SUPPLEMENTARY INFORMATION:

Notice of proposed rulemaking (NPRM) acronyms and abbreviations. The EPA uses multiple acronyms and terms in this NPRM. While this list may not be exhaustive, to ease the reading of this preamble and for reference purposes, the EPA defines the following terms and acronyms here:

CAA Clean Air Act ( printed page 53559)

CFR Code of Federal Regulations

CO Carbon Monoxide

EPA Environmental Protection Agency

FR Federal Register

MMBtu Million British Thermal Units

MSA Metropolitan Statistical Area

NAAQS National Ambient Air Quality Standard or Standards

NEI National Emissions Inventory

NO_X  Nitrogen Oxides

NNSR Nonattainment New Source Review

NPRM Notice of Proposed Rulemaking

NSPS New Source Performance Standards

NSR New Source Review

PM Particulate Matter

PM_2.5  Fine PM

PM₁₀  Coarse PM

PSD Prevention of Significant Deterioration

PTE Potential to Emit

SIP State Implementation Plan

SO₂  Sulfur Dioxide

TPY Tons Per Year

VOC Volatile Organic Compound

Table of Contents

I. Executive Summary

A. What action is the EPA taking?

B. What is the legal authority and what are the requirements?

II. Proposed Action

III. Background

A. Minor NSR Program Background

B. South Carolina's Minor Source Permitting Program

C. The EPA's August 17, 2017, and January 21, 2025, Proposals

IV. Summary of South Carolina's Submittals

V. The EPA's Evaluation of the State's Submittals

A. Subparagraph II(B)(2)(h)

B. Paragraph II(K)(5)

C. South Carolina's CAA Section 110(l) Demonstration

1. CAA Section 110(l) Demonstration—South Carolina's Minor Source Permitting Exemptions

2. CAA Section 110(l) Demonstration—South Carolina's Automatic Exemption Thresholds

3. The EPA's Analysis

i. Ozone, NO₂, and CO NAAQS

1. Ozone NAAQS

2. NO₂ NAAQS

3. CO NAAQS

4. 2020 NO_X, VOCs, and CO NEI Data

5. Ozone, NO₂, and CO NAAQS Analysis

ii. Fine Particulate Matter (PM_2.5), SO₂, and NO₂ NAAQS

1. PM_2.5 NAAQS

2. SO₂ NAAQS

3. NO₂ NAAQS

4. 2020 PM_2.5, SO₂, and NO₂ NEI Data

5. PM_2.5, SO₂, and NO₂ Analysis

iii. Coarse Particulate Matter (PM₁₀) NAAQS

1. PM₁₀ NAAQS

2. 2020 PM₁₀ NEI Data

3. PM₁₀ Analysis

4. Summary of the EPA's Findings From South Carolina's CAA Section 110(l) Demonstration

VI. Incorporation by Reference

VII. Statutory and Executive Order Reviews

I. Executive Summary

A. What action is the EPA taking?

On October 1, 2007, July 18, 2011, August 8, 2014, and April 24, 2020, SC DHEC ^[1] submitted SIP revisions to the EPA for approval that include changes to South Carolina's minor source permitting regulations to revise the State's federally approved minor source preconstruction and operating permit program. This federally approved program requires minor stationary sources of air pollutants planning to construct or modify to first obtain a construction permit and then obtain and maintain operating permits in accordance with the South Carolina Code of Regulations Annotated (S.C. Code Ann. Regs.) (hereinafter “Regulation”) 61-62.1, Section II, Permit Requirements. The portion of the SIP-approved minor source permitting program covering construction permits is generally referred to as the minor NSR program.^[2]

SC DES subsequently submitted a SIP revision on July 23, 2025, updating references to reflect the restructuring of South Carolina DHEC to the South Carolina Department of Public Health and the South Carolina DES.^[3] As discussed in the July 23, 2025, SIP submittal and in a letter from South Carolina to the EPA Region 4 dated June 20, 2024, all functions, powers, and duties of the environmental divisions, offices, and programs of DHEC are retained and continued in full force and effect under DES. This includes the authority to administer and enforce SIPs. Therefore, the changes within Regulation 61-62.1, Section II, reflecting the restructuring, are merely administrative in nature.

On May 13, 2026, SC DES submitted supplemental materials, including a letter requesting that the EPA conditionally approve portions of the State's minor source permitting SIP revisions in Regulation 61-62.1 based on a commitment under CAA section 110(k)(4) to adopt and submit corrective revisions to portions of the SIP provisions currently before the EPA no later than one year after the EPA's conditional approval of South Carolina's submissions. Additionally, the supplemental materials included a CAA section 110(l) demonstration to support the corrective changes that the State intended to submit in a corrective SIP revision. The CAA section 110(l) demonstration also applies to a portion of the SIP submittals for which the State did not request conditional approval.

Subsequently, on July 21, 2026,^[4] SC DES submitted a letter removing from EPA consideration the subset of provisions in Regulation 61-62.1, Section II, for which the State, in its May 13, 2026, letter, requested conditional approval. That letter supersedes the May 13, 2026, request for conditional approval of those same provisions. Specifically, the July 21, 2026, letter removes from EPA consideration two sentences within subparagraph II(B)(2)(h) ^[5] and paragraphs II(B)(3), II(B)(5), and II(B)(6), as submitted through the April 24, 2020, SIP revision. South Carolina states that “the specific text . . . is not before EPA at this time.”

In this proposed action, the EPA is proposing only to approve the portions of the SIP revisions that make changes to South Carolina's minor NSR requirements, as detailed herein. Specifically, the EPA is proposing to proposing to approve minor, administrative, and clarifying changes to South Carolina Regulation 61-62.1, Section II, Permit Requirements, subparagraph II(B)(2)(h), as described below, and to approve changes to the State's exemptions from the requirement to obtain a permit at subparagraph II(B)(2)(h), except for the second and third sentences of subparagraph ( printed page 53560) II(B)(2)(h),^[6] for the reasons discussed in section V of this NPRM. Additionally, the EPA is also proposing to approve minor and ministerial changes to South Carolina Regulation 61-62.1, Section II, Permit Requirements, paragraph II(K)(5), to reflect the restructuring of SC DHEC to the South Carolina Department of Public Health and SC DES. Section V.C., below, provides the EPA's analysis of the State's CAA section 110(l) non-interference demonstration for the portions that the EPA is proposing to approve.^[7]

B. What is the legal authority and what are the requirements?

Under CAA section 110(k)(3), the EPA has a statutory obligation to approve SIP submittals that meet all applicable CAA requirements.^[8] Pursuant to CAA section 110(k)(3), the EPA may approve portions of a SIP submittal if those portions meet all the applicable CAA requirements.

Additionally, under CAA section 110(l), the EPA cannot approve a SIP revision if it would interfere with any applicable requirement concerning attainment and reasonable further progress (as defined by CAA section 171), or any other applicable requirement of the CAA.^[9] Section V.C. of this notice of proposed rulemaking NPRM discusses South Carolina's CAA section 110(l) analysis supporting the changes proposed for approval. The EPA evaluates CAA section 110(l) non-interference demonstrations on a case-by-case basis considering the circumstances of each SIP revision.

II. Proposed Action

The EPA is proposing to approve minor, administrative, and clarifying changes to South Carolina Regulation 61-62.1, Section II, Permit Requirements, subparagraph II(B)(2)(h), as described above, and to approve changes to the State's exemptions from the requirement to obtain a permit at subparagraph II(B)(2)(h), except for the second and third sentences of subparagraph II(B)(2)(h).^[10] The EPA is proposing to approve the portions of the SIP revisions consisting of the aforementioned changes to subsection II(B) for the reasons discussed in section V of this NPRM. Additionally, the EPA is also proposing to approve minor and ministerial changes to South Carolina Regulation 61-62.1, Section II, Permit Requirements, paragraph II(K)(5), to reflect the restructuring of SC DHEC to the South Carolina Department of Public Health and SC DES.

III. Background

A. Minor NSR Program Background

CAA section 110(a)(2)(C) requires that SIPs include a program to regulate the construction and modification of any stationary source as necessary to assure that the national ambient air quality standards (NAAQS) are achieved. Additionally, CAA section 110(a)(2)(C) cites to more detailed CAA permitting requirements that pertain to the construction and modification of major sources of air pollution. These CAA requirements for regulating the construction and modification of stationary sources are known collectively as the NSR program. The NSR program is comprised of the Prevention of Significant Deterioration (PSD) program, established in part C of title I of the CAA and applicable to major stationary sources and major modifications in attainment and unclassifiable areas; the Nonattainment NSR (NNSR) program, established in part D of title I of the CAA and applicable to major stationary sources and major modifications located in nonattainment areas; and the minor NSR program, applicable to a universe of new sources and modifications, as defined in a State's SIP, that fall below major NSR thresholds in any area.^[11] Pursuant to CAA section 110(a)(2)(C) and 40 CFR 51.160, SIPs must contain a minor NSR program regulating the modification and construction of stationary sources as necessary to assure that NAAQS are achieved.

The minor NSR program is established under CAA section 110(a)(2)(C). Section 110(a)(2)(C) is the statutory foundation for the portion of the Code of Federal Regulations (CFR) at 40 CFR 51.160-164, which generally applies to all NSR programs but, because of more specific implementing regulations for the PSD and NNSR programs found, respectively, at 40 CFR 51.166 and 40 CFR 51.165, the implementing regulations at 40 CFR 51.160-51.164 serve primarily as the basis for the EPA's evaluation of minor NSR programs. The requirements at 40 CFR 51.160-164 apply to all new minor sources and modifications under a state's minor NSR program in accordance with 40 CFR 51.160.^[12] States have discretion to define the scope of their minor NSR programs within the bounds of CAA section 110 and 40 CFR 51.160-164. The EPA's implementing regulations at 40 CFR 51.160 set forth requirements for “legally enforceable procedures” applicable to minor NSR programs. 40 CFR 51.160(a) requires SIPs to set forth minor NSR programs with legally enforceable procedures that enable a state to determine whether the construction or modification of a source will result in a violation of applicable portions of the control strategy or interference with attainment or maintenance of the NAAQS. 40 CFR 51.160(e) requires such programs to identify the types and sizes of sources subject to review and discuss the basis for determining which sources are subject. Where a state has a defined minor NSR program under 51.160, subject sources cannot subsequently be exempt from that program's requirements barring a demonstration under 51.160(e) that such sources are not needed for the state's program to meet the requirements of section 110(a)(2)(A) and 40 CFR 51.160.

B. South Carolina's Minor Source Permitting Program

South Carolina has a SIP-approved minor source permitting program at Regulation 61-62.1, Section II, that includes requirements for minor NSR permitting.^[13] In the October 1, 2007, SIP revision submittal letter, the State explains that the revisions to Section II clarify and streamline the State's SIP-approved permitting program, which requires stationary sources planning to construct, alter, or add to a source of air pollutants to first obtain a construction permit from the State and to request an ( printed page 53561) operating permit prior to placing the new or altered source into operation. Minor source permitting programs, such as South Carolina's SIP-approved program under Section II, apply to stationary sources that do not require major source permits, e.g., PSD, NNSR, and/or Title V permits.

South Carolina's SIP-approved minor source preconstruction permitting program covers true minor sources ( i.e., sources where the potential to emit (PTE) of regulated NSR pollutants is below applicable major stationary source or major modification thresholds without any enforceable emission limitations to constrain emissions) and synthetic minor sources ( i.e., sources that accept enforceable emission limitations to restrict the PTE of regulated NSR pollutants below major source and major modification applicability thresholds). The EPA originally approved South Carolina's minor NSR regulations into the SIP in 1972 and approved subsequent revisions through June 2, 2008, with additional changes approved on October 13, 2022.^[14]

C. The EPA's August 17, 2017, and January 21, 2025, Proposals

Through NPRMs published on August 17, 2017,^[15] and January 21, 2025,^[16] the EPA proposed to act on changes to South Carolina's minor source permitting provisions involving, in part, the State's minor NSR program regulations. In the August 17, 2017, NPRM, the EPA proposed to approve SIP revisions submitted by the State on October 1, 2007, July 18, 2011, June 17, 2013, August 8, 2014, January 20, 2016, and July 27, 2016. The EPA received adverse comments on portions of the 2017 NPRM. On January 21, 2025, the EPA proposed to disapprove certain provisions that received adverse comment and certain provisions that did not receive adverse comment. In the same NPRM, the Agency also re-proposed approval of certain provisions that received adverse comment. Additionally, the Agency did not reconsider or seek additional comments on certain provisions evaluated in the 2017 NPRM that did not receive comment. In that 2025 NPRM, the EPA also proposed to act on a subsequent SIP revision submitted by the State on April 24, 2020. The EPA's analyses and rationales for those proposed actions are described in the respective 2017 and 2025 NPRMs. Information specific to the August 17, 2017, NPRM, including comments received, is available in Docket No. EPA-R04-OAR-2017-0359.^[17] Docket No. EPA-R04-OAR-2024-0241 contains information specific to the January 21, 2025, NPRM, including comments received.^[18]

In this proposed action, the EPA is not reconsidering or seeking additional comment on certain provisions evaluated in the August 17, 2017, NPRM that did not receive comment.^[19] Likewise, the EPA is also not reconsidering or seeking additional comment on certain provisions evaluated in the January 21, 2025, NPRM that did not receive comment.^[20]

In this NPRM, the EPA is proposing to approve portions of South Carolina's minor source permitting SIP revisions that were proposed for disapproval in the January 21, 2025, NPRM. Specifically, in this NPRM, the EPA is proposing to approve changes to a portion of Regulation 61-62.1, subparagraph II(B)(2)(h) submitted by the State on the following dates: October 1, 2007; July 18, 2011; August 8, 2014; and April 24, 2020.^[21 22]

Furthermore, as described above, SC DES submitted a SIP revision on July 23, 2025, which includes edits in the State's minor source permitting regulation merely to reflect the administrative restructuring of the State's public health and environmental agencies, from DHEC to the Department of Public Health and to SC DES. Therefore, in this NPRM, the EPA is proposing to approve changes to reflect this restructuring within Regulation 61-62.1, paragraph II(K)(5), submitted on July 23, 2025.^[23]

The EPA's analysis of the changes proposed for approval in the previously noted submittals is discussed below.

IV. Summary of South Carolina's Submittals

In this NPRM, the EPA is proposing to approve portions of South Carolina's minor source permitting regulation as submitted in several SIP revisions. The changes cover recodification of portions of the regulation, changes to the scope of sources subject to minor source permitting, and minor and administrative changes to the affected portions of the rule. The following paragraphs describe the changes under consideration in this NPRM in greater detail.

The October 1, 2007, SIP revision revises the State's minor NSR exemption provisions. The 2007 SIP revision renumbers subsection II(F), “Exemptions” to subsection II(B) and revises the subsection title to “Exemptions From the Requirement to Obtain a Construction Permit.” In the 2007 SIP revision, subsection II(B), “Operating Permit,” in the existing SIP is renumbered to subsection II(F). The EPA is not proposing to act on subsection II(F) in this NPRM.^[24] The renumbered subsection II(B), “Exemptions,” sets forth exemptions from the minor source preconstruction permitting program requirements. The October 1, 2007, SIP revision also renumbers subparagraph II(F)(2)(g) to ( printed page 53562) II(B)(2)(h) and expands the existing SIP-approved exemptions from minor NSR permitting therein for sources with uncontrolled emissions of particulate matter (PM) less than one pound per hour (lb/hour) and volatile organic compounds (VOCs) less than 1,000 lb/month to include sources with uncontrolled emissions of sulfur dioxide (SO₂), nitrogen oxides (NO_X), and carbon monoxide (CO) less than one lb/hr. The 2007 SIP revision also modifies the exemption language which requires sources to submit information to the State and currently provides that the State will determine whether the source needs a permit, taking into consideration certain factors to instead provide that sources may require subsequent construction or operating permit review to ensure the NAAQS are not affected and to note that information on exemptions for air toxic pollutants is found in Regulation 61-62.5, Standard No. 8.

The July 18, 2011, SIP revision revises subparagraph II(B)(2)(h) by adding language requiring that sources maintain, and provide to the State on request, emissions calculations and other information needed to document qualification for the exemption. The August 8, 2014, SIP revision further revises subparagraph II(B)(2)(h) to clarify that uncontrolled emission rate means uncontrolled PTE and revises the exemption thresholds for PM, SO₂, NO_X, and CO from one lb/hour to five tons per year (tpy).

In addition to the changes described above, the EPA is proposing to approve minor, administrative, and clarifying edits to subparagraph II(B)(2)(h) submitted through the April 24, 2020, SIP revision, including formatting updates, administrative and minor language changes, and restructuring edits. Finally, the EPA is proposing to approve ministerial changes to paragraph II(K)(5) to reflect the updated structure of South Carolina's environmental agency, SC DES, submitted on July 23, 2025. The EPA is proposing to approve these minor and editorial changes because they are consistent with CAA section 110.

V. The EPA's Evaluation of the State's Submittals

A. Subparagraph II(B)(2)(h)

As noted previously, SC DES submitted changes to recodify and revise subparagraph II(F)(2)(g) in the October 1, 2007, July 18, 2011, and August 8, 2014, submittals. Consistent with South Carolina's May 13, 2026, and July 21, 2026, requests, the EPA is proposing to approve the following text into the SIP under subparagraph II(B)(2)(h):

Sources with a total uncontrolled potential to emit (PTE) of less than five (5) tons per year each of particulates, sulfur dioxide, nitrogen oxides, and carbon monoxide; and a total uncontrolled PTE of less than 1000 pounds per month (lbs/month) of VOCs will not require construction permits. However, these sources may be required to be included in any subsequent construction or operating permit review to ensure that there is no cause or contribution to an exceedance of any ambient air quality standard or limit. For toxic air pollutant exemptions, refer to Regulation 61-62.5, Standard No. 8. Emissions calculations and any other information necessary to document qualification for this exemption must be maintained onsite and provided to the Department upon request.

The EPA is also proposing to approve the change to subparagraph II(B)(2)(h) transmitted in the April 24, 2020, submittal placing the alphanumeric provision divider in parentheses. Thus, if the EPA takes final action to approve the portion of subparagraph II(B)(2)(h) which remains before the Agency, the following phrase will be excluded from the SIP: “Unless otherwise exempt, sources may be exempted under this section at higher emission levels if there is a demonstration that there are no applicable limits or requirements. These applicable requirements include federally applicable limits or requirements.”

B. Paragraph II(K)(5)

Subsection II(K) sets forth factors that the State will consider in determining whether to impose alternative emissions limits, compliance schedules, or other restrictions. South Carolina previously submitted changes to subsection II(K), which the EPA proposed to approve in the January 21, 2025, NPRM. Subsequently, the State submitted final changes to various regulations on July 23, 2025, to reflect the restructuring of South Carolina DHEC to the South Carolina Department of Public Health and the South Carolina DES. Consistent with the State's request in the July 23, 2025, submittal, the EPA is proposing to approve changes to remove the phrase “Upon approval by the Board” and to replace “this” with “the” in the second sentence of paragraph II(K)(5). Thus, if the EPA takes final action to approve these changes, the revised paragraph II(K)(5) text would read “Any request under this section will be subjected to public notice and opportunity for a public hearing. The recommendations of the Department shall be sent to the Administrator, or his designated representative, for approval or disapproval.”

The EPA is proposing to approve these changes because they are administrative in nature and therefore would not interfere with any applicable requirement concerning attainment and reasonable further progress or any other applicable requirement of the CAA.

C. South Carolina's CAA Section 110(l) Demonstration

As previously described, on May 13, 2026, SC DES submitted a supplemental CAA section 110(l) demonstration in support of the State's minor source permitting exemptions requested for approval and its anticipated corrections to the provisions and portions thereof requested for conditional approval.^[25]

Portions of the demonstration apply to the section of subparagraph II(B)(2)(h), as revised through the April 24, 2020, SIP revision, that sets forth the previously described five tpy total uncontrolled PTE exemption thresholds for sources of PM, SO₂, NO_X, and CO and the 1,000 lb/month uncontrolled PTE exemption threshold for sources of VOCs. Additionally, portions of the demonstration apply to the State's anticipated corrections to subparagraph II(B)(2)(h) applicable to the case-by-case exemption for sources with potential emissions greater than the five tpy total uncontrolled PTE exemption thresholds for PM, SO₂, NO_X, and CO and the 1,000 lb/month total uncontrolled PTE exemption threshold for VOCs, which South Carolina committed, in its May 13, 2026, letter, to revise and submit to the EPA in a SIP revision no later than 12 months from a final conditional approval.

However, as detailed above, the State submitted a letter on July 21, 2026, letter which supersedes the May 13, 2026, request for conditional approval of the previously described case-by-case exemption within subparagraph II(B)(2)(h) and related provisions at paragraphs II(B)(3), II(B)(5), and II(B)(6), and instead South Carolina has removed the subset of regulations it requested to be conditionally approved from the EPA's consideration. The Agency's assessment in this NPRM focuses on the State's CAA section 110(l) demonstration supporting the State's exemptions under its minor NSR program as it relates to the defined exemptions of five tpy for PM, NO_X, ( printed page 53563) SO₂ , and CO and 1,000 lb/month for VOCs.^[26]

1. CAA Section 110(l) Demonstration—South Carolina's Minor Source Permitting Exemptions

Generally, South Carolina's CAA section 110(l) demonstration asserts that the exemptions included in the State's regulations are consistent with CAA sections 110(l) and 110(a)(2)(C) and the implementing regulations for minor NSR programs in SIPs under 40 CFR 51.160(a)-(b) and (e).^[27] Further, the State explains that these exemptions include appropriate safeguards to ensure that any exempt source: will comply with the NAAQS; will be below major source or major modification thresholds; and will not be subject to applicable requirements that would necessitate a source permit.

South Carolina's CAA section 110(l) demonstration includes emissions data to support its exemptions, which the State asserts indicates that the exemptions are well-founded without having any meaningful emissions impact. Specifically, the State's demonstration includes a figure juxtaposing economic and aggregate emissions trends with pollutant trends; ^[28] 2020 national emissions inventory (NEI) data pie charts by source category and sector; ^[29] long-term air quality design value trends by highest metropolitan statistical area (MSA) monitor; ^[30] and triennial title V major source emissions from 2008 through 2023.^[31]

First, the State points to economic and aggregate emissions trends from 2008-2024 juxtaposed with common pollutants to support its request for approval of the new five tpy threshold exemptions for SO₂, NO_X , and CO and the revised five tpy threshold exemption for PM. The State explains that, since 2008, air quality monitoring and emissions inventory trends reflect emissions reductions. SC DES also notes that all State ambient air quality monitors reflecting all emissions demonstrate attainment for all pollutants and further explains that, despite significant population growth and resulting higher mobile source emissions, aggregate emissions continue to fall,^[32] and the State remains in attainment for all criteria pollutants.^[33] SC DES also notes that, between 2008 and 2024, the State's gross domestic product (GDP) increased 117 percent, but total emissions of common air pollutants fell 37 percent.

Next, the State points to emissions data in Appendix A to its CAA section 110(l) demonstration, which categorizes NEI emissions in pie charts by source type and sector for NO_X, PM, SO₂ , VOCs, and CO to broadly support that exempt emissions represent an insignificant fraction of State emissions and do not affect ongoing NAAQS attainment. The percentages of pollutant emissions by various sectors in the figures under Appendix A are derived from 2020 NEI emissions data divided into the following source categories: point,^[34] nonpoint, onroad, and nonroad sources. Stationary sources subject to the State's minor NSR program and any sources qualifying for exemptions from minor NSR permitting fall into some sectors of the nonpoint source category ( e.g., stationary source fuel combustion and industrial processes), which includes emissions estimates for sources which are individually too small to report as point sources. Other nonpoint emissions sectors include agricultural emissions, fires, biogenic emissions, commercial marine vessels, locomotives, and road dust. SC DES explains that a limited portion of NEI emissions in 2020 were attributable to minor stationary sources and asserts its available 2020 NEI data indicates that emissions that would be exempt with approval of the requested SIP revisions would comprise a very small portion of overall emissions in the State. The State also notes examples of existing SIP exemptions such as categorical exemptions for certain types and capacities of fuel combustion sources and the existing SIP-approved exemption thresholds for PM and VOCs. SC DES further asserts that, while nonpoint source emissions include some industrial minor stationary sources, those emissions from sources that would be exempt represent such a minimal contribution to total emissions that this small aspect of the Department's minor source permitting program does not have any meaningful emissions impact. The State concludes that emissions attributable to the exemption provisions under review comprise “necessarily a sliver” of the State's emissions as shown in the NEI.

Next, South Carolina points to ambient air quality data in Appendix B to its CAA section 110(l) demonstration, which includes long-term air quality design value trends across the State for ozone, PM_, SO₂, and NO₂ from 2008 through 2025 and for CO from 2010 through 2025, corresponding to the highest monitor design value in each MSA by pollutant and its corresponding NAAQS.^[35] The State also points to emissions data from title V point sources in Appendix C to the demonstration, which contains the State's triennial total point source emissions for CO, PM, NO_X, SO₂, and VOCs from 2008 through 2023. As previously noted, the State explains that since 2008, air quality monitoring and emissions inventory trends reflect emissions reductions across the state, and that all ambient air quality monitors reflecting all emissions demonstrate attainment for all criteria pollutants. The State points to the NEI and other collective data as amply demonstrating that any sources and emissions exempt under these provisions do not and will not affect its attainment. The State's 2020 NEI data for NO_X, PM, SO₂, VOC, and CO emissions; design value trends for ozone, PM, SO₂, CO, and NO₂; and other relevant data are described further in Subsection V.C.3. of this NPRM, which contain the EPA's analyses of the State's emissions data and air quality.

Finally, the State points out that it has implemented these exemptions for more than a decade.^[36] The State asserts that, because its SIP revisions which are the subject of this NPRM are focused on reducing regulatory burdens on industrial sources and the reviewing authority where there was no environmental benefit, these exemptions are a logical step. SC DES asserts that it has and will retain a ( printed page 53564) robust minor source permitting program ^[37] and that the substantial permitting and regulation of minor stationary sources under its program will not change with the EPA's action on the pending SIP revisions.

2. CAA Section 110(l) Demonstration—South Carolina's Automatic Exemption Thresholds

In this section, the EPA discusses its analysis of the portion of the State's CAA section 110(l) demonstration specifically focused on supporting the addition of the five tpy total uncontrolled PTE exemption thresholds for sources of SO₂, NO_X, and CO and the slightly increased exemption threshold for PM, from one lb/hour to five tpy, which the EPA is proposing to approve in this NPRM. The current SIP-approved exemption, found at subparagraph II(F)(2)(g), applies to sources with an uncontrolled PM emission rate less than one lb/hour and/or an uncontrolled VOC emission rate less than 1,000 lb/month. SC DES asserts its “2007 SIP submittal narrowed this exemption” to include only sources with total uncontrolled PTE less than 1,000 lb/month for VOCs and one lb/hour for PM, SO_2, NO_X, and CO (as opposed to exempting sources based solely on uncontrolled PM and/or VOC emission rates, regardless of SO₂, NO_X , and CO emissions under the current SIP-approved rule).^[38] The State adds that, although the August 8, 2014, SIP revision increased the one lb/hour total uncontrolled emission rate exemption thresholds for PM, SO₂, NO_X, and CO from the 2007 revision to five tpy total uncontrolled PTE, the existing PM SIP limit of one lb/hour is “functionally close” to five tpy (1.14 lb/hour), from a mathematical standpoint. Further, it explains that “the added mandate” to exempt only sources that also have total uncontrolled PTE below five tpy SO₂, NO_X, and CO “narrows the scope of sources potentially subject to exemption relative to the approved SIP,” describing the collective changes as “largely SIP-strengthening in nature” compared to the existing exemption, which the State asserts “considers only VOC and PM emissions, as opposed to VOC, PM, SO₂, NO_X, and CO.” The EPA notes that the current SIP does not include specific exemptions from permitting for sources emitting SO₂, NO_X, or CO. The Agency must therefore evaluate the change to the SIP to include the addition of exemptions for sources of these emissions. Regardless, the State's CAA section 110(l) demonstration evaluates the revised exemption to support the five tpy thresholds for each of these pollutants. Finally, to support the new five tpy total uncontrolled PTE exemption thresholds for sources of SO₂, NO_X, and CO, and the slightly increased exemption threshold for PM, South Carolina again points out that it has implemented the five tpy exemption for PM, SO₂, NO_X, and CO over more than a decade with no issues or concerns.

To demonstrate that the revisions would not interfere with attainment or maintenance of the NAAQS, the State points to its emissions data ( i.e., economic and aggregate emissions trends); 2020 NEI pie charts; and long term design values. South Carolina explains that it has maintained attainment of all criteria pollutant standards, despite increases in population and traffic, and asserts that an overall decrease in emissions is reflected in emissions inventory and ambient monitoring data. Based on its data, the State asserts that the level of emissions exempted from permitting due to the revised exemption threshold from one lb/hour for PM to five tpy and the added five tpy exemption thresholds for SO₂, NO_X, and CO has had a statistically insignificant effect on emissions and does not interfere with ongoing NAAQS attainment. The State further asserts that, although precise percentages cannot be quantified, its emissions data indicates that sources below the five tpy exemption thresholds represent a minimal fraction of overall emissions and are inconsequential to the State's ongoing NAAQS attainment.

To further support the five tpy total uncontrolled PTE exemption thresholds for sources of PM, SO₂, NO_X , and CO, the State points to the EPA's Tribal minor NSR FIP. The State cites to the EPA's Tribal minor NSR thresholds, under which sources with lower emissions would typically be exempt from minor NSR, and the Agency's rationale in the preamble to the FIP supporting those thresholds.^[39] Specifically, SC DES asserts that the EPA has recognized the appropriateness of such exemption thresholds by establishing similar, including broader, thresholds for exemption from the federal Tribal minor NSR program. The State points to the Agency's Tribal minor NSR exemption thresholds for sources in attainment areas with CO, NO_X, SO₂ , PM, and VOC emissions.^[40] It also points to the portion of that rulemaking where the EPA stated its belief that sources with emissions below those thresholds will be inconsequential to attainment or maintenance of the NAAQS, based on findings from a national source distribution analysis; that the thresholds would promote an effective balance between environmental protection and source burden; and that, because similar thresholds were included in many minor NSR programs in surrounding States, the thresholds would level the playing field with the surrounding state programs and result in a more cost-effective program by reducing source and reviewing authority burdens.^[41] South Carolina asserts that this rationale for the Tribal minor NSR thresholds applies equally in South Carolina and supports the acceptability of the State's five tpy exemption thresholds for PM, SO₂, NO_X, and CO to reduce source and reviewing authority burdens. The State maintains that its exemption thresholds are comparable to and in some cases narrower than the Tribal minor NSR thresholds and asserts that the revised exemption allows South Carolina to focus its permitting efforts on activities that account for most of the State's regulated emissions.

3. The EPA's Analysis

As previously noted, South Carolina's CAA section 110(l) demonstration evaluates the revised exemption to support the five tpy thresholds for PM, SO₂, NO_X, and CO. For the EPA's analysis of South Carolina's emissions data and air quality with respect to the impacts the five tpy PM, SO₂, NO_X, and CO exemption thresholds are likely to have on its ability to maintain compliance with the ozone, NO₂, CO, PM_2.5, PM₁₀, and SO₂ NAAQS, see Section V.C.3. in this NPRM, below.

South Carolina asserts that the exemption threshold for PM, one lb/hour is functionally close to five tpy, mathematically. The EPA agrees that, when considering uncontrolled PTE, a maximum potential emission rate of one lb/hour (equivalent to 4.38 tpy over the year) is not considerably different than the revised allowable emission rate of 1.14 lb/hour (derived from the five tpy threshold). Additionally, the phrase “total uncontrolled PTE” does not account for any possible controls or limits that sources would have in place. This means that the exemption does not ( printed page 53565) apply to sources with synthetic limits or other control equipment that restricts the maximum potential emissions to less than five tpy. Thus, the 14 percent increase in allowable emission rate for PM remains small, close to the original one lb/hour threshold, and the universe of sources exempt from construction permitting is not likely to be greatly increased as a result of this specific change. The State asserts that the EPA's Tribal minor NSR thresholds support its above-described exemption thresholds for PM, SO₂, NO_X , CO, and VOCs and that the Agency's supporting rationale set forth in the related FIP applies equally in South Carolina, supporting the acceptability of those exemption thresholds to reduce source and reviewing authority burdens. As the State notes, the EPA set similar, and in some cases, higher thresholds for federal permitting of minor NSR sources in Indian Country where the EPA is the permitting authority and broadly considered the applicability thresholds in state minor NSR permitting programs. The EPA also considered a balance between environmental benefit and program efficiency.^[42] The State asserts that this rationale is applicable in South Carolina and mentions the need to reduce administrative burden on the sources and the reviewing authority to allow SC DES to focus permitting efforts on those activities accounting for most of the regulated emissions outside mobile emissions. The EPA agrees that, for similar reasons that supported the adoption of specific emission thresholds for the Tribal Minor NSR FIP, the revisions proposed for approval are consistent with applicable CAA requirements. The EPA agrees that with South Carolina's current air quality status as attainment or attainment/unclassifiable for all NAAQS, and the EPA further agrees that with no violations of the applicable NAAQS at any air quality monitors in the State,^[43] five tpy is an appropriate PTE at which to set the scope of the minor NSR preconstruction review program pursuant to 40 CFR 51.160(e) for these pollutants in South Carolina.^[44] See Section V.C.3. for analysis of the historical compliance with and margins available to the SO₂, NO₂, CO, ozone, and PM NAAQS and comparisons between the estimated emissions from the categories of sources subject to the state's minor NSR program (including sources that would be exempt from that program) and emissions from other sources in the State.

i. Ozone, NO₂, and CO NAAQS

This section discusses South Carolina's emissions and air quality data with respect to the ozone, NO₂, and CO NAAQS. Specifically, in this section, the EPA evaluates the State's ozone, NO₂, and CO NAAQS attainment history; long term and recent ozone, NO₂, and CO air quality design values and NAAQS margins; and 2020 NEI data for ozone precursors.

1. Ozone NAAQS

VOCs and NO_X comprise two main classes of precursor pollutants to tropospheric ( i.e., ground-level) ozone.^[45] When an area has lower levels of sunlight resulting in slower photochemical formation of ozone and NO_X concentrations in excess compared to VOCs, the area is considered a VOC-limited regime. In contrast, when an area has NO_X concentrations that are generally low compared to VOCs and is generally warm and sunny, resulting in relatively faster NO_X photochemistry, the area is considered a NO_X -limited regime. NO_X -limited conditions are more common in portions of the country with high biogenic VOC emissions like the Southeast. While anthropogenic sources are important for VOC emissions, in some locations at certain times ( e.g., Southeastern states in the summer), the majority of VOC emissions come from vegetation. In Southeastern rural areas, the vast majority of VOC emissions come from plants and trees (biogenic emissions).^[46] South Carolina's demonstration references a 2020 EPA integrated science assessment for ozone ^[47] and a study of ground-level ozone chemical formation ^[48] to assert that the State is NO_X -limited. The State asserts that a significant majority of VOC emissions in South Carolina derive from biogenic sources, and as a result, ground-level ozone in the State is primarily and most effectively addressed through control of NO_X.

Since its original promulgation in 1971, the EPA has revised the ozone NAAQS several times. The EPA promulgated the first primary and secondary ozone NAAQS, a 0.12 parts per million (ppm) 1-hour standard, on February 8, 1979.^[49 50] On November 6, 1991, the EPA classified Cherokee County, South Carolina, as a Marginal ozone nonattainment area for the 1979 1-hour ozone NAAQS, effective January 6, 1992.^[51] On December 15, 1992, the EPA redesignated Cherokee County to attainment and classified it as a maintenance area, effective February 16, 1993.^[52]

The EPA promulgated 8-hour primary and secondary ozone standards of 0.080 ppm on July 18, 1997, effective September 16, 1997.^[53 54] On April 30, 2004, the EPA designated three areas—Columbia, South Carolina; Greenville-Spartanburg-Anderson, South Carolina; and Charlotte-Gastonia-Rock Hill, North Carolina-South Carolina—as nonattainment for the revised 1997 8-hour ozone NAAQS, but deferred the effective date for the Columbia and Greenville-Spartanburg-Anderson areas to September 30, 2005, due to their participation in the Early Action Compact program.^[55] On April 2, 2008, the EPA redesignated the Columbia and Greenville-Spartanburg, Anderson areas to attainment for the 1997 8-hour ozone NAAQS, effective April 15, 2008.^[56] On December 26, 2012, the EPA redesignated the South Carolina portion of the Charlotte-Gastonia-Rock Hill bi-state area to attainment for the 1997 8-hour ozone NAAQS.^[57]

On March 27, 2008, the EPA revised the primary and secondary 8-hour ozone NAAQS to 0.075 ppm, effective May 27, 2008.^[58] On May 21, 2012, the EPA designated South Carolina as “Attainment/Unclassifiable,” with the exception of part of York County, which was designated a Marginal nonattainment area as part of the ( printed page 53566) Charlotte-Rock Hill North Carolina-South Carolina bi-state area, effective July 20, 2012.^[59 60] York County, South Carolina was included in the Charlotte bi-state nonattainment area despite the York County air quality monitor showing design values below the level of the 2008 8-hour ozone NAAQS at the time.^[61] On December 11, 2015, the EPA redesignated the York County, South Carolina portion of the Charlotte-Rock Hill bi-state area to attainment for the 2008 8-hour ozone NAAQS.^[62]

On October 26, 2015, the EPA revised the primary and secondary 8-hour ozone NAAQS to 0.070 ppm, effective December 28, 2015.^[63] On November 16, 2017, the Agency designated all counties in South Carolina as “Attainment/Unclassifiable” for the 2015 8-hour ozone standard, effective January 16, 2018, and South Carolina is currently in attainment for each form of the standard.^[64]

The EPA's NAAQS regulations at 40 CFR 50.19 and 40 CFR part 50, Appendix U provide that the primary 8-hour ozone NAAQS is attained when the 3-year average of the annual fourth-highest daily maximum 8-hour average ambient ozone concentration is less than or equal to 70 ppb. Further, a critical fourth-highest daily maximum 8-hour value for ozone is one that would result in a violating 3-year average design value. The most recent (2023-2025) certified design values in South Carolina show that the fourth-highest daily maximum 8-hour average ambient ozone concentrations ranged from 59 ppb (Charleston and Edgefield Counties) to 68 ppb (Spartanburg County).^[65] The 2026 critical fourth-highest daily maximum 8-hour concentrations that would result in a violation of the 2015 ozone NAAQS for Spartanburg, which has the highest value to date, is 79 ppb.^[66] Spartanburg has had recent historic fourth-highest daily maximum 8-hour concentrations of 71 ppb in 2024, 63 ppb in 2025, and 68 ppb, as of July 20, 2026.^[67]

As previously described, South Carolina's CAA section 110(l) demonstration includes the State's long-term air quality design value trends in several figures which depict the margins between the State's ozone emissions design values and the NAAQS from 2008-2025. These figures show that the State has maintained the applicable 8-hour ozone standards since 2011, where valid data is available.^[68 69]

2. NO₂ NAAQS

The EPA uses NO₂ as an indicator for NO_X .^[70] As noted above, NO_X is also considered a primary precursor of tropospheric ozone. Ambient concentrations of NO₂ are influenced by both direct NO₂ emissions and by emissions of NO, with the subsequent conversion of NO to NO₂ primarily through reaction with ozone (NO₂ can also be photolyzed to reform NO, creating new ozone in the process). Anthropogenic sources account for a large majority of NO_X emissions in the U.S., and highway and off-highway vehicles and stationary fuel combustion are the largest contributors.^[71] The EPA originally promulgated primary and secondary NO₂ annual standards in 1971 and, in 2010, promulgated a primary 1-hour NO₂ standard.

The EPA promulgated the first primary and secondary NO₂ NAAQS, 53 parts per billion (ppb) annual standards, on April 30, 1971.^[72] On February 9, 2010, the EPA promulgated a primary 100 ppb 1-hour NO₂ primary standard, effective April 12, 2010.^[73] The Agency retained the existing annual primary NO₂ standard in 2010.^[74] On February 17, 2012, the EPA designated all areas in South Carolina as “Attainment/Unclassifiable” for the 2010 primary 1-hour standard, effective February 29, 2012.^[75]

40 CFR 50.11 and 40 CFR part 50, Appendix S provide that the primary 1-hour NO₂ NAAQS is attained when the 3-year average of the annual 98th percentile of the daily maximum 1-hour average ambient NO₂ concentration is less than or equal to 100 ppb. Under those regulations, the primary annual NO₂ standard is attained when the annual average ambient NO₂ concentration is less than or equal to 53 ppb. The most recent (2023-2025) certified design values for the 1-hour standard in South Carolina show that the daily maximum 1-hour average ambient NO₂ concentrations range from 30 ppb (Richland County) to 39 ppb (Greenville County),^[76] well below the 1-hour NO₂ NAAQS. The most recent (2025) certified design values for the annual standard in South Carolina show that the annual average ambient NO₂ concentrations ranged from 4 ppb (Richland County) to 6 ppb (Charleston and Greenville Counties),^[77] well below the annual NO₂ NAAQS.

As previously described, South Carolina's CAA section 110(l) demonstration includes the State's long-term air quality design value trends in several figures which depict the margins between the State's NO₂, emissions design values and the NAAQS from 2008-2025. These figures show that the State has attained the annual NO₂ standards throughout the timeframes covered by the figures. Further, South Carolina has never been designated nonattainment for any NO₂ NAAQS and continues to attain each applicable form of the standard.

3. CO NAAQS

CO is formed primarily by incomplete combustion of carbon-containing fuels and photochemical reactions in the atmosphere. Oxidation of anthropogenic and biogenic VOCs constitute important secondary sources of CO.^[78] Mobile sources are the largest anthropogenic source of CO emissions in the U.S., and fires ( i.e., wildfires, agricultural field burning, and prescribed burns) are ( printed page 53567) another important source of CO emissions.

The EPA promulgated primary and secondary CO NAAQS on April 30, 1971, at 35 ppm (1-hour standard) and 9 ppm (8-hour standard).^[79] The EPA has since retained the primary standards three times and revoked the secondary standards.^[80]

Under 40 CFR 50.8, the design value for the primary 1-hour CO standard of 35 ppm is based on the second-highest hourly concentration in each year of the most recent 2-year period, and the design value is the higher of these two annual second maximum values. Under this regulation, the design value for the primary 8-hour CO standard of 9 ppm is based on the second-highest non-overlapping 8-hour average concentration for the most recent two years and then calculated as the higher of the two maximum values. The most recent (2024-2025) certified design values for the 1-hour and 8-hour standards in Richland County, South Carolina, are 1.2 ppm ^[81] and 0.7 ppm,^[82] respectively, well below the well below the respective CO NAAQS.

As previously described, South Carolina's CAA section 110(l) demonstration includes the State's long-term air quality design value trends in several figures which depict the margins between the State's CO emissions design values and the NAAQS from 2010-2025 for CO. These figures show that the State has attained the CO 1-hour and 8-hour standards throughout the timeframes covered by the figures. Further, South Carolina has never been designated nonattainment for any CO NAAQS and continues to attain each applicable form of the standard.

4. 2020 NO_X, VOCs, and CO NEI Data

As previously described, South Carolina's CAA section 110(l) demonstration also includes the State's 2020 NEI data for certain pollutants, including the ozone precursors. Appendix A to the CAA section 110(l) demonstration includes Figures A-1, A-5, and A-6, which display the State's NEI emissions data in pie charts by source type and sector with total 2020 pollutant emissions in tons for NO_X, VOCs, and CO, respectively. These figures characterize the proportion of emissions regulated under the State's minor NSR program, which includes the small proportion of emissions that would be exempt from that program with approval of the changes to subparagraph II(B)(2)(h). The charts divide emissions by four primary source categories: point, nonpoint, onroad, and nonroad. NEI point sources include emissions estimates for larger stationary sources ( e.g., large industrial facilities and electric power plants and smaller industrial, non-industrial, and commercial facilities, as defined at 40 CFR 51.50).^[83] NEI nonpoint sources include emissions estimates for sources which are individually too small in magnitude to report as point sources. As noted at 40 CFR 51.50, these sources are typically too small, numerous, or difficult to inventory using methods for other classes of sources. NEI onroad and nonroad sources include emissions from on-road vehicles and off-road mobile sources, respectively, that use gasoline, diesel, and other fuels.

Under South Carolina's minor source permitting SIP revisions that have been proposed for approval thus far,^[84] including those proposed for approval in this NPRM, sources that could qualify for exemption from minor source construction permitting would be those exempt under Regulation 61-62.1, subsection II(B), as revised through the April 24, 2020, SIP revision, with the exception of certain provisions detailing a case-by-case exemption which the State has removed from the EPA's consideration to address through parallel processing. Any sources exempt from minor NSR permitting under these provisions would fall exclusively into the nonpoint source category.^[85] Therefore, all emissions that would be exempt as a result of the changes to the SIP addressed in this NPRM are included as a subset of the nonpoint source category.

Specifically, under the subset of nonpoint source emissions from minor sources, the smaller fraction of exempt sources would be those that are currently approved into the SIP, those proposed for exemption in this NPRM, and those proposed for exemption in previous NPRMs,^[86] at paragraph II(B). This includes those sources under the five tpy uncontrolled PTE thresholds for SO₂, NO_X, CO, and PM proposed for approval in this NPRM, and those proposed to be exempt in the August 17, 2017, and January 21, 2025, NPRMs. This also includes those already exempt under the existing SIP. In the August 17, 2017, NPRM, the EPA proposed to approve the State's changes to clarify that subset of auxiliary boilers and space heaters of less than 1.5 MMBtu/hour rated input capacity that burn only virgin liquid or virgin solid fuels are exempt. In the January 21, 2025, NPRM, the EPA proposed to exempt auxiliary boilers and space heaters of less than 10 MMBtu/hour rated input capacity that burn only virgin gas fuels and proposed to modify the existing exemption for emergency generators. As noted above, the EPA is not taking further comment on these prior proposed approvals. The sources exempt under the existing SIP and which are not otherwise being proposed for modification include certain emergency generators, natural gas-fired boilers, oil-fired boilers rated 50 MMBtu/hour or less, and coal-fired boilers rated 20 MMBtu/hour or less which were constructed prior to February 11, 1971, and which are not located at a facility defined as a major source as defined in South Carolina's federally approved title V (40 CFR part 70) permitting program, and sources with VOC emissions less than 1,000 lb/month.

Figure A-1 indicates that of the 127,711 tons of NO_X emissions reported in the 2020 NEI, on-road, non-road, and point sources comprised 73.42 percent of total NEI NO_X emissions, contributing 93,765 tons, while nonpoint sources comprised only 26.58 percent. The nonpoint emissions are divided into five subcategories, and emissions from minor sources included in the NEI and regulated under the State's minor NSR program are covered by just one sector, stationary source fuel combustion, which is a small fraction of overall nonpoint NO_X emissions.^[87] This one sector includes the small fraction of minor sources proposed for exemption in this NPRM and the 2017 and the 2025 NPRMs, and those already exempt under the existing SIP. Stationary source fuel combustion emissions comprised 6.68 percent of total NEI NO_X ( printed page 53568) emissions (or 25.13 percent of NEI nonpoint source NO_X emissions), meaning 2020 NO_X contributions from minor sources included in the NEI and regulated under the State's minor NSR program were just over 8,531 tons. As noted above, of the 25.13 percent NEI nonpoint NO_X emissions, only a small portion of those emissions are from sources proposed for exemption in this NPRM and the 2017 and the 2025 NPRMs, and those already exempt under the existing SIP.

Figure A-5 indicates that of the 1,005,847 tons of VOC emissions reported in the 2020 NEI, 93.34 percent of NEI nonpoint VOC emissions were from nonpoint sources, and biogenic emissions comprised 86.78 percent of them (or 81.53 percent of total NEI VOC emissions), contributing 814,736 tons. The agricultural emissions and fires subcategory comprised 5.85 percent of NEI nonpoint VOC emissions (or 5.46 percent of total NEI VOC emissions), totaling 54,919 tons. Together, biogenic and agricultural emissions and fires comprised just under 87 percent of total NEI VOC emissions and over 92 percent of NEI nonpoint VOC emissions. Minor sources included in the NEI and regulated under the State's minor NSR program fall under the storage and transport, stationary source fuel combustion, and solvent utilization sectors, which comprised 5.85 percent of total NEI VOC emissions (or 6.27 percent of NEI nonpoint source VOC emissions), meaning 2020 VOC contributions from minor sources included in the NEI and regulated under the State's minor NSR program were just over 58,842 tons.^[88] As noted above, of the 6.27 percent NEI nonpoint VOC emissions, only a small portion of those emissions are from sources proposed for exemption in this NPRM and the 2017, and the 2025 NPRMs, and those already exempt under the existing SIP.

Figure A-6 indicates that of the 968,725 tons of CO emissions reported in the 2020 NEI, on-road, non-road, and point sources comprised 61.06 percent of total NEI CO emissions, contributing 591,503 tons, while nonpoint sources contributed to 38.95 percent of CO emissions, totaling 377,318 tons. The nonpoint sources are divided into the following sectors: agriculture and fires; biogenic emissions; commercial marine vessels, locomotives; industrial processes; stationary source fuel combustion; and open burning. The nonpoint emissions from sources that would be regulated under, or exempt from, the State's minor NSR program represent a small fraction of overall nonpoint CO emissions and would fall under the industrial processes and stationary source fuel combustion subcategories. Figure A-6 indicates that industrial processes and stationary source fuel combustion comprised 2.92 percent of total NEI CO emissions (or 7.5 percent of NEI nonpoint source CO emissions), meaning 2020 CO emissions from minor sources included in the NEI and regulated under the State's minor NSR program were just under 28,287 tons. This includes the small fraction of minor sources proposed for exemption in this NPRM and those already exempt under the existing SIP. Agricultural emissions and fires comprised 23.04 percent of total NEI CO emissions and 59.15 percent of NEI nonpoint source CO emissions, contributing 223,194.24 tons.

As previously noted, South Carolina relies on its 2020 NEI data to broadly support its position that emissions attributable to the exemptions from its minor NSR program, as revised through the April 24, 2020, SIP revision, including the five tpy thresholds for SO₂, NO_X, CO, and PM, comprise a sliver of the State's emissions, as shown in its 2020 NEI data, and represent an insignificant fraction of the State's emissions and do not affect ongoing NAAQS attainment. The State asserts, and the EPA agrees, that its available 2020 NEI data indicates that the proportion of emissions that would be automatically exempt, as described above, comprise a very small portion of overall emissions in the State. More specifically, the State asserts, and the EPA agrees, that only a limited portion of 2020 NEI emissions were attributable to minor stationary sources, both permitted and those that would be exempt, and further that the emissions from the subset of potentially exempt minor stationary sources comprises an even smaller fraction.

The EPA agrees that the previously described 2020 NEI data reflects that the subset of potential emissions contributions that would be exempt under the automatic exemption thresholds for NO_X , VOCs, and CO comprise very small proportions of 2020 NEI emissions across the State. The State acknowledges that not all minor stationary source emissions are accounted for in the NEI, because South Carolina's state emissions inventory is limited to major sources. However, generally, small stationary source sector emissions are accounted for with the NEI nonpoint source category, which utilizes activity data, such as employment or population data, multiplied by emission factors.^[89] South Carolina states that, despite state emissions inventory limitations owing to only major sources submitting emissions inventory information directly, NEI and other collective data amply demonstrate that sources and emissions exempt under the automatic exemption thresholds do not and will not affect attainment in South Carolina.

5. Ozone, NO₂, and CO NAAQS Analysis

With respect to the ozone, NO₂, and CO NAAQS, given the previously described rationale, air quality design value margins, and 2020 NEI data, the EPA does not expect the added five tpy PTE automatic exemption thresholds for NO_X and CO to interfere with the State's attainment or maintenance of the ozone, NO₂, or CO NAAQS. As explained earlier, since South Carolina is a NO_X -limited area, limiting emissions of NO_X, rather than VOCs, is critical to limiting the formation of ozone; therefore, controlling NO_X emissions is more effective than controlling VOCs to reduce ozone formation. As described above, South Carolina has maintained attainment or attainment/unclassifiable status for the ozone NAAQS since York County, SC was redesignated to attainment for the 2008 8-hour NAAQS in 2015 and has never been designated nonattainment for NO₂ or CO. The State's long-term air quality design value figures indicate that the State has maintained the applicable 8-hour ozone standard since 2011, where valid data is available, has maintained the NO₂ and CO NAAQS since at least the starting point in the figures of 2008, and that margins exist between the State's design values and the ozone, NO₂, and CO NAAQS. Additionally, 2020 NEI data indicates that VOC, NO_X, and CO emissions regulated under the State's minor NSR program are relatively small, comprising 2.92-6.68 percent of total 2020 NEI emissions, and the State's rationale demonstrates that, of those minor sources, sources that would be exempt comprise an even smaller fraction.

Based on the State's CAA 110(l) demonstration, including the information described above, the EPA finds that the added five tpy exemption thresholds for NO_X and CO would not interfere with any applicable ( printed page 53569) requirement concerning attainment and reasonable further progress, as defined in section 171, or any other applicable requirement of the CAA.

ii. Fine Particulate Matter (PM_2.5), SO₂, and NO₂ NAAQS

This section discusses South Carolina's emissions and air quality data and the EPA's analysis of that data with respect to the PM_2.5, SO₂, and NO₂ NAAQS. Specifically, in this section, the EPA evaluates the State's PM_2.5, SO₂, and NO₂ NAAQS attainment history, long term and recent PM_2.5, SO₂, and NO₂ air quality design values and NAAQS margins, and 2020 NEI data for PM_2.5, SO₂, and NO₂.

1. PM_2.5 NAAQS

PM is composed of primary and secondary components.^[90] Primary PM is derived from direct particle emissions from specific sources, and secondary PM originates from gas-phase chemical compounds present in the atmosphere. Stationary and mobile sources directly emit primary PM to ambient air, along with secondary PM precursors ( e.g., SO₂, NO_X) that contribute to the secondary formation of PM in the atmosphere. In general, sources of PM vary for different size fractions. PM_2.5 in ambient air is largely emitted directly by sources or through secondary PM formation in the atmosphere and is discussed in this section. PM₁₀ is comprised of PM_2.5 and coarser PM_10-2.5, which is almost entirely emitted from primary sources ( i.e., directly emitted) and is discussed below. Secondary PM accounts for a substantial fraction of PM_2.5 mass and forms through atmospheric photochemical oxidation reactions of precursors including SO₂ and NO_X . Anthropogenic SO₂ and NO_X are the predominant precursor gases in the formation of secondary PM_2.5 sulfate and nitrate. Atmospheric oxidation of VOCs, both anthropogenic and biogenic, is an important source of secondary organic PM, often referred to as secondary organic aerosols (SOA), particularly in summer. Natural emissions sources contributing to PM_2.5 concentrations can be interconnected with anthropogenic emissions through atmospheric chemistry ( e.g., modulation of biogenic SOA production by anthropogenic NO_X and SO₂ emissions).

Since its original promulgation in 1997, the EPA has revised the PM_2.5 NAAQS several times. On July 18, 1997, the EPA established annual primary and secondary PM_2.5 NAAQS of 15.0 micrograms per cubic meter (μg/m^[3] ) and a 24-hour PM_2.5 NAAQS of 65 μg/m^[3] , effective September 16, 1997.^[91] On October 17, 2006, the EPA retained the 1997 annual PM_2.5 NAAQS of 15.0 μg/m^[3] but revised the 24-hour PM_2.5 NAAQS to 35 μg/m^[3] , effective December 18, 2006.^[92] On January 15, 2013, the EPA retained the 2006 24-hour PM_2.5 NAAQS of 35 μg/m^[3] but revised the annual primary PM_2.5 NAAQS to 12.0 μg/m^[3] , effective March 18, 2013.^[93] The Agency retained the existing PM_2.5 standards in 2020 without revision.^[94] On March 6, 2024, the EPA revised the annual primary PM_2.5 NAAQS to 9.0 μg/m^[3] , effective May 6, 2024.^[95]

The EPA's NAAQS regulations at 40 CFR 50.20 and 40 CFR part 50, Appendix N provide that the primary annual PM_2.5 NAAQS is attained when the 3-year average of the annual arithmetic mean ambient PM_2.5 concentration is less than or equal to 9.0 μg/m^[3] , and the primary 24-hour NAAQS is attained when the 3-year average of the 98th percentile 24-hour ambient PM_2.5 concentration is less than or equal to 35 μg/m^[3] . The most recent 2023-2025 certified design values for the annual standard in South Carolina show that the annual arithmetic mean ambient PM_2.5 concentrations range from 7.1 μg/m^[3] (Charleston County) to 8.5 μg/m^[3] (Spartanburg),^[96] below the annual standard with available margin. The most recent 2023-2025 certified design values for the 24-hour standard in South Carolina show that the 24-hour ambient PM_2.5 concentrations range from 16 μg/m^[3] (Charleston County) to 20 μg/m^[3] (Chesterfield County),^[97] well below the 24-hour standard.

As previously described, South Carolina's CAA section 110(l) demonstration includes the State's long-term air quality design value trends in several figures which depict the margins between the State's PM_2.5 emissions design values and the NAAQS from 2008-2025. These figures show that the State has attained the annual and 24-hour PM_2.5 standards throughout the timeframes covered by the figures. Further, South Carolina has never been designated nonattainment for any PM_2.5 NAAQS and continues to attain each form of the standard.

2. SO₂ NAAQS

The EPA uses SO₂ as the NAAQS indicator for sulfur oxides, which include SO₂, sulfur monoxide, disulfur monoxide, and sulfur trioxide. SO₂ is both a primary gas-phase pollutant, ( i.e., when formed during fuel combustion), and a secondary pollutant ( i.e., when formed as the product of reduced sulfur compound oxidation).^[98] As noted above, sulfur oxides also appear in the particle phase, as components of PM, and anthropogenic SO₂ is a predominant precursor gas in the formation of secondary PM_2.5 sulfate. Fossil fuel combustion is the main anthropogenic source of primary SO₂, and anthropogenic SO₂ emissions originate primarily from point sources, including coal-fired electricity generating units and other industrial facilities. Volcanoes and wildfires are the main natural sources of primary SO₂ . Industrial chemical and pulp and paper production, smelter and steel mill operations, natural biological activity, and volcanoes are among many sources of reduced sulfur compounds that contribute to the formation of secondary SO₂ through various oxidation reactions in the atmosphere. Since its original promulgation in 1997, the EPA has revised the SO₂ NAAQS twice.

On April 30, 1971, the EPA established primary and secondary SO₂ standards, with a primary 24-hour SO₂ NAAQS of 0.14 ppm and an annual SO₂ NAAQS of 0.03 ppm.^[99] The EPA revoked the 24-hour and annual primary SO₂ standards on June 22, 2010, and instead established a 1-hour SO₂ standard of 75 ppb, effective August 23, 2010.^[100]

40 CFR 50.17 and 40 CFR part 50, Appendix T provide that the primary 1-hour SO₂ NAAQS is attained when the 3-year average of the annual 99th percentile daily maximum 1-hour average ambient SO₂ concentration is less than or equal to 75 ppb. The most recent 2023-2025 certified design values for the 1-hour standard in South Carolina show that the 1-hour ambient SO₂ concentrations range from 2 ppb (Greenville and Richland Counties) to 6 ( printed page 53570) ppb (Charleston County),^[101] well below the 1-hour SO₂ NAAQS.^[102 103]

As previously described, South Carolina's CAA section 110(l) demonstration includes the State's long-term air quality design value trends in several figures which depict the margins between the State's SO₂ emissions and the NAAQS from 2008-2025. These figures show that the State has attained the 1-hour SO₂ standard throughout the timeframes covered by the figures. Further, South Carolina has never been designated nonattainment for the SO₂ NAAQS and continues to attain the standard.

3. NO₂ NAAQS

As noted above, anthropogenic NO_X is a predominant precursor gas in the formation of secondary PM_2.5 nitrate. For information regarding the history and status of the NO₂ NAAQS and the State's long-term air quality design value trends, please refer to the section of this NPRM discussing the ozone, NO₂, and CO NAAQS. For information regarding South Carolina's recent certified NO₂ design values, please refer to the section of this NPRM discussing the ozone, NO₂, and CO NAAQS.

As previously noted, the EPA agrees with South Carolina's assertion that it has been maintaining attainment of all criteria pollutant standards for more than a decade. The previously described long-term and recent certified design values for PM_2.5, SO₂, and NO₂ demonstrate that the State is attaining the PM_2.5, SO₂, and NO₂ NAAQS and that margins exist between the State's long-term air quality design values and the PM_2.5, SO₂, and NO₂ NAAQS.

4. 2020 PM_2.5, SO₂, and NO₂ NEI Data

As previously described, South Carolina's CAA section 110(l) demonstration also includes the State's 2020 NEI data for certain pollutants, including PM_2.5 and the PM_2.5 precursors SO₂, NO_X , and VOCs.^[104] Appendix A to the CAA section 110(l) demonstration includes Figures A-1, A-3, A-4, and A-5 which display the State's NEI emissions data in pie charts by source type and sector with total 2020 pollutant emissions in tons for NO_X, PM_2.5, SO₂, and VOCs, respectively. These figures characterize the proportion of emissions regulated under the State's minor NSR program which includes the small proportion of emissions which would be exempt from that program ( e.g., the proposed changes at subparagraph II(B)(2)(h) in the NPRM).

Figure A-3 indicates that, of the 71,358 tons of PM_2.5 emissions reported in the 2020 NEI, nonpoint sources contributed 87.48 percent (or 62,424 tons). The nonpoint emissions sources in Figure A-3 are divided into the following sectors: open burning; stationary source fuel combustion; industrial processes; commercial marine vessels, locomotives, and road dust; and agriculture and fires. Emissions from sources that would qualify for exemption from minor NSR permitting would fall, as a small fraction of overall nonpoint PM_2.5 emissions, in the stationary source fuel combustion and industrial process categories, which comprised 22.45 percent of total NEI PM_2.5 emissions (and 25.66 percent of NEI nonpoint source PM_2.5 emissions). This means 2020 PM_2.5 contributions from minor sources included in the NEI and regulated under the State's minor NSR program were less than or equal to approximately 16,020 tons. As mentioned previously, of the 25.66 percent NEI nonpoint PM_2.5 emissions, only a small portion of those emissions are from sources proposed for exemption in this NPRM and the 2017, and the 2025 NPRMs, and those already exempt under the existing SIP.

Figure A-4 indicates that, of the 18,805 tons of SO₂ emissions reported in the 2020 NEI, point sources comprised 77.36 percent of total NEI SO₂ emissions, while nonpoint sources comprised 21.65 percent. Nonpoint sources were divided into the following sectors: agriculture and fires; commercial marine vessels, locomotives, and road dust; stationary source fuel combustion; and open burning. Sources that are exempt in the current SIP or would be exempt based on the changes proposed in this, the 2017, and the 2025 NPRMs fall in the stationary source fuel combustion category, which comprised 6.89 percent of total NEI SO₂ emissions (or 31.82 percent of NEI nonpoint source SO₂ emissions), meaning 2020 SO₂ contributions from minor sources included in the NEI and regulated under the State's minor NSR program were less than or equal to approximately 1,296 tons. As noted above, of the 31.82 percent NEI nonpoint SO₂ emissions, only a small portion of those emissions are from sources proposed for exemption in this NPRM and the 2017 and 2025 NPRMs, and those already exempt under the existing SIP.

As discussed above with respect to the ozone, NO₂, and CO NAAQS, the State relies on its 2020 NEI data to broadly support its position that the proportion of potentially exempt emissions, as described above, comprise a very small portion of overall emissions in the State, and that a limited portion of 2020 NEI emissions were attributable to minor stationary sources. Further, the State asserts, and the EPA agrees, that a very small portion of overall State emissions would be exempt because the subset of potentially exempt minor sources' emissions comprises a smaller fraction of the minor stationary sources under the 2020 NEI.

The EPA agrees that the previously described 2020 NEI data reflects that the subset of potential emissions contributions that would be exempt under the automatic exemption thresholds for NO_X and SO₂ comprise small proportions of 2020 NEI emissions across the State. As noted previously, the State acknowledges its state emissions inventory limitations, but states that, regardless, NEI and other collective data amply demonstrate that sources and emissions exempt under the automatic exemption thresholds do not and will not affect attainment in South Carolina.

5. PM_2.5, SO₂, and NO₂ Analysis

With respect to the PM_2.5, NO₂, and SO₂ NAAQS, given the previously described rationale, air quality design value margins, and 2020 NEI data, the EPA does not expect the five tpy PTE automatic exemption thresholds for PM, NO_X, and SO₂ to interfere with the State's attainment or maintenance of the PM_2.5, NO₂, and SO₂ NAAQS. As described above, South Carolina has never been designated nonattainment for PM_2.5, NO₂, or SO₂ . The State's long-term air quality design value figures indicate that margins exist between the State's design values and the PM_2.5, NO₂, and SO₂ NAAQS. Additionally, 2020 NEI data indicates that NO_X, SO₂, ( printed page 53571) and VOC emissions regulated under the State's minor NSR program are relatively small, comprising 5.85-6.89 percent of total 2020 NEI emissions, and the State's rationale demonstrates that, of those minor sources, sources that would be exempt comprise an even smaller fraction.

While the fraction of PM_2.5 2020 NEI emissions attributable to minor NSR sources (22.45 percent) is relatively higher than the fractions for the other pollutants evaluated, the on-road and non-road emissions are relatively lower for PM_2.5 than for NO_X and VOCs, as expected. Additionally, PM_2.5 emissions are expected to be more disparate across nonpoint sectors than emissions for SO₂, where sulfur is limited in many commercially available fuels that are combusted. As with the added exemption thresholds for the other pollutants, the State's rationale supporting its slightly increased PM exemption threshold demonstrates that, of the subset of nonpoint sources regulated under the State's minor NSR program, sources of PM_2.5 that would be exempt comprise a smaller fraction. However, unlike the new exemption thresholds for CO, SO₂, and NO_X, the current SIP already contains an exemption for sources with an uncontrolled particulate matter emission rate of less than one lb/hour (or 4.38 tpy), and the revised exemption represents a small increase in PM emissions, as discussed above. Moreover, the sources exempt at a five tpy total uncontrolled PTE threshold for PM would need to consider particulate matter emissions, which represents larger fractions of PM than PM_2.5 and PM₁₀ . Thus, a source with a total uncontrolled PTE below five tpy of PM_2.5 may not in itself qualify for the automatic exemption because the source may emit additional forms of particulate matter, all of which may sum to higher than the five tpy threshold. Finally, the nonpoint category covers sources across the entire range of PTE up to the title V major source thresholds, which for PM_2.5 is up to 100 tpy. If a facility is a title V major source for PM₁₀, however, the PM_2.5 emissions are likely also reported as point source emissions.^[105] In sum, the fraction of the PM_2.5 emissions that would be exempt at less than five tpy total uncontrolled PTE over the relevant nonpoint sectors is expected to be significantly smaller than the 22.45 percent of the total inventory of PM_2.5 emissions attributable to minor NSR sources. The EPA therefore agrees that the subset of PM_2.5 emissions contributions that would be exempt under the five tpy PTE automatic exemption threshold for PM comprises a small proportion of 2020 NEI emissions.

Based on the State's CAA section 110(l) demonstration, including the information described above, the EPA finds that the revised five tpy exemption threshold for PM, as it concerns PM_2.5, and the added five tpy exemption thresholds for NO_X and SO₂ would not interfere with any applicable requirement concerning attainment and RFP (as defined in section 171), or any other applicable requirement of the CAA.

iii. Coarse Particulate Matter (PM₁₀) NAAQS

This section discusses South Carolina's emissions and air quality data and the EPA's analysis of that data with respect to the PM₁₀ NAAQS. Specifically, in this section, the EPA evaluates the State's PM₁₀ NAAQS attainment history, long term and recent PM₁₀ air quality design values and NAAQS margins, and PM₁₀ 2020 NEI data.

1. PM₁₀ NAAQS

As previously noted, PM₁₀ is comprised of PM_2.5, and the remaining fraction of more coarse particles, PM_10-2.5, is almost entirely directly emitted from primary sources. The coarse portion of PM₁₀ is produced by surface abrasion or by suspension of sea spray or biological materials and resuspension of dust.

On July 1, 1987, the EPA established a primary 24-hour PM₁₀ NAAQS of 150 μg/m^[3] and a primary annual PM₁₀ NAAQS of 50 μg/m^[3] , effective July 31, 1987.^[106] On July 18, 1997, the EPA retained the annual PM₁₀ standard, and revised the form, but not the level, of the 150 μg/m^[3] 24-hour PM₁₀ standard, effective September 16, 1997.^[107] However, following promulgation of the revised 1997 p.m.₁₀ standards, petitions for review were filed by a large number of parties which ultimately resulted in vacatur of the 1997 p.m.₁₀ standards by the U.S. Court of Appeals for the District of Columbia Circuit,^[108] leaving the 1987 standards in place.^[109] On October 17, 2006, the EPA retained the level and form of the 1987 150 μg/m^[3] 24-hour PM₁₀ standard and revoked the annual PM₁₀ standards.^[110]

As previously described, South Carolina's CAA section 110(l) demonstration includes the State's long-term air quality design value trends in several figures which depicts the margins between the State's PM₁₀ emissions design values and the NAAQS from 2008-2025. These figures show that the State has attained the 24-hour PM₁₀ standard throughout the timeframe covered by the figures. Further, South Carolina has never been designated nonattainment for any PM₁₀ NAAQS and continues to attain the applicable form of the standard.

The EPA's NAAQS regulations at 40 CFR 50.6 and 40 CFR part 50, Appendix K provide that the primary 24-hour PM₁₀ NAAQS is attained when the expected number of days per calendar year with a 24-hour average concentration above 150 µg/m^[3] is less than or equal to one. The most recent 2023-2025 certified design values for the 24-hour standard in Greenville County, South Carolina, show that there were no estimated exceedances of the 24-hour PM₁₀ NAAQS.^[111]

As previously noted, the EPA agrees with South Carolina's assertion that it has been maintaining attainment of all criteria pollutant standards for more than a decade. The previously described long-term and recent certified design values for PM₁₀ demonstrate that the State is attaining the PM₁₀ NAAQS and that a margin exists between the State's long-term air quality design values and the 24-hour PM₁₀ NAAQS.

2. 2020 PM₁₀ NEI Data

As previously described, South Carolina's CAA section 110(l) demonstration also includes the State's 2020 NEI data for certain pollutants, including PM₁₀ . Appendix A to the CAA section 110(l) demonstration includes Figure A-2 which displays the State's PM₁₀ NEI emissions data in a pie chart by source type and sector with total 2020 pollutant emissions in tons. That figure characterizes the proportion of emissions regulated under the State's minor NSR program, including the ( printed page 53572) small proportion of emissions that would be exempt based on the proposed changes at subparagraph II(B)(2)(h) in the NPRM.

Figure A-2 indicates that, of the 209,790 tons of PM₁₀ emissions reported in the 2020 NEI, nonpoint sources (divided into the following subcategories: open burning; agricultural emissions and fires; commercial marine vessels, locomotives, and road dust; stationary source fuel combustion; and industrial processes) comprised 93.89 percent of total NEI PM₁₀ emissions, contributing 196,972 tons. Emissions from sources regulated under the State's minor NSR program fall under the stationary source fuel combustion and industrial processes categories, which, combined, accounted for 14.31 percent of total NEI PM₁₀ emissions (or 15.24 percent of NEI nonpoint source PM₁₀ emissions), meaning 2020 p.m.₁₀ contributions from minor sources included in the NEI and regulated under the State's minor NSR program were less than or equal to approximately 30,021 tons. This includes the small fraction of minor sources proposed for exemption in this NPRM and the 2017 and the 2025 NPRMs, and those already exempt under the existing SIP.

As discussed with respect to the ozone, NO₂, CO, and SO₂ NAAQS, the State relies on its 2020 NEI data to broadly support its position that emissions attributable to the exemption provisions under review represent an insignificant fraction of the State's emissions and do not affect ongoing NAAQS attainment. The State asserts, and the EPA agrees, that a very small portion of overall State emissions are potentially exempt because the subset of potential exempt minor sources comprises an even smaller fraction of the minor stationary sources under the 2020 NEI.

Like the fraction of PM_2.5, discussed above, the EPA notes that the overall fraction of PM₁₀ emissions from minor sources (14.31 percent) is relatively higher than those for NO_X, CO, VOCs, and SO₂, and the on-road and non-road emissions are relatively lower for PM₁₀ than for NO_X and VOCs. Notably, road dust emissions are included in the nonpoint sector for “commercial marine vessels, locomotives, and road dust.” Additionally, the PM_2.5-10 fraction of PM₁₀ is primarily derived from surface abrasion or by suspension of sea spray or biological materials and resuspension of dust, as noted previously. The lower fraction of point source emissions relative to the total 2020 NEI inventory for PM₁₀ compared to other pollutants (save VOCs) reflects that the industrial sources most likely to generate the coarser fraction of PM are more commonly minor sources. As with the added exemption for the other pollutants, the State's rationale supporting its slightly increased PM exemption threshold demonstrates that, of the subset of nonpoint sources regulated under the State's minor NSR program, sources of PM₁₀ that would be exempt comprise a smaller fraction. Likewise, the current SIP contains an existing exemption for sources with an uncontrolled particulate matter emission rate of less than one lb/hour (or 4.38 tpy), and the revised exemption represents a small increase in PM emissions, as discussed above. Moreover, as with PM_2.5, the five tpy total uncontrolled PTE exemption threshold in subparagraph II(B)(2)(h) is based on PM emissions, of which PM₁₀ is a subset. Thus, sources with a total uncontrolled PTE less than five tpy of PM₁₀ may not themselves qualify for the automatic exemption. Finally, the nonpoint category covers sources across the entire range of PTE up to the title V major source thresholds, which for PM₁₀ is up to 100 tpy. In sum, the fraction of the PM₁₀ emissions that would be exempt at less than five tpy total uncontrolled PTE over the relevant nonpoint sectors is expected to be significantly smaller than the 14.31 percent of the total emissions inventory for PM₁₀ . The EPA therefore agrees that the 2020 NEI data reflects that the subset of PM₁₀ emissions contributions that would be exempt under the five tpy PTE automatic exemption threshold for PM comprises a small proportion of 2020 NEI emissions.

3. PM₁₀ Analysis

With respect to the PM₁₀ NAAQS, given the previously described rationale, air quality design value margins, and 2020 NEI data, the EPA does not expect that the revised five tpy PTE automatic exemption threshold would interfere with the State's attainment or maintenance of the PM₁₀ NAAQS. As described above, South Carolina has never been designated nonattainment for PM₁₀ . The State's long-term air quality design value figures indicate that a significant margin exists between the State's design values and the 24-hour PM₁₀ standard, approximately 50 percent of the NAAQS. Additionally, 2020 NEI data indicates that PM₁₀ emissions regulated under the State's minor NSR program are relatively small, comprising 14.31 percent of total 2020 NEI emissions. Further, the State's rationale demonstrates that, of those minor sources, potentially exempt sources comprise an even smaller fraction. Based on the State's CAA section 110(l) demonstration, including the information described above, the EPA finds that the revised five tpy exemption threshold for PM, as it concerns PM₁₀, would not interfere with any applicable requirement concerning attainment and RFP (as defined in section 171), or any other applicable requirement of the CAA.

4. Summary of the EPA's Findings From South Carolina's CAA Section 110(l) Demonstration

The previously described data and the State's supporting rationale, including rationale related to its historical implementation of the minor NSR program exemptions, demonstrate that the added or revised exemption thresholds would not interfere with attainment or maintenance of the NAAQS or with any other applicable CAA requirement. As noted above, the State has implemented the five tpy total uncontrolled PTE exemption thresholds for sources of SO₂, NO_X , CO, and PM for more than a decade. The 1,000 lb/month total uncontrolled PTE exemption threshold for VOCs and the similar one lb/hour PM exemption threshold are currently SIP-approved and have been implemented for an even longer period of time. Further, because the air quality design values described above show the State remains below the relevant NAAQS with available margins, and because the State does not expect significant increases in emissions to result from these exemptions, South Carolina does not expect future interference with attainment or maintenance of the NAAQS. Further information on the State's rationale for its exemptions and the EPA's analyses of the State's emissions data and air quality with respect to each relevant NAAQS ^[112] are found in Section V.C.3. of this NPRM. The EPA agrees, based on the State's rationale and supporting emissions data and air quality, that the revised exemption for PM to five tpy and the new five tpy exemptions for NO_X, CO, and SO₂ would not interfere with attainment or maintenance of the NAAQS. The EPA also agrees that the State has articulated the basis for setting the scope of its minor NSR program pursuant to CAA section 110(a)(2)(C) and 40 CFR 51.160(e).

( printed page 53573)

VI. Incorporation by Reference

In this document, the EPA is proposing to include in a final EPA rule regulatory text that includes incorporation by reference. In accordance with requirements of 1 CFR 51.5, and as discussed in section V of this preamble, the EPA is proposing to incorporate by reference South Carolina Regulation 61-62.1, Section II, Permit Requirements, subparagraph II(B)(2)(h), state effective on April 24, 2020, with the exception of the following two sentences: “Unless otherwise exempt, sources may be exempted under this section at higher emission levels if there is a demonstration that there are no applicable limits or requirements. These applicable requirements include federally applicable limits or requirements.” The EPA is also proposing to incorporate by reference South Carolina Regulation 61-62.1, Section II, Permit Requirements, paragraph II(K)(5), state effective on May 23, 2025. The EPA has made, and will continue to make, these materials generally available through www.regulations.gov and at the EPA Region 4 office (please contact the person identified in the FOR FURTHER INFORMATION CONTACT section of this preamble for more information).

VII. 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.^[113] 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.

Because 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, this proposed action for the State of South Carolina does not have Tribal implications as specified by Executive Order 13175 (65 FR 67249, November 9, 2000). Therefore, this action will not impose substantial direct costs on Tribal governments or preempt Tribal law. The Catawba Indian Nation Reservation is located within the boundary of York County, South Carolina. Pursuant to the Catawba Indian Claims Settlement Act, S.C. Code Ann. 27-16-120 (Settlement Act), “all state and local environmental laws and regulations apply to the [Catawba Indian Nation] and Reservation and are fully enforceable by all relevant state and local agencies and authorities.” The Catawba Indian Nation also retains authority to impose regulations applying higher environmental standards to the Reservation than those imposed by state law or local governing bodies, in accordance with the Settlement Act.

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

91 FR 53558