[Federal Register Volume 88, Number 183 (Friday, September 22, 2023)]
[Proposed Rules]
[Pages 65336-65350]
[FR Doc No: 2023-20555]

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 52

[EPA-R09-OAR-2023-0267; FRL-10958-01-R9]

Second 10-Year Maintenance Plan for the 24-Hour PM10 Standards;
Sacramento County 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 ``Second 10-Year PM10 Maintenance Plan for
Sacramento County'' (``Second 10-Year Maintenance Plan'' or ``Plan'')
as a revision to the state implementation plan (SIP) for the State of
California (``State''). The Second 10-Year Maintenance Plan includes,
among other elements, a base year emissions inventory, a maintenance
demonstration, contingency provisions, and motor vehicle emissions
budgets for use in transportation conformity determinations, to ensure
the continued maintenance of the national ambient air quality standards
(NAAQS) for particulate matter of 10 microns or less (PM10).
With this proposed rulemaking, the EPA is beginning the adequacy
process for the 2024, 2027, and 2033 motor vehicle emissions budgets.
Additionally, as part of the technical basis for this approval, the EPA
is taking comment on our August 1, 2022 concurrence on the wildfire
exceptional events demonstration submitted by the California Air
Resources Board (CARB) on April 26, 2021.

DATES: Written comments must arrive on or before October 23, 2023.

ADDRESSES: Submit your comments identified by Docket ID No. EPA-R09-
OAR-2023-0267 at https://www.regulations.gov. For comments submitted at
Regulations.gov, follow the online instructions for submitting
comments. Once submitted, comments cannot be edited or removed from
Regulations.gov. The EPA may publish any comment received to its public
docket. Do not submit electronically any information you consider to be
Confidential Business Information (CBI) or other information whose
disclosure is restricted by statute. Multimedia submissions (audio,
video, etc.) must be accompanied by a written comment. The written
comment is considered the official comment and should include
discussion of all points you wish to make. The EPA will generally not
consider comments or comment contents located outside of the primary
submission (i.e., on the web, cloud, or other file sharing system). For
additional submission methods, please contact the person identified in
the FOR FURTHER INFORMATION CONTACT section. For the full EPA public
comment policy, information about CBI or multimedia submissions, and
general guidance on making effect comments, please visit

https://www.epa.gov/dockets/commenting-epa-dockets. If you need
assistance in a language other than English or if you are a person with
a disability who needs a reasonable accommodation at no cost to you,
please contact the person identified in the FOR FURTHER INFORMATION
CONTACT.

FOR FURTHER INFORMATION CONTACT: Michael Dorantes, Geographic
Strategies and Modeling Section (AIR-2-2), EPA Region IX, (415) 972-
3934, [email protected].

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

Table of Contents

I. Background
    A. The PM10 National Ambient Air Quality Standards
    B. The Sacramento County Planning Area Nonattainment Designation
and First PM10 Maintenance Plan
II. Air Quality in the Sacramento County Planning Area
    A. Exceedances in the Sacramento County Planning Area
    B. Exceptional Events Demonstration for the 2018 Exceedances in
the Sacramento County Planning Area
    C. Exceedances Occuring After the 2019 Design Value Period
III. The Second 10-Year Maintenance Plan Submittal and Procedural
Requirements
IV. Evaluation of the Second 10-Year Maintenance Plan
    A. Emissions Inventory
    B. Maintenance Demonstration
    C. Monitoring Network Requirements
    D. Verification of Continued Attainment
    E. Contingency Provisions
    F. Motor Vehicle Emissions Budgets for Transportation Conformity
V. Proposed Action and Request for Public Comment
VI. Statutory and Executive Order Reviews

I. Background

A. The PM10 National Ambient Air Quality Standards

    Under section 109 of the Clean Air Act (CAA), the EPA promulgates
NAAQS for pervasive air pollutants, such as particulate matter, and
conducts periodic review of these standards to determine whether they
should be revised or whether new standards should be established. In
1987, the EPA established two PM10 NAAQS: annual standards
of 50 micrograms per cubic meter ([mu]g/m\3\) and 24-hour standards of
150 [mu]g/m\3\.\1\ Upon further review, the annual PM10
standards were subsequently revoked effective December 18, 2006, as the
available evidence did not suggest an association between long-term
exposure to coarse particles at ambient levels and detrimental health
effects.\2\ However, the EPA announced that it was retaining the 24-
hour PM10 NAAQS at 150 micrograms per cubic meter ([micro]g/
m\3\) to provide continued protection against the effects associated
with short-term exposure to coarse particles.\3\ In this document,
``PM10 NAAQS'' or the singular ``PM10 standard''
will henceforth refer to both the primary and secondary 24-hour
PM10 NAAQS, as they are the same.
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    \1\ 52 FR 24634 (July 1, 1987). The EPA established both primary
and secondary standards for the annual NAAQS and the 24-hour NAAQS.
Primary standards provide public health protection, including
protecting the health of ``sensitive'' populations such as
asthmatics, children, and the elderly. Secondary standards provide
public welfare protection, including protection against decreased
visibility and damage to animals, crops, vegetation, and buildings.
The primary and secondary standards were the set at the same level
for the annual PM10 NAAQS (i.e., at 50 [mu]g/m\3\) and
for the 24-hour NAAQS (i.e., at 150 [mu]g/m\3\).
    \2\ 71 FR 61144 (October 17, 2006).
    \3\ 78 FR 3086 (January 15, 2013).
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B. The Sacramento County Planning Area Nonattainment Designation and
First PM10 Maintenance Plan

    Under section 107 of the CAA, the EPA is required to designate all
areas of the country as attainment, nonattainment, or unclassifiable
for each of the NAAQS. Under the CAA Amendments of 1990, the Sacramento
County planning area was initially designated as unclassifiable for the
PM10 NAAQS by operation of law. The EPA then redesignated
and classified the area as a ``Moderate'' nonattainment area on January
20, 1994, due to PM10 NAAQS violations recorded at two
PM10 monitors within the Sacramento County planning area
during 1989 and 1990.\4\ This action established an attainment deadline
of December 31, 2000.
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    \4\ The nonattainment area for PM10 was set as the
same boundaries as Sacramento County, 58 FR 67334 (December 21,
1993).
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    On February 15, 2002, the EPA determined that the Sacramento County
nonattainment area had attained the PM10 NAAQS by the
attainment date.\5\ The determination was based on complete, quality-
assured, and certified ambient air monitoring data from 1998 to 2000.
The 24-hour standard is attained when the recorded number of days with
levels above 150 [micro]g/m\3\ (averaged over a 3-year period) is less
than or equal to one.\6\ The recorded number of exceedances averaged
over a three-year period at any given monitor is known as the
PM10 design value, and the highest design value recorded
within the nonattainment area is used as the area's PM10
design value for the purposes of determining attainment.\7\
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    \5\ 67 FR 7082 (February 15, 2002).
    \6\ An exceedance is defined as a daily value that is above the
level of the 24-hour standard (i.e., 150 [micro]g/m\3\) after
rounding to the nearest 10 [micro]g/m\3\ (i.e., values ending in
five or greater are to be rounded up.) Thus, a recorded value of 154
[micro]g/m\3\ would not be an exceedance as it would be rounded to
150 [micro]g/m\3\. A recorded value of 155 [micro]g/m\3\ would be an
exceedance because it would be rounded to 160 [micro]g/m\3\. 40 CFR
part 50, Appendix K, section 1.0.
    \7\ 40 CFR 50.6 and 40 CFR part 50, appendix K. The comparison
with the allowable expected exceedance rate of one per year is made
in terms of a number rounded to the nearest tenth; e.g., an
exceedance rate of 1.05 would be rounded to 1.1, which is the lowest
rate for nonattainment. 40 CFR part 50, appendix K, section 2.1(b).
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    Section 175A of the CAA dictates that any state that submits a
request for redesignation of a nonattainment area to attainment shall
also submit a SIP revision that provides for the maintenance of the
pertinent NAAQS for at least 10 years after the redesignation. This
maintenance plan must, among other requirements, ensure control
measures are in place such that the area will continue to maintain the
standard for a 10-year period after redesignation, and include
contingency provisions to ensure that violations of the NAAQS will be
promptly remedied.
    In California, CARB is the agency responsible for the adoption and
submission of California SIPs and SIP revisions to the EPA. Working
jointly with CARB, local and regional air pollution control districts
in California are responsible for the development of regional air
quality plans. The Sacramento Metropolitan Air Quality Management
District (``SMAQMD'' or ``District'') develops and adopts plans to
address CAA planning requirements applicable to Sacramento County.
SMAQMD adopts and submits its plans to CARB for state adoption and
submission to the EPA as revisions to the California SIP.
    On December 7, 2010, CARB requested that the EPA redesignate the
Sacramento County PM10 nonattainment area to attainment and
concurrently submitted the Sacramento PM10 Maintenance Plan
and associated motor vehicle emissions budgets (``budgets'') to the EPA
as a revision to the California SIP.\8\ On October 28, 2013, the EPA
approved the Sacramento PM10 Maintenance Plan, which
provided for maintenance of the NAAQS for the area through October 28,
2023.\9\
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    \8\ Letter dated December 7, 2010, from James Goldstene,
Executive Officer, CARB, to Jared Blumenfeld, Regional
Administrator, EPA Region IX.
    \9\ 78 FR 59261 (September 26, 2013).

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II. Air Quality in the Sacramento County Planning Area

A. Exceedances in the Sacramento County Planning Area

    A recent design value showing a maintenance area is continuing to
attain the PM10 NAAQS (i.e., the recorded number of days
with levels above 150 [micro]g/m\3\, averaged over a 3-year period, is
less than or equal to one) is the foundation of a second 10-year
maintenance plan. As described in more detail in Section IV.A of this
document, a base year emissions inventory from the design value period
that represents attainment conditions is used as the basis for
projecting emissions inventories into the future and to demonstrate
that future emissions will not lead to an exceedance of the standards.
The District used the data from calendar years 2017 through 2019 to
calculate a 2019 design value to demonstrate the area had continued to
attain the PM10 standard and selected the 2017 emissions
inventory as its base year inventory.
    Table 1 of this document shows the design values for the Sacramento
County PM10 maintenance area at the monitoring sites active
in the county between 2011 through 2022, accounting for all recorded
exceedances during that time. Specifically, no exceedances of the
PM10 NAAQS were recorded in 2011-2017, numerous exceedances
were recorded in 2018 across all active monitors, a single exceedance
was recorded in 2019 at the Sacramento T Street monitoring site (AQS
ID: 06-067-0010), several exceedances were recorded in 2020 across all
active monitors, and in 2021-2022 no exceedances of the PM10
NAAQS were recorded. As a result of the exceedance days recorded in
2018, the calculated 2019 design value for PM10 is in
violation of the standard.\10\ The District contends that the
exceedances in 2018 were due to uncontrollable wildfire smoke and
submitted a request to exclude the 2018 data from regulatory decisions
on the basis that they are exceptional events.\11\
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    \10\ See EPA AQS Design Value Report, AMP480, for 2011-2022
PM10 Design Values for Sacramento County (Report accessed
August 9, 2023), included in the docket for this rulemaking, for
full details.
    \11\ Letter dated March 31, 2021, from Mark Loutzenhiser,
Division Manager, Program Coordination Division, SMAQMD, to Richard
Corey, Executive Officer, CARB, Subject: ``Exceptional Event
Demonstration for November 2018 PM10 Exceedances in
Sacramento County due to Wildfires.''

  Table 1--Sacramento County 2013-2022 PM10 Monitor Design Values Including 2018 Exceptional Events Exceedances
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                                                                          Monitoring site
                                                 ---------------------------------------------------------------
               Design value period                     North                       Sacramento T     Sacramento
                                                     Highlands    Del Paso Manor    Street \a\     Branch Center
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2011-2013.......................................             0.0             0.0  ..............             0.0
2012-2014.......................................             0.0             0.0  ..............             0.0
2013-2015.......................................             0.0             0.0  ..............             0.0
2014-2016.......................................             0.0             0.0             0.0             0.0
2015-2017.......................................             0.0             0.0             0.0             0.0
2016-2018.......................................             4.1             4.1             2.0             2.0
2017-2019.......................................             4.1             4.1             2.3             2.0
2018-2020.......................................             6.0             6.0             3.7             4.6
2019-2021.......................................             1.9             1.9             1.7             2.6
2020-2022.......................................             1.9             1.9             1.3             2.6
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\a\ The Sacramento T Street monitoring station came into active use in 2013. (North Highlands Air Quality System
  Site ID #:06-067-0002-1; Del Paso Manor (primary) AQS Site ID #: 06-067-0006-1; Sacramento T Street AQS Site
  ID #: 06-067-0010-4; Sacramento Branch Center AQS Site ID #: 06-067-0284-1).

B. Exceptional Events Demonstration for the 2018 Exceedances in the
Sacramento County Planning Area

    Congress has recognized that it may not be appropriate for the EPA
to use certain monitoring data, collected by the ambient air quality
monitoring network and maintained in the EPA's Air Quality System (AQS)
database, 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. To implement this 2005 CAA amendment, the EPA
promulgated the 2007 Exceptional Events Rule.\12\ The 2007 Exceptional
Events Rule created a regulatory process codified at 40 CFR parts 50
and 51 (sections 50.1, 50.14, 51.930). These regulatory sections, which
superseded the EPA's previous guidance on handling data influenced by
exceptional events, contain definitions, procedural requirements,
requirements for air agency demonstrations, criteria for EPA 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 (referred to
herein as the ``Exceptional Events Rule'').\13\ Under the Exceptional
Events Rule, if, for example, a state demonstrates to the EPA's
satisfaction that emissions from a wildfire smoke event caused specific
air pollution concentration in excess of the PM10 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.\14\
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    \12\ 72 FR 13560 (March 22, 2007).
    \13\ 81 FR 68216 (October 3, 2016).
    \14\ 40 CFR 50.14(b)(4).
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    For the EPA to concur with excluding the air quality data from
regulatory decision, the demonstration must satisfy all the Exceptional
Events Rule criteria. Specifically, under 40 CFR 50.14(c)(3)(iv), the
air agency demonstration to justify exclusion of data must include:
    1. a narrative conceptual model that describes the event(s) causing
the exceedance or violation and a discussion of how emissions from the
event(s) led to the exceedance or violation at the affected
monitors(s);
    2. a demonstration that the event affected air quality in such a
way that

there exists a clear causal relationship between the specific event and
the monitored exceedance or violation;
    3. analyses comparing the claimed event-influenced concentration(s)
to concentrations at the same monitoring site at other times to support
requirement in 40 CFR 50.14(c)(3)(iv)(2);
    4. a demonstration that the event was both not reasonably
controllable and not reasonably preventable, and;
    5. a demonstration that the event was a human activity that is
unlikely to recur at a particular location or was a natural event.\15\
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    \15\ A natural event is further described in 40 CFR 50.1(k) as
``[a]n event and its resulting emissions, which may recur at the
same location, in which human activity plays little or no direct
causal role. For purposes of the definition of a natural event,
anthropogenic sources that are reasonably controlled shall be
considered to not play a direct role in causing emissions.''
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    In addition, the air agency must meet several procedural
requirements, including:
    1. submission of an Initial Notification of Potential Exceptional
Event and flagging of the affected data in the EPA's Air Quality System
(AQS) as described in 40 CFR 50.14(c)(2)(i);
    2. completion and documentation of the public comment process
described in 40 CFR 50.14(c)(3)(v); and
    3. implementation of any relevant mitigation requirements as
described in 40 CFR 51.930.
    On August 21, 2019,\16\ CARB submitted an Initial Notification of
Potential Exceptional Events prepared by SMAQMD for numerous
exceedances of the PM10 NAAQS that occurred at the
Sacramento T Street, North Highland, Del Paso Manor, and Sacramento
Branch Center PM10 monitoring sites within the maintenance
area on November 10-12 and November 14-16, 2018.
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    \16\ Email dated August 21, 2019, from Sylvia Vanderspek (CARB)
to Gwen Yoshimura (EPA Region IX) Subject: ``INI Form for Submittal
to EPA--SMAQMD PM10.''
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    The EPA recommended that CARB and SMAQMD determine the relevant
exceedances and associated monitoring sites that may have regulatory
significance with respect to the PM10 NAAQS, and submit an
exceptional event demonstration to the EPA no later than March of
2021.\17\ On March 31, 2021, SMAQMD submitted the ``Exceptional Event
Demonstration for November 2018 Exceedances in Sacramento County due to
Wildfires'' to CARB for transmittal to the EPA.\18\ Then, on April 26,
2021,\19\ CARB submitted the exceptional event demonstration prepared
by SMAQMD for 13 exceedances of the 1987 24-hour PM10 NAAQS
during November 10-12 and November 14-16, 2018.\20\ Table 2 of this
document summarizes the exceedances that SMAQMD included in the
demonstration.
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    \17\ See letter dated March 3, 2020, from Elizabeth Adams, Air
and Radiation Division Director, EPA Region IX, to Sylvia
Vanderspek, Air Quality Planning Branch Chief, CARB.
    \18\ Letter dated March 31, 2021, from Mark Loutzenhiser,
Division Manager, Program Coordination Division, SMAQMD, to Richard
Corey, Executive Officer, CARB, Subject: ``Exceptional Event
Demonstration for November 2018 PM10 Exceedances in
Sacramento County due to Wildfires.''
    \19\ Letter dated April 26, 2021, from David Edwards for Michael
Benjamin, Air Quality Planning and Science Division Chief, CARB, to
Elizabeth Adams, Air and Radiation Division Director, EPA Region IX,
Subject: ``Submittal of Final Documentation for 2018 Exceptional
Events.''
    \20\ SMAQMD Exceptional Event Demonstration For November 2018
PM10 Exceedances in Sacramento County Due to Wildfires,
March 31, 2021.

                        Table 2--Sacramento County PM10 NAAQS Exceedance Summary for 2018
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                                                                                PM10 ([micro]g/
               Exceedance date                         Monitoring site             AQS ID \a\          m\3\)

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November 10, 2018............................  Sacramento T Street............     06-067-0010-4             189
November 10, 2018............................  North Highlands................     06-067-0002-1             222
November 10, 2018............................  Del Paso Manor.................     06-067-0006-1             212
November 10, 2018............................  Del Paso Manor.................     06-067-0006-2             202
November 10, 2018............................  Sacramento--Branch Center......     06-067-0284-1             200
November 11, 2018............................  Sacramento T Street............     06-067-0010-4             176
November 12, 2018............................  Sacramento T Street............     06-067-0010-4             183
November 14, 2018............................  Sacramento T Street............     06-067-0010-4             181
November 15, 2018............................  Sacramento T Street............     06-067-0010-4             292
November 16, 2018............................  Sacramento T Street............     06-067-0010-4             252
November 16, 2018............................  North Highlands................     06-067-0002-1             163
November 16, 2018............................  Del Paso Manor.................     06-067-0006-1             166
November 16, 2018............................  Del Paso Manor.................  \b\ 06-067-0006-             163
                                                                                2
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\a\ The last number in the AQS ID is the Parameter Occurrence Code (POC) and distinguishes between different
  monitors at the same site.
\b\ The Del Paso Manor (POC 2) monitor is a collocated monitor used for quality assurance purposes. Data from
  this monitor are not used for comparison to the NAAQS. However, for completeness, CARB, SMAQMD, and the EPA
  have included this monitor in the demonstration and concurrence process.
Source: Second 10-Year Maintenance Plan, Table 2-5.

    The demonstration submitted by CARB and SMAQMD provides a narrative
conceptual model to describe how emissions from the Camp Fire, in Butte
County, California, caused the PM10 exceedances at the
listed monitoring sites on the listed dates. The narrative conceptual
model includes a description of the Camp Fire and its progression, the
general meteorological conditions in the affected area, and information
regarding how PM10 concentrations measured during this
period compared to normal conditions across the Sacramento Valley. To
support a clear causal relationship between the wildfire event and the
monitored exceedances, the demonstration includes several analyses,
specifically including the following: comparison with historical
PM10 concentrations; Hybrid Single-Particle Lagrangian
Integrated Trajectory (HYSPLIT) analysis; satellite imagery of smoke;
ceilometer data; \21\ regional patterns of PM10
concentrations and PM air quality index (AQI) values; fine particulate
matter (PM2.5) concentrations and comparison with historical
data; concurrent increases in carbon monoxide, black carbon, and
organic carbon concentrations; media reports of wildfire smoke
affecting the monitoring area; and District-issued air quality
advisories.\22\ The documentation also demonstrates that the wildfire

event was not reasonably controllable and not reasonably
preventable.\23\ Furthermore, the Camp Fire event meets the definition
of a natural wildfire event, defined in 40 CFR 50.1(n) as ``a wildfire
that predominantly occurs on wildland.'' \24\
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    \21\ A ceilometer measures the attenuated backscatter of light
due to gradients in particulate matter or other aerosols.
    \22\ See Sections 3 and 4, and Appendices A, B, C, and D of the
Demonstration for full details.
    \23\ Id. at pp. 3-1 to 3-3 and Section 5: p. 5-1.
    \24\ Id. at Section 6: p. 6-1.
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    In addition to the technical demonstration requirements, there are
timing and procedural requirements an air agency must follow to request
data exclusion. The demonstration submitted by CARB includes evidence
of the following: SMAQMD provided prompt public notification of the
events, CARB submitted an Initial Notification of Potential Exceptional
Event in the EPA's AQS system \25\ and met the deadline requirements
for these submissions, and the District allowed for a documented public
comment period in which feedback from the public was solicited,
collected, submitted to the EPA, and considered along with the
submission of the demonstration.
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    \25\ SMAQMD Exceptional Event PM10 Initial
Notification Summary Information 2016-2018, submitted August 21,
2019.
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    The EPA reviewed and concurred on the documentation provided by
CARB and SMAQMD to support claims that the Camp Fire caused exceedances
of the PM10 NAAQS at the Sacramento T Street, North
Highlands, Del Paso Manor, and Sacramento Branch Center monitoring
sites on November 10-12 and November 14-16, 2018.\26\ The demonstration
prepared by SMAQMD and submitted by CARB meets all criteria required by
40 CFR 50.14 (c)(3)(iv). Furthermore, the submittal satisfied all
schedule and procedural requirements specified in 40 CFR 50.14(c) and
40 CFR 51.930. Thus, the EPA is relying on calculated values that
exclude the event-influenced data for the purpose of demonstrating
continued attainment of the PM10 NAAQS. With the exclusion
of the wildfire-related exceedances in 2018, the 2019 design value is
no longer in violation of the PM10 NAAQS.
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    \26\ Details included in ``Technical Support Document for EPA
Concurrence on PM10 Exceedances Measured in the
Sacramento County Maintenance Area on November 10-12 and November
14-16, 2018 as Exceptional Events,'' found within the docket for
this rulemaking, and letter dated July 27, 2022, from Elizabeth
Adams, Director, Air and Radiation Division, EPA Region IX, to
Sylvia Vanderspek, Chief, Air Quality Planning Branch and Air
Quality Planning and Science Division, CARB, Subject: ``EPA
Concurrence with EE exclusion of PM10 exceedances on
November 10-12 and 14-16, 2018.''
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    EPA concurrence is a preliminary step in the regulatory process for
actions that may rely on these data and does not constitute final
agency action. Regulatory actions that rely on the exclusion of
exceptional event data require the EPA to provide an opportunity for
public comment on the technical basis of the proposed action, including
the claimed exceptional events and all supporting data prior to the EPA
taking final agency action. This proposed action provides the public
with an opportunity to comment on the claimed exceptional events for
the 2018 exceedances in Sacramento County and all supporting documents
submitted by CARB, and the EPA's concurrence with the State's request
with regards to our proposed action to approve the Second 10-Year
Maintenance Plan.

C. Exceedances Occuring After the 2019 Design Value Period

    In order to ensure that the area has continued to attain the
standard after 2017-2019 design value period on which the Plan is
based, the District calculated the 2020 design value (based on 2018-
2020 data), and we independently calculated the 2021 and 2022 design
values (based on 2019-2021, and 2020-2022 data, respectively). In all
cases the design values are above the standard.\27\ The 2020
exceedances associated with these violations were initially flagged in
AQS by SMAQMD as wildfire related and the District included information
with the Plan to support these claims.\28\ Appendix A in the Second 10-
Year Maintenance Plan (``Analysis of PM10 Exceedance Days in
2020'') provides a conceptual narrative demonstrating how wildfire
smoke also contributed to the PM10 exceedances in 2020.
Between September 8, 2020, and September 13, 2020, there was a total of
seven recorded exceedances among all monitoring sites located within
the county at the time,\29\ accounting for all exceedances recorded in
2020. Table 3 of this document summarizes the exceedances recorded
during this period.
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    \27\ ``Second 10-Year PM10 Maintenance Plan for
Sacramento County,'' Appendix A.
    \28\ EPA AQS Report of Flagged PM10 Values due to
Wildfire Events in Sacramento County, Report Prepared February 13,
2023.
    \29\ See Section IV.C of the rulemaking for additional details
on the present status of the Sacramento County PM10
monitoring network.

                        Table 3--Sacramento County PM10 NAAQS Exceedance Summary for 2020
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                                                                                PM10 ([micro]g/
               Exceedance date                        Monitoring station           AQS ID \a\          m\3\)

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September 8, 2020............................  Sacramento T Street............     06-067-0010-4             298
September 11, 2020...........................  Sacramento T Street............     06-067-0010-4             231
September 12, 2020...........................  Sacramento T Street............     06-067-0010-4             186
September 12, 2020...........................  Del Paso Manor.................     06-067-0006-1             186
September 12, 2020...........................  Del Paso Manor.................  \b\ 06-067-0006-             188
                                                                                2
September 12, 2020...........................  North Highlands................     06-067-0002-1             187
September 12, 2020...........................  Sacramento--Branch Center......     06-067-0284-1             201
September 13, 2020...........................  Sacramento T Street............     06-067-0010-4             169
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\a\ The last number in the AQS ID is the Parameter Occurrence Code (POC) and distinguishes between different
  monitors at the same site.
\b\ The Del Paso Manor (POC 2) monitor is a collocated monitor for quality assurance purposes, and the data from
  this monitor is not used for comparison to the NAAQS. However, for completeness, CARB, SMAQMD, and the EPA
  included this monitor in the demonstration and concurrence process.
Source: Second 10-Year Maintenance Plan, Table A-1.

    Similar to the exceptional event demonstration for the 2018
exceedances, Appendix A documents several wildfires in the vicinity of
Sacramento County that were active during 2020 and attributes emissions
from these wildfires, concurrent with wind gust events, as having
caused the PM10 exceedances listed in Table 3.\30\

The appendix includes an overview of the wildfires active at the time
of the exceedances, including the start and containment dates, the
geographic proximity and range of each wildfire, and fire containment
levels during the date range of the exceedances. To support a clear
causal relationship between these wildfire events, wind gusts, and the
monitored exceedances, Appendix A includes several analyses including
the following: HYSPLIT analysis; satellite imagery of smoke; regional
patterns of PM10 concentrations and PM AQI; PM2.5
concentrations and comparison with historical data; concurrent
increases in carbon monoxide, black carbon, and organic carbon
concentrations; as well as media reports of wildfire smoke affecting
the monitoring data. In addition, the District notes that the wildfires
listed in Table A-2 of Appendix A were either a result of lightning
strikes or were still under investigation, and the District contends
these wildfire events were not reasonably controllable and not
reasonably preventable. Therefore, in lieu of an exceptional event
demonstration, the EPA proposes to find that this information provided
in Appendix A of the Plan indicates that the 2020 exceedances were
caused by uncontrollable wildfire smoke and wind gusts.
---------------------------------------------------------------------------

    \30\ During the late summer and early fall of 2020, the Slater/
Devils Fire, Red Salmon Complex Fire, August Complex Fire, North
Complex Fire (composed of the Baer and Claremont fires), Fork Fire,
and the Creek Fire were all active at the time of the exceedances.
---------------------------------------------------------------------------

    Because SMAQMD and CARB did not submit an exceptional event
demonstration for the 2020 exceedances from wildfires, we have factored
these exceedances into design value calculations, and the post-2019
design values (2020, 2021, and 2022) remain in violation of the
PM10 NAAQS, as summarized in Table 4 of this document.
However, after reviewing the evidence provided by the District
demonstrating that the exceedances in 2020 were caused by a combination
of uncontrollable wildfire smoke and wind gust events, and therefore
separate from trends in the ambient air quality for PM10, we
propose to find that these exceedances do not call into question the
EPA's proposed approval of the Second 10-Year Maintenance Plan as
providing for maintenance of the PM10 NAAQS. No exceedances
were recorded in 2021, nor 2022, lending additional support to the
claim that the 2020 exceedances were caused by uncontrollable wildfire
smoke and wind gust events. We find that these data are consistent with
the EPA's proposed approval of the Second 10-Year Maintenance Plan as
providing for maintenance of the PM10 NAAQS. Prior to
finalizing this action, we will examine all quality-assured and
certified PM10 monitoring data available to ensure this
trend persists or that the District has implemented its contingency
plan to address any exceedances.

     Table 4--Sacramento County PM10 Monitor Design Values With 2018 Exceptional Events Exceedances Removed
----------------------------------------------------------------------------------------------------------------
                                                                          Monitoring site
                                                 ---------------------------------------------------------------
               Design value period                     North                       Sacramento T     Sacramento
                                                     Highlands    Del Paso Manor    Street \a\     Branch Center
----------------------------------------------------------------------------------------------------------------
2011-2013.......................................             0.0             0.0  ..............             0.0
2012-2014.......................................             0.0             0.0  ..............             0.0
2013-2015.......................................             0.0             0.0  ..............             0.0
2014-2016.......................................             0.0             0.0             0.0             0.0
2015-2017.......................................             0.0             0.0             0.0             0.0
2016-2018.......................................             0.0             0.0             0.0             0.0
2017-2019.......................................             0.0             0.0             0.3             0.0
2018-2020.......................................             1.9             1.9             1.7             2.6
2019-2021.......................................             1.9             1.9             1.7             2.6
2020-2022.......................................             1.9             1.9             1.3             2.6
----------------------------------------------------------------------------------------------------------------
\a\ The Sacramento T Street monitoring station came into active use in 2013. (North Highlands AQS Site ID #:06-
  067-0002-1; Del Paso Manor (primary) AQS Site ID #: 06-067-0006-1; Sacramento T Street AQS Site ID #: 06-067-
  0010-4; Sacramento Branch Center AQS Site ID #: 06-067-0284-1).
Source: TSD for EPA Concurrence on PM10 Exceedances Measured in Sacramento County on Nov 10-12 and Nov 14-16 as
  EE, found within the docket for this rulemaking.

III. The Second 10-Year Maintenance Plan Submittal and Procedural
Requirements

    CAA section 175A(b) requires states to submit a SIP revision to
maintain the NAAQS for an additional ten years after the expiration of
the 10-year period covered by the initial maintenance plan. The
submittal is due eight years after the original redesignation request
and maintenance plan was approved. The deadline to submit the SIP
revision for the Sacramento County PM10 NAAQS maintenance
area was October 28, 2021. On October 21, 2021, CARB submitted the
``Second 10-Year PM10 Maintenance Plan for Sacramento
County'' (``Second 10-Year Maintenance Plan'' or ``Plan'') to meet the
requirement for a subsequent maintenance plan under CAA section
175A(b).\31\ The Second 10-Year Maintenance Plan is intended to provide
for continued maintenance of the PM10 NAAQS for the 10-year
period following the end of the first 10-year period, i.e., from 2024
through 2033.
---------------------------------------------------------------------------

    \31\ Letter dated October 20, 2021, from Richard Corey,
Executive Officer, CARB, to Deborah Jordan, Acting Regional
Administrator, EPA Region IX (submitted electronically October 21,
2021).
---------------------------------------------------------------------------

    In addition, CAA sections 110(a)(1), (2), and 110(l) require states
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 opportunity for a
public hearing consistent with the EPA's implementing regulations in 40
CFR 51.102. CARB's October 21, 2021 SIP submittal package includes
documentation of the public processes used by the District and CARB to
adopt the Second 10-Year Maintenance Plan. Prior to adoption of the
plan, a reasonable notice of a public hearing was provided to the
public, and a public hearing was conducted. Specifically, notices of a
public hearing and the opening of a comment period for the Second 10-
Year Maintenance Plan for Sacramento County were published within the
``News and Notices'' section of the District's website on July 23,
2021, in advance of the August 26, 2021

public hearing.\32\ No comments were received during the District's
comment period.\33\ Following the adoption of a resolution to approve
the Second 10-Year Maintenance Plan,\34\ the District requested that
CARB review and adopt the Plan.\35\ On August 13, 2021, CARB published
on its website a notice of a public hearing to be held on September 23,
2021, to consider adoption of the District's Plan.\36\ No comments were
received during CARB's public comment period. CARB adopted the
Plan,\37\ and subsequently submitted it to the EPA as a revision to the
California SIP on October 21, 2021. Based on the documentation provided
in the Second 10-Year Maintenance Plan submittal, we propose to find
that the SIP revision satisfies the public notice procedural
requirements of the Act.
---------------------------------------------------------------------------

    \32\ SMAQMD affidavit of publication of ``Public Hearing for
Approval of the Second 10-Year PM10 Maintenance Plan for
Sacramento County'' on the District's website on July 23, 2021.
    \33\ See SMAQMD Transmittal Letter from Mark Loutzenhiser,
Division Manager, Program Coordination Division, SMAQMD, to Richard
Corey, Executive Officer, CARB, dated September 2, 2021.
    \34\ SMAQMD Board of Directors Public Hearing and Resolution No.
2021-009 Adopting the ``Second 10-Year PM10 Maintenance
Plan for Sacramento County,'' dated August 26, 2021.
    \35\ Letter dated September 2, 2021, from Mark Loutzenhiser,
Division Manager, Program Coordination Division, SMAQMD, to Richard
Corey, Executive Officer, CARB.
    \36\ CARB Notice of Public Meeting to Consider Sacramento County
PM10 Maintenance Plan State Implementation Plan
Submittal, dated August 13, 2021.
    \37\ CARB Board Resolution 21-20: Sacramento County
PM10 Maintenance Plan State Implementation Plan
Submittal, dated September 23, 2021.
---------------------------------------------------------------------------

    Section 175A of the CAA provides the general framework for a
maintenance plan. The initial 10-year maintenance plan must provide for
maintenance of the NAAQS for at least 10 years after redesignation,
including any control measures necessary to ensure such maintenance. In
addition, maintenance plans are to contain contingency provisions
necessary to ensure the prompt correction of a violation of the NAAQS
that may occur after redesignation. The contingency measures must
include, at a minimum, a requirement that the state will implement all
control measures contained in the nonattainment SIP prior to
redesignation. Beyond these provisions, section 175A of the CAA does
not define the content of a second 10-year maintenance plan.
    The primary guidance on maintenance plans and redesignation
requests is the September 4, 1992 memorandum from John Calcagni, titled
``Procedures for Processing Requests to Redesignate Areas to
Attainment'' (``Calcagni Memo'').\38\ The Calcagni Memo outlines the
key elements of a maintenance plan, which include the following:
attainment emissions inventory, maintenance demonstration, monitoring
network requirements, verification of continued attainment, and
contingency plan elements. We are evaluating the Second 10-Year
Maintenance Plan based on the satisfactory fulfillment of these and all
relevant procedural requirements of the CAA.
---------------------------------------------------------------------------

    \38\ Memorandum dated September 4, 1992, from John Calcagni,
Director, Air Quality Management Division, EPA, to Regional Office
Air Division Directors, Subject: ``Procedures for Processing
Requests to Redesignate Areas to Attainment.''
---------------------------------------------------------------------------

IV. Evaluation of the Second 10-Year Maintenance Plan

A. Emissions Inventory

    A maintenance plan for the PM10 NAAQS should include a
comprehensive, accurate, and current emissions inventory of all sources
of relevant pollutants in the area, to identify a level of emissions
sufficient to attain the PM10 NAAQS. The inventory should
include emissions from stationary point sources, area sources, and
mobile sources and must be based on actual emissions during the
appropriate season, if applicable.\39\ This emissions inventory should
be consistent with the EPA's most recent guidance available at the time
and should represent emissions during the time period associated with
the monitoring data showing attainment, in this case 2017-2019. The
specific PM10 emissions inventory requirements are set forth
in the Air Emissions Reporting Requirements rule.\40\ The EPA has
provided additional guidance for developing PM10 emissions
inventories in ``PM10 Emissions Inventory Requirements,''
\41\ and ``Emissions Inventory Guidance for Implementation of Ozone and
Particulate Matter National Ambient Air Quality Standards (NAAQS) and
Regional Haze Requirements'' (May 2017).
---------------------------------------------------------------------------

    \39\ CAA section 172(c)(3).
    \40\ 40 CFR part 51, subpart A.
    \41\ EPA-454/R-94-033, September 1994.
---------------------------------------------------------------------------

    The SMAQMD Second 10-Year Maintenance Plan includes inventories for
total primary PM10 and nitrogen oxide pollutants
(NOX) in the County for the years 2017, 2024, 2027, and
2033. NOX emissions are discussed in this plan due to the
significant contribution of NOX as a precursor pollutant,
especially toward wintertime ambient PM10 concentrations, as
demonstrated in the first maintenance plan by a chemical mass balance
(CMB) study of PM10 pollution in the County.\42\
Additionally, detailed emissions inventory data for sulfur oxides
(SOX) are not included, but SOX emissions remain
stable throughout the second maintenance period at about 1 ton per day
(tpd).\43\ The Plan also states that volatile organic compounds (VOCs)
are not identified in the CMB study analysis performed for the First
Maintenance Plan as contributing to the PM10 concentrations
and therefore are not included in the emissions inventory. The District
selected the inventory years to include the base year emissions
inventory (2017), an inventory for the first year of the second
maintenance period (2024), an interim year inventory (2027), and an
inventory for the end of the second maintenance period (2033). The base
year is the first year of the Plan's design value. Projected emissions
inventories for future years must account for, among other factors, 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 includes emissions
estimates from all the relevant stationary point, area, and mobile
source categories, and further divides these main categories into more
descriptive subcategories. As these emissions forecasts consider
expected emissions reductions to the base year inventory resulting from
adopted control measures, they similarly consider potential emissions
increases, such as those associated with emissions reduction credits
(ERCs). ERCs are allowances earned through voluntary pollutant
emissions reductions such as equipment shutdowns or voluntarily
installed controls. Emissions within the Plan are listed for an average
winter day when concentrations were shown to be seasonally elevated.
The SMAQMD analysis demonstrates a seasonal occurrence of higher
ambient PM10 concentrations in the fall and winter
months.\44\ The District finds that this trend is a result of increased
residential wood combustion, in conjunction with

winter weather conditions conducive to PM10 pollutant build
up (e.g., greater atmospheric stability, low wind dispersion, and
colder temperatures).
---------------------------------------------------------------------------

    \42\ SMAQMD PM10 Implementation/Maintenance Plan and
Redesignation Request for Sacramento County, p. 4-4. Source
contributions used in the CMB study were based on a technical paper
on wintertime PM2.5 and PM10 source
apportionment for Sacramento (Motallebi, Nehzat. ``Wintertime
PM2.5 and PM10 Source Apportionment at
Sacramento California.'' Air and Waste Management Association,
1999). The CMB study calculated source contributions for ambient air
quality samples (>40 [mu]g/m3) collected from November to January
for 1991-1996.
    \43\ Second 10-Year Maintenance Plan, Table 5-1.
    \44\ Second 10-Year Maintenance Plan For Sacramento County,
Section 2.8.
---------------------------------------------------------------------------

    The emissions inventories used in the Plan are from CARB's
California Emissions Projection Analysis Model (CEPAM): CEPAM 2019:
External Adjustment Reporting Tool--Version 1.02. Because the Second
10-Year Maintenance Plan depends on both PM10 and
NOX emissions to demonstrate continued compliance (discussed
in further detail in Sections III.C and D of this document), the EPA
reviewed both PM10 and NOX emissions inventories.
    Direct PM10 and NOX emissions estimates for
stationary point sources reflect actual emissions reported to the
District by owners or operators of industrial point sources in the
Sacramento County planning area. This category is primarily composed of
fuel combustion, waste disposal, petroleum production and marketing,
and other industrial processes. Areawide sources, such as consumer
products and agricultural burning, occur over a wide geographic area.
Emissions for these categories are calculated from fuel usage, product
sales, population, employment data, and other parameters for the
pertinent range of activities across Sacramento County.
    Emissions from on-road mobile sources, which include passenger
vehicles, buses, and trucks, were estimated using outputs from CARB's
EMFAC2017 model.\45\ Emissions inventories for aircraft, trains, boats,
and off-road vehicles and equipment used for construction, farming,
commercial, industrial, and recreational activities were included in
the ``Other Mobile'' category.
---------------------------------------------------------------------------

    \45\ EMFAC is short for EMission FACtor. The EPA approved
EMFAC2017 for SIP development and transportation conformity purposes
in California on August 15, 2019. 84 FR 41717. EMFAC2017 was the
most recently approved version of the EMFAC model that was available
at the time of preparation of the Second 10-Year Maintenance Plan.
---------------------------------------------------------------------------

    The direct PM10 emissions for the base year emissions
inventory are presented within Table 5 of this document.

                         Table 5--Sacramento County Direct PM10 2017 Base Year Emissions
                                          [Tons per average winter day]
----------------------------------------------------------------------------------------------------------------
        Source category            Subcategory         2017            2024            2027            2033
----------------------------------------------------------------------------------------------------------------
Stationary Point Sources......  Fuel Combustion.            0.26            0.24            0.25            0.24
                                Waste Disposal..            0.02            0.02            0.02            0.02
                                Industrial                  1.14            1.18            1.31            1.35
                                 Processes.
Areawide......................  Residential Fuel            9.15            8.97            8.89            8.83
                                 Combustion.
                                Farming                     1.25            1.16            1.12            1.06
                                 Operations.
                                Construction and            9.42            9.57           10.60           11.29
                                 Demolition.
                                Paved Road Dust.            7.69            8.25            8.52            9.15
                                Unpaved Road                0.65            0.62            0.61            0.59
                                 Dust.
                                Managed Burning             0.16            0.17            0.17            0.16
                                 and Disposal.
                                Cooking.........            0.88            0.94            0.96            1.00
                                Fires...........            0.06            0.07            0.07            0.07
                                Fugitive                    0.11            0.11            0.10            0.10
                                 Windblown Dust.
                                Asphalt Paving/             0.01            0.01            0.01            0.01
                                 Roofing.
On-Road Motor Vehicles........  ................            2.24            2.08            2.15            2.22
Other Mobile..................  Aircraft........            0.07            0.08            0.08            0.08
                                Trains..........            0.02            0.02            0.02            0.02
                                Equipment (Off-             0.29            0.20            0.17            0.15
                                 Road/Farm).
                                Recreational                0.13            0.09            0.08            0.07
                                 Boat.
                                Commercial                  0.01            0.01            0.01            0.01
                                 Harbor Craft.
                                Off-road                   <0.01           <0.01           <0.01           <0.01
                                 Recreational
                                 Vehicles.
                                                 ---------------------------------------------------------------
    Total.....................  All Stationary,            33.58           33.78           35.15           36.43
                                 Areawide, and
                                 Mobile Sources.
----------------------------------------------------------------------------------------------------------------
Source: Second 10-Year Maintenance Plan, Table 3-1.

    The direct NOX emissions for the base year emissions
inventory are presented within Table 6 of this document.

                             Table 6--Sacramento County NOX 2017 Base Year Emissions
                                          [Tons per average winter day]
----------------------------------------------------------------------------------------------------------------
        Source category            Subcategory         2017            2024            2027            2033
----------------------------------------------------------------------------------------------------------------
Stationary Point Sources......  Fuel Combustion.            1.93            1.78            1.80            1.80
                                Waste Disposal..            0.07            0.07            0.08            0.08
                                Industrial                  0.24            0.25            0.27            0.28
                                 Processes.
                                Petroleum                  <0.01           <0.01           <0.01           <0.01
                                 Processing and
                                 Marketing.
Areawide......................  Residential Fuel            3.83            3.75            3.76            3.81
                                 Combustion.
                                Managed Burning             0.06            0.06            0.06            0.05
                                 and Disposal.
                                Fires...........            0.01            0.01            0.01            0.01
On-Road Motor Vehicles........  ................           21.45           10.66            9.33            7.46
Other Mobile..................  Aircraft........            1.75            1.98            2.08            2.30

                                Trains..........            0.85            0.99            1.02            1.05
                                Equipment (Off-             5.00            3.42            2.97            2.69
                                 Road/Farm).
                                Recreational                0.39            0.36            0.35            0.34
                                 Boat.
                                Commercial                  0.25            0.23            0.22            0.19
                                 Harbor Craft.
                                Off-road                    0.01            0.01            0.01            0.01
                                 Recreational
                                 Vehicles.
                                                 ---------------------------------------------------------------
    Total.....................  All Stationary,            35.84           23.57           21,96           20.08
                                 Areawide, and
                                 Mobile Sources.
----------------------------------------------------------------------------------------------------------------
Source: Second 10-Year Maintenance Plan, Table 3-2.

    Based on the estimates for the year 2017 in Table 5, areawide
sources account for a majority (approximately 88 percent) of the total
PM10 emissions in the Sacramento County planning area.
Residential fuel combustion, construction and demolition, and paved
road dust account for the majority of the areawide emissions
(approximately 89 percent). The future year emissions estimates in the
Plan predict an increase in direct PM10 emissions within the
Sacramento County planning area over the second ten-year planning
period. The main source of the overall predicted increase of
PM10 emissions is increased emissions of areawide sources,
with increases from stationary source emissions also acting as a minor
contributor to the overall trend (0.20 tpd). By 2033, total direct
PM10 emissions are estimated to be approximately 2.85 tpd
(8.5 percent) higher than in the 2017 base year. These projected
increases in PM10 emissions are associated with increases in
industrial activity and vehicle miles traveled (VMT) from expected
population growth in the county.
    For precursor NOX emissions estimates, the Plan predicts
an overall decrease of 15.8 tpd (44 percent) between the base year of
2017 and 2033. Reductions to the On-Road Motor Vehicle subcategory, the
most significant contributor to total NOX emissions, is the
primary cause of this trend. Implementation of federal, state, and
local regulations, including fleet turnover, result in a 14.0 tpd
reduction in associated NOX emissions.
    Based on our review of the Second 10-Year Maintenance Plan, we find
that the emissions inventories in the Plan are comprehensive in that
they include estimates of PM10 and its precursors from all
the relevant source categories, which the Plan divides among
stationary, areawide, on-road motor vehicles, and other mobile sources.
The EPA considers the selection of the 2017 base year inventory to be
appropriate given that it was the most recent emissions inventory
associated with the reporting schedule required under the Air Emissions
Reporting Requirements rule at the time of Plan drafting and because it
represents attainment conditions. Moreover, preparation of a seasonal
average daily inventory, as opposed to a yearly or episodic inventory,
is also appropriate given that elevated PM10 concentrations
in Sacramento County exhibit a clear seasonal pattern, with ambient
concentrations peaking in the fall and winter months. Additionally, we
consider the continued use of the CMB analysis from the first
maintenance plan as a technical basis for the emissions inventory to be
appropriate as we have found no evidence that it is invalid or
inaccurate. Based on our review of the documentation provided with the
Plan, we are proposing to find that the 2017 emissions inventory for
PM10 and NOX is based on reasonable assumptions
and methodologies, and that the inventory is comprehensive, current,
accurate, and consistent with applicable CAA provisions and the
Calcagni Memo.

B. Maintenance Demonstration

    Section 175A(a) of the CAA requires that the maintenance plan
provide for maintenance of the NAAQS for such air pollutant in the area
concerned for at least 10 years after the redesignation. A state may
generally demonstrate maintenance of the NAAQS by either showing that
future emissions of a pollutant or its precursors will not exceed the
level of the attainment inventory, or by conducting modeling that shows
that the future mix of sources and emissions rates will not cause a
violation of the NAAQS.\46\
---------------------------------------------------------------------------

    \46\ Calcagni Memo, p. 9-11.
---------------------------------------------------------------------------

    The District demonstrates continued maintenance of the
PM10 NAAQS in its Second 10-Year Maintenance Plan by using a
proportional rollback analysis to show that the future PM10
source concentrations will not cause a violation of the 24-hour
PM10 NAAQS. The District's proportional rollback model
relies on CMB modeling performed in 1995.\47\ In proportional rollback,
each source category's associated proportion of the ambient
PM10 contribution scales with the emissions of the category,
i.e., the source ambient contribution is ``rolled back'' according to
source emissions reductions. Thus, the Plan aims to demonstrate
continued maintenance of the standard by showing that the sum of the
individual source category contributions for future years will not
exceed the PM10 NAAQS as those source category emissions
change.
---------------------------------------------------------------------------

    \47\ Motallebi, Nahzat. ``Wintertime PM2.5 and
PM10 Source Apportionment at Sacramento California.'' Air
and Waste Management Association [1999]. CMB receptor monitor
results from the 1991-1996 wintertime ambient 24-hour
PM10 samples from the Sacramento T Street monitor were
used to determine a CMB for the 1995 ambient PM10. The
CMB modeling used the chemical components of ambient PM10
concentrations, such as fugitive dust, carbonaceous materials from
burning, nitrate, and sulfate, and associated them with broad
emissions source categories having those chemical signatures. This
is a source apportionment, giving a percent ambient contribution for
each source category.
---------------------------------------------------------------------------

    To determine the source category concentration contributions for
future years, the District conducted proportional rollback in two
steps. First the State adjusted the 1995 source apportionment (percent
contributions) to yield an updated source apportionment for the 2017
base year; then the 2017 source concentrations were projected to future
years, including 2033. The ratio of the 2017 base year and the 1995
emissions for each category yields a scaling factor (``2017 Emissions
Projection Factor''), to be applied to the 1995 percentage. This
provides a growth-adjusted source apportionment for 2017
PM10. This scaling factor accounts for the various changes
in the PM10 source categories that have occurred over the
1995-2017 period. For this purpose, the source categories were broad
and included several individual categories with chemically similar
emissions; for example, ``wood burning'' is the sum of Residential Fuel
Combustion, Fires, and

Managed Burning and Disposal in the California Emissions Projection
Analysis Model (CEPAM) 2019 state emissions inventory system. The Plan
lists ammonium nitrate, ammonium sulfate, motor vehicles, wood smoke,
fugitive dust PM10, and all leftover PM10 from
unidentified sources as PM10 ``source categories,''
identified in the CMB. The growth-adjusted source apportionment
percentages for 2017 were then applied to the peak PM10
ambient measurement in 2017 to yield the individual source category
concentration contributions for 2017. In a similar manner, projection
factors for future years were calculated from the ratio of future
emissions estimates and 2017 base year emissions. Those projection
ratios were then applied to the 2017 peak measurement source category
concentrations to yield the peak source category concentrations for
future years, 2024, 2027, and 2033.

   Table 7--Predicted Future Maintenance Year Concentrations Based on 2017 Peak Ambient PM10 Concentration in
                                                Sacramento County
----------------------------------------------------------------------------------------------------------------
                                                     2017 Peak       2024 Peak       2027 Peak       2033 Peak
                                                       conc.           conc.           conc.           conc.
            PM10 CMB source category                ([micro]g/      ([micro]g/      ([micro]g/      ([micro]g/
                                                       m\3\)           m\3\)           m\3\)           m\3\)
----------------------------------------------------------------------------------------------------------------
Ammonium Nitrate................................            27.1            21.7            20.6            19.6
Ammonium Sulfate................................             3.3             4.3             4.5             4.5
Motor Vehicles..................................            32.3            29.0            29.4            29.7
Wood Smoke......................................            27.9            27.4            27.2            27.0
Fugitive Dust...................................            25.4            26.1            27.8            29.4
Unidentified Other..............................            27.4            27.8            28.9            30.0
                                                 ---------------------------------------------------------------
    Total PM10--Background......................           144.3           136.4           138.4           140.3
Background......................................             5.7             5.7             5.7             5.7
                                                 ---------------------------------------------------------------
    Total PM10 (using peak concentration).......             149             142             144             146
----------------------------------------------------------------------------------------------------------------
Source: Second 10-Year Maintenance Plan, p. 5-5, Table 5-4.

    Table 7 of this document presents a summary of the predicted peak
ambient PM10 concentrations for the future maintenance years
for the Second 10-Year Maintenance Plan. The proportional rollback
model predicts a decrease of secondary ammonium nitrate PM10
due to the decrease in NOX emissions.\48\ This decrease
offset the increases in other PM10 source categories such as
ammonium sulfate and fugitive dust for the duration of the second
maintenance period. The resulting projections for the future 24-hour
PM10 concentrations were calculated to be 142 [micro]g/m\3\
for 2024, 144 [micro]g/m\3\ for 2027, and 146 [micro]g/m\3\ for 2033,
all of which demonstrate continued attainment of the PM10
NAAQS of 150 [micro]g/m\3\. As discussed in Section 2.3.1 of the Plan,
the peak concentration in 2017 was suspected to be influenced by
natural events and may not represent ambient conditions in
Sacramento.\49\ The District states that this is supported by CARB
flagging the data with an informational flag, which indicated the data
may have been influenced by wildfire.\50\
---------------------------------------------------------------------------

    \48\ In its analysis, the District applied a scaling factor of
0.7 to reflect the change in ambient ammonium nitrate due to the
change in NOX emissions. i.e., ammonium nitrate
concentration changed by 0.7 percent for every 1 percent change in
NOX emissions. This ratio was based on San Joaquin Valley
Air Pollution Control District photochemical modeling results. The
District cites SJVAPCD, ``2007 PM10 Maintenance Plan and
Request for Redesignation,'' Appendix F. Modeling Analysis, p.61.
    \49\ The District performed additional proportional rollback
analysis using the second highest ambient PM10 value
recorded in 2017 (87 [micro]g/m\3\), which yielded predicted peak
concentrations for 2024, 2027, 2033 that were substantially lower
than those yielded using the highest ambient PM10
concentration for 2017. However, as the future peak values yielded
from the peak 2017 concentration already demonstrated continued
maintenance, the District did not use this additional rollback
analysis to demonstrate continued maintenance of the PM10
NAAQS.
    \50\ Additional discussion of evidence in support of the impact
of natural events on the peak 2017 ambient PM10
concentration is found within Section 2.3.1 of the Plan.
---------------------------------------------------------------------------

    Based on our review, we propose to find that the proportional
rollback analysis performed to demonstrate continued attainment of the
PM10 NAAQS for the years 2017 through 2033 is based on
reasonable methods, growth factors, and assumptions, and is based on
the most current and accurate information available to CARB and SMAQMD
at the time of plan drafting and inventory development. Given that the
projections of combined PM10 sources show continued
attainment through 2033, we are proposing to find that the Second 10-
Year Maintenance Plan provides an adequate basis to demonstrate
maintenance of the PM10 NAAQS within the Sacramento County
planning area. Lastly, we propose to find that by providing projected
peak concentrations through 2033, the Plan demonstrates maintenance of
the PM10 NAAQS for more than 10 years after the expiration
of the first 10-year maintenance plan (i.e., 2023), in accordance with
section 175A(b) of the CAA.

C. Monitoring Network Requirements

    Following redesignation, the EPA determines whether an area's air
quality is maintaining compliance with 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 in the EPA AQS database.\51\ SLAMS
monitors produce data to be compared to the NAAQS, using an approved
federal reference method (FRM), federal equivalent method (FEM), or an
approved regional method. 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.\52\ All valid data are
reviewed to determine the area's air quality status in accordance with
40 CFR part 50, Appendix K.
---------------------------------------------------------------------------

    \51\ For PM10, a ``complete'' set of data include a
minimum of 75 percent of the scheduled PM10 samples per
quarter. See 40 CFR, part 50, appendix K, section 2.3(a).
    \52\ 40 CFR 50.6; 40 CFR part 50, Appendix J; 40 CFR part 53;
and 40 CFR part 58, Appendices A, C, D, and E.
---------------------------------------------------------------------------

    SMAQMD and CARB work together to monitor ambient air quality in
Sacramento County and to submit annual monitoring network plans to the
EPA. The annual monitoring network

plans submitted to the EPA describe the air monitoring network operated
by the District and CARB and its status, as required under 40 CFR
58.10. Once received, the EPA reviews these annual monitoring network
plans for compliance with the applicable reporting requirements in 40
CFR part 58. The EPA examined the Sacramento-Roseville-Folsom
Metropolitan Statistical Area (MSA), in which Sacramento County is
located, to determine if the MSA currently meets the requirements for
the minimum number of SLAMS for PM10 based on the MSA
population and air quality as described in 40 CFR 58, Appendix D. EPA
regulations require six to ten PM10 monitors in an MSA with
the population and air quality of the Sacramento-Roseville-Folsom MSA.
At the time the District drafted the Plan and through July 31, 2022,
there were eight monitoring sites in the MSA, four of which were in
Sacramento County. In 2022, the North Highlands monitoring station in
Sacramento County, which produced air pollution data through 2021 and
part of 2022, was closed.\53\ Because we are evaluating the continued
maintenance of the area using design values through 2022, we include
discussion of the four monitoring sites. However, our evaluation of the
adequacy of the monitoring network is based on the number of
operational monitoring sites at the time of this rulemaking. With the
temporary shutdown of the North Highlands monitoring site, the
Sacramento-Roseville-Folsom MSA is operating a total of seven monitors;
thus, the MSA meets the minimum monitoring requirements.
---------------------------------------------------------------------------

    \53\ On August 1, 2022, the North Highlands monitoring site (AQS
ID: 06-067-0002) was dismantled at the request of the owner of the
property, following a withdrawal of permission for the continued
placement of the monitor on the property. Due to the deteriorating
condition of the station, immediate relocation was deemed not
feasible, and the District discontinued the monitor. SMAQMD will
work with the EPA to identify a relocation site. See email dated
July 28, 2022, from Janice Lam Snyder (SMAQMD) to Gwen Yoshimura
(Air Quality Analysis Office, EPA Region IX), Subject:
``Notification of Shut down of North Highlands Station due to
property owner request.''
---------------------------------------------------------------------------

    During the 2017-2019 design value period covered by the Plan,
SMAQMD operated SLAMS monitors at three sites within Sacramento County
(North Highlands, Del Paso Manor, and Sacramento Branch Center), and
CARB operated a SLAMS monitor at one site (Sacramento T Street). Except
for the North Highlands monitor, these monitors continue to operate.
The Del Paso Manor monitoring site contains two collocated FRM
monitors, while the Sacramento Branch site has, and the North Highlands
site had, one FRM monitor each. The Sacramento T Street monitoring site
has a single FEM monitor. The schedule for PM10 sample
collection is one in six days for the FRM filter-based high-volume
samplers (Del Paso Manor, Sacramento Branch, and North Highlands
monitoring site), while the FEM monitor operates on a daily 24-hour
schedule (Sacramento T Street monitoring site).
    SMAQMD and CARB jointly commit to continuing to operate a
regulatory monitoring network in accordance with 40 CFR part 58 and the
California SIP, to verify the attainment status of the area. The Plan
contains provisions for the continued operation of air quality monitors
that will provide such verification. These provisions include
maintaining the operational procedures of data collection, routine
calibrations, pre-run and post-run test procedures, and routine service
checks. Continued adherence to the annual network plan and annual
reviews of the entire air quality monitoring network will be performed
to determine if the network is effectively meeting the objectives of
the monitoring program. Furthermore, SMAQMD documents any modifications
of its monitoring network in its annual network plan that is submitted
and reviewed annually by the EPA.\54\
---------------------------------------------------------------------------

    \54\ SMAQMD 2022 Annual Network Plan, August 1, 2022.
---------------------------------------------------------------------------

    Therefore, the EPA proposes to determine that the Second 10-Year
Maintenance Plan contains adequate provisions for continued operation
of an air quality monitoring network and a commitment to annually
verify continued attainment of the PM10 NAAQS for Sacramento
County.

D. 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 continued attainment status of the
area.\55\ Data collected by the monitoring network during this time are
also needed to implement the contingency provisions of the maintenance
plan.
---------------------------------------------------------------------------

    \55\ Calcagni Memo, p. 11.
---------------------------------------------------------------------------

    As discussed in Section IV.C of this document, SMAQMD monitors
ambient concentrations of PM10 in the Sacramento County
planning area at three separate monitoring stations. In Section 5.5 of
the Second 10-Year Maintenance Plan, the District commits to continue
to operate a PM10 ambient monitoring network to track
maintenance of the PM10 standard in accordance with 40 CFR
part 58. The EPA also recommends that the state verify continued
attainment through methods supplementary to the ambient air monitoring
program, e.g., through periodic review of the factors used in the
development of the attainment inventory to track any significant
change.\56\ In the Second 10-Year Maintenance Plan, SMAQMD commits to
perform periodic reviews of the air monitoring data and assumptions
used to develop the emissions inventory as part of its effort to verify
that the County will continue to meet the 24-hour PM10
NAAQS. We are therefore proposing to determine that the Second 10-Year
Maintenance Plan contains adequate provisions for continued ambient
PM10 monitoring and for periodic review of emissions
inventory development assumptions to ensure the continued attainment
through the maintenance period.
---------------------------------------------------------------------------

    \56\ Id.
---------------------------------------------------------------------------

E. 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 the redesignation of the
area. Such provisions must include a requirement that the state will
implement all measures with respect to the control of the relevant air
pollutants that were contained in the SIP for the area before
redesignation of the area as an attainment area. These contingency
provisions are distinguished from contingency measures required for
nonattainment areas under CAA section 172(c)(9), in that they are not
required to be fully adopted measures that take effect without further
action by the state. However, the contingency provisions of a
maintenance plan are an enforceable part of the SIP and should ensure
that contingency measures are adopted expeditiously once they are
triggered. The maintenance plan should clearly identify the measures to
be adopted, include a schedule and procedure for adoption and
implementation of the measures, and contain a specific timeline for
action by the state. In addition, the state should identify the
specific indicators or triggers that will be used to determine when the
contingency measures need to be implemented.
    The District has adopted a contingency plan to address possible
future PM10 air quality problems in the Sacramento County
planning area. The contingency plan is included in Section 6 of the
Plan. As noted by the District

in the Second 10-Year Maintenance Plan, contingency measures are to be
triggered to promptly correct any violation of the standard that occurs
during the maintenance period. In this case, these contingency measures
will be triggered when the number of monitored exceedances, averaged
over three years, is greater than 1.05. However, the contingency plan
also includes a detailed screening process that allows the District and
CARB, subject to EPA review and agreement, to exclude exceedances from
the trigger calculation if the agencies collectively determine that
information developed by the District is sufficient to support
exclusion. The purpose of the screening process is to differentiate
between exceedances that are not within the District's or State's
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 therefore should be included in the trigger
calculation. 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 would therefore continue to be
included in design value calculations for the planning area, unless
CARB, following opportunity for public comment, submits a request for
the EPA to concur on the exceedance as an exceptional event pursuant to
40 CFR 50.14, and the EPA reviews the submittal and formally concurs.
    Under the contingency trigger screening process described in the
Plan, the District will analyze any exceedance(s) within the District's
or State's control that leads to a violation of the NAAQS on a
quarterly basis, in order to determine the possible causes and take
appropriate action.\57\ The District will evaluate future emissions
reductions from already-adopted rules to determine if those reductions
would be sufficient to correct any exceedance(s). These rules could
include previously-adopted CARB or District PM10 or
NOX measures used to address ozone or PM10 SIP
requirements. Should the additional reductions resulting from these
measures be insufficient to correct the exceedance(s), the District has
committed to consider the implementation of new rules and/or
modifications to existing rules that would bring the area back into
maintenance.\58\ The District will complete its analysis of the
exceedance(s) that caused the violation and evaluate the most
appropriate control measures to adopt or implement within 6 months of
identifying the violation. This is followed by a 12-month period, in
which the District will adopt and implement the control measures
identified from this process to achieve the necessary reductions. In
total, the District will act to implement the contingency measures
within 18 months of a violation of the PM10 NAAQS. Based on
our review of the Second 10-Year Maintenance Plan, we propose to find
that the contingency provisions of the Plan clearly identify potential
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 were not within the District or State control, and
exceedances that were within the District or State control and for
which new or tightened control measures might be effective. Thus, we
propose to conclude that the contingency plan in the Plan is adequate
to ensure correction of any violation of the PM10 NAAQS that
occurs after redesignation, as required by section 175A(d) of the CAA.
---------------------------------------------------------------------------

    \57\ While not explicitly stated within the Plan, the District
later confirmed that analysis of PM10 monitoring data for
any violation that would trigger the District's contingency plan or
the exceptional event evaluation process would occur on a quarterly
basis. See email dated June 12, 2023 from Michael Dorantes (EPA) to
Janice Lam Snyder (SMAQMD). Subject: ``Sacramento County 2nd
PM10 Maintenance Plan; Inquiry regarding the Contingency
Action Trigger.''
    \58\ Appendix C of the Plan compiles possible control measures
to reduce windblown dust and wood combustion.
---------------------------------------------------------------------------

F. 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 the 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 budgets contained in submitted or approved control
strategy SIPs and maintenance plans.\59\
---------------------------------------------------------------------------

    \59\ Control strategy SIPs refer to reasonable further progress
and attainment demonstration SIPs. 40 CFR 93.101.
---------------------------------------------------------------------------

    These control strategy SIPs and maintenance plans typically set
budgets for criteria pollutants and/or their precursors to address
pollution from on-road vehicles such as cars and trucks. Budgets are
generally established for specific years for those specific pollutants
or precursors. PM10 maintenance plan submittals must
identify budgets for transportation related PM10 emissions
for the last year of the maintenance period.\60\
---------------------------------------------------------------------------

    \60\ Transportation-related emissions of VOC and NOX
must also be specified in PM10 maintenance plans if the
EPA or the state finds 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 (or SIP revision
submission) 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). An analysis of
precursors to PM10 emissions, performed in the first
maintenance plan, indicates that while NOX emissions
contributed significantly to wintertime ambient PM10
concentration, VOCs did not. (See Section 7.4 of the Plan.) Further,
40 CFR 93.118(b)(2)(i) requires that motor vehicle emissions budgets
must be established, at a minimum, for the last year of the
maintenance plan.
---------------------------------------------------------------------------

    For budgets in a maintenance plan to be approvable, they must meet,
at a minimum, the EPA's adequacy criteria.\61\ 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.
---------------------------------------------------------------------------

    \61\ 40 CFR 93.118(e)(4).
---------------------------------------------------------------------------

    The EPA also determines the adequacy of budgets in certain
submitted SIPs. The adequacy process is separate from the approval
process. 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,\62\ or via a Federal Register notice of proposed
rulemaking when the EPA reviews the adequacy of a maintenance plan
budget simultaneously with its review and action on the SIP submittal
itself.\63\
---------------------------------------------------------------------------

    \62\ 40 CFR 93.118(e)(4).
    \63\ 40 CFR 93.118(f)(2).
---------------------------------------------------------------------------

    The Second 10-Year Maintenance Plan includes budgets for direct
PM10 and NOX, on an average winter day, for the
first year of the maintenance plan (2024), an interim year (2027), and
the last year (2033) of the maintenance plan. The applicable source
categories within the budget for PM10 include direct exhaust
(includes tire and brake wear), transportation related (road)
construction emissions, re-entrained paved and unpaved road dust.
NOX budgets are based on combustion activity from on-road
motor vehicles. In developing the budgets, the District also rounded up
the motor vehicle emissions estimates to the nearest tenth of a ton and
included a safety margin of 0.5 tpd of NOX to the 2024
NOX budgets.\64\ The conformity budgets for these categories
and years are provided in Table 8 of this document.
---------------------------------------------------------------------------

    \64\ The District has determined, based on proportional rollback
analysis, that the addition of 0.5 tpd of NOX in 2024
will increase the future PM10 concentrations by less than
0.3 [mu]g/m\3\, which satisfies the requirements outlined in 40 CFR
93.124(a).
    \65\ AP-42 is the EPA's Compilation of Air Pollutant Emission
Factors. It has been published since 1972 as the primary source of
the EPA's emission factor information. It contains emission factors
and process information for more than 200 air pollution source
categories. A source category is a specific industry sector or group
of similar emitting sources. The emission factors have been
developed and compiled from source test data, material balance
studies, and engineering estimates.

                                     Table 8--Transportation Conformity Budgets for the Sacramento County PM10 Area
                                                           [PM10 tons per average winter day]
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                       2024                            2027                            2033
                     Source category                     -----------------------------------------------------------------------------------------------
                                                                NOX            PM10             NOX            PM10             NOX            PM10
--------------------------------------------------------------------------------------------------------------------------------------------------------
Vehicular Exhaust \a\ (includes tire and break wear for            10.68            2.09            9.57            2.17            8.30            2.27
 PM10)..................................................
Re-Entrained Paved Road Dust \b\ (Total)................             N/A            8.25             N/A            8.52             N/A            9.15
Re-Entrained Unpaved Road Dust (City and Country Roads).             N/A            0.62             N/A            0.61             N/A            0.59
Road Construction Dust..................................             N/A            3.65             N/A            4.04             N/A            4.31
Safety Margin...........................................             0.5             N/A             N/A             N/A             N/A             N/A
                                                         -----------------------------------------------------------------------------------------------
    Total \c\...........................................           11.18           14.62            9.57           15.34            8.30           16.32
Motor Vehicle Emissions Budgets \d\.....................            11.2            14.7             9.6            15.4             8.4            16.4
--------------------------------------------------------------------------------------------------------------------------------------------------------
\a\ This reflects the adjustment factor for SAFE Vehicle Rule using EMFAC 2017.
\b\ Paved road dust was not measured directly and is based on CARB's Miscellaneous Process Methodology, which computed paved road dust using the
  emission factor equation provided by EPA's AP-42: Compilation of Air Emissions Factors document.\65\
\c\ Values from California Emissions Projection Analysis Model (CEPAM) 2019: External Adjustment Reporting Tool Version 1.02 may not add up due to
  rounding.
\d\ This reflects the adjustment factor for SAFE Vehicle Rule using EMFAC 2017.
Source: Second 10-Year Maintenance Plan, Table 7-1, extracted from CEPAM 2019: External Adjustments Reporting Tool Version 1.02 and EMFAC2017.

    The District, the Sacramento County MPO, and CARB jointly developed
the budgets, taking into consideration the expected population-related
growth trends for the county since the first maintenance plan.
Specifically, Sacramento Council of Governments (SACOG), the MPO for
the six county Sacramento region,\66\ used both the Sacramento
Activity-Based Simulation Model (SACSIM) program and data contained
within the 2020 Metropolitan Transportation Plan/Sustainable
Communities Strategy (``2020 MTP/SCS'') to develop a travel demand
model to forecast VMT for future years within the area.\67\
Transportation activity data from the 2020 MTP/SCS and emissions
modeling generated by CARB's EMFAC 2017 model were used to calculate
the budgets. CARB further adjusted the budgets in the Plan to account
for the Safer Affordable Fuel-Efficient Vehicle Rule Part 1.\68\
---------------------------------------------------------------------------

    \66\ The six counties are El Dorado, Placer, Sacramento, Sutter,
Yolo, and Yuba counties.
    \67\ Information on SACSIM is located at: https://www.sacog.org/modelingandthe2020MTP/SCS is located at: https://www.sacog.org/2020-metropolitan-transportation-plansustainable-communities-strategy-update.
    \68\ 85 FR 24174 (June 29, 2020).
---------------------------------------------------------------------------

    In contrast to PM2.5, where road dust applies in
transportation conformity only if found to be significant or if budgets
include it, for PM10 road dust is always considered.\69\ The
EPA requires road dust emissions to be included in all transportation
conformity analyses of direct PM10 emissions because
fugitive dust from roadways and other sources dominate PM10
on-road emissions inventories. The budgets in the Second 10-Year
Maintenance Plan, therefore, include paved and unpaved road emissions.
---------------------------------------------------------------------------

    \69\ See 40 CFR 93.102(b)(3).
---------------------------------------------------------------------------

    Regional PM10 emissions analyses for transportation
conformity determinations in PM10 nonattainment and
maintenance areas must also 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 air quality problem.\70\ Emissions estimates developed for the
Second 10-Year Maintenance Plan show that fugitive PM10
emissions from highway and transit project construction are a
significant portion of total regional PM10 emissions for the
Sacramento County planning area. Consequently, the budgets in the Plan
reflect highway and transit project construction-related fugitive dust.
---------------------------------------------------------------------------

    \70\ 40 CFR 93.122(e).
---------------------------------------------------------------------------

    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. 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 Second 10-Year Maintenance Plan for Sacramento
County and are proposing herein to approve the Plan including the
demonstration of maintenance of the PM10 NAAQS in the area
through the year 2033. We have also reviewed the budgets in the 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).\71\ For these reasons, the EPA proposes to
approve the 2024, 2027, and 2033 budgets in the Second 10-Year
Maintenance Plan.
---------------------------------------------------------------------------

    \71\ Technical Support Document for the Adequacy Review of the
Motor Vehicle Emissions Budgets within the Second 10-Year
PM10 Maintenance Plan for Sacramento County can be found
within the docket for this rulemaking.
---------------------------------------------------------------------------

    In addition, in this document the EPA is announcing the beginning
of the adequacy process for these budgets. Under the transportation
conformity regulation, the EPA can begin this process with our proposed
action on the second maintenance plan.\72\ The public has 30 days to
comment on the adequacy of the budgets, per the transportation
conformity rule at 40 CFR 93.118(f)(2)(i) and (ii). Any comments on the
adequacy of the budgets should be submitted to the docket for this
proposed rulemaking.
---------------------------------------------------------------------------

    \72\ See the transportation conformity regulation at 40 CFR
93.119(f).
---------------------------------------------------------------------------

    When we finalize our proposed approval of the budgets, they must be
used by SACOG (i.e., the MPO for this area) for transportation
conformity determinations for the Sacramento County planning area
effective upon the publication date of our finalized approval.\73\
---------------------------------------------------------------------------

    \73\ 40 CFR 93.118(f)(2)(iii).
---------------------------------------------------------------------------

V. Proposed Action and Request for Public Comment

    Under CAA section 110(k)(3), and for the reasons set forth in this
document, the EPA is proposing to approve the Second 10-Year
Maintenance Plan submitted by CARB by letter dated October 21, 2021, as
a revision to the California SIP. 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, and the motor vehicle emissions budgets
for 2024, 2027, and 2033 (shown in Table 8) for transportation
conformity purposes, as we propose to find they meet all applicable
criteria for such budgets including the adequacy criteria under 40 CFR
93.118(e).
    We are soliciting comments on these proposed actions, including our
concurrence on the exceptional events demonstration for the 2018
exceedances in Sacramento County as part of the technical basis for the
approval of the Second 10-Year Maintenance Plan, as well as the
adequacy of the motor vehicle emissions budgets. We will accept
comments from the public for 30 days following publication of this
proposal in the Federal Register and will consider any relevant
comments before taking final action.

VI. Statutory and Executive Order Reviews

    Under the Clean Air Act, the Administrator is required to approve a
SIP submission that complies with the provisions of the Act and
applicable federal regulations. 42 U.S.C. 7410(k); 40 CFR 52.02(a).
Thus, in reviewing SIP submissions, the EPA's role is to approve state
choices, provided that they meet the criteria of the Clean Air Act.
Accordingly, this proposed action merely approves state law as meeting
federal requirements and does not impose additional requirements beyond
those imposed by state law. For that reason, this proposed action:
     Is not a ``significant regulatory action'' subject to
review by the Office of Management and Budget under Executive Orders
12866 (58 FR 51735, October 4, 1993) and 14094 (88 FR 21879April 11,
2023);
     Does not impose an information collection burden under the
provisions of the Paperwork Reduction Act (44 U.S.C. 3501 et seq.);
     Is certified as not having a significant economic impact
on a substantial number of small entities under the Regulatory
Flexibility Act (5 U.S.C. 601 et seq.);
     Does not contain any unfunded mandate or significantly or
uniquely affect small governments, as described in the Unfunded
Mandates Reform Act of 1995 (Pub. L. 104-4);
     Does not have federalism implications as specified in
Executive Order 13132 (64 FR 43255, August 10, 1999);
     Is not an economically significant regulatory action based
on health or safety risks subject to Executive Order 13045 (62 FR
19885, April 23, 1997);
     Is not a significant regulatory action subject to
Executive Order 13211 (66 FR 28355, May 22, 2001); and
     Is not subject to requirements of Section 12(d) of the
National Technology Transfer and Advancement Act of 1995 (15 U.S.C. 272
note) because application of those requirements would be inconsistent
with the Clean Air Act.
    In addition, the SIP is not approved to apply on any Indian
reservation land or in any other area where the EPA or an Indian tribe
has demonstrated that a tribe has jurisdiction. In those areas of
Indian country, this rulemaking 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).
    Executive Order 12898 (Federal Actions To Address Environmental
Justice in Minority Populations and Low-Income Populations, 59 FR 7629,
Feb. 16, 1994) directs Federal agencies to identify and address
``disproportionately high and adverse human health or environmental
effects'' of their actions on minority populations and low-income
populations to the greatest extent practicable and permitted by law.
The EPA defines environmental justice (EJ) as ``the fair treatment and
meaningful involvement of all people regardless of race, color,
national origin, or income with respect to the development,
implementation, and enforcement of environmental laws, regulations, and
policies.'' The EPA further defines the term fair treatment to mean
that ``no group of people should bear a disproportionate burden of
environmental harms and risks, including those resulting from the
negative environmental consequences of industrial, governmental, and
commercial operations or programs and policies.''
    The State did not evaluate environmental justice considerations as
part of its SIP submittal; the CAA and applicable implementing
regulations neither prohibit nor require such an evaluation. The EPA
did not perform an EJ analysis and did not consider EJ in this action.
If finalized, this action is expected to have a neutral to positive
impact on the air quality of the affected area. Consideration of EJ is
not required as part of this action, and there is no information in the
record inconsistent with the stated goal of E.O. 12898 of achieving
environmental justice for people of color, low-income populations, and
Indigenous peoples.

List of Subjects in 40 CFR Part 52

    Environmental protection, Air pollution control, Incorporation by

reference, Nitrogen dioxide, Particulate matter, Sulfur dioxide,
Reporting and recordkeeping requirements, Volatile organic compounds.

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

    Dated: September 18, 2023.
Martha Guzman Aceves,
Regional Administrator, Region IX.
[FR Doc. 2023-20555 Filed 9-21-23; 8:45 am]
BILLING CODE 6560-50-P