90 FR 155 pgs. 39148-39155 - Air Plan Approval; Michigan; Detroit 2010 Sulfur Dioxide Redesignation and Maintenance Plan
Type: PRORULEVolume: 90Number: 155Pages: 39148 - 39155
Pages: 39148, 39149, 39150, 39151, 39152, 39153, 39154, 39155Docket number: [EPA-R05-OAR-2025-0238; FRL-12841-01-R5]
FR document: [FR Doc. 2025-15458 Filed 8-13-25; 8:45 am]
Agency: Environmental Protection Agency
Official PDF Version: PDF Version
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ENVIRONMENTAL PROTECTION AGENCY
40 CFR Parts 52 and 81
[EPA-R05-OAR-2025-0238; FRL-12841-01-R5]
Air Plan Approval; Michigan; Detroit 2010 Sulfur Dioxide Redesignation and Maintenance Plan
AGENCY:
Environmental Protection Agency (EPA).
ACTION:
Proposed rule.
SUMMARY:
The Environmental Protection Agency (EPA) is proposing to find that the Detroit, Michigan area is attaining the 2010 sulfur dioxide (SO 2 ) National Ambient Air Quality Standard (NAAQS) and to act in accordance with a request from Michigan to redesignate the area to attainment for the 2010 SO 2 NAAQS, because the request meets the statutory requirements for redesignation under the Clean Air Act (CAA). EPA is also proposing to approve Michigan's maintenance plan for the Detroit area. Michigan submitted the request for approval of the Detroit nonattainment area's redesignation and maintenance plan on May 5, 2025. EPA approved Michigan's attainment plan for the Detroit area on May 19, 2025.
DATES:
Comments must be received on or before September 15, 2025.
ADDRESSES:
[top] Submit your comments, identified by Docket ID No. EPA-R05-OAR-2025-0238 at https://www.regulations.gov, or via email to arra.sarah@epa.gov. For comments submitted at Regulations.gov, follow the online instructions for submitting comments. Once submitted, comments cannot be edited or removed from the docket. EPA may publish any comment received to its public docket. Do not submit to EPA's docket at https://www.regulations.gov any information you consider to be Confidential Business Information (CBI), Proprietary Business Information (PBI), or other information whose disclosure is restricted by statute. Multimedia submissions (audio, video, etc.) must be accompanied by a written comment. The written comment is considered the official comment and should include discussion of all points you wish to make. EPA will generally not consider comments or comment contents located outside of the primary submission ( i.e., on the web, cloud, or other file sharing system). For additional submission methods, please contact the person identified in the FOR FURTHER INFORMATION CONTACT section. For the full EPA public comment policy, information about CBI, PBI, or
FOR FURTHER INFORMATION CONTACT:
Abigail Teener, Air and Radiation Division (AR-18J), Environmental Protection Agency, Region 5, 77 West Jackson Boulevard, Chicago, Illinois 60604, (312) 353-7314, teener.abigail@epa.gov. The EPA Region 5 office is open from 8:30 a.m. to 4:30 p.m., Monday through Friday, excluding Federal holidays.
SUPPLEMENTARY INFORMATION:
I. Background and Redesignation Requirements
On June 22, 2010 (75 FR 35520), EPA published a new SO 2 NAAQS of 75 parts per billion (ppb), which is met at an ambient air quality monitoring site when the 3-year average of the annual 99th percentile of daily maximum 1-hour average concentrations does not exceed 75 ppb, as determined in accordance with appendix T of 40 CFR part 50.
Upon promulgation of a new or revised NAAQS, section 107(d)(1)(B) of the CAA requires EPA to designate as nonattainment any areas that are violating the NAAQS. On August 5, 2013 (78 FR 47191), EPA designated the Detroit area, a portion of Wayne County, Michigan, as nonattainment for the 2010 SO 2 NAAQS based on ambient air quality data collected at the Detroit SW monitoring site (AQS ID 26-163-0015) from 2009 to 2011. The nonattainment area designation became effective on October 4, 2013. Section 191 of the CAA directs states to submit a State Implementation Plan (SIP) for an area designated as nonattainment for the 2010 SO 2 NAAQS to EPA within 18 months of the effective date of the designation, i.e., by no later than April 4, 2015, in this case. The SIP must demonstrate attainment of the NAAQS as expeditiously as practicable, but no later than five years from the effective date of designation, which was October 4, 2018, for the Detroit nonattainment area.
On March 18, 2016 (81 FR 14736), EPA published an action finding that Michigan had failed to submit the required SO 2 nonattainment plan by the submittal deadline. This finding initiated deadlines under CAA section 179(a) for the potential imposition of 2-to-1 New Source Review (NSR) offset and Federal highway funding sanctions. Additionally, under CAA section 110(c), the finding triggered a requirement that EPA promulgate a Federal Implementation Plan (FIP) within two years of the finding unless, by that time, (a) the State had made the necessary complete submittal, and (b) EPA had approved the submittal as meeting applicable requirements.
On May 31, 2016, Michigan submitted a Detroit SO 2 attainment plan and on June 30, 2016, submitted associated final enforceable measures. Michigan's submission of a complete attainment plan terminated the deadlines for imposing sanctions, pursuant to 40 CFR 52.31(d)(5), but it did not terminate EPA's FIP obligation. On March 19, 2021 (86 FR 14827), EPA partially approved and partially disapproved Michigan's SO 2 plan as submitted in 2016. EPA's March 19, 2021, action approved the enforceable control measures for two facilities, approved the base-year emissions inventory, and affirmed that the NSR requirements for the area had previously been met. In the same March 19, 2021, action, EPA disapproved the attainment demonstration, as well as the requirements for meeting reasonable further progress (RFP) toward attainment of the NAAQS, reasonably available control measures/reasonably available control technology (RACM/RACT), and contingency measures. Additionally, EPA disapproved the plan's control measures for two facilities as insufficient to demonstrate attainment. These disapprovals started a new sanctions clock under CAA section 179(a).
On January 28, 2022 (87 FR 4501), EPA issued a finding of failure to attain for the Detroit SO 2 nonattainment area, determining that the area failed to attain the 2010 SO 2 NAAQS by the applicable attainment date of October 4, 2018, and established a requirement that Michigan submit a revised SIP by January 30, 2023, that would provide for expeditious attainment of the NAAQS within the time period specified in CAA sections 179(d)(3) and 172(a)(2).
On October 12, 2022 (87 FR 61514), EPA promulgated a FIP for the Detroit SO 2 nonattainment area, which satisfied EPA's duty to promulgate a FIP for the area under CAA section 110(c) that resulted from the March 18, 2016, finding of failure to submit. While EPA's FIP for the Detroit area met the requirements for SO 2 nonattainment area plans, the FIP did not relieve Michigan of the previously discussed CAA requirement to submit a plan that provides for attainment of the 2010 SO 2 NAAQS for the Detroit nonattainment area. On December 20, 2022, Michigan submitted a revised attainment plan for the Detroit SO 2 nonattainment area mirroring EPA's FIP to remedy Michigan's 2016 plan deficiencies specified in EPA's March 19, 2021, rulemaking partially approving and partially disapproving Michigan's SIP.
Michigan's revised plan, as submitted on December 20, 2022, depended, in part, upon permits that had not yet been issued but would include limits and associated requirements for the United States Steel Corporation (U.S. Steel), EES Coke Battery (EES Coke), and Dearborn Industrial Generation (DIG) facilities containing emission limits and associated requirements no less stringent than those set forth in EPA's FIP, codified at 40 CFR 52.1189. On February 21, 2023, Michigan submitted a clarification letter committing to submit the necessary permits by April 30, 2024. On March 23, 2023 (88 FR 17488), EPA proposed to conditionally approve Michigan's plan, conditioned upon the issuance of and submission for incorporation into the SIP the applicable permits for the U.S. Steel, EES Coke, and DIG facilities. Also, on March 23, 2023 (88 FR 17376), EPA issued an interim final determination to stay and defer sanctions in the Detroit SO 2 nonattainment area based on EPA's proposed conditional approval.
On December 14, 2023, Michigan submitted three applicable permits for the U.S. Steel, EES Coke, and DIG facilities. On April 2, 2024, the State submitted the final applicable permit for the DIG facility, along with a request that EPA approve its revised plan. On April 29, 2024, EPA issued a completeness letter, included in the docket for this action, determining that Michigan's submittal had satisfied the completeness criteria set forth at 40 CFR part 51, appendix V and met the requirement for a SIP submittal that provides for expeditious attainment set forth in EPA's January 28, 2022, finding of failure to attain.
[top] On May 19, 2025 (90 FR 21228), EPA approved Michigan's revised SIP submission, which the State submitted to EPA on December 20, 2022, and supplemented on February 21, 2023, December 14, 2023, and April 2, 2024, for attaining the 2010 SO 2 NAAQS for the Detroit area and for meeting other nonattainment area planning requirements of CAA sections 110, 172, 179 and 192. EPA approved Michigan's demonstration that these requirements provide for attainment of the 2010 SO 2 NAAQS in Detroit and concluded that Michigan had satisfied the other applicable requirements for nonattainment areas. In the same action, EPA determined that the conditions articulated in 40 CFR 52.31(d) had been met, thereby terminating the sanctions clock resulting from EPA's March 19,
On May 5, 2025, Michigan submitted a redesignation request and maintenance plan for the Detroit nonattainment area for the 2010 SO 2 NAAQS. Under section 107(d)(3)(E) of the CAA, EPA may promulgate a redesignation of a nonattainment area provided that:
1. EPA has determined that the area has attained the NAAQS;
2. EPA has fully approved the applicable implementation plan for the area under section 110(k) of the CAA;
3. EPA has determined that improvement in air quality is due to permanent and enforceable reductions in emissions resulting from implementation of the applicable implementation plan and applicable Federal air pollution control regulations and other permanent and enforceable reductions;
4. EPA has fully approved a maintenance plan for the area under section 175A of the CAA; and
5. The State containing such area has met all requirements applicable to the area under section 110 of the CAA and part D.
II. Evaluation of Michigan's Redesignation Request and Maintenance Plan
On May 5, 2025, Michigan submitted a request that EPA redesignate the Detroit 2010 SO 2 nonattainment area to attainment and a SIP revision containing a maintenance plan for the area.
EPA's evaluation of Michigan's redesignation request and maintenance plan was based on consideration of the five redesignation criteria provided under CAA section 107(d)(3)(E) and is described in the remainder of this section.
A. Criteria (1)-The Detroit SO 2 Nonattainment Area Has Attained the 2010 SO 2 NAAQS
In accordance with CAA section 107(d)(3)(E)(i), for redesignation of a nonattainment area to attainment, the CAA requires EPA to determine that the area has attained the applicable NAAQS. As stated in EPA's April 23, 2014, "Guidance for 1-Hour SO 2 Nonattainment Area SIP Submissions" ("April 2014 SO 2 Guidance"), there are two components needed to support an attainment determination: (1) a review of representative air quality monitoring data located in the area of maximum concentration; and (2) a further analysis, using air quality dispersion modeling, which will generally be needed to estimate SO 2 concentrations throughout the nonattainment area to demonstrate that the entire area is attaining the applicable NAAQS, based on current actual emissions or the fully implemented control strategy. Michigan's May 5, 2025, redesignation request addresses both components, as described below.
1. Air Quality Monitoring Data
Under 40 CFR 50.17(b), the 2010 SO 2 NAAQS is met at an ambient air quality monitoring site when the three-year average of the annual (99th percentile) daily maximum 1-hour average concentrations is less than or equal to 75 ppb, as determined in accordance with appendix T of 40 CFR part 50, at all relevant monitoring sites in the subject area. In a year with 365 days of valid monitoring data, the 99th percentile would be the fourth highest daily maximum 1-hour value.
Michigan operates five SO 2 monitors in the Detroit nonattainment area: Detroit SW (AQS ID 26-163-0015; 150 Waterman Street), NMH 48217 (AQS ID 26-163-0097; 3225 South Deacon Street), DP4th (AQS ID 26-163-0098; 4700 West Fort Street), Trinity (AQS ID 26-163-0099; 9191 West Fort Street), and Military Park (AQS ID 26-163-0100; 1238 Military Street). Tables 1 and 2 below show the 99th percentile results and three-year average design values, respectively, for the five monitors in the Detroit SO 2 nonattainment area for 2019-2023. The design values for 2019-2021 range from 14-37 ppb, the design values for 2020-2022 range from 16-41 ppb, and the design values for 2021-2023 range from 15-38, which are all below the SO 2 NAAQS. Furthermore, Michigan's redesignation request states that the originally violating monitor, Detroit SW, has shown attainment since 2014, and all other monitors in the nonattainment area have shown attainment since they began monitoring in 2016 and 2018. Documentation of the monitoring data is included as appendix A of Michigan's redesignation request. Therefore, EPA finds that Michigan has demonstrated that the SO 2 monitors in the Detroit area show attainment.
| Site name | Site ID | 2019 | 2020 | 2021 | 2022 | 2023 |
|---|---|---|---|---|---|---|
| Detroit SW | 26-163-0015 | 61 | 43 | 37 | 43 | 35 |
| NMH 48217 | 26-163-0097 | 27 | 17 | 14 | 17 | 18 |
| DP4th | 26-163-0098 | 19 | 17 | 16 | 16 | 14 |
| Trinity | 26-163-0099 | 26 | 16 | 20 | 20 | 15 |
| Military Park | 26-163-0100 | 32 | 33 | 25 | 31 | 30 |
| Site name | Site ID | 2019-2021 | 2020-2022 | 2021-2023 |
|---|---|---|---|---|
| Detroit SW | 26-163-0015 | 47 | 41 | 38 |
| NMH 48217 | 26-163-0097 | 19 | 16 | 16 |
| DP4th | 26-163-0098 | 17 | 16 | 15 |
| Trinity | 26-163-0099 | 21 | 19 | 18 |
| Military Park | 26-163-0100 | 30 | 29 | 29 |
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2. Air Quality Dispersion Modeling
The April 2014 SO 2 Guidance states that EPA may make determinations of attainment based on the modeling, using allowable emissions, from the attainment demonstrations for the applicable SIP for the affected area. Attainment demonstrations for the 2010 SO 2 NAAQS should demonstrate future attainment and maintenance of the NAAQS in the entire area designated as nonattainment ( i.e., not just at the violating monitor) by using air quality dispersion modeling ( see appendix W to 40 CFR part 51) to show that the mix of sources and enforceable control measures and emission rates in an identified area will not lead to a violation of the 2010 SO 2 NAAQS. For a short-term ( i.e., 1-hour) standard, EPA believes that dispersion modeling, using allowable emissions and addressing stationary sources in the affected area (and in some cases those sources located outside the nonattainment area which may affect attainment in the area) is technically appropriate, efficient and effective in demonstrating attainment in nonattainment areas because it takes into consideration combinations of meteorological and emission source operating conditions that may contribute to peak ground-level concentrations of SO 2.
Preferred air quality models for use in regulatory applications are described in appendix A of EPA's Guideline on Air Quality Models (40 CFR part 51, appendix W). In 2005, EPA promulgated the AERMOD model as the Agency's preferred near-field dispersion modeling for a wide range of regulatory applications addressing stationary sources (for example in estimating SO 2 concentrations) in all types of terrain based on extensive developmental and performance evaluation. Supplemental guidance on modeling for purposes of demonstrating attainment of the SO 2 standard is provided in appendix A to the April 23, 2014, SO 2 nonattainment area SIP guidance document referenced above. Appendix A provides extensive guidance on the modeling domain, the source inputs, assorted types of meteorological data, and background concentrations. Consistency with the recommendations in this guidance is generally necessary for the attainment demonstration to offer adequately reliable assurance that the plan provides for attainment.
The meteorological data used in the analysis should generally be processed with the most recent version of the AERMET data preprocessor. Estimated concentrations should include ambient background concentrations, should follow the form of the standard, and should be calculated as described in section 2.6.1.2 of the August 23, 2010, clarification memo on "Applicability of Appendix W Modeling Guidance for the 1-hr SO 2 National Ambient Air Quality Standard" (U.S. EPA, 2010).
Michigan's redesignation request relies upon the air dispersion modeling analysis EPA conducted while developing its FIP to demonstrate attainment of the 2010 SO 2 NAAQS. A more in-depth discussion of EPA's modeling requirements and analysis, including the use of longer-term average limits, may be found in EPA's proposed FIP (87 FR 33095, June 1, 2022) and the associated technical support document, which is included as appendix C of Michigan's May 5, 2025, redesignation request.
In its modeling analysis, EPA explicitly modeled maximum allowable or maximum uncontrolled emissions from the following sources: U.S. Steel, EES Coke, DTE Energy (DTE) Trenton Channel, Carmeuse Lime, DTE Monroe, Cleveland-Cliffs Steel Corporation (formerly known as AK or Severstal Steel), DIG, and Marathon Refinery. The emission limits and associated requirements, including the construction of a 170-foot stack for U.S. Steel Boilerhouse 2, that Michigan's attainment demonstration rely upon are contained in permits specified in Table 3 below.
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| Unit | SO 2 emission limit (lb/hr) | Permit No. and date | SIP incorporation date |
|---|---|---|---|
| U.S. Steel-Zug Island | |||
| Boilerhouse 1 (all stacks combined) A1 Blast Furnace B2 Blast Furnace D4 Blast Furnace A/B Blast Furnace Flares D Furnace Flare | 55.00 0.00 40.18 40.18 60.19 60.19 | Permit to Install 110-23, effective September 26, 2023 | Incorporated into Michigan's SIP as part of May 19, 2025, action (90 FR 21228). |
| Boilerhouse 2 | *?750.00/81.00 | Permit to Install 108-23, effective November 14, 2024 | |
| U.S. Steel-Ecorse | |||
| Hot Strip Mill-Slab Reheat Furnace 1 Hot Strip Mill-Slab Reheat Furnace 2 Hot Strip Mill-Slab Reheat Furnace 3 | 0.31 0.31 0.31 | Permit to Install 110-23, effective September 26, 2023 | Incorporated into Michigan's SIP as part of May 19, 2025, action (90 FR 21228). |
| Hot Strip Mill-Slab Reheat Furnace 4 | 0.31 | ||
| Hot Strip Mill-Slab Reheat Furnace 5 | 0.31 | ||
| No. 2 Baghouse | 3.30 | ||
| Main Plant Boiler No. 8 | 0.07 | ||
| Main Plant Boiler No. 9 | 0.07 | ||
| EES Coke | |||
| Combustion Stack | 544.6 | Permit to Install 51-08C, effective November 21, 2014 | Incorporated into Michigan's SIP as part of May 19, 2025, action (90 FR 21228). |
| DTE Trenton Channel?** | |||
| Trenton Channel Unit 9 | 5,907 | Permit to Install 125-11C, effective January 1, 2017 | Incorporated into Michigan's SIP as part of March 19, 2021, action (86 FR 14827). However, the source has since shut down, and any restart would require a revision to the source's Title V permit, subject to EPA review and possible objection if a permit revision would not ensure compliance with all applicable CAA requirements. |
| Carmeuse Lime | |||
| Carmeuse Lime Stack | 470 | Permit to Install 193-14A, effective October 1, 2018 | Incorporated into Michigan's SIP as part of March 19, 2021, action (86 FR 14827). |
| Cleveland-Cliffs Steel Corporation?** | |||
| Furnace B Baghouse Stack Furnace B Stove Stack Furnace B Baghouse and Stove Stacks (combined) Furnace C Baghouse Stack Furnace C Stove Stack Furnace C Baghouse and Stove Stacks (combined) | 71.9 38.75 77.8 179.65 193.6 271.4 | Permit MI-ROP-A8640-2016a, modified January 19, 2017 | Incorporated into Michigan's SIP as part of May 19, 2025, action (90 FR 21228). |
| DIG?** | |||
| Boilers 1, 2, and 3 (combined) | 420 | Permit 253-02A, effective September 25, 2003 | Incorporated into Michigan's SIP as part of May 19, 2025, action (90 FR 21228). |
| Boilers 1, 2, and 3 and Flares 1 and 2 (combined) | 840 | Permit to Install 109-23, effective September 26, 2023 | Incorporated into Michigan's SIP as part of May 19, 2025, action (90 FR 21228). |
| *?U.S. Steel-Zug Island Boilerhouse 2 shall emit less than 750.00 lbs/hr unless Boilerhouse 1, A1 Blast Furnace, B2 Blast Furnace, D4 Blast Furnace, A/B Blast Furnace Flares, or D Furnace Flare is operating, in which case it shall emit less than 81.00 lbs/hr. In addition to the limit, this permit required a new 170-foot stack to be constructed for Boilerhouse 2 by November 14, 2024. | |||
| **?The limit for Trenton Channel is expressed as a 30-day average limit, and the limits for Cleveland-Cliffs Steel Corporation and DIG are expressed as daily average limits. EPA's FIP proposal addresses the use of these longer-term average limits, both with respect to the general suitability of using such limits for demonstrating attainment and with respect to whether the particular limits included in the plan have been suitably demonstrated to provide for attainment. | |||
EPA evaluated two separate operating scenarios as part of its modeling analysis based on the separate limits for U.S. Steel Boilerhouse 2. In both scenarios, the modeling for the Detroit area showed a maximum concentration of 73.6 ppb (192.7 micrograms per cubic meter (µg/m 3 )), which is below the NAAQS of 75 ppb. This maximum concentration resulted from modeling all units at maximum permitted levels now incorporated into Michigan's SIP or maximum uncontrolled emissions and the background concentration determined using monitoring data from the Allen Park monitor (AQS ID 26-163-0001).
The April 2014 SO 2 Guidance states that a demonstration that the control strategy in the SIP has been fully implemented would be relevant for making a determination of attainment based on modeling from the attainment demonstration of the applicable SIP. All compliance dates included in Michigan's plan have passed. The latest compliance date was for U.S. Steel Boilerhouse 2 on November 14, 2024. Michigan has confirmed that the facilities included in the modeling analysis are currently in full compliance with their emission limits and that the U.S. Steel Boilerhouse 2 stack construction was completed and commenced operation on October 25, 2024, ahead of the November 14, 2024, deadline. Compliance documentation is included as appendix D of Michigan's May 5, 2025, redesignation request.
The modeling analysis was discussed in detail in EPA's proposed FIP (87 FR 33095, June 1, 2022). In this action, EPA proposes to find that this modeling analysis and the monitored air quality data demonstrate that the Detroit area has attained the 2010 SO 2 NAAQS.
B. Criteria (2) and Criteria (5)-Michigan Has Met All Applicable Requirements Under CAA Section 110 and Part D of the CAA, and EPA Has Fully Approved the Applicable Implementation Plan Under CAA Section 110(k)
[top] For redesignating a nonattainment area to attainment under a NAAQS, a State must have met all applicable requirements (CAA section 107(d)(3)(E)(v)), and EPA must have
Many of the section 110 elements that are unrelated to an area's SO 2 attainment status are not applicable requirements for purposes of redesignation. The area will still be subject to these requirements after the area is redesignated to attainment of the 2010 SO 2 NAAQS. For example, the CAA section 110(a)(2)(D) interstate transport requirements for a State are not linked with a nonattainment area's designation and classification in that State and continue to apply to States regardless of the designation status of areas within that State. However, even though many of the section 110 requirements are not applicable for purposes of redesignation, EPA in any case approved Michigan's section 110 infrastructure SIP on November 12, 2015 (80 FR 61311).
EPA proposes to determine that Michigan has met, and EPA has fully approved, those part D requirements that are applicable for purposes of redesignation. Part D is comprised of the general nonattainment area plan requirements in subpart 1 (section 172) as well as pollutant-specific subparts, including section 191 (or subpart 5), which applies to areas designated nonattainment for SO 2 , nitrogen dioxide, or lead. While some nonattainment planning requirements are not applicable for purposes of CAA section 107(d)(3)(E)(ii) and (v) for areas that are attaining the NAAQS, Michigan has in any case submitted a complete attainment plan and EPA has fully approved that plan, including emissions inventories, RACT/RACM, RFP, and contingency measures.
On May 19, 2025 (90 FR 21228), EPA fully approved Michigan's attainment SIP, mirroring EPA's FIP, for the Detroit area including the operation of a new stack at U.S. Steel Boilerhouse 2 and emission limits and associated requirements for U.S. Steel, EES Coke, Carmeuse Lime, Cleveland-Cliffs Steel Corporation, and DIG. In that action, EPA found that Michigan had satisfied requirements for providing for attainment of the 2010 SO 2 NAAQS in the Detroit area. The adopted SO 2 SIP regulations for U.S. Steel, EES Coke, Carmeuse Lime, Cleveland-Cliffs Steel Corporation, and DIG are contained in the permits specified above in Table 3. Michigan has shown that it maintains an active enforcement program to ensure ongoing compliance with these requirements. Michigan's program for NSR, which includes provisions for the Prevention of Significant Deterioration program, will address emissions from potential new sources in the area (78 FR 76064, December 16, 2013).
Section 176(c) of the CAA requires States to establish criteria and procedures to ensure that federally supported or funded projects conform to the air quality planning goals in the applicable SIP. The requirement to determine conformity applies to transportation plans, programs, and projects that are developed, funded, or approved under title 23 of the United States Code (U.S.C.) or the Federal Transit Act (49 U.S.C. 1601) (transportation conformity) as well as to all other federally supported or funded projects (general conformity). State transportation conformity SIP revisions must be consistent with Federal conformity regulations relating to consultation, enforcement, and enforceability that EPA promulgated pursuant to its authority under the CAA. EPA's longstanding interpretation of the CAA is that because CAA section 176(c) conformity requirements continue to apply after areas are redesignated to attainment, meeting those requirements is not a prerequisite to redesignating an area. In addition, based on EPA's April 2014 SO 2 Guidance, transportation conformity only applies to SO 2 SIPs if transportation-related emissions of SO 2 as a precursor are a significant contributor to a fine particulate matter (PM 2.5 ) nonattainment problem or if the SIP has established an approved or adequate budget for such emissions as part of the RFP, attainment, or maintenance strategy, neither of which applies to the Detroit area. EPA concluded that highway and transit vehicles are not significant sources of SO 2 in this area. As a result, transportation conformity determinations are not required in the Detroit SO 2 maintenance area. Therefore, transportation plans, improvement programs, and projects are presumed to conform to applicable implementation plans for SO 2 . Federal agencies are still required to address general conformity in the Detroit SO 2 maintenance area. EPA approved Michigan's general conformity SIP on December 18, 1996 (61 FR 66607).
Based on the above findings, EPA is proposing to find that Michigan has met the applicable requirements of section 110 and part D of title I of the CAA for purposes of the redesignation of the Detroit nonattainment area. Furthermore, EPA has fully approved the applicable implementation plan for the Detroit area.
C. Criteria (3)-The Air Quality Improvement in the Detroit SO 2 Nonattainment Area Is Due to Permanent and Enforceable Emission Reductions
To redesignate an area from nonattainment to attainment, section 107(d)(3)(E)(iii) of the CAA requires EPA to determine that the air quality improvement in the area is due to permanent and enforceable reductions in emissions resulting from the implementation of the SIP and applicable Federal air pollution control regulations and other permanent and enforceable emission reductions.
Michigan's attainment plan (90 FR 21228, May 19, 2025) incorporates the permits for U.S. Steel, EES Coke, DTE Trenton Channel, Carmeuse Lime, Cleveland-Cliffs Steel Corporation, and DIG specified above in Table 3, which include SO 2 emission limits and associated requirements, including the construction of a 170-foot stack for U.S. Steel Boilerhouse 2 by November 14, 2024. Michigan has confirmed that the facilities are currently in full compliance with their emission limits and associated requirements contained in the permits specified in Table 3 and that the U.S. Steel Boilerhouse 2 stack construction has been completed. Compliance documentation is included as appendix D of Michigan's May 5, 2025, redesignation request. EPA has included these emission limits and associated requirements in the March 19, 2021, partial approval of Michigan's SIP (86 FR 14827) and the May 19, 2025, approval of Michigan's SIP (90 FR 21228), which also renders them federally enforceable.
[top] The EPA modeling that Michigan's attainment plan relies upon includes the emission limits for U.S. Steel, EES Coke, DTE Trenton Channel, Carmeuse Lime, Cleveland-Cliffs Steel Corporation, and DIG and shows attainment of the 2010 SO 2 NAAQS throughout the Detroit area. A more in-depth discussion of EPA's modeling may be found in EPA's proposed FIP (87 FR 33095, June 1, 2022) and the associated technical support document, which is included as appendix C of Michigan's May 5, 2025,
D. Criteria (4)-The Detroit SO 2 Nonattainment Area Has a Fully Approved Maintenance Plan Pursuant to Section 175A
To redesignate an area from nonattainment to attainment, section 107(d)(3)(E)(iv) of the CAA requires EPA to determine that the area has a fully approved maintenance plan pursuant to section 175A of the CAA. Section 175A of the CAA sets forth the elements of a maintenance plan for areas seeking redesignation from nonattainment to attainment. Under section 175A, the maintenance plan must demonstrate continued attainment of the NAAQS for at least 10 years after EPA approves a redesignation to attainment. Eight years after the redesignation, the State must submit a revised maintenance plan which demonstrates that attainment of the NAAQS will continue for an additional 10 years beyond the initial 10-year maintenance period. To address the possibility of future NAAQS violations, the maintenance plan must contain contingency measures, as EPA deems necessary, to ensure prompt correction of any future NAAQS violation.
Specifically, the maintenance plan should address five requirements: an attainment emissions inventory, a maintenance demonstration, a commitment for continued air quality monitoring, a process for verification of continued attainment, and a contingency plan. EPA is proposing to determine that Michigan's May 5, 2025, redesignation request contains its maintenance plan and all the necessary components, which Michigan has committed to review eight years after the redesignation.
As a part of a State's maintenance plan, the air agency should develop an attainment emissions inventory to identify the level of emissions in the affected area which is sufficient to attain and maintain the SO 2 NAAQS. 1 In its redesignation request, Michigan provided an emissions inventory for SO 2 in the nonattainment area for 2025, the first year after the latest compliance date included in Michigan's attainment plan and the U.S. Steel Boilerhouse 2 stack construction was completed. Total allowable emissions in the Detroit area for the 2025 attainment year are 11,890 tons. This level of emissions, in combination with the new stack construction at the U.S. Steel facility, is sufficient to maintain the NAAQS, and Michigan has confirmed that the facilities are in full compliance with their emission limits. Compliance documentation is included as appendix D of Michigan's May 5, 2025, redesignation request. In its attainment plan, Michigan reported that total actual SO 2 emissions for the nonattainment area from 2012, a year during which the area was not attaining the NAAQS, were 37,378 tons. The SO 2 emission limits for U.S. Steel, EES Coke, Carmeuse Lime, Cleveland-Cliffs Steel Corporation, and DIG specified in Table 3 above, as well as the shutdown of the DTE Trenton Channel and DTE River Rouge facilities, led to a more than 25,000-ton, or 68 percent, decrease between actual emissions in 2012 and maximum allowable emissions in 2025 in the Detroit area. EPA's modeling that Michigan relied upon for its redesignation request for the Detroit area, based on maximum uncontrolled emissions or SO 2 emission limits now incorporated into Michigan's SIP, resulted in a design value of 73.6 ppb, below the SO 2 NAAQS. See Detroit SO 2 FIP technical support document (87 FR 61514, October 12, 2022).
Footnotes:
1 ? See April 2014 SO 2 Guidance, page 66.
EPA's "Procedures for Processing Requests to Redesignate Areas to Attainment" (Calcagni Memo)? 2 describes two ways for a State to demonstrate maintenance of the NAAQS following the redesignation of the area: (1) the State can show that future emissions of a pollutant will not exceed the level of the attainment inventory, or (2) the State can model to show that the future mix of sources and emission rates will not cause a violation of the standard. In both instances, the demonstration should be for a period of 10 years following the redesignation. Furthermore, the plan should contain a summary of air quality concentrations resulting from control measures implemented where modeling is relied upon to demonstrate maintenance. Michigan's maintenance demonstration consists of the attainment plan air quality modeling analysis showing that the emissions reductions now in effect in the Detroit area will provide for attainment of the 2010 SO 2 NAAQS. The permanent and enforceable SO 2 emission reductions described above ensure that the area emissions will be equal to or less than the emission levels that were evaluated in the air quality modeling analysis, and Michigan's enforceable emission requirements will ensure that the Detroit area SO 2 emission limits are met continuously. Michigan's redesignation request contains an emissions inventory for 2036, the maintenance year, which does not show any increases in maximum allowable emissions from the attainment year. Additionally, Michigan has a fully approved New Source Review (NSR) program (78 FR 76064, December 16, 2013), including requirements to assess the impacts of any plans to construct or resume operations of an emission unit on maintaining NAAQS attainment.
Footnotes:
2 ?Calcagni, John, Director, Air Quality Management Division, EPA Office of Air Quality Planning and Standards, "Procedures for Processing Requests to Redesignate Areas to Attainment," September 4, 1992.
For verification of continued attainment, Michigan has committed to track the emissions and compliance status of the major facilities in the Detroit area so that future emissions will not exceed the allowable emissions-based attainment inventory. All major sources in Michigan are required to submit annual emissions data, which the State uses to update its emission inventories as required by the CAA. Michigan commits to continue monitoring SO 2 levels in the Detroit area and consult EPA prior to making changes to the existing monitoring network, periodically reevaluate assumptions and input data used for the attainment plan modeling analysis, and monitor contingency plan indicators as described below.
[top] Section 175A(d) of the CAA provides that a maintenance plan must contain contingency provisions that will promptly correct any violation of the 2010 SO 2 NAAQS after the area is redesignated to attainment (Calcagni Memo). The maintenance plan should identify the contingency measures to be adopted, a schedule and procedure for adoption and implementation, and a time limit for action by the State. A State should also identify specific indicators to be used to determine when the contingency measures need to be implemented. The maintenance plan must also include a requirement that a State will implement all measures with respect to control of the pollutant that were contained in the SIP before redesignation of the area to attainment in accordance with section 175A(d). Unlike CAA section 172(c)(9), section 175A of the CAA does not explicitly require that contingency measures must take effect without further action by the air agency for the maintenance plan to be approved. However, if this action is finalized, the contingency plan would
Footnotes:
3 ? See April 2014 SO 2 Guidance, page 74.
In the "General Preamble for the Implementation of Title I of the Clean Air Act Amendments of 1990," published on April 16, 1992 (57 FR 13498), EPA provides further discussion of contingency measures for SO 2 . This guidance states that in many cases, attainment revolves around compliance of a single source or a small set of sources with emission limits shown to provide for attainment. Although this guidance applies to contingency measures under section 172(c)(9), EPA applies a similar policy with respect to contingency measures for SO 2 required in maintenance plans under section 175A(d). The requirement to submit contingency measures in accordance with section 175A of the CAA can be adequately addressed for SO 2 by the operation of a comprehensive enforcement program, 4 which can quickly identify and address sources that might be causing exceedances of the NAAQS.
Footnotes:
4 ? See April 2014 SO 2 Guidance, page 41-42.
Michigan's enforcement program is active and capable of prompt action to remedy compliance issues. Michigan commits to ongoing compliance and enforcement of the control measures contained in the federally enforceable permits specified above in Table 3, which have already been incorporated into Michigan's attainment SIP approval (90 FR 21228, May 19, 2025). Michigan also has the necessary resources in the event of violations to enforce its permit provisions and rules. Michigan has the authority to expeditiously adopt, implement, and enforce any subsequent emission control measures deemed necessary to correct any future SO 2 violations. Michigan commits to adopting and implementing such corrective actions as necessary to address violations of the 2010 SO 2 NAAQS. Specifically, Michigan commits to adopt and expeditiously implement necessary corrective actions in the event of a violation of the standard or an annual 99th percentile daily maximum 1-hour SO 2 concentration of 79 ppb or above occurs in a single calendar year in the Detroit area. Based on the foregoing, EPA proposes to find that Michigan has addressed the contingency measure requirement.
EPA is proposing to find that Michigan's maintenance plan adequately addresses the five basic components of a maintenance plan necessary to maintain the SO 2 NAAQS in the Detroit nonattainment area. Therefore, EPA proposes to find that the redesignation and maintenance plan SIP revision submitted by Michigan for the 2010 SO 2 Detroit nonattainment area meets the requirements of section 175A of the CAA and proposes to approve this plan.
III. What action is EPA taking?
EPA is proposing to redesignate the Detroit area from nonattainment to attainment for the 2010 SO 2 NAAQS in accordance with Michigan's May 5, 2025, request. EPA has determined that the area is attaining the 2010 SO 2 NAAQS and that the improvement in air quality is due to permanent and enforceable SO 2 emission reductions in the area. EPA is also proposing to approve Michigan's maintenance plan, which is designed to ensure that the area will continue to maintain attainment of the 2010 SO 2 NAAQS.
IV. Statutory and Executive Order Reviews
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 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).
List of Subjects in 40 CFR Part 52
Environmental protection, Air pollution control, Incorporation by reference, Intergovernmental relations, Reporting and recordkeeping requirements, Sulfur oxides.
Dated: July 31, 2025.
Anne Vogel,
Regional Administrator, Region 5.
[FR Doc. 2025-15458 Filed 8-13-25; 8:45 am]
BILLING CODE 6560-50-P