AGENCY:

Environmental Protection Agency (EPA).

ACTION:

Proposed rule.

SUMMARY:

The Environmental Protection Agency (EPA) is proposing to approve the “Imperial County 2018 Redesignation Request and Maintenance Plan for Particulate Matter Less Than 10 Microns in Diameter (PM₁₀)” (“Imperial PM₁₀ Plan”) as a revision of the California state implementation plan (SIP). The Imperial PM₁₀ Plan includes, among other elements, a demonstration of implementation of best available control measures (BACM) and a maintenance plan that includes an emissions inventory consistent with attainment, a maintenance demonstration, contingency provisions, and motor vehicle emissions budgets for use in transportation conformity determinations. In connection with the proposed approval of the Imperial PM₁₀ Plan, the EPA is proposing to determine that PM₁₀ precursors do not contribute significantly to elevated PM₁₀ levels in the area. The EPA is also proposing to approve the State of California's request to redesignate the Imperial Valley Planning Area from nonattainment to attainment for the PM₁₀ national ambient air quality standards. The EPA is proposing these actions because the SIP revision meets the applicable statutory and regulatory requirements for such plans and motor vehicle emissions budgets and because the area meets the Clean Air Act requirements for redesignation of nonattainment areas to attainment. Lastly, the EPA is beginning the adequacy process for the 2016 and 2030 motor vehicle emissions budgets in the 2018 Imperial PM₁₀ Plan through this proposed rule.

DATES:

Comments must be received on or before May 4, 2020.

ADDRESSES:

Submit your comments, identified by Docket ID No. EPA-R09-OAR-2019-0654, at http://www.regulations.gov. For comments submitted at Regulations.gov, follow the online instructions for submitting comments. Once submitted, comments cannot be edited or removed from Regulations.gov. The EPA may publish any comment received to its public docket. Do not 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 EPA's full 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:

Ginger Vagenas, EPA Region IX, 75 Hawthorne St., San Francisco, CA 94105. By phone at 415-972-3964, or by email at Vagenas.Ginger@epa.gov.

SUPPLEMENTARY INFORMATION:

Throughout this document, the terms “we,” “us,” and “our” mean the EPA.

Table of Contents

I. Background

A. National Ambient Air Quality Standards

B. State Implementation Plans and Area Designations

C. Exceptional Events Rule

D. Imperial Valley Planning Area

E. PM₁₀ Planning in the Imperial Valley Planning Area

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

III. Clean Air Act Requirements for Redesignation to Attainment

IV. Evaluation of the State's Redesignation Request for the Imperial PM₁₀ Nonattainment Area

A. Determination That the Area Has Attained the PM₁₀ National Ambient Air Quality Standards

B. The Area Must Have a Fully Approved State Implementation Plan Meeting the Requirements Applicable for Purposes of Redesignation Under Section 110 and Part D

C. The Area Must Show the Improvement in Air Quality is Due to Permanent and Enforceable Emission Reductions

D. The Area Must Have a Fully Approved Maintenance Plan Under Section 175A

V. Proposed Actions and Request for Public Comment

VI. Statutory and Executive Order Reviews

I. Background

A. National Ambient Air Quality Standards

Under section 109 of the Clean Air Act (CAA or “Act”), the EPA has established national ambient air quality standards (NAAQS or “standards”) for certain pervasive air pollutants (referred to as “criteria pollutants”) and conducts periodic reviews of the NAAQS to determine whether they should be revised or whether new NAAQS should be established. The EPA sets the NAAQS for criteria pollutants at levels required to protect public health and welfare.^[1] Particulate matter is one of the ambient pollutants for which the EPA has established NAAQS.^[2]

In 1987, the EPA established primary and secondary NAAQS for particles with an aerodynamic diameter less than or equal to a nominal ten micrometers (PM₁₀).^[3] At that time, the EPA established two PM₁₀ standards; an annual standard and a 24-hour 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 in excess of the standard (referred to as an exceedance), averaged over three years, is equal to or less than one.^[5] The annual PM₁₀ standard was subsequently revoked.^[6] More recently, the EPA announced that it was retaining the 24-hour PM₁₀ NAAQS as a 24-hour standard of 150 μg/m^[3] .^[7] In this document, “PM₁₀ NAAQS” or “PM₁₀ standard” refer to the 24-hour-average PM₁₀ NAAQS.

B. State Implementation Plans and Area Designations

Following promulgation of a new or revised NAAQS, section 110 of the CAA requires states to adopt and submit a plan, referred to as the SIP, that provides for the implementation, maintenance, and enforcement of each NAAQS within each state. Under CAA section 107(d), the EPA is required to designate areas throughout the nation as nonattainment, attainment, or unclassifiable based on ambient pollutant monitoring data showing whether the area is attaining or not attaining the NAAQS. States with nonattainment areas are required to revise their SIPs to provide for attainment of the NAAQS and to meet other nonattainment area requirements.

C. Exceptional Events Rule

Congress has recognized that it may not be appropriate for the EPA to use certain monitoring data collected by the ambient air quality monitoring network and maintained in the EPA's Air Quality System database (AQS) ^[8] in certain regulatory determinations. Thus, in 2005, Congress provided the statutory authority for the exclusion of data influenced by “exceptional events” meeting specific criteria by adding section 319(b) to the CAA.^[9] To implement this 2005 CAA amendment, the EPA promulgated the 2007 Exceptional Events Rule.^[10] The 2007 Exceptional Events Rule created a regulatory process codified at 40 CFR parts 50 and 51 (sections 50.1, 50.14 and 51.930). These regulatory sections, which superseded the EPA's previous guidance on handling data influenced by events, contain definitions, procedural requirements, requirements for air agency demonstrations, criteria for the EPA's approval of the exclusion of event-affected air quality data from the data set used for regulatory decisions, and requirements for air agencies to take appropriate and reasonable actions to protect public health from exceedances or violations of the NAAQS. In 2016, the EPA promulgated a comprehensive revision to the 2007 Exceptional Events Rule.^[11]

Under the Exceptional Events Rule, if a state demonstrates to the EPA's satisfaction that emissions from a high wind dust event caused a specific air pollution concentration in excess of the NAAQS at a particular air quality monitoring location and otherwise satisfies the requirements of 40 CFR 50.14, the EPA must exclude that data from use in determinations of exceedances and violations.^[12] The EPA considers high wind dust events to be natural events in cases where windblown dust is entirely from natural undisturbed lands in the area or where all anthropogenic sources are reasonably controlled.^[13] For areas in California, the EPA accepts sustained winds of 25 miles per hour as a high wind threshold.^[14]

D. Imperial Valley Planning Area

Through its enactment of the Clean Air Act Amendments of 1990, Congress designated certain areas of the country as nonattainment areas for the PM₁₀ NAAQS. A portion of Imperial County (or “County”), referred to as the Imperial Valley Planning Area, was one of the areas designated as nonattainment.^[15] In 1991, the EPA classified the Imperial Valley Planning Area, also referred to herein as the “Imperial PM₁₀ nonattainment area,” as a “Moderate” PM₁₀ nonattainment area.^[16]

Imperial County encompasses approximately 4,500 square miles in southeastern California. It is home to approximately 190,600 people, and its principal industries are farming and retail trade. It is bordered by Riverside County to the north, Arizona to the east, Mexico to the south, and San Diego County and coastal mountains to the west. The Salton Sea straddles the boundary between Riverside and Imperial counties with most of the lake located in the northwest portion of Imperial County. Winters are mild and dry, and summers are extremely hot, with average annual rainfall of about 3 inches. The topography and meteorology of the area creates conditions conducive to moderate and occasionally extremely high winds that result in elevated levels of particulate matter.^[17]

The Imperial PM₁₀ nonattainment area encompasses the western and central parts of the County and includes the Imperial Valley.^[18] The Imperial Valley runs north-south through the central part of the County. Most of the County's population and industries exist within this relatively narrow land area, which extends about one-fourth the width of the County. The rest of Imperial County is primarily open desert, with little or no human population. The Torres Martinez Desert Cahuilla Indians have reservation land in the northwestern corner of the nonattainment area, and the Quechan Tribe of the Fort Yuma Indian Reservation has reservation land in the southeastern portion of the nonattainment area.

In California, the California Air Resources Board (CARB) is the state agency responsible for the adoption and submission to the EPA of California SIPs and SIP revisions and it has broad authority to establish emissions standards and other requirements for mobile sources. Local and regional air pollution control districts in California are responsible for the regulation of stationary sources and are generally responsible for the development of air quality plans. In Imperial County, the Imperial County Air Pollution Control District (ICAPCD or “District”) develops and adopts air quality plans to address CAA planning requirements applicable to the Imperial Valley Planning Area. Such plans are then submitted to CARB for adoption and submittal to the EPA as revisions to the California SIP.

E. PM ₁₀ Planning in the Imperial Valley Planning Area

Under section 189(a) of the CAA, as amended in 1990, states with Moderate PM₁₀ nonattainment areas were required to develop and submit SIP revisions that, among other things, provide for implementation of reasonably available control measures (RACM) and that demonstrate that the nonattainment area would attain the PM₁₀ NAAQS no later than the applicable attainment date of December 31, 1994. Subsequent to litigation over the extent to which PM₁₀ emissions generated within Mexico contributed to PM₁₀ exceedances over the 1992 to 1994 period, we determined that the Imperial PM₁₀ nonattainment area did not attain the PM₁₀ NAAQS by the Moderate area deadline (December 31, 1994) and reclassified the area from Moderate to “Serious.” ^[19]

Under section 189(b) of the CAA, states with Serious PM₁₀ nonattainment areas are required to submit SIP revisions that, among other things, provide for implementation of BACM and attainment no later than applicable Serious area attainment date (December 31, 2001). In the case of the Imperial PM₁₀ nonattainment area, we determined that the area did not attain the PM₁₀ NAAQS by the Serious area deadline (December 31, 2001), which triggered the requirement under CAA section 189(d) for the State to revise the SIP to provide for attainment of the PM₁₀ NAAQS in the Imperial PM₁₀ nonattainment area and to provide at least five percent annual reductions in PM₁₀ or PM₁₀ precursor emissions until attainment is reached.^[20]

Meanwhile, in response to the designation of the Imperial Valley Planning Area as a Moderate, then Serious, nonattainment area, the District and CARB developed several air quality plans to address applicable CAA requirements for the area. In developing the plans and control strategies, the District and CARB identified direct PM₁₀ sources, such as fugitive dust sources (e.g., farming, construction, and vehicle travel over paved and unpaved roads) and windblown dust as two principal sources of PM₁₀ emissions causing or contributing to PM₁₀ exceedances in the nonattainment area.^[21] The District and CARB found that secondarily-formed PM₁₀ (i.e., PM₁₀ derived from PM₁₀ precursors such as NO_X and SO₂) contributed little to exceedances in the nonattainment area.

To address fugitive dust sources in the nonattainment area and to address the Serious area requirement for implementation of BACM, the District adopted a set of rules in Regulation VIII establishing emission control requirements for such fugitive sources as construction and earthmoving, bulk materials, carry out and track out, open areas, paved and unpaved roads, and agricultural activities. In 2010, the EPA approved the rules, but also identified certain deficiencies with respect to the BACM requirement in some of the rules that prevented full approval.^[22] In response, in 2012, the District amended certain Regulation VIII rules, including the rules for open areas, paved and unpaved roads, and agricultural activities.

In the following year, the EPA found that the deficiencies had been corrected and approved the amended rules as revisions to the Imperial County portion of the California SIP.^[23] In our 2013 final rule, we indicated our preliminary view that the Regulation VIII rules, as revised in 2012, constitute reasonable control of the sources covered by Regulation VIII for the purpose of evaluating whether an exceedance of the PM₁₀ NAAQS is an exceptional event pursuant to the Exceptional Events Rule, including reasonable and appropriate control measures on significant contributing anthropogenic sources.^[24]

More recently, the District and CARB reviewed the PM₁₀ ambient monitoring data collected within the Imperial Valley Planning Area and preliminarily determined that the Imperial Valley Planning Area has attained the PM₁₀ NAAQS based on 2014-2016 data. Their preliminary determination assumes the EPA's concurrence, under the Exceptional Events Rule, on the District's and CARB's determination that nearly all the exceedances during that period were exceptional events caused by emissions due to high winds. Attainment of the NAAQS is one of the criteria for redesignation of a nonattainment area to attainment, and the District and CARB developed the Imperial PM₁₀ Plan to address all the redesignation criteria, including the attainment criterion.

Following approval by the District in October 2018 and by CARB in December 2018, CARB submitted the Imperial PM₁₀ Plan to the EPA under cover of letter dated February 6, 2019, as a revision to the Imperial County portion of the California SIP. We received the SIP submittal on February 13, 2019. In addition to the Imperial PM₁₀ Plan itself, the SIP revision submittal package includes the District Board Minute Order approving the plan and related District staff report, the CARB Board Resolution 18-58 adopting the plan and related CARB staff report, and documentation of public participation. In this action, for the reasons discussed in the following sections of this document, we are proposing to approve the Imperial PM₁₀ Plan and to approve CARB's request to redesignate the Imperial Valley Planning Area from nonattainment to attainment for the PM₁₀ NAAQS.

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

CAA sections 110 (a)(1) and (2) and section 110(l) require a state to provide reasonable notice and opportunity for public hearing prior to adoption and submission of a SIP or SIP revision. To meet these procedural requirements, every SIP submission should include evidence that the state provided adequate public notice and an opportunity for a public hearing consistent with the EPA's implementing regulations in 40 CFR 51.102.

CARB's February 6, 2019 SIP submittal package includes documentation of the public processes used by the District and CARB to adopt the Imperial PM₁₀ Plan. As documented in the SIP revision submittal package, on September 20, 2018, the District published a notice in a newspaper of general circulation in Imperial County that a public hearing to consider adoption of the plan would be held on October 23, 2018. As documented in the Minute Order of the Air Pollution Control Board that is included in the SIP revision submittal package, the Imperial County Air Pollution Control Board of Directors adopted the Imperial PM₁₀ Plan on October 23, 2018, following the public hearing.

Following transmittal by the District of the adopted Imperial PM₁₀ Plan to CARB, on November 9, 2018, CARB published on its website a notice of a public hearing to be held on December 13, 2018, to consider adoption of the plan. As evidenced by CARB Resolution 18-58, CARB adopted the Imperial PM₁₀ Plan on December 13, 2018, following a public hearing. Based on documentation included in the February 6, 2019 SIP revision submittal package, we find that both the District and CARB have satisfied the applicable statutory and regulatory requirements for reasonable public notice and hearing prior to the adoption and submission of the Imperial PM₁₀ Plan. Therefore, we find that the submission of the Imperial PM₁₀ Plan meets the procedural requirements for public notice and hearing in CAA sections 110(a) and 110(l) and in 40 CFR 51.102.

III. Clean Air Act Requirements for Redesignation to Attainment

The CAA establishes the requirements for redesignation of a nonattainment area to attainment. Specifically, section 107(d)(3)(E) allows for redesignation provided that the following criteria are met: (1) The EPA determines that the area has attained the applicable NAAQS; (2) the EPA has fully approved the applicable implementation plan for the area under 110(k); (3) the EPA determines that the improvement in air quality is due to permanent and enforceable reductions; (4) the EPA has fully approved a maintenance plan for the area as meeting the requirements of CAA 175A; and (5) the state containing such area has met all requirements applicable to the area under section 110 and part D of the CAA. Section 110 identifies a comprehensive list of elements that SIPs must include and part D establishes the SIP requirements for nonattainment areas. Part D is divided into six subparts. The generally-applicable nonattainment SIP requirements are found in part D, subpart 1, and the particulate matter-specific SIP requirements are found in part D, subpart 4.

The EPA provided guidance on redesignations in a document entitled “State Implementation Plans; General Preamble for the Implementation of Title I of the Clean Air Act Amendments of 1990,” published in the Federal Register on April 16, 1992,^[25] and supplemented on April 28, 1992 ^[26] (referred to herein as the “General Preamble”). We issued additional guidance on September 4, 1992, in a memorandum from John Calcagni, Director, Air Quality Management Division, EPA Office of Air Quality Planning and Standards, entitled “Procedures for Processing Requests to Redesignate Areas to Attainment” (referred to herein as the “Calcagni memo”). On August 16, 1994, the EPA published guidance for Serious PM₁₀ nonattainment areas in a document entitled “State Implementation Plans for Serious PM₁₀ Nonattainment Areas, and Attainment Date Waivers for PM₁₀ Nonattainment Areas Generally; Addendum to the General Preamble for the Implementation of Title I of the Clean Air Act Amendments of 1990,” (herein referred to as the “Addendum”).^[27]

Maintenance plan submittals are SIP revisions, and as such, the EPA is obligated under CAA section 110(k) to approve them or disapprove them depending upon whether they meet the applicable CAA requirements for such plans.

For reasons set forth in Section IV of this document, we propose to approve the Imperial PM₁₀ Plan and to approve CARB's request for redesignation of the Imperial Valley Planning Area from nonattainment to attainment for the PM₁₀ NAAQS based on our conclusion that all the criteria under CAA section 107(d)(3)(E) have been satisfied.

IV. Evaluation of the State's Redesignation Request for the Imperial PM₁₀ Nonattainment Area

A. Determination That the Area Has Attained the PM ₁₀ National Ambient Air Quality Standards

Section 107(d)(3)(E)(i) of the CAA states that, for an area to be redesignated to attainment, the EPA must determine that the area has attained the relevant NAAQS. In this case, the relevant standard is the PM₁₀ NAAQS. Generally, the EPA determines whether an area's air quality is meeting the PM₁₀ NAAQS based upon complete, quality-assured, and certified data gathered at established state and local air monitoring stations (SLAMS) in the nonattainment area and entered into the EPA's AQS database.^[28]

Data from air monitors operated by state, local, or tribal agencies in compliance with EPA monitoring requirements must be submitted to AQS. These monitoring agencies certify annually 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.^[29] All valid data are reviewed to determine the area's air quality status in accordance with 40 CFR part 50, Appendix K.

The PM₁₀ standard is attained when the expected number of exceedances per year, averaged over a three-year period, is less than or equal to one. The expected number of exceedances averaged over a three-year period at any given monitor is known as the PM₁₀ design value. The PM₁₀ design value for the area is the highest design value within the nonattainment area. Three consecutive years of air quality data are required to show attainment of the PM₁₀ standard.^[30] The demonstration of attainment in the Imperial PM₁₀ Plan is based on data from 2014-2016. In order to ensure the area has continued to attain, the EPA is also considering data collected subsequent to the time frame of the Plan.

ICAPCD is a monitoring organization within the CARB Primary Quality Assurance Organization (PQAO). ICAPCD and CARB are jointly responsible for monitoring ambient air quality within the Imperial PM₁₀ nonattainment area. CARB submits annual monitoring network plans to the EPA describing the monitoring network operated by ICAPCD and CARB within Imperial County and discussing the status of the air monitoring network, as required under 40 CFR 58.10.

The EPA reviews these annual plans for compliance with the applicable reporting requirements in 40 CFR part 58. With respect to PM₁₀, the EPA has found that CARB's network plans meet the applicable reporting requirements for the area under 40 CFR part 58.^[31] The EPA also concluded from its 2018 Technical System Audit that CARB and ICAPCD's monitoring network currently meets or exceeds the requirements for the minimum number of SLAMS for PM₁₀ in the El Centro, CA Metropolitan Statistical Area, which includes the Imperial PM₁₀ nonattainment area.^[32] ICAPCD and CARB annually certify that the data they submit to AQS are complete and quality-assured.^[33]

During the 2014-2016 time period, CARB operated one and ICAPCD operated four PM₁₀ SLAMS monitoring sites within the Imperial PM₁₀ nonattainment area. These sites are oriented along a roughly north-south axis in the central, populated part of the nonattainment area.^[34] Historically, all five sites monitored PM₁₀ concentrations using filter-based designated Federal Reference Method (FRM) monitors. Two sites have also monitored concentrations using continuous Federal Equivalent Method (FEM) monitors since 2009.

Between 2015 and 2016, data from FEM monitors became available at the remaining stations, while the filter-based FRM monitors at all five stations were gradually retired.^[35] The PM₁₀ monitoring sites have been established to monitor for population exposure in the middle or neighborhood scale.^[36]

Consistent with the requirements contained in 40 CFR part 50, the EPA has reviewed the quality-assured and certified PM₁₀ ambient air monitoring data as recorded in AQS for the applicable monitoring period collected at the monitoring sites in the Imperial PM₁₀ nonattainment area and determined that the data are of sufficient completeness for the purposes of making comparisons with the PM₁₀ standards.

The monitoring data for the PM₁₀ standard for the Imperial PM₁₀ nonattainment area include exceedances of the standard recorded during the 2014-2016 time period and in 2017 and 2018. However, the EPA is excluding most of the exceedances of the standard in these years from the attainment determination because they were the result of exceptional events as defined in section 319(b) of the Act and its implementing regulations, referred to herein as the Exceptional Events Rule.^[37] The Exceptional Events Rule defines an exceptional event as an event that the EPA determines affects air quality in such a way that there is a clear causal relationship between the event and a monitored exceedance (or violation) that is not reasonably controllable or preventable. Such events can be natural (for example, high winds or wildfires) or can be caused by human activity that is unlikely to recur.^[38]

On various dates, CARB submitted demonstrations for high wind PM₁₀ exceptional events covering the exceedances recorded at various monitoring sites in the nonattainment area during the 2014—2018 time period.^[39] The demonstrations include a narrative conceptual model of each event that describes the event-specific characteristics, evidence showing the exceedances were not reasonably controllable or preventable, and evidence of the clear causal relationship between the high wind events and the exceedances flagged as exceptional events.

The EPA reviewed the documentation that CARB and the District developed to demonstrate that the exceedances on these days met the criteria for an exceptional event under the Exceptional Events Rule. As conveyed in the EPA's concurrence letters included in the docket for this action, we have concurred with 91 exceedance days that the State requested for determinations that, based on the weight of evidence, exceedances were caused by high wind exceptional events.^[40] Accordingly, the EPA has determined that the monitored exceedances associated with these exceptional events should be excluded from use in determinations of exceedances and violations, including the evaluation of whether the Imperial PM₁₀ nonattainment area has attained the standard for the purposes of redesignation under CAA section 107(d)(3)(E)(i). Table 1 presents a summary of the PM₁₀ design values for 2016, 2017, and 2018 at the various monitors within the Imperial Valley Planning Area, excluding the exceedances for which the EPA has issued concurrences, based on the data for 2014-2016, 2015-2017 and 2016-2018 data, respectively.^[41] The PM₁₀ design value for the area is the PM₁₀ design value at the monitor with the highest design value in a given year.

Based on a review of air quality data during the three-year period covered by the Plan (2014-2016) (summarized above in Table 1), excluding the exceedances flagged by CARB and ICAPCD and concurred with by the EPA as exceptional events, we find that the 2016 design value for the Imperial PM₁₀ nonattainment area is 0.0 and that the area attained the standard by that year. We have also evaluated the certified data for 2017 and 2018 and find that that the 2017 design value for the Imperial PM₁₀ nonattainment area is 0.7 and the 2018 design value is 1.0, which demonstrates that the area continues to attain the standard. Therefore, based on complete, quality-assured, and certified data for 2014-2018, we find that the Imperial County PM₁₀ nonattainment area attained the PM₁₀ NAAQS in 2016 and has continued to attain since that time.

We have also reviewed preliminary data for 2019 that have been entered in AQS and have determined that they are consistent with attainment.^[42] We will review any additional data that becomes available prior to final action to ensure that they are consistent with continued attainment.^[43]

B. The Area Must Have a Fully Approved State Implementation Plan Meeting the Requirements Applicable for Purposes of Redesignation Under Section 110 and Part D

Sections 107(d)(3)(E)(ii) and (v) require the EPA to determine that the area has a fully approved applicable SIP under section 110(k) that meets all applicable requirements under section 110 and part D for the purposes of redesignation. The EPA may rely on prior SIP approvals in approving a redesignation request ^[44] as well as any additional measure it may approve in conjunction with a redesignation action. ^[45] In this instance, we are proposing to approve two part D elements as part of this action—the emissions inventory under CAA section 172(c)(3) and the BACM demonstration under CAA section 189(b)(1)(B). With full approval of those two elements, the Imperial County portion of the California SIP will be fully approved under section 110(k) for the purposes of redesignation of the area to attainment.

1. Basic State Implementation Plan Requirements Under Section 110

The general SIP elements and requirements set forth in section 110(a)(2) include, but are not limited to, the following: Submittal of a SIP that has been adopted by the state after reasonable public notice and hearing; provisions for establishment and operation of appropriate procedures needed to monitor ambient air quality; implementation of a source permitting program; provision for the implementation of part C requirements for prevention of significant deterioration; provisions for the implementation of part D requirements for nonattainment new source review permit programs; provisions for air pollution modeling; and provisions for public and local agency participation in planning and emission control rule development.

We note that SIPs must be fully approved only with respect to applicable requirements for purposes of redesignation in accordance with section 107(d)(3)(E)(ii). The section 110(a)(2) (and part D) requirements that are linked to a particular nonattainment area's designation and classification are the relevant measures to evaluate in reviewing a redesignation request. Requirements that apply regardless of the designation of any particular area of a state are not applicable requirements for the purposes of redesignation, and the State will remain subject to these requirements after the Imperial PM₁₀ nonattainment area is redesignated to attainment.

For example, CAA section 110(a)(2)(D) requires that SIPs contain certain measures to prevent sources in a state from significantly contributing to air quality problems in another state: These SIPs are often referred to as “transport SIPs.” Because the section 110(a)(2)(D) requirements for transport SIPs are not linked to a particular nonattainment area's designation and classification, but rather apply regardless of the area's attainment status, these are not applicable requirements for the purposes of redesignation under section 107(d)(3)(E).

Similarly, the EPA considers other section 110(a)(2) (and part D) requirements that are not linked to nonattainment plan submissions or to an area's attainment status as not applicable requirements for purposes of redesignation. The EPA evaluates the section 110 (and part D) requirements that relate to a particular nonattainment area's designation and classification as the relevant measures to evaluate in reviewing a redesignation request. This is consistent with the EPA's existing policy on applicability of the conformity SIP requirement for redesignations.^[46]

On numerous occasions, CARB and ICAPCD have submitted and we have approved provisions addressing the basic CAA section 110 provisions. The Imperial County portion of the California SIP contains enforceable emissions limitations; requires monitoring, compiling and analyzing of ambient air quality data; requires preconstruction review of new or modified stationary sources; provides for adequate funding, staff, and associated resources necessary to implement its requirements; and provides the necessary assurances that the State maintains responsibility for ensuring that the CAA requirements are satisfied in the event that Imperial County is unable to meet its CAA obligations.^[47] There are no outstanding or disapproved applicable SIP submittals with respect to the Imperial County portion of the SIP that prevent redesignation of the Imperial PM₁₀ nonattainment area for the PM₁₀ NAAQS. Therefore, we find that CARB and ICAPCD have met all general SIP requirements for Imperial that are applicable for purposes of redesignation under section 110 of the CAA.

2. State Implementation Plan Requirements Under Part D

Subparts 1 and 4 of part D, title 1 of the CAA contain air quality planning requirements for PM₁₀ nonattainment areas. Subpart 1 contains general requirements for all nonattainment areas of any pollutant, including PM₁₀, governed by a NAAQS. The subpart 1 requirements include, in relevant part, provisions for implementation of RACM, a demonstration of reasonable further progress (RFP), emissions inventories, a program for preconstruction review and permitting of new or modified major stationary sources, contingency measures, transportation conformity, and for areas that fail to attain the standard by the applicable attainment date, a plan meeting the requirements of section 179(d).

Subpart 4 contains specific planning and scheduling requirements for PM₁₀ nonattainment areas. Section 189(a), (c), and (e) requirements apply specifically to Moderate PM₁₀ nonattainment areas and include the following: An approved permit program for construction of new and modified major stationary sources; provisions for RACM; an attainment demonstration; quantitative milestones demonstrating RFP toward attainment by the applicable attainment date; and provisions to ensure that the control requirements applicable to major stationary sources of PM₁₀ also apply to major stationary sources of PM₁₀ precursors, except where the Administrator has determined that such sources do not contribute significantly to PM₁₀ levels that exceed the NAAQS in the area.

Under CAA section 189(b), Serious PM₁₀ nonattainment areas such as the Imperial PM₁₀ nonattainment area, must meet the subpart 1 and Moderate area requirements discussed above and, in addition, must develop and submit provisions to assure the implementation of BACM for the control of PM₁₀.^[48] Under CAA section 189(d), Serious PM₁₀ nonattainment areas that fail to attain the standard by the applicable attainment date, such as Imperial County, must develop and submit plan revisions that provide for attainment of the PM₁₀ standard and, from the date of such submission until attainment, for an annual reduction in PM₁₀ of not less than 5 percent of the amount of such emissions.

In the context of evaluating an area's eligibility for redesignation, the EPA has interpreted CAA requirements associated with attainment of the NAAQS (such as attainment and RFP demonstrations) as not being applicable for purposes of redesignation.^[49] The Calcagni memo similarly provides that requirements for RFP and other measures needed for attainment will not apply for redesignations because they have meaning and applicability only where areas do not meet the NAAQS.^[50] With respect to contingency measures, the EPA explained that the section 172(c)(9) contingency measure requirements are directed at ensuring RFP and attainment by the applicable date and that, consequently, these requirements no longer apply when an area has attained the standard and is eligible for redesignation. Furthermore, CAA section 175A(d) provides for specific requirements for maintenance plan contingency measures that effectively supersede the requirements of section 172(c)(9) for these areas.^[51]

Thus, the requirements associated with attainment do not apply for purposes of evaluating whether an area that has attained the standard qualifies for redesignation. The EPA has enunciated this position since the General Preamble was published more than 25 years ago, and it represents the Agency's interpretation of what constitutes applicable requirements under section 107(d)(3)(E). The courts have recognized the scope of the EPA's authority to interpret “applicable requirements” in the redesignation context.^[52]

The remaining applicable Part D requirements for Serious PM₁₀ areas include the following: (1) An emissions inventory under section 172(c)(3); (2) a permit program for the construction and operation of new and modified major stationary sources of PM₁₀ under sections 172(c)(5), 189(a)(1)(A) and 189(b)(3); (3) provisions to assure the implementation of BACM under section 189(b)(1)(B); (4) control requirements for major stationary sources of PM₁₀ precursors under section 189(e), except where the Administrator determines that such sources do not contribute significantly to PM₁₀ levels that exceed the standard in the area; (5) requirements under section 172(c)(7) that meet the applicable provisions of section 110(a)(2); and (6) provisions to ensure that federally supported or funded transportation projects conform to the air quality planning goals in the applicable SIP under section 176(c). We discuss each of these requirements below.

a. PM₁₀ Precursors

While CAA section 189(e) expressly requires control of precursors from major stationary sources, it is clear that subpart 4 and other CAA provisions collectively require the control of direct PM_2.5 and PM_2.5 precursors from all types of sources (i.e., stationary sources, area sources and mobile sources) as may be needed for the purposes of demonstrating attainment as expeditiously as practicable in a given nonattainment area. See CAA requirements for states to demonstrate attainment “as expeditiously as practicable.” CAA section 188(c)(1) and section 172(a)(1).

For the purposes of the redesignation request and development of the maintenance plan, CARB undertook an analysis of mass and speciation data to determine the extent to which PM₁₀ precursors contribute to ambient concentrations of PM₁₀ in the Imperial Valley Planning Area.^[53] CARB identified five days within the period of 2007 to 2016 where concentrations of PM₁₀ were greater than 95% of the NAAQS and for which PM₁₀ mass and PM₁₀ and PM_2.5 speciation data were available.^[54] Values for PM₁₀ mass on these dates ranged from 144 μg/m^[3] to 305 μg/m^[3] .^[55] Using this information, CARB calculated that for these five days, on average, SO_X ^[56] contributes 4.5 μg/m³ or 2 percent (%) of the PM₁₀ mass, NO_X contributes 3 μg/m³ or 1.3% of the PM₁₀ mass, ammonia contributes 4.7 μg/m³ or 2.1% of the PM₁₀ mass, and VOC contributes 4.1 μg/m³ or 1.8% of the PM₁₀ mass.

In its evaluation of whether precursors are significant contributors to PM₁₀ nonattainment, CARB relied upon a significance threshold of 3.7%, which CARB derived by adapting for PM₁₀ the recommended significance threshold of 1.3 μg/m^[3] for the 24-hour PM_2.5 standard of 35 μg/m^[3] .^[57] CARB concluded that, because each of the precursors contribute less than 2.1% of the PM₁₀ standard,^[58] they do not contribute significantly to elevated PM₁₀ concentrations in the Imperial Valley Planning Area.

CARB also plotted PM_2.5 and PM₁₀ from the Calexico monitoring site collected from 2007 through 2016 to illustrate the relationship between PM₁₀concentrations and PM_2.5 concentrations in the area. The data generally show that elevated PM_2.5 concentrations correspond to PM₁₀ concentrations below the PM₁₀ NAAQS and that PM_2.5 contributes a small percentage of the PM₁₀ mass when PM₁₀ levels exceed the PM₁₀ NAAQS. This suggests that high PM₁₀ concentrations are driven by fugitive dust and that secondarily-formed particulate matter does not increase as a percentage of mass as PM₁₀ concentration exceed the NAAQS. The data also show that PM_2.5 represents about 11% of the total PM₁₀ mass when PM₁₀ concentrations approach the level of the PM₁₀ NAAQS.

We have reviewed the precursor analysis prepared by CARB and agree that precursors do not contribute significantly to elevated PM₁₀ concentrations in the Imperial Valley Planning Area. First, we generally recommend using 5 µg/m^[3] as the threshold for identifying potentially significant contributions to elevated PM₁₀ concentrations.^[59] The contribution of precursors to PM₁₀ concentrations is not significant using either CARB's 3.7% threshold or the 5 µg/m³ threshold. As CARB notes, the highest average precursor contribution based on data for the five specific analysis days presented in Appendix A of the Imperial PM₁₀ Plan is less than 2.1%, and the highest average estimated precursor contribution is approximately 4.7 µg/m³ (i.e., for NH₃).

Second, as described in section IV.A of this notice, exceedances of the PM₁₀ standard in Imperial County are caused by windblown dust that is generated during high wind events. When such days are removed from consideration in accordance with the EPA's Exceptional Events Rule, the area is attaining the PM₁₀ standard. In this context, we believe it is appropriate to evaluate the contribution of precursors on days that are close to the level of the standard rather than days on which elevated levels of PM₁₀ are likely associated with high wind exceptional events. CARB's analysis includes two such days. On October 21, 2007, the total PM₁₀ mass was 144 μg/m³ and on July 18, 2009, the total PM₁₀ mass was 147.9 μg/m³. The estimated contribution of each precursor on each of these two dates ranges from 1.4 μg/m³ to 4.1 μg/m³. All values are below the 5 μg/m³ threshold established in the Addendum.

Thus, for the reasons stated above, we propose to find that PM₁₀ precursors do not significantly contribute to elevated PM₁₀ concentrations in the Imperial Valley Planning Area. With respect to future conditions, we note that the emissions inventories prepared for the Imperial PM₁₀ Plan show a downward trend in the County for the PM₁₀ precursor emissions through the initial maintenance period (i.e., through 2030),^[60] and thus, we also find that PM₁₀ precursors will not significantly contribute to elevated PM₁₀ concentrations within the Imperial Valley Planning Area through the initial maintenance period.

b. Emissions Inventory

Section 172(c)(3) of the CAA requires states to submit a comprehensive, accurate, current inventory of actual emissions from all sources of the relevant pollutant(s) within the nonattainment area. The EPA interprets the Act such that the emissions inventory requirement of section 172(c)(3) is satisfied by the inventory requirement of the maintenance plan.^[61] In section IV.D.1 of this document, we are proposing to approve the 2016 attainment inventory submitted as part of the Imperial PM₁₀ Plan as satisfying the emissions inventory requirement under section 172(c)(3) for the Imperial Valley Planning Area for the PM₁₀ NAAQS.

c. Permits for New and Modified Major Stationary Sources

CAA sections 172(c)(5) and 189(a)(1)(A) require that states submit SIP revisions that establish certain requirements for new or modified major stationary sources in nonattainment areas, including provisions to ensure that new major sources or major modifications of existing sources of nonattainment pollutants incorporate the highest level of control, referred to as the lowest achievable emission rate, and that increases in emissions from such stationary sources are offset so as to provide for reasonable further progress towards attainment in the nonattainment area. The major source threshold for Serious PM₁₀ nonattainment areas is 70 tons per year of PM_10.^[62]

The process for reviewing permit applications and issuing permits for new or modified major stationary sources of air pollution is referred to as new source review (NSR). With respect to nonattainment pollutants in nonattainment areas, this process is referred to as nonattainment NSR (NNSR). Areas that are designated as attainment or unclassifiable for one or more NAAQS are required to submit SIP revisions that ensure that new major stationary sources or major modifications of existing stationary sources meet the federal requirements for prevention of significant deterioration (PSD), including application of best available control technology for each applicable pollutant emitted in significant amounts, among other requirements.^[63]

The District is responsible for the regulation of stationary sources, and its rules govern air permits issued for such units. In 2017, the EPA approved ICAPCD's NNSR rule, Rule 207 (“New and Modified Stationary Source Review”) as satisfying the statutory and regulatory requirements for a NNSR permit program for Serious PM₁₀ nonattainment areas as set forth in the applicable provisions of part D of title I of the Act (sections 172 and 173), and in 40 CFR 51.165 and 40 CFR 51.307.^[64]

If we finalize the redesignation action proposed herein, the Imperial PM₁₀ nonattainment area will become an attainment area, and new or modified major sources in the area will be subject to the PSD permitting requirements rather than the NNSR requirements.

The District has a SIP-approved PSD program (Rule 904, “Prevention of Significant Deterioration (PSD) Permit Program”) that will apply to PM₁₀ emissions from new major sources or major modifications upon redesignation of the area to attainment.^[65] Thus, new PM₁₀ major sources and major modifications with significant PM₁₀ emissions at major sources will be required to obtain a PSD permit or address PM₁₀ emissions in their existing PSD permit.

d. Best Available Control Measures

Clean Air Act section 189(b)(1)(B) requires that Serious areas implement BACM for the control of PM₁₀ for all source categories that contribute significantly to nonattainment of the NAAQS.^[66] The EPA has long interpreted this requirement to apply independent of attainment.^[67] Consequently, the requirement for BACM level controls continues to apply, even when the area has attained the standard.

The Imperial PM₁₀ plan addresses the BACM requirement by first, providing a detailed emissions inventory and determining which source categories of directly emitted PM₁₀ contribute significantly; second, by identifying the rules that apply to significantly contributing source categories and documenting that those rules require BACM level controls; and third, by documenting compliance with CAA best available control technology requirements by major sources of PM₁₀ that are located within the nonattainment area.

Identification of Significant Contributors

The Imperial PM₁₀ Plan's BACM demonstration includes an analysis that establishes which sources of directly emitted PM₁₀ contribute significantly to ambient levels of PM₁₀. It does this by calculating the percent contribution of sources in Imperial County's average annual daily emissions inventory and then performing a sensitivity analysis to determine if reducing the contribution of windblown dust to the inventory would alter the conclusions of the analysis.^[68] Because the 5 μg/m³ significant contribution threshold equates to 3.25% of the PM₁₀ NAAQS, the District concludes that any source category that contributes more than 3.25% of the inventory would be significant and therefore subject to BACM.

Based on the Imperial County 2016 average annual daily PM₁₀ emissions inventory, the only source categories that contribute more than 3.25% of the total direct PM₁₀ emissions are entrained unpaved road dust from city and county roads (6.47%) and canal roads (10.82%), and windblown dust from open areas (70.37%) and non-pasture agricultural lands (3.79%).^[69] If windblown dust is reduced by 25% (i.e., to 75% of its average annual daily contribution), there are no changes to significantly contributing categories. When windblown dust is reduced by 50%, the only change is that the PM₁₀ contribution from non-pasture agricultural lands drops below the significance threshold. If windblown dust is reduced by 75% (i.e., to 25% of its average annual daily contribution), the contribution from tilling operations increases to 3.9%. If windblown dust is removed entirely, the source categories that exceed the 3.25% threshold are mineral processes (5.12%), tilling (6.8%), cattle operations (3.66%), and entrained unpaved road dust from city and county roads (25.65%) and canal roads (42.90%).

The District plotted PM₁₀ concentrations against wind speed for 2014 to 2016 monitoring data.^[70] Each value that exceeds the PM₁₀ standard has been flagged by the District as an exceptional event. To evaluate the contribution of sources of non-windblown dust, the District analyzed January 15, 2016, which was a low-wind day that approached but did not exceed the standard. Although the average hourly wind speed was 4.28 miles per hour, an examination of the hourly wind speeds for that date show there were periods of elevated wind speed that indicate the date “could not reasonably be categorized as a `no-wind' day.” ^[71] Based on this analysis, ICAPCD concludes that “it is unlikely that a day with low winds and 0% windblown dust contributions would result in an exceedance of the PM₁₀ NAAQS at a monitor in Imperial County.” Consequently, the District determined that mineral processes, cattle, and construction, which only exceed the 3.25% threshold on days where windblown dust is completely eliminated from the inventory, do not contribute significantly to exceedances of the NAAQS.

We find the District's analysis to be sound and, based on a conservative determination of the percent contribution of source categories when windblown dust is reduced by 75%, agree that the source categories that contribute significantly are tilling, entrained unpaved road dust, and windblown dust from open areas. We note that the BACM demonstration in the Imperial PM₁₀ Plan does not address PM₁₀ precursor emissions, but we find that the decision to exclude PM₁₀ precursors in this instance is acceptable in light of our proposed determination in section IV.B.2.a of this document that PM₁₀ precursors do not contribute significantly to elevated PM₁₀ concentrations in the Imperial Valley Planning Area.

BACM Analysis for Significantly Contributing Source Categories

The Imperial PM₁₀ Plan provides documentation showing that the source categories that contribute significantly to exceedances of the PM₁₀ NAAQS in Imperial County are subject to the provisions of Regulation VIII, which form the core of the ICAPCD's control strategy for PM₁₀. Specifically, the following rules apply to the significantly contributing source categories: Rule 800 (“General Requirements for Control of Fine Particulate Matter (PM₁₀)”), Rule 804 (“Open Areas”), Rule 805 (“Paved and Unpaved Roads”), and Rule 806 (“Conservation Management Practices”).^[72] ICAPCD's Regulation VIII rules were originally adopted by the District in 2005. The EPA partially approved and partially disapproved these rules after identifying certain deficiencies in rules 800, 804, 805, and 806.^[73] The District subsequently revised and strengthened the rules by addressing these deficiencies and on April 23, 2013, the EPA approved the revised rules and found that they established BACM-level controls for the categories they regulate.^[74] Based on our prior approval of these rules and our conclusion that they cover all significant PM₁₀ source categories in the Imperial PM₁₀ nonattainment area, we propose to approve ICAPCD's demonstration as satisfying the requirement to ensure implementation of BACM under CAA section 189(b)(1)(B).

e. Control Requirements for Major Sources of PM₁₀ Precursors

CAA section 189(e) provides that control requirements for major stationary sources of direct PM₁₀ also apply to major stationary sources of PM precursors, except where the EPA determines that major stationary sources of such precursors do not contribute significantly to PM₁₀ levels that exceed the standard in the area. In general, a major stationary source in a PM₁₀ Serious area is a stationary source that emits, or has the potential to emit, 70 tons per year of PM₁₀. As described in more detail in section IV.B.2.a of this action, we are proposing to approve the demonstration the Imperial PM₁₀ plan that precursors do not contribute significantly to PM₁₀ levels that exceed the standard.

f. Compliance With Section 110(a)(2)

Section 172(c)(7) requires the SIP to meet the applicable provisions of section 110(a)(2). As described above in Section IV.B., we conclude the California SIP meets the requirements of section 110(a)(2) applicable for purposes of this redesignation.

g. General and Transportation Conformity Requirements

Under section 176(c) of the CAA, states are required to revise their SIPs to establish criteria and procedures to ensure that federally supported or funded projects in nonattainment areas and formerly nonattainment areas subject to a maintenance plan (referred to as “maintenance areas”) conform to the air quality planning goals in the applicable SIP. Section 176(c) further provides that state conformity provisions must be consistent with federal conformity regulations that the CAA requires the EPA to promulgate. The EPA's conformity regulations are codified at 40 CFR part 93, subparts A (referred to herein as “transportation conformity”) and B (referred to herein as “general conformity”). Transportation conformity applies to transportation plans, programs, and projects developed, funded, and approved under title 23 U.S.C. or the Federal Transit Act, and general conformity applies to all other federally-supported or funded projects. SIP revisions intended to address the conformity requirements are referred to herein as “conformity SIPs.” In 2005, Congress amended section 176(c) of the CAA. Under the amended conformity statutory provisions, states are no longer required to submit conformity SIPs for general conformity, and the conformity SIP requirements for transportation conformity have been reduced to include only those relating to consultation, enforcement and enforceability.^[75]

In 1999, before the general conformity SIP requirement was eliminated by Congress, we approved the District's general conformity rule, Rule 925 (“General Conformity”) as a revision to the Imperial County portion of the California SIP.^[76] We have not approved a transportation conformity SIP for the Imperial PM₁₀ nonattainment area. However, we consider it reasonable to interpret the conformity SIP requirements as not applying for purposes of a redesignation request under section 107(d) because the conformity SIP requirement continues to apply post-redesignation (because conformity applies in maintenance areas as well as nonattainment areas) and because the federal conformity rules (set forth in 40 CFR part 93, subparts A and B) apply where state rules have not been approved.^[77]

C. The Area Must Show the Improvement in Air Quality is Due to Permanent and Enforceable Emission Reductions

In order to approve a redesignation to attainment, section 107(d)(3)(E)(iii) of the CAA requires the EPA to determine that the improvement in air quality is due to emissions reductions that are permanent and enforceable, and that the improvement results from the implementation of the applicable SIP and applicable federal air pollution control regulations and other permanent and enforceable regulations. Attainment resulting from temporary reductions in emissions rates (e.g., reduced production or shutdown due to temporary adverse economic conditions) or unusually favorable meteorology would not qualify as an air quality improvement due to permanent and enforceable emissions reductions.^[78]

The 2018 Imperial PM₁₀ Plan concludes that the improvement in PM₁₀ air quality in the Imperial Valley Planning Area is due to emissions reductions from implementation of the District's Regulation VIII fugitive dust rules, adopted in 2005, based on data for years 2000 to 2016 that show a gradual decline in annual average PM₁₀ concentrations that cannot be explained by adverse economic conditions or usually favorable meteorology. With respect to economic conditions, the data presented in the 2018 Imperial PM₁₀ Plan show a gradual increase in population over the 2000 to 2016 period and a very gradual decline in harvested acres over that period suggesting little change in the agricultural sector of the economy during this time. With respect to meteorological conditions, the plan presents annual rainfall totals for Imperial County from 2000 through 2016 ranging from less than 1 inch to approximately 5 inches with rainfall totals during the 2014-2016 attainment period of approximately 2 inches each year.

First, we agree that the implementation of the District's Regulation VIII fugitive dust rules has reduced PM₁₀ emissions within the Imperial Valley Planning Area. More specifically, we find that emissions of the largest contributors to ambient PM₁₀ concentrations (i.e., fugitive windblown dust and unpaved road dust) declined significantly after Regulation VIII was adopted in 2005. For instance, in 2005, PM₁₀ emissions from unpaved road dust and fugitive windblown dust totaled approximately 288 tons per day (tpd) in Imperial County. After implementation of Regulation VIII, emissions attributable to these categories declined by approximately 16 tpd, or about 6 percent by 2008. While the amount of fugitive windblown dust has remained relatively constant since 2008, unpaved road dust has continued to decline until, by 2017, it accounted for an additional 7 tpd reduction of PM₁₀.^[79] Overall, between 2005 and 2016, PM₁₀ emissions within Imperial County have declined from approximately 313 tpd to approximately 284 tpd in 2016. The most significant reductions from 2005 and 2016 occurred in the farming operations, unpaved road dust and fugitive windblown dust source categories, all of which are subject to one or more Regulation VIII rules.

Second, because we have approved the Regulation VIII fugitive dust rules, the associated emissions reductions are permanent and enforceable. Table 2 lists the District's Regulation VIII rules with most recent adoption or amendment dates and most recent EPA approval dates.

Third, based on the data on population growth, harvested acreage, and rainfall totals in the 2018 Imperial PM₁₀ Plan, we agree that the reduction in PM₁₀ emissions within Imperial County is due largely to the District's Regulation VIII fugitive dust rules and is not due to adverse economic conditions or favorable meteorology. In this regard, we note that we are proposing herein to find that the area attained the standard during the 2014 to 2016 period. During that time, Imperial County saw a slight increase in population, relatively steady economic activity, and lower than average rainfall. Therefore, attainment of the PM₁₀ NAAQS in that period could not have been the result of adverse economic conditions or favorable meteorology. Moreover, the determination of attainment relies upon the implementation of Regulation VIII rules, without which high-wind-caused exceedances would not have been deemed to be exceptional events under the EPA's Exceptional Events Rule.

Therefore, for the above reasons, we find that attainment of the PM₁₀ NAAQS in the Imperial Valley Planning Area is due to permanent and enforceable emissions reductions resulting from implementation of the applicable SIP, namely the District's Regulation VIII fugitive dust rules. Consequently, we propose to find that the criterion for redesignation set forth at CAA section 107(d)(3)(E)(iii) is satisfied.

D. The Area Must Have a Fully Approved Maintenance Plan Under Section 175A

Section 107(d)(3)(E)(iv) of the CAA requires that, in order to approve a redesignation to attainment, the EPA must fully approve a maintenance plan for the area as meeting the requirements of section 175A of the Act. Section 175A sets forth the required elements of a maintenance plan for areas seeking redesignation from nonattainment to attainment. Under section 175A, the plan must demonstrate continued attainment of the applicable NAAQS for at least 10 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 as the EPA deems necessary to promptly correct any violation of the NAAQS that occurs after redesignation of the area. The Calcagni memo provides further guidance on the content of a maintenance plan, explaining that a maintenance plan should include an attainment emissions inventory, maintenance demonstration, monitoring and verification of continued attainment, and a contingency plan. For the reasons provided below, we are proposing to approve the Imperial PM₁₀ Plan as meeting the requirements for maintenance plans under CAA section 175A.

1. Attainment Inventory

A maintenance plan for the PM₁₀ NAAQS should include an inventory of direct PM₁₀ emissions in the area to identify a level of emissions sufficient to attain the PM₁₀ NAAQS.^[80] This inventory should be consistent with the EPA's most recent guidance on emissions inventories for nonattainment areas available at the time and should represent emissions during the time period associated with the monitoring data showing attainment. The inventory must also be comprehensive, including emissions from stationary point sources, area sources, and mobile sources and must be based on actual emissions during the appropriate season, if applicable. See CAA section 172(c)(3).

The specific PM₁₀ emissions inventory requirements are set forth in the Air Emissions Reporting Rule (40 CFR 51, subpart A). The EPA has provided additional guidance for developing PM₁₀ emissions inventories in “PM₁₀ Emissions Inventory Requirements,” EPA-454/R-94-033 (September 1994) and “ Emissions Inventory Guidance for Implementation of Ozone and Particulate Matter National Ambient Air Quality Standards (NAAQS) and Regional Haze Regulations” (July 2017) (“EPA 2017 EI Guidance”).^[81]

The Imperial PM₁₀ Plan provides an emissions inventory of actual emissions from all direct PM₁₀ sources within Imperial County on an average annual day in 2016. The District and CARB developed this inventory based on the methods and assumptions presented in detail in Appendix G (“Emission Inventory Documentation for the Imperial County PM₁₀ Nonattainment Maintenance Plan”) and Appendix H (“PM₁₀ and PM₁₀ Precursor Emission Inventories”). Appendix H also identifies the specific filterable and condensable components of the direct PM₁₀ emissions estimates. Table 3 below provides a summary of the 2016 direct PM₁₀ emissions inventory for Imperial County. As shown in Table 3, fugitive dust sources, particularly fugitive windblown dust and entrainment of dust from vehicle travel over unpaved roads, are the predominant sources of direct PM₁₀ emissions in the County.

As discussed in Appendix G of the Imperial PM₁₀ Plan, direct PM₁₀ emissions estimates for stationary point sources reflect actual emissions reported to the District in 2012 by owners or operators of industrial point sources in the County and then adjusted to 2016 based on applicable growth surrogates. Areawide sources occur over a wide geographic area. Examples of these sources are consumer products, paved and unpaved road dust, fireplaces, farming operations, and prescribed burning. Emissions for these categories are estimated by both CARB and the ICAPCD using various models and methodologies. Emissions estimates for the fugitive dust source categories also reflect implementation of the District's various Regulation VIII rules.

Emissions from on-road mobile sources, which include passenger vehicles, buses, and trucks, were estimated using outputs from CARB's EMFAC2014 model.^[82] These emissions were calculated by applying EMFAC2014 emissions factors to the transportation activity data provided by the Southern California Association of Governments (SCAG) from their 2016 adopted Regional Transportation Plan/Sustainable Communities Strategy (2016 RTP/SCS).^[83] SCAG is the metropolitan planning organization representing Imperial County, along with five other counties in Southern California.

Emissions from off-road mobile sources, which include cargo handling equipment, pleasure craft, recreational vehicles, and locomotives, were estimated using a suite of category-specific models or, where a new model was not available, the OFFROAD2007 model. Many of the newer models were developed to support recent regulations, including in-use offroad equipment.

The EPA considers the selection of 2016 for the attainment year inventory to be appropriate given that the design value for 2016, excluding exceedances caused by exceptional events, is consistent with attainment of the PM₁₀ NAAQS. Moreover, preparation of an annual average daily inventory, as opposed to a seasonal or episodic inventory, is appropriate given that elevated PM₁₀ concentrations in Imperial County do not exhibit a clear seasonal or episodic pattern. Also, we find that the county-wide basis for the inventory is appropriate in this instance even though the County is larger than the nonattainment area because the nonattainment area encompasses the vast majority of the population and vehicular activity within the County. Based on our review of the documentation provided with the plan, we find that the 2016 emissions inventory for direct PM₁₀ is based on reasonable assumptions and methodologies, and that the inventory is comprehensive, current and accurate. We therefore propose to approve the inventory of actual emissions in 2016 in the Imperial PM₁₀ Plan as meeting the requirements of CAA section 172(c)(3). We also find the 2016 inventory in the plan to be acceptable for use in demonstrating maintenance of the PM₁₀ NAAQS in the future.

2. PM₁₀ Maintenance Demonstration

Section 175A requires a state seeking redesignation to attainment to submit a SIP revision to provide for maintenance of the NAAQS for a period of at least ten years following redesignation. This can be shown either by demonstrating that future emissions of a pollutant and its precursors will not exceed the level of the attainment inventory or by conducting modeling that shows the future emissions will not cause a violation of the standard. In accordance with EPA guidance, the state should project emissions for the 10-year period following redesignation, for either purpose.^[84] Projected emissions inventories for future years must account for, among other things, the ongoing effects of economic growth and adopted emissions control requirements, and the inventories are expected to be the best available representation of future emissions. The plan submission should include documentation explaining how the state calculated the emissions data for the base year and projected inventories.

The Imperial PM₁₀ Plan demonstrates that the Imperial Valley Planning Area will maintain the PM₁₀ NAAQS through 2030 by projecting the direct PM₁₀ emissions in the County for years 2018-2030 and by estimating the proportional change in the design concentration ⁸⁵ based on the change in future emissions relative to the 2016 attainment inventory. The last year for which a maintenance plan demonstrates maintenance of the NAAQS is referred to as the horizon year, and for the Imperial PM₁₀ Plan, 2030 is the horizon year.

Projected inventories are derived by applying expected growth trends for each source category and are based on data that reflect historical trends, current conditions, and recent economic and demographic forecasts with expected emissions reductions resulting from adopted control measures to the base year inventory. For the Imperial PM₁₀ Plan, emissions projections for 2018 through 2030 were generated by applying growth and control profiles to the 2016 attainment inventory. Growth forecasts for most point and areawide sources were developed either by CARB or by SCAG and provided to CARB through the South Coast Air Quality Management District. Mobile sources were forecast using total vehicle miles traveled projections provided by SCAG. Off-road sources were forecast using various growth surrogates as shown in Table 5 of Appendix G of the plan. Appendix G of the plan documents the methods and assumptions used to develop the emissions projections upon which the maintenance demonstration relies, and Appendix H of the plan presents the detailed source-category-specific estimates for each of the analysis years.

Table 4 presents a summary of the Imperial PM₁₀ Plan's estimates of direct PM₁₀ emissions in an interim year (2025) and the horizon year (2030) along with the corresponding emissions estimates for the attainment year (2016). For the sake of simplicity, Table 4 shows emissions for just one of the interim years (i.e., 2025) between the attainment year and the horizon year, but the plan itself provides emissions estimates for each year from 2018 through 2030.^[86] The emissions estimates in the plan predict a gradual change in emissions within the County over time with slight decreases in certain categories (e.g., farming operations and unpaved road dust) nearly offsetting slight increases in certain other source categories (e.g., construction and demolition and paved road dust). By 2030, overall direct PM₁₀ emissions are estimated to be approximately 2 tpd (0.6 percent) higher than in the 2016 attainment year.

For the Imperial PM₁₀ Plan, based on 2014-2016 ambient PM₁₀ concentration data (excluding exceedances from high wind exceptional events), the District identified a design concentration of 149 μg/m^[3] , which is about 3.8% less than the level at which the PM₁₀ NAAQS is exceeded.^[87] The Imperial PM₁₀ Plan concludes that maintenance is demonstrated through the horizon year because the projected increase in emissions through the horizon year (0.6%) is less than the margin between the design concentration and an exceedance of the PM₁₀ NAAQS (3.8%).

We note that over the initial maintenance period (i.e., through 2030), the lake surface of the Salton Sea is expected to shrink, and that the future emissions projections in the Imperial PM₁₀ Plan used as the basis for the maintenance demonstration do not include any emissions increases directly related to the increased exposure of previously submerged lakebed, known as playa, as the lake surface shrinks. However, the Imperial PM₁₀ Plan recognizes the potential for emissions increases from windblown dust from the exposed playa and describes the various efforts underway to evaluate and control this emerging source.^[88] These efforts include the establishment in 2015 of the Salton Sea Task Force, which has developed a 10-year plan that endeavors to expedite wildlife habitat construction and to suppress dust from playa that will be exposed in the future. The Imperial Irrigation District's Salton Sea Air Quality Mitigation Program, which applies in addition to other programs and requirements, represents another of these efforts. It includes three components: A monitoring program and development of an emissions inventory; a dust control strategy that includes the development and testing of dust control measures; and the implementation of an annual proactive dust control plan that includes performance modeling. The District also notes that state law and water transfer permits include requirements to control PM₁₀ emissions from exposed lake bed, and that District Rule 804, which requires the control of fugitive dust from open areas, also applies to the playa.^[89] Therefore, we find that the Imperial PM₁₀ Plan adequately addresses the potential for an increase in PM₁₀ emissions from newly exposed playa along the shores of the Salton Sea to interfere with maintenance of the PM₁₀ NAAQS through the initial maintenance period.^[90]

Based on our review of the documentation provided with the Imperial PM₁₀ Plan, we find that the projected emissions inventories for direct PM₁₀ for years 2018 through 2030 are based on reasonable methods, growth factors, and assumptions, and are based on the most current and accurate information available to CARB and ICAPCD at the time the plan and its inventories were being developed. Given that the projections of direct PM₁₀ emissions show future emissions increases through 2030 that would be less than the margin between the design concentration and an exceedance of the standard, we find that Imperial PM₁₀ Plan provides an adequate basis to demonstrate maintenance of the PM₁₀ NAAQS within the Imperial Valley Planning Area through 2030.^[91] Lastly, section 175A of the CAA requires that a maintenance plan provide for maintenance of the NAAQS in the area for at least ten years after redesignation. If we finalize this proposed approval of CARB's redesignation request and such approval becomes effective in 2020, the projected 2030 inventory in the Imperial PM₁₀ Plan demonstrates that the Imperial Valley Planning Area will maintain the PM₁₀ NAAQS for at least 10 years beyond redesignation.

3. 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 attainment status of the area.^[92] Data collected by the monitoring network are also needed to implement the contingency plan element of the maintenance plan. As discussed in section IV.A. of this document, CARB and the District monitor ambient concentrations of PM₁₀ at five monitoring sites within the Imperial PM₁₀ nonattainment area. In section 4.2 (“Future Monitoring Network”) of the Imperial PM₁₀ Plan, the District states that, in conjunction with CARB, it will assure the quality of the data using various quality assurance procedures and notes that, under federal regulations, the monitoring network is reviewed annually. ICAPCD also commits to continuing to assure PM₁₀ monitoring is conducted in accordance with 40 CFR part 58. We find that the Imperial PM₁₀ Plan contains adequate provisions for continued operation of an appropriate air quality monitoring network that will provide a basis to verify the attainment status of the area.

The EPA also recommends that the state verify continued attainment through methods in addition to the ambient air monitoring program, e.g., through periodic review of the factors used in developing the attainment inventory to show no significant change.^[93] In the Imperial PM₁₀ Plan, the District commits to periodic review of the inputs and assumptions used for the emissions inventory on an annual basis and, if the District finds that these inputs have changed significantly, to request that CARB update the existing inventory and take other appropriate measures.^[94] We find that the District's commitments to verify continued attainment of the PM₁₀ NAAQS through continued ambient air monitoring and annual review of the inputs and assumptions used for the emission inventory in the Imperial PM₁₀ plan are acceptable.

4. Contingency Provisions

Section 175A(d) of the CAA requires that maintenance plans include contingency provisions, as the EPA deems necessary, to promptly correct any violations of the NAAQS that occur after redesignation of the area. Such provisions must include a requirement that the state will implement all measures with respect to the control of the air pollutant concerned that were contained in the SIP for the area before redesignation of the area as an attainment area.^[95] These contingency provisions are distinguished from those generally required for nonattainment areas under CAA section 172(c)(9) in that they are not required to be fully-adopted measures that will take effect without further action by the state for the maintenance plan to be approved. However, the contingency plan is considered to be an enforceable part of the SIP and it should ensure that the contingency measures are adopted expeditiously once the requirement for contingency measures has been triggered. 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. As a necessary part of the plan, the state should also identify the specific indicators or triggers that will be used to determine when the contingency measures need to be implemented.

The District has adopted a contingency plan to address future PM₁₀ exceedances occurring after redesignation of the area to attainment. The contingency plan is contained in Section 4.4 of the Imperial PM₁₀ Plan.

As noted by the District in the Imperial PM₁₀ Plan, contingency provisions are typically implemented when air quality deteriorates beyond a specified level, such as a certain number of exceedances of the standard or a violation of the standard. In this case, the contingency provisions will be triggered when the number of exceedances at a monitor, averaged over three years, is greater than 1.05. However, because PM₁₀ exceedances in Imperial County are largely driven by high wind dust events that may be eligible for consideration under the Exceptional Events Rule,^[96] the contingency plan includes a screening process that allows the District and CARB, subject to EPA review, to exclude exceedances from the trigger calculation if the agencies show that the exceedances meet certain criteria indicating they are likely eligible for treatment as an exceptional event.^[97] The purpose of the screening process is to differentiate between exceedances that are not within the District or State control (i.e., exceedances that occur despite the implementation of reasonable measures), and exceedances that are within the District's or State's control and should be included in the trigger calculation. It is important to note that, should the District or State exclude an exceedance from the contingency trigger calculation using this process, it would not constitute the EPA's concurrence that the exceedance was caused by an exceptional event. The exceedance will therefore continue to be included in design value calculations for the Imperial Valley Planning Area unless CARB, 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.

Under the contingency trigger screening process, within 60 days of the end of each calendar quarter, the District will complete the following: Provide a list of exceedances that occurred during that previous quarter to CARB, identify those exceedances that meet the criteria specified in the contingency measure screening process, flag the relevant data, and provide an initial description in AQS. The State then has 60 days to review the information, during which time it may request additional information from the District to supplement the District's analysis. Following CARB's review, CARB will transmit the information to the EPA, including information for those exceedances the District believes should be excluded from the contingency plan trigger calculation.

The Imperial PM₁₀ Plan anticipates that, within 60 days of receipt, the EPA will review the submitted information, notify the District if the submitted information is insufficient to support exclusion from the contingency plan trigger calculation, include such exceedances in calculating the trigger for the contingency plan, and notify the District if the contingency plan has been triggered. The EPA intends to notify the District, within 60 days of receipt, whether submitted information is sufficient or insufficient to support the exclusion of a given exceedance from the contingency plan trigger calculation and to take the other actions described in the plan. If the submitted information is not sufficient, the EPA will include the exceedance in the calculation to determine if the contingency plan has been triggered. If the State or District subsequently provide additional information sufficient to support the conclusion that the exceedance meets the criteria for exclusion from the trigger calculation, the EPA will notify the District that the calculation will be adjusted.

Under the contingency plan, if the EPA determines that contingency provisions have been triggered (i.e., the number of exceedances at any single monitor, averaged over three years, is greater than 1.05 excluding those exceedances identified through the screening process), ICAPCD commits to the following steps:

(1) Within six months of EPA notification, ICAPCD will complete an analysis of the exceedances and the available contingency measures. During this time, the District will determine the possible cause of the exceedances and will consult with community and local industry members to determine if any voluntary or incentive measures could be implemented to reduce the magnitude of or eliminate the source of emissions.

If voluntary and incentive-based measures do not adequately address the problem, the ICAPCD will evaluate its Regulation VIII fugitive dust rules, or other rules as appropriate, to determine where such rules could be improved or expanded to achieve additional emissions reductions. The measures that ICAPCD would consider and analyze include but are not limited to those listed in Table 4-6 in the Plan.

(2) Within 12 months of completing its analysis, the District will adopt and implement the new contingency measures.

Based on our review of the Imperial PM₁₀ Plan, as summarized above, we propose to find that the contingency provisions of the Imperial PM₁₀ Plan clearly identify specific 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 are the type that have been deemed exceptional events in the past and exceedances for which new or tightened control measures might be effective. Our assessment indicates that the screening process is an appropriate element of the contingency plan for the Imperial Valley Planning Area because of the frequency of exceedances related to high wind dust events in this area. Thus, we propose to conclude that the contingency plan in the Imperial PM₁₀ Plan is adequate to ensure prompt correction of any violation of the PM₁₀ NAAQS that occurs after redesignation, as required by section 175A(d) of the CAA.

5. Motor Vehicle Emissions Budgets for Transportation Conformity

Section 176(c) of the CAA 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 (MPOs) 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 done 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.

Budgets are generally established for specific years and specific pollutants or precursors. PM₁₀ maintenance plan submittals should identify budgets for transportation-related PM₁₀ emissions in the last year of the maintenance period.^[98] 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 (40 CFR 93.118(e)(4)). 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 the motor vehicle control measures relied upon for the maintenance demonstration.

The EPA's process for determining adequacy of a budget consists of three basic steps: (1) Notifying the public of a SIP submittal; (2) providing the public the opportunity to comment on the budget 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 (40 CFR 93.118(f)(1)), or via a Federal Register notice of proposed rulemaking when the EPA reviews the adequacy of an maintenance plan budget simultaneously with its review and action on the SIP submittal itself (40 CFR 93.118(f)(2)).

The Imperial PM₁₀ Plan includes budgets for direct PM₁₀ for the attainment year (2016) and the last year of the maintenance plan (2030). The applicable source categories included in the budgets include vehicle emissions (including exhaust, brake wear, and tire wear), and entrained dust from vehicle travel over paved and unpaved roads. With respect to unpaved road dust, the budgets include only those emissions generated by vehicle travel over city- and county-owned unpaved roads, not canal roads, farm roads or those owned by the U.S. Bureau of Land Management or the U.S. Forest Service. In addition, the budgets apply to the entire County, including the portion of the County that lies outside of the PM₁₀ nonattainment area.^[99] As noted previously, an estimated 95% of the vehicle activity within the County occurs within the PM₁₀ nonattainment area, and thus, the budgets reasonably correspond to the nonattainment area even though they are county-wide values. The 2016 and 2030 annual average day conformity budgets for PM₁₀ are provided in Table 5.

CARB developed the on-road mobile portion of the emissions inventory for the maintenance plan using California's on-road mobile source emission projection model, EMFAC2014, and vehicle activity data provided by SCAG from its 2016 RTP/SCS. The EMFAC2014 model calculated tire wear, brake wear, and exhaust emissions. Paved road dust emissions were estimated using AP-42 with California-specific silt loading data.^[100] The unpaved road dust emissions were estimated using CARB's methodology 7.10, updated in 2012 for non-farm roads.

As discussed in the March 10, 2006 final Transportation Conformity rulemaking, the conformity rule does not include an exception for PM₁₀ for paved and unpaved road dust emissions to be determined significant, like the exception for such emissions in PM_2.5 analyses in 40 CFR 93.102(b)(3). The EPA intends for road dust emissions to be included in all conformity analyses of direct PM₁₀ emissions because fugitive dust from roadways and other sources dominate PM₁₀ emissions inventories. The budgets in the Imperial PM₁₀ Plan, therefore, include paved and unpaved road emissions.

Regional PM₁₀ emissions analyses for transportation conformity determinations in PM₁₀ nonattainment and maintenance areas must account for highway and transit project construction-related fugitive PM₁₀ emissions if the control strategy or maintenance plan identifies such emissions as a contributor to the nonattainment problem, but are not required to do so if such emissions are not identified as a contributor to the nonattainment problem.^[101 102] Emissions estimates developed for the Imperial PM₁₀ Plan show that fugitive PM₁₀ emissions from highway and transit project construction represent approximately 0.2% and 0.3% of the total annual-average daily PM₁₀ emissions in 2016 and 2030, respectively.^[103] Based on these emissions estimates, the Imperial PM₁₀ Plan concludes that fugitive PM₁₀ emissions from highway and transit project construction are not a contributor to the nonattainment problem and thus need not be accounted for in regional emissions analyses for transportation conformity determinations made for the Imperial PM₁₀ nonattainment area. Consequently, the budgets in the Imperial PM₁₀ Plan do not reflect highway or transit project construction-related fugitive dust.

We 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 and expect to complete the adequacy review of the budgets concurrent with our final action on the Imperial PM₁₀ Plan. The EPA is not required under its transportation conformity rule to find budgets adequate prior to proposing approval of them.^[104] Today, the EPA is announcing that the adequacy process for these budgets begins, and the public has 30 days to comment on their adequacy, per the transportation conformity rule at 40 CFR 93.118(f)(2)(i) and (ii).

As documented in the separate memorandum included in the docket for this rulemaking, we preliminarily conclude that the budgets in the Imperial PM₁₀ Plan meet each adequacy criterion.^[105] 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 Imperial PM₁₀ Plan and are proposing herein to approve the maintenance plan including the demonstration of maintenance of the PM₁₀ NAAQS in the area through year 2030. We have also reviewed the budgets in the Imperial PM₁₀ 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). Moreover, we agree with the conclusion in the Imperial PM₁₀ Plan that highway and transit project construction-related PM₁₀ emissions are not a contributor to the nonattainment problem in the Imperial PM₁₀ nonattainment area and need not be accounted for in regional emissions analyses for transportation conformity determinations for this area. For these reasons, the EPA proposes to approve the 2016 and 2030 motor vehicle emissions budgets in the Imperial PM₁₀ Plan. At the point when we either finalize the adequacy process or approve the budgets as proposed (whichever occurs first; note that they could also occur concurrently per 40 CFR 93.118(f)(2)(iii)), the budgets must be used by the SCAG (i.e., the MPO for this area) for transportation conformity determinations for the Imperial PM₁₀ nonattainment area.

The transportation conformity rule allows us to limit the approval of budgets, and CARB requested that we limit the duration of our approval of the budgets in the Imperial PM₁₀ Plan to the period before the effective date of the EPA's adequacy finding for any subsequently submitted budgets.^[106 107] However, we will consider the State's request to limit an approval of its budgets only if the request includes the following elements: ^[108]

• An acknowledgement and explanation as to why the budgets under consideration have become outdated or deficient;
• A commitment to update the budgets as part of a comprehensive SIP update; and
• A request that the EPA limit the duration of its approval to the time when new budgets have been found to be adequate for transportation conformity purposes.

Because CARB's request does not address these elements, we cannot at this time propose to limit the duration of our approval of the submitted budgets. In order to limit the approval, we would need the information described above in order to determine whether such limitation is reasonable and appropriate in this case. If CARB provides the necessary information, we intend to review it and take appropriate action. If we propose to limit the duration of our approval of the budgets in the Imperial PM₁₀ Plan, we will provide the public an opportunity to comment. The duration of the approval of the budgets, however, would not be limited until we complete such a rulemaking.

6. Conclusion

Based on the review presented above of the various elements of the maintenance plan portion of the Imperial PM₁₀ Plan, we are proposing to approve the Imperial PM₁₀ Plan as a revision to the California SIP. In doing so, we find that the Imperial PM₁₀ Plan, submitted by CARB by letter dated February 6, 2019, satisfies the requirements of section 175A of the Act. If finalized as proposed, our approval of the Imperial PM₁₀ Plan will satisfy the criterion for redesignation under CAA section 107(d)(3)(E)(iv).

V. Proposed Actions and Request for Public Comment

Under CAA section 110(k)(3), and for the reasons set forth above, the EPA is proposing to approve the Imperial PM₁₀ Plan submitted by CARB by letter dated February 6, 2019, as a revision to the California SIP. In so doing, the EPA is proposing to approve the BACM demonstration and attainment inventory included as part of the Imperial PM₁₀ Plan as meeting the requirements of CAA sections 189(b)(1)(B) and 172(c)(3), respectively. 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. The EPA is also proposing to approve the motor vehicle emissions budgets for 2016 and 2030 (shown in Table 5 above) for transportation conformity purposes because we find they meet all applicable criteria for such budgets including the adequacy criteria under 40 CFR 93.118(e).

In addition, under CAA section 107(d)(3)(D), we are proposing to approve the state's request to redesignate the Imperial PM₁₀ nonattainment area to attainment for the PM₁₀ NAAQS. We are doing so based on our conclusion that the area has met, or will meet as part of this action, all the criteria for redesignation under CAA section 107(d)(3)(E). More specifically, we propose to find the following: That the Imperial PM₁₀ nonattainment area has attained the PM₁₀ standard based on the most recent three-year period (2016-2018) of quality-assured, certified, and complete PM₁₀ data; that relevant portions of the California SIP are, or will be as part of this action, fully approved; that the improvement in air quality is due to permanent and enforceable reductions in emissions; that California has met all requirements applicable to the Imperial PM₁₀ nonattainment area with respect to section 110 and part D of the CAA if we finalize our approvals of the BACM demonstration and the attainment inventory in the Imperial PM₁₀ Plan, as proposed herein; and that the Imperial PM₁₀ nonattainment area will have a fully approved maintenance plan meeting the requirements of CAA section 175A if we finalize our approval of it, also as proposed herein.

In connection with the above proposed approvals and determinations, and as authorized under CAA section 189(e), we are proposing to determine that PM₁₀ precursors do not contribute significantly to PM₁₀ exceedances in the Imperial PM₁₀ nonattainment area based on the information included in Appendix A of the Imperial PM₁₀ Plan.

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

VI. Statutory and Executive Order Reviews

Under the CAA, redesignation of an area to attainment and the accompanying approval of a maintenance plan under section 107(d)(3)(E) are actions that affect the status of a geographic area and do not impose any additional regulatory requirements on sources beyond those imposed by state law. Redesignation to attainment does not in and of itself create any new requirements, but rather results in the applicability of requirements contained in the CAA for areas that have been redesignated to attainment. Moreover, 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, these proposed actions merely propose to approve a State plan and redesignation request as meeting federal requirements and do not impose additional requirements beyond those imposed by state law. For these reasons, these proposed actions:

• Are 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);
• Are not an Executive Order 13771 (82 FR 9339, February 2, 2017) regulatory action because SIP approvals are exempted under Executive Order 12866;
• Do not impose an information collection burden under the provisions of the Paperwork Reduction Act (44 U.S.C. 3501 et seq.);
• Are 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.);
• Do 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);
• Do not have Federalism implications as specified in Executive Order 13132 (64 FR 43255, August 10, 1999);
• Are not an economically significant regulatory action based on health or safety risks subject to Executive Order 13045 (62 FR 19885, April 23, 1987);
• Are not a significant regulatory action subject to Executive Order 13211 (66 FR 28355, May 22, 2001);
• Are 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
• Do 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 State plan for which the EPA is proposing approval does not apply on any Indian reservation land or in any other area where the EPA or an Indian tribe has demonstrated that a tribe has jurisdiction. In those areas of Indian country, the proposed rule, as it relates to the maintenance plan, 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). However, the proposed redesignation would apply to Indian country within the nonattainment area. In those areas of Indian country, the proposed redesignation action will not result in the relaxation of measures and programs currently in place to protect air quality 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). The EPA has invited the Torres Martinez Desert Cahuilla Indians and the Quechan Tribe of the Fort Yuma Indian Reservation, who have lands within the Imperial PM₁₀ nonattainment area, to consult on today's proposed action.

List of Subjects

40 CFR Part 52

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

40 CFR Part 81

• Environmental protection
• Air pollution control
• National parks
• Wilderness areas

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

Footnotes