27050 Federal Register / Vol. 87, No. 88 / Friday, May 6, 2022 / Proposed Rules 

includes incorporation by reference. As 

described in Sections II, III, and V of 

this preamble and set forth below in the 

proposed amendments to 40 CFR part 

52, the EPA is proposing to remove 

provisions of the EPA-Approved 

Missouri Regulations from the Missouri 

State Implementation Plan, which is 

incorporated by reference in accordance 

with the requirements of 1 CFR part 51. 

VII. Statutory and Executive Order 

Reviews 

Under the CAA, the Administrator is 

required to approve a SIP submission 

that complies with the provisions of the 

Act and applicable Federal regulations. 

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

Thus, in reviewing SIP submissions, the 

EPA’s role is to approve state choices, 

provided that they meet the criteria of 

the CAA. Accordingly, this action 

merely approves state law as meeting 

Federal requirements and does not 

impose additional requirements beyond 

those imposed by state law. For that 

reason, this action: 

• Is not a significant regulatory action 

subject to review by the Office of 

Management and Budget under 

Executive Orders 12866 (58 FR 51735, 

October 4, 1993) and 13563 (76 FR 3821, 

January 21, 2011); 

• Does not impose an information 

collection burden under the provisions 

of the Paperwork Reduction Act (44 

U.S.C. 3501 et seq.); 

• Is certified as not having a 

significant economic impact on a 

substantial number of small entities 

under the Regulatory Flexibility Act (5 

U.S.C. 601 et seq.); 

• Does not contain any unfunded 

mandate or significantly or uniquely 

affect small governments, as described 

in the Unfunded Mandates Reform Act 

of 1995 (Pub. L. 104–4); 

• Does not have federalism 

implications as specified in Executive 

Order 13132 (64 FR 43255, August 10, 

1999); 

• Is not an economically significant 

regulatory action based on health or 

safety risks subject to Executive Order 

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

• Is not a significant regulatory action 

subject to Executive Order 13211 (66 FR 

28355, May 22, 2001); 

• Is not subject to requirements of the 

National Technology Transfer and 

Advancement Act (NTTA) because this 

rulemaking does not involve technical 

standards; and 

• Does not provide EPA with the 

discretionary authority to address, as 

appropriate, disproportionate human 

health or environmental effects, using 

practicable and legally permissible 

methods, under Executive Order 12898 

(59 FR 7629, February 16, 1994). 

The SIP is not approved to apply on 

any Indian reservation land or in any 

other area where EPA or an Indian tribe 

has demonstrated that a tribe has 

jurisdiction. In those areas of Indian 

country, the rule does not have tribal 

implications and will not impose 

substantial direct costs on tribal 

governments or preempt tribal law as 

specified by Executive Order 13175 (65 

FR 67249, November 9, 2000). 

List of Subjects in 40 CFR Part 52 

Environmental protection, Air 

pollution control, Incorporation by 

reference, Ozone, Volatile organic 

compounds. 

Dated: April 27, 2022. 

Meghan A. McCollister, 

Regional Administrator, Region 7. 

For the reasons stated in the 

preamble, the EPA proposes to amend 

40 CFR part 52 as set forth below: 

PART 52—APPROVAL AND 

PROMULGATION OF 

IMPLEMENTATION PLANS 

■ 1. The authority citation for part 52 

continues to read as follows: 

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

Subpart AA—Missouri 

§ 52.1320 [Amended] 

■ 2. In § 52.1320, the table in paragraph 

(c) is amended by removing the entry 

‘‘10–5.440’’ under the heading ‘‘Chapter 

5—Air Quality Standards and Air 

Pollution Control Regulations for the St. 

Louis Metropolitan Area’’. 

[FR Doc. 2022–09468 Filed 5–5–22; 8:45 am] 

BILLING CODE 6560–50–P 

ENVIRONMENTAL PROTECTION 

AGENCY 

40 CFR Part 52 

[EPA–R08–OAR–2019–0140; EPA–HQ– 

OAR–2021–0663; FRL–9782–01–R8] 

Air Plan Approval; Colorado; 

Addressing Remanded Portions of the 

Previously Approved Infrastructure 

Requirements for the 2015 Ozone 

National Ambient Air Quality 

Standards 

AGENCY: Environmental Protection 

Agency (EPA). 

ACTION: Proposed rule. 

SUMMARY: On January 5, 2021, the 

United States Court of Appeals for the 

Tenth Circuit granted the 

Environmental Protection Agency’s 

(EPA) motion for a voluntary remand 

without vacatur of two parts of EPA’s 

2020 final rule approving Colorado’s 

infrastructure state implementation plan 

(SIP) submission for the 2015 8-hour 

ozone national ambient air quality 

standards (NAAQS) (2020 final rule). In 

this document, EPA proposes to address 

those two remanded parts of the 2020 

final rule: EPA’s conclusion that 

Colorado’s infrastructure SIP 

submission met the State’s good 

neighbor obligation under Clean Air Act 

(CAA) section 110(a)(2)(D)(i)(I); and 

EPA’s conclusion that Colorado’s 

infrastructure SIP submission provided 

‘‘necessary assurances’’ of the State’s 

authority to regulate agricultural sources 

under CAA section 110(a)(2)(E)(i). EPA 

is proposing to approve Colorado’s 

infrastructure SIP submission pursuant 

to CAA section 110. 

DATES: Written comments must be 

received on or before June 6, 2022. 

ADDRESSES: You may send comments, 

identified as Docket No. EPA–R08– 

OAR–2019–0140, using the Federal 

eRulemaking Portal at https://

www.regulations.gov, following the 

online instructions for submitting 

comments. Include Docket ID No. EPA– 

R08–OAR–2019–0140 in the subject line 

of the message. 

Instructions: All submissions received 

must include Docket ID No. EPA–R08– 

OAR–2019–0140. Comments received 

may be posted without change to 

https://www.regulations.gov, including 

any personal information provided. For 

detailed instructions on sending 

comments and additional information 

on the rulemaking process, see the 

‘‘Public participation’’ heading of the 

SUPPLEMENTARY INFORMATION section of 

this document. Out of an abundance of 

caution for members of the public and 

our staff, EPA Docket Center and 

Reading Room are open to the public by 

appointment only to reduce the risk of 

transmitting COVID–19. Our 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 us online at https://www.epa.gov/ 

dockets. Please email or call a person 

listed in the FOR FURTHER INFORMATION

CONTACT section if you need to make 

alternative arrangements for access to 

the docket. 

FOR FURTHER INFORMATION CONTACT: 

Amrita Singh, Air and Radiation 

Division, EPA, Region 8, Mailcode 

8ARD–IO, 1595 Wynkoop Street, 

Denver, Colorado, 80202–1129, 

telephone number: (303) 312–6103, 

email address: singh.amrita@epa.gov; or 


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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 submissions 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 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 the 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). 

Ellen Schmitt, telephone number: (303) 

312–6728, email address: schmitt.ellen@

epa.gov. 

SUPPLEMENTARY INFORMATION: Public 

participation: Submit your comments, 

identified by Docket No. EPA–R08– 

OAR–2019–0140, 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). 

There are two dockets supporting this 

proposed action, EPA–R08–OAR–2019– 

0140 and EPA–HQ–OAR–2021–0663. 

Docket No. EPA–R08–OAR–2019–0140 

contains information specific to 

Colorado, including the 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 proposed 

action. All comments regarding 

information in either of these dockets 

must be made in Docket No. EPA–R08– 

OAR–2019–0140. For additional 

submission methods, please email or 

call a person listed in the FOR FURTHER

INFORMATION CONTACT. 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. 

The index to Docket No. EPA–HQ– 

OAR–2021–0663 is available 

electronically at https://

www.regulations.gov. While all 

documents in that docket are listed in 

the index, some information may not be 

publicly available due to docket file size 

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

Throughout this document wherever 

‘‘we,’’ ‘‘us,’’ or ‘‘our’’ is used, we mean 

EPA. 

Table of Contents 

I. Background 

A. Statutory and Regulatory Background 

1. Ozone Transport 

a. Background on EPA’s Ozone Transport 

Modeling Information 

2. Necessary Assurances of State Authority 

B. EPA’s 2020 Action and the 2021 

Voluntary Remand 

II. EPA’s Evaluation and Proposed Approval 

of Colorado’s Infrastructure SIP 

Submission Under CAA Section 

110(a)(2)(D)(i)(I) and (E)(i) 

A. Good Neighbor Provision 

1. EPA’s Approach to Evaluating Interstate 

Transport SIP Submissions for the 2015 

8-Hour Ozone NAAQS 

2. Selection of Analytic Year 

3. Step 1 of the 4-Step Interstate Transport 

Framework 

4. Step 2 of the 4-Step Interstate Transport 

Framework 

5. Step 3 of the 4-Step Interstate Transport 

Framework 

6. Step 4 of the 4-Step Interstate Transport 

Framework 

7. EPA’s Evaluation of Colorado’s CAA 

Section 110(a)(D)(i)(I) Submission 

8. Emissions Assumptions Used in 

Modeling 

B. Colorado’s Authority To Regulate 

Agricultural Emissions 

1. EPA’s Prior Approval 

2. EPA’s Revised Analysis on Remand 

Under CAA Section 110(a)(2)(E)(i) 

III. Proposed Action 

IV. Statutory and Executive Order Reviews 

I. Background 

A. Statutory and Regulatory 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 three 

years after promulgation of a new or 

revised standard, SIP submissions 

meeting the applicable requirements of 

CAA section 110(a)(2).2

1. Ozone Transport 

One of the applicable requirements of 

section 110(a)(2) is found in CAA 

section 110(a)(2)(D)(i)(I), otherwise 

known as the ‘‘interstate transport’’ or 

‘‘good neighbor’’ 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 

submission 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

EPA is using the 4-step interstate 

transport framework (or 4-step 

framework) to evaluate state SIP 

submissions 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 and the 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 


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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). 

9 82 FR 1735. 

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, available in 

Docket No. EPA–HQ–OAR–2021–0663 or at https:// 

www.epa.gov/node/194139/. 

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/ 

airmarkets/memo-and-supplemental-informationregarding-interstate-transport-sips-2015-ozonenaaqs. 

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.’’ March 2018 memorandum 

at 2. 

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, available in Docket 

No. EPA–HQ–OAR–2021–0663 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 Revised CSAPR Update for the 2008 Ozone 

NAAQS, 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 the 

Headquarters 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. 

18See Technical Support Document (TSD) 

Preparation of Emissions Inventories for the 2016v2 

North American Emissions Modeling Platform. 

Dated: February 2022. (2016v2 TSD). Included 

under Docket No. EPA–HQ–OAR–2021–0663. 

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 

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. 

a. 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 (VOC) in individual 

upwind states. 

EPA has released several documents 

containing projected ozone 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 we 

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, we 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, we 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 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 ozone 

NAAQS concerning, respectively, 

potential contribution thresholds that 

may be appropriate to apply in Step 2 

of the 4-step framework, and 

considerations for identifying 

downwind areas that may have 

problems maintaining the standard at 

Step 1 of the 4-step 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, the 

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 ozone 

NAAQS.16

Following the final Revised CSAPR 

Update, EPA made further updates to 

the 2016 emissions platform to include 

mobile emissions from EPA’s Motor 

Vehicle Emission Simulator MOVES3 

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 an 

emissions modeling technical support 

document (TSD).18 EPA performed air 


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19Ramboll Environment and Health, January 

2021, www.camx.com. 

20 42 U.S.C. 7410(a)(2)(E)(i). 

21Promulgation of State Implementation Plan 

Revisions; Infrastructure Requirements for the 2015 

Ozone National Ambient Air Quality Standards; 

Colorado and North Dakota, 84 FR 36516 (July 29, 

2019). In the same rulemaking EPA also proposed 

to act on North Dakota’s infrastructure SIP 

submission for the 2015 ozone NAAQS. EPA’s final 

action with respect to North Dakota’s SIP 

submission was neither challenged nor remanded 

and thus is not addressed in this action. 

22 84 FR 36516, 36524–25. 

23 Id. n.24. 

24 84 FR 36524–25. 

25 938 F.3d at 313. 

26Approval and Promulgation of State 

Implementation Plan Revisions; Infrastructure 

Requirements for the 2015 Ozone National Ambient 

Air Quality Standards; Colorado and North Dakota, 

85 FR 20169, 20169–71 (April 10, 2020). 

27 Id. at 20169. 

28 958 F.3d 1185, 1203–04 (D.C. Cir. 2020). 

29Center for Biological Diversity v. EPA, No. 20– 

9560 (Tenth Cir.). 

30Center for Biological Diversity v. EPA, No. 20– 

9560 (Tenth Cir.), Petitioner’s Opening Brief at 10– 

11. 

31 Id. 

32 Id. 

quality modeling of the 2016v2 

emissions using the most recent public 

release version of the Comprehensive 

Air-quality Model with extensions 

(CAMx) photochemical modeling, 

version 7.10.19

EPA now 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 framework and generally 

references it within this action as 

2016v2 modeling for 2023. By using the 

updated modeling results, EPA is using 

the most current and technically 

appropriate information for this 

proposed rulemaking. Section III of this 

document and the Air Quality Modeling 

TSD for 2015 Ozone NAAQS Transport 

SIP Proposed Actions, included in 

Docket No. EPA–HQ–OAR–2021–0663 

for this proposal, contain additional 

detail on EPA’s 2016v2 modeling. EPA 

is accepting public comment on this 

updated 2023 modeling, which uses a 

2016v2 emissions platform as the 

modeling pertains to this proposed 

action. Comments on EPA’s air quality 

modeling as used in this proposed 

action should be submitted in the 

Regional docket for this action, Docket 

No. EPA–R08–OAR–2019–0140. EPA is 

not accepting comments in Docket No. 

EPA–HQ–OAR–2021–0663. 

2. Necessary Assurances of State 

Authority 

CAA section 110(a)(2)(E)(i) requires 

that a state provide ‘‘necessary 

assurances’’ that it will have, among 

other things, adequate authority under 

state law to carry out its SIP to meet 

CAA requirements with respect to the 

relevant NAAQS.20 Specifically, a 

state’s infrastructure SIP submission 

should show that the state has the legal 

authority to carry out the provisions 

identified in the state’s infrastructure 

SIP submission and is not prohibited by 

federal or state law from carrying out 

the SIP submission. 

B. EPA’s 2020 Action and the 2021 

Voluntary Remand 

On September 17, 2018, the State of 

Colorado submitted to EPA its 

infrastructure SIP submission for the 

2015 ozone NAAQS. On July 29, 2019, 

EPA proposed to approve Colorado’s 

submission with respect to all relevant 

CAA elements.21 EPA proposed 

approval of the portion of Colorado’s 

infrastructure SIP related to prongs 1 

and 2 of CAA section 110(a)(2)(D)(i)(I), 

primarily relying on the 2023 modeling 

(2011 base year platform) presented in 

the March 2018 memorandum.22 EPA’s 

analysis of the 2023 modeling indicated 

that Colorado’s largest impacts at any 

identified downwind receptor would be 

less than 1 percent (0.70 ppb) of the 

2015 ozone NAAQS.23 Thus, EPA 

proposed to find that Colorado’s 

emissions would not significantly 

contribute to nonattainment or interfere 

with maintenance of the 2015 ozone 

NAAQS in any other state.24

On September 13, 2019, the United 

States Court of Appeals for 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).25

In our 2020 final rule (published on 

April 10, 2020), EPA defended the use 

of the 2023 analytical year on the basis 

of what was then, in the Agency’s view, 

a position consistent with Wisconsin— 

specifically that the Wisconsin holding 

did not apply with respect to the 

attainment date for marginal areas.26

However, EPA also offered an 

alternative rationale. EPA used linear 

interpolation to estimate Colorado’s 

maximum contribution to a potential 

receptor in 2021 and concluded that 

even if it were appropriate to use the 

2021 marginal area date rather than the 

2023 moderate area date, Colorado’s 

impacts would be similar to those 

projected for 2023 and thus it would not 

significantly contribute to 

nonattainment or interfere with 

maintenance in other states.27

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

issued a ruling 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).28 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). 

On June 9, 2020, the Center for 

Biological Diversity (Center) filed a 

petition for review of the 2020 final rule 

in the United States Court of Appeals 

for the Tenth Circuit (Tenth Circuit).29

The Center challenged two sub-elements 

of the SIP approval: (1) EPA’s 

conclusion that Colorado’s 

infrastructure SIP submission satisfies 

the good neighbor provision, CAA 

section 110(a)(2)(D)(i)(I); and (2) EPA’s 

conclusion that the State’s infrastructure 

SIP submission satisfies Colorado’s 

obligation to provide necessary 

assurances that the State has authority 

to regulate all agricultural sources of air 

pollution as may be required by the 

CAA section 110(a)(2)(E)(i).30

In challenging EPA’s approval of the 

portion of Colorado’s infrastructure SIP 

submission addressing CAA section 

110(a)(2)(D)(i)(I), the Center argued that 

EPA’s analysis focused on the wrong 

analytical year, failed to adequately 

analyze all of the relevant potential outof-state receptor locations, and should 

have accounted for air quality impacts 

from various proposed and final federal 

rules.31

With respect to the state authority 

issue, the Center argued that a provision 

of state law, Colo. Rev. Stat. § 25–7– 

109(8)(a), bars Colorado from regulating 

agricultural sources other than those 

that are major sources. The Center 

argued that this means that Colorado’s 

infrastructure SIP submission failed to 

provide ‘‘necessary assurances’’ of the 

State’s authority to regulate all 

agricultural sources, as may be needed 

to comply with CAA requirements for 

SIPs, pursuant to CAA section 

110(a)(2)(E)(i).32

On December 31, 2020, EPA filed a 

motion for a voluntary remand without 

vacatur of the two challenged parts of 

the 2020 final rule. EPA stated that it 


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33Center for Biological Diversity v. EPA, No. 20– 

9560 (Tenth Cir.), EPA’s Motion for Voluntary 

Remand, Ex. 1, Declaration in Support of Motion for 

Voluntary Remand, at ¶ 8–10. 

34Center for Biological Diversity v. EPA, No. 20– 

9560 (Tenth Cir.), January 5, 2021 Order. 

35See EME Homer City Generation, LP v. EPA, 

572 U.S. 489, 519 (2014). As discussed later in this 

section, EPA recognizes that the nature of high 

ozone levels due to wintertime inversion conditions 

in the Uinta Basin in Utah raises unique analytical 

challenges in assessing whether there is transport 

from Colorado during those wintertime episodes. 

EPA has separately analyzed that unique situation 

and proposes to conclude that emissions from 

Colorado do not contribute to high ozone levels in 

Utah. That analysis, however, is separate from the 

generally applicable 4-step analytical framework for 

ozone transport described here. 36 42 U.S.C. 7410(a)(2)(D)(i). 37For attainment dates for the 2015 8-hour ozone 

NAAQS, refer to 42 U.S.C. 7511(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). 38See 42 U.S.C. 7511(a); 40 CFR 51.1303; 83 FR 

25776. 

39See 86 FR 23074; see also Wisconsin, 938 F.3d 

at 322. 

40Nor does EPA view 2022 as a reasonable 

analytic year for a similar reason: it would be 

impossible to finalize this action and implement 

any emissions reductions measures that could be 

shown to be needed by the 2022 ozone season. 

Thus, 2023 is the appropriate analytic year and also 

aligns with the next attainment date. 

intended to consider additional 

information, including the Maryland 

decision and new information 

developed after EPA issued the 2020 

final rule that was not available in the 

administrative record for the 2020 final 

rule.33 The Tenth Circuit granted EPA’s 

motion on January 5, 2021.34

In this document, EPA proposes to 

address the two remanded portions of 

EPA’s 2020 final rule by proposing to 

approve Colorado’s infrastructure SIP 

submission for the 2015 ozone 

standards with respect to CAA section 

110(a)(2)(D)(i)(I) and (E)(i). EPA seeks 

comment on its conclusions under CAA 

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

this proposed approval. We are not 

otherwise addressing or reopening for 

comment any of the other portions of 

our 2020 final rule. We will deem any 

comments on such portions beyond the 

scope of this action. 

II. EPA’s Evaluation and Proposed 

Approval of Colorado’s Infrastructure 

SIP Submission Under CAA Section 

110(a)(2)(D)(i)(I) and (E)(i) 

A. Good Neighbor Provision 

1. EPA’s Approach to Evaluating 

Interstate Transport SIP Submissions 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 

submissions for the 2015 8-hour ozone 

NAAQS. These policy judgments reflect 

consistency with relevant case law and 

past agency practice as reflected in the 

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.35

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. 

2. 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].’’ 36

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).37 As discussed in Section I of 

this proposed rulemaking, recent case 

law makes clear that the states and the 

Agency are obligated, under the good 

neighbor provision, to assess downwind 

air quality as expeditiously as 

practicable and no later than the next 

applicable attainment date. This 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, 2024.38 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, including 

Colorado, 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). EPA appreciates that among the 

arguments raised by the Center in 

challenging the 2020 final rule was the 

failure to analyze a year earlier than 

2023. However, EPA must act on SIP 

submissions—even in this action on 

remand—using the information 

available at the time it takes such action. 

In this circumstance, EPA does not 

believe it would be appropriate to 

evaluate Colorado’s 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.39 It would not make sense to 

analyze air quality, contribution levels, 

or emissions control strategies for the 

2021 attainment date, for purposes of 

interstate transport obligations, when no 

emissions reductions, if shown to be 

needed, could be implemented by that 

date anyway.40 Consequently, in this 

proposal EPA will use the analytical 

year of 2023 to evaluate Colorado’s CAA 

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

with respect to the 2015 8-hour ozone 

NAAQS. 

3. 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, we 

proceed to the next step of our 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 


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41See 531 F.3d at 910–11 (holding that EPA must 

give ‘‘independent significance’’ to each prong of 

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

42See 81 FR 74504. 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). 

43 795 F.3d 118, 136 (D.C. Cir. 2015); see 76 FR 

48208 (August 8, 2011). CSAPR Update and Revised 

CSAPR Update also used this approach. See 81 FR 

74504 and 86 FR 23054. 

44See 81 FR 74518. See also 86 FR 23085 

(reviewing and explaining rationale from CSAPR, 

76 FR 48237–38, for selection of 1 percent 

threshold). 

D.C. Circuit’s direction in North 

Carolina v. EPA.41

For 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).42

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 the 

CSAPR and upheld by the D.C. Circuit 

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

EPA.43 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. 

4. 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 

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 Clean 

Air Interstate Rule (CAIR), CSAPR, and 

CSAPR Update, a portion of the 

nonattainment problems from 

anthropogenic sources in the United 

States results 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.44

5. 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 focused primarily 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 


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45As 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. 

46See 42 U.S.C. 7410(a)(2)(D) (‘‘Each such [SIP] 

shall . . . contain adequate provisions . . . .’’); see 

also 42 U.S.C. 7410(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 state to 

meet CAA requirements must be included in the 

SIP). 

47Letter from Dr. Larry Wolk, Executive Director, 

Colorado Department of Health & Environment, to 

Douglas Benevento, Regional Administrator, EPA 

Region 8, Attachment 9, Adopted SIP at 4–5 

(August 16, 2018) (Colorado SIP Submission). 

48 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. 

49Both 0.06 ppb and 0.20 ppb are below the 1 

percent threshold of the 2015 ozone NAAQS (.70 

ppb). 

50Center for Biological Diversity v. EPA, No. 20– 

9560 (Tenth Cir.), Petitioner’s Opening Brief at 29– 

31. 

51As described in the Air Quality Modeling 

Technical Support Document 2015 Ozone NAAQS 

Transport SIP Proposed Actions, EPA’s method for 

calculating an average contribution metric for use 

in Step 2 of the 4-step transport framework is based 

on the average of daily contributions on the top 10 

ozone concentrations days as modeled in 2023. 

However, in order to avoid including contributions 

on days with low ozone concentrations, EPA 

requires at least 5 days with model-predicted 

maximum daily average 8-hour ozone 

concentrations greater than or equal to 60 ppb. In 

EPA’s method, contribution metric values are not 

calculated for monitors with fewer than 5 days that 

meet the 60 ppb threshold. As a result of applying 

this criterion, there were three monitoring sites in 

the areas identified by the Center, excluding the 

Uinta Basin, that are projected to have problems 

attaining and/or maintaining the NAAQS in 2023 

for which EPA did not calculate contribution metric 

values. These monitors include two sites in Dona 

Ana County, New Mexico, and one site in Toole 

County, Utah. Although EPA does not have 

contribution data for these specific monitors, the 

data at near-by monitors indicate that the 

contributions from Colorado to Dona Ana and Toole 

Counties are expected to be well below the 1 

percent threshold. Specifically, the contribution 

from Colorado to a monitoring site in El Paso, 

Texas, which is in the Dona Ana-El Paso interstate 

nonattainment area, is 0.04 ppb and, as indicated 

in Table 1, the contributions from Colorado to 

monitoring sites in Salt Lake County, which is 

closer to Colorado than Toole County, are 0.03 ppb. 

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.45

6. 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 SIP so that it is 

permanent and federally enforceable.46

7. EPA’s Evaluation of Colorado’s CAA 

Section 110(a)(2)(D)(i)(I) Submission 

As mentioned above, the State of 

Colorado submitted a SIP submission to 

EPA on September 17, 2018, to meet the 

good neighbor requirements for the 2015 

ozone NAAQS. In its prong 1 and prong 

2 analysis, Colorado’s SIP submission 

relies on analysis of the year 2023 (using 

a 2011 base year platform), among other 

things, to conclude that the State does 

not significantly contribute to 

nonattainment or interfere with 

maintenance of the 2015 ozone NAAQS 

in any other state.47 As explained in 

Section I of this proposed rulemaking, 

EPA has conducted an updated analysis 

for the 2023 analytical year (using a 

2016 base year platform) and proposes 

to rely primarily on this updated 

modeling to evaluate Colorado’s 

transport SIP submission. 

As described in Section I, EPA 

performed air quality modeling to 

project design values and contributions 

for 2023 using the 2016v2 emissions 

platform. EPA examined these data to 

determine if emissions in Colorado 

contribute 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 

in this most recent round of modeling. 

The data 48 indicate that the highest 

contribution in 2023 from Colorado to a 

downwind nonattainment or 

maintenance receptor is 0.06 ppb and 

0.20 ppb, respectively.49 Specifically, 

EPA’s analysis indicates that Colorado 

will have a 0.06 ppb impact at the 

projected nonattainment receptor in 

Kenosha County, Wisconsin (Site ID 

550590019), which has a 2023 projected 

average design value of 72.8 ppb and a 

2023 projected maximum design value 

of 73.7 ppb. EPA’s analysis further 

indicates that Colorado will have a 0.20 

ppb impact at a projected maintenance 

receptor in Denton County, Texas (Site 

ID 481210034), which has a projected 

2023 average design value of 70.4 ppb 

and a 2023 projected maximum design 

value of 72.2 ppb. The data also indicate 

that the only contribution in 2023 from 

Colorado to any downwind monitor 

above the 1 percent threshold is to a 

monitor in San Juan, New Mexico (0.99 

ppb). This monitor’s 2023 average and 

maximum design values are projected to 

be below the 2015 ozone NAAQS and 

the monitor is therefore not projected to 

be a nonattainment and/or maintenance 

receptor for the 2015 ozone NAAQS. 

Accordingly, EPA proposes to conclude 

that the most recent data support EPA’s 

conclusion that Colorado does not 

contribute to nonattainment or interfere 

with maintenance of the 2015 ozone 

NAAQS in any other state. 

In its comments on the 2020 rule and 

in its brief in the Tenth Circuit 

litigation, the Center identified several 

downwind areas that it argued may have 

been in nonattainment in 2020 but that 

EPA had screened out by using the 

incorrect analytic year of 2023. These 

included: Tarrant and Denton County, 

Texas; the Northern and Southern 

Wasatch Fronts in Utah; and monitors 

in New Mexico.50 In response to this 

argument, EPA is providing in Table 1 

the projected 2023 design values (DV) 

and associated contributions from 

Colorado for all monitors located in 

these areas for which EPA’s modeling 

provides valid contribution data.51


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52See monitors 481210034, 490110004, 

490353006, 490353013, 490570002, and 490571003. 

53Center for Biological Diversity v. EPA, No. 20– 

9560 (Tenth Cir.), Petitioner’s Opening Brief at 30. 

54EPA, Technical Support Document, Ozone 

Transport Analysis: Colorado and the Uinta Basin 

Nonattainment Area, April 2022 (Uinta Basin TSD). 

55 Id. 

56 Id. 

57Center for Biological Diversity v. EPA, No. 20– 

9560 (Tenth Cir.), Petitioner’s Opening Brief at 33– 

37. 

58See generally 2016v2 TSD; see also, e.g., 

2016v2 TSD Section 4, 157–213. 

TABLE 1—COLORADO CONTRIBUTIONS AND SELECT MONITORS

Monitor 

(AQS site ID) State County Projected 2023 average DV 

Projected 2023 

maximum DV 

Colorado 

contribution 

(ppb) 

350010029 .......................... New Mexico ....................... Bernalillo ............................ 62.0 62.7 0.27 

350450018 .......................... New Mexico ....................... San Juan ............................ 64.7 66.6 1.00 

350610008 .......................... New Mexico ....................... Valencia ............................. 62.2 63.9 0.30 

481210034 .......................... Texas ................................. Denton ............................... 70.4 72.2 0.20 

481211032 .......................... Texas ................................. Denton ............................... 67.2 69.0 0.22 

484393009 .......................... Texas ................................. Tarrant ............................... 68.0 68.7 0.17 

481410029 .......................... Texas ................................. El Paso .............................. 62.3 64.6 0.04 

490030003 .......................... Utah ................................... Box Elder ........................... 65.2 66.5 0.02 

490110004 .......................... Utah ................................... Davis .................................. 72.9 75.1 0.03

490353006 .......................... Utah ................................... Salt Lake ............................ 73.6 75.3 0.03 

490353013 .......................... Utah ................................... Salt Lake ............................ 74.4 74.9 0.03 

490570002 .......................... Utah ................................... Weber ................................ 70.6 72.5 0.02 

490571003 .......................... Utah ................................... Weber ................................ 70.5 71.5 0.02 

Table 1 shows that there are six 

monitors predicted to be violating the 

2015 ozone NAAQS in 2023, one in 

Texas and five in Utah.52 However, 

Colorado’s projected contribution to 

each of these monitors is below the 1 

percent threshold. Thus, no further 

analysis is required to address 

Colorado’s good neighbor obligations for 

the areas relevant to the listed monitors 

at Step 3. 

The Center also claimed that it could 

not find any documents in the record 

which address Colorado’s contribution 

to nonattainment in the Uinta Basin.53

EPA projected the design values for 

several of the monitoring sites in 

Duchesne County and Uintah County, 

Utah, but the Agency’s modeling 

represents summertime ozone 

conditions and is not designed to 

capture the conditions that result in the 

high wintertime ozone concentrations in 

the Uinta Basin nonattainment area. 

In order to characterize potential 

transport from Colorado to the Uinta 

Basin nonattainment area in the absence 

of reliable modeling to inform 

wintertime ozone levels and 

contributions, EPA conducted a separate 

analysis for the Uinta Basin, which is 

provided in a Uinta Basin TSD 

accompanying this action and included 

in Docket EPA–R08–OAR–2019–0140.54

To summarize EPA’s TSD findings, the 

ozone levels in the Uinta Basin 

nonattainment area are caused by a 

combination of meteorological inversion 

conditions, the unique topography of 

the Uinta Basin, and significant 

emissions of ozone precursors from 

sources within Utah. Generally, EPA 

concludes that ozone-precursor 

emissions do not transport into the 

Uinta Basin from outside the area 

during wintertime inversion episodes 

that produce high ozone conditions. 

Further, with respect to the portion of 

Colorado located within the regional 

Uinta Basin, available data shows that, 

because of low wind speed during 

wintertime inversion conditions and the 

unique topographical features within 

the regional Uinta Basin, emissions from 

the relevant area of Colorado are 

unlikely to transport to the Utah portion 

of the Uinta Basin.55

EPA reaches these conclusions 

recognizing the unique challenges 

associated with characterizing 

wintertime ozone concentrations and 

contributions in the Uinta Basin. As 

such, for this portion of the analysis, 

EPA is supplementing the consistently 

applied 4-step interstate transport 

framework used to characterize ozone 

transport at a broader, regional scale and 

during the summertime ozone season. 

Based on the information and analysis 

presented in the Uinta Basin TSD, EPA 

proposes to find that it is reasonable to 

conclude that Colorado does not 

significantly contribute to 

nonattainment or interfere with 

maintenance of the 2015 ozone NAAQS 

in the Utah portion of the Uinta Basin.56

In summary, based on the analyses 

provided in this document and in the 

Uinta Basin TSD, EPA proposes to 

conclude that emissions from sources in 

Colorado will not contribute to 

nonattainment or interfere with 

maintenance of the 2015 ozone NAAQS 

in any other state. Accordingly, EPA 

proposes to approve Colorado’s 

infrastructure SIP submission for the 

2015 ozone NAAQS under CAA section 

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

8. Emissions Assumptions Used in 

Modeling 

The Center argued that in the context 

of evaluating Colorado’s good neighbor 

SIP submission, EPA should have 

accounted for air quality impacts from 

various proposed and final federal 

rules.57 EPA’s normal practice is to 

include in its modeling only changes in 

emissions from final regulatory actions 

because, until such rules are finalized, 

any potential changes in NOX or VOC 

emissions are speculative. EPA’s 

updated 2023 modeling using the 

2016v2 platform reflects an updated 

assessment of the emissions inventory 

nationwide based on changes in federal 

and state rules and other relevant 

changes in the emissions inventory 

known at the time this latest modeling 

was conducted. All assumptions that 

formed the basis of the updated 2023 

modeling (2016v2) are available in the 

emissions modeling TSD.58 EPA 

encourages commenters to review this 

information, which supports the 

updated basis for this proposed action. 

This information supersedes the older 

modeling of 2023 that had been used in 

the 2020 final rule (2011 base year 

platform). 

B. Colorado’s Authority To Regulate 

Agricultural Emissions 

1. EPA’s Prior Approval 

CAA section 110(a)(2)(E)(i) requires 

that a state must provide ‘‘necessary 

assurances’’ that it has, among other 

things, adequate authority under state 

law to carry out the provisions of its SIP 

with respect to the relevant NAAQS. In 

the context of an infrastructure SIP 

submission, EPA expects states to 


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27058 Federal Register / Vol. 87, No. 88 / Friday, May 6, 2022 / Proposed Rules 

59Colorado SIP Submission, Attachment 9, 

Adopted SIP at 6. 

60 85 FR 20171. 

61Center for Biological Diversity v. EPA, No. 20– 

9560 (Tenth Cir.), Petitioner’s Opening Brief at 38– 

44. 

62Emissions from agricultural sources make up a 

very small portion of NOX and VOC emissions 

statement in the Denver Metro/Northern Front 

Range nonattainment area. See 2017 NEI NOX VOC 

table, which is included in the docket for this 

action. 

63 85 FR 20171. 

64C.R.S. 25–7–109(8)(a). 

65Letter to Deb Thomas, Regional Administrator 

(Acting) and Deputy Regional Administrator, U.S. 

Environmental Protection Agency, Region 8, from 

Garrison Kaufman, Director, Air Pollution Control 

Division, July 29, 2021. 

provide such necessary assurances for 

the new or revised NAAQS at issue. 

In its September 17, 2018 

infrastructure SIP submission, Colorado 

stated that ‘‘[t]here are no state or 

federal provisions prohibiting the 

implementation of any provision of the 

Colorado SIP.’’ Specifically, Colorado 

cited to its ‘‘general authority to adopt 

the rules and regulations necessary to 

implement the SIP’’ as ‘‘set out in the 

Colorado Air Pollution Prevention and 

Control Act Section 25–7–105 of the 

Colorado Revised Statutes (C.R.S);’’ 

general authority to administer and 

enforce the program in C.R.S. 25–7–111; 

additional authority to regulate air 

pollution and implement provisions in 

the SIP in the Colorado Air Pollution 

Prevention and Control Act, Article 7 of 

title 25; and authority delegated under 

C.R.S. 42–4–301 through 42–4–414 

(concerning motor vehicle emissions) 

and 42–4–414, C.R.S. (concerning 

emissions from diesel-powered 

vehicles).59

The Center commented on EPA’s 

proposed approval of the State’s 

infrastructure SIP submission, stating 

that C.R.S. 25–7–109(8)(a) prohibits 

Colorado from regulating agricultural 

sources of air pollution unless they are 

major sources. EPA evaluated the 

Center’s concern with respect to 

Colorado’s authority. In response, EPA 

explained that the provision cited by the 

Center does not bar the State from 

carrying out its existing SIP, and that in 

fact, the provision requires regulation of 

agricultural sources if they are major 

stationary sources, or if regulation is 

required by Part C, Part D, or title V of 

the CAA. In other words, EPA 

interpreted the provision to mean that if 

it is necessary to regulate agricultural 

sources beyond those that are major 

sources in order to attain and maintain 

the NAAQS, then the State has authority 

to do so. EPA noted that whether 

Colorado will need additional emission 

limitations and other control measures 

for areas designated nonattainment for 

the 2015 ozone NAAQS will be 

evaluated by the State and EPA as part 

of the State’s attainment plan under 

CAA title I part D through a separate 

process. Thus, EPA found that Colorado 

does not lack authority to implement 

the SIP and concluded instead that 

Colorado’s infrastructure SIP satisfied 

CAA section 110(a)(2)(E)(i).60

2. EPA’s Revised Analysis on Remand 

Under CAA Section 110(a)(2)(E)(i) 

In its brief filed in the Tenth Circuit 

litigation, the Center renewed its 

argument challenging EPA’s approval of 

Colorado’s infrastructure SIP 

submission as meeting CAA section 

110(a)(2)(E)(i) for the 2015 ozone 

NAAQS. The Center argued that EPA 

erred in approving Colorado’s 

infrastructure SIP submittal under CAA 

section 110(a)(2)(E)(i) because C.R.S. 

25–7–109(8)(A) bars Colorado from 

regulating agricultural sources other 

than those that are major sources. In 

particular, the Center argued that 

agricultural emissions are largely not 

from major stationary sources, but rather 

from fugitive emissions due to pesticide 

application, gases emitted from soil after 

fertilizer application, minor stationary 

sources, and mobile sources. The Center 

argued that Colorado state law thus is 

inadequate to provide authority to 

control these sources of pollution.61

As explained in the 2020 final rule, 

EPA disagreed with the Center’s 

interpretation of the C.R.S. 25–7– 

109(8)(A) and instead concluded that 

Colorado is not prohibited under state 

law from regulating emissions from 

agricultural sources (however small) 62

as necessary to implement the 2015 

ozone NAAQS.63 In relevant part, the 

agricultural provision states that ‘‘the 

[State] shall regulate emissions from 

[agriculture, horticultural, or 

floricultural production, including 

pesticide application] . . . if they are 

‘major stationary sources’, . . . or are 

required by Part C (prevention of 

significant deterioration), Part D 

(nonattainment), or Title V (minimum 

elements of a permit program), 

. . . .’’ 64 Thus, as stated in the 2020 

final rule, the statute plainly requires 

regulation of emissions from 

agricultural sources, including from 

nonpoint sources, soils and pesticides, 

mobile sources, and minor sources, if 

required under the CAA, including as 

necessary under Part D for attainment of 

the NAAQS. 

On remand, EPA verified that it 

properly interpreted Colorado law with 

respect to the State’s authority to 

regulate agricultural sources, and, in 

particular, that Colorado law does not 

limit that regulatory authority to major 

sources. Indeed, Colorado has 

confirmed that it agrees with EPA’s 

interpretation of C.R.S. 25–7–109(8)(A). 

In a letter submitted to EPA on July 29, 

2021, Colorado acknowledged that 

C.R.S. 25–7–109(8)(A) includes a 

‘‘limited restriction’’ on the State’s 

authority to regulate emissions from 

agricultural production activities but 

explains that there are ‘‘important carveouts’’ to that limited restriction. 

Colorado confirmed that the State has 

explicit authority to regulate major 

stationary sources. Colorado further 

explained that the sources that qualify 

as ‘‘major stationary sources’’ depends 

on the classification of the 

nonattainment area at issue—the higher 

the classification the lower the 

emissions threshold to qualify as a 

major stationary source. Additionally, 

Colorado confirmed in the letter that the 

State has ‘‘authority to regulate 

emissions from agricultural production, 

regardless of the size of the source, to 

the extent that such regulations are 

required by Part C (prevention of 

significant deterioration), Part D 

(nonattainment), or Title V (minimum 

elements of a permit program) of the 

federal [CAA].’’ Moreover, Colorado 

confirmed that the State has explicit 

authority to regulate emissions from 

agricultural production to the extent 

that such regulation is required by CAA 

section 111 (new source performance 

standards) and explained that such 

regulation is conducted through the 

State’s minor source, Prevention of 

Significant Deterioration, New Source 

Review, and Title V permitting 

programs. Finally, Colorado explained 

that the State has authority to 

promulgate, administer, and enforce 

emissions regulations that impact 

emissions from agricultural production, 

including mobile sources.65

Based on the above analysis and 

Colorado’s July 29, 2021 letter, EPA has 

now verified its interpretation of the 

State’s authority to regulate agricultural 

sources, as necessary to meet CAA 

requirements. Colorado has thus 

provided necessary assurances of the 

State’s authority to regulate agricultural 

sources as required in 42 U.S.C. 

7410(a)(2)(E)(i). Accordingly, EPA is 

again proposing to approve Colorado’s 

infrastructure SIP submission for the 

2015 ozone NAAQS with respect to the 

requirements of CAA section 

110(a)(2)(E)(i). 


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Federal Register / Vol. 87, No. 88 / Friday, May 6, 2022 / Proposed Rules 27059 

III. Proposed Action 

In this action, EPA proposes to 

conclude that Colorado’s infrastructure 

SIP satisfies the interstate transport 

provision of the CAA, section 

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

NAAQS, and that the State has provided 

the necessary assurances of the State’s 

authority to regulate all agricultural 

sources as may be required by the CAA 

under section 110(a)(2)(E)(i). 

IV. Statutory and Executive Order 

Reviews 

Under the CAA, the Administrator is 

required to approve a SIP submission 

that complies with the provisions of the 

Act and applicable Federal regulations. 

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

Thus, in reviewing SIP submissions, 

EPA’s role is to approve state choices, 

provided that they meet the criteria of 

the CAA. Accordingly, this action 

merely proposes to approve state law as 

meeting Federal requirements and does 

not impose additional requirements 

beyond those imposed by state law. For 

that reason, this action: 

• Is not a ‘‘significant regulatory 

action’’ subject to review by the Office 

of Management and Budget under 

Executive Orders 12866 (58 FR 51735, 

October 4, 1993) and 13563 (76 FR 3821, 

January 21, 2011); 

• Does not impose an information 

collection burden under the provisions 

of the Paperwork Reduction Act (44 

U.S.C. 3501 et seq.); 

• Is certified as not having a 

significant economic impact on a 

substantial number of small entities 

under the Regulatory Flexibility Act (5 

U.S.C. 601 et seq.); 

• Does not contain any unfunded 

mandate or significantly or uniquely 

affect small governments, as described 

in the Unfunded Mandates Reform Act 

of 1995 (Pub. L. 104–4); 

• Does not have Federalism 

implications as specified in Executive 

Order 13132 (64 FR 43255, August 10, 

1999); 

• Is not an economically significant 

regulatory action based on health or 

safety risks subject to Executive Order 

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

• Is not a significant regulatory action 

subject to Executive Order 13211 (66 FR 

28355, May 22, 2001); 

• Is not subject to requirements of 

section 12(d) of the National 

Technology Transfer and Advancement 

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

application of those requirements would 

be inconsistent with the CAA; and 

• Does not provide EPA with the 

discretionary authority to address, as 

appropriate, disproportionate human 

health or environmental effects, using 

practicable and legally permissible 

methods, under Executive Order 12898 

(59 FR 7629, February 16, 1994). 

In addition, the SIP is not approved 

to apply on any Indian reservation land 

or in any other area where EPA or an 

Indian tribe has demonstrated that a 

tribe has jurisdiction. In those areas of 

Indian country, the proposed rule does 

not have tribal implications and will not 

impose substantial direct costs on tribal 

governments or preempt tribal law as 

specified by Executive Order 13175 (65 

FR 67249, November 9, 2000). 

List of Subjects in 40 CFR Part 52 

Environmental protection, Air 

pollution control, Incorporation by 

reference, Intergovernmental relations, 

Nitrogen dioxide, Ozone, Reporting and 

recordkeeping requirements, Volatile 

organic compounds. 

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

Dated: April 26, 2022. 

K.C. Becker, 

Regional Administrator, Region 8. 

[FR Doc. 2022–09449 Filed 5–5–22; 8:45 am] 

BILLING CODE 6560–50–P 

ENVIRONMENTAL PROTECTION 

AGENCY 

40 CFR Part 152 

[EPA–HQ–OPP–2019–0701; FRL–7542–03– 

OCSPP] 

RIN 2070–AK56 

Pesticides; Proposal To Add Chitosan 

to the List of Active Ingredients 

Permitted in Exempted Minimum Risk 

Pesticide Products; Notice of Data 

Availability on Chitosan and Chitosan 

Salts 

AGENCY: Environmental Protection 

Agency (EPA). 

ACTION: Notification of data availability. 

SUMMARY: The Environmental Protection 

Agency (EPA) is announcing the 

availability of and soliciting comment 

on data related to the aquatic toxicity of 

chitosan salts. The EPA seeks public 

comment on these data. 

DATES: Comments must be received on 

or before June 6, 2022. 

ADDRESSES: Submit your comments, 

identified by docket identification (ID) 

number EPA–HQ–OPP–2006–0766, 

through the Federal eRulemaking Portal 

at https://www.regulations.gov. Follow 

the online instructions for submitting 

comments. Do not submit electronically 

any information you consider to be 

Confidential Business Information (CBI) 

or other information whose disclosure is 

restricted by statute. Additional 

instructions on commenting or visiting 

the docket, along with more information 

about dockets generally, is available at 

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

Due to the public health concerns 

related to COVID–19. The EPA Docket 

Center (EPA/DC) and Reading Room is 

open to visitors by appointment only. 

The staff continues to provide remote 

customer service via email, phone, and 

webform. For the latest status 

information on EPA/DC services and 

docket access, visit https://

www.epa.gov/dockets. 

FOR FURTHER INFORMATION CONTACT: 

Charles Smith, Director, Biopesticides 

and Pollution Prevention Division 

(7511P), Office of Pesticide Programs, 

Environmental Protection Agency, 1200 

Pennsylvania Ave. NW, Washington, DC 

20460–0001; main telephone number: 

(703) 305–7090; email address: 

BPPDFRNotices@epa.gov. 

SUPPLEMENTARY INFORMATION: 

I. General Information 

The EPA is making two aquatic 

toxicity reports, submitted by Tidal 

Vision Products, LLC, available for 

public comment. The EPA seeks input 

from stakeholders on how these reports 

may be used to inform the Agency’s 

assessment of the aquatic toxicity of 

chitosan and its salts. 

On November 2, 2020, the EPA 

published ‘‘Pesticides; Proposal to Add 

Chitosan to the List of Active 

Ingredients Permitted in Exempted 

Minimum Risk Pesticide Product,’’ 85 

FR 69307 (FRL–10009–24). The 

proposed rule addressed the subject 

matter of a 2018 petition by Tidal Vision 

Products LLC that requested that the 

substance commonly known as chitosan 

(also known by its chemical name polyD-glucosamine) (CAS Reg. No. 9012–76– 

4) be added to the list of active 

ingredients allowed in exempted 

minimum risk pesticide products under 

40 CFR 152.25(f)(1). 

Public comments on the proposed 

rule discussed these salts. The EPA 

notes that chitosan may form as a salt 

(e.g., acetate, lactate, hydrochloride, and 

salicylate) when it is solubilized in 

acids for end use product formulation 

and subsequently applied in the 

environment. The new information 

submitted by Tidal Vision pertains to 

these salts. 

As authorized by the Federal 

Insecticide, Fungicide, and Rodenticide 

Act (FIFRA) section 25(b), the EPA has 

exempted from the requirement of 

registration certain pesticide products if 

they are composed of specified 


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