Proposed approval of the Illinois Alton Township 2010 SO2 Redesignation and Maintenance Plan

Air Plan Approval; Illinois; Alton Township 2010 Sulfur Dioxide Redesignation and Maintenance Plan

Supplementary Information

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

I. Background and Redesignation Requirements

On June 22, 2010 (75 FR 35520), EPA revised the primary SO ₂ NAAQS, establishing a new health-based 1-hour standard of 75 parts per billion (ppb). EPA promulgated designations for this standard in four rounds. On September 18, 2015, Illinois submitted its recommendations to EPA to designate certain areas of the State as part of the Round 2 designations. Illinois recommended a portion of southern Alton Township in Madison County be designated as nonattainment for the 2010 SO ₂ NAAQS. EPA concurred with Illinois' analysis and published a final action designating the area as nonattainment for the 2010 SO ₂ NAAQS effective September 12, 2016 (81 FR 45039).

Illinois submitted an attainment plan for the Alton Township nonattainment area on December 3, 2018. Under section 192(a) of the CAA, these plans are required to demonstrate that areas will attain the NAAQS as expeditiously as practicable, but no later than five years from the effective date of designation. The plan included modeling from emissions associated with the Alton Steel Inc. (Alton Steel) facility in Alton, Illinois, and emissions from the Ameren Missouri-Sioux Energy Center (Ameren-Sioux) power plant in Missouri, located about 13 kilometers west-northwest of the nonattainment area. The modeled emissions showed the nonattainment status of the area was mainly attributed to these two SO ₂ sources. Unlike the Round 2 designations modeling, the Alton Township attainment demonstration did not include the Wood River Power Station among the sources modeled due to the retirement of the facility in June 2016 and its demolition in February 2021. On March 14, 2019, after Illinois' submission of the attainment plan, the Illinois Environmental Protection Agency issued Construction Permit #18020009 for the Alton Steel facility to operate a new ladle metallurgy facility (LMF) stack, removing the downfacing vents that were contributing to modeled nonattainment at the facility. EPA included additional dispersion modeling to supplement Illinois' attainment demonstration to demonstrate that the emission limits required by the Illinois SIP and submitted for EPA approval provide for modeled concentrations meeting the 2010 SO ₂ NAAQS. EPA approved Illinois' attainment plan revision on February 21, 2023 (88 FR 10464). Additionally, under section 179(c)(1) of the CAA, EPA is required to determine whether a nonattainment area attained a standard by the applicable attainment date based on the area's air quality as of the attainment date. EPA is to issue this determination within six months of the attainment date. Thus, EPA had a mandatory duty under CAA section 179(c) to determine by March 12, 2022, whether the Alton Township area attained by September 12, 2021. As an additional action, EPA is proposing to determine the Alton Township area did attain the 2010 SO ₂ NAAQS by the attainment date of September 12, 2021.

On October 2, 2023, Illinois submitted a redesignation request and maintenance plan for the Alton Township nonattainment area for the 2010 SO ₂ NAAQS. Additionally, on March 31, 2022, Missouri adopted into its SIP a Consent Agreement between the Missouri Department of Natural Resources' Air Pollution Control Program and Ameren-Sioux, APCP-2021-018. EPA approved the revision to incorporate the Ameren-Sioux Consent Agreement on November 16, 2022 (87 FR 68634), establishing an enforceable SO ₂ emissions limit for two coal-fired boilers at the facility. See Appendix B of the State's submittal included in the public docket of this action-Ameren-Sioux Consent Agreement. The submitted redesignation request and maintenance plan includes the Construction Permit issued to Alton Steel and the Consent Agreement issued to Ameren-Sioux approved into the Missouri SIP (87 FR 68634, November 16, 2022) with accepted SO ₂ emissions limits. While the Ameren-Sioux facility is not in the Alton Township nonattainment area, Illinois included this facility in their modeling due to its close proximity to the nonattainment area and high SO ₂ emissions, using information provided by the Missouri Department of Natural Resources. EPA's supplemental modeling with the updated limit of 7,342 pounds per hour (lbs/hr) averaged over a 24-hour block period for the Ameren-Sioux facility outlined in the Consent Agreement, provided for attainment of the 2010 SO ₂ NAAQS, and thus is included in Illinois' submittal.

Under section 107(d)(3)(E) of the CAA, EPA may not promulgate a redesignation of a nonattainment area (or portion thereof) unless:

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 Illinois' Redesignation Request and Maintenance Plan

On October 2, 2023, Illinois submitted a redesignation request for the Alton Township 2010 SO ₂ nonattainment area to attainment and a SIP revision containing a maintenance plan for the area.

EPA's evaluation of Illinois' redesignation request and maintenance plan was based on consideration of the five redesignation criteria provided under CAA section 107(d)(3)(E).

Criteria (1)-The Alton Township SO

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. An area is attaining the 2010 SO ₂ NAAQS at an ambient air quality monitoring site, in accordance with 40 CFR 50.17 and appendix T of part 50, when the three-year average of the annual (99th percentile) of the daily maximum 1-hour average concentrations is less than or equal to 75 ppb. 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, where there are no monitors, 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. ⁽¹⁾ The April 2014 SO ₂ Guidance further states that dispersion modeling should be conducted to estimate SO ₂ concentrations throughout the nonattainment area using actual emissions and meteorological information for the most recent 3 calendar years. EPA considered Illinois' modeling analyses submitted in the State's attainment plan which incorporated reductions in allowable emissions without the LMF stack changes to Alton Steel, which showed Alton Steel was the principal contributor to the highest modeled violations. Subsequently, EPA considered the modeling analyses with changes to the LMF exhaust configuration as described in Illinois' Construction Permit issued to Alton Steel. This analysis determined that after changes to the LMF exhaust stack in Alton Steel, the analysis still modeled violations of the 2010 SO ₂ NAAQS that were primarily due to the Ameren-Sioux facility. New SO ₂ emission limits were established under the Ameren-Sioux Consent Agreement (87 FR 68634, November 16, 2022), and EPA conducted supplementary modeling that incorporated both of these new limits and the changes to the LMF exhaust stack at Alton Steel. The supplementary modeling showed design values that are below the 2010 SO ₂ NAAQS for the Alton Township area.

The April 2014 SO ₂ Guidance provides an extensive discussion of EPA's view that appropriately set comparably stringent limits based on averaging times as long as 30 days can be found to provide for attainment of the 2010 SO ₂ NAAQS. The April 2014 SO ₂ Guidance also offers specific recommendations for determining an appropriate longer-term average limit. Illinois' plan applies 1-hour average emission limits to Alton Steel. However, Illinois' attainment plan also considers the impact of an additional facility, Ameren-Sioux, that is subject to a 24-hour block average limit. In response, EPA provided additional discussion of its rationale for approving the use of longer-term average limits in plans designed to provide for attainment. More detail on EPA's analysis of the attainment plan for the Alton Township area can be found in the attainment plan approval (88 FR 10464, February 21, 2023).

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. 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. Illinois' redesignation request for the Alton Township nonattainment area relied upon the demonstration of attainment based on air dispersion modeling, which Illinois submitted to EPA as part of its December 2018 attainment SIP submittal. For a short-term ( i.e., 1-hour) standard, 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 AERMOD 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. To support the SIP for bringing the Alton area into attainment of the 2010 SO ₂ NAAQS, EPA assisted Illinois by conducting a modeling demonstration of the Alton area with updated emissions data relied upon in the model and by correcting the source characterization. Because Illinois' submittal predated the updated SO ₂ emissions limit at the Ameren-Sioux facility necessary to model attainment in the area, EPA updated the emissions data at Ameren-Sioux in the supplemental model and corrected any other deficiencies in the emissions data. Additional updates and modifications in EPA's modeling analysis included: updated AERMOD version from version 18081 to 21112 (the most recent available version at the time), updated stack parameters to current operating conditions, and adjusted emission rates for the Ameren-Sioux facility to account for longer-term average limits. EPA used Illinois' receptor grid, meteorological surface and upper air stations, model settings, and some source parameters to develop the modeling demonstration. See Alton SO ₂ Nonattainment Plan TSD, 87 FR 80509 (December 30, 2022). EPA used AERMOD version 21112, the most recent version of the AERMOD Modeling System available at the time, for the modeling analysis. In the time since the modeling was conducted by Illinois and later supplemented by EPA using AERMOD version 21112, EPA has released two AERMOD version updates. AERMOD 22112 was released in 2022 to replace the regulatory version 21112 and was a routine release that does not include any scientific updates to the regulatory formulation of AERMOD as described in appendix W. ⁽²⁾ In 2023, AERMOD 23132 replaced the regulatory version 22112 which included small bug fixes and enhancements. ⁽³⁾ Currently, AERMOD 23132 is the most recent available version. However, EPA does not require Illinois to use the current AERMOD version as Illinois used the AERMOD version that was most recent at the time it was developing the SIP and determining SO ₂ emission limits.

Illinois' modeled demonstration of attainment for the Alton Township area was discussed in detail in EPA's proposed approval of the Alton Township SO ₂ attainment plan. See 87 FR 80509, (December 30, 2022). Illinois' original modeling submitted included Ameren-Sioux maximum allowable emissions and the reconfigured LMF stack emissions for Alton Steel, which yielded a maximum predicted 99th percentile 1-hour average concentration of 298.5 micrograms per cubic meter (µg/m ³ ). EPA conducted a supplemental modeling run to evaluate the reconfigured stack requirements at Alton Steel in combination with Ameren-Sioux's updated 7,342 lbs SO ₂ /hr 24-hour block limit found in the Missouri SIP (87 FR 68634, November 16, 2022). EPA's modeling demonstrated that the Alton area showed a design value of 74.9 ppb (196.2 µg/m ³ ) with the revised SO ₂ emission limits that will provide for attainment based on the new requirements for Alton Steel and Ameren-Sioux, which are both permanently and federally enforceable. As mentioned above, the changes at the Alton Steel facility were construction changes to the LMF stack parameters to be completed by July 31, 2019, modifying the dispersion of emissions, and they did not alter existing operating emission limit conditions that the reconfigured LMF stack was already subject to and approved for in the approved attainment plan. Stack test results of the LMF at the Alton Steel facility prior to construction of the modified LMF stack show compliance with the permitted values, as do updated stack test results of the LMF stack upon construction completion as shown in Table 1. EPA concluded that Illinois' modeling is a suitable demonstration that its requirements in the Construction Permit for Alton Steel and all other Illinois sources in the nonattainment area were properly addressed in the attainment plan. EPA's supplemental modeling demonstrated that the updated 24-hour block limit for Ameren-Sioux of 7,342 lbs/hr in combination with updated emissions at Alton Steel provide for attainment and is the primary basis to conclude that the area is attaining the 2010 SO ₂ NAAQS.

EPA has also considered additional information which supports its proposed determination that the area has attained the NAAQS, including annual SO ₂ emissions from the Alton Steel facility shown in Table 2. The annual tons per year emissions at the Alton facility show a decreasing trend overall. Annual SO ₂ emissions from the Ameren-Sioux facility found in Table 2 also show a decreasing trend overall. EPA included data from the Ameren-Sioux facility showing that hourly emissions with a 24-hour average, are at or below the newly established limit of 7,342 lbs/hr, and have been since 2017. These data are included in the docket of this action. ⁽⁴⁾ In this action, EPA is proposing to find that the Alton Township area has attained and will continue to attain the 2010 SO ₂ NAAQS with respect to the redesignation criteria under CAA section 107(d)(3)(E)(i).

Additionally, with respect to nonattainment area requirements under CAA section 179(c), EPA is proposing to determine the Alton Township area attained the 2010 SO ₂ NAAQS by the area's attainment date of September 12, 2021. This is based on the information provided above, including the stack construction date in 2019 and emissions data shown to be below emission limits during and after the attainment period. Because this a separate CAA requirement, EPA may choose to finalize this determination separately, as this is not a redesignation criterion, but rather, just relying on the same set of facts.

Criteria (2) and Criteria (5)-Illinois 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)

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 fully approved the applicable implementation plan (CAA section 107(d)(3)(E)(ii)). EPA's long-standing interpretation of the CAA is that not every requirement under CAA section 110 and part D are applicable for purposes of CAA section 107(d)(3)(E)(ii) and (v). The Agency's interpretation of the statute limiting evaluation of section 110 and part D requirements to only those that are applicable for purposes of redesignation was first articulated shortly after the passage of the 1990 CAA Amendments in Agency guidance documents, and has been consistently applied in notice-and-comment redesignation actions over the last three decades.

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 has in any case approved most elements of Illinois' section 110 infrastructure SIP. See infrastructure SIP approval, 79 FR 62042 (October 16, 2014); revisions to Prevention of Significant Deterioration (PSD) and Nonattainment New Source Review (NSR) programs, 87 FR 20715 (April 8, 2022); State board requirements, 84 FR 49671 (September 23, 2019); and emission limits of pollutants relevant to the 2010 SO ₂ NAAQS, 80 FR 29535 (May 22, 2015).

EPA also proposes to determine that Illinois 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, Illinois has in any case submitted a complete attainment plan and EPA has fully approved that plan, including emissions inventories, Reasonably Available Control Technology/Reasonably Available Control Measures, Reasonable Further Progress (RFP), and contingency measures.

On February 21, 2023 (88 FR 10464), EPA approved Illinois' attainment SIP for the Alton Township area including the operation of a new LMF stack at Alton Steel and revised emission limits for Ameren-Sioux, which are the main SO ₂ sources affecting the Alton Township area. In that action, EPA found that Illinois had satisfied requirements for providing for attainment of the 2010 SO ₂ NAAQS in the Alton Township area. The adopted SO ₂ SIP regulations for Alton Steel and Ameren-Sioux are contained in the Construction Permit for Alton Steel and the Ameren-Sioux Consent Agreement, respectively. Illinois has shown that it maintains an active enforcement program to ensure ongoing compliance with these requirements. Illinois' programs for NSR and PSD will address emissions from potential new sources in the area (57 FR 59928, December 17, 1992; 60 FR 49780, September 27, 1995; 68 FR 25504, May 13, 2003). Missouri also maintains an active enforcement program under the Revised Statutes of Missouri section 643.080 to ensure ongoing compliance.

In its attainment plan, Illinois chose 2017 for its base year emissions inventory as comprehensive data were available and updated that year, satisfying the requirements of section 172(c)(3) of the CAA. Illinois additionally examined whether any large sources beyond 10 kilometers of the nonattainment area might also have significant air quality impacts in the area, resulting in the addition of Ameren-Sioux to the inventory. Illinois' SO ₂ emissions data identified Alton Steel and Ameren-Sioux as the main contributors to the nonattainment status for the Alton Township area.

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 requirements 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, whether or not the area has met that requirement is not a prerequisite to getting redesignated. 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 apply to the Alton Township 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 Alton Township SO ₂ maintenance area. Therefore, transportation plans, transportation improvement programs and projects are presumed to conform to applicable implementation plans for SO ₂ . With respect to general conformity, Federal agencies are still required to address general conformity in the Alton Township SO ₂ maintenance area.

Based on the above findings, EPA is proposing to find that Illinois has met the applicable requirements of section 110 and part D of title I of the CAA for purposes of the redesignation of the Alton Township nonattainment area, and EPA has fully approved the applicable implementation plan for such area.

Criteria (3)-The Air Quality Improvement in Alton Township SO

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. Illinois' attainment plan incorporates the Alton Steel Construction Permit (88 FR 10464, February 21, 2023) which requires the operation of a new LMF stack and does not change any existing requirements that apply to the furnace in the LMF, including the permitted emission unit limits which the Alton Steel facility was already subject to. The permit approved the construction of a new LMF stack to be finalized no later than July 31, 2019. The facility continues to meet existing SO ₂ emission limits that do not exceed 0.10 pound per ton of steel produced, 11.20 lbs/hr, and 37.50 tons per year as shown in Table 1 above. EPA has included these emission limits and source configuration requirements in the approval of Illinois' SIP on February 21, 2023 (88 FR 10464), which will also render them federally enforceable. For Ameren-Sioux, a new limit was approved into the Missouri SIP establishing a more stringent limit of 7,342 lbs/hr averaged over a 24-hour block period. EPA approved Ameren-Sioux's new limit in a different rulemaking on November 16, 2022 (87 FR 68634). The updated EPA modeling in Illinois' attainment plan approval (88 FR 10464, February 21, 2023) included the change in emissions at both Alton Steel and Ameren-Sioux and showed attainment of the 2010 SO ₂ standard throughout the Alton Township area. EPA is proposing to find, consistent with our approval of the State's attainment plan, that the modeling results demonstrate attainment and continued maintenance of the 2010 SO ₂ NAAQS and that the air quality improvement in the Alton Township nonattainment area is due to permanent and enforceable reductions in emissions.

Criteria (4)-The Alton Township SO

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. ⁽⁵⁾ In its redesignation request, Illinois provided an emissions inventory for SO ₂ in the nonattainment area for 2022, one of the years making up the attaining design value. Total actual emissions in the Alton Township area for the 2022 attainment year were 2,691.88 tons. This level of emissions, in combination with modifications at the Alton Steel facility, are sufficient to maintain the NAAQS. In its attainment plan, Illinois reported that total actual SO ₂ emissions for the nonattainment area from 2017, a year during which the area was not attaining the NAAQS, were 4,280.97 tons. Construction of a new LMF stack at the Alton Steel facility to replace four downward facing vents, as well as the Consent Order limit of 7,342 lbs/hr averaged over a 24-hour block period accepted by the Ameren-Sioux power plant, led to decreases in actual SO ₂ emissions by over 1,580 tons in the Alton Township area between 2017 and 2022. Previously, EPA's modeling for the Alton Township area based on maximum allowable levels at Alton Steel and updated limits on Ameren-Sioux already incorporated into the Illinois SIP and Missouri SIP respectively, resulted in a design value of 74.9 ppb, below the SO ₂ NAAQS. See Alton SO ₂ Nonattainment Plan TSD, 87 FR 80509 (December 30, 2022).

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 plan must demonstrate continued attainment of the applicable NAAQS for at least ten years after the nonattainment area is redesignated to attainment. Eight years after the redesignation, the State must submit a revised maintenance plan demonstrating that attainment will continue to be maintained for the ten years following the initial ten-year period. To address the possibility of future NAAQS violations, the maintenance plan must contain contingency measures, which EPA deems necessary to ensure prompt correction of any future 2010 SO ₂ NAAQS violations.

Specifically, the maintenance plan should address five requirements: the attainment emissions inventory, maintenance demonstration, monitoring, verification of continued attainment, and a contingency plan. EPA is proposing to determine that Illinois' redesignation request of October 2, 2023, contains its maintenance plan and all the necessary components, which Illinois 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. ⁽⁶⁾ In its redesignation request, Illinois provided an emissions inventory for SO ₂ in the nonattainment area for 2022, one of the years making up the attaining design value. Total actual emissions in the Alton Township area for the 2022 attainment year were 2,691.88 tons. This level of emissions, in combination with modifications at the Alton Steel facility, are sufficient to maintain the NAAQS. In its attainment plan, Illinois reported that total actual SO ₂ emissions for the nonattainment area from 2017, a year during which the area was not attaining the NAAQS, were 4,280.97 tons. Construction of a new LMF stack at the Alton Steel facility to replace four downward facing vents, as well as the Consent Order limit of 7,342 lbs/hr averaged over a 24-hour block period accepted by the Ameren-Sioux power plant, led to decreases in actual SO ₂ emissions by over 1,580 tons in the Alton Township area between 2017 and 2022. Previously, EPA's modeling for the Alton Township area based on maximum allowable levels at Alton Steel and updated limits on Ameren-Sioux already incorporated into the Illinois SIP and Missouri SIP respectively, resulted in a design value of 74.9 ppb, below the SO ₂ NAAQS. See Alton SO ₂ Nonattainment Plan TSD, 87 FR 80509 (December 30, 2022).

EPA's "Procedures for Processing Requests to Redesignate Areas to Attainment" (Calcagni Memo)  ⁽⁷⁾ 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 rate 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. Illinois' maintenance demonstration consists of the attainment SIP air quality modeling analysis showing that the emissions reductions now in effect in the Alton Township 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 Illinois' enforceable emission requirements will ensure that the Alton Township area SO ₂ emission limits are met continuously.

By providing actual emissions data from Alton Steel and Ameren-Sioux, the main sources of SO ₂ , from a time period when the area was not meeting the NAAQS and from a time period when the area was attaining the NAAQS, Illinois demonstrates a 52 percent and 38 percent reduction in actual annual SO ₂ emissions at Alton Steel and Ameren-Sioux, respectively. Illinois' submittal shows that actual annual Alton Steel SO ₂ emissions in 2022 were 48 percent of the actual emissions in 2017 and shows actual annual 2022 Ameren-Sioux SO ₂ emissions were 62 percent of the actual emissions in 2017. EPA's modeling described in the Criteria 4 section above, shows by modeling that modified LMF exhaust configuration at Alton Steel in addition to the newly imposed consent agreement SO ₂ limits for Ameren-Sioux, which are federally enforceable, result in the area maintaining attainment of the SO ₂ NAAQS.

For continuing verification, Illinois has committed to track the emissions and compliance status of the major facilities in the Alton Township area so that future emissions will not exceed the allowable emissions-based attainment inventory. All major sources in Illinois are required to submit annual emissions data, which the State uses to update its emission inventories as required by the CAA. The Alton Steel facility must submit annual compliance certifications to ensure the facility is meeting its SIP limits and the facility must submit a semi-annual Monitoring Report to the Illinois EPA, Air Compliance Section, summarizing required monitoring done and identifying all instances of deviation from the permit.

Illinois has also committed to continue operating an "appropriate air quality monitoring network to verify maintenance of the attainment status" of the Alton Township area. However, the closest monitor to the Alton area is the East St. Louis monitor (AQS ID: 17-163-0010, coordinates: 38.61203-90.16048) approximately 30 kilometers south of the Alton Steel facility. As such, Illinois commits to providing EPA with annual emissions report of the newly constructed Alton Steel LMF stack as part of Illinois' annual network plan submittal to provide ongoing verification of attainment. The Ameren-Sioux facility is subject to annual emissions data reporting under EPA's Federal emissions trading programs and, therefore, data are readily accessible via EPA's Clean Air Markets Program Division's database. ⁽⁸⁾

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 l75A of the CAA does not explicitly require that contingency measures must take effect without further action by the air agency in order for the maintenance plan to be approved. However, the maintenance plan's contingency plan would become an enforceable part of the SIP and should ensure that contingency measures are adopted and implemented as expeditiously as practicable once they are triggered. ⁽⁹⁾ 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, ⁽¹⁰⁾ which can quickly identify and address sources that might be causing exceedances of the NAAQS. Illinois' enforcement program is active and capable of prompt action to remedy compliance issues. Illinois commits to ongoing compliance and enforcement of the control measures contained in the federally enforceable Construction Permit issued to Alton Steel approved and incorporated into the Illinois' attainment SIP approval (88 FR 10464, February 21, 2023). Illinois also has the necessary resources in the event of violations to enforce its permit provisions and rules. Illinois has the authority to expeditiously adopt, implement, and enforce any subsequent emission control measures deemed necessary to correct any future SO ₂ violations. Illinois commits to adopting and implementing such corrective actions as necessary to address violations of the 2010 SO ₂ NAAQS. Another contingency measure option is the implementation of a PSD program for new or modified existing sources of SO ₂ , which includes requirements for Best Available Control Technology, in the Alton nonattainment area once redesignated to attainment. The Ameren-Sioux Consent Agreement has been adopted into the Missouri SIP and includes monitoring, recordkeeping, and reporting requirements that will be used to confirm ongoing compliance incorporated into the Missouri SIP (87 FR 68634, November 16, 2022). Based on the foregoing, EPA proposes to find that Illinois has addressed the contingency measure requirement.

EPA is proposing to find that Illinois' maintenance plan adequately addresses the five basic components of a maintenance plan necessary to maintain the SO ₂ NAAQS in the Alton Township nonattainment area. Therefore, EPA proposes to find that the redesignation and maintenance plan SIP revision submitted by Illinois for the 2010 SO ₂ Alton Township 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 Alton Township area from nonattainment to attainment for the 2010 SO ₂ NAAQS in accordance with Illinois' October 2, 2023, 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 Illinois' maintenance plan, which is designed to ensure that the area will continue to maintain attainment of the 2010 SO ₂ NAAQS. Additionally, EPA is proposing to determine the Alton Township area attained the 2010 SO ₂ NAAQS by the September 12, 2021, attainment date addressing EPA's obligation under CAA section 179(c).

IV. Environmental Justice Concerns

To identify environmental burdens and potentially susceptible populations in the Alton Township area, EPA performed a screening-level analysis using EPA's environmental justice (EJ) screening and mapping tool (EJScreen). ⁽¹¹⁾ The results of EPA's screening analysis are being provided for informational and transparency purposes, and EPA did not rely on these findings in its action on Illinois' submissions. EPA utilized the EJScreen tool to review environmental and demographic data, which provides an assessment of individual demographic groups of the populations living within the Alton Township area in Madison County. The tool output report is contained in the docket for this action. Due to the localized nature of SO ₂ , EPA considered a 1.5-mile radius of the Alton Steel facility in its assessment. EPA's screening-level analysis indicates that communities affected by this action score above the national percent average for the EJScreen "Demographic Index", which is the average of an area's percent minority and percent low-income populations, i.e., the two demographic indicators explicitly named in Executive Order 12898. Additionally, the results indicate that the area scores below the 80th percentile (in comparison to the nation as a whole) for 8 out of the 13 EJ indexes established by EPA, which include a combination of environmental and demographic information. The Alton Township area scored at or above the 80th percentile for the ozone, toxic releases to the air, lead paint, RMP facility proximity, and wastewater discharge indexes. The analysis was done for the purpose of providing additional context and information about this rulemaking to the public, and not as a basis of the action. Due to the nature of the action being taken here, this action is expected to have a neutral to positive impact on the air quality of the affected area.

V. Statutory and Executive Order Reviews

Under the CAA, redesignation of an area to attainment and the accompanying approval of a maintenance plan are actions that affect the status of a geographical area and do not impose any additional regulatory requirements on sources beyond those imposed by State law. A redesignation to attainment does not in and of itself create any new requirements, but rather results in the applicability of requirements contained in the CAA for areas that have been redesignated to attainment. Moreover, 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 these reasons, this 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), and 14094 (88 FR 21879, April 11, 2023);

• 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).

Executive Order 12898 (Federal Actions to Address Environmental Justice in Minority Populations and Low-Income Populations, 59 FR 7629, February 16, 1994) directs Federal agencies to identify and address "disproportionately high and adverse human health or environmental effects" of their actions on communities with EJ concerns to the greatest extent practicable and permitted by law. EPA defines EJ as "the fair treatment and meaningful involvement of all people regardless of race, color, national origin, or income with respect to the development, implementation, and enforcement of environmental laws, regulations, and policies." EPA further defines the term fair treatment to mean that "no group of people should bear a disproportionate burden of environmental harms and risks, including those resulting from the negative environmental consequences of industrial, governmental, and commercial operations or programs and policies."

Illinois did not include an evaluation of EJ considerations as part of its SIP submittal; the CAA and applicable implementing regulations neither prohibit nor require such an evaluation. EPA performed an EJ analysis, as is described above in the section titled, "Environmental Justice Considerations." The analysis was done for the purpose of providing additional context and information about this rulemaking to the public, and not as a basis of the action. Due to the nature of the action being taken here, this action is expected to have a neutral to positive impact on the air quality of the affected area. In addition, there is no information in the record upon which this decision is based inconsistent with the stated goal of E.O. 12898 of achieving EJ for communities with EJ concerns.

⁽¹⁾  EPA's "Guidance for 1-Hour Sulfur Dioxide (SO ₂ ) Nonattainment Area State Implementation Plans (SIP) Submissions" can be found at https://www.epa.gov/so2-pollution/guidance-1-hour-sulfur-dioxide-so2-nonattainment-area-state-implementation-plans-sip.

⁽²⁾ See AERMOD Modeling System Transmittal Memorandum (v22112) https://gaftp.epa.gov/Air/aqmg/SCRAM/models/preferred/aermod/AERMOD_22112_Transmittal_Memo.pdf.

⁽³⁾ See AERMOD Modeling System Transmittal Memorandum (v23132) https://gaftp.epa.gov/Air/aqmg/SCRAM/models/preferred/aermod/AERMOD_23132_Transmittal_Memo.pdf.

⁽⁴⁾ See Ameren Sioux (MO) Facility Emissions Data 2016-2023.xlsx in the docket.

⁽⁵⁾ See April 2014 SO ₂ Guidance, page 66.

⁽⁶⁾ See April 2014 SO ₂ Guidance, page 66.

⁽⁷⁾  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.

⁽⁸⁾ See Ameren-Sioux emissions data at https://campd.epa.gov/data/custom-data-download.

⁽⁹⁾ See April 2014 SO ₂ Guidance, page 74.

⁽¹⁰⁾ See April 2014 SO ₂ Guidance, page 41-42.

⁽¹¹⁾ See https://www.epa.gov/ejscreen.