Proposed Rule2026-04339
Air Plan Approval; Arizona; Attainment Plan for the Hayden SO2 Nonattainment Area for the 1971 and 2010 Sulfur Dioxide National Ambient Air Quality Standards
Primary source
Metadata and text below are from the Federal Register, a public-domain U.S. government work. Always verify the official published version before relying on it for any legal matter.
Published
March 4, 2026
Issuing agencies
Environmental Protection Agency
Abstract
The Environmental Protection Agency (EPA) is proposing to approve revisions to the Arizona state implementation plan (SIP) for attaining the 1971 and 2010 sulfur dioxide (SO<INF>2</INF>) national ambient air quality standards (NAAQS or "standards") in the Hayden SO<INF>2</INF> nonattainment area. These SIP revisions, collectively referred to as the "Hayden SO<INF>2</INF> Plan" or "Plan," include Arizona's attainment demonstration and other elements required under Clean Air Act (CAA or "Act") sections 110, 172, 191, and 192. In addition to an attainment demonstration, the revisions address the requirements for meeting reasonable further progress (RFP) toward attainment of the NAAQS, reasonably available control measures and reasonably available control technology (RACM/RACT), base-year and projection-year emissions inventories, nonattainment new source review (NSR), emissions limitations necessary to provide for attainment, and contingency measures. The EPA is proposing to approve the SIP revisions as meeting the CAA requirements. This action is being taken under the CAA. We are taking comments on this proposal and plan to follow with a final action.
Full Text
<html>
<head>
<title>Federal Register, Volume 91 Issue 42 (Wednesday, March 4, 2026)</title>
</head>
<body><pre>
[Federal Register Volume 91, Number 42 (Wednesday, March 4, 2026)]
[Proposed Rules]
[Pages 10531-10544]
From the Federal Register Online via the Government Publishing Office [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[FR Doc No: 2026-04339]
=======================================================================
-----------------------------------------------------------------------
ENVIRONMENTAL PROTECTION AGENCY
40 CFR Part 52
[EPA-R09-OAR-2025-3821; FRL-13144-01-R9]
Air Plan Approval; Arizona; Attainment Plan for the Hayden SO2
Nonattainment Area for the 1971 and 2010 Sulfur Dioxide National
Ambient Air Quality Standards
AGENCY: Environmental Protection Agency (EPA).
ACTION: Proposed rule.
-----------------------------------------------------------------------
SUMMARY: The Environmental Protection Agency (EPA) is proposing to
approve revisions to the Arizona state implementation plan (SIP) for
attaining the 1971 and 2010 sulfur dioxide (SO<INF>2</INF>) national
ambient air quality standards (NAAQS or ``standards'') in the Hayden
SO<INF>2</INF> nonattainment area. These SIP revisions, collectively
referred to as the ``Hayden SO<INF>2</INF> Plan'' or ``Plan,'' include
Arizona's attainment demonstration and other elements required under
Clean Air Act (CAA or ``Act'') sections 110, 172, 191, and 192. In
addition to an attainment demonstration, the revisions address the
requirements for meeting reasonable further progress (RFP) toward
attainment of the NAAQS, reasonably available control measures and
reasonably available control technology (RACM/RACT), base-year and
projection-year emissions inventories, nonattainment new source review
(NSR), emissions limitations necessary to provide for attainment, and
contingency measures. The EPA is proposing to approve the SIP revisions
as meeting the CAA requirements. This action is being taken under the
CAA. We are taking comments on this proposal and plan to follow with a
final action.
DATES: Comments must be received on or before April 3, 2026.
ADDRESSES: Submit your comments, identified by Docket ID No. EPA-R09-
OAR-2025-3821, at <a href="https://www.regulations.gov">https://www.regulations.gov</a>. For comments submitted
at <a href="http://Regulations.gov">Regulations.gov</a>, follow the online instructions for submitting
comments. Once submitted, comments cannot be edited or removed from
<a href="http://Regulations.gov">Regulations.gov</a>. The EPA may publish any comment received to its public
docket. Do not submit electronically any information you consider to be
Confidential Business Information (CBI) or other information whose
disclosure is restricted by statute. Multimedia submissions (audio,
video, etc.) must be accompanied by a written comment. The written
comment is considered the official comment and should include
discussion of all points you wish to make. The EPA will generally not
consider comments or comment contents located outside of the primary
submission (i.e., on the web, cloud, or other file sharing system). For
additional submission methods, please contact the person identified in
the FOR FURTHER INFORMATION CONTACT section. For the full EPA public
comment policy, information about CBI or multimedia submissions, and
general guidance on making effective comments, please visit <a href="https://www.epa.gov/dockets/commenting-epa-dockets">https://www.epa.gov/dockets/commenting-epa-dockets</a>. If you need assistance in a
language other than English or if you are a person with a disability
who needs a reasonable accommodation at no cost to you, please contact
the person identified in the FOR FURTHER INFORMATION CONTACT section.
FOR FURTHER INFORMATION CONTACT: Ashley Graham, Geographic Strategies
and Modeling Section (AIR-2-2), EPA Region IX, 75 Hawthorne Street, San
Francisco, CA 94105; telephone number: (415) 972-3877; email address:
<a href="/cdn-cgi/l/email-protection#9ff8edfef7fef2b1feecf7f3fae6eddffaeffeb1f8f0e9"><span class="__cf_email__" data-cfemail="7116031019101c5f1002191d140803311401105f161e07">[email protected]</span></a>.
SUPPLEMENTARY INFORMATION: Throughout this document, ``we,'' ``us,''
and ``our'' refer to the EPA.
Table of Contents
I. Background
II. Requirements for SO<INF>2</INF> Attainment Plans
III. Review of Arizona's SIP Submissions
IV. Review of Modeled Attainment Demonstration
A. Modeling Approach and Receptor Grid
B. Meteorological Data
C. Emissions Data
D. Emission Limits
E. Background Concentrations
F. Summary of Results
V. Review of Emissions and Emission Controls
A. Emissions Inventory and the Quantification of Emissions
B. Reasonably Available Control Measures/Reasonably Available
Control Technology
C. Nonattainment New Source Review
D. Reasonable Further Progress
E. Contingency Measures
VI. Additional Elements of Arizona's Submittal
VII. Proposed Action
VIII. Incorporation by Reference
IX. Statutory and Executive Order Reviews
I. Background
Under section 109 of the CAA, the EPA has established primary and
secondary NAAQS for certain pervasive air pollutants (referred to as
``criteria pollutants'') and conducts periodic reviews of the NAAQS to
determine whether they should be revised or whether new NAAQS should be
established. The primary NAAQS represent ambient air quality standards
the attainment and maintenance of which the EPA has determined are
requisite to protect public health with an adequate margin of safety.
The secondary NAAQS represent ambient air quality standards the
attainment and maintenance of which the EPA has determined are
requisite to protect public welfare from any known or anticipated
adverse effects associated with the presence of such an air pollutant
in the ambient air.
Under the CAA, the EPA must establish NAAQS for criteria
pollutants, including SO<INF>2</INF>. SO<INF>2</INF> is released to the
atmosphere primarily through the burning of fossil fuels by power
generation and certain industrial processes. Short-term exposure to
SO<INF>2</INF> can damage the human respiratory system and increase
breathing difficulties. Small children and people with respiratory
conditions, such as asthma, are more sensitive to the effects of
SO<INF>2</INF>. Sulfur oxides at high concentrations in ambient air can
also react with compounds to form small particulates (fine particulate
matter) that can penetrate deeply into the lungs and cause health
problems.
The EPA first established primary SO<INF>2</INF> standards in
1971.\1\ The short-term (24-hour) standard of 0.140 parts per million
(ppm) was not to be exceeded more than once per calendar year. The
long-term standard specifies an annual arithmetic mean not to exceed
0.030 ppm. The level of the secondary SO<INF>2</INF> NAAQS is 0.5 ppm
over a 3-hour averaging period (not to be exceeded more than once per
year).\2\
---------------------------------------------------------------------------
\1\ 36 FR 8186 (April 30, 1971). See 40 CFR 50.4.
\2\ See 40 CFR 50.5. The 1971 final rule also included a
secondary annual standard of 0.02 ppm and a 24-hour SO<INF>2</INF>
standard of 0.1 ppm (not to be exceeded more than once per year) as
a guide to be used in assessing implementation plans to achieve the
annual standard. In 1973, the secondary 3-hour SO<INF>2</INF>
standard was retained without revision and the secondary annual
SO<INF>2</INF> standard was revoked (38 FR 25678, September 14,
1973).
---------------------------------------------------------------------------
On March 3, 1978, for lack of a state recommendation, the EPA
designated Pinal County as a primary SO<INF>2</INF> nonattainment area
based on monitored violations of the primary SO<INF>2</INF> NAAQS in
[[Page 10532]]
the county between 1975 and 1977.\3\ At the request of the Arizona
Department of Environmental Quality (ADEQ), the nonattainment area was
subsequently reduced to nine townships in and around Hayden,
Arizona.\4\
---------------------------------------------------------------------------
\3\ 43 FR 8962 (March 3, 1978).
\4\ 44 FR 21261 (April 10, 1979). The nonattainment area is
composed of the following townships in southern Gila County and
northeastern Pinal County: T4S, R14E; T4S, R15E; T4S, R16E; T5S,
R14E; T5S, R15E; T5S, R16E; T6S, R14E; T6S, R15E; and T6S, R16E. The
following townships were designated ``cannot be classified:'' T4S,
R13E; T4S, R17E; T5S, R13E; T5S, R17E; T6S, R13E; and T6S, R17E.
---------------------------------------------------------------------------
On the date of enactment of the 1990 CAA Amendments, SO<INF>2</INF>
areas meeting the conditions of section 107(d) of the Act were
designated nonattainment for the SO<INF>2</INF> NAAQS by operation of
law. Section 107(d) of the CAA describes the processes by which
nonattainment areas are designated, including the pre-existing
SO<INF>2</INF> nonattainment areas. Thus, the Hayden area remained
nonattainment for the primary SO<INF>2</INF> NAAQS following enactment
of the 1990 CAA Amendments on November 15, 1990.
On June 22, 2010, the EPA promulgated a new 1-hour primary
SO<INF>2</INF> NAAQS of 75 parts per billion (ppb).\5\ This standard is
met at an ambient air quality monitoring site when the 3-year average
of the annual 99th percentile of daily maximum 1-hour average
concentrations does not exceed 75 ppb, as determined in accordance with
Appendix T of 40 CFR part 50.\6\ The EPA provided that the 24-hour and
annual standards established in 1971 were to remain in place for those
areas designated nonattainment for the 2010 SO<INF>2</INF> NAAQS until
such time that the state submits, and the EPA approves, an
implementation plan providing for attainment of the 2010 SO<INF>2</INF>
NAAQS.\7\
---------------------------------------------------------------------------
\5\ 40 CFR 50.17(a).
\6\ 75 FR 35520 (June 22, 2010), codified at 40 CFR 50.17(a) and
(b).
\7\ See 40 CFR 50.4(e). 75 FR 35520, 35581 (June 22, 2010).
---------------------------------------------------------------------------
Under CAA section 107(d)(1), the EPA is required to designate areas
as ``nonattainment,'' ``attainment,'' or ``unclassifiable'' within two
years of establishing a new standard or revising an existing standard.
The Hayden nonattainment area for the 2010 SO<INF>2</INF> NAAQS was
established effective October 4, 2013.\8\ The dominant source of
SO<INF>2</INF> emissions in the Hayden SO<INF>2</INF> nonattainment
area is the Hayden copper smelter (``Hayden Smelter'' or ``Smelter''),
owned and operated by ASARCO LLC (``Asarco'').\9\ This final area
designation triggered a requirement for Arizona to submit by April 4,
2015 (within 18 months per CAA section 191(a)), a SIP revision with an
attainment plan for how the Hayden SO<INF>2</INF> nonattainment area
would attain the 2010 SO<INF>2</INF> NAAQS as expeditiously as
practicable, but no later than October 4, 2018, per CAA section 192(a)
in accordance with CAA sections 110(a), 172(c), 191, and 192.
---------------------------------------------------------------------------
\8\ 78 FR 47191 (August 5, 2013), codified at 40 CFR part 81,
subpart C.
\9\ ASARCO LLC was organized in 1899 as the American Smelting
And Refining COmpany.
---------------------------------------------------------------------------
As required by CAA section 110(k)(1)(B), the EPA published a final
rule on March 18, 2016, finding that Arizona had failed to submit the
required SO<INF>2</INF> nonattainment area plan by the submittal
deadline.\10\ This finding initiated a deadline under CAA section
179(a) for the potential imposition of new source and highway funding
sanctions. Additionally, under CAA section 110(c), the finding
triggered a requirement that the EPA promulgate a Federal
implementation plan (FIP) within two years of the effective date of the
finding unless by that time the State had made the necessary complete
submittal and the EPA had approved the submittal as meeting applicable
requirements.
---------------------------------------------------------------------------
\10\ 81 FR 14736 (March 18, 2016).
---------------------------------------------------------------------------
In response to the requirement for SO<INF>2</INF> nonattainment
area plan submittals, ADEQ submitted a SIP revision on March 9, 2017,
titled ``Arizona State Implementation Plan Revision: Hayden Sulfur
Dioxide Nonattainment Area for the 2010 SO<INF>2</INF> NAAQS'' (``2017
Hayden SO<INF>2</INF> Plan''). The emission limits that were intended
to provide for attainment of the 2010 SO<INF>2</INF> NAAQS for the
Hayden area were codified in the Arizona Administrative Code (AAC),
Title 18, Chapter 2, Article 13, section R18-2-B1302 (``Limits on
SO<INF>2</INF> Emissions from the Hayden Smelter'') (``Rule B1302'').
ADEQ submitted Rule B1302 to the EPA on April 6, 2017.\11\ The EPA
issued letters dated July 17, 2017, and September 26, 2017, finding the
submittals complete and stopping the sanctions clocks under CAA section
179(a).\12\
---------------------------------------------------------------------------
\11\ Letter dated March 8, 2017, from Timothy S. Franquist,
Director, Air Quality Division, ADEQ, to Alexis Strauss, Acting
Regional Administrator, EPA Region IX, Subject: ``Submittal of the
State Implementation Plan Revision, Sulfur Dioxide National Ambient
Air Quality Standards, Hayden Nonattainment Area,'' (submitted
electronically on March 9, 2017); and letter dated April 6, 2017,
from Timothy S. Franquist, Director, Air Quality Division, ADEQ, to
Alexis Strauss, Acting Regional Administrator, EPA Region IX,
Subject: ``RE: Submittal of the Final Rules for the State
Implementation Plans for Hayden Sulfur Dioxide Nonattainment Area,
Hayden Lead Nonattainment Area, and Miami Sulfur Dioxide
Nonattainment Area,'' (submitted electronically on April 6, 2017).
\12\ Letter dated July 17, 2017, from Elizabeth J. Adams, Acting
Director, Air Division, EPA Region IX, to Timothy S. Franquist,
Director, Air Quality Division, ADEQ; and letter dated September 26,
2017, from Elizabeth J. Adams, Acting Director, Air Division, EPA
Region IX, to Timothy S. Franquist, Director, Air Quality Division,
ADEQ.
---------------------------------------------------------------------------
On November 5, 2020, the EPA finalized a limited approval and
limited disapproval of Arizona Rule B1302,\13\ and on November 10,
2020, the EPA finalized a partial approval and partial disapproval of
the 2017 Hayden SO<INF>2</INF> Plan.\14\ The EPA finalized a limited
disapproval of Rule B1302 because we found that some of the rule
provisions conflicted with the requirements of CAA sections 110 and
172(c)(6), including that the rule did not contain any numeric
emissions limit(s) or ongoing monitoring requirements corresponding to
the levels of fugitive emissions that were modeled in the 2017 Hayden
SO<INF>2</INF> Plan.\15\ The EPA finalized a partial disapproval of the
2017 Hayden SO<INF>2</INF> Plan because we found that the plan did not
meet the attainment demonstration, RACM/RACT, enforceable emission
limitations, RFP, and contingency measure requirements of the CAA for
the 2010 SO<INF>2</INF> NAAQS.\16\ The final limited disapproval of
Rule B1302 and partial disapproval of the 2017 Hayden SO<INF>2</INF>
Plan became effective on December 7, 2020, and December 10, 2020,
respectively, and initiated deadlines under CAA section 179(a) for the
imposition of new source review offset and highway funding sanctions
unless the State had made the necessary complete submittal and the EPA
approved the submittal as meeting applicable requirements prior to
those deadlines.\17\
---------------------------------------------------------------------------
\13\ 85 FR 70483 (November 5, 2020).
\14\ 85 FR 71547 (November 10, 2020). As part of our November
10, 2020 final action, the EPA approved the emissions inventory
element of the plan and affirmed that the State had met the new
source review requirements for the area.
\15\ 85 FR 70483, 70484 (November 5, 2020).
\16\ 85 FR 71547, 71552 (November 10, 2020).
\17\ On June 7, 2022, offset sanctions were imposed in the
Hayden SO<INF>2</INF> nonattainment area, and on December 7, 2022,
highway sanctions were imposed in the area.
---------------------------------------------------------------------------
On January 31, 2022, the EPA determined that the Hayden
SO<INF>2</INF> nonattainment area failed to attain the 2010 1-hour
primary SO<INF>2</INF> NAAQS by the October 4, 2018 applicable
attainment date, which triggered a requirement under CAA section 179(d)
for Arizona to submit a revised SIP by January 31, 2023, that provides
for expeditious attainment of the 2010 SO<INF>2</INF> NAAQS in the
Hayden SO<INF>2</INF> nonattainment area by January 31, 2027.\18\
---------------------------------------------------------------------------
\18\ 87 FR 4805 (January 31, 2022).
---------------------------------------------------------------------------
The remainder of this document describes the requirements that
nonattainment area plans must meet to
[[Page 10533]]
obtain EPA approval, provides a review of the Hayden SO<INF>2</INF>
Plan with respect to these requirements, and describes the EPA's
proposed action on the Plan.
II. Requirements for SO2 Attainment Plans
Nonattainment area SO<INF>2</INF> SIPs must meet the applicable
requirements of the CAA, specifically CAA sections 110, 172, 191, and
192. The EPA's regulations governing nonattainment area SIP submissions
are set forth at 40 CFR part 51, with specific procedural requirements
and control strategy requirements residing at subparts F and G,
respectively. Soon after Congress enacted the 1990 amendments to the
CAA, the EPA issued comprehensive guidance on SIP revisions in the
``General Preamble for the Implementation of Title I of the Clean Air
Act Amendments of 1990'' (``General Preamble'').\19\ Among other
things, the General Preamble addressed SO<INF>2</INF> SIP submissions
and fundamental principles for SIP control strategies.\20\ On April 23,
2014, the EPA issued guidance and recommendations for meeting the
statutory requirements in SO<INF>2</INF> SIP submissions, in a document
titled, ``Guidance for 1-Hour SO<INF>2</INF> Nonattainment Area SIP
Submissions'' (``2014 SO<INF>2</INF> Guidance'').\21\ In the 2014
SO<INF>2</INF> Guidance, the EPA described the statutory requirements
for the elements of a nonattainment area plan as listed at CAA section
172(c), which include an accurate emissions inventory of current
emissions for all sources of SO<INF>2</INF> within the nonattainment
area; an attainment demonstration; a demonstration of RFP;
implementation of RACM (including RACT); emission limitations and
control measures necessary to provide for attainment; nonattainment
NSR; and adequate contingency measures. This guidance supplements the
EPA's 1994 ``SO<INF>2</INF> Guideline Document,'' which remains
applicable unless specifically altered by the 2014 SO<INF>2</INF>
Guidance.\22\
---------------------------------------------------------------------------
\19\ 57 FR 13498 (April 16, 1992).
\20\ Id. at 13548-13549, 13567-13568.
\21\ Available at <a href="https://www.epa.gov/sites/production/files/2016-06/documents/20140423guidance_nonattainment_sip.pdf">https://www.epa.gov/sites/production/files/2016-06/documents/20140423guidance_nonattainment_sip.pdf</a>.
\22\ 2014 SO<INF>2</INF> Guidance, p. 2.
---------------------------------------------------------------------------
In general, the EPA's duties in reviewing state attainment plans
are described in CAA sections 110(k) and 110(l). The EPA is first
required to determine whether a SIP submission meets certain minimum
criteria for completeness. Once a SIP submission has been determined to
be complete, the EPA is required to approve the submission, as a whole,
if it meets all applicable requirements of the CAA. State attainment
plans are approved by the EPA as meeting the minimum requirements of
the CAA if they fully address the requirements of CAA sections 110,
172, 191, and 192, and the EPA's regulations at 40 CFR part 51.
Also, under CAA section 110(l), the EPA may not approve a SIP
revision that would interfere with any applicable requirement
concerning NAAQS attainment and RFP, or any other applicable
requirement. Further, under CAA section 193, no control requirement in
effect before November 15, 1990 (or required to be adopted by an order,
settlement, agreement, or plan in effect before November 15, 1990), in
any area that is a nonattainment area for any air pollutant, may be
modified in any manner unless the modification insures equivalent or
greater emission reductions of such air pollutant.
CAA sections 172(c)(1) and 172(c)(6) direct states with areas
designated as nonattainment to demonstrate that the submitted plan and
its emissions limitations and control measures provide for attainment
of the NAAQS. The EPA's regulations at 40 CFR part 51, subpart G
further delineate the control strategy requirements that plans must
meet, and that all SIPs and control strategies reflect the four
fundamental principles of quantification, enforceability,
replicability, and accountability.\23\ SO<INF>2</INF> nonattainment
area plans must consist of two components: (1) enforceable emission
limits and other control measures that assure implementation of
permanent, enforceable, and necessary emission controls, and (2) a
modeling analysis that meets the requirements of 40 CFR part 51,
appendix W and demonstrates that these emission limits and control
measures provide for timely attainment of the primary SO<INF>2</INF>
NAAQS as expeditiously as practicable, but by no later than the
attainment date for the affected area. In all cases, the emission
limits and control measures must be accompanied by appropriate methods
and conditions to determine compliance with the respective emission
limits and control measures and must be quantifiable (i.e., a specific
amount of emission reduction can be ascribed to the measures), fully
enforceable (i.e., specifying clear, unambiguous, and measurable
requirements for which compliance can be practicably determined),
replicable (i.e., the procedures for determining compliance are
sufficiently specific and non-subjective so that two independent
entities applying the procedures would obtain the same result), and
accountable (i.e., source specific limits must be permanent and must
reflect the assumptions used in the plan demonstrations).
---------------------------------------------------------------------------
\23\ See General Preamble, 13567-13568 (April 16, 1992).
---------------------------------------------------------------------------
The EPA's 2014 SO<INF>2</INF> Guidance recommends that the emission
limits established for an attainment demonstration be expressed as
short-term average limits (e.g., addressing emissions averaged over one
hour consistent with the averaging time of the 1-hour SO<INF>2</INF>
NAAQS), but also describes the option to utilize emission limits with
longer averaging times of up to 30 days so long as the limit is
demonstrated by the state to assure comparable stringency to a 1-hour
average limit that demonstrates attainment of the 1-hour SO<INF>2</INF>
NAAQS. The 2014 SO<INF>2</INF> Guidance includes suggested criteria and
procedures for making this demonstration.\24\ The 2014 SO<INF>2</INF>
Guidance recommends that, should states and sources utilize longer
averaging times, the longer-term average limit should be set at an
adjusted level that reflects a stringency comparable to the 1-hour
average limit at the critical emission value shown to provide for
attainment.
---------------------------------------------------------------------------
\24\ See 2014 SO<INF>2</INF> Guidance, pp. 22-39.
---------------------------------------------------------------------------
The 2014 SO<INF>2</INF> Guidance provides an extensive discussion
of the EPA's rationale for concluding that appropriately set,
comparable stringent limitations based on averaging times as long as 30
days can be found to provide for attainment of the 2010 SO<INF>2</INF>
NAAQS. In evaluating this option, the EPA considered the nature of the
standard, conducted detailed analyses of the effect of 30-day average
limits on the prospects for attaining the standard, and carefully
reviewed how best to achieve an appropriate balance among the various
factors that warrant consideration in judging whether a state's plan
provides for attainment.\25\
---------------------------------------------------------------------------
\25\ Id. at 22-39, and Appendices B, C, and D.
---------------------------------------------------------------------------
As specified in 40 CFR 50.17(b), the 1-hour primary SO<INF>2</INF>
NAAQS is met at an ambient air quality monitoring site when the 3-year
average of the annual 99th percentile of daily maximum 1-hour average
concentrations is less than or equal to 75 ppb. In a year with 365 days
of valid monitoring data, the 99th percentile would be the fourth
highest daily maximum 1-hour value. Because the standard has this form,
a single hourly exceedance of the 75 ppb NAAQS level does not by itself
result in a violation of the standard. Instead, at issue is whether a
source operating in compliance with a properly set longer-term average
could cause multiple hourly exceedances over multiple days in a year,
and if so, the resulting
[[Page 10534]]
frequency and magnitude of such exceedances, and in particular, whether
the EPA can have reasonable confidence that a properly set longer-term
average limit will provide that the 3-year average of annual fourth
highest daily maximum hourly values will be at or below 75 ppb. A
synopsis of how the EPA evaluates whether such plans ``provide for
attainment,'' based on modeling of projected allowable emissions and in
light of the form of the SO<INF>2</INF> NAAQS for determining
attainment at monitoring sites, follows.
For SO<INF>2</INF> attainment plans based on 1-hour emission
limits, the standard approach is to conduct modeling using fixed 1-hour
emission rates. The maximum modeled emission rate that results in
attainment is labeled the ``critical emission value'' (CEV). The
modeling process for identifying this CEV inherently considers the
numerous variables that affect ambient concentrations of
SO<INF>2</INF>, such as meteorological data, background concentrations,
and topography. In the standard approach, the state would then provide
for attainment by setting a continuously applicable 1-hour emission
limit for each stationary SO<INF>2</INF> source at this CEV.
The EPA recognizes that some SO<INF>2</INF> sources have highly
variable emissions, for example due to variations in fuel sulfur
content and operating rate, that can make it extremely difficult, even
with a well-designed control strategy, to ensure in practice that
emissions for any given hour do not exceed the CEV. The EPA also
acknowledges the concern that longer-term emission limits can allow
short periods with emissions above the CEV, which, if coincident with
meteorological conditions conducive to high SO<INF>2</INF>
concentrations, could in turn create the possibility of an hourly NAAQS
exceedance occurring on a day when an exceedance would not have
occurred if emissions were continuously controlled at the level
corresponding to the CEV. However, for several reasons, the EPA
believes that the approach recommended in its guidance document
suitably addresses this concern.
First, from a practical perspective, the EPA expects the actual
emission profile of a source subject to an appropriately set longer-
term average limit to be similar to the emission profile of a source
subject to an analogous 1-hour average limit. The EPA expects this
similarity because it has recommended that the longer-term average
limit be set at a level that is comparably stringent to the otherwise
applicable 1-hour limit (reflecting a downward adjustment from the CEV)
and that takes the source's emissions profile (and inherent level of
emissions variability) into account. As a result, the EPA expects
either form of emission limit to yield comparable air quality.
Second, from a more theoretical perspective, the EPA has compared
the likely air quality with a source having maximum allowable emissions
under an appropriately set longer-term limit, to the likely air quality
with the source having maximum allowable emissions under the comparable
1-hour limit. In this comparison, in the 1-hour average limit scenario,
the source is presumed at all times to emit at the CEV, and in the
longer-term average limit scenario, the source is presumed occasionally
to emit more than the CEV, but on average, and presumably at most
times, to emit well below the CEV. In an ``average year,'' \26\
compliance with the 1-hour limit is expected to result in three
exceedance days (i.e., three days with maximum hourly values above 75
ppb) and a fourth day with a maximum hourly value at 75 ppb. By
comparison, with the source complying with a longer-term limit, it is
possible that additional hourly exceedances would occur that would not
occur in the 1-hour limit scenario (if emissions exceed the CEV at
times when meteorology is conducive to poor air quality). However, this
comparison must also factor in the likelihood that exceedances that
would be expected in the 1-hour limit scenario would not occur in the
longer-term limit scenario. This result arises because the longer-term
limit requires lower emissions most of the time (because the limit is
set below the CEV), so a source complying with an appropriately set
longer-term limit is likely to have lower emissions at critical times
than would be the case if the source were emitting as allowed with a 1-
hour limit.
---------------------------------------------------------------------------
\26\ An ``average year'' is used to mean a year with average air
quality. While 40 CFR part 50, appendix T, provides for averaging
three years of annual 99th percentile daily maximum hourly values
(e.g., the fourth highest maximum daily hourly concentration in a
year with 365 days with valid data), this discussion and the example
discussed herein uses a single ``average year'' in order to simplify
the illustration of relevant principles.
---------------------------------------------------------------------------
To illustrate this point, the EPA conducted a statistical analysis
using a range of scenarios using actual plant data. This analysis is
described in Appendix B of the EPA's 2014 SO<INF>2</INF> Guidance.
Based on the analysis described in the 2014 SO<INF>2</INF> Guidance,
the EPA expects that an emission profile with maximum allowable
emissions under an appropriately set, comparably stringent 30-day
average limit is likely to have the net effect of having a lower number
of hourly exceedances and better air quality than an emission profile
with maximum allowable emissions under a 1-hour emission limit at the
CEV. This result provides a compelling policy rationale for allowing
the use of a longer averaging period, in appropriate circumstances
where the facts indicate this result can be expected to occur.
The 2014 SO<INF>2</INF> Guidance offers specific recommendations
for determining an appropriate longer-term average limit. The
recommended method starts with determination of the 1-hour emission
limit that would provide for attainment (i.e., the CEV), and applies an
adjustment factor to determine the (lower) level of the longer-term
average emission limit that would be estimated to have a stringency
comparable to the otherwise necessary 1-hour emission limit. This
method uses a database of continuous emission data reflecting the type
of control that the source will be using to comply with the plan's
emission limits, which (if compliance requires new controls) may
require use of an emission database from another source. The
recommended method involves using these data to compute a complete set
of emission averages, computed according to the averaging time and
averaging procedures of the prospective emission limitation (i.e.,
using 1-hour historical emission values from the emissions database to
calculate 30-day average emission values). In this recommended method,
the ratio of the 99th percentile among these longer-term averages to
the 99th percentile of the 1-hour values represents an adjustment
factor that may be multiplied by the candidate 1-hour emission limit
CEV to determine a longer-term average emission limit that may be
considered comparably stringent.\27\
---------------------------------------------------------------------------
\27\ For example, if the CEV is 1000 pounds of SO<INF>2</INF>
per hour, and a suitable adjustment factor is determined to be 70
percent, the recommended longer-term average limit would be 700 lb/
hr.
---------------------------------------------------------------------------
The 2014 SO<INF>2</INF> Guidance also addresses a variety of
related topics, including the potential utility of setting supplemental
emission limits, such as mass-based limits or work practice
requirements for the operation of SO<INF>2</INF> control equipment, to
reduce the likelihood and/or magnitude of elevated emission levels that
might occur under the longer-term emission rate limit.
Preferred air quality models for use in regulatory applications are
described in Addendum A of the EPA's ``Guideline on Air Quality
Models'' (``Appendix W'').\28\ In 2005, the EPA promulgated the
American Meteorological Society/Environmental Protection Agency
Regulatory Model (AERMOD) as the
[[Page 10535]]
Agency's preferred near-field dispersion model for a wide range of
regulatory applications addressing stationary sources (e.g., in
estimating SO<INF>2</INF> concentrations) in all types of terrain based
on an extensive developmental and performance evaluation. Supplemental
guidance on modeling for purposes of demonstrating attainment of the
SO<INF>2</INF> standard is provided in Appendix A of the 2014
SO<INF>2</INF> Guidance. Appendix A provides extensive guidance on the
modeling domain, the source inputs, assorted types of meteorological
data, and background concentrations. Consistency with the
recommendations in the 2014 SO<INF>2</INF> Guidance would generally
ensure that the attainment demonstration offers adequately reliable
assurance that the plan provides for attainment.
---------------------------------------------------------------------------
\28\ 40 CFR part 51, appendix W.
---------------------------------------------------------------------------
Attainment demonstrations for the 2010 1-hour primary
SO<INF>2</INF> NAAQS must demonstrate future attainment and maintenance
of the NAAQS in the entire area designated as nonattainment (i.e., not
just at the violating monitor) by using air quality dispersion modeling
(see Appendix W) to show that the mix of sources and enforceable
control measures and emission rates in an identified area will not lead
to a violation of the SO<INF>2</INF> NAAQS. For a short-term (i.e., 1-
hour) standard, the EPA believes that dispersion modeling, using
allowable emissions and addressing stationary sources in the affected
area (and in some cases those sources located outside the nonattainment
area that may affect attainment in the area) is technically
appropriate, efficient, and effective in demonstrating attainment in
nonattainment areas because it takes into consideration combinations of
meteorological and emission source operating conditions that may
contribute to peak ground-level concentrations of SO<INF>2</INF>.
The meteorological data used in the analysis should generally be
processed with the most recent version of AERMET. AERMET is a
meteorological data preprocessor that incorporates air dispersion based
on planetary boundary layer turbulence structure and scaling concepts.
Estimated concentrations should include ambient background
concentrations, should follow the form of the standard, and should be
calculated as described in section 2.6.1.2 of the August 23, 2010,
clarification memo on ``Applicability of Appendix W Modeling Guidance
for the 1-hour SO<INF>2</INF> National Ambient Air Quality Standard.''
\29\
---------------------------------------------------------------------------
\29\ Memorandum dated August 23, 2010, from Tyler Fox, Leader,
Air Quality Modeling Group, C439-01, to Regional Air Division
Directors, Subject: ``Applicability of Appendix W Modeling Guidance
for the 1-hour SO<INF>2</INF> National Ambient Air Quality
Standard.'' Available at <a href="https://www.epa.gov/sites/default/files/2020-10/documents/clarificationmemo_appendixw_hourly-so2-naaqs_final_08-23-2010.pdf">https://www.epa.gov/sites/default/files/2020-10/documents/clarificationmemo_appendixw_hourly-so2-naaqs_final_08-23-2010.pdf</a>.
---------------------------------------------------------------------------
Finally, CAA section 123(a) provides that the degree of emission
limitation required for control of any air pollutant under an
applicable implementation plan shall not be affected in any manner by
so much of the stack height of any source as exceeds good engineering
practice (GEP) (as determined under regulations promulgated by the
Administrator). The EPA's regulations implementing section 123 reside
at 40 CFR 51.118 to 51.119, and in a series of definitions at 40 CFR
51.100(ff) to (nn). GEP stack height is defined as the greatest among
three values, based on three defined approaches for determining GEP
stack height. As relevant here, under the third approach the creditable
stack height is defined in 40 CFR 51.100(ii)(3) as ``[t]he height
demonstrated by a fluid model . . . which ensures that the emissions
from a stack do not result in excessive concentrations of any air
pollutant as a result of atmospheric downwash, wakes, or eddy effects
created by the source itself, nearby structures or nearby terrain
features.'' ``Nearby'' is defined in 40 CFR 51.100(jj)(2) as not
greater than 0.8 kilometers (km) (\1/2\ mile) with a set of exceptions
applying to terrain features. ``Excessive concentrations'' is defined
in 40 CFR 51.100(kk)(1), which also specifies that, ``[t]he allowable
emission rate to be used in making demonstrations under this part shall
be prescribed by the new source performance standard that is applicable
to the source category unless the owner or operator demonstrates that
this emission rate is infeasible.'' Since this demonstration must rely
on allowable emissions, the SIP must include the appropriate limit,
either the new source performance standard (NSPS) limit or an
alternative limit if the NSPS limit is infeasible, as an adopted part
of the plan.\30\
---------------------------------------------------------------------------
\30\ See 67 FR 22168, 22209 to 22218 (May 2, 2002) (explaining
that the EPA's stack height regulations require sources that wish to
obtain above-formula stack height credit to have a SIP limit that is
no higher than the NSPS limit used in modeling) and Montana Sulphur
& Chemical Co. v. EPA, 666 F.3d 1174, 1187-1188 (9th Cir. 2012)
(upholding this interpretation).
---------------------------------------------------------------------------
III. Review of Arizona's SIP Submissions
Arizona submitted the ``Final SIP Revision: 2023 Hayden Sulfur
Dioxide Nonattainment Area for the 1971 and 2010 SO<INF>2</INF> NAAQS''
(``2023 Hayden SO<INF>2</INF> Plan'') to the EPA as a revision to the
Arizona SIP on October 3, 2023.\31\ The 2023 Hayden SO<INF>2</INF> Plan
includes a copy of Significant Permit Revision No. 96410, Attachment
``I'' Hayden Smelter Site-Specific SIP Requirements (``Hayden
SO<INF>2</INF> Permit Revision''), which includes numerical fugitive
emissions limits, work practice standards, and recordkeeping/reporting
requirements to ensure attainment of the SO<INF>2</INF> NAAQS in the
Hayden SO<INF>2</INF> nonattainment area. ADEQ's letter adopting and
submitting the 2023 Hayden SO<INF>2</INF> Plan for inclusion in the
Arizona SIP clarifies that the SIP revision is intended to satisfy the
CAA requirements for the Hayden SO<INF>2</INF> planning area for both
the 1971 and 2010 SO<INF>2</INF> NAAQS.\32\ The October 3, 2023
submittal became complete by operation of law on April 3, 2024. On May
2, 2024, the EPA issued a completeness letter, determining that
Arizona's October 3, 2023 submittal includes all SIP elements required
as a result of the January 31, 2022 finding of failure to attain and
that the submittal meets the minimum completeness criteria in 40 CFR
part 51, appendix V.\33\
---------------------------------------------------------------------------
\31\ Letter dated October 3, 2023, from Daniel Czecholinski,
Director, Air Quality Division, ADEQ, to Martha Guzman, Regional
Administrator, EPA Region 9, Subject; ``RE: Submittal of the Arizona
Department of Environmental Quality's SIP revision: 2023 Hayden
Sulfur Dioxide Nonattainment Area for the 1971 and 2010
SO<INF>2</INF> NAAQS,'' with enclosures (submitted electronically on
October 3, 2023).
\32\ Id.
\33\ Letter dated May 2, 2024, from Matthew Lakin, Director, Air
and Radiation Division, EPA Region IX, to Karen L. Peters, Cabinet
Executive Officer, ADEQ, Subject: ``Re: Completeness Finding for the
State Implementation Plan (SIP) Submission for the Hayden
Nonattainment Area for the 1971 and 2010 Sulfur Dioxide
(SO<INF>2</INF>) National Ambient Air Quality Standards (NAAQS).''
---------------------------------------------------------------------------
On December 8, 2025, ADEQ submitted for parallel processing the
proposed ``SIP Revision: Rules Incorporating Hayden Smelter Permit
Conditions to Supplement Arizona's 2023 SO<INF>2</INF> SIP'' as a
supplement to the 2023 Hayden SO<INF>2</INF> Plan (``Hayden
SO<INF>2</INF> Supplement'').\34\ In addition to addressing attainment
planning requirements, the Hayden SO<INF>2</INF> Supplement includes
revisions to Rule B1302 and AAC Title 18, Chapter 2, Appendix 14
(``Procedures for Sulfur Dioxide and Lead Fugitive Emissions Studies
for the Hayden Smelter'') (``Appendix 14'') that establish certain
enforceable control requirements that are relied upon in the attainment
demonstration. ADEQ's December 5, 2025 letter accompanying the Hayden
SO<INF>2</INF> Supplement explains that the rule
[[Page 10536]]
revisions ``replace the existing references to the Hayden Smelter
permitting conditions in Permit No. 39945 (as amended by Significant
Permit Revision No. 92168 and Significant Permit Revision No. 96410)
with direct incorporation by reference of the equivalent requirements
now codified in the A.A.C.,'' and that where the 2023 Hayden
SO<INF>2</INF> Plan referred to the conditions in the permit, ADEQ now
requests that EPA instead refer to the applicable rules.\35\ These rule
revisions have been adopted under State law.\36\ However, ADEQ notes
that the State is requesting parallel processing of these submissions
to help facilitate timely EPA action on the 2023 Hayden SO<INF>2</INF>
Plan, given the additional administrative steps required before
codification of the rule revisions in the AAC.
---------------------------------------------------------------------------
\34\ Letter dated December 5, 2025, from Daniel Czecholinski,
Director, Air Quality Division, ADEQ, to Michael Martucci, Acting
Regional Administrator, U.S. EPA, Region 9 (submitted electronically
on December 8, 2025).
\35\ The Hayden SO<INF>2</INF> Supplement further clarifies that
ADEQ intends to withdraw the previously submitted Hayden
SO<INF>2</INF> Permit Revision from the 2023 Hayden SO<INF>2</INF>
Plan now that they have incorporated the relevant permit conditions
into state rule. Hayden SO<INF>2</INF> Supplement, p. 1.
\36\ On December 10, 2025, ADEQ submitted an updated version of
the Hayden SO<INF>2</INF> Supplement, which noted in Exhibit A-II
that ``[o]n December 2, 2025, the Arizona Governor's Regulatory
Review Council (Arizona GRRC) approved the Hayden Pb and
SO<INF>2</INF> rulemaking. Accordingly, the Arizona GRRC-approved
Notice of Final Rulemaking (NFRM) package was submitted to the
Arizona Secretary of State (SOS) on December 9, 2025.'' The NFRM was
published in the Arizona Administrative Register on January 2, 2026
(Vol. 32, Issue 1, p. 93) with an effective date of February 7,
2026. However, the codified version of the rules has not yet been
published in the AAC.
---------------------------------------------------------------------------
Parallel processing refers to a process where the state submits a
SIP revision prior to actual adoption by the state.\37\ The EPA reviews
the proposed SIP revision and prepares a notice of proposed rulemaking
under Federal law. Any final rule action by the EPA will occur only
after the state formally adopts and submits its final submission to the
EPA.
---------------------------------------------------------------------------
\37\ 40 CFR part 51, appendix V, section 2.3.
---------------------------------------------------------------------------
Section 110(k)(1)(B) of the CAA requires the EPA to determine
whether a SIP submission is complete within 60 days of receipt. This
section also provides that if the EPA has not affirmatively determined
a SIP submission to be complete or incomplete, it will become complete
by operation of law six months after the date of submission. The EPA's
SIP completeness criteria are found in 40 CFR part 51, appendix V. The
EPA has reviewed the Hayden SO<INF>2</INF> Supplement and finds that it
fulfills the completeness criteria of appendix V, with the exception of
the requirements of paragraphs 2.1(e)-2.1(h), which do not apply to
plans submitted for parallel processing.
CAA sections 110(a)(1) and (2) and 110(l) require each state to
provide reasonable public notice and opportunity for public hearing
prior to the adoption and submission of a SIP submission to the EPA. To
meet this requirement, a state's SIP submission must 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. However, because ADEQ submitted the Hayden
SO<INF>2</INF> Supplement for parallel processing, this initial
submission is exempt from this requirement pursuant to 40 CFR part 51,
appendix V, section 2.3.1. ADEQ is required to meet these procedural
criteria during the parallel processing period and prior to adopting
and submitting the final SIP submission to the EPA. The EPA will
evaluate whether the final submission meets these requirements at the
time of any final action on the Hayden SO<INF>2</INF> Supplement.
In addition to the 2023 Hayden SO<INF>2</INF> Plan and Hayden
SO<INF>2</INF> Supplement, ADEQ previously submitted amendments to AAC
Title 18, Chapter 2, Article 13, section R18-2-715 (``Standards of
Performance for Existing Primary Copper Smelters: Site-Specific
Requirements'') (``Rule 715'') and section R18-2-715.01 (``Standards of
Performance for Existing Primary Copper Smelters; Compliance and
Monitoring'') (``Rule 715.01'') on April 6, 2017.\38\ We have not yet
acted on these amendments to Rules 715 and 715.01, which are related to
the revisions to Rule B1302. These amendments sunset Rule 715 and
715.01 requirements upon the approval and effective date of Rule B1302.
Further details can be found in the technical support document (TSD)
titled ``Technical Support Document for Rule Revisions in the Hayden
SO<INF>2</INF> Supplement to the 2023 Hayden SO<INF>2</INF> Plan''
included in the docket for this proposed action.\39\ On July 17, 2017,
the EPA issued a completeness letter for Rules 715 and 715.01, finding
that they fulfill the completeness criteria in 40 CFR part 51, appendix
V.\40\ In the December 5, 2025 letter submitting the revised rules for
parallel processing, ADEQ requests that EPA act on the previously
submitted Rules 715 and 715.01.
---------------------------------------------------------------------------
\38\ Letter dated April 6, 2017, from Timothy S. Franquist,
Director, Air Quality Division, ADEQ, to Alexis Strauss, Acting
Regional Administrator, EPA Region IX, Subject: ``RE: Submittal of
the Final Rules for the State Implementation Plans for Hayden Sulfur
Dioxide Nonattainment Area, Hayden Lead Nonattainment Area, and
Miami Sulfur Dioxide Nonattainment Area,'' (submitted electronically
on April 6, 2017).
\39\ EPA Region IX, ``Technical Support Document for Rule
Revisions in the Hayden SO<INF>2</INF> Supplement to the 2023 Hayden
SO<INF>2</INF> Plan,'' December 2025.
\40\ Letter dated July 17, 2017, from Elizabeth J. Adams, Acting
Director, Air Division, EPA Region IX, to Timothy S. Franquist,
Director, Air Quality Division, ADEQ.
---------------------------------------------------------------------------
Table 1 lists the rules addressed by this proposal with the dates
that they were adopted and submitted by ADEQ.
Table 1--Submitted Rules
----------------------------------------------------------------------------------------------------------------
Rule No. Rule title Effective date Submitted
----------------------------------------------------------------------------------------------------------------
R18-2-715.......................... Standards of Performance May 7, 2017........... April 6, 2017.
for Existing Primary
Copper Smelters; Site-
specific Requirements.
R18-2-715.01....................... Standards of Performance May 7, 2017........... April 6, 2017.
for Existing Primary
Copper Smelters;
Compliance and Monitoring.
R18-2-B1302........................ Limits on SO2 Emissions February 7, 2026...... December 8, 2025 (for
from the Hayden Smelter. parallel processing).
Appendix 14........................ Procedures for Sulfur February 7, 2026...... December 8, 2025 (for
Dioxide and Lead Fugitive parallel processing).
Emissions Studies for the
Hayden Smelter.
----------------------------------------------------------------------------------------------------------------
[[Page 10537]]
The remainder of this document discusses the EPA's review of and
proposed action on the rules summarized in Table 1 and Arizona's Hayden
SO<INF>2</INF> Plan for attaining the 1971 and 2010 SO<INF>2</INF>
NAAQS.
IV. Review of Modeled Attainment Demonstration
ADEQ provided a summary of the modeled attainment demonstration in
section 5 of the 2023 Hayden SO<INF>2</INF> Plan and section 2.2.1 of
the Hayden SO<INF>2</INF> Supplement and provided more details in
Appendix C (``Modeling Technical Support Document for the Hayden Sulfur
Dioxide (SO<INF>2</INF>) Nonattainment Area'') of the Plan (``ADEQ's
Modeling TSD''). The submission contains an air quality modeling
analysis used to demonstrate that the emission limits in the plan will
suffice to provide for timely attainment. This section discusses the
EPA's review of the State's attainment demonstration. A more detailed
discussion of our evaluation is contained in the EPA's modeling TSD for
this proposed action, titled ``Technical Support Document, EPA
Evaluation of the Modeled Attainment Demonstration in the 2023 Hayden
SO<INF>2</INF> Plan.'' \41\
---------------------------------------------------------------------------
\41\ EPA Region IX, ``Technical Support Document, EPA Evaluation
of the Modeled Attainment Demonstration in the 2023 Hayden
SO<INF>2</INF> Plan,'' December 2025.
---------------------------------------------------------------------------
A. Modeling Approach and Receptor Grid
ADEQ's attainment demonstration used AERMOD, the preferred model
for this application. The State used AERMOD version 22112 (``v22112''),
the regulatory version at the time it conducted its nonattainment
planning, for all emission sources. For all emission sources, the State
used regulatory default options. The EPA proposes to find this
selection appropriate.
The modeling domain was centered on the Hayden Smelter facility and
extended to the edges of the Hayden SO<INF>2</INF> nonattainment area.
ADEQ used a grid spacing of 25 meters to resolve AERMOD model
concentrations along the ambient air boundary surrounding the Smelter
with increased grid spacing toward the edges of the nonattainment area.
Receptors were placed outside the ambient air boundary, which is
defined by the facility's physical fence line, except in several
segments where there is no fence, and the State inspected and concluded
steep topography precludes public access. The area is further secured
by regular security patrols. We propose to find this selection
appropriate.
B. Meteorological Data
ADEQ conducted its modeling using five years of on-site surface
meteorological data collected by the State, specifically 2015 to 2016
and 2018 to 2020 at a 10-meter tower located approximately 0.35 km
south of the Smelter. The State provided audit reports for the years
2015, 2016, 2018, 2019, and 2020 for the monitoring station to document
that the station's installation and data collection were consistent
with the EPA's recommendations.<SUP>42 43</SUP> The anemometer and
solar radiation sensor were found to be faulty in 2017 and 2021,
respectively, leading to their replacement. These issues prevented both
years from meeting the 90 percent data completeness requirement for
regulatory modeling. The State used upper air data from the National
Weather Service station in Tucson, Arizona (Weather Bureau Army Navy
station number 23160), which is 100 km south of the Smelter. The State
used AERMET v22112 to process meteorological data for use with AERMOD.
---------------------------------------------------------------------------
\42\ ADEQ's Modeling TSD, appendix G.
\43\ EPA, ``EPA Meteorological Monitoring Guidance for
Regulatory Modeling Applications,'' Publication No. EPA-454/R-99-005
(February 2000).
---------------------------------------------------------------------------
The State used AERSURFACE version 20060, relying on data from the
onsite location to estimate the surface characteristics (i.e., albedo,
Bowen ratio, and surface roughness). The State calculated the
parameters for twelve compass sectors of 30 degrees each out to 1 km at
a seasonal temporal resolution.
The State used the Auer (1978) land use method, with land cover
data from the United States Geological Survey National Land Cover Data
1992 archives, to determine that the 3-km area around the Hayden
Smelter is composed of 89.9 percent rural land types. Therefore, the
State selected rural dispersion coefficients for modeling.
Based on our review, the EPA proposes to find the selection and use
of these meteorological inputs to be appropriate and in accordance with
appendix W and the 2014 SO<INF>2</INF> Guidance.
C. Emissions Data
ADEQ developed a modeling emissions inventory for sources within
the Hayden SO<INF>2</INF> nonattainment area and a 50 km buffer zone
extending from the nonattainment area boundary based on the 2017 base
year emission inventory data. In 2017, the Hayden Smelter emitted
20,498.8 tons of SO<INF>2</INF>, accounting for more than 99.9 percent
of SO<INF>2</INF> emissions in the nonattainment area. No other sources
had SO<INF>2</INF> emissions greater than 25 tons per year (tpy) in the
nonattainment area in 2017. The Freeport-McMoRan Miami Inc. (FMMI)
copper smelter is located 46 km north of the Hayden Smelter and had
2017 SO<INF>2</INF> emissions of 3,930.3 tpy. The two smelters are
separated by large mountains, making these two airsheds distinct. The
State modeled the FMMI stack emissions and determined that the modeled
concentrations from the source were negligible in the Hayden
SO<INF>2</INF> nonattainment area. Additionally, the State determined
that all other sources were sufficiently represented by background
monitored concentrations.
The State evaluated the stack height of the main stack of the
Hayden Smelter in section 5.3 (``Good Engineering Practice (GEP) Stack
Height'') of Appendix C of the 2023 Hayden SO<INF>2</INF> Plan. ADEQ
relied upon fluid modeling performed in 1979 and an updated 2022
analysis based on the current stack height regulations to determine
that the 1,000 foot stack remains an appropriate stack height, pursuant
to 40 CFR 51.100(ii)(3). ADEQ also incorporated the NSPS limit for
SO<INF>2</INF> of 0.065 percent by volume (applicable to all roasters,
smelting furnaces and copper converters),\44\ into Rule B1302.
---------------------------------------------------------------------------
\44\ 40 CFR 60.163(a).
---------------------------------------------------------------------------
Since 2014, Asarco has undertaken substantial upgrades to the
Smelter facility that have reduced SO<INF>2</INF> emissions and has
proposed several additional upgrades that have been incorporated into
the Hayden SO<INF>2</INF> Permit Revision and revised Rule B1302 as
required controls.\45\ The State estimated post-upgrade maximum 1-hour
SO<INF>2</INF> emissions and used those estimates to model facility
sources subject to additional control. The State provided a
justification for the control efficiencies assumed in the
adjustments.\46\ The State modeled all sources within the Smelter
complex, including the main stack, anode furnace roof monitors,
converter aisle roof monitors, flash furnace building roof monitors,
and outdoor slag pouring. Additionally, the modeling included emissions
from the acid plant preheater, anode boiler, and oxygen plant boiler as
three non-trivial pieces of auxiliary equipment that collectively
[[Page 10538]]
account for an additional 61.69 pounds per hour (lb/hr) of
SO<INF>2</INF> emissions.\47\
---------------------------------------------------------------------------
\45\ ADEQ's Modeling TSD, section 5-1.
\46\ See letter dated August 12, 2022, from William B. Jones,
Blue Sky Modeling LLC., to Feng Mao, ADEQ, Subject: ``Re: Response
to ADEQ comments on ASARCO SO<INF>2</INF> SIP Modeling,'' included
as Appendix D of ADEQ's Modeling TSD, Appendix F.
\47\ ADEQ's Modeling TSD, Table 5-1 and Table 8-4.
---------------------------------------------------------------------------
The hourly emission rates used in the attainment modeling in the
2023 Hayden SO<INF>2</INF> Plan are shown in Table 2. The main stack
CEV (1,518 lb/hr) was used to derive a 14-operating day average
emission limit, as described in section IV.D of this document.
Table 2--Projected Maximum Smelter SO2 Emissions After Additional
Controls
------------------------------------------------------------------------
SO2
Source emissions
(lb/hr)
------------------------------------------------------------------------
Main Stack.................................................. 1,518
Slag Pouring................................................ 4.05
Anode Furnace............................................... 10.0
Converter Aisle............................................. 9.0
Flash Furnace............................................... 38.5
Acid Plant Preheater........................................ 0.12
Anode Boiler................................................ 0.002
Oxygen Plant Boiler......................................... 0.01
-----------
Total................................................... 1,580
------------------------------------------------------------------------
Source: ADEQ's Modeling TSD, Table 5-1 and Table 8-4.
In addition to modeling the fugitive emission limits in Table 2,
the State included additional modeling results in the Hayden
SO<INF>2</INF> Supplement for a series of alternative fugitive
emissions limit scenarios that vary emissions among the anode furnace,
converter aisle, and flash furnace.\48\ The State conducted modeling
for these additional scenarios to account for a provision that ADEQ
included in Rule B1302. Subsection (C)(3)(d) of Rule B1302 allows the
owner or operator to apply for a significant permit revision to change
the applicable fugitive emissions limits for the three fugitive sources
to those of an alternative scenario. The alternative fugitive emissions
limit scenarios and resulting modeled SO<INF>2</INF> concentrations are
shown in Table 3 of this document. The modeled design values for these
alternative scenarios are all below the NAAQS.
---------------------------------------------------------------------------
\48\ Hayden SO<INF>2</INF> Supplement, section 2.2.1.
Table 3--Alternative Emissions Limit Scenarios
----------------------------------------------------------------------------------------------------------------
Resulting AERMOD
Scenario Flash furnace (lb/ Converter aisle Anode furnace (lb/ concentrations
hr) (lb/hr) hr) ([micro]g/m\3\) *
----------------------------------------------------------------------------------------------------------------
1................................... 37 10 10 195.8
2................................... 35.5 10 11 195.3
3................................... 34 10 12 194.8
4................................... 36.5 11 9 195.3
5................................... 35 11 10 194.8
6................................... 34 11 11 195.8
7................................... 32.5 11 12 195.3
8................................... 35 12 9 195.8
9................................... 33.5 12 10 195.3
10.................................. 32 12 11 194.9
11.................................. 30.5 12 12 194.7
12.................................. 33 13 9 194.9
13.................................. 32 13 10 195.8
14.................................. 30.5 13 11 195.7
15.................................. 29.1 13 12 195.8
----------------------------------------------------------------------------------------------------------------
Source: Hayden SO2 Supplement, Table 1-2.
* Modeled values have been rounded to the nearest tenth.
The State asserts that the emission limit for the main stack and
limits for each of the fugitive emission limit scenarios will
adequately regulate emissions from the Hayden Smelter facility.\49\ We
propose to find the selection and use of these emissions inputs to
AERMOD to be appropriate and in accordance with Appendix W and the 2014
SO<INF>2</INF> Guidance. The EPA also proposes to find that the State
adequately characterized source parameters for the emissions described
above, as well as the Hayden Smelter's building layout and location in
its modeling. Where appropriate, the AERMOD component Building Profile
Input Program for Plume Rise Model Enhancements was used to assist in
addressing building downwash. We propose to find the selection and use
of these emissions inputs to AERMOD to be appropriate and in accordance
with Appendix W and the 2014 SO<INF>2</INF> Guidance.
---------------------------------------------------------------------------
\49\ Id. at 6.
---------------------------------------------------------------------------
D. Emission Limits
Section 172(c)(6) of the CAA requires that a state's attainment
plan include enforceable emission limitations, and such other control
measures, means, or techniques (including economic incentives such as
fees, marketable permits, and auctions of emission rights), as well as
schedules and timetables for compliance, as may be necessary or
appropriate to provide for attainment of the standard in the area by
the applicable attainment date.\50\ Part of the review of a state's
attainment plan must address the use of these limits, both with respect
to the general suitability of using such limits for the purpose of
meeting the requirements of CAA section 172(c)(6) and with respect to
whether the particular limits included in the plan have been suitably
demonstrated to provide for attainment. As specified in sections
172(c)(6) and 110(a)(2)(A) of the CAA and in the preamble to the EPA's
final rule establishing the 2010 1-hour SO<INF>2</INF> NAAQS,\51\
emission limitations, control measures, and other elements in the SIP
must be enforceable by the state and the EPA.
---------------------------------------------------------------------------
\50\ See General Preamble, 13567-13568 (April 16, 1992).
\51\ 75 FR 35520 (June 22, 2010).
---------------------------------------------------------------------------
The first subsection that follows addresses the enforceability of
the limits in the Plan and the second subsection that follows addresses
in particular the
[[Page 10539]]
longer-term 14-operating day average limit.
1. Enforceability
The emission limits for the main stack and fugitive emissions
sources (i.e., the flash furnace, converter aisle, and anode furnace)
of the Asarco Hayden Smelter are codified in revisions to section (C)
of Rule B1302. ADEQ submitted the revised rule to the EPA for
incorporation into the Arizona SIP via parallel processing on December
8, 2025. We are proposing to approve Rule B1302 as part of this action
and we intend to finalize action on the rule prior to or
contemporaneously with our final action on the Hayden SO<INF>2</INF>
Plan.
Rule B1302's 14-operating day average emission limit of 1,069.1 lb/
hr applies to emissions vented to the Smelter's main stack from several
control devices, including the acid plant, secondary and tertiary
converter ventilation gas baghouses, vent gas baghouse, and anode
furnace baghouses.\52\ To ensure compliance with the main stack limit,
the rule requires that continuous emissions monitoring systems be
operated at the exit of each of the aforementioned control devices.\53\
In addition, Rule B1302 requires the owner or operator to develop, keep
current, and submit for ADEQ review and approval an operations and
maintenance plan covering each of the emissions capture and control
systems to ensure that these systems are functioning properly and are
adequately maintained.\54\
---------------------------------------------------------------------------
\52\ 2023 Hayden SO<INF>2</INF> Plan, p. 58.
\53\ Rule B1302, section (E).
\54\ Id. at section (D).
---------------------------------------------------------------------------
To ensure compliance with the fugitive emissions limits, Rule B1302
requires that the owner or operator operate continuous emissions
monitoring systems for continuous monitoring along the roofline of the
flash furnace building and above the converter aisle and anode
furnaces.\55\ Rule B1302 also requires the owner or operator to develop
and submit to ADEQ and the EPA for review and approval, within 90 days
of smelter restart, a roofline monitoring system operations and
maintenance plan to ensure the systems function properly and are
maintained.\56\ In addition, Rule B1302 subsection (C)(3)(e) makes
clear that any alternative fugitive limits would apply only following
approval into a permit revision.
---------------------------------------------------------------------------
\55\ Id. at section (F).
\56\ Id. at subsections (F)(4) and (F)(5).
---------------------------------------------------------------------------
Rule B1302 includes provisions for determining compliance with the
emission limits, and the necessary monitoring, recordkeeping, and
reporting requirements to ensure that the regulation as a whole is
enforceable.\57\ Further discussion on the enforceability of Rule B1302
is included in a separate TSD for this proposed action titled
``Technical Support Document for Rule Revisions in the Hayden
SO<INF>2</INF> Supplement to the 2023 Hayden SO<INF>2</INF> Plan.''
\58\
---------------------------------------------------------------------------
\57\ Id. at sections (H), (I), (J), (K), and (L).
\58\ EPA Region IX, ``Technical Support Document for Rule
Revisions in the Hayden SO<INF>2</INF> Supplement to the 2023 Hayden
SO<INF>2</INF> Plan,'' December 2025.
---------------------------------------------------------------------------
In accordance with the EPA's guidance on the use of federally
enforceable limits, we find that the limits in Rule B1302 will be
enforceable upon our approval of the rule, are supportive of
attainment, and are suitable for inclusion into the Arizona SIP. We
also find that the 14-day average emission limit is set at a lower
level than the shorter-term CEV used in the attainment demonstration;
the relationship between these two values is discussed in more detail
in the following section.
2. Longer-Term Average Limits
The State modeled emissions from the Hayden Smelter as described in
section IV.C of this document to determine a 1-hour average CEV for the
main stack of 1518 lb/hr. To derive a longer-term average emission
limit, the State used hourly SO<INF>2</INF> data collected using
continuous emission monitors from 2005-2007 and 2010 through early
2014, adjusted to account for facility upgrades, as a representative
emission profile for the Smelter's forecasted configuration.\59\ ADEQ
used the forecasted hourly emissions data to calculate a corresponding
distribution of longer-term emission averages, including 30-day, 14-
day, and 24-hour averages. The 99th percentile of the 14-day and 1-hour
SO<INF>2</INF> emission rates are 943.24 lb/hr and 1,339.27 lb/hr,
respectively. The ratio of these two values (i.e., the computed
adjustment factor) is 0.70.\60\ The adjustment factor was multiplied by
the main stack CEV (i.e., 1,518 lb/hr) to derive a longer-term 14-day
average emission limit of 1,069.1 lb/hr. ADEQ included an updated
analysis to examine whether the forecasted hourly emissions reflect
actual operating conditions post-upgrades. Based on this analysis, the
State concludes that the forecasted emissions were a conservative
estimate and that the existing 1069.1 lb/hr 14-day average limit
remains appropriate and protective.
---------------------------------------------------------------------------
\59\ ASARCO_EMISSION_LIMIT_TSD_10222018.xlsx. Data available
from prior to 2005 and from 2008-2009 were excluded because they
were determined to not be fully representative of Smelter
operations.
\60\ Using the same technique, the State also computed the 99th
percentile of the 30-day and 24-hour SO<INF>2</INF> emission rates,
which are 929.91 lb/hr and 991.83 lb/hr, resulting in computed
adjustment factors of 0.69 and 0.74, respectively. These values are
within the range of the national average 30-day average adjustment
factors (i.e., 0.63-0.79) and lower than the range of 24-hour
average adjustment factors (i.e., 0.81-0.93) estimated for
electrical generating units (EGUs) and listed in Table 1 of Appendix
D of the 2014 SO<INF>2</INF> Guidance. Although the 24-hour average
adjustment factor is outside of the range derived for EGUs, this is
expected, as smelters exhibit a greater range of variability due to
feed and operational variability. In general, we expect operations
with large variability to require bigger adjustments (lower
adjustment factors) and result in lower long-term average emissions
limits relative to the 1-hour CEV.
---------------------------------------------------------------------------
Based on a review of the State's submittal, the EPA proposes to
find that the 14-day average limit for the main stack of the Hayden
Smelter provides a suitable alternative to establishing a 1-hour
average emission limit for the main stack. The State has used a
suitable database in an appropriate manner and has thereby applied an
appropriate adjustment factor, yielding an emission limit that has
comparable stringency to the 1-hour average limit that the State
determined would otherwise have been necessary to provide for
attainment. While the 14-day average limit for the main stack allows
occasions in which emissions may be higher than the level that would be
allowed with the 1-hour limit, the State's limit compensates by
requiring average emissions to be lower than the level that would
otherwise have been required by a 1-hour average limit. For reasons
described herein and explained in more detail in the EPA's 2014
SO<INF>2</INF> Guidance, the EPA has found that appropriately set
longer-term average limits provide a reasonable basis by which
nonattainment plans may provide for attainment. Based on our review of
this general information as well as the particular information in
ADEQ's plan, the EPA proposes to find that the 14-day average limit for
the main stack of the Hayden Smelter, in combination with other
emissions limitations in the State's plan, will provide for attainment
of the NAAQS. The EPA is proposing to conclude that the modeling and
comparably stringent longer-term emission limit in Arizona's plan
adequately demonstrate that it, along with the 1-hour fugitive limits,
provides for attainment of the 1971 and 2010 SO<INF>2</INF> NAAQS in
the Hayden SO<INF>2</INF> nonattainment area.
E. Background Concentrations
The 2014 SO<INF>2</INF> Guidance recommends developing a uniform
monitored background concentration based on monitored design values for
the latest
[[Page 10540]]
three-year period, regardless of the years of meteorological data used
in the modeling. The guidance further states that in cases of
nonattainment areas designated based on a monitor's data showing a
NAAQS violation, it may be necessary to use a different representative
monitor outside of the nonattainment area, particularly where the
monitor has a high number of observations affected by modeled sources.
The EPA's ``Guidance on Developing Background Concentration for Use in
Modeling Demonstrations'' \61\ provides guidance on the selection of
nearby sources to explicitly model in the demonstration and the
representativeness of the background concentration of sources not
modeled explicitly.
---------------------------------------------------------------------------
\61\ EPA, ``Guidance on Developing Background Concentrations for
Use in Modeling Demonstrations'' (November 2024). Publication No.
EPA-454/R-24-003. Available at <a href="https://www.epa.gov/system/files/documents/2024-11/background-concentrations.pdf">https://www.epa.gov/system/files/documents/2024-11/background-concentrations.pdf</a>.
---------------------------------------------------------------------------
ADEQ selected background SO<INF>2</INF> concentrations using
ambient air measurements recorded for the years 2020 and 2021 at the
Hayden Old Jail monitor (Air Quality System (AQS) \62\ ID: 04-007-1001)
following the start of the temporary shutdown at the Hayden Smelter
facility. The Hayden Old Jail monitor is uniquely positioned to capture
ambient SO<INF>2</INF> levels reflective of background conditions
during the closure period, as it is the only AQS monitor in the
nonattainment area and is located just to the west of the facility's
ambient air boundary. This location ensures that the monitor is
influenced by the same topographically driven diurnal flows governing
ambient SO<INF>2</INF> concentrations throughout the nonattainment
area. The shutdown period provides a dataset free from facility
influence, as the Asarco Hayden Smelter is the sole major
SO<INF>2</INF> source in the area. No hourly exceedances of the
SO<INF>2</INF> NAAQS occurred during the temporary closure period,
underscoring the reliability of these background concentrations for
accurately representing ambient conditions in the absence of smelter
emissions. The State calculated the 2-year averages of the 99th
percentile of SO<INF>2</INF> concentrations for each hour of the day
and season at the Hayden Old Jail site. The State chose to use these
concentrations to establish temporally varying background
concentrations of SO<INF>2</INF> to add to modeled design values.
---------------------------------------------------------------------------
\62\ The EPA maintains the AQS, a database that contains ambient
air pollution data collected by the EPA, state, local, and tribal
air pollution control agencies. The AQS also contains meteorological
data, descriptive information about each monitoring station
(including its geographic location and its operator) and data
quality assurance/quality control information. The AQS data are used
to (1) assess air quality, (2) assist in attainment/non-attainment
designations, (3) evaluate SIPs for non-attainment areas, (4)
perform modeling for permit review analysis, and (5) prepare reports
for Congress as mandated by the CAA. Access is through the website
at <a href="https://www.epa.gov/aqs">https://www.epa.gov/aqs</a>.
---------------------------------------------------------------------------
The EPA is proposing to find that the State's specification of
temporally varying SO<INF>2</INF> background concentrations provide for
representative background SO<INF>2</INF> levels in the Hayden
SO<INF>2</INF> nonattainment area and is appropriate and consistent
with the modeling guidance.
F. Summary of Results
The State's modeling indicates that with CEVs of 1,518 lb/hr for
the main stack, 38.5 lb/hr for the flash furnace fugitives, 10 lb/hr
for the converter aisle fugitives, and 9 lb/hr for the anode furnace
fugitives, the highest predicted 99th percentile daily maximum 1-hour
concentration within the Hayden SO<INF>2</INF> nonattainment area would
be 195.97 [micro]g/m\3\, which is below the 196.4 [micro]g/m\3\ (75
ppb) level of the 2010 1-hour SO<INF>2</INF> NAAQS.\63\ Likewise the
State's modeling indicates that with these CEVs, the controlling
concentrations for the 1971 NAAQS would be 170.8 [micro]g/m\3\ (3-hour
average), compared to the 3-hour secondary standard of 1300 [micro]g/
m\3\ (0.5 ppm); 51.7 [micro]g/m\3\ (24-hour average), compared to the
24-hour primary standard of 512 [micro]g/m\3\ (0.14 ppm); and 11.9
[micro]g/m\3\ (annual average) compared to the annual primary standard
of 80 [micro]g/m\3\ (0.03 ppm).\64\ The modeled concentrations include
the background concentration, slag pouring emissions, non-trivial
equipment emissions, and fugitive emissions of SO<INF>2</INF>. The
modeling indicates that the Smelter facility upgrades, resulting 14-day
emission limit of 1,069.1 lb/hr for the main stack, and fugitive
emissions limits of 38.5 lb/hr for the flash furnace, 10 lb/hr for the
converter aisle, and 9 lb/hr for the anode furnace, are sufficient for
the Hayden SO<INF>2</INF> nonattainment area to attain the 1971 and
2010 SO<INF>2</INF> NAAQS. Additionally, the State's attainment
modeling for the alternative fugitive emissions limit scenarios
detailed in Table 3 of this document indicates that each of the
alternative scenarios, coupled with the 14-day limit for the main
stack, would also provide for attainment of the 1971 and 2010
SO<INF>2</INF> NAAQS in the Hayden SO<INF>2</INF> nonattainment area.
---------------------------------------------------------------------------
\63\ 2023 Hayden SO<INF>2</INF> Plan, p. 82.
\64\ Id.
---------------------------------------------------------------------------
The EPA is proposing to determine that the attainment modeling
demonstration meets the technical requirements of Appendix W and the
2014 SO<INF>2</INF> Guidance.
V. Review of Emissions and Emission Controls
A. Emissions Inventory and the Quantification of Emissions
Section 172(c)(3) of the CAA requires that a state's attainment
plan include a comprehensive, accurate, current inventory of actual
emissions from all sources of the relevant pollutant or pollutants in
the area, including such periodic revisions as the Administrator may
determine necessary to assure that the requirements of the CAA are met.
Section 172(c)(4) of the CAA requires that a state's attainment plan
expressly identify and quantify the emissions, if any, of any pollutant
or pollutants that will be allowed, in accordance with section
173(a)(1)(B) of the CAA, from the construction and operation of major
new or modified stationary sources in the area. Section 172(c)(4) of
the CAA also requires the plan demonstrate that the quantified
emissions are consistent with the achievement of RFP and will not
interfere with attainment of the NAAQS by the attainment date.
The emissions inventory and source emission rate data for an area
serve as the foundation for air quality modeling and other analyses
that enable states to estimate the degree to which different sources
within a nonattainment area contribute to violations within the
affected area and assess the expected improvement in air quality within
the nonattainment area due to the adoption and implementation of
control measures. As noted above, the state must develop and submit to
the EPA a comprehensive, accurate, and current inventory of actual
emissions from all sources of SO<INF>2</INF> emissions in each
nonattainment area, as well as any sources located outside the
nonattainment area that may affect attainment in the area.\65\
---------------------------------------------------------------------------
\65\ See CAA section 172(c)(3) and the EPA's 2014 SO<INF>2</INF>
Guidance.
---------------------------------------------------------------------------
The ADEQ used 2017 as the base year for emissions inventory
preparation. At the time of preparation of the Plan, 2017 reflected the
most recent triennial National Emission Inventory (NEI) available for a
year in which the Hayden Smelter was operational \66\ and therefore is
representative of a year with violations of the primary SO<INF>2</INF>
NAAQS. Emissions in the year 2017 also reflect a time prior to
implementation of the
[[Page 10541]]
control strategy in the 2023 Hayden SO<INF>2</INF> Plan.
---------------------------------------------------------------------------
\66\ As discussed in the 2023 Hayden SO<INF>2</INF> Plan, on
October 13, 2019, the Hayden Smelter ``shut down due to the
declaration of a work stoppage by the ASARCO bargaining unit.'' As
of the writing of this document, the Hayden Smelter has not resumed
operations.
---------------------------------------------------------------------------
To develop the 2017 base year emissions inventory, ADEQ reviewed
and compiled actual emissions information from all sources of
SO<INF>2</INF> in the nonattainment area. The ADEQ used information
from state and local permits and surveys to estimate emissions from
point sources and derived nonpoint source emissions from the 2017 NEI.
In addition to developing an emissions inventory of SO<INF>2</INF>
emission sources within the nonattainment area, ADEQ provided an
SO<INF>2</INF> emissions inventory for those emission sources within a
50 km buffer zone of the nonattainment area. Table 4 of this document
summarizes 2017 base year SO<INF>2</INF> emissions inventory data for
the nonattainment area, categorized by emission source type (rounded to
the nearest whole number).
Table 4--Base Year SO2 Emissions Inventory for the Hayden SO2 Nonattainment Area
[Tons per year]
--------------------------------------------------------------------------------------------------------------------------------------------------------
Year Point Nonpoint On-road mobile Non-road mobile Total
--------------------------------------------------------------------------------------------------------------------------------------------------------
2017............................................................... 20,499 5 <1 <1 20,504
--------------------------------------------------------------------------------------------------------------------------------------------------------
Source: 2023 Hayden SO2 Plan, Table 3-13.
As shown in Table 4, the majority of SO<INF>2</INF> emissions in
the 2017 base year inventory can be attributed to the point source
category. Emissions for this category are from the Hayden Smelter.
A projected attainment year emissions inventory should also be
included in the SIP submission according to the 2014 SO<INF>2</INF>
Guidance. This emissions inventory should include, in a manner
consistent with the attainment demonstration, estimated emissions for
all SO<INF>2</INF> emission sources that were determined to have an
impact on the affected nonattainment area for the projected attainment
year. Table 5 of this document summarizes Arizona's projected 2026
SO<INF>2</INF> emissions inventory data for the nonattainment area,
categorized by source type. The 2017 base year emissions, as well as
the projected change between base year and projected year emissions
(rounded to the nearest whole number), are also summarized in Table 5.
Table 5--Projected 2026 Emissions Inventory for the Hayden SO2 Nonattainment Area
[Tons per year]
--------------------------------------------------------------------------------------------------------------------------------------------------------
Year Point Nonpoint On-road mobile Non-road mobile Total
--------------------------------------------------------------------------------------------------------------------------------------------------------
2017.............................................................. 20,499 5 <1 <1 20,504
2026.............................................................. 3,007 5 <1 <1 3,012
-------------------------------------------------------------------------------------
Change........................................................ -17,492 0 0 0 -17,492
--------------------------------------------------------------------------------------------------------------------------------------------------------
Source: 2023 Hayden SO2 Plan, Appendix B, Tables 5-6 and 7-6.
As shown in Table 5, the majority of SO<INF>2</INF> emissions in
the projected 2026 emission inventory are attributed to the point
source emissions category. Emissions for this category were estimated
based on a potential to emit at maximum throughput or federally
enforceable limits for the Hayden Smelter. These emission projections
include emission reduction estimates from the capture efficiencies of
control measures that have already been implemented, or are required to
be implemented under the Hayden SO<INF>2</INF> Permit Revision and
revised Rule B1302.
The EPA has evaluated ADEQ's 2017 base year inventory and projected
2026 emissions inventory for the Hayden SO<INF>2</INF> nonattainment
area and finds these inventories and the methodologies used for their
development to be consistent with EPA guidance. As a result, the EPA is
proposing to determine that the emissions inventories in the 2023
Hayden SO<INF>2</INF> Plan satisfy the requirements of CAA section
172(c)(3) and (4) for the Hayden SO<INF>2</INF> nonattainment area for
the 1971 and 2010 SO<INF>2</INF> NAAQS.
B. Reasonably Available Control Measures/Reasonably Available Control
Technology
CAA section 172(c)(1) states that nonattainment plans should
``provide for the implementation of all reasonably available control
measures as expeditiously as practicable (including such reductions in
emissions from existing sources in the area as may be obtained through
the adoption, at a minimum, of reasonably available control technology)
and shall provide for attainment of the [NAAQS].'' In this case,
pursuant to CAA section 179(d)(3), following the EPA's determination
that the Hayden SO<INF>2</INF> nonattainment area failed to attain by
the October 4, 2018 attainment date, Arizona's revised plan must
provide for attainment by January 31, 2027.\67\
---------------------------------------------------------------------------
\67\ 87 FR 4805 (January 31, 2022).
---------------------------------------------------------------------------
ADEQ's control strategy for attaining the 1971 and 2010
SO<INF>2</INF> NAAQS in the Hayden SO<INF>2</INF> nonattainment area is
based on implementation of the controls in the 2017 Hayden
SO<INF>2</INF> Plan and the 2023 Hayden SO<INF>2</INF> Plan at the
Hayden Smelter. The controls implemented as part of the 2017 Hayden
SO<INF>2</INF> Plan include the replacement of five converter units
with three larger units; the installation of more extensive, efficient,
and effective fugitive gas control ducting around the converters; and
the installation of additional process gas controls before venting to
the main stack. Installation of these controls, collectively referred
to as the ``Converter Retrofit Project,'' was completed in May 2018.
In the 2017 Hayden SO<INF>2</INF> Plan, ADEQ compared controls at
the Hayden Smelter with those at eight other facilities and determined
that the Smelter's use of an acid plant, the Converter Retrofit
Project, and dry lime scrubbing were comparable to SO<INF>2</INF>
control measures employed by similar
[[Page 10542]]
sources.\68\ Thus, ADEQ concluded that the controls for the Hayden
Smelter, including the Converter Retrofit Project, were representative
of RACM/RACT level control.
---------------------------------------------------------------------------
\68\ 85 FR 31118, 31122 (May 22, 2020).
---------------------------------------------------------------------------
The State's updated RACM/RACT analysis can be found in section
4.5.2.2 of the 2023 Hayden SO<INF>2</INF> Plan. ADEQ conducted the
RACM/RACT analysis by comparing the requirements at the Hayden Smelter
with controls for SO<INF>2</INF> and particulate matter at twelve
facilities across the U.S. that (1) have similar control technologies
as the Hayden Smelter; and (2) have been determined to meet the
requirements for best available control measures for prevention of
significant deterioration permitting purposes. The State chose to
examine a diversity of sources because of the small number of primary
copper smelting facilities operating in the United States. ADEQ
compared the projected control efficiencies for the proposed control
measures for the Hayden Smelter with the control efficiencies for the
measures identified at the other large sources and, based on the
efficiency of these sources as provided in the EPA's RACT/BACT/LAER
Clearinghouse,\69\ ADEQ reaffirmed its prior finding that the control
technology implemented by Asarco as part of the Converter Retrofit
Project is achieving similar or higher control efficiencies as those
used by other industries. Thus, ADEQ concluded that these control
technologies are representative of RACM/RACT level of control.
---------------------------------------------------------------------------
\69\ Available at <a href="https://cfpub.epa.gov/rblc/index.cfm?action=Home.Home">https://cfpub.epa.gov/rblc/index.cfm?action=Home.Home</a>.
---------------------------------------------------------------------------
Because the requirements in the 2017 Hayden SO<INF>2</INF> Plan did
not ultimately provide for attainment of the 2010 1-hour primary
SO<INF>2</INF> NAAQS by the original October 4, 2018 attainment date,
ADEQ included additional controls for the Hayden Smelter in the 2023
Hayden SO<INF>2</INF> Plan to provide for attainment by the January 31,
2027 applicable attainment date. These controls include three projects
aimed at reducing fugitive emissions during peak processing periods:
<bullet> The ``Uptake Improvement Project'' involves the addition
of a partial enclosure around the flash furnace to improve emissions
capture during matte tapping and slag skimming activities;
<bullet> The ``Fuming Ladle Capture Project'' involves the addition
of a hood and retaining walls to capture emissions from ``fuming''
ladles; and
<bullet> The ``Anode Furnace Secondary Hood System'' involves the
addition of secondary hooding around the anode furnaces to improve
capture during operations.
Arizona's Hayden SO<INF>2</INF> Permit Revision and revised Rule
B1302 require compliance with the Uptake Improvement Project (also
known as the ``Flash Furnace Area Capture Improvements''), Fuming Ladle
Capture Project (also known as the ``Converter and Material Transfer
Area Capture Improvements''), and Anode Furnace Secondary Hood System
within 180 days of smelter restart. Arizona has determined that these
measures, in combination with the Converter Retrofit Project and a
redesigned acid plant preheater,\70\ will suffice to provide for timely
attainment. The EPA concurs and proposes to conclude that the State has
satisfied the requirement in CAA section 172(c)(1) to adopt and submit
all RACM as needed to attain the standards as expeditiously as
practicable.
---------------------------------------------------------------------------
\70\ In April 2018, Asarco commissioned a new acid plant
preheater to reduce acid plant SO<INF>2</INF> emissions. Asarco
subsequently discovered a malfunction at the preheater that resulted
in loss of some process gas to the preheater exhaust stream and some
exceedances of the 1-hour SO<INF>2</INF> NAAQS. Asarco redesigned
and replaced the preheater to correct the issue. 2023 Hayden
SO<INF>2</INF> Plan, pp. 49, 100.
---------------------------------------------------------------------------
C. Nonattainment New Source Review
Section 172(c)(5) of the CAA requires that a state's attainment
plan provisions shall require permits for the construction and
operation of new or modified major stationary sources anywhere in the
nonattainment area, in accordance with CAA section 173.
On November 2, 2015, the EPA published a final limited approval and
limited disapproval of revisions to ADEQ's new source review (NSR)
rules.\71\ On May 4, 2018, the EPA approved rule revisions to address
many of the deficiencies identified in the 2015 action,\72\ and on June
16, 2021, the EPA approved additional rule revisions and determined
that all outstanding deficiencies identified in the 2015 action had
been corrected.\73\ On April 3, 2024, the EPA approved further rule
revisions submitted by ADEQ governing the issuance of permits for
stationary sources in accordance with changes that the EPA had made to
its NSR program regulations under the CAA.\74\ Collectively, these rule
revisions ensure that ADEQ's rules provide for appropriate NSR for
SO<INF>2</INF> sources undergoing construction or major modification in
the Hayden SO<INF>2</INF> nonattainment area without need for further
modification. The EPA has already concluded that the NSR requirement
has been met for this area,\75\ and we are not reopening that
determination in this proposed action. We note that Rule B1302, section
(M) (``Preconstruction review'') indicates that the smelter emission
limits contained in the rule are determined to be SO<INF>2</INF> RACT
for purposes of minor NSR requirements. This provision does not
interfere with or adversely affect existing nonattainment NSR rules.
---------------------------------------------------------------------------
\71\ 80 FR 67319 (November 2, 2015).
\72\ 83 FR 19631 (May 4, 2018).
\73\ 86 FR 31927 (June 16, 2021).
\74\ 89 FR 22963 (April 3, 2024).
\75\ 85 FR 71547, 71552 (November 10, 2020).
---------------------------------------------------------------------------
D. Reasonable Further Progress
Section 172 of the CAA requires that attainment plans include
provisions to address RFP. As discussed in the EPA's 2014
SO<INF>2</INF> Guidance, this requirement is more practically relevant
and important for NAAQS pollutants affected by emissions from numerous
and diverse sources, where the relationship between any individual
source and overall air quality is not easily discernable, and where
NAAQS attainment may require inventory-wide emissions reductions. The
relationship between ambient SO<INF>2</INF> concentrations and
SO<INF>2</INF> emission sources is more directly quantifiable as
compared to other NAAQS pollutants, and there is frequently only one
(or few) primary source of SO<INF>2</INF> emissions responsible for
poor air quality in a nonattainment area. Consequently, full progress
to attainment is achieved as soon as the one (or few) emission source
is subject to an enforceable emission limitation. Therefore, for
SO<INF>2</INF> SIP submittals that address a small number of affected
sources, requiring expeditious compliance with attainment emission
limits is sufficient to address the RFP requirement. CAA section 192(a)
requires that SO<INF>2</INF> attainment plans provide for future
attainment of the NAAQS as expeditiously as practicable, but no later
than five years from the effective date of the area's designation as
nonattainment. As discussed earlier in this document, following the
EPA's determination that the Hayden SO<INF>2</INF> nonattainment area
failed to attain by the October 4, 2018 attainment date, Arizona's plan
must provide for attainment by January 31, 2027.\76\
---------------------------------------------------------------------------
\76\ 87 FR 4805 (January 31, 2022).
---------------------------------------------------------------------------
ADEQ discusses the State's RFP demonstration, including the
compliance schedule for the Hayden Smelter's operational controls and
emission limits, in section 5.5 of the 2023 Hayden SO<INF>2</INF> Plan.
As discussed in section V.B of this document, ADEQ's control
strategy for attaining the SO<INF>2</INF> NAAQS includes the
implementation of the Converter
[[Page 10543]]
Retrofit Project, the Uptake Improvement Project, the Fuming Ladle
Capture Project, and the Anode Furnace Secondary Hood System, as well
as compliance with the emissions limits for the main stack and fugitive
emissions sources. The Converter Retrofit Project was completed in
2018.\77\ The operational controls and limitations associated with the
Uptake Improvement Project, Fuming Ladle Capture Project, and Anode
Furnace Secondary Hood System are generally required to be implemented
upon smelter restart, with some specific operational controls to be
implemented by later deadlines specified in Rule B1302, section (D)
(``Operational Standards'').\78\ The SO<INF>2</INF> emission limits for
the main stack and fugitive emissions sources are to be effective 60
days after the Hayden Smelter achieves maximum production after restart
or 180 days after smelter restart, whichever occurs first.\79\
---------------------------------------------------------------------------
\77\ 2023 Hayden SO<INF>2</INF> Plan, p. 83.
\78\ Id.
\79\ Id.
---------------------------------------------------------------------------
ADEQ finds that the 2023 Hayden SO<INF>2</INF> Plan requires
affected sources to implement appropriate control measures as
expeditiously as practicable to ensure attainment of the standards by
the applicable attainment date.\80\ ADEQ concludes that the Plan
provides for RFP in accordance with the approach to RFP described in
the EPA's 2014 SO<INF>2</INF> Guidance.\81\ The EPA proposes to
conclude that Arizona has satisfied the requirement in CAA section
172(c)(2) to provide for RFP toward attainment of the 1971 and 2010
SO<INF>2</INF> NAAQS in the Hayden SO<INF>2</INF> nonattainment area.
---------------------------------------------------------------------------
\80\ Id. at 70.
\81\ Id. at 83.
---------------------------------------------------------------------------
E. Contingency Measures
Section 172(c)(9) of the CAA requires that a state's attainment
plan include additional measures, called contingency measures, that
will take effect if the area fails to meet RFP or fails to attain the
NAAQS by the attainment date. The EPA's 2014 SO<INF>2</INF> Guidance
describes special features of SO<INF>2</INF> attainment planning that
influence the suitability of alternative means of addressing the
requirement in CAA section 172(c)(9) for contingency measures for
SO<INF>2</INF>.\82\ That is, SO<INF>2</INF> control measures are based
on what is directly and quantifiably necessary to attain the
SO<INF>2</INF> NAAQS, and consequently, an area that implements such
control measures would be unlikely to fail to attain the NAAQS.\83\
Therefore, the EPA's longstanding approach is that an appropriate means
of satisfying the contingency measures requirement for the
SO<INF>2</INF> NAAQS is for the state to have a comprehensive
enforcement program that identifies sources of violations of the
SO<INF>2</INF> NAAQS and for the state to undertake aggressive follow-
up for compliance and enforcement.
---------------------------------------------------------------------------
\82\ 2014 SO<INF>2</INF> Guidance, pp. 41-42.
\83\ See 75 FR 35520, 35576 (June 22, 2010) and the 2014
SO<INF>2</INF> Guidance.
---------------------------------------------------------------------------
ADEQ explains its rationale for concluding that the Plan meets the
requirement for contingency measures in section 6 of the 2023 Hayden
SO<INF>2</INF> Plan. Specifically, ADEQ relies on the approach outlined
in the 2014 SO<INF>2</INF> Guidance of having a comprehensive program
to identify sources of violations of the SO<INF>2</INF> NAAQS and, as
needed, of undertaking an aggressive follow-up for compliance and
enforcement of applicable emission limitations. ADEQ states in the 2023
Hayden SO<INF>2</INF> Plan that it has such an enforcement program
pursuant to State law in Arizona Revised Statutes (ARS) sections 49-
461, 49-402, 49-404, and 49-406.\84\ ADEQ also describes the process
under State law to apply contingency measures for failure to make RFP
and/or for failure to attain the SO<INF>2</INF> NAAQS by the attainment
date and concludes that ADEQ's Plan satisfies contingency measure
requirements.\85\
---------------------------------------------------------------------------
\84\ 2023 Hayden SO<INF>2</INF> Plan, p. 85.
\85\ Id. at sections 6.1 and 6.2.
---------------------------------------------------------------------------
We note that the EPA has approved ARS 49-402, 49-404, 49-406, and
49-461 into the Arizona SIP.\86\ In addition, we have approved ARS 49-
422(A) (``Powers and Duties''), which authorizes ADEQ to require
sources of air contaminants to ``monitor, sample or perform other
studies to quantify emissions of air contaminants or levels of air
pollution that may reasonably be attributable to that source'' for
purposes of determining whether the source is in violation of a control
requirement. We have also approved ARS 49-460 through 49-463, which
authorize ADEQ to request compliance-related information from sources,
to issue orders of abatement upon reasonable cause to believe a source
has violated or is violating an air pollution control requirement, to
establish injunctive relief, to establish civil penalties of up to
$10,000 per day per violation, and to conduct criminal enforcement, as
appropriate, through the Attorney General.\87\
---------------------------------------------------------------------------
\86\ 40 CFR 52.120(e), Table 3.
\87\ 77 FR 66398 (November 5, 2012).
---------------------------------------------------------------------------
As noted above, the EPA's 2014 SO<INF>2</INF> Guidance describes
special features of SO<INF>2</INF> planning that influence the
suitability of alternative means of addressing the requirement in CAA
section 172(c)(9) for contingency measures for SO<INF>2</INF>, such
that in particular an appropriate means of satisfying this requirement
is for the state to have a comprehensive enforcement program that
identifies sources of violations of the SO<INF>2</INF> NAAQS and to
undertake an aggressive follow-up for compliance and enforcement.
Arizona's plan provides for satisfying the contingency measure
requirement in this manner for the nonattainment area. Consequently,
the EPA is proposing to find that Arizona's comprehensive enforcement
program is an appropriate contingency measure for this area and meets
the requirement of CAA section 172(c)(9) for the 1971 and 2010
SO<INF>2</INF> NAAQS.
VI. Additional Elements of Arizona's Submittal
ADEQ addressed conformity requirements for the SO<INF>2</INF>
NAAQS, including both general conformity and transportation conformity,
in section 7 of the 2023 Hayden SO<INF>2</INF> Plan.
Generally, as set forth in section 176(c) of the CAA, conformity
requires that actions by Federal agencies do not cause new air quality
violations, worsen existing violations, or delay timely attainment of
the relevant NAAQS. General conformity applies to Federal actions,
other than certain highway and transportation projects, if the action
takes place in a nonattainment or maintenance area (i.e., an area that
submitted a maintenance plan that meets the requirements of section
175A of the CAA and has been redesignated to attainment) for ozone,
particulate matter, nitrogen dioxide, carbon monoxide, lead, or
SO<INF>2</INF>. The EPA's General Conformity Rule establishes the
criteria and procedures for determining if a Federal action conforms to
the SIP.\88\ With respect to the 2010 SO<INF>2</INF> NAAQS, Federal
agencies are expected to continue to estimate emissions for conformity
analyses in the same manner as they estimated emissions for conformity
analyses under the previous NAAQS for SO<INF>2</INF>. The EPA's General
Conformity Rule includes the basic requirement that a Federal agency's
general conformity analysis be based on the latest and most accurate
emission estimation techniques available.\89\ When updated and improved
emission estimation techniques become available, the EPA expects the
Federal agency to use these techniques.
---------------------------------------------------------------------------
\88\ 40 CFR 93.150 through 93.165.
\89\ 40 CFR 93.159(b).
---------------------------------------------------------------------------
Transportation conformity determinations are not required in
SO<INF>2</INF> nonattainment and maintenance areas. The EPA concluded
in its 1993
[[Page 10544]]
transportation conformity rule that highway and transit vehicles are
not significant sources of SO<INF>2</INF>. Therefore, transportation
plans, transportation improvement programs, and projects are presumed
to conform to applicable implementation plans for SO<INF>2</INF>.\90\
---------------------------------------------------------------------------
\90\ 58 FR 3768, 3776 (January 11, 1993).
---------------------------------------------------------------------------
VII. Proposed Action
The EPA is proposing to approve the 2023 Hayden SO<INF>2</INF>
Plan, which ADEQ submitted to the EPA on October 3, 2023, and the
Hayden SO<INF>2</INF> Supplement, including amendments to Rule B1302
and Appendix 14, submitted for parallel processing on December 8, 2025.
We find that these submittals provide for attainment of the 1971 and
2010 SO<INF>2</INF> NAAQS for the Hayden SO<INF>2</INF> nonattainment
area and for meeting other nonattainment planning requirements. This
SO<INF>2</INF> attainment plan includes Arizona's attainment
demonstration for the Hayden SO<INF>2</INF> nonattainment area. In
addition to an attainment demonstration, the State's plan addresses the
requirements for meeting RFP toward attainment of the NAAQS, RACM/RACT,
base year and projection year emission inventories, nonattainment NSR,
emission limitations necessary to provide for attainment, and
contingency measures. In addition, the EPA is also proposing to approve
amendments to Rules 715 and 715.01, which ADEQ submitted to the EPA on
April 6, 2017. We find that these amendments, which would sunset the
requirements in these rules, will not result in any relaxation of SIP
requirements based on the revisions to Rule B1302.
The EPA is proposing to determine that Arizona's Hayden
SO<INF>2</INF> Plan meets the applicable requirements of section 172 of
the CAA for the 1971 and 2010 SO<INF>2</INF> NAAQS. The EPA proposes to
determine that the Hayden SO<INF>2</INF> Plan meets the emissions
inventory requirements under CAA section 172(c)(3) and (4) and to
affirm that the State has met the NSR requirements for the Hayden
SO<INF>2</INF> nonattainment area under CAA section 172(c)(5). We also
propose to determine that the Hayden SO<INF>2</INF> Plan meets the
attainment demonstration, RACM/RACT, enforceable emission limitations,
RFP, and contingency measure requirements of the CAA for the 1971 and
2010 SO<INF>2</INF> NAAQS. The EPA's analysis is discussed in this
proposed rulemaking. In addition, the TSDs for this proposal are
available at <a href="http://www.regulations.gov">www.regulations.gov</a>, Docket No. EPA-R09-OAR-2025-3821. The
EPA's TSDs for this action provide additional explanation of the EPA's
analysis supporting this proposal.
If approval of the Hayden SO<INF>2</INF> Plan, including amendments
to Rule B1302 and Appendix 14, is finalized as proposed, all sanctions
triggered by our November 5, 2020 limited disapproval and November 10,
2020 partial disapproval actions would be permanently terminated.\91\
Final approval would also satisfy the FIP obligation triggered by the
March 18, 2016 finding of failure to submit and would terminate the
associated FIP obligation for the Hayden SO<INF>2</INF> nonattainment
area under the consent decree in Center for Biological Diversity et al.
v. Regan, No. 4:24-cv-01900 (N.D. Cal.), doc. 28, paragraphs 1.b and 2.
In addition, if the EPA takes final action to fully approve the Hayden
SO<INF>2</INF> Plan, the 1971 SO<INF>2</INF> NAAQS would no longer
apply to the Hayden SO<INF>2</INF> nonattainment area.\92\
---------------------------------------------------------------------------
\91\ 85 FR 70483 (November 5, 2020) and 85 FR 71547 (November
10, 2020).
\92\ See 40 CFR 50.4(e) (``for areas designated nonattainment
for the [1971 SO<INF>2</INF> NAAQS] as of [August 23, 2010] . . .
the [1971 SO<INF>2</INF> NAAQS] will apply until that area submits .
. . and EPA approves, an implementation plan providing for
attainment of the [2010 SO<INF>2</INF> NAAQS].''
---------------------------------------------------------------------------
The EPA is soliciting public comments for 30 days following the
publication of this proposed action in the Federal Register and will
take all relevant timely comments into consideration in our final
action.
VIII. Incorporation by Reference
In this document, the EPA is proposing to include in a final EPA
rule regulatory text that includes incorporation by reference. In
accordance with requirements of 1 CFR 51.5, the EPA is proposing to
incorporate by reference the ADEQ rules listed in Table 1 of this
document. The EPA has made, and will continue to make, these materials
available at <a href="https://www.regulations.gov">https://www.regulations.gov</a> and at the EPA Region IX
Office (please contact the person identified in the FOR FURTHER
INFORMATION CONTACT section of this preamble for more information).
IX. Statutory and Executive Order Reviews
Under the CAA, 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, this
proposed action merely proposes to approve State law as meeting Federal
requirements and does not impose additional requirements beyond those
imposed by State law. For that reason, this proposed action:
<bullet> Is not a significant regulatory action subject to review
by the Office of Management and Budget under Executive Order 12866 (58
FR 51735, October 4, 1993);
<bullet> Is not subject to Executive Order 14192 (90 FR 9065,
February 6, 2025) because SIP actions are exempt from review under
Executive Order 12866;
<bullet> Does not impose an information collection burden under the
provisions of the Paperwork Reduction Act (44 U.S.C. 3501 et seq.);
<bullet> Is certified as not having a significant economic impact
on a substantial number of small entities under the Regulatory
Flexibility Act (5 U.S.C. 601 et seq.);
<bullet> Does not contain any unfunded mandate or significantly or
uniquely affect small governments, as described in the Unfunded
Mandates Reform Act of 1995 (Pub. L. 104-4);
<bullet> Does not have federalism implications as specified in
Executive Order 13132 (64 FR 43255, August 10, 1999);
<bullet> Is not subject to Executive Order 13045 (62 FR 19885,
April 23, 1997) because it proposes to approve a state program;
<bullet> Is not a significant regulatory action subject to
Executive Order 13211 (66 FR 28355, May 22, 2001); and
<bullet> Is not subject to requirements of section 12(d) of the
National Technology Transfer and Advancement Act of 1995 (15 U.S.C. 272
note) because application of those requirements would be inconsistent
with the CAA.
In addition, the SIP is not approved to apply on any Indian
reservation land or in any other area where the EPA or an Indian Tribe
has demonstrated that a Tribe has jurisdiction. In those areas of
Indian country, the rule 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).
List of Subjects in 40 CFR Part 52
Environmental protection, Air pollution control, Incorporation by
reference, Intergovernmental relations, Reporting and recordkeeping
requirements, Sulfur oxides.
Dated: February 23, 2026.
Michael Martucci,
Acting Regional Administrator, Region IX.
[FR Doc. 2026-04339 Filed 3-3-26; 8:45 am]
BILLING CODE 6560-50-P
</pre><script data-cfasync="false" src="/cdn-cgi/scripts/5c5dd728/cloudflare-static/email-decode.min.js"></script></body>
</html>Indexed from Federal Register on March 4, 2026.
This is legal information, not legal advice. Laws vary by jurisdiction and change frequently. Always verify current law with official sources and consult a licensed attorney in your jurisdiction for advice on your specific situation.