38630 Federal Register / Vol. 86, No. 138 / Thursday, July 22, 2021 / Proposed Rules 

consultation with tribal governments and 

discussions with the state of Oklahoma as part of 

this review. EPA also notes that the October 1, 2020 

approval is the subject of a pending challenge in 

federal court. (Pawnee v. Regan, No. 20–9635 (10th 

Cir.)). Pending completion of EPA’s review, EPA is 

proceeding with this proposed action in accordance 

with the October 1, 2020 approval. EPA’s final 

action on the approved revisions to the Oklahoma 

SIP that include revisions to OAC Title 252 Chapter 

100 Subchapter 39 (OAC 252:100–39) Sections 4, 

16, 40, and 41 will address the scope of the state’s 

program with respect to Indian country, and may 

make any appropriate adjustments, based on the 

status of our review at that time. If EPA’s final 

action on Oklahoma’s SIP is taken before our review 

of the SAFETEA approval is complete, EPA may 

make further changes to the approval of Oklahoma’s 

program to reflect the outcome of the SAFETEA 

review. 

IV. Proposed Action 

In this action, we are proposing to 

approve revisions to OAC 252:100–39, 

Emission of VOCs in Nonattainment 

Areas and Former Nonattainment Areas, 

in Section 4 (Exemptions), Section 16 

(Petroleum refinery process unit 

turnaround), Section 40 (Cutback 

asphalt), and Section 41 (Storage, 

loading and transport/delivery of VOCs) 

as submitted to us by a letter dated May 

20, 2020 (Submittal). The submittal 

covers Oklahoma’s 2019 regulatory 

update. We are proposing to approve 

these revisions in accordance with 

section 110 of the Act. 

V. 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 Oklahoma regulations, 

as described in the Proposed Action 

section above. 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). 

VI. Statutory and Executive Order 

Reviews 

Under the CAA, the Administrator is 

required to approve a SIP submission 

that complies with the provisions of the 

Act and applicable Federal regulations. 

42 U.S.C. 7410(k); 40 CFR 52.02(a). 

Thus, in reviewing SIP submissions, the 

EPA’s role is to approve state choices, 

provided that they meet the criteria of 

the CAA. Accordingly, this action 

merely proposes to approve state law as 

meeting Federal requirements and does 

not impose additional requirements 

beyond those imposed by state law. For 

that reason, this action: 

• 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 13563 (76 FR 3821, 

January 21, 2011); 

• Is not an Executive Order 13771 (82 

FR 9339, February 2, 2017) regulatory 

action because SIP approvals are 

exempted under Executive Order 12866; 

• 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 an economically significant 

regulatory action based on health or 

safety risks subject to Executive Order 

13045 (62 FR 19885, April 23, 1997); 

• Is not a significant regulatory action 

subject to Executive Order 13211 (66 FR 

28355, May 22, 2001); 

• Is not subject to requirements of 

section 12(d) of the National 

Technology Transfer and Advancement 

Act of 1995 (15 U.S.C. 272 note) because 

application of those requirements would 

be inconsistent with the CAA; and 

• Does not provide EPA with the 

discretionary authority to address, as 

appropriate, disproportionate human 

health or environmental effects, using 

practicable and legally permissible 

methods, under Executive Order 12898 

(59 FR 7629, February 16, 1994). 

This proposal to approve revisions to 

the Oklahoma SIP that include 

amendments to OAC Title 252 Chapter 

100 Subchapter 39 (OAC 252:100–39) 

Sections 4, 16, 40, and 41 will apply, if 

finalized as proposed, to certain areas of 

Indian country in Tulsa and Oklahoma 

counties as discussed in the preamble, 

and therefore has tribal implications as 

specified in E.O. 13175 (65 FR 67249, 

November 9, 2000). However, this 

action will neither impose substantial 

direct compliance costs on federally 

recognized tribal governments, nor 

preempt tribal law. This action will not 

impose substantial direct compliance 

costs on federally recognized tribal 

governments because no actions will be 

required of tribal governments. This 

action will also not preempt tribal law 

as no Oklahoma tribe implements a 

regulatory program under the CAA, and 

thus does not have applicable or related 

tribal laws. Consistent with the EPA 

Policy on Consultation and 

Coordination with Indian Tribes (May 4, 

2011), the EPA has offered consultation 

to tribal governments that may be 

affected by this action. 

List of Subjects in 40 CFR Part 52 

Environmental protection, Air 

pollution control, Incorporation by 

reference, Intergovernmental relations, 

Reporting and recordkeeping 

requirements, Volatile organic 

compounds. 

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

Dated: July 15, 2021. 

David Gray, 

Acting Regional Administrator, Region 6. 

[FR Doc. 2021–15396 Filed 7–21–21; 8:45 am] 

BILLING CODE 6560–50–P 

ENVIRONMENTAL PROTECTION 

AGENCY 

40 CFR Part 52 

[EPA–R06–OAR–2021–0032; FRL–8688–01– 

R6] 

Air Plan Approval; Oklahoma; 

Interstate Visibility Transport 

AGENCY: Environmental Protection 

Agency (EPA). 

ACTION: Proposed rule. 

SUMMARY: Pursuant to the Federal Clean 

Air Act (CAA or the Act), the 

Environmental Protection Agency (EPA) 

is proposing to approve elements of a 

State Implementation Plan (SIP) 

submission from the State of Oklahoma 

for the 2015 Ozone National Ambient 

Air Quality Standard (NAAQS), and 

proposing to disapprove elements of 

two SIP submissions for the 2010 sulfur 

dioxide (SO2) and the 2012 fine 

particulate matter (PM2.5) NAAQS. 

These infrastructure SIP (i-SIP) 

submissions address how the existing 

SIP provides for implementation, 

maintenance, and enforcement of these 

NAAQS. The i-SIP requirements are to 

ensure that the Oklahoma SIP is 

adequate to meet the state’s 

responsibilities under the CAA for these 

NAAQS. Specifically, this proposed rule 

addresses the interstate visibility 

transport requirements of the i-SIP for 

the 2010 SO2, 2012 PM2.5, and 2015 

Ozone NAAQS under CAA section 

110(a)(2)(D)(i)(II). We are also proposing 

to find that the deficiencies in the 

Oklahoma SIP that form the basis of our 

proposed disapproval of the interstate 

visibility transport portions of the 

Oklahoma i-SIP submissions for the 

2010 SO2 and 2012 PM2.5 NAAQS are 


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1Stephen D. Page, Director, Office of Air Quality 

Planning and Standards. ‘‘Guidance on 

Infrastructure State Implementation Plan (SIP) 

Elements under Clean Air Act Section 110(a)(1) and 

110(a)(2).’’ Memorandum to EPA Air Division 

Directors, Regions 1 through 10, September 13, 

2013 (hereinafter ‘‘2013 i-SIP Guidance’’). 

2 78 FR 3085 (Jan. 15, 2013). 

3 81 FR 83184 (November 21, 2016). 

4 82 FR 27121 (June 14, 2017). 

5 75 FR 35520 (June 22, 2010). 

6 81 FR 83184. 

remedied by the existing Federal 

Implementation Plan (FIP) in place for 

the Oklahoma Regional Haze program, 

and that no further federal action is 

required to address the proposed 

disapproval. 

DATES: Comments must be received on 

or before August 23, 2021. 

ADDRESSES: Submit your comments, 

identified by Docket No. EPA–R06– 

OAR–2021–0032, at https://

www.regulations.gov or via email to 

medina.dayana@epa.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 Dayana Medina, 214–665–7341, 

medina.dayana@epa.gov. 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 due to docket file size 

restrictions or content (e.g., CBI). 

FOR FURTHER INFORMATION CONTACT: 

Dayana Medina, EPA Region 6 Office, 

Regional Haze and SO2 Section, 214– 

665–7341, medina.dayana@epa.gov. 

Out of an abundance of caution for 

members of the public and our staff, the 

EPA Region 6 office will be closed to the 

public to reduce the risk of transmitting 

COVID–19. We encourage the public to 

submit comments via https://

www.regulations.gov, as there will be a 

delay in processing mail and no courier 

or hand deliveries will be accepted. 

Please call or email the contact listed 

above if you need alternative access to 

material indexed but not provided in 

the docket. 

SUPPLEMENTARY INFORMATION: 

Throughout this document, ‘‘we,’’ ‘‘us,’’ 

and ‘‘our’’ means the EPA. 

I. Background 

Whenever a new or revised NAAQS is 

promulgated, the Clean Air Act (CAA) 

requires states to submit a plan for the 

implementation, maintenance, and 

enforcement of the standard, commonly 

referred to as infrastructure 

requirements. Section 110(a)(2) lists 

specific requirements that infrastructure 

SIPs, or i-SIPs, must include to 

adequately address such new or revised 

NAAQS, as applicable. Section 

110(a)(2)(D)(i) includes four distinct 

elements related to interstate transport 

of air pollution, commonly referred to as 

prongs, that must be addressed in i-SIP 

submissions. The first two prongs are 

codified in section 110(a)(2)(D)(i)(I) and 

the third and fourth prongs are codified 

in section 110(a)(2)(D)(i)(II). These four 

prongs prohibit any source or type of 

emission activities in one state from: 

• Contributing significantly to 

nonattainment of the NAAQS in another 

state (prong 1); 

• Interfering with maintenance of the 

NAAQS in another state (prong 2); 

• Interfering with measures that 

prevent significant deterioration of air 

quality in another state (prong 3); and 

• Interfering with measures that 

protect visibility in another state (prong 

4 or ‘‘visibility transport’’). 

We are only addressing the prong 4 

element in this proposal. In an effort to 

assist states in complying with the i-SIP 

requirements, EPA issued guidance in 

2013.1 In the 2013 i-SIP guidance, EPA 

discussed its interpretation of prong 4 

and its relationship to the Regional Haze 

program under CAA sections 169A and 

169B, which require each state to 

address its share of emission reductions 

needed to meet reasonable progress 

goals (RPGs) for surrounding Class I 

areas. EPA suggested two options states 

may have to demonstrate that the 

requirements of prong 4 are met. One 

way in which prong 4 may be satisfied 

for any relevant NAAQS is through 

confirmation in the state’s i-SIP 

submission that it has an approved 

regional haze SIP that fully meets the 

requirements of 40 CFR 51.308 or 

51.309. Alternatively, a state may 

demonstrate in its i-SIP submission that 

emissions within its jurisdiction do not 

interfere with other states’ plans to 

protect visibility. The demonstration 

should show that the state has sufficient 

measures that have been approved into 

its SIP to prevent emissions within its 

jurisdiction from interfering with the 

visibility protection plans of other 

states. 

A. Oklahoma’s Infrastructure SIP 

Submittals for 2010 SO2, 2012 PM2.5, 

and 2015 Ozone NAAQS 

EPA has regulated particulate matter 

(PM) since the first NAAQS for PM were 

published in 1971. (36 FR 8186 (April 

30, 1971)). Most recently, by notice 

dated January 15, 2013, following a 

periodic review of the NAAQS for 

PM2.5, EPA revised the primary annual 

PM2.5 NAAQS to 12.0 mg/m3 and 

retained the secondary annual PM2.5

standard of 15 mg/m3 as well as the 

primary and secondary 24-hour PM2.5

standards of 35 mg/m3 (2012 PM2.5

NAAQS).2 The primary NAAQS is 

designed to protect human health, and 

the secondary NAAQS is designed to 

protect the public welfare. On June 16, 

2016, the Oklahoma Secretary of Energy 

and Environment submitted a SIP 

revision to address most of the i-SIP 

elements for this revised 2012 PM2.5

NAAQS. On November 21, 2016, we 

proposed to approve all elements 

included in the 2012 PM2.5 i-SIP 

submission except for the 

110(a)(2)(D)(i)(II) prong 4 portion, which 

we proposed to disapprove.3 On June 

14, 2017, we took final action to 

approve all elements included in this 

i-SIP submission, but deferred taking 

final action on the 110(a)(2)(D)(i)(II) 

prong 4 portion.4 In this notice, we are 

once again proposing to disapprove the 

prong 4 visibility transport portion of 

the June 16, 2016 i-SIP submission for 

the 2012 PM2.5 NAAQS. 

On June 22, 2010, we revised the 

primary NAAQS for SO2 to establish a 

new 1-hour standard at a level of 75 

parts per billion (ppb), based on the 

3-year average of the annual 99th 

percentile of 1-hour daily maximum 

concentrations.5 On January 28, 2015, 

the Oklahoma Secretary of Energy and 

Environment submitted a SIP revision to 

address i-SIP elements for this revised 

NAAQS. On November 21, 2016, we 

proposed to disapprove the 

110(a)(2)(D)(i)(II) prong 4 portion of the 

2010 SO2 i-SIP submission, but we did 

not finalize this disapproval.6 In this 

notice, we are once again proposing to 

disapprove the prong 4 visibility 


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7 82 FR 65291 (Oct. 26, 2015). Additional 

information on the history of the NAAQS for ozone 

is available at https://www.epa.gov/ozonepollution/table-historical-ozone-national-ambientair-quality-standards-naaqs. 

8See 85 FR 17502 (March 30, 2020). 

9 76 FR 81728 (December 28, 2011). 

10 In a final rule published in the Federal Register 

on January 5, 2016, we disapproved Oklahoma’s 

2018 RPGs on the 20% least impaired and 20% 

most impaired days for the Wichita Mountains 

Class I area because Oklahoma did not adequately 

demonstrate that its RPGs provide for reasonable 

progress towards meeting the national visibility 

goal. Specifically, Oklahoma did not satisfy several 

of the requirements at section 51.308(d)(1) with 

regard to setting RPGs, including the requirement 

to adequately consult with other states that may 

reasonably be anticipated to cause or contribute to 

visibility impairment at the Wichita Mountains and 

the requirement to adequately justify RPGs that are 

less stringent than the uniform rate of progress 

(URP). However, that final rulemaking was 

challenged, and in December 2016, following the 

submittal of a request by the EPA for a voluntary 

remand of the parts of the rule under challenge, the 

Fifth Circuit Court of Appeals remanded the rule in 

its entirety without vacatur. Texas v. EPA, 829 F.3d 

405 (5th Cir. 2016). 

11 76 FR 81728. 

12 Id. 

13 79 FR 12944, 12954 (March 7, 2014). 

14EPA approved the NOX BART determinations 

for the AEP/PSO Northeastern Units 3 and 4 and 

all other subject-to-BART sources in Oklahoma in 

the December 28, 2011 final rule, but Oklahoma 

revised the EPA-approved NOX BART 

determinations for Northeastern Units 3 and 4 in 

the 2013 Oklahoma Regional Haze SIP Revision to 

require earlier installation and compliance with 

reduced NOX emission limits prior to the original 

SIP-imposed deadline. This is discussed in more 

detail in section III.C of this notice. 

15 79 FR at 12945. 

transport portion of the January 28, 2015 

i-SIP submission for the 2010 SO2

NAAQS. 

EPA has regulated ozone since 1971, 

when we published the first NAAQS for 

Photochemical Oxidants (36 FR 8186 

(April 30, 1971)). Most recently, 

following a periodic review of the 2008 

NAAQS for ozone, the EPA promulgated 

a revision to the ozone NAAQS in 2015 

lowering the level of both the primary 

and secondary standards to 0.070 parts 

per million.7 On October 25, 2018, the 

Oklahoma Secretary of Energy and 

Environment submitted a SIP revision to 

address i-SIP elements for this revised 

NAAQS. On March 30, 2020, we 

approved most infrastructure elements 

of the 2015 ozone i-SIP submission but 

deferred taking final action on the 

110(a)(2)(D)(i)(II) prong 4 portion.8

In this notice, we refer to each of 

these NAAQS by the year promulgated, 

e.g., ‘‘the 2008 ozone standard.’’ For 

more information on these standards, 

please visit https://www.epa.gov/ 

criteria-air-pollutants. 

B. Regional Haze and Visibility 

Transport in Oklahoma 

On February 17, 2010, Oklahoma 

submitted a regional haze SIP (the 2010 

Regional Haze SIP) to the EPA that 

included best available retrofit 

technology (BART) requirements for 

SO2, NOX, and PM for Oklahoma 

sources. On December 28, 2011, we took 

final action to partially approve and 

partially disapprove the 2010 Regional 

Haze SIP.9 In this final action, we 

disapproved Oklahoma’s SO2 BART 

determinations for the Oklahoma Gas 

and Electric (OG&E) Sooner Units 1 and 

2, the OG&E Muskogee Units 4 and 5, 

and the American Electric Power/Public 

Service Company of Oklahoma (AEP/ 

PSO) Northeastern Units 3 and 4 

because they do not comply with our 

regional haze regulations under 40 CFR 

51.308(e). We approved Oklahoma’s 

remaining SO2 BART determinations as 

well as all nitrogen oxide (NOX) and PM 

BART determinations. Additionally, we 

approved all remaining portions of the 

2010 Regional Haze SIP, with the 

exception of (1) the long-term strategy to 

the extent it relied on the BART 

emission limits that we disapproved 

and (2) Oklahoma’s 2018 RPGs on the 

20% least impaired and 20% most 

impaired days for the Wichita 

Mountains Class I area.10

In the December 28, 2011 final rule, 

we also evaluated whether Oklahoma’s 

SIP ensures that emissions from sources 

within Oklahoma do not interfere with 

the visibility programs of other states 

with respect to the 1997 8-hour Ozone 

NAAQS and the 1997 PM2.5 NAAQS. In 

developing their respective regional 

haze SIPs and reasonable progress goals 

(RPGs), the Central Regional Air 

Planning Association (CENRAP) states 

consulted with each other through 

CENRAP’s work groups. As a result of 

this process, the understanding was that 

each CENRAP state would take action to 

achieve the emissions reductions relied 

upon by other states in their reasonable 

progress demonstrations. CENRAP 

states consulted in the development of 

RPGs, using the products of the 

technical consultation process to codevelop their RPGs. In developing their 

visibility projections using 

photochemical grid modeling, CENRAP 

states assumed a certain level of 

emissions from sources within 

Oklahoma. The CENRAP modeling 

assumed SO2 reductions from the OG&E 

Sooner Units 1 and 2, the OG&E 

Muskogee Units 4 and 5, and the AEP/ 

PSO Northeastern Units 3 and 4, which 

Oklahoma did not secure when making 

its BART determinations for these 

sources and were thus not required by 

the 2010 Oklahoma Regional Haze SIP. 

Since this modeling was used by other 

states and Oklahoma in establishing 

their RPGs, we made the finding that the 

Oklahoma SIP does not ensure that 

emissions from sources within 

Oklahoma do not interfere with 

measures required in the SIP of any 

other state under Part C of the CAA to 

protect visibility.11 In the December 28, 

2011 final rule, we finalized a FIP 

(Oklahoma SO2 BART FIP) that controls 

SO2 emissions from the six units to 

address the deficiencies identified in 

our disapproval of these SO2 BART 

determinations and the disapproval of 

the SIP submission addressing its prong 

4 visibility transport obligations for the 

1997 8-hour Ozone NAAQS and the 

1997 PM2.5 NAAQS.12

On June 20, 2013, Oklahoma 

submitted a regional haze SIP revision 

to replace the FIP’s SO2 BART 

requirements for the AEP/PSO 

Northeastern Units 3 and 4 and a related 

revision to the SIP addressing interstate 

visibility transport requirements (the 

2013 Oklahoma Regional Haze SIP 

Revision). On March 7, 2014, we 

approved this SIP revision and 

concurrently withdrew the FIP’s 

applicability to these two units.13 In 

addition to approving the SO2 BART 

determinations for the AEP/PSO 

Northeastern Units 3 and 4 in that final 

rule, we also approved revised NOX

BART requirements for these two 

units,14 and approved the portion of the 

2013 Oklahoma Regional Haze SIP 

Revision concerning Oklahoma’s 

interstate visibility transport obligations 

of CAA section 110(a)(2)(D)(i)(II) with 

respect to the 1997 8-hour ozone and 

1997 PM2.5 NAAQS as applied to this 

source and its associated impacts on 

other states’ programs to protect 

visibility in Class I Areas.15 The FIP 

provisions applicable to the OG&E 

Muskogee and Sooner plants remain in 

place. 

II. Oklahoma Infrastructure SIP 

Submittals 

On January 28, 2015, Oklahoma 

submitted a SIP revision to address the 

infrastructure requirements for the 2010 

1-hour SO2 NAAQS, including the 

interstate visibility transport 

requirements. In its evaluation, 

Oklahoma stated that the 2010 Regional 

Haze SIP describes Oklahoma’s 

measures to protect visibility and ensure 

that emissions do not interfere with any 

other state’s measures to protect 

visibility. Oklahoma stated that these 

measures include provisions in the 

Oklahoma Administrative Code 

252:100–8, Part 11. Oklahoma noted 

that EPA partially approved and 


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16See ‘‘Oklahoma Demonstration of Compliance 

with the Good Neighbor Requirements of Clean Air 

Act Section 110(a)(2)(D)(i)(I) for the 2015 Ozone 

National Ambient Air Quality Standard,’’ which is 

part of Oklahoma’s October 25, 2018 Infrastructure 

SIP submittal for the 2015 Ozone NAAQS. 

partially disapproved Oklahoma’s 

Regional Haze SIP and partially 

approved and partially disapproved 

Oklahoma’s SIP submission addressing 

its prong 4 visibility transport 

requirements for the 1997 8-hour Ozone 

NAAQS and the 1997 PM2.5 NAAQS on 

December 28, 2011. Oklahoma noted 

that in the same action, EPA 

promulgated a FIP addressing the 

disapproved portions of Oklahoma’s 

2010 Regional Haze SIP and the 

interstate visibility transport SIP 

revisions for the 1997 8-hour Ozone 

NAAQS and the 1997 PM2.5 NAAQS, 

and that EPA found that the controls 

under this FIP, in combination with the 

controls required by the portion of the 

Oklahoma Regional Haze SIP submittal 

approved by EPA, will serve to prevent 

sources in Oklahoma from emitting 

pollutants in amounts that will interfere 

with efforts to protect visibility in other 

states. Oklahoma also noted that it 

submitted a revision to its regional haze 

and interstate visibility transport SIPs 

(2013 Oklahoma Regional Haze SIP 

Revision) on June 14, 2013, to replace 

the FIP as it relates to the AEP/PSO 

Northeastern Units 3 and 4, and that 

EPA approved this revision effective 

April 7, 2014. Oklahoma asserted that 

any contribution to visibility 

impairment or interference with any 

other state’s measures to protect 

visibility attributable to SO2 emissions 

are addressed through Oklahoma’s 2010 

Regional Haze SIP as revised in the 2013 

Oklahoma Regional Haze SIP Revision 

and through EPA’s related regional haze 

actions in Oklahoma. This includes 

EPA’s FIP action that currently 

addresses the OG&E Sooner Units 1 and 

2 and the OG&E Muskogee Units 4 and 

5. Oklahoma also noted that although no 

additional visibility protection 

obligations are anticipated on 

Oklahoma’s part as a result of the 

revised 2010 1-hour SO2 NAAQ, other 

program actions taken to ensure 

maintenance of the revised SO2 NAAQS 

will indirectly assist in avoiding 

interference with any other state’s 

measures to protect visibility. 

On June 16, 2016, Oklahoma 

submitted a SIP revision to address the 

infrastructure requirements for the 2012 

PM2.5 NAAQS, including the transport 

requirements. In its evaluation, 

Oklahoma stated that the 2010 Regional 

Haze SIP describes Oklahoma’s 

measures to protect visibility and ensure 

that emissions do not interfere with any 

other state’s measures to protect 

visibility. Oklahoma stated that these 

measures include provisions in the 

Oklahoma Administrative Code 

252:100–8, Part 11. Oklahoma noted 

that EPA partially approved and 

partially disapproved Oklahoma’s 

Regional Haze SIP and partially 

approved and partially disapproved 

Oklahoma’s SIP submission addressing 

the visibility prong of interstate 

transport for the 1997 8-hour Ozone 

NAAQS and the 1997 PM2.5 NAAQS on 

December 28, 2011. Oklahoma noted 

that in the same action, EPA 

promulgated a FIP addressing the 

disapproved portions of Oklahoma’s 

2010 Regional Haze SIP and the 

interstate visibility transport SIP 

submittals for the 1997 8-hour Ozone 

NAAQS and the 1997 PM2.5 NAAQS, 

and that EPA found that the controls 

under this FIP, in combination with the 

controls required by the portion of the 

Oklahoma Regional Haze SIP submittal 

approved by EPA, will serve to prevent 

sources in Oklahoma from emitting 

pollutants in amounts that will interfere 

with efforts to protect visibility in other 

states. Oklahoma also noted that it 

submitted a revision to its regional haze 

and interstate visibility transport SIPs 

on June 14, 2013, to replace the FIP as 

it relates to the AEP/PSO Northeastern 

Units 3 and 4, and that EPA approved 

this revision effective April 7, 2014. In 

its evaluation, Oklahoma asserted that 

any contribution to visibility 

impairment or interference with any 

other state’s measures to protect 

visibility attributable to emission of 

PM2.5 or its precursors (e.g., SO2) are 

addressed through Oklahoma’s 2010 

Regional Haze SIP as revised in the 2013 

Oklahoma Regional Haze SIP Revision 

and through EPA’s related regional haze 

actions in Oklahoma. This includes 

EPA’s FIP action that currently 

addresses the OG&E Sooner Units 1 and 

2 and the OG&E Muskogee Units 4 and 

5. Oklahoma also noted that although no 

additional visibility protection 

obligations are anticipated on 

Oklahoma’s part as a result of the 

revised 2012 PM2.5 NAAQS, other 

program actions taken to assure 

maintenance of the revised PM2.5

NAAQS will indirectly assist in 

avoiding interference with any other 

state’s measures to protect visibility. 

On October 25, 2018, Oklahoma 

submitted a SIP revision to address the 

CAA section 110(a)(1) and 110(a)(2) 

infrastructure and transport 

requirements for the 2015 Ozone 

NAAQS. In its evaluation, Oklahoma 

stated that the 2010 Regional Haze SIP 

describes Oklahoma’s measures to 

protect visibility and ensure that 

emissions do not interfere with any 

other state’s measures to protect 

visibility. Oklahoma stated that these 

measures include provisions in the 

Oklahoma Administrative Code 

252:100–8, Part 11. Oklahoma noted 

that EPA partially approved and 

partially disapproved Oklahoma’s 

Regional Haze SIP and partially 

approved and partially disapproved 

Oklahoma’s SIP submission addressing 

the visibility prong of interstate 

transport for the 1997 8-hour Ozone 

NAAQS and the 1997 PM2.5 NAAQS on 

December 28, 2011. Oklahoma noted 

that in the same action, EPA 

promulgated a FIP addressing the 

disapproved portions of Oklahoma’s 

2010 Regional Haze SIP and the 

interstate visibility transport SIP 

submittals for the 1997 8-hour Ozone 

NAAQS and the 1997 PM2.5 NAAQS, 

and that EPA found that the controls 

under this FIP, in combination with the 

controls required by the portion of the 

Oklahoma Regional Haze SIP submittal 

approved by EPA, will serve to prevent 

sources in Oklahoma from emitting 

pollutants in amounts that will interfere 

with efforts to protect visibility in other 

states. Oklahoma also noted that it 

submitted a revision to its regional haze 

and interstate visibility transport SIPs 

on June 14, 2013, to replace the FIP as 

it relates to the AEP/PSO Northeastern 

Units 3 and 4, and that EPA approved 

this revision effective April 7, 2014. In 

its evaluation, Oklahoma asserted that 

ozone from ozone precursor emissions 

are not believed to contribute 

significantly to visibility impairment 

and that Oklahoma’s 2010 Regional 

Haze SIP demonstrates that Oklahoma’s 

PM2.5 emissions do not interfere with 

any other state’s measures to protect 

visibility. Oklahoma noted that this 

portion of the 2010 Regional Haze SIP 

was approved by EPA on December 28, 

2011. Additionally, the submission 

includes a technical support document 

(TSD) 16 intended to address the 

requirements of CAA section 

110(a)(2)(D)(i)(I), which requires a 

state’s SIP to contain adequate 

provisions prohibiting any source or 

other type of emissions activity within 

the state from emitting any air pollutant 

in amounts which will contribute 

significantly to nonattainment in, or 

interfere with maintenance by, any 

other state with respect to any such 

national primary or secondary ambient 

air quality standard (i.e., prongs 1 and 

2). In that document, Oklahoma asserted 

that the Oklahoma Department of 

Environmental Quality (ODEQ) has 

determined that Oklahoma meets the 


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17Letter from Michael Feldman, Chief, SO2 and 

Regional Haze Section, U.S. Environmental 

Protection Agency, Region 6, to Melanie Foster, 

Manager, Rules & Planning Section, Air Quality 

Division, Oklahoma Department of Environmental 

Quality, (December 1, 2020). A copy of this letter 

is included in the docket associated with this 

proposed rulemaking. 

18Letter from Kendal Stegmann, Director, Air 

Quality Division, Oklahoma Department of 

Environmental Quality, to Michael Feldman, Chief, 

SO2 and Regional Haze Section, U.S. Environmental 

Protection Agency, Region 6 (January 5, 2021). A 

copy of this letter is included in the docket 

associated with this proposed rulemaking. 

19See 2013 i-SIP Guidance at 32–35. 

20 76 FR 81728. 

21 79 FR 12954. 

prong 4 visibility transport provisions 

for the 2015 Ozone NAAQS, as the state 

is not contributing significantly to 

nonattainment or maintenance issues in 

any other state. 

In summary, Oklahoma relied on the 

following points to support its 

conclusion that Oklahoma meets the 

prong 4 visibility transport provision for 

the 2015 Ozone NAAQS: (1) The 

modeling and technical analysis in the 

State’s interstate transport SIP revision 

(as to ‘‘prongs 1 and 2’’ under section 

110(a)(2)(D)(i)(I)) purportedly 

demonstrating that Oklahoma does not 

significantly contribute to 

nonattainment or maintenance in 

another state for the 2015 Ozone 

NAAQS; (2) the fact that ozone formed 

from ozone precursor emissions is not 

believed to contribute significantly to 

visibility impairment; and (3) 

Oklahoma’s 2010 Regional Haze SIP, 

which Oklahoma says demonstrates that 

PM2.5 emissions from Oklahoma do not 

interfere with any other state’s measures 

to protect visibility. 

On December 1, 2020, EPA sent a 

letter to ODEQ requesting clarification 

on how the Oklahoma SIP satisfies the 

prong 4 interstate visibility transport 

requirement with respect to the 2015 

Ozone NAAQS.17 In a letter dated 

January 5, 2021, ODEQ pointed out that 

EPA approved the NOX BART 

determinations in the 2010 Oklahoma 

Regional Haze SIP and also clarified that 

the SIP addressed NOX and VOC 

emissions, which are ozone precursors, 

using an approach that is consistent 

with what was anticipated under the 

CENRAP process for the first regional 

haze planning period.18 In the letter, 

ODEQ noted that Sections VII and IX of 

the 2010 Oklahoma Regional Haze SIP 

explain that the SIP requires NOX

reductions resulting from BART and 

other program requirements, as well as 

other factors, that are consistent with 

what was anticipated under the 

CENRAP consultation process for 

regional haze SIP development for the 

first planning period. In the letter, 

ODEQ further noted that Section VIII of 

the 2010 Oklahoma Regional Haze SIP 

explains that the CENRAP modeling 

used to project the visibility impacts in 

2018 as a result of growth and control 

of emissions from the baseline for Class 

I areas in CENRAP states included 

emission adjustments made by ODEQ to 

reflect presumptive BART controls for 

the OG&E Sooner Plant, the OG&E 

Muskogee Plant, and the AEP/PSO 

Northeastern Plant. For NOX emissions, 

this presumptive control level is 

equivalent to 0.15 lb/MMBtu for NOX

BART and is consistent with the NOX

emission limits required by the 2010 

Oklahoma Regional Haze SIP for 

subject-to-BART units at these three 

power plants. 

In the January 5, 2021 letter, ODEQ 

also explains that the 2010 Oklahoma 

Regional Haze SIP did not include 

additional control requirements to 

address VOC emissions under regional 

haze for the first planning period. In the 

letter, ODEQ points to Section VI(A) of 

the 2010 Oklahoma Regional Haze SIP, 

which explains that ODEQ determined 

that the visibility impairing pollutants 

in Oklahoma include SO2, NOX, PM10, 

and PM2.5, while CENRAP modeling 

showed that anthropogenic VOCs do not 

significantly impair visibility at the 

Wichita Mountains. ODEQ also notes 

that Section IX(E)(4) of the 2010 

Oklahoma Regional Haze SIP explains 

that the emissions inventory associated 

with the SIP assigns most emissions of 

VOCs to biogenic sources, which ODEQ 

considers to be natural and therefore 

uncontrollable. ODEQ explains that 

Section IX(E)(4) of the 2010 Oklahoma 

Regional Haze SIP noted that a minority 

of VOC emissions in Oklahoma 

originate from area, industrial, point, 

and mobile sources, and that most of 

these sources already employ controls 

under various federal mandates. The 

2010 Oklahoma Regional Haze SIP 

explained that considering the small 

and uncertain contribution of 

anthropogenic sources of VOC to 

visibility impairment at the Wichita 

Mountains, ODEQ did not find further 

VOC controls reasonable. In the letter, 

ODEQ explains that these 

determinations similarly apply to the 

approach taken in the 2010 Oklahoma 

Regional Haze SIP regarding potential 

VOC-related impacts of and remedies 

for visibility impairment at other states’ 

Class I areas, and that this approach is 

consistent with what was anticipated 

under the CERNAP process for the first 

regional haze planning period. Further, 

ODEQ notes that Section VIII of the 

2010 Oklahoma Regional Haze SIP 

presented model output data that 

demonstrates that Oklahoma emissions 

are projected to impair visibility only 

insignificantly at all Class I areas in 

other states, and ODEQ therefore 

concluded that additional emission 

reduction action was not needed to 

protect other Class I areas, including for 

NOX and VOC as ozone precursors. 

Thus, ODEQ clarifies in the letter that 

the EPA-approved portion of the 2010 

Oklahoma Regional Haze SIP addressed 

NOX and VOC emissions using an 

approach that is consistent with what 

was anticipated in the CENRAP process 

for the first regional haze planning 

period and ODEQ states that it believes 

that, considering the clarifications in the 

January 5, 2021 letter, and as certified 

in the October 25, 2018 submittal, the 

Oklahoma SIP satisfies the interstate 

visibility transport CAA requirement of 

section 110(a)(2)(D)(i)(II) with respect to 

the 2015 Ozone NAAQS. 

III. The EPA’s Evaluation 

Our 2013 i-SIP guidance addresses the 

requirements for prong 4 and lays out 

two ways in which a state’s 

infrastructure SIP submittal may satisfy 

these requirements.19 The first method 

is through a state’s confirmation in its 

infrastructure SIP submittal that it has a 

fully approved regional haze SIP in 

place. As previously discussed, EPA 

promulgated a partial approval and 

partial disapproval of the 2010 

Oklahoma Regional Haze SIP in 2011 

because the SO2 BART determinations 

for the OG&E Sooner Units 1 and 2, the 

OG&E Muskogee Units 4 and 5, and the 

AEP/PSO Northeastern Units 3 and 4 

did not comply with our regional haze 

regulations under 40 CFR 51.308(e), and 

EPA concurrently promulgated a FIP to 

address these deficiencies.20 On June 

20, 2013, Oklahoma submitted a SIP 

revision to address this deficiency with 

respect to the AEP/PSO Northeastern 

Units 3 and 4, and the FIP with respect 

to these two units was withdrawn on 

March 7, 2014.21 However, the FIP 

remains in place with SO2 BART 

requirements for the OG&E Sooner Units 

1 and 2 and the OG&E Muskogee Units 

4 and 5. Therefore, Oklahoma cannot 

rely on a fully approved Regional Haze 

SIP as the basis for meeting its prong 4 

visibility transport obligations for the 

2010 SO2, 2012 PM2.5, and the 2015 

Ozone NAAQS. 

In the absence of a fully approved 

Regional Haze SIP, the second method 

provided by the 2013 i-SIP guidance to 

meet prong 4 requirements is a 

demonstration that emissions within a 

state’s jurisdiction do not interfere with 


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22See 2013 i-SIP Guidance at 34. 

23See 2013 i-SIP Guidance at 33. 

24See 2013 i-SIP Guidance at 34. See also 76 FR 

22036 (April 20, 2011) (containing EPA’s approval 

of the visibility requirement of 110(a)(2)(D)(i)(II) 

based on a demonstration by Colorado that did not 

rely on the Colorado Regional Haze SIP). 

25See 2013 i-SIP Guidance at 32–33. 

26The BART Guidelines direct states to address 

SO2, NOX and direct PM (including both PM10 and 

PM2.5) emissions as visibility-impairment 

pollutants, and states must exercise their ‘‘best 

judgment to determine whether VOC or ammonia 

emissions from a source are likely to have an 

impact on visibility in an area.’’ See 70 FR 39162. 

27 76 FR 81728. 

28 79 FR 12954. 

29See 2013 i-SIP Guidance at 33 (‘‘The EPA 

interprets [prong 4] to be pollutant-specific, such 

that the infrastructure SIP submission need only 

address the potential for interference with 

protection of visibility caused by the pollutant 

(including precursors) to which the new or revised 

NAAQS applies.’’) 

other states’ plans to protect visibility.22

EPA interprets prong 4 to be pollutantspecific such that the state need only 

address the potential for interference 

with visibility protection caused by the 

pollutant (including precursors) to 

which the new or revised NAAQS 

applies.23 According to the guidance, 

such a demonstration for the first 

planning period should establish or 

identify the measures in the approved 

SIP that limit visibility-impairing 

pollutants and ensure that the resulting 

reductions conform with any mutually 

agreed emission reductions under the 

relevant regional haze regional planning 

organization (RPO) process.24 As 

explained below, Oklahoma did not 

make such a demonstration in the i-SIP 

submittals for the 2010 SO2 and 2012 

PM2.5 NAAQS. The i-SIP submittal for 

the 2015 Ozone NAAQS as clarified by 

Oklahoma’s January 5, 2021 letter, 

provides a demonstration identifying 

the measures in the approved SIP that 

limit visibility-impairing ozone 

precursor emissions and clarifies that 

the resulting reductions conform with 

mutually agreed emission reductions 

under the relevant regional haze RPO 

process with respect to the 2015 Ozone 

NAAQS. We discuss this in the 

subsections that follow. 

A. Analysis of Oklahoma’s January 28, 

2015 Prong 4 Submittal for the 2010 SO2

NAAQS 

The portion of the 2015 infrastructure 

SIP submittal for the 2010 1-hour SO2

NAAQS that addresses interstate 

visibility transport relied on both 

Oklahoma’s 2010 Regional Haze SIP 

submittal, as revised in the 2013 

Regional Haze SIP revision that 

addresses the AEP/PSO facility, and 

EPA’s FIP that currently applies to the 

OG&E Sooner Units 1 and 2 and the 

OG&E Muskogee Units 4 and 5. As 

explained above, the prong 4 

requirements are pollutant specific. 

Some portions of the 2010 Oklahoma 

Regional Haze SIP that address SO2

emissions have been disapproved and 

thus cannot be relied upon by 

Oklahoma to satisfy the prong 4 

requirements. Further, the EPA’s 2013 

i-SIP guidance states, ‘‘Under section 

110(a)(2)(D(i)(II), an i-SIP submission 

cannot be approved with respect to 

prong 4 (visibility transport) until the 

EPA has issued final approval of SIP 

provisions that the EPA has found to 

adequately address any contribution of 

that state’s sources to impacts on 

visibility program requirements in other 

states.’’ 25 Thus, Oklahoma cannot rely 

on the existing SO2 BART FIP to satisfy 

the prong 4 requirements for the 2010 

1-hour SO2 NAAQS. Moreover, the 2015 

i-SIP submittal does not provide any 

additional information to demonstrate 

that the measures in the SIP are 

sufficient to prohibit emissions from 

sources within Oklahoma from 

interfering with measures that have 

been developed by other states to 

protect visibility with respect to the 

2010 1-hour SO2 NAAQS. Therefore, 

while the FIP provides an appropriate 

level of SO2 control to prohibit 

emissions from sources within 

Oklahoma from interfering with 

measures that have been developed by 

other states to protect visibility (as 

discussed in Section III.E.), the SIP 

submittal does not; Thus, we are 

proposing to disapprove the 

110(a)(2)(D)(i)(II) prong 4 portion of 

Oklahoma’s 2015 i-SIP submittal for the 

2010 1-hour SO2 NAAQS. 

B. Analysis of Oklahoma’s June 16, 2016 

Prong 4 Submittal for the 2012 PM2.5

NAAQS 

The portion of the 2016 infrastructure 

SIP submittal for the 2012 PM2.5

NAAQS that addresses interstate 

visibility transport relied on both 

Oklahoma’s 2010 Regional Haze SIP 

submittal, as revised in the June 20, 

2013 SIP revision with respect to the 

AEP/PSO facility, and EPA’s FIP that 

currently applies to the OG&E Sooner 

Units 1 and 2 and the OG&E Muskogee 

Units 4 and 5. The portions of 

Oklahoma’s 2010 Regional Haze SIP that 

address PM BART have been approved, 

but portions of the SIP that address PM 

precursor emissions (i.e., SO2) have not, 

and thus cannot be relied upon to 

satisfy the prong 4 requirements. PM 

emissions can be emitted directly from 

sources and can also form in the 

atmosphere as a result of complex 

reactions of other pollutants (i.e., 

precursors) such as SO2 and NOX, 

which are visibility impairing pollutants 

themselves and are required to be 

addressed under regional haze.26 As 

discussed above, EPA disapproved the 

SO2 BART determinations for the OG&E 

Sooner Units 1 and 2, the OG&E 

Muskogee Units 4 and 5, and the AEP/ 

PSO Northeastern Units 3 and 4, and 

promulgated a FIP to address these 

deficiencies.27 EPA approved the 2013 

Oklahoma Regional Haze SIP Revision 

that addressed SO2 BART for the AEP/ 

PSO Northeastern Units 3 and 4, and 

EPA withdrew the FIP with respect to 

these two units on March 7, 2014.28

However, the FIP remains in place with 

SO2 BART requirements for the OG&E 

Sooner Units 1 and 2 and the OG&E 

Muskogee Units 4 and 5. As explained 

above, Oklahoma cannot rely upon the 

portions of the 2010 Oklahoma Regional 

Haze SIP that address SO2 emissions 

that have been disapproved or on the 

existing SO2 BART FIP to satisfy the 

prong 4 requirements for the 2012 PM2.5

NAAQS. The 2016 i-SIP submittal does 

not provide any additional information 

to demonstrate that the measures in the 

SIP are sufficient to prohibit emissions 

from sources within Oklahoma from 

interfering with measures that have 

been developed by other states to 

protect visibility with respect to the 

2012 PM2.5 NAAQS. We are therefore 

proposing to disapprove the 

110(a)(D)(2)(i)(II) prong 4 portion of 

Oklahoma’s 2016 infrastructure SIP 

submittal for the 2012 PM2.5 NAAQS. 

C. Analysis of Oklahoma’s 2018 Prong 

4 Submittal for the 2015 Ozone NAAQS 

In Oklahoma’s 2018 infrastructure SIP 

submittal for the 2015 Ozone NAAQS, 

Oklahoma asserted that it meets the 

visibility transport provisions under 

section 110(a)(2)(D)(i)(II) for the 2015 

Ozone NAAQS given that it has 

determined the state is not contributing 

significantly to nonattainment or 

maintenance issues in any other state 

under section 110(a)(2)(D)(i)(I). The 

analysis in the SIP submittal that 

purports to find that Oklahoma 

emissions do not significantly 

contribute to nonattainment or interfere 

with maintenance in another state under 

section 110(a)(2)(D)(i)(I) focuses on the 

potential impact of ozone-precursor 

emissions at certain ozone monitor 

locations in other states as related to the 

attainment and maintenance of the 

ozone NAAQS (i.e., prongs 1 and 2), but 

does not provide an analysis of visibility 

impacts at Class I areas due to emissions 

of ozone precursors as visibility 

pollutants (prong 4).29 This basis is 


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30 Id. 

31 During consultation ODEQ indicated that 

Sooner Units 1 and 2, Muskogee Units 4 and 5, and 

Northeastern Units 3 and 4 would have emission 

limits based on 0.15 lb of NOX per MMBtu. ODEQ’s 

January 5, 2021 letter noted that Section VIII of the 

2010 Oklahoma Regional Haze SIP explained that 

these emissions reductions for these six units were 

included in the CENRAP 2018 modeling projections 

that other CENRAP states relied on in developing 

their regional haze SIPs. 

32 76 FR 81728. 

33 76 FR at 81729. 

34 78 FR 51686, 51690 (August 21, 2013). 

35 76 FR 16168, 16181, 16182 (March 22, 2011). 

36 79 FR at 12944. 

37See 2010 Oklahoma Regional Haze SIP, Section 

IX.E.4, page 113. A copy of the submittal is 

included in the docket associated with this 

proposed rulemaking. 

38 Id at Section VI.A, page 69. 

39 Id. 

40 Id. 

41See 76 FR at 81729 77 FR (proposed rule) and 

76 FR 81728 (final rule). 

inadequate for approval of the visibility 

transport requirements. 

In the 2018 submittal, Oklahoma also 

stated that ozone formed from ozone 

precursor emissions is not believed to 

contribute significantly to visibility 

impairment. Oklahoma asserted that the 

2010 Regional Haze SIP demonstrates 

that PM2.5 emissions from Oklahoma do 

not interfere with any other state’s 

measures to protect visibility, and that 

this portion of the SIP was approved by 

EPA on December 28, 2011. Here, 

Oklahoma is referring to EPA’s approval 

of all the PM BART determinations in 

Oklahoma’s 2010 Regional Haze SIP. 

However, it is unclear in the submittal 

how the SIP fulfills the prong 4 

requirements for the 2015 Ozone 

NAAQS.30

The EPA has not established a 

separate visibility transport standard for 

ozone because it does not directly 

impair visibility or substantially 

produce or contribute to the production 

of the secondary air contaminants that 

cause visibility impairment or regional 

haze. As stated above, section 

110(a)(2)(D)(i)(II) prong 4 requirements 

apply to all pollutants (including 

precursors) for which EPA has 

promulgated a NAAQS. As such, 

Oklahoma is required to demonstrate to 

EPA that it has approved measures in its 

SIP that ensure that ozone-precursor 

emissions within its jurisdiction do not 

interfere with other states’ visibility 

protection plans. While ozone itself 

does not directly impair visibility, 

ozone precursors (i.e., NOX and in some 

cases volatile organic compounds) can 

react to generate visibility impairing 

pollutants. Thus, the pertinent question 

is whether Oklahoma’s SIP adequately 

controls emissions of ozone precursors 

that may contribute to visibility 

impairment in other states and whether 

the level of control of these emissions is 

consistent with mutually-agreed 

emissions reductions under the 

CENRAP regional haze planning process 

for the first planning period. 

As explained in Oklahoma’s January 

5, 2021 clarification letter, EPA 

approved all NOX BART determinations 

in Oklahoma’s 2010 Regional Haze SIP 

and these EPA-approved NOX BART 

determinations conform with the 

mutually-agreed emission reductions 31

under the CENRAP regional haze 

planning process that Oklahoma and 

other Midwestern states participated in 

for regional haze SIP development for 

the first regional haze planning 

period.32 In the 2013 Oklahoma 

Regional Haze SIP Revision, Oklahoma 

revised the NOX BART requirements for 

the Northeastern Units 3 and 4 that EPA 

approved in the December 28, 2011 final 

rule.33 The revisions require earlier 

installation and compliance with 

reduced NOX emission limits prior to 

the original SIP-imposed deadline.34

Our December 2011 approval of NOX

BART for Units 3 and 4 required that 

these units meet a NOX emission limit 

of 0.15 lb/MMBtu (based on a 30-day 

rolling average) within five years from 

the effective date of EPA’s approval, or 

by January 27, 2017.35 However, under 

the 2013 Oklahoma Regional Haze SIP 

Revision, which EPA approved on 

March 7, 2014, both units are required 

to meet an initial NOX emission limit of 

0.23 lb/MMBtu (based on a 30-day 

rolling average) by December 31, 2013, 

with additional limits of 1,098 lb/hr per 

unit on a 30-day rolling average basis 

and a 9,620 tpy combined cap for both 

units.36 By April 16, 2016, one unit is 

required to be permanently shut down, 

while the remaining unit is required to 

meet a NOX emission limit of 0.15 lb/ 

MMBtu (based on a 30-day rolling 

average), with an additional limit of 716 

lb/hr on a 30-day rolling average basis 

and a cap of 3,137 tpy on a 12-month 

rolling basis. Finally, this second unit is 

required to shut down by December 31, 

2026. Thus, these revised NOX BART 

determination for the Northeastern 

Units 3 and 4 are more stringent than 

the determinations that we previously 

approved given that they require 

compliance with the 0.15 lb/MMBtu 

limit on a more expeditious schedule. 

The Oklahoma SIP contains NOX BART 

determinations for all subject-to-BART 

sources in Oklahoma, which have been 

approved by EPA in previous actions 

and conform with the mutually-agreed 

emission reductions under the CENRAP 

regional haze planning process that 

Oklahoma and other Midwestern states 

participated in for regional haze SIP 

development for the first regional haze 

planning period. 

In the January 5, 2021 letter, ODEQ 

also explained that VOC emissions, 

which are an ozone precursor, were 

addressed in the 2010 Oklahoma 

Regional Haze SIP in a manner 

consistent with what was anticipated 

under the CENRAP process for the first 

regional haze planning period. 

Specifically, in the 2010 Oklahoma 

Regional Haze SIP, ODEQ asserted that 

the emissions inventory associated with 

that SIP submittal assigns most VOC 

emissions to biogenic sources, which 

ODEQ considers to be uncontrollable; 37

The CENRAP modeling shows that 

anthropogenic VOC emissions do not 

significantly impair visibility at the 

Wichita Mountains; 38 And, only a 

minority of VOC emissions in Oklahoma 

originate from area, industrial, point, 

and mobile sources, which ODEQ 

asserted are sources that are already 

controlled under various federal 

mandates.39 ODEQ stated in the 2010 

Oklahoma Regional Haze SIP that 

considering the small and uncertain 

contribution of anthropogenic sources of 

VOC to visibility impairment at the 

Wichita Mountains, ODEQ did not find 

further controls for VOC sources to be 

reasonable.40 The CENRAP modeling 

used to project the visibility impacts in 

2018 for Class I areas in CENRAP states, 

which reflects the mutually-agreed 

emissions reductions in CENRAP states, 

did not assume additional control of 

VOC emissions in Oklahoma. In the 

December 28, 2011 final rule on the 

2010 Oklahoma Regional Haze SIP, EPA 

agreed with ODEQ’s decision to not 

further evaluate or require additional 

controls for VOC emissions in 

Oklahoma.41 Thus, Oklahoma’s 

approach for VOC emissions in the 2010 

Oklahoma Regional Haze SIP has been 

approved by EPA and conforms with the 

mutually-agreed emission reductions 

under the CENRAP regional haze 

planning process that Oklahoma and 

other Midwestern states participated in 

for regional haze SIP development for 

the first regional haze planning period. 

Therefore, we are proposing to find 

that the Oklahoma SIP includes the 

necessary emission reductions to satisfy 

the 110(a)(2)(D)(i)(II) prong 4 

requirements for the 2015 Ozone 

NAAQS and are proposing to approve 

the portion of the 2018 infrastructure 

SIP submittal that addresses interstate 

visibility transport for the 2015 Ozone 

NAAQS. 


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42 76 FR at 16189 and 76 FR at 81735. 

43 70 FR 39104, 39131 (July 6, 2005). 

44 76 FR at 81730. 

45 76 FR 81728. 

46 79 FR 12954. 

47 79 FR at 12945. 

48Northeastern Units 3 and 4 are similar design 

capacity so comparing them as the same is a 

reasonable approximation for this contextual 

assessment. Specific assessment is included later in 

this notice and in docket materials. 49See Attachment A, paragraph 1(f) of the ‘‘AEP/ 

PSO Settlement Agreement,’’ which is presented in 

Appendix I of the June 20, 2013 Oklahoma Regional 

Haze SIP revision. A copy of the submittal is found 

in the docket for this proposed rulemaking. 50 Id. 

51 79 FR at 12945. 

52 79 FR at 12945 

53 79 FR at 12945. 

54 79 FR at 12945. 

55A copy of the June 25, 2019 ‘‘BART SO2

Monitoring Program for Northeastern Power Station 

Unit 3’’ can be found in the docket for this 

proposed rulemaking. 

56The 0.37 lb/MMBtu emission rate is 60 percent 

of the difference between 0.40 and the 

demonstrated emission rate (0.35 lb/MMBtu), per 

the terms of the AEP/PSO Settlement Agreement. 

D. AEP/PSO Northeastern SO2 Emission 

Reductions Assumed in the CENRAP 

Modeling 

As discussed earlier in this notice, 

Oklahoma engaged in a regional 

planning process with other CENRAP 

states to develop their regional haze SIP 

for the first planning period. This 

regional planning process included a 

forum in which state representatives 

built emission inventories that assumed 

that specific pollution sources would be 

controlled to specific levels. This 

included adjustments to projected 

emissions by ODEQ to reflect the 

assumption that the OG&E Sooner Units 

1 and 2, the OG&E Muskogee Units 4 

and 5, and the AEP/PSO Northeastern 

Units 3 and 4 would each be controlled 

to presumptive BART emission levels 

for SO2,42 which is equivalent to 0.15 

lb/MMBtu.43 Visibility modeling 

projections conducted by CENRAP 

subsequently included those emission 

reductions, and other states relied on 

them as part of their reasonable progress 

demonstrations. However, Oklahoma, in 

its subsequent 2010 Regional Haze SIP, 

did not include these promised 

reductions on which the other states 

relied on in developing their own RPGs 

and regional haze SIPs. Instead, 

Oklahoma determined that SO2 BART 

for these units was no additional control 

and specified an SO2 limit of 0.65 lbs/ 

MMBtu on a 30-day rolling average. In 

a final rule published on December 28, 

2011, we disapproved the SIP’s SO2

BART determinations for these six units 

because they do not comply with our 

regulations under 40 CFR 51.308(e).44 In 

the same final rule, we promulgated a 

FIP establishing an emission limit of 

0.06 lb/MMBtu for each of the six units 

for purposes of complying with SO2

BART.45

On June 20, 2013, Oklahoma 

submitted a regional haze SIP revision 

to replace the FIP’s SO2 BART 

requirements for the AEP/PSO 

Northeastern Units 3 and 4. On March 

7, 2014, we approved this SIP revision 

and concurrently withdrew the sections 

of the FIP that applied to those two 

units.46 The 2013 Oklahoma Regional 

Haze SIP Revision requires one of the 

two Northeastern units to shut down no 

later than April 16, 2016, while the 

remaining unit is required to install dry 

sorbent injection (DSI) to meet an SO2

emission limit of 0.4 lb/MMBtu.47

However, the SO2 emission reductions 

for the AEP/PSO Northeastern facility 

contained in the 2013 Oklahoma 

Regional Haze SIP Revision fall short of 

the levels assumed in other states’ 

regional haze plans through the 

CENRAP RPO process. In order to 

achieve emission levels equivalent to 

the levels assumed in other states’ 

regional haze plans through the 

CENRAP RPO process, the remaining 

Northeastern unit would have to meet 

an emission limit of 0.3 lb/MMBtu (0.15 

+ 0.15).48 To address this, the 2013 

Oklahoma Regional Haze SIP Revision 

also requires the source operators to 

optimize the performance of DSI on the 

remaining unit to ensure that the best 

possible performance is achieved and 

adjust the limit accordingly. The ‘‘AEP/ 

PSO Settlement Agreement’’ included in 

the 2013 Oklahoma Regional Haze SIP 

Revision requires the company to 

develop and propose a monitoring 

program to test various operating 

profiles and other measures in order to 

determine whether increased SO2

removal efficiencies can be achieved 

during normal operations.49 AEP/PSO 

was required to implement this 

monitoring program and to evaluate and 

report the results to EPA and ODEQ. If 

the evaluation demonstrated that the 

technology is capable of sustainably 

achieving an emission rate of less than 

0.37 lbs/MMBtu on a 30-day rolling 

average basis without (i) altering the 

unit’s fuel supply, (ii) incurring 

additional capital costs, (iii) increasing 

operating expenses by more than a 

negligible amount, and/or (iv) adversely 

impacting overall unit operations, 

ODEQ would have to propose to revise 

the emission rate for the remaining 

Northeastern unit by 60 percent of the 

difference between 0.40 and the 

demonstrated emission rate.50

If it is determined that the remaining 

operating unit still cannot meet the 

emission limit of 0.3 lb/MMBtu, then 

the 2013 Oklahoma Regional Haze SIP 

Revision contains an enforceable 

commitment obligating ODEQ to 

‘‘obtain and/or identify additional SO2

reductions within the State of Oklahoma 

to the extent necessary to achieve the 

anticipated visibility benefits 

estimated’’ by CENRAP.51 As explained 

in our March 7, 2014 final rule 

approving the 2013 Oklahoma Regional 

Haze SIP Revision, any additional SO2

emissions reductions that can be 

obtained or identified from the 

northeast quadrant of the State will be 

presumed to count toward the emission 

reductions necessary to achieve the 

anticipated visibility benefits associated 

with a 0.30 lb/MMBtu emission limit at 

Northeastern Power Station.52

Emissions reductions obtained outside 

the northeast quadrant that are 

technically justified will also be 

counted.53 We explained in our March 

7, 2014 final rule that if necessary, 

additional emissions reductions are to 

be obtained via enforceable emission 

limits or control equipment 

requirements where necessary and 

submitted to EPA as a SIP revision as 

expeditiously as practicable, but in no 

event later than the end of the first full 

Oklahoma legislative session occurring 

subsequent to AEP/PSO’s submission of 

the evaluation and report for the 

monitoring program required under the 

AEP/PSO Settlement Agreement.54

On June 25, 2019, AEP/PSO 

submitted to ODEQ the ‘‘BART SO2

Monitoring Program for Northeastern 

Power Station Unit 3’’ (SO2 Monitoring 

Program), pursuant to one of the 

requirements in the AEP/PSO 

Settlement Agreement.55 Based on the 

results of the SO2 Monitoring Program, 

AEP/PSO concluded that the lowest 

target emission rate sustainably 

achieved consistent with the conditions 

in the AEP/PSO Agreement is 0.35 lb/ 

MMBTU on a 30-day rolling average 

basis, and that the resulting federally 

enforceable emission rate should be 0.37 

lb/MMBtu on a 30-day rolling average 

basis.56 However, an emission limit of 

0.37 lb/MMBtu for AEP/PSO 

Northeastern Unit 3 would still fall 

short of the 0.3 lb/MMBtu emission 

limit necessary to achieve emission 

levels equivalent to the levels assumed 

in other states’ regional haze plans 

through the CENRAP RPO process. 

Following final disapproval of a SIP 

revision in whole or in part, EPA has an 

obligation under section 110(c) of the 

Act to either approve a SIP revision 

and/or promulgate a FIP to address the 

disapproval within 24 months. We 

believe EPA’s FIP obligation under 


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57 76 FR 81728. 

58 76 FR 16193. 

59 79 FR 12954 (March 7, 2014). 

60 76 FR at 16189 and 76 FR at 81735. 

61Although the FIP requires an SO2 emission 

limit of 0.06 lb/MMBtu for the OG&E Muskogee 

Units 4 and 5, the company elected to convert the 

units to natural gas in 2019 to comply with this 

emission limit. Therefore, these two units have 

actual SO2 emissions near zero. 

62See the Excel spreadsheet ‘‘NE SIP vs FIP 

visibility review calcs.xlsx’’ which can be found in 

the docket for this proposed rulemaking. 

63 79 FR 12945. 

section 110(c) could be addressed 

through a demonstration that the 

deficiencies in the Oklahoma SIP that 

form the basis of our proposed 

disapproval of the interstate visibility 

transport portions of the Oklahoma i-SIP 

submissions for the 2010 SO2 and 2012 

PM2.5 NAAQS are already addressed by 

the existing FIP in place for the 

Oklahoma Regional Haze program. As 

discussed in the next section, we have 

assessed whether the emissions 

reductions secured by the existing SO2

BART emission limits for the OG&E 

Sooner Units 1 and 2 and the OG&E 

Muskogee Units 4 and 5, required under 

the existing FIP, are sufficient to make 

up for any shortfall to achieve the 

necessary anticipated visibility benefits 

associated with a 0.30 lb/MMBtu 

emission limit at Northeastern Power 

Station that CENRAP states agreed on 

and relied upon in their regional haze 

plans. We discuss our technical analysis 

in the subsection that follows. 

E. Proposed Finding That EPA’s Prong 

4 FIP Obligations Are Satisfied for the 

2010 SO2 and 2012 PM2.5 NAAQS 

For the reasons explained above, 

Oklahoma’s reliance on both its 2010 

Regional Haze SIP submittal as revised 

in its 2013 Regional Haze SIP revision 

and EPA’s FIP that applies to the OG&E 

Sooner Units 1 and 2 and OG&E 

Muskogee Units 4 and 5 is insufficient 

to satisfy its prong 4 requirements in 

accordance with EPA’s 2013 i-SIP 

guidance. EPA is thus proposing to 

disapprove the submissions with regard 

to CAA section 110(a)(2)(D)(i)(II). EPA’s 

disapproval triggers its obligation to 

promulgate a FIP under CAA section 

111(c)(1) to address the deficiencies in 

the state’s SIP. However, as discussed 

below, EPA finds that its FIP obligation 

with respect to prong 4 for these two 

NAAQS is already satisfied, and no 

further action is required. 

The FIP we published on December 

28, 2011,57 included SO2 emission 

limitations for the OG&E Sooner Units 

1 and 2, the OG&E Muskogee Units 4 

and 5, and the AEP/PSO Northeastern 

Units 3 and 4 based on EPA’s analysis 

of the five BART statutory factors, and 

these emission limitations reflected a 

level of control more stringent than 

what was assumed in the CENRAP 

modeling.58 On June 20, 2013, 

Oklahoma submitted a regional haze SIP 

revision to replace the FIP’s SO2 BART 

requirements for the AEP/PSO 

Northeastern Units 3 and 4. On March 

7, 2014, we approved this SIP revision 

and concurrently withdrew the FIP’s 

applicability to these two units.59 The 

FIP provisions applicable to the OG&E 

Sooner Units 1 and 2 and the OG&E 

Muskogee Units 4 and 5 remain in 

place. 

As discussed in the previous 

subsection, based on the results of the 

SO2 Monitoring Program that was 

required under the AEP/PSO Settlement 

Agreement and part of the 2013 

Regional Haze SIP Revision, AEP/PSO 

concluded that the federally enforceable 

emission rate for AEP/PSO Northeastern 

Unit 3 should be 0.37 lb/MMBtu on a 

30-day rolling average basis. However, 

this level of control falls short of the 0.3 

lb/MMBtu emission limit necessary to 

achieve emission levels equivalent to 

the levels assumed in other states’ 

regional haze plans through the 

CENRAP RPO process. To address this 

issue, EPA assessed whether the SO2

emissions reductions secured from other 

facilities under the existing FIP 

promulgated on December 28, 2011, 

would be sufficient to make up for the 

shortfall in emissions reductions and 

associated visibility benefit from the 

AEP/PSO Northeastern facility 

compared to what was assumed in the 

CENRAP modeling. Under the CENRAP 

regional haze planning process, 

CENRAP included emissions for these 

sources based upon Oklahoma’s 

indications that the OG&E Sooner Units 

1 and 2, the OG&E Muskogee Units 4 

and 5, and the AEP/PSO Northeastern 

Units 3 and 4 would each be controlled 

to presumptive BART emission levels 

for SO2, which is 0.15 lb/MMBtu.60

Further, the FIP EPA promulgated on 

December 28, 2011, which continues to 

apply to the OG&E Sooner Units 1 and 

2 and the OG&E Muskogee Units 4 and 

5, requires each of these four units to 

comply with an emission limit of 0.06 

lb/MMBtu for purposes of complying 

with the SO2 BART requirements.61

In Table 1 below, we present the 

controlled SO2 annual emission levels 

included in the CENRAP chemical 

transport modeling using the 

Comprehensive Air Quality Model with 

Extensions (CAMx) for the six units and 

the controlled SO2 annual emission 

levels required by both the FIP for 4 

units and the 2013 Oklahoma Regional 

Haze SIP Revision for the AEP/PSO 

Northeastern facility’s 2 units.62 These 

SO2 annual emissions were based on 

annual firing rate information for the 

base period (2002) and the appropriate 

lb/MMBtu emission limit. The CENRAP 

CAMx modeling assumed that AEP/PSO 

Northeastern Units 3 and 4 would have 

combined controlled SO2 emissions of 

5,921 tpy, while the 2013 Oklahoma 

Regional Haze SIP revision includes 

control requirements that result in 

combined controlled SO2 emissions of 

7,895 tpy using the same annual firing 

rate information used in CENRAP’s 

CAMx modeling. This results in a 

shortfall of 1,974 tpy between the 

controlled emission level assumed in 

the CENRAP CAMx modeling and the 

level of control required by the 2013 SIP 

Revision. The CENRAP CAMx modeling 

also assumed that the OG&E Muskogee 

Units 4 and 5 would have combined 

controlled SO2 emissions of 5,249 tpy, 

while the FIP requires SO2 controls that 

result in combined controlled SO2

emissions of 2,100 tpy using the same 

annual firing rate information used in 

CENRAP’s CAMx modeling. The FIP 

results in SO2 controlled emissions on 

Muskogee units that are 3,150 SO2 tpy 

lower than the level assumed in the 

CENRAP modeling, which is greater 

than the 1,974 tpy shortfall from the 

AEP/PSO Northeastern facility. 

Focusing on the OG&E Muskogee Units 

4 and 5 alone, the level of SO2 control 

required by the FIP at these two units 

is sufficient to make up for the shortfall 

in emission reductions from the AEP/ 

PSO Northeastern facility. This is 

significant because the OG&E Muskogee 

facility is located in the northeast 

quadrant of Oklahoma, which is where 

the AEP/PSO Northeastern facility is 

located. In our final rule approving the 

2013 Oklahoma Regional Haze SIP 

revision, we explained that any 

additional SO2 emissions reductions 

that can be obtained or identified from 

the northeast quadrant of the State will 

be presumed to count toward the 

emission reductions necessary to 

achieve the anticipated visibility 

benefits associated with a 0.30 lb/ 

MMBtu emission limit at Northeastern 

Power Station.63 The OG&E Sooner 

Units 1 & 2 also provide additional 

surplus emissions (3,304 tpy of SO2) 

that provide benefit beyond the net 

surplus of 1,176 tpy of SO2 from the net 

of Muskogee units surplus and 

Northeastern units shortfall (3,150 tpy 

¥ 1,974 tpy). The level of SO2 controls 

within EPA’s FIP is therefore sufficient 


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to make up for the shortfall from the 

AEP/PSO Northeastern facility. 

TABLE 1—COMPARISON OF CONTROLLED SO2 EMISSIONS REDUCTIONS IN SIP/FIP VS. CENRAP CAMX MODELING

Facility/unit 

Annual avg. 

heat input rate 

used in CAMx 

modeling for 

SIP 

(MMBtu/hr) 

CENRAP 

modeling SO2

emission limit 

assumption 

(lb/MMBtu) 

CENRAP 

Modeling 

Controlled 

SO2 emissions 

assumption 

(tpy) * 

SIP/FIP SO2

emission limit 

(lb/MMBtu) 

SIP/FIP 

controlled 

SO2 emissions 

(tpy) * 

OG&E Sooner Unit 1 .................................................................................. 4,548 0.15 2,988.2 0.06 1,195.3 

OG&E Sooner Unit 2 .................................................................................. 3,835 0.15 2,519.4 0.06 1,007.7 

OG&E Muskogee Unit 4 ............................................................................. 4,112 0.15 2,701.7 0.06 ** 1,440.1 

OG&E Muskogee Unit 5 ............................................................................. 3,877 0.15 2,547.5 0.06 ** 1,080.7 

AEP/PSO Northeastern Unit 3 .................................................................... 4,506 0.15 2,960.6 0.40 7,895.0 

AEP/PSO Northeastern Unit 4 .................................................................... 4,506 0.15 2,960.6 0 0 

Total Controlled SO2 Emissions .......................................................... .......................... .......................... 16,678 .......................... 12,198 

* Controlled SO2 emissions calculated based on the 2002 annual heat input rate (MMBtu/yr) of the unit used in CENRAP’s CAMx modeling that was included in 

CENRAP states SIPs. 

** The controlled SO2 emissions we have calculated in this table for the OG&E Muskogee Units 4 and 5 are based on the FIP emission limits and the actual annual 

heat input rate (MMBtu/yr). However, OG&E Muskogee Units 4 and 5 converted to natural gas to comply with their SO2 BART emission limits in the FIP. Therefore, 

even though the FIP requires SO2 emission limits of 0.06 lb/MMBtu, these two units are actually emitting SO2 at much lower (near negligible) levels. 

Since hourly emission estimates for 

these six units were also used in 

CALPUFF modeling that was part of the 

BART analyses in the 2010 Oklahoma 

Regional Haze SIP, the FIP and the 2013 

SIP revision, we also evaluated the 

difference in modeled emission rates 

and emissions used in the CALPUFF 

modeling to compare the estimated 

hourly emission rates between the 0.15 

lb/MMBtu presumptive rate utilized in 

the CENRAP RPO process and the rates 

required by the FIP and 2013 SIP 

revision. The CALPUFF modeling 

provides visibility impact information 

for each of the three facilities to further 

support that the net changes in 

emissions at these three facilities result 

in a net surplus of emission reductions 

and visibility benefits that supports 

EPA’s proposed conclusion that 

visibility transport is adequately 

addressed for SO2. Below we discuss the 

difference in emissions followed by a 

discussion of the modeled visibility 

impacts. 

Single source modeling with the 

CALPUFF model was conducted for 

each of these facilities using maximum 

firing rates (instead of the actual annual 

firing rate used in CAMx analysis). The 

use of maximum firing rate rather than 

the actual annual rate that was utilized 

in the CENRAP CAMx modeling results 

in a higher estimate of hourly emission 

rates and also annual emission rates. 

Since these maximum hourly emission 

rates used for CALPUFF modeling give 

a larger difference (larger potential 

shortfall) for the Northeastern Units 3 & 

4 and also are the emission rates 

evaluated for individual visibility 

assessments, we perform our evaluation 

on these rates as well as the annual 

CAMx modeled rates discussed above 

and in Table 1. In Table 2, these 

controlled SO2 maximum hourly 

emission levels were calculated 

assuming the maximum heat input rate 

(MMBtu/hr) of each unit, which is also 

the heat input rate used in EPA’s 

CALPUFF BART modeling for the FIP, 

multiplied by the applicable emission 

rate (lb/MMBtu). A comparison of these 

numbers shows that even though the 

AEP/PSO Northeastern Unit 3 is 

required to comply with an emission 

limit of 0.40 lb/MMBtu under the 2013 

Oklahoma Regional Haze SIP Revision, 

which is higher (less stringent) than the 

0.30 lb/MMBtu level (0.15 + 0.15 for 

Northeastern Units 3 and 4) needed in 

order to achieve hourly emission levels 

equivalent to the levels relied upon in 

other states’ regional haze plans through 

the CENRAP RPO process, the total 

maximum hourly controlled SO2

emissions levels for the six units under 

the FIP and the 2013 Oklahoma 

Regional Haze SIP Revision are lower 

than the total controlled maximum 

hourly SO2 emissions levels based on 

the presumptive control level included 

in the CENRAP RPO consultation and 

modeling. In other words, the FIP and 

the 2013 Oklahoma Regional Haze SIP 

Revision result in greater SO2 emission 

reductions for these three facilities for 

the maximum hourly emissions 

compared to the maximum hourly 

emissions based on the 0.15 lb/MMBtu 

emission limit used in the CENRAP 

RPO consultation process. Specifically, 

the combination of the FIP and the 2013 

Oklahoma Regional Haze SIP Revision 

result in combined maximum hourly 

controlled SO2 emissions of 3,596.3 lb/ 

hr from the six units, which is 1,293.4 

lb/hr less than the levels estimated from 

the rate (4,889.7 lb/hr) based on the 0.15 

lb of SO2/MMBtu controlled emission 

rate that Oklahoma shared in 

consultation and was used in the 

CENRAP RPO process, including the 

CENRAP CAMx modeling. This is 

because the FIP requires a greater level 

of SO2 control for the OG&E Sooner 

Units 1 and 2 and the OG&E Muskogee 

Units 4 and 5 than the presumptive rate 

included in consultation and in the 

CENRAP CAMx modeling. The more 

stringent level of SO2 controls required 

by EPA’s FIP is therefore sufficient to 

make up for the shortfall from the AEP/ 

PSO Northeastern facility. Using the 

0.15 lb/MMBtu controlled emission rate 

from the CENRAP CAMx modeling, the 

maximum hourly emission rate using 

the higher firing rate (maximum firing 

rate) calculated that AEP/PSO 

Northeastern Units 3 and 4 would have 

combined controlled SO2 emissions of 

1710.9 lb/hr, while the 2013 Oklahoma 

Regional Haze SIP revision includes 

control requirements that result in 

combined controlled SO2 maximum 

hourly emissions of 2324.8 lb/hr, 

resulting in a shortfall of 613.9 lb/hr. 

Using the 0.15 lb/MMBtu from the 

CENRAP CAMx modeling, the OG&E 

Muskogee Units 4 and 5 would have 

combined maximum hourly controlled 

SO2 emissions of 1644 lb/hr, while the 

FIP requires SO2 controls that result in 

combined maximum hourly controlled 

SO2 emissions of 657.6 lb/hr, a 

difference of 986.4 lb/hr. This surplus of 

986.4 lb/hr of SO2 is greater than the 

613.9 lb/hr shortfall from the AEP/PSO 

Northeastern facility. Focusing on the 

OG&E Muskogee Units 4 and 5 alone, 

the level of SO2 control required by the 

FIP at these two units is sufficient to 

make up for the shortfall from the AEP/ 

PSO Northeastern facility. This is 

significant because the OG&E Muskogee 

facility is located in the northeast 

quadrant of Oklahoma, which is where 


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64 79 FR 12945. 

65See ‘‘CALPUFF tpy’’ tab of the Excel 

spreadsheet ‘‘NE SIP vs FIP visibility review 

calcs.xlsx,’’ which can be found in the docket for 

this proposed rulemaking. 

66Our calculations are found in the Excel 

spreadsheet ‘‘NE SIP vs FIP visibility review 

calcs.xlsx,’’ which can be found in the docket for 

this proposed rulemaking. 

67See ‘‘Summary Visibility’’ tab of the Excel 

spreadsheet ‘‘NE SIP vs FIP visibility review 

calcs.xlsx,’’ which can be found in the docket for 

this proposed rulemaking. 

68See ‘‘Summary Visibility’’ tab of the Excel 

spreadsheet ‘‘NE SIP vs FIP visibility review 

calcs.xlsx,’’ which can be found in the docket for 

this proposed rulemaking. 

the AEP/PSO Northeastern facility is 

located. In our final rule approving the 

2013 Oklahoma Regional Haze SIP 

revision, we explained that any 

additional SO2 emissions reductions 

that can be obtained or identified from 

the northeast quadrant of the State will 

be presumed to count toward the 

emission reductions necessary to 

achieve the anticipated visibility 

benefits associated with a 0.30 lb/ 

MMBtu emission limit at Northeastern 

Power Station.64 The OG&E Sooner 

Units 1 & 2 also provide an additional 

surplus of maximum hourly emission 

reductions (920.9 lb/hr of SO2) that 

provide benefit beyond the net surplus 

of 372.5 lb/hr of SO2 from Muskogee 

units surplus and Northeastern units 

shortfall (986.4 lb/hr¥613.9 lb/hr). The 

level of SO2 controls within EPA’s FIP 

is therefore sufficient to make up for the 

shortfall from the AEP/PSO 

Northeastern facility when comparing 

maximum hourly emissions. In the 

spreadsheet in the docket we also 

evaluated using these maximum hourly 

emission estimates on an annual basis 

(tpy) for general comparison and it also 

indicated that EPA’s FIP requirements 

result in a net surplus of annual 

emissions.65

TABLE 2—COMPARISON OF CONTROLLED SO2 EMISSIONS REDUCTIONS IN SIP/FIP VS. CENRAP CALPUFF MODELING

Facility/unit 

Maximum heat 

input rate 

used in BART 

modeling 

for FIP 

(MMBtu/hr) 

CENRAP 

modeling SO2

emission limit 

assumption 

(lb/MMBtu) 

CENRAP 

modeling controlled SO2

emissions 

assumption (lb/ 

hr) * 

SIP/FIP SO2

emission 

limit 

(lb/MMBtu) 

SIP/FIP 

controlled 

SO2

emissions (lb/ 

hr) * 

OG&E Sooner Unit 1 .................................................................................. 5,116 0.15 767.40 0.06 306.96 

OG&E Sooner Unit 2 .................................................................................. 5,116 0.15 767.40 0.06 306.96 

OG&E Muskogee Unit 4 ............................................................................. 5,480 0.15 822.0 0.06 ** 328.8 

OG&E Muskogee Unit 5 ............................................................................. 5,480 0.15 822.0 0.06 ** 328.8 

AEP/PSO Northeastern Unit ....................................................................... 5,812 0.15 871.8 0.40 2,324.8 

AEP/PSO Northeastern Unit ....................................................................... 5,594 0.15 839.1 0 0 

Total Controlled SO2 Emissions .......................................................... .......................... .......................... 4,889.7 .......................... 3,596.3 

* Controlled SO2 emissions calculated based on the maximum heat input rate (MMBtu/hr) of the unit used in EPA’s BART modeling for the FIP. 

** The controlled SO2 emissions we have calculated in this table for the OG&E Muskogee Units 4 and 5 are based on the FIP emission limits. However, OG&E 

Muskogee Units 4 and 5 converted to natural gas to comply with their SO2 BART emission limits in the FIP. Therefore, even though the FIP requires SO2 emission 

limits of 0.06 lb/MMBtu, these two units are actually emitting SO2 at much lower (near negligible) levels. 

We also assessed whether the 

visibility benefits resulting from the SO2

controls for the OG&E Sooner Units 1 

and 2 and the OG&E Muskogee Units 4 

and 5 under the FIP are estimated to 

make up for any visibility benefit 

shortfall from the AEP/PSO 

Northeastern Units 3 and 4 by scaling 

modeled visibility improvements from 

the CALPUFF modeling that was 

performed as part of the 2011 Oklahoma 

SO2 BART FIP.66 Based on previous 

modeling performed for these sources 

and other sources in other Region 6 FIPs 

and SIPs linear scaling within the 

ranges performed is a reasonable 

approach to estimate impacts. We scaled 

modeled visibility improvements for 

Wichita Mountains as well as Class I 

areas in other states affected by 

Oklahoma: Caney Creek Wilderness 

Area and Upper Buffalo Wilderness 

Area in Arkansas and Hercules-Glades 

Wilderness Area in Missouri. We used 

the 2001–2003 average of the 98th 

percentile of daily maximum dv as the 

visibility impact values for our 

calculations and assumed linear 

concentration and linear visibility 

impairment calculations. Based on our 

calculations, the SO2 emission 

reduction shortfall in the 2013 

Oklahoma Regional Haze SIP Revision 

for the AEP/PSO Northeastern Units 3 

and 4 (difference between visibility 

impacts under the 2013 SIP 

requirements and the CENRAP 

consultation and modeling assumptions 

of 0.15 lb/MMBtu for each unit) is 

estimated to result in a visibility benefit 

shortfall of 0.096 dv for the four affected 

Class I areas combined (See Table 3 

below).67 On the other hand, the FIP’s 

estimated visibility benefits in excess of 

the assumptions in the CENRAP 

consultation and modeling (i.e., 

comparing 0.15 lb/MMBtu emission 

limit from the CENRAP consultation 

and CAMx modeling with 0.06 lb/ 

MMBtu emission limit required under 

the FIP) with respect to the OG&E 

Muskogee Units 4 and 5 are 0.332 dv 

and the OG&E Sooner Units 1 and 2 are 

0.190 dv for the four affected Class I 

areas combined.68 The excess benefit 

from OG&E Muskogee Units 4 and 5 

alone is enough to more than offset the 

Northeastern shortfall at each Class I 

area, including the nearby areas in other 

states. In addition, the cumulative 

benefit at all four Class I areas is greater 

than the cumulative shortfall, resulting 

in an overall benefit of 0.236 dv (0.332 

dv excess¥0.096 dv shortfall = 0.236 

dv). Including the benefits from the four 

OG&E Muskogee and Sooner units 

results in t a net estimated excess 

visibility benefit of 0.425 dv at the four 

affected Class I areas combined. These 

results are summarized in the Table 3 

below. 


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69 Due to litigation over the FIP, the deadline by 

which these units were required to meet their SO2

emission limits contained in the FIP is January 4, 

2019. The necessary control equipment was 

installed by the compliance deadline and these 

units are currently meeting their SO2 emission 

limits. 70 76 FR 81728. 

71See 2013 i-SIP Guidance at 33. 

72 Id at 34–35. 

73A copy of the Governor’s July 22, 2020 request 

can be found in the docket for this proposed 

rulemaking. 

74 In ODEQ v. EPA, the D.C. Circuit held that 

under the CAA, a state has the authority to 

implement a SIP in non-reservation areas of Indian 

country in the state, where there has been no 

demonstration of tribal jurisdiction. Under the D.C. 

Circuit’s decision, the CAA does not provide 

authority to states to implement SIPs in Indian 

reservations. ODEQ did not, however, substantively 

address the separate authority in Indian country 

provided specifically to Oklahoma under 

SAFETEA. That separate authority was not invoked 

until the State submitted its request under 

SAFETEA, and was not approved until EPA’s 

decision, described in this section, on October 1, 

2020. 

75A copy of EPA’s October 1, 2020 approval can 

be found in the docket for this proposed 

rulemaking. 

TABLE 3—ESTIMATED SHORTFALL AND EXCESS VISIBILITY BENEFITS AT AFFECTED CLASS I AREAS DUE TO SO2

CONTROLS

Class I Area 

2001–2003 Average 98th percentile value 

(Ddv) 

AEP/PSO 

Northeastern 

estimated 

visibility 

benefit 

shortfall 1

(Ddv) 

OG&E Sooner 

estimated 

visibility 

benefit 

excess 2

(Ddv) 

OG&E 

Muskogee 

estimated 

visibility 

benefit 

excess 2

(Ddv) 

Sum of OG&E 

Sooner and 

Muskogee estimated 

visibility benefit excess 2

(Ddv) 

Estimated net 

excess visibility 

benefit 3

(Ddv) 

Wichita Mountains ....................................................................................... 0.033 0.097 0.091 0.187 0.154 

Caney Creek ............................................................................................... 0.025 0.035 0.072 0.107 0.082 

Upper Buffalo .............................................................................................. 0.017 0.033 0.094 0.127 0.110 

Hercules-Glades .......................................................................................... 0.022 0.026 0.076 0.102 0.081 

Total ..................................................................................................... 0.096 0.190 0.332 0.522 0.425 

1Based on a comparison of SO2 control requirements for the AEP/PSO Northeastern facility in the 2013 Regional Haze SIP (i.e., zero emissions for one unit and 

0.4 lb/MMBtu for the remaining unit) against the CENRAP consultation and modeling assumptions (0.15 lb/MMBtu for each unit). 2Based on a comparison of SO2 control requirements in the FIP (0.06 lb/MMBtu for each unit) against the CENRAP consultation and modeling assumptions (0.15 

lb/MMBtu for each unit). 3Based on a comparison of the ‘‘Sum of OG&E Sooner and Muskogee Estimated Visibility Benefit Excess’’ column against the ‘‘AEP/PSO Northeastern Estimated 

Visibility Benefit Shortfall’’ column. 

The FIP SO2 emission limits for the 

OG&E Sooner Units 1 and 2 and the 

OG&E Muskogee Units 4 and 5 are 

permanent and federally enforceable.69

Therefore, we are proposing to find that 

the existing SO2 emission limits for the 

OG&E Sooner Units 1 and 2 and the 

OG&E Muskogee Units 4 and 5, required 

under the FIP, are sufficient to make up 

for the shortfall in the 2013 Oklahoma 

Regional Haze SIP Revision to secure 

the emission reductions necessary to 

achieve the anticipated visibility 

benefits associated with a 0.30 lb/ 

MMBtu emission limit at Northeastern 

Power Station. 

The CENRAP modeling did not 

assume there would be any PM 

emission reductions from sources in 

Oklahoma for the first planning period. 

Therefore, the PM BART determinations 

in Oklahoma’s 2010 Regional Haze SIP, 

which EPA approved on December 28, 

2011,70 conform with the mutually 

agreed emission reductions under the 

CENRAP regional haze planning 

process. Based on our assessment 

presented in the preceding paragraphs, 

we believe that the SO2 controls 

required by the existing FIP, in 

combination with the SO2 controls 

required by the EPA-approved 2013 

Oklahoma Regional Haze SIP Revision, 

constitute an assemblage of SO2 controls 

that conform with the mutually agreed 

emission reductions under the CENRAP 

regional haze planning process. This 

ensures that the existing FIP, together 

with the approved SIP, prevents sources 

in Oklahoma from emitting pollutants in 

amounts that will interfere with efforts 

to protect visibility in other states with 

respect to the 2010 1-hour SO2 and the 

2012 PM2.5 NAAQS. Under EPA’s 2013 

i-SIP guidance, this is sufficient to 

satisfy prong 4 requirements for the first 

planning period.71 Thus, there are no 

additional practical consequences from 

this disapproval for the state, the 

sources within its jurisdiction, or the 

EPA.72 EPA is proposing to find that its 

prong 4 obligations in Oklahoma for the 

2010 1-hour SO2 and 2012 PM2.5

NAAQS are satisfied. 

F. Impact on Areas of Indian Country 

Following the U.S. Supreme Court 

decision in McGirt v. Oklahoma, 140 

S.Ct. 2452 (2020), the Governor of the 

State of Oklahoma requested approval 

under Section 10211(a) of the Safe, 

Accountable, Flexible, Efficient 

Transportation Equity Act of 2005: A 

Legacy for Users, Public Law 109–59, 

119 Stat. 1144, 1937 (August 10, 2005) 

(‘‘SAFETEA’’), to administer in certain 

areas of Indian country (as defined at 18 

U.S.C. 1151) the State’s environmental 

regulatory programs that were 

previously approved by the EPA outside 

of Indian country.73 The State’s request 

excluded certain areas of Indian country 

further described below. In addition, the 

State only sought approval to the extent 

that such approval is necessary for the 

State to administer a program in light of 

Oklahoma Dept. of Environmental 

Quality v. EPA, 740 F.3d 185 (D.C. Cir. 

2014).74

On October 1, 2020, the EPA 

approved Oklahoma’s SAFETEA request 

to administer all of the State’s EPAapproved environmental regulatory 

programs, including the Oklahoma SIP, 

in the requested areas of Indian 

country.75 As requested by Oklahoma, 

the EPA’s approval under SAFETEA 

does not include Indian country lands, 

including rights-of-way running through 

the same, that: (1) Qualify as Indian 

allotments, the Indian titles to which 

have not been extinguished, under 18 

U.S.C. 1151(c); (2) are held in trust by 

the United States on behalf of an 

individual Indian or Tribe; or (3) are 

owned in fee by a Tribe, if the Tribe (a) 

acquired that fee title to such land, or 

an area that included such land, in 

accordance with a treaty with the 

United States to which such Tribe was 

a party, and (b) never allotted the land 

to a member or citizen of the Tribe 

(collectively ‘‘excluded Indian country 

lands’’). 

EPA’s approval under SAFETEA 

expressly provided that to the extent 

EPA’s prior approvals of Oklahoma’s 

environmental programs excluded 


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76EPA’s prior approvals relating to Oklahoma’s 

SIP frequently noted that the SIP was not approved 

to apply in areas of Indian country (consistent with 

the D.C. Circuit’s decision in ODEQ v. EPA) located 

in the state. See, e.g., 85 FR 20178, 20180 (April 10, 

2020). Such prior expressed limitations are 

superseded by the EPA’s approval of Oklahoma’s 

SAFETEA request. 

77 In accordance with Executive Order 13990, 

EPA is currently reviewing our October 1, 2020 

SAFETEA approval and is engaging in further 

consultation with tribal governments and 

discussions with the state of Oklahoma as part of 

this review. EPA also notes that the October 1, 2020 

approval is the subject of a pending challenge in 

federal court. (Pawnee v. Regan, No. 20–9635 (10th 

Cir.)). Pending completion of EPA’s review, EPA is 

proceeding with this proposed action in accordance 

with the October 1, 2020 approval. EPA’s final 

action on the approved interstate visibility transport 

portion of the Oklahoma i-SIP for the 2015 Ozone 

NAAQS will address the scope of the state’s 

program with respect to Indian country, and may 

make any appropriate adjustments, based on the 

status of our review at that time. If EPA’s final 

action on Oklahoma’s SIP is taken before our review 

of the SAFETEA approval is complete, EPA may 

make further changes to the approval of Oklahoma’s 

program to reflect the outcome of the SAFETEA 

review. 

Indian country, any such exclusions are 

superseded for the geographic areas of 

Indian country covered by the EPA’s 

approval of Oklahoma’s SAFETEA 

request.76 The approval also provided 

that future revisions or amendments to 

Oklahoma’s approved environmental 

regulatory programs would extend to 

the covered areas of Indian country 

(without any further need for additional 

requests under SAFETEA). 

As explained above, the EPA is 

proposing to disapprove the interstate 

visibility transport portions of the 

Oklahoma i-SIP submittals for the 2010 

SO2 and the 2012 PM2.5 NAAQS because 

they do not meet the interstate visibility 

transport requirements of CAA Section 

110(a)(2)(D)(i)(II) with respect to these 

NAAQS; however, the EPA is also 

proposing to make the determination 

that the deficiencies forming the basis of 

the proposed disapproval of these SIPs 

are met through the existing Federal 

Implementation Plan (FIP) in place for 

the Oklahoma Regional Haze program. 

The FIP applies to all lands within the 

State regardless of land status. In 

practice, the FIP requirements, as 

discussed previously, only apply to the 

OG&E facilities, Sooner Station Units 1 

and 2, and Muskogee, Units 4 and 5. 

Additionally, EPA is proposing to 

approve the interstate visibility 

transport element of the Oklahoma i-SIP 

for the 2015 Ozone NAAQS. Consistent 

with the D.C. Circuit’s decision in 

ODEQ v. EPA and with EPA’s October 

1, 2020, SAFETEA approval, if this 

approval is finalized as proposed, this 

portion of the SIP will apply in certain 

areas of Indian country. Under EPA’s 

October 1, 2020 SAFETEA approval, the 

SIP will apply to all Indian country 

within the State of Oklahoma, other 

than the excluded Indian country lands. 

Because—per the State’s request under 

SAFETEA—EPA’s October 1, 2020 

approval does not displace any SIP 

authority previously exercised by the 

State under the CAA as interpreted in 

ODEQ v. EPA, the SIP will also apply 

to any Indian allotments or dependent 

Indian communities located outside of 

an Indian reservation over which there 

has been no demonstration of tribal 

authority. 77

This action will not result in the 

imposition of new requirements for the 

affected sources. Rather, it proposes to 

approve Oklahoma’s determination that 

the regional haze measures that have 

already been approved and are currently 

being implemented satisfy the visibility 

transport requirements for the 2015 

Ozone NAAQS and also proposes to 

make the determination that the 

regional haze measures promulgated by 

EPA in the Oklahoma FIP that are 

currently being implemented address 

the deficiencies in the Oklahoma SIP 

with respect to visibility transport 

requirements for the 2010 SO2 and 2012 

PM2.5 NAAQS. 

IV. Proposed Action 

We are proposing to approve the 

interstate visibility transport element of 

Oklahoma’s infrastructure SIP 

submission for the 2015 Ozone NAAQS. 

We are also proposing to disapprove the 

interstate visibility transport elements of 

two SIP submissions from Oklahoma: 

One for the 2010 1-hour SO2 NAAQS 

and the other for the 2012 PM2.5

NAAQS. In order to address EPA’s FIP 

obligation under section 110(c) of the 

Act, we are proposing to find that the 

deficiencies in the Oklahoma SIP that 

form the basis of our proposed 

disapproval of the interstate visibility 

transport portions of the Oklahoma i-SIP 

submissions for the 2010 SO2 and 2012 

PM2.5 NAAQS are already addressed by 

the existing FIP in place for the 

Oklahoma Regional Haze program, and 

no further federal action is required. 

V. Statutory and Executive Order 

Reviews 

A. Executive Order 12866: Regulatory 

Planning and Review and Executive 

Order 13563: Improving Regulation and 

Regulatory Review 

This action is not a significant 

regulatory action and was therefore not 

submitted to the Office of Management 

and Budget for review. 

B. Paperwork Reduction Act (PRA) 

This proposed action does not impose 

an information collection burden under 

the PRA because it does not contain any 

information collection activities. 

C. Regulatory Flexibility Act (RFA) 

I certify that this action will not have 

a significant economic impact on a 

substantial number of small entities 

under the RFA. This action merely 

proposes to disapprove a SIP 

submission as not meeting the CAA. 

D. Unfunded Mandates Reform Act 

(UMRA) 

This action does not contain any 

unfunded mandate as described in 

UMRA, 2 U.S.C. 1531–1538, and does 

not significantly or uniquely affect small 

governments. The action imposes no 

enforceable duty on any state, local or 

tribal governments or the private sector. 

E. Executive Order 13132: Federalism 

This action does not have federalism 

implications. It will not have substantial 

direct effects on the states, on the 

relationship between the national 

government and the states, or on the 

distribution of power and 

responsibilities among the various 

levels of government. 

F. Executive Order 13175: Consultation 

and Coordination With Indian Tribal 

Governments 

This proposal to approve the 

interstate visibility transport element of 

the Oklahoma i-SIP submission for the 

2015 Ozone NAAQS and to disapprove 

the interstate visibility transport 

elements of the Oklahoma i-SIP 

submissions for the 2010 1-hour SO2

NAAQS and the 2012 PM2.5 NAAQS 

(and to propose a determination that no 

further action is required to address the 

deficiencies identified in the proposed 

disapproval) will apply, if finalized as 

proposed, to certain areas of Indian 

country as discussed in the preamble, 

and therefore has tribal implications as 

specified in E.O. 13175 (65 FR 67249, 

November 9, 2000). However, this 

action will neither impose substantial 

direct compliance costs on federally 

recognized tribal governments, nor 

preempt tribal law. This action will not 

impose substantial direct compliance 

costs on federally recognized tribal 

governments because no actions will be 

required of tribal governments. This 

action will also not preempt tribal law 

as no Oklahoma tribe implements a 

regulatory program under the CAA, and 

thus does not have applicable or related 

tribal laws. Consistent with the EPA 

Policy on Consultation and 

Coordination with Indian Tribes (May 4, 


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Federal Register / Vol. 86, No. 138 / Thursday, July 22, 2021 / Proposed Rules 38643 

2011), the EPA has offered consultation 

to tribal governments that may be 

affected by this action. 

G. Executive Order 13045: Protection of 

Children From Environmental Health 

Risks and Safety Risks 

EPA interprets Executive Order 13045 

as applying only to those regulatory 

actions that concern environmental 

health or safety risks that the EPA has 

reason to believe may 

disproportionately affect children, per 

the definition of ‘‘covered regulatory 

action’’ in section 2–202 of the 

Executive Order. This action is not 

subject to Executive Order 13045 

because it merely proposes to 

disapprove a SIP submission as not 

meeting the CAA. 

H. Executive Order 13211, Actions That 

Significantly Affect Energy Supply, 

Distribution or Use 

This action is not subject to Executive 

Order 13211, because it is not a 

significant regulatory action under 

Executive Order 12866. 

I. National Technology Transfer and 

Advancement Act 

This rulemaking does not involve 

technical standards. 

J. Executive Order 12898: Federal 

Actions To Address Environmental 

Justice in Minority Populations and 

Low-Income Populations 

EPA believes the human health or 

environmental risk addressed by this 

action will not have potential 

disproportionately high and adverse 

human health or environmental effects 

on minority, low-income or indigenous 

populations. This action merely 

proposes to disapprove a SIP 

submission as not meeting the CAA. 

List of Subjects in 40 CFR Part 52 

Environmental protection, Air 

pollution control, Incorporation by 

reference, Intergovernmental relations, 

Nitrogen dioxide, Ozone, Particulate 

matter, Sulfur oxides, Visibility 

transport. 

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

Dated: July 15, 2021. 

David Gray, 

Acting Regional Administrator, Region 6. 

[FR Doc. 2021–15467 Filed 7–21–21; 8:45 am] 

BILLING CODE 6560–50–P 

ENVIRONMENTAL PROTECTION 

AGENCY 

40 CFR Part 52 

[EPA–R05–OAR–2021–0256; FRL–8692–01– 

R5] 

Air Plan Approval; Wisconsin; 

Attainment Plan for the Rhinelander 

SO2 Nonattainment Area 

AGENCY: Environmental Protection 

Agency (EPA). 

ACTION: Proposed rule. 

SUMMARY: The Environmental Protection 

Agency (EPA) is proposing to approve 

the State Implementation Plan (SIP) 

revision submitted by Wisconsin on 

March 29, 2021, which amends a SIP 

submission previously submitted to 

EPA on January 22, 2016 and 

supplemented on July 18, 2016, and 

November 29, 2016, for attaining the 1- 

hour sulfur dioxide (SO2) primary 

national ambient air quality standard 

(NAAQS) for the Rhinelander SO2

nonattainment area. This plan (herein 

referred to as Wisconsin’s Rhinelander 

SO2 plan or plan) includes Wisconsin’s 

attainment demonstration and other 

elements required under the Clean Air 

Act (CAA). In addition to an attainment 

demonstration, the plan addresses the 

requirement for meeting reasonable 

further progress (RFP) toward 

attainment of the NAAQS, reasonably 

available control measures and 

reasonably available control technology 

(RACM/RACT), and contingency 

measures. This action supplements a 

prior action which found that 

Wisconsin had satisfied emission 

inventory and new source review (NSR) 

requirements for this area, but had not 

met requirements for the elements 

proposed to be approved here. EPA is 

proposing to conclude that Wisconsin 

has appropriately demonstrated that the 

plan provisions provide for attainment 

of the 2010 1-hour primary SO2 NAAQS 

in the Rhinelander SO2 nonattainment 

area and that the plan meets the other 

applicable requirements under the CAA. 

DATES: Comments must be received on 

or before August 23, 2021. 

ADDRESSES: Submit your comments, 

identified by Docket ID No. EPA–R05– 

OAR–2021–0256 at http://

www.regulations.gov, or via email to 

leslie.michael@epa.gov. For comments 

submitted at Regulations.gov, follow the 

online instructions for submitting 

comments. Once submitted, comments 

cannot be edited or removed from 

Regulations.gov. For either manner of 

submission, 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. 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 the person 

identified in the FOR FURTHER

INFORMATION CONTACT section. For the 

full EPA public comment policy, 

information about CBI or multimedia 

submissions, and general guidance on 

making effective comments, please visit 

http://www2.epa.gov/dockets/ 

commenting-epa-dockets. 

FOR FURTHER INFORMATION CONTACT: 

Abigail Teener, Environmental 

Engineer, Attainment Planning and 

Maintenance Section, Air Programs 

Branch (AR–18J), Environmental 

Protection Agency, Region 5, 77 West 

Jackson Boulevard, Chicago, Illinois 

60604, (312) 353–7314, teener.abigail@

epa.gov. The EPA Region 5 office is 

open from 8:30 a.m. to 4:30 p.m., 

Monday through Friday, excluding 

Federal holidays and facility closures 

due to COVID–19. 

SUPPLEMENTARY INFORMATION: This 

SUPPLEMENTARY INFORMATION section is 

arranged as follows: 

I. Why was Wisconsin required to submit an 

SO2 plan for the Rhinelander area? 

II. Requirements for SO2 Nonattainment Area 

Plans 

III. Attainment Demonstration and Longer 

Term Averaging 

IV. Review of Modeled Attainment Plan 

A. Model Selection 

B. Simulation of Downwash 

C. Meteorological Data 

D. Emissions Data 

E. Emission Limits 

F. Background Concentrations 

G. Summary of Results 

V. Review of Other Plan Requirements 

A. RACM/RACT 

B. Reasonable Further Progress (RFP) 

C. Contingency Measures 

VI. What action is EPA taking? 

VII. Incorporation by Reference 

VIII. Statutory and Executive Order Reviews 

I. Why was Wisconsin required to 

submit an SO2 plan for the Rhinelander 

area? 

On June 22, 2010, EPA promulgated a 

new 1-hour primary SO2 NAAQS of 75 

parts per billion (ppb), which is met at 

an ambient air quality monitoring site 

when the 3-year average of the annual 

99th percentile of daily maximum 1- 


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