National Emission Standards for Hazardous Air Pollutants From Hazardous Waste Combustors: Residual Risk and Technology Review

Federal RegisterJun 3, 2026

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 63

[EPA-HQ-OAR-2004-0022; FRL-10654-02-OAR]

RIN 2060-AV96

National Emission Standards for Hazardous Air Pollutants From Hazardous Waste Combustors: Residual Risk and Technology Review

AGENCY:

Environmental Protection Agency (EPA).

ACTION:

Final rule.

SUMMARY:

The U.S. Environmental Protection Agency (EPA) is finalizing the residual risk and technology review (RTR) conducted for the National Emission Standards for Hazardous Air Pollutants (NESHAP) from Hazardous Waste Combustors (HWC). Specifically, the EPA is finalizing that risks due to emissions of hazardous air pollutants (HAP) from this source category are adequately addressed by the existing standards; that the NESHAP provides an ample margin of safety to protect public health; and that no developments in practices, processes, or control technologies necessitate revision of the standards. In addition, the EPA is promulgating emission standards for hydrogen fluoride (HF) and hydrogen cyanide (HCN) emissions from major source HWC incinerators, cement kilns, solid fuel boilers, and liquid fuel boilers under Clean Air Act (CAA) sections 112(d)(2) and (3) and 112(h). These final amendments also include work practice standards under CAA section 112(h) for periods of startup, shutdown, and malfunction (SSM); new electronic reporting provisions and requirements; provisions allowing States to choose to exempt area source HWCs from certain permitting requirements; and certain typographical and technical corrections and clarifications.

DATES:

This final rule is effective on June 3, 2026. The incorporation by reference of certain material listed in the rule was approved by the Director of the Federal Register as of September 8, 2020.

ADDRESSES:

The EPA established a docket for this action under Docket ID No. EPA-HQ-OAR-2004-0022. All documents in the docket are listed in

https://www.regulations.gov/.

Although listed, some information is not publicly available,

e.g.,

Confidential Business Information or other information whose disclosure is restricted by statute. The EPA does not place certain other material, such as copyrighted material, on the internet; this material is publicly available only as Portable Document Format (PDF) versions and accessible only on EPA computers in the docket office reading room. The public cannot download certain databases and physical items from the docket but may request these items by contacting the docket office by telephone at (202) 566-1744. The docket office has 10 business days to respond to such requests. Except for these items, publicly available docket materials are available electronically at

https://www.regulations.gov

or on EPA computers in the docket office reading room at the EPA Docket Center, WJC West Building, Room Number 3334, 1301 Constitution Ave. NW, Washington, DC. The Public Reading Room hours of operation are 8:30 a.m. to 4:30 p.m. Eastern Time (ET), Monday through Friday. The telephone number for the Public Reading Room is (202) 566-1744, and the telephone number for the EPA Docket Center is (202) 566-1742.

FOR FURTHER INFORMATION CONTACT:

For information about this final rule, contact U.S. EPA, Attn: Rachel Smoak, Mail Drop: Natural Resources Division (E143-02), 109 T.W. Alexander Drive, P.O. Box 12055, RTP, North Carolina 27711; telephone number: (919) 541-0253; and email address:

smoak.rachel@epa.gov.

Individuals who are deaf or hard of hearing, as well as individuals who have speech or communication disabilities, may use a telecommunications relay service. To learn more about how to make an accessible telephone call to any of the telephone numbers shown in this preamble, please visit the web page

for the relay service of the Federal Communications Commission, and a list of relay services is available on their directory page.

See

https://www.fcc.gov/trs.

See

https://www.fcc.gov/general/trs-state-and-territories.

SUPPLEMENTARY INFORMATION:

Preamble acronyms and abbreviations.

Throughout this preamble, the use of “we,” “us,” or “our” refers to the EPA. We use multiple acronyms and terms in this preamble. While this list may not be exhaustive, to ease the reading of this preamble and for reference purposes, the EPA defines the following terms and acronyms here:

APCD air pollution control device

AWFCO automatic waste feed cutoff

CAA Clean Air Act

CDX Central Data Exchange

CEDRI Compliance and Emissions Data Reporting Interface

CEMS continuous emission monitoring system(s)

CISWI commercial and industrial solid waste incinerator

CFR Code of Federal Regulations

CfPT confirmatory performance test

CMAS chemical manufacturing area sources

CMS continuous monitoring system(s)

COMS continuous opacity monitoring system(s)

CPT comprehensive performance test

DRE destruction and removal efficiency

°F degrees Fahrenheit

EPA Environmental Protection Agency

ERT Electronic Reporting Tool

GACT generally available control technology

GMCS GORE Mercury Control System

HAP hazardous air pollutants(s)

HBEL health-based emission limit

HCl hydrochloric acid

HCN hydrogen cyanide

HF hydrogen fluoride

Hg mercury

HQ hazard quotient

HWC hazardous waste combustor

ICR Information Collection Request

MACT maximum achievable control technology

MMBTU/hr million British thermal units per hour

MTEC maximum theoretical emissions concentration

NESHAP national emission standards for hazardous air pollutants

NSPS new source performance standards

NOC Notification of Compliance

NTTAA National Technology Transfer and Advancement Act

OMB Office of Management and Budget

OPL operating parameter limit

PAH polycyclic aromatic hydrocarbons

PCB polychlorinated biphenyls

PCDD/PCDF polychlorinated dibenzo-

-dioxins and polychlorinated dibenzofurans

PM particulate matter

POM polycyclic organic matter

ppmv parts per million by volume

RATA relative accuracy test audit

RCRA Resource Conservation and Recovery Act

RFA Regulatory Flexibility Act

RTR risk and technology review

SDDS Shell Dioxin Destruction System

SSM startup, shutdown, and malfunction

TEQ toxic equivalency quotient

THC total hydrocarbons

TOSHI target organ-specific hazard index

UMRA Unfunded Mandates Reform Act

UPL upper prediction limit

Table of Contents

I. General Information

A. Executive Summary

B. Does this action apply to me?

C. What is the statutory authority for this final action?

D. Where can I get a copy of this document and other related information?

E. Judicial Review and Administrative Reconsideration

F. Severability

II. Background

A. What is the HWC NESHAP source category and how does the HWC

NESHAP regulate HAP emissions from the source category?

B. What changes did we propose for the HWC NESHAP source category in our November 10, 2025, proposal?

III. What is included in this final rule?

A. What are the final rule amendments based on the risk review for the HWC NESHAP source category?

B. What are the final rule amendments based on the technology review for the HWC NESHAP source category?

C. What are the final rule amendments pursuant to CAA sections 112(d)(2) and (3) and 112(h) for the HWC NESHAP source category?

D. What are the final rule amendments addressing emissions during periods of startup, shutdown, and malfunction?

E. What other changes have been made to the NESHAP?

F. What are the effective and compliance dates of the standards?

IV. What is the rationale for our final decisions and amendments for the HWC NESHAP source category?

A. Residual Risk Review for the HWC NESHAP Source Category

B. Technology Review for the HWC NESHAP Source Category

C. Amendments Pursuant to CAA Sections 112(d)(2) and (3) and 112(h) for the HWC NESHAP Source Category

D. Changes to Provisions for Periods of Startup, Shutdown, and Malfunction

E. Other Amendments to the HWC NESHAP

V. Summary of Cost, Environmental, and Economic Impacts and Additional Analyses Conducted

A. What are the affected facilities?

B. What are the air quality impacts?

C. What are the cost impacts?

D. What are the economic impacts?

E. What are the benefits?

VI. Statutory and Executive Order Reviews

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

B. Executive Order 14192: Unleashing Prosperity Through Deregulation

C. Paperwork Reduction Act (PRA)

D. Regulatory Flexibility Act (RFA)

E. Unfunded Mandates Reform Act (UMRA)

F. Executive Order 13132: Federalism

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

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

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

J. National Technology Transfer and Advancement Act (NTTAA)

K. Congressional Review Act (CRA)

I. General Information

A. Executive Summary

The EPA promulgated the current HWC NESHAP to address emissions of HAP from hazardous waste burning incinerators, cement kilns, lightweight aggregate kilns, solid fuel-fired boilers, liquid fuel-fired boilers, and HCl production furnaces under CAA section 112 in 2005.

This followed the vacatur

of the 1999 standards

and a period of regulation under a 2002 interim final rule

while the EPA developed the updated HWC NESHAP. In response to multiple petitions for reconsideration, the EPA sought and received a full voluntary remand of the rule in 2009 to reexamine the HWC NESHAP.

70 FR 59402 (Oct. 12, 2005).

Cement Kiln Recycling Coal.

EPA, 255 F.3d 855, 872 (D.C. Cir. 2001)

64 FR 52828 (Sept. 30, 1999).

67 FR 6792 (Feb. 13, 2002).

Sierra Club

EPA

, Docket No. 05-1441 (consolidated with Docket Nos. 05-1442, 05-1443, 05-1445, 05-1449) (D.C. Cir. 2008).

CAA section 112(f)(2) requires the EPA to review the standards initially promulgated for this source category within eight years to identify and address residual risk to human health and the environment. CAA section 112(d)(6) also requires the EPA to review and revise the standards “as necessary” at least every eight years to address developments in practices, processes, and control technologies.

The EPA conducted the required RTR and proposed those results in 2025.

In the same action, the EPA withdrew a previous proposal regarding emission standards during periods of malfunction

and proposed new standards for HF and HCN for HWCs with demonstrated emissions of those HAP, which had not previously been regulated by the HWC NESHAP; revisions to the SSM provisions; electronic reporting provisions; provisions regarding area source HWC title V permitting requirements; and other technical, typographical, and clarifying corrections.

90 FR 50814 (Nov. 10, 2025).

89 FR 59867 (July 24, 2024).

90 FR 50814 (Nov. 10, 2025).

In this final rule, the EPA is finalizing the results of the RTR, determining that the risks due to HAP emissions from the HWC NESHAP are adequately addressed by the existing standards, that the HWC NESHAP provides an ample margin of safety to protect public health, and that there are no developments in practices, processes, or control technologies that warrant revisions to the standards pursuant to the technology review. The EPA is finalizing a new work practice standard for HF for HWC incinerators, numerical emission limits for HCN for HWC cement kilns, numerical emission limits for HF and HCN for HWC solid fuel boilers, and a work practice standard for HF and numerical emission limits for HCN for HWC liquid fuel boilers. The EPA is also finalizing new work practice standards for periods of SSM; electronic reporting provisions; provisions that title V air permitting authorities may choose to exempt area sources not otherwise subject to title V air permitting requirements on a case-by-case basis; and other technical, typographical, and clarifying corrections to the HWC NESHAP.

Following consideration of comments and evaluation of additional information received on the proposed rule, the EPA is revising our assessment of the emission limits for HF and HCN for HWC cement kilns. The EPA received additional data on the emission of HF from cement kilns demonstrating that the HF emissions the EPA relied upon to propose a work practice standard for HF were artifacts of the measurement technique, not data demonstrating HF emissions from HWC cement kilns. The EPA does not currently have any credible data demonstrating that HWC cement kilns measurably emit HF. Accordingly, the EPA is not finalizing any emission standard for HF emissions from HWC cement kilns. The EPA is also revising the HCN emission limit for new source HWC cement kilns based on information about the best similar source for new cement kilns. The EPA has also made other minor revisions in response to comments.

The EPA estimates that this final rule will result in present value costs of $2.4 million at a three percent discount rate and $1.8 million at a seven percent discount rate over the 2027 to 2041 time frame, with equivalent annualized values of $200,000 per year for both discount rates (in 2024 dollars). Averaged over the first three years, the EPA does not expect any affected entity to incur an annual cost of more than 0.16 percent of their revenues, and the Agency expects nine affected parent entities to have cost savings associated with this final rule.

B. Does this action apply to me?

Regulated entities.

Table 1 of this preamble presents categories and entities that this action potentially regulates.

ER03JN26.072

Table 1 of this preamble, although not exhaustive, provides a guide for readers regarding entities that this final action likely affects for the source categories listed. To determine if this action affects your facility, you should examine the applicability criteria in title 40 of the Code of Federal Regulations (CFR), part 63, subpart EEE. If you have any questions regarding the applicability of any aspect of this NESHAP, please contact the appropriate person listed in the preceding

FOR FURTHER INFORMATION CONTACT

section of this preamble. To our knowledge, State, local, and Tribal government entities do not own or operate sources that would be affected by this action.

C. What is the statutory authority for this final action?

CAA sections 112, as amended, and 502(a) provide the statutory authority for this action.

CAA section 112 establishes a multi-stage regulatory process to develop standards for emission of HAP from stationary sources. Generally, the first stage involves the EPA establishing technology-based standards that reflect the maximum achievable control technology (MACT) or an appropriate alternative.

The second stage involves evaluating those standards within eight years pursuant to CAA section 112(f)(2) to determine whether additional standards are needed to address remaining risk associated with HAP emissions.

This second stage is commonly referred to as the “residual risk review.” In addition to the residual risk review, CAA section 112(d)(6) also requires the EPA to review the standards every eight years and “revise as necessary” taking into account “developments in practices, processes, and control technologies.”

This review is commonly referred to as the “technology review.” The following discussion identifies the most relevant statutory sections and briefly explains the contours of the methodology used to implement these statutory requirements.

42 U.S.C. 7412, 7601(a), 7661a(a).

. 7412(d)(1)-(4).

. 7412(f)(2).

. 7412(d)(6).

In the first stage of the CAA section 112 standard-setting process, the EPA promulgates technology-based standards under CAA section 112(d) for categories of sources identified as emitting one or more of the HAP listed in CAA section 112(b). Sources of HAP emissions are either major sources or area sources, and CAA section 112 establishes different requirements for major source standards and area source standards. The HWC NESHAP regulates both major and area sources, but only the requirements for establishing emissions limitations for major sources are relevant to the present rulemaking. “Major sources” are those that emit or have the potential to emit 10 tons per year or more of a single HAP or 25 tons per year or more of any combination of HAP.

All other sources are “area sources.”

For major sources, CAA section 112(d)(2) provides that the technology-based NESHAP must reflect the maximum degree of reduction in emissions of HAP achievable (after considering cost, energy requirements, and non-air quality health and environmental impacts). These standards are commonly referred to as MACT standards. CAA section 112(d)(3) also establishes a minimum control level for MACT standards, known as the MACT “floor,” which is based on emission control achieved in practice by the best performing sources. For new sources, the MACT floor cannot be less stringent than the emission control achieved in practice by the best-controlled similar source. The MACT standards for existing sources can be less stringent than floors for new sources, but they cannot be less stringent than the average emission limitation achieved by the best-performing 12 percent of existing sources in the category or subcategory (or the best-performing five sources for categories or subcategories with fewer than 30 sources). The EPA also considers control options that are more stringent than the floor and may establish standards more stringent than the floor, based on the consideration of the cost of achieving the emissions reductions, any non-air quality health and environmental impacts, and energy requirements.

Standards that are more stringent than the floor are commonly referred to as “beyond-the-floor” standards.

42 U.S.C. 7412(a)(1).

Id.

7412(a)(2).

Id.

7412(d)(2).

Nat'l Lime Ass'n

EPA,

233 F.3d 625, 634 (D.C. Cir. 2000) (“Once the Agency sets statutory floors, it then determines, considering cost and the other factors listed in section 7412(d)(2), whether stricter standards are `achievable.' The Agency calls such stricter requirements `beyond-the-floor' standards.”).

In certain instances, as provided in CAA section 112(h), the EPA may set work practice standards in lieu of numerical emission standards. Under CAA section 112(h), the EPA may adopt a work practice standard in lieu of a numerical emission standard if it is “not feasible in the judgment of the Administrator to prescribe or enforce an emission standard for control of a hazardous air pollutant.”

42 U.S.C. 7412(h)(1);

Sierra Club

EPA,

479 F.3d 875, 883-84 (D.C. Cir. 2007). The EPA may “adopt[ ] a method to account for measurement imprecision that has a rational basis in the correlation between increased emission values and increased testing precision.”

Nat'l Ass'n of Clean Water Agencies (NACWA)

EPA,

734 F.3d 1115, 1154-55 (D.C. Cir. 2013).

The next stage in standard-setting focuses on identifying and addressing any remaining (

i.e.,

“residual”) risk within eight years pursuant to CAA

section 112(f)(2). The approach incorporated into the CAA and used by the EPA to evaluate residual risk and develop standards under CAA section 112(f)(2) is also a two-step approach. In the first step, the EPA determines whether risks are adequately addressed by existing standards. This determination “considers all health information, including risk estimation uncertainty, and includes a presumptive limit on maximum individual lifetime [cancer] risk (MIR) of approximately 1 in 10 thousand.”

If risks are unacceptable, the EPA determines the emission standards necessary to reduce risk to an acceptable level without considering costs. In the second step of the approach, the EPA considers whether the emission standards provide an ample margin of safety to protect public health “in consideration of all health information, including the number of persons at risk levels higher than approximately 1 in 1 million, as well as other relevant factors, including costs and economic impacts, technological feasibility, and other factors relevant to each particular decision.”

The EPA promulgates emission standards necessary to provide an ample margin of safety to protect public health or determine that the standards being reviewed provide an ample margin of safety without any revisions. After conducting the ample margin of safety analysis, the EPA considers whether a more stringent standard is necessary to prevent an adverse environmental effect, taking into consideration costs, energy, safety, and other relevant factors.

54 FR 38045 (Sept. 14, 1989). Although defined as “maximum individual risk,” MIR refers only to cancer risk. MIR, one metric for assessing cancer risk, is the estimated risk if an individual were exposed to the maximum level of a pollutant for a lifetime.

Id.

CAA section 112(d)(6) separately requires the EPA to review MACT standards promulgated under CAA section 112 and revise them “as necessary (taking into account developments in practices, processes, and control technologies)” no less frequently than every eight years. In conducting this review, the EPA is not required to recalculate the MACT floors that were established in earlier rulemakings.

Louisiana Environmental Action Network (LEAN)

EPA,

the D.C. Circuit held that the EPA must address previously unregulated HAP known to be emitted from a major source category as part of its periodic review under CAA section 112(d)(6).

See Ass'n of Battery Recyclers, Inc.

EPA,

716 F.3d 667 (D.C. Cir. 2013);

NRDC

EPA,

529 F.3d 1077, 1084 (D.C. Cir. 2008).

955 F.3d 1088 (D.C. Cir. 2020).

CAA section 112(d)(6) and relevant case law provide the EPA with flexibility to consider additional relevant factors other than those enumerated in CAA section 112(d)(6) when deciding whether revisions to existing standards are “necessary.” The D.C. Circuit has held that the CAA section 112(d)(6) requirement to periodically review and revise CAA section 112 emission standards “as necessary” is not limited to the consideration of “developments in practices, processes and control technologies.”

Rather, “the operative standard is `revise as necessary,' with the parenthetical pointing to a non-exhaustive list of considerations.”

The Supreme Court also emphasized in

Michigan

EPA

that unless the statute provides otherwise, broad terms such as “necessary” direct the relevant agency to consider all relevant factors, including cost.

That decision is particularly relevant here because the Court was interpreting a provision of CAA section 112 that instructs the Administrator to determine whether it is “appropriate and necessary” to regulate HAP emissions from electric utility steam generating units.

Thus, under relevant case law, when the EPA is deciding whether it is “necessary” to revise standards pursuant to CAA section 112(d)(6), the Agency considers the costs of any developments in practices, processes, and control technologies.

LEAN,

955 F.3d at 1097.

Id.; see also Nat'l Ass'n for Surface Finishing

EPA,

795 F.3d 1, 11 (D.C. Cir. 2015); Ass'n of Battery Recyclers, 716 F.3d at 673-74.

576 U.S. 743, 752-53 (2015).

See id.

(interpreting 42 U.S.C. 7412(n)(1)(A)).

The EPA is also required to specify relevant test methods, best practices, procedures, or protocols and recordkeeping requirements for standards promulgated under CAA section 112. Finally, CAA section 502(d)(l) requires each State to develop and submit to the EPA an operating permit program to meet the requirements of title V of the CAA and the EPA's implementing regulations at 40 CFR part 70 (“title V”). Major stationary sources of air pollution and certain other non-major sources are required to apply for and operate in accordance with title V operating permits that include emission limitations and other conditions as necessary to assure compliance with applicable requirements of the CAA, including the requirements of the applicable implementation plan.

D. Where can I get a copy of this document and other related information?

In addition to the docket, an electronic copy of this final action is available on the internet. A brief summary of this rule is available at

https://www.regulations.gov,

Docket ID No. EPA-HQ-OAR-2004-0022. Following signature by the EPA Administrator, the EPA will post a copy of this rule at:

https://www.epa.gov/hazardous-waste-combustors-national-emission-standards-hazardous.

Following publication in the

Federal Register

, the EPA will post the

Federal Register

version and key technical documents at this same website.

Additional information is available on the RTR website at

https://www.epa.gov/stationary-sources-air-pollution/risk-and-technology-review-national-emissions-standards-hazardous.

This information includes an overview of the RTR program and links to project websites for the RTR source categories.

E. Judicial Review and Administrative Reconsideration

Under CAA section 307(b)(1), judicial review of this final action is available only by filing a petition for review in the United States Court of Appeals for the District of Columbia Circuit by August 3, 2026. CAA section 307(b)(2) prohibits a party from challenging this final rule separately in any civil or criminal proceedings brought by the EPA for enforcement.

CAA section 307(d)(7)(B) further provides that only an objection to a rule or procedure that was raised with reasonable specificity during the period for public comment (including any public hearing) may be raised during judicial review. This section also requires the EPA to reconsider the rule if the person raising an objection can demonstrate to the Administrator that it was impracticable to raise such objection within the period for public comment or if the grounds for such objection arose after the period for public comment (but within the time specified for judicial review) and if such objection is of central relevance to the outcome of the rule. Any person seeking to make such a demonstration should submit a Petition for Reconsideration to the Office of the Administrator, U.S. EPA, Room 3000, WJC South Building, 1200 Pennsylvania Ave. NW, Washington, DC 20460, with a copy to both the person(s) listed in the preceding

FOR FURTHER INFORMATION CONTACT

section, and the Associate General Counsel for the Air and

Radiation Law Office, Office of General Counsel (Mail Code 2344A), U.S. EPA, 1200 Pennsylvania Ave. NW, Washington, DC 20460.

F. Severability

This final rule contains several discrete components, which the EPA views as severable as a practical matter—

i.e.,

they are functionally independent and will operate in practice independently of the other components. These discrete components are detailed in sections III.A through III.E of this preamble and the technical memoranda available in the docket.

For example, the outcome of the risk review, the outcome of the technology review, the final emission limits for HF and HCN for each type of HWC, and the final work practice standards for periods of SSM generally function independently of one another and would not be impacted if a reviewing court were to vacate one or more of the other final provisions. In addition, as this final rule revises an existing NESHAP, the EPA notes that if a reviewing court were to vacate one or more of the standards finalized here, the affected standards will revert to those present in the 2005 HWC NESHAP as revised in 2005, 2006, and 2008.

See

Docket ID. No. EPA-HQ-OAR-2004-0022.

See

70 FR 59402 (Oct. 12, 2005); 70 FR 75042 (Dec. 19, 2005); 71 FR 62388 (Oct. 25, 2006); 73 FR 18970 (Apr. 8, 2008); 73 FR 64068 (Oct. 28, 2008).

II. Background

A. What is the HWC NESHAP source category and how does the HWC NESHAP regulate HAP emissions from the source category?

HWCs are units that combust hazardous waste and they can be located at many types of facilities including those listed in table 1 of this preamble. The source category covered by the HWC NESHAP currently includes approximately 160 HWCs located at approximately 90 facilities in the United States. HWCs are incinerators, cement kilns, lightweight aggregate kilns, boilers, or HCl production furnaces that combust hazardous waste for waste reduction, thermal energy recovery, and/or production of a product. Hazardous waste is defined under the Resource Conservation and Recovery Act (RCRA), which establishes a comprehensive regulatory structure overseeing the treatment, storage, and disposal of hazardous waste.

In 2023, approximately 32.2 million tons of hazardous waste were generated in the United States, all of which must be treated or disposed of in a manner that protects human health and the environment.

Hazardous waste incineration provided that manner of disposal for approximately 1.1 million tons of that hazardous waste, and energy recovery in units like hazardous waste burning boilers accounted for an additional 1.4 million tons.

42 U.S.C. 6901-6992k.

U.S. Environmental Protection Agency. (Last updated Dec. 30, 2024). Biennial Report Summary:

https://rcrapublic.epa.gov/rcra-hwip/trends-and-analysis/details/4.

U.S. Environmental Protection Agency. (Last updated July 10, 2025). Biennial Report Management Methods:

https://rcrapublic.epa.gov/rcra-hwip/trends-and-analysis/details/3.

The key HAP that the HWC NESHAP regulates include polychlorinated dibenzodioxins and furans (PCDD/PCDF); mercury (Hg); cadmium and lead as semi-volatile metals; arsenic, beryllium, and chromium as low-volatile metals; antimony, cobalt, manganese, nickel, and selenium as non-enumerated metal HAP; HCl and chlorine gas; and other hydrocarbon HAP, including polychlorinated biphenyls (PCB) and polycyclic aromatic hydrocarbons (PAH). The HWC NESHAP also includes several other emission limits used as surrogate standards to regulate emissions of other HAP such as a carbon monoxide (CO) or total hydrocarbon (THC) limit associated with demonstrating good combustion practices, a destruction and removal efficiency (DRE) standard also for demonstrating good combustion practices, and a particulate matter (PM) emission limit for some subcategories.

For more information about the HWC NESHAP, see the notice of proposed rulemaking associated with this final action at 90 FR 50814 (Nov. 10, 2025).

The EPA originally promulgated the HWC NESHAP, codified at 40 CFR part 63, subpart EEE, in 1999.

It regulated incinerators, cement kilns, and lightweight aggregate kilns that burned hazardous waste. These standards were vacated in 2001

and replaced with interim standards in 2002.

The EPA promulgated replacement standards for hazardous waste incinerators, cement kilns, and lightweight aggregate kilns and first-time standards for hazardous waste solid fuel boilers, liquid fuel boilers, and HCl production furnaces in 2005.

In response to multiple petitions for reconsideration, the EPA sought and received a voluntary remand of the rule in 2009 to reexamine the HWC NESHAP.

64 FR 52828 (Sept. 30, 1999).

Cement Kiln Recycling Coal.,

255 F.3d at 872.

67 FR 6792 (Feb. 13, 2002).

70 FR 59402 (Oct. 12, 2005).

Sierra Club

EPA,

Docket No. 05-1441 (consolidated with Docket Nos. 05-1442, 05-1443, 05-1445, 05-1449) (D.C. Cir.).

In October 2022, Earthjustice filed an action in the U.S. District Court for the District of Columbia to compel the EPA to review and revise the HWC NESHAP under CAA sections 112(d)(6) and (f)(2) (

i.e.,

complete the RTR). In December 2024, the district court issued an order requiring that the EPA sign the final RTR rule for this source category by December 31, 2025.

In response to the EPA's request for an extension of time, the district court subsequently extended the deadline from December 31, 2025, to May 29, 2026.

The EPA is finalizing this action in response to the court order.

Order,

Blue Ridge Envtl. Def. League

Regan,

22-cv-3134 (APM), at 4 (D.D.C. Dec. 12, 2024).

Order, Blue Ridge Envtl. Def. League

Regan,

22-cv-3134 (APM), at 3-4 (D.D.C. Dec. 23, 2025).

In finalizing standards for previously unregulated HAP as part of this rulemaking, the EPA is exercising its authority under CAA section 112(d)(6) to revise the standards as necessary. Nothing in this final rule should be taken as endorsing the language in the district court's order discussing the EPA's obligations under CAA section 112 or the

LEAN

decision. The D.C. Circuit has exclusive jurisdiction to review final action taken by the EPA to promulgate standards pursuant to CAA section 112, including, when appropriate, to interpret relevant statutory provisions, see 42 U.S.C. 7607(b)(1), while district courts have jurisdiction, subject to standing, venue, and other requirements, to order the performance of “any act or duty under [the CAA] which is not discretionary with the Administrator,”

see id.

7604(a). In context, the district court's order was addressing the parties' arguments about the appropriate remedy, that is, the appropriate timeline for completing the RTR, for plaintiffs' claim that the EPA had failed to act by the statutory deadline.

B. What changes did we propose for the HWC NESHAP source category in our November 10, 2025, proposal?

On November 10, 2025, the EPA published a proposed rule in the

Federal Register

for the HWC NESHAP, 40 CFR part 63, subpart EEE, that discussed the results of the RTR and proposed actions reflecting those results. Specifically, the EPA proposed: that the results of the risk review demonstrated that no revisions to the existing standards were required to address residual risk; that no revisions to the existing standards were necessary based on developments in practices, processes, or control technologies under the technology review; numeric emission limits for HF and HCN for major source HWC solid fuel boilers; a work practice standard for HF for major source HWC incinerators; a work practice standard for HF and numeric emission limits for HCN for major source HWC cement kilns; a work practice standard for HF and numeric emission limits for HCN for major source liquid fuel boilers; work practice standards for periods of SSM; electronic reporting provisions; allowing title V air

permitting authorities to choose to exempt area sources from the requirement to obtain a title V permit if such area sources are not otherwise subject to title V air permitting requirements; and other items and technical corrections.

For more information about what was proposed, see the notice of proposed rulemaking associated with this final rule at 90 FR 50814 (Nov. 10, 2025).

III. What is included in this final rule?

This action finalizes the EPA's determinations pursuant to the RTR provisions of CAA section 112 for the HWC NESHAP source category. This action also finalizes other changes to the NESHAP, including emission limits and work practice standards for HF and HCN from major source HWC incinerators, cement kilns, solid fuel boilers, and liquid fuel boilers; work practice standards for periods of SSM; new electronic reporting provisions and requirements; provisions allowing title V air permitting authorities to choose to exempt area source HWCs from the requirement to have a title V air permit if such area sources are not otherwise subject to title V air permitting requirements; and minor corrections and clarifications to a number of other rule provisions. This action also reflects several changes to the November 2025 proposal in consideration of comments received during the public comment period, as described in section IV of this preamble.

A. What are the final rule amendments based on the risk review for the HWC NESHAP source category?

The EPA is finalizing, as proposed, that pursuant to CAA section 112(f), risks from this source category are adequately addressed by the existing standards and therefore acceptable, the existing standards provide an ample margin of safety to protect public health, and more stringent standards are not necessary to prevent an adverse environmental effect. The EPA is not promulgating any additional control requirements pursuant to CAA section 112(f)(2) but instead reaffirming the existing standards.

The D.C. Circuit upheld this approach to CAA section 112(f)(2) in

NRDC:

“If EPA determines that the existing technology-based standards provide an `ample margin of safety,' then the Agency is free to readopt those standards during the residual risk rulemaking.” 529 F.3d at 1083.

Sections IV.A.2 through IV.A.4 of this preamble provide a more in-depth analysis of the decision to finalize that the risks from the source category are acceptable and provide an ample margin of safety pursuant to CAA section 112(f).

B. What are the final rule amendments based on the technology review for the HWC NESHAP source category?

The EPA is finalizing, as proposed, that pursuant to CAA section 112(d)(6), there are no developments in practices, processes, and control technologies that warrant revisions to the MACT standards for this source category. Sections IV.B.2 through IV.B.4 of this preamble provide a more in-depth analysis of the decision not to revise the existing MACT standards under CAA section 112(d)(6).

C. What are the final rule amendments pursuant to CAA sections 112(d)(2) and (3) and 112(h) for the HWC NESHAP source category?

Consistent with our authority to review and revise the HWC NESHAP and with the proposed rule,

the EPA is finalizing regulatory provisions to address previously unregulated HAP emissions within the source category in this rule. Based on a review of available information, the EPA is finalizing the following pursuant to CAA sections 112(d)(2), (d)(3), and (h)(1):

See 90 FR 50814 (Nov. 10, 2025).

See

LEAN,

955 F.3d at 1091-99.

• Numeric emission limits for HF and HCN for major source HWC solid fuel boilers.

• Work practice standard for HF for major source HWC incinerators.

• Numeric emission limit for HCN for major source HWC cement kilns.

• Work practice standard for HF for all major source HWC liquid fuel boilers and numeric emission limits for HCN for some major source HWC liquid fuel boilers.

The EPA presents the results and final decisions based on the analyses performed pursuant to CAA sections 112(d)(2), (d)(3), and (h)(1) below, with separate discussion for each subcategory and HAP. All emission standards discussed here regulate only HWCs at facilities that are major sources of HAP. Sections IV.C.2 through IV.C.4 of this preamble provide a more in-depth discussion of the HF and HCN emission limitations.

1. Solid Fuel Boilers

a. Hydrogen Fluoride

The EPA is promulgating standards for HF emissions from major source HWC solid fuel boilers pursuant to CAA sections 112(d)(2) and (3). The EPA is promulgating a limit at the MACT floor of 6.2 parts per million by volume (ppmv) HF, dry basis and corrected to seven percent oxygen, for both existing and new solid fuel boilers.

The EPA is finalizing these standards as proposed.

New source standards apply to major source HWC solid fuel boilers for which construction or reconstruction commences after November 10, 2025.

The EPA is finalizing as proposed that existing sources must comply with the HF emission limits for solid fuel boilers within three years after June 3, 2026, and must conduct an initial compliance test demonstrating compliance no later than six months after the compliance date using EPA Methods 26A or 320. For affected facilities that commence construction or reconstruction after November 10, 2025, owners or operators must comply with all requirements of the subpart, including the HF emission limits, no later than the effective date of the final rule or upon startup, whichever is later, and must demonstrate compliance no later than six months after the compliance date using the same methods. All sources must subsequently demonstrate compliance once every five years during the comprehensive performance test (CPT).

b. Hydrogen Cyanide

The EPA is promulgating standards for HCN emissions from major source HWC solid fuel boilers pursuant to CAA sections 112(d)(2) and (3). The EPA is promulgating a limit at the MACT floor of 5.0 ppmv HCN, dry basis and corrected to seven percent oxygen, for both existing and new solid fuel boilers.

The EPA is finalizing these standards as proposed.

New source standards apply to major source HWC solid fuel boilers for which construction or reconstruction commences after November 10, 2025.

The EPA is finalizing as proposed that existing sources must comply with the HCN emission limits for solid fuel boilers within three years after June 3, 2026, and must conduct an initial compliance test demonstrating compliance no later than six months after the compliance date using EPA Method 320 or, if there are entrained water droplets in the flue gas, an alternative test method submitted and approved by the Administrator.

For affected facilities that commence construction or reconstruction after November 10, 2025, owners or operators must comply with all requirements of the subpart, including the HCN emission limits, no later than the effective date of the final rule or upon startup, whichever is later, and must demonstrate compliance no later than six months after the compliance date

using the same methods. Sources must subsequently demonstrate compliance once every five years during the CPT.

40 CFR 63.7(f).

2. Incinerators

a. Hydrogen Fluoride

The EPA is promulgating a work practice standard with multiple compliance options for HF emissions from major source HWC incinerators pursuant to CAA section 112(h) because it is not feasible to prescribe or enforce a standard of performance.

The same work practice standard is applicable to both new and existing sources.

In response to comments, the EPA is finalizing the requirement that one automatic waste feed cutoff (AWFCO)-interlocked operating parameter limit (OPL) other than chlorine feed rate, rather than two, is appropriate for complying with the work practice standard.

See

CAA section 112(h)(2) for more information about the circumstances under which prescribing or enforcing a standard of performance is not reasonable and the notice of proposed rulemaking associated with this final action for discussion of why it is not feasible in this circumstance (90 FR 50814 (Nov. 10, 2025)).

New source standards apply to major source HWC incinerators for which construction or reconstruction commences after November 10, 2025.

The work practice standard requires a source to comply with their choice of one of three options. The options of the work practice standard are as follows:

Option 1:

If a source actively controls HCl emissions and the source has at least one AWFCO-interlocked OPL other than chlorine feed rate to control HCl, then the source may comply with the HCl and chlorine gas OPL or limits and indicate in the CPT report and Notification of Compliance (NOC) that they are demonstrating compliance with the HF work practice standard by complying with the HCl and chlorine gas OPL requirements.

Option 2:

If a facility does not feed any material with detectable levels of fluorine to the source, then the source may certify in the CPT report that no fluorine is fed and indicate in the CPT report and NOC that they are demonstrating compliance with the HF work practice standard through the certification.

Option 3:

If a facility feeds fluorine to a source and the source has no active HCl control with at least one AWFCO-interlocked OPL other than chlorine feed rate to control HCl emissions (Option 1), then the facility must monitor and record the total fluorine fed to the unit as a 12-hour rolling average. If at any point the feed rate suggests that HF emissions may exceed the solid fuel boiler existing source emission limit for HF (6.2 ppmv HF as calculated according to the HWC NESHAP's maximum theoretical emissions concentration (MTEC) procedure), then the source must complete a one-time HF emissions test during the next CPT at the maximum recorded fluorine feed rate and include the test results in the CPT report. The source must include the comparison of the HF MTEC to the solid fuel boiler existing source emission limit for HF in the CPT plan.

The EPA is finalizing as proposed that existing sources must comply with the HF work practice standard for incinerators within three years after June 3, 2026, and must demonstrate compliance through a certification, test plan, or initial compliance test no later than six months after the compliance date. Emission testing for HF must use EPA Methods 26A or 320. For affected facilities that commence construction or reconstruction after November 10, 2025, owners or operators must comply with all requirements of the subpart, including the HF work practice standard, no later than the effective date of the final rule or upon startup, whichever is later, and must demonstrate compliance no later than six months after the compliance date. Sources must subsequently demonstrate compliance once every five years during the CPT.

b. Hydrogen Cyanide

The EPA did not propose and is not finalizing standards for HCN emissions from major source HWC incinerators because the EPA does not have credible data indicating that major source HWC incinerators measurably emit HCN.

90 FR 50814 (Nov. 10, 2025).

3. Cement Kilns

a. Hydrogen Fluoride

As explained in sections IV.C.2 through IV.C.4 of this preamble, the EPA is not finalizing standards for HF emissions from major source HWC cement kilns because the Agency does not have credible data indicating that HWC cement kilns measurably emit HF.

b. Hydrogen Cyanide

The EPA is promulgating standards for HCN emissions from major source HWC cement kilns pursuant to CAA sections 112(d)(2) and (3). For existing sources, the EPA is finalizing as proposed a limit at the MACT floor of 56 ppmv HCN, dry basis and corrected to seven percent oxygen. As explained in sections IV.C.2 through IV.C.4 of this preamble, for new sources the EPA is finalizing for new sources a limit at the revised MACT floor of 5.5 ppmv HCN, dry basis and corrected to seven percent oxygen.

New source standards apply to major source HWC cement kilns for which construction or reconstruction commences after November 10, 2025.

The EPA is finalizing as proposed that existing sources must comply with the HCN emission limits for cement kilns within three years after June 3, 2026, and must demonstrate compliance through an initial compliance test no later than six months after the compliance date using EPA Method 320 or, if there are entrained water droplets in the flue gas, an alternative test method submitted and approved by the Administrator.

For affected facilities that commence construction or reconstruction after June 3, 2026, owners or operators must comply with all requirements of the subpart, including the HCN emission limits, no later than the effective date of the final rule or upon startup, whichever is later, and must demonstrate compliance no later than six months after the compliance date using the same methods. Sources must subsequently demonstrate compliance once every five years during the CPT using EPA Method 320 or, if there are entrained water droplets in the flue gas, an alternative test method submitted and approved by the Administrator.

40 CFR 63.7(f).

Id.

4. Liquid Fuel Boilers

a. Hydrogen Fluoride

The EPA is promulgating a work practice standard with multiple compliance options for HF emissions from major source HWC liquid fuel boilers pursuant to CAA section 112(h) because it is not feasible to prescribe or enforce a standard of performance.

This is the same work practice standard with multiple compliance options described in section III.C.2.a of this preamble for incinerators. The same work practice standard is applicable to both new and existing sources.

The EPA is finalizing these standards as proposed.

See

New source standards apply to major source HWC liquid fuel boilers for which construction or reconstruction commences after November 10, 2025.

The EPA is finalizing as proposed that existing sources must comply with the HF work practice standard for liquid

fuel boilers within three years after the publication of the final rule and that demonstration through a certification, test plan, or initial compliance test would occur no later than six months after the compliance date. For affected facilities that commence construction or reconstruction after June 3, 2026, owners or operators must comply with all requirements of the subpart, including the HF work practice standard, no later than the effective date of the final rule or upon startup, whichever is later, and must demonstrate compliance no later than six months after the compliance date. Sources must subsequently demonstrate compliance once every five years during the CPT. Emission testing for HF must use EPA Methods 26A or 320.

b. Hydrogen Cyanide

The EPA is promulgating standards for HCN emissions from two subcategories of major source HWC liquid fuel boilers pursuant to CAA sections 112(d)(2) and (3). The EPA is finalizing as proposed the subcategorization of liquid fuel boilers by size, under CAA section 112(d)(1), for the purposes of the HCN emission standard.

The size categories are as follows: capacity less than or equal to 50 million british thermal units per hour (MMBTU/hr), capacity greater than 50 MMBTU/hr but less than or equal to 250 MMBTU/hr, and capacity greater than 250 MMBTU/hr.

42 U.S.C. 7412(d)(1); see also

U.S. Sugar Corp.

EPA

830 F.3d 579, 593-94 (D.C. Cir. 2016) (“[T]he EPA has discretion to differentiate among classes, types, and sizes of sources within a category or subcategory.” (internal citations omitted)).

The EPA did not propose and is not finalizing standards for HCN emissions from major source HWC liquid fuel boilers with a capacity that is less than or equal to 50 MMBTU/hr because the Agency does not have credible data indicating that major source HWC incinerators measurably emit HCN.

For existing major source HWC liquid fuel boilers with capacity greater than 50 MMBTU/hr but less than or equal to 250 MMBTU/hr, the EPA is finalizing as proposed a limit at the MACT floor of 2.7 ppmv HCN, dry basis and corrected to seven percent oxygen. For new major source HWC liquid fuel boilers with capacity greater than 50 MMBTU/hr but less than or equal to 250 MMBTU/hr, the EPA is finalizing as proposed a limit at the MACT floor of 1.2 ppmv HCN, dry basis and corrected to seven percent oxygen.

New source standards apply to major source HWC liquid fuel boilers for which construction or reconstruction commences after November 10, 2025.

For existing major source HWC liquid fuel boilers with capacity greater than 250 MMBTU/hr, the EPA is finalizing as proposed a limit at the MACT floor of 3.4 ppmv HCN, dry basis and corrected to seven percent oxygen. For new major source HWC liquid fuel boilers with capacity greater than 250 MMBTU/hr, the EPA is finalizing as proposed a limit at the MACT floor of 1.1 ppmv HCN, dry basis and corrected to seven percent oxygen.

The EPA is finalizing as proposed that existing sources must comply with the HCN emission limits for liquid fuel boilers within three years after June 3, 2026, and must demonstrate compliance through an initial compliance test no later than six months after the compliance date using EPA Method 320 or, if there are entrained water droplets in the flue gas, an alternative test method submitted and approved by the Administrator.

40 CFR 63.7(f).

Id.

5. HCl Production Furnaces

a. Hydrogen Fluoride

The EPA did not propose and is not finalizing standards for HF emissions from major source HWC HCl production furnaces because the Agency does not have credible data indicating that major source HWC HCl production furnaces measurably emit HF.

90 FR 50814 (Nov. 10, 2025).

b. Hydrogen Cyanide

The EPA did not propose and is not finalizing standards for HCN emissions from major source HWC HCl production furnaces because the Agency does not have credible data indicating that major source HWC HCl production furnaces measurably emit HCN.

Id.

6. Lightweight Aggregate Kilns

The EPA did not propose and is not finalizing standards for HF or HCN emissions from lightweight aggregate kilns because the EPA has no credible emissions data on which to base decisions about whether or how to regulate such emissions.

If an HWC lightweight aggregate kiln begins operating after the promulgation of this final rule, the EPA expects to collect emissions testing data from them and address potential emissions in a subsequent action.

Id.

D. What are the final rule amendments addressing emissions during periods of startup, shutdown, and malfunction?

Consistent with

Sierra Club

EPA

and the proposed rule,

the EPA is finalizing revisions to the SSM provisions of the NESHAP to ensure that HWCs meet MACT standards at all times when controlling HAP emissions. The EPA is promulgating work practice standards for periods of SSM. These work practice standards include the following: (1) a clean fuel requirement for periods of startup and shutdown; (2) a requirement to follow an approved SSM plan during periods of SSM; and (3) the AWFCO system requirement. The EPA is also finalizing as proposed various other changes to modify recordkeeping and reporting requirements as a result of the SSM provisions.

551 F.3d 1019 (D.C. Cir. 2008).

90 FR 50814 (Nov. 10, 2025).

The EPA is finalizing a work practice standard for periods of startup and shutdown. This work practice standard is the combination of firing prescribed supplemental clean fuels during periods of startup and shutdown and operating in accordance with an approved SSM plan during periods of startup and shutdown. The EPA is also finalizing a work practice standard for periods of malfunction. This work practice standard is the combination of AWFCO system requirements and operating in accordance with an approved SSM plan during periods of malfunction. Because the SSM plan also includes a description of potential causes of malfunctions that may result in significant releases of HAP and actions the source takes to minimize the frequency and severity of those malfunctions, the source must also comply with any requirements to minimize the frequency and severity of malfunctions prescribed in the SSM plan for periods of normal operation.

The EPA is also finalizing that owners or operators must submit SSM plans to the Administrator for approval within 180 days of the effective date of this rule or upon initial startup, whichever is

later, and that sources must begin complying with the SSM plan immediately upon submittal. While the EPA expects SSM plans to be reviewed within no more than 90 days of submittal, commenters pointed out, and the Agency agrees, that owners or operators of HWCs can only control the submittal date, not the approval date of an SSM plan, and so the EPA considers that it is more appropriate to tie the compliance timeline to the action that HWC owners or operators can control.

In response to comments, the EPA is also finalizing that if changes are made to the SSM plan as a result of the approval process, sources must begin complying with the revised SSM plan upon notification of approval.

See

40 CFR 63.1206(c)(2)(ii)(B) for information about SSM plan review.

As discussed in sections IV.D.2 through IV.D.4 of this preamble, the EPA is finalizing revised definitions of startup, shutdown, and supplemental fuel in response to comments received on the proposal.

Commenters requested, and the EPA is finalizing, separate definitions of startup and shutdown for different types of HWCs and is clarifying that transitioning from operating under the requirements of an otherwise applicable requirement constitutes a period of startup.

The definitions of startup are:

See

the revised 40 CFR 63.1206(c)(10) and (c)(11).

See

40 CFR 63.1206(b)(1)(ii) for information about operating according to an otherwise applicable requirement.

• For incinerators, startup begins with the firing of supplemental fuel in the combustion chamber or with transitioning from a period of shutdown. All air pollution control devices (APCDs) must be in operation as expeditiously as possible and prior to the introduction of any waste material that is not supplemental fuel into the HWC. Startup ends once the system has stabilized but no later than 15 minutes after either hazardous waste that is not fed in accordance with the AWFCO requirements when burning hazardous waste during startup and shutdown or any waste material that is not supplemental fuel is fed into the HWC, whichever occurs first.

See

40 CFR 63.1206(c)(2)(v)(B) for the AWFCO requirements when burning hazardous waste during startup and shutdown.

• For cement kilns and lightweight aggregate kilns, startup begins when a kiln either begins firing supplemental fuel or transitions from a period of shutdown. All APCDs must be in operation as expeditiously as possible and prior to the introduction of kiln feed or any waste material that is not supplemental fuel into the kiln. Startup ends 120 minutes after the continuous introduction of kiln feed, when the feed rate exceeds 60 percent of the kiln design limitation rate, or 15 minutes after hazardous waste that is not fed in accordance with the AWFCO requirements when burning hazardous waste during startup and shutdown is fed into the HWC, whichever occurs first.

Cement kilns may fire traditional fuels as defined in 40 CFR 241.2 once the HWC achieves 1200 degrees Fahrenheit (°F) measured at a location that best represents, as practicable, the bulk gas temperature in the combustion zone and all APCDs are operational.

See

40 CFR 63.1206(c)(2)(v)(B) for the AWFCO requirements when burning hazardous waste during startup and shutdown.

• For solid fuel boilers and liquid fuel boilers, startup begins with either the first-ever firing of supplemental fuel in a boiler for the purpose of supplying useful thermal energy (such as heat or steam) for heating, cooling, or process purposes, or producing electricity or the firing of fuel in a boiler for any purpose after a shutdown event. All APCDs must be in operation as expeditiously as possible and prior to the introduction of any waste material that is not supplemental fuel into the boiler. Startup ends at the earliest of the following: four hours after when the boiler supplies useful thermal energy (such as heat or steam) for heating, cooling, or process purposes; the boiler produces electricity; or 15 minutes after either hazardous waste that is not fed in accordance with the AWFCO requirements when burning hazardous waste during startup and shutdown or any waste material that is not supplemental fuel is fed into the boiler.

See

40 CFR 63.1206(c)(2)(v)(B) for the AWFCO requirements when burning hazardous waste during startup and shutdown.

• For HCl production furnaces, startup begins when the HCl production furnace either begins firing supplemental fuel or transitions from a period of shutdown. All APCDs must be in operation as expeditiously as possible and prior to the introduction of any waste material that is not supplemental fuel into the HCl production furnace. Startup ends either 120 minutes after the continuous introduction of materials intended to produce HCl to the HCl production furnace or 15 minutes after either hazardous waste that is not fed in accordance with the AWFCO requirements when burning hazardous waste during startup and shutdown or any waste material that is not supplemental fuel is fed into the HCl production furnace, whichever is earlier.

See

40 CFR 63.1206(c)(2)(v)(B) for the AWFCO requirements when burning hazardous waste during startup and shutdown.

• Notwithstanding the previous definitions, transitioning from an otherwise applicable standard initiates a period of startup lasting no more than 15 minutes in duration.

The definitions of shutdown are:

• For incinerators, shutdown begins when hazardous waste feed to the combustion chamber has been cut off for a period of time not less than the hazardous waste residence time and the feed of non-hazardous waste materials to the combustion chamber is cut off. Shutdown ends when fire is extinguished in the combustion chamber, the incinerator enters another mode of operation, or when a startup is initiated.

• For cement kilns and lightweight aggregate kilns, shutdown begins when hazardous waste feed to the combustion chamber has been cut off for a period of time not less than the hazardous waste residence time and kiln feed is halted. Shutdown ends when continuous kiln rotation ceases, the kiln enters another mode of operation, or when a startup is initiated.

• For solid fuel boilers and liquid fuel boilers, shutdown begins when the boiler no longer supplies useful thermal energy (such as heat or steam) for heating, cooling, or process purposes and/or generates electricity or when no fuel is being fed to the boiler, whichever is earlier, and when hazardous waste feed to the combustion chamber has been cut off for a period of time not less than the hazardous waste residence time. Shutdown ends when the boiler no longer supplies useful thermal energy (such as steam or heat) for heating, cooling, or process purposes and/or generates electricity, and no fuel is being combusted in the boiler, the boiler enters another mode of operation, or when startup is initiated.

• For HCl production furnaces, shutdown begins when hazardous waste feed to the combustion chamber has been cut off for a period of time not less than the hazardous waste residence time and raw material feed to the HCl production furnace is halted. Shutdown ends when the HCl production furnace flame is extinguished, the HCl production furnace enters another mode of operation, or when a startup is initiated.

The EPA defines supplemental fuel as one or a combination of the following fuels: natural gas, synthetic natural gas,

propane, other gas 1 fuels, distillate oil, syngas, ultra-low sulfur diesel, kerosene, hydrogen, refinery gas, liquified petroleum gas, and any other fuel approved in the SSM plan. For solid fuel boilers, the definition of supplemental fuel includes coal. The EPA also defines other gas 1 fuels as gaseous fuel that is not natural gas, refinery gas, or a hazardous waste and does not exceed a maximum Hg concentration of 40 micrograms per cubic meter of gas. The SSM plan must specify the basis for determining that any gas qualifies as other gas 1 fuel.

The EPA is also finalizing as proposed changes in recordkeeping requirements that are associated with periods of SSM. In accordance with this final action, sources must retain in the operating record the start date, start time, and duration (hours) of each startup, shutdown, or malfunction of affected process, air pollution control, and monitoring equipment and whether the source followed the SSM plan. For periods of SSM when the SSM plan was not followed, sources must record and retain a list of the affected sources or equipment; actions taken to minimize emissions in accordance with 40 CFR 63.6(e)(1)(i) and 40 CFR 63.8(c)(1)(i); any corrective actions taken to return the affected unit to its normal or usual manner of operation; whether the failure occurred during a period of SSM; an estimate of the quantity of each regulated pollutant emitted; and a description of the method used to estimate the emissions.

The EPA is finalizing as proposed changes to the HWC NESHAP General Provisions table related to periods of SSM by revising the applicability of 40 CFR 63.10. The following general provisions remain applicable to the HWC NESHAP: 40 CFR 63.10(a), (b)(1), (b)(2)(iii), (b)(2)(v)-(xiv), (b)(3), (c), (d)(1), (d)(3), (d)(4), (e), and (f). The following general provisions are no longer applicable to the HWC NESHAP: 40 CFR 63.10(b)(2)(i) and (ii), (b)(2)(iv), and (d)(2).

Sections IV.D.2 through IV.D.4 of this preamble provide a more in-depth analysis of the EPA's decisions regarding work practice standards for periods of SSM.

E. What other changes have been made to the NESHAP?

The EPA is promulgating other changes to the HWC NESHAP. Regarding electronic reporting, the EPA is finalizing as proposed the requirement to electronically report performance test results, NOC reports, and certain other submissions. Regarding technical corrections, the EPA is finalizing, as proposed, the removal of the requirement that CO is kept between the average and maximum reported values during the confirmatory performance test (CfPT) and the never-implemented requirement that sources install and operate PM continuous emission monitoring systems (PM CEMS). Regarding clarifications, the EPA is finalizing the following issues as proposed: explicitly allowing incorporation by reference of OPLs determined during the CPT in air permits, removing references that were incorrectly incorporated by reference and have since expired, clarifying the demonstration of compliance timeframe for new standards by removing an outdated demonstration of compliance timeline for the 2005 HWC NESHAP, and other minor editorial corrections. The EPA is also clarifying that a relative accuracy test audit (RATA) must be performed within 180 days before every CPT. The EPA is also finalizing that title V air permitting authorities including but not limited to States may choose to exempt area sources not otherwise subject to title V air permitting requirements from the requirement to obtain a title V permit on a case-by-case basis. Section IV.E of this preamble provides a more in-depth analysis of the EPA's decisions regarding these revisions.

EPA Method 0023A is referenced in the amendatory text of this document and was previously approved for § 63.1208.

F. What are the effective and compliance dates of the standards?

The revisions to the HWC NESHAP standards promulgated in this action are effective on June 3, 2026. The EPA is finalizing the timeline for compliance with the HF and HCN limits as proposed. Existing sources must comply with the HF and HCN emission limits as applicable by June 3, 2029, which is three years after publication of this final rule. For existing sources, CAA section 112(i) provides that the compliance date for standards promulgated under CAA section 112(d) shall be as expeditious as practicable, but no later than three years after the effective date of the standard.

As the EPA explained in the proposal, and as some commenters agreed, owners and operators need at least three years to implement the requirements that the EPA is finalizing under CAA section 112(d)(2), (3), and (6).

For example, sources that complete performance testing to demonstrate compliance with the HF or HCN emission limits must determine if they need to make any modifications to comply with the limits, implement any changes, submit a performance test plan at least one year before testing commences, get the performance test plan approved, and schedule and conduct a performance test to demonstrate compliance. Owners or operators may also require modifications to their title V, other air, or RCRA permits if they modify operations of their HWC to comply with the HF or HCN emission limits. As provided in CAA section 112(i) and 5 U.S.C. 801(3), all new affected sources, which are for the purposes of the HF and HCN standards sources constructed or reconstructed after November 10, 2025, must comply with all requirements under CAA sections 112(d)(2), (3), (6), and 112(h) immediately upon the effective date, which is June 3, 2026, or upon startup, whichever is later. Both new and existing sources must commence performance testing to demonstrate compliance with the HF and HCN emission limits no later than six months after their respective compliance dates. The EPA provided additional rationale for these compliance dates in the preamble to the proposed rule.

The EPA is clarifying in this final rule that the Administrator may grant an extension of the compliance timeline, as appropriate.

U.S. Sugar Corp.

EPA,

113 F.4th 984, 995 (D.C. Cir. 2024) (CAA section 112(i)(3)(A) “permits EPA to establish a delayed `compliance date' for any existing-source emission standard, which may fall up to 3 years after the effective date of such standard”);

see also Ass'n of Battery Recyclers,

716 F.3d at 672 (“Section 112(i)(3)'s three-year maximum compliance period applies generally to any emission standard . . . promulgated under [section 112].”).

See

chapter 1 of U.S. EPA,

Summary of Public Comments and Responses for the National Emission Standards for Hazardous Air Pollutants from Hazardous Waste Combustors,

available in the docket for this rulemaking.

90 FR 50814, 50851 (Nov. 10, 2025).

See 40 CFR 63.6(i) and 40 CFR 63.1213 for more information about an extension of the compliance timeline.

The EPA is promulgating new electronic reporting requirements for all sources, and the Agency is finalizing all electronic reporting compliance dates as proposed. Owners and operators must submit notifications of intent to comply, eligibility demonstrations, periodic SSM reports, and compliance progress reports electronically through a PDF upload in Compliance and Emissions Data Reporting Interface (CEDRI) beginning 60 days from the effective date of the final rule, which is August 3, 2026. As the EPA is not changing the contents and structure of these reports, but only the manner of submission, the Agency believes that 60 days is sufficient time for facilities to enroll in

CEDRI if not already enrolled and to submit these reports electronically. Owners and operators must submit performance tests and performance evaluations including RATA electronically using the Electronic Reporting Tool (ERT) beginning 90 days after the effective date of the final rule, which is September 1, 2026. In the EPA's experience, since the ERT has been available for use for over a decade and stack testing firms are well acquainted with its use, 90 days is sufficient time to begin electronic reporting using the ERT. Owners and operators must submit the NOC and the excess emissions and continuous monitoring system (CMS) performance reports and summary reports electronically in CEDRI using a spreadsheet template beginning one year from the effective date of the final rule, which is June 3, 2027, or one year from the date the EPA makes the template available on the CEDRI homepage, whichever is later. The EPA believes that one year is necessary to ensure that facilities can become acquainted with the spreadsheet template and begin entering data into the new format.

The EPA is promulgating new work practice standards for periods of SSM, which are described in sections III.D and IV.D of this preamble. In response to comments, the EPA is finalizing that all facilities must submit the SSM plan to the Administrator for approval either postmarked within 180 days of June 3, 2026, or upon initial startup, whichever is later. For clarity, November 30, 2026, is 180 days after the date of this rule's effective date. The EPA anticipates that most facilities are already operating in accordance with their SSM plan. Based on the EPA's experience and comments received from affected entities, the 180-day compliance period is a reasonable timeframe for facilities to review their SSM plans, revise them, if required, based on the contents of this action, and submit them for approval. All facilities already implement the AWFCO system requirement of the SSM work practice standards and so HWC owners and operators do not require additional time for compliance.

The EPA is finalizing as proposed that all other revisions to the HWC NESHAP would become applicable on the effective date of the final rule, which is June 3, 2026, or as otherwise indicated in the regulatory text. These revisions are technical corrections, clarifications, and deregulatory actions that do not require demonstrations of compliance or immediate action on the part of regulated entities.

IV. What is the rationale for our final decisions and amendments for the HWC NESHAP source category?

For each issue, this section provides a description of what the EPA proposed and what the Agency is finalizing, the Agency's rationale for the final decisions and amendments, and a summary of key comments and responses. For all comments not discussed in this preamble, comment summaries and the EPA's responses are in the document titled

Summary of Public Comments and Responses for the National Emission Standards for Hazardous Air Pollutants from Hazardous Waste Combustors

(“Comment Response Document”), which is in the docket for this rulemaking.

See

Docket ID. No. EPA-HQ-OAR-2004-0022.

A. Residual Risk Review for the HWC NESHAP Source Category

1. What did we propose pursuant to CAA section 112(f) for the HWC NESHAP source category?

On November 10, 2025, the EPA proposed that risks posed by HAP emissions from HWCs are adequately address by existing standards and acceptable, that the current NESHAP provides an ample margin of safety to protect public health, and that additional standards are not necessary to prevent an adverse environmental effect.

The EPA's residual risk review found that the estimated cancer risks were below the presumptive limit of acceptability and that the noncancer risk results indicates a minimal likelihood of adverse noncancer health effects due to HAP emissions from HWCs. The EPA based the proposed decision on ample margin of safety on a weighing of relevant factors, including the risk posed by HWCs, the costs and effectiveness of additional controls to further reduce risk, and uncertainties and conservative assumptions in the emission rates used in estimating risk.

90 FR 50814 (Nov. 10, 2025).

In the proposed review, the EPA evaluated risk based on estimates of current actual HAP emissions from HWCs, maximum allowable HAP emissions from HWCs, and facility-wide risk based on reported actual HAP emissions to characterize the risk from HWCs in the context of whole facility risk. The EPA modeled several metrics for risk due to HAP inhalation in the proposed review, including cancer risk to the individual most exposed, total cancer incidence, population within 50 kilometers of an HWC facility exposed to cancer risk greater than or equal to one in one million, modeled chronic noncancer target organ-specific hazard index (TOSHI), and maximum modeled acute noncancer hazard quotient (HQ). The EPA also evaluated in the proposed review multipathway human health risks including the cancer risk for the highest exposed individual, the maximum chronic noncancer HQ for persistent and bioaccumulative HAP, and if the Agency expected an adverse environmental effect as a result of HAP emissions from HWCs based on the results of an environmental risk screening analysis. Table 2 of this preamble presents a summary of the results of the proposed risk analysis. The EPA estimates that no people will be at an increased risk of cancer greater than or equal to 100-in-1 million based on source category actual or allowable emissions.

ER03JN26.073

The EPA also considered the uncertainty associated with the proposed risk assessment. Some of the major uncertainties in the proposed risk assessment were associated with the RTR emissions dataset, dispersion modeling, inhalation exposure estimates, and dose-response relationships.

Considering all of the health risk information, including the uncertainties, the EPA proposed to conclude that the risks for this source category under the current NESHAP provisions are acceptable.

See

the preamble to the proposed rule at 90 FR 50830 (Nov. 10, 2025), section III.C.8, and the memorandum

Residual Risk Assessment for the Hazardous Waste Combustor Source Category in Support of the Risk and Technology Review 2025 Proposed Rule

, which is available in the docket for this rulemaking.

As part of the ample margin of safety analysis performed for the proposal, the EPA evaluated additional potential technologies for controlling emissions to further reduce risk from HWCs, taking into consideration costs and economic impacts of controls, technological feasibility, uncertainties, and other relevant factors.

The EPA evaluated the installation of a Shell Dioxin Destruction System (SDDS) for control of PCDD/PCDF in the proposal. The EPA estimated in the proposal that emissions reductions of PCDD/PCDF due to SDDS installation would have no impact on the cancer maximum individual risk or the maximum noncancer TOSHI, a minimal impact on the cancer incidence, and little impact on the number of people exposed to cancer risks greater than or equal to one, but could potentially lower the cancer risks that the EPA estimated in the multipathway risk screening. The EPA did not propose revisions based on this control scenario pursuant to CAA section 112(f) because of the relatively high capital and annualized costs compared to relatively low reductions in cancer risks and emissions reductions.

The EPA similarly evaluated the installation of a GORE Mercury Control System (GMCS) for control of Hg in the proposal. The EPA estimated in the proposal that the emission reductions due to GMCS installation would have no impact on the cancer maximum individual risk, maximum TOSHI, cancer incidence, or number of people exposed to cancer risk levels of greater than or equal to one in one million but could potentially lower the cancer risks estimated in the multipathway risk screening. Like the SDDS, the EPA did not propose revisions based on this control scenario pursuant to CAA section 112(f) because of the relatively high capital and annualized costs compared to relatively low reductions in cancer risk and emissions reductions.

Based on the EPA's weighing of all the relevant factors presented in the risk analyses for the HWC NESHAP and all of the other information discussed earlier in this section, the Agency proposed to conclude that the current standards provide an ample margin of safety to protect public health. Therefore, the EPA did not propose any changes to the HWC NESHAP in order to provide an ample margin of safety to protect public health or to prevent an adverse environmental effect.

2. How did the risk review for the HWC NESHAP source category change since proposal?

The EPA did not make any changes to the risk review in this final rule and is finalizing the residual risk assessment as proposed.

3. What key comments did we receive on the risk review, and what are our responses?

The EPA received comments in support of and against the proposed risk

review. Commenters generally discussed the statutory requirements for the residual risk review, the methodology used to conduct the residual risk review, and the EPA's conclusions concerning the residual risk review. This section provides a summary of and response to key comments received regarding the statutory requirements for the residual risk review. Comment summaries and the EPA's responses for additional issues raised regarding the residual risk review for the HWC NESHAP are in the Comment Response Document, which is available in the docket for this rulemaking.

Comment

: Two commenters asserted that the D.C. Circuit previously affirmed the EPA's interpretation of CAA section 112(f)(2) in

NRDC

EPA

under the second step of the

Chevron

framework and that, per

Loper Bright

, the Agency's interpretations must now reflect the best reading of the statute.

The commenters stated that the proposed rule does not reflect the best reading of the statute because CAA section 112(f)(2)(A) requires the EPA to promulgate risk-based standards to reduce the maximum individual lifetime cancer risk to less than one in one million, which they assert the Agency has not done. The commenters further argued that the EPA's interpretation of CAA section 112(f)(2)(B), which they characterized as a savings provision, makes CAA section 112(f)(2)(A) meaningless because the maximum individual cancer risk for the HWC source category would remain above one in one million. Additionally, the EPA's interpretation allows for readopting standards that have “already been promulgated,” which is contrary to language contained in CAA section 112(f)(2)(A). One commenter further asserted that since the EPA has not promulgated any standards under CAA section 112(f) for this source category, it is in violation of the best reading of the statute.

529 F.3d 1077.

Chevron U.S.A., Inc.

Natural Res. Def. Council

, 467 U.S. 837 (1984);

Loper Bright Enters.

Raimondo

, 603 U.S. 369 (2024).

Response

: The EPA disagrees with the commenters' assertion that the best reading of CAA section 112(f)(2) requires the EPA to promulgate risk-based standards to reduce the maximum individual lifetime cancer risk to less than one in one million. As described in the preamble for the notice of proposed rulemaking,

CAA section 112(f)(2)(B) expressly preserves the EPA's use of the two-step approach for developing standards to address any residual risk and the Agency's interpretation of “ample margin of safety” developed in the

National Emissions Standards for Hazardous Air Pollutants: Benzene Emissions from Maleic Anhydride Plants, Ethylbenzene/Styrene Plants, Benzene Storage Vessels, Benzene Equipment Leaks, and Coke By-Product Recovery Plants

(“Benzene NESHAP”).

Specifically, CAA section 112(f)(2)(B) states that nothing in CAA section 112(f)(2)(A) or in any other provision of CAA section 112 shall be construed as affecting or applying to the Administrator's interpretation of CAA section 112 as set forth in the Benzene NESHAP final rule.

The commenters cite language in CAA section 112(f)(2)(A), which is subject to the plain language of CAA section 112(f)(2)(B). The best interpretation of CAA section 112(f)(2)(B) indicates that the Administrator's interpretation of a residual risk review as set forth in the Benzene NESHAP should be used for the residual risk review conducted by the EPA for the HWC source category. The EPA does not agree that CAA section 112(f)(2)(A) is best read as compelling the Agency to promulgate standards pursuant to subsection (f)(2) where, as here, the residual risk is acceptable and there is an ample margin of safety.

See

90 FR 50814 sections II.A, III.A, III.C, IV.B, and IV.C (Nov. 10, 2025).

See

54 FR 38044 (Sept. 14, 1989).

42 U.S.C. 7412(f)(2)(B).

The EPA further disagrees that the D.C. Circuit precedents rejecting commenters' argument are no longer valid under

Loper Bright

. The D.C. Circuit has rejected the commenters' alternative reading of CAA section 112(f)(2) on multiple occasions, and the court's reasoning makes clear that the EPA's longstanding position is at least the better reading of the statute. In any event, the Supreme Court noted in

Loper Bright

that it did “not call into question prior cases that relied on the

Chevron

framework.”

603 U.S. at 412.

The EPA also disagrees with the commenters' assertion that the Agency is not promulgating standards pursuant to CAA section 112(f)(2). As described in the preamble to the proposed rule, the EPA completed the residual risk review pursuant to CAA section 112(f)(2), proposed to determine that the risks are acceptable with an ample margin of safety under the statutory authority of CAA section 112(f)(2), and is finalizing that determination under the same authority. As previously discussed, CAA section 112(f)(2)(B) dictates that the Administrator may continue to use the interpretation set forth in the Benzene NESHAP for the residual risk review conducted pursuant to CAA section 112(f)(2). In the Benzene NESHAP, the Administrator determined that existing levels of control provided an ample margin of safety for ethylbenzene/styrene process vents and benzene equipment leaks and so the Administrator did not promulgate a new standard for those processes, instead drawing a conclusion that additional standards were not warranted for those processes.

The conclusion that no new standards were warranted and so no new standards were promulgated in the Benzene NESHAP combined with CAA section 112(f)(2)(B) leads the EPA to determine that the best plain language reading of CAA section 112(f)(2) allows for the Administrator to affirm or readopt existing standards for the HWC source category under CAA section 112(f)(2).

See

54 FR 38044 (Sept. 14, 1989).

NRDC

, 529 F.3d at 1083 (“If EPA determines that the existing technology-based standards provide an ‘ample margin of safety,’ then the Agency is free to readopt those standards during the residual risk rulemaking.”).

4. What is the rationale for our final approach and final decisions for the risk review?

The EPA's residual risk review focused on whether risks due to HAP emissions from HWCs are acceptable and if the standards provide an ample margin of safety to protect public health. The EPA considered multiple measures of health risk, including cancer risks and incidence rates, the presence of non-cancer health effects due to chronic or acute exposure, the potential for an adverse environmental effect, and the uncertainties of the risk assessment. Based on consideration of all of the health risk information, factors, results, and uncertainties discussed in section IV.A.1 of this preamble and in the proposal, the EPA concludes that the risks due to HAP emissions from the HWC NESHAP source category are acceptable.

Furthermore, based on the analyses described in the proposal and elsewhere in this preamble, including the evaluation of the costs and effectiveness of potential controls to reduce emissions and risks, the EPA concludes that the HWC NESHAP provides an ample margin of safety to protect public health. Finally, based on our evaluation of environmental risks, the EPA concludes that more stringent standards are not necessary to prevent an adverse environmental effect. Therefore, the EPA is not promulgating any additional control requirements pursuant to CAA section 112(f)(2) but

instead reaffirming the existing standards.

90 FR 50814 (Nov. 10, 2025).

The D.C. Circuit upheld this approach to CAA section 112(f)(2) in NRDC: “If EPA determines that the existing technology-based standards provide an `ample margin of safety,' then the Agency is free to readopt those standards during the residual risk rulemaking.” 529 F.3d at 1083.

B. Technology Review for the HWC NESHAP Source Category

1. What did we propose pursuant to CAA section 112(d)(6) for the HWC NESHAP source category?

The EPA's technology review under CAA section 112(d)(6) focused on the identification and evaluation of potential developments in practices, processes, and control technologies that have occurred since the promulgation of the HWC NESHAP in 2005. The EPA reviewed various sources of information to identify any such developments and found that since 2005, two new control technologies have been employed in the HWC NESHAP source category on one incinerator, the SDDS for control of PCDD/PCDF and the GMCS for control of Hg. Based on an evaluation of the capital cost, annualized cost, potential emission reductions, and HAP cost effectiveness, the EPA proposed not to consider either the SDDS or the GMCS a cost-effective technology to further reduce HAP emissions from sources subject to the HWC NESHAP.

In summary, the EPA did not identify any additional relevant cost-effective developments in technologies, practices, or processes since promulgation of the HWC NESHAP in 2005 to further reduce HAP emissions. Therefore, the EPA did not propose any changes to the MACT standards in this action as a result of our technology review under CAA section 112(d)(6).

See

section IV.D of the proposed rule (90 FR 50814 (Nov. 10, 2025)) and the memorandum

Clean Air Act Section 112(d)(6) Technology Review for the Hazardous Waste Combustor Source Category

, which is available in the docket for this rulemaking, for a more detailed discussion of the EPA's findings.

2. How did the technology review for the HWC NESHAP source category change since proposal?

The EPA did not make any changes to the technology review in this final rule and is finalizing the technology review as proposed.

The EPA provided one additional scenario to estimate the cost-effectiveness of the SDDS at the average rate of HWC PCDD/PCDF emissions, which is available in the document titled

Clean Air Act Section 112(d)(6) Technology Review for the Hazardous Waste Combustor Source Category

in the docket for this rulemaking.

90 FR 50814 (Nov. 10, 2025).

3. What key comments did we receive on the technology review, and what are our responses?

The EPA received comments in support of and against the proposed technology review results. Commenters generally discussed the criteria used to evaluate potential developments, the developments evaluated, and the scope of the technology review. This section provides a summary of and response to key comments received regarding the EPA's evaluation criteria for the technology review for the HWC NESHAP. Comment summaries and the EPA's responses for additional issues raised regarding the technology review for the HWC NESHAP are in the Comment Response Document, which is available in the docket for this rulemaking.

Comment:

A commenter disagreed with both the proposed technology review's calculation of cost-effectiveness for new HAP control technologies and the conclusion that there would be high cost and low potential emissions reductions for the identified pollution control technologies. The commenter was concerned about the social and economic harm caused by exposure to toxic chemicals on human health, including families dealing with radiation and chemotherapy treatments, impacts on child development, reproductive harm, and funeral costs. The commenter asserted that “petrochemical polluters” can easily absorb the costs from more stringent standards.

Response:

The EPA disagrees with the commenter's assertion that the Agency's calculations of emissions reduction, cost, and cost-effectiveness in the technology review were inappropriate. As described in the preamble for the proposed rule, the EPA based its technology review decisions on the criteria described in CAA section 112(d)(6), that is, to review and revise the standards as necessary taking into account developments in practices, processes, and control technologies.

The EPA's decision on whether it is “necessary” to revise the HWC NESHAP emission standards was based on cost, cost-effectiveness, technical feasibility, energy implications, non-air environmental impacts, and emission reductions associated with the potential application of each development.

See

90 FR 50814 (Nov. 10, 2025) section III.B for more information about what factors the EPA considers in the technology review.

See

90 FR 50814 (Nov. 10, 2025) section IV.D and Document ID No. EPA-HQ-OAR-2004-0022-0720 entitled

Clean Air Act Section 112(d)(6) Technology Review for the Hazardous Waste Combustor Source Category

for more information about the analyses conducted for the technology review.

The EPA estimated that the SDDS could reduce emissions of PCDD/PCDF by between 7.66 and 211 milligrams of PCDD/PCDF toxic equivalency quotient (TEQ) per year per unit, with the average reduction on the low end of the range.

Because the EPA does not expect an adverse environmental effect resulting from HAP emissions from HWCs, as described in the environmental risk screening results, the EPA also does not expect a positive non-air environmental effect from these modest emission reductions of PCDD/PCDF.

The EPA also estimated a total capital investment cost of $1,776,000 and a total annualized cost of $299,000 per year (2024$) per unit. This results in an annualized cost-effectiveness of between $1.4 million and $39 million (2024$) per gram of PCDD/PCDF TEQ emission.

Given the modest emission reductions, lack of non-air environmental effects, high cost of installation, and lack of cost-effectiveness, the EPA is determining that the SDDS does not constitute a development that makes it necessary to revise the HWC NESHAP emission limits.

See

the document entitled

Clean Air Act Section 112(d)(6) Technology Review for the Hazardous Waste Combustor Source Category Final Rule

, which is available in the docket for this rulemaking.

See

90 FR 50814 (Nov. 10, 2025) section IV.B.4 for discussion of ample margin of safety.

See

the document entitled

Clean Air Act Section 112(d)(6) Technology Review for the Hazardous Waste Combustor Source Category Final Rule

, which is available in the docket for this rulemaking.

The EPA estimated that the GMCS could reduce emissions of Hg by approximately 13 pounds of Hg per year per unit.

The EPA also estimated a total capital investment cost of $4,143,000 and a total annualized cost of $804,000 per year (2024$) per unit. This results in an annualized cost-effectiveness of $62,000

(2024$) per pound of Hg emission.

Given the modest emission reductions, lack of non-air environmental effects, high cost of installation, and lack of cost-effectiveness, the EPA is determining that the GMCS does not constitute a development that makes it necessary to revise the HWC NESHAP emission limits.

Id.

See

90 FR 50814 (Nov. 10, 2025) section IV.B.4 for discussion of ample margin of safety.

See

the document entitled

Clean Air Act Section 112(d)(6) Technology Review for the Hazardous Waste Combustor Source Category Final Rule

, which is available in the docket for this rulemaking.

4. What is the rationale for our final approach for the technology review?

The EPA's technology review focused on the identification and evaluation of developments in practices, processes, and control technologies that have occurred since the EPA promulgated the 2005 HWC NESHAP. In the proposal, the EPA identified two potential developments but proposed that they did not necessitate a change in the HWC NESHAP standards. During the public comment period, the EPA received several comments on the Agency's proposed determinations for the technology review. The comments and the EPA's specific responses and rationale for the Agency's final decisions are in section IV.B.3 of this preamble and in the Comment Response Document, which is in the docket for this rulemaking.

No information presented by commenters has led the EPA to change the Agency's proposed determination under CAA section 112(d)(6). For the reasons explained in the proposed rule and in this final rule preamble, the EPA is finalizing that there are no developments in practices, processes, or control technologies to further reduce HAP emissions that warrant revisions to the standards.

100

Consequently, the EPA is not promulgating any new or revised standards in this action for the HWC NESHAP as a result of our technology review under CAA section 112(d)(6).

100

For more information, see the preamble to the proposed rule, 90 FR 50814 (Nov. 10, 2025), and section IV.B.1 of this preamble.

C. Amendments Pursuant to CAA Sections 112(d)(2) and (3) and 112(h) for the HWC NESHAP Source Category

1. What did we propose pursuant to CAA sections 112(d)(2) and (3) and 112(h) for the HWC NESHAP source category?

On November 10, 2025, the EPA proposed emission standards for HF and HCN pursuant to CAA sections 112(d)(2), (d)(3), and (h)(1) for major source HWC solid fuel boilers, incinerators, cement kilns, and liquid fuel boilers. For existing and new major source solid fuel boilers, the EPA proposed a MACT floor emission limit of 6.2 ppmv HF, dry basis and corrected to seven percent oxygen. The EPA proposed that existing sources must comply with the HF emission limit within three years after publication of the final rule, and that new sources must comply with the HF emission limits no later than the effective date of the final rule or upon startup, whichever is later. For both existing and new sources, the EPA proposed that owners or operators must demonstrate compliance with this limit through an initial compliance test using EPA Methods 26A or 320 occuring no later than six months after the applicable compliance date.

101

The EPA also proposed that subsequent performance testing would be required once every five years during the CPT using the same methods.

101

New sources are affected facilities that commence construction or reconstruction after November 10, 2025.

For existing and new major source HWC incinerators, cement kilns, and liquid fuel boilers, the EPA proposed a work practice standard for HF emissions with multiple compliance options. The EPA proposed that a source would have a choice of complying with only one of the three following options:

•

Option 1:

If a source actively controls HCl emissions and the source has at least two AWFCO-interlocked OPLs other than chlorine feed rate to control HCl, then the facility must comply with the HCl and chlorine gas OPLs and indicate in the CPT report and NOC that compliance is demonstrated by complying with the HCl and chlorine gas OPLs.

•

Option 2:

If a facility does not feed any material with detectable levels of fluorine to the source, then the facility must certify in the CPT report that no fluorine is fed and indicate in the CPT report and NOC that compliance is demonstrated through the certification.

•

Option 3:

If a facility feeds fluorine to a source and the source has no active HCl control with at least two AWFCO-interlocked OPLs other than chlorine feed rate to control HCl emissions, then the facility must monitor and record the total fluorine fed to the unit as a 12-hour rolling average. If at any point the feed rate suggests that HF emissions may exceed the solid fuel boiler existing source emission limit for HF (as calculated according to the HWC NESHAP's MTEC procedure), then the source would complete a one-time HF emissions test using EPA Methods 26A or 320 during the next CPT at the maximum recorded fluorine feed rate and include the test results in the CPT report. The demonstration that HF MTEC does not exceed the solid fuel boiler existing source emission limit for HF would be included in the CPT plan.

The EPA proposed that existing sources must comply with the work practice standard for HF within three years after publication of the final rule, and that new sources must comply with the work practice standard for HF no later than the effective date of the final rule or upon startup, whichever is later. For both existing and new sources, owners or operators must demonstrate compliance with this work practice through a certification, test plan, or initial compliance test occuring no later than six months after the applicable compliance date. The EPA also proposed to require subsequent demonstration of compliance once every five years during the CPT.

The EPA also proposed emission standards for HCN pursuant to CAA sections 112(d)(2) and (d)(3) for major source HWC solid fuel boilers, cement kilns, liquid fuel boilers with capacity greater than 50 MMBTU/hr but less than or equal to 250 MMBTU/hr, and liquid fuel boilers with capacity greater than 250 MMBTU/hr. The EPA did not propose emission standards for HCN for major source HWC incinerators, liquid fuel boilers with capacity less than or equal to 50 MMBTU/hr, HCl production furnaces, or lightweight aggregate kilns.

For existing and new major source HWC solid fuel boilers, the EPA proposed a MACT floor emission limit of 5.0 ppmv HCN. For existing major source HWC cement kilns, the EPA proposed a MACT floor emission limit of 56 ppmv HCN. For new major source HWC cement kilns, the EPA proposed a MACT floor emission limit of 1.8 ppmv HCN. For existing major source HWC liquid fuel boilers with capacity greater than 50 MMBTU/hr but less than or equal to 250 MMBTU/hr, the EPA proposed a MACT floor emission limit of 2.7 ppmv. For new major source HWC liquid fuel boilers with capacity greater than 50 MMBTU/hr but less than or equal to 250 MMBTU/hr, the EPA proposed a MACT floor emission limit of 1.2 ppmv HCN. For existing major source HWC liquid fuel boilers with capacity greater than 250 MMBTU/hr, the EPA proposed a MACT floor emission limit of 3.4 ppmv HCN. For new major source HWC liquid fuel boilers with capacity greater than 250 MMBTU/hr, the EPA proposed a MACT floor emission limit of 1.1 ppmv HCN. All proposed emission limits are on a dry basis and corrected to seven percent oxygen.

For all subcategories with proposed limits, the EPA proposed that existing sources must comply with the applicable HCN emission limit within three years after publication of the final rule, and that new sources must comply with the HCN emission limits no later than the effective date of the final rule or upon startup, whichever is later. For both existing and new sources, the EPA proposed that owners or operators must demonstrate compliance with this limit through an initial compliance test occuring no later than six months after the applicable compliance date using EPA Method 320 or, if there are entrained water droplets in the flue gas, an alternative test method submitted and approved by the Administrator.

102

The EPA also proposed that subsequent performance testing would be required once every five years during the CPT using the same methods.

103

102

See

40 CFR 63.7(f) for information about alternative test methods. New sources are affected facilities that commence construction or reconstruction after November 10, 2025.

103

Section IV.A of the preamble to the proposed rule contains a complete discussion of the EPA's proposed requirements for HWC sources under CAA sections 112(d)(2), (3) and 112(h). 90 FR 50814 (Nov. 10, 2025).

2. How did the revisions pursuant to CAA sections 112(d)(2) and (3) and 112(h) for the HWC NESHAP source category change since proposal?

The EPA is finalizing as proposed the numeric emission limits for HF and HCN for solid fuel boilers and the numeric emission limits for HCN for liquid fuel boilers with capacity greater than 50 MMBTU/hr but less than or equal to 250 MMBTU/hr and liquid fuel boilers with capacity greater than 250 MMBTU/hr.

104

The EPA is finalizing the proposed work practice standard for HF for incinerators and liquid fuel boilers with one minor revision in response to comment. Specifically, sources must have one AWFCO-interlocked OPL other than chlorine feed rate to control HCl to use Option 1 of the work practice standard. For cement kilns, in response to information submitted by commenters, the EPA is finalizing a revised numeric emission limit for HCN. Further, the EPA is not finalizing the work practice standard for HF for cement kilns. In addition, the EPA is clarifying that the Administrator may extend the timeline for compliance with these standards.

105

104

90 FR 50814 (Nov. 10, 2025).

105

See

CAA section 112(i)(3)(B) and (i)(5), 40 CFR 63.6(i), and 40 CFR 63.1213.

3. What key comments did we receive on the proposed revisions pursuant to CAA sections 112(d)(2) and (3) and 112(h), and what are our responses?

This section provides summaries of and responses to key comments received regarding the EPA's proposed emission standards for HF and HCN. The comments are organized as: (1) the EPA's beyond-the-floor evaluation methodology, (2) HF work practice standard, (3) HF emissions from cement kilns, (4) HCN emission limits for cement kilns, and (5) health-based emission limits (HBELs). Comment summaries and the EPA's responses for additional issues raised regarding the revisions pursuant to CAA sections 112(d)(2) and (3) and 112(h) for the HWC NESHAP are in the Comment Response Document, which is available in the docket for this rulemaking.

a. The EPA's Beyond-the-Floor Evaluation Methodology

Comment:

One commenter stated that the EPA did not establish emission limits or evaluate potential beyond-the-floor options for HF for incinerators, cement kilns, liquid fuel boilers, HCl production furnaces or lightweight aggregate kilns, which according to the commenter encompasses 157 out of 164 sources in the HWC category. The commenter also argued that the EPA did not evaluate beyond-the-floor controls for HCN emissions at incinerators, HCl production furnaces, and lightweight aggregate kilns, which according to the commenter encompasses 81 out of 164 sources in the HWC category. The commenter noted that there is a “self-created lack of data,” but that the EPA can still determine whether there are additional controls that should be implemented, and that the EPA must consider what beyond-the-floor controls are available for these sources.

Response:

The EPA did not propose and, as such, is not finalizing numeric emission limits for HF emissions from HWC incinerators, cement kilns, lightweight aggregate kilns, liquid fuel boilers, and HCl production furnaces and for HCN emissions from incinerators, lightweight aggregate kilns, and HCl production furnaces.

106

Thus, the commenter's count of sources appears to be a combination of subcategories the EPA did not propose to establish emission limits or evaluate beyond-the-floor options for because of no demonstrated emissions of HF or HCN and subcategories that the EPA proposed to regulate through a work practice standard. The EPA disagrees that the Agency must consider beyond-the-floor standards where we are not setting emission limits.

107

106

90 FR 50841 (Nov. 10, 2025).

107

See NACWA, 734 F.3d at 1157 (noting that “Congress gave EPA broad discretion in considering whether to go beyond-the-floor”).

The EPA collected emissions data regarding emissions of HCN from HWC incinerators and HCl production furnaces. The emissions data indicated in all test runs for both subcategories that HCN is not emitted from HWC incinerators and HCl production furnaces.

108

Under CAA section 112(d)(1), the EPA is required to set emissions standards for major source categories and subcategories that emit HAP.

109

Under the EPA's historic approach to standard setting, the first step requires the establishment of the MACT standard developed under CAA section 112(d)(3). In the second step, which is after establishing the MACT standard, the EPA then determines whether to set more stringent standards that control emissions beyond-the-floor considering criteria and methods contained in CAA section 112(d)(2) (

i.e.,

cost, non-air quality health and environmental impacts, and energy requirements).

110

The EPA has no obligation or statutory authority to establish emissions limitations for HAP that are not emitted from a source category and as such the EPA is also under no obligation to undertake a beyond-the-floor analysis under CAA section 112(d)(2).

108

For discussion about the EPA's emissions data collection for HCN from these sources, see section 3.2.2 of the Comment Response Document, which is available in the docket for this rulemaking.

109

42 U.S.C. 7412(d)(1).

110

42 U.S.C. 7412(d)(2)-(3); Nat'l Lime Ass'n, 233 F.3d at 634 (“Once the Agency sets statutory floors, it then determines, considering cost and the other factors listed in section 7412(d)(2), whether stricter standards are `achievable.' The Agency calls such stricter requirements `beyond-the-floor' standards.”).

As previously explained, the EPA made a reasonable attempt to collect emissions data where the Agency had reason to believe that a type of HWC could emit a given HAP. At proposal, the EPA did not have any credible emissions data regarding HF emissions from lightweight aggregate kilns and HCl production furnaces and HCN emissions from lightweight aggregate kilns.

111

Therefore, the EPA did not propose MACT standards for HF emissions from HCl production furnaces. Additionally, the EPA did not propose MACT standards for HF and

HCN emissions for lightweight aggregate kilns.

112

As such, the EPA did not conduct a beyond-the-floor analysis pursuant to CAA section 112(d)(2) for HF emissions from lightweight aggregate kilns or HCl production furnaces or HCN emissions from lightweight aggregate kilns.

111

For discussion about the EPA's emissions data collection for HCl production furnaces and lightweight aggregate kilns, see sections 3.2.3 and 3.2.4, respectively, of the Comment Response Document, which is available in the docket for this rulemaking.

112

90 FR 50841 (Nov. 10, 2025).

The EPA is finalizing work practice standards for HF emissions from HWC incinerators and liquid fuel boilers. The EPA requested and analyzed data on HF emissions

113

and practices used to control HF emissions from incinerators and liquid fuel boilers.

114

The EPA generally considers a work practice standard to be justified if a significant majority (

e.g.,

more than 55 percent of test runs) of emissions data available indicate that emissions are so low that they cannot be reliably measured (

i.e.,

emissions are below detection limit). Emissions testing data showed that 94 percent of HF measurements from HWC incinerators and 75 percent of HF measurements from HWC liquid fuel boilers were below the detection limit.

115

The EPA identified the best performing incinerators and liquid fuel boilers as those where all HF measurements were below the detection limit. Sources with non-detectable HF emissions reported that they used the following methods that control HF emissions: not feeding fluorinated organics, various control devices that control HCl emissions, and tracking the feedrate of fluorine.

116

Based on this data, the EPA determined that the best performing HWC incinerators and liquid fuel boilers control HF emissions through one or a combination of not feeding fluorinated organics, actively controlling HCl emissions, and tracking the feedrate of fluorine, which forms the basis of the EPA's work practice standard for HF emissions.

113

See

Document ID No. EPA-HQ-OAR-2004-0022-0724.

114

See

Document ID No. EPA-HQ-OAR-2004-0022-0651.

115

See

Document ID No. EPA-HQ-OAR-2004-0022-0724.

116

See

Document ID No. EPA-HQ-OAR-2004-0022-0651, responses to questions 39, 48, and 69. Note that no liquid fuel boilers reported tracking the feedrate of fluorine.

The EPA also considered additional measures that would be more stringent than those reported by HWCs. The EPA proposed expanding the scope of the feed restrictions from not feeding fluorinated organics to not feeding fluorine-containing materials. Chemically, if no fluorine enters an HWC, then the HWC cannot produce HF; this control cannot be improved upon. As explained in the preamble to the proposed rule, APCDs that control HCl are equally or more effective at controlling HF than HCl. As these HWCs already control HF emissions, there is no need for further control requirements. The information collection indicated that some HWCs are monitoring fluorine content in their combustor feed; it did not indicate that HWCs routinely report on the amount of fluorine fed to the HWC or perform emissions testing for HF. The EPA proposed and is finalizing the requirement that HWCs tracking fluorine input would need to calculate a theoretical HF output and if that theoretical output exceeds the numerical emission limit for existing solid fuel boilers, perform a one-time HF emission test at their next CPT. This one-time test performs at least three important functions. First, it provides data for the EPA to consider in a future technology review if HF emissions are more common or higher than the current data suggests.

117

Second, it provides State regulators with information they can use to determine if State emission limits for HF are warranted. Third, it provides the public with transparent information about HWC emissions of HF. There was no single best performer from this pool of sources with all HF measurements below detection limit, so the EPA proposed and is finalizing the same work practice standard for existing and new sources.

117

See

e.g.,

Sierra Club

EPA

, 884 F.3d 1185, 1203 (D.C. Cir. 2018) (“[D]ata EPA gathers while these rules are in effect should inform . . . future refinements of these rules when they are periodically reviewed.”).

b. HF Work Practice Standard

Comment:

Four commenters supported the work practice standards for HF emissions. One commenter suggested modifying Option 1 to require one AWFCO-interlocked operating parameter instead of two.

118

According to the commenter, a single AWFCO-interlocked operating parameter would cut off waste feed as appropriate. The commenter gave the example of a hazardous waste incinerator that uses HCl CEMS interlocked with the AWFCO system as the control and concluded that a failure of any OPL or CEM would trigger an AWFCO. The commenter also questioned the EPA's proposed numerical emission limit for solid fuel boilers and suggested the same work practice options for solid fuel boilers because the fundamental principles for the three options are also valid for solid fuel boilers. Finally, the commenter reinforced their conclusions by explaining the technical aspects of HCl and HF control in HWCs.

118

See

proposed 40 CFR 63.1209(s)(1)(i) in Document ID No. EPA-HQ-OAR-2004-0022-0708.

One commenter pointed out that the AWFCO system requirements in the proposed work practice standards are already in use by many hazardous waste incinerators.

One commenter suggested that the EPA should allow owners or operators to demonstrate compliance for Option 1 or 2 with a notification to the Administrator (

e.g.,

NOC Status Report) without necessarily including it in the CPT report.

Response:

The EPA acknowledges the commenter's support for the work practice standard for HF emissions from incinerators and liquid fuel boilers and the many HWCs incinerators that are already in compliance. In response to comment, the EPA is modifying the work practice standard option to actively control HCl emissions by finalizing that the HWC must have at least one AWFCO-interlocked OPL other than chlorine feed rate and then comply with the HCl and chlorine gas OPLs. The EPA agrees that complying with one interlocked parameter other than chlorine feedrate meets the objective of an OPL controlling chlorine emissions; controlling only chlorine feed rate does not control HF emissions.

The EPA disagrees with the commenter that solid fuel boilers should be able to use the work practice standard for HF, given that the emissions test data from solid fuel boilers demonstrated measurable HF emissions. CAA section 112(h)(1) authorizes the EPA to promulgate a work practice standard where it is not feasible to prescribe and enforce a standard.

119

Because it is feasible to prescribe and enforce a numerical standard for HF emissions from solid fuel boilers, the EPA is doing so.

119

42 U.S.C. 7412(h)(1).

HWCs must report the option they select to comply with the work practice standard for HF in both the NOC and the CPT report to reduce confusion and for completeness. The NOC is a streamlined summary of the outcomes of a CPT, which is in a more readable format. The CPT report contains all the information needed to determine how a source is complying with the HWC NESHAP, and so the EPA believes that it is reasonable to include this compliance information in the CPT report. Given the minimal burden associated with stating how an HWC incinerator or liquid fuel boiler is complying with the HF work practice standard, the EPA is finalizing as proposed the requirement to state the

method of compliance in both the CPT report and NOC.

c. HF Emissions From Cement Kilns

Comment:

One commenter asserted that cement kilns do not emit HF and provided information to show that HF from cement kiln stack tests during testing for the EPA's emissions testing request was invalid data because of calibration gas contamination. The commenter challenged the EPA's conclusion at proposal that 71 percent of HF data were below the detection limit for cement kilns, asserting that this 71 percent included invalid data and, without the invalid data, 100 percent of the remaining HF data were below the detection limit. The commenter referenced previous communications with the EPA warning against using HF reference gas and explaining why HF contaminates the performance tests. The commenter also cited a previous emissions testing request for the Portland Cement NESHAP to support these conclusions.

The commenter identified the following issues with the EPA's proposed approach for HF emissions from cement kilns:

• The inability to identify facilities with HCl controls.

• Non-compliance with an HCl OPL would lead to an automatic non-compliance for HF even though cement kilns do not emit HF.

• Incinerators can certify that there is no fluorine fed, but there might be a detectable amount of HF in the raw materials including fluorine found in limestone.

• Comparing MTEC against the solid fuel boiler numeric HF limit is inappropriate for cement kilns because they are not boilers.

• Fluorine monitoring would be needlessly burdensome because it would require updates to feedstream analysis, data acquisition and handling systems to calculate, and procuring new lab equipment and training staff on new lab methods.

Response:

After reviewing the information provided by the commenter, the EPA agrees that HF was not measurably present in cement kiln emissions and further agrees that the long period of time necessary for HF to purge from the sample system when there is no measurable HF in the sample stream caused the few values that were above detection limit. The EPA disagrees with the commenter that it is always inappropriate to calibrate using HF, as the “sticky” nature of HF makes it more important to demonstrate that the sampling system can accurately quantify HF in the gas stream. This is a not an otherwise unknown situation with certain gases in stack sampling and is analogous to SO

CEMS calibrations on low emitting SO

sources, where purging SO

from a system post calibration requires an atypically long time compared to other typical CEMS gases. The EPA is not promulgating any final HF work practice for cement kilns as HWC cement kilns do not emit measurable quantities of HF.

d. HCN Emission Limits for Cement Kilns

Comment:

One commenter challenged the EPA's proposed HCN emission limit for new cement kilns. The commenter highlighted that the limit was based on a single best performing HWC cement kiln for HCN, which is a long wet-process kiln with no APCD for HCN. The commenter attested that this type of kiln has the worst emission profile for criteria pollutants. The commenter cautioned that there are no feasible controls to reduce HCN and explained why caustic scrubbers and RTOs are not feasible control measures for cement kilns. The commenter concluded that new and modified sources would be unable to simultaneously meet the proposed HCN new source limit and the criteria pollutant standards, even with pollution controls, and that existing hazardous waste cement kilns could not modernize and would have to close. The commenter recommended requiring sources to develop site-specific HBELs if necessary, in the future.

Response:

In response to comment, the EPA is finalizing an HCN emission limit for new HWC cement kilns of 5.5 ppmv, dry basis at seven percent oxygen. The EPA agrees with the commenter that the Agency calculated the proposed HCN limit for new HWC cement kilns, 1.8 ppmv, dry basis at seven percent oxygen, based on data from a long wet-process kiln. In a follow-up conversation with representatives of all companies that own or operate HWC cement kilns, the EPA learned about the low likelihood of future construction of long wet process cement kilns based on industry clarification that included long wet-process kiln emitting more criteria pollutants than preheater/precalciner cement kilns, along with energy inefficiencies of long wet-process kilns in comparison to other kiln types.

120

The EPA further confirmed that the HWC wet process kilns owned by Heidelberg Materials in Logansport, IN were built between 1961 and 1965

121

while the HWC wet process kilns owned by Amrize in Paulding, OH were constructed in the 1950s.

122

To the EPA's knowledge, no other long wet-process HWC cement kilns have been constructed since 1965. Additionally, companies are even replacing wet-process kilns with dry process kilns.

123

120

See the memorandum entitled Meeting and Communication Record Between the U.S. EPA and Representatives of the Cement Kiln Recycling Coalition,

which is available in the docket for this rulemaking.

121

See

Document ID No. EPA-HQ-OAR-2004-0022-0695, attachments 8 and 11.

122

See https://edocpub.epa.ohio.gov/publicportal/ViewDocument.aspx?docid=928108.

123

See

Document ID No. EPA-HQ-OAR-2004-0022-0650.

CAA section 112(d)(3) requires “that the maximum degree of reduction in emissions that is deemed achievable for new sources in a category or subcategory shall not be less stringent than the emission control that is achieved in practice by the best controlled similar source, as determined by the Administrator.”

124

Based on comments received at proposal, the EPA reasonably believes that owners or operators of HWC cement kilns will not construct new long wet-process kilns in the future. Accordingly, the EPA does not view a long wet-process kiln as an appropriate “best controlled similar source” for new HWC cement kilns.

125

Instead, the EPA views the best performing dry cement kiln as the “best controlled similar source” for new HWC cement kilns.

126

The EPA has the “discretion to determine what metric to use in defining the `best' source, so long as it is reasonable.”

127

Additionally, the D.C. Circuit “has generally acknowledged that EPA may exercise discretion and utilize its expertise when calculating emission standards for categories of sources” under CAA sections 112(d)(2) and (d)(3).

128

Accordingly, the MACT floor emission limit for HCN emissions from new HWC cement kilns is 5.5 ppmv, dry basis at seven percent oxygen. It is also worth noting that the EPA solicited comment on this limit as a new source HCN limit for a potential subcategory of dry cement kilns in the preamble to the proposed rule.

129

124

42 U.S.C. 7412(d)(3).

125

Cement Kiln Recycling Coal.,

255 F.3d at 871(explaining that “[f]loors need not be perfect mirrors of the best performers' emissions”).

126

See Ne. Md. Waste Disposal Auth.

EPA,

358 F.3d 936, 945 (D.C. Cir. 2004) (“The word `similar' [in CAA section 129(a)(2)] may reasonably be read as referring to a unit that is in the same subcategory.”).

127

Sierra Club,

895 F.3d at 15.

128

U.S. Sugar Corp.,

113 F.4th at 999.

129

90 FR 50814 (Nov. 10, 2025).

At proposal, the EPA evaluated whether the incremental emissions reduction achievable with RTO would be cost-effective. The EPA estimated

that RTO would achieve approximately 95 percent reduction of HCN. This may be an overestimation of effectiveness given the relatively high HCN emissions from one Portland cement kiln with RTO installed.

130

A 95 percent reduction from the UPL MACT floor due to RTO results in an emission limit of 0.275 ppmv, which is below three times the RDL value for HCN for cement kilns (1.1 ppmv, dry basis at seven percent oxygen). Therefore, the evaluated beyond-the-floor-limit for new sources is 1.1 ppmv, dry basis at seven percent oxygen. This is the same beyond-the-floor new source limit that the EPA evaluated in the preamble to the proposed rule at section IV.A.3.b with the same associated costs and benefits.

131

For the reasons explained in the preamble to the proposed rule, the EPA does not consider that installation and operation of RTO for the beyond-the-floor control of HCN emissions from HWC cement kilns is cost-effective for new HWC cement kilns and would have additional non-air quality health and environmental impacts and energy requirements.

132

Therefore, the EPA is finalizing a new source limit for HCN emissions from HWC cement kilns as 5.5 ppmv, dry basis at seven percent oxygen.

130

U.S. Environmental Protection Agency. (Last updated Mar. 30, 2026). Portland Cement Manufacturing Industry: Information Collection Request Data:

https://www.epa.gov/stationary-sources-air-pollution/portland-cement-manufacturing-industry-information-collection

131

90 FR 50814 (Nov. 10, 2025).

132

90 FR 50837-39. For additional discussion about RTO cost-effectiveness, see section 3.6 of the Comment Response Document, which is available in the docket for this rulemaking.

e. Health-Based Emission Limits

Comment:

Several commenters supported adopting HBELs for HF and HCN under CAA section 112(d)(4). Some of these commenters suggested that the EPA should adopt the site-specific risk assessment approach currently used for the alternative HCl HBEL.

133

Two commenters pointed out that emissions of HF and HCN from sites electing to implement an HBEL will necessarily be at a level that provides an ample margin of safety. Similarly, another commenter argued that using HBELs provides a flexible alternative that allows the EPA to ensure standards remain protective of public health with an ample margin of safety without unnecessarily locking future HBELs into a particular form of limit or method for establishing them.

133

40 CFR 63.1215.

Many commenters argued that CAA section 112(d)(4) allows the EPA to set risk-based standards in lieu of the technology-based standards. The commenters said that rather than relying on the MACT floor approach in CAA section 112(d)(2) and (3) and (h), which can overregulate by emphasizing technological performance instead of actual risk reduction, Congress intentionally allows the EPA, in CAA section 112(d)(4), to avoid unnecessary over-regulation by tailoring the stringency of emission limits for a given threshold HAP to the specific health risks posed by that pollutant in a particular source category. A commenter elaborated that given that CAA section 112(d)(4) is under the same subsection as 112(d)(1), the EPA's authority to utilize a health threshold approach is in addition to its authority to promulgate an emissions standard; therefore, the EPA may elect to establish a health threshold with an ample margin of safety under CAA section 112(d)(4) or adopt a MACT standard as set forth under CAA section 112(d)(2). The commenter pointed out that in

Sierra Club

EPA,

the Court recognized that the “EPA may use a health threshold rather than MACT standards for `pollutants for which a health threshold has been established.' Such a health-based standard must include an `ample margin of safety.' ”

134

The commenter said that according to the EPA, an HBEL does not need to be as stringent as a MACT standard.

135

The commenter added that the D.C. Circuit Court has confirmed the EPA's understanding that HBELs can be less stringent than MACT standards.

136

134

See Sierra Club

EPA,

895 F.3d 1, 8 (D.C. Cir. 2018);