[Federal Register: March 10, 2006 (Volume 71, Number 47)]
[Proposed Rules]
[Page 12591-12610]
[DOCID:fr10mr06-23]

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Part V

Environmental Protection Agency

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40 CFR Parts 50 and 51

The Treatment of Data Influenced by Exceptional Events; Proposed Rule

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Parts 50 and 51

[EPA-HQ-OAR-2005-0159; FRL-8042-5]
RIN 2060-AN40

The Treatment of Data Influenced by Exceptional Events

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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SUMMARY: Today, EPA is proposing a rule to govern the review and
handling of air quality monitoring data influenced by exceptional
events. Exceptional events are events for which the normal planning and
regulatory process established by the Clean Air Act (CAA) is not
appropriate. In this rulemaking action, EPA is proposing to: Implement
section 319(b)(3)(B) and section 107(d)(3) authority to exclude air
quality monitoring data from regulatory determinations related to
exceedances or violations of the National Ambient Air Quality Standards
(NAAQS) and avoid designating an area as nonattainment, redesignating
an area as nonattainment, or reclassifying an existing nonattainment
area to a higher classification if a State adequately demonstrates that
an exceptional event has caused an exceedance or violation of a NAAQS.
Also, EPA is proposing four options with respect to whether, and to
what extent, States should be required to take additional actions to
address public health impacts related to the event.

DATES: Comments must be received on or before May 9, 2006. Comments
must be postmarked by the last day of the comment period.

ADDRESSES: Submit your comments, identified by Docket ID No. EPA-HQ-
OAR-2005-0159, by one of the following methods:
     http://www.regulations.gov. Follow the on-line

instructions for submitting comments.
     E-mail: Comments may be sent by electronic mail (e-mail)
to<EMAIL_ADDRESS>Attention Docket ID No. EPA-HQ-OAR-2005-
0159.
     Fax: Fax your comments to:<PHONE_NUMBER>, Attention Docket
ID no. EPA-HQ-OAR-2005-0159.
     Mail: Send your comments to: Air and Radiation Docket and
Information Center, U.S. Environmental Protection Agency, Mail Code:
6102T, 1200 Pennsylvania Ave., NW., Washington, DC 20460, Attention
Docket ID No. EPA-HQ-OAR-2005-0159.
     Hand Delivery: Air and Radiation Docket and Information
Center, U.S. Environmental Protection Agency, 1301 Constitution Avenue,
NW., Room B102, Washington, DC, Attention Docket ID No. EPA-HQ-OAR-
2005-0159. Such deliveries are only accepted during the Docket's normal
hours of operation, and special arrangements should be made for
deliveries of boxed information.
    Instructions: Direct your comments to Docket ID No. EPA-HQ-OAR-
2005-0159. The EPA's policy is that all comments received will be
included in the public docket without change and may be made available
online at http://www.regulations.gov, including any personal

information provided, unless the comment includes information claimed
to be Confidential Business Information (CBI) or other information
whose disclosure is restricted by statute. Do not submit information
that you consider to be CBI or otherwise protected information through
http://www.regulations.gov, or e-mail. The http://www.regulations.gov
Web site is an ``anonymous access'' system, which means that EPA will
not know your identity or contact information unless you provide it in
the body of your comment. If you send an e-mail comment directly to EPA
without going through http://www.regulations.gov, your e-mail address

will be automatically captured and included as part of the comment that
is placed in the public docket and made available on the Internet. If
you submit an electronic comment, EPA recommends that you include your
name and other contact information in the body of your comment and with
any disk or CD-ROM you submit. If EPA cannot read your comment due to
technical difficulties and cannot contact you for clarification, EPA
may not be able to consider your comment. Electronic files should avoid
the use of special characters, any form of encryption, and be free of
any defects or viruses. For additional instructions on submitting
comments, go to SUPPLEMENTARY INFORMATION.
    Docket: All documents in the docket are listed in the http://www.regulations.gov
 index. Although listed in the index, some

information is not publicly available, e.g., CBI or other information
whose disclosure is restricted by statute. Certain other material, such
as copyrighted material, will be publicly available only in hard copy.
Publicly available docket materials are available either electronically
in http://www.regulations.gov or in hard copy at the Office of Air and

Radiation Docket and Information Center, EPA West, Room B102, 1301
Constitution Ave., NW., Washington, DC. The Public Reading Room is open
from 8:30 a.m. to 4:30 p.m., Monday through Friday, excluding legal
holidays. The telephone number for the Public Reading Room is (202)
566-1744, and the telephone number for the Office of Air and Radiation
Docket and Information Center is<PHONE_NUMBER>.

FOR FURTHER INFORMATION CONTACT: General questions concerning this
proposed rule should be addressed to Mr. Larry D. Wallace, Ph.D.,
Office of Air Quality Planning and Standards, Air Quality Policy
Division, Mail Code C539-01, Research Triangle Park, NC 27711;
telephone<PHONE_NUMBER>, and e-mail address<EMAIL_ADDRESS>    Questions concerning technical and analytical issues related to
this proposed rule should be addressed to Mr. Neil Frank, Office of Air
Quality Planning and Standards, Air Quality Assessment Division, Mail
Code C304-04, Research Triangle Park, NC 27711; telephone (919) 541-
5560, and e-mail address<EMAIL_ADDRESS>
SUPPLEMENTARY INFORMATION:

Public Hearing

    The EPA will hold two public hearings on today's proposal during
the comment period. The details of the public hearings, including the
times, dates, and locations will be provided in a future Federal
Register notice. The public hearings will provide interested parties
the opportunity to present data, views, or arguments concerning the
proposed rule. The EPA may ask clarifying questions during the oral
presentations, but will not respond to the presentations or comments at
that time. Written statements and supporting information submitted
during the comment period will be considered with the same weight as
any oral comments and supporting information presented at the public
hearings. Under CAA section 307(d)(1)(A), the procedural requirements
of section 307(d) apply to this proposal. In addition, under section
307(d)(1)(U), the Administrator determines that this action is subject
to the provisions of section 307(d). Section 307(d)(1)(U) provides that
the provisions of section 307(d) apply to ``such other actions as the
Administrator may determine.'' The EPA is including the proposals in
today's proposed rulemaking under sections 307(d)(1)(A) and (U).

Comments

    1. Submitting CBI. Do not submit this information to EPA through
http://www.regulations.gov or e-mail. Clearly mark the part or all of

the information that you claim to be CBI. For CBI information in a disk
or CD-ROM that

you mail to EPA, mark the outside of the disk or CD-ROM as CBI and then
identify electronically within the disk or CD-ROM the specific
information that is claimed as CBI. In addition to one complete version
of the comment that includes information claimed as CBI, a copy of the
comment that does not contain the information claimed as CBI must be
submitted for inclusion in the public docket. Information so marked
will not be disclosed except in accordance with procedures set forth in
40 CFR part 2.
    2. Tips for Preparing Your Comments. When submitting comments,
remember to:
     Identify the rulemaking by docket number and other
identifying information (subject heading, Federal Register date and
page number).
     Follow directions--The agency may ask you to respond to
specific questions or organize comments by referencing a Code of
Federal Regulations (CFR) part or section number.
     Explain why you agree or disagree; suggest alternatives
and substitute language for your requested changes.
     Describe any assumptions and provide any technical
information and/or data that you used.
     If you estimate potential costs or burdens, explain how
you arrived at your cost estimate in sufficient detail to allow for it
to be reproduced.
     Provide specific examples to illustrate your concerns, and
suggest alternatives.
     Explain your views as clearly as possible, avoiding the
use of profanity or personal threats.
     Make sure to submit your comments by the comment period
deadline identified.
    In addition, please send a copy of your comments to: Mr. Larry D.
Wallace, Ph.D., U.S. Environmental Protection Agency, by one of the
means listed below:
    1. E-Mail<EMAIL_ADDRESS>    2. Fax:<PHONE_NUMBER>, Attention: Mr. Larry D. Wallace, Ph.D.
    3. Mail: Mr. Larry D. Wallace, Ph.D., U.S. Environmental Protection
Agency, Office of Air Quality Planning and Standards, Mail Code: C539-
01, Research Triangle Park, NC 27711.
    4. Hand Delivery: Mr. Larry D. Wallace, Ph.D., U.S. Environmental
Protection Agency, Office of Air Quality Planning and Standards, 109
T.W. Alexander Drive, Research Triangle Park, NC 27709.

Table of Contents

    The following is an outline of the preamble.

I. Preamble Glossary of Terms and Acronyms
II. Background and Purpose of Today's Rulemaking
    A. Legislative Requirements
    B. Historical Experience Concerning Exceptional and Natural
Events
III. Today's Proposed Action
    A. To Whom and to What Pollutants Does Today's Proposed Rule
Apply?
    B. How Does This Rule Relate to Indian Tribes?
    C. What Is an Exceptional Event?
    D. Examples of Exceptional Events
    1. Chemical Spills and Industrial Accidents
    2. Structural Fires
    3. Exceedances Due to Transported Pollution
    4. Exceedances Due to a Terrorist Attack
    5. Natural Events
    a. Volcanic and Seismic Activities
    b. Natural Disasters and Associated Clean-up Activities
    c. High Wind Events
    d. Unwanted Fires
    e. Stratospheric Ozone Intrusions
IV. The Management of Air Quality Data Affected by Exceptional
Events
    A. Flagging of Data in the AQS Database
    B. What Does It Mean for an Event To ``Affect Air Quality''?
    1. Option 1: 95th Percentile Criterion
    2. Option 2: 75th Percentile/95th Percentile Tiered Approach
    3. Option 3: Case-by-Case Approach Based On Weight of Evidence
    C. Use of a ``But For'' Test
    D. Schedules and Procedures for Flagging and Requesting
Exclusion of Data
    1. Option 1: Early Data Flagging and Demonstration Submission
    2. Option 2: Early Data Flagging and Delayed Demonstration
Submission
    3. Option 3: Delayed Data Flagging and Demonstration Submission
    E. Exclusion of Entire 24-Hour Value as Opposed to a Partial
Adjustment of the 24-Hour Value
    F. What Should States be Required To Submit in Their Exceptional
Events Demonstrations?
    G. Special Considerations Relevant to Proposed Standards for
PM10-2.5
    H. Public Availability of Air Quality Data and Demonstrations
Related to Exceptional Events
V. Additional Requirements
    A. Option 1: Proposed Option: Require Public Notification,
Education and Appropriate and Reasonable Measures
    B. Option 2: The Development of a Mitigation Plan by States
Under Section 110 of the CAA
    C. Option 3: The Development of a Mitigation Plan for Episodic
Events
    D. Option 4: Do Not Require States To Adopt and Implement
Specific Mitigation Plans or Measures Under This Rule
VI. Special Treatment of Certain Events Under This Rule
    A. Volcanic and Seismic Activities
    B. High Wind Events
    C. Stratospheric Ozone Intrusion
VII. Treatment of Fireworks Displays
VIII. Statutory and Executive Order Reviews
    A. Executive Order 12866: Regulatory Planning and Review
    B. Paperwork Reduction Act
    C. Regulatory Flexibility Act
    D. Unfunded Mandates Reform Act
    E. Executive Order 13132: Federalism
    F. Executive Order 13175: Consultation and Coordination With
Indian Tribal Governments
    G. Executive Order 13045: Protection of Children From
Environmental Health and Safety Risks
    H. Executive Order 13211: Actions that Significantly Affect
Energy Supply, Distribution, or Use
    I. National Technology Transfer Advancement Act

I. Preamble Glossary of Terms and Acronyms

    The following are abbreviations of terms used in the preamble.

AQS Air Quality System
BACM Best Available Control Measures
CAA Clean Air Act
CAAA Clean Air Act Amendments
EPA Environmental Protection Agency
FIP Federal Implementation Plan
FMP Fire Mitigation Plan
NAAQS National Ambient Air Quality Standards
NEAP Natural Event Action Plan
OAQPS Office of Air Quality Planning and Standards
PM10 Particles with a nominal mean aerodynamic diameter less
than or equal to 10 micrometers
PM10-2.5 Particles with a nominal mean aerodynamic diameter
greater than 2.5 micrometers and less than or equal to 10 micrometers
PM2.5 Particles with a nominal mean aerodynamic diameter
less than or equal to 2.5 micrometers
RACM Reasonably Available Control Measures
SIP State Implementation Plan
SAFE-TEA-LU Safe Accountable Flexible Efficient-Transportation Equity
Act--A Legacy for Users
SMP Smoke Management Plan
TAR Tribal Authority Rule
TIP Tribal Implementation Plan

II. Background and Purpose of Today's Rulemaking

A. Legislative Requirements

    Today, EPA is proposing a rule to govern the review and handling of
air quality monitoring data influenced by exceptional events. As
discussed below, these are events for which the normal planning and
regulatory process established by the CAA is not appropriate. Section
319 of the CAA, as amended by section 6013 of the Safe Accountable
Flexible Efficient-Transportation Equity Act: A Legacy for Users (SAFE-
TEA-LU) of 2005, requires EPA to publish this rule in the Federal

Register no later than March 1, 2006.\1\ Further, EPA is required to
issue the final rule no later than 1 year from the date of proposal.
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    \1\ All subsequent references to section 319 of the CAA in this
proposal are to section 319 as amended by SAFE-TEA-LU unless
otherwise noted.
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    The EPA is proposing to establish procedures and criteria related
to the identification, evaluation, interpretation, and use of air
quality monitoring data related to any NAAQS where States petition EPA
to exclude data that are affected by exceptional events. Section 319
defines an event as an exceptional event if the event affects air
quality; is a natural event or an event caused by human activity that
is unlikely to recur at a particular location; and is determined by the
Administrator to be an exceptional event. The statutory definition of
exceptional event specifically excludes stagnation of air masses or
meteorological inversions; a meteorological event involving high
temperature or lack of precipitation; or air pollution relating to
source noncompliance.
    Section 319(b)(3)(B)(i) requires a State air quality agency to
demonstrate through ``reliable, accurate data that is promptly
produced'' that an exceptional event occurred.\2\ Section
319(b)(3)(B)(ii) requires that ``a clear causal relationship'' be
established between a measured exceedance of a NAAQS and the
exceptional event demonstrating ``that the exceptional event caused a
specific air pollution concentration at a particular location.'' In
addition, section 319(b)(3)(B)(iii) requires a public process to
determine whether an event is an exceptional event. Finally, section
319(b)(3)(B)(iv) requires criteria and procedures for a Governor to
petition the Administrator to exclude air quality monitoring data that
is directly due to exceptional events from use in determinations with
respect to exceedences or violations of the NAAQS.
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    \2\ While this document refers primarily to States as the entity
responsible for flagging data impacted by exceptional events, other
agencies, such as local or Tribal government agencies, may also have
standing to flag data as being affected by these types of events,
and the criteria and procedures that are discussed in this
rulemaking also apply to these entities.
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    Section 319 also contains a set of five principles for EPA to
follow in developing regulations to implement section 319:
    (i) Protection of public health is the highest priority;
    (ii) Timely information should be provided to the public in any
case in which the air quality is unhealthy;
    (iii) All ambient air quality data should be included in a timely
manner in an appropriate Federal air quality data base that is
accessible to the public;
    (iv) Each State must take necessary measures to safeguard public
health regardless of the source of the air pollution; and
    (v) Air quality data should be carefully screened to ensure that
events not likely to recur are represented accurately in all monitoring
data and analyses (42 U.S.C. 7619(b)(3)(A)).
    In adopting revisions to section 319, EPA believes that Congress
sought to provide statutory relief to States to allow them to avoid
being designated as nonattainment or to avoid continuing to be
designated nonattainment as a result of exceptional events in
appropriate circumstances. In addition, Congress indicated that States
should not have to prepare and implement regulatory strategies when
their air quality is affected by events beyond their reasonable
control. To accomplish this goal, Congress enumerated certain minimum
requirements for this rulemaking. In addition, Congress provided
certain statutory principles for EPA to follow in promulgating
regulations to exclude data affected by exceptional events.
    Section 319 also includes an interim provision, section 319(b)(4),
that addresses the transition period between the present and the date
that a final regulation governing the treatment of data related to
exceptional events is promulgated. The provision indicates that
following EPA guidance documents continues to apply until the effective
date of a final regulation promulgated under section 319(b)(2):
``Guidance on the Identification and Use of Air Quality Data Affected
by Exceptional Events'' (July 1986); ``Areas Affected by
PM10 Natural Events,'' May 30, 1996; and appendices I, K,
and N to 40 CFR part 50, which describe how air quality monitoring data
are to be used and interpreted to determine compliance with the
applicable NAAQS. The statute requires the promulgation of the final
rule no later than 1 year following the publication of this proposed
rule.

B. Historical Experience Concerning Exceptional and Natural Events

    Since 1977, EPA guidance and regulations have either implied or
documented the need for a flagging system for data affected by an
exceptional event. The first EPA guidance related to the exclusion or
discounting of data affected by an exceptional event was an Office of
Air Quality Planning and Standards (OAQPS) guidance document entitled,
``Guidelines for the Interpretation of Air Quality Standards,''
Guideline No. 1.2-008 (revised February 1977).\3\
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    \3\ ``Guideline for Interpretation of Air Quality Standards,''
U.S. Environmental Protection Agency, Office of Air Quality Planning
and Standards, Research Triangle Park, N.C. OAQPS No. 1.2-008
(Revised February 1977). The guidance indicated the need for a data
flagging system which would require the submittal of detailed
information establishing that a violation was due to uncontrollable
natural sources and that the information could be used in decision-
making related to the feasibility of modifying control strategies.
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    In July 1986, EPA issued the guidance entitled, ``Guideline on the
Identification and Use of Air Quality Data Affected by Exceptional
Events'' (the Exceptional Events Policy). The Exceptional Events Policy
provided criteria for States to use in making decisions related to
identifying data that have been influenced by an exceptional event.
    In addition to the Exceptional Events Policy, on July 1, 1987, EPA
promulgated the NAAQS for PM10 (particulate matter with an
aerodynamic diameter of 10 micrometers or less) which also addressed
the issue of excluding or discounting data affected by exceptional
events.\4\ Appendix K of that rule allows for special consideration of
data determined to be affected by an exceptional event. Section 2.4 of
appendix K authorizes EPA to discount from consideration in making
attainment or nonattainment determinations for air quality data that
are attributable to ``an uncontrollable event caused by natural
sources'' of PM10, or ``an event that is not expected to
recur at a given location.'' Section 2.4 of appendix K, together with
EPA guidance contained in the Exceptional Events Policy, describes the
steps that should be taken for flagging PM10 data that a
State believes are affected by an exceptional or natural event.
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    \4\ Federal Register (52 FR 24667), July 1, 1987.
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    In 1990, section 188(f) was added to the CAA. This section of the
CAA provided EPA authority to waive either a specific attainment date
or certain planning requirements for serious PM10
nonattainment areas that were affected by nonanthropogenic sources. In
response to section 188(f), and in consideration of the CAA
consequences for areas affected by elevated concentrations caused by
natural events, in 1996 EPA issued a policy to address data affected by
natural events entitled, ``Areas Affected by PM10 Natural
Events,'' (the PM10 Natural Events Policy).\5\
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    \5\ Memorandum from Mary D. Nichols, Assistant Administrator for
Air and Radiation, to EPA Regional Offices entitled, ``Areas
Affected by PM10 Natural Events,'' May 30, 1996.

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    On July 18, 1997, EPA issued revised NAAQS for ozone and a new
NAAQS addressing PM2.5. For ozone, the revised NAAQS
provided for an 8-hour averaging period (versus 1 hour for the previous
NAAQS), and the level of the standard was changed from 0.12 ppm to 0.08
ppm (62 FR 38856). For the PM2.5 NAAQS, EPA established both
a new 24-hour standard and a new annual standard. In that Federal
Register, EPA also promulgated appendices I and N to 40 CFR part 50.
Appendices I and N provided the methodologies for determining whether
an area is in attainment of the 8-hour ozone and PM2.5 NAAQS
respectively, using ambient air quality data. Section 1.0 of appendix
I, and section 1.0(b) of appendix N provide the authority for EPA to
give special consideration to data determined to be affected by an
exceptional or natural event.
    Appendices K, I, and N, which are a part of the NAAQS for the
affected pollutants as described above, provide that, while States must
submit all valid ambient air quality data to EPA's Air Quality System
(AQS) data base for use in making regulatory decisions, in some cases
it may be appropriate for the Regional Administrator to exclude,
discount, weight, or make adjustments to data that have been
appropriately flagged from calculations in determining whether or not
an area has attained the standard. These decisions are to be made on a
case-by-case basis using all available information related to the event
in question, and are required to be made available to the public for
review. It should also be noted that, while it would be desirable to be
able to adjust the daily value to exclude only those portions of the
data that are attributable to the exceptional event, due to technical
limitations, such subtraction has not been possible, and EPA's
historical practice has been to exclude a daily measured value in its
entirety when that value is found to be largely caused by an
exceptional event.
    Following the promulgation of the 8-hour ozone and the
PM2.5 NAAQS, EPA provided additional guidance to States on
how to address data affected by exceptional and natural events.\6\ That
guidance directed the States to follow three specific EPA guidance
documents in making determinations related to data influenced by
exceptional and natural events: (1) The Exceptional Events Policy; (2)
The PM10 Natural Events Policy; and (3) The Interim Air
Quality Policy on Wildland and Prescribed Fires, Memorandum from
Richard D. Wilson, Acting Assistant Administrator for Air and
Radiation, to EPA Regional Administrators, May 15, 1998. The Interim
Air Quality Policy on Wildland and Prescribed Fires addressed the
treatment of air quality monitoring data that are affected by wildland
and prescribed fires that are managed for resource benefits.\7\ The EPA
will continue to use these policies to address issues related to the
existing and/or revised PM2.5 NAAQS pending EPA's final
action on today's proposed rulemaking. Similarly, issues related to
exceptional and natural events affecting the ozone standard will
continue to be addressed under the 1986 Exceptional Events Policy until
EPA issues a final exceptional events rule.
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    \6\ ``Guideline on Data Handling Conventions for the PM NAAQS,''
United States Environmental Protection Agency, Office of Air Quality
Planning and Standards, Research Triangle Park, N.C. 27711, EPA-454/
R-99-008, April 1999.
    ``Guideline on Data Handling Conventions for the 8-hour Ozone
NAAQS,'' United States Environmental Protection Agency, Office of
Air Quality Planning and Standards, Research Triangle Park, N.C.
27711, EPA-454/R-99-008, April 1999.
    \7\ Following the promulgation of this rule, EPA will revise the
``Interim Air Quality Policy on Wildland and Prescribed Fires'' to
be consistent with current policies related to wildland and
prescribed fires as well as the final rulemaking on exceptional
events.
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III. Today's Proposed Action

A. To Whom and to What Pollutants Does Today's Proposed Rule Apply?

    Under the statutory scheme established by the CAA, States are
primarily responsible for the administration of air quality management
programs within their borders. This includes the monitoring and
analysis of ambient air quality and submission of monitoring data to
EPA, which are then stored in EPA's AQS data base. The EPA retains an
important oversight responsibility for ensuring compliance with CAA
requirements. With respect to the treatment of air quality monitoring
data, States are responsible for ensuring data quality and validity and
for identifying measurements that they believe warrant special
consideration, while EPA is responsible for reviewing and approving or
disapproving any requests for such consideration. Therefore, if
adopted, today's proposed rule would apply 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, as discussed below, to Tribal air
quality agencies where appropriate. This proposed rule would also
govern EPA's actions in reviewing and approving or disapproving the
relevant actions taken or requested by States. Where EPA implements air
quality management programs on Tribal lands, this proposed rule would
govern those actions as well.
    At present, only the NAAQS for ozone and PM contain provisions
which allow for the special handling of air quality data affected by
exceptional events (40 CFR part 50, appendices K, I, and N). The
language of section 319 of the CAA is broad in terms of making its
provisions applicable to events that ``affect air quality'' and to
exceedances or violations of ``the national ambient air quality
standards'' (42 U.S.C. 7619(b)(1)(A)(i), (b)(3)(B)(iv)). Thus, its
provisions can apply to the NAAQS for any criteria pollutant. Because
the NAAQS established for other criteria pollutants do not currently
contain provisions permitting the discounting or exclusion of data due
to exceptional events, we are proposing to only apply the provisions of
this rule initially to ozone and PM. As we review and consider the need
for revisions to the NAAQS for other pollutants, we will include
provisions to address exceptional events in those NAAQS in accordance
with section 319, as appropriate at that time. Because issuance of a
new or revised NAAQS will necessitate the initiation of the designation
process, EPA believes that the NAAQS rules are an appropriate place to
make provision for exceptional events in the evaluation of air quality
data. In the interim, where exceptional events result in exceedances or
violations of NAAQS that do not currently provide for special treatment
of the data, we intend to use our discretion as outlined under section
107(d)(3) not to redesignate affected areas as nonattainment based on
these events.

B. How Does This Rule Relate to Indian Tribes?

    Under the CAA and the Tribal Authority Rule (TAR), eligible Indian
Tribes may develop and submit Tribal Implementation Plans (TIPs) for
EPA approval, to administer requirements under the CAA on their
reservations and other areas under their jurisdiction. However, Tribes
are not required to develop TIPs or otherwise implement relevant
programs under the CAA. The EPA has stated that it will continue to
ensure the protection of air quality throughout the nation, including
in Indian country, and will issue Federal Implementation Plans (FIPs)
as necessary or appropriate to fill gaps in program implementation in
affected areas of Indian country (63 FR 7254, 7265; February 12, 1998).

    In cases where a Tribal air quality agency has implemented an air
quality monitoring network which is affected by emissions from
exceptional events, the criteria and procedures identified in this
proposed rule may be used to exclude or discount data for regulatory
purposes. Certain Tribes may implement all relevant components of an
air quality program for purposes of meeting the various requirements of
this proposed rule. In some cases, however, a Tribe may implement only
portions of the relevant program and may not be in a position to
address each of the procedures and requirements associated with
excluding or discounting emissions data (e.g., a particular Tribe may
operate a monitoring network for purposes of gathering and identifying
appropriate data, but may not implement relevant programs for the
purpose of mitigating the effects of exceptional events required under
this proposed rule). The EPA intends to work with Tribes on the
implementation of this proposed rule, which may include appropriate
implementation by EPA of program elements ensuring that any exclusion
or discounting of data in Indian country areas with air quality
affected by exceptional events comports with the procedures and
requirements of this proposed rule.

C. What Is an Exceptional Event?

    In accordance with the language in section 319, EPA is proposing to
define the term ``exceptional event'' to mean an event that:
    (i) Affects air quality;
    (ii) Is not reasonably controllable or preventable;
    (iii) Is an event caused by human activity that is unlikely to
recur at a particular location or a natural event; and
    (iv) Is determined by the Administrator through the process
established in these regulations to be an exceptional event.

It is important to note that natural events, which are one form of
exceptional events according to this definition, may recur, sometimes
frequently (e.g., western wildfires). For purposes of this rule, EPA is
proposing to define ``natural event'' as an event in which human
activity has no substantial or direct causal connection to the event in
question. We recognize that over time, certain human activities may
have had some impact on the conditions which later give rise to a
``natural'' air pollution event. However, we do not believe that small
historical human contributions should preclude an event from being
deemed ``natural.''
    In this proposed rule, EPA also defines the term ``exceedance''
with respect to compliance with the NAAQS and establishes criteria for
determining when an event can be said to ``affect air quality.'' We are
not proposing more detailed requirements for determining when an event
is ``not reasonably controllable or preventable'' because we believe
that such determinations will necessarily be dependent on specific
facts and circumstances that cannot be prescribed by rule. In adopting
section 188(f) of subpart 4 of the 1990 amendments to the CAA, Congress
recognized and provided for distinctions between these types of
activities, while discussing circumstances under which events should or
should not be considered natural (see Public Law 101-549, CAA
Amendments of 1990 House Report No. 101-290(l), May 17, 1990; and
discussion of Mono Lake, California therein).

D. Examples of Exceptional Events

    The EPA believes that the following types of events meet the
definition of exceptional events, as defined above. This means that air
quality data affected by these types of events may qualify for
exclusion under this proposed rule if all other requirements of the
rule are met. The AQS data base also contains a more detailed list of
other similar events that may be flagged for special consideration
(http://www.epa.gov/ttn/airs/airsaqs/manuals/ codedescs.htm).

1. Chemical Spills and Industrial Accidents
    Emissions that result from accidents such as fires, explosions,
power outages, train derailments, vehicular accidents, or combinations
of these may be flagged as an exceptional event.
2. Structural Fires
    Structural fires include any accidental fire involving a manmade
structure.
3. Exceedances Due to Transported Pollution
    Transported pollution, whether national or international in origin
and whether from natural or anthropogenic sources, may cause
exceedances which are eligible for exclusion under this rule as long as
the other criteria and requirements for exceptional events under this
rule are met. For example, States may flag, and EPA may exclude, data
associated with fires occurring outside of the borders of the United
States, such as forest fires in Mexico, Central America, and Canada; or
transport events such as African dust and Asian dust which contribute
significantly to ambient concentrations of a pollutant, leading to
exceedances or violations of the NAAQS. An example of interstate
transported emissions which may be flagged as due to an exceptional
event would be emissions due to smoke from wildland fires which cause
exceedances or violations at monitoring sites in other States. Other
types of events may be considered on a case-by-case basis.
4. Exceedances Due to a Terrorist Attack
    Emissions that result from a terrorist attack such as smoke from
fires, dust, explosions, power outages, train derailments, vehicular
accidents, or combinations of these may be flagged as an exceptional
event.
5. Natural Events
    The natural events addressed by this proposed rule are: (1)
Volcanic and seismic activities; (2) natural disasters and associated
cleanup activities; (3) high wind events; (4) unwanted fires; and (5)
stratospheric ozone intrusions. The EPA will consider other types of
natural events on a case-by-case basis.
    a. Volcanic and Seismic Activities. Ambient concentrations of
particulate matter for which volcanic eruptions or seismic activity
caused or contributed to high levels of particulate matter in an
affected area will be treated as natural events. While not occurring
frequently, volcanic and seismic activity can affect air quality data
related to the particulate matter NAAQS for an extended period of time
after an event. Volcanic eruptions contribute to ambient concentrations
in two ways; concentrations due to primary emissions (e.g., ash); and
emissions of precursor pollutants (e.g., sulfur dioxide) that
contribute to the secondary formation of particulate matter. Seismic
activity (e.g., earthquakes) can also contribute to ambient particulate
matter concentrations by shaking the ground, causing structures to
collapse and otherwise raising dust.
    b. Natural Disasters and Associated Clean-up Activities. For the
purpose of flagging, major natural disasters, such as hurricanes and
tornados for which State, local, or Federal relief has been granted,
and clean-up activities associated with these events may be considered
exceptional events.
    c. High Wind Events. High wind events are events that affect
ambient particulate matter concentrations through re-entrainment of
material, i.e., by raising dust. Concentrations of coarse particles,
i.e., PM10-2.5 and PM10 in some locations, are
most likely affected by these types of events, although
PM2.5

standards may be exceeded under such circumstances as well.
    d. Unwanted Fires. Ambient particulate matter concentrations caused
by smoke from wildland fires will be treated as due to natural events
if the fires are determined to be unwanted fires, designated wildland
fire use fires, not designated or managed as prescribed fires, or
requiring appropriate suppression action by a wildland manager.\8\
---------------------------------------------------------------------------

    \8\ It should be noted that this rule does not cover
agricultural burning. To the extent that it is necessary for EPA to
address this issue, we will do so in the future via separate
guidance or rulemaking.
---------------------------------------------------------------------------

    The question of what is a natural versus an anthropogenic fire has
particular significance in considering the impacts of wildland fires on
air quality and how they should be regarded under today's proposed
rule. Federal land managers have given recognition to several different
types of wildland fires, depending on their causal circumstances and
the role that such fires play in the affected ecosystems. ``Wildfires''
are described as unplanned, unwanted wildland fires, and include
unauthorized burns (such as arson or acts of carelessness by campers),
prescribed burns that escape control due to unforeseen circumstances,
or other wildland fires where the primary objective is to suppress the
fire as quickly as possible.
    In contrast, ``wildland fire use'' fires are those which were
ignited naturally or unintentionally (e.g., as the result of lightning)
and are allowed to continue burning without suppression efforts in
locations that have been designated in fire management plans as areas
where fires are necessary and desirable to accomplish specific resource
management objectives. ``Prescribed fires'' are those ignited purposely
to accomplish specific management objectives, and have been subject to
written, approved prescribed fire plans (``Interagency Strategy for
Directives Task Group,'' Memorandum from National Fire and Aviation
Executive Board to Agency Personnel: Bureau of Indian Affairs, Bureau
of Land Management, National Park Service, U.S. Fish and Wildlife
Service, USDA Forest Service, April 18, 2005). Under these
classifications, we believe that wildfires due to whatever causes them
clearly fall within the meaning of ``natural events'' as that term is
used in section 319. Similarly, we believe that wildland fire use fires
qualify as ``natural events'' by virtue of their natural origins.
    Prescribed fires, however, cannot be classified as ``natural,''
given their clearly anthropogenic origins. Nonetheless, we believe that
prescribed fires are not automatically excluded from the definition of
exceptional events. If a prescribed fire meets the statutory criteria
of being ``unlikely to recur at the same location'' or ``not reasonably
controllable or preventable,'' and the measures specified below, it may
qualify as an exceptional event.
    Prescribed fires carried out for resource management objectives are
frequently designed to restore the role of wildland fires as they once
occurred under natural conditions. As such, their expected frequency
can vary widely, depending on the fire regenerative cycle of a
particular landscape or wildland ecosystem. The natural fire cycle can
range from once every year to less frequently than once in 35-60 years.
Thus in many, though not all, cases it may be demonstrated that the
likelihood of recurrence is sufficiently small that these events should
be accorded special consideration under the rule.
    Since a prescribed fire is being deliberately ignited, it does not
qualify as ``natural,'' and one view is that it cannot qualify as ``not
reasonably controllable or preventable.'' However, a different
interpretation of this provision of section 319 examines whether there
are any reasonable alternatives to the use of fire in light of the
needs and objectives to be served by it. For instance, there may be a
sufficient build-up of forest fuels in a particular area that if left
unaddressed would pose an unacceptable risk of catastrophic wildfire,
which result in adverse impacts of much greater magnitude and severity
than would result from the careful use of prescribed fires. A
particular ecosystem may also be highly dependent on a natural fire
cycle to maintain a sustainable natural species composition.
Alternatively, pest or disease outbreaks in an area may be such that
there are no reasonable alternatives to fire. In some cases, other
legal requirements may preclude the use of mechanical fuel reduction
methods such as in designated wilderness or National Parks. Where such
ecological conditions exist, or where mechanical or other treatments
are not reasonably feasible for reasons that include, but are not
limited to, a lack of access or severe topography, we believe that it
would be appropriate to exclude the impacts from well-managed
prescribed fires to address them. Well-managed prescribed fires are
those that consider smoke impacts prior to and during the burn, barring
unforeseen circumstances, and when the prescribed fire is in compliance
with a Smoke Management Plan (SMP).
    The EPA is proposing in this action that States continue to follow
the smoke management provisions described in the ``Interim Air Quality
Policy on Wildland and Prescribed Fires,'' issued May 15, 1998
(Wildland and Prescribed Fire Policy). This policy provides that EPA
will allow exceedances to be discounted that have been flagged by a
State as having been caused by prescribed fires used for purposes of
resource management provided that the State certifies that it has
adopted and is implementing a certified SMP as described in our policy.
Under our proposal, if a State, local, or Tribal air quality agency
does not certify that a basic SMP is being implemented, or that basic
smoke management practices are being employed by burners, EPA would not
exclude data related to exceedances or violations attributed to
prescribed fires managed for resource benefits.
    We request comments on the interpretation of prescribed fire
described above on the proposed requirements for SMPs, and on any
additional criteria or conditions that should be considered in
determining whether and under what circumstances prescribed fires
should be considered to be exceptional events.
    e. Stratospheric Ozone Intrusions. Stratospheric ozone intrusion is
considered to be a natural event. A stratospheric ozone intrusion
occurs when a parcel of air originating in the stratosphere, which is
at an average height of 20 km or 12.4 miles, is re-entrained directly
to the surface of the earth. Stratospheric ozone intrusions are very
infrequent, localized events of short duration. They are typically
associated with strong frontal passages and, thus, may occur primarily
during the spring season.

IV. The Management of Air Quality Data Affected by Exceptional Events

    The EPA is proposing that, in order to exclude air quality data
from consideration for regulatory purposes, States must follow the
procedures, timelines, and other requirements described in this
proposed rule. Specifically, States must clearly identify, or ``flag,''
data they believe to be influenced by such events; they must show that
they have flagged days on which air quality has been ``affected'' by
exceptional events according to EPA criteria; and they must submit
appropriate documentation demonstrating that the exceptional event
caused the exceedance or violation of the NAAQS in question. Each of
these steps is described in detail below.

A. Flagging of Data in the AQS Data Base

    Air quality data are required, pursuant to 40 CFR part 58.35, to be
submitted to EPA by each State on a calendar quarterly basis, with
submissions due not later than 90 days after the end of a quarterly
reporting period. Once air quality data have been submitted to EPA, it
is possible to ``flag'' specific values for various purposes. ``Data
flagging'' refers to the act of making a notation in a designated field
of an electronic data record. The principal purpose of the data
flagging system in the AQS data base is to identify those air quality
measurements for which special attention or handling is warranted.
These include, but are not limited to, those measurements that are
influenced by exceptional events. In the case of exceptional events,
States place the initial flag on the data in the AQS data base.
Following an evaluation of the supporting documentation, EPA will
decide whether to concur with the flag; concurrence will be marked by
the placement of a second flag in the AQS data base by EPA. Once EPA
has concurred on the flag, the data will be excluded from regulatory
decisions such as determinations of attainment or nonattainment.
    While the flagging of data by the State is the first step in an
exceptional events demonstration, it is insufficient by itself to allow
for the exclusion of data. In order to have EPA concur on a flag,
States must meet the additional requirements described below. As
explained, the State has the responsibility to document both the
occurrence of the event and the causal connection to the monitoring
data under consideration. Because the initial step of flagging the data
is a relatively simple one, States may flag many more days than the
number of days for which they ultimately submit documentation to
support exclusion.

B. What Does It Mean for an Event To ``Affect Air Quality''?

    It is important to recognize that any emissions-producing event has
the potential to have some influence on downwind air quality. Indeed,
on any given day, measured air quality at any given location will
reflect the influences of a variety of activities, including both
natural and anthropogenic emissions from both local and remote upwind
sources. The EPA believes that it would be unreasonable to exclude data
affected by an exceptional event simply because of a trivial
contribution of the event to air quality. Furthermore, we also believe
that it would be unreasonable to exclude more significant, but routine
background air quality impacts, as this would disregard an important
part of the public's exposure to air pollution upon which EPA's air
quality standards are based. The effect of such exclusion would be an
inappropriate reduction in the stringency of the NAAQS, rather than
providing specific relief under the circumstances provided in section
319 for which States should not be designated nonattainment or be
required to prepare control strategies.
    Neither section 319 nor its legislative history provides precise
guidance on what should be considered when determining whether an event
``affects air quality'' and thus qualifies to be considered for
exclusion or special treatment. However, section 319(b)(3)(B)(ii) and
(iv) provide that there must be a ``clear causal relationship'' between
a measured exceedance of a standard and the event to show that the
event ``caused a specific air pollution concentration;'' and it must be
shown that the data in question are ``directly due'' to an exceptional
event. Moreover, one of the principles provided by section 319(b)(3)(A)
indicate that the protection of public health is the highest priority.
For these reasons, we are proposing that for an event to qualify as
``exceptional'' for purposes of special regulatory consideration, its
air quality impact must fall both above the level of the applicable
standard (i.e., must be an ``exceedance'' as required by section 319)
and significantly beyond the normal fluctuating range of air quality,
including background air quality concentrations, and should be large
enough so that without it there would have been no exceedance. We next
provide several alternative approaches to determining whether and when
air quality is ``affected by'' exceptional events, and request comment
on which of these approaches is most suitable for demonstrating such
impacts.
1. Option 1: 95th Percentile Criterion
    The first proposed approach is essentially a test for statistical
deviations from the norm. For measurement days on which the event can
be shown to have an air quality impact, the measurement would be
compared to the 95th percentile of measurements typical of days in the
particular calendar quarter that are not influenced by exceptional
events (``non-event days''). The typical days could be based on a 3-5
year period of record which exclude days influenced by exceptional
events. Under this option, only an event whose resulting concentrations
meet or exceed the 95th percentile criterion, along with meeting the
other criteria in this proposed rule would qualify for exclusion from
regulatory consideration.
    In evaluating available air quality data, we have found that by
limiting consideration to those concentrations above the 95th
percentile, only those concentrations that fall approximately two
standard deviations above the mean of concentrations for that quarter
would generally be excluded (See memo from Mark Schmidt, OAQPS, to
docket entitled ``Analysis of Flagged Particulate Matter Data,''
February 10, 2006). Excluding days on which concentrations caused by
exceptional events exceed the 95th percentile threshold employs a
general test of statistical significance and has the effect of ensuring
that such concentrations would clearly fall beyond the range of normal
expectations for air quality during a particular time of year.
    In our analysis of flagged and excluded air quality data for the
period 1999-2004, we found that application of the 95th percentile
criterion would result in the exclusion of approximately 85 percent of
data previously flagged by States and concurred on by EPA. Thus, this
approach would result in a somewhat more rigorous qualification
requirement than is reflected in EPA's past case-by-case approach.
Previously, EPA did not have a concentration threshold or other
quantitative criteria to determine which days would be eligible for
exclusion due to exceptional events. As indicated above, approximately
15 percent of the flags that were concurred on were concentrations that
were not necessarily statistically distinguishable from routine levels.
The 95th percentile approach could also help to eliminate some of the
variability from State to State and Region to Region: as described in
Schmidt (2006), rates of flagging and the severity of pollution on
flagged days have varied significantly among States and regions in the
past. For PM2.5, for example, many States flagged no days
between 1999-2004, while Puerto Rico flagged 15 percent of all of its
PM2.5 data. Also, while most PM2.5 flags during
this period were above the 95th percentile, some States flagged data at
the 75th percentile or lower. (See memo from Mark Schmidt, OAQPS, to
docket entitled ``Analysis of Flagged Particulate Matter Data,''
February 10, 2006.)
2. Option 2: 75th Percentile/95th Percentile Tiered Approach
    Under this approach, we propose to retain flexibility to determine
whether concentrations less than the 95th percentile but above the norm
should

qualify for exclusion as ``affecting air quality.'' In particular,
multiple measurement values over time with relatively small individual
event impacts may collectively affect an annual average concentration
to a significant degree. States may wish to consider whether to exclude
such impacts if the average concentration is close to the level of the
annual NAAQS. Therefore, we are soliciting comment on a second approach
whereby measured values are compared both to the historical 95th
percentile of non-event days and to the 75th percentile of such days.
    Where concentrations caused by an exceptional event meet or exceed
the 95th percentile criterion, they would be conclusively determined to
qualify for exclusion subject to the other requirements of this
proposed rule. Where concentrations caused by an exceptional event do
not meet the 95th percentile criterion, we would provide a further
opportunity for States to make demonstrations which satisfy the other
criteria in this proposed rule, so long as values exceeded the 75th
percentile of non-event days. This approach would provide for a more
flexible approach and would rely on a weight-of-evidence demonstration
that would permit States to make other sorts of showings that the
concentrations caused by the event were in some way unusual or not
representative of normal air quality and thus should not result in
additional regulatory requirements.
    When we applied the 75 percent percentile criterion to our analysis
of flagged and excluded air quality data for the period 1999-2004, we
found that this criterion would make nearly all of the data previously
flagged by States and concurred on by EPA eligible for exclusion. Thus,
we expect this approach would have a result that is roughly consistent
with EPA's past case-by-case approach.
3. Option 3: Case-by-Case Approach Based on Weight of Evidence
    The third option is to permit the more general case-by-case
evaluation, without threshold criteria, that may be guided by the
magnitude of the measured concentration on days affected by exceptional
events relative to historical, seasonally adjusted air quality levels.
This approach is most nearly analogous to our historical treatment of
exceptional events but, in contrast to Options 1 and 2, provides the
least definitive guidance to assist States in their evaluations.
Nevertheless, the case-by-case approach allows for consideration of
days with ambient concentrations which are not necessarily among the
highest concentrations that have been historically observed. In fact,
25 percent of days have concentrations greater than the median value
but less than the 75th percentile. While such days are unlikely to
impact short-term standards, discounting such days can certainly have
an impact on an annual average concentration. In general, however,
demonstration that an event caused a concentration which is essentially
indistinguishable from routine air quality would be very difficult to
document, and this approach may make it difficult for EPA regions to be
consistent when determining whether to concur on a flag.
    We request comment on which of these proposed options should be
included in the final rule, including the appropriateness of proposed
statistical criteria, the period of record on which to base the 95th
and 75th percentile and conclusions about normal air quality
expectations (e.g., 3 years, 5 years, or some longer period of record),
and any other criteria or procedures we should consider adopting along
with one of these options.

C. Use of a ``But For'' Test

    There may be instances in which exceptional events may have a
significant impact on air quality on days when concentrations are
already above the applicable standard in the absence of the influence
of such events. In such cases, it is important to preserve and consider
all valid air quality data influenced by activities which properly fall
within the responsibilities of States to manage for purposes of air
quality attainment and maintenance. For this reason, we are proposing
to require that air quality data may not be excluded except where
States show that exceedances or violations of applicable standards
would not have occurred ``but for'' the influence of exceptional
events. In other words, to the extent it is possible to determine that
the resulting air quality concentrations and appropriate design values
for an area would be above the level of the standards even without the
influence of the exceptional event, the air quality data for the day(s)
in question should not be excluded. However, consideration of the
impacts of exceptional events on air quality values for control
strategy planning purposes may be appropriate, and States are
encouraged to consult with the appropriate EPA regional offices to
further discuss this issue.

D. Schedules and Procedures for Flagging and Requesting Exclusion of
Data

    In establishing procedures and timetables for States to request,
and EPA to grant, exclusion of data affected by exceptional events, we
are guided by two competing considerations: ensuring States have
adequate time and opportunity to compile and evaluate all relevant and
available information in support of such requests; and making
determinations in a timely manner so that all pertinent and valid air
quality data would be appropriately considered in regulatory
determinations. To assist EPA in determining the best approach to
managing the data flagging process and submissions of demonstrations
for the final rule, we are proposing three alternatives for public
review and comment.
1. Option 1: Early Data Flagging and Demonstration Submission
    The first approach would establish a two-step process for
identification of data and submission of demonstrations. This process
provides for the early flagging of data and the notification of the
appropriate EPA Regional Office concerning the State's intention to
seek exclusion of data, followed by a longer timeframe for States to
prepare and submit their demonstrations.
    Under this approach, we would require a State to flag the data that
they believe to be affected by exceptional events at the time of
submission of the air quality data to EPA's AQS data base, in
accordance with the schedule described in 40 CFR part 50.35, which is
generally no later than 90 days after the end of the calendar quarter.
This approach would ensure that the flagging process remains consistent
with the timeline set forth in rules governing data submission
requirements.
    Just as the scope and substance of demonstrations in support of
requests for exclusion will vary depending on facts and circumstances
(see section IV.F. below), so, too, will the time required for such
demonstrations. Where air quality in an area is influenced by a
relatively small set of emission sources with well-defined emission
profiles and limited pollutant species, a demonstration that an air
quality measurement influenced by a particular event merits exclusion
may be relatively simple to make. In other cases, such as where the
number and types of sources contributing to measured air quality
concentrations are extremely complex and varied, making it more
difficult to distinguish between the effects of routine activities and

unusual ones, more time and effort will be needed for a State to
provide an adequate demonstration in support of its request.
    For these reasons, we are proposing under this option to require
States to notify the appropriate EPA Regional Office of their intent to
seek exclusion of data due to exceptional events at the time of
submission of quarterly air quality data to the AQS data base. We are
also proposing to require the State to consult with the EPA Regional
Office as soon as reasonably possible after notification about the
event, its suspected air quality impact, and the demonstration needed
to justify a decision to exclude the data from regulatory
consideration. This is intended to enable the State and EPA to work
together during the process of data analysis and documentation to
ensure that a complete and well-supported demonstration is submitted in
a timely manner.
    With respect to demonstrations in support of requests for exclusion
of data, we are proposing under this option to provide States with more
time to submit the necessary demonstration. We propose that States
submit complete demonstrations to EPA not later than 180 days following
the close of the quarter in which the event occurred. Based on past
experience with exceptional events and associated data analyses, we
believe that this will provide adequate time in most cases for States
to identify, compile, and evaluate all relevant factors pertaining to
an exceptional event and its impacts. However, in special circumstances
where additional time is required to make a complete submission, and
where the outcome of such additional efforts is likely to have a
substantial impact on the demonstration, we are proposing to allow
States to request extensions of up to 90 additional days. We expect
that such extensions under this option would be the exception, rather
than the rule, and that they will be limited to special circumstances
necessitating more complex and sophisticated analyses, such as where
the collection and analysis of species-specific data in urban areas may
be needed in order to characterize and quantify an event's contribution
to air quality at a particular location. Under this option, as well as
the options addressed below, once EPA receives a State's demonstration,
EPA will then have a 30-day period to review the demonstration and
provide a concurrence or nonconcurrence on the flag in the AQS data
base. The EPA expects that, in most cases, a period of 30 days will be
enough time to review and provide a concurrence related to a State's
request to exclude data affected by an exceptional event. However, for
more complex demonstrations, EPA may require more time for its review.
In such cases, EPA may extend the time for its review by not more than
an additional 30 days.
2. Option 2: Early Data Flagging and Delayed Demonstration Submission
    Under this option, we are proposing the same requirements for the
flagging of data and notification of the appropriate EPA Regional
Office as described in Option 1. However, under Option 2, we propose to
allow up to 3 years following the quarter in which the event occurred
for the submission of exceptional events demonstrations. The reason for
providing more time under this option is that for most existing air
quality standards, decisions regarding whether or not an area is
attaining the applicable standard are based on the most recent 3 years
of air quality data. Providing 3 years for submission of demonstrations
would provide States with an opportunity to evaluate whether the
influence of one or more exceptional events will be relevant to
determinations of attainment or nonattainment before undertaking the
effort of preparing and submitting demonstrations.
3. Option 3: Delayed Data Flagging and Demonstration Submission
    Under this option, we are proposing to decouple the process of
flagging and demonstrations from the regular submission of air quality
data to the AQS data base and to require instead that data be flagged
and exceptional events demonstrations be submitted not later than 6
months prior to the date when regulatory decisions using the air
quality data must be made. This option is based on the recognition that
while data flagging itself may not be a particularly burdensome
exercise, it triggers a more extensive process of collection and
analysis of other information to determine and demonstrate whether, in
fact, an exceptional event has occurred which affects air quality data
in a way that justifies exclusion of the data. It may be that although
certain events occurred which do indeed affect air quality in
significant ways, their impact on regulatory decisions may not be known
for a significant period of time, i.e., until a relevant 3-year period
of record is compiled and the need for a regulatory decision is
identified. Thus under this option, it would be less burdensome for the
States and EPA if demonstrations were not required unless and until it
became apparent that potentially affected measurements would be used in
making regulatory findings of attainment or nonattainment (e.g., where
a State with an existing area designated as nonattainment seeks to have
that area redesignated as attainment and the existence of one or more
exceptional events may affect its ability to provide the requisite 3
years of clean air quality data).
    We request comment on which of the above three proposed options EPA
should promulgate and on what, if any, modifications to these options
we should make prior to the final rule.

E. Exclusion of Entire 24-Hour Value as Opposed to a Partial Adjustment
of the 24-Hour Value

    The EPA's historical practice has been to exclude a daily measured
value in its entirety when that value is found to be largely caused by
an exceptional event, and we are proposing to retain this approach in
today's proposed rule. With this approach, a determination is made that
emissions from the event are largely responsible for the resultant
ambient air pollutant concentration. For example, if the observed
concentration is 200 [mu]g/m3 PM2.5 and is
associated with a nearby forest fire, then EPA would concur with the
claim that the event was responsible for the ambient concentration. The
measured value would be excluded in its entirety from the data used to
judge attainment (as per 40 CFR 50, appendix N), although the
measurement day would still count towards meeting minimum data capture
requirements.
    We believe it would be desirable to adjust the daily value to
exclude only those portions of the data that are attributable to the
exceptional event in question, and to retain the remainder of the day's
measurement if appropriate and accurate methods were available to make
such adjustments. For example, if an area affected by a forest fire had
a measured 24-hour PM2.5 concentration of 50 [mu]g/
m3 and the estimated event impact was 30 [mu]g/
m3, then the expected value which would have occurred but
for the event would have been 20 [mu]g/m3. Normal air
quality for this location might be 16 [mu]g/m3 and,
therefore, the ``but-for'' concentration of 20 [mu]g/m3 is
above average. Discounting the entire event day could, therefore,
inappropriately bias a determination of nonattainment with the annual
PM2.5 NAAQS (currently set at 15 [mu]g/m3). We
are currently seeking to develop and evaluate new analytical methods
that would allow us to discount only the portion of the daily value
attributable to the exceptional event. However, at present, we are not
aware of the existence of adequate and universally

applicable techniques that are administratively and technically
feasible and that could support partial adjustment of air quality data
except perhaps in limited cases, such as where the number and type of
pollutant species and contributing sources are relatively less complex
or potentially, when sufficient spatial, temporal, meteorological and
chemical data are available [See memo to docket, Husar et al. 2006,
(http://www.regulations.gov, Epa-HQ-Oar-2003-0061-0733 thru 0733.5)].

When we determine that techniques for adjustment of air quality data
are sufficiently well-demonstrated for use in exceptional events
determinations, we will publish a notice of proposed rulemaking to seek
comment on the appropriateness and scope of such use.

F. What Should States Be Required To Submit in Their Exceptional Events
Demonstrations?

    Section 319 requires that, in order to have a flagged value
excluded from regulatory determinations, a State must make an
affirmative demonstration that an event occurred (as shown by reliable
and accurate data that is promptly produced) and that there is a clear
causal relationship between measured exceedances or violations of a
standard and the exceptional event in question to ``demonstrate that
the exceptional event caused a specific air pollution concentration.''
(42 U.S.C. 7619(b)(3)(B)(ii), (iv)). Section 319 also indicates that
regulations promulgated under the section should provide for criteria
and procedures to exclude air quality monitoring data ``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.''
    Therefore, after flagging data in the AQS data base, States are
expected to develop appropriate documentation to support each
individual flag. As a general matter, we believe that such
demonstrations should include documentation showing that the event in
fact occurred and that emissions related to the event were transported
in the direction of the monitor(s) where measurements were recorded;
the size of the area affected by the transported emissions; the
relationship in time between the event, transport of emissions, and
recorded concentrations; and, as appropriate, pollutant species-
specific information supporting a causal relationship between the event
and the measured concentration. The latter information could be based
on available data provided by routine speciation, monitoring networks,
or from selective laboratory analysis of archived particulate matter
filters for the day thought to be impacted by specific events. In
certain situations, such data might be useful for evaluation of impacts
from exceptional events, e.g., to distinguish between impacts caused by
natural fires versus impacts caused by industrial sources. Depending on
which option is finalized pursuant to section V below, States may also
need to show that appropriate mitigation actions were taken at the time
that the event occurred, or after an event occurred in order to protect
public health.
    The following examples are intended to further illustrate the kinds
of information that States could consider in preparing their
demonstrations:
    1. Information demonstrating the occurrence of the event and its
subsequent transport to the affected monitors. This could include, for
instance, documentation from land owners/managers, satellite-derived
pixels (portions of digital images) indicating the presence of fires;
satellite images of the dispersing smoke and smoke plume transport or
trajectory calculations (calculations to determine the direction of
transport of pollutant emissions from their point of origin) connecting
fires with the receptors.
    2. Identification of the spatial pattern of the affected area (the
size, shape, and area of geographic coverage). This could include, for
instance, the use of satellite or surface measurement data.
    3. Information about temporal patterns (e.g., the time and duration
of an event in relation to measured downwind concentrations, air
quality trends over time and space). This could include, for instance,
observed sequential concentration spikes at multiple locations in a
downwind direction.
    4. Identification of the chemical composition of measured
concentrations. This could include, for instance, organic or crustal
material in excess of typically observed quantities to differentiate
from other high concentration events.
    5. Extremely high wind speeds, or unusual transport conditions
relative to historically typical levels for the season of the year in
which the claimed event occurred.
    This list is not exhaustive and not all of these kinds of
information and/or documentation will need to be provided in every
instance. A particular instance may require more or less documentation,
depending on the particular facts or circumstances in that instance.
The simplest demonstrations could consist of newspaper accounts or
satellite images to demonstrate that an event occurred together with
daily and seasonal average ambient concentrations to demonstrate an
unusually high ambient concentration level which is clearly indicative
of an exceptional impact. Such is the case with events such as volcanic
eruptions and nearby forest fires. In one instance, we determined that
wildfires upwind of the San Diego area caused high concentrations of
particulate matter measured in October 2003 based on the actual
physical damage caused by fire to the ambient monitor. Depending on the
nature of the event, meteorological conditions, severity and spatial
extent of measured ambient concentrations (including relevant chemical
components when available) relative to what typically occurs in the
area, and on emissions of pollutants from the exceptional event which
have similar characteristics to those of other sources in the area,
additional showings could be required on a case-by-case basis. In
particular, we anticipate that significantly more effort will be needed
to establish that an exceptional event caused a particular
concentration in an urban area in which there are numerous and diverse
sources and complex meteorology and topography, and where the emissions
from the event in question may well be similar to those from other
sources contributing to measured concentrations, as compared to an area
that has relatively few sources, simple terrain and less complex
meteorology, and where emissions associated with the event are both
substantially greater than and different in composition from those of
other nearby sources. Because of the variability in the nature of
exceptional events and the resulting demonstration requirements, States
should consult with the appropriate EPA Regional Office early in the
process of preparing their demonstrations.
    We are not proposing to specify what will be required as a minimum
level of documentation in all cases because facts and circumstances
will vary significantly based on, among other things, geography,
meteorology and the relative complexity of source contributions to
measured concentrations in any particular location. However, we request
comment on whether we should adopt a set of minimum demonstration
requirements to ensure a reasonable degree of national consistency in
approaches to demonstrating exceptional events, and if so, what
elements should be included in the demonstration. We believe, however,
that at a minimum, the elements of such a demonstration

should include a showing that an event occurred at a time when
meteorological conditions were conducive to transporting emissions from
the event downwind to the monitor recording a high concentration of one
or more criteria pollutants.

G. Special Considerations Relevant to Proposed Standards for
PM10-2.5

    As noted in EPA's notice of proposed rulemaking reviewing the NAAQS
for particulate matter (71 FR 2620; January 17, 2006), fine particles
(PM2.5) are produced chiefly by combustion processes and by
atmospheric reactions of various gaseous pollutants, whereas thoracic
coarse particles (PM10-2.5) are generally emitted directly
as particles as a result of mechanical processes that crush or grind
larger particles or the resuspension of dusts. Sources of fine
particles include, for example, motor vehicles, power generation,
combustion sources at industrial facilities, and residential fuel
burning. Sources of thoracic coarse particles include, for example,
resuspension of traffic-related emissions such as tire and brake lining
materials, and direct emissions from industrial operations,
construction and demolition activities. Fine particles can remain
suspended in the atmosphere for days to weeks and can be transported
thousands of kilometers, whereas thoracic coarse particles generally
deposit rapidly on the ground or other surfaces and are not readily
transported across urban or broader areas (71 FR 2620, 2625; January
17, 2006).
    Based on preliminary analysis, we generally anticipate that
demonstrations that ambient concentrations of PM10-2.5 have
been affected by exceptional events will involve similar analytical
steps to demonstrations for PM2.5 but will be simpler than
demonstrations for PM2.5.\9\ This conclusion is based on
preliminary evaluation of estimated PM10-2.5 concentrations
derived from historical PM10 and PM2.5 data. We
examined those days on which PM10 exceedances were flagged
as due to exceptional events but where PM2.5 concentrations
were not also flagged, indicating that the event in question was
dominated by coarse particles. The results of this analysis suggest
that exceptional events related to PM10-2.5 are relatively
infrequent, occur predominantly in the western States and are
overwhelmingly high wind events. Thus, with the exception of western
areas, we do not anticipate that exceptional events will be a
predominate factor in decisions made related to attainment or
nonattainment determinations for the proposed PM10-2.5
standards (See memo from Mark Schmidt, OAQPS, to docket entitled
``Analysis of Flagged Particulate Matter Data,'' February 10, 2006).
Moreover, in light of the above analysis and the evidence on which it
is based, we believe that exceptional events demonstrations for
PM10-2.5 will involve relatively straightforward showings
that when high concentrations occurred at the affected monitors,
concentrations at available rural monitors (e.g., IMPROVE network
monitors) were also elevated and that meteorological conditions (i.e.,
wind speed and wind direction) were conducive to transport from upwind
sources of re-entrained coarse particles. It may be beneficial to
examine continuous PM10-2.5 monitoring data as well, as they
may indicate extremely high short-term values (e.g., 1 hour or less)
that heavily influence 24-hour concentrations and are consistent with
extreme high wind events. For instance, when we examined air quality
concentrations recorded in El Paso, Texas during a dust storm that
occurred on April 26-27, 2002 we found two consecutive 24-hour average
concentrations of PM10 (654 [mu]g/m\3\) and PM2.5
(56 [mu]g/m\3\) which were dominated by a peak 1-hour concentration of
2700 [mu]g/m\3\ which occurred in the late evening of April 26-27.
---------------------------------------------------------------------------

    \9\ The demonstrations related to PM10-2.5 are
contingent upon the final outcome related to the rulemaking on the
NAAQS for PM10-2.5.
---------------------------------------------------------------------------

H. Public Availability of Air Quality Data and Demonstrations Related
to Exceptional Events

    Sections 40 CFR parts 58.35 and 58.28 of EPA's air quality
monitoring rules state that all data, flagged or unflagged, should be
available to the public for comparison to the NAAQS to determine if
exceedances have occurred. The EPA is proposing to require that all
relevant flagged data, along with the reasons for the data being
flagged, and a demonstration that the flagged data are caused by
exceptional events be made available by the State for public review and
comment prior to the demonstration being submitted to EPA for a
decision concerning whether to exclude the data from regulatory
consideration. Notice and availability of such data and demonstrations
must be adequate and consistent with States' administrative procedures
governing similar submissions. EPA is not proposing to require that
public hearings be held on exceptional events demonstrations, but
leaves this matter to the States' discretion.

V. Additional Requirements

    Pursuant to section 319, EPA is proposing new regulations to
address exceptional events. Also EPA is proposing one option, and is
taking comments on three alternative options, to address the issue of
whether, and to what extent, States might be required to adopt specific
mitigation plans or measures. Section 319 states that EPA must
promulgate regulations that are consistent with paragraph 3 which
enumerates certain principles and minimum regulatory requirements. The
first part of paragraph 3 states that in promulgating regulations under
section 319, EPA shall follow five principles, including the principle
that each State ``must take necessary measures to safeguard public
health regardless of the source of air pollution.'' Section
319(b)(3)(A). This section does not, however, specify what measures may
be ``necessary'' in this context. In order to address this principle,
EPA is proposing to exclude trivial and more routine background air
quality impacts from qualifying as an exceptional event and is also
proposing a ``but for'' test as a precondition to qualification as an
exceptional event (See: section IV). In addition, EPA is also proposing
one approach and is taking comments on three other alternative options
concerning State actions in anticipation of or in response to
exceptional events. These proposed options range from being very
detailed and more prescriptive to very flexible and less prescriptive.
While EPA does not believe section 319(b)(3)(A) explicitly requires, in
and of itself, that States develop mitigating measures or plans under
options (1), (2), and (3) as discussed below, EPA solicits comment on
whether this subparagraph supports the exertion of other legal
authority to require mitigating actions or plans and solicits comment
on issues regarding its legal authority to require mitigation measures
and plans, and the legal basis for not requiring mitigation measures or
plans. We are also requesting comments on the proposed approach and the
three alternatives, and on any modifications to or combinations of any
of the four approaches.

A. Option 1: Proposed Option: Require Public Notification, Education
and Appropriate and Reasonable Measures

    In cases where exceedances or violations of a NAAQS are caused by
an exceptional event, EPA is proposing that once a State becomes aware
that an exceptional event is occurring, is predicted to occur, or has
occurred, the State must take appropriate action to:

    1. Provide notice to the public of the event. This may include, but
is not limited to, using the media to alert the public of the event.
    2. Provide public education concerning the potential health risks
associated with being exposed to high ambient concentrations of
pollutant(s) related to the event. This may include, but is not limited
to, providing information to sensitive populations related to the
health risks associated with the event.
    3. Take appropriate and reasonable measures to abate or minimize
the exposure of the public to high concentrations of air pollution
associated with the exceptional event. This may include, but is not
limited to, taking reasonable and appropriate actions to implement
control measures on significant contributing anthropogenic sources to
reduce potential exposure of the public to emissions associated with
natural events. For example, in the case of volcanic or seismic
activity, this may include, but is not limited to, providing for prompt
clean up of the ash deposits related to the event to prevent re-
entrainment.
    Under this option, where a State is requesting that air quality
data be excluded as an exceptional event, the State must submit, as
part of its demonstration, the appropriate documentation to show that
the State provided appropriate public notice and public education
concerning the event in question, and that the State took reasonable
measures to abate or minimize the exposure of the public, where
appropriate.
    The concept of having States take steps to reduce emissions, where
appropriate, and to develop mitigation plans to address impacts
associated with exceptional events was first instituted under the
PM10 Natural Events Policy. The mitigation plans required
under the PM10 Natural Events Policy were called Natural
Events Action Plans (NEAPS). In instances where a State requested that
air quality data influenced by a natural event be excluded, the State
was required to develop and implement a NEAP.
    In developing a NEAP, States were expected to: Establish a public
notification and education program related to natural events; minimize
public exposure to high concentrations of pollutants related to natural
events; provide a process for abatement of controllable anthropogenic
sources related to natural events; identify, study, and implement
practical mitigation measures as necessary; and provide for a periodic
re-evaluation of the NEAP every 3-5 years.
    Due to past success with the implementation of NEAPs, EPA is
proposing to base the requirements to mitigate the impact of
exceptional events on the general concepts and elements described above
from the PM10 Natural Events Policy. The EPA is proposing
this approach to provide flexibility to the States to implement those
measures that it considers to be reasonable and appropriate under
particular circumstances to protect public health in the event of an
exceptional event. The EPA believes that this approach allows States to
use their experience in addressing those exceptional events that occur
most frequently in their respective jurisdictions, and in providing
notice to sensitive populations concerning the harmful effects of
prolonged exposure to high concentrations of pollution associated with
various types of exceptional events, yet could be consistent with both
the principles and requirements of section 319. The proposed approach
also allows EPA to fulfill its oversight responsibility, while still
providing flexibility to States to implement reasonable measures to
address the effects of exceptional events on public health. A possible
disadvantage of this option is that it has the potential to result in
inconsistencies in the way that exceptional events are addressed by
States and in the actions that are taken to mitigate public health
impacts associated with exceptional events, although such
inconsistencies exist in any program that allows flexibility of any
kind. We believe that despite this, such flexibility makes for a better
and more efficient program in terms of taking specific mitigation
actions that fit the circumstances of each case.

B. Option 2: The Development of a Mitigation Plan by States Under
Section 110 of the CAA

    Under this option, States would be required to adopt a general
mitigation plan to address exceptional events before the occurrence of
an event as a part of the State's SIP required under section 110(a)(1)
of the CAA. Section 110(a)(1) requires States to adopt and submit to
EPA, within 3 years following the promulgation of a new or revised
NAAQS, a plan which provides for the implementation, maintenance, and
enforcement of the standard in each air quality region within the
State. The EPA believes that section 110(a)(1) of the CAA provides EPA
with the statutory authority to require States to submit plans to
address the mitigation of public health impacts due to exceptional
events that cause exceedances or violations of the NAAQS, because such
plans assist in the maintenance and enforcement of the NAAQS and could
be consistent with both the principles and requirements of section 319.
Under this alternative, States would be required to develop and adopt
the general requirements and procedures necessary for the
implementation of a mitigation plan as a part of its section 110(a)(1)
SIP to address a new or revised NAAQS. As a part of this plan, EPA
would require States to identify the actions the State intends to take
to reduce the impact of exceptional events on public health. Since the
precise nature and cause of exceptional events may not be foreseeable,
in many cases, these requirements would be general, and similar to the
types of actions that States have already identified and adopted in
their section 110 plans intended to address emergency episodes as
required under section 110(g) and 40 CFR part 51.152. Once the general
requirements of the mitigation plan are in place under section 110, the
State would only need to take action on an episodic basis to implement
the requirements of the mitigation plan for the affected area following
the occurrence of an exceptional event.
    The general plan requirements would include provisions for
providing public notification of an event; providing a program to
educate the public on the harmful effects of prolonged exposure to
emissions associated with an exceptional event; and implementing
reasonable measures to mitigate the public health impacts of an
exceptional event (e.g., the implementation of control measures to
abate or minimize the effect of high concentrations of emissions
associated with an exceptional event). In cases where control measures
are required to address the impacts associated with an exceptional
event, the State would implement the required measures on an episodic
basis, meaning in response to a specific event that affects the air
quality of a particular area.
    In cases where anthropogenic sources contribute to emissions
related to a recurring natural event, appropriate control measures
would have to be implemented on all significant contributing
anthropogenic sources related to the event in the affected area.\10\
Natural events, which are

defined as a class of exceptional events under this rule, may recur
frequently in affected areas. Under this option, as well as under
Option 3 below, after a natural event occurs, and it is determined that
anthropogenic sources have significantly contributed to the emissions
associated with that event, EPA is proposing that at a minimum,
Reasonably Available Control Measures (RACM) must be implemented on the
anthropogenic sources that contributed to the emissions associated with
the event. Reasonable Available Control Measures are defined as those
control measures that are considered to be reasonable, and economically
feasible, to implement in an area for a given source type. States
should consult the most recent EPA control guidance for the affected
pollutant to determine what control measures might be considered as
RACM for the affected source types associated with emissions due to a
natural event. This requirement is also consistent with the policy
currently being implemented under the ``PM10 Natural Events
Policy.''
---------------------------------------------------------------------------

    \10\ In the case of the proposed NAAQS for PM10-2.5,
these options would not apply to sources which are proposed to be
excluded from consideration, e.g., agriculture and mining
activities.
---------------------------------------------------------------------------

    Also, EPA requests comments on whether, instead of RACM, the
appropriate level of controls that should be implemented on these
source types is Best Available Control Measures (BACM). Best Available
Control Measures is a term first identified in the CAA under part D,
subpart 4, related to the implementation of the PM10
standard. For PM10, BACM are defined as techniques that
achieve the maximum degree of emissions reductions from a source as
determined on a case-by-case basis, considering both the technological
and economic feasibility of implementing the control measures for the
affected source (59 FR 42010; August 16, 1994). Currently, EPA requires
the implementation of BACM on contributing anthropogenic sources under
the PM10 Natural Events Policy for high wind events. Under
this option, as well as under Option 3 below, the State would also be
required to submit the mitigation plan for the affected area to the
appropriate EPA Regional Office for review and concurrence. Once the
State has received concurrence from the Regional Office on the control
measures identified for the anthropogenic sources contributing to
exceedances associated with natural events, the State would be required
to include the measures as a part of its section 110(a)(1) SIP related
to the mitigation plan for the area. As is the case with the control
plans required for emergency episode plans under section 110(g), the
State will not be required to submit the specific control measures as a
part of the mitigation plan to EPA to be made federally enforceable.
Pursuant to section 107(d)(3)and section 319 (b)(3)(B) of the CAA, it
is EPA's intention to adopt a flexible approach and not redesignate an
area as nonattainment, or seek a SIP call for an area, so long as the
State continues to implement the requirements related to the mitigation
plan for the area, as well as the control measures for significant
contributing anthropogenic sources related to a natural event.
    Where a State provides adequate documentation to show that RACM was
being implemented for the affected sources at the time that the natural
event in question occurred, a State need not implement further control
measures in the area related to the natural event. In cases where RACM
was not implemented for contributing anthropogenic sources at the time
of the natural event, the State would be required to implement RACM as
expeditiously as practicable, but in no case later than 18 months from
the end of the calendar quarter in which the event occurred. The EPA
requests comments on whether this proposed time period is appropriate
for the implementation of RACM for significant contributing
anthropogenic sources under this option or whether another time period
is more appropriate.
    The advantage of this particular option is that all States would
have a general plan in place for how to address exceptional events once
they occur and could take immediate action to protect public health. It
would also allow States to evaluate proactively what actions need to be
taken to address anthropogenic sources related to exceptional events,
and to consider the most efficient and effective ways to educate the
sensitive populations most likely to be harmed should an event occur.
    It is important to note that if we selected Option 3 regarding the
timeline for flagging of data and submission of demonstrations, a
disadvantage would be that flagging and demonstrations could
potentially be delayed significantly past the time when States would be
required to implement RACM under this option for mitigation plans. We
request comment on when RACM should be implemented by States in the
event that we select Flagging and Demonstration Option 3.

C. Option 3: The Development of a Mitigation Plan for Episodic Events

    Under this option, where appropriate, EPA would require a State to
develop and implement a mitigation plan for an area following the
occurrence of an exceptional event. This is in contrast to Option 2
above, which would require each State to adopt a plan under section 110
of the CAA containing the general provisions of a mitigation plan in
advance of the occurrence of any exceptional event. Under this third
option, the mitigation plan would only be developed by the State
following the occurrence of an exceptional event for which a State
requested exclusion of air quality data. The mitigation plan would be
required to address the actions that would be taken by the State
related to future similar events, yet could be consistent with the
principles and requirements of section 319. The mitigation plan under
this option would have the same provisions to plans developed under
Option 2 above, including the requirements to notify the public that an
event is expected to occur, or is occurring, or has occurred, to
provide for public education related to the health effects associated
with the event, and to identify the actions that would be taken by the
State to mitigate the impact of any recurrence of the event on public
health. The mitigation plan must include a detailed description of
planned actions that would be implemented if the event recurs. It would
also provide for an implementation schedule which identifies the
actions that would be taken related to the recurrence of an event, and
it should identify the principal parties that would be responsible for
carrying out the stated actions under the mitigation plan.
    In cases where a State intends to request that EPA exclude data
from regulatory consideration that has been affected by an exceptional
event under this option, the State must submit the plan to EPA for
review and concurrence. However, EPA will not take action to make the
mitigation plan federally enforceable. Under this option States would
develop a mitigation plan for an area where an exceptional event has
caused an exceedance or violation of a NAAQS no later than 18 months
following the end of the calendar quarter in which the event occurred.
The EPA requests comments on whether 18 months is an appropriate time
period for the development and adoption of a mitigation plan under this
option or whether another time period is more appropriate.
    As stated in Option 2 above, in cases where anthropogenic sources
contribute to emissions related to a recurring natural event, RACM must
be implemented for all significant contributing anthropogenic sources.
Where a State provides adequate documentation to show that RACM was
being implemented for the affected

sources in the area at the time that the event occurred, no action
would be required by the State to implement further control measures
related to the event for the affected area. In cases where a
determination is made that RACM was not being implemented for
significant contributing anthropogenic sources at the time of the
event, the State would be required to adopt and implement RACM as
expeditiously as practicable, but in no case later than 3 years
following the end of the calendar quarter in which the event occurred.
The EPA requests comment on the appropriateness of the time period
being proposed for the implementation of control measures related to
significant contributing anthropogenic sources associated with a
recurring natural event under this option.
    An advantage of this alternative is that a State can more carefully
tailor the actions that it will take to mitigate the effect of the
exceptional event based on its prior experience, which will help ensure
protection of public health. However, the disadvantage of this
particular option is that it would apply more specifically to one type
of event, so that if a new or different type of exceptional event
occurred, there would be no provisions in place under the mitigation
plan to address it. Each time a new type of event occurs, the State
would need to submit or revise the plan to address the new event.

D. Option 4: Do Not Require States To Adopt and Implement Specific
Mitigation Plans or Measures Under This Rule

    Under this option, EPA would not require a State to develop and
implement a mitigation plan for exceptional events, or to take specific
mitigation measures as described in options 1-3 in order for EPA to
exclude data from regulatory consideration because it results from an
exceptional event. This approach would allow States to have the maximum
degree of flexibility in determining what actions should be taken to
mitigate the impacts of exceptional events, e.g., public notification,
public education, efforts to reduce exposures, or other necessary
measures to safeguard public health. Thus, States would not be
obligated to take any particular actions to mitigate exposures such as
those in Option 1, to develop and implement a formal mitigation plan as
part of the SIP such as that in proposed Option 2, or to develop a more
formal plan with requirements not a part of the SIP such as that in
proposed Option 3.
    This proposed approach would require a much less formal method for
States to take necessary measures to safeguard public health, yet could
be consistent with both the principles and requirements of section 319.
The statute does not identify specific ways in which EPA must satisfy
its principles and requirements. Moreover, as detailed above, EPA is
proposing to exclude only certain types of exceptional events from
regulatory determinations with respect to the NAAQS. In section IV, EPA
is proposing options for percentile criteria, case-by-case evaluation,
and establishment of a ``but for'' test in order for an event to
qualify as an exceptional event for which data can be excluded with
respect to exceedences or violations of the NAAQS. These requirements,
in and of themselves, may offer appropriate protection of public
health. Under this view, EPA should give States broad flexibility in
determining how best to respond to individual exceptional events. Given
the States' concern with the health of their citizens, and taking into
consideration the other requirements of this rule, in this view States
would have sufficient incentive to take appropriate actions to protect
public health.
    One benefit of this option is that it would allow States to
maintain the maximum degree of flexibility to respond to exceptional
events and to take appropriate actions to protect public health without
unnecessarily limiting their ability to seek exceptional events
treatment for the data. One potential limitation of this proposed
approach is that it might result in inconsistencies among States in
addressing exceptional events and in mitigating the impacts of those
events.
    The EPA requests comments on all options described above.
Additionally, EPA requests comments on specific modifications that
should be made to one or more of the options provided above, or on any
combination of these options.

VI. Special Treatment of Certain Events Under This Rule

    As stated in section III.C., above, this proposed rule applies to
data affected by natural events, which are a subset of exceptional
events, at air quality monitoring sites where it has been determined
that concentrations due to these events have caused or substantially
contributed to exceedances or violations of the NAAQS in an affected
area. This proposed rule applies to several types of natural events,
including volcanic and seismic actives, natural disasters, high wind
events, unwanted fires, and stratospheric ozone intrusions, and to
transported pollution originating from national and international
sources that otherwise meets the criteria and requirements for
exceptional events. Some types of exceptional events have unusual
characteristics which require special consideration in the context of
this proposed rulemaking. We discuss each of these special issues, and
the necessary accommodations, below.

A. Volcanic and Seismic Activities

    Volcanic and seismic activities may affect air quality for an
extended period of time after the initial occurrence of the event in
question. Therefore, EPA believes it is appropriate to consider an
extended timeframe for flagging and exclusion of data associated with
such events. Specifically, EPA is proposing that emissions attributed
to anthropogenic activities that re-entrain volcanic ash and dust from
seismic activity during the first year (12 months) following an event
will be treated as due to the natural event. Based on prior
experiences, and on consultation with States, we believe that 1 year is
an adequate amount of time for cleaning ash deposits from areas where
anthropogenic activities (e.g., vehicle traffic) may cause re-
entrainment and possible exceedances of the particulate matter NAAQS.
After a year, however, exceedances or violations due to re-entrainment
of ash deposits will not be provided special consideration under this
rule. The EPA, however, requests comments on whether another time
period is more appropriate and reasonable to allow for clean up of ash
deposits following volcanic or seismic activity.

B. High Wind Events

    Where high wind events result in exceedances or violations of
PM2.5 standards, we are proposing that they will be treated
as natural events pursuant to this proposed rule if there is a clear
causal relationship demonstrated between the exceedances measured and
the high wind event in question, and if anthropogenic activities which
contribute to PM2.5 emissions in conjunction with the high
wind event are reasonably well controlled.
    For the proposed 24-hour PM10-2.5 standard, we propose
to exclude measured exceedances from consideration if it is
demonstrated that high winds resulted in the transport of airborne
particulate matter in concentrations that caused an exceedance or
violation of the NAAQS.\11\ States would be expected to

control emissions from contributing anthropogenic sources as
appropriate under the definition of the proposed PM10-2.5
indicator.
---------------------------------------------------------------------------

    \11\ As discussed in rules proposed at 71 FR 2665-2668, January
17, 2006, and 71 FR 2710 and 2731, 2736-40, January 17, 2006, where
properly sited monitors show exceedances or violations of proposed
PM10-2.5 standards, it will generally be presumed that
such concentrations are due to emissions of urban origin and
therefore subject to regulations, unless shown to be due to an
exceptional event.
---------------------------------------------------------------------------

C. Stratospheric Ozone Intrusion

    Consideration of stratospheric ozone intrusions applies only to the
8-hour ozone standard. The occurrence of such inversions is extremely
difficult to measure or document given currently measured
meteorological parameters. The infrequence, short duration, and
localized nature of such events makes it difficult to use currently
available, general meteorological data, which are usually collected at
isolated locations like airports, to determine whether a stratospheric
ozone intrusion has occurred. The EPA believes it is important to
differentiate between stratospheric ozone intrusion, which is an
exceptional event for the purpose of flagging data, and other non-
exceptional meteorological events. Although data have been identified
in the past showing the result of stratospheric ozone intrusion, no
standard definition or criteria have been established for concrete
identification. Therefore, EPA's determination of whether a
stratospheric ozone intrusion has occurred is a case-by-case decision
based on reasonable judgment considering the season of the year; time
of day; persistence, duration, type and severity of accompanying
meteorological conditions associated with the ozone measurement in
question; and other data showing that conditions were not conducive to
local high ozone production but for this intrusion.

VII. Treatment of Fireworks Displays

    While we are not including fireworks displays in our proposed rule
governing exceptional events, we are proposing as a policy matter to
address certain displays in a manner similar to exceptional events.
Some national and/or cultural traditions, such as July 4th Independence
Day and Chinese New Year, have long included fireworks displays as
important--indeed, many might assert essential--elements of their
observances. While this issue is not specifically covered in CAA
section 319, EPA believes that Congress did not intend to require EPA
to consider air quality violations associated with such cultural
traditions in regulatory determinations to prohibit these activities.
    We are not aware of any information showing adverse air quality
impacts caused by individual use of fireworks in relatively small
quantities. However, analyses of monitoring data collected on July 4th
and July 5th indicates that large fireworks displays, in combination
with other sources, can in some circumstances be potentially
significant sources of air pollutant emissions. For this reason, States
are encouraged to take reasonable precautions to minimize exposures to
emissions from fireworks displays, as well as to manage associated
activities that may have significant impact in the areas where these
events are held. Such actions may include alerting the public to the
potential for short-term air quality impacts that may result from the
discharge of fireworks at large displays, monitoring prevailing winds,
and locating displays downwind of concentrations of people. States are
encouraged, too, to explore the use of lower-emitting fireworks, such
as those developed for frequent use at amusement parks.
    For these reasons, where States can show that the use of fireworks
displays is integral to significant traditional national, ethnic, or
other cultural events, we are proposing that air quality data
associated with such events could be excluded. We request comments on
alternative approaches to addressing emissions from fireworks at such
events.

VIII. Statutory and Executive Order Reviews

A. Executive Order 12866: Regulatory Planning and Review

    Under Executive Order 12866 (58 FR 51735, October 4, 1993), EPA
must determine whether the regulatory action is ``significant'' and,
therefore, subject to the Office of Management and Budget (OMB) review
and the requirements of the Executive Order. The order defines
``significant regulatory action'' as one that is likely to result in a
rule that may:
    (1) Have an annual effect on the economy of $100 million or more or
adversely affect in a material way the economy, a sector of the
economy, productivity, competition, jobs, the environment, public
health or safety, or State, local, or Tribal governments or
communities;
    (2) Create a serious inconsistency or otherwise interfere with an
action taken or planned by another agency;
    (3) Materially alter the budgetary impact of entitlements, grants,
user fees, or loan programs or the rights and obligations of recipients
thereof; or
    (4) Rraise novel legal or policy issues arising out of legal
mandates, the President's priorities, or the principles set forth in
the Executive Order.
    Pursuant to the terms of Executive Order 12866, it has been
determined that the proposed rule is a ``significant regulatory
action.'' As such, this proposed rule was submitted to OMB for review
under Executive Order 12866.

B. Paperwork Reduction Act

    This action does not impose an information collection burden. The
information being requested under this rule is consistent with current
requirements related to information needed to verify the authenticity
of monitoring data submitted to EPA's AQS data base, and to justify
data that has been flagged as being affected by exceptional or natural
events. The OMB has previously approved the information collection
requirements contained in the existing regulations at 40 CFR part
58.01, subparts A through E, under the provisions of the Paperwork
Reduction Act, 44 U.S.C. 3501 et seq. and assigned OMB control number
2060-0084, EPA ICR number 940.17. A copy of the OMB approved
Information Collection Request (ICR) may be obtained from Susan Auby,
Collection Strategies Division; U.S. Environmental Protection Agency
(2822T); 1200 Pennsylvania Ave., NW., Washington, DC 20460 or by
calling<PHONE_NUMBER>.
    Burden means that total time, effort, or financial resources
expended by persons to generate, maintain, retain, or disclose or
provide information to or for a Federal agency. This includes the time
needed to review instructions; develop, acquire, install, and utilize
technology and systems for the purposes of collecting, validating, and
verifying information, processing and maintaining information, and
disclosing and providing information; adjust the existing ways to
comply with any previously applicable instructions and requirements;
train personnel to be able to respond to a collection of information;
search data sources; complete and review the collection of information;
and transmit or otherwise disclose the information. An Agency may not
conduct or sponsor, and a person is not required to respond to a
collection of information unless it displays a currently valid OMB
control number. The OMB control numbers for EPA's regulations in the
CFR are listed in 40 CFR part 9.

C. Regulatory Flexibility Act

    The Regulatory Flexibility Act (RFA) generally requires an agency
to prepare a regulatory flexibility analysis of any rule subject to
notice and comment rulemaking requirements under the Administrative
Procedures Act (APA) or any other statute unless the EPA certifies that
the rule will not have a significant economic impact on a substantial
number of small entities. Small entities include small businesses,
small organizations, and small governmental jurisdictions. For the
purpose of assessing the impacts of today's proposed rule on small
entities, small entity is defined as: (1) A small business that is a
small industry entity as defined in the U.S. Small Business
Administration (SBA) size standards. (See 13 CFR 121); (2) a small
governmental jurisdiction that is a government of a city, county, town,
school district or special district with a population of less than
50,000; and (3) a small organization that is any not-for-profit
enterprise which is independently owned and operated and is not
dominate in its field.
    Courts have interpreted the RFA to require a regulatory flexibility
analysis only when small entities will be subject to the requirements
of the rule. See, Michigan v. EPA, 213 F.3d 663, 668-69 (D.C. Cir.,
2000), cert. den., 532 U.S. 903 (2001). This rule would not establish
requirements applicable to small entities. Instead, this rule provides
the criteria necessary for State, local, or Tribal air quality agencies
to meet in order to properly flag data as being influenced by an
exceptional or natural event. The rule also provides information
concerning what action should be taken by a State, local, or Tribal air
quality agency to protect public health once EPA has provided a
concurrence on data that has been flagged as being influenced by an
exceptional or natural event. Because affected States would have
discretion to choose the sources that may need to be regulated and the
emissions reductions each selected source would have to achieve using
RACM or BACM related to anthropogenic sources in the area determined to
be influenced by an exceptional or natural event, EPA could not predict
the effect of the rule on small entities.
    After considering the economic impacts of today's proposed rule on
small entities, I certify that this rule will not have a significant
economic impact on a substantial number of small entities.

D. Unfunded Mandates Reform Act

    Title II of the Unfunded Mandates Reform Act of 1995 (UMRA), Public
Law 104-4, establishes requirements for Federal Agencies to assess the
effects of their regulatory actions on State, local and Tribal
governments and the private sector. Under section 202 of the UMRA, EPA
generally must prepare a written statement, including a cost-benefit
analysis, for proposed and final rules with ``Federal mandates'' that
may result in expenditures to State governments, in the aggregate, or
to the private sector, of $100 million or more in any 1 year. Before
promulgating an EPA rule for which a written statement is needed,
section 205 of the UMRA generally requires EPA to identify and consider
a reasonable number of regulatory alternatives and adopt the least
costly, most cost-effective or least burdensome alternative that
achieves the objectives of the rule. The provisions of section 205 do
not apply when they are inconsistent with applicable law. Moreover,
section 205 allows EPA to adopt an alternative other than the least
costly, most cost-effective or least burdensome alternative if the
Administrator publishes with the final rule an explanation of why that
alternative was not adopted. Before EPA establishes any regulatory
requirements that may significantly or uniquely affect small
governments, including Tribal governments, it must have developed under
section 203 of the UMRA a small government agency plan. The plan must
provide for notifying potentially affected small governments to have
meaningful and timely input in the development of EPA regulatory
proposals with significant Federal intergovernmental mandates, and
informing, educating, and advising small government on compliance with
regulatory requirements.
    Today's action does not include a Federal mandate within the
meaning of UMRA that may result in expenditures of $100 million or more
in any 1 year by either State, local, or Tribal governments in the
aggregate or to the private sector, and therefore, is not subject to
the requirements of sections 202 and 205 of the UMRA.
    Inasmuch as this action simply provides the criteria for State,
local, or Tribal air quality agencies to flag data to be discounted for
regulatory purposes that is being influenced by exceptional or natural
events, this proposed Federal action will not impose mandates that will
require expenditures of $100 million or more in the aggregate in any 1
year.

E. Executive Order 13132: Federalism

    Executive Order 13132, entitled ``Federalism'' (64 FR 43255, August
10, 1999), requires EPA to develop an accountable process to ensure
``meaningful and timely input by State and local officials in the
development of regulatory policies that have federalism implications.''
``Policies that have federalism implications'' is defined in the
Executive Order to include regulations that have ``substantial direct
effects on the States, or the relationship between the national
government and the States, or on the distribution of power and
responsibilities among the various levels of government.''
    This proposed rule does not have federalism implications. It will
not have substantial direct effects on the States, on the relationship
between the national government and the States, or on the distribution
of power and responsibilities among the various levels of government,
as specified in Executive Order 13132. The CAA establishes the scheme
whereby States take the lead in developing plans to meet the NAAQS.
This rule will not modify the relationship of the States and EPA for
purposes of developing programs to implement the NAAQS. Thus, Executive
Order 13132 does not apply to this rule.

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

    Executive Order 13175, entitled ``Consultation and Coordination
with Indian Tribal Governments'' (65 FR 67249, November 9, 2000),
requires EPA to develop an accountable process to ensure ``meaningful
and timely input by Tribal officials in the development of regulatory
policies that have Tribal implications.'' This proposed rule does not
have ``Tribal implications'' as specified in Executive Order 13175. The
rule provides information concerning what action should be taken by a
State, local, or Tribal air quality agency implementing relevant air
quality programs to protect public health once EPA has provided a
concurrence on data that has been flagged as being influenced by an
exceptional or natural event. The CAA and the Tribal Authority Rule
(TAR) give Tribes the opportunity to develop and implement CAA
programs, but it leaves to the discretion of the Tribe whether to
develop these programs and which programs, or appropriate elements of a
program, the Tribe will adopt.
    This rule does not have Tribal implications as defined by Executive
Order 13175. It does not have a

substantial direct effect on one or more Indian Tribes, because no
Tribe has implemented an air quality management program related to the
PM NAAQS at this time. Furthermore, this rule does not affect the
relationship or distribution of power and responsibilities between the
Federal government and Indian Tribes. The CAA and the TAR establish the
relationship of the Federal government and Tribes in developing plans
to attain the NAAQS, and this rule does nothing to modify that
relationship. Because this rule does not have Tribal implications,
Executive Order 13175 does not apply.

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

    Executive Order 13045: ``Protection of Children From Environmental
Health and Safety Risks'' (62 FR 19885, April 23, 1997) applies to any
rule that (1) is determined to be ``economically significant'' as
defined under Executive Order 12866, and (2) concerns an environmental
health and safety risk that EPA has reason to believe may have a
disproportionate effect on children. If the regulatory action meets
both criteria, EPA must evaluate the environmental health or safety
effects of the planned rule on children, and explain why the planned
regulation is preferable to other potentially effective and reasonably
feasible alternatives considered by EPA.
    This action is not subject to Executive Order 13045 because it is
not economically significant as defined in Executive Order 12866, and
because EPA does not have reason to believe that the environmental
health risks or safety risks addressed by this rule present a
disproportionate risk or safety risk to children. The rule provides
information concerning what action should be taken by a State, local,
or Tribal air quality agency to protect public health once EPA has
provided a concurrence on data that has been flagged as being
influenced by an exceptional or natural event.

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

    This rule is not a ``significant energy action'' as defined in
Executive Order 13211, ``Actions that Significantly Affect Energy
Supply, Distribution, or Use,'' (66 FR 28355, May 22, 2001) because it
is not likely to have a significant adverse effect on the supply,
distribution, or use of energy. Further, we have concluded that this
rule is not likely to have any adverse energy effects.

I. National Technology Transfer Advancement Act

    Section 12(d) of the National Technology Transfer Advance ment Act
of 1995 (NTTAA), Public Law No. 104-113, section 12(d) (15 U.S.C. 272
note) directs EPA to use voluntary consensus standards (VCS) in its
regulatory activities unless to do so would be inconsistent with
applicable law or otherwise impracticable. Voluntary consensus
standards are technical standards (e.g., materials specifications, test
methods, sampling procedures, and business practices) that are
developed or adopted by VCS bodies. The NTTAA directs EPA to provide
Congress, through OMB, explanations when EPA decides not to use
available and applicable VCS.
    This action does not involve technical standards. Therefore, EPA
did not consider the use of any VCS.

List of Subjects in 40 CFR Parts 50 and 51

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

    Dated: March 1, 2006.
Stephen L. Johnson,
Administrator.

    In consideration of the foregoing, the Environmental Protection
Agency proposes to amend 40 CFR parts 50 and 51 as follows:

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

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

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

    2. Amend Sec.  50.1 to add paragraphs (j), (k), and (l) to read as
follows:

Sec.  50.1  Definitions.

* * * * *
    (j) Exceptional event means an event that affects air quality; is
not reasonably controllable or preventable; is a natural event or an
event caused by human activity that is unlikely to recur at a
particular location; and is determined by the Administrator in
accordance with 40 CFR 50.13 to be an exceptional event; it does not
include stagnation of air masses or meteorological inversions; a
meteorological event involving high temperatures or lack of
precipitation; or air pollution relating to source noncompliance.
    (k) Natural event means an event in which human activity plays
little or no direct causal role.
    (l) 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.
    3. Add Sec.  50.14 to read as follows:

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

    (a) Requirements. (1) A State may request EPA to exclude data
showing exceedances or violations of the national ambient air quality
standards that are directly due to an exceptional event from use in
determinations by demonstrating to EPA's satisfaction that such event
caused a specific air pollution concentration at a particular air
quality monitoring location.
    (2) Demonstrations may include any reliable and accurate data, but
must demonstrate a clear causal relationship between the measured
exceedance or violation of such standards and the event.
    (b) Determinations by EPA. (1) EPA shall exclude data due to such
event from use in determinations where a State demonstrates:
    (i) That an exceptional event caused a specific air pollution
concentration resulting in an exceedance or violation of the national
ambient air quality standards at a particular air quality monitoring
location; and
    (ii) That it has taken appropriate actions to protect public
health.
    (2) [Reserved]
    (c) Schedules and procedures--(1) Public notification. (i) All
States and, where applicable, their political subdivisions must notify
the public promptly whenever an event occurs or is reasonably
anticipated to occur which may result in the exceedance of an
applicable air quality standard.
    (ii) [Reserved]
    OPTION 1 for paragraphs (c)(2) through (c)(4):
    (2) Flagging of data. (i) A State shall notify EPA of its intent to
exclude one or more measured exceedances of an applicable ambient air