SUPPLEMENTARY INFORMATION:

Table of Contents

I. Summary of the EPA's Proposed Action

II. Background

III. North Carolina's SIP Submittal

IV. The EPA's Evaluation of North Carolina's SIP Submittal

A. Attainment Emissions Inventory

B. Maintenance Demonstration

C. Monitoring Network

D. Verification of Continued Attainment

E. Contingency Plan

V. The EPA's Analysis of North Carolina's Proposed NO_X and VOC Sub-Area Budgets for the Charlotte Area

VI. The EPA's Adequacy Determination for the Proposed NO_X and VOC Sub-Area Budgets

VII. Effect of EPA's Proposed Action

VIII. Proposed Action

IX. Statutory and Executive Order Reviews

I. Summary of the EPA's Proposed Action

In accordance with the Clean Air Act (CAA or Act), the EPA is proposing to approve the second 10-year Charlotte Area maintenance plan for the 2008 8-hour ozone NAAQS, submitted by NCDAQ as a revision to the North Carolina SIP on February 28, 2025.^[1] The ( printed page 60350) Charlotte Area includes all of Mecklenburg County and portions of Cabarrus, Gaston, Iredell, Lincoln, Rowan, and Union Counties.^[2]

The February 28, 2025, submittal is designed to maintain the 2008 8-hour ozone NAAQS within the Charlotte Area through the end of the second 10-year portion of the maintenance period beyond redesignation. The EPA is proposing to approve the plan because it meets all applicable requirements under CAA sections 110 and 175A. The EPA is also proposing to approve the 2018 and 2035 NO_X and VOC sub-area budgets in the Charlotte Area Maintenance Plan because the sub-area budgets meet the applicable transportation conformity requirements under 40 CFR 93.118(e).

II. Background

On March 12, 2008, the EPA promulgated a revised 8-hour ozone NAAQS of 0.075 parts per million (ppm) to provide increased protection of public health and the environment.^[3] Under the EPA's regulations at 40 CFR part 50, the 2008 8-hour ozone NAAQS is attained when the 3-year average of the annual fourth-highest daily maximum 8-hour average ambient air quality ozone concentrations is less than or equal to 0.075 ppm.^[4] Ambient air quality monitoring data for the 3-year period must meet a data completeness requirement. The ambient air quality monitoring data completeness requirement is met when the average percent of days with valid ambient monitoring data is greater than 90 percent, and no single year has less than 75 percent data completeness as determined in Appendix I of part 50.

Upon promulgation of a new or revised NAAQS, section 107(d)(1) of the CAA requires the EPA to designate as nonattainment any area that is violating the NAAQS, based on the three most recent years of complete, quality-assured, and certified ambient air quality data at the conclusion of the designation process. The bi-state Charlotte Area was designated nonattainment for the 2008 8-hour ozone NAAQS on May 21, 2012, effective July 20, 2012, using 2009-2011 ambient air quality data.^[5] At the time of designation, the bi-state Charlotte Area was classified as a marginal nonattainment area for the 2008 8-hour ozone NAAQS. In the final implementation rule for the 2008 8-hour ozone NAAQS,^[6] the EPA established ozone nonattainment area attainment dates based on Table 1 of CAA section 181(a). This rule established an attainment date three years after the July 20, 2012, effective date for areas classified as marginal areas for the 2008 8-hour ozone nonattainment designations. Therefore, the bi-state Charlotte Area's attainment date was July 20, 2015. In 2015, the Charlotte Area was redesignated to attainment for the 2008 8-hour ozone NAAQS, the first 10-year maintenance plan was approved, and the public was notified that the EPA found the 2014 and 2026 sub-area budgets for NO_X and VOC adequate.^[7]

The primary guidance on maintenance plans and redesignation requests is the September 4, 1992, memorandum from John Calcagni, titled “Procedures for Processing Requests to Redesignate Areas to Attainment” (Calcagni Memo).^[8] The Calcagni Memo outlines the key elements of a maintenance plan, which include the following: attainment emissions inventory, maintenance demonstration, monitoring network requirements, verification of continued attainment, and contingency plan elements.

Since 2015, three SIP revisions to the first 10-year maintenance plan have been approved. Two supplements updated the 2026 budgets for NO_X and VOC,^[9] and one supplement revised the motor vehicle model year coverage of the emissions inspection and maintenance program (I/M).^[10]

The EPA has revised the ozone NAAQS once since the 2008 standards were finalized. On October 1, 2015, the Agency revised both the primary and secondary NAAQS for ozone to a level of 0.070 ppm (annual fourth-highest daily maximum 8-hour average concentration, averaged over 3 years).^[11] On November 16, 2017, the EPA published a final rule establishing initial area designations for the 2015 8-hour ozone NAAQS.^[12] The bi-state Charlotte Area was designated attainment for that standard with an effective date of August 3, 2018.^[13]

III. North Carolina's SIP Submittal

On February 28, 2025, NCDAQ submitted a second 10-year maintenance plan to the EPA as a revision to the North Carolina SIP. The submittal includes the maintenance plan, air monitor data, emissions inventory information, and appendices.^[14] Appendices include emissions inventory documentation for onroad, nonroad, point, and nonpoint (area) source emissions, as well as documentation of public notice, comments received, and comment responses.

IV. The EPA's Evaluation of North Carolina's SIP Submittal

The EPA has reviewed the second 10-year maintenance plan for the Charlotte Area, which is designed to maintain the 2008 8-hour ozone NAAQS within the bi-state Charlotte Area through the end of the 20-year period beyond redesignation, as required under CAA section 175A(b). The following is a summary of the EPA's interpretation of the section 175A requirements ^[15] and the Agency's evaluation of how each requirement is met.

A. Attainment Emissions Inventory

As discussed above, the EPA determined in 2015 that the bi-state Charlotte Area had attained the 2008 8-hour ozone NAAQS at the time that it redesignated the Charlotte Area to attainment.^[16] The bi-state Charlotte Area continues to attain the 2008 8-hour ozone NAAQS. For the second 10-year ( printed page 60351) maintenance plan, NCDAQ selected 2018 as the base year ( i.e., attainment emissions inventory year) for developing a comprehensive emissions inventory for NO_X and VOC, for which projected emissions could be developed for 2026 and 2035. The attainment inventory identifies a level of emissions in the bi-state Charlotte Area that is sufficient to attain the 2008 8-hour ozone NAAQS. North Carolina began development of the attainment inventory by first generating a baseline emissions inventory for the State's portion of the bi-state Charlotte Area. The projected summer day emission inventories have been estimated using projected rates of growth in population, traffic, economic activity, and other parameters. In addition to comparing the final year of the plan (2035) to the base year (2018), North Carolina compared an interim year (2026) to the baseline to demonstrate that the years in between are also expected to show continued maintenance of the 2008 8-hour ozone standard.

The emissions inventory is composed of four major types of sources: point, nonpoint (area), onroad mobile, and nonroad mobile. The complete descriptions of how the inventories were developed are discussed in Appendices A, B, C, and D of the February 28, 2025, submittal, which can be found in the docket for this proposed action.

i. Point Sources

Point sources are those large, stationary (non-mobile), identifiable sources of emissions that release pollutants into the atmosphere. Point source emissions are tabulated from data collected by direct on-site measurements of emissions or from mass balance calculations utilizing emission factors from the EPA's AP-42 or stack test results. Emission data are collected for each point source at a facility and reported to NCDAQ through its online system.

For Electricity Generating Units (EGUs) with a Continuous Emissions Monitoring System (CEMS), 2018 base year NO_X emissions for July were obtained from the EPA's Clean Air Markets Division (CAMD) database for the G.G. Allen Steam Station in Gaston County, Lincoln County Combustion Turbine Station in Lincoln County, and Buck Steam Station and Plant Rowan in Rowan County. Base year 2018 summer day VOC emissions were calculated for each unit using annual emissions that Duke Energy Carolinas reported to NCDAQ. Duke Energy Carolinas provided NCDAQ with 2026 and 2035 July day NO_X and VOC emissions forecasts for Lincoln Combustion Turbine Station and Buck Steam Station.^[17] For Plant Rowan, NCDAQ used the Eastern Regional Technical Advisory Committee (ERTAC) model v22.0 AEO2023 reference case's July 2026 and July 2035 NO_X emissions forecast to develop summer day NO_X emissions. NCDAQ calculated 2018 to 2026 and 2018 to 2035 summer day NO_X emission growth rates and applied the growth rates to 2018 VOC summer day emissions to estimate VOC emissions for 2026 and 2035.

NCDAQ compiled annual NO_X and VOC emissions from the 2022 North Carolina point source inventory for the list of relevant non-CEMS EGUs, and these emissions were used to estimate emissions in 2026. For 2018 and 2035, NCDAQ compiled annual 2018 and 2032 VOC and NO_X emissions from the 2018v2 Emissions Modeling Platform (EMP) ^[18] for the non-CEMS EGUs included in this plan. Given the proximity of 2032 to 2035 and the lack of emission projections for 2035,^[19] the 2032 projections were used to represent 2035 emissions. For non-EGU point sources, aircraft, and wild/prescribed/agricultural fires, the 2018 inventory reflects county emissions from the EPA's 2018v2 EMP.^[20] Emissions for 2026 were estimated by interpolating between the 2018 and 2032 emission estimates provided in the 2018v2 EMP.

ii. Nonpoint Sources

Nonpoint sources collectively represent individual sources that have not been inventoried as specific point or mobile sources. These individual sources treated collectively as nonpoint sources are typically too small, numerous, or difficult to inventory using the methods for the other classes of sources. In general, emissions for nonpoint sources are estimated by multiplying an emission factor by some known indicator of collective activity such as production, number of employees, or population. These types of emissions are estimated at the county level. North Carolina's nonpoint source emissions inventory is based on the EPA's 2018v2 EMP. Given the proximity of 2032 to 2035 and the lack of emission projections for 2035, the 2018v2 EMP projections for 2032 are used to represent 2035 emissions. Emissions for 2026 were estimated by interpolating between the 2018 and 2032 emission estimates provided in the 2018v2 EMP.

iii. Onroad Sources

Onroad mobile sources are vehicles licensed to operate on public roadways, including a wide range of vehicle types, from motorcycles and passenger cars to the largest buses and trucks. For these sources, historical input data were used for modeling 2018 emissions, whereas 2026 and 2035 emissions were modeled using the EPA's MOtor Vehicle Emissions Simulator (MOVES) 4.0.1 mobile model. Modeling inputs were developed by projecting the latest available data to the needed future years. NCDAQ used local county-level, partial county-level, and State model input data in lieu of the MOVES4.0.1 default data, wherever possible, to represent local vehicle fleet and emissions characteristics more accurately.

On February 12, 2026, the EPA finalized the rescission of the GHG Endangerment Finding and repealed all greenhouse gas (GHG) emission standards for light-duty, medium-duty, and heavy-duty vehicles and engines (“Endangerment Finding Rescission Rule”).^[21] Due to this action, aspects of the State's planning assumptions from the EPA's MOVES model versions 4 MOVES4.0.1 are no longer entirely consistent with the latest information. The EPA recognizes that States have relied on MOVES4 and MOVES5, including the national default electric vehicle (EV) projections tied in part to the implementation of these now-repealed standards, in developing some SIP actions that have been submitted to the EPA.

This action was developed using MOVES4 and the latest EPA guidance on the use of MOVES in SIP development that was available at the time. Per the EPA's MOVES Policy Guidance, States “should use the latest ( printed page 60352) version of MOVES that is available at the time that a SIP is developed.” ^[22] In this guidance, the EPA also stated that an earlier version of MOVES can be used in SIP development if significant work has already been completed on a SIP using that earlier version.^[23] Therefore, the State developed this SIP based on an emissions model that the EPA expected States to use. In addition, the EPA indicated that for fuel type distributions for onroad vehicles that include estimates of EVs, States should use local data if available and could rely on the default information within the model as planning assumptions.^[24] Therefore, based on the EPA's statements in the Agency's MOVES Policy and Technical Guidance, the State reasonably relied on the assumptions in MOVES4.

As a general principle, the SIP is an iterative document, subject to various revisions over time. This is because the SIP revision process is cyclical by nature per the different obligations under the CAA. The EPA acknowledges the significant amount of time and resources required by States to develop a SIP revision. In the evaluation of this SIP submittal, the EPA is considering the modeling and information provided by North Carolina and affirming that North Carolina relied on the latest EPA model and guidance information available at the time it developed the SIP. To acknowledge and accommodate reliance interests States may have had in MOVES4 based on the EPA's statements in Agency's MOVES Policy and Technical Guidance, and to treat all States consistently that submitted SIPs prior to or shortly after the Endangerment Finding Rescission Rule where significant work had been completed, the EPA is proposing to find that North Carolina appropriately estimated onroad mobile source emissions for this SIP based on MOVES4.

iv. Nonroad Sources

The nonroad mobile source inventory contains emissions from mobile vehicles and equipment not licensed for use on public roadways. Emissions of NO_X and VOC were estimated by running the nonroad mobile source module of MOVES4.0.1. Model runs were performed for each county and year of interest. The default data were used for the input files used in the MOVES4.01 Nonroad model. The MOVES RunSpec file (wherein all modeling variables are set) was tailored to reflect North Carolina-specific information. NCDAQ estimated 2026 emissions values by interpolating between the 2018 and 2032 emissions estimates.

The 2018 NO_X and VOC emissions for the Charlotte Area, as well as the emissions for other years, were developed with methods consistent with the EPA guidance and are summarized in Tables 1 through 3 of the following subsection.

B. Maintenance Demonstration

The maintenance plan includes a maintenance demonstration that:

(i) Shows compliance with and maintenance of the 2008 8-hour ozone NAAQS by providing information to support the demonstration that current and future emissions of NO_X and VOC remain at or below 2018 emissions levels through 2035, the end of the second 10-year portion of the maintenance period.

(ii) Uses 2018 as the attainment year and includes future emissions inventory projections for 2026 and 2035.

(iii) Per 40 CFR part 93, NO_X and VOC sub-area budgets were established for the last year (2035) of the maintenance plan ( see section V below). Additionally, NCDAQ opted to establish sub-area budgets for an interim year (2018).

(iv) Provides actual (2018) and projected emissions inventories, in tons per ozone season day (tons/summer day), for the Charlotte Area, as shown in Tables 1 through 3, below.

Tables 1 through 3 summarize the 2018 and future projected emissions of NO_X and VOC from the Charlotte Area. In situations where local emissions are the primary contributor to nonattainment, the NAAQS should not be violated in the future as long as emissions from within the area remain at or below the baseline with which attainment was achieved. North Carolina has projected emissions as described previously and determined that emissions in the Charlotte Area will remain below those in 2018—the attainment year inventory for the duration of the maintenance plan.

A safety margin is the difference between the attainment level of emissions from all source categories ( i.e., point, nonpoint, onroad, and nonroad) and the projected level of emissions in the maintenance plan from all source categories.^[25] The attainment level of emissions is the level of emissions during one of the years in which the area met the NAAQS. NCDAQ selected 2018 as the attainment emissions inventory year for the Charlotte Area and calculated safety margins for the years 2018, 2026, and 2035. Table 4 displays the established safety margins for the Charlotte Area in tons per ozone season day (tons/summer day).

The State has decided to allocate a portion of the available safety margin to the 2035 budgets to allow for unanticipated growth in Vehicle Miles Traveled, changes, and uncertainty in vehicle mix assumptions, and uncertainty associated with mobile modeling. NCDAQ developed and implemented a five-step approach for determining a factor to use to calculate the amount of safety margin to allocate to the budgets for 2035. Based on this approach, NCDAQ allocated 50 percent of the total NO_X safety margin emissions and 100 percent of the total VOC safety margin emissions to the 2035 budgets. After allocation of the available safety margin, the remaining safety margin was calculated as 25.03 tons/summer day for NO_X and 0.0 tons/summer day for VOC. This allocation and the resulting available safety margin for the Charlotte Area are discussed further in section V of this notice of proposed rulemaking, along with the sub-area budgets to be used for transportation conformity purposes.

C. Monitoring Network

There are currently five ozone monitors in the bi-State Charlotte Area: one in Lincoln County, North Carolina; two in Mecklenburg County, North Carolina; one in Rowan County, North Carolina; and one in Union County, North Carolina.^[26] No monitors are located within the South Carolina portion of the bi-state Charlotte Area. Table 5 presents the design values (DV) ^[27] (in ppm) for the currently active monitors in the bi-state Charlotte Area over the 2012-2025 period.

As shown in Table 5, the design values derived from the monitors in the bi-State Charlotte Area have been below the level of the 2008 8-hour ozone NAAQS since redesignation. Furthermore, the overall ozone concentrations for the Area decreased by 15 ppb between the 2010-2012 and 2023-2025 design values at three of the five monitors (AQS ID 37-119-0041, 37-119-0046, and 37-159-0021). As the ozone levels have dropped and remain ( printed page 60354) relatively stable, it is reasonable to conclude that the bi-State Charlotte Area will not exceed the 2008 8-hour ozone NAAQS during the second 10-year maintenance period.

The EPA periodically reviews the ozone monitoring networks operated and maintained by the states in accordance with 40 CFR part 58. The network plans are submitted annually to the EPA, and network assessments are submitted every five years. NCDAQ operates a network plan with monitors within the boundary of the Charlotte Area. The annual network plan developed by NCDAQ follows a public notification and review process. The local network plan from the Mecklenburg County Air Quality (MCAQ) local air agency was also provided to the public for inspection and comment, as required by 40 CFR 58.10(d). Known potential monitor shutdowns or relocations are noted in these documents and will only be made with the approval of the EPA. No plans are underway that will affect the integrity of the ambient monitoring network in place. The current monitors are operated consistent with 40 CFR part 58, and no changes will be made that are inconsistent with 40 CFR part 58. The EPA has reviewed and approved ^[28] the North Carolina 2025-2026 Ambient Air Monitoring Network Plan.

Through state and local agencies, North Carolina has committed to continue operation of the current ozone monitors in the Charlotte Area in compliance with 40 CFR part 58, provided that sufficient funding is available for continued operation. For further details on monitoring, see the 2025-2026 Annual Monitoring Network Plan which can be found in the docket for this proposed action.

D. Verification of Continued Attainment

The State of North Carolina, through NCDAQ, has the legal authority to enforce and implement the maintenance plan for the North Carolina portion of the Area. This includes the authority to adopt, implement, and enforce any subsequent emissions control contingency measures determined to be necessary to correct future ozone attainment problems.

In addition, North Carolina has adopted State rules to implement and enforce Federal and State air pollution control requirements to ensure that ozone precursor emissions reductions are permanent and enforceable in the Charlotte Area. The State rules are codified at 15A NCAC Subchapter 2D (Air Pollution Control Requirements) and Subchapter 2Q (Air Quality Permit Procedures). The MCAQ has also adopted rules reflecting the State and Federal rules which are codified as Mecklenburg County Air Pollution Control Ordinance (MCAPCO) Article 1.0000 (Sections 1.5100-1.5700, Permitting Provisions for Air Pollution Sources; Rules and Operating Regulations) and MCAPCO Article 2.0000 (Sections 2.0100-2.2600, Air Pollution Control Regulations and Procedures).

E. Contingency Plan

CAA section 175A 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 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).

In the February 28, 2025, submittal, North Carolina affirms that all programs instituted by the State will remain enforceable and that sources are prohibited from reducing emissions controls following the redesignation of the Charlotte Area. The contingency plan included in the submittal includes a triggering mechanism to determine when contingency measures are needed and a process of developing and implementing appropriate control measures. The State includes a tertiary, a secondary, and a primary trigger to evaluate and implement contingency measures. The tertiary trigger will not be an actual violation of the 2008 8-hour ozone standard. This trigger will be a first alert as to a potential air quality problem on the horizon. The trigger will be activated when a monitor in the bi-state Charlotte Area has a 4th highest value of 0.076 ppm or greater, starting the first year after the maintenance plan has been approved. The trigger date will be 60 days from the date on which an ozone monitor in the bi-state Charlotte Area records a 4th highest value of 0.076 ppm or greater. Once the tertiary trigger is activated, the Planning Section of NCDAQ, in consultation with the South Carolina Department of Environmental Services (SCDES) ^[29] and MCAQ, shall commence analyses including meteorological evaluation, trajectory analyses of high ozone days, and emissions inventory assessment to understand why a 4th highest exceedance of the standard has occurred. Once the analyses are completed, NCDAQ will work with SCDES, MCAQ and the local air awareness program to develop an outreach plan identifying any additional voluntary measures that can be implemented. If the 4th highest exceedance occurs early in the ozone season,^[30] the NCDAQ will work with entities identified in the outreach plan to determine if the measures can be implemented during the current season; otherwise, NCDAQ will work with SCDES, MCAQ, and the local air awareness coordinator to implement the plan for the following ozone season.

The secondary trigger will then apply where no actual violation of the 2008 8-hour ozone NAAQS has occurred, but where the State finds monitored ozone levels indicating that an actual ozone NAAQS violation may be imminent. North Carolina explains that a pattern will be deemed to exist when there are two consecutive ozone seasons in which the 4th highest values are 0.076 ppm or greater at a single monitor within the Area. The trigger date will be 60 days from the date on which an ozone monitor in the bi-state Charlotte Area records a 4th highest value of 0.076 ppm or greater for which the previous season had a 4th highest value of 0.076 ppm or greater.

Finally, the primary trigger of the contingency plan will be a violation of the 2008 8-hour ozone NAAQS or when the 3-year average of the 4th highest values is equal to or greater than 0.076 ppm at a monitor in the bi-state Charlotte Area. The trigger date will be 60 days from the date on which an ozone monitor in the bi-state Charlotte Area records a 4th highest value that, ( printed page 60355) when averaged with the two previous ozone seasons' fourth highest values, results in a 3-year average equal to or greater than 0.076 ppm.

Once the primary or secondary trigger is activated, which would occur after the tertiary trigger, the Planning Section of NCDAQ, in consultation with the SCDES and MCAQ, shall commence analyses including trajectory analyses of high ozone days, and an emissions inventory assessment to determine emission control measures that will be required for maintaining the 2008 8-hour ozone standard. The analysis will include an evaluation of any future Federal, State, and local measures that will be implemented after the trigger is activated to determine their effectiveness for bringing the area into attainment and assure maintenance going forward. If deemed applicable, NCDAQ will submit to the EPA an analysis supporting the conclusion that control measures will be adequate to reduce ozone concentrations to attain and maintain the 2008 8-hour ozone NAAQS. If additional State and local control measures are determined to be necessary, NCDAQ will perform an analysis to determine the most effective measure(s) to bring the area back into attainment of and/or maintain compliance with the NAAQS. The analysis of State and local control measures will focus on NO_X controls because North Carolina is NO_X limited for ozone formation.^[31]

The measures that will be considered for adoption upon a primary or secondary trigger of the contingency plan include:

• NO_X Reasonably Available Control Technology (RACT) on stationary sources with a potential to emit less than 100 tons per year in the Charlotte Area;
• Implementation of diesel retrofit programs, including incentives for performing retrofits;
• Reinstatement of the emissions I/M program ^[32] for on-road light-duty gasoline vehicles in the counties subject to the maintenance plan; and
• Additional controls in upwind areas.

By May 1 of the year following the ozone season in which the primary or secondary trigger has been activated, North Carolina will complete sufficient analyses to begin adoption of necessary rules for ensuring attainment and maintenance of the 2008 8-hour ozone NAAQS. These rules would become effective by the following March 1 (the beginning of the ozone season) unless legislative review is required.

North Carolina commits to begin implementing as expeditiously as practicable, but no later than 24 months after the primary or secondary trigger, at least one control measure that is determined to be most appropriate for reducing NO_X emissions in order to attain and maintain the NAAQS based on the analyses performed.

The EPA proposes to find that the contingency provisions in North Carolina's second 10-year maintenance plan for the Charlotte Area for the 2008 8-hour Ozone NAAQS meet the requirements of CAA section 175A(d).

V. The EPA's Analysis of North Carolina's Proposed NO X and VOC Sub-Area Budgets for the Charlotte Area

Under CAA section 176(c), new transportation plans, programs, and projects, such as the construction of new highways, must “conform” to ( i.e., be consistent with) the part of the state's air quality plan that addresses pollution from cars and trucks. Conformity to the SIP means that transportation activities will not cause or contribute to new air quality violations, worsen existing violations, or delay timely attainment of the NAAQS or any required interim milestones. If a transportation plan does not conform, most new projects that would expand the capacity of roadways cannot go forward because they would not meet the requirements of CAA section 176(c). Regulations at 40 CFR part 93 set forth the EPA policy, criteria, and procedures for demonstrating and assuring conformity of such transportation activities to a SIP. The regional emissions analysis is one, but not the only, requirement for implementing transportation conformity. Transportation conformity is a requirement for nonattainment and maintenance areas.

Under Title I of the CAA, states are required to submit, at various times, control strategy SIPs and maintenance plans for nonattainment areas and redesignated attainment areas. These control strategy SIPs (including reasonable further progress (RFP) and attainment demonstration requirements) and maintenance plans create budgets ^[33] (or in this case, sub-area budgets) for criteria pollutants and/or their precursors to address pollution from cars and trucks. The budgets serve as a ceiling on emissions from an area's planned transportation system. The budget concept is further explained in the preamble to the November 24, 1993, Transportation Conformity Rule.^[34] The preamble also describes how to establish the budgets in the SIP and how to revise the budgets.

As part of the interagency consultation process on setting sub-area budgets,^[35] NCDAQ held three conference calls with the Charlotte Regional Transportation Planning Organization (CRTPO)-Rocky River Rural Planning Organization (RRRPO), Gaston-Cleveland-Lincoln Metropolitan Planning Organization (GCLMPO), and Cabarrus Rowan Metropolitan Planning Organization (CRMPO) to determine what years to set sub-area budgets for the second Charlotte Area maintenance plan. According to the transportation conformity rule, a maintenance plan must establish budgets for the last year of the maintenance plan (in this case, 2035). The state may set a budget for an interim year (in this case, 2026), but it is not a requirement.^[36] In the February 28, 2025, submittal, North Carolina requests that the EPA replace the 2014 and 2026 NO_X and VOC sub-area budgets associated with the first 10-year maintenance plan with the 2018 and 2035 sub-area budgets. After the EPA finds the 2018 and 2035 sub-area budgets adequate or approves them, whichever is completed first, they must be used for future conformity determinations. The previous 2014 and 2026 sub-area budgets will no longer apply for transportation conformity purposes. Tables 6 through 8 below provide the NO_X and VOC sub-area ( printed page 60356) budgets ^[37] in kilograms per day (kg/day),^[38] for 2018 and 2035.

Because the initial budget year of 2018 is also the base year for the maintenance plan inventory, there is no safety margin, therefore, no adjustments were made to the budgets for 2018. As shown in Tables 6 through 8, above, North Carolina has chosen to allocate a portion of the available safety margin to the NO_X and VOC sub-area budgets for 2035.

Through this rulemaking, the EPA is proposing to approve the 2018 and 2035 sub-area NO_X and VOC budgets for the Charlotte Area because the Agency believes that the Charlotte Area will maintain the 2008 8-hour ozone NAAQS with the emissions at the levels of the sub-area budgets. The EPA is also proposing to replace the previous 2014 and 2026 NO_X and VOC sub-area budgets from the first 10-year maintenance plan. If the EPA finalizes that replacement, the 2014 and 2026 budgets will no longer apply for transportation conformity purposes. The EPA intends to make its determination on the adequacy of the 2018 and 2035 sub-area budgets for the Charlotte Area for transportation conformity purposes in the near future by completing the adequacy process that was started on February 28, 2025. If the EPA finds the 2018 and 2035 sub-area budgets adequate or approves them, whichever is completed first, they must be used for future conformity determinations. The EPA is proposing to approve the budgets because they are consistent with maintenance of the 2008 8-hour ozone NAAQS through 2035.

VI. The EPA's Adequacy Determination for the Proposed NO X and VOC Sub-Area Budgets

When reviewing submitted “control strategy” SIPs or maintenance plans containing sub-area budgets, the EPA may affirmatively find the budgets contained therein adequate for use in determining transportation conformity. Once the EPA affirmatively finds the submitted budgets adequate for transportation conformity purposes, those budgets must be used by state and Federal agencies in determining whether proposed transportation projects conform to the SIP as required by CAA section 176(c).

The EPA's substantive criteria for determining adequacy of budgets are set out in 40 CFR 93.118(e)(4). The process for determining adequacy consists of three basic steps: Public notification of a SIP submission, a public comment period, and the EPA's adequacy determination. This process for determining the adequacy of submitted budgets for transportation conformity purposes was initially outlined in the EPA's May 14, 1999, guidance, “Conformity Guidance on Implementation of March 2, 1999, Conformity Court Decision.” ^[39] The EPA adopted regulations to codify the adequacy process in the Transportation Conformity Rule Amendments for the “New 8-Hour Ozone and PM_2.5 National Ambient Air Quality Standards and Miscellaneous Revisions for Existing Areas; Transportation Conformity Rule Amendments—Response to Court Decision and Additional Rule Change.” ^[40] Additional information on the adequacy process for transportation ( printed page 60357) conformity purposes is available in the proposed rule entitled, “Transportation Conformity Rule Amendments: Response to Court Decision and Additional Rule Changes.” ^[41]

As discussed earlier, North Carolina's second 10-year maintenance plan includes NO_X and VOC sub-area budgets for the Charlotte Area for 2018, an interim year of the maintenance plan (2026), and the last year of the maintenance plan (2035). The EPA is reviewing the NO_X and VOC sub-area budgets through the adequacy process. The Charlotte Area NO_X and VOC sub-area budgets were opened for public comment on the EPA's adequacy website on May 2, 2025, found at: www.epa.gov/​state-and-local-transportation/​adequacy-review-state-implementation-plan-sip-submissions-conformity. The EPA public comment period on adequacy for the sub-area budgets for 2018 and 2035 for the Charlotte Area closed on June 2, 2025. No comments, adverse or otherwise, were received during that public comment period.

The EPA intends to make its determination on the adequacy of the 2018 and 2035 sub-area budgets for the Charlotte Area for transportation conformity purposes in the near future by completing the adequacy process that was started on May 2, 2025. If the EPA finds the 2018 and 2035 sub-area budgets adequate or approves them, the new sub-area budgets for NO_X and VOC must be used for future transportation conformity determinations. For required regional emissions analysis that involves years 2018 through 2034, the applicable 2018 sub-area budgets will be used. For regional emissions analysis years 2035 and beyond, the 2035 sub-area budgets will be used, as defined in section V of this notice of proposed rulemaking.

VII. Effect of the EPA's Proposed Action

The EPA's proposed action establishes the basis upon which the EPA may take final action on the issues being proposed for approval. Approval of North Carolina's SIP revisions would incorporate a plan for maintaining the 2008 8-hour ozone NAAQS in the Charlotte Area through 2035 into the SIP. This second 10-year maintenance plan includes contingency measures to remedy any future violations of the 2008 8-hour ozone NAAQS and procedures for evaluation of potential violations. The second 10-year maintenance plan also removes the budgets for 2014 and 2026, associated with the first 10-year maintenance plan, and establishes new NO_X and VOC budgets for 2018 and 2035 for the Charlotte Area. The budgets are listed in Tables 6 through 8 in section V of this notice. Additionally, the EPA is notifying the public of the status of Agency's adequacy determination for the newly established Charlotte Area NO_X and VOC sub-area budgets for 2018 and 2035.

VIII. Proposed Action

The EPA is proposing to approve the second 10-year maintenance plan for the 2008 8-hour ozone NAAQS for the Charlotte Area, including the NO_X and VOC sub-area budgets for 2018 and 2035 (to replace the previous NO_X and VOC sub-area budgets for 2014 and 2026 from the first 10-year maintenance plan), into the North Carolina SIP under CAA section 175A. The second 10-year maintenance plan meets all applicable requirements for maintenance plans and related contingency provisions in CAA section 175A, including a demonstration that the Charlotte Area will continue to maintain the 2008 8-hour ozone NAAQS until August 27, 2035, the end of the 20-year maintenance period. Further, as part of this proposed action, the EPA is describing the status of its adequacy determination for the NO_X and VOC sub-area budgets for 2018 and 2035 in accordance with 40 CFR 93.118(f)(1). Within 24 months from the publication date of the EPA's final rule for this action (if the EPA approves this maintenance plan and the underlying budgets), or the effective date of the EPA's adequacy determination for the budgets, whichever is earlier, the transportation partners ^[42] will need to demonstrate conformity to the new NO_X and VOC sub-area budgets pursuant to 40 CFR 93.104(e)(3).

IX. Statutory and Executive Order Reviews

Under the CAA, the Administrator is required to approve a SIP submission that complies with the provisions of the CAA and applicable Federal regulations.^[43] Thus, in reviewing SIP submissions, the EPA's role is to approve state choices, provided that they meet the criteria of the CAA. Accordingly, this proposed action merely proposes to approve 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 underExecutive Order 12866 (58 FR 51735, October 4, 1993);
• Is not anExecutive Order 14192 (90 FR 9065, February 6, 2025) regulatory action because this 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.);
• 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 CAA.

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

(Authority: 42 U.S.C. 7401 et seq.)

91 FR 60349