[Federal Register Volume 83, Number 116 (Friday, June 15, 2018)]
[Proposed Rules]
[Pages 27938-27948]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[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, (520) 999-7880 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

[[Page 27939]]

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

[[Page 27940]]

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

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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

[[Page 27942]]

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

[[Page 27943]]

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

[[Page 27944]]

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

[[Page 27945]]

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).

[[Page 27946]]



                      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

[[Page 27947]]

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,

[[Page 27948]]

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