Proposed Rule2026-17502
Air Plan Approval; Kentucky; Cincinnati-Hamilton Area Limited Maintenance Plan for the 1997 8-Hour Ozone NAAQS
Primary source
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Published
August 27, 2026
Issuing agencies
Environmental Protection Agency
Abstract
The U.S. Environmental Protection Agency (EPA or Agency) is proposing to approve a State Implementation Plan (SIP) revision submitted by the Commonwealth of Kentucky through the Energy and Environment Cabinet (Cabinet), Division of Air Quality (Division), on July 23, 2024. The SIP revision consists of a Limited Maintenance Plan (LMP) for the Kentucky portion of the tri-state Cincinnati-Hamilton 1997 8-hour ozone nonattainment area (the "tri-state Cincinnati-Hamilton Area"). The Kentucky portion of the tri-state Cincinnati-Hamilton Area is composed of Boone, Campbell, and Kenton Counties in Kentucky (hereinafter also referred to as the "Northern Kentucky Area"). The EPA is proposing to approve Kentucky's LMP for the Northern Kentucky Area because it provides for the maintenance of the 1997 8-hour ozone National Ambient Air Quality Standards (NAAQS) within the tri-state Cincinnati-Hamilton Area through the end of the second 10-year portion of the maintenance period. The effect of this proposed action would be to make certain commitments related to maintenance of the 1997 8-hour ozone NAAQS in the Northern Kentucky Area federally enforceable as part of the Kentucky SIP.
Full Text
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<title>Federal Register, Volume 91 Issue 165 (Thursday, August 27, 2026)</title>
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[Federal Register Volume 91, Number 165 (Thursday, August 27, 2026)]
[Proposed Rules]
[Pages 55299-55305]
From the Federal Register Online via the Government Publishing Office [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[FR Doc No: 2026-17502]
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ENVIRONMENTAL PROTECTION AGENCY
40 CFR Part 52
[EPA-R04-OAR-2024-0440; FRL-13324-01-R4]
Air Plan Approval; Kentucky; Cincinnati-Hamilton Area Limited
Maintenance Plan for the 1997 8-Hour Ozone NAAQS
AGENCY: Environmental Protection Agency (EPA).
ACTION: Proposed rule.
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SUMMARY: The U.S. Environmental Protection Agency (EPA or Agency) is
proposing to approve a State
[[Page 55300]]
Implementation Plan (SIP) revision submitted by the Commonwealth of
Kentucky through the Energy and Environment Cabinet (Cabinet), Division
of Air Quality (Division), on July 23, 2024. The SIP revision consists
of a Limited Maintenance Plan (LMP) for the Kentucky portion of the
tri-state Cincinnati-Hamilton 1997 8-hour ozone nonattainment area (the
``tri-state Cincinnati-Hamilton Area''). The Kentucky portion of the
tri-state Cincinnati-Hamilton Area is composed of Boone, Campbell, and
Kenton Counties in Kentucky (hereinafter also referred to as the
``Northern Kentucky Area''). The EPA is proposing to approve Kentucky's
LMP for the Northern Kentucky Area because it provides for the
maintenance of the 1997 8-hour ozone National Ambient Air Quality
Standards (NAAQS) within the tri-state Cincinnati-Hamilton Area through
the end of the second 10-year portion of the maintenance period. The
effect of this proposed action would be to make certain commitments
related to maintenance of the 1997 8-hour ozone NAAQS in the Northern
Kentucky Area federally enforceable as part of the Kentucky SIP.
DATES: Comments must be received on or before September 17, 2026.
ADDRESSES: Submit your comments, identified by Docket ID No. EPA-R04-
OAR-2024-0440 at <a href="https://www.regulations.gov">https://www.regulations.gov</a>. Follow the online
instructions for submitting comments. Once submitted, comments cannot
be edited or removed from <a href="http://Regulations.gov">Regulations.gov</a>. The EPA may publish any
comment received to its public docket. Do not submit electronically any
information you consider to be Confidential Business Information (CBI)
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. The 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, the full EPA
public comment policy, information about CBI 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: Nelsha Athauda, Multi-Air Pollutant
Coordination Section, Air Planning and Implementation Branch, Air and
Radiation Division, U.S. Environmental Protection Agency, Region 4, 61
Forsyth Street SW, Atlanta, Georgia 30303-8960. The telephone number is
(404) 562-9360. Ms. Athauda can also be reached via electronic mail at
<a href="/cdn-cgi/l/email-protection#6e0f1a060f1b0a0f40000b021d060f2e0b1e0f40090118"><span class="__cf_email__" data-cfemail="ec8d98848d99888dc28289809f848dac899c8dc28b839a">[email protected]</span></a>.
SUPPLEMENTARY INFORMATION: Throughout this proposed rule, the use of
``we,'' ``us,'' or ``our'' is intended to refer to the EPA. We use
multiple abbreviations and terms in this proposed rule. While this list
may not be exhaustive, for ease of reading and for reference purposes,
the EPA defines the following terms and acronyms here:
AQS Air Quality System
CAA Clean Air Act
CBI Confidential Business Information
CFR Code of Federal Regulations
CO Carbon Monoxide
DV Design Value
EPA Environmental Protection Agency
FR Federal Register
LMP Limited Maintenance Plan
MOVES EPA's MOtor Vehicle Emission Simulator
NAAQS National Ambient Air Quality Standard
NEI National Emissions Inventory
NO<INF>X</INF> Nitrogen Oxides
OKI Ohio-Kentucky-Indiana
PM<INF>10</INF> Particulate Matter with an aerodynamic diameter less
than 10 microns
ppm Parts per million
RACT Reasonably Available Control Technology
SIP State Implementation Plan
tpsd tons per summer day
VOC Volatile Organic Compounds
Table of Contents
I. Executive Summary
II. Background
III. Kentucky's SIP Submittal
IV. The EPA's Evaluation of Kentucky's SIP Submittal
A. Attainment Emissions Inventory
B. Maintenance Demonstration
C. Monitoring Network and Verification of Continued Attainment
D. Contingency Plan
V. Transportation Conformity
VI. Proposed Action
VII. Statutory and Executive Order Reviews
I. Executive Summary
In accordance with the Clean Air Act (CAA or Act), the EPA is
proposing to approve the Northern Kentucky Area's second 10-year LMP
for the 1997 8-hour ozone NAAQS, adopted by the Cabinet on July 23,
2024, and submitted to the Agency as a revision to the Kentucky SIP on
July 23, 2024.
On April 30, 2004, the tri-state Cincinnati-Hamilton Area, which is
composed of Boone, Campbell, and Kenton Counties in Kentucky; Butler,
Clermont, Clinton, Hamilton, and Warren Counties in Ohio; and a portion
of Dearborn County in Indiana, was designated as nonattainment for the
1997 8-hour ozone NAAQS.\1\ Subsequently, on January 29, 2010, the
Cabinet submitted a redesignation request and the first 10-year
maintenance plan for the Northern Kentucky Area. In 2010, after the
EPA's approval of the maintenance plan, the Northern Kentucky Area was
redesignated to attainment for the 1997 8-hour ozone NAAQS.\2\
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\1\ See 69 FR 23857 (Apr. 30, 2004).
\2\ See 75 FR 47218 (Aug. 5, 2010).
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The Northern Kentucky Area LMP for the 1997 8-hour ozone NAAQS,
submitted by the Cabinet on July 23, 2024, is designed to maintain the
1997 8-hour ozone NAAQS within the Northern Kentucky Area through the
end of the second 10-year portion of the maintenance period beyond
redesignation (through August 5, 2030). The EPA is proposing to approve
the plan because it meets all applicable requirements under CAA
sections 110 and 175A.
II. Background
In 1979, under CAA section 109, the EPA established primary and
secondary NAAQS for ozone at 0.12 parts per million (ppm), averaged
over a 1-hour period.\3\ On July 18, 1997, the EPA revised the primary
and secondary NAAQS for ozone to set the acceptable level of ozone in
the ambient air at 0.08 ppm, averaged over an 8-hour
period.<SUP>4 5</SUP>
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\3\ See 44 FR 8202 (Feb. 8, 1979).
\4\ See 62 FR 38856 (July 18, 1997).
\5\ In March 2008, the EPA completed another review of the
primary and secondary ozone NAAQS and lowered the level for both to
0.075 ppm. See 73 FR 16436 (Mar. 27, 2008). Additionally, in October
2015, the EPA completed another review of the primary and secondary
ozone NAAQS and further lowered the level for both to 0.070 ppm. See
80 FR 65292 (Oct. 26, 2015).
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Following promulgation of a new or revised NAAQS, the EPA is
required by the CAA to designate areas throughout the nation as
attaining or not attaining the NAAQS. On April 30, 2004, the EPA
designated the tri-state Cincinnati-Hamilton Area, which consists of
the Kentucky counties of Boone, Campbell, and Kenton, the Ohio counties
of Butler, Clermont, Clinton, Hamilton, and Warren, and a portion of
Dearborn County of Indiana, as nonattainment for the 1997 8-hour ozone
NAAQS. Those designations became effective on June 15, 2004.\6\
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\6\ See 69 FR 23858 (Apr. 30, 2004).
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The EPA has revised the ozone NAAQS twice since the 1997 standards
were finalized. On July 20, 2012, the EPA designated areas as
unclassifiable/attainment or nonattainment for the 2008 8-hour ozone
NAAQS. At that time, the tri-state Cincinnati-Hamilton
[[Page 55301]]
Area was designated as nonattainment. The EPA redesignated the Kentucky
portion of the tri-state Cincinnati-Hamilton Area to attainment for the
2008 8-hour ozone standard with an effective date of July 5, 2017.\7\
On November 16, 2017, the EPA designated areas for the 2015 8-hour
ozone NAAQS. The tri-state Cincinnati-Hamilton Area was designated as
nonattainment for the 2015 8-hour ozone NAAQS with an effective date of
August 3, 2018.\8\ On June 9, 2022, the EPA designated the Ohio portion
of the tri-state Area attainment for the 2015 8-hour ozone NAAQS with
an effective date of June 9, 2022.\9\ On October 4, 2023, the EPA
designated the Kentucky portion of the tri-state Cincinnati-Hamilton
Area to attainment for the 2015 8-hour ozone standard with an effective
date of November 3, 2023.\10\
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\7\ See 82 FR 30976 (July 5, 2017).
\8\ See 83 FR 25776 (June 4, 2018).
\9\ See 87 FR 35104 (June 9, 2022).
\10\ See 88 FR 68471 (Oct. 4, 2023).
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A State may submit a request that the EPA redesignate a
nonattainment area that is attaining a NAAQS to attainment, and, if the
area has met the criteria described in CAA section 107(d)(3)(E), the
Agency may approve the redesignation request.\11\ One of the criteria
for redesignation is for the area to have an approved maintenance plan
under CAA section 175A. The maintenance plan must demonstrate that the
area will continue to maintain the NAAQS for the period extending ten
years after redesignation, and it must contain such additional measures
as necessary to ensure maintenance and such contingency provisions as
necessary to assure that violations of the NAAQS will be promptly
corrected. Eight years after the effective date of redesignation, the
State must also submit a second maintenance plan to ensure ongoing
maintenance of the NAAQS for an additional ten years pursuant to CAA
section 175A(b) (i.e., ensuring maintenance for 20 years after
redesignation).
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\11\ CAA section 107(d)(3)(E) sets out the requirements for
redesignating a nonattainment area to attainment. They include
attainment of the NAAQS, full approval of the applicable SIP
pursuant to CAA section 110(k), 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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The EPA has published long-standing guidance for states on
developing maintenance plans. The Calcagni memo \12\ 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
projected 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).\13\ The EPA clarified in
three subsequent guidance memos that certain areas can meet the CAA
section 175A requirement to provide for maintenance by showing that
they are unlikely to violate the NAAQS in the future, using information
such as the area design values \14\ when the design values are well
below the standard and have been historically stable.\15\ The EPA
refers to a maintenance plan containing this streamlined demonstration
as an LMP.
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\12\ John Calcagni, Director, Air Quality Management Division,
EPA Office of Air Quality Planning and Standards (OAQPS),
``Procedures for Processing Requests to Redesignate Areas to
Attainment,'' September 4, 1992 (Calcagni memo).
\13\ See Calcagni memo at page 9.
\14\ The ozone design value for a monitoring site is the 3-year
average of the annual fourth-highest daily maximum 8-hour average
ozone concentrations. The design value for an ozone area is the
highest design value of any monitoring site in the area.
\15\ See ``Limited Maintenance Plan Option for Nonclassifiable
Ozone Nonattainment Areas'' from Sally L. Shaver, OAQPS, dated
November 16, 1994; ``Limited Maintenance Plan Option for
Nonclassifiable CO Nonattainment Areas'' from Joseph Paisie, OAQPS,
dated October 6, 1995; and ``Limited Maintenance Plan Option for
Moderate PM<INF>10</INF> Nonattainment Areas'' from Lydia Wegman,
OAQPS, dated August 9, 2001. Copies of these guidance memoranda can
be found in the docket for this proposed rulemaking.
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The EPA has interpreted CAA section 175A as permitting the LMP
option because CAA section 175A does not define how areas may
demonstrate maintenance, and in the Agency's experience implementing
the various NAAQS, areas that qualify for an LMP and have approved LMPs
have rarely, if ever, experienced subsequent violations of the NAAQS.
As noted in the LMP guidance memoranda, states seeking an LMP must
still submit the maintenance plan elements outlined in the Calcagni
memo, including an attainment emissions inventory, provisions for the
continued operation of the ambient air quality monitoring network,
verification of continued attainment, and a contingency plan in the
event of a future violation of the NAAQS. Moreover, a State seeking an
LMP must still submit its section 175A maintenance plan as a revision
to its SIP, with all attendant notice and comment procedures. While the
LMP guidance memoranda were originally written with respect to certain
NAAQS,\16\ the EPA has extended the LMP interpretation of section 175A
to other NAAQS and pollutants not specifically covered by the previous
guidance memos.\17\
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\16\ The prior memos addressed: unclassifiable areas under the
1-hour ozone NAAQS, nonattainment areas for the PM<INF>10</INF>
(particulate matter with an aerodynamic diameter less than 10
microns) NAAQS, and nonattainment areas for the carbon monoxide (CO)
NAAQS.
\17\ See, e.g., 79 FR 41900 (July 18, 2014) (approval of the
second ten-year LMP for the Grant County 1971 sulfur dioxide
maintenance area).
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In this case, the EPA is proposing to approve the Northern Kentucky
Area LMP because the Commonwealth has shown that ozone concentrations
in the tri-state Cincinnati-Hamilton Area are well below the 1997 8-
hour ozone NAAQS, have been historically stable, and that the
Commonwealth has met the other maintenance plan requirements. The
Cabinet submitted the LMP for the Northern Kentucky Area to fulfill the
CAA's second maintenance plan requirement. The EPA's evaluation of the
Northern Kentucky Area LMP is presented in section IV of this document,
below.
On January 29, 2010, the Cabinet submitted a request to the EPA to
redesignate the Northern Kentucky Area to attainment for the 1997 8-
hour ozone NAAQS. This submittal included a plan, for inclusion in the
Kentucky SIP, to provide for maintenance of the 1997 8-hour ozone NAAQS
in the tri-state Cincinnati-Hamilton Area through 2030. The EPA
approved the Northern Kentucky Maintenance Plan and the Commonwealth's
requests to redesignate the Northern Kentucky Area to attainment for
the 1997 8-hour ozone NAAQS, effective August 5, 2010.\18\ Kentucky's
July 23, 2024, submittal contains the second 10-year maintenance plan
for the 20-year maintenance period of the 1997 8-hour ozone NAAQS to
ensure continued maintenance for the tri-state Cincinnati-Hamilton
Area.
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\18\ See 75 FR 47218 (Aug. 5, 2010).
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CAA section 175A(b) requires states to submit a revision to the
first maintenance plan eight years after redesignation to provide for
maintenance of the NAAQS for ten additional years following the end of
the first 10-year period. However, the EPA's final implementation rule
for the 2008 8-hour ozone NAAQS revoked the 1997 8-hour ozone NAAQS and
stated that one consequence of revocation was that areas that had been
redesignated to attainment (i.e., maintenance areas) for the 1997 NAAQS
no longer needed to submit a second 10-year maintenance plan under CAA
section 175A(b).\19\
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\19\ See 80 FR 12264, 12315 (Mar. 6, 2015).
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In South Coast Air Quality Management District v. EPA, the United
States Court of Appeals for the District
[[Page 55302]]
of Columbia Circuit vacated the EPA's interpretation that, because of
the revocation of the 1997 8-hour ozone NAAQS, a second maintenance
plan was not required for ``orphan maintenance areas,'' i.e., areas
that had been redesignated to attainment for the 1997 8-hour ozone
NAAQS maintenance areas and were designated attainment for the 2008
ozone NAAQS.\20\ Thus, states with these ``orphan maintenance areas''
under the 1997 8-hour ozone NAAQS must submit a maintenance plan for
the second maintenance period. Accordingly, on July 23, 2024, Kentucky
submitted a second maintenance plan for the Northern Kentucky Area
which shows that the Area is expected to remain in attainment of the
1997 8-hour ozone NAAQS through 2030.
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\20\ South Coast II, 882 F.3d 1138 (D.C. Cir. 2018).
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In recognition of the continuing record of relatively stable air
quality monitoring data showing ambient 8-hour ozone concentrations in
the tri-state Cincinnati-Hamilton Area well below the 1997 8-hour ozone
NAAQS, the Cabinet chose the LMP option for the development of the
second 1997 8-hour ozone NAAQS maintenance plan.
III. Kentucky's SIP Submittal
As mentioned previously, on July 23, 2024, the Cabinet submitted
the Northern Kentucky Area LMP for the 1997 8-hour ozone NAAQS to the
EPA as a revision to the Kentucky SIP. The submittal includes the LMP,
air quality data, emissions inventory information, and appendices.
Appendices to the plan include monitoring data along with documentation
of public notice and statement of consideration.
IV. The EPA's Evaluation of Kentucky's SIP Submittal
The EPA has reviewed the Northern Kentucky Area LMP, which is
designed to maintain the 1997 8-hour ozone NAAQS within the tri-state
Cincinnati-Hamilton Area through the end of the 20-year period beyond
redesignation, as required under CAA section 175A(b). The following is
a summary of EPA's interpretation of the section 175A requirements \21\
and the Agency's evaluation of how each requirement is met for the
Northern Kentucky Area.
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\21\ See Calcagni memo.
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A. Attainment Emissions Inventory
The July 23, 2024, submittal includes an ozone attainment inventory
that reflects typical summer day emissions in 2019. The submittal also
includes a comparison of the 2019 attainment emissions inventory to the
2008 attainment inventory developed for the first 10-year maintenance
plan.\22\ Comparing these inventories shows an overall decrease in
emissions. Table 1 presents a summary of these inventories.
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\22\ For more information on the development of the 2008
emissions inventories, see 75 FR 26685 (May 12, 2010).
Table 1--Attainment Emissions Inventory for 2008 and 2019 in Tons Per Summer Day (tpsd) for the Northern
Kentucky Area
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NOX VOC
-----------------------------------------------
2008 2019 2008 2019
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Boone Total: 47.84 13.97 20.29 12.83
Point....................................................... 23.27 5.99 2.81 2.75
Nonpoint.................................................... 5.02 2.54 8.41 7.29
Onroad...................................................... 8.53 4.70 4.00 1.30
Nonroad..................................................... 11.02 0.74 5.07 1.49
Campbell Total: 11.56 3.79 8.42 3.95
Point....................................................... 0.02 0.29 0.28 0.40
Nonpoint.................................................... 1.32 0.92 4.34 2.23
Onroad...................................................... 4.88 2.20 2.29 0.80
Nonroad..................................................... 5.34 0.38 1.51 0.52
Kenton Total: 19.79 7.68 14.85 6.78
Point....................................................... 0.03 0.28 1.17 0.43
Nonpoint.................................................... 4.06 1.53 7.88 4.11
Onroad...................................................... 8.37 5.30 3.85 1.50.
Nonroad..................................................... 7.33 0.57 1.95 0.74
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Kentucky Total 79.19 25.44 43.56 23.56
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The Attainment Inventory portion of the July 23, 2024, submittal
describes the methods, models, and assumptions used to develop the 2019
attainment inventory and indicates that this inventory was developed
using the following combination of sources: (1) data from the 2017
National Emissions Inventory (NEI); (2) data required to be submitted
by sources to the Division; \23\ (3) mobile modeling conducted by the
Ohio-Kentucky-Indiana (OKI) Regional Council of Governments; \24\ and
(4) EPA's 2016v2 modeling platform.\25\
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\23\ 401 KAR 52:020, available at <a href="https://apps.legislature.ky.gov/law/kar/401/052/020.pdf">https://apps.legislature.ky.gov/law/kar/401/052/020.pdf</a>; and 401 KAR 52:030,
available at <a href="https://apps.legislature.ky.gov/law/kar/401/052/030.pdf">https://apps.legislature.ky.gov/law/kar/401/052/030.pdf</a>.
\24\ Mobile emissions data was developed by OKI from emission
factors produced by EPA's MOtor Vehicle Emission Simulator (MOVES)
version 3 (MOVES3) software program and data extracted from the
region's updated travel-demand model.
\25\ Documentation and data for the 2016 NEIv2 can be accessed
via the following website: <a href="http://www.epa.gov/air-emissions-inventories/2014-national-emissions-inventory-nei-data">http://www.epa.gov/air-emissions-inventories/2014-national-emissions-inventory-nei-data</a>.
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Based on our review of the methods, models, and assumptions used by
Kentucky to develop the volatile organic compounds (VOC) and oxides of
nitrogen (NO<INF>X</INF>) estimates, the EPA proposes to find that the
Northern Kentucky Area LMP includes a comprehensive, reasonably
accurate inventory of actual ozone precursor emissions in attainment
year 2019 and proposes to conclude that the plan's inventories are
acceptable for the purposes of a subsequent maintenance plan under CAA
section 175A(b).
B. Maintenance Demonstration
The maintenance demonstration requirement is satisfied in a LMP if
the weight of evidence indicates that air quality in the area is well
below the level of the NAAQS, that past air quality trends have been
shown to be stable, and that the probability of the area
[[Page 55303]]
experiencing a violation over the second 10-year maintenance period is
low.\26\ These criteria are evaluated below.
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\26\ See ``Limited Maintenance Plan Option for Nonclassifiable
Ozone Nonattainment Areas'' from Sally L. Shaver, OAQPS, dated
November 16, 1994; ``Limited Maintenance Plan Option for
Nonclassifiable CO Nonattainment Areas'' from Joseph Paisie, OAQPS,
dated October 6, 1995; and ``Limited Maintenance Plan Option for
Moderate PM<INF>10</INF> Nonattainment Areas'' from Lydia Wegman,
OAQPS, dated August 9, 2001.
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1. Evaluation of Ozone Concentrations
To attain the 1997 8-hour ozone NAAQS, the three-year average of
the fourth-highest daily maximum 8-hour average ozone concentrations
(design value or DV) at each monitor within an area must not exceed
0.08 ppm. Based on the rounding convention described in 40 CFR part 50,
appendix I, the 1997 8-hour ozone NAAQS is attained if the design value
is 0.084 ppm or below.
There are currently eleven ozone monitors in the tri-state
Cincinnati-Hamilton Maintenance Area: one in Boone County, Kentucky;
one in Campbell County, Kentucky; three in Butler County, Ohio; one in
Clermont County, Ohio; one in Clinton County, Ohio; three in Hamilton
County, Ohio; and one in Warren County, Ohio. Table 2 of this document
presents the design values (in ppm) for each monitor in the tri-state
Cincinnati-Hamilton Maintenance Area over the 2012-2025 period.
Table 2--1997 8-Hour Ozone NAAQS Design Values (ppm) for Monitors in the Tri-State Cincinnati-Hamilton Area for the 2012-2025 Time Period *
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2010-2012 2011-2013 2012-2014 2013-2015 2014-2016 2015-2017 2016-2018 2017-2019 2018-2020 2019-2021 2020-2022 2021-2023 2022-2024 2023-2025
County AQS Site ID DV DV DV DV DV DV DV DV DV DV DV DV DV DV
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Boone, KY....................................................... 21-015-0008 0.070 0.067 0.065 0.061 0.063 0.062 0.064 0.063 0.064 0.061 ** 0.063 ** 0.068 0.068 0.070
Campbell, KY.................................................... 21-037-3002 0.079 0.078 0.075 0.071 0.070 0.069 0.067 0.065 0.063 0.063 0.063 0.064 0.066 0.069
Butler, OH...................................................... 39-017-0018 0.082 0.078 0.073 0.069 0.071 0.071 0.073 0.071 0.071 0.067 0.067 0.067 0.068 0.068
Butler, OH...................................................... 39-017-0023 0.079 0.076 0.073 0.069 0.072 0.072 0.073 0.070 0.069 0.066 0.067 0.068 0.068 0.068
Butler, OH...................................................... 39-017-9991 (* * *) 0.077 0.074 0.068 0.069 0.069 0.070 0.068 0.066 0.064 0.064 0.066 0.067 0.067
Clermont, OH.................................................... 39-025-0022 0.082 0.079 0.075 0.068 0.070 0.070 0.070 0.069 0.068 0.066 0.064 0.065 0.066 0.068
Clinton, OH..................................................... 39-027-1002 0.082 0.078 0.073 0.068 0.070 0.070 0.069 0.067 0.064 0.063 0.063 0.067 0.070 0.071
Hamilton, OH.................................................... 39-061-0006 0.085 0.081 0.075 0.070 0.072 0.073 0.075 0.074 0.074 0.070 0.069 0.070 0.071 0.072
Hamilton, OH.................................................... 39-061-0010 0.080 0.075 0.073 0.069 0.072 0.070 0.072 0.070 0.070 0.067 0.067 0.068 0.070 0.070
Hamilton, OH.................................................... 39-061-0040 0.080 0.078 0.073 0.069 0.071 0.071 0.072 0.071 0.070 0.069 0.068 0.070 0.071 0.074
Warren, OH...................................................... 39-165-0007 0.079 0.076 0.072 0.069 0.072 0.071 0.072 0.071 0.072 0.070 0.069 0.070 0.072 0.073
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* This notice of proposed rulemaking uses design values generated under the 1997 ozone NAAQS procedures, as provided by the Air Quality System (AQS), as the design value data provided in the July 23, 2024, submittal were
inadvertently generated under the 2015 ozone NAAQS procedures. AQS data is accessible at <a href="https://www.epa.gov/aqs">https://www.epa.gov/aqs</a>.
* * The Boone County, Kentucky, monitor (AQS Site ID: 21-015-0003) was relocated to a new site (AQS Site ID: 21-015-0008) in 2022. The EPA approved combining data for the two sites to calculate design values; value reported is a
combined design value.
* * * The Butler County, Ohio, monitor (AQS Site ID: 39-017-9991) reported no data during 2010. As a result, there is no valid three-year design value during (2010-2012) for this monitor.
In the tri-state Cincinnati-Hamilton Area, all current design
values are below 85 percent of the ozone NAAQS,\27\ with the exception
of two monitors, one in Warren County, OH, (AQS ID: 39-165-0007) and
one in Hamilton, OH (AQS ID: 39-061-0040). The Hamilton County
monitor's 2025 design value is 0.074 ppm, which is 88 percent of the
exceedance levels of the ozone NAAQS. All other monitors in the tri-
state Cincinnati-Hamilton Area are below this 85 percent threshold.
Based on the weight of evidence in support of Kentucky's submittal, the
EPA is proposing to approve this LMP. No design values in the tri-state
Cincinnati-Hamilton Area have exceeded the 1997 ozone NAAQS during the
2013-2025 time period depicted in Table 2. The design value data shown
in Table 2 illustrates an overall downward trend in ozone levels at
each monitor over this timeframe, and the 20-year maintenance period
beyond redesignation ends in 2030, which leaves only a relatively short
amount of remaining time based on the data in Table 2. Thus, the
probability of the tri-state Cincinnati-Hamilton Area experiencing a
violation during this second maintenance period is low. These aspects
of the EPA's proposed approval are discussed in more detail below.
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\27\ See ``Limited Maintenance Plan Option for Nonclassifiable
Ozone Nonattainment Areas'' from Sally L. Shaver, OAQPS, dated
November 16, 1994.
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2. Stability of Ozone Levels
As discussed previously, the tri-state Cincinnati-Hamilton Area has
maintained ozone concentrations below the 1997 8-hour ozone NAAQS over
the past twelve 3-year design value periods. Additionally, the design
value data shown in Table 2 illustrates an overall downward trend in
ozone levels at each monitor over this timeframe. Over the past ten
years, the maximum design value increase was 0.009 ppm, which occurred
at the Boone, Kentucky ozone monitor (AQS ID: 21-015-0003) between the
2019-2021 DV and the 2023-2025 DV. After adding the maximum design
value increase of 0.009 ppm to the maximum most recent design value
(0.070 ppm), the resulting 0.079 ppm remains below the 0.084 ppm
threshold to attain the 1997 8-hour ozone NAAQS. Additionally, the 20-
year maintenance period beyond redesignation ends in 2030, which leaves
a relatively short amount of remaining time during which significant
increases in ozone levels are unlikely based on the data in Table 2. As
a result, the EPA finds that there is a low probability of the tri-
state Cincinnati-Hamilton Area violating the 1997 8-hour ozone NAAQS
during this second maintenance period.
C. Monitoring Network and Verification of Continued Attainment
The EPA annually reviews the ozone monitoring network that the
Cabinet operates and maintains in accordance with 40 CFR part 58. This
network is described in the ambient air monitoring network plan that is
developed by the Cabinet and submitted to the EPA annually, following a
public notification and comment process. For further details on
monitoring, the reader is referred to Kentucky's 2025 Ambient Air
Monitoring Network Plan. The Cabinet submitted the 2025 Network Plan on
July 1, 2025, and it received approval from the EPA on October 28,
2025.\28\
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\28\ Kentucky's 2025 Annual Ambient Air Monitoring Network Plan
(submitted to the EPA on July 1, 2025) and the EPA's Approval Letter
(transmitted by October 28, 2025) are both available in the docket
for this proposed action.
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As noted previously, the Cabinet's monitoring network in the
Northern
[[Page 55304]]
Kentucky Area has been approved by the EPA in accordance with 40 CFR
part 58, and the Cabinet has committed to continue to maintain a
network in accordance with the EPA requirements. The EPA proposes to
find that the Cabinet's monitoring network is adequate to verify
continued attainment of the 1997 ozone NAAQS in the tri-state
Cincinnati-Hamilton Area.
D. Contingency Plan
CAA section 175A(d) requires that a maintenance plan include
contingency provisions. The purpose of such contingency provisions is
to prevent future violations of the NAAQS or to promptly remedy any
NAAQS violations that might occur during the maintenance period.
The Northern Kentucky Area LMP contingency plan includes tracking
and triggering mechanisms to determine when control measures are
needed, and a process for developing and adopting appropriate control
measures. Specifically, any 8-hour ozone monitoring reading of 0.085
ppm or greater in the tri-state Cincinnati-Hamilton Area or periodic
emissions inventory updates \29\ that reveal excessive or unanticipated
growth greater than 10 percent in either NO<INF>X</INF> or VOC
emissions over the attainment inventory for the tri-state Cincinnati-
Hamilton Area will cause the Division to evaluate existing control
measures to see if any further emission reduction measures should be
implemented at that time. Implementation of necessary controls in
response to an initial ``indicator'' will take place as expeditiously
as possible, but no later than twelve months from the conclusion of the
most recent ozone season (October 31) in which the annual fourth-
highest monitored value of 0.085 ppm or greater occurred.
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\29\ The Air Emissions Reporting Rule requires State and local
agencies to collect and submit criteria pollutant emissions data to
the EPA's Emissions Inventory System according to the schedule in 40
CFR 51.30.
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If a three-year average of annual fourth-highest monitored values
of 0.085 ppm or greater (i.e., a violation of the standard) occurs
within the tri-state Cincinnati-Hamilton Area, an ``action level''
response will take effect. The Division, in conjunction with the
metropolitan planning organization or regional council of governments,
will determine additional control measures needed to ensure future
attainment of the NAAQS for ozone. Appropriate contingency measures
will be selected to be in place within twenty-four months of a
monitored violation.
The contingency measures chosen will be selected based on their
ability to bring the tri-state Cincinnati-Hamilton Area back into
attainment. The LMP contains the following list of potential
contingency measures:
<bullet> Implementation of a program to require additional emission
reductions on stationary sources, including Reasonably Available
Control Technology (RACT) for point sources of VOC and NO<INF>X</INF>,
and, specifically, the adoption of new and revised RACT rules based on
Groups II, III, and IV Control Technique Guidelines;
<bullet> Implementation of a program to enhance inspection of
stationary sources;
<bullet> Implementation of fuel programs, including incentives for
alternative fuels;
<bullet> Restriction of certain roads or lanes to, or construction
of such roads or lanes for use by, passenger buses or high-occupancy
vehicles;
<bullet> Trip-reduction ordinances;
<bullet> Employer-based transportation management plans, including
incentives;
<bullet> Programs for new construction and major reconstructions of
paths or tracks for use by pedestrians or by non-motorized vehicles
when economically feasible and in the public interest;
<bullet> Implementation of a modern vehicle inspection/maintenance
program;
<bullet> Implementation of diesel retrofit programs, including
incentives for performing retrofits for fleet vehicle operations;
<bullet> Additional engine idling reduction programs.
The Northern Kentucky LMP includes updates to the list of potential
contingency measures in the first 10-year maintenance plan. New
potential contingency measures include the implementation of a program
to enhance inspection of stationary sources, a modern vehicle
inspection/maintenance program, diesel retrofit programs with
incentives for retrofitting fleet vehicles, and additional engine
idling reduction programs. The second 10-year LMP no longer lists the
programs from the first 10-year maintenance plan aimed at limiting or
restricting vehicle use in downtown areas or other high-emission zones
during peak periods as potential contingency measures.
The EPA proposes to find that the contingency provisions in
Kentucky's second maintenance plan for Northern Kentucky for the 1997
8-hour Ozone NAAQS meet the requirements of the CAA section 175A(d).
V. Transportation Conformity
Transportation conformity is required by CAA section 176(c).
Conformity to a SIP means that transportation activities will not
produce new air quality violations, worsen existing violations or delay
timely attainment of the NAAQS.\30\ The EPA's transportation conformity
rule at 40 CFR part 93, subpart A, requires that transportation plans,
programs, and projects conform to SIPs, and establishes the criteria
and procedures for determining whether they conform.
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\30\ See CAA 176(c)(1)(A) and (B).
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Due to the decision in South Coast Air Quality Management v. EPA,
the parts of the 1997 maintenance area that are also in maintenance for
the 2008 and 2015 8-hour ozone NAAQS are not required to demonstrate
conformity with the 1997 standard as they are currently demonstrating
conformity with the more stringent 2008 and 2015 NAAQS with their
respective approved motor vehicle emissions budgets.
The parts of the 1997 maintenance area that are not included in the
maintenance area for the subsequent 2008 and 2015 NAAQS are considered
a partial orphan area.\31\ Transportation conformity continues to apply
for the 1997 NAAQS in the partial maintenance area. Within the partial
orphan area, transportation conformity for transportation plans and
transportation improvement programs for the 1997 ozone NAAQS can be
demonstrated without a regional emissions analysis pursuant to 40 CFR
93.109(c) because the South Coast II court decision upheld EPA's
revocation of the 1997 ozone NAAQS.
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\31\ The 1997 partial orphan area is made up of the southern
portions of Boone, Campbell, and Kenton counties that were excluded
from the nonattainment designations for the 2008 and 2015 NAAQS. See
77 FR 30088 (May 21, 2012) and 83 FR 25776 (June 4, 2018),
respectively.
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The Northern Kentucky 2008 8-hour ozone and 2015 8-hour ozone NAAQS
Areas need to continue to meet all applicable requirements of the
transportation conformity regulations, including the need for a
regional emissions analysis and comparison of the results of the
regional emissions analysis to the applicable budget for the respective
8-hour ozone NAAQS. A budget was approved for the 2008 8-hour ozone
NAAQS,\32\ effective July 5, 2017.\33\ A budget was approved for the
2015 8-hour ozone NAAQS, effective November 3, 2023.\34\
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\32\ See 82 FR 30976 (July 5, 2017).
\33\ On July 3, 2025, the Cabinet submitted a second 10-year
maintenance plan for the 2008 8-hour ozone maintenance area. This
will be addressed in a separate future action.
\34\ See 88 FR 68471 (Oct. 4, 2023).
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[[Page 55305]]
VI. Proposed Action
Under CAA sections 110(k) and 175A and for the reasons set forth
above, the EPA is proposing to approve the Northern Kentucky LMP for
the 1997 8-hour ozone NAAQS, submitted by the Cabinet on July 23, 2024,
as a revision to the Kentucky SIP. The EPA is proposing to approve the
Northern Kentucky LMP because it includes an acceptable update of the
various elements of the 1997 8-hour ozone NAAQS maintenance plan
approved by the EPA for the first 10-year period (including emissions
inventory, assurance of adequate monitoring and verification of
continued attainment, and contingency provisions).
The EPA also finds that the Northern Kentucky Area qualifies for
the LMP option and that, therefore, the Northern Kentucky Area LMP
adequately demonstrates maintenance of the 1997 8-hour ozone NAAQS
through documentation of monitoring data showing design values well
below the NAAQS and continuation of existing control measures. The EPA
believes that the Northern Kentucky Area LMP is sufficient to provide
for maintenance of the 1997 8-hour ozone NAAQS in the tri-state
Cincinnati-Hamilton Area over the remainder of the second 10-year
maintenance period, through 2030, and thereby satisfies the
requirements for such a plan under CAA section 175A(b).
VII. Statutory and Executive Order Reviews
Under the CAA, the Administrator is required to approve a SIP
submission that complies with the provisions of the CAA and applicable
Federal regulations.\35\ 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 rulemaking:
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\35\ See 42 U.S.C. 7410(k); 40 CFR 52.02(a).
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<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 an Executive Order 14192 (90 FR 9065, February 6,
2025) regulatory action because this action is not significant 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 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).
List of Subjects in 40 CFR Part 52
Environmental protection, Air pollution control, Incorporation by
reference, Intergovernmental relations, Ozone, Reporting and
recordkeeping requirements, Volatile organic compounds.
Authority: 42 U.S.C. 7401 et seq.
Dated: August 20, 2026.
Kristy Eubanks,
Deputy Regional Administrator performing the functions and duties of
the Regional Administrator, Region 4.
[FR Doc. 2026-17502 Filed 8-26-26; 8:45 am]
BILLING CODE 6560-50-P
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</html>Indexed from Federal Register on August 27, 2026.
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.