Proposed Rule2025-20672
Air Plan Approval; Indiana; Second Maintenance Plan for 2008 Ozone NAAQS
Primary source
Metadata and text below are from the Federal Register, a public-domain U.S. government work. Always verify the official published version before relying on it for any legal matter.
Published
November 21, 2025
Issuing agencies
Environmental Protection Agency
Abstract
The Environmental Protection Agency (EPA) is proposing to approve a revision to the Indiana State Implementation Plan (SIP). On April 1, 2025, the Indiana Department of Environmental Management (IDEM) submitted a revision to the State's plan for maintaining the 2008 ozone National Ambient Air Quality Standard (NAAQS or standard) in the Indiana portion of the Cincinnati, Ohio-Kentucky-Indiana area. EPA is proposing to approve this maintenance plan because it provides for the maintenance of the 2008 ozone NAAQS for the area for 10 additional years as required by the Clean Air Act (CAA). EPA is also initiating the adequacy review process for motor vehicle emission budgets (Budgets) for the area. This action, if finalized, would make certain commitments related to maintenance of the 2008 ozone NAAQS in this area federally enforceable as part of the Indiana SIP.
Full Text
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<title>Federal Register, Volume 90 Issue 223 (Friday, November 21, 2025)</title>
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[Federal Register Volume 90, Number 223 (Friday, November 21, 2025)]
[Proposed Rules]
[Pages 52582-52587]
From the Federal Register Online via the Government Publishing Office [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[FR Doc No: 2025-20672]
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ENVIRONMENTAL PROTECTION AGENCY
40 CFR Part 52
[EPA-R05-OAR-2025-0167; FRL-12839-01-R5]
Air Plan Approval; Indiana; Second Maintenance Plan for 2008
Ozone NAAQS
AGENCY: Environmental Protection Agency (EPA).
ACTION: Proposed rule.
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SUMMARY: The Environmental Protection Agency (EPA) is proposing to
approve a revision to the Indiana State Implementation Plan (SIP). On
April 1, 2025, the Indiana Department of Environmental Management
(IDEM) submitted a revision to the State's plan for maintaining the
2008 ozone National Ambient Air Quality Standard (NAAQS or standard) in
the Indiana portion of the Cincinnati, Ohio-Kentucky-Indiana area. EPA
is proposing to approve this maintenance plan because it provides for
the maintenance of the 2008 ozone NAAQS for the area for 10 additional
years as required by the Clean Air Act (CAA). EPA is also initiating
the adequacy review process for motor vehicle emission budgets
(Budgets) for the area. This action, if finalized, would make certain
commitments related to maintenance of the 2008 ozone NAAQS in this area
federally enforceable as part of the Indiana SIP.
DATES: Comments must be received on or before December 22, 2025.
ADDRESSES: Submit your comments, identified by Docket ID No. EPA-R05-
OAR-2025-0167 at <a href="https://www.regulations.gov">https://www.regulations.gov</a>, or via email to
<a href="/cdn-cgi/l/email-protection#600c010e070d010e4e0d09030801050c200510014e070f16"><span class="__cf_email__" data-cfemail="93fff2fdf4fef2fdbdfefaf0fbf2f6ffd3f6e3f2bdf4fce5">[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: Delaney Kilgour, Air and Radiation
Division (AR18J), Environmental Protection Agency, Region 5, 77 West
Jackson Boulevard, Chicago, Illinois 60604, (312) 886-1493,
<a href="/cdn-cgi/l/email-protection#e08b898c878f9592ce84858c818e8599a0859081ce878f96"><span class="__cf_email__" data-cfemail="2c4745404b43595e024849404d4249556c495c4d024b435a">[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: Throughout this document whenever ``we,''
``us,'' or ``our'' is used, we mean EPA. This SUPPLEMENTARY INFORMATION
section is arranged as follows:
I. Summary of EPA's Proposed Action
II. Background
III. EPA's Evaluation of Indiana's SIP Submittal
A. Second Maintenance Plan
B. Transportation Conformity
IV. What action is EPA taking?
V. Statutory and Executive Order Reviews
I. Summary of EPA's Proposed Action
EPA is proposing to approve, as a revision to the Indiana SIP, the
2008 ozone NAAQS maintenance plan for the Indiana portion of the
Cincinnati, Ohio-Kentucky-Indiana area. The Cincinnati area includes
Lawrenceburg Township in Dearborn County in Indiana; Butler, Clermont,
Clinton, Hamilton, and Warren Counties in Ohio; and parts of Boone,
Campbell, and Kenton Counties in Kentucky. The maintenance plan is
designed to keep the Cincinnati area in attainment of the 2008 ozone
NAAQS through 2037.
II. Background
Ground-level ozone is formed when nitrogen oxides (NO<INF>X</INF>)
and volatile organic compounds (VOC) react in the presence of sunlight.
These two pollutants are referred to as ozone precursors. Scientific
evidence indicates that adverse public health effects occur following
exposure to ozone.
On March 12, 2008, under section 109 of the CAA, EPA promulgated a
revised primary and secondary 8-hour ozone NAAQS of 0.075 parts per
million (ppm). See 73 FR 16436 (March 27, 2008). Under EPA's
regulations at 40 CFR part 50, the 2008 ozone NAAQS is attained in an
area when the 3-year average of the annual fourth highest daily maximum
8-hour average concentration is equal to or less than 0.075 ppm, when
truncated after the thousandth decimal place, at all of the ozone
monitoring sites in the area. See 40 CFR 50.15 and appendix P to 40 CFR
part 50.
Following promulgation of a new or revised NAAQS, EPA is required
by the CAA to designate areas throughout the nation as attaining or not
attaining the NAAQS. On May 21, 2012 (77 FR 30088), EPA designated
areas for the 2008 ozone NAAQS, including the Cincinnati, Ohio-
Kentucky-Indiana area as nonattainment. These designations became
effective on July 20, 2012. Under the CAA, States are also required to
adopt and submit SIPs to implement, maintain, and enforce the NAAQS in
designated nonattainment areas and throughout the State.
When a nonattainment area has three years of complete, certified
air quality data that has been determined to attain the 2008 ozone
NAAQS, and the area has met other required criteria described in
section 107(d)(3)(E) of the CAA, the State can submit to EPA a request
to be redesignated to attainment, referred to
[[Page 52583]]
as a ``maintenance area.'' \1\ One of the criteria for redesignation is
to have an approved maintenance plan under section 175A of the CAA. The
maintenance plan must demonstrate that the area will continue to
maintain the standard for the period extending 10 years after
redesignation, and it must contain such additional measures as
necessary to ensure maintenance and such contingency provisions as
necessary to ensure that violations of the standard will be promptly
corrected. At the end of the eighth year after the effective date of
the redesignation, the State must also submit a second maintenance plan
to ensure ongoing maintenance of the standard for an additional 10
years. See CAA section 175A.
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\1\ Section 107(d)(3)(E) of the CAA sets out the requirements
for redesignation. They include attainment of the NAAQS, full
approval of the SIP under section 110(k) of the CAA, determination
that improvement in air quality is a result of permanent and
enforceable reductions in emissions, demonstration that the State
has met all applicable section 110 and part D requirements, and a
fully approved maintenance plan under CAA section 175A.
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EPA has published long-standing guidance for States on developing
maintenance plans.\2\ The Calcagni Memorandum provides that States may
generally demonstrate maintenance by either performing air quality
modeling to show that the future mix of sources and emission rates will
not cause a violation of the NAAQS or by showing that future emissions
of a pollutant and its precursors will not exceed the level of
emissions during a year when the area was attaining the NAAQS (i.e.,
attainment year inventory). See Calcagni Memorandum at 9.
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\2\ ``Procedures for Processing Requests to Redesignate Areas to
Attainment,'' Memorandum from John Calcagni, Director, Air Quality
Management Division, September 4, 1992 (the ``Calcagni
Memorandum'').
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On February 23, 2016, IDEM submitted a request to EPA to
redesignate the Indiana portion of the Cincinnati nonattainment area to
attainment for the 2008 ozone NAAQS. This submittal included a plan to
maintain the 2008 ozone NAAQS in the Cincinnati area through 2030 as a
revision to the Indiana SIP. EPA approved the Cincinnati maintenance
plan and the State's request to redesignate the Indiana portion of the
area to attainment for the 2008 ozone NAAQS on April 7, 2017 (82 FR
16940).
Under section 175A(b) of the CAA, States must submit a revision to
the first maintenance plan eight years after redesignation to provide
for maintenance of the NAAQS for 10 additional years following the end
of the first 10-year period. IDEM submitted a second maintenance plan
on April 1, 2025, and supplemented the submission on October 8, 2025.
The second maintenance plan shows attainment of the 2008 ozone NAAQS
for Cincinnati through 2037, i.e., through the end of the full 20-year
maintenance period for the area.
III. EPA's Evaluation of Indiana's SIP Submittal
A. Second Maintenance Plan
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 the Administrator
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 determines necessary, to
ensure prompt correction of the future NAAQS violation.
The Calcagni Memorandum provides further guidance on the content of
a maintenance plan, explaining that a maintenance plan should address
five elements: (1) an attainment emission inventory; (2) a maintenance
demonstration; (3) a commitment for continued air quality monitoring;
(4) a process for verification of continued attainment; and (5) a
contingency plan.
On April 1, 2025, IDEM submitted, as a SIP revision, a plan to
provide for maintenance of the 2008 ozone standard in the Indiana
portion of the Cincinnati area through 2037, more than 20 years after
the effective date of the redesignation to attainment. On October 8,
2025, IDEM submitted a supplement to the April 1 SIP revision
submittal, revising the emission inventories. As discussed below, EPA
proposes to find that IDEM's second maintenance plan includes the
necessary components and to approve the maintenance plan as a revision
to the Indiana SIP.
1. Attainment Inventory
The CAA section 175A maintenance plan approved by EPA for the first
10-year period included an attainment inventory for the Cincinnati area
that reflected typical summer day VOC and NO<INF>X</INF> emissions in
2014. In addition, because the area continued to monitor attainment of
the 2008 ozone NAAQS in 2016, 2016 is an appropriate year to use for an
attainment year inventory. For the Cincinnati attainment inventory,
Ohio and Indiana emissions of area, nonroad, and point sources, and
Kentucky emissions of area and nonroad sources were based upon the
2016v2 Emissions Modeling Platform provided by EPA.\3\ Kentucky point
source emissions (electric generating unit (EGU) and non-EGU) were
derived from the Kentucky emissions reporting system, provided in tons
per year (tpy), and based upon the actual locations of the sources
within the partial areas of Kentucky counties in the maintenance area.
Kentucky point source emissions were converted to tons per day (tpd) by
multiplying by the ratio of average July day emissions to annual
emissions for the point sector from the 2016v2 Emissions Modeling
Platform. On-road mobile source emissions for the Cincinnati area were
developed in conjunction with the Ohio-Kentucky-Indiana Regional
Council of Governments and were calculated from emission factors
produced by EPA's 2023 Motor Vehicle Emission Simulator (MOVES4) \4\
and data extracted from the region's travel demand model. All sectors
of Kentucky emissions were multiplied by fractions representing the
maintenance portions of the Kentucky counties. On-road mobile source
emissions for Indiana were based on the partial maintenance area in
Dearborn County, and remaining source sectors were based on the entire
county. Attainment inventories for the Cincinnati area are in Tables 1
and 2.
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\3\ The inventory documentation for this modeling platform can
be found here: <a href="https://gaftp.epa.gov/Air/emismod/2016/v2/">https://gaftp.epa.gov/Air/emismod/2016/v2/</a>.
\4\ The documentation for MOVES4 can be found here: <a href="https://www.epa.gov/moves/moves-versions-limited-current-use">https://www.epa.gov/moves/moves-versions-limited-current-use</a>.
[[Page 52584]]
Table 1--Cincinnati-OH-KY-IN Area Typical Summer Day VOC Emissions for Attainment Year 2016
[Tons/day (tpd)]
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Point Area Nonroad On-road Total
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Indiana:
Dearborn County............. 6.21 1.37 0.37 0.20 8.15
Entire Area..................... 13.38 65.80 17.39 27.30 123.87
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Table 2--Cincinnati-OH-KY-IN Area Typical Summer Day NOX Emissions for Attainment Year 2016
[Tons/day (tpd)]
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Point Area Nonroad On-road Total
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Indiana:
Dearborn County............. 1.75 0.26 0.38 0.57 2.96
Entire Area..................... 58.92 11.90 15.60 64.90 151.32
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2. Maintenance Demonstration
IDEM demonstrates maintenance through 2037 for the Cincinnati area
by showing that future VOC and NO<INF>X</INF> emissions remain at or
below attainment year emission levels. 2037 is an appropriate
maintenance year for the Cincinnati area because this year is more than
10 years beyond the first 10-year maintenance period. The maintenance
year emissions inventories of area, nonroad, and point sources are
projected from the EPA 2016v2 Emissions Modeling Platform, which
includes emissions for the modeling years of 2016, 2023, 2026, and
2032. The 2037 maintenance year emissions were projected from the
platform by linear extrapolation. If the extrapolation resulted in a
negative value, IDEM assumed that maintenance year emissions would
remain at the levels from the 2032 modeling year included in the 2016v2
platform, which is a conservative assumption as emissions have been
shown to be decreasing. On-road mobile source emissions for maintenance
years were calculated from EPA's 2023 MOVES4. All sectors of Kentucky
emissions were multiplied by fractions representing the maintenance
portions of the Kentucky counties. On-road mobile source emissions for
Indiana were based on the partial maintenance area in Dearborn County,
and remaining source sectors were based on the entire county. The 2037
summer day emission inventories for the Cincinnati area are in Tables 3
and 4, and changes in VOC and NO<INF>X</INF> emissions in the
Cincinnati area between 2016 and 2037 are summarized in Table 5.
In summary, the maintenance demonstration shows maintenance of the
2008 ozone standard by providing emissions information to support the
demonstration that future emissions of NO<INF>X</INF> and VOC will
remain at or below 2016 emission levels when considering both future
source growth and implementation of future controls. In the Indiana
portion of the Cincinnati area, Table 5 shows that VOC emissions are
projected to increase by 0.01 tpd between 2016 and 2037, and NOx
emissions are projected to decrease by 1.00 tpd between 2016 and 2037.
In the entire Cincinnati area, Table 5 shows that VOC and
NO<INF>X</INF> emissions are projected to decrease by 18.16 tpd and
102.23 tpd, respectively, between 2016 and 2037.
Table 3--Cincinnati-OH-KY-IN Area Typical Summer Day VOC Emissions for Maintenance Year 2037
[Tons/day (tpd)]
----------------------------------------------------------------------------------------------------------------
Point Area Nonroad On-road Total
----------------------------------------------------------------------------------------------------------------
Indiana:
Dearborn County............. 6.24 1.58 0.27 0.07 8.16
Entire Area..................... 11.75 69.90 12.59 11.47 105.71
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Table 4--Cincinnati-OH-KY-IN Area Typical Summer Day NOX Emissions for Maintenance Year 2037
[Tons/day (tpd)]
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Point Area Nonroad On-road Total
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Indiana:
Dearborn County............. 1.51 0.19 0.17 0.09 1.96
Entire Area..................... 22.54 8.97 7.49 10.09 49.09
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[[Page 52585]]
Table 5--Change in Typical Summer Day VOC and NOX Emissions in the Cincinnati Area Between 2016 and 2037
[Tons/day (tpd)]
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VOC NOX
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Net change Net change
2016 2037 (2016-2037) 2016 2037 (2016-2037)
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Indiana Portion of the Area:
Point............................................... 6.21 6.24 0.03 1.75 1.51 -0.24
Area................................................ 1.37 1.58 0.21 0.26 0.19 -0.07
Nonroad............................................. 0.37 0.27 -0.10 0.38 0.17 -0.21
On-road............................................. 0.20 0.07 -0.13 0.57 0.09 -0.48
-----------------------------------------------------------------------------------------------
Total........................................... 8.15 8.16 0.01 2.96 1.96 -1.00
Entire Area:
Point............................................... 13.38 11.75 -1.63 58.92 22.54 -36.38
Area................................................ 65.80 69.90 4.10 11.90 8.97 -2.93
Nonroad............................................. 17.39 12.59 -4.80 15.60 7.49 -8.11
On-road............................................. 27.30 11.47 -15.83 64.90 10.09 -54.81
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Total........................................... 123.87 105.71 -18.16 151.32 49.09 -102.23
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3. Continued Air Quality Monitoring
IDEM has committed to continue to work with neighboring agencies to
operate an approved ozone monitoring network in the Cincinnati area.
IDEM has committed to consult with EPA prior to making changes to the
existing monitoring network should changes become necessary in the
future. Indiana remains obligated to meet monitoring requirements and
to continue to quality assure monitoring data in accordance with 40 CFR
part 58, and to enter all data into the Air Quality System in
accordance with Federal guidelines.
4. Verification of Continued Attainment
Indiana has the legal authority to enforce and implement the
requirements of the maintenance plan for the Indiana portion of the
Cincinnati area. This includes the authority to adopt, implement, and
enforce any subsequent emission control measures determined to be
necessary to correct future ozone attainment problems.
Verification of continued attainment is accomplished through
operation of the ambient ozone monitoring network and the periodic
update of the area's emission inventories. IDEM will continue to work
with neighboring agencies to operate an approved ozone monitoring
network in the Cincinnati maintenance area. There are no plans to
discontinue operation, relocate, or otherwise change the existing ozone
monitoring network other than through revisions in the network approved
by EPA.
In addition, to track future levels of emissions, IDEM will
continue to develop and submit to EPA updated emission inventories for
all source categories at least once every three years, consistent with
the requirements of 40 CFR part 51, subpart A, and in 40 CFR 51.122.
5. Contingency Plan
Section 175A of the CAA requires that the State must adopt a
maintenance plan, as a SIP revision, that includes such contingency
measures as EPA deems necessary to ensure that the State will promptly
correct a violation of the NAAQS that occurs after redesignation of the
area to attainment of the NAAQS. The maintenance plan must identify:
the contingency measures to be considered and, if needed for
maintenance, adopted and implemented; a schedule and procedure for
adoption and implementation; and a time limit for action by the State.
The State should also identify specific indicators to be used to
determine when the contingency measures need to be considered, adopted,
and implemented. The maintenance plan must include a commitment that
the State will implement all measures with respect to the control of
the pollutant that were contained in the SIP before redesignation of
the area to attainment in accordance with section 175A(d) of the CAA.
See Calcagni Memorandum at 12-13.
As required by section 175A of the CAA, IDEM has adopted a
contingency plan for the Cincinnati area to address possible future
ozone air quality problems. The contingency plan adopted by IDEM has
two levels of response: a warning level response and an action level
response.
In IDEM's plan, a warning level response will be triggered when an
annual (1-year) fourth highest 8-hour average ozone concentration of
0.079 ppm or higher or a 2-year fourth highest 8-hour average ozone
concentration of 0.076 ppm or higher is monitored within the
maintenance area. A warning level response will consist of IDEM
conducting a study to determine whether the ozone value indicates a
trend toward higher ozone values or whether emissions appear to be
increasing. The study will evaluate whether the trend, if any, is
likely to continue, and if so, the control measures necessary to
reverse the trend. The study will consider ease and timing of
implementation as well as economic and social impacts. Implementation
of necessary controls in response to a warning level response trigger
will take place within 12 months from the conclusion of the most recent
ozone season.
In IDEM's plan, an action level response will be triggered whenever
a violation of the standard (3-year average of the annual fourth
highest 8-hour average ozone concentration equal to 0.076 ppm or
higher) is monitored within the maintenance area. When an action level
response is triggered, IDEM will determine what additional control
measures are needed to ensure future attainment of the ozone standard
and will adopt these measures through the necessary administrative and
legal process, including the opportunity for a public hearing. Control
measures selected will be adopted and implemented within 18 months from
the close of the ozone season that prompted the action level. IDEM may
also consider if significant new regulations not currently included as
part of the maintenance provisions will be implemented in a timely
manner and
[[Page 52586]]
would thus constitute an adequate contingency measure response.
IDEM included the following list of potential contingency measures
in its maintenance plan:
a. Lower-Reid vapor pressure gasoline program.
b. Broader geographic applicability of existing measures.
c. Tighten VOC Reasonably Available Control Technology (RACT) on
existing sources covered by EPA Control Technique Guidelines issued
after the 1990 CAA.
d. Apply VOC RACT to smaller existing sources.
e. One or more transportation control measures sufficient to
achieve at least half a percent reduction in actual area wide VOC
emissions. Transportation measures will be selected from the following,
based upon the factors listed above, after consultation with affected
local governments:
i. Trip reduction programs, including, but not limited to,
employer-based transportation management plans, area-wide rideshare
programs, work schedule changes, and telecommuting;
ii. Traffic flow and transit improvements; and
iii. Other new or innovative transportation measures, not yet in
widespread use, that affected local governments deem appropriate.
f. Alternative fuel and diesel retrofit programs for fleet vehicle
operations.
g. Apply controls on consumer products consistent with those
adopted elsewhere in the U.S.
h. Require VOC or NO<INF>X</INF> emission offsets for new and
modified major sources.
i. Require VOC or NO<INF>X</INF> emission offsets for new and
modified minor (less than 100 tpy) sources.
j. Increase the ratio of emission offsets required for new sources.
k. Require VOC or NO<INF>X</INF> controls on new minor sources
(less than 100 tons).
EPA concludes that the maintenance plan adequately addresses the
five basic components of a maintenance plan required under section 175A
of the CAA: an attainment emissions inventory, a maintenance
demonstration, a commitment for continued air quality monitoring, a
verification of continued attainment, and a contingency plan. As such,
EPA proposes to find that the maintenance plan SIP revision submitted
by IDEM for the Cincinnati area meets the requirements of section 175A
of the CAA.
B. Transportation Conformity
Under section 176(c) of the CAA, new transportation plans,
programs, or projects that receive Federal funding or support, such as
the construction of new highways, must ``conform'' to (i.e., be
consistent with) the SIP. Conformity to the SIP means that
transportation activities will not cause or contribute to any new air
quality violations, increase the frequency or severity of any existing
air quality problems, or delay timely attainment or any required
interim emissions reductions or any other milestones. Regulations at 40
CFR part 93 set forth EPA policy, criteria, and procedures for
demonstrating and ensuring conformity of transportation activities to a
SIP. Transportation conformity is a requirement for nonattainment and
maintenance areas.
Under the CAA, States are required to submit, at various times,
control strategy SIPs for nonattainment areas and maintenance plans for
areas seeking redesignations to attainment of the ozone standard and
for continuing maintenance of attainment. See the SIP requirements for
the 2008 ozone standard in EPA's March 6, 2015, implementation rule (80
FR 12264). These control strategy SIPs and maintenance plans must
include Budgets for criteria pollutants, including ozone, and their
precursor pollutants (VOC and NO<INF>X</INF>) to address pollution from
on-road transportation sources. The Budgets are the portion of the
total allowable emissions that are allocated to highway and transit
vehicle use that, together with emissions from other sources in the
area, will provide for attainment or maintenance. See 40 CFR 93.101.
Under 40 CFR part 93, Budgets for a maintenance area must be
established for the last year of the maintenance period. The Budgets
serve as a ceiling on emissions from an area's planned transportation
system. The Budgets concept is further explained in the Preamble to the
November 24, 1993 (58 FR 62188), Transportation Conformity Rule. The
Preamble also describes how to establish the Budgets in the SIP and how
to revise the Budgets, if needed, after initially establishing them in
the SIP.
Indiana's maintenance plan includes NO<INF>X</INF> and VOC Budgets
for the last year of the maintenance period (2037) for the Cincinnati
area. Indiana's April 1, 2025, maintenance plan submission, including
the Budgets for the maintenance area, is available for public comment
via this proposed rulemaking. The submission was endorsed by the
Governor's designee and IDEM provided opportunity for a public hearing.
The Budgets were developed as part of an interagency consultation
process which includes Federal, State, and local agencies. The Budgets
were clearly identified and precisely quantified. These Budgets, when
considered together with all other emission sources, are consistent
with maintenance of the 2008 ozone NAAQS.
The Budgets for the Ohio and Indiana portions of the Cincinnati
multi-state area are in Table 6. For ease of planning, the smaller
Dearborn County, Indiana area is combined with the Ohio Budget. As
shown, the 2037 Budgets exceed the estimated 2037 on-road sector
emissions. To accommodate future variations in travel demand models and
vehicle miles traveled forecast, IDEM allocated a portion of the safety
margin, described further below, to the mobile source sector. IDEM has
demonstrated that the Cincinnati area can maintain the 2008 ozone NAAQS
in the 2037 maintenance year with mobile source emissions in the Ohio
and Indiana portions of the area of 11.01 tpd of VOC and 9.32 tpd of
NO<INF>X</INF>. Despite partial allocation of the safety margin for
each area, emissions will remain under attainment year emission levels.
A ``safety margin'' is the amount by which the total projected
emissions from all sources of a given pollutant are less than the total
emissions that would satisfy the applicable requirement for
maintenance. See 40 CFR 93.101. As noted in Table 5, the emissions in
the Cincinnati area are projected to have safety margins of 102.23 tpd
of NO<INF>X</INF> and 18.16 tpd of VOC in 2037. The safety margin is
calculated as the difference between emissions in the 2016 attainment
year and projected emissions in the 2037 maintenance year for all
sources in the Cincinnati area. Even if emissions exceeded projected
levels by the full amount of the safety margin, the area would still
demonstrate maintenance since emission levels would equal those in the
attainment year.
IDEM is allocating a portion of that safety margin to the mobile
source sector. More specifically, in the Ohio and Indiana portions of
the multi-state Cincinnati area, in 2037, IDEM is allocating 1.22 tpd
and 1.44 tpd of the NO<INF>X</INF> and VOC safety margins,
respectively, shown in Table 6. IDEM is not requesting allocation to
the Budgets of the entire available safety margins reflected in the
demonstration of maintenance. In fact, the amount allocated to the
Budgets represents only a portion of the maintenance year safety
margins. Therefore, even though the State is requesting Budgets that
exceed the projected on-road mobile source emissions for the
maintenance years contained in the demonstration of maintenance, the
increase in on-road
[[Page 52587]]
mobile source emissions that can be considered for transportation
conformity purposes is within the safety margins of the ozone
maintenance demonstration. Further, once allocated to mobile sources,
these safety margins will not be available for use by other sources.
Table 6--Budgets for the Ohio and Indiana Portions of the Cincinnati OH-KY-IN Area
[Tons/day (tpd)]
----------------------------------------------------------------------------------------------------------------
Attainment year 2037 Mobile
2016 on-road 2037 Estimated on- safety margin 2037 Budgets
emissions road emissions allocation
----------------------------------------------------------------------------------------------------------------
VOC................................. 23.56 9.57 1.44 11.01
NOX................................. 51.63 8.10 1.22 9.32
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EPA is proposing to find adequate and approve the Budgets for use
to determine transportation conformity in the Cincinnati area because
EPA has determined that the area can maintain attainment of the 2008
ozone NAAQS for the maintenance year period with mobile source
emissions at the levels of the Budgets. Also, EPA has reviewed the
submitted Budgets and proposes to find that they meet the adequacy
criteria in the transportation conformity regulations (40 CFR
93.118(e)(4)). As required by the transportation conformity rule (40
CFR 93.118(f)(2)), EPA is using this proposal to notify the public that
EPA is beginning a 30-day comment period on the adequacy of the
submitted motor vehicle emissions budgets. Comments on the adequacy of
the Budgets should be submitted to the docket for this proposal. EPA
will make a final determination on the adequacy of the submitted
Budgets either in a final action on this proposal or by notifying the
State in writing, notifying the public by publishing a Federal Register
notice, and announcing the determination on EPA's adequacy web page.\5\
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\5\ EPA's adequacy web page can be found here: <a href="https://www.epa.gov/state-and-local-transportation/conformity-adequacy-review-region-5">https://www.epa.gov/state-and-local-transportation/conformity-adequacy-review-region-5</a>.
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IV. What action is EPA taking?
EPA is proposing to approve the second maintenance plan for the
2008 ozone NAAQS submitted by IDEM on April 1, 2025, and supplemented
on October 8, 2025, under sections 110(k) and 175A of the CAA for the
reasons set forth above, for the Indiana portion of the Cincinnati area
as a revision to the Indiana SIP. This second maintenance plan is
designed to keep the Cincinnati area in attainment of the 2008 ozone
NAAQS through 2037. EPA is also proposing to find adequate and approve
the newly established Budgets for the Indiana portion of the Cincinnati
maintenance area.
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, 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:
<bullet> 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);
<bullet> Is not subject to Executive Order 14192 (90 FR 9065,
February 6, 2025) because SIP actions are exempt from review under
Executive Order 12866;
<bullet> Does not impose an information collection burden under the
provisions of the Paperwork Reduction Act (44 U.S.C. 3501 et seq.);
<bullet> 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.);
<bullet> 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);
<bullet> Does not have federalism implications as specified in
Executive Order 13132 (64 FR 43255, August 10, 1999);
<bullet> Is not subject to Executive Order 13045 (62 FR 19885,
April 23, 1997) because it approves a State program;
<bullet> Is not a significant regulatory action subject to
Executive Order 13211 (66 FR 28355, May 22, 2001); and
<bullet> 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 Clean Air Act.
In addition, the SIP is not approved to apply on any Indian
reservation land or in any other area where EPA or an Indian Tribe has
demonstrated that a Tribe has jurisdiction. In those areas of Indian
country, the rulemaking 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).
List of Subjects in 40 CFR Part 52
Environmental protection, Air pollution control, Incorporation by
reference, Intergovernmental relations, Nitrogen oxides, Ozone,
Reporting and recordkeeping requirements, Volatile organic compounds.
Dated: November 19, 2025.
Anne Vogel,
Regional Administrator, Region 5.
[FR Doc. 2025-20672 Filed 11-20-25; 8:45 am]
BILLING CODE 6560-50-P
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</html>Indexed from Federal Register on November 21, 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.