# Identification of plan.
**AGENCY:**
Environmental Protection Agency (EPA).
**ACTION:**
Proposed rule.
**SUMMARY:**
The Environmental Protection Agency (EPA) is proposing to approve the regional haze state implementation plan (SIP) submission submitted by the State of Montana on August 10, 2022, under the Clean Air Act (CAA) and the EPA's Regional Haze Rule (RHR) for the program's second implementation period. Montana's 2022 SIP submission addresses the requirement that states revise their long-term strategies every implementation period to make reasonable progress towards the national goal of preventing any future, and remedying any existing, anthropogenic impairment of visibility, including regional haze, in mandatory Class I Federal areas. Montana's 2022 SIP submission also addresses other applicable requirements for the second implementation period of the regional haze program. The EPA is also proposing to approve the prong 4 visibility portion of Montana's October 1, 2018 Infrastructure SIP submission for the 2015 ozone National Ambient Air Quality Standards (NAAQS). The EPA is taking these actions pursuant to the CAA.
**DATES:**
Written comments must be received on or before October 14, 2025.
**ADDRESSES:**
Submit your comments, identified by Docket ID No. EPA-R08-OAR-2024-0608, to the Federal Rulemaking Portal: *https://www.regulations.gov.* Follow the online instructions for submitting comments. Once submitted, comments cannot be edited or removed from *https://www.regulations.gov.* The EPA may publish any comment received to its public docket. Do not submit electronically any information you consider to be Confidential Business Information (CBI) or other information whose disclosure is restricted by statute. Multimedia submissions (audio, video, etc.) must be accompanied by a written comment. The written comment is considered the official comment and should include discussion of all points you wish to make. The EPA will generally not consider comments or comment contents located outside of the primary submission ( *i.e.,* on the web, cloud, or other file sharing system). For additional submission methods, the full EPA public comment policy, information about CBI or multimedia submissions, and general guidance on making effective comments, please visit *https://www.epa.gov/dockets/commenting-epa-dockets.*
*Docket:* All documents in the docket are listed in the *https://www.regulations.gov* index. Although listed in the index, some information is not publicly available, *e.g.,* CBI or other information whose disclosure is restricted by statute. Certain other material, such as copyrighted material, will be publicly available only in hard copy. Publicly available docket materials are available electronically in *https://www.regulations.gov.* Please email or call the person listed in the *FOR FURTHER INFORMATION CONTACT* section if you need to make alternative arrangements for access to the docket.
**FOR FURTHER INFORMATION CONTACT:**
Jaslyn Dobrahner, Air and Radiation Division, EPA, Region 8, Mailcode 8ARD-IO, 1595 Wynkoop Street, Denver, Colorado 80202-1129, telephone number: (303) 312-6252; email address: *[email protected].*
**SUPPLEMENTARY INFORMATION:**
Throughout this document wherever “we,” “us,” or “our” is used, we mean the EPA.
**Table of Contents**
I. What action is the EPA proposing?
II. Background and Requirements for Regional Haze Plans
A. Regional Haze
B. Roles of Agencies in Addressing Regional Haze
C. Status of Montana's Regional Haze Plan for the First Implementation Period
D. Montana's Regional Haze Plan for the Second Implementation Period
III. Requirements for Regional Haze Plans for the Second Implementation Period
IV. The EPA's Evaluation of Montana's Regional Haze Plan for the Second Implementation Period
A. Identification of Class I Areas
B. Calculation of Baseline, Current, and Natural Visibility Conditions; Progress to Date; and Uniform Rate of Progress for Class I Areas Within the State
C. Long-Term Strategy
1. Montana's Long-Term Strategy Four-Factor Analysis
a. Summary of Montana's Long-Term Strategy Four-Factor Analysis
b. The EPA's Evaluation of Montana's Long-Term Strategy Four-Factor Analysis
2. Other Long-Term Strategy Requirements
D. Reasonable Progress Goals
E. Reasonably Attributable Visibility Impairment (RAVI)
F. Monitoring Strategy and Other State Implementation Plan Requirements
G. Requirements for Periodic Reports Describing Progress Towards the Reasonable Progress Goals
H. Requirements for State and Federal Land Manager Coordination
V. Interstate Transport Prong 4 (Visibility) for the 2015 Ozone NAAQS Infrastructure SIP
A. Background on Infrastructure SIPs
B. Prong 4 Requirements
C. Montana's Infrastructure SIP Submission
D. The EPA's Evaluation of Montana's Infrastructure SIP Submission
VI. Proposed Action
VII. Statutory and Executive Order Reviews
**I. What action is the EPA proposing?**
The EPA is proposing to approve a SIP submission submitted by the State of Montana to the EPA on August 10, 2022, addressing the requirements of the second implementation period of the RHR. Specifically, the EPA is proposing approval for the portions of Montana's 2022 SIP submission relating to 40 CFR 51.308(f)(1): calculations of baseline, current, and natural visibility conditions, progress to date, and the uniform rate of progress; 40 CFR 51.308(f)(2): long-term strategy; 40 CFR 51.308(f)(3): reasonable progress goals; 40 CFR 51.308(f)(4): reasonably attributable visibility impairment; 40 CFR 51.308(f)(5) and 40 CFR 51.308(g): progress report requirements; 40 CFR 51.308(f)(6): monitoring strategy and other implementation plan requirements; and 40 CFR 51.308(i): Federal Land Manager (FLM) consultation. The EPA is also proposing to approve the CAA section 110(a)(2)(D)(i) prong 4 (visibility) portion of Montana's October 1, 2018 Infrastructure SIP submission addressing the 2015 ozone NAAQS.
**II. Background and Requirements for Regional Haze Plans**
A detailed history and background of the regional haze program is provided in multiple prior EPA proposal actions. [^1] For additional background on the 2017 RHR revisions, please refer to section III. Overview of Visibility Protection Statutory Authority, Regulation, and Implementation of “Protection of Visibility: Amendments to Requirements for State Plans” of the 2017 RHR. [^2] The following is an abbreviated history and background of the regional haze program and 2017 Regional Haze Rule as it applies to the current action.
[^1]*See* 90 FR 13516 (March 24, 2025).
[^2]*See* 82 FR 3078 (January 10, 2017, located at *https://www.federalregister.gov/documents/2017/01/10/2017-00268/protection-of-visibility-amendments-to-requirements-for-State-plans#h-16* ).
**A. Regional Haze**
In the 1977 CAA amendments, Congress created a program for protecting visibility in the nation's mandatory Class I Federal areas, which include certain national parks and wilderness areas. [^3] CAA section 169A. The CAA establishes as a national goal the “prevention of any future, and the remedying of any existing, impairment of visibility in mandatory Class I Federal areas which impairment results from manmade air pollution.” CAA section 169A(a)(1).
[^3] Areas statutorily designated as mandatory Class I Federal areas consist of national parks exceeding 6,000 acres, wilderness areas and national memorial parks exceeding 5,000 acres, and all international parks that were in existence on August 7, 1977. CAA section 162(a). There are 156 mandatory Class I areas. The list of areas to which the requirements of the visibility protection program apply is in 40 CFR part 81, subpart D.
Regional haze is visibility impairment that is produced by a multitude of anthropogenic sources and activities that are located across a broad geographic area and that emit pollutants that impair visibility. Visibility impairing pollutants include fine and coarse particulate matter (PM) ( *e.g.,* sulfates, nitrates, organic carbon, elemental carbon, and soil dust) and their precursors ( *e.g.,* sulfur dioxide (SO <sub>2</sub> ), nitrogen oxides (NO <sub>X</sub> ), and, in some cases, volatile organic compounds (VOC) and ammonia (NH <sub>3</sub> )). Fine particle precursors react in the atmosphere to form fine particulate matter (PM <sub>2.5</sub> ), which impairs visibility by scattering and absorbing light. Visibility impairment reduces the perception of clarity and color, as well as visible distance. [^4]
[^4] There are several ways to measure the amount of visibility impairment, *i.e.,* haze. One such measurement is the deciview, which is the principal metric used by the RHR. Under many circumstances, a change in one deciview will be perceived by the human eye to be the same on both clear and hazy days. The deciview is unitless. It is proportional to the logarithm of the atmospheric extinction of light, which is the perceived dimming of light due to its being scattered and absorbed as it passes through the atmosphere. Atmospheric light extinction (b [^ext] ) is a metric used for expressing visibility and is measured in inverse megameters (Mm <sub>−1</sub> ). The formula for the deciview is 10 ln (b [^ext] )/10 Mm <sub>−1</sub> ). 40 CFR 51.301.
To address regional haze visibility impairment, the 1999 RHR established an iterative planning process that requires states containing Class I areas and states containing sources whose emissions “may reasonably be anticipated to cause or contribute to any impairment of visibility” in a Class I area in another state to periodically submit SIP revisions to address such impairment. CAA section 169A(b)(2); see also 40 CFR 51.308(b), (f) (establishing submission dates for iterative regional haze SIP revisions); (64 FR at 35768, July 1, 1999).
On January 10, 2017, the EPA promulgated revisions to the RHR (82 FR 3078, January 10, 2017) that apply for the second and subsequent implementation periods. The reasonable progress requirements as revised by the 2017 rule (referred to here as the 2017 RHR Revisions) are codified at 40 CFR 51.308(f).
**B. Roles of Agencies in Addressing Regional Haze**
Because the air pollutants and pollution affecting visibility in Class I areas can be transported over long distances, successful implementation of the regional haze program requires long-term, regional coordination among multiple jurisdictions and agencies that have responsibility for Class I areas and the emissions that impact visibility in those areas. To address regional haze, states need to develop strategies in coordination with one another, considering the effect of emissions from one jurisdiction on the air quality in another. Five regional planning organizations (RPOs), which include representation from state and Tribal governments, the EPA, and FLMs, were developed in the lead-up to the first implementation period to address regional haze. RPOs evaluate technical information to better understand how emissions from state and Tribal land impact Class I areas across the country, pursue the development of regional strategies to reduce emissions of particulate matter and other pollutants leading to regional haze, and help states meet the consultation requirements of the RHR.
The Western Regional Air Partnership (WRAP), one of the five regional planning organizations described in the previous paragraph, is a collaborative effort of state governments, local air agencies, Tribal governments, and various federal agencies established to initiate and coordinate activities associated with the management of regional haze, visibility, and other air quality issues in the Western United States. Members include the states of Alaska, Arizona, California, Colorado, Hawaii, Idaho, Montana, Nevada, New Mexico, North Dakota, Oregon, South Dakota, Utah, Washington, Wyoming, and 28 Tribal governments. [^5] The federal partner members of WRAP are the EPA, U.S. National Parks Service, U.S. Fish and Wildlife Service, U.S. Forest Service, and the Bureau of Land Management.
[^5] A full list of WRAP members is available at *https://www.westar.org/wrap-council-members/.*
WRAP formed a workgroup to develop a planning framework for state regional haze second planning period SIPs. Based on emissions and monitoring data supplied by its membership, WRAP produced a technical system to support regional modeling of visibility impacts at Class I areas across the West. The WRAP Technical Support System consolidated air quality monitoring data, meteorological and receptor modeling data analyses, emissions inventories and projections, and gridded air quality/visibility regional modeling results. The Technical Support System is accessible by member states and allows for the creation of maps, figures, and tables to export and use in state plan development. It also maintains the original source data for verification and further analysis. Montana collaborated with WRAP on various aspects of the State's 2022 SIP submission, including the identification of Class I areas outside of Montana that may be affected by sources in the state, source selection, analysis of air quality monitoring data, preparation of emission inventories, development of reasonable progress goals, and air quality modeling, which together informed the development of its long-term strategy.
**C. Status of Montana's Regional Haze Plan for the First Implementation Period**
The CAA requires that regional haze plans for the first implementation period (2008 through 2018) include, among other things, a long-term strategy for making reasonable progress and BART requirements for certain older stationary sources, where applicable. [^6]
[^6] Requirements for regional haze SIPs for the first implementation period are also contained in CAA section 169A(b)(2).
On September 18, 2012, the EPA promulgated a federal implementation plan (FIP) that included NO <sub>X</sub> , SO <sub>2</sub> , and PM BART emission limits for three electricity generating units (EGUs) at two power plants and two cement kilns, as well as an emission limit for a natural gas compressor station to satisfy the reasonable progress requirements. [^7] The EPA promulgated a FIP in this instance because Montana did not submit a regional haze SIP as required under section 110 of the CAA. [^8]
[^7] 77 FR 57864 (September 18, 2012).
[^8] Letter from Richard H. Opper, Director Montana Department of Environmental Quality to Laurel Dygowski, EPA Region 8 Air Program, June 19, 2006. Based off this letter, EPA made a determination finding of failure to submit a SIP by Montana. This triggered a mandatory duty clock to have EPA either promulgate a FIP or approve a SIP within two years of the EPA finding. *See* 74 FR 2392 (January 15, 2009).
Several parties challenged the portion of the FIP addressing the EPA's NO <sub>X</sub> and SO <sub>2</sub> BART determinations at the power plants, Colstrip Units 1 and 2 and Corette. [^9] On June 9, 2015, the U.S. Court of Appeals for the Ninth Circuit vacated and remanded the portions of the FIP related to the NO <sub>X</sub> and SO <sub>2</sub> BART emission limits for J.E. Corette and Colstrip Units 1 and 2 and remanded the EPA's response to a public comment in the 2012 final rule regarding the use of visibility modeling in determining BART for Colstrip Units 1 and 2. [^10] The BART emission limits for the Ash Grove and Trident cement kilns, the PM emission limits for the EGUs, and the reasonable progress requirements for the Blaine Compressor Station were not at issue in the petitions filed with the Ninth Circuit Court of Appeals. [^11]
[^9] Several parties petitioned the Ninth Circuit Court of Appeals to review EPA's NO <sub>X</sub> and SO <sub>2</sub> BART determinations at the power plants, Colstrip and Corette (PPL Montana, LLC, the National Parks Conservation Association, Montana Environmental Information Center, and the Sierra Club). *National Parks Conservation Association* v. *EPA,* 788 F.3d 1134 (9th Cir. 2015).
[^10]*Id.*
[^11]*Id.*
On September 12, 2017, the EPA amended aspects of the remaining 2012 FIP by (1) revising the BART NO <sub>X</sub> emission limit for the Trident cement kiln, and (2) correcting errors in our original FIP regarding the reasonable progress determination for the Blaine Compressor Station and the instructions for compliance determinations for PM BART emission limits at the EGUs and cement kilns. [^12] Ultimately, the EPA removed the reasonable progress requirements for the natural gas compressor station from the FIP after correcting the error that resulted in the source no longer being subject to reasonable progress requirements.
[^12] 82 FR 42738 (September 12, 2017).
On June 26, 2023, the EPA approved a SIP revision that addressed NO <sub>X</sub> and SO <sub>2</sub> BART requirements for the J.E. Corette and Colstrip (Units 1 and 2) power plants and replaced portions of the original FIP promulgated by the EPA in 2012. <sub>13 14</sub>
[^13] 88 FR 41320 (June 26, 2023).
[^14] The June 26, 2023, action also addressed the U.S. Court of Appeals for the Ninth Circuit's June 9, 2015 remand of portions of the 2012 regional haze FIP, including the EPA's response to a public comment regarding the use of the CALPUFF visibility model in determining BART at Colstrip Units 1 and 2.
**D. Montana's Regional Haze Plan for the Second Implementation Period**
On August 10, 2022, Montana submitted a SIP submission to address its regional haze obligations for the second implementation period (2018-2028). Montana's 2022 SIP submission contains the State's long-term strategy to address regional haze visibility impairment for each Class I area within the State and each Class I area outside the State that may be affected by emissions from the State. In developing its long-term strategy, the State examined the need to implement additional enforceable emission limitations, compliance schedules, and other measures that are necessary to make reasonable progress since the first implementation period. Specifically, Montana's 2022 SIP submission contains an assessment of visibility progress made at Class I areas since the first implementation period and a long-term strategy to address regional haze visibility impairment at Class I areas the State identified, including: Montana's selection of sources that may affect visibility in Class I areas within the State and outside the State for four-factor analysis; its evaluation of the selected sources to determine what emission reduction measures constitute reasonable progress for the long-term strategy; regional scale modeling of the State's long-term strategy to set reasonable progress goals for 2028; and ultimately, Montana's determinations on what control measures are necessary for the long-term strategy to address regional haze visibility impairment in the Class I areas. The State concluded that no additional emission reduction measures for Montana facilities are required for the second implementation period under its long-term strategy.
**III. Requirements for Regional Haze Plans for the Second Implementation Period**
Under the CAA and the EPA's regulations, all 50 states, the District of Columbia, and the U.S. Virgin Islands were required to submit regional haze SIPs satisfying the applicable requirements for the second implementation period of the regional haze program by July 31, 2021. Each SIP must contain a long-term strategy for making reasonable progress toward meeting the national goal of remedying any existing and preventing any future anthropogenic visibility impairment in Class I areas. CAA section 169A(b)(2)(B). To this end, 40 CFR 51.308(f) lays out the process by which states determine what constitutes their long-term strategies, with the order of the requirements in 40 CFR 51.308(f)(1) through (3) generally mirroring the order of the steps in the reasonable progress analysis [^15] and (f)(4) through (6) containing additional, related requirements.
[^15] The EPA explained in the 2017 RHR revisions that we were adopting new regulatory language in 40 CFR 51.308(f) that, unlike the structure in 51.308(d), “tracked the actual planning sequence.” (82 FR at 3091).
Broadly speaking, a state first must identify the Class I areas within the state and determine the Class I areas outside the state in which visibility may be affected by emissions from the state. These are the Class I areas that must be addressed in the state's long-term strategy. See 40 CFR 51.308(f), (f)(2). For each Class I area within its borders, a state must then calculate the baseline (five-year average period of 2000-2004), current, and natural visibility conditions ( *i.e.,* visibility conditions without anthropogenic visibility impairment) for that area, as well as the visibility improvement made to date and the “uniform rate of progress” (URP). The URP is the linear rate of progress needed to attain natural visibility conditions, assuming a starting point of baseline visibility conditions in 2004 and ending with natural conditions in 2064. This linear interpolation is used as a tracking metric to help states assess the amount of progress they are making towards the national visibility goal over time in each Class I area. See 40 CFR 51.308(f)(1).
Each state having a Class I area and/or emissions that may affect visibility in a Class I area must then develop a long-term strategy that includes the enforceable emission limitations, compliance schedules, and other measures that are necessary to make reasonable progress in such areas. A reasonable progress determination is based on applying the four factors in CAA section 169A(g)(1) to sources of visibility impairing pollutants that the state has selected to assess for controls for the second implementation period. Additionally, as further explained below, the RHR at 40 CFR 51.3108(f)(2)(iv) separately provides five “additional factors” [^16] that states must consider in developing their long-term strategies. See 40 CFR 51.308(f)(2). A state evaluates potential emission reduction measures for those selected sources and determines which are necessary to make reasonable progress. Those measures are then incorporated into the state's long-term strategy.
[^16] The five “additional factors” for consideration in 40 CFR 51.308(f)(2)(iv) are distinct from the four factors listed in CAA section 169A(g)(1) and 40 CFR 51.308(f)(2)(i) that states must consider and apply to sources in determining reasonable progress.
After a state has developed its long-term strategy, it then establishes reasonable progress goals (RPGs) for each Class I area within its borders by modeling the visibility impacts of all reasonable progress controls at the end of the second implementation period, *i.e.,* in 2028, as well as the impacts of other requirements of the CAA. The RPGs include reasonable progress controls not only for sources in the state in which the Class I area is located, but also for sources in other states that contribute to visibility impairment in that area. The RPGs are then compared to the baseline visibility conditions and the URP to ensure that progress is being made towards the statutory goal of preventing any future and remedying any existing anthropogenic visibility impairment in Class I areas. 40 CFR 51.308(f)(2)-(3). There are additional requirements in the rule, including FLM consultation, that apply to all visibility protection SIPs and SIP revisions. *See e.g.,* 40 CFR 51.308(i).
While states have discretion to choose any source selection methodology that is reasonable, whatever choices they make should be reasonably explained. To this end, 40 CFR 51.308(f)(2)(i) requires that a state's SIP submission include “a description of the criteria it used to determine which sources or groups of sources it evaluated.” The technical basis for source selection, which may include methods for quantifying potential visibility impacts such as emissions divided by distance metrics, trajectory analyses, residence time analyses, and/or photochemical modeling, must also be appropriately documented, as required by 40 CFR 51.308(f)(2)(iii).
Once a state has selected the set of sources, the next step is to determine the emissions reduction measures for those sources that are necessary to make reasonable progress for the second implementation period. [^17] This is accomplished by considering the four factors—“the costs of compliance, the time necessary for compliance, the energy and non-air quality environmental impacts of compliance, and the remaining useful life of any existing source subject to such requirements.” CAA section 169A(g)(1). The EPA has explained that the four-factor analysis is an assessment of potential emission reduction measures ( *i.e.,* control options) for sources; “use of the terms `compliance' and `subject to such requirements' in section 169A(g)(1) strongly indicates that Congress intended the relevant determination to be the requirements with which sources would have to comply to satisfy the CAA's reasonable progress mandate.” 82 FR at 3091. Thus, for each source it has selected for four-factor analysis, [^18] a state must consider a “meaningful set” of technically feasible control options for reducing emissions of visibility impairing pollutants. *Id.* at 3088.
[^17] The CAA provides that, “[i]n determining reasonable progress there shall be taken into consideration” the four statutory factors. CAA section 169A(g)(1). However, in addition to four-factor analyses for selected sources, groups of sources, or source categories, a state may also consider additional emission reduction measures for inclusion in its long-term strategy, *e.g.,* from other newly adopted, on-the-books, or on-the-way rules and measures for sources not selected for four-factor analysis for the second implementation period.
[^18] “Each source” or “particular source” is used here as shorthand. While a source-specific analysis is one way of applying the four factors, neither the statute nor the RHR requires states to evaluate individual sources. Rather, states have “the flexibility to conduct four-factor analyses for specific sources, groups of sources or even entire source categories, depending on state policy preferences and the specific circumstances of each state.” 82 FR at 3088.
The EPA has also explained that, in addition to the four statutory factors, states have flexibility under the CAA and RHR to reasonably consider visibility benefits as an additional factor alongside the four statutory factors. [^19] Ultimately, while states have discretion to reasonably weigh the factors and to determine what level of control is needed, 40 CFR 51.308(f)(2)(i) provides that a state “must include in its implementation plan a description of . . . how the four factors were taken into consideration in selecting the measures for inclusion in its long-term strategy.”
[^19]*See, e.g.,* Responses to Comments on Protection of Visibility: Amendments to Requirements for State Plans; Proposed Rule (81 FR 26942, May 4, 2016), Docket ID No. EPA-HQ-OAR-2015-0531, U.S. Environmental Protection Agency at 186.
As explained above, 40 CFR 51.308(f)(2)(i) requires states to determine the emission reduction measures for sources that are necessary to make reasonable progress by considering the four factors. Pursuant to 40 CFR 51.308(f)(2), measures that are necessary to make reasonable progress towards the national visibility goal must be included in a state's long-term strategy and in its SIP. If the outcome of a four-factor analysis is that an emissions reduction measure is necessary to make reasonable progress towards remedying existing or preventing future anthropogenic visibility impairment, that measure must be included in the SIP.
The characterization of information on each of the factors is also subject to the documentation requirement in 40 CFR 51.308(f)(2)(iii). The reasonable progress analysis is a technically complex exercise, and also a flexible one that provides states with bounded discretion to design and implement approaches appropriate to their circumstances. Given this flexibility, 40 CFR 51.308(f)(2)(iii) plays an important function in requiring a state to document the technical basis for its decision making so that the public and the EPA can comprehend and evaluate the information and analysis the state relied upon to determine what emission reduction measures must be in place to make reasonable progress. The technical documentation must include the modeling, monitoring, cost, engineering, and emissions information on which the state relied to determine the measures necessary to make reasonable progress.
Additionally, the RHR at 40 CFR 51.3108(f)(2)(iv) separately provides five “additional factors” that states must consider in developing their long-term strategies: (1) Emission reductions due to ongoing air pollution control programs, including measures to address reasonably attributable visibility impairment; (2) measures to reduce the impacts of construction activities; (3) source retirement and replacement schedules; (4) basic smoke management practices for prescribed fire used for agricultural and wildland vegetation management purposes and smoke management programs; and (5) the anticipated net effect on visibility due to projected changes in point, area, and mobile source emissions over the period addressed by the long-term strategy.
Because the air pollution that causes regional haze crosses state boundaries, 40 CFR 51.308(f)(2)(ii) requires a state to consult with other states that also have emissions that are reasonably anticipated to contribute to visibility impairment in a given Class I area. If a state, pursuant to consultation, agrees that certain measures ( *e.g.,* a certain emission limitation) are necessary to make reasonable progress at a Class I area, it must include those measures in its SIP. 40 CFR 51.308(f)(2)(ii)(A). Additionally, the RHR requires that states that contribute to visibility impairment at the same Class I area consider the emission reduction measures the other contributing states have identified as being necessary to make reasonable progress for their own sources. 40 CFR 51.308(f)(2)(ii)(B). If a state has been asked to consider or adopt certain emission reduction measures, but ultimately determines those measures are not necessary to make reasonable progress, that state must document in its SIP the actions taken to resolve the disagreement. 40 CFR 51.308(f)(2)(ii)(C). Under all circumstances, a state must document in its SIP submission all substantive consultations with other contributing states. 40 CFR 51.308(f)(2)(ii)(C).
Reasonable progress goals “measure the progress that is projected to be achieved by the control measures states have determined are necessary to make reasonable progress based on a four-factor analysis.” 82 FR at 3091. For the second implementation period, the RPGs are set for 2028. Reasonable progress goals are not enforceable targets. 40 CFR 51.308(f)(3)(iii). While states are not legally obligated to achieve the visibility conditions described in their RPGs, 40 CFR 51.308(f)(3)(i) requires that “[t]he long-term strategy and the reasonable progress goals must provide for an improvement in visibility for the most impaired days since the baseline period and ensure no degradation in visibility for the clearest days since the baseline period.”
RPGs may also serve as a metric for assessing the amount of progress a state is making towards the national visibility goal. To support this approach, the RHR requires states with Class I areas to compare the 2028 RPG for the most impaired days to the corresponding point on the URP line (representing visibility conditions in 2028 if visibility were to improve at a linear rate from conditions in the baseline period of 2000-2004 to natural visibility conditions in 2064). If the most impaired days RPG in 2028 is above the URP ( *i.e.,* if visibility conditions are improving more slowly than the rate described by the URP), each state that contributes to visibility impairment in the Class I area must demonstrate, based on the four-factor analysis required under 40 CFR 51.308(f)(2)(i), that no additional emission reduction measures would be reasonable to include in its long-term strategy. 40 CFR 51.308(f)(3)(ii). To this end, 40 CFR 51.308(f)(3)(ii) requires that each state contributing to visibility impairment in a Class I area that is projected to improve more slowly than the URP provide “a robust demonstration, including documenting the criteria used to determine which sources or groups [of] sources were evaluated and how the four factors required by paragraph (f)(2)(i) were taken into consideration in selecting the measures for inclusion in its long-term strategy.”
Section 51.308(f)(6) requires states to have certain strategies and elements in place for assessing and reporting on visibility. Individual requirements under this section apply either to states with Class I areas within their borders, states with no Class I areas but that are reasonably anticipated to cause or contribute to visibility impairment in any Class I area, or both. Compliance with the monitoring strategy requirement may be met through a state's participation in the Interagency Monitoring of Protected Visual Environments (IMPROVE) monitoring network, which is used to measure visibility impairment caused by air pollution at the 156 Class I areas covered by the visibility program. 40 CFR 51.308(f)(6), (f)(6)(i), (f)(6)(iv).
All states' SIPs must provide for procedures by which monitoring data and other information are used to determine the contribution of emissions from within the state to regional haze visibility impairment in affected Class I areas, as well as a statewide inventory documenting such emissions. 40 CFR 51.308(f)(6)(ii), (iii), (v). All states' SIPs must also provide for any other elements, including reporting, recordkeeping, and other measures, that are necessary for states to assess and report on visibility. 40 CFR 51.308(f)(6)(vi).
Section 51.308(f)(5) requires a state's regional haze SIP revision to address the requirements of paragraphs 40 CFR 51.308(g)(1) through (5) so that the plan revision due in 2021 will serve also as a progress report addressing the period since submission of the progress report for the first implementation period. The regional haze progress report requirement is designed to inform the public and the EPA about a state's implementation of its existing long-term strategy and whether such implementation is in fact resulting in the expected visibility improvement. See 81 FR 26942, 26950 (May 4, 2016), (82 FR at 3119, January 10, 2017). To this end, every state's SIP revision for the second implementation period is required to assess changes in visibility conditions and describe the status of implementation of all measures included in the state's long-term strategy, including BART and reasonable progress emission reduction measures from the first implementation period, and the resulting emissions reductions. 40 CFR 51.308(g)(1) and (2).
CAA section 169A(d) requires that before a state holds a public hearing on a proposed regional haze SIP revision, it must consult with the appropriate FLM or FLMs; pursuant to that consultation, the state must include a summary of the FLMs' conclusions and recommendations in the notice to the public. Consistent with this statutory requirement, the RHR also requires that states “provide the [FLM] with an opportunity for consultation, in person and at a point early enough in the State's policy analyses of its long-term strategy emission reduction obligation so that information and recommendations provided by the [FLM] can meaningfully inform the State's decisions on the long-term strategy.” 40 CFR 51.308(i)(2). For the EPA to evaluate whether FLM consultation meeting the requirements of the RHR has occurred, the SIP submission should include documentation of the timing and content of such consultation. The SIP revision submitted to the EPA must also describe how the state addressed any comments provided by the FLMs. 40 CFR 51.308(i)(3). Finally, a SIP revision must provide procedures for continuing consultation between the state and FLMs regarding the state's visibility protection program, including development and review of SIP revisions, five-year progress reports, and the implementation of other programs having the potential to contribute to impairment of visibility in Class I areas. 40 CFR 51.308(i)(4).
Finally, the state SIP must meet the approval requirements in CAA section 110(a)(2) for plans “submitted by a State under this chapter” to the extent not already addressed in the regulations described previously. As relevant here, the state must provide “necessary assurances” that the state has adequate personnel, funding, and authority to carry out the implementation plan, that the state “is not prohibited by any provision of Federal or State law from carrying out such implementation plan or portion thereof,” and that the state can lawfully rely on regional and local instrumentalities to implement the SIP, as applicable. CAA section 110(a)(2)(E)(i)-(iii).
**IV. The EPA's Evaluation of Montana's Regional Haze Plan for the Second Implementation Period**
In section IV. of this document, we describe Montana's 2022 SIP submission and evaluate it against the requirements of the CAA and RHR for the second implementation period of the regional haze program.
**A. Identification of Class I Areas**
Section 169A(b)(2) of the CAA requires each state in which any Class I area is located or “the emissions from which may reasonably be anticipated to cause or contribute to any impairment of visibility” in a Class I area to have a long-term strategy for making reasonable progress toward the national visibility goal. The RHR implements this statutory requirement in 40 CFR 51.308(f) for the second and subsequent planning periods for regional haze. 40 CFR 51.308(f)(2) requires states to submit a long-term strategy that addresses regional haze visibility impairment for each mandatory Class I area within the state and for each mandatory Class I area located outside the state that may be affected by emissions from the state.
There are 12 designated Class I areas within the State of Montana, including two national parks managed by the U.S. National Park Service (Glacier National Park and Yellowstone National Park) and ten wilderness areas managed by the U.S. Forest Service (Anaconda-Pintler Wilderness Area, Bob Marshall Wilderness Area, Cabinet Mountains Wilderness Area, Gates of the Mountains Wilderness Area, Medicine Lake Wilderness Area, Mission Mountain Wilderness Area, Red Rock Lakes Wilderness Area, Scapegoat Wilderness Area, Selway-Bitterroot Wilderness Area, UL Bend Wilderness Area). [^20] In its 2022 submission, Montana acknowledges that emissions from in-state sources contribute to visibility impairment at its 12 Class 1 areas. [^21] Montana demonstrated in their 2022 SIP submission that all of their Class I areas are projected to be below the 2028 URP for each area. [^22]
[^20] Montana 2022 SIP submission at 3.
[^21]*Id.* at 91-103.
[^22]*Id.* at 298-305.
Montana also evaluated Class I areas outside the State where visibility may be affected by Montana sources. Using the WRAP's 2028OTBa2 source apportionment modeling Montana identified three Class I areas where the State contributes 0.11 deciviews or greater: Wind Cave (0.12 deciviews, 1.2%); Theodore Roosevelt (0.11 deciviews, 0.8%); and Lostwood (0.11 deciviews; 0.7%) based on combined percentages of nitrate + sulfate impairment at these Class I areas from Montana sources. [^23]
[^23]*Id.* at 291-293, Table 7-5.
All Class I areas in Montana as well as the three out-of-state Class I areas most impacted by Montana sources are projected to be below the adjusted glidepath for 2028. [^24]
[^24]*https://views.cira.colostate.edu/tssv2/Express/ModelingTools.aspx* .
**B. Calculation of Baseline, Current, and Natural Visibility Conditions; Progress to Date; and Uniform Rate of Progress for Class I Areas Within the State**
Section 51.308(f)(1) requires states to determine the following for “each mandatory Class I Federal area located within the State”: baseline visibility conditions for the most impaired and clearest days, natural visibility conditions for the most impaired and clearest days, progress to date for the most impaired and clearest days, the differences between current visibility conditions and natural visibility conditions, and the URP. This section also provides the option for states to propose adjustments to the URP line for a Class I area to account for visibility impacts from anthropogenic sources outside the United States and/or the impacts from wildland prescribed fires that were conducted for certain specified objectives. 40 CFR 51.308(f)(1)(vi)(B).
The IMPROVE monitoring network measures visibility impairment caused by air pollution at Class I areas. Montana's 2022 SIP submission provides visibility conditions for each IMPROVE monitor and associated Class I area in Montana (table 1). [^25]
[^25] Montana 2022 SIP submission at 73-77.
| Monitor ID | Class I areas | Baseline | Period (2008-2012) | Current | Natural (2064) | Progress | Progress | Difference |
| --- | --- | --- | --- | --- | --- | --- | --- | --- |
| | | | | | | | | |
| CABI1 | Cabinet Mountains Wilderness Area | 10.73 | 10.23 | 9.87 | 5.64 | 0.86 | 0.36 | 4.23 |
| GAMO1 | Gates of the Mountains Wilderness Area | 8.95 | 7.74 | 7.47 | 4.53 | 1.48 | 0.27 | 2.94 |
| GLAC1 | Glacier National Park | 15.89 | 14.07 | 13.77 | 6.90 | 2.12 | 0.30 | 6.87 |
| MELA1 | Medicine Lake Wilderness Area | 16.62 | 16.60 | 15.30 | 5.95 | 1.32 | 1.30 | 9.35 |
| MONT1 | Bob Marshall Wilderness Area, Mission Mountain Wilderness Area, Scapegoat Wilderness Area | 11.00 | 10.24 | 10.06 | 5.53 | 0.94 | 0.18 | 4.53 |
| SULA1 | Anaconda-Pintler Wilderness Area, Selway-Bitterroot Wilderness Area | 10.06 | 8.86 | 8.37 | 5.45 | 1.69 | 0.49 | 2.92 |
| ULBE1 | UL Bend Wilderness Area | 12.76 | 12.16 | 10.93 | 5.87 | 1.83 | 1.23 | 5.06 |
| YELL2 | Red Rock Lakes National Wildlife Refuge, Yellowstone National Park | 8.30 | 7.49 | 7.52 | 3.97 | 0.78 | −0.03 | 3.55 |
| | | | | | | | | |
| CABI1 | Cabinet Mountains Wilderness Area | 3.62 | 2.58 | 2.46 | 1.48 | 1.16 | 0.12 | 0.98 |
| GAMO1 | Gates of the Mountains Wilderness Area | 1.71 | 0.75 | 0.66 | 0.32 | 1.05 | 0.09 | 0.34 |
| GLAC1 | Glacier National Park | 7.22 | 5.68 | 5.38 | 2.43 | 1.84 | 0.30 | 2.95 |
| MELA1 | Medicine Lake Wilderness Area | 7.27 | 6.42 | 6.19 | 2.96 | 1.08 | 0.23 | 3.23 |
| MONT1 | Bob Marshall Wilderness Area, Mission Mountain Wilderness Area, Scapegoat Wilderness Area | 3.86 | 2.79 | 2.56 | 1.48 | 1.30 | 0.23 | 1.08 |
| SULA1 | Anaconda-Pintler Wilderness Area, Selway-Bitterroot Wilderness Area | 2.57 | 1.95 | 1.60 | 1.12 | 0.97 | 0.35 | 0.48 |
| ULBE1 | UL Bend Wilderness Area | 4.75 | 4.14 | 3.71 | 2.46 | 1.04 | 0.43 | 1.25 |
| YELL2 | Red Rock Lakes National Wildlife Refuge, Yellowstone National Park | 2.58 | 1.51 | 1.43 | 0.43 | 1.15 | 0.08 | 1.00 |
The State also determined the URP for the most impaired and clearest days for Montana Class I areas. [^26] Montana also provided haze indices and the URP for IMPROVE monitors and associated Class I areas outside the State. [^27]
[^26] Montana 2022 SIP submission at 86-91.
[^27]*Id.* at 86-91.
Based on the information provided in Montana's 2022 SIP submission, the EPA is proposing to approve the State's visibility condition calculations for Cabinet Mountains Wilderness Area, Gates of the Mountains Wilderness Area, Glacier National Park, Medicine Lake Wilderness Area, Bob Marshall Wilderness Area, Mission Mountains Wilderness Area, Scapegoat Wilderness Area, Anaconda-Pintler Wilderness Area, Selway-Bitterroot Wilderness Area, UL Bend Wilderness Area, Red Rock Lakes National Wildlife Refuge, and Yellowstone National Park [^28] as meeting the requirements of 40 CFR 51.308(f)(1) related to the calculation of baseline, current, and natural visibility conditions; progress to date; and the URP.
[^28] Bob Marshall Wilderness Area, Mission Mountains Wilderness Area, and Scapegoat Wilderness Area are subject to the same visibility calculation. Anaconda-Pintler Wilderness Area and Selway-Bitterroot Wilderness Area are subject to the same visibility calculation. Red Rock Lakes National Wildlife Refuge and Yellowstone National Park are subject to the same visibility calculation.
**C. Long-Term Strategy**
Each state having a Class I area within its borders or emissions that may affect visibility in any Class I area outside the state must develop a long-term strategy for making reasonable progress towards the national visibility goal for each impacted Class I area. CAA section 169A(b)(2)(B). As explained in the Background section of this document, reasonable progress is achieved when all states contributing to visibility impairment in a Class I area are implementing the measures determined—through application of the four statutory factors to sources of visibility impairing pollutants—to be necessary to make reasonable progress. 40 CFR 51.308(f)(2)(i). Each state's long-term strategy must include the enforceable emission limitations, compliance schedules, and other measures that are necessary to make reasonable progress. 40 CFR 51.308(f)(2). After considering the four statutory factors, all measures that are determined to be necessary to make reasonable progress must be in the long-term strategy. In developing its long-term strategy, a state must also consider the five additional factors in 40 CFR 51.308(f)(2)(iv). As part of its reasonable progress determinations, the state must describe the criteria used to determine which sources or group of sources were evaluated ( *i.e.,* subject to four-factor analysis) for the second implementation period and how the four factors were taken into consideration in selecting the emission reduction measures for inclusion in the long-term strategy. 40 CFR 51.308(f)(2)(iii).
**1. Montana's Long-Term Strategy Four-Factor Analysis**
**a. Summary of Montana's Long-Term Strategy Four-Factor Analysis**
Under 40 CFR 51.308(f)(2)(i), SIP submittals must include a description of the criteria a state used to determine which sources or groups of sources to evaluate through four-factor analysis. Montana used a Q/d screening approach to identify sources for four-factor analysis. The Q/d screening metric uses a source's annual emissions in tons (Q) divided by the distance in kilometers (d) between the source and the nearest Class I area, along with a reasonably selected threshold for this metric. The larger the Q/d value, the greater the source's expected effect on visibility in each associated Class I area.
Using a WRAP-devised screening threshold of Q/d > 4 and emissions information from the 2014-2017 average annual emissions, Montana identified sources in the State that may be affecting visibility at Class I areas. [^29] Montana first categorized all permitted stationary sources into two groups based on average combined annual NO <sub>X</sub> and SO <sub>2</sub> emissions. [^30] The first group included 24 facilities emitting 100 tons per year or more, which were automatically selected for further evaluation using a Q/d > 4 to represent the point source emissions impacting Class I areas, resulting in 15 selected sources. Montana then applied the Q/d > 4 to the second group of smaller sources, identifying an additional two sources with lower emissions but close proximity to Class 1 areas. In total, Montana selected 17 point sources for four-factor analysis (table 2). <sub>31 32</sub> These 17 point sources contributed approximately 36,620 tons per year of NO <sub>X</sub> and SO <sub>2</sub> emissions, representing about 90% of total emissions from point sources in the state.
[^29] Montana 2022 SIP submission at 161-164, Appendix C.
[^30] Based on emission trend analysis and light extinction budgets, Montana chose to focus the potential additional control analysis on point source emissions of NO <sub>X</sub> and SO <sub>2</sub> only. Montana 2022 SIP submission at 151-152; 160-161.
[^31] Montana 2022 SIP submission at 162-164, Appendix C.
[^32] Montana did not include Colstrip Units 1 and 2 among the sources screened for four-factor analysis because the units were scheduled to close. The EPA finalized the enforceable closures of Colstrip Units 1 and 2 into the SIP in 2023 (88 FR 41320).
| Facility name | Closest Class I area | (d) | (Q) | Q/d |
| --- | --- | --- | --- | --- |
| Weyerhaeuser NR—Columbia Falls Facility | Glacier | 13.3 | 984.36 | 74.01 |
| Talen Montana LLC—Colstrip Steam Electric Station Units #3 and 4 | UL Bend | 198.9 | 12,716.57 | 63.93 |
| Ash Grove Cement Company | Gates of the Mountains | 30.6 | 1,235.11 | 40.36 |
| Montana Dakota Utilities CO—Lewis & Clark Station | Teddy Roosevelt | 51.8 | 1,052.28 | 20.31 |
| GCC Trident, LLC | Yellowstone | 97.4 | 1,488.39 | 15.28 |
| Yellowstone Energy Limited Partnership—Yellowstone Power Plant | Absaroka | 143.8 | 2,136.33 | 14.86 |
| Roseburg Forest Products CO | Selway Bitterroot | 26.6 | 302.61 | 11.38 |
| Colstrip Energy Ltd Partnership | UL Bend | 188.7 | 1,935.61 | 10.26 |
| Montana Sulphur & Chemical CO | Absaroka | 137.5 | 1,310.27 | 9.53 |
| Graymont Western US Inc—Indian Creek Facility | Gates of the Mountains | 57.1 | 524.23 | 9.18 |
| ExxonMobil Fuels & Lubricants Company—ExxonMobil Billings Refinery | Absaroka | 143.7 | 1,034.41 | 7.20 |
| Cenex Harvest States Cooperative Inc—CHS Inc Refinery Laurel | Absaroka | 113.5 | 628.73 | 5.54 |
| F H Stoltze Land & Lumber CO | Glacier | 14 | 75.22 | 5.37 |
| Sidney Sugars Inc—Sidney Sugar Facility | Teddy Roosevelt | 51.9 | 268.79 | 5.18 |
| Phillips 66 CO—Billings Refinery | Absaroka | 143 | 644.92 | 4.51 |
| Weyerhaeuser NR Kalispell—Weyerhaeuser Evergreen Facility | Glacier | 30.5 | 134.32 | 4.40 |
| Northern Border Pipeline CO—N. Border Pipeline CO Station #3 | Medicine Lake | 22.8 | 95.76 | 4.20 |
The State requested that each of the 17 point sources conduct a four-factor analysis that evaluated controls for NO <sub>X</sub> and SO <sub>2</sub> emissions for its review and consideration. [^33] For one of these sources, Montana Dakota Utilities (MDU) Lewis and Clark Station, the State determined that the source's four-factor analysis was no longer relevant because the source had been permanently removed from service prior to the State's finalization of the SIP. [^34] For the remaining sources, Montana then evaluated what is necessary to make reasonable progress by considering the four statutory factors for each source:
[^33] Montana 2022 SIP submission at 166-167; Appendix A.
[^34]*Id.* at 197-198; Appendix D.
• Cost of compliance;
• Time necessary for compliance;
• Energy and non-air quality environmental impacts of compliance; and
• Remaining useful life of any potentially affected sources.
The State documented these analyses in Montana's 2022 SIP submission and associated technical support documents. Chapter 6 of Montana's SIP submission contains Montana's evaluation of the four statutory factors for each source and Montana's determinations of the source-specific emission reduction measures necessary to make reasonable progress. [^35]
[^35]*Id.* at 166-270.
As part of its long-term strategy evaluation of what emission control measures are necessary to make reasonable progress by 2028, Montana considered the previous approved BART determinations and emission limits for J.E. Corette power plant and Colstrip power plant, Unit 1 and 2. [^36] Ultimately, the State concluded that no additional regional haze controls or measures are required of any of the evaluated sources for the long-term strategy measures necessary to make reasonable progress by 2028 during the second implementation period. [^37]
[^36]*Id.* at 280-281; Appendix D.
[^37]*Id.* at 280.
**b. The EPA's Evaluation of Montana's Long-Term Strategy Four-Factor Analysis**
Section 169A(b)(2) of the CAA requires each state in which any Class I area is located or “the emissions from which may reasonably be anticipated to cause or contribute to any impairment of visibility” in a Class I area to have a plan for making reasonable progress toward the national visibility goal. CAA section 169A(g)(1) specifies: “[I]n determining reasonable progress there shall be taken into consideration the costs of compliance, the time necessary for compliance, and the energy and nonair quality environmental impacts of compliance, and the remaining useful life of any existing source subject to such requirements.” [^38] The RHR implements this statutory requirement in 40 CFR 51.308(f) for the second and subsequent planning periods for regional haze. 40 CFR 51.308(f) requires states to submit a long-term strategy that addresses regional haze visibility impairment for each mandatory Class I area within the state and for each mandatory Class I area located outside the state that may be affected by emissions from the state. 40 CFR 51.308(f)(2)(i) lays out the CAA 169A four-factor criteria for the evaluation and development of the long-term strategy.
[^38] We refer to the CAA section 169A(g)(1) requirements as the four factors.
Based on the EPA's review, we find that Montana's 2022 SIP submission satisfies the requirements under 51.308(f)(2)(i) because Montana's selection of 17 point sources, evaluation of the four statutory factors, and determinations of the emission reductions necessary to make reasonable progress as described in section IV.C.1.a. of this document, were reasonable.
With respect to source selection, Montana used the 2014-2017 average annual emissions of NO <sub>X</sub> and SO <sub>2</sub> in tons divided by distance in kilometers between a source and the nearest Class I area as a surrogate for baseline visibility impact. This metric is also known as Q/d. The state then analyzed the 271 permitted stationary sources in the state and relied on its screening protocol, using a Q/d threshold > 4, to evaluate facilities that account for ninety percent of the NO <sub>X</sub> plus SO <sub>2</sub> emissions from the permitted stationary facilities. Applying this protocol, Montana selected 17 point sources for analysis. As previously stated, 40 CFR 51.308(f)(2)(i) requires that a state's SIP submission include a “description of the criteria it used to determine which sources or groups of sources it evaluated,” and it must be appropriately documented, as required by 40 CFR 51.308(f)(2)(iii). Because Montana provided a detailed description of how the State used technical information to select a reasonable set of sources for an analysis of control measures for the second implementation period, we find that Montana's source selection was reasonable and consistent with the requirements of 40 CFR 51.308(f)(2). [^39]
[^39] Montana 2022 SIP submission at 151-166.
Montana submitted four-factor analyses for the selected sources and demonstrated that its determination of declining additional measures necessary for reasonable progress, as part of its long-term strategy, were an outgrowth of its consideration of the four statutory factors in accordance with 40 CFR 51.308(f)(2)(i). [^40] Ultimately, Montana's 2022 SIP submission relied on previously approved and adopted measures. [^41]
[^40]*Id.* at 166-281.
[^41]*Id.* at 296.
The EPA reviewed the State's long-term strategy to address regional haze visibility impairment for each Class I area affected by emissions from the State. The State included in its implementation plan a description of the criteria it used to determine which sources it evaluated and how the four factors were taken into consideration in selecting the measures for inclusion in its long-term strategy including existing emission control measures and compliance schedules that had been previously codified in Montana Board of Environmental Review Orders and 40 CFR 52.1370(d). <sub>42 43</sub> In addition, the projected 2028 visibility conditions for Class I areas both in Montana and those areas influenced by emissions from Montana sources, are all below the 2028 URP. The EPA's recently implemented URP policy is that so long as the Class I areas impacted by a state are below the URP and the State considers the four factors, the State will have presumptively demonstrated it has already made reasonable progress for the second planning period for that area. [^44] Thus, we are concluding that Montana's long-term strategy contains the enforceable emission limitations, compliance schedules, and other measures that are necessary to make reasonable progress.
[^42] Montana Board of Environmental Review Order: In the Matter of an Order Setting Air Pollutant Emission Limits that the State of Montana may Submit to the Federal Environmental Protection Agency for Revision of the State Implementation Plan Concerning Protection of Visibility, Affecting the Following Facilities: Talen Montana, LLC's Colstrip Steam Electric Station, Units 1 and 2, and J.E. Corette Steam Electric Station. Board Order Findings of Fact, Conclusions of Law, and Order. October 18, 2019, Exhibit A.
[^43] 88 FR 41320 (June 26, 2023).
[^44]*See* 90 FR 29737, 29738 (July 7, 2025); 90 FR 20425, 20434 (May 14, 2025).
Because the State evaluated and determined the emission reduction measures that are necessary to make reasonable progress by considering the costs of compliance, the time necessary for compliance, the energy and non-air quality environmental impacts of compliance, and the remaining useful life of the sources selected as is required under 40 CFR 51.308(f)(2)(i), and the projected 2028 visibility conditions for Class I areas influenced by emissions from Montana sources are all below the URP, we find that Montana's determination of the emission reduction measures that are necessary to make reasonable progress was reasonable and consistent with the requirements of 40 CFR 51.308(f)(2)(i).
**2. Other Long-Term Strategy Requirements**
States must meet the additional requirements specified in 40 CFR 51.308(f)(2)(ii)-(iv) when developing their long-term strategies. 40 CFR 51.308(f)(2)(ii) requires states to consult with other states that have emissions that are reasonably anticipated to contribute to visibility impairment in Class I areas to develop coordinated emission management strategies. Specifically, 40 CFR 51.308(f)(2)(ii)(A) requires a state to demonstrate that its SIP includes all measures agreed upon during the state-to-state consultations. Montana considered facilities affecting out of state Class I areas for additional controls through a four-factor analysis and determined that no additional controls on Montana sources will be required at this time. The states consulted agreed with Montana's conclusion. 40 CFR 51.308(f)(ii)(B) requires a state to consider emission reduction measures identified by other states as being necessary to make reasonable progress in a Class I area. Montana did not receive recommendations for any of the sources within the State from other states. Chapter 7.2 of Montana's 2022 SIP submission describes Montana's consultation with other states throughout the development of its regional haze plan. [^45]
[^45] Montana 2022 SIP submission at 293-296.
40 CFR 51.308(f)(2)(iii) requires states to document the technical basis, including modeling, monitoring, costs, engineering, and emissions information, on which the state is relying to determine the emission reduction measures that are necessary to make reasonable progress in each mandatory Class I area it impacts. Montana relied on WRAP technical information, modeling, and analysis to support development of its long-term strategy. [^46]
[^46]*Id.* at 31-43.
40 CFR 51.308(f)(2)(iv) specifies five additional factors states must consider in developing their long-term strategies. The five additional factors are: emission reductions due to ongoing air pollution control programs, including measures to address reasonably attributable visibility impairment; measures to mitigate the impacts of construction activities; source retirement and replacement schedules; basic smoke management practices for prescribed fire used for agricultural and wildland vegetation management purposes and smoke management programs; and the anticipated net effect on visibility due to projected changes in point, area, and mobile source emissions over the period addressed by the long-term strategy.
Chapter 7.1 of Montana's 2022 SIP submission describes each of the five additional factors it is required to consider under 40 CFR 51.308(f)(2)(iv) and explains how it considered them. [^47] Pursuant to 40 CFR 51.308(f)(2)(iv)(A), Montana detailed the existing and ongoing State and Federal emission control programs that contribute to emission reductions, including the designation status for all current and former non-attainment areas. [^48] Montana's Airborne Particulate Matter rule in Administrative Rules of Montana (ARM) 17.8.308 mitigates the impacts of construction activities as required by 40 CFR 51.308(f)(2)(iv)(B). [^49] Pursuant to 40 CFR 51.308(f)(2)(iv)(C), source retirement schedules are found in table 7-2 of the Montana 2022 SIP submission as well as in a board order codified in 40 CFR 52.1370(d). [^50] In considering smoke management as required in 40 CFR 51.308(f)(2)(iv)(D), Montana explained that it addresses smoke management through its EPA-approved Smoke Management Program [^51] as well as Best Available Control Technology requirements for burners found in ARM 17.8.601 which limits smoke impacts due to burning. <sup>52</sup> Montana considered the anticipated net effect of projected changes in emissions on visibility due to projected changes in point, area and mobile source emissions as required by 40 CFR 51.308(f)(2)(iv)(E) in tables 8-2 and 8-4 of the State's 2022 SIP submission. [^53]
[^47]*Id.* at 271-281.
[^48]*Id.* at 271-277.
[^49]*Id.* at 278.
[^50] Montana 2022 SIP submission at 278-281; Montana Board of Environmental Review Orders.
[^51] Consistent with the EPA's *Interim Air Quality Policy on Wildland Prescribed Fire, May 1998.*
[^52] Montana 2022 SIP submission at 281.
[^53]*Id.* at 297-299.
After reviewing Montana's 2022 SIP chapters addressing 40 CFR 51.308(f)(2)(ii)-(iv), the EPA finds that Montana has satisfied these additional long-term strategy requirements of 40 CFR 51.308(f)(2)(ii)-(iv).
**D. Reasonable Progress Goals**
Section 51.308(f)(3)(i) requires a state in which a Class I area is located to establish RPGs—one each for the most impaired and clearest days—reflecting the visibility conditions that will be achieved at the end of the implementation period as a result of the emission limitations, compliance schedules and other measures required under paragraph (f)(2) in states' long-term strategies, as well as implementation of other CAA requirements.
After establishing its long-term strategy, Montana developed reasonable progress goals for each Class I area for the 20% most impaired days and 20% clearest days based on the results of 2028 WRAP modeling (table 3). [^54]
[^54] Montana 2022 SIP submission at 298-299.
| Class I area | 20% Most impaired days | Average | 2028 | 2028 | 20% Clearest days | Average | 2028 |
| --- | --- | --- | --- | --- | --- | --- | --- |
| | Deciviews | | | | | | |
| Anaconda-Pintler Wilderness Area, Selway-Bitterroot Wilderness Area (SULA1) | 10.06 | 9.12 | 8.01 | 2.57 | 1.51 | | |
| Bob Marshall Wilderness Area, Mission Mountains Wilderness Area, Scapegoat Wilderness Area (MONT1) | 11 | 10.02 | 9.51 | 3.86 | 2.33 | | |
| Cabinet Mountains Wilderness Area (CABI1) | 10.73 | 10.36 | 9.41 | 3.62 | 2.21 | | |
| Gates of the Mountains Wilderness Area (GAMO1) | 8.95 | 8.31 | 7.12 | 1.71 | 0.53 | | |
| Glacier National Park (GLAC1) | 15.89 | 13.78 | 12.92 | 7.22 | 5.10 | | |
| Medicine Lake Wilderness Area (MELA1) | 16.62 | 14.92 | 14.85 | 7.27 | 6.12 | | |
| Red Rock Lakes National Wildlife Refuge, Yellowstone National Park (YELL2) | 8.3 | 7.26 | 6.97 | 2.58 | 1.21 | | |
| UL Bend Wilderness Area (ULBE1) | 12.76 | 12.05 | 10.62 | 4.75 | 3.58 | | |
The reasonable progress goals are based on Montana's long-term strategy, the long-term strategy of other states that may affect Class I areas in Montana, and other CAA requirements. In accordance with 51.308(f)(3)(ii)(A)-(B), if the RPG in 2028 for the most impaired days is above the URP ( *i.e.,* if visibility conditions are improving more slowly than the rate described by the URP), each state that contributes to visibility impairment in the Class I area must demonstrate, based on the four-factor analysis required under 40 CFR 51.308(f)(2)(i), that no additional emission reduction measures would be reasonable to include in its long-term strategy. [^55] Because Montana demonstrated in their 2022 SIP submission that all of their Class I areas are projected to be below the 2028 URP, no additional requirements apply under 40 CFR 51.308(f)(3)(ii). [^56]
[^55] 40 CFR 51.308(f)(3)(ii).
[^56] Montana 2022 SIP submission at 298-305.
Per 40 CFR 51.308(f)(3)(iv), the EPA must evaluate the demonstrations the State developed pursuant to 40 CFR 51.308(f)(2) to determine whether the State's reasonable progress goals for visibility improvement provide for reasonable progress towards natural visibility conditions. As previously explained in section IV.C., we are proposing to approve Montana's long-term strategy for meeting the requirements of 40 CFR 51.308(f)(2) to meet the national goal of preventing future as well as existing visibility impairment due to manmade sources. Montana's reasonable progress goals incorporate Montana's long-term strategy requirements. Thus, we find that Montana's reasonable progress goals provide for an improvement in visibility for the most-impaired days since the baseline period and ensure no degradation in visibility on the clearest days since the baseline period. [^57] Therefore, we propose to approve Montana's reasonable progress goals under 40 CFR 51.308(f)(3).
[^57]*Id.* at 297.
**E. Reasonably Attributable Visibility Impairment (RAVI)**
The RHR contains a requirement at 40 CFR 51.308(f)(4) related to any additional monitoring that may be needed to address visibility impairment in Class I areas from a single source or a small group of sources. This is called “reasonably attributable visibility impairment,” [^58] also known as RAVI. Under this provision, if the EPA or the FLM of an affected Class I area has advised a state that additional monitoring is needed to assess RAVI, the state must include in its SIP revision for the second implementation period an appropriate strategy for evaluating such impairment. The EPA has not advised the State to that effect; nor did the State indicate that FLMs for Class I areas identified any RAVI from Montana sources. For this reason, the EPA proposes to approve the portions of Montana's 2022 SIP submission relating to 40 CFR 51.308(f)(4).
[^58] The EPA's visibility protection regulations define “reasonably attributable visibility impairment” as “visibility impairment that is caused by the emission of air pollutants from one, or a small number of sources.” 40 CFR 51.301.
**F. Monitoring Strategy and Other State Implementation Plan Requirements**
Section 51.308(f)(6) specifies that each comprehensive revision of a state's regional haze SIP must contain or provide for certain elements, including monitoring strategies, emissions inventories, and any reporting, recordkeeping and other measures needed to assess and report on visibility. A main requirement of this section is for states with Class I areas to submit monitoring strategies for measuring, characterizing, and reporting on visibility impairment. Compliance with this requirement may be met through participation in the IMPROVE network.
Under 40 CFR 51.308(f)(6)(i), states must provide for the establishment of additional monitoring sites or equipment needed to assess whether reasonable progress goals to address regional haze for all mandatory Class I Federal areas within the state are being achieved. For states with Class I areas (including Montana), § 51.308(f)(6)(ii) requires SIPs to provide for procedures by which monitoring data and other information are used in determining the contribution of emissions from within the state to regional haze visibility impairment at mandatory Class I Federal areas both within and outside the state. Section 51.308(f)(6)(iv) requires the SIP to provide for the reporting of all visibility monitoring data to the Administrator at least annually for each Class I area in the state. 40 CFR 51.308(f)(6)(v) requires SIPs to provide for a statewide inventory of emissions of pollutants that are reasonably anticipated to cause or contribute to visibility impairment, including emissions for the most recent year for which data are available. Section 51.308(f)(6)(v) also requires states to include estimates of future projected emissions. Finally, 40 CFR 51.308(f)(6)(vi) requires the SIP to provide for any other elements, including reporting, recordkeeping, and other measures, that are necessary for states to assess and report on visibility.
Montana describes its participation in the IMPROVE network, which comprises 110 monitoring sites across the nation, eight of which are in Montana. The State relied on the IMPROVE monitoring network to assess visibility at Class I areas across Montana [^59] and considered the ten monitoring sites CABI1, GAMO1, GLAC1, MELA1, MONT1, NOAB1, SULA1, THRO1, ULBE1, and YELL2 to be adequate for assessing reasonable progress goals at the State's 12 Class I areas. [^60] Using the monitoring data procedures described in its 2022 SIP submission along with other technical information supplied by WRAP, <sub>61 62</sub> Montana determined the contribution of in-State emissions to Class I areas inside and outside Montana. [^63] In addition, Montana also provided a statewide inventory of emissions that are reasonably anticipated to cause or contribute to visibility impairment in Class I areas; Montana relied primarily on 2014-2017 data but also estimated future projected emissions. [^64]
[^59] Montana 2022 SIP submission at 18-27.
[^60]*Id.* at 21.
[^61]*Id.* at 33-43.
[^62] Montana relied on the WRAP Technical Support System (TSS) “Analysis and Planning” section to determine baseline, natural, and current conditions for Class I areas in Montana. *https://views.cira.colostate.edu/tssv2/.*
[^63] Montana 2022 SIP submission at 282-296.
[^64]*Id.* at 126-150.
The EPA finds that Montana has met the requirements of 40 CFR 51.308(f)(6), including through its continued participation in the IMPROVE network and WRAP RPO and its ongoing compliance with the Air Emissions Reporting Requirements (AERR). There is no indication that further SIP elements are necessary at this time for Montana to assess and report on visibility. Therefore, the EPA proposes to approve the monitoring strategy and other state implementation plan elements of Montana's 2022 SIP submission as meeting the requirements of 40 CFR 51.308(f)(6).
**G. Requirements for Periodic Reports Describing Progress Towards the Reasonable Progress Goals**
40 CFR 51.308(f)(5) requires that periodic comprehensive revisions of states' regional haze plans also address the progress report requirements of 40 CFR 51.308(g)(1) through (5). The purpose of these requirements is to evaluate progress towards the applicable RPGs for each Class I area within the state and each Class I area outside the state that may be affected by emissions from within that state. Sections 51.308(g)(1) and (2) apply to all states and require a description of the status of implementation of all measures included in a state's first implementation period regional haze plan and a summary of the emission reductions achieved through implementation of those measures. Section 51.308(g)(3) applies only to states with Class I areas within their borders and requires such states to assess current visibility conditions, changes in visibility relative to baseline (2000-2004) visibility conditions, and changes in visibility conditions relative to the period addressed in the first implementation period progress report. Section 51.308(g)(4) applies to all states and requires an analysis tracking changes in emissions of pollutants contributing to visibility impairment from all sources and sectors since the period addressed by the first implementation period progress report. This provision further specifies the year or years through which the analysis must extend depending on the type of source and the platform through which its emission information is reported. Finally, 40 CFR 51.308(g)(5), which also applies to all states, requires an assessment of any significant changes in anthropogenic emissions within or outside the state that have occurred since the period addressed by the first implementation period progress report, including whether such changes were anticipated and whether they have limited or impeded expected progress towards reducing emissions and improving visibility.
In its 2022 SIP submission, Montana included the elements of the periodic progress report specified in 40 CFR 51.308(f)(5) and 40 CFR 51.308(g)(1)-(5). Montana summarized the facility improvements made during and after the first implementation period, including emission control measures installed and emission reductions achieved by the facilities that most affected each Class I area, and summarized the associated emission reductions. [^65] In addition, the State summarized the implementation status of ongoing air pollution control programs, measures to mitigate construction activities, source retirement and replacement schedules, and smoke management practices and programs. [^66] The EPA finds that Montana has met the requirements of 40 CFR 51.308(g)(1) and (2) because Montana's 2022 SIP submission describes the measures included in the long-term strategy from the first implementation period, as well as the status of their implementation and the emission reductions achieved through such implementation.
[^65]*Id.* at 47-52.
[^66]*Id.* at 54-55; 130-132.
Visibility conditions (in deciviews) are reported in Montana's 2022 SIP submission for the most impaired and clearest days. Visibility conditions are expressed in terms of 5-year averages for the baseline period (2000-2004), “natural visibility conditions” for the 2000-2014 period, previous implementation period (2008-2012), and current period (2014-2018), as well as the progress made since the baseline period ((2000-2004)-(2008-2012)) and during the last implementation period ((2008-2012)-(2014-2018)). [^67] The EPA therefore finds that Montana has satisfied the requirements of 40 CFR 51.308(g)(3).
[^67]*Id.* at 73-77.
The State used the most current emissions inventory available—the 2017 national emissions inventory—to provide emissions inventories for NO <sub>X</sub> , SO <sub>2</sub> , VOC, ammonia (NH <sub>3</sub> ), and PM that identify the type of source, activity, and pollutant. [^68] Montana also provided an assessment and discussion of the significant changes in anthropogenic emissions since the first implementation period. [^69] The EPA finds that the requirements of 40 CFR 51.308(g)(4) and (g)(5) are satisfied by providing emissions of pollutants contributing to visibility impairment within the State and assessing any significant changes in anthropogenic emissions within or outside the State that have occurred since the period addressed in the most recent plan.
[^68]*Id.* at 127-136.
[^69]*Id.* at 63-67.
Because Montana's 2022 SIP submission addresses the requirements of 40 CFR 51.308(g)(1) through (5), the EPA finds that Montana has met the progress report requirements of 40 CFR 51.308(f)(5). Therefore, we propose to approve Montana's 2022 SIP submission as meeting the requirements of 40 CFR 51.308(f)(5) and 40 CFR 51.308(g) for periodic progress reports.
**H. Requirements for State and Federal Land Manager Coordination**
Section 169A(d) of the CAA requires states to consult with FLMs before holding the public hearing on a proposed regional haze SIP, and to include a summary of the FLMs' conclusions and recommendations in the notice to the public. In addition, the 40 CFR 51.308(i)(2) FLM consultation provision requires a state to provide FLMs with an opportunity for consultation that is early enough in the state's policy analyses of its emission reduction obligation so that information and recommendations provided by the FLMs can meaningfully inform the state's decisions on its long-term strategy. If the consultation has taken place at least 120 days before a public hearing or public comment period, the opportunity for consultation will be deemed early enough. Regardless, the opportunity for consultation must be provided at least 60 days before a public hearing or public comment period at the state level. Section 51.308(i)(2) also lists two substantive topics on which FLMs must be provided an opportunity to discuss with states: assessment of visibility impairment in any Class I area and recommendations on the development and implementation of strategies to address visibility impairment. Section 51.308(i)(3) requires states, in developing their implementation plans, to include a description of how they addressed FLMs' comments.
Montana's 2022 SIP submission summarizes the State's consultation and coordination with the FLMs. Montana consulted and coordinated with the FLMs during the development of its regional haze SIP through WRAP participation and direct FLM engagement. [^70] On September 27, 2021, Montana submitted the State's draft regional haze plan to the FLMs for consultation and received comments thereafter. Montana subsequently analyzed the FLMs comments, modified the draft regional haze plan, summarized and responded to each comment, and included the information in an appendix to its SIP submission which was made available for public comment. [^71] The State explained how it is committed to coordinating and consulting with the FLMs during the development of future progress reports and SIP submissions, as well as during the implementation of programs having the potential to contribute to visibility impairment in Class I areas. [^72]
[^70]*Id.* at 30, 44.
[^71]*Id.* at appendix F, I.
[^72]*Id.* at 306.
Montana took administrative steps to provide the FLMs the opportunity to review and provide feedback on the State's draft regional haze plan. Therefore, the EPA proposes to approve the FLM consultation component of Montana's SIP submission which meets the requirements of 40 CFR 51.308(i) and CAA 169A(d), as outlined in this section.
**V. Interstate Transport Prong 4 (Visibility) for the 2015 Ozone NAAQS Infrastructure SIP**
**A. Background on Infrastructure SIPs**
Under CAA sections 110(a)(1) and 110(a)(2), each state is required to submit a SIP that provides for the implementation, maintenance, and enforcement of each primary or secondary NAAQS. Moreover, CAA sections 110(a)(1) and 110(a)(2) require each state to make this new SIP submission within three years (or less, if the Administrator so prescribes) after promulgation of a new or revised NAAQS. This type of SIP submission is commonly referred to as an “infrastructure SIP.” The overall purpose of the infrastructure SIP requirements is to ensure that the necessary structural components of each state's air quality management program are adequate to meet the state's responsibilities for the new or revised NAAQS. Overall, the infrastructure SIP submission process provides an opportunity for the responsible air agency, the public, and the EPA to review the basic structural requirements of the air agency's air quality management program in light of each new or revised NAAQS.
CAA section 110(a)(2)(D) has two components: 110(a)(2)(D)(i) and 110(a)(2)(D)(ii). CAA section 110(a)(2)(D)(i) includes four distinct components, commonly referred to as “prongs,” that must be addressed in infrastructure SIP submissions. The first two prongs, which are codified in CAA section 110(a)(2)(D)(i)(I), prohibit any source or other type of emissions activity in one state from contributing significantly to nonattainment of the NAAQS in another state (prong 1) and from interfering with maintenance of the NAAQS in another state (prong 2). The third and fourth prongs, which are codified in CAA section 110(a)(2)(D)(i)(II), prohibit emissions activity in one state from interfering with measures required to prevent significant deterioration of air quality in another state (prong 3) or from interfering with measures to protect visibility in another state (prong 4).
**B. Prong 4 Requirements**
CAA section 110(a)(2)(D)(i)(II) requires SIPs to contain provisions prohibiting sources in a state from emitting pollutants in amounts that interfere with any other state's efforts to protect visibility under part C of the CAA (which includes sections 169A and 169B). The EPA issued guidance on infrastructure SIPs in a September 13, 2013 memorandum from Stephen D. Page titled “Guidance on Infrastructure State Implementation Plan (SIP) Elements under Clean Air Act sections 110(a)(1) and 110(a)(2)” (“2013 Guidance”). The 2013 Guidance states that these prong 4 requirements can be satisfied by approved SIP provisions that the EPA has found to adequately address any contribution of that state's sources that impact the visibility program requirements in other states. [^73] The 2013 Guidance also states that “[t]he EPA interprets this prong to be pollutant-specific, such that the infrastructure SIP submission need only address the potential for interference with protection of visibility caused by the pollutant (including precursors) to which the new or revised NAAQS applies.” [^74]
[^73] 2013 Guidance at 32-33.
[^74]*Id.* at 33.
The 2013 Guidance lays out how a state's infrastructure SIP may satisfy prong 4. In the second implementation period, confirmation that the state has a fully approved regional haze SIP that fully meets the requirements of 40 CFR 51.308 or 51.309 will satisfy the requirements of prong 4. [^75] The regulations at 40 CFR 51.308 and 51.309 “specifically require that a state participating in a regional planning process include all measures needed to achieve its apportionment of emission reduction obligations agreed upon through that process.” [^76] A fully approved regional haze SIP [^77] will ensure that emissions from sources under an air agency's jurisdiction are not interfering with measures required to be included in other air agencies' plans to protect visibility.
[^75] The EPA acknowledges that in the 2013 Guidance, we indicated that the EPA may find it appropriate to supplement the guidance regarding the relationship between regional haze SIPs and prong 4 after second implementation period SIPs become due, which occurred on July 31, 2021. After a review of the 2013 Guidance and the second implementation period regional haze requirements, the EPA maintains the interpretation that a fully approved regional haze SIP satisfies prong 4 requirements in the second implementation period.
[^76] 2013 Guidance at 33.
[^77] Since second implementation period SIPs became due, a “fully approved regional haze SIP” would necessarily include fully approved first and second implementation period regional haze SIPs.
On October 26, 2015, the EPA revised the 8-hour ozone NAAQS to 70 parts per billion. [^78] States were required to submit infrastructure SIPs within three years of promulgation of the revised NAAQS. On October 1, 2018, Montana submitted an infrastructure SIP to address the CAA section 110(a)(1) and (2) requirements for the 2015 ozone NAAQS (hereafter “2018 Infrastructure SIP”). Through this action, the EPA is proposing to approve the prong 4 portion of Montana's 2018 Infrastructure SIP submission. All other applicable infrastructure SIP requirements for this submission have been or will be addressed in separate rulemakings. [^79]
[^78] 80 FR 65929 (October 26, 2015).
[^79] 87 FR 21578 (April 12, 2022), 90 FR 31911 (July 16, 2025).
**C. Montana's Infrastructure SIP Submission**
To satisfy the prong 4 requirements for the 2015 ozone NAAQS, Montana's 2018 Infrastructure SIP points to their Visibility Plan, and to the EPA's FIP for the first planning period. [^80] Montana's 2018 Infrastructure SIP cites language from the EPA's 2013 Guidance which stated that a FIP could not be relied upon to meet the requirements of element 110(a)(2)(D)(i)(II) related to visibility. [^81] However, subsequent to Montana's 2018 Infrastructure SIP submission, Montana submitted a SIP revision addressing regional haze for the first implementation period to replace portions of EPA's FIP on March 25, 2020. The EPA approved Montana's 2020 SIP submission on June 26, 2023. [^82] As will be discussed further in the following section, the EPA is proposing to find that the first implementation period requirements are covered by the EPA's approval of Montana's March 25, 2020 SIP revision.
[^80] 77 FR 57864 (September 18, 2012).
[^81] Montana's 2018 Infrastructure SIP at 22.
[^82] 88 FR 41320 (June 26, 2023).
**D. The EPA's Evaluation of Montana's Infrastructure SIP Submission**
With this action, the EPA is proposing to approve Montana's 2022 SIP Submission addressing the regional haze requirements for the second implementation period. Regarding the first implementation period, the EPA is proposing to find that Montana's SIP is fully approved for the purposes of meeting the prong 4 requirements. Because Montana's March 25, 2020 SIP submission replaced all of the enforceable requirements from the 2012 FIP, the entire FIP as previously codified at 40 CFR 52.1396 [^83] was removed. [^84] Specifically, the EPA stated in our June 26, 2023 final approval of Montana's 2020 SIP revision that we were “approving the emission limits, compliance determination requirements, and other monitoring, reporting, and recordkeeping requirements associated with BART into Montana's SIP,” but that “other regional haze requirements for the first implementation period, including requirements related to reasonable progress and analytical requirements related to BART remain satisfied by EPA's FIP (with no enforceable FIP requirements left in the CFR).” [^85] Although the FIP previously satisfied certain BART-related requirements for the first implementation period, the EPA finds that the final 2023 full approval of all of the enforceable first implementation period requirements into the Montana SIP represents a fully approved regional haze SIP for that period that “will ensure that emissions from sources under an air agency's jurisdiction are not interfering with measures required to be included in other air agencies' plans to protect visibility.” [^86] For these reasons, the EPA is also proposing to find that Montana's SIP fulfills the prong 4 requirement for the 2015 ozone NAAQS, and thus proposes to approve this portion of Montana's 2018 Infrastructure SIP.
[^83] 77 FR 57915-57919 (September 18, 2012)
[^84] 88 FR 41326 (June 26, 2023).
[^85] 88 FR 41322 (June 26, 2023).
[^86] 2013 Guidance at 33.
**VI. Proposed Action**
The EPA is proposing approval of Montana's 2022 SIP submission addressing the requirements of the second implementation period of the RHR. Specifically, the EPA is proposing approval for the portions of Montana's 2022 SIP submission relating to 40 CFR 51.308(f)(1): calculations of baseline, current, and natural visibility conditions, progress to date, and the uniform rate of progress; 40 CFR 51.308(f)(2): long-term strategy; 40 CFR 51.308(f)(3): reasonable progress goals; 40 CFR 51.308(f)(4): reasonably attributable visibility impairment; 40 CFR 51.308(f)(5) and 40 CFR 51.308(g): progress report requirements; 40 CFR 51.308(f)(6): monitoring strategy and other implementation plan requirements; and 40 CFR 51.308(i): FLM consultation. The EPA is also proposing approval of the CAA section 110(a)(2)(D)(i) prong 4 (visibility) portion of Montana's October 1, 2018 Infrastructure SIP submission addressing the 2015 ozone NAAQS.
**VII. Statutory and Executive Order Reviews**
Under the CAA, the Administrator is required to approve a SIP submission that complies with the provisions of the CAA and applicable Federal regulations. 42 U.S.C. 7410(k); 40 CFR 52.02(a). Thus, in reviewing SIP submissions, the EPA's role is to approve state choices, provided that they meet the criteria of the CAA. Accordingly, this action merely proposes to approve state law as meeting Federal requirements and does not impose additional requirements beyond those imposed by state law. For that reason, this action:
• Is not a significant regulatory action subject to review by the Office of Management and Budget under Executive Order 12866 (58 FR 51735, October 4, 1993);
• Is not subject to Executive Order 14192 (90 FR 9065, February 6, 2025) because SIP actions are exempt from review under Executive Order 12866;
• Does not impose an information collection burden under the provisions of the Paperwork Reduction Act (44 U.S.C. 3501 *et seq.* );
• Is certified as not having a significant economic impact on a substantial number of small entities under the Regulatory Flexibility Act (5 U.S.C. 601 *et seq.* );
• Does not contain any unfunded mandate or significantly or uniquely affect small governments, as described in the Unfunded Mandates Reform Act of 1995 (Pub. L. 104-4);
• Does not have federalism implications as specified in Executive Order 13132 (64 FR 43255, August 10, 1999);
• Is not subject to Executive Order 13045 (62 FR 19885, April 23, 1997) because it approves a state program;
• Is not a significant regulatory action subject to Executive Order 13211 (66 FR 28355, May 22, 2001); and
• Is not subject to requirements of section 12(d) of the National Technology Transfer and Advancement Act of 1995 (15 U.S.C. 272 note) because application of those requirements would be inconsistent with the CAA.
In addition, the SIP is not approved to apply on any Indian reservation land or in any other area where the EPA or an Indian Tribe has demonstrated that a Tribe has jurisdiction. In those areas of Indian country, the rule does not have Tribal implications and will not impose substantial direct costs on Tribal governments or preempt Tribal law as specified by Executive Order 13175 (65 FR 67249, November 9, 2000).
**List of Subjects in 40 CFR Part 52**
Environmental protection, Air pollution control, Carbon monoxide, Greenhouse gases, Incorporation by reference, Intergovernmental relations, Lead, Nitrogen dioxide, Ozone, Particulate matter, Reporting and recordkeeping requirements, Sulfur oxides, Volatile organic compounds.
**Authority:**
42 U.S.C. 7401 *et seq.*
Dated: August 28, 2025.
Cyrus M. Western,
Regional Administrator, Region 8.
For the reasons stated in the preamble, the Environmental Protection Agency proposes to amend 40 CFR part 52 as follows:
**PART 52—APPROVAL AND PROMULGATION OF IMPLEMENTATION PLANS**
1. The authority citation for part 52 continues to read as follows:
**Authority:**
42 U.S.C. 7401 *et seq.*
**Subpart BB—Montana**
2. In § 52.1370:
a. In the table in paragraph (e):
i. Under the center heading “(1) Statewide”, add the entries “Montana Regional Haze State Implementation Plan” and “Interstate Transport Requirements of the CAA, section 110(a)(2)(D)(i)(II) prong 4, for the 2015 Ozone NAAQS” after the entry “Interstate Transport Requirements of the CAA, section 110(a)(2)(D)(i)(I), for the 2015 Ozone NAAQS” to read as follows:
§ 52.1370
(e) * * *
| Title/subject | State | Notice of final rule date | NFR citation |
| --- | --- | --- | --- |
| | | | |
| | | | |
| * * * * * * * | | | |
| Montana Regional Haze State Implementation Plan | 8/10/2022 | [date of publication of the final rule in the
] | 90 FR [
page where the document begins of the final rule]. |
| Interstate Transport Requirements of the CAA, section 110(a)(2)(D)(i)(II) prong 4, for the 2015 Ozone NAAQS | 8/22/2018 | [date of publication of the final rule in the
] | 90 FR [
page where the document begins of the final rule]. |
| | | | |
| * * * * * * * | | | |