentrations of other
                                          pollutants expected to be in
                                          the event plume.
Spatial relationship between the event,  Map showing likely source area,
 sources, transport of emissions and      wind speed/direction and
 recorded concentrations.                 pollutant concentrations for
                                          affected area during the time
                                          of the event, trajectory
                                          analyses.
Temporal relationship between the event  Hourly time series showing
 and elevated pollutant concentrations    pollutant concentrations at
 at the monitor in question.              the monitor in question in
                                          combination with wind speed/
                                          direction data in the area
                                          where the pollutant originated/
                                          was entrained or transported.
Chemical composition and/or size         Chemical speciation data from
 distribution (for PM2.5 to PM10) of      the monitored exceedance(s)
 measured pollution that links the        and sources, size distribution
 pollution at the monitor(s) with         data.
 particular sources or phenomenon.
Comparison of event-affected day(s) to   Comparison of concentration and
 specific non-event days.                 meteorology to days preceding
                                          and following the event,
                                          comparison to high
                                          concentration days in the same
                                          season (if any) without
                                          events, comparison to other
                                          event days without elevated
                                          concentrations (if any),
                                          comparison of chemical
                                          speciation data.
------------------------------------------------------------------------

    As explained in additional detail in the EPA's Interim Exceptional 
Events Implementation Guidance, what has previously been called the 
``historical fluctuations'' showing (i.e., now referred to as the 
comparison to historical concentrations) consists of analyses and 
statistics showing how the observed event-affected concentration 
compares to the distribution or time series of historical 
concentrations of the same pollutant.
    A demonstration may be less compelling if some evidence is 
inconsistent with the description of how the event caused the 
exceedance. For example, if an air agency describes an event as a 
regional dust storm or wildfire, then the EPA anticipates that most or 
all monitors within the same regional scale to be similarly affected by 
the event. That is, the EPA expects that the demonstration elements and 
factors (e.g., clear causal relationship, reasonable controls, 
meteorology, wind speeds) would also support the case for a regional 
event. Comparison of concentrations and conditions at other monitors 
could thus be very important for the demonstration of a clear causal 
relationship. Alternatively, eliminating plausible non-event causes may 
also support a causal relationship between the event and the elevated 
concentration.
    The EPA has been recommending that the clear causal relationship 
section of the demonstration should conclude with this type of 
statement: ``On [day/time] an [event type] occurred which generated 
pollutant X or its precursors resulting in elevated concentrations at 
[monitoring location(s)]. The monitored [pollutant] concentrations of 
[ZZ] were [describe the comparison to historical concentrations 
including the percentile rank over an annual (seasonal) basis]. 
Meteorological conditions were not consistent with historically high 
concentrations, etc.'' and ``Analyses X, Y and Z support Agency A's 
position 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 and thus satisfies the clear causal 
relationship criterion.''
b. Proposed Changes
    As previously noted, the EPA is proposing to revise the 2007 
Exceptional Events Rule text as follows:

 To move the ``clear causal relationship'' element into the 
list of criteria that explicitly must be met for data to be excluded
 To subsume the ``affects air quality'' element into the 
``clear causal relationship'' element
 To remove the term ``historical fluctuations'' and replace it 
with text referring to a comparison to historical concentrations
 To clarify that the comparison to historical concentrations is 
not a fact that must be proven
 To clearly identify the types of analyses that are necessary 
and sufficient in a demonstration to address the comparison to 
historical concentrations
 To remove the ``but for'' element (as discussed in section 
V.B.2)

    Additionally, the EPA proposes to reiterate in guidance the example 
analyses to support the clear causal relationship criterion, shown in 
Table 1 above, and first summarized in the

[[Page 72863]]

EPA's Interim Exceptional Events Implementation Guidance. As noted 
previously, the EPA does not expect air agencies to include all of the 
evidence and analyses identified in Table 2 below, but rather to use 
available information to build a weight of evidence showing.
    The EPA's rationale for proposing the previously identified changes 
to the clear causal relationship criterion is presented in section V.B. 
The remainder of this section focuses on the types of analyses that an 
air agency must provide in its demonstration to make the comparison to 
historical concentrations. As noted in the Current Situation section, 
the EPA has included an entry in Table 1 for the comparison to 
historical concentrations showing.
    The comparison to historical concentrations, referred to as the 
``historical fluctuations'' showing in the 2007 Exceptional Events Rule 
and the Interim Exceptional Events Implementation Guidance, is a 
requirement in the 2007 Exceptional Events Rule but it is not a 
statutory requirement. The EPA's intent with this regulatory element 
was to require air agencies to present event-influenced concentration 
data along with historical data and to quantify the difference, if any, 
between the event and the non-event concentrations. Comparing event-
influenced concentrations to historical concentrations bolsters the 
weight of evidence within the clear causal relationship determination. 
The EPA proposes to re-phrase and incorporate the current regulatory 
requirement at 40 CFR 50.14(c)(3)(iv)(C), which requires that a 
demonstration to justify data exclusion provide evidence that ``[t]he 
event is associated with a measured concentration in excess of normal 
historical fluctuations, including background,'' within the ``clear 
causal relationship'' criterion. In using this approach, we propose to 
remove from the regulatory text the ``in excess of normal historical 
fluctuations, including background'' phrase and to subsume the concept 
of historical comparisons into what will effectively be a 
``completeness'' requirement within the ``clear causal relationship'' 
criterion. As noted above, we specifically propose to remove the phrase 
``in excess of normal historical fluctuations, including background'' 
as we believe this language is vague and provides no additional value 
to historical concentration comparisons.
    To aid the EPA's review, reduce our need to request additional 
information from air agencies and facilitate our understanding of the 
air agency's position, we are proposing rule text changes to indicate 
that an air agency submitting a demonstration must provide the 
following types of statistics, graphics and explanatory text regarding 
comparisons to past data. The rule change would also indicate that this 
information is sufficient to satisfy the rule's requirement regarding 
the comparison to historical concentration data. Table 2 below 
identifies appropriate analyses and examples for comparing event-
related concentrations to historical concentrations within the clear 
causal relationship criterion.

                 Table 2--Evidence and Analyses for the Comparison to Historical Concentrations
----------------------------------------------------------------------------------------------------------------
    Historical concentration evidence      Types of analyses/supporting information      Required or optional?
----------------------------------------------------------------------------------------------------------------
1. Comparison of concentrations on the    Seasonal (appropriate if exceedances occur  Required seasonal and/or
 claimed event day with past historical    primarily in one season, but not in         annual analysis
 data.                                     others).                                    (depending on which is
                                                                                       more appropriate).
                                           Use all available seasonal data
                                           over the previous 5 years (or more, if
                                           available).
                                           Discuss the seasonal nature of
                                           pollution for the location being
                                           evaluated.
                                           Present monthly maximums of the
                                           NAAQS relevant metric (e.g., maximum
                                           daily 8-hour average ozone or 1-hr SO2)
                                           vs monthly or other averaged daily data
                                           as this masks high values.
                                          Annual (appropriate if exceedances are
                                           likely throughout the year).
                                           Use all available data over the
                                           previous 5 years (or more, if available).
                                                 Seasonal and Annual Analyses
                                           Provide the data in the form
                                           relevant to the standard being considered
                                           for data exclusion.
                                           Label ``high'' data points as
                                           being associated with concurred
                                           exceptional events, suspected exceptional
                                           events, other unusual occurrences, or
                                           high pollution days due to normal
                                           emissions.
                                           Describe how emission control
                                           strategies have decreased pollutant
                                           concentrations over the 5-year window, if
                                           applicable.
                                           Include comparisons omitting
                                           known or suspected exceptional events
                                           points, if applicable.
                                           See examples at http://www.epa.gov/ttn/analysis/docs/IdeasforShowingEEEvidence.ppt and
                                           Question 3 in the Interim Q&A document
                                           provides additional detail. \a\
2. Comparison of concentrations on the     Include neighboring days at the    Optional analysis.
 claimed event day with a narrower set     same location (e.g., a time series of two
 of similar days.                          to three weeks) and/or other days with
                                           similar meteorological conditions
                                           (possibly from other years) at the same
                                           or nearby locations with similar
                                           historical air quality along with a
                                           discussion of the meteorological
                                           conditions during the same timeframe. \b\
                                           Use this comparison to
                                           demonstrate that the event caused higher
                                           concentrations than would be expected for
                                           given meteorological and/or local
                                           emissions conditions.
3. Percentile rank of concentration when   Provide the percentile rank of     Required analysis when
 compared to annual data. \c\              the event-day concentration relative to     comparison is made on an
                                           all measurement days over the previous 5    annual basis (see item
                                           years to ensure statistical robustness      #1).
                                           and capture non-event variability over
                                           the appropriate seasons or number of
                                           years. \d\

[[Page 72864]]

 
                                           Use the daily statistic (e.g., 24-
                                           hour average, maximum daily 8-hour
                                           average, or maximum 1-hour) appropriate
                                           for the form of the standard being
                                           considered for data exclusion.
4. Percentile rank of concentration        Provide the percentile rank of     Required analysis when
 relative to seasonal data. \c\            the event-day concentration relative to     comparison is made on a
                                           all measurement days for the season (or     seasonal basis (see item
                                           appropriate alternative 3-month period)     #1).
                                           of the event over the previous 5 years.
                                           Use the same time horizon as used
                                           for the percentile rank calculated
                                           relative to annual data, if appropriate.
----------------------------------------------------------------------------------------------------------------
\a\ 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.
\b\ If an air agency compares the concentration on the claimed event day with days with similar meteorological
  conditions from other years, the agency should also verify and provide evidence that the area has not
  experienced significant changes in wind patterns, and that no significant sources in the area have had
  significant changes in their emissions of the pollutant of concern.
\c\ The EPA does not intend to identify a particular historical percentile rank point in the seasonal or annual
  historical data that plays a critical role in the analysis or conclusion regarding the clear causal
  relationship.
\d\ Section 8.4.2.e of appendix W (proposed revisions at 80 FR 45374, July 29, 2015) recommends using 5 years of
  adequately representative meteorology data from the National Weather Service to ensure that worst-case
  meteorological conditions are represented. Similarly, for exceptional events purposes, the EPA believes that 5
  years of ambient air data, whether seasonal or annual, better represent the range of ``normal'' air quality
  than do shorter periods.

    As with other evidence in an exceptional events demonstration 
submittal, the EPA will use a holistic weight of evidence approach in 
reviewing submitted demonstration packages and will consider the 
``clear causal relationship'' information, including the comparison to 
historical concentrations showing, along with evidence supporting the 
other Exceptional Events Rule criteria.

F. Treatment of Certain Events Under the Exceptional Events Rule

    As we stated in the preamble to the 2007 Exceptional Events Rule, 
we maintain that air quality data affected by the following event types 
are among those that could meet the definition of an exceptional event 
and qualify for data exclusion provided all requirements of the rule 
are met: (1) Chemical spills and industrial accidents,\57\ (2) 
structural fires, (3) terrorist attacks, (4) volcanic and seismic 
activities, (5) natural disasters and associated cleanup and (6) 
fireworks.\58\ We are not proposing any changes to the definition or 
discussion of these event types. The AQS database contains a more 
detailed list of other similar events that may be identified for 
special consideration. The EPA will consider other types of events on a 
case-by-case basis.
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    \57\ A malfunction at an industrial facility could be considered 
to be an exceptional event if it has not resulted in source 
noncompliance, which is statutorily excluded from consideration as 
an exceptional event, see CAA 319(b)(1)(b)(iii), and if it otherwise 
meets the requirements of the Exceptional Events Rule.
    \58\ Of these noted event types, only fireworks are currently 
identified in the regulatory language at 40 CFR 50.14. We are not 
proposing any revisions to the exclusion at 40 CFR 50.14(b)(2) for 
fireworks that are demonstrated to be significantly integral to 
traditional national, ethnic, or other cultural events.
---------------------------------------------------------------------------

    Based on our implementation experience, the following other 
potential exceptional events categories warrant additional discussion: 
Exceedances due to transported pollution, wildland fires including 
wildfires and prescribed fires, stratospheric ozone intrusions and high 
wind dust events. We discuss each of these event categories in the 
following sections.
1. Exceedances Due to Transported Pollution
a. Current Situation
    The 2007 Exceptional Events Rule implements one important CAA 
provision related to transported pollution. Certain events, national or 
international in origin and from natural or anthropogenic sources, may 
cause exceedances that are eligible for exclusion under the 2007 
Exceptional Events Rule if an air agency satisfies the rule criteria. 
We discuss in this section our position regarding exceedances due to 
event-related transported pollution. We also clarify in part c of this 
section how the Exceptional Events Rule provisions currently relate to 
other CAA mechanisms that address or involve transported pollution. We 
are not proposing any changes to these relationships.
    The EPA believes that the Exceptional Events Rule will often be the 
most appropriate mechanism to use when addressing transported emissions 
from out-of-state natural events and/or events due to human activity 
that is unlikely to recur at a particular location, because the 
Exceptional Events Rule may be used during the initial area 
designations process and may make a difference between an attainment 
versus a nonattainment designation. It is important to note, however, 
that the transported natural emissions must be event-related (e.g., 
wildfires or stratospheric ozone intrusion) versus ongoing on a daily 
basis.
b. Proposed Changes
    If an air agency determines that the Exceptional Events Rule is the 
most suitable approach to address contributions from transported 
emissions, then the air agency must consider the point of origin and 
the sources contributing to the exceedance or violation to determine 
how to address individual Exceptional Events Rule criteria, 
specifically the not reasonably controllable or preventable criterion 
and the human activity unlikely to recur or a natural event criterion. 
The analyses to satisfy the clear causal relationship criterion (which 
would subsume the CAA's affects air quality criterion, if promulgated 
as proposed and discussed in section V.B) are largely independent of 
whether the point of origin and contributing sources are within the air 
agency's jurisdiction. The EPA first addressed these concepts in its 
Interim Q&A document and now proposes to clarify these intrastate and 
interstate scenarios.
    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 intrastate scenarios when an event in one part of a 
state, such as a county or air district, affects air quality in another 
part of the same

[[Page 72865]]

state, assuming that the event occurs on land subject to state 
authority (versus tribal government authority). For cases involving 
intrastate transport, the state or local air agency should evaluate 
whether contributing event emissions from all parts of the state were 
not reasonably controllable or preventable. Section V.E.2 discusses the 
assessment of the not reasonably controllable or preventable criterion. 
Because there may be special considerations regarding air agencies' 
authority to regulate activity on federally-owned and managed lands 
(e.g., national parks within the state), states and tribes should 
consult with the appropriate FLM or other federal agency and their EPA 
Regional office early in the development of an exceptional events 
demonstration package if they believe that sources on federally-owned 
and managed land contributed event-related emissions to a degree that 
raises issues of reasonable control.
    Interstate and international transport events are different than 
intrastate events. As noted in section V.E.2, 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 nor does the EPA believe that Congress intended to deny 
the downwind state or tribe of relief in the form of data exclusion. As 
with any demonstration submittal, the submitting (downwind) state 
should identify all natural and anthropogenic contributing sources of 
emissions (both local/in-state and out-of-state) to show the causal 
connection between an event and the affected air concentration values. 
A submitting state may provide a less detailed characterization of 
sources in the upwind state or foreign country than of sources within 
its jurisdiction. After completing the source characterization, the 
submitting state should assess whether emissions from sources within 
its state were not reasonably controllable or preventable (see section 
V.E.2 of this proposal). Although the downwind state must still assess 
potential contribution from in-state sources, we propose that the 
event-related emissions that were transported in the downwind state are 
``not reasonably controllable or preventable'' for purposes of data 
exclusion. The EPA does not expect air agencies to submit analyses to 
satisfy the not reasonably controllable or preventable criterion for 
those upwind, out-of-state sources that contribute to the exceedance as 
part of a submitted demonstration. Rather, with respect to this element 
for such sources, an air agency would merely point to the relevant 
provision we propose to add to the Exceptional Events Rule. Submitting 
states are, however, still required to assess the contribution and 
potential controls from local/in-state sources and submit evidence/
statements supporting the other exceptional events criteria (i.e., 
clear causal relationship, human activity unlikely to recur or a 
natural event). If the event-related emissions are international in 
origin and affect monitors in multiple states or regions, the EPA may 
assist affected agencies in identifying approaches for evaluating the 
potential impacts of international transport and determining the most 
appropriate information and analytical methods for each area's unique 
situation.
    The EPA proposes a similar approach to significant out-of-state 
anthropogenic sources in the case of a mixed natural/anthropogenic 
event that the submitting state wishes to have treated as a natural 
event on the grounds that all significant anthropogenic sources were 
reasonably controlled. That is, if a mixture of natural and 
anthropogenic sources in an upwind state contributed to an event, the 
downwind state is not required to demonstrate that the anthropogenic 
sources in the upwind state were reasonably controlled for those 
sources to be considered to not have directly caused the event. The 
submitting state could consider the event to be a natural event based 
on the situation within the state requesting the data exclusion (that 
is, the contributing sources within the jurisdiction of the submitting 
state were either natural or reasonably controlled anthropogenic 
sources).
    As with all exceptional events demonstrations, the EPA will 
evaluate the information on a case-by-case basis based on the facts of 
a particular exceptional event including any information and arguments 
presented in public comments received by the state in its public 
comment process or by the EPA in a notice-and-comment regulatory action 
that depends on the data exclusion.
c. Relationship Between Exceptional Events Rule Provisions and Other 
CAA Transport Mechanisms
    Two provisions of the CAA other than section 319(b) also provide 
regulatory relief for transported pollution, for different 
circumstances than those addressed by the 2007 Exceptional Events Rule. 
These provisions are briefly described here as context for 
understanding the role of the Exceptional Events Rule itself.
     CAA section 179B, International Transport--CAA section 
179B allows states to consider in their attainment demonstrations 
whether a nonattainment area might have met the NAAQS by the attainment 
date ``but for'' emissions contributing to the area originating outside 
the U.S. This provision addresses sources of emissions originating 
outside of the U.S. and provides qualifying nonattainment areas some 
regulatory relief from otherwise-applicable additional planning and 
control requirements should the area fail to reach attainment by its 
deadline. It does not provide a pathway for regulatory relief from 
designation as a nonattainment area.
     CAA section 182(h), Rural Transport Areas--CAA section 
182(h) authorizes the EPA Administrator to determine that an ozone 
nonattainment area can be treated as a rural transport area, which 
provides relief from more stringent requirements associated with higher 
nonattainment area classifications (i.e., classifications above 
Marginal). Under CAA section 182(h), a nonattainment area may qualify 
as a Rural Transport Area if it does not contain emissions sources that 
make a significant contribution to monitored ozone concentrations in 
the area or in other areas, and if the area does not include and is not 
adjacent to a Metropolitan Statistical Area. Generally, an area 
qualifies as a Rural Transport Area because it does not contribute to 
its own or another area's nonattainment problem; rather, ozone 
exceedances are due to transported emissions, which could be 
international, interstate or intrastate in origin. The Rural Transport 
Area determination can be made during or after the initial area 
designations and classifications process.
    Two additional provisions of the CAA specifically address and 
appropriately regulate transported pollution that does not qualify for 
data exclusion under the Exceptional Events Rule or for regulatory 
relief under CAA section 179B or CAA section 182(h). These provisions 
are briefly described here as context for understanding the role of the 
Exceptional Events Rule itself.
     CAA section 110(a)(2)(D)(i)(I), Interstate Transport--CAA 
section 110(a)(2)(D)(i)(I) requires states to develop and implement 
SIPs to address the interstate transport of emissions. Specifically, 
this provision requires each state's SIP to prohibit ``any source or 
other type of emissions activity within the State from emitting any air 
pollutant in amounts which will significantly contribute to

[[Page 72866]]

nonattainment'' of any NAAQS in another state, or which will 
``interfere with maintenance'' of any NAAQS in another state. When the 
EPA promulgates or revises a NAAQS, each state is required to submit a 
SIP addressing this interstate transport provision as to that NAAQS 
within 3 years. The EPA interprets this interstate transport provision 
to address anthropogenic sources of emissions from other states; we 
believe that is not intended to address natural sources of emissions.
     CAA section 126, Interstate Transport--CAA section 126 
provides states and political subdivisions with a mechanism to petition 
the Administrator for a finding that ``any major source or group of 
stationary sources emits or would emit any air pollution in violation 
of the prohibition of CAA 110(a)(2)(D)(i).'' \59\ Where the EPA grants 
such a petition, an existing source may operate beyond a 3-month period 
only if the EPA establishes emissions limitations and compliance 
schedules to bring about compliance with CAA section 110(a)(2)(D)(i) as 
expeditiously as practicable, but no later than 3 years after such 
finding. Similar to our interpretation above for CAA section 
110(a)(2)(D)(i), the EPA interprets the reference to ``major source or 
group of stationary sources'' in section 126 to refer to anthropogenic 
sources of emissions from other states. The EPA's interpretation is 
that this provision is not intended to address natural sources of 
emissions. This mechanism is available to all downwind states, and 
political subdivisions, regardless of area designations, that may be 
affected by anthropogenic sources of emissions from upwind states in 
violation of the prohibition in CAA section 110(a)(2)(D)(i).
---------------------------------------------------------------------------

    \59\ The text of section 126 codified in the United States Code 
cross references section 110(a)(2)(D)(ii) instead of section 
110(a)(2)(D)(i). The courts have confirmed that this is a 
scrivener's error and the correct cross reference is to section 
110(a)(2)(D)(i), See Appalachian Power Co. v. EPA, 249 F.3d 1032, 
1040-44 (D.C. Cir. 2001).
---------------------------------------------------------------------------

    As noted previously, in most cases, the mechanisms in the 
Exceptional Events Rule often provide the most regulatory flexibility 
in that air agencies can use these provisions to seek relief from 
designation of an area as nonattainment. The CAA section 179B 
(International Transport) and section 182(h) (Rural Transport Areas) 
apply following, or concurrent with, the initial area designations 
process.
2. Wildland Fires
    Fires on wildland play an important ecological role across the 
globe, benefiting those plant and animal species that depend upon 
natural fires for propagation, habitat restoration and reproduction. 
Wildland can include forestland,\60\ shrubland,\61\ grassland \62\ and 
wetlands.\63\ Fires on wildland can be of two types: wildfire 
(unplanned) and prescribed fire (intentionally ignited for management 
purposes). Since promulgation of the 2007 Exceptional Events Rule, the 
EPA has received and acted upon exceptional events demonstrations for 
both wildfires and prescribed fires. The EPA anticipates receiving 
increasing numbers of fire-related demonstrations in the future due to 
the natural accumulation of fuels in the absence of fire, due to 
climate change that is leading to increased incidence of wildfire,\64\ 
which may necessitate land managers employing prescribed fire more 
frequently to manage fuel loads and achieve other benefits as described 
below,\65\ \66\ and due to the potential for fire-related 
demonstrations to affect near-term regulatory decisions such as the 
initial area designations decisions associated with a revised 8-hour 
ozone NAAQS. Consequently, the EPA is proposing revisions to the 2007 
Exceptional Events Rule and developing additional guidance to make the 
preparation and review of demonstrations for wildland fire events more 
efficient and predictable for all parties.
---------------------------------------------------------------------------

    \60\ Forestland is land on which the vegetation is dominated by 
trees or, if trees are lacking, the land shows historic evidence of 
former forest and has not been converted to other uses. Definition 
available at https://globalrangelands.org/rangelandswest/glossary.
    \61\ Shrubland is land on which the vegetation is dominated by 
shrubs. Definition available at https://globalrangelands.org/rangelandswest/glossary.
    \62\ Grassland is land on which the vegetation is dominated by 
grasses, grass like plants, and/or forbs. Definition available at 
https://globalrangelands.org/rangelandswest/glossary.
    \63\ Wetlands, as defined in 40 CFR 230.3(t), means those areas 
that are inundated or saturated by surface or ground water at a 
frequency and duration sufficient to support, and that under normal 
circumstances do support, a prevalence of vegetation typically 
adapted for life in saturated soil conditions. Wetlands generally 
include swamps, marshes, bogs and similar areas.
    \64\ The Administrator's finding on the adverse effects of 
greenhouse gases included the observation that wildfires have 
increased, and that there are potential serious adverse impacts from 
further wildfire occurrence. 74 FR 66530 (December 15, 2009).
    \65\ Climate Change in the United States: Benefits of Global 
Action, U.S. EPA, EPA-430-R-15-001, June 2015. Available at http://www2.epa.gov/cira.
    \66\ The National Strategy: The Final Phase in the Development 
of the National Cohesive Wildland Fire Management Strategy, Report 
to Congress developed by the U.S. Department of Agriculture and the 
U.S. Department of the Interior, April 2014. Available at http://www.forestsandrangelands.gov/strategy/thestrategy.shtml.
---------------------------------------------------------------------------

    Wildfire emissions account for a large portion of direct 
PM2.5 emissions nationally and can contribute to periodic 
high PM2.5 and PM10 levels. Wildfires also emit 
volatile organic compounds (VOC) and nitrogen oxides (NOX), 
which are precursors to PM2.5, PM10 and ozone. 
Besides their effect on air quality, wildfires pose a direct threat to 
public safety. Changes in wildfire risk and occurrence are closely 
associated with the lack of periodic fire in fire-dependent ecosystems, 
demographic changes and associated infrastructure investment at the 
margins of wildland and, as already noted, climate change and climate 
variability. The threat from wildfires can be mitigated through 
management of wildland vegetation. Attempts to suppress wildfires have 
resulted in unintended consequences, especially the buildup of fuel 
loads, which can create a lingering fire liability that will eventually 
find resolution, unplanned or planned. Unplanned fires in areas with 
high fuel loads present high risks to both humans and ecosystems.\67\ 
Planned prescribed fires and letting some wildfires proceed naturally 
(typically those with lower fire intensity and severity) are tools that 
land managers can use to reduce fuel load, unnatural understory and 
tree density, thus helping to reduce the risk of catastrophic 
wildfires. Allowing some wildfires to continue to burn even though they 
could be suppressed and the thoughtful use of prescribed fire can 
influence the occurrence, size and severity of catastrophic wildfires, 
which may lead to improved public safety, improved protection of 
property and an overall reduction in fire-induced smoke impacts and 
subsequent health effects. Thus, appropriate use of prescribed fire may 
help manage the contribution of wildfires to both background and peak 
PM and ozone air pollution. However, prescribed fires themselves can 
affect monitored air quality at some times and places affecting public 
health, and thus give rise to exceptional events issues. This action 
proposes a workable approach to addressing these prescribed fire 
exceptional events issues.
---------------------------------------------------------------------------

    \67\ Indeed, ``fire policy that focuses on [wildfire] 
suppression only, delays the inevitable, promising more dangerous 
and destructive future . . . fires.'' Stephens, SL; Agee, JK; Fule, 
PZ; North, MP; Romme, WH; Swetnam, TW. (2013). Managing Forests and 
Fire in Changing Climates. Science 342: 41-42.
---------------------------------------------------------------------------

    In addition to reducing wildfire risks to humans and ecosystems and 
wildfire contributions to air pollution, prescribed fires can have 
benefits to those plant and animal species that

[[Page 72867]]

depend upon natural fires for propagation, habitat restoration and 
reproduction, as well as benefits to a myriad of ecosystem functions 
(e.g., carbon sequestration, maintenance of water supply systems and 
endangered species habitat maintenance). The EPA understands the 
importance of prescribed fire, which mimics a natural process necessary 
to manage and maintain fire-adapted ecosystems and climate change 
adaptation, while reducing risk to public safety and the risk of 
uncontrolled emissions and ecosystem damage from catastrophic 
wildfires. The EPA is committed to working with federal land managers, 
other federal agencies, tribes, states and private landowners to 
effectively manage prescribed fire use to reduce the impact of 
catastrophic wildfire-related emissions on ozone, PM10 and 
PM2.5.
a. Current Situation
    When the EPA promulgated the 2007 Exceptional Events Rule, we 
included definitions for fire-related terms (e.g., wildfire, prescribed 
fire and wildland) in the preamble and attributed these definitions to 
the National Wildland Fire Coordinating Group (now the National 
Wildfire Coordinating Group or NWCG) Glossary of Wildland Fire 
Terminology, 2003. The EPA did not, however, codify these definitions 
in regulatory text. Since promulgation of the 2007 Exceptional Events 
Rule, the NWCG has modified some of its recommended definitions and the 
EPA used slightly different definitions in its Interim Exceptional 
Events Implementation Guidance, creating some confusion for air 
agencies and other entities working with air agencies who have tried to 
use fire-related definitions and concepts when preparing and submitting 
exceptional events demonstrations for fires.
    The preamble to the 2007 Exceptional Events Rule discussed how the 
EPA expected to apply the rule to wildfires and prescribed fires. The 
EPA stated that wildfires would be considered natural events, while 
prescribed fires would be considered events caused by human activity. 
As events caused by human activity, prescribed fires are subject to the 
``not likely to recur'' criterion, and the preamble to the rule 
discussed the considerations that would apply for this criterion. 
Section V.F.2.d provides a more detailed summary of the current 
situation and planned changes for this criterion.
    Demonstrations for wildfires and those prescribed fires claimed to 
be exceptional events must also address the ``not reasonably 
controllable or preventable'' criterion. Neither the 2007 Exceptional 
Events Rule nor its preamble addressed this criterion in any depth for 
wildfires. Since promulgating the rule in 2007, the EPA has concluded 
that short, general statements in demonstrations for fire events 
satisfy this criterion. The EPA has been advising air agencies that 
when documenting the ``not reasonably controllable or preventable'' 
criterion in a wildfire exceptional events demonstration submittal, air 
agencies should identify the origin and evolution of the wildfire, 
describe local efforts to prevent fires due to unauthorized activity or 
accidental human-caused actions (if relevant given the origin of the 
fire) and explain any efforts to limit the duration or extent (and thus 
the emissions) of the wildfire.68 69 70 We have also advised 
air agencies that if the wildfire originated outside of the 
jurisdiction of the air agency submitting the exceptional events 
demonstration, then the submitting air agency should identify this fact 
in its demonstration.\71\
---------------------------------------------------------------------------

    \68\ 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. See 
question 20b.
    \69\ Prevention/control efforts could include posting High Fire 
Danger signs to make people more careful and prevent accidental 
fires, and/or taking reasonable action to contain a fire once it has 
started.
    \70\ Example language to limit the duration and extent of the 
wildfire might include, ``During wildfires, fire management 
resources were deployed to the fire event giving first priority to 
protecting life and property.''
    \71\ 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 2007 Exceptional Events Rule and its preamble gave more 
extensive treatment to the not reasonably controllable or preventable 
criterion for prescribed fires. The rule text tied the eligibility of 
prescribed fires as approved exceptional events to the air agency 
having a ``certified'' SMP in place or, in the alternative, to using 
BSMP for the prescribed fire(s) in question. In the preamble, the EPA 
did not provide detailed guidance on SMPs or BSMP, but committed to 
defining and developing these concepts when we updated the guidance 
contained in the 1998 Interim Air Quality Policy on Wildland and 
Prescribed Fires.\72\ However, the EPA has not revised this guidance 
document. Although some states have developed demonstrations that 
incorporate BSMP employed for a specific prescribed fire and/or have 
referenced BSMP in their SMPs, the EPA has not in any other more recent 
guidance clarified what it means for an air agency or burner to have a 
certified SMP in place and/or to implement BSMP. Like the inconsistency 
that has developed since 2007 in fire-related definitions, the absence 
of further clarifying guidance on SMPs and BSMP has created confusion 
for air agencies trying to develop these plans and/or apply these 
practices for purposes of developing and submitting exceptional events 
demonstrations for prescribed fires.
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    \72\ 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.
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b. Proposed Changes
    In this action, the EPA proposes to codify in regulatory language 
certain fire-related definitions and SMP/BSMP factors necessary for 
exceptional events demonstration and program implementation purposes. 
Codifying these definitions in 40 CFR 50.1 will promote understanding 
and standardize terminology for the purposes of characterizing an event 
for exceptional events demonstration purposes.
    Finalizing these proposed changes will also decouple implementation 
of the exceptional events process from potential future revisions to 
the Interim Policy on Wildland and Prescribed Fires. Although the EPA 
solicits comment on the regulatory process associated with developing 
exceptional events demonstrations for fire-related events, the EPA does 
not intend to take comment on any aspects of the 1998 Interim Policy on 
Wildland and Prescribed Fires as part of this effort to revise the 
Exceptional Events Rule.
    The proposed new definitions, along with other proposed changes, 
are described in detail in the separate sections on wildfires (section 
V.F.2.c) and prescribed fire (section V.F.2.d) that follow immediately 
below this section.
c. Wildfires
    Current Situation. The preamble to the 2007 Exceptional Events Rule 
defined a wildfire as ``an unplanned, unwanted wildland fire (such as a 
fire caused by lightning), [to] include unauthorized human-caused fires 
(such as arson or acts of carelessness by humans), escaped prescribed 
fire projects (escaped control due to unforeseen circumstances), where 
the appropriate management response includes the objective to suppress 
the fire.'' The 2007 Exceptional Events Rule preamble also defined a 
``wildland fire use'' as ``the application of the appropriate 
management response to a naturally-ignited (e.g., as the result of 
lightning) wildland fire to accomplish specific resource management 
objectives in predefined and designated areas

[[Page 72868]]

where fire is necessary and outlined in fire management or land 
management plans.'' The 2007 Exceptional Events Rule preamble further 
clarified that the EPA believed that both wildfires and wildland fire 
use fires fall within the meaning of ``natural events'' as that term is 
used in CAA section 319(b).
    In the 2013 Interim Q&A Document, after consulting with other 
federal agencies that manage wildfires and prescribed fires, the EPA 
defined a wildfire as ``[a]ny fire started by an unplanned ignition 
caused by lightning; volcanoes; unauthorized activity; accidental, 
human-caused actions; and escaped prescribed fires.'' \73\
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    \73\ 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.
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    Building off of the principles in the February 2009 Guidance for 
Implementation of Federal Wildland Fire Management Policy,\74\ the NWCG 
defines ``wildland'' as ``an area in which development is essentially 
non-existent, except for roads, railroads, power lines, and similar 
transportation facilities. Structures, if any, are widely scattered.'' 
\75\
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    \74\ Guidance for Implementation of Federal Wildland Fire 
Management Policy, developed cooperatively by the Fire Executive 
Council, February 13, 2009. Available at http://wildfiretoday.com/documents/Federal%20Wildland%20Fire%20Management%20Policy%2002-13-2009.pdf.
    \75\ National Wildfire Coordinating Group. Glossary of Wildland 
Fire Terminology, PMS 205. October 2014. Available at http://www.nwcg.gov/sites/default/files/products/pms205.pdf.
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    Proposed Changes. Although the EPA has previously approved 
exceptional events demonstrations for wildfires,\76\ the EPA recognizes 
air agencies preparing exceptional events demonstrations for future 
wildfires will benefit from additional clarification and guidance 
related to wildfire terminology. This section discusses the EPA's 
proposed changes.
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    \76\ See submitted exceptional events demonstrations available 
on the EPA's Web site at http://www2.epa.gov/air-quality-analysis/exceptional-events-submissions-table.
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    (i) Definition of wildland and wildfire. For purposes of this 
action, the EPA proposes to codify in regulatory language the 
definition of ``wildland'' by using the October 2014 NWCG Glossary 
definition that a wildland is ``an area in which human activity and 
development is essentially non-existent, except for roads, railroads, 
power lines, and similar transportation facilities. Structures, if any, 
are widely scattered.'' As previously noted, wildland can include 
forestland, shrubland, grassland and wetlands. This proposed definition 
of wildland would include lands that are predominantly wildland, such 
as land in the wildland-urban interface.77 78
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    \77\ The wildland-urban interface is the line, area or zone 
where structures and other human development meet or intermingle 
with undeveloped wildland or vegetative fuels. The term describes an 
area within or adjacent to private and public property where 
mitigation actions can prevent damage or loss from wildfire. See, 
Glossary of Wildland Fire Terminology, PMS 205. October 2014. 
Available at http://www.nwcg.gov/sites/default/files/products/pms205.pdf.
    \78\ We would generally treat a large prescribed fire in a 
wildland-urban interface area as a prescribed fire on wildland, 
subject to the prescribed fire provisions described in this 
proposal. We do not expect a small prescribed fire in an interface 
area (e.g., a prescribed burn ignited by a single landowner on his/
her personal property) to generate emissions that would raise 
exceptional events issues.
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    In proposing this definition for wildland, the EPA considered the 
types of human intervention that could affect whether a land is 
considered a ``wildland.'' In our view and the view of other federal 
agencies with which we have consulted in the development of this 
proposed action, the presence of fences to limit the movement of 
grazing animals, or of infrastructure to provide water to grazing 
animals, does not prevent a land area from being wildland. Cultivated 
cropland (i.e., a field that is plowed or disked or from which crops 
are removed on an annual or more frequent basis) is not wildland. Land 
areas on which nursery stock is grown to marketable size (e.g., 
Christmas tree farms) are generally not wildland unless they are 
``wild'' in terms of a having only limited human entrance and 
intervention for management or removal purposes thereby resulting in a 
complex ecosystem. Generally, managed timber lands may be considered 
wildland if they have a complex ecosystem affected by only limited 
human entrance and intervention. The EPA invites comment on whether it 
would be appropriate to incorporate these examples of land use types 
that can be considered to be (or not to be) wildland into the 
regulatory definition of wildland or whether or it is adequate to 
discuss them in the preamble only.
    Also for purposes of this action, the EPA proposes to codify in 
regulatory language the following definition of ``wildfire,'' which 
slightly modifies the definition of ``wildfire'' with respect to 
prescribed fires that appeared in the Interim Q&A document.

    A wildfire is any fire started by an unplanned ignition caused 
by lightning; volcanoes; other acts of nature; unauthorized 
activity; or accidental, human-caused actions; or a prescribed fire 
that has been declared to be a wildfire. A wildfire that 
predominantly occurs on wildland is a natural event.

    This proposed definition of wildfire does not require that the 
objective be to put out a fire for the fire to be categorized as a 
wildfire. When an unplanned fire on wildland does not threaten 
catastrophic consequences, it may be very appropriate to allow it to 
continue. The proposed definition therefore encompasses the type of 
activity previously referred to as a wildland fire use (i.e., a 
situation in which a fire manager deliberately allows a wildfire to 
continue to burn over a certain land area rather than immediately 
extinguish it or block its progress into that area). This inclusion is 
consistent with the approach taken in 2007 that all types of wildfire 
were considered to be natural. We note here, as guidance, that the part 
of the proposed definition referring to a prescribed fire that has been 
declared to be a wildfire refers to specific instances in which the 
conditions of a particular prescribed fire have developed in a way that 
leads the fire manager to decide that the fire should be treated as a 
wildfire, for example if it has escaped secure containment lines and 
requires suppression along all or part of its boundary or no longer 
meets the resource objectives (e.g., smoke impact, flame height). It is 
not the intention that land managers may categorically re-define some 
types of prescribed fire to be wildfires.
    Because the EPA is proposing in rule text that all wildfires on 
wildland are always considered natural events, the proposed definition 
of wildland will in turn determine which fires are considered to be 
natural events. This is consistent with the approach in the 2007 
Exceptional Events Rule. The EPA realizes that some wildfires are 
initiated by human actions (e.g., careless use of campfires or leaf and 
brush pile fires). The EPA also realizes that past human activity in 
the form of decades of suppressing wildfires has influenced the size 
and emissions of wildfires that do occur. However, wildfire is mostly 
dominated by natural factors, and the EPA believes that treating all 
wildfires on wildland as natural events is in keeping with 
Congressional intent and not contradictory to any plain meaning of CAA 
section 319(b). Therefore, because a wildfire on wildland is a natural 
event and because natural events can recur, an air agency would not 
need to address event recurrence in the ``human activity unlikely to 
recur at a particular location or a natural event'' portion of its 
exceptional events demonstration.
    (ii) Not reasonably controllable or preventable. Although a 
wildfire is unplanned, the ``not reasonably

[[Page 72869]]

controllable or preventable'' criterion still applies. Another function 
of the definition of wildland is that the EPA is proposing that the 
treatments of wildfires and prescribed fires on wildland with regard to 
the not reasonably controllable or preventable criterion have a number 
of common aspects, as described here and below in the section on 
prescribed fires, because a wildland situation presents particular 
considerations applicable to both fire types with respect to what 
prevention or control measures may be reasonable. The EPA is not 
proposing any general approach for wildfires or prescribed fires that 
are not on wildland.\79\
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    \79\ While we are proposing special provisions only for fires 
that occur predominantly on wildland, we do not intend to restrict 
fires on other types of land from receiving similar treatment. In 
addressing the not reasonably controllable or preventable criterion 
in a demonstration for a wildfire that is not on wildland, air 
agencies should state that available resources were reasonably aimed 
at suppression and avoidance of loss of life and property and that 
no further efforts to control air emissions from the fire would have 
been reasonable.
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    Because wildfires on wildland are unplanned, fire management 
agencies generally have either no advanced notice or limited and 
uncertain notice, of wildfire ignition and location. In addition, many 
areas of wildland are very remote and rugged, and thus not easily 
reached and traversed. These factors generally limit preparation time 
and on-site resources to prevent or control the initiation, duration or 
extent of a wildfire. Also, by their nature, catastrophic wildfires 
typically present some risk of property damage, ecosystem damage and/or 
loss of life (of the public or firefighters), which is a strong 
motivation for appropriate suppression and control efforts. The EPA 
believes that land managers and other fire management entities have the 
motivation and the best information for taking action to reasonably 
prevent and limit the extent of wildfires on wildland, thus also 
controlling the resulting emissions. Therefore, the EPA believes that 
it is not useful to require air agencies to include in their individual 
wildfire exceptional events demonstrations descriptions of prevention 
and control efforts employed by burn managers to support a position 
that such efforts were reasonable. To increase the efficiency of the 
exceptional events process, the EPA proposes a new approach for 
wildfires on wildland, under which there would be a rebuttable 
presumption that every wildfire on wildland satisfies the ``not 
reasonably controllable or preventable'' criterion, unless evidence in 
the record demonstrates otherwise. Applying this categorical 
presumption of not reasonably controllable for wildfires would involve 
referencing the appropriate regulatory citation in the demonstration.
    As previously stated, there will be situations in which a fire 
manager could have suppressed or contained a wildfire but has allowed 
the fire to continue burning through an area with a current, in-place 
land management plan calling for restoration through natural fire or 
mimicking the natural role of fire. The EPA recognizes that this 
scenario could occur when a fire manager has a plan for acquiring 
personnel and equipment to address the wildfire (either coincidentally 
or because the wildfire was originally a prescribed fire) but the 
manager determines that allowing the wildfire to continue burning is 
safe and will conserve overall fire management resources compared to 
suppressing or containing the current wildfire and then conducting a 
separate prescribed burn at a later time. In such a scenario, even 
though the fire would meet the definition of a wildfire and even though 
we are proposing that in general wildfires will not need to be reviewed 
individually against the not reasonably controllable or preventable 
criterion, we would expect the fire manager to employ appropriate BSMP 
as described in section V.F.2.d when possible.
    (iii) Coordinated communications. Regardless of the above 
considerations for wildfires, the EPA urges land managers and air 
agencies to coordinate, as appropriate, in developing plans and 
appropriate public communications regarding public safety and reducing 
exposure in instances where wildfires are potential exceptional events 
and contribute to exceedances of the NAAQS. Coordinated efforts can 
help air agencies satisfy the Exceptional Events Rule obligation at 40 
CFR 51.930 that air agencies must provide public notice and public 
education and must provide for implementation of reasonable measures to 
protect public health when an event occurs.\80\ Also, when wildfire 
impacts are frequent and significant in a particular area, land 
managers, land owners, air agencies and communities may be able to 
lessen the impacts of wildfires by working collaboratively to take 
steps to minimize fuel loading in areas vulnerable to fire.\81\ Fuel 
load minimization steps can consist of both prescribed fire and 
mechanical treatments, such as using mechanical equipment to reduce 
accumulated understory.
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    \80\ 72 FR 13575 (March 22, 2007).
    \81\ One example of this collaborative approach is the evolving 
interagency Wildland Fire Air Quality Response Program, which has 
developed resources to help address and predict smoke impacts from 
wildfires to reduce public exposure to wildfire smoke. Additional 
information is available at http://www.westar.org/Docs/Business%20Meetings/Spring14/Boise/12.3%20Lahm_WFAQRP_5_28_14.pdf.
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d. Prescribed Fires
    As noted previously, the EPA recognizes and acknowledges the 
potential significant impact on air quality posed by catastrophic 
wildfires. The use of prescribed fire on wildland can influence the 
occurrence, severity, behavior and effects of catastrophic wildfires, 
which may help manage the contribution of wildfires to measured ambient 
pollutant levels (particularly ozone and PM concentrations). 
Additionally, prescribed fires can benefit the plant and animal species 
that depend upon natural fires for propagation, habitat restoration and 
reproduction, as well as a myriad of ecosystem functions (e.g., carbon 
sequestration, maintenance of water supply systems and endangered 
species habitat maintenance). The EPA formally recognized in the 1998 
Interim Air Quality Policy on Wildland and Prescribed Fires that 
federal, tribal and state owners and land managers use prescribed fire 
on wildland to achieve some of these resource benefits, to correct the 
undesirable conditions created by past wildfire suppression management 
strategies and to reduce the risk of wildfires to the public. Although 
the 1998 Interim Air Quality Policy on Wildland and Prescribed Fires 
focused on the role of federal, tribal and state owners/land managers, 
it also recognized that prescribed fires on private lands achieve some 
of the same goals. These concepts, also noted in the preamble to the 
2007 Exceptional Events Rule, are summarized in more detail immediately 
below. In recent regulatory actions,\82\ the EPA has continued to 
express an understanding of the importance of prescribed fire, noting 
that it can be used to mimic the natural process necessary to manage 
and maintain existing fire-adapted ecosystems and/or return an area to 
its historical ecosystem (or another natural ecosystem if the 
historical ecosystem is no longer attainable) while reducing the risk 
to public safety and the risk of uncontrolled emissions from 
catastrophic wildfires.
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    \82\ See, for example, National Ambient Air Quality Standards 
for Ozone; Proposed Rule (79 FR 75234, December 17, 2014) and 
Implementation of the 2008 National Ambient Air Quality Standards 
for Ozone: State Implementation Plan Requirements; Final Rule (80 FR 
12264, March 6, 2015).
---------------------------------------------------------------------------

    Current Situation. The 2007 Exceptional Events Rule recognized the 
benefits of prescribed fire as

[[Page 72870]]

summarized earlier in this section and included provisions for these 
event types in both the preamble to the final rule and in regulatory 
language. The preamble to the 2007 Exceptional Events Rule defined a 
prescribed fire as ``a fire ignited by management objectives to meet 
specific resource management needs.'' This was consistent with the 
definition of prescribed fire in general use by the fire management 
community at the time.\83\ Also in the preamble language, the EPA 
explained that prescribed fire cannot be classified as natural given 
the extent of the direct human causal connection. However, the preamble 
explained that a prescribed fire that causes or contributes to an 
exceedance or violation of an ambient air quality standard could still 
be considered an exceptional event if it satisfies all core statutory 
elements of CAA section 319(b), including the ``human activity that is 
unlikely to recur at a particular location'' and the ``not reasonably 
controllable or preventable'' criteria.
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    \83\ The October 2014 NWCG definition of ``prescribed fire'' is 
similar but includes the concept that the fire is not illegal: 
``[a]ny fire intentionally ignited by management actions in 
accordance with applicable laws, policies, and regulations to meet 
specific objectives.''
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    The 2007 Exceptional Events Rule preamble further explained that 
air agencies should take into account the natural fire return interval 
\84\ as part of the basis for establishing that the human activity 
(i.e., the prescribed fire) is ``unlikely to recur at a particular 
location.'' The preamble acknowledged that the natural fire return 
interval can vary widely and range from once every year to less 
frequently than once every 200 years.
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    \84\ The natural fire return interval is the typical number of 
years between two successive naturally-occurring fires in a 
specified area or ecosystem. The historical rate of return of these 
fires resulted in plant communities that evolved with recurring fire 
and therefore became dependent on fire for maintenance.
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    When addressing the ``not reasonably controllable or preventable'' 
criterion, the 2007 Exceptional Events Rule preamble instructed 
agencies to examine whether there are ``reasonable alternatives,'' such 
as mechanical or other (e.g., chemical) treatments to the use of 
prescribed fire. The preamble language recognized that, although case- 
and area-specific, any number of conditions could exist that would 
favor the use of prescribed fire rather than alternate treatments. Such 
scenarios identified in the preamble included: significant build-up of 
forest fuels in a particular area that if left unaddressed would pose 
an unacceptable risk of catastrophic wildfire; pest or disease 
outbreak; natural species composition dependent on a specific fire 
return interval; and legal requirements precluding the use of 
mechanical fuel reduction methods.
    The 2007 Exceptional Events Rule also indicated, in both preamble 
discussion and rule text, that to further satisfy the ``not reasonably 
controllable or preventable'' criterion for prescribed fires and to 
address the principle at section 319(b)(3)(A) of the CAA that the 
protection of public health is the highest priority, a prescribed fire 
would be considered to be an exceptional event only if the state has 
certified to the EPA that it has adopted and is implementing a SMP or 
the state has ensured that the burner has employed BSMP. While the EPA 
did not identify in the 2007 Exceptional Events Rule the necessary 
components of an SMP or what SMP certification entails, the preamble 
cited the 1998 Interim Air Quality Policy on Wildland and Prescribed 
Fires.\85\ This policy identified the following basic components of a 
certifiable SMP: \86\
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    \85\ The discussion of the 1998 Interim Air Quality Policy on 
Wildland and Prescribed Fires recommendations regarding SMPs appears 
in the preamble to the 2007 Exceptional Events Rule at 72 FR 13567 
(March 22, 2007).
    \86\ The language associated with the six basic components of a 
certifiable SMP was taken directly from the 1998 Interim Air Quality 
Policy on Wildland and Prescribed Fires. For context, the EPA notes 
that the identified components of a certifiable SMP apply to 
managing smoke from prescribed fires managed for resource benefits. 
The EPA would expect burn managers to consider actions and 
approaches where applicable or where appropriate rather than in all 
prescribed fire scenarios.
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     Authorization to Burn--includes a process for authorizing 
or granting approval to manage fires for resource benefits within a 
region, state or on Indian lands and identify a central authority 
responsible for implementing the program. The authorization process 
could include burn plans that consider air quality and the ability of 
the airshed to disperse emissions from all burning activities on the 
day of the burn.
     Minimizing Air Pollutant Emissions--encourages wildland 
owners/managers to consider and evaluate alternative treatments to 
fire, but if fire is the selected approach to follow emission reduction 
techniques.
     Smoke Management Components of Burn Plans--identifies the 
following components if the SMP requires burn plans: Actions to 
minimize fire emissions, evaluate smoke dispersion, public notification 
and exposure reduction procedures and air quality monitoring.
     Public Education and Awareness--establishes the criteria 
for issuing health advisories when necessary and procedures for 
notifying potentially affected populations.
     Surveillance and Enforcement--includes procedures to 
ensure that wildland owners/managers comply with the SMP.
     Program Evaluation--provides for periodic review by all 
stakeholders of the SMP effectiveness and program revision as 
necessary.
    The 1998 Interim Air Quality Policy on Wildland and Prescribed 
Fires also noted, regarding the certification process for SMPs, that to 
receive special consideration for air quality data whose concentrations 
were influenced by prescribed fires, ``[t]he State/tribal air quality 
manager must certify in a letter to the Administrator of EPA that at 
least a basic [smoke management] program has been adopted and 
implemented . . . .'' The 1998 Interim Air Quality Policy on Wildland 
and Prescribed Fires further identified that federal agencies intending 
to use prescribed fire should operate under an approved prescribed fire 
plan and meet the National Environmental Policy Act (NEPA) 
requirements, where applicable, prior to ignition.\87\
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    \87\ In specifying the basic components of certifiable SMPs that 
would include the requirement for agency approval of prescribed fire 
plans, the 1998 Interim Air Quality Policy on Wildland and 
Prescribed Fires noted that SMPs can mitigate the nuisance and 
public safety hazards associated with smoke from prescribed fires 
intruding into populated areas, prevent deterioration of air quality 
and NAAQS violations and address visibility impacts in mandatory 
Class I Federal areas. Since the EPA issued the Interim Policy in 
1998, some federal agencies have reported to us their assessment 
that some states and/or local air agencies have managed their SMP 
(or other regulatory programs) in such a way as to exclude the use 
of prescribed fires in areas to such an extent that fuels have 
continued to accumulate to levels that increase the likelihood of 
catastrophic wildfires.
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    The EPA did not use the preamble to the 2007 Exceptional Events 
Rule to expand on the concept of using BSMP in lieu of an SMP. Rather, 
the EPA only noted that burners could use BSMP to minimize emissions 
and control the impacts of fire. Although the EPA identified several 
example BSMP in a footnote in the preamble (footnote 12 at 72 FR 
13567), we also committed to developing the concept when we updated the 
guidance in the 1998 Interim Air Quality Policy on Wildland and 
Prescribed Fires. The EPA has not revised this guidance and does not 
currently plan to do so. Although some states have developed 
demonstrations that incorporate BSMP employed for a specific prescribed 
fire and/or referenced BSMP in their SMPs, the EPA has not in any other 
more recent guidance clarified what it means for an

[[Page 72871]]

air agency or burner to have a certified SMP in place and/or to 
implement BSMP.
    In addition to conditioning the approval of a prescribed fire as an 
exceptional event on the existence and implementation of a certified 
SMP or the actual use of BSMP, as described above, the 2007 Exceptional 
Events Rule also requires that ``[i]f an exceptional event occurs using 
the basic smoke management practices approach, the State must undertake 
a review of its approach to ensure public health is being protected and 
must include consideration of development of a SMP.'' To date, air 
agencies have submitted few exceptional events demonstrations for 
prescribed fires. One recent submission came from Kansas, a state 
already operating an SMP.\88\
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    \88\ Treatment of Data Influenced by Exceptional Events: 
Exceptional Events Submissions Table. U.S. Environmental Protection 
Agency, Research Triangle Park, NC. See links associated with 
``April 2011 Fires'' in the ozone section of the table available at 
http://www2.epa.gov/air-quality-analysis/exceptional-events-submissions-table.
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    The 2007 Exceptional Events Rule at 40 CFR 50.14(b)(3) allows for 
the exclusion of data where a state demonstrates to the EPA's 
satisfaction that emissions from prescribed fires caused a specific air 
pollution concentration in excess of one or more NAAQS at a particular 
air quality monitoring location and otherwise satisfies the 
requirements in the Exceptional Event Rule. The regulatory language 
also requires that the subject prescribed fire meets the definition in 
40 CFR 50.1(j) and requires that the state has certified to EPA that it 
has adopted and is implementing a Smoke Management Program or the state 
has ensured that the burner employed basic smoke management practices. 
The definition of an exceptional event at 40 CFR 50.1(j) includes the 
requirement that an event ``is not reasonably controllable or 
preventable.'' Thus, the EPA has interpreted that a demonstration for a 
prescribed fire independently address both the SMP/BSMP element and the 
not reasonably controllable or preventable criterion. We have not 
indicated that meeting the SMP/BSMP condition is sufficient to satisfy 
the not reasonably controllable or preventable criterion.
    Proposed Changes. As previously noted, the EPA has not to date 
clarified fire-related definitions or its expectations regarding SMPs 
or BSMP in rule or preamble form. This uncertainty has created 
confusion for air and fire management agencies trying to develop fire-
related plans and/or apply fire management practices for prescribed 
fires. It has also created confusion for air agencies when developing 
and submitting exceptional events demonstrations for both wildfires and 
prescribed fires.
    To assist air agencies in documenting an exceptional events package 
for a prescribed fire on wildland, the EPA proposes to clarify its 
expectations for a satisfactory demonstration, as follows.
    (i) Definition of a prescribed fire. We are proposing to adopt in 
rule language the current NWCG-recommended definition of a prescribed 
fire: ``[a]ny fire intentionally ignited by management actions in 
accordance with applicable laws, policies and regulations to meet 
specific objectives.'' In this definition, ``management'' refers to the 
owner or manager of the land area to which prescribed fire is applied, 
and ``specific objectives'' refers to specific land or resource 
management objectives.
    (ii) Events caused by human activity. We are proposing to say in 
rule form that prescribed fires are events caused by human activity. 
Thus, to be considered an exceptional event, every prescribed fire 
demonstration must address the ``human activity unlikely to recur at a 
particular location'' criterion.
    (iii) Unlikely to recur at a particular location. As discussed in 
more detail in section V.E.1 of this proposal, this requirement of CAA 
section 319(b) is not specific and 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.
    As was our position in 2007, we continue to believe that the 
natural fire return interval is a useful and appropriate benchmark for 
a satisfactory demonstration that a prescribed fire is unlikely to 
recur at a particular location, in the sense that if a planned program 
of prescribed fire calls for the application of prescribed fire at a 
similar interval to the natural fire return interval at given locations 
then each prescribed fire conducted in that program can be considered 
not likely to recur at its particular location. However, we now believe 
based on experience and further consideration that the natural fire 
return interval is not the only appropriate benchmark. It can be 
difficult in some cases to determine what fire return interval 
prevailed under natural conditions, which may not have existed for 
decades or even hundreds of years in a particular area. Also, in some 
cases environmental conditions may have changed, for example due to 
climate change, such that the original natural ecosystem cannot 
realistically be restored and the well-considered land management goal 
instead may be the development and maintenance of a sustainable and 
resilient ecosystem that is different than what historically existed 
and that will likely reduce the risk of catastrophic wildfire. In such 
a case, the frequency of prescribed fire needed to establish or restore 
such an ecosystem during a transitional period and/or the frequency 
needed to sustain the resilient ecosystem may be different than the 
natural fire return interval that once prevailed. It is also important 
to consider issues of fire personnel and public safety and protection 
of nearby property. Land managers may need to apply prescribed fire at 
a frequency that maintains the accumulation of fuel loading between 
prescribed fires at a level that does not create the risk of a 
dangerous wildfire.
    Accordingly, the first proposed change for prescribed fires on 
wildland is to include in the rule text two benchmarks for the expected 
future frequency of prescribed fires on wildland to meet the not likely 
to recur criterion: (1) The natural fire return interval as articulated 
in the 2007 preamble and (2) the prescribed fire frequency needed to 
establish, restore and/or maintain a sustainable and resilient wildland 
ecosystem. If finalized, an air agency could include information 
provided by the land manager with respect to the appropriate benchmark 
for a prescribed fire on wildland as the basis for satisfying the human 
activity unlikely to recur at a particular location criterion in its 
exceptional events demonstration.\89\
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    \89\ The benchmarks for the expected frequency of prescribed 
fires not on wildland would be assessed on a case-by-case basis.
---------------------------------------------------------------------------

    Successfully implementing one of these benchmarks for prescribed 
fire frequency necessitates that the air agency and the land manager 
collaborate to establish and document the appropriate fire return 
interval or frequency in a submitted demonstration. Federal agencies 
that use prescribed fire to manage lands for which they are responsible 
generally prepare multi-year plans for the use of prescribed fire in a 
given national park, national forest, armed forces base or other land 
area. Many of these plans include an

[[Page 72872]]

objective to establish, restore and/or maintain a sustainable and 
resilient wildland ecosystem and incorporate the best science available 
to determine what prescribed fire cycle will accomplish this.\90\ Some 
tribes, private landowners (and federal, state and local agencies 
working with private landowners) and state agencies that manage state-
owned lands (e.g., state parks) also prepare multi-year management 
plans. While plans developed by public agencies (i.e., state and 
federal agencies) often undergo public comment prior to being 
finalized, the plans developed by tribes and private landowners may not 
follow a public comment process. However, public agencies often work 
with tribes and private owners to develop these plans, which are based 
on conservation practices and standards that have often undergone 
public comment as part of the state or federal agency process.
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    \90\ An example of a federal land management plan that considers 
the need for the use of prescribed fire is the Land and Resource 
Management Plan for the Kaibab National Forest, Coconino, Yavapai, 
and Mojave Counties, Arizona, USDA Forest Service Southwestern 
Region, MB-R3-07-17, February 2014, available at http://www.fs.usda.gov/Internet/FSE_DOCUMENTS/stelprd3791580.pdf.
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    The EPA understands that multi-year plans incorporate factors 
relevant to identifying and selecting the areas and times under which 
management will initiate a specific prescribed fire. The EPA also 
recognizes that evaluating the behavior and results of prior prescribed 
fires aids in determining the frequency and need for future prescribed 
fire in a given area. In addition, personnel and equipment must be 
available on site, which cannot be specifically planned far in advance. 
Thus, it is typical for multi-year plans to identify somewhat general 
targets for the frequency of prescribed fire use and for specific burn 
plans. Even then, unexpected differences between planned and actual 
fire behavior, landscape or ecosystem characteristics, fuel loading 
patterns and weather patterns may cause management to deviate from the 
general plan and/or the specific burn plan. Therefore, when the EPA 
reviews an exceptional events demonstration for a prescribed fire 
conducted under a wildland management plan, we intend to compare the 
actual time pattern of prescribed fires on the land with the pattern 
described in the applicable multi-year plan in a general way, rather 
than treating the multi-year plan as containing a specific schedule to 
which management must adhere. For example, if the wildland management 
plan identified an approximate 5-year burn interval, the EPA would not 
disapprove a demonstration if the burn occurred on a 4-year or a 6-year 
interval.
    Therefore, we are proposing in rule text that we will consider a 
demonstration's referencing of a multi-year land or resource management 
plan \91\ (and including either a copy or an internet link to the plan) 
with a stated objective to establish, restore and/or maintain a 
sustainable and resilient wildland ecosystem and/or to preserve 
endangered or threatened species that also identifies the subject area 
as a candidate for prescribed fire to be dispositive evidence that a 
particular fire conducted in accordance with such a plan satisfies the 
``unlikely to recur at a particular location'' criterion. We would also 
consider a demonstration's referencing of a fire management plan for 
tribal or private lands that has been reviewed and certified by the 
appropriate fire and/or resource management professionals and agreed to 
and followed by the land owner/manager to be sufficient evidence 
satisfying the ``unlikely to recur at a particular location'' 
criterion.
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    \91\ These plans could also include fire management plans, 
prescribed fire on wildland management plans, landscape management 
plans or equivalent public planning documents.
---------------------------------------------------------------------------

    (iv) Not reasonably controllable or preventable. Consistent with 
current practice and 2007 preamble/rule language, the EPA considers it 
appropriate to allow air agencies to rely on an in-place and 
implemented state-certified SMP to satisfy the controllability prong of 
the ``not reasonably controllable or preventable'' criterion. The EPA 
proposes to incorporate the six elements of SMPs discussed in the 1998 
Interim Air Quality Policy on Wildland and Prescribed Fires and 
referenced in the preamble to the 2007 Exceptional Events Rule into the 
preamble of the final rule for this proposal, where it would serve as 
guidance. That is, at a minimum, a state-certified SMP would include 
provisions for (i) authorization to burn, (ii) minimizing air pollutant 
emissions, (iii) smoke management components of burn plans, (iv) public 
education and awareness, (v) surveillance and enforcement, and (vi) 
program evaluation. Certification would require that the air agency 
certify in a letter to the Administrator of the EPA, or a Regional 
Administrator, that it has adopted and is implementing a SMP.\92\ 
Alternatively, the EPA solicits comment on incorporating these SMP 
elements into rule text language. The EPA proposes to accept as 
sufficient the testimony of the air agency submitting an exceptional 
events demonstration that the SMP is being implemented, provided that 
prior to the EPA's acting on a demonstration, the record contains no 
clear evidence to the contrary.
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    \92\ The EPA anticipates that any person within an air agency 
responsible for submitting exceptional events demonstrations or SIP 
revisions could also be responsible for certifying a Smoke 
Management Program.
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    Consistent with current practice and 2007 preamble and rule 
language, the EPA also considers it appropriate to allow air agencies 
to rely on a burn manager's use of BSMP that minimize emissions and 
control impacts, in lieu of a state-certified SMP, to satisfy the 
controllability prong of the ``not reasonably controllable or 
preventable'' criterion. To provide clarity and reduce uncertainty for 
air agencies and burn managers, the EPA proposes to identify in the 
rule text six BSMP practices as being generally applicable for 
exceptional events purposes for prescribed fires on wildland as well as 
other prescribed fires. The six BSMP, listed and described in more 
detail in Table 3, come from guidance on BSMP for prescribed burns 
provided by the U.S. Department of Agriculture (USDA) Forest Service 
(USFS) and USDA Natural Resources Conservation Service (NRCS).\93\ Land 
managers of other federal, state and local agencies and private land 
owners generally endorse and follow this BSMP guidance.\94\ While the 
listed practices are broadly stated, fire managers use site-specific 
considerations to select the exact actions of each type and apply them 
to specific burn projects. There may be situations in which one or more 
of the six BSMP is clearly not applicable for a particular prescribed 
burn--for example, if a prescribed fire is so remote that there are no 
neighbors to be notified. The EPA generally does not intend to 
challenge a burn manager's selection of the intensity or specific 
measure within the BSMP categories when we review a particular 
exceptional events demonstration. As part of the on-going assessment of 
our

[[Page 72873]]

regulatory programs, we intend to generally review those practices 
commonly employed by federal agencies and other users of prescribed 
fire.
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    \93\ USDA Forest Service and Natural Resources Conservation 
Service, Basic Smoke Management Practices Tech Note, October 2011, 
http://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb1046311.pdf.
    \94\ The EPA also addressed how federal agencies may use basic 
smoke management practices to establish a presumption of conformity 
in the preamble to the EPA's General Conformity Rule at 40 CFR 
93.153(g)-(i) (75 FR 17264, April 5, 2010). The six practices 
identified in Table 3 are not a presumed to conform action for 
purposes of a federal agency satisfying their General Conformity 
responsibilities. For basic smoke management practices to provide a 
presumption of conformity, the identified basic smoke management 
practices must be publicly and state reviewed as part of a presumed 
to conform action under 40 CFR 93.153(g) or (f) of the General 
Conformity Rule.
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    As another component of the approach for prescribed fires on 
wildland, the EPA is proposing to accept as evidence of the actual use 
of BSMP the fire manager's statement that he or she employed applicable 
BSMP for a prescribed fire. Documentation of such statement for an 
exceptional events demonstration could consist of a copy of the routine 
post-burn report or a letter prepared by the fire manager (see example 
content of a burn report in Table 4). The EPA and other federal 
agencies will work collaboratively to provide access to such post-burn 
reports by air agencies that need them. We encourage land managers and 
other organizations that employ prescribed fires to work with states 
and tribes to develop an efficient process to provide air agencies with 
documentation that BSMP were employed for particular prescribed fires.

 Table 3--Summary of Basic Smoke Management Practices, Benefit Achieved
                  With the BSMP, and When It Is Applied
           [before, during or after ignition of the burn] \a\
------------------------------------------------------------------------
                                                      When the BSMP is
   Basic smoke management       Benefit achieved      applied--before/
          practice                with the BSMP       during/after the
                                                            burn
------------------------------------------------------------------------
Evaluate Smoke Dispersion     Minimize smoke        Before, During,
 Conditions.                   impacts.              After.
Monitor Effects on Air        Be aware of where     Before, During,
 Quality.                      the smoke is going    After.
                               and degree it
                               impacts air quality.
Record-Keeping/Maintain a     Retain information    Before, During,
 Burn/Smoke Journal.           about the weather,    After.
                               burn and smoke. If
                               air quality
                               problems occur,
                               documentation helps
                               analyze and address
                               air regulatory
                               issues.
Communication--Public         Notify neighbors and  Before, During.
 Notification.                 those potentially
                               impacted by smoke,
                               especially
                               sensitive receptors.
Consider Emission Reduction   Reducing emissions    Before, During,
 Techniques.                   through mechanisms    After.
                               such as reducing
                               fuel loading can
                               reduce downwind
                               impacts.
Share the Airshed--           Coordinate multiple   Before, During,
 Coordination of Area          burns in the area     After.
 Burning.                      to manage exposure
                               of the public to
                               smoke.
------------------------------------------------------------------------
\a\ The EPA believes that elements of these BSMP could also be practical
  and beneficial to apply to wildfires for areas likely to experience
  recurring wildfires.


   Table 4--Elements That may be Included in Burn Plans and Post-Burn
      Reports for Prescribed Fires Submitted as Exceptional Events
------------------------------------------------------------------------
           Element                  Burn plan         Post-burn report
------------------------------------------------------------------------
Fire Name \a\...............  X...................  X.
Permit number (if             X...................  X.
 appropriate).
Latitude/longitude and        X...................  X.
 physical description.
Date of burn, ignition time   X...................  X.
 and completion time
 (duration of burn).
AQI status on burn day, if    Predicted...........  Actual.
 available (both in the
 vicinity of the fire and in
 the affected upwind area).
Acres burned................  Planned.............  Actual (blackened).
Description of fuel loading.  Estimated...........  Actual (tons
                                                     consumed).
Meteorological data (weather  Predicted conditions  Actual conditions
 conditions, wind speed and    (including            (including actual
 direction, dispersion).       predicted             dispersion).
                               dispersion).
Smoke Impacts...............  Anticipated smoke     Observed or reported
                               impacts.              smoke impacts
                                                     (include nature,
                                                     duration, spatial
                                                     extent and copies
                                                     of received
                                                     complaints).
BSMP actions to reduce        Expected BSMP         Actual BSMP actions.
 impacts.                      actions.
Recommendations for future    ....................  X.
 burns in similar areas.
Analytics (modeled/actual     ....................  X.
 fire spread, satellite
 imagery and analysis,
 webcam/video, PM/ozone
 concentrations over the
 course of the fire).
------------------------------------------------------------------------
\a\ The ``Fire Name'' should be unique and referenced, to the greatest
  extent possible, in all exceptional events-related documentation,
  including the event name in AQS. The fire name could simply consist of
  the county and state in which the burn occurred (e.g., County X, State
  Y Prescribed Burn on Date Z) if no other name has been assigned.

    States with certified SMPs typically have robust communications 
between officials concerned with air quality impacts and officials and 
members of the public who use prescribed fire. These groups communicate 
during the development of the SMP, during the day-to-day burn 
authorization process and in the periodic review and potential revision 
of the SMP. States that instead rely on fire managers employing BSMP on 
a more individual basis may not have

[[Page 72874]]

such regularly occurring communications processes, particularly in 
states in which state legislation gives the leadership of fire 
management to a forestry or public safety agency rather than to an air 
agency. We encourage all agencies and managers/owners involved in land, 
air quality and fire management to develop good communications about 
both fire use practices in general and plans for specific prescribed 
fires with use of BSMP. This will, among other benefits, allow them to 
better coordinate on public air quality notice efforts and, if 
necessary, public health advisories should smoke enter an inhabited 
area. Additionally, the EPA encourages the development of ``prescribed 
fire councils,'' comprised of federal, state, tribal, private and other 
stakeholders to coordinate activities involving fire planning issues 
and, thus, minimize or prevent smoke impacts while using prescribed 
fire to accomplish land management objectives.\95\ However, we are not 
proposing that notifications between prescribed fire users and specific 
types of state agencies be a condition for approval of a prescribed 
fire as an exceptional event.
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    \95\ See additional information on prescribed fire councils on 
the Coalition of Prescribed Fire Councils, Inc. Web site at http://www.prescribedfire.net/membership/state-councils.
---------------------------------------------------------------------------

    As previously stated, to date we have considered the existence and 
implementation of a SMP or the use of BSMP to be a necessary part of 
the supporting evidence needed to satisfy the not reasonably 
controllable or preventable criterion, but we have not clearly 
addressed what conditions are minimally sufficient to satisfy the 
criterion. The remainder of this section focuses on that issue.
    Because prescribed fires are intentionally initiated, clarifying 
the minimal conditions for the not reasonably preventable prong is 
particularly relevant. The detailed USFS/NRCS guidance on the fifth 
listed BSMP, Consider Emission Reduction Techniques, includes the 
potential to reduce the fuel loading. It does not suggest that it may 
be reasonable to not ignite a particular prescribed fire (i.e., that 
the fire be prevented), because this guidance is aimed at those fires 
that are already planned to happen. Similarly, SMPs address 
coordination of previously planned prescribed fires and typically do 
not ask SMP participants to consider whether particular prescribed 
fires are reasonably preventable. Therefore, we do not believe that the 
existence of an SMP or the use of BSMP is a sufficient basis for 
concluding that a prescribed fire is not reasonably preventable. A 
prescribed fire should be concluded to be not reasonably preventable on 
the basis of the benefits that would be foregone if it were not 
conducted, as described below.
    For federal agencies, the planning of prescribed fire programs 
typically happens through the development of multi-year plans that 
focus on specific land or resource management objectives. This planning 
process, and the resulting multi-year plan, typically considers the 
importance of a prescribed fire program to achieving land management 
goals, which may include an objective to establish, restore and/or 
maintain a sustainable and resilient wildland ecosystem, in light of 
the availability, cost and effectiveness of other approaches to fuel 
management. The final multi-year plans thus generally identify the 
level of prescribed fire use necessary to achieve those goals. As noted 
previously, some tribes, private landowners (and federal, state and 
local agencies working with private landowners) and state agencies that 
manage state-owned lands (e.g., state parks) also prepare multi-year 
management plans. While plans developed by public agencies (i.e., state 
and federal agencies) often undergo public comment prior to being 
finalized,\96\ the plans developed by tribes and private landowners may 
not follow a public comment process. However, public agencies often 
work with tribes and private owners to develop these plans, which are 
based on conservation practices and standards that have often undergone 
public comment as part of the state or federal agency process. Not 
conducting the prescribed fire programs described in such plans could 
mean forgoing important ecosystem services and other benefits. 
Accordingly, the EPA is proposing in rule text form to consider a 
prescribed fire on wildland conducted in accordance with a multi-year 
fire management plan that has an objective to establish, restore and/or 
maintain a sustainable and resilient wildland ecosystem to be not 
reasonably preventable, provided there is no compelling evidence to the 
contrary in the record when the EPA approves the associated exceptional 
events demonstration.\97\
---------------------------------------------------------------------------

    \96\ Many multi-year plans developed by state and federal 
agencies are available electronically online or can be requested 
directly from the preparing agency. Interested parties can also 
request electronic versions of project level plans, if they are not 
available online.
    \97\ On a case-by-case basis, in the absence of a multi-year 
plan, the EPA would also consider a prescribed fire on wildland 
conducted on a fire return interval established according to 
scientific literature to satisfy the not reasonably controllable or 
preventable criterion provided the prescribed fire was also 
conducted with the objective to establish, restore and/or maintain a 
sustainable and resilient wildland ecosystem and conducted in 
compliance with either a state-certified SMP or BSMP. This case-by-
case approach is similar to the approach currently used under the 
2007 Exceptional Events Rule.
---------------------------------------------------------------------------

    We also propose in rule text that compliance with either a state-
certified SMP or BSMP is sufficient to establish that a prescribed fire 
was not reasonably controllable, provided there is no compelling 
evidence to the contrary in the record when the EPA concurs with the 
associated exceptional events demonstration. This is an appropriate 
approach to implementing CAA section 319(b), because SMPs and BSMP aim 
to reasonably control the air quality impacts of prescribed fires.\98\
---------------------------------------------------------------------------

    \98\ With respect only to the not reasonably controllable prong, 
we also believe that the SMP and BSMP approach each is sufficient 
for prescribed fires that are not on wildland.
---------------------------------------------------------------------------

    This two-part categorical approach would reduce the length of 
exceptional events demonstrations for prescribed fires on wildland and 
make the demonstration preparation and review process more resource 
efficient. In summary, to satisfy the not reasonably controllable or 
preventable criterion for a prescribed fire on wildland, a 
demonstration would need to identify that the prescribed burn was 
conducted in accordance with a multi-year plan that has an objective of 
the establishment, restoration and/or maintenance of a sustainable and 
resilient wildland ecosystem and was conducted in compliance with 
either a state-certified SMP or BSMP.
    Finally, we are proposing to remove the phrase ``and must include 
consideration of development of a SMP'' from the sentence of the 
existing text of 40 CFR 50.14(b)(3) that reads, ``If an exceptional 
event occurs using the basic smoke management practices approach, the 
State must undertake a review of its approach to ensure public health 
is being protected and must include consideration of development of a 
SMP.'' While the EPA supports states considering the development of a 
SMP in the situation described in this sentence, we believe states have 
had ample opportunity to develop such a program since 2007. This rule 
language effectively requires an ongoing consideration to develop an 
SMP every time a prescribed fire causes a NAAQS exceedance or violation 
that merits exclusion as an exceptional event. We do not believe 
Congress intended this ongoing consideration to be a requirement 
flowing from CAA section 319(b). In addition, we believe that an

[[Page 72875]]

SMP is most appropriate when multiple parties wish to employ prescribed 
fire at about the same time in the same airshed, which is a more narrow 
situation than specified in this sentence. We also do not want our 
rules to be open to an inference that development of a SMP should only 
be considered following a NAAQS exceedance or violation, because the 
impacts from fires may affect public health in areas without NAAQS-
compliance air monitoring stations. Also, we believe that when air 
agencies observe NAAQS exceedances or violations attributed to a 
prescribed fire, air agencies should consider a wide range of 
alternatives including, but not limited to, the development of a SMP. 
For example, agencies might also consider the more frequent or 
intensive use of BSMP to limit the fuel available to burn in each fire.
    The EPA solicits comment on all aspects of the identified fire-
related approaches.
3. Stratospheric Ozone Intrusions
a. Current Situation
    Stratospheric ozone intrusions are natural events that occur when a 
parcel of air originating in the stratosphere is re-entrained into the 
troposphere, and in some cases mixes directly to the surface of the 
earth. These relatively rare events can create elevated ozone 
concentrations that affect areas ranging from a single monitoring site 
to a wider area as the air mass with a high ozone concentration moves 
across the landscape.
    Normally, the tropopause, the temperature inversion layer of air 
that separates the troposphere from the stratosphere, limits the 
transport of stratospheric air into the troposphere, the lowest layer 
of the Earth's atmosphere.\99\ In some cases, however, parcels or 
ribbons of ozone-rich air from the stratosphere can be transported 
rapidly to the surface during deep mixing events, such as thunderstorms 
or strong frontal passages, by a process known as tropopause folding. 
Although this ``folding'' process can occur throughout the year, it is 
typically associated with frontal passages and upper level low pressure 
systems during the spring season.100 101 The ozone 
transported through these ``folds,'' or through other less significant 
mechanisms, may disperse within and be destroyed in the upper 
troposphere or it may mix down to the surface.\102\ The ``intrusion'' 
of stratospheric ozone is identified most frequently at high elevation 
sites where upper tropospheric air is more likely to reach the surface 
than at lower elevation sites where more downward movement would be 
needed for a monitoring site to be affected. At these high elevation 
sites in particular, stratospheric ozone intrusion has been estimated 
to contribute about 20 to 25 percent of the total tropospheric ozone 
budget and can cause relatively short-term (i.e., ranging from several 
hours to 2-3 days in duration) increases of surface ozone of 10 to 50 
ppb above normal background levels.\103\ Stratospheric intrusions with 
short-lived surface ozone concentrations of several hundred ppb have 
also been observed, although these events are extremely rare.
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    \99\ The height of the tropopause varies with latitude and 
season but the average height at mid-latitudes is about 11 
kilometers (km) (7 miles or 36,000 feet). The stratosphere, the 
second layer of the Earth's atmosphere, is located above the 
tropopause at 13 to 50 km (8-31 miles or 43,000 to 160,000 feet) 
above the Earth's surface.
    \100\ Pan, L. L., et al. (2014), ``Thunderstorms enhance 
tropospheric ozone by wrapping and shedding stratospheric air.'' 
Geophys. Res. Lett., 41, 7785-7790, doi:10.1002/2014GL061921.
    \101\ A. O. Langford, K. C. Aikin, C. S. Eubank and E. J. 
Williams. Stratospheric Contribution to High Surface Ozone in 
Colorado During Springtime, Geophysical Research Letters, Vol. 36, 
Issue 12, June 2009.
    \102\ Other mechanisms by which stratospheric ozone is 
transported into the troposphere include cutoff cyclones, streamers 
(long filamentary structures that often roll into vortices), and 
clear air turbulence (see http://www.atmos.umd.edu/~dkuhl/documents/
Kuhl_Tropopause_Folding.ppt).
    \103\ Integrated Science Assessment of Ozone and Related 
Photochemical Oxidants (Final Report). U.S. EPA.Washington, DC EPA/
600/R-10/076F. Available at: http://www3.epa.gov/ttn/naaqs/standards/ozone/s_o3_2008_isa.html.
---------------------------------------------------------------------------

    Because stratospheric intrusion events are relatively infrequent 
and because identifying and monitoring these events are challenging, 
there have been few direct measurements showing that a given parcel of 
surface air contains stratospheric ozone (versus ozone generated by 
local natural or anthropogenic sources). Interpreting these direct 
measurements is also challenging. One approach to confirm the presence 
of stratospheric ozone in surface air is through the use of the 
beryllium tracers, beryllium isotopes Be-7 and Be-10, which are 
produced primarily in the stratosphere by cosmic ray collisions with 
atmospheric gas atoms.\104\ Beryllium isotope measurements are, 
however, rare and expensive, and, consequently not normally available.
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    \104\ Cristofanelli, P. A 6-year analysis of stratospheric 
intrusions and their influence on ozone at Mt. Cimone (2165 m above 
sea level). Journal of Geophysical Research, Vol. 111, D03306, 
doi:10.1029/2005JD006553, 2006.
---------------------------------------------------------------------------

    More common approaches to identify stratospheric ozone in surface 
air can include evaluating measurements at the potentially influenced 
ozone monitoring site for very low concentrations of CO and/or relative 
humidity. Both can be strong indicators of stratospheric air because, 
relative to tropospheric air, stratospheric air has very low relative 
humidity and very low concentrations of other air pollutants such as 
CO, NOX and PM. The concurrent impacts on CO and relative 
humidity can be subtle, however, when stratospheric air has mixed with 
tropospheric air as the mixing process dilutes the ozone enhancement 
and increases CO and water vapor concentrations relative to 
stratospheric conditions. Typical CO monitors used for ambient air 
monitoring have operational ranges of 500 to 50,000 ppb (0.5 to 50 ppm) 
and are not sufficiently sensitive to reliably measure the very low CO 
levels found in stratospheric air (50 to 150 ppb). Additionally, few 
rural high altitude monitoring sites have both ozone and CO 
monitors.\105\ The EPA urges air agencies to provide concurrent 
readings of ozone and CO and/or relative humidity in their exceptional 
events demonstrations if they have these data. The EPA will evaluate 
these data as a part of a weight of evidence showing alongside other 
qualitative evidence in a clear causal relationship showing.
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    \105\ A recent review of AQS data revealed 216 sites in the 
United States with collocated ozone and carbon monoxide monitors in 
operation after January 1, 2014. Most of these sites are located in 
either urban or suburban locations. In these settings, local 
emissions would likely hide the stratospheric CO suppression.
---------------------------------------------------------------------------

    A third measurement-based approach to identifying stratospheric 
ozone could include measurements of ozone above ground level (i.e., 
measurements in the troposphere). This approach is also uncommon. 
Currently, five sites in the U.S. conduct ozone sonde (balloon) 
launches two or more times per week and an additional few research 
locations operate ozone lidars to vertically measure ozone 
profiles.106 107
---------------------------------------------------------------------------

    \106\ Lidar, which stands for Light Detection and Ranging, is a 
remote sensing method that uses light in the form of a pulsed laser 
to measure ranges (variable distances) to the Earth. These light 
pulses, combined with other data recorded by the airborne system, 
generate precise, three-dimensional information about the shape of 
the Earth and its surface characteristics. See, NOAA definition at 
http://oceanservice.noaa.gov/facts/lidar.html.
    \107\ See NOAA data available at ftp://aftp.cmdl.noaa.gov/data/ozwv/Ozonesonde. On April 30, 2015, NOAA's site identified the 
following five sites in the U.S. that conduct bi-weekly ozone sonde 
launchings: Hilo, HI; Huntsville, AL; Narragansett, RI; Trinidad 
Head, CA; and Boulder, CO. Additional launchings occur in Pago Pago, 
American Samoa, and outside of the U.S. in Greenland, Antarctica and 
Fiji.
---------------------------------------------------------------------------

    In the absence of direct measurements of stratospheric tracers at 
ground level,

[[Page 72876]]

meteorological models can indicate conditions under which stratospheric 
air parcels may reach the surface. Meteorological models such as the 
National Oceanic and Atmospheric Administration (NOAA)/National Weather 
Service (NWS) North American Mesoscale Forecast System (NAM) or the 
NOAA Rapid Update Cycle (RUC) models simulate parameters characteristic 
of stratospheric air such as isentropic potential vorticity (IPV) and 
potential temperature (PT) that can be used to identify tropopause 
folding. Visualization tools using the model output can show spatially 
where stratospheric air is located in proximity to or in contact with 
the surface. Similarly, atmospheric chemistry models, such as the 
National Aeronautics and Space Administration (NASA)/NOAA Real-time Air 
Quality Modeling System (RAQMS) \108\ can provide both real time 
intrusion forecasting and retrospective analysis of ozone from 
intrusions. Finally, satellite observation of atmospheric ozone and CO 
can be used to validate predictions based on atmospheric modeling.
---------------------------------------------------------------------------

    \108\ See http://raqms-ops.ssec.wisc.edu/.
---------------------------------------------------------------------------

    Although as of the date of this proposal the EPA has concurred with 
only one stratospheric ozone intrusion exceptional events demonstration 
prepared under the provisions of the 2007 Exceptional Events Rule (and 
disapproved none),\109\ the EPA has been communicating that we consider 
it appropriate to use the previously mentioned stratospheric ozone 
tools with other event/pollutant exceptional events analyses (e.g., 
seasonal analysis of ozone data, comparison of event days with non-
event days, trajectory analysis, ozone measurement time series and 
spatial distribution analysis, meteorological analysis to show the 
presence of weather systems associated with typical intrusions and 
balloon soundings of the NWS Upper Air Observation Program to detect 
parcels of dry air aloft) to successfully demonstrate stratospheric 
ozone exceptional events.
---------------------------------------------------------------------------

    \109\ Wyoming Department of Environmental Quality, Air Quality 
Division. Big Piney and Boulder, Wyoming Ozone Standard Exceedance, 
June 14, 2012. Available at http://www2.epa.gov/air-quality-analysis/exceptional-events-submissions-table.
---------------------------------------------------------------------------

b. Proposed Changes
    As is true for all exceptional events and pollutant combinations, 
when submitting a demonstration for stratospheric ozone intrusion 
events, air agencies must address all of the Exceptional Events Rule 
criteria. As noted in this action, 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 a human activity that is unlikely to 
recur at a particular location or was a natural event. The EPA suggests 
the following approach when addressing these technical criteria for an 
ozone exceedance or violation caused by a stratospheric intrusion.
    An air agency should begin by showing the geographic extent of 
elevated or exceedance-level ozone concentrations associated with the 
intrusion event in conjunction with an evaluation of the historical 
measured surface ozone levels for the same season (see section V.E.3 of 
this proposal for example analyses of how to present the comparison to 
historical concentrations within the clear causal relationship 
criterion). If the intrusion happened at a time of year when local or 
transported photochemical ozone is generally low, evidence that the 
intrusion affected ground level air quality may be relatively brief and 
still be sufficient, compared to an intrusion occurring at the height 
of the historical ozone season.
    If intrusion claims coincide with historically high photochemistry 
seasons, then the air agency may need additional evidence to support 
the clear causal relationship criterion by showing the relative 
contribution estimates to the exceedance from local and transported 
anthropogenic pollutants compared to the intrusion contribution. An air 
agency can provide additional analyses supporting the clear causal 
relationship by showing that an intrusion occurred at or near the 
location of an identified monitor by using atmospheric models such at 
RAQMS, NAM or RUC, with additional data from satellite observations of 
total column ozone and CO.
    The EPA intends to accept a short statement in a demonstration that 
because stratospheric ozone intrusions are purely natural events and 
are large in scale, they are not reasonably controllable or 
preventable.
4. High Wind Dust Events
a. Current Situation
    The 2007 Exceptional Events Rule preamble noted that ``[t]he EPA's 
final rule concerning high wind events states that ambient particulate 
matter concentrations due to dust being raised by unusually high winds 
will be treated as due to uncontrollable natural events where (1) The 
dust originated from nonanthropogenic sources, or (2) the dust 
originated from anthropogenic sources within the State, that are 
determined to have been reasonably well-controlled at the time that the 
event occurred, or from anthropogenic sources outside the State.'' As 
noted in section IV.B of this document, although this language still 
reflects the EPA's interpretation of what might be appropriate under 
the Exceptional Events Rule, the D.C. Circuit determined the language 
to be a legal nullity because the EPA did not specifically address high 
winds or ambient particulate matter concentrations in the promulgated 
regulatory language in 40 CFR 50.14.
    The preamble to the 2007 Exceptional Events Rule also noted that 
because ``. . . the conditions that cause or contribute to high wind 
events vary from area to area with soil type, precipitation, and the 
speed of wind gusts, [air agencies] should provide appropriate 
documentation which indicates what types of circumstances contributed 
to the exceedances or violation at the monitoring site in question.'' 
The EPA declined to identify a specific high wind threshold to qualify 
as being an exceptional event and instead relied on air agencies to 
submit appropriate documentation supporting their position.
    Because of the uncertainty associated with these high wind 
statements and stakeholder feedback asking the EPA to interpret this 
language and provide examples of applying the provisions in the 2007 
Exceptional Events Rule to high wind dust events, the EPA clarified 
many concepts related to high wind dust events in its May 2013 Interim 
Exceptional Events Implementation Guidance, specifically the Interim 
High Winds Guidance document.\110\ In this guidance, the EPA defined a 
high wind dust event as including the high wind and the dust that the 
wind entrains and transports to a monitoring site, clarified our 
expectations regarding ``reasonable controls'' for high wind events 
with contribution from both natural and anthropogenic sources and 
introduced the concept of establishing a value for a high wind 
threshold, up to which reasonable windblown dust controls are

[[Page 72877]]

expected to be effective in the absence of site specific data or 
analyses.
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    \110\ 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.
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    As identified in the Interim High Winds Guidance document, dust 
phenomena are experienced primarily in the western U.S. where rainfall 
is seasonal, creating dry and dusty landscapes.\111\ In high wind dust 
events, the meteorological phenomenon (i.e., wind) is purely natural, 
but the pollution from the event may be a mixture of natural sources 
(e.g., undisturbed soil) and anthropogenic sources (e.g., soil 
disturbed by human activity, emissions from sand and gravel facilities, 
etc.). The EPA generally classifies high wind dust events as ``natural 
events'' in cases where windblown dust is entirely from natural sources 
or where all significant anthropogenic sources of windblown dust have 
been reasonably controlled.\112\ This long-standing policy was first 
established in the PM10 Natural Events Policy, which 
provided that:
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    \111\ We use ``Western U.S.'' to refer to states in the Great 
Plains (North Dakota, South Dakota, Nebraska, Kansas, Oklahoma and 
Texas) and those farther west including Arizona, California, 
Colorado, Nevada, New Mexico, Utah, and Wyoming.
    \112\ As identified in section V.D of this proposal, the EPA 
will generally consider human activity to have played little or no 
direct role in causing emissions of the dust generated by high wind 
for purposes of the regulatory definition of ``natural event'' if 
contributing anthropogenic sources of the dust are reasonably 
controlled, regardless of the amount of dust coming from these 
reasonably controlled anthropogenic sources, and thus the event 
could be considered a natural event. In such cases, the EPA believes 
that it would generally be a reasonable interpretation to find that 
the anthropogenic source had ``little'' direct causal role. If 
anthropogenic sources of windblown dust that are reasonably 
controllable but that did not have those reasonable controls applied 
at the time of the high wind event have contributed significantly to 
a measured concentration, the event would not be considered a 
natural event.

    Ambient PM-10 concentrations due to dust raised by unusually 
high winds will be treated as due to uncontrollable natural events 
under the following conditions: (1) The dust originated from 
nonanthropogenic sources, or (2) the dust originated from 
anthropogenic sources controlled with best available control 
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measures (BACM).\113\

    \113\ Areas Affected by PM-10 Natural Events (the 
PM10 Natural Events Policy), memorandum from Mary D. 
Nichols, Assistant Administrator for Air and Radiation, to EPA 
Regional Offices, May 30, 1996.

    Also integral to definition of a high wind dust event is that the 
wind speed be ``high,'' or, as indicated in the PM10 Natural 
Events Policy, ``unusually high.'' Only ``high wind'' dust events are 
exceptional events and ``high'' is area-specific.
    Typically, undisturbed desert landscapes in the western U.S. have a 
natural crust that protects the surface and tends to limit emissions of 
windblown dust. The wind speed capable of causing emissions from these 
natural undisturbed areas varies by location, depending on 
characteristics of the local landscape (e.g., soil type and 
characteristics, vegetation). Numerous studies have been conducted to 
determine the minimum wind speed capable of causing emissions from 
natural undisturbed areas and/or overwhelming reasonable controls on 
anthropogenic sources.\114\ In the Interim High Winds Guidance, the EPA 
called the minimum threshold wind speed capable of causing emissions 
from natural undisturbed areas or overwhelming reasonable controls on 
anthropogenic sources the ``high wind threshold.''
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    \114\ See Appendix A1 of 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. U.S. EPA. May 2013. Available at http://www2.epa.gov/sites/production/files/2015-05/documents/exceptevents_highwinds_guide_130510.pdf.
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    In the Interim High Winds Guidance, the EPA articulated its 
expectations regarding the development and application of high wind 
thresholds. In this guidance, the EPA encouraged air agencies to 
identify an appropriate high wind threshold for each area experiencing 
high wind dust events within their exceptional events submissions for 
high wind dust events.\115\ The guidance recommended that these 
thresholds should consider local conditions and specify a minimum wind 
speed capable of causing emissions from those natural undisturbed areas 
or overwhelming reasonable controls on contributing anthropogenic 
sources (see section V.E.2 for additional discussion regarding 
reasonable controls). This approach was consistent with the 
PM10 Natural Events Policy in which the EPA recommended that 
air agencies define the conditions in which BACM level controls were 
overwhelmed. The area-specific high wind threshold should be 
representative of conditions (i.e., sustained wind speeds \116\) that 
are capable of overwhelming reasonable controls (whether RACM, BACM or 
other) on anthropogenic sources and/or causing emissions from natural 
undisturbed areas. The threshold was not intended to represent the 
minimum wind speed at which any level of emissions could occur (e.g., 
aerodynamic entrainment), but rather when significant emissions begin 
due to reasonable controls or natural undisturbed areas becoming 
overwhelmed. We have stated that if an agency is unable to develop an 
area-specific high wind threshold, we generally will accept a threshold 
of a sustained wind of 25 mph for areas in the western U.S. provided 
the agencies support this as the level at which they expect stable 
surfaces (i.e., controlled anthropogenic and undisturbed natural 
surfaces) to be overwhelmed.\117\ We did not indicate what form such 
support could take. We also have said that if we receive specific 
information based on relevant studies to choose an alternative high 
wind threshold for an identified area, we will notify the affected air 
agency.
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    \115\ See Appendices A2 and A3 in 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. U.S. EPA. May 2013. Available at http://www2.epa.gov/sites/production/files/2015-05/documents/exceptevents_highwinds_guide_130510.pdf for additional information 
on the development of a high wind threshold.
    \116\ Section 6.3.2.2 in 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. U.S. EPA. May 2013. Available at http://www2.epa.gov/sites/production/files/2015-05/documents/exceptevents_highwinds_guide_130510.pdf for details on the 
calculation of sustained wind speed. Generally, the EPA will accept 
that high winds could be the cause of a high 24-hour average 
PM10 or PM2.5 concentration if there was at 
least one full hour in which the hourly average wind speed was above 
the area-specific high wind threshold.
    \117\ The 25 mph threshold is based on studies conducted on 
natural surfaces. See additional information relevant to 
establishing this threshold in Appendix A1 in 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. U.S. EPA. May 2013. Available at http://www2.epa.gov/sites/production/files/2015-05/documents/exceptevents_highwinds_guide_130510.pdf.
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    Also as noted in the Interim High Winds Guidance document, the EPA 
has expected air agencies to provide relevant wind data (e.g., wind 
speed and direction) as part of an exceptional events submission for 
high wind dust events. Wind speed data consist of analyses and 
statistics showing how the observed high wind dust event wind speed 
compares to the distribution of historical wind speeds and the 
established high wind threshold. The EPA has recommended that air 
agencies show these historical comparisons on an annual and/or seasonal 
basis, depending on which is more appropriate, using a format similar 
to the recommended format of the comparison to historical 
concentrations showing as part of the clear causal relationship 
criterion discussed in section V.E.3 of this proposal. The EPA has 
encouraged air agencies to discuss wind direction in the narrative and 
to present wind direction information graphically in

[[Page 72878]]

maps/plots in the clear causal relationship section of the high wind 
dust exceptional events demonstration.
    In considering past high wind dust event demonstrations, the EPA 
has found that the ``not reasonably controllable or preventable'' and 
the ``clear causal relationship'' (to include the comparison to 
historical concentrations showing) criteria play significant roles in 
the supporting exceptional events documentation. The EPA has generally 
found that for high wind dust events, air agencies can meet the ``human 
activity or natural event'' criterion by satisfying the requirements 
for not reasonably controllable or preventable and clear causal 
relationship as well as addressing the additional components of 
exceptional events demonstration packages as discussed in section V.G.
    As is the case with all demonstration packages, air agencies with 
agricultural sources that potentially contribute to high wind event-
related emissions should address the question of source contribution 
and associated reasonable controls on these sources within the not 
reasonably controllable or preventable portion of the demonstration. 
The EPA has noted in previous guidance that when considering the 
anthropogenic sources that contribute to event-related emissions and 
the appropriate ``reasonable controls'' on these sources, air agencies 
should be aware of USDA/NRCS-approved Best Management Practices (BMPs) 
(also referred to as conservation management practices) that are 
designed to effectively reduce fugitive dust air emissions and prevent 
soil loss in agricultural applications.\118\ We have stated that these 
BMPs could be included in the collection of controls determined to 
constitute reasonable controls for wind-blown dust events in areas in 
which they have been implemented.
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    \118\ Reference Guide for Cropping Systems and General Land 
Management. USDA, NRCS and U.S. EPA. October 2012. Available at 
http://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb1049502.pdf.
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b. Proposed Changes
    The EPA proposes to include in the preamble to the final rule for 
this action a modified version of some of the language that first 
appeared in the Interim High Winds Guidance document and to incorporate 
into the rule text the revisions proposed in this section. We also 
intend to revise the Interim High Winds Guidance to be consistent 
following promulgation of final Exceptional Events Rule revisions.
    Definition of an Event. Consistent with the EPA's proposal to 
revise the regulatory definition of an exceptional event to include 
both the event and its associated resulting emissions, the EPA proposes 
to define a high wind dust event as an event that includes the high-
speed wind and the dust that the wind entrains and transports to a 
monitoring site. Consistent with the nullified language in the 2007 
Exceptional Events Rule preamble, the PM10 Natural Events 
Policy and the Interim High Winds Guidance, the EPA proposes to define 
high wind dust events in the rule text as ``natural events'' in cases 
where windblown dust is entirely from natural sources or where all 
significant anthropogenic sources of windblown dust have been 
reasonably controlled.
    High Wind Threshold. To facilitate clearer expectations regarding 
the evidence needed to demonstrate which controls constitute 
``reasonable controls,'' the EPA proposes to codify in rule language 
the definition of ``high wind threshold'' as the minimum threshold wind 
speed capable of causing particulate matter emissions from natural 
undisturbed lands in the area affected by a high wind dust event. The 
EPA proposes to accept a threshold of a sustained wind of 25 mph for 
areas in the western U.S. provided this value is not contradicted by 
evidence in the record when we review a demonstration. If the EPA 
receives specific information based on relevant studies that suggest a 
different high wind threshold for an identified area, the EPA will 
notify the affected air agency so that the agency may consider basing 
its demonstration on that threshold value. The EPA would consider such 
information as part of the weight of evidence analysis for a submitted 
demonstration. In lieu of using the default 25 mph high wind threshold, 
air agencies would have the option to identify an area-specific high 
wind threshold that is more representative of local/regional 
conditions.
    The high wind threshold concept will continue to apply to the 
review of demonstrations for events in a nonattainment or maintenance 
area for which the dust controls in a recently approved SIP are 
generally accepted as sufficient to satisfy the not reasonably 
controllable criterion. For such a demonstration, the controls 
specified in the SIP should be considered reasonable, while 
acknowledging the possibility that the controls are not being complied 
with and that uncontrolled anthropogenic sources of PM could be the 
contributing to the exceedance. For events with sustained wind speeds 
above the high wind threshold, it is very plausible that SIP controls 
were being implemented and the high PM concentrations are due to 
emissions generated from sources in the area despite implementation of 
the SIP measures. Conversely, for events with sustained wind speeds 
below the high wind threshold, it becomes more plausible that there may 
be noncompliance with control measures or that uncontrolled 
anthropogenic sources are contributing to the exceedance. Therefore, 
the comparison of sustained wind speeds during an event to the high 
wind threshold will help the EPA Regional offices determine what 
evidence is required to be included in a demonstration regarding 
reasonable controls, the possibility of non-compliance, or non-event 
sources.
    Large-Scale or High-Energy High Wind Dust Events. The EPA proposes 
to codify in rule language to apply a case-specific approach when 
considering reasonableness of controls for remote, large-scale, high-
energy and/or sudden high wind dust events, such as ``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. The 
proposed rule text provides that in these situations, the event will be 
considered not reasonably preventable or controllable. Therefore, a 
demonstration limited to such event(s) will not need to substantively 
address this criteria. The EPA solicits comment on this proposed, case-
specific approach when considering reasonableness of controls for 
remote, large-scale, high-energy and/or sudden high wind dust events.
    Other Types of High Wind Dust Events. Any demonstration for a non-
high-energy event would be evaluated on a case-by-case basis. In doing 
so, the EPA would consider what controls are reasonable in light of an 
area's attainment status and associated CAA control requirements, the 
frequency, and range of non-high energy wind events known (at the time 
of the particular event that is the subject of the demonstration) to 
occur in the area.
    The Role of the EPA-approved SIP in Nonattainment and Maintenance 
Areas. As stated in section V.E.2, 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 satisfy the not reasonably 
controllable or

[[Page 72879]]

preventable criterion.\119\ Otherwise, the air agency and the EPA would 
evaluate the not reasonably controllable or preventable criterion on a 
case-by-case basis.
---------------------------------------------------------------------------

    \119\ 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.
---------------------------------------------------------------------------

    We describe below one potential scenario in which deference to the 
SIP for purposes of ``reasonable controls'' (versus a case-by-case 
analysis) satisfies the not reasonably controllable or preventable 
criterion. We also provide two other scenarios needing a case-by-case 
analysis for purposes of satisfying the not reasonably controllable or 
preventable criterion. We identify these scenarios below and then 
discuss them in more detail in sequence.
     Nonattainment Area Scenario 1--The EPA approved the SIP 
with the enforceable control measures as meeting attainment or 
maintenance planning requirements within 5 years of the date of 
submittal of the event AND the air agency is not under an obligation to 
revise the SIP for the reason listed in Scenario 2 or any other reason. 
Additionally, the sustained winds during the event are above the high 
wind threshold. The SIP includes enforceable control measures that 
address the event-related pollutant and all sources necessary to 
fulfill the requirements of the CAA for the SIP that have or may have 
contributed to event-related emissions. This indicates that in the 
development and approval of the SIP, both the EPA and the state 
considered what event-related controls were sufficient to meet the 
attainment or maintenance plan requirements of the CAA.
     Nonattainment Area Scenario 2--The air agency is under an 
obligation to revise the SIP as a result of a SIP call based on failing 
to provide for attainment and maintenance of the relevant NAAQS as 
evidenced by current violations.\120\
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    \120\ Other possible reasons for an area to be in a Scenario 2 
situation would be if it has been designated nonattainment for a 
revised NAAQS for the relevant pollutant or is subject to a SIP call 
for the relevant pollutant following the EPA's determination that 
the SIP is inadequate for some other reason.
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     Maintenance Area Scenario 3--The EPA approved the SIP more 
than 5 years prior to the date of submittal of a demonstration.
Details for Nonattainment Area Scenario 1
    In this scenario, where the sustained winds during the event are 
above the high wind threshold, the EPA would apply a non-rebuttable 
presumption that the controls in the existing SIP represent reasonable 
measures to prevent or control any event of the given type that occurs 
in the 5-year window. To satisfy the not reasonably controllable or 
preventable criterion, the EPA would expect the submitting air agency 
to identify the emission sources that contribute to the event emissions 
and exceedance and identify the associated SIP controls plus any other 
enforceable control measures required by state laws or rules. The air 
agency would also identify the implementation status of these controls 
and provide evidence of effective implementation and enforcement.
    Example: An air agency submits a demonstration for a high wind dust 
event in a PM10 nonattainment area that occurred in October 
2015. The air agency has an EPA-approved attainment plan SIP for the 
affected area that was approved in October 2010 and that SIP includes 
enforceable controls implemented in accordance with the SIP that 
address the event-related pollutant (i.e., PM) and all sources 
necessary to fulfill the requirements of the CAA. The sustained winds 
during the event were above the high wind threshold. In the not 
reasonably controllable or preventable portion of its high wind dust 
demonstration, the air agency would describe the event-related wind 
characteristics and identify the natural and anthropogenic emission 
sources that contributed to the event emissions and the associated SIP 
and other control measures. The air agency would then describe the 
implementation status of these controls and provide evidence of 
effective implementation and enforcement. The air agency would conclude 
the ``not reasonable controllable or preventable'' portion of the 
demonstration by affirmatively stating that because the EPA had 
approved the SIP within 5 years of the event and because the SIP 
measures and other measures specific to the pollutant and at least some 
anthropogenic emission sources that contributed to the event emissions 
were implemented, the agency has satisfied the not reasonably 
controllable or preventable criterion.
    In reviewing the demonstration in this scenario, the EPA would 
generally concur that the air agency met the not reasonably 
controllable or preventable criterion during the 5-year period provided 
the SIP was implemented and the event was not attributable to 
noncompliance. Thus, assuming the demonstration also satisfied the 
remaining technical and procedural elements in the Exceptional Events 
Rule, the EPA would concur with the air agency's request to exclude 
data for purposes of regulatory actions within the scope of the final 
revised Exceptional Events Rule. If, however, the air agency 
experienced an exceedance or violation during the 5-year period for 
reasons other than those attributable to the successful exceptional 
events demonstration (e.g., industrial source noncompliance or another 
type of event), the EPA may take one of these actions. In addition, the 
EPA may issue a SIP call because the SIP is inadequate with regard to a 
requirement of the CAA that is not tied to the occurrence of NAAQS 
violations related to exceptional events. If the EPA issues a SIP call 
during the 5-year window, the situation would switch to Scenario 2.
Details for Nonattainment Area Scenario 2
    In this scenario (where the SIP is being revised to respond to a 
SIP call involving the PM10 or PM2.5 NAAQS), the 
existing SIP controls should not be presumed to satisfy the not 
reasonably controllable or preventable criterion regardless of whether 
the event-related wind speeds are above or below the high wind 
threshold. The EPA recommends that as the first step in preparing an 
exceptional events demonstration, the air agency should assess the 
case-specific effectiveness of the controls that were in place at the 
time of the event and consider potential controls that are more 
comprehensive and effective than those in the SIP that the agency could 
have implemented before or during the event. This case-specific 
assessment should apply the concept that if a set of control measures 
should reasonably have been in place for emission sources that 
contribute to the event emissions in light of the information in the 
record of the EPA action that has created the obligation to revise the 
SIP, then those controls must have been in place for the event to 
satisfy the not reasonably controllable or preventable criterion.
    The submitting air agency preparing a case-specific assessment 
should first identify the natural and anthropogenic emission sources 
that significantly contribute to the event emissions and exceedance. 
The air agency should categorize sources as those that are addressed 
through SIP or other state or local laws or rules and those sources 
that are not addressed by SIP measures or other measures. Where the 
contributing source has SIP or other controls, the air agency would 
identify the implementation status of these controls and provide 
evidence of effective implementation and

[[Page 72880]]

enforcement. The air agency should also consider whether those SIP 
controls should have been made more stringent and effective prior to 
the event. For emission sources that contribute to the event emissions 
but are not specifically addressed in the SIP or other laws or rules, 
the air agency should identify and document why it was reasonable to 
have not implemented controls.
    We invite comment on whether there should be a grace or 
grandfathering period before a SIP call involving a relevant NAAQS has 
the effect of ending the deference that applied prior to the SIP call, 
such that for an event occurring during the grace period the SIP would 
be given the deference described for the first scenario. We believe 
that such a grace period should not extend beyond the due date for the 
required SIP revision in response to the SIP call.
    Example: An air agency has an EPA-approved attainment plan SIP for 
a PM10 nonattainment area that was approved in 1994 and 
includes controls for some of the anthropogenic emission sources that 
contribute fugitive dust during high wind events. The nonattainment 
area did not include fugitive dust controls for gravel operations in 
its 1994 SIP and has not required any controls of these operations in 
the years since SIP approval. The area does not have an approved 
maintenance plan, in part because it has been experiencing unresolved 
exceedances since 1994. The air agency alerts the reviewing EPA 
Regional office that it wishes to submit an exceptional events 
demonstration for a high wind dust event that occurred in 2015 and 
affected several of the area's monitoring sites. This is the second 
high wind dust event associated with an exceedance in the past 3 years. 
After the first event, the EPA issued a SIP call for the air agency to 
revise its PM10 SIP, but the air agency has not yet 
submitted a new SIP. Because the EPA issued a SIP call, the air agency 
is required to show on a case-specific basis that the not reasonably 
controllable or presentable criterion has been met. Applying the 
concept that if a set of control measures should reasonably have been 
in place for emission sources that contribute to the event emissions to 
the information in the record supporting the SIP call would likely 
result in a determination that those controls must have been in place 
for the event to satisfy the not reasonably controllable or preventable 
criterion. Because the gravel operations are not controlled and because 
the high wind dust event was the second in 3 years, the air agency had 
a basis for understanding the possible need for better controls. Given 
the air agency's knowledge of recurring events, the air agency may not 
be able to make a sufficient showing for the not reasonably 
controllable or preventable criterion and the reviewing EPA Regional 
office may not be able to concur with the air agency's request to 
exclude data. If, however, the air agency can show that the gravel 
operations did not contribute to the event-related emissions, the 
reviewing EPA Regional office might be able to concur with the air 
agency's request to exclude data.
Details for Maintenance Area Scenario 3
    In this scenario (where the SIP was approved more than 5 years 
prior to the date of submittal of a demonstration and the air agency is 
not under an obligation to revise the SIP), because of the passage of 
time the SIP controls should not be presumed to satisfy the not 
reasonably controllable or preventable criterion regardless of whether 
the event-related wind speeds are above or below the high wind 
threshold. In this case, the air agency should complete a case-specific 
assessment of the reasonableness of controls to satisfy the not 
reasonably controllable or preventable criterion. The assessment should 
consider controls beyond those required by the existing SIP and other 
state or local laws and rules. The case-specific assessment should 
apply the concept 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 
satisfy the not reasonably controllable or preventable criterion. The 
submitting air agency should first identify the natural and 
anthropogenic emission sources that contribute to the event emissions 
and exceedance. The air agency should categorize sources as those that 
are addressed through SIP or other state or local laws or rules and 
those sources that are not addressed by SIP measures or other measures. 
Where the contributing source has SIP or other controls, the air agency 
would identify the implementation status of these controls and provide 
evidence of effective implementation and enforcement. The air agency 
should also consider whether those SIP controls should have been made 
more stringent and effective prior to the event. For emission sources 
that contribute to the event emissions but are not specifically 
addressed in the SIP or other laws or rules, the air agency should 
identify and document why it was reasonable to have not implemented 
controls.
    Example: An air agency has an EPA-approved attainment plan SIP for 
a PM10 former nonattainment area that was approved in 2008 
and includes controls for anthropogenic emission sources that 
contribute fugitive dust during high wind events. The area has an 
approved maintenance plan. Between 2008 and 2014 it has not been 
experiencing exceedances related to high winds. In 2014 there is a 
single high wind dust event with sustained wind speeds above the high 
wind threshold that results in two exceedance days, sufficient to 
constitute a 3-year NAAQS violation. The air agency submits a 
demonstration covering both exceedances. In the not reasonably 
controllable or preventable portion of its demonstration, the air 
agency would identify all sources contributing to the event emissions, 
including natural sources, sources identified and controlled in the 
SIP, and any sources not controlled by the SIP. The air agency would 
then identify the applicable controls, the implementation status of 
these controls and evidence of enforcement. The air agency should also 
consider whether those SIP controls should have been made more 
stringent and effective prior to the event. Given the area's past 
history of not having events and the fact that the sustained wind speed 
during the event was above the high wind threshold, it is likely that 
the air agency could make a sufficient showing for the not reasonably 
controllable or preventable criterion. In this case, provided the air 
agency satisfies the other rule criteria, the EPA Regional office would 
likely concur with an air agency's request for data exclusion.
    However, in this maintenance area scenario, another possible 
outcome of an event that causes an exceedance or violation is that the 
EPA determines that the not reasonably controllable or preventable 
criterion is not met and the event-affected data are retained for 
regulatory actions within the scope of the Exceptional Events Rule. 
This may lead to the EPA taking an action that places the air agency 
under an obligation to revise the SIP, in which case the situation 
would change into the second scenario for any later events of the same 
type.
    Best Management Practices. The EPA solicits comment on whether or 
not, as part of the assessment of local sources and reasonable 
controls, USDA/NRCS-approved BMPs constitute sufficient reasonable 
controls in any or in all high wind event-affected areas and whether 
these measures should therefore be specifically and categorically 
identified in preamble or rule language as constituting reasonable 
controls. As discussed in the ``Current Situation'' section, the EPA 
has noted in previous guidance that USDA/NRCS-approved BMPs designed to 
effectively reduce

[[Page 72881]]

fugitive dust air emissions and prevent soil loss in agricultural 
applications could be included in the collection of controls determined 
to constitute reasonable controls for wind-blown dust events in areas 
in which they have been implemented.\121\ Although the EPA has 
addressed the sufficiency of BMPs in decisions on individual 
exceptional events demonstrations when the BMPs were part of a SIP-
approved BACM determination, we have not previously addressed whether 
or not BMPs individually or in some combination with each other 
constitute sufficient reasonable controls nationally or in any 
particular types of areas. We recognize that this question may be 
difficult to answer because BMPs often describe general types of 
practices (e.g., installing wind breaks) rather than specifying the 
penetration, scale or intensity of use of these practices by the 
landowners who adopt them. Therefore we also solicit comment on the 
evidence for degree of penetration, scale and intensity that would be 
appropriate in demonstrations to consider BMPs individually or in some 
combination with each other to be reasonable controls.
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    \121\ 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 and Interim 
Guidance to Implement Requirements for the Treatment of Air Quality 
Monitoring Data Influenced by Exceptional Events. U.S. EPA. May 
2013. Available at http://www2.epa.gov/sites/production/files/2015-05/documents/exceptevents_guidememo_130510.pdf.
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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?
a. Current Situation
    Before addressing the schedule and mechanics of flagging event-
influenced data and preparing demonstrations, the EPA believes it is 
necessary to first clarify which parties can submit an exceptional 
events demonstration package to the EPA. The CAA language at section 
319(b)(3)(B)(i) 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.'' As noted in section V.A of this proposal, state, local and 
some tribal agencies administer air quality management programs within 
their jurisdiction, which includes monitoring and analyzing ambient air 
quality and submitting monitoring data to the EPA, which are then 
stored in the EPA's AQS database. Also, FLMs and other federal agencies 
operate air quality monitoring stations on some lands they manage, and 
some of these monitors meet the technical specifications and quality 
assurance requirements for their data to be used in regulatory 
determinations. As operators of regulatory monitors, each of these 
agencies can flag their own data within AQS for consideration as an 
exceptional event.
    As discussed in section V.F.1 of this proposed action, however, the 
EPA generally considers a state, exclusive of tribal lands, to be a 
single responsible actor, and, as the state is the entity primarily 
responsible for administering air quality planning and management 
activities, the state has been ultimately responsible for submitting 
exceptional events demonstrations for exceedances that occur at all 
regulatory monitoring sites within the boundary of the state, including 
exceedances occurring at monitoring sites operated by local air quality 
agencies to whom a state has delegated relevant responsibilities or at 
regulatory monitoring sites operated by any other entity within the 
state, such as FLMs of Class I areas, other federal agencies and/or 
industrial facilities. Although the state is responsible, a local 
agency, an FLM, another federal agency or another entity operating a 
regulatory monitor with an event-influenced exceedance can develop a 
demonstration for submittal by the state. If a state disagrees with the 
local agency's, FLM's, other federal agency's or other entity's 
exceptional events claim, the state can decide not to act on or forward 
that submittal to the EPA. A state can request that operators of other 
regulatory monitors experiencing event-influenced exceedances prepare 
or assist in the preparation of demonstration analyses for ultimate 
submittal by the state.
    Because some tribal air quality agencies also operate regulatory 
ambient air quality monitoring sites and submit these data to the EPA's 
AQS database, as appropriate, these tribal agencies may also submit 
exceptional events demonstrations for exceedances that occur at their 
monitoring sites.
b. Proposed Changes
    As indicated in section V.A of this proposal, because FLMs and 
other federal agencies may operate regulatory monitors and submit 
collected data to the EPA's AQS database and these same monitors could 
be affected by emissions from exceptional events, 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 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 manage land on which an exceptional event 
originates or that operate a monitor that has been affected by an 
event. 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. This discussion might 
instead result in an agreement that the federal agency (or another 
party) will provide a draft demonstration document to the appropriate 
state air agency for adoption and submission by the state 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 \122\ 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.
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    \122\ 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.
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2. Aggregation of Events for NAAQS With Periods Longer Than 24 Hours 
and Demonstrations With Respect to Multiple NAAQS for the Same 
Pollutant
a. Current Situation
    The EPA's AQS database houses ambient air quality monitoring and 
related data. The data in AQS are maintained as individual reported 
measurements, which can range from 5-minute maximum concentrations per 
hour for SO2, to hourly data for ozone,

[[Page 72882]]

CO, NO2, SO2 and some PM measurements to 24-hour 
measurements for lead and other particulate matter measurements. Air 
agencies identify and the EPA concurs with exceptional event-related 
data in AQS that are reported as individual measurements.
    Some NAAQS have long averaging periods, such that multiple 
independent events may affect the period-average concentration of the 
NAAQS pollutant. In the aggregate, a clear causal relationship may 
exist between the events and an exceedance or violation, but no single 
event satisfies the clear causal relationship criterion because each 
event has too small of an effect on the longer-period metric to do so 
by itself. CAA section 319(b) and the 2007 Exceptional Events Rule do 
not clearly allow the aggregation of events for purposes of the clear 
causal relationship criterion, yet aggregation seems consistent with 
the intent of section 319(b). The EPA has not to date indicated that 
actual aggregation of events is permitted. However, Question 30 in the 
Interim Q&A document provided guidance that can be of some help in this 
situation. This guidance was that 24-hour concentrations of Pb, 
NO2, or SO2 can be individually compared to the 
NAAQS level defined for a longer period, for purposes of meeting ``but 
for'' with respect to both the 24-hour NAAQS, if applicable, and for 
purposes of meeting ``but for'' with respect to the NAAQS with the 
longer averaging period. This guidance focused on the intention of a 
passage in the preamble to the 2007 Exceptional Events Rule addressing 
the PM2.5 NAAQS in particular, and extended the approach of 
the 2007 preamble to other cases of NAAQS for the same pollutant that 
have different averaging periods. The practical effect of this approach 
is that several events that individually have effects too small to have 
a causal connection to a longer-period exceedance or violation might be 
excluded one-by-one, and the net effect of the exclusions may make a 
difference to compliance with the longer-period NAAQS. As guidance, 
however, the Interim Q&A document does not provide full certainty that 
an air agency may rely on the recommended approach.
    As noted in section IV.B of this proposal, the 2007 Exceptional 
Events Rule requires that for data exclusion, among other requirements, 
an air agency must demonstrate that there would have been no exceedance 
or violation of the NAAQS ``but for'' the event. The ``but for'' 
criterion necessarily requires comparing the individual measurements in 
AQS to the averaging period of the relevant NAAQS to determine whether 
an exceedance or violation occurred. When the averaging period for the 
NAAQS is the same as the measurement duration period, this comparison 
is relatively straightforward. For example, air agencies and the EPA 
can directly compare 1-hour ozone, 1-hour CO, 1-hour SO2, 
and 1-hour NO2 measurements to the respective 1-hour NAAQS. 
This comparison becomes more complicated, however, when there is a 
difference between the pollutant measurement duration and the averaging 
time of the NAAQS, which is the case when comparing a 1-hour 
measurement to an 8-hour, 24-hour, 3-month or annual NAAQS (or in the 
case of 1-hour ozone the previously existing NAAQS). In fact, the EPA 
devoted Questions 29-31 in the Interim Q&A document to explaining how 
to make these complicated comparisons.\123\ The Interim Q&A document 
also explained that because these comparisons are NAAQS-specific, air 
agencies should request and support the exclusion of a measured air 
concentration separately for each NAAQS that applies to the pollutant 
and the EPA will similarly provide separate concurrences. Under the 
2007 Exceptional Events Rule provisions, this means, for example, that 
an air agency with several 24-hour measurements of event-influenced 
PM2.5 data measuring 75 micrograms per cubic meter ([mu]g/
m\3\) would need to separately flag the data within AQS on a NAAQS-
specific basis, and submit separate requests, analyses and 
demonstration components to support exclusion of the identified event-
influenced data for the 1997 annual secondary PM2.5 NAAQS of 
15 [mu]g/m\3\, the 2012 annual primary PM2.5 NAAQS of 12 
[mu]g/m\3\ and the 2006 primary and secondary 24-hour PM2.5 
NAAQS of 35 [mu]g/m\3\. Depending on the outcome of the ``but for'' 
criterion with respect to each PM2.5 NAAQS, it could be that 
the data would be excluded for purposes of determinations with respect 
to only some of these NAAQS.
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    \123\ 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.
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    This current situation can result in complicated demonstrations for 
air agencies seeking data exclusion from determinations with respect to 
multiple NAAQS for the same pollutant. This complexity may make it more 
difficult for the public to comment, and requires time for the EPA to 
review such a demonstration.
b. Proposed Changes
    The EPA is taking comment on proposed rule text allowing 24-hour 
concentrations of any NAAQS pollutant to be compared to a NAAQS level 
defined for a longer period as part of a weight of evidence showing for 
the clear causal relationship with respect to the NAAQS with the longer 
period. This approach would be more amenable to less quantified weight 
of evidence demonstrations, since only one day would be examined at a 
time.
    The EPA is also proposing that for NAAQS with averaging or 
cumulative periods longer than 24 hours, events occurring on different 
days may be aggregated for the purpose of determining whether their 
collective effect has caused an exceedance or violation, without regard 
to whether the events are of the same type (e.g., stratospheric ozone 
intrusion followed by a wildfire). The EPA notes that such aggregation 
may be very difficult if the effects of the individual events on their 
individual days are not fully quantified. Proposed rule text for this 
change is provided for comment.
    Finally, to simplify some demonstrations, the EPA is also taking 
comment on whether a successful demonstration with respect to any NAAQS 
for a given pollutant would suffice to qualify the data in question for 
exclusion with respect to all NAAQS for that pollutant. The EPA 
believes it is useful to invite public comment on this ``approved for 
one NAAQS approved for all NAAQS for the same pollutant'' concept.
    The EPA will carefully consider the comments it receives on these 
concepts and may finalize all, some or none of the three proposals 
described in this section.
3. Exclusion of Entire 24-Hour Value Versus Partial Adjustment of the 
24-Hour Value for Particulate Matter
a. Current Situation
    As indicated in Question 29 of the Interim Q&A document, we have 
advised air agencies preparing demonstrations to support requests to 
exclude PM2.5 and PM10 data obtained via monitor 
instruments that provide 1-hour measurements that they should flag all 
24 1-hour values within a given event-affected day, even if the event 
did not last all these hours. If concurred upon, flagging all 1-hour 
values will ultimately result in the same available remaining data for 
regulatory analysis and calculation as would be the case had the 24-
hour PM2.5 or PM10 measurement data been 
collected from filter-based (24-hour) monitoring

[[Page 72883]]

instruments.\124\ Another reason we have taken the position that 
flagging all 24 1-hour values is appropriate is because flagging only 
peak or selected hours could result in the remaining 1-hour values 
still meeting the data completeness requirements because flagged and 
excluded data do not count against completeness even though they cannot 
be used in calculating an average concentration for a 24-hour period. 
Under the rules for data interpretation, exclusion of only the event-
affected 1-hour concentrations could result in AQS calculating a 
seemingly valid 24-hour concentration that is actually highly uncertain 
because it is based on only a few hours and thus may be biased.\125\
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    \124\ Filter based instruments typically record a single value 
within a 24-hour period while continuous monitors typically collect 
24 1-hour measurements. Because AQS can calculate a valid 24-hour 
average concentration with as few as 18 hours, it may be necessary 
to exclude hours not actually affected by the event to ensure the 
same data exclusion outcome as if the measurement had been made with 
a 24-hour filter.
    \125\ The form of the 24-hour PM2.5 NAAQS of 35 
[mu]g/m\3\ is 98th percentile averaged over 3 years. The form of the 
primary annual PM2.5 NAAQS of 12 [mu]g/m\3\ is an annual 
mean averaged over 3 years. The form of the 24-hour PM10 
NAAQS of 150 [mu]g/m\3\ is not to be exceeded more than once per 
year on average over 3 years. Biased concentrations can potentially 
skew the determination of the 98th percentile and/or the annual mean 
for PM2.5 and the averages for PM2.5 or 
PM10 calculated to determine compliance with the relevant 
NAAQS.
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b. Proposed Changes
    The EPA solicits comment on codifying its current approach in the 
rule text to eliminate any regulatory uncertainty. If finalized, this 
modification to the data handling procedures will be made to occur 
automatically within AQS.
4. Flagging of Data
    While neither the preamble to nor the rule text contained within 
the 2007 Exceptional Events Rule discuss data handling within AQS, 
explaining certain AQS processes and functions will be useful to an 
understanding of the data flagging situation that has developed in 
implementing the requirements in 40 CFR 50.14(c)(2) and why we are 
proposing changes.
a. Current Situation
    Within AQS, monitoring agencies can use two types of data 
validation, or data qualifier, codes related to exceptional events: The 
Request Exclusion flags (R) and the Informational Only flags (I).\126\ 
The EPA has advised air agencies to use the I series flags when 
identifying informational data and the R series flags to identify data 
points for which the agency intends to request an exceptional events 
exclusion and the EPA's concurrence. As an example, air agencies may 
currently use an I series flag to initially identify values they 
believe were affected by an event. Once the air agency collects 
additional supporting data, it may change the flag to an R series flag 
and submit an initial event description. Or, the air agency may find 
that additional information does not support flagging the data as an 
exceptional event, and the air agency may, therefore, delete the flag 
or retain the I series flag. Air agencies may also use the I series 
flags simply to note activities or conditions occurring on the data 
collection day that are unrelated to exceptional events or that do not 
result in an exceedance or violation of a NAAQS. Air agencies have 
previously indicated that they generally see little value in the use of 
I series flags.\127\
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    \126\ ``Flag'' is the common terminology for a data qualifier 
code in the EPA's AQS. Unless explicitly noted, the process of 
``flagging'' data refers to adding Request Exclusion (R) data 
qualifier codes to selected data in AQS. R flags are the only AQS 
flags that satisfy the 2007 Exceptional Events Rule requirement for 
initial data flagging. The current design of the AQS software is 
such that EPA can act/concur only on an R flag.
    \127\ 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.
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    Flagging of event-influenced data has traditionally also involved 
associating a one- or two-character code with a monitored value within 
AQS indicating that the data have potentially been influenced by a 
particular type of exceptional event (e.g., ``RT'' is the character 
code used to request exclusion for data that have been influenced by 
wildfires in the U.S.). The 2007 Exceptional Events rule added a 
requirement to include a more detailed initial description of the 
particular event associated with such a character code. This 
description consists of text of variable length.
    The EPA does not review or concur on the I series flags. Rather, an 
air agency must use an R flag to request data exclusion. The language 
at 40 CFR 50.14(c)(2), Flagging of Data, requires that an air agency 
notify the EPA of its intent to exclude one or more measured 
exceedances of an applicable NAAQS as being due to an exceptional event 
by placing a flag and an initial event description in the appropriate 
fields in AQS for the data record(s) of concern no later than July 1 of 
the calendar year following the year in which the flagged measurement 
occurred. Only R flags fulfill this requirement. This ``general'' 
schedule date of July 1 applies unless the data are associated with the 
initial area designations process for a new or revised NAAQS in which 
case the specific schedule in Sec.  50.14(c)(2)(vi) applies.
    Air agencies have previously expressed concern that the timelines 
for event flagging and demonstration submittal are not always 
appropriate.\128\ While the EPA has historically promulgated revised 
flagging and demonstration submittal schedules in the regulatory 
actions for new and revised NAAQS for those data years that might be 
used in the initial area designations process for those NAAQS, the EPA 
does not promulgate revised schedules for other regulatory actions such 
as clean data or attainment determinations. Rather, the EPA has relied 
upon the ``general'' flagging and demonstration submittal schedules in 
40 CFR 50.14(c)(2) and (c)(3)(i). Meeting the requirement at 40 CFR 
50.14(c)(2)(iii) to submit R flags and an initial description of the 
event ``not later than July 1st of the calendar year following the year 
in which the flagged measurement occurred'' can be difficult in the 
case of an annual standard where an air agency needs all 12 months of 
data to calculate an annual average and then needs 3 years of annual 
averages to identify whether or not the event-influenced data results 
in a violation of a 3-year design values. An air agency may not know 
that data influenced by an exceptional event caused the design value to 
become a NAAQS violation until 3 years after the event occurred.
---------------------------------------------------------------------------

    \128\ 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.
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    Some air agencies have used and applied I and R flags in AQS 
inconsistently with this intended scheme, by including applying 
numerous R flags in AQS with no real intention to submit an exceptional 
events demonstration. Also, R flags may be set immediately before a 
demonstration is submitted or even as late as when the EPA needs to 
indicate in AQS our approval of a request for data exclusion. As a 
result, neither the presence nor the absence of these flags provide the 
EPA with an indication of anticipated exceptional events 
demonstrations.
b. Proposed Changes
    As part of this action, the EPA proposes to revise the ``general'' 
schedule language contained within 40 CFR 50.14(c)(2) by removing the 
timelines associated with initial event flagging. The EPA also proposes 
to modify the associated data flagging process within AQS to correspond 
with

[[Page 72884]]

these proposed regulatory changes. These proposed changes would include 
eliminating the use of the current exceptional events data validation/
data qualifier codes: The Request Exclusion flags (R) and the 
Informational Only flags (I). The one- or two-character event type 
codes would be retained. The EPA solicits comment on the approach that 
is discussed below in additional detail.
    The EPA is proposing to change the definition and process for 
flagging exceptional event data. Flagging would in effect become the 
application of the one- or two-character event type and event 
description text as described below, along with a concurrent or 
subsequent request for data exclusion communicated to the EPA through 
other channels.
    Because the flagging of data necessarily begins with the 
identification of an event, the EPA proposes to retain, with 
modifications, the AQS free-form text field for an initial event 
description. As is currently the practice, we request that air agencies 
use the ``initial event description'' to identify a unique, real-world 
event. We propose that this ``initial event description'' be expanded 
to contain a unique event name; the type of the event (e.g., high wind 
dust, volcanic eruption, other); a brief description of the event; and, 
to the extent known, the scope of the event in terms of geography and 
time (e.g., likely affected area using latitude and longitude and a 
radius of influence and beginning day/time and ending day/time).\129\ 
AQS would also be modified to allow the air agency to associate 
specific AQS sites and potentially affected monitors and specific data 
points with a given event as so described. This will enable air 
agencies and the EPA to ``flag'' or add qualifier codes to selected 
data in a single step rather than adding this information or the 
necessary codes on a per entry basis. Historically, when events have 
influenced the concentrations at multiple monitors for multiple days, 
the air agency has added initial event descriptions and set flags on 
each monitored concentration, sometimes resulting in hundreds of 
identical individual entries. ``Associating'' monitors with an event 
defined in time and space will save resources.
---------------------------------------------------------------------------

    \129\ The EPA is proposing that air agencies select the ``type 
of event'' from a pre-set list of event types, which would likely 
consist of those event types currently identified by existing 
Informational and Request Exclusion flags within AQS.
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    Once an air agency has identified an event and created the initial 
event description within AQS, the agency should begin the process of 
requesting exclusion for identified data, which will consist of two 
discrete operations: (1) Indicating in a separate communication to the 
EPA that specific ambient air quality measurements are affected by a 
defined event (see section V.G.5 related to Initial Notification of 
Potential Exceptional Event), and (2) requesting that these identified 
ambient air quality measurements be excluded from regulatory actions 
according to the terms of the revised Exceptional Events Rule and EPA 
guidance for other applications of air quality data. AQS would retain a 
field to allow the EPA to concur or not concur with a given request for 
exclusion for one or more of the data points associated with a 
described event, once review of the air agency's request and 
demonstration is completed.
    In addition to the proposed AQS modifications described above, the 
EPA is proposing to remove the ``general'' flagging schedule in 40 CFR 
50.14(c)(2)(iii). This regulatory language currently requires that air 
agencies submit [R] flags and an initial description of the event by 
July 1 of the calendar year following the year in which the flagged 
measurement occurred or by the other deadlines identified with 
individual NAAQS. As noted earlier in this section, an air agency may 
not know that data influenced by an exceptional event caused a 
violation of a NAAQS until after the initial event flagging deadline 
has passed. The EPA proposes to remove and reserve the current language 
at 40 CFR 50.14(c)(2)(iii). Additional changes to the regulatory 
language in 40 CFR 50.14(c)(2) will be discussed in the next section.
    The EPA notes that the recent ozone NAAQS action \130\ also removed 
and reserved the subsequent sections at 40 CFR 50.14(c)(2)(iv) and (v), 
which addressed the submittal of exceptional events demonstrations that 
could affect regulatory determinations associated with initial area 
designations for the 2006 24-hour PM2.5 NAAQS and the 2010 
Lead NAAQS and were made obsolete by the passage of time. The EPA will 
retain these removed and reserved sections as promulgated in the ozone 
NAAQS and proposes no additional changes to these sections.
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    \130\ 80 FR 65292 (October 26, 2015).
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5. Initial Notification of Potential Exceptional Event
a. Current Situation
    As the EPA acknowledged in the Interim Exceptional Events 
Implementation Guidance and in discussions with stakeholders, the EPA 
understands that the initial identification of data affected by 
exceptional events and the subsequent preparation, submittal and review 
of demonstration packages is a resource intensive process both for the 
preparing air agency and the reviewing EPA Regional office.\131\ Delays 
in processing and making decisions on submitted packages create 
regulatory uncertainty and potentially increase the workload for both 
the submitting air agency and the EPA. In addition, the backlog of 
pending actions makes selection of the best information to support new 
submittals potentially more uncertain. Further, air agencies and the 
EPA often face timelines by which they must make regulatory decisions 
that can be affected by the inclusion or exclusion of event-affected 
data. In the Interim Exceptional Events Implementation Guidance and 
through the EPA's best practices discussions identified in section 
IV.E, the EPA committed to work with air agencies as they prepare 
complete demonstration packages and we developed some guidelines to 
increase the efficiency of the process.
---------------------------------------------------------------------------

    \131\ Interim Guidance to Implement Requirements for the 
Treatment of Air Quality Monitoring Data Influenced by Exceptional 
Events. Memorandum from Stephen D. Page, U.S. EPA Office of Air 
Quality Planning and Standards, to Regional Air Directors, Regions 
I-X. May 10, 2013. Available at http://www2.epa.gov/sites/production/files/2015-05/documents/exceptevents_guidememo_130510.pdf.
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    One of the efficiency-increasing measures we suggested in the 
Interim Exceptional Events Implementation Guidance was the Letter of 
Intent. The guidance explained that the Letter of Intent was a 
voluntary process by which the submitting air agency notifies the 
reviewing EPA Regional office of the air agency's intent to submit a 
demonstration for an identified exceptional event. The purpose of the 
letter was to promote early communication between the submitting air 
agency and the reviewing EPA Regional office. In the time since issuing 
the Interim Exceptional Events Implementation Guidance, several air 
agencies and the EPA Regional offices have successfully used this 
voluntary process to discuss expectations regarding specific 
exceptional events demonstrations.
b. Proposed Changes
    As part of the best practices for communications during the 
exceptional events process and to aid all agencies in resource planning 
and prioritization, the EPA proposes that air agencies and the EPA 
engage in regular communications

[[Page 72885]]

to identify those data that have been potentially influenced by an 
exceptional event, to determine whether the identified data affect a 
regulatory determination, and to discuss whether an air agency should 
develop and submit an exceptional events demonstration. In most 
instances, these discussions will be between individual air agencies 
and the reviewing EPA Regional office. In other cases, the EPA regional 
office, or an individual air agency within the purview of the EPA 
Regional office, may initiate and/or host a general discussion with all 
air agencies in the region followed by individual discussions, as 
needed. In still other cases, such as where large events cross state 
lines and when two or more states are pursuing exclusion for the same 
event(s), the EPA region or regions may initiate discussions will all 
potentially affected states/agencies to assist in coordinating states 
affected by regional events.
    For purposes of this proposed action, the EPA is referring to these 
communications as the ``Initial Notification of Potential Exceptional 
Event'' (Initial Notification) process. The EPA has changed the name of 
this process from the Letter of Intent in recognition of the fact that 
effective communication may have multiple formats and does not 
necessarily consist of a formal, written letter to convey important 
information. As with the voluntary Letter of Intent, the ultimate 
purpose of the Initial Notification process is to initiate 
conversations between an air agency and the EPA if not already on-
going, or engage in more detailed discussions if a process is currently 
in place, regarding specific data and whether the identified data are 
ripe for submittal as exceptional events. As stakeholders have 
repeatedly expressed and as the EPA acknowledges, the identification of 
data affected by exceptional events and the subsequent preparation, 
submittal and review of demonstration packages is a resource intensive 
process both for the preparing air agency and the reviewing EPA 
Regional office.
    However, in considering the exceptional events process, it is 
important to note that if these data do not have regulatory 
significance, then engaging in the development and review of an 
exceptional events demonstration is generally not an efficient use of 
an air agency's or the EPA's limited resources. The Initial 
Notification process will focus efforts on the relevant data and 
provide the EPA with the opportunity to convey to the affected air 
agency our initial thoughts regarding the identified event and analyses 
that may or may not be appropriate for inclusion in a demonstration, 
and, with respect to regulatory significance, which demonstrations the 
EPA will consider for review. We believe that this approach will help 
air agencies make the best use of their available resources.
    As noted earlier, the Initial Notification could include any form 
of communication (e.g., letter, email, in-person meeting with an 
attendees' list and discussion summary or phone conversation with 
follow-up email) that ultimately identifies the potential need to 
develop an exceptional events demonstration and communicates key 
information related to the data identified for potential exclusion. 
Where an air agency independently identifies event-affected data and 
the need to submit an exceptional events demonstration outside of its 
regular, on-going communications with the EPA Regional office, the air 
agency could prepare a letter or email communicating its Initial 
Notification. Generally, the EPA anticipates that air agencies would 
develop and provide an Initial Notification as soon as the agency 
identifies event-influenced data that potentially influence a 
regulatory decision or when an agency wants the EPA's input on whether 
or not to prepare a demonstration.\132\ The EPA further proposes that 
each Initial Notification would include the following components:
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    \132\ The EPA recognizes that air agencies can immediately 
identify those events that result in an exceedance of a NAAQS with a 
short averaging time (e.g., 1-hour, 8-hour or 24-hour standards) but 
may need additional time for an annual average standard. An air 
agency could also submit an annual Initial Notification if annual 
submittal makes sense for resource planning or for recurring 
seasonal events.
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     Unique event name (field in AQS)--facilitates future 
communication and understanding between the submitting air agency and 
the reviewing EPA Regional office, particularly if an air agency has 
submitted multiple exceptional events demonstration packages.
     Initial event description (field in AQS)--provides a brief 
narrative of the event that could also include maps or graphs similar 
to what an air agency might include in the proposed conceptual model 
discussed in section V.G.6 of this proposed action; the event 
description would include a qualitative description of the event and, 
at a minimum, briefly describe the agency's current understanding of 
interaction of emissions with the event, transport and meteorology 
(e.g., wind patterns such as strength, convergence, subsidence, 
recirculation) and pollutant formation in the area.
     Affected regulatory decision--provides a description of 
the regulatory action or actions potentially affected by the claimed 
event-influenced data and the anticipated timing of this action.
     Proposed target date for demonstration submittal--
identifies the proposed target date by which the air agency would 
submit a demonstration package to the reviewing EPA Regional office.
     Most recent design value including and excluding the 
event-affected data (optional)--the air agency's assessment of the most 
recent design value both with and without the identified event(s) is 
helpful when assessing regulatory significance. The EPA cannot 
calculate this value (and therefore may not be able to determine 
significance) if the air agency has flagged more data than it intends 
to include in an exceptional events demonstration.
     Information specific to each monitored day--see Table 5, 
which would be developed by the submitting air agency and generated 
from the initial event description in AQS (see discussion in section 
V.G.4).

                                        Table 5--Initial Notification Information Specific to Each Monitored Day
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                                         Monitor AQS
      Agency/planning area            State        County      Event name      Type of        NAAQS      ID and site   Date(s) of    Monitor exceedance
                                                                 in AQS         event                       name          event         concentration
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                  ............  ............  ............  ............  ............  ............  ............  ....................
                                                                                                                     -----------------------------------
                                  ............  ............  ............  ............  ............  ............  ............  ....................
                                                                                                                     -----------------------------------
                                  ............  ............  ............  ............  ............  ............  ............  ....................
--------------------------------------------------------------------------------------------------------------------------------------------------------


[[Page 72886]]

    The EPA anticipates promptly acknowledging an air agency's Initial 
Notification and then formally responding within 90 days of receipt via 
letter, email or in-person meeting with an attendees' list and 
discussion summary. We also anticipate having informal phone 
conversations with the air agency prior to this formal response. As 
previously discussed, the EPA will generally prioritize exceptional 
events determinations that affect near-term regulatory decisions.\133\ 
Where the data are to be used in initial area designations, the EPA 
proposes to rely on the promulgated documentation submission schedule 
in Table 1 at Sec.  50.14(c)(2)(vi). Where the data will influence 
another near-term regulatory decision, the EPA proposes to rely on the 
case-by-case timelines by which the air agency should submit the 
demonstration. For case-by-case demonstrations, the EPA's recommended 
date for demonstration submittal would consider the nature of the 
event, the anticipated timing of the regulatory decision, and would 
allow time for both an air agency's preparation of the demonstration 
and the EPA's review. The EPA may not be able to review and act on 
demonstrations submitted after the recommended submittal date. 
Additionally, the EPA will request in its response that, if the 
submitting air agency has not already identified the affected data 
within AQS, that it undertake this effort according to the process 
described in section V.G.4. If the data identified in the Initial 
Notification do not have regulatory significance (and there is no 
compelling reason for excluding data), then the EPA will indicate this 
in its correspondence back to the air agency and will discourage the 
air agency from devoting resources to developing a demonstration 
because the EPA will likely not review or act upon the submittal.
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    \133\ ``Regulatory decisions'' include findings as to whether 
the area has met the applicable NAAQS, classification 
determinations, attainment demonstrations, the development of 
Limited Maintenance Plans and clean data findings.
---------------------------------------------------------------------------

    If after discussing the content of a submitted Initial Notification 
and/or receiving the EPA's response to the Initial Notification, the 
EPA acknowledges that identified data have regulatory significance (or 
some other compelling reason for excluding data), then the air agency 
should proceed with the development of a technical demonstration 
package that satisfies the requirements in 40 CFR 50.14 and accounts 
for any case-specific advice from the EPA and additional information in 
the EPA's guidance documents.\134\ Although air agencies can submit 
demonstrations for events that do not affect a regulatory action, the 
EPA will likely not review or act on such submittals.
---------------------------------------------------------------------------

    \134\ Interim Guidance to Implement Requirements for the 
Treatment of Air Quality Monitoring Data Influenced by Exceptional 
Events. Memorandum from Stephen D. Page, U.S. EPA Office of Air 
Quality Planning and Standards, to Regional Air Directors, Regions 
I-X. May 10, 2013. Available at http://www2.epa.gov/sites/production/files/2015-05/documents/exceptevents_guidememo_130510.pdf.
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    For these reasons described in this section and in section V.G.4, 
the EPA proposes to revise the language in 40 CFR 50.14(c)(2)(i) as 
follows: ``A State shall notify EPA of its intent to request exclusion 
of one or more measured exceedances of an applicable ambient air 
quality standard as being due to an exceptional event by creating an 
initial event description and flagging the associated data that have 
been submitted to the AQS database and by engaging in the Initial 
Notification of Potential Exceptional Event process.'' Specific steps 
in the Initial Notification process are identified in rule text at the 
end of this document. The EPA solicits comment on the proposed rule 
text revision (in 40 CFR 50.14(c)(2)) to require an Initial 
Notification of Potential Exceptional Event, with a provision that the 
EPA can waive the Initial Notification requirement on a case-by-case 
basis. Alternatively, the EPA solicits comment on making the Initial 
Notification of Potential Exceptional Event a voluntary process.
    Additional proposed revisions would continue at (ii): ``The data 
shall not be excluded from determinations with respect to exceedances 
or violations of the national ambient air quality standards unless and 
until, following the State's submittal of its demonstration pursuant to 
paragraph (c)(3) of this section and EPA review, EPA notifies the State 
of its concurrence by placing a concurrence flag in the appropriate 
field for the data record in the AQS database.''
    As noted in section V.G.4, the EPA is proposing to remove the 
``general'' flagging schedule in 40 CFR 50.14(c)(2)(iii). The EPA seeks 
comments on these proposed changes to the language at 40 CFR 
50.14(c)(2), which more clearly identify the process for flagging data 
in AQS and requesting exclusion of one or more measured exceedances of 
an applicable ambient air quality standard.
    The EPA notes that the recent final rule to revise the ozone NAAQS 
also removed and reserved the subsequent sections at 40 CFR 
50.14(c)(2)(iv) and (v), which addressed the submittal of exceptional 
events demonstrations that could affect regulatory determinations 
associated with initial area designations for the 2006 24-hour 
PM2.5 NAAQS and the 2010 Lead NAAQS and were made obsolete 
by the passage of time. The EPA will retain these removed and reserved 
sections as promulgated in the ozone NAAQS and proposes no additional 
changes to these sections.
6. Submission of Demonstrations
a. Current Situation
    With the recent ozone NAAQS, the EPA proposed and promulgated 
changes to the current exceptional events regulatory language at 40 CFR 
50.14(c)(2) and (3) to include finalizing exceptional events flagging 
and demonstration submittal schedules related to implementing the 
revised ozone standards and future revised NAAQS and removing obsolete 
regulatory language for expired exceptional events deadlines. Sections 
V.G.4 and V.G.5 discuss the current situation and additional proposed 
changes to 40 CFR 50.14(c)(2). This section discusses the current 
situation and proposed revisions to 40 CFR 50.14(c)(3).
    As part of the recent final rule to revise the ozone NAAQS, the 
regulatory language at 40 CFR 50.14(c)(3)(i) now refers to a revised 
exceptional events flagging and demonstration submittal schedule for 
data that could be used in initial area designation decisions following 
promulgation of any future revised NAAQS. However, the language at 40 
CFR 50.14(c)(3)(i) still requires air agencies to ``. . . submit a 
demonstration to justify data exclusion to EPA not later than the 
lesser of, 3 years following the end of the calendar quarter in which 
the flagged concentration was recorded or, 12 months prior to the date 
that a regulatory decision must be made by EPA.''
    As identified in section V.G.4 of this proposal, air agencies have 
previously expressed concern that the timelines for event flagging and 
demonstration submittal are not always appropriate because an air 
agency may not know that data influenced by an exceptional event caused 
the design value exceedance until 3 years after the event 
occurred.\135\ The EPA acknowledges that this scenario can occur.
---------------------------------------------------------------------------

    \135\ 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.

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[[Page 72887]]

    In addition to establishing a general schedule for demonstration 
submittal, the regulatory language at 40 CFR 50.14(c)(3)(i) requires 
that ``A State must submit the public comments it received along with 
its demonstration to EPA.'' Although this language is included in 40 
CFR 50.14(c)(3)(i), it refers to the regulatory language at 40 CFR 
50.14(c)(3)(v), which requires the air agency to document, and submit 
with its demonstration, evidence that it followed the public comment 
process. Regarding this requirement to ``document that the public 
comment process was followed,'' neither the Exceptional Events Rule 
language in 40 CFR 50.14 nor the preamble to the promulgated 2007 
Exceptional Events Rule specifies a minimum timeframe for public 
comment. Many air agencies have been posting draft demonstrations for 
public review on their Web sites. The EPA has reviewed several of these 
postings and identified 30-days as an often cited timeframe for public 
comment on a draft exceptional events demonstration submittal.
    The current rule also provides at 40 CFR 50.14(c)(3)(iv) that the 
demonstration to justify data exclusion shall provide evidence that the 
event satisfies the definition of an exceptional event provided at 40 
CFR 50.1(j); that there is a clear causal relationship between the 
monitored exceedance and the event that is claimed to have affected the 
air quality in the area; that the event is associated with a measured 
concentration in excess of normal historical fluctuations, including 
background; and that there would have been no exceedance or violation 
but for the event. Air agencies have found this section of the 2007 
Exceptional Events Rule to be confusing because it contains a mix of 
statutory requirements and regulatory language without clearly 
identifying the components that the EPA expects to see in an 
exceptional events demonstration. As the EPA expressed in the Interim 
Exceptional Events Implementation Guidance, all parties would benefit 
from clear expectations regarding demonstration components.
    The EPA further believes, and recommended in the Interim High Winds 
Guidance document, that each demonstration begin with 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). As described in the Interim 
High Winds Guidance document, the narrative conceptual model could 
include varying levels of detail depending on the event complexity, but 
in all cases would provide a qualitative description of the event, 
interaction of the event-generated emissions with transport and 
meteorology (e.g., wind patterns such as strength, convergence, 
subsidence, recirculation) and pollutant formation in the area with the 
exceeding monitor. Because, in some cases, monitored data or technical 
analyses may seem to contradict the event claim, particularly the clear 
causal relationship, an air agency can use the conceptual model to 
explain, with a weight of evidence approach, why the majority of the 
data or analyses are consistent with the event's impact on a measured 
exceedance or violation (for example, for a wildfire, why most of the 
meteorology would have indicated a lower ozone day without the fire 
emissions, even if the temperature were high). A useful conceptual 
model also includes (1) a description of the regulatory decision 
impacted by the exceptional event, (2) a summary table of the data 
requested for exclusion and (3) maps and/or summary tables of event-
related information including location; size and extent; point and 
explanation of origin. A conceptual model can additionally include 
examples of media coverage of the event.\136\ Since releasing the 
Interim High Winds Guidance document in 2013, the EPA has received 
several demonstrations that included a conceptual model. The EPA has 
found it very helpful to understand the event formation and the event's 
influence on monitored pollutant concentrations before beginning to 
review the individual technical evidence to support the requested data 
exclusion.
---------------------------------------------------------------------------

    \136\ The EPA expects that air agencies could use some of the 
same information and tables in both the conceptual model and the 
Initial Notification of Potential Exceptional Event, which is 
discussed in section V.G.5 of this proposal.
---------------------------------------------------------------------------

b. Proposed Changes
    For the previously mentioned reasons, the EPA is proposing and 
soliciting comment on the following changes to the regulatory language 
in 40 CFR 50.14(c)(3) regarding the submission of demonstrations:
     Removing the general schedule provisions in 40 CFR 
50.14(c)(3)(i) for submitting demonstrations.
     Moving the language requiring a state to include the 
comments it received during the public comment period for the subject 
demonstration from 40 CFR 50.14(c)(3)(i) to 40 CFR 50.14(c)(3)(v).
     Modifying the language at 40 CFR 50.14(c)(3)(iv) to more 
clearly identify the required elements of an exceptional events 
demonstration to include (1) a narrative conceptual model and (2) 
demonstrations and analysis that address the core statutory technical 
criteria [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 (as indicated by the comparison to 
historical concentrations showing and other analyses), the event was a 
human activity that is unlikely to recur at a particular location or 
was a natural event, the event was not reasonably controllable or 
preventable].
     Modifying the language at 40 CFR 50.14(c)(3)(v) to 
identify that a demonstration submittal must include (1) documentation 
that the air agency conducted a public comment process on its draft 
exceptional events demonstration that was a minimum of 30 days, which 
could be concurrent with the EPA's review, (2) any public comments 
received during the public comment period and (3) an explanation of how 
the air agency addressed the public comments.
    To elaborate on removing the general schedule provisions in 40 CFR 
50.14(c)(3)(i), the EPA proposes to remove the provision in 40 CFR 
50.14(c)(3)(i) that requires air agencies to submit a demonstration 
``not later than the lesser of 3 years following the end of the 
calendar quarter in which the flagged concentration was recorded or 12 
months prior to the date that a regulatory decision must be made by 
EPA.'' In place of this language, the EPA proposes to rely on the 
promulgated documentation submission schedule in Table 1 at 
50.14(c)(2)(vi) in those cases where the data are to be used in initial 
area designations. If the data could influence a regulatory 
determination other than initial area designations, the EPA proposes to 
rely on the case-by-case timelines established by the reviewing EPA 
Regional office as part of the Initial Notification of Potential 
Exceptional Event process.
    With respect to the public comment provisions for a developed 
demonstration, for the reasons stated previously, the EPA proposes to 
move the language requiring an air agency to include the comments it 
received during the public comment period for the subject demonstration 
from 40 CFR 50.14(c)(3)(i) to 40 CFR 50.14(c)(3)(v) to consolidate the 
required elements of the public comment process for exceptional events 
demonstrations within a single regulatory provision. The EPA also 
proposes to specify a minimum 30-day public comment process, which 
provides sufficient time for exchange between the reviewing public and 
the

[[Page 72888]]

air agency. Shorter comment periods may not provide necessary time for 
the public to research the identified event and associated supporting 
data while longer timeframes may not be possible where a near-term 
regulatory decision relies on an exceptional events decision. The EPA 
notes that in very limited cases where the air agency is relying on 
exceptional events claims as part of a near-term regulatory action, 
such as a demonstration for events in the third year of a 3-year design 
value that will be used in initial area designations for a new or 
revised NAAQS under a 2-year designation schedule, the public comment 
period could be concurrent with the EPA's review provided the 
submitting air agency sends any public comments and responses to the 
EPA by a specified date should comments be submitted. If an air agency 
receives public comment disputing the technical elements of a 
demonstration during a comment period that runs concurrent with the 
EPA's review and these comments result in the air agency's need to 
reanalyze or reassess the validity of a claimed event, a second public 
comment period may be necessary.
    The EPA also proposes to revise the language at 40 CFR 
50.14(c)(3)(iv) so that it more clearly identifies the required 
elements of an exceptional events demonstration. As previously 
described, the EPA proposes that each demonstration begin with a 
narrative conceptual model, which summarizes the event in question and 
provides context for required statutory technical criteria analyses. 
The EPA further proposes, consistent with other proposed changes in 
this action, that an air agency include in its demonstration to justify 
data exclusion evidence that the following statutory technical criteria 
are satisfied:
     The event was a human activity that is unlikely to recur 
at a particular location or was a natural event.
     The event was not reasonably controllable or preventable.
     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 (supported in part by the comparison 
to historical concentrations and other analyses).
    The EPA seeks comments on the identified proposed changes to the 
language at 40 CFR 50.14(c)(3)(i), (iv) and (v), which more clearly 
identify the required elements of an exceptional events demonstration.
    The EPA notes that the recent final rule to revise the ozone NAAQS 
also removed and reserved the subsequent sections at 40 CFR 
50.14(c)(3)(ii) and (iii), which addressed the submittal of exceptional 
events demonstrations that could affect regulatory determinations 
associated with initial area designations for the 2006 24-hour 
PM2.5 NAAQS and the 2010 Lead NAAQS and were made obsolete 
by the passage of time. The EPA will retain these removed and reserved 
sections as promulgated in the ozone NAAQS and proposes no additional 
changes to this language.
7. Timing of the EPA's Review of Submitted Demonstrations
a. Current Situation
    Since promulgation of the Exceptional Events Rule in 2007, 
stakeholders have questioned the process by which the EPA reviews 
submitted demonstrations.\137\ Specifically, stakeholders have 
expressed concern that the EPA has a backlog of submittals but acts 
only on EPA-prioritized packages. Stakeholders have stated that because 
the EPA has not acted on all submissions, the air quality values used 
for planning and regulatory purposes are higher than they would be if 
the effects of non-controllable emissions were removed from the data 
set. Air agencies have also noted that without feedback, they do not 
know the EPA's expectations regarding future submittals.
---------------------------------------------------------------------------

    \137\ See comment letters in Docket ID No. EPA-HQ-OAR-2011-0887 
for the July 2012 notice of availability for the Draft Exceptional 
Events Implementation Guidance, which the EPA has incorporated into 
the record for this action.
---------------------------------------------------------------------------

    The EPA addressed these questions and comments in the Interim 
Exceptional Events Implementation Guidance. In Question 27 of the 
Interim Q&A document, the EPA identified the general process and timing 
for demonstration reviews. In this document, the EPA clarified the 
process by which it prioritizes submittals and indicated that we may 
not act on submittals with no regulatory significance. The guidance 
also presented the voluntary Letter of Intent concept as a mechanism to 
aid in planning and prioritization. Additionally, we stated that we 
intend to make a decision regarding concurrence with an air agency's 
request to exclude data as expeditiously as necessary following 
submittal of a complete package if required by a near-term regulatory 
action. We also indicated our intent to communicate with the submitting 
agency, as needed, during the demonstration review period.
b. Proposed Changes
    In this proposal, the EPA is clarifying some of our previous 
statements regarding the prioritization and submittal of 
demonstrations. As noted in several subsections within section V.G of 
this proposal, we also propose to codify in regulatory language 
approaches to increase the efficiency of preparing, submitting and 
reviewing exceptional events demonstrations. Although the EPA is not 
proposing to codify in regulatory language any changes pertaining to 
the timing of the EPA review process, the EPA offers the following 
discussion to clarify expectations and facilitate communications, which 
are at the center of timing-related issues.
    As noted in the Interim Exceptional Events Implementation Guidance 
and in the EPA's best practices discussions described in section IV.E, 
the EPA is committed to working with air agencies as they prepare 
complete demonstration packages. The EPA encourages ongoing discussions 
between the reviewing EPA Regional office and the submitting air agency 
from the onset of the Initial Notification of Potential Exceptional 
Event process through official package submittal. Since renewing our 
focus on improved communications, the EPA has received positive 
feedback from engaged agencies that have used this approach. 
Additionally, these communications have resulted in decreased instances 
of submissions containing insufficient or unnecessary information.
    In reviewing submitted demonstration packages, the EPA will 
generally give priority to exceptional events determinations that may 
affect near-term regulatory decisions, such as EPA action on SIP 
submittals, NAAQS designations and clean data determinations. The EPA 
intends to make a decision regarding event status expeditiously 
following submittal of a complete package if required by a near-term 
regulatory action. If during the review process the EPA identifies the 
need for additional information to determine whether the exceptional 
events criteria are met, the EPA will notify the submitting air agency 
and encourage the agency to provide the supplemental information. If 
the information needed is minor and a natural outgrowth of what was 
previously submitted, the EPA will not require the air agency to 
undergo an additional public notice-and-comment process. However, if 
the needed information is significant, the EPA may request that the air 
agency re-notice the demonstration before resubmitting it to the EPA, 
thus requiring an additional

[[Page 72889]]

EPA review following resubmittal. The EPA will work with air agencies 
on supplemental timeframes; however, the mandatory timing of the EPA 
actions may limit the response time the EPA allows. The EPA proposes to 
include as rule text a requirement for the air agency to submit 
additional information within 12 months. If additional information is 
not received in 12 months, then the EPA will consider the submitted 
demonstration inactive, and will not continue the review or take 
action. In effect, an air agency's lack of response within a 12-month 
period will ``void'' the submittal. In these cases, the EPA does not 
intend to issue a formal notice of deferral. If the air agency later 
decides to pursue the exceptional events claim after a 12-month period 
of inactivity, it may re-initiate the exceptional events process by 
submitting a new Initial Notification of Potential Exceptional Event 
followed by a new demonstration, which could simply be revising the 
original submittal to include the additional information previously 
requested by the EPA.
    At the conclusion of the EPA's review, the EPA will make a 
determination regarding the status of a submitted exceptional events 
demonstration. The EPA's decision could result in concurrence, 
nonconcurrence or deferral.\138\ In acting on a submitted demonstration 
covering multiple event days and/or multiple flags, the EPA could 
concur with part of a demonstration and nonconcur or defer other 
flagged values. If the EPA determines that the events addressed in an 
exceptional events demonstration are not anticipated to affect any 
future regulatory decision, the EPA could defer review of these events 
and notify the submitting agency if a subsequent review results in a 
determination that the events do affect a regulatory decision.\139\ 
Formal mechanisms for deferral could include the EPA's indicating this 
decision by letter, by email to a responsible official or during a 
high-level meeting with an attendees' list and discussion summary.
---------------------------------------------------------------------------

    \138\ The EPA anticipates a reduced number of deferrals and/or 
nonconcurrences for demonstrations associated with the Initial 
Notification of Potential Exceptional Event process as discussed in 
section V.G.5 because the EPA and the affected air agency would have 
discussed issues/concerns prior to the EPA's decision on a submitted 
demonstration.
    \139\ Routine status calls between the reviewing EPA Regional 
office and air agencies could include an agenda item to review the 
status of all submitted demonstrations, including those that the EPA 
has deferred.
---------------------------------------------------------------------------

8. Dispute Resolution Mechanisms
    Since promulgation of the 2007 Exceptional Events Rule and through 
the development of the Interim Exceptional Events Implementation 
Guidance, some interested parties have asked the EPA to identify a 
process by which submitting air agencies can formally dispute the EPA's 
decision regarding requests for additional information to support 
submitted demonstration packages and/or decisions regarding 
concurrence, nonconcurrence or deferral of submitted demonstration 
packages. While the EPA acknowledges the expressed concerns and desire 
for a formally identified dispute resolution process, the EPA also 
believes that several mechanisms currently exist that air agencies can 
use at various points in the exceptional events process. These 
mechanisms include engaging in early dialogue with the reviewing EPA 
Regional office, submitting requests for reconsideration to the 
official who made the determination if a request identifies a clear 
error or if the reviewing EPA regional office overlooked information 
submitted by the affected air agency, and/or elevating the concern 
within the EPA's chain of command. Additionally, air agencies can raise 
any unresolved event-related issues during the regulatory process that 
relies upon the claimed event-influenced data by participating in 
related public notice-and-comment processes and/or challenging in an 
appropriate court the regulatory decision subsequently made based in 
part on the EPA's exceptional events determination. These currently 
available dispute resolution approaches to address exceptional events 
decisions are consistent with the mechanisms available for other EPA 
actions. With exceptional events decisions, however, the air agency has 
opportunities to elevate concerns during two processes: the exceptional 
events determination and the subsequent regulatory action that relies 
on the exceptional events decision.
    The EPA believes that the existing mechanisms identified above 
combined with the EPA's commitment to focus on communication and 
collaboration with the submitting air agency through the exceptional 
events demonstration process, and the clarifications that would be in 
effect with these proposed revisions to the 2007 Exceptional Events 
Rule and associated guidance, will avoid the need for a formal dispute 
resolution mechanism for exceptional events. Therefore, the EPA does 
not intend to address dispute resolution within these proposed rule 
revisions and does not intend to respond to comments on this issue.

VI. Mitigation

A. Current Situation

    Section 319(b)(3)(A) of the CAA identifies five principles for the 
EPA to follow in developing implementing regulations for exceptional 
events:
    (i) Protection of public health is the highest priority;
    (ii) Timely information should be provided to the public in any 
case in which the air quality is unhealthy;
    (iii) All ambient air quality data should be included in a timely 
manner in an appropriate federal air quality database that is 
accessible to the public;
    (iv) Each state must take necessary measures to safeguard public 
health regardless of the source of the air pollution; and
    (v) Air quality data should be carefully screened to ensure that 
events not likely to recur are represented accurately in all monitoring 
data and analyses.
    The regulatory requirements implementing (iii) and (v) of this part 
of the statute are found only in 40 CFR 50.14 while the regulatory 
requirements implementing (i) and (iv) are found only in 40 CFR 51.930, 
Mitigation of Exceptional Events. Both Sec. Sec.  50.14(c)(1) and 
51.930(a)(1) require states to provide notice of events to the public 
(the second of the five principles).
    The language at 40 CFR 51.930 requires air agencies requesting data 
exclusion to ``take appropriate and reasonable actions to protect 
public health from exceedances or violations of the NAAQS'' and at a 
minimum do each of the following:
     Provide for prompt public notification whenever air 
quality concentrations exceed or are expected to exceed the NAAQS.
     Provide for public education concerning actions that 
individuals may take to reduce exposures to unhealthy levels of air 
quality during and following an exceptional event.
     Provide for the implementation of appropriate measures to 
protect public health from exceedances or violations of ambient air 
quality standards caused by exceptional events.
    The EPA promulgated the existing requirements in 2007 after 
considering and proposing several approaches to implementing CAA 
section 319(b)(3)(A). Some of the proposed approaches would have 
established a more formal structure by which air agencies prepared and 
submitted to the EPA mitigation plans to protect public health during 
events. These plans would have

[[Page 72890]]

been subject to the EPA's approval and/or the approval of the exclusion 
of event-affected data would have been contingent on the approval of 
such a plan. Comments on these proposed options varied 
widely.140 141
---------------------------------------------------------------------------

    \140\ The Treatment of Data Influenced by Exceptional Events; 
Proposed Rule, 71 FR 12592 (March 10, 2006).
    \141\ See Comments and Responses related to ``Requirements for 
States To Provide Public Notification, Public Education, and 
Appropriate and Reasonable Measures To Protect Public Health'' in 
Treatment of Data influenced by Exceptional Events; Final Rule, 72 
FR 13574-13576 (March 22, 2007).
---------------------------------------------------------------------------

    In the final 2007 Exceptional Events Rule, ``mitigation'' measures 
\142\ became part of the 2007 Exceptional Events Rule, but they were 
not incorporated into the criteria and processes by which data are 
excluded from use in regulatory determinations. There is no requirement 
to submit such measures to the EPA for either prospective or 
retrospective review and approval as a condition for approval for 
exclusion of event-affected data. Neither are air agencies required to 
notify the EPA of the measures an air agency plans to take or has 
taken. In the preamble to the 2007 Exceptional Events Rule, we stated 
that states should take ``reasonable and appropriate measures'' to 
protect public health related to the occurrence of an event and that 
states should determine what measures constitute those that are 
``reasonable and appropriate.'' \143\ We did not clarify how measures 
should be determined to be ``appropriate'' measures.
---------------------------------------------------------------------------

    \142\ The term ``mitigation'' does not appear in CAA section 
319(b). It appears in the title but not the text of 40 CFR 51.930.
    \143\ 72 FR 13574 (March 22, 2007).
---------------------------------------------------------------------------

    The mitigation measures that the EPA sees states most commonly 
practicing are ones related to the requirement that air agencies 
``provide for prompt public notification whenever air quality 
concentrations exceed or are expected to exceed the NAAQS.'' Often, 
these public notifications include public health alerts for high wind 
dust events or wildfires. We believe that other aspects of mitigation, 
including implementing appropriate measures to protect public health 
beyond notification, are also important in implementing the CAA guiding 
principle that ``each State must take necessary measures to safeguard 
public health regardless of the source of the air pollution.''

B. Proposed Changes

    Given the EPA's and the states' experience implementing the 2007 
Exceptional Events Rule as indicated above, we consider it appropriate 
to consider possible changes to the mitigation-related rule components 
with the benefit of additional public input. We are seeking comment on 
approaches ranging from retaining the existing rule requirements at 40 
CFR 51.930 to the various possible new components described in this 
section. We invite comment on these alternatives and on other concepts. 
We may make no change; we may adopt all of the described new 
components; or we may adopt only some features or variations of the 
described options. Note that we are not considering requiring all 
states to develop formal mitigation plans. We are seeking comment on 
the concept of only some states being required to develop mitigation 
plans for their particular ``historically documented'' or ``known 
seasonal'' exceptional events, defined below in section VI.B.1; on 
recommended elements for such mitigation plans described below in 
section VI.B.2; and on options for implementing mitigation plans 
described in section VI.B.3. Section VI.B.4 summarizes the EPA's 
potential options for mitigation elements for exceptional events 
purposes.
1. Defining Historically Documented or Known Seasonal Events
    The EPA seeks comment on whether an air agency should develop a 
mitigation plan for its particular type of ``historically documented'' 
or ``known seasonal'' exceptional events, if any. The EPA would 
consider ``historically documented'' or ``known seasonal'' exceptional 
events to include events of the same type and pollutant (e.g., high 
wind dust/PM or wildfire/ozone) that meet any of the following 
criteria: an event for which an air agency has previously submitted 
exceptional events demonstrations; an event that an air agency has 
previously flagged for concurrence in AQS (regardless of whether the 
air agency submitted a demonstration); or an event that has been the 
subject of local news articles, public health alerts or published 
scientific journal articles. The EPA would not require an air agency to 
develop a mitigation plan for the first event of a given type (e.g., if 
an area is prone to wildfires but has never experienced a high wind 
dust event, then it would not be expected to develop a mitigation plan 
for its first high wind dust event, but it would be expected to develop 
a mitigation plan for wildfires). A second event of a given type within 
a 3-year period would subject the area to ``having a history'' and, 
therefore, needing a mitigation plan.\144\ This option avoids plan 
development for a one-of-a-kind occurrence.\145\ In defining ``first'' 
and ``second'' events, the EPA could consider events that affect the 
same AQCR, but not necessarily the same monitor.\146\ For example, high 
wind dust events occur seasonally in the Phoenix, Arizona metropolitan 
area, which is part of the Maricopa Intrastate Air Quality Control 
Region (see 40 CFR 81.36). These events have influenced particulate 
matter concentrations at multiple monitors within the Maricopa 
Intrastate AQCR. Under this proposal, high wind dust events in Phoenix 
(i.e., the Maricopa Intrastate AQCR) are known events requiring a 
mitigation plan. On the other hand, a high wind dust event in Sedona, 
Arizona, part of the Northern Arizona Intrastate Air Quality Control 
Region (see 40 CFR 81.270), would be a first event and not subject to 
the development of a mitigation plan. As a variation of this concept on 
which we also seek comment, the EPA could consider a first season of 
events as one of three required seasons of events, so that a mitigation 
plan would be required only when an event type persists across several 
years. For example, an area may not have previously experienced 
wildfires in the past 10 years, but then experiences multiple wildfires 
and multiple exceedances in a single wildfire season. If these multiple 
wildfires affect the same general geographic area and monitors in a 
relatively short period of time (e.g. 2-3 months), then they could be 
considered a single event for purposes of developing a mitigation plan 
and would not trigger the requirement for a mitigation plan.
---------------------------------------------------------------------------

    \144\ A 3-year period is determined based on the submittal date 
of an exceptional events demonstration.
    \145\ Because the form of the NAAQS varies by pollutant, it is 
possible that multiple events in a 3-year period may not cause a 
NAAQS violation. An air agency that identifies multiple events of 
the same type (e.g., wildfire/ozone) in AQS, but prepares and 
submits a demonstration for only one of these events, would trigger 
the proposed requirement to develop a mitigation plan.
    \146\ Air Quality Control Regions are defined in 40 CFR part 81, 
subpart B, Designation of Air Quality Control Regions.
---------------------------------------------------------------------------

2. Mitigation Plan Components
    The EPA solicits comment on the following three plan components 
that could be recommended or required in order to implement the 
mitigation principles found in section 319(b)(3)(A) of the CAA: Public 
notification and education; steps to identify, study and implement 
mitigating measures and provision for periodic revision of the 
mitigation plan (to include public

[[Page 72891]]

review of plan elements). This section discusses these elements in more 
detail. A mitigation plan should address actions that would be taken 
within a state's own territory for events that happen within its own 
territory or that of another jurisdiction.
    a. Public notification to and education programs for affected or 
potentially affected communities. Air agencies could be required or 
encouraged to include in their mitigation plans steps to activate 
public notification and education systems whenever air quality 
concentrations exceed or are expected to exceed an applicable national 
ambient air quality standard. If possible, air agencies would notify 
the public of the actual or anticipated event at least 48 hours in 
advance of the event using methods appropriate to the community being 
served. Outreach mechanisms could include Web site alerts, National 
Weather Service alerts, telephone or text bulletins, television or 
radio campaigns or other messaging campaigns. Public notification and 
education programs could be encouraged or required to include some or 
all of the following actions to support the outreach system: adoption 
of methods for forecasting/detection, consultation with appropriate 
health department personnel regarding issuing health advisories and 
suggested actions for exposure minimization for sensitive populations 
(e.g., remain indoors, avoid vigorous outdoor activity, avoid exposure 
to tobacco smoke and other respiratory irritants and, in extreme cases, 
evacuation or public sheltering procedures).
    b. Steps to identify, study and implement mitigating measures, 
including approaches to address each of the following:
    (i) Mandatory or voluntary measures to abate or minimize 
contributing controllable sources of identified pollutants. A state 
could be required to include or encouraged to consider full-time or 
contingent controls on event-related sources as well as non-event 
related sources. For example, these measures might include continuously 
operating control measures during an extreme event for identified 
sources that normally operate these same controls on an intermittent 
basis. It could also involve including work practices (e.g., water 
spray for dust suppression) or contingent limits during extreme events 
on emissions from non-event related sources that, under non-event 
periods, have no or less stringent emissions limits or work practices.
    (ii) Methods to minimize public exposure to high concentrations of 
identified pollutants.
    (iii) Processes to collect and maintain data pertinent to the event 
(e.g., to identify the data to be collected, the party responsible for 
collecting and maintaining the data and when, how and to whom the data 
will be reported).
    (iv) Mechanisms to consult with other air quality managers in the 
affected area regarding the appropriate responses to abate and minimize 
impacts. Consultation could include collaboration between potentially 
affected local, state, tribal and federal air quality managers and/or 
emergency response personnel.
    c. Provision for periodic review and evaluation of the mitigation 
plan and its implementation and effectiveness by the air agency and all 
interested stakeholders (e.g., public and private land owners/managers, 
air quality, agriculture and forestry agencies, the public). For 
example, air agencies could be required to use this review process and 
to revise, if appropriate, and certify the mitigation plan every 3 
years or every three events, whichever is longer. The air agency could 
be required to submit a summary and response to the comments received 
during the public plan review process to the EPA along with the 
recertification statement and/or revised mitigation plan. If the 
historically documented or known seasonal exceptional events continue 
to result in elevated pollutant concentrations above the relevant 
NAAQS, thus showing that the combination of the existing SIP and the 
existing mitigation plan does not effectively safeguard public health, 
the mitigation plan might need to be strengthened during this review.
    If the EPA adopts requirements like those described above, it would 
not necessarily mean that all affected air agencies would have to 
prepare new plans. If an air agency has developed and implemented a 
contingency plan under 40 CFR part 51, subpart H, Prevention of Air 
Pollution Emergency Episodes, that meets the requirements of 40 CFR 
51.152, and that includes provisions for events that could be 
considered ``exceptional events'' under the provisions in 40 CFR 50.14, 
then the subpart H contingency plan would likely satisfy the mitigation 
requirements described above. If the identified basic elements are 
included and addressed, including the element for public comment, then 
other types of existing mitigation or contingency plans may satisfy the 
possible mitigation plan requirement described above. For example, if 
an area has developed a natural events action plan or a high wind 
action plan covering high wind dust events, this plan likely would 
satisfy mitigation elements for high wind dust events. Smoke management 
plans and/or forest management plans might also satisfy the mitigation 
elements for prescribed fires and wildfires. Most air agencies 
generally have sufficient, established processes that meet the public 
notification and education element, which can be easily adapted or 
modified to meet the mitigation elements proposed in this action. The 
EPA is requesting comment on how much time air agencies should be 
allowed to develop a plan.
3. Options for Implementing Mitigation Plans
    The EPA is seeking comment on two options for tying the proposed 
mitigation plan components discussed in section VI.B.2 to the EPA 
review of exceptional events demonstrations. Option 1 includes the 
EPA's review for completeness but not substantive approval or 
disapproval, while Option 2 includes the EPA's approval of the 
substance of the mitigation plan. These options are discussed below in 
more detail, but neither option would require a mitigation plan to be 
included in a SIP or to be otherwise federally-enforceable.
    Under both options, air agencies with historically documented or 
known seasonal exceptional events could submit the mitigation plan to 
the EPA in advance of an event, or submit a mitigation plan along with 
an exceptional events demonstration. The EPA would concur with a 
demonstration for the relevant event type only if a mitigation plan has 
passed the type of EPA review described in the option. Given that the 
air agency would have advance notification of the need to develop a 
plan, the air agency could develop and submit the mitigation plan in 
advance of any exceptional events demonstration so that the EPA could 
pre-review the mitigation plan and take faster action on an exceptional 
events submittal once one is submitted.
    Option 1: Under this option, the EPA would review for inclusion of 
required elements as described above and to ensure that the development 
of the mitigation plan included a public comment process. We would not 
formally review the substance of the plan in the sense of approving the 
details of the specific measures and commitments in the plan.
    Option 2: Under this option, EPA approval of the substance of the 
mitigation plan would be a precondition for EPA concurrence on an 
exceptional events demonstration. Because the EPA would approve the 
content, completeness and sufficiency of a mitigation plan, the EPA's 
disapproval

[[Page 72892]]

of the plan could result in the EPA's nonconcurrence on a current or 
future exceptional events demonstration.

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?

    The Exceptional Events Rule contains the regulatory requirements 
and criteria necessary for the EPA's approval of the exclusion of air 
quality data from regulatory determinations related to NAAQS 
exceedances or violations. During the implementation of the 2007 
Exceptional Events Rule, the EPA and stakeholders have identified a 
need for implementation guidance that provides an interpretation of and 
examples for addressing the regulatory requirements specific to the 
most common event types. One event type that has been identified by the 
EPA and stakeholders is wildfire influence on ozone concentrations. In 
2013, the EPA finalized the Interim Exceptional Events Implementation 
Guidance documents (see section IV.D), which included the Interim High 
Winds Guidance document and an Interim Overview document that also 
committed to the preparation of a Draft Wildfire Ozone Guidance 
document. The EPA intends to address this need and commitment via the 
Draft Guidance on the Preparation of Exceptional Events Demonstrations 
for Wildfire Events that May Influence Ozone Concentrations (``Draft 
Wildfire Ozone Guidance document''), which accompanies this proposed 
rule and is also available for comment.
    This Draft Wildfire Ozone Guidance document includes example 
analyses, conclusion statements and technical tools that air agencies 
can use to provide evidence that the wildfire event influenced the 
monitored ozone concentration. The Draft Wildfire Ozone Guidance 
document also identifies fire and monitor-based characteristics that 
might allow for a simpler and less resource-consuming demonstration 
package. The EPA has developed the Draft Wildfire Ozone Guidance 
document concurrently with the proposed Exceptional Events Rule 
revisions so that the Draft Wildfire Ozone Guidance reflects the 
proposed rule changes. Once finalized, this guidance will provide the 
EPA regional offices and air agencies with guidance on how to prepare 
and submit evidence to meet the Exceptional Events Rule requirements 
for monitored ozone exceedances caused by wildfires. The guidance, when 
finalized, will not be an EPA rule, and in specific cases the EPA may 
depart from the guidance for reasons that the EPA will explain at the 
time of the action.

B. What scenarios are addressed in the draft guidance?

    The EPA has prepared the Draft Wildfire Ozone Guidance document to 
provide assistance and example analyses for wildfire events that may 
influence ozone concentrations. Though many of the technical analyses 
included in the draft document may also be applied to prescribed fire 
events, the draft guidance document available for comment at this time 
does not provide guidance specific on how prescribed fire events can 
address all proposed rule requirements. Limiting the scope to wildfire 
events is intended to make the document easier to use for wildfire 
events. With this notice, the EPA invites comment on the content of 
this guidance document and whether it is appropriate to expand the 
scope of the guidance to include prescribed fire events. If commenters 
believe it is necessary to expand the scope of the EPA's final new 
guidance beyond the scope of the Draft Wildfire Ozone Guidance 
document, the EPA seeks comment on whether wildfire and prescribed fire 
events should be addressed in a single fire ozone guidance document or 
in separate guidance documents.

VIII. Environmental Justice Considerations

    The Exceptional Events Rule provides the criteria by which state, 
local and tribal air agencies identify air quality data they believe 
have been influenced by exceptional events, which by statutory 
definition are not reasonably controllable or preventable. Because 
these events are not reasonable to prevent or control, they can affect 
all downwind populations including minority and low-income populations. 
For this reason, in adding section 319(b) to the CAA, Congress 
identified as a guiding principle in developing regulations, ``the 
principle that protection of public health is the highest priority.'' 
The 2007 Exceptional Events Rule at 40 CFR 50.14 requires air agencies 
to seek public comment on prepared exceptional events demonstrations 
prior to submitting them to the reviewing EPA regional office. The 
public can also comment on rulemakings that include decisions related 
to the exclusion of event-influenced data. The mitigation of 
exceptional events language at 40 CFR 51.930 also requires that air 
agencies provide public notification and education programs related to 
events. To protect all people and communities, notably minority and 
low-income populations, air agencies should ensure that notifications 
and education programs are communicated using the language (e.g., 
English and Spanish) and media (e.g., radio and postings in local 
community centers) best suited to the target audience(s). Additionally, 
these proposed revisions are part of a public notice-and-comment 
rulemaking effort, which will include a public hearing. These 
opportunities for public input and education ensure that all those 
residing, working, attending school or otherwise present in areas 
affected by exceptional events, regardless of minority and economic 
status, are protected.

IX. Statutory and Executive Order Reviews

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

    This action is a significant regulatory action that was submitted 
to the Office of Management and Budget (OMB) for review because it 
raises novel policy issues. Any changes made in response to OMB 
recommendations have been documented in the docket.

B. Paperwork Reduction Act

    This action does not impose any new information collection burden 
under the PRA. The information being requested under these proposed 
rule revisions is consistent with current requirements related to 
information needed to verify the authenticity of monitoring data 
submitted to the EPA's AQS database, and to justify exclusion of data 
that have been flagged as being affected by exceptional events. OMB has 
previously approved the information collection activities for ambient 
air monitoring data and other supporting measurements reporting and 
recordkeeping activities associated with the 40 CFR part 58 Ambient Air 
Quality Surveillance rule and has assigned OMB control number 2060-
0084.

C. Regulatory Flexibility Act (RFA)

    I certify that this action will not have a significant economic 
impact on a substantial number of small entities under the RFA. This 
action will not impose any requirements on small entities. Instead, the 
proposed rule revisions provide the criteria and increase the 
efficiency of the process by which state, local and tribal air agencies 
identify air quality data they believe

[[Page 72893]]

have been influenced by an exceptional event. The proposed rule 
revisions also clarify those actions that state, local and tribal air 
agencies should take to protect public health during and following an 
exceptional event. Because affected air agencies would have discretion 
to implement controls on sources that may need to be regulated due to 
anthropogenic contribution in the area determined to be influenced by 
an exceptional event, the EPA cannot predict the indirect effect of the 
rule on sources that may be small entities.

D. Unfunded Mandates Reform Act (UMRA)

    This action does not contain an unfunded mandate of $100 million or 
more as described in UMRA, 2 U.S.C. 1531-1538, and does not 
significantly or uniquely affect small governments. The action imposes 
no enforceable duty on any state, local or tribal governments or the 
private sector.

E. Executive Order 13132: Federalism

    This action does not have federalism implications. The EPA 
believes, however, that this action may be of significant interest to 
states and to local air quality agencies to whom a state has delegated 
relevant responsibilities for air quality management. Consistent with 
the EPA's policy to promote communications between the EPA and state 
and local governments, the EPA consulted with representatives of state 
and local governments early in the process of developing this action to 
permit them to have meaningful and timely input into its development. A 
summary of the concerns raised during that consultation is provided in 
section IV of this preamble.

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

    This action does not have tribal implications as specified in 
Executive Order 13175. It would not have a substantial direct effect on 
one or more Indian tribes. Furthermore, these proposed regulation 
revisions do not affect the relationship or distribution of power and 
responsibilities between the federal government and Indian tribes. The 
CAA and the TAR establish the relationship of the federal government 
and tribes in characterizing air quality and developing plans to attain 
the NAAQS, and these revisions to the regulations do nothing to modify 
that relationship. Thus, Executive Order 13175 does not apply to this 
action.
    Although Executive Order 13175 does not apply to this action, the 
EPA held public meetings attended by tribal representatives and 
separate meetings with tribal representatives to discuss the revisions 
proposed in this action. The EPA also provided an opportunity for all 
interested parties to provide oral or written comments on potential 
concepts for the EPA to address during the rule revision process. 
Summaries of these meetings are included in the docket for this 
proposed rule. The EPA specifically solicits additional comment on this 
proposed action from tribal officials.

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

    The EPA interprets Executive Order 13045 as applying only to those 
regulatory actions that concern environmental health or safety risks 
that the EPA has reason to believe may disproportionately affect 
children, per the definition of ``covered regulatory action'' in 
section 2-202 of the Executive Order. This action is not subject to 
Executive Order 13045 because it does not concern an environmental 
health risk or safety risk.

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

    This action is not a ``significant energy action'' because it is 
not likely to have a significant adverse effect on the supply, 
distribution or use of energy. The purpose of this proposed rule is to 
provide the criteria, and increase the efficiency of the process, by 
which state, local and tribal air agencies may identify air quality 
data they believe have been influenced by an exceptional event. The EPA 
does not expect these activities to affect energy suppliers, 
distributors or users.

I. National Technology Transfer and Advancement Act

    This rulemaking does not involve technical standards.

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

    The EPA believes the human health or environmental risk addressed 
by this action will not have potential disproportionately high and 
adverse human health or environmental effects on minority, low-income 
or indigenous populations. The results of this evaluation are contained 
in the section of the preamble titled ``Environmental Justice 
Considerations.'' This proposed action provides the criteria and 
increases the efficiency of the process by which state, local and 
tribal air agencies identify air quality data they believe have been 
influenced by exceptional events, which, by statutory definition, are 
not reasonably controllable or preventable. These proposed regulatory 
provisions do, however, provide information concerning actions that 
state, local or tribal air agencies might take to uniformly protect 
public health once the EPA has concurred with an air agency's request 
to exclude data influenced by an exceptional event. The mitigation 
component of the proposed rule could ultimately provide additional 
protection for minority, low income and other populations located in 
areas affected by exceptional events. Therefore, the EPA finds that 
this proposed action would not adversely affect the health or safety of 
minority or low-income populations, and that it is designed to protect 
and enhance the health and safety of these and other populations.

X. Statutory Authority

    The statutory authority for this action is provided by 42 U.S.C. 
7401, et seq.

List of Subjects in 40 CFR Part 50

    Environmental protection, Air pollution control, National parks, 
Wilderness areas.

    Dated: November 10, 2015.
Gina McCarthy,
Administrator.

    For the reasons set forth in the preamble, it is proposed that 40 
CFR part 50 be amended as follows:

PART 50--NATIONAL PRIMARY AND SECONDARY AMBIENT AIR QUALITY 
STANDARDS

0
1. The authority citation for part 50 continues to read as follows:

    Authority:  42 U.S.C. 7401, et seq.

0
2. Amend Sec.  50.1 by:
0
a. Revising paragraphs (j) and (k).
0
b. Adding paragraphs (m), (n), (o), (p), (q) and (r).
    The revisions and additions read as follows:


Sec.  50.1  Definitions.

* * * * *
    (j) Exceptional event means an event and its resulting emissions 
that affect air quality in such a way that there exists a clear causal 
relationship between the specific event and the monitored exceedance or 
violation, is not reasonably controllable or preventable, is an event 
caused by human activity that is unlikely to recur at a particular 
location or a natural event, and is determined by the Administrator in 
accordance with 40 CFR 50.14 to be an

[[Page 72894]]

exceptional event. It does not include stagnation of air masses or 
meteorological inversions, a meteorological event involving high 
temperatures or lack of precipitation, or air pollution relating to 
source noncompliance.
    (k) Natural event means an event and its resulting emissions, which 
may recur, in which human activity plays little or no direct causal 
role. Anthropogenic sources that are reasonably controlled shall be 
considered to not play a direct role in causing emissions.
* * * * *
    (m) Prescribed fire is any fire intentionally ignited by management 
actions in accordance with applicable laws, policies, and regulations 
to meet specific land or resource management objectives.
    (n) Wildfire is any fire started by an unplanned ignition caused by 
lightning; volcanoes; other acts of nature; unauthorized activity; or 
accidental, human-caused actions, or a prescribed fire that has been 
declared to be a wildfire. A wildfire that predominantly occurs on 
wildland is a natural event.
    (o) Wildland means an area in which human activity and development 
is essentially non-existent, except for roads, railroads, power lines, 
and similar transportation facilities. Structures, if any, are widely 
scattered.
    (p) High wind dust event is an event that includes the high-speed 
wind and the dust that the wind entrains and transports to a monitoring 
site.
    (q) High wind threshold is the minimum wind speed capable of 
causing particulate matter emissions from natural undisturbed lands in 
the area affected by a high wind dust event.
    (r) Federal land manager means, consistent with the definition in 
40 CFR 51.301, the Secretary of the department with authority over the 
Federal Class I area (or the Secretary's designee) or, with respect to 
Roosevelt-Campobello International Park, the Chairman of the Roosevelt-
Campobello International Park Commission.
0
3. Amend Sec.  50.14, as amended on October 26, 2015, at 80 FR 65452, 
effective December 28, 2015, as follows:
0
a. Revise paragraphs (a) and (b);
0
b. Revise paragraphs (c)(1), (c)(2)(i) through (v), and (c)(3).
    The revisions read as follows:


Sec.  50.14  Treatment of air quality monitoring data influenced by 
exceptional events.

    (a) Requirements--(1) Scope. (i) This section applies to the 
treatment of data showing exceedances or violations of any national 
ambient air quality standard for purposes of the following types of 
regulatory determinations by the Administrator:
    (A) An action to designate an area, pursuant to Clean Air Act 
section 107(d)(1), or redesignate an area, pursuant to Clean Air Act 
section 107(d)(3), for a particular national ambient air quality 
standard;
    (B) The assignment or re-assignment of a classification category to 
a nonattainment area where such classification is based on a comparison 
of pollutant design values, calculated according to the specific data 
handling procedures in 40 CFR part 50 for each national ambient air 
quality standard, to the level of the relevant national ambient air 
quality standard;
    (C) A determination regarding whether a nonattainment area has 
attained the level of the appropriate national ambient air quality 
standard by its specified deadline;
    (D) A determination that an area has had only one exceedance in the 
year prior to its attainment deadline and thus qualifies for a 1-year 
attainment date extension, if applicable; and
    (E) A determination under Clean Air Act section 110(k)(5), if based 
on an area violating a national ambient air quality standard, that the 
state implementation plan is inadequate to the requirements of Clean 
Air Act section 110.
    (ii) A State, federal land manager or other federal agency may 
request the Administrator to exclude data showing exceedances or 
violations of any national ambient air quality standard that are 
directly due to an exceptional event from use in determinations by 
demonstrating to the Administrator's satisfaction that such event 
caused a specific air pollution concentration at a particular air 
quality monitoring location.
    (A) For a federal land manager or other federal agency to be 
eligible to initiate such a request for data exclusion, the federal 
land manager or other federal agency must:
    (1) Either operate a regulatory monitor that has been affected by 
an exceptional event or manage land on which an exceptional event 
occurred that influenced a monitored concentration at a regulatory 
monitor; and
    (2) Initiate such a request only after discussing such submittal 
with the State in which the affected monitor is located; and
    (B) When initiating such a request, all provisions in this section 
that are expressed as requirements applying to a State shall, except as 
noted, be requirements applying to the federal land manager or other 
federal agency.
    (2) A demonstration to justify data exclusion may include any 
reliable and accurate data, but must specifically address the elements 
in paragraphs (c)(3)(iv) and (v) of this section.
    (b) Determinations by the Administrator--(1) Generally. The 
Administrator shall exclude data from use in determinations of 
exceedances and violations where a State demonstrates to the 
Administrator's satisfaction that an exceptional event caused a 
specific air pollution concentration in excess of one or more national 
ambient air quality standards at a particular air quality monitoring 
location and otherwise satisfies the requirements of this section.
    (2) Fireworks displays. The Administrator shall exclude data from 
use in determinations of exceedances and violations where a State 
demonstrates to the Administrator's satisfaction that emissions from 
fireworks displays caused a specific air pollution concentration in 
excess of one or more national ambient air quality standards at a 
particular air quality monitoring location and otherwise satisfies the 
requirements of this section. Such data will be treated in the same 
manner as exceptional events under this rule, provided a State 
demonstrates that such use of fireworks is significantly integral to 
traditional national, ethnic, or other cultural events including, but 
not limited to, July Fourth celebrations that satisfy the requirements 
of this section.
    (3) Prescribed fires. (i) The Administrator shall exclude data from 
use in determinations of exceedances and violations, where a State 
demonstrates to the Administrator's satisfaction that emissions from 
prescribed fires caused a specific air pollution concentration in 
excess of one or more national ambient air quality standards at a 
particular air quality monitoring location and otherwise satisfies the 
requirements of this section.
    (ii) In addressing the requirements set forth in paragraph 
(c)(3)(iv)(D) of this section regarding the not reasonably controllable 
or preventable criterion:
    (A) With respect to the requirement that a prescribed fire be not 
reasonably controllable, the State must either certify to the 
Administrator that it has adopted and is implementing a smoke 
management plan or the State must demonstrate that the burn manager 
employed the generally applicable basic smoke management practices 
identified in Table 2 to Sec.  50.14. To make the latter demonstration, 
the State may rely on a statement or other documentation provided by 
the burn manager that he or she employed those practices. If an 
exceptional event occurs using the basic

[[Page 72895]]

smoke management practices approach, the State must undertake a review 
of its approach to ensure public health is being protected.
    (B) With respect to the requirement that a prescribed fire be not 
reasonably preventable, provided the Administrator determines that 
there is no compelling evidence to the contrary in the record, the 
State may rely upon and reference a multi-year land or resource 
management plan for a wildland area with a stated objective to 
establish, restore and/or maintain a sustainable and resilient wildland 
ecosystem and/or to preserve endangered or threatened species through a 
program of prescribed fire, but also provided that the use of 
prescribed fire in the area has not exceeded the frequency indicated in 
that plan.
    (iii) Provided the Administrator determines that there is no 
compelling evidence to the contrary in the record, in addressing the 
requirements set forth in paragraph (c)(3)(iv)(E) of this section 
regarding the human activity unlikely to recur at a particular location 
criterion for demonstrations involving prescribed fires on wildland, 
the State must describe the actual frequency with which a burn was 
conducted, but may rely upon and reference an assessment of the natural 
fire return interval or the prescribed fire frequency needed to 
establish, restore, and/or maintain a sustainable and resilient 
wildland ecosystem contained in a multi-year land or resource 
management plan with a stated objective to establish, restore, and/or 
maintain a sustainable and resilient wildland ecosystem and/or to 
preserve endangered or threatened species through a program of 
prescribed fire.

 Table 2 to Sec.   50.14--Summary of Basic Smoke Management Practices, Benefit Achieved With the BSMP, and When
                         It Is Applied Before, During or After Ignition of the Burn \a\
----------------------------------------------------------------------------------------------------------------
                                         Benefit achieved with the     When the BSMP is  applied--before/during/
   Basic smoke management practice                  BSMP                            after  the burn
----------------------------------------------------------------------------------------------------------------
Evaluate Smoke Dispersion Conditions.  Minimize smoke impacts.......  Before, During, After.
Monitor Effects on Air Quality.......  Be aware of where the smoke    Before, During, After.
                                        is going and degree it
                                        impacts air quality.
Record-Keeping/Maintain a Burn/Smoke   Retain information about the   Before, During, After.
 Journal.                               weather, burn and smoke. If
                                        air quality problems occur,
                                        documentation helps analyze
                                        and address air regulatory
                                        issues.
Communication--Public Notification...  Notify neighbors and those     Before, During.
                                        potentially impacted by
                                        smoke, especially sensitive
                                        receptors.
Consider Emission Reduction            Reducing emissions through     Before, During, After.
 Techniques.                            mechanisms such as reducing
                                        fuel loading can reduce
                                        downwind impacts.
Share the Airshed--Coordination of     Coordinate multiple burns in   Before, During, After.
 Area Burning.                          the area to manage exposure
                                        of the public to smoke.
----------------------------------------------------------------------------------------------------------------
\a\ Elements of these BSMP could also be practical and beneficial to apply to wildfires for areas likely to
  experience recurring wildfires.

    (4) Wildfires. The Administrator shall exclude data from use in 
determinations of exceedances and violations where a State demonstrates 
to the Administrator's satisfaction that emissions from wildfires 
caused a specific air pollution concentration in excess of one or more 
national ambient air quality standard at a particular air quality 
monitoring location and otherwise satisfies the requirements of this 
section. Provided the Administrator determines that there is no 
compelling evidence to the contrary in the record, the Administrator 
will determine every wildfire occurring predominantly on wildland to 
have met the requirements identified in paragraph (c)(3)(iv)(D) of this 
section regarding the not reasonably controllable or preventable 
criterion.
    (5) High wind dust events. (i) The Administrator shall exclude data 
from use in determinations of exceedances and violations, where a State 
demonstrates to the Administrator's satisfaction that emissions from a 
high wind dust event caused a specific air pollution concentration in 
excess of one or more national ambient air quality standards at a 
particular air quality monitoring location and otherwise satisfies the 
requirements of this section provided that such emissions are from high 
wind dust events.
    (ii) The Administrator will consider high wind dust events to be 
natural events in cases where windblown dust is entirely from 
undisturbed natural lands or where all anthropogenic sources are 
reasonably controlled as determined in accordance with paragraph (b)(7) 
of this section.
    (iii) The Administrator will accept a high wind threshold of a 
sustained wind of 25 mph for areas in the States of Arizona, 
California, Colorado, Kansas, Nebraska, Nevada, New Mexico, North 
Dakota, Oklahoma, South Dakota, Texas, Utah, and Wyoming provided this 
value is not contradicted by evidence in the record at the time the 
State submits a demonstration.
    (iv) In addressing the requirements set forth in paragraph 
(c)(3)(iv)(D) of this section regarding the not reasonably preventable 
criterion, the State shall not be required to provide a case-specific 
justification for a high wind dust event.
    (v) With respect to the not reasonably controllable criterion of 
paragraph (c)(3)(iv)(D) of this section, dust controls on an 
anthropogenic source shall be considered reasonable in any case in 
which the controls render the anthropogenic source as resistant to high 
winds as a natural undisturbed land area. The Administrator may 
determine lesser controls reasonable on a case-by-case basis.
    (vi) For remote, large-scale, high-energy and/or sudden high wind 
dust events, such as ``haboobs'' in the southwest, the Administrator 
will generally consider a demonstration documenting the nature and 
extent of the event to be sufficient with respect to the not reasonable 
controllable criterion of paragraph (c)(3)(iv)(D) of this section.
    (6) Determinations with respect to event aggregation and multiple 
national ambient air quality standards for the same pollutant. (i) 
Where a State demonstrates to the Administrator's satisfaction that for 
national ambient air quality standards with averaging or cumulative 
periods longer than 24-hours the aggregate effect of events occurring 
on different days has caused an exceedance or violation, the 
Administrator shall determine such collective data to satisfy the 
requirements in paragraph (c)(3)(iv)(B) of this section regarding the 
clear causal relationship criterion and otherwise satisfies the 
requirements of this section.

[[Page 72896]]

    (ii) The Administrator shall accept as part of a demonstration for 
the clear causal relationship in paragraph (c)(3)(iv)(B) of this 
section, a State's comparison of a 24-hour concentration of any 
national ambient air quality standard pollutant to the level of a 
national ambient air quality standard for the same pollutant with a 
longer averaging period.
    (7) Determinations with respect to the not reasonably controllable 
or preventable criterion. (i) The Administrator shall determine that an 
event is not reasonably preventable if the State shows that reasonable 
measures to prevent the event were applied at the time of the event.
    (ii) The Administrator shall determine that an event is not 
reasonably controllable if the State shows that reasonable measures to 
control the impact of the event on air quality were applied at the time 
of the event.
    (iii) The Administrator shall assess the reasonableness of 
available controls for anthropogenic sources based on information 
available as of the date of the event.
    (iv) Except where a State is obligated to revise its state 
implementation plan, the Administrator shall consider enforceable 
control measures implemented in accordance with a state implementation 
plan, 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 Clean Air Act for the 
state implementation plan to be reasonable controls with respect to all 
anthropogenic sources that have or may have contributed to event-
related emissions.
    (v) The Administrator shall not require a State to provide case-
specific justification to support the not reasonably controllable or 
preventable criterion for emissions-generating activity that occurs 
outside of the State's jurisdictional boundaries within which the 
concentration at issue was monitored. In the case of a tribe with 
treatment as a state status with respect to exceptional events 
requirements, the tribe's jurisdictional boundaries for purposes of 
requiring or directly implementing emission controls apply. In the case 
of a federal land manager or other federal agency submitting a 
demonstration under the requirements of this section, the 
jurisdictional boundaries that apply are those of the State or the 
tribe depending on which has jurisdiction over the area where the event 
has occurred.
    (c) Schedules and procedures--(1) Public notification. (i) All 
States and, where applicable, their political subdivisions must notify 
the public promptly whenever an event occurs or is reasonably 
anticipated to occur which may result in the exceedance of an 
applicable air quality standard.
    (ii) [Reserved]
    (2) Initial notification of potential exceptional event. (i) A 
State shall notify the Administrator of its intent to request exclusion 
of one or more measured exceedances of an applicable national ambient 
air quality standard as being due to an exceptional event by creating 
an initial event description and flagging the associated data that have 
been submitted to the AQS database and by engaging in the Initial 
Notification of Potential Exceptional Event process as follows:
    (A) The State and the appropriate EPA regional office shall engage 
in regular communications to identify those data that have been 
potentially influenced by an exceptional event, to determine whether 
the identified data may affect a regulatory determination and to 
discuss whether the State should develop and submit an exceptional 
events demonstration according to the requirements in this section;
    (B) For data that may affect an anticipated regulatory 
determination or where circumstances otherwise compel the Administrator 
to prioritize the resulting demonstration, the Administrator shall 
respond to a State's Initial Notification of Potential Exceptional 
Event with a due date for demonstration submittal that considers the 
nature of the event and the anticipated timing of the associated 
regulatory decision;
    (C) The Administrator may waive the Initial Notification of 
Potential Exceptional Event process on a case-by-case basis.
    (ii) The data shall not be excluded from determinations with 
respect to exceedances or violations of the national ambient air 
quality standards unless and until, following the State's submittal of 
its demonstration pursuant to paragraph (c)(3) of this section and the 
Administrator's review, the Administrator notifies the State of its 
concurrence by placing a concurrence flag in the appropriate field for 
the data record in the AQS database.
    (iii) [Reserved]
    (iv) [Reserved]
    (v) [Reserved]
* * * * *
    (3) Submission of demonstrations. (i) Except as allowed under 
paragraph (c)(2)(vi) of this section, a State that has flagged data as 
being due to an exceptional event and is requesting exclusion of the 
affected measurement data shall, after notice and opportunity for 
public comment, submit a demonstration to justify data exclusion to the 
Administrator according to the schedule established under paragraph 
(c)(2)(i)(B).
    (ii) [Reserved]
    (iii) [Reserved]
    (iv) The demonstration to justify data exclusion must include:
    (A) A narrative conceptual model that describes the event(s) 
causing the exceedance or violation and a discussion of how emissions 
from the event(s) led to the exceedance or violation at the affected 
monitor(s);
    (B) A demonstration 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;
    (C) Analyses identified in Table 3 to Sec.  50.14 comparing the 
claimed event-influenced concentration(s) to concentrations at the same 
monitoring site at other times consistent with Table 3 to Sec.  50.14 
to support the requirement at paragraph (c)(3)(iv)(B) of this section. 
The Administrator shall not require a State to prove a specific 
percentile point in the distribution of data;
    (D) A demonstration that the event was both not reasonably 
controllable and not reasonably preventable; and
    (E) A demonstration that the event was a human activity that is 
unlikely to recur at a particular location or was a natural event.
    (v) With the submission of the demonstration containing the 
elements in paragraph (c)(3)(iv) of this section, the State must:
    (A) Document that the public comment process was followed and that 
the comment period was open for a minimum of 30 days, which could be 
concurrent with the Administrator's review of the associated 
demonstration provided the State can meet all requirements in this 
paragraph;
    (B) Submit the public comments it received along with its 
demonstration to the Administrator; and
    (C) Address in the submission to the Administrator those comments 
disputing or contradicting factual evidence provided in the 
demonstration.
    (vi) Where the State has submitted a demonstration according to the 
requirements of this section and the Administrator has reviewed such 
demonstration and requested additional evidence to support one of the 
elements in paragraph (c)(3)(iv) of this section, the State shall have 
12 months from the date of the Administrator's request to submit such 
evidence. At the

[[Page 72897]]

conclusion of this time, if the State has not submitted the requested 
additional evidence, the Administrator will consider the demonstration 
to be inactive and will not pursue additional review of the 
demonstration. After a 12-month period of inactivity, if a State 
desires to pursue the inactive demonstration, it must reinitiate its 
request to exclude associated data by following the process beginning 
with paragraph (c)(2)(i) of this section.

         Table 3 to Sec.   50.14. Evidence and Analyses for the Comparison to Historical Concentrations
----------------------------------------------------------------------------------------------------------------
    Historical concentration evidence      Types of analyses/supporting information      Required or optional?
----------------------------------------------------------------------------------------------------------------
1. Comparison of concentrations on the    Seasonal (appropriate if exceedances occur  Required seasonal and/or
 claimed event day with past historical    primarily in one season, but not in         annual analysis
 data.                                     others).                                    (depending on which is
                                           Use all available seasonal data     more appropriate).
                                           over the previous 5 years (or more, if
                                           available).
                                           Discuss the seasonal nature of
                                           pollution for the location being
                                           evaluated.
                                           Present monthly maximums of the
                                           NAAQS relevant metric (e.g., maximum
                                           daily 8-hour average ozone or 1-hr SO2)
                                           vs monthly or other averaged daily data
                                           as this masks high values.
                                          Annual (appropriate if exceedances are
                                           likely throughout the year).
                                           Use all available data over the
                                           previous 5 years (or more, if available).
                                          Seasonal and Annual Analyses..............
                                           Provide the data in the form
                                           relevant to the standard being considered
                                           for data exclusion.
                                           Label ``high'' data points as
                                           being associated with concurred
                                           exceptional events, suspected exceptional
                                           events, other unusual occurrences, or
                                           high pollution days due to normal
                                           emissions.
                                           Describe how emission control
                                           strategies have decreased pollutant
                                           concentrations over the 5-year window, if
                                           applicable.
                                           Include comparisons omitting
                                           known or suspected exceptional events
                                           points, if applicable.
2. Comparison of concentrations on the     Include neighboring days at the    Optional analysis.
 claimed event day with a narrower set     same location (e.g., a time series of two
 of similar days.                          to three weeks) and/or other days with
                                           similar meteorological conditions
                                           (possibly from other years) at the same
                                           or nearby locations with similar
                                           historical air quality along with a
                                           discussion of the meteorological
                                           conditions during the same timeframe. \a\
                                           Use this comparison to
                                           demonstrate that the event caused higher
                                           concentrations than would be expected for
                                           given meteorological and/or local
                                           emissions conditions.
3. Percentile rank of concentration when   Provide the percentile rank of     Required analysis when
 compared to annual data. \b\              the event-day concentration relative to     comparison is made on an
                                           all measurement days over the previous 5    annual basis (see item
                                           years to ensure statistical robustness      #1).
                                           and capture non-event variability over
                                           the appropriate seasons or number of
                                           years.\c\
                                           Use the daily statistic (e.g., 24-
                                           hour average, maximum daily 8-hour
                                           average, or maximum 1-hour) appropriate
                                           for the form of the standard being
                                           considered for data exclusion.
4. Percentile rank of concentration        Provide the percentile rank of     Required analysis when
 relative to seasonal data. \b\            the event-day concentration relative to     comparison is made on a
                                           all measurement days for the season (or     seasonal basis (see item
                                           appropriate alternative 3-month period)     #1).
                                           of the event over the previous 5 years.
                                           Use the same time horizon as used
                                           for the percentile rank calculated
                                           relative to annual data, if appropriate.
----------------------------------------------------------------------------------------------------------------
\a\ If an air agency compares the concentration on the claimed event day with days with similar meteorological
  conditions from other years, the agency should also verify and provide evidence that the area has not
  experienced significant changes in wind patterns, and that no significant sources in the area have had
  significant changes in their emissions of the pollutant of concern.
\b\ The EPA does not intend to identify a particular historical percentile rank point in the seasonal or annual
  historical data that plays a critical role in the analysis or conclusion regarding the clear causal
  relationship.
\c\ Section 8.4.2.e of appendix W (proposed revisions at 80 FR 45374, July 29, 2015) recommends using 5 years of
  adequately representative meteorology data from the National Weather Service to ensure that worst-case
  meteorological conditions are represented. Similarly, for exceptional events purposes, the EPA believes that 5
  years of ambient air data, whether seasonal or annual, better represent the range of ``normal'' air quality
  than do shorter periods.

[FR Doc. 2015-29350 Filed 11-19-15; 8:45 am]
BILLING CODE 6560-50-P