Document ID: EPA-R09-OAR-2019-0654-0001
Agency: epa
Document Type: Proposed Rule
Title: Particulate Matter Less Than 10 Microns in Diameter Maintenance Plan and Redesignation Request: Imperial Valley Planning Area; California
Posted Date: 2020-04-02T04:00Z

[Federal Register Volume 85, Number 64 (Thursday, April 2, 2020)]
[Proposed Rules]
[Pages 18509-18527]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[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

[[Page 18510]]

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

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

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

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

SUPPLEMENTARY INFORMATION: Throughout this document, the terms ``we,'' 
``us,'' and ``our'' mean the EPA.

Table of Contents

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

I. Background

A. National Ambient Air Quality Standards

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

[[Page 18511]]

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

[[Page 18512]]

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-

[[Page 18513]]

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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[[Page 18514]]

    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.
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    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.
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    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

[[Page 18515]]

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.
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    \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

[[Page 18516]]

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

    \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\
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    \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.
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    \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

[[Page 18517]]

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.
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    \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.
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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\
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    \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,

[[Page 18518]]

even when the area has attained the standard.
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    \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

[[Page 18519]]

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.

[[Page 18520]]

                         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.

[[Page 18521]]

                    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

[[Page 18522]]

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

[[Page 18523]]

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.
---------------------------------------------------------------------------

    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.
---------------------------------------------------------------------------

    \92\ Calcagni memo, 11.
---------------------------------------------------------------------------

    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.
---------------------------------------------------------------------------

    \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

[[Page 18524]]

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.
---------------------------------------------------------------------------

    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.
---------------------------------------------------------------------------

    \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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[[Page 18525]]

    For budgets in a maintenance plan to be approvable, they must meet, 
at a minimum, the EPA's adequacy criteria (40 CFR 93.118(e)(4)). To 
meet these requirements, the budgets must be consistent, when 
considered with emissions from all other sources, with maintenance of 
the NAAQS and reflect all the motor vehicle control measures relied 
upon for the maintenance demonstration.
    The EPA's process for determining adequacy of a budget consists of 
three basic steps: (1) Notifying the public of a SIP submittal; (2) 
providing the public the opportunity to comment on the budget during a 
public comment period; and (3) making a finding of adequacy or 
inadequacy. The process for determining the adequacy of a submitted 
budget is codified at 40 CFR 93.118(f). The EPA can notify the public 
by either posting an announcement that the EPA has received SIP budgets 
on the EPA's adequacy website (40 CFR 93.118(f)(1)), or via a Federal 
Register notice of proposed rulemaking when the EPA reviews the 
adequacy of an maintenance plan budget simultaneously with its review 
and action on the SIP submittal itself (40 CFR 93.118(f)(2)).
    The Imperial PM10 Plan includes budgets for direct 
PM10 for the attainment year (2016) and the last year of the 
maintenance plan (2030). The applicable source categories included in 
the budgets include vehicle emissions (including exhaust, brake wear, 
and tire wear), and entrained dust from vehicle travel over paved and 
unpaved roads. With respect to unpaved road dust, the budgets include 
only those emissions generated by vehicle travel over city- and county-
owned unpaved roads, not canal roads, farm roads or those owned by the 
U.S. Bureau of Land Management or the U.S. Forest Service. In addition, 
the budgets apply to the entire County, including the portion of the 
County that lies outside of the PM10 nonattainment area.\99\ 
As noted previously, an estimated 95% of the vehicle activity within 
the County occurs within the PM10 nonattainment area, and 
thus, the budgets reasonably correspond to the nonattainment area even 
though they are county-wide values. The 2016 and 2030 annual average 
day conformity budgets for PM10 are provided in Table 5.
---------------------------------------------------------------------------

    \99\ The Imperial PM10 plan (at 4-6) indicates that 
the budgets are derived from PM10 emissions estimates and 
projections within the PM10 nonattainment area rather 
than the entire County. However, we understand that the budgets 
reflect county-wide emissions estimates and projections. The county-
wide basis for the budgets does not, however, affect the geographic 
area for which transportation conformity determinations must be made 
with respect to PM10. The applicable geographic area for 
such determinations remains the Imperial Valley Planning Area 
portion of Imperial County.

    Table 5--Transportation Conformity Budgets for the PM10 NAAQS in
                             Imperial County
                 [PM10 tpd, annual average, county-wide]
------------------------------------------------------------------------
                 Source                        2016            2030
------------------------------------------------------------------------
Tire Wear, Brake Wear and Exhaust.......             0.4             0.5
Paved Road Dust.........................             1.2             1.5
Unpaved City-County Road Dust...........            18.4            16.8
                                         -------------------------------
    Total...............................            20.0            18.8
Motor Vehicle Emission Budget \a\.......              20              19
------------------------------------------------------------------------
\a\ Rounded up to the nearest integer.
Source: Imperial PM10 Plan, Table 4-5.

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

    \100\ AP-42 is an EPA document that includes a compilation of 
emission factors.
---------------------------------------------------------------------------

    As discussed in the March 10, 2006 final Transportation Conformity 
rulemaking, the conformity rule does not include an exception for 
PM10 for paved and unpaved road dust emissions to be 
determined significant, like the exception for such emissions in 
PM2.5 analyses in 40 CFR 93.102(b)(3). The EPA intends for 
road dust emissions to be included in all conformity analyses of direct 
PM10 emissions because fugitive dust from roadways and other 
sources dominate PM10 emissions inventories. The budgets in 
the Imperial PM10 Plan, therefore, include paved and unpaved 
road emissions.
    Regional PM10 emissions analyses for transportation 
conformity determinations in PM10 nonattainment and 
maintenance areas must account for highway and transit project 
construction-related fugitive PM10 emissions if the control 
strategy or maintenance plan identifies such emissions as a contributor 
to the nonattainment problem, but are not required to do so if such 
emissions are not identified as a contributor to the nonattainment 
problem.101 102 Emissions estimates developed for the 
Imperial PM10 Plan show that fugitive PM10 
emissions from highway and transit project construction represent 
approximately 0.2% and 0.3% of the total annual-average daily 
PM10 emissions in 2016 and 2030, respectively.\103\ Based on 
these emissions estimates, the Imperial PM10 Plan concludes 
that fugitive PM10 emissions from highway and transit 
project construction are not a contributor to the nonattainment problem 
and thus need not be accounted for in regional emissions analyses for 
transportation conformity determinations made for the Imperial 
PM10 nonattainment area. Consequently, the budgets in the 
Imperial PM10 Plan do not reflect highway or transit project 
construction-related fugitive dust.
---------------------------------------------------------------------------

    \101\ 40 CFR 93.122(e).
    \102\ Fugitive PM10 emissions associated with road 
and transit construction are not required to be included in 
conformity unless the state identifies construction-related fugitive 
dust as a contributor to the nonattainment problem per 93.122(e).
    \103\ Imperial PM10 Plan, Table 4-4.
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    We evaluated the budgets against our adequacy criteria in 40 CFR 
93.118(e)(4) and (5) as part of our review of the budget's 
approvability and expect to complete the adequacy review of the budgets 
concurrent with our final action on the Imperial PM10 Plan. 
The EPA is not required under its transportation conformity rule to 
find budgets

[[Page 18526]]

adequate prior to proposing approval of them.\104\ Today, the EPA is 
announcing that the adequacy process for these budgets begins, and the 
public has 30 days to comment on their adequacy, per the transportation 
conformity rule at 40 CFR 93.118(f)(2)(i) and (ii).
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    \104\ Under the transportation conformity rule, the EPA may 
review the adequacy of submitted budgets simultaneously with the 
EPA's approval or disapproval of the submitted control strategy or 
maintenance plan. 40 CFR 93.118(f)(2).
---------------------------------------------------------------------------

    As documented in the separate memorandum included in the docket for 
this rulemaking, we preliminarily conclude that the budgets in the 
Imperial PM10 Plan meet each adequacy criterion.\105\ While 
adequacy and approval are two separate actions, reviewing the budgets 
in terms of the adequacy criteria informs the EPA's decision to propose 
to approve the budgets. We have completed our detailed review of the 
Imperial PM10 Plan and are proposing herein to approve the 
maintenance plan including the demonstration of maintenance of the 
PM10 NAAQS in the area through year 2030. We have also 
reviewed the budgets in the Imperial PM10 Plan and found 
that they are consistent with the maintenance demonstration for which 
we are proposing approval, are clearly identified and precisely 
quantified, are based on control measures that have already been 
adopted and implemented, and meet all other applicable statutory and 
regulatory requirements including the adequacy criteria in 40 CFR 
93.118(e)(4) and (5). Moreover, we agree with the conclusion in the 
Imperial PM10 Plan that highway and transit project 
construction-related PM10 emissions are not a contributor to 
the nonattainment problem in the Imperial PM10 nonattainment 
area and need not be accounted for in regional emissions analyses for 
transportation conformity determinations for this area. For these 
reasons, the EPA proposes to approve the 2016 and 2030 motor vehicle 
emissions budgets in the Imperial PM10 Plan. At the point 
when we either finalize the adequacy process or approve the budgets as 
proposed (whichever occurs first; note that they could also occur 
concurrently per 40 CFR 93.118(f)(2)(iii)), the budgets must be used by 
the SCAG (i.e., the MPO for this area) for transportation conformity 
determinations for the Imperial PM10 nonattainment area.
---------------------------------------------------------------------------

    \105\ Memorandum dated November 13, 2019, from Karina O'Connor 
(EPA), to Rulemaking Docket ID EPA-R09-OAR-2019-0654, Subject: 
``Adequacy Documentation for Plan Motor Vehicle Emissions Budgets in 
October 2018 Imperial PM10 Plan.''
---------------------------------------------------------------------------

    The transportation conformity rule allows us to limit the approval 
of budgets, and CARB requested that we limit the duration of our 
approval of the budgets in the Imperial PM10 Plan to the 
period before the effective date of the EPA's adequacy finding for any 
subsequently submitted budgets.106 107 However, we will 
consider the State's request to limit an approval of its budgets only 
if the request includes the following elements: \108\
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    \106\ 40 CFR 93.118(e)(1).
    \107\ Letter dated February 6, 2019, from Richard W. Corey, 
Executive Officer, California Air Resources Board, to Michael 
Stoker, Regional Administrator, EPA, Region IX.
    \108\ 67 FR 69141 (November 15, 2002), limiting our prior 
approval of budgets in certain California SIPs.
---------------------------------------------------------------------------

     An acknowledgement and explanation as to why the budgets 
under consideration have become outdated or deficient;
     A commitment to update the budgets as part of a 
comprehensive SIP update; and
     A request that the EPA limit the duration of its approval 
to the time when new budgets have been found to be adequate for 
transportation conformity purposes.
    Because CARB's request does not address these elements, we cannot 
at this time propose to limit the duration of our approval of the 
submitted budgets. In order to limit the approval, we would need the 
information described above in order to determine whether such 
limitation is reasonable and appropriate in this case. If CARB provides 
the necessary information, we intend to review it and take appropriate 
action. If we propose to limit the duration of our approval of the 
budgets in the Imperial PM10 Plan, we will provide the 
public an opportunity to comment. The duration of the approval of the 
budgets, however, would not be limited until we complete such a 
rulemaking.
6. Conclusion
    Based on the review presented above of the various elements of the 
maintenance plan portion of the Imperial PM10 Plan, we are 
proposing to approve the Imperial PM10 Plan as a revision to 
the California SIP. In doing so, we find that the Imperial 
PM10 Plan, submitted by CARB by letter dated February 6, 
2019, satisfies the requirements of section 175A of the Act. If 
finalized as proposed, our approval of the Imperial PM10 
Plan will satisfy the criterion for redesignation under CAA section 
107(d)(3)(E)(iv).

V. Proposed Actions and Request for Public Comment

    Under CAA section 110(k)(3), and for the reasons set forth above, 
the EPA is proposing to approve the Imperial PM10 Plan 
submitted by CARB by letter dated February 6, 2019, as a revision to 
the California SIP. In so doing, the EPA is proposing to approve the 
BACM demonstration and attainment inventory included as part of the 
Imperial PM10 Plan as meeting the requirements of CAA 
sections 189(b)(1)(B) and 172(c)(3), respectively. We are proposing to 
approve the maintenance demonstration and contingency provisions as 
meeting all applicable requirements for maintenance plans and related 
contingency provisions in CAA section 175A. The EPA is also proposing 
to approve the motor vehicle emissions budgets for 2016 and 2030 (shown 
in Table 5 above) for transportation conformity purposes because we 
find they meet all applicable criteria for such budgets including the 
adequacy criteria under 40 CFR 93.118(e).
    In addition, under CAA section 107(d)(3)(D), we are proposing to 
approve the state's request to redesignate the Imperial PM10 
nonattainment area to attainment for the PM10 NAAQS. We are 
doing so based on our conclusion that the area has met, or will meet as 
part of this action, all the criteria for redesignation under CAA 
section 107(d)(3)(E). More specifically, we propose to find the 
following: That the Imperial PM10 nonattainment area has 
attained the PM10 standard based on the most recent three-
year period (2016-2018) of quality-assured, certified, and complete 
PM10 data; that relevant portions of the California SIP are, 
or will be as part of this action, fully approved; that the improvement 
in air quality is due to permanent and enforceable reductions in 
emissions; that California has met all requirements applicable to the 
Imperial PM10 nonattainment area with respect to section 110 
and part D of the CAA if we finalize our approvals of the BACM 
demonstration and the attainment inventory in the Imperial 
PM10 Plan, as proposed herein; and that the Imperial 
PM10 nonattainment area will have a fully approved 
maintenance plan meeting the requirements of CAA section 175A if we 
finalize our approval of it, also as proposed herein.
    In connection with the above proposed approvals and determinations, 
and as authorized under CAA section 189(e), we are proposing to 
determine that PM10 precursors do not contribute 
significantly to PM10 exceedances in the Imperial 
PM10 nonattainment area based

[[Page 18527]]

on the information included in Appendix A of the Imperial 
PM10 Plan.
    We are soliciting comments on these proposed actions. We will 
accept comments from the public on this proposal for 30 days following 
publication of this proposal in the Federal Register and will consider 
these comments before taking final action.

VI. Statutory and Executive Order Reviews

    Under the CAA, redesignation of an area to attainment and the 
accompanying approval of a maintenance plan under section 107(d)(3)(E) 
are actions that affect the status of a geographic area and do not 
impose any additional regulatory requirements on sources beyond those 
imposed by state law. Redesignation to attainment does not in and of 
itself create any new requirements, but rather results in the 
applicability of requirements contained in the CAA for areas that have 
been redesignated to attainment. Moreover, the Administrator is 
required to approve a SIP submission that complies with the provisions 
of the Act and applicable federal regulations. 42 U.S.C. 7410(k); 40 
CFR 52.02(a). Thus, in reviewing SIP submissions, the EPA's role is to 
approve state choices, provided that they meet the criteria of the CAA. 
Accordingly, these proposed actions merely propose to approve a State 
plan and redesignation request as meeting federal requirements and do 
not impose additional requirements beyond those imposed by state law. 
For these reasons, these proposed actions:
     Are not a ``significant regulatory action'' subject to 
review by the Office of Management and Budget under Executive Orders 
12866 (58 FR 51735, October 4, 1993) and 13563 (76 FR 3821, January 21, 
2011);
     Are not an Executive Order 13771 (82 FR 9339, February 2, 
2017) regulatory action because SIP approvals are exempted under 
Executive Order 12866;
     Do not impose an information collection burden under the 
provisions of the Paperwork Reduction Act (44 U.S.C. 3501 et seq.);
     Are certified as not having a significant economic impact 
on a substantial number of small entities under the Regulatory 
Flexibility Act (5 U.S.C. 601 et seq.);
     Do not contain any unfunded mandate or significantly or 
uniquely affect small governments, as described in the Unfunded 
Mandates Reform Act of 1995 (Pub. L. 104-4);
     Do not have Federalism implications as specified in 
Executive Order 13132 (64 FR 43255, August 10, 1999);
     Are not an economically significant regulatory action 
based on health or safety risks subject to Executive Order 13045 (62 FR 
19885, April 23, 1987);
     Are not a significant regulatory action subject to 
Executive Order 13211 (66 FR 28355, May 22, 2001);
     Are not subject to requirements of Section 12(d) of the 
National Technology Transfer and Advancement Act of 1995 (15 U.S.C. 272 
note) because application of those requirements would be inconsistent 
with the Clean Air Act; and
     Do not provide the EPA with the discretionary authority to 
address disproportionate human health or environmental effects with 
practical, appropriate, and legally permissible methods under Executive 
Order 12898 (59 FR 7629, February 16, 1994).
    In addition, the State plan for which the EPA is proposing approval 
does not apply on any Indian reservation land or in any other area 
where the EPA or an Indian tribe has demonstrated that a tribe has 
jurisdiction. In those areas of Indian country, the proposed rule, as 
it relates to the maintenance plan, does not have tribal implications 
and will not impose substantial direct costs on tribal governments or 
preempt tribal law as specified by Executive Order 13175 (65 FR 67249, 
November 9, 2000). However, the proposed redesignation would apply to 
Indian country within the nonattainment area. In those areas of Indian 
country, the proposed redesignation action will not result in the 
relaxation of measures and programs currently in place to protect air 
quality and will not impose substantial direct costs on tribal 
governments or preempt tribal law as specified by Executive Order 13175 
(65 FR 67249, November 9, 2000). The EPA has invited the Torres 
Martinez Desert Cahuilla Indians and the Quechan Tribe of the Fort Yuma 
Indian Reservation, who have lands within the Imperial PM10 
nonattainment area, to consult on today's proposed action.

List of Subjects

40 CFR Part 52

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

40 CFR Part 81

    Environmental protection, Air pollution control, National parks, 
Wilderness areas.

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

    Dated: March 26, 2020.
John Busterud,
Regional Administrator, Region IX.
[FR Doc. 2020-06818 Filed 4-1-20; 8:45 am]
 BILLING CODE 6560-50-P