SUPPLEMENTARY INFORMATION:

Throughout this document, “we,” “us,” and “our” refer to the EPA. We use multiple abbreviations in this preamble. While the following list may not be exhaustive, for ease of reading and for reference purposes, the EPA defines the following abbreviations here:

Act: Clean Air Act

AERR: Air Emissions Reporting Requirements rule

AQMD: Air Quality Management Division

AQS: EPA Air Quality System database

CAA: Clean Air Act

Calcagni Memo: September 4, 1992 EPA memorandum from John Calcagni, titled “Procedures for Processing Requests to Redesignate Areas to Attainment”

CBI: Confidential Business Information

CMTC: Contingency Measure Trigger Calculation

DBOH: District Board of Health

EPA: U.S. Environmental Protection Agency

FHWA: Federal Highway Administration

FTA: Federal Transit Administration

lbs/day: Pounds per Day

μg/m³ : micrograms per cubic meter

NAAQS: National Ambient Air Quality Standard

NDEP: Nevada Division of Environmental Protection

NEI: National Emissions Inventory

NNPH: Northern Nevada Public Health

NO_X: Nitrogen Oxides

Plan: Second 10-Year Maintenance Plan for the Truckee Meadows 24-Hour PM₁₀ Attainment Area or Truckee Meadows Second PM₁₀ Maintenance Plan

PM₁₀: Inhalable particles with diameters that are 10 micrometers or less.

SIP: State Implementation Plan

SLAMS: State and Local Air Monitoring Stations

SO_X: Sulfur Oxides

VOC: Volatile Organic Compound

Table of Contents

I. Background

A. What action is the EPA proposing to take?

B. What is the legal authority and what are the requirements?

C. The PM₁₀ National Ambient Air Quality Standards

D. The Truckee Meadows PM₁₀ Planning Area

E. PM₁₀ Planning in the Truckee Meadows Area

II. Air Quality in the Truckee Meadows Area

III. Procedural Requirements for Adoption and Submittal of State Implementation Plan Revisions

IV. Evaluation of the Truckee Meadows Second PM₁₀ Maintenance Plan

A. Emissions Inventory

B. Maintenance Demonstration

C. PM₁₀ Air Quality Monitoring Network

D. Verification of Continued Attainment

E. Contingency Provisions

F. Motor Vehicle Emissions Budgets for Transportation Conformity

V. Proposed Action and Request for Public Comment

VI. Statutory and Executive Order Reviews

I. Background

A. What action is the EPA proposing to take?

The EPA is proposing to approve the Truckee Meadows Second PM₁₀ Maintenance Plan as a revision to the Washoe County portion of the SIP for the State of Nevada. We are also initiating the adequacy process for the 2025, 2030, and 2040 motor vehicle emissions budgets.

B. What is the legal authority and what are the requirements?

Clean Air Act (CAA or “Act”) section 175A(b) requires States to submit an additional SIP revision (a second 10-year maintenance plan) to maintain the national ambient air quality standards (NAAQS or “standards”) for an additional 10 years after the expiration of the 10-year period covered by the initial maintenance plan approved in ( printed page 62372) connection with the redesignation of the area from nonattainment to attainment.

CAA section 176(c) requires Federal actions in nonattainment and maintenance areas to conform to the SIP's goals of eliminating or reducing the severity and number of violations of the NAAQS and achieving expeditious attainment of the standards. The EPA's transportation conformity rule, which implements CAA section 176(c), is codified at 40 CFR part 93, subpart A.

C. The PM₁₀ National Ambient Air Quality Standards

CAA section 109 grants the EPA the authority to set NAAQS for certain ambient air pollutants to protect public health and welfare.^[1] Particulate matter (PM) refers to the mixture of solid particles and liquid droplets found in the air. PM is among the ambient air pollutants for which the EPA has established health-based standards. PM₁₀ is defined as inhalable particles with diameters that are 10 micrometers or less. PM₁₀ can cause adverse health effects by penetrating deep into the lungs and blood stream, leading to lung damage, increased respiratory disease, and premature death. Children, the elderly, and people with asthma and heart conditions are the most vulnerable.

On July 1, 1987, the EPA established primary and secondary NAAQS for PM₁₀ .^[2] At that time, the EPA established two PM₁₀ standards: an annual standard and a 24-hour standard.^[3] Effective December 18, 2006, the EPA revoked the annual PM₁₀ standard but retained the 24-hour PM₁₀ standard.^[4] An area attains the 24-hour standard of 150 micrograms per cubic meter (µg/m^[3] ) when the expected number of days per calendar year with a 24-hour concentration above the standard (referred to as an “exceedance”),^[5] averaged over three years, is equal to or less than one. The expected number of exceedances averaged over a three-year period at any regulatory monitor is known as the PM₁₀ design value. The PM₁₀ design value for the area is the highest design value within the nonattainment area.^[6]

Generally, the EPA determines whether an area's air quality is meeting the PM₁₀ NAAQS based on the most recent complete,^[7] quality-assured, and certified data measured at established State and local air monitoring stations (SLAMS) in the nonattainment area and entered into the EPA Air Quality System (AQS) database. Data from air monitoring sites operated by State, local, or Tribal agencies in compliance with the EPA's monitoring requirements must be submitted to AQS. These monitoring agencies annually certify that these data are accurate to the best of their knowledge. Accordingly, the EPA relies primarily on data in AQS when determining the attainment status of an area.^[8] All valid data are reviewed to determine the area's air quality status in accordance with 40 CFR part 50, appendix K.

D. The Truckee Meadows PM₁₀ Planning Area

Through its enactment of the CAA Amendments of 1990, Congress designated certain areas of the country, including the Reno planning area, commonly referred to as “Truckee Meadows,” as nonattainment areas for the PM₁₀ NAAQS. Truckee Meadows lies in the far southern part of Washoe County, Nevada.^[9] Located at an average elevation of 4,500 feet above sea level, Truckee Meadows encompasses a land area of approximately 200 square miles and is surrounded by mountain ranges, which can lead to persistent wintertime temperature inversions where a layer of cold air is trapped in the valley. Warmer air above the inversion acts as a lid, containing and concentrating air pollutants at ground level. Emissions from anthropogenic activities such as automobile use and residential wood combustion are also concentrated here. The two major cities in Truckee Meadows are Reno and Sparks.

E. PM₁₀ Planning in the Truckee Meadows Area

In 1991, the Reno planning area ( i.e., Truckee Meadows) was designated as a nonattainment area for PM₁₀ by operation of law.^[10] Truckee Meadows was initially classified as a “Moderate” PM₁₀ nonattainment area with an applicable attainment date of December 31, 1994.^[11] Truckee Meadows was later reclassified by operation of law to “Serious” upon the EPA's determination that, based on ambient PM₁₀ data for the 1992 through 1994 period, the area had failed to attain the standard by the Moderate area attainment date.^[12] The State was required under CAA section 188(c) to submit revisions to its SIP to, among other things, demonstrate attainment of the PM₁₀ standard as expeditiously as practicable, but no later than December 31, 2001. Despite further improvements, in a 2011 rulemaking, the EPA found that Truckee Meadows failed to attain by the December 31, 2001 attainment date, based on ambient PM₁₀ data for the 1999 through 2001 period.^[13] Under such circumstances, the State would usually be required to submit a new attainment plan under CAA section 189(d). However, in the same 2011 rulemaking, the EPA determined that the area was currently attaining the PM₁₀ NAAQS based on complete, quality-assured, and certified ambient air monitoring data that showed the area monitored attainment of the 1987 p.m.₁₀ NAAQS for the 2007 through 2009 monitoring period. Consequently, the requirement to submit a new SIP was suspended.

When a nonattainment area attains the NAAQS, the State may request redesignation to attainment, in conjunction with submission of a maintenance plan showing how it will continue to attain the NAAQS. CAA section 175A provides the general framework for a maintenance plan. The maintenance plan must provide for continued attainment of the NAAQS for at least 10 years after redesignation, including any additional control measures necessary to ensure such maintenance. In addition, maintenance plans must contain contingency provisions necessary to ensure the ( printed page 62373) prompt correction of a violation of the NAAQS that occurs after redesignation.^[14] The contingency provisions must include, at a minimum, a requirement that the State will implement all control measures contained in the nonattainment SIP prior to redesignation.

After verifying the area continued to attain the NAAQS and that Nevada had submitted an approvable plan to continue maintenance of the NAAQS through 2026, the EPA redesignated the Truckee Meadows area from nonattainment to attainment and approved the first maintenance plan for the Truckee Meadows area for the PM₁₀ NAAQS, effective January 7, 2016.^[15]

CAA section 175A(b) requires States to submit an additional SIP revision (a second 10-year maintenance plan) to maintain the NAAQS for an additional 10 years after the expiration of the 10-year period covered by the initial maintenance plan approved in connection with the redesignation of the area from nonattainment to attainment. The revision is to be submitted eight years after the original redesignation request and maintenance plan have been approved. The deadline to submit the second PM₁₀ maintenance plan for Truckee Meadows was January 7, 2024.

II. Air Quality in the Truckee Meadows Area

A recent design value showing a maintenance area is continuing to attain the PM₁₀ NAAQS ( i.e., the recorded number of days with levels above 150 µg/m^[3] , averaged over a 3-year period, is less than or equal to one) is the foundation of a second 10-year maintenance plan. As described in more detail in section IV.A of this document, a base year emissions inventory from the design value period that represents attainment conditions is used as the basis for projecting emissions inventories into the future and to demonstrate that future emissions will not lead to an exceedance of the standards. Northern Nevada Public Health ^[16] (NNPH), which administers air quality programs through its Air Quality Management Division (AQMD), used the data from calendar years 2017 through 2019 to calculate a 2019 design value to demonstrate the area had continued to attain the PM₁₀ standard and selected the 2017 emissions inventory as its base year inventory.

Table 1 of this document shows the design values for the Truckee Meadows PM₁₀ maintenance area at the monitoring sites active in the maintenance area from 2016 through 2025, accounting for all recorded exceedances during that time. Table 2 of this document shows the number of exceedances recorded at active monitors for the years 2016 through 2025.^[17]

Between 2016 and 2025, exceedances occurred during three years—2020, 2021, and 2022—which led to violations of the PM₁₀ NAAQS. Because the PM₁₀ design value is based on a 3-year average, exceedances from the prior two years are factored into the design value for the current year, resulting in design values that violated the PM₁₀ NAAQS in 2023 and 2024, even though no exceedances occurred in those years.

CAA section 175A(d) requires that maintenance plans contain contingency provisions as deemed necessary by the EPA that assure the air agency will promptly correct violations of the standard that occur after an area is redesignated.^[18] During the first 10-year maintenance period, for violations that occur outside the design value period on which the second maintenance plan is based, air agencies typically evaluate exceedances to determine the cause and to determine any necessary steps, including rulemaking, they should take to correct the violation. If violations are caused by events that are not reasonably controllable or preventable, e.g., wildfires, air agencies are not required to adopt maintenance plan contingency measures.

NNPH analyzed the exceedances that contributed to violations of the PM₁₀ standard during the first maintenance period to ascertain the cause and what ( printed page 62374) (if any) actions they should take to address the causes, and concluded that wildfire events led to the exceedances.^[19] The EPA has reviewed the information included in the Truckee Meadows Second PM₁₀ Maintenance Plan regarding the exceedances that occurred during the first maintenance period, and we agree that this information does not call into question the EPA's proposed approval of this Plan. We also note that NNPH's analysis and the EPA's evaluation are consistent with the contingency provisions of the maintenance plan that we are proposing to approve in this rulemaking to evaluate data that may have been influenced by certain events in determining whether contingency provisions should be triggered.

III. Procedural Requirements for Adoption and Submittal of State Implementation Plan Revisions

The Nevada Division of Environmental Protection (NDEP) is the State agency with overall responsibility for the Nevada SIP and is the designated agency for submitting SIPs and SIP revisions to the EPA for approval. NNPH is empowered under State law to develop air quality plans within Washoe County. After it adopts an air quality plan for Washoe County, NNPH submits the plan to NDEP for adoption as part of the Nevada SIP and then for submittal to the EPA for approval.

On September 12, 2024, NDEP submitted a second PM₁₀ 10-year maintenance plan for the Truckee Meadows 24-hour PM₁₀ attainment area to meet the requirement for the subsequent maintenance plan under CAA section 175A(b).^[20] On January 22, 2026, NNPH adopted revisions to that plan and on March 12, 2026, NDEP submitted the revised version of the second PM₁₀ 10-year maintenance plan, which superseded the initial September 2024 submittal.^[21] In this action, we are proposing to approve NDEP's March 12, 2026 submittal of its second PM₁₀ 10-year maintenance plan (referred to herein as the “Truckee Meadows Second PM₁₀ Maintenance Plan” or “Plan”) as a revision to the Nevada SIP. The Plan is intended to provide for continued maintenance of the 1987 p.m.₁₀ NAAQS for the 10-year period following the end of the first 10-year period, i.e., from 2026 through 2035.

CAA sections 110(a)(1) and (2) and CAA section 110(1) require States to provide reasonable notice and public hearing prior to adoption of SIP revisions. On November 26, 2025, NNPH posted a media release to the NNPH website announcing the proposed revision to the previously submitted second PM₁₀ Maintenance Plan, informing the public of a public comment period ending December 26, 2025, and the option to request a public hearing that would take place on January 22, 2026. NNPH also notified via email all subscribers to its mailing list of the public comment period.^[22] No comments were submitted and a public hearing was not requested.^[23] Consequently, the adoption of the plan was listed as a consent item on the NNPH District Board of Health (DBOH) agenda for its January 22, 2026 meeting.^[24] At that meeting, no comments were offered by the public, and the NNPH DBOH adopted the Truckee Meadows Second PM₁₀ Maintenance Plan.^[25] Following adoption, NNPH forwarded the plan to NDEP, the Governor of Nevada's designee for SIP matters. NDEP then submitted the plan as a revision to the Nevada SIP to the EPA for approval on March 12, 2026.

Based on the documentation included in the Plan, we find that the Truckee Meadows Second PM₁₀ Maintenance Plan submittal satisfies the procedural requirements of CAA section 110(l).

IV. Evaluation of the Truckee Meadows Second PM 10 Maintenance Plan

CAA section 175A provides the general framework for a maintenance plan. We interpret this section of the Act to require, in general, the following core elements: attainment inventory, maintenance demonstration, monitoring network, verification of continued attainment, and contingency plan.^[26] Under CAA section 175A, a maintenance plan must demonstrate continued attainment of the applicable NAAQS for at least ten years after the EPA approves a redesignation to attainment. Eight years after redesignation, the State must submit a revised maintenance plan that demonstrates continued attainment for the subsequent ten-year period following the initial ten-year maintenance period. To address the possibility of future NAAQS violations, the maintenance plan must contain such contingency provisions that the EPA deems necessary to promptly correct any violation of the NAAQS that occurs after redesignation of the area.

The primary guidance on maintenance plans and redesignation requests is a September 4, 1992 memorandum from John Calcagni, titled “Procedures for Processing Requests to Redesignate Areas to Attainment” (“Calcagni Memo”). The Calcagni Memo outlines the key elements of a maintenance plan, which include verification of continued attainment, monitoring network requirements, attainment emissions inventory, maintenance demonstration, and a contingency plan. We evaluate maintenance plans based on the satisfactory fulfillment of these and all relevant procedural requirements of the CAA.

Based on our review and evaluation of the Plan, as detailed below, we are proposing to approve the Truckee Meadows Second PM₁₀ Maintenance Plan submittal because we believe that it meets the requirements of CAA section 175A.

( printed page 62375)

A. Emissions Inventory

A maintenance plan for the PM₁₀ NAAQS should include an inventory of emissions of PM₁₀ in the area that identifies a level of emissions sufficient to attain the PM₁₀ NAAQS.^[27] This inventory should be consistent with the EPA's most recent guidance on emissions inventories for nonattainment areas available at the time and represent emissions during the time period associated with the monitoring data showing attainment, in this case, 2017 through 2019. The inventory should also be comprehensive, including emissions from stationary sources, area sources, nonroad mobile sources, and on-road mobile sources, and be based on actual emissions during the appropriate season or episode, if applicable.^[28] The specific PM₁₀ emissions inventory requirements are set forth in the Air Emissions Reporting Requirements rule (AERR).^[29] The EPA has provided additional guidance for developing PM₁₀ emissions inventories in “PM₁₀ Emissions Inventory Requirements,” ^[30] and “Emissions Inventory Guidance for Implementation of Ozone and Particulate Matter National Ambient Air Quality Standards (NAAQS) and Regional Haze,” (May 2017).

The Truckee Meadows Second PM₁₀ Maintenance Plan provides an attainment emissions inventory of actual emissions from all sources of direct PM₁₀ within the Truckee Meadows area, based on the 2017 National Emissions Inventory (NEI),^[31] adjusted using seasonal adjustment factors. Updated methodologies and emissions factors were applied to the residential wood combustion and unpaved roads categories to ensure accuracy.^[32] Table 3 of this document summarizes the 2017 attainment inventory provided in the Truckee Meadows Second PM₁₀ Maintenance Plan.

In addition to showing the estimated actual emissions in 2017, Table 3 of this document shows the baseline emissions inventory used to demonstrate maintenance through 2036. The only difference between the 2017 actual emissions and the maintenance plan baseline emissions is in the wildfire source category. Table 3 of the Truckee Meadows Second PM₁₀ Maintenance Plan lists wildfire emissions inventories from NEI years from 1999 through 2020. The Truckee Meadows area experienced unusually high smoke impacts from wildfires in 2011, 2014, and 2020. For the purposes of developing a baseline attainment inventory for demonstrating ongoing attainment, NNPH replaced the actual PM₁₀ emissions from wildfires in 2017 (26 lbs/day) with the average of wildfire emissions from previous typical years (1999, 2002, 2005, and 2008) (21 lbs/day). The difference between 26 lbs/day and 21 lbs/day represents 0.06 percent of the non-point source emissions inventory. NNPH notes that future year planning should not be driven by wildfire emissions, and that PM₁₀ exceedances and violations caused by natural events ( e.g., wildfires) will be treated as exceptional events.^[33] We find this adjustment to be reasonable.

Information regarding the development of the emissions inventories, such as the methodology NNPH uses to develop growth factors for future-year inventories for stationary and mobile sources, is included in appendices A through F of the Plan.

The Plan does not provide emissions inventories for precursors to PM₁₀ and instead addresses direct PM₁₀ only. NNPH notes that precursor emissions were “determined to be negligible in the First 10-Year Maintenance Plan, in reference to the 2011 emissions inventory” on which the plan was based.^[34] In its approval of the first maintenance plan, the EPA concluded that the absence of PM₁₀ precursors from the attainment inventory was acceptable.^[35]

In support of continuing this approach, NNPH asserts that there have not been any substantial changes in the emissions inventory or new major sources of volatile organic compounds (VOCs), nitrogen oxides (NO_X), and sulfur oxides (SO_X) within the maintenance area since 2011 and notes that the control strategy for maintaining compliance with the NAAQS relies on ( printed page 62376) control of direct PM₁₀ .^[36] The NNPH also states that sources of precursor emissions are not correlated with reductions in PM₁₀ emissions and ambient concentrations of PM₁₀ .^[37]

The EPA believes that the selection of 2017 as the attainment year inventory is appropriate given that it represents emissions from an attainment year and it is the most recent emissions inventory representative of normal conditions available at the time of preparation of the maintenance plan. Moreover, preparation of a seasonal (winter) inventory in this instance is appropriate given that winter is typically the season when the highest ambient PM₁₀ concentrations are monitored in the Truckee Meadows. We find that NNPH's 2017 emissions inventory for direct PM₁₀ is based on reasonable assumptions and methodologies, as described in the Truckee Meadows Second PM₁₀ Maintenance Plan and 2017 Periodic Emissions Inventory,^[38] and that the inventory is comprehensive, current, and accurate. We therefore propose to approve the inventory of actual emissions in 2017 as meeting the requirements of CAA section 172(c)(3) and find the 2017 inventory, as adjusted for wildfire emissions, acceptable for use in demonstrating maintenance of the PM₁₀ standard in the future.

B. Maintenance Demonstration

CAA section 175A(a) requires that the maintenance plan provide for maintenance of the NAAQS for at least 10 years after redesignation. A State may generally demonstrate maintenance of the NAAQS by either showing that future emissions of a pollutant or its precursors will not exceed the level of the attainment inventory, or by conducting modeling that shows that the future mix of sources and emissions rates will not cause a violation of the NAAQS.³⁹

The Truckee Meadows Second PM₁₀ Maintenance Plan demonstrates that the Truckee Meadows area will maintain the PM₁₀ NAAQS by comparing the adjusted 2017 attainment inventory (also referred to as the maintenance plan baseline) against the projected emissions for 2025, 2030, and 2040.⁴⁰ NNPH demonstrates continued maintenance of the PM₁₀ NAAQS by showing that future emissions of PM₁₀ will not exceed the level of the 2017 maintenance year baseline. Using the adjusted 2017 emissions inventory as a baseline and appropriate growth and control factors described in Appendix A, “Growth Factors for Emissions Projections”, and Table A-1 of the Truckee Meadows Second PM₁₀ Maintenance Plan, NNPH projected emissions inventories for 2020, 2025, 2030, and 2040. Source specific growth factors were developed based on various demographic, climate, and other data projections. Control factors were developed based on historic data and reasonable assumptions.

Despite expected growth in the area, the Plan's projected future PM₁₀ emissions in the Truckee Meadows area are below the 2017 maintenance inventory of 10,064 lbs/day.⁴¹ The downward trend in total expected emissions is due to federally enforceable PM₁₀ control programs targeting mobile sources and residential wood combustion. Table 4 of this document illustrates that while there are some increases in point source and on-road mobile source emissions, declining emissions from non-road mobile and nonpoint source categories drive a decrease in overall PM₁₀ emissions through 2040. As discussed in section IV.D of this document, NNPH has chosen to include “safety margins” in the motor vehicle emissions budgets for 2025 (857 lbs/day), 2030 (904 lbs/day), and 2040 (1,173 lbs/day).⁴² We find that the overall emissions projections, including the safety margins, continue to demonstrate maintenance because they do not exceed the emissions in 2017. Therefore, the safety margins are consistent with maintenance through 2036.

CAA section 175A(b) requires that eight years after redesignation, the State must submit to EPA an additional revision of the SIP for maintaining the NAAQS for an additional 10 years after the expiration of the first 10-year maintenance plan, in this case, until 2036. The projected emissions inventories for 2025, 2030, and 2040 sufficiently demonstrate that the Truckee Meadows area will continue to maintain the PM₁₀ standard throughout the second 10-year maintenance period. The EPA therefore concludes that the Truckee Meadows Second PM₁₀ Maintenance Plan demonstrates maintenance of the standard through 2036.

( printed page 62377)

C. PM₁₀ Air Quality Monitoring Network

After an area has been redesignated, the State should continue to operate an appropriate air quality monitoring network, in accordance with 40 CFR part 58, to verify the attainment status of the area.^[43] NNPH monitors ambient PM₁₀ concentrations through a network of three State and local air monitors (SLAMS) in the Truckee Meadows area. The network is reviewed annually under 40 CFR 58.20(d) to ensure it continues to meet the applicable monitoring objectives. The currently active network monitors are listed in Table 5 of this document.^[44] The EPA approved NNPH's air quality network plan for 2025 on December 5, 2025.^[45] The approved plan and the EPA approval letter are included in the docket for this proposed action.

In the Truckee Meadows Second PM₁₀ Maintenance Plan, the NNPH commits to continue to operate and maintain a PM₁₀ ambient air quality monitor in the planning area, in accordance with 40 CFR part 58, to verify attainment of the PM₁₀ NAAQS within the Truckee Meadows area. Data collected by the monitoring network are also used to implement the contingency measures trigger calculation, discussed in section IV.E. of this proposed action. We propose that the Second PM₁₀ Maintenance Plan contains adequate provisions for continued ambient PM₁₀ monitoring to verify continued attainment through the full maintenance period.

D. Verification of Continued Attainment

Once an area has been redesignated, the State should continue to operate an appropriate air quality monitoring network, in accordance with 40 CFR part 58, to verify the continued attainment status of the area.^[46] As discussed in section IV.C of this document, NNPH monitors ambient concentrations of PM₁₀ in the Truckee Meadows planning area at three separate monitoring stations. NNPH indicates its intention to continue operation of the air quality monitoring network in accordance with 40 CFR part 58 to verify the attainment status of the area. The NNPH notes that the monitoring network will be reviewed annually to ensure the network meets all relevant monitoring requirements defined in 40 CFR part 58.^[47]

In addition to continued air monitoring, NNPH describes its tracking of actual emissions through periodic emissions inventories and commits to continuing to comply with the rules governing these emissions reporting requirements. Finally, NNPH describes various control strategies and enforcement actions that will ensure continued verification of attainment and maintenance of the PM₁₀ NAAQS.^[48] We are proposing to determine that these efforts are sufficient to verify continued attainment through the maintenance period.

E. Contingency Provisions

CAA section 175A(d) requires that maintenance plans include contingency provisions, as the EPA deems necessary, to promptly correct any violations of the NAAQS that occur after the redesignation of the area. Such provisions must include a requirement that the State will implement all measures with respect to the control of the relevant air pollutants that were contained in the SIP for the area before redesignation of the area as an attainment area.

Under CAA section 175A(d), contingency measures identified in the contingency plan do not have to be fully adopted at the time of redesignation. However, the contingency plan is an enforceable part of the SIP and should ensure that the contingency measures are adopted expeditiously once they are triggered by a specified event. The maintenance plan should clearly identify the measures to be adopted, a schedule and procedure for adoption and implementation, and a specific timeline for action by the State. In addition, the State should identify the specific indicators or triggers that will be used to determine when the contingency measures need to be implemented.

The NNPH has adopted a contingency plan to address possible future PM₁₀ air quality problems in the Truckee Meadows area. As noted by NNPH, contingency measures are to be triggered to promptly correct any violation of the standard that occurs during the maintenance period. The contingency plan for the Truckee Meadows area will be triggered when the number of exceedances recorded at a monitor, averaged over three consecutive years, is greater than 1.05.^[49] The contingency plan also includes a screening process that allows NNPH, subject to EPA review and agreement, to exclude certain exceedances from the contingency measure trigger calculation (CMTC) if the agencies agree that the information developed by the NNPH, through its AQMD, is sufficient to support exclusion.

The purpose of the screening process is to differentiate between exceedances that are not within the NNPH's control ( i.e., exceedances that occur despite the implementation of reasonable measures), and exceedances that are within the NNPH's or State's control and therefore should be included in the trigger calculation. Should the EPA agree with NNPH's exclusion of an exceedance from the CMTC using this process, it would not constitute the EPA's concurrence that the exceedance was caused by an exceptional event. The exceedance would therefore continue to be included in design value calculations for the planning area, unless the State, following opportunity for public comment, submits a request for the EPA to concur on the exceedance as an exceptional event pursuant to 40 CFR 50.14, and the EPA reviews the submittal and formally concurs. ( printed page 62378)

Under the contingency trigger screening process described in the Plan, the NNPH will analyze any exceedance(s) that leads to a violation of the NAAQS on a quarterly basis. Using the screening criteria set forth in the plan, NNPH will evaluate exceedances to determine if any exceedances qualify for exclusion from the CMTC.^[50] If the NNPH believes an exceedance should be excluded, it will submit an exclusion request to the EPA within 90 days of the end of the calendar quarter.

If the EPA reviews and agrees with the exclusion request, NNPH can exclude that exceedance from the CMTC. If the EPA rejects the request and NNPH disagrees with the EPA's determination, it can submit an exceptional events demonstration. Due to the need to promptly address violations, NNPH will proceed with the contingency process while the exceptional event process is under way. NNPH will make recommendations, including a timeline for adoption and implementation of measures, to the DBOH within 45 days of reaching the trigger level, with the exceedance in question included in the CMTC.^[51] Contingency measures should be adopted by the DBOH and implemented as expediently as possible, prior to the next PM₁₀ season.^[52]

The Truckee Meadows Second PM₁₀ Maintenance Plan includes a list of the source categories that typically contribute significantly to PM₁₀ season emissions along with potential contingency measures applicable to each category.^[53] The list of categories includes paved and unpaved roads, dust control, residential wood combustion, and mobile sources of diesel emissions.

Based on our review of the Truckee Meadows Second PM₁₀ Maintenance Plan, we propose to find that the contingency provisions of the Plan clearly identify potential contingency measures, contain a triggering mechanism to determine when contingency measures are needed, contain a description of the process of recommending and implementing contingency measures, and contain specific and appropriate timelines for action. We also propose to find that the contingency trigger screening process, including the associated EPA review, is reasonably designed to distinguish between exceedances that were not within the NNPH or State control, and exceedances that were within the NNPH or State control and for which new or tightened control measures might be effective. Thus, we propose to conclude that the contingency plan in the Plan is adequate to ensure correction of any violation of the PM₁₀ NAAQS that occurs after redesignation, as required by CAA section 175A(d).

F. Motor Vehicle Emissions Budgets for Transportation Conformity

CAA section 176(c) requires Federal actions in nonattainment and maintenance areas to conform to the SIP's goals of eliminating or reducing the severity and number of violations of the NAAQS and achieving expeditious attainment of the standards. Conformity to the SIP's goals means that such actions will not: (1) cause or contribute to violations of a NAAQS, (2) worsen the severity of an existing violation, or (3) delay timely attainment of any NAAQS or any interim milestone.

Actions involving Federal Highway Administration (FHWA) or Federal Transit Administration (FTA) funding or approval are subject to the EPA's transportation conformity rule, codified at 40 CFR part 93, subpart A. Under this rule, metropolitan planning organizations in nonattainment and maintenance areas coordinate with State and local air quality and transportation agencies, the EPA, FHWA, and FTA to demonstrate that an area's regional transportation plans and transportation improvement programs conform to the applicable SIP. This demonstration is typically accomplished by showing that estimated emissions from existing and planned highway and transit systems are less than or equal to the motor vehicle emissions budgets (“budgets”) contained in submitted or approved control strategy plans or maintenance plans.

Control strategy SIPs and maintenance plans typically establish budgets for criteria pollutants and precursors to address pollution from on-road vehicles such as cars and trucks.^[54] Budgets are generally established for specific years for the relevant pollutants or precursors. PM₁₀ maintenance plan submittals must identify budgets for transportation-related PM₁₀ emissions in the last year of the maintenance period.^[55] Budgets may also be specified for additional years during the maintenance period.

For budgets in a maintenance plan to be approvable, they must meet, at a minimum, the EPA's adequacy criteria.^[56] To meet these requirements, the budgets must be consistent, when considered with emissions from all other sources, with maintenance of the NAAQS and reflect all of the motor vehicle control measures relied upon for the maintenance demonstration.

The EPA also determines the adequacy of budgets in certain submitted SIPs. The adequacy process is separate from the approval process. The EPA's process for determining adequacy of a budget consists of three basic steps: (1) providing public notification of a SIP submission; (2) providing the public the opportunity to comment on the budgets during a public comment period; and (3) making a finding of adequacy or inadequacy. The process for determining the adequacy of a submitted budget is codified at 40 CFR 93.118(f). The EPA can notify the public by either posting an announcement that the EPA has received SIP budgets on the EPA's adequacy website ^[57] or via a Federal Register notice of proposed rulemaking when the EPA reviews the adequacy of a maintenance plan budget simultaneously with its review and action on the SIP submittal itself.^[58]

The Truckee Meadows Second PM₁₀ Maintenance Plan provides budgets, which include PM₁₀ emissions estimates for transportation-related emissions and a safety margin, for direct PM₁₀ for 2025, 2030, and 2040.^[59] Transportation-related emissions include emissions from on-road vehicles, road construction, and re-entrained paved and unpaved road dust.^[60] The difference between the transportation-related emissions estimates in the projected emissions inventory and the budgets is defined as a safety margin. ^[61] ( printed page 62379) The transportation-related emissions and safety margins represent a level of emissions consistent with attainment of the PM₁₀ NAAQS.^[62] The applicable PM₁₀ budgets for the Truckee Meadows area are presented in Table 6 of this document.

While transportation conformity is typically not required after the completion of the 20-year maintenance period, which ends in 2036, NNPH has chosen to provide a budget for 2040. If approved, conformity will continue to apply in the Truckee Meadows area through 2040.^[63]

NNPH consulted with Federal, State, and local agencies during the development of the budgets.^[64] NNPH used the EPA's Motor Vehicle Emissions Simulator (MOVES2014b) to develop on-road and non-road mobile source emissions estimates for the 2017 emissions inventory.^[65] On-road mobile source emissions were modeled for 2025, 2030, and 2040 using MOVES3,^[66] incorporating the most recent planning assumptions for the transportation network.

The EPA evaluated the budgets against our adequacy criteria in 40 CFR 93.118(e)(4) and (5) as part of our review of the budget's approvability. While adequacy and approval are two separate actions, reviewing the budgets in terms of the adequacy criteria informs the EPA's decision to propose to approve the budgets. We have completed our detailed review of the Truckee Meadows Second PM₁₀ Maintenance Plan and are proposing herein to approve the Plan including the demonstration of maintenance of the PM₁₀ NAAQS in the area through the year 2036. We have also reviewed the budgets in the Plan and found that they are consistent with the maintenance demonstration for which we are proposing approval, are clearly identified and precisely quantified, are based on control measures that have already been adopted and implemented, and meet all other applicable statutory and regulatory requirements, including the adequacy criteria in 40 CFR 93.118(e)(4) and (5).^[67] For these reasons, the EPA proposes to approve the 2025, 2030, and 2040 budgets in the Truckee Meadows Second PM₁₀ Maintenance Plan.

In addition, in this document the EPA is announcing the beginning of the adequacy process for these budgets. Under the transportation conformity regulation, the EPA can begin this process with our proposed action on the second maintenance plan.^[68] The public has 30 days to comment on the adequacy of the budgets, per the transportation conformity rule at 40 CFR 93.118(f)(2)(i) and (ii). Any comments on the adequacy of the budgets should be submitted to the docket for this proposed rulemaking.

If the EPA issues a final rulemaking action to approve the budgets, they will be effective on the date of the publication date of the EPA's final rulemaking in the Federal Register .^[69] The approved budgets must be used by the Regional Transportation Commission of Washoe County in future transportation conformity determinations for Truckee Meadows for the PM₁₀ NAAQS.

V. Proposed Action and Request for Public Comment

Under CAA section 110(k)(3), and for the reasons set forth in this document, the EPA is proposing to approve the Truckee Meadows Second PM₁₀ Maintenance Plan submitted by NDEP on March 12, 2026, as a revision to the Nevada SIP. We are proposing to approve the maintenance demonstration and contingency provisions as meeting all applicable requirements for maintenance plans and related contingency provisions in CAA section 175A, and the budgets for 2025, 2030, and 2040 for transportation conformity purposes as we find they meet all applicable criteria for such budgets including the adequacy criteria under 40 CFR 93.118(e).

We are soliciting comments on these proposed actions. We will accept comments from the public for 30 days following publication of this proposal in the Federal Register and will consider any relevant comments before taking final action.

VI. Statutory and Executive Order Reviews

Under the CAA, the Administrator is required to approve a SIP submission that complies with the provisions of the Act and applicable Federal regulations. 42 U.S.C. 7410(k); 40 CFR 52.02(a). Thus, in reviewing SIP submissions, the EPA's role is to approve State choices, provided that they meet the criteria of the CAA. Accordingly, this 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 ( printed page 62380) Executive Order 12866 (58 FR 51735, October 4, 1993);
• Is not anExecutive Order 14192 (90 FR 9065, February 6, 2025) regulatory action because this action is not significant 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 inExecutive Order 13132 (64 FR 43255, August 10, 1999);
• Is not subject toExecutive Order 13045 (62 FR 19885, April 23, 1997) because it proposes to approve a State program;
• Is not a significant regulatory action subject toExecutive Order 13211 (66 FR 28355, May 22, 2001); and
• Is not subject to requirements of section 12(d) of the National Technology Transfer and Advancement Act of 1995 (15 U.S.C. 272 note) because application of those requirements would be inconsistent with the CAA.

The Reno-Sparks Indian Colony, a federally recognized Tribe, has reservation lands located within the boundaries of the Truckee Meadows PM₁₀ maintenance area. This proposal, if finalized, will not change the designation or classification of the maintenance area, including areas of Indian country within the maintenance area. Additionally, it will neither impose substantial direct compliance costs on federally recognized Tribal governments, nor preempt Tribal law as specified by Executive Order 13175 (65 FR 67249, November 9, 2000). The EPA will notify the Tribe about this proposal.

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

91 FR 62371