SUPPLEMENTARY INFORMATION:

Throughout this document wherever “we,” “us,” or “our” is used, we mean the EPA.

I. Background

On October 26, 2015, the EPA revised the national standards for ground-level ozone, promulgating identical primary and secondary ozone standards that specified an 8-hour ozone level of 0.070 parts per million (ppm).^[1] In a separate action, the EPA assigned classification thresholds and attainment dates based on each NAA's monitored ozone levels.^[2] Consistent with CAA section 181(a), the EPA established attainment dates based on nonattainment classification; with the attainment date for Marginal areas as August 3, 2021 and Moderate areas as August 3, 2024.

Upon promulgation of the revised 2015 ozone NAAQS, the State of Utah submitted initial designations to the EPA based on monitored air quality data from 2013-2015 and recommended that Salt Lake and Davis Counties, and portions of Weber and Tooele Counties be designated as nonattainment. The EPA did not modify the State's initial designation and, effective August 3, 2018, the EPA designated the NWF as a Marginal NAA.^[3]

On October 7, 2022, the EPA determined that the NWF did not attain the NAAQS by the Marginal attainment date, and the area was subsequently reclassified by operation of law to a Moderate NAA.^[4] A State Implementation Plan (SIP) outlines how states will implement controls to satisfy statutory and regulatory requirements under the 2015 ozone NAAQS and demonstrate how the area will attain the ozone standard by the attainment date. The submission deadline for a majority of the required ozone SIP elements was established as January 1, 2023 for Moderate ozone NAA's. The EPA's implementing regulations at 40 Code of Federal Regulations (CFR) 51.1308-51.1315 address ozone SIP requirements including attainment demonstrations, Reasonable Further Progress (RFP) and associated milestone demonstrations, reasonably available control technology (RACT), reasonably available control measures (RACM), major nonattainment new source review, emission inventories, the timing of required SIP submissions, and compliance with emission control measures in the SIP.

In 2020 and 2021, the State of Utah submitted Marginal SIP elements to the EPA, which were approved in 2021 and 2022 respectively.^[5] On December 12, 2024, Utah submitted a Moderate ozone SIP to meet CAA section 182(b) and which was deemed complete by operation of law on June 12, 2025.^[6] The EPA is currently reviewing the submitted Moderate SIP elements and will be acting on them in future actions.

In December 2024, the NWF NAA was reclassified to Serious by operation of law due to an EPA finding of failure to attain by the Moderate attainment date. That action reclassified the area to Serious by operation of law with an effective date of January 8, 2025.^[7] However, the Final Rule was stayed by the 10th Circuit Court of Appeals in April 2025 due to petitions for review that were filed by the State of Utah and the Utah Petroleum Association (UPA) and the EPA is currently in the process of reconsidering the final action.^[8] The practical implication of this judicial stay is that the NWF NAA is currently classified as Moderate as of the date of this proposal. The stay will be lifted pending EPA concluding its reconsideration. In the event the classification of Serious is retained, the NWF would again be subject to Serious Area planning requirements consistent with CAA section 182(c). The classification and applicable requirements for the current NAA will also apply to the newly redesignated area, if this proposal is finalized.

II. Utah's Submittal

The State's modeling efforts associated with the Moderate SIP development for the 2015 ozone NAAQS showed that large amounts of nitrogen oxides (NO_X) and volatile organic compound (VOC) emissions from a source located upwind of the NAA, namely US Magnesium LLC (US Magnesium), was directly impacting high ozone levels within the NWF NAA. Located in Tooele County on the southwestern edge of the Great Salt Lake, US Magnesium has significant amounts of precursor emissions that contribute to both ozone and fine ( printed page 46130) particulate matter (PM_2.5 ) formation along the Wasatch Front in addition to also producing halogen emissions which further increase ozone formation.^[9]

On February 27, 2023, the State of Utah submitted a request to the EPA to expand the NAA boundary of the NWF to include the US Magnesium facility.^[10] US Magnesium was initially omitted from the NWF NAA based on the State's recommendation that the ozone nonattainment boundary be identical to the 2006 24-hour PM_2.5 nonattainment boundary for Davis, Salt Lake, Tooele, and Weber Counties.^[11] This recommendation was based on assessing the impact of emissions during the winter months since that is when the Salt Lake City region tends to experience PM_2.5 exceedances. As detailed in the State's 2023 boundary expansion request and associated analysis, this point source has likely been contributing to elevated ozone levels in the NWF.^[12] The State determined that tighter emission controls on its highest emitting units will benefit the NWF and therefore submitted to the EPA the NAA boundary expansion request.^[13]

III. EPA Evaluation

When the Governor of any State, on the Governor's own motion, submits a revised designation of areas in the state designated as nonattainment, attainment, or unclassifiable, the Administrator shall act on such designations in accordance with the procedures under section 107(d)(3)(D). In its request to expand the boundary of the NWF, the State of Utah conducted a five-factor analysis, which evaluated emissions, air quality data, meteorology, jurisdictional boundaries, and geography/topography. This analysis concluded that, “emissions from US Magnesium extend to nearly the entire Wasatch Front with plumes emitted from the plant observed across a wide sector of the populated regions of the valleys, and that secondary chemistry from these plumes result in a 10-20% increase in PM_2.5 in the urban regions of the valleys as well as an increase of up to 10% in ozone formation due to the production of additional oxidants.” ^[14] Additionally, preliminary modeling by the State of Utah found increases in summertime ozone concentrations at a number of monitoring sites in the NAA downwind of US Magnesium due to halogens emissions, which, “clearly show that uncontrolled emissions from within the proposed new boundary are regularly transported to the current NAA, and directly contribute to the area's air quality challenges”.^[15]

The EPA supports the State's conclusion and concurs with the State's request to include additional townships and US Magnesium within the NWF ozone NAA for the 2015 ozone NAAQS. Utah's full technical analysis is provided in Utah's supporting documentation titled, “Request for Adjustment of the Northern Wasatch Front Nonattainment Area Boundary for the 2015 8-hour Ozone National Ambient Air Quality Standard”. The EPA's review supporting our proposed action is discussed in an accompanying Technical Support Document (TSD).^[16] Both documents are available in the docket for this action (see https://www.regulations.gov, Docket ID No. EPA-R08-OAR-2025-0001).

IV. Proposed Action

The EPA is proposing to approve Utah's boundary expansion request for the NWF 2015 8-hour ozone NAAQS NAA under section 107(d)(3)(D) of the CAA. The request was submitted on February 27, 2023. This proposed action will expand the boundary of the existing Moderate NAA and does not create any new NAA's. Upon finalization of this rule, the Moderate area classification and August 3, 2024 attainment date will apply to the entirety of the newly expanded NWF Moderate NAA per 40 CFR 51.1303.

Specifically, the State is requesting to add 12 additional western townships in Tooele County into the ozone NAA.^[17] Upon the effective date of the boundary expansion, source emissions from these new townships within the NAA, including from US Magnesium, will need to be included in a revised 2017 base year emissions inventory. Emission reductions that occurred after the 2017 base year, and that are the result of federally enforceable controls, can be credited in the State's Moderate ozone SIP. US Magnesium, and any other sources that are determined to be major stationary sources based on the area's nonattainment classification and annual emissions of NO_X and/or VOC, will be required to apply for a CAA Title V permit, conduct a RACT analysis, and adhere to applicable New Source Review offsets.^[18] More information on the initial designation process for PM_2.5 and ozone is discussed in the accompanying TSD for this proposal.

As a result of being in nonattainment for a criteria pollutant, including ozone, the CAA requires specific elements be developed and submitted to the EPA for approval. Deadlines for ozone SIP elements are set forth in 40 CFR 51.1402. To satisfy CAA requirements for the requested new portion of the NAA, the EPA is proposing to require revisions for certain Marginal and Moderate SIP elements as outlined in table 1. A detailed discussion and rationale for the proposed Marginal and Moderate area SIP revisions is below, including discussion about each element, what is required, and the EPA's rationale for proposing whether to require the State to update each element to reflect the new portion of the ( printed page 46131) NAA. The elements proposed to be resubmitted are based on the EPA's determination of whether the addition of new territory to the NAA would have any impact on already submitted Marginal and Moderate SIP elements. Some elements do not need resubmission as the elements are not affected by the inclusion of new sources in the expanded NAA boundary area. Elements such as emissions inventories and the implementation of reasonably available control technologies will need to be resubmitted to include new sources in the expanded NAA boundary area and are therefore required to be addressed for the new portion of the NAA. The EPA's proposal to require revisions for some, but not all submitted SIP elements is not an indication of the EPA's determination of approvability of said elements or the Agency's intention to approve or disapprove any specific element. Approval of submitted Moderate SIP elements for the NWF will be addressed in future Federal Register documents and actions.

Given the deadlines for Marginal and Moderate SIP elements are years in the past, EPA is proposing to set the deadline for applicable Marginal and Moderate SIP revisions for the new portion of the NAA as 12 months after the effective date of this rule but are taking comments on an alternative timeline.

A. Marginal Area SIP Elements

1. Element Needing Updates Due to Revised NAA Boundary

Base Year Emissions Inventory

The State of Utah was required to submit a 2017 base year inventory as defined by § 51.1300(p), to meet the emissions inventory requirement of CAA section 182(a)(1), no later than 24 months after the effective date of designation. The State met this requirement for the initial Marginal NAA, which was approved by the EPA July 2021.^[19] As proposed, for the expanded area, the State will need to, submit a revised comprehensive, accurate, 2017 base year inventory of actual emissions from all sources of the relevant pollutants to include additional NO_X and VOC emissions for the new portion of the NAA.^[20] The EPA is proposing that this element be due 12 months from the effective date of the final rule expanding the NWF NAA.

2. Elements Not Needing Updates Due to Revised NAA Boundary

a. Certified NNSR

The State of Utah was required to submit a NNSR plan no later than 36 months after the effective date of the area's designation of nonattainment for the 2015 ozone NAAQS. The State's NNSR plan requires permits for the construction and operation of new or modified major stationary sources anywhere in the NAA, and sets emission offset thresholds in accordance with 40 CFR 51.1314. The State met this requirement for the initial Marginal NAA, which was approved by the EPA April 2022.^[21] As proposed, this requirement will not need to be resubmitted as the approved State regulation applies to all NAA's and classifications and will therefore apply to the new portion of the boundary upon finalization of the expansion.

b. Emissions Statement Rule

The State of Utah was required to implement an emissions statement rule in its Marginal NAA's that requires the owner or operator of each stationary source of NO_X or VOCs to provide the State with an annual statement showing the actual emissions from the source.^[22] The State met this requirement, which was approved by the EPA April 2022.^[23] As proposed, this requirement will not need to be resubmitted as the approved State regulation applies to all NAA's and will therefore apply to the new portion of the boundary upon finalization of the expansion.

B. Moderate Area SIP Elements

1. Elements Needing Updates Due to Revised NAA Boundary

a. Baseline Emissions Inventory for Reasonable Further Progress Plans

For Moderate ozone NAA's, a baseline emissions inventory is required to be submitted to the EPA, under the provisions of the Air Emissions Reporting Rule (AERR), to demonstrate compliance with the ROP/RFP requirement (see section IV.B.1.b below).^[24] The emission values included in the inventory required by this section shall be actual ozone season day ( printed page 46132) emissions as defined by § 51.1300(q). The State submitted a SIP revision in 2024 to meet this requirement for the original Moderate NAA. However, as proposed, for the expanded area, the State will need to submit a revised, comprehensive, accurate, 2017 base year inventory of actual emissions from all sources of the relevant pollutants to include additional NO_X and VOC emissions for the new portion of the NAA. It is presumed that this element can be submitted for purposes of meeting both this requirement and the revised 2017 base year emissions inventory requirement (see section IV.A.1 above). The EPA is proposing that this element be due 12 months from the effective date of the final rule expanding the NWF NAA.

b. 15% ROP/RFP

Per CAA section 182(b)(1)(A)(i) and 40 CFR 51.1310(a)(4), under the 2015 ozone NAAQS, Moderate NAA's must show a 15% reduction in emissions in 6 years starting from a 2017 base year through the 2023 Moderate area attainment year. The State submitted a SIP revision in 2024 to meet this requirement for the original Moderate NAA. However, as proposed, the State will need to submit a revised ROP plan to the EPA due to an adjusted base year inventory as well as to take SIP credit for emission reductions from SIP measures implemented in the newly expanded area. The EPA is proposing that this element be due 12 months from the effective date of the final rule expanding the NWF NAA.

c. RACT for Newly Designated Major Sources

For purposes of determining whether a source is a major stationary source as defined in CAA section 182(b)(2) and section 182(f), the amount of VOC and NO_X emissions are to be considered separately.^[25] For the NWF NAA, Utah submitted a SIP revision in 2024 to meet this requirement for the original Moderate NAA. However, Utah has identified one stationary source, US Magnesium, that will become a major source for NO_X and VOC as part of the boundary request and Utah will need to complete a RACT analysis for this source. Utah will also need to determine if any other sources in the new portion of the NAA exceed the Moderate NAA threshold for major sources, and conduct a RACT analysis if any are identified. The CAA requires that RACT be implemented as expeditiously as practicable, but no later than January 1 of the fifth year after the effective date of designation.^[26] Given that this date is now in the past, the EPA is proposing that implementation of RACT for newly determined major sources under 40 CFR 51.1312(b) be due 12 months from the effective date of the final rule expanding the NWF NAA.

d. Non-Major Source CTG RACT

CTG RACT is required for Moderate and above ozone NAA's. The State submitted a SIP revision in 2024 to meet this requirement for the original Moderate NAA. However, as proposed, the State will need to reevaluate all CTGs for which it submitted a negative declaration and either reconfirm that CTGs listed are still accurate for the expanded NWF NAA or provide analysis for any emission sources in the newly added area that are subject to a CTG that was previously on the negative declarations list. Per 40 CFR 51.1312(a)(3)(iii), Utah shall provide for implementation of CTG RACT as expeditiously as practicable, but no later than January 1 of the third year after the associated SIP submission deadline or the deadline established by the Administrator in the final action issuing the CTG. Given both dates are now in the past, the EPA is proposing that the deadline for implementation of CTG RACT for sources located within the new portion of the NWF NAA be 12 months from the effective date of the final rule expanding the NWF NAA.

2. Elements Not Needing Updates Due to Revised NAA Boundary

a. Modeled Attainment Demonstration

The State of Utah was required to submit an attainment demonstration that provides for reductions in emissions of VOCs and NO_X as necessary to attain the 2015 ozone NAAQS by the Moderate area attainment date of August 3, 2024.^[27] The State submitted a SIP revision in 2024 to meet this requirement for the original Moderate NAA. Due to the Moderate attainment date being in the past, the EPA does not see a rational need for a revised modeled attainment demonstration. This is because emissions from the new area were already included in the regional modeling domain and would not change the outcome regarding whether the area was able to model attainment for the 2023 ozone season. Therefore, the EPA is proposing that this Moderate area SIP element does not need to be revised and resubmitted for the NWF NAA.

b. RACM

For each NAA required to submit an attainment demonstration under 40 CFR 51.1308(a) and (b), Utah needs to submit a SIP revision demonstrating that it has adopted all RACM necessary to demonstrate attainment as expeditiously as practicable and to meet any RFP requirements.^[28] The goal of this SIP requirement is to identify feasible control measures that will advance attainment.^[29] Utah submitted a SIP revision in 2024 to meet this requirement for the original Moderate NAA. Similar to the rationale given for the modeled attainment demonstration in section IV.B.2.a above, since the Moderate attainment date is in the past, requiring the State to submit a RACM analysis for the new portion of the NAA to demonstrate whether any new strategies could advance attainment by one year ( i.e., by summer 2022) is illogical and impossible. Therefore, the EPA is proposing that this Moderate area SIP element does not be revised and resubmitted for the NWF NAA.

c. Contingency Measures

This element is required under CAA section 172(c)(9) and is intended to provide for the implementation of specific measures to be undertaken if the area fails to make ROP/RFP or to attain the NAAQS by the attainment date. Such measures shall be included in the plan revision as contingency measures to take effect in any such case without further action by the State or the Administrator. The State submitted a SIP revision in 2024 to meet this requirement. Since contingency measures only need apply “within” the NAA, the EPA is proposing that this Moderate area SIP element does not be revised and resubmitted for the NWF NAA.

d. Motor Vehicle I/M Program

I/M programs are required for certain urbanized NAA's classified as Moderate and above based on criteria detailed in the CAA and the federal I/M rule at 40 CFR part 51, subpart S. The CAA establishes two performance levels of I/M programs: “Basic” and “Enhanced” I/M. Moderate ozone NAA's are to implement Basic I/M in any 1990 Census-defined urbanized areas with a population of 200,000 or more. The ( printed page 46133) State submitted a SIP revision in 2024 to meet this requirement and as a Moderate ozone NAA, the NWF is currently operating Basic I/M programs in all areas that meet the urbanized population criteria.

Pursuant to 40 CFR 51.350(a)(6), if the boundaries of a Moderate ozone NAA are changed, Basic I/M shall be implemented in any additional urbanized areas with a population of 200,000 or more. Since the new territory being proposed for addition to the NWF NAA is rural (and below the population threshold), the EPA is proposing that this Moderate area SIP element does not be revised and resubmitted for the NWF NAA.^[30]

e. NSR Offsets

For purposes of satisfying the emission offset requirements of CAA section 182(b)(5), the ratio of total emission reductions of VOCs to total increased emissions of such air pollutant shall be at least 1.15 to 1 for Moderate NAA's. The State's Marginal SIP submittal demonstrated that this requirement is being met and will continue to be met for all possible NAA's and classifications were this area or any new area to be reclassified to a higher classification in the future.^[31] The EPA approved regulation applies to any and all current and future ozone NAA's, including the new portion of the boundary upon finalization of the expansion. Therefore, the EPA is proposing that this Moderate area SIP element does not be revised and resubmitted for the NWF NAA.

V. Statutory Authority and Procedural Requirements

State of Utah, section 19-2-104 of the Utah Code gives the Utah Air Quality Board the authority to promulgate rules “regarding the control, abatement, and prevention of air pollution from all sources and the establishment of the maximum quantity of air pollutants that may be emitted by an air pollutant source.” The Utah Division of Air Quality (UDAQ) develops, prepares, and submits SIPs to the Utah Air Quality Board for consideration and promulgation. UDAQ is the primary State agency responsible for the development and implementation of SIPs once they are approved by the Utah Air Quality Board, and associated administrative rules, as required by the CAA.

The statutory authority for the requested NAA boundary expansion is provided by the CAA, as amended (42 United States Code (U.S.C.) 7401, et seq.). For areas seeking to change the boundary of an already designated NAA, CAA section 107(d)(3)(D) states, “The Governor of any state may, on the Governor's own motion, submit to the Administrator a revised designation of any area or portion thereof within the State. Within 18 months of receipt of a complete state redesignation submittal, the Administrator shall approve or deny such redesignation. The submission of a redesignation by a Governor shall not affect the effectiveness or enforceability of the applicable implementation plan for the State.” The State was not required to take public comment on the requested boundary expansion.

The EPA is soliciting public comments on the issues discussed in this proposed rule (see DATES section). We will accept comments from the public on this proposal for the next 30 days and will consider comments before taking final action. CAA section 107(d)(1)(B)(ii) lays out a particular process when the EPA disagrees with a state's recommended designations. Because the EPA is agreeing with the State of Utah's recommended boundary expansion and is proposing to approve the State's request, the EPA did not send a 120-day letter to the State prior to this proposed action. Under CAA section 107(d)(2)(B), the EPA is not required to provide an Administrative Procedure Act public comment period for designation actions, however, public comment is being accepted as part of this proposal.

VI. Statutory and Executive Order Reviews

A. Executive Order 12866: Regulatory Planning and Review

This action is not a significant regulatory action as defined in Executive Order 12866 and was therefore not subject to a requirement for Executive Order 12866 review.

B. Executive Order 14192: Unleashing Prosperity Through Deregulation

This action is not subject to Executive Order 14192 (90 FR 9065, February 6, 2025) because NAA boundary revision actions under the CAA are exempt from review under Executive Order 12866.

C. Paperwork Reduction Act

This proposed rule does not impose an information collection burden under the provisions of the Paperwork Reduction Act of 1995 (44 U.S.C. 3501 et seq.).

D. Regulatory Flexibility Act

This action merely approves state law as meeting Federal requirements and imposes no additional requirements beyond those imposed by state law. Accordingly, the Administrator certifies that this rule will not have a significant economic impact on a substantial number of small entities under the Regulatory Flexibility Act (5 U.S.C. 601 et seq.).

E. Unfunded Mandates Reform Act (UMRA)

This action does not contain any unfunded mandate as described in UMRA, 2 U.S.C. 1531-1538, and does not significantly or uniquely affect small governments. This action does not impose additional requirements beyond those imposed by state law. Accordingly, no additional costs to State, local, or Tribal governments, or to the private sector, will result from this action.

F. Executive Order 13132: Federalism

This action does not have federalism implications. It will not have substantial direct effects on the states, on the relationship between the national government and the states, or on the distribution of power and responsibilities among the various levels of government.

G. Executive Order 13175: Consultation and Coordination With Indian Tribal Governments

Executive Order 13175 (65 FR 67249, November 9, 2000), requires EPA to develop an accountable process to ensure “meaningful and timely input by Tribal officials in the development of regulatory policies that have Tribal implications.” This proposed rule does not have Tribal implications, as specified in Executive Order 13175. It will not have substantial direct effects on Tribal governments. Thus, Executive Order 13175 does not apply to this rule.

H. Executive Order 13045: Protection of Children From Environmental Health and Safety Risks

This action is not subject to Executive Order 13045 because it is not 3(f)(1) significant as defined in Executive Order 12866, and because EPA does not believe the environmental health or safety risks addressed by this action present a disproportionate risk to children because it approves a state program. ( printed page 46134)

I. Executive Order 13211: Actions That Significantly Affect Energy Supply, Distribution, or Use

This action is not subject to Executive Order 13211 (66 FR 28355 (May 22, 2001)), because it is not a significant regulatory action under Executive Order 12866.

J. National Technology Transfer Advancement Act

This rulemaking does not involve technical standards.

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

90 FR 46128