[Federal Register Volume 86, Number 5 (Friday, January 8, 2021)]
[Proposed Rules]
[Pages 1347-1362]
[FR Doc No: 2020-29092]

=======================================================================
-----------------------------------------------------------------------

ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 52

[EPA-R09-OAR-2020-0618; FRL-10018-46-Region 9]

Partial Approval and Partial Disapproval of Air Quality
Implementation Plans; Arizona; West Pinal County; 1987 PM10
Nonattainment Area Requirements

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

-----------------------------------------------------------------------

SUMMARY: The Environmental Protection Agency (EPA) is proposing to
approve in part and to disapprove in part the state implementation plan
(SIP) revision submitted by the State of Arizona to meet Clean Air Act
(CAA or ``Act'') requirements for the 1987 PM10 national
ambient air quality standards (NAAQS or ``standard'') in the West Pinal
County PM10 nonattainment area. The State of Arizona's
``2015 West Pinal Moderate PM10 Nonattainment Area SIP''
(``West Pinal County PM10 Plan'') addresses the CAA
nonattainment area requirements for the 1987 PM10 NAAQS,
including requirements for an emissions inventory, an attainment
demonstration, reasonable further progress, reasonably available
control measures, contingency measures, and motor vehicle emissions
budgets. The EPA is proposing to approve the base year 2008 emissions
inventory for direct PM10 and to disapprove the remaining
elements of the West Pinal County PM10 Plan.

DATES: Written comments must arrive on or before February 8, 2021.

ADDRESSES: Submit your comments, identified by Docket ID No. EPA-R09-
OAR-2020-0618 at https://www.regulations.gov. For comments submitted at
Regulations.gov, follow the online instructions for submitting
comments. Once submitted, comments cannot be edited or removed from
Regulations.gov. The EPA may publish any comment received to its public

docket. Do not submit electronically any information you consider to be
Confidential Business Information (CBI) or other information whose
disclosure is restricted by statute. Multimedia submissions (audio,
video, etc.) must be accompanied by a written comment. The written
comment is considered the official comment and should include
discussion of all points you wish to make. The EPA will generally not
consider comments or comment contents located outside of the primary
submission (i.e., on the web, cloud, or other file sharing system). For
additional submission methods, or if you need assistance in a language
other than English or if you are a person with disabilities who needs a
reasonable accommodation at no cost to you, please contact the person
identified in the FOR FURTHER INFORMATION CONTACT section. For the full
EPA public comment policy, information about CBI or multimedia
submissions, and general guidance on making effective comments, please
visit https://www.epa.gov/dockets/commenting-epa-dockets. If you need
assistance in a language other than English or if you are a person with
disabilities who needs a reasonable accommodation at no cost to you,
please contact the person identified in the FOR FURTHER INFORMATION
CONTACT section.

FOR FURTHER INFORMATION CONTACT: Jerry Wamsley, Air Planning Office
(ARD-2), EPA Region IX, 75 Hawthorne Street, San Francisco, CA 94105,
(415) 947-4111, or by email at<EMAIL_ADDRESS>
SUPPLEMENTARY INFORMATION: Throughout this document, ``we,'' ``us,''
and ``our'' refer to the EPA.

Table of Contents

I. Regulatory Context
    A. PM10 Standard, Area Designations, and SIPs
    B. CAA and Regulatory Requirements for Moderate PM10
Nonattainment Area SIPs
II. Submissions From the State of Arizona To Address 1987
PM10 Standard Requirements in the West Pinal County
Nonattainment Area
    A. Summary of State Submissions
    B. CAA Procedural Requirements for Adoption and Submission of
SIP Revisions
III. Evaluation of the West Pinal County PM10 Plan
    A. Emissions Inventories
    B. PM10 Precursors
    C. Reasonably Available Control Measures Demonstration
    D. Attainment Demonstration
    E. Reasonable Further Progress Demonstration
    F. Contingency Measures
    G. Motor Vehicle Emissions Budgets for Transportation Conformity
IV. Proposed Action
V. Statutory and Executive Order Reviews

I. Regulatory Context

A. PM10 Standard, Area Designations, and SIPs

    The EPA sets the National Ambient Air Quality Standard (NAAQS) for
certain ambient air pollutants at levels required to protect human
health and the environment. Particulate matter with an aerodynamic
diameter less than or equal to a nominal ten micrometers, or
PM10, is one of these ambient air pollutants for which the
EPA has established health-based standards. On July 1, 1987, the EPA
promulgated two primary standards for PM10: A 24-hour
standard of 150 micrograms per cubic meter ([micro]g/m\3\); and an
annual PM10 standard of 50 [micro]g/m\3\. The EPA also
promulgated secondary PM10 standards that were identical to
the primary standards.\1\ Because they are identical, we refer to the
primary and secondary standards using the singular term, NAAQS.
Effective December 18, 2006, EPA revoked the annual PM10
NAAQS but retained the 24-hour PM10 NAAQS.\2\
---------------------------------------------------------------------------

    \1\ 52 FR 24634 (July 1, 1987).
    \2\ 71 FR 61144 (October 17, 2006).
---------------------------------------------------------------------------

    An area attains the 24-hour PM10 NAAQS when the expected
number of days per calendar year with a 24-hour concentration in excess
of 150 micrograms per cubic meter ([micro]g/m\3\) (referred to herein
as an ``exceedance''), is equal to or less than one as determined in
accordance with 40 CFR part 50, appendix K.\3\ Conversely, a violation
of the PM10 NAAQS occurs when the number of expected annual
exceedances of the 24-hour NAAQS is greater than one.
---------------------------------------------------------------------------

    \3\ See 40 CFR 50.6 and 40 CFR part 50, appendix K.
---------------------------------------------------------------------------

    Most of Pinal County, Arizona, including what is now the West Pinal
County PM10 nonattainment area, was included in the ``rest
of state'' area, which was designated ``unclassifiable'' for the 24-
hour PM10 NAAQS by operation of law upon enactment of the
CAA, consistent with section 107(d)(4)(B)(iii). Until recently, this
area in Arizona remained designated ``unclassifiable'' for the 1987 24-
hour PM10 NAAQS. The CAA, under section 107(d)(3),
authorizes the EPA to revise the designation of, or ``redesignate,''
areas (or portions thereof) based on air quality data, planning and
control considerations, or any other air-quality-related considerations
that the EPA deems appropriate.
    On October 14, 2009, under CAA section 107(d)(3)(A), the EPA
notified the Governor of Arizona and four tribal leaders (whose areas
of Indian country are located entirely, or in part, within Pinal
County) that the designation for Pinal County, and any nearby areas
that may be contributing to the monitored violations in Pinal County,
should be revised.\4\ Our decision to initiate the redesignation
process was due to ambient data for 2006-2008 from PM10
monitoring sites within the County showing widespread, frequent, and in
some instances, severe, violations of the PM10 standard.
---------------------------------------------------------------------------

    \4\ Letter from Laura Yoshii, Acting Regional Administrator to
Governor Jan Brewer dated October 14, 2009. The EPA notified the
tribal leaders of the Ak-Chin Indian Community, Gila River Indian
Community, San Carlos Apache Tribe by letters dated December 30,
2009, and Tohono O'odham Nation by letter dated September 21, 2010.
---------------------------------------------------------------------------

    Effective July 2, 2012, the EPA designated a portion of state lands
in Pinal County, Arizona (``West Pinal County'') as nonattainment for
the 1987 PM10 NAAQS based on monitoring data from 2006-
2008.\5\ West Pinal County is located in central Arizona, southeast of
the Phoenix metropolitan area and northwest of the city of Tucson.
Pinal County covers 5,365 square miles and has two distinct western and
eastern regions with different characteristics relevant to pollution
formation. The West Pinal County PM10 nonattainment area is
located within the western region, characterized by low desert valleys
and an arid climate. The eastern region is mountainous, with elevations
up to 6,441 feet.
---------------------------------------------------------------------------

    \5\ 77 FR 32024 (May 31, 2012). The precise boundaries for the
West Pinal County nonattainment area are described in 40 CFR 81.303.
---------------------------------------------------------------------------

    As a result of the nonattainment designation, EPA classified West
Pinal County as a ``Moderate'' PM10 nonattainment area.
Consequently, by January 2, 2014, Arizona was required to submit a
nonattainment plan SIP revision for the 24-hour PM10 NAAQS
meeting relevant CAA requirements. The State submitted a SIP revision
intended to meet these requirements on December 21, 2015, and this
``2015 West Pinal Moderate PM10 Nonattainment Area SIP'' is
the subject of this proposed action. For a PM10
nonattainment area classified as Moderate, section 188(c) of the CAA
provides that the Moderate area attainment date is ``as expeditiously
as practicable, but no later than the end of the sixth calendar year
after the area's designation as nonattainment.'' Consequently, the
applicable attainment date for the West Pinal County area, designated
nonattainment in 2012, was as expeditiously as practicable, but no
later than December 31, 2018.
    CAA section 188(b)(2) requires the EPA to determine whether a state
has

attained the 24-hour PM10 NAAQS in a Moderate
PM10 nonattainment area by the applicable attainment date
and requires the EPA to make such a determination within six months
after that date. If the EPA determines that a Moderate area has not
attained the NAAQS by the relevant attainment date, then the area is
reclassified as a Serious area by operation of law. On June 24, 2020,
the EPA determined that the West Pinal County nonattainment area had
not attained the 1987 24-hour PM10 NAAQS by December 31,
2018, the outermost permissible statutory attainment date for the
area.\6\ This determination was based on our calculation of the
PM10 design value for the West Pinal County nonattainment
area over the 2016-2018 period, using complete, quality-assured, and
certified PM10 monitoring data.
---------------------------------------------------------------------------

    \6\ 85 FR 37756 (June 24, 2020).
---------------------------------------------------------------------------

    The basis for the EPA's June 24, 2020 finding of failure to attain
the PM10 NAAQS and the margin by which the area failed to
attain indicate that the Moderate plan's modeled attainment
demonstration, which incorrectly predicted attainment of the
PM10 NAAQS by December 31, 2018, is not approvable. Because
the modeled attainment demonstration is not approvable, as described in
section III.D, other elements of the West Pinal County PM10
Plan that are dependent upon the modeled attainment demonstration are
likewise not approvable, e.g., the emission controls imposed by the
State to meet reasonably available control measure/reasonably available
control technology (RACM/RACT) requirements based on the predicted
sufficiency of those controls to result in attainment by the intended
attainment date. If finalized as we propose, our disapproval of most
elements of the Moderate plan will start sanctions and Federal
implementation plan (FIP) clocks, which can be turned off by the EPA's
approval of new plan elements for the PM10 NAAQS that
correct the deficiencies within the Moderate plan. With the EPA's
reclassification of the West Pinal County area to Serious, Arizona now
has an obligation to submit, by January 24, 2022, a nonattainment plan
SIP revision that complies with the statutory and regulatory
requirements for Serious PM10 nonattainment plans and that
demonstrates attainment of the PM10 NAAQS as expeditiously
as practicable, but no later than December 31, 2022. Although
reclassification of an area from Moderate to Serious does not eliminate
a state's obligation to meet Moderate area nonattainment plan
requirements, the EPA anticipates that Arizona's submission of an
approvable Serious area nonattainment plan would also satisfy the
State's Moderate area nonattainment plan obligations. For example, an
approvable Serious area nonattainment plan would satisfy the Act's
requirements for imposing best available control measures, including
best available control technology (BACM/BACT), which would presumably
satisfy the less stringent requirements for RACM/RACT.

B. CAA and Regulatory Requirements for Moderate PM10
Nonattainment Area SIPs

    Along with the new designations, classifications, and attainment
dates, the Clean Air Act Amendments of 1990 established new
nonattainment area planning requirements. The air quality planning
requirements for Moderate PM10 nonattainment areas are set
out in subparts 1 and 4 of the CAA, including sections 110, 172, and
189 of the statute. We discuss these sections of the Act in more detail
later during our review of each plan element. Also, the EPA has issued
guidance, in a document we refer to as the General Preamble, describing
how we will review state nonattainment plan SIP submissions under Title
I of the CAA, including such SIP submissions for Moderate
PM10 nonattainment areas.\7\ In general, states must include
the following elements in nonattainment plans for Moderate areas for
purposes of the 1987 24-hour PM10 NAAQS: A comprehensive,
accurate, and current emissions inventory of emissions sources in the
nonattainment area; provisions to implement RACM/RACT for the
appropriate sources and pollutants in the nonattainment area;
provisions demonstrating reasonable further progress (RFP), including
quantitative milestones towards attainment of the PM10 NAAQS
as expeditiously as practicable, along with quantitative milestones for
evaluation of RFP at set times; contingency measures that will provide
for additional emissions reductions automatically in the event that the
state fails to meet RFP or to attain the NAAQS by the applicable
attainment date in the area; and, a motor vehicle emissions budget for
the purpose of determining the conformity of transportation programs
and plans developed by state transportation agencies.
---------------------------------------------------------------------------

    \7\ 57 FR 13498 (April 16, 1992) and 57 FR 18070 (April 28,
1992).
---------------------------------------------------------------------------

II. Submissions From the State of Arizona To Address the 1987 PM10
Standard Requirements in the West Pinal County Nonattainment Area

A. Summary of State Submissions

    As a result of the May 31, 2012 nonattainment designation, West
Pinal County was classified as a Moderate PM10 nonattainment
area. Within 18 months from the July 2, 2012 effective date of the
designation, or January 2, 2014, the State was required to submit a
nonattainment plan meeting Moderate area plan requirements, including
emission control measures for West Pinal County designed to attain the
1987 24-hour PM10 NAAQS as expeditiously as practicable, but
no later than December 31, 2018.
    On December 21, 2015, Arizona submitted the West Pinal County
PM10 Plan, intended to address the Moderate area
nonattainment requirements, to the EPA as a revision to the Arizona
SIP.\8\ The West Pinal County PM10 Plan is organized into
seven chapters and nine appendices. The nine appendices provide support
for the plan and are divided into the following categories: Technical
support and documentation (appendices A-D, F), SIP adoption authority
and public notice and hearing documentation (appendix E) and control
measure submittals (appendices G-I).
---------------------------------------------------------------------------

    \8\ Letter dated December 21, 2015, from Eric C. Massey,
Director, Air Quality Division, Arizona Department of Environmental
Quality, to Jared Blumenfeld, Regional Administrator, EPA Region IX.
---------------------------------------------------------------------------

    Appendices G, H, and I contain control measures submitted with the
West Pinal County PM10 Plan in the form of rules, statutes,
and other supporting documents. We are not proposing to act on the
submitted control measures in this proposed action on the West Pinal
County PM10 Plan. Previously, the EPA approved into the
Arizona SIP the submitted control measures that regulate fugitive dust,
construction dust, and crop operations.\9\ In a separate Federal
Register notice, we intend to take action on the remainder of the
State's submitted rules, namely, an update to its agricultural best
management practices (AgBMP) statute, and the AgBMP rules for animal
operations in Pinal County.
---------------------------------------------------------------------------

    \9\ 82 FR 20267 (May 1, 2017).
---------------------------------------------------------------------------

B. CAA Procedural Requirements for Adoption and Submission of SIP
Revisions

    CAA sections 110(a) and 110(l) require a state to provide
reasonable public notice and opportunity for public hearing prior to
the adoption and submission of a SIP revision to the EPA

for evaluation under section 110(k) and other applicable substantive
requirements. To meet this procedural requirement, a state must include
evidence that it provided adequate public notice and an opportunity for
a public hearing, consistent with the EPA's implementing regulations in
40 CFR 51.102.
    The Arizona Department of Environmental Quality (ADEQ) provided
public notice and opportunity for public comment on the West Pinal
County PM10 Plan. On October 19, 2015, ADEQ released the
West Pinal County PM10 Plan for public review and published
a notice of public meeting to be held on November 19, 2015, to consider
adoption of the West Pinal County PM10 Plan.\10\ On November
19, 2015, ADEQ held the public hearing and subsequently adopted the
West Pinal County PM10 Plan as a revision to the Arizona
SIP.\11\ Under authority provided by Arizona state law, on December 21,
2015, Eric Massey, Director of the Air Quality Division, ADEQ,
submitted the West Pinal County PM10 Plan to the EPA.\12\ On
June 21, 2016, the West Pinal County PM10 Plan became
complete by operation of law.\13\
---------------------------------------------------------------------------

    \10\ ``Arizona Department of Environmental Quality and Public
Comment Period and Hearing on the Proposed Arizona State
Implementation Plan Revision, Attainment Plan for the West Pinal
County PM10 Planning Area (1987 NAAQS)'' published in the
Arizona Republic October 19 and 20, 2015; Exhibit E-III, Appendix E,
West Pinal County PM10 Plan.
    \11\ ``Public Hearing Presiding Officer Certification'' signed
by Naveen Savarirvayan, Presiding Officer, November 19, 2015 and
notarized; Exhibit E-VI, Appendix E, West Pinal County
PM10 Plan. The hearing transcript and the public comments
and State responses are found at Exhibit E-VIII and Exhibit E-VII,
respectively, within Appendix E, West Pinal County PM10
Plan.
    \12\ Letter dated December 21, 2015 from Eric C. Massey,
Director, Air Quality Division, ADEQ to Jared Blumenfeld, Regional
Administrator, EPA Region IX.
    \13\ 42 U.S.C. 7410(k)(1)(B).
---------------------------------------------------------------------------

    Based on information provided in the SIP submissions summarized
above, the EPA has determined that the public hearing was properly
noticed. Therefore, we find that the submittal of the West Pinal County
PM10 Plan meets the procedural requirements for public
notice and hearing in CAA sections 110(a) and 110(l) and 40 CFR 51.102.

III. Evaluation of the West Pinal County PM10 Plan

A. Emissions Inventories

1. Statutory and Regulatory Requirements
    CAA section 172(c)(3) requires a state to submit for each
PM10 nonattainment area a ``base year inventory'' that is a
comprehensive, accurate, current inventory of actual emissions from all
sources of the relevant pollutant or pollutants in the area. Also, the
state should submit a second projected ``attainment year inventory''
for the year in which the state projects that the area will attain the
PM10 standards. The state should include documentation
explaining how it calculated the emissions data. When estimating mobile
source emissions, states should use the latest emissions models and
planning assumptions available at the time the SIP is developed.\14\
---------------------------------------------------------------------------

    \14\ See 81 FR 58032 (August 24, 2016).
---------------------------------------------------------------------------

    The state must meet several general requirements for base year
emissions inventories, consistent with CAA section 172(c)(3). First,
the emissions inventory year must be one of the 3 years used for the
EPA PM10 nonattainment designation for the area, or an
alternative year agreed upon by the EPA and the state as more
reflective of the causes and sources of violations of the
PM10 standard that meet the criteria in CAA section
172(c)(3). Second, the state must reflect actual emissions from all
sources of PM10 in the inventory. Third, the state should
report the emissions inventory in the form of the PM10
standard it is intended to address, e.g., in tons or pounds per day to
be consistent with the averaging period of the 24-hour PM10
NAAQS.\15\
---------------------------------------------------------------------------

    \15\ See 81 FR 58027-58032.
---------------------------------------------------------------------------

    A state must meet similar CAA section 172(c)(3) requirements in the
projected attainment year inventory for the most expeditious year in
which the state can show attainment of the PM10 standard in
the modeled attainment demonstration portion of the nonattainment plan.
At a minimum, the state must choose an attainment year consistent with
the outermost applicable deadline required by CAA section 188(c). As
with the baseline year inventory, the state must reflect emissions from
all sources of PM10 in this inventory and report them in the
form of the PM10 standard. In addition, the attainment year
inventory must be consistent with the source categories and level of
detail reported by the state in the base year inventory.
    Future attainment year and related baseline emissions inventories
must reflect the most recent population, employment, travel and
congestion estimates for the area. In this context, ``baseline''
emissions inventories refer to emissions estimates for a given year and
area that reflect rules and regulations and other measures that are
already adopted in a state's EPA approved SIP and assumed within the
attainment demonstration. Future baseline emissions inventories are
necessary to show the projected effectiveness of SIP control measures
designed to result in attainment by the applicable attainment year.
Both the base year and future year, baseline and attainment inventories
are necessary inputs to any modeling or other analyses required to
demonstrate attainment of the PM10 standard, as required by
section 189(a)(1)(B).
2. Summary of State's Submission
    The West Pinal County PM10 Plan includes a base year
(2008) inventory, and future year (2018) baseline and attainment
emissions inventories for direct PM10 in the West Pinal
County area. The State provided documentation for the emissions
inventories in Chapter 5 (``Annual Emissions Inventory'') of the West
Pinal County PM10 Plan and its two-part Appendix B (``Pinal
County PM10 Nonattainment Area Emissions Inventories for
2008 and 2018 Base Years and Design Days'', and its supporting
``Exhibits'').\16\ The emissions inventories are provided in two parts,
one representing windblown PM10 emissions on high-wind days
(including both entrained dust and windblown dust from human
activities), and the second representing PM10 emissions on
low-wind days (including dust due to human activity that stagnates near
its point of origin). The State presents the annual emissions
inventories on a tons per year basis that it later converts to a tons
or pounds per day basis for use within the attainment demonstration
modeling for the 24-hour NAAQS at issue.
---------------------------------------------------------------------------

    \16\ As needed, we will refer to the primary document as
``Appendix B'' and the secondary document as ``Appendix B-
Exhibits.''
---------------------------------------------------------------------------

    The 2018 attainment year emissions inventories reflect State of
Arizona and Pinal County rules adopted concurrently with the West Pinal
County PM10 Plan in late 2015.\17\ The Plan's emissions
reductions are based on continuing implementation of existing Federal
controls along with new state and local control measures submitted with
the Plan. The 2008 base year and projected 2018 baseline and attainment
year inventories use the most recent EPA-approved mobile source
emissions model at the time the plan was developed, MOVES2014, for
estimating on-road motor vehicle emissions.\18\ Future emissions
forecasts in the West Pinal County PM10 Plan, particularly
on-road mobile source emissions, are based primarily on

demographic and economic growth projections provided by Arizona
Department of Administration and the Maricopa Association of
Governments (MAG).\19\
---------------------------------------------------------------------------

    \17\ Please refer to Appendices G, H, and I, West Pinal County
PM10 Plan for rule adoption information.
    \18\ Appendix B, 62.
    \19\ West Pinal County PM10 Plan, 27-28, Table 3-3;
Appendix B, 120, 132, and 132 at footnote 97.
---------------------------------------------------------------------------

    In general, the term ``point sources'' typically refers to
permitted facilities that have one or more identified and fixed pieces
of equipment and emissions points. ``Area sources'' typically consist
of widespread and numerous smaller emissions sources, such as small
permitted facilities and households. The ``mobile sources'' category
refers to vehicles and is typically divided into two major
subcategories, ``on-road'' and ``non-road'' mobile sources. On-road
mobile sources include light-duty automobiles, light-, medium-, and
heavy-duty trucks, and motorcycles. In addition to tailpipe, brake, and
tire wear, on-road mobile emissions estimates for PM10 also
include re-entrained dust from vehicles driven on paved and unpaved
roads. Non-road mobile sources include aircraft and related support
vehicles, locomotives, construction equipment, agricultural equipment,
mobile equipment, and recreational vehicles.
    In the West Pinal County PM10 Plan, the State based the
point source emissions for the 2008 base year emissions inventory on
reported data from facilities using the permit file reporting programs
of the Pinal County Air Quality Control District (PCAQCD). Area
sources, as noted above, include smaller emissions sources distributed
across the nonattainment area. ADEQ estimated emissions for area
sources using established inventory methods, including publicly
available emissions factors and activity information. The State derived
activity data from national survey data, such as the Energy Information
Administration or from local sources and PCAQCD databases. Emissions
factors used for the estimates come from many sources, such as facility
and equipment source tests, compliance reports, and the EPA's
compilation of emissions factors document known as ``AP-42.''
    ADEQ calculated the 2008 base year on-road emissions inventories in
the West Pinal PM10 Plan using the MOVES2014 model and a
back-casting of 2015 modeling of vehicle travel activity data provided
by MAG.\20\ ADEQ estimated emissions inventories for non-road equipment
using the EPA's NONROAD Model, including construction and mining
equipment, industrial and commercial equipment, lawn and garden
equipment, agricultural equipment, and recreational vehicles.\21\
Locomotive emissions were estimated from EPA published emission factors
and local track-mileage, train speed, and throughput data.\22\ The
State developed aircraft and related ground support vehicle emissions
estimates in conjunction with activity data from local airports in the
region.
---------------------------------------------------------------------------

    \20\ Appendix B, 62-75.
    \21\ Appendix B, 87-90. EPA NONROAD Model, Version 2008a,
released July 2009.
    \22\ Appendix B, 96.
---------------------------------------------------------------------------

    As described previously, the State grouped direct PM10
emissions estimates in the West Pinal County PM10 Plan into
two general categories and emissions inventories, windblown dust and
human activity-based emissions; \23\ we present these inventories in
Tables 1 and 2, respectively. In general, emission inventories can be
broken into four basic categories: Stationary sources, area sources,
non-road sources and mobile sources. Instead of a summary emissions
inventory consisting of these four general categories, ADEQ provided a
more detailed 2008 base year emissions inventory. In some cases, a
source category will appear in both emissions inventories and tables.
For example, an unpaved road and an agricultural field will emit
PM10 when wind speeds become high enough to pick up and
carry disturbed earth, as well as due to vehicle and equipment traffic
on the unpaved road or agricultural activity in a field, such as
harvesting or tilling.
---------------------------------------------------------------------------

    \23\ Tables 5-1, 5-2, and 5-3, West Pinal County PM10
Plan.

 Table 1--West Pinal County PM10 Plan, Windblown Dust/Fugitive Emissions
                                Inventory
                             [Tons per year]
------------------------------------------------------------------------
                                                              2008  base
                       Source category                           year
------------------------------------------------------------------------
Developed Urban Lands.......................................       200.7
Developed Rural Lands.......................................     1,959.7
Unpaved Roads...............................................     4,688.6
Cleared Areas...............................................       398.1
Residential Construction....................................     1,302.4
Dairies.....................................................       449.6
CAFOs.......................................................       273.7
Desert Shrubland............................................    38,276.7
Agriculture.................................................    19,510.1
Commercial Construction.....................................       686.4
Other.......................................................     4,243.9
Site Development............................................       858.7
                                                             -----------
    Total...................................................    72,848.6
------------------------------------------------------------------------
Source: West Pinal County PM10 Plan, Table 5-3; Appendix B, Tables 5-31,
  5-33.

    Table 2 presents ADEQ's direct PM10 emissions inventory related to
human activity. Stationary sources are broken out into permitted
sources and fuel combustion. Area sources are disaggregated into
several source categories: Fires, open burning, unpaved parking, and
construction sites and activities. Agricultural sources are also
disaggregated into several source categories: on field harvesting, on
field tilling, confined animal feed operations (CAFOs), and dairies. In
contrast, mobile sources are included within the ``unpaved roads'' and
``paved roads'' source categories. Each of these two source categories
aggregate direct (vehicle exhaust, tire and brake wear) and fugitive
PM10 emissions from motor vehicles on unpaved and paved
roads. Finally, nonroad equipment and railroad emissions are assigned
to their own respective source categories.

  Table 2--West Pinal County PM10 Plan, Human Activity-Based Emissions
                                Inventory
                             [Tons per year]
------------------------------------------------------------------------
                                                              2008  base
                       Source category                           year
------------------------------------------------------------------------
Ag Fields--Harvesting.......................................       312.9
Ag Fields--Tilling..........................................     2,540.3
CAFOs.......................................................     2,614.3
Paved Road *................................................     1,180.7
Unpaved Road--All Road Types *..............................    45,127.8
Fuel Combustion.............................................        28.3
Fires.......................................................        19.9
Open Burning................................................        13.6
Nonroad.....................................................       121.3
Railroad....................................................        85.9
Construction................................................    12,955.3
Dairy.......................................................       186.6
Permitted Sources...........................................       781.3
Unpaved Parking.............................................       251.5
                                                             -----------
    Total...................................................    66,219.7
------------------------------------------------------------------------
Source: West Pinal County PM10 Plan, Table 5-3; Appendix B, Tables 5-31,
  5-33.
* Paved and Unpaved Road emissions estimates include direct vehicle
  emissions and fugitive dust emissions from vehicle re-entrainment.

    Tables 1 and 2 provide a summary of the West Pinal County 2008 base
year direct PM10 emissions in tons per year. Appendix B,
Chapters 3 and 5 also provide source category estimates in a pounds per
day format consistent with the 24-hour PM10 NAAQS. Where
appropriate, within the attainment demonstration, ADEQ used these daily
estimates or developed more focused daily emissions estimates to
provide the basis for the control measure analysis and the modeled
attainment demonstrations in the West Pinal County PM10
Plan.\24\ Within the windblown PM10 emissions inventory, the
largest source after desert shrubland

is agricultural emissions. Within the human activity-based emissions
inventory, the largest source is unpaved roads, followed by
construction fugitive emissions.
---------------------------------------------------------------------------

    \24\ Appendix B, chapters 3 and 5.
---------------------------------------------------------------------------

3. The EPA's Review of the State's Submission
    We have reviewed the 2008 base year emissions inventory for direct
PM10 in the West Pinal County PM10 Plan and
emissions inventory estimation methodologies used by ADEQ for
consistency with CAA requirements and EPA guidance. We address the
State's analysis for PM10 precursors in Section III.B.
    First, we find that although the 2008 base year inventory reports
annual PM10 emissions estimates, the Plan also provides and
uses daily emissions estimates within the attainment demonstration
modeling and the related modeling domain micro-emissions inventories;
therefore, the Plan is consistent with the requirement that ADEQ must
use an emissions inventory in a form consistent with the 24-hour
PM10 standard.\25\ ADEQ has provided adequate documentation
explaining how it calculated the 2008 base year emissions estimates,
both as annual and daily inventories.\26\
---------------------------------------------------------------------------

    \25\ As discussed in Section III.G Motor Vehicle Emissions
Budgets and Transportation Conformity, an annual emissions inventory
introduces difficulties with determining and presenting a motor
vehicle emissions budget.
    \26\ Chapter 5 and Appendix B of the West Pinal County
PM10 Plan.
---------------------------------------------------------------------------

    Second, we find that the 2008 base year emissions inventory in the
West Pinal County PM10 Plan used emissions models, emission
factors, and methodologies for estimating PM10 emissions
that were accurate and appropriate to the time that the Plan was
written. Also, the 2008 base year inventory for direct PM10
is comprehensive in scope and coverage. Therefore, the submitted
emissions inventory represents a comprehensive, accurate, and current
inventory of actual emissions of direct PM10 during that
year in the West Pinal County Area.
    Third, we find that ADEQ's selection of 2008 for the base year
emissions inventory is appropriate because it is chosen from one of the
three years, 2006-2008, in which the area was designated nonattainment.
The 2008 emissions inventory is representative of the sources of direct
PM10 pollution contributing to exceedances of the
PM10 NAAQS that caused the area to be designated
nonattainment. Consequently, the EPA is proposing to approve the 2008
base year emissions inventory for direct PM10 in the West
Pinal County PM10 Plan as meeting the requirements for a
base year inventory set forth in CAA section 172(c)(3).

B. PM10 Precursors

1. Statutory and Regulatory Requirements
    Section 189(e) of the Act requires that the control requirements
for major stationary sources of direct PM10 also apply to
major stationary sources of PM10 precursors, except where
the Administrator determines that such sources do not contribute
significantly to PM10 levels that exceed the standard in the
area. While CAA section 189(e) expressly requires control of precursors
from major stationary sources, subpart 4 and other CAA provisions
collectively require the control of direct PM10 and
PM10 precursors from all types of sources (i.e., stationary
sources, area sources and mobile sources) as may be needed for the
purposes of demonstrating attainment as expeditiously as practicable in
a given nonattainment area.\27\
---------------------------------------------------------------------------

    \27\ See CAA requirements for states to demonstrate attainment
``as expeditiously as practicable,'' CAA section 188(c)(1) and
section 172(a)(1).
---------------------------------------------------------------------------

    The provisions of subpart 4 of part D, title I of the CAA do not
define the term ``precursor'' for purposes of PM10, nor do
they explicitly require the control of any specific PM precursor. The
statutory definition of ``air pollutant'' in CAA section 302(g),
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.'' EPA has identified sulfur
dioxide (SO2), oxides of nitrogen (NOX), volatile
organic compounds (VOC), and ammonia (NH3) as precursors to
the formation of PM.\28\ Accordingly, a state must include emissions of
direct PM emissions and these four precursors in emissions inventories
and must control emissions from sources of all of these pollutants,
unless the state demonstrates to EPA's satisfaction that control of one
or more of these pollutants is not needed for expeditions attainment of
the NAAQS in the nonattainment area at issue.
---------------------------------------------------------------------------

    \28\ See 81 FR 58010, 58018.
---------------------------------------------------------------------------

2. Summary of the State's Submission
    Appendix B, Exhibit BXVI contains ADEQ's demonstration that
emissions of SO2, NOX, and NH3 from
existing sources in the West Pinal County nonattainment area do not
contribute significantly to PM10 levels that exceed the
NAAQS. For this analysis, ADEQ estimated the impact of these three
PM10 precursors on PM10 concentrations at two
sites, Cowtown (CWT) and Pinal County Housing (PCH), using ``worst
impact day monitored data'' from a year-long chemical mass balance
characterization (CMBC) study (Desert Southwest Coarse Particulate
Matter Study) and emissions data from the 2008 National Emission
Inventory (NEI).\29\ ADEQ evaluated these data to determine which, if
any, source categories had precursor emissions that contribute more
than 5 micrograms per cubic meter ([micro]g/m\3\) on specific design
days. \30\
---------------------------------------------------------------------------

    \29\ Clements, A.L., Fraser, M.P., Upadhyay, N., Herckes, P.,
Sundblom, M., Lantz, J., and Solomon, P.A., ``Chemical
characterization of coarse particulate matter in the Desert
Southwest--Pinal County Arizona, USA'', Atmospheric Pollution
Research, 5 (2014) 52-61.
    \30\ ADEQ focused their attainment demonstration on a set of
``design days'' and monitors that have experienced, or are conducive
to, the highest concentrations. See EPA TSD, p. 11. Two design days
were examined in ADEQ's PM10 precursor demonstration.
---------------------------------------------------------------------------

    Appendix B, Exhibit BXVI, Table BXVI-1 provides the maximum
particle mass concentration and chemical composition (i.e., crustal,
organic material, nitrate, sulfate, ammonium, other species, and
unidentified particle fractions) measured during the CMBC study for CWT
and PCH. ADEQ then calculated the percentage of each chemical
constituent to the summed total of the chemical constituent parts. ADEQ
assumed the design days for each monitor had the same relative chemical
composition as the ``worst impact day'' identified in the CMBC study.
The State calculated design day concentrations for each chemical
constituent by multiplying the study-derived percentages by a design
day concentration for CWT (244.5 [mu]g/m\3\) and PCH (178.0 [mu]g/
m\3\). The CMBC study estimated that summed nitrate, sulfate, and
ammonium impacts on the CWT and PCH monitors were 3.4 percent and 4.0
percent, respectively. These percentages suggest that 8.4 [mu]g/m\3\
and 7.2 [mu]g/m\3\ of the design day ambient PM10
concentrations at the CWT and PCH monitors resulted from emissions of
the three PM10 precursors examined.
    Next, ADEQ processed Pinal County 2008 EPA NEI reported emissions
for NOX, SO2, and NH3 to determine the
percent contribution of each source sector to the total emissions of
these pollutants for the county. \31\ ADEQ apportioned the precursor
concentrations derived above to individual source sectors based on the
relative contribution of each sector to the annual emission inventory.
Based

on this analysis, no precursor emissions from any source category
exceeded the 5 [mu]g/m\3\ threshold.\32\ The largest contributing
source category was ``On-road Mobile,'' contributing less than 3.5
[mu]g/m\3\ of PM10 from precursor emissions to either
monitor on the design days.
---------------------------------------------------------------------------

    \31\ Appendix B, Exhibit BXVI, Table BXVI-2.
    \32\ Appendix B, Exhibit BXVI, Table BXVI-3.
---------------------------------------------------------------------------

3. The EPA's Review of the State's Submission
    We identified several issues with the analysis that ADEQ presented.
First, SO2, NOX, VOC, and ammonia are precursors
to the formation of PM10. ADEQ does not address VOC
emissions in its analysis; therefore, we cannot evaluate whether
sources of VOC emissions contribute significantly to PM10
levels that exceed the NAAQS in the West Pinal County PM10
nonattainment area.
    Second, it is unclear whether the chemical composition values
presented in Appendix B, Exhibit BXVI, Table BXVI-1 reflect one maximum
day sample, or the maximum chemical composition measured for each
individual component during the entire CMBC study. If the latter
approach was used, then the resulting percentages would not reflect
percentages measured on any actual exceedance day and could
overrepresent or underrepresent the various chemicals when compared to
actual exceedance days. If the chemical composition values represent
one maximum day sample, then: (a) The individual components listed in
Table BXVI-1 when totaled together should equal that day's total mass,
which they do not; and (b) this would only represent a single day--
therefore, a single type of exceedance day. ADEQ modeled two
meteorological scenarios causing exceedances, high wind conditions and
stagnant or low wind conditions. The emission sources affecting the
PM10 composition would vary between these two scenarios,
making use of a single maximum value at each site for each chemical
component likely insufficient. Therefore, ADEQ's approach of assuming
the chemical composition of the two design days match those reported in
the study likely does not address all conditions affecting
nonattainment for the area.
    Third, ADEQ applied the 5 [mu]g/m\3\ threshold from the Serious
PM10 nonattainment area addendum to the General
Preamble.\33\ The Serious area addendum states that, for purposes of
evaluating best available control measures (BACM), a source category
will be presumed to contribute significantly to a violation of the
NAAQS if its PM10 impact at the location of the expected
violation would exceed 5 [mu]g/m\3\. This guidance is not precursor
guidance and was intended to apply to the total impact of a source
category (including direct PM and precursor emissions). It is not clear
from the State's submission why the application of this threshold to
the impact of precursor emissions from individual source categories is
an appropriate method of evaluating the significance of PM10
precursor emissions for the West Pinal County PM10
nonattainment area.\34\
---------------------------------------------------------------------------

    \33\ Appendix B, Exhibit BXVI, BXVI-2. See 59 FR at 42011.
    \34\ For more recent guidance on precursor significance, see
Memorandum from Scott Mathias, Acting Director, Air Quality Policy
Division and Richard Wayland, Director, Air Quality Assessment
Division, ``Fine Particulate Matter (PM2.5) Precursor
Demonstration Guidance'' (May 30, 2019).
---------------------------------------------------------------------------

    Finally, ADEQ used an annual inventory to partition the source
category contribution to PM10. High wind affected days would
likely have a different composition of sources than what would be
reflected in an annual inventory, potentially by a substantial margin.
ADEQ did not address this issue, and used the annual inventory
composition to represent all exceedance days.
    The State has not adequately shown that PM10 precursors
do not contribute significantly to concentrations above the NAAQS in
the West Pinal County PM10 nonattainment area. As described
elsewhere in this notice, due to the deficiencies with the State's
precursor analysis, the State has not shown that it was unnecessary to
regulate emissions of precursors in its RACM and modeled attainment
demonstration. As explained in Section III.C., the State has only
evaluated sources of direct PM emissions within the West Pinal County
PM10 Plan. The EPA anticipates that ADEQ could develop an
improved precursor analysis for the area, and this analysis may
ultimately confirm that it is not necessary to regulate one or all of
the PM10 precursors; however, we find that the precursor
analysis submitted with the Plan does not provide a sufficient basis
for that conclusion.
    In conclusion, because of the omissions and uncertainties in ADEQ's
PM10 precursor analysis, we are unable to determine whether
precursor emissions contribute significantly to PM10 levels
that exceed the NAAQS in the West Pinal County nonattainment area.
Consequently, we are proposing to disapprove the precursor
demonstration in the West Pinal County PM10 Plan because the
demonstration is inadequate to show that emissions reductions from all
PM10 precursors do not contribute significantly to
PM10 levels exceeding the NAAQS, as required by CAA Section
189(e). As explained in section III.C, the deficiencies in the State's
precursor analysis mean that the State failed to establish in its RACM/
RACT analysis that it was unnecessary to regulate PM10
precursor emissions.

C. Reasonably Available Control Measures Demonstration

1. Statutory and Regulatory Requirements
    CAA section 172(c)(1) requires that each attainment plan provide
for the implementation of all RACM/RACT as expeditiously as practicable
(including such reductions in emissions from sources in the area
through implementation of reasonably available control technology) and
for attainment of the NAAQS. Consistent with section 189(a)(1)(C), each
state with a Moderate PM10 nonattainment area is required to
submit provisions to assure implementation of reasonably available
control measures no later than 4 years after the date of designation of
the area. Taken together, these CAA provisions require that Moderate
area attainment plans must provide for the implementation of RACM and
RACT in the nonattainment area as expeditiously as practicable but no
later than 4 years after designation.
    Section 189(a)(1)(B) of the CAA requires states to demonstrate
attainment of the PM10 standard by the applicable attainment
date (or demonstrate that attainment by such date is impracticable) and
Section 188(c)(1) requires that the attainment date for a Moderate area
shall be as expeditiously as practicable, but no later than the end of
the sixth calendar year after the year of the nonattainment area's
designation.
    To address this requirement to adopt all RACM/RACT and meet the
PM10 NAAQS as expeditiously as practicable, states should
consider all potentially reasonable control measures for source
categories in the nonattainment area to determine whether they are
reasonably available for implementation in that area and whether they
would, if implemented individually or collectively, advance the area's
applicable attainment date by one year or more.\35\ Any measures that
are necessary to meet these requirements that are not either federally
promulgated, or part of the state's SIP, must be submitted in
enforceable form

as part of the state's nonattainment plan SIP submission for the area.
---------------------------------------------------------------------------

    \35\ 44 FR 20372 (April 4, 1979) and 57 FR 13498 (April 16,
1992).
---------------------------------------------------------------------------

    The EPA has provided guidance interpreting the RACM requirement in
the General Preamble for the Implementation of the Clean Air Act
Amendments of 1990 (``General Preamble''). This guidance includes the
following elements and concepts: A recommended list of potential
PM10 measures for states to consider; \36\ an emphasis on a
state's evaluation of the technological and economic feasibility of
potential control measures to determine if such measures are reasonably
available for implementation in a given nonattainment area; an
expectation that the state will provide a reasoned explanation for a
decision not to adopt a given control measure, including a review of
any control measures recommended to the state during public comment or
public hearing; and, a discussion that in some cases partial
implementation of an emissions reduction program may be considered RACM
when full implementation would be infeasible within the given Moderate
area timeframe.\37\
---------------------------------------------------------------------------

    \36\ 57 FR 18070.
    \37\ 57 FR 13540, 13541.
---------------------------------------------------------------------------

2. Summary of the State's Submission
    For the West Pinal County PM10 Plan, ADEQ worked through
a process to identify and evaluate potential RACM/RACT that could
contribute to expeditious attainment of the PM10 NAAQS in
the West Pinal County nonattainment area. Chapter 6 of the West Pinal
County PM10 Plan provides an overview and description of the
Plan's constituent control measures. ADEQ's RACM/RACT analysis for the
PM10 standard is described in Appendix F--RACM Analysis for
the West Pinal County PM10 Nonattainment Area (``Appendix
F''). Appendix F contains summary analyses of potential control
measures for emissions reduction opportunities, as well as the economic
and technological feasibility and comparability with control
requirements in other states and localities.
    As a first step in the RACM/RACT analysis, ADEQ prepared a detailed
inventory of direct PM10 emissions sources to identify
source categories from which emissions reductions would contribute to
attaining the PM10 standard.\38\ In this analysis, ADEQ
identified point sources, unpaved roads and agriculture on tribal land,
dairy operations, nonroad vehicles, residential fuel combustion, and
open burning as insignificant sources of emissions in the area.\39\
Then, ADEQ identified agricultural operations, confined animal feeding
operations, fugitive dust from cleared area and unpaved parking lots,
construction fugitive dust, and re-entrained dust from paved and
unpaved roads as significant sources in the nonattainment area and
determined a list of available control measures. ADEQ determined that a
source category was significant if those sources contributed more than
5 [mu]g/m\3\ on a 24-hour basis on a given design day. Conversely, ADEQ
determined that source categories contributing less than the 5 [mu]g/
m\3\ threshold were insignificant; furthermore, ADEQ determined these
insignificant sources would not advance attainment of the NAAQS, given
their small collective contribution to nonattainment.\40\ Finally, ADEQ
evaluated the efficacy, cost, and technical feasibility of these
identified control measures within the nonattainment area.\41\ As part
of this review, ADEQ also compared the control requirements of its
proposed rules with those requirements in other PM10
nonattainment areas or similar state and local provisions.\42\ ADEQ did
not identify sources or analyze potential RACM/RACT for PM10
precursors because it concluded that such precursors did not contribute
significantly to a violation of the NAAQS.
---------------------------------------------------------------------------

    \38\ Appendix F, Chapters 2 and 3.
    \39\ Appendix F, 4-12.
    \40\ Appendix F, Chapter 2 and Table 1.
    \41\ Appendix F, Chapters 2-4.
    \42\ Appendix F, Chapter 4; Exhibit F-I, Available Measures;
Exhibit F-II, Construction Comparison; Exhibit F-III, Agricultural
Comparison; and, Exhibit F-IV, Fugitive Dust Comparison.
---------------------------------------------------------------------------

    With this process, ADEQ attempted to evaluate and analyze the
universe of potential RACM/RACT level controls for sources of direct
PM10 emissions and identify the subset of control measures
that were available to include within the West Pinal County
PM10 Plan. ADEQ identified a set of control measures that it
determined would be sufficient to enable the area to attain by December
31, 2018, and additional controls that it determined were not necessary
for attainment or RFP to serve as contingency measures.\43\ ADEQ based
this conclusion on: (1) The practical feasibility of adopting control
measures over the latter half of 2015 with the State's desired
implementation date of no later than January 1, 2016; and (2) the
ability of these control measures to produce immediate emissions
reductions and contribute to attainment of the PM10 NAAQS by
2018.\44\ As discussed earlier, the State submitted the following
control measures with the West Pinal County PM10 Plan: The
AgBMP Rules for Pinal County, the Pinal County Fugitive Dust Rule, and
the Pinal County Construction Dust Rule. ADEQ relied only on the
following portions of the AgBMP Rules for Pinal County to meet the
RACM/RACT requirements and demonstrate attainment of the
PM10 standard: AgBMP rule R18-2-610 and -610.03, commercial
farms; AgBMP rule R18-2-611 and -611.03, commercial animal operations
(except for dairy operations); and R18-2-612 and -612.01, irrigation
districts.\45\
---------------------------------------------------------------------------

    \43\ West Pinal County PM10 Plan, Chapter 7; Table 7-
4; Appendix D, Table D5-1.
    \44\ Appendix F, 29, 47, 51.
    \45\ West Pinal County PM10 Plan, Chapters 6 and 7.
---------------------------------------------------------------------------

    ADEQ did not provide a complete or systematic analysis of whether
the control measures it did not adopt based on concerns about a lack of
immediate emission reduction effect, if taken together, would advance
the area's attainment date. Nonetheless, ADEQ did adopt those control
measures, implemented them over the 2016-2018 timeframe, and allocated
them to serve as contingency measures in the Plan. ADEQ designated the
portion of the AgBMP Rules for Pinal County applicable to dairy
operations (R18-2-611 and -611.03), along with the Pinal County
Fugitive Dust Rule and the Pinal County Construction Dust Rule, as
contingency measures because these rules provided additional emissions
reductions not relied upon within the Plan's attainment
demonstration.\46\
---------------------------------------------------------------------------

    \46\ West Pinal County PM10 Plan, Chapter 6; Chapter
7, Table 7-4.
---------------------------------------------------------------------------

3. The EPA's Review of the State's Submission
    As described above, ADEQ evaluated a wide range of potentially
available measures for the West Pinal County PM10 Plan. ADEQ
identified portions of the AgBMP Rules for Pinal County as RACM/RACT
and the State adopted them to provide for attainment of the
PM10 standard.\47\ The remaining adopted control measures,
some of which were identified as significant sources and potential
RACM/RACT, were assigned to provide for contingency measures within the
Plan.\48\ In sum, all source categories identified as significant were
covered by controls either as a control measure for attainment, or as
contingency measures, and implemented over the 2016-2018 timeframe. As
has been confirmed by subsequent monitoring data, however,

these adopted control measures were insufficient to attain the
PM10 NAAQS by the applicable attainment date, in part
because the State overestimated the effectiveness of the RACM/RACT-
designated adopted controls. As an example, ADEQ assumed high and
insufficiently conservative compliance rates for agricultural
operations that had either no previous experience implementing control
measures, or little to no reliable documented compliance history. We
review the State's analysis and attainment demonstration in Section
III.D and provide detailed discussion in the Technical Support Document
(TSD).
---------------------------------------------------------------------------

    \47\ West Pinal County PM10 Plan, Chapters 6 and 7.
    \48\ West Pinal County PM10 Plan, Chapter 6; Chapter
7, Table 7-4.
---------------------------------------------------------------------------

    The Plan described the adopted control measures and concluded that
a subset was reasonable and would achieve the NAAQS by the attainment
date; therefore, the State concluded that the RACM/RACT-designated
subset of adopted control measures constituted the necessary RACM/RACT
for the area.\49\ The State adopted several additional measures beyond
the RACM/RACT measures to serve as contingency measures in the Plan. If
the RACM/RACT-designated adopted controls actually sufficed to achieve
attainment, then these control measures could have constituted
sufficient RACM, as additional measures beyond those necessary for
attainment need not necessarily be considered as RACM/RACT.\50\ Because
the adopted controls designated as RACM/RACT in the West Pinal County
PM10 Plan were insufficient, however, to achieve attainment,
due in part to overestimates of the control efficiency of these rules,
we find that the State terminated its RACM/RACT analysis prematurely.
The control measures reserved for contingency measures that the State
did not include as RACM/RACT should have been included and justified as
RACM. Furthermore, because the State's determination regarding
PM10 precursors failed to demonstrate that precursors do not
contribute significantly to a violation of the NAAQS, the State remains
obligated to demonstrate that additional PM10 precursor
control measures are not required RACM/RACT.
---------------------------------------------------------------------------

    \49\ Appendix F, Chapter 4.
    \50\ See 81 FR 58010, 58035. Although such controls should be
evaluated to determine if their adoption could advance attainment.
---------------------------------------------------------------------------

    Despite the RACM/RACT-designated rules and contingency measures
adopted and implemented by the State, we find that the State failed to
adopt RACM/RACT sufficient to achieve the PM10 NAAQS, due in
part, to overestimating the control effectiveness of these RACM/RACT
control measures. Our conclusion is confirmed by the failure of the
Plan's adopted and designated measures to result in attainment of the
PM10 NAAQS by the applicable attainment date of December 31,
2018. Because the adopted controls were insufficient to meet the
PM10 NAAQS by the attainment date, and the State excluded
source categories, including sources of precursors, from its RACM/RACT
demonstration without sufficient justification, we propose to
disapprove the RACM/RACT demonstration in the West Pinal County
PM10 Plan and determine that the Plan does not provide for
the implementation of all RACM/RACT as required by CAA section
172(c)(1) and section 189(a)(1)(C).

D. Attainment Demonstration

1. Statutory and Regulatory Requirements
    Section 189(a)(1)(B) of the CAA requires that a plan for a Moderate
PM10 nonattainment area include a ``demonstration (including
air quality modeling) that the plan will provide for attainment [of the
PM10 NAAQS] by the applicable attainment date.'' An
attainment demonstration consists of several elements including
technical analyses, such as base year and future year modeling, to
locate and identify sources of emissions that are contributing to
violations of the PM10 NAAQS within the nonattainment area
(i.e., analyses related to the emissions inventory for the
nonattainment area and the emissions reductions necessary to attain the
standard). Section 188(c)(1) of the CAA requires Moderate areas to meet
the PM10 standard as expeditiously as practicable, but no
later than the sixth calendar year from the area designation.
    In addition to reviewing the attainment demonstration modeling and
related analyses, we evaluate the Plan's control strategy and the
efficacy of the Plan's adopted controls to meet the PM10
NAAQS by the applicable date.
2. Summary of the State's Submission
    ADEQ applied a form of proportional roll back and dispersion
modeling using a micro-emissions inventory method to model attainment
of the PM10 NAAQS. ADEQ modeled two meteorological scenarios
causing ambient air values in excess of the 24-hour PM10
NAAQS of 150 [mu]g/m\3\, high wind conditions and stagnant or low wind
conditions, at a representative subset of the monitoring sites in the
nonattainment area.\51\ Under ``stagnation'' conditions, wind speeds
are typically below 3 mph and particles accumulate in the air without
any meteorological reprieve. Under ``high wind'' conditions, elevated
wind speeds (e.g., over 12 mph) generate dust from disturbed soil
surfaces, elevating PM10 concentrations. Each selected
monitoring site in each modeling scenario had design day specific
micro-emissions inventories consistent with the chosen areal modeling
domain and application. ADEQ calculated the 2008 Base, 2018 Base, and
2018 Attainment micro-emissions inventories for the given requirements
of the modeling application at the respective monitoring site domain
and meteorological day scenario.
---------------------------------------------------------------------------

    \51\ West Pinal PM10 Plan County, Section 7.1.
---------------------------------------------------------------------------

    The State's attainment demonstration approach is described in the
Plan within the following documents: Chapter 7, ``Attainment
Demonstration and Reasonable Further Progress''; Appendix A, ``Pinal
County PM Inventory Preparation Plan'' (``IPP''); Appendix B, ``Pinal
County PM10 Nonattainment Area Emissions Inventories for
2008 and 2018 Base Years and Design Days'' (``Modeling EI''); Appendix
C, ``Pinal County PM10 Nonattainment Area Source
Apportionment Modeling for 2008 and 2018 Base Scenario Design Days''
(``Modeling TSD''); and, Appendix D, ``Pinal County PM10
Nonattainment Area 2018 Attainment Demonstration and Controlled
Emissions Inventories.''
    The West Pinal County PM10 Plan discusses the control
strategy within Chapter 6 of the Plan and in more detail within
Appendix D of the Plan.
a. Modeling
    As noted, the West Pinal County PM10 Plan's attainment
demonstration considers two specific problems contributing to
nonattainment of the PM10 standard in West Pinal County: (1)
PM10 emissions from windblown dust and human activity on
days with elevated wind speeds; and (2) PM10 emissions from
human activity, particularly on days with very low wind or ``stagnant''
meteorological conditions.
     ADEQ developed a high wind day scenario for Cowtown,
Maricopa, Pinal County Housing, and Stanfield monitors and surrounding
area micro-emissions inventories. Each monitor has its own two domain
micro-emissions inventory for modeling: High wind hours/windblown dust;
and, low wind hours/activity-based emissions. The high wind scenario
used a proportional rollback approach that accounts for the timing

and geographic location of emissions contributing to NAAQS
exceedances.\52\
---------------------------------------------------------------------------

    \52\ The term ``rollback'' refers to the assumption that the
PM10 concentrations are directly proportional to
emissions. To predict the ambient effect of an emissions change, the
concentration can be scaled, or ``rolled back,'' by the same
percentage by which emissions are reduced. In ``proportional
rollback,'' each source category is rolled back separately, since
emissions from each will have a different level of control, and in
general a different degree of dispersion. As in simple rollback, the
ambient contribution of each individual source category scales with
its emissions. For the ``weighted proportional rollback,'' source-
to-monitor distance was accounted for via an inverse distance factor
(1/d). For example, a source with only small emissions may
nevertheless have a large contribution to the concentration if it
was very close to the monitor. A change in a source's emissions
causes a change in total concentration in proportion to that
source's contribution to that particular monitor.
---------------------------------------------------------------------------

     ADEQ developed a stagnation day scenario for Cowtown,
Pinal County Housing, and Stanfield monitors and surrounding area
micro-emissions inventories. The stagnant day scenarios used dispersion
modeling from the American Meteorological Society (AMS)/EPA Regulatory
Model (AERMOD). ADEQ chose design days from the fall season, September
through November 2008 for this analysis.
b. Control Strategy for Attainment
    ADEQ relied on the following portions of the AgBMP Rules for Pinal
County to provide for attainment of the PM10 standard: R18-
2-610 and -610.03, commercial farms; AgBMP rule R18-2-611 and -611.03,
commercial animal operations (except for dairy operations); and, R18-2-
612 and -612.01, irrigation districts.\53\ Tables 3 and 4 show the
annual nonattainment area emissions inventories for the 2018 baseline
estimate and the 2018 attainment estimate by source category and the
control strategies' predicted emissions reductions. Within the
windblown fugitive dust emissions inventories, ADEQ predicted almost
all the emission reductions, 93 percent, to come from soil
stabilization control measures on agricultural land. Within the
activity-based emissions inventories, ADEQ predicted most of the
emission reductions, 87 percent, to come from control measures applied
to unpaved road operations on private agricultural land and canal
roads; the remainder of predicted emission reductions come from control
measures to reduce PM10 emissions from on-field agriculture
and animal feeding operations. As noted, the regulatory vehicle for
these emissions reductions is the AgBMP rule provisions the State
relied on to provide for attainment of the PM10 standard and
to implement RACM/RACT in the area.
---------------------------------------------------------------------------

    \53\ West Pinal County PM10 Plan, Chapters 6 and 7.

    Table 3--Windblown Dust/Fugitive Emissions, 2018 Base and Attainment Emissions Inventories With Estimated
                                               Emission Reductions
                                                      [tpy]
----------------------------------------------------------------------------------------------------------------
                     Source category                         Base 2018     Attainment 2018   Emission reductions
----------------------------------------------------------------------------------------------------------------
Developed Urban Lands...................................           248.1             248.1  ....................
Developed Rural Lands (low density).....................         1,959.7           1,959.7  ....................
Unpaved Roads...........................................         4,653.0           3,803.1                 849.9
Cleared Areas...........................................           457.0             457.0  ....................
Residential Construction................................           837.5             837.5  ....................
Dairies.................................................           449.6             449.6  ....................
CAFOs...................................................           155.2             125.3                  29.9
Desert Shrubland........................................  ..............  ................  ....................
Agriculture.............................................        19,510.1           7,122.0              12,388.1
Commercial Construction.................................           441.4             441.4  ....................
Other...................................................         4,243.9           4,243.9  ....................
Site Development........................................           552.2             552.2  ....................
                                                         -------------------------------------------------------
    Total...............................................        33,507.7          20,239.8              13,267.9
----------------------------------------------------------------------------------------------------------------
Source: West Pinal County PM10 Plan, Table 5-3; Appendix B, Tables 5-31, 5-32, 5-33, 5-34.

    Table 4--Activity Based Emissions, 2018 Base and Attainment Emissions Inventories With Estimated Emission
                                                   Reductions
                                                      [tpy]
----------------------------------------------------------------------------------------------------------------
                     Source category                         Base 2018     Attainment 2018   Emission reductions
----------------------------------------------------------------------------------------------------------------
Ag--Harvesting..........................................           312.9             207.1                 105.8
Ag--Tilling.............................................         2,540.3           1,658.0                 882.3
CAFOs...................................................         1,620.6           1,369.2                 251.4
Paved Road *............................................         1,408.0           1,408.0  ....................
Unpaved Road *..........................................        45,105.3          37,186.4               7,918.9
Fuel Combustion.........................................            34.9              34.9  ....................
Fires...................................................            22.2              22.2  ....................
Open Burning............................................            16.8              16.8  ....................
Nonroad.................................................           144.4             144.4  ....................
Railroad................................................            45.4              45.4  ....................
Construction............................................         8,499.8           8,499.8  ....................
Dairy...................................................           184.0             184.0  ....................
Permitted Sources.......................................           781.3             781.3  ....................
Unpaved Parking.........................................           251.5             251.5  ....................
                                                         -------------------------------------------------------
    Total...............................................        60,967.4          51,809.0               9,158.4
----------------------------------------------------------------------------------------------------------------
Source: West Pinal County PM10 Plan, Table 5-3; Appendix B, Tables 5-31, 5-32, 5-33, 5-34
* Paved and Unpaved Road emissions estimates include direct vehicle emissions and fugitive dust emissions from
  vehicle re-entrainment.

    The State adopted and pre-implemented control measures to meet the
contingency measures requirement within the Plan: The portion of the
AgBMP Rules for Pinal County applicable to dairy operations (R18-2-611
and -611.03), along with the Pinal County Fugitive Dust Rule and the
Pinal County Construction Dust Rule.\54\ We address the contingency
measures requirement of the Act more completely in Section III.F, where
we point out that pre-implemented contingency measures are not
approvable under CAA section 172(c)(9). Here, we mention the control
measures, adopted and subsequently implemented as contingency measures,
to emphasize two points: (1) Given the shortfall in attaining the
PM10 NAAQS, these control measures designated for
contingency should have been evaluated and designated RACM/RACT, as we
discussed in Section III.C; and (2) despite implementing the RACM/RACT
control measures for attainment and the designated contingency
measures, the West Pinal County area still failed to attain the
PM10 NAAQS, by a large margin.
---------------------------------------------------------------------------

    \54\ West Pinal County PM10 Plan, Chapter 6; Chapter
7, Table 7-4.
---------------------------------------------------------------------------

3. The EPA's Review of the State's Submission
    As previously discussed, the EPA issued a finding that the West
Pinal County area failed to attain the PM10 NAAQS by the
outermost statutory attainment date of December 31, 2018.\55\ In
addition to our previous regulatory review of the air monitoring data
from 2016-2018, detailed in our June 24, 2020 notice, we reviewed
ambient air monitoring data collected from 2006-2018 to examine
PM10 values over time and recent trends over the 2016-2018
control strategy period of Plan implementation. Our detailed review of
PM10 data is included in our TSD provided in the docket for
this proposal. We provide two general conclusions from our data review.
---------------------------------------------------------------------------

    \55\ 85 FR 37756.
---------------------------------------------------------------------------

    First, when considering the number of exceedances of the
PM10 standard, the data show that the West Pinal County
monitoring sites have consistently measured many exceedances in every
year between the start of the base year period, 2006-2008, and in 2018,
the attainment year. While the number of exceedances each year has
generally and gradually decreased over time, there is no clear evidence
of a sustained decrease in recent years as ADEQ implemented control
measures. For example, over the 2016 through 2018 period that would
have been relevant to attainment by December 31, 2018, the annual
number of exceedances of the 24-hour PM10 NAAQS ranged from
29 to 38.\56\ The form of the NAAQS allows for no more than one
exceedance per year, averaged over a three year period. Furthermore,
all eight monitors in the West Pinal County nonattainment area showed
violations of the PM10 NAAQS as determined by their 2018
design values.\57\
---------------------------------------------------------------------------

    \56\ See Table 2 in the TSD.
    \57\ See Table 1 in the TSD.
---------------------------------------------------------------------------

    Second, design value trends show that the number of expected
exceedances remain well above the PM10 NAAQS of one
exceedance per year. The high concentrations and number of exceedances
clearly show that PM10 concentrations well above the level
of the NAAQS (150 [mu]g/m\3\) continue to be a major air quality
problem in the West Pinal County nonattainment area despite the
implementation of control measures meant to reduce PM10
levels. For example, the design concentration for 2016-2018, the period
in which values should be at or under 150 [mu]g/m\3\ to show attainment
by 2018, is 403 [mu]g/m\3\, or 269 percent of the standard.\58\
---------------------------------------------------------------------------

    \58\ See Table 3 and further discussion in Section II.B of the
TSD.

                        Table 5--Three-Year PM10 Monitoring Data Statistics for the Cowtown and Hidden Valley Monitoring Sites a
--------------------------------------------------------------------------------------------------------------------------------------------------------
         3-Year period           2006-2008  2007-2009  2008-2010  2009-2011  2010-2012  2011-2013  2012-2014  2013-2015  2014-2016  2015-2017  2016-2018
--------------------------------------------------------------------------------------------------------------------------------------------------------
Design Concentration ([mu]g/           916        653        539       1064       1064       1064        521        510    \b\ 357    \b\ 303        403
 m\3\).........................
3-year Design Value............      201.2      139.8       86.1       60.7         63       75.7         64       50.5   \b\ 38.3   \b\ 29.8       32.8
--------------------------------------------------------------------------------------------------------------------------------------------------------
Sources: EPA AQS Quick Look Report, December 10, 2020, and EPA AQS Design Value Report, December 10, 2020. The design concentration for these sites is
  the 4th highest 24-hour concentration measured over each three-year period, as detailed in Section 6.3.1 of the PM10 SIP Development Guideline, EPA-
  450/2-86-001 (June 1987).
\a\ Data collected prior to 2016 were collected from the Cowtown monitoring site; data since 2016 were collected at the Hidden Valley monitoring site,
  as described in our TSD, page 6, within the docket for this rulemaking.
\b\ The EPA's relocation approval letter stated that the data from Cowtown and Hidden Valley would be combined to form one continuous data record for
  design value calculations. Consequently, the 2014-2016 and 2015-2017 design values are each a composite data record consisting of 2014 and/or 2015
  data from the Cowtown monitoring site, and 2016 and/or 2017 data from the Hidden Valley monitoring site, as applicable.

    The West Pinal County 2015 PM10 design value was 50.5
exceedances. For the area to meet the PM10 standard by 2018,
it could not have more than three exceedances of the PM10
NAAQS across the three years, 2016-2018, to show a design value of 1.0
exceedances, averaged over three years. Instead, the Plan's control
strategy resulted in the following number of primary exceedances: 30 in
2016; 38 in 2017; and 29 in 2018.\59\ Not only did the Plan's control
strategy fail to produce the effect intended in 2016, the designated
control strategy rules and pre-implemented contingency measures failed
to reduce PM10 exceedances to a level needed to attain the
PM10 standard by December 31, 2018.
---------------------------------------------------------------------------

    \59\ TSD, Table 2; EPA AQS Quick Look Report, December 10, 2020,
in the docket for this rulemaking action.
---------------------------------------------------------------------------

    Given the ambient monitoring data unequivocally indicate that the
Plan was insufficient to achieve attainment by the 2018 attainment
date, we do not provide an exhaustive evaluation of the attainment
demonstration analyses in the West Pinal County PM10 Plan.
Instead, we focused our review on two major deficiencies that preclude
our approval of this Plan element. Our review of these two deficiencies
is illustrative of the insufficiently conservative analyses or
assumptions underlying the Plan's failed attainment demonstration.
Specifically, we evaluated the ``design days'' ADEQ selected to conduct
the modeling exercises and the specific design day micro-emissions
inventories and rule control effectiveness assumptions ADEQ made to
model the Plan's control strategy within the 2018 attainment modeling
analyses. Next, we provide a short summary of our review. We also
provide a more detailed review in our TSD.
    First, we find the design days that ADEQ selected for modeling the
Cowtown monitor under stagnation

conditions, and several monitors under high wind conditions, were
chosen with inconsistent criteria and/or have data inaccuracies. In
turn, these inconsistencies and inaccuracies led to design day
concentration values that were likely too low to address adequately the
range of exceedances experienced in the nonattainment area. For
example, in selecting the stagnation scenario design day for Cowtown,
ADEQ limited selection to fall 2008 (September to November) exceedance
days despite the higher PM10 concentrations and a comparable
number of exceedance days in the spring season (March to May).
Ultimately, the selected 2008 design day was the 68th highest out of
the 137 total low wind/stagnation exceedance days identified by the
State (i.e., approximately 49% of the low wind/stagnation exceedance
days had higher concentrations than the design day selected).\60\ This
middle range day was insufficiently conservative and was inadequate to
represent the attainment issues during stagnation conditions and to
address the range and severity of exceedances experienced at CWT.\61\
---------------------------------------------------------------------------

    \60\ ``Low wind/stagnation exceedance days'' for purposes of
this document are the exceedance days that remain once days
identified by ADEQ as high wind day exceedances in IPP, Appendix C,
Table C-1 are removed. See ``Cowtown 2008 Exceedances.xlxs'' in the
docket for this action.
    \61\ See Section III.B.1. of the TSD for our complete review of
design day selection for stagnation scenario at the Cowtown monitor.
Also, see Section III.B.2 of the TSD for our complete review of
design day selection for the high wind scenario.
---------------------------------------------------------------------------

    Second, we conclude that several data inputs and assumptions
associated with modeling the control strategy were unsupported,
overstated, or insufficiently conservative leading to an overestimate
of the overall efficacy of the control strategy within the attainment
demonstration. Specifically, in calculating the control effectiveness
of the rules in the control strategy, two component assumptions or
estimates were the primary cause of this overestimate: (1) Rule
effectiveness, i.e., the percentage of compliant facilities; and, (2)
aggregate or net best management practices (BMP) control efficiencies.
For example, we found that despite limited or no compliance data, the
lack of compliance assistance program efficacy figures, the lack of
automatic reporting requirements, and little to no farm experience
implementing BMPs, ADEQ assumed high compliance rates with the AgBMP
rule; in turn, this unjustifiably inflated the overall control
effectiveness calculations. In addition, we found that the domain
modeling micro-emissions inventory estimates that ADEQ derived from
this limited BMP implementation data were not appropriately documented
or supported and were insufficiently conservative due to overly
optimistic or simplifying assumptions used to aggregate BMP control
efficiency estimates, such as assuming that farms will either choose
not to operate or will routinely implement higher cost and higher
control efficiency BMPs on high risk days. Consequently, ADEQ assumed
farms reduced emissions from cropland operations and unpaved roads to a
greater extent than what could be supported by the documentation in the
Plan.\62\
---------------------------------------------------------------------------

    \62\ See Section III.C. of the TSD for our complete review of
control effectiveness estimates.
---------------------------------------------------------------------------

    Based on our evaluation of the design days and modeling and control
effectiveness assumptions in the Plan, we find that these several
deficiencies in the analyses preclude approval of the attainment
demonstration. In addition, after reviewing past and recent
PM10 data against the West Pinal County PM10
Plan's attainment demonstration predictions, we conclude that:
     There is no clear evidence of a sustained decrease in the
number of exceedances in recent years as control measures have been
implemented (2015-2018);
     PM10 concentrations well above the level of the
24-hour PM10 NAAQS (150 [mu]g/m\3\) continue to be a major
air quality problem in the West Pinal County nonattainment area despite
the implementation of control measures designed to reduce
PM10 levels thus far; and
     The Plan's control strategy, whether considered as adopted
RACM/RACT or as the entire suite of rules submitted with the Plan, was
inadequate to attain the PM10 NAAQS by December 31, 2018, as
evidenced by the ambient PM10 data.
    Consequently, we propose to disapprove the modeled attainment
demonstration in the West Pinal County PM10 Plan because it
does not meet the requirements of CAA section 189(a)(1)(B) and section
188(c)(1).

E. Reasonable Further Progress Demonstration

1. Statutory and Regulatory Requirements
    The requirement for RFP in PM10 nonattainment areas is
specified in CAA section 172(c)(2) and is described in the General
Preamble.\63\ Under CAA section 171(1), RFP is defined as meaning such
annual incremental reductions in emissions of the relevant air
pollutant as are required under part D (``Plan Requirements for
Nonattainment Areas'') of the CAA or as may reasonably be required by
the EPA for the purpose of ensuring attainment of the applicable NAAQS
by the applicable date. In addition, CAA section 189(c)(1) requires
quantitative milestones that demonstrate RFP and must be achieved every
3 years until the nonattainment area is redesignated to attainment,
beginning 4.5 years after a Moderate area's designation to
nonattainment of the PM10 NAAQS.\64\ Therefore, Moderate
area plans should contain quantitative milestones for 4.5 and 7.5 years
after designation. These quantitative milestones should be constructed
so that they can be tracked, quantified and/or measured adequately, and
provide for an objective evaluation of RFP toward attainment of the
NAAQS, particularly as part of milestone reporting.\65\
---------------------------------------------------------------------------

    \63\ 57 FR at 13539.
    \64\ Ibid.
    \65\ 81 FR 58063-64.
---------------------------------------------------------------------------

2. Summary of the State's Submission
    The West Pinal County PM10 Plan discusses how the Plan
provides for RFP in Section 7.2 and Appendix D and provides visual
representation in Figure 7-1 and Figure D 5-1.\66\ For the purposes of
calculating annual increments of emission reductions for RFP, ADEQ
assumed a linear ``glidepath'' with equal annual emissions reductions
over the 2016-2018 implementation timeframe. This annual increment
representing RFP is 7,475 tons per year.\67\ The implementation of the
Plan's control strategy is projected to produce almost all the needed
emissions reductions in the first year, 2016, with slight and
incremental emission reductions to follow in 2017 and 2018. Because
ADEQ projected that most of the emissions reductions would come in the
first year, the projected emissions were below the ``glidepath'' and
ADEQ concluded that RFP was demonstrated.
---------------------------------------------------------------------------

    \66\ West Pinal County PM10 Plan, 99 and Figure 7-1,
101; Appendix D, 45.
    \67\ West Pinal County PM10 Plan, 100. Expected
emission reductions from 2015 to 2018, 22,426 tons per year, are
divided into 3 annual increments of 7,475 tons per year.
---------------------------------------------------------------------------

3. The EPA's Review of the State's Submission
    Based in part on our review of the 2016-2018 ambient data and in
part on the flaws identified in the West Pinal County PM10
Plan attainment demonstration, we find that ADEQ did not adequately
provide for annual increments of emissions reductions needed to attain
the PM10 NAAQS by 2018. Because the West Pinal County

PM10 plan failed to achieve attainment by the attainment
date, the RFP demonstration based on the rate by which these reductions
were to occur is also necessarily deficient. This was borne out by the
monitoring data; no real rate of reduction of exceedances can be
demonstrated over the period of implementation of the Plan's control
measures, 2016-2018. Indeed, even with the early implementation of
additional controls designated by the State as contingency measures to
provide emissions reductions in the event of a failure to show RFP or
to attain, West Pinal County still exceeded the PM10
standard by a large margin as evidenced by the data in Table 5.
    Regarding quantitative milestones, given the EPA's 2012 designation
of nonattainment for West Pinal County, the State should have included
quantitative milestones for mid-2016 and mid-2019 within the West Pinal
County PM10 Plan. Aside from the two glidepath depictions in
Figure 7-1, the Plan provides no further discussion of quantitative
milestones. What is presented in Figure 7-1 does not meet the criteria
that the Plan's quantitative milestones should be trackable,
quantified, and provide for an objective evaluation of RFP toward
attainment of the NAAQS, by mid-2016. The West Pinal County
PM10 Plan does not address RFP or quantitative milestones in
mid-2019.
    For these reasons, we have determined that the West Pinal County
PM10 Plan fails to demonstrate RFP, consistent with
applicable CAA requirements and EPA guidance. Therefore, we propose to
disapprove the RFP demonstration and quantitative milestones for the
West Pinal County area for the 24-hour PM10 NAAQS under
sections 172(c)(2) and 189(c)(1).

F. Contingency Measures

1. Statutory and Regulatory Requirements
    Under the CAA, states must include contingency measures consistent
with section 172(c)(9) in their nonattainment plan SIP submissions.
Contingency measures are additional controls or measures to be
implemented in the event the area fails to meet RFP or to attain the
NAAQS by the applicable attainment date. The SIP should contain trigger
mechanisms for the contingency measures, specify a schedule for
implementation, and indicate that the measure will be implemented
without significant further action by the state or the EPA.\68\
---------------------------------------------------------------------------

    \68\ 81 FR 58066 (August 24, 2016).
---------------------------------------------------------------------------

    Neither the CAA nor the EPA's implementing regulations establish a
specific level of emissions reductions that implementation of
contingency measures must achieve, but the General Preamble reiterates
the EPA's guidance recommendation that contingency measures should
generally provide for emissions reductions approximately equivalent to
one year's worth of RFP in the area.\69\ Where a failure to attain or
to meet RFP can be corrected in less than one year, the EPA may accept
a proportionally lesser amount sufficient to correct the identified
failure.\70\
---------------------------------------------------------------------------

    \69\ 57 FR 13498, 13543-13544.
    \70\ Id. at 13511.
---------------------------------------------------------------------------

    It has been the EPA's longstanding interpretation of CAA section
172(c)(9) that states may meet the contingency measure requirement by
relying on Federal measures (e.g., Federal mobile source measures based
on the incremental turnover of the motor vehicle fleet each year) and
state or local measures already scheduled for implementation that
provide emissions reductions in excess of those needed to meet any
other nonattainment plan requirements, such as RACM/RACT, RFP, or
expeditious attainment. The key is that the Act requires that
contingency measures provide for additional emissions reductions that
are not relied on for RFP or attainment and that are not included in
the RFP or attainment demonstrations as meeting part of or all the
contingency measure requirements. The purpose of contingency measures
is to provide continued emissions reductions while a plan is being
revised to meet the missed milestone or attainment date.
    In Bahr v. EPA, the Ninth Circuit Court of Appeals rejected the
EPA's interpretation of CAA section 172(c)(9) as allowing for early
implementation of contingency measures.\71\ The Ninth Circuit concluded
that contingency measures must take effect at the time the area fails
to make RFP or attain by the applicable attainment date, not
before.\72\ Consequently, within the geographic jurisdiction of the
Ninth Circuit, states cannot rely on early-implemented measures to
comply with the contingency measure requirements under CAA section
172(c)(9).\73\
---------------------------------------------------------------------------

    \71\ Bahr v. EPA, 836 F.3d 1218, 1235-1237 (9th Cir. 2016).
    \72\ Id. at 1235-1237.
    \73\ The Bahr v. EPA decision involved a challenge to an EPA
approval of contingency measures under the general nonattainment
area plan provisions for contingency measures in CAA section
172(c)(9), but, given the similarity between the statutory language
in section 172(c)(9) and the ozone-specific contingency measure
provision in section 182(c)(9), we find that the decision affects
how both sections of the Act must be interpreted.
---------------------------------------------------------------------------

2. Summary of the State's Submission
    ADEQ developed the West Pinal County PM10 Plan prior to
the Bahr v. EPA decision, and the plan relies solely upon surplus
emissions reductions from already implemented control measures during
the 2016-2018 period to demonstrate compliance with the contingency
measure requirements of CAA section 172(c)(9). The West Pinal County
PM10 Plan included the following early implemented state and
local regulations to meet the contingency measures requirement for the
PM10 standard: The portion of the AgBMP Rules for Pinal
County applicable to dairy operations (R18-2-611 and -611.03), and the
Pinal County Fugitive Dust Rule and Construction Dust Rule.\74\
Contingency Measures are also discussed in Appendix D.\75\
---------------------------------------------------------------------------

    \74\ West Pinal County PM10 Plan, Chapter 6; Chapter
7, Table 7-4.
    \75\ Appendix D, 45, Table D5-1.
---------------------------------------------------------------------------

3. The EPA's Review of the State's Submission
    Arizona is within the geographic jurisdiction of the Ninth Circuit
Court of Appeals; therefore, after the Bahr v. EPA decision, the State
cannot rely on already-implemented control measures to comply with the
contingency measure requirement of CAA section 172(c)(9). To comply
with CAA section 172(c)(9), as interpreted in the Bahr v. EPA decision,
a state must develop, adopt and submit contingency measures to be
triggered upon a failure to meet RFP milestones or failure to attain
the NAAQS by the applicable attainment date regardless of the extent to
which already-implemented measures would achieve surplus emissions
reductions beyond those necessary to meet RFP milestones and beyond
those predicted to achieve attainment of the NAAQS. Arizona's adopted
and pre-implemented contingency measures do not comply with these
requirements for failure to make RFP and failure to meet attainment
contingency measures. Section 172(c)(9) requires contingency measures
to address potential failures to achieve RFP milestones or failure to
attain the NAAQS by the applicable attainment date. For these reasons,
we propose to disapprove the contingency measures element of the West
Pinal County PM10 Plan as failing to meet the contingency
measure requirements of CAA sections 172(c)(9).

G. Motor Vehicle Emissions Budgets for Transportation Conformity

1. Statutory and Regulatory Requirements
    Section 176(c) of the CAA requires Federal actions in nonattainment
and maintenance areas to conform to the goals of the state's SIP to
eliminate or reduce the severity and number of violations of the NAAQS
and achieve timely attainment of the standards. Conformity to the goals
of the SIP means that such actions will not: (1) Cause or contribute to
violations of a NAAQS, (2) worsen the severity of an existing
violation, or (3) delay timely attainment of any NAAQS or any interim
milestone.
    Actions involving Federal Highway Administration (FHWA) or Federal
Transit Administration (FTA) funding or approval are subject to the
EPA's transportation conformity rule, codified at 40 CFR part 93,
subpart A. Under this rule, metropolitan planning organizations (MPOs)
in nonattainment and maintenance areas coordinate with state and local
air quality and transportation agencies, the EPA, the FHWA, and the FTA
to demonstrate that an area's regional transportation plans and
transportation improvement programs conform to the applicable SIP. This
demonstration is typically done by showing that estimated emissions
from existing and planned highway and transit systems are less than or
equal to the motor vehicle emissions budgets (MVEBs or ``budgets'')
contained in all control strategy attainment plans designed to attain
the NAAQSs. Budgets are generally established for specific years and
specific pollutants or precursors. Attainment plans for PM10
nonattainment areas should identify budgets for mobile source emissions
of PM10, i.e., vehicle and fugitive dust emissions, in the
area for each RFP milestone year, as appropriate, and the attainment
year, if the plan demonstrates attainment.\76\
---------------------------------------------------------------------------

    \76\ 40 CFR 93.102(b)(1).
---------------------------------------------------------------------------

    For budgets to be approvable, they must meet, at a minimum, the
EPA's adequacy criteria at 40 CFR 93.118(e)(4). To meet these
requirements, the budgets must be consistent with the attainment and
RFP requirements and reflect all the motor vehicle control measures
contained in the attainment and RFP demonstrations.\77\ Budgets may
include a safety margin representing the difference between projected
emissions and the total amount of emissions estimated to satisfy any
requirements for attainment or RFP.
---------------------------------------------------------------------------

    \77\ 40 CFR 93.118(e)(4)(iii), (iv) and (v). For more
information on the transportation conformity requirements and
applicable policies on MVEBs, please visit our transportation
conformity website at: http://www.epa.gov/otaq/stateresources/transconf/index.htm.
---------------------------------------------------------------------------

    The EPA's process for determining adequacy of a budget consists of
three basic steps: (1) Providing public notification of a SIP
submission; (2) providing the public the opportunity to comment on the
budget during a public comment period; and (3) making a finding of
adequacy or inadequacy.\78\
---------------------------------------------------------------------------

    \78\ 40 CFR 93.118(f)(2).
---------------------------------------------------------------------------

2. Summary of the State's Submission
    The West Pinal County PM10 Plan includes a budget for
the 2018 attainment year. As discussed in Section III.E, we are
proposing to disapprove the RFP and quantitative milestones elements of
the Plan. No interim RFP budget was submitted for 2016. The State's
submitted 2018 conformity budget for PM10 for the West Pinal
County Area is provided in Table 6.

 Table 6--2018 Motor Vehicle Emissions Budget for the West Pinal County
                         PM10 Nonattainment Area
                             [Tons per year]
------------------------------------------------------------------------
                           Source                              Emissions
------------------------------------------------------------------------
Direct On-Road Mobile Sources (exhaust, tire and brake wear)       173.7
Unpaved Road Fugitive Dust..................................    26,433.5
Paved Road Fugitive Dust....................................     1,211.1
Road Construction/Maintenance...............................       168.8
                                                             -----------
    Total...................................................    27,987.1
------------------------------------------------------------------------
Source: West Pinal County PM10 Plan, Table 5-4.

    The methodologies ADEQ used to develop the motor vehicle emissions
budget are provided in Appendix B of the West Pinal County
PM10 Plan.\79\ As discussed in section III.A. of this
proposal, ADEQ used MOVES2014 in the development of this budget; this
emissions factor model was the latest EPA approved version at the time
the West Pinal County PM10 Plan was developed. Paved road
vehicle miles traveled (VMT) estimates for estimating direct and
fugitive PM10 emissions were provided by MAG using an
interpolation methodology where 2018 VMT was estimated from 2015 and
2025 regional transportation modeling runs.\80\ ADEQ used the most
recently approved EPA provided AP-42 emissions factor equations to
develop paved and unpaved road fugitive dust emissions estimates.\81\
In addition to the line item source categories in the 2018 budget
presented in Table 6, ADEQ specified that the budget includes an 81 ton
per year safety margin.\82\
---------------------------------------------------------------------------

    \79\ Appendix B, 120-137, and 166-180.
    \80\ Appendix B, 120.
    \81\ ADEQ used the appropriate AP-42 guidance in sections 13.2.1
and 13.2.2 to calculate fugitive dust from paved and unpaved roads.
The AP-42 emission factor equation inputs for estimating unpaved
road fugitive dust emissions can be found in Appendix B, Table 5-11.
The most recent EPA revision and approval of these AP-42 emission
factor equations occurred in 2011 and are reflected in the Plan's
estimates; 76 FR 6328 (February 4, 2011).
    \82\ West Pinal County PM10 Plan, 62.
---------------------------------------------------------------------------

    The EPA has neither found this 2018 budget to be adequate, nor have
we acted on it in the past.
3. The EPA's Review of the State's Submission
    As part of our review of the approvability of the motor vehicle
emissions budget in the West Pinal County PM10 Plan, we have
evaluated the budget using the adequacy criteria specified in the
transportation conformity rule.\83\ Reviewing the budget against the
criteria in the transportation conformity rule informs the EPA's
decision to propose our action on the budget. We have determined that
the 2018 budget submitted by Arizona for the West Pinal County area has
not met several of these criteria.
---------------------------------------------------------------------------

    \83\ 40 CFR 93.118(e)(4) and (5).
---------------------------------------------------------------------------

    First and foremost, Sec.  93.118(e)(4)(iv) requires that a budget,
when considered together with all other emissions sources, be
consistent with applicable requirements for RFP, attainment, or
maintenance (whichever is relevant to a given implementation plan
submission). In this case, the West Pinal County area budget is not
consistent with the requirements for attainment and RFP, as discussed
in Sections III.D and E of this proposal and our proposed disapproval
of these two Plan elements. Secondly, the West Pinal County budget is
presented in a tons per year format for an attainment plan intended to
meet the 24-hour PM10 NAAQS. The budget must be consistent
with the 24-hour timeframe of the attainment demonstration and
PM10 standard, and therefore should be presented in a tons
per day format. Finally, Sec.  93.118(e)(4)(iii) requires that the
budget be clearly identified and precisely quantified. Although ADEQ
describes an ``allowance or safety margin'' in the West Pinal County
PM10 Plan, the submitted budget does not clearly and
explicitly identify this safety margin in its presentations of the
budget.\84\ Also, a safety margin, as

defined in the Transportation Conformity rule, Sec.  93.101, must be
clearly presented and demonstrated to be outside and above the
emissions level demonstrating attainment, but below the threshold of
the applicable NAAQS.
---------------------------------------------------------------------------

    \84\ West Pinal County PM10 Plan, Table 5-4; Appendix
D, Table D4-4.
---------------------------------------------------------------------------

    We have reviewed the motor vehicle emissions budget in the West
Pinal County PM10 Plan and find that it does not meet
applicable statutory and regulatory requirements including the adequacy
criteria in 40 CFR 93.1118(e)(4) and (5). The primary deficiency is
that the submitted 2018 budget is not consistent with, or derived from,
a demonstration of attainment and RFP meeting the requirements of the
Act. As discussed earlier in sections III.D and III.E, we are proposing
herein to disapprove the Plan's attainment and RFP demonstrations.
Therefore, we are proposing to disapprove the 2018 budget in the West
Pinal County PM10 Plan. In addition, because we are
disapproving the attainment and RFP demonstrations, the 2018 budget is
not eligible for a protective finding.\85\
---------------------------------------------------------------------------

    \85\ 40 CFR 93.120(a)(3).
---------------------------------------------------------------------------

    If our proposed disapproval of the 2018 budget is finalized, upon
the effective date of our final rule, the area would be subject to a
conformity freeze under Sec.  93.120 of the Transportation Conformity
rule. No transportation project outside of the first four years of the
currently conforming transportation plan and transportation improvement
plan (TIP) or that meets the requirements of Sec.  93.104(f) during the
resulting conformity freeze may be found to conform until Arizona
submits a new PM10 control strategy/attainment plan, the EPA
finds the submitted budget adequate per Sec.  93.118 or approves the
new control strategy/attainment plan and conformity to the new control/
strategy implementation plan is determined.\86\ Furthermore, if, as a
result of our final disapproval action, the EPA imposes highway
sanctions under section 179(b)(1) of the Act two years from the
effective date of our final rule, then the conformity status of the
transportation plan and TIP will lapse on that date and no new
transportation plan, TIP, or project may be found to conform until
Arizona submits a new PM10 attainment plan, and conformity
to this attainment plan is determined.\87\
---------------------------------------------------------------------------

    \86\ 40 CFR 93.120(a)(2).
    \87\ 40 CFR 93.120(a)(1).
---------------------------------------------------------------------------

IV. Proposed Action

    For the reasons discussed in this notice, under CAA section
110(k)(3), the EPA is proposing to approve and disapprove the following
portions of the West Pinal County PM10 Plan, submitted by
the State on December 21, 2015. Our proposed approval and disapproval
actions are as follows:
     We propose to approve the 2008 base year emissions
inventory element for direct PM10 in the West Pinal County
PM10 Plan as meeting the requirements of CAA sections
172(c)(3) for the 1987 p.m.10 NAAQS;
     We propose to disapprove the precursor demonstration in
the West Pinal County PM10 Plan because the demonstration is
inadequate to show that emissions reductions from all PM10
precursors do not contribute significantly to PM10 levels
exceeding the NAAQS, as required by CAA Section 189(e) for the 1987
p.m.10 NAAQS;
     We propose to disapprove the RACM/RACT demonstration
element in the West Pinal County PM10 Plan because it does
not meet the requirements of CAA section 172(c)(1) and section
189(a)(1)(C) for the 1987 p.m.10 NAAQS; furthermore, the
deficiencies in the State's precursor analysis mean that the State
failed to establish in its RACM/RACT analysis that it was unnecessary
to regulate PM10 precursor emissions;
     We propose to disapprove the modeled attainment
demonstration element for the 1987 p.m.10 NAAQS in the West
Pinal County PM10 Plan because it does not meet the
requirements of CAA section 189(a)(1)(B) and section 188(c)(1) to
demonstrate attainment of the 1987 p.m.10 NAAQS;
     We propose to disapprove the RFP demonstration element in
the West Pinal County PM10 Plan because it does not meet the
requirements of CAA sections 172(c)(2) for the 1987 p.m.10
NAAQS;
     We propose to disapprove the quantitative milestones
element in the West Pinal County PM10 Plan because it does
not meet the requirements of CAA section 189(c)(1) for the 1987
p.m.10 NAAQS;
     We propose to disapprove the contingency measures element
of the West Pinal County PM10 Plan because it does not meet
the requirements of CAA section 172(c)(9) for the 1987
p.m.10 NAAQS; and,
     We propose to disapprove the motor vehicle emissions
budget in West Pinal County PM10 Plan for the attainment
year of 2018 (see Table 6) because it is not consistent with or derived
from, approvable RFP or and attainment demonstrations for the 1987
PM10 NAAQS meeting the requirements of the Act.
    The EPA is soliciting public comments on the issues discussed in
this proposed rule. We will accept comments from the public on this
proposal for the next 30 days and will consider those comments before
taking final action.

V. Statutory and Executive Order Reviews

    Additional information about these statutes and Executive orders
can be found at http://www.epa.gov/laws-regulations/laws-and-executive-orders.

A. Executive Order 12866: Regulatory Planning and Review and Executive
Order 13563: Improving Regulation and Regulatory Review

    This action is not a significant regulatory action and was
therefore not submitted to the Office of Management and Budget (OMB)
for review.

B. Executive Order 13771: Reducing Regulations and Controlling
Regulatory Costs

    This action is not an Executive Order 13771 regulatory action
because SIP approvals, including partial approvals, are exempted under
Executive Order 12866.

C. Paperwork Reduction Act (PRA)

    This action does not impose an information collection burden under
the PRA because this action does not impose additional requirements
beyond those imposed by state law.

D. Regulatory Flexibility Act (RFA)

    I certify that this action will not have a significant economic
impact on a substantial number of small entities under the RFA. This
action will not impose any requirements on small entities beyond those
imposed by state law.

E. Unfunded Mandates Reform Act (UMRA)

    This action does not contain any unfunded mandate as described in
UMRA, 2 U.S.C. 1531-1538, and does not significantly or uniquely affect
small governments. This action does not impose additional requirements
beyond those imposed by state law. Accordingly, no additional costs to
state, local, or tribal governments, or to the private sector, will
result from this action.

F. Executive Order 13132: Federalism

    This action does not have federalism implications. It will not have
substantial direct effects on the states, on the relationship between
the National Government and the states, or on the

distribution of power and responsibilities among the various levels of
government.

G. Executive Order 13175: Coordination With Indian Tribal Governments

    This action does not have tribal implications, as specified in
Executive Order 13175, because the SIP is not approved to apply on any
Indian reservation land or in any other area where the EPA or an Indian
tribe has demonstrated that a tribe has jurisdiction, and will not
impose substantial direct costs on tribal governments or preempt tribal
law. Thus, Executive Order 13175 does not apply to this action.

H. Executive Order 13045: Protection of Children From Environmental
Health Risks and Safety Risks

    The EPA interprets Executive Order 13045 as applying only to those
regulatory actions that concern environmental health or safety risks
that the EPA has reason to believe may disproportionately affect
children, per the definition of ``covered regulatory action'' in
section 2-202 of the Executive order. This action is not subject to
Executive Order 13045 because it does not impose additional
requirements beyond those imposed by state law.

I. Executive Order 13211: Actions That Significantly Affect Energy
Supply, Distribution, or Use

    This action is not subject to Executive Order 13211, because it is
not a significant regulatory action under Executive Order 12866.

J. National Technology Transfer and Advancement Act (NTTAA)

    Section 12(d) of the NTTAA directs the EPA to use voluntary
consensus standards in its regulatory activities unless to do so would
be inconsistent with applicable law or otherwise impractical. The EPA
believes that this action is not subject to the requirements of section
12(d) of the NTTAA because application of those requirements would be
inconsistent with the CAA.

K. Executive Order 12898: Federal Actions To Address Environmental
Justice in Minority Populations and Low-Income Populations

    The EPA lacks the discretionary authority to address environmental
justice in this rulemaking.

List of Subjects in 40 CFR Part 52

    Environmental protection, Air pollution control, Incorporation by
reference, Intergovernmental relations, Particulate matter, Reporting
and recordkeeping requirements.

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

    Dated: December 23, 2020.
John Busterud,
Regional Administrator, Region IX.
[FR Doc. 2020-29092 Filed 1-7-21; 8:45 am]
BILLING CODE 6560-50-P