Air Plan Approval; Utah; Interstate Transport of Air Pollution for the 2008 8-Hour Ozone National Ambient Air Quality Standard

ENVIRONMENTAL PROTECTION AGENCY <CFR>40 CFR Part 52</CFR> <DEPDOC>[EPA-R08-OAR-2025-0054; FRL-12595-01-R8]</DEPDOC> <SUBJECT>Air Plan Approval; Utah; Interstate Transport of Air Pollution for the 2008 8-Hour Ozone National Ambient Air Quality Standard</SUBJECT> <HD SOURCE="HED">AGENCY:</HD> Environmental Protection Agency (EPA). <HD SOURCE="HED">ACTION:</HD> Proposed rule. <SUM> <HD SOURCE="HED">SUMMARY:</HD> Pursuant to the Federal Clean Air Act (CAA or the Act), the Environmental Protection Agency (EPA) is proposing to approve a portion of a Utah State Implementation Plan (SIP) submission addressing interstate transport for the 2008 8-hour ozone national ambient air quality standard (NAAQS). The “interstate transport” provision requires that each state's SIP contain adequate provisions to prohibit emissions from within the state from significantly contributing to nonattainment or interfering with maintenance of the NAAQS in other states. In this action, EPA is only addressing the requirement prohibiting interference with maintenance, referred to as “prong 2,” for the 2008 ozone NAAQS. </SUM> <EFFDATE> <HD SOURCE="HED">DATES:</HD> Written comments must be received on or before July 18, 2025. </EFFDATE> <HD SOURCE="HED">ADDRESSES:</HD> Submit your comments, identified by Docket ID No. EPA-R08-OAR-2025-0054, to the Federal Rulemaking Portal: <E T="03">https://www.regulations.gov.</E> Follow the online instructions for submitting comments. Once submitted, comments cannot be edited or removed from <E T="03">https://www.regulations.gov.</E> EPA may publish any comment received to its public docket. Do not submit electronically any information you consider to be Confidential Business Information (CBI) or other information whose disclosure is restricted by statute. Multimedia submissions (audio, video, etc.) must be accompanied by a written comment. The written comment is considered the official comment and should include discussion of all points you wish to make. The EPA will generally not consider comments or comment contents located outside of the primary submission ( <E T="03">i.e.,</E> on the web, cloud, or other file sharing system). For additional submission methods, the full EPA public comment policy, information about CBI or multimedia submissions, and general guidance on making effective comments, please visit <E T="03">https://www.epa.gov/dockets/commenting-epa-dockets.</E> <E T="03">Docket:</E> All documents in the docket are listed in the <E T="03">https://www.regulations.gov</E> index. Although listed in the index, some information is not publicly available, <E T="03">e.g.,</E> CBI or other information whose disclosure is restricted by statute. Certain other material, such as copyrighted material, will be publicly available only in hard copy. Publicly available docket materials are available electronically in <E T="03">https://www.regulations.gov.</E> Please email or call the person listed in the <E T="02">FOR FURTHER INFORMATION CONTACT</E> section if you need to make alternative arrangements for access to the docket. <FURINF> <HD SOURCE="HED">FOR FURTHER INFORMATION CONTACT:</HD> Adam Clark, Air and Radiation Division, EPA, Region 8, Mailcode 8ARD-IO, 1595 Wynkoop Street, Denver, Colorado 80202-1129, telephone number: (303) 312-7104, email address: <E T="03">clark.adam@epa.gov.</E> </FURINF> <SUPLINF> <HD SOURCE="HED">SUPPLEMENTARY INFORMATION:</HD> Throughout this document whenever “we,” “us,” or “our” is used, we mean EPA. <HD SOURCE="HD1">Table of Contents</HD> <EXTRACT> <FP SOURCE="FP-2">I. Background</FP> <FP SOURCE="FP-2">II. EPA's Ozone Transport Modeling Information</FP> <FP SOURCE="FP-2">III. Selection of Analytic Year</FP> <FP SOURCE="FP-2">IV. Summary of Utah's Submission</FP> <FP SOURCE="FP-2">V. EPA's Evaluation</FP> <FP SOURCE="FP-2">VI. Proposed Action</FP> <FP SOURCE="FP-2">VII. Statutory and Executive Order Reviews</FP> </EXTRACT> <HD SOURCE="HD1">I. Background</HD> On March 12, 2008, EPA strengthened the NAAQS for ozone. (73 FR 16436; March 27, 2008). EPA revised the level of the 8-hour ozone NAAQS from 80 parts per billion (ppb) to 75 ppb. EPA also revised the secondary 8-hour standard to the level of 75 ppb making it identical to the revised primary standard. Section 110(a)(1) of the CAA imposes an obligation upon states to submit SIP submissions that provide for the implementation, maintenance, and enforcement of a new or revised NAAQS within 3 years following the promulgation of that NAAQS. Section 110(a)(2) lists specific requirements that states must meet in these SIP submissions, as applicable. EPA refers to this type of SIP submission as the “infrastructure” SIP because the SIP ensures that states can implement, maintain, and enforce the air quality standards. Within these requirements, CAA section 110(a)(2)(D)(i)(I) contains requirements to address interstate transport of NAAQS pollutants or their precursors. CAA section 110(a)(2)(D)(i)(I), which is also known as the “interstate transport” provision, requires SIPs to contain provisions prohibiting any source or other type of emissions activity within the State from emitting any air pollutant in amounts that will contribute significantly to nonattainment of the NAAQS in any other state (commonly referred to as prong 1) or interfere with maintenance of the NAAQS in any other state (prong 2). A SIP addressing this provision is often referred to as an “interstate transport SIP.” Through the development and implementation of several previous rulemakings, <SU>1</SU> <FTREF/> EPA, working in partnership with states, established the following 4-step framework to address the requirements of the interstate transport provision for ground-level ozone NAAQS: (1) identifying downwind ozone air quality monitors, termed “receptors,” that are expected to have problems attaining or maintaining the NAAQS; (2) determining which upwind states contribute to these identified problems in amounts sufficient to “link” them to downwind air quality problems; (3) for states linked to downwind air quality problems, identifying upwind emissions that significantly contribute to downwind nonattainment or interfere with downwind maintenance of the NAAQS; and (4) for states that are found to have emissions that significantly contribute to downwind nonattainment or interfere with maintenance of the NAAQS downwind, implementing the necessary emissions reductions through enforceable measures. <FTNT> <SU>1</SU>  See, <E T="03">e.g.,</E> the Cross-State Air Pollution Rule (CSAPR) at 76 FR 48208 (August 8, 2011), the CSAPR Update at 81 FR 74504 (October 26, 2016), and the Revised CSAPR Update at 86 FR 23054 (April 30, 2021). </FTNT> On August 4, 2015, EPA issued a Notice of Data Availability (NODA) containing air quality modeling to assist states with meeting section 110(a)(2)(D)(i)(I) requirements for the 2008 ozone NAAQS within the context of the 4-step framework. <SU>2</SU> <FTREF/> Specifically, the air quality modeling helped states address steps 1 and 2 of the framework by (1) identifying locations in the United States where EPA anticipated nonattainment or maintenance issues in 2017 for the 2008 ozone NAAQS, and (2) quantifying the projected contributions from emissions from upwind states to downwind ozone concentrations at the receptors in 2017. EPA used this modeling to support the Cross-State Air Pollution Rule Update for the 2008 Ozone NAAQS (“CSAPR Update”) proposed rule (80 FR 75706; December 3, 2015), and updated this modeling in 2016 to support the CSAPR Update final rule (81 FR 74504; October 26, 2016). The 2017 projections in this updated version of the modeling (hereon referred to as the “CSAPR Update modeling”) were part of the technical record for EPA's final action disapproving the prong 2 portion of the Utah 2008 Ozone Infrastructure SIP (81 FR 71991; October 19, 2016), which is discussed in more detail later in this document. <FTNT> <SU>2</SU>   <E T="03">See</E> Notice of Availability of the Environmental Protection Agency's Updated Ozone Transport Modeling Data for the 2008 Ozone National Ambient Air Quality Standard (NAAQS), 80 FR 46271 (August 4, 2015); <E T="03">see also</E> “Updated Air Quality Modeling Technical Support Document for the 2008 Ozone NAAQS Transport Assessment,” August 2015 (included in the docket to the NODA). </FTNT> In the CSAPR Update, EPA used the CSAPR Update modeling to identify downwind nonattainment and maintenance receptors at step 1 of the 4-step framework ( <E T="03">see</E> 81 FR 74530-74532; October 26, 2016). Specifically, EPA identified nonattainment receptors as those monitoring sites with current measured design values exceeding the NAAQS that also have projected ( <E T="03">i.e.,</E> in 2017) average design values exceeding the NAAQS. <SU>3</SU> <FTREF/> EPA identified maintenance receptors as those monitoring sites with projected maximum design values exceeding the NAAQS. EPA considered all nonattainment receptors to also be maintenance receptors because a monitoring site with a projected average design value above the standard necessarily also has a projected maximum design value above the standard. Monitoring sites with projected maximum design values that exceed the standard and which are not also nonattainment receptors were thus referred to as maintenance-only receptors. <FTNT> <SU>3</SU>  For the 2008 ozone NAAQS, the air quality design value for a monitoring site is the 3-year average annual fourth-highest daily maximum 8-hour average ozone concentration. <E T="03">See</E> 73 FR 16513 (March 27, 2008). </FTNT> At step 2 of the 4-step framework in the CSAPR Update, EPA used the CSAPR Update modeling to determine whether states' impact on each projected downwind air quality problem would be considered significant ( <E T="03">s ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ Preview showing 10k of 39k characters. Full document text is stored and available for version comparison. ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━