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[Federal Register Volume 89, Number 233 (Wednesday, December 4, 2024)]
[Proposed Rules]
[Pages 96152-96166]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2024-27635]

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 52

[EPA-R05-OAR-2024-0215; FRL-12351-01-R5]

Air Plan Approval; Michigan and Minnesota; Revision to Taconite 
Federal Implementation Plan

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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SUMMARY: The Environmental Protection Agency (EPA) is proposing to 
finalize nitrogen oxide (NOX) and/or sulfur dioxide 
(SO2) limits for the indurating furnaces at five taconite 
facilities in accordance with the procedures set forth in the Federal 
implementation plan (FIP) addressing the requirement for best available 
retrofit technology (BART) at taconite facilities. EPA is also 
proposing to modify the Upper Predictive Limit (UPL) equations used to 
establish NOX and SO2 emission limits under the 
FIP. Finally, EPA is proposing to revise reporting provisions to 
require reports to be submitted to EPA electronically. EPA is proposing 
these actions pursuant to sections 110 and 169A of the Clean Air Act 
(CAA).

[[Page 96153]]

DATES: Comments must be received on or before January 21, 2025.
    Virtual Public Hearing. EPA will hold a virtual public hearing to 
solicit comments on December 19, 2024. The last day to pre-register to 
present at the hearing will be December 16, 2024. On December 16, 2024, 
EPA will post a general agenda for the hearing that will list pre-
registered presenters in approximate order at https://www.epa.gov/mn/revision-taconite-regional-haze-federal-implementation-plan-mi-and-mn. 
If you require the services of a translator or a special accommodation 
such as audio description/closed captioning, please pre-register for 
the hearing and describe your needs by December 11, 2024.
    For more information on the virtual public hearing, see 
SUPPLEMENTARY INFORMATION.

ADDRESSES: Submit your comments, identified by Docket ID No. EPA-R05-
OAR-2024-0215 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 the docket. EPA may publish 
any comment received to its public docket. Do not submit to EPA's 
docket at https://www.regulations.gov any information you consider to 
be Confidential Business Information (CBI), Proprietary Business 
Information (PBI), 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, 
PBI, or multimedia submissions, and general guidance on making 
effective comments, please visit https://www.epa.gov/dockets/commenting-epa-dockets.

FOR FURTHER INFORMATION CONTACT: Kathleen D'Agostino, Environmental 
Scientist, Air and Radiation Division (AR18J), Environmental Protection 
Agency, Region 5, 77 West Jackson Boulevard, Chicago, Illinois 60604, 
(312) 886-0266, [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.

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

Virtual Public Hearing

    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 December 19, 2024. The hearing will convene at 9:00 a.m. 
Central Standard Time (CST) and will conclude at 1:00 p.m. CST, 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/mn/revision-taconite-regional-haze-federal-implementation-plan-mi-and-mn.
    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/mn/revision-taconite-regional-haze-federal-implementation-plan-mi-and-mn 
or contact Mayesha Choudhury at 312-886-5909 or by email at 
[email protected]. The last day to pre-register to present at 
the hearing will be December 16, 2024. On December 16, 2024, EPA will 
post a general agenda for the hearing that will list pre-registered 
presenters in approximate order at https://www.epa.gov/mn/revision-taconite-regional-haze-federal-implementation-plan-mi-and-mn. 
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.
    EPA is asking all hearing attendees to pre-register, even those who 
do not intend to present. This will help EPA prepare for the virtual 
hearing.
    Please note that any updates made to any aspect of the hearing will 
be posted online at https://www.epa.gov/mn/revision-taconite-regional-haze-federal-implementation-plan-mi-and-mn. While EPA expects the 
hearing to go forward as set forth above, please monitor our website or 
contact Mayesha Choudhury at 312-886-5909 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 Mayesha Choudhury at 312-886-5909 or 
[email protected] and describe your needs by December 11, 2024. 
EPA may not be able to arrange accommodations without advance notice.

I. Background

A. Requirements of the Clean Air Act and EPA's Regional Haze Rule

    In section 169A of the 1977 Amendments to the CAA, Congress created 
a program for protecting visibility in the nation's national parks and 
wilderness areas. This section of the CAA establishes as a national 
goal the ``prevention of any future, and the remedying of any existing, 
impairment of visibility in mandatory Class I Federal areas \1\ which 
impairment results from manmade air pollution.'' Congress added section 
169B to the CAA in 1990 to address regional haze issues. EPA 
promulgated a rule to address regional haze on July 1, 1999

[[Page 96154]]

(64 FR 35714), codified at 40 CFR part 51, subpart P (herein after 
referred to as the ``Regional Haze Rule''). The Regional Haze Rule 
codified and clarified the BART provisions in the CAA and revised the 
existing visibility regulations to add provisions addressing regional 
haze impairment and to establish a comprehensive visibility protection 
program for Class I areas. The requirements for regional haze, found at 
40 CFR 51.308 and 51.309, are included in EPA's visibility protection 
regulations at 40 CFR part 51, subpart P.
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    \1\ Areas designated as mandatory Class I Federal areas consist 
of national parks exceeding 6000 acres, wilderness areas and 
national memorial parks exceeding 5000 acres, and all international 
parks that were in existence on August 7, 1977. 42 U.S.C. 7472(a). 
In accordance with section 169A of the CAA, EPA, in consultation 
with the Department of Interior, promulgated a list of 156 areas 
where visibility is identified as an important value. 44 FR 69122 
(November 30, 1979). The extent of a mandatory Class I area includes 
subsequent changes in boundaries, such as park expansions. 42 U.S.C. 
7472(a). Although states and Tribes may designate as Class I 
additional areas which they consider to have visibility as an 
important value, the requirements of the visibility program set 
forth in section 169A of the CAA apply only to ``mandatory Class I 
Federal areas.'' Each mandatory Class I Federal area is the 
responsibility of a ``Federal Land Manager.'' 42 U.S.C. 7602(i). 
When we use the term ``Class I area'' in this action, we mean a 
``mandatory Class I Federal area.''
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    Section 169A of the CAA directs states, or EPA if developing a FIP, 
to evaluate the use of retrofit controls at certain larger, often 
uncontrolled, older stationary sources to address visibility impacts 
from these sources. Specifically, section 169A(b)(2)(A) of the CAA 
requires that implementation plans contain such measures as may be 
necessary to make reasonable progress toward the natural visibility 
goal, including a requirement that certain categories of existing major 
stationary sources \2\ built between 1962 and 1977 procure, install, 
and operate BART as determined by EPA.
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    \2\ The set of ``major stationary sources'' potentially subject 
to BART is listed in CAA section 169A(g)(7) and includes ``taconite 
ore processing facilities.''
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    Under the Regional Haze Rule, states (or in the case of a FIP, EPA) 
are directed to conduct BART determinations for such ``BART-eligible'' 
sources that may reasonably be anticipated to cause or contribute to 
any visibility impairment in a Class I area.
    On July 6, 2005, 70 FR 39104, EPA published the Guidelines for BART 
Determinations Under the Regional Haze Rule at appendix Y to 40 CFR 
part 51 (hereinafter referred to as the ``BART Guidelines'') to assist 
states and EPA in determining which sources should be subject to the 
BART requirements and in determining appropriate emission limits for 
each source subject to BART.
    The process of establishing BART emission limitations follows three 
steps. First, states, or EPA if developing a FIP, must identify and 
list ``BART-eligible sources.'' \3\ Once the state or EPA has 
identified the BART-eligible sources, the second step is to identify 
those sources that may ``emit any air pollutant which may reasonably be 
anticipated to cause or contribute to any impairment of visibility'' in 
a Class I area. (Under the Regional Haze Rule, a source which fits this 
description is ``subject to BART.''). Third, for each source subject to 
BART, the state or EPA must identify the level of control representing 
BART after considering the five factors set forth in CAA section 
169A(g). The BART Guidelines provide a process for making BART 
determinations that states can use in implementing the BART 
requirements on a source-by-source basis. See 40 CFR part 51, appendix 
Y, at IV.D.
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    \3\ ``BART-eligible sources'' are those sources that have the 
potential to emit 250 tons or more of a visibility-impairing air 
pollutant, were not in operation prior to August 7, 1962, but were 
in existence on August 7, 1977, and whose operations fall within one 
or more of 26 specifically listed source categories. 40 CFR 51.301.
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    States, or EPA if developing a FIP, must address all visibility-
impairing pollutants emitted by a source in the BART determination 
process. The most significant visibility impairing pollutants are 
SO2, NOX, and particulate matter (PM).
    A state implementation plan (SIP) or FIP addressing regional haze 
must include source-specific BART emission limits and compliance 
schedules for each source subject to BART. Once a state or EPA has made 
a BART determination, the BART controls must be installed and operated 
as expeditiously as practicable, but no later than five years after the 
date of the final SIP or FIP. See CAA section 169A(g)(4) and 40 CFR 
51.308(e)(1)(iv). In addition to what is required by the Regional Haze 
Rule, general SIP requirements mandate that the SIP or FIP include all 
regulatory requirements related to monitoring, recordkeeping, and 
reporting for the BART controls on the source. See CAA section 110(a).

B. BART FIP for Taconite Facilities in Michigan and Minnesota

    EPA is proposing to finalize NOX and/or SO2 
limits for the indurating furnaces at five taconite facilities in 
accordance with the procedures set forth in the FIP addressing the 
requirement for BART at taconite facilities. These facilities include 
Tilden Mining Company (Tilden) located at 101 Cci Mine Road, Ishpeming, 
Michigan; Hibbing Taconite Company (Hibbing) located at 4950 Highway 5 
North, Hibbing, Minnesota; Minorca Mine (Minorca) located at 5950 Old 
Highway 53, Virginia, Minnesota; Northshore Mining Company--Silver Bay 
(Northshore) located at 10 Outer Drive, Silver Bay, Minnesota, and 
United Taconite (UTAC) located at 8470 Townline Road, Forbes, 
Minnesota. Tilden, Minorca, Northshore, and UTAC are owned by 
Cleveland-Cliffs, Inc. (Cliffs), formerly known as Cliffs Natural 
Resources, and Hibbing is jointly owned by Cliffs and United States 
Steel. The primary units identified as being subject to BART at Tilden, 
Hibbing, Minorca, UTAC, and Northshore include the following 
pelletizing, or indurating, furnaces: Tilden Grate Kiln Line 1, Hibbing 
Straight-Grate Lines 1-3, Minorca Straight-Grate Line 1, UTAC Grate 
Kiln Lines 1 and 2, and Northshore Straight-Grate Furnaces 11 and 
12.\4\ The U.S. taconite iron ore industry uses two types of 
pelletizing machines or processes: straight-grate kilns and grate 
kilns. In a straight-grate kiln, a continuous bed of agglomerated green 
pellets is carried through different temperature zones with upward 
draft or downward draft blown through the pellets on the metal grate. 
The grate kiln system consists of a traveling grate, a rotary kiln, and 
an annular cooler. A significant difference between these designs is 
that straight-grate kilns do not burn coal and therefore have a much 
lower potential for emitting SO2. Further, even within the 
same kiln type or process, individual furnaces (referred to as 
indurating or pelletizing) or processes have distinct equipment and 
process characteristics that may affect the compatibility and 
performance of certain types of burners.
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    \4\ Fuel sulfur content BART limits were also set for two 
process boilers and a line dryer at Tilden. Those limits are not 
impacted by this action.
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    On February 6, 2013 (78 FR 8706), EPA promulgated a FIP that set 
BART limits for NOX and SO2 emissions from 
furnaces at seven taconite facilities in Michigan and Minnesota 
(``Original FIP''). EPA took this action because Michigan and Minnesota 
had failed to meet a statutory deadline to submit their Regional Haze 
SIPs and subsequently failed to require BART at the taconite facilities 
within their borders. BART limits for NOX were based upon 
the performance of high stoichiometric (high-stoich) low-NOX 
burners (LNBs) \5\ at two of the taconite furnaces at U.S. Steel's 
Minntac facility, while BART for SO2 was established as no 
additional controls, apart from a limit on the sulfur content of coal 
used in co-firing furnaces.
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    \5\ Stoichiometry refers to the relationship between the actual 
quantity of combustion air to the theoretical minimum quantity of 
air needed for 100 percent combustion of the fuel.
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    In a related action, EPA published a final partial disapproval of 
Michigan's and Minnesota's Regional Haze SIPs on September 30, 2013 (78 
FR 59825), due to the states' failure to require BART for taconite 
facilities within these states.
    ArcelorMittal USA LLC (``ArcelorMittal'') \6\ and Cliffs, owners of 
several taconite facilities affected by the FIP, along with the State 
of Michigan,

[[Page 96155]]

filed timely petitions for review of the Original FIP. ArcelorMittal 
and Cliffs also filed a joint motion seeking a stay of the Original 
FIP, which was granted by the Eighth Circuit on June 14, 2013.\7\ 
ArcelorMittal, Cliffs, the State of Michigan, and others also submitted 
petitions for reconsideration of the Original FIP, pursuant to CAA 
section 307(d)(7)(B). 42 U.S.C. 7607(d)(7)(B).
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    \6\ Cliffs acquired ArcelorMittal Steel Production Company in 
2020. Previously, Minorca was owned by ArcelorMittal and Hibbing was 
jointly owned by ArcelorMittal, Cliffs and United States Steel. 
Currently, Minorca is owned by Cliffs and Hibbing is jointly owned 
by Cliffs and United States Steel.
    \7\ On November 15, 2016, the 8th Circuit Court of Appeals 
terminated the June 14, 2013, stay and extended the deadlines in the 
Original FIP by one day for each day the court's stay was in place. 
From the day the 2013 FIP was effective to the day it was stayed, 98 
days elapsed (March 8, 2013, to June 14, 2013). See Order dated 
November 15, 2016, in response to U.S. EPA's Petition to reconsider 
the Original FIP, EPA-R05OAR-2017-0066-0009 (8th Cir. 2016). As a 
result, the deadlines contained in the Original FIP still apply 
(e.g., 6 months after March 8, 2013), only now from the date the 
stay was terminated, minus the number of days that elapsed prior to 
the stay being issued.
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    On October 22, 2015 (80 FR 64160), in response to the petitions for 
reconsideration and due to new information submitted to EPA after 
promulgation of the Original FIP, EPA proposed to revise the Original 
FIP to revise NOX and SO2 emission limits for 
certain taconite facilities. On April 16, 2016 (81 FR 21672), EPA 
promulgated the final 2016 revised FIP (``2016 FIP''). With respect to 
NOX, the emission limits in the 2016 FIP were based on 
information submitted to EPA by Cliffs and ArcelorMittal that suggested 
high-stoich LNBs, which formed the basis for the NOX limits 
in the Original FIP, posed serious technical hurdles. In the 2016 FIP, 
EPA revised the NOX emission limits for Tilden, Hibbing, 
Minorca, and UTAC, and set forth a process to confirm or modify those 
emission limits using continuous emissions monitoring system (CEMS) 
data that was to be collected after the installation of the selected 
low-NOX technology. Under the 2016 FIP, the NOX 
emission limits do not become enforceable until EPA confirms or 
modifies the emission limits in accordance with procedures set forth in 
the FIP. The NOX emission limits in the 2016 FIP were based 
upon low-stoich LNBs (for grate kilns) and LNBs that utilize a 
combination of water and steam injection and pre-combustion 
technologies (for straight-grate kilns).
    With respect to SO2, EPA granted reconsideration of the 
SO2 limit for Tilden's grate kiln due to information that 
became available after the close of the public comment period on the 
2013 FIP regarding Tilden's intent to burn mixed fuels. Cliffs' intent 
to burn mixed fuels at Tilden was not considered in the Original FIP 
and would have led to an inability to meet the established BART limit. 
The 2016 FIP limits the sulfur content of the coal combusted on Tilden 
Line 1 and sets an SO2 emission limit for the furnace.
    Cliffs and ArcelorMittal filed petitions for review of the 2016 FIP 
due to a dispute over the UPL equation in the final rule. The 2016 FIP 
requirements for each facility are set forth in 40 CFR 52.1183 for 
Michigan and 40 CFR 52.1235 for Minnesota and discussed further in the 
remainder of this action.

II. Basis for NOX Limits

    The 2016 FIP set emission limits in pounds (lbs) of NOX 
per million British Thermal Unit (MMBtu), based on a 30-day (720-hour) 
rolling average, and established a process to either confirm or modify 
the NOX emission limits within established ranges based on 
CEMS data that Tilden, Hibbing, Minorca, and UTAC were required to 
submit to EPA by dates specified in the 2016 FIP.\8\ The FIP also 
specified that the NOX emission limits for these facilities 
would become enforceable only after EPA's confirmation or modification 
of the NOX emission limits reflecting EPA's expectation that 
the owner or operator of each facility would provide the requisite data 
to EPA by the dates specified in the FIP. EPA's efforts to finalize 
NOX emission limits for these facilities by the deadlines 
established in the FIP were complicated by several implementation 
issues, including challenges with installation of control technology, 
delays in receipt of requisite data, and emission limit modification 
requests not conforming to the requirements set forth in the FIP.
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    \8\ Taconite facilities typically operate 24 hours per day and 
720 is the number of hours in a 30-day period; therefore, a 720-hour 
average is essentially equivalent to a 30-day average.
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    The NOX emission limits established for each furnace and 
the ranges of limits allowable under the limit modification process are 
set forth in Table 1. As indicated in Table 1, the emission limits for 
certain furnaces vary by the type of fuel being used (natural gas or 
``co-fire,'' which is a combination of natural gas and coal).

  Table 1--NOX Limits and Limit Modification Ranges Established in the
                                2016 FIP
------------------------------------------------------------------------
                                                       Emission limit
           Furnace            Emission limit  (lbs   modification range
                                   NOX/MMBtu)          (lbs NOX/MMBtu)
------------------------------------------------------------------------
Tilden Line 1:
    Natural Gas.............                   2.8               2.8-3.0
    Co-fire.................                   1.5               1.5-2.5
Hibbing Line 1..............                   1.2               1.2-1.8
Hibbing Line 2..............                   1.2               1.2-1.8
Hibbing Line 3..............                   1.2               1.2-1.8
    Minorca.................                   1.2               1.2-1.8
UTAC Line 1:
    Natural Gas.............                   2.8               2.8-3.0
    Co-fire.................                   1.5               1.5-2.5
UTAC Line 2:
    Natural Gas.............                   2.8               2.8-3.0
    Co-fire.................                   1.5               1.5-2.5
------------------------------------------------------------------------

    For Tilden, Hibbing, Minorca, and UTAC, the process specified in 
the 2016 FIP to either confirm or modify the NOX emission 
limits within the established ranges included the installation of a 
CEMS, submission of an engineering report to EPA, installation of 
NOX reduction control technology, submission of pellet 
quality analyses to EPA, and submission to EPA of a report to either 
confirm or modify the limit. For any furnace without CEMS already 
installed, CEMS installation was required for each furnace by 6 months 
after May 12, 2016, and the owner or operator was required to submit 
quarterly CEMS data to EPA after May 12, 2016, for the time periods 
specified

[[Page 96156]]

below in Table 2. Engineering reports containing detailed engineering 
analyses and modeling of the selected NOX reduction 
technology for each furnace demonstrating that the technology was 
designed to meet an emission limit equal to the lower bound of the 
established range were required to be submitted to EPA by the deadlines 
specified in Table 2. NOX reduction technology was required 
to be installed two months after the engineering report submission 
deadline. Beginning on the earlier of six months after the installation 
of NOX reduction technology or the deadline for installation 
of the NOX reduction technology, the owner or operator was 
required to submit quarterly pellet quality analyses to EPA, including 
an explanation of causes for pellet samples that failed to meet the 
acceptable range for any pellet quality analysis factor, for the time 
periods specified in Table 2. At the end of the CEMS and pellet quality 
data collection periods, the owner or operator of each furnace may 
submit a report to EPA to either confirm or modify the NOX 
limits within the bounds described in the 2016 FIP (and above in this 
section). The 2016 FIP also allows the owner or operator to submit a 
report proposing a single NOX limit for all fuels. The 
process for confirming or modifying limits detailed in the 2016 FIP 
specifies that EPA's determinations shall be based on the appropriate 
UPL equation, using CEMS data that meet pellet quality specifications 
and proper furnace/burner operation. For a more detailed description of 
the process set forth in the 2016 FIP to confirm or modify the emission 
limits, see 40 CFR 52.1183 and 40 CFR 52.1235.

                           Table 2--Timelines of Processes To Confirm or Modify Limits
----------------------------------------------------------------------------------------------------------------
                                                                                     Period of
                                  Period of CEMS                   NOX reduction      pellet         Report to
                                   data required    Engineering     technology     quality data     confirm or
             Furnace                    for           report       installation    required for    modify limit
                                  submission  to     deadline        deadline      submission to     deadline
                                        EPA                                            EPA *
----------------------------------------------------------------------------------------------------------------
                                                             Months after May 12, 2016
                                 -------------------------------------------------------------------------------
Tilden Line 1...................            0-57              48              50           50-57              57
Hibbing Line 1..................            6-34              24              26           26-34              34
Hibbing Line 2..................            6-52              42              44           44-52              52
Hibbing Line 3..................            6-57              48              50           50-57              57
Minorca's Indurating Furnace....            6-52              42              44           44-52              52
UTAC Line 1.....................            0-34              24              26           26-34              34
UTAC Line 2.....................            0-52              42              44           44-52              52
----------------------------------------------------------------------------------------------------------------
* If the owner or operator installed NOX reduction technology more than six months before the required date,
  pellet quality analyses were required to be submitted to EPA beginning six months after installation.

    The 2016 FIP incorporates two UPL equations to calculate emission 
limits. The appropriate equation is determined by the statistical 
distribution of the hourly CEMS data. If the data are normally 
distributed and statistically independent, the equation in 40 CFR 
52.1183(p)(1) and 40 CFR 52.1235(f)(1) is used. If the data are not 
normally distributed or are normally distributed but not statistically 
independent, the non-parametric equation in 40 CFR 52.1183(p)(2) and 40 
CFR 52.1235(f)(2) is used. None of the CEMS data submitted are normally 
distributed and statistically independent, therefore the non-parametric 
equation is the applicable equation for all limit setting in this 
action.\9\
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    \9\ Data distribution analyses are available in the docket for 
this action.
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    The non-parametric equation in the 2016 FIP calculates a 95th 
percentile UPL by ranking 720-hour averages of NOX emissions 
in lbs/MMBtu from lowest to highest and identifying the value at the 
95th percentile of the data set as the UPL and emission limit.\10\ 
While a 95th percentile UPL establishes an emission rate that a source 
is predicted to be below during at least 95 out of 100 averaging 
periods, it was not EPA's intent to set a limit that a source would be 
expected to exceed five percent of the time once the limit was in 
place. Rather, EPA used the 95th percentile UPL to ensure that the 
final emission limits would be consistent with the actual emission 
reduction capabilities of the BART controls, as required by 40 CFR 
51.301, which defines BART as ``the degree of reduction achievable.'' 
\11\ EPA expected that during the eight-month CEMS data collection 
period, furnace operators would be adjusting numerous variables to 
optimize control technology performance, which would result in higher 
emissions at times during the initial ``shakedown'' period. Once the 
eight-month data collection period was over, EPA expected that the 
operators would have gained sufficient experience to run the furnaces 
and control technologies with fewer adjustments, meaning less emission 
variations and lower emissions overall. EPA selected the 95th 
percentile UPL to ensure the elevated emissions expected during the 
initial shakedown period would not become the basis for final emission 
limits.
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    \10\ Taconite facilities typically operate 24 hours per day and 
720 is the number of hours in a 30-day period; therefore, a 720-hour 
average is essentially equivalent to a 30-day average. For 
facilities that both burn natural gas exclusively and co-fire with 
coal, i.e., Tilden and UTAC, a 30-day period may involve operation 
with only natural gas as well as operation with co-firing of coal. 
Therefore, the 2016 FIP established UPL equations based on 720-hour 
averages to allow for the separation of hours when burning only 
natural gas from hours when co-firing with coal. When calculating an 
emission limit that applies only when burning natural gas, emissions 
are averaged over 720 successive hours in which the unit burns only 
natural gas. When calculating a co-firing emission limit, emissions 
are averaged over 720 successive hours in which the unit burns a 
gas/coal mix. All emission limit modifications were calculated based 
on 720-hour averages, consistent with the equations at 40 CFR 
52.1183(p) and 40 CFR 52.1235(f). However, EPA is proposing modified 
emission limits in the form of a 30-day average if the facility 
burns only one fuel or if the modified limit applies to all fuels. 
In those circumstances, there is no need to be able to separate the 
hourly data to determine compliance with the emission limit.
    \11\ April 16, 2016, 81 FR 21672, 21680.
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    However, once continuous data collection began, the CEMS data did 
not show the expected elevated emissions levels during the shakedown 
period and emissions were not consistently lower toward the end of the 
data collection period as compared to the beginning of the period.\12\ 
Therefore, EPA has

[[Page 96157]]

determined that using the UPL equation at the 99th percentile is more 
appropriate to establish an emission limit consistent with the actual 
emission reduction capabilities of the BART controls and is proposing 
to modify the UPL equations used to calculate both the NOX 
and SO2 emission limits to reflect use of the 99th 
percentile. The emission limits EPA is proposing in this action were 
calculated using the UPL equations at 40 CFR 52.1183(p) and 40 CFR 
52.1235(f) at the 99th percentile.\13\
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    \12\ See emission limit calculation files in the docket for this 
action.
    \13\ Data analyses and emissions calculations are available in 
the docket for this action.
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A. Tilden

    For Tilden's indurating furnace, Tilden Line 1 (EUKILN1), the 2016 
FIP established a specific NOX BART emission limit of 2.8 
pounds of NOX/MMBtu when burning natural gas, while allowing 
for potential modification of the limit within the range of 2.8-3.0 lbs 
NOX/MMBtu. Similarly, the 2016 FIP established a specific 
NOX BART emission limit of 1.5 lbs NOX/MMBtu when 
co-firing coal and natural gas, with an allowance for potential 
modification of the limit within the range of 1.5-2.5 lbs 
NOX/MMBtu.\14\ The 2016 FIP also allowed for the 
establishment of a single NOX limit for all fuels.\15\
---------------------------------------------------------------------------

    \14\ 40 CFR 52.1183(k)(1).
    \15\ 40 CFR 52.1183(k)(1)(viii).
---------------------------------------------------------------------------

    Tilden submitted a partially complete engineering report on May 21, 
2020, and submitted the final engineering report on July 30, 2020. 
Tilden implemented low-stoichiometry LNBs designed to achieve an 
emission rate of 2.8 lbs NOX/MMBtu when firing exclusively 
natural gas and 1.5 lbs NOX/MMBtu when co-firing with coal, 
as described in the engineering report submitted to EPA.
    On February 12, 2021, Tilden submitted a report requesting 
modification of the NOX limits for Line 1 pursuant to 40 CFR 
52.1183 (k)(1)(vi). Tilden requested an emission limit of 3.0 lbs 
NOX/MMBtu for all fuels. Tilden's limit modification request 
was accompanied by CEMS data (in 30-day rolling averages) from 
September 12, 2020, to February 2, 2021. On May 21, 2021, Tilden 
provided hourly emission data for July 1, 2020, to February 11, 2021. 
Approximately half of these data were collected when Tilden was co-
firing with coal and half were collected when Tilden was burning 
exclusively natural gas. Tilden demonstrated that when burning natural 
gas, NOX emission rates recorded were higher than the 
modeling results presented in the engineering report, and above the 
high end of the limit range established in the 2016 FIP (2.8-3.0 lbs/
MMBtu). The CEMS data submitted to EPA when burning coal recorded 
emission rates within the range specified in the 2016 FIP (1.5-2.5 lbs/
MMBtu). Tilden explained that the furnace is unable to achieve 3.0 lbs 
NOX/MMBtu when burning exclusively natural gas and would 
need to burn a minimum of 80% coal when co-firing to meet a limit of 
2.0 lbs NOX/MMBtu. Tilden stated a preference to maximize 
natural gas usage and supplement with solid fuel as needed to meet 
NOX limits.\16\
---------------------------------------------------------------------------

    \16\ See ``Tilden NOX limit modification report (Feb. 
12, 2021)_Redacted.pdf,'' available in the docket for this action.
---------------------------------------------------------------------------

    The 2016 FIP provides Tilden the option to propose, for EPA's 
consideration and approval, a single NOX emission limit for 
all fuels based on a 30-day rolling average. Citing the CEMS data, 
Tilden requested a revised NOX BART limit of 3.0 lbs 
NOX/MMBtu for all fuels that would apply on a rolling 30-day 
average, contending that this emission limit is the most stringent 
limit that can be met without substantial increases in coal usage, 
while maintaining pellet quality standards.
    Based on the equation set forth at 40 CFR 52.1183(p)(2), EPA 
calculated a 720-hour average NOX emission limit of 3.8 lbs 
NOX/MMBtu when burning exclusively natural gas, and 
separately, an emission limit of 1.9 lbs NOX/MMBtu when 
burning mixed fuel.\17\ While CEMS data show the installed emission 
control measures reduced NOX emissions, the selected 
technology failed to achieve emission rates within the specified FIP 
ranges when burning only natural gas (2.8-3.0 lbs NOX/
MMBtu). Using the non-parametric equation with the full data set, 
unseparated by fuel type, EPA calculated a 720-hour average UPL of 3.7 
lbs NOX/MMBtu. EPA evaluated these CEMS data and considered 
Tilden's requested single NOX emission limit of 3.0 lbs 
NOX/MMBtu for all fuels based on a 30-day rolling average, 
as allowed at 40 CFR 52.1183(k)(1)(viii). EPA has concluded that 
Tilden's requested emission limit of 3.0 lbs NOX/MMBtu for 
all fuels based on a 30-day rolling average is appropriate and reflects 
BART. It allows Tilden to select a fuel mix that maximizes natural gas 
usage and minimizes coal usage if the facility so chooses without 
exceeding the natural gas emission limit range established in the 2016 
FIP. This has the duel environmental (visibility) benefit of minimizing 
NOX emissions by setting an emissions limit that is below 
the calculated natural gas-only rate, and also potentially minimizing 
the use of coal and the associated SO2 emissions from coal 
burning. Therefore, based on these data and as provided at 40 CFR 
52.1183(k)(1)(viii), EPA is proposing that a modified limit of 3.0 lbs 
NOX/MMBtu for all fuels, with compliance to be determined on 
a rolling 30-day average basis, reflects BART for the Tilden Line 1 
indurating furnace.
---------------------------------------------------------------------------

    \17\ See Tilden Emission Limit Calculations, available in the 
docket for this action.
---------------------------------------------------------------------------

B. Hibbing

    For Hibbing Lines 1, 2, and 3, the 2016 FIP established 
NOX BART emission limits of 1.2 lbs NOX/MMBtu 
that applied to each furnace individually, with provisions allowing for 
potential modification of the limits within the range of 1.2-1.8 lbs 
NOX/MMBtu.\18\
---------------------------------------------------------------------------

    \18\ See 40 CFR 52.1235((b)(1)(ii).
---------------------------------------------------------------------------

    Hibbing implemented the NOX reduction measures described 
in its engineering report, submitted to EPA on May 11, 2018, identified 
as LNBs in conjunction with water injection, at Hibbing Lines 1, 2, and 
3. Hibbing installed CEMS on Lines 1, 2, and 3 and provided EPA with 
hourly NOX emissions data on March 12, 2019, September 11, 
2020, and February 12, 2021, for Lines 1, 2 and 3, respectively, 
documenting actual emissions after installation of LNB technology. 
Hibbing's submittals included CEMS data from July 12, 2018, to March 
11, 2019, for Line 1; January 12, 2020, through September 1, 2020, for 
Line 2; and August 3, 2020, to February 11, 2021, for Line 3. The 
hourly CEMS data identified hours excluded from the limit-setting 
calculations because pellets failed to meet pellet quality 
specifications. Although the limit-setting period for Line 3 
established in the 2016 FIP began August 3, 2020, Line 3 did not 
operate during the period between July 12 to August 3, 2020, due to 
COVID-related reasons. Line 2 did not operate from May 1, 2020, to July 
31, 2020, during the limit setting period for similar reasons. On 
November 25, 2020, Hibbing provided additional information requested by 
EPA, including hourly CEMS data for Lines 1, 2, and 3 in Excel format 
to facilitate independent calculation of emission limits and 
identification of hours when the burner was not operated within the 
parameters modeled in the engineering report.
    The requirements at 40 CFR 52.1235((b)(1)(ii)(A)(6), (B)(6), and 
(C)(6) set forth the process for submitting data to support limit 
modifications under the 2016 FIP. At the time of the initial

[[Page 96158]]

CEMS data submissions, Hibbing requested NOX emission limits 
of 1.7, 1.5, and 1.6 lbs NOX/MMBtu on Lines 1, 2, and 3, 
respectively. The facility cited sub-zero temperatures and other 
factors that may have affected the calculated emission rates and 
restricted production. Further, Hibbing provided regression analyses 
assessing the relationship between furnace feed rates and 
NOX emission rates during the limit-setting periods to 
support the requested limit increases.
    On October 22, 2021, Hibbing submitted a request to EPA to 
establish a crossline average emission limit for Lines 1, 2, and 3 of 
1.6 lbs NOX/MMBtu, with compliance to be determined on a 30-
day rolling average basis. The submittal included hourly CEMS data for 
the same time periods as Hibbing's initial limit modification 
submittals and a regression analysis assessing the relationship between 
furnace feed rates and NOX emission rates during the limit-
setting periods to support the requested limit increases. The hourly 
CEMS data submitted to EPA included a description of the failure 
analyses identifying potential reasons for pellets failing to meet 
pellet quality specifications for hours excluded in the limit-setting 
calculation.
    There is no basis in the FIP for adjusting emission limits to 
account for possible future production levels based upon an assumed 
correlation between feed rates and emissions. Therefore, in accordance 
with 40 CFR 52.1235(f)(2), EPA calculated 720-hour average 
NOX emission limits of 1.5 lbs NOX/MMBtu for Line 
1, 1.4 lbs NOX/MMBtu for Line 2, and 1.5 lbs NOX/
MMBtu for Line 3.\19\ Under the BART Guidelines, a source may be 
permitted to `` `average' emissions across any set of BART-eligible 
emission units within a fenceline, so long as the emission reductions 
from each pollutant being controlled for BART would be equal to those 
reductions that would be obtained by simply controlling each of the 
BART-eligible units that constitute BART-eligible sources.'' \20\ EPA 
averaged the single line limits described above and calculated a 
crossline 720-hour average emission limit of 1.5 lbs NOX/
MMBtu. The NOX controls have been installed and are being 
operated on all three lines. Based on EPA's analysis, this crossline 
average emission limit is equal to the reductions that would be 
obtained by controlling each line separately. Therefore, based on these 
data and as provided at 40 CFR 52.12335(b)(1)(ii)(A)(7), (B)(7), and 
(C)(7), and consistent with 40 CFR 51.308(e) and 40 CFR part 51, 
appendix Y, at V, EPA is proposing that a crossline average emission 
limit of 1.5 lbs NOX/MMBtu for Hibbing Lines 1, 2, and 3, 
with compliance to be determined on a 30-day rolling average basis, 
reflects NOX BART for Hibbing Lines 1, 2, and 3.
---------------------------------------------------------------------------

    \19\ See Hibbing Emission Limit Calculations, available in the 
docket for this action.
    \20\ 40 CFR part 51, appendix Y, at V.
---------------------------------------------------------------------------

C. Minorca

    For Minorca's indurating furnace, the 2016 FIP established a 
NOX BART emission limit of 1.2 lbs NOX/MMBtu, 
while allowing for potential modification of the limit within the range 
of 1.2-1.8 lbs NOX/MMBtu.\21\
---------------------------------------------------------------------------

    \21\ See 40 CFR 52.1235((b)(1)(v).
---------------------------------------------------------------------------

    On November 12, 2019, Minorca submitted an engineering report to 
EPA which identified the low NOX technology to be installed 
on Line 1 as an LNB, water injection, and utilization of specific 
operating parameters. The combined use of these measures was projected 
to meet an emission limit of 1.2 lbs NOX/MMBtu based on a 
30-day average. On September 11, 2020, Minorca submitted CEMS data for 
the period January 12, 2020, to September 10, 2020, excluding the CEMS 
values that did not meet pellet quality specifications, consistent with 
the 2016 FIP.\22\
---------------------------------------------------------------------------

    \22\ CEMS data in the September 11, 2020, submittal was 
presented as 720-hour rolling averages. On November 25, 2020, 
Minorca provided the hourly CEMS data for the same January 12, 2020, 
to September 10, 2020, time period to allow for independent 
calculation of 720-hour averages.
---------------------------------------------------------------------------

    On October 22, 2021, Minorca submitted supplemental information 
consisting of 720-hour averages of CEMS data from January 12, 2020, 
through September 30, 2021. Adding the data from September 10, 2020, 
through September 30, 2021, to the original data set, Minorca 
calculated an emission limit of 1.6 lbs NOX/MMBtu using the 
equation at 40 CFR 52.1235(f)(2). Minorca then performed a regression 
analysis assessing the relationship between furnace pellet production 
rates and NOX emission rates during the limit-setting period 
to support the requested limit increase. Minorca cited the climate in 
Minnesota and other factors that may have affected production rates in 
its explanation of why the emission limit should be adjusted to 1.7 lbs 
NOX/MMBtu.
    Based on the non-parametric equation at 40 CFR 52.1235(f)(2), EPA 
evaluated the 720-hour average NOX emission data for the 
full data set submitted and calculated an emission limit of 1.6 lbs 
NOX/MMBtu.\23\ There is no basis in the FIP for adjusting 
emission limits to account for possible future production levels based 
upon an assumed correlation between feed rates and emissions. 
Therefore, based on these data and as provided at 40 CFR 
52.1235(b)(1)(v)(7), EPA is proposing that a modified limit of 1.6 lbs 
NOX/MMBtu, with compliance to be determined on a rolling 30-
day average basis, reflects BART for the Minorca Line 1 indurating 
furnace.
---------------------------------------------------------------------------

    \23\ See Minorca Emission Limit Calculations, available in the 
docket for this action.
---------------------------------------------------------------------------

D. UTAC

    For UTAC's indurating furnaces, Grate Kiln Line 1 (EU040) and Grate 
Kiln Line 2 (EU042), the 2016 FIP established specific NOX 
BART limits of 2.8 pounds of NOX/MMBtu when burning natural 
gas, while allowing for potential modification of the limits within the 
range of 2.8-3.0 lbs NOX/MMBtu. Similarly, the 2016 FIP 
established specific NOX BART limits of 1.5 lbs 
NOX/MMBtu when co-firing coal and natural gas, while 
allowing for potential modification of the limits within the range of 
1.5-2.5 lbs NOX/MMBtu.\24\ The 2016 FIP also allowed for the 
establishment of a single NOX limit for all fuels.
---------------------------------------------------------------------------

    \24\ 40 CFR 52.1235(b)(1)(iv).
---------------------------------------------------------------------------

    UTAC submitted an engineering report for Line 1 on May 11, 2018. 
UTAC installed and began operating the sub-stoichiometric staged 
combustion LNB designed to achieve an emission rate of 2.8 lbs 
NOX/MMBtu when firing exclusively natural gas and 1.5 lbs 
NOX/MMBtu when co-firing with coal, as described in the 
engineering report submitted to EPA. UTAC subsequently made 
modifications to the Line 1 LNB in September 2018. On March 12, 2019, 
UTAC submitted a report requesting modification of the co-firing 
NOX limit for Line 1 to 2.5 lbs NOX/MMBtu, based 
upon 720-hour averages from February 2019.
    On November 12, 2019, UTAC submitted a report to EPA to address the 
requirement for an engineering report for Line 2. On November 12, 2021, 
UTAC submitted information on the LNB selected for Line 2, a modified 
version of the LNB installed on Line 1. This submittal included a 
report on computational fluid dynamics modeling demonstrating the 
burner was designed to achieve an emission rate of 2.8 lbs 
NOX/MMBtu when firing exclusively natural gas and 1.5 lbs 
NOX/MMBtu when co-firing with coal. On April 11, 2023, UTAC 
submitted an analysis of Line 1 and Line 2 NOX performance

[[Page 96159]]

post LNB installations and requested a crossline average limit of 3.0 
lb NOX/MMBtu for all fuels, based on a 30-day rolling 
average. Along with the analysis, UTAC submitted 720-hour averages of 
total lbs NOX/MMBtu for Lines 1 and 2 combined for the time 
period of January 25, 2022, to March 26, 2023. UTAC also submitted 
hourly CEMS and process information for this time period, which UTAC 
claimed as confidential business information, so that EPA could verify 
the calculations.
    Based on the equation set forth at 40 CFR 52.1235(f)(2), EPA 
calculated 720-hour average NOX emission limits of 2.3 lbs 
NOX/MMBtu and 3.6 lbs NOX/MMBtu when burning 
exclusively natural gas for Lines 1 and 2, respectively. Separately, 
EPA calculated an emission limit of 3.1 lbs NOX/MMBtu when 
burning mixed fuel on Line 2. There were 475 hours of co-firing data 
for Line 1, which is not sufficient to calculate a 720-hour average 
NOX emission limit. EPA also calculated an emission limit of 
3.1 lbs NOX/MMBtu when combining hourly emissions data for 
both lines and all fuels.\25\ While CEMS data show the installed 
emission control measures reduced NOX emissions, the 
selected technology failed to achieve emission rates within the 
specified FIP ranges, particularly when evaluating separate limits for 
each fuel type.
---------------------------------------------------------------------------

    \25\ See United Taconite Emission Limit Calculations, available 
in the docket for this action.
---------------------------------------------------------------------------

    As discussed in II.B., under the BART Guidelines, a source may be 
permitted to `` `average' emissions across any set of BART-eligible 
emission units within a fenceline, so long as the emission reductions 
from each pollutant being controlled for BART would be equal to those 
reductions that would be obtained by simply controlling each of the 
BART-eligible units that constitute BART-eligible sources.'' \26\ EPA 
evaluated the CEMS data and considered UTAC's requested crossline 
average NOX emission limit of 3.0 lbs NOX/MMBtu 
for all fuels, for Lines 1 and 2, with compliance to be determined on a 
30-day rolling average basis. Based on EPA's analysis, this crossline 
average emission limit is equal to the reductions that would be 
obtained by controlling each line separately and is within the natural 
gas NOX emission limit range established in the 2016 FIP. A 
single fuel-neutral emission limit allows UTAC to select a fuel mix 
that maximizes natural gas usage and minimizes coal usage without 
exceeding the natural gas emission limit range established in the 2016 
FIP. This has the dual environmental (visibility) benefit of minimizing 
NOX emissions by setting an emissions limit that is below 
the calculated natural gas-only rate, and also potentially minimizing 
the use of coal and the associated SO2 emissions from 
burning coal. Therefore, based on these data and as provided at 40 CFR 
52.1235(b)(1)(iv)(A)(8) and (B)(8), and consistent with 40 CFR 
51.308(e) and 40 CFR part 51, appendix Y, at V, EPA is proposing that a 
crossline emission limit of 3.0 lbs NOX/MMBtu for all fuels 
for UTAC Lines 1 and 2, based on a rolling 30-day average, reflects 
BART for UTAC Lines 1 and 2.
---------------------------------------------------------------------------

    \26\ 40 CFR part 51, appendix Y, at V.
---------------------------------------------------------------------------

III. Basis for SO2 Limits

    As previously described, the Original FIP determined that existing 
controls reflected SO2 BART for Minorca, Hibbing, and 
Northshore, and established SO2 emission limits for each 
furnace, with the option or requirement, depending on the facility, 
that the owner or operator submit one year of CEMS data to EPA to set a 
revised SO2 emission limit calculated using the appropriate 
UPL equation. The 2016 FIP limited the sulfur content of the coal 
burned at Tilden, set an SO2 emission limit, and required 
Tilden to submit one year of CEMS data to EPA to set a revised 
SO2 emission limit calculated using the appropriate UPL 
equation. For a more detailed description of the existing 
SO2 emission limits and the process set forth to modify the 
emission limits, see 40 CFR 52.1235 (Hibbing, Minorca, and Northshore) 
and 40 CFR 52.1183 (Tilden). As discussed above in II., EPA has 
calculated the emission limits using the appropriate UPL equation at 
the 99th percentile.

A. Tilden

    For Tilden, the 2016 FIP established a specific SO2 BART 
emission limit of 500 pounds of SO2 per hour (lbs/hr) for 
Grate Kiln Line 1, with no more than 0.60 percent sulfur by weight 
based on a monthly block average for any coal usage. The 2016 FIP also 
required that the owner or operator of Tilden calculate an 
SO2 emission limit based on one year of hourly CEMS 
emissions data using the appropriate UPL equation provided in 40 CFR 
52.1183(p) and submit such calculations and data to EPA by 36 months 
after May 12, 2016. The 2016 FIP provides that EPA may revise the 
emission limit downward to reflect the calculated SO2 
emission rate; however, EPA may not increase the SO2 limit 
above 500 lbs SO2/hr.
    On October 1, 2018, Tilden submitted SO2 emissions data 
to EPA reflecting Tilden burning exclusively natural gas during the 
period March 28, 2017, through March 27, 2018. Citing various 
production-related concerns, Tilden adjusted its calculated limit to 
account for expected higher production capacity and higher ore sulfur 
content, which resulted in an adjusted expected emission rate of 568 
lbs SO2/hr. Tilden requested an SO2 emission 
limit of 500 lbs/hour for all fuels, regardless of natural gas or coal 
fuel usage, as established in the 2016 FIP. On November 10, 2022, 
Tilden submitted hourly SO2 data for Line 1 from the same 
time period of March 28, 2017, through March 27, 2018, during which 
time Tilden was exclusively burning natural gas. On March 1, 2023, 
Tilden provided hourly co-firing CEMS data for July 12, 2018, through 
July 11, 2019. On March 30, 2023, Tilden provided hourly CEMS data for 
the time period March 27, 2018, through March 26, 2019, which included 
both co-firing and natural gas-only operation.
    The 2016 FIP established a single SO2 emission limit to 
apply regardless of natural gas or coal fuel usage, which Tilden must 
meet at all times. Consistent with this approach, and because 
SO2 emissions are higher when Tilden is co-firing and the 
emission limit must be met at all times, EPA is proposing to base the 
emission limit modification calculations on all co-firing data included 
in Tilden's March 1, 2023, and March 30, 2023, CEMS data submissions. 
Based on the equation set forth at 40 CFR 52.1183(p)(2), EPA calculated 
an emission limit of 189 lbs SO2/hour consistent with this 
approach.\27\ There is no basis in the FIP for adjusting emission 
limits to account for possible future production levels or possible 
higher ore sulfur content. Therefore, based on these data and as 
provided at 40 CFR 52.1183(k)(3), EPA is proposing that an 
SO2 limit of 189 lbs SO2/hr for the Tilden Line 1 
indurating furnace, with compliance to be determined on a 30-day 
rolling average basis, reflects SO2 BART for Tilden Line 1.
---------------------------------------------------------------------------

    \27\ See Tilden Emission Limit Calculations, available in the 
docket for this action.
---------------------------------------------------------------------------

B. Hibbing

    For Hibbing Lines 1, 2, and 3, the Original FIP set an aggregate 
emission limit of 247.8 lbs SO2/hr, based on a 30-day 
rolling average and excluding emissions resulting from the combustion 
of fuel oil, and provided Hibbing the option of calculating a revised 
SO2 emission limit by 20 months after March 8, 2013, based 
on one year of hourly CEMS emissions data and the non-parametric UPL 
equation. If any fuel oil is burned after the first day

[[Page 96160]]

that SO2 CEMS were required to be operational, the 2016 FIP 
requires Hibbing to submit the gallons of fuel oil burned per hour, the 
sulfur content of the fuel oil, and the SO2 emissions in 
pounds per hour, so that EPA can establish an SO2 emissions 
limit for fuel oil. Hibbing chose not to calculate a revised 
SO2 emission limit.\28\
---------------------------------------------------------------------------

    \28\ While Hibbing's SO2 BART limit is not being 
modified, the regulatory text at 40 CFR 52.1235(b)(2)(ii) is being 
revised to remove the original limit modification provisions and 
clarify that Hibbing's SO2 BART limit is final.
---------------------------------------------------------------------------

C. Minorca

    For Minorca, the Original FIP set an emission limit of 38.16 lbs 
SO2/hour, based on a 30-day rolling average and excluding 
emissions when Minorca is combusting fuel oil, with an allowance for 
potential modification of the limit based on one year of hourly CEMS 
data submitted to EPA by 20 months after March 8, 2013. If any fuel oil 
is burned after the first day that SO2 CEMS were required to 
be operational, the 2016 FIP requires Minorca to submit the gallons of 
fuel oil burned per hour, the sulfur content of the fuel oil, and the 
SO2 emissions in pounds per hour so that EPA can establish 
an SO2 emissions limit for fuel oil.
    On April 6, 2018, Minorca submitted a request to modify the 
SO2 limit established in the 2016 FIP. Minorca ranked hourly 
data from the period March 1, 2017, through March 31, 2018, adjusted 
the calculated limit based on potential increased production rates, and 
requested an emission limit of 73.79 lbs SO2/hour. On 
October 14, 2019, Minorca submitted additional hourly SO2 
CEMS emission data for the time period of September 8, 2018, through 
September 7, 2019, revising their request to an emission limit of 
208.66 lbs SO2/hr. Minorca adjusted the calculated limit 
based on potential increased production rates, maximum ore sulfur 
content based on a ratio of maximum percent sulfur, and pellet type.
    Using the equation set forth at 40 CFR 52.1235(f)(2) and the most 
recent CEMS data from September 8, 2018, through September 7, 2019, EPA 
calculated an SO2 emission limit of 68.2 lbs SO2/
hour.\29\ There is no basis in the FIP for adjusting emission limits to 
account for possible future production levels or possible higher ore 
sulfur content. Therefore, based on these data and as provided at 40 
CFR 52.1235(b)(2)(v) and 40 CFR 51.308(e), EPA is proposing that an 
emission limit of 68.2 lbs SO2/hr, based on a 30-day rolling 
average, reflects SO2 BART for the Minorca indurating 
furnace.
---------------------------------------------------------------------------

    \29\ See Minorca Emission Limit Calculations, available in the 
docket for this action.
---------------------------------------------------------------------------

D. Northshore

    For Northshore, the Original FIP set an aggregate emission limit of 
39.0 lbs SO2/hour for Furnace 11 (EU100/EU104) and Furnace 
12 (EU110/EU114), based on a 30-day rolling average and excluding 
emissions resulting from the combustion of fuel oil, with a requirement 
that the owner or operator calculate a revised limit based on one year 
of hourly CEMS data and submit such data and calculations to EPA by 20 
months after March 8, 2013.
    On April 11, 2018, Northshore submitted an SO2 emission 
limit modification request which included CEMS data from January 16, 
2017, through January 15, 2018. Northshore adjusted the calculated 
emission limit based on potential increased production rates and 
requested a limit of 22.1 lbs SO2/hour.
    On November 21, 2018, Northshore submitted a revised limit 
modification request of 49 lbs SO2/hr. This limit 
modification request included data for the time period of January 16, 
2017, through January 15, 2018, and adjusted the calculated limit based 
on potential increased production rates and potential increases in ore 
sulfur content. On November 10, 2022, Northshore submitted hourly 
SO2 CEMS data for the period of January 16, 2017, through 
January 15, 2018, as requested by EPA, to allow for EPA's independent 
calculation of emission limits.
    Using the equation set forth at 52.1235(f)(2) and the hourly 
SO2 CEMS data from January 16, 2017 through January 15, 
2018, EPA calculated an aggregate SO2 emission limit of 17.0 
lbs SO2/hour for Furnaces 11 and 12.\30\ There is no basis 
in the FIP for adjusting emission limits to account for possible future 
production levels or possible higher ore sulfur content. Therefore, 
based on these data and as provided at 40 CFR 52.1235(b)(2)(vi), EPA is 
proposing that an aggregate SO2 emission limit of 17.0 lbs 
SO2/hr for Northshore Furnaces 11 and 12, based on a 30-day 
rolling average, reflects SO2 BART for Northshore.
---------------------------------------------------------------------------

    \30\ See Northshore Emission Limit Calculations, available in 
the docket for this action.
---------------------------------------------------------------------------

IV. CAA Section 110(l)

    Under CAA section 110(l) (sometimes referred to as an ``anti-
backsliding'' provision), EPA cannot approve a plan revision ``if the 
revision would interfere with any applicable requirement concerning 
attainment and reasonable further progress (as defined in section 7501 
of this title), or any other applicable requirement of this chapter.'' 
Based on the following analysis, we find that our revisions to the 2016 
FIP are consistent with CAA section 110(l) because they will not 
interfere with any applicable requirement concerning attainment or 
reasonable further progress or any other applicable requirements of the 
CAA.

A. NOX Emission Limits

    When the 2016 FIP was promulgated, NOX control 
technology had not yet been installed on the furnaces at Tilden, 
Hibbing, Minorca, and UTAC. Therefore, EPA established initial emission 
limitations based on the modeled (estimated) performance of the 
proposed technology along with a procedure to refine and modify the 
emission limits within a specified range based upon CEMS data collected 
after installation of the NOX control technology. The 2016 
FIP also allowed for the establishment of a single NOX limit 
for all fuels. However, the NOX emission limits in the 2016 
FIP are not enforceable and final until EPA takes action to confirm or 
modify the initial emission limits established in the 2016 FIP. Because 
the NOX limits established in the 2016 FIP have not been 
confirmed and made enforceable through the procedures set forth in the 
2016 FIP, and are not currently enforceable, the proposed 
NOX emission limits do not alter any existing enforceable 
limits, since there are no current enforceable limits. Therefore, 
approval of the proposed NOX limits would not interfere with 
any applicable requirement concerning attainment or reasonable further 
progress, or any other applicable requirement of the CAA.
    Additionally, even if EPA were to evaluate the proposed 
NOX emission limits in relation to the relevant provisions 
of the 2016 FIP, we believe the FIP will not interfere with any 
applicable requirement concerning attainment or reasonable further 
progress, or any other applicable requirements of the CAA.\31\ EPA's 
proposed action will complete the process set forth in the 2016 FIP to 
finalize enforceable NOX emission limits for Tilden, 
Hibbing, UTAC, and Minorca within ranges previously established. The 
NOX emission limits EPA is proposing reflect BART because 
they were calculated using the corrected UPL equation and actual 
emission data recorded by CEMS, after installation of the required low-
NOX technology, pursuant to the procedures set forth in

[[Page 96161]]

the 2016 FIP. While crossline averaging was not addressed in the 2016 
FIP, under the BART Guidelines, a source may be permitted to `` 
`average' emissions across any set of BART-eligible emission units 
within a fenceline, as long as the emission reductions from each 
pollutant being controlled for BART would be equal to those reductions 
that would be obtained by simply controlling each of the BART-eligible 
units that constitute BART-eligible sources.'' \32\ Based on EPA's 
analysis, the crossline average emission limits proposed for Hibbing 
and UTAC are equal to the reductions that would be obtained by 
controlling each line separately.
---------------------------------------------------------------------------

    \31\ 40 CFR 52.1183(k)(1)(viii), 52.1235(b)(1)(iv)(A)(8) and 
52.1235(b)(1)(iv)(B)(8).
    \32\ 40 CFR part 51, appendix Y, at V.
---------------------------------------------------------------------------

    The proposed NOX emission limits do not reflect a change 
in EPA's BART determination. Rather, the proposed limits were 
calculated using CEMS data and the corrected UPL equation, following 
the procedure set forth in the 2016 FIP, to more accurately reflect an 
emission limit consistent with the actual emission reduction 
capabilities of the BART controls and within the natural gas ranges 
established in the 2016 FIP. Therefore, there are no expected increases 
in NOX emissions compared to the ranges set in the 2016 FIP.

B. SO2 Emission Limits

    EPA is proposing to revise the SO2 emission limits 
applicable to Minorca, Northshore, and Tilden. Minorca and Northshore 
are straight-grate furnaces that do not co-fire with coal; 
SO2 emissions from these sources result from sulfur in the 
ore processed in the furnaces. As discussed previously, when the 
Original FIP was promulgated, SO2 BART for Minorca and 
Northshore was established as no further controls. EPA set initial 
SO2 emission limits based on limited stack test data and 
established a procedure to refine those limits when CEMS data became 
available. EPA is proposing to modify the Minorca emission limit from 
38.16 lbs SO2/hour to 68.2 lbs SO2/hour and the 
Northshore emission limit from 39.0 lbs SO2/hour to 17.0 lbs 
SO2/hour. These proposed revised emission limits do not 
reflect a change in EPA's BART determination or in operations at the 
facilities that would lead to an increase or decrease in SO2 
emissions. Rather, the emission limits EPA is proposing establish 
emission limits that more accurately reflect BART because they were 
calculated using the corrected UPL equation and actual emission data 
recorded by CEMS, pursuant to the procedures set forth in the Original 
FIP.
    Similarly, the 2016 FIP established SO2 BART for Tilden 
as a limit on the sulfur content of the coal and no further controls, 
and set an SO2 emission limit for Tilden along with a 
process to modify that limit when CEMS data became available. EPA is 
not proposing to revise any limits on the sulfur content of coal at 
Tilden. EPA is only proposing to modify Tilden's emissions limit from 
500 lbs SO2/hour to 189 lbs SO2/hour. The revised 
emission limit was calculated using the corrected UPL equation and 
actual emission data recorded by CEMS, pursuant to the procedures set 
forth in the 2016 FIP.
    In sum, as a result of the revised SO2 emissions limits 
described above, EPA does not expect changes in SO2 
emissions from these sources. The limits do not reflect a change in 
EPA's BART determination or in operations at the facilities. Rather, 
the proposed limits more accurately reflect actual emissions that were 
calculated using newly available CEMS data and the corrected UPL 
equation.

C. Regional Haze SIPs

    On June 12, 2012 (77 FR 34801), EPA approved Minnesota's regional 
haze plan for the first implementation planning period as satisfying 
the applicable requirements in 40 CFR 51.308, except for BART emission 
limits for the taconite facilities. Among the regional haze plan 
elements approved were Minnesota's long-term strategy for making 
reasonable progress toward visibility goals. Minnesota's long-term 
strategy did not rely on the achievement of any particular degree of 
emission control from the taconite plants to achieve reasonable 
progress goals.
    On December 3, 2012 (77 FR 71533), EPA approved Michigan's regional 
haze plan for the first implementation planning period as satisfying 
the applicable requirements in 40 CFR 51.308, except for BART emission 
limits for Tilden, St. Mary's Cement, and Escanaba Paper Company. Among 
the regional haze plan elements approved was Michigan's long-term 
strategy for making reasonable progress toward visibility goals. 
Michigan's long-term strategy did not rely on the achievement of any 
particular degree of emission control from the taconite plants to 
achieve reasonable progress goals.
    On August 23, 2021, Michigan submitted a revision to their regional 
haze SIP for the second implementation planning period. Michigan's 
submittal provided a long-term strategy and reasonable progress goals 
that included 2028 emission projections for Tilden based on a 2016 
modeling platform developed by LADCO that did not rely on emission 
limits or ranges in the 2016 FIP.
    On December 20, 2022, Minnesota submitted a revision to its 
regional haze SIP for the second implementation period. Minnesota's 
long-term strategy included implementation of the current applicable 
limits and ranges in the Original FIP and 2016 FIP for Hibbing, 
Minorca, UTAC, and Northshore. However, in applying the long-term 
strategy to develop its reasonable progress goals, Minnesota used 2028 
projected emissions modeling that relied on the 2016 FIP limits only 
for UTAC and not for Hibbing, Minorca, or Northshore. For Hibbing and 
Minorca, Minnesota's modeling utilized 2028 projected emissions 
provided by LADCO using the 2016 emissions modeling platform since CEMS 
data was not available at the time. For Northshore, Minnesota accounted 
for the facility being idled until 2031, which was incorporated into an 
enforceable agreement as an Administrative Order by Consent issued by 
the Minnesota Pollution Control Agency to Northshore and Cleveland-
Cliffs, Inc. To project 2028 emissions for UTAC, Minnesota used 2017 
CEMS data to convert NOX and SO2 emissions and 
associated heat input into emission rates that allowed for a comparison 
to the limits and ranges in the 2016 FIP. Minnesota kept heat input 
rates the same and assumed compliance at the least stringent end of the 
emission limit ranges (e.g., for an emission limit range of 2.8-3.0 lbs 
NOX/MMBtu, Minnesota assumed 3.0 lbs NOX/MMBtu in 
the emission calculations), resulting in conservative emission 
projections for 2028. Using a photochemical model based on the 2028 
emission projections for all selected sources in their regional haze 
plan, including the taconite facilities, Minnesota estimated future 
visibility and established their reasonable progress goals.
    Although EPA has not yet taken final action on the regional haze 
SIP revisions submitted by Michigan and Minnesota for the second 
implementation period, the assumptions used in the long-term strategies 
and reasonable progress goals were no more stringent than the currently 
applicable Original FIP and 2016 FIP emission limits and ranges or the 
revised limits we are proposing in this action. Therefore, the revised 
NOX emission limits for Tilden, Hibbing, UTAC, Minorca, and 
Northshore represent greater control overall than was assumed in 
Michigan's and Minnesota's long-term strategy and would not result in a 
degradation of the reasonable progress goals required by 40 CFR 
51.308(d)(1).

[[Page 96162]]

D. National Ambient Air Quality Standards (NAAQS) and Reasonable 
Further Progress

    With respect to requirements concerning attainment of the NAAQS and 
reasonable further progress, EPA is proposing to finalize 
NOX BART emission limits for seven subject-to-BART units at 
four facilities within the ranges established in the 2016 FIP. EPA is 
also proposing to finalize SO2 emission limits for three 
facilities which will not result in an increase in SO2 
emissions. Thus, the proposed FIP revision will not interfere with 
attainment and reasonable further progress requirements.

E. Conclusion

    We find that these revisions are consistent with CAA section 
110(l). The previous sections of the notice explain how the proposed 
FIP revision will comply with applicable regional haze requirements and 
general implementation plan requirements and demonstrate that it will 
not interfere with any regional haze program requirements, attainment 
and reasonable further progress, or any other requirement of the CAA.

V. Environmental Justice Considerations

    Executive Order 12898 (59 FR 7629, February 16, 1994) directs 
Federal agencies, to the greatest extent practicable and permitted by 
law, to make environmental justice (EJ) 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 communities with EJ concerns.
    EPA believes that the human health and environmental conditions 
that exist prior to this action do not result in disproportionate and 
adverse effects on communities with EJ concerns. To identify 
environmental burdens and susceptible populations in communities nearby 
the Tilden, Hibbing, Minorca, Northshore, and UTAC facilities, and to 
examine the implications of the proposed NOX and 
SO2 emission limits, EPA utilized the EJScreen tool to 
evaluate environmental and demographic indicators within a 3-mile 
buffer, a 10-mile buffer, and the county that each facility is located 
in (Marquette County, Michigan for Tilden; St. Louis County, Minnesota 
for Hibbing, Minorca, and UTAC; and Lake County, Minnesota for 
Northshore).
    EPA's screening-level analysis indicates that communities near the 
facilities affected by this action score below the national average for 
the EJScreen ``Demographic Index'', which is the average of an area's 
percent minority and percent low-income populations, i.e., the two 
demographic indicators explicitly named in Executive Order 12898. 
Additionally, the results indicate that these areas score below the 
80th percentile (in comparison to the nation as a whole) in the 13 EJ 
Indexes established by EPA, which include a combination of 
environmental and demographic information. EPA has provided that if any 
of the EJ indexes for the areas under consideration are at or above the 
80th percentile nationally, then further review may be appropriate. As 
discussed in the EPA's EJ technical guidance, communities with EJ 
concerns often experience greater exposure and disease burdens than the 
general population, which can increase their susceptibility to adverse 
health effects from environmental stressors.
    EPA believes that this action is not likely to result in new 
disproportionate and adverse effects on communities with EJ concerns. 
This action proposes to set final NOX and SO2 
emission limits which are not expected to result in new or increased 
burdens on residents, including those in communities of EJ concern, as 
specified in Executive Order 12898.
    EPA invited the identification of EJ and other concerns during its 
Tribal consultations which occurred prior to proposing emission limits 
for all five taconite facilities. No EJ concerns were raised in the 
context of this action. We have determined that this rulemaking will 
not have disproportionately high and adverse human health or 
environmental effects on communities with EJ concerns. The information 
supporting this Executive Order review is contained in the docket for 
this action, including the EJSCREEN reports considering a 3-mile 
buffer, a 10-mile buffer, and the county that each taconite facility is 
in.

VI. Proposed Action

    EPA is proposing to modify the UPL equations used to establish 
NOX and SO2 emission limits and to finalize 
NOX and/or SO2 limits for the indurating furnaces 
at five taconite facilities in accordance with the procedure set forth 
in the 2016 FIP. Specifically, EPA is proposing to approve the 
following NOX limits, with compliance to be determined on a 
rolling 30-day average: 3.0 lbs NOX/MMBtu for all fuels for 
Tilden Line 1; a crossline average limit of 1.5 lb NOX/MMBtu 
for Hibbing Lines 1, 2, and 3; a crossline average emission limit of 
3.0 lbs NOX/MMBtu for all fuels for UTAC Lines 1 and 2; and 
1.6 lbs NOX/MMBtu for Minorca's indurating furnace. EPA is 
proposing to approve the following SO2 limits, with 
compliance to be determined on a rolling 30-day average: 189 lbs 
SO2/hr for all fuels for Tilden Line 1; an aggregate 
emission limit of 247.8 lbs SO2/hr for Hibbing Lines 1, 2, 
and 3; 68.2 lbs SO2/hr for Minorca's indurating furnace; and 
an aggregate limit of 17.0 lbs SO2/hr for Northshore 
Furnaces 11 and 12.

VII. Statutory and Executive Order Reviews

A. Executive Order 12866: Regulatory Planning and Review and Executive 
Order 14094: Modernizing Regulatory Review

    This action is not a significant regulatory action as defined in 
Executive Order 12866, as amended by Executive Order 14094, and was 
therefore not subject to a requirement for Executive Order 12866 
review.

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. Because the FIP applies to just the taconite facilities in 
Michigan and Minnesota, the Paperwork Reduction Act does not apply. See 
5 CFR 1320.3(c).

C. Regulatory Flexibility Act

    I certify that this proposed action will not have a significant 
economic impact on a substantial number of small entities under the 
RFA. This proposed action will not impose any requirements on small 
entities. This action, if finalized, will add 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 proposed 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 proposed action imposes no 
enforceable duty on any state, local or Tribal governments or the 
private sector.

E. Executive Order 13132: Federalism

    This proposed 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.

[[Page 96163]]

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

    This proposed action 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 action. Consistent with the EPA Policy on Consultation 
and Coordination with Indian Tribes, EPA did discuss this action in 
conference calls with the Michigan and Minnesota Tribes.

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

    This action is not subject to Executive Order 13045 because it is 
not 3(f)(1) significant as defined in Executive Order 12866, and 
because EPA does not believe the environmental health or safety risks 
addressed by this action present a disproportionate risk to children. 
To the extent this action, if finalized, will limit emissions of 
NOX and 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 and 
Executive Order 14096: Revitalizing Our Nation's Commitment to 
Environmental Justice for All

    EPA believes that the human health and environmental conditions 
that exist prior to this action do not result in disproportionate and 
adverse effects on communities with Environmental Justice concerns. 
This proposed FIP limits emissions of NOX and SO2 
from five taconite facilities in Michigan and Minnesota. EPA believes 
that this action is not likely to result in new disproportionate and 
adverse effects on communities with environmental justice concerns.
    EPA performed an EJ analysis, as is described above in the section 
titled, ``Environmental Justice Considerations.'' The analysis was done 
for the purpose of providing additional context and information about 
this rulemaking to the public, not as a basis of the action. Due to the 
nature of the action being taken here, this action is expected to have 
a neutral to positive impact on the air quality of the affected area. 
In addition, there is no information in the record upon which this 
decision is based inconsistent with the stated goal of E.O. 12898 of 
achieving EJ for communities with EJ concerns.

List of Subjects in 40 CFR Part 52

    Environmental protection, Air pollution control, Incorporation by 
reference, Intergovernmental relations, Nitrogen dioxide, Regional 
haze, Reporting and recordkeeping requirements, Sulfur oxides.

Michael S. Regan,
Administrator.

    For the reasons stated in the preamble, EPA proposes to amend title 
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 52.1183 is amended by:
0
a. in paragraph (k) revising (1), (3), (4) and (5);
0
b. in paragraph (l) revising (3), (4)(v) and (4)(xii);
0
c. in paragraph (n) revising (1) and (2); and
0
d. removing and reserving paragraph (p).
    The revisions read as follows:

Sec.  52.1183  Visibility protection.

* * * * *
    (k) Tilden Mining Company, or any subsequent owner/operator of the 
Tilden Mining Company facility in Ishpeming, Michigan, shall meet the 
following requirements:
    (1) NOX Emission Limits.
    (i) An emission limit of 3.0 lbs NOX/MMBTU, based on a 
30-day rolling average, shall apply to Tilden Grate Kiln Line 1 
(EUKILN1) beginning January 3, 2025.
    (ii) Compliance with this emission limit shall be demonstrated with 
data collected by a continuous emissions monitoring system (CEMS) for 
NOX.
    (2) SO2 Emission Limits. * * *
    (3) The owner or operator of the Tilden Grate Kiln Line 1 (EUKILN1) 
furnace shall meet an emission limit of 189.0 lbs SO2/hr, 
based on a 30-day rolling average, beginning on January 3, 2025. 
Compliance with this emission limit shall be demonstrated with data 
collected by a continuous emissions monitoring system (CEMS) for 
SO2. Beginning November 12, 2016, any coal burned on Tilden 
Grate Kiln Line 1 shall have no more than 0.60 percent sulfur by weight 
based on a monthly block average. The sampling and calculation 
methodology for determining the sulfur content of coal must be 
described in the monitoring plan required for this furnace.
    (4) Emissions resulting from the combustion of fuel oil are not 
included in the calculation of the 30-day rolling average. However, if 
any fuel oil is burned after the first day that SO2 CEMS are 
required to be operational, then the information specified in (k)(5) 
must be submitted, for each calendar year, to the Regional 
Administrator at [email protected] no later than 30 days after the 
end of each calendar year so that a limit can be set.
    (5) Records shall be kept for any day during which fuel oil is 
burned as fuel (either alone or blended with other fuels) in Grate Kiln 
Line 1. These records must include, at a minimum, the gallons of fuel 
oil burned per hour, the sulfur content of the fuel oil, and the 
SO2 emissions in pounds per hour. If any fuel oil is burned 
after the first day that SO2 CEMS are required to be 
operational, then the records must be submitted, for each calendar 
year, to the Regional Administrator at [email protected] no later 
than 30 days after the end of each calendar year.
    (l) Testing and monitoring.
     * * *
    (3) The owner or operator shall install, certify, calibrate, 
maintain, and operate one or more continuous diluent monitor(s) 
(O2 or CO2) and continuous stack gas flow rate 
monitor(s) on Tilden Grate Kiln Line 1 to allow conversion of the 
NOX and SO2 concentrations to units of the 
standard (lbs/MMBTU and lbs/hr, respectively) unless a demonstration is 
made that a diluent monitor and/or continuous flow rate monitor are not 
needed for the owner or operator to demonstrate compliance with 
applicable emission limits in units of the standard.
    (4) * * *
* * * * *
    (v) The owner or operator of each CEMS must furnish the Regional 
Administrator a written report of the results of each quarterly 
performance evaluation and a data accuracy assessment pursuant to 40 
CFR part 60 appendix F within 60 days after the calendar quarter in 
which the

[[Page 96164]]

performance evaluation was completed. These reports shall be submitted 
to the Regional Administrator at [email protected].
* * * * *
    (xii) Data substitution must not be used for purposes of 
determining compliance under this regulation. If CEMS data is measuring 
only a portion of the NOX or SO2 emitted during 
startup, shutdown, or malfunction conditions, the CEMS data may be 
supplemented, but not modified, by the addition of calculated emission 
rates using procedures set forth in the site specific monitoring plan.
* * * * *
    (n) Reporting requirements.
    (1) Unless instructed otherwise, all requests, reports, submittals, 
notifications, and other communications required by this section shall 
be submitted to the Regional Administrator at [email protected]. 
References in this section to the Regional Administrator shall mean the 
EPA Regional Administrator for Region 5.
    (2) The owner or operator of each BART affected unit identified in 
this section and CEMS required by this section must provide to the 
Regional Administrator the written notifications, reports, and plans 
identified at paragraphs (n)(2)(i) through (viii) of this section.
     * * *
* * * * *
    (p) [Reserved]
* * * * *
0
3. Section 52.1235 is amended by:
0
a. in paragraph (b) revising (1)(ii), (1)(iv), (1)(v), (1)(vi), 
(2)(ii), (2)(v) and (2)(vi);
0
b. in paragraph (c) revising (1), (2), (3), (4)(ii), (4)(v), and 
(4)(xii); and
0
c. in paragraph (e) revising (1) and (2); and
0
d. revising paragraph (f).
    The revisions read as follows:

Sec.  52.1235  Regional haze.

* * * * *
    (b) * * *
    (1) NOX emission limits.
    (i) * * *
    (ii) Hibbing Taconite Company
    (A) An aggregate emission limit of 1.5 lbs NOX/MMBtu, 
based on a 30-day rolling average, shall apply to the combined 
NOX emissions from the three indurating furnaces, Line 1 
(EU020), Line 2 (EU021), and Line 3 (EU022), beginning on January 3, 
2025. To determine the aggregate emission rate, the combined 
NOX emissions from Lines 1, 2, and 3 shall be divided by the 
total heat input to the three lines (in MMBtu) during every rolling 30-
day period.
    (B) Compliance with this emission limit shall be demonstrated with 
data collected by a continuous emissions monitoring system (CEMS) for 
NOX.
    (iii) * * *
    (iv) United Taconite
    (A) An aggregate emission limit of 3.0 lbs NOX/MMBtu, 
based on a 30-day rolling average, shall apply to the combined 
NOX emissions from the two indurating furnaces, Grate Kiln 
Line 1 (EU040) and Grate Kiln Line 2 (EU042), beginning on January 3, 
2025. To determine the aggregate emission rate, the combined 
NOX emissions from Grate Kiln Line 1 and Grate Kiln Line 2 
shall be divided by the total heat input to the two lines (in MMBtu) 
during every rolling 30-day period.
    (B) Compliance with this emission limit shall be demonstrated with 
data collected by a continuous emissions monitoring system (CEMS) for 
NOX.
    (v) Minorca Mine
    (A) An emission limit of 1.6 lbs NOX/MMBtu, based on a 
30-day rolling average, shall apply to the Minorca Mine indurating 
furnace (EU026). This emission limit will become enforceable on January 
3, 2025.
    (B) Compliance with this emission limit will be demonstrated with 
data collected by a continuous emissions monitoring system (CEMS) for 
NOX.
    (vi) Northshore Mining Company--Silver Bay: An emission limit of 
1.5 lbs NOX/MMBtu, based on a 30-day rolling average, shall 
apply to Furnace 11 (EU100/EU104) beginning October 10, 2018. An 
emission limit of 1.5 lbs NOX/MMBtu, based on a 30-day 
rolling average, shall apply to Furnace 12 (EU110/114) beginning 
October 11, 2019. However, for any 30, or more, consecutive days when 
only natural gas is used at either Northshore Mining Furnace 11 or 
Furnace 12, a limit of 1.2 lbs NOX/MMBtu, based on a 30-day 
rolling average, shall apply. An emission limit of 0.085 lbs 
NOX/MMBtu, based on a 30-day rolling average, shall apply to 
Process Boiler #1 (EU003) and Process Boiler #2 (EU004) beginning 
October 10, 2021. The 0.085 lbs NOX/MMBtu emission limit for 
each process boiler applies at all times a unit is operating, including 
periods of start-up, shut-down and malfunction.
    (2) SO2 Emission Limits.
    (i) * * *
    (ii) Hibbing Taconite Company
    (A) An aggregate emission limit of 247.8 lbs SO2/hour, 
based on a 30-day rolling average, shall apply to the combined 
SO2 emissions from the three indurating furnaces, Line 1 
(EU020), Line 2 (EU0021), and Line 3 (EU022), beginning on February 10, 
2017. To determine the aggregate emission rate, the combined 
SO2 emissions from Lines 1, 2, and 3 shall be divided by the 
total hours of operation of the three lines during every rolling 30-day 
period.
    (B) Compliance with this emission limit shall be demonstrated with 
data collected by a continuous emissions monitoring system (CEMS) for 
SO2.
    (C) Emissions resulting from the combustion of fuel oil are not 
included in the calculation of the 30-day rolling average. However, if 
any fuel oil is burned after the first day that SO2 CEMS are 
required to be operational, then the information specified in 
(b)(2)(vii) must be submitted, for each calendar year, to the Regional 
Administrator at [email protected] no later than 30 days after the 
end of each calendar year so that a limit can be set.
    (iii) * * *
    (iv) * * *
    (v) Minorca Mine
    (A) An emission limit of 68.2 lbs SO2/hr, based on a 30-
day rolling average, shall apply to the indurating furnace (EU026) 
beginning January 3, 2025.
    (B) Compliance with this emission limit shall be demonstrated with 
data collected by a continuous emissions monitoring system (CEMS) for 
SO2.
    (C) Emissions resulting from the combustion of fuel oil are not 
included in the calculation of the 30-day rolling average. However, if 
any fuel oil is burned after the first day that SO2 CEMS are 
required to be operational, then the information specified in 
(b)(2)(vii) must be submitted, for each calendar year, to the Regional 
Administrator at [email protected] no later than 30 days after the 
end of each calendar year so that a limit can be set.
    (vi) Northshore Mining Company--Silver Bay
    (A) An aggregate emission limit of 17.0 lbs SO2/hr, 
based on a 30-day rolling average, shall apply to Furnace 11 (EU100/
EU104) and Furnace 12 (EU110/EU114) beginning January 3, 2025. To 
determine the aggregate emission rate, the combined SO2 
emissions from Furnace 11 and Furnace 12 shall be divided by the total 
hours of operation of the two furnaces during every rolling 30-day 
period.
    (B) Compliance with these emission limits shall be demonstrated 
with data collected by a continuous emissions monitoring system (CEMS) 
for SO2.
    (C) Emissions resulting from the combustion of fuel oil are not 
included in the calculation of the 30-day rolling average. However, if 
any fuel oil is burned after the first day that SO2 CEMS are 
required to be operational, then the information specified in 
(b)(2)(vii) must

[[Page 96165]]

be submitted, for each calendar year, to the Regional Administrator at 
[email protected] no later than 30 days after the end of each 
calendar year so that a limit can be set.
    (D) The owner or operator may submit to EPA for approval an 
alternative monitoring procedure request. The request shall include at 
least one year of CEMS data demonstrating consistent values at or below 
5 lbs SO2/hr. The alternative monitoring procedure request 
shall not remove the obligation to maintain and operate a flow rate 
monitor in the stack. If approved, the owner or operator would not be 
required to operate the SO2 CEMS and may demonstrate 
continuous compliance using an emission factor derived from the average 
of at least one year of existing SO2 data using the 
procedure set forth in the site specific monitoring plan, and verified 
by annual stack tests using EPA approved test methods, multiplied by 
the daily measured flow rate as recorded by the flow rate monitor and 
recorded as the daily lb/hr SO2 emission rate.
    (vii) * * *
    (c) Testing and monitoring.
    (1) The owner or operator of the respective facility shall install, 
certify, calibrate, maintain and operate continuous emissions 
monitoring systems (CEMS) for NOX on United States Steel 
Corporation, Keetac unit EU030; Hibbing Taconite Company units EU020, 
EU021, and EU022; United States Steel Corporation, Minntac units EU225, 
EU261, EU282, EU315, and EU334; United Taconite units EU040 and EU042; 
Minorca Mine unit EU026; and Northshore Mining Company-Silver Bay units 
Furnace 11 (EU100/EU104) and Furnace 12 (EU110/EU114). Compliance with 
the emission limits for NOX shall be determined using data 
from the CEMS.
    (2) The owner or operator shall install, certify, calibrate, 
maintain, and operate CEMS for SO2 on United States Steel 
Corporation, Keetac unit EU030; Hibbing Taconite Company units EU020, 
EU021, and EU022; United States Steel Corporation, Minntac units EU225, 
EU261, EU282, EU315, and EU334; United Taconite units EU040 and EU042; 
Minorca Mine unit EU026; and Northshore Mining Company-Silver Bay units 
Furnace 11 (EU100/EU104) and Furnace 12 (EU110/EU114).
    (3) The owner or operator shall install, certify, calibrate, 
maintain, and operate one or more continuous diluent monitor(s) 
(O2 or CO2) and continuous stack gas flow rate 
monitor(s) on the BART affected units to allow conversion of the 
NOX and SO2 concentrations to units of the 
standard (lbs/MMBTU and lbs/hr, respectively) unless a demonstration is 
made that a diluent monitor and/or continuous flow rate monitor are not 
needed for the owner or operator to demonstrate compliance with 
applicable emission limits in units of the standards.
    (4) * * *
    (i) * * *
    (ii) CEMS must be installed and operational such that the 
operational status of the CEMS identified in paragraphs (c)(1) and (2) 
of this section shall be verified by, as a minimum, completion of the 
manufacturer's written requirements or recommendations for 
installation, operation, and calibration of the devices.
* * * * *
    (v) The owner or operator of each CEMS must furnish the Regional 
Administrator a written report of the results of each quarterly 
performance evaluation and a data accuracy assessment pursuant to 40 
CFR part 60 appendix F within 60 days after the calendar quarter in 
which the performance evaluation was completed. These reports shall be 
submitted to the Regional Administrator at [email protected].
* * * * *
    (xii) Data substitution must not be used for purposes of 
determining compliance under this section. If CEMS data is measuring 
only a portion of the NOX or SO2 emitted during 
startup, shutdown, or malfunction conditions, the CEMS data may be 
supplemented, but not modified, by the addition of calculated emission 
rates using procedures set forth in the site specific monitoring plan.
     * * *
* * * * *
    (e) Reporting Requirements
    (1) Unless instructed otherwise, all requests, reports, submittals, 
notifications, and other communications required by this section shall 
be submitted to the Regional Administrator at [email protected]. 
References in this section to the Regional Administrator shall mean the 
EPA Regional Administrator for Region 5.
    (2) The owner or operator of each BART affected unit identified in 
this section and CEMS required by this section must provide to the 
Regional Administrator the written notifications, reports and plans 
identified at paragraphs (e)(2)(i) through (viii) of this section.
     * * *
* * * * *
    (f) Equations for establishing the upper predictive limit--
    (1) Equation for normal distribution and statistically independent 
data.
[GRAPHIC] [TIFF OMITTED] TP04DE24.035

Where:

x = average or mean of hourly test run data;
t[(n-1),(0.99)] = t score, the one-tailed t 
value of the Student's t distribution for a specific degree of 
freedom (n-1) and a confidence level (0.99, to reflect the 99th 
percentile)
s\2\ = variance of the hourly data set;
n = number of values (e.g., 5,760 if 8 months of valid lbs 
NOX/MMBTU hourly values)
m = number of values used to calculate the test average (m = 720 as 
per averaging time)

    (i) To determine if statistically independent, use the Rank von 
Neumann Test on p. 137 of data Quality Assessment: Statistical Methods 
for Practitioners EPA QA/G-9S.
    (ii) Alternative to Rank von Neumann test to determine if data are 
dependent, data are dependent if t test value is greater than t 
critical value, where:
[GRAPHIC] [TIFF OMITTED] TP04DE24.036

r = correlation between data points
t critical = t[(n-2),(0.95)] = t score, the two-tailed t 
value of the Student's t distribution for a specific degree of 
freedom (n-2) and a confidence level (0.95)

    (iii) The Anderson-Darling normality test is used to establish 
whether the data are normally distributed. That is, a distribution is 
considered to be normally distributed when p > 0.05.
    (2) Non-parametric equation for data not normally distributed and 
normally distributed but not statistically independent.

m = (n+1) * [alpha]
m = the rank of the ordered data point, when data are sorted 
smallest to largest. The data points are 720-hour averages for 
establishing NOX limits.
n = number of data points (e.g., 5040 720-hourly averages for eight 
months of valid NOX lbs/MMBTU values)
[alpha] = 0.99, to reflect the 99th percentile

    If m is a whole number, then the limit, UPL, shall be computed as:

UPL = Xm

Where:

Xm = value of the mth data point in terms of lbs SO2/hr 
or lbs NOX/MMBtu, when the data are sorted smallest to 
largest.

    If m is not a whole number, the limit shall be computed by linear 
interpolation according to the following equation.

[[Page 96166]]

UPL = xm = xmi[middot]md= xmi + 0.md(xm(i+1) - xmi)

Where:

mi = the integer portion of m, i.e., m truncated at zero decimal 
places, and
md = the decimal portion of m

[FR Doc. 2024-27635 Filed 12-3-24; 8:45 am]
BILLING CODE 6560-50-P
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