[Federal Register Volume 84, Number 212 (Friday, November 1, 2019)]
[Proposed Rules]
[Pages 58641-58666]
[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,<PHONE_NUMBER><EMAIL_ADDRESS>
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-

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

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

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

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\
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    \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

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

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

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

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.

    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\
---------------------------------------------------------------------------

    \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.
---------------------------------------------------------------------------

    \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

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,

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.

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

    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

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.
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    \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.
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    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

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.
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    \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

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