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 Environmental Protection Agency 40 CFR Part 52
[EPA-R05-OAR-2024-0215; FRL-12351-01-R5]
 AGENCY: Environmental Protection Agency (EPA).
 ACTION: Proposed rule.
 SUMMARY: The Environmental Protection Agency (EPA) is proposing to finalize nitrogen oxide (NOX) and/or sulfur dioxide (SO2) limits for the indurating furnaces at five taconite facilities in accordance with the procedures set forth in the Federal implementation plan (FIP) addressing the requirement for best available retrofit technology (BART) at taconite facilities. EPA is also proposing to modify the Upper Predictive Limit (UPL) equations used to establish NOX
                         and SO2
                         emission limits under the FIP. Finally, EPA is proposing to revise reporting provisions to require reports to be submitted to EPA electronically. EPA is proposing these actions pursuant to sections 110 and 169A of the Clean Air Act (CAA).
 DATES: Comments must be received on or before January 21, 2025. *Virtual Public Hearing.*
                         EPA will hold a virtual public hearing to solicit comments on December 19, 2024. The last day to pre-register to present at the hearing will be December 16, 2024. On December 16, 2024, EPA will post a general agenda for the hearing that will list pre-registered presenters in approximate order at 
                        *https://www.epa.gov/​mn/​revision-taconite-regional-haze-federal-implementation-plan-mi-and-mn.*
                         If you require the services of a translator or a special accommodation such as audio description/closed captioning, please pre-register for the hearing and describe your needs by December 11, 2024. For more information on the virtual public hearing, see 
                        **SUPPLEMENTARY INFORMATION**
                        .
 ADDRESSES: Submit your comments, identified by Docket ID No. EPA-R05-OAR-2024-0215 at 
                        *https://www.regulations.gov,*
                         or via email to 
                        *arra.sarah@epa.gov.*
                         For comments submitted at 
                        *Regulations.gov*, follow the online instructions for submitting comments. Once submitted, comments cannot be edited or removed from 
                        *the docket.*
                         EPA may publish any comment received to its public docket. Do not submit to EPA's docket at 
                        *https://www.regulations.gov*
                         any information you consider to be Confidential Business Information (CBI), Proprietary Business Information (PBI), or other information whose disclosure is restricted by statute. Multimedia submissions (audio, video, etc.) must be accompanied by a written comment. The written comment is considered the official comment and should include discussion of all points you wish to make. EPA will generally not consider comments or comment contents located outside of the primary submission (
                        *i.e.*
                         on the web, cloud, or other file sharing system). For additional submission methods, please contact the person identified in the 
                        **FOR FURTHER INFORMATION CONTACT**
                         section. For the full EPA public comment policy, information about CBI, PBI, or multimedia submissions, and general guidance on making effective comments, please visit 
                        *https://www.epa.gov/​dockets/​commenting-epa-dockets.*
 FOR FURTHER INFORMATION CONTACT: Kathleen D'Agostino, Environmental Scientist, Air and Radiation Division (AR18J), Environmental Protection Agency, Region 5, 77 West Jackson Boulevard, Chicago, Illinois 60604, (312) 886-0266, 
                        *dagostino.kathleen@epa.gov.*
                         The EPA Region 5 office is open from 8:30 a.m. to 4:30 p.m., Monday through Friday, excluding Federal holidays.


SUPPLEMENTARY INFORMATION: Throughout this document whenever “we,” “us,” or “our” is used, we mean EPA. Virtual Public Hearing EPA is holding a virtual public hearing to provide interested parties the opportunity to present data, views, or arguments concerning the proposal. EPA will hold a virtual public hearing to solicit comments on December 19, 2024. The hearing will convene at 9:00 a.m. Central Standard Time (CST) and will conclude at 1:00 p.m. CST, or 15 minutes after the last pre-registered presenter in attendance has presented if there are no additional presenters. EPA will announce further details, including information on how to register for the virtual public hearing, on the virtual public hearing website at 
                    *https://www.epa.gov/​mn/​revision-taconite-regional-haze-federal-implementation-plan-mi-and-mn.* EPA will begin pre-registering presenters and attendees for the hearing upon publication of this document in the 
                    **Federal Register**
                    . To pre-register to attend or present at the virtual public hearing, please use the online registration form available at 
                    *https://www.epa.gov/​mn/​revision-taconite-regional-haze-federal-implementation-plan-mi-and-mn*
                     or contact Mayesha Choudhury at 312-886-5909 or by email at 
                    *choudhury.mayesha@epa.gov.*
                     The last day to pre-register to present at the hearing will be December 16, 2024. On December 16, 2024, EPA will post a general agenda for the hearing that will list pre-registered presenters in approximate order at 
                    *https://www.epa.gov/​mn/​revision-taconite-regional-haze-federal-implementation-plan-mi-and-mn.*
                     Additionally, requests to present will be taken on the day of the hearing as time allows. EPA will make every effort to follow the schedule as closely as possible on the day of the hearing; however, please plan for the hearing to run either ahead of schedule or behind schedule. Each commenter will have 5 minutes to provide oral testimony. EPA encourages commenters to provide EPA with a copy of their oral testimony electronically by including it in the registration form or emailing it to 
                    *choudhury.mayesha@epa.gov.*
                     EPA may ask clarifying questions during the oral presentations but will not respond to the presentations at that time. Written statements and supporting information submitted during the comment period will be considered with the same weight as oral comments and supporting information presented at the virtual public hearing. EPA is asking all hearing attendees to pre-register, even those who do not intend to present. This will help EPA prepare for the virtual hearing. Please note that any updates made to any aspect of the hearing will be posted online at 
                    *https://www.epa.gov/​mn/​revision-taconite-regional-haze-federal-implementation-plan-mi-and-mn.*
                     While EPA expects the hearing to go forward as set forth above, please monitor our website or contact Mayesha Choudhury at 312-886-5909 or 
                    *choudhury.mayesha@epa.gov*
                     to determine if there are any updates. EPA does not intend to publish a document in the 
                    **Federal Register**
                     announcing updates. If you require the services of a translator or a special accommodation such as audio description/closed captioning, please pre-register for the hearing with Mayesha Choudhury at 312-886-5909 or 
                    *choudhury.mayesha@epa.gov*
                     and describe your needs by December 11, 2024. EPA may not be able to arrange accommodations without advance notice. I. Background A. Requirements of the Clean Air Act and EPA's Regional Haze Rule In section 169A of the 1977 Amendments to the CAA, Congress created a program for protecting visibility in the nation's national parks and wilderness areas. This section of the CAA establishes as a national goal the “prevention of any future, and the remedying of any existing, impairment of visibility in mandatory Class I Federal areas [1]
                    
                     which impairment results from manmade air pollution.” Congress added section 169B to the CAA in 1990 to address regional haze issues. EPA promulgated a rule to address regional haze on July 1, 1999 
                    ( print page 96154)
                    (64 FR 35714), codified at 40 CFR part 51, subpart P (herein after referred to as the “Regional Haze Rule”). The Regional Haze Rule codified and clarified the BART provisions in the CAA and revised the existing visibility regulations to add provisions addressing regional haze impairment and to establish a comprehensive visibility protection program for Class I areas. The requirements for regional haze, found at 40 CFR 51.308 and 51.309, are included in EPA's visibility protection regulations at 40 CFR part 51, subpart P. Section 169A of the CAA directs states, or EPA if developing a FIP, to evaluate the use of retrofit controls at certain larger, often uncontrolled, older stationary sources to address visibility impacts from these sources. Specifically, section 169A(b)(2)(A) of the CAA requires that implementation plans contain such measures as may be necessary to make reasonable progress toward the natural visibility goal, including a requirement that certain categories of existing major stationary sources [2]
                    
                     built between 1962 and 1977 procure, install, and operate BART as determined by EPA. Under the Regional Haze Rule, states (or in the case of a FIP, EPA) are directed to conduct BART determinations for such “BART-eligible” sources that may reasonably be anticipated to cause or contribute to any visibility impairment in a Class I area. On July 6, 2005, 70 FR 39104, EPA published the Guidelines for BART Determinations Under the Regional Haze Rule at appendix Y to 40 CFR part 51 (hereinafter referred to as the “BART Guidelines”) to assist states and EPA in determining which sources should be subject to the BART requirements and in determining appropriate emission limits for each source subject to BART. The process of establishing BART emission limitations follows three steps. First, states, or EPA if developing a FIP, must identify and list “BART-eligible sources.” [3]
                    
                     Once the state or EPA has identified the BART-eligible sources, the second step is to identify those sources that may “emit any air pollutant which may reasonably be anticipated to cause or contribute to any impairment of visibility” in a Class I area. (Under the Regional Haze Rule, a source which fits this description is “subject to BART.”). Third, for each source subject to BART, the state or EPA must identify the level of control representing BART after considering the five factors set forth in CAA section 169A(g). The BART Guidelines provide a process for making BART determinations that states can use in implementing the BART requirements on a source-by-source basis. 
                    *See*40 CFR part 51, appendix Y, at IV.D. States, or EPA if developing a FIP, must address all visibility-impairing pollutants emitted by a source in the BART determination process. The most significant visibility impairing pollutants are SO2, NOX, and particulate matter (PM). A state implementation plan (SIP) or FIP addressing regional haze must include source-specific BART emission limits and compliance schedules for each source subject to BART. Once a state or EPA has made a BART determination, the BART controls must be installed and operated as expeditiously as practicable, but no later than five years after the date of the final SIP or FIP. 
                    *See*
                     CAA section 169A(g)(4) and 40 CFR 51.308(e)(1)(iv). In addition to what is required by the Regional Haze Rule, general SIP requirements mandate that the SIP or FIP include all regulatory requirements related to monitoring, recordkeeping, and reporting for the BART controls on the source. 
                    *See*
                     CAA section 110(a). B. BART FIP for Taconite Facilities in Michigan and Minnesota EPA is proposing to finalize NOX
                     and/or SO2
                     limits for the indurating furnaces at five taconite facilities in accordance with the procedures set forth in the FIP addressing the requirement for BART at taconite facilities. These facilities include Tilden Mining Company (Tilden) located at 101 Cci Mine Road, Ishpeming, Michigan; Hibbing Taconite Company (Hibbing) located at 4950 Highway 5 North, Hibbing, Minnesota; Minorca Mine (Minorca) located at 5950 Old Highway 53, Virginia, Minnesota; Northshore Mining Company—Silver Bay (Northshore) located at 10 Outer Drive, Silver Bay, Minnesota, and United Taconite (UTAC) located at 8470 Townline Road, Forbes, Minnesota. Tilden, Minorca, Northshore, and UTAC are owned by Cleveland-Cliffs, Inc. (Cliffs), formerly known as Cliffs Natural Resources, and Hibbing is jointly owned by Cliffs and United States Steel. The primary units identified as being subject to BART at Tilden, Hibbing, Minorca, UTAC, and Northshore include the following pelletizing, or indurating, furnaces: Tilden Grate Kiln Line 1, Hibbing Straight-Grate Lines 1-3, Minorca Straight-Grate Line 1, UTAC Grate Kiln Lines 1 and 2, and Northshore Straight-Grate Furnaces 11 and 12.[4]
                    
                     The U.S. taconite iron ore industry uses two types of pelletizing machines or processes: straight-grate kilns and grate kilns. In a straight-grate kiln, a continuous bed of agglomerated green pellets is carried through different temperature zones with upward draft or downward draft blown through the pellets on the metal grate. The grate kiln system consists of a traveling grate, a rotary kiln, and an annular cooler. A significant difference between these designs is that straight-grate kilns do not burn coal and therefore have a much lower potential for emitting SO2. Further, even within the same kiln type or process, individual furnaces (referred to as indurating or pelletizing) or processes have distinct equipment and process characteristics that may affect the compatibility and performance of certain types of burners. On February 6, 2013 (78 FR 8706), EPA promulgated a FIP that set BART limits for NOX
                     and SO2
                     emissions from furnaces at seven taconite facilities in Michigan and Minnesota (“Original FIP”). EPA took this action because Michigan and Minnesota had failed to meet a statutory deadline to submit their Regional Haze SIPs and subsequently failed to require BART at the taconite facilities within their borders. BART limits for NOX
                     were based upon the performance of high stoichiometric (high-stoich) low-NOX
                     burners (LNBs) [5]
                    
                     at two of the taconite furnaces at U.S. Steel's Minntac facility, while BART for SO2
                     was established as no additional controls, apart from a limit on the sulfur content of coal used in co-firing furnaces. In a related action, EPA published a final partial disapproval of Michigan's and Minnesota's Regional Haze SIPs on September 30, 2013 (78 FR 59825), due to the states' failure to require BART for taconite facilities within these states. ArcelorMittal USA LLC (“ArcelorMittal”) [6]
                    
                     and Cliffs, owners of several taconite facilities affected by the FIP, along with the State of Michigan, 
                    ( print page 96155)
                    filed timely petitions for review of the Original FIP. ArcelorMittal and Cliffs also filed a joint motion seeking a stay of the Original FIP, which was granted by the Eighth Circuit on June 14, 2013.[7]
                    
                     ArcelorMittal, Cliffs, the State of Michigan, and others also submitted petitions for reconsideration of the Original FIP, pursuant to CAA section 307(d)(7)(B). 42 U.S.C. 7607(d)(7)(B). On October 22, 2015 (80 FR 64160), in response to the petitions for reconsideration and due to new information submitted to EPA after promulgation of the Original FIP, EPA proposed to revise the Original FIP to revise NOX
                     and SO2
                     emission limits for certain taconite facilities. On April 16, 2016 (81 FR 21672), EPA promulgated the final 2016 revised FIP (“2016 FIP”). With respect to NOX, the emission limits in the 2016 FIP were based on information submitted to EPA by Cliffs and ArcelorMittal that suggested high-stoich LNBs, which formed the basis for the NOX
                     limits in the Original FIP, posed serious technical hurdles. In the 2016 FIP, EPA revised the NOX
                     emission limits for Tilden, Hibbing, Minorca, and UTAC, and set forth a process to confirm or modify those emission limits using continuous emissions monitoring system (CEMS) data that was to be collected after the installation of the selected low-NOX
                     technology. Under the 2016 FIP, the NOX
                     emission limits do not become enforceable until EPA confirms or modifies the emission limits in accordance with procedures set forth in the FIP. The NOX
                     emission limits in the 2016 FIP were based upon low-stoich LNBs (for grate kilns) and LNBs that utilize a combination of water and steam injection and pre-combustion technologies (for straight-grate kilns). With respect to SO2, EPA granted reconsideration of the SO2
                     limit for Tilden's grate kiln due to information that became available after the close of the public comment period on the 2013 FIP regarding Tilden's intent to burn mixed fuels. Cliffs' intent to burn mixed fuels at Tilden was not considered in the Original FIP and would have led to an inability to meet the established BART limit. The 2016 FIP limits the sulfur content of the coal combusted on Tilden Line 1 and sets an SO2
                     emission limit for the furnace. Cliffs and ArcelorMittal filed petitions for review of the 2016 FIP due to a dispute over the UPL equation in the final rule. The 2016 FIP requirements for each facility are set forth in 40 CFR 52.1183 for Michigan and 40 CFR 52.1235 for Minnesota and discussed further in the remainder of this action. II. Basis for NO
                    X
                     Limits The 2016 FIP set emission limits in pounds (lbs) of NOX
                     per million British Thermal Unit (MMBtu), based on a 30-day (720-hour) rolling average, and established a process to either confirm or modify the NOX
                     emission limits within established ranges based on CEMS data that Tilden, Hibbing, Minorca, and UTAC were required to submit to EPA by dates specified in the 2016 FIP.[8]
                    
                     The FIP also specified that the NOX
                     emission limits for these facilities would become enforceable only after EPA's confirmation or modification of the NOX
                     emission limits reflecting EPA's expectation that the owner or operator of each facility would provide the requisite data to EPA by the dates specified in the FIP. EPA's efforts to finalize NOX
                     emission limits for these facilities by the deadlines established in the FIP were complicated by several implementation issues, including challenges with installation of control technology, delays in receipt of requisite data, and emission limit modification requests not conforming to the requirements set forth in the FIP. The NOX
                     emission limits established for each furnace and the ranges of limits allowable under the limit modification process are set forth in Table 1. As indicated in Table 1, the emission limits for certain furnaces vary by the type of fuel being used (natural gas or “co-fire,” which is a combination of natural gas and coal). Table 1—NO
                        X
                         Limits and Limit Modification Ranges Established in the 2016 FIP
Furnace
Emission limit 
                             
                                (lbs NO
                                X
                                /MMBtu)
Emission limit 
                             modification range  
                             
                                (lbs NO
                                X
                                /MMBtu)Tilden Line 1:Natural Gas
2.8
2.8-3.0Co-fire
1.5
1.5-2.5Hibbing Line 1
1.2
1.2-1.8Hibbing Line 2
1.2
1.2-1.8Hibbing Line 3
1.2
1.2-1.8Minorca
1.2
1.2-1.8UTAC Line 1:Natural Gas
2.8
2.8-3.0Co-fire
1.5
1.5-2.5UTAC Line 2:Natural Gas
2.8
2.8-3.0Co-fire
1.5
1.5-2.5
 For Tilden, Hibbing, Minorca, and UTAC, the process specified in the 2016 FIP to either confirm or modify the NOX
                     emission limits within the established ranges included the installation of a CEMS, submission of an engineering report to EPA, installation of NOX
                     reduction control technology, submission of pellet quality analyses to EPA, and submission to EPA of a report to either confirm or modify the limit. For any furnace without CEMS already installed, CEMS installation was required for each furnace by 6 months after May 12, 2016, and the owner or operator was required to submit quarterly CEMS data to EPA after May 12, 2016, for the time periods specified 
                    ( print page 96156)
                    below in Table 2. Engineering reports containing detailed engineering analyses and modeling of the selected NOX
                     reduction technology for each furnace demonstrating that the technology was designed to meet an emission limit equal to the lower bound of the established range were required to be submitted to EPA by the deadlines specified in Table 2. NOX
                     reduction technology was required to be installed two months after the engineering report submission deadline. Beginning on the earlier of six months after the installation of NOX
                     reduction technology or the deadline for installation of the NOX
                     reduction technology, the owner or operator was required to submit quarterly pellet quality analyses to EPA, including an explanation of causes for pellet samples that failed to meet the acceptable range for any pellet quality analysis factor, for the time periods specified in Table 2. At the end of the CEMS and pellet quality data collection periods, the owner or operator of each furnace may submit a report to EPA to either confirm or modify the NOX
                     limits within the bounds described in the 2016 FIP (and above in this section). The 2016 FIP also allows the owner or operator to submit a report proposing a single NOX
                     limit for all fuels. The process for confirming or modifying limits detailed in the 2016 FIP specifies that EPA's determinations shall be based on the appropriate UPL equation, using CEMS data that meet pellet quality specifications and proper furnace/burner operation. For a more detailed description of the process set forth in the 2016 FIP to confirm or modify the emission limits, 
                    *see*40 CFR 52.1183 and 40 CFR 52.1235. Table 2—Timelines of Processes To Confirm or Modify Limits
Furnace
Period of
                             CEMS data 
                             required for  
                             submission  
                             to EPA
Engineering 
                             report  
                             deadline
NO
                            X
                             reduction 
                             technology  
                             installation  
                             deadline
Period of 
                             pellet  
                             quality data  
                             required for  
                             submission 
                             to EPA *
Report to 
                             confirm or  
                             modify limit  
                             deadlineMonths after May 12, 2016Tilden Line 1
0-57
48
50
50-57
57Hibbing Line 1
6-34
24
26
26-34
34Hibbing Line 2
6-52
42
44
44-52
52Hibbing Line 3
6-57
48
50
50-57
57Minorca's Indurating Furnace
6-52
42
44
44-52
52UTAC Line 1
0-34
24
26
26-34
34UTAC Line 2
0-52
42
44
44-52
52* If the owner or operator installed NO
                        X
                         reduction technology more than six months before the required date, pellet quality analyses were required to be submitted to EPA beginning six months after installation.
 The 2016 FIP incorporates two UPL equations to calculate emission limits. The appropriate equation is determined by the statistical distribution of the hourly CEMS data. If the data are normally distributed and statistically independent, the equation in 40 CFR 52.1183(p)(1) and 40 CFR 52.1235(f)(1) is used. If the data are not normally distributed or are normally distributed but not statistically independent, the non-parametric equation in 40 CFR 52.1183(p)(2) and 40 CFR 52.1235(f)(2) is used. None of the CEMS data submitted are normally distributed and statistically independent, therefore the non-parametric equation is the applicable equation for all limit setting in this action.[9] The non-parametric equation in the 2016 FIP calculates a 95th percentile UPL by ranking 720-hour averages of NOX
                     emissions in lbs/MMBtu from lowest to highest and identifying the value at the 95th percentile of the data set as the UPL and emission limit.[10]
                    
                     While a 95th percentile UPL establishes an emission rate that a source is predicted to be below during at least 95 out of 100 averaging periods, it was not EPA's intent to set a limit that a source would be expected to exceed five percent of the time once the limit was in place. Rather, EPA used the 95th percentile UPL to ensure that the final emission limits would be consistent with the actual emission reduction capabilities of the BART controls, as required by 40 CFR 51.301, which defines BART as “the degree of reduction achievable.” [11]
                    
                     EPA expected that during the eight-month CEMS data collection period, furnace operators would be adjusting numerous variables to optimize control technology performance, which would result in higher emissions at times during the initial “shakedown” period. Once the eight-month data collection period was over, EPA expected that the operators would have gained sufficient experience to run the furnaces and control technologies with fewer adjustments, meaning less emission variations and lower emissions overall. EPA selected the 95th percentile UPL to ensure the elevated emissions expected during the initial shakedown period would not become the basis for final emission limits. However, once continuous data collection began, the CEMS data did not show the expected elevated emissions levels during the shakedown period and emissions were not consistently lower toward the end of the data collection period as compared to the beginning of the period.[12]
                    
                     Therefore, EPA has 
                    ( print page 96157)
                    determined that using the UPL equation at the 99th percentile is more appropriate to establish an emission limit consistent with the actual emission reduction capabilities of the BART controls and is proposing to modify the UPL equations used to calculate both the NOX
                     and SO2
                     emission limits to reflect use of the 99th percentile. The emission limits EPA is proposing in this action were calculated using the UPL equations at 40 CFR 52.1183(p) and 40 CFR 52.1235(f) at the 99th percentile.[13] A. Tilden For Tilden's indurating furnace, Tilden Line 1 (EUKILN1), the 2016 FIP established a specific NOX
                     BART emission limit of 2.8 pounds of NOX
                    /MMBtu when burning natural gas, while allowing for potential modification of the limit within the range of 2.8-3.0 lbs NOX
                    /MMBtu. Similarly, the 2016 FIP established a specific NOX
                     BART emission limit of 1.5 lbs NOX
                    /MMBtu when co-firing coal and natural gas, with an allowance for potential modification of the limit within the range of 1.5-2.5 lbs NOX
                    /MMBtu.[14]
                    
                     The 2016 FIP also allowed for the establishment of a single NOX
                     limit for all fuels.[15] Tilden submitted a partially complete engineering report on May 21, 2020, and submitted the final engineering report on July 30, 2020. Tilden implemented low-stoichiometry LNBs designed to achieve an emission rate of 2.8 lbs NOX
                    /MMBtu when firing exclusively natural gas and 1.5 lbs NOX
                    /MMBtu when co-firing with coal, as described in the engineering report submitted to EPA. On February 12, 2021, Tilden submitted a report requesting modification of the NOX
                     limits for Line 1 pursuant to 40 CFR 52.1183 (k)(1)(vi). Tilden requested an emission limit of 3.0 lbs NOX
                    /MMBtu for all fuels. Tilden's limit modification request was accompanied by CEMS data (in 30-day rolling averages) from September 12, 2020, to February 2, 2021. On May 21, 2021, Tilden provided hourly emission data for July 1, 2020, to February 11, 2021. Approximately half of these data were collected when Tilden was co-firing with coal and half were collected when Tilden was burning exclusively natural gas. Tilden demonstrated that when burning natural gas, NOX
                     emission rates recorded were higher than the modeling results presented in the engineering report, and above the high end of the limit range established in the 2016 FIP (2.8-3.0 lbs/MMBtu). The CEMS data submitted to EPA when burning coal recorded emission rates within the range specified in the 2016 FIP (1.5-2.5 lbs/MMBtu). Tilden explained that the furnace is unable to achieve 3.0 lbs NOX
                    /MMBtu when burning exclusively natural gas and would need to burn a minimum of 80% coal when co-firing to meet a limit of 2.0 lbs NOX
                    /MMBtu. Tilden stated a preference to maximize natural gas usage and supplement with solid fuel as needed to meet NOX
                     limits.[16] The 2016 FIP provides Tilden the option to propose, for EPA's consideration and approval, a single NOX
                     emission limit for all fuels based on a 30-day rolling average. Citing the CEMS data, Tilden requested a revised NOX
                     BART limit of 3.0 lbs NOX
                    /MMBtu for all fuels that would apply on a rolling 30-day average, contending that this emission limit is the most stringent limit that can be met without substantial increases in coal usage, while maintaining pellet quality standards. Based on the equation set forth at 40 CFR 52.1183(p)(2), EPA calculated a 720-hour average NOX
                     emission limit of 3.8 lbs NOX
                    /MMBtu when burning exclusively natural gas, and separately, an emission limit of 1.9 lbs NOX
                    /MMBtu when burning mixed fuel.[17]
                    
                     While CEMS data show the installed emission control measures reduced NOX
                     emissions, the selected technology failed to achieve emission rates within the specified FIP ranges when burning only natural gas (2.8-3.0 lbs NOX
                    /MMBtu). Using the non-parametric equation with the full data set, unseparated by fuel type, EPA calculated a 720-hour average UPL of 3.7 lbs NOX
                    /MMBtu. EPA evaluated these CEMS data and considered Tilden's requested single NOX
                     emission limit of 3.0 lbs NOX
                    /MMBtu for all fuels based on a 30-day rolling average, as allowed at 40 CFR 52.1183(k)(1)(viii). EPA has concluded that Tilden's requested emission limit of 3.0 lbs NOX
                    /MMBtu for all fuels based on a 30-day rolling average is appropriate and reflects BART. It allows Tilden to select a fuel mix that maximizes natural gas usage and minimizes coal usage if the facility so chooses without exceeding the natural gas emission limit range established in the 2016 FIP. This has the duel environmental (visibility) benefit of minimizing NOX
                     emissions by setting an emissions limit that is below the calculated natural gas-only rate, and also potentially minimizing the use of coal and the associated SO2
                     emissions from coal burning. Therefore, based on these data and as provided at 40 CFR 52.1183(k)(1)(viii), EPA is proposing that a modified limit of 3.0 lbs NOX
                    /MMBtu for all fuels, with compliance to be determined on a rolling 30-day average basis, reflects BART for the Tilden Line 1 indurating furnace. B. Hibbing For Hibbing Lines 1, 2, and 3, the 2016 FIP established NOX
                     BART emission limits of 1.2 lbs NOX
                    /MMBtu that applied to each furnace individually, with provisions allowing for potential modification of the limits within the range of 1.2-1.8 lbs NOX
                    /MMBtu.[18] Hibbing implemented the NOX
                     reduction measures described in its engineering report, submitted to EPA on May 11, 2018, identified as LNBs in conjunction with water injection, at Hibbing Lines 1, 2, and 3. Hibbing installed CEMS on Lines 1, 2, and 3 and provided EPA with hourly NOX
                     emissions data on March 12, 2019, September 11, 2020, and February 12, 2021, for Lines 1, 2 and 3, respectively, documenting actual emissions after installation of LNB technology. Hibbing's submittals included CEMS data from July 12, 2018, to March 11, 2019, for Line 1; January 12, 2020, through September 1, 2020, for Line 2; and August 3, 2020, to February 11, 2021, for Line 3. The hourly CEMS data identified hours excluded from the limit-setting calculations because pellets failed to meet pellet quality specifications. Although the limit-setting period for Line 3 established in the 2016 FIP began August 3, 2020, Line 3 did not operate during the period between July 12 to August 3, 2020, due to COVID-related reasons. Line 2 did not operate from May 1, 2020, to July 31, 2020, during the limit setting period for similar reasons. On November 25, 2020, Hibbing provided additional information requested by EPA, including hourly CEMS data for Lines 1, 2, and 3 in Excel format to facilitate independent calculation of emission limits and identification of hours when the burner was not operated within the parameters modeled in the engineering report. The requirements at 40 CFR 52.1235((b)(1)(ii)(A)(6), (B)(6), and (C)(6) set forth the process for submitting data to support limit modifications under the 2016 FIP. At the time of the initial 
                    ( print page 96158)
                    CEMS data submissions, Hibbing requested NOX
                     emission limits of 1.7, 1.5, and 1.6 lbs NOX
                    /MMBtu on Lines 1, 2, and 3, respectively. The facility cited sub-zero temperatures and other factors that may have affected the calculated emission rates and restricted production. Further, Hibbing provided regression analyses assessing the relationship between furnace feed rates and NOX
                     emission rates during the limit-setting periods to support the requested limit increases. On October 22, 2021, Hibbing submitted a request to EPA to establish a crossline average emission limit for Lines 1, 2, and 3 of 1.6 lbs NOX
                    /MMBtu, with compliance to be determined on a 30-day rolling average basis. The submittal included hourly CEMS data for the same time periods as Hibbing's initial limit modification submittals and a regression analysis assessing the relationship between furnace feed rates and NOX
                     emission rates during the limit-setting periods to support the requested limit increases. The hourly CEMS data submitted to EPA included a description of the failure analyses identifying potential reasons for pellets failing to meet pellet quality specifications for hours excluded in the limit-setting calculation. There is no basis in the FIP for adjusting emission limits to account for possible future production levels based upon an assumed correlation between feed rates and emissions. Therefore, in accordance with 40 CFR 52.1235(f)(2), EPA calculated 720-hour average NOX
                     emission limits of 1.5 lbs NOX
                    /MMBtu for Line 1, 1.4 lbs NOX
                    /MMBtu for Line 2, and 1.5 lbs NOX
                    /MMBtu for Line 3.[19]
                    
                     Under the BART Guidelines, a source may be permitted to “ `average' emissions across any set of BART-eligible emission units within a fenceline, so long as the emission reductions from each pollutant being controlled for BART would be equal to those reductions that would be obtained by simply controlling each of the BART-eligible units that constitute BART-eligible sources.” [20]
                    
                     EPA averaged the single line limits described above and calculated a crossline 720-hour average emission limit of 1.5 lbs NOX
                    /MMBtu. The NOX
                     controls have been installed and are being operated on all three lines. Based on EPA's analysis, this crossline average emission limit is equal to the reductions that would be obtained by controlling each line separately. Therefore, based on these data and as provided at 40 CFR 52.12335(b)(1)(ii)(A)(7), (B)(7), and (C)(7), and consistent with 40 CFR 51.308(e) and 40 CFR part 51, appendix Y, at V, EPA is proposing that a crossline average emission limit of 1.5 lbs NOX
                    /MMBtu for Hibbing Lines 1, 2, and 3, with compliance to be determined on a 30-day rolling average basis, reflects NOX
                     BART for Hibbing Lines 1, 2, and 3. C. Minorca For Minorca's indurating furnace, the 2016 FIP established a NOX
                     BART emission limit of 1.2 lbs NOX
                    /MMBtu, while allowing for potential modification of the limit within the range of 1.2-1.8 lbs NOX
                    /MMBtu.[21] On November 12, 2019, Minorca submitted an engineering report to EPA which identified the low NOX
                     technology to be installed on Line 1 as an LNB, water injection, and utilization of specific operating parameters. The combined use of these measures was projected to meet an emission limit of 1.2 lbs NOX
                    /MMBtu based on a 30-day average. On September 11, 2020, Minorca submitted CEMS data for the period January 12, 2020, to September 10, 2020, excluding the CEMS values that did not meet pellet quality specifications, consistent with the 2016 FIP.[22] On October 22, 2021, Minorca submitted supplemental information consisting of 720-hour averages of CEMS data from January 12, 2020, through September 30, 2021. Adding the data from September 10, 2020, through September 30, 2021, to the original data set, Minorca calculated an emission limit of 1.6 lbs NOX
                    /MMBtu using the equation at 40 CFR 52.1235(f)(2). Minorca then performed a regression analysis assessing the relationship between furnace pellet production rates and NOX
                     emission rates during the limit-setting period to support the requested limit increase. Minorca cited the climate in Minnesota and other factors that may have affected production rates in its explanation of why the emission limit should be adjusted to 1.7 lbs NOX
                    /MMBtu. Based on the non-parametric equation at 40 CFR 52.1235(f)(2), EPA evaluated the 720-hour average NOX
                     emission data for the full data set submitted and calculated an emission limit of 1.6 lbs NOX
                    /MMBtu.[23]
                    
                     There is no basis in the FIP for adjusting emission limits to account for possible future production levels based upon an assumed correlation between feed rates and emissions. Therefore, based on these data and as provided at 40 CFR 52.1235(b)(1)(v)(7), EPA is proposing that a modified limit of 1.6 lbs NOX
                    /MMBtu, with compliance to be determined on a rolling 30-day average basis, reflects BART for the Minorca Line 1 indurating furnace. D. UTAC For UTAC's indurating furnaces, Grate Kiln Line 1 (EU040) and Grate Kiln Line 2 (EU042), the 2016 FIP established specific NOX
                     BART limits of 2.8 pounds of NOX
                    /MMBtu when burning natural gas, while allowing for potential modification of the limits within the range of 2.8-3.0 lbs NOX
                    /MMBtu. Similarly, the 2016 FIP established specific NOX
                     BART limits of 1.5 lbs NOX
                    /MMBtu when co-firing coal and natural gas, while allowing for potential modification of the limits within the range of 1.5-2.5 lbs NOX
                    /MMBtu.[24]
                    
                     The 2016 FIP also allowed for the establishment of a single NOX
                     limit for all fuels. UTAC submitted an engineering report for Line 1 on May 11, 2018. UTAC installed and began operating the sub-stoichiometric staged combustion LNB designed to achieve an emission rate of 2.8 lbs NOX
                    /MMBtu when firing exclusively natural gas and 1.5 lbs NOX
                    /MMBtu when co-firing with coal, as described in the engineering report submitted to EPA. UTAC subsequently made modifications to the Line 1 LNB in September 2018. On March 12, 2019, UTAC submitted a report requesting modification of the co-firing NOX
                     limit for Line 1 to 2.5 lbs NOX
                    /MMBtu, based upon 720-hour averages from February 2019. On November 12, 2019, UTAC submitted a report to EPA to address the requirement for an engineering report for Line 2. On November 12, 2021, UTAC submitted information on the LNB selected for Line 2, a modified version of the LNB installed on Line 1. This submittal included a report on computational fluid dynamics modeling demonstrating the burner was designed to achieve an emission rate of 2.8 lbs NOX
                    /MMBtu when firing exclusively natural gas and 1.5 lbs NOX
                    /MMBtu when co-firing with coal. On April 11, 2023, UTAC submitted an analysis of Line 1 and Line 2 NOX
                     performance 
                    ( print page 96159)
                    post LNB installations and requested a crossline average limit of 3.0 lb NOX
                    /MMBtu for all fuels, based on a 30-day rolling average. Along with the analysis, UTAC submitted 720-hour averages of total lbs NOX
                    /MMBtu for Lines 1 and 2 combined for the time period of January 25, 2022, to March 26, 2023. UTAC also submitted hourly CEMS and process information for this time period, which UTAC claimed as confidential business information, so that EPA could verify the calculations. Based on the equation set forth at 40 CFR 52.1235(f)(2), EPA calculated 720-hour average NOX
                     emission limits of 2.3 lbs NOX
                    /MMBtu and 3.6 lbs NOX
                    /MMBtu when burning exclusively natural gas for Lines 1 and 2, respectively. Separately, EPA calculated an emission limit of 3.1 lbs NOX
                    /MMBtu when burning mixed fuel on Line 2. There were 475 hours of co-firing data for Line 1, which is not sufficient to calculate a 720-hour average NOX
                     emission limit. EPA also calculated an emission limit of 3.1 lbs NOX
                    /MMBtu when combining hourly emissions data for both lines and all fuels.[25]
                    
                     While CEMS data show the installed emission control measures reduced NOX
                     emissions, the selected technology failed to achieve emission rates within the specified FIP ranges, particularly when evaluating separate limits for each fuel type. As discussed in II.
                    *B.,*
                     under the BART Guidelines, a source may be permitted to “ `average' emissions across any set of BART-eligible emission units within a fenceline, so long as the emission reductions from each pollutant being controlled for BART would be equal to those reductions that would be obtained by simply controlling each of the BART-eligible units that constitute BART-eligible sources.” [26]
                    
                     EPA evaluated the CEMS data and considered UTAC's requested crossline average NOX
                     emission limit of 3.0 lbs NOX
                    /MMBtu for all fuels, for Lines 1 and 2, with compliance to be determined on a 30-day rolling average basis. Based on EPA's analysis, this crossline average emission limit is equal to the reductions that would be obtained by controlling each line separately and is within the natural gas NOX
                     emission limit range established in the 2016 FIP. A single fuel-neutral emission limit allows UTAC to select a fuel mix that maximizes natural gas usage and minimizes coal usage without exceeding the natural gas emission limit range established in the 2016 FIP. This has the dual environmental (visibility) benefit of minimizing NOX
                     emissions by setting an emissions limit that is below the calculated natural gas-only rate, and also potentially minimizing the use of coal and the associated SO2
                     emissions from burning coal. Therefore, based on these data and as provided at 40 CFR 52.1235(b)(1)(iv)(A)(8) and (B)(8), and consistent with 40 CFR 51.308(e) and 40 CFR part 51, appendix Y, at V, EPA is proposing that a crossline emission limit of 3.0 lbs NOX
                    /MMBtu for all fuels for UTAC Lines 1 and 2, based on a rolling 30-day average, reflects BART for UTAC Lines 1 and 2. III. Basis for SO
                    2
                     Limits As previously described, the Original FIP determined that existing controls reflected SO2
                     BART for Minorca, Hibbing, and Northshore, and established SO2
                     emission limits for each furnace, with the option or requirement, depending on the facility, that the owner or operator submit one year of CEMS data to EPA to set a revised SO2
                     emission limit calculated using the appropriate UPL equation. The 2016 FIP limited the sulfur content of the coal burned at Tilden, set an SO2
                     emission limit, and required Tilden to submit one year of CEMS data to EPA to set a revised SO2
                     emission limit calculated using the appropriate UPL equation. For a more detailed description of the existing SO2
                     emission limits and the process set forth to modify the emission limits, 
                    *see*40 CFR 52.1235 (Hibbing, Minorca, and Northshore) and 40 CFR 52.1183 (Tilden). As discussed above in II., EPA has calculated the emission limits using the appropriate UPL equation at the 99th percentile. A. Tilden For Tilden, the 2016 FIP established a specific SO2
                     BART emission limit of 500 pounds of SO2
                     per hour (lbs/hr) for Grate Kiln Line 1, with no more than 0.60 percent sulfur by weight based on a monthly block average for any coal usage. The 2016 FIP also required that the owner or operator of Tilden calculate an SO2
                     emission limit based on one year of hourly CEMS emissions data using the appropriate UPL equation provided in 40 CFR 52.1183(p) and submit such calculations and data to EPA by 36 months after May 12, 2016. The 2016 FIP provides that EPA may revise the emission limit downward to reflect the calculated SO2
                     emission rate; however, EPA may not increase the SO2
                     limit above 500 lbs SO2
                    /hr. On October 1, 2018, Tilden submitted SO2
                     emissions data to EPA reflecting Tilden burning exclusively natural gas during the period March 28, 2017, through March 27, 2018. Citing various production-related concerns, Tilden adjusted its calculated limit to account for expected higher production capacity and higher ore sulfur content, which resulted in an adjusted expected emission rate of 568 lbs SO2
                    /hr. Tilden requested an SO2
                     emission limit of 500 lbs/hour for all fuels, regardless of natural gas or coal fuel usage, as established in the 2016 FIP. On November 10, 2022, Tilden submitted hourly SO2
                     data for Line 1 from the same time period of March 28, 2017, through March 27, 2018, during which time Tilden was exclusively burning natural gas. On March 1, 2023, Tilden provided hourly co-firing CEMS data for July 12, 2018, through July 11, 2019. On March 30, 2023, Tilden provided hourly CEMS data for the time period March 27, 2018, through March 26, 2019, which included both co-firing and natural gas-only operation. The 2016 FIP established a single SO2
                     emission limit to apply regardless of natural gas or coal fuel usage, which Tilden must meet at all times. Consistent with this approach, and because SO2
                     emissions are higher when Tilden is co-firing and the emission limit must be met at all times, EPA is proposing to base the emission limit modification calculations on all co-firing data included in Tilden's March 1, 2023, and March 30, 2023, CEMS data submissions. Based on the equation set forth at 40 CFR 52.1183(p)(2), EPA calculated an emission limit of 189 lbs SO2
                    /hour consistent with this approach.[27]
                    
                     There is no basis in the FIP for adjusting emission limits to account for possible future production levels or possible higher ore sulfur content. Therefore, based on these data and as provided at 40 CFR 52.1183(k)(3), EPA is proposing that an SO2
                     limit of 189 lbs SO2
                    /hr for the Tilden Line 1 indurating furnace, with compliance to be determined on a 30-day rolling average basis, reflects SO2
                     BART for Tilden Line 1. B. Hibbing For Hibbing Lines 1, 2, and 3, the Original FIP set an aggregate emission limit of 247.8 lbs SO2
                    /hr, based on a 30-day rolling average and excluding emissions resulting from the combustion of fuel oil, and provided Hibbing the option of calculating a revised SO2
                     emission limit by 20 months after March 8, 2013, based on one year of hourly CEMS emissions data and the non-parametric UPL equation. If any fuel oil is burned after the first day 
                    ( print page 96160)
                    that SO2
                     CEMS were required to be operational, the 2016 FIP requires Hibbing to submit the gallons of fuel oil burned per hour, the sulfur content of the fuel oil, and the SO2
                     emissions in pounds per hour, so that EPA can establish an SO2
                     emissions limit for fuel oil. Hibbing chose not to calculate a revised SO2
                     emission limit.[28] C. Minorca For Minorca, the Original FIP set an emission limit of 38.16 lbs SO2
                    /hour, based on a 30-day rolling average and excluding emissions when Minorca is combusting fuel oil, with an allowance for potential modification of the limit based on one year of hourly CEMS data submitted to EPA by 20 months after March 8, 2013. If any fuel oil is burned after the first day that SO2
                     CEMS were required to be operational, the 2016 FIP requires Minorca to submit the gallons of fuel oil burned per hour, the sulfur content of the fuel oil, and the SO2
                     emissions in pounds per hour so that EPA can establish an SO2
                     emissions limit for fuel oil. On April 6, 2018, Minorca submitted a request to modify the SO2
                     limit established in the 2016 FIP. Minorca ranked hourly data from the period March 1, 2017, through March 31, 2018, adjusted the calculated limit based on potential increased production rates, and requested an emission limit of 73.79 lbs SO2
                    /hour. On October 14, 2019, Minorca submitted additional hourly SO2
                     CEMS emission data for the time period of September 8, 2018, through September 7, 2019, revising their request to an emission limit of 208.66 lbs SO2
                    /hr. Minorca adjusted the calculated limit based on potential increased production rates, maximum ore sulfur content based on a ratio of maximum percent sulfur, and pellet type. Using the equation set forth at 40 CFR 52.1235(f)(2) and the most recent CEMS data from September 8, 2018, through September 7, 2019, EPA calculated an SO2
                     emission limit of 68.2 lbs SO2
                    /hour.[29]
                    
                     There is no basis in the FIP for adjusting emission limits to account for possible future production levels or possible higher ore sulfur content. Therefore, based on these data and as provided at 40 CFR 52.1235(b)(2)(v) and 40 CFR 51.308(e), EPA is proposing that an emission limit of 68.2 lbs SO2
                    /hr, based on a 30-day rolling average, reflects SO2
                     BART for the Minorca indurating furnace. D. Northshore For Northshore, the Original FIP set an aggregate emission limit of 39.0 lbs SO2
                    /hour for Furnace 11 (EU100/EU104) and Furnace 12 (EU110/EU114), based on a 30-day rolling average and excluding emissions resulting from the combustion of fuel oil, with a requirement that the owner or operator calculate a revised limit based on one year of hourly CEMS data and submit such data and calculations to EPA by 20 months after March 8, 2013. On April 11, 2018, Northshore submitted an SO2
                     emission limit modification request which included CEMS data from January 16, 2017, through January 15, 2018. Northshore adjusted the calculated emission limit based on potential increased production rates and requested a limit of 22.1 lbs SO2
                    /hour. On November 21, 2018, Northshore submitted a revised limit modification request of 49 lbs SO2
                    /hr. This limit modification request included data for the time period of January 16, 2017, through January 15, 2018, and adjusted the calculated limit based on potential increased production rates and potential increases in ore sulfur content. On November 10, 2022, Northshore submitted hourly SO2
                     CEMS data for the period of January 16, 2017, through January 15, 2018, as requested by EPA, to allow for EPA's independent calculation of emission limits. Using the equation set forth at 52.1235(f)(2) and the hourly SO2
                     CEMS data from January 16, 2017 through January 15, 2018, EPA calculated an aggregate SO2
                     emission limit of 17.0 lbs SO2
                    /hour for Furnaces 11 and 12.[30]
                    
                     There is no basis in the FIP for adjusting emission limits to account for possible future production levels or possible higher ore sulfur content. Therefore, based on these data and as provided at 40 CFR 52.1235(b)(2)(vi), EPA is proposing that an aggregate SO2
                     emission limit of 17.0 lbs SO2
                    /hr for Northshore Furnaces 11 and 12, based on a 30-day rolling average, reflects SO2
                     BART for Northshore. IV. CAA Section 110(l) Under CAA section 110(l) (sometimes referred to as an “anti-backsliding” provision), EPA cannot approve a plan revision “if the revision would interfere with any applicable requirement concerning attainment and reasonable further progress (as defined in section 7501 of this title), or any other applicable requirement of this chapter.” Based on the following analysis, we find that our revisions to the 2016 FIP are consistent with CAA section 110(l) because they will not interfere with any applicable requirement concerning attainment or reasonable further progress or any other applicable requirements of the CAA. A. NO*X*
                     Emission Limits When the 2016 FIP was promulgated, NOX
                     control technology had not yet been installed on the furnaces at Tilden, Hibbing, Minorca, and UTAC. Therefore, EPA established initial emission limitations based on the modeled (estimated) performance of the proposed technology along with a procedure to refine and modify the emission limits within a specified range based upon CEMS data collected after installation of the NOX
                     control technology. The 2016 FIP also allowed for the establishment of a single NOX
                     limit for all fuels. However, the NOX
                     emission limits in the 2016 FIP are not enforceable and final until EPA takes action to confirm or modify the initial emission limits established in the 2016 FIP. Because the NOX
                     limits established in the 2016 FIP have not been confirmed and made enforceable through the procedures set forth in the 2016 FIP, and are not currently enforceable, the proposed NOX
                     emission limits do not alter any existing enforceable limits, since there are no current enforceable limits. Therefore, approval of the proposed NOX
                     limits would not interfere with any applicable requirement concerning attainment or reasonable further progress, or any other applicable requirement of the CAA. Additionally, even if EPA were to evaluate the proposed NOX
                     emission limits in relation to the relevant provisions of the 2016 FIP, we believe the FIP will not interfere with any applicable requirement concerning attainment or reasonable further progress, or any other applicable requirements of the CAA.[31]
                    
                     EPA's proposed action will complete the process set forth in the 2016 FIP to finalize enforceable NOX
                     emission limits for Tilden, Hibbing, UTAC, and Minorca within ranges previously established. The NOX
                     emission limits EPA is proposing reflect BART because they were calculated using the corrected UPL equation and actual emission data recorded by CEMS, after installation of the required low-NOX
                     technology, pursuant to the procedures set forth in 
                    ( print page 96161)
                    the 2016 FIP. While crossline averaging was not addressed in the 2016 FIP, under the BART Guidelines, a source may be permitted to “ `average' emissions across any set of BART-eligible emission units within a fenceline, as long as the emission reductions from each pollutant being controlled for BART would be equal to those reductions that would be obtained by simply controlling each of the BART-eligible units that constitute BART-eligible sources.” [32]
                    
                     Based on EPA's analysis, the crossline average emission limits proposed for Hibbing and UTAC are equal to the reductions that would be obtained by controlling each line separately. The proposed NOX
                     emission limits do not reflect a change in EPA's BART determination. Rather, the proposed limits were calculated using CEMS data and the corrected UPL equation, following the procedure set forth in the 2016 FIP, to more accurately reflect an emission limit consistent with the actual emission reduction capabilities of the BART controls and within the natural gas ranges established in the 2016 FIP. Therefore, there are no expected increases in NOX
                     emissions compared to the ranges set in the 2016 FIP. B. SO*2*
                     Emission Limits EPA is proposing to revise the SO2
                     emission limits applicable to Minorca, Northshore, and Tilden. Minorca and Northshore are straight-grate furnaces that do not co-fire with coal; SO2
                     emissions from these sources result from sulfur in the ore processed in the furnaces. As discussed previously, when the Original FIP was promulgated, SO2
                     BART for Minorca and Northshore was established as no further controls. EPA set initial SO2
                     emission limits based on limited stack test data and established a procedure to refine those limits when CEMS data became available. EPA is proposing to modify the Minorca emission limit from 38.16 lbs SO2
                    /hour to 68.2 lbs SO2
                    /hour and the Northshore emission limit from 39.0 lbs SO2
                    /hour to 17.0 lbs SO2
                    /hour. These proposed revised emission limits do not reflect a change in EPA's BART determination or in operations at the facilities that would lead to an increase or decrease in SO2
                     emissions. Rather, the emission limits EPA is proposing establish emission limits that more accurately reflect BART because they were calculated using the corrected UPL equation and actual emission data recorded by CEMS, pursuant to the procedures set forth in the Original FIP. Similarly, the 2016 FIP established SO2
                     BART for Tilden as a limit on the sulfur content of the coal and no further controls, and set an SO2
                     emission limit for Tilden along with a process to modify that limit when CEMS data became available. EPA is not proposing to revise any limits on the sulfur content of coal at Tilden. EPA is only proposing to modify Tilden's emissions limit from 500 lbs SO2
                    /hour to 189 lbs SO2
                    /hour. The revised emission limit was calculated using the corrected UPL equation and actual emission data recorded by CEMS, pursuant to the procedures set forth in the 2016 FIP. In sum, as a result of the revised SO2
                     emissions limits described above, EPA does not expect changes in SO2
                     emissions from these sources. The limits do not reflect a change in EPA's BART determination or in operations at the facilities. Rather, the proposed limits more accurately reflect actual emissions that were calculated using newly available CEMS data and the corrected UPL equation. C. Regional Haze SIPs On June 12, 2012 (77 FR 34801), EPA approved Minnesota's regional haze plan for the first implementation planning period as satisfying the applicable requirements in 40 CFR 51.308, except for BART emission limits for the taconite facilities. Among the regional haze plan elements approved were Minnesota's long-term strategy for making reasonable progress toward visibility goals. Minnesota's long-term strategy did not rely on the achievement of any particular degree of emission control from the taconite plants to achieve reasonable progress goals. On December 3, 2012 (77 FR 71533), EPA approved Michigan's regional haze plan for the first implementation planning period as satisfying the applicable requirements in 40 CFR 51.308, except for BART emission limits for Tilden, St. Mary's Cement, and Escanaba Paper Company. Among the regional haze plan elements approved was Michigan's long-term strategy for making reasonable progress toward visibility goals. Michigan's long-term strategy did not rely on the achievement of any particular degree of emission control from the taconite plants to achieve reasonable progress goals. On August 23, 2021, Michigan submitted a revision to their regional haze SIP for the second implementation planning period. Michigan's submittal provided a long-term strategy and reasonable progress goals that included 2028 emission projections for Tilden based on a 2016 modeling platform developed by LADCO that did not rely on emission limits or ranges in the 2016 FIP. On December 20, 2022, Minnesota submitted a revision to its regional haze SIP for the second implementation period. Minnesota's long-term strategy included implementation of the current applicable limits and ranges in the Original FIP and 2016 FIP for Hibbing, Minorca, UTAC, and Northshore. However, in applying the long-term strategy to develop its reasonable progress goals, Minnesota used 2028 projected emissions modeling that relied on the 2016 FIP limits only for UTAC and not for Hibbing, Minorca, or Northshore. For Hibbing and Minorca, Minnesota's modeling utilized 2028 projected emissions provided by LADCO using the 2016 emissions modeling platform since CEMS data was not available at the time. For Northshore, Minnesota accounted for the facility being idled until 2031, which was incorporated into an enforceable agreement as an Administrative Order by Consent issued by the Minnesota Pollution Control Agency to Northshore and Cleveland-Cliffs, Inc. To project 2028 emissions for UTAC, Minnesota used 2017 CEMS data to convert NOX
                     and SO2
                     emissions and associated heat input into emission rates that allowed for a comparison to the limits and ranges in the 2016 FIP. Minnesota kept heat input rates the same and assumed compliance at the least stringent end of the emission limit ranges (
                    *e.g.,*
                     for an emission limit range of 2.8-3.0 lbs NOX
                    /MMBtu, Minnesota assumed 3.0 lbs NOX
                    /MMBtu in the emission calculations), resulting in conservative emission projections for 2028. Using a photochemical model based on the 2028 emission projections for all selected sources in their regional haze plan, including the taconite facilities, Minnesota estimated future visibility and established their reasonable progress goals. Although EPA has not yet taken final action on the regional haze SIP revisions submitted by Michigan and Minnesota for the second implementation period, the assumptions used in the long-term strategies and reasonable progress goals were no more stringent than the currently applicable Original FIP and 2016 FIP emission limits and ranges or the revised limits we are proposing in this action. Therefore, the revised NOX
                     emission limits for Tilden, Hibbing, UTAC, Minorca, and Northshore represent greater control overall than was assumed in Michigan's and Minnesota's long-term strategy and would not result in a degradation of the reasonable progress goals required by 40 CFR 51.308(d)(1).
                    ( print page 96162) D. National Ambient Air Quality Standards (NAAQS) and Reasonable Further Progress With respect to requirements concerning attainment of the NAAQS and reasonable further progress, EPA is proposing to finalize NOX
                     BART emission limits for seven subject-to-BART units at four facilities within the ranges established in the 2016 FIP. EPA is also proposing to finalize SO2
                     emission limits for three facilities which will not result in an increase in SO2
                     emissions. Thus, the proposed FIP revision will not interfere with attainment and reasonable further progress requirements. E. Conclusion We find that these revisions are consistent with CAA section 110(l). The previous sections of the notice explain how the proposed FIP revision will comply with applicable regional haze requirements and general implementation plan requirements and demonstrate that it will not interfere with any regional haze program requirements, attainment and reasonable further progress, or any other requirement of the CAA. V. Environmental Justice Considerations Executive Order 12898 (59 FR 7629, February 16, 1994) directs Federal agencies, to the greatest extent practicable and permitted by law, to make environmental justice (EJ) part of their mission by identifying and addressing, as appropriate, disproportionately high and adverse human health or environmental effects of their programs, policies, and activities on communities with EJ concerns. EPA believes that the human health and environmental conditions that exist prior to this action do not result in disproportionate and adverse effects on communities with EJ concerns. To identify environmental burdens and susceptible populations in communities nearby the Tilden, Hibbing, Minorca, Northshore, and UTAC facilities, and to examine the implications of the proposed NOX
                     and SO2
                     emission limits, EPA utilized the EJScreen tool to evaluate environmental and demographic indicators within a 3-mile buffer, a 10-mile buffer, and the county that each facility is located in (Marquette County, Michigan for Tilden; St. Louis County, Minnesota for Hibbing, Minorca, and UTAC; and Lake County, Minnesota for Northshore). EPA's screening-level analysis indicates that communities near the facilities affected by this action score below the national average for the EJScreen “Demographic Index”, which is the average of an area's percent minority and percent low-income populations, 
                    *i.e.,*
                     the two demographic indicators explicitly named in Executive Order 12898. Additionally, the results indicate that these areas score below the 80th percentile (in comparison to the nation as a whole) in the 13 EJ Indexes established by EPA, which include a combination of environmental and demographic information. EPA has provided that if any of the EJ indexes for the areas under consideration are at or above the 80th percentile nationally, then further review may be appropriate. As discussed in the EPA's EJ technical guidance, communities with EJ concerns often experience greater exposure and disease burdens than the general population, which can increase their susceptibility to adverse health effects from environmental stressors. EPA believes that this action is not likely to result in new disproportionate and adverse effects on communities with EJ concerns. This action proposes to set final NOX
                     and SO2
                     emission limits which are not expected to result in new or increased burdens on residents, including those in communities of EJ concern, as specified in Executive Order 12898. EPA invited the identification of EJ and other concerns during its Tribal consultations which occurred prior to proposing emission limits for all five taconite facilities. No EJ concerns were raised in the context of this action. We have determined that this rulemaking will not have disproportionately high and adverse human health or environmental effects on communities with EJ concerns. The information supporting this Executive Order review is contained in the docket for this action, including the EJSCREEN reports considering a 3-mile buffer, a 10-mile buffer, and the county that each taconite facility is in. VI. Proposed Action EPA is proposing to modify the UPL equations used to establish NOX
                     and SO2
                     emission limits and to finalize NOX
                     and/or SO2
                     limits for the indurating furnaces at five taconite facilities in accordance with the procedure set forth in the 2016 FIP. Specifically, EPA is proposing to approve the following NOX
                     limits, with compliance to be determined on a rolling 30-day average: 3.0 lbs NOX
                    /MMBtu for all fuels for Tilden Line 1; a crossline average limit of 1.5 lb NOX
                    /MMBtu for Hibbing Lines 1, 2, and 3; a crossline average emission limit of 3.0 lbs NOX
                    /MMBtu for all fuels for UTAC Lines 1 and 2; and 1.6 lbs NOX
                    /MMBtu for Minorca's indurating furnace. EPA is proposing to approve the following SO2
                     limits, with compliance to be determined on a rolling 30-day average: 189 lbs SO2
                    /hr for all fuels for Tilden Line 1; an aggregate emission limit of 247.8 lbs SO2
                    /hr for Hibbing Lines 1, 2, and 3; 68.2 lbs SO2
                    /hr for Minorca's indurating furnace; and an aggregate limit of 17.0 lbs SO2
                    /hr for Northshore Furnaces 11 and 12. VII. Statutory and Executive Order Reviews A. Executive Order 12866: Regulatory Planning and Review and Executive Order 14094: Modernizing Regulatory Review This action is not a significant regulatory action as defined in Executive Order 12866, as amended by Executive Order 14094, and was therefore not subject to a requirement for Executive Order 12866 review. B. Paperwork Reduction Act This proposed action does not impose an information collection burden under the provisions of the Paperwork Reduction Act, 44 U.S.C. 3501 
                    *et seq.*
                     Because the FIP applies to just the taconite facilities in Michigan and Minnesota, the Paperwork Reduction Act does not apply. 
                    *See*5 CFR 1320.3(c). C. Regulatory Flexibility Act I certify that this proposed action will not have a significant economic impact on a substantial number of small entities under the RFA. This proposed action will not impose any requirements on small entities. This action, if finalized, will add additional controls to certain sources. None of these sources are owned by small entities, and therefore are not small entities. D. Unfunded Mandates Reform Act (UMRA) This proposed action does not contain any unfunded mandate as described in UMRA, 2 U.S.C. 1531-1538, and does not significantly or uniquely affect small governments. The proposed action imposes no enforceable duty on any state, local or Tribal governments or the private sector. E. Executive Order 13132: Federalism This proposed action does not have federalism implications. It will not have substantial direct effects on the states, on the relationship between the national government and the states, or on the distribution of power and responsibilities among the various levels of government.
                    ( print page 96163) F. Executive Order 13175: Consultation and Coordination With Indian Tribal Governments This proposed action does not have Tribal implications, as specified in Executive Order 13175. It will not have substantial direct effects on Tribal governments. Thus, Executive Order 13175 does not apply to this action. Consistent with the EPA Policy on Consultation and Coordination with Indian Tribes, EPA did discuss this action in conference calls with the Michigan and Minnesota Tribes. G. Executive Order 13045: Protection of Children From Environmental Health Risks and Safety Risks This action is not subject to Executive Order 13045 because it is not 3(f)(1) significant as defined in Executive Order 12866, and because EPA does not believe the environmental health or safety risks addressed by this action present a disproportionate risk to children. To the extent this action, if finalized, will limit emissions of NOX
                     and SO2
                     emissions, the rule will have a beneficial effect on children's health by reducing air pollution. H. Executive Order 13211: Actions Concerning Regulations That Significantly Affect Energy Supply, Distribution, or Use This action is not subject to Executive Order 13211 (66 FR 28355, May 22, 2001), because it is not a significant regulatory action under Executive Order 12866. I. National Technology Transfer and Advancement Act This rulemaking does not involve technical standards. J. Executive Order 12898: Federal Actions To Address Environmental Justice in Minority Populations and Low-Income Populations and Executive Order 14096: Revitalizing Our Nation's Commitment to Environmental Justice for All EPA believes that the human health and environmental conditions that exist prior to this action do not result in disproportionate and adverse effects on communities with Environmental Justice concerns. This proposed FIP limits emissions of NOX
                     and SO2
                     from five taconite facilities in Michigan and Minnesota. EPA believes that this action is not likely to result in new disproportionate and adverse effects on communities with environmental justice concerns. EPA performed an EJ analysis, as is described above in the section titled, “Environmental Justice Considerations.” The analysis was done for the purpose of providing additional context and information about this rulemaking to the public, not as a basis of the action. Due to the nature of the action being taken here, this action is expected to have a neutral to positive impact on the air quality of the affected area. In addition, there is no information in the record upon which this decision is based inconsistent with the stated goal of E.O. 12898 of achieving EJ for communities with EJ concerns. List of Subjects in 40 CFR Part 52 Environmental protection
Air pollution control
Incorporation by reference
Intergovernmental relations
Nitrogen dioxide
Regional haze
Reporting and recordkeeping requirements
Sulfur oxides
 Michael S. Regan, Administrator.
 For the reasons stated in the preamble, EPA proposes to amend title 40 CFR part 52 as follows: PART 52—APPROVAL AND PROMULGATION OF IMPLEMENTATION PLANS
 1.The authority citation for part 52 continues to read as follows: Authority:
                    42 U.S.C. 7401 
                        *et seq.* 2.Section 52.1183 is amended by: a.in paragraph (k) revising (1), (3), (4) and (5); b.in paragraph (l) revising (3), (4)(v) and (4)(xii); c.in paragraph (n) revising (1) and (2); and d.removing and reserving paragraph (p). The revisions read as follows: § 52.1183
  
 (k) Tilden Mining Company, or any subsequent owner/operator of the Tilden Mining Company facility in Ishpeming, Michigan, shall meet the following requirements: (1) 
                        *NO**X**Emission Limits.* (i) An emission limit of 3.0 lbs NOX
                        /MMBTU, based on a 30-day rolling average, shall apply to Tilden Grate Kiln Line 1 (EUKILN1) beginning January 3, 2025. (ii) Compliance with this emission limit shall be demonstrated with data collected by a continuous emissions monitoring system (CEMS) for NOX. (2) 
                        *SO**2**Emission Limits.*
                         * * * (3) The owner or operator of the Tilden Grate Kiln Line 1 (EUKILN1) furnace shall meet an emission limit of 189.0 lbs SO2
                        /hr, based on a 30-day rolling average, beginning on January 3, 2025. Compliance with this emission limit shall be demonstrated with data collected by a continuous emissions monitoring system (CEMS) for SO2. Beginning November 12, 2016, any coal burned on Tilden Grate Kiln Line 1 shall have no more than 0.60 percent sulfur by weight based on a monthly block average. The sampling and calculation methodology for determining the sulfur content of coal must be described in the monitoring plan required for this furnace. (4) Emissions resulting from the combustion of fuel oil are not included in the calculation of the 30-day rolling average. However, if any fuel oil is burned after the first day that SO2
                         CEMS are required to be operational, then the information specified in (k)(5) must be submitted, for each calendar year, to the Regional Administrator at 
                        *R5ARDReporting@epa.gov*
                         no later than 30 days after the end of each calendar year so that a limit can be set. (5) Records shall be kept for any day during which fuel oil is burned as fuel (either alone or blended with other fuels) in Grate Kiln Line 1. These records must include, at a minimum, the gallons of fuel oil burned per hour, the sulfur content of the fuel oil, and the SO2
                         emissions in pounds per hour. If any fuel oil is burned after the first day that SO2
                         CEMS are required to be operational, then the records must be submitted, for each calendar year, to the Regional Administrator at 
                        *R5ARDReporting@epa.gov*
                         no later than 30 days after the end of each calendar year. (l) 
                        *Testing and monitoring.* * * * (3) The owner or operator shall install, certify, calibrate, maintain, and operate one or more continuous diluent monitor(s) (O2
                         or CO2) and continuous stack gas flow rate monitor(s) on Tilden Grate Kiln Line 1 to allow conversion of the NOX
                         and SO2
                         concentrations to units of the standard (lbs/MMBTU and lbs/hr, respectively) unless a demonstration is made that a diluent monitor and/or continuous flow rate monitor are not needed for the owner or operator to demonstrate compliance with applicable emission limits in units of the standard. (4) * * * 
 (v) The owner or operator of each CEMS must furnish the Regional Administrator a written report of the results of each quarterly performance evaluation and a data accuracy assessment pursuant to 40 CFR part 60 appendix F within 60 days after the calendar quarter in which the 
                        ( print page 96164)
                        performance evaluation was completed. These reports shall be submitted to the Regional Administrator at 
                        *R5AirEnforcement@epa.gov.* 
 (xii) Data substitution must not be used for purposes of determining compliance under this regulation. If CEMS data is measuring only a portion of the NOX
                         or SO2
                         emitted during startup, shutdown, or malfunction conditions, the CEMS data may be supplemented, but not modified, by the addition of calculated emission rates using procedures set forth in the site specific monitoring plan. 
 (n) 
                        *Reporting requirements.* (1) Unless instructed otherwise, all requests, reports, submittals, notifications, and other communications required by this section shall be submitted to the Regional Administrator at 
                        *R5AirEnforcement@epa.gov.*
                         References in this section to the Regional Administrator shall mean the EPA Regional Administrator for Region 5. (2) The owner or operator of each BART affected unit identified in this section and CEMS required by this section must provide to the Regional Administrator the written notifications, reports, and plans identified at paragraphs (n)(2)(i) through (viii) of this section. * * * 
 (p) [Reserved]
 3.Section 52.1235 is amended by: a.in paragraph (b) revising (1)(ii), (1)(iv), (1)(v), (1)(vi), (2)(ii), (2)(v) and (2)(vi); b.in paragraph (c) revising (1), (2), (3), (4)(ii), (4)(v), and (4)(xii); and c.in paragraph (e) revising (1) and (2); and d.revising paragraph (f). The revisions read as follows: § 52.1235
  
 (b) * * * (1) NOX
                         emission limits. (i) * * * (ii) Hibbing Taconite Company (A) An aggregate emission limit of 1.5 lbs NOX
                        /MMBtu, based on a 30-day rolling average, shall apply to the combined NOX
                         emissions from the three indurating furnaces, Line 1 (EU020), Line 2 (EU021), and Line 3 (EU022), beginning on January 3, 2025. To determine the aggregate emission rate, the combined NOX
                         emissions from Lines 1, 2, and 3 shall be divided by the total heat input to the three lines (in MMBtu) during every rolling 30-day period. (B) Compliance with this emission limit shall be demonstrated with data collected by a continuous emissions monitoring system (CEMS) for NOX. (iii) * * * (iv) United Taconite (A) An aggregate emission limit of 3.0 lbs NOX
                        /MMBtu, based on a 30-day rolling average, shall apply to the combined NOX
                         emissions from the two indurating furnaces, Grate Kiln Line 1 (EU040) and Grate Kiln Line 2 (EU042), beginning on January 3, 2025. To determine the aggregate emission rate, the combined NOX
                         emissions from Grate Kiln Line 1 and Grate Kiln Line 2 shall be divided by the total heat input to the two lines (in MMBtu) during every rolling 30-day period. (B) Compliance with this emission limit shall be demonstrated with data collected by a continuous emissions monitoring system (CEMS) for NOX. (v) Minorca Mine (A) An emission limit of 1.6 lbs NOX
                        /MMBtu, based on a 30-day rolling average, shall apply to the Minorca Mine indurating furnace (EU026). This emission limit will become enforceable on January 3, 2025. (B) Compliance with this emission limit will be demonstrated with data collected by a continuous emissions monitoring system (CEMS) for NOX. (vi) Northshore Mining Company—Silver Bay: An emission limit of 1.5 lbs NOX
                        /MMBtu, based on a 30-day rolling average, shall apply to Furnace 11 (EU100/EU104) beginning October 10, 2018. An emission limit of 1.5 lbs NOX
                        /MMBtu, based on a 30-day rolling average, shall apply to Furnace 12 (EU110/114) beginning October 11, 2019. However, for any 30, or more, consecutive days when only natural gas is used at either Northshore Mining Furnace 11 or Furnace 12, a limit of 1.2 lbs NOX
                        /MMBtu, based on a 30-day rolling average, shall apply. An emission limit of 0.085 lbs NOX
                        /MMBtu, based on a 30-day rolling average, shall apply to Process Boiler #1 (EU003) and Process Boiler #2 (EU004) beginning October 10, 2021. The 0.085 lbs NOX
                        /MMBtu emission limit for each process boiler applies at all times a unit is operating, including periods of start-up, shut-down and malfunction. (2) 
                        *SO**2**Emission Limits.* (i) * * * (ii) Hibbing Taconite Company (A) An aggregate emission limit of 247.8 lbs SO2
                        /hour, based on a 30-day rolling average, shall apply to the combined SO2
                         emissions from the three indurating furnaces, Line 1 (EU020), Line 2 (EU0021), and Line 3 (EU022), beginning on February 10, 2017. To determine the aggregate emission rate, the combined SO2
                         emissions from Lines 1, 2, and 3 shall be divided by the total hours of operation of the three lines during every rolling 30-day period. (B) Compliance with this emission limit shall be demonstrated with data collected by a continuous emissions monitoring system (CEMS) for SO2. (C) Emissions resulting from the combustion of fuel oil are not included in the calculation of the 30-day rolling average. However, if any fuel oil is burned after the first day that SO2
                         CEMS are required to be operational, then the information specified in (b)(2)(vii) must be submitted, for each calendar year, to the Regional Administrator at 
                        *R5ARDReporting@epa.gov*
                         no later than 30 days after the end of each calendar year so that a limit can be set. (iii) * * * (iv) * * * (v) Minorca Mine (A) An emission limit of 68.2 lbs SO2
                        /hr, based on a 30-day rolling average, shall apply to the indurating furnace (EU026) beginning January 3, 2025. (B) Compliance with this emission limit shall be demonstrated with data collected by a continuous emissions monitoring system (CEMS) for SO2. (C) Emissions resulting from the combustion of fuel oil are not included in the calculation of the 30-day rolling average. However, if any fuel oil is burned after the first day that SO2
                         CEMS are required to be operational, then the information specified in (b)(2)(vii) must be submitted, for each calendar year, to the Regional Administrator at 
                        *R5ARDReporting@epa.gov*
                         no later than 30 days after the end of each calendar year so that a limit can be set. (vi) Northshore Mining Company—Silver Bay (A) An aggregate emission limit of 17.0 lbs SO2
                        /hr, based on a 30-day rolling average, shall apply to Furnace 11 (EU100/EU104) and Furnace 12 (EU110/EU114) beginning January 3, 2025. To determine the aggregate emission rate, the combined SO2
                         emissions from Furnace 11 and Furnace 12 shall be divided by the total hours of operation of the two furnaces during every rolling 30-day period. (B) Compliance with these emission limits shall be demonstrated with data collected by a continuous emissions monitoring system (CEMS) for SO2. (C) Emissions resulting from the combustion of fuel oil are not included in the calculation of the 30-day rolling average. However, if any fuel oil is burned after the first day that SO2
                         CEMS are required to be operational, then the information specified in (b)(2)(vii) must 
                        ( print page 96165)
                        be submitted, for each calendar year, to the Regional Administrator at 
                        *R5ARDReporting@epa.gov*
                         no later than 30 days after the end of each calendar year so that a limit can be set. (D) The owner or operator may submit to EPA for approval an alternative monitoring procedure request. The request shall include at least one year of CEMS data demonstrating consistent values at or below 5 lbs SO2
                        /hr. The alternative monitoring procedure request shall not remove the obligation to maintain and operate a flow rate monitor in the stack. If approved, the owner or operator would not be required to operate the SO2
                         CEMS and may demonstrate continuous compliance using an emission factor derived from the average of at least one year of existing SO2
                         data using the procedure set forth in the site specific monitoring plan, and verified by annual stack tests using EPA approved test methods, multiplied by the daily measured flow rate as recorded by the flow rate monitor and recorded as the daily lb/hr SO2
                         emission rate. (vii) * * * (c) Testing and monitoring. (1) The owner or operator of the respective facility shall install, certify, calibrate, maintain and operate continuous emissions monitoring systems (CEMS) for NOX
                         on United States Steel Corporation, Keetac unit EU030; Hibbing Taconite Company units EU020, EU021, and EU022; United States Steel Corporation, Minntac units EU225, EU261, EU282, EU315, and EU334; United Taconite units EU040 and EU042; Minorca Mine unit EU026; and Northshore Mining Company-Silver Bay units Furnace 11 (EU100/EU104) and Furnace 12 (EU110/EU114). Compliance with the emission limits for NOX
                         shall be determined using data from the CEMS. (2) The owner or operator shall install, certify, calibrate, maintain, and operate CEMS for SO2
                         on United States Steel Corporation, Keetac unit EU030; Hibbing Taconite Company units EU020, EU021, and EU022; United States Steel Corporation, Minntac units EU225, EU261, EU282, EU315, and EU334; United Taconite units EU040 and EU042; Minorca Mine unit EU026; and Northshore Mining Company-Silver Bay units Furnace 11 (EU100/EU104) and Furnace 12 (EU110/EU114). (3) The owner or operator shall install, certify, calibrate, maintain, and operate one or more continuous diluent monitor(s) (O2
                         or CO2) and continuous stack gas flow rate monitor(s) on the BART affected units to allow conversion of the NOX
                         and SO2
                         concentrations to units of the standard (lbs/MMBTU and lbs/hr, respectively) unless a demonstration is made that a diluent monitor and/or continuous flow rate monitor are not needed for the owner or operator to demonstrate compliance with applicable emission limits in units of the standards. (4) * * * (i) * * * (ii) CEMS must be installed and operational such that the operational status of the CEMS identified in paragraphs (c)(1) and (2) of this section shall be verified by, as a minimum, completion of the manufacturer's written requirements or recommendations for installation, operation, and calibration of the devices. 
 (v) The owner or operator of each CEMS must furnish the Regional Administrator a written report of the results of each quarterly performance evaluation and a data accuracy assessment pursuant to 40 CFR part 60 appendix F within 60 days after the calendar quarter in which the performance evaluation was completed. These reports shall be submitted to the Regional Administrator at 
                        *R5AirEnforcement@epa.gov.* 
 (xii) Data substitution must not be used for purposes of determining compliance under this section. If CEMS data is measuring only a portion of the NOX
                         or SO2
                         emitted during startup, shutdown, or malfunction conditions, the CEMS data may be supplemented, but not modified, by the addition of calculated emission rates using procedures set forth in the site specific monitoring plan. * * * 
 (e) Reporting Requirements (1) Unless instructed otherwise, all requests, reports, submittals, notifications, and other communications required by this section shall be submitted to the Regional Administrator at 
                        *R5AirEnforcement@epa.gov*. References in this section to the Regional Administrator shall mean the EPA Regional Administrator for Region 5. (2) The owner or operator of each BART affected unit identified in this section and CEMS required by this section must provide to the Regional Administrator the written notifications, reports and plans identified at paragraphs (e)(2)(i) through (viii) of this section. * * * 
 (f) Equations for establishing the upper predictive limit— (1) Equation for normal distribution and statistically independent data.  Where: *x*
                             = average or mean of hourly test run data; *t*[(*n*−1),(0.99)]
                             = t score, the one-tailed t value of the Student's t distribution for a specific degree of freedom (n−1) and a confidence level (0.99, to reflect the 99th percentile) *s*2
                             = variance of the hourly data set; *n*
                             = number of values (
                            *e.g.,*
                             5,760 if 8 months of valid lbs NOX
                            /MMBTU hourly values) *m*
                             = number of values used to calculate the test average (m = 720 as per averaging time) (i) To determine if statistically independent, use the Rank von Neumann Test on p. 137 of data Quality Assessment: Statistical Methods for Practitioners EPA QA/G-9S. (ii) Alternative to Rank von Neumann test to determine if data are dependent, data are dependent if t test value is greater than t critical value, where:  r
                             = correlation between data points *t critical*
                             = t[(n−2),(0.95)]
                             = t score, the two-tailed t value of the Student's t distribution for a specific degree of freedom (n−2) and a confidence level (0.95) (iii) The Anderson-Darling normality test is used to establish whether the data are normally distributed. That is, a distribution is considered to be normally distributed when p > 0.05. (2) Non-parametric equation for data not normally distributed and normally distributed but not statistically independent. *m*
                             = (n+1) * α *m*
                             = the rank of the ordered data point, when data are sorted smallest to largest. The data points are 720-hour averages for establishing NOX
                             limits. *n*
                             = number of data points (
                            *e.g.,*
                             5040 720-hourly averages for eight months of valid NOX
                             lbs/MMBTU values) α = 0.99, to reflect the 99th percentile If 
                        *m*
                         is a whole number, then the limit, 
                        *UPL,*
                         shall be computed as: *UPL*
                         = 
                        *X**m* Where: *X**m*
                             = value of the 
                            *m**th*
                             data point in terms of lbs SO2
                            /hr or lbs NOX
                            /MMBtu, when the data are sorted smallest to largest. If 
                        *m*
                         is not a whole number, the limit shall be computed by linear interpolation according to the following equation. 
 
 *UPL*
                         = 
                        *x**m*
                         = 
                        *x**m*i
                        ·*m*d
                        = 
                        *x**m*i
                         + 0.
                        *m**d**(x**m*(i+1)
                         − 
                        *x**m*i
                        *)* Where: *m**i*
                             = the integer portion of 
                            *m, i.e., m*
                             truncated at zero decimal places, and *m**d*
                             = the decimal portion of 
                            *m*


# Footnotes

1.
    
                         Areas designated as mandatory Class I Federal areas consist of national parks exceeding 6000 acres, wilderness areas and national memorial parks exceeding 5000 acres, and all international parks that were in existence on August 7, 1977. 42 U.S.C. 7472(a). In accordance with section 169A of the CAA, EPA, in consultation with the Department of Interior, promulgated a list of 156 areas where visibility is identified as an important value. 44 FR 69122 (November 30, 1979). The extent of a mandatory Class I area includes subsequent changes in boundaries, such as park expansions. 42 U.S.C. 7472(a). Although states and Tribes may designate as Class I additional areas which they consider to have visibility as an important value, the requirements of the visibility program set forth in section 169A of the CAA apply only to “mandatory Class I Federal areas.” Each mandatory Class I Federal area is the responsibility of a “Federal Land Manager.” 42 U.S.C. 7602(i). When we use the term “Class I area” in this action, we mean a “mandatory Class I Federal area.” Back to Citation
 2.
    
                         The set of “major stationary sources” potentially subject to BART is listed in CAA section 169A(g)(7) and includes “taconite ore processing facilities.” Back to Citation
 3.
    
                         “BART-eligible sources” are those sources that have the potential to emit 250 tons or more of a visibility-impairing air pollutant, were not in operation prior to August 7, 1962, but were in existence on August 7, 1977, and whose operations fall within one or more of 26 specifically listed source categories. 40 CFR 51.301. Back to Citation
 4.
    
                         Fuel sulfur content BART limits were also set for two process boilers and a line dryer at Tilden. Those limits are not impacted by this action. Back to Citation
 5.
    
                         Stoichiometry refers to the relationship between the actual quantity of combustion air to the theoretical minimum quantity of air needed for 100 percent combustion of the fuel. Back to Citation
 6.
    
                         Cliffs acquired ArcelorMittal Steel Production Company in 2020. Previously, Minorca was owned by ArcelorMittal and Hibbing was jointly owned by ArcelorMittal, Cliffs and United States Steel. Currently, Minorca is owned by Cliffs and Hibbing is jointly owned by Cliffs and United States Steel. Back to Citation
 7.
    
                         On November 15, 2016, the 8th Circuit Court of Appeals terminated the June 14, 2013, stay and extended the deadlines in the Original FIP by one day for each day the court's stay was in place. From the day the 2013 FIP was effective to the day it was stayed, 98 days elapsed (March 8, 2013, to June 14, 2013). See Order dated November 15, 2016, in response to U.S. EPA's Petition to reconsider the Original FIP, EPA-R05OAR-2017-0066-0009 (8th Cir. 2016). As a result, the deadlines contained in the Original FIP still apply (
                        *e.g.,*
                         6 months after March 8, 2013), only now from the date the stay was terminated, minus the number of days that elapsed prior to the stay being issued. Back to Citation
 8.
    
                         Taconite facilities typically operate 24 hours per day and 720 is the number of hours in a 30-day period; therefore, a 720-hour average is essentially equivalent to a 30-day average. Back to Citation
 9.
    
                         Data distribution analyses are available in the docket for this action. Back to Citation
 10.
    
                         Taconite facilities typically operate 24 hours per day and 720 is the number of hours in a 30-day period; therefore, a 720-hour average is essentially equivalent to a 30-day average. For facilities that both burn natural gas exclusively and co-fire with coal, 
                        *i.e.,*
                         Tilden and UTAC, a 30-day period may involve operation with only natural gas as well as operation with co-firing of coal. Therefore, the 2016 FIP established UPL equations based on 720-hour averages to allow for the separation of hours when burning only natural gas from hours when co-firing with coal. When calculating an emission limit that applies only when burning natural gas, emissions are averaged over 720 successive hours in which the unit burns only natural gas. When calculating a co-firing emission limit, emissions are averaged over 720 successive hours in which the unit burns a gas/coal mix. All emission limit modifications were calculated based on 720-hour averages, consistent with the equations at 40 CFR 52.1183(p) and 40 CFR 52.1235(f). However, EPA is proposing modified emission limits in the form of a 30-day average if the facility burns only one fuel or if the modified limit applies to all fuels. In those circumstances, there is no need to be able to separate the hourly data to determine compliance with the emission limit. Back to Citation
 11.
    
                         April 16, 2016, 81 FR 21672, 21680. Back to Citation
 12.
    
                         See emission limit calculation files in the docket for this action. Back to Citation
 13.
    
                         Data analyses and emissions calculations are available in the docket for this action. Back to Citation
 14.
    
                         40 CFR 52.1183(k)(1). Back to Citation
 15.
    
                         40 CFR 52.1183(k)(1)(viii). Back to Citation
 16.
    
                         
                        *See*
                         “Tilden NOX
                         limit modification report (Feb. 12, 2021)_Redacted.pdf,” available in the docket for this action. Back to Citation
 17.
    
                         
                        *See*
                         Tilden Emission Limit Calculations, available in the docket for this action. Back to Citation
 18.
    
                         
                        *See*40 CFR 52.1235((b)(1)(ii). Back to Citation
 19.
    
                         
                        *See*
                         Hibbing Emission Limit Calculations, available in the docket for this action. Back to Citation
 20.
    
                         40 CFR part 51, appendix Y, at V. Back to Citation
 21.
    
                         
                        *See*40 CFR 52.1235((b)(1)(v). Back to Citation
 22.
    
                         CEMS data in the September 11, 2020, submittal was presented as 720-hour rolling averages. On November 25, 2020, Minorca provided the hourly CEMS data for the same January 12, 2020, to September 10, 2020, time period to allow for independent calculation of 720-hour averages. Back to Citation
 23.
    
                         
                        *See*
                         Minorca Emission Limit Calculations, available in the docket for this action. Back to Citation
 24.
    
                         40 CFR 52.1235(b)(1)(iv). Back to Citation
 25.
    
                         
                        *See*
                         United Taconite Emission Limit Calculations, available in the docket for this action. Back to Citation
 26.
    
                         40 CFR part 51, appendix Y, at V. Back to Citation
 27.
    
                         
                        *See*
                         Tilden Emission Limit Calculations, available in the docket for this action. Back to Citation
 28.
    
                         While Hibbing's SO2
                         BART limit is not being modified, the regulatory text at 40 CFR 52.1235(b)(2)(ii) is being revised to remove the original limit modification provisions and clarify that Hibbing's SO2
                         BART limit is final. Back to Citation
 29.
    
                         
                        *See*
                         Minorca Emission Limit Calculations, available in the docket for this action. Back to Citation
 30.
    
                         
                        *See*
                         Northshore Emission Limit Calculations, available in the docket for this action. Back to Citation
 31.
    
                         40 CFR 52.1183(k)(1)(viii), 52.1235(b)(1)(iv)(A)(8) and 52.1235(b)(1)(iv)(B)(8). Back to Citation
 32.
    
                         40 CFR part 51, appendix Y, at V. Back to Citation


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