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Federal Register / Vol. 86, No. 39 / Tuesday, March 2, 2021 / Rules and Regulations 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 commenters 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. EPAs 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
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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 20122017 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.
Comment 7: Although EPAs 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
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
8 See Minntac CEMS Data and Analysis, included in the docket.
9 See Lines 3, 4, and 5 Data-L4_7 NO CEMS
X Data files combined.
10 Commenter refers to a figure provided by commenter that purports to show 2002 baseline emissions from Minnesotas state implementation plan SIP submittal along with plots of facilitywide NOX emissions in tons per year tpy and
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Response: Commenter references a figure provided by commenter that: 1
Shows the 2002 baseline annual emissions for Minntac included in Minnesotas December 30, 2014 FiveYear 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. Steels implementation and optimization of low NOX burners at Minntac. First, the annual NOX emissions included in the commenters 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 ratebased 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.
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 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.
11 Note commenter used incorrect numbers 14,294 vs 14,924.
12 See 40 CFR 51.301.

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