AGENCY:

Environmental Protection Agency (EPA).

ACTION:

Proposed rule.

SUMMARY:

The Environmental Protection Agency (EPA) is proposing to approve State Implementation Plan (SIP) submissions from the State of Utah regarding certain interstate transport requirements of the Clean Air Act (CAA or “Act”). These submissions respond to the EPA's promulgation of the 2010 nitrogen dioxide (NO₂) national ambient air quality standards (NAAQS), the 2010 sulfur dioxide (SO₂) NAAQS, and the 2012 fine particulate matter (PM_2.5) NAAQS. The submissions address the requirement that each SIP contain adequate provisions prohibiting air emissions that will significantly contribute to nonattainment or interfere with maintenance of these NAAQS in any other state.

DATES:

Written comments must be received on or before July 22, 2019.

ADDRESSES:

Submit your comments, identified by Docket ID No. EPA-R08-OAR-2019-0180, 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 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 http://www2.epa.gov/​dockets/​commenting-epa-dockets.

Docket: All documents in the docket are listed in the 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 either electronically in www.regulations.gov or in hard copy at the Air and Radiation Division, Environmental Protection Agency (EPA), Region 8, 1595 Wynkoop Street, Denver, Colorado 80202-1129. The EPA requests that if at all possible, you contact the individual listed in the FOR FURTHER INFORMATION CONTACT section to view the hard copy of the docket. You may view the hard copy of the docket Monday through Friday, 8:00 a.m. to 4:00 p.m., excluding federal holidays.

FOR FURTHER INFORMATION CONTACT:

Adam Clark, Air Quality Planning Branch, EPA, Region 8, Mailcode 8ARD-QP, 1595 Wynkoop Street, Denver, Colorado 80202-1129, (303) 312-7104, clark.adam@epa.gov.

SUPPLEMENTARY INFORMATION:

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

Table of Contents

I. Background

A. Interstate Transport

B. Utah's Submissions

II. Interstate Transport Evaluation

A. Evaluation for the 2010 1-Hour NO₂ NAAQS

1. EPA's General Approach to Evaluating the 2010 NO₂ NAAQS

2. State's Submission

3. EPA's Analysis

B. Evaluation for the 2010 1-Hour SO₂ NAAQS

1. EPA's General Approach to Evaluating the 2010 SO₂ NAAQS

2. State's Submission

3. EPA's Analysis

C. Evaluation for the 2012 Annual PM_2.5 NAAQS

1. EPA's General Approach to Evaluating the 2012 PM_2.5 NAAQS

2. State's Submission

3. EPA's Analysis

III. Proposed Action

IV. Statutory and Executive Order Reviews

I. Background

Section 110(a)(1) of the CAA requires states to submit SIPs meeting the applicable requirements of section 110(a)(2) within 3 years after promulgation of a new or revised NAAQS or within such shorter period as the EPA may prescribe. Section 110(a)(2) requires states to address structural SIP elements such as requirements for monitoring, basic program requirements, and legal authority that are designed to provide for implementation, maintenance, and enforcement of the NAAQS. The EPA refers to the SIP submissions required by these provisions as “infrastructure SIPs.” Section 110(a) imposes the obligation upon states to make an infrastructure SIP submission to the EPA for a new or revised NAAQS, but the contents of individual state submissions may vary depending upon the facts and circumstances. This proposed rule pertains to the infrastructure SIP requirements for interstate transport of air pollution.

A. Interstate Transport

Section 110(a)(2)(D)(i) of the CAA requires SIPs to include provisions prohibiting any source or other type of emissions activity in one state from emitting any air pollutant in amounts that will contribute significantly to nonattainment, or interfere with maintenance, of the NAAQS, or interfere with measures required to prevent significant deterioration of air quality or to protect visibility in any other state. This proposed rule addresses the two requirements under section 110(a)(2)(D)(i)(I), which we refer to as prong 1 (significant contribution to nonattainment of the NAAQS in any other state) and prong 2 (interference with maintenance of the NAAQS in any other state).^[1] The EPA often refers to SIP revisions addressing the requirements of section 110(a)(2)(D)(i)(I) as “interstate transport SIPs.”

The EPA evaluates each state's interstate transport SIP to see how the state evaluates the transport of air pollution to other states for a given air pollutant; what types of information the state used in its analysis; how that analysis compares with prior EPA rulemakings, modeling, monitoring, and guidance; and what conclusions were drawn by the state. If the EPA concludes that the SIP contains adequate provisions to prohibit sources from emitting air pollutants that significantly contribute to nonattainment, or interfere with maintenance, of a given NAAQS in any other state, we will approve the state's submission with regard to prongs 1 and 2 of CAA section 110(a)(2)(D)(i)(I).

Each of the following NAAQS revisions triggered the requirement for states to submit infrastructure SIPs, including provisions to address interstate transport prongs 1 and 2. On January 22, 2010, the EPA promulgated a new 1-hour primary NAAQS for NO₂ at a level of 100 parts per billion (ppb) while retaining the annual standard of 53 ppb.^[2] On June 2, 2010, the EPA promulgated a new primary 1-hour SO₂ standard of 75 ppb and retained the secondary 3-hour standard of 0.5 parts per million (ppm).^[3] Finally, on December 14, 2012, the EPA revised the primary annual PM_2.5 standard by lowering the level to 12.0 micrograms per cubic meter (μg/m^[3] ) and retained the secondary annual PM_2.5 standard of 15.0 µg/m^[3] and the primary and secondary 24-hour PM_2.5 standards of 35 μg/m^[3] .^[4]

As discussed further in this notice, the EPA proposes to determine that Utah's SIP contains adequate provisions to prohibit sources from emitting air pollutants in amounts that significantly contribute to nonattainment or interfere with maintenance of the 2010 NO₂, 2010 SO₂ and 2012 PM_2.5 NAAQS.

B. Utah's Submissions

The State of Utah submitted infrastructure SIPs for the 2010 NO₂ NAAQS on January 31, 2013, and for the 2010 SO₂ NAAQS on June 2, 2013. In both of these submissions, the State addressed interstate transport prongs 1 and 2 by referencing the EPA's November 19, 2012 Memorandum ^[5] which outlined the EPA's intention to abide by the August 21, 2012 decision of the U.S. Court of Appeals for the D.C. Circuit, holding that a SIP cannot be deemed deficient for failing to meet the prong 1 and 2 requirements in Section 110(a)(2)(D)(i) before the EPA quantifies the state's obligation. EME Homer City Generation, L.P. v. EPA, 696 F.3d 7 (D.C. Cir. 2012). Utah stated that the EPA had not yet quantified Utah's interstate transport obligation under the 2010 NO₂ or 2010 SO₂ NAAQS and therefore Utah's infrastructure SIPs were adequate for section 110(a)(2)(D)(i)(I).^[6]

On April 29, 2014, the U.S. Supreme Court reversed and remanded the D.C. Circuit's EME Homer City ruling and upheld the EPA's approach in the Cross-State Air Pollution Rule. EPA v. EME Homer City Generation, L.P., 572 U.S. 489 (2014). As a result of the Supreme Court reversal, each state was again required to address the interstate transport requirements of 110(a)(2)(D)(i) regardless of whether the EPA had quantified the state's obligation. In accordance with the Supreme Court's decision, on May 8, 2018 Utah submitted to the EPA 2010 NO₂ and 2010 SO₂ infrastructure SIPs, both of which contained new analyses addressing interstate transport prongs 1 and 2 of Section 110(a)(2)(D)(i) for the respective NAAQS. These submissions supplement the State's prior 2013 interstate transport SIP submissions for both NAAQS. Utah submitted an infrastructure SIP for the 2012 PM_2.5 NAAQS, including an interstate transport SIP, on December 22, 2015. The EPA will discuss these submissions in further detail later in this proposed action.

II. Interstate Transport Evaluation

A. Evaluation for the 2010 1-Hour NO₂ NAAQS

1. EPA's General Approach To Evaluating the 2010 NO₂ NAAQS

Unlike certain other NAAQS like ozone and PM_2.5, the EPA has not developed a recommended approach for states to use when addressing prongs 1 and 2 for the 2010 NO₂ NAAQS. Following promulgation of the 2010 NO₂ NAAQS, the EPA designated all areas of the United States as “unclassifiable/attainment” for this NAAQS because monitors throughout the country had indicated no violations of the NAAQS from 2008-2010.^[7] 77 FR 9532, February 17, 2012. Additionally, no violations occurred at any monitor in the country in the most recent available design value period of 2015-2017.^[8] For these reasons, 110(a)(2)(D)(i)(I) demonstrations for states have been relatively straightforward because the EPA has not identified areas in any state to which emissions from another state would likely contribute significantly to nonattainment or interfere with maintenance.

2. State's Submission

Utah conducted a weight of evidence analysis to examine whether NO₂ emissions from Utah adversely affect attainment or maintenance of the 2010 NO₂ NAAQS in downwind states. In this analysis, the State reviewed ambient monitoring data in Utah and neighboring states, which all indicated that no monitor values in Utah or neighboring states approach the level of the 2010 NO₂ NAAQS. Based on this monitoring data, Utah concluded that the emissions from the State will not contribute significantly to nonattainment or interfere with maintenance of the 2010 NO₂ NAAQS in any other state, and therefore the SIP meets the requirements of section 110(a)(2)(D)(i)(I) prongs 1 and 2 for this NAAQS.

3. EPA's Analysis

In addition to the information provided in the SIP, the EPA notes that the highest monitored valid NO₂ design values in each state bordering Utah are well below the NAAQS (see Table 1, below), as are the maximum single year 98th percentile values from each neighboring state between 2015-2017 (see Table 2, below). These facts further support the State's assertion that significant contribution to nonattainment or interference with maintenance of the NO₂ NAAQS from Utah is very unlikely. With respect to prong 2 (interference with maintenance), specifically, in addition to the lack of areas violating the NO₂ NAAQS, there are also no areas in neighboring states approaching a violation of the 2010 NO₂ NAAQS (i.e., 100 ppb) which might therefore be expected to have difficulty maintaining the standard. With respect to both prongs, we also note that there are no areas elsewhere in the United States approaching a violation of the 2010 NO₂ NAAQS.^[9]

Based on all of these factors, the EPA proposes to concur with the State's conclusion in its January 31, 2013 and supplemental May 8, 2018 submissions that emissions from Utah will not contribute significantly to nonattainment or interfere with maintenance of the 2010 NO₂ NAAQS in other states. The EPA is therefore proposing to approve Utah's January 31, 2013 and supplemental May 8, 2018 NO₂ submissions.

B. Evaluation for the 2010 1-Hour SO₂ NAAQS

1. EPA's General Approach To Evaluating the 2010 SO₂ NAAQS

Although SO₂ is emitted from a similar universe of point and nonpoint sources as is directly emitted PM_2.5 and the precursors to ozone and PM_2.5, interstate transport of SO₂ is unlike the transport of PM_2.5 or ozone because SO₂ emissions sources usually do not have long range SO₂ impacts. The transport of SO₂ relative to the 1-hour NAAQS is more analogous to the transport of Pb relative to the Pb NAAQS in that emissions of SO₂ typically result in 1-hour pollutant impacts of possible concern only near the emissions source. However, ambient 1-hour concentrations of SO₂ do not decrease as quickly with distance from the source as do 3-month average concentrations of Pb, because SO₂ gas is not removed by deposition as rapidly as are Pb particles and because SO₂ typically has a higher emissions release height than Pb. Moreover, while emitted SO₂ has wider ranging impacts than emitted Pb, it does not have such wide-ranging impacts that treatment in a manner similar to ozone or PM_2.5 would be appropriate. The approaches that the EPA has adopted for ozone or PM_2.5 transport are too regionally focused and the approach for Pb transport is too tightly circumscribed to the source. SO₂ transport is therefore a unique case and requires a different approach.

In SO₂ transport analyses, we focus on a 50 km-wide zone because the physical properties of SO₂ result in relatively localized pollutant impacts near an emissions source that drop off with distance. Given the physical properties of SO₂, the EPA selected the “urban scale”—a spatial scale with dimensions from 4 to 50 kilometers (km) from point sources—as that scale has been an appropriate range both for monitoring SO₂ concentrations and for modeling SO₂ impacts from such sources.^[10] As such, the EPA utilized an assessment up to 50 km from point sources in order to assess trends in area-wide air quality that might impact downwind states.

2. State's Submission

Utah conducted a weight of evidence analysis to examine whether SO₂ emissions from Utah contribute significantly to nonattainment or interfere with maintenance of the 2010 SO₂ NAAQS in downwind states. Utah's analysis first reviewed monitoring data in neighboring states to determine whether there were cross-state areas to which Utah could potentially contribute significantly to nonattainment. Utah concluded that the only monitors in neighboring states near or above the NAAQS were violating monitors located in the Miami, Arizona and Hayden, Arizona SO₂ nonattainment areas.^[11] Utah then analyzed the SO₂ source within the State with the closest proximity to the Arizona nonattainment areas. The State determined the distance (531 km) between this source (Cci Paradox Midstream, Llc: Lisbon Natural Gas Processing Plant) and the nearest nonattainment area (Miami, Arizona) showed that Utah will not contribute significantly to nonattainment in Arizona. For its analysis of interference with maintenance, Utah reviewed the sources with over 100 ton per year (tpy) SO₂ emissions in the State within 50 km of a state border, the distance from the nearest cross-state SO₂ monitors to Utah sources, and its proximity to the nearest former 2010 SO₂ nonattainment area in Billings, Montana. Utah also pointed to the significant decrease in SO₂ emissions from sources in the State over time, and its current low levels of monitored SO₂, as further evidence that Utah will not significantly contribute to nonattainment of the 2010 SO₂ NAAQS in any other state.

3. EPA's Analysis

Prong 1: Significant Contribution to Nonattainment

The EPA proposes to approve Utah's June 2, 2013 and supplemental May 8, 2018 submittals with respect to the interstate transport requirements of CAA section 110(a)(2)(D)(i)(I), prong 1 for the 2010 SO₂ NAAQS, as discussed below. We have analyzed the air quality, emission sources and emission trends in Utah and neighboring states, i.e., Arizona, Colorado, Idaho, New Mexico, Nevada and Wyoming. Based on that analysis, we propose to find that Utah will not significantly contribute to nonattainment of the 2010 SO₂ NAAQS in any other state.

We first reviewed 2015-2017 1-hour SO₂ design value concentrations for Utah and neighboring states.^[12] In Table 3, below, we have included monitoring data from four scenarios: (1) All of the monitor data from Utah; ^[13] (2) the monitor with the highest SO₂ level in each neighboring state; (3) the monitor in each neighboring state located closest to the Utah border; and (4) all monitors in each neighboring state within 50 km of the Utah border.^[14] For monitors without a valid 2015-2017 design value, we have instead elected to present the highest annual 99th percentile daily maximum 1-hour SO₂ concentration between 2015 and 2017. These values are shown in the far-right column of Table 3, below. As the table indicates, all of these concentrations are below the level of the 2010 SO₂ NAAQS.

The EPA reviewed these data to see whether there were any regulatory monitoring sites, particularly near the Utah border, with elevated SO₂ concentrations that might warrant further investigation with respect to interstate transport of SO₂ from emission sources near any given monitor. As shown, at the monitors with valid design values, there are no violating design values in Utah or neighboring states apart from Arizona, and the nearest monitor with the violating design value in Arizona is 443 km from the Utah border.

The data presented in Table 3, above, show that Utah's network of SO₂ monitors, while limited, indicates that monitored 1-hour SO₂ levels in Utah were 9% of the 75 ppb level of the NAAQS. As shown, there are no Utah monitors located within 50 km of a neighboring state's border, nor are there any monitors in neighboring states located within 50 km of the Utah border. Thus, these air quality data do not, by themselves, indicate any particular location that would warrant further investigation with respect to SO₂ emission sources that might significantly contribute to nonattainment in the neighboring states. However, because the monitoring network is not necessarily designed to find all locations of high SO₂ concentrations, we have also conducted a source-oriented analysis.

As noted, the EPA finds that it is appropriate to examine the impacts of emissions from stationary sources in Utah in distances ranging from 0 km to 50 km from the facility. Utah assessed point sources up to 50 km from state borders to evaluate SO₂ transport. The list of sources emitting 100 tpy ^[16] or more of SO₂ in 2017 within 50 km from Utah state borders is shown in Table 4 below.

Table 4 also shows the distance from Utah sources located near a neighboring state to the nearest out-of-state SO₂ source emitting above 100 tpy of SO₂, because elevated levels of SO₂, to which SO₂ emitted in Utah may have a downwind impact, are most likely to be found near such sources. As shown, both Utah sources within 50 km of a neighboring state are beyond 50 km from the nearest major out-of-state source, with the shortest distance between such cross-state SO₂ sources at 68 km.^[18] Given the localized range of potential 1-hour SO₂ impacts and the distance between sources, Table 4 suggests that emissions from these Utah sources are unlikely to contribute significantly to nonattainment of the 2010 SO₂ NAAQS in neighboring states. Additionally, the largest neighboring-state source in Table 4, Naughton Power Plant, was modeled and showed attainment with the 2010 SO₂ NAAQS.^[19] Based on this modeling, the EPA designated Lincoln County, Wyoming as attainment/unclassifiable for this NAAQS. See 83 FR 1170, January 9, 2018. This provides additional support for our proposed conclusion that emissions from the Utah sources in Table 4 do not significantly contribute to nonattainment of the 2010 SO₂ NAAQS in neighboring states.^[20]

The EPA also reviewed the location of sources in neighboring states emitting more than 100 tpy of SO₂ and located within 50 km of the Utah border (see Table 5) that were not already addressed in Table 4. As shown in Table 5, there is only one such source, and the shortest distance between it and any Utah source that emits 100 tpy or more of SO₂ is 233 km. The distance shown in Table 5 indicates that there are no locations in neighboring states that would warrant further investigation with respect to Utah SO₂ emission sources that might contribute significantly to nonattainment of the 2010 SO₂ NAAQS. The Hayden and Miami, Arizona 2010 SO₂ nonattainment areas, which Utah reviewed as part of its analysis, are over 380 km from the nearest Utah border and so were not included in Table 5. Utah asserted that the significant distance between its border and these nonattainment areas indicates that it is highly unlikely that SO₂ emissions generated in Utah are contributing significantly to either nonattainment area in Arizona, and the EPA proposes to agree with this conclusion.

In conclusion, for interstate transport prong 1, we reviewed ambient SO₂ monitoring data and SO₂ emission sources both within Utah and in neighboring states. Based on this analysis, we propose to determine that emissions from Utah will not significantly contribute to nonattainment of the 2010 SO₂ NAAQS in any other state and therefore propose to approve the June 2, 2013 and supplemental May 8, 2018 SO₂ submissions with respect to this requirement.

Prong 2: Interference With Maintenance

The EPA also proposes to approve the June 2, 2013 and supplemental May 8, 2018 submissions with respect to the prong 2 requirement. In its prong 2 analysis, Utah reviewed ambient SO₂ monitoring data, emissions trends within Utah, and potential SO₂ impacts on the Billings, Montana area, which is currently in “maintenance” status for the 2010 SO₂ NAAQS, noting the large distance between the nearest Utah border and the Billings area (457 km). However, in previous actions the EPA has analyzed prong 2 by evaluating the potential impact of a state's emissions on areas that are currently measuring data below the NAAQS, but that may have issues maintaining that air quality, rather than only former nonattainment areas which are in maintenance status.^[21] Therefore, we focused our review on SO₂ monitoring data and emission trends to evaluate the State's conclusion that Utah will not interfere with maintenance of the 2010 SO₂ NAAQS in downwind states. This evaluation builds on the analysis regarding significant contribution to nonattainment (prong 1). Specifically, the low monitored ambient concentrations of SO₂ in Utah and neighboring states shown in Table 3, and the large distances between cross-state SO₂ sources shown in Tables 4 and 5, do not indicate any potential inability to maintain the SO₂ NAAQS that could be attributed in part to sources in Utah.

Table 6, below, shows emission trends for Utah and neighboring states.^[22]

As shown in Table 6, the statewide SO₂ emissions from Utah and neighboring states have decreased substantially over time, per our review of the EPA's emissions trends data. This trend of decreasing SO₂ emissions does not by itself demonstrate that areas in Utah and neighboring states will maintain the 2010 SO₂ NAAQS. However, as a piece of this weight of evidence analysis for prong 2, it provides further indication (when considered alongside low monitor values in neighboring states and large distances between SO₂ emissions sources) that maintenance issues are unlikely. The geographic scope and large relative size of these reductions strongly suggest that they are not transient effects from reversible causes, and thus there is low likelihood that a strong upward trend in emissions will occur that might cause areas presently in attainment to violate the NAAQS in the future.

In conclusion, for interstate transport prong 2, we reviewed additional information about emission trends, as well as the technical information considered for interstate transport prong 1. We propose to find that the combination of low ambient concentrations of SO₂ in Utah and neighboring states, the large distances between cross-state SO₂ sources, and the downward trend in SO₂ emissions from Utah and neighboring states, show no interference with maintenance of the 2010 SO₂ NAAQS from Utah. Accordingly, we propose to approve Utah's June 2, 2013 and supplemental May 8, 2018 SO₂ submissions with respect to the prong 2 requirement.

C. Evaluation for the 2012 Annual PM_2.5 NAAQS

1. EPA's General Approach To Evaluating the 2012 PM_2.5 NAAQS

The EPA has developed a consistent framework for addressing interstate transport with respect to the PM_2.5 NAAQS. This framework includes the following four steps: (1) Identify downwind areas that are expected to have problems attaining or maintaining the NAAQS; (2) Identify which upwind states contribute to these air quality problems in amounts sufficient to warrant further review and analysis; (3) Identify any emissions reductions necessary to prevent an identified upwind state from significantly contributing to downwind nonattainment or interfering with downwind maintenance of the NAAQS; and (4) Adopt permanent and enforceable measures needed to achieve those emissions reductions.

To help states identify the receptors expected to have problems attaining or maintaining the 2012 annual PM_2.5 NAAQS, the EPA released a memorandum titled, “Information on the Interstate Transport `Good Neighbor' Provision for the 2012 Fine Particulate Matter National Ambient Air Quality Standards under Clean Air Act Section 110(a)(2)(D)(i)(I)” on March 17, 2016 (hereon “2016 Memo”).^[23] The 2016 Memo provides projected future year annual PM_2.5 design values for monitors throughout the country based on quality-assured and certified ambient monitoring data and recent air quality modeling and explains the methodology used to develop these projected design values. The 2016 Memo also provides recommendations on how states can use the projected values to determine which monitors should be further evaluated as potential receptors under step 1 of the interstate transport framework described above, so that states can determine whether their emissions significantly contribute to nonattainment or interfere with maintenance of the 2012 annual PM_2.5 NAAQS at these monitoring sites.

To develop the projected values presented in the 2016 Memo, the EPA used the results of nationwide photochemical air quality modeling that it recently performed to support two ozone NAAQS-related rulemakings. We performed base year modeling for 2011 and future year modeling for 2017 to support the Cross-State Air Pollution Rule (CSAPR) Update for the 2008 Ozone NAAQS. See 81 FR 74504 (October 26, 2016). We also performed future year modeling for 2025 to support the Regulatory Impact Assessment of the final 2015 Ozone NAAQS.^[24] The outputs from these model runs included hourly concentrations of PM_2.5 that the EPA used in conjunction with measured data to project annual average PM_2.5 design values for 2017 and 2025.

Areas that were designated as Moderate PM_2.5 nonattainment areas for the 2012 annual PM_2.5 NAAQS in 2014 must attain the NAAQS by December 31, 2021, or as expeditiously as practicable. Since modeling results are only available for 2017 and 2025, the 2016 Memo explains that one way to assess potential receptors for 2021 ^[25] is to assume that receptors projected to have average and/or maximum design values above the NAAQS in both 2017 and 2025 are also likely to be either nonattainment or maintenance receptors in 2021. Similarly, the EPA stated that it may be reasonable to assume that receptors that are projected to attain the NAAQS in both 2017 and 2025 are also likely to be attainment receptors in 2021. Where a potential receptor is projected to be nonattainment or maintenance in 2017, but projected to be attainment in 2025, further analysis of the emissions and modeling may be needed to make a further judgement regarding the receptor status in 2021.^[26]

Based on this approach, the EPA identified nineteen potential nonattainment and/or maintenance receptors.^[27] Seventeen of these are located in California. One of the potential maintenance-only receptors is located in Shoshone County, Idaho, and the other potential maintenance-only receptor is located in Allegheny County, Pennsylvania.

After identifying potential receptors, the next step is to identify whether upwind states contribute to air pollution at each of the identified receptors in other states. In the 2016 Memo, the EPA did not calculate the portion of any downwind state's predicted PM_2.5 concentrations that would result from emissions from individual states. Accordingly, the EPA will evaluate Utah's prong 1 and 2 submissions using a weight of evidence analysis. This analysis is based on a review of the State's submission and other available information, including air quality trends; topographical, geographical, and meteorological information; local emissions in downwind states and emissions from the upwind state; and contribution modeling from prior interstate transport analyses. While none of these factors is by itself dispositive, together they may be used in weight of evidence analyses to determine whether the emissions from Utah will significantly contribute to nonattainment or interfere with maintenance of the 2012 annual PM_2.5 NAAQS at the 19 potential nonattainment and/or maintenance receptors identified in the 2016 Memo.

2. State's Submission

Utah conducted a weight of evidence analysis to examine whether PM_2.5 emissions from Utah adversely affect attainment or maintenance of the 2012 PM_2.5 NAAQS in downwind states. The State's analysis primarily focused on potential contribution to the West Silver Valley, Idaho 2012 PM_2.5 nonattainment area,^[28] which is also the location of the Shoshone County, Idaho potential maintenance-only receptor identified in the 2016 Memo and the only area in a state bordering Utah that contained a nonattainment or maintenance receptor. Utah considered the distance from the State to West Silver Valley, as well as meteorological information and PM_2.5 speciation data, and on this basis concluded that the State will not contribute significantly to nonattainment or interfere with maintenance of the 2012 PM_2.5 NAAQS in Idaho or any other state.

The EPA notes that, because Utah's analysis focused on designated nonattainment areas, it does not independently address whether the SIP contains adequate provisions prohibiting emissions that will interfere with maintenance of the 2012 PM_2.5 NAAQS in any other state. In remanding the Clean Air Interstate Rule (CAIR) to the EPA in North Carolina v. EPA, the D.C. Circuit explained that the regulating authority must give the “interfere with maintenance” clause of section 110(a)(2)(D)(i)(I) “independent significance” by evaluating the impact of upwind state emissions on downwind areas that, while currently in attainment, are at risk of future nonattainment, considering historic variability.^[29] While Utah's submittal pre-dates the 2016 Memo, which provided the states with information about potential maintenance-only receptors, Utah was still required to evaluate the potential impact of its emissions on areas that are currently measuring data below the NAAQS, but that may have issues maintaining that air quality, and the State did not do so. The EPA also notes that while Utah elected to address areas in neighboring states designated as nonattainment for the 2012 PM_2.5 NAAQS, the State did not also address such areas in non-neighboring states, such as California, and should have done so because directly emitted PM_2.5 and PM_2.5 precursors can have long-ranging impacts.

When, as here, the EPA determines that a state's SIP has not addressed all of the statutory requirements or provided a technical analysis to justify its conclusion regarding the state's impact on downwind air quality problems, the EPA identifies those deficiencies in acting upon the state's SIP submission. However, if the EPA has supplemental analysis available that nonetheless supported a state's conclusion despite these deficiencies in the state's SIP submission, the EPA can nonetheless propose to approve the state's SIP submission. See 82 FR 9142, 9149 (Feb. 3, 2017).

3. EPA's Analysis

The EPA reviewed the information in Utah's submittal, as well as the 2016 Memo and additional information for our evaluation, and we propose to come to the same conclusion as the State, including (based on our supplemental information) Utah's conclusion that emissions from the State will not interfere with maintenance in downwind states. The EPA therefore proposes to approve the December 22, 2015 submission with respect to both the prong 1 and 2 requirements for the 2012 PM_2.5 NAAQS. In our evaluation, we identified potential downwind nonattainment and maintenance receptors using the modeling results presented in the 2016 Memo. We then evaluated these receptors to determine whether Utah emissions could significantly contribute to nonattainment or interfere with maintenance at them. Below, we provide an overview of our analysis. A more detailed evaluation of how the SIP revision meets the requirements of CAA section 110(a)(2)(D)(i)(I) may be found in our 2012 PM_2.5 technical support document (TSD) in the docket for this action.

Our prong 1 analysis focused on the 17 California receptors, which include the only nonattainment receptors modeled in the 2016 Memo. As shown in Table 1 of the 2016 Memo, 12 of the 17 California receptors are projected as nonattainment in both 2017 and 2025, while the remaining 5 receptors are projected as maintenance in either 2017 or 2025. Because all of the 17 California receptors are located in either the San Joaquin Valley or South Coast 2012 PM_2.5 nonattainment area, we have elected to analyze all of the California receptors together rather than separate the California nonattainment and maintenance receptor analyses. Our analysis of these receptors showed that elevated PM_2.5 levels in California are driven primarily by local emissions.^[30] Additionally, Utah's southwestern border is more than 290 miles to the east and downwind of the California receptors, with intervening mountainous topography which tends to impede interstate pollution transport. Finally, as shown in Table 7, below, monitoring data from Interagency Monitoring of Protected Visual Environment (IMPROVE) monitors tend to show that the air in remote areas between Utah and the California nonattainment and maintenance receptors is well below the level of the 2012 PM_2.5 NAAQS.^[31] All of these factors indicate that emissions from Utah are not likely to reach California in amounts that could impact the air quality at the California nonattainment and maintenance receptors. Thus, the EPA is proposing to find that Utah emissions will not significantly contribute to nonattainment or interfere with maintenance of the 2012 PM_2.5 NAAQS at any California projected receptor.

For the EPA's prong 2 analysis, we reviewed potential impacts from Utah emissions at the two projected maintenance-only receptors outside of California identified in the 2016 Memo. With regard to the Shoshone County, Idaho receptor, our analysis showed that elevated PM_2.5 levels in the area are driven primarily by local emissions from wood burning in the wintertime, specifically when the West Silver Valley experiences the combination of cold surface temperatures, low wind speeds, and constrained vertical mixing.^[33] The deep, narrow mountain valley magnifies this effect relative to other nearby areas. The combination of these meteorological effects and the mountainous terrain confine the geographical area that could contribute emissions to elevated wintertime PM_2.5 concentrations at the Shoshone County receptor.^[34] Utah's prong 1 analysis noted that speciation data in the Utah 2006 PM_2.5 nonattainment areas ^[35] indicate that ammonium nitrate drives high PM_2.5 levels in north-central Utah, which contrasts with carbon-driven speciation data at the Shoshone County receptor during the winter and indicates emissions originating in Utah are not contributing to elevated PM_2.5 at the Shoshone County receptor. Additionally, Utah's nearest border is approximately 400 miles to the southeast and generally downwind of this receptor. Finally, the IMPROVE monitoring data in Table 7 tend to show that the air in remote areas in Idaho between Utah and the Shoshone County receptor is well below the level of the 2012 PM_2.5 NAAQS. This provides further indication that elevated PM_2.5 at the Shoshone County receptor is primarily driven by local emissions. All of these factors indicate that emissions from Utah will not interfere with maintenance of the 2012 PM_2.5 NAAQS at the projected Shoshone County maintenance receptor.

With regard to the Allegheny County, Pennsylvania potential maintenance receptor, our analysis included review of previous modeling data conducted for the EPA's 2011 CSAPR, which addressed the 1997 and 2006 PM_2.5 NAAQS.^[36] For the 2011 CSAPR, the EPA modeled contribution from states in the eastern U.S. to air quality monitors also located in the eastern U.S.^[37] Therefore, the 2011 CSAPR modeling did not project downwind contribution of emissions from Utah, but projected contributions from states east of Utah, including Kansas and Nebraska. The CSAPR modeling indicated that Kansas and Nebraska, states located much closer to the Allegheny County receptor and with higher PM_2.5 precursor emissions than Utah,^[38] were modeled to be below 1% (the contribution level at which eastern states were considered “linked” to downwind receptors in the CSAPR and CSAPR Update rulemakings) of the 1997 annual and 2006 24-hr PM_2.5 NAAQS at the Allegheny County receptor. These factors, in addition to the very large distance (1,525 miles) from the Allegheny County receptor to the Utah border, indicate that emissions from Utah will not interfere with maintenance of the 2012 PM_2.5 NAAQS at the projected Allegheny County receptor.

Based on these analyses, the EPA is proposing to determine that Utah emissions will not contribute significantly to nonattainment or interfere with maintenance of the 2012 PM_2.5 NAAQS in any other state, and we therefore propose to approve the December 22, 2015 submittal.

III. Proposed Action

Based on our review of Utah's January 31, 2013, June 2, 2013, December 22, 2015 and May 8, 2018 infrastructure submissions, and our analysis of additional relevant information, we propose to determine that emissions from Utah will not significantly contribute to nonattainment, or interfere with maintenance, of the 2010 NO₂, 2010 SO₂, and 2012 PM_2.5 NAAQS in any other state. Accordingly, we propose to approve the January 31, 2013, June 2, 2013, December 22, 2015 and May 8, 2018 Utah SIP submissions as satisfying the requirements of CAA section 110(a)(2)(D)(i)(I) for these NAAQS. The EPA is soliciting public comments on this proposed action and will consider public comments received during the comment period.

IV. Statutory and Executive Order Reviews

Under the CAA, the Administrator is required to approve a SIP submission that complies with the provisions of the Act and applicable federal regulations. 42 U.S.C. 7410(k); 40 CFR 52.02(a). Thus, in reviewing SIP submissions, 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 Orders 12866 (58 FR 51735, October 4, 1993) and 13563 (76 FR 3821, January 21, 2011);
• Is not an Executive Order 13771 (82 FR 9339, February 2, 2017) regulatory action because SIP approvals are exempted 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 an economically significant regulatory action based on health or safety risks subject to Executive Order 13045 (62 FR 19885, April 23, 1997);
• Is not a significant regulatory action subject to Executive Order 13211 (66 FR 28355, May 22, 2001);
• Is not subject to requirements of section 12(d) of the National Technology Transfer and Advancement Act of 1995 (15 U.S.C. 272 note) because application of those requirements would be inconsistent with the CAA; and
• Does not provide the EPA with the discretionary authority to address, as appropriate, disproportionate human health or environmental effects, using practicable and legally permissible methods, under Executive Order 12898 (59 FR 7629, February 16, 1994).

In addition, the SIP is not approved to apply on any Indian reservation land or in any other area where the EPA or an Indian tribe has demonstrated that a tribe has jurisdiction. In those areas of Indian country, the proposed rule does not have tribal implications and will not impose substantial direct costs on tribal governments or preempt tribal law as specified by Executive Order 13175 (65 FR 67249, November 9, 2000).

List of Subjects in 40 CFR Part 52

• Environmental protection
• Air pollution control
• Incorporation by reference
• Intergovernmental relations
• Nitrogen dioxide
• Ozone
• Particulate matter
• Reporting and recordkeeping requirements
• Sulfur dioxide
• Volatile organic compounds

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

Footnotes