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Federal Register / Vol. 86, No. 39 / Tuesday, March 2, 2021 / Rules and Regulations
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, its 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 20122017 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. Steels 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, 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.

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and in doing so achieved the NOX
reductions at Line 7. EPAs 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.
Response: U.S. Steels 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 EPAs 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

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and 5, adjusted and optimized each of those burners to reduce NOX, and collected CEMS data for each of the lines.
EPAs proposal to set an aggregate emission limit averaged across Minntacs 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.
EPAs apparent reliance on confidential information not disclosed as a part of this proposal, contravenes the Acts 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 EPAs 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, EPAs emission limitation proposal appears to be based on negotiations, rather than a technical analysis, since EPA did not consider the
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