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Proposed Rule2025-13342

Air Plan Partial Approval and Partial Disapproval; Colorado; Regional Haze Plan for the Second Implementation Period

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Published

July 16, 2025

Issuing agencies

Environmental Protection Agency

Abstract

The Environmental Protection Agency (EPA) is proposing to partially approve and partially disapprove a regional haze state implementation plan (SIP) submission submitted by the State of Colorado under the Clean Air Act (CAA) and the EPA's Regional Haze Rule (RHR) for the program's second implementation period. Colorado'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. We propose to base our partial disapproval of Colorado's long-term strategy on its inclusion of insufficiently justified enforceable source closures that are not consistent with statutory requirements. Colorado's 2022 SIP submission also addresses other applicable requirements for the second implementation period of the regional haze program. Concurrently, the EPA is proposing to approve a revision to Colorado's SIP consolidating existing regional haze provisions into the same regulation where the State's new, second planning period provisions are located.

Full Text

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<title>Federal Register, Volume 90 Issue 134 (Wednesday, July 16, 2025)</title>
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[Federal Register Volume 90, Number 134 (Wednesday, July 16, 2025)]
[Proposed Rules]
[Pages 31926-31945]
From the Federal Register Online via the Government Publishing Office [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[FR Doc No: 2025-13342]

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 52

[EPA-R08-OAR-2024-0607; FRL-12598-01-R8]

Air Plan Partial Approval and Partial Disapproval; Colorado;
Regional Haze Plan for the Second Implementation Period

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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SUMMARY: The Environmental Protection Agency (EPA) is proposing to
partially approve and partially disapprove a regional haze state
implementation plan (SIP) submission submitted by the State of Colorado
under the Clean Air Act (CAA) and the EPA's Regional Haze Rule (RHR)
for the program's second implementation period. Colorado'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. We propose to base our
partial disapproval of Colorado's long-term strategy on its inclusion
of insufficiently justified enforceable source closures that are not
consistent with statutory requirements. Colorado's 2022 SIP submission
also addresses other applicable requirements for the second
implementation period of the regional haze program. Concurrently, the
EPA is proposing to approve a revision to Colorado's SIP consolidating
existing regional haze provisions into the same regulation where the
State's new, second planning period provisions are located.

DATES: Written comments must be received on or before September 15,
2025.

ADDRESSES: Submit your comments, identified by Docket ID No. EPA-R08-
OAR-2024-0607, 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,

[[Page 31927]]

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#fd99929f8f9c9593988fd3979c8e918493bd988d9cd39a928b">[email&#160;protected]</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 Colorado's Regional Haze Plan for the First
Implementation Period
D. Colorado'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 Colorado'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. Colorado's Long-Term Strategy Four-Factor Analysis
a. Summary of Colorado's Long-Term Strategy Four-Factor Analysis
b. The EPA's Evaluation of Colorado'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. Proposed Action
VI. Incorporation by Reference
VII. Statutory and Executive Order Reviews

I. What action is the EPA proposing?

Pursuant to CAA section 110(k)(3), the EPA is proposing to
partially approve and partially disapprove a SIP submission submitted
by the State of Colorado to the EPA on May 20, 2022, and supplemented
on August 2, 2022, and June 23, 2023, addressing the requirements of
the second implementation period of the RHR.\1\ Specifically, the EPA
is proposing approval for the portions of Colorado'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)(ii)-(iv): 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.
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\1\ The EPA may partially approve portions of a submittal if
those elements meet all applicable requirements and may disapprove
the remainder so long as the elements are fully separable. See CAA
section 110(k)(3) and July 1992 EPA memorandum titled ``Processing
of State Implementation Plan (SIP) Submittals'' from John Calcagni,
at <a href="https://www.epa.gov/sites/default/files/2015-07/documents/procsip.pdf">https://www.epa.gov/sites/default/files/2015-07/documents/procsip.pdf</a>. The EPA proposes to conclude that the elements at issue
are fully separable, as described in greater detail later in this
preamble.
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For the reasons described in section IV.C.1.b. of this document,
the EPA is proposing to disapprove portions of Colorado's 2022 SIP
submission relating to 40 CFR 51.308(f)(2)(i). The submission relies on
enforceable source closures that the EPA proposes to disapprove on the
basis that they were adopted without full information about grid
reliability concerns, particularly because the Class I areas Colorado
emissions contribute to are below the Uniform Rate of Progress and the
state conducted four-factor analyses. The EPA also proposes to find
that the State has not provided necessary assurances required by CAA
section 110(a)(2)(E) that unconsented enforceable source closures would
not be prohibited by state or federal law.
Concurrently, the EPA is proposing to approve a revision to
Colorado's SIP consolidating existing regional haze provisions into the
same regulation where the State's new, second planning period
provisions are located. Together, these SIP revisions establish updated
emission reduction requirements for nitrogen oxides (NO<INF>X</INF>),
sulfur dioxide (SO<INF>2</INF>), and particulate matter (PM) emissions
from certain sources identified as impacting Class I areas under the
RHR for the second 10-year planning period.\2\
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\2\ The EPA uses the terms ``implementation period'' and
``planning period'' interchangeably.
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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.\3\ For additional
background on the 2017 RHR revisions, please refer to section III.
Overview of Visibility Protection Statutory Authority, Regulation, and
Implementation of ``Protection of Visibility: Amendments to
Requirements for State Plans'' of the 2017 RHR.\4\ 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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\3\ See 90 FR 13516 (March 24, 2025).
\4\ 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.\5\ 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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\5\ 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

[[Page 31928]]

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., SO<INF>2</INF>,
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.\6\
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\6\ 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-1). The formula for the deciview is 10 ln (b\ext\)/10
Mm-1). 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.\7\ The
federal partner members of WRAP are the EPA, U.S. National Parks
Service (NPS), U.S. Fish and Wildlife Service (USFWS), U.S. Forest
Service (USFS), and the Bureau of Land Management (BLM). 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. Colorado collaborated with WRAP on various aspects of the
State's 2022 SIP submission, including the identification of Class I
areas outside of Colorado 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.
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\7\ 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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C. Status of Colorado'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 Best Available
Retrofit Technology (BART) requirements for certain older stationary
sources, where applicable.\8\ On December 31, 2012, the EPA approved a
regional haze SIP revision submitted May 25, 2011, by the State of
Colorado as meeting the requirements of the CAA and RHR.\9\ On February
25, 2013, the National Parks Conservation Association (NPCA) and Wild
Earth Guardians (Guardians) filed petitions for review in the U.S.
Court of Appeals for the Tenth Circuit of the EPA's final approval of
the Colorado regional haze SIP.\10\ Among other things, Guardians and
NPCA challenged the NO<INF>X</INF> BART limit for Craig Unit 1. The
parties settled the challenge regarding Craig Unit 1.\11\ Separately,
on May 26, 2015, the EPA reissued its final approval of the May 25,
2011, SIP submission with respect to the State's BART determination for
the Comanche Generating Station in response to a petition for review
and as part of a voluntary remand, without vacatur, to more adequately
respond to public comments concerning the Comanche Generating
Station.\12\
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\8\ Requirements for regional haze SIPs for the first
implementation period are also contained in CAA section 169A(b)(2).
\9\ 77 FR 76871 (December 31, 2012).
\10\ WildEarth Guardians v. EPA, No. 13-9520 (10th Cir.) and
National Parks Conservation Association v. EPA, No. 13-9525 (10th
Cir.).
\11\ Following that settlement, on July 5, 2018, the EPA
approved a SIP revision to include source-specific revisions to the
NO<INF>X</INF> BART determination for Craig Station Unit 1 and to
the NO<INF>X</INF> reasonable progress determination for the Nucla
Station. 83 FR 31332 (July 5, 2018).
\12\ 80 FR 29953 (May 26, 2015).
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D. Colorado's Regional Haze Plan for the Second Implementation Period

On May 20, 2022, Colorado submitted a SIP submission to address its
regional haze obligations for the second implementation period (2018-
2028). Colorado'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

[[Page 31929]]

examined the need to implement additional enforceable emission
limitations, compliance schedules, and other measures that may be
necessary to make reasonable progress since the first implementation
period. Specifically, Colorado'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 the twelve Class I areas the State identified,
including: Colorado'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,
Colorado's determinations on what control measures are necessary for
the long-term strategy to address regional haze visibility impairment
in the twelve Class I areas. The State concluded that additional
emission reduction measures for Colorado facilities are required for
the second implementation period under its long-term strategy.
On May 20, 2022, Colorado submitted a separate SIP submission to
move the regional haze provisions currently contained in Regulation
Number 3 to Regulation Number 23. The Colorado Air Quality Control
Commission previously approved regional haze requirements under
Regulation Number 3, which included emission reduction requirements for
sources subject to BART and reasonable progress determinations during
the first planning period of the regional haze program. As part of
Colorado's 2022 SIP submission, the State adopted revisions to
Regulation Number 3 (Part F) to the newly created Regulation Number 23
which will serve as the central repository for new and existing
provisions that comply with the RHR. Regulation Number 23 includes BART
and reasonable progress determinations from the first planning period
as well as emission reduction requirements to meet the reasonable
progress goals for the second 10-year planning period.

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 \13\ and (f)(4)
through (6) containing additional, related requirements.
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\13\ 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'' \14\ that states must consider in
developing their long-term strategies. See 40 CFR 51.308(f)(2). A 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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\14\ 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 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.\15\ This is

[[Page 31930]]

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,\16\ 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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\15\ 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.
\16\ ``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.\17\ 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 measure for inclusion in
its long-term strategy.''
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\17\ 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 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

[[Page 31931]]

[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 Colorado's Regional Haze Plan for the
Second Implementation Period

In section IV of this document, we describe Colorado'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 of visibility'' in
a Class I area to have a plan for making reasonable progress toward the
national visibility goal. The RHR implements this statutory requirement
at 40 CFR 51.308(f), which provides that each state's plan ``must
address regional haze in each mandatory Class I Federal area located
within the State and in each mandatory Class I Federal area located
outside the State that may be affected by emissions from within the
State,'' and (f)(2), which requires each state's plan to include a
long-term strategy that addresses regional haze in such Class I areas.
There are twelve designated Class I areas within the State of
Colorado, including four national parks managed by the U.S. National
Park Service (Black Canyon of the Gunnison National Park, Great Sand
Dunes National Park, Mesa Verde National Park, Rocky Mountain National
Park) and eight wilderness areas managed by the U.S. Forest Service
(Eagles Nest Wilderness Area, Flat Tops Wilderness Area, La Garita
Wilderness Area, Maroon Bells-Snowmass Wilderness Area, Mount Zirkel
Wilderness Area, Rawah Wilderness Area, Weminuche Wilderness Area, West
Elk Wilderness Area).\18\
---------------------------------------------------------------------------

\18\ Colorado 2022 SIP submission at 7.
---------------------------------------------------------------------------

Using the 2021 Particulate Source Apportionment Technology (PSAT)
product from the WRAP, Colorado identified five Class I areas outside
the State where visibility may be affected by Colorado sources:
Canyonland National Park in Utah (9.4%), Capitol Reef National Park in
Utah (3.6%), Badlands National Park in South Dakota (7.5%), Wind Cave
National Park in South Dakota (2.9%), and Wheeler Peak Wilderness in
New Mexico (4.1%) based on combined percentages of nitrate + sulfate
impairment at these Class I areas from Colorado sources. The State
further highlighted that these Class I areas also experience visibility
impairment due to five other aerosol species (sea salt, elemental
carbon, organic carbon, fine soil, and coarse mass) which were not
included in the 2021 PSAT modeling the State relied on to determine its
contributions to Class I areas outside of the State.\19\ Therefore,
according to the State, Colorado's contribution to overall light
extinction is less than the results of the 2021 PSAT modeling which
only

[[Page 31932]]

evaluated nitrate + sulfate impairment. Furthermore, Colorado notes
that the already announced retirements of coal-fired power plants
driven by Colorado state rules and associated with the State's regional
haze long-term strategy and incorporated into the SIP, along with state
regulations for ozone, greenhouse gases, and other regulatory programs
not part of the State's regional haze long-term strategy, will further
reduce nitrate and sulfate contributions from Colorado sources.\20\
Because Colorado addressed regional haze visibility impairment for each
Class I area within the State, and each mandatory Class I area located
outside the State that may be affected by emissions from the State, we
find that Colorado did not unreasonably exclude any Class I areas from
its analysis.
---------------------------------------------------------------------------

\19\ Colorado 2022 SIP submission at 142.
\20\ Colorado 2022 SIP submission at 142.
---------------------------------------------------------------------------

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. Colorado's 2022 SIP
submission provides visibility conditions for each IMPROVE monitor and
associated Class I area in Colorado (table 1).\21\
---------------------------------------------------------------------------

\21\ Colorado 2022 SIP submission at 21-22 and 157.

Table 1--Visibility Conditions (Deciviews) for Colorado IMPROVE Stations
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Difference
between
Baseline Period (2008- Current Natural Progress since baseline Progress during last current (2014-
Monitor ID Class I areas (2000-2004) 2012) (2014-2018) (2064) (2000-2004)--(2014-2018) implementation period 2018) and
\1\ (2008-2012)-(2014-2018) natural (2064)

------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Most Impaired Days
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
GRSA1............................... Great Sand Dunes.................. 9.66 8.88 8.02 4.45 -1.64 -0.86 3.57
MEVE1............................... Mesa Verde........................ 9.22 8.13 6.51 4.20 -2.71 -1.62 2.31
MOZI1............................... Mount Zirkel, Rawah............... 7.29 6.26 5.47 3.16 -1.82 -0.79 2.31
ROMO1............................... Rocky Moutain National Park....... 11.12 9.36 8.41 4.94 -2.71 -0.95 3.47
WEMI1............................... Weminuche, La Garita, Black Canyon 7.78 6.94 6.55 3.97 -1.23 -0.38 2.58
of Gunnison.
WHRI1............................... Eagles Nest, Flat Tops, Maroon 6.30 5.89 4.98 3.02 -1.32 -0.91 1.96
Bells, White River, West Elk.
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Clearest Days
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
GRSA1............................... Great Sand Dunes.................. 4.50 3.65 2.74 1.24 -1.76 -0.91 1.5
MEVE1............................... Mesa Verde........................ 4.32 2.96 2.28 1.02 -2.04 -0.68 1.26
MOZI1............................... Mount Zirkel, Rawah............... 1.61 0.49 0.23 -0.47 -1.38 -0.26 0.7
ROMO1............................... Rocky Moutain National Park....... 2.29 1.69 1.37 0.28 -0.92 -0.32 1.09
WEMI1............................... Weminuche, La Garita, Black Canyon 3.11 2.11 1.61 0.98 -1.5 -0.50 0.63
of Gunnison.
WHRI1............................... Eagles Nest, Flat Tops, Maroon 0.70 0.04 -0.16 -0.81 -0.86 -0.20 0.65
Bells, White River, West Elk.
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
\1\ Natural visibility conditions for the clearest days from EPA Memo, Data for regional haze technical addendum. June 3, 2020.

The State also determined the uniform rate of progress for the most
impaired and clearest days for Colorado Class I areas.\22\ Colorado
also provided haze indices and the uniform rate of progress for IMPROVE
monitors and associated Class I areas outside the State.\23\
---------------------------------------------------------------------------

\22\ Colorado 2022 SIP submission at 27, 42.
\23\ Colorado 2022 SIP submission at 18-28.
---------------------------------------------------------------------------

Based on the information provided in Colorado's 2022 SIP
submission, the EPA is proposing to approve the State's visibility
condition calculations for Great Sand Dunes, Mesa Verde, Mount Zirkel,
Rawah, Rocky Mountain National Park, Weminuche, La Garita, Black Canyon
of the Gunnison, Eagles Nest, Flat Tops, Maroon Bells, White River, and
West Elk \24\ 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.
---------------------------------------------------------------------------

\24\ Mount Zirkel and Rawah are subject to the same visibility
calculation. Weminuche, La Garita, and Black Canyon of the Gunnison
are subject to the same visibility calculation. Eagles Nest, Flat
Tops, Maroon Bells, White River, and West Elk 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 a Class I area must develop a long-term
strategy for making reasonable progress towards the national visibility
goal. CAA section 169A(b)(2)(B). 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., subjected 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).

[[Page 31933]]

1. Colorado's Long-Term Strategy Four-Factor Analysis
a. Summary of Colorado's Long-Term Strategy Four-Factor Analysis
Colorado identified twelve Class I areas that must be addressed in
its long-term strategy.\25\ 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. Colorado 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.
---------------------------------------------------------------------------

\25\ Colorado 2022 SIP submission at 7.
---------------------------------------------------------------------------

Specifically, the WRAP Reasonable Progress Screening protocol
recommends a three-step process for screening sources that involves an
initial screening of identifying stationary sources that emit combined
NO<INF>X</INF>, SO<INF>2</INF>, SO<INF>4</INF>, and PM<INF>10</INF>
emissions of over 25 tons/year, a secondary screening of assessing the
Q/d for those stationary sources to determine whether a source Q/d
exceeds ``10'' for a specific Class I area, and the use of the 2028
Weighted Emissions Potential (WEP) to determine the possible
contribution of the source to visibility impairment in Class I areas
for the 20% most impaired days. Using the WRAP-devised screening
threshold of Q/d > 10 and emissions information from the 2014 National
Emission Inventory (NEI), Colorado initially identified twenty-three
sources in the State that may be affecting visibility at Class I areas
in Colorado.26 27 The State reduced the number of facilities
subject to a reasonable progress four-factor analysis to nineteen
because two facilities have actual emissions below the WRAP screening
protocol's threshold of 25 tons/year, one coal mine closed in 2015, and
two adjacent coal mines were combined into one facility.\28\
Ultimately, the State selected nineteen sources subject to a four-
factor analysis (table 2).\29\
---------------------------------------------------------------------------

\26\ Colorado 2022 SIP submission at 51.
\27\ WRAP Reasonable Progress Source Identification and Analysis
Protocol For Second 10-year Regional Haze State Implementation
Plans. February 27, 2019.
\28\ Colorado 2022 SIP submission at 51. The WRAP RP Screening
protocol recommends a three step process for screening sources that
involves (1) identifying stationary sources with combined
NO<INF>X</INF>, SO<INF>2</INF>, SO<INF>4</INF>, and PM<INF>10</INF>
emissions of over 25 tons/year, (2) assessing the Q/d for those
stationary sources to determine whether a source Q/d exceeds ``10''
for a specific Class I area and (3) using the 2028 Weighted
Emissions Potential (WEP) to confirm whether the identified source
is located in a grid cell that impacts the specific Class I area for
the 20% most impaired days.
\29\ Colorado 2022 SIP submission at 52.

Table 2--Facilities Screened in Using Q/d
----------------------------------------------------------------------------------------------------------------
(d) Minimum of (Q) Maximum of
Facility name Closest Class I area distance (km) to emissions (tons/ Q/d
Class I area year)
----------------------------------------------------------------------------------------------------------------
Craig Power Plant (Tri-State Flat Tops Wilderness...... 47.85 17,665.13 369.17
Generation).
Hayden Power Plant (Public Service Mount Zirkel Wilderness... 31.59 8,435.17 267.04
Co).
Cherokee Power Plant (Public Rocky Mountain National 65.09 8,194.22 125.89
Service Co). Park.
Comanche Power Plant (Public Great Sand Dunes 91.63 8,101.48 88.42
Service Co). Wilderness.
Valmont Power Plant \1\ (Public Rocky Mountain National 34.69 2,986.64 86.10
Service Co). Park.
Lyons Cement Kiln (Cemex Rocky Mountain National 24.74 1,193.48 48.25
Construction Materials). Park.
Pawnee Power Plant (Public Service Rocky Mountain National 155.67 7,340.60 47.15
Co). Park.
Nixon Power Plant (Colorado Great Sand Dunes 113.48 5,350.98 47.15
Springs Utilities). Wilderness.
Rawhide Power Plant (Platte River Rocky Mountain National 56.45 2,438.39 43.20
Power Authority). Park.
Martin Drake Power Plant \2\ Great Sand Dunes 125.41 5,214.47 41.58
(Colorado Springs Utilities). Wilderness.
Denver International Airport \3\.. Rocky Mountain National 82.84 3,112.60 37.57
Park.
Molson Coors Boiler Support Rocky Mountain National 54.23 1,825.35 33.66
Facility \4\. Park.
Nucla Power Plant \5\ (Tri State Black Canyon of the 70.53 1,619.96 22.97
Generation). Gunnison Wilderness.
Portland Plant (Holicm (Us) Inc.). Great Sand Dunes 75.39 1,548.00 20.53
Wilderness.
Denver Refinery (Suncor Energy)... Rocky Mountain National 67.03 1,278.79 19.08
Park.
South Taylor Mine/Colorado Mine Flat Tops Wilderness...... 40.44/39.29 685.00/652.92 16.94/16.62
(Colowyo Coal Co.).
Pueblo Cement Plant (GCC Rio Great Sand Dunes 85.31 1,080.60 12.67
Grande). Wilderness.
Rocky Mountain Bottle Company..... Rocky Mountain National 56.97 712.94 12.51
Park.
Evraz Rocky Mountain Steel Mill... Great Sand Dunes 90.41 967.11 10.70
Wilderness.
----------------------------------------------------------------------------------------------------------------
\1\ Valmont Power Plant closed in September 2017.
\2\ Martin Drake Unit 5 closed in January 2017.
\3\ After reviewing emissions for the point sources, Colorado determined that emissions from each point fell
below the 10 tons/year for a full analysis of additional control options. Therefore, no point sources were
subject to a full emissions control analysis.
\4\ The Molson Coors Boiler Support Facility was formerly the Colorado Energy Nations Company (CENC).
\5\ Nucla Power Plant closed in September 2019.

The State requested that each of the nineteen sources submit cost
information for its review and consideration.\30\ For three of these
sources, the State determined that it was not necessary to conduct
further review because those sources had closed prior to the State's
development of its SIP.\31\ For the remaining sources, Colorado then
evaluated what is necessary to make reasonable progress by considering
the four statutory factors \32\ for each source:
---------------------------------------------------------------------------

\30\ Colorado 2022 SIP submission at 52.
\31\ Martin Drake Unit 5, Nucla, and Valmont.
\32\ 40 CFR 51.308(f)(2)(i)
---------------------------------------------------------------------------

<bullet> Cost of compliance;
<bullet> Time necessary for compliance;

[[Page 31934]]

<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 Colorado's 2022 SIP
submission and associated technical support documents. Chapter 7 of the
SIP submission contains Colorado's evaluation of the four statutory
factors for each source and Colorado's determinations of the source-
specific emission reduction measures necessary to make reasonable
progress. As part of its four-factor evaluation, Colorado considered
the already announced retirements of several units and facilities as
part of its ``remaining useful life'' analysis and incorporated those
retirements into the SIP.\33\ Ultimately, the State concluded that the
following enforceable reasonable progress source retirements (table 3)
and emission limits (table 4) satisfy and exceed regional haze
requirements for the second implementation period and that no other
regional haze analyses or regional haze controls will be required by
the State during the second regional haze implementation period.
---------------------------------------------------------------------------

\33\ Colorado 2022 SIP submission at 56.
\34\ Colorado Regulation Number 23, Part A, IV.F.1.
\35\ Colorado Regulation Number 23, Part A, IV.F.3.

Table 3--Reasonable Progress Determinations for the Second Implementation Period in the Colorado Regional Haze
SIP--Source Closures \34\
----------------------------------------------------------------------------------------------------------------
Emission unit Closure date Additional requirements/notes
----------------------------------------------------------------------------------------------------------------
Rawhide Unit 1.......................... December 31, 2029.......... Maintain existing emission limits until
closure.
Martin Drake Unit 6..................... December 31, 2022.......... Maintain existing emission limits until
closure.
Martin Drake Unit 7..................... December 31, 2022.......... Maintain existing emission limits until
closure.
Nixon Unit 1............................ December 31, 2029.......... Maintain existing emission limits until
closure.
Nixon Coal Handling..................... December 31, 2029.......... Cessation of coal unloading and crushing.
Comanche Unit 1......................... December 31, 2022.......... Maintain existing emission limits until
closure.
Comanche Unit 2......................... December 31, 2025.......... Maintain existing emission limits until
closure. Comply with additional NOX and
SO2 limits when Comanche Unit 1 closes--
see table 4.
Hayden Unit 1........................... December 31, 2028.......... Maintain existing emission limits until
closure.
Hayden Unit 2........................... December 31, 2027.......... Maintain existing emission limits until
closure.
Craig Unit 2............................ September 30, 2028......... Maintain existing emission limits until
closure.
Craig Unit 3............................ December 31, 2029.......... Maintain existing emission limits until
closure.
ColoWyo Coal Mine....................... December 31, 2031.......... Not applicable.
Cherokee Unit 4......................... December 31, 2028.......... Maintain existing emission limits until
closure.
----------------------------------------------------------------------------------------------------------------

Table 4--Reasonable Progress Determinations for the Second Implementation Period in the Colorado Regional Haze
SIP--Emissions Limits \35\
----------------------------------------------------------------------------------------------------------------
Emission unit NOX emission limit SO2 emission limit PM emission limit
----------------------------------------------------------------------------------------------------------------
Nixon Coal Handling.................. N/A \1\................ N/A \1\................ 1.46 tons PM10 per
year, unloading,
transfer, conveying,
processing, and
crushing (12-month
rolling total).
Cessation of coal
unloading and crushing
no later than 12/31/
2029.
Nixon--Front Range Power Plant 111 ppmvd at 15% O2 (4- N/A \2\................ N/A.\2\
Turbine 1 and Turbine 2. hour rolling average).
Nixon--Clear Spring Ranch Solids N/A \2\................ 186.4 lb/hr (12-month N/A.\2\
Handling and Disposal Facility rolling calculation).
(SDHF). 52.20 tons/year (12-
month rolling total)..
5,000 ppmv H2S in
digester gas..
Comanche Unit 2 \3\.................. 0.20 lb/MMBtu (30-day 0.12 lb.MMBtu (30-day .......................
rolling average). rolling average).
3,050 tons/year (12- 1,830 tons/year (12-
month rolling average). month rolling average).
Comanche Unit 3...................... 0.08 lb/MMBtu (30-day 0.10 lb/MMBtu (30-day 0.02 lb/MMBtu.
rolling average). rolling average). 0.012 lb/MMBtu (24-hour
0.07 lb/MMBtu (annual average).
average).
Hayden Coal Ash Handling and Disposal N/A \1\................ N/A \1\................ 22.39 tons/year from
and Unpaved Roads. coal ash, sorbent
loading, unloading
only (12-month rolling
total).
Cherokee Turbine 5................... Applicable limits in 40 N/A \2\................ 0.1 lb/MMBtu.
CFR 60.4300 Table 1
(NSPS KKKK).
Cherokee Turbine 6................... Applicable limits in 40 N/A \2\................ 0.1 lb/MMBtu.
CFR 60.4300 Table 1
(NSPS KKKK).
Pawnee Unit 1........................ 0.07 lb/MMBtu (30-day 0.11 lb/MMBtu (30-day 0.03 lb/MMBtu.
rolling average). rolling average).
Pawnee Cooling Tower................. N/A \1\................ N/A \1\................ 36.5 tons/year (12-
month rolling total).
Manchief Turbine 1................... 15 ppmvd at 15% O2 (1- N/A \2\................ N/A.\2\
hr average).
100 ppmvd at 15% O2 and
186 lb/hr during
startup (1-hour
average).
100 ppmvd at 15% O2 and
140 lb/hr during
shutdown (1-hour
average).
25 ppmvd at 15% O2 low
load operation between
March 1 and October 31
(1-hour average).

[[Page 31935]]

Manchief Turbine 2................... 15 ppmvd at 15% O2 (1- N/A \2\................ N/A.\2\
hr average).
100 ppmvd at 15% O2 and
186 lb/hr during
startup (1-hour
average).
100 ppmvd at 15% O2 and
140 lb/hr during
shutdown (1-hour
average).
25 ppmvd at 15% O2 low
load operation between
March 1 and October 31
(1-hour average).
CEMEX Lyons Kiln..................... 1.85 lb/ton of clinker 25.3 lb/hour (12-month N/A.\2\
(30-day rolling rolling average).
average). 95.0 tons/year (12-
901.0 tons/year (12- month rolling total)..
month rolling average).
CEMEX Dowe Flats and Lyons Quarries.. N/A \1\................ N/A \1\................ 58.4 tons/year (Dowe
Flats Quarry, 12-month
rolling total).
Current permitted limit
for Lyons Quarry below
10 tons/year screening
threshold.
CEMEX Raw Materials Grinding......... N/A \1\................ N/A \1\................ Reporting based on the
following factors:
S010 (Raw Mill)--0.012
lb/ton of clinker
S011 (Raw Mill Air
Separator)--0.032 lb/
ton of clinker.
S012 (Raw Mill Weigh
Feeders)--0.019 lb/ton
of clinker.
S013 (Iron/Silica Feed
Belt--0.0031 lb/ton of
clinker).
Holcim Florence Kiln................. 2.73 lb/ton of clinker 1.3 lb/ton of clinker 247.6 tons/year (12-
(30-day rolling (30-day rolling month rolling total).
average). average).
2,086.8 tons/year (12- 721.4 tons/year (12-
month rolling total). month rolling total).
Holcim Florence Quarry............... N/A \2\................ N/A \2\................ 67.3 tons/year (12-
month rolling total).
Holcim Florence Finish Mill.......... N/A \1\................ N/A \1\................ 34.3 tons/year (12-
month rolling total).
GCC Pueblo Kiln...................... 2.70 lb/ton of clinker N/A \2\................ 36.01 tons/year
(30-day rolling (Filterable, 12-month
average). rolling total).
2.32 lb/ton of clinker 293.56 tons/year
(12-month rolling (Condensable, 12-month
average). rolling total).
1,100 tons/year (12-
month rolling average).
GCC Pueblo Clinker Cooler............ N/A \1\................ N/A \1\................ 33.92 tons/year (12-
month rolling total).
Molson Coors Boiler Support Facility 0.20 lb/MMBtu.......... N/A \2\................ N/A.\2\
Boiler 1. 625.4 tons/year
(Combined 12-month
rolling total for
Boilers 1, 2, 4, and
5).
Molson Coors Boiler Support Facility 0.20 lb/MMBtu.......... N/A \2\................ N/A.\2\
Boiler 2. 625.4 tons/year
(Combined 12-month
rolling total for
Boilers 1, 2, 4, and
5).
Molson Coors Boiler Support Facility 0.12 lb/MMBtu (30-day N/A \2\................ N/A.\2\
Boiler 4. rolling average).
242.9 tons/year (12-
month rolling total,
Boiler 4 only).
625.4 tons/year
(Combined 12-month
rolling total for
Boilers 1, 2, 4, and
5).
Molson Coors Boiler Support Facility 0.10 lb/MMBtu (30-day N/A \2\................ N/A.\2\
Boiler 5. rolling average).
256.3 tons/year (12-
month rolling total,
Boiler 5 only).
625.4 tons/year
(Combined 12-month
rolling total for
Boilers 1, 2, 4, and
5).
EVRAZ Electric Arc Furnace (EAF)..... 0.28 lb/ton of steel 0.15 lb/ton of steel 0.0018 grains/dscf
(30-day rolling (30-day rolling (filterable).
average). average). 0.0052 grains/dscf
189.0 tons/year (12- 101.25 tons/year (12- (filterable+condensabl
month rolling total). month rolling total). e).
163.11 tons/year (12-
month rolling total).
EVRAZ Ladle Metallurgy Station (LMS). 84.1 tons/year (12- 2 tons/day (3-hour N/A.\2\
month rolling total). rolling average).
234.3 tons/year (12-
month rolling total).
EVRAZ Round Caster................... 35.6 tons/year (12- N/A \2\................ 19.10 tons/year (12-
month rolling total). month rolling total).
EVRAZ Seamless Mill Rotary Furnace... 169.26 tons/year (12- N/A \2\................ N/A.\2\
month rolling total).
EVRAZ Seamless Mill Quench Furnace... Reporting based on 280 N/A \2\................ N/A.\2\
lbs/MMscf AP-42
emission factor.
EVRAZ Seamless Mill Tempering Furnace Reporting based on 280 N/A \2\................ N/A.\2\
lbs/MMscf AP-42
emission factor.
EVRAZ Rod/Bar Mill Furnace........... 0.07 lb/MMBtu.......... N/A \2\................ N/A.\2\
30.28 tons/year (12-
month rolling total).
EVRAZ Rail Mill Furnace.............. 0.07 lb/MMBtu (30-day N/A \2\................ N/A.\2\
rolling average).
32.34 tons/year (12-
month rolling total).
EVRAZ Haul Roads..................... N/A \1\................ N/A \1\................ Compliance with
Fugitive Dust Control
Plan.
EVRAZ Vacuum Tank Degasser Boiler.... 16.21 tons/year (12- N/A \2\................ N/A.\2\
month rolling total).
EVRAZ Ladle Preheaters............... 23.91 tons/year (12- N/A \2\................ N/A.\2\
month rolling total,
combined for 6
preheaters).

[[Page 31936]]

Rocky Mountain Bottle Company 157.8 tons/year (12- 114.8 tons/year (12- 0.27 lb/ton of glass
Furnaces B+ and C (common stack). month rolling total). month rolling total). (Performance testing
every 5 years).
38.7 tons/year
(filterable +
condensable, 12-month
rolling total).
Suncor Plant 1 Fluidized Catalytic 58.7 ppmvd at 0% O2 25 ppmvd at 0% O2 (365- 85.4 tons/year (12-
Cracking Unit Catalyst Regenerator (365-day rolling day rolling average). month rolling total).
(FCCU). average).
Suncor Plant 2 Fluidized Catalytic 160 ppmvd at 0% O2 (7- 37.2 ppmvd at 0% O2 53.1 tons/year (12-
Cracking Unit Catalyst Regenerator day rolling average). (365-day rolling month rolling total).
(FCCU). 80 ppmvd at 0% O2 (365- average).
day rolling average).
Suncor Plant 1 Sulfur Recovery Unit N/A \2\................ 59.7 tons/year (12- N/A.\2\
Tail Gas Unit (SRC TGU). month rolling total).
Suncor Plant 2 Sulfur Recovery Unit N/A \2\................ 1.20% volume SO2 (12- N/A.\2\
Tail Gas Incinerator (SRC TGI). hour rolling average)
\4\.
271 tons/year (12-month
rolling total)..
120 tons/year (12-month
rolling total).\5\.
Optimization no later
than 12/31/2023 and
compliance with 12-
month rolling total 12
months after
optimization is
complete and no later
than 12/31/2024.
Application for permit
modifications and
limits based on
operating data no
later than 18 months
after optimization
project implementation
or comply with
alternative.\6\.
Suncor Plant 1 Main Plant Flare...... ....................... 162 ppmv H2S (3-hour N/A.\2\
rolling average).
Suncor Heater H-11................... 12.78 tons/year (12- N/A \2\................ N/A.\2\
month rolling total).
Suncor Heater H-17................... 24.83 tons/year (12- N/A \2\................ N/A.\2\
month rolling total).
Suncor Heater H-27................... 32.84 tons/year (12- N/A \2\................ N/A.\2\
month rolling total).
Suncor Heater H-28/29/30............. 20.40 tons/year (12- N/A \2\................ N/A.\2\
month rolling total).
Suncor Heater H-37................... 10.41 tons/year (12- N/A \2\................ N/A.\2\
month rolling total).
Suncor Heater H-101.................. 55.85 tons/year (12- N/A \2\................ N/A.\2\
month rolling total).
Suncor Heater H-402.................. 21.16 tons/year (12- N/A \2\................ N/A.\2\
month rolling total).
Suncor Heater H-2101................. 52.19 tons/year (12- N/A \2\................ N/A.\2\
month rolling total).
Suncor Boiler 4...................... 0.06 lb/MMBtu (30-day N/A \2\................ N/A.\2\
rolling average).
Suncor Boiler 505.................... 0.044 lb/MMBtu (30-day N/A \2\................ N/A.\2\
rolling average).
----------------------------------------------------------------------------------------------------------------
\1\ This pollutant is not emitted.
\2\ Emissions did not meet the screening threshold. Thus, this unit was not subject to a four-factor analysis
for this pollutant.
\3\ Compliance with NOX and SO2 emission limits beginning when Comanche Unit 1 closes and until Comanche Unit 2
closes.
\4\ Beginning February 14, 2022, the Plant 2 sulfur recovery unit tail gas incinerator will meet a 1.20% volume
SO2 (12-hour rolling average) and an annual SO2 limit of 271 tons per year (12-month rolling total).
\5\ The owner/operator must implement optimization of air flow through the Plant 2 sulfur recovery unit no later
than December 31, 2023. The Plant 2 sulfur recovery unit tail gas incinerator will meet an SO2 limit of 120
tons per year (12 month rolling total) within twelve (12) months after optimization and by no later than
December 31, 2024.
\6\ Alternative for Suncor Plant 2 sulfur recovery unit tail gas incinerator: If the owner/operator fails to
implement air flow optimization or fails to achieve the limit by the specified timeline, the owner/operator
will install SUPERCLAUS 2+1 on the sulfur recovery unit by no later than December 31, 2028. The sulfur
recovery unit must achieve at least a 98.65% sulfur recovery efficiency, by no later than December 31, 2029.
The sulfur recovery unit tail gas incinerator will meet an SO2 limit of 120 tons per year (12-month rolling
total) within twelve (12) months after SUPERCLAUS 2+1 installation and by no later than December 31, 2029.

According to Colorado's 2022 SIP submission, each source must
comply as expeditiously as practicable with the limits and averaging
times, record keeping, and reporting requirements in addition to its
applicable permit requirements, but in no event later than five years
after EPA approval of Colorado's 2022 SIP submission.\36\
---------------------------------------------------------------------------

\36\ Colorado Regulation Number 23, Part A, IV.F.4.
---------------------------------------------------------------------------

Section 51.308(f)(2) of the RHR requires states to include in their
SIPs the enforceable emission limitations, compliance schedules, and
other measures necessary to make reasonable progress. In addition to
what is required by the RHR, general SIP requirements mandate that the
SIP must also include adequate monitoring, recordkeeping, and reporting
requirements for the regional haze emission limits and requirements.
(See CAA section 110(a)). Colorado's 2022 SIP submission requires that
sources maintain control equipment or operational practices required to
comply with the limits and averaging times, recordkeeping, and
reporting requirements, and establish procedures to ensure that such
equipment or operational practices are properly operated and
maintained.\37\ Tables 3 and 4 specify reasonable progress emission
limits and compliance schedules found in Colorado Regulation Number 23,
Part A, IV. Regional Haze Determinations, which was submitted as part
of Colorado's 2022 SIP submission.
---------------------------------------------------------------------------

\37\ Id.
---------------------------------------------------------------------------

Colorado's 2022 SIP submission also included Colorado Regulation
Number 23, Part A, V. Monitoring, Recordkeeping, and Reporting for
Regional Haze Limits which specifies the monitoring, recordkeeping, and
reporting requirements for the State's regional haze determinations.
Specifically, for NO<INF>X</INF> and SO<INF>2</INF> emission limits,
sources with continuous emission monitoring systems (CEMS) must operate
and maintain CEMS in accordance with relevant EPA regulations, in
particular, 40 CFR part 75 or 40 CFR part 60. Sources without
NO<INF>X</INF> and SO<INF>2</INF> emission CEMS are required to use
stack testing, fuel sampling, fuel consumption, and associated emission
factors, as applicable, and in accordance with EPA and ASTM test
methods. For PM emission limits, sources must perform testing in
accordance with EPA approved test methods, in particular, 40 CFR part
60 or 40 CFR part 63, and

[[Page 31937]]

other PM monitoring/compliance determinations, as applicable, including
compliance assurance monitoring plans developed and approved in
accordance with 40 CFR part 64. In addition, sources must keep relevant
records for five years and report relevant emissions.
b. The EPA's Evaluation of Colorado'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 Colorado's 2022 SIP
submission satisfies the requirements of 40 CFR 51.308(f)(2)(i) insofar
as Colorado's selection of nineteen sources, evaluation of the cost of
compliance, time necessary for compliance, remaining useful life of any
potentially affected sources statutory factors, and determinations of
the emission reductions necessary to make reasonable progress contained
in table 4 of section IV.C.1.a of this document, were reasonable.
However, we find that Colorado's long-term strategy does not adequately
consider the ``energy and nonair quality environmental impacts of
compliance'' statutory factor as it pertains to the enforceable source
closures contained in table 3 of section IV.C.1.a. of this document.
With respect to source selection, Colorado followed and provided a
detailed description of the WRAP Reasonable Progress Screening protocol
the State used to determine sources subject to four-factor
analysis.\39\ Applying this protocol, Colorado selected nineteen
sources for 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). In addition, states may rely on technical
information developed by the RPOs of which they are members to select
sources for four-factor analysis and to conduct that analysis, as well
as to satisfy the documentation requirements under 40 CFR 51.308(f).
Where an RPO has performed source selection and/or four-factor analyses
(or considered the five additional factors in 40 CFR 51.308(f)(2)(iv))
for its member states, those states may rely on the RPO's analyses for
the purpose of satisfying the requirements of 40 CFR 51.308(f)(2)(i) so
long as the states have a reasonable basis to do so and all state
participants in the RPO process have approved the technical
analyses.\40\ Because Colorado 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 and reasonably relied on the selection of sources
from the WRAP analysis, we find that Colorado's source selection was
reasonable and consistent with the requirements of 40 CFR 51.308(f)(2).
---------------------------------------------------------------------------

\39\ Colorado 2022 SIP Submission at 51-52.
\40\ 40 CFR 51.308(f)(2)(iii).
---------------------------------------------------------------------------

Colorado submitted four-factor analyses for the selected sources
and demonstrated that its determination of controls necessary for
reasonable progress, and ultimately for inclusion in 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). Ultimately,
Colorado's 2022 SIP submission included both emission limits at
fourteen facilities (covering over seventy emission units) and
enforceable closures for already announced retirements at an additional
eight facilities across 13 units in its long-term strategy under the
regional haze program.
These measures are codified in Colorado Regulation Number 23, Part
A, IV. Regional Haze Determinations. The State also included compliance
schedules and other measures (i.e., recordkeeping and reporting)
codified in Colorado Regulation Number 23, Part A, V. Monitoring,
Recordkeeping, and Reporting for Regional Haze Limits.
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 and concluded that the long-term strategy contains the
enforceable emission limitations, compliance schedules, and other
measures that are necessary to make reasonable progress. 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 as well as adoption of the emission
limitations and compliance schedules codified in Colorado Regulation
Number 23, Part A, IV. Regional Haze Determinations and Colorado
Regulation Number 23, Part A, V. Monitoring, Recordkeeping, and
Reporting for Regional Haze Limits. Because the State evaluated and
determined the emission reduction measures contained in table 4 of
section IV.C.1.a of this document 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 in
accordance with 40 CFR 51.308(f)(2)(i), we find that Colorado's
determination of the emission reduction measures contained in table 4
of section IV.C.1.a of this document that are necessary to make
reasonable progress was reasonable and consistent with the requirements
of 40 CFR 51.308(f)(2)(i).
However, the EPA proposes to partially disapprove Colorado's long-
term strategy to the extent the SIP includes insufficiently justified
enforceable source closures. As detailed in the paragraphs below, the
EPA has substantial concerns that these enforceable source closures are
inconsistent with applicable regulations and CAA sections 110 and 169A,
including because the State has not provided necessary assurances that
the enforceable closures would not violate State and Federal law as
required by CAA section 110(a)(2)(E)(i).
First, we find that Colorado's long-term strategy did not
adequately consider the energy impacts associated with the source
closures contained in table 3 of section IV.C.1.a. of this document and
therefore does not fully satisfy the requirements of CAA section
169A(g)(1) and 40 CFR 51.308(f)(2)(i). More specifically, we find
Colorado did not sufficiently assess the closures'

[[Page 31938]]

impacts on maintaining grid reliability and utilities' ability to meet
energy demand. This finding is supported by documentation from an
electrical utility regarding risk to energy availability and grid
reliability due to source closures incorporated into Colorado's long-
term strategy.
Colorado's 2022 SIP submission partially addressed the ``energy and
nonair quality environmental impacts of compliance'' statutory factor
by describing the increasing need to fluctuate the utilization of
traditional, coal-fired power plants, which have historically provided
baseload electric generating capacity, to balance the inherent
variability of available capacity generated from renewable resources.
Thus, as more baseload coal-fired power plant units retire, more
renewable generation will be added to the grid, thereby increasing the
demands on remaining baseload resources to respond to variations in
electrical load and maintain a balanced grid.\41\ According to the
State, ``[m]aintaining grid reliability and meeting demand during this
transition is critical to allow for flexibility.'' \42\ However, the
State did not adequately evaluate and address grid reliability and
electrical demand associated with the closures of the coal-fired power
plants. Although the State did recognize that accommodating concerns
about grid reliability and electrical demand was ``key to the closure
date announcements'' \43\ of the coal-fired power plants, particularly
related to the need for further tightening of existing interim emission
limits on retiring units, the State's evaluation of the energy and
nonair quality environmental impacts of compliance factor did not
include how grid reliability and electrical demand was evaluated
related to the closure of these units. Nor did the evaluation discuss
what safeguards, if any, the State considered to ensure concerns about
grid reliability and electrical demand would be addressed.
---------------------------------------------------------------------------

\41\ Colorado 2022 SIP submission at 68.
\42\ Colorado 2022 SIP submission at 68, 71, 73, 80, 84, 85, 86,
88, 90, 95, 96, 97, 99.
\43\ Colorado Regulation Number 23, Part B at 32.
---------------------------------------------------------------------------

During the EPA's review of Colorado's assessment of its long-term
strategy's energy impacts, the EPA learned some of those closures were
more likely to impair grid reliability than had been previously
evaluated. For example, Colorado Springs Utilities submitted
information to the EPA on April 2, 2025, regarding the enforceable
closure of Nixon Unit 1 in Colorado's 2022 SIP submission.\44\ Colorado
Springs Utilities asked the EPA to exclude the SIP's proposed closure
of Nixon Unit 1 by December 29, 2029, from the EPA's final action on
Colorado's 2022 SIP submission. In addition, Colorado Springs Utilities
met with the State of Colorado on April 23, 2025, and asked the State
to remove the December 29, 2029 closure of Nixon Unit 1 from its
submission amid concerns regarding grid reliability.\45\ According to
Colorado Springs Utilities, the continued operation of Nixon Unit 1 is
``critically important'' for Colorado Springs Utilities to meet
projected electricity demand and thereby ensure the reliability of the
electric grid. Furthermore, Colorado Springs Utilities explained that
``potentially dire'' electric grid reliability impacts would likely
result from Nixon Unit 1's retirement. The risks to grid reliability,
according to Colorado Springs Utilities, are being driven by
increasingly unfavorable market conditions for renewable energy
development, the lack of immediately viable electricity transmission
developments in Colorado, and increasing load demands for new
electricity. Together, these factors compound Colorado Springs
Utilities' inability to bring sufficient resources online prior to the
Nixon Unit's planned retirement date of December 29, 2029, ultimately
resulting in projected capacity deficits of 173 MW in 2030 and 257 MW
in 2034, according to the utility.
---------------------------------------------------------------------------

\44\ Colorado Springs Utilities meeting with EPA_April 2, 2025.
\45\ Overview of Colorado Springs Utilities meeting with
CDPHE_April 23, 2025.
---------------------------------------------------------------------------

In addition to accounting for this new information, we reviewed
Colorado's assessment of these measures' energy impacts in light of the
rise in electricity demand due to the resurgence of domestic
manufacturing and the construction of artificial intelligence data
processing centers. As noted in Executive Order 14241, this
Administration has found as a matter of national interest, national
security, and energy policy that power generated from coal resources is
critical to addressing this surging demand.\46\ In this instance, the
EPA finds that Colorado did not adequately account for the energy
impacts of including these source closures in its long-term strategy
for regional haze as required by the CAA.
---------------------------------------------------------------------------

\46\ Executive Order 14241, ``Reinvigorating America's Beautiful
Clean Coal Industry and Amending Executive Order 14241,'' The White
House (April 8, 2025), <a href="https://www.whitehouse.gov/presidential-actions/2025/04/reinvigorating-americas-beautiful-clean-coal-industry-and-amending-executive-order-14241/">https://www.whitehouse.gov/presidential-actions/2025/04/reinvigorating-americas-beautiful-clean-coal-industry-and-amending-executive-order-14241/</a>.
---------------------------------------------------------------------------

Second, even with all source closures removed from the SIP,
Colorado is unlikely to contribute to visibility impairment at any
Class I areas projected to be above the adjusted 2028 URP.\47\ Because
Colorado lacked material information about grid reliability, later
provided to the EPA by Colorado Springs Utilities, we propose to find
the State did not appropriately weigh the energy impacts of the closure
measures against its substantial progress toward natural visibility
conditions in a manner consistent with issued executive orders'
priority on energy generation.
---------------------------------------------------------------------------

\47\ As the EPA has announced in recent SIP rulemakings, the
Agency is proposing to adopt a policy whereby states that are not
contributing to visibility impairment at Class I areas projected to
be above the Uniform Rate of Progress are presumed to be making
reasonable progress toward natural visibility conditions provided
they have considered the four statutory factors. See Air Plan
Approval, West Virginia; Regional Haze Plan for the Second
Implementation Period, 90 FR 16478 (April 18, 2025); Air Plan
Approval; South Dakota; Regional Haze Plan for the Second
Implementation Period, 90 FR 20425 (May 14, 2025).
---------------------------------------------------------------------------

We also propose to find that Colorado has not provided the
assurances required by CAA section 110 that implementing the SIP's
forced closure provisions is not prohibited by state or federal law.
CAA section 110(a)(2)(E)(i) provides that state plans must provide
``necessary assurances'' that the State ``is not prohibited by any
provision of Federal or State law from carrying out such implementation
plan or portion thereof.'' The best reading of this provision is that
the EPA may not approve a SIP that risks violating Federal or State law
in the course of implementation. This reading is consistent with the
EPA's independent obligation to follow Federal constitutional and
statutory law and with the structure of CAA section 110 as a whole,
which sets out detailed requirements for state plans and for the EPA's
review of such plans. The EPA proposes to find there is a risk that
enforceable source closure provisions, without just compensation, would
violate the Federal Takings Clause and possibly comparable provisions
of State law, and that Colorado has not provided the necessary
assurances that such violations would not occur.\48\
---------------------------------------------------------------------------

\48\ U.S. Const. amends. V, XIV; see also Colo. Const. art. II,
Sec. 15.
---------------------------------------------------------------------------

Although the application of the Takings Clause is necessarily fact-
specific, an unconsented source closure could constitute either a per
se or regulatory taking. The EPA notes that there is a lack of
controlling precedent on application of the Takings Clause to forced
source closures under CAA

[[Page 31939]]

section 110 because states typically do not seek to implement their
SIPs in a manner that forces closure on a nonconsenting source.\49\
U.S. Supreme Court precedent suggests, however, that the EPA's approval
of this course of action could amount to a per se taking. In Cedar
Point Nursery v. Hassid, 594 U.S. 139 (2021), the U.S. Supreme Court
explained that government action that appropriates property ``is no
less a physical taking because it arises from a regulation.''
Particularly relevant here, the Court applied the per se bar on
uncompensated takings in Horne v. Department of Agriculture, 576 U.S.
351 (2015), to a complex regulatory regime that required regulated
parties to set aside a portion of their output to achieve governmental
aims. The EPA proposes to conclude that Colorado has not provided the
necessary assurances required by CAA section 110(a)(2)(E)(i) that the
submitted closure provisions would not result in uncompensated per se
takings in violation of Federal law.
---------------------------------------------------------------------------

\49\ The EPA is not aware of any prior state submission under
CAA section 110 that sought to force closure of a currently
operating source without that source's consent. We seek comment on
whether any such examples exist and request that commenters identify
such an example with enough specificity to allow us to evaluate the
circumstances in which such a forced closure was attempted through a
CAA section 110 submission.
---------------------------------------------------------------------------

Relatedly, a total regulatory taking could occur if the closure
would fully deprive the source owner of all economic use of the land
under the standard described in Lucas v. S.C. Coastal Council, 505 U.S.
1003, 1116 (1992). A partial regulatory taking could occur if the
closure inflicted a significant economic impact upon the source owner,
undermined distinct, investment-backed expectations, and shared
characteristics with actions conventionally regarded as government
takings. These factors and how courts should balance them are detailed
in Penn Central Transp. Co. v. New York City, 438 U.S. 104, 123 (1978),
and subsequent cases. The EPA proposes to find that Colorado has not
provided the necessary assurances required by CAA section
110(a)(2)(E)(i) that Federal law would not prohibit the State from
implementing the submitted closure provisions, including whether such
unconsented source closures would amount to a taking without just
compensation.
Finally, the EPA also proposes to conclude that the forced source
closure contained in this portion of the State's submission is
inconsistent with the structure of CAA sections 110 and 169A, which do
not contemplate forced closures as a means to achieve compliance. In
this context, we are referring to a source closure opposed by the
source in question that would be made federally enforceable as a result
of a SIP approval. The EPA is referring to such a closure as
``unconsented'' or ``forced.''
CAA section 110(a)(1)(A) provides that, as a general matter, a SIP
must ``include enforceable emission limitations and other control
measures, means, or techniques (including economic incentives such as
fees, marketable permits, and auctions of emissions rights)'' as ``may
be necessary or appropriate to meet the applicable requirements of this
chapter.'' The EPA is proposing that the ordinary meaning of ``emission
limitations'' does not include forced closures that prohibit all
operations against the will of the owner/operator, or in a timeframe
unconsented to by the owner/operator. Similarly, we are proposing that
the best reading of the phrase ``other control measures, means, or
techniques'' does not encompass the authority to force a source to
close, or to close on timeframe not agreed to by the owner/operator.
This proposal is supported by reading the terms ``measures'' and
``means'' in context and informed by the surrounding statutory terms,
including the parenthetical phrase discussing market-based incentives
that contemplate ongoing operations. ``Measures'' and ``means'' must
also be ``necessary or appropriate'' to meet applicable CAA
requirements. As noted above, the EPA is proposing that unconsented
closures are neither ``necessary'' under the circumstances here nor
otherwise required by the CAA, and that such closures are not
``appropriate'' when they could amount to an uncompensated taking in
violation of Federal and State law. The EPA seeks comment on this
interpretation.
CAA section 169A similarly does not contemplate use of unconsented
closures as part of the regional haze program. The statute provides
that state plans must contain ``emission limits, schedules of
compliance and other measures as may be necessary to make reasonable
progress,'' including through the use of ``retrofit technology'' and
long-term strategies. Consistent with the interpretation of CAA section
110 proposed above, the EPA proposes that the best reading of the
statute does not require or authorize the use of forced source closures
to attain the statutory goals listed in CAA section 169A. The EPA seeks
comment on this interpretation as well.
The EPA notes that at least one of the sources slated for closure
in the SIP--Nixon Unit 1--has expressly stated that it does not consent
to closing by the enforceable deadline. Additionally, we note that the
North American Electric Reliability Corporation (NERC) stated in their
2024 Long-Term Reliability Assessment that ``most of the North American
bulk power system faces mounting resource adequacy challenges over the
next 10 years as surging demand growth continues and thermal generators
announce plans for retirement.'' Ultimately, according to NERC, ``[t]he
trends point to critical reliability challenges facing the industry:
satisfying escalating energy growth, managing generator retirements,
and accelerating resource and transmission development.'' \50\ Industry
assessments relied on by Colorado utilities indicate that increasing
energy demand in the region may cause additional sources to reverse
course on previously agreed-to closure provisions, and Colorado has not
sufficiently addressed the legal implications of forcing these plants
to close under the SIP provisions submitted by the State.
---------------------------------------------------------------------------

\50\ North American Electric Reliability Corporation, 2024 Long-
Term Reliability Assessment. December 2024 at 6.
---------------------------------------------------------------------------

In summary, we are proposing to partially disapprove Colorado's
long-term strategy under CAA section 169A and 40 CFR 51.308(f)(2)(i)
because Colorado's 2022 SIP submission does not adequately consider the
energy impacts associated with the state's enforceable source closures
of coal and gas-fired power plants and associated units to energy
availability and grid reliability and contains provisions that are
inconsistent with the CAA and its implementing regulations. Our
proposed disapproval would encompass, and therefore decline to
incorporate, the enforceable source closures contained in Colorado's
2022 SIP submission (listed in table 3 of section IV.C.1.a. of this
document) and in Colorado's Regulation Number 23.\51\ If we receive
information during the comment period that a source is permanently
decommissioned (i.e., rendered fully inoperable and its operating
permit has been revoked), we could reevaluate our proposed disapproval
of these units.
---------------------------------------------------------------------------

\51\ IV.F.1.; IV.F.3. pertaining to the cessation of coal
handling at Nixon, Coal Handling, Hayden Units 1 and 2, and Pawnee
Unit 1; IV.F.5.; and I.V.F.6.
---------------------------------------------------------------------------

Despite our proposed partial disapproval of the State's long-term
strategy as it pertains to source closures, we find that the regional
haze requirements are satisfied by the portion of Colorado's 2022 SIP
submission that we are approving. Therefore, because no outstanding
obligations remain, there

[[Page 31940]]

will be no additional regulatory action needed, either in the form of a
federal implementation plan or another SIP revision, as a result of the
partial disapproval.
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. Chapter 2.3 of Colorado's 2022 SIP submission
describe the State's consultation with other states throughout the
development of its regional haze plan.
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. The State relied on
WRAP technical information, modeling, and analysis to support
development of its long-term strategy.\52\
---------------------------------------------------------------------------

\52\ Colorado 2002 SIP submission at 8, 51-52, 150-157.
---------------------------------------------------------------------------

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 8.4 of Colorado'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.\53\ Pursuant to
40 CFR 51.308(f)(2)(iv)(A), Colorado 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.\54\ Many of these same measures, particularly the
provisions found in Colorado's Regulation Number 1 and Regulation
Number 3, also mitigate the impacts of construction activities as
required by 40 CFR 51.308(f)(2)(iv)(B).\55\ Pursuant to 40 CFR
51.308(f)(2)(iv)(C), the State considered source retirements schedules
in the Colorado 2022 SIP submission \56\ as well as in Colorado
Regulation Number 23. In considering smoke management as required in 40
CFR 51.308(f)(2)(iv)(D), Colorado explained that it addresses smoke
management through its smoke management program \57\ as well as
Colorado Regulation Number 9 which addresses open burning, prescribed
fire, and permitting.\58\ Colorado considered the anticipated net
effect of projected changes in emissions on visibility as required by
40 CFR 51.308(f)(2)(iv)(E) by discussing the analytical results from
the air quality monitoring, emission inventories, and air quality
modeling for the second implementation period that it conducted in
collaboration with the WRAP.\59\
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\53\ Colorado 2022 SIP submission at 143-155.
\54\ Colorado 2022 SIP submission at 143-147.
\55\ Colorado 2022 SIP submission at 148.
\56\ Colorado 2022 SIP submission at 59-67; Regulation Number
23, Part A, IV.F.
\57\ Consistent with the EPA's Interim Air Quality Policy on
Wildland Prescribed Fire, May 1998.
\58\ Colorado 2022 SIP submission at 148-150.
\59\ Colorado 2022 SIP submission at 150-155.
---------------------------------------------------------------------------

After reviewing Colorado's 2022 SIP submission chapters addressing
40 CFR 51.308(f)(2)(ii)-(iv), the EPA finds that Colorado 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, Colorado 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 5).\60\
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\60\ Colorado 2022 SIP submission at 156.

Table 5--Reasonable Progress Goals for the 20% Most Impaired Days and 20% Clearest Days for Colorado Class I
Areas
----------------------------------------------------------------------------------------------------------------
20% Most impaired days 20% Clearest days
-------------------------------------------------------------------------------
Average 2028 2028 Average
Class I area baseline Unadjusted \1\ Reasonable baseline 2028
conditions uniform progress goal conditions Reasonable
(2000-2004) progress goal \2\ (2000-2004) progress goal
----------------------------------------------------------------------------------------------------------------
Deciviews
----------------------------------------------------------------------------------------------------------------
Great Sand Dunes................ 9.66 7.58 7.50 4.5 2.44
Mesa Verde...................... 9.22 7.21 6.10 4.32 2.01
Mount Zirkel, Rawah............. 7.29 5.64 4.93 1.61 0.02
Rocky Mountain National Park.... 11.12 8.65 7.56 2.29 1.17
Weminuche, La Garita, Black 7.78 6.26 6.03 3.11 1.39
Canyon of Gunnison.............
Eagles Nest, Flat Tops, Maroon 6.30 4.99 4.49 0.70 -0.35
Bells, White River, West Elk...
----------------------------------------------------------------------------------------------------------------
\1\ Colorado did not rely on the adjusted URP for either international emissions or international emissions plus
wildland prescribed fire.
\2\ Based on WRAP 2028OTBa2.

[[Page 31941]]

The reasonable progress goals are based on Colorado's long-term
strategy, the long-term strategy of other states that may affect Class
I areas in Colorado, and other CAA requirements. 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.1.b., we are proposing to
partially disapprove Colorado's long-term strategy relating to 40 CFR
51.308(f)(2)(i) and the associated source closures. The RPGs in table 5
are based on modeling of the measures included in the long-term
strategy, namely the closures of Comanche Units 1 and 2, Craig Unit 1,
and Nucla.\61\ The closures of Craig Unit 1 and Nucla have already
occurred and were previously incorporated into Colorado's federally
enforceable SIP.\62\ The closures of Comanche Units 1 and 2 are part of
Colorado's 2022 SIP submission and are not proposed to be incorporated
into this rulemaking. While the RPGs in Colorado's 2022 SIP submission
are all below the unadjusted 2028 URP, and Colorado is not known to
contribute to any Class I areas that are above the 2028 URP, our
proposed action does not include the incorporation of the closures of
Comanche Units 1 and 2 into the federally enforceable SIP and therefore
may impact whether all Class I areas remain below the URP. The Class I
area closest to the URP is Great Sand Dunes where the unadjusted 2028
URP is 7.58 and the 2028 RPG, based on Colorado's long-term strategy
which includes the four aforementioned source closures, is 7.50.
However, when we evaluate Colorado's 2028 RPG against the adjusted
glidepaths, either adjusted for international emissions (2028 URP is
8.30) or adjusted for international emissions plus wildland prescribed
fire (2028 URP is 8.36), Colorado's 2028 RPG without the closures of
Comanche Units 1 and 2 would very likely remain below either adjusted
glidepath.\63\ If, on the other hand, Colorado's 2028 RPG provides for
a slower rate of improvement in visibility due to the absence of the
enforceable closures of Comanche Units 1 and 2 in Colorado's federally
enforceable SIP, the EPA finds that in accordance with 40 CFR
51.308(f)(3)(ii)(A), Colorado: (1) demonstrated that there are no
additional emission reduction measures that would be reasonable to
include in its long-term strategy, and (2) provided a robust
demonstration, including documenting the criteria used to determine
which sources or groups of sources were evaluated and how the four-
factors were taken into consideration in selecting the measures for
inclusion in its long-term strategy. Specifically, Colorado selected
nineteen sources to evaluate, resulting in over seventy emission
control measures in the State's long-term strategy. Given the
comprehensive set of sources selected and evaluated, the consideration
of the four statutory factors for those sources, and the large number
of emission control measures included in the SIP, the EPA agrees that
there are no additional emissions reduction measures that would be
necessary to include in the long-term strategy. Therefore, no
additional requirements apply under 40 CFR 51.308(f)(3)(ii). Based on
having satisfied the RPG rule requirements, we propose to approve
Colorado's reasonable progress goals under 40 CFR 51.308(f)(3).
---------------------------------------------------------------------------

\61\ Colorado 2022 SIP submission at 150.
\62\ 83 FR 31332 (July 5, 2018).
\63\ WRAP, Visibility Progress and Projections. ``Adjustments to
Uniform Rate of Progress Glidepath--Most Impaired Days. Great Sand
Dunes.'' <a href="https://views.cira.colostate.edu/tssv2/Express/ModelingTools.aspx">https://views.cira.colostate.edu/tssv2/Express/ModelingTools.aspx</a>.
---------------------------------------------------------------------------

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,'' \64\ 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 Great
Sand Dunes National Park, Mesa Verda National Park, Mount Zirkel
Wilderness, Rawah Wilderness, Rocky Mountain National Park, Weminuche
Wilderness, Black Canyon of Gunnison NP, La Garita Wilderness, Eagles
Nest Wilderness, Flat Tops Wilderness, Maroon Bells-Snowmass
Wilderness, and West Elk Wilderness identified any RAVI from Colorado
sources. For this reason, the EPA proposes to approve the portions of
Colorado's 2022 SIP submission relating to 40 CFR 51.308(f)(4).
---------------------------------------------------------------------------

\64\ 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.
---------------------------------------------------------------------------

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 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 Colorado), 40 CFR
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.
Colorado describes its participation in the IMPROVE network, which
comprises 110 monitoring sites across the nation, six of which are in
Colorado. The State relied on the IMPROVE monitoring network to assess
visibility at Class I areas across Colorado \65\ and considered the six
monitoring sites GRSA1, MEVE1, MOZI1, ROMO1, WEMI1 and WHRI1 to be
adequate for

[[Page 31942]]

assessing reasonable progress goals at the State's twelve Class I
areas.\66\ Using the monitoring data procedures described in its 2022
SIP submission along with other technical information supplied by
WRAP,67 68 the State determined the contribution of in-State
emissions to Class I areas inside and outside Colorado.\69\ In
addition, the State also provided a statewide inventory of emissions
that are reasonably anticipated to cause or contribute to visibility
impairment in Class I areas; the State relied primarily on 2014-2018
data but also estimated future projected emissions.\70\
---------------------------------------------------------------------------

\65\ Colorado 2022 SIP submission at 12-17.
\66\ Id. at 12-16.
\67\ Id. at 13.
\68\ Colorado relied on the WRAP Technical Support System (TSS)
``Analysis and Planning'' section to determine baseline, natural,
and current conditions for Class I areas in Colorado. <a href="https://views.cira.colostate.edu/tssv2/">https://views.cira.colostate.edu/tssv2/</a>.
\69\ Colorado 2022 SIP submission at 13 and 143.
\70\ Id. at 13, 17 and 29-38.
---------------------------------------------------------------------------

The EPA finds that Colorado 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 Colorado to assess
and report on visibility. Therefore, the EPA proposes to approve the
monitoring strategy and other state implementation plan elements of
Colorado'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,\71\ Colorado included the elements of
the periodic progress report specified in 40 CFR 51.308(f)(5) and 40
CFR 51.308(g)(1)-(5). Colorado 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.\72\ 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.\73\
The EPA finds that Colorado has met the requirements of 40 CFR
51.308(g)(1) and (2) because Colorado'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.
---------------------------------------------------------------------------

\71\ Colorado's June 2023 supplement contained the elements of
the periodic progress report.
\72\ Colorado 2022 SIP submission, Regional Haze Progress Report
at E-1-E-11.
\73\ Colorado 2022 SIP submission, Regional Haze Progress Report
at E-4-E-8.
---------------------------------------------------------------------------

Visibility conditions (in deciviews) are reported in Colorado'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), 2010-2014 period, and current period (2015-2019),
as well as the progress made since the baseline period ((2000-2004)-
(2015-2019)) and during the last implementation period ((2010-2014)-
(2015-2019)) for each Class I area.\74\ The EPA therefore finds that
Colorado has satisfied the requirements of 40 CFR 51.308(g)(3).
---------------------------------------------------------------------------

\74\ Colorado 2022 SIP submission, Regional Haze Progress Report
at E-12-E-23.
---------------------------------------------------------------------------

The State used the most current emissions inventory available-the
2017 NEI--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.\75\ Colorado also provided an
assessment and discussion of the significant changes in anthropogenic
emissions since the first implementation period.\76\ 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.
---------------------------------------------------------------------------

\75\ Colorado 2022 SIP submission, Regional Haze Progress Report
at E-26-E-35.
\76\ Colorado 2022 SIP submission, Regional Haze Progress Report
at E-33-E-35.
---------------------------------------------------------------------------

Because Colorado's 2022 SIP submission addresses the requirements
of 40 CFR 51.308(g)(1) through (5), the EPA finds that Colorado has met
the progress report requirements of 40 CFR 51.308(f)(5). Therefore, we
propose to approve Colorado'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

[[Page 31943]]

provided at least sixty 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.
Colorado's 2022 SIP submission summarizes the State's consultation
and coordination with the FLMs. Colorado consulted and coordinated with
the FLMs during the development of its regional haze SIP through WRAP
participation and direct FLM engagement. Colorado facilitated both in-
person and virtual public stakeholder meetings in 2019 and 2020 to
gather input early in the planning stages. The State also held multiple
consultations directly with the FLMs in June 2019 to discuss Q/d
thresholds and potential sources for analysis. Subsequent discussions
occurred in August and October 2020, as well as in April, May, and June
2021 to refine analyses and address concerns raised by FLMs concerning
additional control measures. These discussions occurred prior to the
State's public hearing on the draft regional haze plan in November
2020. The State also held a public information meeting in August 2021
to provide information on its draft regional haze SIP prior to holding
a public hearing in November 2021.\77\ The State further shared the
regional haze plan's technical support documents with the FLMs.
---------------------------------------------------------------------------

\77\ Colorado 2022 SIP submission at 8-11.
---------------------------------------------------------------------------

Colorado 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 Colorado's SIP submission which meets the
requirements of 40 CFR 51.308(i), as outlined in this section.

V. Proposed Action

The EPA is proposing partial approval and partial disapproval of
Colorado'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 Colorado'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)(ii)-(iv): 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 proposing disapproval of
portions of Colorado's 2022 SIP submission relating to 40 CFR
51.308(f)(2)(i) and its corresponding regulatory provisions (Colorado
Regulation Number 23 section IV.F.1.; IV.F.3. pertaining to the
cessation of coal handling at Nixon, Coal Handling, Hayden Units 1 and
2, and Pawnee Unit 1; IV.F.5.; and IV.F.6.). Despite our proposed
disapproval of the State's long-term strategy as it pertains to source
closures, we find that the regional haze requirements are satisfied by
the portion of Colorado's 2022 SIP submission that we are approving.
Because no outstanding obligations remain, there will be no additional
regulatory action needed, either in the form of a federal
implementation plan or another SIP revision, as a result of the partial
disapproval. Concurrently, the EPA is proposing to approve a revision
to Colorado's SIP that moves the regional haze provisions in Regulation
Number 3 to the newly adopted Regulation Number 23. Together, these SIP
revisions establish updated emission reduction requirements for
NO<INF>X</INF>, SO<INF>2</INF>, and PM emissions from certain
reasonable progress sources identified as impacting Class I areas under
the RHR for the second ten-year planning period.

VI. Incorporation by Reference

In this document, the EPA is proposing to include regulatory text
in an EPA final rule that includes incorporation by reference. In
accordance with requirements of 1 CFR 51.5, and as discussed in
sections I. through V. of this preamble and set forth below in the
proposed amendments to part 52, the EPA is proposing: to remove 5 CCR
1001-05, Regulation Number 3, Part F, Regional Haze Limits--Best
Available Retrofit Technology (BART) and Reasonable Progress (RP) and
the associated entries for VI. Regional Haze Determinations and VII.
Monitoring, Recordkeeping, and Reporting for Regional Haze Limits, from
the Colorado SIP; and to incorporate by reference 5 CCR 1001-27,
Regulation Number 23, Part A, Regional Haze Limits--Best Available
Retrofit Technology (BART) and Reasonable Progress (RP) and the
associated entries for IV. Regional Haze Determinations and V.
Monitoring, Recordkeeping, and Reporting for Regional Haze Limits. The
EPA has made, and will continue to make, these materials generally
available through <a href="https://www.regulations.gov">https://www.regulations.gov</a> and at the EPA Region 8
Office (please contact the person identified in the FOR FURTHER
INFORMATION CONTACT section of this preamble for more information).

VII. Statutory and Executive Order Reviews

This action proposes to partially approve and partially disapprove
state law as meeting Federal requirements and does not impose
additional requirements beyond those imposed by state law. For that
reason, this action:
<bullet> Is not a significant regulatory action subject to review
by the Office of Management and Budget under Executive Order 12866 (58
FR 51735, October 4, 1993);
<bullet> Is not subject to Executive Order 14192 (90 FR 9065,
February 6, 2025) because SIP actions are exempt from review under
Executive Order 12866;
<bullet> Does not impose an information collection burden under the
provisions of the Paperwork Reduction Act (44 U.S.C. 3501 et seq.);
<bullet> Is certified as not having a significant economic impact
on a substantial number of small entities under the Regulatory
Flexibility Act (5 U.S.C. 601 et seq.);
<bullet> Does not contain any unfunded mandate or significantly or
uniquely affect small governments, as described in the Unfunded
Mandates Reform Act of 1995 (Pub. L. 104-4);
<bullet> Does not have federalism implications as specified in
Executive Order 13132 (64 FR 43255, August 10, 1999);
<bullet> Is not subject to Executive Order 13045 (62 FR 19885,
April 23, 1997) because it approves a state program;
<bullet> Is not a significant regulatory action subject to
Executive Order 13211 (66 FR 28355, May 22, 2001); and
<bullet> Is not subject to requirements of section 12(d) of the
National Technology Transfer and Advancement Act of 1995 (15 U.S.C. 272
note) because application of those requirements would be inconsistent
with the 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

[[Page 31944]]

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: _July 9, 2025.
Cyrus M. Western,
Regional Administrator, Region 8.

For the reasons stated in the preamble, the Environmental
Protection Agency is proposing 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 G--Colorado

0
2. Amend Sec. 52.320 by:
0
a. In the table in paragraph (c):
0
i. Removing the center heading ``5 CCR 1001-05, Regulation Number 3,
Part F, Regional Haze Limits--Best Available Retrofit Technology (BART)
and Reasonable Progress (RP)'' and the entries ``VI. Regional Haze
Determinations'' and ``VII. Monitoring, Recordkeeping, and Reporting
for Regional Haze Limits''; and
0
ii. Adding the center heading ``5 CCR 1001-27, Regulation Number 23,
Part A, Regional Haze Limits--Best Available Retrofit Technology (BART)
and Reasonable Progress (RP)'' and the entries ``IV. Regional Haze
Determinations'' and ``V. Monitoring, Recordkeeping, and Reporting for
Regional Haze Limits'' at the end of the table.
0
b. In the table in paragraph (e):
0
i. Adding the entry ``Colorado Visibility and Regional Haze State
Implementation Plan for the Twelve Mandatory Class I Federal Areas in
Colorado, Revised Regional Haze State Implementation Plan for the
Second Implementation Period'' at the end of the table.
The additions read as follows:

Sec. 52.320 Identification of plan.

* * * * *
(c) * * *

----------------------------------------------------------------------------------------------------------------
State
Title effective EPA effective date Final rule citation/ Comments
date date
----------------------------------------------------------------------------------------------------------------

* * * * * * *
----------------------------------------------------------------------------------------------------------------
5 CCR 1001-27, Regulation Number 23, Part A, Regional Haze Limits--Best Available Retrofit Technology (BART) and
Reasonable Progress (RP)
----------------------------------------------------------------------------------------------------------------
IV. Regional Haze Determinations. 2/14/2021 [date 30 days after 90 FR [Federal Except for IV.F.1.;
date of publication Register page where IV.F.3. pertaining
of the final rule the document begins to the cessation of
in the Federal of the final rule], coal handling at
Register]. [date of Nixon, Coal
publication of the Handling, Hayden
final rule in the Units 1 and 2, and
Federal Register]. Pawnee Unit 1;
IV.F.5.; and
I.V.F.6.
V. Monitoring, Recordkeeping, and 2/14/2021 [date 30 days after 90 FR [Federal ....................
Reporting for Regional Haze date of publication Register page where
Limits. of the final rule the document begins
in the Federal of the final rule],
Register]. [date of
publication of the
final rule in the
Federal Register].
----------------------------------------------------------------------------------------------------------------

* * * * *
(e) * * *

* * * * * * *
----------------------------------------------------------------------------------------------------------------
Visibility
----------------------------------------------------------------------------------------------------------------

* * * * * * *
Colorado Visibility and Regional 1/30/22 [date 30 days after 90 FR [Federal Excluding the
Haze State Implementation Plan date of publication Register page where sections
for the Twelve Mandatory Class I of the final rule the document begins disapproved in this
Federal Areas in Colorado, in the Federal of the final rule], action. EPA
Revised Regional Haze State Register]. [date of disapproved the
Implementation Plan for the publication of the portions of
Second Implementation Period. final rule in the Colorado's 2022 SIP
Federal Register]. submission relating
to CAA section 169A
and 40 CFR
51.308(f)(2)(i):
long-term strategy
corresponding to
source closures.
----------------------------------------------------------------------------------------------------------------

[[Page 31945]]

[FR Doc. 2025-13342 Filed 7-15-25; 8:45 am]
BILLING CODE 6560-50-P

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