[Federal Register Volume 84, Number 212 (Friday, November 1, 2019)]
[Proposed Rules]
[Pages 58641-58666]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2019-23134]


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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 52

[EPA-R09-OAR-2018-0562; FRL-10001-51-Region 9]


Clean Air Plans; 2008 8-Hour Ozone Nonattainment Area 
Requirements; Determination of Attainment by the Attainment Date; 
Imperial County, California

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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SUMMARY: The Environmental Protection Agency (EPA) is proposing to 
approve two state implementation plan (SIP) revisions submitted by the 
State of California to meet Clean Air Act (CAA or ``Act'') requirements 
for the 2008 ozone national ambient air quality standards (NAAQS) in 
the Imperial County nonattainment area, as follows. The EPA proposes to 
approve the ``Imperial County 2017 State Implementation Plan for the 
2008 8-Hour Ozone Standard'' (``Imperial Ozone Plan'' or ``Plan'') and 
the portions of the ``2018 Updates to the California State 
Implementation Plan'' (``2018 SIP Update'') that address the 
requirement for a reasonable further progress (RFP) demonstration for 
the Imperial County for the 2008 ozone standards. In addition, the EPA 
is proposing to determine, based on a separate demonstration submitted 
by the State of California, that the Imperial County nonattainment area 
would have attained the 2008 ozone NAAQS by the ``Moderate'' area 
attainment date of July 20, 2018, but for emissions emanating from 
outside of the United States, and therefore would no longer be subject 
to the CAA requirements pertaining to reclassification upon failure to 
attain. If we finalize these proposed actions, the Imperial County 
nonattainment area would remain classified as a Moderate nonattainment 
area for the 2008 ozone NAAQS.

DATES: Any comments must arrive by December 2, 2019.

ADDRESSES: Submit your comments, identified by Docket ID No. EPA-R09-
OAR-2018-0562, at https://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 full EPA public 
comment policy, information about CBI or multimedia submissions, and 
general guidance on making effective comments, please visit https://www.epa.gov/dockets/commenting-epa-dockets.

FOR FURTHER INFORMATION CONTACT: Rory Mays, Air Planning Office (AIR-
2), EPA Region IX, (415) 972-3227, [email protected].

SUPPLEMENTARY INFORMATION: Throughout this document, ``we,'' ``us,'' 
and ``our'' refer to the EPA. The EPA proposes to approve the portions 
of the Imperial Ozone Plan that address the requirements for emissions 
statements, a base year emissions inventory, a reasonably available 
control measures (RACM) demonstration, a demonstration of attainment of 
the standards by the applicable attainment date but for emissions 
emanating from outside of the United States, and motor vehicle emission 
budgets. The EPA proposes that the requirements for contingency 
measures for failing to meet RFP would be moot if we finalize our 
proposed determination that Imperial County has met its 2017 RFP 
targets. The EPA also proposes that contingency measures for failing to 
attain the standards would not be required if we finalize our proposed 
approval of the State's demonstrations of attainment by the attainment 
date but for international emissions. The EPA proposes to approve the 
portions of the 2018 SIP Update that address the requirement for a 
reasonable further progress (RFP) demonstration for the Imperial County 
for the 2008 ozone standards.

Table of Contents

I. Background
    A. Ozone Standards, Area Designations, and SIPs
    B. Imperial County Ozone Nonattainment Area
II. Imperial Ozone Plan and 2018 SIP Update
    A. Overarching Requirements
    B. Requirements for International Border Areas
    C. Summary of the Imperial Ozone Plan and 2018 SIP Update
    D. Emissions Statement Certification
    E. Emissions Inventories
    F. Reasonably Available Control Measures Demonstration
    G. Demonstration of Attainment but for International Emissions
    H. Rate of Progress and Reasonable Further Progress 
Demonstration
    I. Motor Vehicle Emission Budgets
    J. Contingency Measures
    K. Other Requirements
III. Imperial County Ozone Determination of Attainment but for 
International Emissions
    A. Statutory and Regulatory Requirements
    B. Summary of State's Submission
    C. EPA Review of State's Submission
IV. Proposed Action
V. Statutory and Executive Order Reviews

I. Background

A. Ozone Standards, Area Designations, and SIPs

    Ground-level ozone pollution is formed from the reaction of 
volatile organic compounds (VOC) and oxides of nitrogen 
(NOX) in the presence of sunlight. These two pollutants, 
referred to as ozone precursors, are emitted by many types of sources, 
including on-

[[Page 58642]]

and non-road motor vehicles and engines, power plants and industrial 
facilities, and smaller area sources such as lawn and garden equipment 
and paints.
    Scientific evidence indicates that adverse public health effects 
occur following exposure to ozone, particularly in children and adults 
with lung disease. Breathing air containing ozone can reduce lung 
function and inflame airways, which can increase respiratory symptoms 
and aggravate asthma or other lung diseases.\1\
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    \1\ ``Fact Sheet--2008 Final Revisions to the National Ambient 
Air Quality Standards for Ozone,'' March 2008.
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    Under CAA section 109, the EPA promulgates NAAQS (or ``standards'') 
for pervasive air pollutants, such as ozone. The EPA has previously 
promulgated NAAQS for ozone in 1979 and 1997.\2\ In 2008, the EPA 
revised and further strengthened the ozone NAAQS by setting the 
acceptable level of ozone in the ambient air at 0.075 parts per million 
(ppm) averaged over an 8-hour period.\3\ Although the EPA tightened the 
8-hour ozone standards in 2015 (to 0.070 ppm), this action relates to 
the requirements for the 2008 ozone standards.\4\
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    \2\ The ozone NAAQS promulgated in 1979 was 0.12 parts per 
million (ppm) averaged over a 1-hour period. 44 FR 8202 (February 8, 
1979). The ozone NAAQS promulgated in 1997 was 0.08 ppm averaged 
over an 8-hour period. 62 FR 38856 (July 18, 1997).
    \3\ 73 FR 16436 (March 27, 2008).
    \4\ Information on the 2015 ozone standards is available at 80 
FR 65292 (October 26, 2015).
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    Following promulgation of a new or revised NAAQS, the EPA is 
required under CAA section 107(d) to designate areas throughout the 
country as attaining or not attaining the NAAQS. Under the CAA, after 
the EPA designates areas as nonattainment for a NAAQS, states with 
nonattainment areas are required to submit SIP revisions that provide 
for, among other things, attainment of the NAAQS within certain 
prescribed periods that vary depending on the severity of 
nonattainment. Areas classified as Moderate must attain the NAAQS 
within 6 years of the effective date of the nonattainment 
designation.\5\
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    \5\ CAA section 181(a)(1), 40 CFR 51.1102 and 40 CFR 51.1103(a).
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    The EPA designated Imperial County, California, as nonattainment 
for the 2008 ozone standards on May 21, 2012, and classified the area 
as ``Marginal.'' \6\ Within 6 months of the applicable attainment date, 
the EPA is required under CAA section 181(b)(2) to determine whether an 
area has attained the NAAQS based on the design value of the area as of 
the area's attainment date. Based on 2012-2014 ozone monitoring data, 
on May 4, 2016, the EPA determined that Imperial County had not 
attained the 2008 ozone NAAQS by the July 20, 2015 Marginal area 
attainment date and reclassified the area as Moderate with an 
attainment date of no later than July 20, 2018.\7\
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    \6\ 77 FR 30088 (May 21, 2012).
    \7\ 81 FR 26697 (May 4, 2016).
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    In California, the California Air Resources Board (CARB) is the 
state agency responsible for the adoption and submission to the EPA of 
the California SIP and revisions to the SIP and has broad authority to 
establish emission 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 regional air quality plans. The 
Imperial County Air Pollution Control District (Imperial County APCD or 
``District'') develops and adopts air quality management plans to 
address CAA planning requirements applicable to Imperial County. Such 
plans are then submitted to CARB for adoption and submitted to the EPA 
as revisions to the California SIP.

B. Imperial County Ozone Nonattainment Area

    The Imperial County nonattainment area for the 2008 ozone standards 
includes the whole county as well as Indian country within the 
geographic boundary of Imperial County pertaining to the Quechan Tribe 
of the Fort Yuma Indian Reservation and the Torres Martinez Desert 
Cahuilla Indians.\8\ The County encompasses over 4,000 square miles in 
southeastern California.\9\ It is home to approximately 184,000 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 to the west. The Imperial Valley 
runs north-south through the central part of the County and includes 
the County's three most populated cities: Brawley, El Centro, and 
Calexico. Most of the County's population and industries exist within 
this relatively narrow land area that extends about one-fourth the 
width of the County. The rest of Imperial County is primarily desert, 
with little or no human population.
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    \8\ 40 CFR 81.305.
    \9\ Imperial Ozone Plan, 2-1 to 2-3.
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    Ambient 8-hour ozone concentrations in Imperial County are above 
the level of the 2008 8-hour ozone NAAQS of 0.075 ppm. The maximum 
design value for the area, based on certified monitoring data at the 
Calexico monitor (Air Quality System (AQS) ID: 06-025-0005), was 0.077 
ppm for the 2015-2017 period.\10\
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    \10\ AQS Design Value Report (AMP480) for Imperial County for 
2008 ozone NAAQS for 2015-2017, August 10, 2018. We also note that 
the maximum design value for the area in 2016-2018 is 0.077 ppm at 
Calexico. AQS Design Value Report (AMP480) for Imperial County for 
2008 ozone NAAQS for 2016-2018, August 8, 2019.
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II. Imperial Ozone Plan and 2018 SIP Update

A. Overarching Requirements

    States must implement the 2008 ozone standards under Title 1, part 
D of the CAA, which includes the ozone specific requirements for 
attainment plans in sections 181-185 of subpart 2 (``Additional 
Provisions for Ozone Nonattainment Areas'') and, to the extent not 
amended by subpart 2, the general requirements for attainment plans in 
section 172 (``Nonattainment plan provisions in general''). To assist 
states in developing plans to address ozone nonattainment problems, in 
2015, the EPA issued a SIP Requirements Rule for the 2008 ozone 
standards (``2008 Ozone SRR'') that addresses statutory obligations 
pertaining to implementation of the NAAQS, including requirements for 
emissions inventories and attainment and RFP demonstrations.\11\ The 
2008 Ozone SRR is codified at 40 CFR part 51 subpart AA.
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    \11\ 80 FR 12264 (March 6, 2015).
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    Following a challenge to the EPA's 2008 Ozone SRR, on February 16, 
2018, the U.S. Court of Appeals for the D.C. Circuit (``D.C. Circuit'') 
published its decision in South Coast Air Quality Management District 
v. EPA (``South Coast II'').\12\ The primary aspect of the South Coast 
II decision that affects the 2017 Imperial Ozone Plan is the vacatur of 
a provision in the 2008 Ozone SRR that allowed states to demonstrate 
RFP using baseline years other than 2011. The 2017 Imperial Ozone 
Plan's RFP demonstration used 2008 as the baseline year; following 
South Coast II, CARB submitted the 2018 SIP Update, which includes an 
RFP demonstration for Imperial County that uses 2011 as the RFP 
baseline year.
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    \12\ South Coast Air Quality Management District v. EPA, 882 
F.3d 1138 (D.C. Cir. 2018). The term ``South Coast II'' is used in 
reference to the 2018 court decision to distinguish it from a 
decision published in 2006 with the same lead plaintiff. The earlier 
decision involved a challenge to the EPA's Phase 1 implementation 
rule for the 1997 ozone standards. South Coast Air Quality 
Management Dist. v. EPA, 472 F.3d 882 (D.C. Cir. 2006).
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    Pursuant to CAA Title I, Part D, the District's nonattainment new 
source

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review (NSR) program must regulate new major sources and major 
modifications of NOX and VOC as ozone precursors. The EPA 
recently approved Imperial County APCD rules addressing various permit 
rule requirements, including Rules 204 (``Applications''), 206 
(``Processing of Applications''), and 207 (``New and Modified 
Stationary Source Review'') into the California SIP.\13\ Therefore, the 
EPA is not proposing any further action on nonattainment NSR 
requirements for Imperial County in this notice.
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    \13\ 82 FR 27125 (June 14, 2017), for Rules 204 and 206; 84 FR 
44545 (August 26, 2019), for Rule 207.
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    We discuss the CAA and regulatory requirements for 2008 ozone plans 
that are relevant to this proposal in more detail in the following 
sections of this proposed rule.

B. Requirements for International Border Areas

    For a nonattainment area affected by emissions emanating from 
outside the U.S., CAA section 179B(a) provides that, notwithstanding 
any other provision of law, the EPA Administrator shall approve a SIP 
revision required under Title I of the CAA for such an area if (i) the 
SIP revision meets all of the applicable requirements other than the 
requirement to demonstrate attainment and maintenance of the relevant 
NAAQS by the applicable attainment date; and (ii) the state establishes 
to the Administrator's satisfaction that the SIP revision would be 
adequate to attain and maintain the relevant NAAQS by the applicable 
attainment date, but for emissions emanating from outside of the U.S. 
Moreover, for any state that establishes to the Administrator's 
satisfaction that the state would have attained the ozone NAAQS by the 
applicable attainment date, but for emissions emanating from outside 
the U.S., CAA section 179B(b) provides that the area shall not be 
subject to section 181(b)(2), which obligates the Administrator to 
determine whether the area attained by its attainment date and if not, 
to reclassify such area to a higher classification.\14\
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    \14\ The actual text of CAA section 179B(b) refers to section 
181(a)(2); however, the EPA has long understood this reference to be 
erroneous and that Congress intended to refer to section 181(b)(2). 
``State Implementation Plans; General Preamble for the 
Implementation of Title I of the Clean Air Act Amendments of 1990,'' 
57 FR 13498, 13569, n. 41 (April 16, 1992) (``General Preamble'').
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    It is important to note that the EPA's approval of a state's CAA 
section 179B(a) demonstration that a nonattainment area would attain 
the standards but for emissions emanating from outside the U.S. does 
not affect the area's nonattainment designation--the area retains its 
nonattainment designation and remains subject to requirements 
applicable to nonattainment areas, such as nonattainment new source 
review and conformity.\15\ Similarly, where the EPA approves a state's 
CAA section 179B(b) demonstration that the nonattainment area would 
have attained the standards by the applicable attainment date but for 
emissions emanating from outside of the U.S., the area retains its 
nonattainment designation and is still subject to all applicable 
requirements, based on the area's classification.
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    \15\ 78 FR 34178, 34205 (June 6, 2013).
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    The 2008 Ozone SRR does not include regulatory requirements 
specific to CAA section 179B. Instead, the preamble of the 2008 Ozone 
SRR recommends that states work with relevant EPA Regional Offices ``on 
a case-by-case basis to determine the most appropriate information and 
analytical methods for each area's unique situation.'' \16\
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    \16\ 2008 Ozone SRR, 12293. See also 78 FR 34178, 34204.
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    In addition, both the EPA's 1992 General Preamble and 1994 General 
Preamble Addendum provide general guidance on CAA section 179B.\17\ The 
General Preamble Addendum describes several types of information that 
may be relevant, such as analyzing monitoring data where a dense 
network exists, meteorological influences, particle composition, 
comparison of U.S. and international emissions inventories, and 
modeling that can be used to evaluate the impact of emissions emanating 
from outside the U.S. In the General Preamble Addendum, the EPA 
indicated that it is appropriate to consider this information ``for 
individual nonattainment areas on a case-by-case basis in determining 
whether an area may qualify for treatment under section 179B.'' \18\ 
While the focus of the EPA's discussion in the General Preamble 
Addendum is on particulate matter (e.g., evaluation of particle 
composition), the EPA is applying these general principles for 
evaluation of international impacts on ambient ozone levels to the 
Imperial County nonattainment area.
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    \17\ General Preamble, 13569; and ``State Implementation Plans 
for Serious PM10 Nonattainment Areas, and Attainment Date 
Waivers for PM-10 Nonattainment Areas Generally; Addendum to the 
General Preamble for the Implementation of Title I of the Clean Air 
Act Amendments of 1990,'' 59 FR 41998, 42000 (August 16, 1994) 
(``General Preamble Addendum'').
    \18\ General Preamble Addendum, 42001.
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C. Summary of the Imperial Ozone Plan and 2018 SIP Update

    On November 14, 2017, CARB submitted the Imperial Ozone Plan as a 
revision to the Imperial County portion of the California SIP.\19\ The 
Imperial Ozone Plan addresses the requirements for base year 
inventories for attainment planning, baseline emissions inventories for 
RFP plans, and periodic emission inventories at 3-year intervals. It 
also includes air quality modeling demonstrating that the area would 
attain the 2008 ozone standards by the July 20, 2018 Moderate area 
attainment date (based on a modeled attainment year of 2017), but for 
emissions emanating from Mexico (pursuant to section 179B(a)), 
demonstrations for implementation of reasonably available control 
technology (RACT) and RACM, a demonstration for RFP, motor vehicle 
emission budgets for 2017, and contingency measures for failure to make 
RFP. The Plan also includes a certification that an existing SIP-
approved rule from the District meets the CAA's emission statement 
requirements for the 2008 ozone NAAQS.
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    \19\ Letter dated November 14, 2017, from Richard Corey, 
Executive Officer, CARB, to Alexis Strauss, Acting Regional 
Administrator, EPA Region 9.
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    On December 11, 2018, CARB submitted the 2018 SIP Update to the EPA 
as a revision to the California SIP for several ozone nonattainment 
areas.\20\ In part, CARB developed the 2018 SIP Update in response to 
the court's decision in South Coast II vacating the 2008 Ozone SRR with 
respect to the use of an alternate baseline year for demonstrating RFP. 
For Imperial County, the 2018 SIP Update includes a revised RFP 
demonstration for the 2008 ozone NAAQS using 2011 as the baseline year, 
as well as an updated emissions inventory for 2017 that is also used 
for the revised RFP demonstration (to reflect actual emissions data for 
2017 for certain sources, and updated activity data for certain other 
sources that were not available when the Imperial Ozone Plan was 
adopted in 2017). The 2018 Update also addresses aspects of contingency 
measure and motor vehicle emission budget requirements.
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    \20\ Letter dated December 5, 2018, from Richard Corey, 
Executive Officer, CARB, to Michael Stoker, Regional Administrator, 
EPA Region 9.
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    Sections 110(a)(1) and (2) and 110(l) of the CAA require a state to 
provide reasonable public notice and opportunity for public hearing 
prior to the adoption and submission of a SIP or SIP revision. To meet 
this requirement, every SIP submittal should include evidence that 
adequate public notice was given and an opportunity for a public 
hearing was provided consistent with the EPA's implementing regulations 
in 40 CFR 51.102.
    Both the District and CARB satisfied applicable statutory and 
regulatory requirements for reasonable public

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notice and hearing prior to adoption and submission of the Imperial 
Ozone Plan. The District provided a public comment period and held a 
public hearing prior to the adoption of the SIP submission on September 
12, 2017.\21\ CARB provided the required public notice and opportunity 
for public comment prior to its October 26, 2017 public hearing and 
adoption of the SIP submission.\22\ The submission includes proof of 
publication of notices for the respective public hearings. Therefore, 
we find that the Imperial Ozone Plan meets the procedural requirements 
for public notice and hearing in CAA sections 110(a) and 110(l) and 40 
CFR 51.102.
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    \21\ Imperial County APCD, ``Notice of Public Hearing for 
Adoption of the 2017 Imperial County State Implementation Plan for 
8-Hour Ozone (Ozone SIP),'' August 9, 2017; and Imperial County Air 
Pollution Control Board, Minute Order #20, September 12, 2017.
    \22\ CARB, ``Notice of Public Meeting to Consider the Ozone 
State Implementation Plan for Imperial County,'' September 22, 2017; 
and CARB Board Resolution 17-18, ``Ozone State Implementation Plan 
for Imperial County,'' October 26, 2017.
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    Similarly, CARB satisfied applicable statutory and regulatory 
requirements for reasonable public notice and hearing prior to adoption 
and submission of the 2018 SIP Update. CARB provided the required 
public notice and opportunity for public comment prior to its October 
25, 2018 public hearing and adoption of the SIP submission.\23\ The 
submission includes proof of publication of notices for the respective 
public hearings. Therefore, we find that the Imperial Ozone Plan meets 
the procedural requirements for public notice and hearing in CAA 
sections 110(a) and 110(l) and 40 CFR 51.102.
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    \23\ CARB, ``Notice of Public Meeting to Consider the 2018 
Updates to the California State Implementation Plan,'' September 21, 
2018; and CARB Board Resolution 18-50, ``2018 Updates to the 
California State Implementation Plan,'' October 25, 2018.
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    CAA section 110(k)(1)(B) requires the EPA to determine whether a 
SIP submission is complete within 60 days of receipt. This section of 
the CAA also provides that any plan that the EPA has not affirmatively 
determined to be complete or incomplete will become complete by 
operation of law six months after the date of submission. The EPA's SIP 
completeness criteria are found in 40 CFR part 51, Appendix V. The 
Imperial Ozone Plan submission, dated November 14, 2017, became 
complete by operation of law on May 14, 2018. The 2018 SIP Update, 
submitted December 11, 2018, was found complete as part of the EPA's 
completeness review for purposes of another ozone nonattainment area 
addressed in the 2018 SIP Update.\24\
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    \24\ 84 FR 11198, 11199 (March 25, 2019).
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D. Emissions Statement Certification

1. Statutory and Regulatory Requirements
    Section 182(a)(3)(B)(i) of the Act requires states to submit a SIP 
revision requiring owners or operators of stationary sources of VOC or 
NOX to provide the state with statements of actual emissions 
from such sources. Statements must be submitted at least every year and 
must contain a certification that the information contained in the 
statement is accurate to the best knowledge of the individual 
certifying the statement. Section 182(a)(3)(B)(ii) allows states to 
waive the emissions statement requirement for any class or category of 
stationary sources that emits less than 25 tons per year of VOCs or 
NOX if the state provides an inventory of emissions from 
such class or category of sources as part of the base year or periodic 
inventories required under CAA sections 182(a)(1) and 182(a)(3)(A) that 
is based on the use of emission factors established by the EPA or other 
methods acceptable to the EPA.
    The preamble of the 2008 Ozone SRR states that if the EPA has 
previously approved an emissions statement rule for the 1997 ozone 
NAAQS or the 1-hour ozone NAAQS that covers all portions of the 
nonattainment area for the 2008 ozone NAAQS, then such rule should be 
sufficient for purposes of the emissions statement requirement for the 
2008 ozone NAAQS.\25\ The state should review the existing rule to 
ensure it is adequate and, if so, may rely on it to meet the emissions 
statement requirement for the 2008 ozone NAAQS. In cases when an 
existing emissions statement requirement is still adequate to meet this 
requirement for the 2008 ozone NAAQS, states can provide the rationale 
for that determination to the EPA in a written statement in the SIP 
submission explaining how it meets this requirement. States should 
identify the various requirements within the emissions statement 
requirement and indicate how each is met by the existing emissions 
statement program. In cases when an emissions statement requirement is 
modified for any reason, states must provide the revisions to the 
emissions statement as part of their SIP submission.
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    \25\ 2008 Ozone SRR, 12291.
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2. Summary of State's Submission
    The Imperial Ozone Plan explains that Imperial County APCD adopted 
Rule 116 (``Emissions Statement and Certification'') in 2010 to address 
the emissions statement requirements for the 1997 ozone NAAQS.\26\ The 
District notes that Rule 116 applies to the nonattainment area for the 
1997 ozone NAAQS, which covers the same area as the nonattainment area 
for the 2008 ozone NAAQS, and that EPA approved the rule into the 
California SIP in 2012 for purposes of meeting the 1997 ozone NAAQS 
planning requirements.\27\ The Plan then includes a summary of the 
requirements of CAA section 182(a)(3)(B) and how the District reviewed 
Rule 116 against those requirements for the 2008 ozone NAAQS.
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    \26\ Imperial Ozone Plan, 10-1.
    \27\ 77 FR 72968 (December 7, 2012).
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    The District states that the explicit purpose of Rule 116 is to 
address the requirement for owners and operators of stationary sources 
of NOX or VOC to provide a statement of actual emissions of 
such pollutants; that the rule requires such statements to be submitted 
annually with a certification by a responsible company official; and 
that the rule addresses the provision of CAA section 182(a)(3)(B)(ii) 
that allows states to waive the application of the emissions statement 
requirements for sources emitting less than 25 tons per year (tpy) or 
NOX or VOC so long as the state provides emissions 
inventories for such classes or categories of sources. Based on this 
review, the District concludes that Rule 116 fulfills the emissions 
statement requirements for the 2008 ozone NAAQS.
3. EPA Review of State's Submission
    The EPA evaluated Imperial County APCD Rule 116 and the Plan's 
assessment of Rule 116 for compliance with the specific requirements 
for emissions statements under CAA section 182(a)(3)(B)(i). We find 
that Rule 116 applies within the entire nonattainment area for the 2008 
ozone NAAQS; applies to all permitted sources of VOC and 
NOX; requires the submittal, on an annual basis, of the 
types of information necessary to estimate actual emissions from the 
subject stationary sources; and requires certification by the 
responsible officials representing the owners and operators of 
stationary sources. Therefore, we propose to find that Rule 116 meets 
the requirements of CAA section 182(a)(3)(B)(i).
    We also note that, while Rule 116 provides authority to the 
District to waive the requirement for any class or category of 
stationary sources that emit less than 25 tons per year, such a waiver 
is allowed under CAA section 182(a)(3)(B)(ii) so long as the state 
includes estimates of such class or

[[Page 58645]]

category of stationary sources in base year emissions inventories and 
periodic inventories submitted under CAA sections 182(a)(1) and 
182(a)(3)(A) based on EPA emission factors or other methods acceptable 
to the EPA. We recognize that emissions inventories developed by CARB 
for Imperial County routinely include actual emissions estimates for 
all stationary sources or classes or categories of such sources, 
including those less than 25 tons per year, and that such inventories 
provide the basis for inventories submitted to meet the requirements of 
CAA sections 182(a)(1) and 182(a)(3)(A). By approval of emissions 
inventories as meeting the requirements of CAA sections 182(a)(1) and 
182(a)(3)(A), the EPA is accepting the methods and factors used by CARB 
to develop those emissions estimates. For example, in 2014, the EPA 
approved the 2002 base year emissions inventory for Imperial county for 
the 1997 ozone NAAQS,\28\ and in this notice we are proposing to 
approve the Imperial Ozone Plan's 2012 base year emissions inventory 
for the 2008 ozone NAAQS.
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    \28\ 79 FR 63332 (October 23, 2014).
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    Thus, for the reasons stated herein, we propose to approve the 
Imperial Ozone Plan's certification that Rule 116 (adopted February 23, 
2010) meets the emissions statement requirements under CAA section 
182(a)(3)(B) for the 2008 ozone NAAQS.\29\
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    \29\ For further background on our evaluation of Rule 116, see 
``Technical Support for the Imperial County Air Pollution Control 
District Rule 116, Emissions Statement and Certification,'' EPA 
Region IX, January 2012, included in the docket for today's action.
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E. Emissions Inventories

1. Statutory and Regulatory Requirements
    Sections 172(c)(3) and 182(a)(1) of the CAA require states to 
submit for each ozone nonattainment area a ``base year inventory'' that 
is a comprehensive, accurate, current inventory of actual emissions 
from all sources of the relevant pollutant or pollutants in the area. 
In addition, the 2008 Ozone SRR requires that the inventory year 
selected be consistent with the baseline year for the RFP 
demonstration, which is the most recent calendar year for which a 
complete triennial inventory is required to be submitted to the EPA 
under the Air Emissions Reporting Requirements (AERR).\30\
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    \30\ 2008 Ozone SRR at 40 CFR 51.1115(a) and the Air Emissions 
Reporting Requirements at 40 CFR part 51, subpart A.
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    The EPA has issued guidance on the development of emissions 
inventories for ozone and other pollutants.\31\ Emissions inventories 
for ozone must include emissions of VOC and NOX and 
represent emissions for a typical ozone season weekday.\32\ States 
should include documentation explaining the approaches used to 
calculate emissions data. In estimating mobile source emissions, states 
should use the latest emissions models and planning assumptions 
available at the time it develops the SIP revision.\33\
---------------------------------------------------------------------------

    \31\ ``Emissions Inventory Guidance for Implementation of Ozone 
and Particulate Matter National Ambient Air Quality Standards 
(NAAQS) and Regional Haze Regulations,'' EPA-454/B-17-002, May 2017. 
At the time the emission inventory for the Imperial Ozone Plan was 
developed, the following EPA emissions inventory guidance applied: 
``Emissions Inventory Guidance for Implementation of Ozone and 
Particulate Matter National Ambient Air Quality Standards (NAAQS) 
and Regional Haze Regulations,'' EPA-454-R-05-001, August 2005.
    \32\ 40 CFR 51.1115(a) and (c), and 40 CFR 51.1100(bb) and (cc).
    \33\ 2008 Ozone SRR, 12290.
---------------------------------------------------------------------------

    The base year inventory required by sections 172(c)(3) and 
182(a)(1) serves as the starting point for attainment demonstration air 
quality modeling, assessing RFP, and determining the need for 
additional SIP control measures. Future year emissions inventories 
(also referred to as baseline inventories) are necessary to show the 
projected effectiveness of SIP control measures and must reflect the 
most recent population, employment, travel and congestion estimates for 
the area. Both base year and future year inventories are necessary for 
photochemical modeling to demonstrate attainment and RFP.
2. Summary of State's Submission
    The Imperial Ozone Plan includes a base year inventory (using 2012 
as the base year) and future year baseline inventories (2008, 2014, and 
2017) \34\ for NOX and VOC.\35\ Documentation for the 
emissions inventories appears in Chapter 4, which also contains summary 
inventories in Tables 4-6 through 4-9; Appendix A contains more 
detailed inventories.\36\ The Plan explains that the inventories 
represent a joint effort by staff from both CARB and the District. The 
Plan also explains the reason for selecting 2012 as the base year as 
related an on-going data collection effort by the South Coast Air 
Quality Management District to study exposure to air toxics and a 
desire to maintain consistency for plans developed in the State.\37\ 
The Plan states that the inventories reflect average summer day 
emissions because ozone levels in Imperial County are typically higher 
from May through October.\38\
---------------------------------------------------------------------------

    \34\ The 2018 SIP Update contains a new baseline inventory, 
using 2011 as the baseline year, to demonstrate RFP. We discuss the 
baseline emission inventory in the 2018 SIP Update as part of our 
RFP evaluation in section II.H of this proposed rule.
    \35\ The Plan uses the term ``reactive organic gases'' (ROG) to 
refer to VOCs. Imperial Ozone Plan, 4-1. In general, ROG represent a 
slightly broader group of compounds than those in the EPA's list of 
VOCs and pertain to common chemical species (e.g., benzene, xylene, 
etc.) as VOCs. Therefore, this proposed rulemaking refers to this 
set of gases as VOCs.
    \36\ The 2012 base year inventory included in the Imperial Ozone 
Plan updates a previous submittal from CARB, the ``8-Hour Ozone 
State Implementation Plan Emission Inventory Submittal'' (the Multi-
area Emission Inventory). The Multi-area Emission Inventory was 
submitted by CARB on July 17, 2014, and included inventories for 16 
nonattainment areas, including Imperial County. The base year 
inventory submitted with the Imperial Ozone Plan in November 2017 
revises and updates the base year emission inventory for Imperial 
County included in the Multi-area Emission Inventory submitted in 
July 2014. Because we understand the State intended the November 
2017 submittal to replace the July 2014 submittal (at least with 
respect to Imperial County), we plan no further action on the 
inventory for Imperial County submitted by CARB in July 2014.
    \37\ Imperial Ozone Plan, 4-2.
    \38\ Id. at 4-3.
---------------------------------------------------------------------------

    The Imperial Ozone Plan presents VOC and NOX emissions 
estimates in two general categories: stationary sources and mobile 
sources. Stationary sources are subdivided into point sources and 
areawide sources. The Plan first explains that point sources typically 
include permitted facilities that have one or more identified and fixed 
pieces of equipment and emissions points. The Plan's 2012 base year 
inventory for these types of point sources uses actual emissions for 
2012 as reported by regulated entities consistent with the AERR and may 
be based on testing, continuous emissions monitoring, or 
calculations.\39\ In addition, the Plan explains that the term ``point 
source'' includes ``stationary area sources,'' which are smaller 
sources such as internal combustion engines (e.g., agricultural diesel 
irrigation pumps) and gasoline dispensing facilities (gas stations) for 
which emissions are estimated as a group and included in the 
inventories as an aggregated total.\40\ The Plan provides information 
regarding the methodologies used to estimate base year and forecasted 
emissions for the various categories of stationary area sources.\41\ 
Areawide sources are small sources that produce emissions over a wide 
geographic area (e.g., consumer products, architectural coatings, 
asphalt paving/roofing, residential wood combustion, fires, and 
agricultural burning). Similar to the approach for stationary area 
sources, the Plan

[[Page 58646]]

provides information for each of the various categories of areawide 
sources regarding the methods used to estimate emissions.\42\
---------------------------------------------------------------------------

    \39\ Id.
    \40\ Id. at 4-4
    \41\ Id. at 4-4 to 4-5.
    \42\ Id. at 4-6 to 4-8.
---------------------------------------------------------------------------

    The Plan divides mobile sources into ``on-road sources'' and ``off-
road sources.'' \43\ On-road mobile sources include automobiles, light-
, medium-, and heavy-duty trucks, and motorcycles. Off-road sources 
include aircraft, locomotives, cargo handling equipment, farm 
equipment, and recreational vehicles. Emissions from on-road sources 
were calculated using CARB's EMFAC2014 model \44\ and travel activity 
data from Southern California Association of Governments (SCAG) using 
the 2016 Regional Transportation Plan/Sustainable Communities 
Strategy.\45\ Off-road emissions were developed using different 
category-specific models developed to support District regulations or 
the OFFROAD2007 model where specific models were not available.\46\
---------------------------------------------------------------------------

    \43\ In general, CARB uses the term ``off-road'' to refer to 
sources to which the EPA typically applies the term ``non-road.''
    \44\ EMFAC is short for EMission FACtor. The EPA announced the 
availability of the EMFAC2014 model for use in state implementation 
plan development and transportation conformity in California on 
December 14, 2015. 80 FR 77337. The EPA's approval of the EMFAC2014 
emissions model for SIP and conformity purposes was effective on the 
date of publication of the notice in the Federal Register. On August 
15, 2019, the EPA approved and announced the availability of 
EMFAC2017, the latest update to the EMFAC model for use by State and 
local governments to meet CAA requirements. See 84 FR 41717.
    \45\ Imperial Ozone Plan, 4-10. SCAG is the metropolitan 
planning organization for six counties in Southern California, 
including Imperial County. Imperial Ozone Plan, 4-1.
    \46\ Id. at 4-11.
---------------------------------------------------------------------------

    With respect to future year baseline inventories, the Plan explains 
the approaches used to forecast emissions for various categories of 
both stationary and mobile sources.\47\ Forecasted emissions rely on 
assumptions regarding growth and reductions from adopted control 
measures, and information used to forecast emissions of stationary 
sources includes on data regarding economic activity, fuel usage, 
population and residential housing (i.e., growth and control profiles), 
whereas projections of mobile source emissions are accomplished through 
the use of models that predict activity and vehicle turnover rates and 
also reflect adopted regulatory measures.\48\
---------------------------------------------------------------------------

    \47\ Id. at 4-8 to 4-10 and 4-12 to 4-13.
    \48\ Id. at 4-2.
---------------------------------------------------------------------------

    The Plan also explains how the emissions inventories reflect 
emissions reduction credits (ERCs) generated by facilities that 
voluntarily reduced emissions or ceased operation of equipment prior to 
the base year of 2012.\49\ District Rule 207 (``New and Modified 
Stationary Source Review'') allows voluntarily reduced emissions to be 
banked for future use as offsets to meet nonattainment permitting 
requirements.\50\ As noted in the Plan, EPA regulations require 
inclusion of ERCs banked prior to the base year in the base year and 
forecasted emission inventories.\51\
---------------------------------------------------------------------------

    \49\ Id. at 4-16 to 4-17.
    \50\ The rule governing the use of such emission reduction 
credits for new of modified major sources of NOX or VOC 
in Imperial County is District Rule 207. The EPA has approved Rule 
207, as amended on September 11, 2018, including applicable major 
source thresholds and offset ratios, into the California SIP. 84 FR 
44545.
    \51\ 40 CFR 51.165(a)(3)(ii)(C)(1)(ii).
---------------------------------------------------------------------------

    The detailed inventories in Appendix A provide emissions of point 
sources (including stationary area sources) in five primary categories 
(Fuel Combustion, Waste Disposal, Cleaning and Surface Coatings, 
Petroleum Production and Marketing, and Industrial Processes) and 
various subcategories; emissions for areawide sources in two primary 
categories (Solvent Evaporation and Miscellaneous Processes) and 
various subcategories; and emissions for mobile sources in two 
categories (On-Road and Off-Road).
3. EPA Review of State's Submission
    We have reviewed the 2012 base year inventory developed for the 
Imperial Ozone Plan and the inventory methodologies used by CARB and 
the District for consistency with CAA requirements and the EPA's 
guidance. First, as required by EPA regulation, we find that that the 
2012 base year inventory includes estimates for NOX and VOCs 
for a typical ozone season weekday, and that the Plan includes adequate 
information to determine how emissions were calculated. Second, we find 
that the 2012 base year inventory reflects appropriate emissions models 
and methodologies, and therefore represents a comprehensive, accurate, 
and current inventory of actual emissions for that year in Imperial 
County. Third, we find that the selection of 2012 for the base year 
emissions inventory is appropriate because it is consistent with the 
2011 baseline year inventory in the 2018 SIP Update used to demonstrate 
RFP for Imperial County, as both inventories are derived from a common 
set of models and methods.
    Table 1 presents a summary of ozone precursor summer emissions by 
source category for the 2012 base year. Based on the 2012 inventory of 
anthropogenic emissions, which used tons per day (tpd), mobile sources 
account for 89 percent (%) of NOX emissions and 49% of VOC 
emissions. The next largest categories include stationary sources (6% 
of NOX emissions) and area sources (44% of VOC emissions).

 Table 1--Summary of Ozone Precursor Summer Emissions for the 2012 Base
                                  Year
------------------------------------------------------------------------
                                                     2012
           Source category           -----------------------------------
                                         NOX  (tpd)        VOC  (tpd)
------------------------------------------------------------------------
Stationary Sources..................              1.73              1.33
Area Sources........................              0.67              8.51
On-road Mobile Sources..............             10.01              4.25
Non-road Mobile Sources.............              9.43              5.10
Total for Imperial County...........             21.83             19.20
------------------------------------------------------------------------
Source: Imperial Ozone Plan, App. A, Table A-2. Totals may not add up
  due to rounding.

    With respect to future baseline projections, we reviewed the 
approaches used and find them acceptable and conclude that the future 
baseline emissions projections in the Imperial Ozone Plan reflect 
appropriate methods and assumptions. With respect to nonattainment NSR 
requirements for offsets,\52\ we find that the District properly 
included emissions reductions generated before the base year (i.e., 
pre-base year emission reduction credits) in

[[Page 58647]]

the forecasted year inventory and thus satisfied this requirement.\53\
---------------------------------------------------------------------------

    \52\ 40 CFR 51.165(a)(3)(ii)(C)(1)(ii).
    \53\ Imperial Ozone Plan, 4-16 to 4-17.
---------------------------------------------------------------------------

    Therefore, the EPA is proposing to approve the 2012 emissions 
inventory in the Imperial Ozone Plan as meeting the requirements for a 
base year inventory set forth in CAA sections 172(c)(3) and 182(a)(1) 
and 40 CFR 51.1115.

F. Reasonably Available Control Measures Demonstration

1. Statutory and Regulatory Requirements
    Section 172(c)(1) of the CAA requires that each attainment plan 
provide for the implementation of all RACM as expeditiously as 
practicable, including such reductions in emissions from existing 
sources in the area as may be obtained through implementation of 
RACT.\54\ EPA regulations governing implementation of the 2008 ozone 
NAAQS require that, for each nonattainment area required to submit an 
attainment demonstration, the state concurrently submit a SIP revision 
demonstrating that it has adopted all RACM necessary to demonstrate 
attainment as expeditiously as practicable and to meet any RFP 
requirements.\55\ The 2008 Ozone SRR provided that the determination of 
whether a SIP contains all RACM requires an area-specific analysis 
establishing that there are no additional economically and technically 
feasible control measures (alone or cumulatively) that will provide for 
expeditious attainment or advance the attainment date by one year.'' 
\56\
---------------------------------------------------------------------------

    \54\ For ozone nonattainment areas classified as Moderate or 
above, CAA section 182(b)(2) also requires implementation of RACT 
for all major sources of VOC and for each VOC source category for 
which EPA has issued a Control Techniques Guideline (CTG). Section 
182(f) of the Act requires that RACT under section 182(b)(2) also 
apply to major stationary sources of NOX. In a separate 
action, the EPA has proposed to approve in part and conditionally 
approve in part the portions of the Imperial Ozone Plan (Chapter 7, 
``Reasonably Available Control Technology Assessment'' and App. B, 
``Reasonably Available Control Technology Analysis for the 2017 
Imperial County State Implementation Plan for the 2008 8-Hour Ozone 
Standard'') that relate to the RACT requirements under CAA section 
182(b)(2) and 40 CFR 51.1112. 84 FR 49202 (September 19, 2019).
    \55\ 40 CFR 51.1112(c).
    \56\ 2008 Ozone SRR, 12286. EPA has previously provided 
additional guidance interpreting the RACM requirement for ozone 
nonattainment areas. General Preamble, 13498; Memorandum from John 
Seitz, Director, OAQPS, to Regional Air Directors, ``Guidance on the 
Reasonably Available Control Measure Requirement and Attainment 
Demonstration Submissions for Ozone Nonattainment Areas,'' November 
30, 1999; and Memorandum from John S. Seitz, Director, OAQPS, to 
Regional Air Directors, ``Additional Submission on RACM From States 
with Severe One-Hour Ozone Nonattainment Area SIPs,'' December 14, 
2000.
---------------------------------------------------------------------------

    The 2008 ozone NAAQS implementation regulations require that all 
control measures needed for attainment must be implemented no later 
than the beginning of the attainment year ozone season.\57\ The 
attainment year ozone season is defined as the ozone season immediately 
preceding a nonattainment area's maximum attainment date.\58\
---------------------------------------------------------------------------

    \57\ 40 CFR 51.1108(d).
    \58\ 40 CFR 51.1100(h).
---------------------------------------------------------------------------

2. Summary of State's Submission
    When the EPA acted to reclassify Imperial County (and certain other 
areas) from Marginal to Moderate, the EPA established a deadline of 
January 1, 2017, for the submission of a SIP revision to address the 
Moderate area requirements for the 2008 ozone NAAQS, including the RACM 
requirement of CAA section 172. Imperial County APCD and CARB undertook 
a process to identify and evaluate potential RACM in Imperial County. 
They present their assessment of RACM in Chapter 6 of the Imperial 
Ozone Plan, which is further explained and supported in Appendix C 
(area source RACM), Appendix D (key mobile source regulations and 
programs), and Appendix E (compilation of CARB control measures, 1985-
2016) of the Plan. This assessment describes how the state and local 
control measures address the RACM requirements for purposes of 
demonstrating RFP (in Chapter 5 of the Plan) and in support of the 
demonstration that the reductions from such measures would be adequate 
to bring Imperial County into attainment of the 2008 ozone NAAQS but 
for emissions from Mexico (in Chapter 8 of the Plan).\59\ CARB and the 
District conclude in their RACM evaluations that no additional measures 
are necessary in accordance with EPA regulations and RACM guidance.\60\
---------------------------------------------------------------------------

    \59\ Imperial Ozone Plan, 6-1.
    \60\ Id. at 6-11.
---------------------------------------------------------------------------

    The District also describes strategic efforts to understand and 
address air quality and emissions sources at the U.S.-Mexico border and 
in Mexico (in Chapter 9 of the Plan).\61\ The Plan does not relate 
these efforts to specific CAA requirements for Moderate ozone 
nonattainment areas, and, accordingly, we are not evaluating this 
portion of the Plan.
---------------------------------------------------------------------------

    \61\ Id., Chapter 9.
---------------------------------------------------------------------------

    The following paragraphs of this proposed rule separately describe 
the Plan's RACM analyses as prepared by the District for certain source 
categories and by CARB for other source types.
a. District's RACM Analysis
    Stationary sources emitted an estimated 8% of the NOX 
and 8% of the VOC in Imperial County in 2017.\62\ The largest portions 
of stationary source emissions are from fuel combustion (e.g., 
manufacturing and industrial, and electric utility sources) for 
NOX and from cleaning and surface coatings, and petroleum 
marketing for VOC.
---------------------------------------------------------------------------

    \62\ Imperial Ozone Plan, App. A (``Ozone Precursor Emission 
Inventories for Imperial County''), Table A-4.
---------------------------------------------------------------------------

    For stationary sources subject to RACT as major sources of 
NOX or VOC and non-major point sources subject to CTGs under 
RACT, the District states that RACM can be achieved through the 
adoption of RACT and includes its RACT evaluation and summary.\63\ The 
EPA has in a separate action proposed to approve in part and 
conditionally approve in part the portions of the Imperial Ozone Plan 
that relate to the RACT requirements under CAA section 182(b)(2) and 40 
CFR 51.1112, and thus we do not re-summarize those portions herein.\64\ 
The District's RACM analysis also describes its nonattainment NSR rule 
for stationary sources (Rule 207).\65\
---------------------------------------------------------------------------

    \63\ Id., at 6-2.
    \64\ 84 FR 49202.
    \65\ Id. We note that the Imperial Ozone Plan refers to versions 
of Rule 207 that were adopted on November 10, 1980 and October 10, 
2006. Imperial County APCD most recently amended Rule 207 on 
September 11, 2018 and the EPA has approved such amended rule into 
the California SIP. 84 FR 44545.
---------------------------------------------------------------------------

    CARB estimated that area sources would emit 3% of the 
NOX and 46% of the VOC in Imperial County in 2017.\66\ The 
largest portions of these emissions are from managed burning and 
disposal for NOX and from farming operations, pesticides, 
consumer products, and managed burning and disposal for VOC. For these 
area sources, the District's RACM analysis indicates that the District 
evaluated its area source control measures against EPA's Menu of 
Control Measures for NOX and VOC.\67\ The District presents 
a summary of that evaluation in Appendix C of the Plan where, for most 
source categories, the District found either that the District has 
rules in place for such measures or that Imperial County has no sources 
within a source category. For the latter situation, the Plan includes 
negative declarations.\68\
---------------------------------------------------------------------------

    \66\ Imperial Ozone Plan, App. A, Table A-4.
    \67\ Imperial Ozone Plan, 6-2 to 6-3 and App. C. See also, EPA 
Menu of Control Measures for NAAQS Implementation, https://www.epa.gov/air-quality-implementation-plans/menu-control-measures-naaqs-implementation.
    \68\ Id., App. C, Table C-1, pages 5 to 8.
---------------------------------------------------------------------------

    Table 2 identifies the District's area source control measures (as 
listed in

[[Page 58648]]

Appendix C of the Imperial Ozone Plan) that contribute toward 
attainment of the 2008 ozone NAAQS by 2017. The EPA has approved each 
of these measures into the California SIP.

                            Table 2--Area Source Measures for RACM in Imperial County
----------------------------------------------------------------------------------------------------------------
                                                    Date adopted/  Citation for EPA approval into the California
         Rule No.                 Rule title           amended                          SIP
----------------------------------------------------------------------------------------------------------------
400.2.....................  Boilers, Process            2/23/2010  78 FR 896 (1/7/2013).
                             Heaters, and Steam
                             Generators.
424.......................  Architectural               2/23/2010  76 FR 39303 (7/6/2011).
                             Coatings.
426.......................  Cutback Asphalt and         9/14/1999  66 FR 20084 (4/19/2001).
                             Emulsified Paving
                             Materials.
427.......................  Automotive                  2/23/2010  76 FR 67369 (11/1/2011).
                             Refinishing
                             Operations.
414.......................  Storage of Reactive         5/18/2004  73 FR 70883 (11/24/2008).
                             Organic Compound
                             Liquids.
n/a.......................  CARB Consumer                     (*)  Various rulemakings.
                             Products Program,
                             various rules.
----------------------------------------------------------------------------------------------------------------
Note: This table is adapted from Table C-1 of the Imperial Ozone Plan. See also, Imperial Ozone Plan, section
  8.3 (``Weight of Evidence Analysis''), which provides a weight of evidence analysis that describes how the
  overall emission reduction trends for NOX and VOC support reduction in ambient ozone concentrations.
* Various dates.

    The Plan provides a discussion of the District's and CARB's Smoke 
Management Programs, under which the District and CARB may call no-burn 
days in Imperial County, and states that these programs are more 
protective of public health compared to the EPA's episodic burning 
control measure.\69\ The District also states that it does not have a 
rule for municipal solid waste landfills, but instead issues permits 
that must comply with CARB and EPA waste management statutes and 
regulations.\70\ Though not described in the RACM portion of the Plan, 
the District also refers to its Rule 217 (``Large Confined Animal 
Facilities'') as a stationary source control rule in the Plan's 
inventory.\71\
---------------------------------------------------------------------------

    \69\ Imperial Ozone Plan, App. C, Table C-1, page 2.
    \70\ Id. at 4.
    \71\ Id., Table 4-4.
---------------------------------------------------------------------------

    In addition to the source categories described above, the District 
states that it was not feasible to adopt and implement control measures 
for three source categories before the attainment year given the short 
time between the area's reclassification to Moderate, effective June 3, 
2016, and the 2017 attainment year.\72\ The District also states that 
it was determined that these measures were not necessary to demonstrate 
expeditious attainment or to meet RFP.\73\
---------------------------------------------------------------------------

    \72\ Id., App. C, Table C-1, pages 1, 2, and 4. The District 
states that, in 2019, it will adopt new limits on NOX 
emissions from (i) boilers, steam generators, and process heaters 
rated 0.075 to 5 MMBtu per hour (a new limit of 14 nanograms (ng) 
NOX per joule of heat output or 20 ppm), and (ii) new and 
replacement residential water heaters rated less than 0.075 MMBtu 
per hour (a new limit of 10 ng NOX per joule of heat 
output). The District intends to implement both new limits by 
January 1, 2020. Imperial Ozone Plan, App. C, 1-2. See also, 
sections 5.5.4 and 5.5.2, respectively, of CARB and Imperial County 
APCD's SIP revision for the 2012 PM2.5 NAAQS, submitted 
July 18, 2018. ``Imperial County 2018 Annual Particulate Matter Less 
Than 2.5 Microns in Diameter State Implementation Plan,'' Imperial 
County APCD, April 2018 (``Imperial PM2.5 Plan'').
    \73\ Imperial Ozone Plan, 6-3.
---------------------------------------------------------------------------

    The Plan also discusses regional and local transportation control 
measures (TCMs) that address the portion of the NOX and VOC 
emissions sources under regional and local jurisdictions.\74\ For 
regional measures, the District refers to the current quadrennial 
regional transportation plan applicable to Imperial County, the ``2016-
2040 Regional Transportation Plan/Sustainable Communities Strategy 
(2016 RTP/SCS),'' and the biennial ``Federal Transportation Improvement 
Plan (FTIP).'' The District states that the 2016 RTP/SCS addresses the 
long-term planning requirements for how transportation projects, plans, 
and programs will conform with applicable air quality plans, while the 
FTIP addresses the associated short-term planning implementation 
requirements. For local measures, the District refers to the Imperial 
County ``CEQA Air Quality Handbook'' that provides guidance to 
determine emissions from residential, commercial, and industrial 
projects and feasible measures to mitigate the effect of such 
emissions.
---------------------------------------------------------------------------

    \74\ Id. at 6-3 to 6-7.
---------------------------------------------------------------------------

    The District states that to be considered RACM, TCMs must be 
technologically and economically feasible in the area, and able to be 
implemented by the attainment year. The District notes that CAA section 
108(f)(1)(A) provides a list of TCMs that could potentially qualify as 
RACM, and that there are currently no on-going TCMs in Imperial County. 
The District concludes that no new TCMs are being proposed in the Plan 
due to the short time between the area's reclassification to Moderate, 
effective June 3, 2016, and the 2017 attainment year.
b. CARB's RACM Analysis
    The Plan notes that CARB provided the RACM analysis for certain 
sources, including consumer products, pesticides, and mobile 
sources.\75\
---------------------------------------------------------------------------

    \75\ Imperial Ozone Plan, 6-6.
---------------------------------------------------------------------------

    CARB states that CARB's Consumer Products Program has established 
regulations that limit VOC emissions from 129 consumer product 
categories and that each applies in Imperial County.\76\ These include 
product categories such as antiperspirants and deodorants and aerosol 
coatings. The Plan also refers to a voluntary Alternative Control Plan 
that provides compliance flexibilities to companies. The Plan also 
notes that the EPA's consumer products regulation was promulgated in 
1998 \77\ and states that California's requirements for general 
consumer products and aerosol coatings are more stringent than those 
EPA standards.\78\
---------------------------------------------------------------------------

    \76\ Imperial Ozone Plan, 6-10 and App. C, Table C-1, page 3.
    \77\ 63 FR 8819 (September 11, 1998).
    \78\ Imperial Ozone Plan, 6-10. Regarding the EPA's more recent 
2008 rule on VOC emission standards for aerosol coatings, 73 FR 
15604 (March 24, 2008), the District states that the rule was aimed 
primarily at manufacturers of such coatings, which are not present 
in Imperial County. Imperial Ozone Plan, App. C, Table C-1, page 3.
---------------------------------------------------------------------------

    CARB states that California Department of Pesticide Regulation 
(DPR) is responsible for regulating the application of pesticides, and 
that DPR has adopted and implemented regulations to limit VOC emissions 
from use of agricultural pesticides in certain areas of California.\79\ 
In May 2019, CARB provided additional technical clarifications 
(``CARB's Technical Clarification Letter'') with respect to the RACM 
conclusion for not regulating

[[Page 58649]]

pesticides in the Imperial Ozone Plan.\80\ While acknowledging the 
``relative significance'' of VOC emissions from pesticides, CARB 
presented its position that implementation of pesticide regulations in 
the area would not contribute to RFP and is not necessary for 
expeditious attainment.
---------------------------------------------------------------------------

    \79\ Imperial Ozone Plan, 6-10 and App. C, Table C-1, page 4.
    \80\ Letter dated May 20, 2019 from Michael Benjamin, Chief, Air 
Quality Planning and Science Division, CARB to Amy Zimpfer, 
Associate Director, Air Division, EPA Region 9, 3 and Attachment B.
---------------------------------------------------------------------------

    CARB provides three bases for this position. First, CARB argues 
that implementation would not have been feasible given the short 
timeframe between reclassification in June 2016 and the attainment year 
of 2017. Second, CARB relies on data in the Imperial Ozone Plan to 
estimate that a 1.0 tpd reduction in NOX or VOC emissions 
would result in 0.2 parts per billion (ppb) reduction in ambient ozone 
concentration at the modeled high site (El Centro). Based on a 
conservative assumption of 100% reduction of the pesticide VOC 
emissions in 2017 of 2.21 tpd VOC, CARB estimates that the modeled 
2015-2017 design value of 79 ppb would decrease by no more than 0.44 
ppb and concludes that such reductions would not result in attainment 
of the 2008 ozone NAAQS by the 2017 attainment year. Third, CARB also 
states that annual emissions data demonstrate that Imperial County has 
achieved a level of VOC reductions in the pesticide/fertilizer category 
that is comparable to VOC reduction levels in five other areas 
(Sacramento Metro, San Joaquin Valley, South Coast, Southeast Desert, 
and Ventura County) where pesticide regulations are in effect as a 
result of an earlier ozone SIP obligation.
    For mobile sources, CARB discusses how California's mobile source 
measures for NOX and VOC emissions meet RACM in Imperial 
County.\81\ Given the need for substantial emissions reductions from 
mobile and area sources to meet the NAAQS in California nonattainment 
areas, the State of California has developed stringent control measures 
for on-road and non-road mobile sources and the fuels that power them. 
California has unique authority under CAA section 209 (subject to a 
waiver by the EPA) to adopt and implement new emissions standards for 
many categories of on-road vehicles and engines and new and in-use non-
road vehicles and engines. The EPA has approved such mobile source 
regulations for which waiver authorizations have been issued as 
revisions to the California SIP.\82\
---------------------------------------------------------------------------

    \81\ Imperial Ozone Plan, 6-6 and App. D.
    \82\ E.g., 81 FR 39424 (June 16, 2016); 82 FR 14447 (March 21, 
2017); and 83 FR 23232 (May 18, 2018).
---------------------------------------------------------------------------

    CARB's mobile source program extends beyond regulations that are 
subject to the waiver or authorization process set forth in CAA section 
209 to include standards and other requirements to control emissions 
from in-use heavy-duty trucks and buses, gasoline and diesel fuel 
specifications, and many other types of mobile sources. Generally, 
these regulations have been submitted and approved as revisions to the 
California SIP.\83\
---------------------------------------------------------------------------

    \83\ E.g., EPA approval of standards and other requirements to 
control emissions from in-use heavy-duty diesel trucks, 77 FR 20308 
(April 4, 2012), and revisions to the California on-road 
reformulated gasoline and diesel fuel regulations, 75 FR 26653 (May 
12, 2010).
---------------------------------------------------------------------------

    CARB identifies the key mobile source regulations and programs that 
provide emissions reductions in Imperial County.\84\ These key measures 
include requirements for light-duty vehicles,\85\ heavy-duty 
vehicles,\86\ non-road sources,\87\ and incentive programs for a 
variety of sources \88\ that applied through the Imperial County 
attainment year of 2017. CARB also describes its Mobile Source 
Strategy, which was adopted in November 2016 and included a suite of 
actions to address federal air quality standards and other state air 
quality goals, and its State SIP Strategy, which was adopted by CARB on 
March 23, 2017 and submitted to the EPA as a revision to the California 
SIP on April 27, 2017.\89\
---------------------------------------------------------------------------

    \84\ Imperial Ozone Plan, App. D, 1, 2, 4, and 7.
    \85\ Id., App. D, 2. E.g., On-Board Diagnostics and Reformulated 
Gasoline.
    \86\ Id. at 4. E.g., Heavy-duty Engine Standards, Clean Diesel 
Fuel, and the Cleaner In-Use Heavy-Duty Trucks (Truck and Bus 
Regulation).
    \87\ Id. at 7. E.g., Off-road Engine Standards, (Federal) 
Locomotive Engine Standards, Clean Diesel Fuel, Cleaner In-Use Off-
road Regulation, and the In-Use Large Spark-Ignition Fleet 
Regulation.
    \88\ Id. at 1, 2, and 4. E.g., Carl Moyer Program; Goods 
Movement Emission Reduction Program, funded by Prop. 1B; Lower-
Emissions School Bus Program; Air Quality Improvement Program 
(AQIP), including the Hybrid and Zero-Emission Truck and Bus Voucher 
Program, and the Clean Vehicle Rebate Project; and the Truck Loan 
Assistance Program.
    \89\ ``Revised Proposed 2016 State Strategy for the State 
Implementation Plan,'' CARB, March 7, 2017 (``State SIP Strategy''). 
We note that the State SIP Strategy only briefly discusses the 
Imperial County nonattainment area for the 2008 ozone NAAQS (State 
SIP Strategy, 21-22) and includes no specific emissions reduction 
commitments for Imperial County.
---------------------------------------------------------------------------

    CARB concludes that, considering the comprehensiveness and 
stringency of its mobile source program, all RACM for mobile sources 
under CARB's jurisdiction are being implemented, and that no additional 
measures are being proposed in the Plan due to the short time between 
the area's reclassification to Moderate and the attainment year.\90\
---------------------------------------------------------------------------

    \90\ Imperial Ozone Plan, 6-7 and 6-10.
---------------------------------------------------------------------------

3. EPA Review of State's Submission
    The process followed by CARB and the District in the Imperial Ozone 
Plan to identify RACM is generally consistent with the EPA's 
regulations and guidance. The process included compiling a 
comprehensive list of potential control measures for sources of 
NOX and VOC in Imperial County.\91\ As part of this process, 
CARB and the District evaluated potential controls for relevant source 
categories and provided justifications for the rejection of certain 
identified measures.
---------------------------------------------------------------------------

    \91\ Id., App. C.
---------------------------------------------------------------------------

    The EPA has reviewed the Imperial Ozone Plan's determination that 
current stationary, area, and mobile source control measures represent 
RACM for NOX and VOC. For the reasons presented below, we 
propose that the State and District's rules provide for the 
implementation of RACM for sources of NOX and VOC for the 
2008 ozone NAAQS.
    With respect to mobile sources, CARB has developed and implemented 
stringent control measures for on-road and non-road mobile sources, and 
its current program addresses the full range of mobile sources in 
Imperial County through regulatory programs for both new and in-use 
vehicles. With respect to transportation controls, we note that the 
SCAG has a program to fund cost-effective TCMs. Overall, we propose to 
determine that the programs developed and administered by CARB and SCAG 
provide for the implementation of RACM for NOX and VOC in 
Imperial County.

[[Page 58650]]

    For area-wide sources and stationary sources not subject to RACT, 
we reviewed Chapter 6 and Appendix C and found that the measures 
identified by the District, as reflected in Table 2 of this proposed 
action, meet RACM for each source category.\92\ Regarding consumer 
products, the EPA has approved many CARB measures into the California 
SIP that limit VOC emissions from a wide array of products, including 
antiperspirants and deodorants, aerosol coating products, and other 
consumer products.\93\
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    \92\ We also note that while the EPA's Menu of Control Measures 
is periodically updated with examples of reasonable measures, it 
should not be relied on as the sole source of comparison for 
determining RACM for any given source category.
    \93\ CARB's consumer product measures are found in the 
California Code of Regulations, Title 17 (``Public Health''), 
Division 3 (``Air Resources''), Chapter 1 (``Air Resources Board''), 
Subchapter 8.5 (``Consumer Products''). The compilation of such 
measures that have been approved into the California SIP, including 
Federal Register citations, is available at: https://www.epa.gov/sips-ca/epa-approved-regulations-california-sip. EPA's most recent 
approval of amendments to California's consumer products regulations 
was in 2014. 79 FR 62346 (October 17, 2014).
---------------------------------------------------------------------------

    For open burning, we reviewed the District's SIP-approved measures 
that address managed burning and disposal,\94\ which account for 0.54 
tpd of NOX and 1.10 tpd of VOC in the Plan's 2017 emissions 
inventory.\95\ The District has SIP-approved rules for open burning in 
general, open burning of wood wastes, agricultural burning, and range 
improvement burning.
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    \94\ Imperial County Rule 421 (``Open Burning,'' adopted 
September 14, 1999), 66 FR 36170 (July 11, 2001); Rule 422 (``Open 
Burning of Wood Wastes,'' adopted November 19, 1985), 54 FR 5448 
(February 3, 1989); Rule 701 (``Agricultural Burning,'' adopted 
August 13, 2002), 68 FR 4929 (January 31, 2003); and Rule 702 
(``Range Improvement Burning,'' adopted September 14, 1999), 66 FR 
36170 (July 11, 2001).
    \95\ Imperial Ozone Plan, App. A, Table A-4.
---------------------------------------------------------------------------

    Regarding landfills, the District stated that it does not have a 
rule for municipal solid waste landfills and instead permits such 
facilities. We found that there are no major source landfills in 
Imperial County, which is consistent with the Plan's 2017 emissions 
inventory for this source category.\96\ We note that methane, which 
comprises a large portion of landfill organic carbon emissions, is 
excluded from the EPA's definition of VOCs due to its negligible 
photochemical reactivity.\97\
---------------------------------------------------------------------------

    \96\ Id.
    \97\ 40 CFR 51.100(s)(1).
---------------------------------------------------------------------------

    In reviewing the Plan's 2017 emissions inventory, we also found 
that farming operations were projected to emit 2.53 tpd of VOC, which 
is 15% of the total 2017 VOC emissions inventory.\98\ According to 
CARB's California Emissions Projection Analysis Model (CEPAM), such VOC 
emissions in Imperial County largely come from agricultural waste from 
livestock husbandry, particularly feedlot cattle.\99\ Imperial County 
Rule 217 (adopted February 9, 2016) was developed to limit such VOC 
emissions by requiring the use of best management practices for 
activities relating to livestock waste, and it is included in the 
Imperial Ozone Plan's table of stationary source rules in the Plan's 
emissions inventory.\100\ The EPA approved this rule into the 
California SIP in June 2017, including a determination that the rule 
represented RACT-level controls.\101\ A review of other areas shows 
that there is no change to the set of reasonable controls that may 
apply to such sources.
---------------------------------------------------------------------------

    \98\ Imperial Ozone Plan, App. A, Table A-4.
    \99\ CEPAM data accessed October 12, 2018 at https://www.arb.ca.gov/app/emsinv/fcemssumcat/fcemssumcat2016.php and 
included in the docket of this proposed rule. Of the 2.53 tpd 
estimated for the farming operations source category, 2.22 tpd are 
estimated to come from agricultural waste from feedlot cattle.
    \100\ Imperial Ozone Plan, Table 4-4.
    \101\ 82 FR 26594 (June 8, 2017).
---------------------------------------------------------------------------

    We also evaluated the Plan's determinations for three source 
categories (i.e., commercial and institutional natural gas water 
heaters; residential, commercial, and institutional low-NOX 
water heaters and low-NOX burner space heaters; and 
pesticides).
    For commercial and institutional natural gas water heaters and 
residential, commercial, and institutional low-NOX water 
heaters and low-NOX burner space heaters, we considered 
whether there are additional economically and technically feasible 
control measures that could have been adopted into the SIP by the 
attainment year of 2017 to meet RACM. While Imperial County APCD plans 
to adopt new rules for these two source categories in 2019 to limit 
NOX emissions from such sources,\102\ no additional measures 
were proposed for adoption prior to the attainment date due to the 
short time between the area's reclassification to Moderate and the 
attainment year of 2017. Based on CEPAM data, these source categories 
emitted a combined 0.88 tpd of NOX in 2017,\103\ which 
amounts to 5.4% of the 2017 total NOX emissions in Imperial 
County. The combined estimated emissions reductions from both measures 
constitute 0.27 tpd of NOX or 1.5% of the total 2017 
NOX emissions of 18.0 tpd.\104\ The EPA notes that although 
not considered RACM, these anticipated new control measures could 
contribute to a small air quality improvement in the area in the 
future.
---------------------------------------------------------------------------

    \102\ Imperial Ozone Plan, App. C, 1-2, and Imperial 
PM2.5 Plan, sections 5.5.2 and 5.5.4.
    \103\ CEPAM data accessed April 15, 2019 at https://www.arb.ca.gov/app/emsinv/fcemssumcat/fcemssumcat2016.php and 
included in the docket of this proposed rule.
    \104\ Imperial Ozone Plan, Table 8-1.
---------------------------------------------------------------------------

    For the pesticides category VOC emissions are 2.2 tpd in 2017,\105\ 
which amounts to 13% of the total VOC emissions of 16.9 tpd in Imperial 
County.\106\ CARB concluded that implementation of additional pesticide 
emissions reduction measures would not be feasible given the short 
timeframe between reclassification in June 2016 and the attainment year 
of 2017. CARB also estimated that, even if there were a 100% reduction 
in pesticide VOC emissions, resulting in a maximum reduction in the 
ozone design value of 0.44 ppb, and even if such reductions had been 
achieved by 2017, those reductions would not have been sufficient to 
attain the standards but for international emissions.\107\
---------------------------------------------------------------------------

    \105\ Imperial Ozone Plan, App. A, Table A-4. We note that 
2.2075 tpd of the 2.21 tpd of VOC emissions from the pesticides/
fertilizer category are agricultural pesticides. CEPAM data accessed 
October 12, 2018 at https://www.arb.ca.gov/app/emsinv/fcemssumcat/fcemssumcat2016.php.
    \106\ Imperial Ozone Plan, Table 8-1.
    \107\ CARB also examined whether the conditions at each Imperial 
County ozone monitor in 2012 represented a NOX-limited 
regime (where VOC emission reductions have minimal effect on ozone 
concentrations) or a transitional regime (where both NOX 
and VOC emission reductions can reduce ozone concentrations). 
Imperial Ozone Plan, App. F, 36. CARB found that the modeled 2012 
baseline ozone values showed a prevalence of NOX-limited 
conditions at the Niland and El Centro sites, and that the observed 
2012 values were consistent with a more transitional ozone chemistry 
at the Calexico site. Regarding the presentation, in CARB's 
Technical Clarification Letter, of reductions in pesticide VOC 
emissions from 1990 to 2016 in Imperial County relative to other 
areas of California where pesticide regulations have been imposed, 
CARB does not state how the similar scale of past reductions 
supports a RACM determination. Accordingly, the EPA is not relying 
on Imperial County's historic pesticide VOC emission reductions as a 
basis for evaluating RACM.
---------------------------------------------------------------------------

    Consistent with the EPA's past guidance interpreting the RACM 
requirement, the EPA has considered which of the above-discussed 
control measures were technologically and economically feasible and 
could be adopted by the attainment year of 2017, and if implemented 
collectively, would achieve sufficient emissions reductions to provide 
for attainment by the attainment date but for international emissions. 
As described in the preceding paragraphs, we have considered potential 
emissions reductions from two NOX source categories and one 
VOC category.
    The District estimated that adoption of controls on commercial and

[[Page 58651]]

institutional natural gas water heaters and residential, commercial, 
and institutional low-NOX water heaters and low-
NOX burner space heaters would not be feasible given the 
short timeframe between reclassification in June 2016 and the 
attainment year of 2017. However, the District estimated that rules to 
be adopted soon after the attainment date for these source categories 
would result in a combined emissions reduction of 0.27 tpd of 
NOX over more than a decade. CARB's Technical Clarification 
Letter also evaluated a conservative reduction of 2.21 tpd of VOC 
emissions on the basis of zeroing out the 2017 emissions for the 
pesticide source category. Thus, as a conservatively high estimate, 
these emissions reductions sum to 0.27 tpd of NOX and 2.21 
tpd of VOC, or 2.48 tpd combined.
    Based on estimates available in the Imperial Ozone Plan, we have 
applied the modeled relationship between ozone concentrations in 
Imperial County and reductions in NOX or VOC emissions in 
Mexico to the combined 2.48 tpd of emission reductions, given the 
proximity (9 miles and 1 mile, respectively) of the El Centro and 
Calexico monitoring sites to the Mexican border and the Mexicali 
region. This relationship estimates that a 1.0 tpd reduction in 
NOX or VOC emissions would result in a 0.2 ppb reduction in 
ambient ozone concentration at the modeled high site (El Centro). Thus, 
based on conservative assumptions, the combined potential emissions 
reductions would be estimated to result in no more than a 0.50 ppb 
reduction in the modeled 8-hour ozone concentration and thus would not 
be sufficient to provide for attainment by the attainment date.
    As noted at the outset of this section, the EPA's regulations 
governing implementation of the 2008 ozone NAAQS require that, for each 
nonattainment area required to submit an attainment demonstration, the 
state concurrently submit a SIP revision demonstrating that it has 
adopted all RACM necessary to demonstrate attainment as expeditiously 
as practicable and to meet any RFP requirements.\108\ The 2008 Ozone 
SRR provided that ``[t]he determination of whether a SIP contains all 
RACM requires an area-specific analysis establishing that there are no 
additional economically and technically feasible control measures 
(alone or cumulatively) that will advance'' attainment.\109\ Based on 
our evaluation, we propose to determine that the two NOX 
source categories and pesticides measures analyzed above are not 
technologically and economically feasible control measures that could 
have been adopted by the attainment year of 2017, and therefore would 
not have provided for expeditious attainment of the 2008 ozone NAAQS in 
Imperial County by the attainment date. Thus, we propose to find that 
the Imperial Ozone Plan provides for implementation of all RACM for the 
2008 ozone NAAQS as required by CAA section 172(c)(1) and 40 CFR 
51.1112(c).
---------------------------------------------------------------------------

    \108\ 40 CFR 51.1112(c).
    \109\ 2008 Ozone SRR, 12286.
---------------------------------------------------------------------------

G. Demonstration of Attainment but for International Emissions

1. Statutory and Regulatory Requirements
    Section 172(c)(1) of the CAA requires that plans for nonattainment 
areas provide for expeditious attainment of the NAAQS, and section 
182(b)(1)(A) requires that such plans for areas classified as Moderate 
nonattainment for an ozone NAAQS demonstrate attainment by the 
applicable attainment date for Moderate areas. To implement these 
requirements for Moderate areas, the 2008 Ozone SRR requires that 
states submit an attainment demonstration based on photochemical 
modeling or another equivalent method that is at least as effective as 
the method required of ozone nonattainment areas classified Serious and 
above.\110\ The attainment demonstration predicts future ambient 
concentrations for comparison to the NAAQS, making use of available 
information on measured concentrations, meteorology, and current and 
projected emissions inventories of ozone precursors, including the 
effect of control measures in the plan.
---------------------------------------------------------------------------

    \110\ 40 CFR 51.1108(c); 2008 Ozone SRR, 12268.
---------------------------------------------------------------------------

    These requirements for the 2008 ozone NAAQS are codified at 40 CFR 
51.1108 (``Modeling and attainment demonstration requirements'') and, 
in turn, rely on the requirements of 40 CFR 51.112 (``Demonstration of 
adequacy''). The latter section requires such a plan to demonstrate 
that its measures, rules, and regulations are adequate to provide for 
timely attainment and maintenance of the NAAQS and includes a list of 
specific requirements for the content of such demonstration.
    As described in section I.A of this proposed rule, the EPA 
designated Imperial County as nonattainment for the 2008 ozone NAAQS 
and classified the area as Marginal, effective July 20, 2012. On May 4, 
2016, the EPA published its determination that Imperial County had not 
attained the 2008 ozone NAAQS by the July 20, 2015 Marginal area 
attainment date and reclassified the area as Moderate with an 
attainment date of no later than July 20, 2018. An attainment 
demonstration must show attainment of the standards for the ozone 
season immediately preceding the area's outermost attainment date.\111\ 
As applied to areas in California, where the ozone season is the full 
calendar year, the State must demonstrate attainment for any Moderate 
nonattainment area in 2017.
---------------------------------------------------------------------------

    \111\ 40 CFR 51.1100(h) defining ``attainment year ozone 
season'' as ``the ozone season immediately preceding a nonattainment 
area's maximum attainment date.'' Due to California's predominately 
temperate climate, the term ``ozone season'' is understood to mean 
the full calendar year. Therefore, an attainment date of July 20, 
2018 requires attainment to be demonstrated by calendar year 2017.
---------------------------------------------------------------------------

    As discussed in section II.B of this proposed rule, for a 
nonattainment area affected by emissions emanating from outside the 
U.S., CAA section 179B(a) provides that, notwithstanding any other 
provision of law, the EPA Administrator shall approve an attainment 
plan SIP submission if it (1) meets all of the applicable nonattainment 
area requirements other than the requirement to demonstrate attainment 
and maintenance of the relevant NAAQS by the applicable attainment 
date, and (2) establishes to the Administrator's satisfaction that the 
SIP revision would be adequate to attain and maintain the relevant 
NAAQS by the applicable attainment date but for emissions emanating 
from outside of the U.S.\112\
---------------------------------------------------------------------------

    \112\ In addition, as explained below in section III of this 
proposed rule, CAA section 179B(b) provides that for the purposes of 
the ozone NAAQS, any state that establishes to the Administrator's 
satisfaction that the state would have attained the NAAQS by the 
applicable attainment date, but for emissions emanating from outside 
the U.S., the area shall not be subject to section 181(b)(2), which 
requires the EPA to determine whether an area attained the standards 
by its attainment date and reclassify to a higher classification 
those areas that fail to attain.
---------------------------------------------------------------------------

    The 2008 Ozone SRR does not establish specific requirements for how 
states should demonstrate attainment but for emissions emanating from 
outside the U.S., and instead recommends as ``the best approach'' that 
states work with EPA regional offices ``on a case-by-case basis to 
determine the most appropriate information and analytical methods for 
each area's unique situation.'' \113\
---------------------------------------------------------------------------

    \113\ 2008 Ozone SRR, 12293.
---------------------------------------------------------------------------

    The EPA's recommended procedures for modeling ozone as part of an 
attainment demonstration are relevant to such a section 179B 
demonstration,

[[Page 58652]]

in terms of their modeling and adequacy criteria and their purpose in 
predicting future ambient concentrations for comparison to the NAAQS, 
making use of available information on measured concentrations, 
meteorology, and current and projected emissions inventories of ozone 
precursors, including the effect of control measures in the plan. These 
recommended procedures are contained in the EPA's ``Modeling Guidance 
for Demonstrating Attainment of Air Quality Goals for Ozone, 
PM2.5, and Regional Haze,'' (``Modeling Guidance'').\114\ 
The Modeling Guidance includes recommendations for a modeling protocol, 
model input preparation, model performance evaluation, use of model 
output for the numerical NAAQS attainment test, and modeling 
documentation.
---------------------------------------------------------------------------

    \114\ ``Modeling Guidance for Demonstrating Air Quality Goals 
for Ozone, PM2.5, and Regional Haze,'' EPA-454/R-18-009, 
November 2018; available at: https://www.epa.gov/scram/state-implementation-plan-sip-attainment-demonstration-guidance. During 
development of the Imperial Ozone Plan, CARB relied on the draft 
version of this guidance update: ``Draft Modeling Guidance for 
Demonstrating Attainment of Air Quality Goals for Ozone, 
PM2.5, and Regional Haze,'' December 3, 2014 Draft, EPA 
OAQPS. Additional EPA modeling guidance can be found in 40 CFR 51 
Appendix W (``Guideline on Air Quality Models''), 82 FR 5182 
(January 17, 2017); available at https://www.epa.gov/scram/clean-air-act-permit-modeling-guidance.
---------------------------------------------------------------------------

    As described in the Modeling Guidance, the modeling process starts 
with the development of base year emissions and meteorology inputs, 
which are then used to assess model performance by comparing predicted 
concentrations from this base case to air quality monitoring data. Once 
the model performance is determined to be acceptable, future year 
emissions are simulated with the model. The relative (or percent) 
change in modeled concentration due to future emissions reductions 
provides a Relative Response Factor (RRF). Each monitoring site's RRF 
is applied to its monitored base year design value to project the 
future design value, which can then be compared to the NAAQS. The 
Modeling Guidance also recommends supplemental air quality analyses 
that may corroborate the attainment demonstration by considering 
evidence other than the main air quality modeling attainment test, such 
as trends and additional monitoring and modeling analyses.
    Neither the 2008 Ozone SRR nor the Modeling Guidance specify that a 
particular year be used as the base year to demonstrate attainment with 
the 2008 ozone standards.\115\ The Modeling Guidance explains that the 
most recent year of the National Emission Inventory may be appropriate 
for use as the base year for modeling, but that other years may be more 
appropriate when considering meteorology, transport patterns, 
exceptional events, or other factors that may vary from year to 
year.\116\
---------------------------------------------------------------------------

    \115\ See generally, 40 CFR 51.1108; 2008 Ozone SRR, 12268-
12271; Modeling Guidance at Section 2.7.1.
    \116\ Modeling Guidance at Section 2.7.1.
---------------------------------------------------------------------------

2. Summary of State's Submission
    The Imperial Ozone Plan includes a demonstration prepared by CARB 
and Imperial County APCD that Imperial County would attain the 2008 
ozone NAAQS by the Moderate area attainment date, but for emissions 
emanating from outside the United States. Using several lines of 
evidence, CARB evaluated whether, and the extent to which, ambient 
ozone levels in Imperial County would be affected by Mexican emissions, 
including photochemical air quality modeling, back trajectory analysis, 
and emissions inventory comparisons. The modeling relies on a 2012 base 
year and projects that, (i) when the Mexican emissions inventory is 
included in the model, the highest predicted 2017 ozone design value is 
79 ppb, which exceeds the 2008 8-hour ozone NAAQS of 75 ppb; and (ii) 
removal of the anthropogenic emissions inventory from Mexico lowers 
2017 predicted ozone design values to below 75 ppb. CARB also conducted 
additional analyses, described in section III.B of this proposed rule, 
that scaled CARB's photochemical air quality modeling, scaled separate 
photochemical air quality modeling performed by the EPA (using 
monitored data from 2015-2017), and updated CARB's back trajectory 
modeling.
    CARB's modeling and modeled attainment demonstration are described 
in Chapter 8 of the Imperial Ozone Plan, and in more detail in 
Appendices F-I. Appendix F provides a description of model input 
preparation procedures and various model configuration options.\117\ 
The Plan's modeling protocol is in Appendix G \118\ and contains all 
the elements recommended in the Modeling Guidance, including selection 
of model, time period to model, modeling domain, and model boundary 
conditions and initialization procedures; a discussion of emissions 
inventory development and other model input preparation procedures; 
model performance evaluation procedures; selection of days and other 
details for calculating RRFs. Appendix H explains the modeling emission 
inventories.\119\ Appendix I discusses the use of anthropogenic 
emissions inventories, photochemical modeling, and other factors to 
assess the impact of emissions emanating from Mexico and whether the 
area would have attained but for Mexican emissions.\120\
---------------------------------------------------------------------------

    \117\ Imperial Ozone Plan, App. F (``Modeling Attainment 
Demonstration: Photochemical Modeling for the Imperial County 
Nonattainment Area 8-Hour Ozone State Implementation Plan'').
    \118\ Id., App. G (``Photochemical Modeling Protocol: 
Photochemical Modeling for the 8-Hour Ozone and Annual/24-hour 
PM2.5 State Implementation Plans'').
    \119\ Id., App. H (``Modeling Emission Inventory for the 8-Hour 
Ozone State Implementation Plan in the Imperial Nonattainment 
Area'').
    \120\ Id., App. I (``179B Attainment Demonstration for the 2017 
Imperial County State Implementation Plan for the 2008 8-Hour Ozone 
Standard'').
---------------------------------------------------------------------------

    For photochemical modeling for the Imperial Ozone Plan's attainment 
demonstration, CARB and Imperial County APCD used the Community 
Multiscale Air Quality (CMAQ) model developed by the EPA.\121\ The 
overall CMAQ air quality modeling domain covering the entire State of 
California has a horizontal grid size resolution of 12 kilometer (km) 
with 107 x 97 lateral grid cells for each vertical layer and extends 
from the Pacific Ocean in the west to eastern Nevada in the east and 
from the U.S.-Mexico border in the south to the California-Oregon 
border in the north. The smaller nested domain used to model the 
Imperial County nonattainment area covers southern California 
(including the South Coast, San Diego, and Salton Sea air basins), has 
a finer scale 4 km grid resolution, and includes 156 x 102 lateral grid 
cells.
---------------------------------------------------------------------------

    \121\ CMAQ model version 5.0.2, released by the EPA in May 2014. 
Further information on CMAQ is available at: https://www.cmascenter.org/cmaq/.
---------------------------------------------------------------------------

    To prepare meteorological input for CMAQ, CARB and the District 
used the Weather and Research Forecasting (WRF) model version 3.6.1 
from the National Center for Atmospheric Research.\122\ The WRF 
modeling used routinely available meteorological and air quality data 
collected during 2012.
---------------------------------------------------------------------------

    \122\ The overall WRF meteorological modeling domain covers 
California's neighboring states, and major portions of the next 
outer ring of states, with 36-kilometer (km) resolution (i.e., grid 
cell size); it has nested domains with 12 km and 4 km resolution, 
with the latter, innermost covering the entire State of California; 
and it has 30 vertical layers extending up to 16 km.

---------------------------------------------------------------------------

[[Page 58653]]

    The peak ozone levels in California for a given year at any monitor 
tend to occur between May and September. Therefore, the Imperial Ozone 
Plan's attainment demonstration modeled the May to September period for 
both 2012 and 2017 to ensure simulation for the top ozone days in 
Imperial County.
    The ozone model (CMAQ) and meteorological model (WRF) results and 
performance statistics are described in Appendix F of the Imperial 
Ozone Plan. Tables of statistics recommended in the Modeling Guidance 
for 8-hour ozone are provided for each of the three Imperial ozone 
monitoring sites.\123\ Time series plots of the hourly, 1-hour daily 
maximum, and 8-hour daily maximum ozone data for each of the three 
monitors located in the Imperial County can be found in the 
supplementary material.
---------------------------------------------------------------------------

    \123\ Imperial Ozone Plan, App. F, Table 8.
---------------------------------------------------------------------------

    After CARB and Imperial County APCD confirmed the model performance 
for the 2012 base case, they applied the model to develop RRFs for the 
attainment demonstration.\124\ CARB and the District conducted four 
sets of simulations for this purpose: (1) A base year simulation for 
2012 to verify that the model reasonably reproduced the observed air 
quality; (2) a reference year simulation for 2012, which was the same 
as the base year simulation but excluded event-influenced data such as 
wildfires; \125\ (3) a future year simulation for 2017 with Mexican 
emissions that were the same as the reference year simulation, except 
that projected anthropogenic emissions for 2017 were used in lieu of 
2012 emissions; and (4) a future year simulation for 2017 without 
Mexican emissions that was the same as the reference year simulation, 
except that projected anthropogenic emissions for 2017 were used in 
lieu of 2012 emissions and Mexican anthropogenic emissions in the 
modeling domain were removed.
---------------------------------------------------------------------------

    \124\ Id., section 8.2 (``Attainment Demonstration''), and App. 
F, Section 5.3 (``Relative Response Factors, Future Design Values, 
and the Impact from Mexico Anthropogenic Emissions'').
    \125\ Certain data modification and exclusion is allowed, as 
described in the EPA's ``Modeling Guidance for Demonstrating Air 
Quality Goals for Ozone, PM2.5 and Regional Haze,'' 
November 29, 2018, section 4.1.1 (``Establishing the Base Design 
Value'').
---------------------------------------------------------------------------

    The modeled attainment test carried out by CARB and the District is 
consistent with the Modeling Guidance. The RRFs were calculated as the 
ratio of future to base year concentrations. This calculation was done 
for each monitor using the top 10 ozone days over 60 ppb, i.e., using 
the base year concentration in the highest of the three by three 
modeling grid cells centered on the monitor, and the future 
concentration from the same day and grid cell, with some exclusions, 
e.g., if there were too few days above 60 ppb.
    The resulting RRFs were then applied to 2012 weighted base year 
design values \126\ for each monitor to arrive at 2017 future year 
design values.\127\ The results based on CARB modeling are listed in 
Table 3 of this proposed rule. The highest predicted 2017 ozone design 
value (including the Mexican emissions inventory) is 79 ppb at the El 
Centro site, which exceeds the 2008 8-hour ozone NAAQS of 75 ppb. When 
the anthropogenic emissions inventory from Mexico (within the modeling 
domain) is removed, the resulting 2017 ozone design values at each of 
the three sites (Niland, El Centro, and Calexico) are below 75 ppb. 
CARB concludes that this supports a demonstration of attainment of the 
2008 ozone NAAQS but for emissions from Mexico.\128\
---------------------------------------------------------------------------

    \126\ The Modeling Guidance recommends that RRFs be applied to 
the average of three 3-year design values centered on the base year. 
In this case the RRFs were applied to the design values for 2010-
2012, 2011-2013, and 2012-2014. This amounts to a 5-year weighted 
average of individual year 4th high concentrations, centered on the 
base year of 2012, and so is referred to as a weighted design value.
    \127\ Imperial Ozone Plan, Table 8-2.
    \128\ Imperial Ozone Plan, 8-5.
    \129\ CARB Staff Report, September 22, 2017, App. A 
(``Supplemental Weight of Evidence Analysis: 2014-2016 Exceedance 
Day Hysplit Analysis'').
    \130\ According to the Imperial Ozone Plan, the Mexicali Region 
includes the City of Mexicali and surrounding metropolitan area, has 
five times the population of Imperial County, and emits about four 
times the NOX and VOC of Imperial County. Imperial Ozone 
Plan, 1-2 and Table 8-1.

                       Table 3--CARB's Estimated 2017 Design Values Based on CARB Modeling
----------------------------------------------------------------------------------------------------------------
                                                                               Predicted 2017    Predicted 2017
                                                             2012 base year     design value      design values
                 Monitoring site (AQS ID)                     design value      with Mexican     without Mexican
                                                                  (ppb)           emission          emission
                                                                               inventory (ppb)   inventory (ppb)
----------------------------------------------------------------------------------------------------------------
Niland (06-025-4004)......................................              70.3                67                64
El Centro (06-025-1003)...................................              81.0                79                68
Calexico (06-025-0005)....................................              76.3                75                62
----------------------------------------------------------------------------------------------------------------

    The ``CARB Review of the Imperial County 2017 State Implementation 
Plan for the 2008 8-Hour Ozone Standard'' (``CARB's Staff Report'') for 
the Imperial Ozone Plan includes an analysis of back trajectories 
modeled using the National Oceanic and Atmospheric Administration's 
(NOAA) Hybrid Single Particle Lagrangian Integrated Trajectory 
(HYSPLIT) Model.\129\ The analysis focused on exceedance days at the 
Calexico and El Centro sites for the years 2014, 2015, and 2016. The 
analysis shows that the majority of exceedance days at each site had 
back trajectories for at least 4 of the 6 hours leading up to the last 
hour that exceeded 75 ppb that originated from or went through Northern 
Mexico, indicating influence from sources in the Mexicali Region.\130\
    Finally, the Plan contains additional analysis in Appendix I, which 
is summarized in section 8.3 of the Plan. The analysis presents trends 
from 1995-2000 in NOX and VOC emissions, ozone 
concentrations, design values, exceedance days, and the top 30 daily 
maximum 8-hour ozone concentrations.
3. EPA Review of State's Submission
    The EPA has evaluated the several lines of evidence presented by 
CARB and proposes that together they support the conclusion that 
Imperial County would attain the 2008 ozone NAAQS by the Moderate area 
attainment date but for emissions emanating from Mexico. We present our 
evaluation of CARB's photochemical modeling from the Imperial Ozone 
Plan in this section of this proposed rule. We present our evaluation 
of CARB's scaling of its own modeling and EPA modeling, back trajectory 
modeling, and emissions inventory comparison from CARB's additional 
analyses in section III of this proposed rule, as described further 
below.
    Regarding CARB's photochemical modeling from the Imperial Ozone 
Plan, the EPA reviewed CARB's attainment demonstration and agrees that 
it supports the conclusion that the 8-hour

[[Page 58654]]

ozone design values at each ozone monitoring site in Imperial County 
would have predicted attainment for the 2008 ozone NAAQS of 75 ppb by 
2017 but for emissions emanating from Mexico. We include a technical 
support document (TSD), ``Imperial County Ozone Plan and Determination 
Regarding Attainment,'' August 2019 (``EPA's 179B TSD for Imperial 
County Ozone''), which provides further information regarding our 
evaluation of the Imperial Ozone Plan's demonstration of attainment but 
for emissions from Mexico, in the docket of this proposed rule.
    The Modeling Guidance recognizes both CMAQ and WRF as technically 
sound, state-of-the-science models. The size of the modeling domain and 
the horizontal and vertical grid resolution used in these models are 
sufficient to model ozone in Imperial County.
    CARB calculated the model performance statistics using simulated 
data at Niland, El Centro, and Calexico, respectively, from the 
modeling in the Imperial Ozone Plan. The modeling performance 
statistical metrics for hourly, daily maximum 1-hour, and daily maximum 
8-hour ozone from this work are consistent with, and in many cases 
superior to, values reported by other studies in the literature.\131\ 
The mean bias for daily maximum 8-hour ozone ranged from approximately 
-7 ppb to +13 ppb, while the mean error ranged from around 4 ppb to 22 
ppb, and the root mean squared error ranged from approximately 8 ppb to 
23 ppb. The 8-hour maximum performance statistics during the 2012 ozone 
season for each monitor in Imperial County fall within these ranges. 
Each of these ranges is similar in magnitude to the statistics 
presented in the Imperial Ozone Plan.\132\ The Modeling Guidance 
cautions against using comparisons to performance benchmarks as pass/
fail tests and stresses their use in assessing general confidence and 
in guiding refinement of model inputs when statistics fall outside 
benchmark ranges. In summary, the Imperial Ozone Plan's modeling 
performance statistics appear satisfactory, and support CARB's 
determination that Imperial County would attain the 2008 ozone NAAQS by 
the 2017 attainment year but for emissions from Mexico.
---------------------------------------------------------------------------

    \131\ Imperial Ozone Plan, App. F, Figure 15, 34.
    \132\ Id., App. F, Table 10 and App. F, page 33. See also, 
Simon, H., Baker, K.R., and Phillips, S., ``Compilation and 
interpretation of photochemical model performance statistics 
published between 2006 and 2012,'' Atmospheric Environment, 2012, 
Vol. 61, 124 to 139.
---------------------------------------------------------------------------

    In addition to the analysis in CARB's Staff Report for the Imperial 
Ozone Plan of back trajectories for the exceedance days that occurred 
during 2014-2016,\133\ CARB also provided updated 8-hour trajectories 
for 2015-2017 in the ``Imperial County Clean Air Act Section 179B(b) 
Retrospective Analysis for the 75 ppb 8-hour Ozone Standard'' 
(``Imperial Ozone Retrospective Demonstration,''), submitted July 3, 
2018.\134\ This updated analysis includes the three years in the 2015-
2017 attainment design value period, and also includes back 
trajectories for each hour of the high 8-hour ozone period (i.e., 8 
back trajectories per exceedance), rather than the 6 back trajectories 
leading to the last 1-hour that exceeded 75 ppb, as presented in the 
CARB Staff Report. While both the original and updated analyses serve 
to investigate the degree to which Mexican emissions may affect 
Imperial County, we focused our evaluation on CARB's updated analysis 
given that it addresses the attainment year design value period and a 
fuller complement of hours per exceedance.\135\ Our evaluation of 
CARB's updated back trajectory analysis is included in sections III.B.3 
and III.C of this proposed rule that are part of our overall 
presentation of the Imperial Ozone Retrospective Demonstration.
---------------------------------------------------------------------------

    \133\ CARB Staff Report, App. A (``Supplemental Weight of 
Evidence Analysis: 2014-2016 Exceedance Day Hysplit Analysis). In a 
general case, back trajectories may not be available as part of a 
section 179B(a) demonstration because they rely on having monitored 
data. However, due to the timing of the Imperial Ozone Plan 
development, monitored data for 2015 and 2016 were available and 
CARB included back trajectory modeling in its section 179B(a) 
demonstration.
    \134\ Imperial Ozone Retrospective Demonstration, App. A.
    \135\ CARB also noted that 8 hours of data better represented 
the hours of the day that contributed to 8-hour ozone exceedance. 
Imperial Ozone Retrospective Demonstration, 9.
---------------------------------------------------------------------------

    The Imperial Ozone Retrospective Demonstration also includes CARB's 
emissions inventory comparison, which is also relevant to our 
evaluation of the Imperial Ozone Plan's attainment demonstration. The 
emissions inventory comparison describes the small scale of Imperial 
County emissions relative to those from Mexico. These results support 
the conclusion that Imperial County would attain the 2008 ozone NAAQS 
by the 2017 attainment year but for emissions from Mexico. Our 
evaluation of CARB's emissions inventory comparison is included in 
sections III.B.4 and III.C below as part of our discussion of the 
Imperial Ozone Retrospective Demonstration.
    In addition, Appendix I of the Plan contains other analyses, 
including trends in ambient air quality and emissions and additional 
emissions controls and reductions summarized in section 8.3 of the 
Plan. These analyses support and corroborate the modeling used in the 
attainment demonstration of attainment in 2017 but for emissions 
emanating from Mexico. For example, the trends analyses show long-term 
downward trends that continue through 2015, the latest year available 
prior to development of the Imperial Ozone Plan.\136\
---------------------------------------------------------------------------

    \136\ Imperial Ozone Plan, App. I, Appendix (to App. I) entitled 
``Imperial County Nonattainment Area 8-hour Ozone Plan,'' section 
2.3 (``Daily Maximum 8-hour Ozone Air Quality Trends'').
---------------------------------------------------------------------------

    Also, EPA modeling conducted in support of other actions is useful 
for estimating the amount of ozone resulting from ozone precursors 
emitted in Mexico. The EPA modeled interstate air pollution transport 
across the continental United States with ozone source apportionment 
technology for the Cross-State Air Pollution Rule (CSAPR) Update.\137\ 
The ozone contribution at each receptor \138\ was tracked from 
different sources, such as individual states, Mexico and Canada, as 
well as boundary conditions. Two sets of modeling results have been 
released, one for year 2017 and one for year 2023. Both cases were 
simulated using a 2011 base year modeling platform, which means the 
2011 meteorology and boundary conditions were applied to both future 
years' (2017 and 2023) cases. The predicted design values with and 
without Mexican contribution at each Imperial County site are shown in 
Table 4.\139\ When the contribution of Mexican anthropogenic

[[Page 58655]]

emissions (within the modeling domain) is removed, the resulting 2017 
ozone design values at each of the three sites (Niland, El Centro, and 
Calexico) are below 75 ppb, which supports the Imperial Ozone Plan's 
demonstration of attainment for the 2008 ozone NAAQS but for emissions 
from Mexico.
---------------------------------------------------------------------------

    \137\ 81 FR 74504 (October 26, 2016); ``Air Quality Modeling 
Technical Support Document for the Final Cross State Air Pollution 
Rule Update,'' OAQPS, EPA, August 2016, including 2017 modeling 
results (``CSAPR Update Air Quality Modeling TSD''), and associated 
spreadsheet with design values and contributions (``CSAPR Update 
2008 Ozone Design Values and Contributions Spreadsheet''); and 
Memorandum from Stephen D. Page, Director, OAQPS, EPA, 
``Supplemental Information on the Interstate Transport State 
Implementation Plan Submissions for the 2008 Ozone National Ambient 
Air Quality Standards under Clean Air Act Section 
110(a)(2)(D)(i)(I),'' October 27, 2017, including 2023 modeling 
results (``Supplemental 2008 Ozone Transport Memo''). Further 
information on the CSAPR Update rule and the Supplemental 2008 Ozone 
Transport Memo are available at the following websites, 
respectively: https://www.epa.gov/airmarkets/final-cross-state-air-pollution-rule-update; and https://www.epa.gov/airmarkets/october-2017-memo-and-supplemental-information-interstate-transport-sips-2008-ozone-naaqs.
    \138\ Receptors were regulatory monitors at each ambient air 
quality monitoring site for ozone.
    \139\ The CSAPR Update 2008 Ozone Design Values and 
Contributions Spreadsheet lists Mexican and Canadian contribution as 
one value for each receptor. However, for purposes of this proposed 
rule, the EPA assumes that the Canadian influence is negligible at 
Imperial County receptors given that Imperial County is about 1,700 
km from Canada whereas the County borders Mexico. Thus, we express 
the Mexican and Canadian contribution as ``Contribution from Mexican 
Emissions'' in Table 4.

                      Table 4--EPA's 2015-2017 Design Value Estimates Based on EPA Modeling
----------------------------------------------------------------------------------------------------------------
                                                             Predicted 2015-
                                             2011 CSAPR        2017 design                       Predicted 2015-
                                          update base year     value with       Contribution       2017 design
                  Site                      design value         Mexican        from Mexican     values without
                                                (ppb)           emissions      emissions (ppb)  Mexican emission
                                                             inventory (ppb)                     inventory (ppb)
----------------------------------------------------------------------------------------------------------------
Niland..................................              71.3              66.7              6.95              59.8
El Centro...............................              81.0              79.3             12.19              67.1
Calexico................................              74.0                73              13.9              59.1
----------------------------------------------------------------------------------------------------------------

    In conclusion, the EPA finds that the various lines of evidence 
described above support the demonstration of attainment by 2017 but for 
emissions emanating from Mexico. Given the extensive discussion of 
modeling procedures, tests, and performance analyses called for in the 
Modeling Guidance and the good performance of CARB's model, the EPA 
agrees that CARB's modeling supports the demonstration of attainment 
but for Mexican emissions. CARB's model shows that, in 2017, with 
Mexican emissions included, the ozone design value at one monitor would 
exceed the 75 ppb standard, but by removing the contribution of Mexican 
anthropogenic emissions, the ozone design values at each of the three 
sites (Niland, El Centro, and Calexico) would be below 75 ppb. 
Therefore, the EPA agrees that CARB's modeling of the projected year 
2017 both with and without anthropogenic emission inventory from Mexico 
(within the modeling domain) supports the conclusion that Imperial 
County would attain the 2008 ozone NAAQS but for Mexican emissions.
    Regarding CARB's analyses of back trajectories, emissions, and EPA 
air quality modeling, we incorporate our evaluation and discussion 
presented in section III of this proposed rule into our evaluation of 
the State's section 179B(a) demonstration. These lines of evidence, as 
well as CARB's modeling discussed above, together support the 
conclusion that Imperial County would attain the 2008 ozone NAAQS in 
2017 but for emissions emanating from Mexico.

H. Rate of Progress and Reasonable Further Progress Demonstration

1. Statutory and Regulatory Requirements
    Requirements for RFP for Moderate ozone nonattainment areas are 
specified in CAA section 182(b)(1).\140\ CAA section 182(b)(1) requires 
that ozone nonattainment areas that are classified as Moderate or above 
demonstrate a 15% reduction in VOC within the first six years of the 
planning period. The EPA has typically referred to section 182(b)(1) as 
the Rate of Progress (ROP) requirement.\141\ Except as specifically 
provided in CAA section 182(b)(1)(C), emissions reductions from all 
SIP-approved, federally promulgated, or otherwise SIP-creditable 
measures that occur after the baseline year are creditable for purposes 
of demonstrating that the RFP targets are met.\142\
---------------------------------------------------------------------------

    \140\ CAA section 182(b)(1) is the specific requirement 
regarding RFP in Part D, Subpart 2, and is applicable to ozone 
nonattainment areas classified Moderate and higher. CAA sections 
171(1) and 172(c)(2) in Part D, Subpart 1 address RFP for all 
nonattainment pollutants. E.g., CAA section 171(1), which defines 
RFP as annual incremental reductions in emissions of the relevant 
air pollutant as are required under part D (``Plan Requirements for 
Nonattainment Areas'') or may reasonably be required by the EPA for 
the purpose of ensuring attainment of the applicable NAAQS by the 
applicable attainment date.
    \141\ The 2008 Ozone SRR provides that, for areas classified 
Moderate or higher for the 2008 8-hour ozone standard, the ROP 
requirements of CAA section 182(b)(1) will be met if the area has a 
fully approved 15% ROP plan for the 1979 1-hour or 1997 8-hour ozone 
standards (provided the boundaries of the ozone nonattainment areas 
are the same). For more information about how the RFP requirement of 
section 172(c)(2) applies in such areas, see 84 FR 28157 (June 17, 
2019). Imperial County does not have a fully approved 15% ROP plan 
for either the 1979 1-hour or the 1997 8-hour ozone standards. For 
the 1979 1-hour ozone NAAQS, the EPA classified Imperial County as a 
CAA section 185A (or ``transitional'') area and, thus, it was not 
subject to the ROP requirement. For the 1997 8-hour ozone NAAQS, the 
EPA initially designated Imperial County as a Marginal nonattainment 
area and later reclassified the area to Moderate, triggering the ROP 
requirement, but subsequently issued a clean data determination, 
which suspended attainment-related planning requirements, including 
the ROP requirement. 73 FR 8209 (February 13, 2008); 74 FR 63309 
(December 3, 2009). Therefore, the 15% ROP requirement of section 
182(b)(1) remains applicable to Imperial County.
    \142\ Because the EPA has determined that the passage of time 
has caused the effect of certain exclusions to be de minimis, the 
RFP demonstration is no longer required to calculate and 
specifically exclude reductions from measures related to motor 
vehicle exhaust or evaporative emissions promulgated by January 1, 
1990; regulations concerning Reid vapor pressure promulgated by 
November 15, 1990; measures to correct previous RACT requirements; 
and, measures required to correct previous inspection and 
maintenance (I/M) programs. 40 CFR 51.1110(a)(7).
---------------------------------------------------------------------------

    As noted in section II.E of this proposed rule, future year 
emissions inventories are necessary to show the projected effectiveness 
of SIP control measures and must reflect the most recent population, 
employment, travel, and congestion estimates for the area. EPA 
regulations require that the base year emissions inventory be 
consistent with the baseline year for the RFP demonstration.\143\ 
Furthermore, the 2008 Ozone SRR requires the RFP baseline year to be 
the most recent calendar year for which a complete triennial inventory 
was required to be submitted to the EPA.\144\ For the purposes of 
developing RFP demonstrations for the Imperial County nonattainment 
area for the 2008 ozone standards, the applicable triennial inventory 
year is 2011. As discussed previously, the South Coast II decision 
vacated the 2008 Ozone SRR's provision allowing states to use an 
alternative baseline year for RFP.\145\
---------------------------------------------------------------------------

    \143\ 40 CFR 51.1115(a).
    \144\ 2008 Ozone SRR, 12272; 40 CFR 51.1110(b); and the Air 
Emissions Reporting Requirements at 40 CFR part 51 subpart A.
    \145\ South Coast Air Quality Management District v. EPA, 882 
F.3d 1138 (D.C. Cir. 2018).
---------------------------------------------------------------------------

2. Summary of State's Submission
    CARB developed the 2018 SIP Update and submitted it to the EPA on 
December 5, 2018, in part to address the impacts of the South Coast II 
decision on several plans for ozone nonattainment areas in California 
that, like the Imperial Ozone Plan, had relied

[[Page 58656]]

on the provision in the 2008 Ozone SRR that states could use years 
other than 2011 as the RFP baseline year to demonstrate RFP. The 
portions of 2018 SIP Update related to Imperial County include an 
emissions inventory consistent with the new RFP baseline year of 2011, 
an updated inventory for the RFP milestone year of 2017, and a revised 
RFP demonstration using 2011 as the RFP baseline year and the updated 
2017 RFP milestone inventory.\146\
---------------------------------------------------------------------------

    \146\ 2018 SIP Update, section II (``SIP Elements for Imperial 
County''), 11-13, and App. A (``Nonattainment Area Inventories''), 
A-3 to A-6.
---------------------------------------------------------------------------

    To develop the 2011 and 2017 inventories, CARB used emissions as 
reported by larger point sources to the District and, for smaller point 
sources (stationary area sources), areawide sources and mobile sources, 
back-casted emissions from the base year inventory of 2012.\147\ CARB 
explains that back-casted emissions rely on the same assumptions 
regarding growth and emissions reductions from adopted control measures 
(i.e., ``growth parameters and control profiles'') that are used to 
project emissions inventories in future years.\148\ CARB also explains 
that the 2011 RFP baseline emissions inventory and the 2012 base year 
emissions inventory are consistent with one another, as required by the 
2008 Ozone SRR: Both inventories use actual emissions as reported to 
the District by larger point sources, and emissions for other sources 
(stationary area sources, areawide sources, and mobile sources) in the 
2011 baseline inventory are back-casted from the 2012 base year 
inventory.\149\
---------------------------------------------------------------------------

    \147\ 2018 SIP Update, 5, 11.
    \148\ Id. at 5.
    \149\ Id.
---------------------------------------------------------------------------

    Table 5 presents a summary of the 2011 RFP baseline inventory and 
the updated 2017 RFP milestone inventory.

                     Table 5--Summary of Ozone Precursor Summer Emissions for 2011 and 2017
----------------------------------------------------------------------------------------------------------------
                                                         2011                                2017
             Source category             -----------------------------------------------------------------------
                                              NOX (tpd)        VOC  (tpd)         NOX (tpd)        VOC  (tpd)
----------------------------------------------------------------------------------------------------------------
Stationary Sources......................               1.7               1.3               1.3               1.2
Area Sources............................               0.7               8.4               0.2               5.7
On-road Mobile Sources..................              11.3               4.5               6.5               3.1
Non-road Mobile Sources.................               9.2               5.2               7.1               3.5
rrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrr
    Total for Imperial County...........              23.0              19.5              15.2              13.5
----------------------------------------------------------------------------------------------------------------
Source: 2018 SIP Update, Table II-1 (noting that numbers may not add up due to rounding) and App. A, A-3 to A-6.

    The 2018 SIP Update's RFP demonstration calculates future year VOC 
targets from the 2011 baseline, consistent with CAA 182(b)(1), which 
requires a 15% reduction in VOC within six years of the RFP baseline 
year for a Moderate ozone nonattainment area as shown in Table 6.

                 Table 6--Rate of Progress Demonstration
------------------------------------------------------------------------
                                       VOC (tpd, unless otherwise noted)
                                     -----------------------------------
                                            2011              2017
------------------------------------------------------------------------
1. Baseline VOC.....................              19.5              13.5
2. Transportation conformity safety   ................               0.8
 margin \a\.........................
3. Baseline VOC + safety margin       ................              14.3
 (Line 1 + Line 2)..................
4. Required VOC emission reduction,   ................               15%
 % \b\..............................
5. Target VOC Level (Line 1 (2011)-   ................              16.6
 Line 4 (2017) x Line 1 (2011)).....
6. Apparent Surplus in VOC emission   ................               2.3
 reductions (Line 5-Line 3) \c\.....
7. Apparent Surplus in VOC emission   ................             11.7%
 reductions, % (Line 6/Line 1
 (2017)) \c\........................
RFP Met?............................  ................               YES
------------------------------------------------------------------------
Note: This table is adapted from the 2018 SIP Update, Table II-2 and
  CARB's Technical Clarification Letter, Attachment A.
\a\ CARB Technical Clarification Letter, Attachment A.
\b\ While the 2018 SIP Update characterizes the % change as (VOC or
  NOX), in fact, the required change is just for VOC, per our discussion
  of the ROP requirement herein.
\c\ The CARB Technical Clarification Letter identifies 2.2 tpd and 11.4%
  as the apparent surplus in VOC emission reductions. The difference
  between the values in the CARB Technical Clarification Letter and this
  table is due to rounding. Numbers listed here in Table 6 are
  calculated as shown in the table.

    CARB concludes that the RFP demonstration for Imperial County in 
the 2018 SIP Update meets the CAA's applicable requirements for RFP.
3. EPA Review of State's Submission
    We have reviewed the portions of the 2018 SIP Update relating to 
Imperial County, including the 2011 baseline and 2017 emissions 
inventories and the updated RFP demonstration that uses a 2011 baseline 
year, and CARB's Technical Clarification Letter for consistency with 
CAA and regulatory requirements and EPA guidance. Based on our review 
of the emissions inventory documentation in the 2018 SIP Update, as 
well as the Imperial Ozone Plan, we find that CARB and the District 
used the most recent planning and activity assumptions, emissions 
models, and methodologies in developing the RFP baseline and milestone 
year inventories.
    Regarding the 2008 Ozone SRR's requirement that the base year 
inventory be consistent with the baseline year for

[[Page 58657]]

the RFP demonstration, we note that 2012 is the year used for the base 
year inventory, while 2011 is the year used for the baseline inventory 
for the RFP demonstration. However, both the 2012 base year inventory 
and 2011 RFP baseline inventory use actual emissions reported by larger 
point sources, and, for other sources (e.g., stationary area sources, 
areawide sources, and mobile sources), the 2011 RFP baseline inventory 
is back-casted from the 2012 base year inventory, and therefore based 
on the same data. Therefore, we find that selection of 2012 as the base 
year for the emissions inventory is consistent with the 2011 baseline 
year for the RFP demonstration for this nonattainment area as required 
by 40 CFR 51.1115(a).
    In addition to the 2011 RFP baseline inventory, the 2018 SIP Update 
also includes an inventory for the RFP milestone year of 2017. Similar 
to the 2011 RFP baseline inventory, the 2017 RFP milestone inventory 
includes actual emissions reported for 2017 for certain stationary 
sources and forecasted emissions for other sources using updated 
activity data, where available. The 2017 RFP milestone inventory from 
the 2018 SIP Update (13.5 tpd of VOC) is smaller than the 2017 
emissions inventory from the Imperial Ozone Plan (16.85 tpd of VOC). 
These emission inventory updates are directionally consistent with the 
observed 2015-2017 design value of 77 ppb as compared to the modeled 
2015-2017 design value of 79 ppb and suggest that Imperial County made 
greater progress towards attaining the 2008 ozone NAAQS than was 
originally predicted, even though the area did not actually attain the 
standards.
    We also reviewed the calculations in Table II-2 of the 2018 SIP 
Update and CARB's Technical Clarification Letter, Attachment A, as 
presented in Table 6 of this proposed rule, and find that CARB and the 
District used an appropriate calculation method to demonstrate RFP. 
Specifically, we reviewed the 2011 and 2017 emissions inventories 
included in the 2018 SIP Update, as discussed in the preceding 
paragraphs of this evaluation subsection; the inclusion of a safety 
margin in the 2017 VOC motor vehicle emission budgets and whether the 
area still achieves sufficient emissions reductions to demonstrate RFP 
with such safety margin; \150\ and the comparison of the VOC emissions 
reductions against the 15% ROP requirement. As shown in Table 6, the 
RFP demonstration shows a 26.7% reduction in VOC emissions from 2011 to 
2017 (i.e., 15% required reduction plus 11.7% surplus reduction). Such 
reductions satisfy the ROP requirement for Imperial County for the 2008 
ozone NAAQS.
---------------------------------------------------------------------------

    \150\ A safety margin is ``the amount by which the total 
projected emissions from all sources of a given pollutant are less 
than the total emissions that would satisfy the applicable 
requirement for reasonable further progress, attainment, or 
maintenance.'' 40 CFR 93.101. A safety margin allows future 
transportation projects to increase on-road mobile source emissions 
provided they satisfy applicable requirements (e.g., support a 
demonstration of RFP in Imperial County in 2017) and the emissions 
from such future projects are calculated using the same method.
---------------------------------------------------------------------------

    For these reasons, we propose to determine that the State has 
demonstrated RFP in the applicable milestone year of 2017, consistent 
with CAA requirements and EPA guidance. We therefore propose to approve 
the RFP demonstrations under section 182(b)(1) of the CAA and 40 CFR 
51.1110(a)(4)(i).

I. Motor Vehicle Emission Budgets

1. Statutory and Regulatory Requirements
    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 timely attainment of the standards. Conformity to the SIP's 
goals means that such actions will not: (1) Cause or contribute to 
violations of a NAAQS, (2) worsen the severity of an existing 
violation, or (3) delay timely attainment of any NAAQS or any interim 
milestone.
    Actions involving Federal Highway Administration (FHWA) or Federal 
Transit Administration (FTA) funding or approval are subject to the 
EPA's transportation conformity rule, codified at 40 CFR part 93, 
subpart A. Under this rule, metropolitan planning organizations in 
nonattainment and maintenance areas coordinate with state and local air 
quality and transportation agencies, the EPA, the FHWA, and the 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 emission budgets (MVEBs or ``budgets'') 
contained in all control strategy SIPs. Budgets are generally 
established for specific years and specific pollutants or precursors. 
Ozone plans should identify budgets for on-road emissions of ozone 
precursors (NOX and VOC) in the area for each RFP milestone 
year and the attainment year, if the plan demonstrates attainment.\151\
---------------------------------------------------------------------------

    \151\ 40 CFR 93.102(b)(2)(i).
---------------------------------------------------------------------------

    For budgets to be approvable, they must meet, at a minimum, the 
EPA's adequacy criteria in 40 CFR 93.118(e)(4). To meet these 
requirements, the budgets must be consistent with the attainment and 
RFP requirements and reflect all the motor vehicle control measures 
contained in the attainment and RFP demonstrations.\152\
---------------------------------------------------------------------------

    \152\ 40 CFR 93.118(e)(4)(iii), (iv) and (v). For more 
information on the transportation conformity requirements and 
applicable policies on MVEBs, please visit our transportation 
conformity website at: http://www.epa.gov/otaq/stateresources/transconf/index.htm.
---------------------------------------------------------------------------

    The EPA's process for determining adequacy of a budget consists of 
three basic steps: (1) Providing public notification of a SIP 
submission; (2) providing the public the opportunity to comment on the 
budget during a public comment period; and, (3) making a finding of 
adequacy or inadequacy.\153\
---------------------------------------------------------------------------

    \153\ 40 CFR 93.118(f)(2).
---------------------------------------------------------------------------

2. Summary of State's Submission
    The Imperial Ozone Plan includes NOX and VOC budgets for 
Imperial County for 2017 and states that they are consistent with the 
emissions inventory used in the Plan's section 179B(a) 
demonstration.\154\ The budgets were calculated by SCAG using updated 
vehicle miles traveled estimates and speed distribution data in the 
SCAG's 2016 RTP/SCS and updated emission rates and planning assumptions 
from EMFAC2014.\155\ They reflect average summer weekday emissions 
consistent with the 2017 RFP milestone year for the 2008 ozone NAAQS. 
The 2017 on-road mobile source emissions are 6.53 tpd of NOX 
and 3.13 tpd of VOC, and the 2017 budgets in the Imperial Ozone Plan 
are 7 tpd of NOX and 4 tpd of VOC. In CARB's Technical 
Clarification Letter, CARB identifies the difference between the 2017 
on-road mobile source emissions and the 2017 budgets as a

[[Page 58658]]

safety margin of 0.4 tpd of NOX and 0.8 tpd of VOC.\156\
---------------------------------------------------------------------------

    \154\ Imperial Ozone Plan, 10-3. We note that the 2018 SIP 
Update simply states that the 2017 budgets in the Imperial Ozone 
Plan are still applicable. 2018 SIP Update, 13.
    \155\ At the time the Imperial Ozone Plan was developed, 
EMFAC2014 was CARB's latest version of the EMFAC model for 
estimating emissions from on-road vehicles operating in California 
that had been approved into the California SIP. 80 FR 77337. It was 
the appropriate model to use for SIP development purposes, as noted 
in the EPA's implementation rule for the 2015 ozone NAAQS. 83 FR 
62998, 63022, n. 54 (December 6, 2018).
    \156\ CARB's Technical Clarification Letter, Attachment A. We 
note that the hundredths place of the 2017 emissions amounts are 
rounded up to the nearest whole number (i.e., 6.53 tpd + 0.4 tpd = 
6.93 tpd, rounded to 7 tpd NOX; and 3.13 tpd + 0.8 tpd = 
3.93 tpd, rounded up to 4 tpd VOC).
---------------------------------------------------------------------------

    CARB also asked that the EPA limit the duration of the approval of 
the 2017 budgets in the Imperial Ozone Plan and includes an explanation 
for why the budgets have become, or will become, outdated or 
deficient.\157\ In short, CARB has requested that we limit the duration 
of the approval of the budgets in anticipation, in the near term, of 
the EPA's approval of EMFAC2017, which is an updated version of the 
model (EMFAC2014) used for the budgets in the Imperial Ozone Plan.\158\ 
EMFAC2017 updates vehicle mix and emissions data of the currently 
approved version of the model, EMFAC2014.
---------------------------------------------------------------------------

    \157\ Letter dated December 5, 2018 from Richard Corey, 
Executive Officer, CARB, to Mike Stoker, Regional Administrator, EPA 
Region IX, 2, and CARB's Technical Clarification Letter, 1-2.
    \158\ The EPA has approved EMFAC2017 for use in SIP development 
and transportation conformity decisions in California. 84 FR 41717.
---------------------------------------------------------------------------

    CARB explains that, upon approval of EMFAC2017, the budgets from 
the Imperial Ozone Plan, for which we are proposing approval in today's 
action, will become outdated and will need to be revised using 
EMFAC2017 within the grace period established in our approval of 
EMFAC2017. This in turn would allow for the EPA to use the adequacy 
process to review and replace the budgets proposed for approval in this 
notice so that they can be used in future conformity determinations for 
the SCAG regional transportation plan and program, as applied to 
Imperial County. In addition, CARB states that, without the ability to 
replace the budgets using the budget adequacy process, the benefits of 
using the updated data may not be realized for a year or more after the 
updated SIP (with the EMFAC2017-derived budgets) is submitted, due to 
the length of the SIP approval process.
3. EPA Review of State's Submission
    We have evaluated the budgets in the Imperial Ozone Plan against 
our adequacy criteria in 40 CFR 93.118(e)(4) as part of our review of 
the budgets' approvability and will complete the adequacy review 
concurrent with our final action on the ozone plan.\159\ The EPA is not 
required under its transportation conformity rule to find budgets 
adequate prior to proposing approval of them.\160\
---------------------------------------------------------------------------

    \159\ Memorandum from Karina O'Connor, Air Planning Office, EPA 
Region IX, ``Adequacy Documentation for Plan Motor Vehicle Emission 
Budgets in September 2017 Imperial Ozone Plan,'' May 24, 2019.
    \160\ Under the transportation conformity regulations, the EPA 
may review the adequacy of submitted motor vehicle emission budgets 
simultaneously with the EPA's approval or disapproval of the 
submitted implementation plan. 40 CFR 93.118(f)(2).
    \161\ 40 CFR 93.118(e)(1).
    \162\ 67 FR 69141 (November 15, 2002), limiting our prior 
approval of MVEB in certain California SIPs.
---------------------------------------------------------------------------

    As discussed in section II.H of this proposed rule, the 2011 RFP 
baseline and 2017 RFP emissions inventories, including the figures for 
mobile sources, were back-casted and forecasted, respectively, from the 
2012 base year emissions inventory. For the reasons discussed in 
section II.H of this proposed rule, we are proposing to approve the RFP 
demonstration in the 2018 SIP Update, including the safety margins 
identified in CARB's Technical Clarification Letter. While only the VOC 
emissions reductions are required for ROP, the Imperial Ozone Plan's 
demonstration of attainment but for emissions emanating from Mexico 
relies on reductions of both NOX and VOC emissions. As 
described in our summary of the State's submission, the 2017 budgets, 
including safety margins, are shown in Table 7, below.

Table 7--2017 Motor Vehicle Emission Budgets for Imperial County for the
                            2008 Ozone NAAQS
------------------------------------------------------------------------
                                                     2017
                                     -----------------------------------
                                          NOX (tpd)         VOC (tpd)
------------------------------------------------------------------------
On-road Mobile Sources..............              6.53              3.13
Safety Margin.......................               0.4               0.8
Motor Vehicle Emission Budget                        7                 4
 (rounded to nearest whole number)..
------------------------------------------------------------------------
Source: 2018 SIP Update, Table II-2 and CARB's Technical Clarification
  Letter, Attachment A.

    The EPA has determined that these budgets are consistent with 
emissions control measures in the SIP and RFP for the 2008 ozone NAAQS. 
They are clearly identified and precisely quantified, and meet all 
other applicable statutory and regulatory requirements, including the 
adequacy criteria in 40 CFR 93.118(e)(4) and (5). In addition, we 
conclude that CARB has identified an appropriate safety margin for the 
2017 NOX and VOC MVEBs and demonstrated how such budgets 
remain consistent with demonstrating RFP, as discussed in section II.F 
of this proposed rule. For these reasons, the EPA is proposing to 
approve the 2017 budgets in the Imperial Ozone Plan for transportation 
conformity purposes for the 2008 ozone NAAQS. Also, we anticipate 
completing the budget adequacy process upon our final rule.
    Under our transportation conformity rule, as a general matter, once 
budgets are approved, they cannot be superseded by revised budgets 
submitted for the same CAA purpose and the same period of years 
addressed by the previously approved SIP until the EPA approves the 
revised budgets as a SIP revision. In other words, as a general matter, 
such approved budgets cannot be superseded by revised budgets found 
adequate, but rather only through approval of the revised budgets, 
unless the EPA specifies otherwise in its approval of a SIP by limiting 
the duration of the approval to last only until subsequently submitted 
budgets are found adequate.\161\
    In this instance, CARB has requested that we limit the duration of 
our approval of the budgets in the Imperial Ozone Plan only until the 
effective date of the EPA's adequacy finding for any subsequently 
submitted budgets. Generally, we will consider a state's request to 
limit an approval of an MVEB only if the request includes the following 
elements: \162\
     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.
    We find that CARB's explanation for why the budgets will become 
outdated

[[Page 58659]]

and why limiting the duration of the approval of the budgets is 
appropriate. This information provides us with a reasonable basis on 
which to limit the duration of the approval of the budgets.
    We note that CARB has not committed to update the budgets as part 
of a comprehensive SIP update, but as a practical matter, CARB must 
submit a SIP revision that includes updated demonstrations as well as 
the updated budgets to meet the adequacy criteria in 40 CFR 
93.118(e)(4); \163\ and thus, we do not need a specific commitment for 
such a plan at this time. For the reasons provided above, and in light 
of CARB's explanation for why the budgets will become outdated and 
should be replaced upon an adequacy finding for updated budgets, we 
propose to limit the duration of our approval of the budgets in the 
Imperial Ozone Plan until new budgets have been found adequate.
---------------------------------------------------------------------------

    \163\ Under 40 CFR 93.118(e)(4), the EPA will not find a budget 
in a submitted SIP to be adequate unless, among other criteria, the 
budgets, when considered together with all other emissions sources, 
are consistent with applicable requirements for RFP and attainment. 
40 CFR 93.118(e)(4)(iv).
---------------------------------------------------------------------------

J. Contingency Measures

1. Statutory and Regulatory Requirements
    Under the CAA, ozone nonattainment areas classified under subpart 2 
as Moderate must include in their SIPs contingency measures consistent 
with section 172(c)(9).\164\ Contingency measures are additional 
controls or measures to be implemented in the event the area fails to 
meet RFP requirements or to attain the NAAQS by the attainment date. 
The SIP should contain trigger mechanisms for the contingency measures, 
specify a schedule for implementation of the measures, and indicate 
that the measures will be implemented without significant further 
action by the state or the EPA.\165\
---------------------------------------------------------------------------

    \164\ Contingency measures in ozone nonattainment areas 
classified under CAA Title I, subpart 2 as Serious or higher must 
also be consistent with CAA section 182(c)(9). However, this 
requirement does not apply to the Imperial County nonattainment 
area, which is classified as Moderate for the 2008 ozone NAAQS.
    \165\ 2008 Ozone SRR, 12285.
---------------------------------------------------------------------------

    Neither the CAA nor the EPA's implementing regulations establish a 
specific amount of emissions reductions that implementation of 
contingency measures must achieve, but the 2008 Ozone SRR reiterates 
the EPA's recommendation that contingency measures should provide for 
emissions reductions approximately equivalent to one year's worth of 
RFP, thus amounting to reductions of 3% of the baseline emissions 
inventory for the nonattainment area.\166\
---------------------------------------------------------------------------

    \166\ Id.
---------------------------------------------------------------------------

    It has been the EPA's longstanding interpretation of section 
172(c)(9) that states may rely on existing federal measures (e.g., 
federal mobile source measures based on the incremental turnover of the 
motor vehicle fleet each year) and state or local measures in the SIP 
already scheduled for implementation that provide emissions reductions 
in excess of those needed to meet any other nonattainment plan 
requirements, such as meeting RACM/RACT, RFP, or expeditious attainment 
requirements. The key is that the statute requires that contingency 
measures provide for additional emissions reductions that are not 
relied on for RFP or attainment and that are not included in the RFP or 
attainment demonstrations as meeting part or all of the contingency 
measure requirements. The purpose of contingency measures is to provide 
continued emissions reductions while the state revises the SIP to meet 
the missed milestone or attainment date.
    The EPA has approved numerous nonattainment area plan SIP 
submissions under this interpretation, i.e., SIPs that use as 
contingency measures one or more federal or state control measures that 
are already in place and provide reductions that are in excess of the 
reductions required to meet other requirements or relied upon in the 
modeled attainment demonstration,\167\ and there is case law supporting 
the EPA's interpretation in this regard.\168\ However, in Bahr v. EPA, 
the Ninth Circuit rejected the EPA's interpretation of CAA section 
172(c)(9) as allowing for approval of already implemented control 
measures as contingency measures.\169\ The Ninth Circuit concluded that 
contingency measures must be measures that would take effect at the 
time the area fails to make RFP or to attain by the applicable 
attainment date, not before.\170\ Thus, within the geographic 
jurisdiction of the Ninth Circuit, states cannot rely on already 
implemented control measures to comply with the contingency measure 
requirements under CAA section 172(c)(9).
---------------------------------------------------------------------------

    \167\ E.g., 62 FR 15844 (April 3, 1997) (direct final rule 
approving an Indiana ozone SIP revision); 62 FR 66279 (December 18, 
1997) (final rule approving an Illinois ozone SIP revision); 66 FR 
30811 (June 8, 2001) (direct final rule approving a Rhode Island 
ozone SIP revision); 66 FR 586 (January 3, 2001) (final rule 
approving District of Columbia, Maryland, and Virginia ozone SIP 
revisions); and 66 FR 634 (January 3, 2001) (final rule approving a 
Connecticut ozone SIP revision).
    \168\ E.g., LEAN v. EPA, 382 F.3d 575 (5th Cir. 2004) (upholding 
contingency measures that were previously required and implemented 
where they were in excess of the attainment demonstration and RFP 
SIP).
    \169\ Bahr v. EPA, 836 F.3d 1218, 1235-1237 (9th Cir. 2016).
    \170\ Id.
---------------------------------------------------------------------------

2. Summary of State's Submission
    Imperial County APCD and CARB adopted the Imperial Ozone Plan after 
the Bahr v. EPA decision. Nevertheless, the Plan relies upon surplus 
emissions reductions from already implemented control measures in the 
2017 RFP year to demonstrate compliance with the RFP contingency 
measure requirements of CAA sections 172(c)(9).\171\ With respect to 
the attainment contingency measure requirements, the Imperial Ozone 
Plan stated that such measures are not required.\172\
---------------------------------------------------------------------------

    \171\ Imperial Ozone Plan, 5-1 to 5-2.
    \172\ Imperial Ozone Plan, Table 11-1.
---------------------------------------------------------------------------

    In the 2018 SIP Update, CARB revised the RFP demonstration for the 
2008 ozone standards for Imperial County. Based on that demonstration 
and the fact that 2017 had passed, CARB concludes that Imperial County 
successfully met applicable RFP requirements in 2017 and, therefore, 
the RFP contingency measure requirement in CAA section 172(c)(9) is 
irrelevant for Imperial County for the 2008 ozone NAAQS.\173\
---------------------------------------------------------------------------

    \173\ Imperial Ozone Plan, 13.
---------------------------------------------------------------------------

3. EPA Review of State's Submission
    The EPA has reviewed the Imperial Ozone Plan and the 2018 SIP 
Update and proposes that the contingency measure requirement of CAA 
section 172(c)(9) for RFP is moot, as described below. Regarding the 
contingency measure requirement of section 172(c)(9) for failure to 
attain by the applicable attainment date, we propose that such measures 
would no longer be required if the EPA were to finalize our proposed 
approval of the section 179B demonstrations for Imperial County for the 
2008 ozone NAAQS, as also described below.
    The contingency measure portion of the Imperial Ozone Plan, based 
on the Plan's RFP demonstration from a 2008 RFP baseline emission 
inventory through the 2017 RFP emission inventory, relies upon 
emissions reductions that are surplus to those needed to demonstrate 
RFP. As noted in our summary of the statutory and regulatory 
requirements for contingency measures, states in the Ninth Circuit 
cannot rely on already implemented control measures to comply with the 
contingency measure requirements under CAA sections 172(c)(9), and thus 
we do not propose to approve such an

[[Page 58660]]

approach for Imperial County for the 2008 ozone NAAQS.
    However, as described in section II.H of this proposed rule, we 
reviewed the revised 2017 RFP emissions inventory and RFP demonstration 
for Imperial County in the 2018 SIP Update. Given that the revised RFP 
demonstration is based upon actual emissions reported for 2017 for 
stationary point sources, and forecasted emissions for other sources 
using updated activity data, consistent with the Imperial Ozone Plan's 
section 179B(a) demonstration, using the appropriate metric (summer 
emissions of ozone precursor pollutants) and that the area achieved 
greater than 3% annual emissions reductions in VOC, we agree with CARB 
that Imperial County has met applicable RFP requirements for 2017. 
Because the area met RFP for 2017, and because no RFP demonstration is 
required for a year beyond 2017 for Imperial County for the 2008 ozone 
NAAQS, the event that would otherwise trigger implementation of RFP 
contingency measures did not occur and will not occur in the future. 
Accordingly, we propose that the RFP contingency measure requirement is 
moot as applied to Imperial County for purposes of the 2008 ozone 
NAAQS.
    With respect to attainment contingency measures, CARB and Imperial 
County APCD state that attainment contingency measures are not required 
due to the area's attainment but for the impacts of international 
emissions. We agree that such measures are not required for Imperial 
County for the 2008 ozone NAAQS as follows.
    Attainment contingency measures under CAA section 172(c)(9) are 
triggered upon the EPA's determination that an area failed to attain a 
given NAAQS by its applicable attainment date. However, section 179B(b) 
provides that where a state demonstrates to the EPA that the area would 
have attained the ozone NAAQS by the applicable attainment date but for 
emissions emanating from outside the U.S., the area is not subject to 
the reclassification provisions in section 181(b)(2) and will not be 
reclassified to a higher nonattainment level.\174\ It is therefore 
consistent with section 179B(b) to conclude that the EPA's approval of 
a demonstration of attainment but for international emissions under 
section 179B(b) means that the EPA is not required to make 
determinations of attainment by the attainment date for that area. 
Therefore, contingency measures would not be triggered for the area's 
failure to attain by the attainment date, provided that the EPA has 
approved the area's demonstration that it would have attained by the 
applicable attainment date but for emissions emanating from outside the 
U.S. Given these considerations, the EPA interprets the CAA not to 
require contingency measures for failure to attain in an area with an 
approved section 179B demonstration.
---------------------------------------------------------------------------

    \174\ The EPA's long held view is that CAA section 179B(b)'s 
reference to section 181(a)(2) was made in error, and that Congress 
actually intended to refer to section 181(b)(2). 83 FR 62998, 63009, 
n.24; ``State Implementation Plans; General Preamble for the 
Implementation of Title I of the Clean Air Act Amendments of 1990,'' 
57 FR 13498, 13569 n.41 (April 16, 1992).
---------------------------------------------------------------------------

    As described in sections II.G and III of this proposed rule, the 
EPA proposes to approve the Imperial Ozone Plan, the 2018 SIP Update 
(with respect to Imperial County), and the Imperial Ozone Retrospective 
Demonstration under section 179B(b) that Imperial County would have 
attained the 2008 ozone NAAQS by July 20, 2018, but for emissions from 
Mexico. Thus, if the EPA were to finalize this proposed action, there 
would be no requirement for the EPA to determine whether the area 
attained the NAAQS, and therefore no requirement for the state to 
submit attainment contingency measures. Accordingly, we propose that 
the attainment contingency measure requirement does not apply to 
Imperial County for the 2008 ozone NAAQS.

K. Other Requirements

    The Imperial Ozone Plan notes that the Moderate area requirements 
of CAA section 182(b)(3) (``Gasoline vapor recovery'') no longer apply 
since the promulgation of the Onboard Refueling Vapor Recovery Rule, 
and that the requirements of section 182(b)(4) (``Motor vehicle 
inspection and maintenance'') do not apply to Imperial County because 
its population is below the 200,000 persons threshold.\175\ The EPA 
agrees with CARB's assessment and proposes that these two requirements 
do not apply in Imperial County for the 2008 ozone NAAQS.
---------------------------------------------------------------------------

    \175\ Imperial Ozone Plan, 1-1, n. 4. See also, 59 FR 16262 
(April 6, 1994) (known as the Onboard Refueling Vapor Recovery Rule) 
and 40 CFR 51.350(a)(8) (population threshold for applicability of 
motor vehicle inspection and maintenance requirements).
---------------------------------------------------------------------------

III. Imperial County Ozone Determination of Attainment but for 
International Emissions

A. Statutory and Regulatory Requirements

    Section 181(b)(2)(A) of the CAA requires that within 6 months 
following the applicable attainment date, the EPA Administrator shall 
determine whether an ozone nonattainment area attained the ozone 
standards based on the area's design value as of that date.\176\ In the 
event an area fails to attain the relevant ozone NAAQS by the 
applicable attainment date, CAA section 181(b)(2)(A) requires the 
Administrator to make the determination that the area failed to attain 
the ozone standards and requires the area to be reclassified by 
operation of law to the higher of (i) the next higher classification 
for the area, or (ii) the classification applicable to the area's 
design value as of the determination of failure to attain.
---------------------------------------------------------------------------

    \176\ We note that CAA section 181(a)(5) gives the Administrator 
the discretion to grant a 1-year extension of the attainment date 
specified in CAA section 181(a) upon application by any state if 
certain criteria are met. However, CARB is not seeking such an 
extension for Imperial County but rather invokes the provisions of 
section 179B(b).
---------------------------------------------------------------------------

    Section 179B(b), however, provides that if a state demonstrates to 
the EPA that an area would have attained the ozone NAAQS by the 
applicable attainment date, but for emissions emanating from outside 
the U.S., the area is not subject to the reclassification provisions in 
section 181(b)(2) and will not be reclassified to a higher 
nonattainment level. The EPA interprets section 179B(b) to involve an 
analysis of the relationship between past exceedances (i.e., those used 
in determining attainment) and international emissions.

B. Summary of State's Submission

    CARB submitted the Imperial Ozone Retrospective Demonstration to 
the EPA on July 3, 2018.\177\ CARB states that despite air quality 
improvement in Imperial County due to wide-ranging controls on 
NOX and VOC sources, the area would not attain the 2008 
ozone NAAQS by the July 20, 2018 attainment deadline.\178\ In the 
Imperial Ozone Retrospective Demonstration, CARB presents an analysis 
that estimated the ozone levels in Imperial County, without the 
influence of emissions in the Mexicali Region, for 2017. The Imperial 
Ozone Retrospective Demonstration is based on a number of factors, 
including two modeling exercises: (1) Photochemical modeling in the 
Imperial Ozone Plan, discussed in section II.G of this proposed rule; 
and (2) the EPA's interstate air pollution transport modeling for the 
2008 ozone NAAQS, including the CSAPR Update modeling results for 2017 
and supplemental modeling results for

[[Page 58661]]

2023.\179\ CARB also presented a back trajectory analysis for each day 
in 2015, 2016, and 2017 when the ozone level was above 75 ppb at any of 
the three monitoring sites. CARB presented additional supporting 
information, including a comparison of the emissions inventory for 
ozone precursors in Imperial County to the emissions inventory to the 
Mexicali Municipality, the ozone design value trends from 1996 to 2017, 
and a discussion of the conditions that influence ozone formation in 
Imperial County.
---------------------------------------------------------------------------

    \177\ Letter dated July 3, 2018, from Richard Corey, Executive 
Officer, CARB, to Michael Stoker, Regional Administrator, EPA Region 
9.
    \178\ Imperial Ozone Retrospective Demonstration, 1.
    \179\ 81 FR 74504; CSAPR Update Air Quality Modeling TSD; and 
CSAPR Update 2008 Ozone Design Values and Contributions Spreadsheet; 
and Supplemental 2008 Ozone Transport Memo.
---------------------------------------------------------------------------

1. Imperial Ozone Plan Attainment Demonstration Modeling
    To show the effect of emissions emanating from Northern Mexico on 
ozone levels in Imperial County in 2017, CARB relied in part on 
modeling conducted for the attainment demonstration in the Imperial 
Ozone Plan. Specifically, CARB performed an exercise using existing 
modeling results to estimate the effect of Mexican emissions within the 
Southern California Modeling domain (i.e., a subset of the Mexican 
emissions sources nearest Imperial County) and applied those estimates 
to 2015-2017 design values.
    As discussed in section II.G of this proposed rule, the attainment 
demonstration for the Imperial Ozone Plan includes two modeling 
scenarios (or cases) for the year 2017. Case one was a ``base'' run 
that used projected 2017 anthropogenic emissions for both the U.S. and 
Mexicali Municipality within the modeling domain, while all other model 
inputs were based on the year 2012. Case two was a ``sensitivity'' run, 
where the only difference from the base run was that Mexican 
anthropogenic emissions (within the modeling domain) were zeroed out. 
The sensitivity run analysis estimated the ozone contribution from 
Mexican emissions to Imperial County monitoring sites based on the 
change in the predicted design values due to the removal of the Mexican 
anthropogenic emissions (within the modeling domain). CARB then applied 
the estimated ozone reduction from the removal of the Mexican emissions 
as generated by the sensitivity run analysis to the measured 2015-2017 
design value at each of the monitoring sites. The results are shown 
here in Table 8.

         Table 8--CARB's 2015-2017 Design Values Estimates Based on Scaling Exercise From CARB Modeling
----------------------------------------------------------------------------------------------------------------
                                                                               Estimated 2015-
                                                                                 2017 design
                                                             Measured 2015-     value without   Change in design
                      Monitoring site                          2017 design      anthropogenic    value (percent)
                                                               value (ppb)         Mexican
                                                                               emissions (ppb)
----------------------------------------------------------------------------------------------------------------
Niland....................................................                63              60.7               3.7
El Centro.................................................                76              65.9              13.3
Calexico..................................................                77              64.3              16.5
----------------------------------------------------------------------------------------------------------------
Source: Imperial Ozone Retrospective Demonstration, Table 2.

2. CARB's Estimate of Ozone Transport Based on the EPA's Air Quality 
Modeling
    As part of the CSAPR Update rule, the EPA conducted air quality 
modeling to project ozone concentrations at individual monitoring sites 
in 2017 and to estimate state-by-state contributions to those 2017 
concentrations.\180\ The EPA used the Comprehensive Air Quality Model 
with Extensions (CAMx),\181\ including state-level ozone source 
apportionment modeling using the OSAT/APCA technique.\182\ This 
exercise involved tracking the ozone contribution at each receptor from 
different sources (e.g., individual states, Mexico and Canada), as well 
as boundary conditions. As noted in section II.G.3 of this proposed 
rule, the EPA has released two sets of modeling results, one for year 
2017 and one for year 2023.\183\ Both cases were simulated using a 2011 
base year modeling platform, which means the 2011 meteorology and 
boundary conditions were applied to both future year cases (2017 and 
2023).
---------------------------------------------------------------------------

    \180\ 81 FR 74504; Air Quality Modeling Technical Support 
Document for the Final Cross State Air Pollution Update (CSAPR 
Update AQM TSD); and CSAPR Update 2008 Ozone Design Values and 
Contributions Spreadsheet; and Supplemental 2008 Ozone Transport 
Memo.
    \181\ For the final CSAPR Update rule, the EPA used CAMx version 
6.20 (Ramboll Environ, 2015), which was the latest public release 
version of CAMx available at the time the air quality modeling was 
performed. CSAPR Update AQM TSD, 2, n.5.
    \182\ Id. at 15.
    \183\ Results for 2017 are available at: https://www.epa.gov/sites/production/files/2017-05/documents/aq_modeling_tsd_final_csapr_update.pdf. Results for are 2023 
available at: https://www.epa.gov/airmarkets/october-2017-memo-and-supplemental-information-interstate-transport-sips-2008-ozone-naaqs.
---------------------------------------------------------------------------

    CARB's Imperial Ozone Retrospective Demonstration lists the 
measured 8-hour ozone design value for 2015-2017 at each Imperial 
County site.\184\ It also lists the estimated contribution to ozone in 
Imperial County resulting from Mexican anthropogenic emissions based on 
the CSAPR Update 2017.\185\ The Mexican contributions to the design 
values at the Niland, El Centro, and Calexico sites are estimated to be 
11%, 15%, and 17% respectively.\186\ Then, CARB estimated the 2015-2017 
design values without the influence Mexican emissions for each site by 
reducing the measured ozone design value by the percentage estimated by 
the interstate transport modeling developed as part of the CSAPR Update 
for that site. The results are shown in Table 9.
---------------------------------------------------------------------------

    \184\ Imperial Ozone Retrospective Demonstration, Table 4.
    \185\ The Canadian influence is assumed to be negligible.
    \186\ Imperial Ozone Retrospective Demonstration, Table 3. Due 
to a major update of the Mexican emission inventory used in the 2023 
modeling, the modeling results show higher ozone contributions from 
Mexico at all Imperial County sites in 2023. This larger 
contribution is likely due to an increase in Mexican emissions with 
the update to the inventory, as well as a reduction in local 
Imperial County emissions between 2017 and 2023.

[[Page 58662]]



            Table 9--CARB's 2017 Design Value Estimates Based on Scaling EPA's CSAPR Update Modeling
----------------------------------------------------------------------------------------------------------------
                                                                               Estimated 2015-
                                                                                 2017 design
                                                             Measured 2015-     value without   Change in design
                      Monitoring site                          2017 design      anthropogenic    value (percent)
                                                               value (ppb)    Mexican emission
                                                                               inventory (ppb)
----------------------------------------------------------------------------------------------------------------
Niland....................................................                63              56.1              11.0
El Centro.................................................                76              64.4              15.3
Calexico..................................................                77              63.7              17.3
----------------------------------------------------------------------------------------------------------------
Source: Imperial Ozone Retrospective Demonstration, Table 4.

3. CARB's Back Trajectory Model Analysis
    CARB provided a trajectory analysis for each day that exceeded the 
ozone standards at the Calexico and El Centro monitoring sites for the 
years 2015, 2016, and 2017. There were no days that exceeded the 2008 
Ozone NAAQS at the Niland monitoring site in that period. CARB used the 
NOAA HYSPLIT model for its back trajectory modeling and identified the 
hours of each exceedance day with the maximum 8-hour average ozone 
value. CARB then used the HYSPLIT model to draw an 8-hour back 
trajectory for each of the 8 hours of data that contributed to the 
maximum 8-hour ozone value where each line drawn represents the back 
trajectory for one hour at the air quality monitor.\187\
---------------------------------------------------------------------------

    \187\ Id., App. A.
---------------------------------------------------------------------------

    CARB listed each site and each exceedance day for which at least 5 
out of 8 of the eight-hour back trajectories originated from or went 
through the Mexicali region of Mexico (``CARB's 5 of 8 Back Trajectory 
Test'').\188\ CARB determined that for Calexico, 11 of the 14 days were 
likely to have an influence from sources in the Mexicali region since 
they each had 5 or more hours with back trajectories passed through the 
Mexicali region. For El Centro, CARB determined that 8 of the 12 days 
were likely influenced by sources in the Mexicali region. CARB then 
excluded the 8-hour monitoring values for the days for which there was 
a likely influence from Mexico (i.e., 11 days for Calexico and 8 days 
for El Centro) and calculated new design values for each site. CARB 
listed the maximum 8-hour average ozone values on all exceedance days 
at each site, resulting in 2015-2017 design values of 73 ppb in both 
cases, as shown here in Table 10.
---------------------------------------------------------------------------

    \188\ Id., Table 6.

 Table 10--CARB's Predicted 2015-2017 Design Values Excluding Days With Likely Mexican Influence Based on CARB's
                                           5 of 8 Back Trajectory Test
----------------------------------------------------------------------------------------------------------------
                                                       Calexico                            El Centro
                                         -----------------------------------------------------------------------
                                                                4th high                            4th high
                  Year                                      excluding Mexico                    excluding Mexico
                                           4th high (ppb)    influenced days   4th high (ppb)    influenced days
                                                                  (ppb)                               (ppb)
----------------------------------------------------------------------------------------------------------------
2015....................................                77                74                77                72
2016....................................                74                73                74                73
2017....................................                82                74                79                75
2015-2017 Design Value..................                77                73                76                73
----------------------------------------------------------------------------------------------------------------
Source: Imperial Ozone Retrospective Demonstration, Table 7.

4. CARB's Additional Supporting Information
    The comparison of the emissions inventory shows that the Mexicali 
Municipality and the NOX emissions (summer planning 
inventory) are 3.8 times greater than those of Imperial County, and the 
ROG emissions are 3.1 times greater, as shown in Table 11.

[[Page 58663]]



                                   Table 11--CARB's 2012 Imperial County and Mexicali Municipality Emissions Inventory
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                Imperial County                          Mexicali Municipality
                                                                 ---------------------------------------------------------------------------------------
                             Source                               NOX (tpd)   NOX (%)                         NOX (tpd)   NOX (%)
                                                                                        ROG (tpd)   ROG (%)                         ROG (tpd)   ROG (%)
--------------------------------------------------------------------------------------------------------------------------------------------------------
Stationary......................................................          2          8          1          7         15         18         14         24
Area-wide.......................................................          1          3          9         44         10         12         27         46
On-Road Mobile..................................................         10         46          4         22         56         66         17         29
Other Mobile....................................................          9         43          5         27          4          4        0.4          1
                                                                 ---------------------------------------------------------------------------------------
    Total.......................................................         22        100         19        100         85        100         59        100
--------------------------------------------------------------------------------------------------------------------------------------------------------
Source: Imperial Ozone Retrospective Demonstration, Table 1.\189\

    CARB also included a figure displaying the 8-hour ozone design 
value trend, which shows a decrease from 0.112 ppm 1996 to 0.079 ppm in 
2010, and fairly consistent values from 2010 to 2017, with a design 
value of 0.077 ppm for 2015-2017.\190\
---------------------------------------------------------------------------

    \189\ See also Imperial Ozone Plan, Table 8-1. Mexicali 
emissions based on the EPA's 2011 Version 6.3 Platform inventory. 
The 2011 Version 6.3 Platform is based on the 2011 NEI version 2 and 
includes projected future years of 2017, 2023, and 2028. The 2011 
Version 6.3 Platform supported the CSAPR Update, a rule related to 
interstate transport for the 2008 ozone NAAQS.
    \190\ Imperial Ozone Retrospective Demonstration, Figure 3, 5.
---------------------------------------------------------------------------

C. EPA Review of State's Submission

    The EPA has reviewed CARB's analyses and agrees that, despite CARB 
and Imperial County APCD's measures to reduce NOX and VOC 
emissions, the 8-hour ozone design values at each ozone monitoring site 
in Imperial County would have been below the 2008 ozone NAAQS of 75 ppb 
for the 2015-2017 design value period, but for emissions emanating from 
Mexico. We include the EPA's 179B TSD for Imperial County Ozone, which 
provides further information regarding our evaluation of the Imperial 
Ozone Retrospective Demonstration, in the docket of this proposed rule.
    First, we reviewed CARB's analysis of the contribution to ozone 
from Mexican emissions based on CARB's modeling for demonstrating 
attainment as part of the Imperial Ozone Plan. This scaling exercise 
first estimated the contribution of Mexican anthropogenic emissions to 
ozone formation on the measured 2015-2017 ozone design values by 
assuming that the contribution to the 2015-2017 observed design values 
was the same proportion as the contribution to the projected 2017 year 
in the attainment demonstration. The scaling exercise then subtracted 
this estimated contribution to ozone formation of Mexican anthropogenic 
emissions from the measured 2015-2017 ozone design values, which 
resulted in an Imperial County maximum design value of 65 ppb.\191\
---------------------------------------------------------------------------

    \191\ Imperial Ozone Plan, Table 8-2.
---------------------------------------------------------------------------

    The EPA believes the modeling that served as a basis for estimating 
the contribution was sound. As discussed in section II.G.3 of this 
proposed rule, CARB and the District implemented the modeling 
procedures, tests, and performance analyses consistent with the EPA's 
Modeling Guidance, discussed that modeling in detail, and found that 
the model performed well. Also, CARB modeled attainment of the 2008 
ozone NAAQS but for emissions from Mexico by modeling the year 2017, 
both with and without the anthropogenic emissions inventory from Mexico 
(within the modeling domain); given the availability of data to perform 
such analyses, this is a reasonable method of assessing the degree to 
which Mexican emissions affect ozone concentrations in Imperial County, 
together with other lines of evidence.
    Second, we reviewed CARB's estimation of the contribution to ozone 
from Mexican emissions based on modeling results from the EPA's 
interstate air pollution transport modeling developed to estimate ozone 
design values in the Moderate area attainment year of 2017 for the 2008 
ozone NAAQS. We note that this is a similar yet distinct analysis from 
the analysis described in section II.G.3 of this proposed rule. This 
scaling exercise on the actual 2015-2017 design values use EPA's CSAPR 
Update modeling to remove the estimated effect of Mexican emissions and 
resulted in a maximum design value of 64 ppb for Imperial County. The 
EPA's CSAPR Update modeling considered multiple aspects of the 
transport of ozone, including consideration of measured and modeled 
ambient ozone concentrations; estimated NOX and VOC 
emissions inventories for the continental U.S., Mexico, Canada, and 
boundary conditions; application of state of the science modeling tools 
for regional air pollution analysis and appropriate model validation; 
existing and planned emissions control regimes; and meteorology. While 
the EPA did not design that modeling specifically to assess the degree 
to which Mexican emissions may affect ozone concentrations in Imperial 
County, CARB's method of employing the CSAPR Update data among several 
other lines of evidence is reasonable and estimates that the effect of 
the Mexican emissions (11% to 17%) would be in a similar range as 
CARB's analysis of its own modeling (3.7% to 16.5%).
    Thus, each of the two modeling exercises indicates that the 
measured 2015-2017 design values with the predicted impact from Mexican 
emissions removed would be below the 2008 ozone NAAQS for all three 
monitoring sites. These analyses make use of detailed and appropriate 
modeling techniques and data sets and support CARB's conclusion that 
Imperial County would have attained the 2008 Ozone NAAQS by the 2017 
attainment year but for emissions emanating from Mexico.
    Third, we reviewed CARB's back trajectory analyses, wherein CARB 
studied each day that exceeded the 2008 ozone NAAQS at the Calexico and 
El Centro monitoring sites for the years 2015, 2016, and 2017, and 
determined which days at the Calexico and El Centro sites were likely 
to have been influenced by sources in the Mexicali region. As a 
complement to Table 10 of this proposed rule, we summarized the count 
of exceedance days that were likely influenced by Mexican emissions 
based on CARB's 5 of 8 Back Trajectory Test and the count of such days 
likely to be influenced to a lesser degree by Mexican emissions (4 or 
less of 8 back trajectories). These counts are shown in Table 12.

[[Page 58664]]



    Table 12--EPA's Count of Days Influenced by Mexican Emissions Based on CARB's 5 of 8 Back Trajectory Test
----------------------------------------------------------------------------------------------------------------
                                                       Calexico                            El Centro
                                         -----------------------------------------------------------------------
                                            Count of days                       Count of days
                  Year                       with likely      Count of days      with likely      Count of days
                                           influence from   with less likely   influence from   with less likely
                                           Mexico (5 of 8    influence from    Mexico (5 of 8    influence from
                                                Test)            Mexico             Test)            Mexico
----------------------------------------------------------------------------------------------------------------
2015....................................                 4                 0                 6                 0
2016....................................                 2                 1                 1                 1
2017....................................                 8                 2                 5                 3
----------------------------------------------------------------------------------------------------------------

    The EPA finds that CARB's methodology for assessing the potential 
effect of Mexican emissions on recorded ozone exceedances in Imperial 
County is a reasonable means, among several lines of evidence, for 
identifying exceedance days and the highest 8-hour period within each 
such day and examining the origin and pathway of air traveling each 
hour to the Imperial County monitoring sites within that 8-hour period.
    In addition to reviewing the approach and results of CARB's 5 of 8 
Back Trajectory Test, the EPA considered a more stringent test that 
would only remove an exceedance day if 75% (6 of 8) of the back 
trajectories originated in or passed through Mexico (``EPA's 6 of 8 
Back Trajectory Test'') as this would reflect a more conservative 
approach to examining how many days may have been affected by emissions 
from sources in the Mexicali region.
    The EPA reanalyzed the data and determined that 8 of the 14 days 
for Calexico and 5 of the 12 days for El Centro were likely to have an 
influence from sources in the Mexicali region.\192\ As CARB had done, 
the EPA excluded the days for which there was a likely influence from 
Mexico (i.e., 8 days at Calexico and 5 days for El Centro) and 
calculated new design values for each site. This more stringent 
analysis resulted in an Imperial County design value of 75 ppb, as 
shown here in Table 13, supporting the conclusion that Imperial County 
would have attained the 2008 ozone NAAQS by the 2017 attainment year 
but for emissions emanating from Mexico. This estimated design value is 
higher than the estimated design value from the modeling exercises 
discussed herein because many of the days with fewer than 6 
trajectories emanating from Mexico are likely to have some contribution 
from Mexico. This approach is also conservative because there is likely 
Mexico influence on all days and this method only removes days where 
the Mexico influence is expected to be largest.
---------------------------------------------------------------------------

    \192\ For the days identified for El Centro with trajectories as 
having a likely influence from Mexico, the EPA has conducted 
additional trajectory analyses to further assess the influence of 
the Mexicali emissions. This information is provided in the EPA's 
179B TSD for Imperial County Ozone.

 Table 13--EPA's Predicted 2015-2017 Design Values Excluding Days With Likely Mexican Influence Based on EPA's 6
                                            of 8 Back Trajectory Test
----------------------------------------------------------------------------------------------------------------
                                                       Calexico                            El Centro
                                         -----------------------------------------------------------------------
                                                                4th high                            4th high
                  Year                                          excluding                           excluding
                                           4th high (ppb)        Mexico        4th high (ppb)        Mexico
                                                             influenced days                     influenced days
                                                                  (ppb)                               (ppb)
----------------------------------------------------------------------------------------------------------------
2015....................................                77                74                77                73
2016....................................                74                74                74                73
2017....................................                82                75                79                79
2015-2017 Design Value..................                77                74                76                75
----------------------------------------------------------------------------------------------------------------

    For comparison, we also include a count of exceedance days that 
were likely influenced by Mexican emissions based on EPA's 6 of 8 Back 
Trajectory Test and the count of such days likely to be influenced to a 
lesser degree by Mexican emissions (5 or less of 8 back trajectories). 
These counts are shown in Table 14.

[[Page 58665]]



    Table 14--EPA's Count of Days Influenced by Mexican Emissions Based on EPA's 6 of 8 Back Trajectory Test
----------------------------------------------------------------------------------------------------------------
                                                       Calexico                            El Centro
                                         -----------------------------------------------------------------------
                                            Count of days                       Count of days
                  Year                       with likely      Count of days      with likely      Count of days
                                           influence  from  with less likely   influence  from  with less likely
                                           Mexico  (6 of 8   influence from    Mexico (6 of 8    influence from
                                                Test)            Mexico             Test)            Mexico
----------------------------------------------------------------------------------------------------------------
2015....................................           \193\ 4                 0                 4                 2
2016....................................                 0                 3                 1                 1
2017....................................                 7                 3                 0                 8
----------------------------------------------------------------------------------------------------------------

    The additional information provided by the State also supports the 
conclusion that Imperial County would have attained the 2008 ozone 
NAAQS by the attainment date of July 20, 2018, but for emissions 
emanating from Mexico. In brief, the emission inventory data presented 
indicate that the Mexicali Municipality emits three times the amount of 
ozone precursors emitted in Imperial County, such emissions could have 
had a substantial effect on Imperial County ozone concentrations, and 
Imperial County ozone concentrations would have been lower in the 
absence of Mexican emissions. In addition, the proximity of the Mexican 
border to the monitoring sites (1 mile from Calexico and 9 miles from 
El Centro) and the shared topography and meteorology of Imperial Valley 
also support the potential of Mexican emissions having a substantial 
and immediate effect on ozone concentrations in Imperial County.
---------------------------------------------------------------------------

    \193\ September 23, 2015 has 5 of the 6 trajectories (83%) for 
which data was available originating in Mexico. Thus, we included 
this exceedance day in the count of days with likely influence from 
Mexico.
---------------------------------------------------------------------------

    In conclusion, the EPA evaluated the information provided by CARB 
and applied a more conservative test using CARB's back trajectory 
method. CARB's modeling estimates of Mexican contribution based on 
modeling data from the Imperial Ozone Plan attainment demonstration and 
the EPA's CSAPR Update modeling, and the EPA's application of a more 
conservative test using CARB's back trajectory method to analyze 
exceedance days in the 2015-2017 design value period together support 
the conclusion that Imperial County would have attained the standards 
but for the impacts of emissions from Mexico. Furthermore, the 
emissions inventory, showing that the ozone precursor emissions for 
Mexicali Municipality are over three times those emitted in Imperial 
County, and the proximity and shared airshed of the Calexico and El 
Centro monitor to these emissions, also support the conclusion that the 
Mexican emissions affected the ozone concentrations at these sites.
    Thus, based on our evaluation of these several lines of evidence 
and analyses that together support the same conclusion, the EPA 
proposes to determine, under CAA sections 179B(b) and 181(b)(2)(A), 
that Imperial County would have attained the 2008 ozone NAAQS by the 
Moderate area attainment date of July 20, 2018, but for emissions 
emanating from Mexico.

IV. Proposed Action

    For the reasons discussed in this notice, under CAA section 
110(k)(3), the EPA is proposing to approve, as a revision to the 
California SIP, the Imperial Ozone Plan and the Imperial County portion 
of the 2018 SIP Update related to:
     Emissions statement certification as meeting the 
requirements of CAA section 182(a)(3)(B);
     Base year emissions inventory as meeting the requirements 
of CAA sections 172(c)(3) and 182(a)(1) and 40 CFR 51.1115 with respect 
to attainment planning;
     RACM demonstration as meeting the requirements of CAA 
section 172(c)(1) and 40 CFR 51.1112(c);
     RFP demonstration as meeting the requirements of CAA 
section 182(b)(1) and 40 CFR 51.1110(a)(4)(i); and
     Motor vehicle emission budgets for the 2017 RFP milestone 
year because they are consistent with the RFP demonstration and the 
demonstration of attainment but for international emissions that are 
proposed for approval herein and meet the other criteria in 40 CFR 
93.118(e).
    We also propose that finalization of this action would render the 
RFP contingency measure requirement of CAA section 172(c)(9) moot and 
that attainment contingency measures would no longer be required, as 
discussed in section II.J of this proposed rule.
    Given our proposal that the Imperial Ozone Plan meets all 
requirements for the Imperial County Moderate ozone nonattainment area, 
other than the requirement to demonstrate attainment, and our 
evaluation of the State's lines of evidence that together support the 
conclusion that Imperial County would attain the 2008 ozone NAAQS by 
the July 20, 2018 attainment date but for emissions emanating from 
Mexico, the EPA proposes to approve the Imperial Ozone Plan's section 
179B attainment demonstration as meeting the requirements of CAA 
sections 172(c)(1), 182(b)(1)(A), and 179B(a) and 40 CFR 51.1108.
    Concurrently, we are proposing to determine, consistent with our 
evaluation of the Imperial Ozone Plan, the 2018 Update, and Imperial 
Ozone Retrospective Demonstration, that the Imperial County 
nonattainment area would have attained the 2008 ozone NAAQS by the 
Moderate area attainment date of July 20, 2018, but for emissions 
emanating from outside of the United States, under CAA sections 
179B(b). Therefore, if finalized, the EPA's obligation under section 
181(b)(2)(A) to determine whether the area attained by its attainment 
date would no longer apply and the area would not be reclassified.
    The EPA is soliciting public comments on the issues discussed in 
this document. We will accept comments from the public on this proposal 
for the next 30 days and will consider comments before taking final 
action.

V. Statutory and Executive Order Reviews

    With respect to our proposal on the Imperial Ozone Plan and the 
2018 SIP Update, under the Clean Air Act, the Administrator is required 
to approve a SIP submission that complies with the provisions of the 
Act and applicable federal regulations. 42 U.S.C. 7410(k); 40 CFR 
52.02(a). Thus, in reviewing SIP submissions, the EPA's role is to 
approve state choices, provided that they meet the criteria of the 
Clean Air Act. Accordingly, this proposed action merely proposes to 
approve state plans

[[Page 58666]]

as meeting federal requirements and does not impose additional 
requirements beyond those imposed by state law.
    With respect to our proposed determination that Imperial County 
attained the 2008 ozone NAAQS by July 20, 2018 but for emissions from 
Mexico, the purpose of this rule is to determine whether Imperial 
County attained the 2008 ozone standards by its Moderate area 
attainment date, which is required under the CAA for purposes of 
implementing the 2008 ozone standards.
    For these reasons, this proposed action:
     Is not a ``significant regulatory action'' subject to 
review by the Office of Management and Budget under Executive Orders 
12866 (58 FR 51735, October 4, 1993) and 13563 (76 FR 3821, January 21, 
2011);
     Is not an Executive Order 13771 (82 FR 9339, February 2, 
2017) regulatory action because SIP approvals are exempted under 
Executive Order 12866;
     Does not impose an information collection burden under the 
provisions of the Paperwork Reduction Act (44 U.S.C. 3501 et seq.);
     Is certified as not having a significant economic impact 
on a substantial number of small entities under the Regulatory 
Flexibility Act (5 U.S.C. 601 et seq.);
     Does not contain any unfunded mandate or significantly or 
uniquely affect small governments, as described in the Unfunded 
Mandates Reform Act of 1995 (Pub. L. 104-4);
     Does not have Federalism implications as specified in 
Executive Order 13132 (64 FR 43255, August 10, 1999);
     Is not an economically significant regulatory action based 
on health or safety risks subject to Executive Order 13045 (62 FR 
19885, April 23, 1997);
     Is not a significant regulatory action subject to 
Executive Order 13211 (66 FR 28355, May 22, 2001);
     Is not subject to requirements of Section 12(d) of the 
National Technology Transfer and Advancement Act of 1995 (15 U.S.C. 272 
note) because application of those requirements would be inconsistent 
with the Clean Air Act; and
     Does not provide the EPA with the discretionary authority 
to address disproportionate human health or environmental effects with 
practical, appropriate, and legally permissible methods under Executive 
Order 12898 (59 FR 7629, February 16, 1994).
    In addition, with respect to our proposal on the Imperial Ozone 
Plan and the 2018 SIP Update, the SIP is not approved to apply on any 
Indian reservation land or in any other area where the EPA or an Indian 
tribe has demonstrated that a tribe has jurisdiction. In those areas of 
Indian country, the proposed rule does not have tribal implications and 
will not impose substantial direct costs on tribal governments or 
preempt tribal law as specified by Executive Order 13175 (65 FR 67249, 
November 9, 2000).
    However, with respect to our proposed determination that Imperial 
County attained the 2008 ozone NAAQS by July 20, 2018, but for 
emissions from Mexico, this action has tribal implications. 
Nonetheless, it will neither impose substantial direct compliance costs 
on federally recognized tribal governments, nor preempt tribal law. Two 
tribes have areas of Indian country within or directly adjacent to the 
Imperial County: Quechan Tribe of the Fort Yuma Indian Reservation and 
the Torres Martinez Desert Cahuilla Indians. The EPA intends to 
communicate with potentially affected tribes located within or directly 
adjacent to the boundaries of Imperial County on this proposed action.

List of Subjects in 40 CFR Part 52

    Environmental protection, Air pollution control, Carbon monoxide, 
Incorporation by reference, Intergovernmental relations, Nitrogen 
dioxide, Ozone, Particulate matter, Reporting and recordkeeping 
requirements, Volatile organic compounds.

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

    Dated: September 30, 2019.
 Deborah Jordan,
Acting Regional Administrator, Region IX.
[FR Doc. 2019-23134 Filed 10-31-19; 8:45 am]
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