[Federal Register Volume 89, Number 149 (Friday, August 2, 2024)]
[Proposed Rules]
[Pages 63117-63134]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2024-17053]


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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 52

[EPA-R06-OAR-2022-0311; FRL-12123-01-R6]


Air Plan Limited Approval and Limited Disapproval; Texas; 
Attainment Plan for the Rusk and Panola Counties 2010 Sulfur Dioxide 
Primary National Ambient Air Quality Standard Nonattainment Area; 
Finding of Failure To Attain the Primary 2010 One-Hour Sulfur Dioxide 
Standard for Rusk and Panola Counties

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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SUMMARY: The Environmental Protection Agency (EPA) is proposing two 
actions in this notice. First, EPA is proposing to determine that the 
Rusk-Panola Counties, Texas nonattainment area failed to attain the 
2010 1-hour primary sulfur dioxide (SO2) national ambient 
air quality standard (NAAQS) by the applicable attainment date of 
January 12, 2022. Second, EPA is proposing a limited approval and 
limited disapproval of the State Implementation Plan (SIP) revision for 
the Rusk-Panola 2010 1-hour SO2 Primary NAAQS nonattainment 
area. EPA is proposing a limited disapproval because the SIP contains a 
force majeure clause that, if triggered, is such that the emissions 
limitations are not continuously applicable or enforceable. EPA is 
proposing limited approval because the SIP revision strengthens the SIP 
but does not fully meet the Act's requirements and provides for 
attainment, albeit not by the required deadline and with the exception 
of the force majeure clause. Under this limited approval action, if 
finalized, all provisions will be fully incorporated into the SIP. The 
limited disapproval, if finalized, will start sanctions clocks until 
the deficiency is corrected by the State and approved by EPA. EPA plans 
to address the deficiency in the SIP through a separate action 
promulgating a Federal Implementation Plan (FIP).

DATES: Written comments must be received on or before September 3, 
2024.

ADDRESSES: Submit your comments, identified by Docket No. EPA-R06-OAR-
2022-0311, at https://www.regulations.gov. Follow the online 
instructions for submitting comments. Once submitted, comments cannot 
be edited or removed from Regulations.gov. The EPA may publish any 
comment received to its public docket. Do not submit electronically any 
information you consider to be Confidential Business Information (CBI) 
or other information whose disclosure is restricted by statute. 
Multimedia submissions (audio, video, etc.) must be accompanied by a 
written comment. The written comment is considered the official comment 
and should include discussion of all points you wish to make. The EPA 
will generally not consider comments or comment contents located 
outside of the primary submission (i.e., on the web, cloud, or other 
file sharing system). For additional submission methods, please contact 
Andrew Lee, 214-665-6750, [email protected]. For the full EPA public 
comment policy, information about CBI or multimedia submissions, and 
general guidance on making effective comments, please visit https://www.epa.gov/dockets/commenting-epa-dockets.
    Docket: The index to the docket for this action is available 
electronically at www.regulations.gov. While all documents in the 
docket are listed in the index, some information may not be publicly 
available in the electronic docket due to docket file size and/or file 
type restrictions or content (e.g., modeling files, model code, 
copyrighted material, CBI).

FOR FURTHER INFORMATION CONTACT: Andrew Lee, EPA Region 6 Office, Ozone 
and Infrastructure section, 214-665-6750, [email protected]. We 
encourage the public to submit comments via https://www.regulations.gov. Please call or email the contact listed above if 
you need alternative access to material indexed but not provided in the 
docket. Modeling files and other files related to the alternative model 
review are

[[Page 63118]]

available upon request. Copyrighted materials are available for review 
in person at EPA Region 6 office in Dallas.

SUPPLEMENTARY INFORMATION: Throughout this document wherever ``we,'' 
``us,'' or ``our'' is used, we mean the EPA.

Table of Contents

I. Background
    A. Rusk and Panola Counties SO2 Nonattainment Area
    B. SO2 Nonattainment Area Plans
    C. Attainment Demonstration for SO2 Nonattainment 
Area Plan
II. Proposed Determination--Finding of Failure To Attain the Primary 
2010 One-Hour Sulfur Dioxide Standard
    A. Applicable Statutory and Regulatory Provisions
    B. Monitoring Network Considerations
    C. Data Considerations and Proposed Determination
III. Limited Approval/Limited Disapproval
    A. Force Majeure Provision Deficiency
    B. Compliance Date Deficiency
    C. Limited Approval
    D. Limited Disapproval and Consequences
IV. Attainment Demonstration and Longer-Term Averaging
V. Review of Modeled Attainment Plan
    A. Model Selection
    B. Meteorological Data
    C. Emissions Data
    D. Receptor Grid
    E. Emission Limits
    F. Background Concentrations
    G. Summary of Results
VI. Review of Other Plan Requirements
    A. Emissions Inventory
    B. Reasonably Available Control Measures and Reasonably 
Available Control Technology (RACM/RACT)
    C. New Source Review (NSR)
    D. Reasonable Further Progress (RFP)
    E. Contingency Measures
    F. Conformity
VII. Proposed Action
VIII. Incorporation by Reference
IX. Environmental Justice Considerations
X. Statutory and Executive Order Reviews

I. Background

A. Rusk and Panola Counties SO2 Nonattainment Area

    On June 22, 2010, the EPA published a new 1-hour primary 
SO2 NAAQS of 75 parts per billion (ppb), which is met at an 
ambient air quality monitoring site (or in the case of dispersion 
modeling, at an ambient air quality receptor location) when the 3-year 
average of the annual 99th percentile of 1-hour daily maximum 
concentrations does not exceed 75 ppb, as determined in accordance with 
appendix T of 40 CFR part 50.\1\ On December 13, 2016, the EPA 
designated portions of Rusk and Panola Counties, Texas as nonattainment 
for the 2010 1-hour primary SO2 NAAQS, effective January 12, 
2017.\2\ The primary major source of emissions in the area is the 
Martin Lake Steam Electric Station (Martin Lake), a coal-fired power 
plant owned by Luminant Generation Company LLC (Luminant), a subsidiary 
of Vistra Energy Corporation (Vistra). Section 191 of the CAA directs 
states to submit SIPs for nonattainment areas to the EPA within 18 
months of the effective date of the designation, i.e., by no later than 
July 12, 2018 for the Rusk-Panola area. Under CAA section 192, these 
SIPs are required to demonstrate that their respective areas will 
attain the NAAQS as expeditiously as practicable, but no later than 5 
years from the effective date of designation, i.e., January 12, 2022.
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    \1\ See 75 FR 35520. See also 40 CFR 50.17(a)-(b).
    \2\ See 81 FR 89870 See also 40 CFR part 81, subpart C.
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    On August 10, 2020, the EPA published a ``Findings of Failure to 
Submit State Implementation Plans Required for Attainment of the 2010 
1-Hour Primary Sulfur Dioxide (SO2) National Ambient Air 
Quality Standard (NAAQS)'' that found that Texas failed to submit the 
required SO2 attainment plan for the Rusk-Panola area by the 
July 12, 2018 CAA deadline.\3\ This finding, effective on September 9, 
2020, triggered 18-month and 24-month deadlines (March 9, 2022 and 
September 9, 2022) under CAA section 179(a) for the imposition of 
mandatory emission offsets and highway funding sanctions, respectively, 
unless and until the state submits a SIP revision satisfying the CAA's 
completeness criteria. Additionally, this finding triggered the CAA 
section 110(c) requirement for EPA to promulgate a federal 
implementation plan (FIP) within two years of the finding (September 9, 
2022) unless the state submits and obtains EPA approval of a SIP 
revision which corrects the deficiency before EPA promulgates a FIP.
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    \3\ See 85 FR 48111
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    On February 28, 2022, the Texas Commission on Environmental Quality 
(TCEQ) submitted a Nonattainment SIP for the Rusk-Panola area. TCEQ's 
SIP includes an Agreed Order for the Martin Lake facility in the area, 
adopted on February 14, 2022, which includes emission limits and 
monitoring requirements. On August 24, 2022, EPA determined that the 
February 28, 2022 submittal was complete under 40 CFR part 51, App. V, 
which stopped the mandatory emissions offsets sanctions that were in 
effect and the 24-month sanction clock for the imposition of highway 
funding sanctions.\4\ However, EPA's completeness determination did not 
have an effect on EPA's FIP obligation, which is only satisfied by the 
promulgation of a FIP or the full approval of a SIP.
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    \4\ August 24, 2022 Completeness Determination Letter from David 
Garcia, EPA Region 6 to Jon Niermann, TCEQ, available in the docket 
for this action.
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B. SO2 Nonattainment Area Plans

    SO2 Nonattainment area SIPs must meet the applicable 
requirements of CAA sections 110, 172, 191, and 192. The EPA's 
regulations governing nonattainment area SIPs are set forth at 40 CFR 
part 51, with specific procedural requirements and control strategy 
requirements found at subparts F and G, respectively. Soon after 
Congress enacted the 1990 Amendments to the CAA, the EPA issued 
comprehensive guidance on SIPs, 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 
SO2 SIPs and fundamental principles for SIP control 
strategies. Id., at 13545-49, 13567-68. On April 23, 2014, the EPA 
issued additional guidance for meeting the statutory requirements in 
SO2 SIPs in a document titled, ``Guidance for 1-Hour 
SO2 Nonattainment Area SIP Submissions'' (April 2014 
SO2 Guidance).\5\ In this guidance, the EPA describes how a 
nonattainment area SIP can satisfy the following CAA requirements: an 
accurate emissions inventory of current emissions for all sources of 
SO2 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)), an 
approvable nonattainment new source review (NNSR) program, enforceable 
emissions limitations and control measures, and adequate contingency 
measures for the affected area.\6\
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    \5\ ``Guidance for 1-Hour SO2 Nonattainment Area SIP 
Submissions'' available at: https://www.epa.gov/sites/production/files/2016-06/documents/20140423guidance_nonattainment_sip.pdf.
    \6\ See section V. of ``Guidance for 1-Hour SO2 
Nonattainment Area SIP Submissions''.
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    Under CAA sections 110(l) and 193, the EPA may not approve a SIP 
that would interfere with any applicable requirement concerning NAAQS 
attainment and RFP, or any other applicable requirement under the Act.

[[Page 63119]]

C. Attainment Demonstration for SO2 Nonattainment Area Plan

    CAA section 172(c)(1) requires a State's nonattainment area SIP to 
provide for attainment of the NAAQS. 40 CFR part 51, subpart G further 
delineates the control strategy requirements that SIPs must meet. The 
EPA has long required that all SIPs and control strategies reflect four 
fundamental principles of quantification, enforceability, 
replicability, and accountability.\7\ Generally, SO2 
attainment demonstrations consist of two components: (1) emission 
limits and other control measures that assure implementation of 
permanent, enforceable and necessary emission controls and (2) a 
modeling analysis which demonstrates that the emission limits and 
control measures provide for attainment as expeditiously as 
practicable, but no later than the attainment date, and meets the 
requirements of 40 CFR part 51, appendix W (Guideline on Air Quality 
Models).
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    \7\ See General Preamble at 13567-68.
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    In all cases, the emission limits and control measures must be 
accompanied by appropriate methods and conditions to determine 
compliance and 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 limits must be 
permanent and must reflect the assumptions used in the SIP 
demonstrations).\8\
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    \8\ See General Preamble at 13567-68.
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    40 CFR part 51.112(a)(1) states that all applications of air 
quality modeling shall be based on the applicable models specified in 
the Guideline on Air Quality Models (Modeling Guideline). Appendix A to 
the Guideline on Air Quality Models delineates EPA's preferred models 
and other recommended techniques, as well as guidance for their use in 
estimating ambient concentrations of air pollutants.9 10 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 (e.g., for estimating SO2 
concentrations) in all types of terrain based on extensive 
developmental and performance evaluation.\11\
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    \9\ See 80 FR 45340 (July 29, 2015).
    \10\ The EPA published revisions to the Guideline on Air Quality 
Models on January 17, 2017. See 82 FR 5182 (January 17, 2017).
    \11\ See 70 FR 68218 (November 9, 2005).
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    The Modeling Guideline is periodically updated, with the most 
recent revisions adopted in a Federal Register action on January 17, 
2017, effective May 22, 2017.\12\ This most recent version of the 
Modeling Guideline was in effect at the time Texas developed and 
submitted its SIP to EPA.
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    \12\ 82 FR 5182 (January 17, 2017) and 82 FR 14324 (March 20, 
2017).
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    While appendix A contains EPA's preferred models, 51.112(a)(2) also 
provides that on a case-by-case basis, an alternative air quality model 
may be used following written approval from EPA. In addition, the use 
of an alternative model is subject to notice and opportunity for public 
comment. The Modeling Guideline, in sections 4.2.2 and 4.2.2.1 and 
appendix A, identifies AERMOD as EPA's preferred model for development 
of a 1-hour SO2 attainment demonstration SIP.
    EPA's Modeling Guideline requires written approval finding that the 
criteria in section 3.2 Alternative Models to utilize any modification 
or substitution of EPA's preferred model, AERMOD, in a modeling 
demonstration have been satisfied. The Modeling Guideline section 
3.2.2(a) specifies that the determination of acceptability of an 
alternative model is a Regional Office responsibility in consultation 
with the Model Clearinghouse (MCH). Modeling Guideline section 3.2.2(b) 
(sometimes referred to as ``Condition 2'') states the alternative model 
shall be evaluated from both a theoretical and performance perspective 
before regulatory use and outlines the three separate conditions that 
may justify use of an alternative model.\13\ TCEQ's alternative model 
request uses a statistical performance evaluation (Condition 2) to 
justify AERMOD-HBP.\14\ A Condition 2 Alternative Model Request must 
satisfy the Modeling Guideline requirements, including sections 
3.2.2(b)(2), 3.2.2(d),\15\ and 3.2.2(e),\16\ While not specifically 
cross-referenced, section 3.2.2(e) sets forth five conditions that 
provide part of the framework and analytical process for evaluating 
alternative model performance from both a theoretical and performance 
perspective under 3.2.2 (b)(3)(sometimes referred to as Condition 3), 
but that also provide guidance for what should be considered in any 
alternative model approval in general, including for alternative model 
approval under 3.2.2(b)(2) to help address the requirements of appendix 
W 3.2.2(d) and as part of the elements of a modeling protocol and 
submission of an alternative model request.
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    \13\ See Modeling Guideline, section 3.2.2.(b)(1) (Condition 1) 
(``If a demonstration can be made that the model produces 
concentration estimates equivalent to the estimates obtained using a 
preferred model''); section 3.2.2.(b)(2) (Condition 2) (``If a 
statistical performance evaluation has been conducted using air 
quality data and the results of that evaluation indicate the 
alternative model performs better for the given application than a 
comparable model in appendix A''); and section 3.2.2.(b)(3) 
(Condition 3) (``If there is no preferred model'').
    \14\ TCEQ submitted a letter dated May 24, 2021 from Ms. Tonya 
Baer (Director of the Office of Air) to Mr. David Garcia (Air and 
Radiation Division Director) of EPA Region 6 requesting approval of 
an alternative model request for use AERMOD with Highly Buoyant 
Plume (HBP) code modifications in the Rusk-Panola 2010 1-Hour 
SO2 NAAQS attainment demonstration. This document is 
available in the Docket for this action.
    \15\ App. W 3.2.2(d) states, ``For condition (2) in paragraph 
(b) of this subsection [above], established statistical performance 
evaluation procedures and technique for determining the 
acceptability of a model for an individual case based on superior 
performance should be followed, as appropriate. Preparation and 
implementation of an evaluation protocol that is acceptable to both 
control agencies and regulated industry is an important element in 
such an evaluation.''
    \16\ App. W 3.2.2(e) states, ``Finally, for condition (3) in 
paragraph (b) of this subsection, an alternative model or technique 
may be approved for use provided that: The model or technique has 
received a scientific peer review; ii. The model or technique can be 
demonstrated to be applicable to the problem on a theoretical basis; 
iii. The databases which are necessary to perform the analysis are 
available and adequate; iv. Appropriate performance evaluations of 
the model or technique have shown that the model or technique is not 
inappropriately biased for regulatory application; and v. A protocol 
on methods and procedures to be followed has been established.''
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    As required by the Modeling Guideline, EPA Region 6 has consulted 
and coordinated with the EPA's Model Clearinghouse on TCEQ's 
alternative model AERMOD-HBP request and received concurrence from the 
Model Clearinghouse with EPA Region 6's approval of the AERMOD-HBP.\17\ 
While the Regional Administrators are delegated authority to issue such 
approvals under section 3.2 of the Modeling Guideline, all alternative 
model approvals will only be issued after consultation with the EPA's 
MCH and formal documentation through a concurrence memorandum which 
demonstrates that the requirements within section 3.2 for use of an 
alternative model have been met.
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    \17\ EPA Region 6 Concurrence request memorandum to MCH dated 
July 11, 2024 and MCH Concurrence memorandum to EPA Region 6 dated 
July 24, 2024 that are included in the docket for this action.
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    In addition to the Modeling Guideline's requirements, EPA has

[[Page 63120]]

issued supplemental guidance on modeling for purposes of demonstrating 
attainment of the 2010 SO2 NAAQS as part of the April 2014 
SO2 Guidance titled ``appendix A. Modeling Guidance for 
Nonattainment Areas'' (April 2014 SO2 Guidance appendix A) 
which is based on and is consistent with the Modeling Guideline. April 
2014 SO2 Guidance appendix A provides specific 
SO2 modeling guidance on the modeling domain, the source 
inputs, assorted types of meteorological data, and background 
concentrations.
    As stated previously, attainment demonstrations for the 2010 
SO2 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 in 
accordance with the Modeling Guideline and April 2014 SO2 
Guidance 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 SO2 NAAQS.\18\ For a short-term (i.e., 1-
hour) standard, the EPA has stated 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 SO2. 
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-hr SO2 National Ambient Air Quality Standard.'' 
\19\
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    \18\ April 2014 SO2 Guidance Pages 11-12.
    \19\ See https://www3.epa.gov/ttn/naaqs/aqmguide/collection/cp2/20100823_page_1-hr_so2_naaqs_psd_program.pdf.
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II. Proposed Determination--Finding of Failure To Attain the Primary 
2010 One-Hour Sulfur Dioxide Standard

A. Applicable Statutory and Regulatory Provisions

    CAA section 179(c)(1) requires the EPA to determine whether a 
nonattainment area has attained the NAAQS by the applicable attainment 
date based on the area's air quality as of the attainment date. A 
determination of whether an area's air quality meets applicable 
standards is generally based upon the most recent three years of 
complete, quality-assured monitoring data gathered at established state 
and local air monitoring stations (SLAMS) in a nonattainment area and 
entered into the EPA's Air Quality System (AQS) database. The accuracy 
of that data is annually certified by monitoring agencies and the EPA 
relied on that certified air monitoring data to calculate the design 
values used to determine the area's air quality status.
    Under EPA regulations in 40 CFR 50.17 and in accordance with 40 CFR 
part 50 appendix T, the 2010 SO2 NAAQS is met when the 
design value is less than or equal to 75 ppb. Design values are 
calculated by computing the three-year average of the annual 99th 
percentile daily maximum one-hour average concentrations.\20\ An 
SO2 one-hour primary standard design value is valid if it 
encompasses three consecutive calendar years of complete monitoring 
data. A year is considered complete when all four quarters are 
complete, and a quarter is complete when at least 75 percent of the 
sampling days are complete. A sampling day is considered complete if 75 
percent of the hourly concentration values are reported; this includes 
data affected by exceptional events that have been approved for 
exclusion by the Administrator.\21\ We note that when determining the 
attainment status of SO2 nonattainment areas, in addition to 
ambient monitoring data, the EPA may also consider air quality 
dispersion modeling and/or a demonstration that the control strategy in 
the SIP has been fully implemented.\22\
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    \20\ As defined in 40 CFR part 50, appendix T section 1(c), 
daily maximum 1-hour values refer to the maximum one-hour SO 2 
concentration values measured from midnight to midnight that are 
used in the NAAQS computations.
    \21\ See 40 CFR part 50, appendix T sections 1(c), 3(b), 4(c), 
and 5(a).
    \22\ EPA, April 23, 2014, Guidance for 1-Hour SO 2 Nonattainment 
Area SIP Submissions (``SO2 Nonattainment Area 
Guidance''), page 49.
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    With regard to the use of monitoring data for such determinations, 
the EPA's SO2 Nonattainment Area Guidance specifically notes 
that ``if the EPA determines that the air quality monitors located in 
the affected area are located in the area of maximum concentration, the 
EPA may be able to use the data from these monitors to make the 
determination of attainment without the use of air quality modeling 
data.'' \23\ If there are no air quality monitors located in the 
affected area or there are air quality monitors located in the area, 
but analyses show that none of the monitors are located in the area of 
maximum concentration, then air quality dispersion modeling will 
generally be needed to estimate SO2 concentrations in the 
area. \24\ This language might be read to suggest that the EPA must 
always assess whether the air quality monitors in the affected area are 
located in the area of maximum concentration prior to using monitoring 
data to determine area's attainment status. However, this language was 
intended to refer to a situation where the EPA is considering making a 
determination that the area has attained the NAAQS based on a finding 
that all of the monitoring sites within the affected area had an 
attaining design value for the relevant period.
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    \23\ See page 50 of the SO2 Nonattainment Area 
Guidance.
    \24\ See section VIII.A of the SO2 Nonattainment Area 
Guidance
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    As described in section II.C of this notice, in this instance, the 
monitoring sites in the Rusk-Panola SO2 NAAs did not have 
attaining design values for the relevant period. Consequently, even if 
the monitoring sites are not located in the area of maximum 
concentration, any monitors that would be located in the area of 
maximum concentration could not record concentrations lower than those 
recorded at the existing monitor at the Martin Creek site (EPA AQS Site 
ID 48-401-1082). Accordingly, since the Martin Creek monitor was 
violating the 2010 1-hour primary SO2 NAAQS during the 
relevant time period, it is not necessary to consider whether the 
monitors are located in the area of maximum concentration in order to 
determine that the Rusk-Panola area did not attain the 2010 1-hour 
primary SO2 NAAQS by the January 12, 2022, attainment date. 
However, in any future assessment of whether these areas have attained 
the NAAQS, the EPA may assess whether the monitors are located in the 
area of maximum concentration and may also consider modeling and/or 
control implementation information, as appropriate.

B. Monitoring Network Considerations

    Section 110(a)(2)(B)(i) of the CAA requires states to establish and 
operate air monitoring networks to compile data on ambient air quality 
for all criteria pollutants. The EPA's monitoring requirements are 
specified by regulation in 40 CFR part 58. These requirements are 
applicable to state, and where delegated, local air monitoring agencies 
that operate criteria pollutant monitors. In 40 CFR part 58, the EPA 
specifies the minimum requirements for SO2 monitoring sites 
to be classified as state or local air monitoring stations (SLAMS)

[[Page 63121]]

or special purpose monitors (SPM). SLAMS and SPM produce data that are 
eligible for comparison with the NAAQS and, therefore, the monitor must 
be an approved federal reference method (FRM) or federal equivalent 
method (FEM) per section 2 of appendix C to 40 CFR part 58. In the 
Rusk-Panola Area, TCEQ operates a SPM monitor at Martin Creek site (EPA 
AQS Site ID 48-401-1082, 9515 County Road 2181d).

C. Data Considerations and Proposed Determination

    Under 40 CFR 58.15, monitoring agencies must annually certify that 
prior year data collected by FRM and FEM at all SLAMS and special 
purpose monitors (SPMs) meet EPA quality assurance requirements. 
Monitoring agencies must also certify that the previous year of data 
was completely submitted to AQS and is accurate to the best of their 
knowledge.
    The one-hour SO2 design values, based on certified data 
at the Martin Creek site (AQS ID: 48-401-1082) within the Rusk-Panola 
nonattainment area for the 2019-2021 and 2020-2022 periods, are shown 
in table 1.

 Table 1--2019-2022 One-Hour SO2 Design Values for the Rusk-Panola Area
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                                                           Martin Creek
                          Years                            design value
                                                               (ppb)
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2019-2021...............................................              93
2020-2022...............................................              81
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    The attainment date for the area was January 12, 2022. In order for 
the EPA to determine that the area attained by the January 12, 2022, 
attainment date based solely on air quality monitoring data, the design 
value must be based upon complete, quality-assured monitored air 
quality data from three consecutive years (2019-2021) at each eligible 
monitoring site and equal to or less than the 75 ppb standard.
    The one-hour SO2 design value at the Martin Creek 
monitoring site located within the Rusk-Panola area shows a violation 
of the 1-hour primary SO2 NAAQS with a concentration greater 
than 75 ppb for the 2019-2021 design value, and thus, EPA is making the 
determination that the Rusk-Panola area did not attain by its January 
12, 2022, attainment date. We also note that the 2020-2022 design value 
also shows a violation of the NAAQS.
    Under CAA section 179(d)(2), if the EPA determines that an area did 
not attain the NAAQS by the applicable deadline, the responsible air 
agency has up to 12 months from the effective date of the determination 
to submit a revised SIP for the area demonstrating attainment and 
containing any additional measures that the EPA may reasonably 
prescribe that can be feasibly implemented in the area in light of 
technological achievability, costs, and any non-air quality and other 
air quality-related health and environmental impacts as required. 
According to CAA section 179(d)(3), this revised SIP is to achieve 
attainment of the one-hour SO2 NAAQS as expeditiously as 
practicable, but no later than 5 years from the effective date of the 
area's failure to attain (i.e., 5 years after the EPA publishes a final 
action in the Federal Register determining that the nonattainment area 
failed to attain the SO2 NAAQS). In addition to triggering 
requirements for a new SIP submittal, a final determination that a 
nonattainment area failed to attain the NAAQS by the attainment date 
would trigger the implementation of contingency measures adopted under 
172(c)(9).

III. Limited Approval/Limited Disapproval

    Under CAA sections 110(k)(3) and 301(a) and EPA's long-standing 
guidance,\25\ the EPA is proposing a Limited Approval/Limited 
Disapproval action. A limited approval is appropriate when a SIP 
contains provisions that are SIP strengthening, but also contains a 
non-severable deficiency that prevents EPA from granting a full 
approval of the SIP. EPA's limited approval action allows the EPA to 
codify SIP requirements, in this case, that would meet all requirements 
of the CAA but for the noted force majeure and timely compliance 
deficiencies. Under this limited approval, the area would make progress 
toward attaining the NAAQS, even if the SIP cannot be fully approved as 
meeting all applicable requirements for demonstrating NAAQS attainment 
by the attainment date. EPA's limited disapproval action will ensure 
that the deficient portions of the SIP submittal will be addressed, 
either through an EPA approved SIP or a FIP. This subsection will 
discuss the deficiencies identified in the SIP, the reasoning for and 
impact of a limited approval and limited disapproval, and EPA's plan to 
cure the deficiency.
---------------------------------------------------------------------------

    \25\ Processing of State Implementation Plan (SIP) Revisions, 
EPA Memorandum from John Calcagni, Director, Air Quality Management 
Division, OAQPS, to Air Division Directors, EPA Regional Offices I-X 
(1992 Calcagni Memorandum) located at https://www3.epa.gov/ttn/naaqs/aqmguide/collection/cp2_old/19920721_calcagni_sip_submittal_processing.pdf.
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    Section 172(c)(6) of the CAA requires that nonattainment area SIP's 
``include enforceable emission limitations, and such other control 
measures means or techniques . . . . as well as schedules and 
timetables for compliance, as may be necessary or appropriate to 
provide for attainment of such standard in such area by the applicable 
attainment date . . .''. Further, CAA section 302(k) defines ``emission 
limitation'' to mean a requirement which limits the quantity, rate, or 
concentration of air pollutant emissions on a continuous basis.
    For an SO2 attainment plan to be fully approvable, a 
modeled attainment demonstration must be based on the maximum allowable 
emissions permitted under the SIP's emission limitations and under 
172(c)(6) those limitations must be practically and legally enforceable 
and under 302(k) must be continuous. The same is true for the 
demonstration of RACM/RACT, RFP, and contingency measures. Satisfying 
the enforceability criteria ensures that NAAQS attainment will be 
achieved via compliance with the SIP as adopted.

A. Force Majeure Provision Deficiency

    The control strategy for the Rusk-Panola area is found in the 
February 14, 2022, Agreed Order between TCEQ and Luminant for the 
Martin Lake Facility incorporated into the SIP submittal. The Agreed 
Order establishes emissions limits and control requirements for the 
source which are necessary for the area to attain the NAAQS. However, 
the Agreed Order also includes a force majeure provision which states 
that, under a triggering event, the facility's failure to comply with 
an emissions limitation or other provision is not a violation of the 
Agreed Order.\26\ This provision allows exceedances of emission 
limitations of unknown frequency, duration, and magnitude, and thus 
impermissibly interferes with the ability to continuously enforce the 
emissions limitations relied upon to provide for attainment. The 
provision is not contemplated in the attainment modeling which relies 
on the emissions limits being continuously and permanently applied, 
and, therefore, makes the modeling not representative of actual air 
quality in the area should this provision of the SIP be triggered. In 
all cases, the emission limits and control measures must be 
continuously applicable and accompanied by

[[Page 63122]]

appropriate methods and conditions to determine compliance and 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 limits must be permanent and 
must reflect the assumptions used in the SIP demonstrations).\27\ As 
written, emissions associated with a force majeure event may increase 
with unknown frequency, duration, and magnitude notwithstanding the 
emission limitations because if the force majeure provision is 
triggered it is no longer a violation to emit above the limitations set 
in the SIP.
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    \26\ See page 9 of the Agreed Order. The full text of the Agreed 
Order can be found in the docket for this rulemaking action.
    \27\ See General Preamble at 13567-68.
---------------------------------------------------------------------------

    Emissions reductions under this SIP submission are quantifiable, 
except if the force majeure provision is triggered and the facility is 
exempted from complying with emissions limitations to an unknown 
extent. The emissions limitations outlined in the SIP are enforceable 
by the state, EPA, and citizens, except in the case of a force majeure 
event when lack of compliance with the emission limitations does not 
constitute a violation and therefore cannot be enforced. There are no 
clear, unambiguous, and measurable requirements for emissions that 
occur once the force majeure provision is triggered. This could result 
in excess emissions and periods of non-compliance which are ``not a 
violation of [the] Agreed Order.'' \28\ These unaccounted emissions 
could jeopardize the ability of the area to attain and maintain the 
NAAQS while also cutting off the ability to enforce emissions 
limitations necessary to attain. The provisions of this SIP are 
replicable and are written sufficiently specific and non-subjective, 
except for the force majeure provision that does not provide specific 
procedures on how the provision should be interpreted, when compliance 
should be exempt, or for how long compliance should be exempt. 
Accountability is also an issue as the impact of triggering the force 
majeure provision may exempt compliance with SIP requirements and lead 
to unknowable, unaccounted for emissions associated with that event.
---------------------------------------------------------------------------

    \28\ See page 9 of the Agreed Order.
---------------------------------------------------------------------------

    If the control strategy in the SIP fails to adhere to these 
principles, then the attainment demonstration relying on that control 
strategy, that contemplates no such force majeure event, may no longer 
be representative of the nonattainment area when the provision is 
triggered. The force majeure provision impacts the enforceability of 
the agreed order and thus, cannot be severed from the emissions 
limitations contained in the Agreed Order and consequently impacts the 
entirety of the SIP revision. The provision could interfere with the 
SIP revision's ability to provide for attainment and maintenance of the 
NAAQS, RFP, implementation of RACM/RACT, enforceable emission 
limitations as necessary to provide for timely attainment, and 
implementation of contingency measures. Therefore, the force majeure 
provision included in the SIP submission warrants a limited 
disapproval.

B. Compliance Date Deficiency

    Second, EPA proposes a limited disapproval on the basis that the 
date for compliance with the emission limitations as written in the 
Agreed Order and SIP submittal is several months after the attainment 
date for the area. Under CAA section 172(c)(6), the nonattainment plan 
must include provisions as necessary or appropriate to provide for the 
attainment by the applicable attainment date. Here, the applicable 
attainment date for the Rusk-Panola Nonattainment area was January 12, 
2022, but the Martin Lake Facility was not required to comply with all 
of the emissions limitations set forth in the SIP submission's control 
strategy until 180 days later, July 11, 2022. Therefore, because the 
compliance date for the full control strategy is not until after the 
attainment date for the area, EPA proposes a limited disapproval for 
this SIP submission.

C. Limited Approval

    Despite these deficiencies, and as further elaborated on in section 
V with the full analysis of the attainment plan, EPA proposes that 
absent this force majeure provision and the compliance date deficiency, 
the SIP's attainment modeling, controls, emissions limitations, and 
other requirements would otherwise be adequate to provide the needed 
emission reductions to provide for attainment in the Rusk-Panola area. 
Currently, there are no federally enforceable requirements that will 
bring the Rusk/Panola area into attainment for the 2010 SO2 
NAAQS. Therefore, despite the enforceability concerns, EPA is proposing 
a limited approval to make these new requirements federally enforceable 
as a SIP strengthening measure that will result in emissions reductions 
and provide for progress towards attainment of the 1-hour primary 
SO2 NAAQS.
    The Limited Approval encompasses the entire submittal, both the SIP 
strengthening and deficient provisions, making all provisions federally 
enforceable. The major source in the area will have to additionally 
incorporate the control requirements and emissions limits prescribed in 
the SIP into their CAA title V operating permit, which will also be 
subject to federal enforcement.

D. Limited Disapproval and Consequences

    On the basis of the deficiencies noted above, EPA is also proposing 
a Limited Disapproval, which carries the same consequences as a full 
disapproval. In accordance with CAA section 179, this Limited 
Disapproval triggers an 18-month NSR emissions offset sanction clock 
and a 24-month federal highway sanction clock. This action also 
establishes a requirement under CAA section 110(c) for the EPA to 
promulgate a FIP within two years. However, because of EPA's previous 
Finding of Failure to Submit, EPA is past due to issue a FIP revision. 
The sanctions are terminated when EPA fully approves a corrective SIP 
revision. The FIP clock obligation is addressed when EPA issues a FIP 
or fully approves the required SIP revision. Issuing a Limited 
Approval/Limited Disapproval ensures that the area is subject to 
federally enforceable requirements that will provide for progress 
toward attainment, while simultaneously providing for the correction of 
the deficient portion of the SIP submittal.
    As stated previously in this section, the force majeure provision, 
exempts enforcement of the emissions limitations and controls during a 
specific type of event. To remedy this deficiency in the SIP, the EPA 
plans to promulgate a FIP that reflects the control strategy included 
in TCEQ's SIP submission but does not include the force majeure 
provision.

IV. Attainment Demonstration and Longer-Term Averaging

    In accordance with CAA section 172(c)(1), nonattainment SIPs must 
include provisions that provide for attainment of the NAAQS. Please see 
section I. Background, C. Attainment Demonstration for SO2 
Nonattainment Areas subsection for a more detailed discussion of the 
Attainment Demonstration requirements. An area can achieve attainment 
by

[[Page 63123]]

implementing the appropriate control strategy identified to reduce 
pollution at the requisite sources. 40 CFR part 51, subpart G further 
delineates the control strategy requirements that SIPs must meet, and 
EPA has long required that all SIPs and control strategies reflect the 
four fundamental principles of quantification, enforceability, 
replicability, and accountability. See General Preamble, at 13567-68. 
Generally, for 1-hour standards control strategies include requirements 
that are based on 1-hour averaging times as this is the most straight 
forward way to ensure variability in the emission rate will not 
interfere with attainment of the standard. However, EPA does allow 
states to adopt requirements using longer-term averaging limits as long 
as they can demonstrate they are comparably stringent to modeled 1-hour 
critical emissions values (CEV) that would, if adopted as emission 
limits, provide for attainment of the one-hour standard.
    Texas' plan applies a 24-hour block average emission limit to 
Martin Lake. Therefore, EPA is providing the following discussion of 
its rationale for approving the use of longer-term average limits in 
plans designed to provide for attainment. EPA's April 2014 
SO2 Guidance recommends that the emission limits be 
expressed as short-term average limits (e.g., addressing emissions 
averaged over one or three hours), but also allows for emission limits 
with longer averaging times, up to 30 days, if certain criteria are 
met. See April 2014 SO2 Guidance, pp. 22 to 39. The guidance 
recommends that, should states and sources utilize a longer-term 
average limit, the limit should be set at an adjusted level that 
reflects a comparable degree of stringency as the modeled 1-hour CEVs 
(lb/hr and lb/MMBtu limits) {Note MMBtu is million British Thermal 
Units{time} .
    In evaluating this option, EPA considered the nature of the 
standard, conducted detailed analyses of the impact of the use of up to 
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. See April 2014 SO2 Guidance at 
appendices B, C and D.
    As stated above and specified in 40 CFR 50.17(b), the 1-hour 
primary SO2 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. For 
longer-term average limits, States must demonstrate with adequate 
assurance that a longer-term averaging limit will have comparable 
stringency as the one-hour average CEV and provide for attainment. 
Critical to this demonstration is the frequency and magnitude of hourly 
exceedances occurring under a longer-term average limit and the control 
level needed to constrain those occurrences to provide for attainment 
comparable to a strategy based on a one-hour emission standard. The 
following is a synopsis of EPA's review of whether such plans provide 
for attainment based on modeling of the one-hour CEV (1-hour CEV 
emission rates lb/hr and lb/MMBtu) and in light of the NAAQS form for 
determining attainment.
    For plans relying on longer-term averaging limits, EPA's guidance 
recommends that States establish a CEV based off of a continuously 
applicable 1-hour emissions limit before determining their longer-term 
averaging period and limits using fixed emission rates. The maximum 
emission rate that would be modeled to result in attainment (i.e., in 
an ``average year'' \29\ shows three, not four days with maximum hourly 
levels exceeding 75 ppb, over three consecutive years) is labeled the 
``critical emission value.'' The modeling process for identifying this 
critical emission value considers the numerous variables that affect 
ambient concentrations of SO2, 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 at this critical emission value.
---------------------------------------------------------------------------

    \29\ An ``average year'' is used to mean a year with average air 
quality. While 40 CFR 50 appendix T provides for averaging three 
years of 99th percentile daily maximum values (e.g., the fourth 
highest maximum daily 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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    EPA recognizes that some sources have highly variable emissions, 
for example, due to variations in fuel sulfur content and operating 
rate, that 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 critical emissions value. EPA also acknowledges 
the concern that longer-term emission limits can allow short periods 
with emissions above the critical emissions value, which, if coincident 
with meteorological conditions conducive to high SO2 
concentrations, could in turn create the possibility of a NAAQS level 
exceedance occurring on a day when an exceedance would not have 
occurred if emissions were continuously controlled at the level 
corresponding to the critical emissions value. However, for several 
reasons, EPA believes that the approach recommended in its April 2014 
SO2 Guidance document suitably addresses this concern. 
First, from a practical perspective, EPA expects the actual emission 
profile of a source subject to an appropriately set longer-term average 
limit to be like the emission profile of a source subject to an 
analogous 1-hour average limit. 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 critical emissions value) 
and that takes the source's emissions profile into account. As a 
result, EPA expects either form of emissions limit to yield comparable 
air quality.
    Second, from a more theoretical perspective, EPA has compared the 
likely air quality from a source that has maximum allowable emissions 
under an appropriately set longer-term limit, to the likely air quality 
from a source that has 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 critical emissions 
level. In the longer-term average limit scenario, the source is 
presumed occasionally to emit more than the critical emissions value 
but on average, and presumably at most times, to emit well below the 
critical emissions value. In an ``average year,'' compliance with the 
1-hour limit is expected to result in three exceedance days (i.e., 
three days with an hourly value above 75 ppb) and a fourth day with a 
maximum hourly value at 75 ppb. By comparison, for the source complying 
with a longer-term limit, it is possible that additional exceedances 
would occur that would not occur in the 1-hour limit scenario (if 
emissions exceed the critical emissions value 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 since the limit is set well below the 
critical emissions value, so a source complying

[[Page 63124]]

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.
    As a hypothetical example to illustrate these points, suppose a 
source that always emits 1,000 pounds of SO2 per hour and 
this results in air quality at the level of the NAAQS (i.e., results in 
a design value of 75 ppb). Suppose further that in an ``average year,'' 
these emissions cause the 5 highest maximum daily average 1-hour 
concentrations to be 100 ppb, 90 ppb, 80 ppb, 75 ppb, and 70 ppb. Then 
suppose that the source becomes subject to a 30-day average emission 
limit of 700 pounds per hour. It is theoretically possible for a source 
meeting this limit to have emissions that occasionally exceed 1,000 
pounds per hour, but with a typical emissions profile, emissions would 
much more commonly be between 600 and 800 pounds per hour. This 
simplified example assumes a zero-background concentration, which 
allows one to assume a linear relationship between emissions and air 
quality. A nonzero background concentration would make the mathematics 
more difficult but would give similar results. Air quality will depend 
on what emissions happen at what critical hours but suppose that 
emissions at the relevant times on these 5 days are 800 pounds per 
hour, 1,100 pounds per hour, 500 pounds per hour, 900 pounds per hour, 
and 1,200 pounds per hour, respectively. This is a conservative example 
because the average of these emissions, 900 pounds per hour, is well 
over the 30-day average emission limit. These emissions would result in 
daily maximum 1-hour concentrations of 80 ppb, 99 ppb, 40 ppb, 67.5 
ppb, and 84 ppb. In this example, the fifth day would have an 
exceedance that would not otherwise have occurred, but the third day 
would not have an exceedance that otherwise would have occurred, and 
the fourth day would have been below, rather than at, 75 ppb. In this 
example, the fourth highest maximum daily concentration under the 30-
day average would be 67.5 ppb.
    This simplified example encapsulates the findings of a more 
complicated statistical analysis that EPA conducted using a range of 
scenarios using actual plant data. As described in appendix B of EPA's 
April 2014 Guidance, EPA found that the requirement for a lower long 
term average emission limit is highly likely to yield better air 
quality than is required with a comparably stringent 1-hour limit. 
Based on analyses described in appendix B of its 2014 Guidance, EPA 
expects that an emissions profile with maximum allowable emissions 
under an appropriately set, comparably stringent 30-day average limit 
is likely to produce the net effect of having a lower number of hourly 
exceedances of the NAAQS level and better air quality than an emission 
profile with maximum allowable emissions under a 1-hour emission limit 
at the critical emissions value.\30\ 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.
---------------------------------------------------------------------------

    \30\ See also further analyses described in rulemaking on the 
SO2 attainment plan for Southwest Indiana. In response to 
comments expressing concern that the emissions profiles analyzed for 
appendix B represented actual rather than allowable emissions, EPA 
conducted additional work formulating sample allowable emission 
profiles and analyzing the resulting air quality impact. These 
analyses provided further support for the conclusion that an 
appropriately set longer term average emission limit in appropriate 
circumstances can suitably provide for attainment. The rulemaking 
describing these further analyses was published on August 17, 2020, 
at 85 FR 49967. A more detailed description of these analyses is 
available in the docket for that action, specifically at https://www.regulations.gov/document?D=EPA-R05-OAR-2015-0700-0023.
---------------------------------------------------------------------------

    The question then becomes whether this approach--which is likely to 
produce a lower number of overall hourly NAAQS level exceedances even 
though it may produce some unexpected exceedances above the critical 
emission value--meets the requirement in section 110(a)(1) and 
172(c)(1) for state implementation plans to ``provide for attainment'' 
of the NAAQS. For SO2, a variety of factors can cause a 
well-designed attainment plan to fail and unexpectedly not result in 
attainment. For example, this can occur if meteorology occurs that is 
more conducive to poor air quality than was anticipated in the plan. 
Therefore, the plan must provide an adequate level of confidence that 
it will provide for attainment of the NAAQS. Additionally, when 
evaluating longer-term average limits, EPA must weigh the likely net 
effect on air quality. This evaluation must consider the risk that 
occasions with meteorology conducive to high concentrations will have 
elevated emissions leading to NAAQS level exceedances that would not 
otherwise have occurred and must also weigh the likelihood that the 
requirement for lower emissions on average will result in days not 
having hourly exceedances that would have been expected with emissions 
at the critical emissions value. Additional policy considerations, 
including the desirability of accommodating real world emissions 
variability without significant risk of NAAQS violations, are also 
appropriate factors for EPA to weigh in judging whether a plan provides 
for attainment with a reasonable degree of confidence. Based on these 
considerations, especially given the high likelihood that a 
continuously enforceable limit averaged over as long as 30 days, 
determined in accordance with EPA's guidance, will result in 
attainment, EPA believes as a general matter that such limits, if 
appropriately determined, can reasonably be considered to provide for 
attainment of the 2010 SO2 NAAQS.
    EPA's April 2014 SO2 Guidance appendix B prescribes how 
a state's SIP should develop and demonstrate that an appropriate 
longer-term average limit provides for attainment. Development of 
longer-term average limits starts with a determination of the 1-hour 
emission limit that would provide for attainment (i.e., the critical 
emissions value), establishment of an adjustment factor to determine 
the (lower) level of the longer-term average emission limit that would 
be estimated to have a stringency comparable to the otherwise necessary 
1-hour emission limit, and application of the adjustment factor to the 
emissions limits. The method for deriving an appropriate adjustment 
factor 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 this data to compute a complete set 
of emission averages, computed according to the averaging time and 
averaging procedures of the prospective emissions limit. In this 
recommended method, the ratio of the 99th percentile among these long-
term averages to the 99th percentile of the 1-hour values represents an 
adjustment factor that may be multiplied by the candidate 1-hour 
emission limit to determine a longer-term average emission limit that 
may be considered comparably stringent.\31\ The guidance also addresses 
a variety of related topics, such as the potential utility of setting 
supplemental emission limits, such as mass-based limits, to reduce the 
likelihood and/or magnitude of elevated emission levels that might 
occur under the longer-term emission rate limit.
---------------------------------------------------------------------------

    \31\ For example, if the critical emission value is 1,000 pounds 
of SO2 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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[[Page 63125]]

V. Review of Modeled Attainment Plan

    This section discusses EPA's review and analysis of the modeled 
attainment plan, including model selection, meteorological data, 
emissions data, receptor grid, emissions limits, and background 
concentrations. As discussed in detail in prior section III., EPA is 
proposing that a limited approval and limited disapproval action is 
necessary because, but for the presence of the force majeure provision 
in the SIP submission, the modeled attainment plan satisfies the EPA's 
CAA requirements and would adequately demonstrate the SIP requirements 
will provide for attainment absent the force majeure provision.
    TCEQ's SIP submittal relies on an alternative model, which modifies 
the version of AERMOD approved for regulatory modeling. EPA reviewed 
the TCEQ's alternative model and also performed its own additional 
modeling analysis to determine whether the emission limits and control 
measures in the State's SIP, absent the force majeure provision, would 
provide for attainment in the Rusk-Panola area. The EPA's additional 
modeling analysis used the Alternative Model AERMOD v.21112 with Highly 
Buoyant Plume (TCEQ's alternative model AERMOD-HBP) and reflecting what 
was done in the TCEQ modeling. EPA modeled two of the highest modeled 
concentration scenarios utilizing the AERMOD-HBP v.21112 with HBP. 
Those scenarios produced a modeled maximum design value, with 
background concentration included, of 73.6 ppb of SO2, 
confirming TCEQ's modeling results for these two scenarios. EPA also 
ran these same two scenarios with the most recent version of AERMOD 
v.23132 with HBP code. EPA has included the HBP code for scientific 
testing and investigation as an alpha option in AERMOD v.23132, but it 
is important to note that alpha options are for scientific 
investigation and not approved for regulatory use. EPA compared the HBP 
code in AERMOD v.23132 with TCEQ's AERMOD-HBP, and it appears to be the 
same exact code. This modeling was performed by EPA to confirm that any 
other changes in AERMOD between v.21112 and v.23132 would not result in 
significant changes to TCEQ's attainment demonstration modeling, and 
the maximum modeled results for these two scenarios were the same. This 
modeling also confirms that the HBP code included in TCEQ's AERMOD-HBP 
and the alpha option implemented in AERMOD v.23132 resulted in the same 
maximum modeled concentrations. Additional, more detailed discussion of 
the State's modeling and EPA's modeling of these two highest 
concentration scenarios with both versions of AERMOD (TCEQ's v.21112 
with HBP and EPA's v.23132 with non-regulatory alpha option HBP code) 
are contained in the Technical Support Document (TSD) for this proposed 
action. For EPA's alternative model review of the TCEQ's AERMOD-HBP see 
the AERMOD-HBP TSD.

A. Model Selection

    According to the Modeling Guideline, alternative models may only be 
used instead of AERMOD with EPA review and approval. Texas' attainment 
demonstration used an alternative model instead of the Modeling 
Guideline preferred model, AERMOD v.21112.\32\ TCEQ's alternative model 
modifies AERMOD's treatment of penetrated plumes which affects the 
resultant modeled concentrations by delaying mix down of the penetrated 
plume component under certain circumstances resulting in less emissions 
mixing down to add to surface level concentrations. The modified code 
added is referred to as the Highly Buoyant Plume Model Code \33\ and 
the resultant alternative model is called AERMOD-Highly Buoyant Plume 
(AERMOD-HBP). Along with the AERMOD-HBP, Texas used the regulatory 
versions of AERMOD preprocessors (AERMET, AERMINUTE, AERSURFACE, 
AERMAP, and Building Profile Input Program for PRIME (BPIPPRM)), and 
where applicable, used the preprocessor's regulatory default 
parameters.
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    \32\ The most current version of AERMOD is version 23132, and 
version 21112 was the version of AERMOD available at the time TCEQ 
developed and adopted the SIP. See https://www.epa.gov/scram/air-quality-dispersion-modeling-preferred-and-recommended-models.
    \33\ Weil, J.C., Corio, L.A., and Brower, R.P., 1997, A PDF 
Dispersion Model for Buoyant Plumes in the Convective Boundary 
Layer, Journal of Applied Meteorology. 36, 982-1003.Weil, J.C., 
January 2, 2020, New Dispersion Model for Highly-Buoyant Plumes in 
the Convective Boundary Layer, Preliminary Draft v4.
---------------------------------------------------------------------------

    Texas requested use of an alternative model in a letter dated May 
24, 2021. Vistra's consultant, AECOM, performed initial dispersion 
modeling for the Rusk-Panola area using AERMOD v. 19191. AECOM asserted 
its initial modeling showed that AERMOD v. 19191 can overpredict 
SO2 concentrations relative to available SO2 
observations at the Longview and Martin Creek monitors some of the 
time.\34\ Based on AECOM's initial modeling, TCEQ and Vistra approached 
EPA Region 6 in Fall 2020, that led to TCEQ requesting and having 
discussions with EPA, TCEQ's contractor, Vistra, and Vistra's 
contractor AECOM to develop an understanding of what information and 
analysis were needed to support a potential alternative model request 
with modified treatment of penetrated plumes. TCEQ formally requested 
EPA's review and approval of an alternative model in a letter dated May 
24, 2021.\35\ TCEQ's request did not include all of the necessary 
components previously discussed between October 2020 through April 2021 
for the EPA to complete an alternative model review. The EPA continued 
to receive materials from TCEQ through August 2021, and EPA provided 
some feedback and clarification on some technical analyses that were 
needed for EPA to conduct its review of the alternative model request. 
EPA did not receive all necessary components until August 2021. Those 
components included the necessary information and modeling analysis to 
enable EPA to perform a full review in accordance with the alternative 
model review and approval guidelines. Several of these technical 
analyses are based on the available data including: AERMOD v.21112 
regulatory version and AERMOD-HBP modeling results comparisons using 
actual emissions and meteorological data for the 2016-2020 period 
coupled with available SO2 monitoring data at the Martin 
Creek and Longview monitors.\36\
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    \34\ TCEQ SIP appendix M Alternative Model Documentation PDF, 
page 222.
    \35\ TCEQ submitted a letter dated May 24, 2021 from Ms. Tonya 
Baer (Director of the Office of Air) to Mr. David Garcia (Air and 
Radiation Division Director) of EPA Region 6 requesting approval of 
an alternative model request for use AERMOD with Highly Buoyant 
Plume (HBP) code modifications in the Rusk-Panola 2010 1-Hour 
SO2 NAAQS attainment demonstration. This document is 
available in the Docket for this action.
    \36\ Martin Creek monitor (AQS 484011082) is located 
approximately 2 km to the north of Martin Lake EGU facility and 
Longview Monitor (AQS 481830001) is located approximately 19 km to 
the northwest of the Martin Lake EGU facility. While the Longview 
monitor is relatively far away from the Martin Lake facility it was 
found to have elevated SO2 data when Martin Lake's 
emissions were transported to the monitor, that was not 
representative of maximum ambient concentrations from Martin Lake 
facility emissions, was still useful to consider in evaluating the 
alternative model request since there was limited monitoring data in 
the area.
---------------------------------------------------------------------------

    EPA Region 6 performed a detailed analysis of the alternative model 
request materials, including evaluating the theoretical rationale for 
modifying how penetrated plumes are treated in AERMOD. TCEQ and EPA's 
analysis centered on evaluation of the modeling results centered at the 
two monitors in the area, the Martin Creek monitor and Longview 
monitor, in order to compare modeled concentrations to monitored

[[Page 63126]]

values. The evaluation and technical analysis of regulatory AERMOD 
results and the alternative model AERMOD-HBP results at receptors 
placed at the two monitor locations were compared with the monitored 
data for these two monitors using actual emissions, meteorology, and 
monitored concentrations in the 2016-2020 timeframe for the Longview 
monitor and 2018-2020 for the Martin Creek monitor. In addition to 
TCEQ's submittal materials, EPA also performed several technical 
analyses, including its own Cox-Tikvart statistical analysis to confirm 
the conclusions. Overall, EPA's review of TCEQ's submittal materials 
and EPA's own analyses confirmed TCEQ's conclusion that based on the 
data available, AERMOD-HBP performed better than AERMOD in this one 
case-specific and location-specific situation in the area around the 
Martin Lake Electric Generating Facility (EGF) facility. Full details 
of EPA's review and conclusions related to the alternative model 
approval are provided in the ``EPA's Review of TCEQ's Alternative Model 
Request of AERMOD with Highly Buoyant Plume Treatment (HBP)'' (AERMOD-
HBP TSD), included in the docket for this action.
    Once EPA Region 6 modelers and Office of Air Quality Planning and 
Standards' Air Quality Modeling Group (OAQPS-AQMG) modelers were in 
agreement that the Alternative Model could be approved in accordance 
with the Modeling Guideline section 3.2.2, EPA Region 6 sent a 
memorandum with the detailed AERMOD-HBP TSD attached (dated July 11, 
2024) to the Model Clearinghouse (part of OAQPS-AQMG) that proposed 
approval of the Alternative Model and requested concurrence from the 
Model Clearinghouse. The Model Clearinghouse sent a memorandum (dated 
July 24, 2024) to EPA Region 6 concurring with the case specific 
approval of the Alternative Model in this case-specific situation. The 
AERMOD-HBP approval is limited specifically to only allow AERMOD-HBP to 
be used in the attainment demonstration modeling for this Rusk-Panola 
attainment demonstration. This approval limited to the specific 
attainment demonstration at Martin Lake is based on the location and 
situation-specific factors, including available monitoring data, that 
were considered when evaluating this alternative model for this 
specific case. The EPA notes that attempting to use this alternative 
model for any other purposes at the Martin Lake facility, or any other 
facility, would require a separate, stand-alone evaluation and approval 
in accordance with EPA's alternative model requirements. Please see the 
TSD, the Model Clearinghouse Memorandums, and EPA's AERMOD-HBP TSD for 
more details.

B. Meteorological Data

    The State's modeling utilized surface meteorological data obtained 
from the Longview East Texas Regional Airport and upper air data from 
the Shreveport, Louisiana station from 2015-2019. The Longview East 
Texas Regional Airport is the closest National Weather Service (NWS) 
site to the Martin Lake facility and monitor at Tatum County Road, 
2181d Martin Creek Lake site (Air Quality System (AQS) 484011082), 
approximately 19 kilometers (km) away and is representative of the 
meteorology in the Rusk-Panola area due to its proximity. The 
Shreveport, Louisiana NWS upper air site is the closest site of upper 
air data. TCEQ processed the surface and upper air data using the 
meteorological processing tools: AERMINUTE (v.15272), AERMET (v.21112), 
and AERSURFACE (v.20060). AERMINUTE was used to include measured one-
minute wind averages, AERMET was used to generate meteorological data 
files, and AERSURFACE was used to determine the surface characteristics 
for the meteorological station. The current version of each 
preprocessor at the time the modeling demonstration was performed was 
AERMINUTE v.15272, AERMET v.21112, and AERSURFACE v. 20060. While the 
most recent versions of AERMINUTE and AERSURFACE were used, AERMET has 
been updated since the State conducted its modeling. However, based on 
the changes that the EPA made to AERMET, we would not expect to see any 
significant changes to modeling results if the data were processed with 
the latest version of AERMET, and EPA finds that TCEQ's data are still 
representative. EPA recommends using the closest NWS sites for surface 
and upper air data if they are considered representative of the area 
being modeled. In this situation, EPA concurs with the use of these two 
sites for this modeling as meeting EPA's criteria as being nearby and 
representative. EPA also finds that TCEQ adequately processed the data 
in accordance with the Modeling Guideline and EPA's Guidance to 
generate the necessary modeling data to be used in the AERMOD model 
runs. Therefore, the EPA is proposing to find the selection and 
processing of this data to be acceptable.

C. Emissions Data

    The SIP revision identifies the Martin Lake facility as the primary 
SO2 source in the Rusk-Panola area. As there were no 
monitors in the area at the time of designation, EPA relied on modeling 
to designate the area and found that Martin Lake is likely producing 
almost all, if not 100%, of the emissions causing the maximum modeled 
design values that were above the NAAQS.\37\ This information is also 
confirmed by review the of SO2 sources in the Rusk-Panola 
area provided in the SIP revision's emission inventory analysis. The 
emissions inventory analysis shows that there are no other major 
sources of SO2 within the boundary of the Rusk-Panola area. 
TCEQ appropriately modeled the maximum hourly emission rate for the 
Martin Lake facility emission sources. The only nearby SO2 
source with emissions greater than 100 tons per year within 50 km of 
Martin Lake is the American Electric Power Pirkey Power Plant (Pirkey) 
located approximately 17 km outside of the Rusk-Panola area boundary in 
Harrison County. Since Pirkey is a background source outside of the 
Rusk-Panola NAA that could potentially contribute to concentrations in 
the Rusk-Panola NAA, pursuant to the Modeling Guideline table 8-1, a 
hybrid of actual and allowable emission factors was used for emissions 
from Pirkey in TCEQ's modeling for the Rusk-Panola area. The remainder 
of the sources are captured by using monitoring data that is 
representative of background concentrations. The inclusion of Pirkey 
assures that Texas incorporated all sources in the modeling that are 
considered to possibly create SO2 concentrations and/or 
concentration gradients anywhere in the Rusk-Panola NAA that are not 
represented by the background monitoring data.
---------------------------------------------------------------------------

    \37\ See 81 FR 45039.
---------------------------------------------------------------------------

    The other facility, Pirkey, that is located outside of the Rusk-
Panola area included in the modeling, is not located in a direction 
such that it can contribute to the maximum SO2 
concentrations in the Rusk-Panola area (not upwind), and thus, would 
have a negligible impact on maximum modeled concentrations within the 
Rusk-Panola area. Therefore, TCEQ did not require new SO2 
emission limits on Pirkey. EPA has reviewed the facility's data and 
notes that the Pirkey facility is 17 km away from Martin Lake and the 
nearby Martin Creek monitor near Tatum County Road, and thus adding 
emission limits to Pirkey are not critical to demonstrating attainment 
in the area. EPA concurs with TCEQ's

[[Page 63127]]

approach of including Martin Lake (allowable emissions modeled) and 
Pirkey (hybrid of actual and allowable emission related factors to 
generate emissions modeled) emission sources, which comports with EPA's 
Modeling Guideline, including table 8-1, that provides guidance on what 
sources to include in the modeling and whether to model actuals or 
allowable emissions.
    TCEQ used site specific building and stack data and modeled all 
stacks in Martin Lake at the lesser of actual stack height or Good 
Engineering Practice (GEP) stack height. The State's modeling included 
building downwash influences for all sources except for Pirkey because 
the effects of downwash from Pirkey are localized and would not affect 
modeled concentrations in the Rusk-Panola area. The EPA has determined 
that the SIP's selection of sources and preprocessing of that source 
data satisfies the requirements of the Modeling Guideline. For a more 
detailed analysis and conclusions on what sources were included in the 
modeling and how they were modeled, see the TSD.
    As discussed in the TSD, Martin Lake was identified as the primary 
contributor to NAAQS violations in the Rusk-Panola area. Martin Lake is 
an EGF, with four point sources and one fugitive area source for 
SO2; the four point sources consist of three EGF boiler unit 
stacks and one combined stack for two auxiliary boilers. Modeling 
indicated emission reductions for Martin Lake were necessary to provide 
for attainment, and based on the modeling emission limitations were 
developed and included in the Agreed Order between TCEQ and Luminant 
that was submitted as part of this SIP revision. The modeling covers 42 
operating scenarios in total. These different scenarios were developed 
based on a combination of an emissions limit specific to each EGF 
boiler, an overall emission cap on emissions from the three main EGF 
boiler stacks, and four different operating loads. There are four 
different operating loads for the EGF boilers: (1) high load, (2) 
medium load, (3) low load, and (4) a maintenance, startup and shutdown 
(MSS) load. TCEQ modeled control measures using the critical emission 
value of 8,208 lbs/hour as the one-hour averaging period emission cap 
for the three EGF boilers that correlates with the Agreed Order's 
longer-term averaging emissions limit of 7,469 lb/hr over a 24-hour 
block averaging period. TCEQ's modeling also modeled the critical 
emission value of 0.33 lb/MMBtu limit for each boiler that correlates 
to the agreed order limit of 0.32 lb/MMBtu limit on a 24-hour block 
averaging period for each boiler. TCEQ developed the 42 different 
emission scenarios based on these limits as discussed in the TSD. For 
more detailed discussion and evaluation of the Agreed Order 24-hour 
block averaging limits and the critical emission value comparably 
stringent 1-hour averaging limitation values used in the modeling, see 
section V.E. In conclusion, the EPA is proposing to find that Texas' 
choice of included sources and the scenarios modeled to cover the 
potential range of operating scenarios that could occur with the new 
limits in place to be appropriate and inclusive of worst-case 
scenarios, in the absence of the force majeure provision.

D. Receptor Grid

    Within AERMOD, air quality concentration results are calculated at 
discrete locations identified by the user; these locations are called 
receptors. Receptors are placed in areas and outside the plant 
boundaries and areas within the plant boundary where the public has 
access. Areas within the plant where public access is restricted, are 
not considered ambient air for the purposes of compliance with NAAQS. 
TCEQ's modeling domain for this demonstration consisted of a 25.5 km by 
24.5 km rectangular area centered around Martin Lake with three nested 
receptor grids. TCEQ placed receptors within and outside the Rusk-
Panola nonattainment area: (1) receptors at 25 meter (m) spacing along 
the non-ambient air fence/boundary lines, (2) the innermost grid 
spanning 0 to 3 km from the center point, encompassing Martin Lake, 
with 50m spacing between receptors; (3) the middle-nested grid extended 
from 3 km to 9 km, with 100 m spacing between receptors; and (4) the 
outermost grid, which extends beyond the nonattainment boundary covers 
the rest of the modeled domain, had 500 m spacing. The TCEQ, after 
discussions with EPA and Vistra, removed receptors from the grid found 
within the property owned and controlled (public access is restricted) 
by Vistra,\38\ Vistra restricts public access to this area through 
fencing, posting, and patrolling. Again, the air in the area controlled 
by Vistra is considered non-ambient air relative to its own emissions, 
and thus, they are not required to place receptors within these 
boundaries. Receptors with 25m spacing were also added along a section 
of public road within Vistra's property, and an additional receptor was 
placed at the location of the Martin Creek monitor. TCEQ determined 
receptor elevations using AERMAP in its modeling. EPA proposes that the 
receptor grid is consistent with EPA's Modeling Guideline and is 
adequate for demonstrating attainment within the NAA and the 
immediately surrounding area in this attainment demonstration modeling.
---------------------------------------------------------------------------

    \38\ See TCEQ's SIP appendix L--``Documentation from Vistra 
Energy Corporation for Property Boundaries''.
---------------------------------------------------------------------------

E. Emission Limits

    As part of its control strategy for the Rusk-Panola area, Texas 
entered an Agreed Order with Luminant set emissions limitations for the 
Martin Lake facility, adopted on February 14 2022, pursuant to 
Sec. Sec.  382.011, 382.012, 382.023, and 382.024 of the Texas Clean 
Air Act, Texas Health & Safety Code, Chapter 382, and the CAA. TCEQ 
incorporated the Agreed Order as part of its SIP revision submittal as 
a source-specific SIP revision seeking to establish federally 
enforceable emission limits. The limits in table 2 are hourly limits, 
and compliance with the limits is determined using the longer-term 24-
hour block averaging period.
    As stated in subsection C of this notice, there are no other major 
sources of SO2 within the nonattainment area that could 
contribute to nonattainment in the Rusk-Panola area. The Agreed Order 
set the compliance date for emission limits as ``the date by which the 
State of Texas is required to demonstrate compliance with the 2010 1-
hour SO2 NAAQS for the Rusk-Panola SO2 
Nonattainment Area.'' This means that the compliance date for the 
Agreed Order would be the attainment date, January 12, 2022 for limits 
other than the lb/MMBtu limits, which require compliance 180 days later 
(July 11, 2022).\39\ EPA proposes to find that the source specific 
emissions limits as laid out in the Agreed Order submitted with this 
SIP revision would be sufficient, based on the above described modeling 
and recognizing the longer than 1 hour averaging period, to provide for 
attainment in the Rusk-Panola area absent the force majeure provision.
---------------------------------------------------------------------------

    \39\ Vistra and TCEQ signed the Agreed Order on January 19, 
2022. TCEQ formally adopted the Agreed Order on February 14, 2022.

[[Page 63128]]



                             Table 2--Martin Lake Agreed Order Emission Limitations
----------------------------------------------------------------------------------------------------------------
               Source ID                          Source description               Sulfur Dioxide (SO2) limit
----------------------------------------------------------------------------------------------------------------
S-1, S-2, S-3.........................  EGF Boiler Units......................  II.a.(i)
                                                                                (1) Burn only subbituminous
                                                                                 coal, No. 2 fuel oil, or
                                                                                 natural gas;
                                                                                (2) limit the firing rate (when
                                                                                 fired) for all three EGF boiler
                                                                                 units to a combined rate not to
                                                                                 exceed 27,000 million British
                                                                                 thermal units (MMBtu) per hour
                                                                                 (the firing rate is an
                                                                                 operating cap for all three EGF
                                                                                 boiler units combined); and
                                                                                (3) Optimize the FGD systems to
                                                                                 ensure compliance with a
                                                                                 combined SO2 emission rate not
                                                                                 to exceed 7,469 lb/hr on a
                                                                                 block 24-hour average basis for
                                                                                 the three EGF boiler units (the
                                                                                 7,469 lb/hr is an emission cap
                                                                                 for all three EGF boiler units
                                                                                 combined). The emission cap of
                                                                                 7,469 lb/hr applies at all
                                                                                 times when fuel of any type is
                                                                                 fired in any EGF boiler unit.
                                                                                (ii) . . . the Company shall
                                                                                 ensure compliance with an SO2
                                                                                 emission rate not to exceed
                                                                                 0.32 lb/MMBtu on a block 24-
                                                                                 hour average basis for each EGF
                                                                                 boiler unit. This emission rate
                                                                                 applies at all times when fuel
                                                                                 of any type is fired in any EGF
                                                                                 boiler unit.
S-1A and B............................  Auxiliary Boilers.....................  II.b.
                                                                                (i) Fire only No. 2 fuel oil
                                                                                 with a sulfur content of 0.10%
                                                                                 by weight or less;
                                                                                (ii) Not exceed an SO2 emission
                                                                                 rate of 51.46 lbs/hr on a one-
                                                                                 hour basis and 22.54 tpy on an
                                                                                 annual basis, combined for the
                                                                                 two Auxiliary Boilers (the
                                                                                 51.46 lbs/hr and 22.54 tpy are
                                                                                 emission caps for the two
                                                                                 auxiliary boilers combined);
                                                                                 and
                                                                                (iii) Comply with a 10 percent
                                                                                 annual capacity factor for each
                                                                                 of the two Auxiliary Boilers.
                                                                                 Annual capacity factor is the
                                                                                 ratio between the actual heat
                                                                                 input from all fuels burned
                                                                                 during a calendar year and the
                                                                                 potential heat input had the
                                                                                 boiler been operated for 8,760
                                                                                 hours during a year at the
                                                                                 maximum steady state design
                                                                                 heat input capacity. The 10
                                                                                 percent annual capacity factor
                                                                                 limit corresponds to a heat
                                                                                 input of 219,000 MMBtu per
                                                                                 calendar year, per Auxiliary
                                                                                 Boiler.
                                                                                (iv) The Company shall monitor
                                                                                 the sulfur content of the
                                                                                 liquid fuel in accordance with
                                                                                 fuel sampling requirements
                                                                                 specified in 40 CFR part 75,
                                                                                 appendix D, 2.2 Oil Sampling
                                                                                 and Analysis.
----------------------------------------------------------------------------------------------------------------

1. Enforceability
    An attainment plan must include emission limits that provide for 
attainment and that are: quantifiable, fully enforceable, replicable, 
and accountable.\40\ Full enforceability includes the ability to 
enforce emissions limitations by the state, the EPA, or by private 
citizens through a citizen suit.\41\ As discussed in detail in section 
III. of this notice, EPA proposes to find that the force majeure 
provision included in the SIP submission interferes with enforceability 
such that the Agreed Order and attainment plan may not be fully 
approved as meeting the requirements of CAA sections 110, 172, 191 and 
192.
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    \40\ See General Preamble at 13567-68.
    \41\ 42 U.S.C. 7604.
---------------------------------------------------------------------------

2. Longer-Term Average Emission Limits
    As noted in section IV. and section V.C, the Texas SIP is using 
longer-term lb/hr and lb/MMBtu emission limits with 24-hour block 
averaging compliance limits for three EGF boilers at the Martin Lake 
facility. Therefore, the critical emissions values are the modeled 
emission rates/limits based on 1-hour averaging period and serve as the 
basis for developing emission rate limits for longer averaging period 
and the limits used in the attainment modeling for the area. Modeled 
emission rates of 8,208 lb/hr and 0.33 lbs/MMBtu (one hour averaging 
period) were calculated by Vistra to convert to 7,469 lbs/hour and 0.32 
lbs/MMBtu averaged over a 24-hour block period. Martin Lake will be 
switching fuels from lignite and lignite blend operations to 
subbituminous coal, and therefore, Vistra and Texas evaluated other 
similar subbituminous coal fired units elsewhere in Texas with similar 
SO2 control devices that would be more representative of 
operating conditions rather than comparing to the past performance of 
the Martin Lake units operating on lignite coal. As such, Vistra and 
Texas determined that the NRG Limestone units would be appropriate 
sources to derive an adjustment factor to apply to the EGF boilers at 
Martin Lake due to the use of subbituminous coal at the NRG Limestone 
units and both facilities have wet FGD controls. In the SIP, Texas 
utilized three years of NRG Limestone (located near Jewett, Texas) 
emissions data from October 2018 through September 2021 to conduct the 
variability analysis, which coincides with when NRG Limestone burned 
only subbituminous coal. Texas employed the method detailed in our 2014 
SO2 Guidance appendices B, C, and D for deriving an 
appropriate adjustment factor to adjust the lb/hr modeled emission 
rates and the lb/MMBtu emission limit, to result in equivalent 24-hour 
block averaging lb/hr and lb/MMBtu emission limits. Texas followed 
EPA's guidance and evaluated the historic 1-hour 99th percentile of 
SO2 emissions information (lb/hr and lb/MMBtu) against the 
99th percentile 24-hour block average for the lb/hr and lb/MMBtu data 
to derive the appropriate adjustment factors of 0.91 for lb/hr and 0.97 
lb/MMBtu. These factors were used by Texas to derive the emission 
limits of 7,469 lbs/hour and 0.32 lbs/MMBtu averaged over a 24-hour 
block period that were included in the Agreed Order for Martin Lake. 
EPA has reviewed TCEQ's information supporting the 24-hour block 
averaging limits and is proposing to find the analysis acceptable and 
that these represent comparably stringent limits that would, absent the 
force majeure clause be protective of the NAAQS. For a more detailed 
discussion of our analysis please see the TSD prepared for this action.

F. Background Concentrations

    To develop background concentrations for the NAA, Texas relied on 
2015-2019 SO2 data from the Midlothian OFW monitor in Ellis 
County (CAMS C52), approximately 220 km west of the NAA.\42\ Texas 
determined that there were no representative nearby monitors to capture 
background concentrations, as the nearby monitors were all 
SO2 Data Requirements Rule (DRR) monitors sited to capture 
the impacts of major SO2 sources or other monitors with data 
significantly impacted by large SO2 sources (e.g., Longview 
monitor in Gregg County is 19 km from Martin Lake but Martin Lake's 
emissions have historically had a large impact on this

[[Page 63129]]

monitor's data). Therefore, Texas used a monitor located away from the 
source but still considered to be representative of background 
concentrations in the area. The Midlothian OFW monitor in Ellis County, 
Texas was chosen as it had complete SO2 Design Values (DVs) 
for the 2015 through 2019 period and had a more stable DV across recent 
years.
---------------------------------------------------------------------------

    \42\ Data is available in EPA's Air Quality System (AQS). 
(https://www.epa.gov/aqs).
---------------------------------------------------------------------------

    A fixed background concentration of 15.72 [micro]g/m\3\ was added 
to modeled concentrations to result in maximum modeled concentrations 
for all 42 scenarios. These background values are representative of the 
contribution due to other sources within the Rusk-Panola area and 
surrounding areas that were not explicitly modeled combined with 
regional continental background in this area. See the TSD for 
additional information. Using this approach, the EPA is proposing to 
find the State's treatment of SO2 background levels to be 
acceptable for adding to modeled concentrations to represent background 
SO2 levels in this attainment demonstration modeling.

G. Summary of Results

    The State's alternative modeling demonstration, which incorporates 
emissions scenarios based on the February 14, 2022, Agreed Order 
emission limits for the Martin Lake facility but recognizing the longer 
than 1 hour averaging time, resulted in modeled concentrations below 
the 1-hour primary SO2 NAAQS using the alternative model 
AERMOD-HBP. As noted, EPA Region 6 proposed approval and obtained 
concurrence from the Model Clearinghouse for the use of the alternative 
model for this specific application. TCEQ modeled 42 different 
scenarios representing the range of operations, emissions, and 
dispersion that could occur, incorporating the Agreed Order's required 
emission limits. These 42 modeled scenarios had maximum ambient air 
modeled DVs ranging from 40 ppb to 73.6 ppb (104.8 [micro]g/m\3\ to 
192.8 [micro]g/m\3\) that all demonstrated attainment of the 1-hour 
SO2 NAAQS, without accounting for the possible excused non-
compliant emissions periods under the force majeure provision.\43\
---------------------------------------------------------------------------

    \43\ TSD pages 24-26.
---------------------------------------------------------------------------

    As part of EPA's modeling review, EPA modeled the two scenarios 
that resulted in the highest maximum DV of 73.6 ppb using the AERMOD-
HBP alternative model (based on AERMOD v.21112), and the results 
duplicated TCEQ's results with the same maximum modeled design values. 
The only differences between EPA's model runs and TCEQ's model runs for 
these two scenarios were that EPA modeled all of the receptors in one 
AERMOD run using a single CPU processor, and EPA relied on AERMOD to 
generate the maximum DVs with inclusion of the background 
concentrations instead of all of the post-processing steps that TCEQ 
performed. TCEQ modified a prior version of AERMOD that was the current 
version at the time TCEQ developed their SIP, version v.21112. Since 
TCEQ submitted their SIP, there have been two updates to AERMOD, and 
the most recent version is AERMOD v.23132. EPA ran these same two 
scenarios using the current version of AERMOD, v.23132, with the non-
regulatory alpha option HBP code (same as TCEQ's HBP code). The EPA has 
included the HBP code in AERMOD as an alpha option that is only for 
scientific testing and investigation, and the HBP code is not approved 
for any regulatory modeling. EPA did these model runs to see if the 
current version of AERMOD with the alternative HBP model code (not 
approved for use in regulatory modeling) would still result in the same 
maximum DV values obtained using the AERMOD HBP Alternative Model 
(AERMOD v.21112 with HBP code). This test is to verify that the code 
changes in the regulatory version of the model (non-HBP code) did not 
result in any model concentration changes. The more recent version of 
AERMOD with the non-regulatory HBP code included resulted in the same 
modeled results as TCEQ's AERMOD v.21112 with HBP code. This test 
confirms that the updates in the regulatory version of AERMOD between 
v.21112 and v.23132 do not result in any differences in the maximum 
design value when both AERMOD versions were run with the non-regulatory 
alternative model code HBP.
    With the exception of the HBP code that is an alternative model, 
EPA's review of the rest of TCEQ's modeling components indicated that 
TCEQ used the regulatory AERMOD preprocessors (AERMET, AERMINUTE, 
AERSURFACE, AERMAP, and Building Profile Input Program for PRIME 
(BPIPPRM) for building/structure downwash). TCEQ's submitted modeling, 
where applicable, used the regulatory default parameters, and the 
options and settings for AERMOD and the processors used are acceptable. 
TCEQ broke up the receptor grid into multiple runs and post-processed 
the results outside of AERMOD, which complicated review. The EPA 
reviewed model input and output files for all 42 modeling runs and 
modeled two of the scenarios that had the highest design value and 
confirmed that TCEQ's approach resulted in the same maximum modeled 
concentration results. For more detailed information, explanation, and 
analysis of TCEQ's modeling please see the following documents included 
in this docket: TSD, AERMOD-HBP TSD, Model Clearing House memoranda.
    After reviewing Texas' attainment demonstration and conducting 
additional modeling runs, the EPA agrees that Texas' submittal and 
supplemental materials, along with the Agreed Order (February 14, 2022) 
limits, constitute an attainment plan that would strengthen the SIP and 
sufficiently reduce emissions to meet the NAAQS in the Rusk-Panola 
area, but for the force majeure provision. However, due to the untimely 
compliance date for aspects of the attainment plan and the impacts of 
the force majeure provision of the Agreed Order on all of the Agreed 
Order's emission limits for the Martin Lake facility, Texas' attainment 
plan is insufficient to fully provide for attainment in the Rusk-Panola 
area or fully meet the requirements of CAA sections 110, 172, 191 and 
192. EPA therefore proposes to issue a limited approval and limited 
disapproval for this attainment plan SIP revision. See section III. 
Limited Approval/Limited Disapproval for additional discussion. We 
therefore propose to determine that, absent the force majeure 
provision, Texas' plan would provide for attaining air quality under 
the 2010 1-hour primary SO2 NAAQS in the Rusk-Panola 
nonattainment area.

VI. Review of Other Plan Requirements

    Section VI includes EPA's review of the following SIP elements: 
Emissions inventory, RACM and RACT, NSR, RFP, contingency measures, and 
conformity. EPA proposes that the SIP adequately satisfies the 
requirements for a baseline emissions inventory and nonattainment NSR, 
but due to the presence of the force majeure provision affecting the 
enforceability of the limits relied upon in the attainment 
demonstration, cannot otherwise meet the requirements of CAA sections 
110, 172, 191 and 192, particularly for RACM/RACT, RFP, emissions 
limits necessary to provide for attainment, and contingency measures.

A. Emissions Inventory

    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

[[Page 63130]]

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. A nonattainment SIP 
must include a comprehensive, accurate, and current inventory of actual 
emissions from all sources of SO2 in the 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). In its 
submittal, Texas included a current emissions inventory for the Rusk-
Panola area covering the 2017-2022 period, which can be found below at 
table 3.
    The State of Texas compiles a statewide emissions inventory for 
stationary sources in accordance with Texas regulations at 30 Texas 
Administrative Code (TAC) Sec.  101.10, CAA requirements, and EPA 
guidance. The submitted data is then reviewed for quality assurance 
purposes and stored in the State of Texas Air Reporting System (STARS) 
database. In its submittal, Texas confirmed that stationary point 
sources (i.e., Martin Lake) comprised over 99% of the SO2 
emissions in the Rusk-Panola area. Texas determined the forecasted 2022 
emissions for Martin Lake through historical point source heat input 
and a future year emissions limit that accounts for enforceable 
emissions reductions as required in the Agreed Order. According to the 
2014 SO2 Guidance, nearby sources outside the NAA (Pirkey) 
should also be included in the emissions inventory.
    TCEQ chose the year 2017 as the base year for its analyses as the 
most complete and representative record of annual SO2 
emissions because (1) it was the most recent periodic inventory year 
available and (2) it was also the year that the EPA designated the 
Rusk-Panola area as nonattainment for the 2010 SO2 NAAQS.
    The 2017 baseline area source emissions inventories were developed 
in accordance with the requirements of the Air Emissions Reporting 
Requirements (AERR) rule and developed using EPA-generated EIs, TCEQ-
contracted projects, TCEQ staff projects, and 2014 EIs by applying 
growth factors derived from different sources.\44\ TCEQ also developed 
non-road and on-road mobile source emissions inventories by using EPA's 
mobile source emissions models, Texas-specific utility of the EPA 
mobile source models, and EPA-approved methods and guidance.
---------------------------------------------------------------------------

    \44\ Eastern Research Group (ERG) study data, the Economy and 
Consumer Credit Analytics website (https://www.economy.com/default.asp), and the United States Energy Information 
Administration's Annual Energy Outlook publication.
---------------------------------------------------------------------------

    A summary of the State's submitted emissions inventory is provided 
in the following table:
---------------------------------------------------------------------------

    \45\ AEP Pirkey Power Plant was retired in Spring of 2023.

                 Table 3-1--Rusk-Panola Nonattainment Area SO2 Emissions in Tons per Year (TPY)
----------------------------------------------------------------------------------------------------------------
                                                                                                   Agreed order
                                               2017 Base       2018         2019         2022        federally
               Source category                    year       Reported     Reported    Attainment    enforceable
                                                reported    emissions    emissions       year         maximum
                                               emissions                              emissions      emissions
----------------------------------------------------------------------------------------------------------------
Point--Martin Lake..........................    36,441.46    56,198.55    46,549.50    22,269.31       32,736.76
Non-point...................................         0.31          N/A          N/A         0.43             N/A
On-road Mobile..............................         0.14          N/A          N/A         0.14             N/A
Non-road Mobile.............................         0.02          N/A          N/A         0.02             N/A
                                             -------------------------------------------------------------------
    Total...................................    36,441.93    56,198.55    46,549.50    22,269.90       32,736.76
----------------------------------------------------------------------------------------------------------------


               Table 3-2--AEP Pirkey Power Plant SO2 EI Annual and Permitted Emissions in TPY \45\
----------------------------------------------------------------------------------------------------------------
                                                                                          2022
                                                2017          2017          2017       Attainment     Permitted
                  Source                      Reported      Reported      Reported        year        emissions
                                              emissions     emissions     emissions     emissions
----------------------------------------------------------------------------------------------------------------
Point--AEP Pirkey.........................     3,959.80      5,084.80      3,073.00      4,039.20     35,820.00
----------------------------------------------------------------------------------------------------------------

    The EPA agrees that the State's emissions inventories for point, 
nonpoint, and mobile sources are appropriate because they have been 
accumulated and reported in accordance with established methods and 
criteria. EPA proposes that the base year emissions inventory is 
representative and satisfies the EI requirement, however, EPA cannot 
fully approve the future year emission inventory due to enforceability 
concerns arising from the force majeure provision included in the 
Agreed Order.

B. Reasonably Available Control Measures and Reasonably Available 
Control Technology (RACM/RACT)

    Section 172(c)(1) of the CAA requires states to adopt and submit 
all RACM, including RACT, as needed to attain the standards as 
expeditiously as practicable. Section 172(c)(6) requires the SIP to 
contain enforceable emission limits and control measures necessary to 
provide for timely attainment of the standard. The plan relies on 
ambient SO2 concentration reductions achieved by 
implementation of the Agreed Order's control requirements and emissions 
limits at Martin Lake. Martin Lake plans to implement SO2 
emission limits (lb/hr and lb/MMBtu) for the three EGF boilers.
    The control strategy at Martin Lake incorporates pre-combustion and 
post- combustion controls for the three EGF boilers and sets 
SO2 emission limits for the two auxiliary boilers. The EGF 
boilers will be limited to burning subbituminous coal, No. 2 fuel oil, 
and natural gas during operations and additionally have a combined cap 
on their firing rate (MMBtu/hr). Martin Lake intends for the 
subbituminous coal to be the primary fuel burned, which is lower in 
sulfur content compared to the lignite and lignite-blended mix of coals 
historically used by the facility. TCEQ

[[Page 63131]]

additionally provides that the existing SO2 wet limestone 
scrubber system for the EGF boilers will be optimized to increase 
efficiency to meet the limits in the Agreed Order.
    The final emission limitations as included in the February 14, 
2022, Agreed Order are provided earlier in this document in section 
V.E., Emission Limitations. Texas has provided modeling which 
demonstrates that these measures for Martin Lake provide for timely 
attainment and meet the RACM and RACT requirements, without accounting 
for excused emissions not in compliance with the limits during force 
majeure periods. The EPA proposes that, but for the presence of the 
force majeure provision, the state would satisfy the requirements in 
section 172(c)(1) to adopt and submit all RACM, including RACT, as 
needed to attain the standard as expeditiously as practicable and in 
section 172(c)(6) to include emission limits as necessary to attain. 
However, due to the presence of the force majeure provision, at this 
time EPA can only propose a limited approval of the emission limits for 
SIP strengthening purposes.

C. New Source Review (NSR)

    In its submittal, TCEQ provided a certification statement that 
Texas already has EPA-approved rules that address nonattainment NSR 
requirements. EPA initially approved Texas' nonattainment NSR 
regulations for SO2 on November 27, 1995 (60 FR 49781). TCEQ 
determined that because previously approved revisions to the Texas SIP 
already includes 30 TAC section 116.12 (Nonattainment and Prevention of 
Significant Deterioration Review Definitions) and 30 TAC section 
116.151 (New Major Source or Major Modification in Nonattainment Area 
Other Than Ozone), Texas has satisfied the nonattainment NSR SIP 
requirements for the Rusk-Panola nonattainment area. Further, TCEQ 
already certified that Texas has EPA-approved rules that cover 
nonattainment NSR requirements with the timely-submitted 2010 
SO2 NAAQS Infrastructure and Transport SIP Revision. 
Therefore, EPA concludes that the SIP satisfies the CAA's NSR 
requirements.

D. Reasonable Further Progress (RFP)

    Section 171(1) of the CAA defines RFP as ``such annual incremental 
reductions in emissions of the relevant air pollutant as are required 
by [part D] or may reasonably be required by the [EPA] for the purpose 
of ensuring attainment of the applicable [NAAQS] by the applicable 
attainment date.'' For purposes of SO2, the EPA issued 
guidance prescribing how states could satisfy this requirement when 
developing their nonattainment SIPs.\46\ Since pollutants like 
SO2 usually have a limited number of sources affecting areas 
of air quality that are relatively well defined, and emissions control 
measures for such sources generally provide significant and immediate 
improvements in air quality, there is usually a single ``step'' between 
pre-control nonattainment and post-control attainment. Therefore, due 
to the discernible relationship between emissions and air quality, EPA 
interprets RFP in the SO2 context as ``adherence to an 
ambitious compliance schedule'' which ``ensures that affected sources 
implement appropriate control measures as expeditiously as 
practicable'' to ensure attainment by the applicable attainment date. 
See General Preamble, 74 FR 13498, 13547 (April l6, 1992).
---------------------------------------------------------------------------

    \46\ See ``Guidance for 1-Hour SO2 Nonattainment Area 
SIP Submissions'', U.S. Environmental Protection Agency, Office of 
Air Quality Planning and Standards, April 23, 2014, which can be 
accessed at: https://www.epa.gov/sites/production/files/2016-06/documents/20140423guidance_nonattainment_sip.pdf.
---------------------------------------------------------------------------

    In its submittal, TCEQ provided its rationale for concluding that 
the plan met the requirement for RFP in accordance with EPA guidance. 
According to TCEQ, the Rusk-Panola area contains a single source with 
well-defined emissions, such that emissions controls for this source 
should result in a ``swift and dramatic improvement in air quality.'' 
TCEQ further explained that enforceable emission limitations would be 
implemented for the source (Martin Lake) in this area and, therefore, 
this compliance schedule fulfills the RFP requirement for the Rusk-
Panola area. In its submittal, TCEQ sets two compliance deadlines for 
Vistra to meet its emissions limits from the Agreed Order. For limits 
expressed in lbs/hr, compliance is required no later than the date by 
which Texas is required to demonstrate compliance with the 2010 
SO2 NAAQS, which would be the area's attainment date of 
January 12, 2022. For limits expressed in lbs/MMBtu, compliance is 
required by July 11, 2022. EPA has determined that once control 
requirements and emissions limits have been implemented, these measures 
will provide for attainment in the area. This meets the requirement for 
RFP for the Rusk-Panola area. EPA proposes a limited approval/limited 
disapproval for this SIP submission in part because the compliance date 
is several months after the attainment date for this area. EPA proposes 
that, but for the presence of the force majeure provision, the SIP 
submittal would provide for RFP. However, due to the force majeure 
provision and untimely compliance date, EPA proposes a limited approval 
and limited disapproval of the SIP limits Texas relied upon for its RFP 
demonstration for SIP strengthening purposes and to apply federally 
enforceable limits to the area as expeditiously as possible.

E. Contingency Measures

    As discussed in our 2014 SO2 Guidance, section 172(c)(9) 
of the CAA defines contingency measures as such measures in a SIP that 
are to be implemented in the event that an area fails to make RFP, or 
fails to attain the NAAQS, by the applicable attainment date. 
Contingency measures are to become effective without further action by 
the state or the EPA, where the area has failed to (1) achieve RFP or 
(2) attain the NAAQS by the statutory attainment date for the affected 
area. These control measures are to consist of other available control 
measures that are not included in the control strategy for the 
nonattainment area SIP. EPA guidance describes special features of 
SO2 planning that influence the suitability of alternative 
means of addressing the requirement in section 172(c)(9) for 
contingency measures. Because SO2 control measures are by 
definition based on what is directly and quantifiably necessary for 
emissions controls, any violations of the NAAQS are likely related to 
source violations of a source's permit or agreed order terms. 
Therefore, an appropriate means of satisfying this requirement for 
SO2 is for the state to have a comprehensive enforcement 
program that identifies sources of violations of the SO2 
NAAQS and to undertake an aggressive follow-up for compliance and 
enforcement.
    For its contingency plan, Texas stated that TCEQ's comprehensive 
program to (1) identify sources of violations of the NAAQS is satisfied 
through its monitoring network and (2) follow-up for compliance and 
enforcement is satisfied through TCEQ's enforcement programs authorized 
under the Texas Water Code and Texas Health and Safety Code. If EPA 
makes the determination that that the Rusk-Panola Area has failed to 
attain, TCEQ will notify Martin Lake and upon notification the owner or 
operator will be required to do a full system audit of all 
SO2 emissions from Martin Lake within 90 days. The owner or 
operator of Martin Lake must conduct a root cause analysis for the 
reason why the area failed to attain and recommend provisional 
SO2 emission controls as

[[Page 63132]]

necessary. Additionally, Texas has the authority to issue orders 
pursuant to the Texas Clean Air Act and Texas Health and Safety Code 
for the purpose of supporting attainment and maintenance of the 2010 
SO2 NAAQS. EPA believes that this approach generally 
continues to be a valid approach for the implementation of contingency 
measures to address the 2010 SO2 NAAQS. However, as 
previously discussed, the presence of the force majeure provision 
undermines the enforceability of the emission limits in the SIP 
submission, and consequently undermines the utility of Texas' 
enforcement authority to address periods of non-compliance with the 
limits. Therefore, EPA is proposing that but for the presence of the 
force majeure provision, Texas' plan would adequately provide for 
contingency measures as required by the CAA. As a result, EPA can only 
propose limited approval of the limits upon which the SIP relies for 
SIP strengthening purposes.

F. Conformity

    Generally, as set forth in section 176(c) of the CAA, conformity 
requires that actions by federal agencies do not cause new air quality 
violations, worsen existing violations, or delay timely attainment of 
the relevant NAAQS. General conformity applies to federal actions, 
other than certain highway and transportation projects, if the action 
takes place in a nonattainment area or maintenance area (i.e., an area 
which submitted a maintenance plan that meets the requirements of 
section 175A of the CAA and has been redesignated to attainment) for 
ozone, particulate matter, nitrogen dioxide, carbon monoxide, lead, or 
SO2. EPA's General Conformity Rule (40 CFR 93.150 to 93.165) 
establishes the criteria and procedures for determining if a federal 
action conforms to the SIP. With respect to the 2010 SO2 
NAAQS, federal agencies are expected to continue to estimate emissions 
for conformity analyses in the same manner as they estimated emissions 
for conformity analyses under the previous SO2 NAAQS. EPA's 
General Conformity Rule includes the basic requirement that a federal 
agency's general conformity analysis be based on the latest and most 
accurate emission estimation techniques available (40 CFR 93.159(b)). 
When updated and improved emissions estimation techniques become 
available, EPA expects the federal agency to use these techniques. EPA 
finds that the Rusk-Panola SO2 Attainment Plan SIP Revision 
submission meets these conformity requirements.
    Transportation conformity determinations are not required in 
SO2 nonattainment and maintenance areas. EPA concluded in 
its 1993 transportation conformity rule that highway and transit 
vehicles are not significant sources of SO2. Therefore, 
transportation plans, transportation improvement programs and projects 
are presumed to conform to applicable implementation plans for 
SO2. (See 58 FR 3776, January 11, 1993.)

VII. Proposed Action

    For Texas' February 28, 2022 SIP revision submittal, we are 
proposing a limited approval which will incorporate all of the 
submissions requirements, including the emission limits and associated 
control requirements such as monitoring, recordkeeping and reporting 
requirements into the State Implementation Plan. We have determined 
that the revision provides for emissions controls and limits that 
strengthen the existing EPA-approved Texas SIP and would satisfy the 
applicable CAA requirements of sections 110, 172, 191 and 192. We are 
proposing limited disapproval due to the enforceability deficiency 
caused by the force majeure provision in the SIP and the timing of the 
compliance date for the emissions limitations several months after the 
attainment date for this nonattainment area, as is necessary under the 
CAA and associated regulations. The State has demonstrated that its 
current Nonattainment NSR program covers this NAAQS; therefore, no 
revision to the SIP is required for the Nonattainment NSR element. 
Under CAA section 179(c)(1), EPA also proposes to determine that the 
Rusk-Panola SO2 NAA failed to attain the 2010 1-hour 
SO2 standard by the applicable attainment date of January 
12, 2022 based on monitored data from 2019-2021.

VIII. Incorporation by Reference

    In this action, we are proposing to include in a final rule 
regulatory text that includes incorporation by reference. In accordance 
with the requirements of 1 CFR 51.5, we are proposing to incorporate by 
reference revisions to the Texas source-specific requirements for 
Vistra's Martin Lake Electrical Station (Martin Lake) as described in 
section VII of this preamble, Proposed Action. These source-specific 
requirements for Martin Lake include SO2 emission limits and 
fuel limitations for the facility as well as other monitoring, 
recordkeeping, and reporting requirements. We have made, and will 
continue to make, these documents generally available electronically 
through www.regulations.gov (please contact the person identified in 
the FOR FURTHER INFORMATION CONTACT section of this preamble for more 
information).

IX. Environmental Justice Considerations

    Information on Executive Order 12898 (Federal Actions To Address 
Environmental Justice in Minority Populations and Low-Income 
Populations, 59 FR 7629, February 16, 1994), and how EPA defines 
environmental justice (EJ) can be found in the section titled ``VII. 
Statutory and Executive Order Reviews,'' in this proposed rulemaking. 
EPA is providing additional analysis of environmental justice 
associated with this action. The results of this analysis are being 
provided for informational and transparency purposes only, not as a 
basis of our proposed action.
    The EPA conducted a screening analysis using EJSCREEN, an 
environmental justice mapping and screening tool that provides EPA with 
a nationally consistent dataset and approach for combining various 
environmental and demographic indicators.\47\ The EJSCREEN tool 
presents these indicators at a Census block group (CBG) level or a 
larger user-specified ``buffer'' area that covers multiple CBGs.\48\ An 
individual CBG is a cluster of contiguous blocks within the same census 
tract and generally contains between 600 and 3,000 people. EJSCREEN is 
not a tool for performing in-depth risk analysis, but is instead a 
screening tool that provides an initial representation of indicators 
related to environmental justice and is subject to uncertainty in some 
underlying data (e.g., some environmental indicators are based on 
monitoring data which are not uniformly available; others are based on 
self-reported data).\49\ To help mitigate this uncertainty, we have 
summarized EJSCREEN data within larger ``buffer'' areas covering 
multiple block groups and representing the average resident within the 
buffer area surrounding Martin Lake. We present EJSCREEN environmental 
indicators to help screen

[[Page 63133]]

for locations where residents may experience a higher overall pollution 
burden than would be expected for a block group with the same total 
population. These indicators of overall pollution burden include 
estimates of ambient particulate matter (PM2.5) and ozone 
concentration, a score for traffic proximity and volume, percentage of 
pre-1960 housing units (lead paint indicator), and scores for proximity 
to Superfund sites, risk management plan (RMP) sites, and hazardous 
waste facilities.\50\ EJSCREEN also provides information on demographic 
indicators, including percent low-income, communities of color, 
linguistic isolation, and less than high school education.
---------------------------------------------------------------------------

    \47\ The EJSCREEN tool is available at https://www.epa.gov/ejscreen.
    \48\ See https://www.census.gov/programs-surveys/geography/about/glossary.html.
    \49\ In addition, EJSCREEN relies on the five-year block group 
estimates from the U.S. Census American Community Survey. The 
advantage of using five-year over single-year estimates is increased 
statistical reliability of the data (i.e., lower sampling error), 
particularly for small geographic areas and population groups. For 
more information, see https://www.census.gov/content/dam/Census/library/publications/2020/acs/acs_general_handbook_2020.pdf.
    \50\ For additional information on environmental indicators and 
proximity scores in EJSCREEN, see ``EJSCREEN Environmental Justice 
Mapping and Screening Tool: EJSCREEN Technical Documentation for 
Version 2.2,'' Chapter 3 (July 2023) at https://www.epa.gov/system/files/documents/2023-06/ejscreen-tech-doc-version-2-2.pdf.
---------------------------------------------------------------------------

    The EPA prepared an EJSCREEN report covering a buffer area of 
approximately a 6-mile radius around the Martin Lake facility. Table 4 
presents a summary of results from the EPA's screening-level analysis 
for Martin Lake compared to the U.S. as a whole. From that report, 
Martin Lake did not show EJ indices greater than the 80th percentiles. 
The full, detailed EJSCREEN report is provided in the docket for this 
rulemaking.

           Table 4--EJSCREEN Analysis Summary for Martin Lake
------------------------------------------------------------------------
                                EJSCREEN values for buffer area (radius)
                                for Martin Lake and the U.S. (percentile
                                      within U.S. where indicated)
          Variables           ------------------------------------------
                                 Martin Lake
                                 (Rusk-Panola             U.S.
                                Area, 6 miles)
------------------------------------------------------------------------
Pollution Burden Indicators:
    Particulate matter         9.57 [micro]g/   8.67 [micro]g/m\3\ (--).
     (PM2.5), annual average.   m\3\ (77th
                                %ile).
Ozone, summer seasonal         40.1 ppb (32nd   42.5 ppb (--).
 average of daily 8-hour max.   %ile).
    Traffic proximity and      0.72 (2nd %ile)  760 (--).
     volume score *.
    Lead paint (percentage     0.12% (37th      0.27% (--).
     pre-1960 housing).         %ile).
    Superfund proximity score  0.048 (42nd      0.13 (--).
     *.                         %ile).
    RMP proximity score *....  0.17 (32nd       0.77 (--).
                                %ile).
    Hazardous waste proximity  0.059 (11th      2.2 (--).
     score *.                   %ile).
Demographic Indicators:
    People of color            31% (52nd %ile)  40% (--).
     population.
    Low-income population....  25% (46th %ile)  30% (--).
    Linguistically isolated    2% (62nd %ile).  5% (--).
     population.
    Population with less than  13% (65th %ile)  12% (--).
     high school education.
    Population under 5 years   9% (82nd %ile).  6%.
     of age.
    Population over 64 years   14% (44th %ile)  16% (--).
     of age.
------------------------------------------------------------------------
* The traffic proximity and volume indicator is a score calculated by
  daily traffic count divided by distance in meters to the road. The
  Superfund proximity, RMP proximity, and hazardous waste proximity
  indicators are all scores calculated by site or facility counts
  divided by distance in kilometers.

    This proposed action is proposing limited approval and limited 
disapproval of Texas' February 28, 2022, SIP submittal to strengthen 
the SIP requirements for the Rusk-Panola NAA for the 2010 1-hour 
primary SO2 NAAQS. Information on SO2 and its 
relationship to negative health impacts can be found at final Federal 
Register notice titled ``Primary National Ambient Air Quality Standard 
for Sulfur Dioxide'' (75 FR 35520, June 22, 2010).\51\ We expect that 
this action and resulting emissions reductions will generally be 
neutral or contribute to reduced environmental and health impacts on 
all populations in the Rusk-Panola NAA, including people of color and 
low-income populations in the Rusk-Panola nonattainment area. At a 
minimum, this action would not worsen any existing air quality and is 
expected to help the area make progress towards meeting requirements to 
attain air quality standards. Further, there is no information in the 
record indicating that this action is expected to have 
disproportionately high or adverse human health or environmental 
effects on a particular group of people.
---------------------------------------------------------------------------

    \51\ See https://www.federalregister.gov/d/2010-13947.
---------------------------------------------------------------------------

X. Statutory and Executive Order Reviews

    Under the Clean Air Act, the Administrator is required to approve a 
SIP submission that complies with the provisions of the Clean Air Act 
and applicable Federal regulations. 42 U.S.C. 7410(k); 40 CFR 52.02(a). 
Thus, in reviewing SIP submissions, EPA's role is to approve state 
choices, provided that they meet the criteria of the Clean Air Act. 
Accordingly, this proposed action is proposing a limited approval and 
limited disapproval of state law as meeting Federal requirements and 
does not impose additional requirements beyond those imposed by state 
law. For that reason, this action:
     Is not a significant regulatory action subject to review 
by the Office of Management and Budget under Executive Orders 12866 (58 
FR 51735, October 4, 1993) and 14094 (88 FR 21879, April 11, 2023);
     Does not impose an information collection burden under the 
provisions of the Paperwork Reduction Act (44 U.S.C. 3501 et seq.);
     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.);
     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);
     Does not have federalism implications as specified in 
Executive Order 13132 (64 FR 43255, August 10, 1999);
     Is not subject to Executive Order 13045 (62 FR 19885, 
April 23, 1997) because it approves a state program;
     Is not a significant regulatory action subject to 
Executive Order 13211 (66 FR 28355, May 22, 2001); and

[[Page 63134]]

     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 Clean Air Act.
     Executive Order 12898 (Federal Actions To Address 
Environmental Justice in Minority Populations and Low-Income 
Populations, 59 FR 7629, February 16, 1994) directs Federal agencies to 
identify and address ``disproportionately high and adverse human health 
or environmental effects'' of their actions on minority populations and 
low-income populations to the greatest extent practicable and permitted 
by law. EPA defines environmental justice (EJ) as ``the fair treatment 
and meaningful involvement of all people regardless of race, color, 
national origin, or income with respect to the development, 
implementation, and enforcement of environmental laws, regulations, and 
policies.'' EPA further defines the term fair treatment to mean that 
``no group of people should bear a disproportionate burden of 
environmental harms and risks, including those resulting from the 
negative environmental consequences of industrial, governmental, and 
commercial operations or programs and policies.''
    TCEQ did not evaluate environmental justice considerations as part 
of its SIP submittal; the CAA and applicable implementing regulations 
neither prohibit nor require such an evaluation. EPA performed an 
environmental justice analysis, as is described above in the section 
titled, ``Environmental Justice Considerations.'' The analysis was done 
for the purpose of providing additional context and information about 
this rulemaking to the public, not as a basis of the action. Due to the 
nature of the action being taken here, this action is expected to have 
a neutral to positive impact on the air quality of the affected area. 
In addition, there is no information in the record upon which this 
decision is based inconsistent with the stated goal of E.O. 12898 of 
achieving environmental justice for people of color, low-income 
populations, and Indigenous peoples.
    In addition, the SIP is not approved to apply on any Indian 
reservation land or in any other area where EPA or an Indian tribe has 
demonstrated that a tribe has jurisdiction. In those areas of Indian 
country, the proposed 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.

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

    Dated: July 29, 2024.
Earthea Nance,
Regional Administrator, Region 6.
[FR Doc. 2024-17053 Filed 8-1-24; 8:45 am]
BILLING CODE 6560-50-P