2024-28536. Air Plan Approval; Pennsylvania; Redesignation of the Allegheny County Nonattainment Area to Attainment and Approval of the Area's Maintenance Plan for the 2010 1-Hour Primary Sulfur Dioxide National Ambient Air Quality Standard

Table 1—2014-2023 SO ₂ Design Values for Allegheny County Nonattainment Area Monitor Sites

[Parts per billion]

Monitor site	2012-2014	2013-2015	2014-2016	2015-2017	2016-2018	2017-2019	2018-2020	2019-2021	2020-2022	2021-2023
Liberty	101	99	94	97	103	109	85	59	56	63
North Braddock *	89	71	64	55	61	63	64	58	56	54
* North Braddock design values from the 2012-2014 and 2013-2015 periods are comprised of less than three years of data as the monitor began operating in 2014.

Pennsylvania's 2017 attainment plan contained an attainment demonstration which utilized allowable SO₂ emission limits from stationary sources within the Allegheny County NAA to inform several modeling analyses for SO₂ emissions.^[16] These modeling analyses were based on emissions limits for large, stationary sources of SO₂, which, if enacted, would ensure that the Allegheny 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.^[17] The source characteristics are still reasonably represented ^[18] and from 2020-2021, large, stationary SO₂ sources ^[19] within the Allegheny County NAA were meeting their allowable emission limits for attainment.^[20] As such, the 2017 attainment demonstration modeling submitted by Pennsylvania will allow for the EPA's determination of attainment. 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. The specific measures identified in the control strategy include upgrades to the Vacuum Carbonate Unit equipment at the U.S. Steel (USS) Clairton Plant, the implementation of a tail gas recycling project at the USS Clairton Plant, and a new stack and combined flue system for select boilers at the USS Edgar Thomson Plant.^[22] Additionally, lower permitted SO₂ emission rates were implemented for nearly all processes at the primary stationary SO₂ sources in the Allegheny County NAA, including the USS Clairton Plant, the USS Edgar Thomson Plant, the USS Irvin Plant, and Harsco Metals. These implemented, permanent and federally enforceable control measures have aided in reducing the actual total emissions from large, stationary USS SO₂ sources to 2,373 tons per year (as of 2021),^[23] which is below the revised total emissions limits proposed for USS facilities in the 2017 attainment demonstration modeling (2,669 tons per year),^[24] thus contributing to bringing the Allegheny County NAA into attainment.

In this action, the EPA proposes to find that the air quality monitoring data and air quality modeling data demonstrate that the Allegheny County NAA has attained the 2010 1-hour primary SO₂ NAAQS.

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

CAA section 107(d)(3)(E)(ii) 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. The EPA has fully approved the applicable Pennsylvania SIP for the Allegheny County NAA under section 110(k) of the CAA for all requirements applicable for purposes of redesignation. 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.^[25] The 2017 attainment plan SIP was initially proposed for EPA approval on November 19, 2018 ^[26] and received final EPA approval on April 23, 2020.^[27] 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) ( print page 99793) analysis, a reasonable further progress (RFP) analysis, contingency measures, and nonattainment new source review (NNSR) regulations.

C. Criterion (3)—The Air Quality Improvement in the Allegheny 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, 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.

Specifically, the implementation of multiple permanent and federally enforceable control measures at stationary point sources of SO₂ identified in the EPA-approved 2017 attainment demonstration aided in a substantial decrease in SO₂ emissions, and consequently lower SO₂ concentrations in the Allegheny County NAA. These measures include upgrades to the Vacuum Carbonate Unit equipment at the USS Clairton Plant, the implementation of a tail gas recycling project at the USS Clairton Plant, and a new stack and combined flue system for select boilers at the USS Edgar Thomson Plant. Furthermore, the Guardian Glass Plant ceased operations in August 2015 and its operating permit was terminated in November 2015.^[28] The Calcagni Memo states that “[e]mission reductions from source shutdowns can be considered permanent and enforceable to the extent that those shutdowns have been reflected in the SIP and all applicable permits have been modified accordingly,” and therefore the Guardian shutdown is considered permanent and enforceable.^[29] Any future operations at this location would require a new permit and a new source evaluation, as described in ACHD Article XXI, sections 2102.04 and 2103.13.^[30] Additionally, Emissions Reductions Credits for SO₂ were not requested for the Guardian Glass Plant, preventing the transfer or sale of associated emission credits to another entity in Pennsylvania or some surrounding states.

Allegheny County also established lower SO₂ emissions limits for nearly all processes at the USS facilities in the Allegheny County NAA, including USS Clairton, USS Edgar Thomson, and USS Irvin, as well as the Harsco (Braddock Recovery) facility, located on the property of USS Edgar Thomson. These emissions limits are embedded in the installation permits issued by ACHD for these facilities and are federally enforceable as they have been approved into Pennsylvania's SIP, and they are permanent because they cannot be altered without an additional SIP submittal.^[31] Details on the imposed emissions limits were included as copies of the installation permits in Appendix K of the 2017 attainment plan submittal and are available in the docket for this action.^[32]

Collectively, the implemented controls and lower permitted SO₂ emissions rates resulted in an actual decrease of 835 tons of SO₂ emitted per year from 2011 to 2017. This is approximately a 25% reduction from 2011 levels of 3,418 tons of SO₂ emitted per year.^[33] As this reduction comes from EPA-approved SIP controls and permit-controlled emission limits, the EPA finds the air quality improvement in the Allegheny County NAA to be due to permanent and enforceable reductions in emissions.

D. Criterion (4)—The Allegheny 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 Allegheny County NAA to attainment for the 2010 1-hour primary SO₂ NAAQS, the State 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. What is required in a maintenance plan?

CAA section 175A sets forth the elements of a maintenance plan. Under 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 2010 1-hour primary SO₂ NAAQS violations. The Calcagni Memo provides further guidance on the content of a maintenance plan, explaining that a maintenance plan should address five requirements: the attainment emissions inventory, maintenance demonstration, monitoring, verification of continued attainment, and a contingency plan.^[34] As is discussed more fully later in this section, the EPA is proposing to determine that Pennsylvania's maintenance plan meets the requirements in CAA section 175A and is thus proposing to approve it as a revision to the Allegheny 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 SO₂ 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 2017 SO₂ emissions inventory as the attainment inventory with its maintenance plan. The year 2017 was selected because it was the first year in which emissions were at levels required to demonstrate attainment of the 2010 SO₂ NAAQS, with the exception of emissions associated with malfunctions of the desulfurization facility at the USS Clairton Plant. Additionally, 2017 was a year in which a fully reviewed National Emission Inventory (NEI) was released. The NEI is a comprehensive, triennial estimate of emissions. Generally, the ( print page 99794) attainment year is selected as a year within the attaining design value period ( i.e., 2019-2021). However, alternate years from 2018-2022 were less ideal than 2017 for the attainment year for a variety of factors, including excess emissions from sources due to equipment breakdowns, atypical emissions during the COVID pandemic, and incomplete emissions compilations for recent years. Additional details for choosing 2017 as the attainment year are available in the submitted redesignation request.^[35]

For the 2017 attainment year inventory, Pennsylvania directly used point and area source emissions reported in the 2017 NEI, except for corrections identified in Appendix B of the submitted redesignation request.^[36] The point source emissions for the Allegheny County NAA were verified against the EPA's emissions inventory system (EIS) and the EPA found them to be acceptable.^[37] Area source emissions were estimated based on the relative percentage of the Allegheny County population residing in the Allegheny County NAA and the resulting factor allocated the appropriate fraction of the County's total emissions to the Allegheny County NAA.

Nonroad and onroad mobile source emissions for 2017 were obtained from the EPA's Motor Vehicle Emissions Simulator (MOVES) model, specifically the MOVES3 version. PADEP executed the MOVES3 modeling runs for nonroad mobile sources and utilized a contractor to run the model for onroad mobile source emissions.

Natural SO₂ emission sources, such as fires and biogenics, were also compiled. Fire emissions data was pulled from the EPA's Fires ^[38] inventory, while biogenic emissions from soils and vegetation were predicted by the Biogenic Emission Inventory System ^[39] (BEIS) model.

Projection inventories predicted from the attainment inventory demonstrate that the area will continue to remain in attainment during the maintenance period. Pennsylvania developed 2026 and 2035 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 from the 2017 base year emissions and growth factors developed by the Mid-Atlantic Regional Air Management Association, Inc., and other sources. These growth factors are developed based on forecasts from various databases and tools, including the Energy Information Administration's Annual Energy Outlook 2022, Pennsylvania Industry Employment 2018-2028 Long-Term Projections, National Inventory Collaborative 2016v1 Emissions Modeling Platform, and the Federal Aviation Administration's Terminal Area Forecast. Projected emissions were subject to the same corrections utilized in the 2017 base year inventory for consistency. Furthermore, point sources with implemented enforceable controls or shutdowns since the 2017 base year were excluded from the 2026 and 2035 projections. Specifically, the Koppers Clairton tar refining facility ceased operation in 2017 and its permit expired in 2021. Additionally, Coke Batteries 1, 2, and 3 at the USS Clairton Plant ceased operation in March 2023. Conversely, projections for the 2026 and 2035 inventories included the permitted plantwide SO₂ emissions limit of 23.89 tons/year for a new major source facility—the Invenergy Allegheny Energy Center. However, the permit for this facility was terminated on November 9, 2023,^[40] and construction of this facility is not expected to proceed at this time. As such, the actual emissions in 2026 and 2035 should be even lower than the anticipated values reported in the maintenance year projections. Nonroad and onroad mobile source emissions for the projected years 2026 and 2035 were also obtained from the MOVES3 version. MOVES3 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 Appendix B.^[41] Fire and biogenic sources are typically not projected for future case scenarios and therefore emissions were held constant from 2017 to 2026 and 2035.

Table 2—Emissions Inventories for the Allegheny County Nonattainment Area

[Tons per year]

Sector	2017 Actual emissions (base year)	2026 Projected emissions (interim year)	2035 Projected emissions (maintenance year)
Point Sources	2,556	2,511	2,472
Area Sources	22	26	27
Nonroad Mobile Sources	0	0	0
Onroad Mobile Sources	5	2	2
Fires	0	0	0
Biogenics	0	0	0
Total	2,583	2,539	2,501