[Federal Register Volume 88, Number 183 (Friday, September 22, 2023)]
[Proposed Rules]
[Pages 65336-65350]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[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

[[Page 65337]]

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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[[Page 65338]]

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

[[Page 65339]]

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

[[Page 65340]]

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\

[[Page 65341]]

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

[[Page 65342]]

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

[[Page 65343]]

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

[[Page 65344]]

 
                                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

[[Page 65345]]

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.
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    \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.
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    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

[[Page 65346]]

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.
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    \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.''
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    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\
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    \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.
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    \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.
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    \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

[[Page 65347]]

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\
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    \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:

[[Page 65348]]

(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\
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    \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,

[[Page 65349]]

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\
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    \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

[[Page 65350]]

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