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Proposed Rule2026-09054

Air Plan Approval; Missouri; Attainment Plan for the New Madrid Nonattainment Area for the 2010 1-Hour Sulfur Dioxide National Ambient Air Quality Standard

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Published

May 7, 2026

Issuing agencies

Environmental Protection Agency

Abstract

The Environmental Protection Agency (EPA) is proposing to approve the State Implementation Plan (SIP) revision, submitted by the State of Missouri, on May 3, 2023. This revision pertains to the attainment plan for the New Madrid nonattainment area for the 2010 1- hour sulfur dioxide (SO<INF>2</INF>) primary National Ambient Air Quality Standard (NAAQS). This plan (herein called an "attainment plan") includes the State's attainment demonstration and other elements required under Clean Air Act (CAA). In addition to an attainment demonstration, the plan addresses emission limitations necessary to provide for attainment, base-year and projection-year emission inventories, reasonably available control measures and reasonably available control technology (RACM/RACT), nonattainment new source review (NNSR), the requirements for meeting reasonable further progress (RFP) toward attainment of the NAAQS, and contingency measures. The EPA is proposing to approve Missouri's submission as meeting these relevant CAA requirements. This action is being taken pursuant to the CAA.

Full Text

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<title>Federal Register, Volume 91 Issue 88 (Thursday, May 7, 2026)</title>
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[Federal Register Volume 91, Number 88 (Thursday, May 7, 2026)]
[Proposed Rules]
[Pages 24768-24782]
From the Federal Register Online via the Government Publishing Office [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[FR Doc No: 2026-09054]

[[Page 24768]]

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 52

[EPA-R07-OAR-2026-2938; FRL-13334-01-R7]

Air Plan Approval; Missouri; Attainment Plan for the New Madrid
Nonattainment Area for the 2010 1-Hour Sulfur Dioxide National Ambient
Air Quality Standard

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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SUMMARY: The Environmental Protection Agency (EPA) is proposing to
approve the State Implementation Plan (SIP) revision, submitted by the
State of Missouri, on May 3, 2023. This revision pertains to the
attainment plan for the New Madrid nonattainment area for the 2010 1-
hour sulfur dioxide (SO<INF>2</INF>) primary National Ambient Air
Quality Standard (NAAQS). This plan (herein called an ``attainment
plan'') includes the State's attainment demonstration and other
elements required under Clean Air Act (CAA). In addition to an
attainment demonstration, the plan addresses emission limitations
necessary to provide for attainment, base-year and projection-year
emission inventories, reasonably available control measures and
reasonably available control technology (RACM/RACT), nonattainment new
source review (NNSR), the requirements for meeting reasonable further
progress (RFP) toward attainment of the NAAQS, and contingency
measures. The EPA is proposing to approve Missouri's submission as
meeting these relevant CAA requirements. This action is being taken
pursuant to the CAA.

DATES: Comments must be received on or before June 8, 2026.

ADDRESSES: Submit your comments, identified by Docket ID No. EPA-R07-
OAR-2026-2938 to <a href="https://www.regulations.gov">https://www.regulations.gov</a>. Follow the online
instructions for submitting comments. Once submitted, comments cannot
be edited or removed from <a href="http://Regulations.gov">Regulations.gov</a>. The EPA may publish any
comment received to its public docket. Do not submit electronically any
information you consider to be Confidential Business Information (CBI)
or other information whose disclosure is restricted by statute.
Multimedia submissions (audio, video, etc.) must be accompanied by a
written comment. The written comment is considered the official comment
and should include discussion of all points you wish to make. The EPA
will generally not consider comments or comment contents located
outside of the primary submission (i.e. on the web, cloud, or other
file sharing system). For additional submission methods, the full EPA
public comment policy, information about CBI or multimedia submissions,
and general guidance on making effective comments, please visit <a href="https://www.epa.gov/dockets/commenting-epa-dockets">https://www.epa.gov/dockets/commenting-epa-dockets</a>.

FOR FURTHER INFORMATION CONTACT: Ashley Keas, Environmental Protection
Agency, Air and Radiation Division, 11201 Renner Boulevard, Lenexa,
Kansas 66219, telephone number: (913) 551-7629, email address:
<a href="/cdn-cgi/l/email-protection#99f2fcf8eab7f8eaf1f5fce0d9fce9f8b7fef6ef"><span class="__cf_email__" data-cfemail="462d2327356827352e2a233f0623362768212930">[email&#160;protected]</span></a>.

SUPPLEMENTARY INFORMATION: Throughout this document whenever ``we,''
``us,'' and ``our'' is used, we mean the EPA.
Organization of this document. The following outline is provided to
aid in locating information in this preamble.

Table of Contents

I. Background
II. Requirements for SO<INF>2</INF> Attainment Plans
III. Review of Missouri's SIP Submission
A. Termination of the Consent Agreements Upon Action by the EPA
B. Modification of Emission Limits in the Magnitude 7 Metals
Consent Agreement
C. Relocation of Monitors in the Magnitude 7 Metals Consent
Agreement
D. Choice of Law Provisions
E. Force Majeure Provisions
IV. Review of Modeled Attainment Demonstration
A. Modeling Approach and Receptor Grid
B. Meteorological Data
C. Emissions Data
D. Emissions Limits
E. Background Concentrations
F. Summary of Results
V. Review of Emissions and Emissions Controls
A. Emissions Inventory and the Quantification of Emissions
B. Reasonably Available Control Measures/Reasonably Available
Control Technology
C. Nonattainment New Source Review
D. Reasonable Further Progress
E. Contingency Measures
VI. Proposed Action
VII. Incorporation by Reference
VIII. Statutory and Executive Order Reviews

I. Background

Under section 109 of the CAA, the EPA has established primary and
secondary NAAQS for certain pervasive air pollutants (referred to as
``criteria pollutants'') and conducts periodic reviews of the NAAQS to
determine whether they should be revised or whether new NAAQS should be
established. The primary NAAQS represent ambient air quality standards,
the attainment and maintenance of which the EPA has determined,
including an adequate margin of safety, are requisite to protect the
public health. The secondary NAAQS represent ambient air quality
standards, the attainment and maintenance of which the EPA has
determined are requisite to protect the public welfare from any known
or anticipated adverse effects associated with the presence of such air
pollutant in the ambient air.
Under the CAA, the EPA must establish NAAQS for criteria
pollutants, including SO<INF>2</INF>. SO<INF>2</INF> is primarily
released to the atmosphere through the burning of fossil fuels by power
plants and other industrial facilities. Short-term exposure to
SO<INF>2</INF> can damage the human respiratory system and increase
breathing difficulties. Small children and people with respiratory
conditions, such as asthma, are more sensitive to the effects of
SO<INF>2</INF>. Sulfur oxides at high concentrations in ambient air can
also react with other compounds to form small particulates that can
penetrate deeply into the lungs and cause health problems.
On June 22, 2010, the EPA published a new 1-hour primary
SO<INF>2</INF> NAAQS of 75 parts per billion (ppb) at 40 CFR 50.17(a),
which is met at an ambient air quality monitoring site when the 3-year
average of the annual 99th percentile of daily maximum 1-hour average
concentrations does not exceed 75 parts per billion (ppb), as
determined in accordance with appendix T of 40 CFR part 50 (75 FR
35520). Under CAA section 107(d)(1), the EPA is required to designate
areas as ``nonattainment,'' ``attainment,'' or ``unclassifiable''
within two years of establishing a new or revising an existing
standard. As part of this process, states must submit recommendations
for initial area designations and boundaries to the EPA within one year
of the effective date of the standard. The EPA evaluates the state
recommendations and promulgates the area designations based on the
relevant information. On March 26, 2021, the EPA published a document
in the Federal Register designating 9 areas in 7 states as
nonattainment for the 2010 1-hour SO<INF>2</INF> NAAQS, including a
portion of New Madrid County in the State of Missouri. This set of
designations is known as Round 4. See 86 FR 16055, codified at 40 CFR
part 81, subpart C. These area designations were effective April 30,
2021. This Round 4 of designations was based on data from newly
installed monitoring sites placed in the area of maximum concentration
in the respective source areas. As noted later in this document, there
were three new monitoring sites installed in the

[[Page 24769]]

New Madrid area designed to capture the maximum impact from the
relevant sources in the area. Based in part on monitoring data from
these monitors, the EPA designated a portion of New Madrid County as
nonattainment for the 2010 SO<INF>2</INF> NAAQS on April 30, 2021 (86
FR 16055). This designation triggered a requirement for Missouri to
submit by October 30, 2022 (within 18 months per CAA section 191(a)), a
SIP revision containing an attainment plan for how the New Madrid area
would attain the 2010 SO<INF>2</INF> NAAQS as expeditiously as
practicable, but no later than April 30, 2026, per CAA section 192(a)
in accordance with CAA sections 110(a), 172(c) and 191-192.
In response to this requirement, Missouri submitted an attainment
plan for the New Madrid nonattainment area on May 3, 2023. The
remainder of this document describes the requirements that such
attainment plans must meet in order for the EPA to approve the plan
provisions into the federally enforceable SIP, provides a review of the
state's plan with respect to these requirements, and describes the
EPA's proposed action on Missouri's plan. For reasons described in the
following sections, the EPA is proposing to approve Missouri's
attainment plan for the New Madrid area.

II. Requirements for SO<INF>2</INF> Attainment Plans

SO<INF>2</INF> attainment plans must meet the applicable
requirements of the CAA, including specifically CAA sections 110, 172,
191 and 192. The EPA's regulations governing attainment plans are set
forth at 40 CFR part 51, with specific procedural requirements and
control strategy requirements residing at subparts F and G,
respectively. Soon after Congress enacted the 1990 Amendments to the
CAA, the EPA issued comprehensive guidance on SIP requirements, in a
document entitled the ``General Preamble for the Implementation of
Title I of the Clean Air Act Amendments of 1990,'' published at 57 FR
13498 (April 16, 1992) (General Preamble). Among other things, the
General Preamble addressed SO<INF>2</INF> attainment plan requirements
and fundamental principles for SIP emission control strategies. Id., at
13545-49, 13567-68. On April 23, 2014, the EPA issued guidance and
recommendations for meeting the statutory requirements for
SO<INF>2</INF> attainment plans addressing the 2010 primary
SO<INF>2</INF> NAAQS, in a document entitled, ``Guidance for 1-Hour
SO<INF>2</INF> Nonattainment Area SIP Submissions'' (hereafter referred
to as ``2014 SO<INF>2</INF> Nonattainment Guidance'').\1\ In this
guidance, the EPA described the statutory requirements for the elements
of an attainment plan as provided in CAA section 172(c), which include:
an accurate emissions inventory of current emissions for all sources of
SO<INF>2</INF> within the nonattainment area; an attainment
demonstration; demonstration of Reasonable Further Progress (RFP);
implementation of Reasonably Available Control Measures (RACM)
(including Reasonably Available Control Technology (RACT)); emission
limitations and control measures necessary to provide for attainment;
nonattainment new source review (NNSR); and adequate contingency
measures.
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\1\ Available at <a href="https://www.epa.gov/sites/default/files/2016-06/documents/20140423guidance_nonattainment_sip.pdf">https://www.epa.gov/sites/default/files/2016-06/documents/20140423guidance_nonattainment_sip.pdf</a>.
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In general, the EPA's duties in reviewing state attainment plans
are described in CAA sections 110(k) and 110(l). The EPA is required to
determine whether a SIP submission meets certain minimum criteria for
completeness, or it is deemed complete by operation of law six months
after the state submits it. Once a SIP submission is complete, the EPA
is required to approve or disapprove the submission, in whole or in
part, depending upon whether it meets all applicable requirements of
the CAA. The EPA may also conditionally approve a state's attainment
plan submission, in whole or in part, under certain circumstances.
State attainment plans are approved by the EPA as meeting the
requirements of the CAA if they fully address the requirements of CAA
sections 110, 172, 191 and 192, and the EPA's regulations at 40 CFR
part 51.
Also, under CAA section 110(l), the EPA may not approve a SIP
revision that would interfere with any applicable requirement
concerning NAAQS attainment and RFP, or any other applicable
requirement of the CAA. Further, under CAA section 193, no control
requirement in effect before November 15, 1990 (or required to be
adopted by an order, settlement, agreement, or plan in effect before
November 15, 1990), in any area which is a nonattainment area for any
air pollutant, may be modified in any manner unless the modification
ensures equivalent or greater emission reductions of such air
pollutant.
CAA sections 172(c)(1) and 172(c)(6) direct states with areas
designated as nonattainment to demonstrate that the submitted plan and
its emission limitations and control measures provide for attainment of
the NAAQS. The EPA's regulations at 40 CFR part 51, subpart G further
delineates the control strategy requirements that attainment plans must
meet, and provide that all attainment plan control strategies reflect
the four fundamental principles of quantification, enforceability,
replicability, and accountability. See General Preamble, at 13567-
13568. In addition to the attainment plan elements discussed above,
attainment plans for the SO<INF>2</INF> NAAQS must include: (1)
enforceable emission limitations and other control measures that assure
implementation of permanent, enforceable and necessary emission
controls, and (2) a modeling analysis which meets the requirements of
40 CFR part 51, appendix W and demonstrates that necessary emission
limitations and control measures provide for timely attainment of the
primary SO<INF>2</INF> NAAQS as expeditiously as practicable, but by no
later than the applicable attainment date for the affected area. In all
cases, these emission limitations and control measures must be
accompanied by appropriate methods and conditions to determine
compliance with the respective emission limitations and control
measures. Further, these emissions limitations must be quantifiable
(i.e., a specific amount of emission reduction can be ascribed to the
measures), fully enforceable (specifying clear, unambiguous and
measurable requirements for which compliance can be practicably
determined), replicable (the procedures for determining compliance are
sufficiently specific and non-subjective so that two independent
entities applying the procedures would obtain the same result), and
accountable (source-specific emission limitations and control measures
must be permanent and must reflect the assumptions used in the RFP and
modeled attainment demonstrations).
The EPA's 2014 SO<INF>2</INF> Nonattainment Guidance recommends
that the emission limitations established for the attainment
demonstration be expressed as short-term average limits (e.g.,
addressing emissions averaged over one hour consistent with the
averaging time of the 2010 1-hour SO<INF>2</INF> NAAQS), but also
describes the option to utilize emission limitations with longer
averaging times of up to 30 days so long as the limit is demonstrated
by the state to assure comparable stringency to a 1-hour average limit
that demonstrates attainment of the 1-hour SO<INF>2</INF> NAAQS. The
EPA's guidance provides suggested criteria and procedures for making
this demonstration. See 2014 SO<INF>2</INF> Nonattainment Guidance, pp.
22-39.

[[Page 24770]]

The guidance recommends that--should states and sources seek to utilize
longer averaging times--the longer-term average limit should be set at
an adjusted level that reflects a stringency comparable to the 1-hour
average limit at the critical emission value (CEV) shown to provide for
attainment that the plan otherwise would have set.
The 2014 SO<INF>2</INF> Nonattainment Guidance provides an
extensive discussion of the EPA's rationale for concluding that
appropriately set, comparably stringent limitations based on averaging
times as long as 30 days can be found to provide for attainment of the
2010 SO<INF>2</INF> NAAQS. In evaluating this option, the EPA
considered the nature of the standard, conducted detailed analyses of
the impact of 30-day average limits on the prospects for attaining the
standard, and carefully reviewed how best to achieve an appropriate
balance among the various factors that warrant consideration in judging
whether a state's plan provides for attainment. Id. at pp. 22-39, and
appendices B, C, and D.
As specified in 40 CFR 50.17(b), the 2010 1-hour primary
SO<INF>2</INF> NAAQS is met at an ambient air quality monitoring site
when the 3-year average of the annual 99th percentile of daily maximum
1-hour average concentrations is less than or equal to 75 ppb. In a
year with 365 days of valid monitoring data, the 99th percentile would
be the fourth highest daily maximum 1-hour value. Because the standard
has this form, a single hourly exceedance of the 75 ppb NAAQS level
does not by itself result in a violation of the standard. Instead, at
issue is whether a source operating in compliance with a properly set
longer-term average could cause multiple hourly exceedances over
multiple days in a year, and if so, the resulting frequency and
magnitude of such exceedances, and in particular, whether the EPA can
have reasonable confidence that a properly set longer-term average
limit will provide that the 3-year average of annual fourth highest
daily maximum hourly values will be at or below 75 ppb. A synopsis of
how the EPA evaluates whether such plans ``provide for attainment,''
based on modeling of projected allowable emissions and in light of the
SO<INF>2</INF> NAAQS' form for determining attainment at monitoring
sites, follows.
For SO<INF>2</INF> NAAQS attainment plans based on emission
limitations that impose 1-hour emission limits, the standard approach
is to conduct modeling using fixed 1-hour emission rates. The maximum
modeled emission rate that results in attainment is labeled the
``critical emissions value'' (CEV). The modeling process for
identifying this CEV inherently considers the numerous variables that
affect ambient concentrations of SO<INF>2</INF>, such as meteorological
data, background concentrations, and topography. In the standard
approach, the state would then provide for attainment by setting a
continuously applicable 1-hour emission limit for each stationary
SO<INF>2</INF> source at this CEV.
The EPA recognizes that some SO<INF>2</INF> sources have highly
variable emissions, for example due to variations in fuel sulfur
content and operating rate, which can make it extremely difficult, even
with a well-designed control strategy, to ensure in practice that
emissions for any given hour do not exceed the CEV. The EPA also
acknowledges the concern that longer-term emission limits can allow
short periods with emissions above the CEV, which, if coincident with
meteorological conditions conducive to high SO<INF>2</INF>
concentrations, could in turn create the possibility of an hourly NAAQS
exceedance occurring on a day when an exceedance would not have
occurred if emissions were continuously controlled at the level
corresponding to the CEV. However, for several reasons, the EPA
believes that the approach recommended in its guidance document
suitably addresses this concern.
First, from a practical perspective, the EPA expects the actual
emission profile of a source subject to an appropriately set longer-
term average limit to be similar to the emission profile of a source
subject to an analogous 1-hour average limit. The EPA expects this
similarity because it has recommended that the longer-term average
limit be set at a level that is comparably stringent to the otherwise
applicable 1-hour limit (reflecting a downward adjustment from the CEV)
and that takes the source's emissions profile (and inherent level of
emissions variability) into account. As a result, the EPA expects
either form of emission limit to yield comparable air quality.
Second, from a more theoretical perspective, the EPA has compared
the likely air quality with a source having maximum allowable emissions
under an appropriately set longer-term limit, to the likely air quality
with the source having maximum allowable emissions under the comparable
1-hour limit. In this comparison, in the 1-hour average limit scenario,
the source is presumed at all times to emit at the CEV, and in the
longer-term average limit scenario, the source is presumed occasionally
to emit more than the CEV, but on average, and presumably at most
times, to emit well below the CEV. In an ``average year,'' \2\
compliance with the 1-hour limit is expected to result in three
exceedance days (i.e., three days with maximum hourly values above 75
ppb) and a fourth day with a maximum hourly value at 75 ppb. By
comparison, with the source complying with a longer-term limit, it is
possible that additional hourly exceedances would occur that would not
occur in the 1-hour limit scenario (if emissions exceed the CEV at
times when meteorology is conducive to poor air quality). However, this
comparison must also factor in the likelihood that exceedances that
would be expected in the 1-hour limit scenario would not occur in the
longer-term limit scenario. This result arises because the longer-term
limit requires lower emissions most of the time (because the limit is
set below the CEV), so a source complying with an appropriately set
longer-term limit is likely to have lower emissions at critical times
than would be the case if the source were emitting as allowed with a 1-
hour limit.
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\2\ An ``average year'' is used to mean a year with average air
quality. While 40 CFR part 50, appendix T, provides for averaging
three years of annual 99th percentile daily maximum hourly values
(e.g., the fourth highest maximum daily hourly concentration in a
year with 365 days with valid data), this discussion and an example
below uses a single ``average year'' in order to simplify the
illustration of relevant principles.
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To illustrate this point, the EPA conducted a statistical analysis
using a range of scenarios using actual plant data. This analysis is
described in appendix B of the EPA's 2014 SO<INF>2</INF> Nonattainment
Guidance. Based on the analysis described in the 2014 SO<INF>2</INF>
Nonattainment Guidance, the EPA expects that an emission profile with
maximum allowable emissions under an appropriately set, comparably
stringent 30-day average limit is likely to have the net effect of
having a lower number of hourly exceedances and better air quality than
an emission profile with maximum allowable emissions under a 1-hour
emission limit at the CEV. This result provides a compelling policy
rationale for allowing the use of a longer averaging period, in
appropriate circumstances where the facts indicate this result can be
expected to occur.
The 2014 SO<INF>2</INF> Nonattainment Guidance offers specific
recommendations for determining an appropriate longer-term average
limit. The recommended method starts with determination of the 1-hour
emission limit that would provide for attainment (i.e., the CEV), and
applies an adjustment factor to determine the (lower) level of the
longer-term average emission limit that would be estimated

[[Page 24771]]

to have a stringency comparable to the otherwise necessary 1-hour
emission limit. This method uses a database of continuous emission data
reflecting the type of control that the source will be using to comply
with the SIP emission limits, which (if compliance requires new
controls) may require use of an emission database from another source.
The recommended method involves using these data to compute a complete
set of emission averages, computed according to the averaging time and
averaging procedures of the prospective emission limitation (i.e.,
using 1-hour historical emission values from the emissions database to
calculate 30-day average emission values). In this recommended method,
the ratio of the 99th percentile among these longer-term averages to
the 99th percentile of the 1-hour values represents an adjustment
factor that may be multiplied to the candidate 1-hour emission limit
(CEV) to determine a longer-term average emission limit that may be
considered comparably stringent.\3\
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\3\ For example, if the CEV is 1000 pounds of SO<INF>2</INF> per
hour, and a suitable adjustment factor is determined to be 70
percent, the recommended longer-term average limit would be 700
pounds per hour.
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The 2014 SO<INF>2</INF> Nonattainment Guidance also addresses a
variety of related topics, including the potential utility of setting
supplemental emission limits, such as mass-based limits or work
practice requirements for the operation of SO<INF>2</INF> control
equipment, to reduce the likelihood and/or magnitude of elevated
emission levels that might occur under the longer-term emission rate
limit.
Preferred air quality models for use in regulatory applications are
described in Addendum A of the EPA's Guideline on Air Quality Models
(40 CFR part 51, appendix W). In 2005, the EPA promulgated AERMOD as
the Agency's preferred near-field dispersion modeling for a wide range
of regulatory applications addressing stationary sources (for example
in estimating SO<INF>2</INF> concentrations) in all types of terrain
based on extensive developmental and performance evaluations.
Supplemental guidance on modeling for purposes of demonstrating
attainment of the SO<INF>2</INF> standard is provided in appendix A to
the 2014 SO<INF>2</INF> Nonattainment Guidance. Appendix A provides
extensive guidance on the modeling domain, the source inputs, assorted
types of meteorological data, and background concentrations.
Consistency with the recommendations in this guidance would generally
ensure that the attainment demonstration offers adequately reliable
assurance that the plan provides for attainment.
Attainment demonstrations for the 2010 1-hour primary
SO<INF>2</INF> NAAQS must demonstrate future attainment of the NAAQS in
the entire area designated as nonattainment (i.e., not just at the
violating monitor) by using air quality dispersion modeling (see
appendix W to 40 CFR part 51) to show that the mix of sources and
enforceable control measures and emission rates in an identified area
will not lead to a violation of the SO<INF>2</INF> NAAQS. For a short-
term (i.e., 1-hour) standard, the EPA finds that dispersion modeling,
using allowable emissions and addressing stationary sources in the
affected area (and in some cases those sources located outside the
nonattainment area which may affect attainment in the area) is
technically appropriate, efficient, and effective in demonstrating
attainment in nonattainment areas because it takes into consideration
combinations of meteorological and emission source operating conditions
that may contribute to peak ground-level concentrations of
SO<INF>2.</INF>
The meteorological data used in the analysis should generally be
processed with the most recent version of AERMET. AERMET is a
meteorological data preprocessor that incorporates air dispersion based
on planetary boundary layer turbulence structure and scaling concepts.
Estimated concentrations should include ambient background
concentrations, should follow the form of the standard, and should be
calculated as described in section 2.6.1.2 of the August 23, 2010,
clarification memo on ``Applicability of Appendix W Modeling Guidance
for the 1-hour SO<INF>2</INF> National Ambient Air Quality Standard''
(U.S. EPA, 2010).

III. Review of Missouri's SIP Submission

The State of Missouri submitted an attainment plan for the New
Madrid area to the EPA on May 3, 2023. Missouri established new consent
agreements (APCP-2022-047A and APCP-2022-048A respectively) with the
following two sources that account for the majority of SO<INF>2</INF>
emissions in the nonattainment area: Magnitude 7 Metals (M7M) and
Associated Electric Cooperative Incorporated (AECI) New Madrid Power
Plant.\4\ The State relies on these new consent agreements as the
enforceable mechanism for satisfying several requirements of the area's
attainment plan, including the control strategy, attainment
demonstration, RFP, RACM/RACT, and contingency measures. These consent
agreements are available in appendices E and F of the State's
submission included in the docket for this action.
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\4\ The State submittal document in the docket for this action
includes the full consent agreements as appendices. M7M's consent
agreement is contained in appendix E, and AECI New Madrid's consent
agreement is contained in appendix F to the state plan.
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M7M is a primary aluminum reduction plant with two principal
operations that emit SO<INF>2</INF>: on-site carbon bake furnaces which
produce carbon block anodes and electrolysis potlines which consume the
anodes to produce metallic aluminum. As the carbon block anodes are
baked in the furnaces, some sulfur in the raw coke and pitch is also
``baked out'' of the carbon block and released as SO<INF>2</INF>
through relatively low-level stacks. In the potline electrolytic
process, sulfur still present in the carbon blocks oxidizes to form
SO<INF>2</INF>. SO<INF>2</INF> emissions from the potlines are routed
under negative pressure through fluoride scrubbers and then to a common
stack, with a portion of the SO<INF>2</INF> also released as fugitive
emissions through roof vents spanning the potline buildings.
The AECI New Madrid Power Plant operates two coal-fired steam
boilers to generate electric power. They are the main sources of
SO<INF>2</INF> emissions for this facility. The emissions from these
boilers are routed through a dual stack that uses continuous emissions
monitoring systems (CEMS) to measure actual hourly SO<INF>2</INF>
emissions from each of the two boilers.
Although the largest sources of SO<INF>2</INF> emissions in the
nonattainment area are the M7M potlines and the New Madrid Power Plant
coal-fired boilers, the State determined based on air dispersion
modeling analyses that the most significant contributions to elevated
ground-level SO<INF>2</INF> concentrations are from SO<INF>2</INF>
emissions released from relatively low-level stacks of the M7M's carbon
bake furnaces. For this reason, the State developed a control strategy
focused on rerouting SO<INF>2</INF> emissions from the existing low-
level carbon bake furnace stacks to a new yet-to-be-constructed taller
stack to improve dispersion of these emissions. The control strategy
also includes new emission limitations and monitoring requirements for
AECI New Madrid that were applicable beginning on January 1, 2023, as
required by the consent agreement.
The requirement for M7M to cease all SO<INF>2</INF> emissions from
the low-level carbon bake stacks was made enforceable by the State
through a consent agreement with M7M. The State also established new
SO<INF>2</INF> emission

[[Page 24772]]

limits for M7M's carbon bake and potline emission release points. The
M7M Consent Agreement paragraph 1.A.v. prohibits any SO<INF>2</INF>
emissions from the existing carbon bake furnaces unless such emissions
have been re-routed to the new stack by December 31, 2023. This
provision applies to emissions from carbon bake furnaces 1, 2, and 3
(in the event carbon bake 3 is restarted and goes through the New
Source Review process), as identified in appendix A of the consent
agreement. It further states that this deadline may be extended up to
but no later than January 1, 2025. In a letter dated August 10, 2023,
MoDNR extended the December 31, 2023, deadline to January 28, 2024.\5\
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\5\ This letter and other relevant correspondence between the
MoDNR and M7M are included in the docket for this action.
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M7M curtailed operations in January 2024 \6\ and has not yet
constructed the new carbon bake stack. M7M retains all of its operating
permits so the facility could restart at any time and remains subject
to the requirements of the state consent agreement. Therefore, should
the company restart operations, it must comply with the hourly
emissions limits and the prohibition to emit any SO<INF>2</INF>
emissions from the carbon bake stacks unless emissions are routed to
the new carbon bake stack, among other requirements.
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\6\ As referenced in a letter dated February 16, 2024, from the
Missouri Attorney General to M7M and in various media articles, the
M7M smelter ceased operations and laid off the majority of remaining
workers on January 28, 2024. The letter can be found in the docket
for this action and at this link: <a href="https://ago.mo.gov/wp-content/uploads/2024.02.16-Magnitude-7-Metals-Letter.pdf">https://ago.mo.gov/wp-content/uploads/2024.02.16-Magnitude-7-Metals-Letter.pdf</a>. Examples of media
articles: Allison Kite, ``One of nation's only aluminum smelters set
to close in Missouri Bootheel,'' Missouri Independent, January 25,
2024 (<a href="https://missouriindependent.com/2024/01/25/one-of-nations-only-aluminum-smelters-set-to-close-in-missouri-bootheel">https://missouriindependent.com/2024/01/25/one-of-nations-only-aluminum-smelters-set-to-close-in-missouri-bootheel</a>); and Jason
Plautz, ``Aluminum shortage threatens US clean energy plans, E&E
News by Politico, March 13, 2024 (<a href="https://www.eenews.net/articles/aluminum-shortage-threatens-us-clean-energy-plans/">https://www.eenews.net/articles/aluminum-shortage-threatens-us-clean-energy-plans/</a>).
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For the reasons discussed throughout this document, the EPA is
proposing to approve the state's attainment plan submittal, including
the M7M and AECI New Madrid source-specific consent agreements, as
meeting the relevant CAA requirements and thereby proposing to
incorporate by reference the underlying requirements to become
federally enforceable. During the state's public comment period, the
EPA notified the state that the consent agreements contain provisions
that could be interpreted to allow the state and the affected source to
modify or terminate them without following the statutorily-mandated
process for SIP revisions.\7\ See sections 110(i) and 110(l).
Modification or termination of the consent agreements is also contrary
to sections 110(a)(2)(a) and 172(c)(7) of the CAA which require the
state to adopt enforceable emission limitations and control measures
which provide for the implementation, maintenance, and enforcement of
the NAAQS. Further, modification or termination of the consent
agreements may complicate future redesignation of the area. The EPA may
only redesignate a nonattainment area if it has determined that the
improvement in air quality is due to ``permanent and enforceable
reductions in emissions'' resulting from implementation of the SIP,
among other requirements in section 107(d)(3)(E) of the CAA. While the
EPA allows consent agreements or permit requirements to be incorporated
by reference into a state's SIP to meet SIP requirements (see 40 CFR
part 51, appendix V, section 2.1.(b)), the state must ensure that any
such approved provisions cannot be altered by subsequent changes to the
underlying agreements or permits unless the SIP is revised. 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.
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\7\ See the EPA's comment letter on the State's public notice
draft dated December 19, 2022, included in the docket for this
action.
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In the sections that follow, the EPA explains its interpretation of
several consent agreement provisions, including those that could result
in a modification of the consent agreement. Specifically, the EPA
explains its interpretation of those provisions in which a revision to
the SIP would be necessary if the consent agreement is modified
following the EPA's codification of the consent agreement into the SIP.

A. Termination of the Consent Agreements Upon Action by the EPA

The EPA has previously expressed its view that termination
provisions that render the consent agreements unenforceable depending
on the nature of the action the EPA takes are inconsistent with the
requirements of the CAA. See 89 FR 55140. The EPA's position is that
enforceable mechanisms relied upon for attainment plan requirements,
such as the consent agreements provided by Missouri as part of the New
Madrid attainment plan, should not include provisions which would
automatically, or at the source's or the State's option, terminate the
agreement based on the EPA's action. For example, the M7M consent
agreement termination provision states that, ``This consent agreement
shall also terminate if the SIP revision for the New Madrid County
SO<INF>2</INF> Nonattainment Area or this Consent Agreement are
disapproved by the U.S. Environmental Protection Agency.'' Further, the
termination-related provisions included in the AECI New Madrid
agreement provide for automatic termination of the agreement upon the
effective date of a full disapproval and for optional termination after
the effective date of a partial disapproval by the EPA.
Several provisions in the consent agreements state that, once the
EPA approves their inclusion into the SIP, the agreements cannot be
terminated or modified unless the SIP is revised. For example,
paragraph 5 in ``Other Provisions'' of the AECI New Madrid agreement
states that, ``The parties further agree that after EPA has approved
the SIP revision that contains this Consent Agreement, any subsequent
modifications to this Consent Agreement, subject to the termination
provisions in paragraph 13 of this Consent Agreement, will require
approval from EPA before such modifications would take effect.''
Similarly, paragraph 7 of the M7M agreement includes this same
language.
Termination provisions that are triggered upon the EPA's exercise
of its statutory partial approval authority found in CAA section
110(k)(3) essentially limits or nullifies the effect of the EPA's
action and is particularly problematic where there is more than one
source and more than one enforceable mechanism. Because the EPA is
proposing to fully approve the New Madrid attainment plan including the
consent agreements for both M7M and AECI New Madrid, these termination
provisions are not triggered by the EPA's full approval, and the
agreements are therefore not terminated outside the EPA SIP approval
process.

B. Modification of Emission Limits in the Magnitude 7 Metals Consent
Agreement

Paragraph 1.A.xii. of the M7M consent agreement details the process
by which the source may request a new 30-day rolling average emission
limit to replace the hourly emission limits contained in paragraph
1.A.vii. in the consent agreement, and for the State to approve these
replacement limits. The process includes updating the source's
operating permit after state approval of the replacement limit. The
State outlines the process by which the comparably stringent 30-day
rolling average limits would be calculated

[[Page 24773]]

based on data collected by the yet to be installed CEMS.
As part of the EPA's proposed approval of the state's attainment
plan, the EPA approves the process for development and state approval
of a new 30-day rolling average emission limit, but not the resulting
30-day rolling average emission limit. Modification of the relevant
emissions limit relied on to meet the requirements of CAA section
172(c)(6) \8\ would materially change the attainment plan and the basis
for the EPA's approval of Missouri's attainment plan. A SIP revision
would be necessary to incorporate a new (or replace the existing)
emissions limit relied upon in the state's attainment plan. Such change
also requires a justification to meet the requirements of section
110(l) of the CAA.
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\8\ CAA section 172(c)(6): ``Such plan provisions shall include
enforceable emission limitations, [. . .] as may be necessary or
appropriate to provide for attainment of such standard in such area
by the applicable attainment date [. . .]''
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Therefore, any 30-day rolling average emission limit established
either under the terms of the consent agreement or otherwise must go
through public notice and comment and must be approved by the EPA
before it could replace the hourly emission limits in the control
strategy. Specifically, the new numeric emissions limit, averaging
period, and the technical basis for such limit must all be made
available for public review and comment before submission to the EPA
for review and approval as a SIP revision.

C. Relocation of Monitors in the Magnitude 7 Metals Consent Agreement

Paragraph 1.B.i. of the M7M consent agreement allows the source to
request and the State to approve the relocation of any of the three
existing ambient air SO<INF>2</INF> monitors surrounding the M7M
property. Paragraph 1.B.ii. clearly limits the ability of the source to
discontinue (or the State to approve such discontinuation) any of the
three existing ambient air monitors surrounding the M7M property
without going through the necessary EPA approval through the State's
adherence to the annual monitoring network plan review process. The EPA
agrees with this wording describing the process the State and source
must follow to discontinue monitors.
The wording of paragraph 1.B.i., however, does not contain such
limitations and therefore appears to circumvent the required process
for review and approval by the EPA before relocation of required
ambient air monitors. Specifically, 40 CFR 58.14(b) and other related
provisions require that state agencies submit monitoring network
changes to the EPA for review and approval, this is typically handled
through annual network plans. The relocation of monitors (or other
modifications to the ambient monitoring network) must be reviewed and
approved by the EPA, per requirements in 40 CFR 58.14. However, 40 CFR
58.14(c)(6) provides that a monitor not eligible for removal under any
of the criteria in paragraphs (c)(1) through (c)(5) may be moved to a
nearby location with the same scale of representation if logistical
problems beyond the State's control make it impossible to continue
operation at its current site. Because the state's attainment plan
relies on the continued operation of these monitors for contingency
measure triggering language, they should not be moved in a manner that
changes the scale of representation for the nonattainment area. The
Data Requirements Rule (DRR) at 40 CFR 51.1203(c) also provides
requirements for monitoring sites established pursuant the DRR,
specifically that they must be operated similarly to SLAMS (state or
local air monitoring stations) and be subject to the same SLAMS
requirements of 40 CFR part 58. If the source or state significantly
relocate any of the monitors as provided for under Paragraph 1.B.i. of
the M7M consent agreement, such that they would no longer be
appropriately sited to capture maximum impacts from the primary sources
in the nonattainment area and therefore to serve as the mechanism for
triggering contingency measures, the EPA finds this would materially
change the attainment plan and the basis for EPA's approval of
Missouri's attainment plan. Therefore, a SIP revision would be
necessary to incorporate a new (or replace the existing) reliance on
the monitors in their current locations as a triggering mechanism for
contingency measures.

D. Choice of Law Provisions

Both the M7M and AECI New Madrid consent agreements include
provisions termed as ``choice of law'' clauses. Specifically, paragraph
10 of the M7M agreement and paragraph 8 of the AECI New Madrid
agreement state, ``This Consent Agreement shall be construed and
enforced according to the laws of the State of Missouri, and the terms
stated herein shall constitute the entire and exclusive agreement of
the parties hereto with respect to the matters addressed herein.'' The
EPA interprets this provision to bind the ``parties'' to the consent
agreement, namely the State of Missouri and AECI New Madrid and
Magnitude 7 Metals, respectively. Furthermore, following approval of
the consent agreements into the SIP by the EPA, enforcement of the
consent agreement under sections 113 or 304 of the CAA would be
governed by federal law.

E. Force Majeure Provisions

Both the Magnitude 7 Metals and AECI New Madrid consent agreements
include ``force majeure'' provisions which excuse a source from
liability if an event, such as a natural disaster, act of terrorism,
labor dispute or stoppage, war, national or regional emergency,
pandemic, epidemic, local disease outbreak, public health emergency, or
quarantine, occurs which causes performance of an obligation under the
consent agreement to be practically impossible, despite the source's
best efforts to fulfill the obligation. If a force majeure event occurs
that meets the criteria of the consent agreement, the consent agreement
requires the source to notify the State within five business days
following commencement of the force majeure event, and include actions
taken to minimize the impact thereof. According to the terms of each
consent agreement, the source and the State agree that the pertinent
obligations and deliverables of the consent agreement will be
rescheduled rather than cancelled.
The EPA has evaluated the force majeure provisions in the consent
agreements in light of CAA requirements for SIP provisions. The EPA
interprets them to provide the sources an affirmative defense to any
form of liability, whether monetary penalties or injunctive relief, in
the event of violations of the emission limitations or other control
requirements applicable to the sources, so long as the source meets the
requirements to qualify for the force majeure provision. As such, these
force majeure provisions constitute a ``complete'' affirmative defense
and are thus consistent with CAA requirements for SIP provisions.
The EPA notes that the U.S. Court of Appeals for the District of
Columbia Circuit (the D.C. Circuit) has issued decisions that are
relevant to affirmative defense provisions. In the first, Env't Comm.
of the Fla Elec. Power Coordinating Grp, Inc. v. EPA, the court held
that affirmative defense type provisions that only preclude monetary
penalties as a remedy for violations of emission limitations or other
SIP requirements, i.e., a ``partial'' affirmative defense, are invalid.
Env't Comm. of the Fla Elec. Power Coordinating Grp, Inc. v. EPA, 94
F.4th

[[Page 24774]]

77, 116 (D.C. Cir. 2024). More recently, in SSM Litigation Group v.
EPA, the court further clarified that an affirmative defense type
provision that instead precludes any form of liability or remedy for
violations of emission limitations or other SIP requirements, i.e., a
``complete'' affirmative defense, is valid. SSM Litigation Group v.
EPA, et al., 150 F.4th 593 (D.C. Circ. 2025). In that decision, the
D.C. Circuit held in part that a complete affirmative defense is
permissible because it does not function as an exemption from
applicable emission standards. 150 F.4th at 600 (``[a]n affirmative
defense allows a defendant to avoid liability, but it does not alter
the underlying legal requirements''). The court reasoned that a
``complete affirmative defense to liability does not render an emission
limitation non-continuous under 42 U.S.C. 7602(k).'' Id. Although the
court's decision in SSM Litigation Group pertained specifically to an
affirmative defense provision that a state may elect to include in
title V permits for sources in such state, the court's reasoning would
apply more broadly to affirmative defenses that a state may elect to
include in its SIP provisions applicable to sources outside of the
title V permit context.
The force majeure provision in each consent agreement at issue in
this attainment plan functions as a complete affirmative defense
because it allows a defendant to avoid liability if the failure to
perform an obligation under the consent agreement has been caused by a
force majeure event, but it does not alter the underlying legal
requirements that are applicable to the source pursuant to the consent
agreement. Accordingly, any emission limitations or other emission
controls requirements in the consent agreements apply continuously, in
accordance with section 302(k) of the CAA. Furthermore, in accordance
with section 110 of the CAA, following approval of the consent
agreement into the SIP, any modification of the consent agreement would
require the state to submit, and the EPA to approve, the revised
consent agreement as a revision to the SIP. Accordingly, the EPA
proposes to approve the force majeure provisions in each consent
agreement as complete affirmative defense provisions.
The state's attainment plan also includes a modeled attainment
demonstration, based on the emissions limits and operational
requirements set through the new source-specific consent agreements,
which is further discussed in section IV. of this preamble as well as
in the TSD included in the docket with this action. The other
requirements addressed through Missouri's attainment plan are discussed
further in section V. of this preamble.

IV. Review of Modeled Attainment Demonstration

The following discussion evaluates various features of the modeling
that Missouri used in its attainment demonstration.\9\ Missouri's
submission contains a modeling demonstration that includes an
assessment of the air quality impacts the State expected to result from
emissions limitations and operational changes governing M7M and the
AECI New Madrid Power Plant. The State's attainment demonstration
modeling shows that the control strategy of a to-be-constructed carbon
bake stack at M7M and new SO<INF>2</INF> emission limitations for both
facilities results in modeled attainment of the 2010 1-hour primary
SO<INF>2</INF> NAAQS throughout the New Madrid nonattainment area. This
section discusses the EPA's review of the state's attainment
demonstration. The EPA's Technical Support Document (TSD) included in
the docket for this action provides greater detail about our technical
review of the state's submission.
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\9\ The input files used in the modeling demonstration are
available by request from the contact listed in the FOR FURTHER
INFORMATION CONTACT section of this document.
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A. Modeling Approach and Receptor Grid

As previously stated, AERMOD is the preferred model for this
application. Missouri's final attainment demonstration modeling
analysis utilized AERMOD version 21112, the most current version
available at the time of plan development. The State asserts that all
analyses were conducted with the EPA's regulatory default options and
considering the EPA's guidance documents, including the 2014
SO<INF>2</INF> SIP guidance and appendix W. The most recently available
version of AERMAP (18081) was used to import terrain and source
elevations from the National Elevation Dataset (NED). All building
downwash analyses were conducted using the most recently available
version (04274) of the EPA's Building Profile Input Program with Plume
Rise Enhancements (BPIPPRM). The EPA finds the selection and use of
these inputs to AERMOD, AERMAP and BPIPPRM to be appropriate and in
accordance with appendix W and the 2014 SO<INF>2</INF> SIP guidance.
The receptor grid for the final attainment demonstration used 100-
meter spacing throughout the nonattainment area outside of M7M's
property boundary and 50-meter spacing along M7M's property boundary.
The State also extended the receptor grid beyond the nonattainment area
using 200-meter spacing to evaluate whether modeled violations occur
outside the nonattainment area boundary. In addition, the State
prepared a second modeling scenario with receptors placed at 100-meter
spacing throughout the nonattainment area, but excluding receptors
inside the New Madrid power plant's property boundary, to evaluate
whether emissions from the power plant contribute to modeled violations
within the M7M's property boundary. The EPA's TSD includes further
detail on the various receptor grid configurations utilized by
Missouri.

B. Meteorological Data

Modeling for the New Madrid area attainment plan was conducted
using the surface station data from the Cape Girardeau airport and
upper air data from the Springfield airport, and used consecutive years
from 2017-2021. This represents the most recent, readily available 5-
year period at the time of the initial analysis per section 8.3.1.2 of
appendix W. The State selected the Cape Girardeau and Springfield
airport stations as best representative of meteorological conditions
within the area of analysis, consistent with the nonattainment boundary
designation. The State utilized meteorological data processed with
AERMET version 21112, in combination with 1-minute Automated Surface
Observing Stations (ASOS) wind data processed with AERMINUTE version
15272, to generate hourly average winds for input to AERMET. The EPA
finds the selection and use of these meteorological inputs to AERMET to
be appropriate and in accordance with appendix W and the 2014
SO<INF>2</INF> SIP guidance.

C. Emissions Data

[[Page 24775]]

Missouri's modeled attainment demonstration and control strategy
focuses on the two largest sources of SO<INF>2</INF> in the area: M7M
and the New Madrid Power Plant. One minor source, Alubar, was also
included in the modeling due to its proximity and relation to M7M.
Alubar produces aluminum rods from molten aluminum purchased from M7M.
The plant's three rod mills and ancillary processes were previously
part of M7M's operations until purchased by Alubar in December 2021.
There are seven additional small point sources of SO<INF>2</INF> within
and nearby the nonattainment area that the State evaluated for their
potential contribution to concentrations in the area. Table 3 in EPA's
TSD lists these sources. The combined total potential to emit for these
seven sources is 1.4 tons per year of SO<INF>2</INF>. Consistent with
section 8.3.3 of appendix W, the State accounted for these minor point
sources, as well as mobile and area (i.e., stationary non-point)
sources of SO<INF>2</INF> emissions, through the use of a background
SO<INF>2</INF> concentration in the modeling because they do not cause
significant concentration gradients in the vicinity of the sources of
interest. Section V.A. of this preamble contains more information on
the emissions inventory element of the New Madrid attainment plan.
To determine the SO<INF>2</INF> emission rates to use in the
attainment demonstration modeling, the State followed appendix W
section 8.2.2.b and table 8-1, which specify that stationary point
sources should be modeled at maximum allowable emissions levels
assuming continuous operation (i.e., all hours of the time period under
consideration) to demonstrate NAAQS compliance and/or establish
appropriate SIP emission limits. The modeled hourly SO<INF>2</INF>
emission rates used for M7M's main SO<INF>2</INF> emission release
points (potline stack, potline roof vents, and proposed new carbon bake
stack) and the New Madrid power plant stack are consistent with
SO<INF>2</INF> emission limits established in the new consent
agreements for M7M and the New Madrid Power Plant. Specifically, the
State used hourly SO<INF>2</INF> emission rates for M7M of 1,015.42 lb/
hr for the potline stack (EP61), 111.11 lb/hr for the potline fugitives
roof vents (EP59A, 59B, 60A, and 60B), and 1,390.52 lb/hr for the new
carbon back stack (EPAAA, to be constructed) in the attainment
demonstration modeling, which are equivalent to the 1-hour
SO<INF>2</INF> emission limits in section 1.A.vii of the M7M Consent
Agreement. In addition, the State used a modeled hourly SO<INF>2</INF>
emission rate of 6,412.8 lb/hr for both units at New Madrid Power Plant
combined, which the State asserts is of comparable stringency to the
30-day rolling average SO<INF>2</INF> emission limit of 5,523 lb/hour
in paragraph 1.A. of the consent agreement for New Madrid Power Plant.
For the remainder of the explicitly modeled sources (the smaller
SO<INF>2</INF> emission units at M7M and Alubar), the State based the
modeled emission rates on potential to emit. All modeled hourly
emission rates were held constant assuming continuous operation over
the entire five-year period, 2017-2021. The final attainment
demonstration modeling assumes the New Madrid Power Plant is operating
both of its units at 100% load. The State also conducted a series of
supplemental modeling runs that assumed the power plant is operating at
50% and 75% loads to ensure that the attainment demonstration modeling
accounts for maximum potential impacts from the power plant. The
additional load scenarios are intended to address section 8.2.2.d. of
appendix W, which specifies that at a minimum, a source should be
modeled using the design capacity (100% load). It further states that
sources which operate at substantially less than design capacity should
also be modeled at loads such as 50% and 75% if the changes in the
stack parameters associated with the operating conditions could lead to
higher ground level concentrations.
The attainment demonstration modeling used good engineering
practice (GEP) stack heights \10\ as determined by BPIPPRM in
accordance with appendix W and the 2014 SO<INF>2</INF> SIP guidance.
M7M provided stack parameters for the facility's emission release
points, including engineering design parameters for the proposed new
carbon bake stack (to be constructed). AECI provided stack parameters
for the various load scenarios for the New Madrid Power Plant. The
state characterized emissions from the two New Madrid units as a
combined stack in the modeling. BPIPPRM was used to input building
parameters into AERMOD for M7M, New Madrid Power Plant, and Alubar.
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\10\ See 40 CFR 51.118 and 40 CFR 51.100(hh) for more
information on the EPA's stack height regulations and definition of
good engineering practice stack height.
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The derivation of the modeled emission rates, modeled stack
parameters, and the various load scenarios for the New Madrid Power
Plant are discussed further in the TSD.

D. Emissions Limits

Section 172(c)(6) of the CAA requires that the State's attainment
plan include enforceable emission limitations, and such other control
measures, means or techniques (including economic incentives such as
fees, marketable permits, and auctions of emission rights), as well as
schedules and timetables for compliance, as may be necessary or
appropriate to provide for attainment of the standard in the area by
the applicable attainment date. See General Preamble at 13567-68. Part
of the review of the State's attainment plan must address the use of
these limits, both with respect to the general suitability of using
such limits for the purpose of meeting the requirements of CAA section
172(c)(6) and with respect to whether the particular limits included in
the plan have been suitably demonstrated to provide for attainment. As
specified in section 172(c)(6) and section 110(a)(2)(A) of the CAA and
the 2010 1-hour SO<INF>2</INF> NAAQS at 75 FR 35520, emission
limitations, control measures and other elements in the SIP must be
enforceable by the State and the EPA.
1. Enforceability
Working with M7M and AECI New Madrid, the State developed a control
strategy designed to bring the area into attainment of the 1-hour
SO<INF>2</INF> NAAQS. Missouri's attainment plan for the New Madrid
area relies on new consent agreements between the State and M7M and
AECI New Madrid, respectively, as the enforceable mechanisms for the
control strategy. The control strategy establishes source-specific
control measures that include more stringent SO<INF>2</INF> emissions
limits at both facilities and operational changes, specifically
rerouting of emissions from the carbon bake furnaces through
construction of a new stack at M7M. The M7M consent agreement prohibits
emissions from the existing carbon bake stacks after December 31, 2023,
unless those emissions have been re-routed to a new Carbon Bake stack.
The consent agreement states that this deadline may be extended by
MoDNR up to but no later than January 1, 2025. As noted previously,
MoDNR extended the December 31, 2023, deadline to January 28, 2024.\11\
The state's attainment plan relies on these new source consent
agreements to satisfy required elements such as the control strategy
and modeled attainment demonstration, RFP, RACM/RACT, and contingency
measures.
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\11\ See correspondence between MoDNR and M7M related to
deadline extensions as included in the docket for this action.

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[[Page 24776]]

The State relied on the final attainment demonstration modeling to
determine the necessary emission limits for the New Madrid Power Plant
and M7M that would result in modeled attainment of the NAAQS.\12\ In
addition to the 1-hour SO<INF>2</INF> emission limits established for
M7M, the State also established a 5,000 tons per year (tpy) facility-
wide SO<INF>2</INF> emission limit for the facility in the consent
agreement.\13\ This annual facility-wide SO<INF>2</INF> emission limit
was not set based on the attainment demonstration modeling and is not
linked to attainment of the 2010 1-hour SO<INF>2</INF> NAAQS. The
purpose of establishing a 5,000 tpy SO<INF>2</INF> limit for M7M is to
allow credit in the attainment demonstration modeling for the
dispersion characteristics of the proposed new carbon bake stack. Per
the federal definition of dispersion technique at 40 CFR
51.100(hh)(2)(v), credit for certain dispersion techniques, including
but not limited to increasing final exhaust gas plume rise by
manipulating source process parameters, exhaust gas parameters, stack
parameters, or combining exhaust gases from several existing stacks
into one stack, is allowed in the model if the resulting total
allowable SO<INF>2</INF> emissions from the facility do not exceed
5,000 tons per year. The EPA agrees that M7M could merge multiple
uncontrolled SO<INF>2</INF> emission streams from its carbon bake
furnaces into a single, taller stack constructed at GEP height in
accordance with federal stack regulations, as long as the facility is
subject to a 5,000 tpy SO<INF>2</INF> emission limit. The AECI New
Madrid Power Plant emissions limits contained in the consent agreements
and relied on as part of the area's control strategy are 30-day average
emission limits. In accordance with EPA policy, the 30-day average
limit is set at a lower level than the shorter-term emission rate used
in the attainment demonstration; the relationship between these two
values is discussed in more detail in the following section.
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\12\ The modeled attainment demonstration accounts for emissions
from the two carbon bake furnaces as operating at their full hourly
emissions limits as emitted from the yet-to-be-constructed Carbon
Bake stack. This is conservative in nature because per the
requirements and deadlines of the consent agreement, M7M is
currently prohibited from operating the carbon bake furnaces.
\13\ Paragraph 1.A.vi of the M7M Consent Agreement states:
Facility-wide SO<INF>2</INF> emissions from Magnitude 7 shall not
exceed 4,999.99 tons in any rolling 12-month period. This is
referred to as a 5,000 tpy emission limit for the purpose of this
NPRM.
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2. Longer-Term Average Limits
Table 13 in the TSD for this rulemaking presents results of the
different load scenarios for the New Madrid Power Plant. Based on this
table and our review, the EPA agrees that the 100% load scenario
captures the maximum modeled impacts from the power plant and that
using the modeled emissions rate from the 100% load scenario as the
basis for establishing the emission limit for the power plant is
appropriate.
The State followed the procedure in appendix C of the 2014
SO<INF>2</INF> guidance to convert the New Madrid Power Plant's modeled
hourly SO<INF>2</INF> emission rate to a 30-day rolling average
SO<INF>2</INF> emission limit. The procedure is based on determining
the ratio between 99th percentile emission rates for the applicable
averaging time (30 days in this case) and 1-hour 99th percentile
emission rates. The State first determined that a modeled hourly
SO<INF>2</INF> emission rate of 6,412.80 lb/hr for the New Madrid Power
Plant's units 1 and 2 combined is equivalent to the CEV in the
attainment demonstration modeling, taking into account all other
explicitly modeled sources (M7M and Alubar) and the background
SO<INF>2</INF> concentration. Based on CEMS data for New Madrid Power
Plant units 1 and 2 for the 5-year period from 2016-2020, the ratio
between 99th percentile 30-day rolling average and 1-hour 99th
percentile emission rates for both units combined was determined to be
0.86. This ratio is higher than the average ratio of 0.79 for sources
with no control equipment listed in table 1 in appendix D of the EPA's
2014 SO<INF>2</INF> SIP Guidance, which indicates that the operations
of New Madrid Power Plant's units are generally less variable than the
average uncontrolled unit. The modeled hourly SO<INF>2</INF> emission
rate of 6,412.80 lb/hr was then multiplied by 0.86, which results in a
30-day rolling average of 5,523 lb/hr for the two units combined.
Based on a review of the state's submittal, the EPA believes that
the 5,523 lb/hr 30-day rolling average limit for both units 1 and 2
combined that is included in paragraph 1.A. of the Consent Agreement
for the New Madrid Power Plant provides a suitable alternative to
establishing a 1-hour average emission limit for this source. The state
has used a suitable data base in an appropriate manner and has thereby
applied an appropriate adjustment factor, yielding an emission limit
that has comparable stringency to the 1-hour average limit that the
state determined would otherwise have been necessary to provide for
attainment. While the 30-day rolling-average limit allows occasions in
which emissions may be higher than the level that would be allowed with
the 1-hour limit, the state's limit compensates by requiring average
emissions to be lower than the level that would otherwise have been
required by a 1-hour average limit. For reasons described above and
explained in more detail in the EPA's 2014 SO<INF>2</INF> Nonattainment
Guidance, the EPA has found that appropriately set longer-term average
limits provide a reasonable basis by which nonattainment plans may
provide for attainment. Based on its review of this general information
as well as the particular information in Missouri's plan, the EPA finds
that the 30-day rolling average limit for the New Madrid Power Plant,
in combination with other limitations for M7M in the state's plan, will
provide for attainment of the NAAQS. The EPA concludes that the
modeling and comparably stringent longer-term emission limits in
Missouri's plan adequately demonstrate that they provide for attainment
of the 2010 primary 1-hour SO<INF>2</INF> NAAQS in the New Madrid
County Nonattainment Area.
Notably, the State provided both the New Madrid Power Plant's CEV
and the 30-day limit, along with the underlying analysis used to derive
the 30-day limit, for public notice and comment prior to submission to
the EPA for inclusion in the SIP. The State's calculations used to
convert the New Madrid Power Plant's CEV to a 30-day rolling average
limit of comparable stringency are discussed in greater detail in the
TSD.
For M7M, the State determined the maximum hourly emissions rate for
each emission point that would result in modeled attainment.
Specifically, the State determined that maximum hourly SO<INF>2</INF>
emission rates of 317.47 lb/hr for the new carbon bake furnace stack
(to be constructed), 1,015.42 lb/hr for the existing pot line stack for
pot lines 1 and 2, and 111.11 lb/hr for the pot line roof vents, which
are equivalent to the hourly limits included in paragraph 1.A.vii of
the M7M Consent Agreement, result in modeled attainment in combination
with the SO<INF>2</INF> emission limits for the New Madrid Power Plant.
These hourly limits are also presented as the CEV that the State would
use to derive longer-term average limits once enough hourly data is
recorded by the yet-to-be-installed CEMS. However, as described further
in section III. above, it is the EPA's interpretation that the State
may not revise the applicable emissions limit in the control strategy
after EPA approval which codifies the emissions limits and operational
requirements into federal regulations ensuring the limits as approved
remain permanent and federally enforceable. Therefore, in order for any
revised emissions limits to become federally enforceable or replace

[[Page 24777]]

limits that were already approved into the SIP, the state would need to
follow the SIP revision process including public notice and EPA review
and approval. Any subsequent changes made by the state to the control
strategy or aspects of the attainment plan after approval by the EPA,
would only change state enforceability not federal enforceability until
approved as a formal SIP revision by the EPA.

E. Background Concentrations

The 2014 SO<INF>2</INF> Nonattainment Area SIP guidance recommends
developing a uniform monitored background concentration based on
monitored design values for the latest three-year period, regardless of
the years of meteorological data used in the modeling. The guidance
further states that in cases of nonattainment areas designated based on
a monitor's data showing a NAAQS violation, it may be necessary to use
a different representative monitor outside of the nonattainment area,
particularly where the monitor has a high number of observations
impacted by modeled sources. The 2024 Guidance on Developing Background
Concentration for Use in Modeling Demonstrations \14\ (2024 Background
Concentration Guidance) provides guidance on the selection of nearby
sources to explicitly model in the demonstration and the
representativeness of the background concentration of sources not
modeled explicitly.
---------------------------------------------------------------------------

\14\ U.S. Environmental Protection Agency, 2024. Guidance on
Developing Background Concentrations for Use in Modeling
Demonstrations. Publication No. EPA-454/R-24-003. Office of Air
Quality Planning and Standards, Research Triangle Park, NC. (<a href="https://www.epa.gov/system/files/documents/2024-11/background-concentrations.pdf">https://www.epa.gov/system/files/documents/2024-11/background-concentrations.pdf</a>).
---------------------------------------------------------------------------

Because the New Madrid nonattainment area was designated based on
monitoring data and the SO<INF>2</INF> monitors in the area are
impacted by the modeled sources, the State chose to rely on the
regional rural background monitor located at Mark Twain State Park,
which is approximately 236 miles (380 kilometers) northwest of the
nonattainment area. Based on the Mark Twain State Park's 3-year design
value for 2019-2021, the State selected a background SO<INF>2</INF>
concentration of 13.08 micrograms per cubic meter ([mu]g/m\3\),
equivalent to 5.0 ppb, which was held constant throughout the modeled
time period.
Section 3.3 of the 2024 Background Concentration Guidance lists
criteria to consider when determining representativeness of ambient
monitoring data, including whether the monitor is located in an urban
or rural setting similar to the project area, consistency of the wind
and terrain patterns at the monitor to the project area, and whether
data from the monitor have been used in previous analysis for the
project area, among other factors. The EPA finds that the West Entrance
monitor would be more representative of SO<INF>2</INF> background
concentrations in the New Madrid nonattainment area based on the
consistency of the wind and terrain patterns at this monitor due to its
location within the nonattainment area. The EPA performed an analysis
of 2020-2022 SO<INF>2</INF> concentrations measured at the West
Entrance monitor when the monitor was not impacted by SO<INF>2</INF>
emissions from explicitly modeled sources (the New Madrid Power Plant,
M7M, or Alubar). Namely, the EPA performed a wind sector analysis at
this monitor to determine ambient concentrations when winds originate
from sectors not impacted by the modeled sources, in this case when
winds originate from the south. Based on our analysis, we calculated an
SO<INF>2</INF> background concentration of 10.5 [micro]g/m\3\ (4 ppb).
The EPA's TSD included in the docket for this action includes more
details on our analysis.
The EPA finds that an SO<INF>2</INF> concentration of 10.5
[micro]g/m\3\ (4 ppb) is representative of background SO<INF>2</INF>
levels in the New Madrid nonattainment area. In addition, the EPA
agrees that it is appropriate to represent SO<INF>2</INF> emissions
from all sources in the area other than M7M, New Madrid Power Plant,
and Alubar with the background concentration included in the modeling
analysis, and that further consideration of these other sources/sectors
as part of the area's control strategy is unnecessary.

F. Summary of Results

As described in this section of the preamble, the State's final
attainment demonstration modeling relied on maximum allowable hourly
SO<INF>2</INF> emission limits for the M7M potline stack, potline roof
vents, and proposed new carbon bake stack (yet to be constructed), as
contained in the M7M Consent Agreement paragraph 1.A.vii. The modeling
similarly relied on both of the New Madrid Power Plant's units
operating at 100% load using an hourly SO<INF>2</INF> emission rate of
comparable stringency to the 30-day rolling average SO<INF>2</INF>
emission limit in the New Madrid Power Plant Consent Agreement
paragraph 1.A. for both units combined. Hourly SO<INF>2</INF> emission
rates based on potential to emit (PTE) for the smaller SO<INF>2</INF>
sources at M7M and the Alubar rod mill were also included in the model.
The final attainment demonstration modeling results show a maximum
total modeled SO<INF>2</INF> concentration of 195.7 [micro]g/m\3\
(equivalent to 74.7 ppb). Table 14 of the TSD summarizes the results
for the final attainment demonstration modeling, including the maximum
modeled SO<INF>2</INF> contributions from individual sources, as well
as the background SO<INF>2</INF> concentration. These results indicate
that the control strategy established in the consent agreements for M7M
and AECI New Madrid Power Plant result in modeled concentrations
throughout the nonattainment area that comply with the 2010 1-hour
SO<INF>2</INF> NAAQS of 75 ppb . The attainment modeling demonstration
meets the technical requirements of appendix W and the 2014
SO<INF>2</INF> Nonattainment Area SIP guidance and shows modeled
attainment throughout the nonattainment area, therefore the EPA is
proposing to approve the attainment demonstration as meeting CAA
sections 172(c)(1), (2), (6) and (9).

V. Review of Emissions and Emissions Controls

A. Emissions Inventory and the Quantification of Emissions

Section 172(c)(3) of the CAA requires that the state's attainment
plan include a comprehensive, accurate, current inventory of actual
emissions from all sources of the relevant pollutant or pollutants in
the area, including such periodic revisions as the Administrator may
determine necessary to assure that the requirements of the CAA are met.
Section 172(c)(4) of the CAA requires that the state's attainment plan
expressly identify and quantify the emissions, if any, of any pollutant
or pollutants which will be allowed, in accordance with section
703(a)(1)(B) of the CAA, from the construction and operation of major
new or modified stationary sources in the area. Section 172(c)(4) of
the CAA also requires the plan demonstrate that the quantified
emissions are consistent with the achievement of reasonable further
progress and will not interfere with attainment of the NAAQS by the
attainment date.
The emissions inventory and source emission rate data for an area
serve as the foundation for air quality modeling and other analyses
that enable states to: (1) estimate the degree to which different
sources within a nonattainment area contribute to violations within the
affected area; and (2) assess the expected improvement in air quality
within the nonattainment area due to the adoption and implementation of
control measures. As

[[Page 24778]]

noted above, the state must develop and submit to the EPA a
comprehensive, accurate and current inventory of actual emissions from
all sources of SO<INF>2</INF> emissions in each nonattainment area, as
well as any sources located outside the nonattainment area which may
affect attainment in the area. See CAA section 172(c)(3) and the EPA's
2014 SO<INF>2</INF> Nonattainment Guidance.
Section 3 of the New Madrid attainment plan contains the emissions
inventory element pursuant to the requirements of CAA section 172(c)(3)
and 172(c)(4). The base year inventory establishes a baseline that is
used to evaluate emissions reductions achieved by the control strategy
and to assess reasonable further progress requirements. According to
the EPA's 2014 SO<INF>2</INF> guidance, the SIP should also include a
projected attainment year inventory that includes estimated emissions
for all emission sources of SO<INF>2</INF> that were determined to have
an impact on the affected nonattainment area for the year in which the
area is expected to attain the standard, consistent with the attainment
demonstration. The inventory should reflect projected emissions for the
attainment year for all SO<INF>2</INF> sources in the nonattainment
area.
The State's attainment SIP noted that, at the time, the most recent
and available triennial inventory year was 2017, and the State found
that it served as a suitable base year. Because the attainment date for
this area is April 30, 2026, Missouri selected 2026 as the attainment
year. Table 1 summarizes the 2017 base year SO<INF>2</INF> emissions
inventory data for all emissions categories covering the entirety of
New Madrid County. Table 2 summarizes the 2026 attainment year
SO<INF>2</INF> emissions inventory data for all emissions categories
covering the entirety of New Madrid county. The full emissions
inventories for base and attainment years are included in the State's
submission, included in the docket for this action, in appendices A and
B, respectively. The State also confirms it meets the CAA section
172(c)(3) requirement for periodic revisions to such inventories by its
continued compliance with 40 CFR part 51, subpart A, the air emissions
reporting rule (AERR) and through submitting the relevant emissions
data to the triennial national emissions inventory (NEI).
The State's attainment plan acknowledges that, although
SO<INF>2</INF> emissions in and near the nonattainment area are
principally attributable to point sources, a comprehensive emissions
inventory should include an assessment of the other source sectors. The
State asserted that it accomplished this by using estimates of air
emissions for the onroad, nonroad, and nonpoint (area) sources from the
EPA's 2017 National Emissions Inventory (NEI) datasets.\15\ According
to the State's sector summary analyses using the EPA's SCC (source
classification code) full detail data files from the 2017 NEI,
approximately 4.18 tons of SO<INF>2</INF> were emitted by onroad mobile
sources in all of New Madrid County (this includes areas within and
outside of the nonattainment area) which accounts for 0.02% of the
county's total emissions. Nonroad mobile sources (which include non-
road equipment, locomotives, commercial marine vessels, and aircraft)
contributed approximately 1.10 tpy of SO<INF>2</INF>, or 0.01% of the
total. Nonpoint (area) contributed approximately 9.25 tpy of
SO<INF>2</INF>, or 0.05% of the total. As with the mobile sectors, the
nonpoint totals also represent sums across all of New Madrid County. In
contrast, the point source total emissions account for 17,254.74 tpy of
SO<INF>2</INF>, or 99.92% of the total emissions in New Madrid County.
In 2017, M7M was not operating, so this point source estimate includes
2017 actual emissions from all other point sources and actual emissions
from Magnitude 7 as reported for 2019. For the 2026 attainment year,
the state relied on projected emissions data from the EPA's 2016v2
modeling platform.\16\
---------------------------------------------------------------------------

\15\ Data, summaries, and documentation of the 2017 NEI are
available at <a href="https://www.epa.gov/air-emissions-inventories/2017-national-emissions-inventory-nei-data">https://www.epa.gov/air-emissions-inventories/2017-national-emissions-inventory-nei-data</a>.
\16\ Data, summaries, and documentation of the EPA's 2016v2
modeling platform are available at <a href="https://www.epa.gov/air-emissions-modeling/2016v2-platform">https://www.epa.gov/air-emissions-modeling/2016v2-platform</a>.

Table 1--New Madrid County Base Year SO2 Emissions Inventory Summary
----------------------------------------------------------------------------------------------------------------
Emission category 2017 SO2 emissions (tpy) Percent of total emissions
----------------------------------------------------------------------------------------------------------------
Point Source Total (does not include Magnitude 7 13,548.73 78.46
since they did not operate in 2017)................
Magnitude 7 (2019 emissions)........................ 3,706.01 21.46
Point source total with Magnitude 7 2019 emissions.. 17,254.74 99.92
Non-point total..................................... 9.25 0.05
Nonroad total....................................... 1.10 0.01
On road total....................................... 4.18 0.02
-----------------------------------------------------------
Total........................................... 17,269.27
----------------------------------------------------------------------------------------------------------------

Table 2--New Madrid County Attainment Year SO2 Emissions Inventory Summary
----------------------------------------------------------------------------------------------------------------
Difference between 2026
2026 SO2 emissions Percent of total and 2017 (negative
Emission category (tpy) emissions value indicates
decrease)
----------------------------------------------------------------------------------------------------------------
Point Source Total................... 21,440.75 99.98 4,186.01
Non-point total...................... 2.30 0.01 -6.95
Nonroad total........................ 0.52 0.00 -0.58
Onroad total......................... 1.73 0.01 -2.45
--------------------------------------------------------------------------
Total............................ 21,445.30 ....................... 4,176.03
----------------------------------------------------------------------------------------------------------------

[[Page 24779]]

Table 2 shows a projected SO<INF>2</INF> emissions increase of
4,176 tons per year between the 2017 base year inventory and 2026. The
State describes this projected increase is due to projected emissions
from the New Madrid Power Plant as estimated by the EPA's Integrated
Planning Model (IPM) projection tool in the 2016v2 modeling platform
for 2026. Despite the projected increase in actual SO<INF>2</INF>
emissions, the State points to the attainment demonstration which shows
modeled attainment of the 2010 SO<INF>2</INF> NAAQS based on new
emissions limits for both New Madrid Power Plant and M7M (totaling
approximately 34,400 tons per year) and potential to emit for other
point sources in the nonattainment area.\17\
---------------------------------------------------------------------------

\17\ For M7M, annualized SO<INF>2</INF> emissions totaling
6,325.3 tons/year were included in the attainment demonstration
modeling (6,324.7 tons/year based on SO<INF>2</INF> emission limits
in the Consent Agreement for the potline and carbon bake processes
plus 0.6 tons/year potential to emit for other smaller
SO<INF>2</INF> sources at the facility). For the New Madrid Power
Plant, annualized SO<INF>2</INF> emissions totaling 28,088.1 tons/
year were included in the attainment demonstration modeling
consistent with the SO<INF>2</INF> limits in the Consent Agreement.
See the TSD for more details on modeled emission rates for these
facilities, in particular section 3 and tables 4, 5, and 6.
---------------------------------------------------------------------------

As already noted, the State's attainment SIP must identify and
quantify the emissions which will be allowed from the construction and
operation of major new or modified stationary sources in the area (see
CAA section 172(c)(4)). The State must demonstrate that such emissions
will be consistent with RFP requirements and will not interfere with
attainment of the 1-hour SO<INF>2</INF> NAAQS. These requirements are
met by the state's preconstruction permitting program and
implementation of the Nonattainment New Source Review Rules (NNSR). See
section V.C. Nonattainment New Source Review of this document below,
for more information. The EPA is proposing to determine that the State
has met the requirements of CAA section 172(c)(3) and 172(c)(4).
Therefore, the EPA proposes to approve the emission inventory element
of Missouri's SO<INF>2</INF> attainment SIP for New Madrid.

B. Reasonably Available Control Measures/Reasonably Available Control
Technology

CAA section 172(c)(1) states that attainment plans should ``provide
for the implementation of all reasonably available control measures as
expeditiously as practicable (including such reductions in emissions
from existing sources in the area as may be obtained through the
adoption, at a minimum, of reasonably available control technology) and
shall provide for attainment of the [NAAQS].'' CAA section 192(a)
requires that attainment plans for the SO<INF>2</INF> NAAQS provide for
future attainment as expeditiously as practicable, but no later than 5
years from the effective date of the area's designation as
nonattainment. For areas designated nonattainment effective April 30,
2021, attainment plans were required to contain demonstrations that the
area would attain as expeditiously as practicable, but no later than
April 30, 2026.
Missouri's plan for attaining the 1-hour SO<INF>2</INF> NAAQS in
the New Madrid nonattainment area is based on a variety of control
measures and emissions limits at M7M and AECI New Madrid. Those
measures were included in the State's attainment SIP as consent
agreements between the State and the relevant source.\18\ Missouri's
plan required compliance with these measures no later than January 1,
2025. Missouri has determined that these measures suffice to provide
for timely attainment.
---------------------------------------------------------------------------

\18\ Appendices E and F to the state's attainment SIP contain
the source specific consent agreements which define the RACM/RACT
requirements.
---------------------------------------------------------------------------

Table 3 below lists all the sources included in the control
strategy, contains descriptions of the control measures, and provides
effective dates. Source specific allowable emission rates, compliance
and monitoring obligations, reporting and recordkeeping requirements,
and implementation deadlines are detailed in each source's consent
agreement included with the SIP submittal, in the docket for this
action.

Table 3--Summary of New Madrid Attainment Plan Control Strategy
----------------------------------------------------------------------------------------------------------------
Consent agreement SO2 emission limit/
Source reference operational change Effective date
----------------------------------------------------------------------------------------------------------------
Magnitude 7 Metals................. 1.A.v................. Magnitude 7 shall not emit December 31, 2023,
any SO2 emissions from the which may be extended
current emission release up to but no later
points for the carbon than January 1, 2025.
bakes (EP 98, EP 99 and EP
AA, as identified in
appendix A) unless such
emissions have been re-
routed to the new stack
(EP AAA) included in the
Engineering Control Plan.
1.A.vi................ Facility-wide SO2 emissions State effective date
from Magnitude 7 shall not of consent agreement,
exceed 4,999.99 tons in April 13, 2023.
any rolling 12-month
period.
1.A.vii............... Magnitude 7 shall meet or January 1, 2025.
emit less than the maximum
1-hour average SO2
emissions rate limits in
pounds per hour (``lbs/
hr'') as follows:
Pot Line Stack (EP 61):
1,015.42 lbs/hr.
Pot Line Fugitives (Roof
Vents--EP's.
59A, 59B, 60A, and 60B):
111.11 lbs/hr *.
New Carbon Bake Stack
(EPAAA): 317.47 lbs/hr.
* The limit applies to the
combined emissions from
the identified roof vent
emission points.
AECI New Madrid Power Plant........ 1.A................... New Madrid Power Plant January 1, 2023.
agrees to a combined
maximum 30-day daily-
rolling average SO2
emissions rate of 5,523
lbs/hr for boilers EP-01
and EP-02.
----------------------------------------------------------------------------------------------------------------

Table 4--Air Monitoring Data From the New Madrid Nonattainment Area Monitors
--------------------------------------------------------------------------------------------------------------------------------------------------------
Design values (ppb) 99th percentile daily max 1-hour SO2
----------------------------------------------------------------------------------------------------- concentrations (ppb)
1-hour SO2 ---------------------------------------------------
Monitor site name NAAQS (ppb) 2019-2021 2020-2022 2021-2023 2022-2024
2021 2022 2023 2024
--------------------------------------------------------------------------------------------------------------------------------------------------------
AECI Water Tower................... 75 376 417 452 396 405 479 473 235

[[Page 24780]]

East Graveyard..................... 75 333 291 291 241 285 304 283 136
West Entrance...................... 75 83 95 115 94 88 128 128 26
--------------------------------------------------------------------------------------------------------------------------------------------------------

The EPA concludes that the measures relied on by the State to
satisfy the requirement in CAA section 172(c)(1) to adopt and submit
all RACM as needed to attain the standards as expeditiously as
practicable meet the relevant CAA requirements and therefore the EPA
proposes to approve this element of the state's attainment plan.

C. Nonattainment New Source Review

Section 172(c)(5) requires that the State's attainment plan
provisions shall require permits for the construction and operation of
new or modified major stationary sources anywhere in the nonattainment
area, in accordance with section CAA section 173. The EPA most recently
approved revisions to the State's nonattainment new source review
provisions as part of the state's construction permits required rule,
10 Code of State Regulations (CSR) 10-6.060, on April 23, 2026. (91 FR
21724) These provisions provide for appropriate new source review for
SO<INF>2</INF> sources undergoing construction or major modification in
the New Madrid nonattainment area without need for modification of the
SIP-approved rule. Therefore, the EPA concludes that the requirements
of CAA section 172(c)(5) have been met and therefore proposes to
approve this element of the State's SO<INF>2</INF> attainment plan.

D. Reasonable Further Progress

Section 172 of the CAA requires that attainment plans include
provisions to address reasonable further progress (RFP). As discussed
in the EPA's 2014 SO<INF>2</INF> Nonattainment Area SIP Guidance, this
requirement is more practically relevant and important for NAAQS
pollutants impacted by emissions from numerous and diverse sources,
where the relationship between any individual source and overall air
quality is not easily discernable, and where NAAQS attainment may
require inventory-wide emissions reductions. The relationship between
ambient SO<INF>2</INF> concentrations and SO<INF>2</INF> emission
sources is more directly quantifiable as compared to other NAAQS
pollutants, and there is frequently only one (or few) primary source of
SO<INF>2</INF> emissions responsible for poor air quality in a
nonattainment area. Consequently, full progress to attainment is
achieved as soon as the one (or few) emission source is subject to an
enforceable emission limitation. Therefore, for SO<INF>2</INF> SIPs,
which address a small number of affected sources, requiring expeditious
compliance with attainment emission limits is sufficient to address the
RFP requirement. CAA section 192(a) requires that SO<INF>2</INF>
attainment plans provide for future attainment of the NAAQS as
expeditiously as practicable, but no later than 5 years from the
effective date of the area's designation as nonattainment. As noted in
the State's attainment SIP, the EPA has interpreted that RFP is best
construed as ``adherence to an ambitious compliance schedule'' in
previous rulemakings.\19\
---------------------------------------------------------------------------

\19\ See 57 FR 13498, at 13547 (April 16, 1992).
---------------------------------------------------------------------------

Table 3 in section V.B. RACM/RACT notes the SO<INF>2</INF> emission
limits and application of control technologies established for M7M and
AECI New Madrid. The State asserts that this plan requires that
affected sources implement appropriate control measures as
expeditiously as practicable in order to ensure attainment of the
standard by the applicable attainment date. The State again relies on
the consent agreements established for M7M and AECI New Madrid to
satisfy the RFP requirements. The State concludes that its plan
provides for RFP in accordance with the approach to RFP described in
the EPA's 2014 SO<INF>2</INF> Nonattainment Area SIP guidance, and the
EPA proposes that Missouri's plan meets the requirements for RFP as
contained in CAA section 172(c)(2).

E. Contingency Measures

Section 172(c)(9) of the CAA requires that the state's attainment
plan include additional measures, called contingency measures, which
will take effect if an area fails to meet RFP or fails to attain the
NAAQS by the applicable attainment date. The EPA's 2014 SO<INF>2</INF>
Nonattainment Guidance describes special features of SO<INF>2</INF>
attainment planning that influence the suitability of alternative means
of addressing the requirement in CAA section 172(c)(9) for contingency
measures for SO<INF>2</INF>. That is, an SO<INF>2</INF> NAAQS
attainment plan contains the emission limitations and other control
measures that are directly and quantifiably necessary to attain the
SO<INF>2</INF> NAAQS in the area, and consequently, the area would be
unlikely to fail to attain the NAAQS if the state implements such
attainment plan requirements.\20\ Therefore, the EPA's longstanding
approach is that an appropriate means of satisfying the contingency
measures requirement for the SO<INF>2</INF> NAAQS is for the state to
have a comprehensive enforcement program that identifies sources of
violations of the SO<INF>2</INF> NAAQS and for the state to undertake
aggressive follow-up for compliance and enforcement. See the Indiana,
PA NFRM (89 FR 74836, Sept. 13, 2024). States may additionally or
alternatively include other forms of contingency measures as part of
the attainment plan.
---------------------------------------------------------------------------

\20\ See 75 FR 35520 at 35576 (June 22, 2010) and the 2014
SO<INF>2</INF> Nonattainment Guidance.
---------------------------------------------------------------------------

While the state's attainment plan contains specific contingency
measures that apply to M7M, the State of Missouri submitted a
clarification letter to the EPA on December 11, 2025, explaining that
its enforcement program would also serve as a contingency measure. The
letter is included in the docket for this action. In that letter, the
State provides that the existing SIP-approved enforcement program is
authorized to identify sources of violations of the SO<INF>2</INF>
NAAQS and to undertake aggressive follow-up for compliance and
enforcement. As noted previously, the EPA's policy is that a State may
reference its comprehensive enforcement program as an appropriate means
of satisfying the contingency measures requirement for the
SO<INF>2</INF> NAAQS.
The State also included specific contingency measures in the M7M
agreement. Paragraph 1.D.i. and ii. of the M7M agreement contains the
contingency measure triggering language, which states, ``i. Beginning
60 calendar days after commencement of operation of the new Carbon Bake
stack, Magnitude 7 shall be subject to contingency measures in the
event the fourth highest 1-hour daily maximum SO<INF>2</INF>
concentration recorded at any of the individual three ambient
SO<INF>2</INF>

[[Page 24781]]

monitors surrounding the facility exceeds 75 ppb in a single calendar
year. ii. Contingency Measure 1. Following Department notification to
Magnitude 7 that the first triggering event has occurred, Magnitude 7
shall respond in writing within 14 calendar days of the notification
acknowledging the triggering event and committing to the following
contingency measure--'' Subparagraph 1.D.ii.a. contains the first
measure which includes an enhanced leak detection plan including
inspections and repair requirements. If another triggering event occurs
nine months or more after implementation of this first measure, the
facility must implement additional contingency measures, including
purchasing anodes offsite and cessation of the carbon bake furnaces or
more stringent sulfur limits either with or without installation of
flue gas desulfurization control technology (see subparagraphs 1.D.iii.
through vi. of the M7M consent agreement).
At the time of the State's SIP development and negotiations with
M7M, the triggering language specifying the measures would be triggered
beginning 60 calendar days after commencement of operation of the new
Carbon Bake stack, was reasonable. Specifically, the language was
drafted under the assumption that M7M would fully implement and comply
with the control strategy requirements of the attainment plan, such as
constructing the new stack, on the established deadlines. However, due
to events occuring after the State submitted its attainment plan to the
EPA, the source curtailed operations and has not yet constructed the
new Carbon Bake stack. Should the source restart operations, the source
would immediately be subject to the requirements of the consent
agreement including the prohibition to emit from the existing carbon
bake furnace stacks unless the emissions are re-routed to the new
carbon bake stack.\21\ In this situation where the source resumes
operations and complies with the control strategy by constructing and
operating the new carbon bake stack, the contingency measures and
triggering language would apply as originally intended by the state.
---------------------------------------------------------------------------

\21\ See paragraph 1.A.v. of the M7M consent agreement.
---------------------------------------------------------------------------

If the source chose to resume operations without building the new
Carbon Bake stack and instead purchases anodes offsite (which is listed
as Contingency Measure Option A in 1.D.iii.a.), operation of the
existing carbon back furnaces would not be necessary.\22\ It is unclear
as to whether an exceedance would trigger contingency measures since
the new stack has not been constructed. In this hypothetical scenario,
the requirements of the consent agreement alone would not satisfy the
contingency measure requirements of CAA Sec. 172(c)(9). However, the
EPA finds that the robust enforcement program described in the State's
December 11, 2025, letter operates as an adequate contingency measure
in any operating scenario.
---------------------------------------------------------------------------

\22\ M7M requested to pursue this option of purchasing offsite
anodes in January 2024, but did not pursue this and curtailed
operations. See correspondence between M7M and MoDNR included in the
docket for this action.
---------------------------------------------------------------------------

The State's December 11, 2025, clarification letter also commits to
revising the M7M consent agreement and submitting a formal SIP revision
should the company restart operations without building the stack. This
subsequent agreement and associated SIP revision would then codify the
revised control strategy requirements and commensurate contingency
measures.
As explained previously, the EPA finds the control strategy
contained in the state's attainment plan, which primarily relies on
construction of a new carbon bake stack and associated emissions
limits, meets the relevant CAA requirements for attainment plans. The
attainment plan includes contingency measures required by CAA section
172(c)(9) that are commensurate with the control strategy. In addition,
the state's December 11, 2025, clarification letter describes how its
comprehensive enforcement program identifies sources of violations of
the SO<INF>2</INF> NAAQS and the process it will undertake in the event
the M7M facility resumes operations without constructing the new stack.
The EPA proposes to approve the state's robust enforcement program and
the contingency measures provisions of the M7M consent agreement as
meeting the requirements of CAA section 172(c)(9).

VI. Proposed Action

The EPA is proposing to approve Missouri's SIP submission, which
the state submitted to the EPA on May 3, 2023, as it provides for
attainment of the 2010 1-hour SO<INF>2</INF> NAAQS for the New Madrid
SO<INF>2</INF> nonattainment area and satisfies other nonattainment
area planning requirements. This SO<INF>2</INF> attainment plan
includes Missouri's attainment demonstration for the New Madrid area.
In addition to an attainment demonstration, Missouri's plan addresses
the requirements for meeting reasonable further progress (RFP) toward
attainment of the NAAQS, reasonably available control measures and
reasonably available control technology (RACM/RACT), base-year and
projection-year emission inventories, nonattainment new source review
(NNSR), emission limitations necessary to provide for attainment, and
contingency measures.
The EPA has determined that Missouri's SO<INF>2</INF> attainment
plan meets applicable requirements of section 172 of the CAA. The EPA's
analysis is discussed in this proposed rulemaking. In addition, the
technical support document (TSD) is also available in the docket for
this action. The TSD provides additional explanation of the EPA's
analysis supporting this proposal.
The EPA is soliciting public comments for 30 days following the
publication of this proposed action in the Federal Register and will
take these comments into consideration in its final action.

VII. Incorporation by Reference

In this document, the EPA is proposing to include regulatory text
in an EPA final rule that includes incorporation by reference. In
accordance with requirements of 1 CFR 51.5, the EPA is proposing to add
incorporation by reference of the following source-specific consent
agreements as requested by the State of Missouri: APCP-2022-047A and
APCP-2022-048A. These agreements are discussed in sections III. through
V. of this preamble and as set forth below in the proposed amendments
to 40 CFR part 52. The EPA has made, and will continue to make, these
materials generally available through <a href="https://www.regulations.gov">https://www.regulations.gov</a> and
at the EPA Region 7 Office (please contact the person identified in the
FOR FURTHER INFORMATION CONTACT section of this preamble for more
information).

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 approve state choices,
provided that they meet the criteria of the CAA. Accordingly, this
action merely approves state law as meeting Federal requirements and
does not impose additional requirements beyond those imposed by state
law. For that reason, this action:
<bullet> Is not a significant regulatory action subject to review
by the Office of Management and Budget under

[[Page 24782]]

Executive Order 12866 (58 FR 51735, October 4, 1993);
<bullet> Is not an Executive Order 14192 (90 FR 9065, February 6,
2025) regulatory action because this action is not significant under
Executive Order 12866;
<bullet> Does not impose an information collection burden under the
provisions of the Paperwork Reduction Act (44 U.S.C. 3501 et seq.);
<bullet> Is certified as not having a significant economic impact
on a substantial number of small entities under the Regulatory
Flexibility Act (5 U.S.C. 601 et seq.);
<bullet> Does not contain any unfunded mandate or significantly or
uniquely affect small governments, as described in the Unfunded
Mandates Reform Act of 1995 (Pub. L. 104-4);
<bullet> Does not have federalism implications as specified in
Executive Order 13132 (64 FR 43255, August 10, 1999);
<bullet> Is not subject to Executive Order 13045 (62 FR 19885,
April 23, 1997) because it approves a state program;
<bullet> Is not a significant regulatory action subject to
Executive Order 13211 (66 FR 28355, May 22, 2001); and
<bullet> Is not subject to requirements of section 12(d) of the
National Technology Transfer and Advancement Act of 1995 (15 U.S.C. 272
note) because application of those requirements would be inconsistent
with the CAA.
In addition, the SIP is not approved to apply on any Indian
reservation land or in any other area where the EPA or an Indian Tribe
has demonstrated that a Tribe has jurisdiction. In those areas of
Indian country, the rule does not have Tribal implications and will not
impose substantial direct costs on Tribal governments or preempt Tribal
law as specified by Executive Order 13175 (65 FR 67249, November 9,
2000).

List of Subjects in 40 CFR Part 52

Environmental protection, Air pollution control, Incorporation by
reference, Intergovernmental relations, Reporting and recordkeeping
requirements, Sulfur oxides.

Dated: April 28, 2026.
James Macy,
Regional Administrator, Region 7.

For the reasons stated in the preamble, EPA proposes to amend 40
CFR part 52 as set forth below:

PART 52--APPROVAL AND PROMULGATION OF IMPLEMENTATION PLANS

0
1. The authority citation for part 52 continues to read as follows:

Authority: 42 U.S.C. 7401 et seq.

Subpart AA--Missouri

0
2. In Sec. 52.1320:
0
a. The table in paragraph (d) is amended by adding the entries ``(39)''
and ``(40)'' in numerical order.
0
b. The table in paragraph (e) is amended by adding the entry ``(86)''
in numerical order.
The additions read as follows:

Sec. 52.1320 Identification of plan.

* * * * *
(d) * * *

EPA-Approved Missouri Source-Specific Permits and Orders
----------------------------------------------------------------------------------------------------------------
State
Name of source Order/Permit number effective EPA Approval date Explanation
date
----------------------------------------------------------------------------------------------------------------

* * * * * * *
(39) Magnitude 7 Metals.......... APCP-2022-047A...... 4/13/2023 [Date of publication [EPA-R07-OAR-2026-29
of the final rule 38; FRL-13334-01-
in the Federal R7].
Register], 91 FR
[Federal Register
page where the
document begins of
the final rule].
(40) AECI New Madrid............. APCP-2022-048A...... 4/13/2023 [Date of publication [EPA-R07-OAR-2026-29
of the final rule 38; FRL-13334-01-
in the Federal R7].
Register], 91 FR
[Federal Register
page where the
document begins of
the final rule].
----------------------------------------------------------------------------------------------------------------

* St Louis County.
(e) * * *

EPA-Approved Missouri Nonregulatory SIP Provisions
----------------------------------------------------------------------------------------------------------------
Applicable State
Name of nonregulatory SIP geographic or submittal EPA approval date Explanation
provision nonattainment area date
----------------------------------------------------------------------------------------------------------------

* * * * * * *
(86) 2010 1-hour Primary SO2 A portion of New 5/3/2023 [Date of publication [EPA-R07-OAR-2026-29
National Ambient Air Quality Madrid County. of the final rule 38; FRL-13334-01-
Standard Attainment Plan for the in the Federal R7].
New Madrid Nonattainment Area. Register], 91 FR
[Federal Register
page where the
document begins of
the final rule].
----------------------------------------------------------------------------------------------------------------

[FR Doc. 2026-09054 Filed 5-6-26; 8:45 am]
BILLING CODE 6560-50-P

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