6560-50-P
ENVIRONMENTAL PROTECTION AGENCY
40 CFR Part 52
[EPA-R07-OAR-2024-0286; FRL-12046-01-R7]
Air Plan Partial Approval and Partial Disapproval; Missouri; Regional Haze
AGENCY: Environmental Protection Agency (EPA).
ACTION: Proposed rule.
SUMMARY: The Environmental Protection Agency (EPA) is proposing to partially approve
and partially disapprove a revision to Missouri’s State Implementation Plan (SIP) submitted on
August 26, 2022, to satisfy applicable requirements under the Clean Air Act (CAA) and the
EPA’s Regional Haze Rule (RHR) for the program’s second planning period. As required by
section 169A of the Clean Air Act, the Federal Regional Haze Rule calls for state and Federal
agencies to work together to improve visibility, including Regional Haze, in 156 national parks
and wilderness areas. The rule requires the states, in coordination with the EPA, the National
Parks Service (NPS), the U.S. Fish and Wildlife Service (FWS), the U.S. Forest Service (FS),
and other interested parties, to develop and implement air quality protection plans in which states
revise their long-term strategies (LTS) for making reasonable progress towards the national goal
of preventing any future, and remedying any existing, anthropogenic impairment of visibility in
these mandatory Class I Federal areas. Disapproval does not start a mandatory sanctions clock.
DATES: Comments must be received on or before [INSERT DATE 30 DAYS AFTER DATE
OF PUBLICATION IN THE FEDERAL REGISTER].
ADDRESSES: You may send comments, identified by Docket ID No. EPA-R07-OAR-20240286 to https://www.regulations.gov. Follow the online instructions for submitting comments.
Instructions: All submissions received must include the Docket ID No. for this
rulemaking. Comments received will be posted without change to https://www.regulations.gov/,
including any personal information provided. For detailed instructions on sending comments and

additional information on the rulemaking process, see the “Written Comments” heading of the
SUPPLEMENTARY INFORMATION section of this preamble.
FOR FURTHER INFORMATION CONTACT: Ashley Keas, Environmental Protection
Agency, Region 7 Office, Air and Radiation Division, 11201 Renner Boulevard, Lenexa, Kansas
66219; telephone number: (913) 551-7629; email address: keas.ashley@epa.gov.
SUPPLEMENTARY INFORMATION: Throughout this document “we,” “us,” and “our”
refer to the EPA.
Table of Contents
I. Written Comments
II. What is Being Addressed in this Document?
III. Background and Requirements for Regional Haze Plans
A. Regional Haze Background
B. Roles of Agencies in Addressing Regional Haze
IV. Requirements for Regional Haze Plans for the Second Implementation Period
A. Identification of Class I Areas
B. Calculation of Baseline, Current, and Natural Visibility Conditions; Progress to Date;
and the Uniform Rate of Progress
C. Long-Term Strategy for Regional Haze
D. Reasonable Progress Goals
E. Monitoring Strategy and Other State Implementation Plan Requirements
F. Requirements for Periodic Reports Describing Progress Towards the Reasonable
Progress Goals
G. Requirements for State and Federal Land Manager Coordination
V. The EPA’s Evaluation of Missouri’s Regional Haze Submission for the Second
Implementation Period
A. Background on Missouri’s First Implementation Period SIP Submission
B. Missouri’s Second Implementation Period SIP Submission and the EPA’s Evaluation
C. Identification of Class I Areas
D. Calculations of Baseline, Current, and Natural Visibility Conditions; Progress to
Date; and the Uniform Rate of Progress
E. Long-Term Strategy for Regional Haze
1. Source Selection
2. Four-Factor Analysis
3. Additional Long-Term Strategy Requirements
F. Reasonable Progress Goals
G. Monitoring Strategy and Other Implementation Plan Requirements
H. Requirements for Periodic Reports Describing Progress Towards the Reasonable
Progress Goals
I. Requirements for State and Federal Land Manager Coordination
VI. What Action is the EPA Proposing to Take?
VII. Environmental Justice Considerations
VIII. Statutory and Executive Order Reviews
I. Written Comments

Submit your comments, identified by Docket ID No. EPA-R07-OAR-2024-0286, at
https://www.regulations.gov. Once submitted, comments cannot be edited or removed from
Regulations.gov. The EPA may publish any comment received to its public docket. Do not
submit electronically any information you consider to be Confidential Business Information
(CBI) or other information whose disclosure is restricted by statute. Multimedia submissions
(audio, video, etc.) must be accompanied by a written comment. The written comment is
considered the official comment and should include discussion of all points you wish to make.
The EPA will generally not consider comments or comment contents located outside of the
primary submission (i.e., on the web, cloud, or other file sharing system). For additional
submission methods, the full EPA public comment policy, information about CBI or multimedia
submissions, and general guidance on making effective comments, please visit
https://www.epa.gov/dockets/commenting-epa-dockets.
II. What is Being Addressed in this Document?
On August 26, 2022, the Missouri Department of Natural Resources (MoDNR) submitted
a plan to the EPA to satisfy the regional haze program requirements pursuant to CAA sections
169A and 40 CFR 51.308. The EPA is proposing to partially approve and partially disapprove
Missouri’s Regional Haze plan for the second planning period. Consistent with section 110(k)(3)
of the CAA, 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.1 As required by section 169A of the CAA, the Federal RHR calls for state and Federal
agencies to work together to improve visibility in 156 national parks and wilderness areas. The
rule requires the states, in coordination with the EPA, NPS, FWS, FS, and other interested
parties, to develop and implement air quality protection plans to reduce the pollution that causes
visibility impairment. Visibility impairing pollutants include fine and coarse particulate matter

See CAA section 110(k)(3) and July 1992 EPA memorandum titled “Processing of State Implementation Plan
(SIP) Submittals” from John Calcagni, at https://www.epa.gov/sites/default/files/2015-07/documents/procsip.pdf.
(PM) (e.g., sulfates, nitrates, organic carbon, elemental carbon, and soil dust) and their
precursors (e.g., sulfur dioxide (SO2), nitrogen oxides (NOx), and, in some cases, volatile organic
compounds (VOC) and ammonia (NH3)). As discussed in further detail below, the EPA is
proposing to find that Missouri has submitted a Regional Haze plan that does not meet all the
Regional Haze requirements for the second planning period. For the reasons described in this
document, the EPA is proposing to approve the elements of Missouri’s plan related to
requirements contained in 40 CFR 51.308(f)(1), (f)(5), (f)(6), and (g)(1) through (g)(5). The EPA
is proposing to disapprove the elements of Missouri’s plan related to requirements contained in
40 CFR 51.308(f)(2), (f)(3), and (i). The State’s submission can be found in the docket for this
action.
III. Background and Requirements for Regional Haze Plans
A. Regional Haze Background
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.2 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). The CAA
further directs the EPA to promulgate regulations to assure reasonable progress toward meeting
this national goal. CAA section 169A(a)(4). On December 2, 1980, the EPA promulgated
regulations to address visibility impairment in mandatory Class I Federal Areas (hereinafter
referred to as “Class I Areas”) that is “reasonably attributable” to a single source or small group
of sources. (45 FR 80084, December 2, 1980). These regulations, codified at 40 CFR 51.300
through 51.307, represented the first phase of the EPA’s efforts to address visibility impairment.

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.
In 1990, Congress added section 169B to the CAA to further address visibility impairment,
specifically, impairment from Regional Haze. CAA section 169B. The EPA promulgated the
RHR, codified at 40 CFR 51.308,3 on July 1, 1999. (64 FR 35714, July 1, 1999). These Regional
Haze regulations are a central component of the EPA’s comprehensive visibility protection
program for Class I Areas.
Regional Haze is visibility impairment that is produced by a multitude of anthropogenic
sources and activities which are located across a broad geographic area and that emit pollutants
that impair visibility. Visibility impairing pollutants include fine and coarse PM (e.g., sulfates,
nitrates, organic carbon, elemental carbon, and soil dust) and their precursors (e.g., SO2, NOx,
and, in some cases, VOC and NH3). Fine particle precursors react in the atmosphere to form fine
particulate matter (PM2.5), which impairs visibility by scattering and absorbing light. Visibility
impairment reduces the perception of clarity and color, as well as visible distance.4
To address Regional Haze visibility impairment, the 1999 RHR established an iterative
planning process that requires both states in which Class I areas are located and states “the
emissions from which may reasonably be anticipated to cause or contribute to any impairment of
visibility” in a Class I Area to periodically submit SIP revisions to address such impairment.
CAA section 169A(b)(2);5 see also 40 CFR 51.308(b), (f) (establishing submission dates for

3 In addition to the generally applicable regional haze provisions at 40 CFR 51.308, the EPA also promulgated
regulations specific to addressing regional haze visibility impairment in Class I areas on the Colorado Plateau at 40
CFR 51.309. The latter regulations are applicable only for specific jurisdictions’ regional haze plans submitted no
later than December 17, 2007, and thus are not relevant here.
4 There are several ways to measure the amount of visibility impairment, i.e., haze. One such measurement is the
deciview, which is the principal metric used by the RHR. Under many circumstances, a change in one deciview will
be perceived by the human eye to be the same on both clear and hazy days. The deciview is unitless. It is
proportional to the logarithm of the atmospheric extinction of light, which is the perceived dimming of light due to
its being scattered and absorbed as it passes through the atmosphere. Atmospheric light extinction (bext) is a metric
used to for expressing visibility and is measured in inverse megameters (Mm-1). The EPA’s Guidance on Regional
Haze State Implementation Plans for the Second Implementation Period (“2019 Guidance”) offers the flexibility for
the use of light extinction in certain cases. Light extinction can be simpler to use in calculations than deciviews,
since it is not a logarithmic function. See, e.g., 2019 Guidance at 16, 19, https://www.epa.gov/visibility/guidanceregional-haze-state-implementation-plans-second-implementation-period, The EPA Office of Air Quality Planning
and Standards, Research Triangle Park (August 20, 2019). The formula for the deciview is 10 ln (bext)/10 Mm−1). 40
CFR 51.301.
5 The RHR expresses the statutory requirement for states to submit plans addressing out-of-state class I areas by
providing that states must address visibility impairment “in each mandatory Class I Federal area located outside the
State that may be affected by emissions from within the State.” 40 CFR 51.308(d), (f).

iterative Regional Haze SIP revisions); (64 FR 35714 at 35768, July 1, 1999). Under the CAA,
each SIP submission must contain “a long-term (ten to fifteen years) strategy for making
reasonable progress toward meeting the national goal,” CAA section 169A(b)(2)(B); the initial
round of SIP submissions also had to address the statutory requirement that certain older, larger
sources of visibility impairing pollutants install and operate the best available retrofit technology
(BART). CAA section 169A(b)(2)(A); 40 CFR 51.308(d), (e). States’ first Regional Haze SIPs
were due by December 17, 2007, 40 CFR 51.308(b), with subsequent SIP submissions
containing updated long-term strategies originally due July 31, 2018, and every ten years
thereafter. (64 FR 35714 at 35768, July 1, 1999). The EPA established in the 1999 RHR that all
states either have Class I Areas within their borders or “contain sources whose emissions are
reasonably anticipated to contribute to Regional Haze in a Class I Area”; therefore, all states
must submit Regional Haze SIPs.6 Id. at 35721.
Much of the focus in the first implementation period of the Regional Haze program,
which ran from 2007 through 2018, was on satisfying states’ BART obligations. First
implementation period SIPs were additionally required to contain long-term strategies for
making reasonable progress toward the national visibility goal, of which BART is one
component. The core required elements for the first implementation period SIPs (other than
BART) are laid out in 40 CFR 51.308(d). Those provisions required that states containing Class I
Areas establish reasonable progress goals (RPGs) that are measured in deciviews and reflect the
anticipated visibility conditions at the end of the implementation period including from
implementation of states’ long-term strategies. The first planning period RPGs were required to
provide for an improvement in visibility for the most impaired days over the period of the
implementation plan and ensure no degradation in visibility for the least impaired days over the
same period. In establishing the RPGs for any Class I Area in a state, the state was required to

In addition to each of the fifty states, the EPA also concluded that the Virgin Islands and District of Columbia must
also submit regional haze SIPs because they either contain a Class I area or contain sources whose emissions are
reasonably anticipated to contribute regional haze in a Class I area. See 40 CFR 51.300(b), (d)(3).
consider four statutory 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 potentially affected sources. CAA section 169A(g)(1); 40 CFR 51.308(d)(1).
States were also required to calculate baseline (using the five year period of 2000-2004)
and natural visibility conditions (i.e., visibility conditions without anthropogenic visibility
impairment) for each Class I Area, and to calculate 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 known as the uniform rate
of progress (URP) and 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.7 40 CFR
51.308(d)(1)(i)(B), (d)(2). The 1999 RHR also provided that States’ long-term strategies must
include the “enforceable emissions limitations, compliance, schedules, and other measures as
necessary to achieve the reasonable progress goals.” 40 CFR 51.308(d)(3). In establishing their
long-term strategies, states are required to consult with other states that also contribute to
visibility impairment in a given Class I Area and include all measures necessary to obtain their
shares of the emission reductions needed to meet the RPGs. 40 CFR 51.308(d)(3)(i) and (ii).
Section 51.308(d) also contains seven additional factors states must consider in formulating their
long-term strategies, 40 CFR 51.308(d)(3)(v), as well as provisions governing monitoring and
other implementation plan requirements. 40 CFR 51.308(d)(4). Finally, the 1999 RHR required
states to submit periodic progress reports—SIP revisions due every five years that contain
information on states’ implementation of their Regional Haze plans and an assessment of

The EPA established the URP framework in the 1999 RHR to provide “an equitable analytical approach” to
assessing the rate of visibility improvement at Class I areas across the country. The start point for the URP analysis
is 2004 and the endpoint was calculated based on the amount of visibility improvement that was anticipated to result
from implementation of existing CAA programs over the period from the mid-1990s to approximately 2005.
Assuming this rate of progress would continue into the future, the EPA determined that natural visibility conditions
would be reached in 60 years, or 2064 (60 years from the baseline starting point of 2004). However, the EPA did not
establish 2064 as the year by which the national goal must be reached. 64 FR at 35731-32. That is, the URP and the
2064 date are not enforceable targets, but are rather tools that “allow for analytical comparisons between the rate of
progress that would be achieved by the state’s chosen set of control measures and the URP.” (82 FR 3078, 3084,
January 10, 2017).
whether anything additional is needed to make reasonable progress, see 40 CFR 51.308(g), (h)—
and to consult with the Federal Land Manager(s)8 (FLMs) responsible for each Class I area
according to the requirements in CAA section 169A(d) and 40 CFR 51.308(i).
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 2017
rulemaking made several changes to the requirements for Regional Haze SIPs to clarify States’
obligations and streamline certain Regional Haze requirements. The revisions to the Regional
Haze program for the second and subsequent implementation periods focused on the requirement
that States’ SIPs contain long-term strategies for making reasonable progress towards the
national visibility goal. The reasonable progress requirements as revised in the 2017 rulemaking
(referred to here as the 2017 RHR Revisions) are codified at 40 CFR 51.308(f). Among other
changes, the 2017 RHR Revisions adjusted the deadline for States to submit their second
implementation period SIPs from July 31, 2018, to July 31, 2021, clarified the order of analysis
and the relationship between RPGs and the long-term strategy, and focused on making visibility
improvements on the days with the most anthropogenic visibility impairment, as opposed to the
days with the most visibility impairment overall. The EPA also revised requirements of the
visibility protection program related to periodic progress reports and FLM consultation. The
specific requirements applicable to second implementation period Regional Haze SIP
submissions are addressed in detail below.
The EPA provided guidance to the states for their second implementation period SIP
submissions in the preamble to the 2017 RHR Revisions as well as in subsequent, stand-alone
guidance documents. In August 2019, the EPA issued “Guidance on Regional Haze State
Implementation Plans for the Second Implementation Period” (“2019 Guidance”).9 On July 8,

The EPA’s regulations define “Federal Land Manager” as “the Secretary of the department with authority over the
Federal Class I area (or the Secretary’s designee) or, with respect to Roosevelt-Campobello International Park, the
Chairman of the Roosevelt-Campobello International Park Commission.” 40 CFR 51.301.
9 Guidance on Regional Haze State Implementation Plans for the Second Implementation Period.
https://www.epa.gov/visibility/guidance-regional-haze-state-implementation-plans-second-implementation-period
The EPA Office of Air Quality Planning and Standards, Research Triangle Park (August 20, 2019).
2021, the EPA issued a memorandum containing “Clarifications Regarding Regional Haze State
Implementation Plans for the Second Implementation Period” (“2021 Clarifications Memo”).10
Additionally, the EPA further clarified the recommended procedures for processing ambient
visibility data and optionally adjusting the URP to account for international anthropogenic and
prescribed fire impacts in two technical guidance documents: the December 2018 “Technical
Guidance on Tracking Visibility Progress for the Second Implementation Period of the Regional
Haze Program” (“2018 Visibility Tracking Guidance”),11 and the June 2020 “Recommendation
for the Use of Patched and Substituted Data and Clarification of Data Completeness for Tracking
Visibility Progress for the Second Implementation Period of the Regional Haze Program” and
associated Technical Addendum (“2020 Data Completeness Memo”).12
As previously explained in the 2021 Clarifications Memo, the EPA intends the second
implementation period of the Regional Haze program to secure meaningful reductions in
visibility impairing pollutants that build on the significant progress states have achieved to date.
The Agency also recognizes that analyses regarding reasonable progress are state-specific and
that, based on states’ and sources’ individual circumstances, what constitutes reasonable
reductions in visibility impairing pollutants will vary from state-to-state. While there exist many
opportunities for states to leverage both ongoing and upcoming emission reductions under other
CAA programs, the Agency expects states to undertake rigorous reasonable progress analyses
that identify further opportunities to advance the national visibility goal consistent with the
statutory and regulatory requirements. See generally 2021 Clarifications Memo. This is

Clarifications Regarding Regional Haze State Implementation Plans for the Second Implementation Period.
https://www.epa.gov/system/files/documents/2021-07/clarifications-regarding-regional-haze-state-implementationplans-for-the-second-implementation-period.pdf. The EPA Office of Air Quality Planning and Standards, Research
Triangle Park (July 8, 2021).
11 Technical Guidance on Tracking Visibility Progress for the Second Implementation Period of the Regional Haze
Program. https://www.epa.gov/visibility/technical-guidance-tracking-visibility-progress-second-implementationperiod-regional The EPA Office of Air Quality Planning and Standards, Research Triangle Park. (December 20,
2018).
12 Recommendation for the Use of Patched and Substituted Data and Clarification of Data Completeness for
Tracking Visibility Progress for the Second Implementation Period of the Regional Haze Program.
https://www.epa.gov/visibility/memo-and-technical-addendum-ambient-data-usage-and-completeness-regionalhaze-program The EPA Office of Air Quality Planning and Standards, Research Triangle Park (June 3, 2020).
consistent with Congress’s determination that a visibility protection program is needed in
addition to the CAA’s National Ambient Air Quality Standards (NAAQS) and Prevention of
Significant Deterioration (PSD) programs, as further emission reductions may be necessary to
adequately protect visibility in Class I areas throughout the country.13
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. In order
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),14 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 PM and other pollutants leading to
Regional Haze, and help states meet the consultation requirements of the RHR.
The Central Regional Air Planning association (CenRAP), one of the five RPOs
mentioned above, that Missouri was a member of during the first planning period, was a
collaborative effort of state governments, tribal governments, and Federal agencies established to
initiate and coordinate activities associated with the management of Regional Haze, visibility,
and other air quality issues in parts of the Great Plains, Midwest, Southwest, and South Regions
of the United States.

See, e.g., H.R. Rep No. 95-294 at 205 (“In determining how to best remedy the growing visibility problem in
these areas of great scenic importance, the committee realizes that as a matter of equity, the national ambient air
quality standards cannot be revised to adequately protect visibility in all areas of the country.”), (“the mandatory
class I increments of [the PSD program] do not adequately protect visibility in class I areas”).
14 RPOs are sometimes also referred to as “multi-jurisdictional organizations,” or MJOs. For the purposes of this
document, the terms RPO and MJO are synonymous.
After the first planning period SIPs were submitted, the CenRAP was disbanded, and the
relevant regulatory entities reorganized as the Central States Air Resources Agencies
(CenSARA). CenSARA is a collaborative effort of state governments established to initiate and
coordinate activities associated with the management of Regional Haze and other air quality
issues in parts of the Great Plains, Midwest, Southwest, and South Regions of the United States.
Member states include: Arkansas, Iowa, Missouri, Louisiana, Kansas, Missouri, Nebraska,
Oklahoma, and Texas. Unlike CenRAP, CenSARA’s voting members are only comprised of
state agency representatives. However, CenSARA continues to include interested Tribal and
Federal partners on communications and regular meetings. The Federal partners of CenSARA
are the EPA, NPS, FWS, and FS.
IV. 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 are 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 state’s 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, § 51.308(f) lays
out the process by which states determine what constitutes their long-term strategies, with the
order of the requirements in § 51.308(f)(1) through (f)(3) generally mirroring the order of the
steps in the reasonable progress analysis15 and paragraphs (f)(4) through (f)(6) containing
additional, related requirements. 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) and (f)(2). For each Class I area within its

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 40 CFR 51.308(d), “tracked the actual planning sequence.” (82 FR 3078 at
3091, January 10, 2017).
borders, a state must then calculate the baseline, current, and natural visibility conditions for that
area, as well as the visibility improvement made to date and the URP. See 40 CFR 51.308(f)(1).
Each state having a Class I area and/or emissions that may affect visibility in a Class I area must
then develop a long-term strategy that includes the enforceable emission limitations, compliance
schedules, and other measures that are necessary to make reasonable progress in such areas. A
reasonable progress determination is based on applying the four factors in CAA section
169A(g)(1) to sources of visibility-impairing pollutants that the state has selected to assess for
controls for the second implementation period. Additionally, as further explained below, the
RHR at 40 CFR 51.3108(f)(2)(iv) separately provides five “additional factors”16 that states must
consider in developing their long-term strategies. See 40 CFR 51.308(f)(2). A state evaluates
potential emission reduction measures for those selected sources and determines which are
necessary to make reasonable progress using the four statutory factors. Those measures are then
incorporated into the state’s long-term strategy. 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).
In addition to satisfying the requirements at 40 CFR 51.308(f) related to reasonable
progress, the Regional Haze SIP revisions for the second implementation period must address the

The five “additional factors” for consideration in section 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.
requirements in § 51.308(g)(1) through (5) pertaining to periodic reports describing progress
towards the RPGs, 40 CFR 51.308(f)(5), as well as requirements for FLM consultation that apply
to all visibility protection SIPs and SIP revisions. 40 CFR 51.308(i).
A state must submit its Regional Haze SIP and subsequent SIP revisions to the EPA
according to the requirements applicable to all SIP revisions under the CAA and the EPA’s
regulations. See CAA section 169(b)(2); CAA section 110(a). Upon EPA approval, a SIP is
enforceable by the Agency and the public under the CAA. If the EPA finds that a state fails to
make a required SIP revision, or if the EPA finds that a state’s SIP is incomplete or if
disapproves the SIP, the Agency must promulgate a Federal Implementation Plan (FIP) that
satisfies the applicable requirements. CAA section 110(c)(1).
A. Identification of Class I Areas
The first step in developing a Regional Haze SIP is for a state to determine which Class I
areas, in addition to those within its borders, “may be affected” by emissions from within the
state. In the 1999 RHR, the EPA determined that all states contribute to visibility impairment in
at least one Class I area, 64 FR 35714 at 35720 through 35722, and explained that the statute and
regulations lay out an “extremely low triggering threshold” for determining “whether States
should be required to engage in air quality planning and analysis as a prerequisite to determining
the need for control of emissions from sources within their State.” Id. at 35721.
A state must determine which Class I areas must be addressed by its SIP by evaluating
the total emissions of visibility impairing pollutants from all sources within the state. While the
RHR does not require this evaluation to be conducted in any particular manner, the EPA’s 2019
Guidance provides recommendations for how such an assessment might be accomplished,
including by, where appropriate, using the determinations previously made for the first
implementation period. 2019 Guidance at 8-9. In addition, the determination of which Class I
areas may be affected by a state’s emissions is subject to the requirement in 40 CFR
51.308(f)(2)(iii) to “document the technical basis, including modeling, monitoring, cost,

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
Federal area it affects.”
B. Calculations of Baseline, Current, and Natural Visibility Conditions; Progress to Date; and
the Uniform Rate of Progress
As part of assessing whether a SIP submission for the second implementation period is
providing for reasonable progress towards the national visibility goal, the RHR contains
requirements in § 51.308(f)(1) related to tracking visibility improvement over time. The
requirements of this subsection apply only to states having Class I areas within their borders; the
required calculations must be made for each such Class I area. The EPA’s 2018 Visibility
Tracking Guidance17 provides recommendations to assist states in satisfying their obligations
under § 51.308(f)(1); specifically, in developing information on baseline, current, and natural
visibility conditions, and in making optional adjustments to the URP to account for the impacts
of international anthropogenic emissions and prescribed fires. See 82 FR 3078 at 3103 through
3105, January 10, 2017.
The RHR requires tracking of visibility conditions on two sets of days: the clearest and
the most impaired days. Visibility conditions for both sets of days are expressed as the average
deciview index for the relevant five-year period (the period representing baseline or current
visibility conditions). The RHR provides that the relevant sets of days for visibility tracking
purposes are the 20% clearest (the 20% of monitored days in a calendar year with the lowest
values of the deciview index) and 20% most impaired days (the 20% of monitored days in a
calendar year with the highest amounts of anthropogenic visibility impairment).18 40 CFR
51.301. A state must calculate visibility conditions for both the 20% clearest and 20% most

The 2018 Visibility Tracking Guidance references and relies on parts of the 2003 Tracking Guidance: “Guidance
for Tracking Progress Under the RHR,” which can be found at
https://www3.epa.gov/ttnamti1/files/ambient/visible/tracking.pdf.
18 This publication also refers to the 20% clearest and 20% most anthropogenically impaired days as the “clearest”
and “most impaired” or “most anthropogenically impaired” days, respectively.
impaired days for the baseline period of 2000-2004 and the most recent five-year period for
which visibility monitoring data are available (representing current visibility conditions). 40 CFR
51.308(f)(1)(i) and (iii). States must also calculate natural visibility conditions for the clearest
and most impaired days,19 by estimating the conditions that would exist on those two sets of days
absent anthropogenic visibility impairment. 40 CFR 51.308(f)(1)(ii). Using all these data, states
must then calculate, for each Class I area, the amount of progress made since the baseline period
(2000-2004) and how much improvement is left to achieve in order to reach natural visibility
conditions.
Using the data for the set of most impaired days only, states must plot a line between
visibility conditions in the baseline period and natural visibility conditions for each Class I area
to determine the URP—the amount of visibility improvement, measured in deciviews, that would
need to be achieved during each implementation period in order to achieve natural visibility
conditions by the end of 2064. The URP is used in later steps of the reasonable progress analysis
for informational purposes and to provide a non-enforceable benchmark against which to assess
a Class I area’s rate of visibility improvement.20 Additionally, in the 2017 RHR Revisions, the
EPA provided states the option of proposing to adjust the endpoint of the URP to account for
impacts of anthropogenic sources outside the United States and/or impacts of certain types of
wildland prescribed fires. These adjustments, which must be approved by the EPA, are intended
to avoid any perception that states should compensate for impacts from international
anthropogenic sources and to give states the flexibility to determine that limiting the use of

The RHR at 40 CFR 51.308(f)(1)(ii) contains an error related to the requirement for calculating two sets of natural
conditions values. The rule says “most impaired days or the clearest days” where it should say “most impaired days
and clearest days.” This is an error that was intended to be corrected in the 2017 RHR Revisions but did not get
corrected in the final rule language. This is supported by the preamble text at 82 FR 3078 at 3098, January 10, 2017:
“In the final version of 40 CFR 51.308(f)(1)(ii), an occurrence of ‘‘or’’ has been corrected to ‘‘and’’ to indicate that
natural visibility conditions for both the most impaired days and the clearest days must be based on available
monitoring information.”
20 Being on or below the URP is not a “safe harbor”; i.e., achieving the URP does not mean that a Class I area is
making “reasonable progress” and does not relieve a state from using the four statutory factors to determine what
level of control is needed to achieve such progress. See, e.g., 82 FR 3078 at 3093, January 10, 2017.
wildland-prescribed fire is not necessary for reasonable progress. 82 FR 3078 at 3107 footnote
116, January 10, 2017.
The EPA’s 2018 Visibility Tracking Guidance can be used to help satisfy the 40 CFR
51.308(f)(1) requirements, including in developing information on baseline, current, and natural
visibility conditions, and in making optional adjustments to the URP. In addition, the 2020 Data
Completeness Memo provides recommendations on the data completeness language referenced
in § 51.308(f)(1)(i) and provides updated natural conditions estimates for each Class I area.
C. Long-Term Strategy for Regional Haze
The core component of a Regional Haze SIP submission is a long-term strategy that
addresses Regional Haze in each Class I area within a state’s borders and each Class I area that
may be affected by emissions from the state. The long-term strategy “must include the
enforceable emissions limitations, compliance schedules, and other measures that are necessary
to make reasonable progress, as determined pursuant to paragraphs (f)(2)(i) through (iv).” 40
CFR 51.308(f)(2). The amount of progress that is “reasonable progress” is based on applying the
four statutory factors in CAA section 169A(g)(1) in an evaluation of potential control options for
sources of visibility impairing pollutants, which is referred to as a “four-factor” analysis. The
outcome of that analysis is the emission reduction measures that a particular source or group of
sources needs to implement in order to make reasonable progress towards the national visibility
goal. See 40 CFR 51.308(f)(2)(i). Emission reduction measures that are necessary to make
reasonable progress may be either new, additional control measures for a source, or they may be
the existing emission reduction measures that a source is already implementing. See 2019
Guidance at 43; 2021 Clarifications Memo at 8-10. Such measures must be represented by
“enforceable emissions limitations, compliance schedules, and other measures” (i.e., any
additional compliance tools) in a state’s long-term strategy in its SIP. 40 CFR 51.308(f)(2).
Section 51.308(f)(2)(i) provides the requirements for the four-factor analysis. The first
step of this analysis entails selecting the sources to be evaluated for emission reduction

measures; to this end, the RHR requires states to consider “major and minor stationary sources or
groups of sources, mobile sources, and area sources” of visibility impairing pollutants for
potential four-factor control analysis. 40 CFR 51.308(f)(2)(i). A threshold question at this step is
which visibility impairing pollutants will be analyzed. As the EPA previously explained,
consistent with the first implementation period, the EPA generally expects that each state will
analyze at least SO2 and NOx in selecting sources and determining control measures. See 2019
Guidance at 12, 2021 Clarifications Memo at 4. A state that chooses not to consider at least these
two pollutants should demonstrate why such consideration would be unreasonable. 2021
Clarifications Memo at 4.
While states have the option to analyze all sources, the 2019 Guidance explains that “an
analysis of control measures is not required for every source in each implementation period,” and
that “[s]electing a set of sources for analysis of control measures in each implementation period
is . . . consistent with the RHR, which sets up an iterative planning process and anticipates that a
state may not need to analyze control measures for all its sources in a given SIP revision.” 2019
Guidance at 9. However, given that source selection is the basis of all subsequent control
determinations, a reasonable source selection process “should be designed and conducted to
ensure that source selection results in a set of pollutants and sources the evaluation of which has
the potential to meaningfully reduce their contributions to visibility impairment.” 2021
Clarifications Memo at 3.
The EPA explained in the 2021 Clarifications Memo that each state has an obligation to
submit a long-term strategy that addresses the Regional Haze visibility impairment that results
from emissions from within that state. Thus, source selection should focus on the in-state
contribution to visibility impairment and be designed to capture a meaningful portion of the
state’s total contribution to visibility impairment in Class I areas. A state should not decline to

select its largest in-state sources on the basis that there are even larger out-of-state contributors.
2021 Clarifications Memo at 4.21
Thus, 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.22 This is accomplished by considering the Four Factors—"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.” CAA section 169A(g)(1). The EPA has explained that the fourfactor 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 in order to satisfy the CAA’s reasonable
progress mandate.” 82 FR 3078 at 3091, January 10, 2017. Thus, for each source it has selected

Similarly, in responding to comments on the 2017 RHR Revisions, the EPA explained that “[a] state should not
fail to address its many relatively low-impact sources merely because it only has such sources and another state has
even more low-impact sources and/or some high impact sources.” Responses to Comments on Protection of
Visibility: Amendments to Requirements for State Plans; Proposed Rule. Docket Document ID: EPA-HQ-OAR2015-0531-0635 at pages 87-88.
22 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 planning period.
for four-factor analysis,23 a state must consider a “meaningful set” of technically feasible control
options for reducing emissions of visibility impairing pollutants. Id. at 3088. The 2019 Guidance
provides that “[a] state must reasonably pick and justify the measures that it will consider,
recognizing that there is no statutory or regulatory requirement to consider all technically
feasible measures or any particular measures. A range of technically feasible measures available
to reduce emissions would be one way to justify a reasonable set.” 2019 Guidance at 29.
The EPA’s 2021 Clarifications Memo provides further guidance on what constitutes a
reasonable set of control options for consideration: “A reasonable four-factor analysis will
consider the full range of potentially reasonable options for reducing emissions.” 2021
Clarifications Memo at 7. In addition to add-on controls and other retrofits (i.e., new emission
reduction measures for sources), the EPA explained that states should generally analyze
efficiency improvements for sources’ existing measures as control options in their four-factor
analyses, as in many cases such improvements are reasonable given that they typically involve
only additional operation and maintenance costs. Additionally, the 2021 Clarifications Memo
provides that states that have assumed a higher emission rate than a source has achieved or could
potentially achieve using its existing measures should also consider lower emission rates as
potential control options. That is, a state should consider a source’s recent actual and projected
emission rates to determine if it could reasonably attain lower emission rates with its existing
measures. If so, the state should analyze the lower emission rate as a control option for reducing
emissions. 2021 Clarifications Memo at 7. The EPA’s recommendations to analyze potential
efficiency improvements and achievable lower emission rates apply to both sources that have

“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 3078
at 3088, January 10, 2017. However, not all approaches to grouping sources for four-factor analysis are necessarily
reasonable; the reasonableness of grouping sources in any particular instance will depend on the circumstances and
the manner in which grouping is conducted. If it is feasible to establish and enforce different requirements for
sources or subgroups of sources, and if relevant factors can be quantified for those sources or subgroups, then states
should make a separate reasonable progress determination for each source or subgroup. 2021 Clarifications Memo at
7-8.
been selected for four-factor analysis and those that have forgone a four-factor analysis on the
basis of existing “effective controls.” See 2021 Clarifications Memo at 5, 10.
After identifying a reasonable set of potential control options for the sources it has
selected, a state then collects information on the Four Factors with regard to each option
identified. 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.24 The 2019 Guidance provides recommendations for
the types of information that can be used to characterize the Four Factors (with or without
visibility), as well as ways in which states might reasonably consider and balance that
information to determine which of the potential control options is necessary to make reasonable
progress. See 2019 Guidance at 30-36. The 2021 Clarifications Memo contains further guidance
on how states can reasonably consider modeled visibility impacts or benefits in the context of a
four-factor analysis. 2021 Clarifications Memo at 12-13, 14-15. Specifically, the EPA explained
that while visibility can reasonably be used when comparing and choosing between multiple
reasonable control options, it should not be used to summarily reject controls that are reasonable
given the four statutory factors. 2021 Clarifications Memo at 13. Ultimately, while states have
discretion to reasonably weigh the factors and to determine what level of control is needed, §
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.”
As explained above, § 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 § 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

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 Number EPA-HQ-OAR-2015-0531, U.S. Environmental
Protection Agency at 186; 2019 Guidance at 36-37.
SIP.25 If the outcome of a four-factor analysis is a new, additional emission reduction measure
for a source, that new measure is necessary to make reasonable progress towards remedying
existing anthropogenic visibility impairment and must be included in the SIP. If the outcome of a
four-factor analysis is that no new measures are reasonable for a source, continued
implementation of the source’s existing measures is generally necessary to prevent future
emission increases and thus to make reasonable progress towards the second part of the national
visibility goal: preventing future anthropogenic visibility impairment. See CAA section
169A(a)(1). That is, when the result of a four-factor analysis is that no new measures are
necessary to make reasonable progress, the source’s existing measures are generally necessary to
make reasonable progress and must be included in the SIP. However, there may be
circumstances in which a state can demonstrate that a source’s existing measures are not
necessary to make reasonable progress. Specifically, if a state can demonstrate that a source will
continue to implement its existing measures and will not increase its emission rate, it may not be
necessary to have those measures in the long-term strategy in order to prevent future emission
increases and future visibility impairment. The EPA’s 2021 Clarifications Memo provides
further explanation and guidance on how states may demonstrate that a source’s existing
measures are not necessary to make reasonable progress. See 2021 Clarifications Memo at 8 -10.
If the state can make such a demonstration, it need not include a source’s existing measures in
the long-term strategy or its SIP.
As with source selection, the characterization of information on each of the factors is also
subject to the documentation requirement in § 51.308(f)(2)(iii). The reasonable progress analysis,
including source selection, information gathering, characterization of the four statutory factors

States may choose to, but are not required to, include measures in their long-term strategies beyond just the
emission reduction measures that are necessary for reasonable progress. See 2021 Clarifications Memo at 16. For
example, states with smoke management programs may choose to submit their smoke management plans to the EPA
for inclusion in their SIPs but are not required to do so. See, e.g., 82 FR 3078 at 3108 and 3109, January 10, 2017
(requirement to consider smoke management practices and smoke management programs under 40 CFR
51.308(f)(2)(iv) does not require states to adopt such practices or programs into their SIPs, although they may elect
to do so).
(and potentially visibility), balancing of the Four Factors, and selection of the emission reduction
measures that represent reasonable progress, is a technically complex exercise, but also a flexible
one that provides states with bounded discretion to design and implement approaches appropriate
to their circumstances. Given this flexibility, § 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. This documentation requirement can be met through the provision of and
reliance on technical analyses developed through a regional planning process, so long as that
process and its output has been approved by all state participants. In addition to the explicit
regulatory requirement to document the technical basis of their reasonable progress
determinations, states are also subject to the general principle that those determinations must be
reasonably moored to the statute.26 That is, a state’s decisions about the emission reduction
measures that are necessary to make reasonable progress must be consistent with the statutory
goal of remedying existing and preventing future visibility impairment.
The four statutory factors (and potentially visibility) are used to determine what emission
reduction measures for selected sources must be included in a state’s long-term strategy for
making reasonable progress. Additionally, the RHR at 40 CFR 51.3108(f)(2)(iv) separately
provides five “additional factors”27 that states must consider in developing their long-term
strategies: (1) emission reductions due to ongoing air pollution control programs, including

See Arizona ex rel. Darwin v. U.S. EPA, 815 F.3d 519, 531 (9th Cir. 2016); Nebraska v. U.S. EPA, 812 F.3d 662,
668 (8th Cir. 2016); North Dakota v. EPA, 730 F.3d 750, 761 (8th Cir. 2013); Oklahoma v. EPA, 723 F.3d 1201,
1206, 1208-10 (10th Cir. 2013); cf. also Nat’l Parks Conservation Ass’n v. EPA, 803 F.3d 151, 165 (3d Cir. 2015);
Alaska Dep’t of Envtl. Conservation v. EPA, 540 U.S. 461, 485, 490 (2004).
27 The five “additional factors” for consideration in section 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.
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. The 2019 Guidance provides that a state may satisfy this
requirement by considering these additional factors in the process of selecting sources for fourfactor analysis, when performing that analysis, or both, and that not every one of the additional
factors needs to be considered at the same stage of the process. See 2019 Guidance at 21. The
EPA provided further guidance on the five additional factors in the 2021 Clarifications Memo,
explaining that a state should generally not reject cost-effective and otherwise reasonable
controls merely because there have been emission reductions since the first planning period
owing to other ongoing air pollution control programs or merely because visibility is otherwise
projected to improve at Class I areas. Additionally, states generally should not rely on these
additional factors to summarily assert that the state has already made sufficient progress and,
therefore, no sources need to be selected or no new controls are needed regardless of the
outcome of four-factor analyses. 2021 Clarifications Memo at 13.
Because the air pollution that causes Regional Haze crosses state boundaries, §
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. Consultation
allows for each state that impacts visibility in an area to share whatever technical information,
analyses, and control determinations may be necessary to develop coordinated emission
management strategies. This coordination may be managed through inter- and intra-RPO
consultation and the development of regional emissions strategies; additional consultations
between states outside of RPO processes may also occur. 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). The EPA will consider the technical information and
explanations presented by the submitting state and the state with which it disagrees when
considering whether to approve the state’s SIP. See id.; 2019 Guidance at 53. 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).
D. Reasonable Progress Goals
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 3078 at 3091, January 10, 2017. Their primary purpose is to assist
the public and the EPA in assessing the reasonableness of states’ long-term strategies for making
reasonable progress towards the national visibility goal. See 40 CFR 51.308(f)(3)(iii) and (iv).
States in which Class I areas are located must establish two RPGs, both in deciviews – one
representing visibility conditions on the clearest days and one representing visibility on the most
anthropogenically impaired days – for each area within their borders. 40 CFR 51.308(f)(3)(i).
The two RPGs are intended to reflect the projected impacts, on the two sets of days, of the
emission reduction measures the state with the Class I area, as well as all other contributing
states, have included in their long-term strategies for the second implementation period.28 The

RPGs are intended to reflect the projected impacts of the measures all contributing states include in their longterm strategies. However, due to the timing of analyses and of control determinations by other states, other on-going
RPGs also account for the projected impacts of implementing other CAA requirements,
including non-SIP based requirements. Because RPGs are the modeled result of the measures in
states’ long-term strategies (as well as other measures required under the CAA), they cannot be
determined before states have conducted their four-factor analyses and determined the control
measures that are necessary to make reasonable progress. See 2021 Clarifications Memo at 6.
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); rather, they “provide a way for the
states to check the projected outcome of the [long-term strategy] against the goals for visibility
improvement.” 2019 Guidance at 46. While states are not legally obligated to achieve the
visibility conditions described in their RPGs, § 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.” Thus, states are required to have emission reduction
measures in their long-term strategies that are projected to achieve visibility conditions on the
most impaired days that are better than the baseline period and shows no degradation on the
clearest days compared to the clearest days from the baseline period. The baseline period for the
purpose of this comparison is the baseline visibility condition – the annual average visibility
condition for the period 2000 through 2004. See 40 CFR 51.308(f)(1)(i), 82 FR 3078 at 3097 and
3098, January 10, 2017.
So that RPGs may also serve as a metric for assessing the amount of progress a state is
making towards the national visibility goal, 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

emissions changes, a particular state’s RPGs may not reflect all control measures and emissions reductions that are
expected to occur by the end of the implementation period. The 2019 Guidance provides recommendations for
addressing the timing of RPG calculations when states are developing their long-term strategies on disparate
schedules, as well as for adjusting RPGs using a post-modeling approach. 2019 Guidance at 47-48.

conditions in the baseline period of 2000-2004 to natural visibility conditions in 2064). If the
most impaired days RPG in 2028 is above the URP (i.e., if visibility conditions are improving
more slowly than the rate described by the URP), each state that contributes to visibility
impairment in the Class I area must demonstrate, based on the four-factor analysis required
under 40 CFR 51.308(f)(2)(i), that no additional emission reduction measures would be
reasonable to include in its long-term strategy. 40 CFR 51.308(f)(3)(ii). To this end, 40 CFR
51.308(f)(3)(ii) requires that each state contributing to visibility impairment in a Class I area that
is projected to improve more slowly than the URP provide “a robust demonstration, including
documenting the criteria used to determine which sources or groups [of] sources were evaluated
and how the Four Factors required by paragraph (f)(2)(i) were taken into consideration in
selecting the measures for inclusion in its long-term strategy.” The 2019 Guidance provides
suggestions about how such a “robust demonstration” might be conducted. See 2019 Guidance at
50-51.
The 2017 RHR, 2019 Guidance, and 2021 Clarifications Memo also explain that
projecting an RPG that is on or below the URP based on only on-the-books and/or on-the-way
control measures (i.e., control measures already required or anticipated before the four-factor
analysis is conducted) is not a “safe harbor” from the CAA’s and RHR’s requirement that all
states must conduct a four-factor analysis to determine what emission reduction measures
constitute reasonable progress. The URP is a planning metric used to gauge the amount of
progress made thus far and the amount left before reaching natural visibility conditions.
However, the URP is not based on consideration of the four statutory factors and therefore
cannot answer the question of whether the amount of progress being made in any particular
implementation period is “reasonable progress.” See 82 FR 3078 at 3093, 3099 and 3100,
January 10, 2017; 2019 Guidance at 22; 2021 Clarifications Memo at 15-16.
E. Monitoring Strategy and Other State Implementation Plan Requirements

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 subsection 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.
A state with Class I areas within its borders must submit with its SIP revision a monitoring
strategy for measuring, characterizing, and reporting Regional Haze visibility impairment that is
representative of all Class I areas within the state. SIP revisions for such states must also provide
for the establishment of any additional monitoring sites or equipment needed to assess visibility
conditions in Class I areas, as well as reporting of all visibility monitoring data to the EPA at
least annually. 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), and (f)(6)(iv). The IMPROVE monitoring data is used to determine the 20% most
anthropogenically impaired and 20% clearest sets of days every year at each Class I area and
tracks visibility impairment over time.
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. 40 CFR 51.308(f)(6)(ii) and (iii). Section
51.308(f)(6)(v) further requires that all states’ SIPs provide for a statewide inventory of
emissions of pollutants that are reasonably anticipated to cause or contribute to visibility
impairment in any Class I area; the inventory must include emissions for the most recent year for
which data are available and estimates of future projected emissions. States must also include
commitments to update their inventories periodically. The inventories themselves do not need to
be included as elements in the SIP and are not subject to EPA review as part of the Agency’s

evaluation of a SIP revision.29 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). Per the 2019 Guidance, a state may note in its
Regional Haze SIP that its compliance with the Air Emissions Reporting Rule (AERR) in 40
CFR part 51 subpart A satisfies the requirement to provide for an emissions inventory for the
most recent year for which data are available. To satisfy the requirement to provide estimates of
future projected emissions, a state may explain in its SIP how projected emissions were
developed for use in establishing RPGs for its own and nearby Class I areas.30
Separate from the requirements related to monitoring for Regional Haze purposes under
40 CFR 51.308(f)(6), the RHR also contains a requirement at § 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.”31 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 reasonably attributable visibility
impairment, the state must include in its SIP revision for the second implementation period an
appropriate strategy for evaluating such impairment.
F. Requirements for Periodic Reports Describing Progress Towards the Reasonable Progress
Goals
Section 51.308(f)(5) requires a state’s Regional Haze SIP revision to address the
requirements of 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

See “Step 8: Additional requirements for regional haze SIPs” in 2019 Regional Haze Guidance at 55.
Id.
31 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.
29
and whether such implementation is in fact resulting in the expected visibility improvement. See
81 FR 26942, 26950 (May 4, 2016), (82 FR 3078 at 3119, January 10, 2017). To this end, every
state’s SIP revision for the second implementation period is required to 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).
A core component of the progress report requirements is an assessment of changes in
visibility conditions on the clearest and most impaired days. For second implementation period
progress reports, § 51.308(g)(3) requires states with Class I areas within their borders to first
determine current visibility conditions for each area on the most impaired and clearest days, 40
CFR 51.308(g)(3)(i)(B), and then to calculate the difference between those current conditions
and baseline (2000-2004) visibility conditions in order to assess progress made to date. See 40
CFR 51.308(g)(3)(ii)(B). States must also assess the changes in visibility impairment for the
most impaired and clearest days since they submitted their first implementation period progress
reports. See 40 CFR 51.308 (f)(5) and (g)(3)(iii)(B). Since different states submitted their first
implementation period progress reports at different times, the starting point for this assessment
will vary state by state.
Similarly, states must provide analyses tracking the change in emissions of pollutants
contributing to visibility impairment from all sources and activities within the state over the
period since they submitted their first implementation period progress reports. See 40 CFR
51.308(f)(5) and (g)(4). Changes in emissions should be identified by the type of source or
activity. Section 51.308(g)(5) also addresses changes in emissions since the period addressed by
the previous progress report and requires states’ SIP revisions to include an assessment of any
significant changes in anthropogenic emissions within or outside the state. This assessment must
include an explanation of whether these changes in emissions were anticipated and whether they

have limited or impeded progress in reducing emissions and improving visibility relative to what
the state projected based on its long-term strategy for the first implementation period.
G. Requirements for State and Federal Land Manager Coordination
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). Consultation that occurs 120
days prior to any public hearing or public comment opportunity will be deemed “early enough,”
but the RHR provides that in any event the opportunity for consultation must be provided at least
60 days before a public hearing or comment opportunity. This consultation must include the
opportunity for the FLMs to discuss their assessment of visibility impairment in any Class I area
and their recommendations on the development and implementation of strategies to address such
impairment. 40 CFR 51.308(i)(2). In order 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).

V. The EPA’s Evaluation of Missouri’s Regional Haze Submission for the Second
Implementation Period
A. Background on Missouri’s First Implementation Period SIP Submission
Missouri submitted its Regional Haze SIP for the first implementation period to the EPA
on August 5, 2009, and supplemented on January 30, 2012. Missouri relied on the Clean Air
Interstate Rule (CAIR) to satisfy BART requirements. The EPA approved Missouri’s first
implementation period Regional Haze SIP submission on June 26, 2012 (77 FR 38007, June 26,
2012).32 The requirements for Regional Haze SIPs for the first implementation period are
contained in 40 CFR 51.308(d) and (e). 40 CFR 51.308(b). In July 2008, the CAIR rule was
vacated by the District of Columbia Circuit Court.33 In response on August 8, 2011, the EPA
replaced CAIR with the Cross-State Air Pollution Rule (CSAPR).34 Afterwards, the EPA
promulgated the CSAPR better than BART rule, allowing states to rely on CSAPR to satisfy
BART requirements.35 In that same action, the EPA issued FIPs to replace reliance on CAIR for
BART with reliance on CSAPR to satisfy BART requirements. This action included Missouri.
Pursuant to 40 CFR 51.308(g), Missouri was also required to submit a five-year progress report
as a SIP revision for the first implementation period. On August 5, 2014, Missouri submitted the
required progress report to the EPA. The EPA approved the progress report on September 29,
2015 (80 FR 58410, September 29, 2015). On July 31, 2017, Missouri submitted a SIP revision
to change their reliance on CAIR for BART to relying on CSAPR for BART. The EPA approved
this SIP revision.36
B. Missouri’s Second Implementation Period SIP Submission and the EPA’s Evaluation

The EPA’s action included a limited approval as the state relied on the EPA’s Federal Implementation Plan (FIP)
for the interstate transport program to address the required best available retrofit technology (BART) requirements
for certain electric generating units (EGUs).
33 North Carolina v. EPA, 531 F.3d 896 (D.C. Cir. 2008), modified on rehearing, North Carolina v. EPA, 550 F.3d
1176, 1178 (D.C. Cir. 2008)
34 76 FR 48208 August 8, 2011
35 77 FR 33642 June 7, 2012
36 81 FR 50531 September 24, 2018
In accordance with CAA sections 169A and the RHR at 40 CFR 51.308(f), (g), and (i),
on August 26, 2022, Missouri submitted a revision to Missouri’s SIP to address its Regional
Haze obligations for the second implementation period. Missouri made its second
implementation period Regional Haze SIP submission available for public comment from March
28, 2022, through May 5, 2022. The state held a public hearing for the plan on April 28, 2022.
Missouri received and responded to public comments and included both the comments and
responses to those comments in their submission.
The following sections describe Missouri’s SIP submission as well as the EPA’s
evaluation to determine if Missouri’s submission meets all of the requirements of the CAA and
RHR for the second implementation period of the Regional Haze program.
C. 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 paragraph (f)(2), which
requires each state’s plan to include a long-term strategy that addresses Regional Haze in such
Class I areas.
The EPA explained in the 1999 RHR preamble that the CAA section 169A(b)(2)
requirement that states submit SIPs to address visibility impairment establishes “an ‘extremely
low triggering threshold’ in determining which States should submit SIPs for regional haze.” 64
FR 35714 at 35721, July 1, 1999. In concluding that each of the contiguous 48 states and the

District of Columbia meet this threshold,37 the EPA relied on “a large body of evidence
demonstrat[ing] that long-range transport of fine PM contributes to regional haze,” id., including
modeling studies that “preliminarily demonstrated that each State not having a Class I area had
emissions contributing to impairment in at least one downwind Class I area.” Id. at 35722. In
addition to the technical evidence supporting a conclusion that each state contributes to existing
visibility impairment, the EPA also explained that the second half of the national visibility
goal—preventing future visibility impairment—requires having a framework in place to address
future growth in visibility-impairing emissions and makes it inappropriate to “establish criteria
for excluding States or geographic areas from consideration as potential contributors to regional
haze visibility impairment.” Id. at 35721. Thus, the EPA concluded that the agency’s “statutory
authority and the scientific evidence are sufficient to require all States to develop regional haze
SIPs to ensure the prevention of any future impairment of visibility, and to conduct further
analyses to determine whether additional control measures are needed to ensure reasonable
progress in remedying existing impairment in downwind Class I areas.” Id. at 35722. The EPA’s
2017 revisions to the RHR did not disturb this conclusion. See 82 FR 3078 at 3094, January 10,
2017.
Missouri contains two Class I Areas: Hercules-Glades Wilderness Area and Mingo
National Wildlife Refuge. In Missouri’s Regional Haze plan for the first planning period,
submitted on August 5, 2009, and supplemented on January 30, 2012, Missouri analyzed four
Class I Areas as potentially affected by Missouri emissions. In addition to the two Class I Areas
in Missouri, the state identified Caney Creek Wilderness Area and Upper Buffalo Wilderness
Area located in Arkansas.38 In Missouri’s Regional Haze plan for the second planning period,
submitted August 26, 2022, Missouri identifies nine Class I Areas: Hercules-Glades Wilderness

The EPA determined that “there is more than sufficient evidence to support our conclusion that emissions from
each of the 48 contiguous states and the District of Columba may reasonably be anticipated to cause or contribute to
visibility impairment in a Class I area.” 64 FR 35714 at 35721, July 1, 1999. Hawaii, Alaska, and the U.S. Virgin
Islands must also submit regional haze SIPs because they contain Class I areas.
38 “State of Missouri Air Quality State Implementation Plan Regional Haze, Section D, Plan Revision” Page 47,
submitted November 9, 2009. Available in Docket: EPA–R07–OAR–2012–0153.
Area and Mingo National Wildlife Refuge in Missouri, Upper Buffalo Wilderness Area,
Arkansas, Seney National Wildlife Refuge and Isle Royale Wilderness in Michigan, Mammoth
Cave National Park, Kentucky, Linville Gorge Wilderness Area and Shining Rock Wilderness
Area in North Carolina, and Sipsey Wilderness Area, Alabama; as potentially affected by
Missouri emissions. To make this determination, Missouri primarily relied on the cumulative
sulfate and nitrate extinction weighted residence time (EWRT) multiplied by Q/d (emissions
divided by distance) analysis performed by a CenSARA contractor to identify the sources with
the highest estimated contributions to Class I Areas. As further discussed in section E of this
preamble, Missouri selected sources contributing more than 1 percent to any Class I Area for
further evaluation.39
CenSARA performed technical analyses to help assess source and state-level
contributions to visibility impairment and the need for interstate consultation. CenSARA’s
analyses relied on a back-trajectory model combined with air quality measurement data and
emission inventories to identify the geographic areas and emission sources with a high
probability of contributing to anthropogenically impaired visibility at Class I areas within
CenSARA and nearby states. For the EWRT multiplied by Q/d analysis, back trajectory
residence times were first calculated by summing the amount of time trajectories reside in a
specific geographic area (e.g., modeling grid cell). The trajectory residence times were then
weighted by sulfate and nitrate extinction coefficients to account for the varying contributions of
sulfates and nitrates to total light extinction. To determine the potential impact from sources of
SO2 and NOx emissions (precursors of SO4 and NO3, respectively), the EWRT values for SO4
and NO3 were combined with emissions (Q) from sources of SO2 and NOx, respectively.
CenSARA states chose to focus on electric generating units (EGU) and non-EGU stationary
point sources since these sources comprise major fractions of the NOx and SO2 emissions
inventory. To incorporate the effects of dispersion, deposition and chemical transformation along

See Table 36, starting on page 103 of Missouri’s August 2022 submittal.

the path of the trajectories, emissions were inversely weighted by the distance (d) between the
centers of the grid cell emitting the emissions and the grid cell containing the IMPROVE site.
Missouri also included Class I Areas that were identified through the consultation process
as being affected by sources in Missouri, when the consulting state identified specific Missouri
sources that impact the downwind Class I Area.40 Missouri also consulted with MANE-VU on
Class I Areas in Maine, New Jersey, New Hampshire and Vermont. Neither MANE-VU nor
Missouri specifically list which Areas in those states are affected by Missouri sources. The EPA
believes the affected Class I areas may include: Acadia, Moosehorn, and Roosevelt Campobello
in Maine; Great Gulf and Presidential Range-Dry River in New Hampshire; Brigantine
Wilderness, New Jersey; and Lye Brook, Vermont. New Jersey consulted with Missouri.
Neither MANE-VU nor New Jersey specify a source for which Missouri should conduct a fourfactor analysis for its impact on Brigantine Wilderness. Missouri does not explicitly state why it
treats the MANE-VU Areas different than the other consulted Areas, other than to point out
MANE-VU and New Jersey did not specify a Missouri source to evaluate. While MANE-VU
and New Jersey did not specify a source for Missouri to analyze, MANE-VU did have six
“Asks” of other states. Although Missouri does not include the MANE-VU Class I Areas in the
same way as the other identified Areas, Missouri did consult with MANE-VU and New Jersey
on the “Asks.” Despite the apparent inconsistencies in Missouri’s treatment of Class I Areas, we
find the resulting identification of Class I Areas as being impacted by Missouri sources to be
reasonable. However, the EPA finds this requirement is not separable from the overarching
requirement of 40 CFR 51.308(f)(2) to establish a long-term strategy and as explained in section
V.E. of this preamble, the EPA is proposing to disapprove Missouri’s long-term strategy.
Accordingly, the EPA proposes to disapprove this element of Missouri’s second planning period
regional haze plan.

See Table 37, starting on page 104 of Missouri’s submittal.

D. Calculations of Baseline, Current, and Natural Visibility Conditions; Progress to Date; and
the Uniform Rate of Progress
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).
In Chapter 3 of MoDNR’s submittal, Missouri determines and presents the baseline,
natural, and current visibility conditions as well as the differences between these for both the 20
percent most anthropogenically impaired days and the 20 percent clearest days for the state’s two
Class I Areas consistent with the EPA’s RHR and guidance. Specifically, Missouri presents the
latest available visibility monitoring data as accessed on January 14, 2020, for the most recent 5year period (2014-2018) and the baseline period (2000-2004) as collected at IMPROVE sites and
made available on the Federal Land Manager Environmental Database (FED). Using the EPA’s
revised IMPROVE equation (Pitchford et al., 2007), Missouri also calculated the light extinction
contributions from individual particle components. The state provides the required calculated
visibility data as summarized in Table 1 of this preamble. Missouri also presents the progress
made since the baseline period (2000-2004) as well as the difference between current (20142018) and natural visibility conditions for both the most impaired and clearest days. Missouri
presents the uniform rate of progress data for each Missouri Class I Area and additional light
extinction information for specific particle components in section 3.3.6 of the state’s submittal.
Missouri calculated annual URP values of 0.27 dv/year and 0.29 dv/year needed to reach natural

visibility on the 20% most impaired days at at Hercules-Glades and Mingo, respectively. 41
Missouri’s URP values for 2028 are shown in Table 1 of this preamble. Missouri did not choose
to adjust its URP for international anthropogenic impacts or to account for the impacts of
wildland prescribed fires as allowed in 40 CFR 51.308(f)(1)(vi)(B). Missouri additionally
compares observed and modeled visibility conditions and extinction compositions in section
3.3.9 of the submittal. The EPA further reviews the state’s calculations and visibility data in the
technical support document (TSD) as contained in the docket for this rulemaking. Based on the
EPA’s review, detailed in the TSD, the EPA proposes to find that Missouri appropriately
determined the baseline, current and natural visibility conditions as well as the other required
calculations for the two Missouri Class I Areas and thus meets the requirements of 40 CFR
51.308(f)(1). Therefore, the EPA proposes to approve this element of Missouri’s submission.
Table 1. Missouri Class I Areas Visibility Conditions
Missouri

Baseline 2000-2004

Natural Visibility

Current 2014-2018

2028 Uniform

Class I

Average Visibility

(dv)

Average Visibility (dv)

Rate of Progress

Area

(dv)

Hercules

(dv)

20%

20%

20%

20%

20% Most

20%

Most

Clearest

Most

Clearest Impaired

Clearest

Impaired Days

Impaired

Days

Days

Days

Days

Days

25.17

12.84

9.30

4.69

18.72

9.71

18.82

26.31

14.37

9.24

5.3

20.13

11.08

19.48

Glades
Mingo

See “Table 9. Uniform Annual Rate of Improvements Needed to Reach 2016 Natural Visibility for the Most
Impaired Days” in the MO Regional Haze SIP—Final August 2022.
E. Long-Term Strategy for Regional Haze
1. Source Selection
40 CFR 51.308(f)(2)(i) requires states to “...consider evaluating major and minor
stationary sources or groups of sources, mobile sources, and area sources. The State must include
in its implementation plan a description of the criteria it used to determine which sources or
groups of sources it evaluated and how the four factors were taken into consideration in selecting
the measures for inclusion in its long-term strategy.” 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).
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 § 51.308(f). Where an RPO has performed source
selection and/or four-factor analyses (or considered the five additional factors in §
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 § 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 CFR 51.308(f)(3)(iii). States may also satisfy the requirement of § 51.308(f)(2)(ii) to engage
in interstate consultation with other states that have emissions that are reasonably anticipated to
contribute to visibility impairment in a given Class I area under the auspices of intra- and interRPO engagement.
Missouri explains various methods the state considered when determining which sources
to bring forward for further evaluation. Ultimately, Missouri primarily relied on the cumulative
sulfate and nitrate extinction weighted residence time (EWRT) multiplied by Q/d (emissions
divided by distance) analysis performed by a CenSARA contractor to determine the sources with

the highest estimated contributions to Class I Areas. Missouri selected sources contributing more
than 1 percent to any Class I Area for further evaluation.42 This resulted in the selection of nine
Missouri sources and eighteen out of state sources. Missouri also considered sources identified
by other states, RPOs or FLMs and explained whether they would be further evaluated or not and
the rationale behind that decision. Missouri removed two sources initially selected, Buzzi
Unicem and Ameren Meramec, due to decreasing emissions trends. Specifically, Buzzi Unicem
provided the state with updated emissions information and demonstrated that the reductions were
due to an enforceable consent decree entered in 2017. After the state reevaluated Buzzi Unicem’s
impacts with the updated emissions information, the visibility contribution dropped below the 1
percent threshold used by the state and was therefore removed from further consideration.
Regarding Ameren Meramec, Missouri points out that the facility voluntarily switched two
boilers from burning coal to natural gas in 2016 and that the facility was expected to retire by
December 2022. Due to the expected shutdown date before 2028, Missouri removed Meramec
from consideration of additional control measures. However, the shutdown date cited by
Missouri for Ameren Meramec is not federally enforceable. The EPA independently confirmed
that emissions from the Meramec facility have indeed decreased significantly consistent with
reduced operations preparing for shutdown and with no reported emissions or operating hours in
2023. Given these facts, the EPA finds that removal of these two sources is consistent with the
EPA’s 2019 Guidance and 2021 Clarifications Memo. However, Missouri may also consider in
future planning periods whether evaluation of the removed sources (assuming continued
operation of the sources) would result in a more effective control technology being found
reasonable.
The seven sources Missouri selected for further evaluation are: John Twitty Energy
Center, Associated Electric Cooperative Incorporated (AECI) New Madrid Power Plant, AECI
Thomas Hill Power Plant, Sikeston Power Station, Ameren Labadie Energy Center, Ameren

See Table 36, starting on page 103 of Missouri’s submittal.

Rush Island Energy Center, and Mississippi Lime Company. More information on these sources
is provided here and in the TSD.
John Twitty Energy Center is located in Springfield, Missouri in Greene County. Units 1
and 2 are dry bottom wall fired boilers. Unit 1 has a capacity of 205 megawatts (MW). Unit 2
has a capacity of 309.6 MW. Both units burn Powder River Basin low sulfur coal. Unit 1 does
not utilize SO2 controls. Unit 2 has fluidized bed limestone injection for SO2 control. Both units
have selective catalytic reduction (SCR) for NOx control. Unit 2 also has overfire air (OFA).
Both units have baghouses for particulate control.
AECI New Madrid Power Plant is located near Marston, Missouri in New Madrid
County. Units 1 and 2 are cyclone boilers with capacities of 640 MW each and burn Powder
River Basin low sulfur coal. The units do not utilize SO2 control. For NOx control, both units
have SCR and OFA. For particulate control, both units have electrostatic precipitators (ESP).
AECI Thomas Hill Power Plant is located in Clifton Hill, Missouri in Randolph County.
Units 1 and 2 are cyclone boilers. Unit 3 is a dry bottom wall fired boiler. Unit 1 has capacity of
185 MW. Unit 2 has a capacity of 305 MW. Unit 3 has capacity of 777 MW. All units burn
Powder River Basin low sulfur coal and do not utilize SO2 control. Units 1 and 2 have OFA and
SCR for NOx control. Unit 3 has OFA, low NOx burners, and SCR for NOx control. For
particulate control, all 3 units have ESP.
Sikeston Power Station is located near Sikeston, Missouri in Scott County. Unit 1 is a dry
bottom wall fired boiler with capacity of 235 MW and burns Powder River Basin low sulfur
coal. Unit 1 has a tray/Venturi wet scrubber with control device efficiency of 76% (per state’s
four factor analysis), but the scrubber is not operating and is not easily restarted. The facility
does not currently utilize any SO2 control. For NOx control, Unit 1 has low NOx burners with
OFA. For particulate control, Unit 1 has an ESP.
Ameren Labadie Energy Center is located in Labadie, Missouri in Franklin County. Units
1 and 2 are tangentially fired boilers with capacities of 675 MW each and burn Powder River

Basin low sulfur coal. Units 3 and 4 are tangentially fired boilers with capacities of 690 MW
each and burn Powder River Basin low sulfur coal. None of the units utilize control for SO2. For
NOx control, all of the units have low NOx burners, separated overfire air (SOFA), and neural
network optimization. For particulate control, all of the units have ESP.
Ameren Rush Island Energy Center is located in Festus, Missouri in Jefferson County.
Units 1 and 2 are tangentially fired boilers with capacities of 621 MW each and burn Powder
River Basin low sulfur coal. The units do not utilize SO2 control. For NOx control, both units
have low NOx burners, SOFA, and neural network optimization. For particulate control, both
units have ESP.
Mississippi Lime Company is a lime processing plant located in Ste. Genevieve, Missouri
in Ste. Genevieve County. The following emission units were determined to be the plant’s
primary sources of NOx and SO2 emissions: Peerless Rotary Kilns and Mississippi Rotary Kilns
which fire coal and coke. For SO2 control, the Mississippi Rotary Kilns are equipped with wet
scrubbers. Some kilns have lime injection. The remaining Mississippi Rotary Kiln units do not
have lime injection; however, the facility indicates that the exhaust stream provides inherent
process scrubbing of the exhaust stream due to lime in the process. The facility indicates good
combustion and optimization of processes control of NOx on all the units, and that the Peerless
kilns also utilize a preheater. The units do not have any add-on NOx controls.
Although the EPA finds Missouri’s source selection methodology and the sources
selected for further analysis reasonable for the second planning period, the EPA believes the
RHR requirement at 51.308(f)(2), to consider the four factors in establishing the long-term
strategy, encompasses the selection of sources for further analysis, and therefore is not separable.
For the reasons described in section E.2 of this preamble, the EPA is proposing to disapprove
Missouri’s long-term strategy, which encompasses source selection, in Missouri’s second
implementation period regional haze plan as not meeting the requirements of 40 CFR
51.308(f)(2).

2. Four-Factor Analysis
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). As explained in the Background section of
this document, reasonable progress is achieved when all states contributing to visibility
impairment in a Class I area are implementing the measures determined—through application of
the four statutory factors to sources of visibility impairing pollutants—to be necessary to make
reasonable progress. 40 CFR 51.308(f)(2)(i). Each state’s long-term strategy must include the
enforceable emission limitations, compliance schedules, and other measures that are necessary to
make reasonable progress. 40 CFR 51.308(f)(2). All new (i.e., additional) measures that are the
outcome of four-factor analyses are necessary to make reasonable progress and must be in the
long-term strategy. If the outcome of a four-factor analysis and other measures necessary to
make reasonable progress is that no new measures are reasonable for a source, that source’s
existing measures are necessary to make reasonable progress, unless the state can demonstrate
that the source will continue to implement those measures and will not increase its emission rate.
Existing measures that are necessary to make reasonable progress must also be included as
permanent and federally enforceable43 emissions limits in the long-term strategy. In developing
its long-term strategies, a state must also consider the five additional factors in §
51.308(f)(2)(iv).
In Chapter 4 of Missouri’s submittal, the state explains the four-factor analyses
performed either by the state or the source for the seven Missouri sources that were brought
forward for further evaluation. The state describes how each of the four factors is considered.
First, Missouri explains the cost of compliance is considered by performing a cost analysis for
each source and each technically feasible control measure for both SO2 and NOx. The state also

The EPA also interprets the requirement to be permanent and federally enforceable as being practically
enforceable, i.e., an operational or emissions limit with the necessary reporting and recordkeeping requirements such
that the source reports compliance with and that can practically be measured and enforced.
describes the process used to establish the cost threshold that the state uses to determine whether
the cost effectiveness of each control measure is reasonable and therefore should be included in
the long-term strategy. Specifically, Missouri refers to control cost values from the first
implementation period, compiled by the state of Arkansas, to set a cost threshold derived from
those values. Second, Missouri generally describes how the state assumed the time necessary for
compliance for each control type based on prior EPA studies and literature. Third, Missouri
describes how energy and non-air quality environmental impacts of compliance are considered.
For example, quantifiable energy impacts for a given control type are included in the cost
estimates. Fourth, Missouri explains the two methods used to estimate the remaining useful life
of the sources evaluated while also considering the remaining useful life of the control types. In
response to comment on this point, Missouri included cost estimates assuming the default
remaining useful life values that the EPA recommends using for specific control devices.
Ameren Missouri and Mississippi Lime Company provided full four-factor analyses for
their respective facilities. Missouri performed the four-factor analyses for the remaining sources.
The four-factor analyses presented in Missouri’s SIP cover what Missouri determined to be
technically feasible control measures for both SO2 and NOx for each source. Specifically, the
control technologies evaluated by Missouri are displayed in Table 2 of this preamble.

Table 2. Control Technologies Evaluated by Missouri
SO2 Control Technologies
Flue Gas Desulfurization (FGD) – Wet, Spray Dry, Dry Scrubber (50% to 99% control
efficiency)
• Wet Lime Scrubber, typical control efficiency 90% - 99%
• Wet Limestone Scrubber, typical control efficiency 90% - 99%
• Dual-Alkali Scrubber, typical control efficiency 90%-95%
• Spray Dry Absorber (SDA), typical control efficiency 90%-95%
• Dry Sorbent Injection (DSI), typical control efficiency 50% - 80%
• Circulating Dry Scrubber
• Hydrated Ash Reinjection
Limestone Injection
Low sulfur content coal
Fuel Switch
NOx Control Technologies
Selective Catalytic Reduction (SCR), typical control efficiency 90%
Low NOx Burners (LNB), typical control efficiency 40% - 60%
Selective Non-Catalytic Reduction (SNCR), typical control efficiency 35% - 50%
Overfire Air (OFA), typical control efficiency 20%
Flue Gas Recirculation (FGR)
Low Excess Air (LEA)
The full details for the state and source performed four-factor analyses are included in
Appendix C to the state submittal included in the docket for this action.

Table 3. Summary of Results of Missouri’s Four-Factor Analyses
Annualized Emission Effective
Facility
Unit
Pollutant Control
Technology Cost ($)
Reduction Cost
(tons per
($/ton)
year)
Labadie
SO2
DSI
$27,074,061 7,011
$3,862
B1
Energy Center*
NOx
SNCR
$3,261,106 450
$7,247
B2
SO2
DSI
$27,074,061 7,031
$3,851
NOx
SNCR
$3,261,106 450
$7,247
SO2
DSI
$25,419,801 6,592
$3,856
B3
NOx
SNCR
$3,333,575 425
$7,844
B4
SO2
DSI
$25,419,801 6,854
$3,709
NOx
SNCR
$3,333,575 425
$7,844
SO2
DSI
$28,751,220 6,831
$4,209
Rush Island
B1
Energy Center*
NOx
SNCR
$3,000,218 375
$8,001
B2
SO2
DSI
$28,822,931 7,337
$3,928
NOx
SNCR
$3,000,218 375
$8,001
SO2
DSI
$984,041
11.61
$84,800
EP-069
EP-070 EP- NOx
SNCR
$465,644
24
$19,100
Mississippi
071
Lime
SO2
DSI
$1,344,685 8.62
$156,000
EP-640
Company*
EP-645
NOx
SNCR
$809,506
85
$9,500
EP-180H EPWet Lime
186N
Scrubber
SO2
$1,632,862 171.09
$9,500
EP-187N
B1
SO2
DSI
$20,268,773 5,025
$4,033
New Madrid
Power Plant* B2
SO2
DSI
$22,003,761 5,561
$3,957
Thomas Hill
B1
SO2
DSI
$8,255,270 1,837
$4,494
Energy
B2
SO2
DSI
$12,245,800 2,867
$4,271
Center*
B3
SO2
DSI
$29,936,230 7,698
$3,889
John Twitty
Energy
B1
SO2
DSI
$6,764,511 1,794
$3,771
Center*
SO2
DSI
$13,532,594 3,443
$3,930
Sikeston Power
Station*
B1
NOx
SCR
$7,899,846 774
$10,209
*Missouri noted these cost estimates were calculated assuming a remaining useful life consistent
with the EPA’s control cost manual (CCM), however, some values still do not comport with
EPA’s control cost manual. Specifically, Missouri assumed a 25-year useful life for Wet FGD,
SDA and DSI controls when the EPA recommends a 30-year useful life. Missouri assumed a 30year useful life for SCR and a 20-year useful life for SNCR, consistent with the CCM.
The results of Missouri’s four-factor analyses are shown in Table 3 of this preamble.
Missouri details the cost effectiveness for each control type and unit and categorically concludes
that each control measure is not reasonable because the cost effectiveness exceeds the cost
threshold set by Missouri, as discussed later in this section. Consistent with the finding that new

control measures are not necessary, Missouri finds that current existing operations at each
facility are needed for reasonable progress.
For the reasons described below, the EPA proposes to find that Missouri has not
adequately supported the conclusion that existing measures satisfy the requirement to make
reasonable progress. Missouri has not definitively shown that further reductions of visibility
impairing pollutants are not reasonable and has not adequately explained how its approach is
consistent with the CAA’s requirement to make reasonable progress. The EPA discusses each of
the following lines of evidence that support this proposed finding. First, the state rejected
otherwise reasonable control measures that would reduce tens of thousands of tons of visibility
impairing pollutants and improve visibility at Missouri and other states’ Class I areas. This
decision was based primarily on the unreasonable justification and use of the selected cost
threshold. Second, the state’s cost effectiveness calculations do not fully align with EPA
guidance such as the Control Cost Manual. When the EPA corrects the deficiencies of Missouri’s
cost analysis, we find cost effective controls are available on most if not all sources evaluated by
Missouri. Third, Missouri has not included practically enforceable emissions limits as part of its
long-term strategy to make reasonable progress. Specifically, the included source agreements do
not contain explicit enforceable emissions limits associated with existing operations in addition
to problematic provisions included in the source agreements rendering them unenforceable and
not permanent.
Missouri’s Justification and Use of the Selected Cost Threshold is Unreasonable
Missouri chose to establish a cost threshold based on control cost values from the first
planning period adjusted to 2021 dollars. Using a database of first planning period control
costs,44 Missouri selected a cost threshold of $3,658 per ton specific to SO2 for EGUs by

44Missouri

relied on a dataset compiled by the State of Arkansas. Note that the EPA is not proposing an action with
respect to Arkansas’s regional haze SIP and we are not commenting on the approvability of Arkansas’s use of the
cost methodology, their cost threshold, or their overall SIP. Missouri’s cost threshold dataset is available in
Appendix F to the state submittal, in the docket for this action.

calculating the first planning period mean cost per ton value plus one standard deviation
specifically for new control technologies (i.e., excluding upgrades to existing controls or reliance
on lower sulfur coal). Application of this threshold means that Missouri considers all cost
effectiveness values greater than $3,658 per ton to be not cost effective and therefore rejects the
control measure. Using a similar methodology for NOx controls, Missouri selected a cost
threshold of $5,370 per ton. The EPA commented during both the early engagement period and
the formal comment period requesting further documentation and justification for use of such a
cost threshold. In response to comments, Missouri revised the control cost thresholds to be
slightly higher than originally proposed and provided additional documentation. The EPA also
commented on the fact that multiple sources in the underlying statistical data (in the Appendix F
spreadsheet) installed controls at costs above the state’s threshold including at sources similar to
the sources selected by Missouri. This dataset does not include any Missouri units. By selecting
the mean plus one standard deviation as a cost effectiveness threshold, Missouri appears to
ignore those costs that fall above the threshold, costs that were found reasonable at nine units (or
twenty percent) of the previously analyzed EGUs, most of similar size to the Missouri EGUs.
EPA guidance states that “when the cost/ton of a possible measure is within the range of the
cost/ton values that have been incurred multiple times by sources of similar type to meet regional
haze requirements or any other [Clean Air Act] requirement, this weighs in favor of concluding
that the cost of compliance is not an obstacle to the measure being considered necessary to
make.”45 Missouri states that higher cost/ton values are largely associated with smaller capacity
EGUs and therefore are not directly comparable with cost values for their larger capacity EGUs.
However, in the EPA’s review of the state’s cost threshold statistical data, the EPA finds that
values presented for EGUs greater than 500 MW yield maximum costs in the range of $5,000/ton

45EPA’s

2019 “Guidance on Regional Haze State Implementation Plans for the Second Implementation Period”
https://www.epa.gov/visibility/guidance-regional-haze-state-implementation-plans-second-implementation-period

to $6,000/ton for SO2 control and generally exceed the cost effectiveness of SO2 control at
smaller (less than 500 MW) EGUs.
Additionally, the EPA notes that CenRAP (predecessor organization to CenSARA)
conducted a sensitivity analysis which evaluated controls for sources with a Q/d>5 and costeffectiveness up to $10,000/ton related to the first regional haze planning period. Based on that
analysis, CenRAP suggested that a range from $4,000 to $5,000/ton (in 2005 dollars) would be a
reasonable threshold for controls because of diminishing emission reductions as costs increase
beyond that range.46 In 2021 dollars, the CenRAP range becomes $6,060 to $7,600/ ton.47 As
described earlier, Missouri relied on other analyses performed by CenSARA for this planning
period, as well as considered costs from the prior planning period so the EPA finds this analysis
further undermines the reasonableness of Missouri’s selected cost threshold.
Similarly, the EPA recently proposed a BART FIP for Texas that references past BART
decisions, specifically that several controls were required by either the EPA or States as BART
with average cost-effectiveness values in the $4,200 to $5,100/ton range (escalated to 2020
dollars).48 In 2021 dollars, this range is $5,300/ton to $6,500/ton.
Despite the costs from the first planning period being adjusted to 2021 dollars, the cost
thresholds set by Missouri are lower than historical values found necessary for BART and
reasonable progress determinations as evidenced by the control costs above Missouri’s threshold
in the cost effectiveness spreadsheet.49 Missouri’s cost thresholds are based on costs found
reasonable during the first planning period and therefore do not account for control costs found
reasonable since that time. For example, other states have since found higher control costs to be

See “Sensitivity Run Specifications for CenRAP Consultation.pdf,” available in the docket for this action. See
also “so2_cost_ton.xls” and “nox_cost_ton.xls,” also available in the docket for this action.
47 Based on the Chemical Engineering Plant Cost Index (CEPCI). For 2005 the CEPCI value is 468.2. For 2021, the
CEPCI value is 708.8.
48 See 88 FR 28918, 28963. For 2020 the CEPCI value is 596.2.
49 The sources listed in the cost effectiveness spreadsheet (Appendix F to the state submittal) are accompanied by a
link to the relevant EPA action.
reasonable, such as Oregon50 selecting a $10,000/ton threshold. Additionally, Arkansas’s second
planning period regional haze SIP,51 which relies on the same underlying statistical cost data to
establish a threshold as used by Missouri, sets a threshold of $5,086 per ton for EGUs for both
SO2 and NOx control measures.
One reason for considering higher cost effectiveness thresholds for the second planning
period (compared to the first planning period) is that most of the cheapest available cost-effective
emissions reductions were required and implemented during the first planning period. These
were typically SO2 and NOx controls at the largest uncontrolled point sources (mostly electric
generating units), which in many cases had cost-effectiveness values well under $1,000 per ton.
These relatively cheap controls lead to a low bias when using first planning period cost database
numbers to calculate mean costs (even when adding in one standard deviation). Most remaining
point sources have smaller emissions and do not have cost effective controls at those previously
“cheap” levels. However, by itself, that is not a reasonable justification to reject otherwise
potentially cost-effective controls in the second planning period and beyond. As we move
forward in time to subsequent planning periods, source emissions will get smaller and potential
controls will get more expensive on a cost per ton basis. However, the statute still requires states
to continue to make reasonable progress towards the national goal.
Missouri’s use of the selected cost threshold has the effect of rejecting control measures
that historically have been widely used to meet the regional haze rule requirements, without
requiring additional emissions reductions or enforceable shutdowns beyond existing operations.
The EPA has not established a bright line or a recommended cost effectiveness threshold to be
used by States. However, the EPA finds that Missouri’s justification and use of the selected cost
threshold to summarily reject control measures, often with cost effectiveness values just above
the selected threshold value, is not reasonable and does not comport with the stated goals of the

The EPA proposed approval of Oregon’s second planning period regional haze SIP on February 23, 2024, 89 FR
13622.
51 https://www.adeq.state.ar.us/air/planning/sip/regional-haze.aspx.
CAA and RHR. This is especially apparent when considering the magnitude of available
emissions reductions at Missouri sources and associated visibility improvements at Missouri and
other states’ Class I Areas.
Missouri still has multiple power plants that are uncontrolled for SO2. In fact, Missouri
has had the second highest statewide total SO2 emissions in the country for each of the last five
years (2018-2022). Further, of the EGUs selected by Missouri, three were among the top 15 SO2
emitters in the country in 2023, with Ameren Labadie being the highest SO2 emitter in 2023.52
As described earlier, many states relied on transport programs to satisfy BART in the first
planning period instead of requiring source specific control determinations, including Missouri.53
While trading programs are effective at reducing emissions on a regional scale, they do not
require emission reductions or installation of controls on specific sources. Therefore, individual
sources may avoid installing controls or reducing emissions through the purchase or trading of
allowances from other sources that did opt to install controls or reduce emissions. Many of the
sources selected by Missouri for further evaluation, such as Ameren Labadie, have not installed
post combustion control equipment. Generally, sources that did not install or consistently operate
post combustion control equipment relied on the purchase of allowances for trading program
compliance. And as discussed further below, the EPA proposes to find that sources in Missouri
have the potential for cost-effective control options.
As noted previously, the EPA agrees with FLM assertions that there is the potential for
significant visibility improvement associated with the controls evaluated by Missouri at these
sources. However, MoDNR argues in each four-factor analysis summary that additional controls
are not needed. Among the reasons cited, MoDNR states that “All Class I areas impacted by
sources in Missouri have made steady and significant improvement in visibility, and modeling
shows they are projected to be below, or well below, their uniform rate of progress (URP)

52
According to 2023 reported emissions available at https://campd.epa.gov/.
77 FR 38007, June 26, 2012 and 83 FR 48242, September 24, 2018.

glidepaths in 2028.”54 Although the EPA agrees there has been improvement in the Class I areas
impacted by Missouri sources, several of these Class I areas have the highest remaining
anthropogenic visibility impairment in the country. In particular, based on the latest available
IMPROVE data averaged over the five-year period of 2018-2022, Mammoth Cave, Mingo, and
Hercules-Glades are in the top 10 of Class I areas with the greatest anthropogenic visibility
impairment.55 Furthermore, the EPA’s modeling shows that a significant amount of visibility
impairment is projected to remain in these Class I areas in 2028.56 While not explicitly presented
by the state as a reason for rejecting additional controls, the EPA has reiterated through
regulation and guidance that the URP is not a safe harbor and an area’s position with respect to
the URP should not be a factor in determining whether a control measure is reasonable. See 2019
Guidance at 22, 49, and 50 and 2021 Clarifications Memo at 2, 12, 13 and 15.
The national goal set by Congress outlines both the remedying of any existing visibility
impairment, and also preventing any future visibility impairment. CAA section 169A(a). Further,
the EPA has stated that in order to accomplish the national goal set by Congress, cumulative
progress must be made including relatively small reductions and visibility benefits from many
sources over a wide area over time. To that end, visibility should not be used as the sole factor in
rejecting an otherwise reasonable control measure. See 2021 Clarifications Memo at 13.
CAA section 169A(b)(2) requires states to include in their SIPs “emission limits,
schedules of compliance and other measures as may be necessary to make reasonable progress.”
While these emission limits must apply to individual sources or units, CAA section 169A(g)(1)
does not explicitly require states to consider the four factors on a source-specific basis when
See Appendix C-1-7 to the state’s submission.
Based on “Daily Impairment Values Including Patched Values” IMPROVE data spreadsheet,
sia_impairment_daily_budgets_10_23.csv, updated October 2023, obtained from
https://vista.cira.colostate.edu/Improve/rhr-summary-data/. For the 20% most impaired days from 2018-2022,
Mammoth Cave is the 5th most anthropogenically impaired Class I area with a 5-year average anthropogenic
impairment of 10.4 dv, and Mingo is 6th on the list at 10.1 dv. Hercules-Glades is 10th on the list with a 5-year
average anthropogenic impairment of 8.9 dv.
56 Technical Support Document for EPA’s Updated 2028 Regional Haze Modeling, Office of Air Quality Planning
and Standards, United States Environmental Protection Agency (September 2019). See Table 3-2: Base and future
year deciview values on the 20% clearest and 20% most impaired days at each Class I area for the base model period
(2014-2017) and future year (2028).
54
determining what amount of emission reductions (and corresponding visibility improvement)
constitutes “reasonable progress.” The EPA has consistently interpreted the CAA to provide
states with 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. While the CAA and the RHR provide states with flexibility in
evaluating the four reasonable progress factors, states must exercise reasoned judgment when
choosing which sources, groups of sources, or source categories to analyze. Consistent with the
state's obligation to exercise reasoned judgment in its analysis, the EPA's role in reviewing a SIP
is not limited to accepting at face value a state's analysis in its own SIP submission and its
determination that it has fully satisfied the requirements of the CAA. Rather, Congress tasked the
EPA with the responsibility of ensuring that a SIP submission satisfies the requirements of the
CAA. Abundant case law reflects an understanding that the EPA must evaluate SIP submissions
under CAA section 110(k)(2) and (3).57 If a SIP submission is deficient in whole or in part, the
EPA must so find, and if not corrected, implement the relevant requirements through a FIP under
CAA section 110(c). Courts have held that the EPA's ability to ensure that a SIP submission
satisfies the requirements of the CAA includes the ability to review a state's analysis to ensure
that it is “reasonably moored to the Act's provisions and . . . based on reasoned analysis.”58 Thus,
EPA's oversight role is “more than the ministerial task of routinely approving SIP
submissions.”59 If the EPA's role were otherwise, Congress would not have expressly tasked the
agency with both reviewing SIPs for completeness (CAA section 110(k)(1)(B)) and reviewing
the substance of SIPs (CAA section 110(k)(2)–(4)).

See e.g., Oklahoma v. EPA, 723 F.3d 1201, 1209 (10th Cir. 2013) (upholding EPA’s disapproval of ‘‘best
available retrofit technology’’ (BART) SIP, noting BART ‘‘does not differ from other parts of the CAA—states
have the ability to create SIPs, but they are subject to EPA review’’); see also Westar Energy v. EPA, 608 Fed.
App’x 1, 3 (D.C. Cir. 2015) (‘‘EPA acted well within the bounds of its delegated authority when it disapproved of
Kansas’s proposed [good neighbor] SIP.’’).
58 North Dakota v. EPA, 730 F.3d 750, 761 (8th Cir. 2013).
59 North Dakota v EPA, 730 F.3d 750, 761 (8th Cir. 2013). See also Alaska Department of Environmental
Conservation v. EPA, 540 U.S. 461, (2004) (concluding that EPA was not limited to verifying that a BACT
determination had been made, but rather EPA could examine the substance of the BACT determination).
For these reasons, the EPA finds that Missouri does not sufficiently justify the use of the
selected cost threshold to repeatedly reject otherwise reasonable control measures that would
result in potentially meaningful visibility improvements and significant emissions reductions.
And as explained later in this section, the EPA’s revised cost analyses for many of the selected
Missouri sources result in cost effective controls. For these reasons, the EPA finds that
Missouri’s rejection of new control measures is unreasonable and inconsistent with the goals of
the RHR.
Deficiencies in Missouri’s Cost Analyses
The EPA thoroughly reviewed Missouri’s cost analysis for each selected source. During
both the pre-proposal and formal public comment period, the EPA commented on the cost
analysis presented in the state’s plan. The EPA identified specific errors, over- or
underestimations, inappropriate or unexplained assumptions, and inconsistencies with the EPA
Air Pollution Control Cost Manual.60 In response, Missouri addressed many of the EPA’s
concerns by correcting certain identified errors or assumptions. For example, Missouri removed
disallowed costs from the cost assumptions such as owner’s costs and updated cost estimates to
also include the default remaining useful life as recommended by the EPA. However, the EPA
believes that Missouri did not correct all the deficiencies in the cost assumptions and proposes to
find certain aspects of the cost analyses are not well supported. The EPA further explains these
deficiencies in the state’s cost analyses in the technical support document (TSD), contained in
the docket for this action. For example, the EPA commented on Missouri’s reliance on Ameren’s
four-factor analysis which included a non-default retrofit factor of 1.5 for wet FGD and SDA and
1.2 for SCR evaluated at the Ameren facilities (Labadie and Rush Island). Missouri and Ameren
did provide additional documentation in response to the EPA’s comment. However, Missouri’s
reliance on Ameren’s non-default retrofit factors should include more detailed cost estimates

EPA Air Pollution Control Cost Manual, https://www.epa.gov/economic-and-cost-analysis-air-pollutionregulations/cost-reports-and-guidance-air-pollution.
related to the specific retrofit hardships at each facility. The EPA Air Pollution Control Cost
Manual (CCM) includes a retrofit factor in the control cost calculations to account for the
relative difficulty in installing a control device. The default value of 1 is associated with average
difficulty in retrofitting an existing unit with a control device. A value of 0.77 is generally
assumed for new units. Therefore, the default retrofit factor of 1 already includes a 30% increase
in costs compared to new construction. A retrofit factor of 1.5 is the maximum value allowed in
the Control Cost Manual spreadsheets and has the effect of inflating base cost estimates by 50%.
The Control Cost Manual (CCM) specifically notes that the retrofit factor should be between 0.7
and 1.3 for wet FGD systems and between 0.8 and 1.5 for dry FGD systems61 and documentation
of site congestion, site access, complex ductwork construction and capacity of existing
infrastructure is needed to determine the complexity of the retrofit and associated retrofit factor.
Therefore, to support a retrofit factor above 1 a source should provide site specific
documentation detailing the inflated costs associated with the CCM criteria (site congestion, site
access, ductwork complexity as well as capacity of existing infrastructure that would lead to
above average retrofit difficulty). The EPA commented on Missouri’s reliance on Ameren’s
four-factor analysis which included a non-default retrofit factor of 1.5 for SDA and wet FGD and
1.2 for SCR evaluated at the two Ameren facilities (Labadie and Rush Island). Specifically, the
EPA commented that the state and source needed to provide additional documentation to support
the use of this non-default retrofit factor. In response to the EPA’s comment, Missouri and
Ameren provided additional documentation in the form of aerial imagery documenting the site
congestion and site access as well as engineering plans and schematics of potential control
device location, rerouted ductwork, and other construction projected as part of installation of wet
FGD at Labadie. However, these do not appear to be accompanied by site-specific cost estimates
for the various aspects of the retrofit hardship. Ameren also included cost estimates based on

Section 5 - Chapter 1: Wet and Dry Scrubbers for Acid Gas Control, Section 1.2.3.5.
https://www.epa.gov/sites/default/files/202105/documents/wet_and_dry_scrubbers_section_5_chapter_1_control_cost_manual_7th_edition.pdf.
prior source specific studies for wet FGD and DSI at Labadie and Rush Island (See Table 3 in
Appendices C-6 and C-7 of the state submittal, respectively). However, no specifics are provided
about these prior studies nor are the underlying cost assumptions provided for comparison with
the new CCM calculations provided. Ameren reasoned that a higher retrofit factor was needed
because the prior source-specific studies resulted in cost estimates higher than the estimates
using the CCM assumptions. However, this assumption is not well supported. The EPA does not
have access to and therefore cannot review the necessary underlying cost assumptions from these
prior studies to determine the reasonableness of those estimates. To support the retrofit factor of
1.2 for SCR, the state points to the documentation provided for the wet FGD as supplied by
Ameren but there is no documentation specific to the retrofit factor for SCR. Additionally, these
higher retrofit factors are utilized in the cost calculations for both Ameren facilities (Labadie and
Rush Island) but the documentation including imagery and schematics appear specific to
Labadie. Therefore, there appears to be no site-specific documentation provided for the nondefault retrofit factors used for Rush Island.
Detailed, technical cost information and robust documentation is needed to justify the
inflated costs resulting from the use of the maximum retrofit factor value for SO2 controls at each
Ameren facility. Other electric generating units in the state (and outside the state) do not rely on
such a non-default retrofit factor despite having similar limitations, such as physical space
limitations, to accommodate control device retrofits.62 The EPA invites comment on the
reasonableness of using a non-default retrofit factor and whether other cases of using such a
factor may be instructive to the outcome of this specific scenario.
In addition to reviewing Missouri’s cost analyses, the EPA performed independent cost
calculations for certain control measures at the selected sources to compare with Missouri’s cost
calculations. These calculations are summarized below and further detailed in the TSD included

See the EPA’s response to comment including comment on the range of retrofit factors for wet and dry FGD on
EGUs. https://www.epa.gov/sites/default/files/202105/documents/rtcdocument_wet_and_dry_scrubbers_controlcostmanual_7thedition.pdf).
in the docket for this action. The EPA updated certain aspects of the Missouri cost calculations to
follow EPA guidance. For example, the EPA used the default retrofit factor of 1 in our
calculations for all facilities evaluated. This change, along with the other corrections made in the
EPA’s cost analyses, result in cost effectiveness values of SO2 controls near or within the cost
range established by Missouri. Further, the EPA calculated cost effectiveness numbers are
similar to maximum control costs implemented in the first planning period for several states.
The EPA’s analysis also changed the emissions baseline used in determining the emission
reduction for a given control to arrive at the cost effectiveness (or cost per ton) value. While
Missouri relied on the average of reported annual emissions to define the reduction estimate, the
EPA recommends using the maximum annual emissions for the analyzed time period when
setting the baseline emissions to calculate the cost effectiveness. Similarly, the time period
selected for the baseline emissions also influences the final cost effectiveness value. For this
reason, the EPA performed the cost analyses using both the same time period used by Missouri
(2016-2020) for a direct comparison and the most recent time period (2018-2022) in order to
fully evaluate the range of cost effectiveness values using all currently available data. The
baseline emissions assumption alone makes a significant difference when comparing the EPA’s
cost effectiveness values with the state’s values, but other updates to the cost analysis refine and
generally reduce the overall costs. Further, when the calculations are corrected to be consistent
with EPA guidance, there are control costs near and within the cost range as identified as
reasonable by Missouri. For example, the EPA’s calculations result in SO2 control costs as low
as $2,688 per ton. Therefore, we propose to find there are likely cost-effective control options at
most, if not all, sources selected by Missouri. As noted previously, there are control costs that
were previously found reasonable by states or the EPA, in the dataset used by Missouri to set a
cost threshold, that are similar to the range of costs as calculated by Missouri and the EPA.
States should provide a sufficient justification in order to reject measures that have been required
at similarly situated facilities in a similar cost range.

The Federal land managers commented on the state’s use of an “unreasonably low
threshold” and the inappropriate assumptions utilized in the state’s cost analyses. On page 54 of
Appendix G-2 to the state’s submittal, the National Park Service (NPS) references the aspects of
Missouri’s cost analyses that are inconsistent with the EPA rules or guidance and provides their
own estimates of cost effectiveness for the selected sources, often significantly lower than the
values presented by Missouri. The cost values provided by the NPS further corroborate the
EPA’s revised cost analyses, as contained in the TSD, that result in cost effective controls at
most of the state’s selected sources.
In Table 21 of the TSD, the EPA identifies the cost effectiveness in 2021 dollars for SO2
control measures such as DSI, SDA and wet FGD. For NOx, the EPA evaluates SCR and SNCR.
In Table 29 of the TSD, the EPA identifies the cost effectiveness in 2021 dollars for SCR and
SNCR. The spreadsheets included in the docket contain all the underlying data for the EPA’s
cost analyses including the cost effectiveness values in 2021 dollars using both baseline time
periods as previously mentioned.63 For example, the EPA’s estimated cost effectiveness values
for DSI range from $2,688 per ton to $4,119 per ton. The EPA’s estimated cost effectiveness
values for SDA range from $3,966 per ton to $7,846 per ton. The EPA’s estimated cost
effectiveness values for wet FGD range from $4,081 per ton to $9,201 per ton. The EPA’s
estimated cost effectiveness values for SCR range from $795 per ton to $27,208 per ton. The
lowest costs in this dataset are associated with the units that already have SCR installed. In this
case, the control cost is entirely associated with operation of the existing SCR with no additional
capital cost of installation since they are already installed on those units. The EPA’s estimated
cost effectiveness values for SNCR range from $7,429 per ton to $16,580 per ton. Consistent
with Missouri’s cost analyses, the EPA did not calculate the cost effectiveness of SNCR on units

The following values presented as minimum and maximum cost effectiveness values include the full range of
values for both baseline emission time periods.
that already have SCR installed. Additionally, the EPA did not evaluate SNCR for Sikeston as a
prior technical infeasibility determination was made by the source.64
Table 4 of this preamble below includes an abbreviated summary of the EPA’s cost
analyses for certain SO2 control devices. The EPA’s methodology for the cost calculations is
included in the TSD along with the full table of control cost results. In table 4 of this preamble
below, we present only the values associated with wet FGD with an emissions limit of 0.06
lb/mmBTU. The TSD also presents costs associated with wet FGD with an emissions limit of
0.04 lb/mmBTU. Cost effectiveness values associated with the 0.04 lb/mmBTU emissions limit
are lower due to the greater emissions reductions. To be conservative, this table presents only the
highest cost per ton values (i.e., least cost-effective) from the two time periods evaluated by the
EPA for each control type by unit. Values for both time periods are presented in the TSD.
Generally, the EPA’s resulting cost effectiveness values are lower (more cost effective) than the
values presented by Missouri. The cost effectiveness of wet FGD is higher than SDA. However,
wet FGD delivers significant improvements in cost effectiveness as the tonnage of SO2 removal
increases due to the greater level of control. DSI appears the most cost effective given the lower
capital cost compared with SDA and wet FGD, but also comes with lower control efficiency. For
facilities with higher cost effectiveness values for SDA and wet FGD, DSI may be a reasonable
option. The EPA notes that there are examples nationally of each of these control types being
implemented at large electric generating units such that these types of controls are technically
and economically feasible at such sources. Specifically, these types of SO2 controls were
implemented at the sources included in the underlying data for Missouri’s cost threshold, and in
some cases, with cost effectiveness values higher than the threshold set by Missouri. As
previously discussed, if Missouri would have set the cost threshold for this planning period

In January 2009, Sikeston submitted an applicability determination request to install SNCR. However, after initial
testing, Sikeston determined that SNCR was infeasible at the facility due to stalactite formation, dropping and
damaging the boiler tubes. Based on that information, Missouri removed SNCR from further consideration in
Sikeston’s four-factor analysis. Similarly, the EPA did not evaluate SNCR at Sikeston. See Appendix C-5 to
Missouri’s submittal for more information.
nearer other states thresholds or near the maximum of costs from the first planning period (i.e.,
around $6,000/ton), both the cost effectiveness values presented by Missouri and the EPA’s
revised values would be below that threshold for most SO2 control types.
Table 4. Summary of the EPA’s Cost Effectiveness Values for DSI, SDA and Wet
FGD

Date Range
with Highest
Facility Unit Cost Per Ton
2018-2022
2018-2022
John
Twitty
1
2018-2022
2016-2020
2016-2020
2016-2020
1
2016-2020
2016-2020
2
2016-2020
2016-2020
2016-2020
3
2016-2020
2016-2020
2016-2020
2016-2020
Labadie 4
2018-2022
2016-2020
1
2016-2020
2018-2022
2018-2022
New
2018-2022
Madrid 2
2018-2022
2018-2022
1
2018-2022
2018-2022
2018-2022
Rush
2
2018-2022
Island
2018-2022
2018-2022
Sikeston 1
2018-2022
2018-2022
2018-2022
1
2018-2022
2016-2020
2016-2020
2
2016-2020
2016-2020
2016-2020
Thomas
3
2016-2020
Hill

Control
DSI
SDA
WFGD
DSI
SDA
WFGD
DSI
SDA
WFGD
DSI
SDA
WFGD
DSI
SDA
WFGD
DSI
SDA
WFGD
DSI
SDA
WFGD
DSI
SDA
WFGD
DSI
SDA
WFGD
DSI
SDA
WFGD
DSI
SDA
WFGD
DSI
SDA
WFGD
DSI
SDA
WFGD

SO2 Reduction
(tons per year),
Based on
CCM/RCA Cost
Spreadsheet
Calculations
2392
2520
2520
8177
9008
9008
8308
9023
9023
8497
9100
9100
8255
8692
8692
5657
6104
6104
5953
6518
6518
7668
8264
8264
9159
9689
10114
5661
4809
4809
2006
2248
2248
2864
3210
3210
8316
9371
2021$ Cost Effectiveness
($/ton), based on CCM
Spreadsheet (for
SDA/WFGD) and 2023
Version of RCA for DSI
2928
7011
8205
3609
4780
5038
3608
4774
5048
3606
4825
5010
3614
5019
5212
3774
6444
6730
3739
6057
6322
3629
4732
5055
3580
4111
4209
3711
4292
4901
4119
7846
9201
3982
7559
8520
3658
5300
Table 5 below includes a summary of the EPA’s cost effectiveness values for NOx controls.
Table 5. Summary of the EPA’s Cost Effectiveness Values for SCR and SNCR

Date Range
with Highest
Facility
Unit Cost Per Ton
John Twitty 1
2018-2022
2018-2022
1
2018-2022
2016-2020
2
2018-2022
2018-2022
3
2018-2022
2018-2022
Labadie
4
2018-2022
1
2016-2020
New
Madrid
2
2018-2022
2016-2020
1
2018-2022
2018-2022
Rush Island 2
2018-2022
Sikeston
1
2016-2020
1
2016-2020
2
2016-2020
Thomas Hill 3
2016-2020

Control
SCR
SCR
SNCR
SCR
SNCR
SCR
SNCR
SCR
SNCR
SCR
SCR
SCR
SNCR
SCR
SNCR
SCR
SCR
SCR
SCR

NOx
Reduction
(tons per
year), Based
on
CCM/RCA
Cost
Spreadsheet
Calculations
359
948
302
977
301
1,106
359
971
355
10,691
9,617
869
208
763
130
598
3,237
4,695
4,999

2021$ Cost
Effectiveness
($/ton), based
on CCM
Spreadsheet
for SCR and
2023 Version
of RCA for
SNCR
3,313
24,483
9,064
23,960
9,130
21,747
8,245
23,878
8,306
798
832
23,960
11,181
26,659
15,427
15,520
872
876
1,349

The cost effectiveness of SCR is higher than SNCR for units that do not already have
SCR installed. However, SCR delivers significant improvements in cost effectiveness as the
tonnage of NOx removal increases due to the greater level of control of SCR over SNCR. The
cost effectiveness of operating already installed SCR is extremely cost effective in comparison.
As required in the Missouri source agreements submitted with the SIP, the EPA agrees that
existing SCR should be required to be operated continuously on those units already equipped
with SCR at the John Twitty, Thomas Hill, and New Madrid plants. Similar to the SO2 control
summary, the EPA’s revised cost effectiveness values for NOx controls are generally lower than
the values presented by Missouri. For units that have relatively low inlet NOx values, postcombustion controls have lower removal efficiency and accordingly high cost effectiveness

values. Similar to Missouri’s assessment, the EPA finds the cost effectiveness values for
installing new post combustion NOx controls are considerably higher than the highest cost
effectiveness values found to be reasonable in the first planning period (the dataset underlying
Missouri’s cost threshold) and therefore may not be economically feasible for the second
planning period.
Importantly as part of this action, the EPA is not proposing that any given control
technology or numeric emissions limit as evaluated in our TSD is necessary for a given unit.
Rather, the EPA provided its own cost effectiveness calculations as evidence that Missouri’s
control decisions, that reject what may be otherwise reasonable control measures based solely on
the state’s selected cost threshold, are unreasonable.
Legal Deficiencies of Missouri’s Consent Agreements
To formalize the finding that existing measures are sufficient to make reasonable
progress, Missouri entered into new consent agreements with each source selected and analyzed,
with the exception of Mississippi Lime Company.65 The full source consent agreements are
contained in Appendix E to the state’s plan, available in the docket for this rulemaking.
In the new consent agreements, Missouri required that each facility’s future fuel purchase
be western sub-bituminous coal derived from the powder river basin. In addition, each facility
agreed to operate any existing control devices at all times when burning coal in the boiler(s)
except during periods of start-up, shutdown, or malfunction pursuant to 10 CSR 10-6.050.
Through these consent agreements, the state required two facilities to run their existing selective
catalytic reduction (SCR) technology when burning coal. The EPA reviewed the consent
agreements and provided comment through the state’s public process. The EPA commented on
the significant approvability concerns related to the permanence and enforceability of the

For the Mississippi Lime Company, Missouri’s plan appears to rely on current operational practices consistent
with the parameters and limits in the Mississippi Lime Air Pollution Control Title V Permit to Operate instead of
entering a new consent agreement. The EPA notes that Title V permit requirements are not permanent and therefore
may not be relied upon for SIP requirements unless those components of the permit are submitted for inclusion into
the SIP.
agreements. Specifically, the EPA commented that the agreements do not contain the necessary
numerical emissions limitations associated with the operational requirements needed to be
practically enforceable and, therefore, are not consistent with the relevant CAA and RHR
requirements. For example, CAA section 110(a)(2)(A) states that each implementation plan
submitted by a state shall “include enforceable emission limitations and other control measures,
means, or techniques … as well as schedules and timetables for compliance, as may be necessary
or appropriate to meet the applicable requirements of this chapter.”66 The EPA also commented
that the sole requirement to burn western sub-bituminous coal still allows for a wide variability
in the sulfur content of the coal and, therefore, emissions from the source. Similarly, the
requirement to operate existing SCR technology without a particular numeric emissions limit or
operating parameters allows for a wide variability in the control efficiency and operations of the
SCR and, therefore, emissions from the source.67 Missouri did not amend the agreements in
response to the EPA’s formal comments.
The CAA requires that SIPs, including regional haze SIPs, contain elements sufficient to
ensure emission limitations are practically enforceable. CAA section 110(a)(2) states that the
monitoring, recordkeeping, and reporting provisions of states’ SIPs must: “(A) include
enforceable emissions limitations and other control measures, means, or techniques (including
economic incentives such as fees, marketable permits, and auctions of emissions rights), as well
as schedules and timetables for compliance, as may be necessary or appropriate to meet the
applicable requirements of this chapter;… (C) include a program to provide for the enforcement
of the measures described in subparagraph (A), and regulation of the modification and
construction of any stationary source within the areas covered by the plan as necessary to assure
that national ambient air quality standards are achieved, including a permit program as required

See CAA Section 110(a)(2) and section 110(a)(2)(A); see also Committee for a Better Arvin v. U.S. E.P.A., 786
F.3d 1169, 1175 (9th Cir. 2015)
67 The EPA provided variability analyses to demonstrate how these operational requirements without a numerical
emissions limit do not practically limit emissions to an explicit level. See the EPA’s comment letters on both the
pre-hearing draft (dated September 28, 2021) and the public notice draft (dated May 5, 2022) of Missouri’s second
planning period regional haze SIP.
in parts C and D of this subchapter;… (F) require, as may be prescribed by the Administrator –
(i) the installation, maintenance, and replacement of equipment, and the implementation of other
necessary steps, by owners or operators of stationary sources to monitor emissions from such
sources, (ii) periodic reports on the nature and amounts of emissions and emissions-related data
from such sources, and (iii) correlation of such reports by the State agency with any emissions
limitations or standards established pursuant to this chapter, which reports shall be available at
reasonable times for public inspection.”68
Accordingly, 40 CFR part 51, subpart K, Source Surveillance, requires the SIP to provide
for monitoring the status of compliance with the regulations in the SIP, including “[p]eriodic
testing and inspection of stationary sources,”69 and “legally enforceable procedures” for
recordkeeping and reporting.70 Furthermore, 40 CFR part 51, appendix V, Criteria for
Determining the Completeness of Plan Submissions, states in section 2.2 that complete SIPs
contain: “(g) Evidence that the plan contains emission limitations, work practice standards and
recordkeeping/reporting requirements, where necessary, to ensure emission levels”; and “(h)
Compliance/enforcement strategies, including how compliance will be determined in practice.”71
As previously mentioned, emission reduction measures that are necessary to make
reasonable progress may be either new, additional control measures, or they may be the existing
emission reduction measures that a source is already implementing. See 2019 Guidance at 43;
2021 Clarifications Memo at 8-10. Such measures must be represented by “enforceable
emissions limitations, compliance schedules, and other measures” (i.e., any additional
compliance tools) in a state’s long-term strategy in its SIP. 40 CFR 51.308(f)(2). The EPA
proposes to find that the source agreements, submitted by Missouri to serve as the enforceable
mechanism of the long-term strategy, do not meet the requirements of 40 CFR 51.308(f)(2) to

42 U.S.C. 7410(a)(2)(A), (C), and (F).
40 CFR 51.212.
70 Id. § 51.214.
71 40 CFR part 51, appendix V.
68
include enforceable emissions limitations. Specifically, the source agreements do not contain the
necessary numeric emissions limits to constitute a practically enforceable measure needed for
reasonable progress as required by the RHR.

The EPA also has concerns with the delayed compliance date in the agreements.
Specifically, the consent agreements state that requirements of the agreements must be complied
with “Starting 180 days after the approval of this agreement by the EPA as an attachment to
Missouri’s SIP for the second planning period of the RH program and consistent with the
exemption and termination provisions set forth in the Consent Agreement.” The EPA believes
the agreements should include a reasonable compliance date based on the expected time
necessary to implement controls or other operational requirements. The control requirements
under the consent agreements are premised on operating existing installed emissions controls (for
NOx) and for continued purchase and combustion of low sulfur coal (for SO2). The EPA has
consistently found that such emissions control strategies are capable of being implemented in a
matter of weeks, if not immediately given the nature of the requirements. E.g., 88 FR 36654,
36720-22 (June 5, 2023); 86 FR 23054, 23088-89 (April 30, 2021); and 81 FR 74504, 74561
(October 26, 2016). Instead, the state tied the effectiveness of these emissions reductions to an
event that is irrelevant to substantive compliance with the regional haze program, i.e., the
effective date of any final action by the EPA to approve the Consent Agreements into Missouri’s
SIP. This was improper; as a result of this provision, even at this point in time, Missouri has not
imposed the requirements of the Consent Agreements on the affected sources and, under the
plain terms of the Consent Agreements, to this day the covered sources are under no obligation
to comply with them.
The EPA further has concerns with certain other provisions (including but not limited to
termination provisions) in the agreements. For example, the consent agreements contain
provisions that allow for the state and the affected sources to modify them without following the

statutorily-mandated process for SIP revisions and without requisite analysis by the EPA under
CAA section 110(l). See CAA section 110(i); 110(l). While the EPA will allow for consent
agreements or permitting requirements to be incorporated by reference into a state’s SIP to meet
SIP requirements, 50 CFR Pt. 51 App’x V, para. 2.1.(b), it is important that the state provides
that to the extent such provisions are approved and incorporated into the state’s SIP, such
provisions, as approved, cannot be modified by later changes made to the underlying agreements
or permits outside of the SIP revision process. Once approved by the EPA into the SIP as
meeting the applicable SIP requirements, only changes made through the statutory SIP revision
process may modify the approved requirements of the state’s SIP. In this instance, the terms of
the Consent Agreements explicitly authorize the state and the affected sources to cancel the
agreements in toto and without the EPA’s approval of such a modification, which would in effect
negate the emissions limitations in their entirety. This is antithetical to the requirement that SIP
provisions be permanent and enforceable, and not changed except pursuant to the statutory and
regulatory processes for SIP revisions.
The consent agreements should not be unilaterally terminated by either the source or the
state since the state has presented the consent agreements as necessary to achieve reasonable
progress within the SIP revision submitted to the EPA for approval. Missouri is relying on
Consent Agreements that include termination clauses that render the agreements and any
contained requirements as not permanent and therefore not consistent with CAA and RHR
requirements. Specifically, paragraph 12 of the consent agreements allows for termination of the
agreement upon “mutual written agreement of” the source and the state. Paragraph 12 remains an
unambiguous statement authorizing termination of the Agreements upon agreement of the parties
to them.72 If the source and the MoDNR chose to exercise their rights in Paragraph 12, the
Consent Agreements would be terminated without review or approval from the EPA and without

The courts would also likely interpret this language similarly to the EPA. See, e.g., New York v. U.S. EPA, 525
F.Supp.3d 340, 356 (N.D.N.Y. 2021) (“‘[T]the scope of a consent decree must be discerned within its four corners .
. . .’”) (quoting Firefighters Local Union No. 1784 v. Stotts, 467 U.S. 561, 574 (1984)).

input from the public, and the source would be under no obligation to comply. Therefore, the
EPA concludes that paragraph 12 violates the CAA’s prohibition on modification of SIPs outside
the authorized SIP revision process pursuant to sections 110(i) and (l) of the CAA. SIP
provisions cannot authorize a state to make changes in the EPA-approved and federally
enforceable SIP requirements applicable to sources without going through the statutorily
required SIP-revision process. The EPA refers to SIP provisions that purport to authorize states
to make unilateral changes to existing SIP requirements as impermissible “director’s discretion”
provisions. See, e.g., 86 FR 15104, 15116 (March 22, 2021). However, the EPA interprets the
CAA to allow two types of such provisions: (1) where the provision provides director’s
discretion for the state to make changes, but specifies that such changes have no effect for
purposes of Federal law or alter SIP requirements unless and until the EPA approves the changes
through a SIP revision pursuant to CAA requirements; or (2) where the provision provides
director’s discretion that is adequately bounded, such that at the time the EPA approves the SIP
provision the Agency can evaluate it for compliance with applicable CAA requirements and
evaluate the potential impacts of the state’s exercise of that discretion. The EPA interprets CAA
section 110(l) to allow SIP provisions with director’s discretion of either type. In the case of an
adequately bounded provision, the EPA considers such provisions consistent with section 110(l)
because, at the time of initial approval into the SIP, the Agency will already have evaluated the
provision for compliance with applicable requirements and evaluated the potential impacts from
exercise of the discretion. E.g., 86 FR 15116, March 22, 2021.
In Environ. Comm. Fl. Elec. Power v. EPA, 94 F.4th 77 (D.C. Cir. 2024), the D.C. Circuit
held that the EPA impermissibly issued a SIP call, under CAA section 110(k)(5), in its 2015
SSM SIP Action73 for certain SIP provisions applicable to emissions during SSM events,
including certain director’s discretion type provisions that the EPA had previously approved.
However, the Court did not foreclose that some director’s discretion provisions may be so

See 80 FR 33840, June 12, 2015.

unbounded as to interfere with the Agency’s ability to predict the impact on compliance with the
CAA’s requirements. Id. At 111. Further, Enviro. Comm. Fl. Elec. Power concerns the EPA’s
authority to issue a SIP call for certain provisions that it previously approved and not the EPA’s
authority to approve or disapprove a SIP submission in the first instance. Compare CAA section
110(k)(3) with (k)(5).
Here, Paragraph 12 of the Consent Agreements in effect provides unbounded discretion
to the state to eliminate the requirements, even though the MoDNR has submitted these Consent
Agreements as necessary to satisfy Missouri’s obligation to achieve reasonable progress in the
regional haze program. Thus, Paragraph 12, which allows Missouri and its sources to agree
between themselves to terminate these emissions control requirements at any time for any
reason, is unacceptably too unbounded to meet regional haze obligations. Likewise, the EPA
finds Paragraph 12 to be inconsistent with CAA section 110(i) and (l) because it permits the state
not merely discretion to modify some provision within the overall operation of a broader
regulatory scheme, but the ability to terminate the Agreements completely—i.e., the entirety of
the emissions control program the state has put forward—at will. The EPA agrees that emissions
controls on these sources are necessary (albeit not sufficient as discussed earlier in this section)
for Missouri to achieve reasonable progress and it would be inappropriate for the EPA to
approve as SIP provisions these Consent Agreements that the state could eliminate without
undertaking the necessary SIP revision process mandated by the Act.
Here, Paragraph 12 violates the anti-backsliding provisions of section 110(l) of the CAA,
which requires that the EPA shall not approve any revision of a plan if the revision would
interfere with any applicable requirement concerning attainment and reasonable further progress.
42 U.S.C. 7410(l). The termination provision would allow a unilateral amendment to the SIP,
potentially removing emissions and pollution control limits without an evaluation of whether the
removal would interfere with attainment or reasonable further progress or would interfere with
any other applicable requirement of the Act.

As mentioned above, the Consent Agreements include termination clauses that render
them unenforceable depending on the nature of the action the EPA takes. Even if the EPA could
have explored the possibility of a limited or partial approval of the consent agreements, it is not
able to do this if doing so would render the emissions control measures established through the
consent agreements unenforceable, by triggering the sources’ ability to unilaterally withdraw
from the agreements. Nor does the EPA have discretion to partially approve the consent
agreements by not including within its approval those provisions of the Consent Agreements
such as Paragraph 13 (and others discussed in this section) that are not approvable. To do so
would be to render the SIP revision more stringent than the state intended, which the EPA is not
authorized to do. See Bethlehem Steel Corp. v. Gorsuch, 742 F.2d 1028 (7th Cir. 1984).
Despite this, there remain multiple problematic provisions of the Consent Agreements
that render them non-permanent and unenforceable. It is this language in the Agreements
themselves, in addition to the possibility of a future modification to them, that renders them not
approvable as a SIP revision for the purposes of ensuring reasonable progress under the regional
haze program. However, because the consent agreements are otherwise not approvable, the EPA
need not further evaluate the SSM, force majeure, or other exemption provisions of the
agreements for compliance with the Act. Due to the identified flaws in the consent agreements as
described above, the EPA cannot approve these consent agreements as a revision to Missouri’s
SIP nor as enforceable measures of the long-term strategy under 40 CFR 51.308(f)(2).
For the reasons described in this section and in the TSD, the EPA proposes to find that
Missouri failed to submit an approvable Long-Term Strategy because it (1) failed to reasonably
“evaluate and determine the emission reduction measures that are necessary to make reasonable
progress by considering the costs of compliance, the time necessary for compliance, the energy
and non-air quality environmental impacts of compliance, and the remaining useful life of any
potentially affected anthropogenic source of visibility impairment,” as required by 40 CFR
51.308(f)(2)(i); CAA section 169A(g)(1); (2) has not adequately supported its conclusions that

existing measures satisfy the requirement to make reasonable progress; and (3) has not shown
that further reductions of visibility impairing pollutants are not reasonable and has not
adequately explained how its approach is consistent with the CAA’s requirement to make
reasonable progress. In addition, the state rejected otherwise reasonable control measures based
primarily on the unreasonable justification and use of the selected cost threshold and on cost
effectiveness calculations that do not fully align with EPA guidance. Further, Missouri has not
included practically enforceable emissions limits to ensure that selected sources comply with the
requirements constituting existing measures Missouri determined as needed to make reasonable
progress. Specifically, the included source agreements do not contain explicit enforceable
emissions limits associated with existing operations and include problematic termination or other
exemption provisions, rendering them unenforceable and not permanent. Therefore, the EPA is
proposing to disapprove Missouri’s Long-Term Strategy as required by 40 CFR 51.308(f)(2).
3. Additional Long-Term Strategy Requirements
The consultation requirements of § 51.308(f)(2)(ii) provides that states must consult with
other states that are reasonably anticipated to contribute to visibility impairment in a Class I area
to develop coordinated emission management strategies containing the emission reductions
measures that are necessary to make reasonable progress. Section 51.308(f)(2)(ii)(A) and (B)
require states to consider the emission reduction measures identified by other states as necessary
for reasonable progress and to include agreed upon measures in their SIPs, respectively. Section
51.308(f)(2)(ii)(C) speaks to what happens if states cannot agree on what measures are necessary
to make reasonable progress.
In Appendix G-3, Missouri included documentation of its consultation with other states
and responses to requests from other states as it relates to the state’s development of its longterm strategy. However, because these elements are not separable from the overall requirement at
40 CFR 51.308(f)(2) to develop an enforceable long-term strategy, the EPA accordingly

proposes to disapprove all elements of Missouri’s regional haze SIP submission as it relates to
the 40 CFR 51.308(f)(2) rule requirements.
The documentation requirement of § 51.308(f)(2)(iii) provides that states may meet their
obligations to document the technical bases on which they are relying to determine the emission
reductions measures that are necessary to make reasonable progress through an RPO, as long as
the process has been “approved by all State participants.”
Section 51.308(f)(2)(iii) also requires that the emissions information considered to
determine the measures that are necessary to make reasonable progress include information on
emissions for the most recent year for which the state has submitted triennial emissions data to
the EPA (or a more recent year), with a 12-month exemption period for newly submitted data.
Missouri included emissions information from the most recent national emissions
inventory (NEI) reporting year in its submittal. Section 4.1.1 of Missouri’s submittal details how
the state meets the emissions inventory requirement. Missouri also includes additional
information on the inventory development in Appendix A to the state’s submittal. However,
because these elements are not separable from the overall requirement of 40 CFR 51.308(f)(2) to
develop an enforceable long-term strategy, the EPA accordingly proposes to disapprove all
elements of Missouri’s regional haze SIP submission as it relates to the 40 CFR 51.308(f)(2) rule
requirements.
F. Reasonable Progress Goals
Section 51.308(f)(3) contains the requirements pertaining to RPGs for each Class I area.
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) to be in states’ longterm strategies, as well as implementation of other CAA requirements. The long-term strategies
as reflected by the RPGs must provide for an improvement in visibility on the most impaired

days relative to the baseline period and ensure no degradation on the clearest days relative to the
baseline period. Section 51.308(f)(3)(ii) applies in circumstances in which a Class I area’s RPG
for the most impaired days represents a slower rate of visibility improvement than the uniform
rate of progress calculated under 40 CFR 51.308(f)(1)(vi). Under § 51.308(f)(3)(ii)(A), if the
state in which a mandatory Class I area is located establishes an RPG for the most impaired days
that provides for a slower rate of visibility improvement than the URP, the state must
demonstrate that there are no additional emission reduction measures for anthropogenic sources
or groups of sources in the state that would be reasonable to include in its long-term strategy.
Section 51.308(f)(3)(ii)(B) requires that if a state contains sources that are reasonably anticipated
to contribute to visibility impairment in a Class I area in another state, and the RPG for the most
impaired days in that Class I area is above the URP, the upwind state must provide the same
robust demonstration.
In Chapters 5 and 6 of Missouri’s SIP submission, the state describes the process
followed to determine the RPGs for each of the state’s Class I areas. Missouri relied on the
EPA’s modeling of projected 2028 visibility conditions as the basis for establishing the RPGs.74
Specifically, Missouri established an RPG of 17.44 dv for Hercules-Glades and 18.88 dv for
Mingo. Each of these RPGs is slightly below the 2028 point on the uniform rate of progress line
or glidepath (18.82 dv for Hercules-Glades and 19.48 dv for Mingo), meaning the state did not
trigger the provision to provide a robust demonstration as just described.
At the time Missouri submitted its SIP, the provision triggering a robust demonstration
did not apply because the states with Class I areas that are affected by Missouri sources did not
submit any RPGs above the URP. Because we are proposing to disapprove certain elements of
Missouri’s SIP, if Missouri chooses to submit a revised SIP to the EPA, the state should reevaluate whether the requirement of 40 CFR 51.308(f)(3)(iii) applies to Missouri.

See the EPA’s September 2019 memorandum titled, “Availability of Modeling Data and Associated Technical
Support Document for the EPA’s Updated 2028 Visibility Air Quality Modeling.”
https://www.epa.gov/sites/default/files/2019-10/documents/updated_2028_regional_haze_modeling-tsd-2019_0.pdf.
The RPGs should reflect the visibility conditions as a result of the enforceable emissions
limitations and other measures in the state’s long-term strategy as required under 40 CFR
51.308(f)(2). Because the EPA is proposing to disapprove Missouri’s long-term strategy under
40 CFR 51.308(f)(2) through this proposed rulemaking, the EPA is also proposing to disapprove
the RPGs under 40 CFR 51.308(f)(3). If Missouri elects to submit a new long-term strategy, the
state will also need to provide new RPGs associated with the new long-term strategy.
G. Monitoring Strategy and Other 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 subsection 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
Interagency Monitoring of Protected Visual Environments (IMPROVE) network. As noted in
Chapter 7 of Missouri’s submittal, Missouri continues to rely on participation in the IMPROVE
network for its two Class I areas monitoring strategies.
Section 51.308(f)(6)(i) requires SIPs to provide for the establishment of any 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. In
Chapter 7 of the state plan, Missouri describes how the two IMPROVE program monitors in
Missouri are sufficient for determining progress in reducing visibility in the Missouri Class I
areas due to their locations.
Section 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. In Chapter 7 of the state plan, Missouri explains that the assessments of

visibility impairment and progress in reducing visibility impairment at Missouri’s two Class I
areas, and at Class I areas in other states that Missouri’s emissions may affect, in the future will
use the revised IMPROVE algorithm (Pitchford, 2007) and will use data as prescribed in the
EPA’s RHR (40 CFR part 51, subpart P - Visibility Protection). The assessment will follow, as
appropriate, EPA guidance including Guidance on Regional Haze State Implementation Plans
for the Second Implementation Period (EPA, 2019) and Technical Guidance on Tracking
Visibility Progress for the Second Implementation Period of the Regional Haze Program (EPA,
2018).
Section 51.308(f)(6)(iii) does not apply to Missouri, as it has Class I areas.
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. The
monitoring strategy for Missouri relies upon the continued availability of the IMPROVE
network. The IMPROVE monitor for the Hercules-Glades Wilderness Area (indicated as HEGL
in the IMPROVE monitoring network database) is operated and maintained by the FS and is
contained within the Mark Twain National Forest. The IMPROVE monitor for the Mingo
National Wildlife Refuge (indicated as MING in the IMPROVE monitoring network database) is
operated and maintained by the FWS. Since the state does not collect or handle IMPROVE data
directly, the state commits to continue to participate in the IMPROVE Visibility Information
Exchange Web System (VIEWS). The state considers VIEWS to be a core part of the overall
IMPROVE program and will report IMPROVE data from the two Class I areas in Missouri to the
EPA using the VIEWS web system.
Section 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 and estimates of future
projected emissions. It also requires a commitment to update the inventory periodically. Section
51.308(f)(6)(v) also requires states to include estimates of future projected emissions and include

a commitment to update the inventory periodically. In Chapter 4.1 of the state plan, Missouri
notes that it complies with 40 CFR part 51, subpart A, Air Emissions Reporting Requirements
(AERR) to develop and submit periodic emissions inventories to the EPA every three years. Per
the AERR, the state submitted to the EPA’s National Emissions Inventory (NEI) 2011, 2014, and
2017 periodic emissions inventories as a comprehensive and detailed estimate of statewide air
emissions. The reported pollutants include NOx, VOC, carbon monoxide (CO), SO2, NH3, PM2.5,
and PM10. The type of emissions sources, amount of each pollutant emitted, and the types of
processes and control devices employed at each facility or source category are identified in the
inventory. The AERR emissions inventories are derived from estimates developed for four
general categories of anthropogenic emissions sources: point, area or nonpoint, nonroad mobile,
and onroad mobile. Chapter 4.1 of the state plan discusses general emissions inventory
development for each of the anthropogenic source categories. Appendix A to the state’s plan
describes how the state developed the most recent emissions inventory, 2017, including
compilation and submission to the NEI through the EPA’s Emissions Inventory System (EIS).
The EPA proposes to find that Missouri satisfies the requirements of 40 CFR 51.308(f)(6)(v)
through compliance with the AERR.
For the reasons described in this section, the EPA proposes to find Missouri’s plan
satisfies the requirements of 40 CFR 51.308(f)(6) and proposes to approve this element of the
state plan.
H. Requirements for Periodic Reports Describing Progress Towards the Reasonable Progress
Goals
Section 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, §
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 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.
Missouri addresses the requirements of 40 CFR 51.308(g)(1) through (5) in Chapter 8 of
the state’s submittal. To meet the requirement of 40 CFR 51.308(g)(1), the state points to
Chapter 4 of the submittal which details the existing measures that control emissions in the state
including Federal, state, stationary, and mobile source emissions measures. To address 40 CFR
51.308(g)(2), the state refers to the emissions inventory included in Chapter 4, section 4.1.1.4,
Tables 13 and 14, which depict the NOx and SO2 emissions trends by source type and emission
category for 2011, 2014, and 2017. To meet the requirement of 40 CFR 51.308(g)(3), the state
evaluated the haze index and annual light extinction values for each IMPROVE site in Missouri
between 2000 and 2018 and concluded that visibility conditions for the two Class I areas in
Missouri have improved and are below the uniform rate of progress line. For 40 CFR

51.308(g)(4), the state refers to the emissions inventory in Chapter 4 of the submittal to show the
change in emissions of pollutants contributing to visibility impairment over time. To satisfy 40
CFR 51.308(g)(5), Missouri notes that most visibility impairing pollutants have decreased since
the last planning period submittal with the exception of ammonia (NH3). Missouri refers to
Chapter 4 of which details the existing measures that have resulted in those emissions decreases
such as Federal, state or mobile source emissions programs.
The EPA finds that Missouri satisfactorily refers to the included emissions inventory,
describes the emissions trends or changes as well as the visibility trends for their two Class I
Areas to meet the requirements contained in 40 CFR 51.308(g)(1) through (5). Therefore, the
EPA proposes to approve Missouri’s plan as meeting the requirements of 40 CFR 51.308(g)(1)
through (5).
I. 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.”
Section 51.308(i)(2)’s FLM consultation provision requires a state to provide FLMs with
an opportunity for consultation that is early enough in the state’s policy analyses of its emission
reduction obligation so that information and recommendations provided by the FLMs’ can
meaningfully inform the state’s decisions on its long-term strategy. If the consultation has taken
place at least 120 days before a public hearing or public comment period, the opportunity for
consultation will be deemed early enough, Regardless, the opportunity for consultation must be
provided at least sixty days before a public hearing or public comment period at the state level.
Section 51.308(i)(2) also provides 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. Section 51.308(i)(4) requires
states to provide for ongoing consultation between the state and FLM’s on the implementation of
the given plan and on development of future plan revisions or progress reports.
Missouri included summaries of their consultation with various FLMs as well as
responses to their comments in Appendix G-2 to their submittal. On July 30, 2021, Missouri
shared the pre-proposal draft of its second planning period regional haze plan with the FS, the
FWS, the NPS, and the EPA. On September 21, 2021, Missouri held a formal consultation call
with the three FLM agencies as well as the EPA.
However, because the EPA is proposing to disapprove certain elements of Missouri’s
SIP, namely the long-term strategy under 40 CFR 51.308(f)(2) and the reasonable progress goals
under 40 CFR 51.308(f)(3), the EPA is also proposing to disapprove the FLM consultation
requirements under 40 CFR 51.308(i). The requirements contained in 40 CFR 51.308(i): (i)(2),
(i)(3), and (i)(4) are not separable from one another. While Missouri did take administrative steps
to provide the FLMs the requisite opportunity to review and provide feedback on the state’s draft
plan, the EPA cannot approve the requirements under 40 CFR 51.308(i) because Missouri’s
consultation was based on a SIP revision that did not meet the required statutory and regulatory
requirements of the CAA and the RHR, respectively. In addition, if the EPA were to finalize the
partial approval and partial disapproval of Missouri’s SIP, in the process of correcting the
deficiencies outlined above with respect to the RHR and statutory requirements, the state (or the
EPA in the case of an eventual FIP) will be required to again satisfy the FLM consultation
requirements under 40 CFR 51.308(i). Therefore, the EPA proposes to disapprove the respective
elements of Missouri’s plan as not meeting the requirements of 40 CFR 51.308(i).
VI. What Action is the EPA Proposing to Take?
The EPA is proposing to partially approve and partially disapprove the Missouri SIP

revision relating to Regional Haze for the second planning period received on August 26, 2022,
pursuant to section 110(k)(3) of the CAA and 40 CFR (f)(3)(iv). The EPA is proposing to
approve the elements of Missouri’s plan related to requirements contained in 40 CFR
51.308(f)(1), (f)(5), (f)(6), and (g)(1) through (g)(5). The EPA is proposing to disapprove the
elements of Missouri’s plan related to requirements contained in 40 CFR 51.308(f)(2) and (f)(3),
and (i). The EPA is not proposing a Federal Implementation Plan (FIP) at this time. If the EPA
finalizes the disapproval, that will start a two-year clock for the EPA to propose and finalize a
FIP.75 However, the EPA is already on a two-year FIP clock that began September 29, 2022,
when the EPA published a finding that Missouri failed to submit the required regional haze plan
for the second planning period by the regulatory deadline.76 We are soliciting comments on this
proposed action. Final rulemaking will occur after consideration of any comments.
VII. Environmental Justice Considerations
The EPA defines environmental justice (EJ) as ‘‘the fair treatment and meaningful
involvement of all people regardless of race, color, national origin, or income with respect to the
development, implementation, and enforcement of environmental laws, regulations, and
policies.’’ The EPA further defines the term fair treatment to mean that ‘‘no group of people
should bear a disproportionate burden of environmental harms and risks, including those
resulting from the negative environmental consequences of industrial, governmental, and
commercial operations or programs and policies.’’77 Recognizing the importance of these
considerations to local communities, the EPA conducted an environmental justice screening
analysis around the location of the facilities associated with this action to identify potential
environmental stressors on these communities and the potential impacts of this action. However,
the EPA is providing the information associated with this analysis for informational purposes

75The

EPA is only stating this second FIP clock as a factual result that a disapproval leads to a FIP clock. The FIP
clock from the finding of failure to submit is primary and the FIP clock from a future disapproval does not supersede
or reset the FIP clock from the finding of failure to submit.
76 See 87 FR 52856, August 30, 2022.
77 See https://www.epa.gov/environmentaljustice/learn-about-environmentaljustice.

only. The information provided herein is not a basis of the proposed action. The EPA conducted
the screening analyses using EJScreen, an EJ mapping and screening tool that provides the EPA
with a nationally consistent dataset and approach for combining various environmental and
demographic indicators.78 The EJScreen tool presents these indicators at a Census block group
(CBG) level or a larger user specified ‘‘buffer’’ area that covers multiple CBGs.79 An individual
CBG is a cluster of contiguous blocks within the same census tract and generally contains
between 600 and 3,000 people. EJScreen is not a tool for performing in-depth risk analysis, but
is instead a screening tool that provides an initial representation of indicators related to EJ and is
subject to uncertainty in some underlying data (e.g., some environmental indicators are based on
monitoring data which are not uniformly available; others are based on self-reported data).80 For
informational purposes, we have summarized EJScreen data within larger ‘‘buffer’’ areas
covering multiple block groups and representing the average resident within the buffer areas
surrounding the facilities selected by Missouri for further control analysis. EJScreen
environmental indicators help screen for locations where residents may experience a higher
overall pollution burden than would be expected for a block group with the same total population
in the U.S. These indicators of overall pollution burden include estimates of ambient PM2.5 and
ozone concentration, a score for traffic proximity and volume, percentage of pre-1960 housing
units (lead paint indicator), and scores for proximity to Superfund sites, risk management plan
(RMP) sites, and hazardous waste facilities.81 EJScreen also provides information on
demographic indicators, including percent low-income, communities of color, linguistic
isolation, and less than high school education. The EPA prepared EJScreen reports covering

The EJSCREEN tool is available at https:// www.epa.gov/ejscreen.
See https://www.census.gov/programssurveys/geography/about/glossary.html.
80 In addition, EJSCREEN relies on the five-year block group estimates from the U.S. Census American Community
Survey. The advantage of using five-year over single-year estimates is increased statistical reliability of the data
(i.e., lower sampling error), particularly for small geographic areas and population groups. For more information,
see https://www.census.gov/content/ dam/Census/library/publications/2020/acs/acs_ general_handbook_2020.pdf.
81 For additional information on environmental indicators and proximity scores in EJSCREEN, see ‘‘EJSCREEN
Environmental Justice Mapping and Screening Tool: EJSCREEN Technical Documentation,’’ Chapter 3 and
Appendix C (September 2019) at https://www.epa.gov/sites/ default/files/2021-04/documents/ejscreen_
technical_document.pdf.
78
buffer areas of approximately 6-mile radii around the facilities selected by Missouri for further
analysis. For each facility, the EPA indicates in the following statements whether there is an
environmental or socioeconomic indicator for the selected source area above the 80th percentile
nationally. These indicators are displayed in the table on page 3 of each report. The report for
New Madrid Power Plant showed socioeconomic indicators greater than the 80th national
percentile for low income.82 The report for Sikeston showed environmental and socioeconomic
indicators greater than the 80th national percentiles for wastewater discharge and low life
expectancy. The report for John Twitty showed environmental indicators greater than the 80th
national percentiles for wastewater discharge and superfund proximity. The report for Thomas
Hill showed environmental indicators greater than the 80th national percentiles for wastewater
discharge. The report for Mississippi Lime showed environmental indicators greater than the 80th
national percentiles for risk management plan facility proximity. Other facility reports not
mentioned here do not include environmental or socioeconomic indicators greater than the 80th
national percentiles. The full, detailed EJScreen reports for each facility selected by Missouri for
further analysis are provided in the docket for this rulemaking. This action is proposing to
disapprove certain elements of Missouri’s second planning period regional haze plan as not
meeting the requirements of the CAA or the EPA’s RHR. Exposure to PM and SO2 is associated
with significant public health effects. Short-term exposures to SO2 can harm the human
respiratory system and make breathing difficult. People with asthma, particularly children, are
sensitive to these effects of SO2.83 Exposure to PM can affect both the lungs and heart and is
associated with: premature death in people with heart or lung disease, nonfatal heart attacks,
irregular heartbeat, aggravated asthma, decreased lung function, and increased respiratory
symptoms, such as irritation of the airways, coughing or difficulty breathing. People with heart

For a place at the 80th percentile nationwide, that means 20% of the U.S. population has a higher value. The EPA
identified the 80th percentile filter as an initial starting point for interpreting EJScreen results. The use of an initial
filter promotes consistency for EPA programs and regions when interpreting screening results.
83 See https://www.epa.gov/so2-pollution/sulfurdioxide-basics#effects.
or lung diseases or conditions, children, and older adults are the most likely to be affected by PM
exposure.84 This action which proposes to partially disapprove Missouri’s regional haze plan, if
finalized, will not directly result in a change to emissions or air quality. There is nothing in the
record which indicates that this proposed action, if finalized, would have disproportionately high
or adverse human health or environmental effects on communities with environmental justice
concerns.
VIII. Statutory and Executive Order Reviews
Under the CAA, the Administrator is required to approve a SIP submission that complies
with the provisions of the CAA and applicable Federal regulations. 42 U.S.C. 7410(k); 40 CFR
52.02(a). Thus, in reviewing SIP submissions, the EPA's role is to review state choices, and
approve those choices if they meet the minimum criteria of the CAA. Accordingly, this proposed
action partially approves and partially disapproves state law as meeting Federal requirements and
does not impose additional requirements beyond those imposed by state law.
A. Executive Order 12866: Regulatory Planning and Review and Executive Order 13563:
Improving Regulation and Regulatory Review
This action is not a “significant regulatory action” under the terms of Executive Order
12866 (58 FR 51735, October 4, 1993) and is therefore not subject to review under Executive
Orders 12866, 13563 (76 FR 3821, January 21, 2011) and 14094 (88 FR 21879, April 11, 2023).
B. Paperwork Reduction Act (PRA)
This rule does not impose an information collection burden under the provisions of the
Paperwork Reduction Act of 1995 (44 U.S.C. 3501 et seq.).
C. Regulatory Flexibility Act (RFA)
This action merely proposes to partially approve and partially disapprove state law as
meeting or not meeting Federal requirements and imposes no additional requirements beyond

See https://www.epa.gov/pm-pollution/healthand-environmental-effects-particulate-matter-pm.

those imposed by state law. Accordingly, the Administrator certifies that this rule will not have a
significant economic impact on a substantial number of small entities under the Regulatory
Flexibility Act (5 U.S.C. 601 et seq.).
D. Unfunded Mandates Reform Act (UMRA)
This action does not contain any unfunded mandate as described in UMRA, 2 U.S.C.
1531–1538, and does not significantly or uniquely affect small governments. This action does
not impose additional requirements beyond those imposed by state law. Accordingly, no
additional costs to State, local, or tribal governments, or to the private sector, will result from this
action.
E. Executive Order 13132: Federalism
This action does not have federalism implications. It will not have substantial direct
effects on the states, on the relationship between the national government and the states, or on
the distribution of power and responsibilities among the various levels of government.
F. Executive Order 13175: Consultation and Coordination With Indian Tribal Governments
This action does not have tribal implications as specified in Executive Order 13175. This
action does not apply on any Indian reservation land, any other area where the EPA or an Indian
tribe has demonstrated that a tribe has jurisdiction, or non-reservation areas of Indian country.
This rule does not have tribal implications and will not impose substantial direct costs on tribal
governments or preempt tribal law as specified by Executive Order 13175 (65 FR 67249,
November 9, 2000).
G. Executive Order 13045: Protection of Children From Environmental Health Risks and
Safety Risks
The EPA interprets Executive Order 13045 as applying only to those regulatory actions
that concern environmental health or safety risks that the EPA has reason to believe may
disproportionately affect children, per the definition of “covered regulatory action” in section 2–
202 of the Executive Order. This action is not subject to Executive Order 13045

because it merely proposes to disapprove a SIP submission as not meeting the CAA.
H. Executive Order 13211, Actions That Significantly Affect Energy Supply, Distribution or Use
This action is not subject to Executive Order 13211, because it is not a significant
regulatory action under Executive Order 12866.
I. National Technology Transfer and Advancement Act
This rulemaking does not involve technical standards. Therefore, the EPA is not
considering the use of any voluntary consensus standards.
J. Executive Order 12898: Federal Actions To Address Environmental Justice in Minority
Populations and Low-Income Populations (59 FR 7629, February 16, 1994)
Executive Order 12898 directs Federal agencies to identify and address
“disproportionately high and adverse human health or environmental effects” of their actions on
minority populations and low-income populations to the greatest extent practicable and permitted
by law. The EPA defines environmental justice (EJ) as “the fair treatment and meaningful
involvement of all people regardless of race, color, national origin, or income with respect to the
development, implementation, and enforcement of environmental laws, regulations, and
policies.” The EPA further defines the term fair treatment to mean that “no group of people
should bear a disproportionate burden of environmental harms and risks, including those
resulting from the negative environmental consequences of industrial, governmental, and
commercial operations or programs and policies.” The Missouri Department of Natural
Resources did not evaluate environmental justice considerations as part of its SIP submittal; the
CAA and applicable implementing regulations neither prohibit nor require such an evaluation.
The EPA performed an environmental justice analysis, as is described above in the section titled,
“Environmental Justice Considerations.” The analysis was done for the purpose of providing
additional context and information about this rulemaking to the public, not as a basis of the
action. Due to the nature of the action being taken here, merely proposing to partially approve
and partially disapprove the state’s plan as meeting requirements of the Act or EPA regulations,

this action will not directly impact air quality or emissions in the affected areas. Consideration
of EJ is not required as part of this action, and there is no information in the record inconsistent
with the stated goal of EO 12898 of achieving environmental justice for people of color, lowincome populations, and Indigenous peoples.

List of Subjects in 40 CFR Part 52
Environmental protection, Air pollution control, Carbon monoxide, Incorporation by reference,
Intergovernmental relations, Lead, Nitrogen dioxide, Ozone, Particulate matter, Reporting and
recordkeeping requirements, Sulfur oxides, Volatile organic compounds.

Dated: June 27, 2024.
Meghan A. McCollister,
Regional Administrator,
Region 7.
For the reasons stated in the preamble, the EPA proposes to amend 40 CFR part 52 as set forth
below:
PART 52—APPROVAL AND PROMULGATION OF IMPLEMENTATION PLANS
1. The authority citation for part 52 continues to read as follows:
Authority: 42 U.S.C. 7401 et seq.
Subpart AA-Missouri
2. In § 52.1320, the table in paragraph (e) is amended by adding the entry “(86)” in numerical
order to read as follows:
§52.1320 Identification of plan.
*****

(e) * * *

EPA-APPROVED MISSOURI NONREGULATORY SIP PROVISIONS
Applicable
Name of
geographic or State
EPA
nonregulatory
nonattainment submittal
approval
SIP revision
area
date
date
Explanation
*******
[Date of
This action approves the
publication
plan as only meeting the
of the final
requirements of 40 CFR
rule in the
51.308(f)(1), (f)(5), (f)(6),
(86) Missouri
Federal
and (g)(1) through (g)(5).
Regional Haze
Register],
This action disapproves
Plan for the
[Federal
the plan as not meeting the
Second
Register
requirements of 40 CFR
Implementation
citation of the 51.308(f)(2), (f)(3), and
Period
Statewide
8/26/22
final rule]
(i).
3. Amend § 52.1339 by adding paragraph (b) to read as follows:
§ 52.1339 Visibility protection.
*****

(b) The requirements of section 169A of the Clean Air Act are not fully met for the second
implementation period because the plan does not include approvable measures for meeting the
requirements of 40 CFR 51.308(f)(2), (f)(3), and (i) for protection of visibility in mandatory
Class I Federal areas. The plan does meet the requirements of 40 CFR 51.308(f)(1), (f)(5), (f)(6),
and (g)(1) through (g)(5).

[FR Doc. 2024-14612 Filed: 7/2/2024 8:45 am; Publication Date: 7/3/2024]