RD proposes to rescind the standards in 7 CFR 1924 for its housing programs as existing State and local requirements sufficiently protect Federal investments. Local building codes and permitting systems already ensure structural integrity, safety, and compliance for construction and development. Since these locally administered requirements meet the needs previously addressed in Part 1924, USDA determined that additional Federal standards are unnecessary for housing programs. For RBCS programs, RD proposes amendments to Parts 4280 and 4290 to replace obsolete references to Part 1924 and similar Federal regulatory standards with cross-references to constructions and development standards used in the Community Facilities programs at 7 CFR part 1942.

This proposed rescission advances the administration's priority for regulatory reform by repealing outdated, unnecessary, or ineffective regulations. Part 1924 establishes procedures for construction, site development, and defect resolution across RD programs, but these requirements create duplicative processes, additional paperwork, and extra processing steps for RHS property owners. Part 1924 imposes energy-efficiency and thermal-performance standards, as well as environmental considerations in site planning and design, that often exceed State and local requirements, increase construction and compliance costs, and delay the production and repair of housing in rural communities. RD concluded that these prescriptive regulatory overlays exceed requirements under Title V of the Housing Act of 1949 (42 U.S.C. 1471 et seq. ), which authorizes the Secretary to ensure that dwellings financed under RHS programs are “decent, safe, and sanitary.” The statute does not mandate the sorts of prescriptive design standards found in Part 1924.

Requiring compliance with both Federal and local standards adds redundancy, increases costs, and lengthens construction timelines. The costs and delays are passed directly on to borrowers by increasing home prices. Burdensome regulations restrict the number of developers interested in using RHS programs. A longer timeline for housing production and higher construction costs for low- and moderate-income families reduce the number of loans RHS can make and restricts affordability.

This proposed rule will make conforming amendments to Parts 4280 and 4290 to replace obsolete references to Part 1924 and similar Federal regulatory standards. Certain rescinded references, where necessary, will now point to 7 CFR part 1942 subpart C. Unlike the housing industry, RBCS projects do not have robust state and local standards and thus those programs necessitate continued Federal regulatory standards.

Executive Order 14219 (February 19, 2025), “Ensuring Lawful Governance and Implementing the President's Department of Government Efficiency Deregulatory Initiative,” directs agencies to review their regulations and rescind those that are unlawful or unnecessary. In response, RD reviewed Part 1924 and determined it is no longer needed.

Executive Order 14394 (March 13, 2026), “Removing Regulatory Barriers to Affordable Home Construction,” directs Federal housing agencies to reform or eliminate burdensome energy-efficiency, water-use, and alternative-energy requirements that increase construction costs. RD determined that Part 1924 contains this type of prescriptive energy and construction standards and falls within the scope of the Executive Order's directives.

This rescission also supports Executive Order 14192 (January 31, 2025), “Unleashing Prosperity through Deregulation,” which directs agencies to identify, and repeal outdated, unnecessary, or ineffective regulations that impose costs or hinder economic growth.

Removing obsolete cross-references will further streamline RD's regulatory framework and improve clarity for lenders, builders, and rural borrowers, consistent with the Administration's regulatory reform policies.

RD is rescinding 7 CFR part 1924 and is making conforming changes to RBCS program regulations to remove such references.

This program is not subject to the requirements of Executive Order 12372, “Intergovernmental Review of Federal Programs,” as implemented under USDA's regulations at 2 CFR 415, subpart C.

This rule has been determined to be not significant and therefore was not reviewed by the Office of Management and Budget under Executive Order 12866.

This rule has been reviewed under Executive Order 12988. In accordance with this rule: (1) unless otherwise specifically provided, all State and local laws that conflict with this rule will be preempted; (2) no retroactive effect will be given to this rule except as specifically prescribed in the rule; and (3) administrative proceedings of the National Appeals Division of the Department of Agriculture (7 CFR part 11) must be exhausted before bringing suit in court that challenges action taken under this rule.

The policies contained in this rule do not have any substantial direct effect on States, on the relationship between the National Government and the States, or on the distribution of power and responsibilities among the various levels of government. Nor does this rule impose substantial direct compliance costs on state and local governments. Therefore, consultation with the States is not required.

This proposed rule has been reviewed in accordance with the requirements of Executive Order 13175, Consultation and Coordination with Indian Tribal Governments. Executive Order 13175 requires Federal agencies to consult and coordinate with Tribes on a government-to-government basis on policies that have Tribal implications, including regulations, legislative comments or proposed legislation, and other policy statements or actions that have substantial direct effects on one or more Indian Tribes, on the relationship between the Federal government and Indian Tribes or on the distribution of power and responsibilities between the Federal government and Indian Tribes. Consultation is also required for any regulation that preempts Tribal law or that imposes substantial direct compliance costs on Indian Tribal governments and that is not required by statute.

The Agency has determined that this proposed rule does not, to our knowledge, have Tribal implications that require formal Tribal consultation under Executive Order 13175. If a Tribe requests consultation, the RBCS and/or RHS will work with the Office of Tribal Relations to ensure meaningful consultation is provided where changes, additions and modifications identified herein are not expressly mandated by Congress.

Rural Development has reviewed this rule in accordance with USDA Regulation 4300-4, Civil Rights Impact Analysis, to identify any major civil rights impacts the rule might have on program participants on the basis of age, race, color, national origin, sex, disability, marital or familial status. Based on the review and analysis of the rule and all available data, issuance of this Proposed Rule is not likely to negatively impact low and moderate-income populations, minority populations, women, Indian tribes or persons with disability, by virtue of their age, race, color, national origin, sex, disability, or marital or familial status. No major civil rights impact is likely to result from this proposed rule.

Pursuant to the Congressional Review Act (5 U.S.C. 801 et seq. ), the Office of Information and Regulatory Affairs designated this final rule as not a major rule, as defined by 5 U.S.C. 804(2).

Rural Development is committed to the E-Government Act, which requires Government agencies in general to provide the public the option of submitting information or transacting business electronically to the maximum extent possible and to promote the use of the internet and other information technologies to provide increased opportunities for citizen access to Government information and services, and for other purposes.

In accordance with the National Environmental Policy Act of 1969, Public Law 91-190, this proposed rule has been reviewed in accordance with 7 CFR part 1b (“National Environmental Policy Act”). The Agency has determined that (i) this action meets the criteria established in 7 CFR 1b.4(c)(31) and (ii) no extraordinary circumstances exist. Therefore, the Agency has determined that the action does not have a significant effect on the human environment, and therefore neither an Environmental Assessment nor an Environmental Impact Statement is required.

This rule does not contain reporting or recordkeeping requirements subject to the Paperwork Reduction Act.

The rule has been reviewed with regard to the requirements of the Regulatory Flexibility Act (5 U.S.C. 601-612). The undersigned has determined and certified by signature on this document that this rule will not have a significant economic impact on a substantial number of small entities since this rulemaking action does not involve a new or expanded program, nor does it require any more action on the part of a small business than required of a large entity.

Title II of the UMRA, Public Law 104-4, establishes requirements for Federal Agencies to assess the effects of their regulatory actions on State, local, and Tribal Governments and on the private sector. Under section 202 of the UMRA, Federal Agencies generally must prepare a written statement, including cost-benefit analysis, for proposed and Final Rules with “Federal mandates” that may result in expenditures to State, local, or Tribal Governments, in the aggregate, or to the private sector, of $100 million or more in any one-year. When such a statement is needed for a rule, section 205 of the UMRA generally requires a Federal Agency to identify and consider a reasonable number of regulatory alternatives and adopt the least costly, more cost-effective, or least burdensome alternative that achieves the objectives of the rule.

This rule contains no Federal mandates (under the regulatory provisions of title II of the UMRA) for State, local, and Tribal Governments or for the private sector. Therefore, this rule is not subject to the requirements of sections 202 and 205 of the UMRA.

In accordance with Federal civil rights laws and USDA civil rights regulations and policies, the USDA, its Mission Areas, agencies, staff offices, employees, and institutions participating in or administering USDA programs are prohibited from discriminating based on race, color, national origin, religion, sex, disability, age, marital status, family/parental status, income derived from a public assistance program, political beliefs, or reprisal or retaliation for prior civil rights activity, in any program or activity conducted or funded by USDA (not all bases apply to all programs). Remedies and complaint filing deadlines vary by program or incident.

Persons with disabilities who require alternative means of communication for program information ( e.g., Braille, large print, audiotape, American Sign Language, etc.) should contact the State or local Agency that administers the program or contact USDA through the Telecommunications Relay Service at 711 (voice and TTY). Program information may be made available in languages other than English. To file a program discrimination complaint, complete the USDA Program Discrimination Complaint Form, AD-3027, found online at https://www.usda.gov/sites/default/files/documents/ad-3027.pdf and at any USDA office or write a letter addressed to USDA and provide in the letter all of the information requested in the form. To request a copy of the complaint form, call (866) 632-9992. Submit your completed form or letter to USDA by:

a. Mail: U.S. Department of Agriculture, Office of the Assistant Secretary for Civil Rights, 1400 Independence Avenue SW, Mail Stop 9410, Washington, DC 20250-9410; or

b. Fax: (202) 690-7442; or

c. Email: program.intake@usda.gov.

USDA is an equal opportunity provider, employer, and lender.

For the reasons stated in the preamble, Rural Development proposes to amend 7 CFR parts 1924, 4280, and 4290 as follows:

The FAA invites you to send any written relevant data, views, or arguments about this proposal. Send your comments using a method listed under the ADDRESSES section. Include “Docket No. FAA-2026-8782; Project Identifier MCAI-2025-01560-T” at the beginning of your comments. The most helpful comments reference a specific portion of the proposal, explain the reason for any recommended change, and include supporting data. The FAA will consider all comments received by the closing date and may amend this proposal because of those comments.

Except for Confidential Business Information (CBI) as described in the following paragraph, and other information as described in 14 CFR 11.35, the FAA will post all comments received, without change, to regulations.gov, including any personal information you provide. The agency will also post a report summarizing each substantive verbal contact received about this NPRM.

CBI is commercial or financial information that is both customarily and actually treated as private by its owner. Under the Freedom of Information Act (FOIA) (5 U.S.C. 552), CBI is exempt from public disclosure. If your comments responsive to this NPRM contain commercial or financial information that is customarily treated as private, that you actually treat as private, and that is relevant or responsive to this NPRM, it is important that you clearly designate the submitted comments as CBI. Please mark each page of your submission containing CBI as “PROPIN.” The FAA will treat such marked submissions as confidential under the FOIA, and they will not be placed in the public docket of this NPRM. Submissions containing CBI should be sent to Frank Carreras, Aviation Safety Engineer, FAA, 2200 South 216th St., Des Moines, WA 98198; phone: 206-231-3539; email: frank.carreras@faa.gov. Any commentary that the FAA receives which is not specifically designated as CBI will be placed in the public docket for this rulemaking.

EASA, which is the Technical Agent for the Member States of the European Union, has issued EASA AD 2025-0208, dated September 24, 2025 (EASA AD 2025-0208) (also referred to as the MCAI), to correct an unsafe condition for certain Airbus SAS Model A330-941 airplanes. The MCAI states an occurrence was reported of a triple “PRIM FAULT” at touchdown, leading to the loss of ground spoilers, thrust reversers and autobrake. An investigation determined the root cause was an undue triggering of the rudder order “COM/MON” monitoring in the three FCPCs. This condition, if not corrected, could result in the loss of autobrake and thrust reverser, possibly resulting in reduced control of the airplane. Airbus issued instructions for the installation of a new FCPC standard. The FAA is proposing this AD to address the unsafe condition on these products.

You may examine the MCAI in the AD docket at regulations.gov under Docket No. FAA-2026-8782.

EASA AD 2025-0208 specifies procedures for the installation of a new FCPC standard by replacing the FCPCs, replacing the FCPC on board replaceable module (OBRMs), or reprogramming the FCPC OBRMs. EASA AD 2025-0208 further specifies that applicable concurrent modifications to the FCPC must be done ( i.e., FCPC, flight management, guidance and envelope computer (FMGEC), flight warning computer (FWC), and electronic instrument system (EIS) standard upgrades). EASA AD 2025-0208 also specifies parts installation restrictions allowing installation of only a serviceable FCPC.

This material is reasonably available because the interested parties have access to it through their normal course of business or by the means identified in the ADDRESSES section.

These products have been approved by the civil aviation authority of another country and are approved for operation in the United States. Pursuant to the FAA's bilateral agreement with this State of Design Authority, that authority has notified the FAA of the unsafe condition described in the MCAI referenced above. The FAA is issuing this NPRM after determining that the unsafe condition described previously is likely to exist or develop in other products of the same type design.

This proposed AD would require accomplishing the actions specified in EASA AD 2025-0208 described previously, except for any differences identified as exceptions in the regulatory text of this proposed AD.

In the FAA's ongoing efforts to improve the efficiency of the AD process, the FAA developed a process to use some civil aviation authority (CAA) ADs as the primary source of information for compliance with requirements for corresponding FAA ADs. The FAA has been coordinating this process with manufacturers and CAAs. As a result, the FAA proposes to incorporate EASA AD 2025-0208 by reference in the FAA final rule. This proposed AD would, therefore, require compliance with EASA AD 2025-0208 in its entirety through that incorporation, except for any differences identified as exceptions in the regulatory text of this proposed AD. Using common terms that are the same as the heading of a particular section in EASA AD 2025-0208 does not mean that operators need comply only with that section. For example, where the AD requirement refers to “all required actions and compliance times,” compliance with this AD requirement is not limited to the section titled “Required Action(s) and Compliance Time(s)” in EASA AD 2025-0208. Material required by EASA AD 2025-0208 for compliance will be available at regulations.gov under Docket No. FAA-2026-8782 after the FAA final rule is published.

The FAA estimates that this AD, if adopted as proposed, would affect 39 airplanes of U.S. registry. The FAA estimates the following costs to comply with this proposed AD:

Title 49 of the United States Code specifies the FAA's authority to issue rules on aviation safety. Subtitle I, section 106, describes the authority of the FAA Administrator. Subtitle VII: Aviation Programs, describes in more detail the scope of the Agency's authority.

The FAA is issuing this rulemaking under the authority described in Subtitle VII, Part A, Subpart III, Section 44701: General requirements. Under that section, Congress charges the FAA with promoting safe flight of civil aircraft in air commerce by prescribing regulations for practices, methods, and procedures the Administrator finds necessary for safety in air commerce. This regulation is within the scope of that authority because it addresses an unsafe condition that is likely to exist or develop on products identified in this rulemaking action.

The FAA determined that this proposed AD would not have federalism implications under Executive Order 13132. This proposed AD would not have a substantial direct effect on the States, on the relationship between the national government and the States, or on the distribution of power and responsibilities among the various levels of government.

For the reasons discussed above, I certify this proposed regulation:

(1) Is not a “significant regulatory action” under Executive Order 12866,

(2) Would not affect intrastate aviation in Alaska, and

(3) Would not have a significant economic impact, positive or negative, on a substantial number of small entities under the criteria of the Regulatory Flexibility Act.

Accordingly, under the authority delegated to me by the Administrator, the FAA proposes to amend 14 CFR part 39 as follows:

Under section 721(d)(1) of the Federal Food, Drug, and Cosmetic Act (21 U.S.C. 379e(d)(1)), we are giving notice that we have filed a color additive petition (CAP 5C0338), submitted by GNT USA, LLC., c/o Exponent, Inc., 1150 Connecticut Ave. NW, Suite 1100, Washington, DC, 20036. The petition proposes that we amend our color additive regulations in 21 CFR Part 73 ( Listing of Color Additives Exempt from Certification) to provide for the safe use of safflower ( Carthamus tinctorius L.) extract as a color additive in: (1) tortilla wraps; (2) alcoholic beverages; (3) non-alcoholic beverages and beverage bases; (4) colored extruded breakfast cereals; (5) chewing gum; (6) flavored ready-to-drink tea and tea concentrates; (7) pickles, relish, pickled jalapenos, banana pepper rings, and pepperoncini; (8) sugar decorations, frostings (excluding chocolate frosting), and marshmallows; (9) salad dressings (ready-to-use); (10) frozen dairy desserts and mixes; (11) shelf stable ice pops; (12) fillings (excluding chocolate), and ready-to-eat gelatins and puddings; (13) hard candy; (14) flavored milk and milk shakes, flavored yogurt, yogurt drinks, and non-dairy yogurt; (15) soft candy and candy coated nuts; (16) ready-to-use chicken and vegetable broth; and (17) flavored syrups for beverages and desserts (excluding chocolate syrup), at levels consistent with good manufacturing practices.

The petitioner claims that this action is categorically excluded under 21 CFR 25.32(k) because granting this petition would authorize the use of a substance intended to remain in food through ingestion by consumers and is not intended to replace macronutrients in food. In addition, the petitioner states that, to their knowledge, no extraordinary circumstances exist. If FDA determines a categorical exclusion applies, neither an environmental assessment nor an environmental impact statement is required. If FDA determines a categorical exclusion does not apply, we will request an environmental assessment and make it available for public inspection.

Under section 721(d)(1) of the Federal Food, Drug, and Cosmetic Act (21 U.S.C. 379e(d)(1)), we are giving notice that we have filed a color additive petition (CAP 6C0343), submitted by GBIG, c/o Exponent, Inc., 1150 Connecticut Ave. NW, Suite 1100, Washington, DC 20036. The petition proposes that we amend our color additive regulations in 21 CFR 73.168 (“Gardenia (genipin) blue”) to expand the safe use of gardenia (genipin) blue to include use in: (1) sponge cake; (2) alcoholic mixed drinks; (3) carbonated drinks; (4) powdered beverages; (5) processed breakfast cereals; (6) chewing gum; (7) instant iced tea; (8) wasabi paste and powder; (9) sugar coating; (10) syrup for shaved ice; (11) icing; (12) creamers and whiteners; (13) ice cream and frozen dairy desserts; (14) frozen desserts (edible ices); (15) gelatin, puddings, custards, and pie filling; (16) jam, jellies, and marmalade; (17) flavored milk and both flavored and unflavored yogurt; (18) snack foods; (19) fruit preparation, syrup, and toppings; and (20) chewable tablets, at levels consistent with good manufacturing practice. The petition also proposes to lower the specification for arsenic in gardenia (genipin) blue from ≤2 mg/kg (ppm) to ≤1 mg/kg (ppm). FDA may also consider other changes to the regulation, as appropriate, during the course of our review.

The petitioner claims that this action is categorically excluded under 21 CFR 25.32(k) because granting this petition would authorize the use of a substance intended to remain in food through ingestion by consumers and is not intended to replace macronutrients in food. In addition, the petitioner has stated that, to their knowledge, no extraordinary circumstances exist. If FDA determines a categorical exclusion applies, neither an environmental assessment nor an environmental impact statement is required. If FDA determines a categorical exclusion does not apply, we will request an environmental assessment and make it available for public inspection.

Under section 721(d)(1) of the Federal Food, Drug, and Cosmetic Act (21 U.S.C. 379e(d)(1)), we are giving notice that we have filed a color additive petition (CAP 5C0339), submitted by the International Association of Color Manufacturers, 1101 17th St. NW, Suite 700, Washington, DC 20036. The petition proposes to amend the color additive regulations in § 73.300 (21 CFR 73.300), Listing of Color Additives Exempt from Certification, to provide for the safe use of acetone as a solvent in the manufacture of carrot oil. The petition also proposes to add heavy metal limits and secondary names for carrot oil. FDA may also consider other changes to the regulation, as appropriate, during the course of our review.

We are reviewing the potential environmental impact of this petition. To encourage public participation consistent with regulations issued under the National Environmental Policy Act (40 CFR 1501.5(e)), we are placing the environmental assessment submitted with the petition that is the subject of this notice on public display at the Dockets Management Staff (see ADDRESSES ) for public review and comment.

We will also place on public display, in the Dockets Management Staff and at https://www.regulations.gov, any amendments to, or comments on, the petitioner's environmental assessment without further announcement in the Federal Register . If, based on our review, we find that an environmental impact statement is not required, and this petition results in a regulation, we will publish the notice of availability of our finding of no significant impact and the evidence supporting that finding with the regulation in the Federal Register in accordance with 21 CFR 25.51(b).

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

On October 1, 2007; July 18, 2011; August 8, 2014; July 27, 2016;  1 and April 24, 2020, SC DHEC  2 submitted SIP revisions to the EPA for approval that include changes to South Carolina's minor source permitting regulations to clarify and streamline the State's federally approved minor source preconstruction and operating permit program. These regulations require minor stationary sources of air pollutants planning to construct or modify to first obtain a construction permit and to 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. The portion of the SIP-approved minor source permitting program covering operating permits also includes a program referred to as the federally enforceable State operating permit (FESOP) program. The EPA had previously proposed action on these submitted SIP revisions on January 21, 2025. See 94 FR 41591. This NPRM is intended to be in supplement to, and not replace, that prior proposed action. Here, the EPA is proposing to approve identified portions of the SIP submissions that make changes to South Carolina's minor source permitting program requirements contingent on the EPA finalizing a recently proposed change to relevant national regulations. 3

Under CAA section 110(k)(3), the EPA has a statutory obligation to approve SIP submittals that meet all applicable CAA requirements. 4 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, including CAA section 110(l). 5 The EPA evaluates CAA section 110(l) non-interference on a case-by-case basis considering the circumstances of each SIP revision.

On July 7, 2026, the EPA published a proposal to revise the public participation regulatory requirements for sources subject to NSR programs in SIPs. 6 If the EPA's July 7, 2026, NPRM is finalized as proposed, state and local air agencies would have the discretion to determine whether, and the extent to which, public participation elements are appropriate and reasonable in their minor NSR programs. For more information on the proposed revisions to the Federal minor NSR regulations and the rationale for the July 7, 2026, NPRM, please refer to the July 7, 2026, NPRM  7 and related docket materials. 8 Any comments on those proposed revisions and the EPA's rationale for those changes should be made on the July 7, 2026, NPRM and are not being solicited through this proposed action. If the EPA were to finalize the July 7, 2026, NPRM as proposed, the EPA is proposing to approve changes to South Carolina Regulation 61-62.1, Section II, Permit Requirements, subsections II(D), II(E), II(F), II(G), II(I), and II(N), for the reasons discussed in Section IV of this NPRM. This proposal supplements, and does not replace, previous proposals the EPA published on August 17, 2017, 9 and January 21, 2025. 10

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 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 implementation plan, 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), which is the statutory foundation for the portion of the CFR at 40 CFR 51.16051.164. The regulatory requirements at 40 CFR 51.160-51.164 generally apply 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 51.160-51.164 apply to all new minor sources and modifications under a state's minor NSR program in accordance with 40 CFR 51.160. States have discretion to define the scope of their minor NSR programs within the bounds of CAA section 110 and 40 CFR 51.160-51.164. 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.

On July 7, 2026, the EPA published a NPRM proposing to revise the Federal public participation requirements for minor NSR programs to be approved into SIPs. 12 In that NPRM, the EPA proposed to revise the Agency's regulations at 40 CFR 51.161 to remove the requirement for public notice and comment as a minimum feature of State and local minor source NSR programs. 13 In that NPRM, the EPA stated that the approach proposed within more closely adheres to the statutory language in CAA section 110(a)(2)(C) as it applies to minor NSR, noting section 110(a)(2)(C) requires only that each SIP provide for the “regulation of the modification and construction of” stationary sources “as necessary to assure that [the NAAQS] are achieved,” but does not specify, with respect to minor NSR, specifically what air agencies must include for the SIP to be approvable. 14

If the EPA's July 7, 2026, NPRM is finalized as proposed, state and local air agencies would have the discretion to determine whether, and the extent to which, public participation elements are appropriate and reasonable in their minor NSR programs. For more information on the proposed rule revisions and the rationale for the July 7, 2026, NPRM, please refer to the July 7, 2026, NPRM  15 and related docket materials. 16 Any comments on those proposed revisions and the EPA's rationale for those changes should be made on the July 7, 2026 NPRM and are not being solicited through this proposed action.

In contrast to the requirements in CAA section 110(a)(2)(C) and at 40 CFR 51.160-51.164 applicable to minor source construction permitting, there are no statutory or regulatory requirements applicable to the issuance of minor source operating permits or the evaluation of minor source operating permit programs. 17 Furthermore, although the EPA has the authority to approve such programs into SIPs under CAA section 110(a)(2)(B) and (D), state operating permit programs are not a required element in SIPs. A subset of minor source operating permitting programs comprise FESOP programs. FESOPs are federally enforceable permits issued by a state under a SIP-approved minor source operating permit program meeting the criteria identified by the EPA in the preamble to a June 28, 1989, final rulemaking action (1989 Preamble). 18 The 1989 Preamble notes the flexibility states have in conducting public participation for FESOPs, noting that the EPA would consider the public participation practices sufficient “as long as ample opportunity is provided for comment on permits prior to their final issuance.”  19 Many States, such as South Carolina, adopted FESOPs as an additional mechanism for creating federally enforceable limits to avoid major source requirements like those applicable to CAA title V sources.

Under the CAA, there are no explicit requirements for minor source operating permit programs in SIPs, which are not required minimum elements of SIPs to begin with. 20 That absence, in contrast with the statutory requirements applicable to minor NSR programs and the detailed statutory requirements applicable to major source operating permit programs prescribed by Congress, indicates that the CAA affords maximum discretion to States in developing their minor source operating permit programs for voluntary inclusion in SIPs within the bounds of CAA section 110, to include the discretion to require public participation, and, if so, to what extent. Furthermore, although the 1989 Preamble sets forth criteria for “federal enforceability” applicable to FESOPs, including the criterion that “permits are issued subject to public participation,”  21 all permits issued under a SIP-approved minor source permitting program are federally enforceable. 22 This is true even if a SIP-approved minor source permitting program does not provide for public participation for the operating permits issued.

South Carolina has a SIP-approved minor source permitting program at Regulation 61-62.1, Section II, that includes requirements for minor NSR and minor source operating permitting. In the October 1, 2007, SIP revision submittal letter, the State explains that the revisions to Section II clarify and streamline South Carolina'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 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 two categories of sources: 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 modifications 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. 23

South Carolina's minor source operating permitting program covers two categories of sources: true minor sources, i.e., sources where the PTE of any air pollutant is below applicable major stationary source or major source thresholds without any enforceable emission limitations to constrain emissions; and conditional major sources, i.e., sources where conditional major permits establish enforceable emission limitations to restrict the PTE of any air pollutant below major source applicability thresholds. The EPA originally approved “the addition of a requirement . . . in Section II . . . that an operating permit be obtained in addition to construction permits which were previously required” into South Carolina's SIP in 1974 and subsequently approved revisions to those operating permit provisions, e.g., in 1980, 1982, and 1983. 24

In 1995, South Carolina submitted a voluntary SIP revision to modify its SIP-approved minor source operating permitting program to carve out a FESOP program for “conditional major” operating permits at Regulation 61-62.1, subsection II(G). The State created this FESOP program pursuant to the 1989 Preamble to allow it to issue operating permits restricting a source's potential to emit below major source thresholds. The EPA approved that SIP revision on December 11, 1995, 25 as satisfying the five FESOP criteria. In that action, the Agency also recognized that the FESOP program approved in that rulemaking did not cover all minor source operating permits issued by the State under Regulation 61-62.1, subsection II(B), which is SIP-approved and contains the State's generally applicable operating permit provisions that also cover true minor operating permits. Subsection II(B) is recodified and revised, in part, under subsection II(F) in the SIP submissions which are the subject of this NPRM.

Through NPRMs published on August 17, 2017, 26 and January 21, 2025, 27 the EPA proposed to act on changes to South Carolina's minor source permitting provisions involving, in part, the State's minor source permitting program regulations, including those involving minor source permitting public participation. 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. 28 Docket No. EPA-R04-OAR-2024-0241 contains information specific to the January 21, 2025, NPRM, including comments received. 29

This proposed action is intended to supplement, and not replace, those prior proposed actions. In this NPRM, the EPA is proposing that the Agency would approve portions of South Carolina's minor source permitting SIP revisions related to public participation if EPA were to finalize the Agency's July 7, 2026, NPRM as proposed. Specifically, if the July 7, 2026, NPRM was finalized as proposed, the EPA is proposing that it would approve changes to Regulation 61-62.1, subsections II(D), II(E), II(F), II(G), II(I), and II(N) submitted by the State on the following dates: October 1, 2007; July 18, 2011; August 8, 2014; July 27, 2016; and April 24, 2020. The EPA's analysis of the changes in the previously listed submittals is discussed below. 30

This NPRM covers recodification of portions of the regulation, minor and administrative changes to the affected portions of the rule, and certain substantive changes, described below. Specifically, the following paragraphs describe the substantive changes to subsections II(D), II(E), II(F), II(G), II(I), and II(N) under consideration in this NPRM.

The October 1, 2007, SIP revision adds new subsection II(D), “General Construction Permits.” In the 2007 SIP revision, subsection II(D), “Exceptions,” in the current SIP is renumbered to subsection II(K); however, the EPA is not proposing to act on subsection II(K) in this NPRM. 31 New subsection II(D) allows the State to develop and issue general construction permits applicable to similar stationary sources for new construction projects or minor modifications to existing sources. In the 2007 SIP revision, subsection II(D) provides for the following: (1) general construction permits will incorporate all applicable requirements for construction of similar sources and identify criteria by which sources can qualify for the permit; (2) sources may submit construction permit applications to the State that request coverage under the general permit, the State will grant coverage to sources certifying qualification for and agreeing to the conditions and terms of a general construction permit, and sources later determined not to qualify for a general construction permit are subject to enforcement; (3) authorization to operate under a general construction permit is a final permit action for purposes of judicial review; (4) the application for coverage can deviate from the requirements of subsection II(C) if an application includes all information necessary to determine the source's qualification for and assure compliance with a general construction permit; and (5) sources qualifying for coverage under a general construction permit can apply for an individual construction permit in lieu of coverage under a general permit.

The August 8, 2014, SIP revision makes minor edits to subsection II(D), including administrative and minor language changes and restructuring edits. In the 2014 SIP revision, some of the requirements in paragraph II(D)(1) are restructured into new paragraph II(D)(2), shifting the subsequent paragraphs. Similarly, some of the requirements in paragraph II(D)(3), renumbered from II(D)(2), are restructured into new paragraph II(D)(4), shifting the subsequent paragraphs again.

The April 24, 2020, SIP revision makes minor edits to subsection II(D), including administrative and minor language changes and additional restructuring edits. In the 2020 SIP revision, the requirements in paragraph II(D)(3) are restructured into new subparagraph II(D)(3)(a) under paragraph II(D)(3) and a new heading, “Coverage under a General Construction Permit.” Under that paragraph, new subparagraph II(D)(3)(b) states that a source that has submitted an individual construction permit application to the State that has not requested coverage under the conditions and terms of a general construction permit for similar sources but which is determined to qualify for coverage under a general permit can be granted coverage under the general permit at the State's sole discretion. The April 24, 2020, SIP submittal notes that this change reflects current Department practices and clarifies and streamlines the permit application process.

Under minor NSR, general permitting programs can protect the NAAQS and be an effective method of streamlining permitting requirements and procedures for similar sources. General construction permits are preconstruction permits which establish a category of covered sources or modifications, criteria for such sources or modifications to qualify for coverage under the permit, and standardized requirements applicable to all such sources or modifications. General permits can apply to a number of similar emissions units or sources. The CAA offers states enhanced flexibility in designing their minor NSR programs, including the flexibility to use regulatory mechanisms such as general permits as part of such programs, as long as such programs assure attainment and maintenance of the NAAQS. Although the implementing regulations at 40 CFR 51.160-51.164 do not use the term “general permit” or expressly describe general construction permits, those regulations do not stipulate that programs to regulate construction must require individual construction permits for every regulated source. Rather, the minor NSR regulations require legally enforceable procedures that meet the requirements set forth therein. 32 The EPA interprets the relevant statutory and regulatory provisions to allow States to develop mechanisms including general construction permits to authorize construction for minor sources and modifications, provided such mechanisms assure that the NAAQS are achieved and meet other applicable requirements. 33 The legally enforceable procedures used by States to develop minor source construction general permits are established as components of the States' broader programs addressing CAA requirements for minor source preconstruction permitting, and, like other minor NSR permitting provisions, are submitted as SIP revisions to the EPA for review and incorporation into the SIP, as South Carolina has done here.

The addition of these general permitting provisions, applicable to the construction and modification of true minor sources, is consistent with applicable statutory and regulatory requirements with the exception of the current public participation requirements in 40 CFR 51.161, which the EPA proposed to revise in its July 7, 2026, NPRM. If that NPRM is finalized as proposed, subsection II(D), which does not require that the subject true minor source general permits undergo public participation, would be consistent with the revised requirements in 51.161.

Furthermore, in the current SIP, and as revised through the April 24, 2020, SIP revision, Regulation 61-62.1, Section II requires public participation for synthetic minor (construction permits) and conditional major (operating) permits, by which sources adopt federally enforceable limitations on PTE to avoid major source status and associated requirements. With the cumulative changes to Section II in the SIP revisions submitted through 2020, SC DES may, but is not required to, administer public participation for additional permitting activities, i.e., true minor NSR permits. Therefore, with respect to public participation, the State's added general permitting provisions applicable to true minor sources, which streamline the permitting process for similar source types, are consistent with the level of public participation already required for other true minor source permits in the SIP. In other words, the addition of subsection II(D), where public participation is concerned, is a neutral change that does not result in the addition or removal of public participation requirements already applicable to the sources subject to the minor source permitting program.

The October 1, 2007, SIP revision revises the State's synthetic minor construction permit requirements. Subsection II(E) sets forth requirements for stationary sources requesting enforceable permit emission limits to restrict PTE to avoid qualifying as a major source under the major NSR programs. The 2007 SIP revision renumbers subsection II(H), “Synthetic Minor Plant Permits,” to subsection II(E) and revises the subsection title to “Synthetic Minor Construction Permits.” In the 2007 SIP revision, subsection II(E), “Transfer of Ownership/Operation,” in the current SIP is renumbered to subsection II(M); however, the EPA is not proposing to act on subsection II(M) in this NPRM. 34 The October 1, 2007, SIP revision also makes minor edits to subsection II(E), including administrative and minor language changes ( e.g., clarifying changes to indicate that subsection II(E) pertains to construction permits, to indicate that paragraph II(E)(4) pertains to general synthetic minor construction permits, as distinguished from the general construction permit provisions applicable to true minor sources in new subsection II(D), to further clarify general synthetic minor construction permitting procedures under paragraph II(E)(4), and to add or update cross-references).

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:

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 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

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.

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.

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.

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 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

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.

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 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 (SO 2 ), 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, SO 2 , 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.

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):

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.”

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.

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, SO 2 , 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, SO 2 , 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 , SO 2 , and CO and 1,000 lb/month for VOCs. 26

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 SO 2 , 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, SO 2 , 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 , SO 2 , and NO 2 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 , SO 2 , 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, SO 2 , VOC, and CO emissions; design value trends for ozone, PM, SO 2 , CO, and NO 2 ; 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 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.

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 SO 2 , 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 SO 2 , 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, SO 2 , 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 SO 2 , 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, SO 2 , NO X , and CO.” The EPA notes that the current SIP does not include specific exemptions from permitting for sources emitting SO 2 , 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 SO 2 , 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, SO 2 , 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 SO 2 , 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, SO 2 , 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 , SO 2 , 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, SO 2 , 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.

As previously noted, South Carolina's CAA section 110(l) demonstration evaluates the revised exemption to support the five tpy thresholds for PM, SO 2 , 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, SO 2 , NO X , and CO exemption thresholds are likely to have on its ability to maintain compliance with the ozone, NO 2 , CO, PM 2.5 , PM 10 , and SO 2 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 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, SO 2 , 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 SO 2 , NO 2 , 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.

This section discusses South Carolina's emissions and air quality data with respect to the ozone, NO 2 , and CO NAAQS. Specifically, in this section, the EPA evaluates the State's ozone, NO 2 , and CO NAAQS attainment history; long term and recent ozone, NO 2 , and CO air quality design values and NAAQS margins; and 2020 NEI data for ozone precursors.

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 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

The EPA uses NO 2 as an indicator for NO X . 70 As noted above, NO X is also considered a primary precursor of tropospheric ozone. Ambient concentrations of NO 2 are influenced by both direct NO 2 emissions and by emissions of NO, with the subsequent conversion of NO to NO 2 primarily through reaction with ozone (NO 2 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 NO 2 annual standards in 1971 and, in 2010, promulgated a primary 1-hour NO 2 standard.

The EPA promulgated the first primary and secondary NO 2 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 NO 2 primary standard, effective April 12, 2010. 73 The Agency retained the existing annual primary NO 2 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 NO 2 NAAQS is attained when the 3-year average of the annual 98th percentile of the daily maximum 1-hour average ambient NO 2 concentration is less than or equal to 100 ppb. Under those regulations, the primary annual NO 2 standard is attained when the annual average ambient NO 2 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 NO 2 concentrations range from 30 ppb (Richland County) to 39 ppb (Greenville County), 76 well below the 1-hour NO 2 NAAQS. The most recent (2025) certified design values for the annual standard in South Carolina show that the annual average ambient NO 2 concentrations ranged from 4 ppb (Richland County) to 6 ppb (Charleston and Greenville Counties), 77 well below the annual NO 2 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 NO 2 , emissions design values and the NAAQS from 2008-2025. These figures show that the State has attained the annual NO 2 standards throughout the timeframes covered by the figures. Further, South Carolina has never been designated nonattainment for any NO 2 NAAQS and continues to attain each applicable form of the standard.

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 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.

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 SO 2 , 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 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 SO 2 , 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.

With respect to the ozone, NO 2 , 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, NO 2 , 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 NO 2 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 NO 2 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, NO 2 , 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 requirement concerning attainment and reasonable further progress, as defined in section 171, or any other applicable requirement of the CAA.

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 , SO 2 , and NO 2 NAAQS. Specifically, in this section, the EPA evaluates the State's PM 2.5 , SO 2 , and NO 2 NAAQS attainment history, long term and recent PM 2.5 , SO 2 , and NO 2 air quality design values and NAAQS margins, and 2020 NEI data for PM 2.5 , SO 2 , and NO 2 .

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., SO 2 , 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. PM 10 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 SO 2 and NO X . Anthropogenic SO 2 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 SO 2 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.

The EPA uses SO 2 as the NAAQS indicator for sulfur oxides, which include SO 2 , sulfur monoxide, disulfur monoxide, and sulfur trioxide. SO 2 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 SO 2 is a predominant precursor gas in the formation of secondary PM 2.5 sulfate. Fossil fuel combustion is the main anthropogenic source of primary SO 2 , and anthropogenic SO 2 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 SO 2 . 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 SO 2 through various oxidation reactions in the atmosphere. Since its original promulgation in 1997, the EPA has revised the SO 2 NAAQS twice.

On April 30, 1971, the EPA established primary and secondary SO 2 standards, with a primary 24-hour SO 2 NAAQS of 0.14 ppm and an annual SO 2 NAAQS of 0.03 ppm. 99 The EPA revoked the 24-hour and annual primary SO 2 standards on June 22, 2010, and instead established a 1-hour SO 2 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 SO 2 NAAQS is attained when the 3-year average of the annual 99th percentile daily maximum 1-hour average ambient SO 2 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 SO 2 concentrations range from 2 ppb (Greenville and Richland Counties) to 6 ppb (Charleston County), 101 well below the 1-hour SO 2 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 SO 2 emissions and the NAAQS from 2008-2025. These figures show that the State has attained the 1-hour SO 2 standard throughout the timeframes covered by the figures. Further, South Carolina has never been designated nonattainment for the SO 2 NAAQS and continues to attain the standard.

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 NO 2 NAAQS and the State's long-term air quality design value trends, please refer to the section of this NPRM discussing the ozone, NO 2 , and CO NAAQS. For information regarding South Carolina's recent certified NO 2 design values, please refer to the section of this NPRM discussing the ozone, NO 2 , 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 , SO 2 , and NO 2 demonstrate that the State is attaining the PM 2.5 , SO 2 , and NO 2 NAAQS and that margins exist between the State's long-term air quality design values and the PM 2.5 , SO 2 , and NO 2 NAAQS.

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 SO 2 , 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 , SO 2 , 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 SO 2 emissions reported in the 2020 NEI, point sources comprised 77.36 percent of total NEI SO 2 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 SO 2 emissions (or 31.82 percent of NEI nonpoint source SO 2 emissions), meaning 2020 SO 2 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 SO 2 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, NO 2 , 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 SO 2 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.

With respect to the PM 2.5 , NO 2 , and SO 2 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 SO 2 to interfere with the State's attainment or maintenance of the PM 2.5 , NO 2 , and SO 2 NAAQS. As described above, South Carolina has never been designated nonattainment for PM 2.5 , NO 2 , or SO 2 . 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 , NO 2 , and SO 2 NAAQS. Additionally, 2020 NEI data indicates that NO X , SO 2 , 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 SO 2 , 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, SO 2 , 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 PM 10 . 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 PM 10 , 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 SO 2 would not interfere with any applicable requirement concerning attainment and RFP (as defined in section 171), or any other applicable requirement of the CAA.

This section discusses South Carolina's emissions and air quality data and the EPA's analysis of that data with respect to the PM 10 NAAQS. Specifically, in this section, the EPA evaluates the State's PM 10 NAAQS attainment history, long term and recent PM 10 air quality design values and NAAQS margins, and PM 10 2020 NEI data.

As previously noted, PM 10 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 PM 10 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 PM 10 NAAQS of 150 μg/m 3 and a primary annual PM 10 NAAQS of 50 μg/m 3 , effective July 31, 1987. 106 On July 18, 1997, the EPA retained the annual PM 10 standard, and revised the form, but not the level, of the 150 μg/m 3 24-hour PM 10 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 PM 10 standard and revoked the annual PM 10 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 PM 10 emissions design values and the NAAQS from 2008-2025. These figures show that the State has attained the 24-hour PM 10 standard throughout the timeframe covered by the figures. Further, South Carolina has never been designated nonattainment for any PM 10 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 PM 10 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 PM 10 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 PM 10 demonstrate that the State is attaining the PM 10 NAAQS and that a margin exists between the State's long-term air quality design values and the 24-hour PM 10 NAAQS.

As previously described, South Carolina's CAA section 110(l) demonstration also includes the State's 2020 NEI data for certain pollutants, including PM 10 . Appendix A to the CAA section 110(l) demonstration includes Figure A-2 which displays the State's PM 10 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 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 PM 10 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 PM 10 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 PM 10 emissions (or 15.24 percent of NEI nonpoint source PM 10 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, NO 2 , CO, and SO 2 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 PM 10 emissions from minor sources (14.31 percent) is relatively higher than those for NO X , CO, VOCs, and SO 2 , and the on-road and non-road emissions are relatively lower for PM 10 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 PM 10 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 PM 10 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 PM 10 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 PM 10 is a subset. Thus, sources with a total uncontrolled PTE less than five tpy of PM 10 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 PM 10 is up to 100 tpy. In sum, the fraction of the PM 10 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 PM 10 . The EPA therefore agrees that the 2020 NEI data reflects that the subset of PM 10 emissions contributions that would be exempt under the five tpy PTE automatic exemption threshold for PM comprises a small proportion of 2020 NEI emissions.

With respect to the PM 10 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 PM 10 NAAQS. As described above, South Carolina has never been designated nonattainment for PM 10 . 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 PM 10 standard, approximately 50 percent of the NAAQS. Additionally, 2020 NEI data indicates that PM 10 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 PM 10 , would not interfere with any applicable requirement concerning attainment and RFP (as defined in section 171), or any other applicable requirement of the CAA.

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 SO 2 , 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 SO 2 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).

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:

On October 1, 2007, July 27, 2016, 1 September 5, 2017, 2 and February 4, 2022, 3 SC DES  4 submitted SIP revisions that include changes to South Carolina's NO X control requirements in the South Carolina Code of Regulations Annotated (S.C. Code Ann. Regs.) Regulation 61-62.5, Air Pollution Control Standards, Standard No. 5.2, Control of Oxides of Nitrogen (NO X ) (hereinafter “Regulation 61-62.5, Standard No. 5.2”). 5 Additionally, SC DES submitted a SIP revision on April 24, 2020, that includes changes to the State's source testing requirements in S.C. Code Ann. Regs. Regulation 61-62.1, Definitions and General Requirements, Section IV, Source Tests (hereinafter “Regulation 61-62.1, Section IV”). 6

On May 13, 2026, SC DES submitted supplemental materials, including a letter requesting that the EPA conditionally approve portions of the State's NO X control SIP revisions 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, should the EPA finalize this partial conditional approval as proposed. Additionally, the supplemental materials include a CAA section 110(l) demonstration to support the corrective changes that the State intends to submit in a corrective SIP revision. Section IV, below, provides the EPA's analysis of the State's non-interference demonstration. On May 13, 2026, SC DES also submitted to the EPA a letter addressing subsection III(A) as revised in the July 25, 2016, SIP revision and paragraph I(B)(3) and subsection II(K) as added and revised in the February 4, 2022, SIP revision, respectively, stating that “the specific text identified . . . is no longer before EPA at this time.”

Subsequently, on July 21, 2026, 7 SC DES submitted a letter removing from the EPA's consideration one provision in Regulation 61-62.5, Standard No. 5.2 for which the State, in its May 13, 2026, letter, requested conditional approval. This letter supersedes the May 13, 2026, request for conditional approval of paragraph I(B)(2). The July 21, 2026, letter removes from EPA consideration “I(B)(2), as submitted on July 25, 2016, and February 3, 2022.” The States notes that in planned changes, the State will be “striking the referenced provision within Standard No. 5.2” and that “[t]herefore, the specific text . . . is not before the EPA at this time.”  8 The EPA is therefore proposing to approve or conditionally approve the remainder of the revised Regulation 61-62.5, Standard No. 5.2 provisions and Regulation 61-62.1, Section IV, in its entirety.

In this NPRM, the EPA is proposing to approve changes to South Carolina's regulations regarding source testing. Additionally, the EPA is proposing to approve portions of, and conditionally approve other portions of, the SIP submissions that make changes to South Carolina's NO X control rule requirements. Section IV, below, provides the EPA's analysis of the State's CAA section 110(l) non-interference demonstration for the provisions that the EPA is proposing to act on in this NPRM.

Under CAA section 110(k)(3), the EPA has a statutory obligation to approve SIP submittals that meet all applicable CAA requirements. 9 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.

Under CAA section 110(k)(4), the EPA may conditionally approve a SIP revision based on a commitment from a state to adopt specific enforceable measures by a date certain, but not later than one year from the date of approval. If the state fails to meet its commitment within one year of the final conditional approval, the conditional approval will be treated as a disapproval. If South Carolina fulfills its commitment within one year of final conditional approval, the requirements of the conditionally approved NO X control SIP revision will remain a part of the SIP until the EPA takes final action approving or disapproving the corrective SIP revision.

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 (RFP) (as defined by CAA section 171), or any other applicable requirement of the CAA. 10 Section IV of this NPRM discusses South Carolina's CAA section 110(l) analysis supporting these changes that the EPA is proposing to act on in this NPRM. The EPA evaluates CAA section 110(l) non-interference demonstrations on a case-by-case basis considering the circumstances of each SIP revision. In its May 13, 2026, letter, the State clarifies that it “has not previously implemented” its discretion and commits not to do so “while the regulatory revisions are pending.” Therefore, although the SIP would have discretionary provisions should the EPA finalize this partial conditional approval as proposed, the EPA understands that the State will not exercise its discretion in implementing the provisions of Standard No. 5.2 as the State moves through its process to go through its procedures to adopt the committed changes.

The EPA is proposing to approve the changes to Regulation 61-62.1, Section IV, Source Tests, in the April 24, 2020, SIP revision, as detailed in Section IV of this NPRM. The EPA is proposing to approve these changes for the reasons discussed Section IV of this NPRM.

The EPA is also proposing to approve the changes to Regulation 61-62.5, Standard No. 5.2, Control of Oxides of Nitrogen (NO X ) , in the October 1, 2007, July 27, 2016, September 5, 2017, and February 4, 2022, SIP revisions, 11 as detailed in Section IV of this NPRM, except for the portions of the SIP revisions consisting of the addition of and changes to certain provisions in Regulation 61-62.5, Standard No. 5.2, Section IV, which the EPA is proposing to conditionally approve, as described below. The EPA is proposing to approve the aforementioned changes to the SIP for the reasons discussed Section IV of this notice.

Finally, the EPA is proposing to conditionally approve the portions of the July 27, 2016, September 5, 2017, and February 4, 2022, SIP revisions consisting of the addition of and changes to certain provisions in Regulation 61-62.5, Standard No. 5.2, Section IV, Monitoring, Record Keeping, and Reporting Requirements for New Affected Sources. Specifically, the EPA is proposing to conditionally approve the following provisions submitted by the State in the July 27, 2016; September 5, 2017; and February 4, 2022, SIP revision submittals: paragraph IV(A)(1), specifically IV(A)(1)(a)-(d); subparagraph IV(A)(2)(a)-(c); subparagraph IV(B)(2)(a); subparagraph IV(B)(2)(b); paragraph IV(C)(1), specifically IV(C)(1)(a)-(d); subparagraph IV(C)(3)(c); subparagraph IV(C)(3)(d); the second prefatory paragraph of IV(D); subparagraph IV(D)(2)(a); and subparagraph IV(D)(2)(b). The EPA is proposing to conditionally approve the aforementioned changes to the SIP for the reasons discussed Section IV of this notice.

On April 24, 2020, SC DES submitted a SIP revision to the EPA that includes changes to South Carolina's generally applicable source testing requirements at Regulation 61-62.1, Section IV. 12 13 Regulation 61-62.1, Section IV provides source testing procedures and schedules applicable to certain sources, including those conducting “a source test required under an applicable standard or permit condition” or “from which data will be submitted to the Department for any purpose.” In this NPRM, the EPA is proposing to approve all of the changes to Regulation 61-62.1, Section IV in the April 24, 2020, SIP revision. The EPA discusses its proposed action with respect to the changes to Regulation 61-62.1, Section IV in Section III.A. of this NPRM.

On October 1, 2007, July 27, 2016, September 5, 2017, and February 4, 2022, SC DES submitted SIP revisions to the EPA that include changes to South Carolina's NO X emission standards and control requirements for certain new and modified stationary sources at Regulation 61-62.5, Standard No. 5.2. 14 The State added Regulation 61-62.5, Standard No. 5.2, State effective June 25, 2004, as part of its Early Action Compact (EAC) with the EPA to achieve emission reductions needed to attain the 1997 8-hour ozone National Ambient Air Quality Standards (NAAQS) in certain EAC areas. 15 The regulation is a control measure for new and existing stationary sources that emit or have the potential to emit NO X from fuel combustion, have not undergone a best available control technology (BACT) analysis for NO X via prevention of significant deterioration (PSD) permitting, and meet other applicability criteria in Section I of the regulation. Regulation 61-62.5, Standard No. 5.2, was designed primarily to capture smaller sources that fall below PSD applicability thresholds which, for the most part, would not otherwise be required to install NO X controls.

In a direct final rule published on August 16, 2017, the EPA approved the changes to Regulation 61-62.5, Standard No. 5.2 in the October 1, 2007, SIP revision, subject to the receipt of adverse comment. 16 The EPA's analysis and the rationale for approving the changes to Regulation 61-62.5, Standard No. 5.2 in South Carolina's 2007 SIP revision are described in that direct final rule. Comments on the August 16, 2017, direct final rule were due on or before September 15, 2017. The EPA received one adverse comment on the changes to Regulation 61-62.5, Standard No. 5.2. 17 Due to the receipt of an adverse comment, on October 13, 2017, the EPA withdrew the portion of the August 16, 2017, direct final rule approving the changes to Regulation 61-62.5, Standard No. 5.2 in the October 1, 2007, SIP revision. 18 On August 16, 2017, the EPA also published a NPRM corresponding to the direct final rule, so that, if the EPA received adverse comment on the August 16, 2017, direct final rule and subsequently withdrew that action, any comments received could be addressed in a subsequent final rule based on the NPRM. 19 However, the EPA did not finalize the August 16, 2017, NPRM.

In this NPRM, the EPA is proposing to approve portions and conditionally approve other portions of South Carolina's NO X control SIP revisions. 20 21 Specifically, in this NPRM, EPA is proposing to approve changes to a portion of Regulation 61-62.5, Standard No. 5.2, submitted in SIP revisions dated October 1, 2007; July 27, 2016; September 5, 2017; and February 4, 2022. The EPA is proposing to conditionally approve changes to the following provisions submitted by the State in the July 27, 2016; September 5, 2017; and February 4, 2022, SIP revision submittals: IV(A)(1), including IV(A)(1)(a)-(d); IV(A)(2)(a), (b), and (c); IV(B)(2)(a); IV(B)(2)(b); IV(C)(1), including IV(C)(1)(a)-(d); IV(C)(3)(c); IV(C)(3)(d); IV(D)—the second prefatory paragraph; IV(D)(2)(a); and IV(D)(2)(b). The EPA's analysis of the changes proposed for approval or conditional approval in the aforementioned submittals is discussed below.

The EPA is proposing to approve the changes to Regulation 61-62.1, Section IV in the April 24, 2020, SIP revision. In the April 24, 2020, SIP revision, the changes to Regulation 61-62.1, Section IV revise the State's source testing procedures to make non-substantive administrative and clarifying edits ( e.g., reformatting subsections, paragraphs, subparagraphs, and rule references); correcting citations to the Code of Federal Regulations (CFR) by adding the word “Part,”; clarifying numbers; and substituting the word “standard” with “requirement.” The EPA is proposing to approve these non-substantive administrative and clarifying edits because they will have no impact on air quality.

The April 24, 2020, SIP revision makes further changes to subsection IV(B), which specifies requirements for the submission and approval of site-specific test plans by a source owner, operator, or representative. In the SIP, subparagraph IV(B)(5)(a) requires the submission of test plans, or a letter amending a previously approved test plan, at least 45 days prior to the proposed test date, except for sources testing for substances listed in the State's regulations applicable to emissions of toxic air pollutants in Regulation 61-62.5, Standard No. 8, for which the submission of test plans or such a letter is required at least 60 days prior to the proposed test date. Subparagraph IV(B)(5)(b) exempts sources that are amending only the facility name, address, telephone number, contact, permit number, and/or source identification number from the requirements in subparagraph IV(B)(5)(a) and requires the submission of such amendments at least two weeks prior to the proposed test date. The April 24, 2020, SIP revision adds language at subparagraph IV(B)(5)(a) that allows source owners, operators, or representatives to submit site-specific test plans or a letter which amends a previously approved test plan at least 45 days prior to the proposed test date, “or as otherwise specified by a relevant federal or state requirement.” This change would allow an owner, operator, or representative of a source subject to other applicable Federal or State standards ( e.g., New Source Performance Standards (NSPS) testing requirements under 40 CFR part 60) to comply with an alternate minimum test plan or amendment letter submission deadline specified in those standards. This change pertains to timing of test plan submissions only and therefore will have no impact on air quality. For these reasons, the EPA is proposing to approve the change to subparagraph IV(B)(5)(a) in the April 24, 2020, SIP revision.

The April 24, 2020, SIP revision makes similar changes to subsection IV(D), which specifies requirements for the notification and conduct of source tests. In the SIP, paragraph IV(D)(1) requires a source owner, operator, or representative to submit a complete written notification that a source test will be conducted at least two weeks prior to the test date. The April 24, 2020, SIP revision adds language that allows source owners, operators, or representatives to submit a complete written notification at least two weeks prior to the test date “or as otherwise specified by a relevant federal or state requirement.” Similar to the above-described revision to subparagraph IV(B)(5)(a), the change to paragraph IV(D)(1) would allow a source owner, operator, or representative to comply with an alternate source testing notification deadline specified in an applicable Federal or State standard to which the source is subject. This change pertains to timing of source testing notifications only and therefore will have no impact on air quality. For these reasons, the EPA is proposing to approve the change to paragraph IV(D)(1) in the April 24, 2020, SIP revision.

The April 24, 2020, SIP revision also makes a change to paragraph IV(D)(5), which, in the SIP, requires that source tests be conducted “while the source is operating at the maximum expected production rate or other production rate or operating parameter which would result in the highest emissions for the pollutants being tested,” unless otherwise approved by the Department. The April 24, 2020, SIP revision adds to that requirement “or as otherwise specified in a relevant federal or state requirement.” This change would allow an owner, operator, or representative of a source subject to other applicable Federal or State source testing standards, e.g., performance testing standards NSPS or National Emission Standards for Hazardous Air Pollutants (NESHAPs), to comply with alternate source testing procedures specified in those standards. 22 This change to paragraph IV(D)(5) does not materially alter the existing SIP provision because the discretionary language in SIP-approved paragraph IV(D)(5) already allows the State to authorize such alternate source testing procedures. This change to paragraph IV(D)(5) does not materially alter the existing SIP provision because the discretionary language in SIP-approved paragraph IV(D)(5) already allows the State to authorize such alternative source testing procedures. 23 The State is recognizing that there could be a reason for testing to take place under an operating scenario that differs from the one that results in the highest emissions such as partial load conditions, which would be specified in relevant State or Federal standards. The April 24, 2020, SIP revision explains that this change is being made to clarify the appropriate production rate or operating parameter to be used while conducting a source test for clarity and internal consistency. Under subsection IV(B), the State must approve the test plan, required under subsection IV(C), prior to the source conducting the test. The test plan includes the test objective at paragraph IV(C)(2), which constitutes a description of the overall purpose of the test and the citation of any State or Federal regulation or permit condition requiring the test. Additionally, the State includes in paragraph IV(D)(5) that any source test performed “at a production rate less than the rated capacity may result in permit limits on emission rates, including limits on production if necessary.” Therefore, the State is able to evaluate the procedures and whether they meet the objective prior to the testing being conducted. For these reasons, the EPA is proposing to approve the change to paragraph IV(D)(5) in the April 24, 2020, SIP revision.

The April 24, 2020, SIP revision also makes a change to subsection IV(C), which specifies requirements for the content of site-specific test plans. In the SIP, subparagraph IV(C)(3)(b) requires that process descriptions in site-specific test plans include process design rates and normal operating rates. The April 24, 2020, SIP revision adds language requiring process descriptions to also include “operating rates specified by applicable regulation.” This change ensures that, if any applicable regulations specify other source operating rates, those rates are included in the site-specific test plan. Therefore, the EPA proposes to approve the change to subparagraph IV(C)(3)(b) in the April 24, 2020, SIP revision.

The EPA is proposing to approve the aforementioned changes to Regulation 61-62.1, Section IV because they will not interfere with any applicable requirement concerning attainment and RFP (as defined in section 171), or any other applicable requirement of the CAA.

The EPA is proposing to approve certain changes and conditionally approve certain other changes to Regulation 61-62.5, Standard No. 5.2 (hereinafter “Standard No. 5.2”) in the October 1, 2007, July 27, 2016, September 5, 2017, and February 4, 2022, SIP revisions. 24 25 The EPA discusses the changes to Standard No. 5.2 and the rationale for its proposed action below.

The October 1, 2007, July 27, 2016, September 5, 2017, and February 4, 2022, SIP revisions make several non-substantive edits to Standard No. 5.2 that revise the State's NO X emission standards and control requirements for certain new and modified stationary sources. In the October 1, 2007, SIP revision, the changes to Standard No. 5.2 consist of several minor edits, such as restructuring and clarifying language changes. In the July 27, 2016, SIP revision, the changes to Standard No. 5.2 consist of further administrative changes, such as reformatting subsections and rule references, adjusting punctuation, restructuring, and minor language edits. In the September 5, 2017, SIP revision, changes to Standard No. 5.2 adjust bolded and italicized text, correct a typographical error, and make clarifying language edits. In the February 4, 2022, SIP revision, changes to Standard No. 5.2 reformat subsections and rule references, correct citations to the CFR by adding the words “Parts” and “Part”, adjust punctuation and table headings, correct “million British thermal units” (MMBtu) by removing the word “metric” after “million”, correct typographical errors, including typographical rule reference, language, and punctuation errors, and make restructuring and clarifying language edits. The EPA is proposing to approve these non-substantive edits because they are administrative and/or clarifying in nature and will have no impact on air quality. The EPA's proposed action with respect to other changes to Standard No. 5.2 in the October 1, 2007, July 27, 2016, September 5, 2017, and February 4, 2022, SIP revisions is discussed below.

The October 1, 2007, SIP revision makes changes to Section I, which specifies the applicability of Standard No. 5.2. In the SIP, paragraph I(A)(1) states that subject sources include any new source “permitted to construct after the effective date of this regulation.” The October 1, 2007, SIP revision revises Standard No. 5.2 applicability in paragraph I(A)(1) to provide that subject sources include any new source “constructed after June 25, 2004.” The changes to paragraph I(A)(1) clarify the state effective date of the regulation, June 25, 2004, the date Standard No. 5.2 was finalized in the State Register. The changes are non-substantive and will have no impact on air quality. Therefore, the EPA is proposing to approve the changes to paragraph I(A)(1) in the October 1, 2007, SIP revision.

The July 27, 2016, SIP revision makes changes to subsection I(A) and paragraphs I(A)(2) and (3). In its submittal, South Carolina states that subsection I(A) is revised to explain which sources are subject to Standard No. 5.2. In the SIP, subsection I(A) states that Standard No. 5.2 applies to any stationary source that emits or has the potential to emit (PTE) NO X from fuel combustion that has not undergone a BACT analysis for NO X pursuant to the State's prevention of significant deterioration (PSD) regulations in Regulation 61-62.5, Standard No. 7 and meets one or more of the Standard No. 5.2 applicability criteria outlined in paragraphs I(A)(1)-(3). The July 27, 2016, SIP revision revises Standard No. 5.2 applicability at subsection I(A) to remove language limiting applicability to stationary sources of NO X that have not undergone BACT analyses for NO X in accordance with SC Regulation 61-62.5, Standard No. 7 and meet one or more the criteria listed in paragraphs I(A)(1)-(3). The SIP revision adds language stating that a stationary source becomes an “affected source”  26 under the regulation by meeting one or more of the criteria specified in paragraphs I(A)(1)-(3). Although the revision removes the language specifying applicability to sources that have not undergone PSD BACT for NO X , the July 27, 2016, SIP revision adds language to Standard No. 5.2 at Subsection I(B) which exempts any source that has undergone a BACT analysis for NO X pursuant to the State's PSD regulations. 27 For this reason, the changes are non-substantive and will have no impact on air quality. Therefore, the EPA is proposing to approve the changes to Subsection I(A) in the July 27, 2016, SIP revision.

The July 27, 2016, SIP revision makes clarifying changes to paragraph I(A)(2). In the SIP, paragraph I(A)(2) states that Standard No. 5.2 applies to any existing source where a burner assembly is replaced with another burner assembly after the regulation effective date and specifies that the replacement of individual burner assembly components such as burner heads, nozzles, or windboxes does not trigger regulation applicability. The July 27, 2016, SIP revision adds language clarifying that any existing source where a burner assembly is replaced with another burner assembly after the regulation effective date becomes an “existing affected source” subject to Sections V, VI, and VII in Standard No. 5.2. 28 This change clarifies that the sources identified in paragraph I(A)(2) are existing affected sources subject to those Sections in the SIP. Another change to paragraph I(A)(2) clarifies that the replacement of individual burner assembly components does not trigger “affected source status.”

In the SIP, paragraph I(A)(3) states that Standard No. 5.2 applies to any existing source moved from one permitted facility to another after the regulation effective date, with the exceptions of process equipment and commercial or industrial boilers transferred between in-state facilities under common ownership. Further, in the SIP, paragraph I(A)(3) specifies that such transferred sources are considered existing sources under paragraph I(A)(2). The July 27, 2016, SIP revision adds language clarifying that any existing source moved from one permitted facility “in-state or out-of-state” to another permitted facility “in-state” after the regulation effective date is considered a “new affected source.” New affected sources are subject to requirements for new sources in Section III and the new Section IV in the revised Standard No. 5.2. Other changes to paragraph I(A)(3) modify the exemption from new affected source status for existing process equipment and commercial or industrial boiler sources transferred between in-state facilities under common ownership. The revised provision provides that “[a]ny existing sources”—not just process equipment and commercial or industrial boilers—that are relocated between permitted in-state facilities under common ownership do not become existing affected sources under the regulation until paragraph I(A)(2) “is triggered,” ( i.e., a burner assembly is replaced, consistent with the Standard No. 5.2 applicability to other existing subject sources).

The changes to paragraph I(A)(3) clarify that existing sources relocated from in- or out-of-state permitted facilities to another permitted in-state facility are considered new, rather than existing, affected sources. Standard No. 5.2, Section III, in the SIP, and as revised, prescribes NO X emission limits and/or control requirements applicable to new sources as defined in paragraphs I(A)(1) and I(A)(3). In the SIP, paragraph I(A)(3) identifies a category of existing sources as those where any existing source is “removed from its presently permitted facility and moved to another permitted facility after the effective date of this regulation except process equipment and commercial or industrial boilers that are transferred between facilities within the state under common ownership. Such transfers will be considered as existing sources under (a)(2).” Although subsection III(A) states that sources defined in paragraphs I(A)(1) and I(A)(3) are subject to the requirements for new sources within that subsection, in the SIP, paragraph I(A)(3) itself does not specify whether the affected sources it applies to are considered new sources nor whether the original permitted facility could be out-of-state, except where the previously described exempted process equipment and commercial or industrial boilers are concerned.

In the July 27, 2016, SIP revision, changes to paragraph I(A)(3) clarify that any existing sources transferred from in- or out-of-state to another permitted in-state facility subject to section I(A) are considered new affected sources under Standard No. 5.2, except for any existing sources relocated between facilities within the State under common ownership. For the latter existing sources, the revised language clarifies that they become existing affected sources under Standard No. 5.2 when paragraph I(A)(2) is triggered ( i.e., a burner assembly is replaced). The changes to paragraph I(A)(3) with respect to those sources that are considered new affected sources clarify that such sources must comply with the emission limits and/or control requirements in Section III once they are relocated.

The changes to paragraph I(A)(3) clarify and delineate when a source qualifies as a new affected source as opposed to remaining an existing affected source. The SIP specifies that an existing affected source is one that is moved to another permitted facility within the State under common ownership, after the effective date of the regulation, except for transfers of process equipment and commercial or industrial boilers. The change simply clarifies that the transfer of process equipment and commercial or industrial boilers transferred between in-state facilities under common control does not trigger new affected source status and has no practical effect on regulation applicability. Under Standard No. 5.2, process equipment and commercial and industrial boilers comprise all the relevant sources that could be transferred as described and trigger existing affected source requirements in paragraph I(A)(2). Although “process equipment” is not defined in the regulation or elsewhere in the SIP, a common understanding of the term in the context of Standard No. 5.2 would be equipment that is integral to the process that generates NO X emissions through fuel burning ( e.g., cement kilns). The only new source types listed in Section III that would not be considered “process equipment” and are not commercial or industrial boilers are internal combustion engines and gas turbines. The State notes explicitly in the definition of “Burner Assembly” in Standard No. 5.2 that “[a] self-contained chamber such as is found on a combustion turbine is not a burner assembly for the purposes of this regulation.” Therefore, internal combustion engines and gas turbines, which do not have burner assemblies consistent with the definition in the regulation, cannot trigger existing source applicability under paragraph (I)(A)(2).

In the event that any internal combustion engines or gas turbines are relocated between permitted facilities within the State under common ownership, those units would be considered new affected sources. The changes to the exemption for existing sources relocated between permitted facilities in-state under common ownership in paragraph I(A)(3) do not practically affect the universe of sources subject to the requirements for new or existing affected sources in the regulation and therefore have no impact on air quality. Further, eliminating undefined terms, ( e.g., “process equipment”) and utilizing the broader “any existing source” has no practical effect on the exemption from new affected source requirements. As revised, paragraph I(A)(3) does not exempt any sources relocated as previously described from regulation applicability but merely clarifies that such sources do not become existing affected sources until the qualifying burner replacement trigger under paragraph I(A)(2). For the reasons described above, the EPA is proposing to approve the changes to paragraphs I(A)(2) and (3) in the July 27, 2016, SIP revision. The EPA is proposing to approve the aforementioned changes to Standard No. 5.2, Subsection I(A) through the February 4, 2022, SIP revision, because they will not interfere with any applicable requirement concerning attainment and RFP (as defined in section 171), or any other applicable requirement of the CAA.

The October 1, 2007, SIP revision makes changes to Subsection I(B), which exempts certain sources from all requirements within Standard No. 5.2 unless otherwise specified. The revision expands an exemption for certain emergency power generators. In the SIP, paragraph I(B)(2) exempts emergency power generators of less than 150 kilowatt (kW) rated capacity, as well as larger emergency power generators that operate 250 hours per year or less and have a method to record actual hours of use, such as an hour meter. The October 1, 2007, SIP revision modifies the exemption for emergency power generators to separate the existing exemption in paragraph I(B)(2) by including prefatory text at paragraph I(B)(2) and creating two new subparagraphs, I(B)(2)(a) and I(B)(2)(b). The revision expands the exemption to include emergency power generators of less than or equal to 150 kW rated capacity (subparagraph I(B)(2)(a)), as well as generators greater than 150 kW rated capacity “designated for emergency use only” that are operated “500 hours per year or less for testing and maintenance” and have a method to record actual hours of use, such as an hour meter (subparagraph I(B)(2)(b)). In its submittal, the State notes that paragraph I(B)(2) was amended “to ensure that exemptions are consistent with proposed amendments to Regulation 61-62.1, Section II,” South Carolina's permitting requirements. 29

The changes to paragraph I(B)(2) expand the 250-hour annual operating limit to 500 hours and clarify that these generators designated for emergency use only are limited to testing and maintenance uses. However, the changes to paragraph I(B)(2) in the October 1, 2007, SIP revision are superseded by relevant changes to subsection I(B) in the July 27, 2016, and February 4, 2022, SIP revisions, which the EPA is proposing to approve for reasons explained below or which the State, as previously noted, removed from the EPA's consideration in its July 21, 2026, letter.

In the October 1, 2007, SIP revision, a change to subsection I(B) modifies an exemption for combustion control devices at paragraph I(B)(4). In the SIP, paragraph I(B)(4) exempts any device that functions “solely as a combustion control device” from Standard No. 5.2. A change to paragraph I(B)(4) adds language clarifying that waste heat recovery from combustion control devices “shall not be considered primary grounds for exclusion from this exemption.” Waste heat recovery can help facilities reduce fuel consumption, as well as associated operating costs and pollutant emissions, by utilizing heat energy that would otherwise be lost. For example, combined heat and power (CHP) is an efficient method of providing power and useful thermal energy such as heating or cooling at the point of use with a single fuel source. 30 Although not strictly functioning as “combustion control” devices, those devices that function as combustion control devices that also recover waste heat can further reduce NO X emissions, and the change to paragraph I(B)(4) is expected to have a neutral to positive impact on air quality. Therefore, the EPA proposes to approve the changes to paragraph I(B)(4) in the October 1, 2007, SIP revision.

In the July 27, 2016, SIP revision, changes to subsection I(B) remove exemptions from Standard No. 5.2 for the following sources: (1) fuel-burning sources less than 10 MMBtu/hour (hr) rated input capacity at paragraph I(B)(1); (2) emergency power generators at paragraph I(B)(2), as modified in the October 1, 2007, SIP revision and described above; (3) “Flares” at paragraph I(B)(8); and (4) “Fuel Cell Sources” at paragraph I(B)(10). The July 27, 2016, SIP revision also adds three new exemptions at paragraphs I(B)(1), (2), and (3), described below. The addition of the three new exemptions shift and renumber the remaining paragraphs in subsection I(B). In the July 27, 2016, SIP revision, changes to subsection I(B) also revise renumbered paragraphs I(B)(4), (6)-(8), (10)-(13), and (15). Paragraphs I(B)(5), (14), and (16) are simply renumbered without changes, 31 and paragraph I(B)(9) remains unchanged. In its submittal, the State notes that subsection I(B) was amended to clarify sources exempt from Standard No. 5.2 and for internal consistency.

In the July 27, 2016, SIP revision, the removal of the exemption in paragraph I(B)(1) expands the applicability of the SIP because it results in Standard No. 5.2 applying to fuel-burning sources with less than 10 MMBtu per hour (10 MMBtu/hr) rated input capacity. In the SIP, any fuel-burning source with less than 10 MMBtu/hr rated input capacity is exempt from Standard No. 5.2. However, other relevant changes to subsection I(B) since the July 27, 2016, SIP revision, specifically those in the February 4, 2022, SIP revision, which the EPA is proposing to approve for reasons explained below supersede the removal of paragraph I(B)(1). Specifically, relevant changes to subsection I(B) in the February 4, 2022, SIP revision, which the EPA is proposing to approve, exempt boilers less than 10 MMBtu/hr rated input, nullifying the removal of the exemption as it applies to those boilers. The EPA's evaluation of the superseding revisions to paragraph I(B)(1) can be found in Section IV.B.1.b.iii. of this NPRM.

The July 27, 2016, SIP revision removes paragraph I(B)(2), the provision exempting emergency power generators from Standard No. 5.2 with less than or equal to a 150 kW rated capacity, and emergency power generators with a rated capacity greater than 150 kW designated for emergency use only operated no more than 500 hours annually for testing and maintenance, with a method to record actual hours of use, as previously described. Although new paragraph I(B)(1) in the July 27, 2016, SIP revision essentially maintains the exemption by exempting any NO X -emitting source listed in Regulation 61-62.1, Subsection II(B), 32 under the State's minor source preconstruction permitting regulation, the revision is superseded by relevant changes to subsection I(B) in the February 4, 2022, SIP revision, and the July 21, 2026, letter.

Specifically, the February 4, 2022, SIP revision (1) narrows the scope of the exemption in new paragraph I(B)(1), as added in the 2016 SIP revision, and (2) combines paragraph I(B)(1), as narrowed, and paragraph I(B)(2) into a single exemption at paragraph I(B)(2). The July 21, 2026, letter SC DES submitted removed from the EPA's consideration paragraph I(B)(2), as submitted in the July 27, 2016, SIP revision, and revised in the February 4, 2022, SIP revision. 33

The EPA is proposing to approve the change removing paragraph I(B)(2) from the SIP, as requested in the July 27, 2016, SIP revision. 34 Further, since SC DES' July 21, 2026 letter removes paragraph I(B)(2) as revised in the February 4, 2022, SIP submittal, from the EPA's consideration, this approval results in the removal of the exemption for emergency power generators of less than 150 KW rated capacity, or those that operate 250 hours per year or less and have a method to record the actual hours of use such as an hour meter. Since these emergency generators will be subject to the NO X emission limits and/or control requirements in Standard No. 5.2, the SIP revision is SIP-strengthening. The EPA discusses its proposed action with respect to changes to Standard No. 5.2, Subsection I(B) in the February 4, 2022, SIP revision in Section IV.B.1.b.iii. of this NPRM.

In the July 27, 2016, SIP revision, new paragraph I(B)(3) exempts from Standard No. 5.2 any source which has undergone a BACT analysis or is subject to Lowest Achievable Emission Rate (LAER) for NO X pursuant to the State's PSD regulations in Regulation 61-62.5, Standard No. 7 and Nonattainment New Source Review (NNSR) regulations in Regulation 61-62.5, Standard No. 7.1, respectively. As explained previously in this NPRM, in the current SIP, subsection I(A) provides that Standard No. 5.2 applies to sources of NO X that have not undergone a PSD BACT analysis, and a change to subsection I(A) in the July 27, 2016, SIP revision removes, in part, language capturing stationary sources of NO X that have not undergone BACT analyses for NO X . Therefore, the addition of the exemption for sources having undergone a NO X BACT analysis is a neutral, non-substantive change that has no practical effect on regulation applicability and therefore no impact on air quality.

With respect to the added exemption for sources subject to LAER pursuant to the State's NNSR regulations, these requirements apply to new major sources and major modifications at existing sources for pollutants in areas designated “nonattainment” for one or more NAAQS. LAER for a source is the more stringent emissions rate based on (1) the most stringent emissions limitation in any state's SIP for the source class or category, unless the owner or operator demonstrates that such limitation is not achievable; or (2) the most stringent emission limitation achieved in practice for the source class or category. 35 South Carolina currently has no nonattainment areas, but, if an area in the State were to be designated “nonattainment” and future projects were to trigger NNSR for NO X , those sources exempt from Standard No. 5.2 under new paragraph I(B)(3) would be subject to the State's NNSR requirements, including the requirement to install LAER for NO X , and would be covered by those more stringent requirements. Therefore, the addition of new paragraph I(B)(3) exempting from Standard No. 5.2 sources subject to LAER would not interfere with any applicable requirement concerning attainment and RFP or any other applicable requirement of the Act, and the EPA is proposing to approve the addition of new paragraph I(B)(3) in the July 27, 2016, SIP revision.

In the July 27, 2016, SIP revision, changes to paragraph I(B)(4) clarify that 200-brake horsepower is equivalent to 149 kW. Changes to paragraphs I(B)(6)-(8) replace “NO X controls” and “controls” with “NO X limits” and “limits,” respectively, to clarify that certain sources are exempt from Standard No. 5.2 if they are subject to equivalent or more stringent NO X emission limits in applicable Federal regulations (NSPS or NESHAPs), equivalent or more stringent NO X emission limits in the State's SIP-approved NO X budget program regulations in Regulation 61-62.96, or NO X emission limits in the State's SIP-approved NO X budget program regulations in Regulation 61-62.99 for stationary sources outside the trading program. In the July 27, 2016, SIP revision, the removal from the SIP of the exemptions for flares at paragraph I(B)(8) and fuel cell sources at paragraph I(B)(10) expands Standard No. 5.2 applicability to capture the universe of sources formerly covered by those exemptions. Another change to paragraph I(B)(10) in the July 27, 2016, SIP revision corrects an exemption to clarify that it applies to engine test cells “and/or” stands.

In the July 27, 2016, SIP revision, changes to paragraph I(B)(12) revise an exemption for certain portable and temporary internal combustion engines. In the current SIP, paragraph I(B)(12) exempts from Standard No. 5.2 portable and temporary internal combustion engines, such as those associated with generators, air compressors, or other applications, if they fall in categories listed in 40 CFR part 89, Control of Emissions from New and In-Use Nonroad Compression-Ignition Engines. Changes to paragraph I(B)(12) in the July 27, 2016, SIP revision renumber the paragraph to I(B)(11) and add that portable and temporary internal combustion engines that fall in categories listed in 40 CFR part 1039, Control of Emissions From New and In-Use Nonroad Compression-Ignition Engines, and 40 CFR part 1068, General Compliance Provisions for Highway, Stationary, and Nonroad Programs, are also exempt from Standard No. 5.2. Following the 1990 amendments to the CAA, which authorized the EPA to set emission standards for nonroad engines, the Agency conducted a series of rulemakings to adopt emission control programs for different nonroad sectors. 36 Since then, the Agency has migrated “legacy” emission control programs under title 40 from subchapter C to subchapter U, 37 and, in each case, the migration corresponded to new emission standards and substantially updated compliance and testing provisions. 38 For land-based nonroad diesel engines, the EPA adopted emission standards for model year 1996 and later nonroad compression-ignition engines under 40 CFR part 89 and migrated regulatory requirements for those engines to 40 CFR part 1039, with additional testing and compliance provisions in 40 CFR parts 1065 and 1068. 39 The regulations in 40 CFR part 1039 apply for new compression-ignition nonroad engines, with certain exceptions, 40 and certain in-use land-based compression-ignition nonroad engines, 41 and certain standards applicable to nonroad compression-ignition engines originally adopted under 40 CFR part 89 are identified in Appendix I to 40 CFR part 1039.

40 CFR part 1068 provides general compliance provisions for highway, stationary, and nonroad programs and applies to certain engine and equipment categories described in 40 CFR 1068.1(a), including land-based nonroad compression-ignition engines subject to 40 CFR part 1039, 42 certain stationary compression-ignition engines, large nonroad spark-ignition engines subject to 40 CFR part 1048, certain stationary spark-ignition engines, and small nonroad spark-ignition engines subject to 40 CFR part 1054. 43 A “[n]onroad engine,” as defined in 40 CFR part 1068.30, is an internal combustion engine that meets certain criteria, including the criterion that an engine, by itself or on a piece of equipment, is portable or transportable, which under the definition of nonroad engine means designed to be and capable of being carried or moved from one location to another. 44 The definition of nonroad engine in 40 CFR part 1068.30, also provides that an internal combustion engine is not a nonroad engine if it is regulated under 40 CFR part 60 or otherwise regulated by a Federal NSPS promulgated under CAA section 111, unless that engine meets certain criteria and is voluntarily certified under 40 CFR part 60. The definition also provides that if a portable or transportable engine remains or will remain at a location for more than 12 consecutive months or a shorter period of time for an engine located at a seasonal source, it is not a nonroad engine. 45

In the July 27, 2016, SIP revision, the changes to renumbered paragraph I(B)(11) exempt from Standard No. 5.2 certain portable and temporary internal combustion engines, i.e., large nonroad spark-ignition engines subject to 40 CFR part 1048 and small nonroad spark-ignition engines subject to 40 CFR part 1054. However, because paragraph I(B)(11) exempts portable and temporary internal combustion engines, as distinguished from stationary engines in 40 CFR 1068.31(e), and Standard No. 5.2 was designed to regulate stationary sources of NO X , the expanded exemption applicable to portable and temporary internal combustion engines listed in 40 CFR part 1068 does not affect the universe of stationary sources of NO X subject to the regulation. The changes to paragraph I(B)(11) also update the exemption from Standard No. 5.2 for the universe of portable and temporary nonroad compression-ignition internal combustion engines subject to Federal requirements. For these reasons, the EPA is proposing to approve the changes to paragraph I(B)(11) in the July 27, 2016, SIP revision.

In the July 27, 2016, SIP revision, changes to paragraph I(B)(12), renumbered from I(B)(13), revise an exemption for combustion sources that operate at a capacity of less than 10 percent per year. The changes to renumbered paragraph I(B)(12) exempt combustion sources that operate at an “annual capacity factor” of 10 percent “or less.”  46 The revised provision will exempt combustion sources operating at an annual capacity factor of 10 percent, whereas now, the SIP exempts sources operating at an annual capacity factor of 9.99 percent or lower. This change will have a negligible impact on air quality. Therefore, the EPA is proposing to approve the changes to paragraph I(B)(12) in the July 27, 2016, SIP revision.

A change to paragraph I(B)(13) in the July 27, 2016, SIP revision amends an exemption for special use burners that are operated less than 500 hours a year. In the SIP, any special use burners, such as startup/shutdown burners, that are operated less than 500 hours a year are exempt from the requirements in Standard No. 5.2. The change to paragraph I(B)(13) provides that such special use burners are only exempt from existing source replacement requirements. With this change, special use burners, when operated less than 500 hours annually, are now subject to the requirements for new sources in the regulation, e.g., emission limitations and/or control requirements in Section III. These burners are still exempt from the requirements for existing sources in the regulation, meaning they are not considered existing affected sources when a burner assembly is replaced and therefore are not subject to the requirements in the regulation for such sources pursuant to paragraph I(A)(2). The revised language in paragraph I(B)(13) removing the exemption for certain new affected special use burners from Standard No. 5.2 expands the regulation's applicability and therefore strengthens the SIP.

In the July 27, 2016, SIP revision, changes to paragraph I(B)(16) renumbers the paragraph to I(B)(15) and clarify that portable sources such as asphalt or concrete batch plants are “considered existing sources only and become existing affected sources when the burner assembly is replaced” pursuant to paragraph I(A)(2). In the current SIP, paragraph I(B)(16) states that those sources are only exempt from the requirements in Section III, which specifies emission limits and/or control requirements for new affected sources. The revised language in renumbered paragraph I(B)(15) clarifies that portable sources are exempt from standards for new sources in Standard No. 5.2, but subject to standards for existing affected sources in the regulation when a burner assembly is replaced.

In the July 27, 2016, SIP revision, the removal from the SIP of paragraphs I(B)(8) and I(B)(10) expands regulation applicability and therefore has a neutral to positive impact on air quality. The changes to paragraphs I(B)(4), (6)-(8), (10), and (15) are non-substantive and therefore have no impact on air quality. The changes to renumbered paragraph I(B)(11) do not meaningfully affect the universe of stationary sources of NO X subject to the regulation, and the changes to renumbered paragraph I(B)(12) will have a negligible impact on air quality. The change to renumbered paragraph I(B)(13) (paragraph I(B)(14) in the current SIP) expands Standard No. 5.2 applicability to capture new special use burners operated less than 500 hours a year as new affected sources and therefore has a neutral to positive impact on air quality. Therefore, the EPA is proposing to approve the removal of current paragraphs I(B)(8) and (10) and the changes to paragraphs I(B)(4), renumbered I(B)(6)-(8), renumbered I(B)(10)-(13), and renumbered I(B)(15) in the July 27, 2016, SIP revision.

The February 4, 2022, SIP revision adds exemptions at new paragraphs I(B)(1), (3), and (9), described below, shifting and renumbering the remaining paragraphs. 47 In its February 4, 2022, submittal, the State notes that, in part, paragraph I(B)(1) is replaced with language to ensure consistency and clarify sources that are exempt from Standard No. 5.2, including boilers less than 10 MMBtu/hr rated input.

As noted above, the July 27, 2016, SIP revision removes from Standard No. 5.2 an exemption for any fuel-burning sources less than 10 MMBtu/hr rated input capacity at paragraph I(B)(1) in the SIP, and the February 4, 2022, SIP revision adds an exemption for boilers less than 10 MMBtu/hr rated input at new paragraph I(B)(1). Taken together, the previously described changes narrow the universe of exempt sources under paragraph I(B)(1) from any fuel-burning source less than 10 MMBtu/hr rated input capacity to only boilers of the same input capacity and are expected to have a neutral to positive impact on air quality. Therefore, the EPA is proposing to approve the addition of new paragraph I(B)(1) in the February 4, 2022, SIP revision.

In the February 4, 2022, SIP revision, new paragraph I(B)(9) exempts from Standard No. 5.2 any source subject to equivalent or more stringent NO X emission limits pursuant to requirements in Regulation 61-62.97, the State's Cross-State Air Pollution Rule (CSAPR) trading program regulations in the SIP. New paragraph I(B)(9) only serves to exempt from Standard No. 5.2 sources already subject to equivalent or more stringent NO X limits under the State's SIP-approved CSAPR NO X annual trading program regulations, which adopt and incorporate by reference certain provisions of 40 CFR part 97, subpart AAAAA and include certain other provisions related to South Carolina's CSAPR NO X annual trading program. For this reason, the added exemption under new paragraph I(B)(9) from the requirements in Standard No. 5.2 for sources subject to the State's CSAPR requirements would not interfere with any applicable requirement concerning attainment and reasonable further progress or any other applicable requirement of the Act. Therefore, the EPA is proposing to approve the addition of new paragraph I(B)(9) in the February 4, 2022, SIP revision.

The EPA is proposing to approve the aforementioned changes to Standard No. 5.2, subsection I(B), because they will not interfere with any applicable requirement concerning attainment and RFP (as defined in section 171), or any other applicable requirement of the CAA.

In the July 27, 2016, SIP revision, the changes to Regulation 61-62.5, Standard No. 5.2, Section II add definitions for “Annual Capacity Factor,” “Equivalent Technology,” “Existing affected source,” and “New affected source” at new Subsections II(A), (F), (G), and (I), respectively, and remove the existing SIP-approved definition of “Tune-up,” shifting and renumbering the existing SIP-approved subsections. Additional changes to Section II in the July 27, 2016, SIP revision clarify the definition of “Fuel” in subsection II(H). In its submittal, the State notes that Section II was amended “to strike obsolete definitions and add others to further clarify existing definitions.”

In the current SIP, “Tune-up” is defined as “adjustments made to the combustion process to optimize combustion efficiency of the source in accordance with procedures provided by the manufacturer or in accordance with good engineering practices.” The State's tune-up requirements in new Section IV and in Section VII require new affected sources, with certain exceptions, 48 and existing affected sources, respectively, to perform tune-ups in accordance with manufacturer's specifications or good engineering practices. Therefore, the EPA proposes to approve the removal of the definition of “Tune-up” from Standard No. 5.2 in the July 27, 2016, SIP revision, finding that the change is non-substantive and administrative in nature and therefore has no impact on air quality.

In the July 27, 2016, SIP revision, new subsection II(A) defines “Annual Capacity Factor” as “the ratio between the actual heat input to a combustion unit from the fuels during a calendar year and the potential heat input to the steam generating unit had it been operated for 8,760 hours during a calendar year at the maximum steady state design heat input capacity,” generally consistent with the NSPS definition of “Annual capacity factor” for industrial-commercial-institutional steam generating units at 40 CFR 60.41b. This term is utilized in subsection I(B).

In the July 27, 2016, SIP revision, new subsection II(F) defines “Equivalent Technology” as “any item that is identical or functionally equivalent to the existing component” and states that “[t]his component may serve the same purpose or function as the replaced component, but may be different in some respects or improved in some ways.” This term is utilized under the requirements for new and existing affected sources in Section III in the current SIP and subsection V(A), renumbered from subsection IV(A) in the current SIP, respectively. The addition of this definition helps to clarify the meaning of the phrase included in these sections.

In the July 27, 2016, SIP revision, new Subsections II(G) and (I) define “Existing affected source” and “New affected source,” respectively. New Subsection II(G) defines “Existing affected source” as a source “constructed on or before June 25, 2004,” the Standard No. 5.2 effective date, and that meets the applicability criteria in paragraph I(A)(2), which specifies criteria for existing affected sources. New Subsection II(I) defines “New affected source” as “any affected source” constructed after June 25, 2004, or that meets the applicability criteria in paragraph I(A)(3), which specifies criteria for new affected sources transferred from a permitted facility to another permitted facility in-state after the regulation effective date, with certain exceptions, and clarifies that “[a] new affected source will not be considered an existing affected source at burner assembly replacement” under paragraph I(A)(2). These terms are utilized throughout Standard No. 5.2. New subsections II(A), (F), (G), and (I) in the July 27, 2016, SIP revision clarify the meaning of the terms of “Annual Capacity Factor,” “Equivalent Technology,” “Existing affected source,” and “New affected source,” respectively, as utilized in Standard No. 5.2. Therefore, the EPA proposes to approve the definitions added to Section II in the July 27, 2016, SIP revision.

In the July 27, 2016, SIP revision, changes to Subsection II(H) clarify the definition of “Fuel.” The changes to subsection II(H) separate the existing definition into prefatory text at subsection II(H) and add six new paragraphs to separately define listed fuel types. In the current SIP, subsection II(H) defines “Fuel” as “the following or any combination of the following: virgin fuel, fossil fuel, waste, waste fuel, biomass fuel, biofuel, methanol, ethanol, biodiesel, landfill gas, digester gas, process liquid or gas, or any combustible material the Department determines to be a fuel.” As revised, prefatory subsection II(H) and new paragraphs II(H)(1)-(6) define “Fuel” as “the following fuels, any combination of the following fuels or any combustible material the Department determines to be a fuel including, but not limited to” virgin fuel, waste, waste fuel, and clean wood (biomass fuel) as defined in Regulation 61-62.1; biodiesel; biofuel; digester gas; fossil fuel; and landfill gas. 49

In the July 27, 2016, SIP revision, new paragraphs II(H)(1)-(6) include added explanatory language. New paragraph II(H)(1) clarifies that “[v]irgin fuel, waste, waste fuel, and clean wood (biomass fuel)” in Standard No. 5.2 carry the same meanings as those terms in the State's definitions and general requirements in Regulation 61-62.1 in the SIP.

New paragraph II(H)(2) defines “Biodiesel” as a “mono-alkyl ester derived from vegetable oil and animal fat and conforming to [American Society for Testing and Materials] ASTM D6751,” generally consistent with the definition of that term in regulations for the renewable fuel program under CAA section 211(o) at 40 CFR 80.2. 50

New paragraph II(H)(3) defines “biofuel” as “any biomass-based solid fuel that is not a solid waste. This includes, but is not limited to, animal manure, including litter and other bedding materials; vegetative agricultural and silvicultural materials, such as logging residues (slash), nut and grain hulls and chaff (for example, almond, walnut, peanut, rice, and wheat), bagasse, orchard prunings, corn stalks, coffee bean hulls and grounds.” This definition is consistent with the NESHAP definition of “biomass” for industrial, commercial, and institutional boilers at 40 CFR 63.11237. 51

New paragraph II(H)(4) defines “Digester gas” as “any gaseous by-product of wastewater treatment typically formed through the anaerobic decomposition of organic waste materials and composed principally of methane and CO 2 [carbon dioxide].” This definition is consistent with the NSPS definition of that term for stationary spark ignition internal combustion engines at 40 CFR 60.4248.

New paragraph II(H)(5) defines “Fossil Fuel” as “natural gas, petroleum, coal, and any form of solid, liquid, or gaseous fuel derived from such material for the purpose of creating useful heat.” It also defines “[p]etroleum for facilities constructed, reconstructed, or modified before May 4, 2011,” as “crude oil or a fuel derived from crude oil, including, but not limited to, distillate oil and residual oil. For units constructed, reconstructed, or modified after May 3, 2011, petroleum means crude oil or a fuel derived from crude oil, including, but not limited to, distillate oil, residual oil, and petroleum coke.” These definitions for “fossil fuel” and “petroleum” are consistent with the NSPS definitions of those terms for electric utility steam generating units at 40 CFR 60.41Da.

New paragraph II(H)(6) defines “Landfill Gas” as a “gaseous by-product of the land application of municipal refuse typically formed through the anaerobic decomposition of waste materials and composed principally of methane and CO 2 .” This definition is consistent with the NSPS definition of that term for stationary spark ignition internal combustion engines at 40 CFR 60.4248.

The changes to subsection II(H) in the July 27, 2016, SIP revision clarify the definition of “Fuel” as utilized in Standard No. 5.2 and the fuel types included within the definition and have no impact on air quality. Therefore, the EPA proposes to approve the changes to subsection II(H) in the July 27, 2016, SIP revision.

In the February 4, 2022, SIP revision, the changes to Section II add a definition for “Non-routine maintenance” at new subsection II(J). 52 In its submittal, the State notes that Section II(J) was added “to define the term non-routine maintenance for clarification.” In the February 4, 2022, SIP revision, new Subsection II(J) defines “Non-routine maintenance” as “an unforeseen failure of a single burner assembly in an existing affected source with multiple burner application forcing an unplanned replacement of the existing burner.” This term is utilized in subsection V(A) where existing affected sources as defined in paragraph I(A)(2) are exempt from requirements to replace an existing burner assembly with a low-NO X burner assembly or equivalent technology and to achieve a 30 percent reduction from uncontrolled NO X emission levels based on manufacturer's specifications when a single burner assembly at a source with multiple burners is replaced “due to non-routine maintenance.”  53 New subsection II(J) in the February 4, 2022, SIP revision clarifies the meaning of the term “Non-routine maintenance” as utilized in Standard No. 5.2. Therefore, the EPA proposes to approve that definition added to Section II of Standard No. 5.2 in the February 4, 2022, SIP revision.

In the October 1, 2007, SIP revision, a change to Section III in Table 1, which prescribes NO X emission limits and/or control requirements for new affected boilers, internal combustion engines, gas turbines, and other sources subject to Standard No. 5.2, clarifies that process heaters not meeting the definition of “Boiler” in Regulation 61-62.1, Section I are an example of a fuel combustion source type not otherwise listed in Table 1 to which control requirements apply. 54 Table 1 provides separate standards for various new boilers subject to Standard No. 5.2. The clarifying change to Table 1 in Section III in the October 1, 2007, SIP revision are non-substantive and therefore have no impact on air quality. Therefore, the EPA proposes to approve the change to Section III in the October 1, 2007, SIP Revision.

In the July 27, 2016, SIP revision, changes to Section III clarify and revise requirements for new affected sources in subsections III(B) and(D) and Table 1. 55 In its submittal, the State notes that Section III is amended “to further explain the requirements for new affected sources,” clarify existing requirements, “ensure internal consistency,” and “cite items” pursuant to “the 2014 South Carolina Legislative Council's Standards Manual.” In its submittal, the State also notes that Table 1 is amended to revise emission limit and/or control requirement measurement units to “ensure consistency” with Federal requirements, to clarify source types and existing requirements, and to “ensure internal consistency.”

Changes to the section title and Subsections II(B) and (D) clarify that subject sources are new “affected” sources. Changes throughout Section III also clarify that sources must meet emission standards in Table 1 by replacing “capable of achieving the limitations” with “shall achieve” under the various standards in Table 1.

In the July 27, 2016, SIP revision, clarifying changes to the Table 1 structure (1) remove “Control Technology and/or” from the first level table heading, so the table prescribes an “Emission Limit” that depends on the “Source Type”; (2) remove a second level “Boilers and Water Heaters” heading (which purported to cover various boilers, internal combustion engines, gas turbines, and other fuel- burning sources, e.g., kilns), 56 and (3) add a third level “Other” heading, so the table is partitioned by source type under second level category headings into third level subcategories for various boilers, internal combustion engines, gas turbines, and other fuel-burning sources. The changes to Table 1 also move “Cement Kilns” from the “Combined Cycle—Distillate Oil Combustion” gas turbine subcategory to the “Other” category and replace language to clarify that other fuel combustion sources not otherwise specified are those “burning any non-specified fuel not listed” in Table 1.

Other clarifying changes to Table 1 in the July 27, 2016, SIP revision remove alternate equivalent emission limits, e.g., changes to gas turbine standards remove emission limits in pounds per MMBtu (lb/MMBtu), leaving equivalent limits in parts per million by volume (ppmv) at 15 percent oxygen (O 2 ) dry basis; changes to landfill gas-fired turbine, recovery furnace, and lime kiln standards clarify that those sources are subject to emission limits prescribed in percent O 2 (oxygen) “Dry Basis”; and changes to standards for boilers burning multiple fuels clarify that the “combination of fuels not otherwise listed” in Table 1 will be addressed on a case-by-case basis. Additionally, in the July 27, 2016, SIP revision, a change to Table 1 corrects an emission limit for municipal refuse-fired boilers from 200 to 195 ppmv at 12 percent CO 2 , consistent with the applicable equivalent 0.35 lb/MMBtu emission limit. The EPA is proposing to approve the clarifying changes and correction to Section III in the July 27, 2016, SIP revision, because these changes are non-substantive and administrative in nature and therefore have no impact on air quality. The EPA discusses its proposed action with respect to other changes to Section III revising subsection III(D) and Table 1 below.

In the July 27, 2016, SIP revision, a change to subsection III(D) removes the language “(April 1 through October 31)” describing “ozone season” from the provision, which, as revised, provides that affected sources required to install post-combustion NO X control technology are required to use such technology during the ozone season. This change removes an inconsistency with the ozone monitoring season for South Carolina listed in 40 CFR part 58, appendix D, table D-3. Therefore, the EPA is proposing to approve the change to subsection III(D) in the July 27, 2016, SIP revision.

A change to Table 1 revises a second level heading for “Natural Gas-Fired Boilers” to cover “Propane and/or Natural Gas-Fired Boilers,” expanding Standard No. 5.2 applicability by capturing new affected propane-fired boilers. This change is expected to have positive impact on air quality because the change expands the universe of sources subject to new affected source requirements to those that fire propane and those that fire a combination of propane and natural gas in addition to the natural gas-fired boilers under the current SIP. Therefore, the EPA proposes to approve the revised Section III, Table 1 subheading in the July 27, 2016, SIP revision.

Other changes to Table 1 in the July 27, 2016, SIP revision revise standards for fluidized bed combustion (FBC) boilers to (1) categorize FBC boilers by design instead of fuel type, (2) revise FBC control requirements, and (3) increase an FBC emission limit. In the SIP, the entries under FBC boilers delineate those units by two fuel types, coal-fired and wood-fired. In the SIP, both coal-fired and wood-fired FBC boilers are required to use selective noncatalytic reduction-urea (SNCR-urea) “capable of achieving 51.8 parts per million (ppm) at 3 percent O 2 or an equivalent limit of 0.07 lb/MMBtu.” In the July 27, 2016, SIP revision, the changes to those entries replace the existing FBC boiler entries delineated by fuel type with entries delineating FBC boilers by two different designs, “Bubbling Bed” and “Circulating Bed,” irrespective of the fuel burned. Other changes revise the new entries for bubbling and circulating bed FBC boilers to allow subject boilers to select SNCR systems other than urea-based systems, 57 and to require those units to use SNCR to meet, for circulating bed units, the existing emission limit of 0.07 lb/MMBtu and, for bubbling bed units, an increased emission limit of 0.15 lb/MMBtu (equivalent emission limits prescribed in ppm are also removed).

SNCR is a post-combustion emissions control technology for reducing NO X by injecting an ammonia-type reactant into a furnace at a determined location. 58 According to findings included in the seventh edition of the EPA Air Pollution Control Cost Manual discussing SNCR as a NO X control, based on review of emission reductions for SNCR applications in a variety of industries, operating data indicates higher NO X reductions occur with ammonia reagent. With respect to the revised emission limit for the new bubbling bed FBC boiler entry, in the State's March 23, 2020, letter, the State explains that it consulted the RACT/BACT/LAER Clearinghouse to set the 0.07 lb/MMBtu emission limit in 2004, but all new wood-fired bubbling bed units requested a case-by-case determination because those units could not meet the 0.07 lb/MMBtu emission limit. 59 In the 2020, letter, South Carolina notes that results from these case-by-case determinations led to the development of the higher 0.15 lb/MMBtu emission limit that the State is seeking to incorporate into its SIP under the revised standards for new affected bubbling bed FBC boilers. The State asserts that, in practice, the increased emission limit has not led to a relaxation in emission limits for wood-fired bubbling bed units and the revised limit therefore has no effect on existing sources or NO X emissions within the State. The State also clarifies that any such new units would be regulated and their impacts assessed under the State's NSR program. New bubbling bed units subject to Standard No. 5.2 would be evaluated pursuant to the State's minor NSR program under Regulation 61-62.1, Section II. In the SIP, Regulation 61-62.1, paragraph II(A)(4) prohibits the issuance of any permit “to construct or modify a source . . . if emissions interfere with attainment or maintenance of any state or federal standard.”  60 For these reasons, the changes to the Table 1 standards for FBC boilers in the July 27, 2016, SIP revision would not interfere with any applicable requirement concerning attainment and reasonable further progress, or any other CAA requirement. Therefore, the EPA proposes to approve the changes to the Table 1 standards in Section III for new affected FBC boilers in the July 27, 2016, SIP revision.

In the February 4, 2022, SIP revision, changes to Section III revise the definition of a variable used to calculate certain emission limits for multiple fuel boilers in Table 1. The changes to the Table 1 multiple fuel boilers emission limit variable revise the definition of the variable “H ng ,” used in the formula for calculating NO X emission limits by adding language to specify that H ng is the heat input from the combustion of natural gas “and/or propane.” This change is consistent with changes to Table 1 in the July 27, 2016, SIP revision that expand Standard No. 5.2 applicability to capture new propane-fired boilers. The changes to Table 1 standards for multiple fuel boilers specify that the heat input from the combustion of propane must be accounted for in the listed calculation under the variable that also accounts for the heat input from the combustion of natural gas, consistent with previous changes to Table 1. The changes to the Table 1 standards for multiple fuel boilers are expected to have a neutral to positive impact on air quality. Therefore, the EPA proposes to approve the changes to Table 1 in the February 4, 2022, SIP revision.

As previously noted in this NPRM, on May 13, 2026, SC DES submitted supplemental materials, including a letter requesting that the EPA conditionally approve portions of the State's NO X Control SIP revisions 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, should the EPA finalize this partial conditional approval as proposed. 61 Additionally, the supplemental materials include a CAA section 110(l) demonstration to support the corrective changes that the State intends to submit in a corrective SIP revision. 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. 62 Sections IV.B.4.a.i.4.III., IV.B.4.b.i.3., and IV.B.4.b.ii.3. of this NPRM discuss South Carolina's CAA section 110(l) analysis supporting these changes. The EPA evaluates CAA section 110(l) non-interference demonstrations on a case-by-case basis considering the circumstances of each SIP revision.

As explained below, in this NPRM, the EPA is proposing to conditionally approve changes to the following provisions submitted by the State in the July 27, 2016; September 5, 2017; and February 4, 2022, SIP revision submittals: IV(A)(1), including IV(A)(1)(a)-(d); IV(A)(2)(a), (b), and (c); IV(B)(2)(a); IV(B)(2)(b); IV(C)(1), including IV(C)(1)(a)-(d); IV(C)(3)(c); IV(C)(3)(d); IV(D)—the second prefatory paragraph; IV(D)(2)(a); and IV(D)(2)(b). The EPA's analysis of the changes proposed for approval or conditional approval in the previously listed submittals is discussed below.

In the July 27, 2016, SIP revision, the State adds to Standard No. 5.2 new Section IV, titled Monitoring, Record Keeping, and Reporting Requirements for New Affected Sources, shifting and renumbering the existing, subsequent sections in the SIP. In the July 27, 2016, SIP revision, new Section IV establishes MRR and certain other, e.g., testing, requirements for new affected boilers in subsection IV(A), internal combustion engines in subsection IV(B), turbines in subsection IV(C), and all other source types in subsection IV(D).

In the July 27, 2016, SIP revision, new Section IV includes language in the first prefatory paragraphs under subsections IV(A), IV(B), IV(C), and IV(D) to provide that, “[w]ith the exception of fuel certification and tune-up requirements,” source compliance with NO X monitoring requirements in 40 CFR part 60 constitutes compliance with monitoring requirements in those sections. New affected boilers, internal combustion engines, turbines, and all other affected source types subject to Federal NSPS NO X monitoring requirements in 40 CFR part 60 are not subject to the monitoring requirements in new Section IV but are required to comply with the new fuel certification and tune-up requirements in that section. The EPA is proposing to approve the first prefatory paragraphs under subsections IV(A), IV(B), IV(C), and IV(D) applicable to new affected boilers, internal combustion engines, turbines, and all other new affected source types, respectively, added in the July 27, 2016, SIP revision, because those paragraphs establish new Section IV applicability, i.e., fuel certification and tune-up requirements, for sources subject to NO X monitoring requirements in the Federal NSPS regulations.

Additional text in the second prefatory paragraphs under subsections IV(A), (B), and (C) provides that new affected boilers, internal combustion engines, and turbines, respectively, not subject to 40 CFR part 60 are required to comply with “applicable requirements” in those respective sections. Subsections IV(B) and IV(C) contain third prefatory paragraphs that require the owner or operator of an affected internal combustion engine or turbine, respectively, to comply with one of two alternative requirements. In the third subsection IV(B) prefatory paragraph, affected internal combustion engines are required to comply with either manufacturer's certification or periodic monitoring and/or source testing requirements in paragraphs IV(B)(1) or (2), respectively. In the third subsection IV(C) prefatory paragraph, affected turbines are required to comply with either continuous emissions monitoring system (CEMS) or parametric monitoring requirements in paragraphs IV(C)(1) or (2), respectively. The EPA is also proposing to approve the second prefatory paragraph under subsection IV(A) and the second and third prefatory paragraphs under subsections IV(B) and IV(C), added in the July 27, 2016, SIP revision, because those prefatory paragraphs establish Section IV applicability for subject boilers, internal combustion engines, and turbines not subject to NO X monitoring requirements in the Federal NSPS regulations and certain applicable requirements for such internal combustion engines and turbines.

Subsection IV(D) applies to new affected sources not subject to Federal NSPS NO X monitoring requirements that are not boilers, internal combustion engines, or turbines. The second subsection IV(D) prefatory paragraph states that, for all other new affected source types not required to comply with Federal NO X monitoring requirements in 40 CFR part 60, monitoring requirements “shall be established on a case by case basis.” The EPA is proposing to conditionally approve the second prefatory paragraph under subsection IV(D) for reasons explained below.

As previously described, the language in the second prefatory paragraph under subsection IV(D) provides that non-boiler, non-internal combustion engine, and non-turbine new affected sources not required to comply with NSPS NO X monitoring requirements are subject to monitoring requirements, established on a case-by-case basis. Although the July 27, 2016, SIP revision adds monitoring requirements for such sources, i.e., adds requirements that are SIP-strengthening, the EPA has concerns regarding the practicable enforceability of these requirements.

CAA section 110(a)(2)(A) requires SIPs to contain “enforceable emission limitations and other control measures, means, or techniques.” 40 CFR 51.111 requires SIPs to “set forth a control strategy” that includes, in part, procedures for monitoring compliance with each of the selected control measures. Additionally, as previously noted, CAA section 110(l) prohibits the EPA from approving a SIP revision that would interfere with any applicable requirement concerning attainment and RFP (as defined by CAA section 171), or any other applicable requirement of the CAA, and requires each SIP revision to undergo reasonable notice and public hearing at the state level. Under the second subsection IV(D) prefatory paragraph, which lacks specific monitoring procedures, it is unclear what monitoring requirements would apply for each subject source. Furthermore, the prefatory paragraph would allow the State to establish or change SIP requirements without fulfilling the public notice and hearing requirements of CAA section 110(l), and the EPA cannot evaluate in advance whether such changes would violate the noninterference requirements of that section.

As explained above, CAA section 110(k)(4) authorizes the EPA to conditionally approve a SIP revision based on a commitment from a state to adopt specific enforceable measures by a date certain, but not later than one year from the date of approval. On May 13, 2026, South Carolina submitted a supplemental letter to the Standard No. 5.2 SIP revisions submitted through February 4, 2022, requesting that the EPA conditionally approve portions of the State's SIP revisions to Standard No. 5.2 and committing to “specific enforceable changes” in “a good faith effort to resolve anticipated concerns with discretionary language.” The changes to the second subsection IV(D) prefatory paragraph in the July 27, 2016, SIP Revision are affected by relevant administrative changes to subsection IV(D) in the February 4, 2022, SIP revision, which the EPA is proposing to conditionally approve for reasons explained above and as described in Section IV.B.4.b.ii. of this NPRM.

In the July 27, 2016, SIP revision, new Section IV establishes CEMS requirements for certain new affected boilers in paragraph IV(A)(1) and turbines in paragraph IV(C)(1). Subject boilers not required to use CEMS are required to comply with certain periodic monitoring and/or source testing requirements in paragraph IV(A)(2), and subject turbines not required to use CEMS are required to comply with certain parametric monitoring requirements in paragraph IV(C)(2) applicable to certain turbines, depending on source characteristics, e.g., NO X control technology, and periodic monitoring and/or source testing requirements in paragraph IV(C)(3).

With respect to CEMS requirements applicable to subject boilers and turbines, subparagraphs IV(A)(1)(a) and IV(C)(1)(a) require the owner or operator of a boiler rated 200 MMBtu/hr or greater permitted for solid fuel or a subject turbine, respectively, to “install, calibrate, maintain, and operate CEMS” to measure NO X and O 2 or CO 2 emissions and record the system output, “[e]xcept as allowed by the Department.” Subparagraphs IV(A)(1)(b) and IV(C)(1)(b) require the CEMS to be operated and data recorded “during all periods of operation of the affected source,” except during “CEMS breakdowns and repairs,” and data to also be recorded during “calibration checks and zero and span adjustments.” Subparagraphs IV(A)(1)(c) and IV(C)(1)(c) require that CEMS be “installed, calibrated, maintained, and operated in accordance with approved methods in Regulation 61-62.60 or 61-62.72,” the State's designated facility plan and NSPS or acid rain regulations, respectively, “or as approved by the Department.”

For the new affected boilers and turbines subject to CEMS requirements, excess emissions-related requirements are stipulated under subparagraphs IV(A)(1)(d) and IV(C)(1)(d). In subparagraphs (A)(1)(d) and (C)(1)(d), prefatory language states that “[e]xcess emissions and monitoring systems performance reports shall be submitted semiannually” and postmarked by the 30th day following the end of each six-month period. 63 The prefatory language in those subparagraphs requires written excess emissions reports to include the information contained in subparagraphs IV(A)(1)(d)(i)-(iv) and (C)(1)(d)(i)-(iv), 64 e.g., the magnitude of excess emissions and the nature and cause of any malfunction, if known, etc. However, subsequent relevant changes to paragraph IV(A)(1) in the February 4, 2022, SIP revision, nullify a requirement for boilers required to use CEMS to specifically identify in their written excess emissions reports periods of excess emissions that occur during startup and shutdown. In the February 4, 2022, SIP revision, changes to the requirement for subject boilers to identify each period of excess emissions during startups, shutdowns, and malfunctions require subject boilers to identify each period of excess emissions during malfunctions. Therefore, with respect to the CEMS-related requirements for subject boilers in the July 27, 2016, SIP revision, the EPA is only evaluating the requirement to identify and report semiannually excess emissions during malfunctions. The February 4, 2022, SIP revision does not alter the requirement for turbines required to use CEMS to specifically identify each period of excess emissions during startups, shutdowns, and malfunctions. Subparagraph (A)(1)(d)(i) still requires that semiannual reports include “the date and time of commencement and completion of each time period of excess emissions, and the process operating time during the reporting period” as well as the magnitude of excess emissions. Thus, all periods of excess emissions must be reported for boilers.

The language in subparagraphs IV(A)(1)(a) and IV(C)(1)(a), i.e., “[e]xcept as allowed by the Department,” and subparagraphs IV(A)(1)(c) and IV(C)(1)(c), i.e., “or as approved by the Department,” provides the State with unbounded discretion to grant exceptions from CEMS MRR requirements. The discretionary language would allow the State to exempt from the requirements to install, calibrate, maintain, and operate CEMS as specified any boiler or turbine subject to new CEMS requirements under Standard No. 5.2. Any sources exempt from the requirements to install, calibrate, maintain, and operate CEMS under subparagraphs IV(A)(1)(a) and IV(C)(1)(a) would also be exempted from the requirement to submit excess emissions and monitoring systems performance reports semiannually. Although the July 27, 2016, SIP revision adds CEMS MRR requirements for certain subject boilers and turbines, i.e., adds requirements that are SIP-strengthening, the EPA has concerns with the practicable enforceability of the CEMS-related requirements in these paragraphs under CAA section 110(a)(2)(A), which requires SIPs to contain “enforceable emission limitations and other control measures, means, or techniques,” and under CAA section 110(l), which requires each SIP revision to undergo reasonable public notice and public hearing at the state level and for which the EPA cannot evaluate in advance whether these changes would violate the noninterference requirements of that section.

As explained above, CAA section 110(k)(4) authorizes the EPA to conditionally approve a SIP revision based on a commitment from a state to adopt specific enforceable measures by a date certain, but not later than one year from the date of approval. On May 13, 2026, South Carolina submitted a supplemental letter to the Standard No. 5.2 SIP revisions submitted through February 4, 2022, requesting that the EPA conditionally approve portions of the State's SIP revisions to Standard No. 5.2 and committing to “specific enforceable changes” in “a good faith effort to resolve anticipated concerns with discretionary language.”

In the February 4, 2022, SIP revision, the changes to paragraph IV(A)(1) are affected by relevant substantive and administrative changes to subsection IV(A), and the changes to paragraph IV(C)(1) are affected by relevant administrative changes to subsection IV(C), which the EPA is proposing to conditionally approve for reasons explained above and described in Section IV.B.4.b.i. of this NPRM.

In the July 27, 2016, SIP revision, under new Section IV, paragraph IV(C)(2) requires parametric monitoring for subject turbines not required to use CEMS, depending on source characteristics, e.g., NO X control technology. Parametric monitoring or a continuous parametric monitoring system measures one or more parameters that are a key indicator of system performance. The parameter(s) measured are generally operational parameters of the process or air pollution control device, e.g., temperature, pressure, or flow rate, which are known to affect process emissions levels or the control efficiency of the air pollution control device. Under paragraph IV(C)(2), subparagraph IV(C)(2)(a) requires a source owner or operator “using water or steam injection to control NO X ” to “install, calibrate, maintain, and operate a continuous monitoring system to monitor and record the fuel consumption and the ratio of water or steam to fuel being fired in the turbine.” Subparagraph IV(C)(2)(b) requires a source owner or operator “using a diffusion flame turbine without add-on selective catalytic reduction controls (SCR) to control NO X ” to “define at least four parameters indicative of the unit's NO X formation characteristics” and monitor those parameters continuously. Subparagraph IV(C)(2)(c) requires the owner or operator of “any lean premix stationary combustion turbine” to “continuously monitor the appropriate parameters to determine whether the unit is operating in low-NO X mode.” Subparagraph IV(C)(2)(d) requires the source owner or operator of “any turbine that uses SCR to reduce NO X ” to “continuously monitor appropriate parameters to verify the proper operation of the emission controls.”

In the July 27, 2016, SIP revision, new paragraph IV(C)(2) adds monitoring and record keeping requirements applicable to subject turbines not required to use CEMS to verify and demonstrate compliance with the NO X emission limits and/or control requirements in Standard No. 5.2. Therefore, the EPA is proposing to approve the added parametric monitoring requirements applicable to certain turbines in paragraph IV(C)(2) in the July 27, 2016, SIP revision.

In the July 27, 2016, SIP revision, paragraph IV(B)(1) requires subject internal combustion engines that comply with manufacturer's certification requirements in lieu of periodic monitoring and/or source testing requirements to operate and maintain the internal combustion engine and control device “according to the manufacturer's emission-related written instructions” and to change only emission-related settings “that are permitted by the manufacturer.” In the July 27, 2016, SIP revision, new paragraph IV(B)(1) adds alternative compliance requirements, in lieu of monitoring and record keeping requirements, applicable to subject internal combustion engines not subject to source testing. Therefore, the EPA is proposing to approve the added manufacturer's certification requirements applicable to certain internal combustion engines in paragraph IV(B)(1) in the July 27, 2016, SIP revision.

In the July 27, 2016, SIP revision, new Section IV establishes periodic monitoring and/or source testing requirements for certain new affected boilers, internal combustion engines, turbines, and all other affected source types. Under paragraph IV(A)(2), subparagraph IV(A)(2)(a) provides that, unless required to operate CEMS, testing requirements apply to boilers rated 30 MMBtu/hr or greater permitted for solid fuels and boilers rated greater than 100 MMBtu/hr permitted for any other fuels. 65 Under paragraph IV(C)(3), subparagraph IV(C)(3)(a) provides that testing requirements only apply to subject turbines not required to operate CEMS. Paragraphs IV(B)(2) and IV(D)(2) prescribe periodic monitoring and/or source testing requirements for internal combustion engines and all other affected source types, respectively. Paragraph IV(B)(2) applies to internal combustion engines, unless such engines comply with manufacturer's certification requirements in paragraph IV(B)(1) to operate and maintain the internal combustion engine and control device according to the manufacturer's emission-related written instructions and to change only emission-related settings as permitted by the manufacturer. Paragraph IV(D)(2) requires periodic monitoring and/or source testing for all other subject affected source types. Subparagraphs IV(A)(2)(b), IV(B)(2)(a), IV(C)(3)(c), and IV(D)(2)(a), applicable to subject new affected boilers, internal combustion engines, turbines, and all other subject new affected sources, respectively, require an initial source test for NO X emissions to be conducted within 180 days after startup, “[e]xcept as allowed by the Department.” Subparagraphs IV(A)(2)(c), IV(B)(2)(b), IV(C)(3)(d), and IV(D)(2)(b) require that, for the previously listed sources, periodic source tests for NO X be conducted every 24 months, “or as determined by the Department on a case by case basis in the permit condition for the affected source,” and state that source tests “will be used to show compliance with the NO X standard.” Subparagraphs IV(A)(2)(d), IV(B)(2)(d), IV(C)(3)(e), and IV(D)(2)(c) state that “[t]he Department reserves the right to require periodic source testing for any affected sources” and that all source testing must be conducted in accordance with the State's source testing requirements in Regulation 61-62.1, Section IV.

In the July 27, 2016, SIP revision, for subject internal combustion engines opting to comply with periodic monitoring and/or source testing requirements in lieu of manufacturer's certification requirements, additional unique periodic monitoring and/or source testing requirements apply. Subparagraph IV(B)(2)(c) requires that an engine owner or operator “operate the affected source(s) within the parameter(s) established during the most recent compliant source tests.” The provision also requires that a copy of the most recent Department-issued “source test summary letter(s) that established the parameter(s)” be maintained with a “required permit.”

Similarly, in the July 27, 2016, SIP revision, for subject turbines required to comply with periodic monitoring and/or source testing requirements in lieu of operating CEMS, additional unique periodic monitoring and/or source testing requirements apply. Subparagraph IV(C)(3)(b) requires that the “steam or water to fuel ratio or other parameters that are continuously monitored as described” in the section be monitored during the performance test “to establish acceptable values and ranges.” The provision allows a source owner or operator to supplement performance test data “with engineering analyses, design specifications, manufacturer's recommendations, and other relevant information to define the acceptable parametric ranges more precisely.” Subparagraph IV(C)(3)(b) also requires a source owner or operator to “develop and keep on-site a parameter monitoring plan which explains the procedures used to document proper operation of the NO X emission controls” which includes “the parameter(s) monitored and the acceptable range(s) of the parameter(s) as well as the basis for designating the parameter(s) and acceptable range(s)” and “[a]ny supplemental data such as engineering analyses, design specifications, manufacturer's recommendations, and other relevant information.”

The EPA is proposing to approve portions and conditionally approve portions of the added periodic monitoring and/or source testing requirements applicable to subject boilers, internal combustion engines, turbines, and all other new affected sources, as described individually below. The EPA is proposing to approve portions of the added periodic monitoring and/or source testing requirements applicable to subject internal combustion engines, turbines, and all other new affected sources that do not contain the discretionary language described above Specifically, the EPA is proposing to approve the paragraph IV(A)(2) title (“Periodic Monitoring and/or Source Test”); subparagraph IV(A)(2)(d); the paragraph IV(B)(2) title; subparagraphs IV(B)(2)(c) and (d); the paragraph IV(C)(3) title; subparagraphs IV(C)(3)(a), (b), and (e); the paragraph IV(D)(2) title; and subparagraph IV(D)(2)(c) in the July 27, 2016, SIP Revision. Subparagraph IV(B)(2)(c) specifies that subject internal combustion engines must operate within parameter(s) established during most recent compliant source tests and that a State-issued source test summary letter(s) establishing such parameters must be maintained with the required permit; subparagraph IV(C)(3)(a) states that testing requirements apply to subject turbines not required to operate CEMS; subparagraph IV(C)(3)(b) specifies parametric monitoring requirements during performance testing and parameter monitoring plan requirements for subject turbines; and subparagraphs IV(A)(2)(d), IV(B)(2)(d), IV(C)(3)(e), and IV(D)(2)(c) state that the State “reserves the right to require” periodic source testing “for any affected sources” and that all source testing must be conducted in accordance with the State's source testing requirements. These provisions add to Standard No. 5.2 periodic monitoring and/or source testing and related requirements relevant to subject internal combustion engines, turbines, and other affected sources for the purposes of demonstrating compliance with the NO X emission limits and/or control requirements in Standard No. 5.2.

As previously described, subparagraphs IV(A)(2)(b), IV(B)(2)(a), IV(C)(3)(c), and IV(D)(2)(a) require subject boilers, internal combustion engines, turbines, and other affected sources to conduct initial source tests for NO X emissions within 180 days of startup, and subparagraphs IV(A)(2)(c), IV(B)(2)(b), IV(C)(3)(d), and IV(D)(2)(b) require the previously listed sources to conduct periodic source tests every 24 months to show compliance with NO X standards applicable to subject sources in Standard No. 5.2. Although these requirements are SIP-strengthening, the EPA has concerns with the practicable enforceability of these provisions under CAA section 110(a)(2)(A), which requires SIPs to contain “enforceable emission limitations and other control measures, means, or techniques,” and under CAA section 110(l), which requires each SIP revision to undergo reasonable public notice and public hearing at the state level and for which the EPA cannot evaluate in advance whether these changes would violate the noninterference requirements of that section.

As explained previously, CAA section 110(k)(4) authorizes the EPA to conditionally approve a SIP revision based on a commitment from a state to adopt specific enforceable measures by a date certain, but not later than one year from the date of approval. On May 13, 2026, South Carolina submitted a supplemental letter to the Standard No. 5.2 SIP revisions submitted through February 4, 2022, requesting that the EPA conditionally approve portions of the State's SIP revisions to Standard No. 5.2 and committing to “specific enforceable changes” in “a good faith effort to resolve anticipated concerns with discretionary language.”

In this NPRM, the EPA is proposing to conditionally approve subparagraph IV(A)(2)(a), which requires certain boilers not subject to CEMS to comply with testing requirements in that paragraph, 66 and subparagraphs IV(A)(2)(b) and (c); IV(B)(2)(a) and (b); IV(C)(3)(c) and (d); and IV(D)(2)(a) and (b), which set source testing requirements for certain subject sources and provide that the State may exercise discretion as to whether, or when, source testing is required, submitted in the State's SIP revisions through February 4, 2022, 67 based on the State's commitment in its May 13, 2026, letter, 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 final action on South Carolina's submissions, should the EPA finalize this partial conditional approval as proposed. Additionally, the State's supplemental materials include a CAA section 110(l) demonstration to support these anticipated corrections that the State intends to submit in a final corrective SIP revision to address the provisions currently before the EPA, for which the State requests conditional approval.

Specifically, consistent with South Carolina's May 13, 2026, request, the EPA is proposing to conditionally approve the following text into the SIP under subparagraph IV(A)(2)(a).

(a) Unless required to operate a CEMS, testing requirements apply to boilers rated thirty (30) MMBtu/hr or greater permitted for solid fuels and boilers rated greater than one hundred (100) MMBtu/hr permitted for any other fuels.

Additionally, the EPA is proposing to conditionally approve the following text into the SIP under subparagraph IV(A)(2)(b).

(b) Except as allowed by the Department, an initial source test for NO X emissions shall be conducted within one hundred and eighty (180) days after startup.

The EPA is also proposing to conditionally approve the following text into the SIP under subparagraphs IV(B)(2)(a) and IV(D)(2)(a).

(a) Except as allowed by the Department, an initial source test for NO X shall be conducted within one hundred eighty (180) days after startup.

Furthermore, the EPA is also proposing to conditionally approve the following text into the SIP under subparagraph IV(C)(3)(c).

(c) Except as allowed by the Department, an initial source test for NO X emissions shall be conducted within one hundred eighty (180) days after startup.

Finally, the EPA is proposing to conditionally approve the following text into the SIP under subparagraphs IV(A)(2)(c), IV(B)(2)(b), IV(C)(3)(d), and IV(D)(2)(b).

Periodic source tests for NO X shall be conducted every twenty-four (24) months, 68 or as determined by the Department on a case by case basis in the permit condition for the affected source. Source tests will be used to show compliance with the NO X standard.

As noted previously, although the incorporation of these provisions adds source testing requirements for sources subject to the NO X control regulation, i.e., adds requirements that are SIP-strengthening, the EPA has concerns regarding the practicable enforceability of these requirements under CAA section 110(a)(2)(A), which requires SIPs to contain “enforceable emission limitations and other control measures, means, or techniques,” and under CAA section 110(l), which requires each SIP revision to undergo reasonable public notice and public hearing at the state level and for which the EPA cannot evaluate in advance whether these changes would violate the noninterference requirements of that section.

As noted above, on May 13, 2026, SC DES submitted a supplemental letter to the SIP revisions submitted through February 4, 2022, requesting that the EPA conditionally approve portions of the State's SIP revisions to Standard No. 5.2. Specifically, the State requested conditional approval of subparagraphs IV(A)(2)(b) and (c); IV(B)(2)(a) and (b); IV(C)(3)(c) and (d); and IV(D)(2)(a) and (b) and committed to “making specific enforceable changes to regulatory text in Standard No. 5.2” that include “establishment of specific terms to govern,” in part, “periodic source testing” and “removal of various discretionary provisions,” which the State frames as changes that “are clarifying and SIP-strengthening in nature.”

With the May 13, 2026, letter, South Carolina included draft regulatory changes to subparagraphs IV(A)(2)(b) and (c); IV(B)(2)(a) and (b); IV(C)(3)(c) and (d); and IV(D)(2)(a) and (b) that it committed to submit in a corrective SIP revision. Specifically, SC DES commits to removing the discretionary phrase “[e]xcept as allowed by the Department” from the requirements pertaining to initial source tests in subparagraphs IV(A)(2)(b), IV(B)(2)(a), IV(C)(3)(c), and IV(D)(2)(a). At the same time, the State commits to revise its initial source test requirements to add clarifying language requiring an initial source test to be conducted within 180 “ operating days after startup,” i.e., to indicate the 180-day timeframe refers to operating days (emphasis added). The State also commits to revising the discretionary language in the requirements pertaining to periodic source tests in subparagraphs IV(A)(2)(c), IV(B)(2)(b), IV(C)(3)(d), and IV(D)(2)(b) by removing the phrase “in the permit condition”-which provides that periodic source tests must be conducted every 24 months or on a case-by-case basis at the State's discretion as established in a permit condition—and replacing it with “not to exceed sixty (60) months,” i.e., with a sixty-month upper bound, providing that periodic source tests for NO X emissions must be conducted every 24 months or on a case-by-case basis at the State's discretion “not to exceed” 60 months. With the changes to subparagraphs IV(A)(2)(b) and (c), the State also anticipates renumbering those subparagraphs to subparagraphs IV(A)(2)(a)(i) and (ii) under subparagraph IV(A)(2)(a), which requires certain boilers not subject to CEMS to comply with testing requirements in that paragraph, and renumbering subparagraph IV(A)(2)(d) to IV(A)(2)(b). As noted above, the EPA is also proposing to conditionally approve subparagraph IV(A)(2)(a), because it is not severable from subparagraphs IV(A)(2)(b) and (c).

If South Carolina fulfills its commitment in line with the May 13, 2026, commitment letter and supplement and the EPA approves the corrective SIP revision, subparagraphs IV(A)(2)(b), IV(B)(2)(a), IV(C)(3)(c), and IV(D)(2)(a) would no longer function to allow the State to modify the requirements to conduct initial source tests for NO X , and subparagraphs IV(A)(2)(c), IV(B)(2)(b), IV(C)(3)(d), and IV(D)(2)(b) would no longer allow the State to modify the requirements to conduct periodic source tests for NO X without any upper bound. Instead, initial source tests would be required within 180 operating days of startup, and periodic source tests would be required every 24 months, subject to the State's discretion, on a case-by-case basis not exceeding a 60-month upper bound. If the State fails to meet its commitment within one year of the final conditional approval, should the EPA finalize this partial conditional approval as proposed, the conditional approval of the source testing provisions in subparagraphs IV(A)(2)(a), (b), and (c); IV(B)(2)(a) and (b); IV(C)(3)(c) and (d); and IV(D)(2)(a) and (b), as submitted in the State's SIP revisions through February 4, 2022, will be treated as a disapproval.

With its May 13, 2026, letter and supplement, SC DES submitted a CAA section 110(l) demonstration in support of its corrections to the Standard No. 5.2 provisions requested for partial conditional approval. South Carolina's CAA section 110(l) demonstration asserts that the specific enforceable changes to which the State has committed and which form the basis for the EPA's proposed conditional approval in this NPRM “will not interfere with South Carolina's continued, longstanding attainment of the [NAAQS]” but instead “strengthen the SIP.” Further, the State notes that it “does not expect any emission increases as a result of the changes,” and that, “to the contrary,” its corrections to the provisions requested for partial conditional approval “will enhance transparency” and the State's ability to evaluate compliance with Standard No. 5.2.

The State's CAA section 110(l) demonstration asserts that its anticipated corrections remove “open-ended discretionary language” from its MRR and testing requirements in changes that “bound or entirely remove Department discretion” and add, for its source testing and monitoring requirements, “increased clarity and specificity,” and, as such, strengthen the SIP and ensure practicable enforceability. 69 With respect to subparagraphs IV(A)(2)(b) and (c), IV(B)(2)(a) and (b), IV(C)(3)(c) and (d), and IV(D)(2)(a) and (b), in South Carolina's CAA section 110(l) demonstration, the State explains that it is “bounding the timeframes for initial and periodic source testing, and, therefore, strengthening the SIP.” Finally, regarding the changes before the EPA for conditional approval, in the May 13, 2026, letter, the State clarifies that it “has not previously implemented” its discretion and commits not to do so “while the regulatory revisions are pending.”

The EPA finds that the added provisions requiring initial and periodic source testing for subject sources to demonstrate compliance with the NO X emission limits and/or control requirements in Standard No. 5.2 are SIP-strengthening and, based on the State's May 13, 2026, commitment and supplement, the EPA is proposing to conditionally approve Standard No. 5.2, subparagraphs IV(A)(2)(a), (b), and (c), IV(B)(2)(a) and (b), IV(C)(3)(c) and (d), and IV(D)(2)(a) and (b), submitted through the February 4, 2022, SIP revision, contingent on the State's commitment under CAA section 110(k)(4) to adopt and submit corrective SIP revisions to those provisions no later than one year after the EPA's conditional approval of South Carolina's submissions, should the EPA finalize this partial conditional approval as proposed.

In the July 27, 2016, SIP revision, new Section IV establishes tune-up requirements for new affected sources subject to Standard No. 5.2, including those sources subject to NO X monitoring requirements in 40 CFR part 60, except for affected boilers and internal combustion engines subject to 40 CFR part 63. In prefatory text, paragraphs IV(A)(4) and IV(B)(3) provide that, if the owner or operator of a boiler or internal combustion engine is required to comply with Federal tune-up requirements in 40 CFR part 63, compliance with the Federal requirements constitutes compliance with the tune-up requirements in those paragraphs. Paragraphs IV(A)(4)(a), IV(B)(3)(a), IV(C)(4)(a), and IV(D)(1)(a), which apply to subject boilers and internal combustion engines and turbines and all other affected source types, respectively, require a source owner or operator to perform tune-ups every 24 months in accordance with manufacturer's specifications or with good engineering practices. Paragraphs IV(A)(4)(b), IV(B)(3)(b), IV(C)(4)(b), and IV(D)(1)(b) require all tune-up records to be maintained on-site and available for inspection by SC DES for five years “from the date generated.” Paragraphs IV(A)(4)(c), IV(B)(3)(c), IV(C)(4)(c), and IV(D)(1)(c) require a source owner or operator to develop and retain a tune-up plan on file. These tune-up requirements, applicable to new affected sources with the exceptions of new affected boilers and internal combustion engines subject to tune-up requirements in 40 CFR part 63, are consistent with tune-up requirements in the current SIP.

Section VI, in the current SIP sets forth tune-up requirements applicable to sources subject to Standard No. 5.2 and requires the following: (1) combustion source owners or operators are required to perform tune-ups every two years in accordance with manufacturer's specifications or good engineering practices; all tune-up records must be maintained on-site and available for inspection by the State for a period of five years; and the facility must develop and retain a tune-up plan on file. For more information and a description of changes to those requirements in the State's SIP revisions submitted through February 4, 2022, see Section IV.B.7. of this NPRM. To the extent that certain new affected boilers and internal combustion engines are required to comply with Federal tune-up requirements in 40 CFR part 63 instead of the tune-up requirements under Section IV, the EPA believes that applicable NESHAP tune-up requirements in 40 CFR part 63 are comparable, e.g., tune-up requirements for industrial, commercial, and institutional area source boilers at 40 CFR 63.11223(b). The EPA is proposing to approve the added tune-up and related record keeping requirements for new affected subject boilers and internal combustion engines and turbines and all other affected source types in paragraphs IV(A)(4), IV(B)(3), IV(C)(4), and IV(D)(1) in the July 27, 2016, SIP revision because these provisions establish tune-up requirements applicable to new affected sources, consistent with or comparable to the tune-up requirements for such sources in the existing SIP.

In the July 27, 2016, SIP revision, new Section IV establishes fuel certification requirements in paragraphs IV(A)(3), IV(B)(4), IV(C)(5), and IV(D)(3) for new affected sources subject to Standard No. 5.2, including sources subject to NO X monitoring requirements in 40 CFR part 60. These paragraphs require owners or operators of new affected boilers, internal combustion engines, turbines, and other affected sources to record the amounts and types of each fuel combusted by the affected sources and maintain monthly records of such on site. The EPA is proposing to approve the added fuel certification requirements for the previously listed sources in paragraphs IV(A)(3), IV(B)(4), IV(C)(5), and IV(D)(3) in the July 27, 2016, SIP revision because they add to the regulation certain fuel-related record keeping requirements applicable to subject sources.

In the July 27, 2016, SIP revision, under new Section IV, paragraphs IV(A)(5), IV(B)(5), and IV(C)(6) contain other record keeping requirements for subject boilers, internal combustion engines, and turbines, respectively. These provisions require owners or operators of new affected sources not subject to 40 CFR part 60 to maintain records documenting the occurrence and duration of any startup, shutdown, or malfunction in the operation of an affected source; any air pollution control equipment malfunction; and/or any periods during which a continuous monitoring system or monitoring device is inoperative.

However, changes to paragraphs IV(A)(5), IV(B)(5), and IV(C)(6) in the February 4, 2022, SIP revision nullify the requirements for such sources to maintain records documenting the occurrence and duration of any startup or shutdown in affected source operation. Therefore, the EPA is only evaluating the added requirements to document malfunction occurrences and durations during affected source operation, as well as any air pollution control equipment malfunction, and/or any periods during which a continuous monitoring system or monitoring device is inoperative. The EPA discusses its proposed action with respect to the relevant changes to paragraphs IV(A)(5), IV(B)(5), and IV(C)(6) in the February 4, 2022, SIP revision below, in Section IV.B.4.b.iv. of this NPRM.

As previously described, the July 27, 2016, SIP revision adds CEMS MRR requirements at subparagraphs IV(A)(1) and IV(C)(1) for certain subject boilers and turbines. In the February 4, 2022, SIP revision, a change to Section IV under paragraph IV(A)(1), as added in the July 27, 2016, SIP revision, revises CEMS MRR requirements for certain boilers not subject to 40 CFR part 60. Specifically, in the February 4, 2022, SIP revision, a change to subparagraph IV(A)(1)(d)(ii) revises excess emissions reporting requirements, which, in the July 27, 2016, SIP submittal, require written reports of excess emissions to specifically identify each period of excess emissions during affected source startup, shutdown, and malfunction to require such reports to only identify each period of excess emissions during malfunctions. Taken together, the net changes to subparagraph IV(A)(1)(d)(ii) in the July 27, 2016, and February 4, 2022, SIP revisions would require owners or operators of certain boilers subject to CEMS requirements in the regulation to submit to the State written excess emissions reports identifying, in part, each period of excess emissions during affected source malfunction (as opposed to the requirement for turbines required to use CEMS to specifically identify each period of excess emissions during startups, shutdowns, and malfunctions). Overall, these provisions add to Standard No. 5.2, CEMS MRR requirements applicable to certain boilers and turbines subject to NO X emission limits and/or control requirements in the regulation.

As previously described, paragraphs IV(A)(1) and IV(C)(1) require subject boilers and turbines to install, calibrate, maintain, and operate CEMS to measure NO X and O 2 or CO 2 emissions and to undertake related record keeping and reporting. Although these requirements are SIP-strengthening, the EPA has concerns with the practicable enforceability of these provisions under CAA section 110(a)(2)(A), which requires SIPs to contain “enforceable emission limitations and other control measures, means, or techniques,” and under CAA section 110(l), which requires each SIP revision to undergo reasonable public notice and public hearing at the state level and for which the EPA cannot evaluate in advance whether these changes would violate the noninterference requirements of that section.

In this NPRM, the EPA is proposing to conditionally approve paragraphs IV(A)(1) and IV(C)(1) submitted in the State's SIP revisions through February 4, 2022, 70 71 which set CEMS MRR requirements for certain subject boilers and turbines and provide that the State may exercise discretion to modify the requirements to install, calibrate, maintain, and operate CEMS. The EPA is proposing to conditionally approve these paragraphs based, in part, on the State's commitment in its May 13, 2026, letter, 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 should the EPA finalize this partial conditional approval as proposed. Additionally, the State's supplemental materials include a CAA section 110(l) demonstration to support these anticipated corrections that the State intends to submit in a final corrective SIP revision to address the provisions currently before the EPA, for which the State requests conditional approval.

Specifically, consistent with South Carolina's May 13, 2026, request, the EPA is proposing to conditionally approve the following text into the SIP under paragraph IV(A)(1).

(a) Except as allowed by the Department, the owner or operator of a boiler rated two hundred (200) MMBtu/hr or greater permitted for solid fuel, shall install, calibrate, maintain, and operate CEMS for measuring NO X , and Oxygen (O 2 ) or Carbon Dioxide (CO 2 ) emissions discharged to the atmosphere, and shall record the output of the system.

(b) The CEMS required under this section shall be operated and data recorded during all periods of operation of the affected source except for CEMS breakdowns and repairs. Data is to be recorded during calibration checks and zero and span adjustments.

(c) The CEMS required under this section shall be installed, calibrated, maintained, and operated in accordance with approved methods in Regulation 61-62.60 or 61-62.72, or as approved by the Department.

(d) Excess Emissions

Excess emissions and monitoring systems performance reports shall be submitted semiannually. All reports shall be postmarked by the thirtieth (30th) day following the end of each six (6) month period. Written reports of excess emissions shall include the following information:

(i) The magnitude of excess emissions, any conversion factor(s) used, the date and time of commencement and completion of each time period of excess emissions, the process operating time during the reporting period.

(ii) Specific identification of each period of excess emissions that occurs during malfunctions of the affected source. The nature and cause of any malfunction (if known), the corrective action taken, or preventative measures adopted.

(iii) The date and time identifying each period during which the continuous monitoring system was inoperative except for zero and span checks and the nature of the system repairs or adjustments.

(iv) When no excess emissions have occurred or the continuous monitoring system(s) have not been inoperative, repaired, or adjusted, such information shall be stated in the reports.

Additionally, the EPA is proposing to conditionally approve the following text into the SIP under paragraph IV(C)(1).

(a) Except as allowed by the Department, the owner or operator shall install, calibrate, maintain, and operate CEMS on the turbine for measuring NO X , and Oxygen (O 2 ) or Carbon Dioxide (CO 2 ) emissions discharged to the atmosphere, and shall record the output of the system.

(b) The CEMS required under this section shall be operated and data recorded during all periods of operation of the affected source except for CEMS breakdowns and repairs. Data is to be recorded during calibration checks and zero and span adjustments.

(c) The CEMS required under this section shall be installed, calibrated, maintained, and operated in accordance with approved methods in Regulation 61-62.60 or 61-62.72, or as approved by the Department.

(d) Excess Emissions

Excess emissions and monitoring systems performance reports shall be submitted semiannually. All reports shall be postmarked by the thirtieth (30th) day following the end of each six (6) month period. Written reports of excess emissions shall include the following information:

(i) The magnitude of excess emissions, any conversion factor(s) used, the date and time of commencement and completion of each time period of excess emissions, and the process operating time during the reporting period.

(ii) Specific identification of each period of excess emissions that occurs during startups, shutdowns, and malfunctions of the affected source. The nature and cause of any malfunction (if known), the corrective action taken, or preventative measures adopted.

(iii) The date and time identifying each period during which the continuous monitoring system was inoperative except for zero and span checks and the nature of the system repairs or adjustments.

(iv) When no excess emissions have occurred or the continuous monitoring system(s) have not been inoperative, repaired, or adjusted, such information shall be stated in the reports.

The EPA has concerns with the practicable enforceability of these provisions under CAA section 110(a)(2)(A), which requires SIPs to contain “enforceable emission limitations and other control measures, means, or techniques” and under CAA section 110(l), which requires each SIP revision to undergo reasonable public notice and public hearing at the state level, and for which the EPA cannot evaluate in advance whether these changes would violate the noninterference requirements of that section.

As noted above, on May 13, 2026, SC DES submitted a supplemental letter to the SIP revisions submitted through February 4, 2022, requesting that the EPA conditionally approve portions of the State's SIP revisions to Standard No. 5.2. Specifically, the State requested conditional approval of subparagraphs IV(A)(1)(a) and (c) and IV(C)(1)(a) and (c) and committed to “making specific enforceable changes to regulatory text in Standard No. 5.2” that include “establishment of specific terms to govern,” in part, “specific alternative monitoring provisions” “and removal of various discretionary provisions,” which the State frames as changes that “are clarifying and SIP-strengthening in nature.”

With the May 13, 2026, letter, South Carolina submitted anticipated corrective revisions to subparagraphs IV(A)(1)(a) and (c) and IV(C)(1)(a) and (c). Specifically, SC DES commits to removing the discretionary phrase “[e]xcept as allowed by the Department” from the requirements applicable to certain subject boilers and turbines to install, calibrate, maintain, and operate CEMS in subparagraphs IV(A)(1)(a) and IV(C)(1)(a). At the same time, the State commits to revise those requirements for subject boilers at subparagraph IV(A)(1)(a) to add language providing that, on request, in lieu of CEMS, the State may require Predictive Emissions Monitoring System (PEMS), if a source demonstrates that its use is warranted based on site-specific circumstances. Additionally, the State commits to removing the discretionary phrase “or as approved by the Department” from the requirements to install, calibrate, maintain, and operate CEMS in accordance with approved methods in Regulation 61-62.60 or 61-62.72 in subparagraphs IV(A)(1)(c) and IV(C)(1)(c). At the same time, the State commits to revise those requirements for subject boilers at subparagraph IV(A)(1)(c) to add language providing that sources using PEMS must install, calibrate, maintain, and operate PEMS in accordance with approved methods in Regulation 61-62.60, the State's regulation incorporating by reference designated facility plan and NSPS regulations.

If South Carolina fulfills its commitment in line with the May 13, 2026, commitment letter and supplement and the EPA approves the corrective SIP revision, subparagraphs IV(A)(1)(a) and (c) and IV(C)(1)(a) and (c) would no longer function to allow the State to modify the requirements to install, calibrate, maintain, and operate CEMS for certain subject boilers and turbines. Instead, subject boilers would be required to use CEMS, unless a source demonstrates that the use of PEMS, in lieu of CEMS, is warranted, based on site-specific circumstances, and subject boilers would be required to install, calibrate, maintain, and operate such CEMS or PEMS in accordance with State-approved methods in Regulation 61-62.60 or 61.62.72, as applicable. Similarly, subject turbines not using parametric monitoring would be required to use CEMS and to install, calibrate, maintain, and operate such CEMS in accordance with State- approved methods in Regulation 61-62.60 or 61.62.72.

The changes to which the State has committed would allow subject boilers to elect to use CEMS or PEMS, i.e., parametric monitoring. As previously described, parametric monitoring or a continuous parametric monitoring system measures one or more parameters that are a key indicator of system performance, i.e., generally operational parameters of the process or air pollution control device which are known to affect process emissions levels or the control efficiency of the air pollution control device. The use of PEMS provides for monitoring of key emissions-related parameters that can be correlated with emissions, rather than direct measurement of pollutant emissions. The use of parametric monitoring can provide more flexible and less expensive options than CEMS for demonstrating compliance of regulated sources, while providing reasonable assurance of compliance. 72 CEMS and PEMS are each designed to assess continuous compliance, and possible considerations a source could factor into account when requesting PEMS in lieu of CEMS include cost and space. Additionally, allowing facilities with subject boilers to possibly monitor compliance with CEMS or PEMS requirements is consistent with the requirements in Standard No. 5.2 for subject turbines, which, if not required to use CEMS, are required to use parametric monitoring. This committed change would bound the exercise of discretion by the State such that any subject boiler will have continuous monitoring requirements, either via CEMS or PEMS.

If the State fails to meet its commitment within one year of the final conditional approval, should the EPA finalize this partial conditional approval as proposed, the conditional approval of the CEMS MRR provisions in paragraphs IV(A)(1) and IV(C)(1), as submitted in the State's SIP revisions through February 4, 2022, will be treated as a disapproval.

For a description of the State's May 13, 2026, letter and CAA section 110(l) demonstration as it supports the specific enforceable changes to which the State has committed overall, see Section III.B.4.a.i.4.III. in this NPRM. With respect to subparagraphs IV(A)(1)(a) and IV(A)(1)(c), in South Carolina's CAA section 110(l) demonstration, the State explains that the changes to subparagraph IV(A)(1)(a) “remove discretionary language” to clarify that the subject boilers “may request a specific alternative” to CEMS, rather than leaving the alternative option “open-ended,” noting that, specifically, the State is clarifying that a source may request the use of PEMS, in lieu of CEMS, “if the source demonstrates that site-specific circumstances warrant its use.” Similarly, SC DES explains that the changes to subparagraph IV(A)(1)(c) remove the State's discretion and clarify “approved methods” for monitoring system installation, calibration, maintenance, and operation, by “specifying that all PEMS . . . be installed, calibrated, maintained, and operated in accordance with approved methods in Regulation 61-62.60.” With respect to subparagraphs IV(C)(1)(a) and IV(C)(1)(c), the State explains that those subparagraphs “are also being revised to remove discretionary language and specify the use of CEMS” and “approved methods for installation, calibration, maintenance, and operation.”

The monitoring procedures at subparagraphs IV(A)(1) and IV(C)(1) are expected to cover a small universe of sources subject to Standard No. 5.2, as the first prefatory paragraphs under subsection IV(A) and IV(C) include language stating that, with the exception of fuel certification and tune-up requirements, “compliance with required NO X monitoring in 40 CFR part 60 shall constitute compliance with the monitoring requirements in this section.” Finally, regarding the changes before the EPA for conditional approval, in the May 13, 2026, letter, the State clarifies that it “has not previously implemented” its discretion and commits not to do so “while the regulatory revisions are pending.”

The EPA finds that the added provisions containing CEMS MRR requirements applicable to subject boilers and turbines are SIP-strengthening and, based on the State's May 13, 2026, commitment and supplement, the EPA is proposing to conditionally approve Standard No. 5.2, paragraphs IV(A)(1) and IV(C)(1), submitted through the February 4, 2022, SIP revision, contingent on the State's commitment under CAA section 110(k)(4) to adopt and submit corrective SIP revisions to those provisions no later than one year after the EPA's conditional approval of South Carolina's submissions, should the EPA finalize this partial conditional approval as proposed.

As previously described, the July 27, 2016, SIP revision adds language in the second prefatory paragraph under subsection IV(D) which provides that non-boiler, non-internal combustion engine, and non-turbine new affected sources not subject to NSPS NO X monitoring requirements are subject to case-by-case monitoring requirements. As previously noted, subject boilers, internal combustion engines, and turbines not subject to 40 CFR part 60 are required to comply with applicable requirements in subsections IV(A), (B), and (C), respectively. Overall, the second prefatory paragraph under subsection IV(D) submitted in the State's SIP revisions through February 4, 2022, adds to Standard No. 5.2., discretionary language allowing the State to set, on a case-by-case basis, monitoring requirements for the subject sources.

As previously described, the second prefatory paragraph under subsection IV(D) contains language allowing SC DES to exercise director's discretion to set monitoring requirements for subject sources on a case-by-case basis. Although this provision is SIP-strengthening, it lacks any specific monitoring procedures and would allow the State to set monitoring requirements for the subject sources outside the SIP. The EPA has concerns with the practicable enforceability of these provisions under CAA section 110(a)(2)(A), which requires SIPs to contain “enforceable emission limitations and other control measures, means, or techniques” and under CAA section 110(l), which requires each SIP revision to undergo reasonable public notice and public hearing at the state level, and for which the EPA cannot evaluate in advance whether these changes would violate the noninterference requirements of that section.

In this NPRM, the EPA is proposing to conditionally approve the second prefatory paragraph under subsection IV(D) submitted in the State's SIP revisions through February 4, 2022, 73 which contains discretionary language allowing the State to set, on a case-by-case basis, monitoring requirements for subject sources, based on the State's commitment in its May 13, 2026, letter, 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, should the EPA finalize this partial conditional approval as proposed. Additionally, the State's supplemental materials include a CAA section 110(l) demonstration to support these anticipated corrections that the State intends to submit in a final corrective SIP revision to address the provisions currently before the EPA, for which the State requests conditional approval.

Specifically, consistent with South Carolina's May 13, 2026, request, the EPA is proposing to conditionally approve the following text into the SIP under subsection IV(D) in the second prefatory paragraph.

If the owner or operator is not required to comply with federal requirements in 40 CFR part 60 for monitoring NO X , then the monitoring requirements for the affected source shall be established on a case by case basis.

As noted above, the EPA has concerns with the practicable enforceability of this provision under CAA section 110(a)(2)(A) which requires SIPs to contain “enforceable emission limitations and other control measures, means, or techniques,” and under CAA section 110(l), which requires each SIP revision to undergo reasonable public notice and public hearing at the state level and for which the EPA cannot evaluate in advance whether these changes would violate the noninterference requirements of that section.

As noted above, on May 13, 2026, South Carolina submitted a supplemental letter to the SIP revisions submitted through February 4, 2022, requesting that the EPA conditionally approve portions of the State's SIP revisions to Standard No. 5.2. Specifically, the State requested conditional approval of the second prefatory paragraph under subsection IV(D) and committed to “making specific enforceable changes to regulatory text in Standard No. 5.2” that include “establishment of specific terms to govern,” in part, “specific alternative monitoring provisions” “and removal of various discretionary provisions,” which the State frames as changes that “are clarifying and SIP-strengthening in nature.”

With the May 13, 2026, letter, South Carolina included draft regulatory changes to the second prefatory paragraph under subsection IV(D) that it committed to submit in a corrective SIP revision. SC DES commits to replacing the discretionary language providing that monitoring requirements for all other affected source types not required to comply with NSPS NO X monitoring requirements will be established on a case-by-case basis with language modifying the case-by-case procedures for such sources requiring that the monitoring must be established “by a permit condition after public notice and opportunity for comment.”

If the State fulfills its commitment in line with the May 13, 2026, commitment letter and supplement and the EPA approves the corrective SIP revision, the second prefatory paragraph under subsection IV(D) would no longer provide the State with insufficiently bounded discretion to set monitoring requirements for the subject sources. Instead, any subject non-boiler, non-internal combustion engine, non-turbine new affected sources that would not trigger any NO X monitoring requirements under 40 CFR part 60 would be subject to monitoring requirements established in a permit condition having undergone public notice and the opportunity for public comment. If the State fails to meet its commitment within one year of the final conditional approval, should the EPA finalize this partial conditional approval as proposed, the conditional approval of the added monitoring provision in the second prefatory paragraph under Subsection IV(D), as submitted in the State's SIP revisions through February 4, 2022, will be treated as a disapproval.

For a description of the State's May 13, 2026, letter and CAA section 110(l) demonstration as it supports the specific enforceable changes to which the State has committed overall, see Section III.B.4.a.i.4.III. in this NPRM. With respect to the changes to Subsection IV(D), in South Carolina's CAA section 110(l) demonstration, the State explains that the changes to that subsection “clarify and ensure monitoring constraints on sources not subject to 40 CFR part 60 NO X monitoring by requiring the affected source monitoring requirements to be included in a permit condition that will undergo public notice and opportunity for comment.”

Because subsection IV(D) is intended to capture sources that the State may not reasonably anticipate as belonging to the universe of new affected sources subject to Standard No. 5.2 which would not trigger any relevant NO X monitoring requirements under 40 CFR part 60 and that fraction of subject sources is expected to be small, South Carolina anticipates needing to evaluate the NO X monitoring requirements at the time the facility is undergoing permitting for the subject source. The revised language requires an opportunity for public participation on the State's establishment of these monitoring requirements, which will not change the underlying requirements applicable to those sources in Section III to install low-NO X burners or equivalent technology that achieves 30 percent reduction in NO X from uncontrolled levels. Finally, regarding the changes before the EPA for conditional approval, in the State's May 13, 2026, letter, the State clarifies that it “has not previously implemented” its discretion and commits not to do so “while the regulatory revisions are pending.”

The EPA finds that the added provision providing for the establishment of monitoring requirements for subject non-boiler, non-internal combustion engine, and non-turbine sources is SIP-strengthening and, based on the State's May 13, 2026, commitment and 110(l) demonstration, the EPA is proposing to conditionally approve, in Standard No. 5.2, the second prefatory paragraph under subsection IV(D), submitted through the February 4, 2022, SIP revision, contingent on the State's commitment under CAA section 110(k)(4) to adopt and submit corrective SIP revisions to those provisions no later than one year after the EPA's conditional approval of South Carolina's submissions, should the EPA finalize this partial conditional approval as proposed.

In the February 4, 2022, SIP revision, changes under paragraphs IV(A)(4) and IV(B)(3) clarify tune-up requirements applicable to new affected boilers and internal combustion engines, respectively, that are not required to comply with NESHAP tune-up requirements in 40 CFR part 63. In paragraphs IV(A)(4) and IV(B)(3), added prefatory language clarifies that, if a boiler or internal combustion engine, respectively, is not subject to Federal tune-up requirements in 40 CFR part 63, the subsequent requirements apply. In paragraph IV(A)(4), new subparagraph IV(A)(4)(a) is added, shifting the original subparagraphs, as submitted in the July 27, 2016, SIP revision, and clarifies that, for the subject boilers, an initial tune-up must be conducted no more than 24 months from operation startup. The EPA is proposing to approve the changes to the prefatory language under paragraphs IV(A)(4) and IV(B)(3) and the addition of subparagraph IV(A)(4)(a) in the February 4, 2022, SIP revision because the changes to paragraphs IV(A)(4) and IV(B)(3) clarify tune-up requirements applicable to subject new affected boilers and internal combustion engines, respectively.

In the February 4, 2022, SIP revision, changes to Section IV in paragraphs IV(A)(5), IV(B)(5), and IV(C)(6) revise the requirements to maintain certain other records applicable to subject new affected boilers, internal combustion engines, and turbines, respectively, that are not subject to 40 CFR part 60. The paragraphs, introduced in the July 27, 2016, SIP revision, require a subject source owner or operator to maintain records of the occurrence and duration of any source operation startup, shutdown, or malfunction and, as revised in the February 4, 2022, SIP revision, require such records to document the occurrence and duration of malfunctions only. Taken together, the addition of paragraphs IV(A)(5), IV(B)(5), and IV(C)(6) in the July 27, 2016, SIP revision and the subsequent changes to those paragraphs in the February 4, 2022, SIP revision require owners or operators of subject boilers, internal combustion engines, and turbines, respectively, to maintain records to document each occurrence and the duration of any source malfunction. The EPA is proposing to approve the addition of these other record keeping requirements for the previously listed sources in paragraphs IV(A)(5), IV(B)(5), and IV(C)(6) in the July 27, 2016, SIP revision and the changes to those paragraphs in the February 4, 2022, SIP revision because these provisions add to the regulation certain operation, air pollution control equipment, and/or monitoring system or device malfunction-related recordkeeping requirements applicable to subject sources.

Lastly, in the February 4, 2022, SIP revision, under subsection IV(D), applicable to all other subject new affected sources, new paragraph IV(D)(4) adds requirements to maintain other records that mirror analogous requirements for subject boilers, internal combustion engines, and turbines in paragraphs IV(A)(5), IV(B)(5), and IV(C)(6), respectively. For all other affected source types not subject to NSPS NO X monitoring requirements in 40 CFR part 60, new paragraph IV(D)(4) requires the owner or operator to maintain records documenting the occurrence and duration of any malfunction in the operation of an affected source, any air pollution control equipment malfunction, or any periods during which a continuous monitoring system or monitoring device is inoperative. In its submittal, the State notes that subsection IV(D) is revised to describe recordkeeping requirements for an affected source during malfunction conditions. The EPA is proposing to approve the addition of the other recordkeeping requirements for all other affected source types not subject to 40 CFR part 60 in new paragraph IV(D)(4) in the February 4, 2022, SIP revision because this provision adds certain recordkeeping requirements for the subject sources, consistent with the recordkeeping requirements applicable to subject boilers, internal combustion engines, and turbines in paragraphs IV(A)(5), IV(B)(5), and IV(C)(6), respectively.

In the July 27, 2016, SIP revision, changes to Section V clarify requirements for existing affected sources, as defined in paragraph I(A)(2), subject to Standard No. 5.2 in subsections V(A), V(B), and V(C). In its submittal, the State notes that Sections IV, V, and VI are relocated at the end of Standard No. 5.2, as Sections V, VI, and VII, respectively, “for ease of use and clarity,” and revised and retitled. Changes to the section title and subsections V(A) and V(C) clarify that subject sources are existing “affected” sources. Another change to subsection V(A) replaces “capable of achieving” with “shall achieve.” According to the State, this change clarifies the standard requirements for existing affected sources. In subsection V(A) as revised, when an existing burner assembly is replaced after the regulation effective date, the replacement low-NO X burner assembly or equivalent technology “shall achieve” a 30 percent reduction from uncontrolled NO X emission levels based on manufacturer's specifications. A change to subsection V(B) updates the cross-reference to the burner assembly replacement notification requirements for existing affected sources in Standard 5.2 to reflect the relocation of those requirements. These changes to Section V strengthen the standard requirements for existing affected sources and will have a neutral to positive impact on air quality. Therefore, the EPA is proposing to approve the changes to Section V in the July 27, 2016, SIP revision.

In the July 27, 2016, SIP revision, changes to Section VI clarify notification requirements for existing affected sources subject to Standard No. 5.2 in paragraphs VI(A)(1) and VI(A)(5). Changes to the Section title and paragraphs VI(A)(1) and VI(A)(5) clarify that Section VI and the notification requirements within apply to existing affected sources. New subsection VI(A) adds the subheading, “Burner Assembly Replacement Notifications for Existing Affected Sources,” which clarifies that the notification requirements in Section VI describe burner assembly replacement notification requirements applicable to existing affected sources, shifting and renumbering the existing subsections in the SIP to paragraphs VI(A)(1)-(5). A change to paragraph VI(A)(5) clarifies that affected sources must submit a permit application “prior to replacement of the burner assembly(s)” to receive an emission reduction credit for a control device, if desired. These clarifying changes to Section VI are non-substantive and have no impact on air quality. Therefore, the EPA is proposing to approve the changes to Section VI in the July 27, 2016, SIP revision.

In the July 27, 2016, SIP revision, changes to Section VII revise tune-up requirements applicable to new and existing affected sources subject to Standard No. 5.2, with substantive changes made to paragraph VII(A). A change to the section title reflects that the Section VII tune-up requirements are revised to apply to existing sources, consistent with changes in the July 27, 2016, SIP revision to paragraph I(A)(2) clarifying existing affected source applicability, discussed in Section IV.B.1.a.ii. of this NPRM, and with added tune-up requirements applicable to certain new affected sources in new Section IV, which are comparable to the tune-up requirements formerly applicable to all sources subject to the regulation in the SIP, discussed in Sections IV.B.4.a.ii. and IV.B.4.b.iii. of this NPRM. 74

The changes to subsection VII(A) require new affected sources to conduct an initial tune-up no more than 24 months from operation startup and existing affected sources to conduct an initial tune-up no more than 24 months from burner assembly replacement. Changes to subsection VII(A) also clarify that each subsequent tune-up must be conducted no more than 24 months after the previous tune-up. Although changes to Subsection VII(A) in the July 27, 2016, SIP revision clarify initial and subsequent tune-up timeframes for new affected sources, those provisions were added to subsection VII(A) in error and subsequent relevant changes to Section VII in the February 4, 2022, SIP revision remove the added tune-up provision specific to new affected sources in the July 27, 2016, SIP revision. Therefore, the EPA is only evaluating the added tune-up requirements applicable to existing affected sources and discusses its proposed action with respect to the relevant changes to Section VII in the February 4, 2022, SIP revision below, in Section IV.B.7.b. of this NPRM. The changes to tune-up requirements for existing affected sources are non-substantive and have no impact on air quality. Therefore, the EPA is proposing to approve the changes to Section VII with respect to the tune-up requirements for existing affected sources in the July 27, 2016, SIP revision in subsection VII(A), because those changes clarify tune-up requirements applicable to existing affected sources.

In the February 4, 2022, SIP revision, a change to Section VII revises tune-up requirements to remove language applicable to new affected sources in subsection VII(A), added in the July 27, 2016, SIP revision. In its submittal, the State notes that Section VII was amended to remove “language addressing the deadline for the first tune-up for new affected sources to avoid duplication and to correct for text error.” The change to subsection VII(A) removes the previously described language requiring new affected sources to conduct the first tune-up no more than 24 months from operation startup. Taken together, the addition of language clarifying timeframes for new affected sources in Section VII(A) in the July 27, 2016, SIP revision and the subsequent removal of that language in the February 4, 2022, SIP revision would remove requirements applicable to new affected sources from the tune up requirements for existing affected sources in Standard No. 5.2, which require existing affected sources to conduct initial tune-ups within 24 months of the replacement of a burner assembly and each subsequent tune-up to be conducted no more than 24 months after the previous tune-up. As discussed above, tune-up requirements for new affected sources subject to Standard No. 5.2 are addressed in new Section IV, added in the July 27, 2016, SIP revision. For these reasons, the EPA is proposing to approve the changes to Section VII in the February 4, 2022, SIP revision.

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 Sections I through III of this preamble, the EPA is proposing to incorporate by reference Regulation 61-62.1, Section IV, Source Tests, state effective April 24, 2020. The EPA is also proposing to incorporate by reference Regulation 61-62.5, Standard No. 5.2, Control of Oxides of Nitrogen (NO X ), state effective April 24, 2020, except for paragraphs I(B)(2) and I(B)(3), subsection II(K), 75 and subsection III(A). 76 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).

Under the CAA, the Administrator is required to approve a SIP submission that complies with the provisions of the CAA and applicable Federal regulations. 42 U.S.C. 7410(k); 40 CFR 52.02(a). Thus, in reviewing SIP submissions, 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 under Executive Order 12866 (58 FR 51735, October 4, 1993);

• Is not subject to Executive Order 14192 (90 FR 9065, February 6, 2025) because SIP actions are exempt from review 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 in Executive Order 13132 (64 FR 43255, August 10, 1999);

• Is not subject to Executive Order 13045 (62 FR 19885, April 23, 1997) because it approves a state program;

• Is not a significant regulatory action subject to Executive Order 13211 (66 FR 28355, May 22, 2001); and

• Is not subject to requirements of section 12(d) of the National Technology Transfer and Advancement Act of 1995 (15 U.S.C. 272 note) because application of those requirements would be inconsistent with the CAA.

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 proposed 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.