SUPPLEMENTARY INFORMATION:

Throughout this document whenever “we,” “us,” or “our” is used, we mean the EPA.

Acronyms

CAA Clean Air Act

CBI Confidential Business Information

EPA U.S. Environmental Protection Agency

LADCO Lake Michigan Air Directors Consortium

NAAQS National Ambient Air Quality Standards

PBI Proprietary Business Information

RPO Regional Planning Organization

SIP State Implementation Plan

I. Executive Summary

A. What action is the EPA taking?

The EPA is finalizing an approval of Indiana's November 2, 2018, interstate transport infrastructure SIP submission as satisfying the requirements related to visibility protection contained in CAA section 110(a)(2)(D)(i)(II), also known as Prong 4, for the 2015 ozone NAAQS.

B. What is the legal authority and requirements?

The EPA proposed to approve Indiana's submission into the SIP on April 10, 2026, 91 FR 18347. In this action, EPA is finalizing an approval of Indiana's submittal as meeting the visibility protection requirements of CAA section 110(a)(2)(D)(i)(II) for the 2015 ozone NAAQS.

II. Background

On November 2, 2018, Indiana submitted an infrastructure SIP revision for the 2015 ozone NAAQS addressing the fourth component of CAA section 110(a)(2)(D)(i)(II), also known as “Prong 4.” Prong 4 requires that a State's SIP contain adequate provisions prohibiting any source or other type of emissions activity within the State from emitting any air pollutant in amounts which will interfere with measures required to be included in the applicable SIP for any other State to protect visibility.

Indiana is a member of the Lake Michigan Air Directors Consortium (LADCO) regional planning organization (RPO) and participated in the RPO's regional approach to identifying emission reduction measures necessary to make reasonable progress towards the national visibility goal in LADCO Class I areas. That process also included consultations with States in other RPOs. Indiana responded to requests from non-LADCO States and another RPO to consider additional measures to address visibility impairment in Class I areas outside the LADCO States.

III. CAA Section 110(a)(2)(D)(i)(II)—Visibility Protection

CAA section 110(a)(2)(D)(i)(II), Prong 4, requires SIPs to contain adequate provisions to prohibit emissions in amounts that will interfere with measures required to be included in the applicable implementation plan for any other state under part C of the Act to protect visibility. The EPA issued guidance on infrastructure SIPs in a September 13, 2013, memorandum titled “Guidance on Infrastructure State Implementation Plan (SIP) Elements ( printed page 57263) under Clean Air Act sections 110(a)(1) and 110(a)(2)” (“2013 Guidance”). The 2013 Guidance states that these Prong 4 requirements can be satisfied by approved SIP provisions that the EPA has found to adequately address any contribution of that State's sources that impact the visibility program requirements in other States.^[1]

The 2013 Guidance lays out how a State's infrastructure SIP may satisfy Prong 4. In the second planning period, confirmation that a State has a fully approved regional haze SIP that fully meets the requirements of 40 CFR 51.308 will satisfy the requirements of Prong 4.^[2] A fully approved regional haze SIP ^[3] will ensure that emissions from sources under an air agency's jurisdiction are not interfering with measures required to be included in other air agencies' plans to protect visibility.

In the second planning period, the EPA's Regional Haze regulations under 40 CFR 51.308(f) require that a State consider the emission reduction measures identified by other States as being necessary to make reasonable progress towards meeting the national visibility goal in Class I Federal areas. Specifically, the regulations require a State to include in its Regional Haze SIP all measures agreed to during that process or measures that will provide equivalent visibility improvement ( See40 CFR 51.308(f)(2)(ii)). Thus, in meeting the requirements of 40 CFR 51.308(f), an approved regional haze SIP meeting the requirements of 40 CFR 51.308(f)(2)(ii) will ensure that emissions from sources under an air agency's jurisdiction are not interfering with measures required to be included in other air agencies' plans to protect visibility and will, therefore, satisfy Prong 4.

III. Summary of Public Comments and the EPA's Responses

The EPA received one comment during the comment period for the proposed rule. The commenter did not object to the EPA's proposed action, but rather suggested that the EPA include additional information supporting the determinations of the proposal in the final rule. EPA has provided this additional information in the background section of this final action, and we are finalizing our action as proposed.

The commenter stated, “EPA should strengthen the final rule in three ways.” A synopsis of each comment is given before the response. The comment letter is included in the docket for this rulemaking.

Comment: The commenter suggests that the EPA identify the specific findings from the regional haze plan approval that it believes satisfy prong 4. The commenter contends that the proposal does not explain which findings from the January 26, 2026, approval demonstrate that Indiana emissions will not interfere with the visibility protection measures required in other States' SIPs.

Response: In the proposed rule, the EPA confirms that Indiana has a fully approved regional haze SIP meeting the requirements of 40 CFR 51.308 to satisfy Prong 4. According to the 2013 Guidance, a State's infrastructure SIP may satisfy Prong 4 for any relevant NAAQS through an air agency's confirmation that the State has a fully approved regional haze SIP meeting the requirements of 40 CFR 51.308. Since second implementation period SIPs became due, a “fully approved regional haze SIP” would necessarily include fully approved first and second implementation period regional haze SIPs. Therefore, simply confirming the EPA's approval of Indiana's second implementation period regional haze plan satisfies the requirement.

The Regional Haze Rule's consultation requirement of 40 CFR 51.308(f)(2)(ii) requires a State to consult with other States that also have emissions that are reasonably anticipated to contribute to visibility impairment in each Class I area. The EPA's approval of Indiana's second implementation period regional haze plan confirms it has engaged in consultation to consider the emission reduction measures identified by other States for their sources as being necessary to make reasonable progress in the mandatory Class I Federal area ( See91 FR 3057, January 26, 2026).

Comment: The commenter suggests that the EPA explain the sequencing of the EPA's approvals of Indiana's 2015 ozone standard infrastructure SIP submission made on November 2, 2018. As the Prong 4 portion of the submittal was not included in the EPA's June 29, 2022, approval, the commenter suggests that the EPA state what changed and why that change is sufficient to resolve the previously open Prong 4 issue.

Response: This is the third EPA rulemaking on Indiana's November 2, 2018, submission addressing the 2015 ozone NAAQS. First, the EPA approved most elements of Indiana's submission on November 2, 2022 (87 FR 66091), which addressed the applicable infrastructure requirements in CAA section 110(a)(1) and (2) for the 2015 ozone NAAQS related to the interstate transport element preventing significant deterioration of air quality from CAA section 110(a)(2)(D)(i)(II) (“Prong 3”). The proposed rule details the background, including an analysis of each element ( See87 FR 38693, June 29, 2022). In this rulemaking, EPA did not act on the other interstate transport elements, Prongs 1, 2, and 4.

Second, the EPA acted on the Prongs 1 and 2 interstate transport elements. On February 13, 2023 (88 FR 9336), the EPA disapproved the CAA section 110(a)(2)(D)(i)(I) elements for Indiana and other States. Prongs 1 and 2 require that each State's SIP contain adequate provisions to prohibit emissions from within the State from significantly contributing to nonattainment or interfering with maintenance of the NAAQS in other States. The EPA found that a portion of Indiana's submission did not meet the State's interstate transport obligations, because it did not contain the necessary provisions to eliminate emissions that would contribute significantly to nonattainment or interfere with maintenance of the 2015 ozone NAAQS in any other State. The proposed rulemaking further details the analysis used in evaluating each State's interstate transport provision for the 2015 ozone NAAQS implementation plan submission, including Indiana ( See87 FR 9838, February 22, 2022).

Third, the EPA is approving the Prong 4 element of CAA section 110(a)(2)(D)(i)(II), with this rule. The EPA finds that Indiana's infrastructure submission fulfills CAA requirements for a State's SIP to contain adequate provisions prohibiting emissions that will interfere with required visibility protection measures in any other State's SIP. The 2013 Guidance confirms a State's infrastructure SIP may satisfy Prong 4 ^[4] for any relevant NAAQS ( printed page 57264) through the States's confirmation that it has a fully approved regional haze SIP ^[5] meeting the requirements of 40 CFR 51.308. The EPA approved Indiana's regional haze plan for the second implementation period ( See91 FR 3057, January 26, 2026).

Comment: The commenter suggests that the EPA make the administrative record easier to audit for ordinary readers. The commenter contends that if the Agency's conclusion depends almost entirely on Indiana's regional haze plan approval, then the final rule should include a short summary showing how the plan's interstate visibility findings relate to this Prong 4 determination.

Response: Electronic dockets make the supporting documents readily available to readers. The referenced documents are in the docket for this rulemaking.

As noted in the proposed rule and the previous comment response, a State having a fully approved regional haze plan for the second implementation period will ensure that emissions from sources under an air agency's jurisdiction are not interfering with measures required to be included in other air agencies' plans to protect visibility and will, therefore, satisfy Prong 4. By meeting the statutory and regulatory requirements of the regional haze program, including the interstate consultation requirements in 40 CFR 51.308(f)(2)(ii), Indiana's SIP adequately prohibits emissions from within the State that would interfere with visibility protection measures in any other State's SIP. Thus, now that the EPA has approved Indiana's regional haze plan for the second implementation period, Indiana satisfies the requirements of CAA section 110(a)(2)(D)(i)(II) relating to visibility protection for the 2015 ozone NAAQS, allowing the Prong 4 element of the infrastructure submission to be approved.

IV. What action is the EPA taking?

The EPA is approving Indiana's November 2, 2018, interstate transport infrastructure SIP submission as satisfying the requirements related to visibility protection contained in CAA section 110(a)(2)(D)(i)(II), also known as Prong 4, for the 2015 ozone NAAQS.

V. Statutory and Executive Order Reviews

Under the CAA, the Administrator is required to approve a SIP submission that complies with the provisions of the CAA and applicable Federal regulations. 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 action merely approves State law as meeting Federal requirements and does not impose additional requirements beyond those imposed by State law. For that reason, this action:

• Is not a significant regulatory action subject to review by the Office of Management and Budget underExecutive Order 12866 (58 FR 51735, October 4, 1993);
• Is not anExecutive Order 14192 (90 FR 9065, February 6, 2025) regulatory action because this action is not significant under Executive Order 12866;
• Does not impose an information collection burden under the provisions of the Paperwork Reduction Act (44 U.S.C. 3501 et seq.);
• Is certified as not having a significant economic impact on a substantial number of small entities under the Regulatory Flexibility Act (5 U.S.C. 601 et seq.);
• Does not contain any unfunded mandate or significantly or uniquely affect small governments, as described in the Unfunded Mandates Reform Act of 1995 (Pub. L. 104-4);
• Does not have federalism implications as specified inExecutive Order 13132 (64 FR 43255, August 10, 1999);
• Is not subject toExecutive Order 13045 (62 FR 19885, April 23, 1997) because it approves a State program;
• Is not a significant regulatory action subject toExecutive Order 13211 (66 FR 28355, May 22, 2001); and
• Is not subject to requirements of section 12(d) of the National Technology Transfer and Advancement Act of 1995 (15 U.S.C. 272 note) because application of those requirements would be inconsistent with the CAA.

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

This action is subject to the Congressional Review Act, and the EPA will submit a rule report to each House of the Congress and to the Comptroller General of the United States. This action is not a “major rule” as defined by 5 U.S.C. 804(2).

Under CAA section 307(b)(1), petitions for judicial review of this action must be filed in the United States Court of Appeals for the appropriate circuit by November 9, 2026. Filing a petition for reconsideration by the Administrator of this final rule does not affect the finality of this action for the purposes of judicial review nor does it extend the time within which a petition for judicial review may be filed, and shall not postpone the effectiveness of such rule or action. This action may not be challenged later in proceedings to enforce its requirements (See CAA section 307(b)(2)).

For the reasons stated in the preamble, 40 CFR part 52 is amended as follows:

91 FR 57262