Throughout this document wherever “we,” “us,” or “our” is used, we mean the EPA.

Under section 109 of the Act, the EPA has promulgated NAAQS for certain pollutants, including PM 2.5 (40 CFR 50.2(b)). Once the EPA promulgates a NAAQS, section 107 of the Act specifies a process for the designation of each area within a state, generally as either an attainment area (an area attaining the NAAQS) or as a NAA (an area not attaining the NAAQS, or that contributes to nonattainment of the NAAQS in a nearby area). For PM 2.5 , certain areas have also been designated “unclassifiable.” These various designations, in turn, trigger certain state planning requirements.

For all areas, regardless of designation, section 110 of the Act requires that each state adopt and submit for EPA approval, a plan to provide for implementation, maintenance, and enforcement of the NAAQS. This plan is commonly referred to as a SIP. CAA section 110 contains requirements that a SIP must meet to gain EPA approval. 1 For NAAs, SIPs must meet additional requirements in part D of title I of the Act.

On October 17, 2006 (71 FR 61144), the EPA revised the level of the 24-hour PM 2.5 NAAQS, lowering the primary and secondary standards from the 1997 standard of 65 micrograms per cubic meter (µg/m 3 ) to 35 µg/m 3 . On November 13, 2009 (74 FR 58688), the EPA designated three NAAs in Utah for the 2006 24-hour PM 2.5 NAAQS of 35 µg/m 3 . These are the Salt Lake City; Provo; and Logan, Utah-Idaho  2 NAAs.

The EPA originally issued a rule in 2007  3 regarding implementation of the 2006 24-hour PM 2.5 NAAQS for the NAA plan requirements specified in CAA title I, part D, subpart 1. Under subpart 1, Utah was required to submit an attainment plan for each area no later than three years from the date of nonattainment designation. These plans needed to provide for the attainment of the PM 2.5 standards as expeditiously as practicable, but no later than five years from the date the areas were designated nonattainment.

In 2013, the U.S. Court of Appeals for the District of Columbia held that the EPA should have implemented the 2006 PM 2.5 24-hour standards, as well as the other PM 2.5 NAAQS, based on both subpart 1 and subpart 4 of CAA title I, part D. 4 Under subpart 4, all NAAs are initially classified as Moderate, and Moderate area attainment plans must address the requirements of subpart 4 as well as subpart 1. Additionally, subpart 4 sets a different SIP submittal due date and attainment year. For a Moderate area, the attainment SIP is due 18 months after designation and the attainment year is as expeditiously as practicable, but no later than the end of the sixth calendar year after designation.

On June 2, 2014 (79 FR 31566), the EPA finalized the Identification of Nonattainment Classification and Deadlines for Submission of State Implementation Plan (SIP) Provisions for the 1997 Fine Particulate (PM 2.5 ) National Ambient Air Quality Standard (NAAQS) and 2006 24-hour PM 2.5 NAAQS. This rule classified the areas that were designated as Moderate in 2009 as nonattainment and set the attainment SIP submittal due date for those areas to December 31, 2014. Additionally, this rule established the Moderate area attainment date of December 31, 2015.

On August 24, 2016 (81 FR 58010), the EPA finalized the Fine Particulate Matter National Ambient Air Quality Standards: State Implementation Plan Requirements (“PM 2.5 Requirements Rule”), which partially addressed the 2013 National Resources Defense Council ( NRDC) decision. The final PM 2.5 Requirements Rule details how air agencies can meet the SIP requirements under subparts 1 and 4 that apply to areas designated nonattainment for any PM 2.5 NAAQS, such as: general requirements for attainment plan due dates and attainment demonstrations; provisions for demonstrating reasonable further progress (RFP); quantitative milestones; contingency measures; nonattainment new source review (NNSR) permitting programs; and reasonable available control measures (RACM) (including reasonably available control technologies (RACT)). The statutory attainment planning requirements of subparts 1 and 4 were established to ensure that the following goals of the CAA are met: (i) that states implement measures that provide for attainment of the PM 2.5 NAAQS as expeditiously as practicable; and (ii) that states adopt emissions reduction strategies that will be the most effective at reducing PM 2.5 levels in NAAs.

If an area is reclassified from Moderate to Serious, the area will then be subject to Serious PM 2.5 CAA requirements under subpart 1 and subpart 4, and the CAA requires the state to submit the following Serious area SIP elements: (1) CAA section 172(c)(3); (2) CAA sections 172(c)(1) and 189(b)(1)(B); (3) CAA section 188(c)(2); (4) CAA section 172(c)(2); (5) CAA section 189(c); (6) CAA section 189(e); (7) CAA section 172(c)(9); and (8) CAA section 302(j) and CAA section 189(b)(3).

Serious area 2006 24-hour PM 2.5 plans must also satisfy the general requirements applicable to all SIP submissions under section 110 of the CAA, including the requirement to provide necessary assurances that the implementing agencies have adequate personnel, funding, and authority under CAA section 110(a)(2)(E), and the requirements concerning enforcement in CAA section 110(a)(2)(C).

After the November 13, 2009 designation of nonattainment for the 2006 24-hour PM 2.5 NAAQS, Utah developed draft PM 2.5 attainment plans intended to meet the requirements of subpart 1. Utah submitted these revised 2006 24-hour PM 2.5 attainment plans for the Salt Lake City and Provo NAAs on December 14, 2012.

After the court's 2013 decision, Utah amended its attainment plans to address the requirements of subpart 4. On December 16, 2014, Utah Division of Air Quality (UDAQ) withdrew all prior Salt Lake City and Provo 2006 24-hour PM 2.5 Moderate SIP attainment plan submissions and submitted a subpart 1 and subpart 4 Salt Lake City and Provo 2006 24-hour PM 2.5 Moderate SIP. Additionally, the State of Utah submitted various revisions to the UAC Title R307 (Environmental Quality) area source rules in multiple submissions: February 2, 2012; May 9, 2013; June 8, 2013; February 18, 2014; April 17, 2014; May 20, 2014; July 10, 2014; and August 6, 2014. These area source rules were either new or revised to meet RACM/RACT for the Salt Lake City and Provo 2006 24-hour PM 2.5 SIPs. The EPA acted on these submittals, along with the area source rule revisions in the December 16, 2014, submission, on February 25, 2016 (81 FR 9343), October 19, 2016 (81 FR 71988), October 2, 2019 (84 FR 52368), and February 26, 2020 (85 FR 10989).

On January 19, 2017, the State of Utah submitted revisions to their Part H.11, 12, and 13 emission limits section of the Utah 2006 24-hour PM 2.5 SIP and revised R307-110-17. R307-110-17 incorporation by reference (IBR) section IX., Control Measures for Area and Point Sources, Part H, Emission Limits; which formally incorporates the Salt Lake City and Provo 2006 24-hour PM 2.5 Part H.11, 12, and 13 emission limits into Utah's State regulations. This was undertaken by UDAQ to correlate any overlapping limits between the 2006 24-hour PM 2.5 Part H.11, 12, and 13, to the coarse particulate matter (PM 10 ) Part H.1, 2, 3, and 4.

On May 10, 2017 (82 FR 21711), the EPA published a final rule reclassifying the Salt Lake City and Provo areas to “Serious” nonattainment status, based on the EPA's determination that the areas could not practicably attain the 2006 24-hour PM 2.5 standards by the December 31, 2015 attainment date. This reclassification became effective on June 9, 2017. The reclassification was based on the EPA's evaluation of ambient air quality data from the 2013-2015 period, indicating that it was not practicable for some of the monitoring sites in the Salt Lake City and Provo areas to show PM 2.5 design values at or below the level of the 2006 24-hour PM 2.5 NAAQS by December 31, 2015.

On March 23, 2018, the State of Utah submitted quantitative milestone reports for the Salt Lake City and Provo 2006 24-hour PM 2.5 NAAs, meeting its due date of no later than 90 days after the December 31, 2017, milestone date. On October 24, 2018, the EPA determined that the 2017 quantitative milestone reports for the Salt Lake City and Provo 2006 24-hour PM 2.5 NAAs were adequate. 5

After the Serious reclassification, UDAQ revised certain area source rules in UAC section R307-200 and R307-300 Series and submitted these revisions on April 19, 2018, May 21, 2020, and July 21, 2020. On February 4, 2019, the State of Utah submitted the Serious 2006 24-hour PM 2.5 SIP for the Salt Lake City NAA which included the BACM/BACT analysis for the Provo Serious 2006 PM 2.5 NAA. The analysis was based on the emission limits submitted on January 19, 2017, for only Part H.13. On February 15, 2019, Utah submitted the Serious 2006 24-hour PM 2.5 SIP for the Salt Lake City NAA, which included revisions to Utah SIP Part H.11 and 12, and the accompanying BACM/BACT analysis. The February 4, 2019 and February 15, 2019, submission included BACM/BACT analyses for on-road, off-road, and area source rules; some of these area source rules were revised and others were deemed BACM/BACT without revising. 6

Applying the Clean Data Policy, 7 on April 10, 2019 (84 FR 14267) and September 27, 2019 (84 FR 51055), the EPA finalized a determination that the obligation to submit any remaining attainment-related SIP revisions arising from classification of the Provo and Salt Lake City area, as Moderate NAAs and the subsequent reclassification as Serious NAAs for the 2006 24-hour PM 2.5 NAAQS does not apply for so long as the area continues to attain the 2006 24-hour PM 2.5 NAAQS. 8 The attainment-related SIP revisions that were suspended include: an attainment demonstration (Moderate and Serious), provisions demonstrating timely implementation of RACM/RACT (Moderate), an RFP plan (Moderate and Serious), quantitative milestones and quantitative milestone reports (Moderate and Serious), and contingency measures (Moderate and Serious). The only remaining attainment-related SIP elements for EPA action include baseline emission inventories, NNSR, and BACM/BACT.

For any Serious 2006 24-hour PM 2.5 NAA, section 189(b)(1)(B) of the Act requires that a state submit provisions to assure that BACM/BACT for the control of PM 2.5 and PM 2.5 precursors shall be implemented no later than four years after the date the area is reclassified as a Serious area. The EPA defines BACM (including BACT) as, among other things, the maximum degree of emissions reduction achievable for a source or source category, which is determined on a case-by-case basis considering energy, economic and environmental impacts, and other costs. 9 We consider BACM a control level that goes beyond existing RACM-level controls, for example by expanding the use of RACM controls or by requiring preventative measures instead of remediation. 10 The level of stringency generally refers to the overall level of emissions reductions of a control measure or technology, or of such measures and technologies combined.

The PM 2.5 Requirements Rule explains that BACM/BACT are generally independent requirements, to be determined without regard to the specific attainment analysis ( i.e., attainment demonstration) for the area. 11 The EPA found it reasonable to interpret the statute as requiring a different analysis for determining BACM/BACT, i.e., that while RACM emphasizes the attainment needs of the area, BACM has a greater emphasis on identifying measures that are feasible to implement. The Addendum to the General Preamble noted that the test for BACM puts a “greater emphasis on the merits of the measure or technology alone,” rather than on “flexibility in considering other factors,” in contrast to the approach for RACM/RACT. 12

Section 189(b)(1)(B) of the Act allows states, in appropriate circumstances, to delay implementation of BACM until four years after reclassification. Because the EPA reclassified the Provo and Salt Lake City areas as Serious NAAs for the 2006 24-hour PM 2.5 NAAQS effective June 9, 2017 (82 FR 21711; May 10, 2017), the date four years after reclassification is June 9, 2021. In this case, however, all BACM for direct PM 2.5 and PM 2.5 precursors in the Salt Lake City area must be, and was, implemented no later than December 31, 2019, which is the outermost statutory attainment date for the Salt Lake City area under section 188(c)(2). 13

Under the PM 2.5 Requirements Rule, control measures that can be implemented in whole or in part by the end of the fourth year after an area's reclassification to Serious are considered BACM, and control measures that can only be implemented after this period but before the attainment date are considered “additional feasible measures.”  14 The EPA has defined “additional feasible measures” as “those measures and technologies that otherwise meet the criteria for BACM/BACT but that can only be implemented in whole or in part beginning 4 years after reclassification of an area, but no later than the statutory attainment date of the area.”  15 Given that the statutory attainment date is less than three years from the effective date of the reclassification of the Provo and Salt Lake City areas, additional feasible measures are not required in this case.

The Addendum and the PM 2.5 Requirements Rule explain that the BACM/BACT selection process for implementation of the 2006 24-hour PM 2.5 NAAQS is designed to take into account the local facts and circumstances and the nature of the air pollution problem in a given NAA. The following steps are used in determining BACM/BACT: (1) Develop a comprehensive emission inventory of the sources of directly emitted PM 2.5 and PM 2.5 precursors; (2) Identify existing and potential control measures for the sources in the inventory; (3) Evaluate the technological feasibility of potential control measures; (4) Evaluate the economic feasibility of potential control measures; and (5) Determine the earliest date by which a control measure or technology can be implemented in whole or in part. 16

Additionally, the information found within this action, coupled with the statutory and regulatory requirements, support the EPA's decision that BACT or lowest achievable emission rate (LAER) provisions for new sources (as distinct from BACT for existing sources), or best available retrofit technology (BART) for existing sources, could potentially qualify as BACM or BACT for purposes of meeting the Serious area attainment plan requirements. 17 However, as discussed further in the PM 2.5 Requirements Rule, it is not appropriate for a state to assume that just because a certain control technology was determined to meet BACT, LAER or BART criteria for a new source sometime in the past, that such a control will also automatically meet the criteria for BACM or BACT or additional feasible measures for attainment planning purposes. This is because the regulated pollutant or source applicability may differ and the analyses may be conducted years apart. Thus, a state may not simply rely on prior BACT, LAER or BART analyses for the purposes of showing that a source has also met BACT for the relevant 2006 24-hour PM 2.5 NAAQS. Rather, the EPA expects that in Step 2 (discussed above) of the BACM/BACT determination process, the state would identify such measures as “existing measures” that should be further evaluated as potential BACM or BACT, or additional feasible measures. At the same time, the EPA notes that the presence of previously installed control technology, and the technical and economic considerations that would be associated with upgrading to a measure that achieves greater reductions, is something that should be considered in the assessments of technological and economic feasibility of the newer measure. 18

Once these analyses are complete, a state must use this information to develop enforceable control measures and submit them to the EPA for evaluation under CAA section 110. We use these steps from the Addendum and the PM 2.5 Requirements Rule, as guidelines in our evaluation of the BACM measures and related analyses in the Provo and Salt Lake City 2006 24-hour PM 2.5 Serious SIP.

Parallel processing refers to a process that utilizes concurrent state and Federal proposed rulemaking actions to process state SIP submissions in less time than the standard process. During parallel processing, generally, the state submits a copy of the proposed regulation or other revisions to the EPA before conducting its public hearing and completing its public comment process under state law. The EPA reviews this proposed state action and prepares a notice of proposed rulemaking under Federal Law. In some cases, the EPA's notice of proposed rulemaking is published in the Federal Register during the same time frame that the state is holding its public hearing and conducting its public comment process. The state and the EPA then provide for concurrent public comment periods on both the state action and Federal action. If, after completing the state and EPA's public comment process, the state changes its final submittal from the proposed submittal, the EPA evaluates those changes and decides on whether to publish another notice of proposed rulemaking in light of those changes or to proceed to taking the final action on its proposed action and describe the state's changes in its final rulemaking action. Any final rulemaking action by the EPA will occur only after the final submittal has been adopted by the state and formally provided to the EPA. Parallel processing is designed to require less time than the standard process, in which a state completes its entire state process before submitting a final SIP package to the EPA, only after which the EPA proposes action on the state submission, seeks public comment, and takes final action.

In this case, however, the EPA's and Utah's processes have not been perfectly concurrent. The State submitted the draft SIP revisions on May 20, 2025, with a public comment period starting March 1 and going through March 31, 2025, with a public hearing held online at 2:00 p.m. on March 13, 2025. The State's intention is to submit its final SIP revisions in July 2025. After Utah submits these formal SIP revisions, the EPA will evaluate the submittal. If the State changes the formal submittal from the proposed submittal, the EPA will evaluate those changes for significance. If the EPA finds any such changes to be significant, then the Agency intends to determine whether to re-propose the actions based on the revised submission or to proceed to take final action on the submittal as changed by the State. Although the EPA was unable to have a concurrent public comment process with the State, parallel processing allows the EPA to begin to take action on the State's proposed submittal in advance of a formal and final submission.

The UDAQ's BACM/BACT process and control measure evaluations for the identified sources are described in detail in their draft May 20, 2025 submission. 20 For each identified source, UDAQ identified its adopted control measures and potential additional control measures based on measures implemented in other areas, measures identified in EPA regulations or guidance ( e.g., in control technique guidelines (CTGs), alternative control technique documents (ACTs), new sources performance standards (NSPSs), or in the EPA's “Cost Analysis Models/Tools for Air Pollution Regulations”), or measures identified in prior EPA rulemaking documents ( e.g., recommendations in SIP actions). 21 UDAQ evaluated these potential additional control measures to determine whether implementation of the measures would be technologically and economically feasible in the Salt Lake City area. Based upon their evaluation, UDAQ determined BACM/BACT to be the existing controls for all five facilities listed below.

In the following sections, we review key components of UDAQ's demonstrations concerning BACM/BACT for the identified sources of direct PM 2.5 , nitrogen oxide (NO X ), volatile organic compounds (VOC), sulfur dioxide (SO 2 ), and ammonia (NH 3 ) emissions in the Salt Lake City NAA: (1) Big West Oil LLC Refinery; (2) Chevron Products Company—Salt Lake Refinery; (3) Hexcel Corporation: Salt Lake Operations; (4) Holly Frontier Sinclair Woods Cross Refinery; and (5) Tesoro Refining and Marketing Company LLC Marathon Refinery: Salt Lake City Refinery.

EPA reviewed UDAQ's analysis and determination in the May 20, 2025 draft submission that the five major stationary source control measures represent BACM/BACT for direct PM 2.5 and PM 2.5 precursors within the Provo and Salt Lake City NAAs. As a result, the EPA proposes to determine that UDAQ's Utah SIP Part H emission limits provide for the implementation of BACM/BACT for the five major stationary sources of direct PM 2.5 and PM 2.5 precursors. Additional detail can be found in our technical support document (TSD) located in the docket for this action.

We are proposing to approve, through parallel processing, the May 20, 2025 draft submission of revisions to Utah SIP section IX.H.11. and 12. and to find that the May 20, 2025 draft submission provides for the implementation of BACM/BACT for all sources of direct PM 2.5 and PM 2.5 precursors as expeditiously as practicable, for purposes of the 2006 24-hour PM 2.5 NAAQS in the Salt Lake City area, in accordance with the requirements of CAA section 189(b)(1)(B) and 40 CFR 51.1010. Additional detail can be found in the TSD within the docket.

When certain sections of the Utah state SIP are amended by the Utah Air Quality Board (UAQB), those sections must be incorporated into the Utah Air Quality Rules in the UAC. Utah incorporates its state SIP sections within UAC section R307-110. These rules are amended as needed to change the effective dates to match the UAQB approval date of various amendments to the Utah state SIP. For this proposed action, we are also proposing to approve into the federally approved SIP, through the parallel process based on the information in the May 20, 2025 UDAQ submission, section IX., Control Measures for Area and Point Sources, Part H, Emission Limits, 22 which incorporates all the emission limits in the Utah state SIP section IX.H.11. and 12. Additionally, we are proposing to approve into the federally approved SIP the revisions within Utah SIP sections 11. and 12. through the parallel process based on the information May 20, 2025 UDAQ submission. In section I.C. above, we discuss the process of this type of action.

Section R307-110-17 incorporates the amendments to Utah State SIP section IX., Control Measures for Area and Point Sources, Part H, Emission Limits into the UAC. This is a ministerial provision, which only revises the effective date within the rule to May 7, 2025, and does not by itself change any state SIP control measures.

Utah State SIP section IX.H.11. (General Requirements: Control Measures for Area and Point Sources, Emission Limits and Operating Practices, PM 2.5 ) establishes general requirements for recordkeeping, reporting, good combustion practices for emission minimization, and monitoring for the stationary sources subject to emission limits under Utah State SIP sections IX.H.12. and 13., except as otherwise outlined in individual conditions in sections IX.H.12. and 13. Additionally, this section establishes general refinery requirements, addressing limitations on emitting units common to the refineries in the NAAs. These general refinery requirements include limits at fluid catalytic cracking units, limits on refinery fuel gas and heat exchangers, requirements on tank degassing, restrictions on liquid fuel oil consumption, requirements for leak detections and repairs, and requirements for hydrocarbon flares. Furthermore, section IX.H.11. controls VOCs through catalytic oxidation at internal combustion engines and natural gas combustion turbines.

UDAQ revised IX.H.11.c. where subsections `iv' and `v' were created. These two subsections describe how each source under IX.H.12. and 13. are required to comply with all applicable recordkeeping and reporting sections of the facilities' most recently, federally, approved title V permit, which includes submissions of annual compliance certifications and bi-annual monitoring reports, unless a more stringent requirement is found under IX.H.12. and/or 13. Additionally, subsection `v' requires that each source complies with applicable recordkeeping and reporting found in 40 CFR part 60 and 40 CFR part 63.

Additionally, UDAQ revised subsection IX.H.11.g.vii.B. and created two other subsections under IX.H.11.g. which includes IX.H.11.g.viii. and IX.H.11.g.ix. Subsection IX.H.11.g.vii.B. revised a reference of 40 CFR 80.510 to 1090.305. The two subsections that were created, create good combustion practices, and recordkeeping and reporting requirements specific to refineries located in the PM 2.5 NAAs. To ensure minimization of emissions, each owner/operator shall operate all combustion units in accordance with good combustion practices and maintain all combustion units following the manufacturer's recommendations. The additional recordkeeping and reporting requirements for refineries are in addition to IX.H.11.c. and each refinery shall comply with the listed requirements until such time as a title V operating permit is federally approved:

The detailed analysis of our parallel process on the May 20, 2025 submission of draft revisions to Utah State SIP section IX.H.11., can be found in our TSD in the docket.

Utah State SIP section IX.H.12. (Source-Specific Emission Limitations in Salt Lake City—UT PM 2.5 Nonattainment Area) establishes specific emission limitations for 17 sources. These sources are ATK Launch Systems Inc. Promontory, Big West Oil LLC Refinery, Chemical Lime Company (LHoist North America), Chevron Products Company—Salt Lake Refinery, Compass Minerals Ogden Inc., Holly Frontier Sinclair Woods Cross Refinery, Kennecott Utah Copper (KUC): Mine, Kennecott Utah Copper (KUC): Power Plant, Kennecott Utah Copper: Smelter and Refinery, Nucor Steel Mills, PacifiCorp Energy: Gadsby Power Plant, Tesoro Refining and Marketing Company LLC Marathon Refinery: Salt Lake City Refinery, The Proctor & Gamble Paper Products Company, Utah Municipal Power Association: West Valley Power Plant, University of Utah: University of Utah Facilities, and Hill Air Force Base. Major stationary sources were identified based on their potential to emit (PTE) of 70 tpy or more of PM 2.5 , NO X , SO 2 , VOC, and/or NH 3 . With this draft submittal, UDAQ is completing major revisions to emission limitations for the following five sources in section IX.H.12.: (1) IX.H.12.b. Big West Oil LLC Refinery; (2) IX.H.12.d. Chevron Products Company—Salt Lake Refinery; (3) IX.H.12.f. Hexcel Corporation: Salt Lake Operations; (4) IX.H.11.g. Holly Frontier Sinclair Woods Cross Refinery; and (5) IX.H.12.m. Tesoro Refining and Marketing Company LLC Marathon Refinery: Salt Lake City Refinery. A summary of the proposed new emission limits is outlined below.

The detailed analysis of our parallel process on the May 20, 2025 submission of draft revisions and BACM/BACT analyses to Utah state SIP section IX.H.12., can be found in our TSD in the docket.

We are proposing to approve, through parallel processing, the May 20, 2025 draft submission of revisions to the federally approved Utah SIP as listed in the Utah state SIP section IX.H.11. and 12. We are also proposing to find that the May 20, 2025 draft submission provides for the implementation of BACM/BACT for the five sources of direct PM 2.5 and PM 2.5 precursors listed above as expeditiously as practicable, for purposes of the 2006 24-hour PM 2.5 NAAQS in the Salt Lake City area, in accordance with the requirements of CAA section 189(b)(1)(B) and 40 CFR 51.1010. Additional detail can be found within the TSD in the docket.

Section 110(k) of the CAA addresses our actions on submissions of revisions to a SIP. The Act also requires states to observe procedural requirements in developing implementation plans and plan revisions for submission. Section 110(a)(2) of the Act provides that each implementation plan submitted by a state must be adopted after reasonable notice and public hearing. Section 110(l) of the Act similarly provides that each revision to an implementation plan submitted by a state under the Act must be adopted by the state after reasonable notice and public hearing.

We also must determine whether a submittal is complete and therefore warrants further review and action. 23 Our completeness criteria for SIP submittals is set out at 40 CFR part 51, appendix V. A submittal is deemed complete by operation of law under section 110(k)(1)(B) of the Act if a completeness determination is not made within six months after receipt of the submission.

On May 20, 2025, UDAQ submitted to the EPA for parallel processing a draft SIP revision based upon draft revisions to the Utah state SIP section IX.H.11. and 12., and R307-110-17. The comment period at the State level began March 1 and ended March 31, 2025, with a public hearing held online at 2:00 p.m. on March 13, 2025. UDAQ requested this parallel processing so as not to delay action on the 2006 24-hour PM 2.5 redesignations for the Salt Lake City and Provo NAAs. UDAQ is planning on submitting its final SIP revision early in July 2025. After the State formally submits these final revisions, the EPA will evaluate the final submittal for any changes between the proposed and final versions. As discussed above in section I.C., the EPA will determine if any changes to the draft submission would warrant another proposed rule, or if on the other hand the agency may proceed with a final action. This formal submission from the State of Utah will accompany either the final rule or the new proposed rule under this docket number.

As mentioned in the sections above, we are proposing to approve, through parallel processing, Utah's draft May 20, 2025 submission to revise the federally approved Utah SIP based upon revisions to the Utah state SIP sections IX.H.11. and 12., and the accompanying R307-110-17. Additionally, the EPA is proposing to approve for incorporation into the federally approved Utah SIP the five major stationary sources BACM/BACT analyses/updates for the Salt Lake City 2006 24-hour PM 2.5 NAA that were submitted as a draft on May 20, 2025.

In this document, the EPA is proposing to include regulatory text in an EPA final rule that includes incorporation by reference. In accordance with requirements of 1 CFR 51.5, the EPA is proposing to incorporate by reference R307-110-17 and Utah state SIP section IX.H.11. and 12, as discussed in sections I. and II. of this preamble. The EPA has made, and will continue to make, these materials generally available through https://www.regulations.gov and at the EPA Region 8 Office (please contact the person identified in the FOR FURTHER INFORMATION CONTACT section of this preamble for more information).

Under the CAA, the Administrator is required to approve a SIP submission that complies with the provisions of the CAA and applicable Federal regulations. 42 U.S.C. 7410(k); 40 CFR 52.02(a). Thus, in reviewing SIP submissions, EPA's role is to approve state choices, provided that they meet the criteria of the CAA. Accordingly, this action merely approves state law as meeting Federal requirements and does not impose additional requirements beyond those imposed by state law. For that reason, this action:

• Is not a significant regulatory action subject to review by the Office of Management and Budget under Executive Order 12866 (58 FR 51735, October 4, 1993);

• Is not subject to Executive Order 14192 (90 FR 9065, February 6, 2025) because SIP actions are exempt from review under Executive Order 12866;

• Does not impose an information collection burden under the provisions of the Paperwork Reduction Act (44 U.S.C. 3501 et seq. );

• Is certified as not having a significant economic impact on a substantial number of small entities under the Regulatory Flexibility Act (5 U.S.C. 601 et seq. );

• Does not contain any unfunded mandate or significantly or uniquely affect small governments, as described in the Unfunded Mandates Reform Act of 1995 (Pub. L. 104-4);

• Does not have federalism implications as specified in Executive Order 13132 (64 FR 43255, August 10, 1999);

• Is not subject to Executive Order 13045 (62 FR 19885, April 23, 1997) because it approves a state program;

• Is not a significant regulatory action subject to Executive Order 13211 (66 FR 28355, May 22, 2001); and

• Is not subject to requirements of section 12(d) of the National Technology Transfer and Advancement Act of 1995 (15 U.S.C. 272 note) because application of those requirements would be inconsistent with the CAA.

In addition, the SIP is not approved to apply on any Indian reservation land or in any other area where EPA or an Indian Tribe has demonstrated that a Tribe has jurisdiction. In those areas of Indian country, the rule does not have Tribal implications and will not impose substantial direct costs on Tribal governments or preempt Tribal law as specified by Executive Order 13175 (65 FR 67249, November 9, 2000).

Throughout this document, “we,” “us,” and “our” refer to the EPA.

The Clean Air Act (CAA) requires the EPA to establish primary and secondary NAAQS for certain pervasive pollutants that “may reasonably be anticipated to endanger public health and welfare.”  1 The primary NAAQS is designed to protect public health with an adequate margin of safety, and the secondary NAAQS is designed to protect public welfare and the environment. The EPA has set standards for six common air pollutants, referred to as criteria pollutants. These standards represent the air quality levels an area must meet to comply with the CAA.

PM 2.5 can be particles emitted by sources directly into the atmosphere as a solid or liquid particle (“primary PM 2.5 ” or “direct PM 2.5 ”) or can be particles that form in the atmosphere as a result of various chemical reactions from PM 2.5 precursor emissions emitted by sources (“secondary PM 2.5 ”). The EPA established each of the PM 2.5 NAAQS after considering substantial evidence from numerous health studies demonstrating that serious health effects are associated with exposures to PM 2.5 concentrations above such levels. Epidemiological studies have shown statistically significant correlations between elevated PM 2.5 levels and premature mortality. Other important health effects associated with PM 2.5 exposure include aggravation of respiratory and cardiovascular disease (as indicated by increased hospital admissions, emergency room visits, absences from school or work, and restricted activity dates), changes in lung function and increased respiratory symptoms, and new evidence for more subtle indicators of cardiovascular health. Individuals particularly sensitive to PM 2.5 exposure include older adults, people with heart and lung disease, and children. 2

On July 18, 1997, the EPA revised the NAAQS for particulate matter by establishing new NAAQS for particles with an aerodynamic diameter less than or equal to a nominal 2.5 micrometers (PM 2.5 ). 3 The EPA established primary and secondary annual and 24-hour standards for PM 2.5 . 4 The EPA set the annual primary and secondary standards at 15.0 micrograms per cubic meter (μg/m 3 ), based on a three-year average of annual mean PM 2.5 concentrations. 5 The EPA has since strengthened the primary annual PM 2.5 NAAQS;  6 however, the 1997 primary annual PM 2.5 NAAQS remains in effect in areas designated nonattainment for that NAAQS. 7

Following promulgation of a new or revised NAAQS, the EPA is required under CAA section 107(d) to designate areas throughout the nation as attainment, nonattainment, or unclassifiable for the NAAQS. Effective April 5, 2005, the EPA established the initial air quality designations for the 1997 annual PM 2.5 NAAQS, using air quality monitoring data for the three-year periods of 2001-2003 and 2002-2004. 8 The EPA designated the San Joaquin Valley as nonattainment for the 1997 annual PM 2.5 NAAQS. 9

The San Joaquin Valley PM 2.5 nonattainment area encompasses over 23,000 square miles and includes all or part of eight counties: San Joaquin, Stanislaus, Merced, Madera, Fresno, Tulare, Kings, and the valley portion of Kern. 10 The area is home to four million people and is one of the nation's leading agricultural regions. Stretching over 250 miles from north to south and averaging 80 miles wide, it is partially enclosed by the Coast Mountain range to the west, the Tehachapi Mountains to the south, and the Sierra Nevada range to the east.

The California Air Resources Board (CARB) is the state agency responsible for the adoption and submission to the EPA of California state implementation plan (SIP) submissions. Under California law, air districts in California are generally responsible for the development of regional air quality plans. For the San Joaquin Valley area, the San Joaquin Valley Unified Air Pollution Control District (SJVUAPCD or “District”) develops and adopts air quality management plans to address CAA planning requirements applicable to the region. The District then submits such plans to CARB for adoption and submission to the EPA as proposed revisions to the California SIP.

The EPA approved most of the elements of the State's attainment plan for the San Joaquin Valley for the 1997 annual PM 2.5 NAAQS on December 14, 2023, including the State's demonstration that the area would attain the NAAQS by December 31, 2023. 11 On May 23, 2024, the State of California transmitted a letter to the EPA requesting that the EPA grant a one-year extension under CAA section 172(a)(2)(C) of the applicable “Serious” area attainment date for the San Joaquin Valley from December 31, 2023, to December 31, 2024. 12 In its request, the State certified that it has complied with all requirements and commitments pertaining to the area in the approved implementation plan and that certified monitoring data for the San Joaquin Valley for 2023 were below the level of the 1997 annual PM 2.5 NAAQS. On November 19, 2024, the EPA granted the State's request and extended the applicable attainment date to December 31, 2024. 13

Sections 179(c) and 188(b)(2) of the CAA require that within six months following the applicable attainment date, the EPA shall determine whether a PM 2.5 nonattainment area attained the standard based on the area's design value  14 as of that date. 15 This determination, also referred to as a determination of attainment by the attainment date (DAAD), is based on certified data leading up to the attainment date, i.e., in this case, data for 2022-2024. Section 179(c)(2) of the CAA requires the EPA to publish the determination in the Federal Register .

Under the EPA's longstanding Clean Data Policy, which was reaffirmed in the PM 2.5 Implementation Rule at 40 CFR 51.1015, when an area has attained the relevant PM 2.5 standard(s), the EPA may issue a CDD (also sometimes referred to as a determination of attainment for the purposes of the Clean Data Policy) after notice and comment rulemaking determining that a specific area is attaining the relevant standard(s). A CDD is not linked to any particular attainment deadline and is not necessarily equivalent to a determination that an area has attained the standard by its applicable attainment deadline (i.e., a DAAD). The effect of a CDD is to suspend the requirement for the area to submit an attainment demonstration, a reasonably available control measures demonstration, a reasonable further progress (RFP) plan, contingency measures, and any other planning requirements related to attainment for as long as the area continues to attain the standard. 16 A CDD does not suspend the requirements for an emissions inventory or for new source review. 17

A determination of whether an area is attaining the NAAQS is typically based upon complete, quality-assured data gathered at established State and Local Air Monitoring Stations (SLAMS) and entered into the EPA's Air Quality System (AQS) database. Data from ambient air monitors operated by state/local agencies in compliance with the EPA monitoring requirements must be submitted to AQS. Monitoring agencies annually certify that these data are accurate to the best of their knowledge. Accordingly, the EPA relies primarily on data in AQS when determining compliance with the NAAQS. 18 The EPA reviews all data to determine the area's air quality status in accordance with 40 CFR part 50, appendix N. Under EPA regulations in 40 CFR 50.7 and in accordance with appendix N, the 1997 annual PM 2.5 NAAQS are met when the annual arithmetic mean concentration, as determined in accordance with the rounding conventions in 40 CFR part 50, appendix N, is less than or equal to 15.0 µg/m 3 at each eligible monitoring site within the area.

For the annual PM 2.5 standard, eligible monitoring sites are those monitoring stations that meet the criteria specified in 40 CFR 58.11 and 58.30 and thus are approved for comparison to the annual PM 2.5 NAAQS. 19 Three years of valid annual means are required to produce a valid annual PM 2.5 NAAQS design value. 20 Data completeness requirements for a given year are met when at least 75 percent of the scheduled sampling days for each quarter have valid data. 21 We note that monitors with incomplete data in one or more quarters may still produce valid design values if the conditions for applying the EPA's data substitution test are met. 22 In determining whether data are suitable for regulatory determinations, the EPA uses a “weight of evidence” approach, considering the requirements of 40 CFR part 58, appendix A “in combination with other data quality information, reports, and similar documentation that demonstrate overall compliance with Part 58.”  23

Section 110(a)(2)(B)(i) of the CAA requires states to establish and operate air monitoring networks to compile data on ambient air quality for all criteria pollutants. The monitoring requirements are specified in 40 CFR part 58. These requirements are applicable to state and, where delegated, local air monitoring agencies that operate criteria pollutant monitors. The regulations in 40 CFR part 58 establish specific requirements for operating air quality surveillance networks to measure ambient concentrations of PM 2.5 , including requirements for measurement methods, network design, quality assurance procedures, and, in the case of large urban areas, the minimum number of monitoring sites designated as SLAMS.

In section 4.7 of appendix D to 40 CFR part 58, the EPA specifies minimum monitoring requirements for PM 2.5 to operate at SLAMS. SLAMS produce data comparable to the NAAQS, and therefore, the monitor must be an approved federal reference method (FRM) or federal equivalent method (FEM). The minimum number of SLAMS required is described in section 4.7.1 and can be met by either filter-based or continuous FRMs or FEMs. The monitoring regulations also provide that each core-based statistical area must operate a minimum number of PM 2.5 continuous monitors;  24 however, this requirement can be met by either an FEM or a non-FEM continuous monitor, and the continuous monitors can be located with other SLAMS or at a different location. Consequently, the monitoring requirements for PM 2.5 can be met with filter-based FRMs/FEMs, continuous FEMs, continuous non-FEMs, or a combination of monitors at each required SLAMS.

Under 40 CFR 58.10, states are required to submit annual monitoring network plans to the EPA. 25 Within the San Joaquin Valley, CARB and the District are the agencies responsible for assuring that the area meets PM 2.5 air quality monitoring requirements. CARB and SJVUAPCD submit monitoring network plans to the EPA annually. These plans describe and discuss the status of the air monitoring network, as required under 40 CFR 58.10. Each year, the EPA reviews these annual network plans for compliance with the applicable monitoring requirements in 40 CFR part 58. With respect to PM 2.5 , we have found that the CARB and SJVUAPCD annual network plans meet the applicable requirements under 40 CFR part 58. 26

During the 2022-2024 period, ambient PM 2.5 concentration data that are eligible for use in determining whether an area has attained the PM 2.5 NAAQS were collected at a total of 18 sites within the San Joaquin Valley. The District operates 12 of these sites while CARB operates 6 of these sites. All of the sites are designated SLAMS for PM 2.5 . 27 Based on our review of the PM 2.5 monitoring network, we propose to find that the monitoring network in the San Joaquin Valley is adequate for the purpose of collecting ambient PM 2.5 concentration data for use in determining whether the San Joaquin Valley has attained the 1997 annual PM 2.5 NAAQS.

Under 40 CFR 58.15, monitoring agencies must submit a letter to the EPA each year to certify that all of the ambient concentration and quality assurance data for the previous year have been submitted to AQS and that the ambient concentration data are accurate to the best of their knowledge, taking into consideration the quality assurance findings. The letter must address data for all FRM and FEM monitors at SLAMS and special purpose monitoring stations that meet the criteria specified in 40 CFR part 58, appendix A. CARB annually certifies that the data the agency submits to AQS are quality assured, including the data collected at monitoring sites in the San Joaquin Valley. 28 SJVUAPCD does the same for data submitted to AQS from monitoring sites operated by the District. 29

With respect to data completeness, we determined that the data collected by the CARB and the District met the quarterly completeness criterion for all 12 quarters of the three-year period at most of the PM 2.5 monitoring sites in the San Joaquin Valley. More specifically, among the 18 PM 2.5 monitoring sites from which regulatory data are available, the data from Merced-Vierra (AQS ID: 06-047-2024), Stockton-University (AQS ID: 06-077-1003), and Manteca (AQS ID: 06-077-2010) did not meet the 75 percent completeness criterion for one quarter;  30 however, the data from the sites are sufficient nonetheless to produce valid design values for the 1997 annual PM 2.5 NAAQS pursuant to the rules governing design value validity in 40 CFR part 50, appendix N, section 4.1.

Finally, the EPA conducts regular technical systems audits (TSAs) where we review and inspect state and local ambient air monitoring programs to assess compliance with applicable regulations concerning the collection, analysis, validation, and reporting of ambient air quality data. For the purposes of this proposal, we reviewed the findings from the EPA's most recent TSAs of CARB's and the District's ambient air monitoring programs. 31 The results of the TSAs do not preclude the EPA from determining that the San Joaquin Valley PM 2.5 nonattainment area has attained the 1997 annual PM 2.5 NAAQS.

In summary, based on the EPA's reviews of the relevant annual network plans, certifications, quality assurance data, and TSAs, we propose to find that the PM 2.5 data collected at San Joaquin Valley monitoring sites are suitable for determining whether the San Joaquin Valley PM 2.5 nonattainment area has attained the 1997 annual PM 2.5 NAAQS.

Table 1 of this document provides the PM 2.5 design values at each of the 18 monitoring sites within the San Joaquin Valley PM 2.5 nonattainment area, expressed as a single design value representing the 2022-2024 period and for each individual year. The PM 2.5 data show that the design values at the San Joaquin Valley monitoring sites were below the level of the 1997 annual PM 2.5 NAAQS of 15.0 μg/m 3 . Consequently, the EPA is proposing to determine based upon three years of quality-assured and certified data from 2022 through 2024 that the San Joaquin Valley PM 2.5 nonattainment area attained the 1997 annual PM 2.5 NAAQS by the applicable December 31, 2024 attainment date.

As described in section I.D. of this document, when an area has attained the relevant PM 2.5 standard(s), the EPA may issue a CDD after notice and comment rulemaking determining that a specific area is attaining the relevant standard. 32 Based on quality-assured and certified data for 2022-2024, the San Joaquin Valley PM 2.5 nonattainment area meets the 1997 annual PM 2.5 NAAQS. Furthermore, preliminary data available in AQS for 2025 (January through March) indicate that the area continues to show concentrations consistent with attainment of the 1997 annual PM 2.5 NAAQS. 33 Consequently, the EPA is proposing to issue a CDD.

If we finalize this proposed CDD, the obligation to submit attainment planning provisions to meet the requirements for an attainment plan for the 1997 annual PM 2.5 NAAQS, including an RFP plan, quantitative milestones and quantitative milestone reports, contingency measures, and an attainment demonstration, are suspended until such time as: (1) the area is redesignated to attainment, after which such requirements are permanently discharged; or (2) the EPA determines that the area has re-violated the PM 2.5 NAAQS, at which time the state shall submit such attainment plan elements for the nonattainment area by a future date to be determined by the EPA and announced through publication in the Federal Register at the time the EPA determines the area is violating the PM 2.5 NAAQS.

A CDD does not suspend the requirements for an emissions inventory or new source review (NSR). The EPA previously approved the base year emissions inventory element of the attainment plan for the 1997 annual PM 2.5 NAAQS as meeting the requirements of CAA section 172(c)(3) and 40 CFR 50.1008. 34 On January 21, 2025, the EPA proposed a limited approval and limited disapproval of nonattainment NSR SIP revisions submitted by California for the San Joaquin Valley. 35 We are not taking any further action on the submissions at this time.

For the reasons discussed in this document, the EPA is proposing to determine, based on the most recent three years (2022-2024) of complete (or otherwise validated), quality-assured, and certified data meeting the requirements of 40 CFR part 50, appendix N, that the San Joaquin Valley PM 2.5 nonattainment area attained the 1997 annual PM 2.5 NAAQS by its December 31, 2024 attainment date. This action, when finalized, will fulfill the EPA's statutory obligation to determine whether the San Joaquin Valley PM 2.5 nonattainment area attained the NAAQS by the attainment date.

In accordance with 40 CFR 51.1015, we are also proposing to issue a CDD for the San Joaquin Valley PM 2.5 nonattainment area for the 1997 annual PM 2.5 NAAQS. Accordingly, the EPA is proposing to determine that the obligation to submit any attainment-related SIP revisions is not applicable for so long as the area continues to attain those NAAQS. This CDD does not constitute a redesignation to attainment. The San Joaquin Valley PM 2.5 nonattainment area will remain designated nonattainment for the 1997 annual PM 2.5 NAAQS until such time as the EPA determines, pursuant to sections 107 and 175A of the CAA, that the San Joaquin Valley PM 2.5 nonattainment area meets the CAA requirements for redesignation to attainment, including an approved maintenance plan showing that the area will continue to meet the standard for 10 years.

The EPA is soliciting public comments on the issues discussed in this document. We will accept comments from the public on this proposal for the next 30 days. We will consider these comments before taking final action.

Additional information about these statutes and Executive Orders can be found at https://www.epa.gov/laws-regulations/laws-and-executive-orders.

This action is not a significant regulatory action and was therefore not submitted to the Office of Management and Budget (OMB) for review.

This action is not expected to be an Executive Order 14192 regulatory action because this action is not significant under Executive Order 12866.

This action does not impose an information collection burden under the PRA because this proposed action does not impose additional requirements beyond those imposed by state law.

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 beyond those imposed by state law.

This action does not contain any unfunded mandate as described in UMRA, 2 U.S.C. 1531-1538, and does not significantly or uniquely affect small governments. This action does not impose additional requirements beyond those imposed by state law. Accordingly, no additional costs to state, local, or Tribal governments, or to the private sector, will result from this action.

This action does not have federalism implications. It will not have substantial direct effects on the states, on the relationship between the national government and the states, or on the distribution of power and responsibilities among the various levels of government.

This action does not have Tribal implications, as specified in Executive Order 13175, because the SIP is not approved to apply on any Indian reservation land or in any other area where the EPA or an Indian Tribe has demonstrated that a Tribe has jurisdiction, and it will not impose substantial direct costs on Tribal governments or preempt Tribal law. Thus, Executive Order 13175 does not apply to this action.

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 children, per the definition of “covered regulatory action” in section 2-202 of the Executive Order. Therefore, this action is not subject to Executive Order 13045 because it merely proposes a DAAD and a CDD. Furthermore, the EPA's Policy on Children's Health does not apply to this action.

This action is not subject to Executive Order 13211, because it is not a significant regulatory action under Executive Order 12866.

Section 12(d) of the NTTAA directs the EPA to use voluntary consensus standards in its regulatory activities unless to do so would be inconsistent with applicable law or otherwise impractical. The EPA believes that this action is not subject to the requirements of section 12(d) of the NTTAA because application of those requirements would be inconsistent with the CAA.

Throughout this document wherever “we,” “us,” or “our” is used, we mean the EPA.

Whenever EPA promulgates a new or revised NAAQS, CAA section 110(a)(1) requires states to make SIP submissions to provide for the implementation, maintenance, and enforcement of the NAAQS. This type of SIP submission is commonly referred to as an “infrastructure SIP.” These submissions must meet the various requirements of CAA section 110(a)(2), as applicable. EPA has previously provided states with direction  1 on the application of these CAA provisions and through regional actions on infrastructure submissions. Unless otherwise noted below, we are following that existing approach in acting on this submission. In addition, in the context of acting on such infrastructure submissions, EPA evaluates the submitting state's SIP for factual compliance with statutory and regulatory requirements, not for the state's implementation of its SIP. EPA has other authority to address any issues concerning a state's implementation of the rules, regulations, consent orders, etc. that comprise its SIP.

The Montana Department of Environmental Quality (MDEQ) submitted the following revisions to its infrastructure SIP (ISIP):

• 2015 Ozone ISIP submitted on October 1, 2018, and

• Revisions to appendix W submitted on December 28, 2022.

CAA section 110(a)(1) provides the procedural and timing requirements for SIP submissions after a new or revised NAAQS is promulgated. Section 110(a)(2) lists specific elements the SIP must contain or satisfy. These infrastructure elements include requirements such as modeling, monitoring, and emission inventories, which are designed to ensure attainment and maintenance of the NAAQS. The elements that are subject to this action are listed below:

• Section 110(a)(2)(A): Emission limits and other control measures.

• Section 110(a)(2)(B): Ambient air quality monitoring/data system.

• Section 110(a)(2)(C): Program for enforcement of control measures/minor new source review (NSR)/prevention of significant deterioration (PSD).

• Section 110(a)(2)(D): Interstate transport.

• Section 110(a)(2)(E): Adequate resources and authority, conflict of interest, and oversight of local governments and regional agencies.

• Section 110(a)(2)(F): Stationary source monitoring and reporting.

• Section 110(a)(2)(G): Emergency powers.

• Section 110(a)(2)(H): Future SIP revisions.

• Section 110(a)(2)(I): Plan revisions for nonattainment areas (under part D);

• Section 110(a)(2)(J): Consultation with government officials; public notification; and PSD and visibility protection.

• Section 110(a)(2)(K): Air quality modeling/data.

• Section 110(a)(2)(L): Permitting fees.

• Section 110(a)(2)(M): Consultation/participation by affected local entities.

Montana provided a detailed synopsis of how various components of its SIP meet each of the applicable requirements in section 110(a)(2) for the 2015 ozone NAAQS. The following review evaluates the SIP's submission.

This section requires SIPs to include enforceable emission limits and other control measures, means or techniques, schedules for compliance, and other related matters. EPA has long interpreted emission limits and control measures for attaining the standards as being due when nonattainment planning requirements are due. 2 In the context of an infrastructure SIP, EPA is not evaluating the existing SIP provisions for this purpose. Instead, EPA is only evaluating whether the State's SIP has basic structural provisions for the implementation of the NAAQS.

The Montana Code Annotated (MCA) 75-2-112 gives MDEQ the authority to “adopt, amend, and repeal rules for the administration, implementation, and enforcement of this chapter.

Montana implements a statewide program for permitting major and minor stationary sources of air pollution, including sources of ozone precursors. Specific control measures adopted in Montana Board of Environmental Review (BER) Orders, along with multiple SIP-approved state air quality regulations within the Administrative Rules of Montana (ARM) and cited in Montana's certifications, provide enforceable emission limitations and other control measures, means of techniques, schedules for compliance, and other related matters necessary to meet the requirements of CAA section 110(a)(2)(A) for the 2015 ozone NAAQS. Montana's certifications generally list provisions and enforceable control measures within its SIP which regulate pollutants through various programs, including its stationary permitting program which requires sources to demonstrate that emissions will not cause or contribute to violation of any NAAQS (ARM 17.8.749). In the case of Montana, this meets the requirements of section 110(a)(2)(A) for the 2015 ozone NAAQS.

This section requires SIPs to provide for establishing and operating ambient air quality monitors, collecting, and analyzing ambient air quality data, and upon request, to make these data available to EPA. Submission of annual monitoring network plans (AMNP) consistent with EPA's ambient air monitoring regulations at 40 CFR 58.10 is one way of satisfying requirements to provide EPA information regarding air quality monitoring activities. 3 EPA's review of a state's annual monitoring plan includes EPA's determination that the state: (i) monitors air quality at appropriate locations throughout the state using EPA-approved Federal Reference Methods or Federal Equivalent Method monitors; (ii) submits data to EPA's Air Quality System in a timely manner; and, (iii) provides EPA Regional offices with prior notification of any planned changes to monitoring sites or the network plan.

A comprehensive AMNP, was submitted to EPA by Montana on July 1, 2018, and subsequently approved by the EPA. 4 Montana's SIP-approved regulations provide for the design and operation of its monitoring network, reporting of data obtained from the monitors, and annual network review including notification to the EPA of any changes, and public notification of exceedance of NAAQS. As described in the submission, Montana operates a comprehensive monitoring network, including ozone monitoring, compiles and analyzes collected data, and submits the data to the EPA's Air Quality System on a quarterly basis.

Based on this information, we are proposing to approve the Montana SIP as meeting the requirements of CAA section 110(a)(2)(B) for the 2015 ozone NAAQS.

Section 110(a)(2)(C) requires states to have a plan that includes a program providing for enforcement of all SIP measures, regulation of minor sources and minor modifications, and the regulation of the modification and construction of each stationary source, including a program to meet the Prevention of Significant Deterioration (PSD) of air quality. This section requires SIPs to set forth a program providing for enforcement of all SIP measures, and the regulation of construction of new and modified stationary sources to meet the NSR requirements under PSD and Nonattainment NSR (NNSR) programs. Part C of the CAA (sections 160-169B) addresses PSD, while part D of the CAA (sections 171-193) addresses NSR requirements. A state must also provide for the regulation of minor source and minor modifications (minor NSR). 5 The NNSR requirements of section 110(a)(2)(C) are generally outside the scope of infrastructure SIPs. The EPA is not evaluating nonattainment-related provisions, such as the NNSR program required by Part D of the CAA. The EPA is evaluating the State's PSD program as required by Part C of the CAA and the State's minor NSR programs as required by 110(a)(2)(C).

With respect to Element (C), each state is required to make an infrastructure SIP submission for a new or revised NAAQS demonstrating that the air agency has a complete PSD permitting program meeting the current requirements for all regulated NSR pollutants. 6 The requirements for Element (J) in relation to a comprehensive PSD Permitting Program are the same as the requirements with respect to Element (C). 7

Montana's submission has shown that is has a PSD program  8 in place that covers all regulated NSR pollutants.

The State has adopted a minor NSR program  9 in the approved SIP, which is adopted under section 110(a)(2)(C) of the CAA. The minor NSR program was originally approved by EPA on March 22, 1972. Since approval of the minor NSR program, the State and EPA have relied on the program to assure that new and modified sources not captured by the major NSR permitting programs do not interfere with attainment and maintenance of the NAAQS. Montana's minor NSR program, as approved in the SIP, covers the construction and modification of regulated NSR pollutants, including PM 2.5 , lead, and ozone and its precursors.

The Montana submission refers to the following state rules and regulations which are SIP-approved, that address and provide for meeting all provisions and requirements of CAA section 110(A)(2)(C).

• 75-2-111, MCA.

• 75-2-112, MCA.

• ARM 17.8.130.

• ARM 17.8.801 et seq.

• ARM 17.8.901 et seq.

• ARM 17.8.10001 et seq.

The EPA is proposing to approve Montana's infrastructure SIP for the 2015 ozone NAAQS, with respect to the general requirements in section 110(a)(2)(C) to include a program in the SIP that regulates the enforcement, modification, and construction of any stationary sources as necessary to assure the NAAQS are achieved.

CAA section 110(a)(2)(D)(i) consists of four separate elements, or “prongs”. CAA section 110(a)(2)(D)(i)(I) requires SIPs to contain adequate provisions prohibiting emissions that will contribute significantly to nonattainment of the NAAQS in any other state (prong 1), and adequate provisions prohibiting emissions that will interfere with maintenance of the NAAQS by any other state (prong 2). CAA section 110(a)(2)(D)(i)(II) requires SIPs to contain adequate provisions prohibiting emissions that will interfere with any other state's required measures to prevent significant deterioration of its air quality (prong 3), and adequate provisions prohibiting emissions which will interfere with any others state's required measures to protect visibility (prong 4). Under section 110(a)(2)(D)(i)(I) of the CAA, the EPA and states must give independent consideration to both the prong 1 “significant contribution to nonattainment” requirement and the prong 2 “interference with maintenance” requirement when evaluating downwind air quality problems under section 110(a)(2)(D)(i)(I). 10 For more information on Montana and EPA's analysis of prongs 1 and 2 for this NAAQS, see our proposed approval of the CAA section 110(a)(2)(D)(i)(I) portion of Montana's October 1, 2018 ISIP. 11

The EPA took final action on the prong 1 and prong 2 requirements of the CAA section 110(a)(2)(D)(i)(I) for the 2015 ozone NAAQS for Montana on April 12, 2022 (87 FR 21578). In that rulemaking, the EPA determined that Montana's SIP contains adequate provisions to prohibit emissions that will significantly contribute to nonattainment or interfere with maintenance of the 2015 ozone NAAQs in any other state. 12 The prong 3 (PSD) requirement of the CAA section 110(a)(2)(D)(i)(II) may be met for all NAAQS by a state's confirmation in an infrastructure SIP submission that new major sources and major modifications in the state are subject to a comprehensive EPA-approved PSD permitting program in the SIP that applies to all regulated NSR pollutants and that satisfies the requirements of the EPA's PSD implementation rule(s). 13 EPA is proposing approval of prong 3 in this rulemaking.

To meet the prong 4 (visibility) requirement of the CAA section 110(a)(2)(D)(i)(II) under the 2015 ozone NAAQS, a SIP must address the potential for interference with visibility protection caused by ozone, including precursors. An approved regional haze SIP that fully meets the regional haze requirements in 40 CFR 51.308 satisfies the 110(a)(2)(D)(i)(II) requirement for visibility protection as it ensures that emissions from the state will not interfere with measures required to be included in other state SIPs to protect visibility. In the absence of a fully approved regional haze SIP, a state can still make a demonstration that satisfies the visibility requirement section of 110(a)(2)(D)(i)(II). 14 EPA will consider Montana's visibility provisions through a future rulemaking.

CAA section 110(a)(2)(D)(ii) requires SIPs to include provisions ensuring compliance with the applicable requirements of CAA sections 126 and 115 (relating to interstate and international pollution abatement). CAA section 126 requires notification to neighboring states of potential impacts from a new or modified major stationary source and specifies how a state may petition the EPA when a major source or group of stationary sources in a state is thought to contribute to certain pollution problems in another state. CAA section 115 governs the process for addressing air pollutants emitted in the United States that cause or contribute to air pollution that may reasonably be anticipated to endanger public health or welfare in a foreign country.

To address CAA section 110(a)(2)(D)(ii), Montana states that its SIP-approved PSD program (specifically, ARM 17.8.826(2)(d)) requires the MDEQ to notify potentially affected states, Trbes, and federal land managers (FLMs) of its intent to approve or disapprove a PSD permit application. Montana also states that nothing in its SIP precludes the state from ensuring compliance with CAA sections 126 and 115 with respect to the 2015 ozone NAAQS. Montana asserts that no sources within the state are the subject of an active finding under CAA section 126 with respect to the 2015 ozone NAAQS, nor are there any findings against Montana under CAA section 115 for this NAAQS. For these reasons, Montana concludes that its SIP meets the requirements of CAA section 110(a)(2)(D)(ii) for the 2015 ozone NAAQS.

For the EPA's analysis of CAA section 110(a)(2)(D)(ii), we reviewed the sections of the Montana SIP referenced by the State in its 2015 Ozone infrastructure SIP submission. As required by 40 CFR 51.166(q)(2)(iv), Montana's SIP-approved PSD program requires notice of proposed new sources or modifications to states whose lands may be significantly affected by emissions from the source or modification ( see ARM 17.8.826(2)(d)). This provision satisfies the notice requirement of section 126(a). Montana also has no pending obligations under sections 126(c) or 115(b). Therefore, the Montana SIP currently meets the requirements of those sections. On these bases, the EPA is proposing to find that the Montana SIP meets the requirements of CAA section 110(a)(2)(D)(ii) for the 2015 ozone NAAQS.

Section 110(a)(2)(E)(i) requires each SIP to provide necessary assurances that the state will have adequate personnel, funding, and legal authority under state law to carry out its SIP. In addition, section 110(a)(2)(E)(ii) requires each state to comply with the requirements respecting state boards under CAA section 128. Finally, section 110(a)(2)(E)(iii) requires that, where a state relies upon local or regional governments or agencies for implementation of its SIP provisions, the state retains responsibility for ensuring implementation of SIP obligations with respect to relevant NAAQS.

The provisions contained in 75-2-102, MCA, 75-2-111, MCA, and 75-2-112, MCA, provide adequate authority for the State of Montana and the MDEQ to carry out its SIP obligations with respect to the 2015 ozone NAAQS. The State receives section 103 and 105 grant funds through its Performance Partnership Grant, along with required state matching funds to provide funding necessary to carry out Montana's SIP requirements. Montana's Performance Partnership Agreement with the EPA, documents that the State has the resources to carry out agreed environmental program goals, measures, and commitments, including developing and implementing appropriate SIPs for all areas of the State. Annually, states update these grant commitments based on current SIP requirements, air quality planning, and applicable requirements related to the NAAQS. Therefore, we propose to approve Montana's SIP meeting the requirements of section 110(a)(2)(E)(i) for the 2015 ozone NAAQS.

With respect to section 110(a)(2)(E)(iii), the regulations cited by Montana in their certifications (75-2-111 and 75-2-112, MCA) and contained within this docket also provide the necessary assurances that the state has the responsibility for adequate implementation of SIP provisions by local governments. Therefore, we propose to approve Montana's SIP meeting the requirements of section 110(a)(2)(E)(iii) for the 2015 ozone NAAQS.

Section 110(a)(2)(E)(ii) requires each SIP to contain provisions that comply with the state board requirements of section 128 of the CAA. That provision contains two explicit requirements: (1) that any board or body which approves permits or enforcement orders under this chapter shall have at least a majority of members who represent the public interest and do not derive any significant portion of their income from persons subject to permits and enforcement order under this chapter, and (2) that any potential conflicts of interest by members of such board or body or the head of an executive agency with similar powers be adequately disclosed. Section 128 further provides that a state may adopt more stringent conflicts of interest requirements and require EPA to approve such requirements submitted as part of a SIP.

The New Rules I (ARM 17.8.150), II (17.8.151) and III (ARM 17.8.152) adopted by the BER on October 16, 2015, were submitted and approved by the EPA for inclusion in the SIP on December 17, 2015, and contain provisions that meet the requirements of section 128(a)(1) and section 128(a)(2) ( See 81 FR 4234). Montana's SIP continues to meet the requirements of section 110(a)(2)(E)(ii). EPA proposes that Montana meets the infrastructure requirements of this portion of section 110(a)(2)(E) for the 2015 ozone NAAQS.

States must establish a system to monitor emissions from stationary sources and submit periodic emission reports. Each plan shall also require the installation, maintenance, and replacement of equipment, and the implementation of other necessary steps, by owners, or operators of stationary sources to monitor emissions from such sources. The state plan shall also require periodic reports on the nature and amounts of emissions and emissions-related data from such sources, and correlation of such reports by each state agency with any emission limitations or standards. Lastly, the reports shall be available at reasonable times for public inspection.

The provisions cited by Montana (ARM 17.8.105 and 17.8.106) pertain to testing requirements and protocols. Montana also incorporates by reference 40 CFR part 51, appendix P regarding minimum reporting requirements. ( See ARM 17.8.103(1)(D)). In addition, Montana provides for monitoring, recordkeeping, and reporting requirements for sources subject to minor and major source permitting.

Furthermore, Montana is required to submit emissions data to the EPA for purposes of the National Emissions Inventory (NEI). The NEI is the EPA's central repository for air emissions data. The EPA published the Air Emissions Reporting Rule (AERR) on December 5, 2008, which modified the requirements for collecting and reporting air emissions data ( See 73 FR 76539). The AERR shortened the time states had to report emissions data from 17 months to 12 months, giving states one calendar year to submit emissions data. All states are required to submit comprehensive emission inventories every three years and report emissions for certain larger sources annually through the EPA's online Emissions Inventory System. States report emissions data for the six criteria pollutants and their associated precursors—nitrogen oxides, sulfur dioxides, ammonia, lead, carbon monoxide, particulate matter, and volatile organic compounds. Many states also voluntarily report emissions of hazardous air pollutants. Montana made its latest update to the NEI in 2024, however for purposes of this proposed action the emissions data are based on the 2017 NEI released in February 2019 since that included the State's most recent NEI update at the time of the October 1, 2018 ISIP submittal. Based on the analysis above, we propose to approve the Montana SIP as meeting the requirements of CAA section 110(a)(2)(F) for the 2015 ozone NAAQS.

This section requires that a plan provide for state authority analogous to that provided to the EPA Administrator in section 303 of the CAA, and adequate contingency plans to implement such authority. Section 303 of the CAA provides authority to the EPA administrator to seek a court order to restrain any source from causing or contributing to emissions that present an “imminent and substantial endangerment to public health or welfare or the environment” in the event that “it is not practicable to assure prompt protection. . . . by commencement of such civil action.”

Montana's SIP submittals with regard to the section 110(a)(2)(G) emergency order requirements explain that Montana has an EPA-approved Emergency Episode Avoidance Plan (EEAP) ( See 71 FR 19, Jan. 3, 2006). According to the EEAP, “the Department shall take the necessary precautions to protect public health as set forth in 75-2-402, MCA, “Emergency Powers.” These precautions include, but are not limited to, ordering a halt or curtailment of any operations, activities, processes, or conditions the Department believes are contributing to the air pollutant emergency episode.” Montana's submission cites 75-2-402, MCA, as providing general authority comparable to CAA section 303. The submission also cites 75-2-112(2)(a) and 75-2-111(3), MCA. Under 75-2-111(3) MCA, Montana's environmental review board has broad authority to “issue orders necessary to effectuate the purposes” of Chapter 2. Also, under 75-2-112(2)(a) MCA, the MDEQ has the authority to use “appropriate administrative and judicial proceedings” to enforce orders issued by the board. Any air pollution discharge that created an emergency situation would constitute a violation of the chapter and its purposes; therefore, providing the BER and the MDEQ authority to issue administrative orders to stop discharges that cause emergencies effecting welfare and the environment.

While no single Montana statute mirrors the authorities of CAA section 303, we propose to find that the combination of MCA provisions discussed above provide for authority comparable to section 303 to immediately bring suit to restrain and issue emergency orders for applicable emergencies to take prompt administrative action against any person causing or contributing to air pollution that presents an imminent and substantial endangerment to public health or welfare, or the environment and, therefore are sufficient to meet the authority requirement of CAA section 110(a)(2)(G).

States must also have adequate contingency plans adopted into their SIP to implement the air agency's emergency episode authority (as discussed above). Requirements for contingency plans are provided in 40 CFR part 51, subpart H. The EPA approved Montana's EEAP in 71 FR 19 (Jan. 3, 2006). We find that Montana's air pollution emergency rules include ozone and establish stages of episode criteria; provide for public announcement whenever any episode stage has been determined to exist; and specify emission control actions to be taken at each episode stage. These are consistent with the EPA emergency episode SIP requirements set forth at 40 CFR part 51, subpart H (prevention of air pollution emergency episode) for ozone.

Based on the above analysis, we propose approval of Montana's SIP as meeting the requirements of CAA section 110(a)(2)(G) for the 2015 ozone NAAQS.

This section requires that a state's SIP provide for revision may be necessary, to take account of changes in the NAAQS or availability of improved methods for attaining the NAAQS and whenever EPA finds that the SIP is substantially inadequate.

Montana's statutory provisions in the Montana CAA at 75-2-101 et. seq., give the BER sufficient authority to meet the requirements of 110(a)(2)(H). Therefore, we propose to approve Montana's SIP as meeting the requirements of the CAA section 110(a)(2)(H).

Section 110(a)(2)(I) provides that each plan, or plan revisions for an area designated as a nonattainment area, shall meet the applicable requirements of part D of the CAA. EPA interprets section 110(a)(2)(I) to be inapplicable to the infrastructure SIP process because specific SIP submissions designated nonattainment areas, as required by part D, are subject to different submission schedule under subparts 2 through 5 of part D, extending as far as 10 years following areas of designation for some elements, whereas infrastructure SIP submissions are due within three years after adoption or revision of a NAAQS. Accordingly, EPA takes action on part D attainment plans through separate processes.

Section 110(a)(2)(J) of the CAA requires that each SIP “meet the applicable requirements of section 121 of this title (relating to consultation), section 127 of this title (relating to public notification) and part C of this subchapter (relating to PSD of air quality and visibility protection).”

The Montana submissions reference the following specific laws and regulations relating to consultation with identified officials on certain air agency actions, public notifications, prevention of significant deterioration, and visibility protection:

• MCA 2-3-203.

• ARM 17.8.801 et seq. —Prevention of Significant Deterioration of Air Quality.

• ARM 17.8.901 et seq. —Permit Requirements for Major Stationary Sources of Major Modifications Locating within Nonattainment Areas.

• ARM 17.8.1001 et seq. —Preconstruction Permit Requirements for Major Stationary Sources of Major Modifications Locating within Attainment or Unclassified areas.

• Montana's Emergency Episode Avoidance Plan (EEAP) SIP.

(i) Montana has demonstrated that it has authority and rules in place to provide a process a process of consultation with general purpose local governments, designated organizations of elected officials of local governments, designated organizations of elected officials of local governments and any FLM having authority over federal land to which the SIP applies, consistent with the requirements of CAA section 121 (59 FR 2988, Jan. 20, 1994). Moreover, Montana's Emergency Episode Avoidance Plan, approved into the SIP (71 FR 19, Jan, 3, 2006), meets the general requirements of CAA section 127.

Montana has demonstrated that it has the authority and rules in place to provide a process of consultation with general purpose local governments, designated organizations with elected officials of local governments and any FLM having authority over Federal land to which the SIP applies, consistent with the requirements of CAA section 121 ( See 59 FR 2988, Jan. 20, 1994). Furthermore, Montana's Emergency Episode Avoidance Plan, approved into the SIP ( See 71 FR 19, Jan, 3, 2006), meets the general requirements of the CAA section 127.

Addressing the requirement in CAA section 110 (a)(2)(J) that the SIP meet the applicable requirements of part C, title 1 of the CAA, we have evaluated this requirement in the context of CAA section 110(a)(2)(C). The EPA most recently approved revisions to Montana's PSD program on June 26, 2018 ( See 83 FR 29694), updating the program consistency with CAA requirements. Therefore, we are proposing to approve the Montana SIP as meeting the requirements of CAA 110(a)(2)(J) with respect to PSD for the 2015 Ozone NAAQS.

With regard to applicable visibility protection requirements, the EPA recognizes that states are subject to visibility and regional haze program requirements under part C of the CAA. In the event of an establishment of a new NAAQS, however, the visibility and regional haze program requirements under part C does not change. Consequently, we find that there is no new applicable requirement relating to visibility triggered under CAA section 110(a)(2)(J) when a new NAAQS becomes effective.

Based on the above analysis, we are proposing to approve the Montana SIP as meeting the requirements of CAA section 110(a)(2)(J) for the 2015 Ozone NAAQS.

Section 110(a)(2)(K) of the CAA requires that SIPs provide for (i) the performance of air quality modeling as the Administrator may prescribe for the purpose of predicating the effect on air quality of any emissions of any air pollutant for which the Administrator has established a NAAQS, and (ii) the submission, upon request, of data related to such air quality modeling to the Administrator.

The EPA's requirements for air quality modeling for criteria pollutants are found in 40 CFR part 51, appendix W Guideline on Air Quality Models. On January 17, 2017 ( See 82 FR 5182), the EPA revised appendix W, effective February 16, 2017. The Federal Register document stated: “For all regulatory applications covered under the Guideline, except for transportation conformity, the changes to appendix A preferred models and revisions to the requirements and recommendations of the Guidelines must be integrated into the regulatory processes of respective reviewing authorities and followed by applicants by no later than January 17, 2018.”

In the September 26, 2018 submission, Montana cites ARM 17.8.821 (MT's PSD Program) which requires estimates of ambient air concentrations be based on applicable air quality models specified in appendix W of 40 CFR part 51, pertaining to the Guidelines on Ambient Air Quality Models. Additionally, Montana cites in its State rules and regulations, as contained within ARM 17.8.701, ARM 17.8.801, ARM 17.8.901, and ARM 17.8.1001 (regulating construction of new or modified stationary sources consistent with PSD and NSR requirements) shall demonstrate the facility can be expected to operate in compliance with applicable law and that it will not cause or contribute to a violation of any NAAQS.

ARM 17.8.802(1)(b) incorporates appendix W by reference without a specific date. ARM 17.8.102(1)(a) provides:

In the December 28, 2022 appendix W revision  15 we received, Montana incorporates the most current version of the “Guideline on Air Quality Models”, 40 CFR part 51, appendix W. ARM rule 17.8.802 Incorporation by Reference (b) is updated to comply with EPA's January 17, 2017 revisions to appendix W.

Based on the above information, we are proposing to approve the Montana SIP as meeting the requirements of CAA section 110(a)(2)(K) for the 2015 ozone NAAQS.

CAA section 110(a)(2)(L) provides that the SIP must require each major stationary source to pay permitting fees to cover the cost of reviewing, approving, implementing, and enforcing a permit.

The Montana submission refers to its fully approved title V operating permit program, and references the ARM regulations for the assessment and collection of fees:

• ARM 17.8.504—Air Quality Permit Application Fees.

• ARM 17.8.505—Air Quality Operation Fees.

• ARM 17.8.1701, et seq. —Registration of Air Contaminant Sources.

ARM 17.8.48 requires new and modified sources to pay fees in accordance with ARM 17.8.504. With respect to title V sources, on January 22, 2001, the EPA fully approved Montana's part 70 title V operating permit program ( See 65 FR 80785). Therefore, we are proposing that Montana has satisfied the requirements of CAA section 110(a)(2)(L) for the 2015 ozone NAAQS.

CAA section 110(a)(2)(M) requires states to provide for consultation and participation in SIP development by local political subdivisions affected by the SIP.

Montana refers to the following ARM and MCA regulations, which require the MDEQ to “. . .advise, consult, contract, and cooperate with other agencies of the state, local governments, industries, other states, inter-local agencies, the United States, and any interested persons or groups”. Additionally, Montana law allows potentially affected parties of MDEQ actions to petition for hearings.

• ARM 17.8.140 Rehearing Procedures—Form and Filing of Petition.

• ARM 17.8.141 Rehearing Procedures—Filing Requirements.

• ARM 17.8.142 Rehearing Procedures—Board Review.

• 75-2-112, MCA—Powers and Responsibilities of Department.

The rules and regulations cited by Montana provide for the consultation and participation by local political subdivisions affected by the SIP; therefore, we are proposing to approve the Montana SIP as meeting the requirements of CAA section 110(a)(2)(M) for the 2015 ozone NAAQS.

In this rulemaking, we are proposing to approve multiple elements of the infrastructure SIP requirements for the 2015 ozone NAAQS for Montana along with a proposed no action for three infrastructure elements for Montana. Additionally, we are proposing to approve the revisions to appendix W. Our proposed action is contained in table 1 below.

The EPA is proposing to approve Montana's September 26, 2018, SIP submission for the following CAA section 110(a)(2) infrastructure elements for the 2015 ozone NAAQS: (A), (B), (C), (D)(ii), (E), (F), (G), (H), (J), (K), (L), and (M). The EPA is proposing no action on D(i)(I) Prongs 1 and 2, and D(i)(II) Prong 4.

In the table below, the key is as follows:

Under the CAA, the Administrator is required to approve a SIP submission that complies with the provisions of the CAA and applicable Federal regulations. 42 U.S.C. 7410(k); 40 CFR 52.02(a). Thus, in reviewing SIP submissions, EPA's role is to approve state choices, provided that they meet the criteria of the CAA. Accordingly, this action merely approves state law as meeting Federal requirements and does not impose additional requirements beyond those imposed by state law. For that reason, this action:

• Is not a significant regulatory action subject to review by the Office of Management and Budget under Executive Order 12866 (58 FR 51735, October 4, 1993);

• Is not subject to Executive Order 14192 (90 FR 9065, February 6, 2025) because State Implementation Plan approvals under the CAA are exempt from review under Executive Order 12866;

• Does not impose an information collection burden under the provisions of the Paperwork Reduction Act (44 U.S.C. 3501 et seq. );

• Is certified as not having a significant economic impact on a substantial number of small entities under the Regulatory Flexibility Act (5 U.S.C. 601 et seq. );

• Does not contain any unfunded mandate or significantly or uniquely affect small governments, as described in the Unfunded Mandates Reform Act of 1995 (Pub. L. 104-4);

• Does not have federalism implications as specified in Executive Order 13132 (64 FR 43255, August 10, 1999);

• Is not subject to Executive Order 13045 (62 FR 19885, April 23, 1997) because it approves a state program;

• Is not a significant regulatory action subject to Executive Order 13211 (66 FR 28355, May 22, 2001); and

• Is not subject to requirements of section 12(d) of the National Technology Transfer and Advancement Act of 1995 (15 U.S.C. 272 note) because application of those requirements would be inconsistent with the CAA.

In addition, the SIP is not approved to apply on any Indian reservation land or in any other area where EPA or an Indian Tribe has demonstrated that a Tribe has jurisdiction. In those areas of Indian country, the rule does not have Tribal implications and will not impose substantial direct costs on Tribal governments or preempt Tribal law as specified by Executive Order 13175 (65 FR 67249, November 9, 2000).

Throughout this document whenever “we,” “us,” or “our” is used, we mean EPA.

On October 1, 2021, MPCA submitted a request for a revision of Minnesota's SIP. The submittal includes amendments to permit rules, clarifications of permit requirements for small sources of air emissions, updates to rules governing small air pollution sources and the addition of four categories of conditionally exempt sources. Minnesota completed a State rulemaking to clarify exempt source and insignificant activities rules in 2019. This proposed SIP revision is intended to codify those amendments to State law in the Minnesota SIP. MPCA previously submitted a similar SIP revision in 2018, and EPA approved the revision on July 27, 2020 (85 FR 45094).

The following chapters of Minnesota's air program rules have undergone revisions: Minnesota Rules Chapter 7005 Definitions and Abbreviations; Chapter 7007 Permits and Offsets; Chapter 7008 Conditionally Exempt Stationary Sources and Conditionally Insignificant Activities; Chapter 7011 Standards for Stationary Sources; and Chapter 7019 Emissions Inventory Requirements. All rule changes were made under the MPCA's rulemaking authority and underwent appropriate public participation procedures as required by State law. EPA proposes to approve the revisions to the Minnesota SIP.

Section 110 of the Clean Air Act (CAA), 42 U.S.C 7410, as amended, requires State and local air pollution control agencies to develop and submit for EPA approval, SIPs that provide for the attainment, maintenance, and enforcement of the NAAQS in each air quality control region (or portion thereof) within each State. Section 110(a) requires an assurance that states' air quality management programs contain the structural components in place to meet the state's responsibilities under the CAA. It also requires that the program attain and maintain the NAAQS.

Section 110(a)(2)(C) of the CAA requires that each SIP include a program to provide for the regulation of construction and modification of stationary sources as necessary to ensure that the NAAQS are achieved. Specific elements for an approvable construction permitting plan are found in the implementing regulations at 40 CFR 51 subpart I—Review of New Sources and Modifications. Requirements relevant to minor construction programs are 40 CFR 51.160-51.163. EPA regulations have several specific criteria for State minor new source review (NSR) programs. Generally, State programs must set forth legally enforceable procedures that allow the State to determine if a planned construction activity would result in a violation of the State's SIP or a national standard and prevent any activity that would. In accordance with 40 CFR 51.162, the State plan must identify the responsible agency for making permitting decisions. 40 CFR 51.160 requires the plan to identify the types and sizes of facilities and installations that are subject to review under the plan, provide that sources undertaking an activity submit adequate information regarding the nature and amounts of emissions to be emitted, as well as information on the location, design construction, and operation of facilities to enable the State to make a determination of whether the planned construction would result in a violation of the SIP or a national standard. 40 CFR 51.161 provides specific criteria for public availability of information and opportunity for public comment. Finally, 40 CFR 51.164 requires the plan to identify the administrative procedures that will be followed in making permitting decisions.

Section 110(l) of the CAA states that a SIP revision cannot be approved if the revision would interfere with any applicable requirements concerning attainment and reasonable further progress toward attainment of a NAAQS or any other applicable requirement of the CAA.

The revisions to the Minnesota SIP are intended to recodify, refine and update Minnesota's air quality rules in the Minnesota SIP, at 40 CFR 52.1220. This SIP revision addresses the requirements of section 110 of the CAA.

Chapter 7005 contains numerous definitions and abbreviations relevant to rules throughout the Minnesota SIP. In Chapter 7005, MPCA amended and added definitions in Minn. R. 7005.0100, to define new terms, clarify definitions, and re-number definitions. EPA finds these revisions approvable because they provide clarity to terms used in various rules throughout the SIP and do not change the requirements of the rules themselves. EPA proposes to approve the revisions to Minn. R. 7005.0100 into the Minnesota SIP.

Chapter 7007 contains rules concerning permits and offsets and has undergone various changes. Because Chapter 7007 combines the State's preconstruction and operating permit programs into a single permitting program, MPCA uses the broad term “Part 70 permit” to reference several types of permits, including some permits that authorize construction. As used in this action, “Part 70” denotes preconstruction permits, unless otherwise specified as “federal part 70.” This rulemaking is limited solely to approval of revisions to the state's preconstruction permitting program and federally enforceable State operating permit program. This is not a rulemaking under the Federal rules at 40 CFR part 70.

Minn. R. 7007.0300 relates to sources that are not required to obtain a permit under parts 7007.0100 to 7007.1850. Minn. R. 7007.0300 subpart 1, has been revised to remove item D, which provided that stationary sources listed as insignificant activities, sources that are conditionally insignificant activities, or sources that qualify as both insignificant activities and conditionally insignificant activities, are not required to obtain a permit, subject to certain conditions and recordkeeping requirements. The substantive provisions of item D are now a category of conditionally exempt stationary sources found in Minn. R. 7008.2600, “Insignificant Facility; Technical Standards,” which is discussed further below. Therefore, these revisions simply reorganize the provisions and do not change the substance of the rules. EPA proposes to approve the revisions to Minn. R. 7007.0300 into the Minnesota SIP.

Minn. R. 7007.0400 subpart 2 has been revised to change the timeframe for the owner or operator to submit an application for renewal of a Federal part 70 permit. The revision clarifies that a permit will not require a renewal application sooner than 18 months prior to permit expiration. EPA finds these revisions approvable as they align State and Federal permitting rules. EPA proposes to approve the revisions to Minn. R. 7007.0400 into the Minnesota SIP.

Minn. R. 7007.0850 subpart 2 has been revised with changes to the public notice and comment requirements and procedures. The revisions remove the requirements to give public notice in a newspaper of general circulation in the area nearby the source or in the Minnesota State Register and require electronic posting of the public notice for the duration of the comment period on the MPCA's public notice website.

Revisions have been made to the minimum requirements of what must be included in the electronic notice to now include the draft permit and a statement of whether the facility has filed a pollution prevention progress report with the State commissioner. Revisions have also been made to paragraph numbering and to include electronic contact information for interested parties to request additional information. Minn. R. 7007.0850 subpart 3 revises the process to petition for meetings and hearings by removing the option of placing the permit onto the agenda of a MPCA board meeting. EPA finds these revisions approvable as they add requirements to align the rules with Federal permitting requirements and do not relax any previously approved SIP provisions. EPA proposes to approve the revisions to Minn. R. 7007.0850 into the Minnesota SIP.

Minn. R. 7007.1144 subpart 5 has been revised to clarify procedures for public participation for capped permits (“capped” permits are rule-based permits designed for noncomplex facilities that do not require site-specific permit conditions), and removes the option of petitioning for meetings and hearings by placing the permit onto the agenda of a MPCA board meeting. EPA finds these revisions approvable as they do not conflict with any Federal requirement. EPA proposes to approve the revisions to Minn. R. 7007.1144 into the Minnesota SIP.

Minor language changes were made to Minn. R. 7007.1145, 7007.1147, and 7007.1250. EPA finds these revisions approvable as they do not change the substance of the rules. EPA proposes to approve the revisions to Minn. R. 7007.1145, 7007.1147 and 7007.1250 into the Minnesota SIP.

Revisions have been made to the list of insignificant activities in Minn. R. 7007.1300. The changes clarify whether certain activities, and the calculation of emissions from those activities, must be included in an air emissions permit application. Language clarifications related to heat input capacity are added, and certain processing, cleaning and other miscellaneous activities and operations are added to the list of insignificant activities. These revisions also add language to clarify that the thresholds for hazardous air pollutants listed in 7007.1300, subpart 5 are to be utilized in determining whether an emissions unit qualifies as an insignificant activity under 7007.1300, subpart 4. The intent of the insignificant activities list is to streamline the permit application process by specifying those activities whose emissions are trivial or short-term by their very nature, or activities that fall below a certain size/production rate, and therefore require minimal regulatory oversight. As part of these rule revisions, the MPCA evaluated each of the activities added or moved and their associated emissions. Activities that were added or moved were based on MPCA's estimates of emissions or examples provided by EPA of activities states could add to their insignificant activities list. While the activities listed may have emissions, the rule changes themselves are not expected to change/increase emissions as they do not authorize stationary sources to bypass any other regulations or permitting requirements. Stationary sources that add new insignificant activities are still required to determine whether the change or modification requires a permit amendment or notice to MPCA. EPA finds these revisions approvable as they provide clarity and do not change the stringency of the rule. EPA proposes to approve the revisions to Minn. R. 7007.1300 into the Minnesota SIP.

Chapter 7008 provides the conditions under which stationary sources are exempt from the requirement to apply for and obtain an air emission permit as provided for under Minn. R. 7007.0300. In the Chapter 7008 rule revisions, MPCA expands the conditionally exempt source categories to include auto-body refinishing facilities, coating facilities, woodworking facilities, and insignificant facilities. It establishes a permit by rule approach for these source categories that does not relax air quality standards. The revisions in Chapter 7008 specify applicable emission limitation and control requirements, operational restrictions and monitoring, recordkeeping, and other requirements in a similar manner to a traditional permit. The revisions outline the conditions under which stationary sources are exempt from the requirement to apply for and obtain an air emission permit as provided for under Minn R. 7007.0300. Chapter 7008 requires sources who claim their operations are conditionally exempt or conditionally insignificant to maintain records that demonstrate eligibility with the rule.

Minn. R. 7008.0100 has been revised to renumber several subparts and adds definitions pertinent to this category of conditionally exempt stationary sources and conditionally insignificant activities. EPA finds these revisions approvable as they provide clarity and do not change the stringency of the rule. EPA proposes to approve the revisions to Minn. R. 7008.0100 into the Minnesota SIP.

Minn. R. 7008.0200 establishes general requirements for conditionally exempt stationary sources and conditionally insignificant activities. This part has been revised to add a new item F. Item F has been added to clarify to owners and operators that if there is a change at the facility that affects the amount or type of air pollutants the facility emits, the owner or operator must determine whether a permit is needed and follow the permitting requirements at Minn. R. 7007.0400, subpart 4. EPA finds these revisions approvable as they strengthen current requirements in the SIP. EPA proposes to approve the revisions to Minn. R. 7008.0200 into the Minnesota SIP.

Minn. R. 7008.2100, subpart 1 identifies the eligibility requirements for the owner or operator of a gasoline service station to operate without a permit under chapter 7008. The requirements of this subpart have been renumbered. New item A, in subpart 1, revises existing rule language to clarify who is responsible for compliance with the rule and corrects the reference to the general requirements in Minn. R. 7008.2000, not Minn. R. 7008.0200. Subpart 1, item A has also been revised to remove the term “general operating” as a qualifier in front of requirements. The revisions also refer to the eligibility requirements in Minn. R. 7008.2000 rather than the general requirements of Minn. R. 7008.0200. New item B revises existing rule language to identify the correct rule citation for insignificant activities and conditionally insignificant activities. This revision provides clarification to the owner or operator that emissions from the gasoline service station must be from insignificant activities or conditionally insignificant activities, or both, in order to operate without a permit. Subpart 3, Notification, is revised to establish the requirements for notification when an owner or operator begins construction of a gasoline service station. The revisions also remove obsolete rule language that referred to a transition period for the original implementation of the rules. EPA finds these revisions approvable as they correct, clarify and strengthen current requirements in the SIP. EPA proposes to approve the revisions to Minn. R. 7008.2100 into the Minnesota SIP.

Minn. R. 7008.2200, subpart 1 identifies the eligibility requirements for the owner or operator of a concrete manufacturing stationary source to operate without a permit under chapter 7008. Subpart 1 has been revised to correct the reference to the general requirements in Minn. R. 7008.2000, not Minn. R. 7008.0200. Revisions also include the addition of a new subpart 6 with recordkeeping requirements for concrete manufacturing stationary sources. The recordkeeping requirements in Minn. R. 7008.2250 are proposed for repeal and are moved to a new subpart 6, items A through D. This change consolidates all requirements for concrete manufacturing stationary sources in one rule part. The revisions also modify language of existing recordkeeping requirements but does not change the content of the requirements. The revisions provide consistent language across the different conditionally exempt source categories. EPA finds these revisions approvable as they clarify and strengthen current requirements in the SIP. EPA proposes to approve the revisions to Minn. R. 7008.2200 into the Minnesota SIP.

Minn. R. 7008.2250 is proposed for repeal. This part provided recordkeeping requirements for concrete manufacturing plants. These requirements are moved to new subpart 6 in part 7008.2200. This consolidates and clarifies the rule so owners and operators can more easily locate, understand and comply with the recordkeeping requirements for concrete manufacturing plants. EPA finds these revisions approvable as they clarify current requirements in the SIP. EPA proposes to approve the revisions that repeal Minn. R. 7008.2250 from the Minnesota SIP.

Minnesota has created four new categories of conditionally exempt sources: Minn. R. 7008.2300 (auto-body refinishing); Minn. R. 7008.2400 (coating facilities); Minn. R. 7008.2500 (woodworking facilities); and Minn. R. 7008.2600 (insignificant facilities). For each of the new source categories, the rule amendments establish technical standards, operational and recordkeeping requirements that control and monitor air emissions in a similar manner to conditions that would be found in a site-specific, low-emitting facility permit.

Minn. R. 7008.2300 establishes technical standards for an owner or operator of an auto-body refinishing facility, by which the source may be exempt from an air emissions permit. Subpart 1 establishes the eligibility requirements for an auto-body refinishing facility to operate without a permit under chapter 7008, including limitations on activities and types of equipment allowed, to ensure there are no other significant sources of emissions at the source that would otherwise require an air emissions permit. Revisions also establish the maximum amount of coating and cleaning materials that an auto-body refinishing facility can purchase or use each calendar year to be eligible to operate without a permit under this subpart. The limit is set at 2,000 gallons each calendar year. Subparts 2, 3 and 4 establish operational, recordkeeping and notification requirements.

Minn. R. 7008.2400 establishes technical standards for an owner or operator of a coating facility, that is not an auto-body refinishing facility, by which the source may be exempt from an air emissions permit. Subpart 1 establishes the eligibility requirements for a coating facility to operate without a permit under chapter 7008, including limitations on activities and types of equipment allowed, to ensure there are no other significant sources of emissions at the source that would otherwise require an air emissions permit. Revisions also establish a limit of 2,000 gallons per calendar year of coating and cleaning material usage to be eligible to operate without a permit under this subpart. Subparts 2, 3 and 4 establish operational, recordkeeping and notification requirements.

Minn. R 7008.2500 establishes technical standards for an owner or operator of a woodworking facility, by which the source may be exempt from an air emissions permit. Subpart 1 establishes the eligibility requirements for a woodworking facility to operate without a permit under chapter 7008, including limitations on activities and types of equipment allowed, to ensure there are no other significant sources of emissions at the source that would otherwise require an air emissions permit. Subparts 2, 3 and 4 establish operational, control and notification requirements. Subpart 3 establishes five control options that restrict emissions to below the State permitting thresholds for PM and PM 10 .

Minn R. 7008.2600 establishes a new exempt category for stationary sources that have only insignificant and conditionally insignificant activities. To ensure that the presence of insignificant activities does not exceed a permitting threshold, the rule revision expands and clarifies the conditions that must be met by a stationary source with only insignificant and conditionally insignificant activities by adding conditions that make the technical requirements federally enforceable. Subpart 1 establishes eligibility requirements for an insignificant facility to operate without a permit under chapter 7008 by specifying the insignificant activities and conditionally insignificant activities that qualify and limits the number of emission units such that potential emissions do not exceed the listed permitting thresholds. Subparts 2 and 3 establish operational and recordkeeping requirements to qualify under this category. Subparagraph 4 requires the owner or operator of an insignificant facility to calculate emissions to determine eligibility.

The minor NSR provisions at 40 CFR 51.160 require State programs to determine whether activities would violate an applicable SIP or national standard and to prevent construction of an activity that would violate an applicable SIP provision or national standard. The new provisions exempt certain eligible stationary sources from air permitting requirements. When determining adequacy of State rules, EPA is concerned with the possibility that an exemption might allow an activity that should be subject to major source permitting requirements to escape appropriate review and permitting, that sources are required to maintain information adequate for the State to ensure that exemptions have been applied appropriately, and that the exemptions would not interfere with any applicable requirement concerning attainment and reasonable further progress, or any other applicable requirement of the CAA.

Minnesota Chapter 7008 provides limitations on the use of the specific exemptions in Minn. R. 7008.0050-7008.4110 and requires sources using the exemptions to maintain certain records to demonstrate that the exemptions have been applied appropriately. Specific conditionally exempt sources may be required to implement additional monitoring and recordkeeping as required to ensure that the equipment is operating as required under the exemption. Section 110(l) of the CAA states that a SIP revision cannot be approved if the revision would interfere with any applicable requirement concerning attainment and reasonable further progress toward attainment of a NAAQS or any other applicable requirement of the CAA. These conditionally exempt sources are expected to yield very low levels of actual emissions of regulated pollutants and are not expected to interfere with attainment and maintenance of the NAAQS. The rules also do not interfere with any other applicable requirement of the CAA, including the applicability of other SIP requirements, and those found in the New Source Performance Standards and the National Emission Standards for Hazardous Air Pollutants (NESHAPs). Therefore, EPA proposes to approve the revisions to Minn. R. 7008.2300, 7008.2400, 7008.2500, and 7008.2600.

The revisions to Minn R. 7008.4000 expand and clarify the conditions that must be met by insignificant and conditionally insignificant activities and are intended to improve the enforceability of restrictions on potential to emit for conditionally insignificant activities. This part is further revised to require that calculations from the activities described in parts 7008.4100 and 7008.4110 must be provided in a permit application for a part 70 permit or an amendment to a part 70 permit. EPA finds these revisions approvable as they strengthen current requirements in the SIP. EPA proposes to approve the revisions to Minn. R. 7008.4000.

The title of Minn. R. 7008.4100 is revised to “Conditionally Insignificant Activity: Material Usage” in order to provide clarification that the activities described are a conditionally insignificant activity. Revisions have been made in this part to the material usage emissions limits of volatile organic compounds (VOC) that qualify as an insignificant activity under this rule. Thresholds of eligibility for VOC emissions have been increased from less than 2,000 pounds to less than 10,000 pounds, and VOC-containing material usage limits have increased from less than 200 gallons to less than 1,000 gallons per calendar year. The limits have been increased to provide flexibility to owners and operators of stationary sources that have material usage that qualifies as a conditionally insignificant activity. It is estimated that this rule change would potentially result in maximum emissions of a single volatile HAP by no more than 5 tons per calendar year per source, which corresponds to 50% of the major source HAP threshold defined by the CAA section 112.

The rule also removes accounting of PM 10 and PM 2.5 separately from particulate matter when calculating emissions for annual calculations. The calculation for particulate matter emissions in this part of the rule is based on the solids content (in lbs/gal or weight%) of the material used. Because the data used for this calculation is not specific to each pollutant (PM, PM 10 , and PM 2.5 ), deleting the reference to PM 10 and PM 2.5 simplifies the emission limit and provides consistency across the requirements in Minn. R. 7008.4100 that govern conditionally insignificant material usage.

Subparts 4 and 5 of this rule revise calculation requirements for VOC and particulate matter and add the ability to include control and transfer efficiencies in calculating particulate matter emissions under certain circumstances as allowed under Minn. R. 7011.

The revisions of Minn. R. 7008.4100 are consistent with CAA section 110(l). These revisions are expected to yield very low levels of actual emissions of regulated pollutants and are not expected to interfere with attainment and maintenance of the NAAQS. The revisions also do not interfere with any other applicable requirement of the CAA, including the applicability of other SIP requirements, and those found in the New Source Performance Standards and the National Emission Standards for Hazardous Air Pollutants (NESHAPs). As such, EPA proposes to approve the revisions to Minn. R. 7008.4100.

The title of Minn. R. 7008.4110 has been revised to “Conditionally Insignificant Activity; Finishing Operations.” The revision provides clarification that the activities described are a conditionally insignificant activity. The revision also establishes requirements specific to stationary sources that claim mechanical finishing operations emitting PM as a conditionally insignificant activity. The revisions further clarify that any activity emitting any other pollutant in addition to PM does not qualify under this part, including lead emissions.

Revisions are also made to identify the qualifications for mechanical finishing operations to be considered a conditionally insignificant activity. Revisions to subpart 2 add “mechanical finishing operations” and remove the example finishing activities ( e.g., buffing, polishing, carving, etc.) previously listed in the SIP. Subpart 2 is also revised to remove the requirement that emissions must be vented inside a building 100% of the time and filtered through an air cleaning system, adds control requirements for particulate emissions and limits particulate matter emissions from mechanical finishing operations to less than 10,000 pounds per calendar year.

Clarifying language is added to specify that the limit applies to all finishing operation activities at the stationary source. This revision disallows multiple activities that might qualify independently as conditionally insignificant finishing operations to exceed the emission limit when aggregated. Subparts 3 and 4 of the rule clarify language and add monitoring, recordkeeping and calculation requirements for sources subject to this subpart. EPA finds these revisions approvable as they strengthen current requirements in the SIP. EPA proposes to approve the revisions to Minn. R. 7008.4110.

Minn. R. 7011.0561 makes minor revisions to language, changing the title from “Control of mercury from electric generating units” to “Controlling mercury from electric generating units” and removes a reference to Minnesota Statutes, section 216B.687, subdivision 3. EPA finds these revisions approvable as they are minor language changes that do not affect the requirements of the rule. EPA proposes to approve Minn. R. 7011.0561.

Minn. R. 7011.1201 revises a statutory reference for the definition of refuse-derived fuel. EPA finds these revisions approvable as they do not change the applicability of the rule. EPA proposes to approve Minn. R. 7011.1201.

Minn. R. 7011.2300 makes minor language revisions and allows for an alternative sulfur dioxide limit in a permit or other enforceable document that models compliance with Minn. R. 7009.0090, the National Ambient Air Quality Standards as they are incorporated by reference into Minnesota's rules. EPA finds these revisions approvable as they are minor language changes that do not affect the requirements of the rule and strengthen current requirements in the SIP. EPA proposes to approve Minn. R. 7011.2300.

Minn. R. 7019.3020 has been revised to change the words “shall” to “must” and renumbers a reference to subpart “J” to “G”. EPA finds these revisions approvable as they are minor language changes that do not affect the requirements of the rule. EPA proposes to approve Minn. R. 7019.3020 into the Minnesota SIP.

As part of this submittal, Minnesota is also requesting that rule 7023 be removed from the SIP. This rule is obsolete given the November 2019 expiration of the carbon monoxide maintenance area.

EPA is proposing to approve MPCA's October 1, 2021, submittal, as a revision to its existing SIP.

In this rule, EPA is proposing to include in a final EPA rule regulatory text that includes incorporation by reference. In accordance with requirements of 1 CFR 51.5, EPA is proposing to incorporate by reference revisions to Minnesota Rules Chapter 7005 Definitions and Abbreviations; Chapter 7007 Permits and Offsets; Chapter 7008 Conditionally Exempt Stationary Sources and Conditionally Insignificant Activities; Chapter 7011 Standards for Stationary Sources; and Chapter 7019 Emissions Inventory Requirements, as discussed in sections I. and II. of this preamble. EPA has made, and will continue to make, these documents generally available through www.regulations.gov and at the EPA Region 5 Office (please contact the person identified in the FOR FURTHER INFORMATION CONTACT section of this preamble for more information).

Under the CAA, the Administrator is required to approve a SIP submission that complies with the provisions of the CAA and applicable Federal regulations. 42 U.S.C. 7410(k); 40 CFR 52.02(a). Thus, in reviewing SIP submissions, EPA's role is to approve State choices, provided they meet the criteria of the CAA. Accordingly, this action merely approves State law as meeting Federal requirements and does not impose additional requirements beyond those imposed by State law. For that reason, this action:

• Is not a significant regulatory action subject to review by the Office of Management and Budget under Executive Order 12866 (58 FR 51735, October 4, 1993);

• Is not subject to Executive Order 14192 (90 FR 9065, February 6, 2025) because SIP actions are exempt from review under Executive Order 12866;

• Does not impose an information collection burden under the provisions of the Paperwork Reduction Act (44 U.S.C. 3501 et seq. );

• Is certified as not having a significant economic impact on a substantial number of small entities under the Regulatory Flexibility Act (5 U.S.C. 601 et seq. );

• Does not contain any unfunded mandate or significantly or uniquely affect small governments, as described in the Unfunded Mandates Reform Act of 1995 (Pub. L. 104-4);

• Does not have federalism implications as specified in Executive Order 13132 (64 FR 43255, August 10, 1999);

• Is not subject to Executive Order 13045 (62 FR 19885, April 23, 1997) because it approves a State program;

• Is not a significant regulatory action subject to Executive Order 13211 (66 FR 28355, May 22, 2001); and

• Is not subject to requirements of Section 12(d) of the National Technology Transfer and Advancement Act of 1995 (15 U.S.C. 272 note) because application of those requirements would be inconsistent with the CAA;

In addition, the SIP is not approved to apply on any Indian reservation land or in any other area where EPA or an Indian Tribe has demonstrated that a Tribe has jurisdiction. In those areas of Indian country, the rulemaking does not have Tribal implications and will not impose substantial direct costs on Tribal governments or preempt Tribal law as specified by Executive Order 13175 (65 FR 67249, November 9, 2000).

Throughout this document, “we,” “us,” and “our” refer to the EPA. In the “Rules and Regulations” section of this issue of the Federal Register , the EPA is approving Guam's submission as a direct final rule without prior proposal because we view this as a noncontroversial action and anticipate no adverse comments. A detailed rationale for the action is set forth in the preamble to the direct final rule. If the EPA receives no adverse comments, the EPA contemplates no further action. If the EPA receives adverse comments, the EPA will withdraw the direct final rule and will address all public comments in a subsequent final rule based on this proposed rule. We do not plan to open a second comment period on this action, so anyone interested in commenting should do so at this time. For additional information, see the direct final rule of the same title that is located in the Final Rules section of this Federal Register .

On June 18, 2025, EPA proposed to approve the Indiana regional haze state implementation plan (SIP) revision submitted by the Indiana Department of Environmental Management on December 29, 2021, as satisfying applicable requirements under the Clean Air Act and EPA's Regional Haze Rule for the program's second implementation period. EPA is extending the comment period for an additional 30 days.

In the Final Rules section of this Federal Register , EPA is approving the State's SIP submittal as a direct final rule without prior proposal because the Agency views this as a noncontroversial submittal and anticipates no adverse comments. A detailed rationale for the approval is set forth in the direct final rule. If no relevant adverse comments are received in response to this rule, no further activity is contemplated. If EPA receives such comments, the direct final rule will be withdrawn and all public comments received will be addressed in a subsequent final rule based on this proposed rule. EPA will not institute a second comment period. Any parties interested in commenting on this action should do so at this time. Please note that if EPA receives adverse comment on an amendment, paragraph, or section of this rule and if that provision may be severed from the remainder of the rule, EPA may adopt as final those provisions of the rule that are not the subject of an adverse comment. For additional information, see the direct final rule which is located in the Rules section of this Federal Register .

Throughout this document whenever “we,” “us,” or “our” is used, we mean EPA.

On November 27, 2023, the Connecticut Department of Energy and Environmental Protection (CT DEEP) submitted a revision to its State Implementation Plan (SIP). This action consists of revisions to Regulations of Connecticut State Agencies (RCSA) sections 22a-174-22e and 22a-174-22f, primarily to add compliance dates for sources brought into the applicability of these sections due to a change in the definition of “severe non-attainment area for ozone” in another section of Connecticut's regulations—specifically, RCSA § 22a-174-1. The revisions to RCSA §§ 22a-174-22e and 22a-17422f became effective on November 13, 2023. Connecticut's change to the definition of “severe non-attainment area for ozone” in RCSA § 22a-174-1 became effective the same day, and the Environmental Protection Agency (EPA) previously approved the new definition into the SIP on February 12, 2024 (89 FR 9771).

On March 20, 2023, CT DEEP proposed changes to the definition of “severe non-attainment area for ozone” within RCSA § 22a-174-1. The proposed change to the definition expanded the list of cities and towns in the definition, to include all cities and towns in New Haven County and Middlesex County. CT DEEP also retained the two towns in Litchfield County to ensure classification consistency in these communities and to comply with section 193 of the Clean Air Act (CAA), which prohibits any control measure in effect in a nonattainment area prior to the enactment of the CAA Amendments of 1990 to be modified after enactment, unless such modification yields equivalent or greater emission reductions. As a result of this definition change and as described in 89 FR 9771, the number of towns included in the “severe non-attainment area for ozone” increased, making RCSA §§ 22a-174-22e and 22a-174-22f applicable to more sources.

The entire state of Connecticut is divided into two nonattainment areas for ozone. One area consists of the southwest portion of the state (the Connecticut portion of the New York-New Jersey-Connecticut area), and the remainder of the state (Greater Connecticut) makes up the other nonattainment area. The area in the southwest portion of the state generally experiences higher ozone levels, and on October 7, 2022, the EPA published a final rule to reclassify, among other areas, the southwest Connecticut ozone nonattainment area to severe nonattainment from serious nonattainment based on the area's inability to attain the 2008 ozone National Ambient Air Quality Standard (NAAQS) by the attainment date (87 FR 60926).

Connecticut regulations define nonattainment areas in a geographic manner. The original definition of “severe non-attainment area for ozone” in RCSA § 22a-174-1, was based on the nonattainment area designation under the 1-hour ozone NAAQS of 1979. The area included all towns and cities in Fairfield County, except the town of Shelton, and two towns in Litchfield County (Bridgewater and New Milford). Currently, the southwest Connecticut ozone nonattainment area for the 2008 ozone NAAQS is larger than the older area for the 1979 ozone NAAQS, and it includes all of Fairfield County, New Haven County, and Middlesex County.

Sections 22a-174-22e and 22a-174-22f of the RCSA impose requirements on sources based in part on the classification of the nonattainment area in which the source is located, and the quantity of emissions released. Sources emitting over certain threshold amounts of nitrogen oxides (NO X ) are subject to the control requirements of RCSA section 22a-174-22e. As a result of the revision to the definition of “severe non-attainment area for ozone,” RCSA §§ 22a-174-22e and 22a-174-22f became newly applicable to certain sources in Towns that were added to the definition. As Connecticut's regulatory revisions bring new sources under RCSA section 22a-174-22e, new provisions were necessary to specify the timing of compliance and of certain submissions the new sources must provide to CT DEEP. The main changes for section 22a-174-22e are (1) the addition of a definition for “Bumped-up RACT unit” in subsection (a), and (2) the addition of subsection (n), “Compliance by bumped-up RACT units.” Connecticut defines a “Bumped-up RACT unit” as “an emission unit located at a facility with a potential to emit NO X of not less than twenty-five (25) tons per year whereby such facility becomes a major stationary source of NO X on or after November 7, 2022 solely as a result of the amendment of the definition of `severe non-attainment area for ozone' in RCSA section 22a-174-1 effective on November 13, 2023.” The revisions to § 22a-174-22e require such a bumped-up reasonably available control technology (RACT) unit to comply with emissions limitations already applicable to other sources covered by § 22a-174-22e, providing a timeframe for that compliance, pursuant to certain conditions. Connecticut also made minor corrections or updates to several provisions in RCSA § 22a-174-22e based on the two changes described above. Finally, Connecticut added timing provisions to RCSA § 22a-174-22f coordinated with those of § 22a-174-22e.

This action will ensure that Connecticut is applying RACT requirements and other NO X control requirements to the appropriate sources in the state, thereby meeting nonattainment requirements for ozone as set out in Section 182(d) of the CAA. The EPA has reviewed Connecticut's November 27, 2023, submittal of revisions to RCSA §§ 22a-174-22e and 22a-174-22f and preliminarily determined that they represent approvable revisions to the versions previously approved into the Connecticut SIP. These revisions will appropriately apply requirements to sources in line with Connecticut's change to the definition of “severe non-attainment area for ozone” that the EPA previously approved into the SIP. (89 FR 9771).

The EPA is proposing to approve Connecticut's November 27, 2023, SIP submittal that addresses revisions to RCSA sections 22a-174-22e and 22a-174-22f. The EPA is soliciting public comments on the issues discussed in this notice or on other relevant matters. These comments will be considered before taking final action. Interested parties may participate in the Federal rulemaking procedure by submitting written comments to this proposed rule by following the instructions listed in the ADDRESSES section of this Federal Register .

In this rule, the EPA is proposing to include in a final EPA rule regulatory text that includes incorporation by reference. In accordance with requirements of 1 CFR 51.5, the EPA is proposing to incorporate by reference changes to Connecticut RCSA sections 22a-174-22e and 22a-174-22f as adopted on November 13, 2023. The changes primarily add compliance dates for sources brought into the applicability of these sections due to a change in the definition of “severe non-attainment area for ozone.” The EPA has made, and will continue to make, these documents generally available through https://www.regulations.gov and at the EPA Region 1 Office (please contact the person identified in the FOR FURTHER INFORMATION CONTACT section of this preamble for more information).

Under the Clean Air Act, the Administrator is required to approve a SIP submission that complies with the provisions of the Clean Air Act and applicable Federal regulations. See 42 U.S.C. 7410(k); 40 CFR 52.02(a). Thus, in reviewing SIP submissions, EPA's role is to approve state choices, provided that they meet the criteria of the Clean Air Act. Accordingly, this proposed action merely approves state law as meeting Federal requirements and does not impose additional requirements beyond those imposed by state law. For that reason, this proposed action:

• Is not a significant regulatory action subject to review by the Office of Management and Budget under Executive Orders 12866 (58 FR 51735, October 4, 1993);

• Is not subject to Executive Order 14192 (90 FR 9065, February 6, 2025) because SIP actions are exempt from review under Executive Order 12866;

• Does not impose an information collection burden under the provisions of the Paperwork Reduction Act (44 U.S.C. 3501 et seq. );

• Is certified as not having a significant economic impact on a substantial number of small entities under the Regulatory Flexibility Act (5 U.S.C. 601 et seq. );

• Does not contain any unfunded mandate or significantly or uniquely affect small governments, as described in the Unfunded Mandates Reform Act of 1995 (Pub. L. 104-4);

• Does not have federalism implications as specified in Executive Order 13132 (64 FR 43255, August 10, 1999);

• Is not subject to Executive Order 13045 (62 FR 19885, April 23, 1997) because it approves a state program;

• Is not a significant regulatory action subject to Executive Order 13211 (66 FR 28355, May 22, 2001); and

• Is not subject to requirements of Section 12(d) of the National Technology Transfer and Advancement Act of 1995 (15 U.S.C. 272 note) because application of those requirements would be inconsistent with the Clean Air Act.

In addition, the SIP is not approved to apply on any Indian reservation land or in any other area where EPA or an Indian tribe has demonstrated that a tribe has jurisdiction. In those areas of Indian country, the rule does not have tribal implications and will not impose substantial direct costs on tribal governments or preempt tribal law as specified by Executive Order 13175 (65 FR 67249, November 9, 2000).

Throughout this document wherever “we,” “us,” or “our” is used, we mean the EPA.

Pursuant to CAA section 110(k)(3), the EPA is proposing to partially approve and partially disapprove a SIP submission submitted by the State of Colorado to the EPA on May 20, 2022, and supplemented on August 2, 2022, and June 23, 2023, addressing the requirements of the second implementation period of the RHR. 1 Specifically, the EPA is proposing approval for the portions of Colorado's 2022 SIP submission relating to 40 CFR 51.308(f)(1): calculations of baseline, current, and natural visibility conditions, progress to date, and the uniform rate of progress; 40 CFR 51.308(f)(2)(ii)-(iv): long-term strategy; 40 CFR 51.308(f)(3): reasonable progress goals; 40 CFR 51.308(f)(4): reasonably attributable visibility impairment; 40 CFR 51.308(f)(5) and 40 CFR 51.308(g): progress report requirements; 40 CFR 51.308(f)(6): monitoring strategy and other implementation plan requirements; and 40 CFR 51.308(i): FLM consultation.

For the reasons described in section IV.C.1.b. of this document, the EPA is proposing to disapprove portions of Colorado's 2022 SIP submission relating to 40 CFR 51.308(f)(2)(i). The submission relies on enforceable source closures that the EPA proposes to disapprove on the basis that they were adopted without full information about grid reliability concerns, particularly because the Class I areas Colorado emissions contribute to are below the Uniform Rate of Progress and the state conducted four-factor analyses. The EPA also proposes to find that the State has not provided necessary assurances required by CAA section 110(a)(2)(E) that unconsented enforceable source closures would not be prohibited by state or federal law.

Concurrently, the EPA is proposing to approve a revision to Colorado's SIP consolidating existing regional haze provisions into the same regulation where the State's new, second planning period provisions are located. Together, these SIP revisions establish updated emission reduction requirements for nitrogen oxides (NO X ), sulfur dioxide (SO 2 ), and particulate matter (PM) emissions from certain sources identified as impacting Class I areas under the RHR for the second 10-year planning period. 2

A detailed history and background of the regional haze program is provided in multiple prior EPA proposal actions. 3 For additional background on the 2017 RHR revisions, please refer to section III. Overview of Visibility Protection Statutory Authority, Regulation, and Implementation of “Protection of Visibility: Amendments to Requirements for State Plans” of the 2017 RHR. 4 The following is an abbreviated history and background of the regional haze program and 2017 Regional Haze Rule as it applies to the current action.

In the 1977 CAA amendments, Congress created a program for protecting visibility in the nation's mandatory Class I Federal areas, which include certain national parks and wilderness areas. 5 CAA section 169A. The CAA establishes as a national goal the “prevention of any future, and the remedying of any existing, impairment of visibility in mandatory Class I Federal areas which impairment results from manmade air pollution.” CAA section 169A(a)(1).

Regional haze is visibility impairment that is produced by a multitude of anthropogenic sources and activities that are located across a broad geographic area and that emit pollutants that impair visibility. Visibility impairing pollutants include fine and coarse particulate matter (PM) ( e.g., sulfates, nitrates, organic carbon, elemental carbon, and soil dust) and their precursors ( e.g., SO 2 , NO X , and, in some cases, volatile organic compounds (VOC) and ammonia (NH 3 )). Fine particle precursors react in the atmosphere to form fine particulate matter (PM 2.5 ), which impairs visibility by scattering and absorbing light. Visibility impairment reduces the perception of clarity and color, as well as visible distance. 6

To address regional haze visibility impairment, the 1999 RHR established an iterative planning process that requires states containing Class I areas and states containing sources whose emissions “may reasonably be anticipated to cause or contribute to any impairment of visibility” in a Class I area in another state to periodically submit SIP revisions to address such impairment. CAA section 169A(b)(2); see also 40 CFR 51.308(b), (f) (establishing submission dates for iterative regional haze SIP revisions); (64 FR at 35768, July 1, 1999).

On January 10, 2017, the EPA promulgated revisions to the RHR (82 FR 3078, January 10, 2017) that apply for the second and subsequent implementation periods. The reasonable progress requirements as revised by the 2017 rule (referred to here as the 2017 RHR Revisions) are codified at 40 CFR 51.308(f).

Because the air pollutants and pollution affecting visibility in Class I areas can be transported over long distances, successful implementation of the regional haze program requires long-term, regional coordination among multiple jurisdictions and agencies that have responsibility for Class I areas and the emissions that impact visibility in those areas. To address regional haze, states need to develop strategies in coordination with one another, considering the effect of emissions from one jurisdiction on the air quality in another. Five regional planning organizations (RPOs), which include representation from state and Tribal governments, the EPA, and FLMs, were developed in the lead-up to the first implementation period to address regional haze. RPOs evaluate technical information to better understand how emissions from state and Tribal land impact Class I areas across the country, pursue the development of regional strategies to reduce emissions of particulate matter and other pollutants leading to regional haze, and help states meet the consultation requirements of the RHR.

The Western Regional Air Partnership (WRAP), one of the five regional planning organizations described in the previous paragraph, is a collaborative effort of state governments, local air agencies, Tribal governments, and various federal agencies established to initiate and coordinate activities associated with the management of regional haze, visibility, and other air quality issues in the Western United States. Members include the states of Alaska, Arizona, California, Colorado, Hawaii, Idaho, Montana, Nevada, New Mexico, North Dakota, Oregon, South Dakota, Utah, Washington, Wyoming, and 28 Tribal governments. 7 The federal partner members of WRAP are the EPA, U.S. National Parks Service (NPS), U.S. Fish and Wildlife Service (USFWS), U.S. Forest Service (USFS), and the Bureau of Land Management (BLM). WRAP formed a workgroup to develop a planning framework for state regional haze second planning period SIPs. Based on emissions and monitoring data supplied by its membership, WRAP produced a technical system to support regional modeling of visibility impacts at Class I areas across the West. The WRAP Technical Support System consolidated air quality monitoring data, meteorological and receptor modeling data analyses, emissions inventories and projections, and gridded air quality/visibility regional modeling results. The Technical Support System is accessible by member states and allows for the creation of maps, figures, and tables to export and use in state plan development. It also maintains the original source data for verification and further analysis. Colorado collaborated with WRAP on various aspects of the State's 2022 SIP submission, including the identification of Class I areas outside of Colorado that may be affected by sources in the state, source selection, analysis of air quality monitoring data, preparation of emission inventories, development of reasonable progress goals, and air quality modeling, which together informed the development of its long-term strategy.

The CAA requires that regional haze plans for the first implementation period (2008 through 2018) include, among other things, a long-term strategy for making reasonable progress and Best Available Retrofit Technology (BART) requirements for certain older stationary sources, where applicable. 8 On December 31, 2012, the EPA approved a regional haze SIP revision submitted May 25, 2011, by the State of Colorado as meeting the requirements of the CAA and RHR. 9 On February 25, 2013, the National Parks Conservation Association (NPCA) and Wild Earth Guardians (Guardians) filed petitions for review in the U.S. Court of Appeals for the Tenth Circuit of the EPA's final approval of the Colorado regional haze SIP. 10 Among other things, Guardians and NPCA challenged the NO X BART limit for Craig Unit 1. The parties settled the challenge regarding Craig Unit 1. 11 Separately, on May 26, 2015, the EPA reissued its final approval of the May 25, 2011, SIP submission with respect to the State's BART determination for the Comanche Generating Station in response to a petition for review and as part of a voluntary remand, without vacatur, to more adequately respond to public comments concerning the Comanche Generating Station. 12

On May 20, 2022, Colorado submitted a SIP submission to address its regional haze obligations for the second implementation period (2018-2028). Colorado's 2022 SIP submission contains the State's long-term strategy to address regional haze visibility impairment for each Class I area within the State and each Class I area outside the State that may be affected by emissions from the State. In developing its long-term strategy, the State examined the need to implement additional enforceable emission limitations, compliance schedules, and other measures that may be necessary to make reasonable progress since the first implementation period. Specifically, Colorado's 2022 SIP submission contains an assessment of visibility progress made at Class I areas since the first implementation period and a long-term strategy to address regional haze visibility impairment at the twelve Class I areas the State identified, including: Colorado's selection of sources that may affect visibility in Class I areas within the State and outside the State for four-factor analysis; its evaluation of the selected sources to determine what emission reduction measures constitute reasonable progress for the long-term strategy; regional scale modeling of the State's long-term strategy to set reasonable progress goals for 2028; and ultimately, Colorado's determinations on what control measures are necessary for the long-term strategy to address regional haze visibility impairment in the twelve Class I areas. The State concluded that additional emission reduction measures for Colorado facilities are required for the second implementation period under its long-term strategy.

On May 20, 2022, Colorado submitted a separate SIP submission to move the regional haze provisions currently contained in Regulation Number 3 to Regulation Number 23. The Colorado Air Quality Control Commission previously approved regional haze requirements under Regulation Number 3, which included emission reduction requirements for sources subject to BART and reasonable progress determinations during the first planning period of the regional haze program. As part of Colorado's 2022 SIP submission, the State adopted revisions to Regulation Number 3 (Part F) to the newly created Regulation Number 23 which will serve as the central repository for new and existing provisions that comply with the RHR. Regulation Number 23 includes BART and reasonable progress determinations from the first planning period as well as emission reduction requirements to meet the reasonable progress goals for the second 10-year planning period.

Under the CAA and the EPA's regulations, all 50 states, the District of Columbia, and the U.S. Virgin Islands were required to submit regional haze SIPs satisfying the applicable requirements for the second implementation period of the regional haze program by July 31, 2021. Each SIP must contain a long-term strategy for making reasonable progress toward meeting the national goal of remedying any existing and preventing any future anthropogenic visibility impairment in Class I areas. CAA section 169A(b)(2)(B). To this end, 40 CFR 51.308(f) lays out the process by which states determine what constitutes their long-term strategies, with the order of the requirements in 40 CFR 51.308(f)(1) through (3) generally mirroring the order of the steps in the reasonable progress analysis  13 and (f)(4) through (6) containing additional, related requirements.

Broadly speaking, a state first must identify the Class I areas within the state and determine the Class I areas outside the state in which visibility may be affected by emissions from the state. These are the Class I areas that must be addressed in the state's long-term strategy. See 40 CFR 51.308(f), (f)(2). For each Class I area within its borders, a state must then calculate the baseline (five-year average period of 2000-2004), current, and natural visibility conditions ( i.e., visibility conditions without anthropogenic visibility impairment) for that area, as well as the visibility improvement made to date and the “uniform rate of progress” (URP). The URP is the linear rate of progress needed to attain natural visibility conditions, assuming a starting point of baseline visibility conditions in 2004 and ending with natural conditions in 2064. This linear interpolation is used as a tracking metric to help states assess the amount of progress they are making towards the national visibility goal over time in each Class I area. See 40 CFR 51.308(f)(1).

Each state having a Class I area and/or emissions that may affect visibility in a Class I area must then develop a long-term strategy that includes the enforceable emission limitations, compliance schedules, and other measures that are necessary to make reasonable progress in such areas. A reasonable progress determination is based on applying the four factors in CAA section 169A(g)(1) to sources of visibility impairing pollutants that the state has selected to assess for controls for the second implementation period. Additionally, as further explained below, the RHR at 40 CFR 51.3108(f)(2)(iv) separately provides five “additional factors”  14 that states must consider in developing their long-term strategies. See 40 CFR 51.308(f)(2). A state evaluates potential emission reduction measures for those selected sources and determines which are necessary to make reasonable progress. Those measures are then incorporated into the state's long-term strategy.

After a state has developed its long-term strategy, it then establishes RPGs for each Class I area within its borders by modeling the visibility impacts of all reasonable progress controls at the end of the second implementation period, i.e., in 2028, as well as the impacts of other requirements of the CAA. The RPGs include reasonable progress controls not only for sources in the state in which the Class I area is located, but also for sources in other states that contribute to visibility impairment in that area. The RPGs are then compared to the baseline visibility conditions and the URP to ensure that progress is being made towards the statutory goal of preventing any future and remedying any existing anthropogenic visibility impairment in Class I areas. 40 CFR 51.308(f)(2)-(3). There are additional requirements in the rule, including FLM consultation, that apply to all visibility protection SIPs and SIP revisions. See e.g., 40 CFR 51.308(i).

While states have discretion to choose any source selection methodology that is reasonable, whatever choices they make should be reasonably explained. To this end, 40 CFR 51.308(f)(2)(i) requires that a state's SIP submission include “a description of the criteria it used to determine which sources or groups of sources it evaluated.” The technical basis for source selection, which may include methods for quantifying potential visibility impacts such as emissions divided by distance metrics, trajectory analyses, residence time analyses, and/or photochemical modeling, must also be appropriately documented, as required by 40 CFR 51.308(f)(2)(iii).

Once a state has selected the set of sources, the next step is to determine the emissions reduction measures for those sources that are necessary to make reasonable progress for the second implementation period. 15 This is accomplished by considering the four factors—“the costs of compliance, the time necessary for compliance, the energy and non-air quality environmental impacts of compliance, and the remaining useful life of any existing source subject to such requirements.” CAA section 169A(g)(1). The EPA has explained that the four-factor analysis is an assessment of potential emission reduction measures ( i.e., control options) for sources; “use of the terms `compliance' and `subject to such requirements' in section 169A(g)(1) strongly indicates that Congress intended the relevant determination to be the requirements with which sources would have to comply to satisfy the CAA's reasonable progress mandate.” 82 FR at 3091. Thus, for each source it has selected for four-factor analysis, 16 a state must consider a “meaningful set” of technically feasible control options for reducing emissions of visibility impairing pollutants. Id. at 3088.

The EPA has also explained that, in addition to the four statutory factors, states have flexibility under the CAA and RHR to reasonably consider visibility benefits as an additional factor alongside the four statutory factors. 17 Ultimately, while states have discretion to reasonably weigh the factors and to determine what level of control is needed, 40 CFR 51.308(f)(2)(i) provides that a state “must include in its implementation plan a description of . . . how the four factors were taken into consideration in selecting the measure for inclusion in its long-term strategy.”

As explained above, 40 CFR 51.308(f)(2)(i) requires states to determine the emission reduction measures for sources that are necessary to make reasonable progress by considering the four factors. Pursuant to 40 CFR 51.308(f)(2), measures that are necessary to make reasonable progress towards the national visibility goal must be included in a state's long-term strategy and in its SIP. If the outcome of a four-factor analysis is that an emissions reduction measure is necessary to make reasonable progress towards remedying existing or preventing future anthropogenic visibility impairment, that measure must be included in the SIP.

The characterization of information on each of the factors is also subject to the documentation requirement in 40 CFR 51.308(f)(2)(iii). The reasonable progress analysis is a technically complex exercise, and also a flexible one that provides states with bounded discretion to design and implement approaches appropriate to their circumstances. Given this flexibility, 40 CFR 51.308(f)(2)(iii) plays an important function in requiring a state to document the technical basis for its decision making so that the public and the EPA can comprehend and evaluate the information and analysis the state relied upon to determine what emission reduction measures must be in place to make reasonable progress. The technical documentation must include the modeling, monitoring, cost, engineering, and emissions information on which the state relied to determine the measures necessary to make reasonable progress.

Additionally, the RHR at 40 CFR 51.3108(f)(2)(iv) separately provides five “additional factors” that states must consider in developing their long-term strategies: (1) Emission reductions due to ongoing air pollution control programs, including measures to address reasonably attributable visibility impairment; (2) measures to reduce the impacts of construction activities; (3) source retirement and replacement schedules; (4) basic smoke management practices for prescribed fire used for agricultural and wildland vegetation management purposes and smoke management programs; and (5) the anticipated net effect on visibility due to projected changes in point, area, and mobile source emissions over the period addressed by the long-term strategy.

Because the air pollution that causes regional haze crosses state boundaries, 40 CFR 51.308(f)(2)(ii) requires a state to consult with other states that also have emissions that are reasonably anticipated to contribute to visibility impairment in a given Class I area. If a state, pursuant to consultation, agrees that certain measures ( e.g., a certain emission limitation) are necessary to make reasonable progress at a Class I area, it must include those measures in its SIP. 40 CFR 51.308(f)(2)(ii)(A). Additionally, the RHR requires that states that contribute to visibility impairment at the same Class I area consider the emission reduction measures the other contributing states have identified as being necessary to make reasonable progress for their own sources. 40 CFR 51.308(f)(2)(ii)(B). If a state has been asked to consider or adopt certain emission reduction measures, but ultimately determines those measures are not necessary to make reasonable progress, that state must document in its SIP the actions taken to resolve the disagreement. 40 CFR 51.308(f)(2)(ii)(C). Under all circumstances, a state must document in its SIP submission all substantive consultations with other contributing states. 40 CFR 51.308(f)(2)(ii)(C).

Reasonable progress goals “measure the progress that is projected to be achieved by the control measures states have determined are necessary to make reasonable progress based on a four-factor analysis.” 82 FR at 3091. For the second implementation period, the RPGs are set for 2028. Reasonable progress goals are not enforceable targets, 40 CFR 51.308(f)(3)(iii). While states are not legally obligated to achieve the visibility conditions described in their RPGs, 40 CFR 51.308(f)(3)(i) requires that “[t]he long-term strategy and the reasonable progress goals must provide for an improvement in visibility for the most impaired days since the baseline period and ensure no degradation in visibility for the clearest days since the baseline period.”

RPGs may also serve as a metric for assessing the amount of progress a state is making towards the national visibility goal. To support this approach, the RHR requires states with Class I areas to compare the 2028 RPG for the most impaired days to the corresponding point on the URP line (representing visibility conditions in 2028 if visibility were to improve at a linear rate from conditions in the baseline period of 2000-2004 to natural visibility conditions in 2064). If the most impaired days RPG in 2028 is above the URP ( i.e., if visibility conditions are improving more slowly than the rate described by the URP), each state that contributes to visibility impairment in the Class I area must demonstrate, based on the four-factor analysis required under 40 CFR 51.308(f)(2)(i), that no additional emission reduction measures would be reasonable to include in its long-term strategy. 40 CFR 51.308(f)(3)(ii). To this end, 40 CFR 51.308(f)(3)(ii) requires that each state contributing to visibility impairment in a Class I area that is projected to improve more slowly than the URP provide “a robust demonstration, including documenting the criteria used to determine which sources or groups [of] sources were evaluated and how the four factors required by paragraph (f)(2)(i) were taken into consideration in selecting the measures for inclusion in its long-term strategy.”

Section 51.308(f)(6) requires states to have certain strategies and elements in place for assessing and reporting on visibility. Individual requirements under this section apply either to states with Class I areas within their borders, states with no Class I areas but that are reasonably anticipated to cause or contribute to visibility impairment in any Class I area, or both. Compliance with the monitoring strategy requirement may be met through a state's participation in the Interagency Monitoring of Protected Visual Environments (IMPROVE) monitoring network, which is used to measure visibility impairment caused by air pollution at the 156 Class I areas covered by the visibility program. 40 CFR 51.308(f)(6), (f)(6)(i), (f)(6)(iv).

All states' SIPs must provide for procedures by which monitoring data and other information are used to determine the contribution of emissions from within the state to regional haze visibility impairment in affected Class I areas, as well as a statewide inventory documenting such emissions. 40 CFR 51.308(f)(6)(ii), (iii), (v). All states' SIPs must also provide for any other elements, including reporting, recordkeeping, and other measures, that are necessary for states to assess and report on visibility. 40 CFR 51.308(f)(6)(vi).

Section 51.308(f)(5) requires a state's regional haze SIP revision to address the requirements of paragraphs 40 CFR 51.308(g)(1) through (5) so that the plan revision due in 2021 will serve also as a progress report addressing the period since submission of the progress report for the first implementation period. The regional haze progress report requirement is designed to inform the public and the EPA about a state's implementation of its existing long-term strategy and whether such implementation is in fact resulting in the expected visibility improvement. See 81 FR 26942, 26950 (May 4, 2016), (82 FR at 3119, January 10, 2017). To this end, every state's SIP revision for the second implementation period is required to assess changes in visibility conditions and describe the status of implementation of all measures included in the state's long-term strategy, including BART and reasonable progress emission reduction measures from the first implementation period, and the resulting emissions reductions. 40 CFR 51.308(g)(1) and (2).

CAA section 169A(d) requires that before a state holds a public hearing on a proposed regional haze SIP revision, it must consult with the appropriate FLM or FLMs; pursuant to that consultation, the state must include a summary of the FLMs' conclusions and recommendations in the notice to the public. Consistent with this statutory requirement, the RHR also requires that states “provide the [FLM] with an opportunity for consultation, in person and at a point early enough in the State's policy analyses of its long-term strategy emission reduction obligation so that information and recommendations provided by the [FLM] can meaningfully inform the State's decisions on the long-term strategy.” 40 CFR 51.308(i)(2). For the EPA to evaluate whether FLM consultation meeting the requirements of the RHR has occurred, the SIP submission should include documentation of the timing and content of such consultation. The SIP revision submitted to the EPA must also describe how the state addressed any comments provided by the FLMs. 40 CFR 51.308(i)(3). Finally, a SIP revision must provide procedures for continuing consultation between the state and FLMs regarding the state's visibility protection program, including development and review of SIP revisions, five-year progress reports, and the implementation of other programs having the potential to contribute to impairment of visibility in Class I areas. 40 CFR 51.308(i)(4).

Finally, the state SIP must meet the approval requirements in CAA section 110(a)(2) for plans “submitted by a State under this chapter” to the extent not already addressed in the regulations described previously. As relevant here, the state must provide “necessary assurances” that the state has adequate personnel, funding, and authority to carry out the implementation plan, that the state “is not prohibited by any provision of Federal or State law from carrying out such implementation plan or portion thereof,” and that the state can lawfully rely on regional and local instrumentalities to implement the SIP, as applicable. CAA section 110(a)(2)(E)(i)-(iii).

In section IV of this document, we describe Colorado's 2022 SIP submission and evaluate it against the requirements of the CAA and RHR for the second implementation period of the regional haze program.

Section 169A(b)(2) of the CAA requires each state in which any Class I area is located or “the emissions from which may reasonably be anticipated to cause or contribute to any impairment of visibility” in a Class I area to have a plan for making reasonable progress toward the national visibility goal. The RHR implements this statutory requirement at 40 CFR 51.308(f), which provides that each state's plan “must address regional haze in each mandatory Class I Federal area located within the State and in each mandatory Class I Federal area located outside the State that may be affected by emissions from within the State,” and (f)(2), which requires each state's plan to include a long-term strategy that addresses regional haze in such Class I areas.

There are twelve designated Class I areas within the State of Colorado, including four national parks managed by the U.S. National Park Service (Black Canyon of the Gunnison National Park, Great Sand Dunes National Park, Mesa Verde National Park, Rocky Mountain National Park) and eight wilderness areas managed by the U.S. Forest Service (Eagles Nest Wilderness Area, Flat Tops Wilderness Area, La Garita Wilderness Area, Maroon Bells-Snowmass Wilderness Area, Mount Zirkel Wilderness Area, Rawah Wilderness Area, Weminuche Wilderness Area, West Elk Wilderness Area). 18

Using the 2021 Particulate Source Apportionment Technology (PSAT) product from the WRAP, Colorado identified five Class I areas outside the State where visibility may be affected by Colorado sources: Canyonland National Park in Utah (9.4%), Capitol Reef National Park in Utah (3.6%), Badlands National Park in South Dakota (7.5%), Wind Cave National Park in South Dakota (2.9%), and Wheeler Peak Wilderness in New Mexico (4.1%) based on combined percentages of nitrate + sulfate impairment at these Class I areas from Colorado sources. The State further highlighted that these Class I areas also experience visibility impairment due to five other aerosol species (sea salt, elemental carbon, organic carbon, fine soil, and coarse mass) which were not included in the 2021 PSAT modeling the State relied on to determine its contributions to Class I areas outside of the State. 19 Therefore, according to the State, Colorado's contribution to overall light extinction is less than the results of the 2021 PSAT modeling which only evaluated nitrate + sulfate impairment. Furthermore, Colorado notes that the already announced retirements of coal-fired power plants driven by Colorado state rules and associated with the State's regional haze long-term strategy and incorporated into the SIP, along with state regulations for ozone, greenhouse gases, and other regulatory programs not part of the State's regional haze long-term strategy, will further reduce nitrate and sulfate contributions from Colorado sources. 20 Because Colorado addressed regional haze visibility impairment for each Class I area within the State, and each mandatory Class I area located outside the State that may be affected by emissions from the State, we find that Colorado did not unreasonably exclude any Class I areas from its analysis.

Section 51.308(f)(1) requires states to determine the following for “each mandatory Class I Federal area located within the State”: baseline visibility conditions for the most impaired and clearest days, natural visibility conditions for the most impaired and clearest days, progress to date for the most impaired and clearest days, the differences between current visibility conditions and natural visibility conditions, and the URP. This section also provides the option for states to propose adjustments to the URP line for a Class I area to account for visibility impacts from anthropogenic sources outside the United States and/or the impacts from wildland prescribed fires that were conducted for certain specified objectives. 40 CFR 51.308(f)(1)(vi)(B).

The IMPROVE monitoring network measures visibility impairment caused by air pollution at Class I areas. Colorado's 2022 SIP submission provides visibility conditions for each IMPROVE monitor and associated Class I area in Colorado (table 1). 21

The State also determined the uniform rate of progress for the most impaired and clearest days for Colorado Class I areas. 22 Colorado also provided haze indices and the uniform rate of progress for IMPROVE monitors and associated Class I areas outside the State. 23

Based on the information provided in Colorado's 2022 SIP submission, the EPA is proposing to approve the State's visibility condition calculations for Great Sand Dunes, Mesa Verde, Mount Zirkel, Rawah, Rocky Mountain National Park, Weminuche, La Garita, Black Canyon of the Gunnison, Eagles Nest, Flat Tops, Maroon Bells, White River, and West Elk  24 as meeting the requirements of 40 CFR 51.308(f)(1) related to the calculation of baseline, current, and natural visibility conditions; progress to date; and the URP.

Each state having a Class I area within its borders or emissions that may affect visibility in a Class I area must develop a long-term strategy for making reasonable progress towards the national visibility goal. CAA section 169A(b)(2)(B). After considering the four statutory factors, all measures that are determined to be necessary to make reasonable progress must be in the long-term strategy. In developing its long-term strategy, a state must also consider the five additional factors in 40 CFR 51.308(f)(2)(iv). As part of its reasonable progress determinations, the state must describe the criteria used to determine which sources or group of sources were evaluated ( i.e., subjected to four-factor analysis) for the second implementation period and how the four factors were taken into consideration in selecting the emission reduction measures for inclusion in the long-term strategy. 40 CFR 51.308(f)(2)(iii).

Colorado identified twelve Class I areas that must be addressed in its long-term strategy. 25 Under 40 CFR 51.308(f)(2)(i), SIP submittals must include a description of the criteria a state used to determine which sources or groups of sources to evaluate through four-factor analysis. Colorado used a Q/d screening approach to identify sources for four-factor analysis. The Q/d screening metric uses a source's annual emissions in tons (Q) divided by the distance in kilometers (d) between the source and the nearest Class I area, along with a reasonably selected threshold for this metric. The larger the Q/d value, the greater the source's expected effect on visibility in each associated Class I area.

Specifically, the WRAP Reasonable Progress Screening protocol recommends a three-step process for screening sources that involves an initial screening of identifying stationary sources that emit combined NO X , SO 2 , SO 4 , and PM 10 emissions of over 25 tons/year, a secondary screening of assessing the Q/d for those stationary sources to determine whether a source Q/d exceeds “10” for a specific Class I area, and the use of the 2028 Weighted Emissions Potential (WEP) to determine the possible contribution of the source to visibility impairment in Class I areas for the 20% most impaired days. Using the WRAP-devised screening threshold of Q/d > 10 and emissions information from the 2014 National Emission Inventory (NEI), Colorado initially identified twenty-three sources in the State that may be affecting visibility at Class I areas in Colorado. 26 27 The State reduced the number of facilities subject to a reasonable progress four-factor analysis to nineteen because two facilities have actual emissions below the WRAP screening protocol's threshold of 25 tons/year, one coal mine closed in 2015, and two adjacent coal mines were combined into one facility. 28 Ultimately, the State selected nineteen sources subject to a four-factor analysis (table 2). 29

The State requested that each of the nineteen sources submit cost information for its review and consideration. 30 For three of these sources, the State determined that it was not necessary to conduct further review because those sources had closed prior to the State's development of its SIP. 31 For the remaining sources, Colorado then evaluated what is necessary to make reasonable progress by considering the four statutory factors  32 for each source:

• Cost of compliance;

• Time necessary for compliance;

• Energy and non-air quality environmental impacts of compliance; and

• Remaining useful life of any potentially affected sources.

The State documented these analyses in Colorado's 2022 SIP submission and associated technical support documents. Chapter 7 of the SIP submission contains Colorado's evaluation of the four statutory factors for each source and Colorado's determinations of the source-specific emission reduction measures necessary to make reasonable progress. As part of its four-factor evaluation, Colorado considered the already announced retirements of several units and facilities as part of its “remaining useful life” analysis and incorporated those retirements into the SIP. 33 Ultimately, the State concluded that the following enforceable reasonable progress source retirements (table 3) and emission limits (table 4) satisfy and exceed regional haze requirements for the second implementation period and that no other regional haze analyses or regional haze controls will be required by the State during the second regional haze implementation period.