Approval of Air Quality Implementation Plans; Arizona; Arizona Department of Environmental Quality; Stationary Source Permits; West Pinal County; PM10

ENVIRONMENTAL PROTECTION AGENCY <CFR>40 CFR Part 52</CFR> <DEPDOC>[EPA-R09-OAR-2025-1113; FRL-12927-01-R9]</DEPDOC> <SUBJECT> Approval of Air Quality Implementation Plans; Arizona; Arizona Department of Environmental Quality; Stationary Source Permits; West Pinal County; PM <E T="0735">10</E> </SUBJECT> <HD SOURCE="HED">AGENCY:</HD> Environmental Protection Agency (EPA). <HD SOURCE="HED">ACTION:</HD> Proposed rule. <SUM> <HD SOURCE="HED">SUMMARY:</HD> The Environmental Protection Agency (EPA) is proposing to fully approve the Arizona Department of Environmental Quality's (ADEQ or “State”) State Implementation Plan (SIP) submittal under the Clean Air Act (CAA or “the Act”) that addresses Nonattainment New Source Review (NNSR) permitting of precursor emissions for the 1987 National Ambient Air Quality Standards (NAAQS or “standard”) for particulate matter with a diameter of 10 micrometers or less (PM <E T="52">10</E> ) in the West Pinal PM <E T="52">10</E> nonattainment area. We are taking comments on this proposal and plan to follow with a final action. </SUM> <EFFDATE> <HD SOURCE="HED">DATES:</HD> Comments must be received on or before October 14, 2025. </EFFDATE> <HD SOURCE="HED">ADDRESSES:</HD> Submit your comments, identified by Docket ID No. EPA-R09-OAR-2025-1113 at <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">Regulations.gov</E> . The 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 the disclosure of which 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, please contact the person identified in the <E T="02">FOR FURTHER INFORMATION CONTACT</E> section. For 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> If you need assistance in a language other than English or if you are a person with disabilities who needs a reasonable accommodation at no cost to you, please contact the person identified in the <E T="02">FOR FURTHER INFORMATION CONTACT</E> section. <FURINF> <HD SOURCE="HED">FOR FURTHER INFORMATION CONTACT:</HD> Shaheerah Kelly, U.S. Environmental Protection Agency, Region IX (AIR-3-2), telephone number: (415) 947-4156, email address: <E T="03">kelly.shaheerah@epa.gov.</E> </FURINF> <SUPLINF> <HD SOURCE="HED">SUPPLEMENTARY INFORMATION:</HD> Throughout this document, “we,” “us,” and “our” refer to the EPA. <HD SOURCE="HD1">Table of Contents </HD> <EXTRACT> <FP SOURCE="FP-2">I. Regulatory Context and Background</FP> <FP SOURCE="FP1-2"> A. PM <E T="52">10</E> NAAQS and West Pinal Area Designation and Classification </FP> <FP SOURCE="FP1-2"> B. CAA NNSR Requirements for PM <E T="52">10</E> Nonattainment Area SIPs Under CAA Section 189(e) </FP> <FP SOURCE="FP1-2"> C. The EPA's Previous Actions on the ADEQ's NNSR Program for PM <E T="52">10</E> for the West Pinal PM <E T="52">10</E> Nonattainment Area </FP> <FP SOURCE="FP-2"> II. The ADEQ's 2023 SIP Submission Addressing the Requirements of CAA Section 189(e) for the ADEQ's PM <E T="52">10</E> NNSR Program in the West Pinal PM <E T="52">10</E> Nonattainment Area </FP> <FP SOURCE="FP-2"> III. Evaluation of PM <E T="52">10</E> Precursors in the West Pinal PM <E T="52">10</E> Nonattainment Area for the ADEQ's NNSR Program Under CAA Section 189(e) and 40 CFR 51.165(a)(10) </FP> <FP SOURCE="FP1-2"> A. The EPA's PM <E T="52">10</E> Precursor Evaluation and Determination </FP> <FP SOURCE="FP1-2"> B. Determination Regarding the ADEQ's NNSR Program for PM <E T="52">10</E> in the West Pinal PM <E T="52">10</E> Nonattainment Area </FP> <FP SOURCE="FP-2">IV. Proposed Action</FP> <FP SOURCE="FP-2">V. Statutory and Executive Order Reviews </FP> </EXTRACT> <HD SOURCE="HD1">I. Regulatory Context and Background</HD> <HD SOURCE="HD2"> A. PM <E T="54">10</E> NAAQS and West Pinal Area Designation and Classification </HD> The EPA sets the NAAQS for certain ambient air pollutants at levels required to protect human health and the environment. Particulate matter with an aerodynamic diameter less than or equal to a nominal ten micrometers, or PM <E T="52">10</E> , is one of these ambient air pollutants for which the EPA has established health-based standards. On July 1, 1987, the EPA promulgated two primary standards for PM <E T="52">10</E> : a 24-hour standard of 150 micrograms per cubic meter (µg/m <SU>3</SU> ); and an annual PM <E T="52">10</E> standard of 50 µg/m <SU>3</SU> . The EPA also promulgated secondary PM <E T="52">10</E> standards that were identical to the primary standards. 52 FR 24634 (July 1, 1987). Because they are identical, we refer to the primary and secondary standards using the singular term, NAAQS. Effective December 18, 2006, the EPA revoked the annual PM <E T="52">10</E> NAAQS but retained the 24-hour PM <E T="52">10</E> NAAQS. 71 FR 61144 (October 17, 2006). Effective July 2, 2012, the EPA designated a portion of state lands in Pinal County, Arizona, (“West Pinal”) as nonattainment for the 1987 p.m. <E T="52">10</E> NAAQS. <SU>1</SU> <FTREF/> West Pinal is located in central Arizona, southeast of the Phoenix metropolitan area and northwest of the city of Tucson. Pinal County covers 5,365 square miles and has two distinct western and eastern regions with different characteristics relevant to pollution formation. The West Pinal PM <E T="52">10</E> nonattainment area is located within the western region. <FTNT> <SU>1</SU>  77 FR 32024 (May 31, 2012). The precise boundaries for the West Pinal PM <E T="52">10</E> nonattainment area are described in 40 CFR 81.303. </FTNT> As a result of this nonattainment designation, EPA initially classified West Pinal as a “Moderate” PM <E T="52">10</E> nonattainment area. <SU>2</SU> <FTREF/> Pursuant to CAA section 188(b)(2), the EPA later determined that the West Pinal nonattainment area had not attained the 1987 24-hour PM <E T="52">10</E> NAAQS by the attainment date for the area, which resulted in the area's reclassification as a “Serious” PM <E T="52">10</E> nonattainment area, effective July 24, 2020. <SU>3</SU> <FTREF/> <FTNT> <SU>2</SU>  See 77 FR 32024, 32030, 32032. </FTNT> <FTNT> <SU>3</SU>  85 FR 37756 (June 24, 2020). </FTNT> <HD SOURCE="HD2"> B. CAA NNSR Requirements for PM <E T="54">10</E> Nonattainment Area SIPs Under CAA Section 189(e) </HD> The Act's preconstruction permitting requirements for stationary sources, also called New Source Review (NSR), are found in title I of the Act and in the EPA's implementing regulations addressing the SIP requirements for state NSR programs at 40 CFR part 51, subpart I. The EPA's designation of West Pinal as a nonattainment area for the 1987 PM <E T="52">10</E> NAAQS triggered the requirement for the ADEQ to develop and submit an NNSR program to the EPA for SIP approval for that nonattainment area pursuant to CAA sections 172(c)(5) and 173 and 40 CFR 51.160-51.165, which must satisfy the NNSR requirements applicable to PM <E T="52">10</E> nonattainment areas. Among other CAA requirements applicable to PM <E T="52">10</E> nonattainment areas, section 189(e) of the Act requires that the control requirements for major stationary sources of direct PM <E T="52">10</E> also apply to major stationary sources of PM <E T="52">10</E> precursors, except where the EPA determines that such sources do not contribute significantly to PM <E T="52">10</E> levels that exceed the standard in the area. The EPA's regulations implementing state NNSR program requirements likewise provide that the state NNSR program requirements at 40 CFR 51.165 that are applicable to major stationary sources and major modifications of PM <E T="52">10</E> must also apply to major stationary sources and major modifications of PM <E T="52">10</E> precursors, except where the EPA determines that such sources do not contribute significantly to PM <E T="52">10</E> levels that exceed the PM <E T="52">10</E> NAAQS in the area. 40 CFR 51.165(a)(10). <HD SOURCE="HD2"> C. The EPA's Previous Actions on the ADEQ's NNSR Program for PM <E T="54">10</E> for the West Pinal PM <E T="54">10</E> Nonattainment Area </HD> In November 2015, the EPA issued a final rule taking action on a comprehensive 2012 NSR SIP submittal from the ADEQ that constituted a major update to the ADEQ's NSR program (“2015 NSR action”). 80 FR 67319 (Nov. 2, 2015). The EPA determined that this SIP submittal met most NSR requirements and significantly strengthened ADEQ's NSR program. However, the EPA also identified deficiencies with various aspects of the SIP submittal, and therefore the EPA's 2015 NSR action was a limited approval and limited disapproval of the ADEQ's NNSR program for all areas within the ADEQ's jurisdiction, including but not limited to the West Pinal PM <E T="52">10</E> nonattainment area, based on the program not meeting certain NNSR program requirements. 80 FR 67319, 67321, 67332. The EPA's 2015 NSR action also included additional actions, including a separate limited approval of the ADEQ's NNSR program for PM <E T="52">10</E> only with respect to the West Pinal PM <E T= ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ Preview showing 10k of 30k characters. Full document text is stored and available for version comparison. ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━