[Federal Register Volume 89, Number 74 (Tuesday, April 16, 2024)]
[Proposed Rules]
[Pages 26835-26846]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2024-08004]


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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 63

[EPA-HQ-OAR-2020-0408; FRL-7821-02-OAR]
RIN 2060-AU78


Petition To Remove the Stationary Combustion Turbines Source 
Category From the List of Categories of Major Sources of Hazardous Air 
Pollutants

AGENCY: Environmental Protection Agency (EPA).

ACTION: Notification of denial of petition to delist.

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SUMMARY: The U.S Environmental Protection Agency (EPA) is announcing 
the Agency's decision to deny a petition requesting the removal of the 
Stationary Combustion Turbines source category from the list of 
categories of major sources of hazardous air pollutants (HAP) subject 
to regulation the Clean Air Act (CAA). The petition was submitted 
jointly by American Fuel & Petrochemical Manufacturers, the American 
Petroleum Institute, the American Public Power Association, the Gas 
Turbine Association, the Interstate Natural Gas Association of America, 
and the National Rural Electric Cooperative Association (``the 
petitioners''). The EPA is denying the petition based on the EPA's 
determination that the petition is incomplete and because we have found 
that the submitted information is inadequate to determine that no 
source in the category emits HAP in quantities that may cause a 
lifetime risk of cancer greater than 1-in-1 million to the individual 
in the population who is most exposed to emissions of such pollutants 
from the source. We have reached this decision based on review of the 
risk analysis and other information submitted by petitioners and on 
consideration of turbine testing results received from a CAA 
information request. The EPA is denying the petition with prejudice and 
will deny any future petition to delist as a matter of law unless such 
future petition is accompanied by substantial new information or 
analysis.

DATES: Petitions for judicial review of this action must be filed June 
17, 2024. See SUPPLEMENTARY INFORMATION for filing information.

ADDRESSES: In addition to being available in the docket, an electronic 
copy of this action is available on the internet. Following signature, 
the EPA will post a copy of this action at https://www.epa.gov/stationary-sources-air-pollution/stationary-combustion-turbines-national-emission-standards. Following publication in the Federal 
Register, the EPA will post the Federal Register version of this action 
at this same website.

FOR FURTHER INFORMATION CONTACT: For questions about this action 
contact Ms. Angela M. Ortega, Sector Policies and Programs Division 
(D243-01), Office of Air Quality Planning and Standards, U.S. 
Environmental Protection Agency, P.O. Box 12055, Research Triangle 
Park, North Carolina 27711; telephone number: (919) 541-4197; and email 
address: [email protected].

SUPPLEMENTARY INFORMATION: 
    Docket. The EPA has established a docket for this rulemaking under 
Docket ID No. EPA-HQ-OAR-2020-0408.\1\ 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 (CBI) or other information whose disclosure is restricted 
by statute. Certain other material, such as copyrighted material, is 
not placed on the internet and will be publicly available only in hard 
copy. With the exception of such material, publicly available docket 
materials are available electronically in https://www.regulations.gov.
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    \1\ As explained in a memorandum to the docket, the docket for 
this action includes the documents and information in Docket ID Nos. 
EPA-HQ-OAR-2017-0688 (Stationary Combustion Turbines NESHAP Risk and 
Technology Review), EPA-HQ-OAR-2003-0196 (Proposal to stay the 
enforcement of the combustion turbines National Emission Standards 
Hazardous Air Pollutants for new sources in the lean premix gas-
fired turbines and diffusion flame gas-fired turbines 
subcategories), EPA-HQ-OAR-2003-0189 (Proposal to delist four 
subcategories from the Stationary Combustion Turbines source 
category), and EPA-HQ-OAR-2002-0060 (National Emission Standards for 
Hazardous Air Pollutants for Stationary Combustion Turbines).
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    Judicial review. Section 307(b)(1) of the CAA governs judicial 
review of final actions by the EPA. This section provides, in part, 
that petitions for review must be filed in the United States Court of 
Appeals for the District of Columbia Circuit: (i) when the Agency 
action consists of ``nationally applicable regulations promulgated, or 
final actions taken, by the Administrator,'' or (ii) when such action 
is locally or regionally applicable, but ``such action is based on a 
determination of nationwide scope or effect and if in taking such 
action the Administrator finds and publishes that such action is based 
on such a determination.'' For locally or regionally applicable final 
actions, the CAA reserves to the EPA complete discretion to decide 
whether to invoke the exception in (ii).\2\
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    \2\ Sierra Club v. EPA, 47 F.4th 738, 745 (D.C. Cir. 2022) 
(``EPA's decision whether to make and publish a finding of 
nationwide scope or effect is committed to the agency's discretion 
and thus is unreviewable''); Texas v. EPA, 983 F.3d 826, 834-35 (5th 
Cir. 2020).
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    This final action is ``nationally applicable'' within the meaning 
of CAA section 307(b)(1). In this final action, the Administrator is 
denying a petition to delist the entire Stationary Combustion Turbines 
source category under CAA section 112(c)(9)(B). This action results in 
the continued applicability of the National Emission Standards for 
Hazardous Air Pollutants (NESHAP) for Stationary Combustion Turbines to 
all turbines meeting the rule's applicability criteria located in any 
state in the nation. For these reasons, this final action is nationally 
applicable.
    Under section 307(b)(1) of the CAA, petitions for judicial review 
of this action must be filed in the United States Court of Appeals for 
the District of Columbia Circuit within 60 days from April 16, 2024. 
Filing a petition for reconsideration of this final action by the 
Administrator does not affect the finality of this action for the 
purposes of judicial review, nor does it extend the time within which a 
petition for judicial review must be filed and shall not postpone the 
effectiveness of such rule or action.
    Under CAA section 307(b)(2) (42 U.S.C. 7607(b)(2)), the 
requirements established by this final action may not be challenged 
separately in any civil or criminal proceedings brought by the EPA to 
enforce the requirements.

[[Page 26836]]

    Organization of this document. The information in this preamble is 
organized as follows:

I. General Information
    A. What action is the EPA taking?
    B. Background Information
II. Treatment of Petitions To Delist a Source Category From 
Regulation Under CAA Section 112
    A. What is a source category delisting petition and what are the 
criteria for delisting a source category?
    B. What is the process for delisting a source category?
III. Risk Review Methodology and Findings
    A. The EPA's Risk Assessment Methodology
    B. The EPA's 2020 Risk Review Findings
    C. CAA Section 114 Information Request
IV. Evaluation of the Petition
    A. Description of the Petition
    B. Petitioners' Risk Assessment Methodology
    C. Basis for Emission Estimates
    D. HAP and Turbines Not Included in Petition
V. What is the rationale for denying the petition?

I. General Information

    The EPA has received, has reviewed, and is now denying a petition 
that requests the removal of a source category from the list of major 
source categories of HAP, under CAA section 112. In section I.A., we 
summarize the action we are taking today. In section I.B., we provide 
information about the NESHAP program set forth in CAA section 112 and 
the regulatory history and information for the source category at 
issue. In section II., we discuss the delisting criteria outlined in 
the CAA and the Agency's process for delisting a source category. 
Section III. discusses the EPA's residual risk review methodologies and 
findings in the 2020 Stationary Combustion Turbines NESHAP Risk and 
Technology Review (2020 RTR) as well as the CAA section 114 information 
request that the EPA issued subsequent to the 2020 RTR. Section IV. 
presents the details of the petition to delist and the Agency's 
technical evaluation of the petition. Finally, in section V., we 
discuss the EPA's response to the petition.

A. What action is the EPA taking?

    This action presents the Agency's decision to deny a petition 
requesting the removal of the Stationary Combustion Turbines source 
category from the list of categories of major sources of HAP subject to 
regulation under CAA section 112. The petition was submitted jointly by 
American Fuel & Petrochemical Manufacturers, the American Petroleum 
Institute, the American Public Power Association, the Gas Turbine 
Association, the Interstate Natural Gas Association of America, and the 
National Rural Electric Cooperative Association (``the petitioners'').
    The EPA's decision is governed by CAA section 112(c)(9), which 
provides the EPA's discretionary authority to delist source categories 
and specifies the health risk criteria that must be met for a source 
category to be delisted. These criteria require the EPA to determine 
that no source in the category emits HAP in quantities which may cause 
a lifetime risk of cancer greater than 1-in-1 million to the individual 
in the population who is most exposed to emissions of such pollutants 
from the source and that HAP emissions from such source category would 
not result in adverse effects to human health or the environment before 
delisting a source category.
    The EPA is denying the petition based on the EPA's determination 
that the petition is incomplete and because the petitioners did not 
present adequate information and analyses for each of the necessary 
subject areas, under CAA section 112(c)(9)(B). After receipt of the 
initial petition and the first supplement, the EPA requested that the 
petitioners provide information and data to support the stationary 
combustion turbine emission estimates provided by the petitioners; the 
requested information was not provided. As an additional and separate 
independent basis for the denial of the petition, the EPA has 
determined that the petitioners' requested conclusions are not 
supported by the evidence. The EPA is denying the petition with 
prejudice and will deny any future petition to delist as a matter of 
law unless such future petition is accompanied by substantial new 
information or analysis.

B. Background Information

    In this section, the EPA provides a brief overview of HAP 
regulation under CAA section 112, the regulatory history of the 
Stationary Combustion Turbines source category, information about the 
source category and its HAP emissions, and information about delisting 
petitions concerning this source category.
1. HAP Regulation Under CAA Section 112
    CAA section 112 establishes the framework for regulation of HAP. 
CAA section 112(c)(1) requires the EPA to publish a list of both 
categories and subcategories of major and area sources of HAP. A source 
category on the list is required to meet the specifically defined 
emission standards that depend on the HAP emitted and whether a source 
is a major source or an area source. Major sources of HAP are those 
stationary sources or group of stationary sources under common control 
(e.g., facilities) that emit or that have the potential to emit 10 tons 
per year or more of any specific HAP or 25 tons per year or more of any 
combination of HAP. An area source is any source of HAP that is not a 
major source. CAA section 112(c)(2) further requires the EPA to 
promulgate standards under CAA section 112(d) for all listed source 
categories according to the schedule specified in CAA section 112(e). 
CAA section 112(d)(6) requires the EPA to review these standards and 
revise them as necessary, with consideration of developments in 
practices, processes, and control technologies, every 8 years (the 
``technology review''), and CAA section 112(f)(2) requires the EPA to 
assess the risk to public health remaining after application of the 
technology-based standards and revise the standards, if necessary, to 
provide an ample margin of safety to protect public health or to 
prevent, taking into consideration costs, energy, safety, and other 
relevant factors, an adverse environmental effect. When the two reviews 
are combined into a single rulemaking, it is commonly referred to as 
the ``risk and technology review'' (RTR).
2. Regulatory History of and Information About the Stationary 
Combustion Turbines Source Category
    On July 16, 1992, the EPA published the initial list of source 
categories, which included the Stationary Turbines source category (57 
FR 31576). This source category was subsequently renamed the Stationary 
Combustion Turbines source category (64 FR 63025; November 18, 1999). 
CAA section 112(c)(2) further requires the EPA to promulgate standards 
under CAA section 112(d) for all listed source categories according to 
the schedule specified in CAA section 112(e). The EPA promulgated the 
NESHAP for Stationary Combustion Turbines on March 5, 2004 (69 FR 
10512). The standards are codified at 40 CFR part 63, subpart YYYY and 
apply to stationary combustion turbines at major sources of HAP. There 
are no requirements under 40 CFR part 63, subpart YYYY for stationary 
combustion turbines located at area sources. The RTR for the Stationary 
Combustion Turbines NESHAP was proposed on April 12, 2019 (84 FR 15046) 
and finalized on March 9, 2020 (85 FR 13524).\3\
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    \3\ The EPA readopted the existing standards under CAA section 
112(f)(2) (85 FR 13530).
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    The Stationary Combustion Turbines source category covered by the 
NESHAP

[[Page 26837]]

includes approximately 1,015 turbines at 310 facilities.\4\ Within the 
Stationary Combustion Turbines source category are the following eight 
subcategories: lean premix gas-fired turbines, lean premix oil-fired 
turbines, diffusion flame gas-fired turbines, diffusion flame oil-fired 
turbines, turbines which burn landfill or digester gas or gasified 
municipal solid waste, turbines of less than 1 megawatt (MW) rated peak 
power output, emergency turbines, and turbines operated on the North 
Slope of Alaska. Stationary combustion turbines are typically located 
at power plants, compressor stations, landfills, and industrial 
facilities such as chemical plants. These turbines are generally 
operated using natural gas, distillate oil, landfill gas, jet fuel, or 
process gas.
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    \4\ Turbine NESHAP Unit List--Updated October 2023. Docket ID 
No. EPA-HQ-OAR-2020-0408.
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    Emissions of HAP in the exhaust gases of turbines are the result of 
combustion of the gaseous and liquid fuels. The HAP present in these 
exhaust gases include formaldehyde, toluene, benzene, acetaldehyde, and 
metallic HAP (e.g., cadmium, chromium, manganese, lead, and nickel). Of 
these HAP, benzene, nickel subsulfide, and hexavalent chromium are 
classified as known human carcinogens, and formaldehyde, acetaldehyde, 
lead, nickel carbonyl, and cadmium are classified as probable human 
carcinogens. Exposure to the various HAP emitted by stationary 
combustion turbines is associated with a variety of adverse health 
effects. These adverse health effects include chronic (long-term) 
health disorders (e.g., effects on the central nervous system, damage 
to the kidneys, and irritation of the lung, skin, and mucus membranes); 
and acute health disorders (e.g., effects on the kidney and central 
nervous system, alimentary effects such as nausea and vomiting, and 
lung irritation and congestion).
    Mercury has been measured in the exhaust gas from landfill gas-
fired turbines. Gaseous mercury emitted into the air eventually can be 
deposited into soil and water bodies, where microorganisms can convert 
it into methylmercury, a highly toxic form of mercury that bio-
accumulates in fish tissue and in other aquatic creatures. People are 
primarily exposed to mercury by consuming contaminated fish. 
Methylmercury exposure is a particular concern for people of 
childbearing age, developing fetuses, and young children, because 
studies have linked exposure to high levels of methylmercury to damage 
to the developing nervous system. Children exposed to methylmercury 
while they are in the womb can have negative impacts to their cognitive 
thinking, memory, attention, language, fine motor skills, and visual 
spatial skills. Animals can absorb mercury through water, air, and soil 
or from eating certain plants. Mercury can harm an animal's ability to 
reproduce and to care for their young.
3. Delisting Petitions Concerning the Stationary Combustion Turbines 
Source Category
    During the 2004 Stationary Combustion Turbines NESHAP rulemaking, 
the EPA received a petition from the Gas Turbine Association to delist 
two subcategories of stationary combustion turbines under CAA section 
112(c)(9).\5\ The petitioners requested the EPA to create and delist 
two subcategories--lean premix turbines firing natural gas with limited 
oil backup and a low-risk subcategory where facilities would make site-
specific demonstrations regarding risk levels. On April 7, 2004, the 
EPA proposed to delist the following four subcategories: lean premix 
gas-fired turbines, diffusion flame gas-fired turbines, emergency 
turbines, and turbines located on the North Slope of Alaska (69 FR 
18327). At the same time, the EPA proposed to stay the effectiveness of 
the NESHAP for new lean premix gas-fired and diffusion flame gas-fired 
turbines (69 FR 18338). On August 18, 2004, the EPA finalized the 
administrative stay of the effectiveness of the NESHAP for new lean 
premix gas-fired and diffusion flame gas-fired turbines, pending the 
outcome of the proposed subcategory delisting (69 FR 51184). The 
proposal to delist the four subcategories was never finalized in light 
of the 2007 decision in Natural Resources Defense Council v. EPA, 489 
F.3d 1364 (D.C. Cir. 2007), which addressed limits on the EPA's ability 
to delist subcategories. This court decision is discussed in more 
detail in section II.A.
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    \5\ Petition to Delist Two Subcategories of Combustion Turbines. 
Docket ID No. EPA-HQ-OAR-2003-0189-0014.
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    On August 28, 2019, the EPA received the petition being acted on 
here, which seeks to remove the Stationary Combustion Turbines source 
category from the list of categories of major sources under CAA section 
112. The petitioners submitted a supplement to the source category 
delisting petition on November 21, 2019; a second supplement to the 
source category delisting petition on December 2, 2020; and a revised 
version of the second supplement to the delisting petition on March 15, 
2021. The EPA has fully considered all the petitioners' submissions in 
this final decision to deny the petition. Delisting of the Stationary 
Combustion Turbines source category from the list of major sources 
would result in removal of the regulatory requirements specified in the 
NESHAP for Stationary Combustion Turbines in 40 CFR 63.6080-6175 of 40 
CFR part 63, subpart YYYY.

II. Treatment of Petitions To Delist a Source Category From Regulation 
Under CAA Section 112

    In this section, the EPA sets out the specific criteria under the 
CAA that apply for removing a source category from the list of source 
categories. CAA section 112(c)(9)(B) specifies certain criteria that 
must be satisfied in order for the EPA to grant a petition to remove a 
source category from the list of source categories regulated for HAP 
emissions. The EPA's consideration of petitions to delist is bound by 
these criteria and informed by prior court decisions interpreting this 
provision of the CAA.

A. What is a source category delisting petition and what are the 
criteria for delisting a source category?

    A source category delisting petition is a formal request to the EPA 
from an individual or group to remove a specific source category from 
the CAA section 112 list of categories of major sources and area 
sources under CAA section 112(c)(9)(B). The Administrator must grant or 
deny such a petition to delete a source category within 1 year after a 
petition is filed and is determined to be complete.\6\ See CAA section 
112(c)(9)(B). Delisting of a source category would result in the 
removal of applicable regulatory requirements under CAA section 112 for 
such source category. CAA section 112(c)(9)(B) contains the 
discretionary authority to delist a source category and provides in 
relevant part: ``The Administrator may delete any source category from 
the list under this subsection, on petition of any person or on the 
Administrator's own motion, whenever the Administrator makes the 
following determination or determinations, as applicable: [. . .].''
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    \6\ As stated previously, the EPA has determined that the 
current petition to delist the Stationary Combustion Turbines source 
category is not complete.
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    CAA section 112(c)(9)(B) further specifies three criteria for 
deletion of a source category from the list. The first criterion is 
specific to carcinogenic HAP and is specified in CAA section 
112(c)(9)(B)(i). The criterion states that, in the case of HAP emitted 
by sources in the category that may result in cancer

[[Page 26838]]

in humans, a determination must be made that ``no source in the 
category (or group of sources in the case of area sources) emits such 
hazardous air pollutants in quantities which may cause a lifetime risk 
of cancer greater than one in one million to the individual in the 
population who is most exposed to emissions of such pollutants from the 
source (or group of sources in the case of area sources).''
    The second criterion is specific to non-carcinogenic HAP and the 
third criterion is specific to environmental effects. These criteria 
are specified in CAA section 112(c)(9)(B)(ii). In the case of HAP that 
may result in adverse health effects in humans other than cancer or 
adverse environmental effects, the second criterion states that a 
determination must be made that ``emissions from no source in the 
category or subcategory concerned (or group of sources in the case of 
area sources) exceed a level which is adequate to protect public health 
with an ample margin of safety'' and the third criterion states that a 
determination must be made that ``no adverse environmental effect will 
result from emissions from any source (or from a group of sources in 
the case of area sources).''
    Further, to assist the EPA in making judgments about whether a 
pollutant causes adverse environmental effects, CAA section 112(a)(7) 
defines an ``adverse environmental effect'' as ``[A]ny significant and 
widespread adverse effect, which may reasonably be anticipated, to 
wildlife, aquatic life, or other natural resources, including adverse 
impacts on populations of endangered or threatened species or 
significant degradation of environmental quality over broad areas.''
    For source categories that emit carcinogenic HAP, CAA section 
112(c)(9)(B)(i) sets a lifetime cancer risk threshold for delisting of 
1-in-1 million. This level differs from the acceptable risk 
determination used in other rulemakings under CAA section 112. For 
instance, for standards promulgated under CAA section 112(f)(2), an 
excess lifetime cancer risk to the most exposed individual of 100-in-1 
million is ordinarily the upper bound of acceptability. This level was 
established in the Benzene NESHAP (54 FR 38044; September 14, 1989) and 
was incorporated into the 1990 CAA Amendments in CAA section 
112(f)(2)(B).\7\
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    \7\ The maximum individual lifetime cancer risk is the 
``estimated risk that a person living near a plant would have if he 
or she were exposed to the maximum pollutant concentrations for 70 
years.'' 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) (54 FR 38044, 38045; 
September 14, 1989).
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    When considering delisting decisions under CAA section 
112(c)(9)(B), the EPA construes this provision as calling for a high 
level of confidence before a determination can be made that the 
criteria for delisting are satisfied. For example, for purposes of 
deleting the non-mercury cell chlorine production subcategory under CAA 
section 112(c)(9)(B)(ii), the EPA ``obtained chlorine and HCl emission 
estimates from every known major source facility in the non-mercury 
cell chlorine production subcategory using our authority under section 
114 of the CAA and conducted risk assessments for each facility.'' \8\
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    \8\ National Emission Standards for Hazardous Air Pollutants: 
Chlorine and Hydrochloric Acid Emissions from Chlorine Production: 
Final decision to delete subcategory (68 FR 70948, 70951; December 
19, 2003). See also 66 FR 21933, where the EPA explained and agreed 
with the use of certain health effect studies in delisting petition 
for Methanol. (``As the [Health Effects Institute] Health Review 
Committee noted in its commentary, the experiments in this study 
were `well designed and executed with appropriate quality control 
and quality assurance procedures. Thus, one can have confidence in 
the data.' '').
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    For source categories that emit HAP that may result in adverse 
health effects (non-cancer risks), CAA section 112(c)(9)(B)(ii) 
requires HAP emissions to be below a level providing an ample margin of 
safety. In the context of a source category delisting and CAA section 
112(c)(9)(B)(ii), the EPA interprets an ``ample margin of safety'' as 
such that the chronic and acute concentrations that a person may be 
exposed to should be less than the concentrations that may elicit an 
adverse non-cancer health effect (i.e., each of the ratios should be 
less than one). This interpretation has been applied in a prior 
subcategory delisting action under CAA section 112(c)(9)(B)(ii) for the 
non-mercury cell chlorine production subcategory (68 FR 70947).
    For the purposes of determining whether the delisting criteria 
under CAA section 112(c)(9)(B) are satisfied, risk evaluations must be 
based on emission estimates that assume the controls required under CAA 
section 112 are not in place unless they are also known to be required 
under a different regulatory authority. This is because a final notice 
granting a delisting petition of, for example, the Stationary 
Combustion Turbines source category from the list of major sources 
would result in removal of the regulatory requirements specified in the 
NESHAP for stationary combustion turbines.
    The EPA views CAA section 112(c)(9)(B) as providing discretionary 
authority for delisting source categories that satisfy the criteria 
contained therein. ``The Administrator may delete any source category 
from the list under this subsection, on petition of any person . . . , 
whenever the Administrator makes the following determination or 
determinations, as applicable,'' (CAA section 112(c)(9)(B) (Emphasis 
added)). The Agency reads this provision as allowing for delisting of a 
source category upon the Administrator determining that the statutory 
criteria are satisfied. However, it does not foreclose the exercise of 
the Administrator's discretion in forming a final decision on whether 
to delist. (``The Administrator may delete . . .'' and not ``The 
Administrator [must] delete . . .'' (Emphasis supplied). The EPA 
interprets ``may'' in CAA section 112(c)(9)(B)(i) as being directional 
towards a determination that is based on reasonably health protective 
assumptions to account for uncertainties in any supporting analysis. 
The final decision involves the consideration and balancing of factors 
that are uniquely within the Administrator's expertise, including 
policy choices, and predictions on ``the frontiers of scientific 
knowledge.'' Nat'l Lime Ass'n v. EPA, 627 F.2d 416, 454 (D.C. Cir. 
1980).\9\
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    \9\ ``[A]n agency [has] latitude to exercise its discretion in 
accordance with the remedial purposes of the controlling statute 
where relevant facts cannot be ascertained or are on the frontiers 
of scientific inquiry.'' 627 F.2d 454.
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    Questions as to whether pollutant emissions from a source category 
present adverse health and environmental effects and questions 
regarding the kinds of effects that can come from exposure to those 
emissions may, in certain instances, border on the frontiers of 
scientific knowledge and are given to be quite uncertain due to either 
insufficient or inconsistent data.\10\ For example, there could be 
limited scientific knowledge of the effects of pollutant exposure on 
human health and the environment. There could also be limited emissions 
data from the source category. Further, some

[[Page 26839]]

pollutants have no known safe level of exposure.\11\ The Administrator 
is not required to base his determination solely on a single parameter 
or measure and has the discretion to weigh various factors or data 
differently. The Administrator's decision to delist (or to deny a 
petition to delist) a source category is made on a case-by-case basis 
and involve a thorough and comprehensive review of factual issues, 
scientific evidence, and data provided in support of a delisting 
petition.
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    \10\ ``Where a statute is precautionary in nature, the evidence 
difficult to come by, uncertain, or conflicting because it is on the 
frontiers of scientific knowledge, the regulations designed to 
protect the public health, and the decision that of an expert 
administrator, we will not demand rigorous step-by-step proof of 
cause and effect. Such proof may be impossible to obtain if the 
precautionary purpose of the statute is to be served.'' Id., at 454 
n.143 citing Ethyl Corp. v. EPA, 541 F.2d 1, 28-29 (D.C. Cir. 1976).
    \11\ ``The Administrator may apply his expertise to draw 
conclusions from suspected, but not completely substantiated, 
relationships between facts, from trends among facts, from 
theoretical projections from imperfect data, from probative 
preliminary data not yet certifiable as `fact,' and the like.'' Id.
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    The EPA also views CAA section 112(c)(9)(B) as allowing the 
Administrator to balance the likelihood of adverse health effects 
against limited scientific data and to err on the side of caution in 
making decisions considering uncertainties in scientific data. Any 
projections, assessments, and estimations must be reasonable and not 
based on conjecture. While use of the term ``adequate''' further 
indicates that the Administrator must weigh the potential uncertainties 
and their likely significance, uncertainties concerning the risks of 
adverse health or environmental effects may be mitigated if the 
Administrator can determine that projected exposures are sufficiently 
low to provide reasonable assurance that adverse health effects will 
not occur. Similarly, uncertainties concerning the magnitude of 
projected exposures may be mitigated if the Administrator can determine 
that the levels which might cause adverse health or environmental 
effects are sufficiently high to provide reasonable assurance that 
exposures will not reach harmful levels. But as a part of the requisite 
demonstration called for by CAA section 112(c)((9)(B), a petitioner 
must present data that are adequate to support a delisting decision, 
and thus, resolve any uncertainties associated with missing 
information.
    The Administrator will not remove a source category from the list 
of source categories covered under CAA section 112 merely because of 
the inability to conclude that HAP emissions from sources within that 
source category will cause adverse effects on human health or the 
environment. Thus, the EPA will not grant a petition to remove a source 
category if there are uncertainties relating to health effects or if 
the Administrator does not have sufficient information to make the 
requisite determination under CAA section 112(c)(9)(B).\12\ We note 
that the Administrator's discretion is neither unbounded nor limitless, 
but rather constrained by the EPA's duty to protect human health and 
welfare.\13\ This is because the CAA is a protective or preventive 
statute \14\ considering that one of its stated purposes under CAA 
section 101(b)(1) is ``to protect and enhance the quality of the 
Nation's air resources so as to promote the public health and 
welfare.'' Such statutes do not call for certitude of harm but rather 
accord a decision maker discretion and flexibility in taking regulatory 
action that is protective of both public health and the environment.
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    \12\ See American Forest and Paper Ass'n v. EPA 294 F.3d 113, 
119 (D.C. Cir. 2002) (upholding the EPA's denial of the petition to 
delist methanol as a HAP) ``EPA's interpretation easily passes 
muster under Chevron. The statutory language unambiguously places on 
a delisting petitioner the burden to make a showing that there is 
adequate data about a substance to determine exposure to it may not 
reasonably be anticipated to cause adverse effects. This is 
precisely what EPA has construed it to require.'' (Emphasis in 
original; cleaned up) (66 FR 21930; May 2, 2001) (Where the 
Administrator is acting on a delisting petition, ``the burden 
remains on a petitioner to demonstrate that the available data 
support an affirmative determination that emissions of a substance 
may not be reasonably anticipated to result in adverse effects on 
human health or the environment.'').
    \13\ See Massachusetts v. EPA, 127 S. Ct. 1438, 1462. (The goal 
of the CAA is ``to protect and enhance the quality of the Nation's 
air resources so as to promote the public health and welfare and the 
productive capacity of its population.'' CAA section 101(b)(1)).
    \14\ Ethyl Corp., 541 F.2d at 29 n.56 (``Under the Clean Air Act 
the Administrator's flexibility is derived not from a command to 
act, but from a precautionary statute that necessarily includes risk 
assessment if its preventive purpose is to be achieved.''). The CAA 
is ``to assure that regulatory action can effectively prevent harm 
before it occurs; to emphasize the predominant value of protection 
of public health.'' H.R. Rep. No. 95-294, 95th Cong., 1st Sess. 49 
(1977).
---------------------------------------------------------------------------

    Further, when considering delisting petitions under CAA section 
112(c)(9)(B), the EPA is guided by relevant decisions of the United 
States Court of Appeals for the District of Columbia (D.C. Circuit or 
court). Specifically, in 2007, the court held in Natural Resources 
Defense Council v. EPA, 489 F.3d 1364, 1373 (D.C. Cir. 2007) (vacating 
portions of the Plywood Maximum Achievable Control Technology (MACT) 
standards), that the EPA had no authority to create and delist a ``low-
risk subcategory'' under CAA section 112(c)(9)(B)(i).\15\ According to 
the court, only subcategories with no carcinogenic HAP emissions and 
satisfying CAA section 112(c)(9)(B)(ii) could be removed from the CAA 
section 112(c)(1) list of categories and subcategories (e.g., deletion 
of the non-mercury cell chlorine production subcategory (68 FR 70947; 
December 19, 2003)). Otherwise, subcategories with any carcinogenic HAP 
emissions could only be removed as part of a complete removal of the 
entire source category under CAA section 112(c)(9)(B)(i), noting that 
the criteria in CAA section 112(c)(9)(B)(ii) would also need to be 
satisfied if applicable.
---------------------------------------------------------------------------

    \15\ To accord with this decision, the EPA is denying the 
petition to delist two subcategories of stationary combustion 
turbines that the EPA received during the 2004 Stationary Combustion 
Turbines NESHAP rulemaking.
---------------------------------------------------------------------------

    Further, in another key case, New Jersey v. EPA, 517 F.3d 574, 582 
(D.C. Cir. 2008), the court vacated the EPA's action that delisted 
coal- and oil-fired electric utility steam generating units (EGUs) 
holding that ``because section 112(c)(9) governs the removal of `any 
source category' from the section 112(c)(1) list, and nothing in the 
CAA exempts EGUs from section 112(c)(9), the only way the EPA could 
remove EGUs from the section 112(c)(1) list was by satisfying section 
112(c)(9)'s requirements.'' (Emphasis in original). Since then, the 
court has upheld our reading of CAA section 112(c)(9) as calling for 
application of criteria contained therein.\16\ For instance, in White 
Stallion Energy Ctr., LLC v. EPA, 748 F.3d 1222 (D.C. Cir. 2013) the 
court upheld the EPA's denial of a petition to delist coal-fired EGUs 
finding that the EPA was correct in rejecting a delisting petition 
because it ``did not demonstrate that EPA could make either of the two 
predicate findings required for delisting under section 112(c)(9)(B).'' 
Id., at 1248. Additionally, in American Forest and Paper Ass'n v. EPA, 
294 F.3d at 119 (construing section 112(b) and upholding the EPA's 
denial of the petition to delist methanol as a HAP), the court held 
that ``[t]he statutory language unambiguously places on a delisting 
petitioner the burden to make a showing that there is adequate data 
about a substance to determine exposure to it may not reasonably be 
anticipated to cause adverse effects.''
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    \16\ See U.S. Sugar Corp. v. EPA, 830 F.3d 579 (D.C. Cir. 2016) 
(upholding the EPA's decision to remove source categories from CAA 
section 112(c)(6) without applying CAA section 112(c)(9)).
---------------------------------------------------------------------------

    Finally, an additional relevant decision addresses setting MACT 
standards for listed source categories under CAA section 112. In 
Louisiana Environmental Action Network v. EPA, 955 F.3d 1088 (D.C. Cir. 
2020) (LEAN), the court held that when the ``EPA reviews an existing 
standard that fails to address many of the listed air toxics the source 
category emits, adding limits for those overlooked toxics is a 
`necessary' revision under section 112(d)(6).'' Id., at 1091. The EPA 
must now set MACT

[[Page 26840]]

standards in the context of a CAA section 112(d)(6) review where there 
are gaps in existing MACT standards.

B. What is the process for delisting a source category?

    In this section, the EPA describes the Agency's process for 
consideration of petitions to delist source categories under CAA 
section 112(c)(9)(B).
    Although the delisting action for a listed source category is not 
subject to the formal rulemaking procedures under CAA section 307(d), 
it is the EPA's practice to publish and solicit public comments on 
relevant aspects of the Agency's consideration of such a complete 
petition in the Federal Register. See American Forest and Paper Ass'n 
v. EPA, 294 F.3d 113, 117 n.3 (D.C. Cir. 2002) (``Section 112(b) does 
not contemplate a formal rulemaking and is not among the sections 
enumerated in section 307(d)(1) (although other subsections of section 
112 are included there).'').
    The EPA's petition review process proceeds in two phases: a 
completeness determination and a technical review.\17\ During the 
completeness determination, we conduct a broad review of the petition 
to determine whether all the necessary subject areas are addressed and 
whether reasonable information and analyses are presented for each of 
these subject areas.\18\ Once the petition is determined to be 
complete, we place a notice of receipt of a complete petition in the 
Federal Register.\19\ That Federal Register document announces a public 
comment period on the petition and starts the technical review phase of 
our decision-making process. The technical review involves a thorough 
scientific review of the petition to determine whether the data, 
analyses, interpretations, and conclusions in the petition are 
appropriately supported and technically sound. The technical review 
will also determine whether the petition satisfies the necessary 
requirements of CAA section 112(c)(9)(B) and adequately supports a 
decision to delist the source category. All comments and data submitted 
during the public comment period are considered during the technical 
review. The decision to either grant or deny a petition is made after a 
comprehensive technical review of both the petition and the information 
received from the public to determine whether the petition satisfies 
the requirements of CAA section 112(c)(9)(B). Here, the review process 
is not proceeding to the second phase due to the EPA's determination 
that the petition is incomplete because the petitioners did not address 
all the necessary subject areas under CAA section 112(c)(9)(B) and did 
not present reasonable information and analyses for each these subject 
areas.
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    \17\ See, e.g., 70 FR 30407; May 26, 2005 (Notice of receipt of 
a complete petition to delist 4,4'- methylene diphenyl diisocyanate 
as a HAP); 64 FR 42125; August 3, 1999 (Notice of receipt of a 
complete petition to delist ethylene glycol monobutyl ether as a 
HAP); 64 FR 38668, 38669; July 19, 1999 (Notice of receipt of a 
complete petition to delist methanol as a HAP); 64 FR 33453; June 
23, 1999 (Notice of receipt of a complete petition to delist Methyl 
Ethyl Ketone as a HAP).
    \18\ As an additional and separate independent basis for denial, 
the EPA may deny a petition that is not complete if the petitioners 
did not address all the necessary subject areas under CAA section 
112(c)(9)(B) and did not present reasonable information and analyses 
for each of the subject areas. See, e.g., Notice of denial of 
petition to delist five glycol ethers as a HAP (58 FR 4164, 4165; 
January 13, 1993) (The EPA explained that: ``Although public 
information indicated that over 140 million pounds of these 
substances are used annually in the U.S. and that there is a general 
trend towards greater usage, the petitioner did not provide 
measurements or estimates regarding the emissions associated with 
such use. In the absence of such information, EPA cannot make the 
substantive determination contemplated by CAA Section 112(b)(3)'').
    \19\ The EPA did not make a completeness determination for the 
petition because the petitioners did not address all the necessary 
subject areas under CAA section 112(c)(9)(B) and did not present 
reasonable information and analyses for each these subject areas.
---------------------------------------------------------------------------

    If the Administrator decides to grant a petition, the Agency 
publishes a written explanation of the Administrator's decision, along 
with a proposed rule to delete the source category. The proposed rule 
is open to public comment and public hearing and all additional 
substantive information received is considered prior to the issuance of 
a final rule.\20\ If the Administrator decides to deny the petition, 
the Agency publishes a notice of its denial, along with a written 
explanation of the basis for denial.\21\ A decision to deny a petition 
is a final Agency action subject to review in the Circuit Court of 
Appeals for the District of Columbia under CAA section 307(b).
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    \20\ See, e.g., 68 FR 65648; November 21, 2003 (Proposal to 
Delist Ethylene Glycol Monobutyl Ether: Request for Comment); 68 FR 
32605; May 30, 2003 (Proposed Rule to Delist Methyl Ethyl Ketone 
(MEK): Request for Comment).
    \21\ See, e.g., 66 FR 21929; May 2, 2001 (Denial of the petition 
to delist methanol as a HAP).
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    A denial of a petition may take one of two forms. The EPA may deny 
the petition with prejudice, in which case any future petition will be 
denied as a matter of law unless it is accompanied by substantial new 
evidence; or the EPA may deny the petition without prejudice, in which 
case the EPA will consider future petitions without the presentation of 
substantial new evidence. The EPA will issue a denial with prejudice 
when there are adequate data available that lead the EPA to conclude 
that emissions from a source category may cause a lifetime risk of 
cancer greater than 1-in-1 million to the individual in the population 
who is most exposed to emissions of pollutants from a source category; 
or where there are adequate data available that lead the EPA to 
conclude that emissions from a pollutant can be anticipated to result 
in adverse effects to human health or the environment. Additionally, 
the EPA will issue a denial with prejudice when the EPA concludes that 
the available evidence cannot support a determination that emissions 
from a source category may not cause a lifetime risk of cancer greater 
than 1-in-1 million to the individual in the population who is most 
exposed to emissions of such pollutants; or when the EPA concludes that 
the available evidence cannot support a determination that emissions 
from the source category may not reasonably be anticipated to result in 
adverse effects to human health or the environment and, therefore, that 
substantial new information or analyses would be necessary to allow the 
Agency to make the requisite determination under CAA section 
112(c)(9)(B).\22\
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    \22\ A denial with prejudice serves a vital administrative 
purpose. It prevents the endless resubmission of essentially 
identical petitions (with only peripheral or trivial changes) in the 
wake of an EPA decision on the merits of a petition. Thereby, once 
the EPA has denied a petition to delist based on a full 
consideration of the merits, any future petition to remove the same 
source category will not trigger another full evaluation of the 
merits unless it includes substantial data or analyses that were not 
present in the earlier petition. Conversely, the EPA may issue a 
denial without prejudice, for example, where there has not been a 
complete examination of the merits of a petition, and where, 
therefore, the EPA has not reached a decision on the petition that 
is based on a robust evaluation of the underlying technical data and 
analyses. For example, where a petition obviously lacks some element 
necessary for the EPA to properly evaluate the petition, the EPA may 
deny such petition without prejudice and allow the petitioner to re-
submit the petition with the necessary additional information 
without a determination that the additional information constitutes 
substantial new data or analysis. See, e.g., Notice of Denial (58 FR 
4164; January 13, 1993) (denying without prejudice a petition to 
remove five glycol ethers from the list of HAP).
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III. Risk Review Methodology and Findings

    In this section, the Agency presents the risk assessment and risk 
assessment methodology that are the underpinnings of the findings for 
the 2020 RTR for the Stationary Combustion Turbines source category 
under CAA section 112(f)(2). It bears note that under CAA section 
112(f)(2) the excess lifetime cancer risk to the most exposed 
individual of 100-in-1 million is ordinarily the upper

[[Page 26841]]

bound of acceptability, in contrast to CAA section 112(c)(9)(B)(i) 
which sets out a risk threshold of 1-in-1 million for delisting source 
categories that emit carcinogenic HAP. On April 12, 2019, the EPA 
proposed the RTR for the Stationary Combustion Turbines NESHAP (84 FR 
15046). The EPA finalized the RTR on March 9, 2020, and based on the 
risk assessment performed for this source category readopted the 
existing standards under CAA section 112(f)(2) (85 FR 13524).\23\ 
Additional emissions data collection efforts by the EPA after the 2020 
RTR are also discussed in this section.
---------------------------------------------------------------------------

    \23\ 85 FR at 13530. (See NRDC v. EPA, 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.'').
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A. The EPA's Risk Assessment Methodology

    The EPA's risk assessment methodology for the 2020 RTR is described 
in detail in the Residual Risk Assessment for the Stationary Combustion 
Turbines Source Category in Support of the 2020 Risk and Technology 
Review Final Rule, Docket ID No. EPA-HQ-OAR-2017-0688-0131 (``Risk 
Report''). The risk assessment estimated the maximum individual 
lifetime cancer risk, population at increased cancer risk, total 
estimated cancer incidence, maximum chronic non-cancer hazard index, 
and maximum acute non-cancer risk hazard quotient. The EPA performed a 
three-tier screening assessment of the potential multipathway health 
risks, as well as a three-tier screening assessment of the potential 
adverse environmental risks. The risk modeling dataset includes 
emissions data for three emissions scenarios: actual emissions, 
allowable emissions, and acute emissions.

B. The EPA's 2020 Risk Review Findings

    Pursuant to CAA section 112(f)(2), the EPA conducted a residual 
risk review for the Stationary Combustion Turbines source category. 
Risk modeling was conducted for all the facilities known by the EPA at 
the time to be subject to the Stationary Combustion Turbines NESHAP, 
which totaled 253 stationary combustion turbine facilities. Additional 
information obtained after risk modeling refined our estimate of 
facilities in the source category to 244. The total emissions of HAP 
from modeled facilities were approximately 5,300 tons per year. The HAP 
emitted in the largest quantities were formaldehyde, n-hexane, 
acetaldehyde, toluene, xylenes (mixed), hydrochloric acid, propylene 
oxide, ethyl benzene, benzene, and acrolein. Emissions of these 
pollutants made up over 99 percent of the total HAP emissions by mass. 
Emissions of persistent and bioaccumulative HAP (PB-HAP) included lead 
compounds, arsenic compounds, cadmium compounds and mercury compounds. 
Emissions of environmental HAP included the above PB-HAP plus 
hydrochloric acid.
    The results of the chronic inhalation cancer risk assessment based 
on actual emissions indicated that the estimated maximum individual 
lifetime cancer risk was 3-in-1 million, with formaldehyde, 
acetaldehyde, propylene oxide and arsenic compounds from combustion 
turbines as the major contributors to the risk. The total estimated 
cancer incidence was 0.04 excess cancer cases per year, or one excess 
case in every 25 years. Approximately 153,000,000 people live within 50 
kilometers of the 253 modeled facilities, and 42,000 people were 
estimated to have cancer risks at or above 1-in-1 million. The 2020 
RTR, where the Agency was acting under CAA section 112(f)(2), showed 
that the Stationary Combustion Turbines source category did not meet 
the statutory criteria for delisting described in section II.A. of this 
preamble. More information concerning the risk analysis can be found in 
the Risk Report.

C. CAA Section 114 Information Request

    In May 2020, the EPA received a petition for reconsideration of the 
2020 RTR. One of the issues listed in the petition for reconsideration 
was the EPA's failure to set limits for unregulated HAP in the 
Stationary Combustion Turbines NESHAP, citing LEAN. The EPA granted the 
petition for reconsideration on August 13, 2020. In April 2022, the 
EPA, acting under authority of CAA section 114, requested operating 
information and emissions data from six companies that own and operate 
turbines subject to the Stationary Combustion Turbines NESHAP. A 
request was sent to a seventh company in September 2022. The requests 
were sent for the purpose of obtaining emissions data to be used in an 
upcoming separate rulemaking to establish emission standards for 
turbines subject to the Stationary Combustion Turbines NESHAP that do 
not currently have standards in the rule. Requests for operating 
information included annual hours of turbine operation and annual 
turbine heat input for 2016-2020. Responses were required within 3 
months of receipt of the request. The request mandated testing of 
selected turbines for emissions of formaldehyde, acid gases (hydrogen 
fluoride and hydrogen chloride), metallic HAP, particulate matter (PM), 
and carbon monoxide. The 22 turbines that were tested ranged in size 
from 1 to 269 MW and included both simple cycle and combined cycle 
units. The turbines were operated on natural gas, distillate oil, or 
landfill gas. Some turbines were equipped with an oxidation catalyst. 
Submittal of the required data from emissions testing was required 
within 9 months of receipt of the request. The responses to the 
requests are included in the docket for this action, Docket ID No. EPA-
HQ-OAR-2020-0408.

IV. Evaluation of the Petition

    In this section, the EPA presents the details of the petition to 
delist and of the Agency's technical evaluation of the petition. In 
section IV.A., the EPA presents the details of the petition to delist; 
and, in section IV.B., the EPA presents the petitioners' risk 
assessment methodology. In section IV.C., the EPA discusses 
deficiencies in the petitioners' estimates of HAP emissions for the 
Stationary Combustion Turbines source category; and, in section IV.D., 
the EPA presents the gaps in the petitioners' data that include missing 
emissions data from a large number of affected sources and uncertainty 
in the HAP emission estimates for the Stationary Combustion Turbines 
source category.
    In general, the EPA found that the petitioners did not present 
reasonable and complete information and analyses for each of the 
affected sources, such as HAP emission measurements from stack testing 
or fuel content analyses for all sources subject to the Stationary 
Combustion Turbines source category. In the absence of such requisite 
information, the EPA did not make a completeness determination for the 
petition. And, in conducting the technical review of the information 
provided, the EPA cannot make the substantive determination 
contemplated under CAA section 112(c)(9)(B).

A. Description of the Petition

    As stated previously, on August 28, 2019, the EPA received a joint 
petition from the American Fuel & Petrochemical Manufacturers, the 
American Petroleum Institute, the American Public Power Association, 
the Gas Turbine Association, the Interstate Natural Gas Association of 
America, and the National Rural Electric Cooperative Association to 
remove the Stationary Combustion Turbines source category from the list 
of categories of major sources regulated under CAA section

[[Page 26842]]

112. That petition claimed that the HAP emissions from affected sources 
in the Stationary Combustion Turbines source category that were 
identified in the proposed RTR meet the criteria for delisting. The 
petitioners submitted the first supplement to the petition on November 
21, 2019. That supplement included risk analyses for additional units 
that were identified in a comment to the proposed RTR for the 
Stationary Combustion Turbines NESHAP. The petitioners claimed that all 
three statutory criteria for delisting were satisfied based on the 
results of this risk assessment.
    After receipt of the first supplement to the petition, a second set 
of additional turbines that were not evaluated in either the petition 
or first supplement to the petition were identified by the EPA as being 
subject to the rule. The EPA therefore requested that the petitioners 
provide analyses for the second set of additional units. The EPA also 
asked for further explanation on the following issues: (1) whether the 
petitioners' analyses were based on emission factors without 
corroboration by emissions data and whether it accounted for operation 
of units at partial loads; (2) whether arsenic emission factors used in 
the petition analyses would be adequately justified for oil-fired 
turbines; and (3) whether the acute multiplier used in estimating acute 
risk at two facilities was adequately justified. The petitioners 
submitted a second supplement to the petition on December 2, 2020, in 
response to the EPA's concerns regarding the completeness of the 
petition. Finally, the petitioners submitted a revised version of the 
second supplement on March 15, 2021, correcting an error in the 
estimated hexavalent chromium emissions at one source. The petition and 
all the supplements to the petition are available for review in the 
docket, Docket ID No. EPA-HQ-OAR-2020-0408. The EPA has fully 
considered all the petitioners' submissions in this decision to deny 
the petition.
    In general, the petitioners' initial petition and subsequent 
supplements to the petition provided both revised HAP emission 
estimates and a revised evaluation of the 2020 RTR risk analysis.\24\ 
The petitioners revised HAP emission estimates and revised risk 
evaluation, however, were primarily based on emission factors and 
historical fuel usage data for a subset of the turbines that are 
subject to CAA section 112.
---------------------------------------------------------------------------

    \24\ As described in section III.B. of this preamble, the 2020 
RTR showed that the Stationary Combustion Turbines source category 
did not meet the statutory criteria for delisting.
---------------------------------------------------------------------------

    The initial petition and supplements provided by the petitioners 
contained the following information:
     Revised emission estimates for formaldehyde, which is one 
of the organic HAP that is a contributor to risk for stationary 
combustion turbines firing natural gas or distillate fuel oil;
     Revised emission estimates for arsenic, which is one of 
the metallic HAP that is a contributor to risk for stationary 
combustion turbines;
     Revised emission estimates for other HAP (organic and 
metallic) based on fuel use, emission factors, and permit limits for 
volatile organic compounds (VOCs);
     Measurements of the arsenic content in distillate fuel oil 
at certain facilities;
     Revised acute emission estimates for certain facilities;
     Other revisions including adjustments to stack parameters 
and locations, and removal of sources that were no longer operating;
     Analyses of the inhalation acute and chronic (cancer and 
non-cancer) risks for each source in the category, based on the revised 
HAP emission estimates;
     Analyses of the multipathway chronic (cancer and non-
cancer) risks for each source in the category, based on the revised HAP 
emission estimates;
     Analyses of the environmental effects, based on the 
revised and updated emission estimates; and
     New emission estimates and analyses for the facilities not 
previously reviewed in the 2020 RTR risk analysis.
    The petitioners argued that delisting of the source category was 
warranted based on the following results from their analyses:
     A maximum lifetime inhalation cancer risk for the most 
exposed individual of 0.76-in-1 million;
     A maximum acute inhalation hazard quotient (i.e., the 
ratio of acute exposure concentration to the concentration at which no 
acute adverse health effect is observed) of 0.52;
     A maximum chronic (non-cancer) inhalation hazard index 
(i.e., the ratio of chronic exposure concentration to the concentration 
at which no chronic adverse health effect is observed) of 0.03;
     A maximum multipathway cancer risk for the most exposed 
individual of 0.007-in-1 million; and
     A maximum multipathway chronic hazard index of 0.12.
     All facilities were below environmental screening 
thresholds.

B. Petitioners' Risk Assessment Methodology

    As previously referenced, the petitioners' initial petition and 
subsequent supplements to the petition provided both revised HAP 
emission estimates and a revised evaluation of the 2020 RTR risk 
analysis. The petitioners also included risk analyses that covered 
additional units that were identified by the EPA as subject to the 
Stationary Combustion Turbines NESHAP after submittal of the initial 
petition. The petitioners' risk assessments, however, did not address 
whether the emission controls that reduce HAP emissions, such as 
oxidation catalysts, that are installed on some turbines were installed 
due to the requirements of the Stationary Combustion Turbines NESHAP or 
for other regulatory requirements.\25\ The petitioners' risk 
assessments also did not address the effect of delisting the Stationary 
Combustion Turbines source category on the emission estimates used for 
their analysis. This is requisite information because deleting a source 
category from the list of major sources would result in removal of the 
regulatory requirements specified in the applicable NESHAP.
---------------------------------------------------------------------------

    \25\ As mentioned previously, the EPA proposed to remove the 
stay of effectiveness of the standards for new lean premix gas-fired 
and diffusion flame gas-fired turbines on April 12, 2019 (84 FR 
15046), prior to the submittal of the petition to delist in August 
2019. The EPA finalized the removal of the stay on March 9, 2022 (87 
FR 13183).
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    In some instances, the petitioners performed additional analyses 
that they claimed made their results more conservative. For inhalation 
risks, the petitioners conducted an additional analysis that accounted 
for the effects of building downwash,\26\ which they indicated has the 
potential to increase risk. The petitioners also evaluated the non-
cancer risks by summing the hazard quotients among all HAP regardless 
of the target organ. For multipathway health risks, the petitioners 
further performed a site-specific multipathway risk assessment for one 
facility with five stationary combustion turbines. According to the 
petitioners' multipathway risk assessment, four of those units 
exclusively fire natural gas while one fires refinery fuel gas. This 
facility was evaluated in the initial petition risk analysis and was 
re-evaluated in the first supplement to the petition. All other 
facilities showed low multipathway risks in a more general analysis by 
the petitioners and so they

[[Page 26843]]

did not perform site-specific multipathway risk assessments.
---------------------------------------------------------------------------

    \26\ Downwash means the downward movement of pollutant plumes 
immediately after stack release due to obstacles such as buildings 
or smokestacks.
---------------------------------------------------------------------------

    In general, the risk assessment methodology used in the 
petitioners' analyses estimated the same risk parameters as those used 
by the EPA in the risk assessment for the 2020 RTR, including maximum 
individual lifetime cancer risk, population at increased cancer risk, 
total estimated cancer incidence, maximum chronic non-cancer hazard 
index, maximum acute non-cancer risk hazard quotient, multipathway 
health risks, and adverse environmental risks. However, while the 
petitioners' risk modeling methodology was similar to the EPA's, there 
are deficiencies in the petitioners' estimates of the emissions from 
the source category which were used to determine the values of the 
petitioners' risk modeling results, as discussed further in sections 
IV.C. and IV.D.

C. Basis for Emission Estimates

    The following section discusses deficiencies in the petitioners' 
analyses that support the EPA's conclusions that the petition is 
incomplete and that there are inadequate data to determine that no 
source in the category emits HAP in quantities which may cause a 
lifetime risk of cancer greater than 1-in-1 million to the individual 
in the population who is most exposed to emissions of such pollutants 
from the source.
    The EPA identified several deficiencies in the submitted petition. 
First, the petitioners relied on emission factors and fuel sampling 
which are not adequate for determining site-specific emissions with the 
necessary certainty; and the petitioners failed to provide any site-
specific emissions testing data. Notably, the Agency afforded 
petitioners the opportunity to provide additional information and data, 
which petitioners declined. Second, the petitioners significantly 
underestimated the formaldehyde emissions from some turbines, as 
demonstrated by site-specific turbine formaldehyde emissions testing 
data collected by the EPA. Third, to assess the potential health 
impacts from short-term exposures, the petitioners used a multiplier 
for acute risks that is far lower than the standard multiplier the EPA 
applied in the 2020 RTR, which was supported by measured emissions 
data, and the petitioners did not explain why their multiplier is more 
appropriate than the EPA's own multipliers. And fourth, the petitioners 
failed to explain whether the emission estimates they used would 
continue to be applicable if the source category were delisted.
1. Reliance on Emission Factors
    As stated previously, a source category may be delisted only if the 
EPA has a high level of confidence that emissions from no source in the 
category or subcategory exceed a level which is adequate to protect 
public health with an ample margin of safety. The emission estimates 
used by the petitioners to assess the risks from the source category 
relied almost entirely on emission factors. The EPA has long viewed 
emission factors as not supplying sufficient certainty regarding site-
specific emissions that would provide confidence that no source in the 
category exceeds the criteria for delisting. While emission factors are 
a widely used tool for estimating emissions, the EPA as well as state 
and local air pollution control agencies usually prefer data from 
source-specific emission tests or continuous emission monitoring 
systems (CEMS) for estimating a source's emissions because those data 
provide the best representation of the source's emissions. The EPA 
notes that the introduction to AP-42: Compilation of Air Emission 
Factors from Stationary Sources states that ``[b]ecause emission 
factors essentially represent an average of a range of emission rates, 
approximately half of the subject sources will have emission rates 
greater than the emission factor and the other half will have emission 
rates less than the emission factor.'' \27\ In the same document, the 
EPA also noted that ``[a]verage emissions differ significantly from 
source to source and, therefore, emission factors frequently may not 
provide adequate estimates of the average emissions for a specific 
source.'' Further, for example, the North Carolina Department of 
Environmental Quality states the following regarding estimating 
emissions: ``Usually, results from continuous emission monitoring data 
are the preferred way to establish emissions. However, this is not 
often possible or practical, except for larger facilities such as 
electric utilities. Use of site-specific stack tests under a single or 
a range of representative conditions is usually the next preferable 
method.'' \28\ After receipt of the initial petition and first 
supplement, the EPA requested that the petitioners provide HAP emission 
measurements from stack testing to corroborate the HAP emissions 
estimated by the petitioners based on emission factors and fuel content 
analyses, where possible. In response to the EPA's request, however, 
the petitioners indicated via email that a ``detailed measurement 
campaign is out of the scope for this study.'' \29\
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    \27\ https://www.epa.gov/air-emissions-factors-and-quantification/ap-42-compilation-air-emissions-factors-stationary-sources. Fifth Edition. January 1995.
    \28\ The Basics of Estimating Air Emissions. North Carolina 
Department of Environmental Quality. https://www.deq.nc.gov/about/divisions/air-quality/outreach-education-engagement/air-quality-science-and-data/emission-inventories/general-information-emission-inventories. Accessed on March 29, 2024.
    \29\ Email from Eladio Knipping, Electric Power Research 
Institute to Nick Hutson, Melanie King, and Greg Honda, EPA. 
Subject: FW: Response to EPA Feedback on EPRI CT Reports. April 15, 
2020. Docket ID No. EPA-HQ-OAR-2020-0408.
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    In multiple instances, the petitioners' emission estimates were 
based on permit limits or emission factors of other pollutants (VOC and 
PM) that were then used to approximate the emissions of organic HAP 
(e.g., formaldehyde) and metallic HAP (e.g., arsenic). This introduces 
further uncertainty in the emission estimates for this source category. 
Moreover, the petitioners stated in the petition that ``combustion 
turbines' PM emissions are not a strong predictor of metallic HAP 
emissions.'' Regarding arsenic, in the 2020 RTR, arsenic emissions were 
one of the primary drivers for risk at sources firing distillate oil. 
The petitioners stated that metallic HAP emissions from oil-fired 
turbines are constituents of the fuel, and that the arsenic emissions 
estimated by the EPA for the 2020 RTR were biased upward because 
``regulations requiring lower sulfur content for diesel fuel have 
resulted in lower arsenic content, if any, for these fuels, because the 
techniques used to remove sulfur from fuels necessarily remove metals 
such as arsenic also.'' One example of such regulation is the 15 parts 
per million by weight (ppmw) sulfur standard for ultra-low sulfur 
diesel fuel in 40 CFR 1090.305. The petitioners, however, did not 
provide references supporting the statement that the arsenic content in 
ultra-low sulfur diesel fuel is universally lower or documenting that 
stationary combustion turbines in the source category are required to 
use ultra-low sulfur diesel fuel. Rather, the new source performance 
standards (NSPS) for stationary combustion turbines (units constructed, 
modified, or reconstructed after February 18, 2005) require the use of 
only fuel having a sulfur content that is equivalent to a sulfur 
dioxide content less than 0.06 pounds per million British thermal units 
(lb/MMBtu) (i.e., approximately 500 ppmw of sulfur content in 
distillate fuel oil) for turbines located on the continent and 0.42 lb/
MMBtu (4,000 ppmw) for turbines in non-continental areas (71 FR 38497; 
July

[[Page 26844]]

6, 2006 and 40 CFR part 60, NSPS subpart KKKK, at 40 CFR 60.4300). 
Notably, permitted thresholds for stationary combustion turbines vary, 
but the source identified to have the highest cancer risk in the 2020 
RTR is permitted to combust diesel fuel with a sulfur content up to 
1,500 ppmw (permit available in the docket to this rulemaking, Docket 
ID No. EPA-HQ-OAR-2020-0408), which further demonstrates that there is 
no assurance that turbines are using ultra-low sulfur diesel fuel.
    The petitioners also provided summary fuel analysis reports from a 
few stationary combustion turbines in the source category. In those 
cases, fuel arsenic concentrations reported by the petitioners were 
below the limit of detection of the instruments. The petitioners, 
however, did not provide any information regarding the methods and 
procedures that were used for the fuel sampling and the determination 
of the detection limits for arsenic. Instead, results were only 
indicated by a qualitative statement that the measurement was below the 
limit of detection. Additionally, raw data were not provided. After 
receipt of the first supplement to the petition, the EPA asked the 
petitioners to provide more detail regarding the methods used for the 
fuel measurements, including calibration data and information on the 
determination of non-detects.\30\ The petitioners indicated that such 
information would be provided, but the second supplement only included 
more summary fuel sampling results and did not provide the more 
detailed information requested by the EPA. Without this information, 
the EPA cannot evaluate whether the quality of the data is adequate or 
assess whether the detection limits are accurate and, therefore, cannot 
determine whether the arsenic emissions estimated for these facilities 
are representative of their actual emissions.
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    \30\ Email from Eladio Knipping, Electric Power Research 
Institute to Nick Hutson, Melanie King, and Greg Honda, EPA. 
Subject: FW: Response to EPA Feedback on EPRI CT Reports. April 15, 
2020. Docket ID No. EPA-HQ-OAR-2020-0408.
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2. The Measured Rates for Formaldehyde Emissions
    Formaldehyde was the HAP emitted in the largest quantities from 
stationary combustion turbines evaluated in the EPA's 2020 risk 
analysis (see Table 3.1-1 of Risk Report). An examination of the 
formaldehyde emission rates measured during the CAA section 114 testing 
showed emissions that are significantly higher for some turbines than 
those estimated in the petition analysis (as well as the 2020 RTR). For 
instance, formaldehyde emissions at the two landfill gas-fired turbines 
at the BMW Manufacturing facility averaged 0.28 lb/hour (for unit GT05) 
and 0.65 lb/hour (for unit GT06) during the CAA section 114 testing. 
Multiplying the hourly emission rate by the highest annual hours of 
operation on 100 percent landfill gas for the turbines reported for the 
CAA section 114 request, which occurred in the year 2016, yields annual 
formaldehyde emissions of 0.80 tons/year for unit GT05 and 1.85 tons/
year for unit GT06. The formaldehyde emissions assumed for those units 
in the petition analysis were 0.0096 tons/year for each turbine. The 
measured emissions were 80 times higher than estimated for unit GT05 
and 190 times higher than estimated for unit GT06. A similar analysis 
of the formaldehyde emissions for units 7 and 8 at Northern Natural 
Gas's Waterloo Compressor Station showed that the measured formaldehyde 
emissions were 31 times (unit 7) and 18 times (unit 8) higher than the 
estimated emissions.\31\ These differences in the measured formaldehyde 
emissions versus the petitioners' estimated formaldehyde emissions 
demonstrate that the petitioners' data are not adequate for purposes of 
the Administrator's determination under CAA section 112(c)(9)(B).
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    \31\ Comparison of estimated emissions in delisting petition 
with actual measured emissions from CAA section 114 testing for BMW 
Manufacturing and Waterloo Compressor Station. November 22, 2023. 
Docket ID No. EPA-HQ-OAR-2020-0408. Note that the annual emissions 
for the BMW Manufacturing turbines do not include emissions from the 
additional hours that the turbines were operated on a blend of 80 
percent landfill gas and 20 percent natural gas.
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    These higher measured formaldehyde emissions may also indicate that 
the EPA's finding in the 2020 RTR of a maximum individual lifetime 
cancer risk for the Stationary Combustion Turbines source category of 
3-in-1 million may be a significant underestimation. But the EPA has 
also long acknowledged that the maximum individual lifetime cancer 
risk, under CAA section 112(f)(2), ``does not necessarily reflect the 
true risk, but [rather] displays a conservative risk level which is an 
upper-bound that is unlikely to be exceeded.'' \32\ Moreover, as 
previously explained, for delisting source categories that emit 
carcinogenic HAP, CAA section 112(c)(9)(B)(i) sets a lifetime cancer 
risk to the most exposed individual threshold of 1-in-1 million, which 
differs significantly from the acceptable risk determination for 
standards promulgated under CAA section 112(f)(2), where a lifetime 
cancer risk to the most exposed individual of 100-in-1 million is 
ordinarily the upper bound of acceptability. And, ultimately, sources 
would remain subject to standards promulgated under CAA section 
112(f)(2) in contrast to removal of all CAA section 112 regulatory 
requirements if the EPA grants a delisting petition under CAA section 
112(c)(9)(B).\33\
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    \32\ 54 FR 38045.
    \33\ The EPA readopted existing standards under CAA section 
112(f)(2) (85 FR at 13530).
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3. Acute Multiplier
    The acute multiplier used by the petitioners to assess the health 
impacts from short-term exposures to HAP emissions for two facilities 
is not adequately supported by the evidence. As discussed previously, 
the risk analyses for both the 2020 RTR and the petition evaluated the 
acute health risks posed by actual baseline emissions. To assess the 
potential health impacts from short-term exposures, the petitioners 
estimated worst-case 1-hour HAP emission rates (``acute emissions'') 
from each turbine included in their analysis. For most sources, the 
petitioners' analysis used an acute multiplier of 10 times the average 
annual hourly emission rate for each turbine. Use of this value is 
consistent with the acute multiplier used by the EPA in the 2020 RTR, 
as discussed in the March 6, 2019, memorandum titled Review of the 
Acute Multiplier Used to Derive Hourly Emission Rates for the 
Stationary Combustion Turbines Risk Analysis that reviewed the acute 
multiplier and that is available in the docket for the Stationary 
Combustion Turbines RTR (Docket ID No. EPA-HQ-OAR-2017-0688-0070).
    As discussed in the memorandum, the basis for the use of a default 
acute multiplier of 10 in the 2020 RTR is a study of short-term 
emissions variability in a heavily industrialized four-county area in 
Texas.\34\ At the time of the RTR proposal, the EPA evaluated the 
suitability of the default acute multiplier of 10 by reviewing 
available stack test data for formaldehyde emissions from stationary 
combustion turbines to determine the variability of hourly test runs. 
To determine the emissions variability, the average formaldehyde 
concentration for each unit was calculated using all available

[[Page 26845]]

valid stack test data for that unit, and then the concentration of 
formaldehyde for each hourly test run was divided by that unit's 
average to determine the run-to-average emissions ratio. The highest 
run-to-average ratio in the EPA's analysis for the 2020 RTR was 6.7. 
For two facilities, Salinas River Cogeneration and Sargent Canyon 
Cogeneration, the petitioners stated that using the EPA's default ratio 
of 10 in their analysis yielded acute hazard quotients exceeding 1. The 
petitioners then used a value of 2 for the acute multiplier in their 
analysis for those two facilities and justified this based on the ratio 
of hours in the year to annual operating hours at those facilities, 
rather than on information regarding worst-case emissions data. The 
petitioners did not provide any information to show how a comparison of 
the hours in the year to annual operating hours was relevant for an 
analysis of potential worst-case 1-hour HAP emission rates or how a 
multiplier of 2 was more valid than the multiplier used for the 2020 
RTR, which was based on actual hourly emissions data. The EPA believes 
that the petitioners' approach does not adequately account for spikes 
in emissions and variability in emission rates at non-baseload 
conditions (e.g., startup, part-load operation). At lower loads, more 
incomplete combustion may occur and result in proportionately greater 
organic HAP emissions. Furthermore, the oxidation catalysts used to 
control organic HAP emissions for some turbines may not operate 
effectively during startup until the catalyst reaches its appropriate 
operating temperature.
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    \34\ Allen, D., C. Murphy, Y. Kimura, W. Vizuete, and T. Edgar. 
2004. Variable Industrial VOC Emissions and their impact on ozone 
formation in the Houston Galveston Area. Final Report, Texas 
Environmental Research Consortium Project H-13. April 16, 2004. 
Docket ID No. EPA-HQ-OAR-2017-0688-0005.
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    After receipt of the initial petition and the first supplement, the 
EPA discussed these issues with the petitioners. The petitioners 
indicated that they would provide an expanded justification for the use 
of an acute multiplier of 2.\35\ The discussion of the acute multiplier 
for Salinas River Cogeneration and Sargent Canyon Cogeneration in the 
second supplement did not address the questions raised by the EPA. 
Instead, it just restated the petitioners' previous justification for 
using the ratio of hours in the year to annual operating hours. 
Therefore, the petitioners have not adequately demonstrated that an 
acute multiplier of 2 is appropriate for the turbines at the Salinas 
River Cogeneration and Sargent Canyon Cogeneration facilities and, 
therefore, that the hazard quotients for those two facilities are below 
1.
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    \35\ Email from Eladio Knipping, Electric Power Research 
Institute to Nick Hutson, Melanie King, and Greg Honda, EPA. 
Subject: FW: Response to EPA Feedback on EPRI CT Reports. April 15, 
2020. Docket ID No. EPA-HQ-OAR-2020-0408.
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4. Accounting for Potential Increases in Emissions
    As previously noted, emission estimates in the petition analyses 
were primarily based on emission factors and historical fuel usage 
data. For the purposes of determining whether the delisting criteria 
under CAA section 112(c)(9)(B) are satisfied, risk evaluations must be 
based on emission estimates that assume the controls required under CAA 
section 112 are not in place unless they are also known to be required 
under a different regulatory authority. This is because deleting a 
source category from the list of major sources would result in removal 
of the regulatory requirements specified in the applicable NESHAP. 
However, the petitioners' emission estimates for those units with 
oxidation catalyst were based on controlled emissions, and the 
petitioners did not specify whether those oxidation catalysts were 
installed to meet the Stationary Combustion Turbines NESHAP or to 
satisfy regulatory requirements under other EPA programs (e.g., new 
source review (NSR) or prevention of significant deterioration (PSD) 
permits).\36\ As a result, the petitioners did not explain--and the EPA 
was not able to determine based on the information submitted--whether 
the emissions estimates and risk assessment presented by the 
petitioners account for potential increases in emissions that might 
result from delisting the Stationary Combustion Turbines source 
category.
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    \36\ As discussed previously, the EPA proposed to remove the 
stay of the standards for new lean premix gas-fired and diffusion 
flame gas-fired turbines on April 12, 2019 (84 FR 15046), prior to 
the submittal of the petition to delist in August 2019. The EPA 
finalized the removal of the stay on March 9, 2022 (87 FR 13183).
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D. HAP and Turbines Not Included in Petition

    Regarding HAP emissions, in addition to the deficiencies discussed 
in section IV.C., the emission estimates in the information submitted 
by the petitioners do not include several HAP that have been 
demonstrated to be emitted by stationary combustion turbines and do not 
include one-fourth of the turbines in the source category. As discussed 
in section III.C., the EPA required testing of stationary combustion 
turbines to obtain data on emissions of formaldehyde, acid gases 
(hydrogen fluoride and hydrogen chloride), and metallic HAP. The 
emissions testing showed that there are measurable emissions of 
metallic HAP from turbines operating on natural gas and landfill gas. 
The risk analysis submitted by the petitioners did not include metallic 
HAP emissions for natural gas and landfill gas turbines. Several 
metallic HAP (arsenic, cadmium, lead, and mercury compounds) and acid 
gases are included in both the EPA's health risk analysis and screening 
for adverse environmental effects.
    Regarding the universe of affected sources, the EPA has identified 
an additional 245 turbines that are subject to the Stationary 
Combustion Turbines NESHAP that were not included in the petitioners' 
risk analyses. These additional turbines include units that are owned 
and operated by companies that are members of the organizations that 
submitted the petition to delist.\37\ The EPA has identified a total of 
1,015 turbines that are subject to the NESHAP. Hence, the petitioners' 
analyses do not account for nearly one-fourth of the turbines that are 
subject to the Stationary Combustion Turbines NESHAP. This contrasts 
with, for example, the delisting of the non-mercury cell chlorine 
production subcategory where the EPA ``obtained chlorine and HCl 
emission estimates from every known major source facility in the non-
mercury cell chlorine production subcategory using our authority under 
section 114 of the CAA and conducted risk assessments for each 
facility.'' \38\ As previously noted, a petitioner must provide a 
detailed assessment of the available data concerning the potential 
adverse human health and environmental effects and the potential for 
human and environmental exposures from the source category that is to 
be delisted. Such data must demonstrate that no source in the category 
or subcategory emits HAP in quantities which may cause a lifetime risk 
of cancer greater than 1-in-1 million to the individual in the 
population who is most exposed to emissions of such pollutants from the 
source or that no source in the category exceeds a level which is 
adequate to protect public health with an ample margin of safety and no 
adverse environmental effect will result from emissions from that 
source category.
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    \37\ Turbine NESHAP Unit List--Updated October 2023. Docket ID 
No. EPA-HQ-OAR-2020-0408.
    \38\ 68 FR 70951.
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V. What is the rationale for denying the petition?

    The EPA is denying the petition because the EPA has determined that 
the petition is incomplete. The petitioners did not address all the 
necessary subject areas under CAA

[[Page 26846]]

section 112(c)(9)(B) and did not present adequate information and 
analyses for the requested determination. As stated previously, CAA 
section 112(c)(9)(B)(i) requires the EPA to determine that no source in 
the category emits HAP in quantities which may cause a lifetime risk of 
cancer greater than 1-in-1 million to the individual in the population 
who is most exposed to emissions of such pollutants from the source. 
Here, the petition and all the supplements to the petition did not 
include HAP emissions measurements for all of the HAP emitted by the 
Stationary Combustion Turbines source category.\39\ The risk analysis 
submitted by the petitioners did not include metallic HAP emissions for 
natural gas and landfill gas turbines, which the CAA section 114 
information request results demonstrated are emitted from turbines 
operating on both natural gas and landfill gas. Further, the 
petitioners' analyses did not include nearly one-fourth of the 
stationary combustion turbines that are subject to the Stationary 
Combustion Turbines NESHAP. For the fuel sampling data and the acute 
multiplier, the petitioners did not provide information requested by 
the EPA that is necessary to evaluate the adequacy of the data. The EPA 
also afforded petitioners opportunities to address the above referenced 
identified gaps in the data and information underpinning their 
petition, which petitioners declined. For these reasons, the EPA cannot 
conclude that the petitioners have demonstrated that the maximum 
individual lifetime cancer risk from all stationary combustion turbines 
subject to CAA section 112 is less than the 1-in-1 million delisting 
threshold under CAA section 112(c)(9)(B)(i).
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    \39\ See, e.g., 66 FR at 21933, ``As the [Health Effects 
Institute] Health Review Committee noted in its commentary, the 
experiments in this study were `well designed and executed with 
appropriate quality control and quality assurance procedures. Thus, 
one can have confidence in the data.' '' (The EPA explaining and 
agreeing with the use of certain health effect studies in the 
delisting petition for Methanol).
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    The EPA construes CAA section 112(c)(9)(B)(i) as calling for the 
Administrator to make a determination that the criteria for delisting 
are satisfied. Any such determination must be supported by measured 
emissions data or otherwise reasonably account for operational 
variability.\40\ This is because delisting of a source category would 
result in the removal of applicable regulatory requirements under CAA 
section 112 for such source category. The EPA cannot grant a petition 
to delist a source category if there are major uncertainties that must 
be addressed for the EPA to have sufficient information to make the 
requisite substantive determination, under CAA section 112(c)(9)(B)(i). 
And the burden remains on a petitioner to demonstrate that the 
available data support an affirmative determination that HAP emissions 
from a source category may not be reasonably anticipated to result in 
adverse effects on human health or the environment. See American Forest 
and Paper Ass'n v. EPA, 294 F.3d at 119 (``The statutory language 
unambiguously places on a delisting petitioner the burden to make a 
showing that there is adequate data about a substance to determine 
exposure to it may not reasonably be anticipated to cause adverse 
effects.'' (Emphasis in original; cleaned up)).
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    \40\ ``Although public information indicated that over 140 
million pounds of these substances are used annually in the U.S. and 
that there is a general trend towards greater usage, the petitioner 
did not provide measurements or estimates regarding the emissions 
associated with such use. In the absence of such information, EPA 
cannot make the substantive determination contemplated by CAA 
Section 112(b)(3).'' 58 FR 4165 (The EPA explaining the decision to 
deny the petition to delist five glycol ethers as a HAP for lack of 
emission measurements and HAP estimated use).
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    In addition to the incompleteness of the petition, the EPA's 
technical review identified major uncertainties in the emission 
estimates provided by the petitioners that are an additional and 
separate independent basis for denial of the petition. The results of 
the 2020 RTR risk analysis (based on actual emissions), under CAA 
section 112(f)(2), indicated that the estimated maximum individual 
lifetime cancer risk is 3-in-1 million. The petitioners' analyses 
contained in their submittals claimed a maximum individual lifetime 
cancer risk of 0.76-in-1 million as support for their petition to 
delist under CAA section 112(c)(9). But the petitioners' analyses, 
which included revised HAP emission estimates and a revised evaluation 
of the 2020 RTR risk analysis, were primarily based on emission factors 
and historical fuel usage data for a subset of the turbines that are 
subject to CAA section 112.
    The petitioners also did not include any stack testing on the 
turbines that they analyzed to determine actual emissions. As stated 
previously, emission factors do not provide sufficient certainty 
regarding site-specific emissions that would provide confidence that no 
source in the category exceeds the criteria for delisting. In addition, 
the CAA section 114 emissions testing showed actual formaldehyde 
emissions for some turbines that are significantly higher than those 
estimated by the petitioners. Lastly, the petitioners did not explain 
whether the emission estimates they relied on would continue to be 
applicable if the EPA were to delist the source category. Overall, and 
as shown in section IV., the petitioners did not provide sufficient 
data or analyses for the purpose of estimating maximum offsite 
pollutant concentrations that would enable the Administrator to make 
the substantive determination contemplated by CAA section 
112(c)(9)(B).\41\
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    \41\ 58 FR 4165 (denying petition to delist five glycol ethers 
as a HAP on similar grounds).
---------------------------------------------------------------------------

    The EPA has concluded that the available evidence is inadequate to 
support a determination that no source in the Stationary Combustion 
Turbines source category emits such HAP in quantities which may cause a 
lifetime risk of cancer greater than 1-in-1 million to the individual 
in the population who is most exposed to emissions of such pollutants 
from the source category as called for under CAA section 
112(c)(9)(B)(i). Because the petition is denied under CAA section 
112(c)(9)(B)(i) for the reasons stated above, the EPA finds that it is 
not necessary to make any determinations as to whether any source in 
the category exceeds a level which is adequate to protect public health 
with an ample margin of safety and presents adverse environmental 
effects under CAA section 112(c)(9)(B)(ii).
    For the reasons stated in this section, the EPA concludes that the 
petitioners have not demonstrated that the Stationary Combustion 
Turbines source category may be delisted under CAA section 
112(c)(9)(B)(i). This means that the petitioners have failed to meet 
the delisting criteria outlined in CAA section 112(c)(9)(B)(i), and the 
EPA must deny the petition. Finally, because the EPA has determined 
that the petitioners did not address all the necessary subject areas 
under CAA section 112(c)(9)(B) and did not present adequate information 
and analyses for each of the subject areas, the EPA is denying the 
petition with prejudice. Any future petition to delist will be denied 
as a matter of law unless such future petition is accompanied by 
substantial new information or analysis.

Michael S. Regan,
Administrator.
[FR Doc. 2024-08004 Filed 4-15-24; 8:45 am]
BILLING CODE 6560-50-P