Proposed Rule2025-18594
Air Plan Approval; Indiana; Huntington County 2010 Sulfur Dioxide Redesignation and Maintenance Plan
Primary source
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Published
September 25, 2025
Issuing agencies
Environmental Protection Agency
Abstract
The Environmental Protection Agency (EPA) is proposing to find that Huntington Township, Indiana (referred to in this proposed rule as the Huntington County, Indiana area) is attaining the 2010 sulfur dioxide (SO<INF>2</INF>) National Ambient Air Quality Standard (NAAQS) and to propose approval of Indiana's request to redesignate the area to attainment for the 2010 SO<INF>2</INF> NAAQS, because the request meets the statutory requirements for redesignation under the Clean Air Act (CAA). EPA is also proposing to approve Indiana's maintenance plan for the area, which, once approved, will become part of Indiana's federally enforceable State Implementation Plan (SIP).
Full Text
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<title>Federal Register, Volume 90 Issue 184 (Thursday, September 25, 2025)</title>
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[Federal Register Volume 90, Number 184 (Thursday, September 25, 2025)]
[Proposed Rules]
[Pages 46124-46128]
From the Federal Register Online via the Government Publishing Office [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[FR Doc No: 2025-18594]
[[Page 46124]]
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ENVIRONMENTAL PROTECTION AGENCY
40 CFR Parts 52 and 81
[EPA-R05-OAR-2024-0378; FRL-12933-01-R5]
Air Plan Approval; Indiana; Huntington County 2010 Sulfur Dioxide
Redesignation and Maintenance Plan
AGENCY: Environmental Protection Agency (EPA).
ACTION: Proposed rule.
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SUMMARY: The Environmental Protection Agency (EPA) is proposing to find
that Huntington Township, Indiana (referred to in this proposed rule as
the Huntington County, Indiana area) is attaining the 2010 sulfur
dioxide (SO<INF>2</INF>) National Ambient Air Quality Standard (NAAQS)
and to propose approval of Indiana's request to redesignate the area to
attainment for the 2010 SO<INF>2</INF> NAAQS, because the request meets
the statutory requirements for redesignation under the Clean Air Act
(CAA). EPA is also proposing to approve Indiana's maintenance plan for
the area, which, once approved, will become part of Indiana's federally
enforceable State Implementation Plan (SIP).
DATES: Comments must be received on or before October 27, 2025.
ADDRESSES: Submit your comments, identified by Docket ID No. EPA-R05-
OAR-2024-0378 at <a href="https://www.regulations.gov">https://www.regulations.gov</a>, or via email to
<a href="/cdn-cgi/l/email-protection#97f6e5e5f6b9e4f6e5f6ffd7f2e7f6b9f0f8e1"><span class="__cf_email__" data-cfemail="65041717044b160417040d250015044b020a13">[email protected]</span></a>. For comments submitted at <a href="http://Regulations.gov">Regulations.gov</a>, follow
the online instructions for submitting comments. Once submitted,
comments cannot be edited or removed from the docket. EPA may publish
any comment received to its public docket. Do not submit to EPA's
docket at <a href="https://www.regulations.gov">https://www.regulations.gov</a> any information you consider to
be Confidential Business Information (CBI), Proprietary Business
Information (PBI), or other information whose disclosure is restricted
by statute. Multimedia submissions (audio, video, etc.) must be
accompanied by a written comment. The written comment is considered the
official comment and should include discussion of all points you wish
to make. EPA will generally not consider comments or comment contents
located outside of the primary submission (i.e., on the web, cloud, or
other file sharing system). For additional submission methods, please
contact the person identified in the FOR FURTHER INFORMATION CONTACT
section. For the full EPA public comment policy, information about CBI,
PBI, or multimedia submissions, and general guidance on making
effective comments, please visit <a href="https://www.epa.gov/dockets/commenting-epa-dockets">https://www.epa.gov/dockets/commenting-epa-dockets</a>.
FOR FURTHER INFORMATION CONTACT: Abigail Teener, Air and Radiation
Division (AR-18J), Environmental Protection Agency, Region 5, 77 West
Jackson Boulevard, Chicago, Illinois 60604, (312) 353-7314,
<a href="/cdn-cgi/l/email-protection#443021212a21366a25262d23252d28042134256a232b32"><span class="__cf_email__" data-cfemail="235746464d46510d42414a44424a4f634653420d444c55">[email protected]</span></a>. The EPA Region 5 office is open from 8:30 a.m.
to 4:30 p.m., Monday through Friday, excluding Federal holidays.
SUPPLEMENTARY INFORMATION:
I. Background and Redesignation Requirements
On June 22, 2010 (75 FR 35520), EPA published a new SO<INF>2</INF>
NAAQS of 75 parts per billion (ppb), which is met at an ambient air
quality monitoring site (or in the case of dispersion modeling, at an
ambient air quality receptor location) when the 3-year average of the
annual 99th percentile of daily maximum 1-hour average concentrations
does not exceed 75 ppb, as determined in accordance with appendix T of
40 CFR part 50.
On January 9, 2018 (83 FR 1098), EPA designated Huntington
Township, a partial area of Huntington County, Indiana, as
nonattainment for the 2010 SO<INF>2</INF> NAAQS with an effective date
of April 9, 2018, based on air quality modeling information which
showed that Isolatek International (Isolatek), formerly known as U.S.
Mineral Wool, may have been contributing to violations of the 2010
SO<INF>2</INF> NAAQS. Section 191 of the CAA directs States to submit a
SIP for an area designated as nonattainment for the 2010 SO<INF>2</INF>
NAAQS to EPA within 18 months of the effective date of the designation.
The SIP must demonstrate that the State will achieve the NAAQS for the
nonattainment area as expeditiously as practicable, but no later than
five years from the effective date of designation.
On November 6, 2023, Indiana submitted Commissioner's Order 2023-
Air-01, containing SO<INF>2</INF> emission limits for Isolatek, along
with a revision to the Indiana SIP that provides for attainment of the
2010 SO<INF>2</INF> NAAQS in the Huntington County area. The revision
included an Attainment Demonstration, Reasonably Available Control
Measures/Reasonably Available Control Technology (RACM/RACT)
requirements, Reasonable Further Progress (RFP) provisions, Contingency
Measures, Emissions Inventories for the 2017 Base Year and 2023
Attainment Year, and NSR Certification. On February 12, 2024, Indiana
submitted a supplemental SIP revision including Commissioner's Order
2023-Air-02, effective March 1, 2024, which revised Commissioner's
Order 2023-Air-01 and established compliance requirements for the
SO<INF>2</INF> emission limits. Commissioner's Order 2023-Air-02 is
included as attachment C of Indiana's July 30, 2024, redesignation
request.
On August 14, 2025 (90 FR 39130), EPA approved Indiana's plan for
attaining the 2010 SO<INF>2</INF> NAAQS for the Huntington County area
and for meeting other nonattainment area planning requirements of CAA
sections 110, 172, 179 and 192. EPA approved Indiana's demonstration
that these requirements provide for attainment of the 2010
SO<INF>2</INF> NAAQS in Huntington County and that Indiana had
satisfied the other applicable requirements for nonattainment areas.
II. Evaluation of Indiana's Redesignation Request and Maintenance Plan
On July 30, 2024, Indiana submitted a redesignation request and
maintenance plan for the Huntington County nonattainment area for the
2010 SO<INF>2</INF> NAAQS, and on September 17, 2024, submitted
supplemental information.
Under section 107(d)(3)(E) of the CAA, EPA may promulgate a
redesignation of a nonattainment area provided that:
1. EPA has determined that the area has attained the NAAQS;
2. EPA has fully approved the applicable implementation plan for
the area under section 110(k) of the CAA;
3. EPA has determined that improvement in air quality is due to
permanent and enforceable reductions in emissions resulting from
implementation of the applicable implementation plan and applicable
Federal air pollution control regulations and other permanent and
enforceable reductions;
4. EPA has fully approved a maintenance plan for the area under
section 175A of the CAA; and
5. The State containing such area has met all requirements
applicable to the area under section 110 of the CAA and part D.
EPA's evaluation of Indiana's redesignation request and maintenance
plan was based on consideration of the five redesignation criteria
provided under CAA section 107(d)(3)(E) and is described in the
remainder of this section.
[[Page 46125]]
A. Criterion (1)--The Huntington County SO2 Nonattainment Area Has
Attained the 2010 SO2 NAAQS
CAA section 107(d)(3)(E)(i) requires EPA to determine that an area
has attained the applicable NAAQS in order for EPA to redesignate the
area from nonattainment to attainment. If dispersion modeling is used
to make this determination, an area is attaining the 2010
SO<INF>2</INF> NAAQS when the modeled concentration is at or below the
one-hour SO<INF>2</INF> NAAQS of 196.4 micrograms per cubic meter (or
75 ppb).
As detailed in EPA's April 23, 2014, Guidance for 1-Hour SO2
Nonattainment Area SIP Submissions (``April 2014 SO<INF>2</INF>
Guidance''), there are generally two methods available to support an
attainment determination. The first component relies on air quality
monitoring data. For SO<INF>2,</INF> any available monitoring data
would need to indicate that all monitors in the affected area are
meeting the standard in 40 CFR 50.17. The second component relies on
air quality modeling data. If there are no air quality monitors in the
area, a further analysis using air quality dispersion modeling will
generally be needed to estimate SO<INF>2</INF> concentrations
throughout the nonattainment area to demonstrate that the entire area
is attaining the applicable NAAQS, based on current actual emissions or
the fully implemented control strategy.\1\
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\1\ EPA's Guidance for 1-Hour Sulfur Dioxide (SO2) Nonattainment
Area State Implementation Plans (SIP) Submissions can be found at
<a href="https://www.epa.gov/so2-pollution/guidance-1-hour-sulfur-dioxide-so2-nonattainment-area-state-implementation-plans-sip">https://www.epa.gov/so2-pollution/guidance-1-hour-sulfur-dioxide-so2-nonattainment-area-state-implementation-plans-sip</a>.
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The April 2014 SO<INF>2</INF> Guidance states that EPA may make
determinations of attainment based on the modeling, using allowable
emissions, from the attainment demonstrations for the applicable SIP
for the affected area. Attainment demonstrations for the 2010
SO<INF>2</INF> NAAQS should demonstrate future attainment and
maintenance of the NAAQS in the entire area designated as nonattainment
(i.e., not just at the violating monitor) by using air quality
dispersion modeling (see appendix W to 40 CFR part 51) to show that the
mix of sources and enforceable control measures and emission rates in
an identified area will not lead to a violation of the 2010
SO<INF>2</INF> NAAQS. For a short-term (i.e., 1-hour) standard, EPA
believes that dispersion modeling, using allowable emissions and
addressing stationary sources in the affected area (and in some cases
those sources located outside the nonattainment area which may affect
attainment in the area) is technically appropriate, efficient and
effective in demonstrating attainment in nonattainment areas because it
takes into consideration combinations of meteorological and emission
source operating conditions that may contribute to peak ground-level
concentrations of SO<INF>2.</INF>
As there is no approved SO<INF>2</INF> monitoring network in the
Huntington County area, Indiana's redesignation request relies upon the
air dispersion modeling analysis conducted while developing its
attainment demonstration for the Huntington County area to show that
the area is attaining the SO<INF>2</INF> NAAQS. A more in-depth
discussion of EPA's modeling requirements and Indiana's modeling
analysis may be found in EPA's proposed attainment plan approval (90 FR
25968, June 18, 2025) and Indiana's modeling report, which is included
as attachment D of Indiana's July 30, 2024, redesignation request.
Indiana's modeling analysis confirmed that the primary source of
SO<INF>2</INF> emissions in the Huntington County area is Isolatek.
Therefore, Indiana's modeled demonstration of attainment of the
SO<INF>2</INF> NAAQS relies on Isolatek meeting the permanent and
enforceable SO<INF>2</INF> emission limits established in
Commissioner's Order 2023-Air-02. Commissioner's Order 2023-Air-02
includes limits of 160.0 pounds per hour (lbs/hr) of SO<INF>2</INF>
combined for Cupola units EU #1 and EU #2, exhausting to shared Stack
#1, and 20.0 lbs/hr of SO<INF>2</INF> combined for blow chambers EU #3
and EU #4, exhausting to Screen Houses CE #3 and CE #4, which exhaust
to Stack #3 at Isolatek.
Indiana's modeling demonstrates that the one-hour average hourly
SO<INF>2</INF> emission limits contained in Commissioner's Order 2023-
Air-02 yield a maximum SO<INF>2</INF> concentration of 195.9 micrograms
per cubic meter, which is below the 2010 SO<INF>2</INF> NAAQS level of
75 ppb (or 196.4 micrograms per cubic meter). EPA approved
Commissioner's Order 2023-Air-02 as part of Indiana's Huntington County
attainment plan on August 14, 2025 (90 FR 39130).
The April 2014 SO<INF>2</INF> Guidance states that a demonstration
that the control strategy in the SIP has been fully implemented is
relevant when making an attainment determination based on modeling.
Construction for the control measures selected at Isolatek, including
increasing the cupola stack height, enclosing screenhouses, and
building a new elevated stack, was completed in November 2022.
Indiana's attainment plan for the Huntington County area includes
Commissioner's Order 2023-Air-02, which established a compliance date
of March 1, 2024, for the emission limits included in the plan. On
September 17, 2024, Indiana supplemented its July 30, 2024,
redesignation request with a report containing results from stack
testing at Isolatek to demonstrate that the facility is complying with
the SO<INF>2</INF> emission limits set forth in the order.
Indiana's modeling analysis is discussed in detail in EPA's
proposed approval of Indiana's attainment plan for the Huntington
County area (90 FR 25968, June 18, 2025). In this action, EPA proposes
to find that this modeling analysis demonstrates that the Huntington
County area has attained the 2010 SO<INF>2</INF> NAAQS.
B. Criterion (2) and Criterion (5)--Indiana Has Met All Applicable
Requirements Under CAA Section 110 and Part D of the CAA, and EPA Has
Fully Approved the Applicable Implementation Plan Under CAA Section
110(k)
In order for EPA to redesignate a nonattainment area to attainment
under a NAAQS, the State must have met all applicable requirements (CAA
section 107(d)(3)(E)(v)), and EPA must have fully approved the
applicable implementation plan (CAA section 107(d)(3)(E)(ii)). EPA's
long-standing interpretation of the CAA is that not every requirement
under CAA section 110 and part D are applicable for purposes of CAA
section 107(d)(3)(E)(ii) and (v). EPA's interpretation of the statute
limiting evaluation of section 110 and part D requirements to only
those that are applicable for purposes of redesignation was first
articulated shortly after the passage of the 1990 CAA Amendments in
Agency guidance documents and has been consistently applied in notice-
and-comment redesignation actions over the last three decades.
Many of the section 110 elements that are unrelated to an area's
SO<INF>2</INF> attainment status are not applicable requirements for
purposes of redesignation. The area will still be subject to these
requirements after the area is redesignated to attainment of the 2010
SO<INF>2</INF> NAAQS. For example, the CAA section 110(a)(2)(D)
interstate transport requirements for a State are not linked with a
nonattainment area's designation and classification in that State and
continue to apply to States regardless of the designation status of
areas within that State. Even though many of the section 110
requirements are not applicable for purposes of redesignation, EPA in
any case approved Indiana's section 110
[[Page 46126]]
infrastructure SIP for the 2010 SO<INF>2</INF> NAAQS on August 14, 2015
(80 FR 48733).
EPA proposes to determine that Indiana has met, and EPA has fully
approved, those part D requirements that are applicable for purposes of
redesignation. Part D is comprised of the general nonattainment area
plan requirements in subpart 1 (section 172) as well as pollutant-
specific subparts, including section 191 (in subpart 5), which applies
to areas designated nonattainment for SO<INF>2</INF>. While some
nonattainment planning requirements are not applicable for purposes of
CAA section 107(d)(3)(E)(ii) and (v) for areas that are attaining the
NAAQS, Indiana has in any case submitted a complete attainment plan for
the Huntington County area, including emissions inventories, RACT/RACM,
RFP, and contingency measures, and has therefore met Part D
requirements.
On August 14, 2025 (90 FR 39130), EPA fully approved a revision to
Indiana's SIP intended to provide for attainment of the 2010
SO<INF>2</INF> NAAQS for the Huntington County area, including one-hour
SO<INF>2</INF> emission limits and associated requirements for Isolatek
set forth in Commissioner's Order 2023-Air-02 and described above in
the Criteria 1 section of this notice. Indiana's program for NSR will
address emissions from potential new sources in the area (94 FR 24837,
October 7, 1994).
Section 176(c) of the CAA requires States to establish criteria and
procedures to ensure that federally supported or funded projects
conform to the air quality planning goals in the applicable SIP. The
requirement to determine conformity applies to transportation plans,
programs, and projects that are developed, funded, or approved under
title 23 of the United States Code (U.S.C.) or the Federal Transit Act
(49 U.S.C. 1601) (transportation conformity) as well as to all other
federally supported or funded projects (general conformity). State
transportation conformity SIP revisions must be consistent with Federal
conformity regulations relating to consultation, enforcement, and
enforceability that EPA promulgated pursuant to its authority under the
CAA. EPA's longstanding interpretation of the CAA is that because CAA
section 176(c) conformity requirements continue to apply after areas
are redesignated to attainment, meeting those requirements is not a
prerequisite to redesignating an area. In addition, based on EPA's
April 2014 SO<INF>2</INF> Guidance, transportation conformity only
applies to SO<INF>2</INF> SIPs if transportation-related emissions of
SO<INF>2</INF> as a precursor are a significant contributor to a fine
particulate matter (PM<INF>2.5</INF>) nonattainment problem or if the
SIP has established an approved or adequate budget for such emissions
as part of the attainment or maintenance strategy, neither of which
applies to the Huntington County area. EPA concluded that highway and
transit vehicles are not significant sources of SO<INF>2</INF> in this
area. As a result, transportation conformity determinations are not
required in the Huntington County SO<INF>2</INF> maintenance area.
Therefore, transportation plans, improvement programs, and projects are
presumed to conform to applicable implementation plans for
SO<INF>2</INF>. EPA approved Indiana's general conformity SIP revision
on January 14, 1998 (63 FR 2146). This SIP revision adopted the Federal
general conformity rules set forth at 40 CFR part 51, subpart W.
Based on the above findings, EPA is proposing to find that Indiana
has met the applicable requirements of section 110 and part D of title
I of the CAA for purposes of the redesignation of the Huntington County
nonattainment area. Furthermore, EPA has fully approved a revision to
Indiana's applicable SIP that provides for attainment of the 2010
SO<INF>2</INF> NAAQS for the Huntington County area.
C. Criterion (3)--The Air Quality Improvement in the Huntington County
SO2 Nonattainment Area Is Due to Permanent and Enforceable Emission
Reductions
To redesignate an area from nonattainment to attainment, section
107(d)(3)(E)(iii) of the CAA requires EPA to determine that the air
quality improvement in the area is due to permanent and enforceable
reductions in emissions resulting from the implementation of the SIP
and applicable Federal air pollution control regulations and other
permanent and enforceable emission reductions.
As described in the Criterion 1 section above, Indiana's modeling
analysis confirmed that the primary source of SO<INF>2</INF> emissions
in the Huntington County area is Isolatek. Therefore, Indiana evaluated
control options and established emission limits for Isolatek.
Construction of the relevant control projects was completed in November
2022, and Indiana submitted Commissioner's Order 2023-Air-02 containing
permanent and enforceable SO<INF>2</INF> emission limits for Isolatek
as part of its Huntington County attainment plan.
Commissioner's Order 2023-Air-02, included as attachment C to
Indiana's July 30, 2024, redesignation request, establishes a
compliance date of March 1, 2024, for the emission limits included in
the Huntington County attainment plan and specifies that Isolatek must
incorporate reporting and recordkeeping requirements into its part 70
operating permit within 90 days of EPA's approval of Indiana's
attainment plan for the Huntington County area. On September 17, 2024,
Indiana submitted stack testing to demonstrate that Isolatek is
complying with the SO<INF>2</INF> emission limits set forth in
Commissioner's Order 2023-Air-02. On August 14, 2025 (90 FR 39130), EPA
approved Commissioner's Order 2023-Air-02 as part of Indiana's
Huntington County attainment plan.
The modeling that Indiana's attainment plan relies upon includes
the emission limits for Isolatek and shows attainment of the 2010
SO<INF>2</INF> NAAQS throughout the Huntington County area. EPA is
proposing to find, consistent with the approval of the State's
attainment plan, that the modeling results demonstrate attainment and
continued maintenance of the 2010 SO<INF>2</INF> NAAQS and that the air
quality improvement in the Huntington County nonattainment area is due
to permanent and enforceable reductions in emissions.
D. Criterion (4)--The Huntington County SO2 Nonattainment Area Has a
Fully Approved Maintenance Plan Pursuant to Section 175A
To redesignate an area from nonattainment to attainment, section
107(d)(3)(E)(iv) of the CAA requires EPA to determine that the area has
a fully approved maintenance plan pursuant to section 175A of the CAA.
Section 175A of the CAA sets forth the elements of a maintenance plan
for areas seeking redesignation from nonattainment to attainment. Under
section 175A, the maintenance plan must demonstrate continued
attainment of the NAAQS for at least 10 years after EPA approves a
redesignation to attainment. Eight years after the redesignation, the
State must submit a revised maintenance plan which demonstrates that
attainment of the NAAQS will continue for an additional 10 years beyond
the initial 10-year maintenance period. To address the possibility of
future NAAQS violations, the maintenance plan must contain contingency
measures, as EPA deems necessary, to ensure prompt correction of any
future NAAQS violation.
Specifically, the maintenance plan should address five
requirements: an attainment emissions inventory, a maintenance
demonstration, a commitment for continued air quality monitoring, a
process for verification of continued attainment, and a contingency
plan. EPA is proposing to
[[Page 46127]]
determine that Indiana's July 30, 2024, redesignation request contains
a maintenance plan that includes all the necessary components, which
Indiana has committed to review eight years after the redesignation.
EPA is further proposing to approve the maintenance plan as part of
Indiana's federally enforceable SIP.
As a part of a State's maintenance plan, the air agency should
develop an attainment emissions inventory to identify the level of
emissions in the affected area which is sufficient to attain and
maintain the SO<INF>2</INF> NAAQS.\2\ In its redesignation request,
Indiana provided an emissions inventory for SO<INF>2</INF> in the
nonattainment area for 2023, the first year after construction of the
relevant emissions control projects at Isolatek was completed. Total
SO<INF>2</INF> emissions in the Huntington County area for the 2023
attainment year are 792 tons, including 788 tons from Isolatek, which
was calculated using the maximum allowable hourly emission limits
established in Commissioner's Order 2023-Air-02. This level of
emissions, as shown in Indiana's attainment demonstration, is
sufficient to maintain the NAAQS, and Indiana submitted a stack testing
report on September 17, 2024, to demonstrate that Isolatek is in
compliance with the emission limits set forth in Commissioner's Order
2023-Air-02. The modeling that Indiana relied upon for its
redesignation request for the Huntington County area, based on
SO<INF>2</INF> emission limits set forth in Commissioner's Order 2023-
Air-02, resulted in a design value of 195.9 micrograms per cubic meter,
below the SO<INF>2</INF> NAAQS of 75 ppb (or 196.4 micrograms per cubic
meter). Indiana's modeling report is included as attachment D of its
July 30, 2024, redesignation request.
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\2\ See April 2014 SO<INF>2</INF> Guidance, page 66.
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EPA's ``Procedures for Processing Requests to Redesignate Areas to
Attainment'' (Calcagni Memo) \3\ describes two ways for a State to
demonstrate maintenance of the NAAQS following the redesignation of the
area: (1) the State can show that future emissions of a pollutant will
not exceed the level of the attainment inventory, or (2) the State can
provide modeling to show that the future mix of sources and emission
rates will not cause a violation of the NAAQS. In both instances, the
demonstration should be for a period of 10 years following the
redesignation. Furthermore, where modeling is relied upon to
demonstrate maintenance, the plan should contain a summary of air
quality concentrations expected to result from control measures
implemented. Indiana's maintenance demonstration consists of the
attainment plan air quality modeling analysis showing that the emission
limits now in effect in the Huntington County area will provide for
attainment of the 2010 SO<INF>2</INF> NAAQS. The permanent and
enforceable SO<INF>2</INF> emission limits described above ensure that
the area emissions will be equal to or less than the emission levels
that were evaluated in the air quality modeling analysis, and Indiana's
enforceable emission requirements will ensure that the Huntington
County area SO<INF>2</INF> emission limits are met continuously.
Indiana's redesignation request contains an emissions inventory for
2035, the maintenance year, which does not show any increases in
maximum allowable emissions from the attainment year. Additionally,
Indiana has a fully approved NSR program (94 FR 24837, October 7,
1994), including requirements to assess the impacts of any plans to
construct or resume operations of an emission unit on maintaining NAAQS
attainment.
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\3\ Calcagni, John, Director, Air Quality Management Division,
EPA Office of Air Quality Planning and Standards, ``Procedures for
Processing Requests to Redesignate Areas to Attainment,'' September
4, 1992.
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For verification of continued attainment, Indiana commits to
periodically reevaluate the modeling assumptions and input data used in
its Huntington County attainment plan. As there is no approved
SO<INF>2</INF> monitoring network to characterize air quality in the
Huntington County area, Indiana commits to examine Isolatek's annual
emissions as part of Indiana's annual assessment for ongoing data
requirements for the 2010 SO<INF>2</INF> NAAQS. Indiana has the legal
authority, necessary resources, and structural components to implement
and enforce all measures needed to attain and maintain the 2010
SO<INF>2</INF> NAAQS.
Section 175A(d) of the CAA provides that a maintenance plan must
contain contingency provisions that will promptly correct any violation
of the 2010 SO<INF>2</INF> NAAQS after the area is redesignated to
attainment (Calcagni Memo). The maintenance plan should identify the
contingency measures to be adopted, a schedule and procedure for
adoption and implementation, and a time limit for action by the State.
A State should also identify specific indicators to be used to
determine when the contingency measures need to be implemented. The
maintenance plan must also include a requirement that a State will
implement all measures with respect to control of the pollutant that
were contained in the SIP before redesignation of the area to
attainment in accordance with section 175A(d). Unlike CAA section
172(c)(9), section l75A of the CAA does not explicitly require that
contingency measures must take effect without further action by the air
agency for the maintenance plan to be approved. However, if this action
is finalized, the contingency plan would become an enforceable part of
the SIP and should ensure that contingency measures are adopted and
implemented as expeditiously as practicable once they are triggered.\4\
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\4\ See April 2014 SO<INF>2</INF> Guidance, page 74.
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In the ``General Preamble for the Implementation of Title I of the
Clean Air Act Amendments of 1990,'' published on April 16, 1992 (57 FR
13498), EPA provides further discussion of contingency measures for
SO<INF>2</INF>. This guidance states that in many cases, attainment
revolves around compliance of a single source or a small set of sources
with emission limits shown to provide for attainment. Although this
guidance applies to contingency measures under section 172(c)(9), EPA
applies a similar policy with respect to contingency measures for
SO<INF>2</INF> required in maintenance plans under section 175A(d). The
requirement to submit contingency measures in accordance with section
175A of the CAA can be adequately addressed for SO<INF>2</INF> by the
operation of a comprehensive enforcement program,\5\ which can quickly
identify and address sources that might be causing exceedances of the
NAAQS.
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\5\ See April 2014 SO<INF>2</INF> Guidance, page 41-42.
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Indiana's enforcement program is active and capable of prompt
action to remedy compliance issues. Indiana commits to undertake
aggressive follow-up to ensure compliance with and enforcement of all
rules related to SO<INF>2</INF> emissions in the Huntington County
area, including Commissioner's Order 2023-Air-02, which EPA approved as
part of Indiana's Huntington County attainment plan (90 FR 39130,
August 14, 2025). Indiana has the authority to expeditiously adopt,
implement, and enforce any subsequent emission control measures deemed
necessary to correct any future SO<INF>2</INF> violations. Indiana
commits to adopting and implementing such corrective actions as
necessary to address violations of the 2010 SO<INF>2</INF> NAAQS. Based
on the foregoing, EPA proposes to find that Indiana has addressed the
contingency measure requirement.
EPA is proposing to find that Indiana's maintenance plan adequately
addresses the five basic components of a maintenance plan necessary to
maintain the SO<INF>2</INF> NAAQS in the
[[Page 46128]]
Huntington County nonattainment area. Therefore, EPA proposes to find
that the redesignation and maintenance plan SIP revision submitted by
Indiana for the 2010 SO<INF>2</INF> Huntington County nonattainment
area meets the requirements of section 175A of the CAA and proposes to
approve this plan as part of Indiana's federally enforceable SIP.
III. What action is EPA taking?
EPA is proposing to redesignate the Huntington County area from
nonattainment to attainment for the 2010 SO<INF>2</INF> NAAQS in
accordance with Indiana's July 30, 2024, request. EPA has determined
that the area is attaining the 2010 SO<INF>2</INF> NAAQS and that the
improvement in air quality is due to permanent and enforceable
SO<INF>2</INF> emission reductions in the area. EPA is also proposing
to approve Indiana's maintenance plan, which is designed to ensure that
the area will continue to maintain attainment of the 2010
SO<INF>2</INF> NAAQS. Once approved, the maintenance plan will become a
part of Indiana's federally enforceable SIP.
IV. Statutory and Executive Order Reviews
Redesignation of an area to attainment and the accompanying
approval of a maintenance plan under CAA sections 107 and 175A are
actions that affect the status of a geographical area and do not impose
any additional regulatory requirements on sources beyond those imposed
by State law. A redesignation to attainment does not in and of itself
create any new requirements but rather results in the applicability of
requirements contained in the CAA for areas that have been redesignated
to attainment. Moreover, 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, 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.
A. Executive Order 12866: Regulatory Planning and Review
This action is not a significant regulatory action and was
therefore not submitted to the Office of Management and Budget (OMB)
for review.
B. Executive Order 14192: Unleashing Prosperity Through Deregulation
This action is not subject to Executive Order 14192 (90 FR 9065,
February 6, 2025) because SIP approval and redesignation actions under
the CAA are exempt from review under Executive Order 12866.
C. Paperwork Reduction Act
This rule does not impose an information collection burden under
the provisions of the Paperwork Reduction Act of 1995 (44 U.S.C. 3501
et seq.).
D. Regulatory Flexibility Act
This action merely approves State law as meeting Federal
requirements and imposes no additional requirements beyond those
imposed by State law. Accordingly, the Administrator certifies that
this rule will not have a significant economic impact on a substantial
number of small entities under the Regulatory Flexibility Act (5 U.S.C.
601 et seq.).
E. Unfunded Mandates Reform Act (UMRA)
This action does not contain any unfunded mandate as described in
UMRA, 2 U.S.C. 1531-1538, and does not significantly or uniquely affect
small governments. This action does not impose additional requirements
beyond those imposed by State law. Accordingly, no additional costs to
State, local, or tribal governments, or to the private sector, will
result from this action.
F. Executive Order 13132: Federalism
This action does not have federalism implications. It will not have
substantial direct effects 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.
G. Executive Order 13175: Consultation and Coordination With Indian
Tribal Governments
Executive Order 13175 (65 FR 67249, November 9, 2000), requires EPA
to develop an accountable process to ensure ``meaningful and timely
input by tribal officials in the development of regulatory policies
that have tribal implications.'' This rule does not have Tribal
implications, as specified in Executive Order 13175. It will not have
substantial direct effects on Tribal governments. Thus, Executive Order
13175 does not apply to this rule.
H. Executive Order 13045: Protection of Children From Environmental
Health and Safety Risks
This action is not subject to Executive Order 13045 because it is
not 3(f)(1) significant as defined in Executive Order 12866, and
because EPA does not believe the environmental health or safety risks
addressed by this action present a disproportionate risk to children
because it does not establish an environmental standard intended to
mitigate health or safety risks.
I. Executive Order 13211: Actions That Significantly Affect Energy
Supply, Distribution, or Use
This action is not subject to Executive Order 13211 (66 FR 28355
(May 22, 2001)), because it is not a significant regulatory action
under Executive Order 12866.
J. National Technology Transfer Advancement Act
This rulemaking does not involve technical standards.
List of Subjects
40 CFR Part 52
Environmental protection, Air pollution control, Incorporation by
reference, Intergovernmental relations, Reporting and recordkeeping
requirements, Sulfur oxides.
40 CFR Part 81
Environmental protection, Air pollution control, National parks,
Wilderness areas.
Dated: September 15, 2025.
Anne Vogel,
Regional Administrator, Region 5.
[FR Doc. 2025-18594 Filed 9-24-25; 8:45 am]
BILLING CODE 6560-50-P
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</html>Indexed from Federal Register on September 25, 2025.
This is legal information, not legal advice. Laws vary by jurisdiction and change frequently. Always verify current law with official sources and consult a licensed attorney in your jurisdiction for advice on your specific situation.