[Federal Register Volume 85, Number 216 (Friday, November 6, 2020)]
[Proposed Rules]
[Pages 71023-71046]
[FR Doc No: 2020-24444]

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Parts 52 and 81

[EPA-R08-OAR-2020-0098; FRL-10016-53-Region 8]

Approval and Promulgation of Implementation Plans; State of Utah;
Salt Lake City and Provo, Utah PM2.5 Redesignations to Attainment and
Utah State Implementation Plan Revisions

AGENCY: Environmental Protection Agency.

ACTION: Proposed rule.

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SUMMARY: The Environmental Protection Agency (EPA) is proposing the
redesignation of the Salt Lake City, Utah and Provo, Utah nonattainment
areas (NAAs) to attainment for the 2006 24-hour fine particulate matter
with an aerodynamic diameter less than or equal to a nominal 2.5
microns (PM2.5) National Ambient Air Quality Standard
(NAAQS), and also acting on multiple related State Implementation Plan
(SIP) submissions. We are proposing to approve SIP revisions submitted
by the State of Utah on January 19, 2017; April 19, 2018; February 4
and 15, 2019; and January 13, May 21, and July 21, 2020. These SIP
submissions include revisions to Utah Administrative Code (UAC)
Sections R307-110, R307-200, and R307-300 Series; revisions to Utah SIP
Sections X.B and E; revisions to Utah SIP Sections IX.H.11, 12, and 13;
best available control measures/best available control technologies
(BACM/BACT) PM2.5 determinations for Salt Lake City and
Provo; maintenance plans for the Salt Lake City and Provo areas for
PM2.5; and the request for redesignation under the 2006 24-
hour PM2.5 standard. Additionally, the EPA is proposing to
approve, through parallel processing, a request to remove startup and
shutdown emission limits for Kennecott's Power Plant in the Utah SIP
and the accompanying R307-110-17 revisions (draft dated October 9,
2020). The EPA is taking this action pursuant to the Clean Air Act (CAA
or the Act).

DATES: Written comments must be received on or before December 7, 2020.

ADDRESSES: Submit your comments, identified by Docket ID No. EPA-R08-
OAR-2020-0098, to the Federal Rulemaking Portal: https://www.regulations.gov. Follow the online instructions for submitting
comments. Once submitted, comments cannot be edited or removed from
www.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, the full EPA public comment
policy, information about CBI or multimedia submissions, and general
guidance on making effective comments, please visit http://www2.epa.gov/dockets/commenting-epa-dockets.
    Docket: All documents in the docket are listed in the
www.regulations.gov index. Although listed in the index, some
information is not publicly available, e.g., CBI or other information
whose disclosure is restricted by statute. Certain other material, such
as copyrighted material, will be publicly available only in hard copy.
Publicly available docket materials are available

electronically in www.regulations.gov. To reduce the risk of COVID-19
transmission, for this action we do not plan to offer hard copy review
of the docket. Please email or call the person listed in the FOR
FURTHER INFORMATION CONTACT section if you need to make alternative
arrangements for access to the docket.

FOR FURTHER INFORMATION CONTACT: Crystal Ostigaard, Air and Radiation
Division, Environmental Protection Agency (EPA), Region 8, Mailcode
8ARD-QP, 1595 Wynkoop Street, Denver, Colorado, 80202-1129, (303) 312-
6602<EMAIL_ADDRESS>
SUPPLEMENTARY INFORMATION: Throughout this document wherever ``we,''
``us,'' or ``our'' is used, we mean the EPA.

I. Background

A. Statutory and Regulatory Background for EPA's Regulation of PM2.5

    Under section 109 of the Act, the EPA has promulgated NAAQS for
certain pollutants, including PM2.5 (40 CFR 50.2(b)). Once
the EPA promulgates a NAAQS, section 107 of the Act specifies a process
for the designation of each area within a state, generally as either an
attainment area (an area attaining the NAAQS) or as a NAA (an area not
attaining the NAAQS, or that contributes to nonattainment of the NAAQS
in a nearby area). For PM2.5, certain areas have also been
designated ``unclassifiable.'' These various designations, in turn,
trigger certain state planning requirements.
    For all areas, regardless of designation, section 110 of the Act
requires that each state adopt and submit for EPA approval a plan to
provide for implementation, maintenance, and enforcement of the NAAQS.
This plan is commonly referred to as a SIP. Section 110 contains
requirements that a SIP must meet to gain EPA approval.\1\ For NAAs,
SIPs must meet additional requirements in part D of Title I of the Act.
Usually, SIPs include measures to control emissions of air pollutants
from various sources, including stationary, mobile, and area sources.
For example, a SIP may specify emission limits at power plants or other
industrial sources.
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    \1\ EPA's approval of a SIP has several consequences. For
example, after the EPA approves a SIP, the EPA and citizens may
enforce the SIP's requirements in federal court under section 113
and section 304 of the Act; in other words, the EPA's approval of a
SIP makes the SIP ``federally enforceable.'' Also, once the EPA has
approved a SIP, a state cannot unilaterally change the federally
enforceable version of the SIP. Instead, the state must first submit
a SIP revision to the EPA and gain EPA's approval of that revision.
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    Under section 109 of the Act, the EPA has promulgated NAAQS for
certain pollutants, including PM2.5 (40 CFR 50.2(b)). Once
the EPA promulgates a NAAQS, section 107 of the Act specifies a process
for the designation of each area within a state, generally as either an
attainment area (an area attaining the NAAQS) or as a NAA (an area not
attaining the NAAQS, or that contributes to nonattainment of the NAAQS
in a nearby area). For PM2.5, certain areas have also been
designated ``unclassifiable.'' These various designations, in turn,
trigger certain state planning requirements.
    For all areas, regardless of designation, section 110 of the Act
requires that each state adopt and submit for EPA approval a plan to
provide for implementation, maintenance, and enforcement of the NAAQS.
This plan is commonly referred to as a SIP. Section 110 contains
requirements that a SIP must meet to gain EPA approval.\2\ For NAAs,
SIPs must meet additional requirements in part D of Title I of the Act.
Usually, SIPs include measures to control emissions of air pollutants
from various sources, including stationary, mobile, and area sources.
For example, a SIP may specify emission limits at power plants or other
industrial sources.
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    \2\ EPA's approval of a SIP has several consequences. For
example, after the EPA approves a SIP, the EPA and citizens may
enforce the SIP's requirements in federal court under section 113
and section 304 of the Act; in other words, the EPA's approval of a
SIP makes the SIP ``federally enforceable.'' Also, once the EPA has
approved a SIP, a state cannot unilaterally change the federally
enforceable version of the SIP. Instead, the state must first submit
a SIP revision to the EPA and gain EPA's approval of that revision.
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    On October 17, 2006 (71 FR 61144), the EPA revised the level of the
24-hour PM2.5 NAAQS, lowering the primary and secondary
standards from the 1997 standard of 65 micrograms per cubic meter
([micro]g/m\3\) to 35 [micro]g/m\3\. On November 13, 2009 (74 FR
58688), the EPA designated three NAAs in Utah for the 2006 24-hour
PM2.5 NAAQS of 35 [micro]g/m\3\. These are the Salt Lake
City; Provo; and Logan, Utah-Idaho NAAs.
    The EPA originally issued a rule in 2007 \3\ regarding
implementation of the 2006 24-hour PM2.5 NAAQS for the NAA
requirements specified in CAA title I, part D, subpart 1. Under subpart
1, Utah was required to submit an attainment plan for each area no
later than three years from the date of nonattainment designation.
These plans needed to provide for the attainment of the
PM2.5 standards as expeditiously as practicable, but no
later than five years from the date the areas were designated
nonattainment.
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    \3\ 72 FR 20586 (Apr. 25, 2007).
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    In 2013, the U.S. Court of Appeals for the District of Columbia
held that the EPA should have implemented the 2006 PM2.5 24-
hour standards, as well as the other PM2.5 NAAQS, based on
both subpart 1 and subpart 4 of CAA title I, part D.\4\ Under subpart
4, all NAAs are initially classified as Moderate, and Moderate area
attainment plans must address the requirements of subpart 4 as well as
subpart 1. Additionally, subpart 4 sets a different SIP submittal due
date and attainment year. For a Moderate area, the attainment SIP is
due 18 months after designation and the attainment year is as
expeditiously as practicable, but no later than the end of the sixth
calendar year after designation.
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    \4\ Nat. Res. Def. Council v. EPA, 706 F.3d 428, 437 (D.C. Cir.
2013) (NRDC).
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    On June 2, 2014 (79 FR 31566), the EPA finalized the Identification
of Nonattainment Classification and Deadlines for Submission of State
Implementation Plan (SIP) Provisions for the 1997 Fine Particulate
(PM2.5) National Ambient Air Quality Standard (NAAQS) and
2006 24-hour PM2.5 NAAQS. This rule classified as Moderate
the areas that were designated in 2009 as nonattainment and set the
attainment SIP submittal due date for those areas at December 31, 2014.
Additionally, this rule established the Moderate area attainment date
of December 31, 2015.
    When an area is designated as a Moderate NAA under subpart 1 and
subpart 4, the CAA requires the State to submit the following Moderate
area SIP elements:
    1. A comprehensive, accurate, current inventory of actual emissions
from all sources of PM2.5 and PM2.5 precursors in
the area (CAA section 172(c)(3)).
    2. Provisions to assure that reasonably available control measures
(RACM), including reasonably available control technologies (RACT), for
the control of direct PM2.5 and PM2.5 precursors
shall be implemented no later than four years after the area is
designated (CAA sections 172(c)(1) and 189(a)(1)(C)).
    3. A demonstration (including air quality modeling) that the plan
provides for attainment as expeditiously as practicable but no later
than the Moderate area attainment date (CAA section 188(c)(1).
    4. Plan provisions that require reasonable further progress (RFP)
(CAA section 172(c)(2)).
    5. Quantitative milestones, which are to be achieved every three
years until the area is redesignated to attainment,

and which demonstrate RFP toward attainment by the applicable date. The
State is required to submit, not later than 90 days after the date on
which a milestone applicable to the area occurs, a demonstration that
all measures in the approved SIP have been implemented and the
milestone has been met. These submissions are referred to as
``quantitative milestone reports.'' (CAA section 189(c)).
    6. Provisions to assure that control requirements applicable to
major stationary sources of PM2.5 also apply to major
stationary sources of PM2.5 precursors, except where the
State demonstrates to the EPA's satisfaction that such sources do not
contribute significantly to PM2.5 levels that exceed the
standard in the area (CAA section 189(e)).
    7. Contingency measures to be implemented if the area fails to meet
RFP or fails to attain by the applicable attainment date (CAA section
172(c)(9)).
    8. A revision to the Nonattainment New Source Review (NNSR) program
to set the applicable ``major stationary source'' thresholds to 100
tons per year (tpy) (CAA section 302(j)).
    Moderate area 2006 24-hour PM2.5 plans must also satisfy
the general requirements applicable to all SIP submissions under
section 110 of the CAA, including the requirement to provide necessary
assurances that the implementing agencies have adequate personnel,
funding, and authority under CAA section 110(a)(2)(E), and the
requirements concerning enforcement in CAA section 110(a)(2)(C).
    On August 24, 2016 (81 FR 58010), the EPA finalized the Fine
Particulate Matter National Ambient Air Quality Standards: State
Implementation Plan Requirements (``PM2.5 Requirements
Rule''), which partially addressed the 2013 NRDC decision. The final
PM2.5 Requirements Rule details how air agencies can meet
the SIP requirements under subparts 1 and 4 that apply to areas
designated nonattainment for any PM2.5 NAAQS, such as:
General requirements for attainment plan due dates and attainment
demonstrations; provisions for demonstrating RFP; quantitative
milestones; contingency measures; NNSR permitting programs; and RACM
(including RACT). The statutory attainment planning requirements of
subparts 1 and 4 were established to ensure that the following goals of
the CAA are met: (i) That states implement measures that provide for
attainment of the PM2.5 NAAQS as expeditiously as
practicable; and (ii) that states adopt emissions reduction strategies
that will be the most effective at reducing PM2.5 levels in
NAAs.
    If an area is reclassified from Moderate to Serious, the area will
then be subject to Serious PM2.5 CAA requirements. Serious
area PM2.5 requirements are the same as those listed above
for Moderate areas, except that BACM and BACT are required instead of
RACM and RACT, the NNSR permit threshold drops to 70 tons, and the
relevant attainment date is the Serious area attainment date (CAA
section 188(c)(2). Serious area PM2.5 plans must also
satisfy the Moderate PM2.5 requirements discussed above, and
the general requirements applicable to all SIP submissions under
section 110 of the CAA, including the requirement to provide necessary
assurances that the implementing agencies have adequate personnel,
funding and authority under CAA section 110(a)(2)(E) and the
requirements concerning enforcement in CAA section 110(a)(2)(C).

B. Utah's PM2.5 Attainment Status and SIP Development

    After the November 13, 2009 designation of nonattainment for the
2006 24-hour PM2.5 NAAQS, Utah developed draft
PM2.5 attainment plans intended to meet the requirements of
subpart 1. The EPA submitted written comments dated November 1, 2012,
to UDAQ on the draft PM2.5 SIP, technical support document
(TSD), area source rules, and point source rules in Section IX, Part
H.\5\ Utah submitted revised 2006 24-hour PM2.5 attainment
plans for the Salt Lake City and Provo NAAs on December 14, 2012.
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    \5\ An ``area source'' is ``any small residential, governmental,
institutional, commercial, or industrial fuel combustion operation;
onsite solid waste disposal facility; motor vehicle], aircraft
vessel or other transportation facilit[y] or other miscellaneous
source identified'' through specified inventory techniques. 40 CFR
51.100(l). A ``point source'' is any stationary source emitting
above certain thresholds. 40 CFR 51.100(k).
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    After the court's 2013 decision, Utah amended its attainment plans
to address the requirements of subpart 4. On December 2, 2013, and
October 30, 2014, the EPA provided comments on Utah's revised draft
2006 24-hour PM2.5 SIPs, including the TSD and emissions
limits in Section IX, Part H. On December 16, 2014, UDAQ withdrew all
prior Salt Lake City and Provo 2006 24-hour PM2.5 Moderate
SIP attainment plan submissions and submitted a subpart 1 and subpart 4
Salt Lake City and Provo 2006 24-hour PM2.5 Moderate SIP.
Additionally, the State of Utah submitted various revisions to the UAC
Title R307 (Environmental Quality) area source rules in multiple
submissions: February 2, 2012; May 9, 2013; June 8, 2013; February 18,
2014; April 17, 2014; May 20, 2014; July 10, 2014; and August 6, 2014.
These area source rules were either new or revised to meet RACM/RACT
for the Salt Lake City and Provo 2006 24-hour PM2.5 SIPs.
The EPA acted on these submittals, along with the area source rule
revisions in the December 16, 2014 submission, on February 25, 2016 (81
FR 9343), October 19, 2016 (81 FR 71988), October 2, 2019 (84 FR
52368), and February 26, 2020 (85 FR 10989).
    On January 19, 2017, the State of Utah submitted revisions to their
Part H.11, 12, and 13 emission limits section of the Utah 2006 24-hour
PM2.5 SIP and revises R307-110-17. R307-110-17 incorporates
by reference (IBR) Section IX, Control Measures for Area and Point
Sources, Part H, Emission Limits; which formally incorporates the Salt
Lake City and Provo 2006 24-hour PM2.5 Part H.11, 12, and 13
emission limits into Utah's state regulations. This was undertaken by
UDAQ to correlate any overlapping limits between the 2006 24-hour
PM2.5 Part H.11, 12, and 13, to the coarse particulate
matter (PM10) Part H.1, 2, 3, and 4.
    On May 10, 2017 (82 FR 21711), the EPA published a final rule
reclassifying the Salt Lake City and Provo areas to ``Serious''
nonattainment status, based on the EPA's determination that the areas
could not practicably attain the 2006 24-hour PM2.5
standards by the December 31, 2015 attainment date. This
reclassification became effective on June 9, 2017. The reclassification
was based on the EPA's evaluation of ambient air quality data from the
2013-2015 period, indicating that it was not practicable for some of
the monitoring sites in the Salt Lake City and Provo areas to show
PM2.5 design values at or below the level of the 2006 24-
hour PM2.5 NAAQS by December 31, 2015.
    On March 23, 2018, the State of Utah submitted quantitative
milestone reports for the Salt Lake City and Provo 2006 24-hour
PM2.5 NAAs, meeting its due date of no later than 90 days
after the December 31, 2017 milestone date. On October 24, 2018, the
EPA determined that the 2017 quantitative milestone reports for the
Salt Lake City and Provo 2006 24-hour PM2.5 NAAs were
adequate.\6\
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    \6\ The state's quantitative milestone reports and the adequacy
determination letter from the EPA Administrator to the Governor of
Utah are in the docket for this action.
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    After the Serious reclassification, UDAQ revised certain area
source rules in UAC Section R307-200 and R307-300 Series and submitted
these revisions on April 19, 2018, May 21, 2020, and July 21, 2020. On
February 4,

2019, the State of Utah submitted the BACM/BACT analysis for the Provo
Serious 2006 24-hour PM2.5 NAA, which is based on the
emission limits submitted on January 19, 2017 for only Part H.13. On
February 15, 2019, Utah submitted the Serious 2006 24-hour
PM2.5 SIP for the Salt Lake City NAA, which included
revisions to Utah SIP Part H.11 and 12, and the accompanying BACM/BACT
analysis. The February 4, 2019 and February 15, 2019 submissions
included BACM/BACT analyses for on-road, off-road, and area source
rules; some of these area source rules were revised and others were
deemed BACM/BACT without revising. Our detailed discussion on the
intricacies of these submissions can be found in Section II.B below of
this document.
    Applying the Clean Data Policy,\7\ on April 10, 2019 (84 FR 14267)
and September 27, 2019 (84 FR 51055), the EPA finalized determinations
that the obligation to submit any remaining attainment-related SIP
revisions arising from classification of the Provo and Salt Lake City
areas, respectively, as Moderate NAAs and their subsequent
reclassification as Serious NAAs for the 2006 24-hour PM2.5
NAAQS does not apply for so long as the area continues to attain the
2006 24-hour PM2.5 NAAQS.\8\ The attainment-related SIP
revisions that were suspended include the requirements for the State to
submit: An attainment demonstration (Moderate and Serious), provisions
demonstrating timely implementation of RACM/RACT (Moderate), an RFP
plan (Moderate and Serious), quantitative milestones and quantitative
milestone reports (Moderate and Serious), and contingency measures
(Moderate and Serious). The only remaining SIP elements for EPA action
include baseline emission inventories, NNSR, and BACM/BACT. Our review
of these remaining elements is in Section II.B below of this document
and in our TSD found in the docket.
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    \7\ The EPA codified the Clean Data Policy in the
PM2.5 SIP Requirements Rule for the implementation of
current and future PM2.5 NAAQS. See 81 FR at 58161; 40
CFR 51.1015(a).
    \8\ 40 CFR 51.1015(a) and (b).
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    On October 9, 2020, the State of Utah submitted draft revisions to
Kennecott's Power Plant startup/shutdown emission limits in Subsection
IX.H.12.i.i.C. in Utah's SIP and revisions to R307-110-17, for the EPA
to act on as a parallel process. UDAQ's BACM/BACT analysis submitted on
February 15, 2019 for this source did not support these limits;
therefore, UDAQ proposed with the October 9, 2020 draft revision to
remove these limits. The parallel process is generally described in
more detail in Section I.E below.

C. Redesignation Requests and Related Requirements

    For a NAA to be redesignated to attainment, the following
conditions in section 107(d)(3)(E) of the CAA must be met:
    1. We must determine that the area has attained the NAAQS;
    2. The applicable implementation plan for the area must be fully
approved under section 110(k) of the Act;
    3. We must determine that the improvement in air quality is due to
permanent and enforceable reductions in emissions resulting from
implementation of the applicable implementation plan and applicable
Federal air pollutant control regulations and other permanent and
enforceable reductions;
    4. We must fully approve a maintenance plan for the area as meeting
the requirements of CAA section 175A; and
    5. The state containing the area must meet all requirements
applicable to the area under section 110 and part D of the CAA.
    Our September 4, 1992 guidance entitled ``Procedures for Processing
Requests to Redesignate Areas to Attainment'' (referred to in this
action as the Calcagni Memorandum) outlines how to assess the adequacy
of redesignation requests against the conditions listed above.
    On January 13, 2020, the Governor of Utah submitted revisions to
the SIP for R307-110-10, maintenance plans for the Salt Lake City (Utah
SIP Section IX.A.36) and Provo (Utah SIP Section IX.A.27) areas, and a
request that the EPA redesignate the areas to attainment for the 2006
24-hour PM2.5 NAAQS. R307-110-10 IBRs Section IX, Control
Measures for Area and Point Sources, Part A, Fine Particulate Matter;
which formally incorporates the Salt Lake City and Provo 2006 24-hour
PM2.5 Maintenance Plans (located within the Utah SIP at
Sections IX.A.36 and 27, respectively) into Utah's state regulations.
In Section II.C below, we discuss our review of UDAQs maintenance plans
and redesignation requests for the Salt Lake City and Provo 2006 24-
hour PM2.5 NAAs.

D. SIP Submissions Supporting the Redesignation Request

    Vehicle I/M programs help improve air quality by identifying cars
and trucks with high emissions and that may need repairs. Owners or
operators of vehicles with high emissions are notified to make any
repairs so that emissions are within legal limits. On July 17, 1997 (62
FR 38213), and September 14, 2005 (70 FR 54267), the EPA finalized
approval of revisions to Utah's SIP Section X, Vehicle Inspection and
Maintenance Program for Part B, Davis County, and Part E, Weber County,
respectively. In these actions the EPA also approved into the SIP
revisions to Utah's regulations at R307-110-32 and R307-110-35. These
rules IBR the Utah SIP into state regulations: Rule R307-110-32 IBRs
Utah SIP Section X, Vehicle Inspection and Maintenance Program, Part B,
Davis County; and Rule R307-110-35 IBRs Utah SIP Section X, Vehicle
Inspection and Maintenance Program, Part E, Weber County.\9\
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    \9\ Since promulgating R307-110-32, Utah has renumbered its SIP.
On February 14, 2006 (71 FR 7679), the EPA renumbered the Weber
County I/M Program to R307-110-32. R307-110-35 was last approved on
September 14, 2005.70 FR 54267.
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E. What is parallel processing?

    Parallel processing refers to a process that utilizes concurrent
state and Federal proposed rulemaking actions. Generally, the state
submits a copy of the proposed regulation or other revisions to the EPA
before conducting its public hearing and completing its public comment
process under state law. The EPA reviews this proposed state action and
prepares a notice of proposed rulemaking under Federal Law. In some
cases, the EPA's notice of proposed rulemaking is published in the
Federal Register during the same time frame that the state is holding
its public hearing and conducting its public comment process. The state
and the EPA then provide for concurrent public comment periods on both
the state action and Federal action. If, after completing its public
comment process and after the EPA's public comment process has run, the
state changes its final submittal from the proposed submittal, the EPA
evaluates those changes and decides on whether to publish another
notice of proposed rulemaking in light of those changes or to proceed
to taking the final action on its proposed action and describe the
state's changes in its final rulemaking action. Any final rulemaking
action by the EPA will occur only after the final submittal has been
adopted by the state and formally provided to the EPA.
    In this case, however, the EPA's and Utah's processes have not been
perfectly concurrent. The State submitted the draft SIP revisions on
October 9, 2020, with a public comment period starting October 1 and
going through November 3, 2020, with a public hearing held online at
10am on November 3, 2020.

Utah requested that the EPA parallel process these proposed revisions
while the State finishes the comment period and public hearing, so as
not to delay the 2006 24-hour PM2.5 redesignation of the
Salt Lake City NAA. The State's intention is to submit its final SIP
revisions in early January 2021. After Utah submits these formal SIP
revisions, the EPA will evaluate the submittal. If the State changes
the formal submittal from the proposed submittal, the EPA will evaluate
those changes for significance. If the EPA finds any such changes to be
significant, then the Agency intends to determine whether to re-propose
the actions based on the revised submission or to proceed to take final
action on the submittal as changed by the State. Although the EPA was
unable to have a concurrent public comment process with the State,
Utah's request for parallel processing allows the EPA to begin to take
action on the State's proposed submittal in advance of a formal and
final submission.

II. The EPA's Evaluation

A. Utah's SIP Revisions

    When certain sections of the Utah SIP are amended by the Utah Air
Quality Board (UAQB), those sections must be incorporated into the Utah
Air Quality Rules. Utah incorporates SIP sections within the state's
rule R307-110. These rules are amended as needed to change the
effective dates to match the UAQB approval date of various amendments
to the Utah SIP. For the Salt Lake City and Provo 2006 24-hour
PM2.5 proposed action, we are acting on R307-110-10, which
IBRs Section IX, Control Measures for Area and Point Sources, Part A,
Fine Particulate Matter, and thus incorporates the Salt Lake City and
Provo 2006 24-hour PM2.5 maintenance plans into state
regulations (located within the Utah SIP at Sections IX.A.36 and 27,
respectively). We are also proposing to approve into the SIP R307-110-
17, which IBRs Section IX, Control Measures for Area and Point Sources,
Part H, Emission Limits, and thus incorporates all the emission limits
in Utah SIP Section IX.H.11, 12, and 13, into state regulations. The
state's R307-110-32 and R307-110-35 IBR Section X, Vehicle Inspection
and Maintenance Program, Part B, Davis County, and Section X, Vehicle
Inspection and Maintenance Program, Part E, Weber County, respectively.
These two rules incorporate the I/M Programs of Davis and Weber
Counties into the state regulations.
    Utah Code 41-6a-1642 gives authority to each county in the State to
design and manage a vehicle I/M program when necessary to attain or
maintain any NAAQS. Section X of the Utah SIP incorporates these county
programs. Section X, Part A summarizes I/M requirements that are common
among all I/M programs, while Section X, Parts B through F contain the
requirements for each county's unique I/M program. Below we discuss the
revisions to Utah SIP Section X, Parts B and E, and to the related
Rules R307-110-10, R307-110-32, and R307-110-35, along with our
evaluation. We discuss the revisions done to Utah SIP Section X, Parts
B and E, in greater detail within the TSD. Utah Rule R307-110-17 will
be going through the parallel process based on the informal October 9,
2020 UDAQ submission revising Utah SIP Section IX.H.12.i.i.C, which
requires a revision to R307-110-17 to incorporate the revisions into
the Utah SIP. In Section I.E above, we discuss the process of this type
of action.
1. R307-110-10
    Section R307-110-10 incorporates amendments to Utah SIP Section
IX.A into State regulations, thereby making them effective as a matter
of State law. This is a ministerial provision, which only revises the
effective date within the rule to December 4, 2019 and does not by
itself include any SIP measures.
2. R307-110-17
    Section R307-110-17 incorporates the amendments to Utah SIP Section
IX, Control Measures for Area and Point Sources, Part H, Emission
Limits into State regulations, thereby making them effective as a
matter of State law. This is a ministerial provision, which only
revises the effective date within the rule to December 2, 2020, and
does not by itself include any SIP control measures; however, this
revision is being acted on as a parallel process due to revisions to
Utah SIP Section IX.H.12.i.i.C. In Section I.E above, we discuss the
process of this type of action.
3. R307-110-32
    Section R307-110-32 incorporates the amendments to Utah SIP Section
X, Vehicle Inspection and Maintenance Program, Part B, Davis County
into State rules, thereby making them effective as a matter of State
law. This is a ministerial provision, which only revises the effective
date within the rule to March 4, 2020 and does not by itself include
any control measures.
4. R307-110-35
    Section R307-110-35 incorporates the amendments to Utah SIP Section
X, Vehicle Inspection and Maintenance Program, Part E, Weber County
into State regulations, thereby making them effective as a matter of
State law. This is a ministerial provision, which only revises the
effective date within the rule to March 4, 2020 and does not by itself
include any control measures.
5. SIP Section X, Vehicle Inspection and Maintenance Program, Part B,
Davis County
    The Davis County motor vehicle I/M program was last approved by the
EPA on July 17, 1997 (62 FR 38213). The County has since made numerous
improvements, updates and revisions to the I/M program ordinance, while
removing unnecessary and obsolete provisions and sections. The version
of the Davis County I/M program that we are now proposing to approve
supersedes and replaces the July 17, 1997 version. The Davis County I/M
Ordinance was enacted and adopted by the Davis County Commission on
October 1, 2019 and became effective October 18, 2019, and the
Ordinance was adopted into the SIP by the UAQB on March 4, 2020, at
Section X, part B. This is the version that was submitted to the EPA
and is discussed below.
    Section X, Part B of the SIP contains two main components for the
Davis County I/M program: (a) Language addressing applicability, a
general description of the Davis County I/M program, and the time frame
for implementation of the I/M program; and (b) the Davis County
Emission Inspection/Maintenance Program, as enacted in Davis County
Ordinance 10.12.
    a. State Language Addressing the Davis County I/M Program:
    Under the heading ``1. Applicability'' is a description of the 2019
revised Davis County I/M program, and a history of the Salt Lake and
Davis county federal ozone NAAQS attainment status and the development
of the Davis County I/M program. The section also notes that the Davis
County I/M program was included as a control measure in the 2006 24-
hour PM2.5 NAAQS.
    Under ``2. Summary of Davis County I/M Program,'' the state
describes various aspects of the revised Davis County I/M program:
Network Type, Test Convenience, Subject Fleet, Test Frequency, Station
Inspector Audits, Waivers, Test Equipment, and Test Procedures.
    Under the heading ``3. I/M SIP Implementation,'' the State notes
that the Davis I/M program will continue to apply until a maintenance
plan without an I/M program is approved by the EPA in accordance with
Section 175 of the CAA.

    b. Revisions to Davis County's ``Davis County Vehicle Emissions
Inspection/Maintenance Program Ordinance'' amend the Ordinance's
sections 10.12.020 Definitions, 10.12.030 Purpose, 10.12.040
Jurisdiction of the Division, 10.12.050 Powers and Duties, 10.12.060
Scope, 10.12.070 General Provisions, 10.12.080 Standards and
Specifications for Emissions Inspection Analyzers and Span Gases for
Equipment, 10.12.090 Requirements of the Vehicle Emissions Inspection/
Maintenance Program Stations, 10.12.100 Requirements of the Certified
Emissions Testers and/or Repair Technicians, 10.12.110 Official
Inspection Procedures, 10.12.130 Emissions Standards for Motor
Vehicles, 10.12.140 Certificates of Compliance and Waivers, 10.12.150
Engine Switching, 10.12.160 Right to Appeal, 10.12.170 Recall,
10.12.180 Penalty, 10.12.200 Quality Assurance, 10.12.210 Severability,
10.12.240 Fee Schedule, 10.12.250 Emissions Standards, 10.12.260 Waiver
Cut Points, 10.12.270 Passing Versus Waiver Cut Point Comparison,
10.12.280 Penalty Schedule, and 10.12.290 Conflicts.
    In addition, the State has submitted revisions to: Appendix A,
involving the provisions and requirements for emission inspection
analyzer specifications; Appendix B, involving the Two Speed Idle (TSI)
emissions inspection procedures; Appendix C, involving the OBDII (On-
Board Diagnostics Generation II) inspection procedures; Appendix D,
involving the Davis County Diesel I/M Program, which the EPA notes that
we are not proposing to act on: and Appendix E, involving compressed
natural gas vehicle emissions inspection procedures.
    We have evaluated the Governor's May 21, 2020 submittal of the
above revisions to the Utah SIP Section X Part B and the revised Davis
County Ordinance, with respect to the applicable provisions and
requirements in 40 CFR part 51, subpart S ``Inspection/Maintenance
Program Requirements,'' and are proposing approval. Additional
information and the EPA's more detailed evaluation of the above
materials are found in the accompanying TSD. The entire Davis County
Ordinance is in the Docket for this action.
6. SIP Section X, Vehicle Inspection and Maintenance Program, Part E,
Weber County
    The Weber County motor vehicle I/M program was last approved by the
EPA on September 14, 2005 (70 FR 54267). The County has since made
numerous improvements, updates and revisions to the I/M program
ordinance, while removing unnecessary and obsolete provisions and
sections. The version of the Weber County I/M program that we are now
proposing to approve supersedes and replaces the prior September 14,
2005 EPA-approved version. The Weber County I/M Regulation was enacted
and adopted by the Weber-Morgan Board of Health on September 23, 2019,
and the Weber-Morgan Health Department (WMHD) implements the I/M
program on behalf of Weber County. The Regulation was adopted into the
SIP by the UAQB on March 4, 2020. This is the version that was
submitted to the EPA and is discussed below.
    Section X, Part E of the Utah SIP addresses the provisions and
requirements for the implementation of the motor vehicle I/M program in
Weber County, Utah. Section X, Part E of the SIP contains two main
components for the Weber County I/M program: (a) Language for Section X
Part E that addresses applicability, a general description of the Weber
County I/M program, and the time frame for implementation of the I/M
program; and (b) the WMHD Motor Vehicle I/M Program Regulation.
    a. State Language Addressing the Weber County I/M Program:
    Under the heading ``1. Applicability'' is a description of the 2019
revised Weber County I/M program, a history of the Weber county federal
ozone NAAQS attainment status and the development of the Weber County
I/M program. The section also notes that the Weber County I/M program
was included as a control measure in the 2006 24-hour PM2.5
NAAQS.
    Under the heading ``2. Summary of Weber County I/M Program,'' the
State describes certain aspects of the revised Weber County I/M program
involving: Network Type, Test Convenience, Subject Fleet, Test
Frequency, Station Inspector Audits, Waivers, Test Equipment, and Test
Procedures.
    Under the heading ``3. I/M SIP Implementation'' the State notes
that the Weber I/M program will continue to apply until a maintenance
plan without an I/M program is approved by the EPA in accordance with
Section 175 of the CAA.
    b. Revisions to Weber County's ``Weber-Morgan Health Department
Regulation for Motor Vehicle Inspection and Maintenance Program'' amend
the regulation's: Section 1 Title and Definitions, Section 2 Purpose,
Section 4 Powers and Duties, Section 6 General Provisions, Section 7
Standards and Specifications for Analyzers and Calibration Gases,
Section 8 Permit Requirements of the Vehicle Emissions Station, Section
9 Inspection Procedure, Section 10 Certificate of Waiver, Section 12
Certified Emissions Inspection and Repair Technician/Certified
Emissions Inspection Only Technician Permit, Section 14 Certificate of
Compliance, Certificate of Compliance Numbers, and Certificate of
Waiver, Section 15 Adjudicative Proceedings, and Section 18 Effective
Date.
    In addition, the State has submitted revisions to Appendix A-
Analyzer Specifications, Appendix B- Fee Schedule, Appendix C-Motor
Vehicle Emissions Inspection and Maintenance Program, Appendix D-
Penalty Schedule, Appendix E-OBD IM Test Procedures, Appendix F
entitled ``Diesel Fueled Vehicle Test Procedure,'' which the EPA notes
that we are not taking any action on this Appendix, and a new Appendix
G entitled ``Adjustment Procedures.''
    We have evaluated the Governor's May 21, 2020 submittal of the
above revisions to the Utah SIP Section X Part E and the revised Weber
County Regulation, with respect to the applicable provisions and
requirements in 40 CFR part 51, subpart S ``Inspection/Maintenance
Program Requirements,'' and are proposing approval. Additional
information and the EPA's more detailed evaluation of the above
materials are found in the accompanying TSD. The entire Weber County
Regulation is in the Docket for this action.

B. PM2.5 SIP Plan

    On August 24, 2016 the EPA finalized the PM2.5 SIP
Requirements Rule,\10\ which established regulatory requirements
related to the statutory SIP requirements for areas designated
nonattainment for the PM2.5 standards.
---------------------------------------------------------------------------

    \10\ 81 FR 58010.
---------------------------------------------------------------------------

    As discussed in the PM2.5 SIP Requirements Rule,
sections 189(a), (c), and (e) of the CAA require that Moderate area
attainment plans contain the following: (i) An approved permit program
for construction of new and modified major stationary sources (CAA
section 189(a)(1)(A)); (ii) a demonstration that the plan provides for
attainment by no later than the applicable Moderate area attainment
date or a demonstration that attainment by that date is impracticable
(CAA section 189(a)(1)(B)); (iii) provisions for the implementation of
RACM/RACT no later than 4 years after designation (CAA section
189(a)(1)(C)); (iv) quantitative milestones that will be used to
evaluate compliance with the requirements to demonstrate RFP (CAA
section 189(c));

and (v) evaluation and regulation of PM2.5 precursors (in
general to meet RACM/RACT and other attainment planning requirements,
and also as specifically provided for major stationary sources under
CAA section 189(e)).
    Sections 189(b) and (c) of the CAA include the following
requirements for Serious area attainment plan submissions: (i) An
attainment demonstration (CAA section 189(b)(1)(A)); (ii) provisions
for the implementation of BACM/BACT no later than 4 years after
reclassification of the area to Serious (CAA section 189(b)(1)(B));
(iii) quantitative milestones that will be used to evaluate compliance
with the requirement to demonstrate RFP (CAA section 189(c)); and (iv)
regulation of PM2.5 precursors (in general to meet
attainment and control strategy requirements, and as specifically
required for major stationary sources by CAA section 189(e)).
    Other subpart 1 requirements for attainment plans not otherwise
superseded under subpart 4 also apply to Moderate and Serious areas for
the 2006 24-hour PM2.5 NAAQS, including (i) a description of
the expected annual incremental reductions in emission that will
demonstrate RFP (CAA section 172(c)(2)); (ii) emissions inventories
(CAA section 172(c)(3)); (iii) other control measures (besides RACM/
RACT for Moderate areas and BACM/BACT for Serious areas) needed for
attainment (CAA section 172(c)(6)); and (iv) contingency measures (CAA
section 172(c)(9)).
    In connection with the Moderate area SIP for the 2006 24-hour
PM2.5 NAAQS, the EPA has previously acted on a number of
Utah SIP revisions related to area sources. In particular, on February
2, 2012; May 9, 2013; June 8, 2013; February 18, 2014; April 17, 2014;
May 20, 2014; July 10, 2014; and August 6, 2014, UDAQ submitted either
new area source rules or revisions to rules found in UAC Title R307
(Environmental Quality). We acted on these rule revisions on February
25, 2016 (81 FR 9343), October 19, 2016 (81 FR 71988), October 2, 2019
(84 FR 52368) and February 26, 2020 (85 FR 10989).
    On December 16, 2014, UDAQ submitted additional Moderate 2006 24-
hour PM2.5 SIP revisions for the Provo and Salt Lake City
NAAs. CAA section 110(k)(1)(B) requires the EPA to determine whether a
SIP submission is complete within 60 days of receipt. This section also
provides that any plan that the EPA has not affirmatively determined to
be complete or incomplete will become complete by operation of law six
months after the date of submission. The EPA's SIP completeness
criteria are in 40 CFR part 51, appendix V. The 2014 2006 24-hour
PM2.5 plan became complete by operation of law on June 22,
2014. Additionally, UDAQ submitted revisions to the Utah SIP Part H.11,
12 and 13 of the Moderate 2006 24-hour PM2.5 SIPs for the
Provo and Salt Lake City NAAs on January 19, 2017, which became
complete by operation of law on July 20, 2017.
    On May 10, 2017 (82 FR 21711), the EPA determined that the Provo
and Salt Lake City NAAs failed to attain the 2006 24-hour
PM2.5 NAAQS by the Moderate attainment date of December 31,
2015. With this determination, the Provo and Salt Lake City NAAs were
reclassified as a ``Serious'' area for the 2006 24-hour
PM2.5 NAAQS, with a new attainment date of December 31,
2019. This reclassification triggered an obligation for Utah to submit
a new, Serious area attainment plan including the CAA elements listed
above. Additionally, CAA section 189(b)(1) requires that ``in
addition'' to the attainment plan requirements specific to Serious
areas, states must also meet all Moderate area attainment plan
requirements. The EPA interprets the statutory language of CAA section
189(b)(1) to require states with areas that are reclassified to Serious
to meet Moderate area attainment plan requirements, including all areas
that the EPA reclassifies through rulemaking under its discretionary
authority, even if that occurs before the area has met all of its
Moderate area attainment plan requirements. The following section
describes the EPA's final actions in this rule regarding Serious area
attainment plan requirements in greater detail.
    On April 10, 2019 (84 FR 14267) and September 27, 2019 (84 FR
51055), the EPA finalized clean data determinations (CDD) for the Provo
and Salt Lake City NAAs, respectively. As provided at 40 CFR 51.1015(a)
in the PM2.5 SIP Requirements Rule, this determination by
the EPA that the Provo and Salt Lake City Moderate 2006 24-hour
PM2.5 NAAs suspended the requirements for the State to
submit an attainment demonstration, provisions demonstrating timely
implementation of RACM/RACT, a RFP plan, quantitative milestones and
quantitative milestone reports, and contingency measures. However,
based on the EPA's longstanding policy, the BACM/BACT requirement of
CAA section 189(b)(1)(B) is independent of attainment. Thus, the CDD
did not suspend the obligation for UDAQ to submit any applicable
outstanding BACM/BACT requirements or other requirements that are
independent of attainment (NNSR and base-year emissions inventories).
    On February 15, 2019, UDAQ submitted the Serious 2006 24-hour
PM2.5 SIP for the Salt Lake City NAA. Under CAA section
110(k)(1)(B), the Salt Lake City Serious 2006 24-hour PM2.5
SIP became complete by operation of law on August 15, 2019.
Additionally, UDAQ submitted BACM/BACT analyses on February 4, 2019 for
the Provo NAA. The revisions to area source rules for the NAAs were
submitted on April 19, 2018, May 21, 2020 and July 21, 2020, and
revisions to the Utah SIP Section IX.H.11, 12 and 13 for the NAAs were
submitted on December 16, 2014, January 19, 2017 and February 15, 2019.
The revisions submitted on January 19, 2017 and February 15, 2019, for
Utah SIP Section IX.H.11, 12 and 13, supersede the December 16, 2014
submission; therefore, we are not acting on the December 16, 2014
revisions, but are fully acting on Utah SIP Section IX.H.13 from the
January 19, 2017 submission and Utah SIP Section IX.H.11 and 12 from
the February 15, 2019 submission. Any reference to the December 16,
2014 submission for Utah SIP Sections IX.H.11, 12 and 13, and any
reference to the January 19, 2017 submittal for Utah SIP Section
IX.H.11 and 12, are for informational purposes only. Additionally, on
October 9, 2020, UDAQ submitted draft revisions to Kennecott's Power
Plant in Utah SIP Section IX.H.12.i.i.C and the accompanying R307-110-
17 revisions for the EPA to parallel process.
    We are acting on these remaining Serious 2006 24-hour
PM2.5 SIP elements for the Salt Lake City and Provo NAAs,
that were not suspended with the CDDs, to allow for our action on the
2006 24-hour PM2.5 redesignation requests discussed in
Section II.C below of this document.
1. Base-Year Emissions Inventories
    CAA section 172(c)(3) requires that each SIP include a
comprehensive, accurate, current inventory of actual emissions from all
sources of the relevant pollutant or pollutants in the NAAs. This base-
year emissions inventory should provide a state's best estimate of
actual emissions from all sources of the relevant pollutants in the
area, including all emissions that contribute to the formation of a
particular NAAQS pollutant. For the 2006 24-hour PM2.5
NAAQS, the base-year inventory must include direct PM2.5
emissions, separately reported filterable and condensable
PM2.5 emissions, and emissions of all chemical precursors to
the formation of

secondary PM2.5: Nitrogen oxides (NOX), sulfur
dioxide (SO2), volatile organic compounds (VOC), and ammonia
(NH3).\11\
---------------------------------------------------------------------------

    \11\ 40 CFR 51.1008.
---------------------------------------------------------------------------

    The most current base year for emissions inventories for the Provo
and Salt Lake City NAAs was for 2017, which was made available to the
public for comment (and a public hearing if requested) in the January
13, 2020 PM2.5 maintenance plans/redesignation requests
submittal. The base-year inventories are based on the most current and
accurate information available to UDAQ at the time of the submittal.
The 2017 base-year inventories comprehensively address all source
categories in the Provo and Salt Lake City NAAs and were developed
consistent with the EPA's inventory guidance.
    In Section II.C.4.a below, the EPA provides a detailed analysis of
the 2017 base-year emissions inventories for the Provo and Salt Lake
City NAAs, which were submitted for the 2006 24-hour PM2.5
maintenance plans. Direct PM2.5 and all PM2.5
precursors are included in the 2017 base-year emissions inventories,
and filterable and condensible direct PM2.5 emissions are
identified separately. For these reasons, and with the EPA's detailed
analysis in Section II.C.4.a below, the EPA is proposing to approve the
2017 base-year emissions inventories for the Provo and Salt Lake City
NAAs as meeting the requirements of CAA section 172(c)(3), 40 CFR
51.1008(a)(1) and 40 CFR 51.1008(b)(1).
2. NNSR
    CAA section 172(c)(5) requires preconstruction and operating
permits for new major stationary sources and major modifications
locating in NAAs. Section 173 of the CAA outlines the minimum statutory
requirements for a state's NNSR permit program and serves as the basis
for the EPA's NNSR regulations for PM2.5 as promulgated in
the 2008 PM2.5 NSR Rule published at 73 FR 28321, May 16,
2008.\12\ The 2016 PM2.5 Regulatory Rule amended the
definitions of (1) regulated NSR pollutant with regard to
PM2.5 precursors, (2) major stationary source with regard to
major sources locating in PM2.5 NAAs classified as Moderate
and Serious, and (3) significant with regard to emissions of
PM2.5 precursors. For Moderate 2006 24-hour PM2.5
SIPs, CAA section 189(a)(1)(A) of subpart 4 applies, which requires
states to include in their implementation plan a permit program
addressing major stationary sources of the 2006 24-hour
PM2.5 NAAQS that meets the requirements under CAA section
173 of subpart 1. For a Serious 2006 24-hour PM2.5 SIP, CAA
section 189(b)(3) of subpart 4 applies, which requires that for any
Serious Area the terms ``major source'' and ``major stationary source''
include any stationary source or group of stationary sources located
within a contiguous area and under common control that emits, or has
the potential to emit, at least 70 tpy of PM2.5.
---------------------------------------------------------------------------

    \12\ 81 FR at 58107.
---------------------------------------------------------------------------

    An approvable NNSR program in a state's implementation plan must,
at a minimum, meet the applicable program requirements set forth in the
federal NNSR provisions at 40 CFR 51.165, which for PM2.5
have been based on changes to the section made by the 2008
PM2.5 NSR Rule.\13\ States with designated NAAs for a
particular pollutant are required to adopt regulations consistent with
those applicable plan requirements, including any subsequent rule
changes that the EPA may make, and submit them to the EPA for approval
as part of their SIP.
---------------------------------------------------------------------------

    \13\ Id.
---------------------------------------------------------------------------

    The Provo and Salt Lake City NAAs were classified as a Moderate NAA
for the 2006 24-hour PM2.5 NAAQS on November 13, 2009 (74 FR
58688). On May 10, 2017 (82 FR 21711), the Provo and Salt Lake City
areas were reclassified from Moderate to Serious 2006 24-hour
PM2.5 NAAs. The major source permitting threshold for a
Moderate 2006 24-hour PM2.5 NAA is 100 tpy of direct
PM2.5 or any PM2.5 precursor, and 70 tpy for a
Serious 2006 24-hour PM2.5 NAA.
    On July 25, 2019 (84 FR 35831), the EPA approved revisions to UAC
R307-403 (Permits: New and Modified Sources in Nonattainment Areas and
Maintenance Areas), which satisfies the outstanding NNSR requirement
for the Provo and Salt Lake City Moderate and Serious 2006 24-hour
PM2.5 NAAs.
3. BACM/BACT
a. Requirements for BACM/BACT
    For any Serious 2006 24-hour PM2.5 NAA, section
189(b)(1)(B) of the Act requires that a state submit provisions to
assure that BACM/BACT for the control of PM2.5 and
PM2.5 precursors shall be implemented no later than four
years after the date the area is reclassified as a Serious area. The
EPA defines BACM (including BACT) as, among other things, the maximum
degree of emissions reduction achievable for a source or source
category, which is determined on a case-by-case basis considering
energy, economic and environmental impacts, and other costs.\14\ We
generally consider BACM a control level that goes beyond existing RACM-
level controls, for example by expanding the use of RACM controls or by
requiring preventative measures instead of remediation.\15\ Indeed, as
implementation of BACM and BACT is required when a Moderate NAA is
reclassified as Serious due to its inability to attain the NAAQS
through implementation of ``reasonable'' measures, it is logical that
``best'' control measures should represent a more stringent and
potentially more costly level of control.\16\ The level of stringency
generally refers to the overall level of emissions reductions of a
control measure or technology, or of such measures and technologies
combined.
---------------------------------------------------------------------------

    \14\ State Implementation Plans for Serious PM10
Nonattainment Areas, and Attainment Date Waivers for PM10
Nonattainment Areas Generally; Addendum to the General Preamble for
the Implementation of Title I of the Clean Air Act Amendments of
1990 (``Addendum''), August 16, 1994; 59 FR 41998, 42010, 42013
(Aug. 16, 1994). The General Preamble for the Implementation of
Title I of the Clean Air Act Amendments of 1990 (``General
Preamble'') was published at 57 FR 13498 (Apr. 16, 1992).
    \15\ Id. at 42011, 42013.
    \16\ Id. at 42009-42010.
---------------------------------------------------------------------------

    The PM2.5 SIP Requirements Rule explains that BACM/BACT
are generally independent requirements, to be determined without regard
to the specific attainment analysis (i.e., attainment demonstration)
for the area.\17\ The EPA found it reasonable to interpret the statute
as requiring a different analysis for determining BACM/BACT, i.e., that
while RACM emphasizes the attainment needs of the area, BACM has a
greater emphasis on identifying measures that are feasible to
implement. The Addendum noted that the test for BACM puts a ``greater
emphasis on the merits of the measure or technology alone,'' rather
than on ``flexibility in considering other factors,'' in contrast to
the approach for RACM/RACT.\18\
---------------------------------------------------------------------------

    \17\ 81 FR at 58081.
    \18\ 59 FR at 42011.
---------------------------------------------------------------------------

    Section 189(b)(1)(B) of the Act allows states, in appropriate
circumstances, to delay implementation of BACM until four years after
reclassification. Because the EPA reclassified the Provo and Salt Lake
City areas as Serious NAAs for the 2006 24-hour PM2.5 NAAQS
effective June 9, 2017 (82 FR 21711; May 10, 2017), the date four years
after reclassification is June 9, 2021. In this case, however, all BACM
for direct PM2.5 and PM2.5 precursors in the
Provo and Salt Lake City areas must be implemented no later than
December

31, 2019, which is the outermost statutory attainment date for the
Provo and Salt Lake City areas under section 188(c)(2).\19\
---------------------------------------------------------------------------

    \19\ CAA section 189(b)(1)(B) establishes an outermost deadline
(``no later than four years after the date the area is
reclassified'') and does not preclude an earlier implementation
deadline for BACM where necessary to satisfy the attainment
requirements of the Act.
---------------------------------------------------------------------------

    Under the PM2.5 SIP Requirements Rule, control measures
that can be implemented in whole or in part by the end of the fourth
year after an area's reclassification to Serious are considered BACM,
and control measures that can only be implemented after this period but
before the attainment date are considered ``additional feasible
measures.'' \20\ The EPA has defined ``additional feasible measures''
as ``those measures and technologies that otherwise meet the criteria
for BACM/BACT but that can only be implemented in whole or in part
beginning 4 years after reclassification of an area, but no later than
the statutory attainment date of the area.'' \21\ Given that the
statutory attainment date is less than three years from the effective
date of the reclassification of the Provo and Salt Lake City areas,
additional feasible measures are not required in this case.
---------------------------------------------------------------------------

    \20\ 40 CFR 51.1010(a)(4)(ii). ``Additional feasible measures''
may be necessary in certain circumstances to implement the
requirements of CAA section 172(c)(6), which states that NAA plans
shall include enforceable emission limitations and such other
control measures, means or techniques, as well as schedules and
timetables for compliance, as may be necessary or appropriate to
provide for attainment of the NAAQS by the applicable attainment
date.
    \21\ 40 CFR 51.1000.
---------------------------------------------------------------------------

    The Addendum and the PM2.5 SIP Requirements Rule explain
that the BACM/BACT selection process for implementation of the 2006 24-
hour PM2.5 NAAQS is designed to take into account the local
facts and circumstances and the nature of the air pollution problem in
a given NAA. The following steps are used in determining BACM/BACT: (1)
Develop a comprehensive emission inventory of the sources of directly
emitted PM2.5 and PM2.5 precursors; (2) Identify
existing and potential control measures for the sources in the
inventory; (3) Evaluate the technological feasibility of potential
control measures; (4) Evaluate the economic feasibility of potential
control measures; and (5) Determine the earliest date by which a
control measure or technology can be implemented in whole or in
part.\22\
---------------------------------------------------------------------------

    \22\ Addendum at 42012-42014; 81 FR at 58084-58085.
---------------------------------------------------------------------------

    Additionally, the EPA believes that BACT or lowest achievable
emission rate (LAER) provisions for new sources (as distinct from BACT
for existing sources), or best available retrofit technology (BART) for
existing sources, could potentially quality as BACM or BACT for
purposes of meeting the Serious area attainment plan requirements.\23\
However, as discussed further in the PM2.5 SIP Requirements
Rule, the EPA does not believe it is appropriate for a state to assume
that just because a certain control technology was determined to meet
BACT, LAER or BART criteria for a new source sometime in the past, that
such a control will also automatically meet the criteria for BACM or
BACT or additional feasible measures for attainment planning purposes,
because the regulated pollutant or source applicability may differ and
the analyses may be conducted years apart. Thus, a state may not simply
rely on prior BACT, LAER or BART analyses for the purposes of showing
that a source has also met BACT for the relevant 2006 24-hour
PM2.5 NAAQS. Rather, the EPA expects that in Step 2
(discussed above) of the BACM/BACT determination process, the state
would identify such measures as ``existing measures'' that should be
further evaluated as potential BACM or BACT, or additional feasible
measures. At the same time, the EPA notes that the presence of
previously installed control technology, and the technical and economic
considerations that would be associated with upgrading to a measure
that achieves greater reductions, is something that should be
considered in the assessments of technological and economic feasibility
of the newer measure.\24\
---------------------------------------------------------------------------

    \23\ See 81 FR at 58086.
    \24\ Id.
---------------------------------------------------------------------------

    Once these analyses are complete, a state must use this information
to develop enforceable control measures and submit them to the EPA for
evaluation under CAA section 110. We use these steps as guidelines in
our evaluation of the BACM measures and related analyses in the Provo
and Salt Lake City 2006 24-hour PM2.5 Serious SIP.
b. Requirements for the Control of PM2.5 Precursors
    The composition of PM2.5 is complex and highly variable
due in part to the large contribution of secondary PM2.5 to
total fine particle mass in most locations, and to the complexity of
secondary particle formation processes. A large number of possible
chemical reactions, often non-linear in nature, can convert gaseous
SO2, NOX, VOC, and NH3 to
PM2.5, making them precursors to PM2.5.\25\
Formation of secondary PM2.5 may also depend on atmospheric
conditions, including solar radiation, temperature, and relative
humidity, and the interactions of precursors with preexisting particles
and with cloud or fog droplets.\26\
---------------------------------------------------------------------------

    \25\ Air Quality Criteria for Particulate Matter (EPA/600/P-99/
002aF, Oct. 2004), Chapter 3.
    \26\ Regulatory Impact Analysis for the Final Revisions to the
National Ambient Air Quality Standards for Particulate Matter (EPA/
452/R-12-005, December 2012), at 2-1.
---------------------------------------------------------------------------

    As explained in the PM2.5 SIP Requirements Rule, the Act
requires that the state evaluate all PM2.5 precursors for
regulation unless, for any given PM2.5 precursor, it
demonstrates to the Administrator's satisfaction that the precursor
does not contribute significantly to 2006 24-hour PM2.5
levels that exceed the NAAQS in the NAA.\27\ The CAA does not define
the term ``precursor'' for purposes of PM. The statutory definition of
``air pollutant,'' however, provides that the term ``includes any
precursors to the formation of any air pollutant, to the extent the
Administrator has identified such precursor or precursors for the
particular purpose for which the term `air pollutant' is used.'' \28\
The EPA has identified SO2, NOX, VOC, and
NH3 as precursors to the formation of PM2.5.
Accordingly, the BACM/BACT requirements of subpart 4 apply to emissions
of all four precursor pollutants and direct PM2.5 from all
types of stationary, area, and mobile sources, except as otherwise
provided in the Act (e.g., CAA section 189(e)).
---------------------------------------------------------------------------

    \27\ See 81 FR at 51018-58019.
    \28\ See CAA section 302(g).
---------------------------------------------------------------------------

    Section 189(e) \29\ of the Act requires that the control
requirements for major stationary sources of PM2.5 also
apply to major stationary sources of PM2.5 precursors,
except where the Administrator determines that such sources do not
contribute significantly to PM2.5 levels that exceed the
standard in the area. Although section 189(e) explicitly addresses only
major stationary sources, the EPA interprets the Act as authorizing it
also to determine, under appropriate circumstances, that regulation of
specific PM2.5 precursors from other

source categories in a given NAA is not necessary.\30\
---------------------------------------------------------------------------

    \29\ On Jan. 4, 2013, in NRDC v. EPA, the D.C. Circuit held that
the EPA erred in implementing the 1997 PM2.5 NAAQS
pursuant only to the general implementation requirements of subpart
1, rather than also to the implementation requirements specific to
particulate matter (PM10) in subpart 4, part D of title I
of the CAA. The court reasoned that the plain meaning of the CAA
requires implementation of the 1997 PM2.5 NAAQS under
subpart 4 because PM2.5 particles fall within the
statutory definition of PM10 and thus implementation of
the PM2.5 NAAQS is subject to the same statutory
requirements as the PM10 NAAQS. See 81 FR at 58013.
    \30\ Courts have upheld this approach to the requirements of
subpart 4 for PM10. See, e.g., Assoc. of Irritated
Residents v. EPA, et al., 423 F.3d 989 (9th Cir. 2005).
---------------------------------------------------------------------------

    The PM2.5 SIP Requirements Rule recognizes that the
treatment of PM2.5 precursors is important in developing a
PM2.5 plan.\31\ The rule provides flexibility for areas
where a particular PM2.5 precursor or precursors may not
contribute significantly to PM2.5 levels that exceed the
NAAQS. The rule provides for optional precursor demonstrations that a
state may submit to the EPA to establish that sources of particular
precursors need not be regulated for purposes of attainment planning or
in an NNSR permitting program for a specific NAA.
---------------------------------------------------------------------------

    \31\ See, e.g., 81 FR at 58017.
---------------------------------------------------------------------------

    The February 4, 2019 and February 15, 2019, submissions for the
Provo and Salt Lake City discusses the five primary pollutants that
contribute to the emissions in the NAAs (i.e., NOX,
SO2, VOC, NH3, and directly emitted
PM2.5). The majority of ambient PM2.5 collected
during a typical cold-pool episode of elevated concentration is
secondary particulate matter, generated from gaseous precursor
emissions. The results of speciation studies led UDAQ to the conclusion
that the exceedances of the 2006 24-hour PM2.5 NAAQS were a
result of the increased portion of the secondary PM2.5,
mainly ammonium nitrate, that was chemically formed in the air and not
primary PM2.5 emitted directly into the troposphere.\32\
Because of the major role that precursors play within the Provo and
Salt Lake City NAAs, UDAQ did not include any precursor demonstration.
Thus, the requirement to ensure the implementation of BACM/BACT applies
to direct PM2.5 and each of the four PM2.5
precursors listed above.
---------------------------------------------------------------------------

    \32\ The study results can be found in the TSD for the state's
February 15, 2019 action (available in the docket for this action).
---------------------------------------------------------------------------

    Based on the information provided in the Provo and Salt Lake City
submissions and other information available to the EPA, we agree with
UDAQ's conclusion that all four chemical precursors, including direct
PM2.5, must be regulated for purposes of attaining and
maintaining the 2006 24-hour PM2.5 NAAQS in the Provo and
Salt Lake City NAAs.
c. BACM/BACT Analysis in the Serious PM2.5 SIP
(1) Identifying the Sources of PM2.5 and PM2.5
Precursors
    The first step in determining BACM is to develop a detailed
emissions inventory of the sources of direct PM2.5 and
PM2.5 precursors that can be used with modeling to determine
the effects of these sources on ambient PM2.5 levels. As
discussed above in Section II.B.1 of this proposed rule, Chapter 4
(Emission Inventory Data) of the Salt Lake City February 15, 2019
submission and the General Inventory section of the Provo, February 4,
2019 submission, contain the planning inventories for directly emitted
PM2.5 and for all PM2.5 precursors
(NOX, SO2, VOC, and NH3) for the Salt
Lake City and Provo NAAs, along with supporting documentation to
support these inventories. Based on these inventories, four general
categories were established: Industrial point sources, on-road mobile
sources, off-road mobile sources, and area sources. Area sources
represent smaller, more numerous point sources, residential activities
such as home heating, and some biogenic emissions.
    Based on this identification of stationary, area, and mobile
sources of direct PM2.5, NOX, VOC,
SO2, and NH3 in the Provo and Salt Lake City
areas, we conclude that the February 4, 2019 and February 15, 2019
submissions, respectively, appropriately identify all emission sources
and source categories that must be subject to evaluation for potential
control measures consistent with the requirements of subpart 4.
(2) Identification and Implementation of BACM/BACT
    As part of its process for identifying candidate BACM/BACT and
considering the technical and economic feasibility of additional
control measures, UDAQ reviewed the EPA's guidance documents on BACM,
guidance documents on control measures for direct PM2.5,
NOX, VOC, NH3, and SO2 emissions
sources,\33\ and control measures implemented in other PM2.5
NAAs in other states. UDAQ's evaluations of potential BACM/BACT for
each source category identified above are found in ``Section 8. Control
Strategies'' in the February 4, 2019 Provo submission and in the TSD
supporting the February 15, 2019 Salt Lake City submission. In the
following sections, we review key components of UDAQ's demonstrations
concerning BACM/BACT for the identified sources of direct
PM2.5, NOX, VOC, SO2, and
NH3 emissions in the Provo and Salt Lake City NAAs. We
provide a more detailed evaluation of our review of UDAQ's regulations
in our TSD, which is in the docket.
---------------------------------------------------------------------------

    \33\ This is not an exhaustive list. Please refer to UDAQ's
submittal for detailed references: Control Techniques Guidelines
(CTG); Alternative Control Techniques (ACT); New Source Performance
Standards (NSPS); Ozone Transport Commission's (OTC) model rules;
PM2.5 Requirements Rule, 81 FR 58010; US EPA Fugitive
Dust Background Document and Technical Information Document for BACM
(September 1992); General Preamble, 57 FR 13498; and Addendum, 59 FR
41998.
---------------------------------------------------------------------------

    The UDAQ's BACM/BACT process and control measure evaluations are
described in detail in the February 4, 2019 submission, ``Section 8.
Control Strategies'' for the Provo NAA and in the State's February 15,
2019 TSD for the Salt Lake City NAA. For each identified source
category, UDAQ identified its adopted control measures and potential
additional control measures based on measures implemented in other
areas, measures identified in EPA regulations or guidance (e.g., in
control technique guidelines (CTGs), alternative control technique
documents (ACTs), new sources performance standards (NSPSs), or in the
EPA's ``Cost Analysis Models/Tools for Air Pollution Regulations''), or
measures identified in prior EPA rulemaking documents (e.g.,
recommendations in SIP actions).\34\ UDAQ evaluated these potential
additional control measures to determine whether implementation of the
measures would be technologically and economically feasible in the
Provo and Salt Lake City areas.
---------------------------------------------------------------------------

    \34\ The Cost Analysis Models/Tools for Air Pollution
Regulations can be found at https://www.epa.gov/economic-and-cost-analysis-air-pollution-regulations/cost-analysis-modelstools-air-pollution.
---------------------------------------------------------------------------

    On April 19, 2018, May 21, 2020 and July 21, 2020, UDAQ submitted
revisions and new rules to its area source rules R307-208, Outdoor Wood
Boilers; R307-230, NOX Emission Limits for Natural Gas-Fired
Water Heaters; R307-304, Solvent Cleaning; R307-335, Degreasing; R307-
343, Emissions Standards for Wood Furniture Manufacturing Operations;
R307-344, Paper, Film, & Foil Coating; R307-345, Fabric & Vinyl
Coating; R307-346, Metal Furniture Surface Coating; R307-347, Large
Appliance Surface Coating; R307-348, Magnet Wire Coating; R307-349,
Flat Wood Panel Coating; R307-350, Miscellaneous Metal Parts & Products
Coating; R307-351, Graphic Arts; R307-352, Metal Containers, Closure &
Coating; R307-353, Plastic Parts Coating; R307-354, Auto Body
Refinishing; and R307-355, Control of Emissions from Aerospace
Manufacture & Rework Facilities. Additionally, UDAQ provided BACM
analysis for area source rules that were not revised, which include:
R307-302, Solid Fuel Burning Devices; R307-303, Commercial Cooking;
R307-307, Road Salting & Sanding; R307-309, Nonattainment and
Maintenance Areas

for PM10 and PM2.5: Fugitive Emissions and
Fugitive Dust; R307-312, Aggregate Processing Operations; R307-328,
Gasoline Transfer and Storage; R307-341, Cutback Asphalt; R307-342,
Adhesive and Sealants; R307-356, Appliance Pilot Light; R307-357,
Consumer Products; and R307-361, Architectural Coatings. Our detailed
analysis of these area source rule revisions submitted on April 19,
2018, May 21, 2020, and July 21, 2020, and the BACM analyses for these
area sources submitted on February 4, 2019 and February 15, 2019 for
the Provo and Salt Lake City Serious 2006 24-hour PM2.5 NAAs
can be found in our TSD in the docket.
    On February 15, 2019, Utah submitted revisions to SIP Section
IX.H.11 (General Requirements: Control Measures for Area and Point
Sources, Emission Limits and Operating Practices, PM2.5).
This section of Utah's SIP applies to all sources addressed in Utah SIP
sections IX.H.12 and 13, except as otherwise outlined in individual
conditions in Sections IX.H.12 and 13. Our detailed analysis of the
revisions submitted on February 15, 2019, for the Utah SIP Section
IX.H.11, along with our analysis of UDAQs BACM/BACT analyses specific
to Utah SIP Section IX.H.11, submitted on February 4, 2019 and February
15, 2019 can be found in our TSD in the docket.
    On February 15, 2019, Utah submitted revisions to SIP Section
IX.H.12 (Source-Specific Emission Limitations in Salt Lake City--UT
PM2.5 Nonattainment Area), which sets emission limits and
control measures for major stationary sources in the Salt Lake City
2006 24-hour PM2.5 Serious NAA. These sources, which fall
above the 70 tpy threshold for Serious 2006 24-hour PM2.5
major sources \35\ defined in Utah R307-403 (Permits: New and Modified
Sources in Nonattainment Areas and Maintenance Areas), include: (1) ATK
Launch Systems Inc. Promontory; (2) Big West Oil Refinery; (3) Chemical
Lime Company (Lhoist North America); (4) Chevron Products Company--Salt
Lake Refinery; (5) Compass Minerals Ogden Inc.; (6) Hexel Corporation:
Salt Lake Operations; (7) Holly Corporation: Holly Refining & Marketing
Company (Holly Refinery); (8) Kennecott Utah Copper (KUC): Mine; (9)
Kennecott Utah Copper (KUC): Power Plant; (10) Kennecott Utah Copper
(KUC): Smelter and Refinery; (11) Nucor Steel Mills; (12) PacifiCorp
Energy: Gadsby Power Plant; (13) Tesoro Refining and Marketing Company:
Salt Lake City Refinery; (14) The Proctor & Gamble Paper Products
Company; (15) Utah Municipal Power Association: West Valley Power
Plant; (16) University of Utah: University of Utah Facilities; and (17)
Hill Air Force Base. On February 15, 2019, UDAQ submitted the BACM/BACT
analyses for each of these 17 sources. All other sources fall below the
70 tpy threshold and are covered in the multiple area source rules
discussed above. Our detailed analysis of the revisions submitted on
February 15, 2019, for the Utah SIP Section IX.H.12, along with our
analysis of UDAQs BACM/BACT analyses submitted on February 15, 2019,
specific to Utah SIP Section IX.H.12, can be found in our TSD in the
docket.
---------------------------------------------------------------------------

    \35\ 81 FR at 58152.
---------------------------------------------------------------------------

    Additionally, UDAQ submitted draft revisions on October 9, 2020,
specific to Utah SIP Section IX.H.12.i.i.C (Kennecott Power Plant),
which the state has asked the EPA to act on through parallel
processing. This draft revision removes the startup/shutdown limits for
the Kennecott Power Plant that was not supported within the BACM/BACT
analysis submitted on February 15, 2019. The detailed analysis of our
parallel process on the October 9, 2020, submission of draft revisions
to Utah SIP Section IX.H.12.i.i.C (Kennecott Power Plant), can be found
in our TSD in the docket, and our detailed discussion of how parallel
processing works can be found in Section I.E above.
    On January 19, 2017, Utah submitted revisions to SIP Section
IX.H.13 (Source-Specific Emission Limitations in Provo--UT
PM2.5 Nonattainment Area), which sets emission limits and
control measures for major stationary sources in the Provo 2006 24-hour
PM2.5 Serious NAA. The sources in Section IX.H.13 include:
(1) Brigham Young University: Main Campus; (2) Geneva Nitrogen Inc.:
Geneva Nitrogen Plant; (3) McWane Ductile--Utah; (4) PacifiCorp Energy:
Lake Side Power Plant; (5) Payson City Corporation: Payson City Power;
(6) Provo City Power: Power Plant; and (7) Springville City
Corporation: Whitehead Power Plant. UDAQ submitted BACM/BACT analyses
for only two of these sources, McWane Ductile--Utah and PacifiCorp
Energy: Lake Side Power Plant. The other five sources listed above fall
below the 70 tpy threshold for Serious 2006 24-hour PM2.5
major stationary sources,\36\ which is defined in Utah R307-403
(Permits: New and Modified Sources in Nonattainment Areas and
Maintenance Areas) rule. These remaining five sources (Brigham Young
University, Geneva Nitrogen Plant, Payson City Power, Provo City Power,
and Whitehead Power Plant) were either shut down (Geneva Nitrogen
Plant) or have reduced their emissions to be minor sources (Brigham
Young University, Payson City Power, Provo City Power, and Whitehead
Power Plant). UDAQ uses Utah SIP Section IX.H. only for major
stationary source emission limits or control measures; therefore, UDAQ
has requested that EPA not act on the Utah SIP Section IX.H.13 portions
for these facilities because the limits/measures are out of date and
will be removed in future rulemakings. Since we have never approved
these limits or sources into Utah SIP Section IX.H.13, and this section
was only created in the December 16, 2014 submittal, UDAQ does not need
to complete a 110(l) demonstration. We will only be acting on the
McWane Ductile--Utah and PacifiCorp Energy: Lake Side Power Plant
sections of Utah SIP Section IX.H.13, and on these sources' BACM/BACT
determinations submitted by UDAQ on February 4, 2019. Our detailed
analysis of the revisions submitted on January 19, 2017, along with our
analysis of UDAQ's BACM/BACT analyses submitted on February 4, 2019,
can be found in our TSD in the docket.
---------------------------------------------------------------------------

    \36\ Id.
---------------------------------------------------------------------------

    As to the other facilities originally submitted within Utah SIP
Section IX.H.13, no additional discussion or action is necessary for
the Geneva Nitrogen Plant due to its shutdown. The BACM/BACT analyses
for the other facilities (Brigham Young University, Payson City Power,
Provo City Power, and the Whitehead Power Plant) are now included in
the individual BACM/BACT analyses for each area source rule. No
additional discussion is needed as to these limits in Utah SIP Section
IX.H.13, which as noted above are outdated, or on these facilities as
individual sources. Our detailed analysis of the area source rules,
along with our analysis of UDAQ's BACM/BACT analyses submitted on
February 4, 2019 and February 15, 2019, can be found in our TSD in the
docket.
    Additionally, on February 4, 2019 and February 15, 2019, UDAQ
submitted BACM/BACT analyses for on-road and non-road mobile sources
for the Provo and Salt Lake City Serious 2006 24-hour PM2.5
NAAs, respectively. Our detailed analysis of these analyses can be
found in our TSD in the docket.
(3) The EPA's Evaluation and Conclusion
    We have reviewed UDAQ's determination in the February 4, 2019 and
February 15, 2019 submissions that the major stationary and area source

control measures represent BACM/BACT for direct PM2.5 and
PM2.5 precursors within the Provo and Salt Lake City NAAs,
respectively. In our review, we also considered our previous
evaluations of UDAQ's rules in connection with our approval of
revisions for Utah's R307 area source rules and RACM demonstration for
the Provo and Salt Lake City Moderate 2006 24-hour PM2.5
SIPs that were acted on.\37\ Based on this review, we believe that
UDAQ's area source rules and the Utah SIP Part H emission limits
provide for the implementation of BACM/BACT for major stationary
sources and area sources of direct PM2.5 and
PM2.5 precursors.
---------------------------------------------------------------------------

    \37\ See 81 FR 9343 (Feb. 25, 2016); 81 FR 71988 (Oct. 19,
2016); 84 FR 52368 (Oct. 2, 2019); and 85 FR 10989 (Feb. 26, 2020).
---------------------------------------------------------------------------

    With respect to mobile sources, we believe that the programs
developed and administered by UDAQ, along with the identified Federal
requirements, provide for the implementation of BACM/BACT for direct
PM2.5 and PM2.5 precursors in the Provo and Salt
Lake City NAAs.
    For these reasons we propose to approve the revisions submitted on
January 19, 2017, April 19, 2018, February 4, 2019, February 15, 2019,
May 21, 2020 and July 21, 2020. We also propose to find that these
submissions provide for the implementation of BACM/BACT for all sources
of direct PM2.5 and PM2.5 precursors as
expeditiously as practicable, for purposes of the 2006 24-hour
PM2.5 NAAQS in the Provo and Salt Lake City areas, in
accordance with the requirements of CAA section 189(b)(1)(B) and 40 CFR
51.1010. We are also proposing to approve, through parallel processing,
the October 9, 2020 draft submission of revisions to Utah SIP Section
IX.H.12.i.i.C to remove the startup/shutdown limits that were not
supported in the BACM/BACT determination of the Kennecott Power Plant.
Additionally, we are proposing to approve the area source rule
revisions submitted on April 19, 2018, May 21, 2020 and July 21, 2020,
and to approve the BACM/BACT analyses submitted on February 4, 2019 and
February 15, 2019. We are also proposing to approve the revisions to
Utah SIP Sections IX.H.11 and 12, submitted on February 15, 2019;
revisions to Utah SIP Section IX.H.13, submitted on January 19, 2017;
and draft revisions submitted on October 9, 2020, for the Provo and
Salt Lake City Serious 2006 24-hour PM2.5 NAAs. Our detailed
analyses can be found in the EPA TSD in the docket.

C. Do the redesignation requests and maintenance plans meet CAA
requirements?

    For a NAA to be redesignated to attainment, the following
conditions in section 107(d)(3)(E) of the CAA must be met: (1) We must
determine that the area has attained the NAAQS; (2) The applicable
implementation plan for the area must be fully approved under section
110(k) of the Act; (3) We must determine that the improvement in air
quality is due to permanent and enforceable reductions in emissions
resulting from implementation of the applicable implementation plan and
applicable Federal air pollutant control regulations and other
permanent and enforceable reductions; (4) We must fully approve a
maintenance plan for the area as meeting the requirements of CAA
section 175A; and (5) The state containing such area must meet all
requirements applicable to the area under section 110 and part D of the
CAA.
    The September 4, 1992 Calcagni Memorandum outlines how to assess
the adequacy of redesignation requests against the conditions listed
above. On January 13, 2020, the Governor of Utah submitted revisions to
the SIP for R307-110-10, submitted maintenance plans for the Salt Lake
City and Provo areas (located within Utah SIP Sections IX.A.36 and 27,
respectively), and requested that the EPA redesignate the area to
attainment for 2006 24-hour PM2.5.
    The sections below discuss how Utah's redesignation requests and
maintenance plans meet the requirements of the Act for redesignation of
the Provo and Salt Lake City areas to attainment for the 2006 24-hour
PM2.5 NAAQS.
1. Attainment of the 2006 24-Hour PM2.5 NAAQS
    To redesignate an area from nonattainment to attainment, the EPA
must determine that the area has attained the applicable NAAQS. See CAA
section 107(d)(3)(E)(i). A state must demonstrate that an area has
attained the 2006 24-hour PM2.5 NAAQS through submittal of
ambient air quality data from an ambient air monitoring network
representing maximum PM2.5 concentrations. The data, which
must be quality assured, quality-controlled, and certified in the EPA's
Air Quality System (AQS), must show that the most recent three years
(2017-2019) of valid PM2.5 98th percentile mass
concentrations are below the 2006 PM2.5 24-hour NAAQS (35
[micro]g/m\3\), pursuant to 40 CFR 50.13. In making this showing, three
consecutive years of complete air quality data must be used.
    Between 2017 and 2019, Utah operated two and five PM2.5
monitors in the Provo and Salt Lake City NAAs, respectively. The EPA
reviewed the PM2.5 ambient air monitoring data from the
Provo monitors, Lindon (AQS site 49-049-4001) and Spanish Fork (AQS
site 49-049-5010),\38\ and from the Salt Lake City monitors, Bountiful
(AQS site 49-011-0004), Rose Park (AQS site 49-035-3010), Hawthorn (AQS
site 49-035-3006), Herriman #3 (AQS site 49-035-3013), and Erda (AQS
site 49-045-0004).\39\
---------------------------------------------------------------------------

    \38\ The Provo NAA had one monitor (North Provo, 49-049-0002)
shut down near the end of 2018 due to safety issues at the site, and
UDAQ is working to reestablish the monitor at a new site.
    \39\ The Salt Lake City NAA had two monitors shut down due to
the loss of each site, and UDAQ is working to reestablish the
monitors at new sites. These monitors are Brigham City (49-003-
0003), which shutdown in June 2019, and Ogden 2 (49-057-0002), which
shut down in May 2019. A new site for Ogden 2 was established in
Weber County (Harrisville, 49-057-1003) in September 2019. UDAQ is
still working with Box Elder County on new potential sites.
---------------------------------------------------------------------------

    As part of the redesignation requests for the Provo and Salt Lake
City NAAs, UDAQ submitted ambient air quality data from the monitoring
sites, which had been quality-assured and placed in AQS on a quarterly
basis. The 98th percentile 2017-2019 design values for the monitors in
the Provo and Salt Lake City NAAs are found in Table 1 below, and
support the conclusion that the areas have attained the 2006 24-hour
PM2.5 NAAQS.
---------------------------------------------------------------------------

    \40\ The Salt Lake City near-road PM2.5 monitoring
site (AQS ID 49-035-4002) was established and began recording data
on January 1, 2019. The 98th percentile daily average concentration
for 2019 at this PM2.5 near-road monitor was 31.0
[micro]g/m\3\; however, the one year of available data is not
sufficient for calculating a design value. Additional discussion of
the EPA's position as to Salt Lake City's PM2.5 near-road
monitor can be found in the final rule signed by the Region 8
Regional Administrator on October 29, 2020, determining that the
Salt Lake City Serious 2006 24-hour PM2.5 NAA attained by
the Serious attainment date.

               Table 1--Provo and Salt Lake City 2006 24-Hour PM2.5 NAAs 2017-2019 98th Percentiles and Design Values ([micro]g/m\3\) \40\
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                98th percentiles ([micro]g/m\3\)            2017-2019
                                                                                ------------------------------------------------  Design value
                    NAA                            Monitoring site            AQS ID                                                        ([micro]g/
                                                                                2017            2018            2019            m\3\)
--------------------------------------------------------------------------------------------------------------------------------------------------------
Provo.....................................  Lindon......................     49-049-4001            28.9            28.4            21.2              26
                                            Spanish Fork................     49-049-5010            27.6            49.6            17.5              32
Salt Lake City............................  Bountiful...................     49-011-0004            35.2            25.7            19.3              27
                                            Rose Park...................     49-035-3010            32.4            29.2            27.9              30
                                            Hawthorn....................     49-035-3006            35.7            26.2            27.3              30
                                            Herriman #3.................     49-035-3013            28.2            29.0            18.8              25
                                            Erda........................     49-045-0004            20.9            30.6            22.9              25
--------------------------------------------------------------------------------------------------------------------------------------------------------

    As explained above, quality-assured, quality-controlled, and
certified air quality monitoring data were collected for each year from
2017 through 2019 in accordance with an approved annual monitoring
network plan (AMNP) for each year. The EPA has reviewed this data and
concluded that it shows that the areas attained by the Serious
attainment date of December 31, 2019.\41\
---------------------------------------------------------------------------

    \41\ The final determination of attainment by the Serious 2006
24-hour PM2.5 attainment date was signed by the Region 8
Regional Administrator on October 29, 2020.
---------------------------------------------------------------------------

    Further information on PM2.5 monitoring is in
Subsections IX.A.27.b(1) and IX.A.36.b(1) of the Provo and Salt Lake
City maintenance plans, respectively. Additionally, on October 29,
2020, the Region 8 Regional Administrator signed the final rule, which
finalized a determination that the Provo and Salt Lake City NAAs
attained by the Serious attainment date of December 31, 2019. We have
evaluated the ambient air quality data and believe that Utah has
adequately demonstrated that the 2006 24-hour PM2.5 NAAQS
has been attained in the Provo and Salt Lake City areas and that the
two areas attained by their Serious 2006 24-hour PM2.5
attainment date.
2. State Implementation Plan Approval
    Section 107(d)(3)(E)(ii) of the CAA states that for an area to be
redesignated to attainment, it must be determined that the
Administrator has fully approved the applicable implementation plan for
the area under section 110(k).
    Those states containing Moderate 2006 24-hour PM2.5 NAAs
were required to submit a SIP by December 31, 2014, demonstrating
attainment of the 2006 24-hour PM2.5 NAAQS by December 31,
2015. UDAQ submitted the Moderate 2006 24-hour PM2.5 SIPs
for the Provo and Salt Lake City NAAs on December 16, 2014, with
additional revisions submitted on January 19, 2017. On May 10, 2017 (82
FR 21711), the EPA published a final rule reclassifying the Salt Lake
City and Provo areas as ``Serious'' nonattainment under subpart 4,
based on the EPA's determination that the area could not practicably
attain the 2006 24-hour PM2.5 standards by the December 31,
2015 attainment date. This reclassification became effective on June 9,
2017. The reclassification was based on the EPA's evaluation of ambient
air quality data from the 2013-2015 period, indicating that it was not
practicable for certain monitoring sites within the Salt Lake City and
Provo areas to show PM2.5 design values at or below the
level of the 2006 24-hour PM2.5 NAAQS by December 31, 2015.
    Section 107(d)(3)(E)(ii) of the CAA states that for NAAs to be
redesignated to attainment, it must be determined that the
Administrator has fully approved the applicable implementation plan for
the areas under section 110(k). On February 25, 2016 (81 FR 9343),
October 19, 2016 (81 FR 71988), October 2, 2019 (84 FR 52368) and
February 26, 2020 (85 FR 10989) the EPA approved revisions to several
area source rules, and approved new rules for the 2006 24-hour
PM2.5 NAAs into the Utah SIP. Additionally, we completed a
CDD for the Provo and Salt Lake City 2006 24-hour PM2.5 NAAs
on April 10, 2019 (84 FR 14267) and on September 27, 2019 (84 FR
51055), respectively. With these final rules, the EPA suspended the
obligation for Utah to make submissions to meet certain CAA
requirements related to attainment of the 2006 24-hour PM2.5
NAAQS for Moderate and Serious NAAs. These suspended CAA requirements
are: (1) Attainment demonstration (Moderate and Serious); (2) projected
emissions inventory (Moderate and Serious); (3) RACM/RACT (Moderate);
(4) RFP (Moderate and Serious); (5) motor vehicle emission budgets
(MVEB) (Moderate and Serious); (6) contingency measures (Moderate and
Serious); and (7) quantitative milestones (Moderate and Serious).
    The CDD did not suspend Utah's obligation to submit CAA
requirements not related to demonstrating attainment, which includes
the base-year emission inventory, NNSR revisions, and BACM/BACT for the
Provo and Salt Lake City NAAs. The base-year emission inventory
requirement for the Moderate and Serious Provo and Salt Lake City NAAs,
will be based on our approval of the base-year inventory submitted in
the January 13, 2020 submittal of the maintenance plans. Our analysis
of the base-year inventory is discussed in Section II.C.4.a below and
in Section II.B.1 above.
    On July 25, 2019 (84 FR 35831), the EPA approved revisions to UAC
R307-403 (Permits: New and Modified Sources in Nonattainment Areas and
Maintenance Areas), which satisfies the outstanding NNSR requirement
for the Provo and Salt Lake City Moderate and Serious 2006 24-hour
PM2.5 NAAs and is discussed above in Section II.B.2. above.
    The remaining CAA requirement that was not suspended with the April
10, 2019 (84 FR 14267) and the September 27, 2019 (84 FR 51055), CDD
for the Provo and Salt Lake City 2006 24-hour PM2.5 NAAs,
respectively, is BACM/BACT for the Serious 2006 24-hour
PM2.5 SIPs. Our analysis that completes this remaining
requirement is discussed in our TSD, with a brief discussion in Section
II.B.3. above.
    We have evaluated the actions above and have determined that
through these actions, the State of Utah has a fully approved Provo and
Salt Lake City 2006 24-hour PM2.5 SIP under section 110(k).
3. Improvement in Air Quality Due to Permanent and Enforceable Measures
    Section 107(d)(3)(E)(iii) of the CAA provides that for an area to
be redesignated to attainment, the Administrator must determine that
the improvement in air quality is due to permanent and enforceable
reductions in emissions resulting from implementation of the applicable
implementation plan, implementation of applicable Federal air pollutant

control regulations, and other permanent and enforceable reductions.
    As briefly discussed above in Section II.B.3 and in further detail
in our TSD, Utah has implemented multiple area source rules, I/M
Programs, and emission limits for stationary sources in the Provo and
Salt Lake City NAAs.
    Additionally, within Section IX.A.27.b.1.c. and IX.A.36.b.3.a. of
the Provo and Salt Lake City 2006 24-hour PM2.5 maintenance
plan, respectively, UDAQ provides an assessment of the ambient air
quality data collected at the monitors in these two NAAs from the year
monitoring began (2000) to 2018 (the last year of valid data before the
maintenance plan was submitted), which shows an observable decrease in
the monitored PM2.5. UDAQ observed the 98th percentile
average of the 24-hour data in the Provo and Salt Lake City 2006 24-
hour PM2.5 NAAs, as well as the annual arithmetic mean,
which assisted in understanding the trends. The Provo and Salt Lake
City 2006 24-hour PM2.5 NAAs were only designated
nonattainment for the 2006 24-hour PM2.5 NAAQS, however, the
annual arithmetic mean is useful information in showing the decrease in
emissions. The cold-pool temperature inversions during winter, which
drive and trap secondary PM2.5, vary in strength and
duration from year to year, and the PM2.5 concentrations
measured during these periods reflect this variability more than they
reflect the gradual changes in emissions of direct PM2.5 and
the PM2.5 precursors. This variability is evident in UDAQ's
assessment, but the 24-hour data trend is downward, indicating
improvement of a little less than 1 [micro]g/m\3\ per year for both the
Provo and Salt Lake City 2006 24-hour PM2.5 NAAs. Episodic
variability is reduced when reviewing the annual mean values of
PM2.5 concentrations from 2000-2018. Graphing the annual
mean PM2.5 concentration data reveals a decreasing trend,
which indicates an improvement of 3 [micro]g/m\3\ and 4.3 [micro]g/m\3\
over this 18-year span for the Provo and Salt Lake City NAAs,
respectively.
    We have evaluated the various state and federal control measures,
historical emissions inventories, and the emission trends of the
PM2.5 98th percentiles and annual PM2.5 mean
concentrations presented by UDAQ from 2000 to 2018, and believe that
the improvement in air quality in the Provo and Salt Lake City NAAs has
resulted from emission reductions that are permanent and enforceable.
4. Fully Approved Maintenance Plan Under Section 175A of the Act
    Section 107(d)(3)(E) of the Act requires that, for a NAA to be
redesignated to attainment, we must fully approve a maintenance plan
which meets the requirements of section 175A of the Act. The plan must
demonstrate continued attainment of the relevant NAAQS in the area for
at least 10 years after our approval of the redesignation. Eight years
after our approval of a redesignation, a state must submit a revised
maintenance plan demonstrating attainment for the 10 years following
the initial 10-year period. The maintenance plan must also contain a
contingency plan to ensure prompt correction of any violation of the
NAAQS.\42\ The EPA's interpretations of the CAA section 175A
maintenance plan requirements are generally provided in the General
Preamble \43\ and the Calcagni Memorandum referenced above. The
Calcagni Memorandum outlines five core elements necessary to ensure
maintenance of the relevant NAAQS in an area seeking redesignation from
nonattainment to attainment. Those elements, as well as guidelines for
subsequent maintenance plan revisions, are explained in detail below.
---------------------------------------------------------------------------

    \42\ Sections 175A(b) and (d).
    \43\ 57 FR 13498, at 13563.
---------------------------------------------------------------------------

a. Attainment Inventory
    PM2.5 maintenance plans should include an attainment
emission inventory to identify the level of emissions in the area that
is sufficient to maintain the NAAQS. An emissions inventory was
developed and submitted with the Provo and Salt Lake City 2006 24-hour
PM2.5 maintenance plans for the two NAAs on January 13,
2020. This submittal contains a base year inventory for 2017, interim-
year projection inventory for 2026, and a projected maintenance
inventory of 2035. The emissions in the inventories include sources of
direct PM2.5 and PM2.5 precursor emissions
located within a regional area called a modeling domain. UDAQ modeled
two different domain sizes and grid resolutions: A 4 kilometer (km)
coarse grid and a 1.33 km fine grid.\44\ The 4 km coarse domain covered
the entire State of Utah, a significant portion of Eastern Nevada
(including Las Vegas), and smaller portions of Idaho, Wyoming, Colorado
and Arizona, and was used to show movement of pollutants at the
boundaries of the nested fine grid domain.
---------------------------------------------------------------------------

    \44\ See January 13, 2020 State of Utah submittal for Provo and
Salt Lake City 2006 24-hour PM2.5 Maintenance Plans;
Figures IX.A.27.4. and IX.A.36.4, respectively, titled ``CAMx
Photochemical Modeling Domain in Two-Way Nested Configuration.''
---------------------------------------------------------------------------

    Since the coarse domain was so large, the 1.33 km fine domain or a
``core area'' within this domain was identified, within which a greater
degree of accuracy was applied. Within this core area (which includes
Weber, Davis, Salt Lake, Utah, Box Elder, Tooele, Cache and Franklin,
ID counties), SIP-specific inventories were prepared to include
seasonal adjustments and forecasting to represent each of the
projection years. In the bordering region, outside the core area, the
2014 National Emissions Inventory (NEI) was used in the analysis. There
were four general categories of sources included in these inventories:
Point sources, area sources, on-road mobile sources and non-road mobile
sources.
    For each of these source categories, the pollutants that were
inventoried were PM2.5, SO2, NOX, VOC
and NH3. More detailed descriptions of the 2017 base-year
inventory and the 2026 and 2035 projection inventories can be found in
Sections IX.A.27.c and IX.A.36.c. Maintenance Plan, Subsection (2)
Attainment Inventory, for the Provo and Salt Lake City NAAs,
respectively, and in the State of Utah's TSD. Utah's submittal contains
detailed emission inventory information that was prepared in accordance
with the EPA's emission inventory guidance.\45\ Summary of emission
figures from the 2017 base year and emission projections for 2026 and
2035 are provided in Table 2 and Table 3, below, for the Provo and Salt
Lake City, respectively.
---------------------------------------------------------------------------

    \45\ Emissions Inventory Guidance for Implementation of Ozone
and Particulate Matter National Ambient Air Quality Standards
(NAAQS) and Regional Haze Regulations (EPA-454/B-17-002, May 2017)
(available at https://www.epa.gov/sites/production/files/2017-07/documents/ei_guidance_may_2017_final_rev.pdf).

                                Table 2--Provo NAA; Actual Emissions From 2017 and Emission Projections for 2026 and 2035
                                                                  [tons per day (tpd)]
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                PM2.5         PM2.5       PM2.5
                    Year                              Source category           filterable    condensible    total      NOX      VOC      NH3      SO2
--------------------------------------------------------------------------------------------------------------------------------------------------------
2017 Baseline...............................  Area Sources...................          1.75          0.29      2.04      5.01    13.32     6.54     0.06
                                              Mobile Sources.................  ............  ............      0.83      15.4     9.07     0.43     0.09
                                              Non-Road.......................  ............  ............      0.21      3.07     1.66        0     0.01
                                              Point Sources..................          0.18          0.12       0.3      1.12     0.18     0.42     0.05
                                                                              --------------------------------------------------------------------------
                                                 2017 Total..................  ............  ............      3.38      24.6    24.23     7.39     0.22
--------------------------------------------------------------------------------------------------------------------------------------------------------
2026........................................  Area Sources...................          1.89          0.32      2.21      3.56     14.2     6.38     0.05
                                              Mobile Sources.................  ............  ............      0.42      5.79     4.58     0.36     0.05
                                              Non-Road.......................  ............  ............      0.14      2.14     1.65     0.01     0.01
                                              Point Sources..................          0.19          0.12      0.31      0.97     0.17     0.44     0.06
                                                                              --------------------------------------------------------------------------
                                                 2026 Total..................  ............  ............      3.08     12.46     20.6     7.19     0.17
--------------------------------------------------------------------------------------------------------------------------------------------------------
2035........................................  Area Sources...................          2.06          0.35      2.41      3.67    16.32     6.24     0.05
                                              Mobile Sources.................  ............  ............      1.41      5.74     6.49     0.44     0.05
                                              Non-Road.......................  ............  ............      0.13      1.84      1.8     0.01     0.01
                                              Point Sources..................          0.19          0.12      0.31      0.97     0.17     0.44     0.06
                                                                              --------------------------------------------------------------------------
                                                 2035 Total..................  ............  ............      4.26     12.22    24.78     7.13     0.17
--------------------------------------------------------------------------------------------------------------------------------------------------------

                           Table 3--Salt Lake City NAA; Actual Emissions From 2017 and Emission Projections for 2026 and 2035
                                                                  [tons per day (tpd)]
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                PM2.5         PM2.5       PM2.5
                    Year                              Source category           filterable    condensible    total      NOX      VOC      NH3      SO2
--------------------------------------------------------------------------------------------------------------------------------------------------------
2017 Baseline...............................  Area Sources...................          5.02          1.11      6.13     13.55    45.98    14.21     0.21
                                              Mobile Sources.................  ............  ............      2.28     44.21    30.12     1.28     0.31
                                              Non-Road.......................  ............  ............      0.96     18.12     8.89     0.02     0.35
                                              Point Sources..................          2.97          0.97      3.94     17.01     6.52     0.34     3.78
                                                                              --------------------------------------------------------------------------
                                                 2017 Total..................  ............  ............     13.31     92.89    91.51    15.85     4.65
--------------------------------------------------------------------------------------------------------------------------------------------------------
2026........................................  Area Sources...................          5.19          1.15      6.34      8.54    43.99    14.19      0.2
                                              Mobile Sources.................  ............  ............      1.34     19.63    15.96     1.09     0.16
                                              Non-Road.......................  ............  ............      0.72     14.64     8.85     0.02     0.44
                                              Point Sources..................          4.19          1.38      5.57     22.61     7.26     0.48      3.5
                                                                              --------------------------------------------------------------------------
                                                 2026 Total..................  ............  ............     13.97     65.42    76.06    15.78      4.3
--------------------------------------------------------------------------------------------------------------------------------------------------------
2035........................................  Area Sources...................          5.37          1.19      6.56      8.69    47.17    14.21      0.2
                                              Mobile Sources.................  ............  ............      1.39     18.91    18.93     1.19     0.15
                                              Non-Road.......................  ............  ............      0.67     13.32      9.7     0.03     0.51
                                              Point Sources..................          4.19          1.38      5.57     22.62     7.26     0.48      3.5
                                                                              --------------------------------------------------------------------------
                                                 2035 Total..................  ............  ............     14.19     63.54    83.06    15.91     4.36
--------------------------------------------------------------------------------------------------------------------------------------------------------

    Based on our review, we have determined that Utah prepared an
adequate attainment inventory for the Provo and Salt Lake City 2006 24-
hour PM2.5 NAAs. Additionally, the 2017 base-year inventory
satisfies the outstanding requirement for the Serious Provo and Serious
Salt Lake City NAAs that were not suspended with the CDDs finalized on
April 10, 2019 (84 FR 14267) and September 27, 2019 (84 FR 51055),
respectively.
b. Maintenance Demonstration
    The Calcagni Memorandum explains that where modeling was relied on
to demonstrate maintenance, the plan must contain a summary of the air
quality concentrations expected to result from the application of the
control strategies. Also, the plan should identify and describe the
dispersion model or other air quality model used to project ambient
concentrations. The maintenance demonstration for the Provo and Salt
Lake City areas used a regional photochemical model.
    Before the development of the Provo and Salt Lake City 2006 24-hour
PM2.5 maintenance plans, UDAQ conducted a technical analysis
to support the development of the Serious SIP for the Salt Lake City
2006 24-hour PM2.5 NAA. The analysis included preparation of
emissions inventories and meteorological data, and the evaluation and
application of a regional photochemical model. Part of this process
included episode selection to determine the episode that most
accurately replicates the photochemical formation of ambient
PM2.5 during a persistent cold air pool episode in the
airshed. For the Provo and Salt Lake City maintenance plans, UDAQ used
the same episode that was used for the Serious SIP modeling.
    The Comprehensive Air Quality Model with Extensions (CAMx) version
6.30 for air quality modeling was used for the Provo and Salt Lake City

maintenance plans, with enhancements that included snow chemistry and
topographical and surface albedo refinements. The emissions processing
model that UDAQ used in conjunction with CAMx was the Sparse Matrix
Operator Kernel Emissions Modeling System (SMOKE) version 3.6.5,\46\
which prepares the annual emissions inventory for use in the air
quality model.
---------------------------------------------------------------------------

    \46\ https://www.cmascenter.org/smoke/.
---------------------------------------------------------------------------

    Activity profiles and their associated cross reference files from
the EPA's 2011v6 \47\ modeling platform were used by UDAQ. For
stationary non-point and mobile sources, UDAQ used spatial surrogates
from the EPA Clearinghouse for Inventories and Emissions Factors
(CHIEF),\48\ which were used to distribute emissions in space across
the modeling domain. Emissions from point sources were placed at the
specific location of the sources. Additionally, if reliable local
information was available, UDAQ modified or developed the profiles and
surrogates to reflect this information.
---------------------------------------------------------------------------

    \47\ https://www.epa.gov/air-emissions-modeling/2011-version-6-air-emissions-modeling-platforms.
    \48\ https://www.epa.gov/chief.
---------------------------------------------------------------------------

    Meteorological inputs were derived using the Weather Research and
Forecasting \49\ (WRF) Advanced Research WRF (WRF-ARW) model to prepare
meteorological datasets for UDAQ to use with the photochemical model.
WRF-ARW had reasonable ability to replicate the vertical temperature
structure of the boundary layer (i.e., the temperature inversion);
however, UDAQ found that WRF-ARW had difficulty reproducing the
inversion when the inversion was shallow and strong (i.e., an 8-degree
temperature increase over 100 vertical meters). UDAQ provides
additional information on these models in their TSD.
---------------------------------------------------------------------------

    \49\ https://www.mmm.ucar.edu/weather-research-and-forecasting-model.
---------------------------------------------------------------------------

    Part of the modeling exercise that UDAQ completed for the Provo and
Salt Lake City maintenance plans was to test whether the model could
successfully replicate the PM2.5 mass and composition
observed during prior episodes of elevated PM2.5
concentrations. The selection of an appropriate episode(s) should
determine the meteorological episode that helps produce the best air
quality modeling performance.
    Based on EPA guidance,\50\ UDAQ selected three episodes: (1)
January 1-10, 2011; (2) December 7-19, 2013; and (3) February 1-16,
2016. UDAQ examined the PM2.5 model performance for these
three episodes and concluded that CAMx performed the best when using
the January 2011 WRF-ARW output. UDAQ further confirmed this
determination by using a linear regression analysis showing that
modeled and measured PM2.5 at the Provo monitoring station
(Lindon) was strongly correlated during the January 2011 episode (R\2\
= 0.89) compared to the other episodes (R\2\ = 0.81 for the December
2013 episode; and R\2\ = 0.05 for the February 2016 episode). The Salt
Lake City monitoring station (Hawthorne) linear regression analysis
showed similar results to the Provo monitoring site, in that the
performance of the January 2011 episode was strongly correlated (R\2\ =
0.80) compared to the other episodes (R\2\ = 0.54 for the December 2013
episode and R\2\ = 0.69 for the February 2016 episode). Therefore, UDAQ
selected the January 2011 episode to conduct the modeled maintenance
demonstration work for the Provo and Salt Lake City areas. A
comprehensive discussion of the meteorological model performance for
all three of these episodes can be found in the TSD submitted by UDAQ.
---------------------------------------------------------------------------

    \50\ Guidance on the Use of Models and Other Analyses for
Demonstrating Attainment of Air Quality Goals for Ozone,
PM2.5, and Regional Haze (EPA, Apr. 2007).
---------------------------------------------------------------------------

    UDAQ completed a comparison of the 24-hour average modeled and
observed PM2.5 during the January 1-10, 2011 episode at the
Provo monitoring station (Lindon) and at the Salt Lake City monitoring
station (Hawthorne), and the results showed that the model overall
captured the daily 24 hour average temporal variation in
PM2.5 well. A more detailed analysis of this episode for
both the Provo and Salt Lake City monitoring sites (Lindon and
Hawthorne, respectively) can be found in the TSD submitted by UDAQ.
    Overall, UDAQ concluded that the model performed well in
replicating the buildup and dispersal of PM2.5 in the Provo
and Salt Lake City NAAs, and thus the model could be used for air
quality planning purposes. UDAQ then developed a 2017 baseline model
simulation using 2017 emissions data, but using the WRF-ARW
meteorological data for the 2011 episode. The 2017 baseline modeling
and the 2017 baseline monitoring data design values are used to
simulate possible future PM2.5 levels by projecting from the
2017 emissions to future year emissions. The results of the future year
modeling are described below.
    With acceptable model performance, the model can be used to make
future-year attainment projections. For each future year, an attainment
projection is made by calculating a concentration termed the Future
Design Value (FDV). This calculation is made for each monitor included
in the analysis, and then compared to the NAAQS (35 [micro]g/m\3\).
When the FDV is smaller than the NAAQS at every monitor in the NAA,
this would demonstrate attainment for the area in that specific future
year. A maintenance plan must demonstrate continued attainment of the
NAAQS for a span of ten years. Since this ten-year span is measured
from the time that the EPA finalizes action of the plan, the ten-year
end date is uncertain. To be conservative, UDAQ projected an attainment
date of 2035, which is fifteen years after Utah submitted the Provo and
Salt Lake City maintenance plans. Additionally, UDAQ modeled a ``spot-
check'' assessment of 2026.
    For any monitor, the FDV is greatly influenced by the existing air
quality at the specific location. This can be quantified and expressed
as a Baseline Design Value (BDV). The BDV is consistent with the form
of the 2006 24-hour PM2.5 NAAQS, which is the 98th
percentile value averaged over a three-year period. The quantification
of the BDV for each monitor in Provo and Salt Lake City, is included in
the TSD submitted by UDAQ.
    Several values were excluded when UDAQ calculated the BDVs in the
Provo NAA. UDAQ utilized the EPA's ``Exceptional Events Rule,'' \51\
which allows states to exclude certain air quality data due to
exceptional events (e.g., wildfires, dust storms, etc.). Two large
local wildfires were observed during the summer of 2018 that affected
the PM2.5 values at the Spanish Fork monitor in the Provo
NAA, but even when the atypical wildfire data is included in the
baseline design value the level is still below the 2006 24-hour
PM2.5 NAAQS, at 35.4 [micro]g/m\3\. Since the design value
complies with the NAAQS, the wildfire events are not considered
regulatorily significant exceptional events under the Exceptional
Events Rule because they did not cause an exceedance or a violation of
the NAAQS.\52\
---------------------------------------------------------------------------

    \51\ 81 FR 68216 (Oct 3, 2016).
    \52\ 40 CFR 50.14.
---------------------------------------------------------------------------

    Although the wildfires did not cause exceptional events, which
would have needed the EPA's concurrence under the Exceptional Events
Rule, Utah excluded the values from those days from its modeling, so as
to produce more representative projections of future air quality. This
exclusion was consistent with EPA guidance on addressing instances
where air quality data is influenced by atypical, extreme, or
unrepresentative.\53\ This Additional

Methods Guidance identifies the most common determinations and analyses
not covered by the Exceptional Events Rule, and clarifies for each of
them whether there is a separate, existing mechanism under which the
exclusion, selection, or adjustment of air quality monitoring data may
be appropriate. One example is certain modeling analyses under EPA's
Guideline on Air Quality Models \54\ including modeling analyses used
for estimating base and future year design values for ozone and
PM2.5 attainment demonstrations.
---------------------------------------------------------------------------

    \53\ See Additional Methods, Determinations, and Analyses to
Modify Air Quality Data Beyond Exceptional Events (EPA, Apr. 4,
2019) (the ``Additional Methods Guidance,'' available at https://www.epa.gov/sites/production/files/2019-04/documents/clarification_memo_on_data_modification_methods.pdf).
    \54\ 40 CFR part 51, appendix W.
---------------------------------------------------------------------------

    Table 4 below details the atypical, potentially wildfire-influenced
values recorded at the Spanish Fork monitor, with the specific date the
monitor was impacted and what the potential source could be.

  Table 4--2018 Atypical Event Values Excluded From the Baseline Design
                    Value at the Spanish Fork Monitor
------------------------------------------------------------------------
                                     Value,         Potential wildfire
              Date                [micro]g/m\3\          sources
------------------------------------------------------------------------
8/7/2018.......................            37.8  Coal Hollow.
8/9/2020.......................            50.8  Coal Hollow and other
                                                  western state(s)
                                                  fire(s).
8/10/2018......................            68.8  Coal Hollow and other
                                                  western state(s)
                                                  fire(s).
8/11/2018......................            49.6  Coal Hollow and other
                                                  western state(s)
                                                  fire(s).
8/13/2018......................            58.1  Coal Hollow and other
                                                  western state(s)
                                                  fire(s).
9/14/2018......................            71.5  Pole Creek and Bald
                                                  Mountain.
9/15/2018......................            42.6  Pole Creek and Bald
                                                  Mountain.
9/17/2018......................            74.5  Pole Creek and Bald
                                                  Mountain.
9/18/2018......................            57.7  Pole Creek and Bald
                                                  Mountain.
9/19/2020......................            76.3  Pole Creek and Bald
                                                  Mountain.
9/21/2018......................            39.3  Pole Creek and Bald
                                                  Mountain.
------------------------------------------------------------------------

    UDAQ worked with the EPA to determine whether these atypical values
could be excluded under the approach described in the Additional
Methods Guidance, and based on the specific modeling analysis conducted
in accordance with EPA's Air Quality Models Guideline. We have reviewed
historical data for the area and the HYSPLIT ``back trajectory
analysis'' \55\ in which the State presented an analysis of the
direction and sources of air pollution at the receptor site.\56\ Based
on our review, and considering the provisions of Utah SIP Section
IX.A.27.c.1.d., the EPA agrees with UDAQ's assessment that the atypical
baseline design value of 35.4 [micro]g/m\3\ was exacerbated by local