SUPPLEMENTARY INFORMATION:

I. Background

A. Nonattainment Designation

On June 22, 2010, the EPA revised the primary SO₂ NAAQS, establishing a new 1-hour primary standard of 75 parts per billion (ppb).^[1] Under the EPA's regulations at title 40 of the Code of Federal Regulations (CFR) part 50, the 2010 1-hour SO₂ NAAQS is met at a monitoring site when the design value ^[2] is less than or equal to 75 ppb (based on the rounding convention in 40 CFR part 50, appendix T).^[3] Ambient air quality monitoring data for the 3-year period must meet a data completeness requirement. A year meets data completeness requirements when all four quarters are complete, and a quarter is complete when at least 75 percent of the sampling days in the quarter have complete data. A sampling day has complete data if 75 percent of the hourly concentration values, including state-flagged data affected by exceptional events which have been approved for exclusion by the Administrator, are reported.^[4]

Upon promulgation of a new or revised NAAQS, the CAA requires the EPA to designate as nonattainment any area that does not meet (or that contributes to ambient air quality in a nearby area that does not meet) the NAAQS.^[5] On August 5, 2013, the EPA designated a portion of Warren County, Pennsylvania (hereafter the “Warren County NAA”), as nonattainment for the 2010 1-hour primary SO₂ NAAQS, effective October 4, 2013.^[6] The designation was based on violating air quality monitoring data for calendar years 2009-2011. The Warren County NAA consists of Conewango Township, Glade Township, Pleasant Township, and the City of Warren.^[7] This proposed action established an attainment date five years after the effective date for the areas designated as nonattainment for the 2010 SO₂ NAAQS ( i.e., by October 4, 2018). The Commonwealth was also required to submit an attainment plan SIP revision for the Warren County NAA to the EPA that met the requirements of CAA sections 110, 172(c) and 191-192 within 18 months of the October 4, 2013, effective date of designation ( i.e., by April 4, 2015).

B. Relevant Historical SIP Actions

The EPA did not receive an attainment plan SIP revision for the Warren County NAA by the deadline of April 4, 2015, and subsequently on March 18, 2016, the EPA published a finding of failure to submit indicating that Pennsylvania did not submit the required SO₂ attainment plan.^[8] This finding initiated a clock under CAA section 179(a) for the potential imposition of new source review sanctions 18 months after the effective date of the finding and the potential imposition of highway funding sanctions 6 months following that, in accordance with CAA section 179(b) and 40 CFR 52.31. Additionally, under CAA section 110(c), the finding triggered a requirement for the EPA to promulgate a Federal implementation plan (FIP) within two years of the effective date of the finding unless, by that time, Pennsylvania made the necessary complete submittal, and the EPA approved the submittal.

Ultimately, Pennsylvania did submit an attainment plan SIP revision for the Warren County NAA on September 29, 2017. The EPA issued a letter to Pennsylvania on October 5, 2017, finding the attainment plan submittal complete and noting the stopping of the sanctions' deadline. As a result, these CAA section 179(b) sanctions were not imposed.^[9] The EPA proposed approving the attainment plan SIP revision ( printed page 48035) submittal on March 22, 2018,^[10] and issued a final approval on October 12, 2018.^[11] This approval ended the requirement for the EPA to promulgate a FIP under CAA section 110(c).

Relevant to this proposed action, on September 19, 2025, PADEP submitted a SIP revision to the EPA for the inclusion of a maintenance plan for the 2010 1-hour primary SO₂ NAAQS and requested a concurrent redesignation of the Warren County NAA to attainment for the 2010 1-hour primary SO₂ NAAQS.^[12] The September 19, 2025 SIP revision also requested that the EPA correct source-specific requirements included in the Pennsylvania SIP. The October 12, 2018 final approval of Pennsylvania's attainment plan SIP revision incorporated by reference the entirety of a consent order and agreement between PADEP and United Refining Company,^[13] rather than the intended redacted version and PADEP has provided updated language with the September 19, 2025 revision for inclusion in the SIP to replace the prior error.

C. Redesignation to Attainment Criteria

After a state has submitted a redesignation request for a nonattainment area, the EPA must assess if the statutory criteria identified in CAA section 107(d)(3)(E) have been met to redesignate the area to attainment. These conditions include: (1) the EPA has determined that the applicable NAAQS has been attained; (2) the applicable SIP has been fully approved by the EPA under CAA section 110(k); (3) the EPA has determined that the improvement in the area's air quality is due to permanent and enforceable reductions in emissions; (4) the area has a fully approved maintenance plan, including a contingency plan, under CAA section 175A; and (5) the State has met all applicable requirements for the area under CAA section 110 and part D. The EPA has provided direction for how it would consider if these conditions have been met in the April 23, 2014 memorandum “Guidance for 1-Hour SO₂ Nonattainment Area SIP Submissions” (2014 SO₂ Guidance).^[14]

D. Maintenance Plan Approval Criteria

Section 175A of the CAA and additional EPA guidance, including the September 4, 1992 memorandum “Procedures for Processing Requests to Redesignate Areas to Attainment” (Calcagni Memo),^[15] identify the required elements for an approvable maintenance plan for areas seeking redesignation from nonattainment to attainment. Under CAA section 175A, the plan must demonstrate continued attainment of the applicable NAAQS for at least 10 years after the EPA approves a redesignation request to attainment. Eight years after the redesignation, the State must submit a revised maintenance plan demonstrating that attainment will continue to be maintained for an additional 10 years following the initial 10-year period. To address the possibility of future NAAQS violations, the maintenance plan must contain contingency measures, as the EPA deems necessary, to assure prompt correction of any future NAAQS violations, in this case the 2010 1-hour SO₂ NAAQS. The Calcagni Memo provides further guidance on the content of a maintenance plan, explaining that a maintenance plan should address five requirements: (1) an attainment emissions inventory that identifies the level of emissions in the area which is sufficient to attain the NAAQS; (2) a maintenance demonstration that shows future emissions of a pollutant will not exceed the level of the attainment inventory; (3) the continued operation of a monitoring network that conforms to 40 CFR part 58; (4) a means for verifying the continued attainment of the NAAQS; and (5) a contingency plan to correct any violation of the NAAQS in the area following redesignation of the area.

II. Summary of Redesignation Request and Maintenance Plan and EPA Analysis

The EPA's evaluation of Pennsylvania's redesignation request and maintenance plan for the Warren County NAA is based on consideration of the five redesignation criteria provided under CAA section 107(d)(3)(E) and relevant guidance, including the aforementioned 2014 SO₂ Guidance and Calcagni Memo. The summary and analysis of Pennsylvania's redesignation request and maintenance plan are discussed immediately below, while the summary and analysis of the source-specific requirements revision is discussed in section III in this document.

A. Criterion (1)—The Warren County SO2 Nonattainment Area Has Attained the 2010 1-Hour SO₂ NAAQS

Section 107(d)(3)(E)(i) of the CAA requires that the EPA determine that a nonattainment area has attained the applicable NAAQS in order to redesignate the area to attainment. In assessing if the area has attained the NAAQS, the 2014 SO₂ Guidance stipulates that the EPA can interdependently consider two components to support an attainment determination: air quality monitoring data and air quality modeling data.^[16]

The Warren County NAA contains two operational SO₂ monitor sites: the Warren Overlook site (Air Quality System (AQS) Site ID 42-123-0004) and the Warren East site (AQS Site ID 42-123-0005). The Warren Overlook site is located in Conewango Township, while the Warren East site is located in the City of Warren. The Warren Overlook monitor has been in operation since 1996 and has been in attainment of the 2010 1-hour primary SO₂ NAAQS since 2017, with the most recent design value for the 2022-2024 period measuring 45 parts per billion (ppb). The Warren East monitor does not meet siting criteria established in 40 CFR part 58 and as such its data is not appropriate for assessing NAAQS compliance.^[17] Since it began monitoring in 2012, the Warren East monitor has continuously recorded design values below the 2010 1-hour primary SO₂ NAAQS, with the most recent design value for the 2022-2024 period measuring 32 ppb. Design values for both the Warren Overlock and Warren East monitors are reported in table 1 in this document.

( printed page 48036)

Pennsylvania's 2017 attainment plan contained an attainment demonstration which utilized allowable SO₂ emission limits from stationary sources within the Warren County NAA to inform several modeling analyses for SO₂ emissions.^[18] These modeling analyses were based on emissions limits for large, stationary sources of SO₂, which, when enacted, would ensure that the Warren County NAA would attain the 2010 1-hour primary SO₂ NAAQS. The 2014 SO₂ Guidance states that the EPA may make a determination of attainment based on this attainment plan modeling, eliminating the need for separate actual emissions-based modeling to support a redesignation request—provided that the source characteristics are still reasonably represented and that the control strategy in the SIP has been fully implemented.^[19]

Since Pennsylvania's 2017 submittal of this attainment plan modeling—which EPA approved on October 12, 2018 ^[20] —source characteristics within the Warren County NAA remain reasonably represented. United Refining Company (URC) is still the largest SO₂ emissions stationary source within the nonattainment area and remains relatively unchanged, with the exception of a boiler replacement, a stack height reduction, and the addition of a loading rack. The former boiler at URC was modeled with an SO₂ emissions rate equivalent to 7.21 pounds per hour (lbs/hr), while the replacement boiler is limited to 1.7 lbs/hr of SO₂ emissions. The stack that the new boiler exhausts through was shortened from the height of the prior boiler's exhaust stack, but the new boiler simultaneously was permitted at a lower emissions rate. The newly constructed loading rack is expected to produce minimal SO₂ emissions, with a reported contribution of 0.0001 lbs/hr. The sources characteristics are still reasonably represented and overall, these operational changes lead to a modeled overestimation of actual emissions of SO₂ sources within the Warren NAA.

The 2014 SO₂ Guidance further states that a demonstration that the control strategy in the SIP has been fully implemented will also be pertinent for making the determination of attainment.^[21] Pennsylvania has submitted information detailed in its redesignation request and maintenance plan to confirm that the control strategy outlined in the SIP has been fully implemented. Specific measures identified in the control strategy include a fuel switch to low sulfur fuel in 11 combustion units and heaters at URC, as well as the increased usage of an additive for preventing SO₂ formation in the fluid catalytic cracking unit at URC. These implemented permanent and federally enforceable control measures have aided in reducing the actual total emissions from large, stationary SO₂ sources in the Warren County NAA to 328 tons per year (as of 2018),^[22] which is well below the revised total emissions limits proposed for Warren County NAA facilities in the 2017 attainment demonstration modeling (1,274 tons per year),^[23] thus contributing to bringing the Warren County NAA into attainment.

As the source characteristics within the Warren County NAA are still reasonably represented and the control strategy in the SIP has been fully implemented, the EPA may make a determination of attainment based on this attainment plan modeling. In this proposed rulemaking, the EPA proposes to find that the air quality modeling data demonstrate that the Warren County NAA has attained the 2010 1-hour primary SO₂ NAAQS, with the air quality monitoring data further supporting this conclusion.

B. Criterion (2)—Pennsylvania Has a Fully Approved SIP Under Section 110(k)

Section 107(d)(3)(E)(ii) of the CAA requires that the EPA fully approve the applicable implementation plan for the area under CAA section 110(k) in order to redesignate that area to attainment. An area cannot be redesignated to attainment if a required element of the SIP is the subject of a disapproval; a finding of failure to submit, or failure to implement the SIP; or a partial, conditional, or limited approval.^[24] The 2017 attainment plan SIP was initially proposed for EPA approval on March 22, 2018 ^[25] and received final EPA approval on October 12, 2018.^[26] The approved elements from the 2017 attainment plan include a 2011 base year emissions inventory, a control strategy and air quality modeling demonstration, a reasonable available control measures/reasonably available control technology (RACM/RACT) analysis, a reasonable further progress (RFP) analysis, and contingency measures. The EPA also concluded in the October 12, 2018 final approval that Pennsylvania's existing SIP-approved nonattainment new source review (NNSR) program meets the applicable requirements for SO₂ .^[27] As such, the EPA has fully approved the applicable Pennsylvania SIP for the Warren County NAA under section 110(k) of the CAA for all requirements applicable for purposes of redesignation.

C. Criterion (3)—The Air Quality Improvement in the Warren County SO₂ Nonattainment Area Is Due to Permanent and Enforceable Reductions in Emissions

For redesignating a nonattainment area to attainment, CAA section 107(d)(3)(E)(iii) requires the EPA to determine that the air quality improvement in the area is due to permanent and enforceable reductions in emissions resulting from implementation of the SIP, applicable federal air pollution control regulations, ( printed page 48037) and other permanent and enforceable reductions. The EPA proposes to find that Pennsylvania has demonstrated that the requirements of CAA section 107(d)(3)(E)(iii) have been met.

Collectively, a fuel switch to low sulfur fuel in 11 combustion units and heaters at URC, as well as the increased usage of an additive for preventing SO₂ formation in the fluid catalytic cracking unit at URC resulted in an actual decrease of approximately 664 tons of SO₂ emitted per year from 2011 to 2018.^[28] This is approximately a 67% reduction from 2011 levels of 992 tons of SO₂ emitted per year.^[29] As this reduction is federally enforceable through permit-controlled emission limits,^[30] the EPA proposes to find the air quality improvement in the Warren County NAA to be due to permanent and enforceable reductions in emissions.

D. Criterion (4)—The Warren County SO₂ Nonattainment Area Has a Fully Approved Maintenance Plan Pursuant to Section 175A of the CAA

To redesignate a NAA to attainment, CAA section 107(d)(3)(E)(iv) requires the EPA to determine that the area has a fully approved maintenance plan pursuant to section 175A of the CAA. In conjunction with its request to redesignate the Warren County NAA to attainment for the 2010 1-hour primary SO₂ NAAQS, the Commonwealth submitted a SIP revision to provide for the maintenance of the 2010 1-hour primary SO₂ NAAQS for at least 10 years after the effective date of redesignation to attainment. The EPA is proposing to find that this maintenance plan meets the requirements for approval under section 175A of the CAA.

1. Maintenance Plan Requirements

Section 175A of the CAA sets forth the elements of a maintenance plan. Under CAA section 175A, the plan must demonstrate continued attainment of the applicable NAAQS for at least 10 years after the Administrator approves a redesignation request to attainment. Eight years after the redesignation, the State must submit a revised maintenance plan demonstrating that attainment will continue to be maintained for an additional 10 years following the initial 10-year period. To address the possibility of future NAAQS violations, the maintenance plan must contain contingency measures as the EPA deems necessary to assure prompt correction of any future NAAQS violations, here the 2010 1-hour primary SO₂ NAAQS. As noted above, the Calcagni Memo provides further guidance on the content of a maintenance plan, explaining that a maintenance plan should address five requirements: (1) the attainment emissions inventory; (2) maintenance demonstration; (3) monitoring; (4) verification of continued attainment; and (5) a contingency plan.^[31] As discussed in detail below, the EPA is proposing to determine that Pennsylvania's submitted maintenance plan meets the requirements in CAA section 175A and is thus proposing to approve it as a revision to the Warren County portion of the Pennsylvania SIP.

2. Attainment Emissions Inventory

In a maintenance plan, states are required to submit an emissions inventory to identify the level of emissions in the area which is sufficient to attain and maintain the relevant NAAQS, which is called the attainment inventory. This inventory is used as the basis for future, projected emission inventories that are used to show the area will remain in attainment. Pennsylvania submitted a 2018 SO₂ emissions inventory as the attainment inventory with its maintenance plan. This represented a year in which SO₂ emissions were at levels required to demonstrate attainment of the 2010 SO₂ NAAQS.

For the 2018 attainment year inventory, Pennsylvania directly used point source emissions reported to Pennsylvania for 2018, except for Warren General Hospital and Warren Airpark, which were projected from the 2017 National Emission Inventory (NEI).^[32] The point source emissions for the Warren County NAA were verified against the EPA's emissions inventory system (EIS) and the EPA found them to be acceptable. Projected emissions for area sources in 2018 were estimated from the 2017 NEI emission data and growth factors developed by the Mid-Atlantic Regional Air Management Association (MARAMA), Inc. These growth factors are developed based on forecasts from various databases and tools, including the Energy Information Administration's 2019 and 2020 Annual Energy Outlook, the 2016 NEI Collaborative data for the rail and the oil and gas Source Classification Codes, and other sources that are detailed in the submitted maintenance plan.^[33] Area source emissions were estimated based on the relative percentage of the Warren County population residing in the Warren County NAA and the resulting factor allocated the appropriate fraction of the County's total emissions to the Warren County NAA.

Nonroad and onroad mobile source emissions for 2017 were obtained from the EPA's Motor Vehicle Emissions Simulator (MOVES) model, specifically the MOVES2014b version. PADEP executed the MOVES2014b modeling runs for nonroad mobile sources and utilized a contractor to run the model for onroad mobile source emissions.

Projected inventories from the attainment inventory demonstrate that the area will continue to remain in attainment throughout the first maintenance period. Pennsylvania developed 2028 and 2036 emission projections for the interim and maintenance plan end year, respectively. Projected emissions for these years—as well as the base year inventory—are available in table 2 in this document. Projected emissions for point and area sources were estimated, as previously described for area sources, from the 2017 NEI and growth factors developed by MARAMA. Nonroad and onroad mobile source emissions for the projected years 2028 and 2036 were estimated from the MOVES2014b version. MOVES2014b modeling runs were once again executed by PADEP for nonroad mobile source emissions and by the contractor for onroad mobile source emissions. Additional details on some of the assumptions and inputs to the model are available in the redesignation request and its associated Appendices C4, C5, and C6.^[34]

( printed page 48038)

3. Maintenance Demonstration

The Calcagni memo describes two ways for a state to demonstrate maintenance of the NAAQS for a period of at least 10 years 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.^[35] Pennsylvania's projected actual emissions for the interim year of 2028 and for the maintenance year of 2036 are both below the modeled limits established in the 2017 attainment demonstration, which is acceptable for showing maintenance in the Warren County NAA.

4. Monitoring Network

The 2014 SO₂ Guidance indicates that once an area has been redesignated to attainment, the state should continue to operate an appropriate air quality monitoring network as provided under 40 CFR part 58 to verify the attainment status of the area. Pennsylvania has committed to continued operation of its SO₂ monitoring network in the Warren County NAA to verify the attainment status. Also, Pennsylvania will continue to submit an annual monitoring network plan to the EPA for approval, in accordance with 40 CFR 58.10. No monitoring sites will be retired from the existing network unless pre-approved by the EPA. The EPA proposes to find that these measures are sufficient for purposes of the maintenance plan.

5. Verification of Continued Attainment

The 2014 SO₂ Guidance states that each air agency should ensure that it has the legal authority to implement and enforce all measures necessary to attain and maintain the 2010 SO₂ NAAQS. The air agency's submittal should indicate how it will track the progress of the maintenance plan for the area either through air quality monitoring or modeling.

Pennsylvania Air Pollution Control Act (APCA) section 4(27) grants PADEP the legal authority to implement all measures necessary to enforce the APCA, including maintaining the 2010 1-hour primary SO₂ NAAQS. In addition, PADEP has indicated it will track the progress of the maintenance plan through an integrated approach utilizing air quality monitoring data and emissions inventories.

As previously indicated, PADEP will continue to operate its SO₂ monitoring network to verify the attainment status of the Warren County NAA. PADEP will also use emissions inventories—developed annually for major point sources and triennially for area and mobile sources—to assess emissions trends. PADEP has also committed to submitting an additional SIP revision 8 years following redesignation to establish the Commonwealth's plan for maintaining the 2010 SO₂ NAAQS for an additional 10 years, as required by CAA section 175A(b).

The EPA proposes to find that these proposed measures will provide for verifying continued attainment within the Warren County NAA.

6. Contingency Measures

Section 175A(d) of the CAA requires that a maintenance plan include such contingency measures as the EPA deems necessary to assure that the state will promptly correct a violation of the NAAQS that occurs after redesignation. 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 continue to implement all measures with respect to control of the pollutant that were contained in the SIP before redesignation of the area to attainment.

Pennsylvania has committed to continuing implementation of all applicable measures indicated in the SIP after redesignation of the Warren County NAA.^[36] Furthermore, Pennsylvania has identified triggering indicators for its contingency measures, a schedule for implementing these potential measures, and has specified potential options to correct any NAAQS violation.^[37] These contingency measures include both URC- and PADEP-based contingency measures.

For URC, Pennsylvania has identified two separate triggering indicators for different contingency measures: (1) an exceedance of the permitted SO₂ emission limit (131.5 lbs/hr) for the fluid catalytic cracking (FCC) unit at URC and (2) the occurrence of a third daily max 1-hour SO₂ concentration that exceeds 75 ppb, as measured by PADEP's Warren Overlook SO₂ ambient monitor.^[38] If the FCC unit at URC exceeds its permitted emission limit, URC will initiate a system audit of the FCC unit—which includes a review of the SO₂ emission-controlling additive components, continuous emissions monitoring system, and communications equipment. Within 45 days of the exceedance, URC shall furnish PADEP with a written report that details the operating parameters of the FCC unit and its emission control system. Alternatively, if PADEP's Warren Overlook SO₂ ambient monitor measures a third daily max 1-hour SO₂ concentration that exceeds 75 ppb, PADEP will provide written notice to ( printed page 48039) URC that the facility must produce an “Ambient Action Level Report” within 90 days of the provided notice. This Ambient Action Level Report should identify if any URC sources were beyond their permitted emission limits, the reason for the non-compliance, and if any additional measures have been or will be implemented to reduce the possibility of future non-compliance. If no emission exceedances are identified by URC, then URC must conduct an analysis—which may include meteorological or photochemical modeling—to identify the source of the SO₂ ambient monitor violation. If URC was found to be in compliance with all SO₂ emission limits and no other parties are indicated as the source of the SO₂ monitor violation or if the Ambient Action Level Report identifies that a URC source caused the SO₂ monitor violation, then URC shall also assess if any changes in facility operations are required to avoid a future violation of the 2010 SO₂ NAAQS.

Alongside the URC-based contingency measures, PADEP also has identified a PADEP-based contingency measure. If PADEP identifies a daily maximum SO₂ concentration exceeding 75 ppb at the Warren Overlook SO₂ monitor, PADEP will initiate an investigation and proceed with enforcement as appropriate. This process includes PADEP contacting the PADEP Air Resource Management Division Chief and the PADEP Northwest Regional Office Air Program Manager to report the exceeding monitored value within five business days of the identified exceedance. Within five business days of PADEP's notification, the Northwest Regional Office will contact URC in writing requesting an informal investigation into each observed daily exceedance at the Warren Overlook SO₂ monitor, with a URC response due in writing within 30 days. This PADEP-initiated contingency measure takes effect with the first instance of a 1-hour daily maximum SO₂ concentration at the Warren Overlook monitor exceeding 75 ppb and is intended to proactively identify any issue prior to a violation of the 2010 SO₂ NAAQS. If three instances of daily exceedance events occur within a calendar year, the Ambient Action Level Report contingency measure associated with URC will be enacted to correct for any potential NAAQS violation.

As the 2036 projected inventory estimates approximately 450 tons of SO₂ emissions per year compared to the approximately 1,275 tons of SO₂ emissions per year permitted in the 2017 attainment plan modeling, it is not expected that there will be a future monitor exceedance in the Warren County NAA. Nevertheless, Pennsylvania has committed to adopting and implementing corrective actions, as necessary and appropriate.

The EPA proposes to find that these contingency measures are sufficient. Consistent with the above proposed findings, the EPA proposes to find that Pennsylvania's submitted maintenance plan meets the requirements set forth in CAA section 175A and EPA guidance, and is proposing to approve the maintenance plan as a revision to the Pennsylvania SIP.

E. Criterion (5)—Pennsylvania Has Met All Applicable Requirements Under Section 110 and Part D of Title I of the CAA

In accordance with section 107(d)(3)(E)(v) of the CAA, to redesignate the Warren County NAA to attainment, Pennsylvania must meet all requirements applicable to the Warren County NAA under CAA section 110 (general SIP requirements) and part D of title I of the CAA (SIP requirements for nonattainment areas).

1. Section 110 General Requirements for SIPs

Pursuant to CAA section 110(a)(1), whenever new or revised NAAQS are promulgated, the CAA requires states to submit a plan ( i.e., SIP) for the implementation, maintenance, and enforcement of such NAAQS. Section 110(a)(2) of title I of the CAA contains the general requirements for a SIP, also known as “infrastructure” requirements. These requirements include, but are not limited to, the following: submittal of a SIP that has been adopted by the State after reasonable public notice and hearing; provisions for establishment and operation of appropriate procedures needed to monitor ambient air quality; implementation of a source permit program; provisions for the implementation of part C of title I of the Clean Air Act (CAA) requirements (Prevention of Significant Deterioration (PSD)) and provisions for the implementation of part D of title I of the Clean Air Act (CAA) requirements NNSR permit programs); provisions for air pollution modeling; and provisions for public and local agency participation in planning and emission control rule development.

Section 110(a)(2)(D) of the CAA requires that SIPs contain certain measures to prevent sources in a state from significantly contributing to air quality problems in another state. To implement this provision, the EPA has required certain states to establish programs to address the interstate transport of air pollutants.^[39] The CAA section 110(a)(2)(D) requirements for a State are not linked with a particular nonattainment area's designation and classification in that state. The EPA has concluded that the requirements linked with a particular nonattainment area's designation and classifications are the relevant measures to evaluate in reviewing a redesignation request. The transport SIP submittal requirements, where applicable, continue to apply to a state regardless of the designation of any one particular area in the state. Thus, the EPA has concluded that the CAA's interstate transport requirements should not be construed to be applicable requirements for purposes of redesignation.

In addition, the EPA has concluded other CAA section 110 elements—those that are neither connected with nonattainment plan submissions nor linked with an area's attainment status—are not applicable requirements for purposes of redesignation. The area will still be subject to these requirements after the area is redesignated. The CAA section 110 and part D requirements which are linked with a particular area's designation and classification are the relevant measures to evaluate in reviewing a redesignation request. This approach is consistent with the EPA's existing policy on applicability ( i.e., for redesignations) of conformity and oxygenated fuels requirements, as well as with CAA section 184 ozone transport requirements. See Reading, Pennsylvania, proposed and final rules (61 FR 53174-53176, October 10, 1996), (62 FR 24826, May 7, 2008); Cleveland-Akron-Loraine, Ohio, final rule (61 FR 20458, May 7,1996); and Tampa, Florida, final rule (60 FR 62748, December 7, 1995). See also the discussion on this issue in the Cincinnati, Ohio, redesignation (65 FR 37890, June 19, 2000), and in the Pittsburgh, Pennsylvania, redesignation (66 FR 50399, October 19, 2001).

The EPA approved elements of Pennsylvania's June 15, 2014 SO₂ infrastructure SIP submittal on August 5, 2015.^[40] As explained previously, certain general requirements of CAA section 110(a)(2) are statewide requirements that are not linked to the nonattainment status of the Warren County NAA and are therefore not “applicable requirements” for the purpose of reviewing Pennsylvania's ( printed page 48040) redesignation request. Because Pennsylvania satisfies the general SIP elements and requirements set forth in CAA section 110(a)(2) applicable to and necessary for SO₂ redesignation with the EPA's August 5, 2015 (80 FR 46494) approval of the infrastructure SIP, the EPA proposes to conclude that Pennsylvania has satisfied the criterion of CAA section 107(d)(3)(E)(v) related to section 110(a)(2) of the CAA.

2. Part D Requirements

In addition to the CAA section 110 requirements, CAA section 107(d)(3)(E)(v) requires that the State meet all the requirements applicable to the nonattainment area “under part D of this subchapter” for the nonattainment area to be redesignated. Both CAA section 107 and part D are within title 1 of the CAA. Part D, of title I of the CAA, entitled “Plan Requirements for Nonattainment Areas,” consists of six subparts, of which only subparts 1 and 5 are applicable to SO₂ nonattainment areas. Subpart 1 (sections 171 through 179B) contains provisions that can apply to all nonattainment areas for all criteria pollutants, while subpart 5 (sections 191 and 192) contains additional provisions for SO₂, NO_X, or lead nonattainment areas. The requirements applicable to this redesignation regarding the 2010 SO₂ NAAQS are discussed below, as applicable to SO₂.

a. Subpart 1 Requirements

1. Section 172 Requirements

Section 172 of the CAA requires states with nonattainment areas to submit plans that provide for timely attainment of the NAAQS. More specifically, CAA section 172(c) contains general requirements for nonattainment plans. A thorough discussion of these requirements is found in the General Preamble for Implementation of title I.^[41]

As noted in the General Preamble, certain attainment-related planning requirements under CAA section 172(c) no longer have meaning for an area that is already attaining the NAAQS, and therefore are not applicable for purposes of redesignation. For example, for an area that is already attaining the NAAQS, there would be nothing for the State to provide to show reasonable further progress to attainment in that area. Similarly, the CAA section 172 requirements for the attainment demonstration, implementation of reasonably available control measures, including reasonably available control technology, and contingency measures that are triggered if an area fails to meet RFP or fails to attain are also not applicable for purposes of redesignation.

With respect to CAA section 172(c)(3), Pennsylvania was required to submit an actual current emissions inventory with its attainment plan.^[42] Pennsylvania had submitted a base year inventory with its attainment plan SIP on September 29, 2017 and the EPA approved this element on October 12, 2018.^[43]

2. Section 173 Requirements

Section 173 of the CAA includes requirements for permit programs that are required in a nonattainment area for new sources as required by CAA section 172(c)(5), known as NNSR. However, the EPA has a longstanding interpretation that because the NNSR permit program is replaced by the PSD permit program upon an area's redesignation to attainment, nonattainment areas seeking redesignation to attainment do not need a fully approved part D NNSR program to be redesignated. A more detailed rationale for this view is described in a memorandum from Mary Nichols, Assistant Administrator for Air and Radiation, dated October 14, 1994, entitled, “Part D New Source Review Requirements for Areas Requesting Redesignation to Attainment.” ^[44] Nevertheless, the EPA notes that Pennsylvania's Code has SIP-approved NNSR and PSD programs found at 25 Pa. Code 127.201-127.218 for NNSR and at 25 Pa. Code 127.81-127.83 for PSD. Pennsylvania's PSD regulations merely incorporate by reference the Federal PSD regulations found at 40 CFR part 52. Warren County has therefore addressed all required provisions for the permitting of sources in NAAs, including NNSR. See 40 CFR 52.2020(c). Pennsylvania's PSD program will become applicable for SO₂ in the Warren County NAA if redesignation to attainment is finalized.

3. Section 175A Requirements

CAA section 175A requires that states seeking redesignation of an area to attainment submit a “maintenance plan” containing certain elements. Pennsylvania included a maintenance plan for the Warren County NAA with its September 19, 2025, redesignation request, which the EPA is proposing to approve in conjunction with the redesignation, and it is discussed in detail in section II.D., Criterion (4) of this document.

4. Section 176 Requirements

Section 176(c) of the CAA requires that Federal actions 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 and the Federal Transit Act (transportation conformity) as well as to all other Federally-supported or funded projects (general conformity). Section 176(c) of the CAA also requires that states establish criteria and procedures to ensure that Federally-supported or funded transportation plans, transportation improvement programs (TIPs) and projects conform to the goals of the applicable SIP. This is referred to as a transportation conformity SIP. In the preamble to the January 1993 proposed transportation conformity rule, the EPA stated that, “[b]ased on available emissions information, EPA believes highway and transit motor vehicles are not significant sources of lead or sulfur dioxide. Therefore, transportation plans, TIPs, and projects are presumed to conform to the applicable implementation plans for these pollutants.” ^[45] In November 1993, the EPA finalized its transportation conformity regulations. One section of those regulations addressed the geographic applicability of the transportation conformity regulations. The regulation stated at that time that, “[t]he provisions of this subpart apply with respect to emissions of the following criteria pollutants: Ozone, carbon monoxide, nitrogen dioxide, and particles with an aerodynamic diameter less than or equal to a nominal 10 micrometers (PM₁₀ ).” ^[46] Based on this provision, transportation conformity does not apply in nonattainment or maintenance areas for SO₂ . Therefore, a transportation conformity SIP is not required for SO₂ nonattainment and maintenance areas and is not necessary for an SO₂ nonattainment area to be redesignated to attainment, and the EPA's transportation conformity rules do not apply to SO₂ for the Warren County NAA.

( printed page 48041)

5. Section 179 Requirements

Section 179(a) of the CAA addresses potential sanctions for the failure of a State to submit certain required SIP elements by statutory deadlines. The EPA is not aware of any missing or incomplete Warren County planning elements subject to section 179(a) of the CAA.

b. Subpart 5 Requirements

The subpart 5 requirements, which consist of sections 191 and 192 of the CAA, are specific provisions applicable to SO₂, NO₂ or lead nonattainment areas. Section 191 of the CAA requires states with areas designated nonattainment for SO₂, NO₂ or lead after November 15, 1990, to submit within 18 months of the designation an implementation plan meeting the requirements of part D.^[47] The substance of the required plans is established by CAA section 172(c). Section 192 of the CAA sets forth attainment dates for nonattainment areas under CAA section 191.

For SO₂, CAA section 192(a) requires that attainment plans provide for attainment of the primary Standard as expeditiously as possible, but no later than five years from the date of the nonattainment designation. The EPA designated the Warren County NAA as nonattainment on August 5, 2013 (78 FR 47191), with an attainment date of October 4, 2018. However, because the EPA is reviewing a redesignation request under CAA section 107(d)(3)(E), rather than a determination of attainment under CAA section 179(c), the determination of whether the Area attained by the attainment date set forth in CAA section 192 is not applicable to this proposed action proposing approval of Pennsylvania's redesignation request.

Based on the above, the EPA is proposing to find that Pennsylvania has satisfied the applicable requirements for the redesignation of the Warren County NAA under section 110 and part D of title I of the CAA.

III. Summary of Source-Specific Requirements SIP Revision and EPA Analysis

In the September 19, 2025 redesignation request and maintenance plan submittal, PADEP concurrently requested that the EPA correct source-specific requirements for URC in the Pennsylvania SIP.^[48] With the final approval of the attainment plan for the Warren Nonattainment Area on October 12, 2018,^[49] the EPA incorporated by reference the entirety of a consent order and agreement (COA) between PADEP and URC, as submitted by PADEP. However, a redacted version of the COA was intended to be included in the SIP. PADEP has requested that the previously unredacted language included in the Pennsylvania SIP be removed to align with the redacted version of the COA, as originally intended. Specifically, PADEP has requested that the EPA replace the unredacted COA with an excerpt of the title V permit for URC that contains the provisions identified by the COA.^[50]

The EPA has reviewed the unredacted version of the COA as well as the title V permit excerpt containing the COA provisions and has determined that the title V permit excerpt contains all relevant emission limits, testing, and recordkeeping and reporting requirements as originally identified in the COA. The redacted COA information mainly pertains to historical context, background information on the facility, and details related to the development and execution of the COA. Notably, the title V permit excerpt removes an SO₂ emission limit for Boiler 4 at the URC facility. However, this source was decommissioned on February 14, 2018 and the latest title V permit for URC—issued on December 15, 2025—does not permit operation of this source any longer.^[51] All other emission limits, fuel sulfur content, testing, and recordkeeping and reporting requirements from the original COA remain intact. No emissions increases are anticipated as a result of this SIP revision.

IV. Proposed Action

The EPA's review of this material indicates that the Warren County NAA has met the criteria necessary under CAA section 107(d)(3)(E) for the EPA to redesignate the Warren County NAA from nonattainment to attainment for the 2010 SO₂ NAAQS. Accordingly, the EPA is proposing to approve Pennsylvania's redesignation request for the Warren County NAA, which was submitted on September 19, 2025. Final approval of Pennsylvania's redesignation request would change the legal designation of the portion of Warren County designated nonattainment at 40 CFR 81.339 to attainment for the 2010 1-hour SO₂ NAAQS. Essential to the potential redesignation, the EPA is also proposing to approve Pennsylvania's maintenance plan, which is designed to ensure that the potentially redesignated Warren County NAA will continue to maintain the SO₂ NAAQS for ten years following potential redesignation.

Simultaneously, the EPA is proposing to amend the Pennsylvania SIP by replacing the unredacted version of the 2017 COA between PADEP and URC with an excerpt of the 2025 title V permit for URC that contains the provisions identified by the COA. The entirety of the 2017 COA was initially incorporated into the SIP in error, and this proposed action proposes to correct this error. The title V permit excerpt contains all relevant emission limits, testing, and recordkeeping and reporting requirements as originally identified in the COA.

The EPA is soliciting public comments on the issues discussed in this document. These comments will be considered before taking final action.

V. Statutory and Executive Order Reviews

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. 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 anExecutive Order 14192 (90 FR 9065, February 6, 2025) regulatory action because this proposed action is not significant 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.); ( printed page 48042)
• 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 inExecutive Order 13132 (64 FR 43255, August 10, 1999);
• Is not subject toExecutive Order 13045 (62 FR 19885, April 23, 1997) because it approves a State program;
• Is not a significant regulatory action subject toExecutive 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 the 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).

91 FR 48034