90 FR 116 pgs. 25960-25968 - Air Plan Approval; Colorado; Serious Attainment Plan RACT Requirements for the 2008 8-Hour Ozone National Ambient Air Quality Standards for the Denver Metro/North Front Range Nonattainment Area
Type: PRORULEVolume: 90Number: 116Pages: 25960 - 25968
Pages: 25960, 25961, 25962, 25963, 25964, 25965, 25966, 25967, 25968Docket number: [EPA-R08-OAR-2025-0233; FRL-12746-03-R8]
FR document: [FR Doc. 2025-11263 Filed 6-17-25; 8:45 am]
Agency: Environmental Protection Agency
Official PDF Version: PDF Version
[top]
ENVIRONMENTAL PROTECTION AGENCY
40 CFR Part 52
[EPA-R08-OAR-2025-0233; FRL-12746-03-R8]
Air Plan Approval; Colorado; Serious Attainment Plan RACT Requirements for the 2008 8-Hour Ozone National Ambient Air Quality Standards for the Denver Metro/North Front Range Nonattainment Area
AGENCY:
Environmental Protection Agency (EPA).
ACTION:
Proposed rule.
SUMMARY:
The Environmental Protection Agency (EPA) is proposing to approve state implementation plan (SIP) submittals under the Clean Air Act (CAA) that address Reasonably Available Control Technology (RACT) requirements for the 2008 ozone National Ambient Air Quality Standards (NAAQS) for the Denver Metro/North Front Range (DMNFR) ozone nonattainment area. The requirements at issue relate to the area's previous Serious nonattainment classification. The EPA is proposing approval of the RACT SIP submittals, proposing to find that the State has met the applicable CAA requirements for Serious area RACT, and proposing that the State has addressed EPA's prior disapproval concerning specific RACT determinations. In this issue of the Federal Register the EPA is concurrently making an interim final determination to defer application of CAA sanctions associated with the prior disapproval. The EPA is taking this action pursuant to the CAA.
DATES:
Written comments must be received on or before July 18, 2025.
ADDRESSES:
[top] Submit your comments, identified by Docket ID No. EPA-R08-OAR-2025-0233, to the Federal
Docket: All documents in the docket are listed in the https://www.regulations.gov index. Although listed in the index, some information is not publicly available, e.g., CBI or other information whose disclosure is restricted by statute. Certain other material, such as copyrighted material, will be publicly available only in hard copy. Publicly available docket materials are available electronically in https://www.regulations.gov. Please email or call the person listed in the FOR FURTHER INFORMATION CONTACT section if you need to make alternative arrangements for access to the docket.
FOR FURTHER INFORMATION CONTACT:
Matthew Lang, Air and Radiation Division, EPA, Region 8, Mailcode 8ARD-IO, 1595 Wynkoop Street, Denver, Colorado 80202-1129, telephone number: (303) 312-6709, email address: lang.matthew@epa.gov.
SUPPLEMENTARY INFORMATION:
In this document "we," "us," and "our" refer to the EPA.
Table of Contents
I. What action is the EPA proposing to take?
II. Background
A. 2008 8-Hour Ozone NAAQS Nonattainment Area
B. The EPA's December 8, 2023 Final Rule
III. RACT Requirements
IV. Summary of State's SIP Submittals
A. Revisions to Regulation 7, Part E and Reorganization into Regulation 26
B. RACT Demonstration
1. Landfill/Biogas Fired RICE
2. Process Heaters
3. Cold Rolling Mill
V. Procedural Requirements
VI. The EPA's Evaluation of Colorado's SIP Submittals
A. Revisions to Regulation 7, Part E and Reorganization into Regulation 26
B. RACT Demonstration
1. Landfill/Biogas Fired RICE
2. Process Heaters
3. Cold Rolling Mill
4. Conclusion
VII. Proposed Action
VIII. Consideration of Section 110(l) of the CAA
IX. Incorporation by Reference
X. Statutory and Executive Order Reviews
I. What action is the EPA proposing to take?
As explained below, the EPA is proposing to approve Colorado SIP revisions stemming from four submittals related to Serious ozone nonattainment area RACT requirements for the DMNFR area. These submittals also include organizational SIP revisions affecting the submitted regulations, including the relocation of existing portions of Colorado's Regulation Number 7 ("Reg. 7") into new standalone regulations. The four submittals that are the subject of this action are described below.
First, on June 26, 2023, Colorado submitted SIP revisions related to the Moderate and Severe nonattainment requirements for the 2015 and 2008 ozone NAAQS, respectively, which included revisions to Reg. 7. 1 The June 26, 2023 revisions to Reg. 7 do not specifically address Serious ozone nonattainment area RACT requirements. Because the June 2023 submittal included revisions to Reg. 7, parts A and E that were further revised by the subsequent three submittals by Colorado described below (that are specific to Serious ozone nonattainment area RACT requirements), the EPA is acting on all these revisions collectively. Second, on May 23, 2024, Colorado submitted revisions to Reg. 7 that separate out Part E of that state regulation into a new Regulation 26 ("Reg. 26"). 2 Third, on May 30, 2024, Colorado submitted revisions to Reg. 26 concerning landfill/biogas fired Reciprocating Internal Combustion Engines (RICE), as well as other revisions related to Moderate and Severe ozone nonattainment requirements for the 2015 and 2008 ozone NAAQS, respectively. 3 Fourth, on April 2, 2025, Colorado submitted SIP revisions to address outstanding RACT requirements for Serious ozone nonattainment areas under the 2008 ozone NAAQS, which includes associated revisions to Reg.7 and Reg. 26. 4
Footnotes:
1 ?June 2023 SIP Submittal, Document Set 1 of 7, "Submittal Letter to EPA_Ozone SIP." The letter is dated June 22, 2023, but the SIP was submitted to EPA on June 26, 2023.The portion of the June 2023 SIP Submittal concerning Moderate ozone nonattainment requirements was determined to be complete by EPA on September 7, 2023. The remainder of the submittal was deemed complete by operation of law on December 22, 2023.
2 ?May 23, 2024 SIP Submittal, "Submittal Letter to EPA_Regs 7, 24, 25, 26_signed." The letter is dated May 21, 2024, but the SIP was submitted to EPA on May 23, 2024. The May 23, 2024 SIP Submittal was deemed complete by operation of law on November 23, 2024.
3 ?May 30, 2024 SIP Submittal, "Submittal Letter to EPA_Ozone SIP, Regs 7, 26, AQS_signed." The letter is dated May 21, 2024, but the SIP was submitted to EPA on May 30, 2024. The May 30, 2024 SIP Submittal was deemed complete by operation of law on November 30, 2024.
4 ?April 2025 SIP Submittal, Document Set 1 of 2, "Signed Submittal Letter to EPA."
The EPA had previously finalized disapprovals with respect to SIP revisions related to RACT requirements for refinery fuel process heaters, a cold rolling mill, and landfill/biogas fired RICE. 5 In this action, and as detailed in this preamble, we are proposing to approve the portions of the June 26, 2023, May 23, 2024, May 30, 2024, and April 2, 2025 submittals related to the previously disapproved state RACT regulations.
Footnotes:
5 ?Final Rule, Air Plan Disapproval; Colorado; RACT Elements for the 2008 8-Hour Ozone Standard for the Denver Metro/North Front Range Nonattainment Area; 88 FR 85511 (Dec. 8, 2023).
[top] The EPA is proposing to approve the May 30, 2024 revisions establishing a revised RACT emission limitation for landfill/biogas fired RICE. The EPA is acting on this change as a superseding revision in recognizing that Colorado's intent is for the landfill/biogas fired RICE regulatory provision, that was previously disapproved by the EPA, to now be incorporated into the SIP with subsequent changes that were made to address the disapproval. Therefore, the EPA is proposing to approve all of Reg. 26, Part B, section II.A.4.f., including the revised emission limitation, into the SIP. The EPA is also proposing to approve the April 2, 2025 revisions with respect to the RACT determinations for refinery fuel process heaters and a cold rolling mill. We are also proposing approval of organizational SIP revisions from the June 26, 2023 and May 23, 2024 submittals to Reg. 7 and Reg. 26 that are unrelated to the substance of Colorado's RACT determinations, but which facilitate efficient reorganization of Reg. 7, Part E into Reg. 26 and/or that are clerical or clarifying in nature. The portions of the four SIP submittals that the EPA is proposing approval of in this action are summarized in table 1 of this preamble. The remaining revisions from the June 26, 2023, May 23, 2024, May 30, 2024 and April 2, 2025 submittals will be addressed in future rulemakings.
If the EPA finalizes this rulemaking as proposed, Colorado will have corrected the deficiencies identified in the EPA's December 8, 2023 disapproval with respect to the Serious area RACT requirement for the 2008 ozone NAAQS. Consistent with applicable regulations, 6 the EPA is concurrently making an interim final determination, which also appears in this issue of the Federal Register , to defer application of the CAA emission offset sanction for permitting of new or modified major sources as well as highway sanctions associated with the December 8, 2023 disapproval. The deferral is based on this proposal to approve SIP revisions from Colorado to resolve the RACT requirement deficiencies that were the basis for the December 8, 2023 disapproval. If the EPA does not finalize this approval as proposed and instead disapproves or proposes to disapprove these SIP revisions, then the offset sanction under CAA section 179(b)(2) for permitting new or modified major sources would apply in the DMNFR area on the later of: (1) the date the EPA issues such a proposed or final disapproval; or (2) July 8, 2025 ( i.e., 18 months from the effective date of the finding that started the original sanctions clock). 7 Subsequently, highway sanctions under section 179(b)(1) would apply in the DMNFR area six months after the date the offset sanction is applied. 8
Footnotes:
6 ?40 CFR 52.31(d)(2)(i).
7 ? See id. In this case, the finding that started the original sanctions clock was the disapproval issued on December 8, 2023, which was effective on January 8, 2024.
8 ? See id.
The basis for our proposed action is discussed in more detail below. The State's submittals, including technical information that we are relying on, is in the docket, available at https://www.regulations.gov, Docket ID No. EPA-R08-OAR-2025-0233.
II. Background
A. 2008 8-Hour Ozone NAAQS Nonattainment Area
On March 12, 2008, the EPA revised both the primary and secondary NAAQS for ozone to a level of 0.075 parts per million (ppm) (based on the annual fourth-highest daily maximum 8-hour average concentration, averaged over 3 years). 9 The 2008 ozone NAAQS retains the same general form and averaging time as the 0.08 ppm NAAQS set in 1997, but is set at a more protective level. Specifically, the 2008 8-hour ozone NAAQS is met when the 3-year average of the annual fourth-highest daily maximum 8-hour average ambient air quality ozone concentrations is less than or equal to 0.075 ppm. 10 Effective July 20, 2012, the EPA designated any area as nonattainment that was violating the 2008 8-hour ozone NAAQS based on the three most recent years (2008-2010) of air monitoring data. 11
Footnotes:
9 ?Final rule, National Ambient Air Quality Standards for Ozone, 73 FR 16436 (March 27, 2008). The EPA has since further strengthened the ozone NAAQS, but the 2008 8-hour standard remains in effect. See Final Rule, National Ambient Air Quality Standards for Ozone, 80 FR 65292 (Oct. 26, 2015).
10 ?40 CFR 50.15(b).
11 ?Final rule, Air Quality Designations for the 2008 Ozone National Ambient Air Quality Standards, 77 FR 30088 (May 21, 2012).
Ozone nonattainment areas are classified based on the severity of their ambient ozone levels, as determined using the area's design value. The design value is the 3-year average of the annual fourth-highest daily maximum 8-hour average ozone concentration at a monitoring site. 12 In our July 20, 2012 action, the EPA designated the DMNFR area as nonattainment and classified the area as Marginal. 13 The DMNFR area did not attain the 2008 8-hour ozone NAAQS by the applicable Marginal area attainment deadline, and accordingly was reclassified as Moderate. 14 After not attaining the 2008 ozone NAAQS for subsequent attainment dates, the area was reclassified to Serious, and then to Severe nonattainment status. 15
Footnotes:
12 ?40 CFR part 50, appendix I.
13 ?Final rule, Air Quality Designations for the 2008 Ozone National Ambient Air Quality Standards, 77 FR 30088 (May 21, 2012) at 30110. The nonattainment area includes Adams, Arapahoe, Boulder, Broomfield, Denver, Douglas and Jefferson Counties, and portions of Larimer and Weld Counties. See 40 CFR 81.306.
14 ?Final rule, Determinations of Attainment by the Attainment Date, Extensions of the Attainment Date, and Reclassification of Several Areas for the 2008 Ozone National Ambient Air Quality Standards, 81 FR 26697 (May 4, 2016).
15 ?Final rule, Finding of Failure to Attain and Reclassification of Denver Area for the 2008 Ozone National Ambient Air Quality Standard, 84 FR 70897 (Dec. 26, 2019) (Moderate to Serious); Final rule, Determinations of Attainment by the Attainment Date, Extensions of the Attainment Date, and Reclassification of Areas Classified as Serious for the 2008 Ozone National Ambient Air Quality Standards, 87 FR 60926 (Oct. 7, 2022) (Serious to Severe); see 40 CFR 81.306.
B. The EPA's December 8, 2023 Final Rule
Although the area is currently classified as Severe nonattainment for the 2008 ozone NAAQS, the present action pertains only to outstanding requirements from the prior Serious nonattainment classification. Among the requirements for Serious nonattainment areas, states must submit SIP provisions to impose RACT-level emission limitations on relevant emission sources in the nonattainment area. As described above, on December 8, 2023, the EPA disapproved Colorado's RACT determinations for refinery fuel process heaters, landfill/biogas fired RICE, and a cold rolling mill. The EPA has taken action to approve or conditionally approve other SIP revisions related to Serious ozone nonattainment requirements. 16
Footnotes:
16 ? See 88 FR 29827, 88 FR 76676, and 88 FR 85511.
III. RACT Requirements
CAA sections 172(c)(1) and 182(b)(2) require states to include provisions in the SIP providing for the implementation of RACT in areas classified as Moderate nonattainment or higher for an ozone NAAQS. The EPA has defined RACT as "[t]he lowest emission limitation that a particular source is capable of meeting by the application of control technology that is reasonably available considering technological and economic feasibility."? 17 For a given category of sources, or emission units, RACT may be determined to be work practices, rather than the application of add-on controls and/or numerical emission limitations. 18 The RACT requirement applies to sources of volatile organic compound (VOC) emissions that are covered by an EPA Control Techniques Guideline (CTG), as well as to all major stationary sources of VOC or nitrogen oxides (NO X ) emissions within a nonattainment area. 19 For nonattainment areas classified as Moderate, Serious, or Severe under an ozone NAAQS, a major stationary source that is subject to RACT is one that emits, or has the potential to emit, 100, 50, or 25 tpy or more, respectively, of VOCs or NO X . 20 Therefore, under the DMNFR area's Serious nonattainment classification for the 2008 ozone NAAQS, Colorado was required to submit SIP revisions providing for the implementation of RACT at stationary sources subject to an EPA CTG and at major stationary sources emitting 50 tpy or more of VOC or NO X .
Footnotes:
17 ? See "Guidance for Determining Acceptability of SIP Regulations in Non-Attainment Areas" (Dec. 9, 1976) at p.2, available at https://www3.epa.gov/ttn/naaqs/aqmguide/collection/cp2/19761209_strelow_ract.pdf, and 44 FR 53761, at 53762, footnote 2 (Sep. 17, 1979).
18 ? See "Approval Options for Generic RACT Rules Submitted to Meet the non-CTG VOC RACT Requirement and Certain NO X RACT Requirements" (Nov. 7, 1996), available at https://www.epa.gov/sites/production/files/2016-08/documents/shavermemogenericract_7nov1996.pdf.
19 ? See CAA section 182(b)(2).
20 ? See CAA sections 182(b), 182(c), 182(d), 182(f)(1), and 302(j).
[top]
IV. Summary of State's SIP Submittals
A. Revisions to Regulation 7, Part E and Reorganization Into Regulation 26
Due to the adoption of new rules, revisions, and reorganization on the part of the State, part of this action includes proposing to approve the addition of regulatory provisions that are related to the State's RACT determinations. Specifically, the State of Colorado submitted formal SIP revisions on June 26, 2023, May 23, 2024, May 30, 2024, and April 2, 2025, which included revisions to Reg. 7 and 26.
In the June 26, 2023 submittal, among other revisions, reference dates to the Code of Federal Regulations (CFR) concerning EPA's National Emission Standards for Hazardous Air Pollutants, New Source Performance Standards (NSPS), and test methods were updated in Reg. 7, Part E, sections I.D.4.a.(i)(B), II.A.4.b.(ii), II.A.5.b.(i)(A)(2)-(3), II.A.5.b.(i)(B)(1)-(2), II.A.5.b.(ii)(A), II.A.6.c.(ii), II.A.7.f.(iii), and V.A.6.b.; and compliance dates were moved into the SIP at Reg. 7, Part E, section II.A.4. for natural gas-fired and refinery fuel-fired process heaters subject to applicable emission limitations. 21 Several other revisions that are clerical or clarifying in nature were included in the June 26, 2023 submittal. Of relevance to this proposed action, this includes revisions to Reg. 7, Part E, sections II.A.4.a.(vii), II.A.5.a.(i), II.A.5.b.(ii)(B)(1)-(2), II.A.5.b.(ii)(B)(6)-(7), II.A.5.b.(ii)(D)-(E), II.A.6.a.(i)-(ii), and II.A.6.b.(viii)(F)-(G). The revisions described above are not specific to the RACT determinations at issue in this rulemaking concerning landfill/biogas RICE, refinery fuel process heaters, and the cold rolling mill. However, the EPA is proposing to approve them here to concurrently propose action on revisions from the subsequent May 23, 2024, May 30, 2024, and April 2, 2025 submittals that reorganize and further revise the regulatory provisions.
Footnotes:
21 ?June 2023 SIP Submittal, Document Set 5 of 7, "Reg Lang & SBAP Adopted_R7" at 82-119. The EPA is not proposing action here on the addition to Reg. 7, Part E, section II.A.4. from the June 26, 2023 SIP submittal that concerns the May 1, 2024 compliance date for equipment specified under sections II.A.1.d.-e. The EPA is not yet acting on the revisions to sections II.A.1.d.-e. from the June 26, 2023 SIP submittal and will therefore propose action on the associated revision to section II.A.4. concurrently with the revisions to sections II.A.1.d.-e. in a future action.
In the State's May 23, 2024 submittal, Reg. 7 was retitled from "Control of Ozone via Ozone Precursors and Control of Hydrocarbons via Oil and Gas Emissions (Emissions of Volatile Organic Compounds (VOC) & Nitrogen Oxides (NO X ))" to "Control of Emissions from Oil and Gas Emissions Operations." As a result, Reg. 7, Part E was removed from Reg. 7 and was relocated to the newly established Reg. 26, "Control of Emissions from Engines and Major Stationary Sources."? 22 The State's intent for this revision was to narrow Reg. 7 to be primarily focused on oil and gas emission controls, which necessitated the relocation of provisions in Part E to a new standalone regulation.
Footnotes:
22 ?May 23, 2024 SIP Submittal, "Adopted Language_R7" at 241-292, "Adopted Language_R26."
After the reorganization of Reg. 7, Part E into Reg. 26, Colorado adopted revisions to Reg. 26 parts A and B and submitted the revisions to the EPA on May 30, 2024. The May 30, 2024 submittal includes revisions to Reg. 26, Part B, sections II.A.4.f. and II.A.5.b.(ii)(E) establishing an emission limitation and performance testing/portable analyzer monitoring requirements for landfill or biogas fired RICE; and to Reg. 26, Part B, sections II.A.7.h. and II.A.8.b.(i) relating to recordkeeping and reporting for semi-annual portable analyzer monitoring. 23 Several other revisions that are clerical or clarifying in nature were included in the May 30, 2024 submittal. Of relevance to this proposed action, this includes revisions to Reg. 26, Part A, section I.C. as well as Reg. 26, Part B, sections I.C.1., II.A.5.b.(ii)(F) and V.A.1.a.
Footnotes:
23 ?May 30, 2024 SIP Submittal, "Adopted Language_R26."
Colorado submitted further revisions on April 2, 2025. This submittal makes the following revisions to Reg. 26, Part B: establishes compliance dates for process heaters subject to emission limitations, including for refinery fuel process heaters for which Colorado adopted regulatory revisions to implement RACT at section II.A.4.; establishes emission limitations for refinery fuel process heaters to meet RACT, at sections II.A.4.g.(iv)-(v); sets forth requirements for determining compliance with applicable emission limitations for refinery fuel process heaters, at section II.A.5.a.(iii); requires operation of a NO X continuous emission monitoring system (CEMS) for refinery fuel process heaters subject to emission limits to demonstrate compliance with those limits, at section II.A.5.b.(i)(A); removed a reference to refinery fuel process heaters at section II.A.5.b.(ii)(B)(1) since no units that are not already equipped with CEMS are subject to NO X emission limits that would prompt performance testing; and establishes standards and work practice requirements for the cold rolling mill as RACT at section IX. 24 Other clerical or clarifying revisions are documented in the April 2, 2025 SIP submittal, including to Reg. 26, Part B, section II.A.4.g.(i).
Footnotes:
24 ?April 2025 SIP Submittal, "Reg Language Adopted R26 (redline)."
Several additional revisions are included in Colorado's June 26, 2023, May 23, 2024, May 30, 2024, and April 2, 2025 SIP submittals, but the EPA is not proposing action on them in this rulemaking. We will address the remaining revisions from the four submittals in future rulemakings.
B. RACT Demonstration
As noted previously, the revisions to Reg. 26 that are included in Colorado's May 30, 2024 and April 2, 2025 SIP submittals were made, in part, to implement RACT for landfill/biogas fired RICE, refinery fuel process heaters, and a cold rolling mill. Colorado submitted these SIP revisions to address the EPA's December 8, 2023 disapproval of the State's RACT determinations for these categories. The State also included a narrative discussion and analysis, including relevant technical information, to support its RACT determinations ("2024 RACT Demonstration"). 25
Footnotes:
25 ?April 2025 SIP Submittal, Document Set 1 of 2, Technical Support Documents at 2-36 ("2024 RACT Demonstration"). Subsequent citations to the 2024 RACT Demonstration use the page numbers within that document; so, for example, "2024 RACT Demonstration at 1" refers to the 5th page of the Technical Support Documents file.
1. Landfill/Biogas Fired RICE
[top] Colorado previously adopted as RACT, and EPA previously disapproved, the numerical NO X emission limitation of 2.0 grams of NO X per horsepower-hour (g/hp-hr) from EPA's NSPS at 40 CFR part 60, subpart JJJJ for landfill/digester gas fired engines greater than 500 hp. This applied to units at major stationary sources emitting 50 tons per year of NO X or more, and the emission limitation was based on the emissions profiles of potentially subject sources at the time of the State's rule development in 2020. Due to certain engines being removed from service following rule development in 2020, Colorado has adopted a revised emission limitation of 1.5 g/hp-hr. Colorado's May 30, 2024 submittal determines that this emission limitation is more representative of the engines that are currently in use, and that the limitation, along with periodic performance testing requirements,
Footnotes:
26 ?May 30, 2024 SIP Submittal, "Adopted Language_R26" at 29-30.
2. Process Heaters
Colorado's 2024 RACT Demonstration for refinery fuel process heaters applies to heaters at the Suncor refinery, which is within the DMNFR nonattainment area. The State individually evaluated 23 process heaters with the potential to emit NO X of at least 5 tons per year. 27 The RACT Demonstration evaluates the technological and economic feasibility of NO X control technologies including: (1) combustion controls like low NO X burners (LNB) and ultra-low NO X burners (ULNB); (2) post-combustion controls like selective catalytic reduction (SCR) and selective non-catalytic reduction (SNCR); and (3) work practices, like good combustion practices and combustion process adjustments. 28 As to all 23 heaters, Colorado determined that SNCR was not RACT for these sources because it was not technologically feasible. Colorado determined that SNCR would not be an appropriate control because of the insufficient residence times (the duration of the interaction between reagents and exhaust gases) associated with unit design, and because the exhaust temperatures for the heaters would not be conducive to effective SNCR operation. 29 For 13 units, the 2024 RACT Demonstration states that burner retrofits are not technologically feasible for unit-specific reasons, including the potential for flame length constraints, flame impingement, and coking of burner tubes. 30 These 13 units include the heaters with the designations H-31, H-32, H-10, H-11, H-20, H-27, H-28, H-29, H-30, H-201, H-401, H-402, and H-403. For those units where burner retrofits were deemed technologically feasible, Colorado evaluated the cost effectiveness of burner retrofits, finding that it ranged from $51,000-$669,000 per ton of NO X removed. 31 Therefore, Colorado determined that burner retrofits for the process heaters with the following designations were not economically feasible for implementation as RACT: H-17, H-19, H-22, H-1716, H-1717, H-2410, H-101, and H-103. Concerning SCR post-combustion emission control, Colorado's analysis presumes that SCR is technologically feasible for all units, and instead focuses on the cost effectiveness of retrofitting units with SCR. The State found that this cost effectiveness ranges from $31,000-$586,000 per ton of NO X removed. For all 23 units, Colorado determined that these costs make SCR retrofits not economically feasible for RACT purposes.
Footnotes:
27 ?2024 RACT Demonstration at 5.
28 ? Id. at 19.
29 ? Id. at 21-22.
30 ? Id. at 22-26.
31 ? Id. at 29-30.
Considering the technological or economic infeasibility of additional NO X control technologies, Colorado's 2024 RACT Demonstration establishes RACT on a unit-by-unit basis based on current operational characteristics. 32 For two process heaters (H-1716 and H-2410) that currently operate CEMS, the State determined that a NO X emission limit of 40 parts per million by volume dry (ppmvd) at 0% oxygen on a 30-day rolling average constitutes RACT. Colorado's regulatory revisions included with the April 2, 2025 SIP submittal require these units to continue operating the units' CEMS to determine compliance with the established emission limit. For units that already use LNB or ULNB, Colorado determined RACT to consist of continued operation of the already installed NO X control technology. Finally, for units not subject to a numerical emission limitation, including those that are equipped with LNB/ULNB, Colorado determined RACT to include semi-annual combustion process adjustment requirements. These requirements include inspection of process heater components like burners and combustion controls, and replacing/making adjustments as appropriate.
Footnotes:
32 ? Id. at table 9.
3. Cold Rolling Mill
Colorado's 2024 RACT Demonstration evaluates a range of emission control requirements for VOC emissions produced by the cold rolling mill. This analysis and resulting RACT determination apply to the rolling mill at Golden Aluminum, an aluminum manufacturing facility in the DMNFR nonattainment area. VOC emissions from the cold rolling mill result from volatilization of mineral oil applied as a coolant/lubricant during the milling process that thins aluminum sheets to a specified thickness. The cold rolling mill at the facility currently controls emissions by using low-volatility mineral oil; coolant spray volume and temperature control with excess spray collection using hoods and catch basins; and a purifier for control of particulate matter emissions. 33 The 2024 RACT Demonstration evaluates the feasibility of additional VOC control technologies, including thermal oxidizers, condensers, adsorbers, absorbers, and alternative lubricants. It also estimates the cost effectiveness of controlling VOC emissions from the cold rolling mill, both including and excluding costs from lost production associated with the retrofits. 34 The State arrived at this list of potential emission controls for evaluation after reviewing various resources like EPA's Menu of Control Measures (MCM), 35 CTGs/Alternative Control Techniques (ACTs), 36 and the RACT BACT (best available control technology) LAER (lowest achievable emission rate) Clearinghouse (RBLC). 37 Colorado determined the cost effectiveness of these emission controls as the following: a thermal oxidizer, which can reduce VOCs by more than 95%, would cost $23,520-$39,796 per ton of VOC removed; a condenser, to provide for collection of VOCs through change of phase, would cost $30,713-$48,637 per ton of VOC removed; a carbon adsorber, which traps VOC on a carbon surface, would cost $128,271-$148,551 per ton of VOC removed; and absorption, which involves entraining VOCs within a liquid, would cost $27,211-$74,045 per ton of VOC removed.
Footnotes:
33 ?2024 RACT Demonstration at 4-5.
34 ? Id. at 12-14.
35 ?Available at https://www.epa.gov/sites/default/files/2016-02/documents/menuofcontrolmeasures.pdf.
36 ?Available at https://www.epa.gov/ground-level-ozone-pollution/control-techniques-guidelines-and-alternative-control-techniques.
37 ?Available at https://cfpub.epa.gov/rblc/index.cfm?action=Search.BasicSearch&lang=en.
Colorado's 2024 RACT Demonstration further considers whether an alternative, lower volatility lubricant could be utilized. The State determined that due to a need to ensure food-grade quality of materials produced, and because the lubricant currently in use has a relatively high boiling point and low vapor pressure, selection of a substitute lubricant would not be appropriate as RACT for the cold rolling mill. 38 Given the technological constraints on process materials and the anticipated high costs of retrofitting the facility with additional air pollution control equipment, Colorado's 2024 RACT Demonstration determines that RACT for the cold rolling mill is use of the existing low-volatility lubricant, existing temperature control requirements, and good operational practices like controlling application rates and preventing spills.
Footnotes:
38 ?2024 RACT Demonstration at 10.
V. Procedural Requirements
[top] The CAA requires that states meet certain procedural requirements before submitting a SIP revision to the EPA,
Footnotes:
39 ?CAA section 110(a)(2), 42 U.S.C. 7410(a)(2).
40 ?June 2023 SIP Submittal, Document Set 1 of 7, "Denver Post Legal Ad."
41 ?May 23, 2024 SIP Submittal, "Denver Post Legal Ad."
42 ?May 30, 2024 SIP Submittal, "Denver Post Legal Ad."
43 ?April 2025 SIP Submittal, Document Set 1 of 2, "Denver Post Legal Ad."
VI. The EPA's Evaluation of Colorado's SIP Submittals
A. Revisions to Regulation 7, Part E and Reorganization Into Regulation 26
As discussed in section IV.A. above, and in addition to several clerical revisions to Reg. 7, Part E, Colorado's June 26, 2023 submittal updated various reference dates to the CFR and incorporated compliance dates into the SIP for process heaters subject to emission limitations. While these revisions do not directly relate to the RACT determinations evaluated in subsequent sections, the EPA is proposing to approve them because they are relevant to subsequent submittals that directly implement RACT requirements and/or will, if approved, facilitate efficient relocation of regulatory provisions through Colorado's reorganization of Reg. 7.
The EPA is also proposing to approve revisions from Colorado's May 23, 2024 SIP submittal relocating Reg. 7, Part E to Reg. 26. These organizational revisions also are not specific to the RACT determinations evaluated in subsequent sections, but the EPA is proposing to approve them because subsequent regulatory revisions that Colorado includes in the May 30, 2024 and April 2, 2025 SIP submittals, which do relate to RACT, concern the newly established Reg. 26.
The EPA is proposing approval of the revisions to Reg. 26, parts A and B that were included in the May 30, 2024 and April 2, 2025 SIP submittals. Since the revisions to Reg. 26, Part A, section I.C. and to Reg. 26, Part B, sections I.C.1., II.A.5.b.(ii)(F), and V.A.1.a. are clerical in nature, the EPA is proposing to approve them. The May 30, 2024 revisions to Reg. 26, Part B, sections II.A.4.f. and II.A.5.b.(ii)(E) implement Colorado's RACT determination for landfill/biogas fired RICE. The EPA's evaluation of these revisions, including their sufficiency in meeting RACT, is included below.
The EPA is also proposing approval of the regulatory revisions in Colorado's April 2, 2025 submittal to Reg. 26, Part B. We are proposing approval of the revisions to Reg. 26, Part B, section II.A.4.g.(i) because the revision is clerical in nature. The April 2, 2025 revisions to Reg. 26, Part B, sections II.A.4., II.A.4.g.(iv)-(v), II.A.5.a.(iii), II.A.5.b.(i)(A), II.A.5.b.(ii)(B)(1), and IX. implement Colorado's RACT determinations for either refinery fuel process heaters or the cold rolling mill. These revisions are addressed in the EPA's RACT evaluation below for the respective equipment.
Given that the revisions the EPA is evaluating span multiple SIP submittals from Colorado, we have included table 1, detailing the revisions from each submittal that we are proposing to approve. The revisions in each submittal that we are not proposing action on here will be addressed in later rulemakings. The EPA has previously proposed approval of certain revisions from these submittals in our May 8, 2025 proposed rule at 90 FR 19447.
| Submittal | Revisions included in the EPA's proposed approval |
|---|---|
| June 26, 2023 | Reg. 7, Part E, sections I.D.4.a.(i)(B), II, II.A.4, II.A.4.a.(vii), II.A.4.b.(ii), II.A.5.a.(i), II.A.5.b.(i)(A)(2)-(3), II.A.5.b.(i)(B)(1)-(2), II.A.5.b.(ii)(A), II.A.5.b.(ii)(B)(1)-(2), II.A.5.b.(ii)(B)(6)-(7), II.A.5.b.(ii)(D)-(E), II.A.6.a.(i)-(ii), II.A.6.b.(viii)(F)-(G), II.A.6.c.(ii), II.A.7.f.(iii), V.A.6.b. |
| May 23, 2024 | Removal of Reg. 7, Part E; Relocation of provisions to Reg. 26 parts A and B. |
| May 30, 2024 | Reg. 26, Part A, section I.C, Reg. 26; Part B, sections I.C.1., II.A.4.f, II.A.5.b.(ii)(E)-(F), II.A.7.h, II.A.8.b.(i), V.A.1.a. |
| April 2, 2025 | Reg. 26, Part B, sections II.A.4., II.A.4.g.(i), II.A.4.g.(iv)-(v), II.A.5.a.(iii), II.A.5.b.(i)(A), II.A.5.b.(ii)(B)(1), IX. |
| Note : At this time, the EPA is not proposing action on any of the revisions included in the June 26, 2023, May 23, 2024, May 30, 2024, and April 2, 2025 submittals besides those identified in table 1. Additionally, those sections marked as "state-only" in Colorado's SIP submittals are not included for incorporation into the SIP. Therefore, the EPA is not proposing action on these sections, and any such sections which were relocated from Reg. 7 to Reg. 26 will continue to be "state-only." | |
B. RACT Demonstration
1. Landfill/Biogas Fired RICE
[top] The EPA's December 8, 2023 disapproval of Colorado's RACT determination for landfill and biogas fired RICE found that the engines subject to the selected emission limitation of 2.0 g NO X /hp-hr could in practice, and were currently achieving lower emissions. 44 Additionally, the EPA also found that emissions testing/monitoring requirements to determine compliance with the emission limitation may have been inadvertently excluded from the revised regulation. Colorado's May 30, 2024 SIP submittal includes regulatory revisions that establish an emission limitation of 1.5 g NO X /hp-hr at Reg. 26, Part B, section II.A.4.f.; initial and periodic testing requirements for landfill and biogas fired RICE at Reg. 26, Part B, section II.A.5.b.(ii)(E); and associated recordkeeping and reporting requirements at Reg. 26, Part B, sections II.A.7.h. and II.A.8.b.(i). This emission limitation can be achieved by the impacted engines as currently operated and is more stringent than that established in EPA's NSPS for landfill/digester gas burning engines at 40 CFR part 60, subpart JJJJ. 45 Colorado previously evaluated the cost effectiveness of adopting add-on emission control requirements for landfill/biogas RICE. The State
Footnotes:
44 ? See 88 FR 54975, 54979 (proposed rule; explaining that RACT analyses showed that the subject facilities were meeting a lower emission limit); 88 FR at 85511 (finalizing proposed disapproval).
45 ?40 CFR part 60, subpart JJJJ, table 1.
46 ? See 2008 Serious RACT TSD, available within the docket.
2. Process Heaters
The EPA's prior disapproval of Colorado's categorical RACT determination for refinery fuel process heaters found that the emission limit of 0.1 lb NO X per million British Thermal Units (mmBTU) that the State adopted was not sufficiently supported given the lack of test data for several units. 47 The EPA is now proposing to approve revised determinations since we find that Colorado appropriately established RACT on a case-by-case basis for refinery fuel process heaters. The State made the unit-specific determinations following consideration and subsequent exclusion of LNB/ULNB and SCR retrofits on either the basis of technological or economic infeasibility. 48
Footnotes:
47 ? See 88 FR 54975, 54980-54981.
48 ?2024 RACT Demonstration at 26-27, 29-30, and 32.
The EPA has previously explained that RACT may "vary from source to source due to source configuration, retrofit feasibility, operation procedures, raw materials, and other technical or economic characteristics of an individual source or group of sources."? 49 Colorado's 2024 RACT Demonstration details how the unit-specific configuration of certain process heaters makes burner retrofit technologically infeasible. Among other design challenges, flame length constraints, flame impingement, and coking of burner tubes, are identified as affecting the technological feasibility of burner retrofit. The EPA has previously acknowledged the difficulty that extended flame lengths, and in particular the potential for flame impingement, present for certain process heater LNB/ULNB retrofit applications. 50 The EPA reviewed these acknowledgments and has found them to still be relevant in the context of this SIP action. In consideration of the unit-specific analyses included in Colorado's April 2, 2025 submittal, including the evaluations provided by burner vendors, the EPA is proposing that the aforementioned design challenges are relevant to those process heaters that are identified in Colorado's RACT demonstration as being poor candidates for burner retrofit. Therefore, the EPA is proposing to find that Colorado reasonably excluded burner retrofits as RACT for the following 13 process heaters on the basis of technological infeasibility: H-31, H-32, H-10, H-11, H-20, H-27, H-28, H-29, H-30, H-201, H-401, H-402, and H-403.
Footnotes:
49 ? See "Guidance for Determining Acceptability of SIP Regulations in Non-Attainment Areas," memorandum from Roger Strelow, Assistant Administrator for Air and Waste Management, to Regional Administrators, at 2 (Dec. 9, 1976).
50 ?"Alternative Control Techniques Document-NO X Emissions from Process Heaters (Revised)," EPA-453/R-93-034, September 1993 at 5-13, 5-14, and 5-23.
After determining the units for which burner retrofit may be technologically feasible, the State calculated cost effectiveness at $51,000-$669,000 per ton of NO X removed. While the CAA does not establish a bright line figure for determining the reasonableness of emission controls as RACT, even the most cost-effective potential burner retrofit presented in Colorado's 2024 RACT Demonstration for these sources, at $51,000 per ton of NO X removed, is not economically reasonable for purposes of RACT, based on EPA's historic approach to RACT. Concerning retrofitting units with SCR systems, the calculated cost effectiveness ranged from $25,000-$586,000 per ton of NO X removed. Like the economic feasibility of burner retrofit, the EPA does not consider even the most cost-effective SCR retrofit in Colorado's analysis at $25,000 per ton of NO X removed to be cost effective for purposes of establishing RACT. Colorado's 2024 RACT Demonstration estimated the costs for SCR and burner retrofit in a manner consistent with procedures from the EPA Air Pollution Control Cost Manual. 51 The analysis determined the upfront capital investment of retrofit and annualized this cost by assuming a 20-year equipment life and a 5.5% interest rate. The estimated cost effectiveness of various control options was then calculated by summing this value with the direct annual costs of operating the equipment as well as associated annual administrative costs and dividing the total dollar amount by the amount of NO X removed in tons. Therefore, the EPA is concurring with Colorado's rejection of burner retrofits for the following process heaters for purposes of RACT on the basis of economic infeasibility: H-17, H-22, H-1716, H-1717, H-2410, H-101, and H-103. The EPA also agrees with Colorado's assessment that SCR retrofit is not appropriate for adoption as RACT for all process heaters included in the State's analysis on the basis of economic infeasibility.
Footnotes:
51 ?Available at https://www.epa.gov/economic-and-cost-analysis-air-pollution-regulations/cost-reports-and-guidance-air-pollution.
Due to the technological and/or economic infeasibility of retrofitting affected units, the EPA is proposing to approve Colorado's determination that continued operation of refinery fuel process heaters, as currently configured, represents RACT. In particular, we are proposing to approve the following requirements as meeting RACT: (1) semi-annual combustion process adjustments that will contribute to proper operation and functionality of process heaters and individual components; (2) use of LNB or ULNB as currently in use on heaters H-31, H-37, H-2101, H-1716, H-1717, H-201, H-101, H-401, H-402, H-403, and H-103 that will ensure continued emission reduction associated with these burners; and (3) a numerical NO X emission limit for heaters H-1716 and H-2410 that will ensure emissions are not in excess of 40 ppmvd. We note that in reviewing EPA's RBLC, there are several recent entries with NO X emission limits for similar equipment used in petroleum refining. Listed emission limitations established for purposes of BACT? 52 range from 20 to 80 ppmv depending on emission controls that are in use and supports Colorado's selected RACT emission limit for heaters H-1716 and H-2410. The EPA is also proposing to approve the April 2, 2025 revisions to Reg. 26, Part B, sections II.A.4., II.A.4.g.(iv)-(v), II.A.5.a.(iii), II.A.5.b.(i)(A), II.A.5.b.(ii)(B)(1) that implement the RACT determinations for refinery fuel process heaters evaluated in this section, and which are described in greater detail in section IV.A. of this preamble.
Footnotes:
52 ?BACT emission limitations are required on major new or modified major sources in areas that are in attainment of a NAAQS and are generally more stringent than those required for purposes of RACT for similar sources.
3. Cold Rolling Mill
[top] Concerning the prior disapproval of the RACT SIP revisions for the
The EPA is proposing to find that Colorado reasonably excluded installation of additional air pollution control equipment as RACT, including regenerative thermal oxidizers, refrigerated condensers, carbon adsorber, and heavy oil scrubbers, on the basis of economic infeasibility. As described previously, the CAA does not establish a specific threshold to determine the economic reasonableness of a control technology for implementation of RACT. However, the cost estimates in the 2024 RACT Demonstration for installation of a thermal oxidizer, a condenser, a carbon adsorber and heavy-oil scrubber show that addition of these controls would not be cost-effective. 53 When considering even the more conservative cost estimates in the 2024 RACT Demonstration, which exclude estimated costs associated with lost production during retrofit, the most cost-effective control technology is thermal oxidation, at $23,520 per ton of VOC removed, which the EPA does not consider as reasonable for implementation as RACT. Furthermore, the EPA is proposing to find that Colorado reasonably determined that requiring a lower volatility lubricant does not constitute RACT because, unlike potential alternative lubricants, the characteristics of the lubricant currently in use at the facility are known to be well-suited to specific process conditions and to the production of food-grade quality materials. These operational requirements would prevent the impacted facility from readily adopting an alternative lubricant for purposes of RACT. That is, using an alternative rolling lubricant is not a technologically viable option for this facility because the lubricant currently in use already has characteristics that would minimize volatilization including a low vapor pressure and high boiling point. An alternative lubricant would require testing under the process conditions at the facility to ensure specification requirements are met, such as production of food-grade materials.
Footnotes:
53 ?2024 RACT Demonstration at 12-14.
Accordingly, because of the economic infeasibility of installing additional air pollution control equipment and the technological infeasibility of using an alternative lubricant, the EPA is proposing to approve Colorado's determination that continued operation of the cold rolling mill as currently configured represents RACT. The EPA is proposing the addition of the following operational practices into the SIP, which function to limit emissions to the level determined to represent RACT-level control: (1) use of existing low volatility rolling lubricant, (2) temperature control of lubricant to minimize volatilization, and (3) good operational practices as described in section IV.B.3. of this preamble. The EPA is also proposing to approve the April 2, 2025 addition of Reg. 26, Part B, section IX. that implements the RACT determination evaluated in this section for the cold rolling mill as well as associated recordkeeping and reporting requirements.
4. Conclusion
Based on the RACT determinations, associated regulatory revisions, and supporting analyses submitted by Colorado, the EPA proposes to determine that Colorado's SIP revisions fulfill the RACT requirement for landfill/biogas fired RICE, refinery fuel process heaters, and the cold rolling mill for the Serious nonattainment plan for the DMNFR area for the 2008 ozone NAAQS. Final approval of the RACT determinations for these three categories of sources would cure the EPA's prior disapproval of the State's March 22, 2021 submittal intended to meet the RACT requirement for the 2008 ozone NAAQS for the DMNFR Serious nonattainment area.
VII. Proposed Action
The EPA is proposing to approve SIP revisions submitted by the State of Colorado to address the RACT requirement for the Serious nonattainment plan for the DMNFR area for purposes of the 2008 Ozone NAAQS. The EPA is proposing this action based on our determination that Colorado's RACT determinations for landfill/biogas fired RICE, refinery fuel process heaters, and the cold rolling mill meet the requirements of CAA section 172(c)(1) and 182(b)(2). The EPA is also proposing to approve revisions to Colorado Reg. 7 and 26 related to the RACT requirement, as summarized in section IV.A. of this proposed rulemaking.
In this same issue of the Federal Register , we are also issuing an interim final determination, effective on publication, to defer the imposition of sanctions. Specifically, the determination will defer application of the offset sanction for permitting of new or modified major sources and highway sanctions for which clocks were triggered by the EPA's December 8, 2023 disapproval of SIP revisions submitted to address the RACT requirement for the 2008 ozone NAAQS for the DMNFR Serious classification nonattainment area. 54 The determination to defer sanctions is based upon our proposed approval action detailed in this document, with respect to the SIP submittals addressing the RACT SIP requirement. Please see the interim final determination for further information concerning sanctions and the basis for issuing the interim final determination.
Footnotes:
54 ?See 40 CFR 52.31(d)(2)(ii).
The EPA is soliciting public comments on the proposed action and our rationale for the proposed action. We will accept comments from the public on this proposal for the next 30 days and will consider comments before taking final action.
VIII. Consideration of Section 110(l) of the CAA
Under section 110(l) of the CAA, the EPA cannot approve a SIP revision if the revision would interfere with any applicable requirement concerning attainment and reasonable further progress toward attainment of the NAAQS, or any other applicable requirement of the Act. In addition, section 110(l) requires that each revision to an implementation plan submitted by a state be adopted by the state after reasonable notice and public hearing. The Colorado SIP provisions that the EPA is proposing to approve in this action do not interfere with any applicable requirements of the Act. Thus, the EPA is proposing to find that the approval of portions of the State's June 26, 2024, May 23, 2023, May 30, 2024, and April 2, 2025 SIP submittals as described in this notice of proposed rulemaking is consistent with section 110(l). Therefore, the EPA proposes to determine the CAA section 110(l) requirements are satisfied.
IX. Incorporation by Reference
[top] In this document, the EPA is proposing to include regulatory text in an EPA final rule that includes incorporation by reference. In accordance with requirements of 1 CFR 51.5, the EPA is proposing to incorporate by reference Colorado Air Quality Control Commission Reg. 26 pertaining to the "Control of Emissions from Engines and Major Stationary
X. Statutory and Executive Order Reviews
Under the CAA, the Administrator is required to approve a SIP submission that complies with the provisions of the CAA and applicable Federal regulations.42 U.S.C. 7410(k); 40 CFR 52.02(a).Thus, in reviewing SIP submissions, EPA's role is to approve state choices, provided that they meet the criteria of the CAA.Accordingly, this action merely approves state law as meeting Federal requirements and does not impose additional requirements beyond those imposed by state law.For that reason, this action:
• Is not a significant regulatory action subject to review by the Office of Management and Budget under Executive Order 12866 (58 FR 51735, October 4, 1993);
• Is not subject to Executive Order 14192 (90 FR 9065, February 6, 2025), because SIP actions are exempt from review under Executive Order 12866;
• Does not impose an information collection burden under the provisions of the Paperwork Reduction Act (44 U.S.C. 3501 et seq. );
• Is certified as not having a significant economic impact on a substantial number of small entities under the Regulatory Flexibility Act (5 U.S.C. 601 et seq. );
• Does not contain any unfunded mandate or significantly or uniquely affect small governments, as described in the Unfunded Mandates Reform Act of 1995 (Pub. L. 104-4);
• Does not have federalism implications as specified in Executive Order 13132 (64 FR 43255, August 10, 1999);
• Is not subject to Executive Order 13045 (62 FR 19885, April 23, 1997), because it approves a state program;
• Is not a significant regulatory action subject to Executive Order 13211 (66 FR 28355, May 22, 2001); and
• Is not subject to requirements of section 12(d) of the National Technology Transfer and Advancement Act of 1995 (15 U.S.C. 272 note) because application of those requirements would be inconsistent with the CAA.
In addition, the SIP is not approved to apply on any Indian reservation land or in any other area where the EPA or an Indian Tribe has demonstrated that a Tribe has jurisdiction. The proposed rule does not have Tribal implications and will not impose substantial direct costs on Tribal governments or preempt Tribal law as specified by Executive Order 13175 (65 FR 67249, November 9, 2000).
List of Subjects in 40 CFR Part 52
Environmental protection, Air pollution control, Carbon monoxide, Greenhouse gases, Incorporation by reference, Intergovernmental relations, Lead, Nitrogen dioxide, Ozone, Particulate matter, Reporting and recordkeeping requirements, Sulfur oxides, Volatile organic compounds.
Authority:
42 U.S.C. 7401 et seq.
Dated: June 2, 2025.
Cyrus M. Western,
Regional Administrator, Region 8.
[FR Doc. 2025-11263 Filed 6-17-25; 8:45 am]
BILLING CODE 6560-50-P