[Federal Register Volume 85, Number 108 (Thursday, June 4, 2020)]
[Proposed Rules]
[Pages 34381-34395]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2020-11930]



[[Page 34381]]

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Parts 52 and 81

[EPA-R09-OAR-2019-0609; FRL-10010-26-Region 9]


Maintenance Plan and Redesignation Request for the Ajo PM10 
Planning Area; Arizona

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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SUMMARY: The Environmental Protection Agency (EPA) is proposing to 
approve the ``Ajo PM10 Redesignation Request and Maintenance 
Plan (May 3, 2019)'' (``Ajo PM10 Maintenance Plan'' or 
``Plan'') as a revision to the state implementation plan (SIP) for the 
State of Arizona. The Ajo PM10 Maintenance Plan includes, 
among other elements, an emissions inventory consistent with 
attainment, a maintenance demonstration, contingency provisions, and a 
demonstration that contributions from motor vehicle emissions to 
PM10 in the Ajo planning area are insignificant. The EPA is 
also proposing to approve the State of Arizona's request to redesignate 
the Ajo planning area from nonattainment to attainment for the national 
ambient air quality standards (NAAQS or ``standards'') for particulate 
matter of ten microns or less (PM10). Lastly, the EPA is 
proposing to delete the area designation for Ajo for the revoked NAAQS 
for total suspended particulate (TSP) because the designation is no 
longer necessary. The EPA is proposing these actions because the SIP 
revision meets the applicable requirements under the Clean Air Act (CAA 
or ``Act'') for maintenance plans and because the State has met the 
requirements under the Act for redesignation of a nonattainment area to 
attainment with respect to the Ajo planning area.

DATES: Comments must be received on or before July 6, 2020.

ADDRESSES: Submit your comments, identified by Docket ID No. EPA-R09-
OAR-2019-0609, at https://www.regulations.gov, or via email to Ashley 
Graham, Air Planning Office at [email protected]. For comments 
submitted at Regulations.gov, follow the online instructions for 
submitting comments. Once submitted, comments cannot be removed or 
edited from Regulations.gov. For either manner of submission, 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 (e.g., audio or video) must be 
accompanied by a written comment. The written comment is considered the 
official comment and should include discussion of all points you wish 
to make. The EPA will generally not consider comments or comment 
contents located outside of the primary submission (i.e., on the web, 
cloud, or other file sharing system). For additional submission 
methods, please contact the person identified in the FOR FURTHER 
INFORMATION CONTACT section. For the full EPA public comment policy, 
information about CBI or multimedia submissions, and general guidance 
on making effective comments, please visit https://www.epa.gov/dockets/commenting-epa-dockets.

FOR FURTHER INFORMATION CONTACT: Ashley Graham, EPA Region IX, (415) 
972-3877, [email protected].

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

Table of Contents

I. Background
    A. The PM10 National Ambient Air Quality Standards
    B. The Ajo PM10 Planning Area
II. Procedural Requirements for Adoption and Submittal of State 
Implementation Plan Revisions
III. Substantive Requirements for Redesignation
IV. Evaluation of the State's Redesignation Request for the Ajo 
PM10 Nonattainment Area
    A. Determination That the Area Has Attained the PM10 
National Ambient Air Quality Standards
    B. The Area Must Have a Fully Approved State Implementation Plan 
Meeting the Requirements Applicable for Purposes of Redesignation 
Under Section 110 and Part D of the Clean Air Act
    C. The Area Must Show the Improvement in Air Quality Is Due to 
Permanent and Enforceable Emission Reductions
    D. The Area Must Have a Fully Approved Maintenance Plan Under 
Clean Air Act Section 175A
V. Proposed Deletion of the Total Suspended Particulate Designation 
for Ajo
    A. General Considerations
    B. Deletion of Total Suspended Particulate Nonattainment Area 
Designation for Ajo
VI. Proposed Action and Request for Public Comment
VII. Statutory and Executive Order Reviews

I. Background

A. The PM10 National Ambient Air Quality Standards

    In 1971, pursuant to section 109 of the CAA, the EPA promulgated 
the original NAAQS for the criteria pollutants, which included carbon 
monoxide, hydrocarbons, nitrogen dioxide, photochemical oxidant, sulfur 
dioxide and particulate matter.\1\ The NAAQS are set at concentrations 
intended to protect public health and welfare. Following promulgation 
of the NAAQS, under section 110 of the CAA, each state is required to 
adopt and submit a SIP to provide for the implementation, maintenance 
and enforcement of the NAAQS within such state.
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    \1\ 36 FR 8186 (April 30, 1971).
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    The original NAAQS for particulate matter were defined in terms of 
a reference method that called for measuring particulate matter up to a 
nominal size of 25 to 45 micrometers or microns. This fraction of total 
ambient particulate matter is referred to as ``total suspended 
particulate'' or TSP. In 1987, the EPA revised the NAAQS for 
particulate matter, replacing TSP as the indicator for particulate 
matter for the ambient standards with a new indicator that includes 
only the particles with an aerodynamic diameter less than or equal to 
10 microns in diameter (PM10).\2\ At that time, the EPA 
established two PM10 standards: Primary and secondary 24-
hour standards of 150 micrograms per cubic meter ([micro]g/m\3\) and 
primary and secondary annual standards of 50 [mu]g/m\3\.\3\
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    \2\ 52 FR 24634 (July 1, 1987).
    \3\ For a given air pollutant, ``primary'' standards are those 
determined by the EPA as requisite to protect public health. 
``Secondary'' standards are those determined by the EPA as requisite 
to protect public welfare from any known or anticipated adverse 
effects associated with the presence of such air pollutant in the 
ambient air. CAA section 109(b).
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    In 2006, the EPA retained the 24-hour PM10 standards but 
revoked the annual standards.\4\ More recently, as part of the EPA's 
periodic review of the NAAQS, the EPA reaffirmed the 24-hour 
PM10 NAAQS.\5\ This proposed action relates to the current 
24-hour PM10 NAAQS and the revoked TSP NAAQS.
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    \4\ 71 FR 61144 (October 17, 2006).
    \5\ 78 FR 3086 (January 15, 2013).
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    PM10 contributes to effects that are harmful to human 
health and the environment, including premature mortality, aggravation 
of respiratory and cardiovascular disease, decreased lung function, 
visibility impairment, and damage to vegetation and ecosystems. 
Individuals particularly sensitive to exposure include older adults, 
people with heart and lung disease, and children.\6\ PM10 
can be emitted directly into the atmosphere as a solid or liquid 
particle (``primary PM10'' or ``direct PM10'') or 
can be formed in the atmosphere (``secondary PM10'') as a 
result of various chemical reactions among precursor pollutants such as

[[Page 34382]]

nitrogen oxides (NOX), sulfur dioxide (SO2), 
volatile organic compounds (VOC), and ammonia.\7\
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    \6\ Id. at 3088.
    \7\ EPA, Air Quality Criteria for Particulate Matter, No. EPA/
600/P-99/002aF and EPA/600/P-99/002bF, October 2004.
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B. The Ajo PM10 Planning Area

    Under section 107 of the CAA, the EPA is required to designate all 
areas of the country as attainment, nonattainment, or unclassifiable 
for each of the NAAQS. In response to an area designation of 
nonattainment, states are required to adopt and submit SIP revisions 
that, among other things, provide for attainment of the NAAQS within 
such area. Once a nonattainment area attains the NAAQS and meets 
certain other prerequisites, the state may request that the EPA 
redesignate the area to attainment. For the Ajo planning area, the 
Arizona Department of Environmental Quality (ADEQ) has primary 
responsibility for air quality planning and has permitting jurisdiction 
over certain types of sources, including smelting of metal ores.\8\ The 
Pima County Department of Environmental Quality (PDEQ or ``District'') 
\9\ has primary permitting authority over most types of stationary 
sources within Pima County. The ADEQ worked cooperatively with the 
District in preparing the Ajo PM10 Maintenance Plan.
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    \8\ Arizona Revised Statutes (ARS) Sec.  49-402(A) and (B).
    \9\ The Pima County Board of Supervisors is the governing body 
for the Pima County Air Quality Control District, which operates 
within the PDEQ.
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    In 1979, we designated Township T12S, R6W (``Ajo'') in the 
northwestern portion of Pima County, Arizona as a nonattainment area 
for the TSP NAAQS.\10\ At that time, the Phelps Dodge Corporation 
copper mining, concentrating, and smelting facilities, collectively 
known as the Phelps Dodge ``New Cornelia Branch,'' were the principal 
sources of fugitive dust in the Ajo nonattainment area. The Ajo mine 
ceased operation in 1984 and the smelter deactivated in April 1985.
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    \10\ 44 FR 21261 (April 10, 1979). The unincorporated town of 
Ajo, Arizona, is located approximately 113 miles west northwest of 
Tucson, and is located on the edge of a broad desert valley at an 
elevation of 1,750 feet, bordered by scattered hills and low 
mountain ranges to the west and south.
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    In 1987, the EPA replaced the TSP NAAQS with the PM10 
NAAQS. Under the CAA, as amended in 1990, the EPA designated the Ajo 
planning area as a Moderate nonattainment area for the PM10 
NAAQS.\11\ By the end of 1991, to minimize windblown fugitive dust from 
the inactive tailings impoundments, one of the significant sources of 
fugitive dust in the area, Phelps Dodge covered (or capped) more than 
1,900 acres of the tailings with crushed rock. The smelter and copper 
ore concentrator structures at the facility were effectively dismantled 
by the end of 1996.
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    \11\ 56 FR 11101 (March 15, 1991). The Ajo planning area is 
somewhat larger than the Ajo TSP nonattainment area and includes 
sections 6-8, 17-20 and 29-32 of Township T12S, R5W in addition to 
Township T12S, R6W. Area designations within the State of Arizona 
are codified at 40 CFR 81.303. Currently, the population within the 
Ajo planning area is approximately 3,500 persons, and employment is 
mainly in the commercial, service, and tourism sectors. Ajo 
PM10 Maintenance Plan, 8-9.
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    In 2006, based on ambient monitoring data for 2002-2004, the EPA 
determined that the Ajo PM10 nonattainment area had attained 
the PM10 NAAQS.\12\ Based on that determination, the EPA 
also determined that certain CAA requirements, including obligations to 
demonstrate reasonable further progress, to provide an attainment 
demonstration, and to provide contingency measures pursuant to part D 
of the CAA, were not applicable for so long as the Ajo area continues 
to attain the PM10 NAAQS.
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    \12\ 71 FR 6352 (February 8, 2006).
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    With the closure of the mine and smelter, and the capping of the 
inactive tailings impoundment, only one significant source of fugitive 
dust, a slag reprocessing facility, remained active in the Ajo planning 
area. In 2011 and 2013, the ADEQ's Ajo PM10 monitoring site 
recorded exceedances of the PM10 NAAQS caused in part by 
high winds that entrained fugitive dust from the slag reprocessing 
facility and other fugitive sources in the area. In 2015, the slag 
reprocessing facility was demolished and a slag dust cap was applied on 
certain process areas.
    In 2019, the Pima County Board of Supervisors adopted Pima County 
Code (PCC) Section 17.16.125 (``Inactive Mineral Tailings Impoundment 
and Slag Storage Area within the Ajo PM10 Planning Area'') 
to provide for continued maintenance and enforcement of the measures 
already implemented to control windblown dust from the tailings 
impoundment and the slag storage area. On May 10, 2019, in light of 
renewed attainment of the PM10 NAAQS in the Ajo planning 
area and the adoption of PCC Section 17.16.125, the ADEQ submitted the 
Ajo PM10 Maintenance Plan to the EPA as a revision to the 
Arizona SIP and requested that the EPA redesignate the Ajo planning 
area from nonattainment to attainment for the PM10 
NAAQS.\13\ The ADEQ also requested that the EPA delete the TSP 
nonattainment designation for the Ajo Area.\14\
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    \13\ May 10, 2019 refers to the date on which the ADEQ submitted 
the Ajo PM10 Maintenance Plan electronically to the EPA. 
The ADEQ's transmittal letter to the EPA is dated May 8, 2019.
    \14\ Letter dated May 8, 2019, from Timothy S. Franquist, 
Director, Air Quality Division, ADEQ, to Michael Stoker, Regional 
Administrator, EPA Region IX, submitting the SIP Revision ``Ajo 
PM10 Redesignation Request and Maintenance Plan.''
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    The Ajo PM10 Maintenance Plan includes chapters 
addressing the various criteria for redesignation under CAA section 
107(d)(3)(E); a chapter containing the PM10 maintenance 
plan; a chapter addressing transportation conformity; and three 
appendices that document the emissions inventory estimates relied upon 
by the maintenance plan, the compliance with procedural and legal 
authority requirements, and the process undertaken to adopt PCC Section 
17.16.125 (``Inactive Mineral Tailings Impoundment and Slag Storage 
Area Within the Ajo PM10 Planning Area'').

II. Procedural Requirements for Adoption and Submittal of State 
Implementation Plan Revisions

    Section 110(l) of the CAA requires states to make SIP revisions 
available for public review and comment and to hold a public hearing or 
provide the public the opportunity to request a public hearing. The Act 
requires the plan be adopted by the state and submitted to the EPA by 
the governor or his/her designee. To meet these procedural 
requirements, every SIP submission should include evidence that the 
state provided adequate public notice and an opportunity for a public 
hearing consistent with the EPA's implementing regulations in 40 CFR 
51.102.
    In the ADEQ's May 10, 2019 submittal of the Ajo PM10 
Maintenance Plan, the State verified that it had adhered to its SIP 
adoption procedures in Appendix B, which includes the notice of public 
hearing, the agenda for the January 24, 2019 public hearing, the sign-
in sheet, the public hearing officer certification and transcript of 
the hearing, and the State's responsiveness summary. Specifically, a 
notice of public hearing was published in the Ajo Copper News on 
December 25, 2018 and January 1, 2019, and in the Arizona Daily Star on 
December 26, 2018 and December 27, 2018, newspapers of general 
circulation in the Ajo area. The notices announced the availability of 
the Ajo PM10 Maintenance Plan at the ADEQ Record Center in 
Phoenix, Arizona, on the ADEQ's website, and at the Salazar-Ajo branch 
of the Pima County Public Library in Ajo, Arizona, and opened the 
comment period for 30 days prior to the public hearing. The public 
hearing was held on January 24, 2019. No comments on the Ajo 
PM10 Maintenance Plan were

[[Page 34383]]

made during the public hearing, and no written comments were received 
during the public comment period.
    Through the SIP transmittal letter dated May 8, 2019, the ADEQ's 
Director of the Air Quality Division adopted the Ajo PM10 
Maintenance Plan as a revision to the Arizona SIP. The Director of the 
ADEQ is authorized under state law to adopt and submit SIPs and SIP 
revisions to the EPA, and the Director of the ADEQ has delegated that 
authority to the Director of the Air Quality Division. Based on the 
documentation provided in the SIP submittal and summarized in this 
notice, we find that submittal of the Ajo PM10 Maintenance 
Plan as a revision to the Arizona SIP satisfies the procedural 
requirements of section 110(l) of the Act and of 40 CFR 51.102.\15\
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    \15\ On November 10, 2019, the Ajo PM10 Maintenance 
Plan was deemed complete by operation of law under CAA section 
110(k)(1)(B).
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III. Substantive Requirements for Redesignation

    The CAA establishes the requirements for redesignation of a 
nonattainment area to attainment. Specifically, section 107(d)(3)(E) 
allows for redesignation provided that the following criteria are met: 
(1) The EPA determines that the area has attained the applicable NAAQS; 
(2) the EPA has fully approved the applicable implementation plan for 
the area under CAA section 110(k); (3) the EPA determines that the 
improvement in air quality is due to permanent and enforceable 
reductions in emissions; (4) the EPA has fully approved a maintenance 
plan for the area as meeting the requirements of CAA section 175A; and 
(5) the state has met all requirements applicable to the area under 
section 110 and part D of the CAA. Section 110 identifies a 
comprehensive list of elements that SIPs must include, and part D 
establishes the SIP requirements for nonattainment areas. Part D is 
divided into six subparts. The generally applicable nonattainment SIP 
requirements are found in subpart 1 of part D, and the particulate 
matter-specific SIP requirements are found in subpart 4 of part D.
    The EPA provided guidance on redesignations in a document titled 
``State Implementation Plans; General Preamble for the Implementation 
of Title I of the Clean Air Act Amendments of 1990,'' published in the 
Federal Register on April 16, 1992,\16\ and supplemented on April 28, 
1992 (collectively referred to herein as the ``General Preamble'').\17\ 
Additional guidance was issued on September 4, 1992, in a memorandum 
from John Calcagni, Director, Air Quality Management Division, EPA 
Office of Air Quality Planning and Standards, titled ``Procedures for 
Processing Requests to Redesignate Areas to Attainment'' (referred to 
herein as the ``Calcagni memo''), and a 1994 memorandum from Mary D. 
Nichols, titled ``Part D New Source Review (part D NSR) Requirements 
for Areas Requesting Redesignation to Attainment'' (``Nichols memo'').
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    \16\ 57 FR 13498.
    \17\ 57 FR 18070.
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    As noted above, approval of a maintenance plan is one of the CAA 
prerequisites for redesignation of a nonattainment area to attainment. 
Section 175A of the CAA provides the general framework for maintenance 
plans. The initial 10-year maintenance plan must provide for 
maintenance of the NAAQS for at least 10 years after redesignation, 
including any additional control measures necessary to ensure such 
maintenance. In addition, maintenance plans are to contain contingency 
provisions necessary to assure the prompt correction of a violation of 
the NAAQS that occurs after redesignation. The contingency provisions 
must include, at a minimum, a requirement that the state will implement 
all control measures contained in the nonattainment SIP prior to 
redesignation. Maintenance plan submittals are SIP revisions, and as 
such, the EPA is obligated under CAA section 110(k) to approve them or 
disapprove them depending upon whether they meet the applicable CAA 
requirements for such plans.
    For the reasons set forth in section IV of this document, we 
propose to approve the Ajo PM10 Maintenance Plan and to 
approve the ADEQ's request for redesignation of the Ajo nonattainment 
area to attainment for the PM10 NAAQS based on our 
conclusion that all of the criteria under CAA section 107(d)(3)(E) have 
been satisfied.

IV. Evaluation of the State's Redesignation Request for the Ajo PM10 
Nonattainment Area

A. Determination That the Area Has Attained the PM10 National Ambient 
Air Quality Standards

    Section 107(d)(3)(E)(i) of the CAA requires that for an area to be 
redesignated to attainment, the EPA must determine that the area has 
attained the relevant NAAQS. In this case, the relevant NAAQS is the 
24-hour PM10 NAAQS.\18\ In 2006, the EPA determined that the 
Ajo area had attained the PM10 standards based on ambient 
data from 2002-2004.\19\ This proposed action updates this 
determination based on the most recent available PM10 
monitoring data.
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    \18\ The annual PM10 standards were revoked effective 
December 18, 2006 (71 FR 61144, October 17, 2006). Thus, this 
document discusses only attainment of the 24-hour PM10 
standards.
    \19\ 71 FR 6352 (February 8, 2006).
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    Generally, the EPA determines whether an area's air quality is 
meeting the PM10 NAAQS based on the most recent complete, 
quality-assured, and certified data measured at established state and 
local air monitoring stations (SLAMS) in the nonattainment area and 
entered into the EPA Air Quality System (AQS) database. Data from air 
monitoring sites operated by state, local, or tribal agencies in 
compliance with EPA monitoring requirements must be submitted to AQS. 
These monitoring agencies annually certify that these data are accurate 
to the best of their knowledge. Accordingly, the EPA relies primarily 
on data in AQS when determining the attainment status of an area.\20\ 
All valid data are reviewed to determine the area's air quality status 
in accordance with 40 CFR part 50, appendix K.
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    \20\ 40 CFR 50.6; 40 CFR part 50, appendix J; 40 CFR part 53; 
and 40 CFR part 58, appendices A, C, D, and E.
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    The PM10 NAAQS is attained when the expected number of 
days per calendar year with a 24-hour concentration in excess of the 
standard (referred to herein as an ``exceedance''),\21\ averaged over a 
three-year period, is less than or equal to one. The expected number of 
exceedances averaged over a three-year period at any given monitor is 
known as the PM10 design value. The PM10 design 
value for the area is the highest design value within the nonattainment 
area.\22\ Generally, for purposes of redesignation, the most recent 
three consecutive years

[[Page 34384]]

of complete \23\ air quality data are necessary to show attainment of 
the PM10 NAAQS.
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    \21\ An exceedance is defined as a daily value that is above the 
level of the 24-hour standard (i.e., 150 [mu]g/m\3\) after rounding 
to the nearest 10 [mu]g/m\3\ (i.e., values ending in 5 or greater 
are to be rounded up). Thus, a recorded value of 154 [mu]g/m\3\ 
would not be an exceedance since it would be rounded to 150 [mu]g/
m\3\ whereas a recorded value of 155 [mu]g/m\3\ would be an 
exceedance since it would be rounded to 160 [mu]g/m\3\. 40 CFR part 
50, appendix K, section 1.0.
    \22\ 40 CFR 50.6 and 40 CFR part 50, appendix K. The comparison 
with the allowable expected exceedance rate of one per year is made 
in terms of a number rounded to the nearest tenth (fractional values 
equal to or greater than 0.05 are to be rounded up; e.g., an 
exceedance rate of 1.05 would be rounded to 1.1, which is the lowest 
rate for nonattainment). 40 CFR part 50, appendix K, section 2.1(b).
    \23\ For PM10, a complete year of air quality data 
includes all four calendar quarters with each quarter containing a 
minimum of 75 percent of the scheduled PM10 sampling 
days. 40 CFR part 50, Appendix K, section 2.3(a).
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    The ADEQ operates the PM10 monitoring network in the Ajo 
area. The ADEQ submits annual monitoring network plans to the EPA. 
These network plans describe the monitoring network operated by the 
ADEQ within the Ajo nonattainment area and discuss the status of the 
air monitoring network, as required under 40 CFR 58.10. The EPA 
regularly reviews these annual plans for compliance with the applicable 
reporting requirements in 40 CFR part 58. With respect to 
PM10, the EPA has found that the area's network plans meet 
the applicable reporting requirements under 40 CFR part 58, appendix 
D.\24\ The EPA also concluded from its 2018 Technical Systems Audit 
that the ADEQ's ambient air monitoring program is robust and meets or 
exceeds EPA requirements.\25\ The ADEQ annually certifies that the data 
it submits to AQS are complete and quality-assured.\26\
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    \24\ For example, see letter dated November 8, 2019, from Gwen 
Yoshimura, Manager, Air Quality Analysis Office, EPA Region IX, to 
Daniel Czecholinski, Acting Director, Air Quality Division, ADEQ.
    \25\ Letter dated April 25, 2019, from Elizabeth Adams, 
Director, Air Division, EPA Region IX, to Timothy Franquist, 
Director, Air Quality Division, ADEQ.
    \26\ For example, see letter dated April 13, 2020, from Daniel 
Czecholinski, Director, Air Quality Division, ADEQ, to Gwen 
Yoshimura, Manager, Air Quality Analysis Office, EPA Region IX, 
Subject: ``Certification of 2019 Ambient Air Data.''
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    The ADEQ operates one PM10 SLAMS monitoring site, Ajo 
(AQS ID: 04-019-0001), within the Ajo PM10 nonattainment 
area. The monitor is located at the Arizona Department of 
Transportation (ADOT) maintenance yard (see Figure 1-1 in the Ajo 
PM10 Maintenance Plan) and was sited to monitor the effects 
of the former copper smelter and mine tailings. SLAMS produce data 
comparable to the NAAQS, and therefore the monitor must be an approved 
Federal Reference Method, Federal Equivalent Method (FEM), or Approved 
Regional Method. The Ajo monitor measures hourly PM10 
concentrations on a daily, year-round basis using a method that has 
been designated as an FEM by the EPA.
    Consistent with the requirements contained in 40 CFR part 50, the 
EPA has reviewed the quality-assured and certified PM10 
ambient air monitoring data collected at the Ajo monitoring site, as 
recorded in AQS, for the applicable monitoring period. We have 
determined that the data are of sufficient completeness for the 
purposes of making comparisons with the PM10 NAAQS. The 
EPA's evaluation of whether the Ajo PM10 nonattainment area 
has attained the PM10 NAAQS is based on our review of the 
monitoring data and takes into account the adequacy of the 
PM10 monitoring network in the nonattainment area and the 
reliability of the data collected by the network as discussed earlier 
in this section of this proposal.
    Table 1 shows the highest measured PM10 concentrations 
and number of expected exceedances at the Ajo monitoring site during 
the most recent three-year period (2017-2019). One exceedance of the 
PM10 NAAQS was recorded in 2018 at the Ajo monitor.\27\ 
However, the resulting 24-hour design value for the 2017-2019 period is 
less than 1.0 at the Ajo monitor. Therefore, we find that, based on 
complete, quality-assured, and certified data for 2017-2019, the Ajo 
PM10 nonattainment area has attained the PM10 
NAAQS. Preliminary data available in AQS for 2020 indicate that the 
area continues to attain the PM10 NAAQS.
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    \27\ One exceedance was recorded in 2018; however, the number of 
expected exceedances for 2018 is 1.1 due to an adjustment applied to 
the data. 40 CFR part 50 Appendix K.

               Table 1--Ajo Monitored PM10 Concentrations, Expected Exceedances, and Design Value
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                                       Maximum 24-hour  average        Expected exceedances        PM10  design
                                      concentration ([mu]g/m\3\)          (calendar year)             value
   Monitoring site name (AQS ID)    ----------------------------------------------------------------------------
                                       2017      2018      2019      2017      2018      2019       2017-2019
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Ajo (04-019-0001)..................      109       164        65         0       1.1         0              0.4
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Source: EPA AQS Design Value Report and Quicklook Report, accessed May 6, 2020.

B. The Area Must Have a Fully Approved State Implementation Plan 
Meeting the Requirements Applicable for Purposes of Redesignation Under 
Section 110 and Part D of the Clean Air Act

    Sections 107(d)(3)(E)(ii) and (v) of the CAA require the EPA to 
determine that the area has a fully approved applicable SIP under CAA 
section 110(k) that meets all applicable requirements under section 110 
and part D for the purposes of redesignation. The EPA may rely on prior 
SIP approvals in approving a redesignation request \28\ as well as any 
additional measure or element it may approve in conjunction with a 
redesignation action.\29\ In this instance, we are proposing to approve 
a part D element as part of this action--the emissions inventory under 
CAA section 172(c)(3). With full approval of this element, the Ajo 
planning area portion of the Arizona SIP will be fully approved under 
CAA section 110(k) for the purposes of redesignation of the area to 
attainment.
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    \28\ Calcagni Memo, 3; Wall v. EPA, F.3d 426 (6th Cir. 2001); 
and Southwest Pennsylvania Growth Alliance v. Browner, 114 F.3d 984, 
989-990 (6th Cir. 1998).
    \29\ 68 FR 25418, 25426 (May 12, 2003) and citations within.
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1. Basic State Implementation Plan Requirements Under Section 110
a. Clean Air Act Section 110(a) Requirements
    The general SIP elements and requirements set forth in CAA section 
110(a)(2) include, but are not limited to, the following: Submittal of 
a SIP that has been adopted by the state after reasonable public notice 
and hearing; provisions for establishment and operation of appropriate 
procedures needed to monitor ambient air quality; implementation of a 
source permitting program; provisions for the implementation of part C 
requirements for prevention of significant deterioration (PSD); 
provisions for the implementation of part D requirements for 
nonattainment new source review permit programs; provisions for air 
pollution modeling; and provisions for public and local agency 
participation in planning and emission control rule development.
    We note that SIPs must be fully approved only with respect to 
applicable requirements for purposes of

[[Page 34385]]

redesignation in accordance with CAA section 107(d)(3)(E)(ii). The CAA 
section 110(a)(2) (and part D) requirements that are linked to a 
particular nonattainment area's designation and classification are the 
relevant measures to evaluate in reviewing a redesignation request. 
Requirements that apply regardless of the designation of any particular 
area of a state are not applicable requirements for the purposes of 
redesignation, and the state will remain subject to these requirements 
after the nonattainment area is redesignated to attainment.
    For example, CAA section 110(a)(2)(D) requires that SIPs contain 
certain measures to prevent sources in a state from significantly 
contributing to air quality problems in another state; these SIPs are 
often referred to as ``transport SIPs.'' Because the section 
110(a)(2)(D) requirements for transport SIPs are not linked to a 
particular nonattainment area's designation and classification, but 
rather apply regardless of the area's attainment status, these are not 
applicable requirements for the purposes of redesignation under CAA 
section 107(d)(3)(E).
    Similarly, the EPA considers other section 110(a)(2) (and part D) 
requirements that are not linked to nonattainment plan submissions or 
to an area's attainment status as not applicable requirements for 
purposes of redesignation. The EPA considers the section 110 (and part 
D) requirements that relate to a particular nonattainment area's 
designation and classification as the relevant measures to evaluate in 
reviewing a redesignation request. This is consistent with the EPA's 
existing policy on applicability of the conformity SIP requirement for 
redesignations.\30\
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    \30\ 75 FR 36023, 36026 (June 24, 2010) and citations within.
---------------------------------------------------------------------------

    On numerous occasions, the ADEQ and the PDEQ have submitted, and 
the EPA has approved, provisions addressing the basic CAA section 110 
provisions. The Arizona SIP contains enforceable emission limitations; 
requires monitoring, compiling, and analyzing of ambient air quality 
data; requires preconstruction review of new or modified stationary 
sources; provides for adequate funding, staff, and associated resources 
necessary to implement its requirements; and provides the necessary 
assurances that the State maintains responsibility for ensuring that 
the CAA requirements are satisfied in the event that local or regional 
agencies are unable to meet their CAA obligations.\31\ There are no 
outstanding or disapproved applicable SIP submittals that prevent 
redesignation of the Ajo PM10 nonattainment area for the 
PM10 standards.\32\ Therefore, we propose to conclude that 
the ADEQ and the PDEQ have met all SIP requirements for the Ajo 
planning area that are applicable for purposes of redesignation under 
section 110 of the CAA.
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    \31\ For example, see the EPA's final actions approving 
provisions of the Arizona SIP addressing section 110 elements under 
the 1997 and 2006 PM2.5 NAAQS (77 FR 66398) and the 2008 
lead and 2008 ozone NAAQS (80 FR 47859).
    \32\ On June 30, 2017, Arizona submitted a SIP revision to meet 
the requirements under section 110 of the CAA for the 1987 
PM10 NAAQS. The requirements of section 110(a)(2), 
however, are statewide requirements that are not linked to the 1987 
PM10 NAAQS nonattainment status of the Ajo area. 
Therefore, the EPA concludes that these infrastructure requirements 
are not applicable requirements for purposes of review of the 
State's redesignation request.
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b. Federal Implementation Plan at 40 CFR 52.126
    In 1972, the EPA determined that Arizona's SIP ``does not provide 
for the attainment and maintenance of the national standards for 
particulate matter'' in the Phoenix-Tucson Intrastate Air Quality 
Control Region (AQCR), which includes Pima County.\33\ The following 
year, the EPA promulgated a particulate matter federal implementation 
plan (FIP), based on a finding that the SIP ``was not adequate to 
attain the primary standards for particulate matter'' in the Phoenix-
Tucson Intrastate AQCR.\34\ We explained that the emissions inventory 
``indicated that the problem is the result of emissions from stationary 
source[s] (mainly process sources) and fugitive dust sources'', and 
concluded that ``control of both these source categories is necessary 
to attain the national particulate matter standards.'' \35\ 
Accordingly, we promulgated ``substitute regulations for process 
sources equivalent to reasonable available control technology.'' These 
regulations were put in place as a replacement for Arizona, Maricopa 
County, and Pima County rules.
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    \33\ 37 FR 10842, 10849 (May 31, 1972).
    \34\ 38 FR 12702 (May 14, 1973), codified at 40 CFR 52.126.
    \35\ Id. at 12703.
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    In 1974, Pima County adopted new regulations for process industries 
under its jurisdiction and ADEQ submitted them to the EPA. These new 
regulations incorporated the federal emission rates promulgated in the 
FIP. The EPA proposed to approve the rules on August 21, 1975.\36\ Upon 
final approval, the Pima County jurisdiction was removed from the 
FIP.\37\ As a result, the current FIP only applies to Pima County 
sources under the ADEQ's jurisdiction. There are no process sources 
under ADEQ jurisdiction currently operating within the Ajo 
PM10 nonattainment area. Therefore, the EPA finds that the 
FIP at 40 CFR 52.126 does not apply to any sources in the Ajo area and 
does not preclude redesignation of the area to attainment. As discussed 
in more detail in section IV.B.2.b of this document, upon redesignation 
to attainment, any new major sources with significant PM10 
emissions as defined under 40 CFR 51.166 proposing to locate within the 
Ajo planning area will be subject to the requirements in the EPA's PSD 
regulation at 40 CFR 52.21 unless the new source is subject to the 
ADEQ's jurisdiction in which case the new source will be subject to the 
ADEQ's SIP-approved PSD permitting program requirements.
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    \36\ 40 FR 36577, 36578.
    \37\ 42 FR 46926 (September 19, 1977).
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2. State Implementation Plan Requirements Under Part D
    Subparts 1 and 4 of part D, title I of the CAA contain air quality 
planning requirements for PM10 nonattainment areas. Subpart 
1 contains general requirements for all nonattainment areas of any 
pollutant governed by a NAAQS, including PM10. The subpart 1 
requirements include, in relevant part, provisions for implementation 
of reasonably available control measures (RACM), a demonstration of 
reasonable further progress (RFP), emissions inventories, a program for 
preconstruction review and permitting of new or modified major 
stationary sources, contingency measures, and transportation 
conformity.
    Subpart 4 contains specific planning and scheduling requirements 
for PM10 nonattainment areas. The requirements set forth in 
CAA section 189(a), (c), and (e) apply specifically to Moderate 
PM10 nonattainment areas and include the following: An 
approved permit program for construction of new or modified major 
stationary sources; provisions for RACM; an attainment demonstration; 
quantitative milestones demonstrating RFP toward attainment by the 
applicable attainment date; and provisions to ensure that the control 
requirements applicable to major stationary sources of PM10 
also apply to major stationary sources of PM10 precursors, 
except where the Administrator has determined that such sources do not 
contribute significantly to PM10 levels that exceed the 
NAAQS in the area.

[[Page 34386]]

    As noted in section I.B of this document, the EPA determined in 
2006 that the Ajo PM10 nonattainment area attained the 
PM10 NAAQS based on 2002-2004 data. In accordance with the 
EPA's Clean Data Policy, we determined that the following requirements 
do not apply to the Ajo PM10 nonattainment area for so long 
as the area continues to attain the PM10 standards or until 
the area is redesignated to attainment: an attainment demonstration 
under CAA section 189(a)(1)(B); RACM provisions under sections 172(c) 
and 189(a)(1)(C); RFP provisions under section 189(c)(1); and 
contingency measures under section 172(c)(9).\38\
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    \38\ For other rulemaking actions applying the Clean Data Policy 
in the context of PM10, see 77 FR 31268, May 25, 2012 
(Paul Spur/Douglas, Arizona); 76 FR 10817, February 28, 2011 
(Truckee Meadows, Nevada); 75 FR 13710, March 23, 2010 (Coso 
Junction, California); 73 FR 22307, April 25, 2008 (San Joaquin 
Valley, California). See also 40 CFR 51.1015.
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    Moreover, in the context of evaluating the area's eligibility for 
redesignation, there is a separate and additional justification for 
finding that requirements associated with attainment are not applicable 
for purposes of redesignation. Prior to and independently of the Clean 
Data Policy, and specifically in the context of redesignations, the EPA 
has interpreted CAA SIP submittal requirements associated with 
attainment of the NAAQS (such as attainment and RFP demonstrations) as 
not being applicable for purposes of redesignation.\39\ The Calcagni 
memo similarly provides that requirements for RFP and other measures 
needed for attainment will not apply for redesignations because they 
have meaning and applicability only where areas do not meet the 
NAAQS.\40\ With respect to contingency measures, the EPA explained that 
the section 172(c)(9) contingency measure requirements are directed at 
ensuring RFP and attainment by the applicable date, and that 
consequently, these requirements no longer apply when an area has 
attained the standards and is eligible for redesignation. Furthermore, 
CAA section 175A(d) provides for specific requirements for maintenance 
plan contingency provisions that effectively supersede the requirements 
of section 172(c)(9) for these areas.
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    \39\ General Preamble, 13564.
    \40\ Calcagni memo, 6.
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    Thus, the requirements associated with attainment do not apply for 
purposes of evaluating whether an area that has attained the standards 
qualifies for redesignation. The EPA has enunciated this position since 
the General Preamble was published more than 25 years ago, and it 
represents the Agency's interpretation of what constitutes applicable 
requirements under section 107(d)(3)(E). The courts have recognized the 
scope of the EPA's authority to interpret ``applicable requirements'' 
in the redesignation context.\41\
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    \41\ The Seventh Circuit in Sierra Club v. EPA, 375 F.3d 537 
(7th Cir. 2004) (upholding the EPA's redesignation of the St. Louis 
metropolitan area to attainment) is one such example.
---------------------------------------------------------------------------

    The remaining applicable Part D requirements for Moderate 
PM10 areas include the following: (1) An emissions inventory 
under section 172(c)(3); (2) a permit program for the construction and 
operation of new and modified major stationary sources of 
PM10 under sections 172(c)(5) and 189(a)(1)(A); (3) control 
requirements for major stationary sources of PM10 precursors 
under section 189(e), except where the Administrator determines that 
such sources do not contribute significantly to PM10 levels 
that exceed the standards in the area; (4) requirements under section 
172(c)(7) that meet the applicable provisions of section 110(a)(2); and 
(5) provisions to ensure that federally supported or funded projects 
conform to the air quality planning goals in the applicable SIP under 
section 176(c). We discuss each of these requirements below.
a. Emissions Inventory
    Section 172(c)(3) of the CAA requires states to submit a 
comprehensive, accurate, current inventory of relevant PM10 
pollutants for the baseline year from all sources within the 
nonattainment area. We interpret the Act such that the emissions 
inventory requirement of section 172(c)(3) may be satisfied by the 
inventory included in the maintenance plan.\42\ In section IV.D.1 of 
this document, we are proposing to approve the 2018 attainment 
inventory submitted as part of the Ajo PM10 Maintenance Plan 
as satisfying the emissions inventory requirement under section 
172(c)(3) for the Ajo planning area for the PM10 NAAQS.
---------------------------------------------------------------------------

    \42\ General Preamble, 13498, 13564.
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b. Permits for New and Modified Major Stationary Sources
    CAA sections 172(c)(5) and 189(a)(1)(A) require that states submit 
SIP revisions that establish certain requirements for new or modified 
major stationary sources in nonattainment areas, including provisions 
to ensure that major new sources or major modifications of existing 
sources of nonattainment pollutants incorporate the highest level of 
control (referred to as the lowest achievable emission rate (LAER)), 
and that increases in emissions from such stationary sources are offset 
so as to provide for RFP towards attainment in the nonattainment area. 
The major source threshold for Moderate PM10 nonattainment 
areas is 100 tons per year of PM10.\43\
---------------------------------------------------------------------------

    \43\ CAA section 302(j).
---------------------------------------------------------------------------

    The process for reviewing permit applications and issuing permits 
for new or modified stationary sources of air pollution is referred to 
as new source review (NSR). With respect to nonattainment pollutants in 
nonattainment areas, this process is referred to as nonattainment NSR 
(NNSR). Areas that are designated as attainment or unclassifiable for 
one or more NAAQS are required to submit SIP revisions that ensure that 
major new stationary sources or major modifications of existing 
stationary sources meet the federal requirements for PSD, including 
application of best available control technology for each applicable 
pollutant emitted in significant amounts, among other requirements.\44\
---------------------------------------------------------------------------

    \44\ PSD requirements control the growth of new source emissions 
in areas designated as attainment or unclassifiable for a NAAQS.
---------------------------------------------------------------------------

    The ADEQ and the PDEQ share air permitting responsibilities in Pima 
County. ADEQ has an EPA-approved NNSR program for PM10.\45\ 
With respect to sources subject to PDEQ's jurisdiction, EPA-approved 
regulations include rules for the review of applications for new or 
modified stationary sources. The EPA has not approved PDEQ regulations 
specifically meeting the NNSR requirements of CAA sections 172(c)(5) 
and 189(a)(1)(A). However, the EPA interprets section 107(d)(3)(E)(v) 
of the CAA such that final approval of an NNSR program is not a 
prerequisite to approving a state's redesignation request. The EPA has 
determined in past redesignations that an NNSR program does not have to 
be approved prior to redesignation provided that the area demonstrates 
maintenance of the standards without part D NNSR requirements in 
effect.\46\
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    \45\ 80 FR 67319 (November 2, 2015); 83 FR 19631 (May 4, 2018).
    \46\ See, generally, the Nichols memo; see also, the more 
detailed explanations in the following redesignation rulemakings: 
Detroit, Michigan (60 FR 12467-12468, March 7, 1996); Cleveland-
Akron-Lorrain, Ohio (61 FR 20458, 20469-20470, May 7, 1996); 
Louisville, Kentucky (66 FR 53665, 53669, October 23, 2001); Grand 
Rapids, Michigan (61 FR 31831, 31836-31837, June 21, 1996); and San 
Joaquin Valley, California (73 FR 22307, 22313, April 25, 2008 and 
73 FR 66759, 66766-66767, November 12, 2008).
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    The demonstration of maintenance of the PM10 NAAQS in 
the Ajo PM10 Maintenance Plan relies on projections

[[Page 34387]]

of future emissions based on various growth factors. For the types of 
stationary sources that are subject to PDEQ jurisdiction, future 
emissions are projected based on employment growth projections and do 
not take credit for future control technology requirements, such as 
LAER, or for imposition of emissions offsets.\47\ Thus, we find that 
the maintenance demonstration for the Ajo planning area does not rely 
on an NNSR program, and that the area need not have a fully-approved 
NNSR program prior to approval of the PM10 redesignation 
request for the area.
---------------------------------------------------------------------------

    \47\ Ajo PM10 Maintenance Plan, Appendix A.
---------------------------------------------------------------------------

    If we finalize the redesignation action as proposed herein, the 
requirements of the PSD program will apply with respect to 
PM10 (PSD already applies with respect to the other 
pollutants in the Ajo planning area).
    The ADEQ has an EPA-approved PSD program under 40 CFR 51.166,\48\ 
except for greenhouse gases (GHGs),\49\ and the EPA has delegated the 
PDEQ authority to administer the federal PSD program under 40 CFR 
52.21.\50\ These programs will apply to PM10 emissions from 
new major sources and major modifications upon redesignation of the 
area to attainment. Thus, new major sources with significant 
PM10 emissions and major modifications of major 
PM10 sources, as defined under 40 CFR 51.166 and 52.21, will 
be required to obtain a PSD permit.
---------------------------------------------------------------------------

    \48\ 83 FR 19631 (May 4, 2018).
    \49\ The ADEQ administers the requirements for GHGs under a 
delegation agreement with the EPA.
    \50\ 40 CFR 52.144.
---------------------------------------------------------------------------

    We conclude that the Arizona SIP adequately meets the requirements 
of section 172(c)(5) and 189(a)(1)(A) for purposes of redesignation of 
the Ajo planning area.
c. Control Requirements for PM10 Precursors
    Section 189(e) of the CAA provides that control requirements for 
major stationary sources of direct PM10 also apply to 
PM10 precursors from those sources, except where the EPA 
determines that major stationary sources of such precursors do not 
contribute significantly to PM10 levels that exceed the 
standards in the area. The CAA does not explicitly address whether it 
would be appropriate to include a potential exemption from precursor 
controls for all source categories under certain circumstances. In 
implementing subpart 4, the EPA permitted states to determine that a 
precursor was ``insignificant'' where the state could show in its 
attainment plan that it would expeditiously attain without adoption of 
emission reduction measures aimed at that precursor. This approach was 
upheld in Association of Irritated Residents v. EPA, 423 F.3d 989 (9th 
Cir. 2005). A state may develop its attainment plan and adopt RACM that 
target only those precursors that are necessary to control for purposes 
of timely attainment.
    Therefore, because the requirement of section 189(e) is primarily 
actionable in the context of addressing precursors in an attainment 
plan, a precursor exemption analysis under section 189(e) and the EPA's 
implementing regulations is not an applicable requirement that needs to 
be fully approved in the context of a redesignation under CAA section 
107(d)(3)(E)(ii). As discussed earlier in this document, for areas that 
are attaining the standards, the EPA does not interpret attainment 
planning requirements of subpart 1 and subpart 4 to be applicable 
requirements for the purposes of redesignating the area to attainment.
    As previously noted, the EPA determined in 2006 that the Ajo 
PM10 nonattainment area had attained the PM10 
NAAQS. Therefore, no additional controls of any pollutant, including 
any PM10 precursor, are necessary to bring the area into 
attainment. In section IV.A of this document, we find that the area 
continues to attain the NAAQS. In section IV.C, the EPA is proposing to 
determine that the Ajo PM10 nonattainment area has attained 
the standards due to permanent and enforceable emission reductions. 
Further, as set forth in section IV.D.2, we find that the Ajo 
PM10 Maintenance Plan demonstrates continued maintenance of 
the PM10 standards through 2031. Finally, the Ajo 
PM10 Maintenance Plan demonstrates that historic violations 
of the PM10 NAAQS were the direct result of operations at 
facilities that are no longer in operation, there are no major sources 
of PM10 precursors in the Ajo PM10 nonattainment 
area, and emissions of PM10 precursors from other sources 
are sufficiently low that they are insignificant contributors to 
secondary particle formation in the Ajo PM10 nonattainment 
area. Taken together, these factors support our conclusion that 
PM10 precursors are adequately controlled.
d. Compliance With Section 110(a)(2)
    Section 172(c)(7) requires the SIP to meet the applicable 
provisions of section 110(a)(2). As described in section IV.B.1 of this 
document, we conclude that the Arizona SIP meets the requirements of 
section 110(a)(2) applicable for purposes of this redesignation.
e. General and Transportation Conformity Requirements
    Under section 176(c) of the CAA, states are required to revise 
their SIPs to establish criteria and procedures to ensure that 
federally supported or funded projects in nonattainment areas and 
former nonattainment areas subject to a maintenance plan (referred to 
as ``maintenance areas'') conform to the air quality planning goals in 
the applicable SIP. Section 176(c) further provides that state 
conformity provisions must be consistent with federal conformity 
regulations that the CAA requires the EPA to promulgate. The EPA's 
conformity regulations are codified at 40 CFR part 93, subpart A 
(referred to herein as ``transportation conformity'') and subpart B 
(referred to herein as ``general conformity''). Transportation 
conformity applies to transportation plans, programs, and projects 
developed, funded, and approved under title 23 U.S.C. or the Federal 
Transit Act, and general conformity applies to all other federally-
supported or funded projects. SIP revisions intended to address the 
conformity requirements are referred to herein as ``conformity SIPs.'' 
In 2005, Congress amended section 176(c) of the CAA. Under the amended 
conformity statutory provisions, states are no longer required to 
submit conformity SIPs for general conformity, and the conformity SIP 
requirements for transportation conformity have been reduced to include 
only those relating to consultation, enforcement, and 
enforceability.\51\
---------------------------------------------------------------------------

    \51\ CAA section 176(c)(4)(E).
---------------------------------------------------------------------------

    We have not approved a transportation conformity SIP for the Ajo 
planning area. However, we consider it reasonable to interpret the 
conformity SIP requirements as not applying for purposes of a 
redesignation request under section 107(d) because the conformity SIP 
requirement continues to apply post-redesignation (because conformity 
applies in maintenance areas as well as nonattainment areas) and 
because the federal conformity rules (set forth in 40 CFR part 93, 
subpart A and subpart B) apply where state rules have not been 
approved.\52\
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    \52\ See Wall v. EPA, 265 F.3d 426 (6th Cir. 2001), upholding 
this interpretation. See also, 60 FR 62748 (December 7, 1995).

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[[Page 34388]]

C. The Area Must Show the Improvement in Air Quality Is Due to 
Permanent and Enforceable Emission Reductions

    To approve a redesignation to attainment, section 107(d)(3)(E)(iii) 
of the CAA requires the EPA to determine that the improvement in air 
quality is due to emission reductions that are permanent and 
enforceable, and that the improvement results from the implementation 
of the applicable SIP, applicable federal air pollution control 
regulations, and other permanent and enforceable regulations. Under 
this criterion, a state must be able to reasonably attribute the 
improvement in air quality to permanent and enforceable emission 
reductions. Attainment resulting from temporary reductions in emission 
rates (e.g., reduced production or shutdown due to temporary adverse 
economic conditions) or unusually favorable meteorology would not 
qualify as an air quality improvement due to permanent and enforceable 
emission reductions.\53\
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    \53\ Calcagni memo, 4.
---------------------------------------------------------------------------

    The Ajo PM10 Maintenance Plan addresses the 
redesignation criterion in section 107(d)(3)(E)(iii) by presenting a 
detailed overview of the sources of PM10 emissions in the 
planning area, the emission control measures that have been 
implemented, the emission reductions associated with those measures, 
and an evaluation of the sequence of facility closures and 
implementation of control measures relative to changes in ambient 
PM10 concentrations measured in the planning area since 
1987.\54\ In short, the principal sources of PM10 emissions 
in the Ajo planning area were the operations and facilities associated 
with the Ajo New Cornelia mine and smelter, and the slag reprocessing 
facility located adjacent to the Ajo tailings piles.
---------------------------------------------------------------------------

    \54\ Ajo PM10 Maintenance Plan, Chapter 4.
---------------------------------------------------------------------------

    Phelps Dodge ceased operations at the Ajo New Cornelia mine in 1984 
and deactivated the smelter in 1985. In 1991, Phelps Dodge arranged for 
the capping of the Ajo New Cornelia tailings impoundment with 2-4'' 
diameter crushed rock. In 1996, the smelter and copper ore concentrator 
structures were effectively dismantled and the ADEQ terminated the 
facility's permit. With respect to the slag reprocessing facility, the 
operator closed the facility in 2015, and PDEQ terminated the 
facility's permit in 2016. Stabilization of the slag reprocessing 
worksite, including application of a slag dust cap on select process 
areas, was completed in 2015. In 2019, the Pima County Board of 
Supervisors adopted PCC Section 17.16.125 (``Inactive Mineral Tailings 
Impoundment and Slag Storage Area within the Ajo PM10 
Planning Area'') to provide for continued maintenance and enforcement 
of the measures already implemented to control windblown dust from the 
tailings impoundment and the slag storage area.
    Emissions from active operations of the mine, smelter, and slag 
reprocessing facility ceased with the closure of those facilities, and 
closure has been made permanent and enforceable by termination of the 
facilities permits. PCC Section 17.16.125 ensures that the measures 
already implemented to control windblown dust from the tailings 
impoundment and slag storage area are permanent and enforceable. In a 
separate rulemaking, we have proposed to approve PCC Section 17.16.125 
as a revision to the Arizona SIP.\55\ We will take final action on PCC 
Section 17.16.125 prior to or concurrent with final action on the 
redesignation request for the Ajo planning area for the PM10 
NAAQS. If we take final action to approve PCC Section 17.16.125 as part 
of the Arizona SIP, the requirements contained therein will become 
permanent and enforceable for the purposes of CAA section 
107(d)(3)(E)(iii). Continued implementation of the measures made 
permanent and enforceable through PCC Section 17.16.125 will help to 
ensure that the Ajo planning area maintains the PM10 NAAQS.
---------------------------------------------------------------------------

    \55\ 85 FR 25379 (May 1, 2020).
---------------------------------------------------------------------------

    A sense of the effectiveness of the control measures to reduce 
PM10 emissions can be gained by comparing emissions and 
monitored air quality concentrations prior to and following the capping 
of the tailings impoundment in 1991 and prior to and following the 
stabilization of the slag processing area in 2015. Capping of the 
tailings impoundments led to a 90 percent reduction of windblown 
emissions from that source that has persisted through the present 
day.\56\ Similarly, stabilization of the slag processing and storage 
area led to a reduction in emissions from that source of approximately 
99 percent.\57\
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    \56\ Ajo PM10 Maintenance Plan, Table 4-1.
    \57\ Id. at 27, Table 4-2.
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    With respect to the connection between the emission reductions and 
the improvement in air quality, we also conclude that the air quality 
improvement in the Ajo PM10 nonattainment area is not the 
result of a local economic downturn or unusual or extreme weather 
patterns. Our conclusion is based on the timing of the exceedances of 
the PM10 NAAQS, which occurred in the late 1980's, prior to 
the capping of the tailings impoundments in 1991; and in 2011 and 2013, 
prior to the closure and stabilization of the slag reprocessing 
facility in 2015.
    Thus, we find that the improvement in air quality in the Ajo 
PM10 nonattainment area is the result of permanent and 
enforceable emission reductions from a combination of (1) facility 
closures and termination of permits, and (2) control measures approved 
by the EPA as part of the Arizona SIP. Therefore, we propose to find 
that the criterion for redesignation set forth at CAA section 
107(d)(3)(E)(iii) is satisfied.

D. The Area Must Have a Fully Approved Maintenance Plan Under Clean Air 
Act Section 175A

    Section 107(d)(3)(E)(iv) of the CAA requires that, to approve a 
redesignation to attainment, the EPA must fully approve a maintenance 
plan for the area as meeting the requirements of section 175A of the 
Act. Section 175A of the CAA sets forth the required elements of a 
maintenance plan for areas seeking redesignation from nonattainment to 
attainment. Under CAA section 175A, the plan must demonstrate continued 
attainment of the applicable NAAQS for at least 10 years after the EPA 
approves a redesignation to attainment. Eight years after 
redesignation, a state must submit a revised maintenance plan that 
demonstrates continued attainment for the subsequent 10-year period 
following the initial 10-year maintenance period. To address the 
possibility of future NAAQS violations, the maintenance plan must 
contain such contingency provisions as the EPA deems necessary to 
promptly correct any violation of the NAAQS that occurs after 
redesignation of the area. The Calcagni memo provides further guidance 
on the content of a maintenance plan, explaining that a maintenance 
plan should include an attainment emissions inventory, maintenance 
demonstration, monitoring and verification of continued attainment, and 
a contingency plan. Based on our review and evaluation of the Plan, as 
discussed below, we are proposing to approve the Ajo PM10 
Maintenance Plan as meeting the requirements of CAA section 175A.
1. Attainment Inventory
    A maintenance plan for the PM10 NAAQS should include an 
inventory of direct PM10 emissions in the area to identify a 
level of emissions sufficient to

[[Page 34389]]

attain the PM10 NAAQS.\58\ The inventory should be 
consistent with the EPA's most recent guidance on emissions inventories 
for nonattainment areas available at the time and should represent 
emissions during the time period associated with the monitoring data 
showing attainment. The inventory must also be comprehensive, including 
emissions from stationary point sources, area sources, and mobile 
sources, and must be based on actual emissions during the appropriate 
season, if applicable.\59\
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    \58\ PM10 precursor emissions should also be included 
depending upon the contribution of secondarily-formed particulate 
matter to high ambient PM10 concentrations in the area. 
In this instance, an inventory of PM10 precursor 
emissions is not required because PM10 precursor controls 
were not relied upon to achieve attainment of the PM10 
NAAQS in the Ajo planning area (see section IV.B.2.c of this 
document) nor are they relied upon to demonstrate maintenance of the 
NAAQS. While not required, the Ajo PM10 Maintenance Plan 
includes an inventory of PM10 precursor emissions in 
appendix A (``Ajo PM10 Emission Inventory Technical 
Support Document'').
    \59\ CAA section 172(c)(3).
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    The specific PM10 emissions inventory requirements are 
set forth in Air Emissions Reporting Rule (40 CFR part 51, subpart A), 
which requires that emissions inventories report filterable and 
condensable components, as applicable.\60\ The EPA has provided 
additional guidance for developing PM10 emissions 
inventories in ``PM10 Emissions Inventory Requirements,'' 
EPA-454/R-94-033 (September 1994) and ``Emissions Inventory Guidance 
for Implementation of Ozone and Particulate Matter National Ambient Air 
Quality Standards (NAAQS) and Regional Haze Regulations'' (July 2017) 
(``EPA 2017 EI Guidance'').
---------------------------------------------------------------------------

    \60\ 40 CFR 51.15(a)(1)(vii).
---------------------------------------------------------------------------

    The Ajo PM10 Maintenance Plan's demonstration that the 
area attained the standards is based on monitoring data from 2015-2017, 
the three most recent years with complete air quality data prior to 
adoption and submittal of the redesignation request and maintenance 
plan. The ADEQ selected 2016 for the attainment year inventory, which 
is consistent with this time period. Emissions are also provided for a 
2011 pre-base year and 2014 base year for informational purposes.
    The emissions inventories in the Ajo PM10 Maintenance 
Plan include estimates from all relevant source categories, which the 
Plan divides among point, nonpoint, windblown, and mobile.\61\ The ADEQ 
developed the emissions inventories based on the EPA's National 
Emissions Inventory (NEI) and the ADEQ's internal point source 
database. The year 2014 was selected as the base year because the 2014 
NEIv1 was the most current, accurate, and comprehensive inventory 
available when the Plan was being developed. The 2016 inventory has 
been projected from the 2014 inventory. The Plan includes a description 
of facility types, emitting equipment, permitted emission limits, 
operating rates, and emission calculation methods.
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    \61\ Ajo PM10 Maintenance plan, section 6.1 and 
Appendix A.
---------------------------------------------------------------------------

    The Ajo PM10 Maintenance Plan includes inventories for 
total primary PM10 for 2011, 2014, 2016, 2021, 2026, and 
2031, and for NOX, SO2, VOC, and ammonia as 
PM10 precursors for 2014.\62\ Appendix A to the Ajo 
PM10 Maintenance Plan contains additional details on each of 
the emissions inventories. The ADEQ determined, based on the fact that 
there are no major sources of NOX, SO2, VOC, or 
ammonia in the nonattainment area and the relatively low emissions in 
2014 from other sources of these precursors in the nonattainment area, 
that sources of NOX, SO2, VOC, and ammonia are 
insignificant contributors to secondary particle formation in the Ajo 
PM10 nonattainment area.\63\ Therefore, NOX, 
SO2, VOC, and ammonia emissions are not included in the 
PM10 emissions inventories in the Ajo PM10 
Maintenance Plan. The Plan notes that there are no major sources of 
condensable PM in the area, so condensable PM is not reported in the 
emissions inventory.\64\
---------------------------------------------------------------------------

    \62\ Id., Table 6-1, and Appendix A Tables A-14 through A-18.
    \63\ Id., Appendix A, section A5.1.
    \64\ Id. Because approximately 95 percent of the Ajo 
PM10 emissions inventory is crustal material (which does 
not include condensable particulate matter), we find that not 
including the condensable fraction of PM10 in the 
PM10 inventories for the Ajo PM10 Maintenance 
Plan is acceptable.
---------------------------------------------------------------------------

    Table 2 presents a summary of actual PM10 emissions 
estimates for the 2014 base year, and projected emissions for the 2016 
attainment year, for sources in the Ajo PM10 nonattainment 
area. Based on the estimates for the year 2016 in Table 2, windblown 
dust accounts for approximately 95 percent of total PM10 
emissions in the Ajo nonattainment area. A majority of windblown 
emissions are from open areas, vacant land, and inactive properties 
previously associated with mining and smelting activities. Dust 
associated with construction and unpaved roads are the next largest 
source categories; together, they account for approximately four 
percent of total PM10 emissions in the Ajo nonattainment 
area. As discussed earlier, there are no major PM10 point 
sources in the Ajo nonattainment area.

                    Table 2--2014 and 2016 PM10 Emissions in the Ajo PM10 Nonattainment Area
                                                 [Tons per year]
----------------------------------------------------------------------------------------------------------------
                   Category                                  Source                    2014            2016
----------------------------------------------------------------------------------------------------------------
Point.........................................  Point sources...................           51.86            0.41
Nonpoint......................................  Agriculture--Crops and livestock            0.11            0.11
                                                 dust.
                                                Commercial cooking..............            0.98            0.98
                                                Dust--Construction dust.........           42.80           43.05
                                                Dust--Paved road dust...........            4.58            4.60
                                                Dust--Unpaved road dust.........           28.20           28.37
                                                Fires...........................            0.00            0.00
                                                Fuel combustion.................            3.71            3.73
                                                Industrial processes............            0.58            0.58
                                                Miscellaneous non-industrial NEC            0.17            0.17
                                                Solvent--Industrial surface                 0.00            0.00
                                                 coating and solvent use.
                                                Waste Disposal..................            4.20            4.22
Windblown.....................................  Dust--Windblown.................        1,592.73        1,592.73
Mobile........................................  Mobile--Aircraft................            0.00            0.00
                                                Mobile--Locomotives.............            0.00            0.00
                                                Mobile--Non-road equipment......            1.09            1.09
                                                Mobile--On-road.................            0.29            0.30
                                                                                 -------------------------------

[[Page 34390]]

 
    Total.....................................  ................................        1,731.29        1,680.35
----------------------------------------------------------------------------------------------------------------
Source: Ajo PM10 Maintenance Plan, Tables 6-1 and 6-2.

    Based on our review of the emissions inventories in the Ajo 
PM10 Maintenance Plan, including the supporting information 
in Appendix A, we find that the inventory for year 2016 is 
comprehensive, that the methods and assumptions used by the ADEQ to 
develop the inventories are reasonable, and that the 2016 inventory 
reasonably estimates actual PM10 emissions in that year. 
Therefore, we are proposing to approve the 2016 emissions inventory as 
satisfying the requirements of section 172(c)(3) of the CAA. We also 
find that the 2016 emissions inventory is appropriate for use as the 
attainment inventory for the Ajo PM10 Maintenance Plan 
because the year 2016 is within the 2015-2017 period during which the 
area was attaining the PM10 standards.\65\
---------------------------------------------------------------------------

    \65\ EPA 2018 p.m.10 Design Value Report, 
``pm10_designvalues_20162018_final_07_19_19.xlsx.''
---------------------------------------------------------------------------

2. Maintenance Demonstration
    Section 175A(a) of the CAA requires that the maintenance plan 
``provide for the maintenance of the national primary ambient air 
quality standard for such air pollutant in the area concerned for at 
least 10 years after the redesignation.'' A state may generally 
demonstrate maintenance of the NAAQS by either showing that future 
emissions of a pollutant or its precursors will not exceed the level of 
the attainment inventory, or by conducting modeling that shows that the 
future mix of sources and emission rates will not cause a violation of 
the NAAQS.\66\
---------------------------------------------------------------------------

    \66\ Calcagni memo, 9-11.
---------------------------------------------------------------------------

    The Ajo PM10 Maintenance Plan demonstrates that the Ajo 
planning area will maintain the PM10 NAAQS though 2031 by 
comparing the 2014 base year and 2016 attainment year inventories to 
projected emissions for 2021 (assumed first year of the maintenance 
period), 2026 (interim year), and 2031 (end of the maintenance 
period).\67\ Using the 2014 emissions inventory as a baseline and 
growth factors described in appendix A of the Plan (see section A5), 
the ADEQ projected emissions inventories for 2021, 2026, and 2031. 
These projections were based primarily on Arizona's forecasts of 
population and on the EPA on-road emissions model (i.e., MOVES2014a). 
Table 3 summarizes the ADEQ's 2016 attainment year PM10 
emissions and projected PM10 emission levels for 2021, 2026, 
and 2031.
---------------------------------------------------------------------------

    \67\ Ajo PM10 Maintenance Plan, section 6.2, and 
Appendix A, section A6.

       Table 3--Attainment Year (2016) and Projected (2021, 2026, and 2031) PM10 Emissions in the Ajo PM10
                                               Nonattainment Area
                                                 [Tons per year]
----------------------------------------------------------------------------------------------------------------
            Category                   2014            2016            2021            2026            2031
----------------------------------------------------------------------------------------------------------------
Point a.........................           51.86            0.41            0.41            0.41            0.41
Nonpoint........................           85.33           85.82           91.17           95.98          100.56
Windblown.......................        1,592.73        1,592.73        1,592.73        1,592.73        1,592.73
Mobile b........................            1.38            1.39            1.42            1.50            1.56
                                 -------------------------------------------------------------------------------
    Total.......................        1,731.29        1,680.35        1,685.73        1,690.61        1,695.26
----------------------------------------------------------------------------------------------------------------
a Includes activity-based emissions only. Windblown emissions from point sources are included in the windblown
  category.
b Re-entrained dust from paved and unpaved roads is included in the emissions estimates for nonpoint sources.
Source: Ajo PM10 Maintenance Plan, Table 6-3.

    Despite expected growth in the area, the maintenance plan's 
projected PM10 emissions in Ajo through 2031 are within one 
percent of the 2016 attainment year inventory emissions and are lower 
than emissions in 2014, a year in which there were no recorded 
exceedances of the PM10 NAAQS. The decrease in 
PM10 emissions between 2014 and 2016 reflects the closure 
and stabilization of slag processing activities in the Ajo 
PM10 nonattainment area.
    Given the slight increase in PM10 emissions over the 10-
year maintenance period, the Ajo PM10 Maintenance Plan uses 
a simple rollback modeling approach to further support its conclusion 
that the Ajo planning area will continue to maintain the 
PM10 standards. The Plan's rollback modeling assumes that 
PM10 concentrations scale linearly with PM10 
emissions by scaling the 2017 design concentration by the percentage 
increase in the emissions inventory over the maintenance period. The 
Ajo PM10 Maintenance Plan finds that the projected design 
concentrations for the Ajo planning area over the maintenance period 
are less than 70 percent of the NAAQS, within a margin of safety of the 
PM10 standards.
    Normally in a rollback modeling approach, some portion of the 
observed concentration is assumed to be ``background'' and therefore 
not affected by emissions from local sources. The background can be 
estimated by concentrations from a relatively pristine nearby area. The 
ADEQ's procedure assumes that the entire PM10 concentration 
scales up with local emissions, whereas in reality the background 
portion would not scale up. The result is a conservatively high 
projection for future concentrations.
    Based on our review, we find that the methods, growth factors, and 
assumptions used by the ADEQ to project emissions to 2021, 2026, and 
2031 levels are reasonable. Given that the projections (summarized in 
Table 3) show future emissions through 2031 are within one percent of 
those in 2016 and below those in 2014 (both of which reflect attainment 
conditions), we find that the projections provide an adequate basis to 
demonstrate maintenance of the

[[Page 34391]]

PM10 standards within the Ajo planning area through 2031. We 
further find that the State's rollback modeling provides additional 
support that the area will continue to maintain the standards through 
the end of the 10-year maintenance period.
    Section 175A requires that maintenance plans provide for 
maintenance of the relevant NAAQS in the area for at least 10 years 
after redesignation. If this redesignation becomes effective in 2020, 
the projected 2031 inventory demonstrates that the Ajo area will 
maintain the PM10 NAAQS for more than 10 years beyond 
redesignation. Moreover, the projected emissions inventories for 2021 
and 2026, i.e., milestone years between the attainment inventory and 
the maintenance plan horizon year, sufficiently demonstrate that the 
Ajo planning area will maintain the standards throughout the period 
from redesignation through 2031. Thus, we conclude that the Ajo 
PM10 Maintenance Plan adequately demonstrates maintenance of 
the standards through 2031.
3. Verification of Continued Attainment
    Once an area has been redesignated, the state should continue to 
operate an appropriate air quality monitoring network, in accordance 
with 40 CFR part 58, to verify the attainment status of the area.\68\ 
Data collected by the monitoring network are also needed to implement 
the contingency provisions of the maintenance plan.
---------------------------------------------------------------------------

    \68\ Calcagni memo, 11.
---------------------------------------------------------------------------

    As discussed in section IV.A of this proposal, PM10 is 
currently monitored by the ADEQ within the Ajo PM10 
nonattainment area. In section 6.3 of the Ajo PM10 
Maintenance Plan, the ADEQ commits to continue operating a 
PM10 air quality monitoring network in the Ajo planning area 
and to consult with EPA regarding any potential changes to the network. 
We find that the Ajo PM10 Maintenance Plan contains adequate 
provisions for continued ambient PM10 monitoring to verify 
continued attainment through the maintenance period.
    The EPA also recommends that the state verify continued attainment 
through methods in addition to the ambient air monitoring program, 
e.g., through periodic review of the factors used in development of the 
attainment inventory to show no significant change.\69\ In the Ajo 
PM10 Maintenance Plan, the ADEQ commits to perform a 
comprehensive review of the factors and assumptions used to develop the 
attainment and projected inventories to determine whether significant 
changes have occurred. The ADEQ's review will be conducted for the 2026 
interim projection year and may include the following elements: permit 
applications and source reports, population data, agricultural activity 
information, wildfire/prescribed burning data, and motor vehicle 
activity data.\70\ In the Plan, the ADEQ also identifies the legal 
authority under which the ADEQ and the PDEQ collect the information 
necessary for the ADEQ to conduct the comprehensive review of the 
factors and assumptions used to develop the attainment and projected 
emissions inventories. We find that the ADEQ's commitment to verify 
continued attainment of the NAAQS through a comprehensive review of the 
factors and assumptions used to develop the emissions inventories in 
the Ajo PM10 Maintenance Plan is acceptable.
---------------------------------------------------------------------------

    \69\ Id.
    \70\ Ajo PM10 Maintenance Plan, 45-46.
---------------------------------------------------------------------------

4. Contingency Provisions
    Section 175A(d) of the CAA requires that maintenance plans contain 
contingency provisions, as the EPA deems necessary, to promptly correct 
any violations of the NAAQS that occur after redesignation of the area. 
Such provisions must include a requirement that the state will 
implement all measures with respect to the control of the air pollutant 
concerned that were contained in the SIP for the area before 
redesignation of the area as an attainment area. These contingency 
provisions are distinguished from contingency measures required for 
nonattainment areas under CAA section 172(c)(9) in that they are not 
required to be fully-adopted measures that will take effect without 
further action by the state for the maintenance plan to be approved. 
However, the contingency provisions of a maintenance plan are 
considered to be an enforceable part of the SIP and should ensure that 
contingency measures are adopted expeditiously once they are triggered 
by a specified event. The maintenance plan should clearly identify the 
measures to be adopted, include a schedule and procedure for adoption 
and implementation of the measures, and contain a specific timeline for 
action by the state. In addition, the state should identify the 
specific indicators or triggers that will be used to determine when the 
contingency measures need to be implemented.
    The ADEQ has adopted a contingency plan to address possible future 
PM10 air quality problems in the Ajo planning area. The 
contingency provisions are included in section 6.5 of the Plan. Upon a 
monitored violation of the PM10 NAAQS at the ADEQ's Ajo 
PM10 monitoring site, the ADEQ commits to the following 
steps:
    1. Within 60 days of the NAAQS violation trigger, the ADEQ will 
begin analyzing the cause(s) of the exceedance. The analysis will 
include review and validation of ambient air quality and meteorological 
data, evaluation to determine if the violation qualifies as an 
exceptional event per EPA's Exceptional Event Rule (EER),\71\ and 
assessment of emissions sources contributing to elevated 
PM10 levels.
---------------------------------------------------------------------------

    \71\ 81 FR 68216 (October 3, 2016).
---------------------------------------------------------------------------

    2. If the exceedance qualifies as an exceptional event, the ADEQ 
will prepare and submit to the EPA an exceptional event demonstration. 
If, during their evaluation, the ADEQ determines that new measures are 
needed to satisfy the requirements of the exceptional events rule, the 
ADEQ will adopt and implement new measures that are permanent and 
enforceable and meet the ``reasonable'' level of control described in 
the EER.
    3. If the exceedance does not qualify as an exceptional event, the 
ADEQ will determine which source(s) contributed to the exceedance, 
identify existing control measures for the source(s), verify source(s) 
compliance with existing measures, and if necessary, develop, adopt and 
implement new permanent and enforceable measures or strengthen existing 
measures.
    Under the contingency plan, if new measures are needed, the 
adoption process will begin within 12 months, and final adoption will 
be completed within 18 months, of the triggering event (i.e., a 
monitored violation of the PM10 NAAQS at the Ajo monitoring 
site). The ADEQ would require compliance with new measures within six 
months of final adoption.
    The Ajo PM10 Maintenance Plan includes a list of 
contingency measures, focusing on the principal source categories 
contributing to PM10 emissions in the area, that may be 
considered for implementation in the event the contingency plan is 
triggered.\72\ Table 4 presents the ADEQ's potential PM10 
contingency measures for the Ajo planning area.
---------------------------------------------------------------------------

    \72\ Ajo PM10 Maintenance Plan, 48.

[[Page 34392]]



         Table 4--Ajo PM10 Maintenance Plan Contingency Measures
------------------------------------------------------------------------
      Emissions category             Potential contingency measure
------------------------------------------------------------------------
Paved Roads..................  Increase stabilization of unpaved
                                shoulders.
                               Increase stabilization of access points
                                from unpaved roads.
Unpaved Roads................  Increase stabilization of unpaved roads
                                and shoulders.
                               Post speed limits to decrease vehicle
                                speeds.
                               Restrict access to decrease average daily
                                trips and vehicle miles traveled.
Unpaved Parking..............  Pave or stabilize unpaved parking areas.
Disturbed Open Areas and Lots  Stabilize disturbed open areas.
                               Restrict access to minimize disturbance.
Material Handling and Storage  Review/revise dust control measures for
                                material handling and storage.
Construction.................  Review/revise dust control measures for
                                construction activities.
------------------------------------------------------------------------
Source: Ajo PM10 Maintenance Plan, Table 6-5.

    Upon review of the contingency plan summarized above, we find that 
the ADEQ has established a contingency plan for the Ajo planning area 
that clearly identifies specific contingency measures, contains 
tracking and triggering mechanisms to determine when contingency 
measures are needed, contains a description of the process of 
recommending and implementing contingency measures, and contains 
specific timelines for action. Thus, we conclude that the contingency 
provisions of the Ajo PM10 Maintenance Plan are adequate to 
ensure prompt correction of a violation and to satisfy the requirements 
of the CAA section 175A(d).
5. Transportation Conformity and Motor Vehicle Emissions Budgets
    Section 176(c) of the CAA requires federal actions in nonattainment 
and maintenance areas to conform to the SIP's goals of eliminating or 
reducing the severity and number of violations of the NAAQS and 
achieving expeditious attainment of the standards. Conformity to the 
SIP's goals means that such actions will not: (1) Cause or contribute 
to violations of the NAAQS, (2) worsen the severity of an existing 
violation, or (3) delay timely attainment of any NAAQS or any interim 
milestone.
    Actions involving Federal Highway Administration (FHWA) or Federal 
Transit Administration (FTA) funding or approval are subject to the 
EPA's transportation conformity rule, codified at 40 CFR part 93, 
subpart A. Under this rule, metropolitan planning organizations in 
nonattainment and maintenance areas coordinate with state and local air 
quality and transportation agencies, the EPA, FHWA, and FTA to 
demonstrate that an area's regional transportation plans and 
transportation improvement programs conform to the applicable SIP. This 
demonstration is typically done by showing that estimated emissions 
from existing and planned highway and transit systems are less than or 
equal to the motor vehicle emissions budgets (``budgets'') contained in 
all control strategy SIPs and maintenance plans.\73\
---------------------------------------------------------------------------

    \73\ Control strategy SIPs refer to RFP and attainment 
demonstration SIPs. 40 CFR 93.101.
---------------------------------------------------------------------------

    These control strategy SIPs and maintenance plans typically set 
budgets for criteria pollutants and/or their precursors to address 
pollution from cars and trucks. Budgets are generally established for 
specific years and specific pollutants or precursors and must reflect 
the motor vehicle control measures contained in the RFP plan and the 
attainment or maintenance demonstration. Under the Transportation 
Conformity Rule, budgets must be established for the last year of the 
maintenance plan for direct PM10 and PM10 
precursors subject to transportation conformity analyses.\74\ For motor 
vehicle emissions budgets to be approvable, they must meet, at a 
minimum, the EPA's adequacy criteria.\75\
---------------------------------------------------------------------------

    \74\ Section 93.102(b)(2)(iii) of the conformity rule identifies 
VOC and NOX as PM10 precursor pollutants that 
are presumed insignificant unless the SIP makes a finding that the 
precursor is significant.
    \75\ 40 CFR 93.118(e)(4).
---------------------------------------------------------------------------

    The Transportation Conformity Rule allows areas to forgo 
establishment of budgets where the EPA finds through the adequacy or 
approval process that a control strategy SIP or maintenance plan 
demonstrates that the regional motor vehicle emissions for a particular 
pollutant or precursor are an insignificant contributor to the air 
quality problem in the area. The criteria for insignificance 
determinations can be found in 40 CFR 93.109(f). In order for a 
pollutant or precursor to be considered insignificant, the SIP would 
have to demonstrate that it would be unreasonable to expect that such 
an area would experience enough motor vehicle emissions growth in that 
pollutant/precursor for a NAAQS violation to occur. Insignificance 
determinations are based on a number of factors, including (1) the 
current state of air quality as determined by monitoring data for that 
NAAQS; (2) the absence of SIP motor vehicle control measures; (3) 
historical trends and future projections of the growth of motor vehicle 
emissions; and (4) the percentage of motor vehicle emissions in the 
context of the total SIP inventory. The EPA's rationale for providing 
for insignificance determinations is described in the July 1, 2004, 
revisions to the Transportation Conformity Rule.\76\ Specifically, the 
rationale is explained on page 40061 under the subsection entitled 
``XXIII. B. Areas With Insignificant Motor Vehicle Emissions.''
---------------------------------------------------------------------------

    \76\ 69 FR 40004.
---------------------------------------------------------------------------

    In chapter 7 of the Ajo PM10 Maintenance Plan, the ADEQ 
included a demonstration that on-road emissions of direct 
PM10 are insignificant for conformity purposes, and 
therefore the State did not submit any budgets. The EPA is proposing to 
approve the ADEQ's insignificance demonstration for the on-road motor 
vehicle contribution of PM10 to overall PM10 
emissions in the maintenance plan.
    The information provided by the ADEQ to the EPA as part of the Ajo 
PM10 Maintenance Plan addresses each of the factors listed 
in 40 CFR 93.109(f), and is summarized below. PM10 
concentrations for the area have been decreasing over the past several 
years.\77\ Furthermore, transportation-related emissions in 2031 are 
projected to account for less than three percent of total direct 
PM10 emissions from all sources in the Ajo planning area. 
Our detailed evaluation and conclusions are as follows:
---------------------------------------------------------------------------

    \77\ Ajo PM10 Maintenance Plan, Figure 4-1.
---------------------------------------------------------------------------

(1) The Ajo Planning Area Is Attaining the PM10 NAAQS
    The Ajo PM10 Maintenance Plan demonstrates that the area 
was attaining the PM10 standards during the 2015-2017 period 
upon which the Plan is based. Furthermore, as discussed in

[[Page 34393]]

section IV.A of this proposal, data from the most recent three-year 
period (2017-2019), as well as preliminary 2020 data, indicate that 
area continues to attain the PM10 standards.
(2) Motor Vehicle Control Measures Were Not Adopted for the Purpose of 
Bringing the Area Into Attainment
    As discussed in more detail in section IV.C of this document, the 
control measures relied upon in the Ajo PM10 Maintenance 
Plan to bring the area into attainment are primarily associated with 
fugitive dust control measures applicable to the Ajo mine tailings and 
slag storage areas. The Ajo portion of the Arizona SIP does not rely on 
the control of on-road emissions to demonstrate attainment or 
maintenance of the PM10 NAAQS.
(3) The Percentage of Motor Vehicle Emissions in the Context of the 
Total SIP Inventory Is Low
    As shown in Table 5, the percentage contribution of motor vehicle 
emissions to total emissions for PM10 is small. In the 2016 
attainment year, emissions of PM10 from on-road motor 
vehicles contributed only 1.98 percent of the Ajo total PM10 
emissions inventory. At the end of the 10-year maintenance period 
(2031), motor vehicle PM10 emissions are projected to 
contribute just 2.30 percent.

                  Table 5--Transportation-Related Emissions in the Ajo PM10 Nonattainment Area
                                                 [Tons per year]
----------------------------------------------------------------------------------------------------------------
         Emission sector               2014            2016            2021            2026            2031
----------------------------------------------------------------------------------------------------------------
On-road mobile..................            0.29            0.30            0.26            0.27            0.28
Re-entrained dust...............           32.78           32.97           35.03           36.88           38.63
Road construction...............               0               0               0               0               0
Total--Mobile...................           33.07           33.27           35.29           37.15           38.91
Total--All......................        1,731.29        1,680.35        1,685.37        1,690.61        1,695.26
Percent--Mobile.................           1.91%           1.98%           2.09%           2.20%           2.30%
----------------------------------------------------------------------------------------------------------------
Source: Ajo PM10 Maintenance Plan, Tables 6-3 and 7-1.

(4) Historical Trends and Future Projections Indicate Motor Vehicle 
PM10 Emissions Will Continue To Be a Small Fraction of Total 
Emissions
    Finally, historical trends and future projections of the growth of 
motor vehicle PM10 emissions in the Ajo area suggest that 
motor vehicle-related PM10 emissions are not likely to 
increase and therefore, are not likely to cause or contribute to a 
future violation of the PM10 standards. The Ajo 
PM10 planning area is geographically small and has a 
relatively low population with very modest projected population growth 
through 2031.\78\ According to the US Census Bureau, the population in 
Ajo peaked at approximately 7,000 in the 1960s, declining to 
approximately 3,300 in 2010. The State attributes the reduction to 
waning mining activities and the shutdown of the Ajo copper smelter in 
1985. Since that time, the Ajo area has experienced little growth 
compared to other parts of Pima County. The population is projected to 
increase 17 percent between 2016 and 2031, to approximately 3,900 
inhabitants.
---------------------------------------------------------------------------

    \78\ Ajo PM10 Maintenance Plan, section 1.6.3.
---------------------------------------------------------------------------

    The main traffic corridor through Ajo is State Route 85, which 
connects the Mexican border area with Interstate 8. While traffic 
between the U.S. and Mexico passes through Ajo along this corridor, it 
is less than the traffic along the two major border crossings in the 
Yuma and Nogales areas.\79\ Traffic data from the ADOT shows that 
vehicle miles traveled has not increased substantially over the past 
decade, and emissions from mobile sources are projected to remain 
approximately constant and less than 2.5 percent of total 
PM10 emissions in Ajo through 2031, as shown in Table 5.
---------------------------------------------------------------------------

    \79\ US Department of Transportation, Bureau of Transportation 
Statistics, 2018 border crossing data, available at https://explore.dot.gov/t/BTS/views/BTSBorderCrossingAnnualData/BorderCrossingTableDashboard?:embed=y&:showShareOptions=true&:display_count=no&:showVizHome=no.
---------------------------------------------------------------------------

    In summary, given the small population, historically declining or 
modest population growth, and historical and projected traffic 
information, motor vehicle emissions are not expected to increase in 
the Ajo area to the point where a violation of the PM10 
NAAQS would occur.
    As part of our review of the ADEQ's insignificance demonstration, 
we announced receipt of the Ajo PM10 Maintenance Plan and 
posted an announcement of availability on the EPA Office of 
Transportation and Air Quality's transportation conformity website.\80\ 
We requested public comments by June 24, 2019. We did not receive any 
comments.
---------------------------------------------------------------------------

    \80\ https://www.epa.gov/state-and-local-transportation/adequacy-review-state-implementation-plan-sip-submissions-conformity.
---------------------------------------------------------------------------

    After evaluating the information provided by the ADEQ and weighing 
the factors for the insignificance determination outlined in 40 CFR 
93.109(f), the EPA is proposing to find that the Ajo PM10 
Maintenance Plan adequately demonstrates that the PM10 
contributions from motor vehicle emissions to the PM10 air 
quality problem in the Ajo nonattainment area are insignificant.
    If the EPA's insignificance finding is finalized, the Pima 
Association of Governments would no longer be required to perform 
regional emissions analyses for PM10 as part of future 
PM10 conformity determinations for the PM10 NAAQS 
for the Ajo planning area. The EPA's insignificance finding should, 
however, be noted in the transportation conformity documentation that 
is prepared for this area. Areas with insignificant regional motor 
vehicle emissions for a pollutant or precursor are still required to 
make a conformity determination that satisfies other relevant 
conformity requirements such as financial constraint, timely 
implementation of transportation control measures, and project level 
conformity.

V. Proposed Deletion of the Total Suspended Particulate Designation for 
Ajo

A. General Considerations

    In section I.B of this document, we noted that the ADEQ included in 
its transmittal letter for the Ajo PM10 Maintenance Plan a 
request to the EPA to delete the TSP nonattainment designation for the 
Ajo planning area. Consistent with section 107(d)(4)(B) of the CAA, we 
have considered the continued necessity for retaining the Ajo TSP area 
designation, and as discussed below, we have determined that the TSP 
designation for Ajo is no

[[Page 34394]]

longer necessary. As a result, we are proposing to delete the 
designation from the TSP table in 40 CFR 81.303.
    To evaluate whether the TSP area designation should be retained or 
can be deleted, we have relied upon the final rule implementing the 
PM10 NAAQS,\81\ a policy memorandum on TSP 
redesignations,\82\ and our proposed and final rules establishing 
maximum allowable increases in concentrations (also known as 
``increments'') for PM10.\83\
---------------------------------------------------------------------------

    \81\ 52 FR 24634 (July 1, 1987).
    \82\ Memorandum dated May 20, 1992, from Joseph W. Paisie, 
Acting Chief, SO2/Particulate Matter Programs Branch, EPA 
Office of Air Quality Planning and Standards, to Chief, Air Branch, 
Regions I-X, entitled ``TSP Redesignation Request.''
    \83\ See the proposed rule at 54 FR 41218 (October 5, 1989), and 
the final rule at 58 FR 31622 (June 3, 1993).
---------------------------------------------------------------------------

    Based on the above references, we consider the relevant 
considerations for evaluating the necessity of retaining the TSP area 
designations to depend upon the status of a given area with respect to 
TSP and PM10. For areas that are nonattainment for TSP but 
attainment for PM10, we generally find that the TSP 
designations are no longer necessary and can be deleted when the EPA 
(1) approves a state's revised PSD program containing the 
PM10 increments, (2) promulgates the PM10 
increments into a state's SIP where the state chooses not to adopt the 
increments on its own, or (3) approves a state's request for delegation 
of PSD responsibility under 40 CFR 52.21(u).\84\
---------------------------------------------------------------------------

    \84\ 58 FR 31622, 31635 (June 3, 1993).
---------------------------------------------------------------------------

    For areas that are nonattainment for TSP and nonattainment for 
PM10, an additional consideration is whether deletion of the 
TSP designation would automatically relax any emission limitations, 
control measures, or programs approved into the SIP. If such a 
relaxation would occur automatically with deletion of the TSP area 
designation, then we will not delete the designation until we are 
satisfied that the resulting SIP relaxation would not interfere with 
any applicable requirement concerning attainment, RFP, or maintenance 
of the NAAQS or any other requirement of the CAA in the affected 
areas.\85\
---------------------------------------------------------------------------

    \85\ CAA section 110(l).
---------------------------------------------------------------------------

    In the case of the Ajo planning area, we believe that the 
considerations for both types of areas described above are relevant 
because although Ajo is nonattainment for PM10, we are 
proposing to redesignate the area to attainment for PM10 in 
this action. Thus, we must take into account both the potential for 
relaxation that would be inconsistent with continued maintenance of the 
PM10 NAAQS as well as protection of the PM10 
increments (as applies in areas designated attainment or 
unclassifiable).

B. Deletion of Total Suspended Particulate Nonattainment Area 
Designation for Ajo

    With respect to protection of the PM10 increments, the 
TSP nonattainment designations are no longer necessary in Ajo because 
the EPA's PSD pre-construction permit program promulgated at 40 CFR 
52.21 applies to those sources under the PDEQ's jurisdiction under a 
delegation agreement with the EPA.\86\ We recognize that the ADEQ 
retains jurisdiction over certain types of sources in Pima County but 
note that we have approved the ADEQ's NSR regulations as satisfying the 
related PSD requirements.
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    \86\ 40 CFR 52.144.
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    To ensure that deletion of the TSP nonattainment designation for 
Ajo would not result in any automatic relaxations in SIP emission 
limitations, control measures, or programs that would interfere with 
attainment, RFP, or maintenance of the NAAQS (including 
PM10) or any other requirement of the Act, we reviewed the 
following portions of the Pima County portion of the Arizona SIP:
     Pima County air pollution control regulations: Chapter III 
(``Universal Control Standards''), particularly, Regulation 31 
(``Design or Work Practice Control Standards'')--Rule 315 (``Roads and 
Streets''), Rule 316 (``Particulate Materials''), and Rule 318 
(``Vacant Lots and Open Spaces''); Regulation 32 (``Emissions-Discharge 
Opacity Limiting Standards'')--Rule 321 (``Standards and 
Applicability''); Regulation 34 (``Ambient-Air Standard'')--Rule 343 
(``Visibility Limiting Standard''); Regulation 37 (``Nonattainment/
Attainment Areas'')--Rule 372 (``Ajo Area''); and Regulation 38 
(``Nonattainment-Area Standard'').
     Pima County air pollution control regulations: Chapter IV 
(``Performance Standards for New Major Sources''), particularly, 
Regulation 41 (``Designation of Attainment/Nonattainment Areas'')--Rule 
412 (``Ajo Area'') and Regulation 42 (``Standards for Nonattainment 
Areas'')--Rule 422 (``TSP Clean-Air Plan'').
    We have focused our review on the Pima County portion of the 
Arizona SIP, rather than on state rules in the SIP, because essentially 
all the types of stationary and area sources that remain in the Ajo 
planning area fall under the PDEQ's rather than the ADEQ's 
jurisdiction. Based on our review of the items listed above, we find 
that none are contingent upon continuation of the TSP nonattainment 
designation and thus deletion of the TSP designation would not 
automatically relax any standard.
    In summary, because upon redesignation the PSD PM10 
increments will apply in the Ajo planning area and because deletion of 
the TSP nonattainment designation for Ajo would not automatically relax 
any emission limitations or control measures in the Arizona SIP, we 
find that the TSP nonattainment designation is no longer necessary and 
can be deleted. Based on the above discussion and evaluation, we are 
therefore proposing to delete the TSP nonattainment area designation 
for Ajo from the ``Arizona-TSP'' table in 40 CFR 81.303.

VI. Proposed Action and Request for Public Comment

    Under CAA section 110(k)(3), and for the reasons set forth above, 
the EPA is proposing to approve the Ajo PM10 Maintenance 
Plan submitted by the ADEQ on May 10, 2019, as a revision to the 
Arizona SIP. In so doing, we are proposing to approve the attainment 
inventory as meeting the requirements of CAA section 172(c)(3), the 
maintenance demonstration and contingency provisions as meeting all of 
the applicable requirements for maintenance plans and related 
contingency provisions in CAA section 175A, and the demonstration that 
the PM10 contributions from motor vehicle emissions to the 
PM10 problem in the Ajo planning area are insignificant.
    In addition, under CAA section 107(d)(3)(D), we are proposing to 
approve ADEQ's request to redesignate the Ajo planning area from 
nonattainment to attainment for the PM10 NAAQS. We are doing 
so based on our conclusion that the area has met, or will meet as part 
of this action, all the criteria for redesignation under CAA section 
107(d)(3)(E). More specifically, we propose to find the following: That 
the Ajo planning area has attained the PM10 NAAQS based on 
the most recent three-year period (2017-2019) of quality-assured, 
certified, and complete PM10 data; that relevant portions of 
the Arizona SIP are, or will be as part of this action, fully approved; 
that the improvement in air quality is due to permanent and enforceable 
reductions in emissions; that Arizona has met all requirements 
applicable to the Ajo planning area with respect to section 110 and 
part D of the CAA if we finalize our approval of the attainment 
inventory in the Ajo PM10 Maintenance

[[Page 34395]]

Plan, as proposed herein; and that the Ajo planning area will have a 
fully approved maintenance plan meeting the requirements of CAA section 
175A if we finalize our approval of it, also as proposed herein.
    Lastly, the EPA is proposing to delete the area designation for Ajo 
for the revoked NAAQS for TSP because the designation is no longer 
necessary.
    We are soliciting comments on these proposed actions. We will 
accept comments from the public for 30 days following publication of 
this proposal in the Federal Register and will consider any relevant 
comments before taking final action.

VII. Statutory and Executive Order Reviews

    Under the CAA, redesignation of an area to attainment and the 
accompanying approval of a maintenance plan under section 107(d)(3)(E) 
are actions that affect the status of a geographic area and do not 
impose any additional regulatory requirements on sources beyond those 
imposed by state law. Redesignation to attainment does not in and of 
itself create any new requirements, but rather, results in the 
applicability of requirements contained in the CAA for areas that have 
been redesignated to attainment. Moreover, the Administrator is 
required to approve a SIP submission that complies with the provisions 
of the Act and applicable federal regulations. 42 U.S.C. 7410(k); 40 
CFR 52.02(a). Thus, in reviewing SIP submissions, the EPA's role is to 
approve state choices, provided that they meet the criteria of the CAA. 
Accordingly, these proposed actions merely propose to approve a state 
plan and redesignation request as meeting federal requirements and do 
not impose additional requirements beyond those imposed by state law. 
For these reasons, the proposed actions:
     Are not a ``significant regulatory action'' subject to 
review by the Office of Management and Budget under Executive Orders 
12866 (58 FR 51735, October 4, 1993) and 13563 (76 FR 3821, January 21, 
2011);
     Are not an Executive Order 13771 (82 FR 9339, February 2, 
2017) regulatory action because SIP approvals are exempted under 
Executive Order 12866;
     Do not impose an information collection burden under the 
provisions of the Paperwork Reduction Act (44 U.S.C. 3501 et seq.);
     Are certified as not having a significant economic impact 
on a substantial number of small entities under the Regulatory 
Flexibility Act (5 U.S.C. 601 et seq.);
     Do not contain any unfunded mandate or significantly or 
uniquely affect small governments, as described in the Unfunded 
Mandates Reform Act of 1995 (Pub. L. 104-4);
     Do not have Federalism implications as specified in 
Executive Order 13132 (64 FR 43255, August 10, 1999);
     Are not an economically significant regulatory action 
based on health or safety risks subject to Executive Order 13045 (62 FR 
19885, April 23, 1997);
     Are not a significant regulatory action subject to 
Executive Order 13211 (66 FR 28355, May 22, 2001);
     Are not subject to requirements of section 12(d) of the 
National Technology Transfer and Advancement Act of 1995 (15 U.S.C. 272 
note) because application of those requirements would be inconsistent 
with the CAA; and
     Do not provide the EPA with the discretionary authority to 
address disproportionate human health or environmental effects with 
practicable, appropriate, and legally permissible methods, under 
Executive Order 12898 (59 FR 7629, February 16, 1994).
    In addition, there are no areas of Indian country within the Ajo 
planning area, and the state plan for which the EPA is proposing 
approval does not apply on any Indian reservation land or in any other 
area where the EPA or an Indian tribe has demonstrated that a tribe has 
jurisdiction. In those areas of Indian country, this proposed action 
does not have tribal implications and will not impose substantial 
direct costs on tribal governments or preempt tribal law as specified 
by Executive Order 13175 (65 FR 67249, November 9, 2000), because 
redesignation is an action that affects the status of a geographical 
area and does not impose any new regulatory requirements on tribes, 
impact any existing sources of air pollution on tribal lands, nor 
impair the maintenance of NAAQS in tribal lands.

List of Subjects

40 CFR Part 52

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

40 CFR Part 81

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

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

    Dated: May 27, 2020.
John Busterud,
Regional Administrator, Region IX.
[FR Doc. 2020-11930 Filed 6-3-20; 8:45 am]
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