[Federal Register Volume 85, Number 64 (Thursday, April 2, 2020)]
[Proposed Rules]
[Pages 18509-18527]
[FR Doc No: 2020-06818]

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Parts 52 and 81

[EPA-R09-OAR-2019-0654; FRL 10007-30-Region 9]

PM10 Maintenance Plan and Redesignation Request; Imperial Valley
Planning Area; California

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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SUMMARY: The Environmental Protection Agency (EPA) is proposing to
approve the ``Imperial County 2018 Redesignation Request and
Maintenance Plan for Particulate Matter Less Than 10 Microns in
Diameter (PM10)'' (``Imperial PM10 Plan'') as a
revision of the California state implementation plan (SIP). The
Imperial PM10 Plan includes, among other elements, a
demonstration of implementation of best available control measures
(BACM) and a maintenance plan that includes an emissions inventory
consistent with attainment, a maintenance demonstration, contingency
provisions, and motor vehicle emissions budgets for use in
transportation conformity determinations. In connection with the
proposed approval of the Imperial PM10 Plan, the EPA is
proposing to determine that PM10 precursors do not
contribute significantly to elevated PM10 levels in the
area. The EPA is also proposing to

approve the State of California's request to redesignate the Imperial
Valley Planning Area from nonattainment to attainment for the
PM10 national ambient air quality standards. The EPA is
proposing these actions because the SIP revision meets the applicable
statutory and regulatory requirements for such plans and motor vehicle
emissions budgets and because the area meets the Clean Air Act
requirements for redesignation of nonattainment areas to attainment.
Lastly, the EPA is beginning the adequacy process for the 2016 and 2030
motor vehicle emissions budgets in the 2018 Imperial PM10
Plan through this proposed rule.

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

ADDRESSES: Submit your comments, identified by Docket ID No. EPA-R09-
OAR-2019-0654, at http://www.regulations.gov. For comments submitted at
Regulations.gov, follow the online instructions for submitting
comments. Once submitted, comments cannot be edited or removed from
Regulations.gov. The EPA may publish any comment received to its public
docket. Do not submit electronically any information you consider to be
Confidential Business Information (CBI) or other information whose
disclosure is restricted by statute. Multimedia submissions (audio,
video, etc.) must be accompanied by a written comment. The written
comment is considered the official comment and should include
discussion of all points you wish to make. The EPA will generally not
consider comments or comment contents located outside of the primary
submission (i.e., on the web, cloud, or other file sharing system). For
additional submission methods, please contact the person identified in
the FOR FURTHER INFORMATION CONTACT section. For the EPA's full public
comment policy, information about CBI or multimedia submissions, and
general guidance on making effective comments, please visit http://www.epa.gov/dockets/commenting-epa-dockets.

FOR FURTHER INFORMATION CONTACT: Ginger Vagenas, EPA Region IX, 75
Hawthorne St., San Francisco, CA 94105. By phone at<PHONE_NUMBER>, or by
email at<EMAIL_ADDRESS>
SUPPLEMENTARY INFORMATION: Throughout this document, the terms ``we,''
``us,'' and ``our'' mean the EPA.

Table of Contents

I. Background
    A. National Ambient Air Quality Standards
    B. State Implementation Plans and Area Designations
    C. Exceptional Events Rule
    D. Imperial Valley Planning Area
    E. PM10 Planning in the Imperial Valley Planning Area
II. Procedural Requirements for Adoption and Submittal of State
Implementation Plan Revisions
III. Clean Air Act Requirements for Redesignation to Attainment
IV. Evaluation of the State's Redesignation Request for the Imperial
PM10 Nonattainment Area
    A. Determination That the Area Has Attained the PM10
National Ambient Air Quality Standards
    B. The Area Must Have a Fully Approved State Implementation Plan
Meeting the Requirements Applicable for Purposes of Redesignation
Under Section 110 and Part D
    C. The Area Must Show the Improvement in Air Quality is Due to
Permanent and Enforceable Emission Reductions
    D. The Area Must Have a Fully Approved Maintenance Plan Under
Section 175A
V. Proposed Actions and Request for Public Comment
VI. Statutory and Executive Order Reviews

I. Background

A. National Ambient Air Quality Standards

    Under section 109 of the Clean Air Act (CAA or ``Act''), the EPA
has established national ambient air quality standards (NAAQS or
``standards'') for certain pervasive air pollutants (referred to as
``criteria pollutants'') and conducts periodic reviews of the NAAQS to
determine whether they should be revised or whether new NAAQS should be
established. The EPA sets the NAAQS for criteria pollutants at levels
required to protect public health and welfare.\1\ Particulate matter is
one of the ambient pollutants for which the EPA has established
NAAQS.\2\
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    \1\ For a given air pollutant, ``primary'' standards are those
determined by the EPA as requisite to protect the public health.
``Secondary'' standards are those determined by the EPA as requisite
to protect the public welfare from any known or anticipated adverse
effects associated with the presence of such air pollutant in the
ambient air. CAA section 109(b).
    \2\ Particulate matter is the generic term for a broad class of
chemically and physically diverse substances that exist as discrete
particles (liquid droplets or solids) over a wide range of sizes.
Particles originate from a variety of anthropogenic stationary and
mobile sources as well as from natural sources. Particles may be
emitted directly or form in the atmosphere by transformations of
gaseous emissions such as sulfur dioxide (SO2), oxides of
nitrogen (NOX), volatile organic compounds (VOC), and
ammonia (NH3). The chemical and physical properties of
particulate matter vary greatly with time, region, meteorology, and
source category. SO2, NOX, VOC, and
NH3 are referred to as PM10 precursors. As
discussed later in this proposed rule, precursors do not contribute
significantly to elevated ambient PM10 concentrations in
the Imperial Valley Planning Area. Some California air quality plans
use the term reactive organic gases (ROG) instead of VOC. The terms
cover essentially the same compounds, and herein we use the term
VOC.
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    In 1987, the EPA established primary and secondary NAAQS for
particles with an aerodynamic diameter less than or equal to a nominal
ten micrometers (PM10).\3\ At that time, the EPA established
two PM10 standards; an annual standard and a 24-hour
standard.\4\ An area attains the 24-hour standard of 150 micrograms per
cubic meter ([mu]g/m\3\) when the expected number of days per calendar
year with a 24-hour concentration in excess of the standard (referred
to as an exceedance), averaged over three years, is equal to or less
than one.\5\ The annual PM10 standard was subsequently
revoked.\6\ More recently, the EPA announced that it was retaining the
24-hour PM10 NAAQS as a 24-hour standard of 150 [mu]g/
m\3\.\7\ In this document, ``PM10 NAAQS'' or
``PM10 standard'' refer to the 24-hour-average
PM10 NAAQS.
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    \3\ 52 FR 24634 (July 1, 1987).
    \4\ The primary and secondary standards were set at the same
level for both the 24-hour and the annual PM10 standards.
    \5\ An exceedance is defined as a daily value that is above the
level of the 24-hour standard, 150 [mu]g/m\3\, after rounding to the
nearest 10 [mu]g/m\3\ (i.e., values ending in five or greater are to
be rounded up). Consequently, a recorded value of 154 [mu]g/m\3\
would not be an exceedance because it would be rounded to 150 [mu]g/
m\3\. A recorded value pf 155 [mu]g/m\3\ would be an exceedance
because it would be rounded to 160 [mu]g/m\3\. 40 CFR part 50,
Appendix K, section 1.0.
    \6\ In 2006, the EPA retained the 24-hour PM10
standards but revoked the annual standards. 71 FR 61144 (October 17,
2006).
    \7\ 78 FR 3086 (January 15, 2013).
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B. State Implementation Plans and Area Designations

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

C. Exceptional Events Rule

    Congress has recognized that it may not be appropriate for the EPA
to use certain monitoring data collected by the ambient air quality
monitoring network and maintained in the EPA's Air Quality

System database (AQS) \8\ in certain regulatory determinations. Thus,
in 2005, Congress provided the statutory authority for the exclusion of
data influenced by ``exceptional events'' meeting specific criteria by
adding section 319(b) to the CAA.\9\ To implement this 2005 CAA
amendment, the EPA promulgated the 2007 Exceptional Events Rule.\10\
The 2007 Exceptional Events Rule created a regulatory process codified
at 40 CFR parts 50 and 51 (sections 50.1, 50.14 and 51.930). These
regulatory sections, which superseded the EPA's previous guidance on
handling data influenced by events, contain definitions, procedural
requirements, requirements for air agency demonstrations, criteria for
the EPA's approval of the exclusion of event-affected air quality data
from the data set used for regulatory decisions, and requirements for
air agencies to take appropriate and reasonable actions to protect
public health from exceedances or violations of the NAAQS. In 2016, the
EPA promulgated a comprehensive revision to the 2007 Exceptional Events
Rule.\11\
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    \8\ AQS is the EPA's official repository of ambient air data.
    \9\ Under CAA section 319(b), an exceptional event means an
event that (i) affects air quality; (ii) is not reasonably
controllable or preventable; (iii) is an event caused by human
activity that is unlikely to recur at a particular location or a
natural event; and (iv) is determined by the EPA under the process
established in regulations promulgated by the EPA in accordance with
section 319(b)(2) to be an exceptional event. For the purposes of
section 319(b), an exceptional event does not include (i) stagnation
of air masses or meteorological inversions; (ii) a meteorological
event involving high temperatures or lack of precipitation; or (iii)
air pollution relating to source noncompliance.
    \10\ 72 FR 13560, March 22, 2007.
    \11\ 81 FR 68216 (October 3, 2016). We refer herein to the 2016
revision as the ``Exceptional Events Rule.''
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    Under the Exceptional Events Rule, if a state demonstrates to the
EPA's satisfaction that emissions from a high wind dust event caused a
specific air pollution concentration in excess of the NAAQS at a
particular air quality monitoring location and otherwise satisfies the
requirements of 40 CFR 50.14, the EPA must exclude that data from use
in determinations of exceedances and violations.\12\ The EPA considers
high wind dust events to be natural events in cases where windblown
dust is entirely from natural undisturbed lands in the area or where
all anthropogenic sources are reasonably controlled.\13\ For areas in
California, the EPA accepts sustained winds of 25 miles per hour as a
high wind threshold.\14\
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    \12\ 40 CFR 50.14(b)(5).
    \13\ 40 CFR 50.14(b)(5)(ii).
    \14\ 40 CFR 50.14(b)(5)(iii).
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D. Imperial Valley Planning Area

    Through its enactment of the Clean Air Act Amendments of 1990,
Congress designated certain areas of the country as nonattainment areas
for the PM10 NAAQS. A portion of Imperial County (or
``County''), referred to as the Imperial Valley Planning Area, was one
of the areas designated as nonattainment.\15\ In 1991, the EPA
classified the Imperial Valley Planning Area, also referred to herein
as the ``Imperial PM10 nonattainment area,'' as a
``Moderate'' PM10 nonattainment area.\16\
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    \15\ CAA section 107(d)(4)(B)(i) and 52 FR 29383 (August 7,
1987).
    \16\ 56 FR 56694 (November 6, 1991). On March 19, 2013, we
clarified the description of the Imperial Valley planning area. 78
FR 16792. An exact description of the Imperial PM10
nonattainment area is provided in 40 CFR 81.305.
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    Imperial County encompasses approximately 4,500 square miles in
southeastern California. It is home to approximately 190,600 people,
and its principal industries are farming and retail trade. It is
bordered by Riverside County to the north, Arizona to the east, Mexico
to the south, and San Diego County and coastal mountains to the west.
The Salton Sea straddles the boundary between Riverside and Imperial
counties with most of the lake located in the northwest portion of
Imperial County. Winters are mild and dry, and summers are extremely
hot, with average annual rainfall of about 3 inches. The topography and
meteorology of the area creates conditions conducive to moderate and
occasionally extremely high winds that result in elevated levels of
particulate matter.\17\
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    \17\ Section 1.3 of the Imperial PM10 Plan includes a
description of the geography, climate and meteorology, and
atmospheric stability and dispersion characteristics in Imperial
County.
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    The Imperial PM10 nonattainment area encompasses the
western and central parts of the County and includes the Imperial
Valley.\18\ The Imperial Valley runs north-south through the central
part of the County. Most of the County's population and industries
exist within this relatively narrow land area, which extends about one-
fourth the width of the County. The rest of Imperial County is
primarily open desert, with little or no human population. The Torres
Martinez Desert Cahuilla Indians have reservation land in the
northwestern corner of the nonattainment area, and the Quechan Tribe of
the Fort Yuma Indian Reservation has reservation land in the
southeastern portion of the nonattainment area.
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    \18\ Figure 1-3 of the Imperial PM10 Plan illustrates
the boundary of the nonattainment area. Generally, the nonattainment
area covers that portion of Imperial County that lies west of the
crestline of the Chocolate Mountains.
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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
California SIPs and SIP revisions and it has broad authority to
establish emissions standards and other requirements for mobile
sources. Local and regional air pollution control districts in
California are responsible for the regulation of stationary sources and
are generally responsible for the development of air quality plans. In
Imperial County, the Imperial County Air Pollution Control District
(ICAPCD or ``District'') develops and adopts air quality plans to
address CAA planning requirements applicable to the Imperial Valley
Planning Area. Such plans are then submitted to CARB for adoption and
submittal to the EPA as revisions to the California SIP.

E. PM10 Planning in the Imperial Valley Planning Area

    Under section 189(a) of the CAA, as amended in 1990, states with
Moderate PM10 nonattainment areas were required to develop
and submit SIP revisions that, among other things, provide for
implementation of reasonably available control measures (RACM) and that
demonstrate that the nonattainment area would attain the
PM10 NAAQS no later than the applicable attainment date of
December 31, 1994. Subsequent to litigation over the extent to which
PM10 emissions generated within Mexico contributed to
PM10 exceedances over the 1992 to 1994 period, we determined
that the Imperial PM10 nonattainment area did not attain the
PM10 NAAQS by the Moderate area deadline (December 31, 1994)
and reclassified the area from Moderate to ``Serious.'' \19\
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    \19\ 69 FR 48972 (August 11, 2004). Please see our August 11,
2004 final rule for details concerning the litigation and our
determination that the Imperial PM10 nonattainment area
had failed to attain by the applicable Moderate area attainment
date.
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    Under section 189(b) of the CAA, states with Serious
PM10 nonattainment areas are required to submit SIP
revisions that, among other things, provide for implementation of BACM
and attainment no later than applicable Serious area attainment date
(December 31, 2001). In the case of the Imperial PM10
nonattainment area, we determined that the area did not attain the
PM10 NAAQS by the Serious area deadline (December 31, 2001),
which triggered the requirement under CAA section 189(d) for the State
to revise the SIP to provide for attainment of the PM10
NAAQS in the Imperial PM10 nonattainment area and to provide
at

least five percent annual reductions in PM10 or
PM10 precursor emissions until attainment is reached.\20\
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    \20\ 72 FR 70222 (December 11, 2007).
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    Meanwhile, in response to the designation of the Imperial Valley
Planning Area as a Moderate, then Serious, nonattainment area, the
District and CARB developed several air quality plans to address
applicable CAA requirements for the area. In developing the plans and
control strategies, the District and CARB identified direct
PM10 sources, such as fugitive dust sources (e.g., farming,
construction, and vehicle travel over paved and unpaved roads) and
windblown dust as two principal sources of PM10 emissions
causing or contributing to PM10 exceedances in the
nonattainment area.\21\ The District and CARB found that secondarily-
formed PM10 (i.e., PM10 derived from
PM10 precursors such as NOX and SO2)
contributed little to exceedances in the nonattainment area.
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    \21\ CARB, ``Status Report on Imperial County Air Quality and
Approval of the State Implementation Plan Revision for
PM10,'' Release Date: April 26, 2010.
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    To address fugitive dust sources in the nonattainment area and to
address the Serious area requirement for implementation of BACM, the
District adopted a set of rules in Regulation VIII establishing
emission control requirements for such fugitive sources as construction
and earthmoving, bulk materials, carry out and track out, open areas,
paved and unpaved roads, and agricultural activities. In 2010, the EPA
approved the rules, but also identified certain deficiencies with
respect to the BACM requirement in some of the rules that prevented
full approval.\22\ In response, in 2012, the District amended certain
Regulation VIII rules, including the rules for open areas, paved and
unpaved roads, and agricultural activities.
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    \22\ 75 FR 39366 (July 8, 2010).
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    In the following year, the EPA found that the deficiencies had been
corrected and approved the amended rules as revisions to the Imperial
County portion of the California SIP.\23\ In our 2013 final rule, we
indicated our preliminary view that the Regulation VIII rules, as
revised in 2012, constitute reasonable control of the sources covered
by Regulation VIII for the purpose of evaluating whether an exceedance
of the PM10 NAAQS is an exceptional event pursuant to the
Exceptional Events Rule, including reasonable and appropriate control
measures on significant contributing anthropogenic sources.\24\
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    \23\ 78 FR 23677 (April 22, 2013).
    \24\ Id., at 23682. As stated in our 2013 final rule, our
preliminary view did not extend to exceedances of NAAQS other than
the PM10 NAAQS or to events that differ significantly in
terms of meteorology, sources, or conditions from the events that
were at issue in the EPA's July 2010 final action and associated
litigation, nor was our preliminary statement intended to be a
determination with respect to any specific PM10
exceedances.
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    More recently, the District and CARB reviewed the PM10
ambient monitoring data collected within the Imperial Valley Planning
Area and preliminarily determined that the Imperial Valley Planning
Area has attained the PM10 NAAQS based on 2014-2016 data.
Their preliminary determination assumes the EPA's concurrence, under
the Exceptional Events Rule, on the District's and CARB's determination
that nearly all the exceedances during that period were exceptional
events caused by emissions due to high winds. Attainment of the NAAQS
is one of the criteria for redesignation of a nonattainment area to
attainment, and the District and CARB developed the Imperial
PM10 Plan to address all the redesignation criteria,
including the attainment criterion.
    Following approval by the District in October 2018 and by CARB in
December 2018, CARB submitted the Imperial PM10 Plan to the
EPA under cover of letter dated February 6, 2019, as a revision to the
Imperial County portion of the California SIP. We received the SIP
submittal on February 13, 2019. In addition to the Imperial
PM10 Plan itself, the SIP revision submittal package
includes the District Board Minute Order approving the plan and related
District staff report, the CARB Board Resolution 18-58 adopting the
plan and related CARB staff report, and documentation of public
participation. In this action, for the reasons discussed in the
following sections of this document, we are proposing to approve the
Imperial PM10 Plan and to approve CARB's request to
redesignate the Imperial Valley Planning Area from nonattainment to
attainment for the PM10 NAAQS.

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

    CAA sections 110 (a)(1) and (2) and section 110(l) require a state
to provide reasonable notice and opportunity for public hearing prior
to adoption and submission of a SIP or SIP revision. To meet these
procedural requirements, every SIP submission should include evidence
that the state provided adequate public notice and an opportunity for a
public hearing consistent with the EPA's implementing regulations in 40
CFR 51.102.
    CARB's February 6, 2019 SIP submittal package includes
documentation of the public processes used by the District and CARB to
adopt the Imperial PM10 Plan. As documented in the SIP
revision submittal package, on September 20, 2018, the District
published a notice in a newspaper of general circulation in Imperial
County that a public hearing to consider adoption of the plan would be
held on October 23, 2018. As documented in the Minute Order of the Air
Pollution Control Board that is included in the SIP revision submittal
package, the Imperial County Air Pollution Control Board of Directors
adopted the Imperial PM10 Plan on October 23, 2018,
following the public hearing.
    Following transmittal by the District of the adopted Imperial
PM10 Plan to CARB, on November 9, 2018, CARB published on
its website a notice of a public hearing to be held on December 13,
2018, to consider adoption of the plan. As evidenced by CARB Resolution
18-58, CARB adopted the Imperial PM10 Plan on December 13,
2018, following a public hearing. Based on documentation included in
the February 6, 2019 SIP revision submittal package, we find that both
the District and CARB have satisfied the applicable statutory and
regulatory requirements for reasonable public notice and hearing prior
to the adoption and submission of the Imperial PM10 Plan.
Therefore, we find that the submission of the Imperial PM10
Plan meets the procedural requirements for public notice and hearing in
CAA sections 110(a) and 110(l) and in 40 CFR 51.102.

III. Clean Air Act Requirements for Redesignation to Attainment

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

applicable nonattainment SIP requirements are found in part D, subpart
1, and the particulate matter-specific SIP requirements are found in
part D, subpart 4.
    The EPA provided guidance on redesignations in a document entitled
``State Implementation Plans; General Preamble for the Implementation
of Title I of the Clean Air Act Amendments of 1990,'' published in the
Federal Register on April 16, 1992,\25\ and supplemented on April 28,
1992 \26\ (referred to herein as the ``General Preamble''). We issued
additional guidance on September 4, 1992, in a memorandum from John
Calcagni, Director, Air Quality Management Division, EPA Office of Air
Quality Planning and Standards, entitled ``Procedures for Processing
Requests to Redesignate Areas to Attainment'' (referred to herein as
the ``Calcagni memo''). On August 16, 1994, the EPA published guidance
for Serious PM10 nonattainment areas in a document entitled
``State Implementation Plans for Serious PM10 Nonattainment
Areas, and Attainment Date Waivers for PM10 Nonattainment
Areas Generally; Addendum to the General Preamble for the
Implementation of Title I of the Clean Air Act Amendments of 1990,''
(herein referred to as the ``Addendum'').\27\
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    \25\ 57 FR 13498.
    \26\ 57 FR 18070.
    \27\ 59 FR 41998.
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    Maintenance plan submittals are SIP revisions, and as such, the EPA
is obligated under CAA section 110(k) to approve them or disapprove
them depending upon whether they meet the applicable CAA requirements
for such plans.
    For reasons set forth in Section IV of this document, we propose to
approve the Imperial PM10 Plan and to approve CARB's request
for redesignation of the Imperial Valley Planning Area from
nonattainment to attainment for the PM10 NAAQS based on our
conclusion that all the criteria under CAA section 107(d)(3)(E) have
been satisfied.

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

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

    Section 107(d)(3)(E)(i) of the CAA states that, for an area to be
redesignated to attainment, the EPA must determine that the area has
attained the relevant NAAQS. In this case, the relevant standard is the
PM10 NAAQS. Generally, the EPA determines whether an area's
air quality is meeting the PM10 NAAQS based upon complete,
quality-assured, and certified data gathered at established state and
local air monitoring stations (SLAMS) in the nonattainment area and
entered into the EPA's AQS database.\28\
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    \28\ For PM10, a complete year of air quality data
includes all four calendar quarters with each quarter containing a
minimum of 75 percent of the scheduled PM10 sampling
days. 40 CFR part 50, Appendix K, section 2.3(a).
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    Data from air monitors operated by state, local, or tribal agencies
in compliance with EPA monitoring requirements must be submitted to
AQS. These monitoring agencies certify annually that these data are
accurate to the best of their knowledge. Accordingly, the EPA relies
primarily on data in AQS when determining the attainment status of an
area.\29\ All valid data are reviewed to determine the area's air
quality status in accordance with 40 CFR part 50, Appendix K.
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    \29\ 40 CFR 50.6; 40 CFR part 50, appendices J and K; 40 CFR
part 53; and 40 CFR part 58, appendices A, C, D, and E.
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    The PM10 standard is attained when the expected number
of exceedances per year, averaged over a three-year period, is less
than or equal to one. The expected number of exceedances averaged over
a three-year period at any given monitor is known as the
PM10 design value. The PM10 design value for the
area is the highest design value within the nonattainment area. Three
consecutive years of air quality data are required to show attainment
of the PM10 standard.\30\ The demonstration of attainment in
the Imperial PM10 Plan is based on data from 2014-2016. In
order to ensure the area has continued to attain, the EPA is also
considering data collected subsequent to the time frame of the Plan.
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    \30\ 40 CFR part 50 and Appendix K.
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    ICAPCD is a monitoring organization within the CARB Primary Quality
Assurance Organization (PQAO). ICAPCD and CARB are jointly responsible
for monitoring ambient air quality within the Imperial PM10
nonattainment area. CARB submits annual monitoring network plans to the
EPA describing the monitoring network operated by ICAPCD and CARB
within Imperial County and discussing the status of the air monitoring
network, as required under 40 CFR 58.10.
    The EPA reviews these annual plans for compliance with the
applicable reporting requirements in 40 CFR part 58. With respect to
PM10, the EPA has found that CARB's network plans meet the
applicable reporting requirements for the area under 40 CFR part
58.\31\ The EPA also concluded from its 2018 Technical System Audit
that CARB and ICAPCD's monitoring network currently meets or exceeds
the requirements for the minimum number of SLAMS for PM10 in
the El Centro, CA Metropolitan Statistical Area, which includes the
Imperial PM10 nonattainment area.\32\ ICAPCD and CARB
annually certify that the data they submit to AQS are complete and
quality-assured.\33\
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    \31\ For example, see letter dated November 26, 2018, from Gwen
Yoshimura, Manager, Air Quality Analysis Office, EPA Region IX, to
Ravi Ramalingam, Chief, Consumer Products and Air Quality Assessment
Branch, CARB, approving CARB's 2018 Annual Network Plan.
    \32\ See EPA Region IX, Technical Systems Audit Final Report of
the Ambient Air Monitoring Program: California Air Resources Board,
September-December 2018. Enclosed with letter dated February 3,
2020, from Elizabeth J. Adams, Director, Air and Radiation Division,
EPA Region IX, to Richard Corey, Executive Officer, CARB.
    \33\ See, e.g., letter dated August 12, 2019, from Michael
Benjamin, Chief, Air Quality Planning and Science Division, CARB, to
Mike Stoker, Regional Administrator, EPA Region IX, certifying 2018
ambient air quality data and quality assurance data.
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    During the 2014-2016 time period, CARB operated one and ICAPCD
operated four PM10 SLAMS monitoring sites within the
Imperial PM10 nonattainment area. These sites are oriented
along a roughly north-south axis in the central, populated part of the
nonattainment area.\34\ Historically, all five sites monitored
PM10 concentrations using filter-based designated Federal
Reference Method (FRM) monitors. Two sites have also monitored
concentrations using continuous Federal Equivalent Method (FEM)
monitors since 2009.
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    \34\ Section 2.2 of the Imperial PM10 Plan includes a
description of the monitoring sites and information regarding the
history and timing of the addition of BAM monitors to the network.
Figure 2-1 of the Imperial PM10 Plan shows the locations
of the SLAMS monitoring sites within the Imperial Valley Planning
Area.

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    Between 2015 and 2016, data from FEM monitors became available at
the remaining stations, while the filter-based FRM monitors at all five
stations were gradually retired.\35\ The PM10 monitoring
sites have been established to monitor for population exposure in the
middle or neighborhood scale.\36\
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    \35\ Memorandum dated March 5, 2020, from Jennifer Williams, EPA
Region IX and Brett Gantt, EPA Office of Air Quality Planning and
Standards, to Docket Number EPA-R09-OAR-2019-0654, Subject: Imperial
County, CA PM10 Nonattainment Area Design Value
Calculations.
    \36\ In this context, ``middle scale'' refers to conditions
characteristic of areas from 100 meters to half a kilometer, and
``neighborhood scale'' refers to conditions throughout some
reasonably homogeneous urban sub-region with dimensions of a few
kilometers. 40 CFR part 58, Appendix D, section 4.6.
---------------------------------------------------------------------------

    Consistent with the requirements contained in 40 CFR part 50, the
EPA has reviewed the quality-assured and certified PM10
ambient air monitoring data as recorded in AQS for the applicable
monitoring period collected at the monitoring sites in the Imperial
PM10 nonattainment area and determined that the data are of
sufficient completeness for the purposes of making comparisons with the
PM10 standards.
    The monitoring data for the PM10 standard for the
Imperial PM10 nonattainment area include exceedances of the
standard recorded during the 2014-2016 time period and in 2017 and
2018. However, the EPA is excluding most of the exceedances of the
standard in these years from the attainment determination because they
were the result of exceptional events as defined in section 319(b) of
the Act and its implementing regulations, referred to herein as the
Exceptional Events Rule.\37\ The Exceptional Events Rule defines an
exceptional event as an event that the EPA determines affects air
quality in such a way that there is a clear causal relationship between
the event and a monitored exceedance (or violation) that is not
reasonably controllable or preventable. Such events can be natural (for
example, high winds or wildfires) or can be caused by human activity
that is unlikely to recur.\38\
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    \37\ As noted in Section I.C. of this notice, the EPA
promulgated the Exceptional Events Rule (``Treatment of Data
Influenced by Exceptional Events'') on March 22, 2007 (72 FR 13560)
and later revised it on October 3, 2016 (81 FR 68216).
    \38\ 40 CFR 50.1.
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    On various dates, CARB submitted demonstrations for high wind
PM10 exceptional events covering the exceedances recorded at
various monitoring sites in the nonattainment area during the 2014--
2018 time period.\39\ The demonstrations include a narrative conceptual
model of each event that describes the event-specific characteristics,
evidence showing the exceedances were not reasonably controllable or
preventable, and evidence of the clear causal relationship between the
high wind events and the exceedances flagged as exceptional events.
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    \39\ While submitted by CARB, the demonstrations and addendums
were developed through a joint effort by CARB and ICAPCD. The
exceptional events demonstrations are included in the docket for
this action.
---------------------------------------------------------------------------

    The EPA reviewed the documentation that CARB and the District
developed to demonstrate that the exceedances on these days met the
criteria for an exceptional event under the Exceptional Events Rule. As
conveyed in the EPA's concurrence letters included in the docket for
this action, we have concurred with 91 exceedance days that the State
requested for determinations that, based on the weight of evidence,
exceedances were caused by high wind exceptional events.\40\
Accordingly, the EPA has determined that the monitored exceedances
associated with these exceptional events should be excluded from use in
determinations of exceedances and violations, including the evaluation
of whether the Imperial PM10 nonattainment area has attained
the standard for the purposes of redesignation under CAA section
107(d)(3)(E)(i). Table 1 presents a summary of the PM10
design values for 2016, 2017, and 2018 at the various monitors within
the Imperial Valley Planning Area, excluding the exceedances for which
the EPA has issued concurrences, based on the data for 2014-2016, 2015-
2017 and 2016-2018 data, respectively.\41\ The PM10 design
value for the area is the PM10 design value at the monitor
with the highest design value in a given year.
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    \40\ The EPA's concurrence letters and technical support
documents are located in the docket for this action.
    \41\ More information can be found in the memorandum dated March
5, 2020, from Jennifer Williams, EPA Region IX and Brett Gantt, EPA
Office of Air Quality Planning and Standards, to Docket Number EPA-
R09-OAR-2019-0654, Subject: Imperial County, CA PM10
Nonattainment Area Design Value Calculations.

                                   Table 1--2016, 2017, and 2018 Design Values for the 1987 PM10 NAAQS at Imperial County, CA Air Quality Monitoring Stations
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                PM10 design value
            Station Name                      AQS ID         -----------------------------------------------------------------------------------------------------------------------------------
                                                                         2016                 Valid                  2017                 Valid                  2018                 Valid
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Calexico............................  06-025-0005-3.........  0.0 \a\..................               Y   0.7 \a\..................               Y   1.0......................               Y
Brawley.............................  06-025-0007-1.........  Invalid \b\..............               N   N/A \c\..................               Y   N/A \c\..................               Y
Brawley.............................  06-025-0007-3.........  0.0......................               Y   0.3......................               Y   0.3......................               Y
El Centro...........................  06-025-1003-4.........  0.0 \a\..................               Y   0.0 \a\..................               Y   0.3......................               Y
Westmorland.........................  06-025-4003-3.........  0.0 \a\..................               Y   0.3 \a\..................               Y   0.3......................               Y
Niland..............................  06-025-4004-1.........  0.0......................               Y   N/A \c\..................               Y   N/A \c\..................               Y
Niland..............................  06-025-4004-3.........  0.0......................               Y   0.0......................               Y   0.0......................               Y
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
\a\ The 2016 and 2017 design values for the Westmorland (06-025-4003-3), El Centro (06-025-1003-4), and Calexico (06-025-0005-3) are derived from a combination of data resulting from the
  monitoring agency transitioning from one monitor to a newer monitor at the same monitoring station.
\b\ The 2016 design value for Brawley (06-025-0007-1) is invalid due to insufficient data completeness in 2014.
\c\ The Niland (06-025-4004-1) and Brawley (06-025-0007-1) monitors were approved for closure by the EPA.

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

demonstrates that the area continues to attain the standard. Therefore,
based on complete, quality-assured, and certified data for 2014-2018,
we find that the Imperial County PM10 nonattainment area
attained the PM10 NAAQS in 2016 and has continued to attain
since that time.
    We have also reviewed preliminary data for 2019 that have been
entered in AQS and have determined that they are consistent with
attainment.\42\ We will review any additional data that becomes
available prior to final action to ensure that they are consistent with
continued attainment.\43\
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    \42\ AQS Design Value Report (AMP 480), dated March 5, 2020.
    \43\ We recognize that, on October 22, 2019, the Imperial County
Board of Supervisors adopted a proclamation of local emergency for
air pollution at the Salton Sea. See letter dated November 4, 2019,
from Tony Rouhotas, Jr., County Executive Officer, to Gavin Newsom,
Governor of the State of California. The proclamation was based
primarily on ambient PM10 concentration data collected at
two nonregulatory monitors located immediately west of the Salton
Sea at Salton City and Naval Test Base that showed exceedances of
the PM10 NAAQS. Nonregulatory monitors are those that
have not been determined to comply with the minimum requirements in
40 CFR part 58 (``Ambient Air Quality Surveillance''), such as the
siting criteria. While data from nonregulatory monitors are not
appropriate for use in determining whether an area attained or
failed to attain the NAAQS, the data are appropriate for other
purposes. In this case, under the Salton Sea Air Quality Mitigation
Program, the nonregulatory data are used to produce the annual
emissions inventories, assemble dust control plans, and evaluate the
performances of the dust control plans. Imperial PM10
Plan, 5-5. The State of California's initial response to Imperial
County's November 4, 2019 letter is contained in a letter dated
January 6, 2020, from Wade Crowfoot, Secretary for Natural Resources
and Jared Blumenfeld, Secretary for Environmental Protection, which
is included in the docket for this rulemaking.
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B. The Area Must Have a Fully Approved State Implementation Plan
Meeting the Requirements Applicable for Purposes of Redesignation Under
Section 110 and Part D

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

    \44\ Calcagni Memo, 3; Wall v. EPA, F.3d 416 (6th Cir. 2001);
and Southwestern Pennsylvania Growth Alliance v. Browner, (144 F.3d
984, 989-990 (6th Cir. 1998).
    \45\ 68 FR 25418, 25426 (May 12, 2003) and citations within.
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1. Basic State Implementation Plan Requirements Under Section 110
    The general SIP elements and requirements set forth in section
110(a)(2) include, but are not limited to, the following: Submittal of
a SIP that has been adopted by the state after reasonable public notice
and hearing; provisions for establishment and operation of appropriate
procedures needed to monitor ambient air quality; implementation of a
source permitting program; provision for the implementation of part C
requirements for prevention of significant deterioration; provisions
for the implementation of part D requirements for nonattainment new
source review permit programs; provisions for air pollution modeling;
and provisions for public and local agency participation in planning
and emission control rule development.
    We note that SIPs must be fully approved only with respect to
applicable requirements for purposes of redesignation in accordance
with section 107(d)(3)(E)(ii). The section 110(a)(2) (and part D)
requirements that are linked to a particular nonattainment area's
designation and classification are the relevant measures to evaluate in
reviewing a redesignation request. Requirements that apply regardless
of the designation of any particular area of a state are not applicable
requirements for the purposes of redesignation, and the State will
remain subject to these requirements after the Imperial PM10
nonattainment area is redesignated to attainment.
    For example, CAA section 110(a)(2)(D) requires that SIPs contain
certain measures to prevent sources in a state from significantly
contributing to air quality problems in another state: These SIPs are
often referred to as ``transport SIPs.'' Because the section
110(a)(2)(D) requirements for transport SIPs are not linked to a
particular nonattainment area's designation and classification, but
rather apply regardless of the area's attainment status, these are not
applicable requirements for the purposes of redesignation under section
107(d)(3)(E).
    Similarly, the EPA considers other section 110(a)(2) (and part D)
requirements that are not linked to nonattainment plan submissions or
to an area's attainment status as not applicable requirements for
purposes of redesignation. The EPA evaluates the section 110 (and part
D) requirements that relate to a particular nonattainment area's
designation and classification as the relevant measures to evaluate in
reviewing a redesignation request. This is consistent with the EPA's
existing policy on applicability of the conformity SIP requirement for
redesignations.\46\
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    \46\ 75 FR 36023, 36026 (June 24, 2010) and citations within.
---------------------------------------------------------------------------

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

    \47\ The Imperial County portion of the federally approved
California SIP can be viewed at https://www.epa.gov/sips-ca/epa-approved-imperial-county-apcd-regulations-california-sip.
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2. State Implementation Plan Requirements Under Part D
    Subparts 1 and 4 of part D, title 1 of the CAA contain air quality
planning requirements for PM10 nonattainment areas. Subpart
1 contains general requirements for all nonattainment areas of any
pollutant, including PM10, governed by a NAAQS. The subpart
1 requirements include, in relevant part, provisions for implementation
of RACM, a demonstration of reasonable further progress (RFP),
emissions inventories, a program for preconstruction review and
permitting of new or modified major stationary sources, contingency
measures, transportation conformity, and for areas that fail to attain
the standard by the applicable attainment date, a plan

meeting the requirements of section 179(d).
    Subpart 4 contains specific planning and scheduling requirements
for PM10 nonattainment areas. Section 189(a), (c), and (e)
requirements apply specifically to Moderate PM10
nonattainment areas and include the following: An approved permit
program for construction of new and modified major stationary sources;
provisions for RACM; an attainment demonstration; quantitative
milestones demonstrating RFP toward attainment by the applicable
attainment date; and provisions to ensure that the control requirements
applicable to major stationary sources of PM10 also apply to
major stationary sources of PM10 precursors, except where
the Administrator has determined that such sources do not contribute
significantly to PM10 levels that exceed the NAAQS in the
area.
    Under CAA section 189(b), Serious PM10 nonattainment
areas such as the Imperial PM10 nonattainment area, must
meet the subpart 1 and Moderate area requirements discussed above and,
in addition, must develop and submit provisions to assure the
implementation of BACM for the control of PM10.\48\ Under
CAA section 189(d), Serious PM10 nonattainment areas that
fail to attain the standard by the applicable attainment date, such as
Imperial County, must develop and submit plan revisions that provide
for attainment of the PM10 standard and, from the date of
such submission until attainment, for an annual reduction in
PM10 of not less than 5 percent of the amount of such
emissions.
---------------------------------------------------------------------------

    \48\ In Moderate PM10 nonattainment areas, major
sources include sources that emit or have the potential to emit at
least 100 tons per year of PM10 or its precursors.
Sources that emit less than 100 tons per year are minor sources. In
Serious PM10 nonattainment areas, the threshold
distinguishing major stationary sources from minor stationary
sources is 70 tons per year.
---------------------------------------------------------------------------

    In the context of evaluating an area's eligibility for
redesignation, the EPA has interpreted CAA requirements associated with
attainment of the NAAQS (such as attainment and RFP demonstrations) as
not being applicable for purposes of redesignation.\49\ The Calcagni
memo similarly provides that requirements for RFP and other measures
needed for attainment will not apply for redesignations because they
have meaning and applicability only where areas do not meet the
NAAQS.\50\ With respect to contingency measures, the EPA explained that
the section 172(c)(9) contingency measure requirements are directed at
ensuring RFP and attainment by the applicable date and that,
consequently, these requirements no longer apply when an area has
attained the standard and is eligible for redesignation. Furthermore,
CAA section 175A(d) provides for specific requirements for maintenance
plan contingency measures that effectively supersede the requirements
of section 172(c)(9) for these areas.\51\
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    \49\ General Preamble, 13564.
    \50\ Calcagni memo, 6.
    \51\ Our evaluation of the contingency plan element of the
Imperial PM10 Plan in in Section IV.D.4 of this document.
---------------------------------------------------------------------------

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

    \52\ The Seventh Circuit in Sierra Club v. EPA, 375 F.3d 537
(7th Cir. 2004) (upholding EPA redesignation of the St. Louis
metropolitan area to attainment) is one such example.
---------------------------------------------------------------------------

    The remaining applicable Part D requirements for Serious
PM10 areas include the following: (1) An emissions inventory
under section 172(c)(3); (2) a permit program for the construction and
operation of new and modified major stationary sources of
PM10 under sections 172(c)(5), 189(a)(1)(A) and 189(b)(3);
(3) provisions to assure the implementation of BACM under section
189(b)(1)(B); (4) control requirements for major stationary sources of
PM10 precursors under section 189(e), except where the
Administrator determines that such sources do not contribute
significantly to PM10 levels that exceed the standard in the
area; (5) requirements under section 172(c)(7) that meet the applicable
provisions of section 110(a)(2); and (6) provisions to ensure that
federally supported or funded transportation projects conform to the
air quality planning goals in the applicable SIP under section 176(c).
We discuss each of these requirements below.
a. PM10 Precursors
    While CAA section 189(e) expressly requires control of precursors
from major stationary sources, it is clear that subpart 4 and other CAA
provisions collectively require the control of direct PM2.5
and PM2.5 precursors from all types of sources (i.e.,
stationary sources, area sources and mobile sources) as may be needed
for the purposes of demonstrating attainment as expeditiously as
practicable in a given nonattainment area. See CAA requirements for
states to demonstrate attainment ``as expeditiously as practicable.''
CAA section 188(c)(1) and section 172(a)(1).
    For the purposes of the redesignation request and development of
the maintenance plan, CARB undertook an analysis of mass and speciation
data to determine the extent to which PM10 precursors
contribute to ambient concentrations of PM10 in the Imperial
Valley Planning Area.\53\ CARB identified five days within the period
of 2007 to 2016 where concentrations of PM10 were greater
than 95% of the NAAQS and for which PM10 mass and
PM10 and PM2.5 speciation data were
available.\54\ Values for PM10 mass on these dates ranged
from 144 [mu]g/m\3\ to 305 [mu]g/m\3\.\55\ Using this information, CARB
calculated that for these five days, on average, SOX \56\
contributes 4.5 [mu]g/m\3\ or 2 percent (%) of the PM10
mass, NOX contributes 3 [mu]g/m\3\ or 1.3% of the
PM10 mass, ammonia contributes 4.7 [mu]g/m\3\ or 2.1% of the
PM10 mass, and VOC contributes 4.1 [mu]g/m\3\ or 1.8% of the
PM10 mass.
---------------------------------------------------------------------------

    \53\ Imperial PM10 Plan, Appendix A,
``PM10 Precursor Analysis for Imperial County.''
    \54\ Secondarily-formed particulate matter, i.e., the
particulate matter derived from gases such as NOX and
SO2, is in the fine fraction of particulate matter
(PM2.5).
    \55\ Imperial PM10 Plan, Appendix A,
``PM10 Precursor Analysis for Imperial County,'' Table 1.
    \56\ The Imperial PM10 Plan generally uses ``sulfur
oxides'' or ``SOX'' in reference to SO2 as a
precursor to the formation of PM10. We use SOX
and SO2 interchangeably.
---------------------------------------------------------------------------

    In its evaluation of whether precursors are significant
contributors to PM10 nonattainment, CARB relied upon a
significance threshold of 3.7%, which CARB derived by adapting for
PM10 the recommended significance threshold of 1.3 [mu]g/
m\3\ for the 24-hour PM2.5 standard of 35 [mu]g/m\3\.\57\
CARB concluded that, because each of the precursors contribute less
than 2.1% of the PM10 standard,\58\ they do not contribute
significantly to elevated PM10 concentrations in the
Imperial Valley Planning Area.
---------------------------------------------------------------------------

    \57\ We assume that the 1.3 [mu]g/m\3\ threshold cited by CARB
refers to the recommended contribution threshold in the EPA's draft
``PM2.5 Precursor Demonstration Guidance,'' released for
public review and comment on November 17, 2016. The final guidance,
issued on May 30, 2019, establishes a recommended contribution
threshold for the 24-hour PM2.5 standard of 1.5 [mu]g/
m\3\, which represents about 4.3% of the standard.
    \58\ The estimated contribution of ammonia (2.1%) is rounded up
from 2.05%.
---------------------------------------------------------------------------

    CARB also plotted PM2.5 and PM10 from the
Calexico monitoring site collected from 2007 through 2016 to illustrate
the relationship between PM10

concentrations and PM2.5 concentrations in the area. The
data generally show that elevated PM2.5 concentrations
correspond to PM10 concentrations below the PM10
NAAQS and that PM2.5 contributes a small percentage of the
PM10 mass when PM10 levels exceed the
PM10 NAAQS. This suggests that high PM10
concentrations are driven by fugitive dust and that secondarily-formed
particulate matter does not increase as a percentage of mass as
PM10 concentration exceed the NAAQS. The data also show that
PM2.5 represents about 11% of the total PM10 mass
when PM10 concentrations approach the level of the
PM10 NAAQS.
    We have reviewed the precursor analysis prepared by CARB and agree
that precursors do not contribute significantly to elevated
PM10 concentrations in the Imperial Valley Planning Area.
First, we generally recommend using 5 [micro]g/m\3\ as the threshold
for identifying potentially significant contributions to elevated
PM10 concentrations.\59\ The contribution of precursors to
PM10 concentrations is not significant using either CARB's
3.7% threshold or the 5 [micro]g/m\3\ threshold. As CARB notes, the
highest average precursor contribution based on data for the five
specific analysis days presented in Appendix A of the Imperial
PM10 Plan is less than 2.1%, and the highest average
estimated precursor contribution is approximately 4.7 [micro]g/m\3\
(i.e., for NH3).
---------------------------------------------------------------------------

    \59\ Addendum, 42011.
---------------------------------------------------------------------------

    Second, as described in section IV.A of this notice, exceedances of
the PM10 standard in Imperial County are caused by windblown
dust that is generated during high wind events. When such days are
removed from consideration in accordance with the EPA's Exceptional
Events Rule, the area is attaining the PM10 standard. In
this context, we believe it is appropriate to evaluate the contribution
of precursors on days that are close to the level of the standard
rather than days on which elevated levels of PM10 are likely
associated with high wind exceptional events. CARB's analysis includes
two such days. On October 21, 2007, the total PM10 mass was
144 [mu]g/m\3\ and on July 18, 2009, the total PM10 mass was
147.9 [mu]g/m\3\. The estimated contribution of each precursor on each
of these two dates ranges from 1.4 [mu]g/m\3\ to 4.1 [mu]g/m\3\. All
values are below the 5 [mu]g/m\3\ threshold established in the
Addendum.
    Thus, for the reasons stated above, we propose to find that
PM10 precursors do not significantly contribute to elevated
PM10 concentrations in the Imperial Valley Planning Area.
With respect to future conditions, we note that the emissions
inventories prepared for the Imperial PM10 Plan show a
downward trend in the County for the PM10 precursor
emissions through the initial maintenance period (i.e., through
2030),\60\ and thus, we also find that PM10 precursors will
not significantly contribute to elevated PM10 concentrations
within the Imperial Valley Planning Area through the initial
maintenance period.
---------------------------------------------------------------------------

    \60\ Imperial PM10 Plan, Appendix H, tables H-2--H-5.
---------------------------------------------------------------------------

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

    \61\ General Preamble, 13564.
---------------------------------------------------------------------------

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

    \62\ CAA section 189(b)(3).
---------------------------------------------------------------------------

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

    \63\ PSD requirements control the growth of new source emissions
in areas designated as attainment or unclassifiable for a NAAQS.
---------------------------------------------------------------------------

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

    \64\ 82 FR 41895 (September 5, 2017).
---------------------------------------------------------------------------

    If we finalize the redesignation action proposed herein, the
Imperial PM10 nonattainment area will become an attainment
area, and new or modified major sources in the area will be subject to
the PSD permitting requirements rather than the NNSR requirements.
    The District has a SIP-approved PSD program (Rule 904, ``Prevention
of Significant Deterioration (PSD) Permit Program'') that will apply to
PM10 emissions from new major sources or major modifications
upon redesignation of the area to attainment.\65\ Thus, new
PM10 major sources and major modifications with significant
PM10 emissions at major sources will be required to obtain a
PSD permit or address PM10 emissions in their existing PSD
permit.
---------------------------------------------------------------------------

    \65\ The EPA approved Rule 904 at 77 FR 73316 (December 10,
2012).
---------------------------------------------------------------------------

d. Best Available Control Measures
    Clean Air Act section 189(b)(1)(B) requires that Serious areas
implement BACM for the control of PM10 for all source
categories that contribute significantly to nonattainment of the
NAAQS.\66\ The EPA has long interpreted this requirement to apply
independent of attainment.\67\ Consequently, the requirement for BACM
level controls continues to apply,

even when the area has attained the standard.
---------------------------------------------------------------------------

    \66\ Addendum, 42011.
    \67\ In the Addendum, the EPA provided its rationale for
interpreting the CAA to require BACM be carried out independently
from the analysis to determine the emissions reductions necessary to
attain the NAAQS by the statutory attainment date. 59 FR 41998,
42011-42012.
---------------------------------------------------------------------------

    The Imperial PM10 plan addresses the BACM requirement by
first, providing a detailed emissions inventory and determining which
source categories of directly emitted PM10 contribute
significantly; second, by identifying the rules that apply to
significantly contributing source categories and documenting that those
rules require BACM level controls; and third, by documenting compliance
with CAA best available control technology requirements by major
sources of PM10 that are located within the nonattainment
area.
Identification of Significant Contributors
    The Imperial PM10 Plan's BACM demonstration includes an
analysis that establishes which sources of directly emitted
PM10 contribute significantly to ambient levels of
PM10. It does this by calculating the percent contribution
of sources in Imperial County's average annual daily emissions
inventory and then performing a sensitivity analysis to determine if
reducing the contribution of windblown dust to the inventory would
alter the conclusions of the analysis.\68\ Because the 5 [mu]g/m\3\
significant contribution threshold equates to 3.25% of the
PM10 NAAQS, the District concludes that any source category
that contributes more than 3.25% of the inventory would be significant
and therefore subject to BACM.
---------------------------------------------------------------------------

    \68\ The District notes that the language of the Addendum (``a
source category will be presumed to contribute significantly to a
violation of the 24-hour PM10 NAAQS if its
PM10 Impact at the location of the expected violation
would exceed 5 [mu]g/m\3\'') appears to require information that
could only be obtained through comprehensive air dispersion
modeling. Instead, the District uses ``a more practical alternative
approach that involves evaluating the fractional contribution of
sources in Imperial County's average annual daily inventory and then
performing a sensitivity analysis to determine if variations in the
inventory would alter the conclusions of the analysis.'' Imperial
PM10 Plan, Appendix E, 3.
---------------------------------------------------------------------------

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

    \69\ Imperial PM10 Plan, Appendix E, Table 3-1
summarizes the Plan's significant source sensitivity analysis.
---------------------------------------------------------------------------

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

    \70\ Id., figures 3-1, 3-2, and 3-3.
    \71\ Id. at 8 and Figure 3-4.
---------------------------------------------------------------------------

    We find the District's analysis to be sound and, based on a
conservative determination of the percent contribution of source
categories when windblown dust is reduced by 75%, agree that the source
categories that contribute significantly are tilling, entrained unpaved
road dust, and windblown dust from open areas. We note that the BACM
demonstration in the Imperial PM10 Plan does not address
PM10 precursor emissions, but we find that the decision to
exclude PM10 precursors in this instance is acceptable in
light of our proposed determination in section IV.B.2.a of this
document that PM10 precursors do not contribute
significantly to elevated PM10 concentrations in the
Imperial Valley Planning Area.
BACM Analysis for Significantly Contributing Source Categories
    The Imperial PM10 Plan provides documentation showing
that the source categories that contribute significantly to exceedances
of the PM10 NAAQS in Imperial County are subject to the
provisions of Regulation VIII, which form the core of the ICAPCD's
control strategy for PM10. Specifically, the following rules
apply to the significantly contributing source categories: Rule 800
(``General Requirements for Control of Fine Particulate Matter
(PM10)''), Rule 804 (``Open Areas''), Rule 805 (``Paved and
Unpaved Roads''), and Rule 806 (``Conservation Management
Practices'').\72\ ICAPCD's Regulation VIII rules were originally
adopted by the District in 2005. The EPA partially approved and
partially disapproved these rules after identifying certain
deficiencies in rules 800, 804, 805, and 806.\73\ The District
subsequently revised and strengthened the rules by addressing these
deficiencies and on April 23, 2013, the EPA approved the revised rules
and found that they established BACM-level controls for the categories
they regulate.\74\ Based on our prior approval of these rules and our
conclusion that they cover all significant PM10 source
categories in the Imperial PM10 nonattainment area, we
propose to approve ICAPCD's demonstration as satisfying the requirement
to ensure implementation of BACM under CAA section 189(b)(1)(B).
---------------------------------------------------------------------------

    \72\ The provisions of Regulation VIII, including rules 800,
804, 805, and 806, are summarized in Chapter 3 of the Imperial
PM10 Plan. Rules 800 and 804 apply to windblown dust from
open areas, Rule 805 applies to entrained and windblown dust from
unpaved roads, and Rule 806 applies to windblown dust from non-
pasture agricultural lands and tilling dust from agricultural
operations.
    \73\ 75 FR 39366 (July 8, 2010). On September 11, 2018, the
District again revised Rule 804. The EPA approved the revision on
August 29, 2019 (84 FR 45418).
    \74\ 78 FR 23677.
---------------------------------------------------------------------------

e. Control Requirements for Major Sources of PM10 Precursors
    CAA section 189(e) provides that control requirements for major
stationary sources of direct PM10 also apply to major
stationary sources of PM precursors, except where the EPA determines
that major stationary sources of such precursors do not contribute
significantly to PM10 levels that exceed the standard in the
area. In general, a major stationary source in a PM10
Serious area is a stationary source that

emits, or has the potential to emit, 70 tons per year of
PM10. As described in more detail in section IV.B.2.a of
this action, we are proposing to approve the demonstration the Imperial
PM10 plan that precursors do not contribute significantly to
PM10 levels that exceed the standard.
f. Compliance With Section 110(a)(2)
    Section 172(c)(7) requires the SIP to meet the applicable
provisions of section 110(a)(2). As described above in Section IV.B.,
we conclude the California SIP meets the requirements of section
110(a)(2) applicable for purposes of this redesignation.
g. General and Transportation Conformity Requirements
    Under section 176(c) of the CAA, states are required to revise
their SIPs to establish criteria and procedures to ensure that
federally supported or funded projects in nonattainment areas and
formerly nonattainment areas subject to a maintenance plan (referred to
as ``maintenance areas'') conform to the air quality planning goals in
the applicable SIP. Section 176(c) further provides that state
conformity provisions must be consistent with federal conformity
regulations that the CAA requires the EPA to promulgate. The EPA's
conformity regulations are codified at 40 CFR part 93, subparts A
(referred to herein as ``transportation conformity'') and B (referred
to herein as ``general conformity''). Transportation conformity applies
to transportation plans, programs, and projects developed, funded, and
approved under title 23 U.S.C. or the Federal Transit Act, and general
conformity applies to all other federally-supported or funded projects.
SIP revisions intended to address the conformity requirements are
referred to herein as ``conformity SIPs.'' In 2005, Congress amended
section 176(c) of the CAA. Under the amended conformity statutory
provisions, states are no longer required to submit conformity SIPs for
general conformity, and the conformity SIP requirements for
transportation conformity have been reduced to include only those
relating to consultation, enforcement and enforceability.\75\
---------------------------------------------------------------------------

    \75\ CAA section 176(c)(4)(E).
---------------------------------------------------------------------------

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

    \76\ 64 FR 19916 (April 23, 1999).
    \77\ See Wall v. EPA, 265 F. 3d 426 (6th Cir. 2001), upholding
this interpretation. Also see, for example, 60 FR 62748 (December 7,
1995).
---------------------------------------------------------------------------

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

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

    \78\ Calcagni memo, 4.
---------------------------------------------------------------------------

    The 2018 Imperial PM10 Plan concludes that the
improvement in PM10 air quality in the Imperial Valley
Planning Area is due to emissions reductions from implementation of the
District's Regulation VIII fugitive dust rules, adopted in 2005, based
on data for years 2000 to 2016 that show a gradual decline in annual
average PM10 concentrations that cannot be explained by
adverse economic conditions or usually favorable meteorology. With
respect to economic conditions, the data presented in the 2018 Imperial
PM10 Plan show a gradual increase in population over the
2000 to 2016 period and a very gradual decline in harvested acres over
that period suggesting little change in the agricultural sector of the
economy during this time. With respect to meteorological conditions,
the plan presents annual rainfall totals for Imperial County from 2000
through 2016 ranging from less than 1 inch to approximately 5 inches
with rainfall totals during the 2014-2016 attainment period of
approximately 2 inches each year.
    First, we agree that the implementation of the District's
Regulation VIII fugitive dust rules has reduced PM10
emissions within the Imperial Valley Planning Area. More specifically,
we find that emissions of the largest contributors to ambient
PM10 concentrations (i.e., fugitive windblown dust and
unpaved road dust) declined significantly after Regulation VIII was
adopted in 2005. For instance, in 2005, PM10 emissions from
unpaved road dust and fugitive windblown dust totaled approximately 288
tons per day (tpd) in Imperial County. After implementation of
Regulation VIII, emissions attributable to these categories declined by
approximately 16 tpd, or about 6 percent by 2008. While the amount of
fugitive windblown dust has remained relatively constant since 2008,
unpaved road dust has continued to decline until, by 2017, it accounted
for an additional 7 tpd reduction of PM10.\79\ Overall,
between 2005 and 2016, PM10 emissions within Imperial County
have declined from approximately 313 tpd to approximately 284 tpd in
2016. The most significant reductions from 2005 and 2016 occurred in
the farming operations, unpaved road dust and fugitive windblown dust
source categories, all of which are subject to one or more Regulation
VIII rules.
---------------------------------------------------------------------------

    \79\ These figures are based on data from CARB's Emissions
Inventory Database, California Emissions Projection and Analysis
Model (CEPAM). A print out of the report is included in the docket
for this action.
---------------------------------------------------------------------------

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

                         Table 2--ICAPCD Regulation VIII Rules and Related EPA Approvals
----------------------------------------------------------------------------------------------------------------
                                                                  Most recent adoption
                 Rule                           Title              or amendment date           EPA approval
----------------------------------------------------------------------------------------------------------------
800..................................  General Requirements     October 16, 2012.......  78 FR 23677, April 22,
                                        for Control of Fine                               2013.
                                        Particulate Matter (PM-
                                        10).
801..................................  Construction and         November 8, 2005.......  75 FR 39366, July 8,
                                        Earthmoving Activities.                           2010.
802..................................  Bulk Materials.........  November 8, 2005.......  75 FR 36366, July 8,
                                                                                2010.
803..................................  Carry-Out and Track-Out  November 8, 2005.......  75 FR 36366, July 8,
                                                                                2010.
804..................................  Open Areas.............  September 11, 2018.....  84 FR 45418, August 29,
                                                                                2019.
805..................................  Paved and Unpaved Roads  October 16, 2012.......  78 FR 23677, April 22,
                                                                                2013.
806..................................  Conservation Management  October 16, 2012.......  78 FR 23677, April 23,
                                        Practices.                                        2013.
----------------------------------------------------------------------------------------------------------------

    Third, based on the data on population growth, harvested acreage,
and rainfall totals in the 2018 Imperial PM10 Plan, we agree
that the reduction in PM10 emissions within Imperial County
is due largely to the District's Regulation VIII fugitive dust rules
and is not due to adverse economic conditions or favorable meteorology.
In this regard, we note that we are proposing herein to find that the
area attained the standard during the 2014 to 2016 period. During that
time, Imperial County saw a slight increase in population, relatively
steady economic activity, and lower than average rainfall. Therefore,
attainment of the PM10 NAAQS in that period could not have
been the result of adverse economic conditions or favorable
meteorology. Moreover, the determination of attainment relies upon the
implementation of Regulation VIII rules, without which high-wind-caused
exceedances would not have been deemed to be exceptional events under
the EPA's Exceptional Events Rule.
    Therefore, for the above reasons, we find that attainment of the
PM10 NAAQS in the Imperial Valley Planning Area is due to
permanent and enforceable emissions reductions resulting from
implementation of the applicable SIP, namely the District's Regulation
VIII fugitive dust rules. Consequently, we propose to find that the
criterion for redesignation set forth at CAA section 107(d)(3)(E)(iii)
is satisfied.

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

    Section 107(d)(3)(E)(iv) of the CAA requires that, in order to
approve a redesignation to attainment, the EPA must fully approve a
maintenance plan for the area as meeting the requirements of section
175A of the Act. Section 175A sets forth the required elements of a
maintenance plan for areas seeking redesignation from nonattainment to
attainment. Under section 175A, the plan must demonstrate continued
attainment of the applicable NAAQS for at least 10 years after the EPA
approves a redesignation to attainment. Eight years after
redesignation, the state must submit a revised maintenance plan that
demonstrates continued attainment for the subsequent ten-year period
following the initial ten-year maintenance period. To address the
possibility of future NAAQS violations, the maintenance plan must
contain such contingency provisions as the EPA deems necessary to
promptly correct any violation of the NAAQS that occurs after
redesignation of the area. The Calcagni memo provides further guidance
on the content of a maintenance plan, explaining that a maintenance
plan should include an attainment emissions inventory, maintenance
demonstration, monitoring and verification of continued attainment, and
a contingency plan. For the reasons provided below, we are proposing to
approve the Imperial PM10 Plan as meeting the requirements
for maintenance plans under CAA section 175A.
1. Attainment Inventory
    A maintenance plan for the PM10 NAAQS should include an
inventory of direct PM10 emissions in the area to identify a
level of emissions sufficient to attain the PM10 NAAQS.\80\
This inventory should be consistent with the EPA's most recent guidance
on emissions inventories for nonattainment areas available at the time
and should represent emissions during the time period associated with
the monitoring data showing attainment. The inventory must also be
comprehensive, including emissions from stationary point sources, area
sources, and mobile sources and must be based on actual emissions
during the appropriate season, if applicable. See CAA section
172(c)(3).
---------------------------------------------------------------------------

    \80\ PM10 precursor emissions should also be included
depending upon the contribution of secondarily-formed particulate
matter to high ambient PM10 concentrations in the area.
In this instance, an inventory of PM10 precursor
emissions would not be required based on our proposed determination
in section IV.B.2.a of this document that PM10 precursors
do not contribute significantly to elevated PM10
concentrations in the Imperial Valley Planning Area. While not
required, the Imperial PM10 Plan includes an inventory of
PM10 precursors in Appendix H (``PM10 and
PM10 Precursor Emission Inventories'').
---------------------------------------------------------------------------

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

    \81\ The more recent guidance document is available at https://www.epa.gov/sites/production/files/2017-07/documents/ei_guidance_may_2017_final_rev.pdf.
---------------------------------------------------------------------------

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

                    Table 3--Imperial County PM10 Attainment Year (2016) Emissions Inventory
                                              [annual average, tpd]
----------------------------------------------------------------------------------------------------------------
                Source category                                    Subcategory                       PM10 \a\
----------------------------------------------------------------------------------------------------------------
Stationary Point Sources......................  All.............................................            4.19
Areawide Sources..............................  Farming Operations..............................            8.48
                                                Construction and Demolition.....................            3.02
                                                Paved Road Dust.................................            1.16
                                                Unpaved Road Dust...............................           51.88
                                                Fugitive Windblown Dust.........................          212.52
                                                Other Areawide Sources..........................            1.43
                                                Subtotal--Areawide Sources......................          278.48
Mobile Sources................................  All.............................................            1.50
                                                                                ---------------
    Totals....................................  All Stationary, Areawide, and Mobile Sources....          284.17
----------------------------------------------------------------------------------------------------------------
Source: Imperial PM10 Plan, Table 4-1 and Appendix H (``PM10 and PM10 Precursor Emission Inventories'').
\a\ Emissions inventories are required to include direct PM10 emissions, separately reported as PM10 filterable
  and condensable emissions. 40 CFR 51.15(a)(1)(vii). Table H-1b of Appendix H of the Imperial PM10 plan
  provides this information.

    As discussed in Appendix G of the Imperial PM10 Plan,
direct PM10 emissions estimates for stationary point sources
reflect actual emissions reported to the District in 2012 by owners or
operators of industrial point sources in the County and then adjusted
to 2016 based on applicable growth surrogates. Areawide sources occur
over a wide geographic area. Examples of these sources are consumer
products, paved and unpaved road dust, fireplaces, farming operations,
and prescribed burning. Emissions for these categories are estimated by
both CARB and the ICAPCD using various models and methodologies.
Emissions estimates for the fugitive dust source categories also
reflect implementation of the District's various Regulation VIII rules.
    Emissions from on-road mobile sources, which include passenger
vehicles, buses, and trucks, were estimated using outputs from CARB's
EMFAC2014 model.\82\ These emissions were calculated by applying
EMFAC2014 emissions factors to the transportation activity data
provided by the Southern California Association of Governments (SCAG)
from their 2016 adopted Regional Transportation Plan/Sustainable
Communities Strategy (2016 RTP/SCS).\83\ SCAG is the metropolitan
planning organization representing Imperial County, along with five
other counties in Southern California.
---------------------------------------------------------------------------

    \82\ EMFAC is short for EMission FACtor. The EPA approved
EMFAC2014 for SIP development and transportation conformity purposes
in California at 80 FR 77337 (December 14, 2015). EMFAC2014 was the
most recently approved version of the EMFAC model that was available
at the time of preparation of the Imperial PM10 Plan.
Recently, the EPA approved an updated version of the EMFAC model,
EMFAC2017, for future SIP development and transportation conformity
purposes in California. 84 FR 41717 (August 15, 2019).
    \83\ 2016 RTP/SCS was current as of April 2016.
---------------------------------------------------------------------------

    Emissions from off-road mobile sources, which include cargo
handling equipment, pleasure craft, recreational vehicles, and
locomotives, were estimated using a suite of category-specific models
or, where a new model was not available, the OFFROAD2007 model. Many of
the newer models were developed to support recent regulations,
including in-use offroad equipment.
    The EPA considers the selection of 2016 for the attainment year
inventory to be appropriate given that the design value for 2016,
excluding exceedances caused by exceptional events, is consistent with
attainment of the PM10 NAAQS. Moreover, preparation of an
annual average daily inventory, as opposed to a seasonal or episodic
inventory, is appropriate given that elevated PM10
concentrations in Imperial County do not exhibit a clear seasonal or
episodic pattern. Also, we find that the county-wide basis for the
inventory is appropriate in this instance even though the County is
larger than the nonattainment area because the nonattainment area
encompasses the vast majority of the population and vehicular activity
within the County. Based on our review of the documentation provided
with the plan, we find that the 2016 emissions inventory for direct
PM10 is based on reasonable assumptions and methodologies,
and that the inventory is comprehensive, current and accurate. We
therefore propose to approve the inventory of actual emissions in 2016
in the Imperial PM10 Plan as meeting the requirements of CAA
section 172(c)(3). We also find the 2016 inventory in the plan to be
acceptable for use in demonstrating maintenance of the PM10
NAAQS in the future.
2. PM10 Maintenance Demonstration
    Section 175A requires a state seeking redesignation to attainment
to submit a SIP revision to provide for maintenance of the NAAQS for a
period of at least ten years following redesignation. This can be shown
either by demonstrating that future emissions of a pollutant and its
precursors will not exceed the level of the attainment inventory or by
conducting modeling that shows the future emissions will not cause a
violation of the standard. In accordance with EPA guidance, the state
should project emissions for the 10-year period following
redesignation, for either purpose.\84\ Projected emissions inventories
for future years must account for, among other things, the ongoing
effects of economic growth and adopted emissions control requirements,
and the inventories are expected to be the best available
representation of future emissions. The plan submission should include
documentation explaining how the state calculated the emissions data
for the base year and projected inventories.
---------------------------------------------------------------------------

    \84\ Calcagni memo, 9.
---------------------------------------------------------------------------

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

    \85\ In this context, the design concentration generally refers
to the third or fourth highest 24-hour PM10 concentration
measured at the monitoring site measuring the highest concentrations
over a three-year period, in this case, excluding exceedances caused
by high wind exceptional events.
---------------------------------------------------------------------------

    Projected inventories are derived by applying expected growth
trends for each source category and are based on

data that reflect historical trends, current conditions, and recent
economic and demographic forecasts with expected emissions reductions
resulting from adopted control measures to the base year inventory. For
the Imperial PM10 Plan, emissions projections for 2018
through 2030 were generated by applying growth and control profiles to
the 2016 attainment inventory. Growth forecasts for most point and
areawide sources were developed either by CARB or by SCAG and provided
to CARB through the South Coast Air Quality Management District. Mobile
sources were forecast using total vehicle miles traveled projections
provided by SCAG. Off-road sources were forecast using various growth
surrogates as shown in Table 5 of Appendix G of the plan. Appendix G of
the plan documents the methods and assumptions used to develop the
emissions projections upon which the maintenance demonstration relies,
and Appendix H of the plan presents the detailed source-category-
specific estimates for each of the analysis years.
    Table 4 presents a summary of the Imperial PM10 Plan's
estimates of direct PM10 emissions in an interim year (2025)
and the horizon year (2030) along with the corresponding emissions
estimates for the attainment year (2016). For the sake of simplicity,
Table 4 shows emissions for just one of the interim years (i.e., 2025)
between the attainment year and the horizon year, but the plan itself
provides emissions estimates for each year from 2018 through 2030.\86\
The emissions estimates in the plan predict a gradual change in
emissions within the County over time with slight decreases in certain
categories (e.g., farming operations and unpaved road dust) nearly
offsetting slight increases in certain other source categories (e.g.,
construction and demolition and paved road dust). By 2030, overall
direct PM10 emissions are estimated to be approximately 2
tpd (0.6 percent) higher than in the 2016 attainment year.
---------------------------------------------------------------------------

    \86\ Imperial PM10 Plan, Table 4-2 and Table H-1a.

                     Table 4--Imperial County PM10 Emissions Inventory, 2016, 2025 and 2030
                                              [annual average, tpd]
----------------------------------------------------------------------------------------------------------------
           Source category                Subcategory[thinsp]          2016            2025            2030
----------------------------------------------------------------------------------------------------------------
Stationary Point Sources............  All.......................            4.19            5.46            6.22
Areawide Sources....................  Farming Operations........            8.48            8.11            7.98
                                      Construction and                      3.02            3.82            4.22
                                       Demolition.
                                      Paved Road Dust...........            1.16            1.43            1.50
                                      Unpaved Road Dust.........           51.88           50.20           50.16
                                      Fugitive Windblown Dust...          212.52          212.47          212.45
                                      Other Areawide Sources....            1.43            1.36            1.33
                                      Subtotal--Areawide Sources          278.48          277.39          277.64
Mobile Sources......................  All.......................            1.50            2.03            2.09
                                                                 -----------------------------------------------
    Totals..........................  All Stationary, Areawide,           284.17          284.88          285.96
                                       and Mobile Sources.
----------------------------------------------------------------------------------------------------------------
Source: Imperial PM10 Plan, Appendix H, Table H-1a.
Totals may not add up due to rounding.

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

    \87\ With respect to the PM10 NAAQS, an exceedance is
defined as a daily value that is above the level of the 24-hour
standard, 150 [mu]g/m\3\, after rounding to the nearest 10 [mu]g/
m\3\ (i.e., values ending in five or greater are to be rounded up).
Consequently, exceedances are daily values equal to or greater than
155 [mu]g/m\3\. 40 CFR part 50, Appendix K, section 1.0.
---------------------------------------------------------------------------

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

through the initial maintenance period.\90\
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    \88\ Imperial PM10 Plan, Chapter 5, ``Salton Sea
Considerations''; Appendix I, ``Salton Sea Management Program Phase
I: 10-Year Plan (March 2017)''; and Appendix J, ``Salton Sea Air
Quality Mitigation Program (July 2016).''
    \89\ District Rule 804, ``Open Areas,'' applies to any open area
having 0.5 acres or more within urban areas, or 3.0 acres or more
within rural areas that contain at least 1,000 square feet of
disturbed surface area, excluding certain sites that are subject to
other Regulation VIII rules. Under Rule 804, all persons who own or
otherwise have jurisdiction over an open area must implement one or
more of BACM listed in the rule to achieve a stabilized surface and
to limit visible dust emissions to no more than 20% opacity. One of
the BACM listed in the rule was drafted specifically to allow the
implementation of alternative BACM, with the approval of the ICAPCD
and the EPA, to more effectively control dust from exposed playa at
the Salton Sea (paragraph F.1.d. of the rule) than the standard BACM
otherwise required under the rule.
    \90\ The Imperial PM10 Plan includes contingency
provisions that establish a process for evaluating and remedying
increased emissions from newly-exposed playa if the ongoing efforts
fail to adequately control the emissions such that the related
emissions cause or contribute to exceedances at one of the five
SLAMS PM10 monitoring sites.
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    Based on our review of the documentation provided with the Imperial
PM10 Plan, we find that the projected emissions inventories
for direct PM10 for years 2018 through 2030 are based on
reasonable methods, growth factors, and assumptions, and are based on
the most current and accurate information available to CARB and ICAPCD
at the time the plan and its inventories were being developed. Given
that the projections of direct PM10 emissions show future
emissions increases through 2030 that would be less than the margin
between the design concentration and an exceedance of the standard, we
find that Imperial PM10 Plan provides an adequate basis to
demonstrate maintenance of the PM10 NAAQS within the
Imperial Valley Planning Area through 2030.\91\ Lastly, section 175A of
the CAA requires that a maintenance plan provide for maintenance of the
NAAQS in the area for at least ten years after redesignation. If we
finalize this proposed approval of CARB's redesignation request and
such approval becomes effective in 2020, the projected 2030 inventory
in the Imperial PM10 Plan demonstrates that the Imperial
Valley Planning Area will maintain the PM10 NAAQS for at
least 10 years beyond redesignation.
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    \91\ We recognize that the increased exposure of playa as the
Salton Sea continues to shrink will likely result in higher
windblown PM10 emissions than quantified in the Imperial
PM10 Plan, but we anticipate that, given the federal,
state and local efforts to identify and remedy such emissions
increases, any exceedances to which the emissions would contribute
would be eligible as exceptional events under the Exceptional Events
Rule because, among other reasons, the emissions would be reasonably
controlled for the purposes of the Exceptional Events Rule.
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3. Verification of Continued Attainment
    Once an area has been redesignated, the state should continue to
operate an appropriate air quality monitoring network, in accordance
with 40 CFR part 58, to verify the attainment status of the area.\92\
Data collected by the monitoring network are also needed to implement
the contingency plan element of the maintenance plan. As discussed in
section IV.A. of this document, CARB and the District monitor ambient
concentrations of PM10 at five monitoring sites within the
Imperial PM10 nonattainment area. In section 4.2 (``Future
Monitoring Network'') of the Imperial PM10 Plan, the
District states that, in conjunction with CARB, it will assure the
quality of the data using various quality assurance procedures and
notes that, under federal regulations, the monitoring network is
reviewed annually. ICAPCD also commits to continuing to assure
PM10 monitoring is conducted in accordance with 40 CFR part
58. We find that the Imperial PM10 Plan contains adequate
provisions for continued operation of an appropriate air quality
monitoring network that will provide a basis to verify the attainment
status of the area.
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    \92\ Calcagni memo, 11.
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    The EPA also recommends that the state verify continued attainment
through methods in addition to the ambient air monitoring program,
e.g., through periodic review of the factors used in developing the
attainment inventory to show no significant change.\93\ In the Imperial
PM10 Plan, the District commits to periodic review of the
inputs and assumptions used for the emissions inventory on an annual
basis and, if the District finds that these inputs have changed
significantly, to request that CARB update the existing inventory and
take other appropriate measures.\94\ We find that the District's
commitments to verify continued attainment of the PM10 NAAQS
through continued ambient air monitoring and annual review of the
inputs and assumptions used for the emission inventory in the Imperial
PM10 plan are acceptable.
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    \93\ Id.
    \94\ Imperial PM10 Plan, 4-10 and 4-11.
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4. Contingency Provisions
    Section 175A(d) of the CAA requires that maintenance plans include
contingency provisions, as the EPA deems necessary, to promptly correct
any violations of the NAAQS that occur after redesignation of the area.
Such provisions must include a requirement that the state will
implement all measures with respect to the control of the air pollutant
concerned that were contained in the SIP for the area before
redesignation of the area as an attainment area.\95\ These contingency
provisions are distinguished from those generally required for
nonattainment areas under CAA section 172(c)(9) in that they are not
required to be fully-adopted measures that will take effect without
further action by the state for the maintenance plan to be approved.
However, the contingency plan is considered to be an enforceable part
of the SIP and it should ensure that the contingency measures are
adopted expeditiously once the requirement for contingency measures has
been triggered. The maintenance plan should clearly identify the
measures to be adopted, a schedule and procedure for adoption and
implementation, and a specific timeline for action by the state. As a
necessary part of the plan, the state should also identify the specific
indicators or triggers that will be used to determine when the
contingency measures need to be implemented.
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    \95\ No PM10 controls contained in the SIP would be
relaxed or suspended upon redesignation. All such controls would
continue to be implemented during the maintenance period.
Consequently, the Imperial PM10 Plan meets the
requirement in CAA section 175A(d) for contingency provisions to
require implementation of all measures with respect to the control
of the air pollutant concerned that were contained in the SIP for
the area before redesignation of the area to attainment.
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    The District has adopted a contingency plan to address future
PM10 exceedances occurring after redesignation of the area
to attainment. The contingency plan is contained in Section 4.4 of the
Imperial PM10 Plan.
    As noted by the District in the Imperial PM10 Plan,
contingency provisions are typically implemented when air quality
deteriorates beyond a specified level, such as a certain number of
exceedances of the standard or a violation of the standard. In this
case, the contingency provisions will be triggered when the number of
exceedances at a monitor, averaged over three years, is greater than
1.05. However, because PM10 exceedances in Imperial County
are largely driven by high wind dust events that may be eligible for
consideration under the Exceptional Events Rule,\96\ the contingency
plan includes a screening process that allows the District and CARB,
subject to EPA review, to exclude exceedances from the trigger
calculation if the agencies show that the exceedances meet certain
criteria indicating they are likely eligible for treatment as an
exceptional event.\97\ The purpose of the screening process is to
differentiate between exceedances that are not within the District or
State

control (i.e., exceedances that occur despite the implementation of
reasonable measures), and exceedances that are within the District's or
State's control and should be included in the trigger calculation. It
is important to note that, should the District or State exclude an
exceedance from the contingency trigger calculation using this process,
it would not constitute the EPA's concurrence that the exceedance was
caused by an exceptional event. The exceedance will therefore continue
to be included in design value calculations for the Imperial Valley
Planning Area unless CARB, following opportunity for public comment,
submits a request for the EPA to concur on the exceedance as an
exceptional event pursuant to 40 CFR 50.14, and the EPA reviews the
submittal and formally concurs.
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    \96\ As described in section IV.A. of this action, we have
concurred with 91 exceedance days that the State flagged and
documented as caused by high wind exceptional events.
    \97\ The criteria include: (1) exceedances at multiple monitors
in specified areas; (2) wind speeds in excess of 25 miles per hour
consistent with increasing hourly PM10 concentrations;
(3) reduced visibility (less than 10 miles) consistent with
increasing hourly PM10 concentrations; (4) issuance of
advisories or warnings consistent with increasing hourly
PM10 concentrations; and (5) no dust complaints involving
anthropogenic sources located upwind of an exceeding monitor. If any
of these five criteria are not met, or if other available data
contradict the assessment, additional information and analyses will
be provided to the EPA as described on pages 4-12 and 4-13 of the
Imperial PM10 Plan.
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    Under the contingency trigger screening process, within 60 days of
the end of each calendar quarter, the District will complete the
following: Provide a list of exceedances that occurred during that
previous quarter to CARB, identify those exceedances that meet the
criteria specified in the contingency measure screening process, flag
the relevant data, and provide an initial description in AQS. The State
then has 60 days to review the information, during which time it may
request additional information from the District to supplement the
District's analysis. Following CARB's review, CARB will transmit the
information to the EPA, including information for those exceedances the
District believes should be excluded from the contingency plan trigger
calculation.
    The Imperial PM10 Plan anticipates that, within 60 days
of receipt, the EPA will review the submitted information, notify the
District if the submitted information is insufficient to support
exclusion from the contingency plan trigger calculation, include such
exceedances in calculating the trigger for the contingency plan, and
notify the District if the contingency plan has been triggered. The EPA
intends to notify the District, within 60 days of receipt, whether
submitted information is sufficient or insufficient to support the
exclusion of a given exceedance from the contingency plan trigger
calculation and to take the other actions described in the plan. If the
submitted information is not sufficient, the EPA will include the
exceedance in the calculation to determine if the contingency plan has
been triggered. If the State or District subsequently provide
additional information sufficient to support the conclusion that the
exceedance meets the criteria for exclusion from the trigger
calculation, the EPA will notify the District that the calculation will
be adjusted.
    Under the contingency plan, if the EPA determines that contingency
provisions have been triggered (i.e., the number of exceedances at any
single monitor, averaged over three years, is greater than 1.05
excluding those exceedances identified through the screening process),
ICAPCD commits to the following steps:
    (1) Within six months of EPA notification, ICAPCD will complete an
analysis of the exceedances and the available contingency measures.
During this time, the District will determine the possible cause of the
exceedances and will consult with community and local industry members
to determine if any voluntary or incentive measures could be
implemented to reduce the magnitude of or eliminate the source of
emissions.
    If voluntary and incentive-based measures do not adequately address
the problem, the ICAPCD will evaluate its Regulation VIII fugitive dust
rules, or other rules as appropriate, to determine where such rules
could be improved or expanded to achieve additional emissions
reductions. The measures that ICAPCD would consider and analyze include
but are not limited to those listed in Table 4-6 in the Plan.
    (2) Within 12 months of completing its analysis, the District will
adopt and implement the new contingency measures.
    Based on our review of the Imperial PM10 Plan, as
summarized above, we propose to find that the contingency provisions of
the Imperial PM10 Plan clearly identify specific contingency
measures, contain a triggering mechanism to determine when contingency
measures are needed, contain a description of the process of
recommending and implementing contingency measures, and contain
specific and appropriate timelines for action. We also propose to find
that the contingency trigger screening process, including the
associated EPA review, is reasonably designed to distinguish between
exceedances that are the type that have been deemed exceptional events
in the past and exceedances for which new or tightened control measures
might be effective. Our assessment indicates that the screening process
is an appropriate element of the contingency plan for the Imperial
Valley Planning Area because of the frequency of exceedances related to
high wind dust events in this area. Thus, we propose to conclude that
the contingency plan in the Imperial PM10 Plan is adequate
to ensure prompt correction of any violation of the PM10
NAAQS that occurs after redesignation, as required by section 175A(d)
of the CAA.
5. Motor Vehicle Emissions Budgets for Transportation Conformity
    Section 176(c) of the CAA requires federal actions in nonattainment
and maintenance areas to conform to the SIP's goals of eliminating or
reducing the severity and number of violations of the NAAQS and
achieving expeditious attainment of the standards. Conformity to the
SIP's goals means that such actions will not: (1) Cause or contribute
to violations of a NAAQS, (2) worsen the severity of an existing
violation, or (3) delay timely attainment of any NAAQS or any interim
milestone.
    Actions involving Federal Highway Administration (FHWA) or Federal
Transit Administration (FTA) funding or approval are subject to the
EPA's transportation conformity rule, codified at 40 CFR part 93,
subpart A. Under this rule, metropolitan planning organizations (MPOs)
in nonattainment and maintenance areas coordinate with state and local
air quality and transportation agencies, the EPA, FHWA, and FTA to
demonstrate that an area's regional transportation plans and
transportation improvement programs conform to the applicable SIP. This
demonstration is typically done by showing that estimated emissions
from existing and planned highway and transit systems are less than or
equal to the motor vehicle emissions budgets (``budgets'') contained in
submitted or approved control strategy plans or maintenance plans.
    Budgets are generally established for specific years and specific
pollutants or precursors. PM10 maintenance plan submittals
should identify budgets for transportation-related PM10
emissions in the last year of the maintenance period.\98\ Budgets may
also be specified for additional years during the maintenance period.
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    \98\ Transportation-related emissions of VOC or NOX
must also be specified in PM10 areas if the EPA or the
state find that transportation-related emissions of one or both of
these precursors within the nonattainment area are a significant
contributor to the PM10 nonattainment problem and has so
notified the MPO and the U.S. Department of Transportation (DOT), or
the applicable SIP revision or SIP revision submittal establishes an
approved or adequate budget for such emissions as part of the
reasonable further progress, attainment or maintenance strategy. 40
CFR 93.102(b)(2)(iii). Neither of these conditions apply to the
Imperial PM10 nonattainment area.

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    For budgets in a maintenance plan to be approvable, they must meet,
at a minimum, the EPA's adequacy criteria (40 CFR 93.118(e)(4)). To
meet these requirements, the budgets must be consistent, when
considered with emissions from all other sources, with maintenance of