Document ID: EPA-R05-OAR-2010-0037-0129
Agency: epa
Document Type: Rule
Title: Final Revision to Minnesota Taconite Federal Implementation Plan for U.S. Steel Minntac
Posted Date: 2021-03-02T05:00Z

[Federal Register Volume 86, Number 39 (Tuesday, March 2, 2021)]
[Rules and Regulations]
[Pages 12095-12107]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2021-04108]

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

ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 52

[EPA-R05-OAR-2010-0037; FRL-10019-32-Region 5]

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

AGENCY: Environmental Protection Agency (EPA).

ACTION: Final rule.

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

SUMMARY: The Environmental Protection Agency (EPA) is revising a 
Federal implementation plan (FIP) addressing the requirement for best 
available retrofit technology (BART) for the United States Steel 
Corporation's (U.S. Steel) taconite plant located in Mt. Iron, 
Minnesota (Minntac or Minntac facility). We are revising the nitrogen 
oxides (NOX) limits for U.S. Steel's taconite furnaces at 
its Minntac facility because new information has come to light that was 
not available when we originally promulgated the FIP on February 6, 
2013. The EPA is finalizing this action pursuant to sections 110 and 
169A of the Clean Air Act (CAA or the Act).

[[Page 12096]]

DATES: This final rule is effective April 1, 2021.

ADDRESSES: EPA has established a docket for this action under Docket ID 
No. EPA-R05-OAR-2010-0037. All documents in the docket are listed in 
the http://www.regulations.gov website. Although listed in the index, 
some information is not publicly available, e.g., Confidential Business 
Information or other information whose disclosure is restricted by 
statute. Certain other material, such as copyrighted material, is not 
placed on the internet and will be publicly available only in hard copy 
form. Publicly available docket materials are available either through 
http://www.regulations.gov or at the EPA Region 5 office (please 
contact the person identified in the FOR FURTHER INFORMATION CONTACT 
section for availability information).

FOR FURTHER INFORMATION CONTACT: Kathleen D'Agostino, Environmental 
Scientist, Attainment Planning & Maintenance Section, Air Programs 
Branch (AR-18J), U.S. Environmental Protection Agency, Region 5, 77 
West Jackson Boulevard, Chicago, Illinois 60604, (312) 886-1767, 
dagostino.kathleen@epa.gov.

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

I. Background Information

    On February 6, 2013, EPA promulgated a FIP that included BART 
limits for certain taconite furnaces in Minnesota and Michigan (2013 
Taconite FIP; 78 FR 8706). On February 4, 2020, EPA proposed to revise 
the 2013 Taconite FIP with respect to the NOX BART emission 
limitations and compliance schedules for U.S. Steel's Minntac facility 
in Minnesota. (85 FR 6125).
    Specifically, EPA proposed that an aggregate emission limit of 1.6 
lbs NOX per million British Thermal Unit (MMBtu), based on a 
30-day rolling average, averaged across Minntac's five production 
lines, represents NOX BART for the Minntac facility. An 
explanation of the CAA requirements, a detailed analysis of how these 
requirements apply to U.S. Steel's Minntac facility, and EPA's reasons 
for proposing the revised limit and compliance schedule were provided 
in the notice of proposed rulemaking (NPRM) and will not be restated 
here. The public comment period for this proposed rule ended on March 
5, 2020.
    One commenter stated that EPA did not provide information regarding 
a public hearing and did not ask the public if they were interested in 
a public hearing. To address this comment, EPA held a virtual public 
hearing on October 14, 2020, and reopened the public comment period. 
The second comment period closed on November 13, 2020. The commenter 
also stated that EPA did not demonstrate that the agency consulted with 
Federal Land Managers (FLMs) regarding the proposed FIP revision. In 
response to this comment, EPA engaged with the FLMs on the revision to 
the taconite FIP for Minntac. The FLMs have indicated that they have no 
comments on the FIP revision.

II. Public Comments

    During the first comment period EPA received adverse comments 
submitted on behalf of the National Parks Conservation Association and 
the Minnesota Center for Environmental Advocacy, an adverse comment 
submitted anonymously, and a comment from a private citizen in support 
of the February 4, 2020 proposal. We also received an anonymous comment 
that addresses subjects outside the scope of our proposed action. The 
adverse comments are summarized and addressed below. No one presented 
testimony at the October 14, 2020 virtual public hearing. The 
transcript of the hearing is available in the docket. We received no 
comments during the second comment period.
    Comment 1: The 2013 FIP included case-by-case determinations and 
emission limits for each of the BART units at Minntac, as follows: 1.2 
lbs NOX/MMBtu when burning natural gas and 1.5 lbs 
NOX/MMBtu when co-firing coal and natural gas. This was done 
in accordance with the CAA where BART is defined as ``an emission 
limitation based on the degree of reduction achievable through the 
application of the best system of continuous emission reduction for 
each pollutant which is emitted by an existing stationary facility.'' 
This emission limit is to be established on a case-by-case basis after 
considering the five statutory factors.
    EPA's 2020 proposal would provide a single facility-wide 
NOX BART limit of 1.6 lbs/MMBtu that will apply on a rolling 
30-day basis. Contrary to the CAA and BART Guidelines, for each Minntac 
source subject to BART, EPA abandons its 2013 BART determination and 
now proposes a FIP revision that neglects its obligation to ensure 
limits reflect BART emission rates that are of the appropriate type and 
level for each source subject to BART. Without revised individual BART 
determinations for each of the five Minntac units EPA cannot 
demonstrate that reductions achieved by the facility-wide limit will be 
equal to the reductions obtained by controlling the individual units. 
While the Minntac Spreadsheet in the docket contains information on 
95th and 99th percentile and highest 720-hour averages, it seems EPA 
decided to ignore the percentile values, and rather propose U.S. 
Steel's averaging approach.
    Response: The August 15, 2012 Proposed FIP (77 FR 49312-49313) 
included a five-step BART analysis for Minntac's five lines (Lines 3-
7). The five-step analysis was conducted in accordance with the BART 
Guidelines, appendix Y to 40 CFR part 51. EPA proposed BART emission 
limits of 1.2 lbs NOX/MMBtu measured on a 30-day rolling 
average based on the use of low NOX burners. EPA's analysis 
and proposed determination that BART is based upon the use of low 
NOX burners remains valid. In the February 6, 2013 Final FIP 
(78 FR 8706), based on a comment from U.S. Steel regarding the 
appropriate emission limit when burning solid fuels and supplementary 
data submitted by U.S. Steel on October 15, 2012,\1\ EPA finalized a 
limit for each of Minntac's five lines of 1.5 lbs NOX/MMBtu 
measured on a 30-day rolling average; however, a limit of 1.2 lbs 
NOX/MMBtu measured on a 30-day rolling average would apply 
for any 30 or more consecutive days when only natural gas is used. The 
final 2013 FIP limits reflected what EPA determined could be reasonably 
achieved by the use of low NOX burners at taconite furnaces 
based on the limited emission data available.
---------------------------------------------------------------------------

    \1\ See ``US Steel Comments--Proposed FIP MN and MI'' and ``10-
15-2012 email from C. Bartovich to S. Rosenthal'' and attachments, 
included in the docket.
---------------------------------------------------------------------------

    At the time EPA promulgated the BART emission limits for Minntac, 
low NOX burners had only been in operation on Minntac Lines 
6 and 7 since April 2011 and May 2010, respectively, and there were 
very little emission data available upon which to base a limit. Since 
promulgation of the FIP, however, U.S. Steel submitted continuous 
emission monitoring system (CEMS) data demonstrating that despite 
having optimized each burner,\2\ Minntac is unable to comply with the 
1.2 lbs NOX/MMBtu limit at all times when burning only 
natural gas.
---------------------------------------------------------------------------

    \2\ See ``IV.F. U.S. Steel Minntac Line 6 Low NOX 
Burner Final Report, December 1, 2011,'' ``III.F. U.S. Steel 
Minntac9.m. U.S. Steel Minntac Line 7 Burner Final Report, May 13, 
2011,'' and ``Final Report Line 4 Burner 092917,'' included in the 
docket.
---------------------------------------------------------------------------

    EPA continues to rely on the BART analysis set forth in the August 
15, 2012 proposal concerning the selection of low NOX 
burners as the appropriate BART

[[Page 12097]]

technology. However, since EPA promulgated the BART limits for Minntac, 
U.S. Steel has continued to operate low NOX burners on Lines 
6 and 7 and has installed low NOX burners on Lines 4 and 
5.\3\ There are significantly more data available from which to 
determine whether the BART FIP emission limits are actually achievable 
through the utilization of low NOX burners at Minntac. To 
reevaluate the emission limit achievable by use of low NOX 
burners, EPA analyzed available hourly CEMS data showing emissions in 
lbs NOX/MMBtu by fuel type. These data were available for 
the 2012-2017 time period. From this data set, EPA then compiled the 
emission data available for each line after the installation of low 
NOX burners. For Line 4, this included data from December 
15, 2016 through November 19, 2017. For Line 5, this included data from 
December 12, 2015 through November 11, 2017. For Lines 6 and 7, 
emission data were available from May 8, 2012 and April 27, 2012 
through November 11, 2017, respectively. There are necessarily 
differing amounts of CEMS data for each line since the low 
NOX burners were installed at different times.
---------------------------------------------------------------------------

    \3\ U.S. Steel installed low NOX burners on Lines 4 
and 5 on December 15, 2016, and December 20, 2015, respectively.
---------------------------------------------------------------------------

    To ensure that any revised emission limit would be based upon 
emission reduction capabilities during normal operations, EPA excluded 
hours when a line was idle, when a measurement error was recorded, or 
when process or CEMS codes indicated anything other than normal 
operation. For each line, EPA separated hours when only natural gas was 
burned from hours when the line was co-fired with coal (Lines 6 and 7) 
or co-fired with biomass (Lines 4 and 5). EPA then calculated 720-hour 
rolling averages based upon fuel type.\4\ To establish an achievable 
emission limit, EPA assessed the highest 720-hour average, the 99th 
percentile 720-hour average, and the 95th percentile 720-hour 
average.\5\ The 99th percentile is the emission rate that the source 
would be predicted to be below during 99 out of 100 720-hour averages. 
The 95th percentile is the emission rate that the source would be 
predicted to be below during 95 out of 100 720-hour averages. The 
highest 720-hour average is the emission rate at which the source would 
be predicted to be able maintain continual compliance.
---------------------------------------------------------------------------

    \4\ Operations at Minntac in a given 30-day period, or even a 
single day, may in some cases involve both operation with only 
natural gas and operation with at least some firing of solid fuels. 
To be able to evaluate emissions from all hours when different fuels 
were used within a 30-day period, rather than only the times when a 
line used solely natural gas or solely co-fired for 30 consecutive 
days, EPA evaluated emissions based on 720-hour averages. Note that 
operations are typically 24 hours per day and 720 is the number of 
hours in a 30-day period.
    \5\ See Lines 3, 4, and 5 Data-L4_7 NOX Data files 
combined,'' included in the docket.
---------------------------------------------------------------------------

    Under the BART Guidelines, a source may be permitted to average 
emissions across a 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 the BART-eligible source. See 40 CFR part 51, appendix Y, at 
V. U.S. Steel expressed interest in utilizing this option. As shown in 
Table 1 below, averaging the individual limits across Lines 4 through 7 
for natural gas results in a combined emissions limit of 1.6 lbs 
NOX/MMBtu averaged over 720 hours, regardless of whether the 
single line emission limit basis for the cross-line average was the 
highest 720-hour average, the 99th percentile 720-hour average, or the 
95th percentile 720-hour average.

             Table 1--Individual Line and Cross-Line Averaging Emission Rates for Lines 4 Through 7
----------------------------------------------------------------------------------------------------------------
                                                                   High  720-hr     99%  720-hr     95%  720-hr
                                                  Fuel             average  lbs    average  lbs    average  lbs
                                                                     NOX/MMBtu       NOX/MMBtu       NOX/MMBtu
----------------------------------------------------------------------------------------------------------------
Line 4................................  Natural Gas.............             1.5             1.5             1.5
                                        All Fuels...............             1.5             1.4             1.4
Line 5................................  Natural Gas.............             1.4             1.4             1.4
                                        All Fuels...............             1.4             1.4             1.3
Line 6................................  Natural Gas.............             1.7             1.6             1.6
                                        All Fuels...............             1.7             1.6             1.4
Line 7................................  Natural Gas.............             1.9             1.8             1.8
                                        All Fuels...............             1.9             1.8             1.7
                                                                 -----------------------------------------------
    Cross-line Average................  Natural Gas.............             1.6             1.6             1.6
                                        All Fuels...............             1.6             1.6             1.5
----------------------------------------------------------------------------------------------------------------

    While Line 3 will not become subject to the FIP limits until July 
2021, U.S. Steel has indicated that, when compared to the other lines, 
the Line 3 burner is most similar to Line 4. Line 4 is more similar in 
age, size and design to Line 3 than the other lines. Line 3 utilizes 
the same fuels (natural gas and biomass) as Line 4, and both Lines are 
managed by the same control room operators. In addition, operating 
parameters on Line 3 are similar to Line 4 for such measured parameters 
as Kiln Exit Temperature, Preheat Zone Temperature, Burner Temperature, 
and Pellet Residence time on the grate and in the kiln. Absent an 
engineering study for Line 3, using the emission rates for Line 4 as an 
estimate of the emission rates that would be expected after 
installation of a low NOX burner on Line 3 is reasonable. 
Therefore, EPA also calculated a cross-line average considering actual 
emissions from all four lines currently utilizing low NOX 
burners (Lines 4 through 7), as well as the expected emissions from 
Line 3. The resulting cross-line average is 1.6 lbs NOX/
MMBtu averaged over 720 hours, regardless of selection of statistical 
analyses at the 99th or 95th percentiles, or highest 720-hour average.
    While the 1.6 lbs NOX/MMBtu limit for Minntac is 
reflective of natural gas emission data, in response to the comment 
received, EPA calculated 720-hour rolling averages for each line over 
the entire period without separating fuel types. As provided in Table 
1, the data

[[Page 12098]]

analysis showed that the cross-line averages at the highest 720-hour 
average across all data and also at the 99th percentile is 1.6 lbs 
NOX/MMBtu, and at the 95th percentile is 1.5 lbs 
NOX/MMBtu. In addition, review of the CEMS data shows that 
U.S. Steel has largely transitioned toward firing with natural gas and 
away from co-firing with coal and natural gas. U.S. Steel stated that 
it ``has been primarily combusting natural gas since December 2016.'' 
\6\ As previously stated, only two of Minntac's five lines (Lines 6 and 
7) are capable of burning coal, and CEMS data show that U.S. Steel has 
largely shifted its operations on Lines 6 and 7 away from co-firing 
with coal and natural gas and toward firing exclusively natural gas. 
While Lines 6 and 7 co-fired with coal and natural gas 85% of the time 
in 2012, these lines co-fired with coal and natural gas only 3% of the 
time in 2017.\7\
---------------------------------------------------------------------------

    \6\ See Redacted ``U. S. Steel Confidential Settlement 
Communication--Subject to FRE 408,'' May 1, 2018, included in the 
docket.
    \7\ See ``Minntac CEMS Data and Analysis,'' included in the 
docket.
---------------------------------------------------------------------------

    EPA has determined that the 1.6 lbs NOX/MMBtu cross-line 
emission limit constitutes the appropriate BART emission limit for 
Minntac Lines 3 through 7, regardless of fuel type. As previously 
discussed, the BART Guidelines provide that a source may be permitted 
to average emissions across a set of BART-eligible units within a 
fenceline, so long as the emission reductions from each pollutant 
controlled for BART would be equal to those reductions that would be 
obtained by separately controlling each of the BART-eligible units that 
constitute the BART-eligible source. 40 CFR part 51, appendix Y, at V. 
Minntac Lines 3, 4, 5, 6, and 7 are all BART-eligible units that 
constitute a BART-eligible source within a fenceline. When averaging 
the level of NOX emission reductions achievable on each of 
Minntac Lines 3 through 7 individually, the resulting limit is 1.6 lbs 
NOX/MMBtu when burning natural gas. Therefore, it is 
reasonable for EPA to establish a single cross-line average emission 
limit of 1.6 lbs NOX/MMBtu, to apply at all times, for 
Minntac Lines 3 through 7. 1.6 lbs NOX/MMBtu is the most 
stringent limit the facility can consistently meet while providing for 
operational flexibility with regard to fuel choice, including burning 
exclusively natural gas.
    Comment 2: EPA's proposal lacks alternative BART emission limits 
based on the type of fuel each line will burn under the FIP. Although 
the BART Guidelines are fuel-neutral, where a source wants to operate 
under different scenarios and burn different fuels that create 
different levels of BART pollutant emissions, EPA must first set 
alternative BART emission limits for each unit based on fuel use. EPA's 
2013 FIP promulgated two BART emission limits based on fuel use, which 
apply to all five BART units: A limit when burning natural gas, and 
second limit when co-firing coal and natural gas. The record indicates 
the BART units historically used a variety of fuels, which included: 
Coal; wood; co-firing; biomass; and natural gas. EPA's proposed 
facility-wide BART limit relies on emission data collected when only 
one fuel was used, natural gas. EPA fails to analyze the range of fuels 
burned at Minntac and how the fuel burned impacts revising the prior 
BART determinations.
    Response: EPA disagrees with the commenter's contention that EPA 
must set alternative BART emission limits for each unit based on fuel 
use. Neither the CAA nor the regional haze rule requires EPA to 
establish separate BART limits based on fuel type. While the 1.6 lbs 
NOX/MMBtu limit for Minntac is reflective of natural gas 
emission data, EPA evaluated all available CEMS data for 2012-2017. 
These data are reflective of scenarios where lines were burning 
exclusively natural gas and scenarios when lines were co-firing with 
solid fuels.
    We are under no obligation to set fuel-specific limits and are not 
doing so here. EPA has determined that 1.6 lbs NOX/MMBtu is 
the most stringent limit the facility can consistently meet while 
providing for operational flexibility with regard to fuel choice, 
including burning exclusively natural gas. As discussed previously in 
response to Comment 1, in response to comments received, EPA calculated 
720-hour rolling averages for each line over the entire period without 
separating fuel types (the ``All Fuels'' scenario). The data 
demonstrate that the cross-line averages at the highest 720-hour 
average across all data and also at the 99th percentile is 1.6 lbs 
NOX/MMBtu, and at the 95th percentile is 1.5 lbs 
NOX/MMBtu. However, as previously explained, to allow for 
fuel choice and a scenario in which the facility burns only natural 
gas, 1.6 lbs NOX/MMBtu is the appropriate limit for the 
facility.
    Comment 3: The agency suggests using the new data to revise the 
five BART determinations in its 2013 FIP. EPA fails to provide a 
reasoned analysis for using the new data to revise its prior 
determination. EPA's prior determination found that once low 
NOX burners were installed and burned natural gas, 
NOX emissions were lower than when co-firing coal and 
natural gas, and therefore, based the 2013 FIP BART emission limits on 
its record and findings. EPA's 2020 proposal flips its prior 
determination, contending that NOX emissions are higher when 
burning only natural gas, as compared to co-firing coal and natural 
gas.
    Response: EPA's August 15, 2012 proposed FIP approval includes an 
analysis and proposed determination that BART for Minntac is based upon 
the use of low NOX burners. In the 2013 FIP final rule, EPA 
finalized this determination. EPA's analysis concerning low 
NOX burners as representing BART for Minntac continues to 
remain valid and it is appropriate for EPA to rely on it in this 
action. As discussed above, at the time EPA established limits in the 
2013 FIP, low NOX burners had only been in operation on 
Lines 6 and 7 since April 2011 and May 2010, respectively, and there 
were limited emission data available upon which to base a limit. 
However, since that time, U.S. Steel has continued to operate low 
NOX burners on Lines 6 and 7 and has installed low 
NOX burners on Lines 4 and 5. Therefore, as discussed in the 
response to Comment 1, there are significantly more data available from 
which to determine whether the BART FIP emission limits are actually 
achievable through the utilization of low NOX burners at 
Minntac.
    Comment 4: EPA's approach is not permissible under the Act. Instead 
of proposing BART emission limits based on maximum controls, EPA's 
proposal uses the new data from the operating scenario that is the 
least effective at controlling NOX emissions to derive a 
BART emission limit, and then suggests applying the least effective 
control at all five BART units, regardless of what the unit burns.
    Response: The control technology used as the basis for establishing 
BART limits in the 2013 FIP has not changed. Since promulgation of the 
2013 FIP, however, our understanding of the emissions levels achievable 
through the use of this technology has changed. The emission limits 
initially promulgated under the 2013 FIP were based on the installation 
and optimization of a low NOX burner on Lines 6 and 7, and 
the limited CEMS data available at that time. Since promulgation of the 
2013 FIP, U.S. Steel has continued to collect CEMS data from Lines 6 
and 7. U.S. Steel has also installed low NOX burners on 
Lines 4 and 5, has adjusted and optimized each of those burners to 
reduce NOX, and has collected CEMS data for each of the 
lines. EPA based the 1.6 lbs NOX/MMBtu limit on the

[[Page 12099]]

emission rates demonstrated by the CEMS data to be achievable by low 
NOX burners, which is the technology determined to be the 
basis for BART. The 1.6 lbs NOX/MMBtu limit is the most 
stringent limit the facility can consistently meet while providing for 
operational flexibility with regard to fuel choice. Contrary to 
commenter's assertion, EPA did not base the 1.6 lbs NOX/
MMBtu limit on the projected emission rates achievable by the least 
effective control technology.
    Comment 5: There is nothing in the record to suggest all lines will 
be capable of and restricted to burning natural gas nor that the 
company plans to burn natural gas exclusively.
    Response: The CEMS data clearly demonstrate that all lines are 
capable of burning natural gas. EPA is not restricting U.S. Steel to 
only burning natural gas at Minntac. Should U.S. Steel choose to 
periodically co-fire with coal or biomass on one or more of its lines, 
the facility will remain subject to the 1.6 lbs NOX/MMBtu 
limit regardless of fuel type.
    Comment 6: EPA fails to provide a basis for the cherry-picked and 
incomplete data. EPA's NPRM notes it evaluated six years of CEMS data, 
not specifying which years were evaluated. EPA provides neither an 
analysis of nor a justification for using such disparate data. While 
EPA explains the data represent operations at the taconite furnaces 
under various production scenarios, it fails to explain what these 
scenarios are and whether they represent the full range of future 
scenarios. EPA provides no explanation to justify its use of this 
limited data set.
    Response: As described previously, EPA used the full suite of CEMS 
data available for each line after the installation of low 
NOX burners. The document entitled ``Minntac CEMS Data and 
Analysis,'' included in the docket, identifies the date and hour of 
each emission data point used in the calculations. The earliest data 
available that provided hourly NOX emission data in lbs 
NOX/MMBtu along with the corresponding fuel type began in 
2012 and was provided through 2017. From this data set, EPA then 
compiled the emission data available for each line after the 
installation of low NOX burners. For Line 4, this included 
data from December 15, 2016 through November 19, 2017. For Line 5, this 
included data from December 12, 2015 through November 11, 2017. For 
Lines 6 and 7, emission data were available from May 8, 2012 and April 
27, 2012, respectively, through November 11, 2017. There are 
necessarily differing amounts of data for each line since the low 
NOX burners were installed at different times. To establish 
a limit based on emissions reflective of normal operating conditions, 
EPA excluded hours when the process was idle, when a measurement error 
was recorded, or when process or CEMS codes indicated anything other 
than normal operation.
    With respect to operating scenarios, EPA does not claim that the 
data evaluated represent the full range of possible future operating 
scenarios. Rather, the initial emission limits in the 2013 FIP were 
based upon very limited CEMS data from Lines 6 and 7. Operations at 
Lines 6 and 7 over the 2012-2017 time period showed varying production 
levels, fuels, pellet types and different ore mixes. In addition, we 
now have CEMS data for Lines 4 and 5 reflecting the installation of low 
NOX burners. The available CEMS data provide information on 
NOX emissions over time which encompass more operating 
scenarios than were represented by the limited data available at the 
time EPA promulgated the 2013 FIP. As the CEMS data \8\ available in 
the docket show, the 1.2 lbs NOX/MMBtu limit promulgated 
under the 2013 FIP and intended to apply when burning only natural gas 
cannot be consistently achieved at Minntac during normal operations 
with low NOX burners.
---------------------------------------------------------------------------

    \8\ See ``Minntac CEMS Data and Analysis,'' included in the 
docket.
---------------------------------------------------------------------------

    Comment 7: Although EPA's NPRM explains that U.S. Steel also 
provided hourly NOX emissions data in lbs/MMBtu for Line 3, 
which has not yet installed low NOX burner technology, the 
NPRM provides no information on where this information is available.
    Response: This information was erroneously omitted from the docket. 
The docket has been updated to include this information.\9\
---------------------------------------------------------------------------

    \9\ See ``Lines 3, 4, and 5 Data-L4_7 NOX CEMS Data 
files combined.''
---------------------------------------------------------------------------

    Comment 8: For the past ten years, 2009 through 2018, the 
NOX emissions reported by U.S. Steel have been relatively 
constant. EPA fails to explain why emissions remain constant even 
though U.S. Steel reports it installed low NOX burners on 
four of the five lines subject to BART. EPA also fails to provide an 
explanation for why there has been an increase in NOX 
emissions in the years following installation of the low NOX 
burner. This suggests that U.S. Steel did not optimize the low 
NOX burners from 2014 through 2017.\10\
---------------------------------------------------------------------------

    \10\ Commenter refers to a figure provided by commenter that 
purports to show 2002 baseline emissions from Minnesota's state 
implementation plan (SIP) submittal along with plots of facility-
wide NOX emissions in tons per year (tpy) and facility-
wide production for the period 2007 through 2018. See NPCA and MCEA 
Comments on the Proposed Revision to Minnesota Taconite Federal 
Implementation Plan for U.S. Steel Minntac, at p. 11, Figure 2.
---------------------------------------------------------------------------

    Response: Commenter references a figure provided by commenter that: 
(1) Shows the 2002 baseline annual emissions for Minntac included in 
Minnesota's December 30, 2014 Five-Year Regional Haze Progress Report 
SIP submittal,\11\ and (2) plots annual production and annual 
NOX emissions at Minntac. The figure does not accurately 
reflect U.S. Steel's implementation and optimization of low 
NOX burners at Minntac. First, the annual NOX 
emissions included in the commenter's figure do not represent annual 
emissions from only the indurating furnaces, but rather represent 
facility-wide NOX emissions. Second, by definition, BART is 
``based on the degree of reduction achievable through the application 
of the best system of continuous emission reduction.'' \12\ EPA is 
setting a cross-line average for Minntac Lines 3 through 7 of 1.6 lbs 
NOX/MMBtu, averaged over 30 days, which is a rate-based 
limit based on the degree of reduction achievable through the use of 
low NOX burners. Commenter conflates the rate-based emission 
limit with total annual NOX emissions from the facility. 
Since we are setting a rate-based emission limit, which does not 
constrain production levels, total annual NOX emissions may 
fluctuate in a given year even while the source is in compliance with 
its BART emission rate. For example, if production increases, total 
NOX emissions in tons per year would be expected to increase 
as well. If production decreases, total NOX emissions in 
tons per year (tpy) would be expected to decrease. Under all production 
scenarios, the lbs of NOX/MMBtu rate-based emission limit 
remains applicable. Finally, the production levels shown in the figure 
represent facility-wide production. The figure provided by the 
commenter does not differentiate production contributions by line, 
i.e., what percentage of total production comes from individual lines 
which had low NOX burners installed at the time vs. lines 
which did not have low NOX burners installed at the time.
---------------------------------------------------------------------------

    \11\ Note commenter used incorrect numbers 14,294 vs 14,924.
    \12\ See 40 CFR 51.301.
---------------------------------------------------------------------------

    Notwithstanding the above-noted limitations regarding the figure 
provided by the commenter, nonetheless, some information can be gained 
by looking at the difference between production and emissions over 
time, as represented by the distance

[[Page 12100]]

between the NOX line and production line in the figure. From 
2007 through 2009, before the installation of low NOX 
burners, these lines are relatively close together. In 2010, the year 
when the low NOX burner was installed on Line 7, production 
rose dramatically while annual NOX emissions did not. 
Visually, there is a significant divergence between the NOX 
and production lines in the figure, indicating an increase in 
production without a commensurate increase in emissions. 
Correspondingly, after the low NOX burner was installed on 
Line 6 in 2011, the figure shows production increased between 2010 and 
2011 while emissions decreased. Low NOX burners were 
installed on Lines 5 and 4 in December 2015 and December 2016, 
respectively. Similarly, the figure shows NOX emissions 
between 2015 and 2017 did not increase at the same rate as production.
    Using the available CEMS data for the 2012-2017 time period, EPA 
further evaluated the differences between various NOX 
emission values pre and post-installation of low NOX burners 
on Lines 4 and 5.\13\ Data for both lines showed a decrease in the 
average lbs NOX/MMBtu, high 720-hour average lbs 
NOX/MMBtu, and 99th percentile lbs NOX/MMBtu. 
Even the average lbs NOX/hour, which does not account for 
variations in production levels, decreased. U.S. Steel did not provide 
CEMS data for Lines 6 and 7 for the period prior to the installation of 
low NOX burners, so a similar comparison cannot be made for 
these lines.
---------------------------------------------------------------------------

    \13\ See ``Emission reduction estimates'' and ``Lines 3, 4, and 
5 Data-L4_7 NOX CEMS Data files combined for docket,'' 
included in the docket.
---------------------------------------------------------------------------

    Finally, the commenter asserts that the data suggest that U. S. 
Steel failed to optimize operation of the low NOX burners 
from 2014 through 2017. As discussed in detail in responses to comments 
9 and 14 in this document, after installation of the low NOX 
burner on each line, U.S. Steel optimized burner operation for 
NOX reduction while maintaining pellet quality. In addition, 
Minntac has remained subject to the limits in the 2013 FIP.
    Comment 9: EPA did not explain how U.S. Steel arrived at its 
conclusion that the low NOX burners at each of the lines 
were optimized and functioning at their best. In prior regional haze 
actions, when the level of control has been uncertain at the time of 
EPA's final action, EPA requires a control technology demonstration, 
with explicit requirements for optimization of the control technology 
system. EPA's 2014 final FIP requirements for Arizona plants included a 
control technology demonstration project for the emission control 
system at each plant, which entailed the collection of data and 
preparation of an optimization protocol that would be used to determine 
if a higher control efficiency would be achievable. There is no 
evidence that EPA required and oversaw implementation of a control 
technology project. Moreover, the BART Guidelines require the 
consideration of improvements to the low NOX burner controls 
(40 CFR part 51, appendix Y, at IV. D. Step 1] 9).
    Response: U.S. Steel has documented optimization studies at Lines 
4, 5, 6, and 7 in final testing reports for each line. Final testing 
reports for Lines 6 and 7 and preliminary data for Lines 4 and 5 are 
included in the docket. In addition, U.S. Steel submitted final testing 
reports for Lines 4 and 5, titled ``Final Report Line 4 Burner 
092917.'' This document has also been added to the docket. In each 
report, U.S. Steel describes challenges encountered over the course of 
installing, operating, and testing each low NOX burner, and 
discusses how certain design and operational changes were found to 
optimize operation of each line's low NOX burners. As 
explained in the reports, U.S. Steel evaluated operation of each low 
NOX burner to ensure each burner can operate in a manner 
that reduces NOX emissions while making pellets that meet 
quality specifications. Each burner was evaluated according to hourly 
CEMS data and during expected operating scenarios, including while 
burning natural gas, solid fuels, and a combination of natural gas and 
solid fuels. Over the course of the testing, U.S. Steel identified 
several problems occurring at various stages of low NOX 
burner operation and prescribed specific design and operational changes 
to improve operation in each scenario. U.S. Steel states that each of 
the proposed solutions and design changes--including adding blowers, 
increasing combustion air fan speed and capacity, adding rings to 
combustion air annuli, and adjusting and monitoring atomizing air and 
gas splits--were implemented in consultation with the burner 
manufacturer to optimize low NOX burner operation and 
NOX reduction. In each case, U.S. Steel determined 
optimization of the low NOX burners involves achieving 
stoichiometric ratios of air to fuel at levels that create a tight 
flame shape in order to minimize NOX while ensuring proper 
process operation. U.S. Steel continues to monitor CEMS data and burner 
parameters to ensure the burners are operating effectively.
    As explained in response to Comments 1 and 3, at the time EPA 
established limits in the 2013 FIP, low NOX burners had only 
been in operation on Lines 6 and 7 since April 2011 and May 2010, 
respectively, and there were limited CEMS data available upon which to 
base a limit. However, since EPA promulgated the initial BART limits 
for Minntac in the 2013 FIP, U.S. Steel has continued to operate low 
NOX burners on Lines 6 and 7 and has installed low 
NOX burners on Lines 4 and 5.\14\ There are significantly 
more data available from which to determine whether the 2013 FIP 
emission limits are actually achievable through the utilization of low 
NOX burners at Minntac. In addition, and as noted above, 
U.S. Steel has submitted final testing reports for Lines 4 through 7 
that detail U.S. Steel's optimization efforts for each of these low 
NOX burners. In contrast to the scenario cited by commenter 
where the control technology had not yet been installed and only 
minimal data were available regarding performance of the control 
technology at issue, EPA is basing the revised limit for Minntac on 
actual CEMS data. U.S. Steel has also provided information concerning 
its low NOX burner optimization efforts for Minntac Lines 4 
through 7 and has provided post-optimization emissions data for Lines 4 
through 7.
---------------------------------------------------------------------------

    \14\ U.S. Steel installed low NOX burners on Lines 4 
and 5 on December 15, 2016, and December 20, 2015, respectively.
---------------------------------------------------------------------------

    In the Arizona 2014 Regional Haze FIP (79 FR 52420) cited by the 
commenter, EPA stated the following with regard to Selective Non-
Catalytic Reduction (SNCR) at lime kilns: ``While this type of control 
technology demonstration is not typically required as part of a 
regional haze plan, we consider it to be appropriate here, given the 
minimal data available about the performance of SNCR at lime kilns.'' 
(79 FR 52440). With regard to SNCR at cement kilns, we explained, 
``While this type of control technology demonstration is not typically 
required as part of a regional haze plan, we consider it to be 
appropriate here, given the significant variability in control 
efficiencies achievable with SNCR at cement kilns.'' (79 FR 52456; 79 
FR 52462). The control technologies required for lime kilns and cement 
kilns in the 2014 Arizona FIP had not yet been installed at the time 
the Arizona FIP was promulgated. This is a different scenario than the 
situation we are addressing with regard to Minntac.
    Commenter cites to the BART Guidelines at 40 CFR part 51, appendix

[[Page 12101]]

Y, at IV. D. Step 1] 9. However, section IV.D. addresses the five steps 
of a case-by-case BART analysis, with Step 1 being the identification 
of all available retrofit control technologies. As discussed in 
response to Comment 1, the August 15, 2012 Proposed FIP (77 FR 49312-
49313) included a five-step BART analysis for Minntac's five lines 
(Lines 3-7). The five-step analysis was conducted in accordance with 
the BART Guidelines. EPA's analysis and proposed determination that 
BART is based upon the use of low NOX burners remains valid 
and EPA continues to rely upon that analysis. We are not conducting a 
new five-step BART analysis. In this action, we are only revising the 
NOX emission limits for Minntac to reflect the level of 
emission reductions consistently achievable by low NOX 
burners, which is the control technology determined to represent BART 
for Minntac in the 2013 FIP.
    Comment 10: 42 U.S.C. 7607(d)(2) requires that EPA's proposed 
action include ``the methodology used in obtaining the data.'' While 
the docket includes an Excel spreadsheet of CEMS data, there is no 
explanation provided regarding the methodology and test methods used to 
obtain the data. Furthermore, there is nothing in the record to 
indicate U.S. Steel's recent data was accompanied by a certification 
statement. Therefore, EPA's proposal fails to comply with the Act's 
methodology disclosure requirements and the public is unable to confirm 
accuracy and completeness of the data.
    Response: 42 U.S.C. 7607(d)(2) includes requirements pertaining to 
the establishment of a rulemaking docket. 42 U.S.C. 7607(d)(3), 
however, does require EPA to include a summary of ``the methodology 
used in obtaining the data and in analyzing the data.'' At proposal, we 
explained how EPA obtained the CEMS data. Specifically, we stated, 
``[t]o justify this limit, U.S. Steel provided EPA with hourly 
NOX emissions data in lbs/MMBTU documenting actual emissions 
levels after installation of [low NOX burner] technology on 
Minntac Lines 4-7. U.S. Steel also provided hourly NOX 
emissions data in lbs/MMBTU for Line 3, which has not yet installed 
[low NOX burner] technology.'' (85 FR 6126).
    In response to EPA's CAA section 114 request for information 
regarding Minntac, U.S. Steel provided CEMS data for Lines 3, 4 and 5 
covering the time period from January 1, 2012 through August 9, 2016 as 
well as CEMS data for Lines 6 and 7 covering the time period from July 
24, 2015 through August 9, 2016. The response included a certification 
of the accuracy and completeness of the information provided. U.S. 
Steel's letter responding to the CAA section 114 information request, 
as well as the certification, has been added to the docket.
    In response to additional requests from EPA that were not made 
under CAA section 114, U.S. Steel provided CEMS data for Lines 6 and 7 
for the period of April 27, 2012 through July 24, 2015 and for Lines 4 
through 7 for the period of August 2016 to November 2017. However, 
Minntac's CEMS were certified on Agglomerator Waste Gas Lines 6 & 7 on 
June 2-3, 2005. The CEMS were certified on Waste Gas Lines 3, 4 & 5 on 
January 24, 2007, January 31, 2007 and February 1, 2007, respectively. 
Further, Minntac is subject to the CEMS requirements of the 2013 FIP, 
which may be found at 40 CFR 52.1235(c) and include the requirement 
that CEMS ``be installed, certified, calibrated, maintained, and 
operated in accordance with 40 CFR part 60, appendix B, Performance 
Specification 2 (PS-2) and appendix F, Procedure 1.'' Minntac's title V 
permit also specifies that the CEMS meet the requirements of 40 CFR 
part 60 appendix B and F and Minnesota rule 7017 for monitoring and 
testing requirements. Pursuant to their title V permit, U.S. Steel must 
annually certify its compliance with title V. EPA has no reason to 
question the accuracy and completeness of the CEMS data supplied.
    In addition, the document, Minntac CEMS Data and Analysis, is 
included in the docket and contains EPA's analysis of the data provided 
by U.S. Steel.\15\
---------------------------------------------------------------------------

    \15\ See ``Minntac CEMS Data and Analysis,'' Docket ID # EPA-
R05-OAR-2010-0037-0110, available at https://www.regulations.gov/document?D=EPA-R05-OAR-2010-0037-0110. We note that the document, 
Redacted US Steel Proposal to EPA Minntac 5-1-2018, was erroneously 
listed on regulations.gov as an attachment to Minntac CEMS Data and 
Analysis under Docket ID # EPA-R05-OAR-2010-0037-0110. Minntac CEMS 
Data and Analysis and Redacted US Steel Proposal to EPA Minntac 5-1-
2018 are two distinct documents. Minntac CEMS Data and Analysis is 
an Excel file containing EPA's analysis of CEMS data for Minntac. 
Redacted US Steel Proposal to EPA Minntac 5-1-2018 is a redacted 
version of a settlement communication provided by U.S. Steel to EPA. 
While Redacted US Steel Proposal to EPA Minntac 5-1-2018 remains 
available under Docket ID # EPA-R05-OAR-2010-0037-0110, it may also 
be found under its own Docket ID # EPA-R05-OAR-2010-0037-0109, 
available at https://www.regulations.gov/document?D=EPA-R05-OAR-2010-0037-0109.
---------------------------------------------------------------------------

    Comment 11: While U.S. Steel expressed apprehensions about 
fluctuating emissions due to ``concerns regarding ore blend,'' and EPA 
appears to rely on this in proposing to revise the FIP, there is no 
information in the record to substantiate ore blend variability. Nor is 
there any information in the record that explains how fluctuations in 
ore blend impact the ability of low NOX burners to control 
NOX emissions. EPA's assertions appear to suggest that it 
assumes the fluctuations go in one direction, adding a ``safety 
margin'' to the facility-wide limit, without providing a reasoned 
basis.
    Response: EPA did not consider ore blends in proposing to revise 
the FIP. EPA did provide a reasoned basis for the 1.6 lbs 
NOX/MMBtu emission limit. This is the limit demonstrated by 
the CEMS data to be achievable by low NOX burners, which is 
the technology determined to be the basis for BART. The 1.6 lbs 
NOX/MMBtu limit is the most stringent limit the facility can 
consistently meet while providing for operational flexibility with 
regard to fuel choice. EPA did not add a safety margin to the limit as 
commenter suggests.
    Comment 12: EPA's proposal suggests that given the trajectory of 
fuel markets, EPA has no reason to believe that U.S. Steel will not 
continue to use natural gas at Minntac. EPA provides neither 
information about fuel markets nor a trajectory. Even if such 
information were provided, reliance on market projections is not an 
acceptable justification. Projections are just that, merely 
projections, and EPA lacks authority to rely on them. Moreover, in 
responding to the Petitions for Reconsideration on its 2013 FIP, EPA 
explained that ``the taconite industry has demonstrated that it can re-
engineer furnaces to adapt to market changes (such as fuel prices)'' 
and EPA found that ``at U.S. Steel's Minntac facility, where low 
NOX burners have been installed and are in operation, there 
has been no fuel penalty.''
    Response: The 1.6 lbs NOX/MMBtu limit for Minntac 
represents the most stringent limit the facility can consistently meet 
while providing for operational flexibility to burn exclusively natural 
gas. As discussed previously in response to Comments 2 and 4, U.S. 
Steel's production and fuel use data show that U.S. Steel has been 
moving toward using natural gas rather than co-firing with coal. 
Minntac Lines 6 and 7 (the only lines that capable of burning coal) 
have shifted fuel use dramatically over the six years evaluated, from 
15% natural gas in 2012 to 97% natural gas in 2017. The 1.6 lbs 
NOX/MMBtu limit represents the most stringent limit the 
facility can consistently meet while providing operational flexibility 
with regard to fuel choice--including, for example, in response to 
market changes, the option to burn exclusively natural gas. Should

[[Page 12102]]

U.S. Steel choose to co-fire with coal or biomass on one or more of its 
lines, the facility will remain subject to the 1.6 lbs NOX/
MMBtu limit regardless of fuel type.
    Comment 13: Information in the docket indicates U.S. Steel 
suggested the facility-wide emission limit needs to be set at a level 
that includes approximately two months of historical emission data that 
were above the 1.5 lbs NOx/MMBtu limit EPA offered during 
the negotiations. EPA provides no explanation for what caused the 
elevated levels. In fact, it's unclear whether EPA attempted to 
ascertain the answer to that question. These elevated levels were not 
seen at the other BART units. Without an explanation for this limited 
data, and whether such instances will occur during normal operations, 
it is unreasonable, arbitrary and capricious for EPA to set a limit 
that includes these operations, which has the effect of providing a 
``safety margin.''
    Response: It is unclear what information commenter is referencing. 
However, as discussed in greater detail in response to Comment 1, EPA 
evaluated and analyzed available hourly CEMS data showing emissions in 
lbs NOX/MMBtu and fuel type. These data were available for 
the 2012-2017 time period. From this data set, EPA compiled the 
emission data available for each line after the installation of low 
NOX burners. EPA then evaluated CEMS codes and process codes 
for each line to ensure that the limit would be based upon emission 
reduction capabilities during normal operations. EPA excluded hours 
when the process was idle, when a measurement error was recorded, or 
when process or CEMS codes indicated anything other than normal 
operation. Based upon that data, EPA proceeded to calculate achievable 
limits for the individual lines to use as a basis for the 1.6 lbs 
NOX/MMBtu cross-line average limit proposed.
    Comment 14: Based on its experience with the low NOX 
burner at Minntac Line 6, EPA denied U.S. Steel's Petition for 
Reconsideration (at another facility), explaining that after installing 
Line 6, U.S. Steel was able to make significant design changes before 
installation at the next line planned for BART installation, Minntac 
Line 7.\16\ EPA explained that the company identified the need for 
increased air flow and the need to modify the burner size or physical 
space to best accommodate the installation, and in doing so achieved 
the NOX reductions at Line 7. EPA's current proposal fails 
to explain why U.S. Steel cannot make design changes to all the lines 
that will be capable of burning natural gas to achieve the 
NOX emission limit when burning gas, when earlier it 
demonstrated it was able to do so at Lines 6 and 7.
---------------------------------------------------------------------------

    \16\ Commenter seems to be confusing the order of low-
NOX burner installation on Lines 6 and 7. Low 
NOX burners were installed on Lines 6 and 7 in April 2011 
and May 2010, respectively.
---------------------------------------------------------------------------

    Response: U.S. Steel's final burner reports for Lines 4 and 5, 6, 
and 7 provide detailed explanations of its efforts to optimize 
NOX reduction at each line. As discussed in the reports, 
U.S. Steel has made physical and operational changes and tuned each low 
NOX burner to ensure each can operate in a manner that 
reduces NOX emissions while making pellets that meet quality 
specifications. Specifically, the September 2017 Line 4 final burner 
report highlights how U.S. Steel installed a blower to add additional 
combustion air to optimize stoichiometric ratios at Lines 4 and 5. 
Subsequent information provided by U.S. Steel discusses how U.S. Steel 
implemented a CEMS-based monitoring and process control program to 
monitor NOX emissions at each line and allow for automated 
process control system adjustments to ensure the low NOX 
burners at each line are operating efficiently.
    Comment 15: One of EPA's purported reasons for providing U.S. Steel 
with the higher limit is to provide the company with ``additional 
flexibility.'' This rationale finds no basis in the CAA and is 
therefore not a permissible reason for revising the 2013 FIP 
determinations. Moreover, while EPA suggests that this flexibility is 
appropriate because of ``unique issues U.S. Steel faced in trying to 
comply with the individual limits in the 2013 FIP,'' EPA provides no 
explanation of what those issues are, and what options were explored, 
if any, to resolve those issues. EPA fails to provide an explanation 
for its reversal of opinion and fails to explain the basis for its 
decision.
    Response: As explained in the proposal, U.S. Steel faced issues 
trying to comply with the limits in the 2013 FIP. As discussed in 
response to Comment 1, the emission limits initially promulgated under 
the 2013 FIP were based on the installation and optimization of low 
NOX burners on Lines 6 and 7, and the limited CEMS data 
available at that time. Since promulgation of the 2013 FIP, our 
understanding of the emissions levels achievable through the use of low 
NOX burner has changed. U.S. Steel has continued to collect 
CEMS data from Lines 6 and 7. U.S. Steel has also installed low 
NOX burners on Lines 4 and 5, adjusted and optimized each of 
those burners to reduce NOX, and collected CEMS data for 
each of the lines.
    EPA's proposal to set an aggregate emission limit averaged across 
Minntac's five lines is permissible under the BART Guidelines. As 
discussed in the proposal and in response to Comments 1 and 18, the 
BART Guidelines provide that a source may be permitted to ``average'' 
emissions across a set of BART-eligible emission units within a 
fenceline, so long as the emission reductions from each pollutant 
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. See 40 CFR part 51, appendix Y, at V.
    EPA based the 1.6 lbs NOX/MMBtu cross-line average on 
the emission rates demonstrated by the CEMS data to be achievable 
through the use of low NOX burners. The 1.6 lbs 
NOX/MMBtu limit is the most stringent limit the facility can 
consistently meet while providing for operational flexibility with 
regard to fuel choice. As stated in the proposal, EPA is confident that 
allowing U.S. Steel to average NOX emissions levels across 
Minntac Lines 3 through 7 will achieve NOX emission 
reductions equal to the reductions that would have been obtained had 
EPA revised the individual limits for Minntac Lines 3 through 7 
separately. The ``additional flexibility'' provided by this cross-line 
average is consistent with the BART Guidelines.
    Comment 16: EPA does not disclose that the proposal is apparently 
the result of confidential settlement discussions. EPA's apparent 
reliance on confidential information not disclosed as a part of this 
proposal, contravenes the Act's requirements and does not allow the 
public to review and consider the changes proposed, and is particularly 
problematic in light of the history and level of pollution from these 
sources. EPA has not provided documentation of the reasons for the 
revisions in the form of publicly available information. Without the 
opportunity to review the information EPA relies on, the public is 
prohibited from critiquing the basis for EPA's action and cannot 
meaningfully participate in the comment process. EPA is suppressing 
``meaningful comment by failure to disclose the basic data relied upon 
is akin to rejecting comment altogether.''
    In sum, EPA's emission limitation proposal appears to be based on 
negotiations, rather than a technical analysis, since EPA did not 
consider the

[[Page 12103]]

relevant statutory and regulatory factors in proposing the revisions 
and fails to provide a basis for most of its assertions. It is 
unlawful, arbitrary and capricious for EPA to assert it has authority 
to revise BART emission limitations without the factual and analytical 
support substantiating its decision.
    Response: The revised emission limit is the result of a settlement 
agreement between EPA and U.S. Steel. On September 11, 2019, EPA 
published a notice of proposed settlement agreement in the Federal 
Register and provided the public an opportunity to comment on the 
proposed settlement agreement, in accordance with CAA section 113(g), 
42 U.S.C. 7413(g). (84 FR 47945). EPA did not receive any adverse 
comments relating to the proposed settlement agreement. Contrary to the 
commenter's assertion, EPA did not rely on confidential information in 
determining the appropriate NOX BART emission limits for 
Minntac. Rather, EPA relied upon CEMS data available in the docket.
    As discussed in the response to Comment 1, the five-step BART 
analysis for Minntac in the August 15, 2012 proposed FIP (77 FR 49312-
49313), established low NOX burners as the basis for BART 
emission limits. That analysis and EPA's determination that BART is 
based upon the use of low NOX main burners remains valid and 
EPA continues to rely on the BART analysis set forth in the August 15, 
2012 proposal concerning the selection of low NOX burners as 
the appropriate BART technology. However, since EPA promulgated the FIP 
limits, U.S. Steel has continued to operate low NOX burners 
and to collect CEMS data on Lines 6 and 7. Since promulgation of the 
FIP, U.S. Steel has also installed low NOX burners and 
collected CEMS data on Lines 4 and 5. Therefore, there are 
significantly more data available now from which to evaluate the 
emissions limits actually achievable through the use of low 
NOX burners at Minntac than there were at the time the FIP 
was promulgated. As discussed in greater detail in response to Comments 
1 and 6, it is this combined data set, which has been included in the 
docket, that provides the basis for the revision to the NOX 
BART emission limit for Minntac.
    Comment 17: The proposal lacks clear, well-documented comparisons 
between baseline emissions, the emission limitations from the 2013 
final Taconite FIPs, and the new proposal. In particular, changes in 
annual emissions are not provided, and thus not easily compared by the 
public.
    Response: Upon implementation of limits of 1.5 lbs NOX/
MMBtu and 1.2 lbs NOX/MMBtu, the reductions estimated under 
the 2013 FIP for Minntac range from 5,426 tpy to 6,077 tpy. The 
estimated reductions under a revised Minntac limit of 1.6 lbs 
NOX/MMBtu are 5,209 tpy. These data are included in the 
docket as ``Emission reduction estimates.''
    Comment 18: EPA fails to explain why it now thinks it is reasonable 
to use U.S. Steel's averaging approach, which it earlier found was not 
defensible because it relies on the assumption that all furnaces will 
emit at their highest values. Relying on the assumption that all 
furnaces will emit at their highest values (and be burning natural gas 
100 percent of the time) is yet another assumption that provides an 
additional unjustified ``safety margin.''
    Response: Under the BART Guidelines, a source may be permitted to 
``average'' emissions across a set of BART-eligible emission units 
within a fenceline, so long as the emission reductions from each 
pollutant 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. See 40 CFR part 51, appendix Y, 
at V. As shown in Table 1 in response to Comment 1, averaging the 
individual limits across Lines 4 through 7 results in a combined 
emissions limit of 1.6 lbs NOX/MMBtu averaged over 720 hours 
(30 days).
    In determining the appropriate NOX emission limit for 
Minntac, EPA analyzed CEMS data reflecting 720-hour rolling averages at 
the 95th and 99th percentiles as well as the highest 720-hour rolling 
average at each line. As noted in responses to Comments 1 and 2, while 
the 1.6 lbs NOX/MMBtu limit for Minntac is reflective of 
natural gas emission data, EPA evaluated all available CEMS data for 
2012-2017. Based on this CEMS data, the resulting cross-line average is 
1.6 lbs NOX/MMBtu averaged over 720 hours when the facility 
is burning natural gas, regardless of selection of statistical analyses 
at the 99th or 95th percentiles, or highest 720-hour average. As 
discussed in response to Comments 1 and 13, 1.6 lbs NOX/
MMBtu limit is the most stringent limit the facility can consistently 
meet while providing operational flexibility with regard to fuel 
choice, including the facility's ability to burn natural gas as opposed 
to co-firing. EPA did not add a safety margin to the limit as commenter 
suggests.
    Comment 19: If EPA is already setting a 30-day rolling average 
limit, it is inappropriate to further use the 720-hour values. 
Introducing the hourly values provides additional variability in the 
limit. EPA provides no authority to justify this approach, which 
appears to have increased the BART limit.
    Response: Operations at Minntac in a given 30-day period, or even a 
single day, may in some cases involve both operation with only natural 
gas and operation with at least some firing of solid fuels. To be able 
to evaluate emissions from all hours when different fuels were used 
within a 30-day period, rather than only the times when a line used 
solely natural gas or solely co-fired for 30 consecutive days, EPA 
evaluated emissions based on 720-hour averages. Note that operations 
are typically 24 hours per day and 720 is the number of hours in a 30-
day period.
    Comment 20: 42 U.S.C. 7410(l) prohibits the Administrator from 
approving a SIP/FIP revision if the revisions would interfere with the 
attainment and reasonable further progress requirements of the CAA, and 
``any other applicable requirement.'' In addition to requiring BART, 
each state's regional haze SIP must also set goals, expressed in 
deciviews for each Class I area located within the state that will 
assure reasonable progress toward achieving natural visibility. 
Moreover, the state's haze SIP must establish reasonable progress goals 
that ensure visibility conditions steadily progress, providing for 
improvement in visibility on the most impaired days and ensure no 
degradation in visibility on the least impaired days over the period of 
the implementation plan. 40 CFR 51.308(d)(1). These goals are set after 
considering the anticipated reductions in visibility impairing 
pollution over the planning period of the SIP from anticipated BART 
controls and other Federal or state programs, as well as controls 
imposed on non-BART sources under the regional haze SIP to help achieve 
reasonable progress. EPA's proposal did not consider how relaxing the 
BART emission limits will impact the reasonable progress goals.
    Response: Under section 110(l) of the Act, 42 U.S.C. 7410(l), the 
EPA Administrator may not approve a SIP or FIP revision ``if the 
revision would interfere with any applicable requirements concerning 
attainment and reasonable further progress, or any other applicable 
requirements of [the Act].'' In the proposed action, EPA proposed to 
find that the revisions to the FIP will comply with applicable regional 
haze program requirements and general implementation plan requirements 
such as enforceability.
    On June 12, 2012 (77 FR 34801), EPA approved Minnesota's regional 
haze plan as satisfying the applicable requirements in 40 CFR 51.308, 
except

[[Page 12104]]

for BART emission limits for the taconite facilities. Among the 
regional haze plan elements approved was 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. Therefore, the revised NOX limits 
for Minntac represent greater control than was assumed in Minnesota's 
approved long-term strategy SIP and does not interfere with the 
reasonable progress goals required by 40 CFR 51.308(d)(1). Thus, the 
proposed FIP revision would not interfere with any regional haze 
program requirements.
    Comment 21: The CAA requires that EPA provide a public hearing when 
proposing a FIP. [42 U.S.C. 7607(d)(5)] EPA failed to comply with this 
legislative mandate, since its proposal neither provided information 
regarding a public hearing, nor asked the public if they were 
interested in a hearing.
    Response: In response to this comment, EPA held a virtual public 
hearing on the proposed rule to provide interested persons an 
opportunity for the oral presentation of data, views, or arguments 
concerning the proposed rule. EPA also reopened the comment period on 
the proposed rule. Specifically, on September 29, 2020, EPA published a 
NPRM in the Federal Register announcing the virtual public hearing on 
the proposed rule to be held on October 14, 2020 and reopening the 
public comment period on the proposed rule. (85 FR 60942). EPA held the 
virtual public hearing on October 14, 2020. EPA accepted public 
comments on the proposed rule for 30 days following the virtual public 
hearing, and the public comment period closed on November 13, 2020. No 
individuals presented at the virtual public hearing and EPA did not 
receive any comments during the reopened comment period. The docket has 
been updated with a transcript of the virtual public hearing.\17\
---------------------------------------------------------------------------

    \17\ Minnesota; Revision to Taconite Federal Implementation 
Plan; October 14, 2020 Public Hearing Transcript, Docket ID # EPA-
R05-OAR-2010-0037-0117, available at https://www.regulations.gov/document?D=EPA-R05-OAR-2010-0037-0117.
---------------------------------------------------------------------------

    Comment 22: The CAA and Regional Haze Rule grant the FLMs, 
regardless of whether a FLM manages a Class I area within or beyond the 
state, a special role in the review of regional haze implementation 
plans. There are obligations to consult on plan revisions under 40 CFR 
51.308(i)(3) and EPA has not demonstrated it consulted with the Forest 
Service, the Fish and Wildlife Service and the National Park Service on 
the proposed FIP revision. Therefore, EPA has not met its obligations 
under the Act.
    Response: In response to this comment, EPA contacted the FLMs to 
provide the FLMs an opportunity to consult on the proposed action. EPA 
reached out to representatives from the National Park Service, U.S. 
Forest Service, and U.S. Fish and Wildlife Service. Each representative 
indicated that they did not have any comments on the proposed rule. EPA 
has updated the docket to include the relevant communications with the 
FLMs.\18\
---------------------------------------------------------------------------

    \18\ See emails from March 23, 2020 to June 30, 2020 included in 
the docket as ``3-23-2020 email from K. D'Agostino to D. Shepherd, 
T. Wickman, T. Allen,'' etc.
---------------------------------------------------------------------------

    Comment 23: Should EPA wish to pursue this FIP revision, the agency 
must prepare the required information and analyses, including a 
comprehensive optimization study at Minntac, and then repropose its 
action.
    Response: As noted in responses to Comments 1, 9 and 16, the five-
step BART analysis for Minntac in the August 15, 2012 proposed FIP (77 
FR 49312-49313), established low NOX burners as the basis 
for BART emission limits. That analysis and EPA's determination that 
BART is based upon the use of low NOX main burners remains 
valid and EPA continues to rely on the BART analysis set forth in the 
August 15, 2012 proposal concerning the selection of low NOX 
burners as the appropriate BART technology. However, since EPA 
promulgated the FIP limits, U.S. Steel has continued to operate low 
NOX burners and to collect CEMS data on Lines 6 and 7. Since 
promulgation of the FIP, U.S. Steel has also installed low 
NOX burners and collected CEMS data on Lines 4 and 5. 
Therefore, there are significantly more data available now from which 
to evaluate the emissions limits actually achievable through the use of 
low NOX burners at Minntac than there were at the time the 
FIP was promulgated. As discussed in greater detail in response to 
Comments 1 and 6, it is this combined data set, which has been included 
in the docket, that provides the basis for the revision to the 
NOX BART emission limit for Minntac.
    In addition, as described in greater detail in responses to 
Comments 9 and 14, U.S. Steel's final burner reports for Lines 4 and 5, 
6, and 7 provide detailed explanations of its efforts to optimize 
NOX reduction at each line. As discussed in the reports, 
U.S. Steel has made physical and operational changes and tuned each low 
NOX burner to ensure each can operate in a manner that 
reduces NOX emissions while making pellets that meet quality 
specifications. In each report, U.S. Steel discusses the process of 
optimizing the low NOX burners and tuning each burner and 
ancillary equipment to achieve optimal stoichiometric air to fuel 
ratios. For each line, U.S. Steel determined achieving optimal air to 
fuel ratios requires monitoring the atomizing air and gas split between 
the core and annulus gas to reduce flame turbulence in order to create 
a tight flame shape at each burner. In addition, in some cases, U.S. 
Steel modified capacities of combustion fans and added blowers and 
annulus rings to improve thrust and air to fuel ratios--each of which 
served to minimize NOX emissions as demonstrated by CEMS 
data.
    This action is limited to revising the FIP emission limit for 
Minntac to reflect the level of NOX control achievable for 
the source based on the use of low NOX burners. Regarding 
commenter's assertion that EPA was required to prepare certain 
information and analysis and repropose this action, as noted above, at 
the time of our February 4, 2020 proposal, EPA already had the 
information and analyses necessary to determine the appropriate revised 
emission limit for Minntac. This information included CEMS data for 
Minntac Lines 4 through 7 provided by U.S. Steel and EPA's analysis of 
that information. In addition, U.S. Steel provided to EPA final burner 
reports detailing U.S. Steel's efforts to optimize the low 
NOX burners on Minntac Lines 4 through 7.
    As discussed in response to Comment 1, in the 2013 FIP, EPA 
determined that low NOX burners reflect the appropriate 
level of BART control for Minntac. EPA's analysis and proposed 
determination that BART is based upon the use of low NOX 
burners remains valid. (78 FR 8706). However, the emission limits 
established in the 2013 FIP were based on limited CEMS data. Since 
promulgation of the 2013 FIP, U.S. Steel has continued to collect CEMS 
data on Minntac Lines 6 and 7. U.S. Steel has also installed low 
NOX burners on Lines 4 and 5 and has collected CEMS data 
reflecting the operation of low NOX burners on these lines. 
To determine emission rates that would be consistently achievable at 
each line, EPA evaluated all available CEMS data for 2012-2017, which 
covered a wide range of different operating scenarios.
    Comment 24: How is the increase in NOX emissions at this 
source not affecting nonattainment areas in downwind states such as New 
York or

[[Page 12105]]

Connecticut? East coast states typically point to states like Minnesota 
as significantly contributing to their ozone problems under CAA 
110(a)(2)(D). Is EPA at this point conclusively deciding that this 
increased FIP limit will not cause the state to violate CAA 
110(a)(2)(D) for any of the relevant NAAQS like ozone PM or NO2? Did 
EPA adjust its photochemical modeling performed for good neighbor SIPs 
to account for this relaxation? EPA issued several memos detailing 
Minnesota's contributions before this change, what is the quantitative 
effect of increasing these emissions on Minnesota's contribution to 
downwind states? EPA must figure this out before modifying this FIP 
otherwise EPA is predetermining Minnesota's SIP under 110(a)(2)(D) and 
concluding the state has met its obligations.
    Response: The CAA requires states to submit, within three years 
after promulgation of a new or revised standard, SIPs meeting the 
applicable ``infrastructure'' elements of sections 110(a)(1) and (2). 
One of these applicable infrastructure elements, CAA section 
110(a)(2)(D)(i), requires SIPs to contain ``good neighbor'' provisions 
to prohibit certain adverse air quality effects on neighboring states 
due to interstate transport of pollution. The commenter does not 
specify which element of CAA section 110(a)(2)(D) it believes is 
implicated by this action. Though, in questioning the effect of the FIP 
revision on downwind nonattainment areas, the commenter may be 
referring to the first two sub-elements of the good neighbor 
provisions, at CAA section 110(a)(2)(D)(i)(I). These sub-elements 
require that each SIP for a new or revised standard contain adequate 
provisions to prohibit any source or other type of emissions activity 
within the state from emitting air pollutants that will ``contribute 
significantly to nonattainment'' or ``interfere with maintenance'' of 
the applicable air quality standard in any other state.
    EPA has previously taken action to approve good neighbor SIPs for 
several pollutants and the modifications being made to the FIP are not 
expected to contradict those approvals. On October 20, 2015 (80 FR 
63436), EPA approved Minnesota's SIP as addressing the State's CAA 
section 110(a)(2)(D)(i)(I) obligations under the 2010 NO2 
NAAQS. The approval of Minnesota's 2010 NO2 good neighbor 
SIP was based on low design values for Minnesota and surrounding 
states, with the highest neighboring state showing a design value of 49 
parts per billion (ppb), less than half of the 100 ppb standard. This 
approval was based on monitoring data from 2011 to 2013. Therefore, the 
FIP, promulgated in 2013, but not immediately requiring reductions, 
would not have had an impact on that data set.
    On October 10, 2018 (83 FR 50849), EPA approved Minnesota's SIP as 
addressing the State's CAA section 110(a)(2)(D)(i)(I) obligations under 
the 2012 PM2.5 NAAQS. In the proposed SIP approval, EPA 
explained that Minnesota found, and EPA's review confirmed, that all 
areas in other states where Minnesota emissions had the potential to 
impact monitored PM2.5 air quality, with the exception of 
one monitor in Allegheny County, Pennsylvania, were attaining the 2012 
annual PM2.5 NAAQS based on 2014-2016 data. (83 FR 39970, 
August 13, 2018). The emissions limits promulgated in the 2013 FIP were 
not yet in effect during this period, and thus the associated 
reductions did not impact the EPA's assessment of attainment. Minnesota 
further determined that its impact on air quality monitors in 
Pennsylvania was projected to be less than 1% of the 2012 annual 
PM2.5 NAAQS, an insignificant contribution based on the air 
quality threshold that EPA had previously used to identify linkages 
between upwind states and downwind air quality problems under CAA 
section 110(a)(2)(D)(i)(I). Minnesota's determination was based on 
EPA's source apportionment modeling projecting upwind state 
contributions to downwind monitors using 2011 base case emissions, 
which was also conducted prior to the effectiveness of the emission 
limits promulgated in the 2013 FIP. The revised FIP limit at Minntac 
represents greater control than was assumed in Minnesota's and EPA's 
analysis supporting approval of the 2012 PM2.5 good neighbor 
SIP.
    To the extent EPA has not acted on a pending good neighbor SIP 
under CAA section 110(a)(2)(D)(i)(I), EPA is not in this action pre-
determining its approvability. On October 1, 2018, the State of 
Minnesota submitted to EPA a SIP submittal addressing Minnesota's 
interstate transport requirements under CAA section 110(a)(2)(D)(i)(I) 
with respect to the 2015 ozone NAAQS. EPA has not yet taken action on 
Minnesota's October 1, 2018 SIP submittal. We will consider emissions 
from the state and whether the state is significantly contributing to 
or interfering with maintenance of the 2015 ozone NAAQS in any other 
state when we take action on the SIP.

III. Final Action

    For the reasons stated in the proposed FIP revision, EPA is 
finalizing the revised BART emission limit and related requirements for 
the U.S. Steel Minntac facility as proposed.

IV. Statutory and Executive Order Reviews

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

    This action is exempt from review by the Office of Management and 
Budget (OMB) because it is a rule of particular applicability and only 
affects one facility, U.S. Steel's Minntac taconite plant located in 
Mt. Iron, Minnesota.

B. Executive Order 13771: Reducing Regulations and Controlling 
Regulatory Costs

    This action is not an Executive Order 13771 regulatory action 
because this action is not significant under Executive Order 12866.

C. Paperwork Reduction Act (PRA)

    This action does not impose an information collection burden under 
the provisions of the PRA, 44 U.S.C. 3501 et seq. Under the Paperwork 
Reduction Act, a ``collection of information'' is defined as a 
requirement for ``answers to . . . identical reporting or recordkeeping 
requirements imposed on ten or more persons . . . .'' 44 U.S.C. 
3502(3)(A). Because the FIP applies to just one facility, the PRA does 
not apply. See 5 CFR 1320(c).

D. Regulatory Flexibility Act (RFA)

    After considering the economic impacts of this action on small 
entities, I certify that this action will not have a significant 
economic impact on a substantial number of small entities. EPA's action 
revises control requirements at one source. The Regional Haze FIP that 
EPA is promulgating for purposes of the regional haze program consists 
of imposing Federal control requirements to meet the BART requirement 
for NOX emissions on specific units at one source in 
Minnesota. The net result of the FIP action is that EPA is finalizing 
emission controls on the indurating furnaces at one taconite facilities 
and this source is not owned by small entities, and therefore is not a 
small entity.

E. Unfunded Mandates Reform Act (UMRA)

    EPA has determined that this rule does not contain a Federal 
mandate as

[[Page 12106]]

described in UMRA, 2 U.S.C. 1531-1538, that may result in expenditures 
that exceed the inflation-adjusted UMRA threshold of $100 million by 
State, local, or Tribal governments or the private sector in any one 
year. In addition, this rule does not contain a significant Federal 
intergovernmental mandate as described by section 203 of UMRA nor does 
it contain any regulatory requirements that might significantly or 
uniquely affect small governments.

F. Executive Order 13132: Federalism

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

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

    This rule does not have tribal implications, as specified in 
Executive Order 13175. Thus, Executive Order 13175 does not apply to 
this rule. However, EPA did discuss this action in conference calls 
with the Minnesota Tribes.

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

    EPA interprets E.O. 13045 as applying only to those regulatory 
actions that concern health or safety risks, such that the analysis 
required under section 5-501 of the E.O. has the potential to influence 
the regulation. This action is not subject to E.O. 13045 because it 
does not establish an environmental standard intended to mitigate 
health or safety risks. This action addresses regional haze and 
visibility protection. Further, because this amendment to the current 
regulation will require controls that will cost an amount equal to or 
less than the cost of controls required under the current regulation, 
it is not an economically significant regulatory action. However, to 
the extent this rule will limit emissions of NOX, 
SO2, and PM, the rule will have a beneficial effect on 
children's health by reducing air pollution.

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

    This action is not subject to Executive Order 13211, because it is 
not a significant regulatory action under Executive Order 12866.

J. National Technology Transfer and Advancement Act

    Section 12 of the National Technology Transfer and Advancement Act 
(NTTAA) of 1995 requires Federal agencies to evaluate existing 
technical standards when developing a new regulation. To comply with 
NTTAA, EPA must consider and use ``voluntary consensus standards'' 
(VCS) if available and applicable when developing programs and policies 
unless doing so would be inconsistent with applicable law or otherwise 
impractical.
    VCS are inapplicable to this action because application of those 
requirements would be inconsistent with the CAA.

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

    We have determined that this rule will not have disproportionately 
high and adverse human health or environmental effects on minority or 
low-income populations, as specified in Executive Order 12898 (59 FR 
7629, February 16, 1994), because it increases the level of 
environmental protection for all affected populations without having 
any disproportionately high and adverse human health or environmental 
effects on any population, including any minority or low-income 
population.

L. Congressional Review Act (CRA)

    This rule is exempt from the CRA because it is a rule of particular 
applicability.

M. Determination Under Section 307(d)

    Pursuant to CAA section 307(d)(1)(B), this action is subject to the 
requirements of CAA section 307(d), as it revises a FIP under CAA 
section 110(c).

N. Judicial Review

    Under section 307(b)(1) of the CAA, petitions for judicial review 
of this action must be filed in the United States Court of Appeals for 
the appropriate circuit by May 3, 2021. Filing a petition for 
reconsideration by the Administrator of this final rule does not affect 
the finality of this action for the purposes of judicial review nor 
does it extend the time within which a petition for judicial review may 
be filed, and shall not postpone the effectiveness of such rule or 
action. This action may not be challenged later in proceedings to 
enforce its requirements. See CAA section 307(b)(2).

List of Subjects in 40 CFR Part 52

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

    This document of the Environmental Protection Agency was signed on 
January 11, 2021, by Andrew Wheeler, Administrator, pursuant to a 
settlement agreement between EPA and U.S. Steel that required the final 
rule to be signed no later than January 20, 2021. That document with 
the original signature and date is maintained by EPA. For 
administrative purposes only, and in compliance with requirements of 
the Office of the Federal Register, the undersigned EPA Official re-
signs the document for publication, as an official document of the 
Environmental Protection Agency. This administrative process in no way 
alters the legal effect of this document upon publication in the 
Federal Register.

Jane Nishida,
Acting Administrator.
    For the reasons stated in the preamble, EPA amends 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. In Sec.  52.1235 revise paragraph (b)(1)(iii) to read as follows:

Sec.  52.1235   Regional haze.

* * * * *
    (b)(1) * * *
    (iii) United States Steel Corporation, Minntac: An aggregate 
emission limit of 1.6 lbs NOX/MMBtu, based on a 30-day 
rolling average, shall apply to the combined NOX emissions 
from the five indurating furnaces: Line 3 (EU225), Line 4 (EU261), Line 
5 (EU282), Line 6 (EU315), and Line 7 (EU334). To determine the 
aggregate emission rate, the combined NOX emissions from 
lines 3, 4, 5, 6 and 7 shall be divided by the total heat input to the 
five lines (in MMBTU) during every rolling 30-day period commencing 
either upon notification of a starting date by United States Steel 
Corporation, Minntac, or with the 30-day period from September 1, 2019 
to September 30, 2019, whichever occurs first. The aggregate emission 
rate shall subsequently be determined on each day, 30 days after the 
starting date contained in such

[[Page 12107]]

notification or September 30, 2019, whichever occurs first.
* * * * *
[FR Doc. 2021-04108 Filed 3-1-21; 8:45 am]
BILLING CODE 6560-50-P