2020-06348. Air Quality State Implementation Plan Approval; Nevada; Infrastructure Requirements for the 2010 Sulfur Dioxide National Ambient Air Quality Standard

AGENCY:

Environmental Protection Agency (EPA).

ACTION:

Proposed rule.

SUMMARY:

The Environmental Protection Agency (EPA) is proposing to approve the remaining portion of a state implementation plan (SIP) revision submitted by the State of Nevada. This revision addresses the interstate transport requirements of the Clean Air Act (CAA) with respect to the 2010 1-hour sulfur dioxide (SO₂) primary national ambient air quality standard (NAAQS). In this action, the EPA is proposing to determine that Nevada will not contribute significantly to nonattainment or interfere with maintenance of the 2010 1-hour SO₂ NAAQS in any other state. We are taking comments on this proposal and plan to follow with a final action.

DATES:

Comments must be received on or before April 30, 2020.

ADDRESSES:

Submit your comments, identified by Docket ID No. EPA-R09-OAR-2014-0812 at http://www.regulations.gov,, or via email to [e-mail]. For comments submitted at Regulations.gov, follow the online instructions for submitting comments. Once submitted, comments cannot be removed or edited from Regulations.gov. For either manner of submission, 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, please contact the person identified in the FOR FURTHER INFORMATION CONTACT section. For the full EPA public comment policy, information about CBI or multimedia submissions, and general guidance on making effective comments, please visit http://www.epa.gov/​dockets/​commenting-epa-dockets.

FOR FURTHER INFORMATION CONTACT:

Tom Kelly, EPA Region IX, [phone], [e-mail].

SUPPLEMENTARY INFORMATION:

Throughout this document, “we,” “us,” or “our” refer to the EPA.

Table of Contents

I. Background

II. Section 110(a)(2)(D)(i)(I)—Interstate Transport

A. General Requirements and Historical Approaches for Criteria Pollutants

B. Nevada's SIP Submittal

C. The EPA's Evaluation of Prong 1—Significant Contribution to Nonattainment

D. The EPA's Evaluation of Prong 2—Interference With Maintenance

III. Proposed Action

IV. Statutory and Executive Order Reviews

I. Background

On June 22, 2010, the EPA promulgated a revised primary NAAQS for SO₂ at a level of 75 parts per billion (ppb), based on a 3-year average of the annual 99th percentile of 1-hour daily maximum concentrations.^[1] Pursuant to section 110(a)(1) of the CAA, states are required to submit SIPs meeting the applicable requirements of section 110(a)(2) within three years after promulgation of a new or revised NAAQS or a shorter period as the EPA may prescribe. These SIPs, which the EPA has historically referred to as “infrastructure SIPs,” are to provide for the “implementation, maintenance, and enforcement” of such NAAQS, and the requirements are designed to ensure that the structural components of each state's air quality management program are adequate to meet the state's responsibility under the CAA. Section 110(a) of the CAA imposes the obligation upon states to make a 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. The content of the revisions proposed in SIP submissions may also vary depending upon what provisions are already contained in the state's approved SIP.

On June 3, 2013, the State of Nevada submitted a revision to its SIP addressing the requirements of section 110(a)(2) of the CAA with respect to the 2010 SO₂ NAAQS (“2013 Nevada SIP revision”). On November 3, 2015, the EPA partially approved and partially disapproved portions of the 2013 Nevada SIP revision for the 2010 SO₂ NAAQS.^[2] However, at that time, the EPA did not take action on the section 110(a)(2)(D)(i)(I), interstate transport portion of the 2013 Nevada SIP revision.^[3] The EPA is now proposing to act on that portion of the 2013 Nevada SIP revision for the 2010 SO₂ NAAQS.

II. Section 110(a)(2)(D)(i)(I)—Interstate Transport

A. General Requirements and Historical Approaches for Criteria Pollutants

Section 110(a)(2)(D)(i)(I) requires states to include in their SIPs 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 in another state. The two clauses of this section are referred to as prong 1 (significant contribution to nonattainment) and prong 2 (interference with maintenance of the NAAQS). The EPA commonly refers to SIP revisions addressing the requirements of section 110(a)(2)(D)(i)(I) as “good neighbor SIPs” or “interstate transport SIPs.”

The EPA's most recent infrastructure SIP guidance, the September 13, 2013 “Guidance on Infrastructure State Implementation Plan (SIP) Elements under Clean Air Act Sections 110(a)(1) and 110(a)(2),” did not explicitly include criteria for how the Agency would evaluate infrastructure SIP submissions intended to address section 110(a)(2)(D)(i)(I).^[4] With respect to certain pollutants, such as ozone and particulate matter, the EPA has addressed interstate transport in eastern states in the context of regional rulemaking actions that quantify state emissions reduction obligations.^[5] In other actions, such as the EPA actions on western interstate transport SIPs addressing ozone and particulate matter, the EPA has considered a variety of factors on a case-by-case basis to make a weight of evidence determination as to whether emissions from one state interfere with the attainment and maintenance of the NAAQS in another state. In such actions, the EPA has considered available information such as current air quality, emissions data and trends, meteorology, and topography.^[6]

1. The EPA's Approach for Addressing the Interstate Transport Requirements of the 2010 Primary SO₂ NAAQS in Nevada

As previously noted, section 110(a)(2)(D)(i)(I) requires an evaluation of any source or other type of emissions activity in one state and how emissions from these source categories may impact air quality in other states. The EPA believes that a reasonable starting point for determining which sources and emissions activities in Nevada are likely to impact downwind air quality with respect to the 2010 SO₂ NAAQS is to use information in the National Emissions Inventory (NEI).^[7] The NEI is a comprehensive and detailed estimate of air emissions of criteria pollutants, criteria pollutant precursors, and hazardous air pollutants from air emissions sources, that is updated every three years using information provided by the states. At the time of this proposed rulemaking, the most recently available complete dataset is the 2014 NEI. The analysis in this proposed rulemaking also relies on facility-reported emissions data, the most recent of which is for 2017.^[8] In addition, our analysis uses trends data, which the EPA prepares annually.^[9] Trends data include facility reported emissions data and data extrapolated by the EPA from the most recent NEI year.

Although SO₂ is emitted from similar point and nonpoint sources, as is directly emitted fine particulate matter (PM_2.5) ^[10] and the precursors to both 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 lead (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. Emitted SO₂ has wider ranging impacts than emitted Pb, but it does not have such wide-ranging impacts that its treatment in a manner similar to ozone or PM_2.5 would be appropriate. Accordingly, while the approaches that the EPA has adopted for ozone or PM_2.5 transport would be too regionally focused for SO₂, the approach for Pb transport would be too tightly circumscribed to the source. SO₂ transport is therefore a unique case and requires a different approach.

In this proposed rulemaking, as in prior SO₂ transport analyses, we focus on a 50 kilometer (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 properties of SO₂, the EPA selected a spatial scale with dimensions from four to 50 km from point sources—the “urban scale”—to assess trends in area-wide air quality that might impact downwind states.^[11] As discussed further in section III.B, the EPA selected the urban scale as appropriate for assessing trends in both area-wide air quality and the effectiveness of large-scale pollution control strategies at SO₂ point sources. The EPA's selection of this transport distance for SO₂ is based upon 40 CFR 58, Appendix D, Section 4.4.4(4), “Urban scale”, which states that measurements in this scale would be used to estimate SO₂ concentrations over large portions of an urban area with dimensions from four to 50 km. The American Meteorological Society/Environmental Protection Agency Regulatory Model is the EPA's preferred modeling platform for regulatory purposes for near-field dispersion of emissions for distances up to 50 km. (Appendix W of 40 CFR part 51).^[12] Thus, the EPA has applied the 50-km zone as a reasonable distance to evaluate emissions source impacts into neighboring states and to assess air quality monitors within 50 km of the State's border.

Current implementation strategies for the 2010 primary SO₂ NAAQS include the flexibility to characterize air quality for stationary sources via either data collected at ambient air quality monitors sited to capture the points of maximum concentration, or air dispersion modeling.^[13] The EPA's assessment of SO₂ emissions from fuel combustion categories in Nevada and their potential on neighboring states is informed by all available data at the time of this rulemaking and include: SO₂ ambient air quality; SO₂ emissions and emissions trends; SIP-approved regulations that directly address SO₂; and other SIP-approved regulations, which may yield reductions of SO₂. This notice describes the EPA's weight of evidence evaluation of the 2013 Nevada SIP revision to satisfy the requirements of CAA section 110(a)(2)(D)(i)(I).^[14]

B. Nevada's SIP Submittal

1. Administrative Requirements

On June 3, 2013, the Nevada Division of Environmental Protection (NDEP) submitted to the EPA the 2013 Nevada SIP revision.^[15] The submittal includes the following:

• The Nevada Division of Environmental Protection Portion of the Nevada State Implementation Plan for the 2010 Sulfur Dioxide Primary NAAQS, and appendices, June 3, 2013;
• State Implementation Plan Revision to Meet the Sulfur Dioxide Infrastructure SIP Requirements of the Clean Air Act § 110(a)(2), and attachments Clark County, Nevada, May 29, 2013;
• The Washoe County Portion of the Nevada State Implementation Plan to Meet the Sulfur Dioxide Infrastructure SIP Requirements of Clean Air Act § 110(a)(2), and attachments, March 28, 2013

The submittal was deemed complete by operation of law on December 3, 2013.

The Washoe and the NDEP portions of the submittal state that they are not required to make submittals addressing the requirements of CAA section 110(a)(2)(D)(i)(I) and cite to a November 19, 2012 memo from EPA Administrator Gina McCarthy, which outlined the EPA's intention to abide by a 2012 D.C. Circuit decision.^[16]

Despite stating in the NDEP portion of the submittal that it was not obligated to address the requirements of CAA section 110(a)(2)(D)(i)(I), the NDEP included Appendix C “Interstate Transport Analysis for the 2010 Sulfur Dioxide Primary National Ambient Air Quality Standard” (“Appendix C” or “transport analysis”) to address the aforementioned CAA requirements.

2. The NDEP's Transport Analysis

As the NDEP's portion of the submittal explains, the Clark County Department of Air Quality (Clark County) and Washoe County Board of Health (Washoe County) regulate air pollution within their respective counties, with the exception of fossil-fuel-fired steam generators. The NDEP regulates air pollution in all other counties of the State as well as fossil-fuel-fired steam generators throughout the State, including Clark County and Washoe County.

The following summarizes the NDEP's rationale for concluding that transport of SO₂ from Nevada would not significantly contribute to nonattainment, or interfere with maintenance, of the 2010 SO₂ NAAQS in other states.^[17]

a. Summary of Nevada's transport analysis regarding nonattainment receptors in contiguous states: Arizona and Utah.

The NDEP's transport analysis cites Clean Air Status and Trends Network (CASTNET) monitoring data in Nevada, Utah, Montana, Colorado, and Arizona. CASTNET data measure air quality in areas where urban influences are minimal, and, thus, are representative of regional background levels of air pollution.^[18] According to the NDEP, average weekly and seasonal SO₂ concentrations from six national parks and one national monument in Nevada, Utah, Montana, Colorado, and Arizona were below 2 ppb from 2007 to 2012, “indicating that the regional SO₂ background concentrations are relatively low, which in turn implies that the bulk of the SO₂ in the urban receptor areas is locally generated and not a regional or transport phenomenon.”

The Nevada transport analysis further explains that Arizona's only nonattainment receptors are the Hayden and Miami SO₂ nonattainment planning areas, located in Gila County and Pinal County, respectively. Total SO₂ emissions from Gila and Pinal counties were 29,470 tons from the 2008 NEI. The NDEP notes that Nevada's nearest SO₂ source, the recently closed Reid Gardner Generating Station,^[19] is 305 miles (490 km) from the Miami nonattainment area and 330 miles (530 km) from the Hayden nonattainment area and emitted only 941 tons of SO₂ in 2008, which, for illustrative purposes, was about three percent of the SO₂ emissions originating from the Miami and Hayden copper smelters.^[20] Additionally, the NDEP states that meteorological data show the prevailing wind direction in the southern part of the State is from the south-southwest blowing mainly north-northeast (indicating that winds in Nevada are generally not blowing south-southeast from Nevada toward Hayden and Miami in Arizona).^[21]

For Utah, the NDEP states that Salt Lake and Tooele counties are classified as nonattainment for the 24-hour and annual 1971 SO₂ NAAQS, but that the counties have not violated those NAAQS since 1981.^[22] The Nevada transport analysis concludes that no areas in Utah are likely to exceed the 2010 NAAQS based on monitoring data indicating that elevated SO₂ levels in Salt Lake and Tooele counties ceased decades ago, and CASTNET data demonstrating low levels of regional background SO₂.

b. Summary of Nevada's transport analysis regarding attainment areas in one contiguous western state: Arizona.

Nevada's transport analysis identifies four maintenance areas for the 1971 SO₂ NAAQS in Arizona: The Ajo, Douglas, Morenci, and San Manuel SO₂ planning areas. In its analysis, Nevada summarizes the approved maintenance plans for the areas and states that copper smelters were historically the primary source of SO₂ emissions. The transport analysis states that only one smelter, located in the San Manuel SO₂ maintenance area, remains operational and that there have been no recorded monitoring violations of the SO₂ NAAQS in any of these areas since the mid-1980s.

c. Summary of Nevada's transport analysis regarding nonattainment and maintenance receptor areas in non-contiguous states: Missouri, Montana, and New Mexico.

Nevada's transport analysis also examined transport to nonattainment receptors in Missouri and Montana and determined that SO₂ emissions from Nevada do not contribute to nonattainment in those areas based on a comparison of the emissions inventories in those states and Nevada, wind patterns, and the distance between those states and Nevada.

In addition, the Nevada transport analysis evaluated maintenance receptors in New Mexico and determined that Nevada does not interfere with maintenance in that state based on comparison of the emissions inventories in New Mexico and Nevada, overall regional background levels of SO₂, and the distance between New Mexico and Nevada.

C. The EPA's Evaluation of Prong 1—Significant Contribution to Nonattainment

Prong 1 of the good neighbor provision requires state plans to prohibit emissions that will significantly contribute to nonattainment of a NAAQS in another state. In order to evaluate whether Nevada met prong 1 for the 2010 SO₂ NAAQS, the EPA evaluated the 2013 Nevada SIP revision with respect to the following two factors: (1) SO₂ ambient air quality in Nevada and neighboring states; and (2) SO₂ emissions sources in Nevada and neighboring states. Based on the detailed discussion of these factors below, the EPA proposes to find that Nevada's SIP meets the interstate transport requirements of CAA Section 110(a)(2)(D)(i)(I), prong 1, for the 2010 SO₂ NAAQS.

1. SO₂ Ambient Air Quality in Nevada and Neighboring States

First, the EPA reviewed ambient air quality data in Nevada and neighboring states to see whether there were any monitoring sites with elevated SO₂ concentrations that might warrant further investigation with respect to interstate transport of SO₂ from emissions sources near any given monitor. As shown in Table 1, there are no violating design values ^[23] between 2014 and 2018 in Nevada or neighboring states apart from monitors located in the Hayden and Miami nonattainment areas in Arizona.^[24]

Table 1—SO₂ Design Values for Nevada and Neighboring States

[ppb]

Monitoring site	State	Area	Distance to Nevada border (km)	2014-2016	2015-2017	2016-2018
32-003-0540	NV	Las Vegas	32 km to AZ and 62 km to CA	7	6	6
32-031-0016	NV	Reno	17 km to CA	5	5	4
04-007-1001	AZ	Hayden NAAa	419	280	295	282
04-007-0009	AZ	Miami NAA	391	146	NAb	NA
04-007-0011	AZ	Miami NAA	391	200	221	175
04-007-0012	AZ	Miami NAA	389	194	159	127
04-012-8000	AZ	Wenden	130	3	NA	NA
04-013-3002	AZ	Phoenix	193	7	7	7
04-013-9812	AZ	Phoenix	290	8	9	8
04-013-9997	AZ	Phoenix	287	5	6	6
04-013-1028	AZ	Tucson	452	4	3	2
06-013-0002	CA	Concord	212	8	7	8
06-013-1002	CA	Bethel Island	181	4	4	3
06-019-0011	CA	Fresno	171	6	6	6
06-067-0006	CA	Arden-Arcade	126	7	8	2
06-071-0306	CA	Victorville	210	18	3	3
06-071-1234	CA	Trona	110	6	13	6
(26-31 Other Monitoring Locations)	CA	All Other Monitors in Californiac	216-405	1-18	1-14	1-16
16-001-0010	ID	near Boise	178	4	3	3
16-005-0004	ID	Pocatello	162	39	38	44
16-029-0031	ID	Soda Springs	216	26	30	27
41-051-0080	OR	Portland	442	3	3	3
49-035-3006	UT	Salt Lake City	183	NA	NA	NA
49-035-2005	UT	Midvale	182	NA	NA	NA
49-035-3010	UT	Salt Lake City	178	NA	NA	NA
a NAA—nonattainment area.
b NA—Not available for monitors lacking a valid design value in the given year due to missing or incomplete data.
c This table only includes specific results for monitors within 215 km of the Nevada-California border. Other California monitors are summarized in one row.

Table 2 lists the annual 99th percentiles for SO₂ monitors that collected either three or four complete quarters of data in the specified year but lacked three consecutive years of complete data (i.e., a design value) like the monitors in Table 1. Again, the only monitor exceeding the 2010 SO₂ NAAQS is located in the Miami nonattainment area.

Table 2—Annual SO₂ 99th Percentiles for Monitors in Neighboring States Lacking a Design Value

[ppb]

Monitoring site	State	Area	Distance to Nevada border (km)	2016	2017	2018
04-007-0009	AZ	Miami NAA a	391	120	N/A b	NA
49-035-3006	UT	Salt Lake City	183	N/A	4	3
a NAA—nonattainment area.
b N/A—Not available, less than three complete quarters of data were collected for this monitor in the given year.

In concluding that Nevada would not impact receptors in the Hayden or Miami nonattainment areas in Arizona, Nevada's submittal noted several factors, including the prevailing wind direction in Las Vegas to the south and southwest and the significant distance, more than 300 miles (482 km), between the nonattainment areas and the nearest large generator of SO₂ emissions in southern Nevada, the now closed Reid Gardner Generating Station. At the closest point at Nevada's southern tip, the Hayden and Miami nonattainment areas are 350 km from the Nevada border, far outside the range within which we might expect a potential impact from SO₂ sources located in Nevada, given the localized range of potential 1-hour SO₂ emissions.

The data presented in Table 1 show that Nevada's SO₂ monitors, with sufficient data to produce valid 1-hour SO₂ design values, indicate that monitored 1-hour SO₂ concentrations in Nevada are between 5 percent (%) and 9% of the 75 ppb 1-hour SO₂ NAAQS. The Reno monitor is located within 50 km of the California border and the Las Vegas monitor is located within 50 km of the Arizona border. The highest SO₂ concentration within 300 km of Nevada is the Pocatello Idaho monitor, which is 59% of the NAAQS based on the 2018 design value and 162 km from the Nevada border. The low level of SO₂ at these air quality monitors in and near Nevada do not, by themselves, indicate any particular location that would warrant further investigation with respect to SO₂ emissions sources that might significantly contribute to nonattainment in neighboring states. However, because the monitoring network is not necessarily designed to find all locations of high SO₂ concentrations, this observation 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.

2. Analysis of SO₂ Emissions Sources in Nevada and Neighboring States

To understand the potential for Nevada's emissions to contribute significantly to nonattainment in another state, we begin with a summary of the State's SO₂ emissions in Table 3 from the 2014 NEI.^[25] The EPA believes a reasonable starting point for determining which sources and emissions activities in Nevada are likely to impact downwind air quality in other states with respect to the 2010 1-hour SO₂ NAAQS is by using information in the EPA's 2014 NEI. The NEI is a comprehensive and detailed estimate of air emissions for criteria pollutants, criteria pollutant precursors, and hazardous air pollutants from air emissions sources; it is updated every three years using information provided by the states and other information available to the EPA. The 2014 NEI (version 2) is the most recently available complete and quality assured dataset of the NEI that includes all emissions categories.

Table 3—Summary of 2014 NEI SO₂ Emissions Data for Nevada by Source Category ^a

Category	SO2 emissions (tons per year)
Fuel Combustion, Electric Generation	10,277
Fuel Combustion Industrial	2,967
Fires	840
Mobile	556
Fuel Combustion Commercial	642
Waste Disposal	293
Industrial Processes (non-combustion)	540
Other	61
Total Nevada SO2 Emissions	16,178
a The sum of the categories does not add to the total due to rounding.

As shown in Table 3, the majority of SO₂ emissions in Nevada originate from fuel combustion at point sources. In 2014, SO₂ emissions from fuel combustion point sources accounted for approximately 85% of the State's SO₂ emissions.^[26] With the closure of the Reid Gardner Generating Station, which accounted for over 15% of overall SO₂ emissions in the 2014 NEI, the SO₂ state-wide total should be substantially smaller once the 2017 emissions inventory is released. The next largest category of emissions is fire. According to the 2014 NEI, approximately 92% of fire emissions are from wildfires, which vary in location and quantity of emissions from year to year, while most of the other fire emissions come from prescribed burning. Of the remaining emissions (mobile, waste disposal, non-combustion industrial, and other, which make up approximately 9% of the state total), slightly more than half (about 5% of the state-wide total or 880 tons) originate in Clark County, which contains approximately 75% of Nevada's population, and the rest originate elsewhere throughout the State.

Emissions from the other listed source categories are more dispersed throughout the State, with the exception of McCarran Airport and Sunrise Landfill analyzed later in this notice. Due to the dispersed nature of these other source categories, their emissions are less likely to cause high ambient concentrations when compared to a point source on a ton-for-ton basis. Based on the EPA's analysis of the 2014 NEI SO₂ emissions data, the EPA considers it to be appropriate to focus the discussion on SO₂ emissions from Nevada's larger point sources (i.e., those emitting over 50 tons per year (tpy) of SO₂), which are located within the “urban scale,” i.e., within 50 km of one or more state borders.

Specifically, in 2014 60 percent of the statewide SO₂ emissions came from two facilities.^[27] The first, the North Valmy Generating Station, is 124 km from the state border, well beyond the 50-km threshold zone considered to be a reasonable distance to evaluate emissions source impacts to neighboring states for purposes of this analysis. In addition, EPA recently considered a modeling analysis submitted by the NDEP to support its recommendation that the EPA designate the entire State of Nevada as attainment/unclassifiable for the 2010 SO₂ NAAQS.^[28] The modeling was conducted in response to the Final Data Requirements Rule for the 2010 1-Hour SO₂ Primary NAAQS.^[29] As required by the rule, Nevada identified the North Valmy Generating Station as a facility emitting more than 2,000 tpy of SO₂ in 2014.^[30] Based on modeling that shows a maximum SO₂ concentration of 63 ppb, the EPA determined that the North Valmy Generating Station “is not modeled to cause or contribute to violations of the 2010 SO₂ [NAAQS],” and the EPA designated the area around North Valmy Generating Station, along with the rest of the State, as attainment/unclassifiable for the 2010 SO₂ NAAQS.^[31]

The North Valmy Generating Station is located 124 km from the Nevada-Oregon border and 125 km from the Nevada-Idaho border. Based on 2017 facility reported emissions data, Nevada has no other facilities emitting more than 50 tpy of SO₂ within 50 km of the State's border that could potentially combine with the emissions from the North Valmy Generating Station to contribute to nonattainment in the nearby states of Idaho and Oregon. The closest facility to the North Valmy Generating Station is the TS Power Plant, which is slightly more than 50 km from the North Valmy facility and more than 130 km from the Nevada-Idaho and Nevada-Oregon borders. This information supports the EPA's proposed conclusion that the North Valmy facility, in combination with Nevada's other SO₂ emissions sources, will not contribute significantly to nonattainment of the 2010 SO₂ NAAQS in any other state.

The second facility contributing 60 percent of statewide SO₂ emissions in 2014 is the Reid Gardner Generating Station that ceased operation in 2017. Consequently, this facility does not warrant further investigation with respect to SO₂ emissions sources that might significantly contribute to nonattainment in neighboring states.^[32]

Table 4 below shows all other Nevada sources that generated more than 50 tpy of SO₂ emissions in 2017 located within 50 km of the state border, including Nevada's second largest active source of SO₂ emissions, the McCarran Airport. Table 4 also lists the nearest out-of-state neighboring sources emitting above 50 tpy of SO₂ because elevated levels of SO₂, to which SO₂ emitted in Nevada may have a downwind impact, are most likely to be found near such sources.^[33] As shown in Table 4, the shortest distance between a Nevada source and a neighboring state source, with both emitting more than 50 tpy of SO₂, is 167 km. Furthermore, neighboring states have no sources of SO₂ emissions greater than 50 tpy located within 50 km of the Nevada border. Given the localized range of potential 1-hour SO₂ impacts, the data indicate that there are no additional locations in neighboring states that would warrant further investigation with respect to individual Nevada SO₂ emissions sources that might contribute to nonattainment of the 2010 SO₂ NAAQS.

Table 4—Nevada Sources With SO₂ Emissions Greater than 50 tons in 2017 Within 50 km of a Neighboring State

Nevada source	2017 Emissions a (tons)	Distance to border	Distance to the closest neighboring SO2 source more than 50 tpy (km)	Name of the closest neighboring SO2 source more than 50 tpy	Neighboring state SO2 source 2017 emissions (tons)
McCarran International Airport, Las Vegas	467	37 km (AZ)	178	Lhoist North America (NA), Chemical Lime Nelson Plant	1,678
Republic Services Sunrise (Landfill), Las Vegas	191	23 km (AZ)	167	Lhoist NA, Chemical Lime Nelson Plant	1,678
Lockwood Sanitary Landfill, Sparks	149	33 km (CA)	193	Sacramento International Airport	112
Lhoist NA and Granite Construction (Apex), Las Vegas	140	32 km (AZ)	171	Lhoist NA, Chemical Lime Nelson Plant	1,678
EP Minerals, Clark Plant, Clark	82	45 km (CA)	206	Sacramento International Airport	112
Reno-Tahoe International Airport	53	19 km (CA)	181	Sacramento International Airport	112
a Emissions are based on the 2017 facility reported NEI emissions data for point sources downloaded from https://www.epa.gov/​air-emissions-inventories/​2017-national-emissions-inventory-nei-data on October 9, 2019, and contained in the docket for this notice.

3. Conclusion

In order to determine whether Nevada satisfied prong 1 for the 2010 SO₂ NAAQS, the EPA evaluated the State's 2013 SIP revision with respect to the following two factors: (1) SO₂ ambient air quality in Nevada and neighboring states; and (2) SO₂ emissions sources in Nevada and neighboring states. For the first factor, we identified no violating monitors near the Nevada border, and the only violating monitors in neighboring states are well outside the range within which we might expect them to be significantly impacted by interstate transport of SO₂ from Nevada. For the second factor, we identified no SO₂ sources within 50 km of the Nevada border that are likely contributing to a violation of the standard in another state, and we conclude that it is unlikely that sources farther from the border are leading to violations. Therefore, based on the analysis provided by the State in its SIP submission and the factors discussed above, the EPA proposes to find that Nevada will not cause or contribute significantly to nonattainment of the 2010 1-hour SO₂ NAAQS in any other state.

D. The EPA's Evaluation of Prong 2—Interference With Maintenance

Prong 2 of the good neighbor provision requires state plans to prohibit emissions that will interfere with maintenance of a NAAQS in another state. The EPA considers that reasonable criteria to ensure that sources or emissions activities originating within Nevada will not interfere with its neighboring states' ability to maintain the NAAQS involves a close examination of the following: (1) Air quality trends in Nevada and neighboring states; (2) SIP-approved state and county measures that limit existing and new facility emissions; and (3) ambient concentrations of SO₂ in Nevada and neighboring states.

1. Air Quality Trends for Nevada and Neighboring States

As shown in Table 5 below, the statewide Tier 1 SO₂ emissions trends for Nevada and neighboring states have substantially decreased over time.^[34] Since 2000, overall SO₂ emissions have decreased by 89% in Nevada, 66% in Arizona, 82% in California, 77% in Idaho, 82% in Oregon, and 74% in Utah. The size and geographic scope of these reductions strongly suggest that the reductions are not transient effects from temporary causes and suggest that a trend of increasing emissions is unlikely to occur in these states.

Table 5—Tier 1 SO₂ Emissions Trends for Nevada and Neighboring States (tpy) ^a

State	2000	2005	2010	2015	2017
Arizona	116,207	89,198	71,706	43,623	39,243
California	80,698	155,677	35,769	22,956	22,835
Idaho	23,015	22,962	11,718	5,396	5,386
Nevada	61,689	71,609	14,065	10,352	6,947
Oregon	53,237	24,916	19,625	9,500	8,182
Utah	56,039	51,945	28,932	19,865	14,832
a Data downloaded from https://www.epa.gov/​air-emissions-inventories/​air-pollutant-emissions-trends-data (State Annual Average Emission Trend) and included in the docket for today's notice. See SO2 Trends Tier 1.xlsx.

Table 6 shows the emissions trend since 2008 for all Nevada facilities that emitted more than 100 tpy of SO₂. While some facilities, such as McCarran International Airport, show an increasing trend, the increases are small relative to the decreases at the North Valmy Generating Station and Reid Gardner Generating Station, and the overall downward trend in SO₂ emissions in Nevada is illustrated by the row showing total point source emissions.

Table 6—SO₂ Emission Trends for Nevada Facilities That Have Emitted More Than 50 tpy Since 2008 ^a

Facility name	EIS ID	2008	2011	2014	2017
NV Energy, North Valmy Generating Station	7302011	8,130	3,550	7,430	1,588
McCarran International (Airport)	9392311	264	272	265	467
EP Minerals LLC, Colado Plant	6030011	72	140	26	250
Republic Services Sunrise	9398611	163	197	209	191
Newmont Nevada Energy LLC, TS Power Plant	12758911	364	250	234	152
Lockwood Sanitary Landfill	6030711	0	69	43	149
Lhoist North America and Granite Const. (Apex)	8210711	180	229	152	140
Newmont Mining Corp. Twin Creek Mine	8178211	38	6	6	102
Nevada Cement, Fernley Plant	8179811	282	118	126	90
Barrick Goldstrike Mines Inc., GoldStrike Mine	8177811	40	28	50	70
Reno Tahoe Airport	9376411	NA b	50	25	53
Graymont Western U.S. Pilot Peak Plant	6673911	28	30	23	15
(Newmont) Gold Quarry	8210011	56	59	15	12
Foreland Refining (Eagle Springs)	8179311	76	85	77	7
NV Energy Reid Gardner Generating Station	6815611	941	1,423	2,506	c 0
Halliburton Energy Services Dunphy Plant & Crusher	7200311	194	3	1	0
All Nevada Point Source Emissions	NA	11,598	6,901	11,594	3,710
All Nevada Emissions	NA	20,951	13,578	16,175	NA
a Data from the NEI (files 2008 NEI V3, 2011 NEI V2, 2014 NEI V2, and 2017Oct) downloaded to 2002-2017 NV Facility Data.xlsx.
b NA—Not available.
c No emissions were reported to the EPA's NEI in 2017 for the Reid Gardner Generating Station, but emissions of 168 tons in 2017 were reported to the EPA's Clean Air Markets program (data query on 11/18/2019).

While these trends do not by themselves demonstrate that Nevada and neighboring states will not have issues maintaining the 2010 SO₂ NAAQS, when considered alongside low ambient concentrations in Nevada and neighboring states, as illustrated in Table 1, they provide further evidence that emissions of SO₂ from Nevada are unlikely to interfere with maintenance of the SO₂ NAAQS in other states.

2. Nevada's Air Quality Rules

The 2013 Nevada SIP submittal identifies many rules for controlling current and future SO₂ or sulfur oxides (SO_X) emissions.^[35] The rules identified by the NDEP primarily regulate fuel combustion from large power plants as well as smaller stationary combustion sources (e.g., portable generators). The NDEP retains authority over facilities that generate electricity by using steam produced from fossil fuels, even if located within Clark or Washoe counties. Emissions limits for SO_X are set by Nevada Administrative Code (NAC) 445B.22095 and NAC 445.22096. NAC 445B.22095 identifies factors considered in determining best available control technology (BACT) for major sources, and NAC 445B.22096 provides numeric emissions limits for specific sources where BACT has been established for the Nevada Energy Tracy Generating Station and the Nevada Energy Fort Churchill Generating Station.^[36] NAC 445B.22047 and Article 8.2.1 limit SO₂ emissions from the combustion of fuel based on the heat input of the fuel in British Thermal Units (BTUs). NAC 445B.2205 limits SO₂ emissions from other processes. Nevada also identified many supporting regulations, such as rules covering definitions, calculations, and exemptions, including the following: NAC 445B.22043 (“Sulfur emissions: Calculation of total feed sulfur”); NAC 445B.22083 (“Construction, major modification or relocation of plants to generate electricity using steam produced by burning fossil fuels”); NAC 445B.308 (“Prerequisites and conditions for issuance of certain operating permits; compliance with applicable state implementation plan”); NAC 445B.310 (“Environmental evaluation: Applicable sources and other subjects; exemption”); and NAC 445B.311 (“Environmental evaluation: Contents; and consideration of good engineering practice stack height”).^[37]

Clark County broadly identified permitting rules limiting current and future SO₂ and hydrogen sulfide emissions. More specifically, Clark County permits require the following: Reasonably available control technology (RACT) for minor sources (25 tpy for SO₂) and existing sources with significant emissions increases, if a RACT determination has been made; ^[38] BACT for major new sources and existing sources proposing significant increases in attainment areas; ^[39] and a limit on maximum increment increases of SO₂ for areas with a regional haze designation of Class I, Class II, or Class III.^[40]

For limiting SO₂ emissions, Washoe County identified rules that control trace quantities of SO_X emissions from the storage of petroleum products, gasoline loading, gasoline unloading, and the use of organic solvents.^[41] An additional SIP-approved Washoe County regulation that controls SO_X is Section 040.060 (“Sulfur Content of Fuel”). It limits the sulfur content to 0.7% by weight for solid fuels and 1.0% for liquid fuels burned at less than 250 million BTUs of heat input. For fuels burned at more than 250 million BTUs of heat input per hour, Section 040.060 provides a calculation that sets a maximum quantity of sulfur (in pounds per hour).

In conclusion, for interstate transport prong 2, we reviewed SO₂ emissions trends in Nevada and neighboring states, Nevada's SIP-approved rules regulating SO₂ and SO_X, and the technical information related to SO₂ ambient air quality and SO₂ emissions for interstate transport prong 1, as discussed above. Based on (1) the downward trend in SO₂ emissions in Nevada and neighboring states; (2) SIP-approved State and local measures that limit existing and new facility emissions; and (3) the low ambient concentrations of SO₂ in Nevada and neighboring states, we propose to determine that the 2013 Nevada SIP revision demonstrates that SO₂ emissions in the State will not interfere with maintenance of the 2010 SO₂ NAAQS in any other state, per the requirements of prong 2 of CAA section 110(a)(2)(D)(i)(I).

III. Proposed Action

In light of the above analysis, the EPA is proposing to approve Nevada's infrastructure submittal for the 2010 SO₂ NAAQS as it pertains to section 110(a)(2)(D)(i)(I) of the CAA.

We will accept comments from the public on these proposals for the next 30 days and plan to follow with a final action. The deadline and instructions for submission of comments are provided in the DATE and ADDRESSES sections at the beginning of this proposed rule.

IV. 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 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 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 application of those requirements would be inconsistent with the Clean Air Act; and
• Does not provide the EPA with the discretionary authority to address disproportionate human health or environmental effects with practical, appropriate, 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 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
• Sulfur oxides

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

Dated: March 20, 2020.

John Busterud,

Regional Administrator, Region IX.

Footnotes

1.  75 FR 35520.

2.  The EPA's final rule (80 FR 67652) addressed all elements of the three separate SIP submittals for 2008 ozone, 2010 nitrogen oxides, and 2010 SO₂, with the exception of interstate transport requirements (prongs 1 and 2) for 2008 ozone, addressed in a subsequent rulemaking (82 FR 9164, February 3, 2017), and prongs 1 and 2 of the interstate transport requirements for 2010 SO₂ addressed in this proposal.

3.  In addition to section 110(a)(2)(D)(i)(I) provisions for SO₂, the EPA did not act on the section 110(a)(2)(D)(i)(I) provisions of Nevada's SIP submittal for the 2008 ozone NAAQS that was part of the same rulemaking. The EPA approved the section 110(a)(2)(D)(i)(I) portion of Nevada's submittal for the 2008 ozone NAAQS in a subsequent rulemaking, 82 FR 9164 (February 3, 2017).

4.  At the time the September 13, 2013 guidance was issued, the EPA was litigating challenges raised with respect to its Cross State Air Pollution Rule (“CSAPR”), 76 FR 48208 (Aug. 8, 2011), designed to address the CAA section 110(a)(2)(D)(i)(I) interstate transport requirements with respect to the 1997 ozone and the 1997 and 2006 PM_2.5 NAAQS. CSAPR was vacated and remanded by the D.C. Circuit in 2012 pursuant to EME Homer City Generation, L.P. v. EPA, 696 F.3d 7. The EPA subsequently sought review of the D.C. Circuit's decision by the Supreme Court, which was granted in June 2013. As the EPA was in the process of litigating the interpretation of section 110(a)(2)(D)(i)(I) at the time the infrastructure SIP guidance was issued, the EPA did not issue guidance specific to that provision. The Supreme Court subsequently vacated the D.C. Circuit's decision and remanded the case to that court for further review. 134 S.Ct. 1584 (2014). On July 28, 2015, the D.C. Circuit issued a decision upholding CSAPR, but remanding certain elements for reconsideration. 795 F.3d 118.

5.  See, e.g., NO_X SIP Call, 63 FR 57371 (October 27, 1998); Clean Air Interstate Rule (CAIR), 70 FR 25172 (May 12, 2005); CSAPR, 76 FR 48208 (August 8, 2011); CSAPR Update, 81 FR 74504 (October 26, 2016).

6.  See, e.g., Approval and Promulgation of Implementation Plans; State of California; Interstate Transport of Pollution; Significant Contribution to Nonattainment and Interference With Maintenance Requirements, Proposed Rule, 76 FR 14616, 14616-14626 (March 17, 2011); Final Rule, 76 FR 34872 (June 15, 2011); Approval and Promulgation of State Implementation Plans; State of Colorado; Interstate Transport of Pollution for the 2006 24-Hour PM_2.5 NAAQS, Proposed Rule, 80 FR 27121, 27124-27125 (May 12, 2015); Final Rule, 80 FR 47862 (August 10, 2015).

7.  For additional information, see: https://www.epa.gov/​air-emissions-inventories/​national-emissions-inventory.

8.  Data downloaded on October 9, 2019, from: https://www.epa.gov/​air-emissions-inventories/​2017-national-emissions-inventory-nei-data,, dataset: 2017NEI_Aug2019_PT, and contained in the docket for this notice.

9.  State Annual Emission Trend data can be downloaded from https://www.epa.gov/​air-emissions-inventories/​air-pollutant-emissions-trends-data. Trends data does not include event emissions, such as forest fires.

10.  Includes particles with an aerodynamic diameter of less than or equal to 2.5 micrometers.

11.  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 applies these definitions with respect to interstate transport of SO₂, see the EPA's notice of proposed rulemaking on Connecticut's SO₂ transport SIP. 82 FR 21351, 21352, 21354 (May 8, 2017).

12.  The EPA provided non-binding technical assistance document (i.e., “SO₂ NAAQS Designations Modeling Technical Assistance Document”) to assist states and other parties in their efforts to characterize air quality through air dispersion modeling for sources that emit SO₂. This draft document was first released in spring 2013. Revised drafts were released in February and August of 2016 (see https://www.epa.gov/​sites/​production/​files/​2016-06/​documents/​so2modelingtad.pdf).

13.  Data Requirements Rule for the 2010 1-Hour Sulfur Dioxide (SO₂) Primary National Ambient Air Quality Standard (80 FR 51052, August 21, 2015).

14.  The EPA notes that the evaluation of other states' satisfaction of section 110(a)(2)(D)(i)(I) for the 2010 SO₂ NAAQS can be informed by similar factors found in this proposed rulemaking but may not be identical to the approach taken in this or any future rulemaking for Nevada, depending on available information and state-specific circumstances.

15.  Letter dated June 3, 2013, from Colleen Cripps, Administrator, NDEP, to Jared Blumenfeld, Regional Administrator, EPA Region IX.

16.  EME Homer City Generation, L.P. v. E.P.A. 696 F.3d 7. The EME Homer City Generation, L.P. v. E.P.A. decision addressed CSAPR promulgated by the EPA to address the interstate transport requirements under section 110(a)(2)(D)(i)(I) with respect to the 1997 ozone NAAQS, the 1997 PM_2.5 NAAQS, and the 2006 PM_2.5 NAAQS. Among other things, the D.C. Circuit held that states did not have an obligation to submit SIPs addressing section 110(a)(2)(D)(i)(I) interstate transport requirements as to any NAAQS until the EPA first quantified each state's emissions reduction obligation. On March 25, 2016, the Supreme Court reversed the D.C. Circuit opinion, vacating the EME Homer City Generation, L.P. v. E.P.A. decision.

17.  See C-1 to C-9 (Appendix C) of the NDEP portion of the 2013 Nevada SIP revision.

18.  The NDEP reviewed CASTNET data at six national parks and one national monument in: Nevada (Great Basin National Park), Utah (Canyonlands National Park), Montana (Glacier National Park), Colorado (Mesa Verde National Park), and Arizona (Grand Canyon National Park, Petrified Forest National Park, and Chiricahua National Monument).

19.  As discussed in the EPA's rescission of regional haze federal implementation plan for the Reid Gardner Generating Station, three of the Reid Gardner Generating Station's coal-fired boilers ceased operation in 2014 and the fourth ceased operation in 2017. See 83 FR 24952, May 31, 2018.

20.  This quantity was based on the 2008 NEI.

21.  Discussed at C-2 and documented in Figure C.1, Las Vegas, Nevada, Wind Rose Plot, 2003-2011, of the 2013 SIP submittal.

22.  The entire state of Utah is attainment/unclassifiable for the 2010 SO₂ NAAQS, see https://www.ecfr.gov/​cgi-bin/​text-idx?​SID=​dab140f1447715b3662a38473ba7df7d&​mc=​true&​node=​se40.20.81_​1345&​rgn=​div8 (last visited on May 1, 2019).

23.  The 2010 l-hour SO₂ NAAQS is met at an ambient air quality monitoring site when the three-year average of the annual (99th percentile) of the daily maximum l-hour average concentrations is less than or equal to 75 ppb. This metric is referred to as a “design value” (in this document referred to as the “SO₂ l-hour design value”). The EPA's data handling conventions and computations necessary for determining compliance with the 2010 1-hour SO₂ NAAQS are provided in 40 CFR part 50, appendix T.

24.  Data for Table 1 is contained in the docket for this notice. See SO₂ monitor report 2018.pdf, SO₂ monitor report 2017.pdf, and SO₂ monitor report 2016.pdf.

25.  The EPA's NEI is available at https://www.epa.gov/​air-emissions-inventories/​national-emissions-inventory.

26.  Nevada's fuel combustion point sources listed in Table 3, for the purposes of this action, are comprised of all of the “Fuel Combustion” categories, i.e., Fuel Combustion, Electric Generation; Fuel Combustion, Industrial; and Fuel Combustion, Commercial.

27.  In 2014, the North Valmy Generating Station emitted 7,430 tons of SO₂ and the Reid Gardner Generating Station emitted 2,506 tons of SO₂, per the 2014 NEI.

28.  83 FR 1098 (January 9, 2018). The North Valmy Generating Station is specifically discussed in Chapter 26, Technical Support Document: Intended Round 3 Area Designations for the 2010 1-Hour SO₂ Primary National Ambient Air Quality Standard, EPA, August 2017, which is available in the docket for today's notice.

29.  This Rule required sources emitting more than 2,000 tpy of SO₂ to characterize their air quality impacts through ambient air monitoring or dispersion modeling.

30.  The North Valmy Generating Station generated 1,588 tons of SO₂ emissions in 2017, per the 2017 NEI, which includes only facility reported point source emissions data at this time.

31.  Technical Support Document: Chapter 26 Intended Round 3 Area Designations for the 2010 1-Hour SO₂ Primary National Ambient Air Quality Standard for Nevada, EPA, page 27, August 2017.

32.  As discussed in the EPA's rescission of regional haze federal implementation plan for the Reid Gardner Generating Station, three of the Reid Gardener Generating Station's coal-fired boilers ceased operation in 2014 and the fourth ceased operation in 2017. See 83 FR 24952, May 31, 2018.

33.  Table 4 contains more recent data than Table 3 because the EPA has only released facility reported point source data from the 2017 NEI.

34.  Tier 1 emissions trends data do not include event emissions, which include forest fires and prescribed or intentionally set fires.

35.  SO_X is a group of gases that includes SO₂ and other less common oxides of sulfur in the atmosphere, see https://www.epa.gov/​so2-pollution.

36.  This rule also discusses the Mojave Generation Station, which has been demolished (82 FR 48769, October 20, 2017), and the closed Reid Garner Generating Station.

37.  The NDEP implements its minor source (25 tpy) permitting through Nevada Revised Statutes 445B.310, 311 and NAC 308. See EPA's Technical Support Document, Evaluation of the Nevada Infrastructure SIP for 2008 Ozone, 2010 NO₂ and 2010 SO₂, 19. The NDEP implements its major source permitting through a prevention of significant deterioration federal implementation plan.

38.  See Air Quality Regulation (AQR) 12.1.3.6(c)(1) and (2).

39.  See AQR 12.2.9.1 and 12.2.9.2.

40.  Microgram per meter cubed SO₂ limits for annual mean, 24-hour maximum, and 3-hour maximum, per AQR 12.2.3. The discussion of Element A in the EPA's Technical Support Document, Evaluation of the Nevada Infrastructure SIP for 2008 Ozone, 2010 NO₂, and 2010 SO₂ contains regulatory citations for Clark County rules, with the exception of maximum increment increases that can be found in the Clark County Regulations at AQR 12.2.3. and the variance procedure at 12.2.15.4.

41.  Washoe Rules 040.070, 040.075, 040.080, and 040.085.