Proposed Rule2025-17499
Air Plan Approval; Montana; Regional Haze Plan for the Second Implementation Period; Prong 4 (Visibility) for the 2015 8-Hour Ozone National Ambient Air Quality Standard
Primary source
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Published
September 11, 2025
Issuing agencies
Environmental Protection Agency
Abstract
The Environmental Protection Agency (EPA) is proposing to approve the regional haze state implementation plan (SIP) submission submitted by the State of Montana on August 10, 2022, under the Clean Air Act (CAA) and the EPA's Regional Haze Rule (RHR) for the program's second implementation period. Montana's 2022 SIP submission addresses the requirement that states revise their long-term strategies every implementation period to make reasonable progress towards the national goal of preventing any future, and remedying any existing, anthropogenic impairment of visibility, including regional haze, in mandatory Class I Federal areas. Montana's 2022 SIP submission also addresses other applicable requirements for the second implementation period of the regional haze program. The EPA is also proposing to approve the prong 4 visibility portion of Montana's October 1, 2018 Infrastructure SIP submission for the 2015 ozone National Ambient Air Quality Standards (NAAQS). The EPA is taking these actions pursuant to the CAA.
Full Text
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<title>Federal Register, Volume 90 Issue 174 (Thursday, September 11, 2025)</title>
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[Federal Register Volume 90, Number 174 (Thursday, September 11, 2025)]
[Proposed Rules]
[Pages 43958-43971]
From the Federal Register Online via the Government Publishing Office [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[FR Doc No: 2025-17499]
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ENVIRONMENTAL PROTECTION AGENCY
40 CFR Part 52
[EPA-R08-OAR-2024-0608; FRL-12597-01-R8]
Air Plan Approval; Montana; Regional Haze Plan for the Second
Implementation Period; Prong 4 (Visibility) for the 2015 8-Hour Ozone
National Ambient Air Quality Standard
AGENCY: Environmental Protection Agency (EPA).
ACTION: Proposed rule.
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SUMMARY: The Environmental Protection Agency (EPA) is proposing to
approve the regional haze state implementation plan (SIP) submission
submitted by the State of Montana on August 10, 2022, under the Clean
Air Act (CAA) and the EPA's Regional Haze Rule (RHR) for the program's
second implementation period. Montana's 2022 SIP submission addresses
the requirement that states revise their long-term strategies every
implementation period to make reasonable progress towards the national
goal of preventing any future, and remedying any existing,
anthropogenic impairment of visibility, including regional haze, in
mandatory Class I Federal areas. Montana's 2022 SIP submission also
addresses other applicable requirements for the second implementation
period of the regional haze program. The EPA is also proposing to
approve the prong 4 visibility portion of Montana's October 1, 2018
Infrastructure SIP submission for the 2015 ozone National Ambient Air
Quality Standards (NAAQS). The EPA is taking these actions pursuant to
the CAA.
DATES: Written comments must be received on or before October 14, 2025.
ADDRESSES: Submit your comments, identified by Docket ID No. EPA-R08-
OAR-2024-0608, to the Federal Rulemaking Portal: <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="https://www.regulations.gov">https://www.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>.
Docket: All documents in the docket are listed in the <a href="https://www.regulations.gov">https://www.regulations.gov</a> index. Although listed in the index, some
information is not publicly available, e.g., CBI or other information
whose disclosure is restricted by statute. Certain other material, such
as copyrighted material, will be publicly available only in hard copy.
Publicly available docket materials are available electronically in
<a href="https://www.regulations.gov">https://www.regulations.gov</a>. Please email or call the person listed in
the FOR FURTHER INFORMATION CONTACT section if you need to make
alternative arrangements for access to the docket.
FOR FURTHER INFORMATION CONTACT: Jaslyn Dobrahner, Air and Radiation
Division, EPA, Region 8, Mailcode 8ARD-IO, 1595 Wynkoop Street, Denver,
Colorado 80202-1129, telephone number: (303) 312-6252; email address:
<a href="/cdn-cgi/l/email-protection#30545f524251585e55421e5a51435c495e705540511e575f46"><span class="__cf_email__" data-cfemail="d5b1bab7a7b4bdbbb0a7fbbfb4a6b9acbb95b0a5b4fbb2baa3">[email protected]</span></a>.
SUPPLEMENTARY INFORMATION: Throughout this document wherever ``we,''
``us,'' or ``our'' is used, we mean the EPA.
Table of Contents
I. What action is the EPA proposing?
II. Background and Requirements for Regional Haze Plans
A. Regional Haze
B. Roles of Agencies in Addressing Regional Haze
C. Status of Montana's Regional Haze Plan for the First
Implementation Period
D. Montana's Regional Haze Plan for the Second Implementation
Period
III. Requirements for Regional Haze Plans for the Second
Implementation Period
IV. The EPA's Evaluation of Montana's Regional Haze Plan for the
Second Implementation Period
A. Identification of Class I Areas
B. Calculation of Baseline, Current, and Natural Visibility
Conditions; Progress to Date; and Uniform Rate of Progress for Class
I Areas Within the State
C. Long-Term Strategy
1. Montana's Long-Term Strategy Four-Factor Analysis
a. Summary of Montana's Long-Term Strategy Four-Factor Analysis
b. The EPA's Evaluation of Montana's Long-Term Strategy Four-
Factor Analysis
2. Other Long-Term Strategy Requirements
D. Reasonable Progress Goals
E. Reasonably Attributable Visibility Impairment (RAVI)
F. Monitoring Strategy and Other State Implementation Plan
Requirements
G. Requirements for Periodic Reports Describing Progress Towards
the Reasonable Progress Goals
H. Requirements for State and Federal Land Manager Coordination
V. Interstate Transport Prong 4 (Visibility) for the 2015 Ozone
NAAQS Infrastructure SIP
A. Background on Infrastructure SIPs
B. Prong 4 Requirements
C. Montana's Infrastructure SIP Submission
D. The EPA's Evaluation of Montana's Infrastructure SIP
Submission
VI. Proposed Action
VII. Statutory and Executive Order Reviews
I. What action is the EPA proposing?
The EPA is proposing to approve a SIP submission submitted by the
State of Montana to the EPA on August 10, 2022, addressing the
requirements of the second implementation period of the RHR.
Specifically, the EPA is proposing approval for the portions of
Montana's 2022 SIP submission relating to 40 CFR 51.308(f)(1):
calculations of baseline, current, and natural visibility conditions,
progress to date, and the uniform rate of progress; 40 CFR
51.308(f)(2): long-term strategy; 40 CFR 51.308(f)(3): reasonable
progress goals; 40 CFR 51.308(f)(4): reasonably attributable visibility
impairment; 40 CFR 51.308(f)(5) and 40 CFR 51.308(g): progress report
requirements; 40 CFR 51.308(f)(6): monitoring strategy and other
implementation plan requirements; and 40 CFR 51.308(i): Federal Land
Manager (FLM) consultation. The EPA is also proposing to approve the
CAA section 110(a)(2)(D)(i) prong 4 (visibility) portion of Montana's
October 1, 2018 Infrastructure SIP submission addressing the 2015 ozone
NAAQS.
II. Background and Requirements for Regional Haze Plans
A detailed history and background of the regional haze program is
provided in multiple prior EPA proposal actions.\1\ For additional
background on the 2017 RHR revisions, please refer to section III.
Overview of Visibility Protection
[[Page 43959]]
Statutory Authority, Regulation, and Implementation of ``Protection of
Visibility: Amendments to Requirements for State Plans'' of the 2017
RHR.\2\ The following is an abbreviated history and background of the
regional haze program and 2017 Regional Haze Rule as it applies to the
current action.
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\1\ See 90 FR 13516 (March 24, 2025).
\2\ See 82 FR 3078 (January 10, 2017, located at <a href="https://www.federalregister.gov/documents/2017/01/10/2017-00268/protection-of-visibility-amendments-to-requirements-for-State-plans#h-16">https://www.federalregister.gov/documents/2017/01/10/2017-00268/protection-of-visibility-amendments-to-requirements-for-State-plans#h-16</a>).
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A. Regional Haze
In the 1977 CAA amendments, Congress created a program for
protecting visibility in the nation's mandatory Class I Federal areas,
which include certain national parks and wilderness areas.\3\ CAA
section 169A. The CAA establishes as a national goal the ``prevention
of any future, and the remedying of any existing, impairment of
visibility in mandatory Class I Federal areas which impairment results
from manmade air pollution.'' CAA section 169A(a)(1).
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\3\ Areas statutorily designated as mandatory Class I Federal
areas consist of national parks exceeding 6,000 acres, wilderness
areas and national memorial parks exceeding 5,000 acres, and all
international parks that were in existence on August 7, 1977. CAA
section 162(a). There are 156 mandatory Class I areas. The list of
areas to which the requirements of the visibility protection program
apply is in 40 CFR part 81, subpart D.
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Regional haze is visibility impairment that is produced by a
multitude of anthropogenic sources and activities that are located
across a broad geographic area and that emit pollutants that impair
visibility. Visibility impairing pollutants include fine and coarse
particulate matter (PM) (e.g., sulfates, nitrates, organic carbon,
elemental carbon, and soil dust) and their precursors (e.g., sulfur
dioxide (SO<INF>2</INF>), nitrogen oxides (NO<INF>X</INF>), and, in
some cases, volatile organic compounds (VOC) and ammonia
(NH<INF>3</INF>)). Fine particle precursors react in the atmosphere to
form fine particulate matter (PM<INF>2.5</INF>), which impairs
visibility by scattering and absorbing light. Visibility impairment
reduces the perception of clarity and color, as well as visible
distance.\4\
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\4\ There are several ways to measure the amount of visibility
impairment, i.e., haze. One such measurement is the deciview, which
is the principal metric used by the RHR. Under many circumstances, a
change in one deciview will be perceived by the human eye to be the
same on both clear and hazy days. The deciview is unitless. It is
proportional to the logarithm of the atmospheric extinction of
light, which is the perceived dimming of light due to its being
scattered and absorbed as it passes through the atmosphere.
Atmospheric light extinction (b\ext\) is a metric used for
expressing visibility and is measured in inverse megameters
(Mm<SUP>-1</SUP>). The formula for the deciview is 10 ln (b\ext\)/10
Mm<SUP>-1</SUP>). 40 CFR 51.301.
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To address regional haze visibility impairment, the 1999 RHR
established an iterative planning process that requires states
containing Class I areas and states containing sources whose emissions
``may reasonably be anticipated to cause or contribute to any
impairment of visibility'' in a Class I area in another state to
periodically submit SIP revisions to address such impairment. CAA
section 169A(b)(2); see also 40 CFR 51.308(b), (f) (establishing
submission dates for iterative regional haze SIP revisions); (64 FR at
35768, July 1, 1999).
On January 10, 2017, the EPA promulgated revisions to the RHR (82
FR 3078, January 10, 2017) that apply for the second and subsequent
implementation periods. The reasonable progress requirements as revised
by the 2017 rule (referred to here as the 2017 RHR Revisions) are
codified at 40 CFR 51.308(f).
B. Roles of Agencies in Addressing Regional Haze
Because the air pollutants and pollution affecting visibility in
Class I areas can be transported over long distances, successful
implementation of the regional haze program requires long-term,
regional coordination among multiple jurisdictions and agencies that
have responsibility for Class I areas and the emissions that impact
visibility in those areas. To address regional haze, states need to
develop strategies in coordination with one another, considering the
effect of emissions from one jurisdiction on the air quality in
another. Five regional planning organizations (RPOs), which include
representation from state and Tribal governments, the EPA, and FLMs,
were developed in the lead-up to the first implementation period to
address regional haze. RPOs evaluate technical information to better
understand how emissions from state and Tribal land impact Class I
areas across the country, pursue the development of regional strategies
to reduce emissions of particulate matter and other pollutants leading
to regional haze, and help states meet the consultation requirements of
the RHR.
The Western Regional Air Partnership (WRAP), one of the five
regional planning organizations described in the previous paragraph, is
a collaborative effort of state governments, local air agencies, Tribal
governments, and various federal agencies established to initiate and
coordinate activities associated with the management of regional haze,
visibility, and other air quality issues in the Western United States.
Members include the states of Alaska, Arizona, California, Colorado,
Hawaii, Idaho, Montana, Nevada, New Mexico, North Dakota, Oregon, South
Dakota, Utah, Washington, Wyoming, and 28 Tribal governments.\5\ The
federal partner members of WRAP are the EPA, U.S. National Parks
Service, U.S. Fish and Wildlife Service, U.S. Forest Service, and the
Bureau of Land Management.
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\5\ A full list of WRAP members is available at <a href="https://www.westar.org/wrap-council-members/">https://www.westar.org/wrap-council-members/</a>.
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WRAP formed a workgroup to develop a planning framework for state
regional haze second planning period SIPs. Based on emissions and
monitoring data supplied by its membership, WRAP produced a technical
system to support regional modeling of visibility impacts at Class I
areas across the West. The WRAP Technical Support System consolidated
air quality monitoring data, meteorological and receptor modeling data
analyses, emissions inventories and projections, and gridded air
quality/visibility regional modeling results. The Technical Support
System is accessible by member states and allows for the creation of
maps, figures, and tables to export and use in state plan development.
It also maintains the original source data for verification and further
analysis. Montana collaborated with WRAP on various aspects of the
State's 2022 SIP submission, including the identification of Class I
areas outside of Montana that may be affected by sources in the state,
source selection, analysis of air quality monitoring data, preparation
of emission inventories, development of reasonable progress goals, and
air quality modeling, which together informed the development of its
long-term strategy.
C. Status of Montana's Regional Haze Plan for the First Implementation
Period
The CAA requires that regional haze plans for the first
implementation period (2008 through 2018) include, among other things,
a long-term strategy for making reasonable progress and BART
requirements for certain older stationary sources, where applicable.\6\
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\6\ Requirements for regional haze SIPs for the first
implementation period are also contained in CAA section 169A(b)(2).
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On September 18, 2012, the EPA promulgated a federal implementation
plan (FIP) that included NO<INF>X</INF>, SO<INF>2</INF>, and PM BART
emission limits for three electricity generating units (EGUs) at two
power plants and two cement kilns, as well as an emission limit for a
natural gas compressor station to satisfy the reasonable progress
requirements.\7\ The
[[Page 43960]]
EPA promulgated a FIP in this instance because Montana did not submit a
regional haze SIP as required under section 110 of the CAA.\8\
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\7\ 77 FR 57864 (September 18, 2012).
\8\ Letter from Richard H. Opper, Director Montana Department of
Environmental Quality to Laurel Dygowski, EPA Region 8 Air Program,
June 19, 2006. Based off this letter, EPA made a determination
finding of failure to submit a SIP by Montana. This triggered a
mandatory duty clock to have EPA either promulgate a FIP or approve
a SIP within two years of the EPA finding. See 74 FR 2392 (January
15, 2009).
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Several parties challenged the portion of the FIP addressing the
EPA's NO<INF>X</INF> and SO<INF>2</INF> BART determinations at the
power plants, Colstrip Units 1 and 2 and Corette.\9\ On June 9, 2015,
the U.S. Court of Appeals for the Ninth Circuit vacated and remanded
the portions of the FIP related to the NO<INF>X</INF> and
SO<INF>2</INF> BART emission limits for J.E. Corette and Colstrip Units
1 and 2 and remanded the EPA's response to a public comment in the 2012
final rule regarding the use of visibility modeling in determining BART
for Colstrip Units 1 and 2.\10\ The BART emission limits for the Ash
Grove and Trident cement kilns, the PM emission limits for the EGUs,
and the reasonable progress requirements for the Blaine Compressor
Station were not at issue in the petitions filed with the Ninth Circuit
Court of Appeals.\11\
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\9\ Several parties petitioned the Ninth Circuit Court of
Appeals to review EPA's NO<INF>X</INF> and SO<INF>2</INF> BART
determinations at the power plants, Colstrip and Corette (PPL
Montana, LLC, the National Parks Conservation Association, Montana
Environmental Information Center, and the Sierra Club). National
Parks Conservation Association v. EPA, 788 F.3d 1134 (9th Cir.
2015).
\10\ Id.
\11\ Id.
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On September 12, 2017, the EPA amended aspects of the remaining
2012 FIP by (1) revising the BART NO<INF>X</INF> emission limit for the
Trident cement kiln, and (2) correcting errors in our original FIP
regarding the reasonable progress determination for the Blaine
Compressor Station and the instructions for compliance determinations
for PM BART emission limits at the EGUs and cement kilns.\12\
Ultimately, the EPA removed the reasonable progress requirements for
the natural gas compressor station from the FIP after correcting the
error that resulted in the source no longer being subject to reasonable
progress requirements.
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\12\ 82 FR 42738 (September 12, 2017).
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On June 26, 2023, the EPA approved a SIP revision that addressed
NO<INF>X</INF> and SO<INF>2</INF> BART requirements for the J.E.
Corette and Colstrip (Units 1 and 2) power plants and replaced portions
of the original FIP promulgated by the EPA in 2012.<SUP>13 14</SUP>
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\13\ 88 FR 41320 (June 26, 2023).
\14\ The June 26, 2023, action also addressed the U.S. Court of
Appeals for the Ninth Circuit's June 9, 2015 remand of portions of
the 2012 regional haze FIP, including the EPA's response to a public
comment regarding the use of the CALPUFF visibility model in
determining BART at Colstrip Units 1 and 2.
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D. Montana's Regional Haze Plan for the Second Implementation Period
On August 10, 2022, Montana submitted a SIP submission to address
its regional haze obligations for the second implementation period
(2018-2028). Montana's 2022 SIP submission contains the State's long-
term strategy to address regional haze visibility impairment for each
Class I area within the State and each Class I area outside the State
that may be affected by emissions from the State. In developing its
long-term strategy, the State examined the need to implement additional
enforceable emission limitations, compliance schedules, and other
measures that are necessary to make reasonable progress since the first
implementation period. Specifically, Montana's 2022 SIP submission
contains an assessment of visibility progress made at Class I areas
since the first implementation period and a long-term strategy to
address regional haze visibility impairment at Class I areas the State
identified, including: Montana's selection of sources that may affect
visibility in Class I areas within the State and outside the State for
four-factor analysis; its evaluation of the selected sources to
determine what emission reduction measures constitute reasonable
progress for the long-term strategy; regional scale modeling of the
State's long-term strategy to set reasonable progress goals for 2028;
and ultimately, Montana's determinations on what control measures are
necessary for the long-term strategy to address regional haze
visibility impairment in the Class I areas. The State concluded that no
additional emission reduction measures for Montana facilities are
required for the second implementation period under its long-term
strategy.
III. Requirements for Regional Haze Plans for the Second Implementation
Period
Under the CAA and the EPA's regulations, all 50 states, the
District of Columbia, and the U.S. Virgin Islands were required to
submit regional haze SIPs satisfying the applicable requirements for
the second implementation period of the regional haze program by July
31, 2021. Each SIP must contain a long-term strategy for making
reasonable progress toward meeting the national goal of remedying any
existing and preventing any future anthropogenic visibility impairment
in Class I areas. CAA section 169A(b)(2)(B). To this end, 40 CFR
51.308(f) lays out the process by which states determine what
constitutes their long-term strategies, with the order of the
requirements in 40 CFR 51.308(f)(1) through (3) generally mirroring the
order of the steps in the reasonable progress analysis \15\ and (f)(4)
through (6) containing additional, related requirements.
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\15\ The EPA explained in the 2017 RHR revisions that we were
adopting new regulatory language in 40 CFR 51.308(f) that, unlike
the structure in 51.308(d), ``tracked the actual planning
sequence.'' (82 FR at 3091).
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Broadly speaking, a state first must identify the Class I areas
within the state and determine the Class I areas outside the state in
which visibility may be affected by emissions from the state. These are
the Class I areas that must be addressed in the state's long-term
strategy. See 40 CFR 51.308(f), (f)(2). For each Class I area within
its borders, a state must then calculate the baseline (five-year
average period of 2000-2004), current, and natural visibility
conditions (i.e., visibility conditions without anthropogenic
visibility impairment) for that area, as well as the visibility
improvement made to date and the ``uniform rate of progress'' (URP).
The URP is the linear rate of progress needed to attain natural
visibility conditions, assuming a starting point of baseline visibility
conditions in 2004 and ending with natural conditions in 2064. This
linear interpolation is used as a tracking metric to help states assess
the amount of progress they are making towards the national visibility
goal over time in each Class I area. See 40 CFR 51.308(f)(1).
Each state having a Class I area and/or emissions that may affect
visibility in a Class I area must then develop a long-term strategy
that includes the enforceable emission limitations, compliance
schedules, and other measures that are necessary to make reasonable
progress in such areas. A reasonable progress determination is based on
applying the four factors in CAA section 169A(g)(1) to sources of
visibility impairing pollutants that the state has selected to assess
for controls for the second implementation period. Additionally, as
further explained below, the RHR at 40 CFR 51.3108(f)(2)(iv) separately
provides five ``additional factors'' \16\ that states must consider in
developing their long-term strategies. See 40 CFR 51.308(f)(2). A
[[Page 43961]]
state evaluates potential emission reduction measures for those
selected sources and determines which are necessary to make reasonable
progress. Those measures are then incorporated into the state's long-
term strategy.
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\16\ The five ``additional factors'' for consideration in 40 CFR
51.308(f)(2)(iv) are distinct from the four factors listed in CAA
section 169A(g)(1) and 40 CFR 51.308(f)(2)(i) that states must
consider and apply to sources in determining reasonable progress.
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After a state has developed its long-term strategy, it then
establishes reasonable progress goals (RPGs) for each Class I area
within its borders by modeling the visibility impacts of all reasonable
progress controls at the end of the second implementation period, i.e.,
in 2028, as well as the impacts of other requirements of the CAA. The
RPGs include reasonable progress controls not only for sources in the
state in which the Class I area is located, but also for sources in
other states that contribute to visibility impairment in that area. The
RPGs are then compared to the baseline visibility conditions and the
URP to ensure that progress is being made towards the statutory goal of
preventing any future and remedying any existing anthropogenic
visibility impairment in Class I areas. 40 CFR 51.308(f)(2)-(3). There
are additional requirements in the rule, including FLM consultation,
that apply to all visibility protection SIPs and SIP revisions. See
e.g., 40 CFR 51.308(i).
While states have discretion to choose any source selection
methodology that is reasonable, whatever choices they make should be
reasonably explained. To this end, 40 CFR 51.308(f)(2)(i) requires that
a state's SIP submission include ``a description of the criteria it
used to determine which sources or groups of sources it evaluated.''
The technical basis for source selection, which may include methods for
quantifying potential visibility impacts such as emissions divided by
distance metrics, trajectory analyses, residence time analyses, and/or
photochemical modeling, must also be appropriately documented, as
required by 40 CFR 51.308(f)(2)(iii).
Once a state has selected the set of sources, the next step is to
determine the emissions reduction measures for those sources that are
necessary to make reasonable progress for the second implementation
period.\17\ This is accomplished by considering the four factors--``the
costs of compliance, the time necessary for compliance, the energy and
non-air quality environmental impacts of compliance, and the remaining
useful life of any existing source subject to such requirements.'' CAA
section 169A(g)(1). The EPA has explained that the four-factor analysis
is an assessment of potential emission reduction measures (i.e.,
control options) for sources; ``use of the terms `compliance' and
`subject to such requirements' in section 169A(g)(1) strongly indicates
that Congress intended the relevant determination to be the
requirements with which sources would have to comply to satisfy the
CAA's reasonable progress mandate.'' 82 FR at 3091. Thus, for each
source it has selected for four-factor analysis,\18\ a state must
consider a ``meaningful set'' of technically feasible control options
for reducing emissions of visibility impairing pollutants. Id. at 3088.
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\17\ The CAA provides that, ``[i]n determining reasonable
progress there shall be taken into consideration'' the four
statutory factors. CAA section 169A(g)(1). However, in addition to
four-factor analyses for selected sources, groups of sources, or
source categories, a state may also consider additional emission
reduction measures for inclusion in its long-term strategy, e.g.,
from other newly adopted, on-the-books, or on-the-way rules and
measures for sources not selected for four-factor analysis for the
second implementation period.
\18\ ``Each source'' or ``particular source'' is used here as
shorthand. While a source-specific analysis is one way of applying
the four factors, neither the statute nor the RHR requires states to
evaluate individual sources. Rather, states have ``the flexibility
to conduct four-factor analyses for specific sources, groups of
sources or even entire source categories, depending on state policy
preferences and the specific circumstances of each state.'' 82 FR at
3088.
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The EPA has also explained that, in addition to the four statutory
factors, states have flexibility under the CAA and RHR to reasonably
consider visibility benefits as an additional factor alongside the four
statutory factors.\19\ Ultimately, while states have discretion to
reasonably weigh the factors and to determine what level of control is
needed, 40 CFR 51.308(f)(2)(i) provides that a state ``must include in
its implementation plan a description of . . . how the four factors
were taken into consideration in selecting the measures for inclusion
in its long-term strategy.''
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\19\ See, e.g., Responses to Comments on Protection of
Visibility: Amendments to Requirements for State Plans; Proposed
Rule (81 FR 26942, May 4, 2016), Docket ID No. EPA-HQ-OAR-2015-0531,
U.S. Environmental Protection Agency at 186.
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As explained above, 40 CFR 51.308(f)(2)(i) requires states to
determine the emission reduction measures for sources that are
necessary to make reasonable progress by considering the four factors.
Pursuant to 40 CFR 51.308(f)(2), measures that are necessary to make
reasonable progress towards the national visibility goal must be
included in a state's long-term strategy and in its SIP. If the outcome
of a four-factor analysis is that an emissions reduction measure is
necessary to make reasonable progress towards remedying existing or
preventing future anthropogenic visibility impairment, that measure
must be included in the SIP.
The characterization of information on each of the factors is also
subject to the documentation requirement in 40 CFR 51.308(f)(2)(iii).
The reasonable progress analysis is a technically complex exercise, and
also a flexible one that provides states with bounded discretion to
design and implement approaches appropriate to their circumstances.
Given this flexibility, 40 CFR 51.308(f)(2)(iii) plays an important
function in requiring a state to document the technical basis for its
decision making so that the public and the EPA can comprehend and
evaluate the information and analysis the state relied upon to
determine what emission reduction measures must be in place to make
reasonable progress. The technical documentation must include the
modeling, monitoring, cost, engineering, and emissions information on
which the state relied to determine the measures necessary to make
reasonable progress.
Additionally, the RHR at 40 CFR 51.3108(f)(2)(iv) separately
provides five ``additional factors'' that states must consider in
developing their long-term strategies: (1) Emission reductions due to
ongoing air pollution control programs, including measures to address
reasonably attributable visibility impairment; (2) measures to reduce
the impacts of construction activities; (3) source retirement and
replacement schedules; (4) basic smoke management practices for
prescribed fire used for agricultural and wildland vegetation
management purposes and smoke management programs; and (5) the
anticipated net effect on visibility due to projected changes in point,
area, and mobile source emissions over the period addressed by the
long-term strategy.
Because the air pollution that causes regional haze crosses state
boundaries, 40 CFR 51.308(f)(2)(ii) requires a state to consult with
other states that also have emissions that are reasonably anticipated
to contribute to visibility impairment in a given Class I area. If a
state, pursuant to consultation, agrees that certain measures (e.g., a
certain emission limitation) are necessary to make reasonable progress
at a Class I area, it must include those measures in its SIP. 40 CFR
51.308(f)(2)(ii)(A). Additionally, the RHR requires that states that
contribute to visibility impairment at the same Class I area consider
the emission reduction measures the other contributing states have
identified as being necessary to make reasonable progress for their own
sources. 40 CFR 51.308(f)(2)(ii)(B). If a state has been asked to
consider or adopt certain emission reduction
[[Page 43962]]
measures, but ultimately determines those measures are not necessary to
make reasonable progress, that state must document in its SIP the
actions taken to resolve the disagreement. 40 CFR 51.308(f)(2)(ii)(C).
Under all circumstances, a state must document in its SIP submission
all substantive consultations with other contributing states. 40 CFR
51.308(f)(2)(ii)(C).
Reasonable progress goals ``measure the progress that is projected
to be achieved by the control measures states have determined are
necessary to make reasonable progress based on a four-factor
analysis.'' 82 FR at 3091. For the second implementation period, the
RPGs are set for 2028. Reasonable progress goals are not enforceable
targets. 40 CFR 51.308(f)(3)(iii). While states are not legally
obligated to achieve the visibility conditions described in their RPGs,
40 CFR 51.308(f)(3)(i) requires that ``[t]he long-term strategy and the
reasonable progress goals must provide for an improvement in visibility
for the most impaired days since the baseline period and ensure no
degradation in visibility for the clearest days since the baseline
period.''
RPGs may also serve as a metric for assessing the amount of
progress a state is making towards the national visibility goal. To
support this approach, the RHR requires states with Class I areas to
compare the 2028 RPG for the most impaired days to the corresponding
point on the URP line (representing visibility conditions in 2028 if
visibility were to improve at a linear rate from conditions in the
baseline period of 2000-2004 to natural visibility conditions in 2064).
If the most impaired days RPG in 2028 is above the URP (i.e., if
visibility conditions are improving more slowly than the rate described
by the URP), each state that contributes to visibility impairment in
the Class I area must demonstrate, based on the four-factor analysis
required under 40 CFR 51.308(f)(2)(i), that no additional emission
reduction measures would be reasonable to include in its long-term
strategy. 40 CFR 51.308(f)(3)(ii). To this end, 40 CFR 51.308(f)(3)(ii)
requires that each state contributing to visibility impairment in a
Class I area that is projected to improve more slowly than the URP
provide ``a robust demonstration, including documenting the criteria
used to determine which sources or groups [of] sources were evaluated
and how the four factors required by paragraph (f)(2)(i) were taken
into consideration in selecting the measures for inclusion in its long-
term strategy.''
Section 51.308(f)(6) requires states to have certain strategies and
elements in place for assessing and reporting on visibility. Individual
requirements under this section apply either to states with Class I
areas within their borders, states with no Class I areas but that are
reasonably anticipated to cause or contribute to visibility impairment
in any Class I area, or both. Compliance with the monitoring strategy
requirement may be met through a state's participation in the
Interagency Monitoring of Protected Visual Environments (IMPROVE)
monitoring network, which is used to measure visibility impairment
caused by air pollution at the 156 Class I areas covered by the
visibility program. 40 CFR 51.308(f)(6), (f)(6)(i), (f)(6)(iv).
All states' SIPs must provide for procedures by which monitoring
data and other information are used to determine the contribution of
emissions from within the state to regional haze visibility impairment
in affected Class I areas, as well as a statewide inventory documenting
such emissions. 40 CFR 51.308(f)(6)(ii), (iii), (v). All states' SIPs
must also provide for any other elements, including reporting,
recordkeeping, and other measures, that are necessary for states to
assess and report on visibility. 40 CFR 51.308(f)(6)(vi).
Section 51.308(f)(5) requires a state's regional haze SIP revision
to address the requirements of paragraphs 40 CFR 51.308(g)(1) through
(5) so that the plan revision due in 2021 will serve also as a progress
report addressing the period since submission of the progress report
for the first implementation period. The regional haze progress report
requirement is designed to inform the public and the EPA about a
state's implementation of its existing long-term strategy and whether
such implementation is in fact resulting in the expected visibility
improvement. See 81 FR 26942, 26950 (May 4, 2016), (82 FR at 3119,
January 10, 2017). To this end, every state's SIP revision for the
second implementation period is required to assess changes in
visibility conditions and describe the status of implementation of all
measures included in the state's long-term strategy, including BART and
reasonable progress emission reduction measures from the first
implementation period, and the resulting emissions reductions. 40 CFR
51.308(g)(1) and (2).
CAA section 169A(d) requires that before a state holds a public
hearing on a proposed regional haze SIP revision, it must consult with
the appropriate FLM or FLMs; pursuant to that consultation, the state
must include a summary of the FLMs' conclusions and recommendations in
the notice to the public. Consistent with this statutory requirement,
the RHR also requires that states ``provide the [FLM] with an
opportunity for consultation, in person and at a point early enough in
the State's policy analyses of its long-term strategy emission
reduction obligation so that information and recommendations provided
by the [FLM] can meaningfully inform the State's decisions on the long-
term strategy.'' 40 CFR 51.308(i)(2). For the EPA to evaluate whether
FLM consultation meeting the requirements of the RHR has occurred, the
SIP submission should include documentation of the timing and content
of such consultation. The SIP revision submitted to the EPA must also
describe how the state addressed any comments provided by the FLMs. 40
CFR 51.308(i)(3). Finally, a SIP revision must provide procedures for
continuing consultation between the state and FLMs regarding the
state's visibility protection program, including development and review
of SIP revisions, five-year progress reports, and the implementation of
other programs having the potential to contribute to impairment of
visibility in Class I areas. 40 CFR 51.308(i)(4).
Finally, the state SIP must meet the approval requirements in CAA
section 110(a)(2) for plans ``submitted by a State under this chapter''
to the extent not already addressed in the regulations described
previously. As relevant here, the state must provide ``necessary
assurances'' that the state has adequate personnel, funding, and
authority to carry out the implementation plan, that the state ``is not
prohibited by any provision of Federal or State law from carrying out
such implementation plan or portion thereof,'' and that the state can
lawfully rely on regional and local instrumentalities to implement the
SIP, as applicable. CAA section 110(a)(2)(E)(i)-(iii).
IV. The EPA's Evaluation of Montana's Regional Haze Plan for the Second
Implementation Period
In section IV. of this document, we describe Montana's 2022 SIP
submission and evaluate it against the requirements of the CAA and RHR
for the second implementation period of the regional haze program.
A. Identification of Class I Areas
Section 169A(b)(2) of the CAA requires each state in which any
Class I area is located or ``the emissions from which may reasonably be
anticipated to cause or contribute to any impairment
[[Page 43963]]
of visibility'' in a Class I area to have a long-term strategy for
making reasonable progress toward the national visibility goal. The RHR
implements this statutory requirement in 40 CFR 51.308(f) for the
second and subsequent planning periods for regional haze. 40 CFR
51.308(f)(2) requires states to submit a long-term strategy that
addresses regional haze visibility impairment for each mandatory Class
I area within the state and for each mandatory Class I area located
outside the state that may be affected by emissions from the state.
There are 12 designated Class I areas within the State of Montana,
including two national parks managed by the U.S. National Park Service
(Glacier National Park and Yellowstone National Park) and ten
wilderness areas managed by the U.S. Forest Service (Anaconda-Pintler
Wilderness Area, Bob Marshall Wilderness Area, Cabinet Mountains
Wilderness Area, Gates of the Mountains Wilderness Area, Medicine Lake
Wilderness Area, Mission Mountain Wilderness Area, Red Rock Lakes
Wilderness Area, Scapegoat Wilderness Area, Selway-Bitterroot
Wilderness Area, UL Bend Wilderness Area).\20\ In its 2022 submission,
Montana acknowledges that emissions from in-state sources contribute to
visibility impairment at its 12 Class 1 areas.\21\ Montana demonstrated
in their 2022 SIP submission that all of their Class I areas are
projected to be below the 2028 URP for each area.\22\
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\20\ Montana 2022 SIP submission at 3.
\21\ Id. at 91-103.
\22\ Id. at 298-305.
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Montana also evaluated Class I areas outside the State where
visibility may be affected by Montana sources. Using the WRAP's
2028OTBa2 source apportionment modeling Montana identified three Class
I areas where the State contributes 0.11 deciviews or greater: Wind
Cave (0.12 deciviews, 1.2%); Theodore Roosevelt (0.11 deciviews, 0.8%);
and Lostwood (0.11 deciviews; 0.7%) based on combined percentages of
nitrate + sulfate impairment at these Class I areas from Montana
sources.\23\
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\23\ Id. at 291-293, Table 7-5.
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All Class I areas in Montana as well as the three out-of-state
Class I areas most impacted by Montana sources are projected to be
below the adjusted glidepath for 2028.\24\
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\24\ <a href="https://views.cira.colostate.edu/tssv2/Express/ModelingTools.aspx">https://views.cira.colostate.edu/tssv2/Express/ModelingTools.aspx</a>.
---------------------------------------------------------------------------
B. Calculation of Baseline, Current, and Natural Visibility Conditions;
Progress to Date; and Uniform Rate of Progress for Class I Areas Within
the State
Section 51.308(f)(1) requires states to determine the following for
``each mandatory Class I Federal area located within the State'':
baseline visibility conditions for the most impaired and clearest days,
natural visibility conditions for the most impaired and clearest days,
progress to date for the most impaired and clearest days, the
differences between current visibility conditions and natural
visibility conditions, and the URP. This section also provides the
option for states to propose adjustments to the URP line for a Class I
area to account for visibility impacts from anthropogenic sources
outside the United States and/or the impacts from wildland prescribed
fires that were conducted for certain specified objectives. 40 CFR
51.308(f)(1)(vi)(B).
The IMPROVE monitoring network measures visibility impairment
caused by air pollution at Class I areas. Montana's 2022 SIP submission
provides visibility conditions for each IMPROVE monitor and associated
Class I area in Montana (table 1).\25\
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\25\ Montana 2022 SIP submission at 73-77.
Table 1--Visibility Conditions (Deciviews) for Montana IMPROVE Stations
--------------------------------------------------------------------------------------------------------------------------------------------------------
Difference
Baseline Period (2008- Current Natural Progress since baseline Progress during last between current
Monitor ID Class I areas (2000-2004) 2012) (2014-2018) (2064) (2000-2004)-(2014-2018) implementation period (2014-2018) and
(2008-2012)--(2014-2018) natural (2064)
--------------------------------------------------------------------------------------------------------------------------------------------------------
Most Impaired Days
--------------------------------------------------------------------------------------------------------------------------------------------------------
CABI1........ Cabinet 10.73 10.23 9.87 5.64 0.86 0.36 4.23
Mountains
Wilderness
Area.
GAMO1........ Gates of the 8.95 7.74 7.47 4.53 1.48 0.27 2.94
Mountains
Wilderness
Area.
GLAC1........ Glacier 15.89 14.07 13.77 6.90 2.12 0.30 6.87
National Park.
MELA1........ Medicine Lake 16.62 16.60 15.30 5.95 1.32 1.30 9.35
Wilderness
Area.
MONT1........ Bob Marshall 11.00 10.24 10.06 5.53 0.94 0.18 4.53
Wilderness
Area, Mission
Mountain
Wilderness
Area,
Scapegoat
Wilderness
Area.
SULA1........ Anaconda- 10.06 8.86 8.37 5.45 1.69 0.49 2.92
Pintler
Wilderness
Area, Selway-
Bitterroot
Wilderness
Area.
ULBE1........ UL Bend 12.76 12.16 10.93 5.87 1.83 1.23 5.06
Wilderness
Area.
YELL2........ Red Rock Lakes 8.30 7.49 7.52 3.97 0.78 -0.03 3.55
National
Wildlife
Refuge,
Yellowstone
National Park.
--------------------------------------------------------------------------------------------------------------------------------------------------------
Clearest Days
--------------------------------------------------------------------------------------------------------------------------------------------------------
CABI1........ Cabinet 3.62 2.58 2.46 1.48 1.16 0.12 0.98
Mountains
Wilderness
Area.
GAMO1........ Gates of the 1.71 0.75 0.66 0.32 1.05 0.09 0.34
Mountains
Wilderness
Area.
GLAC1........ Glacier 7.22 5.68 5.38 2.43 1.84 0.30 2.95
National Park.
MELA1........ Medicine Lake 7.27 6.42 6.19 2.96 1.08 0.23 3.23
Wilderness
Area.
MONT1........ Bob Marshall 3.86 2.79 2.56 1.48 1.30 0.23 1.08
Wilderness
Area, Mission
Mountain
Wilderness
Area,
Scapegoat
Wilderness
Area.
[[Page 43964]]
SULA1........ Anaconda- 2.57 1.95 1.60 1.12 0.97 0.35 0.48
Pintler
Wilderness
Area, Selway-
Bitterroot
Wilderness
Area.
ULBE1........ UL Bend 4.75 4.14 3.71 2.46 1.04 0.43 1.25
Wilderness
Area.
YELL2........ Red Rock Lakes 2.58 1.51 1.43 0.43 1.15 0.08 1.00
National
Wildlife
Refuge,
Yellowstone
National Park.
--------------------------------------------------------------------------------------------------------------------------------------------------------
The State also determined the URP for the most impaired and
clearest days for Montana Class I areas.\26\ Montana also provided haze
indices and the URP for IMPROVE monitors and associated Class I areas
outside the State.\27\
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\26\ Montana 2022 SIP submission at 86-91.
\27\ Id. at 86-91.
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Based on the information provided in Montana's 2022 SIP submission,
the EPA is proposing to approve the State's visibility condition
calculations for Cabinet Mountains Wilderness Area, Gates of the
Mountains Wilderness Area, Glacier National Park, Medicine Lake
Wilderness Area, Bob Marshall Wilderness Area, Mission Mountains
Wilderness Area, Scapegoat Wilderness Area, Anaconda-Pintler Wilderness
Area, Selway-Bitterroot Wilderness Area, UL Bend Wilderness Area, Red
Rock Lakes National Wildlife Refuge, and Yellowstone National Park \28\
as meeting the requirements of 40 CFR 51.308(f)(1) related to the
calculation of baseline, current, and natural visibility conditions;
progress to date; and the URP.
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\28\ Bob Marshall Wilderness Area, Mission Mountains Wilderness
Area, and Scapegoat Wilderness Area are subject to the same
visibility calculation. Anaconda-Pintler Wilderness Area and Selway-
Bitterroot Wilderness Area are subject to the same visibility
calculation. Red Rock Lakes National Wildlife Refuge and Yellowstone
National Park are subject to the same visibility calculation.
---------------------------------------------------------------------------
C. Long-Term Strategy
Each state having a Class I area within its borders or emissions
that may affect visibility in any Class I area outside the state must
develop a long-term strategy for making reasonable progress towards the
national visibility goal for each impacted Class I area. CAA section
169A(b)(2)(B). As explained in the Background section of this document,
reasonable progress is achieved when all states contributing to
visibility impairment in a Class I area are implementing the measures
determined--through application of the four statutory factors to
sources of visibility impairing pollutants--to be necessary to make
reasonable progress. 40 CFR 51.308(f)(2)(i). Each state's long-term
strategy must include the enforceable emission limitations, compliance
schedules, and other measures that are necessary to make reasonable
progress. 40 CFR 51.308(f)(2). After considering the four statutory
factors, all measures that are determined to be necessary to make
reasonable progress must be in the long-term strategy. In developing
its long-term strategy, a state must also consider the five additional
factors in 40 CFR 51.308(f)(2)(iv). As part of its reasonable progress
determinations, the state must describe the criteria used to determine
which sources or group of sources were evaluated (i.e., subject to
four-factor analysis) for the second implementation period and how the
four factors were taken into consideration in selecting the emission
reduction measures for inclusion in the long-term strategy. 40 CFR
51.308(f)(2)(iii).
1. Montana's Long-Term Strategy Four-Factor Analysis
a. Summary of Montana's Long-Term Strategy Four-Factor Analysis
Under 40 CFR 51.308(f)(2)(i), SIP submittals must include a
description of the criteria a state used to determine which sources or
groups of sources to evaluate through four-factor analysis. Montana
used a Q/d screening approach to identify sources for four-factor
analysis. The Q/d screening metric uses a source's annual emissions in
tons (Q) divided by the distance in kilometers (d) between the source
and the nearest Class I area, along with a reasonably selected
threshold for this metric. The larger the Q/d value, the greater the
source's expected effect on visibility in each associated Class I area.
Using a WRAP-devised screening threshold of Q/d > 4 and emissions
information from the 2014-2017 average annual emissions, Montana
identified sources in the State that may be affecting visibility at
Class I areas.\29\ Montana first categorized all permitted stationary
sources into two groups based on average combined annual NO<INF>X</INF>
and SO<INF>2</INF> emissions.\30\ The first group included 24
facilities emitting 100 tons per year or more, which were automatically
selected for further evaluation using a Q/d > 4 to represent the point
source emissions impacting Class I areas, resulting in 15 selected
sources. Montana then applied the Q/d > 4 to the second group of
smaller sources, identifying an additional two sources with lower
emissions but close proximity to Class 1 areas. In total, Montana
selected 17 point sources for four-factor analysis (table
2).<SUP>31 32</SUP> These 17 point sources contributed approximately
36,620 tons per year of NO<INF>X</INF> and SO<INF>2</INF> emissions,
representing about 90% of total emissions from point sources in the
state.
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\29\ Montana 2022 SIP submission at 161-164, Appendix C.
\30\ Based on emission trend analysis and light extinction
budgets, Montana chose to focus the potential additional control
analysis on point source emissions of NO<INF>X</INF> and
SO<INF>2</INF> only. Montana 2022 SIP submission at 151-152; 160-
161.
\31\ Montana 2022 SIP submission at 162-164, Appendix C.
\32\ Montana did not include Colstrip Units 1 and 2 among the
sources screened for four-factor analysis because the units were
scheduled to close. The EPA finalized the enforceable closures of
Colstrip Units 1 and 2 into the SIP in 2023 (88 FR 41320).
[[Page 43965]]
Table 2--Facilities Screened in Using Q/d
----------------------------------------------------------------------------------------------------------------
(d) Minimum of
distance (km) (Q) Maximum of
Facility name Closest Class I area to Class I emissions Q/d
area (tons/year)
----------------------------------------------------------------------------------------------------------------
Weyerhaeuser NR--Columbia Falls Facility. Glacier.................... 13.3 984.36 74.01
Talen Montana LLC--Colstrip Steam UL Bend.................... 198.9 12,716.57 63.93
Electric Station Units #3 and 4.
Ash Grove Cement Company................. Gates of the Mountains..... 30.6 1,235.11 40.36
Montana Dakota Utilities CO--Lewis & Teddy Roosevelt............ 51.8 1,052.28 20.31
Clark Station.
GCC Trident, LLC......................... Yellowstone................ 97.4 1,488.39 15.28
Yellowstone Energy Limited Partnership-- Absaroka................... 143.8 2,136.33 14.86
Yellowstone Power Plant.
Roseburg Forest Products CO.............. Selway Bitterroot.......... 26.6 302.61 11.38
Colstrip Energy Ltd Partnership.......... UL Bend.................... 188.7 1,935.61 10.26
Montana Sulphur & Chemical CO............ Absaroka................... 137.5 1,310.27 9.53
Graymont Western US Inc--Indian Creek Gates of the Mountains..... 57.1 524.23 9.18
Facility.
ExxonMobil Fuels & Lubricants Company-- Absaroka................... 143.7 1,034.41 7.20
ExxonMobil Billings Refinery.
Cenex Harvest States Cooperative Inc--CHS Absaroka................... 113.5 628.73 5.54
Inc Refinery Laurel.
F H Stoltze Land & Lumber CO............. Glacier.................... 14 75.22 5.37
Sidney Sugars Inc--Sidney Sugar Facility. Teddy Roosevelt............ 51.9 268.79 5.18
Phillips 66 CO--Billings Refinery........ Absaroka................... 143 644.92 4.51
Weyerhaeuser NR Kalispell--Weyerhaeuser Glacier.................... 30.5 134.32 4.40
Evergreen Facility.
Northern Border Pipeline CO--N. Border Medicine Lake.............. 22.8 95.76 4.20
Pipeline CO Station #3.
----------------------------------------------------------------------------------------------------------------
The State requested that each of the 17 point sources conduct a
four-factor analysis that evaluated controls for NO<INF>X</INF> and
SO<INF>2</INF> emissions for its review and consideration.\33\ For one
of these sources, Montana Dakota Utilities (MDU) Lewis and Clark
Station, the State determined that the source's four-factor analysis
was no longer relevant because the source had been permanently removed
from service prior to the State's finalization of the SIP.\34\ For the
remaining sources, Montana then evaluated what is necessary to make
reasonable progress by considering the four statutory factors for each
source:
---------------------------------------------------------------------------
\33\ Montana 2022 SIP submission at 166-167; Appendix A.
\34\ Id. at 197-198; Appendix D.
---------------------------------------------------------------------------
<bullet> Cost of compliance;
<bullet> Time necessary for compliance;
<bullet> Energy and non-air quality environmental impacts of
compliance; and
<bullet> Remaining useful life of any potentially affected sources.
The State documented these analyses in Montana's 2022 SIP
submission and associated technical support documents. Chapter 6 of
Montana's SIP submission contains Montana's evaluation of the four
statutory factors for each source and Montana's determinations of the
source-specific emission reduction measures necessary to make
reasonable progress.\35\
---------------------------------------------------------------------------
\35\ Id. at 166-270.
---------------------------------------------------------------------------
As part of its long-term strategy evaluation of what emission
control measures are necessary to make reasonable progress by 2028,
Montana considered the previous approved BART determinations and
emission limits for J.E. Corette power plant and Colstrip power plant,
Unit 1 and 2.\36\ Ultimately, the State concluded that no additional
regional haze controls or measures are required of any of the evaluated
sources for the long-term strategy measures necessary to make
reasonable progress by 2028 during the second implementation
period.\37\
---------------------------------------------------------------------------
\36\ Id. at 280-281; Appendix D.
\37\ Id. at 280.
---------------------------------------------------------------------------
b. The EPA's Evaluation of Montana's Long-Term Strategy Four-Factor
Analysis
Section 169A(b)(2) of the CAA requires each state in which any
Class I area is located or ``the emissions from which may reasonably be
anticipated to cause or contribute to any impairment of visibility'' in
a Class I area to have a plan for making reasonable progress toward the
national visibility goal. CAA section 169A(g)(1) specifies: ``[I]n
determining reasonable progress there shall be taken into consideration
the costs of compliance, the time necessary for compliance, and the
energy and nonair quality environmental impacts of compliance, and the
remaining useful life of any existing source subject to such
requirements.'' \38\ The RHR implements this statutory requirement in
40 CFR 51.308(f) for the second and subsequent planning periods for
regional haze. 40 CFR 51.308(f) requires states to submit a long-term
strategy that addresses regional haze visibility impairment for each
mandatory Class I area within the state and for each mandatory Class I
area located outside the state that may be affected by emissions from
the state. 40 CFR 51.308(f)(2)(i) lays out the CAA 169A four-factor
criteria for the evaluation and development of the long-term strategy.
---------------------------------------------------------------------------
\38\ We refer to the CAA section 169A(g)(1) requirements as the
four factors.
---------------------------------------------------------------------------
Based on the EPA's review, we find that Montana's 2022 SIP
submission satisfies the requirements under 51.308(f)(2)(i) because
Montana's selection of 17 point sources, evaluation of the four
statutory factors, and determinations of the emission reductions
necessary to make reasonable progress as described in section IV.C.1.a.
of this document, were reasonable.
With respect to source selection, Montana used the 2014-2017
average annual emissions of NO<INF>X</INF> and SO<INF>2</INF> in tons
divided by distance in kilometers between a source and the nearest
Class I area as a surrogate for baseline visibility impact. This metric
is also known as Q/d. The state then analyzed the 271 permitted
stationary sources in the state and relied on its screening protocol,
using a Q/d threshold > 4, to evaluate facilities that account for
ninety percent of the NO<INF>X</INF> plus SO<INF>2</INF> emissions from
the permitted stationary facilities. Applying this protocol, Montana
selected 17 point sources for
[[Page 43966]]
analysis. As previously stated, 40 CFR 51.308(f)(2)(i) requires that a
state's SIP submission include a ``description of the criteria it used
to determine which sources or groups of sources it evaluated,'' and it
must be appropriately documented, as required by 40 CFR
51.308(f)(2)(iii). Because Montana provided a detailed description of
how the State used technical information to select a reasonable set of
sources for an analysis of control measures for the second
implementation period, we find that Montana's source selection was
reasonable and consistent with the requirements of 40 CFR
51.308(f)(2).\39\
---------------------------------------------------------------------------
\39\ Montana 2022 SIP submission at 151-166.
---------------------------------------------------------------------------
Montana submitted four-factor analyses for the selected sources and
demonstrated that its determination of declining additional measures
necessary for reasonable progress, as part of its long-term strategy,
were an outgrowth of its consideration of the four statutory factors in
accordance with 40 CFR 51.308(f)(2)(i).\40\ Ultimately, Montana's 2022
SIP submission relied on previously approved and adopted measures.\41\
---------------------------------------------------------------------------
\40\ Id. at 166-281.
\41\ Id. at 296.
---------------------------------------------------------------------------
The EPA reviewed the State's long-term strategy to address regional
haze visibility impairment for each Class I area affected by emissions
from the State. The State included in its implementation plan a
description of the criteria it used to determine which sources it
evaluated and how the four factors were taken into consideration in
selecting the measures for inclusion in its long-term strategy
including existing emission control measures and compliance schedules
that had been previously codified in Montana Board of Environmental
Review Orders and 40 CFR 52.1370(d).<SUP>42 43</SUP> In addition, the
projected 2028 visibility conditions for Class I areas both in Montana
and those areas influenced by emissions from Montana sources, are all
below the 2028 URP. The EPA's recently implemented URP policy is that
so long as the Class I areas impacted by a state are below the URP and
the State considers the four factors, the State will have presumptively
demonstrated it has already made reasonable progress for the second
planning period for that area.\44\ Thus, we are concluding that
Montana's long-term strategy contains the enforceable emission
limitations, compliance schedules, and other measures that are
necessary to make reasonable progress.
---------------------------------------------------------------------------
\42\ Montana Board of Environmental Review Order: In the Matter
of an Order Setting Air Pollutant Emission Limits that the State of
Montana may Submit to the Federal Environmental Protection Agency
for Revision of the State Implementation Plan Concerning Protection
of Visibility, Affecting the Following Facilities: Talen Montana,
LLC's Colstrip Steam Electric Station, Units 1 and 2, and J.E.
Corette Steam Electric Station. Board Order Findings of Fact,
Conclusions of Law, and Order. October 18, 2019, Exhibit A.
\43\ 88 FR 41320 (June 26, 2023).
\44\ See 90 FR 29737, 29738 (July 7, 2025); 90 FR 20425, 20434
(May 14, 2025).
---------------------------------------------------------------------------
Because the State evaluated and determined the emission reduction
measures that are necessary to make reasonable progress by considering
the costs of compliance, the time necessary for compliance, the energy
and non-air quality environmental impacts of compliance, and the
remaining useful life of the sources selected as is required under 40
CFR 51.308(f)(2)(i), and the projected 2028 visibility conditions for
Class I areas influenced by emissions from Montana sources are all
below the URP, we find that Montana's determination of the emission
reduction measures that are necessary to make reasonable progress was
reasonable and consistent with the requirements of 40 CFR
51.308(f)(2)(i).
2. Other Long-Term Strategy Requirements
States must meet the additional requirements specified in 40 CFR
51.308(f)(2)(ii)-(iv) when developing their long-term strategies. 40
CFR 51.308(f)(2)(ii) requires states to consult with other states that
have emissions that are reasonably anticipated to contribute to
visibility impairment in Class I areas to develop coordinated emission
management strategies. Specifically, 40 CFR 51.308(f)(2)(ii)(A)
requires a state to demonstrate that its SIP includes all measures
agreed upon during the state-to-state consultations. Montana considered
facilities affecting out of state Class I areas for additional controls
through a four-factor analysis and determined that no additional
controls on Montana sources will be required at this time. The states
consulted agreed with Montana's conclusion. 40 CFR 51.308(f)(ii)(B)
requires a state to consider emission reduction measures identified by
other states as being necessary to make reasonable progress in a Class
I area. Montana did not receive recommendations for any of the sources
within the State from other states. Chapter 7.2 of Montana's 2022 SIP
submission describes Montana's consultation with other states
throughout the development of its regional haze plan.\45\
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\45\ Montana 2022 SIP submission at 293-296.
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40 CFR 51.308(f)(2)(iii) requires states to document the technical
basis, including modeling, monitoring, costs, engineering, and
emissions information, on which the state is relying to determine the
emission reduction measures that are necessary to make reasonable
progress in each mandatory Class I area it impacts. Montana relied on
WRAP technical information, modeling, and analysis to support
development of its long-term strategy.\46\
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\46\ Id. at 31-43.
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40 CFR 51.308(f)(2)(iv) specifies five additional factors states
must consider in developing their long-term strategies. The five
additional factors are: emission reductions due to ongoing air
pollution control programs, including measures to address reasonably
attributable visibility impairment; measures to mitigate the impacts of
construction activities; source retirement and replacement schedules;
basic smoke management practices for prescribed fire used for
agricultural and wildland vegetation management purposes and smoke
management programs; and the anticipated net effect on visibility due
to projected changes in point, area, and mobile source emissions over
the period addressed by the long-term strategy.
Chapter 7.1 of Montana's 2022 SIP submission describes each of the
five additional factors it is required to consider under 40 CFR
51.308(f)(2)(iv) and explains how it considered them.\47\ Pursuant to
40 CFR 51.308(f)(2)(iv)(A), Montana detailed the existing and ongoing
State and Federal emission control programs that contribute to emission
reductions, including the designation status for all current and former
non-attainment areas.\48\ Montana's Airborne Particulate Matter rule in
Administrative Rules of Montana (ARM) 17.8.308 mitigates the impacts of
construction activities as required by 40 CFR 51.308(f)(2)(iv)(B).\49\
Pursuant to 40 CFR 51.308(f)(2)(iv)(C), source retirement schedules are
found in table 7-2 of the Montana 2022 SIP submission as well as in a
board order codified in 40 CFR 52.1370(d).\50\ In considering smoke
management as required in 40 CFR 51.308(f)(2)(iv)(D), Montana explained
that it addresses smoke management through its EPA-approved Smoke
Management Program \51\ as well as Best Available Control Technology
requirements for burners found in ARM 17.8.601 which limits smoke
impacts due to burning.\52\
[[Page 43967]]
Montana considered the anticipated net effect of projected changes in
emissions on visibility due to projected changes in point, area and
mobile source emissions as required by 40 CFR 51.308(f)(2)(iv)(E) in
tables 8-2 and 8-4 of the State's 2022 SIP submission.\53\
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\47\ Id. at 271-281.
\48\ Id. at 271-277.
\49\ Id. at 278.
\50\ Montana 2022 SIP submission at 278-281; Montana Board of
Environmental Review Orders.
\51\ Consistent with the EPA's Interim Air Quality Policy on
Wildland Prescribed Fire, May 1998.
\52\ Montana 2022 SIP submission at 281.
\53\ Id. at 297-299.
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After reviewing Montana's 2022 SIP chapters addressing 40 CFR
51.308(f)(2)(ii)-(iv), the EPA finds that Montana has satisfied these
additional long-term strategy requirements of 40 CFR 51.308(f)(2)(ii)-
(iv).
D. Reasonable Progress Goals
Section 51.308(f)(3)(i) requires a state in which a Class I area is
located to establish RPGs--one each for the most impaired and clearest
days--reflecting the visibility conditions that will be achieved at the
end of the implementation period as a result of the emission
limitations, compliance schedules and other measures required under
paragraph (f)(2) in states' long-term strategies, as well as
implementation of other CAA requirements.
After establishing its long-term strategy, Montana developed
reasonable progress goals for each Class I area for the 20% most
impaired days and 20% clearest days based on the results of 2028 WRAP
modeling (table 3).\54\
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\54\ Montana 2022 SIP submission at 298-299.
Table 3--Reasonable Progress Goals for the 20% Most Impaired Days and 20% Clearest Days for Montana Class I
Areas
----------------------------------------------------------------------------------------------------------------
20% Most impaired days 20% Clearest days
------------------------------------------------------------------
Average 2028 2028 Average 2028
Class I area baseline Uniform Reasonable baseline Reasonable
conditions progress progress conditions progress
(2000-2004) goal goal \1\ (2000-2004) goal
----------------------------------------------------------------------------------------------------------------
Deciviews
----------------------------------------------------------------------------------------------------------------
Anaconda-Pintler Wilderness Area, Selway- 10.06 9.12 8.01 2.57 1.51
Bitterroot Wilderness Area (SULA1)..........
Bob Marshall Wilderness Area, Mission 11 10.02 9.51 3.86 2.33
Mountains Wilderness Area, Scapegoat
Wilderness Area (MONT1).....................
Cabinet Mountains Wilderness Area (CABI1).... 10.73 10.36 9.41 3.62 2.21
Gates of the Mountains Wilderness Area 8.95 8.31 7.12 1.71 0.53
(GAMO1).....................................
Glacier National Park (GLAC1)................ 15.89 13.78 12.92 7.22 5.10
Medicine Lake Wilderness Area (MELA1)........ 16.62 14.92 14.85 7.27 6.12
Red Rock Lakes National Wildlife Refuge, 8.3 7.26 6.97 2.58 1.21
Yellowstone National Park (YELL2)...........
UL Bend Wilderness Area (ULBE1).............. 12.76 12.05 10.62 4.75 3.58
----------------------------------------------------------------------------------------------------------------
\1\ Based on WRAP 2028OTBa2.
The reasonable progress goals are based on Montana's long-term
strategy, the long-term strategy of other states that may affect Class
I areas in Montana, and other CAA requirements. In accordance with
51.308(f)(3)(ii)(A)-(B), if the RPG in 2028 for the most impaired days
is above the URP (i.e., if visibility conditions are improving more
slowly than the rate described by the URP), each state that contributes
to visibility impairment in the Class I area must demonstrate, based on
the four-factor analysis required under 40 CFR 51.308(f)(2)(i), that no
additional emission reduction measures would be reasonable to include
in its long-term strategy.\55\ Because Montana demonstrated in their
2022 SIP submission that all of their Class I areas are projected to be
below the 2028 URP, no additional requirements apply under 40 CFR
51.308(f)(3)(ii).\56\
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\55\ 40 CFR 51.308(f)(3)(ii).
\56\ Montana 2022 SIP submission at 298-305.
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Per 40 CFR 51.308(f)(3)(iv), the EPA must evaluate the
demonstrations the State developed pursuant to 40 CFR 51.308(f)(2) to
determine whether the State's reasonable progress goals for visibility
improvement provide for reasonable progress towards natural visibility
conditions. As previously explained in section IV.C., we are proposing
to approve Montana's long-term strategy for meeting the requirements of
40 CFR 51.308(f)(2) to meet the national goal of preventing future as
well as existing visibility impairment due to manmade sources.
Montana's reasonable progress goals incorporate Montana's long-term
strategy requirements. Thus, we find that Montana's reasonable progress
goals provide for an improvement in visibility for the most-impaired
days since the baseline period and ensure no degradation in visibility
on the clearest days since the baseline period.\57\ Therefore, we
propose to approve Montana's reasonable progress goals under 40 CFR
51.308(f)(3).
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\57\ Id. at 297.
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E. Reasonably Attributable Visibility Impairment (RAVI)
The RHR contains a requirement at 40 CFR 51.308(f)(4) related to
any additional monitoring that may be needed to address visibility
impairment in Class I areas from a single source or a small group of
sources. This is called ``reasonably attributable visibility
impairment,'' \58\ also known as RAVI. Under this provision, if the EPA
or the FLM of an affected Class I area has advised a state that
additional monitoring is needed to assess RAVI, the state must include
in its SIP revision for the second implementation period an appropriate
strategy for evaluating such impairment. The EPA has not advised the
State to that effect; nor did the State indicate that FLMs for Class I
areas identified any RAVI from Montana sources. For this reason, the
EPA proposes to approve the portions of Montana's 2022 SIP submission
relating to 40 CFR 51.308(f)(4).
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\58\ The EPA's visibility protection regulations define
``reasonably attributable visibility impairment'' as ``visibility
impairment that is caused by the emission of air pollutants from
one, or a small number of sources.'' 40 CFR 51.301.
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F. Monitoring Strategy and Other State Implementation Plan Requirements
Section 51.308(f)(6) specifies that each comprehensive revision of
a state's regional haze SIP must contain or provide for certain
elements, including
[[Page 43968]]
monitoring strategies, emissions inventories, and any reporting,
recordkeeping and other measures needed to assess and report on
visibility. A main requirement of this section is for states with Class
I areas to submit monitoring strategies for measuring, characterizing,
and reporting on visibility impairment. Compliance with this
requirement may be met through participation in the IMPROVE network.
Under 40 CFR 51.308(f)(6)(i), states must provide for the
establishment of additional monitoring sites or equipment needed to
assess whether reasonable progress goals to address regional haze for
all mandatory Class I Federal areas within the state are being
achieved. For states with Class I areas (including Montana), Sec.
51.308(f)(6)(ii) requires SIPs to provide for procedures by which
monitoring data and other information are used in determining the
contribution of emissions from within the state to regional haze
visibility impairment at mandatory Class I Federal areas both within
and outside the state. Section 51.308(f)(6)(iv) requires the SIP to
provide for the reporting of all visibility monitoring data to the
Administrator at least annually for each Class I area in the state. 40
CFR 51.308(f)(6)(v) requires SIPs to provide for a statewide inventory
of emissions of pollutants that are reasonably anticipated to cause or
contribute to visibility impairment, including emissions for the most
recent year for which data are available. Section 51.308(f)(6)(v) also
requires states to include estimates of future projected emissions.
Finally, 40 CFR 51.308(f)(6)(vi) requires the SIP to provide for any
other elements, including reporting, recordkeeping, and other measures,
that are necessary for states to assess and report on visibility.
Montana describes its participation in the IMPROVE network, which
comprises 110 monitoring sites across the nation, eight of which are in
Montana. The State relied on the IMPROVE monitoring network to assess
visibility at Class I areas across Montana \59\ and considered the ten
monitoring sites CABI1, GAMO1, GLAC1, MELA1, MONT1, NOAB1, SULA1,
THRO1, ULBE1, and YELL2 to be adequate for assessing reasonable
progress goals at the State's 12 Class I areas.\60\ Using the
monitoring data procedures described in its 2022 SIP submission along
with other technical information supplied by WRAP,<SUP>61 62</SUP>
Montana determined the contribution of in-State emissions to Class I
areas inside and outside Montana.\63\ In addition, Montana also
provided a statewide inventory of emissions that are reasonably
anticipated to cause or contribute to visibility impairment in Class I
areas; Montana relied primarily on 2014-2017 data but also estimated
future projected emissions.\64\
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\59\ Montana 2022 SIP submission at 18-27.
\60\ Id. at 21.
\61\ Id. at 33-43.
\62\ Montana relied on the WRAP Technical Support System (TSS)
``Analysis and Planning'' section to determine baseline, natural,
and current conditions for Class I areas in Montana. <a href="https://views.cira.colostate.edu/tssv2/">https://views.cira.colostate.edu/tssv2/</a>.
\63\ Montana 2022 SIP submission at 282-296.
\64\ Id. at 126-150.
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The EPA finds that Montana has met the requirements of 40 CFR
51.308(f)(6), including through its continued participation in the
IMPROVE network and WRAP RPO and its ongoing compliance with the Air
Emissions Reporting Requirements (AERR). There is no indication that
further SIP elements are necessary at this time for Montana to assess
and report on visibility. Therefore, the EPA proposes to approve the
monitoring strategy and other state implementation plan elements of
Montana's 2022 SIP submission as meeting the requirements of 40 CFR
51.308(f)(6).
G. Requirements for Periodic Reports Describing Progress Towards the
Reasonable Progress Goals
40 CFR 51.308(f)(5) requires that periodic comprehensive revisions
of states' regional haze plans also address the progress report
requirements of 40 CFR 51.308(g)(1) through (5). The purpose of these
requirements is to evaluate progress towards the applicable RPGs for
each Class I area within the state and each Class I area outside the
state that may be affected by emissions from within that state.
Sections 51.308(g)(1) and (2) apply to all states and require a
description of the status of implementation of all measures included in
a state's first implementation period regional haze plan and a summary
of the emission reductions achieved through implementation of those
measures. Section 51.308(g)(3) applies only to states with Class I
areas within their borders and requires such states to assess current
visibility conditions, changes in visibility relative to baseline
(2000-2004) visibility conditions, and changes in visibility conditions
relative to the period addressed in the first implementation period
progress report. Section 51.308(g)(4) applies to all states and
requires an analysis tracking changes in emissions of pollutants
contributing to visibility impairment from all sources and sectors
since the period addressed by the first implementation period progress
report. This provision further specifies the year or years through
which the analysis must extend depending on the type of source and the
platform through which its emission information is reported. Finally,
40 CFR 51.308(g)(5), which also applies to all states, requires an
assessment of any significant changes in anthropogenic emissions within
or outside the state that have occurred since the period addressed by
the first implementation period progress report, including whether such
changes were anticipated and whether they have limited or impeded
expected progress towards reducing emissions and improving visibility.
In its 2022 SIP submission, Montana included the elements of the
periodic progress report specified in 40 CFR 51.308(f)(5) and 40 CFR
51.308(g)(1)-(5). Montana summarized the facility improvements made
during and after the first implementation period, including emission
control measures installed and emission reductions achieved by the
facilities that most affected each Class I area, and summarized the
associated emission reductions.\65\ In addition, the State summarized
the implementation status of ongoing air pollution control programs,
measures to mitigate construction activities, source retirement and
replacement schedules, and smoke management practices and programs.\66\
The EPA finds that Montana has met the requirements of 40 CFR
51.308(g)(1) and (2) because Montana's 2022 SIP submission describes
the measures included in the long-term strategy from the first
implementation period, as well as the status of their implementation
and the emission reductions achieved through such implementation.
---------------------------------------------------------------------------
\65\ Id. at 47-52.
\66\ Id. at 54-55; 130-132.
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Visibility conditions (in deciviews) are reported in Montana's 2022
SIP submission for the most impaired and clearest days. Visibility
conditions are expressed in terms of 5-year averages for the baseline
period (2000-2004), ``natural visibility conditions'' for the 2000-2014
period, previous implementation period (2008-2012), and current period
(2014-2018), as well as the progress made since the baseline period
((2000-2004)-(2008-2012)) and during the last implementation period
((2008-2012)-(2014-2018)).\67\ The EPA therefore finds that Montana has
[[Page 43969]]
satisfied the requirements of 40 CFR 51.308(g)(3).
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\67\ Id. at 73-77.
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The State used the most current emissions inventory available--the
2017 national emissions inventory--to provide emissions inventories for
NO<INF>X</INF>, SO<INF>2</INF>, VOC, ammonia (NH<INF>3</INF>), and PM
that identify the type of source, activity, and pollutant.\68\ Montana
also provided an assessment and discussion of the significant changes
in anthropogenic emissions since the first implementation period.\69\
The EPA finds that the requirements of 40 CFR 51.308(g)(4) and (g)(5)
are satisfied by providing emissions of pollutants contributing to
visibility impairment within the State and assessing any significant
changes in anthropogenic emissions within or outside the State that
have occurred since the period addressed in the most recent plan.
---------------------------------------------------------------------------
\68\ Id. at 127-136.
\69\ Id. at 63-67.
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Because Montana's 2022 SIP submission addresses the requirements of
40 CFR 51.308(g)(1) through (5), the EPA finds that Montana has met the
progress report requirements of 40 CFR 51.308(f)(5). Therefore, we
propose to approve Montana's 2022 SIP submission as meeting the
requirements of 40 CFR 51.308(f)(5) and 40 CFR 51.308(g) for periodic
progress reports.
H. Requirements for State and Federal Land Manager Coordination
Section 169A(d) of the CAA requires states to consult with FLMs
before holding the public hearing on a proposed regional haze SIP, and
to include a summary of the FLMs' conclusions and recommendations in
the notice to the public. In addition, the 40 CFR 51.308(i)(2) FLM
consultation provision requires a state to provide FLMs with an
opportunity for consultation that is early enough in the state's policy
analyses of its emission reduction obligation so that information and
recommendations provided by the FLMs can meaningfully inform the
state's decisions on its long-term strategy. If the consultation has
taken place at least 120 days before a public hearing or public comment
period, the opportunity for consultation will be deemed early enough.
Regardless, the opportunity for consultation must be provided at least
60 days before a public hearing or public comment period at the state
level. Section 51.308(i)(2) also lists two substantive topics on which
FLMs must be provided an opportunity to discuss with states: assessment
of visibility impairment in any Class I area and recommendations on the
development and implementation of strategies to address visibility
impairment. Section 51.308(i)(3) requires states, in developing their
implementation plans, to include a description of how they addressed
FLMs' comments.
Montana's 2022 SIP submission summarizes the State's consultation
and coordination with the FLMs. Montana consulted and coordinated with
the FLMs during the development of its regional haze SIP through WRAP
participation and direct FLM engagement.\70\ On September 27, 2021,
Montana submitted the State's draft regional haze plan to the FLMs for
consultation and received comments thereafter. Montana subsequently
analyzed the FLMs comments, modified the draft regional haze plan,
summarized and responded to each comment, and included the information
in an appendix to its SIP submission which was made available for
public comment.\71\ The State explained how it is committed to
coordinating and consulting with the FLMs during the development of
future progress reports and SIP submissions, as well as during the
implementation of programs having the potential to contribute to
visibility impairment in Class I areas.\72\
---------------------------------------------------------------------------
\70\ Id. at 30, 44.
\71\ Id. at appendix F, I.
\72\ Id. at 306.
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Montana took administrative steps to provide the FLMs the
opportunity to review and provide feedback on the State's draft
regional haze plan. Therefore, the EPA proposes to approve the FLM
consultation component of Montana's SIP submission which meets the
requirements of 40 CFR 51.308(i) and CAA 169A(d), as outlined in this
section.
V. Interstate Transport Prong 4 (Visibility) for the 2015 Ozone NAAQS
Infrastructure SIP
A. Background on Infrastructure SIPs
Under CAA sections 110(a)(1) and 110(a)(2), each state is required
to submit a SIP that provides for the implementation, maintenance, and
enforcement of each primary or secondary NAAQS. Moreover, CAA sections
110(a)(1) and 110(a)(2) require each state to make this new SIP
submission within three years (or less, if the Administrator so
prescribes) after promulgation of a new or revised NAAQS. This type of
SIP submission is commonly referred to as an ``infrastructure SIP.''
The overall purpose of the infrastructure SIP requirements is to ensure
that the necessary structural components of each state's air quality
management program are adequate to meet the state's responsibilities
for the new or revised NAAQS. Overall, the infrastructure SIP
submission process provides an opportunity for the responsible air
agency, the public, and the EPA to review the basic structural
requirements of the air agency's air quality management program in
light of each new or revised NAAQS.
CAA section 110(a)(2)(D) has two components: 110(a)(2)(D)(i) and
110(a)(2)(D)(ii). CAA section 110(a)(2)(D)(i) includes four distinct
components, commonly referred to as ``prongs,'' that must be addressed
in infrastructure SIP submissions. The first two prongs, which are
codified in CAA section 110(a)(2)(D)(i)(I), prohibit any source or
other type of emissions activity in one state from contributing
significantly to nonattainment of the NAAQS in another state (prong 1)
and from interfering with maintenance of the NAAQS in another state
(prong 2). The third and fourth prongs, which are codified in CAA
section 110(a)(2)(D)(i)(II), prohibit emissions activity in one state
from interfering with measures required to prevent significant
deterioration of air quality in another state (prong 3) or from
interfering with measures to protect visibility in another state (prong
4).
B. Prong 4 Requirements
CAA section 110(a)(2)(D)(i)(II) requires SIPs to contain provisions
prohibiting sources in a state from emitting pollutants in amounts that
interfere with any other state's efforts to protect visibility under
part C of the CAA (which includes sections 169A and 169B). The EPA
issued guidance on infrastructure SIPs in a September 13, 2013
memorandum from Stephen D. Page titled ``Guidance on Infrastructure
State Implementation Plan (SIP) Elements under Clean Air Act sections
110(a)(1) and 110(a)(2)'' (``2013 Guidance''). The 2013 Guidance states
that these prong 4 requirements can be satisfied by approved SIP
provisions that the EPA has found to adequately address any
contribution of that state's sources that impact the visibility program
requirements in other states.\73\ The 2013 Guidance also states that
``[t]he EPA interprets this prong to be pollutant-specific, such that
the infrastructure SIP submission need only address the potential for
interference with protection of visibility caused by the pollutant
(including precursors) to
[[Page 43970]]
which the new or revised NAAQS applies.'' \74\
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\73\ 2013 Guidance at 32-33.
\74\ Id. at 33.
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The 2013 Guidance lays out how a state's infrastructure SIP may
satisfy prong 4. In the second implementation period, confirmation that
the state has a fully approved regional haze SIP that fully meets the
requirements of 40 CFR 51.308 or 51.309 will satisfy the requirements
of prong 4.\75\ The regulations at 40 CFR 51.308 and 51.309
``specifically require that a state participating in a regional
planning process include all measures needed to achieve its
apportionment of emission reduction obligations agreed upon through
that process.'' \76\ A fully approved regional haze SIP \77\ will
ensure that emissions from sources under an air agency's jurisdiction
are not interfering with measures required to be included in other air
agencies' plans to protect visibility.
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\75\ The EPA acknowledges that in the 2013 Guidance, we
indicated that the EPA may find it appropriate to supplement the
guidance regarding the relationship between regional haze SIPs and
prong 4 after second implementation period SIPs become due, which
occurred on July 31, 2021. After a review of the 2013 Guidance and
the second implementation period regional haze requirements, the EPA
maintains the interpretation that a fully approved regional haze SIP
satisfies prong 4 requirements in the second implementation period.
\76\ 2013 Guidance at 33.
\77\ Since second implementation period SIPs became due, a
``fully approved regional haze SIP'' would necessarily include fully
approved first and second implementation period regional haze SIPs.
---------------------------------------------------------------------------
On October 26, 2015, the EPA revised the 8-hour ozone NAAQS to 70
parts per billion.\78\ States were required to submit infrastructure
SIPs within three years of promulgation of the revised NAAQS. On
October 1, 2018, Montana submitted an infrastructure SIP to address the
CAA section 110(a)(1) and (2) requirements for the 2015 ozone NAAQS
(hereafter ``2018 Infrastructure SIP''). Through this action, the EPA
is proposing to approve the prong 4 portion of Montana's 2018
Infrastructure SIP submission. All other applicable infrastructure SIP
requirements for this submission have been or will be addressed in
separate rulemakings.\79\
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\78\ 80 FR 65929 (October 26, 2015).
\79\ 87 FR 21578 (April 12, 2022), 90 FR 31911 (July 16, 2025).
---------------------------------------------------------------------------
C. Montana's Infrastructure SIP Submission
To satisfy the prong 4 requirements for the 2015 ozone NAAQS,
Montana's 2018 Infrastructure SIP points to their Visibility Plan, and
to the EPA's FIP for the first planning period.\80\ Montana's 2018
Infrastructure SIP cites language from the EPA's 2013 Guidance which
stated that a FIP could not be relied upon to meet the requirements of
element 110(a)(2)(D)(i)(II) related to visibility.\81\ However,
subsequent to Montana's 2018 Infrastructure SIP submission, Montana
submitted a SIP revision addressing regional haze for the first
implementation period to replace portions of EPA's FIP on March 25,
2020. The EPA approved Montana's 2020 SIP submission on June 26,
2023.\82\ As will be discussed further in the following section, the
EPA is proposing to find that the first implementation period
requirements are covered by the EPA's approval of Montana's March 25,
2020 SIP revision.
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\80\ 77 FR 57864 (September 18, 2012).
\81\ Montana's 2018 Infrastructure SIP at 22.
\82\ 88 FR 41320 (June 26, 2023).
---------------------------------------------------------------------------
D. The EPA's Evaluation of Montana's Infrastructure SIP Submission
With this action, the EPA is proposing to approve Montana's 2022
SIP Submission addressing the regional haze requirements for the second
implementation period. Regarding the first implementation period, the
EPA is proposing to find that Montana's SIP is fully approved for the
purposes of meeting the prong 4 requirements. Because Montana's March
25, 2020 SIP submission replaced all of the enforceable requirements
from the 2012 FIP, the entire FIP as previously codified at 40 CFR
52.1396 \83\ was removed.\84\ Specifically, the EPA stated in our June
26, 2023 final approval of Montana's 2020 SIP revision that we were
``approving the emission limits, compliance determination requirements,
and other monitoring, reporting, and recordkeeping requirements
associated with BART into Montana's SIP,'' but that ``other regional
haze requirements for the first implementation period, including
requirements related to reasonable progress and analytical requirements
related to BART remain satisfied by EPA's FIP (with no enforceable FIP
requirements left in the CFR).'' \85\ Although the FIP previously
satisfied certain BART-related requirements for the first
implementation period, the EPA finds that the final 2023 full approval
of all of the enforceable first implementation period requirements into
the Montana SIP represents a fully approved regional haze SIP for that
period that ``will ensure that emissions from sources under an air
agency's jurisdiction are not interfering with measures required to be
included in other air agencies' plans to protect visibility.'' \86\ For
these reasons, the EPA is also proposing to find that Montana's SIP
fulfills the prong 4 requirement for the 2015 ozone NAAQS, and thus
proposes to approve this portion of Montana's 2018 Infrastructure SIP.
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\83\ 77 FR 57915-57919 (September 18, 2012)
\84\ 88 FR 41326 (June 26, 2023).
\85\ 88 FR 41322 (June 26, 2023).
\86\ 2013 Guidance at 33.
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VI. Proposed Action
The EPA is proposing approval of Montana's 2022 SIP submission
addressing the requirements of the second implementation period of the
RHR. Specifically, the EPA is proposing approval for the portions of
Montana's 2022 SIP submission relating to 40 CFR 51.308(f)(1):
calculations of baseline, current, and natural visibility conditions,
progress to date, and the uniform rate of progress; 40 CFR
51.308(f)(2): long-term strategy; 40 CFR 51.308(f)(3): reasonable
progress goals; 40 CFR 51.308(f)(4): reasonably attributable visibility
impairment; 40 CFR 51.308(f)(5) and 40 CFR 51.308(g): progress report
requirements; 40 CFR 51.308(f)(6): monitoring strategy and other
implementation plan requirements; and 40 CFR 51.308(i): FLM
consultation. The EPA is also proposing approval of the CAA section
110(a)(2)(D)(i) prong 4 (visibility) portion of Montana's October 1,
2018 Infrastructure SIP submission addressing the 2015 ozone NAAQS.
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. 42 U.S.C. 7410(k); 40 CFR 52.02(a). Thus, in
reviewing SIP submissions, the EPA's role is to approve state choices,
provided that they meet the criteria of the CAA. Accordingly, this
action merely 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 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
[[Page 43971]]
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, Carbon monoxide,
Greenhouse gases, Incorporation by reference, Intergovernmental
relations, Lead, Nitrogen dioxide, Ozone, Particulate matter, Reporting
and recordkeeping requirements, Sulfur oxides, Volatile organic
compounds.
Authority: 42 U.S.C. 7401 et seq.
Dated: August 28, 2025.
Cyrus M. Western,
Regional Administrator, Region 8.
For the reasons stated in the preamble, the Environmental
Protection Agency proposes to amend 40 CFR part 52 as follows:
PART 52--APPROVAL AND PROMULGATION OF IMPLEMENTATION PLANS
0
1. The authority citation for part 52 continues to read as follows:
Authority: 42 U.S.C. 7401 et seq.
Subpart BB--Montana
0
2. In Sec. 52.1370:
0
a. In the table in paragraph (e):
0
i. Under the center heading ``(1) Statewide'', add the entries
``Montana Regional Haze State Implementation Plan'' and ``Interstate
Transport Requirements of the CAA, section 110(a)(2)(D)(i)(II) prong 4,
for the 2015 Ozone NAAQS'' after the entry ``Interstate Transport
Requirements of the CAA, section 110(a)(2)(D)(i)(I), for the 2015 Ozone
NAAQS'' to read as follows:
Sec. 52.1370 Identification of plan.
* * * * *
(e) * * *
----------------------------------------------------------------------------------------------------------------
State
Title/subject effective Notice of final rule date NFR citation
date
----------------------------------------------------------------------------------------------------------------
(1) Statewide
----------------------------------------------------------------------------------------------------------------
* * * * * * *
Montana Regional Haze State 8/10/2022 [date of publication of the 90 FR [Federal Register
Implementation Plan. final rule in the Federal page where the document
Register]. begins of the final rule].
Interstate Transport Requirements of the 8/22/2018 [date of publication of the 90 FR [Federal Register
CAA, section 110(a)(2)(D)(i)(II) prong final rule in the Federal page where the document
4, for the 2015 Ozone NAAQS. Register]. begins of the final rule].
* * * * * * *
----------------------------------------------------------------------------------------------------------------
[FR Doc. 2025-17499 Filed 9-10-25; 8:45 am]
BILLING CODE 6560-50-P
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