[Federal Register Volume 81, Number 191 (Monday, October 3, 2016)]
[Rules and Regulations]
[Pages 68216-68282]
[FR Doc No: 2016-22983]

Vol. 81

Monday,

No. 191

October 3, 2016

Part V

Environmental Protection Agency

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40 CFR Parts 50 and 51

Treatment of Data Influenced by Exceptional Events; Final Rule

Federal Register / Vol. 81 , No. 191 / Monday, October 3, 2016 /
Rules and Regulations

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Parts 50 and 51

[EPA-HQ-OAR-2013-0572, EPA-HQ-OAR-2015-0229; FRL-9952-89-OAR]
RIN 2060-AS02

Treatment of Data Influenced by Exceptional Events

AGENCY: Environmental Protection Agency (EPA).

ACTION: Final rule; notification to states with areas subject to
mitigation requirements; final guidance.

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SUMMARY: The Environmental Protection Agency (EPA) is finalizing
revisions to certain sections within the regulations that govern the
exclusion of event-influenced air quality data from certain regulatory
decisions under the Clean Air Act (CAA). The EPA's mission includes
preserving and improving the quality of our nation's ambient air to
protect human health and the environment, and the CAA and the EPA's
regulations rely heavily on ambient air quality data. However, the CAA
also recognizes that it may not be appropriate to use the monitoring
data influenced by ``exceptional'' events that are collected by the
ambient air quality monitoring network when making certain regulatory
determinations. When ``exceptional'' events cause exceedances or
violations of the national ambient air quality standards (NAAQS) that
subsequently affect certain regulatory decisions, the normal planning
and regulatory process established by the CAA may not be appropriate.
This final rule contains definitions, procedural requirements,
requirements for air agency demonstrations, criteria for the EPA's
approval of the exclusion of event-influenced air quality data and
requirements for air agencies to take appropriate and reasonable
actions to protect public health from exceedances or violations of the
NAAQS. It reflects the experiences of the EPA, state, local and tribal
air agencies, federal land managers and other stakeholders in
implementing this program over the past 10 years. These regulatory
revisions, the EPA's commitment to improved communications, our focus
on decisions with regulatory significance, and the expressed non-
binding guidance in the preamble regarding recommendations for
demonstration narrative and analyses to include in demonstration
packages, protect human health and the environment while providing
needed clarity, increasing the administrative efficiency of
demonstration submittal process, and removing some of the challenges
associated with implementing the Exceptional Events Rule. As part of
the EPA's mission to protect public health, this action promulgates new
requirements for mitigation plans for areas with known, recurring
events. We are simultaneously using this action to provide written
notification to those states with areas that are initially subject to
these new requirements. In addition to finalizing revisions to the
Exceptional Events Rule, the EPA is also announcing the availability of
the final version of the non-binding guidance document titled Guidance
on the Preparation of Exceptional Events Demonstrations for Wildfire
Events that May Influence Ozone Concentrations, which applies the rule
revisions to wildfire events that could influence monitored ozone
concentrations.

DATES: This final rule is effective on September 30, 2016.

ADDRESSES: The EPA established Docket ID No. EPA-HQ-OAR-2013-0572 for
this action. All documents in the docket are listed in the http://www.regulations.gov Web site. Although listed in the index, some
information is not publicly available, e.g., Confidential Business
Information or other information whose disclosure is restricted by
statute. Certain other material, such as copyrighted material, is not
placed on the Internet and will be publicly available only in hard
copy. Publicly available docket materials are available electronically
in http://www.regulations.gov.
    The EPA also established Docket ID No. EPA-HQ-OAR-2015-0229 for the
related guidance document titled Guidance on the Preparation of
Exceptional Events Demonstrations for Wildfire Events that May
Influence Ozone Concentrations. All documents in the docket are listed
in the http://www.regulations.gov Web site. Although listed in the
index, some information is not publicly available, e.g., Confidential
Business Information or other information whose disclosure is
restricted by statute. Certain other material, such as copyrighted
material, is not placed on the Internet and will be publicly available
only in hard copy. Publicly available docket materials are available
electronically in http://www.regulations.gov.

FOR FURTHER INFORMATION CONTACT:  For general information regarding
this rule, please contact Beth 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<PHONE_NUMBER>, email at
<EMAIL_ADDRESS>For general information regarding the Guidance
on the Preparation of Exceptional Events Demonstrations for Wildfire
Events that May Influence Ozone Concentrations, please contact Lev
Gabrilovich, U.S. EPA, Office of Air Quality Planning and Standards,
Air Quality Policy Division, Mail Code C539-04, Research Triangle Park,
NC 27711, telephone<PHONE_NUMBER>, email at<EMAIL_ADDRESS>
SUPPLEMENTARY INFORMATION:

I. General Information

A. Executive Summary

    Pursuant to section 319(b) of the CAA, the EPA is taking action to
finalize revisions to the Exceptional Events Rule (codified at 40 CFR
50.1, 50.14 and 51.930), which governs the exclusion of these event-
affected air quality data. The CAA recognizes that it may not be
appropriate to use monitoring data influenced by ``exceptional'' events
collected by the ambient air quality monitoring network when making
certain regulatory determinations. When ``exceptional'' events
influence monitoring data and cause exceedances or violations of the
NAAQS, air agencies can request the exclusion of event-influenced data,
and the EPA can agree to exclude these data, from the data set used for
certain regulatory decisions.
    This section summarizes the purpose of this regulatory action and
its major provisions and provides an overview of the associated
guidance. After considering the comments received during the public
comment period, we are making several changes to the promulgated rule
language and/or the preamble, in which we provide non-binding guidance
to assist air agencies in implementing the rule. In accordance with
section 553(d)(3) of the Administrative Procedures Act, good cause
exists to expedite effectiveness of this final rule, therefore, we are
also establishing the effective date of this action to be the date that
it is published in the Federal Register. See 5 U.S.C. 553(d)(3). Good
cause exists when urgency of conditions are coupled with demonstrated
and unavoidable limitations in time; primary consideration is given to
the convenience or necessity of the people affected. In this
circumstance, prompt effectiveness of this final rule will allow state
governors and tribes, if they wish, to consider the final rule
revisions in advance of submitting recommendations for area
designations for the 2015 Ozone NAAQS, which are due by October 1,
2016, and which could include the consideration of exceptional events.
The

deadline for states and tribes to submit recommendations for area
designations for the 2015 Ozone NAAQS is a demonstrated and unavoidable
time limitation. Prompt effectiveness of this final rule is in the
public interest as it will ensure adequate time for states to develop
their exceptional events demonstrations and time for the public to
comment on those demonstrations. In addition, typically rules are
effective at least 30 days after publication to provide time for
affected parties to adjust their behavior and prepare before the final
rule takes effect. That circumstance does not apply to this final rule
because this rule does not require a behavior change. Rather, this
final rule revises and provides additional clarity with respect to a
previously existing opportunity.
    We are promulgating language to define those regulatory actions
that comprise ``determinations by the Administrator with respect to
exceedances or violations of the [NAAQS].'' In doing so, we apply the
provisions in CAA section 319(b) to a specific set of regulatory
actions (e.g., designations). The final rule language returns to the
three core statutory elements and implicit concepts of CAA section
319(b): (1) 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, (2) the event was not reasonably
controllable or preventable, and (3) the event was caused by human
activity that is unlikely to recur at a particular location or was a
natural event. We clarify in the preamble the general types of analyses
and narrative that the EPA expects to see in demonstrations to address
each of these three core statutory elements. We also clarify how to
apply these criteria in certain scenarios and to certain event types.
    In returning to the first of the three core statutory elements
(i.e., 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), we are promulgating regulatory text that
subsumes the ``affects air quality'' element into the ``clear causal
relationship'' criterion. We are also removing from the rule language
the requirement for air agencies to provide evidence that the event is
associated with a measured concentration in excess of ``normal
historical fluctuations including background'' and replacing it with a
requirement for a comparison of the event-related concentration to
historical concentrations. Additionally, we are removing the 2007
Exceptional Events Rule language commonly referred to as the ``but
for'' criterion and focus instead on the clear causal relationship
criterion.
    With respect to the ``not reasonably controllable or preventable''
criterion, the EPA is promulgating a provision that enforceable control
measures are ``reasonable controls'' with respect to all anthropogenic
sources that have or may have contributed to event-related emissions if
the controls are: (1) Implemented in accordance with an attainment or
maintenance state implementation plan (SIP), a federal implementation
plan (FIP) or a tribal implementation plan (TIP), (2) if the EPA
approved the plan within 5 years of the date of an event, and (3) if
the plan addresses the event-related pollutant and all sources
necessary to fulfill the requirements of the CAA for the SIP, FIP or
TIP.\1\ Also for the ``not reasonably controllable or preventable''
criterion, the EPA is codifying in regulatory text that air agencies
generally have no obligation to specifically address controls if the
event was due to emissions originating outside their jurisdictional
(i.e., state or tribal) border. Of course, a submission based on
emissions originating outside of the submitter's jurisdictional borders
must demonstrate that the event also meets the other exceptional events
criteria.
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    \1\ If the air agency is required to revise its implementation
plan as a result of a SIP Call action pursuant to CAA section
110(k)(5), any deference to the implementation plan's enforceable
control measures will be determined on a case-by-case basis.
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    With respect to the ``human activity that is unlikely to recur at a
particular location or was a natural event'' criterion, we present
options in this preamble that air agencies and the EPA can use to
determine whether the recurrence frequency of an event is ``unlikely to
recur at a particular location.'' We expand on this concept with
regulatory language that defines a specific approach to recurrence
frequency applicable to prescribed fire on wildland. We also clarify in
regulatory language that natural events can recur, sometimes
frequently, without affecting the approvability of a demonstration for
the identified natural event and that we consider reasonably controlled
anthropogenic emissions sources to play little or no direct role in
causing those emissions.
    The final rule preamble and rule text clarify that air agencies
must address all of the core statutory elements and implicit concepts
of CAA section 319(b) within an exceptional events demonstration. To
facilitate early communications and coordination regarding the
identification, development and review of these demonstrations, we are
promulgating a regulatory requirement for an initial notification by
the air agency to the EPA of a potential exceptional event for which
the agency is considering preparing a demonstration as a preliminary
step before submitting a demonstration. We further establish in rule
language that the required demonstration elements include a narrative
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); 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 supported, in part, by a
comparison to historical concentrations; a demonstration that the event
was both not reasonably controllable and not reasonably preventable;
and a demonstration that the event was a human activity that is
unlikely to recur at a particular location or was a natural event.
Additionally, the rule revisions require documentation that the air
agency conducted a public comment process.
    Because affected air agencies have provided feedback regarding the
difficulty associated with meeting the regulatory timelines in the 2007
rule associated with data flagging, initial event descriptions and
demonstration submittals, the EPA is promulgating revisions that remove
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 is promulgating a
provision to terminate the EPA's obligation to review a demonstration
following a 12-month period of inactivity by the air agency. In
addition, although we are not promulgating timelines in rule language
for the EPA's response to submitted demonstrations, we are identifying
in this preamble the following intended response timelines: A formal
response to the Initial Notification (see Section IV.G.5 of this
preamble) within 60 days, initial review of an exceptional events
demonstration with regulatory significance within 120 days of receipt
(see Section IV.G.7 of this preamble), a decision regarding event
concurrence/nonconcurrence within 12 months of receipt of a complete
demonstration (see Section IV.G.7 of this preamble), and a

``deferral letter'' within 60 days of receipt of a demonstration that
the EPA determined during the Initial Notification process to not to
have regulatory significance (see Section IV.G.7 of this preamble).
    Among the questions stakeholders have raised since promulgation of
the 2007 Exceptional Events Rule are those regarding fire-related
components that the preamble to the 2007 Exceptional Events Rule
discussed, but did not fully define or clarify. This final action
promulgates in rule language several fire-related definitions and the
conditions under which prescribed fires could qualify as exceptional
events, which include the use of smoke management programs (SMP) and
the application of basic smoke management practices (BSMP). We also
discuss that while exceptional events demonstrations and data
exclusions requests must be submitted by the affected state/tribal
agency(ies), or with their concurrence, we support and encourage
federal land managers (FLMs), other federal agencies and air agencies
to work collaboratively to prepare and submit exceptional events
demonstrations and data exclusion requests.
    In keeping with the EPA's mission to protect public health and
after seeking comment on approaches ranging from retaining the existing
``mitigation'' rule requirements to promulgating new mitigation-related
rule components, we are promulgating in regulatory language the
requirement to develop mitigation plans in areas with ``historically
documented'' or ``known seasonal'' exceptional events. This action
indicates those areas to which this requirement newly applies and makes
clear that the EPA will not concur with certain exceptional events
demonstrations if an air agency has not submitted the related required
mitigation plan within 2 years of the effective date of this action.
    In addition to finalizing revisions to the 2007 Exceptional Events
Rule, this action simultaneously announces the availability of a final
non-binding guidance document titled Guidance on the Preparation of
Exceptional Events Demonstrations for Wildfire Events that May
Influence Ozone Concentrations (Wildfire Guidance), which applies the
Exceptional Events Rule Revisions to wildfire events that may influence
ozone levels. The EPA prepared this guidance document to further
address specific stakeholder questions regarding the Exceptional Events
Rule and further increase the efficiency of rule implementation.
    The Wildfire Guidance provides air agencies with information on how
to prepare and submit evidence to meet the Exceptional Events Rule
requirements for monitored ozone exceedances caused by wildfires. The
document includes example analyses, conclusion statements, and
technical tools that air agencies can use to provide evidence to
satisfy the Exceptional Events Rule criteria. The Wildfire Guidance
also identifies wildfire and monitor-based characteristics that might
allow for a simpler and less resource-consuming demonstration. The
Wildfire Guidance is not 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. As noted by commenters, while many of the technical
analyses included in the document may also be applied to prescribed
fire events, the guidance document does not specify how demonstrations
for prescribed fire events can address all promulgated rule
requirements. The public comment period for the Draft Guidance on the
Preparation of Exceptional Events Demonstrations for Wildfire Events
that May Influence Ozone Concentrations ran simultaneously with the
comment period on the proposed rule revisions and closed on February 3,
2016. The EPA received 31 comments on the draft guidance during the
public comment period. The EPA summarizes and discusses these comments
in a document that accompanies the final guidance document. Both the
public comments received on the draft guidance and the EPA's discussion
document are available in the docket at http://www.regulations.gov
(Docket ID No. EPA-HQ-OAR-2015-0229).
    Based on feedback from interested parties on the proposed rule
revisions and the draft Wildfire Guidance, we intend to develop
supplementary guidance to assist air agencies in addressing the
Exceptional Events Rule criteria for prescribed fire on wildland. This
guidance will focus on analyses and supporting documentation
recommended to show that prescribed fire events on wildland were
unlikely to recur at a particular location and were not reasonably
controllable or preventable. We intend to post the draft guidance for
prescribed fires and instructions for providing public comment on the
exceptional events Web site at http://www2.epa.gov/air-quality-analysis/treatment-data-influenced-exceptional-events shortly after
finalizing these rule revisions.
    Also based on feedback from interested parties, we intend to
develop supplementary guidance to describe satisfying the Exceptional
Events Rule criteria for stratospheric ozone intrusions. In addition,
as we discussed in the proposal and as discussed in more detail in
Section IV.C of this preamble, we also intend to develop 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, to describe the appropriate additional
pathways for data exclusion for some ``predicted future'' monitoring
data applications. Once available, the EPA intends to post both draft
guidance documents on the exceptional events Web site at http://www2.epa.gov/air-quality-analysis/treatment-data-influenced-exceptional-events.

B. Entities Affected by This Rule

    Entities potentially affected directly by this final rule and
associated guidance include all state air agencies and local air
quality agencies to which 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 final rule
and related guidance include 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.

C. Obtaining a Copy of This Document and Other Related Information

    In addition to being available in the docket, we will post an
electronic copy of this Federal Register document and the final
guidance at http://www2.epa.gov/air-quality-analysis/treatment-data-influenced-exceptional-events.

D. Judicial Review

    Under CAA section 307(b)(1), judicial review of this final action
is available only by filing a petition for review in the United States
Court of Appeals for the District of Columbia Circuit by December 2,
2016. Under CAA section 307(b)(2), the requirements established by this
final rule may not be challenged separately in any civil or criminal
proceedings brought by the EPA to enforce the requirements.

E. Organization of this Federal Register Document

    The information presented in this document is organized as follows:

I. General Information
    A. Executive Summary
    B. Entities Affected by This Rule
    C. Obtaining a Copy of This Document and Other Related
Information
    D. Judicial Review
    E. Organization of this Federal Register Document
II. Glossary of Terms and Acronyms
III. Overview of Exceptional Events Statutory Authority, Regulation
and Implementation
IV. Final Rule Revisions
    A. Applicability of the Exceptional Events Rule: Affected
Entities and Pollutants
    1. Summary of Proposal
    2. Final Rule
    3. Comments and Responses
    B. Definition and Scope of an Exceptional Event
    1. Summary of Proposal
    2. Final Rule
    3. Comments and Responses
    C. Ambient Concentration Data and Data Uses Affected by the
Exceptional Events Rule
    1. Summary of Proposal
    2. Final Rule
    3. Comments and Responses
    D. Definition and Scope of a Natural Event
    1. Summary of Proposal
    2. Final Rule
    3. Comments and Responses
    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. Transported Pollution
    2. Wildland Fires
    3. Stratospheric Ozone Intrusions
    4. High Wind Dust Events
    G. Other Aspects of Identifying Exceptional Events-Influenced
Data and Demonstration Submittal and Review
    1. Aggregation of Events
    2. 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
V. Mitigation
    A. Summary of Proposal
    1. Defining Historically Documented or Known Seasonal Events
    2. Mitigation Plan Components
    3. Options for Implementing Mitigation Plans
    B. Final Rule
    1. Defining Historically Documented or Known Seasonal Events
    2. Mitigation Plan Components
    3. Implementing Mitigation Plans
    C. Comments and Responses
VI. Environmental Justice Considerations
VII. 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 (PRA)
    C. Regulatory Flexibility Act (RFA)
    D. Unfunded Mandates Reform Act (UMRA)
    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 and 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
    K. Congressional Review Act (CRA)
VIII. 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
BACM Best Available Control Measures
BACT Best Available Control Technology
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
CBSA Core based statistical area
CFR Code of Federal Regulations
CO Carbon monoxide
EPA Environmental Protection Agency
FIP Federal implementation plan
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
LAER Lowest Achievable Emission Rate
[mu]g/m\3\ Micrograms per cubic meter
CH4 Methane
Mph Miles per hour
NAAQS National ambient air quality standard or standards
NEAP Natural Events Action Plan
NEI National Emissions Inventory
NH3 Ammonia
NO2 Nitrogen dioxide
NOAA National Oceanic and Atmospheric Administration
NOV Notice of violation
NOX Nitric oxides
NPRM Notice of proposed rulemaking
NPS National Park Service
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
PRA Paperwork Reduction Act
PSD Prevention of significant deterioration
RACM Reasonably available control measures
RACT Reasonably Available Control Technology
RFA Regulatory Flexibility Act
SIP State implementation plan
SMP Smoke management program(s)
SO2 Sulfur dioxide
TAR Tribal Authority Rule
TIP Tribal implementation plan
Tpy Tons per year
UMRA Unfunded Mandates Reform Act
USB U.S. background
USDA U.S. Department of Agriculture
VOC Volatile organic compound or compounds

III. Overview of Exceptional Events Statutory Authority, Regulation and
Implementation

    The EPA's mission includes preserving and improving, when needed,
the quality of our nation's ambient air to protect human health and the
environment as provided by the CAA. To accomplish this, the EPA
develops the NAAQS for criteria pollutants and oversees the states'
programs to improve air quality in areas where the current air quality
is not in attainment with the NAAQS 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
using data collected in the national ambient air quality monitoring
network established under the authority of section 319(a) of the CAA.
    Congress recognized 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 EPA's AQS in certain
regulatory determinations. Thus, in 2005, Congress provided the
statutory authority for the exclusion of data influenced by
``exceptional events'' meeting specific criteria by adding section
319(b) to the CAA. To implement this 2005 CAA amendment, the EPA
promulgated the 2007 Exceptional Events Rule (72 FR 13560, March 22,
2007).
    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, which superseded the
EPA's previous guidance on handling data influenced by events,\2\
contain definitions, procedural requirements, requirements for air
agency demonstrations, criteria for the EPA's approval of the exclusion
of event-affected air quality data from the data set used for
regulatory decisions and requirements for air agencies \3\ to take
appropriate and reasonable actions to protect public health from
exceedances or violations of the NAAQS.\4\
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    \2\ 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 from
the National Service Center for Environmental Publications through
its document search, retrieval and download capabilities at https://www.epa.gov/nscep.
    (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 the 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.
    \3\ References to ``air agencies'' 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 may also apply to federal
land managers of Class I areas and other federal agencies managing
federal land.
    \4\ 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\.
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    Shortly after promulgation, the Natural Resources Defense Council
(NRDC) brought a petition for judicial review challenging certain
aspects of the 2007 rule, including the EPA's definition of a natural
event and several statements in the preamble concerning the types of
events that could qualify as being eligible for exclusion under the
rule provisions.\5\ 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. Because the EPA did
not address the subject high wind preamble language in final rule text,
the D.C. Circuit Court determined the high wind events section of the
2007 preamble to be a legal nullity.
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    \5\ NRDC v. EPA, 559 F.3d 561 (D.C. Cir. 2009).
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    Air agencies affected by the 2007 rule also raised questions
regarding interpretation and implementation. The EPA acknowledges that
applying the provisions of 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. In response to these challenges, in May
2013, after extensive outreach culminating in the EPA issuing a Federal
Register Notice of Availability \6\ seeking broad public review, 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.\7\ The EPA simultaneously acknowledged
the need to consider additional changes through a notice-and-comment
rulemaking effort to revise the 2007 Exceptional Events Rule. Informed
by feedback received during the development of the Interim Exceptional
Events Implementation Guidance \8\ and feedback received during
listening sessions and best practice conference calls,\9\ the EPA
issued a notice of proposed rulemaking (NPRM) on November 20, 2015 (80
FR 72840) titled ``Treatment of Data Influenced by Exceptional Events''
(proposed Exceptional Events Rule Revisions) to address certain
substantive issues raised by state, local and tribal co-regulators and
other stakeholders and to increase the administrative efficiency of the
Exceptional Events Rule criteria and process.
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    \6\ 77 FR 39959 (July 6, 2012).
    \7\ 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).
    \8\ See comments in Docket ID No. EPA-HQ-OAR-2011-0887.
    \9\ 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 also held
conference calls with some air agencies between September 2014 and
March 2015 to further discuss exceptional events implementation
processes and practices. A summary of these implementation ``best
practices'' is available at http://www2.epa.gov/air-quality-analysis/treatment-data-influenced-exceptional-events.
---------------------------------------------------------------------------

    Although the EPA has undertaken this notice-and-comment rulemaking
effort to provide clarity and increase the administrative efficiency of
the Exceptional Events Rule demonstration submittal process, the EPA
recognizes that developing some exceptional events demonstrations may
still be challenging given the case-by-case nature of each event. For
this reason, throughout the preamble to this final action, we provide
recommendations for language and analyses to include in demonstration
packages (see, for example, language in Sections IV.E of this preamble,
Technical Criteria for the Exclusion of Data Affected by Events, and
IV.F, Treatment of Certain Events Under the Exceptional Events Rule).
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 also intends 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. The EPA encourages air agencies
to consult with their EPA Regional office for further guidance on
specific demonstrations.

IV. Final Rule Revisions

    This final action supersedes the 2007 Exceptional Events Rule and
all natural events and exceptional events data handling guidance
developed prior to the 2007 Exceptional Events Rule. This final action
also supersedes the 2013 Interim Exceptional Events Implementation
Guidance until such time as the EPA can revise these documents to
reflect the revisions contained in these Exceptional Events

Rule Revisions. This final action accomplishes the objectives
identified in the proposed Exceptional Events Rule Revisions by
promulgating rule language accompanied by explanation/interpretation in
the preamble and/or presenting non-binding guidance in the preamble.
    The public comment period for the proposed revisions to the
Exceptional Events Rule closed on February 3, 2016. The EPA received 94
unique, timely comments on the proposed rule revisions. The preamble to
this final rule discusses the most significant comments received on the
proposal and how the EPA considered them in developing the agency's
final revisions to the Exceptional Events Rule. The Response to
Comments document that accompanies this final rule provides more
detailed responses to comments. The public comments received on the
proposal and the EPA's Response to Comments document are available in
the docket at http://www.regulations.gov (Docket ID No. EPA-HQ-OAR-
2013-0572).
    As a result of feedback received during the public comment period,
we have changed the proposed regulatory text and/or non-binding
guidance in the preamble in the following ways:
     Modified the provision for FLMs and other federal agencies
to prepare and submit exceptional events demonstrations to include a
step for the concurrence of the affected state/tribal air agency(ies);
     Modified the definition of an exceptional event to more
clearly address drought conditions;
     Modified the list of regulatory actions included within
the scope of the Exceptional Events Rule;
     Revised the provision for reliance on controls in an EPA-
approved SIP to satisfy the not reasonably controllable or preventable
criterion by also including reliance on controls in FIPs and TIPs;
     Modified the required demonstration elements to support
the clear causal relationship criterion by moving the table of analyses
from the rule text to the preamble where it will serve as guidance;
     Added regulatory text requiring air agencies, federal land
managers and burn managers \10\ to collaborate and document a process
for working together to protect public health and manage air quality
during the conduct of prescribed fires on wildland. Such discussions
must include outreach and education regarding general expectations for
the selection and application of appropriate BSMP and goals for
advancing strategies and increasing adoption and communication of the
benefits of appropriate basic smoke management practices;
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    \10\ Throughout this preamble and the associated final rule
text, we use the terminology ``burn manager'' to mean the party
responsible for supervising a prescribed fire from ignition through
fire extinguishing and cleanup, or another party in the same
organization who represents, supervises or is supervised by said
party and can be a communications pathway to and from such person.
Different organizations, states, local agencies and tribes may use
the terms burn manager, burn boss, fire manager or another similar
term to describe the party with this responsibility. Regardless of
the terminology, the actions of the party responsible for prescribed
fire management must conform to and be consistent with any
applicable local, state or federal laws and regulations, where these
laws and regulations exist.
---------------------------------------------------------------------------

     Identified intended timelines for the EPA's response in
this preamble; and
     Added required regulatory elements for mitigation plans
for areas with known, recurring events.
    We discuss all of these changes in more detail in this preamble.

A. Applicability of the Exceptional Events Rule: Affected Entities and
Pollutants

1. Summary of Proposal
    As noted in the proposal, the Exceptional Events Rule applies to
all states, to local air quality agencies to whom a state has delegated
relevant responsibilities for air quality management including air
quality monitoring and data analysis, and to tribal air quality
agencies operating ambient air quality monitors that produce regulatory
data. The proposal also included new provisions to allow FLMs and other
federal agencies to prepare and submit exceptional events
demonstrations and data exclusion requests directly to the EPA. We
included these provisions for the following reasons, which we expressed
in the proposal. First, the CAA language at section 319(b)(3)(B)(i)
provides authority for FLMs to initiate and submit such demonstrations
and data exclusion requests in the language that reads, ``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.'' Second, FLMs and other federal agencies
may operate regulatory monitors \11\ and submit collected data to the
EPA's AQS database,\12\ and emissions from exceptional events could
affect these same monitors. Third, allowing FLMs to prepare and submit
demonstrations directly to the EPA could expedite the exceptional
events demonstration development and submittal process. The EPA
solicited comment on our proposal to allow FLMs and other federal
agencies to prepare and submit exceptional events demonstrations and
data exclusion requests directly to the EPA. In addition, the proposal
explained that the final rule might modify the provision that provided
for FLMs and other federal agencies preparing and submitting
exceptional events demonstrations and data exclusion requests directly
to the EPA (see 80 FR 72848).
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    \11\ 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.
    \12\ 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 https://www3.epa.gov/castnet/docs/CASTNET_Plan_2014_Final.pdf, which applies
to National Park Service (NPS) and Bureau of Land Management (BLM)
site managers operating CASTNET monitors.
---------------------------------------------------------------------------

    The proposal also reiterated the EPA's interpretation that the
Exceptional Events Rule applies to all criteria pollutant NAAQS \13\
based on 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 did not specifically request comment on this
statement.
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    \13\ 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. Final Rule
    The Exceptional Events Rule continues to apply to all state air
agencies and to local air quality agencies to which a state has
delegated relevant responsibilities for air quality management,
including air quality monitoring and data analysis. The Exceptional
Events Rule also continues to apply to tribal air quality agencies
operating ambient air quality monitors that produce regulatory data.
All affected air agencies, including tribal air quality agencies,
should use the Initial Notification of Potential Exceptional Event
process described in more detail in Section IV.G.5 of this preamble, to
discuss with their EPA Regional office the most appropriate approach to
implementing the provisions of the Exceptional Events Rule.

    After considering the public comments, as explained in subsequent
paragraphs and the response to comments below, we are finalizing a
modified version of our proposal, under which FLMs and other federal
agencies could prepare and submit exceptional events demonstrations and
data exclusion requests directly to the EPA if the affected state/
tribal air agency(ies) concurs.\14\ Presumably, demonstrations and
requests for exclusion prepared and submitted by FLMs or other federal
agencies would address prescribed fires or wildfires occurring on
federally-owned and managed land that influence concentrations at
regulatory monitors either on federally-owned and managed land or at
state, local, or tribal regulatory monitors. Although the EPA is
deferring the appropriate mechanism for concurrence to the affected
state or tribal air agency(ies) in accordance with 40 CFR
50.14(a)(1)(ii)(A)(2), the EPA can envision several acceptable
approaches, some of which follow.
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    \14\ We note that any agency, group or individual could submit
an exceptional events demonstration. However, the EPA is obligated
to consider only those submittals that meet the requirements of this
final rule and come from authorized agencies (i.e., all states;
local air quality agencies to whom a state has delegated relevant
responsibilities for air quality management including air quality
monitoring and data analysis; tribal air quality agencies operating
ambient air quality monitors that produce regulatory data; and FLMs
or other federal agencies to whom the relevant state has granted
approval). Further, the EPA cannot take action on material submitted
by an unauthorized party.
---------------------------------------------------------------------------

     An air agency could provide written authorization to the
FLMs or other federal agencies owning land or operating air quality
monitoring stations to prepare and directly submit exceptional events
demonstrations to the EPA. Any such authorization must conform to and
be consistent with any applicable state laws and regulations. The
written authorization (i.e., letter from the air agency official
responsible for preparing demonstrations) would specify the conditions
under which the FLM could submit a demonstration directly to the EPA
and whether the FLM could initiate the Initial Notification of
Potential Exceptional Event (either with or without including the
affected air agency(ies) in this process). The affected air agency
would submit a copy of the authorization to the reviewing EPA Regional
office either in advance of the demonstration submittal and/or with the
Initial Notification of Potential Exceptional Event process associated
with a specific event or events. An air agency selecting this option
would need to provide the submitting FLM or other federal agency with a
case-by-case concurrence in accordance with 40 CFR
50.14(a)(1)(ii)(A)(2), which requires that a demonstration-specific
concurrence from the air agency accompany each submittal. The FLM would
include the concurrence with its submission to the EPA.
     An air agency could agree, on a case-by-case basis, to
allow an FLM or other federal agency to develop and submit a complete
demonstration for an event or events directly to the EPA. Under this
scenario, the air agency could notify the EPA during the Initial
Notification of Potential Exceptional Event process that an FLM will
submit demonstration(s) for a particular event(s) or particular types
of events, specifying the event type(s), pollutant(s) and date(s). An
air agency selecting this option would need to provide the submitting
FLM or other federal agency with a case-by-case concurrence, in
accordance with 40 CFR 50.14(a)(1)(ii)(A)(2), which the FLM would
include with its submission to the EPA.
     The air agency could ask the FLM to prepare the agreed-
upon demonstration for submittal to the affected air agency. The FLM
would then independently prepare the demonstration and submit it to the
affected air agency. The air agency, in turn, could submit the
demonstration to the EPA with a cover letter indicating that the FLM or
federal agency prepared the demonstration, that the affected state/
tribal air agency agrees with the content and the affected state/tribal
air agency requests that the EPA review and take action on the
submitted demonstration.
     Another option might consist of the air agency and the
affected FLM collaboratively developing demonstrations for submittal by
the affected air agency. In this scenario, the air agency and the FLM
would likely agree to a division of responsibilities for specific
analyses or sections of a demonstration.
    If an air agency agrees that FLMs or other federal agencies may
prepare and submit exceptional events demonstrations and data exclusion
requests directly to the EPA, then the FLM-prepared demonstrations must
meet all of the provisions in the Exceptional Events Rule, including
the requirement for a public comment period on a prepared demonstration
\15\ and the requirements related to schedules and procedures for
demonstration submittal that apply to state agencies that operate the
affected monitors. Regardless of the approach selected, the EPA
encourages discussions between the FLM and the affected state/tribal
air agency(ies) similar to those described in the Initial Notification
of Potential Exceptional Event process (see Section IV.G.5 of this
preamble) to ensure that the FLM and the air agency(ies) share a common
understanding regarding the potential event, share relevant information
and data, and understand the timeline for flagging data in AQS and
submitting the demonstration. A number of areas have established local
or regional collaboratives whose goals include improving the health of
local ecosystems (e.g., wildlands), increasing community resiliency to
wildfire, communicating air quality and public health impacts and
communicating the results and benefits of prescribed fire management
and implementation programs.\16\
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    \15\ 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 or non-concurring with an air agency's request to exclude
data. The EPA generally provides a public comment opportunity before
using 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.
    \16\ See, for example, the Fire Memorandum of Understanding
(MOU) Partnership, consisting of multiple state and federal forestry
agencies, prescribed fire councils and conservation agencies, who
work collaboratively with air agencies in California to resolve
issues related to managed fire and protection of public health.
Additional information available at http://www.sierraforestlegacy.org/CF_ManagingFire/FireMOU.php and in
comment number EPA-HQ-OAR-2013-0572-0138.
---------------------------------------------------------------------------

    Also related to the entities affected by the Exceptional Events
Rule, the proposal asserted that, as the single actor responsible for
administering air quality planning and management activities within its
jurisdictional boundaries, the state, exclusive of tribal lands, is
ultimately responsible for submitting exceptional events demonstrations
for exceedances that occur at all regulatory monitoring sites within
the boundary of the state. While the state can request that FLMs or
other federal agencies or local agencies to which a state has
authorized relevant responsibilities develop and submit exceptional
events demonstrations for events that influence concentrations at
regulatory monitors operated by these entities, the state can always
submit demonstrations for events that meet the requirements of the
Exceptional Events Rule for any regulatory monitor within its
jurisdictional bounds, including those operated by FLMs, other federal
agencies and delegated local agencies. The state retains the authority
to decide

whether to concur with and forward an exceptional events submittal
generated by another agency. For example, if a state does not concur
with the local agency's, FLM's, other federal agency's or other
entity's exceptional events claim, the state can decide not to forward
the submittal to the EPA even if the state has authorized the federal
or local government agencies (who are also authorized by the CAA to
produce and provide data) to prepare and submit demonstrations directly
to the EPA. At the suggestion of several commenters, the EPA is adding
regulatory language to 40 CFR 50.14(a)(1)(ii) to clarify this point.
Where questions arise, the reviewing EPA Regional office can provide
assistance and direction as part of the Initial Notification of
Potential Exceptional Event process. In addition to requesting that
FLMs, other federal agencies or delegated local agencies prepare or
assist in the preparation of demonstration analyses, a state can also
request the same of industrial facilities operating regulatory monitors
experiencing event-influenced exceedances. The EPA cannot act on
demonstrations submitted directly by industrial facilities. The
authorizing state is responsible, at its discretion, for submitting
demonstrations prepared by industrial entities.
    Consistent with our proposal, we are also promulgating regulatory
language at 40 CFR 50.14(a)(1)(i) that the Exceptional Events Rule
applies to the treatment of data showing exceedances or violations of
any criteria pollutant NAAQS. AQS retains the capability for air
agencies to flag all criteria pollutant data and for the EPA to concur,
as appropriate, on requests for exclusion.
3. Comments and Responses
    Although three commenters agreed with the EPA's proposal to allow
FLMs and other federal agencies to initiate a request for data
exclusion if the FLM either operates a regulatory monitor that has been
affected by an exceptional event or manages land on which an
exceptional event occurred that influenced a monitored concentration at
a regulatory monitor, the large majority of commenters disagreed with
this proposed provision. State and local air agencies, as well as
several regional planning organizations, commented that it is
inappropriate for the EPA to allow agencies that are not directly
responsible and accountable for managing and/or assuring air quality to
submit exceptional event demonstrations or data exclusion requests.
Several commenters noted that FLMs and other federal agencies may have
different functions and priorities and that the protection of air
quality and public health may not be a primary objective. Some of these
same commenters noted that while the proposed rule language at 40 CFR
50.14(a)(l)(ii)(A)(2) allowed another agency to initiate a request
``only after discussing such submittal with the State in which the
affected monitor is located,'' ``discussing'' does not require
``agreement'' from the state or a requirement that the FLM incorporate
the state's feedback into its submittal. These commenters stated that,
under the proposed requirements, an FLM could submit a request to
exclude data over the objections of the state with primary
responsibility to regulate air quality, which could potentially create
legal conflicts between agencies. Another commenter suggested allowing
FLMs to submit demonstrations only for regulatory monitors owned by the
FLM or located on FLM-managed land rather than for state-owned and
operated monitors influenced by an event (e.g., fire) on FLM-managed
land. Two states and one industry association commenter suggested
following an approach allowing, on a case-by-case basis, FLMs to submit
demonstrations and requests for data exclusion if the affected state/
tribal air agency(ies) agrees and if the FLM works with the affected
state/tribal air agency(ies) through the demonstration development and
submittal process.
    The EPA continues to believe that allowing FLMs to prepare and
submit demonstrations directly to the EPA could expedite the
exceptional events demonstration development and submittal process
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 and because federal entities may
either initiate prescribed fires or fight wildfires on lands managed
and/or owned by federal entities. We also recognize that under the CAA,
states, exclusive of tribal lands, 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. As commenters have noted,
and as the EPA recognizes, FLM submittal of exceptional events
demonstrations and air agency objectives for air quality management may
conflict. Federal land managers do play an important role in helping
states and tribes improve the air quality in those areas that do not
meet the NAAQS. The General Conformity Rule requires that federal
agencies work with state, tribal and local governments in nonattainment
and maintenance areas to ensure that federal actions conform to any
applicable SIP, FIP or TIP. However, because states and tribes are
ultimately responsible for administering air quality management
programs within their borders, which could include addressing air
quality and health impacts from wildfire emissions, the EPA is
finalizing a modified version of our proposal, under which FLMs and
other federal agencies could prepare and submit exceptional events
demonstrations and data exclusion requests directly to the EPA with the
agreement of the affected state/tribal air agency(ies). We believe that
this approach, which requires the agreement of the affected state/
tribal air agency(ies), could encompass all of the alternative
approaches noted by commenters representing state, local and regional
planning organizations. Deferring the approach to achieve agreement to
the affected air agencies provides individual air agencies with the
flexibility to account for any state/tribal-specific authorities that
may limit an agency's ability to regulate certain types of air quality
concerns. Fire plays a critical role in restoring resilient ecological
conditions in our wildlands. In addition, the increased use of
prescribed fire and managed wildfire can reduce the effects of
catastrophic wildfire. The EPA strongly encourages collaboration
between the FLMs and other federal agencies and the appropriate state/
tribal air agency(ies) during the event identification and
demonstration development process regardless of who ultimately submits
the demonstration.
    Also concerning the entities affected by the Exceptional Events
Rule, one commenter asked for clarification regarding whether
industrial facilities operating regulatory monitors can submit
demonstrations directly to the EPA. Other commenters asked that the EPA
clarify whether states and tribes can always submit demonstrations for
any monitors within their jurisdictional bounds. These commenters also
asked whether the EPA would allow and/or evaluate ``competing''
demonstrations.
    The EPA notes in the final rule section of this preamble that while
industrial facilities may operate regulatory monitors that experience
event-influenced exceedances and, at the request of the state, such
facilities may prepare demonstrations for these exceedances, the EPA
cannot act on

demonstrations submitted directly by industrial facilities. The CAA
language at section 319(b)(3)(B)(i) reads, ``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.'' Additionally, the CAA language at
319(b)(3)(B)(iv) requires that the EPA's implementing regulations
provide that ``there are criteria and procedures for the Governor of a
State to petition the Administration to exclude air quality monitoring
data. . . .'' Under the CAA, states, exclusive of tribal lands, are
primarily responsible for the administration of air quality management
programs within their borders. States can delegate relevant
responsibilities for air quality management to local agencies, but the
CAA does not provide for delegation of these responsibilities to
industrial facilities. Where industrial facilities operate regulatory
monitors, the state is ultimately responsible for ensuring that
collected data are uploaded into AQS and for verifying the accuracy of
these data. Thus, the authorizing state, at its discretion, is
responsible for submitting any demonstrations prepared by industrial
entities. The EPA has also clarified in the preamble that a state (or
tribe) can always submit demonstrations for events that meet the
requirements of the Exceptional Events Rule for any regulatory monitor
within its jurisdictional bounds, including those operated by FLMs,
other federal agencies, delegated local agencies, and industrial
facilities. We have added regulatory language to 40 CFR 50.14(a)(1)(ii)
to clarify this point.
    Another commenter noted that CAA section 319(b)(3)(B)(i) provides
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.'' The commenter maintains
that this provision allows federal, state or local government agencies
to produce and provide data, but not to prepare and submit
demonstrations.
    The EPA agrees that the identified CAA language grants specific
authority to state, federal and local government agencies to produce
and provide data. The EPA also notes, however, that nothing in the CAA
language at 319 explicitly restricts federal and local government
agencies from submitting demonstrations if the state agrees. Section
319(b)(3)(B)(iv) of the CAA directs the EPA to develop criteria and
procedures for the ``Governor of a State to petition the Administrator
to exclude air quality monitoring data. . . .'' The EPA's implementing
regulatory language at 40 CFR 50.14(b)(1) says 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 historically been interpreted to mean that only
states can initiate the exceptional events process and submit
demonstrations. A state may delegate the authority for preparing and
submitting demonstrations to local government agencies that are
authorized by the CAA to produce and provide data. In this action, the
EPA is promulgating regulatory language that authorizes federal
agencies to prepare and submit demonstrations if the affected state
concurs, on a case-by-case basis, on the preparation and submission of
demonstrations by those federal agencies. Submissions by delegated
local agencies and/or state-concurred demonstrations by federal
agencies have the effect of a state ``demonstration.'' Additionally,
the state maintains the ultimate responsibility for submitting
exceptional events demonstrations for events influencing concentrations
at any regulatory monitor within its jurisdictional bounds.
    Two tribal commenters asked the EPA to clarify how the provisions
in the Exceptional Events Rule apply to tribes. One of these commenters
asked that this clarification include regulatory text to define
``state'' and ``tribe.'' The EPA is not adding regulatory text to
define ``state'' and ``tribe,'' but instead intends to apply the
definitions set forth in the Tribal Authority Rule (TAR) at 40 CFR
49.2. At 40 CFR 49.2(c), an Indian tribe or tribe is defined as ``any
Indian tribe, band, nation, or other organized group or community,
including any Alaska Native village, which is federally recognized as
eligible for the special programs and services provided by the United
States to Indians because of their status as Indians.'' Section 40 CFR
49.2(e) defines a state as ``a State, the District of Columbia, the
Commonwealth of Puerto Rico, the Virgin Islands, Guam, and American
Samoa and includes the Commonwealth of the Northern Mariana Islands.''
    We further clarify the applicability to tribes by reiterating the
language that appears in Section IV.A.1 of this preamble, which states
that the Exceptional Events Rule applies to all states; to local air
quality agencies to whom a state has delegated relevant
responsibilities for air quality management including air quality
monitoring and data analysis; and to tribal air quality agencies
operating ambient air quality monitors that produce regulatory data.
Throughout the preamble and regulatory language associated with this
final action, we use the terminology ``state,'' ``tribe'' and ``air
agency'' somewhat interchangeably. Footnote 3 in this document
clarifies that 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.'' To be an
affected entity for purposes of this rule, the air agency must first
operate one or more ambient air quality monitors that produce
regulatory data. The provisions of this rule apply uniformly to state
and tribal air agencies (and to authorized federal and local agencies)
that meet this condition. Tribal air quality agencies that operate air
quality monitoring networks that produce regulatory data that are
affected by emissions from exceptional events 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. As we have in the past, the EPA will continue to work with
tribes in implementing the provisions of the Exceptional Events Rule,
including these rule revisions.
    We neither solicited nor received comment regarding applying the
provisions of the Exceptional Events Rule to the treatment of data
showing exceedances or violations of any criteria pollutant NAAQS and
we are making no changes to the rule with respect to this issue.

B. Definition and Scope of an Exceptional Event

1. Summary of Proposal
    The EPA proposed and solicited comment on 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 requirement to provide evidence that the
event is associated with a measured concentration in excess of ``normal
historical fluctuations including background'' and replacing it with a
requirement for a comparison of the event-related concentration to
historical concentrations.

The proposal provided a detailed rationale for each of these proposed
changes, which we summarize here.

    With respect to revising the definition of an exceptional event by
including the combined effects of an event and the resulting emissions,
the proposal noted that a physical event may or may not generate
emissions and these emissions may or may not reach a regulatory monitor
and result in an exceedance or violation of a NAAQS. Each of these
components (i.e., a physical event that generates emissions, transport
of event-generated pollution to a monitor, and an exceedance or
violation at a regulatory monitor) is necessary for an event to qualify
as an exceptional event. The EPA would not consider the physical event
(e.g., a high wind or the wildfire) to be an exceptional event unless
the resulting event-generated pollution (e.g., particulate matter (PM)
or ozone) reached and caused an exceedance or violation at a monitoring
location or locations.
    The EPA elaborated on this concept by providing several examples,
one of which was drought. The proposal stated that while the CAA
definition of an exceptional event excludes ``a meteorological event
involving high temperatures or lack of precipitation,'' the EPA
recognizes that high temperatures and drought conditions can contribute
to exceedances and violations caused by other exceptional events, such
as high wind dust events. The proposal further noted that 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 (e.g., a high wind
event) that falls within the CAA definition of an exceptional event and
meets all of the requirements, provisions and criteria in the
Exceptional Events Rule, then these data could be considered eligible
for exclusion under the provisions of the Exceptional Events Rule. The
proposal also stated that high temperatures, stagnations and inversions
alone would not be eligible for exclusion under the Exceptional Events
Rule by the very clear provisions of the CAA. The proposal stated the
EPA's belief that Congress intended air agencies to compensate for the
effects of high temperature, stagnation and inversions through the
development of SIPs.
    In our November 2015 action, the EPA proposed 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). The proposal explained that in the
2007 Exceptional Events Rule, the EPA derived the ``but for'' criterion
from the language at CAA 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'' \17\ and 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.'' \18\ Air agencies and the EPA have, in some
cases, historically interpreted the ``but for'' criterion as implying
the need for a strict quantitative analysis of the estimated air
quality impact from the event. To clarify the intended approach, the
EPA proposed removing the ``but for'' regulatory language and focusing
on the ``clear causal relationship'' statutory criterion applied to the
specific case, using a weight of evidence approach.
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    \17\ 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.
    \18\ CAA section 319(b)(3)(B)(iv) (emphasis added).
---------------------------------------------------------------------------

    The proposal also modified the regulatory language in 40 CFR
50.14(c)(3)(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. Also
consistent with Congressional intent and air agencies' and the EPA's
experience in implementing the 2007 Exceptional Events Rule, the EPA
proposed to integrate the phrase ``affected air quality'' into the
clear causal relationship criterion. The proposal explained that
separately requiring an air agency to provide evidence to support a
conclusion that an event ``affects air quality'' is unnecessary in
light of a mandatory clear causal relationship showing. The proposal
expressed 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.
    Finally, the EPA proposed to remove the requirement for air
agencies to provide evidence that the event is associated with a
measured concentration in excess of ``normal historical fluctuations
including background'' and replace it with a requirement to compare the
event-influenced concentration to historical concentrations. The
proposal clarified that an air agency does not need to prove a specific
``in excess of'' fact in developing these comparisons to historical
concentrations. The EPA proposed these comparisons to support the clear
causal relationship criterion.
    The proposal stressed that 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,
and
     The event was a human activity that is unlikely to recur
at a particular location or was a natural event.

We proposed to include these core statutory elements in the revised
regulatory definition of an exceptional event.
2. Final Rule
    As proposed, and as supported by numerous commenters, we are
finalizing and incorporating into the regulatory definition of an
exceptional event 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,
and
     The event was a human activity that is unlikely to recur
at a particular location or was a natural event.
    This section of the final rule preamble focuses on the definition
of an

exceptional event particularly as it incorporates these three elements.
We discuss additional detail surrounding the individual criteria (i.e.,
clear causal relationship, not reasonably controllable or preventable
and human activity/natural event) in Section IV.E of this preamble,
Technical Criteria for the Exclusion of Data Affected by Events.
    While we are incorporating the previously identified elements into
the definition of an exceptional event, after considering the public
comments, as discussed more fully in the following paragraphs, we are
finalizing the following slightly modified version of our proposed
definition of an exceptional event: Exceptional event means an event(s)
and its resulting emissions that affect air quality in such a way that
there exists a clear causal relationship between the specific event(s)
and the monitored exceedance(s) or violation(s), is not reasonably
controllable or preventable, is an event(s) caused by human activity
that is unlikely to recur at a particular location or a natural
event(s), and is determined by the Administrator in accordance with 40
CFR 50.14 to be an exceptional event. It does not include air pollution
relating to source noncompliance. Stagnation of air masses and
meteorological inversions do not directly cause pollutant emissions and
are not exceptional events. Meteorological events involving high
temperatures or lack of precipitation (i.e., severe, extreme or
exceptional drought) also do not directly cause pollutant emissions and
are not considered exceptional events. However, events involving high
temperatures or lack of precipitation may promote occurrences of
particular types of exceptional events, such as wildfires or high wind
events, which do directly cause emissions. We presented this concept in
the proposal (see 80 FR 72848), and the EPA is codifying it in the
final rule to prevent confusion, as explained below.
    After considering the public comments received, as discussed as
follows, we have included in the revised regulatory definition the
concept of ``event'' or ``events'' to convey that one or more events
and their resulting emissions could be eligible for consideration in
the aggregate under the provisions in 40 CFR 50.14. We have also
revised the definitional language to ``monitored exceedance(s) or
violation(s)'' to indicate that a single event can cause multiple NAAQS
exceedances or violations either occurring on the same day at multiple
monitors or occurring at one or more monitors on multiple days. The
revised definition also clarifies, at the suggestion of a commenter,
our position with respect to ``meteorological events involving high
temperatures or lack of precipitation'' (i.e., severe, extreme or
exceptional drought). We include the qualifiers ``severe, extreme or
exceptional drought'' to distinguish drought categories from abnormally
dry conditions. In using this language, we incorporate by reference the
conditions described in the U.S. Drought Monitor available at http://droughtmonitor.unl.edu/ and produced through a partnership between the
National Drought Mitigation Center at the University of Nebraska-
Lincoln, the United States Department of Agriculture (USDA) and the
National Oceanic and Atmospheric Administration (NOAA).
3. Comments and Responses
    In considering the three core statutory elements of CAA section
319(b), we note that both the not reasonably controllable or
preventable criterion and the human activity/natural event criterion
are from the statutory language defining the term ``exceptional event''
at CAA section 319(b)(1)(A). The criterion 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
combines the statutory ``affects air quality'' definitional element at
CAA section 319(b)(1)(A) with the ``clear causal relationship''
statutory requirement at CAA section 319(b)(3)(B) and removes the
regulatory-only ``but for'' language. Because this section of the final
rule preamble focuses on the definition of an exceptional event
particularly as it incorporates the statutory elements, we address
comments related to the statutory elements here and discuss the
application of each of these elements in Section IV.E of this preamble.
    Numerous commenters supported, and one commenter representing
several environmental groups opposed, the EPA's incorporating the
``affects air quality'' criterion into the clear causal relationship
element. Commenters supporting this approach agreed with the EPA's
position 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. The commenter opposing this approach noted that the EPA
cannot escape the plain language of the CAA that ``affects air
quality'' and ``clear causal relationship'' are two requirements and
must be addressed individually. The EPA does not disagree that in the
definition of exceptional event, the CAA language at section
319(b)(1)(A)(i) specifically identifies ``affects air quality'' as a
defining term. CAA section 319 does not, however, provide any
indication regarding how an air agency should demonstrate that an event
``affects air quality.'' Rather, the requirements set forth at CAA
section 319(b)(3)(B) indicate that the EPA's implementing regulations
shall provide that (i) the occurrence of an exceptional event must be
demonstrated by reliable, accurate data that are promptly produced and
provided by federal, state or local government agencies; (ii) 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; (iii) there is a public process for
determining whether an event is exceptional; and (iv) there are
criteria and procedures for the Governor of a state to petition the
Administrator to exclude air quality monitoring data that are directly
due to exceptional events from use in determinations by the
Administrator with respect to exceedances or violations of the NAAQS.
In subsuming the ``affects air quality'' element into the ``clear
causal relationship'' criterion we are simply defining the approach by
which an air agency must show that the event affected air quality.
    Similarly, the large majority of commenters supported, and three
commenters representing environmental groups opposed, the EPA's
proposal to remove the ``but for'' criterion. The commenters opposing
the removal of the ``but for'' criterion explain that the EPA correctly
acknowledged in the 2007 rule that the ``but for'' criterion was
derived from the following two statutory requirements: (1) CAA 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'' and (2)
CAA section 319(b)(3)(B)(iv), which requires that the EPA develop
``criteria and procedures for the Governor of a State to petition the
Administrator to exclude . . . data that is directly due to the
exceptional events.'' (Emphasis added.) The commenters argue that the
EPA's proposal to rely more directly upon the ``clear causal
relationship'' statutory

element effectively ignores the statutory requirement that excluded
data be ``. . . directly due to the exceptional events.'' The EPA
disagrees with the commenters on this point. While we are finalizing
our proposal to remove the ``but for'' regulatory requirement, we are
retaining the ``direct causal'' statutory language in the regulatory
definition of exceptional event. This revised regulatory language,
along with our provided example analyses in this preamble (see Section
IV.E.3 of this preamble) and in our associated guidance documents, more
clearly conveys the strength and robustness of our intended weight of
evidence approach \19\ and removes some of the challenges associated
with implementing a strict ``but for'' demonstration.\20\ Further, the
``directly due'' concept is represented through the totality of the
requirements in the revisions to the Exceptional Events Rule that we
are promulgating, including that a demonstration show a ``clear causal
relationship'' between ``an event(s) and its resulting emissions'' and
``the monitored exceedance(s) or violation(s).''
---------------------------------------------------------------------------

    \19\ As we indicated in our November 2015 proposal and in the
preamble to the 2007 Exceptional Events Rule, an air agency's ``but
for'' analysis does not necessarily need to be precise. Rather, we
indicated that the EPA would use a holistic ``weight of evidence''
approach in analyzing submitted demonstration packages. The 2007
preamble further explained 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.'' (See 72 FR 13570, March 22, 2007).
    \20\ Since promulgation of the 2007 rule, the ``but for''
criterion has often been interpreted as implying the need for a
strict quantitative analysis to show a single value, or at least an
explicitly bounded plausible range, of the estimated air quality
impact from the event. As a result, some air agencies began using
burdensome approaches to provide quantitative analyses in their
exceptional events demonstrations to show that the event in question
was 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. In many cases, the ``but for'' role of a single
source or event is difficult to determine with certainty and it is
more often the case that the impact of emissions from events and
other sources cannot be separately quantified and distinguished.
---------------------------------------------------------------------------

    Part of promulgating rule text that is consistent with the core
statutory element 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'' involves removing the
regulatory requirement in 40 CFR 50.14(c)(3)(iv)(C) that a state must
submit evidence that the event is associated with a measured
concentration in excess of normal historical fluctuations, including
background. We are finalizing our proposal to remove this language and
replace it with regulatory text requiring a comparison of the event-
influenced concentration to historical concentrations. We discuss
comments associated with this revision in Section IV.E.3.c of this
preamble.
    Multiple commenters supported the EPA's proposal to revise the
definition of an exceptional event to include the event and resulting
emissions. We have also incorporated the suggestion of one commenter to
indicate in regulatory text, through the plural word ``events,'' that
an aggregation of events and their resulting emissions could be
eligible for consideration under the provisions in 40 CFR 50.14. We
discuss the aggregation of events in more detail in Section IV.G.1 of
this preamble. We believe that this concept also applies to exceedances
and violations, so we extended the use of plural terminology to this
part of the exceptional events definition to more clearly acknowledge
that an event may cause multiple exceedances (e.g., exceedances at
multiple monitors or multiple exceedances at a single monitor) or
violations.
    Regarding exceedances and violations, one commenter asked the EPA
to clarify whether values that are not themselves exceedances or
violations, but raise the design value such that the design value
exceeds the NAAQS can be considered as exceptional events. The EPA
recognizes that events can make an air concentration significantly
higher than it would have been in the absence of the event contribution
and elevate the 3-year design value for a NAAQS pollutant. However, the
concentration values used in calculating a violating 3-year design
value could be considered for exclusion under the Exceptional Events
Rule only if the concentration itself is an exceedance or results in a
violating design value. If the elevated concentration is not itself an
exceedance nor does it result in a violating design value, then the
value in question could not be considered as an exceptional event. As
we explained in the proposal and restate here, while not an exceptional
event, retaining such data in the calculation of a design value can
elevate the design value and, for a nonattainment area seeking the
EPA's approval of an attainment demonstration, make it seem that the
area needs more emissions reduction to attain the NAAQS than is
actually the case. Because these data are not exceptional events, we do
not address exclusion under this rule. We do, however, discuss this
scenario in more detail in Section IV.C of this preamble.
    Another commenter suggested that, for regulatory clarity, we
incorporate our interpretation of ``meteorological events involving
high temperatures or lack of precipitation'' (i.e., drought) into
regulatory text. We agree with the commenter and have clarified,
through the regulatory definition of an exceptional event, the position
that we expressed in the proposal preamble, which is that drought alone
does not create emissions and therefore does not meet the definition of
an exceptional event. Rather, drought can result in arid conditions
that can combine with or exacerbate the effects of events that meet the
requirements, provisions and criteria of the Exceptional Events
Rule.\21\ Because there may be many definitions of drought, we also
clarify that we are referring to ``severe, extreme or exceptional
drought'' as defined by the U.S. Drought Monitor. We are not including
other drought categories in this discussion, nor would other drought
categories alone be considered exceptional events.
---------------------------------------------------------------------------

    \21\ Drought can also exacerbate the air quality impact of
activities that do not meet the criteria of the Exceptional Events
Rule, such as dust from vehicular travel on unpaved roads.
---------------------------------------------------------------------------

    Also related to the definition of an exceptional event, one
commenter asked the EPA to include within the definition of an event
both short-term and long-term contributors to elevated pollutant
concentrations. The commenter further asked the EPA to address the
applicability of the Exceptional Events Rule to ``background'' ozone
and background pollutant concentrations in general. The EPA does not
agree with the commenter's suggestion to add the language or concept of
``short-term and long-term contributors'' to the regulatory definition
of an exceptional event. The EPA believes that the definition that we
are promulgating could include both short- and long-term contributors
provided the contributors meet the operative provisions in the rule.
The EPA will review each request under the Exceptional Events Rule on a
case-by-case basis using a weight of evidence approach.
    With respect to addressing rule applicability to ``background''
ozone, the EPA refers to the recent Implementation of the 2015 Primary
Ozone NAAQS: Issues Associated with Background Ozone White Paper for
Discussion.\22\ As defined in this white paper, U.S. background (USB)
ozone is

any ozone formed from sources or processes other than U.S. manmade
emissions of nitrogen oxides (NOX), volatile organic
compounds (VOC), methane (CH4), and CO.\23\ USB ozone does not include
intrastate or interstate transport of manmade ozone or ozone
precursors. While some sources that contribute to USB (e.g., wildfires,
stratospheric intrusions) may be eligible for treatment as exceptional
events, other sources of USB would not meet the Exceptional Events Rule
criteria. For example, routine or long-term international manmade
emissions are not exceptional events because they are caused by human
activity that is likely to recur at a given location; likewise, routine
biogenic VOC emissions are not exceptional events because they are not
deviations from normal or expected conditions. Thus despite being
natural, they are not ``events.'' The EPA provides additional
information regarding the treatment of certain events under the
Exceptional Events Rule in Section IV.F of this preamble.
---------------------------------------------------------------------------

    \22\ Implementation of the 2015 Primary Ozone NAAQS: Issues
Associated with Background Ozone White Paper for Discussion, U.S.
EPA, December 2015. Available at https://www.epa.gov/sites/production/files/2016-03/documents/whitepaper-bgo3-final.pdf.
    \23\ 80 FR 65292 (October 26, 2015).
---------------------------------------------------------------------------

C. Ambient Concentration Data and Data Uses Affected by the Exceptional
Events Rule

1. Summary of Proposal
    In our November 2015 document, the EPA proposed 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
\24\ 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: \25\
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    \24\ 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.
    \25\ The proposal noted 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 on the
directly 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.
---------------------------------------------------------------------------

     An action to designate or redesignate an area as
attainment, unclassifiable/attainment, nonattainment or unclassifiable
for a particular NAAQS. Such designations rely on the existence or lack
of 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
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.
    In proposing this language, the EPA effectively applied the
exceptional events process to 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 the identified types of determinations, the EPA
proposed 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. The proposal also repeated the EPA's
previous position 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 prevention of significant deterioration
(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.\26\
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    \26\ See Question 14a in the 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 proposal also noted that while data exclusion associated with
the five actions in the previously noted bulleted list must follow the
provisions in the Exceptional Events Rule, there are other actions for
which it may be appropriate to exclude data using mechanisms other than
the Exceptional Events Rule. The proposal differentiated between these
five actions and other actions based on ``past'' versus ``predicted''
exceedances and/or violations. The proposal explained that the five
identified actions involve determinations of whether a NAAQS exceedance
or violation occurred at an ambient monitoring site at a particular
time in the past. We characterized 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 (e.g., the data have already been collected at the monitors,
verified for quality assurance purposes, submitted to AQS, and used in
various regulatory calculations). In short, the collected monitoring
data provide evidence that an exceedance or violation actually
happened. This scenario is different than predicted future NAAQS
violations. The proposal explained that predictions of future NAAQS
violation(s) generally involve reviewing the historical ambient
concentration data that are the evident focus of CAA section 319(b),
estimating expected future emissions, and then using both of these data
sets as inputs to an air quality modeling tool or other analytical
approach that extrapolates these data to predict a future outcome.
While science supports, and the EPA relies on, predictions of future
NAAQS violations in several parts of the clean air program, such as in
the EPA's approval of attainment demonstrations in SIPs, in PSD air
permitting programs and in actions to reclassify a moderate
PM10 or PM2.5 nonattainment area to serious,\27\
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.
---------------------------------------------------------------------------

    \27\ 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.
---------------------------------------------------------------------------

    For these reasons, the EPA proposed requiring that the five types
of determinations that involve data exclusion associated with ``past''
exceedances or violations must follow the provisions in the Exceptional
Events Rule. The EPA also indicated our intent

to develop 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, to describe the appropriate
additional pathways for data exclusion for some ``predicted future''
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).
2. Final Rule
    After considering the public comments we received, as explained
more fully in the following paragraphs, we are finalizing language that
applies the provisions in the Exceptional Events Rule to the treatment
of data showing exceedances or violations of any NAAQS for purposes of
the following types of regulatory determinations by the Administrator.
     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
attained a NAAQS by its CAA deadline. This type of determination
includes ``clean data determinations.''
     A determination that an area has data for the specific
NAAQS that qualify the area for an attainment date extension under the
CAA provisions for the applicable pollutant.
     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.
     Other actions on a case-by-case basis if determined by the
EPA to have regulatory significance based on discussions between the
air agency and the EPA Regional office during the Initial Notification
of Potential Exceptional Event process.
    After considering comments from multiple state and local air
agencies, regional planning organizations and industrial commenters
that requested an option for using the Exceptional Events Rule for
other regulatory determinations, we have added the sixth bullet in the
preamble and in the regulatory text to acknowledge that it may be
appropriate to use the provisions in the Exceptional Events Rule to
exclude data for regulatory determinations not specifically articulated
in the first five bullets. We expect that air agencies and the
appropriate EPA Regional offices will discuss these case-by-case
scenarios as part of the Initial Notification of Potential Exceptional
Event process, described in more detail in Section IV.G.5 of this
preamble.
    Upon further review of the identified determinations by the
Administrator, we also realized that the fourth bullet, formerly ``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'' applies to attainment date extensions only
for PM10 as indicated in CAA section 188(d)(2) because
``only one exceedance'' is specific to PM10. Attainment date
extensions for other NAAQS have other CAA conditions. Our intent was
that this determination would apply to attainment date extensions for
all NAAQS and these NAAQS have CAA conditions other than ``only one
exceedance.'' As a result, we have revised the language as follows to
better convey this concept: ``A determination that an area has data for
the specific NAAQS, which qualify the area for an attainment date
extension under the CAA provisions for the applicable pollutant.''
Using this approach, a state would be required to demonstrate that a
given area had data with respect to the statistical form of that
particular standard in the calendar year prior to the applicable
attainment date for the area (i.e., for the 1997 24-hour
PM10 NAAQS, no more than one exceedance of the 24-hour NAAQS
and the annual mean concentration of PM10 in the area for
such year is less than or equal to the standard level). Revising this
language also accounts for potential future revisions to the form and
level of the NAAQS, data handling provisions and regulatory changes to
state implementation plan requirements.
    As we indicated in the proposal, we still intend to develop 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 for data exclusion for some ``predicted future'' monitoring
data applications. We have delayed the release of this guidance,
however, to allow us to incorporate the content of the final
Exceptional Events Rule revisions. We intend to post the draft guidance
and instructions for providing public comment on the exceptional events
Web site at http://www2.epa.gov/air-quality-analysis/treatment-data-influenced-exceptional-events shortly after finalizing these rule
revisions. As we noted in the proposal, we intend this guidance to do
the following:
     Clarify that data excluded under the procedural and
substantive provisions of the Exceptional Events Rule will also 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.
     Identify potential pathways for data exclusion for
determinations based on ``predicted'' future NAAQS exceedances or
violations (e.g., PSD, transportation conformity).
     Identify the scenarios in which the EPA would not exclude
data, such as when setting priority classifications for emergency plans
under 40 CFR 51.150. 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
even if that elevated concentration is associated with an exceptional
event.
3. Comments and Responses
    While the majority of commenters agreed with the EPA's proposal
that the provisions in the Exceptional Events Rule apply to the
enumerated five actions, many of these same commenters urged the EPA
not to limit the scope of the Exceptional Events Rule to the five
actions that we identified in the proposal as comprising
``determinations by the Administrator with respect to exceedances or
violations of national ambient air quality standards.'' Commenter
suggestions ranged from adding a sixth element to capture other case-
by-case actions deemed to be of regulatory significance to specifically
listing other potential actions (that is, they suggested adding the
following to list of

specifically covered actions: Design value estimates, PSD background
determinations, transportation hot spot analyses, future year
projections for modeled attainment determinations, clean data
determinations (which are included within the third bullet identifying
the types of regulatory determinations by the Administrator included
within the scope of the Exceptional Events Rule), other actions that
rely on design values, monitoring network plans, etc.). The EPA agrees
that the list of actions identified in the regulatory text should allow
for a case-by-case determination in certain circumstances (e.g., such
as when an event is determined during the Initial Notification of
Potential Exceptional Events process to have regulatory significance
for an action not otherwise identified in the regulatory text) and has
added this language to the final regulatory text. The EPA believes that
this language could include any of the specific actions identified by
other commenters. However, as we noted in the proposal, the CAA does
not clearly apply the statutory criteria of section 319(b) to all of
the other actions identified by the commenters. Therefore, under
certain circumstances, we believe that it may be appropriate to exclude
data for some of the other specific actions. Hence, we are not
identifying these actions in the regulatory text. Rather, we intend to
address them in the additional guidance previously mentioned and
discussed further in the following paragraphs.
    As indicated, the majority of commenters agreed with the EPA's
approach to define those actions that constitute ``determinations by
the Administrator.'' A few other commenters, however, indicated that
the EPA cannot narrow the scope of the Exceptional Events Rule nor
agree to exclude event-affected data from other types of regulatory
determinations using another mechanism without first undertaking
notice-and-comment rulemaking. The EPA disagrees with this comment.
First, neither the CAA language at section 319(b)(3)(B)(iv), which
requires regulations allowing 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, nor the implementing language in the 2007 Exceptional Events
Rule at 40 CFR 50.14(a)(1), which allows air agencies to request
exclusions for data showing exceedances or violations of the NAAQS that
are directly due to an exceptional event from use in determinations,
identify the scope of the word ``determinations.'' Second, identifying
the Exceptional Events Rule as the only mechanism by which data may be
excluded from regulatory actions may result in unintended consequences.
As we have noted previously, an event may make a past air concentration
significantly higher than it would have been in the absence of the
event contribution. If the event-influenced data do not result in an
exceedance or violation, they are not eligible for exclusion under the
Exceptional Events Rule. CAA section 319(b) is ambiguous with respect
to how to treat an exceptional event that contributed to a past air
concentration being higher than it would have been without the event,
but the air concentration did not result in an exceedance or violation.
The EPA's decision to not apply the Exceptional Events Rule to data
that does not exceed or violate a NAAQS is consistent with how the rule
has been applied and interpreted and is not inconsistent with CAA
section 319(b). However, we acknowledge that retaining the event-
influenced data could have regulatory implications that seem contrary
to the purpose of CAA section 319(b). For example, retaining such data
in the calculation of background concentrations used in air quality
analysis for a PSD permit may suggest that there will be a NAAQS
violation after construction of a new source and thus could prevent the
permitting authority from issuing the permit.\28\
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    \28\ 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.
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    As previously noted, we intend our 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 to describe the appropriate additional pathways
for data exclusion for some ``predicted future'' monitoring data
applications. Multiple commenters expressed interest in this guidance
and called for its quick release. The EPA recognizes that this guidance
is an important supplement to the revisions to the Exceptional Events
Rule that we are promulgating and we will work towards the quick
release of this document.
    Throughout this preamble and in our proposal, we use the term
``weight of evidence'' to describe the process by which we evaluate
individual exceptional events demonstrations and air agency requests
for data exclusion. Several commenters asked for additional
clarification regarding this terminology, either in preamble or in
regulatory text. Several other commenters asked that we use the ``more
commonly understood'' terminology of ``preponderance of the evidence.''
Another commenter objects to the use of a weight of evidence approach
noting that it could lead to incorrectly granted requests for data
exclusion.
    While we are not adding language to the regulatory text, we are
clarifying in this preamble to the final rule that in applying a
``weight of evidence'' approach to reviewing individual exceptional
events demonstrations, the EPA believes it is appropriate to 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. Courts have found that it is reasonable for the EPA
to use a ``weight of evidence'' analysis when implementing the CAA.
See, e.g., Envtl. Def. v. EPA, 369 F.3d 193 (2d Cir. 2004) (upholding
the EPA's approval of a state's attainment demonstration using
photochemical grid modeling and a weight of evidence analysis) and BCCA
Appeal Group v. EPA, 355 F.3d 817 (5th Cir. 2003) (finding that the
EPA's conclusion that the weight of evidence approach to approving
attainment demonstrations was consistent with the CAA, reasonable and
entitled to deference). In this context, ``weight'' refers to the
relevance of the evidence to the determination and its technical merit,
and not to the amount of documentation. The language ``weight of
evidence'' is consistent with this approach and consistent with the
terminology used in other EPA regulatory actions. ``Preponderance of
the evidence'' conveys many of the same concepts as ``weight of
evidence,'' but because it is a legal term of art, we are not using
that term as part of this rulemaking action. The weight of evidence
approach is an appropriate and reasonable approach, which has been used
historically and successfully under key CAA programs. The commenter did
not present any information showing that this approach is more likely
to yield ``incorrect'' decisions than any other evidentiary approach
that might be applicable to exceptional events demonstrations.

D. Definition and Scope of a Natural Event

1. Summary of Proposal
    In the 2007 Exceptional Events Rule, the EPA defined a natural
event as an event in which human activity plays little or no direct
causal role (see 72 FR 13580). In our 2015 action, the EPA proposed to
revise this definition to include the concept of an event and its
resulting emissions and to acknowledge that natural events can recur.
The EPA also proposed to include language in the regulatory definition
to clarify that anthropogenic emission sources that contribute to the
event emissions (and subsequent exceedance or violation) that are
reasonably controlled do not play a ``direct'' role in causing
emissions. The proposal elaborated on the ``direct causal'' concept by
repeating language that first appeared in the preamble to the 2007
Exceptional Events Rule but not in rule text.
    In the 2007 rule preamble and the November 2015 proposal, the EPA
explained that we generally consider human activity to have played
little or no direct role in causing an event-related exceedance or
violation if anthropogenic emission sources that contribute to the
exceedance are reasonably controlled at the time of the event (see 72
FR 13563-4 and 80 FR 72844). This is the case 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.\29\ Thus, the event could be considered a
natural event by applying the reasonable interpretation that the
anthropogenic source had ``little'' direct causal role. To further
illustrate this concept, as we have noted previously, the EPA considers
wildfires to be natural events even though some accidental human
actions initiate some wildfires and, to some degree, prior land
management practices can influence the frequency and scale of
wildfires. The EPA believes the interpretation that wildfires are
natural events 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, landowners
and managers and government public safety agencies are strongly
motivated to reduce the frequency and severity of human-caused
wildfires. Our proposal further explained that 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.
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    \29\ 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 monitored exceedance or violation.
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2. Final Rule
    After consideration of the public comments and as supported by many
commenters, we are finalizing the following definition: ``natural event
means an event and its resulting emissions, which may recur at the same
location, in which human activity plays little or no direct causal
role. For purposes of the definition of a natural event, anthropogenic
sources that are reasonably controlled shall be considered to not play
a direct role in causing emissions.'' In the final regulatory
definition that we are promulgating, we are adding the language ``at
the same location'' to more clearly indicate that natural events can
recur in the same area or at the same location and still be considered
as exceptional events. The language we are adding in the definition
contrasts the recurrence frequency of natural events with human
activities that must be ``unlikely to recur at a particular location''
to be considered to be an exceptional event (see CAA section
319(b)(1)(A)(iii)). Although several commenters disagreed with our
approach, and stated that a natural event must have no human activity
component at all, we are retaining in the regulatory definition the
concept that we consider reasonably controlled anthropogenic sources to
not play a direct role in causing emissions. We are, however, adding
the language ``[f]or purposes of the definition of a natural event''
prior to the language ``anthropogenic sources that are reasonably
controlled shall be considered to not play a direct role in causing
emissions'' to clarify that the ``direct causal'' language applies to
reasonably controlled anthropogenic sources when considering whether
the event is natural. As we have previously stated, we believe that if
reasonable controls were implemented on contributing anthropogenic
sources at the time of the event and if, despite these efforts and
controls, an exceedance occurred, then we would consider the human
activity to have played little or no direct causal role in causing the
event-related exceedance. Rather, in those cases in which the
anthropogenic source has ``little'' direct causal role, we would
consider the high wind and the emissions arising from the contributing
natural sources (in which human activity has no role) to cause the
exceedance or violation. Additionally, the event would not be natural
if all of the event-related emissions originated from anthropogenic
sources or if anthropogenic emission sources that contributed to the
event-related emissions could have been reasonably controllable but
reasonable controls were not implemented at the time of the event.\30\
We discuss the concept of reasonable control in more detail in Section
IV.E.2 of this preamble.
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    \30\ As we clarify in the final rule discussion in Section
IV.F.2.a of this preamble, when considering prevention/control for
purposes of exceptional event categorization, a prescribed fire
effectively becomes like a wildfire when, for example, the
prescribed fire escapes secure containment due to unforeseen
circumstances (e.g., a sudden shift in prevailing winds). In these
instances, the burn manager would no longer control the path of the
fire. Thus, the fact that the initial fire was deliberately ignited
should not result in the entire burn (e.g., the duration and extent
of the burn) needing to follow the rule requirements for prescribed
fires on wildland.
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3. Comments and Responses
    Commenters providing feedback on the natural events section of the
proposal generally focused on one of the following concepts: The
language in the proposed revised definition of natural event, those
event types considered to be natural events and the concept of
reasonable controls as it relates to contributing anthropogenic
emissions. We address in the explanation of the final rule language in
Section IV.D.2 of this preamble those comments related to the
definition of natural event. We address the types of natural events in
this section and we discuss reasonable controls in Section IV.E.2 of
this preamble.
    Several commenters asked that we clarify those types of events that
could be considered natural events eligible for data exclusion under
the Exceptional Events Rule. Commenters specifically asked for clarity
regarding earthquakes, lightning and biological emissions. Through our
experience implementing the Exceptional Events Rule, we have come to
realize that it may be helpful to think of an event in terms of the
source of its emissions. If the underlying source is natural and the
generated emissions influence a regulatory monitor, then the ensuing
event (i.e., event and resulting

emissions) could be considered a ``natural event'' under the
Exceptional Events Rule. Applying this rationale, as we expressed in
the 2007 rule and the November 2015 proposal (see 72 FR 13565 and 80 FR
72854-72858), the EPA generally considers wildfires, stratospheric
ozone intrusions, volcanic and seismic (e.g., earthquake) activities,
natural disasters (e.g., hurricanes and tornados) and windblown dust
from natural, undisturbed landscapes to be natural events. Natural
events, including, but not limited to, those previously identified, and
their resulting emissions could be considered under the provisions of