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61A finding of nationwide scope or effect is also 

appropriate for actions that cover states in multiple 

judicial circuits. In the report on the 1977 

Amendments that revised section 307(b)(1) of the 

CAA, Congress noted that the Administrator’s 

determination that the ‘‘nationwide scope or effect’’ 

exception applies would be appropriate for any 

action that has a scope or effect beyond a single 

judicial circuit. See H.R. Rep. No. 95–294 at 323, 

324, reprinted in 1977 U.S.C.C.A.N. 1402–03. 

62The EPA may take a consolidated, single final 

action on all the proposed SIP disapproval actions 

with respect to obligations under CAA section 

110(a)(2)(D)(i)(I) for the 2015 ozone NAAQS. 

Should EPA take a single final action on all such 

disapprovals, this action would be nationally 

applicable, and the EPA would also anticipate, in 

the alternative, making and publishing a finding 

that such final action is based on a determination 

of nationwide scope or effect. 

the Administrator intends to exercise 

the complete discretion afforded to him 

under the CAA to make and publish a 

finding that the final action (to the 

extent a court finds the action to be 

locally or regionally applicable) is based 

on a determination of ‘‘nationwide 

scope or effect’’ within the meaning of 

CAA section 307(b)(1). Through this 

rulemaking action (in conjunction with 

a series of related actions on other SIP 

submissions for the same CAA 

obligations), the EPA interprets and 

applies section 110(a)(2)(d)(i)(I) of the 

CAA for the 2015 ozone NAAQS based 

on a common core of nationwide policy 

judgments and technical analysis 

concerning the interstate transport of 

pollutants throughout the continental 

U.S. In particular, the EPA is applying 

here (and in other proposed actions 

related to the same obligations) the 

same, nationally consistent 4-step 

framework for assessing good neighbor 

obligations for the 2015 ozone NAAQS. 

The EPA relies on a single set of 

updated, 2016-base year photochemical 

grid modeling results of the year 2023 

as the primary basis for its assessment 

of air quality conditions and 

contributions at Steps 1 and 2 of that 

framework. Further, the EPA proposes 

to determine and apply a set of 

nationally consistent policy judgments 

to apply the 4-step framework. The EPA 

has selected a nationally uniform 

analytic year (2023) for this analysis and 

is applying a nationally uniform 

approach to nonattainment and 

maintenance receptors and a nationally 

uniform approach to contribution 

threshold analysis.61 For these reasons, 

the Administrator intends, if this 

proposed action is finalized, to exercise 

the complete discretion afforded to him 

under the CAA to make and publish a 

finding that this action is based on one 

or more determinations of nationwide 

scope or effect for purposes of CAA 

section 307(b)(1).62

List of Subjects in 40 CFR Part 52 

Environmental protection, Air 

pollution control, Incorporation by 

reference, Ozone. 

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

Dated: January 31, 2022. 

Lisa Garcia, 

Regional Administrator, Region 2. 

[FR Doc. 2022–02946 Filed 2–18–22; 8:45 am] 

BILLING CODE 6560–50–P 

ENVIRONMENTAL PROTECTION 

AGENCY 

40 CFR Part 52 

[EPA–R04–OAR–2021–0841; EPA–HQ– 

OAR–2021–0663; FRL–9423–01–R4] 

Air Plan Disapproval; Kentucky; 

Interstate Transport Requirements for 

the 2015 8-Hour Ozone National 

Ambient Air Quality Standards 

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 

or Agency) is proposing to disapprove a 

State Implementation Plan (SIP) 

submittal from the Kentucky Energy and 

Environment Cabinet, Department of 

Environmental Quality (DAQ) (herein 

after referred to as Kentucky or the 

Commonwealth) regarding the interstate 

transport requirements for the 2015 8- 

hour ozone national ambient air quality 

standards (NAAQS or standard). The 

‘‘Good Neighbor’’ or ‘‘Interstate 

Transport’’ provision requires that each 

state’s implementation plan contain 

adequate provisions to prohibit 

emissions from within the state from 

significantly contributing to 

nonattainment or interfering with 

maintenance of the NAAQS in other 

states. This requirement is part of the 

broader set of ‘‘infrastructure’’ 

requirements, which are designed to 

ensure that the structural components of 

each state’s air quality management 

program are adequate to meet the state’s 

responsibilities under the CAA. This 

disapproval, if finalized, will establish a 

2-year deadline for EPA to promulgate 

a Federal Implementation Plan (FIP) to 

address the relevant interstate transport 

requirements, unless EPA approves a 

subsequent SIP submittal that meets 

these requirements. Disapproval does 

not start a mandatory sanctions clock. 

DATES: Comments must be received on 

or before April 25, 2022. 

Withdrawals: As of February 22, 2022, 

the proposed rule published in 

December 30, 2019, at 84 FR 71854, is 

withdrawn. 

ADDRESSES: You may submit comments, 

identified by Docket No. EPA–R04– 

OAR–2021–0841, through the Federal 

eRulemaking Portal at https://

www.regulations.gov following the 

online instructions for submitting 

comments. 

Instructions: All submissions received 

must include the Docket No. EPA–R04– 

OAR–2021–0841 for this rulemaking. 

Comments received may be posted 

without change to https://

www.regulations.gov/, including any 

personal information provided. For 

detailed instructions on submitting 

comments and additional information 

on the rulemaking process, see the 

‘‘Public Participation’’ heading of the 

SUPPLEMENTARY INFORMATION section of 

this document. Out of an abundance of 

caution for members of the public and 

staff, the EPA Docket Center and 

Reading Room are open to the public by 

appointment only to reduce the risk of 

transmitting COVID–19. The Docket 

Center staff also continues to provide 

remote customer service via email, 

phone, and webform. For further 

information on EPA Docket Center 

services and the current status, please 

visit EPA online at https://

www.epa.gov/dockets. 

FOR FURTHER INFORMATION CONTACT: 

Evan Adams of the Air Regulatory 

Management Section, Air Planning and 

Implementation Branch, Air and 

Radiation Division, U.S. Environmental 

Protection Agency, Region 4, 61 Forsyth 

Street SW, Atlanta, Georgia 30303–8960. 

Mr. Adams can be reached by telephone 

at (404) 562–9009, or via electronic mail 

at adams.evan@epa.gov. 

SUPPLEMENTARY INFORMATION: Public 

Participation: Submit your comments, 

identified by Docket No. EPA–R04– 

OAR–2021–0841, at https://

www.regulations.gov. Once submitted, 

comments cannot be edited or removed 

from the docket. EPA may publish any 

comment received to its public docket. 

Do not submit to EPA’s docket at 

https://www.regulations.gov 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). 


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1National Ambient Air Quality Standards for 

Ozone, Final Rule, 80 FR 65292 (October 26, 2015). 

Although the level of the standard is specified in 

the units of ppm, ozone concentrations are also 

described in parts per billion (ppb). For example, 

0.070 ppm is equivalent to 70 ppb. 

2SIP revisions that are intended to meet the 

applicable requirements of section 110(a)(1) and (2) 

of the CAA are often referred to as infrastructure 

SIPs and the applicable elements under section 

110(a)(2) are referred to as infrastructure 

requirements. 

3See North Carolina v. EPA, 531 F.3d 896, 909– 

11 (D.C. Cir. 2008). 

4See Federal Implementation Plans: Interstate 

Transport of Fine Particulate Matter and Ozone and 

Correction of SIP Approvals, 76 FR 48208 (August 

8, 2011). 

5Cross-State Air Pollution Rule Update for the 

2008 Ozone NAAQS, 81 FR 74504 (October 26, 

2016). 

6 In 2019, the United States Court of Appeals for 

the District of Columbia Circuit (D.C. Circuit) 

remanded the CSAPR Update to the extent it failed 

to require upwind states to eliminate their 

significant contribution by the next applicable 

attainment date by which downwind states must 

come into compliance with the NAAQS, as 

established under CAA section 181(a). Wisconsin v. 

EPA, 938 F.3d 303, 313 (D.C. Cir. 2019). The 

Revised CSAPR Update for the 2008 Ozone 

NAAQS, 86 FR 23054 (April 30, 2021), responded 

to the remand of the CSAPR Update in Wisconsin 

and the vacatur of a separate rule, the ‘‘CSAPR 

Close-Out,’’ 83 FR 65878 (December 21, 2018), in 

New York v. EPA, 781 F. App’x. 4 (D.C. Cir. 2019). 

7 In addition to CSAPR rulemakings, other 

regional rulemakings addressing ozone transport 

include the ‘‘NOX SIP Call,’’ 63 FR 57356 (October 

27, 1998), and the ‘‘Clean Air Interstate Rule’’ 

(CAIR), 70 FR 25162 (May 12, 2005). 

There are two dockets supporting this 

action, EPA–R04–OAR–2021–0841 and 

EPA–HQ–OAR–2021–0663. Docket No. 

EPA–R04–OAR–2021–0841 contains 

information specific to Kentucky, 

including this notice of proposed 

rulemaking. Docket No. EPA–HQ–OAR– 

2021–0663 contains additional 

modeling files, emissions inventory 

files, technical support documents, and 

other relevant supporting 

documentation regarding interstate 

transport of emissions for the 2015 8- 

hour ozone NAAQS which are being 

used to support this action. All 

comments regarding information in 

either of these dockets are to be made 

in Docket No. EPA–R04–OAR–2021– 

0841. 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-epadockets. Due to public health concerns 

related to COVID–19, the EPA Docket 

Center and Reading Room are open to 

the public by appointment only. The 

Docket Center staff also continues to 

provide remote customer service via 

email, phone, and webform. For further 

information and updates on EPA Docket 

Center services, please visit EPA online 

at https://www.epa.gov/dockets. 

EPA continues to carefully and 

continuously monitor information from 

the Centers for Disease Control and 

Prevention (CDC), local area health 

departments, and Federal partners so 

that EPA can respond rapidly as 

conditions change regarding COVID–19. 

The indices to Docket No. EPA–R04– 

OAR–2021–0841 and Docket No. EPA– 

HQ–OAR–2021–0663 are available 

electronically at www.regulations.gov. 

While all documents in each docket are 

listed in their respective index, some 

information may not be publicly 

available due to docket file size 

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

Table of Contents 

I. Background 

A. Description of Statutory Background 

B. Description of EPA’s Four Step 

Interstate Transport Regulatory Process 

C. Background on EPA’s Ozone Transport 

Modeling Information 

D. EPA’s Approach to Evaluating Interstate 

Transport SIPs for the 2015 8-Hour 

Ozone NAAQS 

II. Summary of Kentucky’s 2015 8-Hour 

Ozone Interstate Transport SIP 

Submission 

A. Information Related to Emission Trends 

From Kentucky Sources 

B. Information Related to Connecticut 

Monitors Provided by Kentucky 

C. Information Related to the Harford, 

Maryland Monitor Provided by Kentucky 

D. Summary of Conclusions From 

Kentucky 

E. Summary of Midwest Ozone Group TSD 

Appended to Kentucky’s Submittal 

III. EPA’s Evaluation of Kentucky’s 2015 8- 

Hour Ozone Interstate Transport SIP 

Submission 

A. Results of EPA’s Step 1 and Step 2 

Modeling and Findings for Kentucky 

B. Evaluation of Information Provided by 

Kentucky Regarding Step 1 

C. Evaluation of Information Provided by 

Kentucky Regarding Step 2 

D. Evaluation of Information Provided by 

Kentucky Regarding Step 3 

E. Evaluation of Information Provided by 

Kentucky Regarding Step 4 

F. Conclusion 

IV. Proposed Action 

V. Statutory and Executive Order Reviews 

I. Background 

The following provides background 

for EPA’s proposed action related to the 

interstate transport requirements for the 

2015 8-hour ozone NAAQS for the 

Commonwealth of Kentucky. 

A. Description of Statutory Background 

On October 1, 2015, EPA promulgated 

a revision to the ozone NAAQS (2015 8- 

hour ozone NAAQS), lowering the level 

of both the primary and secondary 

standards to 0.070 parts per million 

(ppm).1 Section 110(a)(1) of the CAA 

requires states to submit, within 3 years 

after promulgation of a new or revised 

standard, SIP submissions meeting the 

applicable requirements of section 

110(a)(2).2 One of these applicable 

requirements is found in CAA section 

110(a)(2)(D)(i)(I), otherwise known as 

the ‘‘good neighbor’’ or ‘‘interstate 

transport’’ provision, which generally 

requires SIPs to contain adequate 

provisions to prohibit in-state emissions 

activities from having certain adverse 

air quality effects on other states due to 

interstate transport of pollution. There 

are two so-called ‘‘prongs’’ within CAA 

section 110(a)(2)(D)(i)(I). A SIP for a 

new or revised NAAQS must contain 

adequate provisions prohibiting any 

source or other type of emissions 

activity within the state from emitting 

air pollutants in amounts that will 

significantly contribute to 

nonattainment of the NAAQS in another 

state (prong 1) or interfere with 

maintenance of the NAAQS in another 

state (prong 2). EPA and states must give 

independent significance to prong 1 and 

prong 2 when evaluating downwind air 

quality problems under CAA section 

110(a)(2)(D)(i)(I).3

B. Description of EPA’s Four Step 

Interstate Transport Regulatory Process 

EPA is using the 4-step interstate 

transport framework (or 4-step 

framework) to evaluate the states’ 

implementation plan submittals 

addressing the interstate transport 

provision for the 2015 8-hour ozone 

NAAQS. EPA has addressed the 

interstate transport requirements of 

CAA section 110(a)(2)(D)(i)(I) with 

respect to prior ozone NAAQS in 

several regional regulatory actions, 

including the Cross-State Air Pollution 

Rule (CSAPR), which addressed 

interstate transport with respect to the 

1997 ozone NAAQS as well as the 1997 

and 2006 fine particulate matter 

standards,4 the Cross-State Air Pollution 

Rule Update (CSAPR Update) 5 and the 

Revised CSAPR Update, both of which 

addressed the 2008 ozone NAAQS.6

Through the development and 

implementation of the CSAPR 

rulemakings and prior regional 

rulemakings pursuant to the interstate 

transport provision,7 EPA, working in 

partnership with states, developed the 

following 4-step interstate transport 

framework to evaluate a state’s 

obligations to eliminate interstate 

transport emissions under the interstate 

transport provision for the ozone 

NAAQS: (1) Identify monitoring sites 

that are projected to have problems 

attaining and/or maintaining the 

NAAQS (i.e., nonattainment and/or 

maintenance receptors); (2) identify 


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8See Notice of Availability of the Environmental 

Protection Agency’s Preliminary Interstate Ozone 

Transport Modeling Data for the 2015 8-hour Ozone 

National Ambient Air Quality Standard (NAAQS), 

82 FR 1733 (January 6, 2017). 

9See 82 FR 1733, 1735 (January 6, 2017). 

10See Information on the Interstate Transport 

State Implementation Plan Submissions for the 

2008 Ozone National Ambient Air Quality 

Standards under Clean Air Act Section 

110(a)(2)(D)(i)(I), October 27, 2017 (‘‘October 2017 

memorandum’’), available in Docket No. EPA–HQ– 

OAR–2021–0663 or at https://www.epa.gov/ 

interstate-air-pollution-transport/interstate-airpollution-transport-memos-and-notices. 

11See Information on the Interstate Transport 

State Implementation Plan Submissions for the 

2015 Ozone National Ambient Air Quality 

Standards under Clean Air Act Section 

110(a)(2)(D)(i)(I), March 27, 2018 (‘‘March 2018 

memorandum’’), available in Docket No. EPA–HQ– 

OAR–2021–0663 or at https://www.epa.gov/ 

interstate-air-pollution-transport/interstate-airpollution-transport-memos-and-notices. 

12The March 2018 memorandum, however, 

provided, ‘‘While the information in this 

memorandum and the associated air quality 

analysis data could be used to inform the 

development of these SIPs, the information is not 

a final determination regarding states’ obligations 

under the good neighbor provision. Any such 

determination would be made through notice-andcomment rulemaking.’’ 

13See Analysis of Contribution Thresholds for 

Use in Clean Air Act Section 110(a)(2)(D)(i)(I) 

Interstate Transport State Implementation Plan 

Submissions for the 2015 Ozone National Ambient 

Air Quality Standards, August 31, 2018) (‘‘August 

2018 memorandum’’), and Considerations for 

Identifying Maintenance Receptors for Use in Clean 

Air Act Section 110(a)(2)(D)(i)(I) Interstate 

Transport State Implementation Plan Submissions 

for the 2015 Ozone National Ambient Air Quality 

Standards, October 19, 2018 (‘‘October 2018 

memorandum’’), available in Docket No. EPA–HQ– 

OAR–2021–0663 for this action or at https://

www.epa.gov/airmarkets/memo-and-supplementalinformation-regarding-interstate-transport-sips2015-ozone-naaqs. 

14The results of this modeling, as well as the 

underlying modeling files, are included in Docket 

No. EPA–HQ–OAR–2021–0663. 

15See 85 FR 68964, 68981 (October 30, 2020). 

16See the Air Quality Modeling Technical 

Support Document for the Final Revised Cross-State 

Air Pollution Rule Update, included in Docket No. 

EPA–HQ–OAR–2021–0663. 

17Additional details and documentation related 

to the MOVES3 model can be found at https://

www.epa.gov/moves/latest-version-motor-vehicleemission-simulator-moves. 

states that impact those air quality 

problems in other (i.e., downwind) 

states sufficiently such that the states 

are considered ‘‘linked’’ and therefore 

warrant further review and analysis; (3) 

identify the emissions reductions 

necessary (if any), applying a 

multifactor analysis, to eliminate each 

linked upwind state’s significant 

contribution to nonattainment or 

interference with maintenance of the 

NAAQS at the locations identified in 

Step 1; and (4) adopt permanent and 

enforceable measures needed to achieve 

those emissions reductions. 

C. Background on EPA’s Ozone 

Transport Modeling Information 

In general, EPA has performed 

nationwide air quality modeling to 

project ozone design values which are 

used in combination with measured 

data to identify nonattainment and 

maintenance receptors. To quantify the 

contribution of emissions from specific 

upwind states on 2023 ozone design 

values for the identified downwind 

nonattainment and maintenance 

receptors, EPA performed nationwide, 

state-level ozone source apportionment 

modeling for 2023. The source 

apportionment modeling provided 

contributions to ozone at receptors from 

precursor emissions of anthropogenic 

nitrogen oxides (NOX) and volatile 

organic compounds (VOCs) in 

individual upwind states. 

EPA has released several documents 

containing projected design values, 

contributions, and information relevant 

to evaluating interstate transport with 

respect to the 2015 8-hour ozone 

NAAQS. First, on January 6, 2017, EPA 

published a notice of data availability 

(NODA) in which the Agency requested 

comment on preliminary interstate 

ozone transport data including projected 

ozone design values and interstate 

contributions for 2023 using a 2011 base 

year platform.8 In the NODA, EPA used 

the year 2023 as the analytic year for 

this preliminary modeling because that 

year aligns with the expected attainment 

year for Moderate ozone nonattainment 

areas for the 2015 8-hour ozone 

NAAQS.9 On October 27, 2017, EPA 

released a memorandum (October 2017 

memorandum) containing updated 

modeling data for 2023, which 

incorporated changes made in response 

to comments on the NODA, and noted 

that the modeling may be useful for 

states developing SIPs to address 

interstate transport obligations for the 

2008 ozone NAAQS.10 On March 27, 

2018, EPA issued a memorandum 

(March 2018 memorandum) noting that 

the same 2023 modeling data released in 

the October 2017 memorandum could 

also be useful for identifying potential 

downwind air quality problems with 

respect to the 2015 8-hour ozone 

NAAQS at Step 1 of the 4-step interstate 

transport framework.11 The March 2018 

memorandum also included the then 

newly available contribution modeling 

data for 2023 to assist states in 

evaluating their impact on potential 

downwind air quality problems for the 

2015 8-hour ozone NAAQS under Step 

2 of the 4-step interstate transport 

framework.12 EPA subsequently issued 

two more memoranda in August and 

October 2018, providing additional 

information to states developing 

interstate transport SIP submissions for 

the 2015 8-hour ozone NAAQS 

concerning, respectively, potential 

contribution thresholds that may be 

appropriate to apply in Step 2 of the 4- 

step interstate transport framework, and 

considerations for identifying 

downwind areas that may have 

problems maintaining the standard at 

Step 1 of the 4-step interstate transport 

framework.13

Since the release of the modeling data 

shared in the March 2018 

memorandum, EPA performed updated 

modeling using a 2016-based emissions 

modeling platform (i.e., 2016v1). This 

emissions platform was developed 

under the EPA/Multi-Jurisdictional 

Organization (MJO)/state collaborative 

project.14 This collaborative project was 

a multi-year joint effort by EPA, MJOs, 

and states to develop a new, more recent 

emissions platform for use by EPA and 

states in regulatory modeling as an 

improvement over the dated 2011-based 

platform that EPA had used to project 

ozone design values and contribution 

data provided in the 2017 and 2018 

memoranda. EPA used the 2016v1 

emissions to project ozone design values 

and contributions for 2023. On October 

30, 2020, in the Notice of Proposed 

Rulemaking for the Revised CSAPR 

Update, EPA released and accepted 

public comment on 2023 modeling that 

used the 2016v1 emissions platform.15

Although the Revised CSAPR Update 

addressed transport for the 2008 ozone 

NAAQS, the projected design values 

and contributions from the 2016v1 

platform are also useful for identifying 

downwind ozone problems and linkages 

with respect to the 2015 8-hour ozone 

NAAQS.16

Following the Revised CSAPR Update 

final rule, EPA made further updates to 

the 2016 emissions platform to include 

mobile emissions from EPA’s Motor 

Vehicle Emission Simulator (MOVES) 

model 17 and updated emissions 

projections for electric generating units 

(EGUs) that reflect the emissions 

reductions from the Revised CSAPR 

Update, recent information on plant 

closures, and other sector trends. The 

construct of the updated emissions 

platform, 2016v2, is described in the 

Preparation of Emissions Inventories for 

the 2016v2 North American Emissions 

Modeling Platform technical support 

document (TSD) for this proposed rule 

and is included in Docket No. EPA–HQ– 

OAR–2021–0663. EPA performed air 

quality modeling of the 2016v2 

emissions using the most recent public 

release version of the Comprehensive 

Air Quality Modeling with Extensions 

(CAMx) photochemical modeling, 


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18Ramboll Environment and Health, January 

2021, www.camx.com. 

19March 2018 memorandum, Attachment A. 

20 Id. at A–1. 

21 Id. 

22For attainment dates for the 2015 8-hour ozone 

NAAQS, refer to CAA section 181(a), 40 CFR 

51.1303, and Additional Air Quality Designations 

for the 2015 Ozone National Ambient Air Quality 

Standards, 83 FR 25776 (June 4, 2018, effective 

August 3, 2018). 

version 7.10.18 EPA proposes to 

primarily rely on modeling based on the 

updated and newly available 2016v2 

emissions platform in evaluating these 

submissions with respect to Steps 1 and 

2 of the 4-step interstate transport 

framework. By using the updated 

modeling results, EPA is using the most 

current and technically appropriate 

information for this proposed 

rulemaking. Section III of this notice 

and the Air Quality Modeling TSD 

included in Docket No. EPA–HQ–OAR– 

2021–0663 for this proposal contain 

additional detail on the modeling 

performed using the 2016v2 emissions 

modeling. 

In this notice, EPA is accepting public 

comment on this updated 2023 

modeling, which uses the 2016v2 

emissions platform. Details on the air 

quality modeling and the methods for 

projecting design values and 

determining contributions in 2023 are 

described in the Air Quality Modeling 

TSD for 2015 8-hour Ozone NAAQS 

Transport SIP Proposed Actions. 

Comments on EPA’s air quality 

modeling should be submitted in Docket 

No. EPA–R04–OAR–2021–0841. 

Comments are not being accepted in 

Docket No. EPA–HQ–OAR–2021–0663. 

States may have chosen to rely on the 

results of EPA modeling and/or 

alternative modeling performed by 

states or Multi-Jurisdictional 

Organizations (MJOs) to evaluate 

downwind air quality problems and 

contributions as part of their 

submissions. In section III, EPA 

evaluates how Kentucky used air quality 

modeling information in its submission. 

D. EPA’s Approach to Evaluating 

Interstate Transport SIPs for the 2015 8- 

Hour Ozone NAAQS 

EPA proposes to apply a consistent 

set of policy judgments across all states 

for purposes of evaluating interstate 

transport obligations and the 

approvability of interstate transport SIP 

submittals for the 2015 8-hour ozone 

NAAQS. These policy judgments reflect 

consistency with relevant case law and 

past Agency practice as reflected in 

CSAPR and related rulemakings. 

Nationwide consistency in approach is 

particularly important in the context of 

interstate ozone transport, which is a 

regional-scale pollution problem 

involving many smaller contributors. 

Effective policy solutions to the problem 

of interstate ozone transport going back 

to the NOX SIP Call have necessitated 

the application of a uniform framework 

of policy judgments in order to ensure 

an ‘‘efficient and equitable’’ approach. 

See EME Homer City Generation, LP v. 

EPA, 572 U.S. 489, 519 (2014). 

In the March, August, and October 

2018 memoranda, EPA recognized that 

states may be able to establish 

alternative approaches to addressing 

their interstate transport obligations for 

the 2015 8-hour ozone NAAQS that vary 

from a nationally uniform framework. 

EPA emphasized in these memoranda, 

however, that such alternative 

approaches must be technically justified 

and appropriate in light of the facts and 

circumstances of each particular state’s 

submittal. In general, EPA continues to 

believe that deviation from a nationally 

consistent approach to ozone transport 

must be substantially justified and have 

a well-documented technical basis that 

is consistent with relevant case law. 

Where states submitted SIPs that rely on 

any such potential concepts as may 

have been identified or suggested in the 

past, EPA will evaluate whether the 

state adequately justified the technical 

and legal basis for doing so. 

EPA notes that certain potential 

concepts included in an attachment to 

the March 2018 memorandum require 

unique consideration, and these ideas 

do not constitute Agency guidance with 

respect to transport obligations for the 

2015 8-hour ozone NAAQS. Attachment 

A to the March 2018 memorandum 

identified a ‘‘Preliminary List of 

Potential Flexibilities’’ that could 

potentially inform SIP development.19

However, EPA made clear in that 

attachment that the list of ideas were 

not suggestions endorsed by the Agency 

but rather ‘‘comments provided in 

various forums’’ on which EPA sought 

‘‘feedback from interested 

stakeholders.’’ 20 Further, Attachment A 

stated, ‘‘EPA is not at this time making 

any determination that the ideas 

discussed below are consistent with the 

requirements of the CAA, nor [is EPA] 

specifically recommending that states 

use these approaches.’’ 21 Attachment A 

to the March 2018 memorandum, 

therefore, does not constitute agency 

guidance, but was intended to generate 

further discussion around potential 

approaches to addressing ozone 

transport among interested stakeholders. 

To the extent states sought to develop or 

rely on these ideas in support of their 

SIP submittals, EPA will thoroughly 

review the technical and legal 

justifications for doing so. 

The remainder of this section 

describes EPA’s proposed framework 

with respect to analytic year, definition 

of nonattainment and maintenance 

receptors, selection of contribution 

threshold, and multifactor control 

strategy assessment. 

1. Selection of Analytic Year 

In general, the states and EPA must 

implement the interstate transport 

provision in a manner ‘‘consistent with 

the provisions of [title I of the CAA].’’ 

See CAA section 110(a)(2)(D)(i). This 

requires, among other things, that these 

obligations are addressed consistently 

with the timeframes for downwind areas 

to meet their CAA obligations. With 

respect to ozone NAAQS, under CAA 

section 181(a), this means obligations 

must be addressed ‘‘as expeditiously as 

practicable’’ and no later than the 

schedule of attainment dates provided 

in CAA section 181(a)(1).22 Several D.C. 

Circuit court decisions address the issue 

of the relevant analytic year for the 

purposes of evaluating ozone transport 

air-quality problems. On September 13, 

2019, the D.C. Circuit issued a decision 

in Wisconsin v. EPA, remanding the 

CSAPR Update to the extent that it 

failed to require upwind states to 

eliminate their significant contribution 

by the next applicable attainment date 

by which downwind states must come 

into compliance with the NAAQS, as 

established under CAA section 181(a). 

See 938 F.3d 303, 313. 

On May 19, 2020, the D.C. Circuit 

issued a decision in Maryland v. EPA 

that cited the Wisconsin decision in 

holding that EPA must assess the impact 

of interstate transport on air quality at 

the next downwind attainment date, 

including Marginal area attainment 

dates, in evaluating the basis for EPA’s 

denial of a petition under CAA section 

126(b). Maryland v. EPA, 958 F.3d 1185, 

1203–04 (D.C. Cir. 2020). The court 

noted that ‘‘section 126(b) incorporates 

the Good Neighbor Provision,’’ and, 

therefore, ‘‘EPA must find a violation [of 

section 126] if an upwind source will 

significantly contribute to downwind 

nonattainment at the next downwind 

attainment deadline. Therefore, the 

agency must evaluate downwind air 

quality at that deadline, not at some 

later date.’’ Id. at 1204 (emphasis 

added). EPA interprets the court’s 

holding in Maryland as requiring the 

states and the Agency, under the good 

neighbor provision, to assess downwind 

air quality as expeditiously as 

practicable and no later than the next 


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23EPA notes that the court in Maryland did not 

have occasion to evaluate circumstances in which 

EPA may determine that an upwind linkage to a 

downwind air quality problem exists at Steps 1 and 

2 of the interstate transport framework by a 

particular attainment date, but for reasons of 

impossibility or profound uncertainty the Agency is 

unable to mandate upwind pollution controls by 

that date. See Wisconsin, 938 F.3d at 320. The D.C. 

Circuit noted in Wisconsin that upon a sufficient 

showing, these circumstances may warrant 

flexibility in effectuating the purpose of the 

interstate transport provision. 

24See CAA section 181(a); 40 CFR 51.1303; 

Additional Air Quality Designations for the 2015 

Ozone National Ambient Air Quality Standards, 83 

FR 25776 (June 4, 2018, effective August 3, 2018). 

25See North Carolina v. EPA, 531 F.3d 896, 910– 

11 (D.C. Cir. 2008) (holding that EPA must give 

‘‘independent significance’’ to each prong of CAA 

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

26See 81 FR 74504 (October 26, 2016). This same 

concept, relying on both current monitoring data 

and modeling to define nonattainment receptor, 

was also applied in CAIR. See 70 FR at 25241, 

25249 (January 14, 2005); see also North Carolina, 

531 F.3d at 913–14 (affirming as reasonable EPA’s 

approach to defining nonattainment in CAIR). 

27See 76 FR 48208 (August 8, 2011). The CSAPR 

Update and Revised CSAPR Update also used this 

approach. See 81 FR 74504 (October 26, 2016) and 

86 FR 23054 (April 30, 2021). 

applicable attainment date,23 which is 

now the Moderate area attainment date 

under CAA section 181 for ozone 

nonattainment. The Moderate area 

attainment date for the 2015 8-hour 

ozone NAAQS is August 3, 2024.24 EPA 

believes that 2023 is now the 

appropriate year for analysis of 

interstate transport obligations for the 

2015 8-hour ozone NAAQS, because the 

2023 ozone season is the last relevant 

ozone season during which achieved 

emissions reductions in linked upwind 

states could assist downwind states 

with meeting the August 3, 2024, 

Moderate area attainment date for the 

2015 8-hour ozone NAAQS. 

EPA recognizes that the attainment 

date for nonattainment areas classified 

as Marginal for the 2015 8-hour ozone 

NAAQS was August 3, 2021. Under the 

Maryland holding, any necessary 

emissions reductions to satisfy interstate 

transport obligations should have been 

implemented by no later than this date. 

At the time of the statutory deadline to 

submit interstate transport SIPs (October 

1, 2018), many states relied upon EPA 

modeling of the year 2023, and no state 

provided an alternative analysis using a 

2021 analytic year (or the prior 2020 

ozone season). However, EPA must act 

on SIP submittals using the information 

available at the time it takes such action. 

In this circumstance, EPA does not 

believe it would be appropriate to 

evaluate states’ obligations under CAA 

section 110(a)(2)(D)(i)(I) as of an 

attainment date that is wholly in the 

past, because the Agency interprets the 

interstate transport provision as forward 

looking. See 86 FR 23054, 23074; see 

also Wisconsin, 938 F.3d at 322. 

Consequently, in this proposal EPA will 

use the analytical year of 2023 to 

evaluate each state’s CAA section 

110(a)(2)(D)(i)(I) SIP submission with 

respect to the 2015 8-hour ozone 

NAAQS. 

2. Step 1 of the 4-Step Interstate 

Transport Framework 

In Step 1, EPA identifies monitoring 

sites that are projected to have problems 

attaining and/or maintaining the 

NAAQS in the 2023 analytic year. 

Where EPA’s analysis shows that a site 

does not fall under the definition of a 

nonattainment or maintenance receptor, 

that site is excluded from further 

analysis under EPA’s 4-step interstate 

transport framework. For sites that are 

identified as a nonattainment or 

maintenance receptor in 2023, EPA 

proceeds to the next step of the 4-step 

interstate transport framework by 

identifying the upwind state’s 

contribution to those receptors. 

EPA’s approach to identifying ozone 

nonattainment and maintenance 

receptors in this action is consistent 

with the approach used in previous 

transport rulemakings. EPA’s approach 

gives independent consideration to both 

the ‘‘contribute significantly to 

nonattainment’’ and the ‘‘interfere with 

maintenance’’ prongs of CAA section 

110(a)(2)(D)(i)(I), consistent with the 

D.C. Circuit’s direction in North 

Carolina v. EPA.25

For the purpose of this proposal, EPA 

identifies nonattainment receptors as 

those monitoring sites that are projected 

to have average design values that 

exceed the NAAQS and that are also 

measuring nonattainment based on the 

most recent monitored design values. 

This approach is consistent with prior 

transport rulemakings, such as the 

CSAPR Update, where EPA defined 

nonattainment receptors as those areas 

that both currently measure 

nonattainment and that EPA projects 

will be in nonattainment in the future 

analytic year (i.e., 2023).26

In addition, in this proposal, EPA 

identifies a receptor to be a 

‘‘maintenance’’ receptor for purposes of 

defining interference with maintenance, 

consistent with the method used in 

CSAPR and upheld by the D.C. Circuit 

in EME Homer City Generation, L.P. v. 

EPA, 795 F.3d 118, 136 (D.C. Cir. 

2015).27 Specifically, EPA identified 

maintenance receptors as those 

receptors that would have difficulty 

maintaining the relevant NAAQS in a 

scenario that takes into account 

historical variability in air quality at 

that receptor. The variability in air 

quality was determined by evaluating 

the ‘‘maximum’’ future design value at 

each receptor based on a projection of 

the maximum measured design value 

over the relevant period. EPA interprets 

the projected maximum future design 

value to be a potential future air quality 

outcome consistent with the 

meteorology that yielded maximum 

measured concentrations in the ambient 

data set analyzed for that receptor (i.e., 

ozone conducive meteorology). EPA 

also recognizes that previously 

experienced meteorological conditions 

(e.g., dominant wind direction, 

temperatures, air mass patterns) 

promoting ozone formation that led to 

maximum concentrations in the 

measured data may reoccur in the 

future. The maximum design value 

gives a reasonable projection of future 

air quality at the receptor under a 

scenario in which such conditions do, 

in fact, reoccur. The projected 

maximum design value is used to 

identify upwind emissions that, under 

those circumstances, could interfere 

with the downwind area’s ability to 

maintain the NAAQS. 

Recognizing that nonattainment 

receptors are also, by definition, 

maintenance receptors, EPA often uses 

the term ‘‘maintenance-only’’ to refer to 

those receptors that are not 

nonattainment receptors. Consistent 

with the concepts for maintenance 

receptors, as described above, EPA 

identifies ‘‘maintenance-only’’ receptors 

as those monitoring sites that have 

projected average design values above 

the level of the applicable NAAQS, but 

that are not currently measuring 

nonattainment based on the most recent 

official design values. In addition, those 

monitoring sites with projected average 

design values below the NAAQS, but 

with projected maximum design values 

above the NAAQS are also identified as 

‘‘maintenance-only’’ receptors, even if 

they are currently measuring 

nonattainment based on the most recent 

official design values. 

3. Step 2 of the 4-Step Interstate 

Transport Framework 

In Step 2, EPA quantifies the 

contribution of each upwind state to 

each receptor in the 2023 analytic year. 

The contribution metric used in Step 2 

is defined as the average impact from 

each state to each receptor on the days 

with the highest ozone concentrations at 

the receptor based on the 2023 

modeling. If a state’s contribution value 

does not equal or exceed the threshold 

of 1 percent of the NAAQS (i.e., 0.70 

ppb for the 2015 8-hour ozone NAAQS), 

the upwind state is not ‘‘linked’’ to a 


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28As examples of general approaches for how 

such an analysis could be conducted for their 

sources, states could look to the CSAPR Update, 81 

FR 74504, 74539–51; CSAPR, 76 FR 48208, 48246– 

63; CAIR, 70 FR 25162, 25195–229; or the NOX SIP 

Call, 63 FR 57356, 57399–405. See also Revised 

CSAPR Update, 86 FR 23054, 23086–23116. 

Consistently across these rulemakings, EPA has 

developed emissions inventories, analyzed different 

levels of control stringency at different cost 

thresholds, and assessed resulting downwind air 

quality improvements. 

downwind air quality problem, and 

EPA, therefore, concludes that the state 

does not significantly contribute to 

nonattainment or interfere with 

maintenance of the NAAQS in the 

downwind states. However, if a state’s 

contribution equals or exceeds the 1 

percent threshold, the state’s emissions 

are further evaluated in Step 3, 

considering both air quality and cost as 

part of a multi-factor analysis, to 

determine what, if any, emissions might 

be deemed ‘‘significant’’ and, thus, must 

be eliminated under CAA section 

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

EPA is proposing to rely in the first 

instance on the 1 percent threshold for 

the purpose of evaluating a state’s 

contribution to nonattainment or 

maintenance of the 2015 8-hour ozone 

NAAQS (i.e., 0.70 ppb) at downwind 

receptors. This is consistent with the 

Step 2 approach that EPA applied in 

CSAPR for the 1997 ozone NAAQS, 

which has subsequently been applied in 

the CSAPR Update when evaluating 

interstate transport obligations for the 

2008 ozone NAAQS. EPA continues to 

find 1 percent to be an appropriate 

threshold. For ozone, as EPA found in 

the CAIR, CSAPR, and the CSAPR 

Update, a portion of the nonattainment 

problems from anthropogenic sources in 

the U.S. result from the combined 

impact of relatively small contributions 

from many upwind states, along with 

contributions from in-state sources and, 

in some cases, substantially larger 

contributions from a subset of particular 

upwind states. EPA’s analysis shows 

that much of the ozone transport 

problem being analyzed in this 

proposed rule is still the result of the 

collective impacts of contributions from 

many upwind states. Therefore, 

application of a consistent contribution 

threshold is necessary to identify those 

upwind states that should have 

responsibility for addressing their 

contribution to the downwind 

nonattainment and maintenance 

problems to which they collectively 

contribute. Continuing to use 1 percent 

of the NAAQS as the screening metric 

to evaluate collective contribution from 

many upwind states also allows EPA 

(and states) to apply a consistent 

framework to evaluate interstate 

emissions transport under the interstate 

transport provision from one NAAQS to 

the next. See 81 FR at 74518 (August 8, 

2011); see also 86 FR at 23085 (April 30, 

2021) (reviewing and explaining 

rationale from CSAPR, 76 FR at 48237– 

38 (August 8, 2011), for selection of 1 

percent threshold). 

EPA’s August 2018 memorandum 

recognized that in certain 

circumstances, a state may be able to 

establish that an alternative contribution 

threshold of 1 ppb is justifiable. Where 

a state relies on this alternative 

threshold, and where that state 

determined that it was not linked at 

Step 2 using the alternative threshold, 

EPA will evaluate whether the state 

provided a technically sound 

assessment of the appropriateness of 

using this alternative threshold based on 

the facts and circumstances underlying 

its application in the particular SIP 

submission. 

4. Step 3 of the 4-Step Interstate 

Transport Framework 

Consistent with EPA’s longstanding 

approach to eliminating significant 

contribution or interference with 

maintenance, at Step 3, states linked at 

Steps 1 and 2 are generally expected to 

prepare a multifactor assessment of 

potential emissions controls. EPA’s 

analysis at Step 3 in prior Federal 

actions addressing interstate transport 

requirements has primarily focused on 

an evaluation of cost-effectiveness of 

potential emissions controls (on a 

marginal cost-per-ton basis), the total 

emissions reductions that may be 

achieved by requiring such controls (if 

applied across all linked upwind states), 

and an evaluation of the air quality 

impacts such emissions reductions 

would have on the downwind receptors 

to which a state is linked; other factors 

may potentially be relevant if 

adequately supported. In general, where 

EPA’s or alternative air quality and 

contribution modeling establishes that a 

state is linked at Steps 1 and 2, it will 

be insufficient at Step 3 for a state 

merely to point to its existing rules 

requiring control measures as a basis for 

approval. In general, the emissionsreducing effects of all existing emissions 

control requirements are already 

reflected in the air quality results of the 

modeling for Steps 1 and 2. If the state 

is shown to still be linked to one or 

more downwind receptor(s), states must 

provide a well-documented evaluation 

determining whether their emissions 

constitute significant contribution or 

interference with maintenance by 

evaluating additional available control 

opportunities by preparing a multifactor 

assessment. While EPA has not 

prescribed a particular method for this 

assessment, EPA expects states at a 

minimum to present a sufficient 

technical evaluation. This would 

typically include information on 

emissions sources, applicable control 

technologies, emissions reductions, 

costs, cost effectiveness, and downwind 

air quality impacts of the estimated 

reductions, before concluding that no 

additional emissions controls should be 

required.28

5. Step 4 of the 4-Step Interstate 

Transport Framework 

At Step 4, states (or EPA) develop 

permanent and federally enforceable 

control strategies to achieve the 

emissions reductions determined to be 

necessary at Step 3 to eliminate 

significant contribution to 

nonattainment or interference with 

maintenance of the NAAQS. For a state 

linked at Steps 1 and 2 to rely on an 

emissions control measure at Step 3 to 

address its interstate transport 

obligations, that measure must be 

included in the state’s implementation 

plan so that it is permanent and 

federally enforceable. See CAA section 

110(a)(2)(D) (‘‘Each such [SIP] shall . . . 

contain adequate provisions. . . .’’). 

See also CAA section 110(a)(2)(A); 

Committee for a Better Arvin v. EPA, 

786 F.3d 1169, 1175–76 (9th Cir. 2015) 

(holding that measures relied on by a 

state to meet CAA requirements must be 

included in the SIP). 

II. Summary of Kentucky’s 2015 8-Hour 

Ozone Interstate Transport SIP 

Submission 

On January 11, 2019, Kentucky 

submitted a SIP revision, a portion of 

which addressed the CAA section 

110(a)(2)(D)(i)(I) interstate transport 

requirements for the 2015 8-hour ozone 

NAAQS. The Commonwealth’s SIP 

submission provided Kentucky’s 

analysis of its impact to downwind 

states and concluded that the 

Commonwealth had met the 

requirements of CAA section 

l10(a)(2)(D)(i)(I) (i.e., prongs 1 and 2) 

because Kentucky’s SIP contains 

adequate provisions to prevent sources 

and other types of emissions activities 

within the Commonwealth from 

significantly contributing to 

nonattainment, or interfering with the 

maintenance, of downwind states with 

respect to the 2015 8-hour ozone 

NAAQS. 

The Commonwealth’s submission 

relied on the results of EPA’s modeling 

of the year 2023, contained in the March 

2018 memorandum, to identify 

downwind nonattainment and 


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29EPA notes that Kentucky’s SIP submission is 

not organized around EPA’s 4-step framework for 

assessing good neighbor obligations, but EPA 

summarizes the submission using that framework 

for clarity here. 

30See Kentucky’s January 11, 2019, SIP 

submission, at pages 20 through 30 for the list of 

state, SIP-approved regulations and Federal 

programs identified by Kentucky. 

31See the following Appendices to Kentucky’s 

January 11, 2019, submission: Appendix A— 

Information on the Interstate Transport State 

Implementation Plan Submissions for the 2015 

Ozone National Ambient Air Quality Standards 

under Clean Air Act Section 110(a)(2)(D)(i)(I), 

March 27, 2018 (‘‘March 2018 memorandum’’); 

Appendix B—Analysis of Contribution Thresholds 

for Use in Clean Air Act Section 110(a)(2)(D)(i)(I) 

Interstate Transport State Implementation Plan 

Submissions for the 2015 Ozone National Ambient 

Air Quality Standards, August 31, 2018; and 

Appendix D—Public Hearing & Statement of 

Consideration. 

32See Appendix C to Kentucky’s January 11, 

2019, submission—Midwest Ozone Group 

Technical Support Document: ‘‘Good Neighbor 

Modeling Technical Support Document for 8-Hour 

Ozone Implementation Plans.’’ 

33 It is unclear whether Kentucky intends to rely 

on all of the data and policy approaches in 

Appendix C as included in its submittal, or if these 

documents were appended solely to support 

specific policy and technical arguments relied on 

by Kentucky in its submittal. 

34See the following Appendices to Appendix C— 

Midwest Ozone Group Technical Support 

Document: ‘‘Good Neighbor Modeling Technical 

Support Document for 8-Hour Ozone 

Implementation Plans of Kentucky’s January 11, 

2019: Appendix A—4km Modeling Results for MidAtlantic and Lake Michigan Domains Compared to 

EPA 12 km ‘‘No Water’’ Design Value Calculations 

from March 2018 Memorandum; Appendix B— 

Midwest Ozone Group Comments on EPA’s March 

27, 2018 Memorandum Entitled ‘‘Information on 

the Interstate Transport State Implementation Plan 

Submissions for the 2015 Ozone National Ambient 

Air Quality Standards under Clean Air Act Section 

110(a)(2)(D)(i)(I); Appendix C—Presentation— 

Midwest Ozone Group Preview of 2015 Ozone 

NAAQS Good Neighbor SIPs. 

35Table 2 in Kentucky’s SIP provides historic 

annual NOX emissions data for point sources in the 

state from 2008 through 2016, however, the 

associated graph at Chart 1 indicates annual NOX

emissions from 2008 through 2017. 

maintenance receptors that may be 

‘‘linked’’ to emissions from sources in 

Kentucky (which correlates to Step 1 of 

the 4-step framework).29 The March 

2018 modeling indicates that the 

Commonwealth was linked to four 

nonattainment receptors and one 

maintenance monitor above 1% of the 

NAAQS. The largest impact from 

Kentucky sources on any downwind 

nonattainment receptor in the East was 

projected to be 0.89 ppb at the Fairfield 

County, Connecticut (ID: 90013007) site. 

The other nonattainment receptors to 

which Kentucky was linked are: a 

second site in Fairfield County (ID: 

90019003); Milwaukee, Wisconsin (ID: 

550790085); and Sheboygan, Wisconsin 

(ID: 551170006). The impact from 

Kentucky sources on the one downwind 

maintenance-only receptor to which it 

was linked in that modeling was 1.52 

ppb at the Harford County, Maryland 

monitor (ID: 240251001). 

The Commonwealth reviewed EPA’s 

August 2018 memorandum as it related 

to the use of a potential alternative 

contribution threshold of 1 ppb and 

agreed that use of a 1 ppb contribution 

threshold is comparable to the amount 

of collective contribution captured 

using a threshold equivalent to 1 

percent of the NAAQS. Based on the 

March 2018 modeling and application 

of a 1 ppb alternative contribution 

threshold, the Commonwealth found 

that it would not be linked as a 

significant contributor to the four 

nonattainment receptors in Connecticut 

and Wisconsin (which correlates to 

EPA’s Step 2), and therefore concluded 

that no further controls were required to 

address its contribution to those four 

receptors. Thus, the Commonwealth 

concluded that Kentucky’s SIP contains 

adequate provisions to prevent sources 

and other types of emissions activities 

within the Commonwealth from 

contributing significantly to 

nonattainment in any other state (i.e., 

‘‘prong 1’’ of CAA section 

l10(a)(2)(D)(i)(I)) for the 2015 8-hour 

ozone NAAQS. 

After application of the 1 ppb 

contribution threshold, Kentucky 

remained linked to the downwind 

maintenance-only receptor at Harford 

County, Maryland (ID: 240251001) 

because the Commonwealth’s 

contribution of 1.52 ppb to this receptor 

was greater than the 1 ppb alternative 

threshold. Kentucky’s SIP submission 

asserted that the amount of NOX

emission reductions required for an 

upwind state should not be the same for 

a monitor that is already attaining the 

NAAQS as they are for a nonattainment 

monitor. The Commonwealth further 

asserted that local controls should be 

implemented before requiring upwind 

states to control their sources. Thus, 

Kentucky concluded that no further 

reductions other than on-the-books and 

on-the-way measures are required to 

address the Commonwealth’s interstate 

transport obligation to eliminate its 

contribution to the Harford County, 

Maryland maintenance receptor. 

In addition, Kentucky provided 

information intended to demonstrate 

that Kentucky’s SIP contains adequate 

provisions to prevent sources and other 

types of emissions activities within the 

Commonwealth from significantly 

contributing to nonattainment, or 

interfering with the maintenance, of 

downwind states with respect to the 

2015 8-hour ozone NAAQS, and thus, 

no additional emissions reductions from 

Kentucky are necessary. Specifically, 

Kentucky listed existing state, SIPapproved regulations and Federal 

programs for sources in the 

Commonwealth that it concluded 

address the requirements of CAA 

110(a)(2)(D)(i)(I) for the 2015 8-hour 

ozone NAAQS.30 Kentucky provided 

more detailed analyses related to several 

specific topics, which are summarized 

in sections below. 

The Commonwealth also included 

documents attached as appendices to its 

submittal. The March 2018 

memorandum and the August 2018 

memorandum were attached at 

appendices A and B, respectively.31 As 

Appendix C, the Commonwealth 

appended several documents developed 

and/or submitted by the Midwest Ozone 

Group (a consortium of upwind 

industries with emitting facilities).32

This included a modeling analysis 

developed by Alpine Geophysics titled 

‘‘Good Neighbor Modeling Technical 

Support Document for the 8-hour Ozone 

State Implementation Plans,’’ dated June 

2018 (Alpine TSD). The Alpine TSD 

contains alternative modeling of 2023 

performed by Alpine Geophysics 

sponsored by MOG, as well as 

additional policy suggestions that MOG 

suggested states could consider in 

developing good neighbor SIP 

submissions (see section 9 of the Alpine 

TSD).33 The Alpine TSD also appended 

a separate set of MOG comments on 

EPA’s March 2018 memorandum.34

These comments and Alpine’s modeling 

analysis were further summarized in a 

Microsoft PowerPoint Presentation 

titled ‘‘MOG’s Preview of 2015 Ozone 

NAAQS Good Neighbor SIPs.’’ EPA also 

summarizes the materials developed by 

MOG that the Commonwealth included 

as Appendix C to its submittal, although 

it is unclear that Kentucky intended to 

rely on all aspects of these materials. 

A. Information Related to Emission 

Trends From Kentucky Sources 

With respect to ozone precursors 

emitted from Kentucky sources, 

Kentucky focused its analysis on NOX

emissions, as it found that ozone is far 

more sensitive to NOX emissions than 

VOC emissions in the Southeastern 

United States and that controlling NOX

emissions is a more effective strategy in 

reducing ozone. Kentucky reviewed 

NOX emissions trends in the 

Commonwealth, comparing annual NOX

emissions from 2008 to 2016, finding 

that NOX emissions in Kentucky have 

significantly decreased since 2008. The 

Commonwealth asserted that it has 

significantly lowered NOX emissions 

between 2008 and 2017 35 and 

contended that planned shutdowns and 


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36 Kentucky’s SIP acknowledged that the CSAPR 

trading program does not address interstate 

transport for the 2015 standard but nonetheless 

provides NOX emission reductions. 

37See Kentucky’s January 11, 2019, submittal 

located in Docket No. EPA–R04–OAR–2021–0841, 

at pages 32–33 for discussion on implementation of 

CSAPR, the CSAPR Update, EGU retirements, and 

EGU fuel switches. 

38EPA’s designations for the 2015 8-hour ozone 

standard divided the state into two areas, Greater 

Connecticut, CT, with a marginal classification, and 

New York-Northern New Jersey-Long Island, NYNJ-CT (New York Metro Area), with a moderate 

classification. See https://www.epa.gov/ozonedesignations/additional-designations-2015-ozonestandards. 

39According to Kentucky, the HYSPLIT analysis 

were generated using EPA’s 2015 Ozone 

Designation Mapping Tool, available at https://

www.epa.gov/ozone-designations/ozonedesignations-guidance-and-data#:∼:text=The

%20ozone%20designations%20mapping

%20tool,for%20the%202015

%20Ozone%20NAAQS. 

40 Kentucky references NYDEC emission analysis 

entitled ‘‘Background, High Electric Demand Day 

(HEDD) Initiative’’, New York Department of 

Environmental Conservation. 

conversion to natural gas, along with the 

implementation of Federal and State 

programs, ensure Kentucky’s emissions 

will continue to decrease. Based on the 

2014 national emission inventory (NEI), 

Kentucky indicated that the major 

contributor of NOX emissions in the 

Commonwealth are point sources, 

mainly comprised of electric generating 

units (EGUs). 

Kentucky asserted that NOX emissions 

from EGUs in the Commonwealth have 

decreased and would continue to 

decrease based, in part, on the 

implementation of CAIR, CSAPR, and 

the CSAPR Update, as well as 

retirements of several EGUs in the 

Commonwealth. The Commonwealth 

compared Kentucky’s NOX ozone season 

allocations to actual EGU emissions in 

the Commonwealth, concluding that 

Kentucky’s NOX ozone season budgets 

have decreased since the 

implementation of CSAPR and the 

CSAPR Update and actual ozone season 

NOX emissions are significantly lower 

than the trading program budgets.36 The 

SIP submission summarized coal-fired 

unit retirements, shutdowns, and 

repowering from 2015 through 2017 as 

well as on-the-way reductions from 

natural gas conversions and retirements 

from 2017 through 2023.37 Kentucky 

stated that it expected emissions will 

continue to decline in the future due to 

continued implementation of CSAPR, 

the CSAPR Update, and scheduled 

shutdowns, fuel switches, and 

retirements of facilities in the 

Commonwealth. 

B. Information Related to Connecticut 

Monitors Provided by Kentucky 

EPA’s March 2018 modeling showed 

Kentucky linked to the two receptors 

located in Fairfield County, 

Connecticut, which is part of the New 

York-Northern New Jersey-Long Island, 

NY-NJ-CT (New York Metro Area) core 

based statistical area (CBSA).38

Kentucky applied an alternative 

contribution threshold of 1 ppb, and 

thus determined that Kentucky was no 

longer linked to the Connecticut 

receptors. In addition, Kentucky 

provided information intended to 

demonstrate that emissions from local 

sources in the area surrounding the 

monitors contribute significantly to the 

continued nonattainment issues, and 

thus, that local controls should be 

implemented before requesting upwind 

states to control facilities. 

In particular, Kentucky’s SIP 

submission claims that the Westport 

Sherwood, Fairfield, Connecticut (ID: 

90019003) and Stratford Point 

Lighthouse, Fairfield County (ID: 

90013007) monitors are located less 

than three miles from the I–95 interstate 

highway corridor and over 500 miles 

from Kentucky. Kentucky asserted these 

monitors have a consistent pattern of 

violating the 2015 8-hour ozone NAAQS 

from 2007 to 2016. Kentucky also 

pointed out that it is not linked in the 

modeling to two other nonattainment 

receptors (the Greenwich Point Park and 

Criscuolo Park monitoring sites) that are 

in relatively close proximity to the 

Westport and Stratford monitors. 

Kentucky compared the distances 

between these sites with the distances of 

the sites to Kentucky’s nearest border. 

Kentucky’s SIP submission also 

provided information related to the New 

York Metro Area, citing the 2014 NEI to 

state that the on-road source sector 

contributed the highest amount of NOX

emissions and that the nonpoint source 

sector contributed the highest amount of 

VOC emissions in that area. The 

Commonwealth further provided 

information about high vehicle miles 

traveled (VMT) and commuting patterns 

in the New York Metro Area, as well as 

information regarding violating 

monitors along the I–95 corridor and 

outlying monitors that show attainment. 

Additionally, Kentucky’s SIP 

submission includes Hybrid Single 

Particle Lagrangian Integrated Trajectory 

(HYSPLIT) model back trajectory 

analysis to the two Connecticut 

receptors,39 asserting that the HYSPLIT 

analysis indicates that the monitors are 

downwind of nonattainment areas in 

New York, New Jersey, Pennsylvania, 

and Maryland. The Commonwealth also 

asserted there is a consistent pattern of 

violating monitors located along the I– 

95 corridor. In addition, Kentucky 

asserted that pollutants are trapped in 

the marine boundary layer and then 

transported inland to coastal 

Connecticut receptors due to conditions 

on Long Island Sound. 

The Commonwealth’s SIP submission 

also discussed point sources in the New 

York Metro Area, providing information 

regarding the largest point sources in 

that area. In addition, Kentucky 

provided NOX and VOC emission 

information for 13 counties in the New 

York Metro Area that have NOX and 

VOC emission totals above 10,000 tpy, 

finding that three counties that 

surround Fairfield County (Suffolk, 

Queens, and Nassau Counties) had the 

highest NOX emissions. 

Kentucky further evaluated high 

electric demand days in New York, 

discussing a New York Department of 

Environmental Conservation (NYDEC) 

determination that peaking units 

operating on peak electricity demand 

days are a major contributor of NOX

(particularly units installed before 

1987), and that such units can 

contribute 4.8 ppb of ozone on high 

ozone days.40 Kentucky concluded NOX

emission reductions from these EGUs 

point sources would have a significant 

impact on ozone levels in the New York 

Metro Area. 

C. Information Related to the Harford, 

Maryland Monitor Provided by Kentucky 

Kentucky acknowledged that EPA’s 

March 27, 2018 modeling shows the 

potential for Kentucky emissions to 

significantly contribute to the 

Edgewood, Harford County, Maryland 

(ID: 240251001) maintenance-only 

monitor (Edgewood monitor) in 2023. 

However, Kentucky provided air quality 

data designed to demonstrate that 

emissions from local sources in the area 

surrounding the monitors contribute 

significantly to the continued air quality 

issues and concluded that there are 

local controls that should be 

implemented before requesting upwind 

states to control facilities. 

Kentucky provided additional 

information with respect to the 

Edgewood Monitor, which is located 3 

miles from the I–95 corridor and 

approximately 350 miles from 

Kentucky. Kentucky provided data to 

show that the Edgewood monitor 

consistently violated the 2015 8-hour 

ozone standard from 2007 to 2016. 

Kentucky also provided information 

related to other nonattainment monitors 

located in Baltimore County and 

Harford County. 

The Commonwealth’s SIP submission 

provided data related to the BaltimoreVerDate Sep<11>2014 17:03 Feb 18, 2022 Jkt 256001 PO 00000 Frm 00051 Fmt 4702 Sfmt 4702 E:\FR\FM\22FEP1.SGM 22FEP1

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41According to Kentucky, the HYSPLIT analysis 

were generated using EPA’s 2015 Ozone 

Designation Mapping Tool, available at https://

www.epa.gov/ozone-designations/ozonedesignations-guidance-and-data#:∼:text=The

%20ozone%20designations%20mapping

%20tool,for%20the%202015%20Ozone

%20NAAQS. 

42 Kentucky’s SIP references MOG’s comments 

that cite CAA sections 107(a) and 110(a)(1). 

43See Appendix C of Kentucky’s January 11, 

2019, transport SIP submission. 

Columbia-Towson, MD CBSA 

(Baltimore Area), citing to the 2014 NEI 

to state that the on-road source sector 

contributed the highest amount of NOX

emissions and that the nonpoint source 

sector contributed the highest amount of 

VOC emissions in that area. Kentucky 

further provided information about 

VMTs and commuting patterns in the 

Baltimore Area, as well as information 

regarding violating monitors along the 

I–95 corridor and outlying monitors that 

show attainment. The SIP submission 

asserted that local mobile emissions are 

a key contributor to the Edgewood 

monitor, which is also located in close 

proximity to the 1–95 corridor. 

Kentucky further cited to a presentation 

and remarks by Maryland officials, 

discussing programs to reduce 

emissions from local sources, 

specifically focusing on mobile source 

NOX reduction programs. 

Kentucky cited a 2010 case study in 

the Chesapeake Bay that suggests the 

transport of pollution from nearby urban 

areas accumulates over the Bay and 

becomes stagnant, creating a bay breeze 

which is pushed by southerly winds 

northward towards the Edgewood 

monitor. Additionally, Kentucky’s SIP 

submission also provided HYSPLIT 

model back trajectory analysis to the 

Edgewood receptor,41 asserting that the 

HYSPLIT indicates that the monitors are 

downwind of nonattainment areas in 

Baltimore County, Baltimore City, 

Arlington County, and the District of 

Columbia. Kentucky also asserted that 

higher altitude particles from the 

northwest of Baltimore combine with 

lower-level particles from the south and 

southeast. 

Kentucky’s submission used 

information on local mobile emissions 

along the I–95 corridor and coastal air 

pollution formation and accumulation 

along the Maryland coast to support its 

conclusion that local air quality 

problems are the source of ozone 

violations at these monitors. 

Additionally, Kentucky asserted that 

the implementation of local programs to 

reduce emissions should be sufficient 

for monitors in the Maryland area to 

attain the 2015 8-hour ozone NAAQS. 

Kentucky cited claims by MOG 

(appended to the submittal in Appendix 

C) that the modeling in EPA’s March 

2018 memorandum does not account for 

additional retirements, conversions, and 

modifications or emission control 

programs expected to be implemented 

before 2023. Kentucky concluded that 

because the Edgewood monitor is a 

maintenance receptor, the 

Commonwealth believes that no further 

reductions from Kentucky sources other 

than on-the-books controls should be 

required because maintenance receptors 

should be treated differently than 

nonattainment receptors in terms of 

upwind requirements. The 

Commonwealth also asserted that states 

linked to maintenance receptors should 

be held to less stringent standards of 

emissions reductions as compared to 

states linked to a nonattainment 

receptor. 

The Commonwealth also asserted that 

local emission controls should be 

implemented before upwind states are 

required to control their facilities, 

which is based on Kentucky’s 

concurrence with statements from MOG. 

The Commonwealth cited MOG’s 

comments on local controls stating: 

‘‘When an area is measuring 

nonattainment of a NAAQS, as is the 

case with the areas linked to Kentucky, 

the CAA requires that the effects and 

benefits of local controls on all source 

sectors be considered first, prior to 

pursuing controls of sources in upwind 

states.’’ 42 The Commonwealth 

concluded that the emissions reductions 

resulting from on-the-books and on-theway measures are adequate to prohibit 

emissions within Kentucky from 

interfering with the maintenance of 

downwind states with respect to the 

2015 8-hour ozone NAAQS. 

D. Summary of Conclusions From 

Kentucky 

In summary, based on Kentucky’s 

reliance on the modeling results in 

EPA’s March 2018 memorandum, the 

Commonwealth found that emissions 

from Kentucky sources were potentially 

linked to four nonattainment monitors 

in Connecticut and Wisconsin and one 

maintenance receptor in Harford 

County, Maryland. However, after 

utilizing a 1 ppb alternative 

contribution threshold, the 

Commonwealth concluded that it was 

no longer linked to the four 

nonattainment monitors, and thus, that 

the Kentucky SIP contains adequate 

provisions to prevent sources and other 

types of emissions activities within the 

State from contributing significantly to 

nonattainment in any other state (i.e., 

‘‘prong 1’’ of CAA section 

110(a)(2)(D)(i)(I)) for the 2015 8-hour 

ozone NAAQS. Although modeling 

results indicated that Kentucky 

remained linked to the maintenanceonly receptor in Harford County, 

Maryland, even after the application of 

the 1 ppb alternative threshold, 

Kentucky asserted that states should not 

be required to apply the same degree of 

reductions for maintenance receptors as 

nonattainment areas, and determined 

that additional NOX emission 

reductions other than those that are onthe-books or on-the-way are not 

required to address its downwind 

contribution to that receptor. Kentucky 

further provided an assessment of local 

sources in the vicinity of the 

Connecticut and Maryland monitors and 

concluded that local (particularly 

mobile) emissions, high VMTs and 

commuting patterns, and weather 

patterns are the primary cause of 

violating monitors in these areas. 

Therefore, Kentucky concluded that its 

SIP has adequate provisions to prohibit 

emissions from interfering with 

maintenance in another state (i.e., 

‘‘prong 2’’ of CAA section 

110(a)(2)(D)(i)(I)) with respect to the 

2015 8-hour ozone NAAQS. 

E. Summary of Midwest Ozone Group 

TSD Appended to Kentucky’s Submittal 

Kentucky attached several materials 

developed by MOG to its submittal as 

Appendix C, which included a 

document titled ‘‘ ‘Good Neighbor’ 

Modeling Technical Support Document 

for 8-Hour Ozone State Implementation 

Plans’’ prepared by Alpine 

Geophysics.43 The Alpine Geophysics 

document also attached the following 

documents: 4 kilometer (km) modeling 

results for mid-Atlantic and Lake 

Michigan domains compared to EPA 12 

km ‘‘No Water’’ Design Value 

Calculations from March 2018 

memorandum (Appendix A); MOG 

comments on EPA’s March 2018 

memorandum (Appendix B); and a 

Microsoft PowerPoint presentation from 

MOG previewing 2015 8-hour ozone 

NAAQS good neighbor SIPs (Appendix 

C). EPA notes a number of modeling 

results and technical and policy 

arguments provided in the MOG 

attachments are not explicitly discussed 

in Kentucky’s SIP submission narrative. 

Therefore, it is unclear whether 

Kentucky intended to rely on Alpine’s 

modeling or MOG’s policy argument to 

support the Commonwealth’s overall 

transport SIP conclusions. To ensure 

review of all potentially relevant 

technical and policy issues identified in 

Kentucky’s SIP package, this section 

summarizes key arguments presented in 


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44See Section 9.0—Selected SIP Revision 

Approaches in Appendix C—MOG’s TSD of 

Kentucky’s January 11, 2019 transport SIP 

submission. 

45MOG cited to the Georgia Environmental 

Protection Division’s comment on EPA’s March 

2018 Memorandum to support this claim. See 

Section 9.0—Selected SIP Revision Approaches in 

Appendix C—MOG’s TSD of Kentucky’s January 11, 

2019 transport SIP submission, citing Boylan, J. W. 

(May 4, 2018). Georgia EPD Comments on EPA’s 

March 27, 2018 Interstate Transport Memo 

[Memorandum]. 

46The ozone design values and contributions at 

individual monitoring sites nationwide are 

provided in the file ‘‘2016v2_DVs_state_

contributions.xlsx’’ which is included in Docket 

No. EPA–HQ–OAR–2021–0663. 

47These modeling results are consistent with the 

results of a prior round of 2023 modeling using the 

2016v1 emissions platform which became available 

to the public in the fall of 2020 in the Revised 

CSAPR Update, as noted in section I. That modeling 

showed that Kentucky had a maximum contribution 

greater than 0.70 ppb to at least one nonattainment 

or maintenance-only receptor in 2023. These 

modeling results are included in the file ‘‘Ozone 

Design Values And Contributions Revised CSAPR 

Update.xlsx’’ in Docket No. EPA–HQ–OAR–2021– 

0663. 

Appendix C. However, in EPA’s 

evaluation of the SIP submittal in 

section III, EPA will differentiate 

between those positions clearly adopted 

by the Commonwealth and those where 

it is unclear and therefore a position 

espoused by MOG cannot be attributed 

to Kentucky. 

Appendix C included modeling 

results performed by Alpine Geophysics 

as presented in the Alpine TSD. The 

Alpine modeling results identified the 

Harford, Maryland receptor as a 

nonattainment receptor, with Kentucky 

emissions contributing 2.07 ppb. In 

addition, the Alpine modeling results 

identified Kentucky linkages above 1 

percent to the following maintenanceonly receptors: Gloucester, New Jersey 

(ID: 340150002), with a Kentucky 

contribution of 1.69 ppb; Richmond, 

New York (ID: 360850067), with a 

Kentucky contribution of 0.93; and 

Philadelphia, Pennsylvania (ID: 

421010024), with a Kentucky 

contribution of 1.53. (While MOG 

asserts in separate comments that 

emission reductions not accounted for 

in EPA’s modeling suggests there will be 

no receptors by 2023, this is not 

consistent with Alpine’s modeling.) 

The Alpine TSD also evaluated 

additional approaches and flexibilities 

that states could apply in SIP revisions, 

based on the potential concepts 

provided in Appendix A of EPA’s 

March 2018 memorandum.44 These 

included reliance on alterative modeling 

data, evaluation of international 

contributions (both anthropogenic 

contribution and as an additional 

percentage of boundary conditions), 

alternate contribution thresholds, 

proportional control of upwind 

emissions by level of upwind state 

contribution, and addressing 

interference with maintenance 

obligations through use of 10-year 

projections. 

MOG suggested states should be 

allowed to select multiple sources of 

modeling data rather than a single 

modeling simulation if such information 

is considered equally credible when 

making policy decisions related to the 

development of good neighbor SIPs. 

With respect to international 

emissions, MOG cited to an attachment 

to EPA’s 2018 memorandum and asserts 

that EPA’s and Alpine’s contribution 

modeling tracks and reports the relative 

impact contributions of anthropogenic 

emissions located within the 36 km 

modeling domain. Considering this 

information, MOG concluded that states 

seeking to avoid overcontrol may wish 

to consider removing that portion of the 

projected design value that is explicitly 

attributed to international 

anthropogenic contribution, which may 

be enough to demonstrate attainment 

with the 2008 or 2015 8-hour ozone 

NAAQS at multiple monitors in the U.S. 

With respect to potential use of 

alternative contribution thresholds, 

MOG pointed to states raising concerns 

that the 1 percent threshold is more 

stringent than the 2016 EPA Significant 

Impact level (SIL) guidance of 1 ppb, 

which is designed as an individual 

source or group of sources’ contribution 

limit (in the context of prevention of 

significant deterioration (PSD) 

permitting).45 MOG suggested that states 

could submit SIP revisions citing the 

SIL of 1 ppb as an acceptable total state 

anthropogenic contribution threshold 

under Step 2 of the 4-step process, and 

request relief from the 1 percent 

threshold in lieu of using an alternate 

value. 

MOG presented an alternative 

approach to how upwind-state emission 

reduction obligations could be 

allocated. Specifically, MOG proposed 

that upwind reductions could be 

allocated in proportion to the size of 

their contribution to downwind 

nonattainment. To illustrate this 

approach, MOG determined a 

proportional reduction requirement 

associated with the relative contribution 

from each upwind state to the Harford 

County, Maryland monitor. Under this 

analysis, MOG’s approach indicated that 

Kentucky would be responsible for a 

0.02 ppb reduction at the monitor and 

‘‘would then need to craft a [good 

neighbor SIP] revision to generate 

reductions associated with this 

proportional amount.’’ 

With respect to ‘‘interference with 

maintenance’’ obligations, MOG 

suggested that an upwind state could 

choose to indicate that no additional 

controls would be needed to address a 

maintenance monitor if the upwind 

state can show that either the monitor 

is likely to remain in attainment for a 

period of 10 years or that the upwind 

state’s emissions will not increase for 10 

years after the attainment date. 

III. EPA’s Evaluation of Kentucky’s 

2015 8-Hour Ozone Interstate Transport 

SIP Submission 

EPA is proposing to find that 

Kentucky’s January 11, 2019, SIP 

submission does not meet the 

Commonwealth’s obligations with 

respect to prohibiting emissions that 

contribute significantly to 

nonattainment or interfere with 

maintenance of the 2015 8-hour ozone 

NAAQS in any other state based on 

EPA’s evaluation of the SIP submission 

using the 4-step interstate transport 

framework, and therefore EPA is 

proposing to disapprove Kentucky’s SIP 

submission. 

A. Results of EPA’s Step 1 and Step 2 

Modeling and Findings for Kentucky 

As described in section I, EPA 

performed updated air quality modeling 

to project design values and 

contributions for 2023. These data were 

examined to determine if Kentucky 

contributes at or above the threshold of 

1 percent of the 2015 8-hour ozone 

NAAQS (0.70 ppb) to any downwind 

nonattainment or maintenance receptor. 

As shown in Table 1, the data 46 indicate 

that in 2023, emissions from Kentucky 

contribute greater than 1 percent of the 

standard to nonattainment or 

maintenance-only receptors in Bucks 

County, Pennsylvania (ID: 420170012), 

New Haven County, Connecticut (ID: 

90099002), and Fairfield County, 

Connecticut (ID: 90019003 and 

90013007).47


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48The Alpine modeling results identified the 

Harford, Maryland receptor as a nonattainment 

receptor, with Kentucky emissions contributing 

2.07 ppb. In addition, the Alpine modeling results 

identified Kentucky linkages above 1 percent to the 

following maintenance-only receptors: Gloucester, 

New Jersey (ID: 340150002), with a Kentucky 

contribution of 1.69 ppb; Richmond, New York (ID: 

360850067), with a Kentucky contribution of 0.93; 

and Philadelphia, Pennsylvania (ID: 421010024), 

with a Kentucky contribution of 1.53. 

49To the extent that MOG cited Attachment A to 

EPA’s March 2018 memorandum as suggesting 

support for this approach, this is incorrect. As 

discussed in section I.D, the attachment 

summarized ideas from outside stakeholders, and 

EPA did not endorse such approaches as 

technically or legally appropriate. Further, nothing 

in Attachment A suggested that international 

contribution could simply be subtracted from a 

downwind receptor’s projected design value. 

TABLE 1—KENTUCKY LINKAGE RESULTS BASED ON EPA UPDATED 2023 MODELING

Receptor ID Location County Nonattainment/ 

maintenance 

2023 average 

design value 

(ppb) 

2023 

maximum 

design value 

(ppb) 

Kentucky 

contribution 

(ppb) 

420170012 ........................ Pennsylvania .................... Bucks ............................... Maintenance ..................... 70.7 72.2 0.88 

90099002 .......................... Connecticut ...................... New Haven ...................... Nonattainment .................. 71.8 73.9 0.83 

90019003 .......................... Connecticut ...................... Fairfield ............................ Nonattainment .................. 76.1 76.4 0.82 

90013007 .......................... Connecticut ...................... Fairfield ............................ Nonattainment .................. 74.2 75.1 0.77 

B. Evaluation of Information Provided 

by Kentucky Regarding Step 1 

At Step 1 of the 4-step interstate 

transport framework, Kentucky relied 

on EPA modeling released in the March 

2018 memorandum to identify 

nonattainment and maintenance 

receptors in 2023 and also included 

results from modeling performed by 

Alpine. As described previously in this 

notice, EPA has recently updated its 

2023 modeling using the most current 

and technically appropriate 

information. EPA proposes to rely on 

EPA’s most recent modeling to identify 

nonattainment and maintenance 

receptors in 2023. However, even using 

EPA modeling available to Kentucky at 

the time of its SIP submittal, three 

nonattainment receptors and one 

maintenance-only receptor were 

projected in 2023 to which Kentucky 

was linked above 1 percent of the 

NAAQS. In addition, the Alpine 

modeling that Kentucky appended to its 

submittal also indicated that Kentucky 

was linked to several receptors in 

2023.48 Kentucky appended comments 

from MOG arguing that states should be 

allowed to select multiple sources of 

modeling data rather than a single 

modeling simulation if such information 

is considered equally credible when 

making policy decisions related to the 

development of good neighbor SIPs. 

Whether EPA’s most recent 2023 

modeling is relied on, or whether it is 

considered in conjunction with its older 

2023 modeling and/or the Alpine 

modeling, the results consistently 

identify several nonattainment or 

maintenance receptors to which 

Kentucky is linked above 1 percent of 

the 2015 8-hour ozone NAAQS. 

As discussed in section II.E, Kentucky 

attached documents from MOG that 

discussed international transport of 

emissions and their contribution to U.S. 

ozone monitors, and argued that states 

could remove that portion of the 

projected design value explicitly 

attributed to international 

anthropogenic contribution. MOG 

asserted that excluding the international 

anthropogenic contributions could 

result in attainment with the 2008 or 

2015 8-hour ozone NAAQS at ozone 

monitors in the United States, thus 

potentially eliminating 2023 receptors. 

Kentucky did not explicitly discuss in 

its SIP submittal MOG’s arguments 

regarding contributions from 

international emissions and therefore it 

is unclear if the Commonwealth 

intended to rely on this argument to 

support their conclusion, however, EPA 

is providing its analysis related to these 

arguments. 

EPA disagrees that excluding 

international contribution (whether 

from North American international 

anthropogenic, boundary conditions, or 

other international sources) from the 

projected design value of receptors is 

acceptable under the CAA.49 The good 

neighbor provision requires states and 

EPA to address interstate transport of air 

pollution that contributes to downwind 

states’ ability to attain and maintain 

NAAQS. Whether emissions from other 

states or other countries also contribute 

to the same downwind air quality issue 

is irrelevant in assessing whether a 

downwind state has an air quality 

problem, or whether an upwind state is 

significantly contributing to that 

problem. States are not obligated under 

CAA section 110(a)(2)(D)(i)(I) to reduce 

emissions sufficient on their own to 

resolve downwind receptors’ 

nonattainment or maintenance 

problems. Rather, states are obligated to 

eliminate their own ‘‘significant 

contribution’’ or ‘‘interference’’ with the 

ability of other states to attain or 

maintain the NAAQS. 

Indeed, the D.C. Circuit in Wisconsin 

specifically rejected petitioner 

arguments suggesting that upwind states 

should be excused from good neighbor 

obligations on the basis that some other 

source of emissions (whether 

international or another upwind state) 

could be considered the ‘‘but-for’’ cause 

of downwind air quality problem. See 

938 F.3d at 323–324. The court viewed 

petitioners’ arguments as essentially an 

argument ‘‘that an upwind State 

‘contributes significantly’ to downwind 

nonattainment only when its emissions 

are the sole cause of downwind 

nonattainment.’’ See 938 F.3d at 324. 

The court explained that ‘‘an upwind 

State can ‘contribute’ to downwind 

nonattainment even if its emissions are 

not the but-for cause.’’ Id. at 324–325. 

See also Catawba County v. EPA, 571 

F.3d 20, 39 (D.C. Cir. 2009) (rejecting 

the argument ‘‘that ‘significantly 

contribute’ unambiguously means 

‘strictly cause’ ’’ because there is ‘‘no 

reason why the statute precludes EPA 

from determining that [an] addition of 

[pollutant] into the atmosphere is 

significant even though a nearby 

county’s nonattainment problem would 

still persist in its absence’’); Miss. 

Comm’n on Envtl. Quality v. EPA, 790 

F.3d 138, 163 n.12 (D.C. Cir. 2015) 

(observing that the argument that ‘‘there 

likely would have been no violation at 

all . . . if it were not for the emissions 

resulting from [another source]’’ is 

‘‘merely a rephrasing of the but-for 

causation rule that we rejected in 

Catawba County.’’). Therefore, a state is 

not excused from eliminating its 

significant contribution on the basis that 

international emissions also contribute 

some amount of pollution to the same 

receptors to which the state is linked. 

C. Evaluation of Information Provided 

by Kentucky Regarding Step 2 

At Step 2 of the 4-step interstate 

transport framework, Kentucky relied 

on EPA modeling released in the March 

2018 memorandum to identify upwind 

state linkages to nonattainment and 

maintenance receptors in 2023 and 

included results from modeling run by 


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50Although the various modeling runs (EPA’s 

March 2018 modeling, Alpine’s modeling and 

EPA’s updated modeling) indicate that Kentucky is 

linked to different receptors and with differing 

amounts of contribution, all three sets of modeling 

are consistent in that each indicates linkages 

between Kentucky and downwind receptors. 

51See August 2018 memorandum at 1. 52As an example of the type of analysis that EPA 

anticipated states might conduct under the 

guidance, in one instance, EPA itself attempted to 

conduct a state- and receptor-specific analysis that 

could support approval of the use of a 1 ppb 

threshold. See Air Plan Approval; Iowa; 

Infrastructure State Implementation Plan 

Requirements for the 2015 Ozone National Ambient 

Air Quality Standard, 85 FR 12232 (March 2, 2020). 

The Agency received adverse comment on this 

proposed approval and has not taken final action 

with respect to this proposal. 

53 Kentucky applied the 1 ppb contribution 

threshold to the Connecticut, Wisconsin, and 

Maryland receptors, as the Commonwealth found 

that Kentucky was linked to these receptors based 

on the modeling released with the March 2018 

memorandum. Under EPA’s updated modeling, 

Kentucky is no longer linked to the Wisconsin and 

Maryland receptors and is linked to receptors in 

Pennsylvania and New Haven, Connecticut. See 

Table 1. However, as Kentucky did not provide any 

state-specific information, the rationale is also 

applicable to the Pennsylvania and New Haven, 

Connecticut linkages. 

54See Kentucky’s January 11, 2019, submission, 

Appendix D, Summary of Comments and 

Responses, at 6–7. 

55 Id. at 7. EPA directed Kentucky instead to the 

August 2018 memorandum if it wished to rely on 

a 1 ppb threshold; however, EPA’s comments noted 

that this memorandum was only a ‘‘part’’ of the 

rationale the Commonwealth should develop. Id. at 

6. 

56Pursuant to section 107(d) of the CAA, EPA 

must designate areas as either ‘‘nonattainment,’’ 

‘‘attainment,’’ or ‘‘unclassifiable.’’ Historically for 

ozone, the EPA has designated most areas that do 

not meet the definition of nonattainment as 

‘‘unclassifiable/attainment.’’ This category includes 

areas that have air quality monitoring data meeting 

the NAAQS and areas that do not have monitors but 

for which the EPA has no evidence that the areas 

may be violating the NAAQS or contributing to a 

nearby violation. In the designations for the 2015 

ozone NAAQS, the EPA reversed the order of the 

label to be ‘‘attainment/unclassifiable’’ to better 

convey the definition of the designation category 

and so that the category is more easily 

distinguished from the separate unclassifiable 

category. An ‘‘attainment’’ designation is reserved 

for a previous nonattainment area that has been 

redesignated to attainment as a result of the EPA’s 

approval of a CAA section 175A maintenance plan 

submitted by the state air agency. 

Alpine. Both EPA’s modeling released 

in the March 2018 memorandum as well 

as Alpine’s modeling indicate that 

Kentucky is linked to downwind 

monitors.50 As Kentucky attached 

Alpine’s modeling without discussing it 

in the narrative of the submittal, it is 

unclear whether Kentucky intended to 

rely on Alpine’s modeling in its 

submittal. 

As described in section I.C of this 

notice, EPA has recently updated 

modeling to identify upwind state 

contributions to nonattainment and/or 

maintenance receptors in 2023. In this 

notice, EPA proposes to rely on the 

Agency’s most recently available 

modeling to identify upwind 

contributions and ‘‘linkages’’ to 

downwind air quality problems in 2023 

using a threshold of 1 percent of the 

NAAQS. See section I.D for a general 

explanation of the use of 1 percent of 

the NAAQS. 

As shown in Table 1, updated EPA 

modeling identifies Kentucky’s 

maximum contribution to a downwind 

nonattainment or maintenance receptor 

is greater than 1 percent of the standard 

(i.e., 0.70 ppb). 

Kentucky, however, argued in its SIP 

submittal for the use of an alternative 1 

ppb contribution threshold at Step 2 to 

attempt to demonstrate that it was no 

longer ‘‘linked’’ to projected downwind 

nonattainment receptors. Specifically, 

Kentucky cited EPA’s August 2018 

memorandum as supporting the use of 

a 1 ppb alternative contribution 

threshold at Step 2 to assert that the 

Commonwealth was no longer ‘‘linked’’ 

to projected downwind nonattainment 

receptors, while conceding that even 

under this alternative threshold, it was 

linked above 1 ppb to the projected 

Harford, Maryland maintenance-only 

receptor. EPA’s most recent modeling of 

2023 no longer identifies the Harford, 

Maryland monitoring site as either a 

maintenance or nonattainment receptor. 

Nonetheless, Kentucky is linked above 1 

percent of the NAAQS but less than 1 

ppb to the four receptors in EPA’s most 

recent modeling. Therefore, whether 

Kentucky’s use of an alternative 1 ppb 

contribution threshold is approvable is 

potentially a dispositive question in 

EPA’s evaluation. 

EPA proposes to find that Kentucky’s 

reliance on an alternative contribution 

threshold of 1 ppb at Step 2 is not 

approvable. EPA acknowledges that the 

August 2018 memorandum generally 

recognized that a 1 ppb threshold may 

be appropriate for states to use, but also 

made clear that this guidance would be 

applied under the facts and 

circumstances of each particular SIP 

submittal.51 However, Kentucky did not 

provide a technical analysis to 

sufficiently justify use of an alternative 

1 ppb threshold at the linked, 

downwind monitors. Kentucky’s SIP 

submission simply stated that the 

Commonwealth agrees with EPA’s 

rationale set out in the August 2018 

memorandum that the amount of 

upwind collective contribution captured 

with the 1 percent and 1 ppb thresholds 

was generally comparable. But the 

guidance anticipated that states would 

evaluate whether the alternative 

threshold was appropriate under their 

specific facts and circumstances, not 

that the use of the alternative threshold 

would be automatically approvable.52

With respect to the assertion that 1 ppb 

was generally comparable to 1 percent, 

Kentucky did not provide discussion or 

analysis containing information specific 

to Kentucky or a receptor analysis for 

the affected monitors, as anticipated in 

the 2018 memorandum, to evaluate 

whether the alternative threshold was 

appropriate to apply with respect to the 

monitors to which Kentucky was linked. 

Such state-specific information is 

necessary to thoroughly evaluate the 

state-specific circumstances that could 

support approval. Given the absence of 

technical analysis to support the use of 

a 1 ppb threshold under the facts and 

circumstances relevant to Kentucky and 

its linked receptors, EPA proposes that 

the use of 1 ppb as a contribution 

threshold is not approvable.53 (As 

discussed in section III.C.1 below, EPA 

no longer intends to dedicate resources 

to supplement state submittals with 

insufficient analysis in this regard, and 

also has identified other policy and 

programmatic concerns with attempting 

to recognize alternative thresholds at 

Step 2 or otherwise deviating from its 

historical, consistent practice since 

CSAPR of applying a threshold of 1 

percent of the NAAQS at Step 2.) 

The MOG materials appended to 

Kentucky’s submission argued that a 

2016 EPA SIL guidance could be cited 

as acceptable to support a 1 ppb 

contribution threshold. As an initial 

matter, Kentucky appears not to have 

relied on this rationale. In EPA’s 

comments on Kentucky’s draft SIP 

submittal, EPA stated, ‘‘EPA has not 

made a determination that the SIL, 

developed for source-specific (PSD) 

purposes, could be considered an 

appropriate threshold to use when 

assessing contribution from an entire 

state.’’ 54 Kentucky stated in response 

that it ‘‘concurs with the comment’’ and 

had adjusted its SIP submittal 

accordingly.55 Further, even if the State 

had attempted to rely on the SIL as 

support for a 1 ppb threshold, the basis 

supplied by MOG is inadequate. The 

SIL is an analytical metric used in the 

context of PSD permitting, a part of the 

CAA’s ‘‘prevention of significant 

deterioration’’ program, which generally 

is applicable in areas that designated 

attainment 56 or unclassifiable for the 

NAAQS. Good neighbor analysis for the 

ozone NAAQS, by contrast, addresses 

the degree of significant contribution to 

nonattainment and interference with 

maintenance of the NAAQS resulting at 

downwind receptors from the collective 

contribution of many upwind sources. 

Further, it is not correct to conflate the 


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57See August 2018 memorandum at 4. 

58Air Plan Approval; Iowa; Infrastructure State 

Implementation Plan Requirements for the 2015 

Ozone National Ambient Air Quality Standard, 85 

FR 12232 (March 2, 2020). The Agency received 

adverse comment on this proposed approval and 

has not taken final action with respect to this 

proposal. 

59EPA notes that Congress has placed on EPA a 

general obligation to ensure the requirements of the 

CAA are implemented consistently across states 

and regions. See CAA section 301(a)(2). Where the 

management and regulation of interstate pollution 

levels spanning many states is at stake, consistency 

in application of CAA requirements is paramount. 60See August 2018 memorandum at 4. 

use of the term ‘‘significance’’ as used 

in the SIL guidance, with the term 

‘‘contribution,’’ which is the appliable 

statutory term that EPA applies at Step 

2 of the 4-step interstate transport 

framework. (‘‘Significance’’ within the 

4-step framework is evaluated at Step 3 

through a multifactor analysis, for those 

states that are determined to 

‘‘contribute’’ to downwind receptors at 

Steps 1 and 2. See section I.D.4.) Given 

the fundamentally different statutory 

objectives and context, EPA disagrees 

with MOG’s contention that the SIL 

guidance is applicable in the good 

neighbor context. 

1. EPA’s Experience With Alternative 

Step 2 Thresholds 

EPA here shares further evaluation of 

its experience since the issuance of the 

August 2018 memorandum regarding 

use of alternative thresholds at Step 2. 

This experience leads the Agency to 

now believe it may not be appropriate 

to continue to attempt to recognize 

alternative contribution thresholds at 

Step 2. The August 2018 memorandum 

stated that ‘‘it may be reasonable and 

appropriate’’ for states to rely on an 

alternative threshold of 1 ppb threshold 

at Step 2.57 (The memorandum also 

indicated that any higher alternative 

threshold, such as 2 ppb, would likely 

not be appropriate.) However, EPA also 

provided that ‘‘air agencies should 

consider whether the recommendations 

in this guidance are appropriate for each 

situation.’’ Following receipt and review 

of 49 good neighbor SIP submittals for 

the 2015 8-hour ozone NAAQS, EPA’s 

experience has been that nearly every 

state that attempted to rely on a 1 ppb 

threshold did not provide sufficient 

information and analysis to support a 

determination that an alternative 

threshold was reasonable or appropriate 

for that state. 

For instance, in nearly all submittals, 

the states did not provide EPA with 

analysis specific to their state or the 

receptors to which its emissions are 

potentially linked. In one case, the 

proposed approval of Iowa’s SIP 

submittal, EPA expended its own 

resources to attempt to supplement the 

information submitted by the state, in 

order to more thoroughly evaluate the 

state-specific circumstances that could 

support approval.58 It was at EPA’s sole 

discretion to perform this analysis in 

support of the state’s submittal, and the 

Agency is not obligated to conduct 

supplemental analysis to fill the gaps 

whenever it believes a state’s analysis is 

insufficient. The Agency no longer 

intends to undertake supplemental 

analysis of SIP submittals with respect 

to alternative thresholds at Step 2 for 

purposes of the 2015 8-hour ozone 

NAAQS. 

Furthermore, EPA’s experience since 

2018 is that allowing for alternative Step 

2 thresholds may be impractical or 

otherwise inadvisable for a number of 

additional policy reasons. For a regional 

air pollutant such as ozone, consistency 

in requirements and expectations across 

all states is essential. Based on its 

review of submittals to-date and after 

further consideration of the policy 

implications of attempting to recognize 

an alternative Step 2 threshold for 

certain states, the Agency now believes 

the attempted use of different thresholds 

at Step 2 with respect to the 2015 8-hour 

ozone NAAQS raises substantial policy 

consistency and practical 

implementation concerns.59 The 

availability of different thresholds at 

Step 2 has the potential to result in 

inconsistent application of good 

neighbor obligations based solely on the 

strength of a state’s implementation 

plan submittal at Step 2 of the 4-step 

interstate transport framework. From the 

perspective of ensuring effective 

regional implementation of good 

neighbor obligations, the more 

important analysis is the evaluation of 

the emissions reductions needed, if any, 

to address a state’s significant 

contribution after consideration of a 

multifactor analysis at Step 3, including 

a detailed evaluation that considers air 

quality factors and cost. Where 

alternative thresholds for purposes of 

Step 2 may be ‘‘similar’’ in terms of 

capturing the relative amount of upwind 

contribution (as described in the August 

2018 memorandum), nonetheless, use of 

an alternative threshold would allow 

certain states to avoid further evaluation 

of potential emission controls while 

other states must proceed to a Step 3 

analysis. This can create significant 

equity and consistency problems among 

states. 

Further, it is not clear that national 

ozone transport policy is best served by 

allowing for less stringent thresholds at 

Step 2. EPA recognized in the August 

2018 memorandum that there was some 

similarity in the amount of total upwind 

contribution captured (on a nationwide 

basis) between 1 percent and 1 ppb. 

However, EPA notes that while this may 

be true in some sense, that is hardly a 

compelling basis to move to a 1 ppb 

threshold. Indeed, the 1 ppb threshold 

has the disadvantage of losing a certain 

amount of total upwind contribution for 

further evaluation at Step 3 (e.g., 

roughly 7 percent of total upwind state 

contribution was lost according to the 

modeling underlying the August 2018 

memorandum; 60 in EPA’s updated 

modeling, the amount lost is 5 percent). 

Considering the core statutory objective 

of ensuring elimination of all significant 

contribution to nonattainment or 

interference of the NAAQS in other 

states and the broad, regional nature of 

the collective contribution problem with 

respect to ozone, there does not appear 

to be a compelling policy imperative in 

allowing some states to use a 1 ppb 

threshold while others rely on a 1 

percent of the NAAQS threshold. 

Consistency with past interstate 

transport actions such as CSAPR, and 

the CSAPR Update and Revised CSAPR 

Update rulemakings (which used a Step 

2 threshold of 1 percent of the NAAQS 

for two less stringent ozone NAAQS), is 

also important. Continuing to use a 1 

percent of NAAQS approach ensures 

that as the NAAQS are revised and 

made more stringent, an appropriate 

increase in stringency at Step 2 occurs, 

so as to ensure an appropriately larger 

amount of total upwind-state 

contribution is captured for purposes of 

fully addressing interstate transport. See 

76 FR 48208, 48237–38 (August 8, 

2011). 

Therefore, notwithstanding the 

August 2018 memorandum’s 

recognition of the potential viability of 

alternative Step 2 thresholds, and in 

particular, a potentially applicable 1 

ppb threshold, EPA’s experience since 

the issuance of that memorandum has 

revealed substantial programmatic and 

policy difficulties in attempting to 

implement this approach. Nonetheless, 

EPA is not at this time rescinding the 

August 2018 memorandum. The basis 

for disapproval of Kentucky’s SIP 

submission with respect to the Step 2 

analysis is, in the Agency’s view, 

warranted even under the terms of the 

August 2018 memorandum. EPA invites 

comment on this broader discussion of 

issues associated with alternative 

thresholds at Step 2. Depending on 

comment and further evaluation of this 

issue, EPA may determine to rescind the 

August 2018 memorandum in the 

future. 


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61These subsections provide brief summaries of 

the issues as presented in Kentucky’s SIP as 

context; please see section II of this notice for 

additional detail on the contents of Kentucky’s SIP. 

In summary, EPA’s updated modeling 

indicates that emissions from Kentucky 

sources are linked to downwind 

receptors identified in Table 1, and 

application of 1 ppb alternative 

threshold is not supported by 

Kentucky’s SIP submission. Thus, EPA 

preliminarily finds that Kentucky is 

linked to downwind nonattainment and 

maintenance receptors, and proceeds to 

Step 3 of the 4-step framework. 

D. Evaluation of Information Provided 

by Kentucky Regarding Step 3 

At Step 3 of the 4-step interstate 

transport framework, a state’s emissions 

are further evaluated, in light of 

multiple factors, including air quality 

and cost considerations, to determine 

what, if any, emissions significantly 

contribute to nonattainment or interfere 

with maintenance and, thus, must be 

eliminated under CAA section 

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

To effectively evaluate which 

emissions in the state should be deemed 

‘‘significant’’ and therefore prohibited, 

states generally should prepare an 

accounting of sources and other 

emissions activity for relevant 

pollutants and assess potential, 

additional emissions reduction 

opportunities and resulting downwind 

air quality improvements. EPA has 

consistently applied this general 

approach (i.e., Step 3 of the 4-step 

interstate transport framewor46k) when 

identifying emissions contributions that 

the Agency has determined to be 

‘‘significant’’ (or interfere with 

maintenance) in each of its prior 

Federal, regional ozone transport 

rulemakings, and this interpretation of 

the statute has been upheld by the 

Supreme Court. See EME Homer City, 

572 U.S. 489, 518–520 (2014). While 

EPA has not directed states that they 

must conduct a Step 3 analysis in 

precisely the manner EPA has done in 

its prior regional transport rulemakings, 

state implementation plans addressing 

the obligations in CAA section 

110(a)(2)(D)(i)(I) must prohibit ‘‘any 

source or other type of emissions 

activity within the State’’ from emitting 

air pollutants which will contribute 

significantly to downwind air quality 

problems. Thus, states must complete 

something similar to EPA’s analysis (or 

an alternative approach to defining 

‘‘significance’’ that comports with the 

statute’s objectives) to determine 

whether and to what degree emissions 

from a state should be ‘‘prohibited’’ to 

eliminate emissions that will 

‘‘contribute significantly to 

nonattainment in, or interfere with 

maintenance of’’ the NAAQS in any 

other state. Kentucky did not conduct 

such an analysis in its SIP submission. 

Kentucky did not include a 

comprehensive accounting of facilities 

in the Commonwealth and did not 

include a sufficient analysis of potential 

NOX emissions control technologies, 

their associated costs, estimated 

emissions reductions, and downwind 

air quality improvements for the 

purpose of identifying what additional 

emission controls may be necessary to 

eliminate their significant contribution. 

Rather, Kentucky’s SIP included air 

quality analysis related to downwind 

receptors and relied on existing NOX

emission measures in the 

Commonwealth without any rationale to 

show how or why existing measures 

would eliminate the Kentucky’s 

downwind contribution. Further, the 

Commonwealth provided information 

related to programs that it asserted were 

responsible for a 10-year decline in 

ozone season NOX emissions in 

Kentucky, such as regulations and 

Federal programs (including the CSAPR 

Update), EGU shutdowns, retirements, 

and fuel switches. However, Kentucky 

did not quantify the NOx emission 

reduction potential of on-the-books 

regulations or Federal programs or onthe-way measures for 2023, nor does the 

submission consider cost-effectiveness 

of potential emissions controls, the total 

emissions reductions that may be 

achieved by requiring these controls, or 

an evaluation of the air quality impacts 

such emissions reductions would have 

on the downwind receptors to which 

Kentucky is linked. Identifying a range 

of on-the-books emissions control 

measures that have been or may be 

enacted at the state or local level, 

without analysis of the impact of those 

measures on the downwind receptors, is 

not a sufficient analysis. 

Furthermore, the emissions-reducing 

effects of on-the-books emissions 

control requirements are already 

reflected in the air quality results of 

EPA’s modeling under Steps 1 and 2 of 

the 4-step framework. Kentucky, and 

MOG in the materials it submitted to 

Kentucky, maintain that there were 

additional emission reductions that 

have occurred that were not accounted 

for in EPA’s 2023 modeling as presented 

in the March 2018 memorandum. 

Kentucky cites the 2019 retirement of 

units 1 and 2 at the E.W. Brown coalfired power plant (see Appendix D, 

Response to Comments, at 5), and MOG 

claims a variety of unidentified changes 

not accounted for in EPA’s emissions 

inventory at the time of the modeling in 

the March 2018 memorandum, as well 

as certain downwind state measures 

apparently under consideration but not 

adopted, and certain changes in the 

Wisconsin EGU fleet (see Alpine TSD, 

Appendix B, at pages B–5, B–6). In 

general, any changes in the emissions 

inventory and on-the-books controls 

relevant to emissions in 2023 have now 

been incorporated into EPA’s most 

recent modeling of 2023. This includes 

changes in Kentucky EGU emissions. 

As previously discussed, EPA’s 

updated modeling indicates sources in 

Kentucky are linked to downwind air 

quality problems for the 2015 8-hour 

ozone standard. However, Kentucky’s 

SIP submittal did not include a 

sufficient accounting of emissions 

sources or activity in the 

Commonwealth, along with an analysis 

of potential NOX emissions control 

technologies, associated costs, estimated 

emissions reductions, and downwind 

air quality improvements to eliminate 

the Kentucky’s downwind contribution. 

EPA therefore propose to find that 

Kentucky was required to analyze 

emissions from the sources and other 

emissions activity from within the 

Commonwealth to determine whether 

its contributions were significant, and 

EPA proposes to disapprove its 

submission because Kentucky failed to 

do so. 

The subsections below contain 

additional detail with respect to 

arguments made by the Commonwealth 

in its SIP submission.61

1. Evaluation of Kentucky’s Reliance on 

Existing and Future NOX Emission 

Reductions 

The Commonwealth’s SIP submission 

does not contain a Step 3 analysis 

regarding future emissions reduction 

opportunities beyond pointing to NOX

emission reductions from expected 

retirements, fuel switching, and 

shutdowns. While the Commonwealth 

claimed there would be an estimated 

471 tons of NOX emissions from 

potential shutdown of units at the E.W. 

Brown Generating Station facility in 

Harrodsburg, Kentucky, the 

Commonwealth did not clarify how 

these planned reductions would resolve 

the Commonwealth’s downwind 

contribution to the Harford County, 

Maryland maintenance-only receptor by 

2023. (Nor did the Commonwealth 

evaluate whether emissions may 

increase at other sources whose 

generation would replace that lost at 

E. W. Brown.) Further, the E.W. Brown 

facility retired coal-fired units 1 and 2 


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62See Retired Unit exemption forms for E.W. 

Brown Generating station in Docket No.: EPA–R04– 

OAR–2021–0841. 

63The Commonwealth’s submission cites to 

MOG’s statements regarding controls on local 

sources ‘‘When an area is measuring nonattainment 

of a NAAQS, as is the case with the areas linked 

to Kentucky, the CAA requires that the effects and 

benefits of local controls on all source sectors be 

considered first, prior to pursuing controls of 

sources in upwind states.’’ 

in February 2019,62 the units’ retirement 

is included in the recently updated 

modeling for Steps 1 and 2, and yet 

emissions from Kentucky sources 

remain linked to one or more downwind 

receptors. 

While the Commonwealth generally 

asserted that on-the-books or on-the-way 

regulations and programs may provide 

future emissions reductions, Kentucky 

did not quantify these reductions in a 

meaningful way or demonstrate that the 

downwind improvements from these 

regulations and programs would be 

sufficient to eliminate the 

Commonwealth’s significant 

contribution or interference with 

maintenance. In addition, the SIP 

submission did not evaluate or even 

attempt to identify additional control 

measures for EGUs or non-EGUs, nor 

did it include a determination of 

emission reduction potential for these 

potential additional controls or consider 

their cost-effectiveness or downwind air 

quality effects. This is not a sufficient 

Step 3 analysis. 

2. Evaluation of Kentucky’s Reliance on 

Prior Transport FIPs 

The 10-year emission reductions 

discussed by Kentucky relies in part on 

the implementation of CAIR, CSAPR, 

and the CSAPR Update. Kentucky’s SIP 

relied on its EGUs being subject to the 

CSAPR Update (which reflected a 

stringency at the nominal marginal cost 

threshold of $1,400/ton (in 2011 dollars) 

for the 2008 8-hour ozone NAAQS) to 

argue that it has already implemented 

all cost-effective emissions reductions to 

support its conclusion that additional 

NOX emission reductions are not 

necessary from sources in Kentucky. 

Kentucky did not conduct a 

comprehensive Step 3 analysis or 

provide any justification for reliance on 

the CSAPR Update beyond identifying 

the NOX emission reductions that the 

Commonwealth believes are the source 

of the 10-year decline in NOX emissions 

at EGUs in the Commonwealth and 

noting that the actual emissions from 

EGUs in the Commonwealth are well 

below the CSAPR Update NOX ozone 

season trading budget. 

EPA disagrees with the 

Commonwealth. Reliance on the CSAPR 

Update (or the subsequent Revised 

CSAPR Update, which fully resolved 

Kentucky’s good neighbor obligations 

for the 2008 ozone NAAQS, 86 FR 

23056–57), is insufficient because those 

policies addressed section 

110(a)(2)(D)(i)(I) only for the 2008 ozone 

NAAQS. Additionally, reliance on an 

alleged cost-threshold stringency from 

the CSAPR Update is insufficient 

without additional Step 3 analysis and 

justification. First, the CSAPR Update 

did not regulate non-EGUs, and thus 

this analysis would have been 

incomplete, even with respect to 

obligations under the 2008 ozone 

NAAQS. See Wisconsin, 938 F.3d at 

318–20. Second, relying on the CSAPR 

Update’s (or any other CAA program’s) 

determination of cost-effectiveness 

without further Step 3 analysis is not 

approvable. Cost-effectiveness must be 

assessed in the context of the specific 

CAA program; assessing costeffectiveness in the context of ozone 

transport should reflect a more 

comprehensive evaluation of the nature 

of the interstate transport problem 

under the relevant NAAQS, the total 

emissions reductions available at 

alternative cost thresholds, and the air 

quality impacts of the reductions at 

downwind receptors. While EPA has 

not established a benchmark costeffectiveness value for 2015 8-hour 

ozone NAAQS interstate transport 

obligations, because the 2015 8-hour 

ozone NAAQS is a more stringent and 

more protective air quality standard, it 

is reasonable to expect control measures 

or strategies to address interstate 

transport under this NAAQS to reflect 

higher marginal control costs. As such, 

the marginal cost threshold of $1,400/ 

ton for the CSAPR Update (which 

addresses the 2008 ozone 8-hour 

NAAQS and is in 2011 dollars) is not an 

appropriate cost threshold and cannot 

be approved as a benchmark to use for 

interstate transport SIP submissions for 

the 2015 8-hour ozone NAAQS. 

In addition, the updated EPA 

modeling captures all existing CSAPR 

trading programs in the baseline, and 

that modeling confirms that these 

control programs were not sufficient to 

eliminate the Kentucky’s linkage at 

Steps 1 and 2 under the 2015 8-hour 

ozone NAAQS. Kentucky was therefore 

obligated at Step 3 to assess additional 

control measures using a multifactor 

analysis. 

Finally, relying on a FIP at Step 3 is 

per se not approvable if the state has not 

adopted that program into its SIP and 

instead continues to rely on the FIP. 

States may not rely on non-SIP 

measures to meet SIP requirements. See 

CAA section 110(a)(2)(D) (‘‘Each such 

[SIP] shall . . . contain adequate 

provisions. . . .’’). See also CAA 

section 110(a)(2)(A); Committee for a 

Better Arvin v. U.S. E.P.A., 786 F.3d 

1169, 1175–76 (9th Cir. 2015) (holding 

that measures relied on by state to meet 

CAA requirements must be included in 

the SIP). Kentucky has not adopted the 

Group 3 NOX Ozone Season Trading 

Program promulgated in the Revised 

CSAPR Update into its SIP. 

3. Evaluation of Kentucky’s Analysis of 

Air Quality and Emission Reductions 

Near the Linked Monitors 

Kentucky’s SIP also evaluated air 

quality in the vicinity of the Fairfield 

County, Connecticut (IDs: 090013007 

and 090019003) and Harford County, 

Maryland (ID: 240251001) monitors for 

which the Commonwealth is linked 

based on EPA’s modeling in the March 

2018 memorandum. Kentucky’s 

submission asserts that the primary 

cause of nonattainment problems at the 

Connecticut and Maryland monitors are 

due to local emissions of ozone 

precursors (particularly NOX) and 

meteorological conditions. 

Kentucky’s SIP submittal argues 

against control requirements on 

Kentucky sources to address the two 

nonattainment receptors in Fairfield, 

Connecticut (IDs: 090013007, 

090019003) and the maintenance-only 

monitor in Harford County, Maryland 

monitor, claiming that additional 

emission reductions from Kentucky 

EGUs (the only Kentucky source 

category discussed in the submittal) are 

not necessary. Kentucky concludes that 

local emissions reductions should be 

applied before requiring Kentucky to 

control its sources, and that the 

implementation of local programs to 

reduce emissions should be sufficient 

for monitors in the area to attain the 

2015 8-hour ozone NAAQS.63

With respect to the information 

Kentucky provided that is related to 

local emissions and the impact on air 

quality at the Connecticut and Maryland 

receptors, this information is 

insufficient to approve Kentucky’s SIP 

submission. Regardless of whether local 

emissions are the largest contributor to 

a specific nonattainment or 

maintenance receptor, the good 

neighbor provision requires that upwind 

states prohibit emissions that contribute 

significantly to nonattainment or 

interfere with maintenance of the 

NAAQS in downwind states. EPA 

evaluates a state’s obligations to 

eliminate interstate transport emissions 

under the interstate transport provision 

according to EPA’s 4-step process, and 

EPA’s updating modeling at Steps 1 and 


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64 In contrast to the receptors to which Kentucky 

is linked, EPA has found that certain receptors are 

so heavily impacted by local emissions that they 

should not be considered ‘‘transport’’ receptors for 

purposes of the ozone NAAQS. Typically, in such 

cases, only one state is linked above 1 percent to 

that receptor and the total upwind state 

contribution is on the order of 2 percent to 4 

percent of the receptor’s DV. See, e.g., 81 FR 15200 

(March 22, 2016), 81 FR 31513 (May 19, 2016), and 

81 FR 36179 (June 6, 2016) (approving Arizona’s 

transport SIP on basis that certain California 

receptors should not be considered impacted by 

interstate ozone transport). 

65See Area Designations for the 2015 Ozone 

National Ambient Air Quality Standards 

memorandum from Janet G. McCabe to EPA 

Regional Administrators, February 25, 2016 (2015 

ozone Area Designations memorandum). 

66See id. It is important to understand that 

HYSPLIT back trajectory analyses use archived 

meteorological modeling that includes actual 

observed data (surface, upper air, airplane data, 

etc.) and modeled meteorological fields to estimate 

the most likely route of an air parcel transported to 

a receptor at a specified time. The method 

essentially follows a parcel of air backward in 

hourly steps for a specified length of time. HYSPLIT 

Continued 

2 has identified a linkage between 

emission from Kentucky sources and 

downwind nonattainment and 

maintenance receptors. 

Further, EPA disagrees with 

Kentucky’s claims that local emissions 

reductions from the jurisdiction where 

the downwind receptor is located must 

first be implemented and accounted for 

before imposing obligations on upwind 

states under the interstate transport 

provision. There is nothing in the CAA 

that supports that position, and it does 

not provide grounds on which to 

approve Kentucky SIP submission. The 

D.C. Circuit has held on five different 

occasions that the timing framework for 

addressing interstate transport 

obligations must be consistent with the 

downwind areas’ attainment schedule. 

In particular, for the ozone NAAQS, the 

states and EPA are to address interstate 

transport obligations ‘‘as expeditiously 

as practicable’’ and no later than the 

attainment schedule set in accordance 

with CAA section 181(a). See North 

Carolina, 531 F.3d at 911–13; 

Wisconsin, 938 F.3d at 313–20; 

Maryland, 958 F.3d at 1204; New York 

v. EPA, 964 F.3d 1214, 1226 (D.C. Cir. 

2020); New York v. EPA, 781 Fed. App’x 

4, 6–7 (D.C. Cir. 2019). The court in 

Wisconsin explained its reasoning in 

part by noting that downwind 

jurisdictions often may need to heavily 

rely on emissions reductions from 

upwind states in order to achieve 

attainment of the NAAQS, 938 F.3d at 

316–17; such states would face 

increased regulatory burdens including 

the risk of bumping up to a higher 

nonattainment classification if 

attainment is not reached by the 

relevant deadline. Maryland, 958 F.3d at 

1204. The statutory framework of the 

CAA and these cases establish clearly 

that states and EPA must address 

interstate transport obligations in line 

with the attainment schedule provided 

in the Act in order to timely assist 

downwind states in attaining and 

maintain the NAAQS, and this schedule 

is ‘‘central to the regulatory scheme.’’ 

Wisconsin, 938 F.3d at 316 (quoting 

Sierra Club v. EPA, 294 F.3d 155, 161 

(D.C. Cir. 2002)). 

In addition, Kentucky’s SIP does not 

provide a technical justification to 

support its conclusion that local 

emissions reductions at the receptors 

will achieve attainment without upwind 

reductions from sources within 

Kentucky. Specifically, Kentucky does 

not provide any information to support 

its claim that the implementation of 

local programs alone will address the air 

quality problems at the Connecticut and 

Maryland monitors. Even with the 

consideration of on-the-books control 

measures to reduce mobile source 

emissions, EPA’s modeling projects that 

the total contribution from upwind 

states is a substantial part of the ozone 

problem at the nonattainment and 

maintenance receptors to which 

Kentucky is linked. To illustrate this, at 

the four receptors to which Kentucky is 

linked in EPA’s latest 2023 modeling, 

the total percent of U.S. anthropogenic 

emissions from upwind states is 55 

percent (Bucks Co., Pennsylvania), 90 

percent (New Haven Co., Connecticut), 

90 percent (Fairfield Co.—Stratford, 

Connecticut), and 94 percent (Fairfield 

Co.—Westport, Connecticut) of the total 

design values at these receptors. Clearly, 

emissions reductions from upwind 

states would have an impact on the 

design values at the identified 

receptors.64

Additionally, the SIP submission does 

not assess whether the Commonwealth’s 

own emissions contributed to 

nonattainment or interfered with 

maintenance at the linked receptors, or 

rather substantiate that emissions from 

the Commonwealth’s sources were not 

interacting with these monitors. 

Consequently, the application of local 

emission reduction measures does not 

absolve upwind states and sources from 

the responsibility of addressing their 

significant contribution. Moreover, 

Kentucky still has an obligation under 

the Act to address its downwind 

contribution to ozone nonattainment or 

interference with maintenance 

regardless of the emission reduction 

potential for local control measures. 

Furthermore, given that EPA’s updated 

modeling indicates that Kentucky is 

linked to nonattainment and 

maintenance receptors at Step 2 

including the same Fairfield County, 

Connecticut nonattainment receptors as 

were linked in the modeling released 

with the March 2018 memorandum, 

EPA disagrees with Kentucky’s claims 

regarding the application of local 

emission reduction measures with 

respect to its downwind linkages in the 

most recent modeling. 

4. Evaluation of Kentucky’s HYSPLIT 

Analysis 

Kentucky’s SIP submittal also 

included HYSPLIT model back 

trajectory analysis, which Kentucky 

used to emphasize the local nature of 

the ozone precursor emissions at the 

two Connecticut receptors, mobile 

sources along the I–95 Corridor, and the 

proximity of large point sources and 

ozone nonattainment areas in New 

York, New Jersey, Pennsylvania, and 

Maryland. Similarly, Kentucky also 

evaluated HYSPLIT back-trajectory for 

the Harford County, Maryland monitor 

and noted similar localized emissions 

impacts with respect to the Maryland 

monitor as discussed previously for the 

two Fairfield County, Connecticut 

monitors. 

However, the limited information 

provided by Kentucky is not adequate to 

support approval of Kentucky’s SIP on 

this basis and in the absence of a more 

complete Step 3 evaluation. Kentucky’s 

SIP submittal did not address that the 

HYSPLIT back-trajectories indicate that 

ozone precursor emissions sources in 

Kentucky are upwind of the linked 

nonattainment receptors in Connecticut 

(regardless of the existence of other 

upwind nonattainment areas that may 

also be contributing to those receptors). 

Additionally, the HYSPLIT trajectory 

information provided by Kentucky was 

developed by EPA to inform the 2015 

8-hour ozone NAAQS area designations 

and was not intended to evaluate longdistance interstate transport.65

Attachment 3 of the 2015 8-hour 

ozone Area Designations memorandum 

states that the line thickness displayed 

on trajectory plots ‘‘does not imply 

coverage other than to represent the 

centerline of an air parcel’s motion 

calculated to arrive at the starting 

location at the starting time. 

Uncertainties are clearly present in 

these results and these uncertainties 

change with trajectory time and distance 

traveled. One should avoid concluding 

a region is not along a trajectory’s path 

if the center line of that trajectory 

missed the region by a relatively small 

distance.’’ 66


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estimates the central path in both the vertical and 

horizontal planes. The HYSPLIT central path 

represents the centerline with the understanding 

that there are areas on each side horizontally and 

vertically that also contribute to the end point at the 

monitor. The horizontal and vertical areas from the 

centerline grow wider the further back in time the 

trajectory goes. Therefore, a HYSPLIT centerline 

does not have to pass directly over emissions 

sources or emission source areas but merely 

relatively near emission source areas. 

67See Table 1, shown previously in this notice. 

68 Kentucky did not rely on MOG’s proposed 

approach in its SIP submittal, therefore EPA does 

not comprehensively evaluate MOG’s suggestion. 

However, EPA’s definition of maintenance 

receptors already accounts for, and projects 

whether, receptors may have trouble attaining the 

NAAQS, through the use of projected maximum 

design values in the relevant analytic year. Further, 

EPA’s modeling of the relevant analytic year also 

already accounts for projected emissions trends of 

the upwind state (among others) and may (and often 

does) identify a linkage to areas that may struggle 

to maintain the NAAQS despite an overall 

declining emissions trend. This is not surprising. 

First, most maintenance receptors in EPA’s 

projections are currently measuring nonattainment, 

meaning that, despite projecting improved air 

quality in the future analytic year, the receptor 

location is currently, and may continue to be, near 

the level of the NAAQS. Second, ozone levels are 

influenced by meteorological variability and thus 

high ozone levels may persist despite declining 

emissions as a result of recurring or worsening 

ozone-conducive atmospheric conditions (e.g., 

higher temperatures). It is unclear how MOG’s 

approach would account for this variability or 

ensure that projected emissions reductions from 

linked states are rendered certain and enforceable. 

69 In the main text of its SIP submittal conclusion 

regarding interstate transport, Kentucky incorrectly 

attributes statements regarding the ‘‘interfere with 

maintenance’’ prong to the U.S. Supreme Court. See 

Submittal at 45–46. A footnote, however, correctly 

attributes this language to the D.C. Circuit’s original 

opinion in EME Homer City v EPA, 696 F.3d 7 (D.C. 

Cir. 2012). This decision was reversed and 

remanded by the Supreme Court, and on remand, 

the D.C. Circuit affirmed EPA’s approach to 

implementing prong 2, see 795 F.3d at 136. 

Further, the back trajectories used by 

Kentucky were limited to evaluating 

transport of air parcels over a relatively 

short 24-hour period, which limits their 

use for evaluating long-distance 

transport of emissions from Kentucky to 

the Fairfield, Connecticut receptors and 

the Harford, Maryland receptor. In 

contrast, EPA’s analysis of transported 

emissions as discussed in section III.A 

uses updated, photochemical grid 

modeling designed to assess ozone 

transported to downwind monitors 

across the entire region and over 

extended timeframes that fully account 

for fate and transport of ozoneprecursors over longer distances. 

Kentucky’s SIP submission states that 

the Fairfield County ozone monitors are 

located in the New York Metro Area, in 

close proximity to the I–95 

transportation artery. The 

Commonwealth’s analysis asserts a high 

VMT and number of commuters in the 

area indicating the presence of mobile 

emissions that could be the cause of 

violating monitors along the I–95 

corridor. Kentucky’s SIP also mentions 

two additional coastal monitor sites 

(Westport Sherwood and Stratford Point 

Lighthouse) located less than three 

miles from the I–95 corridor that also 

show a pattern of ozone violations. 

Kentucky raises similar points regarding 

the effect of mobile source emissions 

along the I–95 corridor in Maryland 

near the Edgewood receptor. Further, 

Kentucky asserts that both the 

Connecticut and Maryland receptor sites 

may be particularly impacted by unique 

coastal conditions associated with the 

Long Island Sound and the Chesapeake 

Bay. While it is true that both of these 

monitors are affected by coastal 

meteorological conditions such as 

complex land-water wind flows and 

mixing heights, a large portion of 

anthropogenic ozone at these locations 

is the result of transport from upwind 

states. In addition, as noted above, 

EPA’s most recent modeling shows that 

Kentucky is linked to a receptor in 

Bucks County, Pennsylvania which is 

inland and not influenced by coastal 

meteorology. 

The relevance of the points raised by 

Kentucky regarding the HYSPLIT back 

trajectories related to the evaluation of 

Kentucky’s good neighbor obligations is 

not clear. As already discussed, the 

statute and the case law (particularly the 

holdings in Wisconsin and Maryland) 

make clear that good neighbor 

obligations are not merely 

supplementary to or deferable until after 

local emission reductions are achieved. 

Further, all of the receptors to which 

Kentucky is linked are heavily impacted 

by upwind state emissions in addition 

to local sources and conditions. The 

Wisconsin decision’s holding regarding 

international contribution (discussed in 

section III.A) is equally applicable to an 

upwind state’s claims that some other 

state’s emissions, or local emissions, are 

‘‘more to blame’’ than its own 

emissions. See 938 F.3d 303 at 323–25 

(‘‘an upwind State can ‘contribute’ to 

downwind nonattainment even if its 

emissions are not the but-for cause’’). 

5. Evaluation of Kentucky’s Approach to 

Maintenance Receptors 

Kentucky’s SIP argues that states 

linked only to maintenance receptors 

should be held to less stringent 

standards of emissions reductions 

compared to states linked to a 

nonattainment receptor. Thus, as the 

Edgewood monitor was identified as a 

maintenance receptor in EPA’s March 

2018 memorandum modeling, the 

Commonwealth asserts that no further 

reductions from Kentucky sources other 

than on-the-books controls should be 

required. Although the Harford monitor 

is no longer linked to Kentucky based 

on EPA’s updated modeling,67

emissions from the Commonwealth are 

linked to the Bucks County, 

Pennsylvania (ID: 420170012) 

maintenance-only receptor. 

Additionally, MOG argues that states 

should be absolved from additional 

emissions controls to address a 

maintenance monitor if the upwind 

state can show that either the monitor 

is likely to remain in attainment for a 

period of 10 years or that the upwind 

state’s emissions will not increase for 10 

years after the attainment date.68

Under the D.C. Circuit’s decision in 

North Carolina, states and EPA are 

required to give independent 

significance to the ‘‘interference with 

maintenance’’ prong of section 

110(a)(2)(D)(i)(I). See 531 F.3d at 910. 

Since CSAPR, EPA’s nationally 

consistent policy framework for 

addressing interstate ozone transport 

has given meaning to this prong through 

a separate definition of maintenance 

receptors at Step 1 of the 4-step 

interstate transport framework. For 

states linked only to those receptors, 

EPA has found it appropriate to apply 

an emissions control solution that is 

uniform with the strategy applied for 

states that are linked to nonattainment 

receptors. See 76 FR at 48271. EPA’s 

approach to addressing interference 

with maintenance under prong 2 for 

ozone NAAQS has been upheld twice. 

See EME Homer City Generation, L.P., 

795 F.3d at 136; Wisconsin, 938 F.3d at 

325–27. See also 86 FR at 23054 (April 

30, 2021).69

Particularly given this context, 

Kentucky’s SIP submission does not 

provide information sufficient to 

support less stringent standards of 

emissions reductions than would result 

from EPA’s historical approach of 

addressing emissions activities from 

upwind states that are linked to 

maintenance-only receptors. The 

Commonwealth does not explain how 

the obligations of upwind states linked 

to maintenance-only receptors should 

be treated differently than the 

obligations of upwind states linked to 

nonattainment receptors. 

Further, EPA believes it would be 

inconsistent with the CAA for EPA to 

identify receptors that are at risk of 

NAAQS violations given certain 

conditions due to transported upwind 

emissions and then not prohibit the 

emissions that place the receptor at risk. 

The Supreme Court held that it was a 

permissible interpretation of the statute 

to apportion responsibility for states 


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70Pointing to anticipated upcoming emission 

reductions, even if they were not included in the 

analysis at Steps 1 and 2, is not sufficient as a Step 

3 analysis, for the reasons discussed in section III.C. 

In this section, EPA explain that to the extent such 

anticipated reductions are not included in the SIP 

and rendered permanent and enforceable, reliance 

on such anticipated reductions is also insufficient 

at Step 4. 

linked to nonattainment receptors 

considering ‘‘both the magnitude of 

upwind States’ contributions and the 

cost associated with eliminating them.’’ 

EME Homer City, 134 S. Ct. at 1606. It 

is equally reasonable and permissible to 

use these factors to apportion 

responsibility among upwind states 

linked to maintenance receptors because 

the goal in both instances is to prohibit 

the ‘‘amounts’’ of pollution that will 

either significantly contribute to 

nonattainment or interfere with 

maintenance of the NAAQS downwind. 

EPA’s updated modeling indicates that 

the Commonwealth is still linked to 

downwind nonattainment and 

maintenance receptors for the 2015 8- 

hour ozone standard. Consequently, 

EPA believes Kentucky’s assertion that 

upwind states linked to maintenanceonly receptors should be held to less 

stringent standards of emissions 

reductions (as compared to states linked 

to a nonattainment receptor) is also 

inappropriate for new downwind 

linkages. 

6. Evaluation of Weighted Step 3 

Approach 

Although Kentucky did not adopt this 

approach in its SIP submittal, the MOG 

materials Kentucky appended provided 

arguments suggesting a ‘‘weighted’’ 

approach to Step 3 similar to an 

approach that stakeholders had 

identified to EPA (as listed in 

Attachment A to EPA’s March 2018 

memorandum). Under this approach, 

upwind-state emission reduction 

obligations would be allocated in 

proportion to the size of their 

contribution to downwind 

nonattainment. MOG determined the 

proportional reduction requirement 

associated with the relative significant 

contribution from each upwind state to 

the Harford County, Maryland monitor 

including Kentucky, which resulted in 

an additional emission reduction 

obligation for Kentucky of 0.02 ppb, as 

MOG proposed would be the 

appropriate proportion of reductions 

necessary for attainment at the Harford 

receptor. This approach would have 

imposed additional emissions 

reductions for Kentucky sources. 

Kentucky’s final SIP did not consider 

MOG’s proposal, and did not provide an 

explanation for why it was rejecting this 

approach to allocating upwind emission 

reductions, even though it appended 

this recommendation to its SIP 

submittal. 

In summary, EPA has newly available 

information that confirms sources in 

Kentucky are linked to downwind air 

quality problems for the 2015 8-hour 

ozone standard. Kentucky’s SIP 

submittal did not include an accounting 

of emissions sources and activity in the 

Commonwealth along with an analysis 

of potential NOX emissions control 

technologies, their associated costs, 

estimated emissions reductions, and 

downwind air quality improvements. 

Nor did Kentucky present an alternative 

approach to assess which of its 

emissions should be deemed 

‘‘significant.’’ EPA proposes to find that 

Kentucky’s analysis—including reliance 

on on-the-books state and Federal 

measures (including prior CSAPR 

programs) and claimed on-the-way 

emission reductions, as well as other air 

quality, emissions, and geographic 

factors—is insufficient to support the 

Commonwealth’s claim that its SIP 

adequately prohibits emissions within 

Kentucky in a manner sufficient to 

address the State’s interstate transport 

obligations for the 2015 8-hour ozone. 

E. Evaluation of Information Provided 

by Kentucky Regarding Step 4 

Step 4 of the 4-step interstate 

transport framework calls for 

development of permanent and 

federally enforceable control strategies 

to achieve the emissions reductions 

determined to be necessary at Step 3 to 

eliminate significant contribution to 

nonattainment or interference with 

maintenance of the NAAQS. Kentucky 

indicates that certain upcoming planned 

fuel switches or shutdowns at EGUs will 

occur before the end of 2023, for which 

Kentucky cites a press release and a 

closure plan developed by each plant’s 

parent company.70 As discussed in 

section III.D., Kentucky’s analysis is 

insufficient to demonstrate that these 

reductions are sufficient to address the 

Commonwealth’s interstate transport 

obligations; however, the 

Commonwealth also did not provide a 

separate SIP revision to ensure the 

reductions were permanent and 

enforceable. As a result, EPA proposes 

to disapprove Kentucky’s January 11, 

2019, submittal on the separate, 

additional basis that the Commonwealth 

has not developed permanent and 

enforceable emissions reductions 

necessary to meet the obligations of 

CAA section 110(a)(2)(d)(i)(I). 

F. Conclusion 

Based on EPA’s evaluation of 

Kentucky’s SIP submission, EPA is 

proposing to find that the interstate 

transport portion of Kentucky’s January 

11, 2019, SIP submission addressing 

CAA section 110(a)(2)(D)(i)(I) does not 

meet the Commonwealth’s interstate 

transport obligations because it fails to 

contain the necessary provisions to 

eliminate emissions that will contribute 

significantly to nonattainment or 

interfere with maintenance of the 2015 

8-hour ozone NAAQS in any other state. 

IV. Proposed Action 

EPA is proposing to disapprove the 

2015 8-hour ozone good neighbor 

interstate transport SIP revision from 

Kentucky, dated January 11, 2019. 

Under CAA section 110(c)(1), if 

finalized, this disapproval would 

establish a 2-year deadline for EPA to 

promulgate a FIP for Kentucky to 

address the CAA section 

110(a)(2)(D)(i)(I) interstate transport 

requirements pertaining to significant 

contribution to nonattainment and 

interference with maintenance of the 

2015 8-hour ozone NAAQS in other 

states, unless EPA approves a SIP that 

meets these requirements. However, 

under the CAA, a good neighbor SIP 

disapproval does not start a mandatory 

sanctions clock. 

V. Statutory and Executive Order 

Reviews 

A. Executive Order 12866: Regulatory 

Planning and Review and Executive 

Order 13563: Improving Regulation and 

Regulatory Review 

This proposed 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) 

This action merely proposes to 

disapprove a SIP submission as not 

meeting the CAA for Kentucky. EPA 

certifies that this proposed rule will not 

have a significant economic impact on 

a substantial number of small entities 

under the RFA (5 U.S.C. 601 et seq.). 

D. Unfunded Mandates Reform Act 

(UMRA) 

This proposed action does not contain 

any unfunded mandate as described in 

UMRA, 2 U.S.C. 1531–1538, and does 

not significantly or uniquely affect small 

governments. This proposed action 

imposes no enforceable duty on any 

state, local, or tribal governments or the 

private sector. 


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71 In deciding whether to invoke the exception by 

making and publishing a finding that an action is 

based on a determination of nationwide scope or 

effect, the Administrator takes into account a 

number of policy considerations, including his 

judgment balancing the benefit of obtaining the D.C. 

Circuit’s authoritative centralized review versus 

allowing development of the issue in other contexts 

and the best use of agency resources. 

72A finding of nationwide scope or effect is also 

appropriate for actions that cover states in multiple 

judicial circuits. In the report on the 1977 

Amendments that revised section 307(b)(1) of the 

CAA, Congress noted that the Administrator’s 

determination that the ‘‘nationwide scope or effect’’ 

exception applies would be appropriate for any 

action that has a scope or effect beyond a single 

judicial circuit. See H.R. Rep. No. 95–294 at 323, 

324, reprinted in 1977 U.S.C.C.A.N. 1402–03. 

73EPA may take a consolidated, single final 

action on all of the proposed SIP disapproval 

actions with respect to obligations under CAA 

section 110(a)(2)(D)(i)(I) for the 2015 8-hour ozone 

NAAQS. Should EPA take a single final action on 

all such disapprovals, this action would be 

nationally applicable, and EPA would also 

anticipate, in the alternative, making and 

publishing a finding that such final action is based 

on a determination of nationwide scope or effect. 

E. Executive Order 13132: Federalism 

This proposed 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 proposed action does not have 

tribal implications as specified in 

Executive Order 13175. This proposed 

action does not apply on any Indian 

reservation land, any other area where 

EPA or an Indian tribe has demonstrated 

that a tribe has jurisdiction, or nonreservation areas of Indian country. 

Thus, Executive Order 13175 does not 

apply to 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 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 proposed action 

is not subject to Executive Order 13045 

because it merely proposes to 

disapprove a SIP submission from 

Kentucky as not meeting the CAA. 

H. Executive Order 13211, Actions That 

Significantly Affect Energy Supply, 

Distribution or Use 

This proposed 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 proposed 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. 

K. CAA Section 307(b)(1) 

Section 307(b)(1) of the CAA governs 

judicial review of final actions by EPA. 

This section provides, in part, that 

petitions for review must be filed in the 

D.C. Circuit: (i) When the agency action 

consists of ‘‘nationally applicable 

regulations promulgated, or final actions 

taken, by the Administrator,’’ or (ii) 

when such action is locally or regionally 

applicable, if ‘‘such action is based on 

a determination of nationwide scope or 

effect and if in taking such action the 

Administrator finds and publishes that 

such action is based on such a 

determination.’’ For locally or regionally 

applicable final actions, the CAA 

reserves to EPA complete discretion 

whether to invoke the exception in 

(ii).71

If EPA takes final action on this 

proposed rulemaking, the Administrator 

intends to exercise the complete 

discretion afforded to him under the 

CAA to make and publish a finding that 

the final action (to the extent a court 

finds the action to be locally or 

regionally applicable) is based on a 

determination of ‘‘nationwide scope or 

effect’’ within the meaning of CAA 

section 307(b)(1). Through this 

rulemaking action (in conjunction with 

a series of related actions on other SIP 

submissions for the same CAA 

obligations), EPA interprets and applies 

section 110(a)(2)(d)(i)(I) of the CAA for 

the 2015 8-hour ozone NAAQS based on 

a common core of nationwide policy 

judgments and technical analysis 

concerning the interstate transport of 

pollutants throughout the continental 

U.S. In particular, EPA is applying here 

(and in other proposed actions related to 

the same obligations) the same, 

nationally consistent 4-step framework 

for assessing good neighbor obligations 

for the 2015 8-hour ozone NAAQS. EPA 

relies on a single set of updated, 2016- 

base year photochemical grid modeling 

results of the year 2023 as the primary 

basis for its assessment of air quality 

conditions and contributions at Steps 1 

and 2 of that framework. Further, EPA 

proposes to determine and apply a set 

of nationally consistent policy 

judgments to apply the 4-step 

framework. EPA has selected a 

nationally uniform analytic year (2023) 

for this analysis and is applying a 

nationally uniform approach to 

nonattainment and maintenance 

receptors and a nationally uniform 

approach to contribution threshold 

analysis.72 For these reasons, the 

Administrator intends, if this proposed 

action is finalized, to exercise the 

complete discretion afforded to him 

under the CAA to make and publish a 

finding that this action is based on one 

or more determinations of nationwide 

scope or effect for purposes of CAA 

section 307(b)(1).73

List of Subjects in 40 CFR Part 52 

Environmental protection, Air 

pollution control, Incorporation by 

reference, Ozone. 

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

Dated: February 3, 2022. 

Daniel Blackman, 

Regional Administrator, Region 4. 

[FR Doc. 2022–02947 Filed 2–18–22; 8:45 am] 

BILLING CODE 6560–50–P 

ENVIRONMENTAL PROTECTION 

AGENCY 

40 CFR Part 52 

EPA–R03–OAR–2021–0873; EPA–HQ–OAR– 

2021–0663; FRL–9494–01–R3] 

Air Plan Disapproval; West Virginia; 

Interstate Transport of Air Pollution for 

the 2015 8-Hour Ozone National 

Ambient Air Quality Standard 

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 disapprove a State 

Implementation Plan (SIP) submittal 

from West Virginia intended to address 

interstate transport for the 2015 8-hour 

ozone national ambient air quality 

standards (2015 8-hour ozone NAAQS). 

The ‘‘good neighbor’’ or ‘‘interstate 


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