Air Plan Disapproval; Arkansas, Louisiana, Oklahoma, and Texas; Interstate Transport of Air Pollution for the 2015 8-Hour Ozone National Ambient Air Quality Standards

Federal RegisterFeb 22, 2022

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 52

[EPA-R06-OAR-2021-0801, EPA-HQ-OAR-2021-0663; FRL-9338-01-R6]

Air Plan Disapproval; Arkansas, Louisiana, Oklahoma, and Texas; Interstate Transport of Air Pollution 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 State Implementation Plan (SIP) submittals from Arkansas, Louisiana, Oklahoma and Texas regarding interstate transport for the 2015 8-hour ozone national ambient air quality standard (NAAQS). This provision requires that each state's SIP 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. The “good neighbor” or “interstate transport” 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 the EPA to promulgate a Federal Implementation Plan (FIP) to address the relevant interstate transport requirements, unless the EPA approves a subsequent SIP submittal that meets these requirements. Disapproval does not start a mandatory sanctions clock.

DATES:

Written comments must be received on or before April 25, 2022.

ADDRESSES:

You may send comments, identified as Docket No. EPA-R06-OAR-2021-0801, by any of the following methods: Federal eRulemaking Portal at

https://www.regulations.gov

following the online instructions for submitting comments or via email to

fuerst.sherry@epa.gov.

Include Docket ID No. EPA-R06-OAR-2021-0801 in the subject line of the message.

Instructions:

All comments submitted must include the Docket ID No. for this rulemaking. 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, the 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 the EPA Docket Center services and the current status, please visit us online at

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

FOR FURTHER INFORMATION CONTACT:

Sherry Fuerst, EPA Region 6 Office, AR-SI, 214-665-6454,

fuerst.sherry@epa.gov.

We encourage the public to submit comments via

https://www.regulations.gov,

as there will be a delay in processing mail and no courier or hand deliveries will be accepted. Please call or email the contact above if you need alternative access to material indexed but not provided in the docket.

SUPPLEMENTARY INFORMATION:

Public Participation:

Submit your comments, identified by Docket ID No. EPA-R06-OAR-2021-0801, at

https://www.regulations.gov

(our preferred method), or the other methods identified in the

ADDRESSES

section. Once submitted, comments cannot be edited or removed from the docket. The EPA may publish any comment received to its public docket. Do not submit to the 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. The EPA will generally not consider comments or comment contents located outside of the primary submission (

i.e.,

on the web, cloud, or other file sharing system).

There are two dockets supporting this action, EPA-R06-OAR-2021-0801 and EPA-HQ-OAR-2021-0663. Docket No. EPA-R06-OAR-2021-0801 contains information specific to Arkansas, Louisiana, Oklahoma, and Texas, including the notice of proposed rulemaking, submittals from the states, and the EPA Region 6 2015 8-Hour Ozone Transport SIP Proposal Technical Support Document (EPA Region 6 TSD). 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, including Preparation of Emissions Inventories for the 2016v2 North American Emissions Modeling Platform, and Air Quality Modeling TSD for 2015 ozone NAAQS Transport SIP Proposed Actions. All comments regarding information in either of these dockets are to be made in Docket No. EPA-R06-OAR-2021-0801. For additional submission methods, please contact Sherry Fuerst, 214-665-6454,

fuerst.sherry@epa.gov.

For the full EPA public comment policy, information about CBI or multimedia submissions, and general guidance on making effective comments, please visit

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

Due to public health concerns related to COVID-19, the EPA Docket Center and Reading Room are open to the public by appointment only. Our 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 us online at

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

The EPA continues to carefully and continuously monitor information from the Centers for Disease Control and Prevention (CDC), local area health departments, and our Federal partners so that we can respond rapidly as conditions change regarding COVID-19.

The index to the dockets for this action, Docket No. EPA-R06-OAR-2021-0801 and EPA-HQ-OAR-2021-0663, are available electronically at

https://www.regulations.gov.

While all documents in the docket are listed in the index, some information may not be publicly available due to docket file size restrictions or content (

e.g.,

CBI).

Throughout this document, “we,” “us,” and “our” means the EPA.

Table of Contents

I. Background

A. Description of Statutory Background

B. Description of the EPA's 4-Step Interstate Transport Regulatory Process

C. Background on the EPA's Ozone Transport Modeling Information

D. The EPA's Approach to Evaluating Interstate Transport SIPs for the 2015 Ozone NAAQS

1. Selection of Analytic Year

2. Step 1 of the 4-Step Interstate Transport Framework

3. Step 2 of the 4-Step Interstate Transport Framework

4. Step 3 of the 4-Step Interstate Transport Framework

5. Step 4 of the 4-Step Interstate Transport Framework

II. Arkansas SIP Submission Addressing Interstate Transport of Air Pollution for the 2015 Ozone NAAQS and the EPA Evaluation of the SIP Submission

A. Summary of ADEQ SIP Submission Addressing Interstate Transport of Air Pollution for the 2015 Ozone NAAQS

B. EPA Evaluation of the ADEQ SIP Submission

1. Evaluation of Information Provided by ADEQ Regarding Step 1

2. Evaluation of Information Provided by ADEQ Regarding Step 2

3. Results of the EPA's Step 1 and Step 2 Modeling and Findings for Arkansas

4. Evaluation of Information Provided by ADEQ Regarding Step 3

5. Evaluation of Information Provided by ADEQ Regarding Step 4

6. Conclusion

III. Louisiana SIP Submission Addressing Interstate Transport of Air Pollution for the 2015 Ozone NAAQS and the EPA Evaluation of the SIP Submission

A. Summary of LDEQ SIP Submission Addressing Interstate Transport of Air Pollution for the 2015 Ozone NAAQS

B. EPA Evaluation of the LDEQ SIP Submission

1. Evaluation of Information Provided by LDEQ Regarding Steps 1 and 2

2. Results of the EPA's Step 1 and Step 2 Modeling and Findings for Louisiana

3. Evaluation of Information Provided by LDEQ Regarding Step 3

4. Evaluation of Information Provided by LDEQ Regarding Step 4

5. Conclusion

IV. Oklahoma SIP Submission Addressing Interstate Transport of Air Pollution for the 2015 Ozone NAAQS and the EPA Evaluation of the SIP Submission

A. Summary of ODEQ SIP Submission Addressing Interstate Transport of Air Pollution for the 2015 Ozone NAAQS

B. EPA Evaluation of the ODEQ SIP Submission

1. Evaluation of Information Provided by ODEQ Regarding Steps 1 and 2

2. Results of the EPA's Step 1 and Step 2 Modeling and Findings for Oklahoma

3. Evaluation of Information Provided by ODEQ Regarding Step 3

4. Evaluation of Information Provided by ODEQ Regarding Step 4

5. Conclusion

C. Impact on Areas of Indian Country

V. Texas SIP Submission Addressing Interstate Transport of Air Pollution for the 2015 Ozone NAAQS and the EPA Evaluation of the SIP Submission

A. Summary of TCEQ SIP Submission Addressing Interstate Transport of Air Pollution for the 2015 Ozone NAAQS

B. EPA Evaluation of the TCEQ SIP Submission

1. Evaluation of Information Provided by TCEQ Regarding Step 1

i. Evaluation of TCEQ's Methodology for Identifying Maintenance Receptors

ii. Evaluation of the TCEQ Modeling

2. Evaluation of Information Provided by TCEQ Regarding Step 2

3. Results of the EPA's Step 1 and Step 2 Modeling and Findings for Texas

4. Evaluation of Information Provided by TCEQ Regarding Step 3

5. Evaluation of Information Provided by TCEQ Regarding Step 4

6. Conclusion

VI. Proposed Action

VII. Statutory and Executive Order Reviews

I. Background

A. Description of Statutory Background

On October 1, 2015, the EPA promulgated a revision to the 2015 8-hour ozone NAAQS (2015 ozone NAAQS), lowering the level of both the primary and secondary standards to 0.070 parts per million (ppm).

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).

One of these applicable requirements 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 requirements, often referred to as “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). The 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).

“National 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.

SIP 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.

See North Carolina

EPA,

531 F.3d 896, 909-11 (D.C. Cir. 2008).

B. Description of the EPA's 4-Step Interstate Transport Regulatory Process

The EPA is using the 4-Step interstate transport framework (or 4-Step framework) described in detail below to evaluate states' SIP submittals addressing the interstate transport provision for the 2015 ozone NAAQS. The 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,

and the Cross-State Air Pollution Rule Update (CSAPR Update)

and the Revised CSAPR Update, both of which addressed the 2008 ozone NAAQS.

See

“Federal Implementation Plans: Interstate Transport of Fine Particulate Matter and Ozone and Correction of SIP Approvals”, 76 FR 48208 (Aug. 8, 2011).

See

“Cross-State Air Pollution Rule Update for the 2008 Ozone NAAQS”, 81 FR 74504 (Oct. 26, 2016).

In 2019, the D.C. Circuit Court of Appeals 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

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

EPA,

781 F. App'x. 4 (D.C. Cir. 2019).

Through the development and implementation of the CSAPR rulemakings and prior regional rulemakings pursuant to the interstate transport provision,

the EPA, working in partnership with states, developed the following 4-Step 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 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.

In addition to the CSAPR rulemakings, other regional rulemakings addressing ozone transport include the “NO

SIP Call,” 63 FR 57356 (October 27, 1998), and the “Clean Air Interstate Rule” (CAIR), 70 FR 25162 (May 12, 2005).

C. Background on the EPA's Ozone Transport Modeling Information

In general, the EPA has performed nationwide air quality modeling to project ozone design values (DVs)

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 DVs for the identified downwind nonattainment and maintenance receptors, the 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 (NO

) and volatile organic compounds (VOCs) in individual upwind states.

A design value is a statistic that describes the air quality status of a given location relative to the level of the NAAQS. Design values are typically used to designate and classify nonattainment areas, as well as to assess progress towards meeting the NAAQS.

See https://www.epa.gov/air-trends/air-quality-design-values

report.

The EPA has released several documents containing projected ozone design values, contributions, and information relevant to evaluating interstate transport with respect to the 2015 ozone NAAQS. First, on January 6, 2017, the EPA published a notice of data availability (NODA) in which we requested comment on preliminary interstate ozone transport data including projected ozone DVs and interstate contributions for 2023 using a 2011 base year platform.

In the NODA, the 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 NAAQS.

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.

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 ozone NAAQS at Step 1 of the 4-Step framework.

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 ozone NAAQS under Step 2 of the 4-Step framework.

The 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 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.

See

“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).

82 FR at 1735.

See

EPA memorandum, “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 ID No. EPA-HQ-OAR-2021-0663 or at

https://www.epa.gov/interstate-air-pollution-transport/interstate-air-pollution-transport-memos-and-notices.

See

EPA memorandum, “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 ID No. EPA-HQ-OAR-2021-0663 or at

https://www.epa.gov/interstate-air-pollution-transport/interstate-air-pollution-transport-memos-and-notices.

The 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 interstate transport provision. Any such determination would be made through notice-and-comment rulemaking.”

See

EPA memorandums, “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 ID No. EPA-HQ-OAR-2021-0663 or at

https://www.epa.gov/airmarkets/memo-and-supplemental-information-regarding-interstate-transport-sips-2015-ozone-naaqs.

Since the release of the modeling data shared in the March 2018 memorandum, the 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.

This collaborative project was a multi-year joint effort by the EPA, MJOs, and states to develop a new, more recent emissions platform for use by the EPA and states in regulatory modeling as an improvement over the dated 2011-based platform that the EPA had used to project ozone DVs and contribution data provided in the 2017 and 2018 memoranda. The EPA used the 2016v1 emissions to project ozone DVs and contributions for 2023. On October 30, 2020, in the Notice of Proposed Rulemaking for the Revised CSAPR Update, the EPA released and accepted public comment on 2023 modeling that used the 2016v1 emissions platform.

See

85 FR 68964, 68981. Although the Revised CSAPR Update addressed transport for the 2008 ozone NAAQS, the projected DVs and contributions from the 2016v1 platform are also useful for identifying downwind ozone problems and linkages with respect to the 2015 ozone NAAQS.

The results of this modeling, as well as the underlying modeling files, are included in Docket ID No. EPA-HQ-OAR-2021-0663.

See

85 FR 68964, 68981 (Oct. 30, 2020).

See

the Air Quality Modeling Technical Support Document for the Final Revised Cross-State Air Pollution Rule Update, available in Docket ID No. EPA-HQ-OAR-2021-0063 for this action.

Following the Revised CSAPR Update final rule, the EPA made further updates to the 2016 emissions platform to include mobile emissions from the EPA's Motor Vehicle Emission Simulator MOVES3 model

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 Technical Support Document (TSD) Preparation of Emissions Inventories for the 2016v2 North American Emissions Modeling Platform, which is included in Docket ID No. EPA-HQ-OAR-2021-0663. The EPA performed air quality modeling of the 2016v2 emissions using the most recent publicly released version of the Comprehensive Air-quality Model with extensions (CAMx) photochemical modeling, version 7.10.

The EPA now proposes to rely on the air quality modeling performed using CAMx, version 7.10, and the newly available 2016v2 emissions platform in evaluating states' submissions with respect to Steps

1 and 2 of the 4-Step framework and generally referenced within this action as 2016v2 modeling for 2023. By using the updated modeling results, the EPA is using the most current and technically appropriate information for this proposed rulemaking. Sections II-V of this action and the Air Quality Modeling TSD for 2015 ozone NAAQS Transport SIP Proposed Actions, included in Docket ID No. EPA-HQ-OAR-2021-0663 for this proposal, contain additional detail on the EPA's 2016v2 modeling. In this action, the EPA is inviting public comment on this updated 2023 modeling, which uses a 2016v2 emissions platform. Per the instructions in the Supplementary Information section above, all public comments, including comments on the EPA's air quality modeling should be submitted in the Regional docket for this action, Docket ID No. EPA-R06-OAR-2021-0801. Comments are not being accepted in Docket No. EPA-HQ-OAR-2021-0663.

Additional details and documentation related to the MOVES3 model can be found at

https://www.epa.gov/moves/latest-version-motor-vehicle-emission-simulator-moves.

Ramboll Environment and Health, January 2021,

www.camx.com.

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 Sections II-V of this action, we evaluate how the states used air quality modeling information in their submissions.

D. The EPA's Approach to Evaluating Interstate Transport SIPs for the 2015 Ozone NAAQS

The 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 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 1998 NO

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

EPA,

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

See

63 FR 57356. The NO

SIP Call required 22 eastern states and the District of Columbia to submit state implementation plans (SIPs) that set statewide ozone season NOx budgets which would reduce emissions of NO

In the March, August, and October 2018 memoranda, the EPA recognized that states may be able to establish alternative approaches to addressing their interstate transport obligations for the 2015 ozone NAAQS that vary from a nationally uniform framework. The 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, the 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 “flexibilities” as may have been identified or suggested in the past, the EPA will evaluate whether the state adequately justified the technical and legal basis for doing so.

The EPA notes that certain 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 ozone NAAQS. Attachment A to the March 2018 memorandum identified a “Preliminary List of Potential Flexibilities” that could potentially inform SIP development.

However, the EPA made clear in Attachment A that the list of ideas were not suggestions endorsed by the Agency but rather “comments provided in various forums” on which the EPA sought “feedback from interested stakeholders.”

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 are we specifically recommending that states use these approaches.”

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, the EPA will review the technical and legal justifications for doing so.

March 2018 memorandum, Attachment A.

Id.

at A-1.

Id.

The remainder of this section describes the EPA's proposed framework with respect to analytic year, definition of nonattainment and maintenance receptors, selection of contribution threshold, and multifactor control strategy analysis.

1. Selection of Analytic Year

In general, the states and the EPA must implement the interstate transport provision in a manner “consistent with the provisions of [title I of the CAA.]” 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).

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

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). 938 F.3d at 313.

For 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 Aug. 3, 2018).

On May 19, 2020, the D.C. Circuit issued a decision in

Maryland

EPA

that cited the

Wisconsin

decision in holding that the 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 the EPA's denial of a petition under CAA section 126(b).

Maryland

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). The EPA interprets the court's holding in

Maryland

as requiring the states and the Agency, under the interstate transport provision, to assess downwind air quality as expeditiously as practicable and no later than the next applicable

attainment date,

which is now the Moderate area attainment date under CAA section 181 for ozone nonattainment. The Moderate area attainment date for the 2015 ozone NAAQS is August 3, 2024.

The EPA believes that 2023 is now the appropriate year for analysis of interstate transport obligations for the 2015 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 ozone NAAQS.

We note that the court in

Maryland

did not have occasion to evaluate circumstances in which the EPA may determine that an upwind linkage to a downwind air quality problem exists at Steps 1 and 2 of the 4-Step 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.

See

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 Aug. 3, 2018).

The EPA recognizes that the attainment date for nonattainment areas classified as Marginal for the 2015 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 the 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, the EPA must act on SIP submittals using the information available at the time it takes such action. In this circumstance, the 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 at 23074;

See also

86 FR at 23085 (reviewing and explaining rationale from CSAPR); 76 FR at 48237-38 (for selection of 1 percent threshold).

The 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, the 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 the 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 analysis of potential emissions controls. The 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 the 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 emissions-reducing 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 preparing a multifactor assessment that evaluates additional available control opportunities. While the EPA has not prescribed a particular method for this assessment, the 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.

As 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 NO

SIP Call, 63 FR 57356, 57399-405.

See also

Revised CSAPR Update, 86 FR 23054, 23086-23116. Consistently across these rulemakings, the EPA has developed emissions inventories, analyzed different levels of control stringency at different cost thresholds, and assessed resulting downwind air quality improvements.

5. Step 4 of the 4-Step Interstate Transport Framework

In Step 4, states (or the EPA) develop permanent and federally enforceable control strategies to achieve the emissions reductions determined to be necessary in Step 3 to eliminate significant contribution to nonattainment or interference with maintenance of the NAAQS. For a state linked in Steps 1 and 2 to rely on an emissions control measure in 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.

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

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).

II. Arkansas SIP Submission Addressing Interstate Transport of Air Pollution for the 2015 Ozone NAAQS and the EPA Evaluation of the SIP Submission

A. Summary of ADEQ SIP Submission Addressing Interstate Transport of Air Pollution for the 2015 Ozone NAAQS

On October 10, 2019, the Arkansas Division of Environmental Quality (ADEQ) of the Arkansas Department of Energy and Environment made a SIP submission addressing interstate transport of air pollution for the 2015 ozone NAAQS. The ADEQ SIP submission provided an analysis of Arkansas's air emissions impact to downwind states using the EPA's 4-Step framework and an analytic year of 2023 and concluded that the State's air emissions will not contribute significantly to nonattainment or interfere with maintenance of the 2015 ozone NAAQS in other states.

To identify downwind monitors projected to be in nonattainment and/or have maintenance issues in 2023 (Step 1), ADEQ relied on the EPA's interstate transport modeling results that are included as an attachment to the March 2018 memorandum. The EPA modeling results included with the March 2018 memorandum provide: (1) Projected

average DV and maximum DV for the future year 2023 (fy 2023) for ozone monitors projected to be potential nonattainment or maintenance receptors in the 48 contiguous States and (2) the expected contribution of State emissions to the projected ozone concentrations at each ozone monitor.

At Step 2, ADEQ identified those states to which Arkansas contributes emissions and then applied a 1 ppb contribution threshold to determine projected nonattainment and/or maintenance receptors in other states that might be significantly impacted by emissions from Arkansas. ADEQ provided three rationales as a basis to support their decision to rely on a 1 ppb contribution threshold. First, ADEQ cited to the August 2018 memorandum

that compares the collective contribution captured by three different contribution thresholds: 1 Percent of the NAAQS, 1 ppb, and 2 ppb. ADEQ summarized the August 2018 memorandum and concluded that the 1 percent and 1 ppb contribution thresholds are generally comparable. Second, ADEQ referenced an April 2018 memorandum

in which the EPA examined the use of a significant impact level (SIL) value of 1 ppb for determining whether a proposed prevention of significant deterioration (PSD) source causes or contributes to a violation of the corresponding 2015 ozone NAAQS. Despite recognizing that a contribution threshold is not the same as a significance level, ADEQ claimed that a contribution threshold and significance level are sufficiently analogous to support the use of a 1 ppb contribution threshold. The final rationale ADEQ provided was based on the consistency with the reported precision of Federal reference monitors for ozone and the rounding requirements found in 40 CFR part 50, Appendix U, Interpretation of the Primary and Secondary National Ambient Air Quality Standards for Ozone. ADEQ noted that the 1 percent contribution threshold of 0.7 ppb is lower than the manufacturer's reported precision of Federal reference monitors for ozone and that the requirements found in Appendix U truncates monitor values of 0.7 ppb to 0 ppb.

“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, available in Docket ID No. EPA-HQ-OAR-2021-0663 or at

https://www.epa.gov/airmarkets/memo-and-supplemental-information-regarding-interstate-transport-sips-2015-ozone-naaqs.

See

EPA memorandum from Peter Tsirigotis, Director of the Office of Air Quality planning and Standards, April 17, 2018, “Guidance on Significant Impact Levels for Ozone and Fine Particles in the Prevention of Significant Deterioration Permitting Program” (“SILs Guidance” or “April 2018 memorandum”), available at:

https://www.epa.gov/sites/default/files/2018-04/documents/sils_policy_guidance_document_final_signed_4-17-18.pdf.

As stated previously, ADEQ identified all potential nonattainment and maintenance receptors for fy 2023 showing a contribution of emissions from Arkansas.

These receptors are included in Table AR-1.

Table AR-1 lists all sites that the EPA projected to have a fy 2023 average DV or fy 2023 maximum DV greater than 70.9 ppb in our March 2018 memorandum. As Arkansas stated in the SIP submission, the EPA considers sites matching these criteria to be projected nonattainment areas and projected maintenance areas, respectively. ADEQ ranked these sites by Arkansas's potential contribution, which the EPA determined based on the daily eight-hour average contributions on the top ten concentration days in 2023.

Table AR-1—Projected Nonattainment and Maintenance Receptors Identified by Arkansas Based on the EPA's March 2018 Memorandum

Receptor

(site ID, county, state)

2023

average DV

(ppb)

2023

maximum DV

(ppb)

Arkansas

contribution

(ppb)

260050003, Allegan, MI

71.7

1.64

482011039, Harris, TX

71.8

73.5

0.99

480391004, Brazoria, TX

74.9

0.90

484392003, Tarrant, TX

72.5

74.8

0.78

481210034, Denton, TX

69.7

0.58

482011034, Harris, TX

70.8

71.6

0.54

551170006, Sheboygan, WI

72.8

75.1

0.51

550790085, Milwaukee, WI

71.2

0.40

482010024, Harris, TX

70.4

72.8

0.29

261630019, Wayne, MI

0.27

240251001, Harford, MD

70.9

73.3

0.17

90019003, Fairfield, CT

75.9

0.13

90013007, Fairfield, CT

0.13

361030002, Suffolk, NY

75.5

0.12

360810124, Queens, NY

70.2

0.09

90099002, New Haven, CT

69.9

72.6

0.08

90010017, Fairfield, CT

68.9

71.2

0.07

80590006, Jefferson, CO

71.3

73.7

0.03

80590011, Jefferson, CO

70.9

73.9

0.02

81230009, Weld, CO

70.2

71.4

0.02

80350004, Douglas, CO

71.1

73.2

0.01

Based on a 1 ppb contribution threshold, ADEQ identified only one fy 2023 projected maintenance receptor, Allegan County, MI, and no fy 2023 projected nonattainment receptors linked to Arkansas. ADEQ also cited other modeling performed by TCEQ and Midwest Ozone Group, which showed that when different modeling protocols were employed, future year DV projections and contributions could differ considerably. ADEQ therefore elected to consider other evidence regarding its linkage to air quality in Allegan County, MI. Specifically, ADEQ analyzed back trajectory information to infer that there is no consistent or persistent relationship between elevated ozone days in Allegan County, MI and air traveling through Arkansas. ADEQ assessed wind patterns on elevated ozone days—days with a maximum daily average 8-hour ozone (MDA8) greater than 70.9 ppb in Allegan County,

MI. ADEQ used the National Oceanic and Atmospheric Administration (NOAA) HYbrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT)

model to evaluate wind back trajectories from over a 10-year period (2008-2017).

Over the course of the 10-year period, ADEQ identified 95 elevated ozone days (MDA8 > 70.9 ppb) for the Allegan County, MI monitor.

Next, ADEQ identified the maximum ozone value within these elevated ozone days.

Using HYSPLIT, ADEQ ran 72-hour back trajectories using the hour of the maximum ozone value for each elevated day as the back trajectory start time. To consider the effects of vertical variations in wind flows on transport patterns, ADEQ used the following starting heights above ground level: 100m, 500m, 1000m, and 1500m. ADEQ obtained 40 km grid meteorological data for the back trajectory analysis using Eta Data Assimilation System (EDAS) data.

In total, ADEQ ran 152 back trajectories for each mixing height.

ADEQ filtered the back trajectories to determine whether further analysis is warranted using two criteria. First, ADEQ filtered out back trajectories that had a starting hour mixing height below the back trajectory start height because ADEQ asserted these air parcels would not have reached ambient air

at the Allegan County, MI monitor site. Second, ADEQ filtered out any back trajectory that did not have a path through any portion of Arkansas. After ADEQ applied their filter criteria, 41 out of 608 back trajectories (6.74%) remained from 22 out of the 95 elevated ozone days (23%) examined. Of the 10 years examined, ADEQ also found that air passing through Arkansas only reached Allegan County, MI on four or more days in one year: 2012.

For 2012, HYSPLIT analyses indicated 14 Arkansas-Allegan County, MI linked back trajectories for 7 days in total in 2012, whereas for 2011, 2013, 2014, and 2016 the HYSPLIT analyses indicated three, two, zero and one days with Arkansas-Allegan County, MI linked back trajectories, respectively. For the 10 years ADEQ's performed HYSPLITs, ADEQ's HYSPLIT analysis indicated on average 2.2 days per year had trajectories with Arkansas-Allegan County, MI linked back trajectories. ADEQ also noted that these trajectories passed through other states and through Metropolitan Statistical Areas (MSAs)

both before and after traversing through Arkansas. Specifically, ADEQ stated that 37 trajectories passed through the Chicago-Naperville-Elgin, IL-IN-WI MSA prior to reaching Allegan County, MI. Based on these results, ADEQ concluded that other states and MSAs were more likely to have influenced ozone concentrations at the Allegan County, MI monitor on the days with back trajectories linked to Arkansas.

HYbrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model is a complete system for computing both simple air parcel trajectories and complex dispersion and deposition simulations. The model is designed to support a wide range of simulations related to the atmospheric transport and dispersion of pollutants and hazardous materials to the Earth's surface.

ADEQ analyzed ten years of HYSPLIT back trajectories to examine potential relationships between elevated ozone days at the Allegan County, MI monitor and emissions from Arkansas. In the SIP submission ADEQ stated their rationale for looking at an extended period of time is to gain a more complete picture of how Arkansas's emissions might contribute to elevated ozone in Allegan County, MI, rather than relying entirely on the EPA's modeling simulation, which is based on a single base year.

See

the AirNow-Tech website at

https://www.airnowtech.org/.

AirNow-Tech is a website for air quality data management analysis, and decision support used by the Federal, State, Tribal, and local air quality organizations.

If the same maximum eight-hour value occurred multiple times a day, ADEQ evaluated all incidences of the value for that day.

EDAS is an intermittent data assimilation system that uses successive three-hour model forecasts to generate gridded meteorological fields that reflect observations covering the continental United States. EDAS is accessible at

https://ready.arl.noaa.gov/edas40.php.

Mixing heights (m), defined as the height above ground level of the layer adjacent to the ground over which an emitted or entrained inert non-buoyant tracer will be mixed by turbulence.

Ambient air is the “portion of the atmosphere, external to buildings, to which the general public has access.” 40 CFR 50.1(e).

The number of days in a given year and the number of consecutive years is of particular relevance for the ozone NAAQS, which is calculated based the annual fourth-highest daily maximum eight-hour concentration averaged over three consecutive years.

MSA is defined as a geographic region with a high population density at its core and close economic ties throughout the area.

In Step 3, ADEQ also considered air quality trends in Allegan County, MI, emission trends in other upwind states, relative contribution from other upwind states, and cost factors. ADEQ presented that ozone DVs in Allegan County, MI fluctuated over the 2008-2017 period with higher concentration occurring from 2012 through 2014 but declining since 2014. ADEQ also mentioned that despite the most recent 2017 DV for the Allegan County monitor continuing to show an exceedance of the 2015 ozone NAAQS, the EPA-projected 2023 ozone average DV at the Allegan County, MI monitor, based on data provided in the March 2018 memorandum, is 69.0 ppb, which would be in attainment of the 2015 ozone NAAQS in 2023.

Next, ADEQ included an evaluation of the relative contribution and the emission trends from the eight states

with contributions greater than 1 ppb to the Allegan County, MI receptor. The emission trends evaluation examined ozone precursors, nitrogen oxides (NO

) and volatile organic compounds (VOC), from 2011 to 2017 and the model projected fy 2023 emissions level. ADEQ noted that the two states with the highest contributions to Allegan County, MI—Illinois and Indiana—have both experienced year-over-year decreases in NO

emissions in excess of 20,000 tons of NO

reduced per year. Arkansas had also experienced decreases in NO

emissions each evaluated year and emitted less NO

than any other of the potentially linked states. In addition, ADEQ referenced the EPA projections showing that most potentially linked states will continue to realize reductions in NO

, as well as VOCs, through 2023. ADEQ confirmed that based on this analysis, the overall general trends of NO

and VOC emissions are declining from Arkansas and the other linked states. The continuation of trends in the emissions reductions observed, particularly from Illinois and Indiana, are anticipated by ADEQ to result in air quality improvements in Allegan County, MI.

The eight linked states include Illinois, 42%; Indiana, 15%; Michigan, 7%; Missouri, 6%; Texas, 5%; Wisconsin, 4%; Oklahoma, 3% and Arkansas, 4%. The remaining contribution is labeled at “Other”. The linkages are based on the EPA's modeling results that are attached to the March 2018 memorandum.

In terms of cost analysis, ADEQ focused only on the cost of NO

controls at electric generating units (EGUs) in the State because EGUs are the largest source of NO

emissions that ADEQ regulates. In its analysis, ADEQ found that the costs to install additional NO

controls (selective catalytic reduction, SCR and selective noncatalytic reduction, SNCR) at EGUs exceed the EPA's cost thresholds used for the CSAPR and CSAPR Update rules.

Based on ADEQ's evaluation of the evidence, ADEQ concluded that no additional controls beyond pre-existing

state and Federal regulations were warranted for Arkansas sources to satisfy interstate transport obligations for the 2015 ozone NAAQS.

The EPA's Revised CSAPR Update, 86 FR 23054 (April 20, 2021), states “. . . EPA adjusted its representative cost for optimizing existing SNCR control to $1,800 per ton in response to comments received on the proposed rule . . . EPA views $1,600 per ton for optimization of existing SCR control and installation of state-of-the are NO

combustion controls and $1,800 per ton for optimization of existing SNCRs as comparable for policy purposes.” ADEQ's screening analysis using the EPA tools (referencing the EPA's Air Pollution Control Cost Estimation Spreadsheet for SCR) shows that cost-effectiveness values for ozone-season operation of SCR and SNCR are: $12,605-$31,580/ton for SCR and $4,221-$45,581 for SNCR. ADEQ notes that any costs imposed to install controls at the examined EGUs would be passed on to Arkansas ratepayers.

Based on the determinations made by ADEQ at Steps 1 through 3, ADEQ did not include any new control measures in the SIP submission to reduce ozone precursor emissions as part of a Step 4 analysis.

B. EPA Evaluation of the ADEQ SIP Submission

The EPA is proposing to find that ADEQ's October 10, 2019, SIP submission does not meet the State's obligations with respect to prohibiting emissions that contribute significantly to nonattainment or interfere with maintenance of the 2015 ozone NAAQS in any other state based on the EPA's evaluation of the SIP submission using the 4-Step interstate transport framework, and the EPA is therefore proposing to disapprove ADEQ's SIP submission.

1. Evaluation of Information Provided by ADEQ Regarding Step 1

At Step 1 of the 4-Step framework, ADEQ relied on the EPA modeling released in the March 2018 memorandum to identify nonattainment and maintenance receptors in 2023. As described in Section I of this action, the EPA has recently performed updated modeling using the 2016v2 platform to evaluate interstate transport of ozone for a fy 2023.

The EPA proposes to primarily rely on the EPA's modeling using the 2016v2 platform (EPA 2016v2 modeling), to identify projected nonattainment and maintenance receptors in fy 2023. Updating the base period from 2011 (base period used in data included in the March 2018 memorandum) to a more recent year (2016) allows for better projections of which monitors will have problems attaining and/or maintaining the 2015 ozone NAAQS and factors in more recent base year DVs. The EPA notes that with a switch from 2011 base period meteorology to 2016 base period meteorology, it is normal and expected that the potential downwind nonattainment or maintenance receptors would change due to the different weather patterns that occurred in the different base periods, which impacts both the transport of pollutants from upwind states and what receptors have higher monitored values within nonattainment/maintenance regions.

Modeling using both the 2011 and 2016 based years consistently project that certain areas will have problems attaining and/or maintaining the 2015 ozone NAAQS including receptors in Texas.

Per the instructions in the Supplementary Information section above, all public comments, including comments on the EPA's air quality modeling should be submitted in the Regional docket for this action, Docket ID No. EPA-R06-OAR-2021-0801. Comments are not being accepted in Docket No. EPA-HQ-OAR-2021-0663.

We note that ADEQ identified additional modeling performed by TCEQ and Midwest Ozone Group, but simply concluded that different modeling can lead to differences in DV projections and ozone contributions of these two alternative modeling analyses, only TCEQ's modeling using a 2012 base year identified receptors in Texas that projected different DVs for the Texas receptors identified in the EPA's 2011 base year. We discuss the EPA's review of the TCEQ's modeling elsewhere in this action and the Technical Support Document for this action “EPA Region 6 2015 8-Hour Ozone Transport SIP Proposal Technical Support Document” (EPA Region 6 2015 Ozone Transport SIP TSD.pdf) included in the Regional docket for this action (Docket ID No. EPA-R06-OAR-2021-0801), but we do conclude that TCEQ and recent monitoring data indicate that there are problematic receptors that are expected to be either nonattainment or maintenance receptors in 2023 including the Texas receptors that the EPA identified in our March 2018 memorandum with Arkansas linkages.

2. Evaluation of Information Provided by ADEQ Regarding Step 2

As noted earlier, ADEQ utilized a 1 ppb threshold at Step 2 to identify whether the State was “linked” to a projected downwind nonattainment or maintenance receptor. ADEQ identified linkages for Arkansas to one 2023 projected maintenance receptor, Allegan County, MI, and no 2023 projected nonattainment receptors.

As discussed in the EPA's August 2018 memorandum, with appropriate additional analysis it may be reasonable for states to use a 1 ppb contribution threshold as an alternative to a 1 percent threshold, at Step 2 of the 4-Step interstate transport framework, for the purposes of identifying linkages to downwind receptors. However, the EPA's August 2018 memorandum provided that whether or not a 1 ppb threshold is appropriate must be based on an evaluation of state-specific circumstances, and no such evaluation was included in the state's submittal. Instead, ADEQ cited to the EPA's SILs Guidance as a basis to support the use of a 1 ppb threshold; however, ADEQ did not explain the relevance of the SILs Guidance to ADEQ's statutory obligation under the interstate transport provision. The SILs Guidance relates to a different provision of the Clean Air Act regarding implementation of the prevention of significant deterioration (PSD) permitting program,

i.e.,

a program that applies in areas that have been designated attainment of the NAAQS. The SILs Guidance is not applicable to the interstate transport provision, which requires states to eliminate significant contribution or interference with maintenance of the NAAQS at known and ongoing air quality problem areas in other states. The EPA does not, in this action, agree that the State has justified its application of the 1 ppb threshold. In any case, both the EPA's most recent modeling, EPA 2016v2 modeling, and the modeling relied on by ADEQ in its SIP submittal, indicate that the State is projected to contribute greater than both the 1 percent and alternative 1 ppb thresholds. While the EPA does not, in this action, propose to approve of the State's application of the 1 ppb threshold, because the State has linkages greater than 1 ppb to projected downwind nonattainment or maintenance receptors, (as shown in Table AR-2) the State's use of this alternative threshold at Step 2 of the 4-Step interstate framework would not alter our review and proposed disapproval of this SIP submittal.

Additionally, the 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. (The memorandum also indicated that any higher alternative threshold, such as 2 ppb, would likely not be appropriate.) However, the 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 interstate transport SIP submittals for the 2015 ozone NAAQS, the 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 the 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, the 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.

It was at the 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 ozone NAAQS.

“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 comments on this proposed approval and has not taken final action with respect to this proposal.

Furthermore, the 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 ozone NAAQS raises substantial policy consistency and practical implementation concerns.

The availability of different thresholds at Step 2 has the potential to result in inconsistent application of interstate transport obligations based solely on the strength of a state's SIP submittal at Step 2 of the 4-Step interstate transport framework. From the perspective of ensuring effective regional implementation of interstate transport 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.

We note that Congress has placed on the 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.

Further, it is not clear that national ozone transport policy is best served by allowing for less stringent thresholds at Step 2. The 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, the 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 seven percent of total upwind state contribution was lost according to the modeling underlying the August 2018 memorandum;

in EPA 2016v2 modeling, the amount lost is five 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 NAAQS threshold.

See

August 2018 memorandum, at page 4.

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.

Accord

76 FR 48237-38.

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, the EPA's experience since the issuance of that memorandum has revealed substantial programmatic and policy difficulties in attempting to implement this approach. Nonetheless, the EPA is not, at this time, rescinding the August 2018 memorandum. The basis for the EPA's proposed disapproval of ADEQ'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. The EPA invites comment on this broader discussion of issues associated with alternative thresholds at Step 2. (See Supplementary Information section above for details and docket to submit comments). Depending on public comments received in relation to this action and further evaluation of this issue, the EPA may determine to rescind the 2018 memorandum in the future.

ADEQ included information in its SIP submission regarding back trajectories, emissions trends, and EGU cost controls to conclude that emissions from Arkansas should not be considered to contribute significantly to nonattainment or interfere with maintenance of the NAAQS in other states because there is not a persistent and consistent pattern of contribution from the State. While it is not entirely clear whether ADEQ was analyzing these factors under Step 2 or Step 3, the EPA is evaluating such arguments under Step 3, as we view these statements in the SIP submission to speak to whether or not a contribution is “significant” once a linkage is established.

3. Results of the EPA's Step 1 and Step 2 Modeling and Findings for Arkansas

As described in Section I of this action, the EPA performed air quality modeling using the 2016v2 emissions platform to project DVs and contributions for 2023 (EPA 2016v2 modeling). This data was examined to determine if Arkansas contributes at or above the threshold of 1 percent of the 2015 ozone NAAQS (0.70 ppb) to any downwind nonattainment or maintenance receptor. As shown in Table AR-2, the data

indicate that in 2023, emissions from Arkansas contribute greater than 1 percent of the standards to nonattainment or maintenance-only receptors in Texas: Denton County (Monitor ID. 481210034), Brazoria County (Monitor ID. 480391004), Harris County (Monitor ID. 482010055, Monitor ID. 482011034,

and Monitor ID. 482011035).

Therefore, based on the EPA's evaluation of the information submitted by ADEQ, and based on the EPA model 2016v2 results for 2023, the EPA proposes to find that Arkansas is linked at Steps 1 and 2 and has an obligation to assess potential emissions reductions from sources or other emissions activity at Step 3 of the 4-Step framework.

Design values and contributions at individual monitoring sites nationwide are provided in the file: 2016v2_DVs_state_contributions.xlsx which is included in docket ID No. EPA-HQ-OAR-2021-0663.

These 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 of this action. That modeling showed that Arkansas 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 EPA-HQ-OAR-2021-0663.

Allegan County Monitor ID. 260050003 is not a receptor in 2023 in the EPA 2016v2 modeling. 2023 avg DV is 67.3 ppb and 2023 Max. DV is 68.4 ppb, so the Allegan County monitor is not a receptor in 2023 for nonattainment or maintenance.

Table AR-2—Projected Nonattainment and Maintenance Receptors With Arkansas Linkages in 2023 Based on EPA 2016v2 Modeling

Receptor

(site ID, county, state)

Nonattainment/

maintenance

2023

average DV

(ppb)

2023

maximum DV

(ppb)

Arkansas

contribution

(ppb)

481210034, Denton, TX

Maintenance

70.4

72.2

0.76

480391004, Brazoria, TX

Maintenance

70.1

72.3

1.39

482010055, Harris, TX

Nonattainment

71.0

72.0

1.00

482011034, Harris, TX

Maintenance

70.3

71.6

1.38

482011035, Harris, TX

Maintenance

68.0

71.6

1.34

We recognize that the results of the EPA modeling released in the March 2018 memorandum (2011 base year) and the EPA 2016v2 modeling (2016 base year) identified different receptors and linkages at Steps 1 and 2 of the 4-Step framework. These differing results about receptors and linkages can be affected by the varying meteorology from year to year, but we do not think the differing results mean that the modeling or the EPA methodology for identifying receptors or linkages is inherently unreliable. Rather, these separate modeling runs indicated (1) that there were receptors that would struggle with nonattainment or maintenance in the future, and (2) that Arkansas was linked to some set of these receptors, even if the receptors and linkages differed from one another in their specifics (

e.g.,

a different set of receptors were identified to have nonattainment or maintenance problems, or Arkansas was linked to different receptors in one modeling run versus another). We think this common result indicates that Arkansas's emissions were substantial enough to generate linkages at Steps 1 and 2 to some set of downwind receptors, under varying assumptions and meteorological conditions, even if the precise set of linkages changed between modeling runs. Under these circumstances, we think it is appropriate to proceed to a Step 3 analysis to determine what portion of Arkansas's emissions should be deemed “significant.” In doing so, we are not considering our own earlier modeling results included in EPA's March 2018 memorandum to be of equal reliability relative to more recent EPA 2016v2 modeling. However, where alternative or older modeling generated linkages, even if those linkages differ from linkages in EPA 2016v2 modeling, that information provides further evidence, not less, in support of a conclusion that the state is required to proceed to Step 3 to further evaluate its emissions.

4. Evaluation of Information Provided by ADEQ Regarding Step 3

At Step 3 of the 4-Step 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 contribute significantly to nonattainment or interfere with maintenance and, thus, must be eliminated under CAA section 110(a)(2)(D)(i)(I).

ADEQ included in their SIP submission a further analysis of its modeled linkage to Allegan, MI (the only linked receptor it analyzed, based on its application of a 1 ppb threshold). Arkansas stated that the purpose and its conclusion of this analysis was that it would not contribute significantly to the Allegan, MI monitor because the state's emissions did not result in a consistent and persistent pattern of ozone contribution. As stated earlier, EPA 2016v2 modeling projects that the Allegan County, MI receptor will be attaining and is not expected to have difficulty maintaining the standard in 2023. As such, the EPA is not relying on the comparative analysis of emissions trends that ADEQ provided in order to conclude that Arkansas's emissions do not contribute significantly to a nonattainment or maintenance problem in Allegan, MI. We note however, that ADEQ's SIP submission and response to comments do not clearly define what ADEQ considers to be persistent and consistent pattern of contribution. Rather, the SIP submission simply states that contribution should be deemed “significant” only if there is a persistent and consistent pattern of several days with elevated ozone.

To be clear, the modeling establishing linkages of Arkansas to downwind nonattainment and maintenance receptors already establishes that there is a consistent and persistent pattern of contribution on elevated ozone days from Arkansas to other states. That is because EPA's methodology for projecting future year ozone concentrations accounts for precisely these concerns—the relative response factor

that is applied to historic monitored data to generate projections is calculated by looking only at days with elevated ozone levels (ten days is preferred with a minimum of five days). The EPA notes that monitored attainment with the ozone standard is determined by averaging the fourth high value recorded each year for three years. So, the EPA believes it is important to

estimate impacts on the days with highest projected ozone levels. The EPA's approach, as detailed in the Air Quality Modeling Technical Support Document for 2015 Ozone NAAQS Transport SIP Proposed Actions included in Docket ID No. EPA-HQ-OAR-2021-0663, does this by estimating the average fy 2023 impact from an upwind state on the days with the highest projected ozone levels at the downwind nonattainment or maintenance receptor. The days chosen to analyze the future impacts are chosen initially by the selecting the ten highest days in the base period modeling that are projected to be above 65 ppb in the base period. If there are not ten days above 65 ppb at a potential receptor, the number of days above 65 ppb are used as long as there is at least five days above 65 ppb in the base period. If the air quality modeling shows fewer than five days above 65 ppb in the base period, then the data for impacts at that receptor in fy 2023 are not calculated. The base and future year modeling for these five to ten days is then used to project fy 2023 ozone DVs to determine whether it is projected to be a nonattainment or maintenance receptor in 2023. For the same five to ten days identified, the future year modeling provides the estimated daily contribution at a potential receptor's future year daily MDA8 and these daily contributions are averaged for the five to ten days to result in the average contribution from the upwind area.

The relative response factor (RRF) is a ratio developed using the modeled changes between the base case and future case for high ozone modeled days. Typically, the 10 highest MDA8 modeled days in the base case are found and the maximum value from the 3x3 grid centered on the monitor for each day is used to calculate a 10-day average base case modeled value. Then a similar concentration average is developed for same 10 base case days and the same grid cell that provided the base case concentration to calculate a future year 10-day average modeled value using the future year modeling results. The RRF is then calculated by using this future year 10-day average model value divided by the base case year 10-day average model value to develop a ratio representing the change in modeled ozone. The RRF is then multiplied times the base DV value to result in a projected future year DV.

As mentioned previously, ADEQ used HYSPLIT back trajectories to assess wind patterns on elevated ozone days in an attempt to demonstrate that there is not persistent and consistent pattern of contribution from Arkansas to the Allegan County, MI receptor. 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 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 concentration at the end point monitor. The horizontal and vertical areas that potentially contribute to the end point concentration grow wider from the centerline 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 for those areas to contribute to concentrations at the endpoint. The EPA relies on back trajectory analysis as a corollary analysis along with observation-based meteorological wind fields at multiple heights to examine the general plausibility of the photochemical model “linkages.” Since the back trajectory calculations do not account for any air pollution formation, dispersion, transformation, or removal processes as influenced by emissions, chemistry, deposition, etc., the trajectories cannot be used to develop quantitative contributions. Therefore, back trajectories cannot be used to quantitatively evaluate the magnitude of the existing photochemical contributions from upwind states to downwind receptors. Chemical transport models, such as the one relied upon by Arkansas to establish the linkage between Arkansas and those downwind receptors in the first instance, do take these factors into account and therefore provide a more robust assessment of ozone contribution.

During ADEQ's public comment period, the EPA submitted comments noting concerns regarding the methodology ADEQ used in their HYSPLIT back trajectories analysis.

While we are not providing a detailed evaluation of ADEQ's HYSPLIT analysis in this rulemaking, we do note that our review identified a number of concerns with how ADEQ screened out a number of back trajectories, which invalidates ADEQ's conclusions.

While we disagree with ADEQ's methodologies and conclusions, we note that ADEQ's HYSPLIT back trajectory information did not show that the base years used in the EPA modeling (2011 and 2016) demonstrated an unusual amount of transport of air parcels from Arkansas to nonattainment or maintenance receptors in downwind states (

i.e.,

the modeling years used by the EPA do not skew the results toward finding linkages).

Therefore, although Arkansas asserted that its additional air quality factor analysis using back trajectory analysis is a permissible way to interpret which contributions are “significant” because that analysis examines whether there was a “persistent and consistent pattern of contribution on several days with elevated ozone,” the modeled linkage at Step 2 is a superior approach for assessing the persistence of a state's contribution. It is superior because it is based on the average of the contributions on the five to ten highest ozone days. Considering the form of the standard, this is a sufficient number of days to determine if an impact is persistent enough to impact an area's ability to attain or maintain the standard. The modeling is also a better method because it accounts for dispersion while back trajectory analysis as performed by Arkansas only shows the centerline of air parcel travel and otherwise will leave out days when Arkansas would have contributed to downwind problems. Finally, because the modeling accounts for dispersion and chemical reactions, it can provide a quantitative estimate of contribution.

The EPA reviewed the ADEQ SIP submission and provided comments during the State's public comment period for the proposed SIP action. The EPA's comment letter and ADEQ's response to comments are included in ADEQ's October 19, 2019, SIP submission, which is available in the Regional docket for this action (Docket ID No. EPA-R06-OAR-2021-0801).

Concerns included removing of HYSPLIT back trajectories based on start height, the start time that Arkansas used for the back trajectories and removing of back trajectories when the centerline passed near but not through Arkansas because Arkansas has some very large point sources near the Arkansas state line that could be contributing. Texas also screened their HYPSLIT back trajectories similarly to Arkansas and we have further discussed our concerns and why such screening invalidates conclusions from the HYSPLIT back trajectory analyses.

See

EPA's review and conclusions in discussion of TCEQ's HYSPLIT analyses in the “EPA Region 6 2015 8-Hour Ozone Transport SIP Proposal Technical Support Document” (EPA Region 6 2015 Ozone Transport SIP TSD.pdf) included in the Regional docket for this action (Docket ID No. EPA-R06-OAR-2021-0801).

ADEQ's summary of trajectories indicated that 2011 had three linked back trajectories and 2016 had one linked back trajectories and the EPA calculated the average for 2008-2017 in ADEQ's table was 2.2 linked back trajectories per year.

ADEQ also contested the significance of its modeled contribution above 1 ppb based on the relatively larger contributions of other upwind states to the receptor to which it was linked. The EPA disagrees that a state's small contribution relative to other upwind states is a permissible basis for finding no obligation under the interstate transport provision. CAA 110(a)(2)(D)(i)(I) requires states and the EPA to address interstate transport of air pollution that

contributes to

downwind states' ability to attain and maintain the NAAQS. Whether emissions from other states 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 arguments suggesting that upwind states should be excused from interstate transport 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. 938 F.3d 303 at 323-324. The court viewed these 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.” 938 F.3d 303 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

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

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 emissions from other states also contribute some amount of pollution to the same receptors to which the state is linked.

ADEQ did not provide additional analysis for other receptors to which it was linked above 1 percent in the air quality modeling upon which it relied, and to which it continues to be linked in EPA 2016v2 modeling. 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. The EPA has consistently applied this general approach (

i.e.,

Step 3 of the 4-Step interstate transport framework) 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, 519 (2014). While the EPA has not directed states that they must conduct a Step 3 analysis in precisely the manner the 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 the 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. As discussed below, ADEQ did not conduct an adequate analysis in their SIP submission. We therefore propose that ADEQ was required to analyze emissions from the sources and other emissions activity from within the State to determine whether its contributions were significant, and we propose to disapprove its submission because Arkansas failed to adequately do so.

In analyzing potential additional NO

controls, ADEQ found that additional controls on its EGUs would exceed the cost-effectiveness thresholds identified in the CSAPR and CSAPR Update rules. For the cost analysis, Arkansas only focused on the potential costs of NO

controls for EGUs. As stated above, Arkansas found that the costs to install additional NO

controls (selective catalytic reduction, SCR, and selective noncatalytic reduction, SNCR) at electric generating units (EGUs) exceed EPA's cost thresholds used for the CSAPR and CSAPR Update rules. Based on the projected cost of these controls relative to the thresholds used in those two prior EPA rules, Arkansas concluded that no new controls beyond those Federal and State regulations already in existence were cost-effective, especially considering that Allegan County, MI is projected to be in attainment with the 2015 ozone NAAQS and Arkansas's small contribution relative to other states potentially linked to Allegan County, MI based on EPA's modeling.

Arkansas's analysis is inadequate because its focus is only on EGUs.

See Wisconsin,

938 F.3d at 318-20. We also find Arkansas's conclusions as to the availability of cost-effective controls for EGUs to be inadequate. 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 cost-effectiveness in the context of ozone transport should reflect a more comprehensive evaluation of the nature of the interstate transport problem, the total emissions reductions available at several cost thresholds, and the potential air quality impacts of those reductions at downwind receptors. While the EPA has not established a benchmark cost-effectiveness value for 2015 ozone NAAQS interstate transport obligations, because the 2015 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. ADEQ's submission failed to provide a justification for why the $1400/ton threshold used in the CSAPR Update is appropriate to rely on for the 2015 ozone NAAQS. ADEQ's analysis does not consider any air quality impacts of assessed controls at downwind receptors. As stated above, assessing cost-effectiveness in the context of ozone transport requires more than just assessing the cost of controls per ton of NO

removed. As such, ADEQ's assessment of the cost of controls and reliance on the marginal cost threshold of $1,400/ton used for the CSAPR Update is inadequate. Furthermore, EPA 2016v2 modeling captures all existing CSAPR trading programs in the baseline and confirms that these control programs were not sufficient to eliminate Arkansas's linkage at Steps 1 and 2 under the 2015 ozone NAAQS. The State was therefore obligated at Step 3 to assess

additional

control measures using a multifactor analysis.

In 2017, National Emission Inventory (NEI) NO

emissions from EGU sources represent 56% percent of the total NOx emissions categories in Arkansas that report emissions to the NEI.

See

AR NOx.xlsx datasheet included in the Regional docket for this action (Docket ID No. EPA-R06-OAR-2021-0801).

5. Evaluation of Information Provided by ADEQ Regarding Step 4

Step 4 of the 4-Step interstate transport framework calls for the 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. ADEQ's SIP submission, which looked only at additional NO

controls at EGUs and dismissed such controls as not cost-effective relative to the thresholds established in earlier EPA transport rules, did not constitute an adequate emission reduction analysis at Step 3. Based on its conclusions, ADEQ did not revise its SIP to include any emission reductions. As a result, the EPA proposes to disapprove ADEQ's submittal on the separate, additional basis that Arkansas has not developed or included permanent and enforceable emissions reductions in its SIP necessary to meet the obligations of CAA section 110(a)(2)(D)(i)(I).

6. Conclusion

Based on the EPA's evaluation of ADEQ's SIP submission, the EPA is proposing to find that ADEQ's October 19, 2019, SIP submission addressing CAA section 110(a)(2)(D)(i)(I) does not meet the State'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 ozone NAAQS in any other state.

III. Louisiana SIP Submission Addressing Interstate Transport of Air Pollution for the 2015 Ozone NAAQS and the EPA Evaluation of the SIP Submission

A. Summary of LDEQ SIP Submission Addressing Interstate Transport of Air Pollution for the 2015 Ozone NAAQS

On November 13, 2019, the Louisiana Department of Environmental Quality (LDEQ) made a SIP submission addressing the State of Louisiana's interstate transport of air pollution for the 2015 ozone NAAQS. The SIP submission provided LDEQ's analysis of Louisiana's impact to downwind states and concluded that emissions from Louisiana will not contribute significantly to nonattainment or interfere with maintenance of the 2015 ozone NAAQS in other states.

The LDEQ's SIP submission provided an analysis of Louisiana's air emissions impact to downwind states using a 3-Step alternative framework similar to the EPA's 4-Step framework. LDEQ's 3-Step alternative framework includes: Step 1: Identify monitors projected to be in nonattainment or have maintenance issues in a future year; Step 2: Identify projected nonattainment and/or maintenance monitors in other states that might be impacted by emissions from Louisiana, tagging them for further review; and, Step 3: Determine if emissions from Louisiana contribute significantly to nonattainment or interfere with maintenance at the monitors tagged for review in Step 2. LDEQ noted that its Step 1 is identical to the EPA's Step 1, and its Steps 2 and 3 are equivalent to the EPA's Step 2. Louisiana further noted that Steps 3 and 4 of the EPA's 4-Step framework are relevant only if emissions from Louisiana contribute significantly to nonattainment or interfere with maintenance at downwind monitors in another state.

LDEQ's Step 1 was to identify downwind monitors projected to be in nonattainment and/or have maintenance issues in future year 2023 (fy 2023). At this step, LDEQ relied on the EPA's interstate transport modeling results that are included as an attachment to the March 2018 memorandum. The EPA March 2018 modeling results provided: (1) Projected average DV and maximum DV for 2023 for the ozone monitors (or “receptors”) in the 48 contiguous states and (2) the expected contribution of state emissions to the projected ozone concentrations at each ozone monitor.

LDEQ used a contribution threshold of 1 ppb in LDEQ's Step 2 to identify projected nonattainment and/or maintenance receptors in other states that might be impacted by emissions from Louisiana and tagged them for further review. To support a 1 ppb contribution threshold, LDEQ's submission stated that a 1 percent threshold is inappropriate because that value is not detectable by a monitor and the value of 1 percent of the 2015 ozone NAAQS would be truncated to zero if calculated in accordance with the method for determining DVs for the ozone NAAQS. LDEQ also stated that the more stringent threshold of 1 percent of the NAAQS (0.7 ppb) is an order of magnitude smaller than the biases and errors typically documented for regional photochemical modeling.

Based on LDEQ's approach of evaluating linkages at the 1 ppb threshold, five Texas receptors were identified by Louisiana for analysis. The Texas receptors and corresponding receptor data presented in Louisiana's SIP are summarized further in this notice in Table LA-1.

The March 2018 memorandum identified monitors in Allegan, Michigan and Milwaukee and Sheboygan, Wisconsin as potential nonattainment and maintenance-only receptors linked to emissions from Louisiana based on 1 percent of the NAAQS threshold. However, Louisiana did not include the Allegan, Michigan and Milwaukee and Sheboygan, Wisconsin receptors in the State's analysis because the March 2018 memorandum shows that Louisiana's projected modeled contribution values to each receptor is less than 1 ppb.

The Louisiana SIP submittal did not provide a specific citation to the Simon et al., 2012 reference to support this assertion. However, we believe the reference is associated with the following article: Simon, H., Baker, K.R., Phillips, S., 2012. “Compilation and interpretation of photochemical model performance statistics published between 2006 and 2012”. Atmospheric Environment 61, 124-139.

The five potential nonattainment and maintenance receptor monitors identified by LDEQ are from the Dallas-Fort Worth and Houston-Galveston-Brazoria, TX nonattainment areas for the 2015 ozone NAAQS. The Louisiana SIP submittal appears to have inadvertently omitted Harris County, TX Monitor ID No. 482011034 for analysis. EPA's March 2018 memorandum identified this monitor as a maintenance receptor with a contribution of 3.38 ppb from Louisiana emissions.

Table LA-1—Projected Nonattainment and Maintenance Receptors Identified by Louisiana Based on the EPA's March 2018 Memorandum

Receptor

(site ID, county, state)

2023

Average DV

(ppb)

2023

Maximum DV

(ppb)

Louisiana

Contribution

(ppb)

480391004, Brazoria, TX

74.0

74.9

3.80

482011039, Harris, TX

71.8

73.5

4.72

484392003, Tarrant, TX

72.5

74.8

1.71

481210034, Denton, TX

69.7

72.0

1.92

482010024, Harris, TX

70.4

72.8

4.72

For

LDEQ's Step 3, Louisiana

stated that an air emission contribution from the State should only be considered significant if there is a persistent and consistent pattern of contribution on several days with elevated ozone. In trying to determine whether there is a persistent and consistent pattern of contribution, LDEQ analyzed seasonal weather patterns, surface wind directions, and periodic back trajectories. LDEQ used the National Oceanic and Atmospheric Administration (NOAA) Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT)

model to perform 99 back trajectories for exceedances from the receptor monitors identified in Table LA-1 for 2016, 2017, and 2018. Based on an analysis of the HYSPLIT results, LDEQ stated that approximately 28% of the trajectories travel in or through Louisiana, and only 8% of those back trajectories originate in the State. The SIP submission also stated that a comparison of the EPA's modeled contribution between Texas and Louisiana monitors indicates that a far greater proportion of the total ozone detected in Louisiana originates in Texas rather than vice versa. Therefore, Louisiana concluded that the impact from the State's air emissions was insignificant to the overall attainment at the receptor monitors identified in Table LA-1 and does not significantly contribute to nonattainment or interfere with maintenance of the 2015 ozone NAAQS in other states.

Information added from the EPA's March 2018 memorandum.

Id.

See

FN 34.

B. EPA Evaluation of the LDEQ SIP Submission

The EPA is proposing to find that LDEQ's November 13, 2019, SIP submission does not meet the State's obligations with respect to prohibiting emissions that contribute significantly to nonattainment or interfere with maintenance of the 2015 NAAQS in any other state based on the EPA's evaluation of the SIP submission using the 4-Step interstate transport framework, and the EPA is therefore proposing to disapprove Louisiana's SIP submission.

1. Evaluation of Information Provided by LDEQ Regarding Steps 1 and 2

At Step 1 of the 4-Step interstate transport framework, LDEQ relied on EPA modeling released in the March 2018 memorandum to identify nonattainment and maintenance receptors in 2023. At Step 2 of the 4-Step interstate transport framework, LDEQ relied on the EPA modeling released in the March 2018 memorandum to identify upwind state linkages to nonattainment and maintenance receptors in 2023. LDEQ additionally utilized a 1 ppb threshold at Step 2 to identify whether the state was “linked” to a projected downwind nonattainment or maintenance receptor. As discussed in the EPA's August 2018 memorandum, with appropriate additional analysis it may be reasonable for states to use a 1 ppb contribution threshold, as an alternative to a 1 percent threshold, at Step 2 of the 4-Step interstate transport framework, for the purposes of identifying linkages to downwind receptors. In any case, the State is projected to contribute greater than both the 1 percent and the alternative 1 ppb thresholds to receptors in Texas, regardless of whether we look at LDEQ's analysis (which relied on the EPA's older modeling) or updated modeling the EPA has performed in advance of this proposal. As seen in the tables LA-1 and LA-2, Louisiana contributes nearly five times the 1 ppb threshold to nonattainment or maintenance receptors in Texas. Therefore, while the EPA does not, in this action, approve of the State's application of the 1 ppb threshold, because the State has linkages greater than 1 ppb to projected downwind nonattainment or maintenance receptors, the State's use of this alternative threshold at Step 2 of the 4-Step interstate framework would not alter our review and proposed disapproval of this SIP submittal.

The 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.

(The memorandum also indicated that any higher alternative threshold, such as 2 ppb, would likely not be appropriate.) However, the 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 interstate transport SIP submittals for the 2015 ozone NAAQS, the 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.

See

August 2018 memorandum, at page 4.

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 ozone NAAQS.

“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 comments on this proposed approval and has not taken final action with respect to this proposal.

Furthermore, the 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 ozone NAAQS raises substantial policy consistency and practical implementation concerns.

We note that Congress has placed on the 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.

Further, it is not clear that national ozone transport policy is best served by allowing for less stringent thresholds at Step 2. The 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, the EPA notes that while this may be true in some sense, that is not 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 seven percent of total upwind state contribution was lost according to the modeling underlying the August 2018 memorandum;

in the EPA's updated modeling, the amount lost is five 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 NAAQS threshold.

See

August 2018 memorandum, at page 4.

Accord

76 FR 48237-38.

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, the EPA's experience since the issuance of that memorandum has revealed substantial programmatic and policy difficulties in attempting to implement this approach. Nonetheless, the EPA is not at this time rescinding the August 2018 memorandum. The basis for a proposed disapproval of LDEQ's SIP submission with respect to the Step 2 analysis we believe is warranted under the terms of the August 2018 memorandum. The EPA invites comment on this broader discussion of issues associated with alternative thresholds at Step 2. Depending on public comments received and further evaluation of this issue, the EPA may determine to rescind the 2018 memorandum in the future.

2. Results of the EPA's Step 1 and Step 2 Modeling and Findings for Louisiana

As described in Section I of this action, the EPA performed air quality modeling using the 2016v2 emissions platform to project DVs and contributions for 2023.

This data was examined to determine if Louisiana contributes at or above the threshold of 1 percent of the 2015 ozone NAAQS (0.70 ppb) to any downwind nonattainment or maintenance receptor. As shown in Table LA-2, the data

indicate that in 2023, emissions from Louisiana contributed greater than 1 percent of the standards to nonattainment or maintenance-only receptors in Texas.

Therefore, based on the EPA's evaluation of the information submitted by LDEQ, and based on the EPA's most recent modeling results for 2023, the EPA proposes to find that Louisiana is linked at Steps 1 and 2 and has an obligation to assess potential emissions reductions from sources or other emissions activity at Step 3 of the 4-Step framework.

DVs and contributions at individual monitoring sites nationwide are provided in the file: “2016v2_DVs_state_contributions.xlsx”, which is included in Docket ID No. EPA-HQ-OAR-2021-0663.

These 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 of this action. That modeling showed that Louisiana 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 DVs And Contributions Revised CSAPR Update.xlsx” in Docket No. EPA-HQ-OAR-2021-0663.

Table LA-2—Projected Nonattainment and Maintenance Receptors With Louisiana Linkages Based on EPA 2016v2 Modeling

Receptor

(site ID, county, state)

Nonattainment/

maintenance

2023

Average DV

(ppb)

2023

Maximum DV

(ppb)

Louisiana

Contribution

(ppb)

482010024, Harris, TX

Nonattainment

75.2

76.8

4.31

482010055, Harris, TX

Nonattainment

71.0

72.0

5.39

480391004, Brazoria, TX

Maintenance

70.1

72.3

7.03

481210034, Denton, TX

Maintenance

70.4

72.2

3.22

482011034, Harris, TX

Maintenance

70.3

71.6

4.93

482011035, Harris, TX

Maintenance

68.0

71.6

4.77

3. Evaluation of Information Provided by LDEQ 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 contribute significantly 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. The EPA has consistently applied this approach (

i.e.,

See EME Homer City,

572 U.S. 489, 519 (2014). While the EPA has not directed states that they must conduct a Step 3 analysis in precisely the manner the 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 an analysis similar to the EPA's (or an alternative approach to defining “significance” that comports with CAA requirements) to determine whether, and to what degree, emissions from a state should be “prohibited” to eliminate emissions that will “contribute significantly to nonattainment, or interfere with maintenance of” the NAAQS in any other state. LDEQ did not conduct such an analysis in their SIP submission. Instead LDEQ interpreted the Act's requirements as only requiring an analysis of emission reductions where there was a “consistent and persistent” pattern of contribution and conducted an air-quality-only analysis in order to refute such a pattern. We propose to find that LDEQ was required to analyze emissions from the sources and other emissions activity from within Louisiana to determine whether its contributions were significant, and we propose to disapprove its submission because LDEQ did not do so.

As noted, LDEQ stated in its SIP submission that emissions from Louisiana should not be considered to contribute significantly to nonattainment or interfere with maintenance of the NAAQS in other states because there is not a “persistent and consistent” pattern of contribution from the State. The SIP submission does not explain what LDEQ considers to be a persistent and consistent pattern of contribution, even after the LDEQ received a comment during its state comment period that requested that the LDEQ define “persistent and consistent” in terms of impacts on downwind states. The LDEQ responded, “Louisiana has defined the pattern and has provided back trajectories on those monitored exceedances for the 2016-2018 ozone seasons, which will show that the definition is applicable to the conclusion.”

We do not agree that this suffices as an explanation as to why LDEQ does not need to further analyze its potential emission reductions under Step 3 before determining it has no statutory obligation under the interstate transport provision. In the case of Louisiana, modeling in the March 2018 memorandum and the EPA's more recent 2016v2 modeling both project that receptors in the Houston-Galveston-Brazoria (HGB) and Dallas-Fort Worth (DFW) ozone nonattainment areas in Texas will have difficulty attaining or maintaining the 2015 ozone NAAQS, and Louisiana's contribution to these areas exceed both a 1 percent or a 1 ppb threshold. While linkages to specific receptors may change with updated modeling, both modeling analyses consistently show emissions from Louisiana impact both downwind nonattainment receptors and downwind maintenance receptors in Texas.

See

LDEQ SIP Submission, Appendix A, available in the Regional docket for this action (Docket ID No. EPA-R06-OAR-2021-0801).

The LDEQ SIP submission stated that Louisiana's contribution should be deemed “significant” per CAA section 110(a)(2)(D)(i)(I) only if there is a persistent and consistent pattern of contribution on several days with elevated ozone. LDEQ asserted that its linkages to Texas do not warrant further analysis because, according to LDEQ, emissions from Louisiana do not persistently and consistently contribute on several days of elevated ozone. However, the EPA modeling that LDEQ relied upon to demonstrate linkages in the first instance already establishes that there is a consistent and persistent pattern of contribution from Louisiana to Texas receptors on elevated ozone days. The EPA's methodology for projecting future year ozone concentrations accounts for precisely these concerns—the relative response factor

that is applied to historic monitored data to generate projections is calculated by looking only at days with elevated ozone levels. The EPA notes that monitored attainment with the ozone standard is determined by averaging the fourth high value recorded each year for three years. So, the EPA believes it is important to estimate impacts on the days with highest projected ozone levels. The days chosen to analyze the future impacts are chosen initially by the selecting the 10 highest days in the base period modeling that are projected to be above 65 ppb in the base period. If there are not 10 days above 65 ppb at a potential receptor, the number of days above 65 ppb are used so long as there is at least five days above 65 ppb in the base period. If the air quality modeling shows fewer than five days above 65 ppb in the base period, then the data for impacts at that receptor in 2023 are not calculated. The base and future year modeling for these

5-10 days are then used to project 2023 ozone DVs to determine whether it is projected to be a nonattainment or maintenance receptor in 2023. For these same 5-10 days identified, the future year modeling provides the estimated daily contribution at a potential receptor's future year daily MDA8 and these daily contributions are averaged for the 5-10 days to result in the average contribution from the upwind area.

See

FN 53.

LDEQ's air quality analysis used to dismiss its linkages to Texas receptors as not “significant” consists of an evaluation of seasonal weather patterns, surface wind directions, and periodic back trajectories. The State's weather pattern analysis relied on large-scale weather patterns as they relate to commonly observed wind directions rather than weather patterns and conditions that are specifically conducive to ozone formation or tied to specific days when high ozone was monitored in the downwind areas. General weather pattern discussions that are not associated with specific ozone episodes are not generally informative of interstate transport decisions. It is necessary to investigate specific instances of high ozone, because as discussed previously, violations of the ozone standard can be driven by as few as 4 days per year because the compliance with the standard is evaluated based on the average of the fourth high value measured each of three consecutive years.

LDEQ's wind rose analysis is based on surface sites in the Dallas-Fort Worth areas, Houston-Galveston-Brazoria areas, and other areas in Texas and Louisiana, but the analysis does not address transport winds between Louisiana and the Texas areas with receptors on high ozone days at the identified receptors. There are several limitations associated with LDEQ's wind rose analysis: (1) Wind directions measured at the surface are not necessarily good indicators of the wind direction occurring at higher elevations, which tend to have a stronger influence on interstate ozone transport; (2) wind directions change spatially over the range of distance involved in transport from Louisiana to Texas; (3) wind directions change temporally over the range of time involved in ozone transport from Louisiana to Texas; and (4) the wind roses are based on wind data measured throughout the year, not just during either ozone season or monitored ozone episode days. In addition, as discussed previously, LDEQ's wind rose analysis is not limited to the wind conditions that are conducive to high ozone, so it does not provide information directly pertinent to when ozone is high at areas in Texas and whether Louisiana is a contributing area during those specific times.

LDEQ also included 99 back trajectory analyses during the 2016, 2017, and 2018 years for the dates of ozone exceedances at the monitors referenced in Table LA-1 of this action. 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 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 concentrations at the end point. The horizontal and vertical areas that potentially contribute to concentrations at the endpoint grow wider from the centerline 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 for those areas to contribute to concentrations at the trajectory endpoint. The EPA relies on back trajectory analysis as a corollary analysis along with observation-based meteorological wind fields at multiple heights to examine the general plausibility of the photochemical model “linkages.” Since the back trajectory calculations do not account for any air pollution formation, dispersion, transformation, or removal processes as influenced by emissions, chemistry, deposition, etc., the trajectories cannot be used to develop quantitative contributions. Therefore, back trajectories cannot be used to quantitatively evaluate the magnitude of the existing photochemical contributions from upwind states to downwind receptors. LDEQ's HYSPLIT back trajectory analysis for 2016, 2017, and 2018 showed that on high ozone days in Texas at the receptors identified by the EPA in the 2018 memorandum that 28% of the trajectories passed through Louisiana. LDEQ proffered that some of these back trajectories did not pass directly over areas with emissions but did not consider that the back trajectories only represent a centerline and there are areas on either side of the centerline that would be contributing areas. LDEQ's trajectory analysis confirmed that Louisiana is an upwind area for the receptors in Texas often enough to potentially contribute to nonattainment or interfere with maintenance. The analysis did not provide evidence that was contrary to the conclusions of the EPA's photochemical modeling analyses (

i.e.,

the EPA's modeling results in the March 2018 memorandum and EPA 2016v2 model).

Photochemical modeling simulations for ozone interstate transport assessment is relied upon by the EPA to simulate the formation and fate of oxidant precursors, primary and secondary particulate matter concentrations, and deposition over regional and urban spatial scales. Photochemical modeling is the most sophisticated tool available to estimate future ozone levels and contributions to those modeled future ozone levels. Consideration of the different processes that affect primary and secondary pollutants at the regional scale in different locations is fundamental to understanding and assessing the effects of emissions on air quality concentrations. For the 2015 ozone NAAQS interstate transport analysis, the EPA performed nationwide, state-level ozone source apportionment modeling using CAMx to quantify the contribution of NO

and VOC emissions from all sources in each state to project 2023 ozone concentrations at ozone monitoring sites. Detailed information for the EPA's modeling may be found in the Air Quality Modeling TSD in Docket No. EPA-HQ-OAR-2021-0663.

LDEQ concluded in the SIP submittal, citing an article

published in 2012, that the use of 1 percent of the standard for modeled contribution as the sole definition of significant contribution is inappropriate for the 2015 ozone NAAQS. LDEQ's reasoning for this conclusion is that the more stringent 0.7 ppb threshold “is an order of magnitude smaller than the biases and errors typically documented for regional photochemical modeling.” First, the EPA does not use the 1 percent threshold as the sole definition of significant contribution; at Step 2 of the analysis, the 1 percent threshold is used to identify contributions between states and downwind problem areas for further analysis at Step 3. Second, photochemical transport models such as CAMx have been extensively peer reviewed and used to support SIPs and explore relationships between inputs and air quality impacts in the U.S. and beyond. The EPA works to continually develop and update both the guidelines

on using modeling results and the latest versions of photochemical model platforms to support scientific assessments and regulatory determinations. Prior to using photochemical modeling to support a regulatory assessment, a model performance evaluation is completed to establish a benchmark to assess how accurately the model predicts observed concentrations and to identify model limitations. The model performance evaluation provides a better understanding of the model's limitations and biases and serves as a diagnostic evaluation for further model development and improvement. As discussed in Section I of this document and the Air Quality Modeling TSD in Docket No. EPA-HQ-OAR-2021-0663, the EPA follows the most recent established modeling guidance and provides with this action the updated modeling analysis based on the recent CAMx model update. By using the most recent 2016v2 photochemical modeling enhancements (EPA 2016v2 modeling) results are more representative of the projected local and regional air quality as it is based on more recent emission estimates with fewer years between the base case year (2016) and the future year (2023). In addition, to reduce the impact of any potential biases or errors, the EPA uses the modeling results in a relative sense rather than rely on absolute model predictions.

Simon et al.,

supra

FN 58.

See

“Modeling Guidance for Demonstrating Air Quality Goals for Ozone, PM

2.5

and Regional Haze”, Nov. 29, 2018, at 101, available at

https://www.epa.gov/sites/default/files/2020-10/documents/o3-pm-rh-modeling_guidance-2018.pdf

(“2018 Air Quality Modeling Guidance”).

See also

“Draft Modeling Guidance for Demonstrating Attainment of Air Quality Goals for Ozone, PM

2.5,

and Regional Haze”, Dec. 3, 2014, at 97-98, available at

https://www.epa.gov/sites/default/files/2020-10/documents/draft-o3-pm-rh-modeling_guidance-2014.pdf

(“2014 Draft Air Quality Modeling Guidance”).

Furthermore, it is not appropriate to compare the bias/error involved in the estimation of total ozone to the potential error in the estimation of the subset of ozone that is contributed by a single state. For example, on a specific day the modeled vs. monitored ozone value may differ by 2 ppb but that is relatively small percentage of the total modeled ozone, which for a receptor of interest would be on the order of 70 ppb. It would be unrealistic to assign all the 2 ppb, in the above example, to the estimated impact from a single state as the 2 ppb error would be the combination of the error from all sources of ozone that contribute to the total, including estimated impacts from other states, the home state of the receptor and natural background emissions.

In sum, the EPA disagrees that the estimates of potential error in the models estimates of total ozone, call into question the use of 1 percent as a threshold for linkage. As noted earlier, in the case of Louisiana, the difference between a 1 percent threshold and a 1 ppb threshold is irrelevant to the decision here because linkages are present at both threshold levels. As to Louisiana's conclusion that the impacts from Louisiana's emissions are not persistent, the contribution analysis is the average impact for at least 5 days and up to 10 days for the 2016 base period which is sufficiently persistent considering the first through fourth high monitored values set the monitored DV.

We recognize that the results of the EPA (2011 and 2016 base year) modeling indicated different receptors and linkages at Steps 1 and 2 of the 4-Step interstate transport framework. These differing results regarding receptors and linkages can be affected by the varying meteorology from year to year, but we do not think the differing results means that the modeling or the EPA or the state's methodology for identifying receptors or linkages is inherently unreliable. Rather, these separate modeling runs all indicated: (1) That there are receptors that would struggle with nonattainment or maintenance in the future; and (2) that Louisiana is linked to some set of these receptors, even if the receptors and linkages differed from one another in their specifics (

e.g.,

Louisiana was linked to a different set of receptors in one modeling run versus another). These results indicates that Louisiana's emissions were substantial enough to generate linkages at Steps 1 and 2 to at least some set of downwind receptors, under varying assumptions and meteorological conditions, even if the precise set of linkages changed between modeling runs.

4. Evaluation of Information Provided by LDEQ 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. As mentioned previously, LDEQ's SIP submission did not contain an evaluation of additional emission control opportunities (or establish that no additional controls are required), thus, no information was provided at Step 4. To the extent that LDEQ discussed emissions reductions, the State only provided a summary of existing already implemented enforceable control regulations. The EPA's 2016v2 modeling analyses have already accounted for the implementation of the regulations cited by LDEQ's submission—including the CSAPR rulemakings and prior regional rulemakings—and even with those reductions in place, the modeling results consistently show receptors that are projected to be in nonattainment or to struggle with maintenance, and Louisiana contributing to those receptors. Relying only on the existing enforceable control regulations is insufficient to address the Louisiana air emission contributions to linked downwind air quality problems. As a result, the EPA proposes to disapprove LDEQ's submittal on the separate, additional basis that the State has not developed permanent and enforceable emissions reductions necessary to meet the obligations of CAA section 110(a)(2)(D)(i)(I).

5. Conclusion

Based on the EPA's evaluation of LDEQ's SIP submission, the EPA is proposing to find that LDEQ's November 13, 2019, SIP submission pertaining to interstate transport of air pollution does not meet the State'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 ozone NAAQS in any other state.

IV. Oklahoma SIP Submission Addressing Interstate Transport of Air Pollution for the 2015 Ozone NAAQS and the EPA Evaluation of the SIP Submission

A. Summary of ODEQ SIP Submission Addressing Interstate Transport of Air Pollution for the 2015 Ozone NAAQS

On October 25, 2018, the Oklahoma Department of Environmental Quality (ODEQ) made a SIP submission addressing interstate transport of air pollution for the 2015 ozone NAAQS. The SIP submission provided ODEQ's analysis of their impact to downwind states using the EPA's 4-Step framework and an analytic year of 2023 and concluded that emissions from Oklahoma will not contribute significantly to nonattainment or interfere with maintenance of the 2015 ozone NAAQS in other states.

To identify downwind air quality problems that are linked to emissions

from Oklahoma and therefore warrant further review and analysis (Steps 1 and 2), ODEQ used EPA interstate transport modeling results found in the March 2018 memorandum. The EPA modeling results projected: (1) An average DV and a maximum DV for the year 2023 for ozone monitors in the 48 contiguous States and (2) the expected contribution from emissions in each state to the ozone concentrations at each ozone monitor.

ODEQ used the information from the March 2018 EPA memorandum to identify six downwind nonattainment and maintenance receptors

with a contribution from Oklahoma of 1 percent of the 2015 ozone NAAQS (0.70 parts ppb) or greater. ODEQ then applied a 1 ppb threshold to remove from further analysis three receptors with a contribution from Oklahoma of less than 1 ppb. ODEQ noted that the possibility of using an alternative contribution threshold was one of the areas of flexibility identified in the March 2018 EPA memorandum and discussed further in the August 2018 EPA memorandum. To support its alternative contribution threshold, ODEQ referenced an EPA memorandum from April 17, 2018, which recommended a Significant Impact Level (SIL) for ozone of 1.0 ppb for proposed sources subject to the Prevention of Significant Deterioration (PSD) permitting program.

Table OK-1 provides information on the six nonattainment and maintenance receptors identified by ODEQ, including the three receptors ODEQ identified for further analysis.

Nonattainment receptors are monitoring sites that are anticipated to have problems attaining and maintaining the 2015 ozone NAAQS (

i.e.,

average projected 2023 DV greater than 70.9 ppb). Maintenance receptors are monitoring sites that are anticipated to have problems maintaining the 2015 ozone NAAQS (

i.e.,

maximum projected 2023 DV greater than 70.9 ppb).

See

FN 32.

Table OK-1—Nonattainment and Maintenance Receptors Identified by ODEQ Based on the EPA's March 2018 Memorandum

Receptor

(site ID, county, state)

2023

average DV

(ppb)

2023

maximum DV

(ppb)

Oklahoma contribution

(ppb)

ODEQ's step 1 and 2 determination

260050003, Allegan, MI

69.0

71.7

1.31

Maintenance receptor identified for further analysis.

481210034, Denton, TX

69.7

72.0

1.23

Maintenance receptor identified for further analysis.

484392003, Tarrant, TX

72.5

74.8

1.71

Nonattainment receptor identified for further analysis.

480391004, Brazoria, TX

74.0

74.9

0.90

Nonattainment receptor with contribution less than 1 ppb; no further analysis.

550790085, Milwaukee, WI

71.2

73.0

0.76

Nonattainment receptor with contribution less than 1 ppb; no further analysis.

551170006, Sheboygan, WI

72.8

75.1

0.95

Nonattainment receptor with contribution less than 1 ppb; no further analysis.

ODEQ further evaluated the two Texas receptors (Tarrant County and Denton County) and the receptor in Allegan County, MI. ODEQ did not further evaluate the contribution from Oklahoma to the receptors in Brazoria County, TX, Milwaukee County, WI, and Sheboygan County, WI because the contributions from Oklahoma to these receptors were less than 1 ppb.

For the two remaining Texas receptors, ODEQ returned to Steps 1 and 2 of the 4-Step interstate transport framework using modeling performed by the Texas Commission on Environmental Quality (TCEQ). The TCEQ modeling results are included in the Regional docket for this action (Docket ID No. EPA-R06-OAR-2021-0801). ODEQ stated that the primary difference between the EPA modeling and the TCEQ modeling is that the TCEQ modeling used 2012 as the “base year” for assessing interstate transport of ozone pollution in 2023 whereas the EPA modeling used 2011 as the base year for that assessment. In addition, the ODEQ stated that TCEQ used a method different from the EPA's method to identify whether a monitor would have trouble maintaining the 2015 ozone NAAQS (

i.e.,

a maintenance receptor). To identify maintenance receptors, TCEQ calculated a “maintenance future year (fy) DV” by projecting to 2023 the most recent regulatory DV that contains the base year (

i.e.,

the 2012-2014 DV for a base year of 2012), whereas the EPA's methodology for identifying maintenance receptors uses the maximum DV, which is the highest monitored DV from among the three DVs that contain the base year (

i.e.,

the 2009-2011, 2010-2012 and 2011-2013 DVs for a base year of 2011).

To assess whether Oklahoma is linked to nonattainment of the 2015 ozone standard at the Denton and Tarrant County sites, ODEQ switched to using the 2023 average DV projected by TCEQ rather than the EPA's projected average DVs. The ODEQ noted that the projected 2023 average DV was 68 ppb for the Denton County site and 66 ppb for the Tarrant County site based on the TCEQ modeling. ODEQ then claimed that these results demonstrate that both of these sites are in attainment in 2023.

To assess whether Oklahoma interferes with maintenance of the 2015 ozone standard at these two sites, ODEQ used (1) the Texas method to calculate a “maintenance future year DV” for 2023 and (2) a maximum DV calculated using the highest of the three base year DVs multiplied by a relative response factor derived from TCEQ's modeling (

i.e.,

EPA's method for identifying maintenance receptors but using TCEQ's modeling rather than EPA's modeling). This assessment is summarized in Table OK-2.

Table OK-2—Summary of TCEQ Modeling (2012 Base Period) Used by ODEQ To Assess Maintenance Receptors

Receptor

(site ID, county, state)

2023

average DV

(ppb)

2023

maximum DV

(ppb) (EPA method)*

Maintenance DV

(ppb)(TCEQ method)

ODEQ's step 1 and step 2 determination

481210034 Denton, TX

70.7

65.9

Future DVs project no attainment or maintenance problems.

484392003 Tarrant, TX

69.9

62.4

Future DVs project no attainment or maintenance problems.

* These values are not based on calculations made by the EPA. ODEQ calculated these values by using the maximum DV for the 2010-2014 5-year period (

i.e.,

the highest of the DVs in 2012, 2013, and 2014) multiplied by relative response factor for the receptor obtained from TCEQ's modeling.

ODEQ noted in their assessment that based on the TCEQ modeling and TCEQ definition of maintenance receptor, it is expected that the Denton and Tarrant sites will not experience nonattainment or maintenance problems in 2023. Because ODEQ claimed that the Denton and Tarrant County sites will not be nonattainment or maintenance receptors in 2023, ODEQ did not analyze potential emissions reductions at Step 3 to address its contribution to these two sites.

With respect to the remaining receptor at Allegan County, MI, ODEQ provided an analysis of projected 2023 DVs for this site and information on emissions trends in Oklahoma to assert that emissions from Oklahoma do not significantly contribute to nonattainment or interfere with maintenance of the 2015 ozone NAAQS at the Allegan County, MI site.

ODEQ noted that (1) the DV for the Allegan County, MI site has had a substantial reduction in the last 6 years from 84 ppb in 2012 to 73 ppb in 2017, a 1.8 ppb per year decrease, on average and (2) the Allegan County, MI site is substantially influenced by mobile sources from the Chicago area and these emissions are expected to be greatly reduced in the near future, by roughly a 1 ppb per year decrease, leading to attainment of the 2015 ozone standard. The ODEQ then calculated a projected 2023 maintenance DV for the Allegan County, MI site using the EPA's method, but assuming that the base year was 2016 rather than 2011, as in the EPA's modeling or 2012 as in the TCEQ modeling. The ODEQ noted that the maximum DV in the 2016-centered base period (

i.e.,

2014-2016, 2015-2017, and 2016-2018) was 75 ppb at the Allegan County, Michigan site. The ODEQ then calculated the difference between the 2011-centered base period maximum DV of 86 ppb and the 2023 projected maximum DV of 71.7 ppb, using data from the EPA's modeling. The ODEQ calculated a “ppb per year” reduction of 1.1917 ppb per year, based on the 14.3 ppb difference between the 2011-centered and 2023 maximum DVs over the 12 years from 2011 to 2023. Finally, ODEQ applied the 1.1917 ppb per year value to the 2016-centered maximum DV of 75 ppb to estimate a 2023 maximum DV of 66.66 ppb.

ODEQ also asserted that the relatively small contribution from Oklahoma (3% of total upwind state contributions) combined with the distance between Oklahoma sources and the Allegan County, Michigan site, warrants a focus on nearby states with greater proportional contributions as the most prudent approach to addressing interstate transport of ozone precursors for this receptor.

The ODEQ also provided the anthropogenic NO

and VOC data of Oklahoma's emissions from EPA's emission trends and modeling to demonstrate an anticipated substantial reduction of NO

and VOC from 2011 to 2023: (1) Reductions of NO

from 405,000 to 235,000 tons per year and (2) reductions of VOC from 414,000 to 295,000 tons per year.

ODEQ noted these reductions should result in considerable reductions in ozone concentrations. The ODEQ stated that due to the emissions reductions required by rules like CSAPR, the 2016 CSAPR Update, and the regional haze requirements, the NO

emissions from electric generation in Oklahoma have dropped significantly during the ozone season from 38,285 tons per year in 2011 to 10,435 tons per year in 2017. ODEQ also stated that changes in the Southwest Power Pool

, building of additional windfarms, and electric utilities installing solar generation facilities have led to Oklahoma NO

emissions reductions; and that any additional NO

reductions from the electric generation section would require more costly emissions controls. ODEQ concluded that the existing controls in Oklahoma have resulted in significant decreases in ozone DVs in Oklahoma and that additional controls would not be cost-effective. Given their conclusions, ODEQ did not adopt additional controls to reduce ozone precursor emissions (Step 4).

ODEQ used the EPA's emissions data shared alongside the October 2018 memorandum, “state-sector_annual_emissions_data_1.xlsx” available at

https://www.epa.gov/airmarkets/memo-and-supplemental-information-regarding-interstate-transport-sips-2015-ozone-naaqs.

The Southwest Power Pool is a regional electric transmission organization regulated by the Federal Energy Regulatory Commission whose purpose is promoting efficiency and reliability in the operation and planning of the electric transmission grid and ensuring non-discrimination in the provision of electric transmission services. It manages electric transmission in portions of fourteen states: Arkansas, Iowa, Kansas, Louisiana, Minnesota, Missouri, Montana, Nebraska, New Mexico, North Dakota, Oklahoma, South Dakota, Texas and Wyoming.

See

18 CFR 35.34 and

https://www.ferc.gov/electric-power-markets.

B. EPA Evaluation of the ODEQ SIP Submission

The EPA is proposing to find that ODEQ's October 25, 2018, SIP submission does not demonstrate that the State's obligations with respect to prohibiting emissions that contribute significantly to nonattainment or interfere with maintenance of the 2015 ozone NAAQS in any other state based on the EPA's evaluation of the SIP submission using the 4-Step interstate transport framework have been met. The EPA is therefore proposing to disapprove ODEQ's submission.

1. Evaluation of Information Provided by ODEQ Regarding Steps 1 and 2

As noted earlier, ODEQ first used the information from the EPA's March 2018 memorandum to identify nonattainment and maintenance receptors with a contribution from Oklahoma of 0.70 ppb or greater (

i.e.,

ODEQ identified receptors that would be deemed nonattainment and maintenance receptors under the EPA's methodology for Steps 1 and 2). ODEQ then utilized a 1 ppb threshold and elected not to further analyze any receptors to which it did not contribute greater than 1 ppb.

ODEQ provided further evaluation of the State's emissions to those receptors to which Oklahoma contributes greater than 1 ppb (

i.e.,

Allegan County, MI, Denton County, TX and Tarrant County, TX).

As discussed in the EPA's August 2018 memorandum, with appropriate additional analysis it may be reasonable for states to use a 1 ppb contribution threshold, as an alternative to a 1 percent threshold, at Step 2 of the 4-Step interstate transport framework, for the purposes of identifying linkages to downwind receptors. However, the EPA's August 2018 memorandum provided that whether or not a 1 ppb threshold is appropriate must be based on an evaluation of state-specific circumstances, and no such evaluation was included in the ODEQ's submittal. Instead, ODEQ's SIP submission justified the State's use of a 1 ppb threshold based on the threshold's use in the SILs Guidance.

ODEQ did not explain the relevance of the SILs Guidance to Oklahoma's statutory obligation under the interstate transport provision. The SILs Guidance relates to a different provision of the CAA regarding implementation of the prevention of significant deterioration (PSD) permitting program,

i.e.,

a program that applies in areas that have been designated attainment of the NAAQS, and it is not applicable to the interstate transport provision, which requires states to eliminate emissions that contribute significantly or interfere with maintenance of the NAAQS at known, ongoing, or projected air quality problem areas in other states. The EPA does not, in this action, agree that the State has justified its application of the 1 ppb threshold.

See

FN 32.

We note that Congress has placed on the 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.

e.g.,

roughly seven percent of total upwind state contribution was lost according to the modeling underlying the August 2018 memorandum;

See

August 2018 memorandum, at page 4.

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