[Federal Register Volume 83, Number 116 (Friday, June 15, 2018)]
[Proposed Rules]
[Pages 27938-27948]
[FR Doc No: 2018-12913]

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 52

[EPA-R09-OAR-2017-0621; FRL-9979-49--Region 9]

Approval and Promulgation of Air Quality Implementation Plans;
Arizona; Nonattainment Plan for the Miami SO2 Nonattainment Area

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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SUMMARY: The Environmental Protection Agency (EPA) is proposing to
approve an Arizona state implementation plan (SIP) revision for
attaining the 1-hour sulfur dioxide (SO2) primary national
ambient air quality standard (NAAQS or ``standard'') for the Miami
SO2 nonattainment area (NAA). This SIP revision (hereinafter
called the ``Miami SO2 Plan'' or ``Plan'') includes
Arizona's attainment demonstration and other elements required under
the Clean Air Act (CAA or ``Act''). In addition to an attainment
demonstration, the Plan addresses the requirement for meeting
reasonable further progress toward attainment of the NAAQS, reasonably
available control measures and reasonably available control technology,
base-year and projected emission inventories, enforceable emissions
limitations and control measures, and contingency measures. The EPA
proposes to conclude that Arizona has appropriately demonstrated that
the Plan provides for attainment of the 2010 1-hour primary
SO2 NAAQS in the Miami SO2 NAA by the attainment
date of October 4, 2018 and that the Plan meets the other applicable
requirements under the CAA.

DATES: Comments must be received on or before July 16, 2018.

ADDRESSES: Submit your comments, identified by Docket ID No. EPA-R09-
OAR-2017-0621 at http://www.regulations.gov. Follow the online
instructions for submitting comments. Once submitted, comments cannot
be edited or removed from Regulations.gov. The EPA may publish any
comment received to its public docket. Do not submit electronically any
information you consider to be Confidential Business Information (CBI)
or other information whose disclosure is restricted by statute.
Multimedia submissions (audio, video, etc.) must be accompanied by a
written comment. The written comment is considered the official comment
and should include discussion of all points you wish to make. The EPA
will generally not consider comments or comment contents located
outside of the primary submission (i.e., on the web, cloud, or other
file sharing system). For additional submission methods, the full EPA
public comment policy, information about CBI or multimedia submissions,
and general guidance on making effective comments, please visit http://www2.epa.gov/dockets/commenting-epa-dockets.

FOR FURTHER INFORMATION CONTACT:  Krishna Viswanathan, EPA, Region IX,
Air Division, Air Planning Office,<PHONE_NUMBER> or
[email protected].

SUPPLEMENTARY INFORMATION: Throughout this document whenever, ``we,''
``us,'' or ``our'' is used, we mean the EPA.

Table of Contents

I. Why was Arizona required to submit a plan for the Miami
SO2 NAA?
II. Requirements for SO2 Nonattainment Plans
III. Attainment Demonstration and Longer-Term Averaging
IV. Review of Modeled Attainment Demonstration
V. Review of Other Plan Requirements
VI. Conformity
VII. The EPA's Proposed Action
VIII. Statutory and Executive Order Reviews

I. Why was Arizona required to submit a plan for the Miami SO[bdi2]
NAA?

    On June 22, 2010, the EPA promulgated a new 1-hour primary
SO2 NAAQS of 75 parts per billion (ppb). 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.\1\ On August 5, 2013, the EPA designated
a first set of 29 areas of the country as nonattainment for the 2010
SO2 NAAQS, including the Miami SO2 NAA within
Arizona.\2\ These area designations became effective on October 4,
2013. Section 191 of the CAA directs states to submit SIPs for areas

designated as nonattainment for the SO2 NAAQS to the EPA
within 18 months of the effective date of the designation, i.e., by no
later than April 4, 2015, in this case (hereinafter called ``plans'' or
``nonattainment plans''). Under CAA section 192, these plans are
required to have measures that will help their respective areas attain
the NAAQS as expeditiously as practicable, but no later than 5 years
from the effective date of designation, which for the Miami
SO2 NAA is October 4, 2018.
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    \1\ See 75 FR 35520, codified at 40 CFR 50.17(a)-(b).
    \2\ See 78 FR 47191, codified at 40 CFR part 81, subpart C.
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    For a number of areas, including the Miami SO2 NAA, the
EPA published a document on March 18, 2016, finding that Arizona and
other pertinent states had failed to submit the required SO2
nonattainment plan by the submittal deadline.\3\ This finding, which
became effective on April 18, 2016, initiated a deadline under CAA
section 179(a) for the potential imposition of new source review offset
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.
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    \3\ See 81 FR 14736.
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    In response to the requirement for SO2 nonattainment
plan submittals, the Arizona Department of Environmental Quality (ADEQ)
submitted the Miami SO2 Plan on March 9, 2017, and submitted
associated final rules on April 6, 2017.\4\ The EPA issued letters
dated July 17, 2017, and September 26, 2017, finding the submittals
complete and halting the sanctions clock under CAA section 179(a).\5\
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    \4\ Letters from Tim Franquist, ADEQ, to Alexis Strauss, EPA,
dated March 8, 2017, and April 6, 2017. Although the cover letter
for the Miami SO2 Plan was dated March 8, 2017, the Plan
was transmitted to the EPA on March 9, 2017.
    \5\ Letters from Elizabeth Adams, EPA, to Tim Franquist, ADEQ,
dated July 17, 2017, and September 26, 2017.
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    The remainder of this preamble describes the requirements that
nonattainment plans must meet in order to obtain EPA approval, provides
a review of the Miami SO2 Plan with respect to these
requirements, and describes the EPA's proposed action on the Plan.

II. Requirements for SO[bdi2] Nonattainment Plans

    Nonattainment plans for SO2 must meet the applicable
requirements of the CAA, specifically CAA sections 110, 172, 191 and
192. The EPA's regulations governing nonattainment 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.'' \6\ Among other things, the General Preamble
addressed SO2 SIP submissions and fundamental principles for
SIP control strategies.\7\ On April 23, 2014, the EPA issued
recommended guidance for meeting the statutory requirements in
SO2 SIP submissions, in a document entitled, ``Guidance for
1-Hour SO2 Nonattainment Area SIP Submissions'' (``2014
SO2 Guidance''). In the 2014 SO2 Guidance, the
EPA described the statutory requirements for a complete nonattainment
plan, which include: An accurate emissions inventory of current
emissions for all sources of SO2 within the NAA; an
attainment demonstration; demonstration of RFP; implementation of RACM
(including RACT); new source review, enforceable emissions limitations
and control measures, and adequate contingency measures for the
affected area.
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    \6\ See 57 FR 13498 (April 16, 1992) (General Preamble).
    \7\ Id. at 13545-49, 13567-68.
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    For the EPA to fully approve a SIP revision as meeting the
requirements of CAA sections 110, 172 and 191-192 and the EPA's
regulations at 40 CFR part 51, the plan for the affected area needs to
demonstrate to the EPA's satisfaction that each of the aforementioned
requirements has been met. Under CAA section 110(l), the EPA may not
approve a plan that would interfere with any applicable requirement
concerning NAAQS attainment and RFP, or any other applicable
requirement. Under CAA section 193, no requirement in effect (or
required to be adopted by an order, settlement, agreement, or plan in
effect before November 15, 1990) in any area that is a NAA for any air
pollutant may be modified in any manner unless it insures equivalent or
greater emission reductions of such air pollutant.

III. Attainment Demonstration and Longer-Term Averaging

    Section 172(c)(1) and 172(c)(6) of the CAA direct states with areas
designated as nonattainment to demonstrate that the submitted plan
provides for attainment of the NAAQS. 40 CFR part 51, subpart G further
delineates the control strategy requirements that plans must meet, and
the EPA has long required that all SIPs and control strategies reflect
four fundamental principles of quantification, enforceability,
replicability, and accountability.\8\ SO2 nonattainment
plans must consist of two components: (1) 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 SO2 NAAQS as expeditiously as
practicable, but by no later than the attainment date for the affected
area. In cases where the necessary emission limits have not previously
been made a part of the state's SIP, or have not otherwise become
federally enforceable, the plan needs to include the necessary
enforceable limits in adopted form suitable for incorporation into the
SIP in order for the plan to be approved by the EPA. 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 SIP demonstrations).
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    \8\ See 57 FR at 13567-68 (April 16, 1992).
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    The EPA's 2014 SO2 Guidance recommends that the emission
limits be expressed as short-term average limits not to exceed the
averaging time for the applicable NAAQS that the limit is intended to
help maintain (e.g., addressing emissions averaged over one or three
hours), but it also describes the option to utilize emission limits
with longer averaging times of up to 30 days as long as the state meets
various suggested criteria.\9\ The 2014 SO2 Guidance
recommends that--should states and sources utilize longer averaging
times (such as 30 days)--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.
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    \9\ See 2014 SO2 Guidance, pages 22 to 39.
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    The 2014 SO2 Guidance provides an extensive discussion
of the EPA's rationale for concluding that appropriately set,
comparably stringent limitations based on averaging times as long as 30
days can be found to provide for attainment of the 2010 SO2
NAAQS. In evaluating this option, the EPA considered the nature of the
standard, conducted detailed analyses of the impact of use 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.\10\
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    \10\ Id. pages 22 to 39. See also id. at Appendices B and D.
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    As specified in 40 CFR 50.17(b), the 1-hour primary SO2
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. The 2010 SO2 NAAQS,
including this form of determining compliance with the standard, was
upheld by the U.S. Court of Appeals for the District of Columbia
Circuit in Nat'l Envt'l Dev. Ass'n's Clean Air Project v. EPA, 686 F.3d
803 (D.C. Cir. 2012). Because the standard has this form, a single
hourly exceedance does not create a violation of the standard. Instead,
at issue is whether a source operating in compliance with a properly
set longer-term average could cause hourly exceedances, and if so what
the resulting frequency and magnitude of such exceedances would be, and
in particular whether the EPA can have reasonable confidence that a
properly set longer-term average limit will provide that the three-year
average of the annual fourth highest daily maximum hourly value will be
at or below 75 ppb. A synopsis of the EPA's review of how to judge
whether such plans ``provide for attainment,'' based on modeling of
projected allowable emissions and in light of the NAAQS' form for
determining attainment at monitoring sites, follows.
    For SO2 plans based on 1-hour emission limits, the
standard approach is to conduct modeling using fixed emission rates.
The maximum emission rate that would be modeled to result in attainment
(i.e., in an ``average year'' \11\ shows three, not four days with
maximum hourly levels exceeding 75 ppb) is labeled the ``critical
emission value.'' The modeling process for identifying this critical
emissions value inherently considers the numerous variables that affect
ambient concentrations of SO2, 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 at this critical emission value.
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    \11\ 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 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 an example below uses
a single ``average year'' in order to simplify the illustration of
relevant principles.
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    The EPA recognizes that some sources have highly variable emissions
due, for example, 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 critical emission value. The EPA also
acknowledges the concern that longer-term emission limits can allow
short periods with emissions above the critical emissions value, which,
if coincident with meteorological conditions conducive to high
SO2 concentrations, could in turn create the possibility of
a NAAQS exceedance occurring on a day when an exceedance would not have
occurred if emissions were continuously controlled at the level
corresponding to the critical emission value. However, for several
reasons, the EPA believes that the approach recommended in the 2014
SO2 Guidance 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 critical emissions value)
and that takes the source's emissions profile 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, as compared 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
critical emission level, and in the longer-term average limit scenario,
the source is presumed occasionally to emit more than the critical
emission value but on average, and presumably at most times, to emit
well below the critical emission value. In an ``average year,''
compliance with the 1-hour limit is expected to result in three
exceedance days (i.e., three days with 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 exceedances would occur that would not occur in the 1-hour
limit scenario (if emissions exceed the critical emission value 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 well below the critical emission value). Therefore, 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.
    The following hypothetical example illustrates the aforementioned
points. Suppose there is a source that always emits 1000 pounds of
SO2 per hour and these emissions result in air quality at
the level of the NAAQS (i.e., a design value of 75 ppb).\12\ For this
source, in an ``average year'', these emissions cause the five highest
maximum daily average 1-hour concentrations to be 100 ppb, 90 ppb, 80
ppb, 75 ppb, and 70 ppb. Subsequently, the source becomes subject to a
30-day average emission limit of 700 (lb/hr). It is theoretically
possible for a source meeting this limit to have emissions that
occasionally exceed 1000 lb/hr, but with a typical emissions profile,
emissions would much more commonly be between 600 and 800 lb/hr. In
this simplified example, assume a zero-background concentration, which
allows one to

assume a linear relationship between emissions and air quality.\13\ Air
quality will depend on what emissions happen on what critical hours,
but suppose that emissions at the relevant times on these five days are
800 lb/hr, 1100 lb/hr, 500 lb/hr, 900 lb/hr, and 1200 lb/hr,
respectively. (This is a conservative example because the average of
these emissions, 900 lb/hr, is well over the 30-day average emission
limit.) These emissions would result in daily maximum 1-hour
concentrations of 80 ppb, 99 ppb, 40 ppb, 67.5 ppb, and 84 ppb. In this
example, the fifth day would have an exceedance that would not
otherwise have occurred, but the third and fourth days would not have
exceedances that otherwise would have occurred. In this example, the
fourth highest maximum daily concentration under the 30-day average
would be 67.5 ppb.
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    \12\ Design values are the metrics (i.e., statistics) that are
compared to the NAAQS levels to determine compliance. The design
value for the primary 1-hour SO2 NAAQS is the 3-year
average of annual 99th percentile daily maximum 1-hour values for a
monitoring site, calculated as specified in 40 CFR part 50, appendix
T, section 5.
    \13\ A nonzero background concentration would make the
mathematics more difficult but would give similar results.
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    This simplified example illustrates the findings of a more
complicated statistical analysis that the EPA conducted using a range
of scenarios using actual plant data. As described in Appendix B of the
2014 SO2 Guidance, the EPA found that the requirement for
lower average emissions is highly likely to yield better air quality
than is required with a comparably stringent 1-hour limit. Based on
analyses described in appendix B of the 2014 SO2 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 exceedances and better air quality than an emission profile with
maximum allowable emissions under a 1-hour emission limit at the
critical emission value.
    The EPA must evaluate whether a longer-term average emission limit
approach, which is likely to produce a net lower number of overall
exceedances of 75 ppb even though it may produce some exceedances of 75
ppb on occasions when emissions are above the critical emission value,
meets the requirements in sections 110(a)(1) and 172(c)(1) and (6) for
state implementation plans to ``provide for attainment'' of the NAAQS.
For SO2, as for other pollutants, it is generally impossible
to design a nonattainment plan in the present that will guarantee that
attainment will occur in the future. A variety of factors can cause a
well-designed nonattainment plan to fail and unexpectedly not result in
attainment (e.g., if meteorology occurs that is more conducive to poor
air quality than was anticipated in the plan). Therefore, in
determining whether a plan meets the requirement to provide for
attainment, the EPA's task is commonly to judge not whether the plan
provides absolute certainty that attainment will in fact occur, but
rather whether the plan provides an adequate level of confidence of
prospective NAAQS attainment. From this perspective, in evaluating use
of a 30-day average limit, the EPA must weigh the likely net effect on
air quality. Such an evaluation must consider the risk that occasions
with meteorology conducive to high concentrations will have elevated
emissions leading to exceedances that would not otherwise have
occurred, and it must also weigh the likelihood that the requirement
for lower emissions on average will result in days not having
exceedances that would have been expected with emissions at the
critical emissions value. Additional policy considerations, such as in
this case the desirability of accommodating real-world emissions
variability without significant risk of violations, are also
appropriate factors for the EPA to weigh in judging whether a plan
provides a reasonable degree of confidence that the plan will lead to
attainment. Based on these considerations, especially given the high
likelihood that a continuously enforceable limit averaged over as long
as 30 days, determined in accordance with the 2014 SO2
Guidance, will result in attainment, the EPA believes as a general
matter that such limits, if appropriately determined, can reasonably be
considered to provide for attainment of the 2010 SO2 NAAQS.
    The 2014 SO2 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 critical emission
value) 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 SIP emission limits, which may require use of an emission
database from another source (e.g., if compliance requires new
controls). The recommended method involves using these data to compute
a complete set of emission averages, calculated according to the
averaging time and averaging procedures of the prospective emission
limitation. In this recommended method, the ratio of the 99th
percentile among these long-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 to determine a longer-term average
emission limit that may be considered comparably stringent.\14\ The
guidance also addresses a variety of related topics, such as the
potential utility of setting supplemental emission limits (e.g., mass-
based limits) to reduce the likelihood and/or magnitude of elevated
emission levels that might occur under the longer-term emission rate
limit.
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    \14\ For example, if the critical emission value is 1000 pounds
of SO2 per hour, and a suitable adjustment factor is
determined to be 70 percent, the recommended longer-term average
limit would be 700 pounds per hour.
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    Preferred air quality models for use in regulatory applications are
described in appendix A of the EPA's Guideline on Air Quality Models
(40 CFR part 51, appendix W (``appendix W'')).\15\ In general,
nonattainment SIP submissions must demonstrate the adequacy of the
selected control strategy using the applicable air quality model
designated in appendix W.\16\ However, where an air quality model
specified in appendix W is inappropriate for the particular
application, the model may be modified or another model substituted, if
the EPA approves the modification or substitution.\17\ In 2005, the EPA
promulgated the American Meteorological Society/Environmental
Protection Agency Regulatory Model (AERMOD) as the Agency's preferred
near-field dispersion modeling for a wide range of regulatory
applications addressing stationary sources (e.g., in estimating
SO2 concentrations) in all types of terrain based on
extensive developmental and performance evaluation. Supplemental
guidance on modeling for purposes of demonstrating attainment of the
SO2 standard is provided in appendix A to the 2014
SO2 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 SO2 Guidance is generally
necessary for the attainment demonstration to offer adequately reliable
assurance that the plan provides for attainment.
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    \15\ The EPA published revisions to appendix W on January 17,
2017, 82 FR 5182.
    \16\ 40 CFR 51.112(a)(1).
    \17\ 40 CFR 51.112(a)(2); appendix W, section 3.2.
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    As stated previously, attainment demonstrations for the 2010 1-hour

primary SO2 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 SO2 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 NAA which may affect attainment in the area) is technically
appropriate. This approach is also efficient and effective in
demonstrating attainment in NAAs because it takes into consideration
combinations of meteorological and source operating conditions that may
contribute to peak ground-level concentrations of SO2.
    The meteorological data used in the analysis should generally be
processed with the most recent version of AERMET, which is the
meteorological data preprocessor for AERMOD. Estimated concentrations
should include ambient background concentrations, follow the form of
the standard, and be calculated as described in the EPA's August 23,
2010 clarification memo.\18\
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    \18\ ``Applicability of Appendix W Modeling Guidance for the 1-
hr SO2 National Ambient Air Quality Standard'' (August
23, 2010).
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IV. Review of Modeled Attainment Demonstration

    The following discussion evaluates various features of the modeling
that Arizona used in its attainment demonstration.

A. Model Selection

    Arizona's attainment demonstration used a combination of AERMOD and
the Buoyant Line and Point Source model (BLP).\19\ The State used
AERMOD version 14134 (``v14134''), the regulatory version at the time
it conducted its nonattainment planning, for all emission sources
except for those over the Freeport-McMoRan Miami Incorporated (FMMI)
smelter (``Miami Smelter'' or ``Smelter'') building roofline. For
AERMOD-only sources, the State used regulatory default options. To
represent emissions from the Smelter roofline, the State used a
combination of AERMOD v14134 and BLP (``BLP/AERMOD Hybrid Approach'').
BLP was used to estimate hourly final plume rise and sigma-z (a measure
of vertical size of the plume), which were then used to define volume
sources in AERMOD. The State later repeated the simulation using AERMOD
version 16216r, the current regulatory version, and showed no
difference in predicted annual 4th high daily SO2 hourly
concentrations from the previous version.\20\
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    \19\ See Appendix C to Miami SO2 Plan, ``Modeling
Technical Support Document for the Miami Sulfur Dioxide
(SO2) Nonattainment Area'' (Modeling TSD).
    \20\ See letter from Farah Mohammadesmaeili, ADEQ, to Rynda Kay,
EPA Region 9, dated March 16, 2018.
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    The copper smelting process produces large amounts of excess heat.
Fugitive SO2 is released from the Miami Smelter building
roofline at an elevated temperature and velocity, leading to enhanced
plume rise. AERMOD v14134 does not account for buoyant plume rise from
line sources. At the time of preparation of the Miami SO2
Plan, BLP was identified in appendix W as the preferred model for
representing buoyant line sources.\21\ As noted above, where an air
quality model specified in appendix W is inappropriate for the
particular application, the model may be modified or another model
substituted if the EPA approves the modification or substitution.\22\
Appendix W also specifies that for all such approvals, the EPA regional
office will coordinate and seek the concurrence of the EPA's Model
Clearinghouse.\23\ Arizona has sought approval to use the BLP/AERMOD
Hybrid Approach under appendix W, paragraph 3.2.2(b), condition (2),
which allows for use of an alternative model where ``a statistical
performance evaluation has been conducted using measured air quality
data and the results of that evaluation indicate the alternative model
performs better for the given application than a comparable model in
appendix A.'' The State provided a statistical performance evaluation
using measured air quality data that demonstrates the alternative model
performs better than the preferred model for this application.
Additionally, the State provided technical justification for the
validity of the approach for the meteorology and topography affecting
this area. EPA Region 9 requested and received concurrence from the
EPA's Model Clearinghouse that the alternative model is appropriate for
this particular application.24 25 For the reasons described
in the concurrence documents, the EPA finds this selection appropriate
and proposes to approve use of this alternative under 40 CFR
51.112(a)(2).
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    \21\ The EPA has since approved AERMOD, with newly incorporated
BLP algorithms, as the preferred model for buoyant line sources. See
82 FR 5182.
    \22\ 40 CFR 51.112(a)(2); Appendix W, section 3.2.
    \23\ Id. section 3.0(b).
    \24\ Further details can be found in ``Concurrence Request for
Approval of Alternative Model: BLP/AERMOD Hybrid Approach for
Modeling Buoyant Roofline Sources at the FMMI Copper Smelter in
Miami, AZ'' (March 12, 2018).
    \25\ ``Model Clearinghouse Review of a BLP/AERMOD Hybrid
Alternative Model Approach for Modeling Buoyant Roofline Sources at
the FMMI Copper Smelter in Miami, AZ'' (March 26, 2018).
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    The modeling domain was centered on the Miami Smelter facility and
extended to the edges of the Miami SO2 NAA. A grid spacing
of 25 meters was used to resolve AERMOD model concentrations along the
ambient air boundary surrounding the Smelter and increased toward the
edges of the NAA. Receptors were excluded within 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. We
agree with the State's conclusion that the model receptors placed by
the State correspond to ambient air.

B. Meteorological Data

    Arizona conducted its modeling using three years of on-site surface
meteorological data collected by FMMI between 2010 and 2013 at a 30.5-
meter tower located approximately 0.32 kilometer (km) southwest of the
Smelter. The State provided annual audit reports for the monitoring
station to document that the station's installation and data collection
were consistent with the EPA recommendations.26 27 Cloud
cover and relative humidity were not measured at the onsite location
and were taken from the National Weather Service (NWS) station at
Safford Airport (Weather Bureau Army Navy (WBAN) 93084), which is 132
km to the southeast of the Smelter and representative of cloud cover
and relative humidity to the Miami SO2 NAA. The State used
upper air data from the NWS station in Tucson, Arizona (WBAN 23160),
which is 146 km south of the Smelter. The State used AERMET v14134 to
process meteorological data for use with AERMOD and the Meteorological

Processor for Regulatory Models for use with BLP.
---------------------------------------------------------------------------

    \26\ See email from Farah Mohammadesmaeili, ADEQ, to Rynda Kay,
EPA Region 9, dated March 16, 2018.
    \27\ ``EPA Meteorological Monitoring Guidance for Regulatory
Modeling Applications.'' Publication No. EPA-454/R-99-005 (February
2000).
---------------------------------------------------------------------------

    The State used AERSURFACE version 13016 using data from the onsite
location and the NWS Safford site to estimate the surface
characteristics (i.e., albedo, Bowen ratio, and surface roughness
(zo)). The State estimated zo values for 12
spatial sectors out to 1 km at a seasonal temporal resolution for dry
conditions. We conclude that the State appropriately selected
meteorological sites, properly processed meteorological data, and
adequately estimated surface characteristics.
    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 Miami Smelter
is composed of 97.3% rural land types. Therefore, the State selected
rural dispersion coefficients for modeling. We agree with the State's
determination that the facility should be modeled as a rural source.

C. Emissions Data

    Arizona completed a modeling emissions inventory for sources within
the Miami SO2 NAA and a 50-km buffer zone extending from the
NAA boundary based on 2009-2011 data. In 2011, the Miami Smelter
emitted 2,545 tpy SO2, accounting for more than 99.5% of
SO2 emissions in the NAA. Other SO2 sources in
the NAA include the Carlota Copper Pinto Valley Mine (2011
SO2 emissions of 32 tpy) and the Freeport McMoRan Miami Mine
Smelter (2011 SO2 emissions of 7 tpy), located 13 km and 3.3
km southwest of the Miami Smelter, respectively. No other sources had
2011 SO2 emissions greater than 1 tpy SO2 in the
NAA. The ASARCO LLC (ASARCO) copper smelter is located 46 km south of
the Miami Smelter and had 2011 SO2 emissions of 21,747 tpy.
The two smelters are separated by large mountains, making these two
airsheds distinct. The State modeled the ASARCO stack emissions and
determined that the modeled concentrations from that source were
negligible in the Miami SO2 NAA. The State determined that
other than the Miami Smelter, no sources were drivers of nonattainment.
The State also determined that no other sources have the potential to
cause significant concentration gradients in the vicinity of the Miami
SO2 NAA affected by the Miami Smelter. Additionally, the
State determined that all nearby sources are sufficiently captured by
background monitored concentrations. We agree with the State's
determination that only Miami Smelter emissions need to be included in
the attainment modeling.
    FMMI is undertaking substantial upgrades to the Smelter that will
reduce SO2 and other pollutant emissions (see section 4.3 of
the Miami SO2 Plan). The State estimated post-upgrade
maximum 1-hour SO2 emissions and used those estimates to
model all facility emission sources subject to additional control. The
State provided a justification for the control efficiencies assumed in
the adjustments, which we reviewed and agree are reasonable.\28\ The
State also modeled additional sources within the Smelter complex,
including intermittent emergency generators, smelter building leaks,
slag storage area, and other small sources, which will not be subject
to further control. These sources collectively account for an
additional 8 pounds per hour (lb/hr) of SO2 emissions, which
we agree were appropriately calculated.\29\ The resulting hourly
emission rates used in the attainment modeling are shown in Table 1.
Together these emissions accounted for a facility-wide critical
emission value of 393 lb/hr (rounded to nearest whole number). The
facility-wide critical emission value was used to derive a single
facility-wide 30-day average emission limit, as described in section
IV.D below.
---------------------------------------------------------------------------

    \28\ See ``FmmiReponseToEpaReview--20160721--Final w
Signature.pdf'' and ``FMMI--Emissions-Inventory--2015-07-13--Past-
Actuals-Using-Sulfur-Balance.xlsx.''
    \29\ See Appendix K of Modeling TSD.

    Table 1--Projected Maximum Smelter SO2 Emissions After Additional
                                Controls
------------------------------------------------------------------------
                                                           SO2 Emissions
                         Source                               (lb/hr)

------------------------------------------------------------------------
Acid Plant Tail Gas Stack...............................             3.2
Vent Fume Stack.........................................            13.0
Aisle Scrubber Stack--Normal Operations.................            14.3
Aisle Scrubber Stack--Bypass Operations.................           275.0
Isa Roof Vent...........................................            31.8
ELF Roof Vent...........................................            14.2
Converter Roof Vent.....................................            25.6
Anode Roof Vent.........................................             8.0
Additional Sources......................................             8.0
                                                         ---------------
  Total.................................................             393
------------------------------------------------------------------------

    The State asserts that a single facility-wide emission limit will
adequately regulate emissions from each Smelter source. The State
provided an analysis of the Smelter's emissions variability, which
showed that, due to the batch nature of the smelting process, emissions
are independent of one another and therefore do not peak at the same
time. This analysis indicates that the collection of future maximum
potential emission rates for each source listed in Table 1 is a
conservative estimate of the worst-case emission distribution at the
Smelter.\30\ Additionally, the State conducted a sensitivity analysis
increasing the modeled emission rate of each source (except the bypass
stack) by 21%, while proportionally decreasing the emission rate of the
remaining sources so that total facility-wide emissions remained
constant.\31\ The resulting modeled design values were within 1% of
those predicted by the attainment modeling and all below the NAAQS.
These analyses suggest that variations in the location of peak
emissions will not affect attainment so that a facility-wide limit
would be sufficiently protective. We agree with the State that a
facility-wide emission limit is appropriate in this case.
---------------------------------------------------------------------------

    \30\ See Appendix E of Modeling TSD.
    \31\ See Appendix I of Modeling TSD.
---------------------------------------------------------------------------

    The State also adequately characterized source parameters for the
emissions described above, as well as the Miami Smelter's building
layout and location in its modeling. Where appropriate, the AERMOD
component Building Profile Input Program for Plume Rise Model
Enhancements (BPIPPRM) was used to assist in addressing building
downwash.

D. Emission Limits

    An important prerequisite for approval of a nonattainment plan is
that the emission limits that provide for attainment be quantifiable,
fully enforceable, replicable, and accountable.\32\ The numeric
emission limit on which Arizona's Plan relies is expressed as a 30-day
average limit. Therefore, part of the review of Arizona's Plan must
address the use of longer-term average limits, both with respect to the
general suitability of using such limits for this purpose and with
respect to whether the particular numeric emission limit included in
the Plan has been suitably demonstrated to provide for attainment. The
first subsection that follows addresses the enforceability of the
limits in the Plan (including both the numeric 30-day emission limit as
well as operation and maintenance requirements, which also constitute
emission limits),\33\ and the

second subsection that follows addresses the 30-day limit in
particular.
---------------------------------------------------------------------------

    \32\ See 57 FR at 13567-68.
    \33\ See CAA section 302(k)(defining ``emission limit'' to
include ``any requirement relating to the operation or maintenance
of a source to assure continuous emission reduction.'').
---------------------------------------------------------------------------

1. Enforceability
    The emission limits for the Miami Smelter are codified in the
Arizona Administrative Code, Title 18, Chapter 2, Article 13, Section
R18-2-C1302 (``Rule C1302''). After following proper public notice
procedures, Rule C1302 was adopted by the State of Arizona through a
final rulemaking in the Arizona Administrative Register. To ensure that
the regulatory document was consistent with procedures for
incorporating by reference, the EPA subsequently requested that ADEQ
provide the version of this regulation that was codified in the Arizona
Administrative Code as a supplement to the original SIP revision.
    Subsection (A)(2) of Rule C1302 (``Effective Date'') states that,
``(e)xcept as otherwise provided, the provisions of this Section shall
take effect on the later of the effective date of the Administrator's
action approving it as part of the state implementation plan or January
1, 2018.'' Accordingly, the majority of the rule's requirements will
come into effect upon final approval by the EPA of the rule. We
proposed to approve Rule C1302 into the Arizona SIP on March 30, 2018
\34\ and we intend to finalize action on the rule prior to taking final
action on the Miami SO2 Plan.
---------------------------------------------------------------------------

    \34\ 83 FR 13716.
---------------------------------------------------------------------------

    Rule C1302's 30-day rolling average emission limit of 142.45 lbs/hr
applies to emissions from the tail gas stack, vent fume stack, aisle
scrubber stack, and bypass stack, as well as any fugitives that may
come from the roofline of the smelter structure. To ensure that all
emission sources subject to the facility-wide limit are accurately
monitored and reported, the rule also requires that continuous
monitoring systems be installed on each of the aforementioned stacks
and at the roofline to measure fugitive emissions. In addition, under
subsection (E)(8) of Rule C1302, FMMI is required to develop and
implement a roofline fugitive emissions monitoring plan for review and
approval by ADEQ and the EPA. Furthermore, FMMI is required to develop
and submit for EPA review and approval an Operations & Maintenance plan
for capture and control systems at the smelter to ensure that these
systems are functioning properly and are adequately maintained in order
to minimize fugitive emissions. The rule also includes provisions for
determining compliance with the emission limit, and the necessary
monitoring, recordkeeping, and reporting requirements to ensure that
the regulation as a whole is enforceable. As noted above, the EPA
proposed to approve this regulation into the Arizona SIP in a separate
action. Further discussion on the enforceability for Rule C1302 is
included in the Technical Support Document (TSD) for that action.\35\
---------------------------------------------------------------------------

    \35\ ``Technical Support Document for the EPA's Rulemaking for
the Arizona State Implementation Plan; Arizona Administrative Code,
Title 18, Chapter 2, Article 13, Part C--Miami, Arizona, Planning
Area; R18-2-C1302--Limits on SO2 Emissions from the Miami
Smelter'' (March 2018) (Rule C1302 TSD).
---------------------------------------------------------------------------

    In accordance with EPA guidance on the use of federally enforceable
limits, we find that the limits in Rule C1302 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 30-
day average limit is set at a lower level than the critical emission
value used in the attainment demonstration; this relationship is
discussed in detail in the following section.
2. Longer-Term Average Limits
    The State modeled emissions from the Miami Smelter as described in
Section IV.C of this notice to determine a facility-wide critical
emission value of 393 lb/hr. Arizona demonstrated that the Smelter's
``Additional Sources'' listed in Table 1, which account for 8 lb/hr,
have a negligible contribution to the predicted design value
concentration and asserted that these emissions need not be a part of
the facility's enforceable emission limit.\36\ As such, Arizona used an
adjusted critical emission value of 385 lb/hr (i.e., 393 lb/hr minus 8
lb/hr) in the calculation of the facility's longer-term average limit.
---------------------------------------------------------------------------

    \36\ See Appendix K of the Modeling TSD.
---------------------------------------------------------------------------

    To derive a longer-term average emission limit, the State used
hourly SO2 data collected using continuous emission monitors
from May 2013 to October 2014, adjusted to account for facility
upgrades and increased production capacity, as a representative
emission distribution for the Smelter's future configuration. The State
summed the emissions from all point and fugitive sources, which yielded
the hourly emissions data that provided for calculation of the 30-day
average emission rates used to determine an appropriate adjustment
factor. The 99th percentile of the 30-day and 1-hour SO2
emission rates were 102.4 lb/hr and 276.7 lb/hr, respectively. The
ratio of these two values (i.e., the computed adjustment factor) was
0.37. Compared to the national average adjustment factors (i.e., 0.63-
0.79) estimated for Electrical Generating Units (EGUs) and listed in
Table 1 of Appendix D of the 2014 SO2 Guidance, the ratio
reflects the high variability in Smelter emissions. Although the
adjustment factor is out 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 longer-term average emissions limits
relative to the 1-hour critical emission value. The adjustment factor
was multiplied by the adjusted critical emission value (i.e., 385 lb/
hr) to derive a longer-term 30-day average emission limit of 142.45 lb/
hr. Based on a review of the State's submittal, the EPA believes that
the 30-day average limit for the Miami Smelter provides a justified
alternative to establishing a 1-hour average emission limit for this
source.
    The 2014 SO2 Guidance does not directly address the
establishment of limits governing the sum of emissions from multiple
units, and the it provides no specific recommendations for a
methodology for determining appropriate adjustment factors for deriving
comparably stringent longer-term limits in such cases. Nevertheless,
the 2014 SO2 Guidance recommends computing adjustment
factors based on emissions data that have been determined in accordance
with the methods used to determine compliance with the limit.
Therefore, in this case, it is appropriate to use facility total
emissions data as the basis for a statistical analysis of the degree of
adjustment warranted in determining a 30-day facility-wide emission
limit that is comparably stringent to the plant total 1-hour emission
limit that would otherwise have been set.
    The State has used an appropriate data base and the methodology
specified in the 2014 SO2 Guidance to derive 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 30-day average limit 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 above and
explained in more detail in the 2014 SO2 Guidance, the EPA
finds 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 Arizona's Plan,
the EPA finds that the 30 day-average limit will provide for attainment
of the SO2 standard in the Miami SO2 NAA.

E. Background Concentrations

    Arizona selected background SO2 concentrations using
ambient air measurements recorded between 2009 and 2013 during Smelter
shutdown periods at the Jones Ranch (Air Quality System (AQS) ID: 04-
007-0011), Townsite (AQS ID: 04-007-0012) and Ridgeline (AQS ID: 04-
007-0009) monitors. The State calculated the 5-year averages of the
daily maximum 99th percentile 1-hour average SO2 during
Smelter shutdowns at each site, which were 8.1, 6.7, and 7.2 ppb,
respectively. The State chose to use the Jones Ranch value of 8.1 ppb
(21.2 micrograms per cubic meter ([micro]g/m\3\)) as background
concentrations of SO2 to add to modeled design values. We
agree that the State appropriately and conservatively calculated
background concentrations.

F. Summary of Results

    The EPA has reviewed Arizona's submitted modeling supporting the
attainment demonstration for the Miami SO2 NAA and has
preliminarily determined that this modeling is consistent with CAA
requirements, appendix W and the 2014 SO2 Guidance. The
State's modeling indicates that with a critical emission value of 393
lb/hr, the highest predicted 99th percentile daily maximum 1-hour
concentration within the Miami SO2 NAA would be 194.1 [mu]g/
m\3\, below the NAAQS level of 196.4 [mu]g/m\3\ (75 ppb). This modeled
concentration includes the background concentration of SO2
of 21.2 [micro]g/m\3\. The modeling indicates that the Smelter upgrades
and resulting 30-day emission limit of 142.45 lb/hr are sufficient for
the Miami SO2 NAA to attain the 2010 SO2 NAAQS.

V. Review of Other Plan Requirements

A. Emissions Inventory

    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 NAA contribute to violations within the affected area and
assess the expected improvement in air quality within the NAA 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
SO2 emissions in each NAA, as well as any sources located
outside the NAA which may affect attainment in the area.\37\
---------------------------------------------------------------------------

    \37\ See CAA section 172(c)(3).
---------------------------------------------------------------------------

    The base year inventory establishes a baseline that is used to
evaluate emission reductions achieved by the control strategy and to
assess reasonable further progress requirements. Arizona used 2011 as
the base year for emission inventory preparation. At the time of
preparation of the Plan, 2011 reflected the most recent triennial
National Emission Inventory, supported the requirement for timeliness
of data, and was also representative of a year with violations of the
primary SO2 NAAQS. Arizona reviewed and compiled actual
emissions of all sources of SO2 in the NAA in the 2011 base
year emission inventory. In addition to developing an emission
inventory of SO2 emission sources within the NAA, Arizona
also provided an SO2 emission inventory for those emission
sources within a 50 kilometer buffer zone of the NAA. Table 2 below
summarizes 2011 base year SO2 emissions inventory data for
the NAA, categorized by emission source type (rounded to the nearest
whole number).

                                          Table 2--2011 Base Year SO2 Emission Inventory for the Miami SO2 NAA
                                                                       [Tons/year]
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                Mobile source    Mobile source
                                Year                                   Point source   Nonpoint source      (onroad)        (non-road)         Total
--------------------------------------------------------------------------------------------------------------------------------------------------------
2011...............................................................           2,583               13                2               >1            2,598
--------------------------------------------------------------------------------------------------------------------------------------------------------

    As seen above, the majority of SO2 emissions in the 2011
base year inventory can be attributed to the point source category.
Emissions for this category are provided in further detail in Table 3
below.

             Table 3--2011 Base Year SO2 Emission Inventory
                             [Point sources]
------------------------------------------------------------------------
                                                        Emissions (tons/
                     Point source                            year)
------------------------------------------------------------------------
Freeport McMoRan Miami Smelter.......................              2,545
Freeport McMoRan Miami Mine..........................                  7
BHP Copper Pinto Valley Miami Unit...................                 >1
BHP Copper Pinto Valley Mine.........................                 >1
Carlota Copper Pinto Valley Mine.....................                 31
                                                      ------------------
    Total............................................              2,583
------------------------------------------------------------------------

    A projected attainment year emission inventory should also be
included in the SIP submission according to the 2014 SO2
Guidance. This emission inventory should include, in a manner
consistent with the attainment demonstration, estimated emissions for
all SO2 emission sources that were determined to have an
impact on the affected NAA for the projected attainment year. Table 4
below summarizes Arizona's projected 2018 SO2 emissions
inventory data for the NAA, categorized by source type. 2011 base year
emissions, as well as the projected change between base year and
projected year emissions, are also summarized below (rounded to nearest
whole number).

                      Table 4--Projected 2018 SO2 Emission Inventory for the Miami SO2 NAA
                                                   [Tons/year]
----------------------------------------------------------------------------------------------------------------
                                                     Nonpoint      Mobile source   Mobile source
              Year                 Point source       source         (onroad)       (non-road)         Total
----------------------------------------------------------------------------------------------------------------
2011............................           2,583              13               2              >1           2,598
2018............................             685              13               2              >1             700
Change..........................          -1,898               0               0               0          -1,898
----------------------------------------------------------------------------------------------------------------

    As seen above, both the majority of SO2 emissions in the
projected 2018 emission inventory, as well as the majority of projected
SO2 emission reductions, can be attributed to point sources.
Emissions for this category are provided in further detail in Table 5
below.

                                 Table 5--Projected 2018 SO2 Emission Inventory
                                                 [Point sources]
----------------------------------------------------------------------------------------------------------------
                                                                  2011 Base year  2018 Projected
                          Point source                               emissions    year emissions      Change
                                                                    (tons/year)     (tons/year)
----------------------------------------------------------------------------------------------------------------
Freeport McMoRan Miami Smelter..................................           2,545             660          -1,885
Freeport McMoRan Miami Mine.....................................               7               8               1
BHP Copper Pinto Valley Miami Unit..............................              >1              >1               0
BHP Copper Pinto Valley Mine....................................              >1              14              13
Carlota Copper Pinto Valley Mine................................              31               3             -28
                                                                 -----------------------------------------------
    Total.......................................................           2,583             685          -1,898
----------------------------------------------------------------------------------------------------------------

    As seen above, the single largest decrease in emissions is
attributed to the Miami Smelter. The projected 2018 SO2
emissions for the Miami Smelter are consistent with allowable emission
limits for the Miami Smelter that Arizona is requesting that the EPA
approve into the SIP. For other point sources, projected 2018
SO2 emissions were determined by Arizona based on existing
permit allowable SO2 limits or other federally enforceable
SO2 emission limits.
    The EPA has evaluated Arizona's 2011 base year inventory and
projected 2018 emission inventory for the Miami SO2 NAA, and
considers these inventories to have been developed consistent with EPA
guidance. As a result, the EPA is proposing to determine that the Miami
SO2 Plan meets the requirements of CAA Section 172(c)(3) and
(4) for the Miami SO2 NAA.

B. Reasonably Available Control Measures and Reasonably Available
Control Technology

    Arizona's Plan for attaining the 1-hour SO2 NAAQS in the
Miami SO2 NAA is based on implementation of controls at the
Miami Smelter. ADEQ conducted a reasonably available control measures
and reasonably available control technology (RACM/RACT) analysis in the
Miami SO2 Plan, comparing the requirements at the Miami
Smelter with controls in use at other large sources of SO2
to identify potentially available control measures, eliminating any
measures that were not feasible at the Miami Smelter or not more
stringent than those measures already being implemented. ADEQ then
compared the proposed control measures for the Miami Smelter with the
measures not eliminated in the first step of the RACM/RACT analysis,
and concluded that the proposed control measures would be more
stringent. We provide an assessment below of whether ADEQ's RACM/RACT
analysis is consistent with EPA guidance.
    The State's RACM/RACT analysis can be found in section 4.4.3 of the
Miami SO2 Plan. ADEQ compared SO2 controls at
eight different facilities and found that all of these units used an
acid plant to recover or reduce SO2 emissions. Some of these
facilities also used acid absorption equipment (wet and dry scrubbers)
to further control SO2. ADEQ also noted that enhanced
capture systems (such as additional hooding, improved ventilation
systems and enhanced ductwork) at the Miami Smelter would contribute to
reducing uncontrolled fugitive emissions from the smelter structure.
While enhanced capture does not inherently reduce SO2
emissions, these capture systems will route a greater amount of gas to
control devices that do reduce SO2 emissions.
    The State concluded that upgrades to the acid plant, the
installation of additional and improved scrubbers, and the installation
of improved capture systems at the IsaSmelt furnace, electric furnace,
converter department, and anode casting operations at the Miami Smelter
constituted RACM/RACT and would allow the facility to meet the 142.45
lb/hr emission limit and other requirements outlined in Rule C1302. As
explained in the Rule C1302 TSD, we agree that Rule C1302 generally
requires implementation of reasonable controls for the Miami Smelter.
We also find that it was appropriate for Arizona to focus its RACM/RACT
analysis solely on this source, given that the Miami Smelter accounted
for more than 99.5 percent of SO2 emissions in the NAA
during the 2011 base year.\38\
---------------------------------------------------------------------------

    \38\ Miami SO2 Plan, Section 3.1.1, page 33.
---------------------------------------------------------------------------

    As noted above, most of the requirements of Rule C1302 will become
enforceable only after final approval of the rule by the EPA. However,
the Plan itself provides that the owner or operator of the Miami
Smelter will complete construction of the relevant control measures no
later than January 1, 2018, including steps that ADEQ will undertake if
the owner or operator failed to complete construction by January 1,
2018.\39\ On December 19, 2017, FMMI notified the EPA and ADEQ that it
had completed construction of the SO2 capture and control
system upgrades

and had initiated associated commissioning activities.\40\
---------------------------------------------------------------------------

    \39\ Id., page 84.
    \40\ Letter from Byron Belew, FMMI, to Alexis Strauss, EPA, and
Timothy Franquist, ADEQ (December 19, 2017).
---------------------------------------------------------------------------

    As explained above, we find that Arizona has demonstrated that
implementation of the control measures required under the Plan are
sufficient to provide for attainment of the NAAQS. Given that these
controls have already been installed and will be fully operational
prior to October 4, 2018, we propose to conclude that the State has
satisfied the requirement in section 172(c)(1) and (6) to adopt and
submit all RACM and emissions limitations and control measures as
needed to attain the standards as expeditiously as practicable and the
requirement in section 192(b) to provide for attainment by October 4,
2018.

C. New Source Review

    On November 2, 2015, the EPA published a final limited approval and
limited disapproval of revisions to ADEQ's new source review (NSR)
rules.\41\ On May 4, 2018, the EPA approved additional rule revisions
to address many of the deficiencies identified in the 2015 action.\42\
Collectively these rule revisions will ensure that ADEQ's rules provide
for appropriate NSR for SO2 sources undergoing construction
or major modification in the Miami SO2 NAA without need for
further modification. Therefore, the EPA concludes that the NSR
requirement has been met for this area. We note that Rule C1302
subsection (I) indicates that the smelter emission limits contained in
the rule shall be determined to be SO2 RACT for purposes of
minor NSR requirements. This provision does not interfere with or
adversely affect existing nonattainment NSR rules.
---------------------------------------------------------------------------

    \41\ 80 FR 67319 (November 2, 2015).
    \42\ 83 FR 19631 (May 4, 2018).
---------------------------------------------------------------------------

D. Reasonable Further Progress

    In the Miami SO2 Plan, Arizona explained its rationale
for concluding that the Plan meets the requirement for reasonable
further progress (RFP) in accordance with EPA guidance. Specifically,
Arizona's rationale is based on EPA guidance interpreting the RFP
requirement being satisfied for SO2 if the Plan requires
``adherence to an ambitious compliance schedule'' that ``implement[s]
appropriate control measures as expeditiously as practicable.'' Arizona
noted that its Plan provides for attainment as expeditiously as
practicable, i.e., by October 4, 2018, and finds that the Plan thereby
satisfies the requirement for RFP.
    Arizona finds that the Miami SO2 Plan requires affected
sources to implement appropriate control measures as expeditiously as
practicable in order to ensure attainment of the standard by the
applicable attainment date. Arizona concludes that the Plan therefore
provides for RFP in accordance with the approach to RFP described in
the 2014 SO2 Guidance. The EPA concurs and proposes to
conclude that the Plan provides for RFP.

E. Contingency Measures

    In the Miami SO2 Plan, Arizona explained its rationale
for concluding that the Plan meets the requirement for contingency
measures. Specifically, Arizona relies on the 2014 SO2
Guidance, which notes the special circumstances that apply to
SO2 and explains on that basis why the contingency
requirement in CAA section 172(c)(9) is met for SO2 by
having a comprehensive program to identify sources of violations of the
SO2 NAAQS and to undertake an aggressive follow-up for
compliance and enforcement of applicable emissions limitations. Arizona
stated 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. Arizona also describes the process under State law to apply
contingency measures for failure to make RFP and/or for failure to
attain the SO2 NAAQS by the attainment date and concludes
that Arizona's Plan satisfies contingency measure requirements. The EPA
concurs with this assessment. We note that the EPA has approved ARS 49-
402, 49-404, 49-406 and 49-461 into the Arizona SIP.\43\ 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.\44\ Therefore, we agree that the Arizona SIP establishes a
comprehensive enforcement program, allowing for the identification of
sources of SO2 NAAQS violations and aggressive compliance
and enforcement follow-up. We propose to approve Arizona's Plan as
meeting the contingency measure requirement in this manner.
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    \43\ See 40 CFR 52.120(e), Table 3.
    \44\ 77 FR 66398 (November 5, 2012).
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VI. Conformity

    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 area or maintenance area (i.e., an area
which 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
SO2. The EPA's General Conformity Rule establishes the
criteria and procedures for determining if a federal action conforms to
the SIP.\45\ With respect to the 2010 SO2 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 SO2. 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.\46\ When updated and improved
emissions estimation techniques become available, the EPA expects the
federal agency to use these techniques.
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    \45\ 40 CFR 93.150 to 93.165.
    \46\ 40 CFR 93.159(b).
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    Transportation conformity determinations are not required in
SO2 nonattainment and maintenance areas. The EPA concluded
in its 1993 transportation conformity rule that highway and transit
vehicles are not significant sources of SO2. Therefore,
transportation plans, transportation improvement programs and projects
are presumed to conform to applicable implementation plans for
SO2.\47\
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    \47\ See 58 FR 3776 (January 11, 1993).
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VII. The EPA's Proposed Action

    The EPA is proposing to approve the Miami SO2 Plan,
which includes Arizona's attainment demonstration for the Miami
SO2 NAA and addresses requirements for RFP, RACT/RACM,

base-year and projected emission inventories, and contingency measures.
The EPA proposes to determine that the Miami SO2 Plan meets
applicable requirements of sections 110, 172, 191 and 192 of the CAA
for the 2010 SO2 NAAQS.
    The EPA is taking public comments for thirty days following the
publication of this proposed action in the Federal Register. We will
take all relevant comments into consideration in our final action.

VIII. 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 approves state law as meeting Federal
requirements and does not impose additional requirements beyond those
imposed by state law. For that reason, this proposed action:
     Is not a ``significant regulatory action'' subject to
review by the Office of Management and Budget under Executive Order
12866 (58 FR 51735, October 4, 1993) and 13563 (76 FR 3821, January 21,
2011);
     Is not an Executive Order 13771 (82 FR 9339, February 2,
2017) regulatory action because SIP approvals are exempted under
Executive Order 12866;
     Does not impose an information collection burden under the
provisions of the Paperwork Reduction Act (44 U.S.C. 3501 et seq.);
     Is certified as not having a significant economic impact
on a substantial number of small entities under the Regulatory
Flexibility Act (5 U.S.C. 601 et seq.);
     Does not contain any unfunded mandate or significantly or
uniquely affect small governments, as described in the Unfunded
Mandates Reform Act of 1995 (Pub. L. 104-4);
     Does not have Federalism implications as specified in
Executive Order 13132 (64 FR 43255, August 10, 1999);
     Is not an economically significant regulatory action based
on health or safety risks subject to Executive Order 13045 (62 FR
19885, April 23, 1997);
     Is not a significant regulatory action subject to
Executive Order 13211 (66 FR 28355, May 22, 2001);
     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; and
     Does not provide the EPA with the discretionary authority
to address, as appropriate, disproportionate human health or
environmental effects, using practicable and legally permissible
methods, under Executive Order 12898 (59 FR 7629, February 16, 1994).
    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.

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

    Dated: June 4, 2018.
Michael B. Stoker,
Regional Administrator, EPA Region IX.
[FR Doc. 2018-12913 Filed 6-14-18; 8:45 am]
 BILLING CODE 6560-50-P