2020-21741. Air Plan Approval; ID; 2010 Sulfur Dioxide NAAQS Infrastructure Requirements

AGENCY:

Environmental Protection Agency (EPA).

ACTION:

Proposed rule.

SUMMARY:

The Environmental Protection Agency (EPA) is proposing to approve a State Implementation Plan (SIP) submission from the State of Idaho (Idaho or the State) that addresses the Clean Air Act (CAA or Act) interstate transport requirements for the 2010 1-hour Sulfur Dioxide (SO₂) National Ambient Air Quality Standards (NAAQS). In this action, the EPA is proposing to determine that Idaho will not contribute significantly to nonattainment or interfere with maintenance of the 2010 1-hour SO₂ NAAQS in any other state or the Fort Hall Reservation. Therefore, the EPA is proposing to approve Idaho's December 24, 2015, SIP submission as meeting the interstate transport requirements for the 2010 1-hour SO₂ NAAQS.

DATES:

Written comments must be received on or before November 4, 2020.

ADDRESSES:

Submit your comments, identified by Docket ID No. EPA-R10-OAR-2016-0001 at https://www.regulations.gov. Follow the online instructions for submitting comments. Once submitted, comments cannot be edited or removed from Regulations.gov. The EPA may publish any comment received to its public docket. Do not electronically submit any information you consider to be Confidential Business Information (CBI) or other information the disclosure of which 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.

FOR FURTHER INFORMATION CONTACT:

Claudia Vaupel at [phone], or [e-mail].

SUPPLEMENTARY INFORMATION:

Throughout this document whenever “we,” “us,” or “our” is used, it is intended to refer to the EPA.

Table of Contents:

I. Background

II. Relevant Factors To Evaluate 2010 SO₂ Interstate Transport SIPs

III. State Submission and EPA Analysis

A. State Submission

B. EPA Analysis

1. The EPA's Prong 1 Evaluation

2. The EPA's Prong 2 Evaluation

IV. Proposed Action

V. Statutory and Executive Order Reviews

I. Background

On June 2, 2010, the EPA established a new primary 1-hour SO₂ NAAQS of 75 parts per billion (ppb), based on a 3-year average of the annual 99th percentile of 1-hour daily maximum concentrations.^[1] The CAA requires states to submit, within 3 years after promulgation of a new or revised NAAQS, SIPs meeting the applicable “infrastructure” elements of sections 110(a)(1) and (2). One of these applicable infrastructure elements, CAA section 110(a)(2)(D)(i), requires SIPs to contain “good neighbor” provisions to prohibit certain adverse air quality effects on neighboring states due to interstate transport of pollution.

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), require SIPs to contain adequate provisions that 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), require SIPs to contain adequate provisions that 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).

In this action, the EPA is proposing to approve the prong 1 and prong 2 portions of the State of Idaho's December 24, 2015 SIP submission because, based on the information available at the time of this rulemaking, the State demonstrated that Idaho will not contribute significantly to nonattainment or interfere with maintenance of the 2010 SO₂ NAAQS in any other state or the Fort Hall Reservation. All other applicable infrastructure SIP requirements for this SIP submission have been addressed in separate actions. See 79 FR 46707 (August 11, 2014).

II. Relevant Factors To Evaluate 2010 SO₂ Interstate Transport SIPs

Although SO₂ is emitted from a similar universe of point and nonpoint sources, interstate transport of SO₂ is unlike the transport of fine particulate matter (PM_2.5) or ozone, in that SO₂ is not a regional pollutant and does not commonly contribute to widespread nonattainment over a large (and often multi-state) area. The transport of SO₂ is more analogous to the transport of lead (Pb) because its physical properties result in localized pollutant impacts very near the emissions source. However, ambient concentrations of SO₂ do not decrease as quickly with distance from the source as Pb because of the physical properties and typical release heights of SO₂. Emissions of SO₂ travel farther and have wider ranging impacts than emissions of Pb but do not travel far enough to be treated in a manner similar to ozone or PM_2.5. 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 to serve as a model for SO₂ transport. SO₂ transport is therefore a unique case and requires a different approach.

In this proposed rulemaking, as in prior SO₂ transport analyses, the EPA focuses 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—given the usefulness of that range in assessing trends in both area-wide air quality and the effectiveness of large-scale pollution control strategies at such point sources.^[2] 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.

As discussed in section III of this this document, the EPA reviewed Idaho's analysis to assess how it evaluated SO₂ transport to other states, the types of information used in the analysis and the conclusions drawn. The EPA then conducted a weight of evidence analysis, reviewing the submission and other available information, including air quality monitor data, emission sources and emission trends within Idaho and in bordering states to which it could potentially contribute or interfere with attainment or maintenance of the 2010 SO₂ NAAQS.^[3]

III. State Submission and EPA Analysis

On December 24, 2015, Idaho submitted a SIP revision to the EPA documenting that its SIP contains provisions that address CAA section 110(a)(2)(D)(i)(I) interstate transport requirements for the 2010 SO₂ NAAQS. In this section, we provide an overview of Idaho's 2010 SO₂ interstate transport analysis, as well as the EPA's evaluation of prongs 1 and 2.

A. State Submission

Idaho conducted a weight of evidence analysis to examine whether SO₂ emissions from Idaho will adversely affect attainment or maintenance of the 2010 SO₂ NAAQS in downwind states. In the submission, Idaho identified one 2010 SO₂ nonattainment area in Billings, Montana, within Yellowstone County, which has since been redesignated to attainment.^[4] Idaho reviewed 2014 SO₂ emissions data from the largest SO₂ emissions sources in the State and determined that emissions from those sources were hundreds of miles from the SO₂ nonattainment/maintenance areas. Idaho also reviewed 2012-2014 monitoring data from the 3 SO₂ monitoring sites in its monitoring network and from the 14 SO₂ monitoring sites in neighboring states for years 2011-2013. Idaho determined that all design values were below the 2010 SO₂ NAAQS.^[5] In addition, Idaho provided 2009-2011 regional-scale modeling for the State and found that areas of increased SO₂ concentrations were localized in nature.

Based on the weight of evidence analysis, Idaho concluded that emissions within the State will not contribute significantly to nonattainment or interfere with maintenance of the 2010 1-hour SO₂ NAAQS in any other state.

B. EPA Analysis

The EPA proposes to find that Idaho's SIP meets the interstate transport requirements of CAA section 110(a)(2)(D)(i)(I), prong 1 for the 2010 SO₂ NAAQS. We have analyzed the air quality, emission sources and emission trends in Idaho and neighboring states, i.e., Montana, Nevada, Oregon, Utah, Washington, Wyoming, and the Fort Hall Reservation. Based on our analysis, we propose to find that Idaho will not contribute significantly to nonattainment of the 2010 SO₂ NAAQS in any other state or the Fort Hall Reservation.

1. The EPA's Prong 1 Evaluation

The EPA reviewed SO₂ emission data from 2005 to 2017 for Idaho and the six neighboring states.^[6] As shown in Table 1 of this document, SO₂ emissions from Idaho and neighboring states have decreased substantially over time, ranging from 37 to 89 percent. Specifically, over this 13-year period, Idaho's statewide SO₂ emissions decreased by 72 percent.

Table 1—SO₂ Emission Trends in Idaho and Neighboring States

[In tons per year]

State	2005	2008	2011	2014	2017	SO2 reduction, 2005-2017 (%)
Idaho	35,452	20,149	13,791	10,062	10,007	72
Montana	42,085	29,354	29,452	25,046	18,580	56
Nevada	72,474	20,951	13,578	16,178	7,793	89
Oregon	37,204	25,671	30,285	23,606	19,325	48
Utah	52,999	31,609	27,839	26,964	15,442	71
Washington	59,651	34,826	30,492	38,973	37,488	37
Wyoming	122,454	112,791	83,256.1	56,772	52,354	57

We also reviewed the most recent certified air quality data available for 1-hour SO₂ design value concentrations at monitors in Idaho and neighboring states. In Table 2 of this document, we have included the most recent 2017-2019 design values for (1) all monitors in Idaho; (2) the monitor with the highest design value in each neighboring state; and (3) the monitor in each neighboring state located closest to the Idaho border. The EPA notes that no neighboring state has an SO₂ monitor within 50 km of the Idaho border. To assess how air quality has changed over time, we also reviewed 2014-2016, 2015-2017, and 2016-2018 SO₂ design values for these monitors, as shown in Table 2.

Table 2—SO₂ Design Values ⁷ in ppb for AQS Monitors in Idaho and Neighboring States

State/area	AQS site ID	Distance to nearest Idaho border (km) *	Design value
			2014-2016	2015-2017	2016-2018	2017-2019
Idaho/Boise	160010010	55	4	3	3	3
Idaho/Pocatello	160050004	102	39	38	38	40
Idaho/Caribou County	160290031	45	26	30	31	35
Montana/Helena	300490004	180	2	3	5	5
Montana/Billings	301110066	256	53	33	24	24
Nevada/Las Vegas	320030540	644	7	6	6	5
Nevada/Reno	320310016	362	5	5	5	4
Oregon/Portland	410510080	447	3	3	3	3
Washington/Anacortes	530570011	412	5	4	3	3
Wyoming/Casper	560252601	393	25	20	19	19
Wyoming/Rock Springs	560370300	108	21	21	20	12
* All distances throughout this notice are approximations.

We reviewed ambient air quality data in Idaho and neighboring states to see whether there were any monitoring sites, particularly near the Idaho 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 in Table 2 of this document, there are no monitors with violating design values in Idaho or neighboring states. Additionally, the highest monitored 2017-2019 design value in Idaho or neighboring states is 40 ppb, or approximately 54 percent of the level of the 2010 SO₂ NAAQS.

As discussed previously, Idaho analyzed potential impacts to the Billings, Montana area, which was still designated nonattainment at the time of Idaho's submission. The EPA redesignated the former Billings 2010 SO₂ nonattainment area to attainment following the permanent closure of the PPL Corette Plant. See 81 FR 28718 (May 10, 2016). As noted by Idaho, the Billings, Montana area is located far from the nearest Idaho border (256 km). Table 2 of this document also shows that recent monitoring data in the Billings area do not approach the level of the 2010 SO₂ NAAQS. For these reasons, the EPA agrees with Idaho's conclusion that the emissions from Idaho will not contribute significantly to nonattainment in the Billings, Montana area.

The data presented in Table 2 of this document show that 2017-2019 1-hour SO₂ design values in Idaho are between 4 and 54 percent of the 75-ppb level of the NAAQS. The Caribou County SO₂ monitor (AQS Site ID 160290031) is the only Idaho SO₂ monitor that is located within 50 km of a state border—the Idaho-Wyoming border. The 2017-2019 design value at the Caribou County SO₂ monitor is 35 ppb or 47% of the NAAQS. However, these air quality data do not, by themselves, indicate any particular location that would warrant further investigation with respect to SO₂ emission sources in Idaho that might contribute significantly to nonattainment in the bordering states. Because the monitoring network is not necessarily designed to find all locations of high SO₂ concentrations, this observation indicates an absence of evidence of impact at these locations but is not sufficient evidence by itself of an absence of impact at all locations in the neighboring states. We have therefore 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 Idaho in distances ranging from 0 km to 50 km from the facility, based on the “urban scale” definition contained in appendix D to 40 CFR part 58, section 4.4. Therefore, we assessed Idaho and neighboring state point sources that emit 100 tons per year (tpy) of SO₂ ^[8] or more that are located up to 50 km from an Idaho border.

There are four sources in Idaho that emit 100 tpy of SO₂ or more. These sources are located in southeastern Idaho and are listed in Table 3 of this document. Two of the sources, P4 Production and Itafos Conda, are less than 50 km from the Idaho-Wyoming border, 45 km and 40 km, respectively.

Table 3—Idaho SO₂ Sources

[SO₂ ≥ 100 tpy]

Idaho SO2 Source	2017 Emissions (tpy) 9	Distance to nearest state border (km)/state border
J.R. Simplot Company—Don Siding Pocatello (Pocatello, ID)	748	101/ID-NV.
The Amalgamated Sugar Company (Twin Falls, ID)	635	61/ID-NV.
P4 Production (Soda Springs, ID)	488	45/ID-WY.
Itafos Conda (Conda, ID)	387	40/ID-WY.

The Naughton Generating Plant in Lincoln, Wyoming, is the closest neighboring state source to P4 Production and Itafos Conda. The EPA has therefore assessed potential SO₂ impacts from these Idaho sources to the Lincoln, Wyoming area. Table 4 of this document shows SO₂ emissions and approximate distances between the sources. The EPA finds that the 131 to 134 km distance between the two Idaho sources and the Wyoming source, more than twice the 50-km distance the EPA has focused on for this analysis, makes it very unlikely that SO₂ emissions from the Idaho sources will interact with SO₂ emissions from the Wyoming source in such a way as to contribute significantly nonattainment in the Lincoln, Wyoming area.^[10]

Table 4—Idaho SO₂ Sources Within 50 km of a State Border

[SO₂ ≥ 100 tpy]

Idaho SO2 source	2017 SO2 emissions (tpy)	Distance to nearest neighboring state SO2 source (km)/source	Neighboring state source 2017 SO2 emissions (tpy)
Itafos Conda (Conda, Idaho)	387	134/Naughton Generating Plant, Lincoln, WY	4,048
P4 Production (Soda Springs, Idaho)	488	131/Naughton Generating Plant, Lincoln, WY	4,048

The EPA also reviewed the location of neighboring state sources that emit 100 tpy of SO₂ or more and are located within 50 km of the Idaho border. This is because SO₂ emitted by sources in Idaho are most likely to impact elevated levels of SO₂ in neighboring states near such sources. As shown in Table 5 of this document, there are two sources in neighboring states that are located within 50 km of an Idaho border, the previously mentioned Naughton Generating Plant in Lincoln, Wyoming, located in southeastern Idaho, and EP Minerals in Vale, Oregon, located in southwestern Idaho. The shortest distance between any pair of these sources is 131 km, between the Naughton Generating Plant and P4 Production. As just explained, this distance makes it unlikely that SO₂ emissions from the Idaho source will interact with SO₂ emissions from the Wyoming source. This indicates that there is no location in any neighboring state that would warrant further investigation with respect to Idaho SO₂ emission sources that might contribute to problems with attainment of the 2010 SO₂ NAAQS.

Table 5—Neighboring State SO₂ Sources Within 50 km of an Idaho Border

[SO₂ ≥ 100 tpy]

Neighboring state SO2 source	2017 SO2 emissions (tpy)	Distance to Idaho border (km)	Distance to nearest Idaho SO2 source (km)	Idaho Source 2017 SO2 Emissions (tpy)
Naughton Generating Station, Lincoln, WY	4,048	46	131 (P4 Production, Soda Springs, ID)	488
EP Minerals, Vale, OR	182	32	286/The Amalgamated Sugar Company, Twin Falls, ID	635

The Fort Hall Reservation

On January 19, 2017, the EPA determined that the Shoshone-Bannock Tribes of the Fort Hall Reservation were eligible to be treated in the same manner as an affected downwind state for purposes of CAA sections 110(a)(2)(D) and 126.^[11] Idaho submitted the SO₂ interstate transport SIP before this determination and the submission did not analyze SO₂ transport to the Fort Hall Reservation. Therefore, the EPA has conducted the following weight of evidence analysis for potential Idaho SO₂ transport to the Fort Hall Reservation.

The Fort Hall Reservation is located in southeastern Idaho, mostly on the high, flat, cultivated east banks of the Snake River Plain which average around 4,500 feet above sea level. The east portion of the Reservation rests on the northern reaches of the Pocatello range of mountains. The Fort Hall Reservation is bordered on the east and south by the rugged rocky hills of the Pocatello, Chesterfield, and Caribou mountain ranges. These ranges run north-south with peaks rising from 6,000 to 9,000 feet above sea level, generally east and south of the Reservation.

The EPA reviewed ambient air quality data, particularly near the Fort Hall Reservation borders, for any monitoring sites with elevated SO₂ concentrations that might warrant further investigation with respect to interstate transport of SO₂ from Idaho sources. The nearest SO₂ monitor to the Fort Hall Reservation is in Pocatello, Idaho (AQS Site ID 160050004) and is approximately 2 km from the nearest Reservation border. Another SO₂ monitor is located in Caribou County, Idaho (AQS Site ID 160290031) and is approximately 37 km from the southeastern border of the Fort Hall Reservation. Although these monitors are not sited to determine maximum impacts at the Fort Hall Reservation, monitoring data listed in Table 6 of this document, indicate that SO₂ levels in those areas are relatively low. The 2017-2019 design values at the Pocatello and Caribou County monitor sites were 53 at 47 and percent of the 75-ppb level of the NAAQS, respectively.

Table 6—Idaho SO₂ Design Values ¹² in ppb for AQS Monitors Near the Fort Hall Reservation

AQS monitor location (AQS site ID)	Approximate distance to Fort Hall Reservation (km)	Design value
		2012-2014	2013-2015	2014-2016	2015-2017	2016-2018	2017-2019
Pocatello (160050004)	2	51	41	39	38	38	40
Caribou County (160290031)	37	30	26	26	30	31	35

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 contribute significantly to nonattainment at the Fort Hall Reservation. However, data from this monitoring network is not necessarily representative of SO₂ levels throughout the Fort Hall Reservation and we have therefore also conducted a source-oriented analysis.

As discussed previously, the EPA finds that it is appropriate to examine the impacts of emissions from stationary sources in Idaho in distances ranging from 0 km to 50 km from the facility, based on the “urban scale” definition contained in appendix D to 40 CFR part 58, section 4.4. Therefore, we assessed point sources with SO₂ emissions of 100 tpy ^[13] or more within 50 km of the Fort Hall Reservation to evaluate trends and SO₂ concentrations in areawide air quality. We identified three such sources, listed in Table 7 of this document. We note that there are no sources within the Fort Hall Reservation that emit more than 2 tpy of SO₂.

Table 7—SO₂ Emissions Sources Within 50 km of the Fort Hall Reservation

[SO₂ ≥ 100 tpy]

SO2 Source 14 15	2017 SO2 emissions (tpy)	Distance to Fort Hall Reservation (km)	Distance to Pocatello site (AQS site ID 160050004)	Distance to Caribou County site (AQS Site ID 160290031)
J.R. Simplot Company—Don Siding Pocatello (Pocatello, ID)	748	<1	1	80
P4 Production (Soda Springs, ID)	488	38	80	1
Itafos Conda (Conda, ID)	387	38	82	7

J.R. Simplot Company—Don Siding Pocatello

The J.R. Simplot Company—Don Siding Pocatello plant (Simplot Don Siding Plant), in Pocatello, Idaho, is the closest SO₂ source to the Fort Hall Reservation and has the highest SO₂ emissions in the area with 748 tpy in 2017. The Simplot Don Siding Plant is approximately 1 km from the boundary of the Fort Hall Reservation and approximately 1 km from the Pocatello SO₂ monitor (AQS Site ID 160050004). The EPA reviewed SO₂ emissions data for the Simplot Don Siding Plant from 2010 through 2017. As shown in Table 8 of this document, SO₂ emissions have decreased considerably over time and are less than half what they were in 2010.

Table 8—Simplot Don Siding Plant SO₂ Emissions (tpy) From 2010-2017

2010	2011	2012	2013	2014	2015	2016	2017
1,634	1,647	1,563	803	795	732	735	748

The EPA reviewed data from the meteorological station at the Pocatello Regional Airport, which is approximately 6 km west of the Simplot Don Siding Plant. Prevailing winds are from the southwest with an average speed of 4.2 meters per second. Given the close distance of the Pocatello SO₂ monitor to the Simplot Don Siding Plant, the low monitored SO₂ concentrations, and the prevalent wind direction, it is likely that SO₂ emissions from the Simplot Don Siding Plant will be sufficiently dispersed before reaching the Fort Hall Reservation.

In addition to reviewing the 2009-2011 regional scale SO₂ modeling in Idaho's submission, the EPA examined more recent regional-scale SO₂ modeling for the Pocatello area using the same tool Idaho used with updated data from July 2014 to June 2017.^[16] The highest design concentration identified in the area is about 6.8 ppb, well under the 1-hour SO₂ NAAQS of 75 ppb. On the Fort Hall Reservation, the highest design concentration identified in the area is 6.3 ppb and occurs west of the Simplot Don Siding Plant. This analysis indicates that SO₂ emissions impacts from the Simplot Don Siding Plant to the vicinity and the Fort Hall Reservation are likely minimal. While this regional-scale modeling is not dispositive as to the determination of whether impermissible SO₂ transport is occurring, it provides information that along with other factors may be considered in a weight of evidence evaluation.

P4 Production and The Itafos Conda

The EPA also assessed potential SO₂ impacts from other point sources near the Fort Hall Reservation, P4 Production and Itafos Conda, which are approximately 7 km apart. These sources are located in the Soda Springs region on the east side of the high Caribou Valley plain, along the west flanks of the Caribou Range of mountains. The rugged Blackfoot Lava Fields and high, rocky Chesterfield Range of mountains lie between the Fort Hall Reservation and Soda Springs region and rise to peaks exceeding 7,000 feet.

As shown in Table 7 of this document, these sources are approximately 38 km from the Fort Hall Reservation. The closest SO₂ monitor to these sources is the Caribou County monitor (AQS Site ID 160290031), which is 1 km from P4 Production and 7 km from Itafos Conda. The EPA reviewed SO₂ emissions data for P4 Production and Itafos Conda from 2010 to 2017. As shown in Table 9 of this document, SO₂ emissions at P4 Production have decreased by almost half since 2010. At Itafos Conda, SO₂ emissions have not changed substantially since 2010.

Table 9—P4 Production and Itafos Conda SO₂ Emissions (tpy) From 2010-2017

Facility	2010	2011	2012	2013	2014	2015	2016	2017
P4 Production	936	1169	643	615	456	467	478	488
Itafos Conda	341	302	311	410	332	438	364	387

With a 38 km transport distance over complex, rugged terrain, and the low monitored SO₂ concentrations, it is likely that SO₂ emissions from P4 Production and Itafos Conda will be sufficiently dispersed before impacting the Fort Hall Reservation, and that any impacts to the Reservation from these sources would likely be minimal.

The EPA has reviewed SO₂ sources with emissions of 100 tpy or more within 50 km of the Fort Hall Reservation. Based on the available information, the EPA is proposing to find that Idaho will not contribute significantly to nonattainment of the 2010 1-hour SO₂ NAAQS for purposes of CAA section 110(a)(2)(D)(i)(I) in the Fort Hall Reservation.

We are proposing to conclude that, based on our review of the Idaho submission and our supplemental evaluation, Idaho's SIP meets the prong 1 requirements of CAA section 110(a)(2)(D)(i)(I) for purposes of the 2010 SO₂ NAAQS. In summary, for interstate transport prong 1, we reviewed the Idaho submission and conducted a supplemental analysis of ambient SO₂ monitoring data and SO₂ emission sources within Idaho, neighboring states, and the Fort Hall Reservation. Based on this analysis, we propose to determine that Idaho will not contribute significantly to nonattainment of the 2010 SO₂ NAAQS in any other state or the Fort Hall Reservation, per the requirements of CAA section 110(a)(2)(D)(i)(I).

2. The EPA's Prong 2 Evaluation

The EPA has reviewed available information on SO₂ air quality and emission trends to evaluate Idaho's conclusion that emissions from sources in the State will not interfere with maintenance of the 2010 SO₂ NAAQS in any downwind state. The EPA notes that Idaho's analysis does not independently address whether the SIP contains adequate provisions prohibiting emissions that will interfere with maintenance of the 2010 SO₂ NAAQS in any other state, or the Fort Hall Reservation. 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.^[17] While Idaho did not evaluate the potential impact of its emissions on areas that are currently measuring clean data, but that may have issues maintaining that air quality, the EPA reviewed additional information, which builds on the analysis regarding significant contribution to nonattainment (prong 1) to determine potential impacts on areas that are measuring clean data. Specifically, because of the relatively low monitored ambient concentrations of SO₂ in Idaho and neighboring states, the levels of SO₂ emissions of Idaho sources, and the large distances between cross-state SO₂ sources, the EPA's weight of evidence evaluation shows that SO₂ levels in neighboring states near the Idaho border do not indicate any inability to maintain the SO₂ NAAQS that could be attributed, even in part, to sources in Idaho.

Based on our review of the EPA's emissions trends data, as shown in Table 1 of this document, SO₂ emissions from Idaho and neighboring states have decreased substantially over time.^[18] From 2005 to 2017, total statewide SO₂ emissions decreased by the following proportions: Idaho: 72% decrease, Montana: 56% decrease, Nevada: 89% decrease, Oregon: 48% decrease, Utah: 71% decrease, Washington: 37% Decrease, and Wyoming: 57% decrease. This trend of decreasing SO₂ emissions does not by itself demonstrate that areas in Idaho and neighboring states will not have issues maintaining 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) that such maintenance issues are unlikely. This is because the large decrease in SO₂ emissions covers a large geographic area, which strongly suggests that it is not a transient effect from reversible causes and that there is low likelihood that a strong upward trend in emissions will occur that might cause areas that are presently in attainment to violate the NAAQS.

The EPA notes that existing sources are subject to the control requirements in the Idaho SIP discussed in our prong 1 evaluation, and any future new and modified stationary sources of SO₂ emissions will be subject to Idaho's SIP-approved pre-construction permitting (“new source review” or “NSR”) program.^[19] The EPA believes that the permitting regulations contained within these programs will help ensure that ambient concentrations of SO₂ in neighboring states will not be exceeded as a result of new facility construction or modification occurring in Idaho.

In conclusion, for interstate transport prong 2, the EPA has incorporated additional information into our evaluation of Idaho's submission, which did not include an independent analysis of prong 2. In doing so, we have reviewed information about emission trends, as well as the technical information considered for our interstate transport prong 1 analysis. We find that the combination of low ambient concentrations of SO₂ in Idaho and neighboring states, including near the Fort Hall Reservation, the large distances between cross-state SO₂ sources, the downward trend in SO₂ emissions from Idaho and surrounding states, and SIP-approved control measures designed to limit SO₂ emissions from new and modified stationary sources in Idaho, indicates that Idaho sources will not interfere with maintenance of the 2010 SO₂ NAAQS in any other state or the Fort Hall Reservation. Accordingly, we propose to determine that Idaho SO₂ emission sources will not interfere with maintenance of the 2010 SO₂ NAAQS in any other state or the Fort Hall Reservation, per the requirements of CAA section 110(a)(2)(D)(i)(I).

IV. Proposed Action

The EPA is proposing to approve the December 24, 2015 Idaho SIP as meeting the interstate transport requirements of CAA section 110(a)(2)(D)(i)(I) for the 2010 SO₂ NAAQS. The EPA is proposing this approval based on our review of the information and analysis provided by Idaho, as well as additional analyses conducted by the EPA to verify and supplement the Idaho SIP, which indicates that Idaho will not contribute significantly to nonattainment or interfere with maintenance of the 2010 SO₂ NAAQS in any other state or the Fort Hall Reservation. This action is being taken under section 110 of the CAA.

V. Statutory and Executive Order Reviews

Under the Clean Air Act, 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 Clean Air Act. Accordingly, this proposed action merely approves state law as meeting Federal requirements and does not impose additional requirements beyond those imposed by state law. For that reason, this proposed 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 it does not involve technical standards; 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).

The proposed SIP would not be 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). Consistent with EPA policy, the EPA provided a consultation opportunity to the Shoshone-Bannock Tribes concerning the EPA's action on this SIP submission in a letter dated March 7, 2018. The EPA did not receive a request for consultation.

List of Subjects in 40 CFR Part 52

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

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

Dated: September 25, 2020.

Christopher Hladick,

Regional Administrator, Region 10.

Footnotes

1.  75 FR 35520 (June 22, 2010).

2.  For the definition of spatial scales for SO₂, see 40 CFR part 58, appendix D, section 4.4 (“Sulfur Dioxide (SO₂) Design Criteria”). For further discussion on how the EPA is applying these definitions with respect to interstate transport of SO₂, see the EPA's proposal on Connecticut's SO₂ transport SIP. 82 FR 21351, 21352, 21354 (May 8, 2017).

3.  This proposed approval action is based on the information contained in the administrative record for this action and does not prejudge any other future EPA action that may make other determinations regarding any of the subject state's air quality status. Any such future actions, such as area designations under any NAAQS, will be based on their own administrative records and the EPA's analyses of information that becomes available at those times. Future available information may include, and is not limited to, monitoring data and modeling analyses conducted pursuant to the Data Requirements Rule for the 2010 1-Hour SO₂ NAAQS (80 FR 51052, August 21, 2015) and information submitted to the EPA by states, air agencies, and third party stakeholders such as citizen groups and industry representatives.

4.  The Billings, Montana 2010 SO₂ nonattainment area was redesignated to attainment on May 10, 2016 following the state's SIP submission (81 FR 28718).

5.  The design value is the annual 99th percentile of the daily maximum 1-hour concentration values, averaged over three consecutive years. (See 75 FR 35520, June 22, 2010).

6.  We derived the emissions trends information from the EPA's web page https://www.epa.gov/​air-emissions-inventories/​air-pollutant-emissions-trends-data.

7.  Design values are from monitors with sufficient data available in the EPA's Air Quality System (AQS) to produce valid design values. Data retrieved from the EPA's https://www.epa.gov/​air-trends/​air-quality-design-values#report.

8.  We have limited our analysis to sources emitting at least 100 tpy of SO₂ because in the absence of special factors, for example the presence of a nearby larger source or unusual physical factors, Idaho sources emitting less than 100 tpy can appropriately be presumed to not be causing or contributing to SO₂ concentrations above the NAAQS.

9.  Point source emissions data throughout this document were obtained through the EPA's Emissions Inventory System (EIS) Gateway at https://www.epa.gov/​air-emissions-inventories/​emissions-inventory-system-eis-gateway.

10.  In round 3 of 2010 SO₂ designations, the EPA designated Lincoln County in Wyoming as attainment/unclassifiable for the 2010 1-hour SO₂ NAAQS based on modeling of the Naughton source area. See “Technical Support Document: Chapter 45 Final Round 3 Area Designations for the 2010 1-Hour SO₂ Primary National Ambient Air Quality Standard for Wyoming” at https://www.epa.gov/​sites/​production/​files/​2017-12/​documents/​45-wy-so2-rd3-final.pdf. See also “Technical Support Document: Chapter 45 Intended Round 3 Area Designations for the 2010 1-Hour SO₂ Primary National Ambient Air Quality Standard for Wyoming” at https://www.epa.gov/​sites/​production/​files/​2017-08/​documents/​45_​wy_​so2_​rd3-final.pdf.

11.  The EPA's determination that the Shoshone-Bannock Tribes are eligible for treatment in the same manner as a state for CAA sections 110(a)(2)(D) and 126 is available in the docket for this action. See also https://www.epa.gov/​tribal/​tribes-approved-treatment-state-tas.

12.  Design values are from monitors with sufficient data available in the EPA's Air Quality System (AQS) to produce valid design values. Data retrieved from https://www.epa.gov/​air-trends/​air-quality-design-values#report.

13.  We have limited our analysis to Idaho sources emitting at least 100 tpy of SO₂ because in the absence of special factors, for example the presence of a nearby larger source or unusual physical factors, Idaho sources emitting less than 100 tpy can appropriately be presumed to not be causing or contributing to SO₂ concentrations above the NAAQS.

14.  The Simplot Don Siding Plant, P4 Production, and Itafos Conda are title V major stationary sources subject to the applicable limits and controls in the Idaho SIP, including Idaho's SIP-approved stationary source Permit to Construct program (IDAPA 58.01.01.200 through 222). The Simplot Don Siding Plant is owned or operated by J.R. Simplot Company, which is a party to a Federal Consent Decree to resolve CAA violations at the company's sulfuric acid plants. (Consent Decree, USA et al. v. J.R. Simplot Company, Case No. 1:15-cv-00562-CWD (Dist. Idaho 2015). On August 19, 2019, the Idaho Department of Environmental Quality issued a revised Permit to Construct to incorporate the consent decree requirements into the Simplot Don Siding Plant's permit. (P-2016-0055 Project 62103 issued pursuant to IDAPA 58.01.01.200 through 222.)

15.  A schematic map of the sources and their proximity to the Fort Hall Reservation is available in the docket for this action.

16.  The EPA used a tool developed and operated by Washington State University as part of the NW-AIRQUEST consortium. The tool estimates design concentrations from a regionally optimized photochemical air pollutant transport grid model that uses meteorological data and computes air pollutant emissions, transport, and chemistry using the EPA's CMAQ photochemical grid model. The model simulates industrial source emissions from point sources, including the Simplot Don Siding Plant, assuming a constant hourly emission rate of air pollutants based on the annual tons-per-year emissions provided in the 2014 National Emissions Inventory. The technical support document in the docket for this action provides additional information on the NW-AIRQUEST consortium's tool and the EPA's analysis.

17.  North Carolina v. EPA, 531 F.3d 896, 910-11 (D.C. Cir. 2008). The Court held that the EPA must give “independent significance” to each prong of CAA section 110(a)(2)(D)(i)(I). Id.

18.  Additional emissions trends data are available at: https://www.epa.gov/​air-emissions-inventories/​air-pollutant-emissions-trends-data.

19.  The EPA approved a consolidated pre-construction permitting program, including both major and minor source NSR, into the Idaho SIP on June 23, 1986 (51 FR 22810). Since that time, we have approved revisions to the program as consistent with the CAA and Federal NSR requirements codified at 40 CFR 51.160 through 40 CFR 51.166, most recently on August 20, 2018 (83 FR 42033).