*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 1 of 218 6560-50-P ENVIRONMENTAL PRO TECTION AGENCY 40 CFR Part 50 [EPA-HQ-OAR-2013-0572, EPA-HQ-O AR-2015-0229; FRL-9935-73-OAR] RIN 2060-AS02 Treatment of Data Influenced by Exception al Events – Rule Revisions and Notice of Availability for Related Draft Guidance AGENCY: Environmental Protection Agency (EPA). ACTION: Proposed rule; notice of availability. SUMMARY: The Environmental Protection Agency (E PA) is proposing revisions to certain sections within the March 22, 2007, “Treatment of Data Influenced by Exceptional Events; Final Rule” (2007 Exceptional Events Rule) that governs the exclusion of event- affected air quality data from regulatory decisions. The EPA is also providing a noti ce of availability of a draft version of the non-binding guidance document titled, Draft Guidance on the Preparation of Exceptional Events Demonstrations for W ildfire Events that May Influence Ozone
Concentrations

. DATES: Comments . Written comments on this proposal and draft guidance must be received by January 19, 2016. Public hearing: The EPA will hold a public hearing on this proposal on Tuesday, December 8, 2015, in Phoenix, Arizona. Please refer to SUPPLEMENTARY INFORMATION for additional information on the co mment period and public hearing. ADDRESSES: Submit your comments on the EPA’s propos ed revisions to the 2007 Exceptional Events Rule, identified by Dock et ID No. EPA-HQ-OAR-2013-0572, at http://www.regulations.gov . Follow the online instructions for submitting comments. Once*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 2 of 218 submitted, comments cannot be edited or rem oved from Regulations.gov. The EPA may publish any comment received to its public docket. Do not submit electronically any information you consider to be Confidential Busi ness Information (CBI) or other information whose disclosure is restricted by statute. Multimedia submissions (audio, video, etc.) must be accompanied by a written comment. The written comment is consid ered the official comment and should include discussion of all points you wish to make. Th e EPA will generally not consider comments or comment contents located outside of the primary submission ( i.e ., on the web, cloud or other file sharing system). For additional submission methods, the full EPA public comment policy, information about CBI or multimedia submissi ons and general guidance on making effective comments, please visit http://www2.epa.gov/dockets/c ommenting-epa-dockets

. Submit your comments on the EPA’s Draft Guidance on the Preparation of Exceptional Events Demonstrations for Wildfire Events that May Influence Ozone Concentrations, identified by Docket ID No. EPA-HQ-OAR-2015-0229, at http://www.regulations.gov . Follow the online instructions for submitting comments. Once submitted, comments cannot be edited or removed from Regulations.gov. The EPA may publish any comme nt received to its public docket. Do not submit electronically any information you consid er to be CBI or other information whose disclosure is restricted by statute. Multimedia submissions (audio, video, etc.) must be accompanied by a written comment. The written co mment is considered the official comment and should include discussion of all points you wish to make. The EPA will generally not consider comments or comment contents lo cated outside of the primary submission ( i.e ., on the web, cloud or other file sharing system). For ad ditional submission methods, the full EPA public comment policy, information about CBI or mu ltimedia submissions and general guidance on making effective comments, please visit http://www2.epa.gov/dockets /commenting-epa-dockets

.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 3 of 218 Docket . As discussed above, the EPA has esta blished one docket for the proposed revisions to the 2007 Exceptional Events Rule and another docket for the draft guidance document. All documents in th ese dockets are listed on the http://www.regulations.gov website in the respective docket. The rulemaking doc ket is Docket ID No. EPA-HQ-OAR-2013-0572. The separate docket established for the Draft Guidance on the Preparation of Exceptional Events Demonstrations for Wildfire Events t hat May Influence Ozone Concentrations is Docket No. EPA-HQ-OAR-2015-0229. The EPA will not respond to comments relating to the guidance document as part of this rulemaking, but will cons ider these comments in the development of the guidance document. If comments on the draft guidance document are submitted to the rulemaking docket, the EPA will respond only to the portion of such comments that are relevant to the rulemaking. The EPA also relies on th e documents in Docket ID No. EPA-HQ-OAR2011-0887, the docket established for the July 20 12 notice of availability for the Draft Exceptional Events Implementation Guidance, and in corporates this docket into the record for this action. However, no new comments may be directed to Docket ID No. EPA-HQ-OAR-2011- 0887 and the EPA will not respond to comments that have already been submitted to this docket unless they are resubmitted to Dock et ID No. EPA-HQ-OAR-2013-0572. Although listed in the indices to the rulemaking docket and the guida nce docket associated with this action ( i.e ., Docket ID No. EPA-HQ-OAR-2013-0572 and Dock et No. EPA-HQ-OAR-2015-0229), some information is not publicly available, ( e.g. , CBI or other information whose disclosure is restricted by statute). Certain other material, such as copyrighted material, will not be placed on the Internet but may be viewed, with prior arra ngement, at the EPA Docket Center. Publicly available docket materials are av ailable either el ectronically in www.regulations.gov or in hard copy at the Air and Radiation Docket and Info rmation Center, EPA/D. C., EPA William Jefferson*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 4 of 218 Clinton West Building, Room 3334, 1301 Consti tution Avenue, NW, Washington, D.C. The Public Reading Room is open from 8:30 a.m. to 4:30 p.m., Monday through Friday, excluding legal holidays. The telephone number for the Pu blic Reading Room is (202) 566-1744 and the telephone number for the Air and Radiation Do cket and Information Center is (202) 566-1742. For additional information about the EPA’s public docket, visit the EPA Docket Center homepage at: http://www.epa.gov/epahome/dockets.htm

. Public hearing: A public hearing will be held on Tuesday, December 8, 2015, in room 3175 in the Arizona Department of Environmenta l Quality main office building located at 1110 W. Washington Street, Phoenix, Arizona 85007. The public hearing will convene at 10:00 a.m. and continue until the earlier of 6:00 p.m. or 1 hour after the last regi stered speaker has spoken. We have scheduled a lunch break from 12:30 p.m. until 2:00 p.m. People interested in presenting oral testimony should contact Ms. Pamela Long, Air Quality Pl anning Division, Office of Air Quality Planning and Standards (C504-01), U.S. Environmental Protection Agency, Research Triangle Park, NC 27711, telephone (919) 541- 0641, fax number (919) 541-5509, email address long.pam@epa.gov , at least 2 days in adva nce of the public hearing ( see DATES ). People interested in attending the public hearing should also call Ms. Long to verify the time, date and location of the hearing. The public hearing will provide interest ed parties the opportunity to present data, views or arguments concerning the proposed revisions to the 2007 Exceptional Events Rule. The EPA will make every effort to accommodate all speakers who arrive and register. Individuals planning to attend the hear ing will be required to sign in, and may be required to show valid picture identification to the security staff to gain access to the meeting room. In addition, no weapons will be allowed in the facility. Any weapons brought to the site will be stored in a locker at the facility. No large signs will be allowed in the building, cameras*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 5 of 218 may only be used outside of the building. The EP A may ask clarifying ques tions during the oral presentations but will not respond to the presen tations at that time. Written statements and supporting information submitted during the commen t period will be considered with the same weight as oral comments and supporting in formation presented at the public hearing. Commenters must submit written comments on the proposed rule and/or draft guidance by January 19, 2016. Commenters should notify Ms. Long if they will need specific equipment, or if there are other special needs related to providi ng comments at the hearing. The EPA will provide equipment for commenters to show overhead slides or make computerized slide presentations if we receive special requests in advance. Oral testimony will be limited to 5 minutes for each commenter. The EPA encourages commenters to provide the EPA with a copy of their oral testimony electronically (via email or CD) or in hard copy form. The hearing schedule, including the list of speakers, will be posted on the EPA’s website at http://www2.epa.gov/air-qualityanalysis/treatment-data-in fluenced-exceptional-events . Verbatim transcripts of the hearing and written statements will be included in the docket for the rulemaking. The EPA will make every effort to follow the schedule as closely as pos sible on the day of the h earing; however, please plan for the hearing to run either ah ead of schedule or behind schedule. FOR FURTHER INFORMATION CONTACT: For additional information regarding this proposed rule, please contact: Beth W. Palma, U.S. EPA, Office of Air Quality Planning and Standards, Air Quality Policy Division, Mail Code C539-04, Re search Triangle Park, NC 27711, telephone (919) 541–5432, email at palma.elizabeth@epa.gov . For additional information regarding the Draft Guidance on the Preparation of E xceptional Events Demonstrations for Wildfire Events that May Influence Ozone Concentrations , please contact Melinda Beaver, U.S. EPA, Office of Air Quality Planning and Sta ndards, Air Quality Policy Division, Mail Code*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 6 of 218 C539-04, Research Triangle Park, NC 27711, telephone (919) 541-1062, email at beaver.melinda@epa.gov . For information on the public hearing or to register to speak at the hearing, contact Ms. Pamela Long, U.S. Environm ental Protection Agency, Office of Air Quality Planning and Standards, Air Qu ality Planning Division, Mail C ode C504-01, Research Triangle Park, NC 27711, telephone (919) 541-0641, fax number (919) 541-5509, email at long.pam@epa.gov (preferred method for registering). SUPPLEMENTARY INFORMATION: I. General Information A. Does this action apply to me? Entities potentially directly affected by th is proposal and the draft guidance document include all state air agencies a nd any local air quality agency to whom a state has delegated relevant responsibilities for air quality manage ment, including air quali ty monitoring and data analysis. Tribal air agencies operating ambient ai r quality monitors that produce regulatory data may also be directly affected. Entities potential ly affected indirectly by this proposal and the draft guidance document include federal land manage rs (FLMs) of Class I areas, other federal agencies and other entities that operate ambient air quality monitors and submit collected data to the EPA’s Air Quality System (AQS) database.
B. What should I consider as I prepare my comments for the EPA?
1. Submitting CBI . Do not submit this information to the EPA through http://www.regulations.gov or email. Clearly mark the part or all of the information that you claim to be CBI. For CBI information in a disk or CD-ROM that you mail to the EPA, mark the outside of the disk or CD-ROM as CBI and then identify electronically within the disk or CDROM the specific information that is claimed as CBI. In addition to one complete version of the*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 7 of 218 comment that includes information claimed as CBI, a copy of the comment that does not contain the information claimed as CBI must be submitted for inclusion in the public docket. Information so marked will not be disclosed except in accordance with procedures set forth in 40 CFR part 2.
2. Tips for Preparing Your Comments

. When submitting comments, remember to:

● Identify the rulemaking and/or draft guidance document by docket number and other identifying information (subject heading, Federal Register date, page number and guidance document title, if applicable).

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

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

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

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

● Provide specific examples to illustrate your concerns, and su ggest alternatives.

● Explain your views as clearly as possibl e, avoiding the use of profanity or personal threats.

● Make sure to submit your comments by the identified comment period deadline. C. Where can I get a copy of these do cuments and other re lated information?*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 8 of 218 In addition to being available in the docket, an electronic copy of this notice and the draft guidance will be posted at http://www2.epa.gov/air-quality-analysis/treatment-data-influencedexceptional-events

. D. What should I know about the public hearing? The EPA intends to hold a public heari ng on Tuesday, December 8, 2015, in room 3175 in the Arizona Department of Environmental Quality main office building located at 1110 W. Washington Street, Phoenix, Ariz ona 85007. If you would like to at tend or speak at the public hearing, please contact Ms. Pamela Long, U.S. Environmental Protection Agency, Office of Air Quality Planning and Standards, Air Quality Planning Division, Mail Code C504-01, Research Triangle Park, NC 27711, telephone (919) 541-0641, fax number (919) 541-5509, email at long.pam@epa.gov (preferred method for registering) at least 2 days in advance of the public hearing ( see DATES ). Interested parties may submit oral and/or written comments. Interested parties do not need to attend the public hearing to submit written comments. Additional details concerning any public hearing for this proposed rule will be poste d on the EPA’s website for this rulemaking at http://www2.epa.gov/air-quality-analysis /treatment-data-influ enced-exceptionalevents

. E. How is this document organized? The information presented in this document is organized as follows: I. General Information A. Does this action apply to me? B. What should I consider as I pr epare my comments for the EPA? C. Where can I get a copy of these documents and other related information? D. What should I know a bout the public hearing? E. How is this document organized? II. Glossary of Terms and Acronyms III. Executive Summary IV. Background for Proposal A. Purpose of and Statutory Aut hority for this Regulatory Action*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 9 of 218 B. The 2007 Exceptional Events Rule C. Early Experience in Implementi ng the 2007 Exceptional Events Rule D. The EPA’s Interim Exceptional Events Implementation Guidance E. More Recent Implementation Experi ence Including EPA-Recommended Best Practices for the Development of Exceptional Events Demonstrations V. Proposed Rule Revisions A. To whom and to what pollutants does the Exceptional Events Rule apply? 1. Current Situation 2. Proposed Changes B. What is an exceptional event? 1. Current Situation 2. Proposed Changes C. What types of ambient concentration data and data uses may be affected by the Exceptional Events Rule? 1. Current Situation 2. Proposed Changes D. What is a natural event? 1. Current Situation 2. Proposed Changes E. Technical Criteria for the Exclus ion 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 Supporte d by a Comparison to Historical Concentration Data F. Treatment of Certain Events U nder the Exceptional Events Rule 1. Exceedances Due to Transported Pollution 2. Wildland Fires 3. Stratospheric Ozone Intrusions 4. High Wind Dust Events G. Other Aspects of Flagging Exceptional Ev ents-Influenced Data and Demonstration Submittal and Review 1. Who may submit a demonstration a nd request for data exclusion? 2. Aggregation of Events for NAAQS w ith Periods Longer Than 24 Hours and Demonstrations with Respect to Multiple NAAQS for the Same Pollutant 3. Exclusion of Entire 24-hour Value Vers us Partial Adjustment of the 24-hour Value for Particulate Matter 4. Flagging of Data 5. Initial Notification of Potential Exceptional Event 6. Submission of Demonstrations 7. Timing of the EPA’s Review of Submitted Demonstrations 8. Dispute Resolution Mechanisms VI. Mitigation A. Current Situation B. Proposed Changes 1. Defining Historically Document ed or Known Seasonal Events 2. Mitigation Plan Components*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 10 of 218 3. Options for Implementing Mitigation Plans VII. Draft Guidance on the Prep aration of Exceptional Events Demonstrations for Wildfire Events that May Influence Ozone Concentrations A. What is this draft guidan ce about and why is it needed? B. What scenarios are addressed in the draft guidance? VIII. Environmental Justice Considerations IX. Statutory and Executive Order Reviews A. Executive Order 12866: Regulatory Planni ng and Review and Executive Order 13563: Improving Regulation a nd Regulatory Review B. Paperwork Reduction Act C. Regulatory Flexibility Act D. Unfunded Mandates Reform Act E. Executive Order 13132: Federalism F. Executive Order 13175: Consultation a nd Coordination with Indian Tribal Governments G. Executive Order 13045: Protection of Childre n from Environmental Health & Safety Risks H. Executive Order 13211: Actions Concerning Regulations That Si gnificantly Affect Energy Supply, Distribution or Use I. National Technology Transfer and Advancement Act J. Executive Order 12898: Federal Actions to Address Environmental Justice in

Minority Populations and Low-Income Populations X. Statutory Authority II. Glossary of Terms and Acronyms The following are abbreviations of terms used in the preamble. AQCR Air Quality Control Region AQS Air Quality System Be Beryllium BACM Best available control measures BLM Bureau of Land Management BMP Best management practice(s) BSMP Basic smoke management practices CAA Clean Air Act CASTNET Clean Air Status and Trends Network CBI Confidential business information CFR Code of Federal Regulations CO Carbon monoxide EPA Environmental Protection Agency*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 11 of 218 FLM Federal land manager responsible for management of a federally owned area that has been designated a Class I area as codified in 40 CFR part 81, subpart D FR Federal Register IPV Isentropic potential vorticity Lidar A remote sensing techno logy that measures distance by illuminating a target with a laser and analyzing the reflected light μ g/m 3 Micrograms per cubic meter mph Miles per hour NAAQS National ambient air quality standard or standards NAM North American Mesoscale Forecast System NASA National Aeronautics and Space Administration NEPA National Environmental Policy Act NO 2 Nitrogen dioxide NOAA National Oceanic and A tmospheric Administration NOV Notice of violation NOx Nitrogen oxides NPS National Park Service NSR New source review NRCS Natural Resources Conservation Service NRDC Natural Resources Defense Council NWCG National Wildfire Coordinating Group NWS National Weather Service OAQPS Office of Air Quality Pla nning and Standards, U.S. EPA OMB Office of Management and Budget Pb Lead PM Particulate matter PM 10 Particulate matter with a nominal mean aerodynamic diameter less than or equal to 10 micrometers PM 2.5 Particulate matter with a nominal mean aerodynamic diameter less than or equal to 2.5 micrometers ppb Parts per billion PSD Prevention of signi ficant deterioration PT Potential temperature RACM Reasonably available control measures RAQMS Real-time Air Quality Modeling System RUC Rapid Update Cycle*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 12 of 218 SIP State implementation plan SMP Smoke management program SO 2 Sulfur dioxide TAR Tribal Authority Rule TIP Tribal implementation plan UMRA Unfunded Mandates Reform Act USDA U.S. Department of Agriculture USFS U.S. Forest Service VOC Volatile organic compound or compounds III. Executive Summary This section summarizes the purpose of this regulatory action, the major provisions of this action, and the developmen t of associated guidance. Purpose of this Regulatory Action Recognizing that it may not be appropriate for the EPA to use certain monitoring data collected by the ambient air quali ty monitoring network and mainta ined in the air quality data system (AQS) in the EPA’s regulatory determina tions, in 2005 Congress provided the statutory authority for the exclusion of data in specific situations by adding sec tion 319(b) to the CAA. The EPA promulgated the 2007 Exceptional Even ts Rule (March 22, 2007, 72 FR 13560) to implement this 2005 amendment of the CAA. The purpose of this action is to propose revisions to the 2007 Exceptional Events Rule to address certain substantive issues raised by state, local and tribal co-regulators and other stakeholders since promulgation of the rule and to increase the administrative efficiency of the Exceptional Events Rule criteria and process. The EPA intends to promulgate these rule revisions in advance of the date by which states, and any tribes that wish to do so, are required to submit their initial designation recommendations for the revised 2015 ozone NAAQS (expected in October of 2016). In addition, the EPA intends to address a 2008*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 13 of 218 D.C. Circuit Court decision in which the court found that certain preamble language was “legally null” because there was no associated implementing rule language. Interpreting and implementing the 2007 Exceptional Events Rule has been challenging in certain respects both for the air agencies develo ping exceptional events demonstrations and for the EPA regional offices reviewing and acting on these demonstrations. Since 2007, air agencies have submitted exceptional event demonstrations for a variety of pollutant and event combinations ranging from volcanic activity infl uencing sulfur dioxide and particulate matter concentrations to stratospheric ozone intrusions. Air agencies preparing demonstrations have expressed specific concerns and identified challenges associated with preparing analyses to satisfy the “but for” rule crit erion, determining what controls constitute reasonable controls particularly for natural sources and for interstate and internati onal transport and identifying how much documentation to include in a demonstration. As a result of both our experiences and feedback related to implementing the 2007 Exceptional Events Rule received from stat e, local and tribal co-regulators and other stakeholders via letters and nu merous conference calls and m eetings, the EPA developed and released Interim Exceptional Ev ents Implementation Guidance in May of 2013. This guidance has addressed some of the concerns and challe nges raised by interested parties, has helped reduce the burden of preparing demonstrations and has reduced the time needed for review. However, the EPA acknowledged that additiona l changes could only be accomplished through a notice-and-comment rulemaking. Therefore, when the EPA released the Interim Exceptional Events Implementation Guidance in May of 2013, we simultaneously announced our intent to pursue revisions to the Exceptional Events Rule. These changes are reflected in this proposed action.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 14 of 218 Concurrent with preparing this proposed action, the EPA held conference calls with some air agencies to discuss more recent implementation experi ences and to better understand currently employed exceptional events implementa tion processes and practices. As a result of these discussions, the EPA developed a list of best practices for communication and collaboration between the EPA and air agencies. Agencies using these approaches have developed a common understanding of expectations, terminology and interpretation of the EPA’s regulations and policy, which, in turn, helps fo cus efforts, optimize resources and save time during the demonstration devel opment and review process. Based on our experiences and the input we ha ve received from our collaborations with interested parties (including state, local and trib al air agencies) following the promulgation of the 2007 Exceptional Events Rule and since the deve lopment of the Interim Exceptional Events Implementation Guidance and based on the previous legal challenge, we have determined those aspects of the 2007 Exceptional Even ts Rule that most need to be addressed in this proposed action. Summary of Major Provisions For the first time, the EPA proposes to interp ret CAA section 319(b) as applying to only a specific set of regulatory actions ( e.g ., designations) because we belie ve that the criteria and process steps specified in the C AA were not clearly intended by Congr ess to apply to all types of regulatory actions and in some cases certain of the criteria and steps are not appropriate. We address this concept in this document in general te rms, but we also intend to develop a separate guidance document to provide guidance on when da ta can be excluded and when they cannot for other specific types of regulatory actions.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 15 of 218 The EPA proposes to return to the core stat utory elements and implicit concepts of CAA section 319(b): the event affected air quality in such a way th at there exists a clear causal relationship between the specific event and the monitored exceedan ce or violation, the event was not reasonably controllab le or preventable and the event wa s caused by human activity that is unlikely to recur at a particular location or was a natu ral event. Within each of these elements, we are proposing clarifications regarding the desired an alyses to include in exceptional events demonstrations and we discuss the applicability of these clarificat ions to certain event types or categories. As part of this return to the core st atutory elements, we are proposing to remove from the Exceptional Events Rule a paragraph contai ning what is commonly referred to as the “but for” criterion. The EPA is proposing to incorporate the stat utory “affects air quali ty” criterion and the regulatory “historical fluctuations” criterion within the “clear causal relationship” element. We believe that if an air agency demonstrates that an event has a clear cau sal relationship to an exceedance or violation of a NAAQS, then the even t has certainly affected air quality and that a submitting air agency does not need to address “affects air quality” as a distinct component. As we indicated in the Interim Exceptional Events Implementation Guidance (s ee section IV.D), we believe that a comparison of the claimed event-infl uenced concentration(s) to concentrations at the same monitoring site at other times is extr emely useful evidence in an exceptional events demonstration, particularly as part of showi ng a clear causal relations hip, and we propose to continue requiring this type of comparison. This proposed acti on details the minimum set of statistical analyses that the EPA e xpects to see in demonstrations. With respect to the “not reasonably contro llable or preventabl e” criterion, many states have requested that the EPA automatically consider an event to be reasonably controlled if the*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 16 of 218 EPA has approved a state implementation plan (SIP ) that contains controls for anthropogenic sources that contribute to the event that are al so specific to the pollutant of concern in the exceptional events demonstration. In response, the EPA proposes that enforceable control measures implemented in accordance with an attainment or maintenance SIP, approved by the EPA within 5 years of the date of a demonstration submittal, that address the event-related pollutant and all sources necessary to fulfill the requirements of the CAA for the SIP to be reasonable controls with respect to all anthropoge nic sources that have or may have contributed to event-related emissions. Also for this criterion, the EPA clarifies that air agencies generally have no obligation to specifically address controls if the event was natural or if it was due to emissions originating outsi de their jurisdictional ( i.e. , state or trib al) border(s). With respect to the “human activity that is un likely to recur at a part icular location or was a natural event” criterion, we propose a general approach to de termining whether the recurrence frequency of an event is “unlikely to recur at a particular location” and an approach applicable to prescribed fire on wildland only. We also clarify that natural events can recur, sometimes frequently, and reiterate our belief that we generally consider huma n activity to have played little or no direct role in causing emissions if anthr opogenic emission sources th at contribute to the event emissions are reasonably contro lled at the time of the event. Air agencies must address all of the core statutory elements and implicit concepts of CAA section 319(b) within an exceptional events demonstration. In this proposed action, the EPA clarifies the content and organization of exceptional events submittals to include the core statutory elements, but we also pr opose that states be required to include a conceptual model, or narrative, describing the event(s) causing the ex ceedance or violation a nd a discussion of how emissions from the event(s) led to the exceedance at the affected monitor(s) and documentation*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 17 of 218 that the air agency conducted a public comment process. We are proposing to require an initial notification by the state to the EPA of a potential exceptional event as a preliminary step before submitting a demonstration, to ensure the submitti ng air agency and the reviewing EPA regional office share a common understand ing regarding the potential event and are in communication regarding the timeline for the demonstration to be submitted and to be reviewed by the regional office. Because affected air agencies have provided feedback regarding the difficulty associated with meeting the current regulatory timelines as sociated with data flagging, initial event descriptions and demonstration submittals, the EPA proposes to remove the specific deadlines that apply in situations other than initial area designations following pr omulgation of a new or revised NAAQS. Also associated with demonstr ation timing, the EPA proposes to officially terminate review of demonstrations that, due to the passage of time, will have no further regulatory significance specifically fo r the five types of regulatory actions identified in section V.C. of this preamble. Since promulgation of the 2007 Exceptional Ev ents Rule, stakeholders have raised numerous questions about fire-rel ated components that were disc ussed, but not fully defined or clarified, in the preamble to the 2007 Rule. This proposed action addresses fire-related definitions, provides more clarity regarding expectations for smoke management programs (SMPs) and basic smoke management practices (BSMP), and proposes limited scenarios under which federal land managers and other federal agencies may prepare and submit exceptional events demonstrations and data excl usion requests directly to the EPA.
Associated Guidance Documents In addition to proposing revisions to the 2007 Exceptional Events Rule, this proposed*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 18 of 218 action simultaneously provides a notice of availabili ty of a draft non-binding guidance document titled, Draft Guidance on the Preparation of Excep tional Events Demonstrations for Wildfire Events that May Influence Ozone Concentrations , which applies the proposed Exceptional Events Rule revisions to wildfire/ozone events . This guidance document is intended to further address specific stake holder questions regarding the Exceptional Events Rule and further increase the efficiency of rule implementati on. In addition, the EPA is currently developing a guidance document titled, Draft Guidance for Excluding Some Am bient Pollutant Concentration Data from Certain Calculations and Analys es for Purposes Other than Retrospective Determinations of Atta inment of the NAAQS , which will apply to the exclusion of certain data for certain applications using a process and criteria outside of the Exceptional Events Rule. The EPA intends to make this guidance document availa ble shortly after propos ing revisions to the Exceptional Events Rule. The EPA expects to fi nalize these guidance doc uments concurrently with promulgating revisions to the Exceptional Events Rule. IV. Background for Proposal
A. Purpose of and Statutory Authorit y for this Regulatory Action Part of the EPA’s mission is to preserve and improve, when needed, the quality of our nation’s ambient air to protect human health and the environment. As part of accomplishing this, the EPA develops the national ambient air quality standards (NAAQS) for cr iteria pollutants and oversees the states’ programs to improve air qual ity in areas where the current air quality is unacceptable and to prevent deterioration in areas where the air quality meets or exceeds the NAAQS. The EPA then evaluates the status of the ambient air as compared to these NAAQS by using data collected in the national ambient ai r quality monitoring network established under the authority of section 319(a) of the CAA.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 19 of 218 Recognizing that it may not be appropriate for the EPA to use certain monitoring data collected by the ambient air quali ty monitoring network and maintained in AQS in our regulatory determinations, in 2005 Congress pr ovided the statutory authority fo r the exclusion of data in specific situations by adding se ction 319(b) to the CAA in 20 05. The EPA promulgated the 2007 Exceptional Events Rule (March 22, 2007, 72 FR 13560) to implement this 2005 amendment of the CAA. The purpose of this action is to propo se revisions to the 2007 Exceptional Events Rule to address certain issues raised by stakeholders since promulgation of the rule and to increase the administrative efficiency of the Exceptiona l Events Rule criteria and process. In addition to proposing revisions to the 2007 Exceptional Events Rule, we are simultaneously providing a notice of availabi lity of a draft non-bi nding guidance document titled, Draft Guidance on the Preparation of Excep tional Events Demonstrations for Wildfire Events that May Influen ce Ozone Concentrations, which applies the proposed Exceptional Events Rule revisions to wildfire/ozone events . We seek comment on whether the concepts in this guidance document should be finalized as ru le text. We are also currently developing a second guidance document titled, Draft Guidance for Excluding Some Ambient Pollutant Concentration Data from Certain Calculati ons and Analyses for Purposes Other than Retrospective Determinations of Attainment of the NAAQS , which will apply to the exclusion of certain data for certain applicati ons using a process and criteria outside of the Exceptional Events Rule. Both of these draft guidance documents are intended to further addr ess specific stakeholder concerns regarding the Exceptional Events Rule and further increase the efficiency of rule implementation.
B. The 2007 Exceptional Events Rule*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 20 of 218 The 2007 Exceptional Events Rule created a regu latory process codified at 40 CFR parts 50 and 51 (sections 50.1, 50.14 and 51.930). These re gulatory sections contain definitions, procedural requirements, requirements for air agency demonstrations, criteria for the EPA’s approval of the exclusion of event-affected air quality data from the data set used for regulatory decisions, and requirements for air agencies 1 to take appropriate and r easonable actions to protect public health from exceedances or violations of the NAAQS. 2 The 2007 Exceptional Events Rule

1 References to “air agencies” are meant to include state, local and tribal air agencies responsible for implementing the Exceptional Events Rule . The regulatory text in the 2007 Exceptional Events Rule often uses “State” to apply to “air agencies.” In the context of flagging data and preparing and submitting demonstrations, the role of and options available to air agencies would also apply to federal land managers of Class I areas and other federal agencies managing federal land. 2 Per the definition at 40 CFR 50.1(l), an exceedance with respect to a national ambient air quality standard means one occurrence of a measured or modeled concentration that exceeds the specified concentration level of such standard for the averaging period specified by the standard. Violations of a standard are standard-specific and are determ ined by applying the standardspecific 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 μ g/m 3 occurs when the 24-hour concentration is above 35 μ g/m 3 on a single day. A violation of the 2006 24-hour PM 2.5 NAAQS occurs when the 3-year average of the annual 98 th percentile 24-hour concentrations is above 35 μ g/m 3

.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 21 of 218 superseded the EPA’s previous natural events gui dance and those sections of an earlier guidance document that addressed the treatment of data affected by exceptional events. 3 In general, the exceptional events regulatory process consists of the following steps. First, an air agency identifies a potenti al event-related exceedance or vi olation. After noting these data in AQS, the air agency prepares a draft demons tration package to support the exclusion of the identified event-related data and provides an opportunity for public comment. The air agency submits the draft demonstration and any receiv ed public comments to its EPA regional office, which then reviews the submittal and concurs, nonc oncurs or defers a decision related to the air agency’s request to exclude data that have been affected by exceptional events. If the EPA agrees with the air agency’s request, the data are ex cluded. If the EPA does not agree with the air

3 Previous guidance and policy documents that e ither implied or stated the need for special treatment of data affected by an exceptional event include: i) Guideline for the Interpreta tion of Air Quality Standards , U.S. EPA, OAQPS No. 1.2-008, Revised February 1977. Available at http://nepis.epa.gov/Exe/ZyNET.exe/2000YFDB. TXT?ZyActionD=ZyDocument&Client=EPA&I ndex=1976+Thru+1980&Docs=&Query=&Time= &EndTime=&SearchMethod=1&TocRestric t=n&Toc=&TocEntry=&QField=&QFieldYear= &QFieldMonth=&QFieldDay=&IntQFieldOp =0&ExtQFieldOp=0&XmlQuery=&File=D%3 A%5Czyfiles%5CIndex%20Data%5C76thru80% 5CTxt%5C00000007%5C2000YFDB.txt&User=AN ONYMOUS&Password=anonymous&SortM ethod=h%7C- &MaximumDocuments=1&FuzzyDegree=0&Im ageQuality=r75g8/r7 5g8/x150y150g16/i425&D isplay=p%7Cf&DefSeekPage=x &SearchBack=ZyActionL&Back=ZyActionS&BackDesc=Result s%20page&MaximumPages=1&ZyEntry=1&SeekPage=x&ZyPURL. ii) Guideline on the Identification and Use of Air Quality Data Affected by Exceptional Events (the Exceptional Events Policy), U.S. EPA, OAQPS, EPA-450/4-86-007, July 1986. iii) Areas Affected by PM-10 Natural Events (the PM 10 Natural Events Policy), memorandum from Mary D. Nichols, Assistant Administrato r for Air and Radiation, to EPA Regional Offices, May 30, 1996. Available at http://www.epa.gov/ttn/caaa/t1/memoranda/nepol.pdf. iv) Interim Air Quality Policy on Wildland and Prescribed Fires. U.S. EPA. April 23, 1998. Available at http://www.epa.gov/ttn/oarpg/t1/memoranda/firefnl.pdf. v) Guideline on Data Handling Conventions for the PM NAAQS. U.S. EPA, OAQPS, EPA454/R-98-017, December 1998.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 22 of 218 agency claim, or if the EPA decides to defer a decision on the submittal, the data are used in regulatory determinations. The 2007 Exceptional Events Rule was challenged in 2008. In NRDC v. EPA, 559 F.3d 561 (D.C. Cir. 2009), the Natural Resources De fense Council (NRDC) brought a petition for review challenging the EPA’s definition of a natural event and seeking to vacate several statements in the preamble to the final 2007 Ru le concerning the types of events that could qualify as being eligible for excl usion under the rule provisions. In particular, NRDC objected to treating “events in which human activities play ‘ little’ causal role” as na tural events. Regarding the definition of a natural event, the D.C. Circ uit Court determined that NRDC did not identify its objection during the rulemaking process and, therefore, did not ha ve standing under CAA section 307 to challenge the definition. NRDC also challenged the preamble language addressing high wind events. In its decision, the D.C. Circuit stated, In one section of the preamble, EPA refers to its “final rule concerning high wind events,” which “states that ambient particulat e concentrations due to dust being raised by unusually high winds will be treated as due to uncontrollable natural events” when certain conditions apply.... There is no such final rule. The final rule does not mention high wind events or anything about “ambient particulate matter concentrations.” EPA calls this a drafting error. In light of th e error, the high wind ev ents section of the preamble is a legal nullity. The EPA believes it is clear that the “high wind events section of the preamble” to which the court referred is the en tire section titled, “ B. High Wind Events ” beginning at 72 FR 13576. Accordingly, since 2007, the EPA has not relied solely on this section of the preamble when implementing the 2007 Rule. The EPA maintains that certain of the preamble passages determined to be “legally null” are in fact appr opriate interpretations of the Exceptional Events Rule and are consistent with the CAA. For clar ity and regulatory certainty, the EPA is proposing*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 23 of 218 in rule text form some of the interpretative positions originally stated in the High Wind Events section of the preamble to the 2007 Exceptional Events Rule. Within each topical area of th is notice, the EPA has provide d more detailed background information on specific aspects of the 2007 Excepti onal Events Rule and its implementation to allow readers to consider the proposed change s in the context of th e current situation.
C. Early Experience in Implementing the 2007 Exceptional Events Rule Interpreting and implementing the 2007 Exceptional Events Ru le has been a challenging process both for the air agencies developing exce ptional events demonstrations and for the EPA regional offices reviewing and acting on thes e demonstrations. Shortly after the EPA promulgated the rule in 2007, air agencies aske d the EPA to clarify key rule provisions and expectations for these demonstrations. Air agen cies also asked for demonstration templates and/or examples of acceptable demonstrations for various event and pollutant combinations. Although the EPA provided some of this inform ation via the exceptional events website at http://www2.epa.gov/air-quality-analysis/tr eatment-data-influenced-exceptional-events , air agencies noted that, in their view, the in formation provided was insufficient and sought additional guidance to facilitate consistency am ong the EPA regional offices in interpreting and implementing the 2007 Exceptional Events Rule. In the years since rule promulgation, air agencies continued to express concern, through various mechanisms including formal letters, informal emails, interaction at various meetings and C ongressional testimony, about the consistent application of the 2007 Exceptional Events Rule and the resources expended to prepare exceptional even ts demonstrations. The EPA has also faced challenges in re viewing submitted demonstrations. Because exceptional events are fact-specific and thus uni que and varied, providing templates or general*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 24 of 218 guidance was, and still is, ch allenging. The EPA also acknowle dges that the final rule and preamble language for the 2007 Exceptional Events Rule provided room for interpretation, making it difficult for air agencies and the EPA to determine how much ev idence or technical analysis for demonstrations is needed. We do, however, think that providing additional recommendations on appropriate documentation w ould be helpful. Throughout this proposal, for example in section V.E, Technical Criteria for th e Exclusion of Data Affected by Events, and in section V.F, Treatment of Certain Events U nder the Exceptional Events Rule, we provide recommendations for language and analyses to include in demonstration packages. Additional detail regarding specific recommendations is available in the EPA’s guidance documents and on the EPA’s exceptional events website, which the EPA will update to inco rporate the finalized rule changes concurrently with or shortly afte r promulgating the final rule. The EPA will also continue to maintain and update the exceptional events submissions table on its website with examples of approved submissions. These ex amples may help air agencies develop demonstration packages; however, they may not contain the minimum level of data or casespecific analyses necessary for all exceptional even ts demonstrations of the same event type. In addition, commenters on this notice may wish to provide suggestions on the appropriate documentation for specific types of ex ceptional events demonstrations. D. The EPA’s Interim Exceptional Events Implementation Guidance As a result of stakeholder-ide ntified concerns and the EPA’ s own experience related to implementing the 2007 Exceptional Events Rule, in 2010 the EPA began developing additional implementation guidance. In May of 2011, the EPA released the Draft Exceptional Events Implementation Guidance: the Draft Guidance to Impl ement Requirements for the Treatment of Air Quality Monitoring Data In fluenced by Exce ptional Events , the Draft Exceptional Events*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 25 of 218 Rule Frequently Asked Questions document and the Draft Guidance on the Preparation of Demonstrations in Support of Requests to Exclud e Ambient Air Quality Data Affected by High Winds under the Exceptional Events Rule . The EPA provided these draft guidance documents to interested air agencies, FLMs, other federal agencies and other parties upon request, for preliminary review to solicit comment and help en sure that the EPA’s fi nal guidance provided an efficient and effective process to make determinations regarding air quality data affected by exceptional events. The EPA also placed additiona l examples of approved demonstrations on the EPA’s website. The EPA incorporated the commenters’ feedb ack, as appropriate, into revised draft guidance documents, which were made availabl e for broad public review in a July 6, 2012, Federal Register Notice of Availability (77 FR 39959) and in the associated docket (Docket ID No. EPA-HQ-OAR-2011-0887). 4 This docket includes a summary of the comment and response process from the 2011 preliminary review of the draft guidance documents. In addition to identifying specific comments on the draft guidan ce documents, this summary clearly identifies that implementation challenges originated shortly after the EPA promulgated the 2007 Exceptional Events Rule. 5 In May 2013, after a round of re view and comment by the general public, the EPA finalized the Interim Exceptional Events Implementation Guidance and made

4 The EPA established Docket ID No. EP A-HQ-OAR-2011-0887 for the July 2012 notice of availability for the Draft Excepti onal Events Implementation Guidan ce and has incorporated this docket into the record for this action. 5 Responses to Significant First-Round Comme nts on the Draft Guidance Documents on the Implementation of the Exceptional Events Rule , U.S. EPA, June 2012. Available in Docket No. EPA-HQ-OAR-2011-0887.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 26 of 218 these documents publicly available on the exceptional events website at http://www2.epa.gov/air-quality-analysis/tr eatment-data-influenced-exceptional-events

. 6 With the release of the Interim Exceptional Events Implementation Guidance, the EPA simultaneously acknowledged the need to consid er additional changes that could only be accomplished through a notice-and-comment rulemaking to revise the 2007 Exceptional Events Rule. To inform the development of proposed ru le revisions, the EPA hosted exceptional events listening sessions in August and November of 2013 for interested air agencies, FLMs, other federal agencies, regional planning organizati ons, non-governmental organizations and other members of the public. The EPA has considered f eedback from these listening sessions and the previous public comments on the Interim Excep tional Events Implementation Guidance in the development of these proposed revisions to the 2007 Exceptional Events Rule. E. More Recent Implementation Experience In cluding EPA-Recommended Best Practices for the Development of Exceptional Events Demonstrations Because of the passage of time since the 2013 exceptional events listening sessions, the EPA’s Office of Air Quality Planning and Standa rds (OAQPS) held conference calls with some air agencies and the EPA regional offices between September 2014 and March 2015 to ask whether any new implementation concerns ha d arisen and to bette r understand currently employed exceptional events implementation processes and practices.

6 The Interim Exceptional Events Implementation Guidance includes: the Interim Guidance to Implement Requirements for the Treatment of Air Quality Monitoring Data Influenced by Exceptional Events , the Interim Exceptional Events Ru le 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 Qual ity Data Affected by High Winds under the Exceptional Events Rule (the Interim High Winds Guidance document).*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 27 of 218 As a result of these discussions, the EPA developed a list of best practices for communication and collaboration between the EP A and air agencies. These best practices include having discussions before, during a nd after the development and submission of exceptional events demonstration packages. Specif ically, these best practices recommend that the EPA regional offices and their air agencies disc uss, on a mutually agreed upon frequency, those demonstrations that the agencies have deve loped and submitted for the EPA’s action. These regular discussions should focus on whether the demonstrations have regulatory significance ( e.g ., significance for any of the five types of regulatory actions iden tified in section V.C.) and, if not, whether the EPA can provide general technical or policy feedback that the air agency can include in future demonstrations. Prior to an ai r agency’s development of future demonstrations, the air agency and the EPA should identify the relevant days and monitors of focus, the regulatory significance of these monitor days, the an alyses of particular interest for a specific event and pollutant combination and the anticipa ted timeframe for demonstration submission and response. Discussions should continue while the air agency is developing the demonstration and after the agency submits the demonstration and wh ile the EPA is reviewin g the demonstration, to ensure both the air agency and the EPA are aware of status, direction and progress. Finally, after the EPA has acted on the demonstration, the revi ewing EPA regional office and the air agency should discuss elements of the process that should continue a nd those that should be improved, should understand the information in the demonstration that was useful versus the information that was extraneous and should discuss the possi bility of developing a de monstration template(s) for future events of the same type(s). Agencies using this communications appro ach have developed a common understanding of expectations, terminology and interpretation of the EPA’s regulations and policy, which, in*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 28 of 218 turn, helps focus efforts, optimize resources and save time during the demonstration development and review process. A summary of this “best pr actices” approach to implementation is available

at http://www2.epa.gov/air-quality- analysis/treatment-data-in fluenced-exceptional-events

. V. Proposed Rule Revisions
A. To whom and to what pollutants doe s the Exceptional Events Rule apply?
1. Current Situation Under the CAA, states are primarily respons ible for the administ ration of air quality management programs within their borders, wh ich 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 th at may warrant special treatment under the Exceptional Events Rule. The 2007 Exceptional Events Rule applies to all st ate air agencies and to local air quality agencies to whom a state has delegated relevant responsibilities for air quality management, including air quality monitoring and data analysis. Additionally, the 2007 Exceptional Events Rule app lies to some tribal air quality agencies who have been granted treatment as a state fo r section 319 of the CAA. Section 301(d) of the CAA authorizes the EPA to recognize tribal au thority, allowing eligib le, federally-recognized tribal governments to implement provisions of th e CAA. Pursuant to se ction 301(d)(2), the EPA promulgated regulations, known as the Tribal Au thority Rule (TAR), on February 12, 1999 (63 FR 7254, codified at 40 CFR part 49). That rule specifies those provisions of the CAA for which it is appropriate to treat tribes in a similar manner as states. Unde r the TAR, tribes may choose to develop and implement their own CAA programs, but are not required to do so. The TAR also establishes procedures and criter ia by which tribes may request fr om the EPA a determination of eligibility to implement the provisions of the CAA. In cases where a tribal air quality agency is*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 29 of 218 eligible to implement CAA sec tion 319 and has installed and opera tes an air quality monitoring network that produces regulatory da ta that is affected by emissions from exceptional events, the criteria and procedures identifie d in these proposed rule revisions may be used to exclude data for purposes of regulatory decisi ons. Some tribes may implement only portions of the relevant air quality monitoring program and may choose not to address all of the procedures and requirements associated with excluding data th at have been influenced by exceptional events ( e.g ., a particular tribe may ope rate a monitoring network fo r purposes of gathering and identifying data appropriate for informational or educational purposes, but may choose not to implement relevant programs for the purpose of mitigating the effects of exceptional events). Where a tribal air quality agency is not eligible to implement CAA section 319 but operates an air quality monitoring network that produces regula tory data that is aff ected by emissions from exceptional events, the tribal air quality agency should consult with the EPA regional office prior to addressing the procedures and requirements associated with excluding data that have been influenced by exceptional events. 7 In all cases, the EPA will con tinue to work with tribes in implementing any promulgated rule revisions. While air agencies are respons ible for administering air quality management programs within their borders, FLMs of Class I areas, ot her federal agencies an d/or other entities ( e.g ., industrial facilities pursuant to permit conditions) may also operate ambient air quality monitors

7 As of the signature date of this action, only one tribe is eligible to implement all portions of CAA section 319 under the TAR. Several other tr ibes, however, operate air quality monitoring networks that produce regulatory data that coul d be affected by emissions from exceptional events.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 30 of 218 that meet all requirement s of 40 CFR parts 50 and 58. 8 The FLMs, other federal agencies and other entities operating these regu latory monitors may submit collected data to the EPA’s AQS database. 9 These concentration measurements can be affected by exceptional events. The AQS software allows only the entity operating a mon itor (and the EPA data system manager) to apply exceptional events flags to data from that m onitor. Although FLMs and ot her entities can apply exceptional events flags to data from monitors they operate, the Exceptional Events Rule at 40 CFR 50.14(b)(1) states that the EPA shall excl ude data from use in determinations of exceedances and NAAQS violat ions 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 resu lted in an interpretation that only states can initiate the exceptional events process and submit demonstrations. Some stakeholders have asked the EPA to identify the process that the state air agency should follow if the state air agency does not have AQS access rights to place exceptional events flags on event-affected data from monitoring stations located within the state but not operated by the state. The EPA addressed this issue generally in Question 23 of the Interim Q&A document by indicating that air agencies should consult with their EPA regional office ea rly in the development of an exceptional event demonstration package if they believe that monitors on federally-owned and managed land ( e.g .,

8 The Ambient Air Quality Surveillance provisi ons 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 sp ecifically apply to state air pollution control agencies and any local air po llution control agency to which the state has delegated authority to op erate a portion of the stat e’s monitoring network. 9 For a description of one network of mon itoring sites operated by federal agencies, see the 2014 CASTNET (Clean Air Status and Trends Ne twork) Annual Network Plan, available at http://epa.gov/castnet/javawe b/ozone/CASTNET_Plan_2014_Final.pdf , which applies to National Park Service (NPS) and Bureau of La nd Management (BLM) site managers operating CASTNET monitors.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 31 of 218 national parks within the state) have been affected by an event. In these instances, the EPA has assisted in facilitating cross-ag ency coordination regarding the flagging of data, where needed. The 2007 Exceptional Events Rule applie s to all criteria pollutant NAAQS. 10 This is appropriate given the language in CAA secti on 319(b)(3)(B)(iv), which applies to exceedances or violations of “the national ambient air qua lity standards.” The EPA regulations for the interpretation of ambient data with respect to the NAAQS that were in place prior to the 2007 Exceptional Events Rule and that have not been revised do not contain provisions allowing for the special handling of air quality data affected by exceptional even ts or do so without explicit reference to the Exceptional Events Rule as governing such exclusion. One NAAQS without a specific provision for handling event-affected da ta is 40 CFR part 50, appendix K for particulate matter (PM) with a nominal mean aerodynamic diameter less than or equal to 10 micrometers (PM 10 ). Nevertheless, the EPA has enabled in AQS the capability to flag all criteria pollutant data, including the option for the EPA’s concurren ce, as the EPA maintain s that the monitored concentrations of all NAAQS polluta nts have the potential to be elevated by one or more event types and the Exceptional Events Rule should govern the process of data exclusion for certain types of regulatory act ions (see section V.C). 2. Proposed Changes As noted above, because FLMs and other fe deral agencies may operate regulatory monitors and submit collected data to the EPA’ s AQS database and emissions from exceptional

10 There are NAAQS for carbon monoxide (C O), lead (Pb), nitrogen dioxide (NO 2 ), ozone, particle pollution a nd sulfur dioxide (SO 2 ). This applicability include s 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 ev ent situation with resp ect to a non-identical secondary NAAQS.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 32 of 218 events could affect these same monitors, the EPA proposes to allow FLMs and other federal agencies to prepare and submit exceptional events demonstrations and data exclusion requests directly to the EPA. The EPA believes this is appropriate because, in many cases, the lands managed and/or owned by federal entities are not en tirely within the juri sdictional boundary of a single state or local government. Also, as we di scuss in more detail in section V.F.2, federal entities may either initiate prescribed fires or fight wildfires on lands managed and/or owned by federal entities. The EPA could determine both of types of fires to be exceptional events. The EPA expects that allowing FLMs and other federal agencies to submit exclusion requests directly will expedite the exceptional events demonstrat ion development and submittal process. The EPA solicits comment on this proposed addition to the rule text, which appears at the end of this document. Based on comments received, the EPA may retain, modify or not include this provision in the final promulga ted rule. This provision woul d apply only to FLMs and other federal agencies that either operate a monitor that has been affected by an event or that manage land on which an exceptional even t originates. The provision w ould allow such FLMs and other federal agencies to provide demonstrations dire ctly to the EPA only afte r a discussion with the state in which the monitor is operated. Alternativ ely, this discussion might result in an agreement that the federal agency flag the data in AQS at the air agency’s request and then provide a draft demonstration document to the a ppropriate state air agency fo r adoption and submission by the air agency to the EPA, as is currently allowed. If the provision for direct submission to the EPA is included in the final action, demonstrations pr epared by FLMs or other federal agencies would be required to meet all provisions in the Exceptio nal Events Rule, including the requirement for a*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 33 of 218 public comment period on a prepared demonstration 11 and the requirements related to schedules and procedures for demonstration package submittal ( see sections V.G.4, V.G.5 and V.G.6) that apply to state agencies that operate monitors.
B. What is an exceptional event? 1. Current Situation The existing definition of an exceptional event at 40 CFR 50.1(j) repeats the CAA definition, which provides that an exceptional event is one that affects air quality, is not reasonably controllable or preventable, is caused by human activity that is unlikely to recur at a particular location or is a natural event, and is determined by the Administrator in accordance with 40 CFR 50.14 to be an excepti onal event. Also, CAA section 319( b)(3)(B)(ii) requires that a clear causal relationship must exist between the measured exceedances of a NAAQS and the exceptional event to demonstrate that the ex ceptional event caused a specific air pollution concentration at a particular air quality monitoring location. In addition to these defining elements, the 2007 Exceptional Events Rule at 40 CFR 50.14(c)(3)(iv) requires that the demonstration provide evidence that “the event is associated with a measured concentration in excess of normal historical fluctu ations, including bac kground” and evidence that “there would have been no exceedance or violation but for the event.” Both the statutory and regulatory definitions of an exceptional event include the provision that the event affected air qualit y. Many types of events affect ai r quality by causing emissions or

11 A public comment opportunity is important prio r to submission to the EPA because under the Exceptional Events Rule the EPA is not required to provide a public comment opportunity prior to concurring with an air agency’s request to exclude data. The EPA generally provides a public comment opportunity before we use air quality data , with or without such exclusions, in a final regulatory action. States typically provide an opportunity for public comment by posting draft demonstrations on a website. Federal agencies could do the same.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 34 of 218 increasing otherwise occurring emissions. Stratos pheric ozone intrusions, one type of event, differ from most other event types in that they tr ansport ozone already formed in the stratosphere to a surface monitor. High temp eratures, air stagnations and meteorological inversions can increase the level of air pollution formed from a given amount of emissions. However, both the statutory and regulatory definitions of an exceptional event specifically exclude stagnation of air masses, meteorological inversions and meteorological events invol ving high temperatures or lack of precipitation, as well as air pollu tion relating to source noncompliance. While the CAA definition of an exceptional event excludes “a meteorological event involving high temperatures or l ack of precipitation,” high temp eratures and dr ought conditions can contribute to exceedances and violations cau sed by other exceptional events such as high wind dust events. If an air agency submits eviden ce showing that a severe drought that resulted in arid conditions ( e.g ., lower than typical soil moisture c ontent, decreased vegetation, etc.) was combined with an event, such as a high wind even t, that falls within the CAA definition of an exceptional event and has affected air quality data, these data coul d be considered eligible for exclusion under the provisions of the Exceptional Events Rule. Under this scenario, the EPA would consider the high wind event as the critic al exceptional event. The high wind event would need to meet the provisions of the Exceptio nal Events Rule, includi ng assessing whether the event is a natural event or an event due to hum an activity unlikely to recur at a particular location. As another example, if a wildfire exacerbated by drought conditions causes ozone exceedances, then the EPA can consider the ozone exceedances for exclusion under the Exceptional Events Rule because wildfires, unlike lack of precipitation itself, are not excluded from the CAA definition of an exceptional event. However, high temperatures alone that result in elevated ozone concentrations would not be elig ible for exclusion under the Exceptional Events*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 35 of 218 Rule. Elevated temperatures and inversions can affect ambient air quality apart from any interactions with emissions, but such conditions alone are not exceptional events by the very clear provisions of the CAA. The EPA believe s that Congress intend ed air agencies to compensate for the effects of high temperature and inversions on concentrations formed from anthropogenic emissions through the development of SIPs. To summarize, the 2007 Exceptional Events Rule specifies six elements that air agencies must address when requesting that the EPA exclude event-related concentr ations from regulatory determinations:

 The event affected air quality

 The event was not reasonably controllable or preventable

 The event was a human activity that is unlik ely to recur at a pa rticular location, or was a natural event

 There exists a clear causal relationshi p between the specific event and the monitored exceedance

 The event is associated with a measured concentration in excess of normal historical fluctuati ons including background

 There would have been no exceedance or violation but for the event Section 50.14(b)(3) clearly makes the first three of these elements preconditions for the EPA to approve an air agency’s request to ex clude data. However, the last three of these elements are listed only in 50.14(c)(iv), which pr ovides that the state “s hall provide evidence” that they are true. Since prom ulgation of the 2007 Exceptional Events Rule, the EPA has treated all six elements as conditions that air agencies must address in a dem onstration prior to the EPA’s concurring with an air agency’s request to exclude data. In the In terim Exceptional Events*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 36 of 218 Implementation Guidance, the EPA stated th at for the fifth of these elements ( e.g ., the “historical fluctuations” element), there is no bright line th at defines when a concentration is “in excess of historical fluctuations.” With re spect to the sixth element, referre d to as the “but for” criterion, although the EPA has, in some cases, expected dem onstrations to contain a quantitative estimate of the concentration increment caused by the event, more frequently the EPA has considered the “but for” criterion to be satisfied by a more qua litative showing that the measured concentration was much greater than the non-exceedance conc entration that would have normally been expected on the day in question. In addition to considering whether or not an event is “exceptional” under the Exceptional Events Rule, an air agency and the EPA must al so decide whether an “ev ent” has occurred. An event, or anomaly, is a deviation from normal or expected conditions th at contributes to air pollution. In some cases, air agencies or other observers can clearly s ee this “deviation,” for example unusually high wind speeds transporting dus t, fires generating PM or ozone precursors or volcanoes venting plumes of SO 2 , PM and PM precursors. 12 In other cases, such as with stratospheric ozone intrusions, the physical e ffects of the event may not be visible and the occurrence of an event can only be inferred from seeing the eff ect on monitored air quality of emissions associated with the event. As desc ribed in section V.E.3, comparing the ambient pollutant concentrations in question to the histor ical distribution of concentrations of the same pollutant can help an air agency determine wh ether a deviation from normal concentrations occurred. However, such comparisons must consider that multiple factors often contribute to

12 The EPA considers on-going emissions from vol canic activity to be “events” even if they occur every day over a long period. The EPA consid ers this approach to be consistent with Congressional intent, but that extending the same treatment to air pollution due to every day biological processes or lightning would not be consistent with that intent.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 37 of 218 high pollutant concentrations. Some events, such as stratospheric ozone intrusions and high wind dust events, may last only a few hours at any one location. Still other events, such as volcanic activity, may occur and affect pollutant con centrations for a sust ained period of time ( e.g ., multiple days). Some events may create pollutant -increasing conditions that persist after the original event process has ceased, for example high winds or volcanic eruptions that leave deposits of dust on roadways. 2. Proposed Changes The EPA is proposing the following genera lly applicable ch anges to the 2007 Exceptional Events Rule with respect to clarif ying what constitutes an exceptional event:

 Revising the definition of exceptiona l 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 rela tionship” element into the list of criteria that explicitly must be met fo r data to be excluded.

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

 Removing the term “historical fluctuations” and replacing it with text referring to a comparison to historical concentrations, identifying the types of analyses that are necessary in a demonstration to addr ess the comparison of the event-affected concentration to historical concentrations and clarifyi ng that an air agency does not need to prove a speci fic “in excess of” fact.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 38 of 218 Making these changes would re sult in returning to the fo llowing three core statutory elements of CAA section 319(b) that air agenci es must meet when re questing 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 even t and the monitored exceedance or violation.

 The event was not reasonably controllable or preventable.

 The event was a human activity that is unlik ely to recur at a pa rticular location or was a natural event. The implicit intent of CAA section 319(b) is that when the above conditions are met, the data should be excluded from regulatory deci sions so as not to drive SIPs to include unreasonable or additional measures to a ddress the effects of certain events. a. Definition of an Event While an event may have a physical component that is purely natural in origin, for example high wind speeds, human activity either prior to or simultaneous with the event may influence air quality during the event. In im plementing the 2007 Exceptional Events Rule, the EPA’s approach in determining whether an ex ceptional event that affected a monitored concentration was natural or due to human activ ity (an important distinction, as discussed in section V.D) has been to consider both whether the initiating physical event was natural or the result of human activity and whether human activity had any role in strengthening the emissions generation process. In contrast, some parties have argued that only th e naturalness of the initiating physical event should be considered. To clarify that an event is not a “natural event” merely because natural processes initiated the em issions generation process, the EPA proposes to*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 39 of 218 revise the regulatory definition of exceptional event to say that both the naturally occurring physical event and its associated resulting emissi ons are to be considered when applying the definitions and criteria for exclusion provided in the Exceptional Events Rule. For example, an exceptional event might consist of a high wind a nd the subsequently entrained PM that is transported to a monitoring site or a wildfire th at generates ozone or ozone precursors, which are transported to a monitoring site. The EPA would not consider the physical event ( e.g ., in the previous example, the high wind or the wildfire) to be an exceptional event unless the resulting emissions ( e.g. , the PM or ozone) reached and elevat ed the concentration at a monitoring location or locations. b. “But For” Element The EPA proposes to rely more directly upon the statutory requirem ent at CAA section 319(b)(3)(B)(ii) by removing the re gulatory requirement at 40 CFR 50.14(c)(3)(iv)(D) that “there would have been no exceedance or violation but for the event” ( i.e ., the “but for” criterion). In promulgating th e 2007 Exceptional Events Rule, th e EPA derived the “but for” criterion from the language at section 319(b)(3)(B )(ii), which requires “a clear causal relationship...between the measured exceedances...and the exceptional event to demonstrate that the exceptional event caused a specific air pollu tion concentration at a particular air quality monitoring location.” 13 The EPA combined this language w ith the requirement that there be “criteria and procedures for the Governor of a State to petition the Administrator to

13 The EPA believes that the terminology “specifi c air pollution concentr ation” refers to the identified exceedance or violation rather than a specific increment in the measured concentration, which implies quantitative source attributi on and a supporting qua ntitative analysis.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 40 of 218 exclude...data that is directly due to the exceptional events.” 14 Under the EPA’s interpretation of CAA section 319(b) at the time, these words sugges ted that a “but for” causation standard for exceptional events was appropriate. Air agencies have expressed concern that the EPA has, in many cases, historically interpreted the “but for” criterion as implying the need for a strict quantitative analysis to show a single value, or at least an explicitly bounded plausible range 15 , of the estimated air quality impact from the event. While a single event can in some cases clearly be shown to be a “but for” cause of a NAAQS exceedance or violation in the se nse that without the ev ent, the exceedance or violation would not have occurre d, it is more often the case that the impact of emissions from events and other sources cannot be separately quan tified and distinguished, and the “but for” role of a single source or event is difficult to dete rmine with certainty. Even when the effects of events are quantifiable with a sufficient degree of confidence, air agencies have reported expending significant resources to quantify them. The EPA was aware of these concerns in 2007 as a result of public comment on the proposed rule and attempted to allevi ate them by stating in the preamble to the 2007 Exceptional Events Rule that an air agency’s “but for” analysis does

14 CAA section 319(b)(3)(B)(iv) (emphasis a dded). The CAA requires regulations that encompass the following requirements: (1) “the occurrence of an exceptional event must be demonstrated by reliable, accurate data that is promptly produced and provided by the Federal, State, or local government agencies”; (2) “a clear causal relationship must exist between the measured exceedances of a national ambient air qua lity standard and the exceptional event to demonstrate that the exceptional event cause d a specific air pollution concentration at a particular air quality monitoring location...”; (3) “there is a public process for determining whether an event is exceptional”; and (4) there ar e procedures for the states to petition the EPA to exclude monitoring data di rectly due to exceptional ev ents. CAA section 319 (b)(3). 15 The EPA stated in the preamble to the 2007 Exceptional Events Rule that a “weight of evidence demonstration can present a range of possible concentrations, which is not as technically demanding as justif ying a specific adjustment to a measured value.” 72 FR 13570 (March 22, 2007).*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 41 of 218 not necessarily need to be precise and that th e EPA would use a holistic “weight of evidence” approach in analyzing submitted demonstration packages. 16 Without clear examples of what the EPA would accept as satisfying a weight of evid ence approach, some air agencies began using burdensome approaches to provide quantitative “but for” analys es in their exceptional events demonstrations. The reviewing EPA regional offices use similarly resource-intensive approaches to validate these quantitative analyses as they re view demonstrations. In some cases, the detailed quantitative approaches have not produced results any better than what could have been achieved with less burdensome measures. Therefore, the EPA is proposing to remove the “but for” regulatory language and focus on th e “clear causal relationship” stat utory criterion applied to the specific case, using a weight of evidence approach. 17 In so doing, we propose that in their submittals , air agencies demonstrate by the weight of evidence in the record that the event caused th e specific air pollution concentration at issue. 18 Depending on the event characteristics and the ca se-by-case nature of the evaluation, an air agency may or may not need to provide quantita tive analyses or estimate s to support the weight of evidence approach. The EPA will discuss will discuss with an air agency the appropriate approach for a given event demonstration du ring conversations preceding the submittal of a demonstration. For example, when a concentr ation during an event is higher than any concentration previously observed in the same area and time of year, the air agency will

16 72 FR 13570 (March 22, 2007). 17 The term “weight of evidence” means that the EPA will consider all relevant evidence and qualitatively “weigh” this evidence based on its relevance to the Exceptional Events Rule criterion being addressed, the degr ee of certainty, its persuasive ness, and other considerations appropriate to the individu al pollutant and the nature and type of event. 18 This approach is consistent with language in the preambl e to the 2007 Exceptional Events Rule that states, “The final rule permits a cas e-by-case evaluation, without prescribed threshold criteria, to demonstrate that an event aff ected air quality.” 72 FR 13569 (March 22, 2007).*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 42 of 218 generally not need to quantify the event impact to reach the conclusion that the event “caused” the concentration at issue. However, in cases where the concentrations on non-event days during the same season come close to or exceed th e applicable NAAQS, thus providing evidence that non-event pollution sources may produce exceedances of the NAAQS, the EPA would expect an air agency’s clear causa l relationship showing to include a quantitative estimate (or range of estimates) of the specific event’s impact on air po llution concentrations, ev en if uncertain, as a part of a weight of evidence showing alongside ot her qualitative evidence. Section V.E.3 of this proposal clarifies the EPA’s expectations regardi ng analyses associated with the “clear causal” criterion. c. Clear Causal Relationship Element The EPA is proposing to modify the regulator y language in section 50.14(c)(iv) to more clearly indicate, consistent with the CAA directive, the requireme nt to “demonstrate” versus to merely “provide evidence” that a clear causal re lationship must exist between the specific event and the monitored exceedance. The EPA will eval uate this criterion on a weight of evidence basis. d. Affects Air Quality Element As explained above, the EPA has treated the “affects air quality” element as a distinct criterion that air agencies must meet for data to be excluded, and has ex pected exceptional events demonstrations to conclude that the “affects air quality” conditi on has been satisfied. However, after carefully considering Congress’ intent and air agencies’ and the EPA’s experience in implementing the 2007 Exceptional Events Rule, we propose to integrate the phrase “affected air quality” into the clear causal relationship criterio n. We believe that separa tely requiring an air agency to provide evidence to support a conc lusion that an event “affects air quality” is*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 43 of 218 unnecessary if we finalize this proposal to require a mandatory clear causal relationship showing. If an air agency demonstrates that an event ha s a clear causal relationshi p to an exceedance or violation of a NAAQS, then the event has certainl y affected air quality. This proposed approach will reduce the time required to prepare demonstr ations, reduce their length, result in more understandable demonstrations for the public during the notice-and-comment process, and simplify and expedite the EPA’s review process. e. Historical Fluctuations Element As we indicated in the Interim Exceptional Events Implementation Guidance, we believe that a comparison of the claimed event-influenced concentration(s) to concentrations at the same monitoring site at other times is extremely useful evidence in an exceptional events demonstration. The EPA considers these comparis ons as part of the evidence available for determining whether an air agency has satisf ied the statutory and regulatory “clear causal relationship” criterion. Because preparing this type of comparison is within the ability and resources of every air agency, the EPA proposes to continue to require this type of comparison in every demonstration. However, the EPA is propos ing to re-word the requirement to prevent misinterpretation that this comparison must s how that the concentra tion in question was “in excess of normal historical fluctu ations, including bac kground.” This phrase is not clear and has caused confusion and regulatory uncertainty. For ex ample, “fluctuations in concentrations” can convey either day-to-day or hour-to-hour differences in m onitored concentrations. These concentration differentials canno t usefully be compared to an absolute concentration ( i.e ., monitored concentration at a given point in time) because many absolute concentrations will be larger than the differences betw een concentrations. The phrase “in excess” might be interpreted to mean that the concentration at issue must be higher than all historical concentrations, but the*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 44 of 218 EPA maintains that Congress did not intend this, nor would such an interpretation be reasonable. Concentrations that are exceedances of a standa rd but are not higher than all concentrations recorded at a particular monitor may be causally connected to an event of the type that Congress clearly identified for treatment as an excep tional event. Finally, the language “including background” is confusing. In many cases, the monitor or monitors intended to represent “background” concentrations are separated from the event-influenced monitoring site by some distance such that the event-in fluenced monitor and the “backgr ound” monitor reflect a different mixture of emissions sources, which could lead to misinterpretation. Regardless, the EPA sees no clear reason why such “background” concentrations are relevant fo r analyses associated with provisions in the Exceptional Events Rule. The change that the EPA is proposing to th e text of the 2007 Exceptional Events Rule would require demonstrations to include a comparat ive analysis of the concentration data alleged to have been affected by an event and data at other times, and would speci fy certain aspects of the analysis. The change would also make cl ear that there is no specific “in excess of” relationship between the event-aff ected data and other data that must be proven, for example that the event-affected data be above a certain perc entile point in the annua l distribution of data. Section V.E.3 of this proposal contains additiona l detail regarding the minimum set of statistical analyses that the EPA expects to see in demonstrations. C. What types of ambient concentration data and data uses may be affected by the Exceptional Events Rule? The CAA language at 319(b)(3)(B)(iv) requi res the Administrator to promulgate regulations that provide that th ere are criteria and procedures for the Governor of a State to petition the Administrator to ex clude air quality monitoring data that is directly due to*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 45 of 218 exceptional events from use in determinations by the Administra tor with respect to exceedances or violations of the natio nal ambient air quality standards . The implementing language in the 2007 Exceptional Events Rule states at 40 CFR pa rt 50.14(a)(1) that air agencies may request that the EPA exclude data showing exceedances or violations of the NAAQS that are directly due to an exceptional event from use in determin ations without naming those determinations in that paragraph. The rule at 40 CFR part 50.14(b)(1) states that the EPA shall exclude data from use in determinations of exceedances and NAAQS violations where an air agency demonstrates to the EPA’s satisfaction that an exceptional event caused a specific air pollution concentration in excess of one or more NAAQS.” Thus, bot h the statutory language and the 2007 Exceptional Events Rule use the phrase “in determinations of exceedances and NAAQS violations” with no further explanation. In this section, we consider the specific type s of determinations by the Administrator that should be governed by CAA section 319(b). This issue was not specifically addressed in the rulemaking that promulgated the 2007 Exceptional Events Rule and cons equently has caused some confusion and regu latory uncertainty. 1. Current Situation The EPA believes that Congress clearly inte nded the CAA language in section 319(b) to apply to exclusions of ambient data from de terminations of whether a NAAQS exceedance or violation occurred at an ambient mo nitoring site at a particular time in the past. We characterize these exceedances or violations as occurring in the “past” because the process of determining whether an actual exceedance or violation oc curred involves review ing the ambient air monitoring data collected at monitoring sites ove r some historical timeframe. For example, on December 14, 2012, the EPA promulga ted a revised primary annual PM 2.5 NAAQS of 12.0*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 46 of 218 μ g/m 3 , which is attained when the 3-year averag e of the annual arithmetic means does not exceed
12.0 μ g/m 3

. 19 The EPA Administrator made initial ar ea designation decisions for the revised NAAQS in December of 2014 based on air quality m onitoring data for the most recent period 3- year period, which was 2011 through 2013. 20 Historical, or “past,” data were reviewed and assessed to determine whether an exceedance or vi olation had occurred that would influence a current or future regulatory determination. Determ inations of “past” exceedances or violations are key to the EPA’s actions to de signate or redesignate an area, to initially classify an area for a NAAQS (where classifications a pply), to determine if a nonatta inment area has attained the NAAQS for which it has previous ly been designated nonattainm ent, to determine whether a nonattainment area is eligible for an attainment date extension (where ap plicable) and, in some cases, to find that a SIP is inadequate and to issue a SIP call. No affected stakeholders with whom the EPA has interacted since 2007 have disputed this interp retation or approach. It is not as clear whether C AA section 319(b) also means that data should be excluded from determinations of whether a NAAQS exceedance or violation will or is likely to occur in the future. Predictions of future NAAQS violatio n(s) generally involve re viewing 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 i nputs to an air quality modeling tool or other analytical approach that extrapolates th ese data to predict a future outcome. While science supports and the EPA reli es on predictions of fu ture NAAQS violations in several parts of the clean air program, su ch as in the EPA’s approval of attainment demonstrations in SIPs, in prev ention of significant deteriora tion (PSD) air permitting programs

19 78 FR 3086 (January 15, 2013). 20 80 FR 2206 (January 15, 2015).*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 47 of 218 and in actions to reclassify a moderate PM 10 or PM 2.5 nonattainment area to serious, 21 the fact that these predicted future values rely only in pa rt on historical monitori ng data implies that a different standard for data ex clusion may be appropriate. Another interpretation question is whether and under what conditions event-affected data should be excluded from determinations that are ba sed wholly or in part on monitoring data but formally are not determinations of exceedances or violations of the NAAQS. For example, under 40 CFR part 51, subpart H, Prevention of Ai r Pollution Emergency Episodes, the required content of a state’s emergency plan depends on whether the state has experienced air pollution that exceeds a specified threshold level that is well above any NAAQS. Also, under the EPA’s guidance, the eligibility of an area fo r a simplified maintenance plan for PM 10 depends on the difference between the better-than-the-NAAQS air quality in an area and the NAAQS. To date, the EPA has not issued guidance th at explicitly and comprehensively identifies the types of data exclusion that are authorized and required by CAA section 319(b) or that may be otherwise appropriate and permissible. In the 2013 Interim Q&A document, the EPA provided only limited clarification rega rding the meaning of “exclude data.” 22 Question 14a of the Interim Q&A document notes that when the EPA concurs based on the weight of evidence that an air agency has successfully made the demonstrations referred to in 40 CFR 50.14(a)(2) and (b)(1), then the EPA generally excludes th e affected data from the following types of calculations and activities:

21 Projection of future NAAQS exceedances or violations do not necessarily play a role in reclassification of an ozone nonattainmen t area to a higher cl assification level. 22 Interim Exceptional Events Rule Frequently Asked Questions. U.S. EPA. May 2013. Available at http://www2.epa.gov/sites/production/file s/2015-05/documents/eer_qa_doc_5-10-13_r3.pdf

.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 48 of 218  The EPA’s AQS does not count these days as exceedances when generating user reports, and does not include them in design values estimates, 23 unless the AQS user specifically i ndicates that they should be in cluded, which may be appropriate for non-regulatory applications of interest to the user. 24

 The EPA accepts the exclusion of these data for the purposes of selecting appropriate background concentratio ns for PSD air quality analyses 25 and for transportation conformity hot spot analyses. 26

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

 The data continue to be publicly available, but the EPA’s publications and public information statements on the status of ai r quality in the affected area generally do

23 The EPA uses design values in many regulator y decisions, including, but not limited to, when designating areas as attainment, nonattainment or unclassifiable for a NAAQS and when determining whether a nonattainment area has at tained or is still viol ating a NAAQS. A design value is a statistic that describes the ai r quality status of a given loca tion relative to the level of a particular NAAQS. Design values are computed according to the procedures defined in 40 CFR part 50 and published annually by EPA's Office of Air Quality Planning and Standards. Design values are available at http://www.epa.gov/air trends/values.html

. 24 In some cases where the EPA has revise d a NAAQS by strengthening it, the default AQS query will exclude data for the more recent, re vised NAAQS, but may include concurred data for the historical NAAQS. 25 If the EPA is the permitting authority, the EP A will propose permits on this basis. If the EPA is commenting on another permitting authority’s proposed action, the EPA’s comments will be consistent with the determinations in this guidance document and any applicable New Source Review (NSR) permitting and/or modeling guidance. 26 Transportation conformity hot spot analysis is applicable only to PM 10 and PM 2.5 . “Transportation Conformity Guidance for Quantitative Hot-spot Analyses in PM 2.5 and PM 10 Nonattainment and Maintenance Areas,” EPA- 420-B-10-040, US EPA Offi ce of Transportation and Air Quality, December 2010, page 98.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 49 of 218 not reflect these data in any summary stat istic of potential regulatory application, unless such inclusion is specifically noted. 27 Thus, the EPA has maintained that once data are excluded under th e Exceptional Events Rule, these same data should be excluded from th e above-identified calcul ations and activities. The EPA has not clearly addressed whether appr oval for exclusion under the Exceptional Events Rule means that the data may or must be exclude d for the purpose of other types of actions that use monitoring data but are not included in the list above. The EPA has also not clearly addressed whether data that have not been approved for exclusion under the Exceptional Events Rule can nevertheless under some other principle or in terpretation be excluded from any of the various types of calcula tions and activities. The current situation is further complicated by the fact that the conditions for data exclusion in CAA section 319(b) and the Exceptiona l Events Rule, while logical when applied to determinations of NAAQS exceedances or violati ons occurring in the past, may not be logical when applied to predictions of future exceed ances or violations. The EPA recognizes, and acknowledged in Question 13 of the Interim Q&A document, that an event may have made a past air concentration significantly higher than it would have been in th e absence of the event contribution, and thus elevated an exceedance fo r a NAAQS pollutant to an even greater degree of exceedance. This same event-influenced concentration may not be eligible for exclusion under the 2007 Exceptional Events Rule be cause the “but for” criterion is not satisfied because either (1) there would have been a 3-year violation w ith or without the event or (2) there would not

27 These data may be included in statistics intended to describe current status and trends in actual air quality in the area for public information purposes including reporting of the Air Quality Index.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 50 of 218 have been a violation either w ith or without the event. The 2 007 Exceptional Events Rule does not explicitly authorize the exclusion of data a ssociated with such an event because the eventfails to meet the clear causal relationship criterion and “but for” criterion. Retaining the eventinfluenced data could, however, have regulatory implications that seem contrary to the purpose of CAA section 319(b). For example, retaining such data in the calculation of the historical design value for a nonattainment area can make it seem that the area needs more emissions reduction to attain the NAAQS than is actually the case, and could lead to the EPA’s disapproval of an attainment demonstration that is in f act adequate, thus requi ring the state to adopt additional emission controls. 28 As another example, events can make past air concentrations highe r without causing an actual NAAQS exceedance or violation. However, re taining such data in the calculation of background concentrations used in air quality an alysis 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. 29
2. Proposed Changes To remove the ambiguities described in th e preceding section and to provide greater regulatory certainty, the EPA pr oposes in regulatory language to interpret the CAA section 319(b) phrase “determinations by the Administrator with respect to exceedances or violations of

28 The attainment demonstration would be adequate in the sense that if a similar event does not occur during the period on which actual attainment will be based, there would be no monitored NAAQS violation, and if a similar event were to occur during that period the event-affected data could be excluded and thus there would be no “official” violation. 29 If a similar event were to o ccur after completion of constructi on, the event-affected data could be excluded and thus there woul d be no “official” violation.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 51 of 218 national ambient air quality standards” to encompass determinations of current 30 or historical NAAQS exceedances/violations or non-exceedances/non- violations and determinations of the air quality “design value” at particular receptor sites when made as pa rt of the basis for any of the following five types of regulatory actions:

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

 The assignment or re-assignment of a clas sification 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 nona ttainment area has actually attained a NAAQS by its CAA deadline.

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

 A finding of SIP inadequacy leading to a SIP call to the extent the finding hinges on a determination that the area is violating a NAAQS. For these types of actions, the EPA proposes to interpret the CAA to require that data be excluded only if the requirements of secti on 319(b) and the Excepti onal Events Rule are satisfied. In addition, we propose that when one of these determinations is based on a combination of monitoring data a nd air quality modeling, the criter ion requiring that there be a

30 The term “current” denotes the determination at issue in the current analysis. In actual practice, such determinations are based on historical data and thus reflect a past actual condition.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 52 of 218 clear causal relationship between the event and a NAAQS exceed ance or violation will apply to the combined estimate of air pollu tion levels rather than directly to the monitored background air quality data. That is, the event would not be re quired to have caused an actual exceedance or violation at the background ambient monitoring s ite, 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 in creased the background levels that are added to th e air quality modeling output. When the EPA designates or redesignates ar eas as attainment or nonattainment for the NAAQS; initially classifies ozone nonattainment areas as marginal, moderate, serious, severe or extreme; grants a request for a 1-year NAAQS a ttainment date extension where applicable; or determines whether areas designa ted nonattainment for the NAAQS have attained the respective NAAQS by the applicable attainment date, it does so based on monito ring data (where available) or modeling of actual air quality, or a combination thereof, as the evidence of the occurrence or non-occurrence of a NAAQS exceedance or violati on and, in the case of classification actions, the degree of violation. 31 In the case of reclassifying an oz one nonattainment area to a higher classification, the new classifica tion is based on the design value either at the time of the determination of attainment by the attainment dead line under section 181(b)(2), or at the time of the EPA’s grant of a voluntary request for reclas sification from a state under section 181(b)(3). 32 This proposal, if finalized, would in effect appl y the exceptional ev ents process in the same way

31 The EPA’s initial area designati ons process also makes use of ot her information relevant to the CAA criteria for designations, such as po llution contributions between nearby areas. 32 Reclassification of PM 10 and PM 2.5 nonattainment areas, by contrast, do not exclusively rely on area design values (and thus, past monitore d violations) but can also result from the Administrator’s determination that an area cannot practicably attain a standard by the attainment date. See CAA section 188(b)(1).*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 53 of 218 across these related types of determinations and across the NAAQS, which we believe is an appropriate interpretation of the CAA 319(b) phr ase “determinations by the Administrator with respect to exceedances or violatio ns of national ambient air qualit y standards.” For these types of determinations, the EPA proposes to exclude event- affected data only if an air agency satisfies the procedural ( e.g. , event identification, opportunity fo r public comment, demonstration submission) and substantive ( i.e ., clear causal relationship, not reasonably controllable or preventable, and human activity not likely to recur or natura l event) requirements of the exceptional events process. As indicated previously, the EPA has maintained to this point that once data are excluded under the Exceptional Ev ents Rule, these same data also should be excluded from (i) design value estimates and AQS user reports (unless th e AQS user specifically indicates that they should be in cluded), (ii) selecting appropria te background concentrations for PSD air quality analyses and transportation conf ormity hot spot analyses and (iii) selecting appropriate ambient data for projecting future year concentrations as part of a modeled attainment demonstration. As described below, we intend that EPA approval for exclusion of data under the Exceptional Events Rule continue to mean that the same data may be excluded for the three applications listed in the previous senten ce, but that there should be other pathways for exclusion for the second and third of thes e applications (and others) as well. This action proposes to require th at data exclusion associated with the five actions in the above bulleted list ( i.e ., initial area designations, classificat ions, attainment determinations, determinations regarding requests for attainment date extensions and findings of SIP inadequacy leading to a SIP call) must fo llow the provisions in the Exceptional Events Rule. It does not, however, mean that the EPA would never exclude or agree to exclude event-affected data from other types of regulatory determinations. For ex ample, while the EPA would exclude concurred-*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 54 of 218 upon event-affected data from the five types of regulatory actions discussed in V.C.1, the EPA would not exclude these same data when setting pr iority classifications for emergency plans under 40 CFR 51.150 as the EPA believes that im plementing the CAA principle at section 319(b)(3)(A) that “protection of public health is th e highest priority” may necessitate that an air agency address in its emergency plan the a ppropriate planned response for any elevated concentration known to be possible because it has already been observed, although the appropriate type of response may depend on the ca use(s) of the elevated concentration. The concept that the EPA does not consider CAA sec tion 319(b) and the revised Exceptional Events Rule to be the necessary or sole governing authorities for all data exclusions will be discussed further in upcoming, new draft guidance on excludi ng (or in some cases not excluding) data, independent of the Exceptional Events Rule, from several types of determinations and regulatory actions. The EPA is currently developing a supplementary guidance document, Draft Guidance for Excluding Some Ambient Poll utant Concentration Data from Certain Calculations and Analyses for Purposes Other than Retrospective Determinations of Atta inment of the NAAQS, which will describe the appropriate additional pathwa ys that we intend to make available for data exclusion for some monitoring data applications ( e.g ., predicting future attainment that is the basis for approval of an attainment demonstrati on 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 c onformity). The EPA intends to post the draft guidance on the exceptional events website at http://www2.epa.gov/air-qualityanalysis/treatment-data-in fluenced-exceptional-events and expects to fi nalize the document when we finalize these rule revisions. We intend that this guidance will recommend exclusion of data for PSD, transportation conformity and certain other applications in any situation in which*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 55 of 218 exclusion has already been approved under th e Exceptional Events Rule, as well as in applications in which the facts would support exclusion under the crite ria of the Exceptional Events Rule even if an EPA determination ha s not yet been made under the Exceptional Events Rule and in some other situations th at we will describe in the guidance.
D. What is a natural event? 1. Current Situation The CAA definition at section 319(b)(1)(iii) specifies that an exceptional event “is an event caused by human activity that is unlikely to recur at a particular location or a natural event.” Thus, the statute limits the expected oc currence frequency of an event caused by human activity as “unlikely to recur” but does not limit the occurrence frequency of a natural event. Natural events may recur, even frequently. 33 Air agencies can request, and the EPA can agree, to exclude data affected by a natural event if an air agency’s demonstration meets the other requirements of the Exceptional Events Rule. Thus , considering whether an event was a natural event or was caused by human activity is important to the content within and to the approval of a demonstration. As previously discussed, to be considered an exceptional event, an event, whether natural or anthropogenic in origin, must affect air qua lity at the affected monitor. 40 CFR 50.1(k) defines a natural event as one in which human activ ity plays little or no dir ect causal role in the generation of emissions. In some cases, such as stratospheric ozone in trusions or volcanic eruptions, the EPA recognizes that human activity plays no role in the magnitude of emissions or

33 See as examples, Hawaii’s exceptional events demonstration for volcanic activity affecting PM 2.5 concentrations in 2011 – 2012 and California Air Resources Board’s demonstration for wildfire events affecting PM 2.5 concentrations in 2008, both available at http://www2.epa.gov/air-quality-analysis/ exceptional-events-submissions-table

.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 56 of 218 level of air pollution that occurs. In other cases, past or current human ac tivity does influence the magnitude of emissions and hence the level of air pollution. For example, in high wind dust events, the pollution from the event may orig inate from a mixture of natural lands ( e.g ., undisturbed soil), soil that has be en disturbed by human activity and has been made more prone to wind-generated dust emissions ( e.g ., recent construction activity) and materials accumulated and stored by human activity ( e.g ., sand and gravel facilities). The EPA generally considers human ac tivity to have played little or no direct role in causing emissions if anthropogenic emission sources that contribute to th e event emissions are reasonably controlled at the time of the even t, regardless of the magnitude of emissions generated by these reasonably c ontrolled anthropogenic sources a nd regardless of the relative contribution of these emissions and emissions arising from natural sources in which human activity has no role. 34,35 Thus, the event could be considered a natural event. In such cases, the EPA applies the reasonable interp retation that the anthropogenic source had “little” direct causal role. If anthropogenic emission sources that cont ribute to the event emissions can be reasonably controllable but reasonable controls were not implemented at the time of the event, then the

34 For example, if an area affected by a high wind dust event has adequate rules or ordinances for sources of windblown dust ( e.g ., rules that establish restric tions for operating vehicles on unpaved property, rules that cont rol windblown dust emissions asso ciated with lands disturbed by construction, earthwork and land development) and the air agency can provide evidence of implementation and enforcement, then the EPA w ould generally consider human activity to have played little or no direct causal role in causing the event-related emissions. 35 The EPA considers wildfires to be natural even ts even though some wildfires are initiated by human actions and to some degree the frequency and scale of wildfires may be influenced by prior land management practices. The EPA believe s this interpretation best implements the Congressional intent and is a more appropriate ap proach than expecting ai r agencies to determine the initial cause of each wildfire of interest a nd classifying it as natural or anthropogenic based on that cause. In addition, land owners and manage rs and government public safety agencies are strongly motivated to reduce the frequency and se verity of human-caused wildfires and the EPA believes they can be presumed to make reasonable efforts to avoid them.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 57 of 218 event would not be considered a natural event. The EPA explained this concept in the preamble to the 2007 Exceptional Events Rule. 36 However, the rule text di d not reflect the identified concept. This has resulted in some regulatory unc ertainty as to whether the EPA’s interpretation of the CAA and the 2007 Exceptional Events Ru le as described here is appropriate. 2. Proposed Changes Based on the discussion above, the EPA proposes to revise the definition of natural event to clarify that anthropogenic emi ssion sources that contribute to the event emissions that are reasonably controlled do not play a “direct role” in causing emissi ons. Thus, an event with a mix of natural emissions and reasonably controlle d human-affected emission sources may be considered a natural event. However, an event resulting from only reasonably controlled human affected emissions may not be considered a natu ral event. This proposal is consistent with statements made in the preamble to the 2007 Ex ceptional Events Rule, and including it in the rule text provides more regulat ory certainty to all parties. When addressing the not reasona bly controllable or preventa ble criterion for this same event type consisting of a mix of natural emissions and human-affected emission sources ( e.g. , a high wind event affecting both open desert areas and urbanized lands ), air agencies must assess reasonable controls for both the contributi ng natural and anthropogenic sources. While air agencies must “assess” reasonable controls fo r most types of contri buting natural sources because this statutory factor applies to all ev ents, they do not necessari ly need to implement controls for these same sources. Additionally, be cause the rule revisions propose a categorical presumption of not reasonably controllable for wildfires and large-scal e, high-energy and/or sudden high wind dust events, “assessing” thes e events would involve referencing the

36 72 FR 13565-13566 (March 22, 2007).*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 58 of 218 appropriate regulatory ci tation. As we explain in more deta il in section V.E.2, for natural sources, we do not think that air agencies need to have implem ented any controls for windblown dust from never-disturbed, large-scale natural land scapes. Therefore, lack of controls on natural sources that contribute to event-related emissi ons would not disqualify the event from being considered as an exceptional event. When assessing the contribution from anthropogenic sources, similar to the analyses involved in determining whether these same sources play a “direct role” in causing event-related emissions, the air agency should identify the contributing anthropogenic sources, explain why the controls sp ecified in rules or ordi nances are reasonable, and provide evidence of implementation and enforcem ent. Also as explained in section V.E.2, in our view an event is “not reas onably controllable” if an exceeda nce or violation occurs even when reasonable controls were actually in pl ace and any further control would have been beyond what was reasonable. The EPA intends to consid er these aspects when applying the concept of “reasonable controls” on anth ropogenic sources to determin e whether the event can be considered a natural event and to evaluate th e not reasonably controllable or preventable criterion. With respect to determining whether anthr opogenic emission sources that contribute to the event emissions were reasonabl y controlled at the time of the event, the EPA also proposes to revise the definition of a natural event to indica te that the reasonablene ss of available controls should be assessed as of the date of the event. The EPA does not believe that information related to the cost and effectiveness of control measures , or related to the frequency of events, that became available to the air agency after the date of the event should affect the assessment of whether anthropogenic sources were reasonably controlled and thus the identification of an event as natural or caused by human activity.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 59 of 218 When addressing this criterion as part of an exceptional events demonstration, the EPA recommends that the submitting air agency clearly identify whether the event is natural or was a human activity that is unlikely to recur at a particular location. If purely natural ( e.g ., lightningignited wildfire, volcanic or seismic activit y, stratospheric ozone intrusion), the EPA recommends that the submitting air agency identi fy the purely natural status in the “human activity/natural event” section of its demonstr ation; provide the type/source of event, the resulting emissions, and the documented frequency of the event; and affirmatively state that in characterizing the event, the submitting air agency has satisfied the human activity/natural event criterion.
E. Technical Criteria for the Exclusi on of Data Affected by Events As described in section V.B, the EPA proposes to return to the core statutory elements and implicit concepts of CAA sec tion 319(b): that the event affect ed 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 reason ably controllable or preventable and the event was caused by human activity that is unlikely to recur at a partic ular location or was a natural event. All exceptional events dem onstrations, regardless of even t type or rele vant NAAQS, must address each of these technical criteria. This section descri bes the EPA’s proposals for rule revisions and guidance regarding each of thes e technical criteria. Section V.G discusses additional process-related components of ex ceptional events demonstration packages.
1. Human Activity Unlikely to Recur at a Particular Location or a Natural Event The concept of recurrence applies to human ac tivity; the statements in this section are not relevant for natural events. S ection V.D includes a detailed disc ussion of a “natural event.” a. Current Situation*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 60 of 218 According to both the regulator y and statutory definitions, an exceptional event must be “an event caused by human activ ity that is unlikely to recu r at a particular location or a natural event” (emphasis added). For clarity, in this section, the EPA focuses on the language “unlikely to recur at a particular location.” The “unlikely to recur at a particular location” requirement of CAA section 319(b) does not define “unlikely to recur.” Thus, this la nguage requires interpreta tion on a case-by-case or event type-by-event type basis. The term “unlikel y” implies consideration of the expected future frequency of events similar to the event th at has already happened, but does not convey any particular benchmark for what frequency shoul d be low enough to be considered “unlikely.” Also, the term “at a particular lo cation” requires interpretation, as it could refer to the exact area or only to the general area of the event, to the location of th e ambient monitoring station or stations that were affected by the ev ent or to the combination of both. The EPA’s 1986 Guideline on the Identific ation and Use of Air Quality Data Affected by Exceptional Events stated that events can be considered exceptional if they are not expected to “recur routinely at a given location.” 37 This document did not further define or give specific examples of “routinely.” The preamble to the 2007 Exceptional Events Rule did not provide specific guidance on the unlikely to recur cr iterion, except to say th at recurrence is event- specific and should be assessed on a case-by-case basis and that in the particular case of prescribed fires a comparison to the natural fire return interval is a relevant consideration for this criterion.

37 Guideline on the Identification and Use of Air Quality Data Affected by Exceptional Events (the Exceptional Events Policy), U.S. EPA, OAQPS, EPA-450/4-86-007, July 1986.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 61 of 218 The CAA section 319(b) and the 2007 Exceptio nal Events Rule do not specifically address temporary, but multi-day or multi-year activ ities such as construction projects. However, Question 16 in the Interim Q&A document noted th at the 2007 Exceptional Events Rule does not explicitly place a limit on the duration of a singl e event and that a submitting agency could make a showing that a prolonged activity ( e.g ., a multi-year road construction project) is a single event that is not likely to recur at the locati on in question. The Interim High Winds Guidance document addressed recurrence for high wind events , as summarized in section V.F.4 of this document. Other than this, the Interim Excepti onal Events Implementation Guidance did not provide any specific guidance on th e unlikely to recur criterion. b. Proposed Changes While we believe that it is appropriate to c onsider recurrence to be event-specific and for the unlikely to recur criterion to be assessed on a case-by-case basis, we also believe that this proposed action presents an opportunity to clarif y certain points. This section provides general clarifications with respect to the meaning of “ unlikely to recur.” Section V.F.2 addresses this criterion for wildland fires (specifically pres cribed fires on wildland) and section V.F.4 specifically addresses this cr iterion for high wind dust events . Also, under CAA section 319(b) and the 2007 Exceptional Events Rule, air polluti on related to source noncompliance is not an exceptional event regardless of its frequency. The EPA proposes, as guidance, to r ecommend the following boundaries on the interpretation of the unlikely to recur criteri on. If an event type has not previously occurred within a given air quality control region (AQCR) 38 in the 3 years preceding the submittal of an

38 Air Quality Control Regions are defined in 40 CFR part 81, Subpart B, Designation of Air Quality Control Regions.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 62 of 218 exceptional events demonstration, the EPA will c onsider this to be a “first” event and will generally consider it to be unlik ely to recur in the same loca tion. Similarly, a “second” event within the 3 years preceding the submittal of an exceptional events demonstration would also generally be considered unlikely to recur in the same location. If there have been two prior events of a similar type within a 3-year peri od in an AQCR, that woul d generally indicate the third event, for which the demonstration is bein g prepared (or would be prepared), does not satisfy the “human activity that is unlikely to recur at a particul ar location” criterion and, thus, would not qualify as an exceptional event. The term s “first” and “second” events refer to events that affect the same AQCR, even if th ey have not affected the same monitor. 39 This proposed guidance is consistent with the approach ta ken to recurrence in our Interim High Winds Guidance document in which we identified non-recurring ev ents as being less than one event per year in a given area. 40 In the Interim High Winds Guidance, we did not define area other than to differentiate areas by attainme nt status or jurisdiction ( i.e ., intrastate versus interstate or international). The EPA solicits comment on this proposed guida nce regarding recurrence at a particular location, specifically the use of an AQCR to define the bounds for an area subject to event recurrence given that some AQCRs may be qu ite large. The EPA also solicits comments on

39 The EPA will consider previously flagged ex ceedances within AQS with their associated descriptions to be “events” re gardless of whether the EPA ha s received or acted on event demonstrations. The EPA also notes that a si ngle event could influence concentrations on multiple days. 40 See footnote 27 in Table 2 of Interim Guidance on the Prepara tion 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/site s/production/files/2015- 05/documents/exceptevents_highwinds_guide_130510.pdf.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 63 of 218 whether this benchmark of three ev ents in 3 years should be incorpor ated into the rule text, rather than being provided only as guidance. The EPA proposes, as guidance, that to sa tisfy the documentation requirements for the “human activity that is unlikely to recur at a particular location” criterion, the submitting air agency should document and discuss, in a distinct “human activity/natural event” section of the demonstration, the type/source of event ( e.g ., a particular type of chemical spill or other industrial accident or a fire in a particular type of structure), the resulting emissions and the documented frequency of the event in the prior 3 years. The demonstration should affirmatively state that in characterizing the event, the submitt ing air agency has satisfied the “human activity unlikely to recur at a particular loca tion or a natural ev ent” criterion. 2. Not Reasonably Controllable or Preventable The CAA section 319(b) does not restrict the not reasonably controll able or preventable criterion to apply only to events caused by human activity. It al so applies to natural events. Accordingly, the Exceptional Events Rule applies this criterion to all types of events. This section discuss the criterion in general terms. We discuss the cr iterion’s applicability to fire events on wildland in section V.F.2 and to high wind dust events in section V.F.4. a. Current Situation As noted in section V.B of this document, the definition of an exceptional event at 40 CFR 50.1(j) repeats the CAA defini tion and includes the requiremen t at section 319(b)(1)(A)(ii) that an exceptional event, wh ether natural or caused by human activity, is one that “is not reasonably controllable or preventable.” Neither the rule text of the 2007 Exceptional Events Rule nor the preamble to the final rule provided additional clarification regarding this statutory element. Rather, the preamble to the final rule stated, “[w]e are not finalizing more detailed*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 64 of 218 requirements for determining when an event is ‘not reasonably contro llable or preventable’ because we believe that such determinations wi ll necessarily be dependent on specific facts and circumstances that cannot be prescribed by rule.” 41 While we maintain that determining whether or not an event is not reasonabl y controllable or preventable is event-specific and necessarily requires judgment by the air agency and the EPA, we also believe that some concepts regarding this criterion are broadly applicable. To begin, the statutory require ment that an exceptional event is one that “is not reasonably controllable or preven table” contains two factors: prev ention and control. Within the context of the Exceptional Events Rule, we intend that “prevent” means to stop or avert the event, and “control” means to reduce the magnit ude and impact of event-related emissions. We interpret CAA section 319(b) to m ean that to qualify as an exceptional event, the event cannot be reasonably preventable and cannot be reasonably controllable, rath er than that only one of the two elements must be satisfied. It would be contrary to the emphasi s of section 319(b) on protection of public health if there were no re quirement for reasonable control for an event merely because the event could not be reasonably prevented from happening. It is possible for an event to not be reasonably preventabl e, but to be reasonably controllable. 42 In this case, if emissions were reasonably controll ed, then the event could be cons idered for concurrence as an exceptional event. It is also possible that an event be neither preventable nor its air quality impacts to be controllable to any degr ee, such as potential increases in SO 2 concentrations associated with volcanic eruptions.

41 72 FR 13564 (March 22, 2007). 42 For example, in section V.F.2, we propose that under certain circumstan ces a prescribed fire may not be reasonably preventable because of the safety or ecosystem benefits that would be foregone, but emissions and air quality impacts from the fire may be reasonably controllable through the application of basi c smoke management practices.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 65 of 218 The EPA considers the statutory requirement th at an exceptional even t be “not reasonably preventable” to mean that if a set of prevention measures should reasonably have been in place for anthropogenically-influenced emission sources that contribute to the event emissions, then those measures must have been in place for the event to qualify as an excep tional event under the Exceptional Events Rule. Similarly, we consider the statutory requirement that an exceptional event be “not reasonably controllable” to mean that if a set of control measures should reasonably have been in place for emission sources that contribut e to the event emissions, then those controls must have been in place for the event to qualify as an excep tional event under the Exceptional Events Rule. Satisfying the not re asonably controllable element necessitates a showing of reasonable controls. Whether a set of controls constitutes “reasonable controls” is event-, time-, and place-dependent, and involves judgment by the air agency when preparing the demonstration and by the EPA when reviewing the demonstration. 43 We stated in the Interim Exceptional Events Implementation Guidance, and we reiterate in this acti on, that it may not be reasonable to apply any prevention or control efforts for some events. In the course of implementing the 2007 Ex ceptional Events Rule, both the EPA and air agencies have expressed concern regarding th e determination of “reasonable” prevention or control efforts for particular events. When an ai r agency prepares a demonstration, it attempts to show that whatever efforts were made were al l that were reasonable to make. When the EPA reviews a demonstration, we are responsible for determining if the demonstration is credible and convincing. The EPA has been unable to make th is determination regarding reasonableness for some demonstrations because the content rega rding the use and impl ementation of control

43 The EPA has many resources to help states identify appropriate co ntrol technologies and includes links to some of these sources on th e Control Strategies website available at http://www3.epa.gov/airquality/aqmportal/m anagement/control_strategies.htm

.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 66 of 218 measures is insufficient. Given the elasticity of the concept of “reasonab le,” it is not surprising that disagreements have arisen. We have in the past few years, particul arly since issuing the Interim Exceptional Events Implementation Guidance, worked with states to reach mutual understandings of what efforts ar e reasonable and to have those e fforts in place before events happen. However, situations will likely occur in the future, as they have in the past, in which an assessment of reasonableness must be made retrosp ectively, when it is too la te for the air agency to have applied greater efforts. The EPA r ecognizes that our action on the air agency’s demonstration may have important regulatory consequences for the area in question. The EPA has stated that for all types of events , we consider reasonableness in light of the technical information available to the air agency at the time the event occurred. An air agency “caught by surprise” by an event of a given type (or by an unexpected number of such events in a period over which NAAQS compliance is evaluated, ty pically 3 years) should not be expected to have implemented the same controls prior to an ev ent as an air agency that has been aware that events of a certain type occu r with regularity and cause NAAQS exceedances or violations. The EPA anticipates that nonattainment (or maintenan ce) areas have technical information needed to understand those measures that constitute reasona ble control of anthropogenic sources in their jurisdiction for recurring events of the type(s) that cause or contribute to nonattainment (or that did previously). In contrast, th e EPA generally does not expect areas identified as attainment, unclassifiable/attainment or unc lassifiable for a NAAQS to have the same understanding or to have adopted the same level of event-relevant controls as areas that are nonattainment (or maintenance) for the same NAAQS. Also, if an area has been r ecently designated to nonattainment but is still developing its SIP a nd has not yet reached a deadline to implement*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 67 of 218 controls, the EPA expects the level of controls that is appropriate for that planning stage. 44 Regardless of attainment status or natural/ant hropogenic source contribu tion, each demonstration package should address the question of reas onable controls within the not reasonably controllable or preventable por tion of the demonstration. The not reasonably controllable or preventa ble criterion is a source of particular complexity when an event occurs outside the jurisd iction of the state that is requesting that data be excluded. The area outside a state’s jurisdiction may be in an area of Indian country, in another state, or in a foreign country. For thes e cases, the air agency requesting data exclusion, and other government authorities in the state, generally do not have regulatory authority over those who might have been able to prevent or control the event. Th erefore, the EPA believes that event-related emissions that originate outside of the boundaries of the state within which the concentration at issue was monitored are genera lly “not reasonably controllable or preventable” even if no party has made any effort to control or prevent them. To date, we have advised air agencies that an exceptional events demonstration for such a case must nevertheless explicitly address the question of reasonable efforts towards prevention and control. For these situations, we have suggested template language to the effect that satisfying the not reasonably controllable or preventable element could consist of an air agency stating that because the event occurred outside of its jurisdiction, the not reasonably controllable or prev entable criterion is satisfied.

44 The CAA provides different timeframes for developing and implementing SIPs depending on the NAAQS and the nonattainme nt area’s classification ( e.g ., severity of the nonattainment problem). The EPA recognizes that within the SIP development and implementation process, some measures may be implemented relatively quickly ( e.g ., transportation conformity, new source review) whereas other programs, such as de velopment or rules for particular source types, can take time and involve st ate legislative processes.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 68 of 218 Because the reasonableness of controls for ev ent-related emissions is case-specific, the EPA has not issued guidance that particular cont rols are reasonable or are not reasonable. The Interim High Winds Guidance document indicates s ources of information that identify measures that an air agency and the EPA should consider. In that guidance, we said that if the EPA has approved a SIP revision to windblown dust controls within the pa st 3 years of the event, then an air agency can rely on the SIP-approved controls to satisfy a portion of a “prospective controls analysis.” 45 By this, we meant that we would agree with the air agency that for any high wind dust events in the next 3 years, implementation of the controls in the SIP would be sufficient to establish that those events are not reasonabl y controllable. In our discussions during the development of these proposed revisions of the Ex ceptional Events Rule, air agencies have urged us to give more deference to relevant controls in the EPA-approved SIPs. Some air agencies have recommended that we always accept that the cont rols in the approved SIP are all that should have reasonably been in place at the time of the ev ent (and/or that we acce pt no controls if there are no controls in the approved SIP). We understa nd at least some of those recommending this approach to mean it to apply both to nonattainme nt and maintenance areas that have approved attainment or maintenance plans and to areas w hose SIPs have been approved only with respect to less specific infrastructure SIP requirements. b. Proposed Changes The EPA generally plans to continue its past interpretations with respect to the “not reasonably controllable or preventable” criteri on. We propose to codify in regulatory language

45 Interim Guidance on the Preparation of Demons trations in Support of Requests to Exclude Ambient Air Quality Data Affected by Hi gh Winds Under the Exceptional Events Rule. U.S. EPA. May 2013. Available at http://www2.epa.gov/sit es/production/files/2015- 05/documents/exceptevents_highwinds_guide_130510.pdf.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 69 of 218 key aspects of these past interpre tations to reduce uncertainty for air agencies and other parties. Specifically, we are proposing changes to the te xt of the Exceptional Events Rule to indicate that:

 The not reasonably controllable or preventable criterion has two prongs, prevention and control. An air agency mu st demonstrate that an event was both not reasonably preventable a nd 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-specif ic and is to be evaluated in light of information available at the time of the event.

 No case-specific justificati on is needed to support the “n ot reasonably controllable or preventable” criterion for emissions-generating activity that occurs outside of the boundaries of the state (or tribal lands) within which the conc entration at issue was monitored. 46 With regard to the last of these proposed rule text changes, the EPA maintains that it is not reasonable to expect the downwind air agency ( i.e ., the state or tribe submitting the demonstration) to have required or persuaded the upwind foreign c ountry, state or tribe to have

46 Under the CAA, the EPA generall y considers a state (not includi ng 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 author ity). The EPA expects controls appropriate for the designation status of the count y (or portion of the county) in which the emissions originate.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 70 of 218 implemented controls on sources sufficient to limit event-related air concentrations in the downwind state or tribal lands, nor does the EPA believe that Congress intended to deny the downwind state or tribe relief in the form of data exclusion with in the context of the Exceptional Events Rule. Submitting (downwind) air agenci es will, however, need to assess potential contribution from local and state-wide sources and submit evidence and statements supporting the other exceptional events criteria ( i.e ., clear causal relationship a nd human activity unlikely to recur or a natural event). In addition to proposing to codify the five cu rrent interpretations lis ted above, with regard to this criterion, we are proposing and reque sting comments on changes from our current interpretations and changes in the rule text that are explained below in more detail. Natural Events and Natural Sources. The not reasonably controllable or preventable criterion applies to natural ev ents, including natural sources and any cont ributing anthropogenic sources and activities. 47 The EPA proposes, as guidance, that to satisfy the not reasonably controllable or preventable criterion for natural events, air agencies should identify in their demonstration the origin and evolution of the natu ral event, describe any local efforts to prevent the event and explain how any efforts to limit th e duration, intensity or extent (and thus the emissions) from the event were reasonable. Large-scale natural landscapes, such as deserts, are one type of natural source from which emissions can originate and cont ribute to event-related emissions . We propose, as guidance for these types of natural sources, that air agencies would not need to have implemented any controls for windblown dust from never-disturbed, large-scal e natural landscapes. If such a landscape is

47 An event with a significant contribution from anthropogenically-influenced emissions sources that have not themselves been reasonably contro lled cannot be considered a natural event subject to this provision.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 71 of 218 the only source of wind-blown dust, the EPA would c onsider the event in this scenario to be not reasonably controllable or preventable regardless of the past frequency of similar events. Other such cases include vol canic releases of SO 2 and stratospheric ozone intr usions. In these cases, the air agency should affirmatively st ate that the not reasonably contro llable or preventable criterion is satisfied by the fact that the natural even t was of a character that could not have been prevented or controlled and that there were no contributions of event-related emissions from anthropogenic sources. We also propose, as guidance, for events ot her than high wind dust events and wildfire on wildland (for which the proposed ru le revisions take an equivalent approach), to consider the direct effects of remote, large-sc ale, high-energy and/or sudden natu ral events to generally be not reasonable to prevent or control. 48 This concept, as it relates specifically to proposed rule changes addressing high wind dust events, is discu ssed in more detail in section V.F.4. Section V.F.2.c discusses how the same concept relates to proposed rule change s addressing the “not reasonably controllable or preventabl e” criterion for wildfire on wildland. There may, however, be natural events or activities associated with the clean-up following a natural event where some type of control effort woul d be reasonable. For example, while an initial volcanic dust event may not be co ntrollable or preventable, it may be reasonable

48 By “remote” events, we mean events that occu r in locations where the application of control measures is either cost-prohibitive or presents unreasonable risks to worker safety because of the distance of the source from logistic al staging areas, or absence of roads and/or location on rough or steep terrain. By “large-scale” we mean a regional event that i nvolves a significant expanse of land and/or affects all/most monitors in an area. “High-energy” means an event involving levels of kinetic energy that feasible human efforts cannot absorb or redirect. Example large-scale and/or high-energy events might include seismi c events, hurricanes, torn adoes and “haboobs” in the southwest where sustained wind speeds can exceed 40 mph and generate walls of dust several miles wide and more than a mile high.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 72 of 218 to implement a street cleaning program to c ontrol the subsequent re-entrainment of dust deposited on roadways after th e eruption. Also, air quality imp acts during the active period of a weather disaster event generally cannot be preven ted or controlled and it would be reasonable for no effort to have been made to do so. However, air agencies should apply reasonable controls, as applicable, in the recovery period after the event ( e.g ., during the removal or incineration 49 of debris following a hurricane or tornado). There may also be smaller scale natural sources and events for which some control actions would be reasonable. We request comment on additional general and event-specific recommendations that would be consistent with the CAA and the revised Exceptional Events Rule regarding natura l events and sources that the EPA could include in guidance to provide more certainty and allow air agenci es to efficiently prepare demonstrations. The Role of Past Occurrences. When assessing th e controls that should reasonably have been in place in light of information available at the time of the event, both the air agency and the EPA should consider the then-known frequency and severity of recurri ng events of the same type as both characteristics s hould affect decisions regarding t hose measures that constitute reasonable controls. A measure may not be reason able when the event type and severity was known to occur infrequently, but such measures may be reasonable if that event type and severity occurs frequently, because there are greater (more frequent) benefits to balance against the cost of implementation. If the event was the area’s fi rst experienced event of this type, then the submitting air agency would note that fact. The air agency could then rely on measures in the SIP

49 When addressing reasonable controls for the incineration of debris associated with the recovery period following a natural disaster, air agencies may want to consider, as appropriate, the basic smoke management practices discusse d in more detail in section V.F.2.d of this proposal.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 73 of 218 and other controls in place at the time of the event, if any, to satisfy the not reasonably controllable or preventable criterion because, at the time of the event, the air agency did not have a basis for understanding the possibl e need for better controls for this type of event. If, however, the area has previously e xperienced events of the type that are the focus of the demonstration, then the air agency has a basis for understa nding the possible need for better controls. 50 We note that this consideration of past r ecurrence when determini ng what controls would have been sufficient to satisfy the not reasonably controllable or preventa ble criterion is not the same as the consideration of the likelihood of fu ture recurrence for the pu rposes of the unlikely to recur criterion. Past experiences are a general guide to future likelihood but the EPA recognizes that future recurrence may follow a different pattern and may necessitate new measures to prevent events of a given type. The Role of the EPA-approved SIP as th e Benchmark for Reasonable Measures – In General . As already mentioned, some air agencies have urged us to defer to relevant controls in EPA-approved SIPs as always sufficient to satisf y the not reasonably cont rollable or preventable criterion. The EPA could conceivably give “defer ence” to several different types of SIPs. CAA section 110(a)(1) and 110( a)(2) requires every state to de velop and submit to the EPA an “infrastructure SIP” for each NAAQS within 3 ye ars of the promulgation of a new or revised NAAQS. Infrastructure SIPs address a number of CAA requirements, including the requirement to contain emission limits to ensure attainme nt and maintenance of a NAAQS. However, under the EPA’s interpretation of these CAA sections, in frastructure SIPs are not required to include

50 Because a state is considered a single responsib le entity for purposes of SIP development and implementation, there may be state governmental authorities whose knowledge of the need for an availability of controls at the time of the event is also relevant, particular ly for in-state sources outside the geographic area covered by th e air agency’s regulatory authority.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 74 of 218 attainment or maintenance demonstrations and are not required to demonstrate that the controls on particular sources are “reasonable.” Thus, in general, EPA-approved infrastructure SIPs do not necessarily constitute a robus t assessment of those controls th at are reasonable to have in place to address air quality impacts from particular types of events that may become the focus of exceptional events demonstrations. In contrast, states with areas designate d as nonattainment for a NAAQS must prepare attainment plan SIPs, which must include an a ttainment demonstration and reasonably available control measures (RACM), among other requirements. 51 Attainment plans for serious PM 10 or PM 2.5 areas must also contain be st available control measures (BACM). When a nonattainment area reaches attainment, it may be redesignated to maintenance area status if it has implemented all applicable nonattainment area requireme nts and obtains the EPA’s approval for a maintenance plan for a 10-year period. Thus, in both maintenance and nonattainment areas with approved attainment plan SIPs, the air agency and the EPA will have considered what controls are necessary and reasonable to provide for a ttainment, based on information available at the time of plan development and approval. Taken to its furthest limit, the deference recommended by some air agencies would mean that the EPA would always approve a state air ag ency assertion that the control measures in a SIP that has received full approval by the EP A as meeting currently applicable requirements related to the even t-relevant NAAQS constituted the reasonable set of c ontrols for the event in question and thus the event was not reasonably controllable or prev entable. We believe that this degree of deference could, in some cases, result in the approval for data exclusion contrary to

51 Marginal ozone nonattainment areas are excep tions because they are not required to submit attainment demonstrations.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 75 of 218 CAA requirements. Deference to the measures in an EPA-approved SIP is not always appropriate because EPA approval at some time in th e past does not necessarily mean that (1) the control measures in a current SIP address all ev ent-relevant sources of current importance, (2) the control measures that were considered by the air agency and the EPA at the time the EPA last approved the SIP are the same measures that we re known and available at the time of a more recent event, or (3) that conditi ons in the area have not changed in a way that would affect the approvability of the same SIP if it newly needed the EPA’s approval. However, we believe that it may be consistent with the CAA to revise the Ex ceptional Events Rule to identify the conditions under which the EPA and air agencies can rely up on measures in an EPA-approved SIP to satisfy the not reasonably controllable or preventable cr iterion. To clarify these scenarios, the EPA is proposing, and discusses below, various combinati ons of rule provisions and guidance for areas of different designation status. The best time for air agency and federal offi cials to exchange both technical information and views on the balance between costs and bene fits related to the su fficiency of reasonable controls is before an event happens. To avoid the EPA’s retrospective second guessing of an air agency’s consideration of information available to it before an event occurs, we have identified and described below several proposals, which woul d apply when an affected air agency and the EPA have not reached a mutual understanding regarding reasonable controls pr ior to an event. The Role of the EPA-approved SIP in Nonattainment and Maintenance Areas . To satisfy the not reasonably controllable or preventable cr iterion for nonattainment or maintenance areas, the EPA proposes to establish by rule a non-rebuttable presumption that, during a 5-year window (or, alternatively another appropriate timeframe ) following approval of an attainment plan or maintenance plan SIP during which no subsequent new obligation for the air agency to revise the*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 76 of 218 SIP has arisen, the control measures included in the SIP that are specific to the relevant pollutant, sources and event type are sufficient for purpos es of the not reasonably controllable or preventable criterion. 52 The EPA believes that 5 years is an appropriate timeframe upon which to rely for SIP deference for several reasons. As notedearlier, deference to the measures in an EPAapproved SIP is not always appropriate because EPA approval at some time in the past does not necessarily mean that (1) the control measures in a current SIP address all event-relevant sources of current importance, (2) the control measures that were considered by the air agency and the EPA at the time the EPA last approved the SIP are the same measures that were known and available at the time of a more recent event, or (3 ) that conditions in the area have not changed in a way that would affect the approvability of the same SIP if it newly needed the EPA’s approval. A 5-year window provides a reasonable timeframe under which to evaluate the above-identified potential changes. Additionally, as we discuss in section V.E.3 of this proposal, we encourage the use of 5 years of data when developing an alyses to support the clear causal relationship criterion because we believe that 5 years of ambi ent air data represent th e range of “normal” air quality. The EPA would evaluate the not reasonably co ntrollable or preventable criterion on a case-by-case basis for those demonstrations i nvolving an event affec ting a nonattainment or maintenance area with a SIP last approved more th an 5 years prior to the submittal of the subject demonstration. Because the issue of deference to a SIP is most often applicable for high wind events, section V.F.4 further illustrates this proposal.

52 A request for data exclusion must also show that the event was not a result of noncompliance with any existing state or local laws or rules th at have not been incorporated into the SIP.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 77 of 218 The Role of the EPA-approved SIP in A ttainment, Unclassifiable/Attainment or Unclassifiable Areas . Attainment, unclassifiable/attainment and unclassifiable areas should have EPA-approved infrastructure SIPs in place that the EPA approved within a few years following the promulgation of a new or revised NAA QS. Infrastructure SIPs for the 1987 PM 10 NAAQS are likely to be many years old, whil e infrastructure SIPs for ozone, PM 2.5 , 1-hour SO 2 and 1- hour NO 2 have been approved more recently. 53 In addition to the EPA-approved infrastructure SIPs, these areas may have in place other relevant state or local laws and rules, a natural events action plan, a SMP and/or other progra ms based on voluntary participation. Because the development and the EPA’s review of infrastructure SIPs typically do not involve a robust assessment of needed measures to prevent or control the effects of particular types of events and because even in the absence of a pending SIP call the SIP may not reasonably address events of importance, the EPA doe s not propose to establish in rule text or in guidance any form of general deference to the SIP in attainment, unclassifiable/attainment or unclassifiable areas. The EPA will review excep tional events demonstrations on a case-by-case basis, applying the Exceptional Events Rule a nd the EPA’s guidance. A case-by-case review may conclude that the measures that were in pl ace under the SIP, a natural events action plan, an SMP or other state or local progr ams were sufficient or insufficie nt to satisfy the not reasonably controllable or prev entable criterion. If the air agency has hist orically documented recurring events, then the EPA would expect the submitting air agency to identify any anthropogenic em ission sources that contribute to the event emissions and specifically document the controls that were in place for these sources at the time of the event. It is possible that the air agency may no t be able to make a sufficient

53 The NAAQS not mentioned here have rare ly presented exceptional events issues.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 78 of 218 showing for the not reasonably controllable or preventable criterion if it has not implemented reasonable controls for anthropogenic sources that c ontribute to recurring ev ents. In this case, the EPA regional office may not be able to concur with an air agency’s request for data exclusion. If the air agency has no such control plans and has no history of recurri ng events, then the air agency would note this in the not reasonably controllable or preventable portion of its demonstration and would rely on the fact that at the time of the even t, the air agency did not have a basis for understanding the possible need for better reasonable controls. Note that in section V.G.7 of this propos ed action, “Timing of the EPA’s Review of Submitted Demonstrations,” the EPA proposes to wo rk with air agencies to prioritize exceptional events determinations that affect near-term regul atory decisions. In an attainment, unclassifiable/ attainment or unclassifiable ar eas, the only likely non-discretiona ry regulatory action would be an initial designation under a new or revised NAAQS. Possible discretionary actions include a redesignation under a long-standi ng NAAQS or a SIP call. Unde r its planned prioritization approach, the EPA would not expect to act on de monstrations for events in an attainment, unclassifiable/attainment or unc lassifiable areas unless the ar ea could become nonattainment under a new or revised NAAQS, the area is th e subject of a planned EPA discretionary redesignation for a long-standi ng NAAQS where the approval of a demonstration affects the basis for the redesignation, or the area becomes the subject of another EPA discretionary action ( e.g ., a SIP call at the initiative of the EPA or in response to a petition) that hinges on the approval of a demonstration. The Role of Prior Communications with th e EPA in Case-Specific Assessments for Not Reasonably Controllable or Preventable . As already stated, the EPA believes that an air agency must include in its exceptional events demonstration a retrosp ective assessment of whether an*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 79 of 218 event was not reasonably controllable or preventable. The air agency should base this assessment on information available to relevant authorities ( e.g. , the air agency submitting the demonstration and potentially other government authorities in the state, for example an upwind air quality control district where the event occurred) that could have implemented measures to prevent or control the event and its effects prior to and dur ing the event. We are proposing to adopt the following approach as guidance to air agencies su bmitting demonstrations that will be subject to a case-specific assessment ( i.e ., in situations other than when deferring to a nonattainment or maintenance plan SIP). To satisfy the not reasonably controllable or preventable criterion in a case-specific assessment, the EPA proposes to consider comm unications between the EPA and the air agency when assessing “reasonableness” as part of assessing the techni cal information available to the air agency at the time the event occurred and what should reasonably have been in place at the time of the event for anthropogenic emission sources that contribute to the event emissions. It is not the EPA’s intent to retroa ctively apply its current judgmen ts about the reasonableness of controls for past events. Howeve r, it would also be inappropriat e for an air agency to fail to respond to the EPA’s recommendations prior to an event and then claim later in an event demonstration that it was unaware of a reasonable control issue. The EPA recognizes that regulations and an area’s planning status are often evolving and changing. The EPA may have recently promulga ted new or revised federal rules requiring controls on particular sources or promulgated a new or revised nationally applicable standard that will ultimately result in an air agency’s adoption of new control measures. The planning process to implement these new standards ( e.g ., the SIP or maintenance plan approval process) can be lengthy, sometimes spanning several year s and involving multiple rounds of formal and*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 80 of 218 informal communications between the affected air agency and the EPA regarding the appropriateness and completeness of planning elem ents. In some cases, discussion of issues regarding appropriate cont rols, including what controls woul d constitute “reasonable” controls for exceptional events purposes, are part of this iterative co mmunications process. The EPA solicits comment on what form of communication (shor t of a SIP call) would be most effective in conveying the EPA’s views to the affected air agen cy and whether this approach would be most appropriately addressed through guidance or regulatory text. Prospective Agreement on Assessments of Not Reasonably Controllable or Preventable

. In the Interim High Winds Guidance, the EPA sugge sted that an air agency could develop an assessment showing that the controls in place fo r a particular type of event, or a planned enhancement of those controls, were sufficien t to meet the not reas onably controllable or preventable criterion, and then obtain the EPA’ s review and concurren ce with the assessment prior to more events of that type occu rring. This prospective approach would reduce disagreements that might otherwise occur over late r retrospective assessmen ts. To date, most air agencies that face recurring event issues have not pursued this option, but the EPA will work with any air agency expressing an in terest in pursuing this approach. Summary of Requests for Comments Re garding Not Reasonably Controllable or Preventable . The EPA solicits comment on the following clarifications to the “not reasonably controllable or preventable” criterion:

 The EPA solicits comment on recommending as guidance that when addressing the “not reasonably controllable or preven table” criterion within an exceptional events demonstration, air agencies should: (1) identify the natural and anthropogenic sources of emissions cau sing and contributing to the event*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 81 of 218 emissions, including the contribution from lo cal sources, (2) identify the relevant SIP or other enforceable control measur es in place for these sources and the implementation status of these controls , and (3) provide evidence of effective implementation and enforcement of r easonable controls, if applicable. 54 In identifying natural and anthropogenic sour ces, the air agency should assess both potentially contributing lo cal/in-state and upwind s ources. We also request comment on whether we should revise the rule text to require these elements in a demonstration.

 The EPA proposes to codify rule lan guage to specify that no case-specific justification is needed to support the “not reasonably cont rollable or preventable” criterion for emissions-generating activity that occurs outside of the boundaries of the state (or tribal lands) w ithin which the concentration at issue was monitored.

 The EPA solicits comment on specific guida nce or rule requirements regarding what constitutes reasonable control of pa rticular natural events and sources.

 The EPA proposes to codify in rule langua ge that, provided the air agency is not under an obligation to revise the SIP, the EPA would consider ( i.e. , give deference to) enforceable control measures implemented in accordance with a state implementation plan, approved by the EPA within 5 years of the date of a

54 The EPA generally expects eviden ce that the controls determin ed to be reasonable, if any, were effectively implemented a nd appropriately enforced. This assessment of local sources should include a review and description of any know n nearby facility upsets or malfunctions that could have resulted in emissions of the releva nt pollutant(s) that influenced the monitored measurements on the day(s) of the claimed even ts. In the case of a high wind dust event, for example, for the identified poten tially contributing local and upw ind 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.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 82 of 218 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 anthropo genic sources that have or may have contributed to event-related emissions.

 The EPA proposes to codify in rule langua ge the time period for such deference to be 5 years from the date of the SIP approva l measured to the date of an event at issue, but is taking comme nt on whether and what other timeframes might be appropriate. To the extent an altern ative timeframe might be appropriate, comments should explain how it would addr ess the criteria provided above in support of the 5-year timeframe.

 The EPA proposes to consider communi cations and planning status when assessing the status of re asonable controls and propos es to do this through guidance. The EPA solicits comment on met hods 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 addre ssed through rule language. 3. Clear Causal Relationship Supported by a Comp arison to Historical Concentration Data a. Current Situation The CAA at 319(b)(3)(B)(ii) requires that “a clear causal relationship must exist between the measured exceedances of a national ambient air quality standard and the exceptional event to demonstrate that the exceptional event cause d a specific air pollution concentration at a particular air quality monitoring location.” Th e clear causal relationshi p criterion establishes causality between the event and a measured exce edance or violation of a NAAQS. As stated in*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 83 of 218 the preamble to the 2007 Exceptional Events Rule, given the directive in CAA section 319(b)(3)(B)(ii), it would be unreas onable to exclude data affected by an exceptional event simply because of a trivial contri bution of an event to air quality. 55 The EPA does, however, recognize that distinguis hing trivial contributions from more significant contributions to an exceedance may be difficult. As with the other exceptional events criteria, the EPA has used a weight of evidence approach when reviewing anal yses to support a causal relationship between an event and a monitored exceedance. Showing that an event and elevated polluta nt concentrations occurred simultaneously may not establish causality. The clear causal re lationship section of an exceptional events demonstration should include analyses showing that the event occurred and that emissions of the pollutant of interest resulting from the event we re transported to the monitor(s) recording the elevated concentration measurement(s). The example analyses to support the clear causal relationship criterion, shown in Table 1 and first summarized in the EPA’s Interim Exceptional Events Implementation Guidance, are generally appropriate analyses for most event types. 56 The EPA does not expect air agencies to include all of the evidence and analyses identified in the table below, but rather to use available information to build a weight of evidence showing. The

55 72 FR 13569 (March 22, 2007). 56 For purposes of summarizing example clear caus al relationship analyses in one place, the EPA has included an entry for the comparison to hist orical concentrations showing in Table 1. The EPA notes that although the Interim High Winds Guidance an d the Interim Q&A document discussed the comparison to historical concen trations showing, neither of these guidance documents presented this showing as part of the clear causal relationship. See specifically Interim Guidance on the Preparation of Demons trations in Support of Requests to Exclude Ambient Air Quality Data Affected by Hi gh Winds Under the Exceptional Events Rule. U.S. EPA. May 2013. Available at http://www2.epa.gov/sit es/production/files/2015- 05/documents/exceptevents_highwinds_guide_130510.pdf and Interim Exceptional Events Rule Frequently Asked Questions . U.S. EPA. May 2013. Available at http://www2.epa.gov/sites/pr oduction/files/2015-05/docum ents/eer_qa_doc_5-10-13_r3.pdf

.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 84 of 218 EPA may accept limited analyses ( e.g ., a comparison to historical c oncentrations in combination with one or two additional analyses from Table 1) for areas whose monitored ambient air concentrations are generally well below the NAAQS on non-event days. Additional analyses are beneficial if they establish a different facet of the event case and/or if they are used in combination with other analyses with limited da ta. For example, the EPA expects that areas prone to frequent elevated ozone (or other pollutant) concentrati ons, such as nonattainment areas, to have more sophisticated air quality predicti on tools. We would expect these areas could use these tools when supporting an exceptional even ts demonstration and de veloping analyses to support a clear causal relationship. Additionally, photochemical or regression modeling analyses may be beneficial in situations where the causal ity between the event and a measured exceedance of a NAAQS is not clearly established with ev idence and analyses identified in Table 1. For example, if a fire occurs during the normal high ozone season and the ozone level associated with the fire is in the range of otherwise-occu rring ozone levels and/or only slightly above the ozone NAAQS, the causal relationship between the fire and the exceedance or violation may not be clear. In such a situation, modeling may produce a sp ecific estimate of th e ozone contribution from the fire. Air agencies should discuss with th eir EPA regional office those types of analyses that may be adequate to satisfy the weight of evidence requirement in individual exceptional events demonstrations. Table 1. Example Clear Causal Rela tionship Evidence and Analyses

Example of Clear Causal Relationship Evidence Types of Analyses/Inf ormation to Support the Evidence Comparison to Historical Concentrations Analyses and statistics showing how the observed event concentration compares to the distribution or time se ries of historical concentrations of the same pollutant Occurrence and geograp hic extent of the event Special weather statements, advisories, news reports, nearby visibility readings, measurements from regulatory and non-*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 85 of 218 Example of Clear Causal Relationship Evidence Types of Analyses/Inf ormation to Support the Evidence regulatory ( e.g ., special purpose, emergency) monitoring stations th roughout the affected area, satellite imagery Transport of emissions related to the event in the direction of the monitor(s) where the measurements were recorded Wind direction data showing that emissions from sources identified as part of the “not reasonably controllable or preventable” demonstration were upwind of the monitor(s) in question, satellite im agery, monitoring data showing elevated concentrations of other pollutants expected to be in the event plume Spatial relationship between the event, sources, transport of emissions and recorded concentrations Map showing likely source area, wind speed/direction and pollu tant concentrations for affected area during the time of the event, trajectory analyses Temporal relationship between the event and elevated pollutant concentrations at the monitor in question Hourly time series showing pollutant concentrations at the monitor in question in combination with wind speed/direction data in the area where the pollutant originated/was entrained or transported Chemical composition a nd/or size distribution (for PM 2.5 to PM 10 ) of measured pollution that links the pollution at the monitor(s) with particular sources or phenomenon Chemical speciation data from the monitored exceedance(s) and sources, size distribution data Comparison of event-affected day(s) to specific non-event days Comparison of concentration and meteorology to days preceding and following the event, comparison to high concentration days in the same season (if any) without events, comparison to other event days without elevated conc entrations (if any), comparison of chemical speciation data

As explained in additional detail in the EPA’s Interim Exceptional Events Implementation Guidance, what has previously b een called the “historical fluctuations” showing ( i.e. , now referred to as the comparison to histori cal concentrations) cons ists of analyses and statistics showing how the observe d event-affected concentration compares to the distribution or time series of historical concentr ations of the same pollutant.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 86 of 218 A demonstration may be less compelling if some evidence is inconsistent with the description of how the event cause d the exceedance. For example, if an air agency describes an

event as a regional dust storm or wildfire, then the EPA an ticipates that most or all monitors within the same regional scale to be similarly affected by the event. That is, the EPA expects that the demonstration elements and factors ( e.g ., clear causal relationshi p, reasonable controls, meteorology, wind speeds) would also support the case for a regional event. Comparison of concentrations and conditions at other monito rs could thus be very important for the demonstration of a clear causal relationship. A lternatively, eliminating plausible non-event causes may also support a causal re lationship between the event and the elevated concentration. The EPA has been recommending that the cl ear causal relationship section of the demonstration should conclude with this type of statement: “On [day/time] an [event type] occurred which generated pollutant X or its prec ursors resulting in elevated concentrations at [monitoring location(s)]. The monitored [pollutant ] concentrations of [ZZ] were [describe the comparison to historical concentr ations including the percentile rank over an annual (seasonal) basis]. Meteorological conditions we re not consistent with histori cally high concentrations, etc.” and “Analyses X, Y and Z support Agency A’s positi on that the event affected air quality in such a way that there exists a clea r causal relationship between the specific event and the monitored exceedance or violation and thus satisfies the clear cau sal relationship criterion.” b. Proposed Changes As previously noted, the EPA is proposing to revise the 2007 Exceptional Events Rule text as follows:

 To move the “clear causal re lationship” element into the list of criteria that explicitly must be met for data to be excluded*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 87 of 218  To subsume the “affects air quality” element into the “clear causal relationship” element

 To remove the term “historical fluctuations ” and replace it with text referring to a comparison to historical concentrations

 To clarify that the comparison to historical concentrations is not a fact that must be proven

 To clearly identify the types of analyses that are necessary and sufficient in a demonstration to address the compar ison to historical concentrations

 To remove the “but for” element (as discussed in section V.B.2) Additionally, the EPA proposes to reiterate in guidance the example analyses to support the clear causal relationship cr iterion, shown in Table 1 above , and first summarized in the EPA’s Interim Exceptional Events Implementation Guidance. As noted previously, the EPA does not expect air agencies to incl ude all of the evidence and analys es identified in Table 2 below, but rather to use availabl e information to build a weight of evidence showing. The EPA’s rationale for proposi ng the previously identified changes to the clear causal relationship criterion is presente d in section V.B. The remainder of this section focuses on the types of analyses that an air agency must provide in its demonstration to make the comparison to historical concentrations. As not ed in the Current Situation se ction, the EPA has included an entry in Table 1 for the comparison to historical concentrations showing. The comparison to historical concentrations, re ferred to as the “historical fluctuations” showing in the 2007 Exceptional Events Ru le and the Interim Exceptional Events Implementation Guidance, is a requirement in th e 2007 Rule but it is not a statutory requirement. The EPA’s intent with this regulatory element was to require air agencies to present event-*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 88 of 218 influenced concentration data along with historic al data and to quantify the difference, if any, between the event and the non-even t concentrations. Comparing even t-influenced concentrations to historical concentrations bol sters the weight of evidence with in the clear causal relationship determination. The EPA proposes to re-phras e and incorporate the current regulatory requirement at 40 CFR 50.14(c)(3)(iv)(C), which re quires that a demonstration to justify data exclusion provide evidence that “[ t]he event is associated with a measured concentration in excess of normal historical fluctuations, incl uding background,” within the “clear causal relationship” criterion. In using this approach, we propose to rem ove from the regulatory text the “in excess of normal historical fluctuations, including background” phrase and to subsume the concept of historical comparisons into what wi ll effectively be a “completeness” requirement within the “clear causa l relationship” criterion. As noted above, we specifically propose to remove the phrase “in excess of normal historical fluctuations, includin g background” as we believe this language is vague and provides no additional value to historical concentration comparisons. To aid the EPA’s review, reduce our need to request additional information from air agencies and facilitate our understanding of the air agency’s position, we are proposing rule text changes to indicate that an ai r agency submitting a demonstration must provide the following types of statistics, graphics a nd explanatory text regarding comp arisons to past data. The rule change would also indicate that this informati on is sufficient to satisfy the rule’s requirement regarding the comparison to histor ical concentration da ta. Table 2 below identifies appropriate analyses and examples for comparing event-relate d concentrations to historical concentrations within the clear causal relationship criterion.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 89 of 218 Table 2. Evidence and Analyses for the Comparison to Historical Concentrations

Historical Concentration Evidence Types of Analyses/Supporting Information Required or Optional? 1. Comparison of concentrations on the claimed event day with past historical data Seasonal (appropriate if exceedances occur primarily in one season, but not in others)

 Use all available seasonal data over the

previous 5 years (or more, if available)

 Discuss the seasonal nature of pollution for

the location being evaluated

 Present monthly maximums of the NAAQS

relevant metric ( e.g ., maximum daily 8-hour average ozone or 1-hr SO 2 ) vs monthly or other averaged daily data as this masks high values Annual (appropriate if ex ceedances are likely

throughout the year)

 Use all available data over the previous 5

years (or more, if available) Seasonal and Annual Analyses

 Provide the data in the form relevant to the

standard being considered for data exclusion

 Label “high” data points as being associated

with concurred exceptional events, suspected exceptional events, other unusual occurrences, or high pollution days due to normal emissions

 Describe how emission control strategies

have decreased pollutant concentrations over the 5-year window, if applicable

 Include comparisons omitting known or

suspected exceptional events points, if applicable

 See examples at

http://www.epa.gov/ttn/analysis/docs/ IdeasforShowingEEEvidence.ppt and

Question 3 in the Interim Q&A document provides additional detail a Required seasonal and/or annual analysis (depending on which is more appropriate)

2. Comparison of concentrations on the claimed event day with a narrower set of similar days  Include neighboring days at the same location ( e.g., a time series of two to three weeks) and/or other days with similar meteorological conditions (possibly from other years) at the sa me or nearby locations with similar historical air quality along with Optional analysis*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 90 of 218 Historical Concentration Evidence Types of Analyses/Supporting Information Required or Optional? a discussion of the meteorological conditions during the same timeframe b

 Use this comparison to demonstrate that the

event caused higher concentrations than would be expected for given meteorological and/or local emissions conditions 3. Percentile rank of concentration when compared to annual data c  Provide the percentile rank of the event-day concentration relative to all measurement days over the previous 5 years to ensure statistical robustness and capture non-event variability over the a ppropriate seasons or number of years d

 Use the daily statistic ( e.g ., 24-hour average,

maximum daily 8-hour average, or maximum 1-hour) appropriate for the form of the standard being considered for data exclusion Required analysis when comparison is made on an annual basis ( see item #1)

4. Percentile rank of concentration relative to seasonal data c  Provide the percentile rank of the event-day concentration relative to all measurement days for the season (or appropriate alternative 3-month period) of the event over the previous 5 years

 Use the same time horizon as used for the

percentile rank calculate d relative to annual data, if appropriate Required analysis when comparison is made on a seasonal basis ( see item #1)

a Interim Exceptional Events Rule Frequently Asked Questions. U.S. EPA. May 2013. Available at http://www2.epa.gov/sites/production/file s/2015-05/documents/eer_qa_doc_5-10-13_r3.pdf

. b If an air agency compares th e concentration on the claimed even t day with days with similar meteorological conditions from other years, the agency should also verify and provide evidence that the area has not experienced significant changes in wind patterns, and that no significant sources in the area have had signi ficant changes in their emissions of the pollutant of concern.
c The EPA does not intend to iden tify a particular histor ical percentile rank point in the seasonal or annual historical data that play s a critical role in the analysis or conclusion regarding the clear causal relationship. d Section 8.4.2.e of appendix W (proposed re visions at 80 FR 45374, July 29, 2015) recommends using 5 years of adequately representative me teorology data from the National Weather Service to ensure that worst-case meteorological conditio ns are represented. Similarly, for exceptional events purposes, the EPA believes that 5 years of ambient air data, whether seasonal or annual, better represent the range of “normal” air quality than do shorter periods. As with other evidence in an exceptional events demonstration submittal, the EPA will use a holistic weight of evidence approach in reviewing submitted demonstration packages and*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 91 of 218 will consider the “clear causal relationship” in formation, including the comparison to historical concentrations showing, along with evidence su pporting the other Excep tional Events Rule criteria.
F. Treatment of Certain Events Under the Exceptional Events Rule As we stated in the preamble to the 2007 Ex ceptional Events Rule, we maintain that air quality data affected by the following event type s are among those that could meet the definition of an exceptional event and qualif y for data exclusion provided a ll requirements of the rule are met: (1) chemical spills and industrial accidents, 57 (2) structural fires, (3 ) terrorist attacks, (4) volcanic and seismic activities, (5) natural disast ers and associated cleanup and (6) fireworks. 58 We are not proposing any changes to the definiti on or discussion of these event types. The AQS database contains a more detailed list of other similar events that may be identified for special consideration. The EPA will consider other types of events on a case-by-case basis. Based on our implementation experience, the following other potential exceptional events categories warrant additional discussion: exceedan ces due to transported pollution, wildland fires including wildfires and prescribed fires, st ratospheric ozone intrusions and high wind dust events. We discuss each of these event categories in the following sections. 1. Exceedances Due to Transported Pollution a. Current Situation

57 A malfunction at an industrial facility could be considered to be an exceptional event if it has not resulted in source noncompliance, which is statutorily excluded from consideration as an exceptional event, see CAA 319(b)(1)(b)(iii), and if it otherwise meets the requirements of the Exceptional Events Rule. 58 Of these noted event types, only fireworks are currently identified in th e regulatory language at 40 CFR 50.14. We are not proposin g any revisions to the excl usion at 40 CFR 50.14(b)(2) for fireworks that are demonstrated to be significantly integral to traditional national, ethnic, or other cultural events.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 92 of 218 The 2007 Exceptional Events Rule implements one important CAA provision related to transported pollution. Certain even ts, national or international in origin and from natural or anthropogenic sources, may cause exceedances th at are eligible for exclusion under the 2007 Exceptional Events Rule if an air agency satisfies the rule criteria. We discuss in this section our position regarding exceedances due to event-related transported pollution. We also clarify in part c of this section how the Excep tional Events Rule provisions cu rrently relate to other CAA mechanisms that address or involve transporte d pollution. We are not proposing any changes to these relationships. The EPA believes that the Exceptional Events Rule will often be the most appropriate mechanism to use when addressing transported emi ssions from out-of-state natural events and/or events due to human activity that is unlikely to recur at a particul ar location, because the Exceptional Events Rule may be used during the initial area designations process and may make a difference between an attainment versus a nona ttainment designation. It is important to note, however, that the transpor ted natural emissions must be event-related ( e.g ., wildfires or stratospheric ozone intrusion) versus ongoing on a daily basis. b. Proposed Changes If an air agency determines that the Ex ceptional Events Rule is the most suitable approach to address contributions from transported emissions, then the air agency must consider the point of origin and the sour ces contributing to the exceedance or violation to determine how to address individual Exceptional Events Ru le criteria, specifica lly the not reasonably controllable or preventable crite rion and the human activity unlikel y to recur or a natural event criterion. The analyses to satisfy the clear causal relationship crit erion (which would subsume the CAA’s affects air quality criteri on, if promulgated as proposed and discussed in section V.B) are*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 93 of 218 largely independent of whether th e point of origin and contribu ting sources are within the air agency’s jurisdiction. The EPA first addressed th ese concepts in its Interim Q&A document and now proposes to clarify these intras tate and interstate scenarios. Under the CAA, the EPA generally consider s a state (not includi ng areas of Indian country) to be a single responsible actor. A ccordingly, neither the EP A nor the 2007 Exceptional Events Rule provides special considerations for intra state scenarios when an event in one part of a state, such as a county or air district, affects air quality in an other part of the same state, assuming that the event occurs on land subject to state authority (ver sus tribal government authority). For cases involving intr astate transport, the state or local air agency should evaluate whether contributing event emissions from all part s of the state were not reasonably controllable or preventable. Section V.E.2 di scusses the assessment of the not reasonably controllable or preventable criterion. Because there may be sp ecial considerations regarding air agencies’ authority to regulate activity on fe derally-owned and managed lands ( e.g ., national parks within the state), states and tribes s hould consult with the a ppropriate FLM or other federal agency and their EPA regional office early in the developm ent of an exceptional events demonstration package if they believe that sources on fede rally-owned and managed land contributed eventrelated emissions to a degree that ra ises issues of r easonable control.
Inter state and international transpor t events are different than intra state events. As noted in section V.E.2, the EPA maintain s that it is not reasonable to expect the downwind air agency ( i.e ., the state or tribe submitting the demonstrati on) to have required or persuaded the upwind foreign country, state or tribe to have implemented controls on sources sufficient to limit eventrelated air concentrations in the downwind stat e nor does the EPA believe that Congress intended to deny the downwind state or tribe of relief in the form of data exclusion. As with any*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 94 of 218 demonstration submittal, the submitting (downwind) state should identify all natural and anthropogenic contributing sources of emissions (bot h local/in-state and out-of-state ) to show the causal connection between an event and the affect ed air concentration va lues. A submitting state may provide a less detailed char acterization of sources in the upwind state or foreign country than of sources within its jurisdiction. After completing th e source characterization, the submitting state should assess whether emissions from sources within its state were not reasonably controllable or preventable ( see section V.E.2 of this proposal). Although the downwind state must still assess potential contributi on from in-state sources, we propose that the event-related emissions that were transporte d in the downwind state are “not reasonably controllable or preventable” for purposes of data exclusion. The EP A does not expect air agencies to submit analyses to satisfy the not reasonably controllable or preventable criterion for those upwind, out-of-state sources that contribute to the exceedance as part of a submitted demonstration. Rather, with respect to this elemen t for such sources, an air agency would merely point to the relevant provision we propose to add to the Exceptional Events Rule. Submitting states are, however, still required to assess the contribution and potential controls from local/instate sources and submit evidence/statements s upporting the other excepti onal events criteria ( i.e ., clear causal relationship, humanactivity unlikely to recur or a natural event). If the eventrelated emissions are international in origin and a ffect monitors in multiple states or regions, the EPA may assist affected agencies in identifying approaches for evaluating the potential impacts of international transport and determining the most appropriate information and analytical methods for each area’ s unique situation. The EPA proposes a similar approach to signifi cant out-of-state anth ropogenic sources in the case of a mixed natural/anthropogenic event that the submitting state wishes to have treated*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 95 of 218 as a natural event on the grounds that all significant anthropogenic sources were reasonably controlled. That is, if a mixt ure of natural and anthropogeni c sources in an upwind state contributed to an event, the downwind state is not required to demonstrat e that the anthropogenic sources in the upwind state were reasonably controlled for those sources to be considered to not have directly caused the event. The submitting st ate could consider the event to be a natural event based on the situation w ithin the state requesting the data exclusion (that is, the contributing sources within the jurisdiction of the submitting state were either natural or reasonably controlled anthropogenic sources). As with all exceptional events demonstrati ons, the EPA will evaluate the information on a case-by-case basis based on the facts of a particular exceptional event including any information and arguments presented in public comments received by the state in its public comment process or by the EPA in a notice-and- comment regulatory action that depends on the data exclusion. c. Relationship Between Exceptional Events Rule Provisions and Other CAA Transport Mechanisms Two provisions of the CAA other than section 319(b) also provide re gulatory relief for transported pollution, for different circumstan ces than those addre ssed by the 2007 Exceptional Events Rule. These provisions are briefly described here as context for unde rstanding the role of the Exceptional Events Rule itself.

 CAA section 179B, International Transport – CAA section 179B allows states to consider in their attainment demonstrat ions whether a nonattainment area might have met the NAAQS by the attainment da te “but for” emissions contributing to the area originating outside the U.S. This provision addresses sources of*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 96 of 218 emissions originating outside of the U.S. and provides qualifying nonattainment areas some regulatory relief from otherw ise-applicable additional planning and control requirements should the area fail to reach attainment by its deadline. It does not provide a pathway for regulatory relief from designation as a nonattainment area.

 CAA section 182(h), Rural Transport Areas – CAA section 182(h) authorizes the EPA Administrator to determine that an ozone nonattainment area can be treated as a rural transport area, which provides re lief from more stringent requirements associated with higher nonattainment area classifications ( i.e ., classifications above Marginal). Under CAA section 182(h) , a nonattainment area may qualify as a Rural Transport Area if it does not c ontain emissions sources that make a significant contributi on to monitored ozone concentrations in the area or in other areas, and if the area does not include and is not adjacent to a Metropolitan Statistical Area. Generally, an area qualifie s as a Rural Transport Area because it does not contribute to its own or anot her area’s nonattainment problem; rather, ozone exceedances are due to transported emissions, which could be international, interstate or intrastate in origin. The Rural Transport Area determination can be made during or after the initial area de signations and classifi cations process. Two additional provisions of the CAA specifically address and appropriately regulate transported pollution that does not qualify for da ta exclusion under the Exceptional Events Rule or for regulatory relief under CAA section 179B or CAA section 182(h) . These provisions are briefly described here as context for understanding the role of the Exceptional Events Rule itself.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 97 of 218  CAA section 110(a)(2 )(D)(i)(I), Interstate Transport – CAA section 110(a)(2)(D)(i)(I) requir es states to develop and imp lement SIPs to address the interstate transport of emissions. Specif ically, this provision requires each state’s SIP to prohibit “any source or other type of emissions activity within the State from emitting any air pollutant in amounts which will significantly contribute to nonattainment” of any NAAQS in another stat e, or which will “interfere with maintenance” of any NAAQS in another state. When the EPA promulgates or revises a NAAQS, each state is required to submit a SIP addressing this interstate transport provision as to that NAAQS with in 3 years. The EPA interprets this interstate transport provision to address anthropogenic sources of emissions from other states; we believe that is not intended to address natural sources of emissions.

 CAA section 126, Interstate Transport – CAA section 126 provides states and political subdivisions with a mechanism to petition the Administrator for a finding that “any major source or group of stationa ry sources emits or would emit any air pollution in violation of the pr ohibition of CA A 110(a)(2)(D)(i).” 59 Where the EPA grants such a petition, an existing source may operate beyond a 3-month period only if the EPA establishes emissions limitations and compliance schedules to bring about compliance with CAA section 110(a)(2)(D)(i) as expeditiously as practicable, but no later than 3 years after such finding. Similar

59 The text of section 126 codi fied in the United States Code cross references section 110(a)(2)(D)(ii) instead of secti on 110(a)(2)(D)(i). The courts have confirmed that this is a scrivener’s error and the correct cross re ference is to section 110(a)(2)(D)(i), See Appalachian Power Co. v. EPA , 249 F.3d 1032, 1040–44 (D.C. Cir. 2001).*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 98 of 218 to our interpretation above for CAA section 110(a)(2)(D)(i), the EPA interprets the reference to “major source or group of stationary sources” in section 126 to refer to anthropogenic sources of emi ssions from other states. The EPA’s interpretation is that this provision is not intended to address natural sources of emissions. This mechanism is available to all downwind states, and political subdivisions, regardless of area design ations, that may be affected by anthropogenic sources of emissions from upwind states in violation of the prohibition in CAA sec tion 110(a)(2)(D)(i). As noted previously, in most cases, the mechanisms in the Exceptional Events Rule often provide the most regulatory flexibil ity in that air agencies can use these provisions to seek relief from designation of an area as nonattainment. The CAA section 179B (International Transport) and section 182(h) (Rural Transp ort Areas) apply following, or conc urrent with, the initial area designations process. 2. Wildland Fires Fires on wildland play an important ecologi cal role across the globe, benefiting those plant and animal species that depend upon natural fires for propa gation, habitat restoration and*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 99 of 218 reproduction. Wildland can include forestland, 60 shrubland, 61 grassland 62 and wetlands. 63 Fires on wildland can be of two types: wildfire (unpla nned) and prescribed fire (intentionally ignited for management purposes). Since promulgation of the 2007 Exceptional Events Rule, the EPA has received and acted upon excep tional events demonstrations fo r both wildfires and prescribed fires. The EPA anticipates receiving increasing nu mbers of fire-related demonstrations in the future due to the natural accumulation of fuels in the absence of fire, due to climate change that is leading to increased incidence of wildfire, 64 which may necessitate land managers employing prescribed fire more frequently to manage fuel loads and achieve other benefits as described below, 65,66 and due to the potential for fire-related de monstrations to affect near-term regulatory decisions such as the initial ar ea designations decisions associated with a revised 8-hour ozone NAAQS. Consequently, the EPA is proposing revisions to the 2007 Exceptional Events Rule and

60 Forestland is land on which the vegetation is dom inated by trees or, if trees are lacking, the land shows historic evid ence of former forest and has not been converted to other uses. Definition available at https://globalrangelands.org /rangelandswest/glossary

. 61 Shrubland is land on which the vegetation is dominated by shrubs. Definition available at https://globalrangelands.org /rangelandswest/glossary

. 62 Grassland is land on which the vegetation is dominated by grasse s, grass like plants, and/or forbs. Definition available at https://globalrangelands.org/ rangelandswest/glossary

. 63 Wetlands, as defined in 40 CFR 230.3(t), means t hose areas that are inun dated or saturated by surface or ground water at a frequency and durati on sufficient to support, and that under normal circumstances do support, a prevalence of vegetati on typically adapted for life in saturated soil conditions. Wetlands generally include sw amps, marshes, bogs and similar areas. 64 The Administrator’s finding on the advers e effects of greenhouse gases included the observation that wildfires have increased, and th at there are potential serious adverse impacts from further wildfire occurrence. 74 FR 66530 (December 15, 2009). 65 Climate Change in the United Stat es: Benefits of Global Action , U.S. EPA, EPA-430-R-15- 001, June 2015. Available at http://www2.epa.gov/cira. 66 The National Strategy: The Final Phase in the Development of the National Cohesive Wildland Fire Management Strategy, Report to Congress developed by the U.S. Department of Agriculture and the U.S. Department of the Interior, April 2014. Available at http://www.forestsandrangelands.go v/strategy/thes trategy.shtml

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Page 100 of 218 developing additional guidance to make the prep aration and review of demonstrations for wildland fire events more efficient and predictable for all parties. Wildfire emissions account for a large portion of direct PM 2.5 emissions nationally and can contribute to periodic high PM 2.5 and PM 10 levels. Wildfires also emit volatile organic compounds (VOC) and nitrogen oxides (NOx), which are precursors to PM 2.5 , PM 10 and ozone. Besides their effect on air qualit y, wildfires pose a dire ct threat to public safety. Changes in wildfire risk and occurrence are cl osely associated with the lack of periodic fire in fire-dependent ecosystems, demographic changes and associated infrastructure investment at the margins of wildland and, as already noted, climate change and climate variability. The threat from wildfires can be mitigated through management of wildla nd vegetation. Attempts to suppress wildfires have resulted in unintended consequences, especial ly the buildup of fuel loads, which can create a lingering fire liability that will eventually find resolution, unplanned or planned. Unplanned fires in areas with high fuel loads presen t high risks to both humans and ecosystems. 67 Planned prescribed fires and letting some wildfires pro ceed naturally (typically those with lower fire intensity and severity) are tool s that land managers can use to reduce fuel load, unnatural understory and tree density, thus he lping to reduce the risk of ca tastrophic wildfires. Allowing some wildfires to continue to burn even though they could be suppresse d and the thoughtful use of prescribed fire can influen ce the occurrence, size and severity of catastrophic wildfires, which may lead to improved public safety, improved pr otection of property and an overall reduction in fire-induced smoke impacts and subsequent health effects. Thus, appropriate use of prescribed

67 Indeed, “fire policy that focuses on [wildfi re] suppression only, delays the inevitable, promising more dangerous and destructive futu re...fires.” Stephens, SL; Agee, JK; Fule, PZ; North, MP; Romme, WH; Swetnam, TW. (2013). Managing Forests and Fire in Changing Climates. Science 342: 41-42.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 101 of 218 fire may help manage the cont ribution of wildfires to both b ackground and peak PM and ozone air pollution. However, prescribed fires themse lves can affect monitored air quality at some times and places affecting public health, and thus give rise to exceptional events issues. This action proposes a workable approach to addres sing these prescribed fire exceptional events issues. In addition to reducing wildfire risks to humans and ecosystems and wildfire contributions to air pollution, prescr ibed fires can have benefits to those plant and animal species that depend upon natural fires for propagation, ha bitat restoration and reproduction, as well as benefits to a myriad of ecosystem functions ( e.g. , carbon sequestration, maintenance of water supply systems and endangered species habita t maintenance). The EPA understands the importance of prescribed fire, which mimics a na tural process necessary to manage and maintain fire-adapted ecosystems and climate change adap tation, while reducing risk to public safety and the risk of uncontrolled emissions and ecosystem damage from catastrophic wildfires. The EPA is committed to working with federal land managers, other federal agencies, tribes, states and private landowners to effectively manage prescrib ed fire use to reduce the impact of catastrophic wildfire-related emissions on ozone, PM 10 and PM 2.5 . a. Current Situation When the EPA promulgated the 2007 Exceptional Events Rule, we included definitions for fire-related terms ( e.g ., wildfire, prescribed fire and wild land) in the preamble and attributed these definitions to the National Wildland Fire Coordinating Group (now the National Wildfire Coordinating Group or NWCG) Glossary of Wildland Fire Terminology, 2003. The EPA did not, however, codify these definitions in regulator y text. Since promulgation of the 2007 Exceptional Events Rule, the NWCG has modified some of its recommended definitions and the EPA used*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 102 of 218 slightly different definitions in its Interim Exceptional Events Implementation Guidance, creating some confusion for air agencies and othe r entities working with air agencies who have tried to use fire-related definitions and concepts when preparing and submitting exceptional events demonstrations for fires. The preamble to the 2007 Exceptional Events Rule discussed how the EPA expected to apply the rule to wildfires and prescribed fi res. The EPA stated that wildfires would be considered natural events, while prescribed fi res would be considered events caused by human activity. As events caused by huma n activity, prescribed fires are s ubject to the “not likely to recur” criterion, and the preamble to the rule disc ussed the considerations that would apply for this criterion. Section V.F.2.d provides a more detailed summary of th e current situation and planned changes for this criterion. Demonstrations for wildfires and those prescrib ed fires claimed to be exceptional events must also address the “not r easonably controllable or preven table” criterion. Neither the 2007 Exceptional Events Rule nor its preamble addres sed this criterion in a ny depth for wildfires. Since promulgating the rule in 2007, the EPA has c oncluded that short, general statements in demonstrations for fire events satisfy this crit erion. The EPA has been advising air agencies that when documenting the “not reasonably controllab le or preventable” criterion in a wildfire exceptional events demonstration submittal, air agen cies should identify the origin and evolution of the wildfire, describe local e fforts to prevent fires due to unau thorized activity or accidental human-caused actions (if relevant given the origin of the fire) and explain any efforts to limit the*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 103 of 218 duration or extent (and thus th e emissions) of the wildfire. 68,69,70 We have also advised air agencies that if the wildfire originated outside of the jurisdiction of the air agency submitting the exceptional events demonstration, then the submitti ng air agency should identify this fact in its demonstration. 71 The 2007 Exceptional Events Rule and its pr eamble gave more extensive treatment to the not reasonably controllable or preventable criterion for prescribed fires. The rule text tied the eligibility of prescribed fires as approved exceptional events to the air agency having a “certified” SMP in place or, in th e alternative, to using BSMP for the prescribed fire(s) in question. In the preamble, the EPA did not pr ovide detailed guidance on SMPs or BSMP, but committed to defining and developing these con cepts when we updated the guidance contained in the 1998 Interim Air Quality Policy on Wildland and Prescribed Fires

. 72 However, the EPA has not revised this guidance document. Although some states have developed demonstrations that incorporate BSMP employed for a specific pres cribed fire and/or have referenced BSMP in their SMPs, the EPA has not in any other more recent guidance clarified what it means for an air agency or burner to have a certified SMP in place and/or to implement BSMP. Like the inconsistency that has developed since 2007 in fi re-related definitions, the absence of further

68 Interim Exceptional Events Rule Frequently Asked Questions. U.S. EPA. May 2013. Available at http://www2.epa.gov/sites/production/file s/2015-05/documents/eer_qa_doc_5-10-13_r3.pdf

. See question 20b. 69 Prevention/control efforts could include posti ng High Fire Danger signs to make people more careful and prevent accidental fire s, and/or taking reasonable acti on to contain a fire once it has started. 70 Example language to limit the duration and exte nt of the wildfire might include, “During wildfires, fire management resour ces were deployed to the fire event giving first priority to protecting life and property.” 71 Interim Exceptional Events Rule Frequently Asked Questions. U.S. EPA. May 2013. Available at http://www2.epa.gov/sites/production/file s/2015-05/documents/eer_qa_doc_5-10-13_r3.pdf

. 72 Interim Air Quality Policy on Wildland and Prescribed Fires. U.S. EPA. April 23, 1998. Available at http://www.epa.gov/ttn/oarpg/t1/memoranda/firefnl.pdf.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 104 of 218 clarifying guidance on SMPs and BSMP has created confusion for air agencies trying to develop these plans and/or apply these practices for purposes of developing and submitting exceptional events demonstrations fo r prescribed fires. b. Proposed Changes In this action, the EPA proposes to codify in regulatory la nguage certain fire-related definitions and SMP/BSMP factors necessary fo r exceptional events demonstration and program implementation purposes. Codifying these definitions in 40 CFR 50.1 will promote understanding and standardize terminology for th e purposes of characterizing an event for exceptional events demonstration purposes. Finalizing these proposed changes will also decouple implementation of the exceptional events process from potential future revisions to the Interim Policy on Wildland and Prescribed
Fires. Although the EPA solicits comment on the regul atory process associated with developing exceptional events demonstrations for fire-rel ated events, the EPA does not intend to take comment on any aspects of the 1998 Interim Policy on Wildland and Prescribed Fires as part of this effort to revise the Exceptional Events Rule. The proposed new definitions, along with other proposed changes, are described in detail in the separate sections on wildfires (section V. F.2.c) and prescribed fire (section V.F.2.d) that follow immediately below this section. c. Wildfires
Current Situation. The preamble to the 2007 Exceptional Events Rule defined a wildfire as “an unplanned, unwanted wildla nd fire (such as a fire cau sed by lightning), [to] include unauthorized human-caused fires (such as arson or acts of carelessness by humans), escaped prescribed fire projects (escaped control due to unforeseen circumstances), where the appropriate*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 105 of 218 management response includes the objective to suppress the fire.” The 2007 Exceptional Events Rule preamble also defined a “wildland fire us e” as “the applicati on of the appropriate management response to a naturally-ignited ( e.g ., as the result of light ning) wildland fire to accomplish specific resource management objectives in predefined and designated areas where fire is necessary and outlined in fire ma nagement or land management plans.” The 2007 Exceptional Events Rule preamble fu rther clarified that the EPA believed that both wildfires and wildland fire use fires fall within the meaning of “natural events” as that term is used in CAA section 319(b). In the 2013 Interim Q&A Document, after cons ulting with other federal agencies that manage wildfires and prescribed fires, the EPA defined a wildfire as “[a]ny fire started by an unplanned ignition caused by lightning; volcanoes; unauthorized activity ; accidental, humancaused actions; and escaped prescribed fires.” 73 Building off of the principl es in the February 2009 Guidance for Implementation of Federal Wildland Fire Management Policy , 74 the NWCG defines “wildland” as “an area in which development is essentially non-existent, except for roads, railroads, power lines, and similar transportation fac ilities. Structures, if a ny, are widely scattered.” 75

73 Interim Exceptional Events Rule Frequently Asked Questions. U.S. EPA. May 2013. Available at http://www2.epa.gov/sites/production/files/ 2015-05/documents/eer_qa_doc_5-10-13_r3.pdf. 74 Guidance for Implementation of Fede ral Wildland Fire Management Policy , developed cooperatively by the Fire Executive Counc il, February 13, 2009. Available at http://wildfiretoday.com/doc uments/Federal%20Wildland%20Fire%20Management%20Policy %2002-13-2009.pdf

. 75 National Wildfire Coordinating Group. Glo ssary of Wildland Fire Terminology, PMS 205. October 2014. Available at http://www.nwcg.gov/sites/def ault/files/products/pms205.pdf

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Page 106 of 218 Proposed Changes . Although the EPA has previously approved exceptional events demonstrations for wildfires, 76 the EPA recognizes air agencies preparing exceptional events demonstrations for future wildfires will benefit from additional clarification and guidance related to wildfire terminology. This section di scusses the EPA’s proposed changes. (i) Definition of wildland and wildfire. For purposes of this action, the EPA proposes to codify in regulatory language the definiti on of “wildland” by usi ng the October 2014 NWCG Glossary definition that a wild land is “an area in which human activity and development is essentially non-existent, except for roads, railroads, power lin es, and similar transportation facilities. Structures, if any, ar e widely scattered.” As previously noted, wildland can include forestland, shrubland, grassland and wetlands. This proposed definition of wildland would include lands that are predominantly wildland, such as land in the wildland-urban interface. 77,78 In proposing this definition for wildland, the EPA considered the types of human intervention that could affect whether a land is considered a “wildland.” In our view and the view of other federal agencies with which we have consulted in the development of this proposed action, the presence of fences to lim it the movement of grazing animals, or of infrastructure to provide water to grazing an imals, does not prevent a land area from being

76 See submitted exceptional events demonstrations available on the EPA’s website at http://www2.epa.gov/air-quality-analysis/ exceptional-events-submissions-table. 77 The wildland-urban interface is the line, ar ea or zone where structures and other human development meet or intermingle with undevelo ped wildland or vegetative fuels. The term describes an area within or adjacent to private and public property where mitigation actions can prevent damage or loss from wildfire. See , Glossary of Wildland Fire Terminology, PMS 205. October 2014. Available at http://www.nwcg.gov/sites/def ault/files/products/pms205.pdf

. 78 We would generally treat a large prescribed fire in a wildland-urban interface area as a prescribed fire on wildland, subjec t to the prescribed fire provis ions described in this proposal. We do not expect a small prescribed fire in an interface area ( e.g ., a prescribed burn ignited by a single landowner on his/her pers onal property) to generate emissions that would raise exceptional events issues.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 107 of 218 wildland. Cultivated cropland ( i.e ., a field that is plowed or di sked or from which crops are removed on an annual or more frequent basis) is not wildland. Land areas on which nursery stock is grown to marketable size ( e.g ., Christmas tree farms) are generally not wildland unless they are “wild” in terms of a having onl y limited human entrance and intervention for management or removal purposes thereby result ing in a complex ecosystem. Generally, managed timber lands may be considered wildland if they have a comple x ecosystem affected by only limited human entrance and inte rvention. The EPA invites comme nt on whether it would be appropriate to incorporate these ex amples of land use types that can be considered to be (or not to be) wildland into the regulatory definition of w ildland or whether or it is adequate to discuss them in the preamble only. Also for purposes of this action, the EPA propos es to codify in regulatory language the following definition of “wildfire,” which slightly modifies the definiti on of “wildfire” with respect to prescribed fires that app eared in the Interim Q&A document. A wildfire is any fire started by an unpl anned ignition caused by lightning; volcanoes; other acts of nature; unauthorized activity; or accidental, human-caused actions; or a prescribed fire that has been declared to be a wildfire. A wildfire that predominantly occurs on wildland is a natural event. This proposed definition of wildfire does not re quire that the objective be to put out a fire for the fire to be categorized as a wildfire. Wh en an unplanned fire on wildland does not threaten catastrophic consequences, it may be very approp riate to allow it to continue. The proposed definition therefore encompasses the type of activity previously refe rred to as a wildland fire use ( i.e ., a situation in which a fire manager deliberately allows a wildfire to continue to burn over a certain land area rather than immediately extinguish it or block its progress into that area). This inclusion is consistent with the approach taken in 2007 that all type s of wildfire were considered to be natural. We note here, as guidance, that the part of the proposed definition referring to a*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 108 of 218 prescribed fire that has been declared to be a wildfire refers to specific instances in which the conditions of a particular prescribed fire have de veloped in a way that le ads the fire manager to decide that the fire should be treated as a wildfire, for ex ample if it has escaped secure containment lines and requires suppression along a ll or part of its boundary or no longer meets the resource objectives ( e.g ., smoke impact, flame height). It is not the intention that land managers may categorically re-define some type s of prescribed fire to be wildfires. Because the EPA is proposing in rule text that all wildfires on wildland are always considered natural events, the proposed definition of wildland will in turn determine which fires are considered to be natural ev ents. This is consistent with the approach in the 2007 Exceptional Events Rule. The EPA realizes that some wildfires are initiated by human actions ( e.g ., careless use of campfires or leaf and brush pile fires). Th e EPA also realizes that past human activity in the form of decades of suppressi ng wildfires has influenced the size and emissions of wildfires that do occur. However, wildfire is mostly dom inated by natural factors, and the EPA believes that treating all wildfires on wild land as natural events is in ke eping with Congressional intent and not contradictory to any plai n meaning of CAA section 319(b). Therefore, because a wildfire on wildland is a natural event and because natural events can recur, an air agency would not need to address event recurrence in the “human activity unlikely to recur at a particular location or a natural event” portion of its ex ceptional events demonstration. (ii) Not reasonably controllable or preventable. Although a wildfire is unplanned, the “not reasonably controllable or preventable” criterion still applies. Another function of the definition of wildland is that the EPA is proposing that the treatmen ts of wildfires and prescribed fires on wildland with regard to the not reasonab ly controllable or preven table criterion have a number of common aspects, as described here and below in the section on prescribed fires,*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 109 of 218 because a wildland situation presents particular co nsiderations applicable to both fire types with respect to what prevention or c ontrol measures may be reasonabl e. The EPA is not proposing any general approach for wildfires or pres cribed fires that are not on wildland. 79 Because wildfires on wildland are unplanned, fi re management agencies generally have either no advanced notice or limited and uncertain notice, of wildfire ignition and location. In addition, many areas of wildland are very remote and rugged, and thus no t easily reached and traversed. These factors generally limit preparat ion time and on-site resources to prevent or control the initiation, duration or ex tent of a wildfire. Also, by th eir nature, catastrophic wildfires typically present some risk of property damage , ecosystem damage and/or loss of life (of the public or firefighters), which is a strong motivation for appr opriate suppression and control efforts. The EPA believes that land managers and other fire management entities have the motivation and the best information for taking acti on to reasonably prevent and limit the extent of wildfires on wildland, thus also controlling the resulting emissions. Therefore, the EPA believes that it is not useful to require air ag encies to include in their individual wildfire exceptional events demonstrations descriptions of prevention and control efforts employed by burn managers to support a position that such efforts were reasonabl e. To increase the efficiency of the exceptional events proce ss, the EPA proposes a new approach for wildfires on wildland, under which there would be a rebuttable presumption that every wildfire on wildland satisfies the “not reasonably controllable or preventabl e” criterion, unless evid ence in the record

79 While we are proposing special provisions only for fires that occur predominantly on wildland, we do not intend to restrict fires on other type s of land from receiving similar treatment. In addressing the not reasonably controllable or pr eventable criterion in a demonstration for a wildfire that is not on wildland, air agencies should state that available resources were reasonably aimed at suppression a nd avoidance of loss of life a nd property and that no further efforts to control air emissions from the fire would have been reasonable.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 110 of 218 demonstrates otherwise. Applying this categorical presumption of not reasonably controllable for wildfires would involve referenc ing the appropriate re gulatory cita tion in the demonstration. As previously stated, there will be situa tions in which a fire manager could have suppressed or contained a wildfire but has allowed the fire to c ontinue burning through an area with a current, in-place land management plan calling for restoration through natural fire or mimicking the natural role of fire. The EPA recogni zes that this scenario could occur when a fire manager has a plan for acquiring personnel and equipment to address the wildfire (either coincidentally or because the wildfire was originally a prescribed fire) but the manager determines that allowing the wildfire to conti nue burning is safe and will conserve overall fire management resources compared to suppressing or containing th e current wildfire and then conducting a separate prescribed burn at a later time. In such a scenario, even though the fire would meet the definition of a wildfire and even though we are proposing that in general wildfires will not need to be re viewed individually ag ainst the not reasonab ly controllable or preventable criterion, we would expect the fi re manager to employ appropriate BSMP as described in section V.F.2.d when possible. (iii) Coordinated communications. Regardless of the above considerations for wildfires, the EPA urges land managers and air agencies to coordinate, as appropria te, in developing plans and appropriate public communications regard ing public safety and reducing exposure in instances where wildfires are potential exceptional events and contribute to exceedances of the NAAQS. Coordinated efforts can help air agen cies satisfy the Exceptional Events Rule obligation at 40 CFR 51.930 that air agencies mu st provide public noti ce and public education and must provide for implementation of reasonabl e measures to protect public health when an*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 111 of 218 event occurs. 80 Also, when wildfire impacts are frequent and significant in a particular area, land managers, land owners, air agencies and communities may be able to lessen the impacts of wildfires by working collaboratively to take steps to minimize fuel loading in areas vulnerable to fire. 81 Fuel load minimization steps can consist of both prescribed fi re and mechanical treatments, such as using mechanical equi pment to reduce accumulated understory. d. Prescribed Fires As noted previously, the EPA recognizes and acknowledges the potential significant impact on air quality posed by catastrophic wildfire s. The use of prescribed fire on wildland can influence the occurrence, severit y, behavior and effects of catastr ophic wildfires, which may help manage the contribution of wildfires to measured ambient pollutant levels (particularly ozone and PM concentrations). Additiona lly, prescribed fires can benefit the plant and animal species that depend upon natural fires for propagation, ha bitat restoration and reproduction, as well as a myriad of ecosystem functions ( e.g. , carbon sequestration, maintenance of water supply systems and endangered species habitat maintenance) . The EPA formally r ecognized in the 1998 Interim Air Quality Policy on Wildland and Prescribed Fires that federal, tribal and state owners and land managers use prescribed fire on wildland to achieve some of these resource benefits, to correct the undesirable conditions created by past wildfire suppr ession management strategies and to reduce the risk of wild fires to the public. Although the 1998 Interim Air Quality Policy on

80 72 FR 13575 (March 22, 2007). 81 One example of this collaborative approach is the evolving interage ncy Wildland Fire Air Quality Response Program, which has developed re sources to help address and predict smoke impacts from wildfires to reduce public exposure to wildfire smoke. Additional information is available at http://www.westar.org/Docs/Business%20Mee tings/Spring14/Boise/12.3%20Lahm_WFAQRP_5 _28_14.pdf.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 112 of 218 Wildland and Prescribed Fires focused on the role of federa l, tribal and state owners/land managers, it also recognized that prescribed fi res on private lands achieve some of the same goals. These concepts, also noted in the pr eamble to the 2007 Exceptional Events Rule, are summarized in more detail immediately below. In recent regulatory actions, 82 the EPA has continued to express an understand ing of the importance of prescrib ed fire, noting that it can be used to mimic the natural process necessary to manage and maintain existing fire-adapted ecosystems and/or return an area to its historical ecosystem (or another natural ecosystem if the historical ecosystem is no longer a ttainable) while reducing the risk to public safety and the risk of uncontrolled emissions from catastrophic wildfires.
Current Situation . The 2007 Exceptional Events Rule recognized the benefits of prescribed fire as summarized ear lier in this section and included provisions for these event types in both the preamble to the final rule and in regulatory language. Th e preamble to the 2007 Exceptional Events Rule defined a prescribed fire as “a fire ignited by management objectives to meet specific resource management needs.” This wa s consistent with the de finition of prescribed fire in general use by the fire ma nagement community at the time. 83 Also in the preamble language, the EPA explained that pr escribed fire cannot be classifi ed as natural given the extent of the direct human causal connection. However, th e preamble explained that a prescribed fire that causes or contributes to an exceedance or vi olation of an ambient ai r quality standard could

82 See , for example, National Ambient Air Quality Standards for Ozone; Proposed Rule (79 FR 75234, December 17, 2014) and Implementation of the 2008 National Ambient Air Quality Standards for Ozone: State Implementation Plan Requirements; Final Rule (80 FR 12264, March 6, 2015). 83 The October 2014 NWCG definition of “prescribe d fire” is similar but includes the concept that the fire is not illegal: “[ a]ny fire intentionally ignited by management actions in accordance with applicable laws, policies, and re gulations to meet specific objectives.”*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 113 of 218 still be considered an exceptional event if it sati sfies all core statutory elements of CAA section 319(b), including the “human activity that is unlikel y to recur at a partic ular location” and the “not reasonably controllable or preventable” criteria. The 2007 Exceptional Events Rule preamble furt her explained that air agencies should take into account the natu ral fire return interval 84 as part of the basis for establishing that the human activity ( i.e ., the prescribed fire) is “unlikely to recur at a particular location.” The preamble acknowledged that the natural fire return interval can vary widely and range from once every year to less frequently than once every 200 years. When addressing the “not reasonably cont rollable or preventabl e” criterion, the 2007 Exceptional Events Rule preamble instructed agen cies to examine whether there are “reasonable alternatives,” such as mechanical or other ( e.g ., chemical) treatments to the use of prescribed fire. The preamble language recognized that, a lthough case- and area-speci fic, any number of conditions could exist that would favor the use of pr escribed fire rather than alternate treatments. Such scenarios identified in the preamble included: significant build-up of forest fuels in a particular area that if left unaddressed would pos e an unacceptable risk of catastrophic wildfire; pest or disease outbreak; natura l species composition dependent on a specific fire return interval; and legal requirements precluding the use of mechanical fuel reduction methods. The 2007 Exceptional Events Rule also indicat ed, in both preamble discussion and rule text, that to further satisfy th e “not reasonably controllable or preventable” criterion for prescribed fires and to addre ss the principle at section 319( b)(3)(A) of the CAA that the

84 The natural fire return inte rval is the typical number of years between two successive naturally-occurring fires in a specif ied area or ecosystem. The histor ical rate of return of these fires resulted in plant communities that evolve d with recurring fire and therefore became dependent on fire for maintenance.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 114 of 218 protection of public health is the highest priority, a prescribed fire would be considered to be an exceptional event only if the state has certifi ed to the EPA that it has adopted and is implementing a SMP or the state has ensured that the burner has em ployed BSMP. While the EPA did not identify in the 2007 Rule the nece ssary components of an SMP or what SMP certification entails, the preamble cited the 1998 Interim Air Quality Policy on Wildland and
Prescribed Fires. 85 This policy identified the following basic components of a certifiable SMP: 86

 Authorization to Burn - includes a proce ss for authorizing or granting approval to manage fires for resource benefits within a region, state or on Indian lands and identify a central authority responsib le for implementing the program. The authorization process could include burn plans that cons ider air quality and the ability of the airshed to disperse emi ssions from all burning activities on the day of the burn.

 Minimizing Air Pollutant Emissions – en courages wildland owners/managers to consider and evaluate alternative treatments to fire, but if fire is the selected approach to follow emission reduction techniques.

 Smoke Management Components of Burn Plans – identifies the following components if the SMP requires burn plan s: actions to minimize fire emissions, evaluate smoke dispersion, public notific ation and exposure reduction procedures

85 The discussion of the 1998 Interim Air Quality Policy on Wildland and Prescribed Fires recommendations regarding SMPs appears in th e preamble to the 2007 Exceptional Events Rule at 72 FR 13567 (March 22, 2007). 86 The language associated with the six basic com ponents of a certifiable SMP was taken directly from the 1998 Interim Air Quality Policy on Wildland and Prescribed Fires. For context, the EPA notes that the identified components of a certifiable SMP apply to managing smoke from prescribed fires managed for resource benef its. The EPA would expect burn managers to consider actions and approaches where applicab le or where appropriate rather than in all prescribed fire scenarios.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 115 of 218 and air quality monitoring.

 Public Education and Awareness – establ ishes the criteria for issuing health advisories when necessary and procedures for notifying potentially affected populations.

 Surveillance and Enforcement – includes procedures to ensure that wildland owners/managers comply with the SMP.

 Program Evaluation – provides for periodic review by all stakeholders of the SMP effectiveness and program revision as necessary. The 1998 Interim Air Quality Policy on W ildland and Prescribed Fires also noted, regarding the certification process for SMPs, that to receive special consideration for air quality data whose concentrations were influenced by pres cribed fires, “[t]he St ate/tribal air quality manager must certify in a letter to the Admini strator of EPA that at least a basic [smoke management] program has been adopted and implemented....” The 1998 Interim Air Quality Policy on Wildland and Prescribed Fires further identified that federal agencies intending to use prescribed fire should operate under an approved prescribed fire plan and meet the National Environmental Policy Act (NEPA) requireme nts, where applicable, prior to ignition. 87

87 In specifying the basic components of certifiabl e SMPs that would include the requirement for agency approval of prescrib ed fire plans, the 1998 Interim Air Quality Policy on Wildland and Prescribed Fires noted that SMPs can mitigate the nuisanc e and public safety hazards associated with smoke from prescribed fires intruding into populated areas, preven t deterioration of air quality and NAAQS violations and address visibility impacts in mandatory Class I Federal areas. Since the EPA issued the Interim Policy in 1998, some federal agencies have reported to us their assessment that some states and/or local ai r agencies have managed their SMP (or other regulatory programs) in such a way as to exclude th e use of prescribed fires in areas to such an extent that fuels have continued to accumula te to levels that in crease the likelihood of catastrophic wildfires.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 116 of 218 The EPA did not use the preamble to the 2007 Exceptional Events Rule to expand on the concept of using BSMP in lieu of an SMP. Ra ther, the EPA only noted that burners could use BSMP to minimize emissions and control the impacts of fire. Although the EPA identified several example BSMP in a footnote in the preamble (footnote 12 at 72 FR 13567), we also committed to developing the concept when we updated the guidance in the 1998 Interim Air Quality Policy on Wildland and Prescribed Fires. The EPA has not revised this guidance and does not currently plan to do so. Although some states have developed demonstrations that incorporate BSMP employed for a specific prescrib ed fire and/or referenced BSMP in their SMPs, the EPA has not in any other more recent guidance clarified what it means for an air agency or burner to have a certified SM P in place and/or to implement BSMP. In addition to conditioning the approval of a prescribed fire as an exceptional event on the existence and implementation of a certified SM P or the actual use of BSMP, as described above, the 2007 Exceptional Events Rule also re quires that “[i]f an exceptional event occurs using the basic smoke management practices appr oach, the State must undertake a review of its approach to ensure public health is being protected and must include consideration of development of a SMP.” To date, air agencies have submitted few exceptional events demonstrations for prescribed fires. One recen t submission came from Kansas, a state already operating an SMP. 88 The 2007 Exceptional Events Rule at 40 CFR pa rt 50.14(b)(3) allows fo r the exclusion of data where a state demonstrates to the EPA’s sa tisfaction that emissions from prescribed fires

88 Treatment of Data Influenced by Exceptional Events: Exceptional Events Submissions Table. U.S. Environmental Protection Agency, Research Triangle Park, NC. See links associated with “April 2011 Fires” in the ozone sect ion of the table available at http://www2.epa.gov/air-qualityanalysis/exceptional-e vents-submissions-table

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Page 117 of 218 caused a specific air pollution concentration in ex cess of one or more NAAQS at a particular air quality monitoring location and otherwise satisf ies the requirements in the Exceptional Event Rule. The regulatory language also requires that the subject prescr ibed fire meets the definition in 40 CFR part 50.1(j) and requires that the state has certified to EPA that it has adopted and is implementing a Smoke Management Program or th e state has ensured that the burner employed basic smoke management practices. The defin ition of an exceptional event at 40 CFR 50.1(j) includes the requirement that an event “is not r easonably controllable or preventable.” Thus, the EPA has interpreted that a demonstration for a pr escribed fire independently address both the SMP/BSMP element and the not reasonably contro llable or preventable criterion. We have not indicated that meeting the SMP/BSMP condition is sufficient to satisfy the not reasonably controllable or prev entable criterion. Proposed Changes . As previously noted, the EPA has not to date clarified fire-related definitions or its expectations regarding SMPs or BSMP in rule or preamble form. This uncertainty has created confusion for air and fire management ag encies trying to develop firerelated plans and/or apply fire management practi ces for prescribed fires. It has also created confusion for air agencies when developing and submitting exceptional events demonstrations for both wildfires and prescribed fires. To assist air agencies in documenting an ex ceptional events package for a prescribed fire on wildland, the EPA proposes to clarify its exp ectations for a satisfactory demonstration, as follows. (i) Definition of a prescribed fire. We are proposing to adopt in rule language the current NWCG-recommended definition of a prescribed fire: “[a]ny fire intentionally ignited by management actions in accordance with appli cable laws, policies and regulations to meet*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 118 of 218 specific objectives.” In this definition, “managemen t” refers to the owner or manager of the land area to which prescribed fire is applied, and “specific objectives” refe rs to specific land or resource management objectives. (ii) Events caused by human activity. We are proposing to say in rule form that prescribed fires are events caused by human activity. Thus, to be considered an exceptional event, every prescribed fire demonstration must address the “h uman activity unlikely to recur at a particular location” criterion. (iii) Unlikely to recur at a particular location . As discussed in more detail in section V.E.1 of this proposal, this re quirement of CAA section 319(b) is not specific and requires interpretation on a case-by-case or event type-by-ev ent type basis. The term “unlikely” implies consideration of the expected future frequency of events similar to the event that has already happened, but does not convey any particular be nchmark for what frequency should be low enough to be considered “unlikely.” Also, th e term “at a particular location” requires interpretation, as it could refer to the exact area or only to the general area of the event, to the location of the ambient monitoring station or stati ons that were affected by the event or to the combination of both. As was our position in 2007, we con tinue to believe that the natu ral fire return interval is a useful and appropriate benchmar k for a satisfactory demonstrati on that a prescribed fire is unlikely to recur at a particular location, in the se nse that if a planned program of prescribed fire calls for the application of prescribed fire at a similar interval to th e natural fire return interval at given locations then each prescribed fire conducte d in that program can be considered not likely to recur at its particular lo cation. However, we now believe based on experience and further consideration that the natural fire return interval is not the only appropria te benchmark. It can be*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 119 of 218 difficult in some cases to determine what fire re turn interval prevailed under natural conditions, which may not have existed for decades or even hundreds of years in a part icular area. Also, in some cases environmental conditions may have changed, for example due to climate change, such that the original natural ecosystem cannot r ealistically be restored and the well-considered land management goal instead may be the development and maintenance of a sustainable and resilient ecosystem that is different than what hi storically existed and that will likely reduce the risk of catastrophic wildfire. In such a case, the frequency of prescribed fi re needed to establish or restore such an ecosystem during a transitiona l period and/or the frequency needed to sustain the resilient ecosystem may be different than the na tural fire return interval that once prevailed. It is also important to consider i ssues of fire personnel and public safety and protection of nearby property. Land managers may need to apply prescr ibed fire at a frequency that maintains the accumulation of fuel loading between prescribed fire s at a level that does not create the risk of a dangerous wildfire. Accordingly, the first proposed change for pres cribed fires on wildla nd is to include in the rule text two benchmarks for the expected fu ture frequency of prescr ibed fires on wildland to meet the not likely to recur criterion: (1) the natu ral fire return interval as articulated in the 2007 preamble and (2) the prescribed fire frequency ne eded to establish, restore and/or maintain a sustainable and resilient wildland ecosystem. If finalized, an air agency could include information provided by the land manager with respect to the appropriate benchmark for a prescribed fire on wildland as th e basis for satisfying the human activity unlikely to recur at a particular location criterion in its exceptional events demonstration. 89

89 The benchmarks for the expected frequency of prescribed fires not on wildland would be assessed on a case-by-case basis.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 120 of 218 Successfully implementing one of these be nchmarks for prescribed fire frequency necessitates that the air agency and the land manager collaborate to establish and document the appropriate fire return interval or frequency in a submitted demonstration. Federal agencies that use prescribed fire to manage lands for which they are responsible generally prepare multi-year plans for the use of prescribed fire in a given na tional park, national forest, armed forces base or other land area. Many of these plans include an ob jective to establish, restore and/or maintain a sustainable and resilient wildland ecosystem a nd incorporate the best science available to determine what prescribed fire cycle will accomplish this. 90 Some tribes, private landowners (and federal, state and local agencies working with private landowners) and state agencies that manage state-owned lands ( e.g ., state parks) also prepare mul ti-year management plans. While plans developed by public agencies ( i.e. , state and federal agencies) often undergo public comment prior to being finalized, the plans deve loped by tribes and priv ate landowners may not follow a public comment process. However, public agencies often work with tribes and private owners to develop these plans, which are based on conservation practices a nd standards that have often undergone public comment as part of the state or federal agency process. The EPA understands that multi-year plans inco rporate factors relevant to identifying and selecting the areas and times under which manageme nt will initiate a specific prescribed fire. The EPA also recognizes that evalua ting the behavior and results of prior prescribed fires aids in determining the frequency and need for future prescribed fire in a given area. In addition, personnel and equipment must be available on site , which cannot be specifically planned far in

90 An example of a federal land management pl an that considers the need for the use of prescribed fire is the Land and Resource Management Plan fo r the Kaibab National Forest, Coconino, Yavapai, and Mojave Counties, Arizona , USDA Forest Service Southwestern Region, MB-R3-07-17, February 2014, available at http://www.fs.usda.gov/Interne t/FSE_DOCUMENTS/stelprd3791580.pdf

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Page 121 of 218 advance. Thus, it is typical for multi-year plans to identify somewhat general targets for the frequency of prescribed fire use and for specific burn plans. Even then, unexpected differences between planned and actual fire behavior, landsca pe or ecosystem characteristics, fuel loading patterns and weather patterns may cause management to deviate from the general plan and/or the specific burn plan. Therefore, when the EPA revi ews an exceptional even ts demonstration for a prescribed fire conducted under a wildland manage ment plan, we intend to compare the actual time pattern of prescribed fires on the land with th e pattern described in the applicable multi-year plan in a general way, rather th an treating the multi-year plan as containing a specific schedule to which management must adhere. For example, if the wildland management plan identified an approximate 5-year burn interv al, the EPA would not disapprove a demonstration if the burn occurred on a 4-year or a 6-year interval. Therefore, we are proposing in rule text that we will consider a demonstration’s referencing of a multi-year land or resource management plan 91 (and including either a copy or an internet link to the plan) with a stated obj ective to establish, restore and/or maintain a sustainable and resilient wildland ecosystem and/or to preserve endangered or threatened species that also identifies the subject ar ea as a candidate for prescribed fire to be dispositive evidence that a particular fire conducted in accordance with such a plan satis fies the “unlikely to recur at a particular location” criterion. We would also consider a demonstr ation’s referencing of a fire management plan for tribal or private lands that has been reviewed and certified by the appropriate fire and/or resource management professionals and agreed to and followed by the

91 These plans could also include fire manage ment plans, prescribed fire on wildland management plans, landscape management plan s or equivalent public planning documents.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 122 of 218 land owner/manager to be sufficient evidence satis fying the “unlikely to recur at a particular location” criterion. (iv) Not reasonably controllable or preventable . Consistent with current practice and 2007 preamble/rule language, the EPA considers it appr opriate to allow air agencies to rely on an in-place and implemented state-ce rtified SMP to satisfy the controllability prong of the “not reasonably controllable or preventable” crite rion. The EPA proposes to incorporate the six elements of SMPs discussed in the 1998 Interim Air Quality Policy on Wildland and Prescribed
Fires and referenced in the preamble to the 2007 Ex ceptional Events Rule in to the preamble of the final rule for this proposal, where it would se rve as guidance. That is, at a minimum, a statecertified SMP would include provisions for (i) aut horization to burn, (ii) minimizing air pollutant emissions, (iii) smoke management components of burn plans, (iv) public education and awareness, (v) surveillance and enforcement, a nd (vi) program evaluation. Certification would require that the air agency certi fy in a letter to the Administ rator of the EPA, or a Regional Administrator, that it has adopt ed and is implementing a SMP. 92 Alternatively, the EPA solicits comment on incorporating these SMP elements in to rule text language. The EPA proposes to accept as sufficient the testimony of the air agency submitting an exceptional events demonstration that the SMP is being implemente d, provided that prior to the EPA’s acting on a demonstration, the record contains no clear evidence to the contrary. Consistent with current practi ce and 2007 preamble and rule language , the EPA also considers it appropriate to allow air agencies to rely on a burn manager’s use of BSMP that minimize emissions and control impacts, in lieu of a state-certified SMP, to satisfy the controllability prong

92 The EPA anticipates that any person with in an air agency responsible for submitting exceptional events demonstrations or SIP revisi ons could also be responsible for certifying a Smoke Management Program.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 123 of 218 of the “not reasonably controllable or prev entable” criterion. To provi de clarity and reduce uncertainty for air agencies and burn managers, the EPA proposes to identify in the rule text six BSMP practices as being generally applicable for exceptional events purposes for prescribed fires on wildland as well as othe r prescribed fires. The six BSMP , listed and described in more detail in Table 3, come from guidance on BSMP for prescribed burns provided by the U.S. Department of Agriculture (USDA) Forest Service (USFS) and USDA Natural Resources Conservation Service (NRCS). 93 Land managers of other federal, state and local agencies and private land owners generally endor se and follow this BSMP guidance. 94 While the listed practices are broadly stat ed, fire managers use site-specific considerations to select the exact actions of each type and apply them to specific bu rn projects. There may be situations in which one or more of the six BSMP is clearly not ap plicable for a particular prescribed burn--for example, if a prescribed fire is so remote that there are no neighbors to be notified. The EPA generally does not intend to ch allenge a burn manager’s selecti on of the intensity or specific measure within the BSMP categories when we review a particular exceptional events demonstration. As part of the on-going assessment of our regul atory programs, we intend to generally review those practices commonly empl oyed by federal agencies and other users of prescribed fire.

93 USDA Forest Service and Natural Resources Conservation Service, Basic Smoke Management Practices Tech Note, October 2011, http://www.nrcs.usda.gov/Intern et/FSE_DOCUMENTS/stelprdb1046311.pdf

. 94 The EPA also addressed how federal agencies may use basic smoke management practices to establish a presumption of conformity in the prea mble to the EPA’s General Conformity Rule at 40 CFR 93.153(g)-(i) (75 FR 17264, April 5, 2010). The six pract ices identified in Table 3 are not a presumed to conform action for purposes of a Federal agency sa tisfying their General Conformity responsibilities. For basic smoke management practices to provide a presumption of conformity, the identified basic smoke manage ment practices must be publicly and state reviewed as part of a presumed to conform action under 40 CFR 93.153(g) or (f) of the General Conformity Rule.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 124 of 218 As another component of the approach fo r prescribed fires on wildland, the EPA is proposing to accept as evidence of the actual use of BSMP the fire manager’s statement that he or she employed applicable BSMP for a prescribed fire. Documentation of such statement for an exceptional events demonstration could consist of a copy of the routine post-burn report or a letter prepared by the fire manager ( see example content of a burn report in Table 4). The EPA and other federal agencies will work collaboratively to provide access to such post-burn reports by air agencies that need them. We encourag e land managers and othe r organizations that employ prescribed fires to work with states and tr ibes to develop an efficient process to provide air agencies with documentation that BSMP were employed for particular prescribed fires. Table 3. Summary of Basic Smoke Management Practices, benefit achieved with the BSMP, and when it is applied (before, during or after ignition of the burn). a Basic Smoke Management Practice Benefit achieved with the BSMP When the BSMP is Applied – Before/During/After the Burn Evaluate Smoke Dispersion Conditions Minimize smoke impacts Before, During, After
Monitor Effects on Air Quality Be aware of where the smoke is going and degree it impacts air quality Before, During, After

Record-Keeping/Maintain a Burn/Smoke Journal Retain information about the weather, burn and smoke. If air quality problems occur, documentation helps analyze and address air regulatory issues Before, During, After

Communication – Public Notification Notify neighbors and those potentially impacted by smoke, especially sensitive receptors Before, During

Consider Emission Reduction Techniques Reducing emissions through mechanisms such as reducing fuel loading can reduce downwind impacts Before, During, After

Share the Airshed – Coordination of Area Burning Coordinate multiple burns in the area to manage exposure of the public to smoke Before, During, After*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 125 of 218 a The EPA believes that elements of these BSMP c ould also be practical and beneficial to apply to wildfires for areas likely to experience recurring wildfires. Table 4. Elements that May Be Included in Burn Plans and Post-Burn Reports for Prescribed Fires Submitted as Exceptional Events. Element Burn Plan Post-Burn Report Fire Name a X X Permit number (if appropriate) X X Latitude/longitude and physical description X X Date of burn, ignition time and completion time (duration of burn) X X AQI status on burn day, if available (both in the vicinity of the fire and in the affected upwind area) Predicted Actual Acres burned Planned Actual (blackened) Description of fuel loading Estimated Actual (tons consumed) Meteorological data (weather conditions, wind speed and direction, dispersion) Predicted conditions (including predicted dispersion) Actual conditions (including actual dispersion)

Smoke Impacts Anticipated smoke impacts Observed or reported smoke impacts (include nature, duration, spatial extent and copies of received complaints) BSMP actions to reduce impacts Expected BSMP actions Actual BSMP actions Recommendations for future burns in similar areas X Analytics (modeled/actual fire spread, satellite imagery and analysis, webcam/video, PM/ozone concentrations over the course of the fire) X

a The “Fire Name” should be unique and referen ced, to the greatest extent possible, in all exceptional events-related documentation, includi ng the event name in AQS. The fire name could simply consist of the county and state in which the burn occurred ( e.g. , County X, State Y Prescribed Burn on Date Z) if no other name has been assigned. States with certified SMPs typically have robust comm unications between officials concerned with air quality impacts and officials and members of the public who use prescribed*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 126 of 218 fire. These groups communicate during the developm ent of the SMP, during the day-to-day burn authorization process and in the periodic review and pot ential revision of the SMP. States that instead rely on fire managers employing BSMP on a more individual basis may not have such regularly occurring communications pr ocesses, particularly in stat es in which state legislation gives the leadership of fire management to a forest ry or public safety agency rather than to an air agency. We encourage all agencies and managers/owners involved in land, air qua lity and fire management to develop good communications about both fire use practices in general and plans for specific prescribed fires with use of BSMP. This will, among other benefits, allow them to better coordinate on public air qua lity notice efforts and, if nece ssary, public health advisories should smoke enter an inhabited area. Additiona lly, the EPA encourages the development of “prescribed fire councils,” comprised of federal, state, tribal, private a nd other stakeholders to coordinate activities involving fi re planning issues and, thus, mi nimize or prevent smoke impacts while using prescribed fire to a ccomplish land management objectives. 95 However, we are not proposing that notifications between prescribed fire users and specific types of state agencies be a condition for approval of a prescrib ed fire as an exceptional event. As previously stated, to date we have cons idered the existence and implementation of a SMP or the use of BSMP to be a necessary part of the supporting evidence needed to satisfy the not reasonably controllab le or preventable criterion, but we have not clearly addressed what conditions are minimally sufficient to satisfy the criterion. The remainder of this section focuses on that issue.

95 See additional information on prescribed fire co uncils on the Coalition of Prescribed Fire Councils, Inc. website at http://www.prescribedfire.net/membership/state-councils

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Page 127 of 218 Because prescribed fires are intentionally in itiated, clarifying the minimal conditions for the not reasonably preventable pr ong is particularly relevant. The detailed USFS/NRCS guidance on the fifth listed BSMP, Consider Emission Re duction Techniques, includ es the potential to reduce the fuel loading. It does not s uggest that it may be reasonable to not ignite a particular prescribed fire ( i.e ., that the fire be prevented), because this guidance is aimed at those fires that are already planned to happen. Similarly, SMPs address coordination of previously planned prescribed fires and typically do not ask SMP pa rticipants to consider whether particular prescribed fires are reasonably preventable. Theref ore, we do not believe that the existence of an SMP or the use of BSMP is a sufficient basis for concluding that a pr escribed fire is not reasonably preventable. A prescrib ed fire should be concluded to be not reasonably preventable on the basis of the benefits that would be fore gone if it were not conducted, as described below. For federal agencies, the planning of prescrib ed fire programs typi cally happens through the development of multi-year plans that fo cus on specific land or resource management objectives. This planning process, and the resu lting multi-year plan, typically considers the importance of a prescribed fire program to ach ieving land management goals, which may include an objective to establish, restore and/or maintain a sustainable and resi lient wildland ecosystem, in light of the availability, cost and effectiveness of other appr oaches to fuel management. The final multi-year plans thus generally identify the le vel of prescribed fire use necessary to achieve those goals. As noted previously, some tribes, private landowners (and federal, state and local agencies working with private landowners) and state agencies that manage state-owned lands ( e.g ., state parks) also prepare multi-year manage ment plans. While plans developed by public agencies ( i.e. , state and federal agencies) often un dergo public comment prior to being*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 128 of 218 finalized, 96 the plans developed by tribes and pr ivate landowners may not follow a public comment process. However, public agencies ofte n work with tribes a nd private owners to develop these plans, which are based on conserva tion practices and standards that have often undergone public comment as part of the state or federal agency process. Not conducting the prescribed fire programs described in such plans could mean forgoing important ecosystem services and other benefits. Accordingly, the EPA is proposing in rule text form to consider a prescribed fire on wildland conducted in accordance with a multi-year fire management plan that has an objective to establish, restore and/or ma intain a sustainable and resilient wildland ecosystem to be not reasonably preventable, pr ovided there is no compelling evidence to the contrary in the record when the EPA approves the associated exceptional events demonstration. 97 We also propose in rule text that compliance with either a state-certified SMP or BSMP is sufficient to establish that a prescribed fire was not reasonably controllable, provided there is no compelling evidence to the contrary in the reco rd when the EPA concurs with the associated exceptional events demonstration. This is an a ppropriate approach to implementing CAA section 319(b), because SMPs and BSMP aim to reasonably control the air quality impacts of prescribed fires. 98

96 Many multi-year plans developed by state and federal agencies are available electronically online or can be requested directly from the prep aring agency. Interested parties can also request electronic versions of proj ect level plans, if they are not available online. 97 On a case-by-case basis, in the absence of a multi-year plan, the EPA would also consider a prescribed fire on wildland conducte d on a fire return interval esta blished according to scientific literature to satisfy the not reasonably cont rollable or preventable criterion provided the prescribed fire was also conducted with the obj ective to establish, rest ore and/or maintain a sustainable and resilient wildland ecosystem a nd conducted in compliance with either a statecertified SMP or BSMP. This case-by-case approach is similar to the approach currently used under the 2007 Exceptional Events Rule. 98 With respect only to the not r easonably contro llable prong, we also be lieve that the SMP and BSMP approach each is sufficient for pr escribed fires that are not on wildland.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 129 of 218 This two-part categorical approach would reduce the le ngth of exceptional events demonstrations for prescribed fires on wildla nd and make the demonstration preparation and review process more resource efficient. In summar y, to satisfy the not reasonably controllable or preventable criterion for a pres cribed fire on wildland, a demons tration would need to identify that the prescribed burn was conducted in accordan ce with a multi-year plan that has an objective of the establishment, restoration and/or main tenance of a sustainable and resilient wildland ecosystem and was conducted in compliance with either a state-cer tified SMP or BSMP. Finally, we are proposing to remove the phr ase “and must include consideration of development of a SMP” from the sentence of th e existing text of 40 CFR 50.14(b)(3) that reads, “If an exceptional event occurs using the basic smoke management practic es approach, the State must undertake a review of its approach to ensu re public health is being protected and must include consideration of devel opment of a SMP.” While the EPA supports states considering the development of a SMP in the situation described in this sentence, we believe states have had ample opportunity to develop such a program si nce 2007. This rule language effectively requires an ongoing consideration to develop an SMP every time a prescribed fire causes a NAAQS exceedance or violation that merits exclusion as an exceptional event. We do not believe Congress intended this ongoing consideration to be a requirement flowing from CAA section 319(b). In addition, we believe that an SMP is most appropriate when multiple parties wish to employ prescribed fire at about the same time in the same airshed, which is a more narrow situation than specified in this sentence. We also do not want our rules to be open to an inference that development of a SMP should only be considered following a NAAQS exceedance or violation, because the impacts from fires may affect public health in areas without NAAQScompliance air monitoring stations. Also, we be lieve that when air agencies observe NAAQS*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 130 of 218 exceedances or violations attributed to a prescrib ed fire, air agencies should consider a wide range of alternatives including, but not limited to, the development of a SMP. For example, agencies might also consider the more frequent or intensive use of BSMP to limit the fuel available to burn in each fire. The EPA solicits comment on all aspects of the identified fire-related approaches. 3. Stratospheric Ozone Intrusions a. Current Situation Stratospheric ozone intrusions are natural events that occur when a parcel of air originating in the strato sphere is re-entrained into the troposphere, and in some cases mixes directly to the surface of the ea rth. These relatively rare events can create elevated ozone concentrations that affect areas ranging from a single monitoring site to a wider area as the air mass with a high ozone concentra tion moves across the landscape. Normally, the tropopause, the temperature i nversion layer of air that separates the troposphere from the stratosphere, limits the transport of stratos pheric air into the troposphere, the lowest layer of the Earth’s atmosphere. 99 In some cases, however, parcels or ribbons of ozone-rich air from the stratosphere can be tran sported rapidly to the surface during deep mixing events, such as thunderstorms or strong frontal passages, by a process known as tropopause folding. Although this “folding” process can occur th roughout the year, it is typically associated

99 The height of the tropopause varies with latitude and season but the average height at midlatitudes is about 11 kilometers (km) (7 miles or 36,000 feet). Th e stratosphere, the second layer of the Earth’s atmosphere, is located above the tropopause at 13 to 50 km (8-31 miles or 43,000 to 160,000 feet) above the Earth’s surface.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 131 of 218 with frontal passages and upper level low pressure systems during the spring season. 100,101 The ozone transported through thes e “folds,” or through other less significant mechanisms, may disperse within and be destroyed in the upper troposphere or it may mix down to the surface. 102 The “intrusion” of stratospheric oz one is identified most frequently at high elevation sites where upper tropospheric air is more likely to reach th e surface than at lowe r elevation sites where more downward movement would be needed for a monitoring site to be affected. At these high elevation sites in particular, st ratospheric ozone intrus ion has been estimated to contribute about 20 to 25 percent of the total tropospheric ozone budget and can cause relatively short-term ( i.e ., ranging from several hours to 2-3 days in dura tion) increases of surface ozone of 10 to 50 ppb above normal background levels. 103 Stratospheric intrusions wi th short-lived surface ozone concentrations of several hundred ppb have al so been observed, although these events are extremely rare. Because stratospheric intrusion events are relatively infrequent and because identifying and monitoring these events are challenging, there have been few direct measurements showing that a given parcel of surface air contains stra tospheric ozone (versus ozone generated by local natural or anthropogenic sources). Interpreting these direct meas urements is also challenging.

100 Pan, L. L., et al. (2014), “Thunderstorms enhance tropospheric ozone by wrapping and shedding stratospheric air.” Geophys. Res. Lett., 41, 7785–7790, doi:10.1002/2014GL061921. 101 A. O. Langford, K. C. Aikin, C. S. Eubank a nd E. J. Williams. Stratospheric Contribution to High Surface Ozone in Colorado During Springtime, Geophysical Research Letters, Vol. 36, Issue 12, June 2009. 102 Other mechanisms by which stratospheric ozone is transported into the troposphere include cutoff cyclones, streamers (long filamentary structur es that often roll into vortices), and clear air turbulence ( see http://www.atmos.umd.edu/~dkuhl/ documents/Kuhl_Tropopause_Folding.ppt)

. 103 Integrated Science Assessment of Ozone and Re lated Photochemical Oxidants (Final Report). U.S. EPA.Washington, D.C. EPA/ 600/R-10/076F. Available at: http://www3.epa.gov/ttn/naaqs/s tandards/ozone/s_o3_2008_isa.html

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Page 132 of 218 One approach to confirm the presence of strato spheric ozone in surface ai r is through the use of the beryllium tracers, beryllium isotopes Be-7 a nd Be-10, which are produced primarily in the stratosphere by cosmic ray collis ions with atmospheric gas atoms. 104 Beryllium isotope measurements are, however, rare and expensive, and, consequently not normally available. More common approaches to identify stra tospheric ozone in surface air can include evaluating measurements at the potentially infl uenced ozone monitoring site for very low concentrations of CO and/or re lative humidity. Both can be str ong indicators of st ratospheric air because, relative to tropospheric air, stratosphe ric air has very low relative humidity and very low concentrations of other ai r pollutants such as CO, NOx and PM. The concurrent impacts on CO and relative humidity can be subtle, howev er, when stratospheri c air has mixed with tropospheric air as the mixing process dilutes the ozone enhancement and increases CO and water vapor concentrations relative to stratospheric conditio ns. Typical CO monitors used for ambient air monitoring have ope rational ranges of 500 to 50,000 ppb (0.5 to 50 ppm) and are not sufficiently sensitive to reliably measure the very low CO levels found in stratospheric air (50 to 150 ppb). Additionally, few rural high altitude monitoring sites have both ozone and CO monitors. 105 The EPA urges air agencies to provide conc urrent readings of ozone and CO and/or relative humidity in their exceptional events dem onstrations if they have these data. The EPA will evaluate these data as a part of a weight of evidence showing alongside other qualitative evidence in a clear causa l relationship showing.

104 Cristofanelli, P. A 6-year analysis of stratos pheric intrusions and their influence on ozone at Mt. Cimone (2165 m above sea level). Jour nal of Geophysical Research, Vol. 111, D03306, doi:10.1029/2005JD006553, 2006. 105 A recent review of AQS data revealed 216 site s in the United States with collocated ozone and carbon monoxide monitors in op eration after January 1, 2014. Most of these sites are located in either urban or suburban locations. In thes e settings, local emissions would likely hide the stratospheric CO suppression.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 133 of 218 A third measurement-based approach to id entifying stratospheric ozone could include measurements of ozone above ground level ( i.e ., measurements in th e troposphere). This approach is also uncommon. Currently, five s ites in the U.S. conduct ozone sonde (balloon) launches two or more times per week and an additional few research locations operate ozone lidars to vertically measure ozone profiles. 106,107
In the absence of direct measurements of stratospheric tra cers at ground level, meteorological models can indicate conditions un der which stratospheric air parcels may reach the surface. Meteorological models such as the National Oceanic and Atmospheric Administration (NOAA)/National Weather Service (NWS) North American Mesoscale Forecast System (NAM) or the NOAA Rapid Update Cy cle (RUC) models simulate parameters characteristic of stratospheric air such as isentropic potential vorticity (IPV) and potential temperature (PT) that can be us ed to identify tropopause foldi ng. Visualization tools using the model output can show spatially wh ere stratospheric air is located in proximity to or in contact with the surface. Similarly, atmospheric chemistr y models, such as the National Aeronautics and Space Administration (NASA)/NOAA Real-tim e Air Quality Modeling System (RAQMS) 108 can provide both real time intrusion forecasting and retrospective anal ysis of ozone from intrusions.

106 Lidar, which stands for Light Detection and Ranging, is a remote sensing method that uses light in the form of a pulsed laser to measure ra nges (variable distances) to the Earth. These light pulses, combined with other data recorded by the airborne system, generate precise, threedimensional information about the shape of the Earth and its surface characteristics. See , NOAA definition at http://oceanservice .noaa.gov/facts/lidar.html

. 107 See NOAA data available at ftp://aftp.cmdl.noaa.gov/data/ozwv/Ozonesonde/ . On April 30, 2015, NOAA’s site identified the fo llowing five sites in the U.S. that conduct bi-weekly ozone sonde launchings: Hilo, HI; Huntsv ille, AL; Narragansett, RI; Trinidad Head, CA; and Boulder, CO. Additional launchings occur in Pago Pago, American Samoa, and outside of the U.S. in Greenland, Antarctica and Fiji. 108 See http://raqms-ops .ssec.wisc.edu/

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Page 134 of 218 Finally, satellite observation of atmospheric ozon e and CO can be used to validate predictions based on atmospheric modeling. Although as of the date of this propos al the EPA has concurred with only one stratospheric ozone intrusion exceptional events demonstration prepared under the provisions of the 2007 Exceptional Events Rule (and disapproved none), 109 the EPA has been communicating that we consider it appropriate to use the prev iously mentioned stratospheric ozone tools with other event/pollutant exceptional events analyses ( e.g ., seasonal analysis of ozone data, comparison of event days with non-event days, trajectory analysis, ozone measurement time series and spatial distribution anal ysis, meteorological an alysis to show the presence of weather systems associated with typi cal intrusions and balloon sound ings of the NWS Upper Air Observation Program to detect parcels of dry air aloft) to successfully demonstrate stratospheric ozone exceptional events. b. Proposed Changes As is true for all exceptional events a nd pollutant combinations, when submitting a demonstration for stratospheric ozone intrusion events, air agencies must address all of the Exceptional Events Rule criteria. As noted in this action, the EPA proposes to return to the core statutory elements and implicit concepts of CA A section 319(b): that the event affected air quality in such a way that there exists a clear causal relationship between the specific event and the monitored exceedance or violation, the event was not reasonably controllable or preventable and the event was a human activity that is unlikel y to recur at a partic ular location or was a

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

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Page 135 of 218 natural event. The EPA suggests th e following approach when addres sing these technical criteria for an ozone exceedance or violation caused by a stratospheric intrusion. An air agency should begin by showing the ge ographic extent of el evated or exceedancelevel ozone concentrations associated with the intrusion event in conjunc tion with an evaluation of the historical measured surface ozone levels for the same season ( see section V.E.3 of this proposal for example analyses of how to presen t the comparison to historical concentrations within the clear causal relationshi p criterion). If the intrusion ha ppened at a time of year when local or transported photochemical ozone is gene rally low, evidence that the intrusion affected ground level air quality may be rela tively brief and still be suffici ent, compared to an intrusion occurring at the height of the historical ozone season. If intrusion claims coincide with historica lly high photochemistry seasons, then the air agency may need additional ev idence to support the clear cau sal relationshi p criterion by showing the relative contributi on estimates to the exceedance from local and transported anthropogenic pollutants compared to the intrus ion contribution. An air agency can provide additional analyses supporting the clear causal relationship by showi ng that an intrusion occurred at or near the location of an identified monitor by using atmo spheric models such at RAQMS, NAM or RUC, with additional data from satellite observations of total column ozone and CO. The EPA intends to accept a short statement in a demonstration that because stratospheric ozone intrusions are purely natural events and are large in scale, they are not reasonably controllable or preventable. 4. High Wind Dust Events a. Current Situation*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 136 of 218 The 2007 Exceptional Events Rule preamble noted that “[t]he EPA’s final rule concerning high wind events states that ambient particulate matter concentrations due to dust being raised by unusually high winds will be trea ted as due to uncontrollable natural events where (1) the dust originated fr om nonanthropogenic sources, or (2) the dust or iginated from anthropogenic sources within the State, that are determined to have been reasonably wellcontrolled at the time that the event occurred, or from anthropoge nic sources outside the State.” As noted in section IV.B of this document, although this language still reflects the EPA’s interpretation of what might be appropriate unde r the Exceptional Events Rule, the D.C. Circuit determined the language to be a legal nullity because the EPA did not specifically address high winds or ambient particulate matte r concentrations in the promul gated regulatory language in 40
CFR 50.14. The preamble to the 2007 Exceptional Events Rule also noted that because “...the conditions that cause or contri bute to high wind events vary fro m area to area with soil type, precipitation, and the speed of wind gusts, [air agencies] should provide appropriate documentation which indicates what types of circ umstances contributed to the exceedances or violation at the monitoring site in question.” The EPA declined to identify a specific high wind threshold to qualify as being an exceptional event and instead re lied on air agencies to submit appropriate documentation supporting their position. Because of the uncertainty associated with these high wind statements and stakeholder feedback asking the EPA to in terpret this language and provi de examples of applying the provisions in the 2007 Exceptional Events Rule to high wind dust events, the EPA clarified many concepts related to high wind dust events in its May 2013 Interim Exceptional Events*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 137 of 218 Implementation Guidance, specifically th e Interim High Winds Guidance document. 110 In this guidance, the EPA defined a high wind dust event as including the high wind and the dust that the wind entrains and transports to a monitori ng site, clarified our e xpectations regarding “reasonable controls” for high wind events with contribution from both natural and anthropogenic sources and introduced the con cept of establishing a value for a high wind threshold, up to which reasonable windblown dust c ontrols are expected to be effective in the absence of site specific data or analyses. As identified in the Interim High Winds Guidance document, dust phenomena are experienced primarily in the western U.S. wher e rainfall is seasonal, creating dry and dusty landscapes. 111 In high wind dust events, the meteorological phenomenon ( i.e ., wind) is purely natural, but the pollution from the event may be a mixture of natural sources ( e.g ., undisturbed soil) and anthropogenic sources ( e.g ., soil disturbed by human activity, emissions from sand and gravel facilities, etc.). The EPA generally classi fies high wind dust events as “natural events” in cases where windblown dust is entirely from natural sources or where all significant

110 Interim Guidance on the Preparation of Demons trations in Support of Requests to Exclude Ambient Air Quality Data Affected by Hi gh Winds Under the Exceptional Events Rule. U.S. EPA. May 2013. Available at http://www2.epa.gov/sit es/production/files/2015- 05/documents/exceptevents_highwinds_guide_130510.pdf. 111 We use “Western U.S.” to refe r to states in the Great Plains (North Dakota, South Dakota, Nebraska, Kansas, Oklahoma and Texas) and thos e farther west including Arizona, California, Colorado, Nevada, New Mexi co, Utah, and Wyoming.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 138 of 218 anthropogenic sources of windblown dust have been reasonably controlled. 112 This long-standing policy was first established in the PM 10 Natural Events Policy, which provided that: Ambient PM-10 concentrations due to dust ra ised by unusually high winds will be treated as due to uncontrollable natural events under the following conditions: (1) the dust originated from nonanthropogenic sources, or (2) the dust orig inated from anthropogenic sources controlled with best av ailable control measures (BACM). 113 Also integral to definition of a high wind dust event is that the wind speed be “high,” or, as indicated in the PM 10 Natural Events Policy, “unusually high.” Only “high wind” dust events are exceptional events and “high” is area-specific. Typically, undisturbed desert landscapes in the western U.S. have a natural crust that protects the surface and tends to limit emissions of windblown dust. The wind speed capable of causing emissions from these natural undistur bed areas varies by location, depending on characteristics of the local landscape ( e.g ., soil type and characteristics, vegetation). Numerous studies have been conducted to determine the mi nimum wind speed capable of causing emissions from natural undisturbed areas and/or overwhelming reasonable controls on anthropogenic

112 As identified in section V.D of this proposal , the EPA will generally consider human activity to have played little or no direct role in causing emissions of the dust generated by high wind for purposes of the regulatory defin ition of “natural event” if cont ributing anthropogenic sources of the dust are reasonably controll ed, regardless of the amount of dust coming from these reasonably controlled anthropogeni c sources, and thus the event c ould be considered a natural event. In such cases, the EPA believes that it wo uld generally be a reas onable interpretation to find that the anthropogenic source had “little” direct causal role. If anth ropogenic sources of windblown dust that are reasonably controllable but that did not ha ve those reasonable controls applied at the time of the high wind event have contributed significantly to a measured concentration, the even t would not be considered a natural event. 113 Areas Affected by PM-10 Natural Events (the PM 10 Natural Events Policy), memorandum from Mary D. Nichols, Assistant Administrator for Air and Radiation, to EPA Regional Offices, May 30, 1996.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 139 of 218 sources. 114 In the Interim High Winds Guidance, the EPA called the minimum threshold wind speed capable of causing emissions from natura l undisturbed areas or overwhelming reasonable controls on anthropogenic sources the “high wind threshold.” In the Interim High Winds Guidance, the EPA articulated its expectations regarding the development and application of high wind thresholds. In this gui dance, the EPA encouraged air agencies to identify an appropriate high wind threshold for each area experiencing high wind dust events within their exceptional even ts submissions for high wind dust events. 115 The guidance recommended that these thresholds sh ould consider local conditions and specify a minimum wind speed capable of causing emission s from those natural undisturbed areas or overwhelming reasonable controls on contributing anthropogenic sources ( see section V.E.2 for additional discussion regarding reas onable controls). This approach was consistent with the PM 10 Natural Events Policy in which the EPA recommended that air agencies define the conditions in which BACM level controls were overwhelmed. Th e area-specific high wind threshold should be

114 See Appendix A1 of the Interim Guidance on the Preparation of Demonstrations in Support of Requests to Exclude Ambient Air Quality Data Affected by High Winds Under the Exceptional Events Rule. U.S. EPA. May 2013. Available at http://www2.epa.gov/site s/production/files/2015- 05/documents/exceptevents_highwinds_guide_130510.pdf. 115 See Appendices A2 and A3 in the Interim Guidance on the Preparation of Demonstrations in Support of Requests to Exclude Ambient Air Quality Data Affected by High Winds Under the Exceptional Events Rule. U.S. EPA. May 2013. Available at http://www2.epa.gov/site s/production/files/2015- 05/documents/exceptevents_highwinds_guide_130510.pdf for additional information on the development of a high wind threshold

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Page 140 of 218 representative of conditions ( i.e ., sustained wind speeds 116 ) that are capable of overwhelming reasonable controls (whether RACM, BACM or other) on anthropogenic sources and/or causing emissions from natural undisturbed areas. The threshold was not intended to represent the minimum wind speed at which any level of emissions could occur ( e.g ., aerodynamic entrainment), but rather when significant emission s begin due to reasonable controls or natural undisturbed areas becoming overwhelme d. We have stated that if an agency is unable to develop an area-specific high wind threshold, we generally will accept a threshold of a sustained wind of 25 mph for areas in the western U. S. provided the agencies support th is as the level at which they expect stable surfaces ( i.e ., controlled anthropogenic and undisturbed natural surfaces) to be overwhelmed. 117 We did not indicate what form such support could take. We also have said that if we receive specific information based on rele vant studies to choose an alternative high wind threshold for an identified area, we will notify the affected air agency. Also as noted in the Interim High Winds Guidance document, the EPA has expected air agencies to provide relevant wind data ( e.g ., wind speed and direction) as part of an exceptional events submission for high wind dust events. Wind sp eed data consist of analyses and statistics showing how the observed high wind dust event wind speed compares to the distribution of

116 Section 6.3.2.2 in the Interim Guidance on the Preparation of Demonstrations in Support of Requests to Exclude Ambient Air Quality Data Affected by High Winds Under the Exceptional Events Rule. U.S. EPA. May 2013. Available at http://www2.epa.gov/site s/production/files/2015- 05/documents/exceptevents_highwinds_guide_130510.pdf for details on the calculation of sustained wind speed. Generally, the EPA will accept that high winds could be the cause of a high 24-hour average PM 10 or PM 2.5 concentration if there was at least one full hour in which the hourly average wind speed was above the area-specific high wind threshold. 117 The 25 mph threshold is based on studies conducted on natural surfaces. See additional information relevant to establishing th is threshold in Appendix A1 in the Interim Guidance on the Preparation of Demonstrations in Support of Requests to Exclude Ambi ent Air Quality Data Affected by High Winds Under the Exceptional Events Rule. U.S. EPA. May 2013. Available at http://www2.epa.gov/site s/production/files/2015- 05/documents/exceptevents_highwinds_guide_130510.pdf.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 141 of 218 historical wind speeds and the established high wind threshold. The EPA has recommended that air agencies show these historic al comparisons on an annual and/ or seasonal basis, depending on which is more appropriate, using a format sim ilar to the recommended format of the comparison to historical concentrations show ing as part of the clear causal re lationship criterion discussed in section V.E.3 of this proposal. The EPA has encour aged air agencies to discuss wind direction in the narrative and to present wind direction inform ation graphically in maps/plots in the clear causal relationship section of the high wi nd dust exceptional events demonstration. In considering past high wind dust event dem onstrations, the EPA has found that the “not reasonably controllable or preventable” and th e “clear causal relationship” (to include the comparison to historical concentrations showing) criteria play significan t roles in the supporting exceptional events documentation. The EPA has ge nerally found that for high wind dust events, air agencies can meet the “human activity or natural event” criterion by satisfying the requirements for not reasonably controllable or pr eventable and clear causa l relationship as well as addressing the additional components of ex ceptional events demons tration packages as discussed in section V.G. As is the case with all demons tration packages, air agencies with agricultural sources that potentially contribute to high wind event-related emissions shoul d address the question of source contribution and associated reasonable controls on these sources within the not reasonably controllable or preventable por tion of the demonstration. The EPA has noted in previous guidance that when considering the anthropogeni c sources that contribu te to event-related emissions and the appropriate “reasonable contro ls” on these sources, air agencies should be aware of USDA/NRCS-approved Best Management Practices (BMPs) (also referred to as conservation management practices) that are de signed to effectively reduce fugitive dust air*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 142 of 218 emissions and prevent soil loss in agricultural applications. 118 We have stated that these BMPs could be included in the collection of controls determined to constitute reasonable controls for wind-blown dust events in areas in which they have been implemented. b. Proposed Changes The EPA proposes to include in the preamble to the final rule for this action a modified version of some of the language that first appeared in the Interim High Winds Guidance document and to incorporate into the rule text the revisions propos ed in this section. We also intend to revise the Interim High Winds Guidance to be consistent following promulgation of final Exceptional Events Rule revisions. Definition of an Event. Consistent with the EPA’s propos al to revise the regulatory definition of an exceptional event to include both the event and its associated resulting emissions, the EPA proposes to define a high wind dust event as an event that includes the highspeed wind and the dust that the wi nd entrains and transports to a monitoring site. Consistent with the nullified language in the 2007 Exceptional Events Rule preamble, the PM 10 Natural Events Policy and the Interim High Winds Guidan ce, the EPA proposes to define high wind dust events in the rule text as “nat ural events” in cases where windblow n dust is entirely from natural sources or where all significan t anthropogenic sources of windblown dust have been reasonably controlled. High Wind Threshold . To facilitate clearer expectations regarding the evidence needed to demonstrate which controls constitute “reasonable controls,” the EPA proposes to codify in rule language the definition of “high wind threshold” as the minimum threshold wind speed capable

118 Reference Guide for Cropping Syst ems and General Land Management. USDA, NRCS and U.S. EPA. October 2012. Available at http://www.nrcs.usda.gov/Interne t/FSE_DOCUMENTS/stelprdb1049502.pdf.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 143 of 218 of causing particulate matter emissions from natura l undisturbed lands in the area affected by a high wind dust event. The EPA proposes to accept a threshold of a sustained wind of 25 mph for areas in the western U.S. provide d this value is not c ontradicted by evidence in the record when we review a demonstration. If the EPA receives specific information based on relevant studies that suggest a different high wind threshold fo r an identified area, the EPA will notify the affected air agency so that the agency may c onsider basing its demonstration on that threshold value. The EPA would consider such information as part of the weight of evidence analysis for a submitted demonstration. In lieu of using the default 25 mph high wind threshold, air agencies would have the option to identify an area-specifi c high wind threshold that is more representative of local/regional conditions. The high wind threshold concept will continue to apply to the review of demonstrations for events in a nonattainment or maintenance ar ea for which the dust controls in a recently approved SIP are generally accepte d as sufficient to satisfy the not reasonably controllable criterion. For such a demonstration, the controls specified in the SIP should be considered reasonable, while acknowledging th e possibility that the controls are not being complied with and that uncontrolled anthropogeni c sources of PM could be the contributing to the exceedance. For events with sustained wind speeds above the high wind threshold, it is very plausible that SIP controls were being implemented and the high PM concentrations are due to emissions generated from sources in the area despite implem entation of the SIP measures. Conversely, for events with sustained wind speeds below the high wind threshold, it become s more plausible that there may be noncompliance with control measur es or that uncontrolled anthropogenic sources are contributing to the exceedance. Therefore, the comparison of sustained wind speeds during an event to the high wind threshold will help th e EPA regional offices determine what evidence*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 144 of 218 is required to be included in a demonstration regarding reasonable cont rols, the possibility of non-compliance, or non-event sources. Large-Scale or High-Energy High Wind Dust Events . The EPA proposes to codify in rule language to apply a case-specifi c approach when considering reasonableness of controls for remote, large-scale, high-energy and/or sudden high wind dust events, such as “haboobs” in the southwest where sustained wind speeds can excee d 40 mph and generate walls of dust several miles wide and more than a mile high. The proposed rule text provides that in these situations, the event will be considered not reasonably preventable or controllable. Therefore, a demonstration limited to such event(s) will not need to substantively address this criteria. The EPA solicits comment on this proposed, case-specifi c approach when considering reasonableness of controls for remote, large-scale, high- energy and/or sudden hi gh wind dust events. Other Types of High Wind Dust Events . Any demonstration for a non-high-energy event would be evaluated on a case-by-case basis. In do ing so, the EPA would consider what controls are reasonable in light of an area’s attainment status and associated CAA control requirements, the frequency, and range of non-high energy wind ev ents known (at the time of the particular event that is the subject of the demo nstration) to occur in the area. The Role of the EPA-approved SIP in Nonattainment and Maintenance Areas

. As stated in section V.E.2, the EPA proposes to establish by rule a non-rebuttable presumption that, during a 5-year window (or, alternat ively another appropriate timefr ame) following approval of an attainment plan or maintenance plan SIP duri ng which no subsequent new obligation for the air agency to revise the SIP has arisen, the control measures included in the SIP that are specific to the relevant pollutant, sources and event type satisfy the not reasonably controllable or*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 145 of 218 preventable criterion. 119 Otherwise, the air agency and the EPA would evaluate the not reasonably controllable or preventabl e criterion on a case-by-case basis. We describe below one potential scenario in which deferenc e to the SIP for purposes of “reasonable controls” (versus a case-by-case analys is) satisfies the not reasonably controllable or preventable criterion. We also pr ovide two other scenarios needi ng a case-by-case analysis for purposes of satisfying the not re asonably controllable or preven table criterion. We identify these scenarios below and then discuss them in more detail in sequence.

 Nonattainment Area Scenario 1 – The EPA approved the SIP with the enforceable control measures as meeting attainment or maintenance planning requirements within 5 years of the date of submittal of the event AND the air agency is not under an obligation to revise the SIP for the reason listed in Scenario 2 or any other reason. Additionally, the sustained winds during the event are above the high wind threshold. The SIP includes enfor ceable control measures that address the event-related pollutant a nd all sources necessary to fulfill the requirements of the CAA for the SIP that have or may have contributed to event-related emissions. This indicates that in the development a nd approval of the SIP, both the EPA and the state considered what event-related controls were sufficient to meet the attainment or maintenance plan requirements of the CAA.

119 A request for data exclusion must also show that the event was not a result of noncompliance with any existing state or local laws or rules th at have not been incorporated into the SIP.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 146 of 218  Nonattainment Area Scenario 2 – The air ag ency is under an obligation to revise the SIP as a result of a SIP call based on failing to provide for attainment and maintenance of the relevant NAAQS as evidenced by current violations. 120

 Maintenance Area Scenario 3 – The EP A approved the SIP more than 5 years prior to the date of submittal of a demonstration. Details for Nonattainment Area Scenario 1 In this scenario, where the sustained wi nds during the event are above the high wind threshold, the EPA would apply a non-rebuttable presumption that the controls in the existing SIP represent reasonable measures to prevent or control any event of the given type that occurs in the 5-year window. To satisfy the not reason ably controllable or pr eventable criterion, the EPA would expect the submitting air agency to id entify the emission sources that contribute to the event emissions and exceedance and identify the associated SIP controls plus any other enforceable control measures required by state laws or rules. The air agency would also identify the implementation status of these controls and provide evidence of effective implementation and enforcement. Example: An air agency submits a demons tration for a high wind dust event in a PM 10 nonattainment area that occurred in Octobe r 2015. The air agency has an EPA-approved attainment plan SIP for the affected area th at was approved in October 2010 and that SIP includes enforceable controls im plemented in accordance with th e SIP that address the eventrelated pollutant ( i.e. , PM) and all sources necessary to fulf ill the requirements of the CAA. The

120 Other possible reasons for an area to be in a Scenario 2 situation would be if it has been designated nonattainment for a revi sed NAAQS for the relevant pollutant or is subject to a SIP call for the relevant pollutant following the EPA’s determination that the SIP is inadequate for some other reason.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 147 of 218 sustained winds during the event were above th e high wind threshold. In the not reasonably controllable or preventable porti on of its high wind dust demons tration, the air agency would describe the event-related wind characteristics and identify the natural and anthropogenic emission sources that contributed to the event em issions and the associated SIP and other control measures. The air agency would then describe th e implementation status of these controls and provide evidence of effective implementation and enforcement. The air agency would conclude the “not reasonable controllable or preventable” portion of the demonstration by affirmatively stating that because the EPA had approved the SI P within 5 years of th e event and because the SIP measures and other measures specific to the pollutant and at le ast some anthropogenic emission sources that contributed to the even t emissions were implemented, the agency has satisfied the not reason ably controllable or preventable criterion. In reviewing the demonstration in this scenar io, the EPA would genera lly concur that the air agency met the not reasonably controllable or preventable criterion during the 5-year period provided the SIP was implemented and the event wa s not attributable to noncompliance. Thus, assuming the demonstration also satisfied the rema ining technical and procedural elements in the Exceptional Events Rule, the EPA wo uld concur with the air agency’s request to exclude data for purposes of regulatory actions with in the scope of the final revise d Exceptional Events Rule. If, however, the air agency experi enced an exceedance or violation during the 5-year period for reasons other than those attri butable to the successful excep tional events demonstration ( e.g. , industrial source noncompliance or another type of event), th e EPA may take one of these actions. In addition, the EPA may is sue a SIP call because the SIP is inadequate with regard to a requirement of the CAA that is not tied to the occurrence of NAAQS violations related to*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 148 of 218 exceptional events. If the EPA issues a SIP call during the 5-year window, the situation would switch to Scenario 2. Details for Nonattainment Area Scenario 2 In this scenario (where the SIP is bei ng revised to respond to a SIP call involving the
PM 10 or PM 2.5 NAAQS), the existing SIP controls should not be presumed to satisfy the not reasonably controllable or preventable criteri on regardless of whethe r the event-related wind speeds are above or below the high wind threshold. The EPA recommends that as the first step in preparing an exceptional events demonstration, the air agency should a ssess the case-specific effectiveness of the controls that were in place at the time of the event and consider potential controls that are more comprehensive and effectiv e than those in the SIP that the agency could have implemented before or during the event. This case-specific assessment should apply the concept that if a set of control measures should reasonably have been in place for emission sources that contribute to the even t emissions in light of the information in the record of the EPA action that has created the obligation to revise the SIP, then those controls must have been in place for the event to satisfy the not reasonabl y controllable or preventable criterion. The submitting air agency preparing a case-sp ecific assessment should first identify the natural and anthropogenic emission sources that significantly contribute to the event emissions and exceedance. The air agency should categoriz e sources as those that are addressed through SIP or other state or local laws or rules and those sources that are not addressed by SIP measures or other measures. Where the contributing source has SIP or other controls, the air agency would identify the implementation status of these controls and provide evidence of effective implementation and enforcement. The air agen cy should also consid er whether those SIP controls should have been made more stringent and effective prior to the event. For emission*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 149 of 218 sources that contribute to the ev ent emissions but are not specifi cally addressed in the SIP or other laws or rules, the air agency should identify and documen t why it was reasonable to have not implemented controls. We invite comment on whether there should be a grace or grandfathering period before a SIP call involving a relevant NAAQS has the effect of ending the deference that applied prior to the SIP call, such that for an event occurring du ring the grace period the SIP would be given the deference described for the first scenario. We believe that such a grace period should not extend beyond the due date for the required SIP revision in respons e to the SIP call. Example: An air agency has an EP A-approved attainment plan SIP for a PM 10 nonattainment area that was approved in 1994 and includes controls for some of the anthropogenic emission sources that contribut e fugitive dust during high wind events. The nonattainment area did not include fugitive dust c ontrols for gravel operations in its 1994 SIP and has not required any controls of these operations in the years since SIP approval. The area does not have an approved maintenance plan, in part because it has been experiencing unresolved exceedances since 1994. The air agency al erts the reviewing EPA regional office that it wishes to submit an exceptional events demons tration for a high wind dust event that occurred in 2015 and affected several of the area’s mon itoring sites. This is the second high wind dust event associated with an exceedance in the past 3 years. After th e first event, the EPA issued a SIP call for the air agency to revise its PM 10 SIP, but the air agency has not yet submitted a new SIP. Because the EPA issued a SIP call, the air agency is required to show on a case-specific basis that the not reason ably controllable or presentable cr iterion has been met. Applying the concept that if a set of control measures should reasonably have been in place for emission sources that contribute to the ev ent emissions to the information in the record supporting the SIP*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 150 of 218 call would likely result in a dete rmination that those controls must have been in place for the event to satisfy the not reasonably controllable or preventable criter ion. Because the gravel operations are not controlled and because the high wind dust event was the second in 3 years, the air agency had a basis for unders tanding the possible need for better controls. Given the air agency’s knowledge of recurring events, the air agency may not be able to make a sufficient showing for the not reasonably controllable or preventable criterion and the reviewing EPA regional office may not be able to concur with the air agency’s request to exclude data. If, however, the air agency can show that the grav el operations did not co ntribute to the eventrelated emissions, the reviewing EPA regional o ffice might be able to concur with the air agency’s request to exclude data. Details for Maintenance Area Scenario 3 In this scenario (where the SIP was approve d more than 5 years pr ior to the date of submittal of a demonstration and the air agency is not under an obligation to revise the SIP), because of the passage of time the SIP controls should not be presumed to satisfy the not reasonably controllable or preventable criteri on regardless of whethe r the event-related wind speeds are above or below the high wind threshold. In this case, th e air agency should complete a case-specific assessment of the reasonableness of controls to satisfy the not reasonably controllable or preventable cr iterion. The assessment should c onsider controls beyond those required by the existing SIP and othe r state or local laws and rule s. The case-specific assessment should apply the concept that if a set of control measures should reasonably have been in place for emission sources that contribute to the event emissions, then those controls must have been in place for the event to satisfy the not reasonabl y controllable or preventable criterion. The submitting air agency should first identify the na tural and anthropogenic emission sources that*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 151 of 218 contribute to the event emissions and exceedance . The air agency should categorize sources as those that are addressed through SI P or other state or local laws or rules and those sources that are not addressed by SIP measures or other meas ures. Where the contributing source has SIP or other controls, the air agency would identify th e implementation status of these controls and provide evidence of effective implementation a nd enforcement. The air agency should also consider whether those SIP contro ls should have been made more stringent and effective prior to the event. For emission sources that contribute to the event emissions but are not specifically addressed in the SIP or other la ws or rules, the air agency should identify and document why it was reasonable to have not implemented controls. Example: An air agency has an EPA- approved attainment plan SIP for a PM 10 former nonattainment area that was approved in 2008 an d includes controls for anthropogenic emission sources that contribute fugitive dust during high wind events. The area has an approved maintenance plan. Between 2008 and 2014 it has not been experiencing exceedances related to high winds. In 2014 there is a single high wind dus t event with sustained wind speeds above the high wind threshold that results in two exceedance days, sufficien t to constitute a 3-year NAAQS violation. The air agency submits a demonstr ation covering both exceedances. In the not reasonably controllable or preven table portion of its demonstrati on, the air agency would identify all sources contributing to the event emissions, including natural sources, sources identified and controlled in the SIP, and any sources not cont rolled by the SIP. The air agency would then identify the applicable controls, the implementa tion status of these co ntrols and evidence of enforcement. The air agency should also consider whether those SIP controls should have been made more stringent and effective prior to the ev ent. Given the area’s past history of not having events and the fact that the sustained wind speed during the event wa s above the high wind*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 152 of 218 threshold, it is likely that the air agency coul d make a sufficient showing for the not reasonably controllable or preventabl e criterion. In this case, provided the air agency satisfies the other rule criteria, the EPA regional office would likely concur with an ai r agency’s request for data exclusion. However, in this maintenance area scenari o, another possible outcome of an event that causes an exceedance or violation is that the EPA determines that the not reasonably controllable or preventable criterion is not me t and the event-affected data ar e retained for regulatory actions within the scope of the Exceptional Events Rule. This may lead to the EPA taking an action that places the air agency under an obligation to revi se the SIP, in which case the situation would change into the second scenario for any later events of the same type. Best Management Practices . The EPA solicits comment on whether or not, as part of the assessment of local sources and reasonable co ntrols, USDA/NRCS-approved BMPs constitute sufficient reasonable controls in any or in all high wind event-affected areas and whether these measures should therefore be specifically and categorically identified in preamble or rule language as constituting reasonable controls. As discussed in the “C urrent Situation” section, the EPA has noted in previous guidance that US DA/NRCS-approved BMPs de signed to effectively reduce fugitive dust air emissions and prevent soil loss in agricultural applications could be included in the collection of c ontrols determined to constitu te reasonable controls for windblown dust events in areas in which they have been implemented. 121 Although the EPA has

121 Interim Guidance on the Preparation of Demons trations in Support of Requests to Exclude Ambient Air Quality Data Affected by Hi gh Winds Under the Exceptional Events Rule. U.S. EPA. May 2013. Available at http://www2.epa.gov/sit es/production/files/2015- 05/documents/exceptevents_highwinds_guide_130510.pdf and Interim Guidance to Implement Requirements for the Treatment of Air Quality Monitoring Data Influenced by Exceptional Events . U.S. EPA. May 2013. Available at http://www2.epa.gov/sites /production/files/2015- 05/documents/exceptevents_guidememo_130510.pdf

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Page 153 of 218 addressed the sufficiency of BMPs in decisions on individual ex ceptional events demonstrations when the BMPs were part of a SIP-approved BACM determination, we have not previously addressed whether or not BMPs individually or in some combination with each other constitute sufficient reasonable controls nation ally or in any particular type s of areas. We recognize that this question may be difficult to answer because BMPs often describe general types of practices ( e.g ., installing wind breaks) rather than specifying the penetration, scale or intensity of use of these practices by the la ndowners who adopt them. Therefor e we also solicit comment on the evidence for degree of penetration, scale and intensity that would be appropriate in demonstrations to consider BMPs individually or in some combination with each other to be reasonable controls.
G. Other Aspects of Flagging Exceptional Events-Influenced Data and Demonstration Submittal and Review 1. Who may submit a demonstration a nd request for data exclusion? a. Current Situation Before addressing the schedule and mechanic s of flagging event-influenced data and preparing demonstrations, the EPA believes it is necessary to first clarify which parties can submit an exceptional events demonstration pack age to the EPA. The CAA language at section 319(b)(3)(B)(i) states that “the occurrence of an exceptional event must be demonstrated by reliable, accurate data that is promptly produced and provided by Federal, State, or local government agencies.” As noted in section V.A of this proposal, state, local and some tribal agencies administer air quality management pr ograms within their juri sdiction, which includes monitoring and analyzing ambient air quality an d submitting monitoring data to the EPA, which are then stored in the EPA’s AQS database. Al so, FLMs and other federal agencies operate air*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 154 of 218 quality monitoring stations on some lands they manage, and some of these monitors meet the technical specifications and quality assurance requirements for their data to be used in regulatory determinations. As operators of regulatory monito rs, each of these agencies can flag their own data within AQS for considerati on as an exceptional event. As discussed in section V.F.1 of this proposed action, however, the EPA generally considers a state, exclusive of tribal lands, to be a single responsi ble actor, and, as the state is the entity primarily responsible for administering ai r quality planning and mana gement activities, the state has been ultimately responsible for subm itting exceptional events demonstrations for exceedances that occur at all regulatory monito ring sites within the boundary of the state, including exceedances occurring at monitoring site s operated by local air quality agencies to whom a state has delegated releva nt responsibilities or at regula tory monitoring sites operated by any other entity within the state, such as FLMs of Class I areas, other federal agencies and/or industrial facilities. A lthough the state is respons ible, a local agency, an FLM, another federal agency or another entity operati ng a regulatory monitor with an event-influenced exceedance can develop a demonstration for submittal by the state. If a state disagrees with the local agency’s, FLM’s, other federal agency’s or other entity’s exceptional events claim, the state can decide not to act on or forward that submittal to the EPA. A state can request that operators of other regulatory monitors experiencing event-influe nced exceedances prepare or assist in the preparation of demonstration analyses for ultimate submittal by the state. Because some tribal air quality agencies al so operate regulatory ambient air quality monitoring sites and submit these data to the EP A’s AQS database, as appropriate, these tribal agencies may also submit exceptional events dem onstrations for exceedances that occur at their monitoring sites.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 155 of 218 b. Proposed Changes As indicated in section V.A of this propos al, because FLMs and other federal agencies may operate regulatory monitors and submit collect ed data to the EPA’s AQS database and these same monitors could be affected by emissions from exceptional events, the EPA proposes to allow FLMs and other federal agen cies to prepare and submit exce ptional events demonstrations and data exclusion requests directly to the EPA. The EPA solicits comment on this proposed addition to the rule text, wh ich appears at the end of this document. Based on comments received, the EPA may retain, modify or not include this provision in the final promulgated rule. This provision would apply only to FLMs and othe r federal agencies that manage land on which an exceptional event originates or that operate a monitor that has been affected by an event. The provision would allow such FLMs and other federal agencies to provide demonstrations directly to the EPA only after a discussion with the st ate in which the monitor is operated. This discussion might instead result in an agreement that the federal agency (or another party) will provide a draft demonstration document to the appropriate state air ag ency for adoption and submission by the air agency to the EPA, as is currently allowed. If the provision for direct submission to the EPA is included in the final action, demonstrations prepared by FLMs or other federal agencies would be required to meet all provisions in the Exceptional Events Rule, including the requirement for a public co mment period on a prepared demonstration 122 and the

122 A public comment opportunity is important prio r to submission to the EPA because under the Exceptional Events Rule the EPA is not required to provide a public comment opportunity prior to concurring with an air agency’s request to exclude data. The EPA generally provides a public comment opportunity before we use air quality data , with or without such exclusions, in a final regulatory action. States typically provide an opportunity for public comment by posting draft demonstrations on a website. Federal agencies could do the same.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 156 of 218 requirements related to schedules and procedures for demonstration package submittal ( see sections V.G.4, V.G.5 and V.G.6) that apply to state agencies that operate monitors. 2. Aggregation of Events for NAAQS with Peri ods Longer Than 24 Hours and Demonstrations with Respect to Multiple NAA QS for the Same Pollutant a. Current Situation The EPA’s AQS database houses ambient air quality monitoring and related data. The data in AQS are maintained as individual re ported measurements, which can range from 5- minute maximum concentr ations per hour for SO 2 , to hourly data for ozone, CO, NO 2 , SO 2 and some PM measurements to 24-hour measuremen ts for lead and other particulate matter measurements. Air agencies identify and the EPA concurs with exceptional event-related data in AQS that are reported as individual measurements. Some NAAQS have long averaging periods, su ch that multiple independent events may affect the period-average concen tration of the NAAQS pollutant. In the aggregate, a clear causal relationship may exist between the events and an exceedance or violation, but no single event satisfies the clear causal relationship criterion because each ev ent has too small of an effect on the longer-period metric to do so by itself. C AA section 319(b) and the 2007 Exceptional Events Rule do not clearly allow the aggr egation of events for purposes of the clear causal relationship criterion, yet aggregation seems consistent with th e intent of section 319(b). The EPA has not to date indicated that actual aggregation of events is permitted. However, Question 30 in the Interim Q&A document provided guidance that can be of some help in this situation. This guidance was that 24-hour concentrations of Pb, NO 2 , or SO 2 can be individually compared to the NAAQS level defined for a longer period, for purpos es of meeting “but for” with respect to both the 24-hour NAAQS, if applicable, and for purpos es of meeting “but for” with respect to the*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 157 of 218 NAAQS with the longer averaging period. This guid ance focused on the intention of a passage in the preamble to the 2007 Exceptional Events Rule addressing the PM 2.5 NAAQS in particular, and extended the approach of the 2007 preamble to other cases of NAAQS fo r the same pollutant that have different averaging peri ods. The practical effect of this approach is that several events that individually have effects too small to have a causal connection to a longer-period exceedance or violation might be excluded one-by- one, and the net effect of the exclusions may make a difference to complian ce with the longer-period NAAQS. As guidance, however, the Interim Q&A document does not provide full certai nty that an air agen cy may rely on the recommended approach. As noted in section IV.B of this proposal, the 2007 Exceptiona l Events Rule requires that for data exclusion, among other requirements, an air agency must demons trate that there would have been no exceedance or violation of the NAAQS “but for” the event. The “but for” criterion necessarily requires comparing th e individual measurements in AQS to the averaging period of the relevant NAAQS to determine whether an exceedance or violation occurred. When the averaging period for the NAAQS is the same as the measurement duration period, this comparison is relatively straightforward. For ex ample, air agencies and the EPA can directly compare 1-hour ozone, 1-hour CO, 1-hour SO 2 , and 1-hour NO 2 measurements to the respective 1-hour NAAQS. This comparison becomes more complicated, however, when there is a difference between the pollutant measurement duration and the averag ing time of the NAAQS, which is the case when comparing a 1-hour m easurement to an 8-hour, 24-hour, 3-month or annual NAAQS (or in the case of 1-hour ozone the previously existing NAAQS). In fact, the EPA devoted Questions 29-31 in the Interim Q&A document to explaining how to make these*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 158 of 218 complicated comparisons. 123 The Interim Q&A document also explained that because these comparisons are NAAQS-specific, air agencies should request a nd support the exclusion of a measured air concentration separately for each NAAQS that applies to th e pollutant and the EPA will similarly provide separate concurrenc es. Under the 2007 Exceptional Events Rule provisions, this means, for example, that an ai r agency with several 24- hour measurements of event-influenced PM 2.5 data measuring 75 micrograms per cubic meter ( μ g/m 3 ) would need to separately flag the data within AQS on a NAAQS- specific basis, and submit separate requests, analyses and demonstration components to support exclusion of the identified event-influenced data for the 1997 annual secondary PM 2.5 NAAQS of 15 μ g/m 3 , the 2012 annual primary PM 2.5 NAAQS of 12 μ g/m 3 and the 2006 primary and secondary 24-hour PM 2.5 NAAQS of 35 μ g/m 3

. Depending on the outcome of the “but fo r” criterion with respect to each PM 2.5 NAAQS, it could be that the data would be excluded for purposes of determinations with respect to only some of these NAAQS. This current situation can result in complicat ed demonstrations for air agencies seeking data exclusion from determinations with respec t to multiple NAAQS for the same pollutant. This complexity may make it more difficult for the p ublic to comment, and requires time for the EPA to review such a demonstration. b. Proposed Changes The EPA is taking comment on proposed rule text allowing 24-hour concentrations of any NAAQS pollutant to be compared to a NAAQS le vel defined for a longer period as part of a weight of evidence showing for the clear causal relationship with respect to the NAAQS with the

123 Interim Exceptional Events Rule Frequently Asked Questions. U.S. EPA. May 2013. Available at http://www2.epa.gov/sites/production/fi les/2015-05/documents/eer_qa_doc_5-10- 13_r3.pdf

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Page 159 of 218 longer period. This approach would be more am enable to less quantified weight of evidence demonstrations, since only one day would be examined at a time. The EPA is also proposing that for NAAQS w ith averaging or cumu lative periods longer than 24 hours, events occurring on different da ys may be aggregated for the purpose of determining whether their collectiv e effect has caused an exceedan ce or violation, without regard to whether the events are of the same type ( e.g. , stratospheric ozone intrusion followed by a wildfire). The EPA notes that such aggregati on may be very difficult if the effects of the individual events on their indivi dual days are not fully quantified. Proposed rule text for this change is provided for comment. Finally, to simplify some demonstrations, th e EPA is also taking comment on whether a successful demonstration with respect to any NAAQS for a given pollutant would suffice to qualify the data in question for exclusion with re spect to all NAAQS for that pollutant. The EPA believes it is useful to invite public commen t on this “approved for one NAAQS approved for all NAAQS for the same pollutant” concept. The EPA will carefully consider the commen ts it receives on these concepts and may finalize all, some or none of the thre e proposals described in this section. 3. Exclusion of Entire 24-hour Value Versus Partial Adjustment of the 24-hour Value for Particulate Matter a. Current Situation As indicated in Question 29 of the Interim Q& A document, we have advised air agencies preparing demonstrations to support requests to exclude PM 2.5 and PM 10 data obtained via monitor instruments that provide 1-hour measurem ents that they should flag all 24 1-hour values within a given event-affected day, even if the event did not last all th ese hours. If concurred*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 160 of 218 upon, flagging all 1-hour values will ultimately resu lt in the same available remaining data for regulatory analysis and calculation as would be the case had the 24-hour PM 2.5 or PM 10 measurement data been collected from f ilter-based (24-hour) monitoring instruments. 124 Another reason we have taken the position that flagging all 24 1-hour values is appropriate is because flagging only peak or selected hou rs could result in the remaining 1-hour values still meeting the data completeness requirements because fla gged and excluded data do not count against completeness even though they cannot be used in calculating an average concentration for a 24- hour period. Under the rules for data interpretation, ex clusion of only the event-affected 1-hour concentrations could result in AQS calculating a seemingly valid 24-hour concentration that is actually highly uncertain because it is base d on only a few hours and thus may be biased. 125 b. Proposed Changes The EPA solicits comment on codifying its current approach in the rule text to eliminate any regulatory uncertainty. If finalized, this modi fication to the data handling procedures will be made to occur automatically within AQS.
4. Flagging of Data While neither the preamble to nor the rule text contained within the 2007 Exceptional Events Rule discuss data handling within AQS, explaining certain AQS processes and functions

124 Filter based instruments typi cally record a single value within a 24-hour period while continuous monitors typically collect 24 1-hour measurements. Because AQS can calculate a valid 24-hour average concentration with as fe w as 18 hours, it may be necessary to exclude hours not actually affected by the event to ensure the same data exclusion outcome as if the measurement had been made with a 24-hour filter. 125 The form of the 24-hour PM 2.5 NAAQS of 35 μ g/m 3 is 98 th percentile averaged over 3 years. The form of the primary annual PM 2.5 NAAQS of 12 μ g/m 3 is an annual mean averaged over 3 years. The form of the 24-hour PM 10 NAAQS of 150 μ g/m 3 is not to be exceeded more than once per year on average over 3 years. Biased concen trations can potentially skew the determination of the 98 th percentile and/or the annual mean for PM 2.5 and the averages for PM 2.5 or PM 10 calculated to determine complian ce with the relevant NAAQS.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 161 of 218 will be useful to an understanding of the data flagging situation that has developed in implementing the requirements in 40 CFR 50.14( c)(2) and why we are proposing changes. a. Current Situation Within AQS, monitoring agencies can use two types of data validati on, or data qualifier, codes related to exceptional events: the Request Exclusion flags ( R ) and the Informational Only flags ( I ). 126 The EPA has advised air agencies to use the I series flags when identifying informational data and the R series flags to identify data poi nts for which the agency intends to request an exceptional events exclusion and th e EPA’s concurrence. As an example, air agencies may currently use an I series flag to initially identify values they believe were affected by an event. Once the air agency collects addition al supporting data, it may change the flag to

an R series flag and submit an initial event de scription. Or, the air agency may find that additional information does not s upport flagging the data as an exceptional event, and the air agency may, therefore, delete the flag or retain the I series flag. Air agencies may also use the I series flags simply to note activities or conditions occurring on the data collection day that are unrelated to exceptional events or that do not result in an exce edance or violation of a NAAQS. Air agencies have previously indicated that they generally see little value in the use of I series flags. 127

126 “Flag” is the common terminology for a data qualifier code in the EPA’s AQS. Unless explicitly noted, the process of “flagging” data refers to adding Request Exclusion ( R ) data qualifier codes to selected data in AQS. R flags are the only AQS fl ags that satisfy the 2007 Exceptional Events Rule requirement for initia l data flagging. The curre nt design of the AQS software is such that EPA can act/concur only on an R flag. 127 Responses to Significant First-Round Comme nts on the Draft Guidance Documents on the Implementation of the Exceptional Events Rule , U.S. EPA, June 2012. Available in Docket No. EPA-HQ-OAR-2011-0887.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 162 of 218 Flagging of event-influenced data has tradit ionally also involved associating a one- or two-character code with a monito red value within AQS indicating th at the data have potentially been influenced by a particular type of exceptional event ( e.g ., “RT” is the character code used to request exclusion for data that have been influenced by wildfires in the US). The 2007 Exceptional Events rule added a requirement to in clude a more detailed initi al description of the particular event associated with such a characte r code. This description consists of text of variable length. The EPA does not revi ew or concur on the I series flags. Rather, an air agency must use

an R flag to request data exclusi on. The language at 40 CFR 50.14(c)(2), Flagging of Data , requires that an air agency no tify the EPA of its intent to exclude one or more measured exceedances of an applicable NAAQS as being du e to an exceptional event by placing a flag and an initial event description in the appropriate fields in AQS for the data record(s) of concern no later than July 1 of the calendar year followi ng the year in which the flagged measurement occurred. Only R flags fulfill this requirement. This “general” schedule date of July 1 applies unless the data are associated with the initial area designations process for a new or revised NAAQS in which case the specific sc hedule in 50.14(c)(2 )(vi) applies. Air agencies have previously expressed con cern that the timelines for event flagging and demonstration submittal are not always appropriate. 128 While the EPA has historically promulgated revised flagging and demonstration submittal schedules in the regulatory actions for new and revised NAAQS for those data year s that might be used in the initial area designations process for those NAAQS, the EPA does not promulgate revised schedules for

128 Responses to Significant First-Round Comme nts on the Draft Guidance Documents on the Implementation of the Exceptional Events Rule , U.S. EPA, June 2012. Available in Docket No. EPA-HQ-OAR-2011-0887.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 163 of 218 other regulatory actions such as clean data or attainment determinations. Rather, the EPA has relied upon the “general” flagging and dem onstration submittal schedules in 40 CFR 50.14(c)(2) and 40 CFR 50.14(c)(3)(i) . Meeting the requirement at 40 CFR 50.14(c)(2)(iii) to submit R flags and an initial descripti on of the event “not later than July 1st of the calendar year following the year in which the flagged measuremen t occurred” can be difficult in the case of an annual standard where an air agency needs all 12 months of data to calculate an annual average and then needs 3 years of annual averages to iden tify whether or not the event-influenced data results in a violation of a 3-year design values. An air agency ma y not know that data influenced by an exceptional event caused the design valu e to become a NAAQS violation until 3 years after the event occurred. Some air agencies have used and applied I and R flags in AQS inconsistently with this intended scheme, by including applying numerous R flags in AQS with no real intention to submit an exceptional events demonstration. Also, R flags may be set immediately before a demonstration is submitted or even as late as when the EPA needs to indicate in AQS our approval of a request for data exclusion. As a result, neither the pres ence nor the absence of these flags provide the EPA with an indi cation of anticipated exceptional events demonstrations. b. Proposed Changes As part of this action, the EPA proposes to revise the “general” schedule language contained within 40 CFR 50.14(c)(2) by removing th e timelines associated with initial event flagging. The EPA also proposes to modify the a ssociated data flagging process within AQS to correspond with these proposed regulatory chan ges. These proposed changes would include eliminating the use of the current exceptional events data validation/data qualifier codes: the*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 164 of 218 Request Exclusion flags ( R ) and the Informational Only flags ( I ). The one- or two-character event type codes would be retained. The EPA solic its comment on the approach that is discussed below in additional detail. The EPA is proposing to change the definiti on and process for flagging exceptional event data. Flagging would in effect become the appli cation of the one- or two-character event type and event description text as desc ribed below, along with a concu rrent or subsequent request for data exclusion communicated to the EPA through other channels. Because the flagging of data necessarily begins with the identificati on of an event, the EPA proposes to retain, with modifications, the AQS free-form text field for an initial event description. As is currently the practice, we re quest that air agencies use the “initial event description” to identify a unique , real-world event. We propos e that this “initial event description” be expanded to contain a uni que event name; the type of the event ( e.g ., high wind dust, volcanic eruption, other); a brief descripti on of the event; and, to the extent known, the scope of the event in terms of geography and time ( e.g ., likely affected area using latitude and longitude and a radius of influence and beginning day/time and ending day/time). 129 AQS would also be modified to allow the air agency to asso ciate specific AQS sites and potentially affected monitors and specific data points with a given event as so described. This will enable air agencies and the EPA to “flag” or add qualifier codes to selected data in a si ngle step rather than adding this information or the necessary codes on a per entry basis. Historically, when events have influenced the concentrations at multiple monitors for multiple days, the air agency has added initial event descriptions and set flag s on each monitored concentration, sometimes

129 The EPA is proposing that air agen cies select the “type of event” from a pre-set list of event types, which would likely consist of those event types currently identified by existing Informational and Request Exclusion flags within AQS.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 165 of 218 resulting in hundreds of identical individual entries. “Associati ng” monitors with an event defined in time and space will save resources. Once an air agency has identified an event and created the initial event description within AQS, the agency should begin the process of requ esting exclusion for iden tified data, which will consist of two discrete operati ons: (1) indicating in a separate communication to the EPA that specific ambient air quality measuremen ts are affected by a defined event ( see section V.G.5 related to Initial Notification of Potential Ex ceptional Event), and (2) requesting that these identified ambient air quality measurements be excluded from regulatory actions according to the terms of the revised Exceptional Events Rule and EPA guidance for other applications of air quality data. AQS would retain a field to allow the EPA to concur or not concur with a given request for exclusion for one or more of the data points associated with a described event, once review of the air agency’s request and demonstration is completed. In addition to the proposed AQS modifications described above, the EPA is proposing to remove the “general” flagging schedule in 40 CFR 50.14(c)(2)(iii). This regulatory language currently requires that air agencies submit [ R ] flags and an initial description of the event by July 1 of the calendar year following the year in wh ich the flagged measurement occurred or by the other deadlines identified with individual NAAQS. As noted earlier in this secti on, an air agency may not know that data influenced by an excep tional event caused a violation of a NAAQS until after the initial event flagging deadline has passe d. The EPA proposes to remove and reserve the current language at 40 CFR 50.14(c)(2)(iii). Additional changes to the regulatory language in 40 CFR 50.14(c)(2) will be discusse d in the next section.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 166 of 218 The EPA notes that the recent ozone NAAQS action 130 also removed and reserved the subsequent sections at 40 CFR 50.14(c)(2)(iv) and (c)(2)(v), which addressed the submittal of exceptional events demonstrations that could affect re gulatory determinations associated with initial area designations for the 2006 24-hour PM 2.5 NAAQS and the 2010 Lead NAAQS and were made obsolete by the passage of time. The EPA will retain these removed and reserved sections as promulgated in the ozone NAAQS and proposes no additi onal changes to these sections. 5. Initial Notification of Potential Exceptional Event a. Current Situation As the EPA acknowledged in the Interim Exceptional Events Implementation Guidance and in discussions with stakehol ders, the EPA understands that the initial identific ation of data affected by exceptional events and the subse quent preparation, submittal and review of demonstration packages is a resource intensive pr ocess both for the preparing air agency and the reviewing EPA regional office. 131 Delays in processing and making decisions on submitted packages create regulatory uncertainty and pot entially increase the workload for both the submitting air agency and the EPA. In addition, the backlog of pending actions makes selection of the best information to support new submitta ls potentially more uncertain. Further, air

130 On October 1, 2015, the EPA Administrator si gned a final action strengthening the groundlevel ozone NAAQS to 70 ppb. The EPA posted a pr e-publication version of this notice on its website at http://www3.epa.gov/ozonepollution/pdfs/20151001fr.pdf . Once the official version of the notice is published in the Federal Register , the EPA will remove the posted pre-publication version and replace it with a link to the official version of the action. 131 Interim Guidance to Implement Requirements for the Treatment of Air Quality Monitoring Data Influenced by Exceptional Events. Memorandum from Stephen D. Page, U.S. EPA Office of Air Quality Planning and Standards, to Re gional Air Directors, Regions I-X. May 10, 2013. Available at http://www2.epa.gov/site s/production/files/2015- 05/documents/exceptevents_guidememo_130510.pdf

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Page 167 of 218 agencies and the EPA often face timelines by which they must make regulatory decisions that can be affected by the inclusion or exclusion of event-affected data. In the Interim Exceptional Events Implementation Guidance and through the EP A’s best practices disc ussions identified in section IV.E, the EPA committed to work with air agencies as they prepare complete demonstration packages and we developed some guidelines to increase the efficiency of the
process. One of the efficiency-increasing measures we suggested in the Interim Exceptional Events Implementation Guidance was the Letter of Intent. The guidance explained that the Letter of Intent was a voluntary process by which the submitting air agency notifies the reviewing EPA regional office of the air agency’s intent to submit a demonstration for an identified exceptional event. The purpose of the letter was to promote early communication between the submitting air agency and the reviewing EPA regional office. In the time since issuing the Interim Exceptional Events Implementation Guidance, several air agencies and the EPA regional offices have successfully used this voluntary process to discuss expectations regarding specific exceptional events demonstrations. b. Proposed Changes As part of the best practices for communi cations during the exceptional events process and to aid all agencies in resource planning and prioritization, the EPA propos es that air agencies and the EPA engage in regular co mmunications to identify those data that have been potentially influenced by an exceptional event, to determine whether the identified data affect a regulatory determination, and to discuss whether an air ag ency should develop and submit an exceptional events demonstration. In most instances, thes e discussions will be between individual air agencies and the reviewing EPA regional office. In other cases, the EPA regional office, or an*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 168 of 218 individual air agency within the purview of th e EPA regional office, may initiate and/or host a general discussion with all air agencies in th e region followed by individual discussions, as needed. In still other cases, such as where large events cross state lines and when two or more states are pursuing exclusion for the same ev ent(s), the EPA region or regions may initiate discussions will all potentially affected states/agenc ies to assist in coordinating states affected by regional events. For purposes of this proposed action, the EPA is referring to these communications as the “Initial Notification of Potential Exceptional Even t” (Initial Notification) process. The EPA has changed the name of this process from the Letter of Intent in recognition of the fact that effective communication may have multiple formats and does not necessarily consist of a formal, written letter to convey important information. As with the voluntary Letter of Intent, the ultimate purpose of the Initial Notification process is to initiate conversations between an air agency and the EPA if not already on-going, or engage in more detailed discussions if a process is currently in place, regarding specific data and whether the identified data are ripe for submittal as exceptional events. As stakeholders have repe atedly expressed and as the EPA acknowledges, the identification of data affected by excepti onal events and the subsequent preparation, submittal and review of demonstration packages is a resource intensive process both for the preparing air agency and the reviewing EPA regional office. However, in considering the exceptional events process, it is importa nt to note that if these data do not have regulator y significance, then engaging in the development and review of an exceptional events demonstrati on is generally not an efficient use of an air agency’s or the EPA’s limited resources. The Initial Notification pr ocess will focus efforts on the relevant data and provide the EPA with the opportunity to conv ey to the affected ai r agency our initial*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 169 of 218 thoughts regarding the identified event and analys es that may or may not be appropriate for inclusion in a demonstration, and, with respect to regulatory significance , which demonstrations the EPA will consider for review. We believe that this approach will help air agencies make the best use of their available resources. As noted earlier, the Initial Notification could include any form of communication ( e.g ., letter, email, in-person meeting with an at tendees’ list and discussion summary or phone conversation with follow-up email) that ultimately identifies the potential need to develop an exceptional events demonstration and communicat es key information related to the data identified for potential exclusion. Where an air agency independently identifies event-affected data and the need to submit an exceptional events demonstration outside of its regular, on-going communications with the EPA regional office, th e air agency could prep are a letter or email communicating its Initial Notification. Generally, the EPA anticipates that air agencies would develop and provide an Initial No tification as soon as the agency identifies event-influenced data that potentially influence a regulatory decision or when an agency wants the EPA’s input on whether or not to prepare a demonstration. 132 The EPA further proposes that each Initial Notification would include the following components:

 Unique event name (field in AQS) - facilitates future communication and understanding between the submitting air ag ency and the reviewing EPA regional office, particularly if an air agency has submitted multiple exceptional events demonstration packages.

132 The EPA recognizes that air agencies can immedi ately identify those events that result in an exceedance of a NAAQS with a short averaging time ( e.g ., 1-hour, 8-hour or 24-hour standards) but may need additional time for an annual average standard. An air agency could also submit an annual Initial Notification if a nnual submittal makes sense for resource planning or for recurring seasonal events.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 170 of 218  Initial event description (field in AQS) – provides a brief narrative of the event that could also include maps or graphs si milar to what an air agency might include in the proposed conceptual model discusse d in section V.G.6 of this proposed action; the event description would include a qualitative descri ption of the event and, at a minimum, briefly describe the agency’s current understanding of interaction of emissions with the event, transport and meteorology ( e.g ., wind patterns such as strength, convergence, s ubsidence, recirculation) and pollutant formation in the area.

 Affected regulatory decision – provides a description of the regulatory action or actions potentially affected by the claimed event-influenced data and the anticipated timing of this action.

 Proposed target date for demonstration submittal – identifies the proposed target date by which the air agency would su bmit a demonstration package to the reviewing EPA regional office.

 Most recent design value including and excluding the event-affected data (optional) – the air agency’s assessment of the most recent design value both with and without the identified event(s) is helpful when assessing regulatory significance. The EPA cannot cal culate this value (and th erefore may not be able to determine significance) if the air agency has flagged more data than it intends to include in an exceptional events demonstration.

 Information specific to each monitored day – see Table 5, which would be developed by the submitting air agency and generated from the initial event description in AQS ( see discussion in section V.G.4).*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 171 of 218 Table 5. Initial Notification Informat ion Specific to Each Monitored Day

Agency/ Planning Area State County Event Name in AQS Type of Event NAAQS Monitor AQS ID and Site Name Date(s) of Event Monitor Exceedance Concentration

The EPA anticipates promptly acknowledging an air agency’s Initial Notification and then formally responding within 90 days of receipt via letter, email or in-person meeting with an attendees’ list and discussion summary. We also anticipate having informal phone conversations with the air agency prior to this formal re sponse. As previously discussed, the EPA will generally prioritize exceptiona l events determinations that affect near-term regulatory decisions. 133 Where the data are to be us ed in initial area designations, the EPA proposes to rely on the promulgated documentati on submission schedule in Table 1 at 50.14(c)(2)(vi). Where the data will influence another near-term regulator y decision, the EPA proposes to rely on the caseby-case timelines by which the air agency shoul d submit the demonstration. For case-by-case demonstrations, the EPA’s recommended date for demonstration submittal would consider the nature of the event, the antic ipated timing of the regulatory decision, and would allow time for both an air agency’s preparation of the demons tration and the EPA’s review. The EPA may not be able to review and act on demonstrations submitted after the recommended submittal date. Additionally, the EPA will request in its respons e that, if the submitti ng air agency has not

133 “Regulatory decisions” include findings as to whether the area has met the applicable NAAQS, classification determinations, attainment demonstrations, the development of Limited Maintenance Plans and clean data findings.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 172 of 218 already identified the aff ected data within AQS, that it undertake this effort according to the process described in section V.G .4. If the data identif ied in the Initial No tification do not have regulatory significance (and there is no compelling reason for excluding data), then the EPA will indicate this in its corresponden ce back to the air agency and w ill discourage the air agency from devoting resources to developing a demonstration because the EPA will likely not review or act upon the submittal. If after discussing the content of a submitted Initial Notification and/or receiving the EPA’s response to the Initial Notification, the EPA acknowledge s that identified data have regulatory significance (or some other compelling r eason for excluding data), then the air agency should proceed with the development of a techni cal demonstration package that satisfies the requirements in 40 CFR 50.14 and accounts for a ny case-specific advice from the EPA and additional information in th e EPA’s guidance documents. 134 Although air agencies can submit demonstrations for events that do not affect a regulatory action, the EPA will likely not review or act on such submittals. For these reasons described in this section and in section V.G.4, the EPA proposes to revise the language in 40 CFR 50.14( c)(2)(i) as follows: “A State sh all notify EPA of its intent to request exclusion of one or more measured exce edances of an applicab le ambient air quality standard as being due to an exceptional even t by creating an initial event description and flagging the associated data that have been submitted to the AQS database and by engaging in the Initial Notification of Potential Exceptional Event process.” Specific steps in the Initial

134 Interim Guidance to Implement Requirements for the Treatment of Air Quality Monitoring Data Influenced by Exceptional Events. Memorandum from Stephen D. Page, U.S. EPA Office of Air Quality Planning and Standards, to Re gional Air Directors, Regions I-X. May 10, 2013. Available at http://www2.epa.gov/site s/production/files/2015- 05/documents/exceptevents_guidememo_130510.pdf.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 173 of 218 Notification process are identified in rule text at the end of this document. The EPA solicits comment on the proposed rule te xt revision (in 40 CFR 50.14(c)(2 )) to require an Initial Notification of Potential Exceptional Event, with a provision that the EP A can waive the Initial Notification requirement on a case-by-case basi s. Alternatively, the EPA solicits comment on making the Initial Notification of Potentia l Exceptional Event a voluntary process. Additional proposed revisions would continue at (ii): “The data shall not be excluded from determinations with respect to exceedances or violations of the national ambient air quality standards unless and until, following the State’s submittal of its demonstration pursuant to paragraph (c)(3) of this secti on and EPA review, EPA notifies the State of its concurrence by placing a concurrence flag in the appropriate fiel d for the data record in the AQS database.” As noted in section V.G.4, the EPA is pr oposing to remove the “general” flagging schedule in 40 CFR 50.14(c)(2)(ii i). The EPA seeks comments on these proposed changes to the language at 40 CFR 50.14(c)(2), wh ich more clearly identify the process for flagging data in AQS and requesting exclusion of one or more m easured exceedances of an applicable ambient air quality standard. The EPA notes that the recent final rule to revise the ozone NAAQS also removed and reserved the subsequent sectio ns at 40 CFR 50.14(c)(2)(iv) and (c)(2)(v), which addressed the submittal of exceptional events demonstrations that could affect regulatory determinations associated with initial area designations for the 2006 24-hour PM 2.5 NAAQS and the 2010 Lead NAAQS and were made obsolete by the passage of time. The EPA will retain these removed and reserved sections as promulgated in the oz one NAAQS and proposes no additional changes to these sections. 6. Submission of Demonstrations*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 174 of 218 a. Current Situation With the recent ozone NAAQS, the EPA proposed and promulgated changes to the current exceptional events regu latory language at 40 CFR 50.14( c)(2) and 40 CFR 50.14(c)(3) to include finalizing exceptional events flagging an d demonstration submittal schedules related to implementing the revised ozone standards and future revised NAAQS and removing obsolete regulatory language for expired ex ceptional events deadlines. Sec tions V.G.4 and V.G.5 discuss the current situation and additional proposed changes to 40 CFR 50.14(c)(2). This section discusses the current situation and pr oposed revisions to 40 CFR 50.14(c)(3). As part of the recent final rule to revise the ozone NAAQS, the re gulatory language at 40 CFR 50.14(c)(3)(i) now refers to a revised ex ceptional events fla gging and demonstration submittal schedule for data that could be used in initial area designation decisions following promulgation of any future revised NAAQS. Ho wever, the language at 40 CFR 50.14(c)(3)(i) still requires air agencies to “...submit a demonstration to justify data exclusion to EPA not later than the lesser of, 3 years following the end of the calendar quarter in which the flagged concentration was recorded or, 12 months prior to the date that a regulatory decision must be made by EPA.” As identified in section V.G.4 of this proposal, air agencies have previously expressed concern that the timelines for event flaggi ng and demonstration submittal are not always appropriate because an air agency may not know that data influenced by an exceptional event caused the design value exceedance un til 3 years after the event occurred. 135 The EPA acknowledges that this scenario can occur.

135 Responses to Significant First-Round Comme nts on the Draft Guidance Documents on the Implementation of the Exceptional Events Rule , U.S. EPA, June 2012. Available in Docket No. EPA-HQ-OAR-2011-0887.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 175 of 218 In addition to establishing a general schedule for demonstration submittal, the regulatory language at 40 CFR 50.14(c)(3)(i) requires that “A State must submit the public comments it received along with its demons tration to EPA.” Although this la nguage is included in 40 CFR 50.14(c)(3)(i), it refers to the regulatory la nguage at 40 CFR 50.14(c)(3)(v), which requires the air agency to document, and submit with its de monstration, evidence that it followed the public comment process. Regarding this requirement to “document that the public comment process was followed,” neither the Exceptional Events Rule language in 40 CFR 50.14 nor the preamble to the promulgated 2007 Exceptional Events Rule specifies a minimum timeframe for public comment. Many air agencies have been posting dr aft demonstrations for public review on their websites. The EPA has reviewed several of thes e postings and identified 30-days as an often cited timeframe for public comment on a draft exceptional events dem onstration submittal. The current rule also provid es at 40 CFR 50.14(c)(3)(iv) that the demonstration to justify data exclusion shall provide evidence that the event satisfies the definition of an exceptional event provided at 40 CFR 50.1(j); that there is a clea r causal relationship be tween the monitored exceedance and the event that is claimed to have affected the air quality in the area; that the event is associated with a measured concentra tion in excess of normal historical fluctuations, including background; and that th ere would have been no exceed ance or violation but for the event. Air agencies have found this section of the 2007 Exceptional Events Rule to be confusing because it contains a mix of statutory require ments and regulatory language without clearly identifying the components that the EPA expects to see in an exceptional events demonstration. As the EPA expressed in the Interim Exceptiona l Events Implementation Guidance, all parties would benefit from clear expectations regarding demonstration components.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 176 of 218 The EPA further believes, and recommended in the Interim High Winds Guidance document, that each demonstration begin with a conceptual model, or narrative, describing the event(s) causing the exceedance or violation and a discussion of how emissions from the event(s) led to the exceedance at the a ffected monitor(s). As descri bed in the Interim High Winds Guidance document, the narrative conceptual mode l could include varyin g levels of detail depending on the event complexity, but in all case s would provide a qualitative description of the event, interaction of the event-generated emissions with transport and meteorology ( e.g ., wind patterns such as strength, convergence, subsidence , recirculation) and pollutant formation in the area with the exceeding monitor. Because, in some cases, monitored data or technical analyses may seem to contradict the event claim, particul arly the clear causal rela tionship, an air agency can use the conceptual model to explain, with a weight of evidence approach, why the majority of the data or analyses are consistent with the event’s impact on a measured exceedance or violation (for example, for a wildfire, why most of the mete orology would have indicated a lower ozone day without the fire emissions, ev en if the temperature were high). A useful conceptual model also includes (1) a description of the regulatory decision impacted by the exceptional event, (2) a summary ta ble of the data requested for exclusion and (3) maps and/or summary tables of event-related information including location; size and extent; point and explanation of origin. A conceptual model can a dditionally include examples of media coverage of the event. 136 Since releasing the In terim High Winds Guidance document in 2013, the EPA has received several demonstra tions that included a conceptu al model. The EPA has found it very helpful to understand the event formation a nd the event’s influence on monitored pollutant

136 The EPA expects that air agenci es could use some of the same information and tables in both the conceptual model and the Initial Notificat ion of Potential Exceptional Event, which is discussed in section V. G.5 of this proposal.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 177 of 218 concentrations before beginni ng to review the individual t echnical evidence to support the requested data exclusion. b. Proposed Changes For the previously mentioned reasons, the EPA is proposing and soliciting comment on the following changes to the regulatory language in 40 CFR 50.14(c)(3) regarding the submission of demonstrations:

 Removing the general schedule provis ions in 40 CFR 50.14(c)(3)(i) for submitting demonstrations.

 Moving the language requiring a state to in clude the comments it received during the public comment period for the su bject demonstration from 40 CFR 50.14(c)(3)(i) to 40 CFR 50.14(c)(3)(v).

 Modifying the language at 40 CFR 50.14(c)(3 )(iv) to more clearly identify the required elements of an exceptional ev ents demonstration to include (1) a narrative conceptual model a nd (2) demonstrations and analysis that address the core statutory technical criteria [the even t affected air quality in such a way that there exists a clear causal relationshi p between the specific event and the monitored exceedance or violation (as indi cated by the comparison to historical concentrations showing and ot her analyses), the event was a human activity that is unlikely to recur at a particular location or was a natural event, the event was not reasonably controllable or preventable].

 Modifying the language at 40 CFR 50.14(c)(3 )(v) to identify that a demonstration submittal must include (1) documentation that the air agency conducted a public comment process on its draft exceptiona l events demonstration that was a*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 178 of 218 minimum of 30 days, which could be conc urrent with the EPA’s review, (2) any public comments received during the public comment period and (3) an explanation of how th e air agency addressed the public comments. To elaborate on removing the general schedule provisions in 40 CF R 50.14(c)(3)(i), the EPA proposes to remove the provision in 40 CF R 50.14(c)(3)(i) that requi res air agencies to submit a demonstration “not late r than the lesser of 3 years fo llowing the end of the calendar quarter in which the flagged concentration was reco rded or 12 months prior to the date that a regulatory decision must be made by EPA.” In pl ace of this language, the EPA proposes to rely on the promulgated documentati on submission schedule in Table 1 at 50.14(c)(2)(vi) in those cases where the data are to be used in initial area designations. If the data could influence a regulatory determination other than initial ar ea designations, the EPA proposes to rely on the case-by-case timelines established by the reviewin g EPA regional office as part of the Initial Notification of Potential Exceptional Event process. With respect to the public comment provisi ons for a developed demonstration, for the reasons stated previously, the EPA proposes to m ove the language requir ing an air agency to include the comments it received during th e public comment period for the subject demonstration from 40 CFR 50.14(c)(3)(i) to 40 CFR 50.14(c)(3)(v) to cons olidate the required elements of the public comment process for exce ptional events demonstrations within a single regulatory provision. The EPA also proposes to specify a minimum 30-day public comment process, which provides sufficient time for exch ange between the reviewing public and the air agency. Shorter comment periods may not provide necessary time for the public to research the identified event and associated supporting data while longer timeframes may not be possible where a near-term regulatory decision relies on an exceptional events decision. The EPA notes*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 179 of 218 that in very limited cases where the air agency is relying on exceptional events claims as part of a near-term regulatory action, such as a demonstrati on for events in the third year of a 3-year design value that will be used in initial area designations for a new or revised NAAQS under a 2- year designation schedule, the public comment period could be concur rent with the EPA’s review provided the submitting air agency sends any public comments and responses to the EPA by a specified date should comments be submitte d. If an air agency receives public comment disputing the technical elements of a dem onstration during a comment period that runs concurrent with the EPA’s review and these comments result in the air agency’s need to reanalyze or reassess the validity of a claime d event, a second public comment period may be
necessary. The EPA also proposes to revise the language at 40 CFR 50.14(c)(3)( iv) so that it more clearly identifies the required elements of an exceptional events demonstration. As previously described, the EPA proposes that each demonstra tion begin with a narrativ e conceptual model, which summarizes the event in question and pr ovides context for require d statutory technical criteria analyses. The EPA further proposes, cons istent with other proposed changes in this action, that an air agency include in its demonstr ation to justify data ex clusion evidence that the following statutory technical criteria are satisfied: (A) The event was a human activity that is unlik ely to recur at a pa rticular location or was a natural event. (B) The event was not reasonably controllable or preventable. (C) The event affected air quality in such a way that there exists a clear causal relationship between the specific event a nd the monitored exceedance or violation (supported in part by the comparison to historical concentrations and other analyses).*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 180 of 218 The EPA seeks comments on the identified prop osed changes to the language at 40 CFR 50.14(c)(3)(i), (iv) and (v), which more clearly identify the required elements of an exceptional events demonstration. The EPA notes that the recent final rule to revise the ozone NAAQS also removed and reserved the subsequent sectio ns at 40 CFR 50.14(c)(3)(ii) and (c)(3)(iii), which addressed the submittal of exceptional events demonstrations that could affect regulatory determinations associated with initial area designations for the 2006 24-hour PM 2.5 NAAQS and the 2010 Lead NAAQS and were made obsolete by the passage of time. The EPA will retain these removed and reserved sections as promulgated in the oz one NAAQS and proposes no additional changes to this language. 7. Timing of the EPA’s Review of Submitted Demonstrations a. Current Situation Since promulgation of the Exceptional Ev ents Rule in 2007, stakeholders have questioned the process by which the EPA reviews submitted demonstrations. 137 Specifically, stakeholders have expressed concern that the EPA has a backlog of submittals but acts only on EPA-prioritized packages. Stakeholders have st ated that because the EPA has not acted on all submissions, the air quality values used for planning and regulatory purposes are higher than they would be if the effects of non-controllable emissions were removed from the data set. Air agencies have also noted that without fee dback, they do not know the EPA’s expectations regarding future submittals.

137 See comment letters in Docket ID No. EPA- HQ-OAR-2011-0887 for the July 2012 notice of availability for the Draft Ex ceptional Events Implementation Guidance, which the EPA has incorporated into the record for this action.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 181 of 218 The EPA addressed these quest ions and comments in the Interim Exceptional Events Implementation Guidance. In Question 27 of the Interim Q&A document, the EPA identified the general process and timing for demonstration revi ews. In this document, the EPA clarified the process by which it prioritizes submittals and indicat ed that we may not act on submittals with no regulatory significance. The guidanc e also presented the voluntary Letter of Intent concept as a mechanism to aid in planning and prioritization. Add itionally, we stated that we intend to make a decision regarding concurrence with an air agency’s request to exclude data as expeditiously as necessary following submittal of a complete package if required by a near-term regulatory action. We also indicated our intent to comm unicate with the submitting agency, as needed, during the demonstration review period. b. Proposed Changes In this proposal, the EPA is clarifying some of our previous statements regarding the prioritization and submittal of demonstrations. As noted in several subs ections within section V.G of this proposal, we also propose to codify in regulatory language approaches to increase the efficiency of preparing, submitting and review ing exceptional events demonstrations. Although the EPA is not proposing to codify in regulator y language any changes pe rtaining to the timing of the EPA review process, the EPA offers the following discussion to clarify expectations and facilitate communications, which are at the center of timing-related issues. As noted in the Interim Exceptional Events Implementation Guidance and in the EPA’s best practices discussions described in section IV.E, the EPA is committed to working with air agencies as they prepare complete demons tration packages. The EPA encourages ongoing discussions between the reviewing EPA regional office and the submitting air agency from the onset of the Initial Notificati on of Potential Exceptional Event process through official package*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 182 of 218 submittal. Since renewing our focus on improved communications, the EPA has received positive feedback from engaged agencies that have used this approach. Additionally, these communications have resulted in decreased instan ces of submissions containing insufficient or unnecessary information. In reviewing submitted demonstration packages , the EPA will generally give priority to exceptional events determinations that may aff ect near-term regulatory decisions, such as EPA action on SIP submittals, NAAQS designations and clean data determinations. The EPA intends to make a decision regarding event status e xpeditiously following submittal of a complete package if required by a near-term regulatory action. If during the re view process the EPA identifies the need for additional information to determine whether the exceptional events criteria are met, the EPA will notify the submitting air agen cy and encourage the agency to provide the supplemental information. If the information need ed is minor and a natural outgrowth of what was previously submitted, the EPA will not requ ire the air agency to undergo an additional public notice and comment process. However, if the needed information is significant, the EPA may request that the air agency re-notice the de monstration before resubmitting it to the EPA, thus requiring an additional EPA review following resubmittal. The EPA will work with air agencies on supplemental timeframes; however, the mandatory timing of the EPA actions may limit the response time the EPA allows. The EPA propos es to include as rule text a requirement for the air agency to submit additional information within 12 months. If additional information is not received in 12 months, then the EPA will c onsider the submitted demonstration inactive, and will not continue the review or ta ke action. In effect, an air agen cy’s lack of response within a 12-month period will “void” the submittal. In these cases, the EPA does not intend to issue a formal notice of deferral. If the air agency late r decides to pursue the exceptional events claim*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 183 of 218 after a 12-month period of inactivity, it may re -initiate the excepti onal events process by submitting a new Initial Notification of Po tential Exceptional Event followed by a new demonstration, which could simply be revising th e original submittal to include the additional information previously requested by the EPA. At the conclusion of the EPA’s review, the EPA will make a determination regarding the status of a submitted exceptional events dem onstration. The EPA’s decision could result in concurrence, nonconcurrence or deferral. 138 In acting on a submitted demonstration covering multiple event days and/or multiple flags, the EPA could concur with part of a demonstration and nonconcur or defer other flagged values. If the EP A determines that the events addressed in an exceptional events demonstration are not anticipate d to affect any future regulatory decision, the EPA could defer review of these events and notif y the submitting agency if a subsequent review results in a determination that the events do affect a regulatory decision. 139 Formal mechanisms for deferral could include the EPA’ s indicating this decision by le tter, by email to a responsible official or during a high-level meeting with an attendees’ list and discussion summary. 8. Dispute Resolution Mechanisms Since promulgation of the 2007 Exceptional Ev ents Rule and through the development of the Interim Exceptional Events Implementation Guid ance, some interested parties have asked the EPA to identify a process by which submitting ai r agencies can formally dispute the EPA’s decision regarding requests for additional info rmation to support submitted demonstration

138 The EPA anticipates a reduced number of deferrals and/or nonconcurrences for demonstrations associated with the Initial Notification of Poten tial Exceptional Event process as discussed in section V.G.5 because the EPA and the affected air agency would have discussed issues/concerns prior to the EPA’s d ecision on a submitted demonstration. 139 Routine status calls between the reviewing EP A regional office and air agencies could include an agenda item to review the status of all s ubmitted demonstrations, including those that the EPA has deferred.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 184 of 218 packages and/or decisions regarding concurrence, nonconcurrence or deferral of submitted demonstration packages. While the EPA acknowledge s the expressed concerns and desire for a formally identified dispute resolution process, the EPA also believes that several mechanisms currently exist that air agencies can use at vari ous points in the exceptiona l events process. These mechanisms include engaging in early dialogue with the reviewing EPA regional office, submitting requests for reconsideration to the official who made the determination if a request identifies a clear error or if the reviewing EPA regional office overlooked information submitted by the affected air agency, and/or elevating the concern within the EPA’s chain of command. Additionally, air agencies can ra ise any unresolved event-related issues during the regulatory process that relies upon the claimed event-influe nced data by participa ting in related public notice and comment processes and/or challenging in an appropriate court the regulatory decision subsequently made based in part on the EPA’s exceptional events determ ination. These currently available dispute resolution approaches to addr ess exceptional events decisions are consistent with the mechanisms available for other EPA actions. With exceptional events decisions, however, the air agency has oppor tunities to elevate concerns during two processes: the exceptional events determination and the subs equent regulatory act ion that relies on the exceptional events decision. The EPA believes that the existing mechanisms identified above combined with the EPA’s commitment to focus on communication and collaboration with the submitting air agency through the exceptional events dem onstration process, and the clar ifications that would be in effect with these proposed revisions to th e 2007 Exceptional Events Rule and associated guidance, will avoid the need for a formal dis pute resolution mechanism for exceptional events.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 185 of 218 Therefore, the EPA does not intend to address dispute resolution within these proposed rule revisions and does not intend to respond to comments on this issue. VI. Mitigation
A. Current Situation Section 319(b)(3)(A) of the CAA identifies five principles for the EPA to follow in developing implementing regulations for exceptional events: (i) Protection of public health is the highest priority; (ii) Timely information should be provided to the public in any case in which the air quality is unhealthy; (iii) All ambient air quality data should be included in a timely manner in an appropriate Federal air qu ality database that is accessible to the public; (iv) Each state must take necessary measures to safeguard public health regardless of the source of the air pollution; and (v) Air quality data should be carefully screen ed to ensure that events not likely to recur are represented accurately in all monitoring data and analyses. The regulatory requirements implementing (iii) and (v) of this part of the statute are found only in 40 CFR 50.14 while the regulatory requirements implementing (i) and (iv) are found only in 40 CFR 51.930, Mitigation of Excep tional Events. Both section 50.14(c)(1) and section 51.930(a)(1) require states to provide notice of events to the public (the second of the five principles). The language at 40 CFR 51.930 requires air agenci es requesting data exclusion to “take appropriate and reasonable actions to protect public health from exceedances or violations of the NAAQS” and at a minimum do each of the following:*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 186 of 218  Provide for prompt public notification when ever air quality c oncentrations exceed or are expected to exceed the NAAQS.

 Provide for public education concerning act ions that individuals may take to reduce exposures to unhealt hy levels of air quality during and following an exceptional event.

 Provide for the implementation of appropria te measures to protect public health from exceedances or violations of ambient air quality standards caused by exceptional events. The EPA promulgated the existing requireme nts in 2007 after considering and proposing several approaches to implementing CAA s ection 319(b)(3)(A). Some of the proposed approaches would have established a more formal structure by which air agencies prepared and submitted to the EPA mitigation plans to protect public health during events. These plans would have been subject to the EPA’s approval and/or the approval of th e exclusion of event-affected data would have been contingent on the appr oval of such a plan. Comments on these proposed options varied widely. 140,141 In the final 2007 rule, “mitigation” measures 142 became part of the 2007 Exceptional Events Rule, but they were not incorporated in to the criteria and processes by which data are excluded from use in regulatory determinati ons. There is no requirement to submit such

140 The Treatment of Data Influenced by Exceptional Events; Proposed Rule, 71 FR 12592 (March 10, 2006). 141 See Comments and Responses related to “Requi rements for States To Provide Public Notification, Public Education, and Appropriate and Reasonable Measures To Protect Public Health” in Treatment of Data influenced by Exceptional Events; Final Rule, 72 FR 13574-13576 (March 22, 2007). 142 The term “mitigation” does not appear in CAA section 319(b). It appear s in the title but not the text of 40 CFR 51.930.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 187 of 218 measures to the EPA for either prospective or retrospective review a nd approval as a condition for approval for exclusion of event-affected data . Neither are air agencies required to notify the EPA of the measures an air agen cy plans to take or has take n. In the preamble to the 2007 Exceptional Events Rule, we stated that stat es should take “reas onable and appropriate measures” to protect public health related to th e occurrence of an event and that states should determine what measures constitute thos e that are “reasonable and appropriate.” 143 We did not clarify how measures should be determ ined to be “appropriate” measures. The mitigation measures that the EPA sees states most commonly practicing are ones related to the requirement that air agencies “provide for prompt public notification whenever air quality concentrations exceed or are expected to exceed the NAAQS.” Often, these public notifications include public health alerts for high wind dust even ts or wildfires. We believe that other aspects of mitigation, including implementing appropriate measures to protect public health beyond notification, are also important in impl ementing the CAA guiding principle that “each State must take necessary measures to safeguard public health regardless of the source of the air pollution.” B. Proposed Changes Given the EPA’s and the states’ experien ce implementing the 2007 Exceptional Events Rule as indicated above, we consider it appropriate to consider possible changes to the mitigation-related rule components with the bene fit of additional public input. We are seeking comment on approaches ranging fr om retaining the existing rule requirements at 40 CFR 51.930 to the various possible new com ponents described in this section. We invite comment on these alternatives and on other concepts. We may make no change; we may adopt all of the described

143 72 FR 13574 (March 22, 2007).*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 188 of 218 new components; or we may adopt only some feat ures or variations of the described options. Note that we are not considering requiring all st ates to develop formal mitigation plans. We are seeking comment on the concept of only some states being required to develop mitigation plans for their particular “historically documented” or “known seasonal” exceptional events, defined below in section VI.B.1; on recommended elements for such mitigation plans described below in section VI.B.2; and on options for implementing mitigation plans descri bed in section VI.B.3. Section VI.B.4 summarizes the EP A’s potential options for mitigation elements for exceptional events purposes. 1. Defining Historically Document ed or Known Seasonal Events The EPA seeks comment on whether an air ag ency should develop a mitigation plan for its particular type of “histori cally documented” or “known seasona l” exceptional events, if any. The EPA would consider “historically documented” or “known seasonal” exceptional events to include events of the same type and pollutant ( e.g ., high wind dust/PM or wildfire/ozone) that meet any of the following criteria: an event for which an air agency has previously submitted exceptional events demonstrations; an event that an air agency has previously flagged for concurrence in AQS (regardless of whether the air agency submitted a demonstration); or an event that has been the subject of local news articles, public health alerts or published scientific journal articles. The EPA would not require an air agency to develop a mitigation plan for the first event of a given type ( e.g ., if an area is prone to wildfire s but has never experienced a high wind dust event, then it would not be expected to develop a mitigation plan for its first high wind dust event, but it would be expected to develop a mitigation plan for wildfires). A second event of a given type within a 3-year period would subj ect the area to “having a history” and, therefore,*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 189 of 218 needing a mitigation plan. 144 This option avoids plan development for a one-of-a-kind

occurrence. 145 In defining “first” and “second” events, th e EPA could consider events that affect the same AQCR, but not neces sarily the same monitor. 146 For example, high wind dust events occur seasonally in the Phoenix, Arizona metropo litan area, which is part of the Maricopa Intrastate Air Quality Control Region ( see 40 CFR 81.36). These events have influenced particulate matter concentrations at multiple m onitors within the Maricopa Intrastate AQCR. Under this proposal, high wi nd dust events in Phoenix ( i.e ., the Maricopa Intrastate AQCR) are known events requiring a mitigation plan. On the other hand, a high wind dust event in Sedona, Arizona, part of the Northern Arizona Intrastate Air Quality Control Region ( see 40 CFR 81.270), would be a first event and not subject to the development of a mitigation plan. As a variation of this concept on whic h we also seek comment, the EP A could consider a first season of events as one of three required seasons of ev ents, so that a mitigation plan would be required only when an event type persists across severa l years. For example, an area may not have previously experienced wildfires in the past 10 y ears, but then experiences multiple wildfires and multiple exceedances in a single wildfire season. If these multiple wildfires affect the same general geographic area and monitors in a relatively short period of time ( e.g . 2-3 months), then they could be considered a single event for purposes of developing a mitigation plan and would not trigger the requirement for a mitigation plan.

144 A 3-year period is determined based on the submittal date of an exceptional events demonstration. 145 Because the form of the NAAQS varies by polluta nt, it is possible that multiple events in a 3- year period may not cause a NAAQS violation. An air agency that identifies multiple events of the same type ( e.g ., wildfire/ozone) in AQS, but prepares and submits a demonstration for only one of these events, would trigger the proposed requirement to develop a mitigation plan. 146 Air Quality Control Regions are defined in 40 CFR part 81, subpart B, Designation of Air Quality Control Regions.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 190 of 218 2. Mitigation Plan Components The EPA solicits comment on the following three plan components that could be recommended or required in order to implem ent the mitigation principles found in section 319(b)(3)(A) of the CAA: public notification and education; steps to identify, study and implement mitigating measures and provision for periodic revision of the mitigation plan (to include public review of plan elements). This se ction discusses these elements in more detail. A mitigation plan should address actions that woul d be taken within a state’s own territory for events that happen within its own territo ry or that of another jurisdiction.

a. Public notification to and e ducation programs for affected or potentially affected communities. Air agencies could be required or encouraged to include in their mitigation plans steps to activate public notification and education systems whenever air quality concentrations exceed or are expected to exceed an applicable national ambient air quality standard. If possible, air agencies would notify the public of the actual or anticipated event at least 48 hours in advance of the event using methods appropriate to the community being served. Outreach mech anisms could include website alerts, National Weather Service alerts, telephone or te xt bulletins, televisi on or radio campaigns or other messaging campaigns. Public notif ication and education programs could be encouraged or required to include some or all of the following actions to support the outreach system: adoption of methods for forecasting/detection, consultation with appropriate health department personnel re garding issuing health advisories and suggested actions for exposure mini mization for sensitive populations ( e.g ., remain indoors, avoid vigorous outdoor activity, av oid exposure to tobacco smoke and other respiratory irritants and, in extreme cases, evacuation or public sh eltering procedures).*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 191 of 218 b. Steps to identify, study and implement mitigat ing measures, including approaches to address each of the following: (i) Mandatory or voluntary measures to abat e or minimize contributing controllable sources of identified pollutants. A st ate could be required to include or encouraged to consider full-time or con tingent controls on ev ent-related sources as well as non-event related sources. For example, these measures might include continuously operating control measures during an extreme event for identified sources that normally operate these same controls on an intermittent basis. It could also involve including work practices ( e.g ., water spray for dust suppression) or contingent limits duri ng extreme events on emissions from nonevent related sources that , under non-event periods, have no or less stringent emissions limits or work practices. (ii) Methods to minimize public exposure to high concentratio ns of identified pollutants. (iii) Processes to collect and maintain data pertinent to the event ( e.g ., to identify the data to be collected, the party responsibl e for collecting and maintaining the data and when, how and to whom the data will be reported). (iv) Mechanisms to consult with other air qua lity managers in the affected area regarding the appropriate responses to abate and minimize im pacts. Consultation could include collaboration between potenti ally affected local, state, tribal and federal air quality managers and/ or emergency response personnel.

c. Provision for periodic review and eval uation of the mitigation plan and its implementation and effectiveness by the air agency and all interested stakeholders ( e.g .,*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 192 of 218 public and private land owners/managers, air quality, agriculture and forestry agencies, the public). For example, air agencies could be required to use this review process and to revise, if appropriate, and certify the mitigati on plan every 3 years or every three events, whichever is longer. The air ag ency could be required to submit a summary and response to the comments received during the public pl an review process to the EPA along with the recertification statement and/or revised mitigation plan. If the historically documented or known seasonal exceptional events continue to result in elevated pollutant concentrations above the relevant NAAQS, thus showing that the combination of the existing SIP and the existing mitigation plan does not effectively safeguard public health, the mitigation plan might need to be strengthened during this review. If the EPA adopts requirements like those desc ribed above, it would not necessarily mean that all affected air agencies would have to pr epare new plans. If an air agency has developed and implemented a contingency plan under 40 CFR part 51, subpart H, Prevention of Air Pollution Emergency Episodes, that meets the requirements of 40 CFR 51.152, and that includes provisions for events that coul d be considered “exceptional ev ents” under the provisions in 40 CFR 50.14, then the subpart H contingency plan w ould likely satisfy the mitigation requirements described above. If the identif ied basic elements are include d and addressed, including the element for public comment, then other types of existing mitigation or contingency plans may satisfy the possible mitigation plan requirement described above. For example, if an area has developed a natural events ac tion plan or a high wind action plan covering high wind dust events, this plan likely would satisfy mitig ation elements for high wind dust events. Smoke management plans and/or forest management plan s might also satisfy the mitigation elements for prescribed fires and wildfires. Most air agencies generally have sufficien t, established processes*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 193 of 218 that meet the public notification and education element, which can be easily adapted or modified to meet the mitigation elements proposed in th is action. The EPA is re questing comment on how much time air agencies should be allowed to develop a plan. 3. Options for Implementing Mitigation Plans The EPA is seeking comment on two options for tying the proposed mitigation plan components discussed in section VI.B.2 to the EP A review of exceptional events demonstrations. Option 1 includes the EPA’s review for comp leteness but not substantive approval or disapproval, while Option 2 includes the EPA’s approval of the substance of the mitigation plan. These options are discussed below in more deta il, but neither option would require a mitigation plan to be included in a SIP or to be otherwise federally-enforceable. Under both options, air agencies with hi storically documented or known seasonal exceptional events could submit the mitigation plan to the EPA in advance of an event, or submit a mitigation plan along with an exceptional events demonstration. The EPA would concur with a demonstration for the relevant event type only if a mitigation plan has passed the type of EPA review described in the option. Gi ven that the air agency would ha ve advance notification of the need to develop a plan, the air agency could de velop and submit the mitigation plan in advance of any exceptional events demonstration so that the EPA could pre-review the mitigation plan and take faster action on an exceptional events submittal once one is submitted. Option 1 : Under this option, the EPA would review for inclusion of required elements as described above and to ensure that the development of the mitigation plan included a public comment process. We would not formally review the substance of the plan in the sense of approving the details of th e specific measures and commitments in the plan.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 194 of 218 Option 2 : Under this option, EPA approval of the substance of the mitigation plan would be a precondition for EPA concurrence on an ex ceptional events demonstration. Because the EPA would approve the content, completeness and sufficiency of a mitigation plan, the EPA’s disapproval of the plan could result in the EPA’s nonconcurre nce on a current or future exceptional events demonstration. VII. Draft Guidance on the Prep aration of Exceptional Events Demonstrations for Wildfire Events that May Influen ce Ozone Concentrations A. What is this draft guidance about and why is it needed? The Exceptional Events Rule contains the re gulatory requirements and criteria necessary for the EPA’s approval of the exclusion of air quality data from regulatory determinations related to NAAQS exceedances or violations. During the implementation of the 2007 Exceptional Events Rule, the EPA and stakeholders have iden tified a need for implementation guidance that provides an interpretation of and examples for addressing the regulatory re quirements specific to the most common event types. One event type that has been identified by the EPA and stakeholders is wildfire influence on ozone concentrations. In 2013, the EPA finalized the Interim Exceptional Events Implementation Guidance documents ( see section IV.D), which included the Interim High Winds Guidance docum ent and an Interim Overview document that also committed to the preparation of a Draf t Wildfire Ozone Guidance document. The EPA intends to address this ne ed and commitment via the Draft Guidance on the Preparation of Exceptional Events Demonstrations for W ildfire Events that May Influence Ozone
Concentrations (“Draft Wildfire Ozone Guidance documen t”), which accompanies this proposed rule and is also available for comment.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 195 of 218 This Draft Wildfire Ozone Guidance document includes example analyses, conclusion statements and technical tools that air agencies can use to provide evidence that the wildfire event influenced the monitored ozone concen tration. The Draft Wildfire Ozone Guidance document also identifies fire a nd monitor-based characteristics that might allow for a simpler and less resource-consuming demonstration package. The EPA has developed the Draft Wildfire Ozone Guidance document concurrently with the proposed Exceptional Events Rule revisions so that the Draft Wildfire Ozone Guidance reflects the proposed rule changes. Once finalized, this guidance will provide the EPA regional offices and air agencies with guidance on how to prepare and submit evidence to meet the Exceptional Ev ents Rule requirements for monitored ozone exceedances caused by wildfires. The guidance, when finalized, will not be an EPA rule, and in specific cases the EPA may depart from the guidan ce for reasons that the EPA will explain at the time of the action. B. What scenarios are addre ssed in the draft guidance? The EPA has prepared the Draft Wildfire Ozone Guidance document to provide assistance and example analyses for wildfire ev ents that may influence ozone concentrations. Though many of the technical analyses included in the draft document may also be applied to prescribed fire events, the dr aft guidance document available fo r comment at this time does not provide guidance specific on how prescribed fire events ca n address all proposed rule requirements. Limiting the scope to wildfire events is intended to make the document easier to use for wildfire events. With this notice, th e EPA invites comment on the content of this guidance document and whether it is appropriate to expand the scope of the guidance to include prescribed fire events. If commenters believe it is necessary to expand the scope of the EPA’s final new guidance beyond the scope of the Draf t Wildfire Ozone Guidance document, the EPA*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 196 of 218 seeks comment on whether wildfire and prescribed fire events should be addressed in a single fire ozone guidance document or in separate guidance documents. VIII. Environmental Justice Considerations The Exceptional Events Rule provides the crit eria by which state, local and tribal air agencies identify air quality data they believe have been influenced by exceptional events, which by statutory definition are not reas onably controllable or preventable. Because these events are not reasonable to prevent or control, they can affect all downwind popula tions including minority and low-income populations. For this reason, in adding section 319(b) to the CAA, Congress identified as a guiding principle in developing regulations, “the pr inciple that protection of public health is the highest priorit y.” The 2007 Exceptional Events Rule at 40 CFR 50.14 requires air agencies to seek public comment on prepared exceptional events dem onstrations prior to submitting them to the reviewing EPA regional office. The public can also comment on rulemakings that include decisions related to the exclusion of event- influenced data. The mitigation of exceptional events language at 40 CFR 51.930 also requires that air agencies provide public notification and e ducation programs related to even ts. To protect all people and communities, notably minority and low-income populations, air agencies should ensure that notifications and education programs ar e communicated using the language ( e.g ., English and Spanish) and media ( e.g ., radio and postings in local community centers) best suited to the target audience(s). Additionally, these proposed revisions are part of a public notice-and-comment rulemaking effort, which will include a public he aring. These opportunities for public input and education ensure that all those residing, working, attending school or otherwise present in areas affected by exceptional events, regardless of minority and economic status, are protected. IX. Statutory and Executive Order Reviews*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 197 of 218 A. Executive Order 12866: Regulatory Planning and Review and Executive Order 13563: Improving Regulation and Regulatory Review This action is a significant regulatory action that was submitted to the Office of Management and Budget (OMB) for review because it raises novel policy issues. Any changes made in response to OMB recommendations have been documented in the docket.
B. Paperwork Reduction Act This action does not impose any new info rmation collection burden under the PRA. The information being requested under these proposed rule revisions is consistent with current requirements related to information needed to verify the authenticity of monitoring data submitted to the EPA’s AQS database, and to justify exclusion of data that have been flagged as being affected by exceptional events. OMB has pr eviously approved the information collection activities for ambient air mon itoring data and other supporting measurements reporting and recordkeeping activities associated with the 40 CFR part 58 Ambient Air Quality Surveillance rule and has assigned OMB control number 2060-0084.
C. Regulatory Flexibility Act I certify that this action will not have a significant economic impact on a substantial number of small entities under the RFA. This action will not impose any requirements on small entities. Instead, the proposed rule revisions provide the criteria a nd increase the efficiency of the process by which state, local and tribal air agencies identify air quality data they believe have been influenced by an exceptional event. The pro posed rule revisions also clarify those actions that state, local and tribal ai r agencies should take to protect public health during and following an exceptional event. Because affected air agenci es would have discretion to implement controls on sources that may need to be regulated due to anthropogenic contribution in the area*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 198 of 218 determined to be influenced by an exceptional ev ent, the EPA cannot predic t the indirect effect of the rule on sources that may be small entities. D. Unfunded Mandates Reform Act This action does not contain an unfunded manda te of $100 million or more as described in UMRA, 2 U.S.C. 1531–1538, and does not significantly or uniquely affect small governments. The action imposes no enforceable duty on any state, local or tribal governments or the private sector.
E. Executive Order 13132: Federalism This action does not have federalism implica tions. The EPA believes, however, that this action may be of significant interest to states and to local air quali ty agencies to whom a state has delegated relevant responsibiliti es for air quality management. C onsistent with the EPA’s policy to promote communications between the EPA and state and local governments, the EPA consulted with representatives of state and loca l governments early in the process of developing this action to permit them to have meaningful and timely input into its development. A summary of the concerns raised during th at consultation is provided in s ection IV of this preamble.
F. Executive Order 13175: Consultation and Coor dination with Indian Tribal Governments This action does not have tribal implicati ons as specified in Executive Order 13175. It would not have a substantial dir ect effect on one or more Indi an tribes. Furthermore, these proposed regulation revisions do not affect th e relationship or dist ribution of power and responsibilities between the federal government and Indian tribes. The CAA and the Tribal Air Rule establish the relationship of the federal gove rnment and tribes in characterizing air quality and developing plans to attain the NAAQS, and these revisions to the regulations do nothing to modify that relationship. Thus, Executive Order 13175 does not appl y to this action.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 199 of 218 Although Executive Order 13175 does not apply to this action, the EPA held public meetings attended by tribal representatives and sepa rate meetings with tribal representatives to discuss the revisions proposed in this action. The EPA also pr ovided an opportunity for all interested parties to provide oral or writte n comments on potential concepts for the EPA to address during the rule revision process. Summaries of these meetings are included in the docket for this proposed rule. The EPA specifically soli cits additional comment on this proposed action from tribal officials. G. Executive Order 13045: Protection of Children from Environmental Health & Safety Risks The EPA interprets Executive Order 13045 as applying only to those regulatory actions that concern environmental health or safety risks that the EPA has reason to believe may disproportionately affect childre n, per the definition of “covered regulatory action” in section 2- 202 of the Executive Order. This action is not subject to Executiv e Order 13045 because it does not concern an environmental h ealth risk or safety risk. H. Executive Order 13211: Actions Concerning Regu lations That Significantly Affect Energy Supply, Distribution or Use This action is not a “significant energy action” because it is not likely to have a significant adverse effect on the supply, distri bution or use of energy. The purpose of this proposed rule is to provide the criteria, and increa se the efficiency of the process, by which state, local and tribal air agencies may identify air qualit y data they believe have been influenced by an exceptional event. The EPA does not expect th ese activities to aff ect energy suppliers, distributors or users. I. National Technology Transfer and Advancement Act This rulemaking does not invol ve technical standards.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 200 of 218 J. Executive Order 12898: Federal Actions to Address Environmental Justice in Minority Populations and Low-Income Populations The EPA believes the human health or envir onmental risk addresse d by this action will not have potential disproportionate ly high and adverse human health or environmental effects on minority, low-income or indigenous populations. The results of this evaluation are contained in the section of the preamble titled “Environmen tal Justice.” This proposed action provides the criteria and increases the efficiency of the proc ess by which state, local and tribal air agencies identify air quality data they believe have been influenced by exceptional events, which by statutory definition, are not reasonably controlla ble or preventable. Th ese proposed regulatory provisions do, however, provide information concer ning actions that state, local or tribal air agencies might take to uniformly protect public health once the EPA has concurred with an air agency’s request to exclude data influenced by an exceptional event. The mitigation component of the proposed rule could ultimately provide ad ditional protection for minority, low income and other populations locat ed in areas affected by exceptional ev ents. Therefore, the EPA finds that this proposed action would not adve rsely affect the health or safe ty of minority or low-income populations, and that it is designe d to protect and enhance the h ealth and safety of these and other populations. X. Statutory Authority The statutory authority for this action is provided by 42 U.S.C. 7401, et seq

.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 201 of 218 Page 201 of 218 - Treatment of Data Influenced by Ex ceptional Events – Rule Revisions and Notice of Availability for Related Draft Guidance

List of Subjects in 40 CFR Part 50 Environmental protection, Air pollution cont rol, National parks, Wilderness areas.

__________________________________ Dated:

__________________________________ Gina McCarthy, Administrator.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 202 of 218 For the reasons set forth in the prea mble, it is proposed that 40 CFR part 50 be amended as follows: PART 50--NATIONAL PRIMARY AND SECONDARY AMBIENT AIR QUALITY STANDARDS 1. The authority citation for part 50 continues to read as follows: Authority: 42 U.S.C. 7401, et seq

. 2. Amend §50.1 by:

a. Revising paragraphs (j) and (k). b. Adding paragraphs (m), (n), (o), (p), (q) and (r). §50.1 Definitions. * * * * * (j) Exceptional event means an event and its resulting emissi ons that affect air quality in such a way that there exists a clear causal relationshi p between the specific event and the monitored exceedance or violation, is not reasonably cont rollable or preventable, is an event caused by human activity that is unlikely to recur at a pa rticular location or a natural event, and is determined by the Administrator in accordance w ith 40 CFR 50.14 to be an exceptional event. It does not include stagnation of air masses or me teorological inversions, a meteorological event involving high temperatures or lack of precipitation, or air pollution relating to source noncompliance. (k) Natural event means an event and its resulting emi ssions, which may recur, in which human activity plays little or no direct causal role. Anthropogenic sour ces that are reas onably controlled shall be considered to not play a direct role in causing emissions.
***** (m) Prescribed fire is any fire intentionally ignited by management actions in accordance with*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 203 of 218 applicable laws, policies, and regulations to meet specific land or resource management objectives. (n) Wildfir e is any fire started by an unplanned i gnition caused by lightning; volcanoes; other acts of nature; unauthorized activit y; or accidental, human-caused actions, or a prescribed fire that has been declared to be a wildfire. A wild fire that predominantly occurs on wildland is a natural event. (o) Wildland means an area in which human activity and development is essentially non-existent, except for roads, railroads, power lines, and similar transportation facilities. Structures, if any, are widely scattered. (p) High wind dust event is an event that includes the high -speed wind and the dust that the wind entrains and transports to a monitoring site. (q) High wind threshold is the minimum wind speed capab le of causing particulate matter emissions from natural undisturbed lands in the area affected by a high wind dust event. (r) Federal land manager means, consistent with the de finition in 40 CFR 51.301, the Secretary of the department with authority over the Federa l Class I area (or the Secretary’s designee) or, with respect to Roosevelt-Campobello Internat ional Park, the Chairman of the RooseveltCampobello International Park Commission. 3. Revise §50.14 to read as follows: §50.14 Treatment of air quality monitoring data influenced by exceptional events. (a) Requirements . (1) Scope . (i) This section applies to the treatment of data showing exceedances or violations of any national ambi ent air quality standard for purposes of the following types of regulatory determ inations by the Administrator: (A) An action to designate an area, pursuant to Clean Air Act section*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 204 of 218 107(d)(1), or redesignate an area, pursuant to Clean Air Act section 107(d)(3), for a particular national ambient air quality standard; (B) The assignment or re-assignment of a classification category to a nonattainment area where such classi fication is based on a comparison of pollutant design values, cal culated according to the specific data handling procedures in 40 CFR part 50 for each na tional ambient air quality standard, to the level of the relevant national ambient air quality standard; (C) A determination regarding whethe r a nonattainment area has attained the level of the appropriate national ambi ent air quality standard by its specified deadline; (D) A determination that an area has had only one exceedance in the year prior to its attainment d eadline and thus qualifies for a 1-year attainment date extension, if a pplicable; and (E) A determination under Clean Air Ac t section 110(k)(5), if based on an area violating a national ambient air quality standard, that the state implementation plan is inadequate to the requirements of Clean Air Act section
110. (ii) A State, federal land mana ger or other federal agency may request the Administrator to exclude data showing exceedances or violations of any national ambient air quality standard that are directly due to an exceptional event from use in determinations by demonstrating to the Administrator’s satisfaction that such event caused a specific air pollution con centration at a particular air quality monitoring location.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 205 of 218 (A) For a federal land manager or ot her federal agency to be eligible to initiate such a request for data exclusi on, the federal land manager or other federal agency must (i) either operate a regulato ry monitor that has been affected by an exceptional event or manage land on whic h an exceptional event occurred that influenced a monitored concentration at a re gulatory monitor, and (ii) initiate such a request only after discussing such submittal with the State in which the affected monitor is located, and (B) When initiating such a request, all provisions in this section that are expressed as requirements applying to a State shall, except as noted, be requirements applying to the federal la nd manager or other federal agency. (2) A demonstration to justify data exclusion may include any reliable and accurate data, but must specifically address the elements in pa ragraphs (c)(3)(iv) and (c)(3)(v) of this section. (b) Determinations by the Administrator . (1) Generally . The Administrator shall exclude data from use in determinations of exceedances and violations where a State demonstrates to the Administrator’s satisfaction that an excep tional event caused a specific air pollution concentration in excess of one or more national ambient air quality standards at a particular air quality monitoring location and otherwise sati sfies the requirements of this section. (2) Fireworks displays . The Administrator shall exclude data from use in determinations of exceedances and violations where a State demons trates to the Administrator’s satisfaction that emissions from fireworks displays cau sed a specific air pollution concentration in excess of one or more national ambient air qua lity standards at a pa rticular air quality monitoring location and otherwise satisfies the requirements of this section. Such data will*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 206 of 218 be treated in the same manner as excepti onal events under this rule, provided a State demonstrates that such use of fireworks is significantly integral to traditional national, ethnic, or other cultural events including, but not limited to, Ju ly Fourth celebrations that satisfy the requirement s of this section. (3) Prescribed fires . (i) The Administrator shall exclude da ta from use in determinations of exceedances and violations, where a State demonstrates to the Administrator’s satisfaction that emissions from prescrib ed fires caused a specific air pollution concentration in excess of one or more na tional ambient air quality standards at a particular air quality monitoring location and otherwise satisfies the requirements of this section. (ii) In addressing the requirements set fort h in paragraph (c)(3)(iv )(D) of this section regarding the not reasonably cont rollable or preventable criterion: (A) With respect to the requirement that a prescribed fire be not reasonably controllable, the State must eith er certify to the Administrator that it has adopted and is implementing a smoke management plan or the State must demonstrate that the burn manager empl oyed the generally applicable basic smoke management practices identifie d in Table 1. To make the latter demonstration, the State may rely on a st atement or other documentation provided by the burn manager that he or she empl oyed those practices. If an exceptional event occurs using the basic smoke mana gement practices approach, the State must undertake a review of its approach to ensure public health is being protected. (B) With respect to the requirement that a prescribed fire be not reasonably preventable, provi ded the Administrator dete rmines that there is no*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 207 of 218 compelling evidence to the contrary in the record, the State may rely upon and reference a multi-year land or resource ma nagement plan for a wildland area with a stated objective to establish, restore and/ or maintain a sustainable and resilient wildland ecosystem and/or to preserve e ndangered or threatened species through a program of prescribed fire, but also provide d that the use of pres cribed fire in the area has not exceeded the frequenc y indicated in that plan. (iii) Provided the Administrator determines that there is no compelling evidence to the contrary in the record, in addressing the requirements set forth in paragraph (c)(3)(iv)(E) of this section regarding th e human activity unlikely to recur at a particular location criterion for demons trations involving pr escribed fires on wildland, the State must describe the actual frequency with which a burn was conducted, but may rely upon and reference an assessment of the natural fire return interval or the prescribed fire fre quency needed to establish, restore, and/or maintain a sustainable and resilient wild land ecosystem contained in a multi-year land or resource management plan with a stated objective to establish, restore, and/or maintain a sustainable and resilient wildland ecosystem and/or to preserve endangered or threatened species th rough a program of prescribed fire. Table 1. Summary of Basic Smoke Management Practices, benefit achieved with the BSMP, and when it is applied (before, during or after ignition of the burn). a Basic Smoke Management Practice Benefit achieved with the BSMP When the BSMP is Applied – Before/During/After the Burn Evaluate Smoke Dispersion Conditions Minimize smoke impacts Before, During, After
Monitor Effects on Air Quality Be aware of where the smoke is going and degree it impacts air quality Before, During, After

Record-Keeping/Maintain a Burn/Smoke Journal Retain information about the weather, burn and smoke. If air Before, During, After*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 208 of 218 Basic Smoke Management Practice Benefit achieved with the BSMP When the BSMP is Applied – Before/During/After the Burn quality problems occur, documentation helps analyze and address air regulatory issues Communication – Public Notification Notify neighbors and those potentially impacted by smoke, especially sensitive receptors Before, During

Consider Emission Reduction Techniques Reducing emissions through mechanisms such as reducing fuel loading can reduce downwind impacts Before, During, After

Share the Airshed – Coordination of Area Burning Coordinate multiple burns in the area to manage exposure of the public to smoke Before, During, After

a E lements of these BSMP could also be practical and be neficial to apply to wildfires for areas likely to experience recurring wildfires.
(4) Wildfires . The Administrator shall exclude data from use in determinations of exceedances and violations where a State demonstrates to the Administrator’s satisfaction that emissions from wildfires caused a specific air pollution concentration in excess of one or more national ambient air quality standard at a particular air quali ty monitoring location and otherwise satisfies the requirements of this section. Provided the Administrator determines that there is no compelling evid ence to the contrary in the record, the Administrator will determine every wildfire occurring predominantly on wildland to have met the requirements identified in paragraph (c)(3)(iv)(D) of this section regarding the not reasonably cont rollable or preventable criterion. (5) High wind dust events . (i) The Administrator shall exclude da ta from use in determinations of exceedances and violations, where a State demonstrates to the Administrator’s satisfaction that emissions from a hi gh wind dust event caused a specific air pollution concentration in excess of one or more national ambient air quality*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 209 of 218 standards at a particular ai r quality monitoring location and otherwise satisfies the requirements of this section provided that such emissions are from high wind dust

events. (ii) The Administrator will consider high wind dust events to be natural events in cases where windblown dust is entirely from undisturbed natural lands or where all anthropogenic sources are reasonably contro lled as determined in accordance with §50.14(b)(7). (iii) The Administrator will accept a high wi nd threshold of a sustained wind of 25 mph for areas in the States of Arizona, California, Colorado, Kansas, Nebraska, Nevada, New Mexico, North Dakota, Okla homa, South Dakota, Texas, Utah, and Wyoming provided this value is not contradicted by eviden ce in the record at the time the State submits a demonstration. (iv) In addressing the requirem ents set forth in paragraph (c)(3)(iv)(D) of this section regarding the not reasonably preventable criterion, the State shall not be required to provide a case-specific justifi cation for a high wind dust event. (v) With respect to the not reasonably contro llable criterion of (c)(3)(iv)(D), dust controls on an anthropogenic source shall be consid ered reasonable in any case in which the controls render the anthropogenic source as resistant to high winds as a natural undisturbed land area. The Administrato r may determine lesser controls reasonable on a case-by-case basis. (vi) For remote, large-scale, high-energy and/or sudden hi gh wind dust events, such as “haboobs” in the southwest, the Admi nistrator will generally consider a demonstration documenting the nature and extent of the event to be sufficient*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 210 of 218 with respect to the not reasonable cont rollable criterion of (c)(3)(iv)(D). (6) Determinations with respect to event aggreg ation and multiple national ambient air quality standards for the same pollutant . (i) Where a State demonstrates to the Administrator’s satisfaction that for national ambient air quality standards with averaging or cumulative periods longer than 24-hours the aggregate effect of events occurring on different days has caused an exceedance or violation, the Administrator shall determine such collective data to satisfy the requirements in paragraph (c)(3)(iv)(B) of this sectio n regarding the clea r causal relationship criterion and otherwise satisfies th e requirements of this section. (ii) The Administrator shall accept as part of a demonstration for the clear causal relationship in paragraph (c)(3)(iv)(B) of this section, a State’s comparison of a 24-hour concentration of any national ambien t air quality standard pollutant to the level of a national ambient air quality standard for the same pollutant with a longer averaging period. (7) Determinations with respect to the not re asonably controllable or preventable criterion . (i) The Administrator shall determine that an event is not reasonably preventable if the State shows that reasonable measures to prevent the event were applied at the time of the event. (ii) The Administrator shall determine that an event is not reasonably controllable if the State shows that reasonable measures to control the impact of the event on air quality were applied at the time of the event. (iii) The Administrator shall assess the reasonableness of ava ilable controls for anthropogenic sources based on information avai lable as of the date of the event.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 211 of 218 (iv) Except where a State is obligated to revise its state implementation plan, the Administrator shall consider enforcea ble control measures implemented in accordance with a state implementation pl an, approved by the EPA within 5 years of the date of a demonstration submittal, that address the event-related pollutant and all sources necessary to fulfill the requirements of the Clean Air Act for the state implementation plan to be reas onable controls with respect to all anthropogenic sources that have or ma y have contributed to event-related emissions. (v) The Administrator shall not require a State to provide case-specific justification to support the not reasonably c ontrollable or preventabl e criterion for emissionsgenerating activity that o ccurs outside of the Stat e’s jurisdictional boundaries within which the concentration at issue wa s monitored. In the case of a tribe with treatment as a state status with respec t to exceptional events requirements, the tribe’s jurisdictional boundaries for purposes of requiring or directly implementing emission controls apply. In the case of a federal land manager or other federal agency submitting a demons tration under the requirements of this section, the jurisdictional boundaries that ap ply are those of the State or the tribe depending on which has jurisdiction over th e area where the event has occurred. (c) Schedules and procedures . (1) Public notification. (i) All St ates and, where applicable, their political subdivisions must notify the public promptly whenever an event occurs or is reasonably anticipated to occur which may result in the exce edance of an applicable air quality standard. (ii) [Reserved] (2) Initial Notification of Potential Exceptional Event.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 212 of 218 (i) A State shall notify the Administrator of it s intent to request exclusion of one or more measured exceedances of an applicable na tional ambient air quality standard as being due to an exceptional event by cr eating an initial event description and flagging the associated data that have been submitted to the AQS database and by engaging in the Initial Notification of Potential Exceptional Event process as follows: (A) The State and the appropriate EPA regional office shall engage in regular communications to identify thos e data that have been potentially influenced by an exceptional event, to determine whether the identified data may affect a regulatory determination and to discuss whether the St ate should develop and submit an exceptional events demonstr ation according to the requirements in this section; (B) For data that may affect an anticipated regulatory determination or where circumstances otherwise compel the Administrator to prioritize the resulting demonstration, the Administra tor shall respond to a State’s Initial Notification of Potential Exceptional Even t with a due date for demonstration submittal that considers the nature of the event and the anticipated timing of the associated regulatory decision; (C) The Administrator may waive the Initial Notification of Potential Exceptional Event process on a case-by-case basis. (ii) The data shall not be excluded from de terminations with respect to exceedances or violations of the national ambient air qua lity standards unless and until, following the State’s submittal of its demonstration pursuant to paragraph (c)(3) of this*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 213 of 218 section and the Administrator’s review, th e Administrator notifies the State of its concurrence by placing a concurrence flag in the appropriate field for the data record in the AQS database. (iii) [Reserved] (iv) [Reserved] (v) [Reserved] (vi) Table 2 identifies the data submission process for a new or revised national ambient air quality standard. This process shall apply to those data that will or may influence the initial designa tion of areas for any new or revised national ambient air quality standard.
Table 2. Schedule for Flagging and Documentation Submission for Data Influenced by Exceptional Events for Use in Initial Area Designations Exceptional Events / Regulatory Action Exceptional Events Deadline Schedule d

Flagging and initial event description deadline for data years 1, 2 and 3. a If state and tribal initial designation recommendations for a new/revised NAAQS are due August through January, then the flagging and initial event description deadline will be the July 1 prior to the recommendation deadline. If state and tribal recommendations for a new/revised NAAQS are due February through July, then the flagging and initial event description deadline will be the Ja nuary 1 prior to the recommendation deadline. Exceptional events demonstration submittal deadline for data years 1, 2 and 3. a No later than the date that state and tribal recommendations are due to EPA.

Flagging, initial even t description and exceptional events demonstration submittal deadline for data year 4 b and, where applicable, data year 5. c By the last day of the month that is 1 year and 7 months after promulgation of a new/revised NAAQS, un less either option a or b applies. a. If the EPA follows a 3-year designation schedule, the deadline is 2 years and 7*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 214 of 218 months after promulgation of a new/revised NAAQS. b. If the EPA notifies th e state/tribe that it intends to complete the initial area designations process according to a schedule between 2 and 3 years, the deadline is 5 months prior to the date specified for final designations decisions in such EPA notification.

a Where data years 1, 2, and 3 are those years e xpected to be considered in state and tribal recommendations. b Where data year 4 is the additional year of data that the EPA may consider when it makes final area designations for a new/revised NAAQS unde r the standard designations schedule.

c Where data year 5 is the additional year of data that the EPA may consider when it makes final area designations for a new/revised NAAQS under an extended designations schedule. d The date by which air agencies must certify thei r ambient air quality monitoring data in AQS is annually on May 1 of the year following the year of data collection as specified in 40 CFR 58.15(a)(2). In some cases, howev er, air agencies may choose to certify a prior year's data in advance of May 1 of the following year, particularly if the EPA has indicated its intent to promulgate final designations in the first 8 mont hs of the calendar year. Data flagging, initial event description and exceptional events demons tration deadlines for “early certified” data will follow the deadlines for “year 4” and “year 5” data. (3) Submission of demonstrati ons. (i) Except as allowed under paragraph (c)(2)(vi) of this section, a State that has flagged data as being due to an exceptional event and is requesting exclusion of the affected m easurement data shal l, after notice and opportunity for public comment, submit a demo nstration to justif y data exclusion to the Administrator according to the schedule established under paragraph (c)(2)(i)(B). (ii) [Reserved] (iii) [Reserved] (iv) The demonstration to justify data exclusion must include: (A) A narrative conceptual model th at describes 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);*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 215 of 218 (B) A demonstration that the event a ffected air quality in such a way that there exists a clear causal relationshi p between the specific event and the monitored exceedance or violation;(C) Analyses identified in Table 3 comparing the claimed eventinfluenced concentration(s) to concentrati ons at the same monitoring site at other times consistent with Table 3 to suppor t the requirement at (3)(iv)(B) of this paragraph. The Administrator shall not require a State to prove a specific percentile point in the distribution of data; (D) A demonstration that the ev ent was both not reasonably controllable and not reasonably preventable; and (E) A demonstration that the event was a human activity that is unlikely to recur at a particular locati on or was a natural event. (v) With the submission of the demonstrati on containing the elements in (c)(3)(iv), the
State must: (A) Document that the public co mment process was followed and that the comment period was open for a minimum of 30 days, which could be concurrent with the Administrator’s review of th e associated demonstration provided the State can meet all requirements in this paragraph; (B) Submit the public comments it re ceived along with its demonstration to the Administrator; and (C) Address in the submission to the Administrator those comments disputing or contradicting factual ev idence provided in the demonstration. (vi) Where the State has submitted a demonstr ation according to the requirements of this*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 216 of 218 section and the Administrator has review ed such demonstration and requested additional evidence to support one of the el ements in (c)(3)(iv), the State shall have 12 months from the date of the Administrator’s request to submit such evidence. At the conclusion of this time, if the State has not submitted the requested additional evidence, the Administrator will consider the demonstration to be inactive and will not pursue additiona l review of the demonstration. After a 12-month period of inactivity, if a St ate desires to pursue the inactive demonstration, it must reinitiate its re quest to exclude a ssociated data by following the process beginning with paragraph (c)(2)(i). Table 3. Evidence and Analyses for the Comparison to Historical Concentrations

Historical Concentration Evidence Types of Analyses/Supporting Information Required or Optional? 1. Comparison of concentrations on the claimed event day with past historical data Seasonal (appropriate if exceedances occur primarily in one season, but not in others)

 Use all available seasonal data over the

previous 5 years (or more, if available)

 Discuss the seasonal nature of pollution for

the location being evaluated

 Present monthly maximums of the NAAQS

relevant metric ( e.g ., maximum daily 8- hour average ozone or 1-hr SO 2 ) vs monthly or other averaged daily data as this masks high values Annual (appropriate if ex ceedances are likely

throughout the year)

 Use all available data over the previous 5

years (or more, if available) Seasonal and Annual Analyses

 Provide the data in the form relevant to the

standard being considered for data exclusion

 Label “high” data points as being

associated with concurred exceptional events, suspected exceptional events, other unusual occurrences, or high pollution days due to normal emissions Required seasonal and/or annual analysis (depending on which is more appropriate)*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 217 of 218 Historical Concentration Evidence Types of Analyses/Supporting Information Required or Optional?

 Describe how emission control strategies

have decreased pollutant concentrations over the 5-year window, if applicable

 Include comparisons omitting known or

suspected exceptional events points, if applicable 2. Comparison of concentrations on the claimed event day with a narrower set of similar days  Include neighboring days at the same location ( e.g., a time series of two to three weeks) and/or other days with similar meteorological conditions (possibly from other years) at the sa me or nearby locations with similar historical air quality along with a discussion of the meteorological conditions during the same timeframe a

 Use this comparison to demonstrate that the

event caused higher concentrations than would be expected for given meteorological and/or local emissions conditions Optional analysis

3. Percentile rank of concentration when compared to annual data b  Provide the percentile rank of the event-day concentration relative to all measurement days over the previous 5 years to ensure statistical robustness and capture non-event variability over the a ppropriate seasons or number of years. c

 Use the daily statistic ( e.g ., 24-hour

average, maximum daily 8-hour average, or maximum 1-hour) appropriate for the form of the standard being considered for data exclusion Required analysis when comparison is made on an annual basis ( see item #1)

4. Percentile rank of concentration relative to seasonal data b  Provide the percentile rank of the event-day concentration relative to all measurement days for the season (or appropriate alternative 3-month period) of the event over the previous 5 years

 Use the same time horizon as used for the

percentile rank calculate d relative to annual data, if appropriate Required analysis when comparison is made on a seasonal basis ( see item #1)

a If an air agency compares th e concentration on the claimed even t day with days with similar meteorological conditions from other years, the agency should also verify and provide evidence that the area has not experienced significant changes in wind pa tterns, and that no significant sources in the area have had signi ficant changes in their emissions of the pollutant of concern.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Exceptional Events_2060-AS02_NPRM_PreambleRule_20151023

Page 218 of 218 b The EPA does not intend to identify a particular historical percentile ra nk point in the seasonal or annual historical data that play s a critical role in the analysis or conclusion regarding the clear causal relationship.
c Section 8.4.2.e of appendix W (proposed re visions at 80 FR 45374, July 29, 2015) recommends using 5 years of adequately representative me teorology data from the National Weather Service to ensure that worst-case meteorological conditio ns are represented. Similarly, for exceptional events purposes, the EPA believes that 5 years of ambient air data, whether seasonal or annual, better represent the range of “normal” air quality than do shorter periods.