[Federal Register Volume 87, Number 105 (Wednesday, June 1, 2022)]
[Proposed Rules]
[Pages 33095-33109]
[FR Doc No: 2022-11269]

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

ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 52

[EPA-R05-OAR-2021-0536; FRL-9802-01-R5]

Approval and Promulgation of Air Quality Implementation Plans;
Michigan; Federal Implementation Plan for the Detroit Sulfur Dioxide
Nonattainment Area

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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

SUMMARY: The Environmental Protection Agency (EPA) is proposing a
Federal Implementation Plan (FIP) for attaining the 2010 sulfur dioxide
(SO2) primary national ambient air quality standard (NAAQS)
for the Detroit SO2 nonattainment area. The FIP includes an
attainment demonstration and other elements required under the Clean
Air Act (CAA). In addition to an attainment demonstration, the FIP
addresses the requirement for meeting reasonable further progress (RFP)
toward attainment of the NAAQS, reasonably available control measures
and reasonably available control technology (RACM/RACT), enforceable
emission limitations and control measures to provide for NAAQS
attainment, and contingency measures. This action supplements a prior
action which found that Michigan had satisfied emission inventory (EI)
and nonattainment new source review (NSR) requirements for this area
but had not met requirements for the elements addressed in the proposed
FIP. EPA is proposing to determine that the FIP provides for attainment
of the 2010 primary SO2 NAAQS in the Detroit SO2
nonattainment area and meets the other applicable requirements under
the CAA.

DATES: Comments must be received on or before July 18, 2022.
    Virtual Public Hearing. In order to comply with current Centers for
Disease Control and Prevention (CDC) recommendations, as well as state
and local orders, for social distancing to limit the spread of COVID-
19, EPA is holding a virtual public hearing to provide interested
parties the opportunity to present data, views, or arguments concerning
the proposal. EPA will hold a virtual public hearing to solicit
comments on June 16, 2022. The hearing will convene at 3:00 p.m.
Eastern Time (ET) and will conclude at 9:00 p.m. ET, or 15 minutes
after the last pre-registered presenter in attendance has presented if
there are no additional presenters. EPA will announce further details,
including information on how to register for the virtual public
hearing, on the virtual public hearing website at https://www.epa.gov/mi/detroit-so2-federal-implementation-plan.
    EPA will begin pre-registering presenters and attendees for the
hearing upon publication of this document in the Federal Register. To
pre-register to attend or present at the virtual public hearing, please
use the online registration form available at https://www.epa.gov/mi/detroit-so2-federal-implementation-plan or contact Abigail Teener at
312-353-7314 or by email at [email protected]. The last day to pre-
register to present at the hearing will be June 13, 2022. On June 13,
2022, EPA will post a general agenda for the hearing that will list
pre-registered presenters in approximate order at https://www.epa.gov/mi/detroit-so2-federal-implementation-plan. Additionally, requests to
present will be taken on the day of the hearing as time allows.
    EPA will make every effort to follow the schedule as closely as
possible on the day of the hearing; however, please plan for the
hearing to run either ahead of schedule or behind schedule. Each
commenter will have 5 minutes to provide oral testimony. EPA encourages
commenters to provide EPA with a copy of their oral testimony
electronically by including it in the registration form or emailing it
to [email protected]. EPA may ask clarifying questions during the oral
presentations but will not respond to the presentations at that time.
Written statements and supporting information submitted during the
comment period will be considered with the same weight as oral comments
and supporting information presented at the virtual public hearing. A
transcript of the virtual public hearing, as well as copies of oral
presentations submitted to EPA, will be included in the docket for this
action.
    EPA is asking all hearing attendees to pre-register, even those who
do not intend to present. EPA will send information on how to join the
public hearing to pre-registered attendees and presenters.
    Please note that any updates made to any aspect of the hearing will
be posted online at https://www.epa.gov/mi/detroit-so2-federal-implementation-plan. While EPA expects the hearing to go forward as set
forth above, please monitor our website or contact Abigail Teener at
312-353-7314 or [email protected] to determine if there are any
updates. EPA does not intend to publish a document in the Federal
Register announcing updates.

    If you require the services of a translator or a special
accommodation such as audio description/closed captioning, please pre-
register for the hearing with Abigail Teener at<PHONE_NUMBER> or
[email protected] and describe your needs by June 8, 2022. EPA may not
be able to arrange accommodations without advance notice.

ADDRESSES: Submit your comments, identified by Docket ID No. EPA-R05-
OAR-2021-0536 at https://www.regulations.gov, or via email to
[email protected]. For comments submitted at Regulations.gov, follow
the online instructions for submitting comments. Once submitted,
comments cannot be edited or removed from Regulations.gov. For either
manner of submission, 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. EPA will
generally not consider comments or comment contents located outside of
the primary submission (i.e., on the web, cloud, or other file sharing
system). For additional submission methods, please contact the person
identified in the FOR FURTHER INFORMATION CONTACT section. For the full
EPA public comment policy, information about CBI or multimedia
submissions, and general guidance on making effective comments, please
visit https://www2.epa.gov/dockets/commenting-epa-dockets.

FOR FURTHER INFORMATION CONTACT: Abigail Teener, Environmental
Engineer, Attainment Planning and Maintenance Section, Air Programs
Branch (AR-18J), Environmental Protection Agency, Region 5, 77 West
Jackson Boulevard, Chicago, Illinois 60604,<PHONE_NUMBER>,
[email protected]. The EPA Region 5 office is open from 8:30 a.m.
to 4:30 p.m., Monday through Friday, excluding Federal holidays and
facility closures due to COVID-19.

SUPPLEMENTARY INFORMATION: This supplementary information section is
arranged as follows:

I. SO2 Background
II. Detroit Background
III. Requirements for SO2 Nonattainment Area Plans
IV. Control Strategy
    A. Existing Control Strategies
    B. New Rules
V. Longer-Term Averaging
VI. Modeling
    A. Model Selection
    B. Meteorological Data
    C. Emissions Data
    D. Emission Limits
    E. Background Concentrations
    F. Comments Made During Previous EPA Rulemakings
    G. Summary of Results
VII. Other Plan Requirements
    A. Emissions Inventory
    B. RACM/RACT and Enforceable Emissions Limitations
    C. New Source Review (NSR)
    D. RFP
    E. Contingency Measures
VIII. What action is EPA taking?
IX. Statutory and Executive Order Reviews
    A. Executive Orders 12866 and 13563: Regulatory Planning and
Review
    B. Paperwork Reduction Act
    C. Regulatory Flexibility Act
    D. Unfunded Mandates Reform Act (UMRA)
    E. Executive Order 13132: Federalism
    F. Executive Order 13175: Consultation and Coordination With
Indian Tribal Governments
    G. Executive Order 13045: Protection of Children From
Environmental Health Risks and Safety Risks
    H. Executive Order 13211: Actions Concerning Regulations That
Significantly Affect Energy Supply, Distribution, or Use
    I. National Technology Transfer and Advancement Act
    J. Executive Order 12898: Federal Actions To Address
Environmental Justice in Minority Populations and Low-Income
Populations

I. SO2 Background

    On June 22, 2010, EPA published a new 1-hour primary SO2
NAAQS of 75 parts per billion (ppb), which 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. See 75 FR 35520, codified at 40 CFR 50.17(a)-(b). On August 5,
2013, EPA designated 29 areas of the country as nonattainment for the
2010 SO2 NAAQS, including the Detroit area within the State
of Michigan. See 78 FR 47191, codified at 40 CFR part 81, subpart C.
These area designations became effective on October 4, 2013. Section
191 of the CAA directs states to submit state implementation plans
(SIPs) for areas designated as nonattainment for the SO2
NAAQS to EPA within 18 months of the effective date of the designation,
i.e., by no later than April 4, 2015 in this case. These SIPs were
required to demonstrate that their respective areas will attain the
NAAQS as expeditiously as practicable, but no later than 5 years from
the effective date of designation, which was October 4, 2018.

II. Detroit Background

    For a number of nonattainment areas, including the Detroit area,
EPA published an action on March 18, 2016, effective April 18, 2016,
finding that Michigan and other pertinent states had failed to submit
the required SO2 nonattainment plan by the submittal
deadline (81 FR 14736). This finding initiated a deadline under CAA
section 179(a) for the potential imposition of 2-to-1 NSR offset and
federal highway funding sanctions. Additionally, under CAA section
110(c), the finding triggered a requirement that EPA promulgate a FIP
within two years of the finding unless, by that time, (a) the state had
made the necessary complete submittal, and (b) EPA had approved the
submittal as meeting applicable requirements.
    Michigan submitted the Detroit SO2 attainment plan on
May 31, 2016, and submitted associated final enforceable measures on
June 30, 2016. Michigan's May 31, 2016, submittal was considered
administratively complete six months after its submission to EPA, which
terminated the sanctions clock per EPA's sanctions regulations at 40
CFR 52.31 but did not satisfy EPA's FIP obligation under CAA section
110(c). As noted previously, EPA's requirement to promulgate a FIP
would remain in place unless (a) the state had made the necessary
complete submittal, and (b) EPA had approved the submittal as meeting
applicable requirements.
    On March 19, 2021, EPA partially approved and partially disapproved
Michigan's SO2 plan as submitted in 2016 (86 FR 14827). EPA
approved the base-year emissions inventory and affirmed that the NSR
requirements for the area had previously been met on December 16, 2013
(78 FR 76064). EPA also approved the enforceable control measures for
two facilities as SIP strengthening. At that time, EPA disapproved the
attainment demonstration, as well as the requirements for meeting RFP
toward attainment of the NAAQS, RACM/RACT, and contingency measures.
Additionally, EPA disapproved the plan's control measures for two
facilities as not demonstrating attainment. (For more details, see
section IV.A of this action.) EPA's March 19, 2021, partial disapproval
started a new sanctions clock which is stopped by meeting the
conditions of EPA's regulations at 40 CFR 52.31. The partial
disapproval did not have any impact on the FIP clock,

which is stopped by a full SIP approval or EPA's promulgation of a FIP.
    As Michigan has not submitted an approvable plan for the Detroit
area, the remainder of this action describes EPA requirements that
SO2 nonattainment plans must meet and proposes a FIP for the
Detroit area with respect to these requirements. Finalizing this action
will satisfy EPA's obligation to promulgate a FIP, which was initiated
by the March 18, 2016 finding that Michigan had failed to submit the
required SO2 nonattainment plan by the submittal deadline
(81 FR 14736). It will also satisfy the requirement in the court order
issued on February 15, 2022, in Center for Biological Diversity, et al.
v Regan, No. 4:21-cv-06166-JST (N.D. Cal.), directing EPA to either
approve a SIP for Detroit meeting the applicable CAA requirements or
promulgate a FIP for Detroit no later than September 30, 2022.

III. Requirements for SO2 Nonattainment Area Plans

    Nonattainment area plans for SO2 must meet the
applicable requirements of the CAA, and specifically CAA sections 110,
172, 191 and 192. EPA's regulations governing nonattainment area plans
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, EPA issued comprehensive guidance on nonattainment plans, in a
document entitled the ``General Preamble for the Implementation of
Title I of the Clean Air Act Amendments of 1990,'' published at 57 FR
13498 (April 16, 1992) (General Preamble). Among other things, the
General Preamble addressed SO2 nonattainment plans and
fundamental principles for control strategies. Id., at 13545-49, 13567-
68. On April 23, 2014, EPA issued recommended guidance for meeting the
statutory requirements in SO2 SIPs, in a document entitled,
``Guidance for 1-Hour SO2 Nonattainment Area SIP
Submissions,'' available at https://www.epa.gov/sites/production/files/2016-06/documents/20140423guidance_nonattainment_sip.pdf. While this
guidance was intended for SIP submissions, the requirements outlined in
the document are also applicable to FIPs. In this guidance, EPA
described the statutory requirements for a complete nonattainment area
plan, which includes: an accurate emissions inventory of current
emissions for all sources of SO2 within the nonattainment
area; an attainment demonstration; demonstration of RFP; implementation
of RACM (including RACT); NSR; emissions limitations and control
measures as necessary to attain the NAAQS; and adequate contingency
measures for the affected area, which are to apply if the area fails to
attain the standard by the attainment date.
    In order for a nonattainment area plan to meet the requirements of
CAA sections 110, 172 and 191-192, and EPA's regulations at 40 CFR part
51, the plan for the affected area needs to demonstrate that each of
the aforementioned requirements have been met. Under CAA sections
110(l) and 193, a nonattainment area plan may not interfere with any
applicable requirement concerning NAAQS attainment and RFP, or any
other applicable requirement, and 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 which is a nonattainment area for
any air pollutant, may be modified in any manner unless it ensures
equivalent or greater emission reductions of such air pollutant.
    CAA section 172(c)(1) requires nonattainment area plans to
demonstrate attainment of the NAAQS. 40 CFR part 51, subpart G, further
delineates the control strategy requirements that nonattainment area
plans must meet, and EPA has long required that all nonattainment area
plans and control strategies reflect four fundamental principles of
quantification, enforceability, replicability, and accountability.
General Preamble at 13567-68. SO2 attainment plans must
consist of two components: (1) Emission limits and other control
measures that ensure implementation of permanent, enforceable and
necessary emission controls, and (2) a modeling analysis which meets
the requirements of 40 CFR part 51 appendix W, which 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 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 (specifying clear,
unambiguous and measurable requirements for which compliance can be
practicably determined), replicable (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 (source specific limits must be permanent and
must reflect the assumptions used in the attainment demonstrations).
    Preferred air quality models for use in regulatory applications are
described in appendix A of EPA's Guideline on Air Quality Models (40
CFR part 51, appendix W). In 2005, EPA promulgated AERMOD as the
Agency's preferred near-field dispersion modeling for a wide range of
regulatory applications addressing stationary sources (for example 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 April 23, 2014
SO2 nonattainment area SIP guidance document referenced
above. 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 this
guidance is generally necessary for the attainment demonstration to
offer adequately reliable assurance that the plan provides for
attainment.
    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). This is demonstrated by
using air quality dispersion modeling (see appendix W to 40 CFR part
51) that shows that the mix of sources, 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,
EPA believes that dispersion modeling, using allowable emissions and
addressing stationary sources in the affected area (and in some cases
those sources located outside the nonattainment area which may affect
attainment in the area) is technically appropriate, efficient and
effective in demonstrating attainment in nonattainment areas because it
takes into consideration combinations of meteorological and emission
source operating conditions that may contribute to peak ground-level
concentrations of SO2.
    The meteorological data used in the analysis should generally be
processed with the most recent version of

AERMET. Estimated concentrations should include ambient background
concentrations, should follow the form of the standard, and should be
calculated as described in section <IP_ADDRESS> of the August 23, 2010
clarification memo on ``Applicability of appendix W Modeling Guidance
for the 1-hr SO2 National Ambient Air Quality Standard''
(U.S. EPA, 2010).

IV. Control Strategy

A. Existing Control Strategies

    Several control strategies for the Detroit area are already in
place as a result of actions taken by the State related to the
development of Michigan's 2016 attainment plan. The remainder of this
sub-section is a discussion of Michigan's 2016 submittal and the
existing control strategies that EPA is proposing to include as part of
the FIP.
    Michigan's 2016 submittal included a modeling demonstration that
contained an assessment of the air quality impacts Michigan expected to
result from emission limitations governing the following sources: U.S.
Steel (Ecorse and Zug Island), EES Coke, DTE Energy (DTE) River Rouge,
DTE Trenton Channel, Carmeuse Lime, DTE Monroe, Cleveland-Cliffs Steel
Corporation (formerly AK or Severstal Steel), Dearborn Industrial
Generation (DIG), and Marathon Refinery. From the base case modeling
scenario, Michigan determined that Carmeuse Lime was causing violations
in the model at a group of receptors surrounding the Carmeuse Lime
facility, and that U.S. Steel, DTE River Rouge, and DTE Trenton Channel
were all contributing to overlapping violations at a group of receptors
near the northeast side of Zug Island.\1\ No other modeled sources in
or nearby the nonattainment area were found to be significantly
contributing to the modeled violations.
---------------------------------------------------------------------------

    \1\ The locations of these violations relative to the
Southwestern High School (SWHS) monitor triggered the Detroit
nonattainment designation. The violating receptors surrounding the
Carmeuse Lime facility were approximately two miles to the southwest
of the SWHS monitor, and the violating receptors near Zug Island
were approximately one mile south of the SWHS monitor. Although the
monitor has now been showing attainment for several years, EPA's
base case modeling continues to show NAAQS violations.
---------------------------------------------------------------------------

    Michigan ran a variety of control scenarios to determine a
reduction strategy for the area and submitted in its attainment
demonstration emission limitations for Carmeuse Lime, DTE Trenton
Channel, DTE River Rouge, and U.S. Steel. Michigan submitted for
approval into the SIP revised construction permits for Carmeuse Lime,
DTE Trenton Channel, and DTE River Rouge.
    For U.S. Steel, Michigan imposed emission limits it had concluded
were necessary to bring the Detroit area into attainment via Michigan
Administrative Code (MAC) 336.1430 (``Rule 430''). Michigan submitted
Rule 430 to EPA as an enforceable limitation element for approval as
part of its SO2 plan.
    Subsequently, U.S. Steel challenged the legality of Rule 430 under
state law in the Michigan Court of Claims, which invalidated Rule 430
on October 4, 2017. United States Steel Corp. v. Dept. of Environmental
Quality, No. 16-000202-MZ, 2017 WL 5974195 (Mich. Ct. Cl. Oct. 4,
2017). Because the State's submitted attainment demonstration relied on
a limitation that is now unenforceable and, therefore, could not meet
the requirements of CAA sections 110 and 172, EPA disapproved the
Detroit SO2 plan on March 19, 2021.
    Although the attainment plan as a whole was not approvable, EPA
approved two of these three permits--for Carmeuse Lime and DTE Trenton
Channel--in its March 19, 2021 action as SIP strengthening, which is
appropriate for limits that improve air quality but do not meet a
specific CAA requirement. This made the two permits permanent and
federally enforceable by EPA and the State of Michigan.
    For Carmeuse Lime, on March 18, 2016, the State issued Permit to
Install 193-14A, which required the construction of and venting of
emissions through a new stack. The permit also established a more
stringent, permanent, and enforceable SO2 limit.\2\ The
State's modeling indicated that the violation caused by Carmeuse Lime
was resolved by this modification, which is well below the creditable
stack height of 65 meters as determined based on EPA's regulatory
definition of ``good engineering practice (GEP)'' per 40 CFR
51.100(ii)(1). Because this enforceable emission limit reduces ground-
level impacts, EPA approved it as SIP strengthening in the March 19,
2021 action. Carmeuse Lime has constructed the new stack and has shown
compliance with its limit since October 1, 2018. As further discussed
below, EPA has now evaluated the Carmeuse Lime permit as part of the
Detroit area attainment plan and is proposing to include it as part of
the FIP analysis.
---------------------------------------------------------------------------

    \2\ The Carmeuse Lime permit (Permit to Install 193-14A)
requires the construction of and venting of emissions through a new
stack with a minimum height above ground of 120 feet (36.6 meters).
The permit also establishes an enforceable hourly SO2
limit of 470 lbs/hr. Compliance must be shown by calculating and
recording hourly SO2 emissions using the most current
emission factor and the hourly limestone feed rate data.
---------------------------------------------------------------------------

    Similarly, EPA approved the DTE Trenton Channel permit (Permit to
Install 125-11C).\3\ EPA's FIP modeling analysis demonstrates that
attainment at the previously modeled violating receptors can be
achieved when the emission limits in the DTE Trenton Channel Permit \4\
are analyzed together with other control strategies included in the
FIP. DTE Trenton Channel has been in compliance with its limit since
its compliance date of January 1, 2017. In addition to the Carmeuse
Lime permit, EPA is also proposing to include the DTE Trenton Channel
permit as part of the FIP analysis.
---------------------------------------------------------------------------

    \3\ Issued April 29, 2016.
    \4\ The DTE Trenton Channel permit (Permit to Install 125-11C)
establishes an enforceable SO2 limit of 5,907 lbs/hr on a
30-day average basis. Compliance must be shown using a continuous
emissions monitoring system (CEMS), which was required to be
operational by January 1, 2017.
---------------------------------------------------------------------------

    Since Michigan's 2016 submittal, all DTE River Rouge units with
SO2 emissions have been shut down and the permit has been
modified to reflect this.\5\ Consequently, the shutdown of the coal-
fired boilers at DTE River Rouge is permanent and enforceable, and no
restart of their operations can occur without undergoing NSR, including
requirements to assess the impacts of future operations on maintaining
NAAQS attainment. Likewise, any such restart would require a revision
to the source's title V permit, subject to EPA review and possible
objection if a permit revision would not ensure compliance with all
applicable CAA requirements. For these reasons, it is reasonable for
the attainment modeling to treat DTE River Rouge's SO2
emissions as zero.
---------------------------------------------------------------------------

    \5\ Permit MI-ROP-B2810-2012c, modified on August 18, 2021.
---------------------------------------------------------------------------

    For EES Coke, Cleveland-Cliffs Steel Corporation, and DIG,
SO2 emission limits are included in their current operating
permits (Permit to Install 51-08C, November 21, 2014, Permit MI-ROP-
A8640-2016a, modified January 19, 2017, and Permit MI-ROP-N6631-2012a,
modified June 28, 2016, respectively). EPA has included these limits
and compliance mechanisms in the FIP regulatory text to ensure
permanence and enforceability, with one exception. In addition to an
existing daily average limit of 420 lbs/hr for DIG Boilers 1, 2 and 3
(combined), EPA is proposing an additional daily average limit of 840
lbs/hr for DIG Boilers 1, 2, and 3 and Flares 1 and 2 (combined). Both
limits will apply at all times. This additional limit is not reflective
of any new control strategies, but rather is

ensuring that maximum operating conditions are protective of the NAAQS.
    The existing control strategies specified in this section are
reflected in current clean monitoring data from both monitors in the
Detroit area. However, EPA's modeling analysis shows that to model
attainment throughout all the receptors in the Detroit area, new
emission limits at U.S. Steel are needed, which are discussed in
section IV.B below and included in the FIP regulatory language.

B. New Rules

    The proposed FIP regulatory language includes new rules for U.S.
Steel, which are described in the remainder of this sub-section.
Additional details on compliance, recordkeeping, and reporting
requirements are included in the FIP proposed regulatory language found
in the proposed amendment to 40 CFR part 52 Sec.  52.1189 in this
action. The emission limits and other requirements in these rules are
reflected in EPA's modeling.
1. U.S. Steel Boilerhouse 2
    EPA is proposing two separate limits for Boilerhouse 2 based on two
different operating scenarios. When Boilerhouse 2 is the only unit
operating at the U.S. Steel facility, EPA is proposing an emission
limit of 750.00 lbs/hr for U.S. Steel Boilerhouse 2. When any unit
identified in section IV.B.2 of this action is operating in addition to
Boilerhouse 2 at the U.S. Steel facility, EPA is proposing an emission
limit of 81.00 lbs/hr for U.S. Steel Boilerhouse 2. These limits would
be effective two years after the effective date of the FIP,
corresponding with the construction compliance schedule described below
in this section. To determine compliance with these limits, the owner
or operator would be required to install and continuously operate an
SO2 continuous emission monitoring system (CEMS) not later
than two years after the effective date of the FIP to measure
SO2 emissions from Boilerhouse 2 in conformance with 40 CFR
part 60 appendix F procedure 1.
    Additionally, EPA is proposing to require that the owner or
operator of Boilerhouse 2 combine all five stacks at U.S. Steel
Boilerhouse 2 into a single larger stack, with a minimum height of 170
feet (51.8 meters), which is well below the maximum creditable stack
height of 65 meters as determined based on EPA's regulatory definition
of de minimis GEP stack height per 40 CFR 51.100(ii)(1). This stack
reconfiguration is not considered a dispersion technique under 40 CFR
51.100(hh) as the allowable SO2 emissions for the entire
U.S. Steel facility do not exceed 5,000 tons per year.\6\ See 40 CFR
51.100(hh)(2)(v). The owner or operator would be required to submit a
construction permit application for the new stack to the State of
Michigan no later than 90 days after the effective date of the FIP and
would be required to commence stack operation not later than two years
after the effective date of the FIP. This compliance schedule allows
time for the State of Michigan to issue the permit, the owner or
operator to send out requests for proposal and award a construction
contract and procure materials, and for completion of construction.
---------------------------------------------------------------------------

    \6\ When Boilerhouse 2 is the only unit operating at the U.S.
Steel facility, EPA is proposing an emission limit of 750.00 lbs/hr
for U.S. Steel Boilerhouse 2. Assuming maximum operation for every
hour in a year, 750.00 lbs/hr equates to 3,285 tons per year. When
any unit identified in section IV.B.2 of this action is operating in
addition to Boilerhouse 2 at the U.S. Steel facility, EPA is
proposing an emission limit of 81.00 lbs/hr for U.S. Steel
Boilerhouse 2. The combined total of all emission limits for U.S.
Steel (Boilerhouse 2 plus all units identified in section IV.B.2) in
this scenario is 341.73 lbs/hr. Assuming maximum operation for every
hour in a year, 341.73 lbs/hr equates to 1,497 tons per year.
Therefore, in both scenarios, the total U.S. Steel allowable
emissions do not exceed 5,000 tons per year.
---------------------------------------------------------------------------

2. Other U.S. Steel Units
    The proposed FIP SO2 emission limits for the remaining
U.S. Steel units are shown below in Table 1. These limits would become
effective on the effective date of the FIP. Compliance with these
limits would be determined hourly by calculating SO2
emissions using all raw material sulfur charged into each affected
emission unit and assuming 100 percent conversion of total sulfur to
SO2. For all units except Boilerhouse 2 and any idled units,
the owner or operator of the units would be required to implement a
compliance assurance plan (CAP) that specifies the calculation
methodology, procedures, and inputs used in these calculations and
would be required to submit the plan to EPA within 30 days after the
effective date of the FIP. The owner or operator would be required to
submit a list of idled units within 30 days of the effective date of
the FIP and would be required to submit a CAP for any idled units
before resuming operation.

        Table 1--Proposed Emission Limits for U.S. Steel Units *
------------------------------------------------------------------------
                                                           Proposed SO2
                                                          emission limit
                          Unit                                (lbs/hr)

------------------------------------------------------------------------
Boilerhouse 1 (all stacks combined).....................           55.00
Hot Strip Mill--Slab Reheat Furnace 1...................            0.31
Hot Strip Mill--Slab Reheat Furnace 2...................            0.31
Hot Strip Mill--Slab Reheat Furnace 3...................            0.31
Hot Strip Mill--Slab Reheat Furnace 4...................            0.31
Hot Strip Mill--Slab Reheat Furnace 5...................            0.31
No. 2 Baghouse..........................................            3.30
Main Plant Boiler No. 8.................................            0.07
Main Plant Boiler No. 9.................................            0.07
A1 Blast Furnace........................................            0.00
B2 Blast Furnace........................................           40.18
D4 Blast Furnace........................................           40.18
A/B Blast Furnace Flares................................           60.19
D Furnace Flare.........................................           60.19
------------------------------------------------------------------------
* This table does not include proposed limits for Boilerhouse 2, which
  are described in section IV.B.1 of this action.

V. Longer-Term Averaging

    EPA's April 2014 guidance recommends that the emission limits be
expressed as short-term average limits (e.g., addressing emissions
averaged over one or three hours), but also describes the option to
utilize emission limits with longer averaging times of up to 30 days so
long as various suggested criteria are met. See 2014 guidance, pp. 22
to 39. The guidance recommends that, should longer-term averaging times
be used, 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 that the
plan otherwise would have set.
    The April 2014 guidance provides an extensive discussion of 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, 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 nonattainment area plan
provides for attainment. Id. at pp. 22 to 39. See also id. at
appendices B, C, and D.
    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
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 of the 75 ppb level 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
exceedances, and if so, the resulting frequency and magnitude of such
exceedances, and in particular whether EPA can have reasonable
confidence that a properly set longer-term average limit will provide
that the 3-year average of annual fourth highest daily maximum hourly
values will be at or below 75 ppb. A synopsis of how EPA judges whether
such plans ``provide for attainment,'' based on modeling of projected
allowable emissions and in consideration of the form of the NAAQS 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'' \7\ which shows three days with a maximum
hourly level 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.
---------------------------------------------------------------------------

    \7\ An ``average year'' is used to mean a year with average air
quality. While 40 CFR 50 appendix T provides for averaging three
years of 99th percentile daily maximum values (e.g., the fourth
highest maximum daily concentration in a year with 365 days with
valid data), this discussion and an example below use a single
``average year'' in order to simplify the illustration of relevant
principles.
---------------------------------------------------------------------------

    EPA recognizes that some sources have highly variable emissions,
for example due to variations in fuel sulfur content and operating
rate, that can make it extremely difficult, even with a well-designed
control strategy, to ensure in practice that emissions for any given
hour do not exceed the critical emission value. 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 emissions value. However, for several
reasons, EPA believes that the approach recommended in its guidance
document suitably addresses this concern. First, from a practical
perspective, 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. 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 such that the
longer-term limit has a lower permissible emission rate than that of
the critical emissions value) and that takes the source's emissions
profile into account. As a result, EPA expects either form of emission
limit to yield comparable air quality.
    Second, from a more theoretical perspective, 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
emissions value but on average, and presumably at most times, to emit
well below the critical emissions 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 emissions 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 emissions value), so a source complying
with an appropriately set longer-term limit is likely to have lower
emissions at critical times than would be the case if the source were
emitting as allowed with a 1-hour limit.
    As a hypothetical example to illustrate these points, suppose a
source always emits 1,000 pounds of SO2 per hour (lbs/hr),
which results in air quality at the level of the NAAQS (i.e., results
in a design value of 75 ppb). Suppose further that in an ``average
year,'' these emissions cause the 5 highest maximum daily average 1-
hour concentrations to be 100 ppb, 90 ppb, 80 ppb, 75 ppb, and 70 ppb.
Then suppose that the source becomes subject to a 30-

day average emission limit of 700 lbs/hr. It is theoretically possible
for a source meeting this limit to have emissions that occasionally
exceed 1,000 lbs/hr, but with a typical emissions profile emissions
would much more commonly be between 600 and 800 lbs/hr. In this
simplified example, assume a zero background concentration, which
allows one to assume a linear relationship between emissions and air
quality. (A nonzero background concentration would make the mathematics
more difficult but would give similar results.) Air quality will depend
on what emissions happen on what critical hours, but suppose that
emissions at the relevant times on these 5 days are 800 lbs/hr, 1,100
lbs/hr, 500 lbs/hr, 900 lbs/hr, and 1,200 lbs/hr, respectively. (This
is a conservative example because the average of these emissions, 900
lbs/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 (84
ppb under the 30-day average limit compared to 70 ppb under the 1-hour
limit). However, the third day would not have an exceedance that
otherwise would have occurred (40 ppb under the 30-day average limit
compared to 80 ppb under the 1-hour limit). The fourth day would have
been below, rather than at, 75 ppb (67.5 ppb under the 30-day average
limit compared to 75 ppb under the 1-hour limit). In this example, the
fourth highest maximum daily concentration under the 30-day average
would be 67.5 ppb.
    This simplified example illustrates the findings of a more
complicated statistical analysis that EPA conducted using a range of
scenarios incorporating actual plant data. As described in appendix B
of EPA's April 2014 SO2 nonattainment planning guidance, EPA
found that the requirement for lower average emissions is likely to
yield as good air quality as is required with a comparably stringent 1-
hour limit. Based on analyses described in appendix B of its 2014
guidance and similar subsequent work, EPA expects that emission
profiles with maximum allowable emissions under an appropriately set
comparably stringent 30-day average limit are likely to have the net
effect of no more exceedances and air quality as good as that of an
emission profile with maximum allowable emissions under a 1-hour
emission limit at the critical emission value.\8\ This result provides
a compelling policy rationale for allowing the use of a longer
averaging period, in appropriate circumstances where the facts indicate
this result can be expected to occur.
---------------------------------------------------------------------------

    \8\ See also further analyses described in rulemaking on the
SO2 nonattainment plan for Southwest Indiana. In response
to comments expressing concern that the emission profiles analyzed
for appendix B represented actual rather than allowable emissions,
EPA conducted additional work formulating sample allowable emission
profiles and analyzing the resulting air quality impact. This
analysis provided further support for the conclusion that an
appropriately set longer-term average emission limit in appropriate
circumstances can suitably provide for attainment. The rulemaking
describing these further analyses was published on August 17, 2020,
at 85 FR 49967, available at https://www.govinfo.gov/content/pkg/FR-2020-08-17/pdf/2020-16044.pdf. A more detailed description of these
analyses is available in the docket for that action, specifically at
https://www.regulations.gov/document?D=EPA-R05-OAR-2015-0700-0023.
---------------------------------------------------------------------------

    The question then becomes whether this approach, which is likely to
produce a lower number of overall exceedances even though it may
produce some unexpected exceedances above the critical emission value,
meets the requirement in section 110(a)(1) and 172(c)(1) for SIPs 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 attainment
plan to fail and unexpectedly not result in attainment, for example 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, 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, 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 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
accommodating real world emissions variability without significant risk
of violations, are also appropriate factors for 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, EPA believes
that a continuously enforceable limit averaged over as long as 30 days,
if determined in accordance with EPA's guidance, can reasonably be
considered to provide for attainment of the 2010 SO2 NAAQS.
    The April 2014 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 emissions value), then
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 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 nonattainment area
plan emission limits, which (if compliance requires new controls) may
require use of an emission database from another source. The
recommended method involves using these data to compute a complete set
of emission averages, computed according to the averaging time and
averaging procedures of the prospective emission limitation. 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.\9\ The guidance also addresses
a variety of related topics, such as the potential utility of setting
supplemental emission limits, such as mass-based limits, to reduce the
likelihood and/or magnitude of elevated emission levels that might
occur under the longer-term emission rate limit.
---------------------------------------------------------------------------

    \9\ For example, if the critical emission value is 1,000 lbs/hr
of SO2, and a suitable adjustment factor is determined to
be 70 percent, the recommended longer term average limit would be
700 lbs/hr.
---------------------------------------------------------------------------

VI. Modeling

    The following discussion is a summary of various features of the
modeling that EPA used in developing the proposed FIP. The modeling
analysis conducted by EPA to support the FIP was adapted from the
modeling analysis conducted by Michigan to support Michigan's 2016
nonattainment plan. A more in-depth discussion of the modeling,
including an explanation of

the differences between EPA's and Michigan's modeling analyses, is
presented in a technical support document (TSD) included in the docket
for this action.

A. Model Selection

    EPA used AERMOD, the preferred model for this application. EPA used
version 21112 of this model, which is the most current version. In its
2016 submittal, Michigan had instead used version 15181, which was the
current version at that time.\10\
---------------------------------------------------------------------------

    \10\ AERMOD version 21112 resolved errors and bugs that were
found in version 15181 and introduced some new modeling options. For
more information on the differences between AERMOD versions, see
https://www.epa.gov/scram/air-quality-dispersion-modeling-preferred-and-recommended-models.
---------------------------------------------------------------------------

    EPA's receptor grid and modeling domain for the Detroit area
followed the recommended approaches from EPA's Guideline on Air Quality
Models (40 CFR part 51, appendix W). A uniform Cartesian receptor grid
was used with receptor spacing of 100 meters throughout the modeled
domain, which was consistent with the grid Michigan used in its 2016
submittal.
    Although EPA's Guideline on Air Quality Models recommends that
areas such as Detroit should be modeled using urban dispersion
coefficients, Michigan found in its 2016 modeling analysis that using
urban dispersion coefficients caused the model to overpredict monitored
concentrations by 2-3 times due to overpredictions with tall
stacks.\11\ As discussed further in the TSD, EPA agrees with Michigan's
use of rural dispersion coefficients and therefore used rural
dispersion options for tall stacks at EES Coke, DTE Trenton Channel,
and DTE Monroe, and urban dispersion option for the remaining modeled
sources.
---------------------------------------------------------------------------

    \11\ More information on dispersion coefficients can be found in
the TSD for this action.
---------------------------------------------------------------------------

B. Meteorological Data

    EPA used the Detroit Metropolitan Wayne County Airport's (KDTW)
meteorological surface data and the White Lake (DTX) meteorological
upper air data for the years 2016-2020 for modeling the Detroit area.
The surface station is located less than 22 kilometers from the
SO2 sources in the Detroit area and is located in similar
terrain.

C. Emissions Data

    EPA included all point sources within 50 kilometers of Detroit in
its modeling analysis. These sources included U.S. Steel (Ecorse and
Zug Island), EES Coke, DTE Trenton Channel, Carmeuse Lime, DTE Monroe,
Cleveland-Cliffs Steel Corporation, DIG, and Marathon Refinery. DTE
River Rouge was not included in the modeling analysis as all the units
with SO2 emissions have been permanently and enforceably
shut down. EPA found that no other sources outside the nonattainment
area were close enough to cause significant concentration gradients.

D. Emission Limits

    An important aspect of an attainment plan is that the emission
limits that provide for attainment be quantifiable, fully enforceable,
replicable, and accountable. See General Preamble at 13567-68. The FIP
analysis includes limits for U.S. Steel, EES Coke, Cleveland-Cliffs
Steel Corporation, DIG, Carmeuse Lime, and DTE Trenton Channel. The
limit for Trenton Channel is expressed as a 30-day average limit, and
the limits for Cleveland-Cliffs Steel Corporation and DIG are expressed
as daily average limits. Therefore, part of the Detroit FIP must
address the use of these longer-term average limits, both with respect
to the general suitability of using such limits for demonstrating
attainment and with respect to whether the particular limits included
in the plan have been suitably demonstrated to provide for attainment.
The first subsection that follows addresses the enforceability of the
limits in the plan, and the second subsection that follows addresses in
particular the 30-day and daily average limits.
1. Enforceability
    In preparing its 2016 plan, Michigan adopted Permit to Install 193-
14A, governing the Carmeuse Lime SO2 emissions, and Permit
to Install 125-11C, governing the DTE Trenton Channel SO2
emissions. These construction permit revisions were adopted by Michigan
following established, appropriate public review procedures. The
Carmeuse Lime permit required the construction of and venting of
emissions through a new stack with a minimum height above ground of 120
feet (36.6 meters). The permit also established a permanent and
enforceable SO2 limit of 470 lbs/hr. EPA's modeling
indicates that the modeling violation caused by Carmeuse has been
resolved by this modification, which is well below the maximum
creditable stack height of 65 meters as determined based on EPA's
regulatory definition of de minimis GEP stack height per 40 CFR
51.100(ii)(1). The DTE Trenton Channel permit established an
enforceable SO2 limit of 5,907 lbs/hr on a 30-day rolling
average basis. EPA modeling demonstrates that attainment at violating
receptors can be achieved when the emission limits in the DTE Trenton
Channel Permit are analyzed together with the shutdown of the River
Rouge facility. In accordance with EPA policy, the 30-day average limit
is set at a lower level than the emission rate used in the attainment
demonstration; the relationship between these two values is discussed
in more detail in the following section. The permit compliance dates
were October 1, 2018 for Carmeuse Lime and January 1, 2017 for DTE
Trenton Channel. Both of these permits were incorporated into
Michigan's SIP as part of EPA's March 19, 2021 action, and both
facilities have been complying with their limits since their compliance
dates.
    Michigan adopted a revision to the renewable operating permit
governing DTE River Rouge emissions, Permit MI-ROP-B2810-2012c, on
August 18, 2021, that reflects the shutdown of the coal-fired boilers.
As explained in section IV.A above, the shutdown of the coal-fired
boilers at DTE River Rouge is permanent and enforceable.
    Emission limits and associated requirements for U.S. Steel, EES
Coke, Cleveland-Cliffs Steel Corporation, and DIG will be made
permanent and enforceable by the inclusion in the FIP regulatory
language. The codification section of the FIP includes new emission
limits and associated requirements for the U.S. Steel units and the DIG
Boilers 1, 2, and 3 and Flares 1 and 2 flexible group, as well as
emission limits and compliance mechanisms for EES Coke, Cleveland-
Cliffs Steel Corporation, and DIG (with the one aforementioned
exception) that are also required by the sources' existing operating
permits.
    As described further in the TSD, EPA modeled the maximum
uncontrolled emission rate for any unit in the nonattainment area that
does not have an SO2 emission limit already incorporated
into the Michigan SIP or included in the codification section of the
FIP.
2. Longer-Term Average Limits
    The following subsection addresses the 30-day average limit for DTE
Trenton Channel and the daily average limits for Cleveland-Cliffs Steel
Corporation and DIG. As previously discussed in detail in Section V of
this notice, EPA supports adoption of longer-term average limits, as
EPA's guidance recommends modeling of a 1-hour ``critical emissions
value'' (CEV) and application of a properly derived adjustment factor
demonstrates that the longer-term limit is comparably stringent to the
modeled 1-hour CEV that would otherwise be reflected in the emission
limit.

    Michigan's 2016 plan included permits with 30-day average emission
limits for DTE River Rouge and Trenton Channel that, when modeled using
comparably stringent 1-hour emission rates, demonstrated attainment of
the SO2 NAAQS in the areas that had previously shown
violations caused by the DTE facilities. Both DTE River Rouge and
Trenton Channel requested limits expressed as a 30-day average in order
to have longer-term limits that allow for ordinary fluctuations in
emissions but are comparably stringent to hourly limits and still
provide for attainment. Although Michigan's 2016 plan included a 30-day
average emission limit for DTE River Rouge, EPA is not evaluating a
longer-term average limit for DTE River Rouge as the facility has since
been shut down.
    DTE submitted to Michigan an analysis supporting the DTE Trenton
Channel Unit 9A 30-day average emission limits using CEMS heat input
data, SO2 emissions factors, and coal blend projections. DTE
calculated an adjustment factor of 0.87 for the DTE Trenton Channel
unit.
    However, as EPA was reviewing Michigan's 2016 submittal, EPA found
that DTE's adjustment factor calculation did not account for fuel
variability, which increased significantly after 2016 when the Mercury
and Air Toxics Standards (MATS) took effect. Therefore, EPA completed
its own adjustment factor analysis following the 2014 SO2
guidance using 2015-2019 DTE Trenton Channel operating data, which was
the most recent data at the time of the analysis and included DTE
Trenton Channel's transition to compliance with the MATS. EPA
calculated an adjustment factor of 0.771.
    For DTE Trenton Channel, EPA used its calculated adjustment factor
of 0.771 and the permitted 30-day-average emission limit of 5,907 lbs/
hr \12\ to calculate the comparably stringent 1-hour emission rate for
DTE Trenton Channel of 7,661 lbs/hr. EPA used the comparably stringent
1-hour emission rate in its modeling analysis to confirm that the DTE
Trenton Channel limit would result in attainment. The 1-hour emission
rate that EPA used for its modeling analysis (7,661 lbs/hr) is more
stringent than the CEV that would otherwise have been necessary to
provide for attainment, as the CEV represents the maximum 1-hour
emission rate that would result in attainment when modeled, and the
maximum concentration that EPA modeled was below the NAAQS.\13\
---------------------------------------------------------------------------

    \12\ The DTE Trenton Channel Unit 9A 30-day average
SO2 emissions are calculated on a rolling basis as
determined at the end of every calendar day.
    \13\ See section VI.G of this action for a summary of EPA's
modeling results.
---------------------------------------------------------------------------

    Although EPA used a more conservative adjustment factor in its FIP
modeling analysis than Michigan used in its 2016 submittal, EPA used
the same permitted 30-day-average emission limit of 5,907 lbs/hr.
Therefore, the comparably stringent 1-hour emission rate that EPA used
was higher than the rate that Michigan used. However, EPA's modeling
analysis shows that this higher 1-hour emission rate for DTE Trenton
Channel still provides for attainment, largely due to EPA's exclusion
of DTE River Rouge emissions in its analysis.
    For Cleveland-Cliffs Steel Corporation and DIG, EPA does not have a
sufficient historical record of CEMS data to be able to evaluate
source-specific emissions variability for purposes of determining
source-specific factors by which to calculate the comparably stringent
1-hour limits from the sources' daily average limits. Instead, EPA
determined the comparably stringent 1-hour emission rates by applying
one of the national average adjustment factors listed in appendix D of
EPA's 2014 SO2 guidance. For Cleveland-Cliffs Steel
Corporation, EPA divided the furnace stove daily average limits by an
adjustment factor of 0.89, reflecting the national average adjustment
factor that EPA found among facilities with wet scrubbers, and the
furnace baghouse daily average limits by an adjustment factor of 0.93,
reflecting the national average adjustment factor that EPA found among
facilities without control equipment. For DIG, EPA divided the daily
average limits by an adjustment factor of 0.93, reflecting the national
average adjustment factor that EPA found among facilities without
control equipment. The Cleveland-Cliffs Steel Corporation and DIG daily
average limits and comparably stringent 1-hour emission rates are shown
below in Table 2.

        Table 2--Cleveland-Cliffs Steel Corporation and DIG Daily Average Limits and Comparably Stringent
                                              1-Hour Emission Rates
----------------------------------------------------------------------------------------------------------------
                                                                                Modeled comparably
                                                                                stringent 1-hour
              Unit(s)                 Daily average emission limit    Adjustment factor     emission rate  (lbs/
                                                                                hr)
----------------------------------------------------------------------------------------------------------------
                                      Cleveland-Cliffs Steel Corporation *
----------------------------------------------------------------------------------------------------------------
``B'' Blast Furnace Baghouse and     77.8 lbs/hr..................  0.93 for Furnace       85.91 lbs/hr (modeled
 Stove Stacks (combined).                                            Baghouse and 0.89      as 33.46 lbs/hr for
                                                                     for Furnace Stove.     the furnace baghouse
                                                                                and 52.45 lbs/hr for
                                                                                the furnace stove).
``C'' Blast Furnace Baghouse and     271.4 lbs/hr.................  0.93 for Furnace       299.70 lbs/hr
 Stove Stacks (combined).                                            Stove and 0.89 for     (modeled as 116.73
                                                                     Furnace Baghouse.      lbs/hr for the
                                                                                furnace baghouse and
                                                                                182.97 lbs/hr for
                                                                                the furnace stove).
----------------------------------------------------------------------------------------------------------------
                                                       DIG
----------------------------------------------------------------------------------------------------------------
Boilers 1, 2, and 3 (combined).....  420 lbs/hr...................  0.93.................  451.62 lbs/hr
                                                                                (modeled as 150.54
                                                                                lbs/hr per boiler).
Boilers 1, 2, and 3, and Flares 1    840 lbs/hr...................  0.93.................  903.24 lbs/hr
 and 2 (combined).                                                                          (modeled as 150.54
                                                                                lbs/hr per boiler
                                                                                and 451.62 lbs/hr
                                                                                for Flare 2, as
                                                                                Flare 1 is no longer
                                                                                operational).
----------------------------------------------------------------------------------------------------------------
* Note: Modeled emissions were split between the furnace stoves and baghouses at a 60:40 ratio, which was the
  most conservative option based on capacity data over the last several years.

    EPA believes that the 30-day-average limit for DTE Trenton Channel
and the daily average limits for Cleveland-Cliffs Steel Corporation and
DIG provide suitable alternatives to establishing 1-hour average
emission limits for these sources. EPA proposes to find that the
adjustment factors of 0.771 for DTE Trenton Channel, 0.89 for
Cleveland-Cliffs Steel Corporation furnace stoves, 0.93 for Cleveland-
Cliffs Steel Corporation furnace baghouses, and 0.93 for DIG are
appropriate. When the longer-term limits were divided by these
adjustment factors, they resulted in modeled comparably stringent 1-
hour emission rates that are equal to or more stringent than the 1-hour
average emission rates represented by the CEV that would otherwise have
been necessary to provide for attainment. While the longer-term average
limits allow occasions in which emissions may be higher than the level
that would be allowed with the 1-hour limits, the longer-term average
limits compensate by requiring average emissions to be lower than the
level that would otherwise have been required by a 1-hour average limit
that would be represented by the CEV. As described above and explained
in more detail in EPA's April 2014 guidance for SO2
nonattainment plans, EPA finds that appropriately set longer-term
average limits provide a reasonable basis by which nonattainment plans
will provide for attainment.

E. Background Concentrations

    EPA determined background concentrations for the Detroit area using
monitoring data from the Allen Park monitor (AQS ID 26-163-0001), which
is approximately 17 kilometers southwest of Detroit. The background
concentration values that EPA used varied by season and hour-of-day and
ranged from 0.1 to 11.9 ppb.

F. Comments Made During Previous EPA Rulemakings

    During the comment period for EPA's March 19, 2021, partial
approval and partial disapproval of Michigan's 2016 plan for the
Detroit area, EPA received 21 supportive comments, nine comments not
directly relevant to the rulemaking, and a joint comment letter from
Sierra Club and Earthjustice that was partially adverse.
    Part of the joint letter from Sierra Club and Earthjustice included
information about alleged flaws in the State's modeling report. While
EPA was not evaluating whether Michigan's modeling report supported
attainment of the Detroit area in its March 19, 2021 action, EPA
believes these comments are relevant to EPA's modeling analysis for the
FIP. Therefore, EPA has considered the comments as part of the FIP
development. The remainder of this section summarizes the portion of
the comment letter that addressed the commenters' modeling concerns as
well as EPA's proposed response to these comments.
    First, the commenters expressed concerns that the State did not use
an appropriate background concentration in its modeling analysis.
Michigan used hourly SO2 data from the Allen Park monitor
for the years 2012-2014 in its 2016 analysis and excluded hourly
concentrations associated with wind directions between and including 40
degrees and 205 degrees using meteorological data from Allen Park. In
the modeling analysis for the FIP, EPA used a similar method to
Michigan's to calculate the background concentration. EPA used hourly
SO2 data from 2018-2020 at the Allen Park monitor, along
with Allen Park wind data to generate Season/Hour-of-Day
concentrations. Concentrations associated with wind directions between
and including 40 degrees and 205 degrees were excluded due to
SO2 concentrations at the Allen Park monitor being
influenced by sources explicitly included in the modeling analysis.
This includes U.S. Steel, DTE River Rouge, EES Coke, Carmeuse Lime,
Marathon, Cleveland-Cliffs Steel Corporation and DIG to the northeast
and DTE Trenton Channel and DTE Monroe to the south and southwest. Wind
direction checks were made for the preceding hour as well. Only days
with eight hours or more of valid observations with wind directions not
between and including 40 and 205 degrees were included, and the second
highest concentration for each season and hour-of-day combination was
selected. EPA's August 2016 ``SO2 NAAQS Designations
Modeling Technical Assistance Document'' (Modeling TAD) discusses that
the use of hour-of-day and season background concentrations based on
the 99th percentile 1-hour SO2 concentrations over three
years is appropriate for use in modeling against the 1-hour
SO2 NAAQS. The Modeling TAD states that ``to calculate the
99th percentile concentration for a season and hour of day combination,
the second highest concentration for that combination should be
selected.'' The Modeling TAD also concurs that it is appropriate to
exclude periods when the source(s) in question is/are expected to
impact the monitored concentrations.
    Second, the commenters stated that the state failed to adjust the
30-day average limits for DTE River Rouge and Trenton Channel to a
level that was comparably stringent to a 1-hour limit that would
achieve the SO2 NAAQS. As described in section VI.D.2 above,
EPA calculated a lower, more conservative adjustment factor than was
used in Michigan's 2016 modeling analysis for the DTE River Rouge and
Trenton Channel facilities. For DTE Trenton Channel, EPA used the lower
adjustment factor and the 30-day average limit to calculate a higher
comparably stringent 1-hour emission rate, which EPA used in its
modeling analysis to show attainment, that is equal to or more
stringent than the 1-hour emission rate represented by the CEV. As all
DTE River Rouge units emitting SO2 have been permanently
shut down, EPA removed the source from the modeling analysis and did
not include the 30-day average SO2 emission limits for DTE
River Rouge in the FIP. EPA believes that the current adjustment factor
being used in the FIP for DTE Trenton Channel is properly calculated
and protective of the NAAQS.
    Finally, the commenters recommended that EPA evaluate the State's
emissions inventory and consider any significant SO2 sources
that were excluded in future modeling. Specifically, the commenters
noted that three DIG natural gas combustion turbines, a DIG boiler co-
firing natural gas and blast furnace gas, the DTE EES Coke Bypass
Bleeder Flare, DTE EES Coke coke oven door leaks, and all Marathon
Refinery flares were not included in Michigan's 2016 modeling analysis.
EPA has evaluated these sources and they have been included in this
modeling analysis for the FIP. The full list of sources included in the
modeling, as well as the enforceability mechanism of each emission
rate, is included in the TSD, which is included in the docket for this
action.

G. Summary of Results

    EPA evaluated two separate operating scenarios as part of its
modeling analysis based on the separate limits proposed for U.S. Steel
Boilerhouse 2. In both scenarios, the modeling for the Detroit area
showed a maximum concentration of 73.6 ppb (192.7 micrograms per cubic
meter ([mu]g/m\3\)). This maximum concentration resulted from modeling
all units at maximum permitted levels based on the proposed emission
limits included in the FIP or already incorporated into Michigan's SIP,
or maximum uncontrolled emissions, newly adjusted comparably stringent
1-hour emission rates for DTE Trenton Channel, Cleveland-Cliffs Steel
Corporation, and DIG, and the

background concentration previously described. Therefore, EPA proposes
to conclude that this FIP provides for attainment in the Detroit area.

VII. Other Plan Requirements

A. Emissions Inventory

    EPA approved the base year emissions inventory for the Detroit area
in its March 19, 2021 action. Therefore, a review of the emissions
inventory is not included in the FIP.

B. RACM/RACT and Enforceable Emission Limits

    CAA section 172(c)(1) states that nonattainment plans shall provide
for the implementation of all RACM as expeditiously as practicable
(including such reductions in emissions from existing sources in the
area as may be obtained through the adoption, at a minimum, of RACT)
and shall provide for attainment of the national primary ambient air
quality standards. For most criteria pollutants, RACT is control
technology as needed to meet the NAAQS that is reasonably available
considering technological and economic feasibility. However, the
definition of RACT for SO2 is, simply, that control
technology which is necessary to achieve the NAAQS (see 40 CFR
51.100(o)). CAA section 172(c)(6) requires plans to include enforceable
emissions limitations, and such other control measures as may be
necessary or appropriate to provide for attainment of the NAAQS. In its
March 19, 2021, rulemaking, EPA disapproved Michigan's 2016 attainment
plan because it relied on Michigan Administrative Code (MAC) 336.1430
(``Rule 430''), which was invalidated and so was no longer an
enforceable mechanism. Therefore, the plan could not be considered to
provide an appropriate attainment demonstration, and it did not
demonstrate RACM/RACT or meet the requirement for necessary emissions
limitations or control measures. The FIP for attaining the 1-hour
SO2 NAAQS in the Detroit area is based on a variety of
measures, including permits for Carmeuse Lime (effective date of
October 1, 2018) and DTE Trenton Channel (effective date of January 1,
2017) that have been incorporated into Michigan's SIP, as well as the
proposed regulatory language regarding U.S. Steel, EES Coke, Cleveland-
Cliffs Steel Corporation, and DIG emissions that will be enforceable
upon finalization of this action. The FIP requires compliance two years
after the effective date of this action for U.S. Steel Boilerhouse 2
and the effective date of this action for all other units. The two-year
compliance schedule for U.S. Steel Boilerhouse 2 allows 90 days for the
owner or operator to submit a construction permit application to the
State of Michigan, as well as time for the State of Michigan to issue
the permit, the owner or operator to send out requests for proposal and
award a construction contract and procure materials, and for completion
of construction. EPA proposes to determine that these measures suffice
to provide for attainment and proposes to conclude that the FIP
satisfies the requirement in sections 172(c)(1) and (6) to adopt and
submit all RACM/RACT and emissions limitations or control measures as
needed to attain the standards as expeditiously as practicable.

C. NSR

    EPA affirmed in its March 19, 2021, action that NSR requirements
had previously been met. Therefore, a review of the NSR requirements is
not included in the FIP.

D. RFP

    Section 171(1) of the CAA defines RFP as such annual incremental
reductions in emissions of the relevant air pollutant as are required
by part D or may reasonably be required by EPA for the purpose of
ensuring attainment of the applicable NAAQS by the applicable
attainment date. This definition is most appropriate for pollutants
that are emitted by numerous and diverse sources, where the
relationship between any individual source and the overall air quality
is not explicitly quantified, and where the emission reductions
necessary to attain the NAAQS are inventory-wide. (See EPA's April 2014
SO2 nonattainment planning guidance, page 40.) For
SO2, there is usually a single ``step'' between pre-control
nonattainment and post-control attainment. Therefore, for
SO2, with its discernible relationship between emissions and
air quality, and significant and immediate air quality improvements,
RFP is best construed as adherence to an ambitious compliance schedule.
(See General Preamble at 74 FR 13547 (April 16, 1992)).
    In its March 19, 2021 rulemaking, EPA concluded that Michigan had
not satisfied the requirement in section 172(c)(2) to provide for RFP
toward attainment. Michigan's 2016 attainment plan did not demonstrate
that the implementation of the control measures required under the plan
were sufficient to provide for attainment of the NAAQS in the Detroit
SO2 nonattainment area, as some control measures were not
enforceable due to the invalidation of Rule 430. Therefore, a
compliance schedule to implement those controls was not sufficient to
provide for RFP. The FIP regulatory language requires compliance by two
years after the effective date of this action for U.S. Steel
Boilerhouse 2 and the effective date of this action for all other
units. As described in section IV.B above, the 2-year compliance
schedule for U.S. Steel Boilerhouse 2 allows 90 days for the owner or
operator to submit a construction permit application to the State of
Michigan, as well as time for the State of Michigan to issue the
permit, the owner or operator to send out requests for proposal and
award a construction contract and procure materials, and for completion
of construction. For DTE Trenton Channel and Carmeuse lime, compliance
was required by January 1, 2017, and October 1, 2018, respectively. EPA
concludes that this is an ambitious compliance schedule, as described
in April 2014 guidance for SO2 nonattainment plans, and that
this plan therefore provides for RFP in accordance with the approach to
RFP described in EPA's 2014 guidance.

E. Contingency Measures

    EPA guidance describes special features of SO2 planning
that influence the suitability of alternative means of addressing the
requirement in section 172(c)(9) for contingency measures for
SO2, such that in particular an appropriate means of
satisfying this requirement is for the air agency to have a
comprehensive enforcement program that identifies sources of violations
of the SO2 NAAQS and to undertake an aggressive follow-up
for compliance and enforcement. (See EPA's April 2014 SO2
nonattainment planning guidance, page 41.) The FIP provides for
satisfying the contingency measure requirement in this manner, and EPA
will be responsible for enforcement unless Michigan seeks to take
delegation of the FIP. EPA's enforcement authority is contained in
section 113(a) of the CAA. Options include: The issuance of an
administrative order requiring compliance with the applicable
implementation plan; the issuance of an administrative order requiring
the payment of a civil penalty for past violations; and the
commencement of a civil judicial action.

VIII. What action is EPA taking?

    EPA is proposing a FIP for attaining the 2010 SO2 NAAQS
for the Detroit area and for meeting other nonattainment area planning
requirements. In accordance with section 172 of the CAA, this FIP

includes an attainment demonstration for the Detroit area and addresses
requirements for RFP, RACT/RACM, enforceable emission limitations and
control measures, and contingency measures. EPA has previously
concluded that Michigan has addressed the requirements for emissions
inventories for the Detroit area and nonattainment area NSR.
    The FIP is based on the Carmeuse Lime emission limits specified in
Permit to Install 193-14A, the DTE Trenton Channel emission limits
specified in Permit to Install 125-11C, and the U.S. Steel, EES Coke,
Cleveland-Cliffs Steel Corporation, and DIG emission limits specified
in the proposed regulatory language of this FIP. The Carmeuse Lime and
DTE Trenton Channel permits have already been incorporated into
Michigan's SIP, so EPA is not proposing to re-incorporate them into 40
CFR part 52 here.
    EPA is taking public comments for forty-five days following the
publication of this proposed action in the Federal Register. EPA will
take all comments into consideration in the final action. If this FIP
is finalized, it would satisfy EPA's duty to promulgate a FIP for the
area under CAA section 110(c) that resulted from the previous finding
of failure to submit. However, it would not affect the sanctions clock
started under CAA section 179 resulting from EPA's partial disapproval
of the prior SIP, which would be terminated by an EPA rulemaking
approving a revised SIP.

IX. Statutory and Executive Order Reviews

    Additional information about these statutes and Executive Orders
can be found at https://www2.epa.gov/laws-regulations/laws-and-executive-orders.

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

    This action is exempt from review by the Office of Management and
Budget (OMB). As discussed in detail in section B below, the proposed
FIP regulatory language contains requirements only for four facilities.
It is therefore not a rule of general applicability.

B. Paperwork Reduction Act

    This proposed action does not impose an information collection
burden under the provisions of the Paperwork Reduction Act, 44 U.S.C.
3501 et seq. Under the Paperwork Reduction Act, a ``collection of
information'' is defined as a requirement for ``answers to . . .
identical reporting or recordkeeping requirements imposed on ten or
more persons . . .'' 44 U.S.C. 3502(3)(A). Because the proposed FIP
applies to just four facilities, the Paperwork Reduction Act does not
apply. See 5 CFR 1320(c).
    Burden means the total time, effort, or financial resources
expended by persons to generate, maintain, retain, or disclose or
provide information to or for a Federal agency. This includes the time
needed to review instructions; develop, acquire, install, and utilize
technology and systems for the purposes of collecting, validating, and
verifying information, processing and maintaining information, and
disclosing and providing information; adjust the existing ways to
comply with any previously applicable instructions and requirements;
train personnel to be able to respond to a collection of information;
search data sources; complete and review the collection of information;
and transmit or otherwise disclose the information.
    An agency may not conduct or sponsor, and a person is not required
to respond to a collection of information unless it displays a
currently valid Office of Management and Budget (OMB) control number.
The OMB control numbers for our regulations in 40 CFR are listed in 40
CFR part 9.

C. Regulatory Flexibility Act

    The Regulatory Flexibility Act (RFA) generally requires an agency
to prepare a regulatory flexibility analysis of any rule subject to
notice and comment rulemaking requirements under the Administrative
Procedure Act or any other statute unless the agency certifies that the
rule will not have a significant economic impact on a substantial
number of small entities. Small entities include small businesses,
small organizations, and small governmental jurisdictions.
    For purposes of assessing the impacts of this proposed rule on
small entities, small entity is defined as: (1) A small business as
defined by the Small Business Administration's (SBA) regulations at 13
CFR 121.201; (2) a small governmental jurisdiction that is a government
of a city, county, town, school district or special district with a
population of less than 50,000; and (3) a small organization that is
any not-for-profit enterprise which is independently owned and operated
and is not dominant in its field.
    After considering the economic impacts of this proposed action on
small entities, I certify that this proposed action will not have a
significant economic impact on a substantial number of small entities.
EPA's proposal adds additional controls to certain sources. None of
these sources are owned by small entities, and therefore are not small
entities.

D. Unfunded Mandates Reform Act (UMRA)

    This action does not contain any unfunded mandate as described in
UMRA, 2 U.S.C. 1531-1538, and does not significantly or uniquely affect
small governments. The action imposes no enforceable duty on any state,
local or tribal governments or the private sector.

E. Executive Order 13132: Federalism

    This action does not have federalism implications. It will not have
substantial direct effects on the states, on the relationship between
the national government and the states, or on the distribution of power
and responsibilities among the various levels of government.

F. Executive Order 13175: Consultation and Coordination With Indian
Tribal Governments

    Executive Order 13175, entitled Consultation and Coordination with
Indian Tribal Governments (65 FR 67249, November 9, 2000), requires EPA
to develop an accountable process to ensure ``meaningful and timely
input by tribal officials in the development of regulatory policies
that have tribal implications.'' This proposed rule does not have
tribal implications, as specified in Executive Order 13175. It will not
have substantial direct effects on tribal governments. Thus, Executive
Order 13175 does not apply to this rule.

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

    Executive Order 13045: Protection of Children from Environmental
Health Risks and Safety Risks (62 FR 19885, April 23, 1997), applies to
any rule that: (1) Is determined to be economically significant as
defined under Executive Order 12866; and (2) concerns an environmental
health or safety risk that we have reason to believe may have a
disproportionate effect on children. EPA interprets E.O. 13045 as
applying only to those regulatory actions that concern health or safety
risks, such that the analysis required under section 5-501 of the E.O.
has the potential to influence the regulation. This action is not
subject to E.O. 13045 because it is not economically significant under
Executive Order 12866 and because it implements specific standards
established by Congress in statutes. However, to the extent this
proposed rule will limit SO2 emissions, the rule will have a
beneficial effect on

children's health by reducing air pollution.

H. Executive Order 13211: Actions Concerning Regulations That
Significantly Affect Energy Supply, Distribution, or Use

    This action is not subject to Executive Order 13211 (66 FR 28355
(May 22, 2001)), because it is not a significant regulatory action
under Executive Order 12866.

I. National Technology Transfer and Advancement Act

    This rulemaking does not involve technical standards.

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

    Executive Order 12898 (59 FR 7629, February 16, 1994), establishes
Federal executive policy on environmental justice. Its main provision
directs Federal agencies, to the greatest extent practicable and
permitted by law, to make environmental justice part of their mission
by identifying and addressing, as appropriate, disproportionately high
and adverse human health or environmental effects of their programs,
policies, and activities on minority populations and low-income
populations in the United States.
    This proposed rule, if finalized, would improve local air quality
by reducing SO2 emissions in a part of the Detroit
metropolitan area that includes a higher proportion of minority and
low-income populations compared to the State or US averages.
Socioeconomic indicators such as low income, unemployment rate and
percentage of people of color \14\ were all at levels at least two
times that of the state-wide averages (in some cases two to five times
higher), within one to six miles from facilities affected by this
action (see EJScreen analyses provided in the docket for this action).
These populations, as well as all affected populations in this area,
will stand to benefit from the increased level of environmental
protection with the implementation of this rule.
---------------------------------------------------------------------------

    \14\ See https://www.epa.gov/ejscreen/overview-demographic-indicators-ejscreen for the definition of each demographic
indicator.
---------------------------------------------------------------------------

List of Subjects in 40 CFR Part 52

    Environmental protection, Air pollution control, Incorporation by
reference, Intergovernmental relations.

Michael Regan,
Administrator.
    For the reasons stated in the preamble, EPA proposes to amend 40
CFR part 52 as follows:

PART 52--APPROVAL AND PROMULGATION OF IMPLEMENTATION PLANS

0
1. The authority citation for part 52 continues to read as follows:

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

0
2. Section 52.1189 is added to read as follows:

Sec.  52.1189  Control strategy: Sulfur Dioxide (SO2).

    (a) The plan submitted by the State on May 31, 2016 to attain the
2010 1-hour primary sulfur dioxide (SO2) national ambient
air quality standard for the Detroit SO2 nonattainment area
does not meet the requirements of Clean Air Act (CAA) section 172 with
respect to SO2 emissions from the U.S. Steel (Ecorse and Zug
Island), EES Coke, Cleveland-Cliffs Steel Corporation (formerly AK or
Severstal Steel), and Dearborn Industrial Generation (DIG) facilities
in the Detroit, Michigan area. These requirements for these four
facilities are satisfied by 40 CFR 52.1189(b)-(e), respectively.
    (b) This section addresses and satisfies CAA section 172
requirements for the Detroit SO2 nonattainment area by
specifying the necessary emission limits and other control measures
applicable to the U.S. Steel (Ecorse and Zug Island) facility. This
section applies to the owner and operator of the facility located at 1
Quality Drive and 1300 Zug Island Road in Detroit, Michigan.
    (1) SO2 Emission Limits.
    (i) Beginning on the effective date of the FIP, no owner or
operator shall emit SO2 from the following units in excess
of the following limits:

------------------------------------------------------------------------
                                                           SO2 emission
                          Unit                            limit (lbs/hr)

------------------------------------------------------------------------
Boilerhouse 1 (all stacks combined).....................           55.00
Hot Strip Mill--Slab Reheat Furnace 1...................            0.31
Hot Strip Mill--Slab Reheat Furnace 2...................            0.31
Hot Strip Mill--Slab Reheat Furnace 3...................            0.31
Hot Strip Mill--Slab Reheat Furnace 4...................            0.31
Hot Strip Mill--Slab Reheat Furnace 5...................            0.31
No. 2 Baghouse..........................................            3.30
Main Plant Boiler No. 8.................................            0.07
Main Plant Boiler No. 9.................................            0.07
A1 Blast Furnace........................................            0.00
B2 Blast Furnace........................................           40.18
D4 Blast Furnace........................................           40.18
A/B Blast Furnace Flares................................           60.19
D Furnace Flare.........................................           60.19
------------------------------------------------------------------------

    (ii) Beginning two years after the effective date of the FIP, no
owner or operator shall emit SO2 from Boilerhouse 2 in
excess of the following limits:
    (A) When Boilerhouse 2 is the only unit operating at the facility,
an emission limit of 750.00 lbs/hr. When any unit identified in
paragraph (b)(1)(i) of this section is operating in addition to
Boilerhouse 2, an emission limit of 81.00 lbs/hr.
    (2) Stack Restrictions and Permit Requirements.
    (i) The owner or operator shall construct a combined stack for all
Boilerhouse 2 emission points. The stack emission point must be at
least 170 feet above ground level. The owner or operator shall submit a
construction permit application for the stack to the State of Michigan
within 90 days of the effective date of the FIP. Where any compliance
obligation under this section requires any other state or local permits
or approvals, the owner or operator shall submit timely and

complete applications and take all other actions necessary to obtain
all such permits or approvals.
    (ii) Beginning two years after the effective date of the FIP, no
owner or operator shall emit SO2 from Boilerhouse 2, except
from the stack emission point at least 170 feet above ground level.
    (3) Monitoring Requirements.
    (i) Not later than two years after the effective date of the FIP,
the owner or operator shall install and continuously operate an
SO2 continuous emission monitoring system (CEMS) to measure
SO2 emissions from Boilerhouse 2 in conformance with 40 CFR
part 60 appendix F procedure 1.
    (ii) The owner or operator shall determine SO2 emissions
from Boilerhouse 1, Hot Strip Mill Slab Reheat Furnaces 1-5, Main Plant
Boiler No. 8, Main Plan Boiler No. 9, A1 Blast Furnace, B2 Blast
Furnace, D4 Blast Furnace, A/B Blast Furnace Flares, and D Furnace
Flare using mass balance calculations as described in paragraph (b)(4)
of this section.
    (iii) Within 180 days of the installation of the CEMS specified in
paragraph (b)(3)(i), the owner or operator shall perform an initial
compliance test for SO2 emissions from Boilerhouse 2 while
the boilerhouse is operating in accordance with requirements identified
in either paragraph (b)(1)(i) or (b)(1)(ii), whichever is applicable
during the period of testing. The initial compliance test shall be
performed using EPA Test Method 6 at 40 CFR part 60 appendix A-4.
    (4) Compliance Assurance Plan. To determine compliance with the
limits in paragraph (b)(1)(i) of this section, the owner or operator
shall calculate hourly SO2 emissions using all raw material
sulfur charged into each affected emission unit and assume 100 percent
conversion of total sulfur to SO2. The owner or operator
shall implement a compliance assurance plan (CAP) for all units except
Boilerhouse 2 and any idled units that shall specify the calculation
methodology, procedures, and inputs used in these calculations and
submit the plan to EPA within 30 days after the effective date of the
FIP. The owner or operator must submit a list of idled units to EPA
within 30 days of the effective date of the FIP. The owner or operator
must submit a CAP for any idled units prior to resuming operations.
    (5) Recordkeeping. The owner/operator shall maintain the following
records continuously for five years beginning on the effective date of
the FIP:
    (i) All records of production for each affected emission unit.
    (ii) All records of hourly emissions calculated in accordance with
the CAP.
    (iii) In accordance with paragraph (b)(3) of this section, all CEMS
data, including the date, place, and time of sampling or measurement;
parameters sampled or measured; and results.
    (iv) Records of quality assurance and quality control activities
for emission monitoring systems including, but not limited to, any
records required by 40 CFR part 60 appendix F Procedure 1.
    (v) Records of all major maintenance activities performed on
emission units, air pollution control equipment, CEMS, and other
production measurement devices.
    (vi) Any other records required by the Quality Assurance
Requirements for Gas Continuous Emission Monitoring Systems Used for
Compliance Determination rule at 40 CFR part 60 appendix F Procedure 1
or the National Emission Standards for Hazardous Air Pollutants for
Integrated Iron and Steel Manufacturing Facilities rule at 40 CFR part
63 Subpart FFFFF.
    (6) Reporting. Beginning on the effective date of the FIP, all
reports under this section shall be submitted quarterly to Compliance
Tracker, Air Enforcement and Compliance Assurance Branch, U.S.
Environmental Protection Agency, Region 5, Mail Code AE-17J, 77 W
Jackson Blvd., Chicago, IL 60604-3590.
    (i) The owner or operator shall submit a CAP in accordance with
paragraph (b)(4) of this section within 30 days of the effective date
of the FIP.
    (ii) The owner or operator shall report CEMS data and hourly mass
balance calculations quarterly in accordance with CEMS requirements in
paragraph (b)(3) of this section and the CAP requirements set forth in
paragraph (b)(4) of this section no later than the 30th day following
the end of each calendar quarter.
    (iii) The owner or operator shall report the results of the initial
compliance test for the Boilerhouse 2 stack within 60 days of
conducting the test.
    (iv) The owner or operator shall submit quarterly excess emissions
reports for all units identified in paragraphs (b)(1)(i) and (ii) of
this section no later than the 30th day following the end of each
calendar quarter. Excess emissions means emissions that exceed the
emission limits specified in paragraph (b)(1) of this section. The
reports shall include the magnitude, date(s), and duration of each
period of excess emissions, specific identification of each period of
excess emissions that occurs during all periods of operation including
startups, shutdowns, and malfunctions of the unit, the nature and cause
of any malfunction (if known), and the corrective action taken or
preventative measures adopted.
    (v) The owner or operator of each unit shall submit quarterly CEMS
performance reports, to include dates and duration of each period
during which the CEMS was inoperative (except for zero and span
adjustments and calibration checks), reason(s) why the CEMS was
inoperative and steps taken to prevent recurrence, and any CEMS repairs
or adjustments no later than the 30th day following the end of each
calendar quarter.
    (vi) The owner or operator shall also submit results of any CEMS
performance tests required by 40 CFR part 60, appendix F, Procedure 1
(e.g., Relative Accuracy Test Audits, Relative Accuracy Audits, and
Cylinder Gas Audits) no later than 30 days after the test is performed.
    (vii) When no excess emissions have occurred or the CEMS has not
been inoperative, repaired, or adjusted during the reporting period,
such information shall be stated in the quarterly reports required by
paragraph (b)(6) of this section.(c) This section addresses and
satisfies CAA section 172 requirements for the Detroit SO2
nonattainment area by specifying the necessary emission limits and
other control measures applicable to the EES Coke facility. This
section applies to the owner and operator of the facility located at
1400 Zug Island Road in Detroit, Michigan.
    (1) SO2 Emission Limits. Beginning on the effective date of the
FIP, no owner or operator shall emit SO2 from the Underfire
Combustion Stack EUCoke-Battery in excess of 544.6 lbs/hr, as a 3-hour
average, or 2,071 tons per year, on a 12-month rolling basis as
determined at the end of each calendar month, or 0.702 pounds per 1,000
standard cubic feet of coke oven gas, as a 1-hour average.
    (2) Monitoring requirements. The owner or operator shall maintain
and operate in a satisfactory manner a device to monitor and record the
SO2 emissions from the Underfire Combustion Stack EUCoke-
Battery on a continuous basis. The owner or operator shall use
Continuous Emission Rate Monitoring (CERM) data for determining
compliance with the hourly limit in paragraph (c)(1) of this section.
The owner or operator shall operate the CERM system in conformance with
40 CFR part 60 Appendix F.
    (d) This section addresses and satisfies CAA section 172
requirements

for the Detroit SO2 nonattainment area by specifying the
necessary emission limits and other control measures applicable to the
Cleveland-Cliffs Steel Corporation (formerly AK or Severstal Steel)
facility. This section applies to the owner and operator of the
facility located at 4001 Miller Road in Dearborn, Michigan.
    (1) SO2 Emission Limits. Beginning on the effective date of the
FIP, no owner or operator shall emit SO2 from the following
units in excess of the following limits:

----------------------------------------------------------------------------------------------------------------
                  Unit                             SO2 emission limit            Time period/operating scenario
----------------------------------------------------------------------------------------------------------------
``B'' Blast Furnace Baghouse Stack......  71.9 lbs/hr.........................  Calendar day average.
``B'' Blast Furnace Stove Stack.........  38.75 lbs/hr........................  Calendar day average.
``B'' Blast Furnace Baghouse and Stove    77.8 lbs/hr.........................  Calendar day average.
 Stacks (combined).
``B'' Blast Furnace Baghouse and Stove    340 tons per year...................  12-month rolling time period as
 Stacks (combined).                                                              determined at the end of each
                                                                                calendar month.
``C'' Blast Furnace Baghouse Stack......  179.65 lbs/hr.......................  Calendar day average.
``C'' Blast Furnace Stove Stack.........  193.6 lbs/hr........................  Calendar day average.
``C'' Blast Furnace Baghouse and Stove    271.4 lbs/hr........................  Calendar day average.
 Stacks (combined).
``C'' Blast Furnace Baghouse and Stove    1188 tons per year..................  12-month rolling time period as
 Stacks (combined).                                                              determined at the end of each
                                                                                calendar month.
----------------------------------------------------------------------------------------------------------------

    (2) Monitoring Requirements. The owner or operator shall maintain
and operate in a satisfactory manner a device to monitor and record the
SO2 emissions and flow from ``B'' Blast Furnace and ``C''
Blast Furnace Baghouse and Stove Stacks on a continuous basis. The
owner or operator shall use CERM data for determining compliance with
the hourly limits in paragraph (d)(1) of this section. The owner or
operator shall operate the CERM system in conformance with 40 CFR part
60 Appendix F.
    (e) This section addresses and satisfies CAA section 172
requirements for the Detroit SO2 nonattainment area by
specifying the necessary emission limits and other control measures
applicable to the Dearborn Industrial Generation (DIG) facility. This
section applies to the owner and operator of the facility located at
2400 Miller Road in Dearborn, Michigan.
    (1) SO2 Emission Limits.
    (i) Beginning on the effective date of the FIP, no owner or
operator shall emit SO2 from the following units in excess
of the following limits:

----------------------------------------------------------------------------------------------------------------
                  Unit                              SO2 emission limit            Time period/operating scenario
----------------------------------------------------------------------------------------------------------------
Boilers 1, 2, and 3 (combined)..........  420 lbs/hr...........................  Daily average.
Boilers 1, 2, and 3 (combined)..........  1,839.6 tons per year................  12-month rolling time period.
Boilers 1, 2, and 3 and Flares 1 and 2    840 lbs/hr...........................  Daily average.
 (combined).
Boilers 1, 2, and 3 and Flares 1 and 2    2,947.7 tons per year................  12-month rolling time period as
 (combined).                                                                      determined at the end of each
                                                                                calendar month.
----------------------------------------------------------------------------------------------------------------

    (2) Monitoring Requirements. The owner or operator shall maintain
and operate in a satisfactory manner a device to monitor and record the
SO2 emissions from Boilers 1, 2, and 3 on a continuous
basis. Installation and operation of each CEMS shall meet the
timelines, requirements and reporting detailed in 40 CFR part 60
Appendix F. If the owner or operator chooses to use a Predictive
Emissions Monitoring System (PEMS) in lieu of a CEMS to monitor
SO2 emissions, the permittee shall follow the protocol
delineated in Performance Specification 16 in Appendix B of 40 CFR part
60.

[FR Doc. 2022-11269 Filed 5-31-22; 8:45 am]
BILLING CODE 6560-50-P