Treatment of Data Influenced by Exceptional Events

Federal RegisterOct 3, 2016

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Parts 50 and 51

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

RIN 2060-AS02

Treatment of Data Influenced by Exceptional Events

AGENCY:

Environmental Protection Agency (EPA).

ACTION:

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

SUMMARY:

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

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

which applies the rule revisions to wildfire events that could influence monitored ozone concentrations.

DATES:

This final rule is effective on September 30, 2016.

ADDRESSES:

The EPA established Docket ID No. EPA-HQ-OAR-2013-0572 for this action. All documents in the docket are listed in the

http://www.regulations.gov

Web site. Although listed in the index, some information is not publicly available,

e.g.,

Confidential Business Information or other information whose disclosure is restricted by statute. Certain other material, such as copyrighted material, is not placed on the Internet and will be publicly available only in hard copy. Publicly available docket materials are available electronically in

http://www.regulations.gov

The EPA also established Docket ID No. EPA-HQ-OAR-2015-0229 for the related guidance document titled

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

All documents in the docket are listed in the

http://www.regulations.gov

Web site. Although listed in the index, some information is not publicly available,

e.g.,

http://www.regulations.gov

FOR FURTHER INFORMATION CONTACT:

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

palma.elizabeth@epa.gov

. For general information regarding the

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

please contact Lev Gabrilovich, U.S. EPA, Office of Air Quality Planning and Standards, Air Quality Policy Division, Mail Code C539-04, Research Triangle Park, NC 27711, telephone (919) 541-1496, email at

gabrilovich.lev@epa.gov

SUPPLEMENTARY INFORMATION:

I. General Information

A. Executive Summary

Pursuant to section 319(b) of the CAA, the EPA is taking action to finalize revisions to the Exceptional Events Rule (codified at 40 CFR 50.1, 50.14 and 51.930), which governs the exclusion of these event-affected air quality data. The CAA recognizes that it may not be appropriate to use monitoring data influenced by “exceptional” events collected by the ambient air quality monitoring network when making certain regulatory determinations. When “exceptional” events influence monitoring data and cause exceedances or violations of the NAAQS, air agencies can request the exclusion of event-influenced data, and the EPA can agree to exclude these data, from the data set used for certain regulatory decisions.

This section summarizes the purpose of this regulatory action and its major provisions and provides an overview of the associated guidance. After considering the comments received during the public comment period, we are making several changes to the promulgated rule language and/or the preamble, in which we provide non-binding guidance to assist air agencies in implementing the rule. In accordance with section 553(d)(3) of the Administrative Procedures Act, good cause exists to expedite effectiveness of this final rule, therefore, we are also establishing the effective date of this action to be the date that it is published in the

Federal Register

See

5 U.S.C. 553(d)(3). Good cause exists when urgency of conditions are coupled with demonstrated and unavoidable limitations in time; primary consideration is given to the convenience or necessity of the people affected. In this circumstance, prompt effectiveness of this final rule will allow state governors and tribes, if they wish, to consider the final rule revisions in advance of submitting recommendations for area designations for the 2015 Ozone NAAQS, which are due by October 1, 2016, and which could include the consideration of exceptional events. The

deadline for states and tribes to submit recommendations for area designations for the 2015 Ozone NAAQS is a demonstrated and unavoidable time limitation. Prompt effectiveness of this final rule is in the public interest as it will ensure adequate time for states to develop their exceptional events demonstrations and time for the public to comment on those demonstrations. In addition, typically rules are effective at least 30 days after publication to provide time for affected parties to adjust their behavior and prepare before the final rule takes effect. That circumstance does not apply to this final rule because this rule does not require a behavior change. Rather, this final rule revises and provides additional clarity with respect to a previously existing opportunity.

We are promulgating language to define those regulatory actions that comprise “determinations by the Administrator with respect to exceedances or violations of the [NAAQS].” In doing so, we apply the provisions in CAA section 319(b) to a specific set of regulatory actions (

e.g.,

designations). The final rule language returns to the three core statutory elements and implicit concepts of CAA section 319(b): (1) The event affected air quality in such a way that there exists a clear causal relationship between the specific event and the monitored exceedance or violation, (2) the event was not reasonably controllable or preventable, and (3) the event was caused by human activity that is unlikely to recur at a particular location or was a natural event. We clarify in the preamble the general types of analyses and narrative that the EPA expects to see in demonstrations to address each of these three core statutory elements. We also clarify how to apply these criteria in certain scenarios and to certain event types.

In returning to the first of the three core statutory elements (

i.e.,

the event affected air quality in such a way that there exists a clear causal relationship between the specific event and the monitored exceedance or violation), we are promulgating regulatory text that subsumes the “affects air quality” element into the “clear causal relationship” criterion. We are also removing from the rule language the requirement for air agencies to provide evidence that the event is associated with a measured concentration in excess of “normal historical fluctuations including background” and replacing it with a requirement for a comparison of the event-related concentration to historical concentrations. Additionally, we are removing the 2007 Exceptional Events Rule language commonly referred to as the “but for” criterion and focus instead on the clear causal relationship criterion.

With respect to the “not reasonably controllable or preventable” criterion, the EPA is promulgating a provision that enforceable control measures are “reasonable controls” with respect to all anthropogenic sources that have or may have contributed to event-related emissions if the controls are: (1) Implemented in accordance with an attainment or maintenance state implementation plan (SIP), a federal implementation plan (FIP) or a tribal implementation plan (TIP), (2) if the EPA approved the plan within 5 years of the date of an event, and (3) if the plan addresses the event-related pollutant and all sources necessary to fulfill the requirements of the CAA for the SIP, FIP or TIP.

Also for the “not reasonably controllable or preventable” criterion, the EPA is codifying in regulatory text that air agencies generally have no obligation to specifically address controls if the event was due to emissions originating outside their jurisdictional (

i.e.,

state or tribal) border. Of course, a submission based on emissions originating outside of the submitter's jurisdictional borders must demonstrate that the event also meets the other exceptional events criteria.

If the air agency is required to revise its implementation plan as a result of a SIP Call action pursuant to CAA section 110(k)(5), any deference to the implementation plan's enforceable control measures will be determined on a case-by-case basis.

With respect to the “human activity that is unlikely to recur at a particular location or was a natural event” criterion, we present options in this preamble that air agencies and the EPA can use to determine whether the recurrence frequency of an event is “unlikely to recur at a particular location.” We expand on this concept with regulatory language that defines a specific approach to recurrence frequency applicable to prescribed fire on wildland. We also clarify in regulatory language that natural events can recur, sometimes frequently, without affecting the approvability of a demonstration for the identified natural event and that we consider reasonably controlled anthropogenic emissions sources to play little or no direct role in causing those emissions.

The final rule preamble and rule text clarify that air agencies must address all of the core statutory elements and implicit concepts of CAA section 319(b) within an exceptional events demonstration. To facilitate early communications and coordination regarding the identification, development and review of these demonstrations, we are promulgating a regulatory requirement for an initial notification by the air agency to the EPA of a potential exceptional event for which the agency is considering preparing a demonstration as a preliminary step before submitting a demonstration. We further establish in rule language that the required demonstration elements include a narrative conceptual model, or narrative, describing the event(s) causing the exceedance or violation and a discussion of how emissions from the event(s) led to the exceedance at the affected monitor(s); a demonstration that the event affected air quality in such a way that there exists a clear causal relationship between the specific event and the monitored exceedance or violation supported, in part, by a comparison to historical concentrations; a demonstration that the event was both not reasonably controllable and not reasonably preventable; and a demonstration that the event was a human activity that is unlikely to recur at a particular location or was a natural event. Additionally, the rule revisions require documentation that the air agency conducted a public comment process.

Because affected air agencies have provided feedback regarding the difficulty associated with meeting the regulatory timelines in the 2007 rule associated with data flagging, initial event descriptions and demonstration submittals, the EPA is promulgating revisions that remove specific deadlines that apply in situations other than initial area designations following promulgation of a new or revised NAAQS. Also associated with demonstration timing, the EPA is promulgating a provision to terminate the EPA's obligation to review a demonstration following a 12-month period of inactivity by the air agency. In addition, although we are not promulgating timelines in rule language for the EPA's response to submitted demonstrations, we are identifying in this preamble the following intended response timelines: A formal response to the Initial Notification (

see

Section IV.G.5 of this preamble) within 60 days, initial review of an exceptional events demonstration with regulatory significance within 120 days of receipt (

see

Section IV.G.7 of this preamble), a decision regarding event concurrence/nonconcurrence within 12 months of receipt of a complete demonstration (

see

Section IV.G.7 of this preamble), and a

“deferral letter” within 60 days of receipt of a demonstration that the EPA determined during the Initial Notification process to not to have regulatory significance (

see

Section IV.G.7 of this preamble).

Among the questions stakeholders have raised since promulgation of the 2007 Exceptional Events Rule are those regarding fire-related components that the preamble to the 2007 Exceptional Events Rule discussed, but did not fully define or clarify. This final action promulgates in rule language several fire-related definitions and the conditions under which prescribed fires could qualify as exceptional events, which include the use of smoke management programs (SMP) and the application of basic smoke management practices (BSMP). We also discuss that while exceptional events demonstrations and data exclusions requests must be submitted by the affected state/tribal agency(ies), or with their concurrence, we support and encourage federal land managers (FLMs), other federal agencies and air agencies to work collaboratively to prepare and submit exceptional events demonstrations and data exclusion requests.

In keeping with the EPA's mission to protect public health and after seeking comment on approaches ranging from retaining the existing “mitigation” rule requirements to promulgating new mitigation-related rule components, we are promulgating in regulatory language the requirement to develop mitigation plans in areas with “historically documented” or “known seasonal” exceptional events. This action indicates those areas to which this requirement newly applies and makes clear that the EPA will not concur with certain exceptional events demonstrations if an air agency has not submitted the related required mitigation plan within 2 years of the effective date of this action.

In addition to finalizing revisions to the 2007 Exceptional Events Rule, this action simultaneously announces the availability of a final non-binding guidance document titled

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

(Wildfire Guidance), which applies the Exceptional Events Rule Revisions to wildfire events that may influence ozone levels. The EPA prepared this guidance document to further address specific stakeholder questions regarding the Exceptional Events Rule and further increase the efficiency of rule implementation.

The Wildfire Guidance provides air agencies with information on how to prepare and submit evidence to meet the Exceptional Events Rule requirements for monitored ozone exceedances caused by wildfires. The document includes example analyses, conclusion statements, and technical tools that air agencies can use to provide evidence to satisfy the Exceptional Events Rule criteria. The Wildfire Guidance also identifies wildfire and monitor-based characteristics that might allow for a simpler and less resource-consuming demonstration. The Wildfire Guidance is not an EPA rule, and in specific cases the EPA may depart from the guidance for reasons that the EPA will explain at the time of the action. As noted by commenters, while many of the technical analyses included in the document may also be applied to prescribed fire events, the guidance document does not specify how demonstrations for prescribed fire events can address all promulgated rule requirements. The public comment period for the

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

ran simultaneously with the comment period on the proposed rule revisions and closed on February 3, 2016. The EPA received 31 comments on the draft guidance during the public comment period. The EPA summarizes and discusses these comments in a document that accompanies the final guidance document. Both the public comments received on the draft guidance and the EPA's discussion document are available in the docket at

http://www.regulations.gov

(Docket ID No. EPA-HQ-OAR-2015-0229).

Based on feedback from interested parties on the proposed rule revisions and the draft Wildfire Guidance, we intend to develop supplementary guidance to assist air agencies in addressing the Exceptional Events Rule criteria for prescribed fire on wildland. This guidance will focus on analyses and supporting documentation recommended to show that prescribed fire events on wildland were unlikely to recur at a particular location and were not reasonably controllable or preventable. We intend to post the draft guidance for prescribed fires and instructions for providing public comment on the exceptional events Web site at

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

shortly after finalizing these rule revisions.

Also based on feedback from interested parties, we intend to develop supplementary guidance to describe satisfying the Exceptional Events Rule criteria for stratospheric ozone intrusions. In addition, as we discussed in the proposal and as discussed in more detail in Section IV.C of this preamble, we also intend to develop a supplementary guidance document,

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

to describe the appropriate additional pathways for data exclusion for some “predicted future” monitoring data applications. Once available, the EPA intends to post both draft guidance documents on the exceptional events Web site at

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

B. Entities Affected by This Rule

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

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

In addition to being available in the docket, we will post an electronic copy of this

Federal Register

document and the final guidance at

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

D. Judicial Review

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

E. Organization of this

Federal Register

Document

The information presented in this document is organized as follows:

I. General Information

A. Executive Summary

B. Entities Affected by This Rule

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

D. Judicial Review

E. Organization of this

Federal Register

Document

II. Glossary of Terms and Acronyms

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

IV. Final Rule Revisions

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

1. Summary of Proposal

2. Final Rule

3. Comments and Responses

B. Definition and Scope of an Exceptional Event

1. Summary of Proposal

2. Final Rule

3. Comments and Responses

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

1. Summary of Proposal

2. Final Rule

3. Comments and Responses

D. Definition and Scope of a Natural Event

1. Summary of Proposal

2. Final Rule

3. Comments and Responses

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

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

2. Not Reasonably Controllable or Preventable

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

F. Treatment of Certain Events Under the Exceptional Events Rule

1. Transported Pollution

2. Wildland Fires

3. Stratospheric Ozone Intrusions

4. High Wind Dust Events

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

1. Aggregation of Events

2. Demonstrations With Respect to Multiple NAAQS for the Same Pollutant

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

4. Flagging of Data

5. Initial Notification of Potential Exceptional Event

6. Submission of Demonstrations

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

8. Dispute Resolution Mechanisms

V. Mitigation

A. Summary of Proposal

1. Defining Historically Documented or Known Seasonal Events

2. Mitigation Plan Components

3. Options for Implementing Mitigation Plans

B. Final Rule

1. Defining Historically Documented or Known Seasonal Events

2. Mitigation Plan Components

3. Implementing Mitigation Plans

C. Comments and Responses

VI. Environmental Justice Considerations

VII. Statutory and Executive Order Reviews

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

B. Paperwork Reduction Act (PRA)

C. Regulatory Flexibility Act (RFA)

D. Unfunded Mandates Reform Act (UMRA)

E. Executive Order 13132: Federalism

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

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

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

I. National Technology Transfer and Advancement Act

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

K. Congressional Review Act (CRA)

VIII. Statutory Authority

II. Glossary of Terms and Acronyms

The following are abbreviations of terms used in the preamble.

AQCR Air Quality Control Region

AQS Air Quality System

BACM Best Available Control Measures

BACT Best Available Control Technology

BLM Bureau of Land Management

BMP Best management practice(s)

BSMP Basic smoke management practices

CAA Clean Air Act

CASTNET Clean Air Status and Trends Network

CBI Confidential business information

CBSA Core based statistical area

CFR Code of Federal Regulations

CO Carbon monoxide

EPA Environmental Protection Agency

FIP Federal implementation plan

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

FR Federal Register

LAER Lowest Achievable Emission Rate

μg/m

Micrograms per cubic meter

Methane

Mph Miles per hour

NAAQS National ambient air quality standard or standards

NEAP Natural Events Action Plan

NEI National Emissions Inventory

Ammonia

Nitrogen dioxide

NOAA National Oceanic and Atmospheric Administration

NOV Notice of violation

Nitric oxides

NPRM Notice of proposed rulemaking

NPS National Park Service

NRCS Natural Resources Conservation Service

NRDC Natural Resources Defense Council

NWCG National Wildfire Coordinating Group

NWS National Weather Service

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

OMB Office of Management and Budget

Pb Lead

PM Particulate matter

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

2.5

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

PRA Paperwork Reduction Act

PSD Prevention of significant deterioration

RACM Reasonably available control measures

RACT Reasonably Available Control Technology

RFA Regulatory Flexibility Act

SIP State implementation plan

SMP Smoke management program(s)

Sulfur dioxide

TAR Tribal Authority Rule

TIP Tribal implementation plan

Tpy Tons per year

UMRA Unfunded Mandates Reform Act

USB U.S. background

USDA U.S. Department of Agriculture

VOC Volatile organic compound or compounds

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

The EPA's mission includes preserving and improving, when needed, the quality of our nation's ambient air to protect human health and the environment as provided by the CAA. To accomplish this, the EPA develops the NAAQS for criteria pollutants and oversees the states' programs to improve air quality in areas where the current air quality is not in attainment with the NAAQS and to prevent deterioration in areas where the air quality meets or exceeds the NAAQS. The EPA then evaluates the status of the ambient air as compared to these NAAQS using data collected in the national ambient air quality monitoring network established under the authority of section 319(a) of the CAA.

Congress recognized that it may not be appropriate for the EPA to use certain monitoring data collected by the ambient air quality monitoring network and maintained in the EPA's AQS in certain regulatory determinations. Thus, in 2005, Congress provided the statutory authority for the exclusion of data influenced by “exceptional events” meeting specific criteria by adding section 319(b) to the CAA. To implement this 2005 CAA amendment, the EPA promulgated the 2007 Exceptional Events Rule (72 FR 13560, March 22, 2007).

The 2007 Exceptional Events Rule created a regulatory process codified at 40 CFR parts 50 and 51 (sections 50.1,

50.14 and 51.930). These regulatory sections, which superseded the EPA's previous guidance on handling data influenced by events,

contain definitions, procedural requirements, requirements for air agency demonstrations, criteria for the EPA's approval of the exclusion of event-affected air quality data from the data set used for regulatory decisions and requirements for air agencies

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

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

(i)

Guideline for the Interpretation of Air Quality Standards,

U.S. EPA, OAQPS No. 1.2-008, Revised February 1977. Available from the National Service Center for Environmental Publications through its document search, retrieval and download capabilities at

https://www.epa.gov/nscep.

(ii)

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

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

(iii)

Areas Affected by PM-10 Natural Events

(the PM

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

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

(iv)

Interim Air Quality Policy on Wildland and Prescribed Fires,

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

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

(v)

Guideline on Data Handling Conventions for the PM NAAQS,

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

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

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

exceedance with respect to a national ambient air quality standard

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

2.5

NAAQS of 35 μg/m

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

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

2.5

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

Shortly after promulgation, the Natural Resources Defense Council (NRDC) brought a petition for judicial review challenging certain aspects of the 2007 rule, including the EPA's definition of a natural event and several statements in the preamble concerning the types of events that could qualify as being eligible for exclusion under the rule provisions.

Regarding the definition of a natural event, the D.C. Circuit Court determined that NRDC did not identify its objection during the rulemaking process and, therefore, did not have standing under CAA section 307 to challenge the definition. NRDC also challenged the preamble language addressing high wind events. Because the EPA did not address the subject high wind preamble language in final rule text, the D.C. Circuit Court determined the high wind events section of the 2007 preamble to be a legal nullity.

NRDC

EPA,

559 F.3d 561 (D.C. Cir. 2009).

Air agencies affected by the 2007 rule also raised questions regarding interpretation and implementation. The EPA acknowledges that applying the provisions of the 2007 Exceptional Events Rule has been a challenging process both for the air agencies developing exceptional events demonstrations and for the EPA Regional offices reviewing and acting on these demonstrations. In response to these challenges, in May 2013, after extensive outreach culminating in the EPA issuing a

Federal Register

Notice of Availability

seeking broad public review, the EPA finalized the Interim Exceptional Events Implementation Guidance and made these documents publicly available on the exceptional events Web site at

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

The EPA simultaneously acknowledged the need to consider additional changes through a notice-and-comment rulemaking effort to revise the 2007 Exceptional Events Rule. Informed by feedback received during the development of the Interim Exceptional Events Implementation Guidance

and feedback received during listening sessions and best practice conference calls,

the EPA issued a notice of proposed rulemaking (NPRM) on November 20, 2015 (80 FR 72840) titled “Treatment of Data Influenced by Exceptional Events” (proposed Exceptional Events Rule Revisions) to address certain substantive issues raised by state, local and tribal co-regulators and other stakeholders and to increase the administrative efficiency of the Exceptional Events Rule criteria and process.

77 FR 39959 (July 6, 2012).

The Interim Exceptional Events Implementation Guidance includes: The

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

the

Interim Exceptional Events Rule Frequently Asked Questions

(the Interim Q&A document), and the

Interim Guidance on the Preparation of Demonstrations in Support of Requests to Exclude Ambient Air Quality Data Affected by High Winds under the Exceptional Events Rule

(the Interim High Winds Guidance document).

See

comments in Docket ID No. EPA-HQ-OAR-2011-0887.

The EPA hosted exceptional events listening sessions in August and November of 2013 for interested air agencies, FLMs, other federal agencies, regional planning organizations, non-governmental organizations and other members of the public. The EPA also held conference calls with some air agencies between September 2014 and March 2015 to further discuss exceptional events implementation processes and practices. A summary of these implementation “best practices” is available at

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

Although the EPA has undertaken this notice-and-comment rulemaking effort to provide clarity and increase the administrative efficiency of the Exceptional Events Rule demonstration submittal process, the EPA recognizes that developing some exceptional events demonstrations may still be challenging given the case-by-case nature of each event. For this reason, throughout the preamble to this final action, we provide recommendations for language and analyses to include in demonstration packages (

see,

for example, language in Sections IV.E of this preamble, Technical Criteria for the Exclusion of Data Affected by Events, and IV.F, Treatment of Certain Events Under the Exceptional Events Rule). Additional detail regarding specific recommendations is available in the EPA's guidance documents and on the EPA's exceptional events Web site, which the EPA will update to incorporate the finalized rule changes concurrently with or shortly after promulgating the final rule. The EPA also intends to maintain and update the exceptional events submissions table on its Web site with examples of approved submissions. These examples may help air agencies develop demonstration packages; however, they may not contain the minimum level of data or case-specific analyses necessary for all exceptional events demonstrations of the same event type. The EPA encourages air agencies to consult with their EPA Regional office for further guidance on specific demonstrations.

IV. Final Rule Revisions

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

Rule Revisions. This final action accomplishes the objectives identified in the proposed Exceptional Events Rule Revisions by promulgating rule language accompanied by explanation/interpretation in the preamble and/or presenting non-binding guidance in the preamble.

The public comment period for the proposed revisions to the Exceptional Events Rule closed on February 3, 2016. The EPA received 94 unique, timely comments on the proposed rule revisions. The preamble to this final rule discusses the most significant comments received on the proposal and how the EPA considered them in developing the agency's final revisions to the Exceptional Events Rule. The Response to Comments document that accompanies this final rule provides more detailed responses to comments. The public comments received on the proposal and the EPA's Response to Comments document are available in the docket at

http://www.regulations.gov

(Docket ID No. EPA-HQ-OAR-2013-0572).

As a result of feedback received during the public comment period, we have changed the proposed regulatory text and/or non-binding guidance in the preamble in the following ways:

• Modified the provision for FLMs and other federal agencies to prepare and submit exceptional events demonstrations to include a step for the concurrence of the affected state/tribal air agency(ies);

• Modified the definition of an exceptional event to more clearly address drought conditions;

• Modified the list of regulatory actions included within the scope of the Exceptional Events Rule;

• Revised the provision for reliance on controls in an EPA-approved SIP to satisfy the not reasonably controllable or preventable criterion by also including reliance on controls in FIPs and TIPs;

• Modified the required demonstration elements to support the clear causal relationship criterion by moving the table of analyses from the rule text to the preamble where it will serve as guidance;

• Added regulatory text requiring air agencies, federal land managers and burn managers

to collaborate and document a process for working together to protect public health and manage air quality during the conduct of prescribed fires on wildland. Such discussions must include outreach and education regarding general expectations for the selection and application of appropriate BSMP and goals for advancing strategies and increasing adoption and communication of the benefits of appropriate basic smoke management practices;

Throughout this preamble and the associated final rule text, we use the terminology “burn manager” to mean the party responsible for supervising a prescribed fire from ignition through fire extinguishing and cleanup, or another party in the same organization who represents, supervises or is supervised by said party and can be a communications pathway to and from such person. Different organizations, states, local agencies and tribes may use the terms burn manager, burn boss, fire manager or another similar term to describe the party with this responsibility. Regardless of the terminology, the actions of the party responsible for prescribed fire management must conform to and be consistent with any applicable local, state or federal laws and regulations, where these laws and regulations exist.

• Identified intended timelines for the EPA's response in this preamble; and

• Added required regulatory elements for mitigation plans for areas with known, recurring events.

We discuss all of these changes in more detail in this preamble.

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

1. Summary of Proposal

As noted in the proposal, the Exceptional Events Rule applies to all states, to local air quality agencies to whom a state has delegated relevant responsibilities for air quality management including air quality monitoring and data analysis, and to tribal air quality agencies operating ambient air quality monitors that produce regulatory data. The proposal also included new provisions to allow FLMs and other federal agencies to prepare and submit exceptional events demonstrations and data exclusion requests directly to the EPA. We included these provisions for the following reasons, which we expressed in the proposal. First, the CAA language at section 319(b)(3)(B)(i) provides authority for FLMs to initiate and submit such demonstrations and data exclusion requests in the language that reads, “the occurrence of an exceptional event must be demonstrated by reliable, accurate data that is promptly produced and provided by Federal, State, or local government agencies.” Second, FLMs and other federal agencies may operate regulatory monitors

and submit collected data to the EPA's AQS database,

and emissions from exceptional events could affect these same monitors. Third, allowing FLMs to prepare and submit demonstrations directly to the EPA could expedite the exceptional events demonstration development and submittal process. The EPA solicited comment on our proposal to allow FLMs and other federal agencies to prepare and submit exceptional events demonstrations and data exclusion requests directly to the EPA. In addition, the proposal explained that the final rule might modify the provision that provided for FLMs and other federal agencies preparing and submitting exceptional events demonstrations and data exclusion requests directly to the EPA (

see

80 FR 72848).

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

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

see

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

https://www3.epa.gov/castnet/docs/CASTNET_Plan_2014_Final.pdf,

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

The proposal also reiterated the EPA's interpretation that the Exceptional Events Rule applies to all criteria pollutant NAAQS

based on the language in CAA section 319(b)(3)(B)(iv), which applies to exceedances or violations of “the national ambient air quality standards.” The EPA did not specifically request comment on this statement.

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

), ozone, particle pollution and sulfur dioxide (SO

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

2. Final Rule

The Exceptional Events Rule continues to apply to all state air agencies and to local air quality agencies to which a state has delegated relevant responsibilities for air quality management, including air quality monitoring and data analysis. The Exceptional Events Rule also continues to apply to tribal air quality agencies operating ambient air quality monitors that produce regulatory data. All affected air agencies, including tribal air quality agencies, should use the Initial Notification of Potential Exceptional Event process described in more detail in Section IV.G.5 of this preamble, to discuss with their EPA Regional office the most appropriate approach to implementing the provisions of the Exceptional Events Rule.

After considering the public comments, as explained in subsequent paragraphs and the response to comments below, we are finalizing a modified version of our proposal, under which FLMs and other federal agencies could prepare and submit exceptional events demonstrations and data exclusion requests directly to the EPA if the affected state/tribal air agency(ies) concurs.

Presumably, demonstrations and requests for exclusion prepared and submitted by FLMs or other federal agencies would address prescribed fires or wildfires occurring on federally-owned and managed land that influence concentrations at regulatory monitors either on federally-owned and managed land or at state, local, or tribal regulatory monitors. Although the EPA is deferring the appropriate mechanism for concurrence to the affected state or tribal air agency(ies) in accordance with 40 CFR 50.14(a)(1)(ii)(A)(2), the EPA can envision several acceptable approaches, some of which follow.

We note that any agency, group or individual could submit an exceptional events demonstration. However, the EPA is obligated to consider only those submittals that meet the requirements of this final rule and come from authorized agencies (

i.e.,

all states; local air quality agencies to whom a state has delegated relevant responsibilities for air quality management including air quality monitoring and data analysis; tribal air quality agencies operating ambient air quality monitors that produce regulatory data; and FLMs or other federal agencies to whom the relevant state has granted approval). Further, the EPA cannot take action on material submitted by an unauthorized party.

• An air agency could provide written authorization to the FLMs or other federal agencies owning land or operating air quality monitoring stations to prepare and directly submit exceptional events demonstrations to the EPA. Any such authorization must conform to and be consistent with any applicable state laws and regulations. The written authorization (

i.e.,

letter from the air agency official responsible for preparing demonstrations) would specify the conditions under which the FLM could submit a demonstration directly to the EPA and whether the FLM could initiate the Initial Notification of Potential Exceptional Event (either with or without including the affected air agency(ies) in this process). The affected air agency would submit a copy of the authorization to the reviewing EPA Regional office either in advance of the demonstration submittal and/or with the Initial Notification of Potential Exceptional Event process associated with a specific event or events. An air agency selecting this option would need to provide the submitting FLM or other federal agency with a case-by-case concurrence in accordance with 40 CFR 50.14(a)(1)(ii)(A)(2), which requires that a demonstration-specific concurrence from the air agency accompany each submittal. The FLM would include the concurrence with its submission to the EPA.

• An air agency could agree, on a case-by-case basis, to allow an FLM or other federal agency to develop and submit a complete demonstration for an event or events directly to the EPA. Under this scenario, the air agency could notify the EPA during the Initial Notification of Potential Exceptional Event process that an FLM will submit demonstration(s) for a particular event(s) or particular types of events, specifying the event type(s), pollutant(s) and date(s). An air agency selecting this option would need to provide the submitting FLM or other federal agency with a case-by-case concurrence, in accordance with 40 CFR 50.14(a)(1)(ii)(A)(2), which the FLM would include with its submission to the EPA.

• The air agency could ask the FLM to prepare the agreed-upon demonstration for submittal to the affected air agency. The FLM would then independently prepare the demonstration and submit it to the affected air agency. The air agency, in turn, could submit the demonstration to the EPA with a cover letter indicating that the FLM or federal agency prepared the demonstration, that the affected state/tribal air agency agrees with the content and the affected state/tribal air agency requests that the EPA review and take action on the submitted demonstration.

• Another option might consist of the air agency and the affected FLM collaboratively developing demonstrations for submittal by the affected air agency. In this scenario, the air agency and the FLM would likely agree to a division of responsibilities for specific analyses or sections of a demonstration.

If an air agency agrees that FLMs or other federal agencies may prepare and submit exceptional events demonstrations and data exclusion requests directly to the EPA, then the FLM-prepared demonstrations must meet all of the provisions in the Exceptional Events Rule, including the requirement for a public comment period on a prepared demonstration

and the requirements related to schedules and procedures for demonstration submittal that apply to state agencies that operate the affected monitors. Regardless of the approach selected, the EPA encourages discussions between the FLM and the affected state/tribal air agency(ies) similar to those described in the Initial Notification of Potential Exceptional Event process (

see

Section IV.G.5 of this preamble) to ensure that the FLM and the air agency(ies) share a common understanding regarding the potential event, share relevant information and data, and understand the timeline for flagging data in AQS and submitting the demonstration. A number of areas have established local or regional collaboratives whose goals include improving the health of local ecosystems (

e.g.,

wildlands), increasing community resiliency to wildfire, communicating air quality and public health impacts and communicating the results and benefits of prescribed fire management and implementation programs.

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

See,

for example, the Fire Memorandum of Understanding (MOU) Partnership, consisting of multiple state and federal forestry agencies, prescribed fire councils and conservation agencies, who work collaboratively with air agencies in California to resolve issues related to managed fire and protection of public health. Additional information available at

http://www.sierraforestlegacy.org/CF_ManagingFire/FireMOU.php

and in comment number EPA-HQ-OAR-2013-0572-0138.

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

whether to concur with and forward an exceptional events submittal generated by another agency. For example, if a state does not concur with the local agency's, FLM's, other federal agency's or other entity's exceptional events claim, the state can decide not to forward the submittal to the EPA even if the state has authorized the federal or local government agencies (who are also authorized by the CAA to produce and provide data) to prepare and submit demonstrations directly to the EPA. At the suggestion of several commenters, the EPA is adding regulatory language to 40 CFR 50.14(a)(1)(ii) to clarify this point. Where questions arise, the reviewing EPA Regional office can provide assistance and direction as part of the Initial Notification of Potential Exceptional Event process. In addition to requesting that FLMs, other federal agencies or delegated local agencies prepare or assist in the preparation of demonstration analyses, a state can also request the same of industrial facilities operating regulatory monitors experiencing event-influenced exceedances. The EPA cannot act on demonstrations submitted directly by industrial facilities. The authorizing state is responsible, at its discretion, for submitting demonstrations prepared by industrial entities.

Consistent with our proposal, we are also promulgating regulatory language at 40 CFR 50.14(a)(1)(i) that the Exceptional Events Rule applies to the treatment of data showing exceedances or violations of any criteria pollutant NAAQS. AQS retains the capability for air agencies to flag all criteria pollutant data and for the EPA to concur, as appropriate, on requests for exclusion.

3. Comments and Responses

Although three commenters agreed with the EPA's proposal to allow FLMs and other federal agencies to initiate a request for data exclusion if the FLM either operates a regulatory monitor that has been affected by an exceptional event or manages land on which an exceptional event occurred that influenced a monitored concentration at a regulatory monitor, the large majority of commenters disagreed with this proposed provision. State and local air agencies, as well as several regional planning organizations, commented that it is inappropriate for the EPA to allow agencies that are not directly responsible and accountable for managing and/or assuring air quality to submit exceptional event demonstrations or data exclusion requests. Several commenters noted that FLMs and other federal agencies may have different functions and priorities and that the protection of air quality and public health may not be a primary objective. Some of these same commenters noted that while the proposed rule language at 40 CFR 50.14(a)(l)(ii)(A)(2) allowed another agency to initiate a request “only after discussing such submittal with the State in which the affected monitor is located,” “discussing” does not require “agreement” from the state or a requirement that the FLM incorporate the state's feedback into its submittal. These commenters stated that, under the proposed requirements, an FLM could submit a request to exclude data over the objections of the state with primary responsibility to regulate air quality, which could potentially create legal conflicts between agencies. Another commenter suggested allowing FLMs to submit demonstrations only for regulatory monitors owned by the FLM or located on FLM-managed land rather than for state-owned and operated monitors influenced by an event (

e.g.,

fire) on FLM-managed land. Two states and one industry association commenter suggested following an approach allowing, on a case-by-case basis, FLMs to submit demonstrations and requests for data exclusion if the affected state/tribal air agency(ies) agrees and if the FLM works with the affected state/tribal air agency(ies) through the demonstration development and submittal process.

The EPA continues to believe that allowing FLMs to prepare and submit demonstrations directly to the EPA could expedite the exceptional events demonstration development and submittal process because, in many cases, the lands managed and/or owned by federal entities are not entirely within the jurisdictional boundary of a single state or local government and because federal entities may either initiate prescribed fires or fight wildfires on lands managed and/or owned by federal entities. We also recognize that under the CAA, states, exclusive of tribal lands, are primarily responsible for the administration of air quality management programs within their borders, which includes monitoring and analyzing ambient air quality, submitting monitoring data to the EPA, which are then stored in the EPA's AQS database, and identifying measurements that may warrant special treatment under the Exceptional Events Rule. As commenters have noted, and as the EPA recognizes, FLM submittal of exceptional events demonstrations and air agency objectives for air quality management may conflict. Federal land managers do play an important role in helping states and tribes improve the air quality in those areas that do not meet the NAAQS. The General Conformity Rule requires that federal agencies work with state, tribal and local governments in nonattainment and maintenance areas to ensure that federal actions conform to any applicable SIP, FIP or TIP. However, because states and tribes are ultimately responsible for administering air quality management programs within their borders, which could include addressing air quality and health impacts from wildfire emissions, the EPA is finalizing a modified version of our proposal, under which FLMs and other federal agencies could prepare and submit exceptional events demonstrations and data exclusion requests directly to the EPA with the agreement of the affected state/tribal air agency(ies). We believe that this approach, which requires the agreement of the affected state/tribal air agency(ies), could encompass all of the alternative approaches noted by commenters representing state, local and regional planning organizations. Deferring the approach to achieve agreement to the affected air agencies provides individual air agencies with the flexibility to account for any state/tribal-specific authorities that may limit an agency's ability to regulate certain types of air quality concerns. Fire plays a critical role in restoring resilient ecological conditions in our wildlands. In addition, the increased use of prescribed fire and managed wildfire can reduce the effects of catastrophic wildfire. The EPA strongly encourages collaboration between the FLMs and other federal agencies and the appropriate state/tribal air agency(ies) during the event identification and demonstration development process regardless of who ultimately submits the demonstration.

Also concerning the entities affected by the Exceptional Events Rule, one commenter asked for clarification regarding whether industrial facilities operating regulatory monitors can submit demonstrations directly to the EPA. Other commenters asked that the EPA clarify whether states and tribes can always submit demonstrations for any monitors within their jurisdictional bounds. These commenters also asked whether the EPA would allow and/or evaluate “competing” demonstrations.

The EPA notes in the final rule section of this preamble that while industrial facilities may operate regulatory monitors that experience event-influenced exceedances and, at the request of the state, such facilities may prepare demonstrations for these exceedances, the EPA cannot act on

demonstrations submitted directly by industrial facilities. The CAA language at section 319(b)(3)(B)(i) reads, “the occurrence of an exceptional event must be demonstrated by reliable, accurate data that is promptly produced and provided by Federal, State, or local government agencies.” Additionally, the CAA language at 319(b)(3)(B)(iv) requires that the EPA's implementing regulations provide that “there are criteria and procedures for the Governor of a State to petition the Administration to exclude air quality monitoring data. . . .” Under the CAA, states, exclusive of tribal lands, are primarily responsible for the administration of air quality management programs within their borders. States can delegate relevant responsibilities for air quality management to local agencies, but the CAA does not provide for delegation of these responsibilities to industrial facilities. Where industrial facilities operate regulatory monitors, the state is ultimately responsible for ensuring that collected data are uploaded into AQS and for verifying the accuracy of these data. Thus, the authorizing state, at its discretion, is responsible for submitting any demonstrations prepared by industrial entities. The EPA has also clarified in the preamble that a state (or tribe) can always submit demonstrations for events that meet the requirements of the Exceptional Events Rule for any regulatory monitor within its jurisdictional bounds, including those operated by FLMs, other federal agencies, delegated local agencies, and industrial facilities. We have added regulatory language to 40 CFR 50.14(a)(1)(ii) to clarify this point.

Another commenter noted that CAA section 319(b)(3)(B)(i) provides that “the occurrence of an exceptional event must be demonstrated by reliable, accurate data that is promptly produced and provided by Federal, State, or local government agencies.” The commenter maintains that this provision allows federal, state or local government agencies to produce and provide data, but not to prepare and submit demonstrations.

The EPA agrees that the identified CAA language grants specific authority to state, federal and local government agencies to produce and provide data. The EPA also notes, however, that nothing in the CAA language at 319 explicitly restricts federal and local government agencies from submitting demonstrations if the state agrees. Section 319(b)(3)(B)(iv) of the CAA directs the EPA to develop criteria and procedures for the “Governor of a State to petition the Administrator to exclude air quality monitoring data. . . .” The EPA's implementing regulatory language at 40 CFR 50.14(b)(1) says that the EPA shall exclude data from use in determinations of exceedances and NAAQS violations where a state demonstrates to the EPA's satisfaction that an exceptional event caused a specific air pollution concentration in excess of one or more NAAQS. The language “where a State demonstrates” has historically been interpreted to mean that only states can initiate the exceptional events process and submit demonstrations. A state may delegate the authority for preparing and submitting demonstrations to local government agencies that are authorized by the CAA to produce and provide data. In this action, the EPA is promulgating regulatory language that authorizes federal agencies to prepare and submit demonstrations if the affected state concurs, on a case-by-case basis, on the preparation and submission of demonstrations by those federal agencies. Submissions by delegated local agencies and/or state-concurred demonstrations by federal agencies have the effect of a state “demonstration.” Additionally, the state maintains the ultimate responsibility for submitting exceptional events demonstrations for events influencing concentrations at any regulatory monitor within its jurisdictional bounds.

Two tribal commenters asked the EPA to clarify how the provisions in the Exceptional Events Rule apply to tribes. One of these commenters asked that this clarification include regulatory text to define “state” and “tribe.” The EPA is not adding regulatory text to define “state” and “tribe,” but instead intends to apply the definitions set forth in the Tribal Authority Rule (TAR) at 40 CFR 49.2. At 40 CFR 49.2(c), an Indian tribe or tribe is defined as “any Indian tribe, band, nation, or other organized group or community, including any Alaska Native village, which is federally recognized as eligible for the special programs and services provided by the United States to Indians because of their status as Indians.” Section 40 CFR 49.2(e) defines a state as “a State, the District of Columbia, the Commonwealth of Puerto Rico, the Virgin Islands, Guam, and American Samoa and includes the Commonwealth of the Northern Mariana Islands.”

We further clarify the applicability to tribes by reiterating the language that appears in Section IV.A.1 of this preamble, which states that the Exceptional Events Rule applies to all states; to local air quality agencies to whom a state has delegated relevant responsibilities for air quality management including air quality monitoring and data analysis; and to tribal air quality agencies operating ambient air quality monitors that produce regulatory data. Throughout the preamble and regulatory language associated with this final action, we use the terminology “state,” “tribe” and “air agency” somewhat interchangeably. Footnote 3 in this document clarifies that references to “air agencies” are meant to include state, local and tribal air agencies responsible for implementing the Exceptional Events Rule. The regulatory text in the 2007 Exceptional Events Rule often uses “State” to apply to “air agencies.” To be an affected entity for purposes of this rule, the air agency must first operate one or more ambient air quality monitors that produce regulatory data. The provisions of this rule apply uniformly to state and tribal air agencies (and to authorized federal and local agencies) that meet this condition. Tribal air quality agencies that operate air quality monitoring networks that produce regulatory data that are affected by emissions from exceptional events should consult with the EPA Regional office prior to addressing the procedures and requirements associated with excluding data that have been influenced by exceptional events. As we have in the past, the EPA will continue to work with tribes in implementing the provisions of the Exceptional Events Rule, including these rule revisions.

We neither solicited nor received comment regarding applying the provisions of the Exceptional Events Rule to the treatment of data showing exceedances or violations of any criteria pollutant NAAQS and we are making no changes to the rule with respect to this issue.

B. Definition and Scope of an Exceptional Event

1. Summary of Proposal

The EPA proposed and solicited comment on the following generally applicable changes to the 2007 Exceptional Events Rule with respect to clarifying what constitutes an exceptional event:

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

• Removing the “but for” element.

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

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

• Removing the requirement to provide evidence that the event is associated with a measured concentration in excess of “normal historical fluctuations including background” and replacing it with a requirement for a comparison of the event-related concentration to historical concentrations.

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

With respect to revising the definition of an exceptional event by including the combined effects of an event and the resulting emissions, the proposal noted that a physical event may or may not generate emissions and these emissions may or may not reach a regulatory monitor and result in an exceedance or violation of a NAAQS. Each of these components (

i.e.,

a physical event that generates emissions, transport of event-generated pollution to a monitor, and an exceedance or violation at a regulatory monitor) is necessary for an event to qualify as an exceptional event. The EPA would not consider the physical event (

e.g.,

a high wind or the wildfire) to be an exceptional event unless the resulting event-generated pollution (

e.g.,

particulate matter (PM) or ozone) reached and caused an exceedance or violation at a monitoring location or locations.

The EPA elaborated on this concept by providing several examples, one of which was drought. The proposal stated that while the CAA definition of an exceptional event excludes “a meteorological event involving high temperatures or lack of precipitation,” the EPA recognizes that high temperatures and drought conditions can contribute to exceedances and violations caused by other exceptional events, such as high wind dust events. The proposal further noted that if an air agency submits evidence showing that a severe drought that resulted in arid conditions (

e.g.,

lower than typical soil moisture content, decreased vegetation) was combined with an event (

e.g.,

a high wind event) that falls within the CAA definition of an exceptional event and meets all of the requirements, provisions and criteria in the Exceptional Events Rule, then these data could be considered eligible for exclusion under the provisions of the Exceptional Events Rule. The proposal also stated that high temperatures, stagnations and inversions alone would not be eligible for exclusion under the Exceptional Events Rule by the very clear provisions of the CAA. The proposal stated the EPA's belief that Congress intended air agencies to compensate for the effects of high temperature, stagnation and inversions through the development of SIPs.

In our November 2015 action, the EPA proposed to rely more directly upon the statutory requirement at CAA section 319(b)(3)(B)(ii) by removing the regulatory requirement at 40 CFR 50.14(c)(3)(iv)(D) that “there would have been no exceedance or violation but for the event” (

i.e.,

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

and the requirement that there be “criteria and procedures for the Governor of a State to petition the Administrator to exclude. . .data that is

directly due

to the exceptional events.”

Air agencies and the EPA have, in some cases, historically interpreted the “but for” criterion as implying the need for a strict quantitative analysis of the estimated air quality impact from the event. To clarify the intended approach, the EPA proposed removing the “but for” regulatory language and focusing on the “clear causal relationship” statutory criterion applied to the specific case, using a weight of evidence approach.

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

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

The proposal also modified the regulatory language in 40 CFR 50.14(c)(3)(iv) to more clearly indicate, consistent with the CAA directive, the requirement to “demonstrate” versus to merely “provide evidence” that a clear causal relationship must exist between the specific event and the monitored exceedance. Also consistent with Congressional intent and air agencies' and the EPA's experience in implementing the 2007 Exceptional Events Rule, the EPA proposed to integrate the phrase “affected air quality” into the clear causal relationship criterion. The proposal explained that separately requiring an air agency to provide evidence to support a conclusion that an event “affects air quality” is unnecessary in light of a mandatory clear causal relationship showing. The proposal expressed that if an air agency demonstrates that an event has a clear causal relationship to an exceedance or violation of a NAAQS, then the event has certainly affected air quality.

Finally, the EPA proposed to remove the requirement for air agencies to provide evidence that the event is associated with a measured concentration in excess of “normal historical fluctuations including background” and replace it with a requirement to compare the event-influenced concentration to historical concentrations. The proposal clarified that an air agency does not need to prove a specific “in excess of” fact in developing these comparisons to historical concentrations. The EPA proposed these comparisons to support the clear causal relationship criterion.

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

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

• The event was not reasonably controllable or preventable, and

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

We proposed to include these core statutory elements in the revised regulatory definition of an exceptional event.

2. Final Rule

As proposed, and as supported by numerous commenters, we are finalizing and incorporating into the regulatory definition of an exceptional event the following three core statutory elements of CAA section 319(b) that air agencies must meet when requesting that the EPA exclude event-related concentrations from regulatory determinations:

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

• The event was not reasonably controllable or preventable, and

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

This section of the final rule preamble focuses on the definition of an

exceptional event particularly as it incorporates these three elements. We discuss additional detail surrounding the individual criteria (

i.e.,

clear causal relationship, not reasonably controllable or preventable and human activity/natural event) in Section IV.E of this preamble, Technical Criteria for the Exclusion of Data Affected by Events.

While we are incorporating the previously identified elements into the definition of an exceptional event, after considering the public comments, as discussed more fully in the following paragraphs, we are finalizing the following slightly modified version of our proposed definition of an exceptional event:

Exceptional event

means an event(s) and its resulting emissions that affect air quality in such a way that there exists a clear causal relationship between the specific event(s) and the monitored exceedance(s) or violation(s), is not reasonably controllable or preventable, is an event(s) caused by human activity that is unlikely to recur at a particular location or a natural event(s), and is determined by the Administrator in accordance with 40 CFR 50.14 to be an exceptional event. It does not include air pollution relating to source noncompliance. Stagnation of air masses and meteorological inversions do not directly cause pollutant emissions and are not exceptional events. Meteorological events involving high temperatures or lack of precipitation (

i.e.,

severe, extreme or exceptional drought) also do not directly cause pollutant emissions and are not considered exceptional events. However, events involving high temperatures or lack of precipitation may promote occurrences of particular types of exceptional events, such as wildfires or high wind events, which do directly cause emissions. We presented this concept in the proposal (

see

80 FR 72848), and the EPA is codifying it in the final rule to prevent confusion, as explained below.

After considering the public comments received, as discussed as follows, we have included in the revised regulatory definition the concept of “event” or “events” to convey that one or more events and their resulting emissions could be eligible for consideration in the aggregate under the provisions in 40 CFR 50.14. We have also revised the definitional language to “monitored exceedance(s) or violation(s)” to indicate that a single event can cause multiple NAAQS exceedances or violations either occurring on the same day at multiple monitors or occurring at one or more monitors on multiple days. The revised definition also clarifies, at the suggestion of a commenter, our position with respect to “meteorological events involving high temperatures or lack of precipitation” (

i.e.,

severe, extreme or exceptional drought). We include the qualifiers “severe, extreme or exceptional drought” to distinguish drought categories from abnormally dry conditions. In using this language, we incorporate by reference the conditions described in the U.S. Drought Monitor available at

http://droughtmonitor.unl.edu/

and produced through a partnership between the National Drought Mitigation Center at the University of Nebraska-Lincoln, the United States Department of Agriculture (USDA) and the National Oceanic and Atmospheric Administration (NOAA).

3. Comments and Responses

In considering the three core statutory elements of CAA section 319(b), we note that both the not reasonably controllable or preventable criterion and the human activity/natural event criterion are from the statutory language defining the term “exceptional event” at CAA section 319(b)(1)(A). The criterion that the event affected air quality in such a way that there exists a clear causal relationship between the specific event and the monitored exceedance or violation combines the statutory “affects air quality” definitional element at CAA section 319(b)(1)(A) with the “clear causal relationship” statutory requirement at CAA section 319(b)(3)(B) and removes the regulatory-only “but for” language. Because this section of the final rule preamble focuses on the definition of an exceptional event particularly as it incorporates the statutory elements, we address comments related to the statutory elements here and discuss the application of each of these elements in Section IV.E of this preamble.

Numerous commenters supported, and one commenter representing several environmental groups opposed, the EPA's incorporating the “affects air quality” criterion into the clear causal relationship element. Commenters supporting this approach agreed with the EPA's position that if an air agency demonstrates that an event has a clear causal relationship to an exceedance or violation of a NAAQS, then the event has certainly affected air quality and that a submitting air agency does not need to address “affects air quality” as a distinct component. The commenter opposing this approach noted that the EPA cannot escape the plain language of the CAA that “affects air quality” and “clear causal relationship” are two requirements and must be addressed individually. The EPA does not disagree that in the definition of exceptional event, the CAA language at section 319(b)(1)(A)(i) specifically identifies “affects air quality” as a defining term. CAA section 319 does not, however, provide any indication regarding how an air agency should demonstrate that an event “affects air quality.” Rather, the requirements set forth at CAA section 319(b)(3)(B) indicate that the EPA's implementing regulations shall provide that (i) the occurrence of an exceptional event must be demonstrated by reliable, accurate data that are promptly produced and provided by federal, state or local government agencies; (ii) a clear causal relationship must exist between the measured exceedances of a NAAQS and the exceptional event to demonstrate that the exceptional event caused a specific air pollution concentration at a particular air quality monitoring location; (iii) there is a public process for determining whether an event is exceptional; and (iv) there are criteria and procedures for the Governor of a state to petition the Administrator to exclude air quality monitoring data that are directly due to exceptional events from use in determinations by the Administrator with respect to exceedances or violations of the NAAQS. In subsuming the “affects air quality” element into the “clear causal relationship” criterion we are simply defining the approach by which an air agency must show that the event affected air quality.

Similarly, the large majority of commenters supported, and three commenters representing environmental groups opposed, the EPA's proposal to remove the “but for” criterion. The commenters opposing the removal of the “but for” criterion explain that the EPA correctly acknowledged in the 2007 rule that the “but for” criterion was derived from the following two statutory requirements: (1) CAA section 319(b)(3)(B)(ii), which requires “a clear causal relationship . . . between the measured exceedances . . . and the exceptional event to demonstrate that the exceptional event caused a specific air pollution concentration at a particular air quality monitoring location” and (2) CAA section 319(b)(3)(B)(iv), which requires that the EPA develop “criteria and procedures for the Governor of a State to petition the Administrator to exclude . . . data that is

directly due

to the exceptional events.” (Emphasis added.) The commenters argue that the EPA's proposal to rely more directly upon the “clear causal relationship” statutory

element effectively ignores the statutory requirement that excluded data be “. . .

directly due

to the exceptional events.” The EPA disagrees with the commenters on this point. While we are finalizing our proposal to remove the “but for” regulatory requirement, we are retaining the “direct causal” statutory language in the regulatory definition of exceptional event. This revised regulatory language, along with our provided example analyses in this preamble (

see

Section IV.E.3 of this preamble) and in our associated guidance documents, more clearly conveys the strength and robustness of our intended weight of evidence approach

and removes some of the challenges associated with implementing a strict “but for” demonstration.

Further, the “directly due” concept is represented through the totality of the requirements in the revisions to the Exceptional Events Rule that we are promulgating, including that a demonstration show a “clear causal relationship” between “an event(s) and its resulting emissions” and “the monitored exceedance(s) or violation(s).”

As we indicated in our November 2015 proposal and in the preamble to the 2007 Exceptional Events Rule, an air agency's “but for” analysis does not necessarily need to be precise. Rather, we indicated that the EPA would use a holistic “weight of evidence” approach in analyzing submitted demonstration packages. The 2007 preamble further explained that a “weight of evidence demonstration can present a range of possible concentrations, which is not as technically demanding as justifying a specific adjustment to a measured value.” (

See

72 FR 13570, March 22, 2007).

Since promulgation of the 2007 rule, the “but for” criterion has often been interpreted as implying the need for a strict quantitative analysis to show a single value, or at least an explicitly bounded plausible range, of the estimated air quality impact from the event. As a result, some air agencies began using burdensome approaches to provide quantitative analyses in their exceptional events demonstrations to show that the event in question was a “but for” cause of a NAAQS exceedance or violation in the sense that without the event, the exceedance or violation would not have occurred. In many cases, the “but for” role of a single source or event is difficult to determine with certainty and it is more often the case that the impact of emissions from events and other sources cannot be separately quantified and distinguished.

Part of promulgating rule text that is consistent with the core statutory element that “the event affected air quality in such a way that there exists a clear causal relationship between the specific event and the monitored exceedance or violation” involves removing the regulatory requirement in 40 CFR 50.14(c)(3)(iv)(C) that a state must submit evidence that the event is associated with a measured concentration in excess of normal historical fluctuations, including background. We are finalizing our proposal to remove this language and replace it with regulatory text requiring a comparison of the event-influenced concentration to historical concentrations. We discuss comments associated with this revision in Section IV.E.3.c of this preamble.

Multiple commenters supported the EPA's proposal to revise the definition of an exceptional event to include the event and resulting emissions. We have also incorporated the suggestion of one commenter to indicate in regulatory text, through the plural word “events,” that an aggregation of events and their resulting emissions could be eligible for consideration under the provisions in 40 CFR 50.14. We discuss the aggregation of events in more detail in Section IV.G.1 of this preamble. We believe that this concept also applies to exceedances and violations, so we extended the use of plural terminology to this part of the exceptional events definition to more clearly acknowledge that an event may cause multiple exceedances (

e.g.,

exceedances at multiple monitors or multiple exceedances at a single monitor) or violations.

Regarding exceedances and violations, one commenter asked the EPA to clarify whether values that are not themselves exceedances or violations, but raise the design value such that the design value exceeds the NAAQS can be considered as exceptional events. The EPA recognizes that events can make an air concentration significantly higher than it would have been in the absence of the event contribution and elevate the 3-year design value for a NAAQS pollutant. However, the concentration values used in calculating a violating 3-year design value could be considered for exclusion under the Exceptional Events Rule only if the concentration itself is an exceedance or results in a violating design value. If the elevated concentration is not itself an exceedance nor does it result in a violating design value, then the value in question could not be considered as an exceptional event. As we explained in the proposal and restate here, while not an exceptional event, retaining such data in the calculation of a design value can elevate the design value and, for a nonattainment area seeking the EPA's approval of an attainment demonstration, make it seem that the area needs more emissions reduction to attain the NAAQS than is actually the case. Because these data are not exceptional events, we do not address exclusion under this rule. We do, however, discuss this scenario in more detail in Section IV.C of this preamble.

Another commenter suggested that, for regulatory clarity, we incorporate our interpretation of “meteorological events involving high temperatures or lack of precipitation” (

i.e.,

drought) into regulatory text. We agree with the commenter and have clarified, through the regulatory definition of an exceptional event, the position that we expressed in the proposal preamble, which is that drought alone does not create emissions and therefore does not meet the definition of an exceptional event. Rather, drought can result in arid conditions that can combine with or exacerbate the effects of events that meet the requirements, provisions and criteria of the Exceptional Events Rule.

Because there may be many definitions of drought, we also clarify that we are referring to “severe, extreme or exceptional drought” as defined by the U.S. Drought Monitor. We are not including other drought categories in this discussion, nor would other drought categories alone be considered exceptional events.

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

Also related to the definition of an exceptional event, one commenter asked the EPA to include within the definition of an event both short-term and long-term contributors to elevated pollutant concentrations. The commenter further asked the EPA to address the applicability of the Exceptional Events Rule to “background” ozone and background pollutant concentrations in general. The EPA does not agree with the commenter's suggestion to add the language or concept of “short-term and long-term contributors” to the regulatory definition of an exceptional event. The EPA believes that the definition that we are promulgating could include both short- and long-term contributors provided the contributors meet the operative provisions in the rule. The EPA will review each request under the Exceptional Events Rule on a case-by-case basis using a weight of evidence approach.

With respect to addressing rule applicability to “background” ozone, the EPA refers to the recent

Implementation of the 2015 Primary Ozone NAAQS: Issues Associated with Background Ozone White Paper for Discussion.

As defined in this white paper, U.S. background (USB) ozone is

any ozone formed from sources or processes

other than

U.S. manmade emissions of nitrogen oxides (NO

), volatile organic compounds (VOC), methane (CH4), and CO.

USB ozone does not include intrastate or interstate transport of manmade ozone or ozone precursors. While some sources that contribute to USB (

e.g.,

wildfires, stratospheric intrusions) may be eligible for treatment as exceptional events, other sources of USB would not meet the Exceptional Events Rule criteria. For example, routine or long-term international manmade emissions are not exceptional events because they are caused by human activity that is

likely to recur

at a given location; likewise, routine biogenic VOC emissions are not exceptional events because they are not deviations from normal or expected conditions. Thus despite being natural, they are not “events.” The EPA provides additional information regarding the treatment of certain events under the Exceptional Events Rule in Section IV.F of this preamble.

Implementation of the 2015 Primary Ozone NAAQS: Issues Associated with Background Ozone White Paper for Discussion,

U.S. EPA, December 2015. Available at

https://www.epa.gov/sites/production/files/2016-03/documents/whitepaper-bgo3-final.pdf

80 FR 65292 (October 26, 2015).

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

1. Summary of Proposal

In our November 2015 document, the EPA proposed in regulatory language to interpret the CAA section 319(b) phrase “determinations by the Administrator with respect to exceedances or violations of national ambient air quality standards” to encompass determinations of current

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

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

The proposal noted that when one of these determinations is based on a combination of monitoring data and air quality modeling, the criterion requiring that there be a clear causal relationship between the event and a NAAQS exceedance or violation will apply to the combined estimate of air pollution levels rather than on the directly monitored background air quality data. That is, the event would not be required to have caused an actual exceedance or violation at the background ambient monitoring site, but rather to have made the critical difference in the combined estimate of air pollution levels (background plus source impact) resulting in a NAAQS exceedance or violation, because the event increased the background levels that are added to the air quality modeling output.

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

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

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

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

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

In proposing this language, the EPA effectively applied the exceptional events process to these related types of determinations and across the NAAQS, which we believe is an appropriate interpretation of the CAA 319(b) phrase “determinations by the Administrator with respect to exceedances or violations of national ambient air quality standards.” For the identified types of determinations, the EPA proposed to exclude event-affected data only if an air agency satisfies the procedural (

e.g.,

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

i.e.,

clear causal relationship, not reasonably controllable or preventable, and human activity not likely to recur or natural event) requirements of the exceptional events process. The proposal also repeated the EPA's previous position that once data are excluded under the Exceptional Events Rule, these same data also should be excluded from (i) design value estimates and AQS user reports (unless the AQS user specifically indicates that they should be included), (ii) selecting appropriate background concentrations for prevention of significant deterioration (PSD) air quality analyses and transportation conformity hot spot analyses, and (iii) selecting appropriate ambient data for projecting future year concentrations as part of a modeled attainment demonstration.

See

Question 14a in the

Interim Exceptional Events Rule Frequently Asked Questions.

U.S. EPA. May 2013. Available at

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

The proposal also noted that while data exclusion associated with the five actions in the previously noted bulleted list

must

follow the provisions in the Exceptional Events Rule, there are other actions for which it may be appropriate to exclude data using mechanisms other than the Exceptional Events Rule. The proposal differentiated between these five actions and other actions based on “past” versus “predicted” exceedances and/or violations. The proposal explained that the five identified actions involve determinations of whether a NAAQS exceedance or violation occurred at an ambient monitoring site at a particular time in the past. We characterized these exceedances or violations as occurring in the “past” because the process of determining whether an actual exceedance or violation occurred involves reviewing the ambient air monitoring data collected at monitoring sites over some historical timeframe (

e.g.,

the data have already been collected at the monitors, verified for quality assurance purposes, submitted to AQS, and used in various regulatory calculations). In short, the collected monitoring data provide evidence that an exceedance or violation actually happened. This scenario is different than predicted future NAAQS violations. The proposal explained that predictions of future NAAQS violation(s) generally involve reviewing the historical ambient concentration data that are the evident focus of CAA section 319(b), estimating expected future emissions, and then using both of these data sets as inputs to an air quality modeling tool or other analytical approach that extrapolates these data to predict a future outcome. While science supports, and the EPA relies on, predictions of future NAAQS violations in several parts of the clean air program, such as in the EPA's approval of attainment demonstrations in SIPs, in PSD air permitting programs and in actions to reclassify a moderate PM

or PM

2.5

nonattainment area to serious,

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

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

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

to develop a supplementary guidance document,

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

to describe the appropriate additional pathways for data exclusion for some “predicted future” monitoring data applications (

e.g.,

predicting future attainment that is the basis for approval of an attainment demonstration in the SIP for a nonattainment area, preparing required air quality analyses in an application for a PSD permit or preparing required air quality analysis for the purposes of transportation conformity).

2. Final Rule

After considering the public comments we received, as explained more fully in the following paragraphs, we are finalizing language that applies the provisions in the Exceptional Events Rule to the treatment of data showing exceedances or violations of any NAAQS for purposes of the following types of regulatory determinations by the Administrator.

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

• A determination regarding whether a nonattainment area has attained a NAAQS by its CAA deadline. This type of determination includes “clean data determinations.”

• A determination that an area has data for the specific NAAQS that qualify the area for an attainment date extension under the CAA provisions for the applicable pollutant.

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

• Other actions on a case-by-case basis if determined by the EPA to have regulatory significance based on discussions between the air agency and the EPA Regional office during the Initial Notification of Potential Exceptional Event process.

After considering comments from multiple state and local air agencies, regional planning organizations and industrial commenters that requested an option for using the Exceptional Events Rule for other regulatory determinations, we have added the sixth bullet in the preamble and in the regulatory text to acknowledge that it may be appropriate to use the provisions in the Exceptional Events Rule to exclude data for regulatory determinations not specifically articulated in the first five bullets. We expect that air agencies and the appropriate EPA Regional offices will discuss these case-by-case scenarios as part of the Initial Notification of Potential Exceptional Event process, described in more detail in Section IV.G.5 of this preamble.

Upon further review of the identified determinations by the Administrator, we also realized that the fourth bullet, formerly “A determination that an area has had only one exceedance in the year prior to its deadline and thus qualifies for a 1-year attainment date extension, if applicable” applies to attainment date extensions only for PM

as indicated in CAA section 188(d)(2) because “only one exceedance” is specific to PM

. Attainment date extensions for other NAAQS have other CAA conditions. Our intent was that this determination would apply to attainment date extensions for all NAAQS and these NAAQS have CAA conditions other than “only one exceedance.” As a result, we have revised the language as follows to better convey this concept: “A determination that an area has data for the specific NAAQS, which qualify the area for an attainment date extension under the CAA provisions for the applicable pollutant.” Using this approach, a state would be required to demonstrate that a given area had data with respect to the statistical form of that particular standard in the calendar year prior to the applicable attainment date for the area (

i.e.,

for the 1997 24-hour PM

NAAQS, no more than one exceedance of the 24-hour NAAQS and the annual mean concentration of PM

in the area for such year is less than or equal to the standard level). Revising this language also accounts for potential future revisions to the form and level of the NAAQS, data handling provisions and regulatory changes to state implementation plan requirements.

As we indicated in the proposal, we still intend to develop a supplementary guidance document,

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

which will describe the appropriate additional pathways for data exclusion for some “predicted future” monitoring data applications. We have delayed the release of this guidance, however, to allow us to incorporate the content of the final Exceptional Events Rule revisions. We intend to post the draft guidance and instructions for providing public comment on the exceptional events Web site at

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

shortly after finalizing these rule revisions. As we noted in the proposal, we intend this guidance to do the following:

• Clarify that data excluded under the procedural and substantive provisions of the Exceptional Events Rule will also be excluded from (i) design value estimates and AQS user reports (unless the AQS user specifically indicates that they should be included), (ii) selecting appropriate background concentrations for PSD air quality analyses and transportation conformity hot spot analyses, and (iii) selecting appropriate ambient data for projecting future year concentrations as part of a modeled attainment demonstration.

• Identify potential pathways for data exclusion for determinations based on “predicted” future NAAQS exceedances or violations (

e.g.,

PSD, transportation conformity).

• Identify the scenarios in which the EPA would

not

exclude data, such as when setting priority classifications for emergency plans under 40 CFR 51.150. The EPA believes that implementing the CAA principle at section 319(b)(3)(A) that “protection of public health is the highest priority” may necessitate that an air agency address in its emergency plan the appropriate planned response for any elevated concentration known to be possible because it has already been observed even if that elevated concentration is associated with an exceptional event.

3. Comments and Responses

While the majority of commenters agreed with the EPA's proposal that the provisions in the Exceptional Events Rule apply to the enumerated five actions, many of these same commenters urged the EPA

not

to limit the scope of the Exceptional Events Rule to the five actions that we identified in the proposal as comprising “determinations by the Administrator with respect to exceedances or violations of national ambient air quality standards.” Commenter suggestions ranged from adding a sixth element to capture other case-by-case actions deemed to be of regulatory significance to specifically listing other potential actions (that is, they suggested adding the following to list of

specifically covered actions: Design value estimates, PSD background determinations, transportation hot spot analyses, future year projections for modeled attainment determinations, clean data determinations (which are included within the third bullet identifying the types of regulatory determinations by the Administrator included within the scope of the Exceptional Events Rule), other actions that rely on design values, monitoring network plans, etc.). The EPA agrees that the list of actions identified in the regulatory text should allow for a case-by-case determination in certain circumstances (

e.g.,

such as when an event is determined during the Initial Notification of Potential Exceptional Events process to have regulatory significance for an action not otherwise identified in the regulatory text) and has added this language to the final regulatory text. The EPA believes that this language could include any of the specific actions identified by other commenters. However, as we noted in the proposal, the CAA does not clearly apply the statutory criteria of section 319(b) to all of the other actions identified by the commenters. Therefore, under certain circumstances, we believe that it may be appropriate to exclude data for some of the other specific actions. Hence, we are not identifying these actions in the regulatory text. Rather, we intend to address them in the additional guidance previously mentioned and discussed further in the following paragraphs.

As indicated, the majority of commenters agreed with the EPA's approach to define those actions that constitute “determinations by the Administrator.” A few other commenters, however, indicated that the EPA cannot narrow the scope of the Exceptional Events Rule nor agree to exclude event-affected data from other types of regulatory determinations using another mechanism without first undertaking notice-and-comment rulemaking. The EPA disagrees with this comment. First, neither the CAA language at section 319(b)(3)(B)(iv), which requires regulations allowing a state to petition the Administrator to exclude air quality monitoring data that is directly due to exceptional events from use in

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

nor the implementing language in the 2007 Exceptional Events Rule at 40 CFR 50.14(a)(1), which allows air agencies to request exclusions for data showing exceedances or violations of the NAAQS that are directly due to an exceptional event from use in determinations, identify the scope of the word “determinations.” Second, identifying the Exceptional Events Rule as the only mechanism by which data may be excluded from regulatory actions may result in unintended consequences. As we have noted previously, an event may make a past air concentration significantly higher than it would have been in the absence of the event contribution. If the event-influenced data do not result in an exceedance or violation, they are not eligible for exclusion under the Exceptional Events Rule. CAA section 319(b) is ambiguous with respect to how to treat an exceptional event that contributed to a past air concentration being higher than it would have been without the event, but the air concentration did not result in an exceedance or violation. The EPA's decision to not apply the Exceptional Events Rule to data that does not exceed or violate a NAAQS is consistent with how the rule has been applied and interpreted and is not inconsistent with CAA section 319(b). However, we acknowledge that retaining the event-influenced data could have regulatory implications that seem contrary to the purpose of CAA section 319(b). For example, retaining such data in the calculation of background concentrations used in air quality analysis for a PSD permit may suggest that there will be a NAAQS violation after construction of a new source and thus could prevent the permitting authority from issuing the permit.

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

As previously noted, we intend our

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

to describe the appropriate additional pathways for data exclusion for some “predicted future” monitoring data applications. Multiple commenters expressed interest in this guidance and called for its quick release. The EPA recognizes that this guidance is an important supplement to the revisions to the Exceptional Events Rule that we are promulgating and we will work towards the quick release of this document.

Throughout this preamble and in our proposal, we use the term “weight of evidence” to describe the process by which we evaluate individual exceptional events demonstrations and air agency requests for data exclusion. Several commenters asked for additional clarification regarding this terminology, either in preamble or in regulatory text. Several other commenters asked that we use the “more commonly understood” terminology of “preponderance of the evidence.” Another commenter objects to the use of a weight of evidence approach noting that it could lead to incorrectly granted requests for data exclusion.

While we are not adding language to the regulatory text, we are clarifying in this preamble to the final rule that in applying a “weight of evidence” approach to reviewing individual exceptional events demonstrations, the EPA believes it is appropriate to consider all relevant evidence and qualitatively “weigh” this evidence based on its relevance to the Exceptional Events Rule criterion being addressed, the degree of certainty, its persuasiveness, and other considerations appropriate to the individual pollutant and the nature and type of event. Courts have found that it is reasonable for the EPA to use a “weight of evidence” analysis when implementing the CAA.

See, e.g., Envtl. Def.

EPA,

369 F.3d 193 (2d Cir. 2004) (upholding the EPA's approval of a state's attainment demonstration using photochemical grid modeling and a weight of evidence analysis) and

BCCA Appeal Group

EPA,

355 F.3d 817 (5th Cir. 2003) (finding that the EPA's conclusion that the weight of evidence approach to approving attainment demonstrations was consistent with the CAA, reasonable and entitled to deference). In this context, “weight” refers to the relevance of the evidence to the determination and its technical merit, and not to the amount of documentation. The language “weight of evidence” is consistent with this approach and consistent with the terminology used in other EPA regulatory actions. “Preponderance of the evidence” conveys many of the same concepts as “weight of evidence,” but because it is a legal term of art, we are not using that term as part of this rulemaking action. The weight of evidence approach is an appropriate and reasonable approach, which has been used historically and successfully under key CAA programs. The commenter did not present any information showing that this approach is more likely to yield “incorrect” decisions than any other evidentiary approach that might be applicable to exceptional events demonstrations.

D. Definition and Scope of a Natural Event

1. Summary of Proposal

In the 2007 Exceptional Events Rule, the EPA defined a natural event as an event in which human activity plays little or no direct causal role (

see

72 FR 13580). In our 2015 action, the EPA proposed to revise this definition to include the concept of an event and its resulting emissions and to acknowledge that natural events can recur. The EPA also proposed to include language in the regulatory definition to clarify that anthropogenic emission sources that contribute to the event emissions (and subsequent exceedance or violation) that are reasonably controlled do not play a “direct” role in causing emissions. The proposal elaborated on the “direct causal” concept by repeating language that first appeared in the preamble to the 2007 Exceptional Events Rule but not in rule text.

In the 2007 rule preamble and the November 2015 proposal, the EPA explained that we generally consider human activity to have played little or no

direct

role in causing an event-related exceedance or violation if anthropogenic emission sources that contribute to the exceedance are reasonably controlled at the time of the event (

see

72 FR 13563-4 and 80 FR 72844). This is the case regardless of the magnitude of emissions generated by these reasonably controlled anthropogenic sources and regardless of the relative contribution of these emissions and emissions arising from natural sources in which human activity has no role.

Thus, the event could be considered a natural event by applying the reasonable interpretation that the anthropogenic source had “little” direct causal role. To further illustrate this concept, as we have noted previously, the EPA considers wildfires to be natural events even though some accidental human actions initiate some wildfires and, to some degree, prior land management practices can influence the frequency and scale of wildfires. The EPA believes the interpretation that wildfires are natural events best implements the Congressional intent and is a more appropriate approach than expecting air agencies to determine the initial cause of each wildfire of interest and classifying it as natural or anthropogenic based on that cause. In addition, landowners and managers and government public safety agencies are strongly motivated to reduce the frequency and severity of human-caused wildfires. Our proposal further explained that if anthropogenic emission sources that contribute to the event emissions can be reasonably controllable but reasonable controls were not implemented at the time of the event, then the event would

not

be considered a natural event.

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

e.g.,

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

2. Final Rule

After consideration of the public comments and as supported by many commenters, we are finalizing the following definition: “

natural event

means an event and its resulting emissions, which may recur at the same location, in which human activity plays little or no direct causal role. For purposes of the definition of a natural event, anthropogenic sources that are reasonably controlled shall be considered to not play a direct role in causing emissions.” In the final regulatory definition that we are promulgating, we are adding the language “at the same location” to more clearly indicate that natural events can recur in the same area or at the same location and still be considered as exceptional events. The language we are adding in the definition contrasts the recurrence frequency of natural events with human activities that must be “unlikely to recur at a particular location” to be considered to be an exceptional event (

see

CAA section 319(b)(1)(A)(iii)). Although several commenters disagreed with our approach, and stated that a natural event must have no human activity component at all, we are retaining in the regulatory definition the concept that we consider reasonably controlled anthropogenic sources to not play a direct role in causing emissions. We are, however, adding the language “[f]or purposes of the definition of a natural event” prior to the language “anthropogenic sources that are reasonably controlled shall be considered to not play a direct role in causing emissions” to clarify that the “direct causal” language applies to reasonably controlled anthropogenic sources when considering whether the event is natural. As we have previously stated, we believe that if reasonable controls were implemented on contributing anthropogenic sources at the time of the event and if, despite these efforts and controls, an exceedance occurred, then we would consider the human activity to have played little or no direct causal role in causing the event-related exceedance. Rather, in those cases in which the anthropogenic source has “little” direct causal role, we would consider the high wind and the emissions arising from the contributing natural sources (in which human activity has no role) to cause the exceedance or violation. Additionally, the event would

not

be natural if all of the event-related emissions originated from anthropogenic sources or if anthropogenic emission sources that contributed to the event-related emissions could have been reasonably controllable but reasonable controls were not implemented at the time of the event.

We discuss the concept of reasonable control in more detail in Section IV.E.2 of this preamble.

As we clarify in the final rule discussion in Section IV.F.2.a of this preamble, when considering prevention/control for purposes of exceptional event categorization, a prescribed fire effectively becomes like a wildfire when, for example, the prescribed fire escapes secure containment due to unforeseen circumstances (

e.g.,

a sudden shift in prevailing winds). In these instances, the burn manager would no longer control the path of the fire. Thus, the fact that the initial fire was deliberately ignited should not result in the entire burn (

e.g.,

the duration and extent of the burn) needing to follow the rule requirements for prescribed fires on wildland.

3. Comments and Responses

Commenters providing feedback on the natural events section of the proposal generally focused on one of the following concepts: The language in the proposed revised definition of natural event, those event types considered to be natural events and the concept of reasonable controls as it relates to contributing anthropogenic emissions. We address in the explanation of the final rule language in Section IV.D.2 of this preamble those comments related to the definition of natural event. We address the types of natural events in this section and we discuss reasonable controls in Section IV.E.2 of this preamble.

Several commenters asked that we clarify those types of events that could be considered natural events eligible for data exclusion under the Exceptional Events Rule. Commenters specifically asked for clarity regarding earthquakes, lightning and biological emissions. Through our experience implementing the Exceptional Events Rule, we have come to realize that it may be helpful to think of an event in terms of the source of its emissions. If the underlying source is natural and the generated emissions influence a regulatory monitor, then the ensuing event (

i.e.,

event and resulting

emissions) could be considered a “natural event” under the Exceptional Events Rule. Applying this rationale, as we expressed in the 2007 rule and the November 2015 proposal (

see

72 FR 13565 and 80 FR 72854-72858), the EPA generally considers wildfires, stratospheric ozone intrusions, volcanic and seismic (

e.g.,

earthquake) activities, natural disasters (

e.g.,

hurricanes and tornados) and windblown dust from natural, undisturbed landscapes to be natural events. Natural events, including, but not limited to, those previously identified, and their resulting emissions could be considered under the provisions of the Exceptional Events Rule. Also, as explained in this section, events that include emissions from both natural and anthropogenic sources, such as high wind dust events, can be considered natural events only if reasonable controls have been applied to the contributing anthropogenic sources. Lightning storms occurring close to a regulatory monitor, such that the particular storm notably affects the monitor close in time to the storm might qualify as natural events that could also be exceptional events. However, the ongoing and delayed aggregate impact of many lightning storms that are not proximate to the monitor is not a deviation from normal or expected conditions and thus would not be an exceptional event. Also, routine biological emissions (

e.g.,

including, but not limited to, emissions from vegetation, microbes and/or animals) are not deviations from normal or expected conditions. Thus despite being natural, they are not “events” and would not qualify as exceptional events. As is true for all exceptional events determinations, the EPA will consider these events, and other event types not identified here, on a case-by-case basis.

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

As described in Section IV.B of this preamble, the EPA is finalizing provisions to return to the core statutory elements and implicit concepts of CAA section 319(b): That the event affected air quality in such a way that there exists a clear causal relationship between the specific event and the monitored exceedance or violation, the event was not reasonably controllable or preventable, and the event was caused by human activity that is unlikely to recur at a particular location or was a natural event.

See, e.g.,

42 U.S.C. 7619(b)(1). All exceptional events demonstrations, regardless of event type or relevant NAAQS, must address each of these technical criteria. The EPA has posted examples of acceptable demonstrations for various event and pollutant combinations on its Web site at

https://www.epa.gov/air-quality-analysis/exceptional-events-submissions-table

. We will update this Web site as additional examples become available. This section summarizes the EPA's proposed revisions, final regulatory language and public comments regarding each of these technical criteria. Section IV.G of this preamble discusses additional process-related components of exceptional events demonstrations.

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

Because Section IV.D of this preamble addresses the definition of a natural event and those event types that can be considered natural events under the Exceptional Events Rule, we focus this section of the preamble on the “human activity unlikely to recur at a particular location” portion of the “human activity unlikely to recur at a particular location or a natural event” technical criterion. In the final rule description section in this part of the preamble, we provide example conclusory language that air agencies can use in the portion of their exceptional events demonstration that addresses this criterion. This example language applies to both human activity and natural events.

a. Summary of Proposal

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

a natural event” (emphasis added,

see

CAA section 319(b)(1)(A)(iii) and 40 CFR 50.1(j)). As we noted in the discussion of a natural event in Section IV.D of this preamble, we have come to realize that it may be helpful to think of an event in terms of the source of its emissions. If the underlying source is natural and the generated emissions influence a regulatory monitor, then the ensuing event (

i.e.,

event and resulting emissions) could be considered a “natural event” under the Exceptional Events Rule. Under this particular criterion, if the underlying source of emissions is anthropogenic, then the event can only be “exceptional” if the original source is “unlikely to recur at a particular location.” The proposal noted that neither the CAA nor the 2007 Exceptional Events Rule defined “unlikely to recur” or “at a particular location.” Therefore, the proposal sought to clarify both of these phrases. In addition to proposing a generally applicable approach for “unlikely to recur,” we also proposed specific approaches for wildland fires, notably prescribed fires on wildland (which we discuss in Section IV.F.2 of this preamble), and high wind dust events (which we discuss in Section IV.F.4 of this preamble). The proposal also clarified that under CAA section 319(b) and a provision of the 2007 Exceptional Events Rule that we did not propose to change, air pollution related to source noncompliance is not an exceptional event regardless of its frequency.

We proposed, as guidance, to interpret the unlikely to recur language as follows. If an event type has not previously occurred within a given air quality control region (AQCR)

in the 3 years preceding the submittal of an exceptional events demonstration for an event that has occurred recently, the EPA will consider this recent event to be a “first” event and will generally consider that event type to be unlikely to recur in the same location.

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

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

In the Interim High Winds

Guidance, we did not define “area” other than to differentiate areas by attainment status or jurisdiction (

i.e.,

intrastate versus interstate or international). The EPA solicited comment on using an AQCR to define the bounds for an area subject to event recurrence and on whether to incorporate into rule text the benchmark of three events in 3 years.

40 CFR part 81, subpart B, Designation of Air Quality Control Regions, defines Air Quality Control Regions.

While we proposed to define event recurrence as occurring in the 3 years preceding the submittal of an exceptional events demonstration, the proposal language should have read in the 3 years preceding the event that is the subject of an exceptional events demonstration. We clarify this 3-year timeframe in the final rule section.

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

See

footnote 27 in table 2 of

Interim Guidance on the Preparation of Demonstrations in Support of

Requests to Exclude Ambient Air Quality Data Affected by High Winds Under the Exceptional Events Rule.

U.S. EPA. May 2013. Available at

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

b. Final Rule

As a result of the feedback from numerous commenters, we are providing clarifications to the “unlikely to recur at a particular location” language as guidance in this preamble and not regulatory text. We note here, as guidance, the benchmark of three events in 3 years to define recurrence. We measure the 3-year period backwards from the date of the most recent event (

e.g.,

for an event occurring on May 1, 2016, the 3-year period would be May 1, 2013, through May 1, 2016). As described previously, if there have been two prior events of a similar type (

i.e.,

a similar event type generating emissions of the same pollutant whether flagged or the subject of a demonstration) within a 3-year period in “a particular location,” the third event, for which the demonstration is being prepared (or would be prepared), would generally not satisfy the “human activity that is unlikely to recur at a particular location” criterion and, thus, would not qualify as an exceptional event. Although under this approach, the third event essentially confirms that the first two events are “routine,” an air agency would not likely recognize the routine nature of the first two events until the third occurrence. Also as noted in our proposal, the EPA will consider previously flagged exceedances within AQS with their associated descriptions to be “events” regardless of whether the affected air agency has submitted or the EPA has acted on these “recurring” event demonstrations. We also note in this final action that the benchmark of three events in 3 years generally applies regardless of an area's designation status with respect to the NAAQS that is the focus of the event demonstration. The EPA could grant exceptions to the benchmark of three events in 3 years benchmark on a case-by-case basis. Several commenters supported, and no commenters opposed, this generally applicable approach.

With regard to the frequency, several commenters asked the EPA to clarify how the concept of recurrence applies to a single event spanning multiple days. First, the EPA notes that for purposes of exceptional events eligibility, the concept of recurrence only applies to “human activity unlikely to recur at a particular location” and not to natural events. Natural events can recur. That said, a single event, natural or caused by human activity, can span multiple days and result in an air agency flagging multiple monitor-day values in AQS (

i.e.,

multiple exceedances of a given NAAQS at a single monitor in a single day or multiple NAAQS exceedances at multiple monitors on multiple days). The EPA considers a single discrete event to be one occurrence even if it extends over more than one day. Applying our benchmark of three events in 3 years, for an area experiencing three authorized and deliberately set structural fires in 2 years, the EPA would not consider a third such structural fire in the third year to be an exceptional event.

Because prescribed fires on wildland eligible for exceptional events consideration involve igniting and managing the fire according to the provisions set forth in either a Smoke Management Program or using basic smoke management practices, we discuss the unique circumstances associated with the recurrence of prescribed fires on wildland in IV.F.2.

A deliberately set structural fire that has been authorized by a responsible government agency is clearly not a natural event. We are not offering guidance at this time on whether accidentally set structural fires or arson-set structural fires should be considered natural or anthropogenic events. We do note, however, that wildfires on wildland initiated by accident or arson are considered natural events, and on a case-by-case basis this treatment for wildfires may bear on the appropriate treatment of accidental and arson-set structural fires.

While we proposed, as guidance, to use an AQCR to define the bounds for an area subject to recurrence, in light of the comments received and issues raised therein, we agree that using AQCRs as the only way in which to define the bounds for an area subject to recurrence is not appropriate. Commenters identified the following reasons why an AQCR may not be suitable: AQCRs can be antiquated and inconsistent with current jurisdictional boundaries; AQCRs may be too large (particularly in some areas of the West) for effective analysis of event recurrence; AQCRs could be subdivided by terrain (

e.g.,

mountains or valleys) that could affect the transport and/or chemical interactions of pollutants; pollutant sources and monitors may not fall within the bounds of the same AQCR. Rather than prescribe an approach to define “a particular location,” commenters suggested that the EPA Regional offices and the affected air agencies could agree to the bounds of “a particular location” as part of regular, on-going conversations and/or as part of the Initial Notification of Potential Exceptional Event process. Commenters suggested that while an AQCR might appropriately define “a particular location” in some areas of the country, other areas may determine one of the following to be more suitable: Counties or other political boundaries, core based statistical areas (CBSAs), nonattainment or unclassifiable area boundaries (if applicable), a density metric (

i.e.,

number of events per thousand square miles calculated using the radius around the subject monitor), and/or distance to the monitor as indicated by a defined radius from the subject monitor. We agree that some of the commenters' suggestions may be appropriate in particular cases and we leave it to the EPA Regional offices and to the affected air agencies to consult on how to characterize “a particular location.”

As stated previously, all exceptional events demonstrations, regardless of event type or relevant NAAQS, must address each of the three technical criteria. We proposed conclusory language associated with the “human activity that is unlikely to recur at a particular location or a natural event” criterion and repeat it here as part of the preamble to the final Exceptional Events Rule revisions. When addressing this criterion as part of an exceptional events demonstration, the EPA recommends that the submitting air agency document and discuss the following in a distinct “human activity/natural event” section of the demonstration: The type/source of event (

e.g.,

a particular type of chemical spill or other industrial accident, fire in a particular type of structure, lightning-ignited wildfire, etc.), clearly identify whether the event is natural or was a human activity that is unlikely to recur at a particular location, the resulting emissions (

e.g.,

characterized in terms of the pollutant and magnitude, if applicable/available), and the documented frequency of the event in the prior 3 years (or other appropriate timeframe as agreed with the reviewing EPA Regional office).

The air agency should then affirmatively state that in characterizing the event, it has satisfied the “human activity unlikely to recur at a particular location or a natural event” criterion.

The frequency of event recurrence is important for both natural and anthropogenic events. For anthropogenic events, frequency can determine whether the event satisfies the “human activity unlikely to recur at a particular location or a natural event” criterion. For a natural event, the frequency

can determine whether a mitigation plan is necessary (

see

Section V of this preamble).

2. Not Reasonably Controllable or Preventable

As noted in the proposal, because CAA section 319(b) does not restrict the applicability of the not reasonably controllable or preventable criterion to certain types of events, this CAA criterion, and the implementing Exceptional Events Rule language, applies to both events caused by human activity and to natural events. This section discusses the criterion in general terms. We discuss the criterion's specific applicability to fire events on wildland in Section IV.F.2 of this preamble and to high wind dust events in Section IV.F.4 of this preamble.

a. Summary of Proposal

The EPA proposed to codify in regulatory language key aspects of the “not reasonably controllable or preventable” criterion to reduce uncertainty for air agencies and other parties. Specifically, we proposed and solicited comment on the following revisions to the Exceptional Events Rule to indicate that:

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

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

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

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

• Air agencies do not need to provide case-specific justification to support the “not reasonably controllable or preventable” criterion for remote, large-scale, high-energy and/or sudden high wind dust events, such as “haboobs.”

• Provided the air agency is not under an obligation to revise the SIP, the EPA would consider (

i.e.,

give deference to) enforceable control measures implemented in accordance with a state implementation plan, approved by the EPA within 5 years of the date of a demonstration submittal, that address the event-related pollutant and all sources necessary to fulfill the requirements of the CAA for the SIP to be reasonable controls with respect to all anthropogenic sources that have or may have contributed to event-related emissions.

• Air agencies do not need to provide case-specific justification to support the “not reasonably controllable or preventable” criterion for emissions-generating activity that occurs outside of the boundaries of the state (or tribal lands) within which the concentration at issue was monitored.

In addition to the identified revisions, the proposal also discussed and solicited feedback on the role of an EPA-approved SIP in nonattainment, maintenance, unclassifiable and attainment areas; prior communications regarding expectations for reasonable controls; prospective agreements regarding assessments of reasonable controls; and components of a not reasonably controllable or preventable showing within a demonstration. We summarize our proposed positions on these topics in the following paragraphs.

The proposal stated that while we would defer to the enforceable control measures in attainment plan SIPs applying to maintenance and nonattainment areas, we would not give this same deference to infrastructure SIPs developed for attainment, unclassifiable/attainment and unclassifiable areas. We differentiated attainment plan SIPs and infrastructure SIPs by the fact that attainment plan SIPs must include an attainment demonstration and reasonably available control measures (RACM), best available control measures (BACM),

and other requirements,

which together constitute an assessment of reasonable controls. Infrastructure SIPs typically rely on maintenance and attainment SIPs to demonstrate compliance with the key infrastructure elements. Therefore, the EPA proposed that the underlying SIPs, which would themselves include the control measures, be the relevant SIPs for exceptional events demonstrations.

BACM applies to attainment plans for serious PM

or PM

2.5

areas.

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

The proposal also recognized that regulations and an area's planning status are often evolving and changing, that these changes can span several years and involve multiple rounds of formal and informal communications between the affected air agency and the EPA, and that these changes could ultimately result in an air agency's adoption of new control measures, which, for exceptional events purposes, could constitute “reasonable” controls. Acknowledging that these conversations could inform what the air agency knew at the time of the event and thus could influence a case-specific assessment of the not reasonably controllable or preventable criterion, the EPA solicited comment on methods to definitively identify the status of communications and planning efforts (

e.g.,

formal correspondence or other documentation, timelines for responding) and whether this approach would be more appropriately addressed through rule language.

First appearing in the Interim High Winds Guidance, the proposal repeated the suggestion that an air agency could prospectively assess and determine that the controls in place for a particular type of event, or a planned enhancement of those controls, are sufficient to meet the not reasonably controllable or preventable criterion, and then obtain the EPA's review and concurrence of this assessment prior to more events of that type occurring. The proposal expressed the EPA's belief that this prospective approach would reduce disagreements that might otherwise occur over later retrospective assessments.

The proposal also solicited comment on recommending as either guidance or rule the following components that an air agency should include within the not reasonably controllable or preventable showing in a demonstration: (1) Identify the natural and anthropogenic sources of emissions causing and contributing to the event emissions, including the contribution from local sources, (2) identify the relevant SIP or other enforceable control measures in place for these sources and the implementation status of these controls, and (3) provide evidence of effective implementation and enforcement of reasonable controls, if applicable.

In identifying natural and anthropogenic sources, we clarified that the air agency should assess both

potentially contributing local/in-state and upwind sources.

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

e.g.,

that controls were overwhelmed by high wind), if appropriate.

b. Final Rule

After considering the public comments we received, we are finalizing the following not reasonably controllable or preventable elements, all of which contain associated regulatory language.

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

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

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

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

intra

state scenarios when an event in one county affects air quality in another county in the same state, assuming that the event occurs on land subject to state authority (versus tribal government authority). The EPA expects controls appropriate for the designation status of the county (or portion of the county) in which the emissions originate.

In addition, as a result of commenter feedback as explained more fully in subsequent paragraphs, we are promulgating in regulatory text the following revised versions of elements that we proposed for the not reasonably controllable or preventable criterion:

• Provided the appropriate federal, state or tribal air agency is not under an obligation to revise the SIP or FIP or TIP for an attainment or maintenance area for the event-related pollutant, the EPA would consider (

i.e.,

give deference to) enforceable control measures implemented in accordance with such a SIP or FIP or TIP, approved by the EPA within 5 years of the date of the event, that address the event-related pollutant and all sources necessary to fulfill the requirements of the CAA for the SIP or FIP or TIP to be reasonable controls with respect to all anthropogenic sources that have or may have contributed to the monitored exceedance or violation.

If the appropriate air agency is under an obligation to revise its implementation plan with respect to the specific enforceable control measures applicable to the exceptional events demonstration due to a SIP call pursuant to CAA section 110(k)(5), the EPA will evaluate on a case-by-case basis the control measures in place to determine whether emissions were reasonably controlled at the time of the event.

Under CAA section 110(c), the EPA is required to issue a nd enforce a federal implementation plan if a state fails to develop, adopt and implement an adequate SIP. States may also choose to adopt the federal plan as an alternative to developing their own plan. If a federal plan is implemented in a state, the state may still, at a later date submit a plan to replace the federal plan either in whole or in part. States may take over the administrative and enforcement aspects of a federal plan rather than leaving it to the EPA. Similarly, under the TAR at 40 CFR 49, tribes can develop their own plans (

i.e.,

tribal implementation plans) to implement the CAA provisions. Rather than develop their own TIPs, tribes can request that the EPA develop a FIP.

• When addressing the “not reasonably controllable or preventable” criterion within an exceptional events demonstration, air agencies should: (1) Identify the natural and anthropogenic sources of emissions causing and contributing to the monitored exceedance or violation, including the contribution from local sources,

(2) identify the relevant SIP, FIP or TIP or other enforceable control measures in place for these sources and the implementation status of these controls, and (3) provide evidence of effective implementation and enforcement of reasonable controls, if applicable.

In specifying “local” sources, we mean those sources that are both within the jurisdiction of the state or tribe and that are in the vicinity of or are located upwind of the monitor with the recorded exceedance or violation. “Local” sources could include, but are not limited to, large point sources (

e.g.,

large industrial sources, electric power plants, airports, etc), nonpoint sources (

e.g.,

residential heating, asphalt paving, etc.), mobile sources (

e.g.,

both on- and off-road vehicles, construction equipment, trains, and vessels), natural sources or biogenic sources (

e.g.,

off-gassing from soil, animals and vegetation).

The EPA recognizes that air agencies have various methods of ensuring source compliance and various methods of permitting and enforcement. We do not expect nor would

all

agencies necessarily need to have enforcement records for

all

events. However, agencies should make a general showing that they are enforcing controls to a reasonable degree (not necessarily on the particular day of the event). If an air agency identifies several categories of anthropogenic sources as significant or likely contributors to an event, the air agency should also describe in the demonstration the means used to determine compliance with reasonable control requirements for each category.

• Air agencies do not need to provide case-specific justification to support the “not reasonably controllable or preventable” criterion for large-scale and high-energy high wind dust events, such as “haboobs.” (We discuss the characteristics of these events in Section IV.F.4 of this preamble.)

In addition, we repeat in this final action our suggestion that an air agency can prospectively assess and determine that the controls in place for a particular type of event, or a planned enhancement of those controls, are sufficient to meet the not reasonably controllable or preventable criterion, and then obtain the EPA's review and concurrence of this assessment prior to the occurrence of similar events (

i.e.,

a similar event type generating emissions of the same pollutant). This prospective approach would reduce disagreements that might otherwise occur over later retrospective assessments. Although air agencies have not historically pursued this option, it is our intent going forward to work with any air agency expressing an interest in pursuing this approach. Air agencies interested in this process should contact their reviewing EPA Regional office.

c. Comments and Responses

While some commenters supported the EPA's stated position in the proposal that the not reasonably controllable or preventable criterion consists of two prongs (

i.e.,

control and prevention), other commenters asserted that the statutory criterion and the implementing language in the 2007 rule is “not reasonably controllable

preventable” (emphasis added). Commenters disagreeing with the EPA's position claim that the EPA's interpretation is contrary to the CAA and that the EPA lacks authority to contravene the precise statutory language in the implementing regulatory language by interpreting the CAA to mean that an exceptional event must be both not reasonably controllable

and

not reasonably preventable.

As previously noted, we maintain that the criterion consists of two factors: Prevention

and

control and that to qualify as an exceptional event, the event must satisfy both factors. CAA section 319(b)(1)(A)(ii) is ambiguous regarding whether “not reasonably controllable or preventable” requires a demonstration to show both criteria, or one or the other. In adopting our interpretation, we have applied a valid rule of inference known as De Morgan's law, which recognizes that the negation of a disjunction is the conjunction of the negations. Stated simply, “not (A or B)” is the same as “(not A) and (not B).”

See, e.g., State

Nelson,

842 NW.2d 433, at 440-41 (Minn. 2014) (finding it reasonable to apply De Morgan's law to

statutory interpretation);

Schane

Int'l Bhd. Of Teamsters,

760 F.3d 585, 589-92 (7th Cir. 2014) (applying De Morgan's law to address a pension plan dispute, focusing on the context in which the “not . . . or” phrase was used). Applied to CAA section 319(b)(1)(A)(ii), an exceptional event means an event that is both not reasonably controllable and not reasonably preventable. The legislative history supports this logical reading of the statutory language. Congress provided the following rationale for promulgating the exceptional events provisions: “Events such as forest fires or volcanic eruptions, should not influence whether a region is meeting its Federal air quality goals.” S. Rep. No. 109-53, at Sec. 1618 (2005) and S. Rep. No. 108-222, at Sec. 1618 (2004). The examples used in the legislative history—forest fires and volcanic eruptions—are

both

not reasonably controllable

and

not reasonably preventable.

This interpretation is also supported by the intent of CAA section 319(b), which identifies the limited circumstances in which it is appropriate to exclude from certain regulatory decisions air monitor data clearly caused by an exceptional event balanced with the CAA's goal of protecting human health and the environment. The language “not reasonably controllable” clearly implicates controls, as does “preventable,” since an event may be “preventable” by mitigating the conditions under which the event occurs—

i.e.,

by applying controls. Thus, consideration of the circumstances of the event and possible application of controls is appropriate in both contexts, and a separate analysis is required for “not reasonably controllable” and “not reasonably preventable.”

We note that the commenters who disagree with the EPA's interpretation failed to identify any scenarios or provide any examples of why it is problematic for the EPA to require that an exceptional event must be both not reasonably controllable

and

not reasonably preventable. While some air agencies that have submitted demonstrations have argued that the “or” in this criterion allows them to choose between showing either prevention or control of the event-related emissions, this type of “or” selection is contrary to the emphasis of CAA section 319(b) on the protection of public health and the exclusion of data associated with emissions from “exceptional events.” The CAA as a whole, and section 319(b) in particular, is premised on the idea that states should undertake reasonable actions to control emissions and protect public health. Exemptions and exceptions apply in addition to, rather than in place of, reasonable controls. The CAA does not allow air agencies to avoid applying reasonable controls to address emissions simply because other factors also contribute to those emissions. For example, for a high wind event, applying “or” might suggest that because the wind is not preventable, the agency has no obligation to address reasonable controls (

e.g.,

the application of water to stockpiles of wood chips) that could reduce emissions in the case of such an event. For prescribed fire, the use of “or” could allow an air agency to argue that a fire is not reasonably preventable because of the safety or ecosystem benefits that would be foregone if the fire were not applied, so the emissions and air quality impacts from the fire do not need to be reasonably controlled through the application of basic smoke management practices. Another example of when applying “or” would be problematic is a situation in which a developer could intentionally set fire to forested land to clear it for development, as that event would be preventable but possibly not controllable; such an event should not be considered an exceptional event. In contrast, elsewhere in the preamble to these final rule revisions we explain that some events may be neither preventable nor their air quality impacts to be controllable to any degree, such as potential increases in SO

concentrations associated with volcanic eruptions, and thus would qualify as exceptional events.

These final rule revisions present that what is “reasonable” for purposes of “not reasonably controllable or preventable” should consider the technical knowledge available to the air agency at the time of the event. While this concept was supported by some commenters, others maintain that “controllable” is forward looking rather than backward looking and that air agencies should anticipate future events and implement controls and measures to account for potential future impacts.

We agree with the commenters that a prospective approach to assessing what might constitute “reasonable controls” could be helpful in some cases, particularly for areas experiencing recurring events. Therefore, we have modified our proposal as it relates to mitigation for areas experiencing historically documented or known seasonal events. We discuss these concepts in Section V of this preamble. We disagree, however, with the commenters' forward-looking approach as it applies to other situations. As we noted in the proposal, an air agency “caught by surprise” by an event of a given type (or by an unexpected number of such events in a period over which NAAQS compliance is evaluated, typically 3 years) should not be expected to have implemented the same controls prior to an event as an air agency that has been aware that events of a ce

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