# American Lung Association v. EPA

> Court of Appeals for the D.C. Circuit · January 19, 2021 · 985 F.3d 914

URL: https://www.frixlaw.com/law-library/cases/4652158

## Case

- **Court:** Court of Appeals for the D.C. Circuit
- **Decided:** January 19, 2021
- **Citations:** 985 F.3d 914
- **Precedential status:** Published
- **Opinion:** Opinion
- **Cited by:** 16 later opinions in the Frix Law Library

## Citator (automated)

- No negative treatment found by the automated citator. That is not the same as a confirmation that the case is good law; read the citing cases.
- Full citator and citing cases: https://www.frixlaw.com/law-library/cases/4652158

## Opinion text

United States Court of Appeals
FOR THE DISTRICT OF COLUMBIA CIRCUIT

Argued October 8, 2020 Decided January 19, 2021

No. 19-1140

AMERICAN LUNG ASSOCIATION AND AMERICAN PUBLIC
HEALTH ASSOCIATION,
PETITIONERS

v.

ENVIRONMENTAL PROTECTION AGENCY AND ANDREW
WHEELER, ADMINISTRATOR,
RESPONDENTS

AEP GENERATING COMPANY, ET AL.,
INTERVENORS

Consolidated with 19-1165, 19-1166, 19-1173, 19-1175,
19-1176, 19-1177, 19-1179, 19-1185, 19-1186, 19-1187,
19-1188

On Petitions for Review of a Final Action
of the Environmental Protection Agency

Steven C. Wu, Deputy Solicitor General, Office of the
Attorney General for the State of New York, argued the cause
for the State and Municipal petitioners and intervenor Nevada.
2
With him on the briefs were Letitia James, Attorney General,
Barbara D. Underwood, Solicitor General, Matthew W.
Grieco, Assistant Solicitor General, Michael J. Myers, Senior
Counsel, Andrew G. Frank, Assistant Attorney General of
Counsel, Xavier Becerra, Attorney General, Office of the
Attorney General for the State of California, Robert W. Byrne,
Senior Assistant Attorney General, David A. Zonana,
Supervising Deputy Attorney General, Jonathan A. Wiener, M.
Elaine Meckenstock, Timothy E. Sullivan, Elizabeth B. Rumsey,
and Theodore A.B. McCombs, Deputy Attorneys General,
William Tong, Attorney General, Office of the Attorney
General for the State of Connecticut, Matthew I. Levine and
Scott N. Koschwitz, Assistant Attorneys General, Kathleen
Jennings, Attorney General, Office of the Attorney General for
the State of Delaware, Valerie S. Edge, Deputy Attorney
General, Philip J. Weiser, Attorney General, Office of the
Attorney General for the State of Colorado, Eric R. Olson,
Solicitor General, Robyn L. Wille, Senior Assistant Attorney
General, Clare E. Connors, Attorney General, Office of the
Attorney General for the State of Hawaii, William F. Cooper,
Deputy Attorney General, Aaron M. Frey, Attorney General,
Office of the Attorney General for the State of Maine, Laura
E. Jensen, Assistant Attorney General, Brian E. Frosh,
Attorney General, Office of the Attorney General for the State
of Maryland, John B. Howard, Jr., Joshua M. Segal, and
Steven J. Goldstein, Special Assistant Attorneys General,
Maura Healey, Attorney General, Office of the Attorney
General for the Commonwealth of Massachusetts, Melissa A.
Hoffer and Christophe Courchesne, Assistant Attorneys
General, Megan M. Herzog and David S. Frankel, Special
Assistant Attorneys General, Dana Nessel, Attorney General,
Office of the Attorney General for the State of Michigan,
Gillian E. Wener, Assistant Attorney General, Keith Ellison,
Attorney General, Office of the Attorney General for the State
of Minnesota, Peter N. Surdo, Special Assistant Attorney
3
General, Aaron D. Ford, Attorney General, Office of the
Attorney General for the State of Nevada, Heidi Parry Stern,
Solicitor General, Gurbir S. Grewal, Attorney General, Office
of the Attorney General for the State of New Jersey, Lisa J.
Morelli, Deputy Attorney General, Hector Balderas, Attorney
General, Office of the Attorney General for the State of New
Mexico, Tania Maestas, Chief Deputy Attorney General,
Joshua H. Stein, Attorney General, Office of the Attorney
General for the State of North Carolina, Asher Spiller,
Assistant Attorney General, Ellen F. Rosenblum, Attorney
General, Office of the Attorney General for the State of
Oregon, Paul Garrahan, Attorney-in-Charge, Steve Novick,
Special Assistant Attorney General, Josh Shapiro, Attorney
General, Office of the Attorney General for the
Commonwealth of Pennsylvania, Ann R. Johnston, Senior
Deputy Attorney General, Aimee D. Thomson, Deputy
Attorney General, Peter F. Neronha, Attorney General, Office
of the Attorney General for the State of Rhode Island, Gregory
S. Schultz, Special Assistant Attorney General, Thomas J.
Donovan, Jr., Attorney General, Office of the Attorney
General for the State of Vermont, Nicholas F. Persampieri,
Assistant Attorney General, Mark Herring, Attorney General,
Office of the Attorney General for the Commonwealth of
Virginia, Donald D. Anderson, Deputy Attorney General, Paul
Kugelman, Jr., Senior Assistant Attorney General and Chief,
Environmental Section, Caitlin Colleen Graham O=Dwyer,
Assistant Attorney General, Robert W. Ferguson, Attorney
General, Office of the Attorney General for the State of
Washington, Christopher H. Reitz and Emily C. Nelson,
Assistant Attorneys General, Joshua L. Kaul, Attorney
General, Office of the Attorney General for the State of
Wisconsin, Gabe Johnson-Karp, Assistant Attorney General,
Karl A. Racine, Attorney General, Office of the Attorney
General for the District of Columbia, Loren L. AliKhan,
Solicitor General, Tom Carr, City Attorney, Office of the City
4
Attorney for the City of Boulder, Debra S. Kalish, Senior
Counsel, Mark A. Flessner, Corporation Counsel, Office of the
Corporation Counsel for the City of Chicago, Benna Ruth
Solomon, Deputy Corporation Counsel, Jared Policicchio,
Supervising Assistant Corporation Counsel, Kristin M.
Bronson, City Attorney, Office of the City Attorney for the
City and County of Denver, Lindsay S. Carder and Edward J.
Gorman, Assistant City Attorneys, Michael N. Feuer, City
Attorney, Office of the City Attorney for the City of Los
Angeles, Michael J. Bostrom, Assistant City Attorney, James
E. Johnson, Corporation Counsel, New York City Law
Department, Christopher G. King, Senior Counsel, Marcel S.
Pratt, City Solicitor, City of Philadelphia Law Department,
Scott J. Schwarz and Patrick K. O’Neill, Divisional Deputy
City Solicitors, and Thomas F. Pepe, City Attorney, City of
South Miami. Morgan A. Costello and Brian M. Lusignan,
Assistant Attorneys General, Office of the Attorney General
for the State of New York, Gavin G. McGabe, Deputy Attorney
General, Anne Minard, Special Assistant Attorney General,
Office of the Attorney General for the State of New Mexico,
Cynthia M. Weisz, Assistant Attorney General, Office of the
Attorney General for the State of Maryland, entered
appearances.

Kevin Poloncarz argued the cause for Power Company
Petitioners. With him on the briefs were Donald L. Ristow and
Jake Levine.

Mark W. DeLaquil argued the cause for Coal Industry
Petitioners. With him on the briefs were Shay Dvoretzky,
Charles T. Wehland, Jeffery D. Ubersax, Robert D. Cheren,
and Andrew Grossman.
5
Theodore Hadzi-Antich argued the cause for Robinson
Enterprises Petitioners. With him on the briefs were Robert
Henneke and Ryan D. Walters.

Sean H. Donahue and Michael J. Myers argued the causes
for Public Health and Environmental Petitioners. On the briefs
were Ann Brewster Weeks, James P. Duffy, Susannah L.
Weaver, Joanne Spalding, Andres Restrepo, Vera Pardee,
Clare Lakewood, Howard M. Crystal, Elizabeth Jones,
Brittany E. Wright, Jon A. Mueller, David Doniger, Benjamin
Longstreth, Melissa J. Lynch, Lucas May, Vickie L. Patton,
Tomas Carbonell, Benjamin Levitan, Howard Learner, and
Scott Strand. Alejandra Nunez entered an appearance.

David M. Williamson argued the cause and filed the briefs
for Biogenic Petitioners.

Gene Grace, Jeff Dennis, and Rick Umoff were on the brief
for petitioners American Wind Energy Association, et al.

Theodore E. Lamm and Sean B. Hecht were on the brief
for amicus curiae Thomas C. Jorling in support of petitioners.

Gabriel Pacyniak, Brent Chapman, and Graciela Esquivel
were on the brief for amici curiae the Coalition to Protect
America=s National Parks and the National Parks Conservation
Association in support of petitioners.

Deborah A. Sivas and Matthew J. Sanders were on the
brief for amici curiae Administrative Law Professors in
support of petitioners.

Hope M. Babcock was on the brief for amici curiae the
American Thoracic Society, et al. in support of petitioners.
6
Richard L. Revesz and Jack Lienke were on the brief for
amicus curiae the Institute for Policy Integrity at New York
University School of Law in support of petitioners.

Steph Tai was on the brief for amici curiae Climate
Scientists in support of petitioners.

Michael Burger and Collyn Peddie were on the brief for
amici curiae the National League of Cities, et al. in support of
petitioners.

Keri R. Steffes was on the brief for amici curiae Faith
Organizations in support of petitioners.

Shaun A. Goho was on the brief for amici curiae
Maximilian Auffhammer, et al. in support of petitioners.

Ethan G. Shenkman and Stephen K. Wirth were on the
brief for amici curiae Patagonia Works and Columbia
Sportswear Company in support of petitioners.

Mark Norman Templeton, Robert Adam Weinstock,
Alexander Valdes, and Benjamin Nickerson were on the brief
for amicus curiae Professor Michael Greenstone in support of
petitioners.

Nicole G. Berner and Renee M. Gerni were on the brief for
amicus curiae the Service Employees International Union in
support of petitioners.

Elizabeth B. Wydra, and Brianne J. Gorod were on the
brief for amici curiae Members of Congress in support of
petitioners.
7
Jonas J. Monast was on the brief for amici curiae Energy
Modelers in support of petitioners.

Katherine Konschnik was on the brief for amici curiae
Former Commissioners of the Federal Energy Regulatory
Commission in support of petitioners.

Michael Landis, Elizabeth S. Merritt, and Wyatt G.
Sassman were on the brief for amici curiae Environment
America and National Trust for Historic Preservation in
support of petitioners.

Cara A. Horowitz was on the brief for amici curiae Grid
Experts in support of petitioners.

Eric Alan Isaacson was on the brief for amici curiae U.S.
Senators in support of petitioners.

Jonathan D. Brightbill, Principal Deputy Assistant
Attorney General, U.S. Department of Justice, and Meghan E.
Greenfield and Benjamin Carlisle, Attorneys, argued the
causes for respondents. With them on the brief was Jeffrey
Bossert Clark, Assistant Attorney General.

Lindsay S. See, Solicitor General, Office of the Attorney
General for the State of West Virginia, argued the cause for
State and Industry intervenors in support of respondents
regarding Affordable Clean Energy Rule. With her on the brief
were Patrick Morrisey, Attorney General, Thomas T.
Lampman, Assistant Solicitors General, Thomas A. Lorenzen,
Elizabeth B. Dawson, Rae Cronmiller, Kevin G. Clarkson,
Attorney General at the time the brief was filed, Office of the
Attorney General for the State of Alaska, Clyde Sniffen Jr.,
Attorney General, Leslie Rutledge, Attorney General, Office of
the Attorney General for the State of Arkansas, Nicholas J.
8
Bronni, Solicitor General, Vincent M. Wagner, Deputy
Solicitor General, Dylan L. Jacobs, Assistant Solicitor General,
Steve Marshall, Attorney General, Office of the Attorney
General for the State of Alabama, Edmund G. LaCour, Jr.,
Solicitor General, Christopher M. Carr, Attorney General,
Office of the Attorney General for the State of Georgia,
Andrew A. Pinson, Solicitor General, Derek Schmidt, Attorney
General, Office of the Attorney General for the State of Kansas,
Jeffrey A. Chanay, Chief Deputy Attorney General, Curtis T.
Hill, Jr., Attorney General, Office of the Attorney General of
Indiana, Thomas M. Fisher, Solicitor General, Andrew
Beshear, Governor, Office of the Governor for the
Commonwealth of Kentucky, S. Travis Mayo, Chief Deputy
General Counsel, Taylor Payne, Deputy General Counsel,
Joseph A. Newberg, Deputy General Counsel and Deputy
Executive Director, Jeff Landry, Attorney General, Office of
the Attorney General for the State of Louisiana, Elizabeth B.
Murrill, Solicitor General, Harry J. Vorhoff, Assistant
Attorney General, Eric S. Schmitt, Attorney General, Office of
the Attorney General for the State of Missouri, D. John Sauer,
Solicitor General, Julie Marie Blake, Deputy Solicitor General,
Timothy C. Fox, Attorney General at the time the brief was
filed, Office of the Attorney General for the State of Montana,
Matthew T. Cochenour, Deputy Solicitor General, Wayne
Stenehjem, Attorney General, Office of the Attorney General
for the State of North Dakota, Paul M. Seby, Special Assistant
Attorney General, Douglas J. Peterson, Attorney General,
Office of the Attorney General for the State of Nebraska, Justin
D. Lavene, Assistant Attorney General, Dave Yost, Attorney
General, Office of the Attorney General of the State of Ohio,
Benjamin M. Flowers, Solicitor General, Cameron F.
Simmons, Principal Assistant Attorney General, Mike Hunter,
Attorney General, Office of the Attorney General for the State
of Oklahoma, Mithun Mansinghani, Solicitor General, Jason
R. Ravnsborg, Attorney General, Office of the Attorney
9
General for the State of South Dakota, Steven R. Blair,
Assistant Attorney General, Alan Wilson, Attorney General,
Office of the Attorney General for the State of South Carolina,
James Emory Smith, Jr., Deputy Solicitor General, Ken
Paxton, Attorney General, Office of the Attorney General for
the State of Texas, Kyle D. Hawkins, Solicitor General, Sean
Reyes, Attorney General, Office of the Attorney General for the
State of Utah, Tyler R. Green, Solicitor General, Bridget Hill,
Attorney General, Office of the Attorney General for the State
of Wyoming, James Kaste, Deputy Attorney General, Todd E.
Palmer, William D. Booth, Obianuju Okasi, Carroll W.
McGuffey, III, Misha Tseytlin, C. Grady Moore, III, Julia
Barber, F. William Brownell, Elbert Lin, Allison D. Wood,
Scott A. Keller, Jeffrey H. Wood, Jeremy Evan Maltz, Steven P.
Lehotsky, Michael B. Schon, Emily Church Schilling, Kristina
R. Van Bockern, David M. Flannery, Kathy G. Beckett, Edward
L. Kropp, Amy M. Smith, Janet J. Henry, Melissa Horne,
Angela Jean Levin, Eugene M. Trisko, John A. Rego, Reed W.
Sirak, Michael A. Zody, Jacob Santini, Robert D. Cheren, Mark
W. DeLaquil, and Andrew M. Grossman. C. Frederick Beckner,
III, James R. Bedell, Margaret C. Campbell, Erik D. Lange,
and John D. Lazzaretti entered an appearance.

James P. Duffy argued the cause for Public Health and
Environmental Intervenors in support of respondents. With
him on the brief were Ann Brewster Weeks, Sean H. Donahue,
Susannah L. Weaver, Joanne Spalding, Andres Restrepo, Vera
Pardee, Clare Lakewood, Elizabeth Jones, Brittany E. Wright,
Jon A. Mueller, David Doniger, Benjamin Longstreth, Melissa
J. Lynch, Lucas May, Vickie L. Patton, Tomas Carbonell,
Benjamin Levitan, Howard Learner, and Scott Strand.

Letitia James, Attorney General, Office of the Attorney
General for the State of New York, Michael J. Myers, Senior
Counsel, Brian Lusignan, Assistant Attorney General of
10
Counsel, Barbara D. Underwood, Solicitor General, Steven C.
Wu, Deputy Solicitor General, Matthew W. Grieco, Assistant
Solicitor General, Xavier Becerra, Attorney General, Office of
the Attorney General for the State of California, Robert W.
Byrne, Senior Assistant Attorney General, David A. Zonana,
Supervising Deputy Attorney General, Jonathan A. Wiener, M.
Elaine Meckenstock, Timothy E. Sullivan, Elizabeth B. Rumsey,
and Theodore A.B. McCombs, Deputy Attorneys General,
William Tong, Attorney General, Office of the Attorney
General for the State of Connecticut, Matthew I. Levine and
Scott N. Koschwitz, Assistant Attorneys General, Kathleen
Jennings, Attorney General, Office of the Attorney General for
the State of Delaware, Valerie S. Edge, Deputy Attorney
General, Philip J. Weiser, Attorney General, Office of the
Attorney General for the State of Colorado, Eric R. Olson,
Solicitor General, Robyn L. Wille, Senior Assistant Attorney
General, Clare E. Connors, Attorney General, Office of the
Attorney General for the State of Hawaii, William F. Cooper,
Deputy Attorney General, Aaron M. Frey, Attorney General,
Office of the Attorney General for the State of Maine, Laura
E. Jensen, Assistant Attorney General, Brian E. Frosh,
Attorney General, Office of the Attorney General for the State
of Maryland, John B. Howard, Jr., Joshua M. Segal, and Steven
J. Goldstein, Special Assistant Attorneys General, Maura
Healey, Attorney General, Office of the Attorney General for
the Commonwealth of Massachusetts, Melissa A. Hoffer and
Christophe Courchesne, Assistant Attorneys General, Megan
M. Herzog and David S. Frankel, Special Assistant Attorneys
General, Dana Nessel, Attorney General, Office of the
Attorney General for the State of Michigan, Gillian E. Wener,
Assistant Attorney General, Keith Ellison, Attorney General,
Office of the Attorney General for the State of Minnesota,
Peter N. Surdo, Special Assistant Attorney General, Aaron D.
Ford, Attorney General, Office of the Attorney General for the
State of Nevada, Heidi Parry Stern, Solicitor General, Gurbir
11
S. Grewal, Attorney General, Office of the Attorney General
for the State of New Jersey, Lisa J. Morelli, Deputy Attorney
General, Hector Balderas, Attorney General, Office of the
Attorney General for the State of New Mexico, Tania Maestas,
Chief Deputy Attorney General, Joshua H. Stein, Attorney
General, Office of the Attorney General for the State of North
Carolina, Asher Spiller, Assistant Attorney General, Ellen F.
Rosenblum, Attorney General, Office of the Attorney General
for the State of Oregon, Paul Garrahan, Attorney-in-Charge,
Steve Novick, Special Assistant Attorney General, Josh
Shapiro, Attorney General, Office of the Attorney General for
the Commonwealth of Pennsylvania, Ann R. Johnston, Senior
Deputy Attorney General, Aimee D. Thomson, Deputy
Attorney General, Peter F. Neronha, Attorney General, Office
of the Attorney General for the State of Rhode Island, Gregory
S. Schultz, Special Assistant Attorney General, Thomas J.
Donovan, Jr., Attorney General, Office of the Attorney
General for the State of Vermont, Nicholas F. Persampieri,
Assistant Attorney General, Mark Herring, Attorney General,
Office of the Attorney General for the Commonwealth of
Virginia, Donald D. Anderson, Deputy Attorney General, Paul
Kugelman, Jr., Senior Assistant Attorney General and Chief,
Environmental Section, Caitlin Colleen Graham O=Dwyer,
Assistant Attorney General, Robert W. Ferguson, Attorney
General, Office of the Attorney General for the State of
Washington, Christopher H. Reitz and Emily C. Nelson,
Assistant Attorneys General, Karl A. Racine, Attorney
General, Office of the Attorney General for the District of
Columbia, Loren L. AliKhan, Solicitor General, Tom Carr,
City Attorney, Office of the City Attorney for the City of
Boulder, Debra S. Kalish, Senior Counsel, Mark A. Flessner,
Corporation Counsel, Office of the Corporation Counsel for the
City of Chicago, Benna Ruth Solomon, Deputy Corporation
Counsel, Jared Policicchio, Supervising Assistant Corporation
Counsel, Kristin M. Bronson, City Attorney, Office of the City
12
Attorney for the City and County of Denver, Lindsay S. Carder
and Edward J. Gorman, Assistant City Attorneys, Michael N.
Feuer, City Attorney, Office of the City Attorney for the City
of Los Angeles, Michael J. Bostrom, Assistant City Attorney,
James E. Johnson, Corporation Counsel, New York City Law
Department, Christopher G. King, Senior Counsel, Marcel S.
Pratt, City Solicitor, City of Philadelphia Law Department,
Scott J. Schwarz and Patrick K. O’Neill, Divisional Deputy
City Solicitors, and Thomas F. Pepe, City Attorney, City of
South Miami were on the brief for the State and Municipal
Intervenors in support of respondents. Jeremiah Langston,
Assistant Attorney General, Office of the Attorney General for
the State of Montana, Stephen C. Meredith, Solicitor, Office of
the Attorney General for the Commonwealth of Kentucky,
Margaret I. Olson, Assistant Attorney General, Office of the
Attorney General for the State of North Dakota, and Erik E.
Petersen, Assistant Attorney General, Office of the Attorney
General for the State of Wyoming, and Robert A. Wolf entered
appearances.

Patrick Morrisey, Attorney General, Office of the
Attorney General for the State of West Virginia, Lindsay S.
See, Solicitor General, Thomas T. Lampman, Assistant
Solicitor General, Scott A. Keller, Jeffrey H. Wood, Jeremy
Evan Maltz, Steven P. Lehotsky, Michael B. Schon, Thomas A.
Lorenzen, Elizabeth B. Dawson, Rae Cronmiller, Steve
Marshall, Attorney General, Office of the Attorney General for
the State of Alabama, Edmund G. LaCour, Jr., Solicitor
General, Kevin G. Clarkson, Attorney General, Office of the
Attorney General for the State of Alaska at the time the brief
was filed, Clyde Sniffen, Jr., Attorney General, Leslie Rutledge,
Attorney General, Office of the Attorney General for the State
of Arkansas, Nicholas J. Bronni, Solicitor General, Vincent M.
Wagner, Deputy Solicitor General, Dylan L. Jacobs, Assistant
Solicitor General, Christopher M. Carr, Attorney General,
13
Office of the Attorney General for the State of Georgia,
Andrew A. Pinson, Solicitor General, Derek Schmidt, Attorney
General, Office of the Attorney General for the State of Kansas,
Jeffrey A. Chanay, Chief Deputy Attorney General, Curtis T.
Hill, Jr., Attorney General, Office of the Attorney General of
Indiana, Thomas M. Fisher, Solicitor General, Andrew
Beshear, Governor, Office of the Governor for the
Commonwealth of Kentucky, S. Travis Mayo, Chief Deputy
General Counsel, Taylor Payne, Deputy General Counsel,
Joseph A. Newberg, Deputy General Counsel and Deputy
Executive Director, Jeff Landry, Attorney General, Office of
the Attorney General for the State of Louisiana, Elizabeth B.
Murrill, Solicitor General, Harry J. Vorhoff, Assistant
Attorney General, Eric S. Schmitt, Attorney General, Office of
the Attorney General for the State of Missouri, D. John Sauer,
Solicitor General, Julie Marie Blake, Deputy Solicitor General,
Timothy C. Fox, Attorney General at the time the brief was
filed, Office of the Attorney General for the State of Montana,
Matthew T. Cochenour, Deputy Solicitor General, Wayne
Stenehjem, Attorney General, Office of the Attorney General
for the State of North Dakota, Paul M. Seby, Special Assistant
Attorney General, Douglas J. Peterson, Attorney General,
Office of the Attorney General for the State of Nebraska, Justin
D. Lavene, Assistant Attorney General, Dave Yost, Attorney
General, Office of the Attorney General of the State of Ohio,
Benjamin M. Flowers, Solicitor General, Cameron F.
Simmons, Principal Assistant Attorney General, Mike Hunter,
Attorney General, Office of the Attorney General for the State
of Oklahoma, Mithun Mansinghani, Solicitor General, Jason
R. Ravnsborg, Attorney General, Office of the Attorney
General for the State of South Dakota, Steven R. Blair,
Assistant Attorney General, Alan Wilson, Attorney General,
Office of the Attorney General for the State of South Carolina,
James Emory Smith, Jr., Deputy Solicitor General, Ken
Paxton, Attorney General, Office of the Attorney General for
14
the State of Texas, Kyle D. Hawkins, Solicitor General, Sean
Reyes, Attorney General, Office of the Attorney General for the
State of Utah, Tyler R. Green, Solicitor General, Bridget Hill,
Attorney General, Office of the Attorney General for the State
of Wyoming, James Kaste, Deputy Attorney General, Todd E.
Palmer, William D. Booth, Obianuju Okasi, Carroll W.
McGuffey, III, Misha Tseytlin, C. Grady Moore, III, Julia
Barber, F. William Brownell, Elbert Lin, Allison D. Wood,
Emily Church Schilling, Kristina R. Van Bockern, David M.
Flannery, Kathy G. Beckett, Edward L. Kropp, Amy M. Smith,
Janet J. Henry, Melissa Horne, Angela Jean Levin, Eugene M.
Trisko, John A. Rego, Reed W. Sirak, Michael A. Zody, Jacob
Santini, Robert D. Cheren, Mark W. DeLaquil, and Andrew M.
Grossman were on the brief for State and Industry Intervenors
in support of respondents regarding Clean Power Plan Repeal.

Wayne Stenehjem, Attorney General, Office of the
Attorney General for the State of North Dakota, and Paul M.
Seby, Special Assistant Attorney General, were on the brief for
intervenor State of North Dakota in support of the respondents.
Jerry Stouck entered an appearance.

Thomas J. Ward, Megan H. Berge, and Jared R. Wigginton
were on the brief for amicus curiae National Association of
Builders in support of respondents.

Before: MILLETT , PILLARD , and WALKER, Circuit Judges.

Opinion for the Court filed PER CURIAM.

Opinion concurring in part, concurring in the judgment in
part, and dissenting in part filed by Circuit Judge WALKER.
15
TABLE OF C ONTENTS
I. Background .........................................................................17
A. The Clean Air Act ..........................................................17
B. Electricity and Climate Change .....................................21
1. Electricity.....................................................................21
2. Climate Change and the Federal Government ..........24
C. The Clean Power Plan ....................................................29
D. The ACE Rule ................................................................32
1. Repeal of the Clean Power Plan .................................32
2. Best System of Emission Reduction ..........................33
3. Degree of Emission Limitation Achievable ..............36
4. Implementing Regulations..........................................38
E. Petitions for Review .......................................................38
F. Jurisdiction and Standard of Review .............................39
II. Section 7411 .......................................................................40
A. Statutory Context............................................................40
1. Text ..............................................................................46
2. Statutory History, Structure, and Purpose .................59
3. Compliance Measures .................................................71
B. The Major Questions Doctrine ......................................74
1. The EPA’s Regulatory Mandate ................................75
2. Best System of Emission Reduction ..........................80
C. Federalism .......................................................................92
III. The EPA’s Authority to Regulate Carbon Dioxide
Emissions Under Section 7411 ..............................................98
A. The Coal Petitioners’ Challenges ..................................98
1. Endangerment Finding................................................99
2. Section 7411 and Section 7412’s
Parallel Operation...................................................... 111
B. The Robinson Petitioners’ Challenges ....................... 132
IV. Amendments to the Implementing Regulations ...... 138
V. Vacatur and Remand .................................................... 146
VI. Conclusion ..................................................................... 147
16
As the Supreme Court recognized nearly fourteen years
ago, climate change has been called “the most pressing
environmental challenge of our time.” Massachusetts v. EPA,
549 U.S. 497, 505 (2007) (formatting modified). Soon
thereafter, the United States government determined that
greenhouse gas emissions are polluting our atmosphere and
causing significant and harmful effects on the human
environment. Endangerment and Cause or Contribute Findings
for Greenhouse Gases Under Section 202(a) of the Clean Air
Act (2009 Endangerment Finding), 74 Fed. Reg. 66,496,
66,497–66,499 (Dec. 15, 2009). And both Republican and
Democratic administrations have agreed: Power plants
burning fossil fuels like coal “are far and away” the largest
stationary source of greenhouse gases and, indeed, their role in
greenhouse gas emissions “dwarf[s] other categories[.]” EPA
Br. 169; see also Standards of Performance for Greenhouse
Gas Emissions from New, Modified, and Reconstructed
Stationary Sources: Electric Utility Generating Units (New
Source Rule), 80 Fed. Reg. 64,510, 64,522 (Oct. 23, 2015)
(fossil-fuel-fired power plants are “by far the largest emitters”
of greenhouse gases).

The question in this case is whether the Environmental
Protection Agency (EPA) acted lawfully in adopting the 2019
Affordable Clean Energy Rule (ACE Rule), 84 Fed. Reg.
32,520 (July 8, 2019), as a means of regulating power plants’
emissions of greenhouse gases. It did not. Although the EPA
has the legal authority to adopt rules regulating those
emissions, the central operative terms of the ACE Rule and the
repeal of its predecessor rule, the Clean Power Plan, 80 Fed.
Reg. 64,662 (Oct. 23, 2015), hinged on a fundamental
misconstruction of Section 7411(d) of the Clean Air Act. In
addition, the ACE Rule’s amendment of the regulatory
framework to slow the process for reduction of emissions is
arbitrary and capricious. For those reasons, the ACE Rule is
17
vacated, and the record is remanded to the EPA for further
proceedings consistent with this opinion.

I. BACKGROUND

A. T HE C LEAN AIR ACT

In 1963, Congress passed the Clean Air Act, 42 U.S.C.
§ 7401 et seq., “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[,]” id.
§ 7401(b)(1). Animating the Act was Congress’ finding that
“growth in the amount and complexity of air pollution brought
about by urbanization, industrial development, and the
increasing use of motor vehicles[] has resulted in mounting
dangers to the public health and welfare[.]” Id. § 7401(a)(2).

Section 111 of the Clean Air Act, which was added in 1970
and codified at 42 U.S.C. § 7411, directs the EPA to regulate
any new and existing stationary sources of air pollutants that
“cause[], or contribute[] significantly to, air pollution” and that
“may reasonably be anticipated to endanger public health or
welfare.” 42 U.S.C. § 7411(b)(1)(A); see id. § 7411(d), (f)
(providing that the EPA Administrator “shall” regulate existing
and new sources of air pollution). A “stationary source” is a
source of air pollution that cannot move, such as a power plant.
See id. § 7411(a)(3) (defining “stationary source” as “any
building, structure, facility, or installation which emits or may
emit any air pollutant[]”). An example of a common non-
stationary source of air pollution is a gas-powered motor
vehicle. See Utility Air Regulatory Group v. EPA (UARG), 573
U.S. 302, 308 (2014).

Within 90 days of the enactment of Section 7411, the EPA
Administrator was to promulgate a list of stationary source
categories that “cause[], or contribute[] significantly to, air
18
pollution[.]” 42 U.S.C. § 7411(b)(1)(A). In 1971, the
Administrator included fossil-fuel-fired steam-generating
power plants on that list. Air Pollution Prevention and Control:
List of Categories of Stationary Sources, 36 Fed. Reg. 5,931
(March 31, 1971); see also New Source Rule, 80 Fed. Reg. at
64,527–64,528. Today’s power plants fall in that same
category. ACE Rule, 84 Fed. Reg. at 32,557 n.250.

Once a stationary source category is listed, the
Administrator must promulgate federal “standards of
performance” for all newly constructed sources in the category.
42 U.S.C. § 7411(b)(1)(B). The Act defines a “standard of
performance” as

a standard for emissions of air pollutants which
reflects the degree of emission limitation achievable
through the application of the best system of emission
reduction which (taking into account the cost of
achieving such reduction and any nonair quality
health and environmental impact and energy
requirements) the Administrator determines has been
adequately demonstrated.

Id. § 7411(a)(1).

Once such a new source regulation is promulgated, the
Administrator also must issue emission guidelines for already-
existing stationary sources within that same source category.
42 U.S.C. § 7411(d)(1)(A)(ii); see also American Elec. Power
Co., Inc. v. Connecticut (AEP), 564 U.S. 410, 424 (2011).

While the new source standards are promulgated and
enforced entirely by the EPA, the Clean Air Act prescribes a
process of cooperative federalism for the regulation of existing
sources. Under that structure, the statute delineates three
distinct regulatory steps involving three sets of actors—the
19
EPA, the States, and regulated industry—each of which has a
flexible role in choosing how to comply. See 42 U.S.C.
§ 7411(a)(1), (d). This allows each State to work with the
stationary sources within its jurisdiction to devise a plan for
meeting the federally promulgated quantitative guideline for
emissions. See id. § 7411(d).

The process starts with the EPA first applying its expertise
to determine “the degree of emission limitation achievable
through the application of the best system of emission
reduction” that “has been adequately demonstrated.” 42 U.S.C.
§ 7411(a)(1); see 40 C.F.R. § 60.22a. That system must “tak[e]
into account the cost of achieving such reduction and any
nonair quality health and environmental impact and energy
requirements[.]” 42 U.S.C. § 7411(a)(1). Once the
Administrator identifies the best system of emission reduction,
she then determines the amount of emission reduction that
existing sources should be able to achieve based on the
application of that system and adopts corresponding emission
guidelines. Id.; see also, e.g., ACE Rule, 84 Fed. Reg. at
32,523; Clean Power Plan, 80 Fed. Reg. at 64,719.

Each State then submits to the EPA a plan that
(i) establishes standards of performance for that State’s
existing stationary sources’ air pollutants (excepting pollutants
already subject to separate federal emissions standards), and
(ii) “provides for the implementation and enforcement of such
standards of performance[]” by the State. 42 U.S.C.
§ 7411(d)(1); see 40 C.F.R. § 60.23a. The standards of
performance must “reflect[]” the emission targets that the EPA
has determined are achievable. 42 U.S.C. § 7411(a)(1). In this
context, a state standard need not adopt the best system
identified by the EPA to “reflect[]” it. Id.; see 40 C.F.R.
§ 60.24a(c). Instead, the Clean Air Act affords States
significant flexibility in designing and enforcing standards that
20
employ other approaches so long as they meet the emission
guidelines prescribed by the Agency.

If a State fails to submit a satisfactory plan, the EPA may
prescribe a plan for that State. 42 U.S.C. § 7411(d)(2)(A); see
40 C.F.R. § 60.27a(c)-(e). Similarly, if the State submits a plan
but fails to enforce it, the EPA itself may enforce the plan’s
terms. Id. § 7411(d)(2)(B).

The third and final set of relevant actors are the regulated
entities themselves, to which, under the Act, the States may
afford leeway in crafting compliance measures. See Clean
Power Plan, 80 Fed. Reg. at 64,666; ACE Rule, 84 Fed. Reg.
at 32,555.

The EPA has exercised its authority under Section 7411
over the years to set emission limitations for different types of
air pollution from various categories of existing sources. See
42 Fed. Reg. 12,022 (March 1, 1977) (fluorides from phosphate
fertilizer plants); 42 Fed. Reg. 55,796 (Oct. 18, 1977) (acid
mist from sulfuric acid plants); 44 Fed. Reg. 29,828 (May 22,
1979) (total reduced sulfur from kraft pulp plants); 45 Fed.
Reg. 26,294 (April 17, 1980) (fluorides from primary
aluminum plants); 60 Fed. Reg. 65,387 (Dec. 19, 1995)
(various pollutants from municipal waste combustors); 61 Fed.
Reg. 9905 (March 12, 1996) (landfill gases from municipal
solid waste landfills); 70 Fed. Reg. 28,606 (May 18, 2005)
(mercury from coal-fired power plants).

The Clean Air Act is a comprehensive statute that includes
a variety of regulatory programs for tackling air pollution in
addition to Section 7411. Regulated parties may be subject to
one or more programs. As relevant here, the National Ambient
Air Quality Standards (NAAQS) provisions, 42 U.S.C.
§§ 7408–7410, govern the levels of specified air pollutants that
may be present in the atmosphere to protect air quality and the
21
public health and welfare. The Hazardous Air Pollutants
program, id. § 7412, directs the EPA to establish strict emission
limitations for the most dangerous air pollutants emitted from
major sources. Section 7411’s cooperative federalism program
for existing sources operates as a gap-filler, requiring the EPA
to regulate harmful emissions not controlled under those other
two programs. Id. § 7411(d)(1)(i).

B. E LECTRICITY AND CLIMATE CHANGE

1. Electricity

Electricity powers the world. Chances are that you are
reading this opinion on a device that consumes electricity. Yet
two distinct characteristics of electricity make its production
and delivery in the massive quantities demanded by consumers
an exceptionally complex process. First, unlike most products,
electricity is a perfectly fungible commodity. Grid Experts
Amicus Br. 6. A watt of electricity is a watt of electricity, no
matter who makes it, how they make it, or where it is
purchased. Second, at least as of now, this highly demanded
product cannot be effectively stored at scale after it is created.
Paul L. Joskow, Creating a Smarter U.S. Electricity Grid, 26
J. ECON. PERSP. 29, 31–33 (2012).1 Instead, electricity must

1
Change in storage capacity is picking up speed. See generally
Richard L. Revesz & Burcin Unel, Managing the Future of the
Electricity Grid: Energy Storage and Greenhouse Gas Emissions,
42 HARV. ENV’T L. REV. 139, 140–141 (2018) (describing ongoing
declines in cost of storage); LAZARD, LAZARD’S LEVELIZED COST
OF STORAGE ANALYSIS—VERSION 6.0 (2020) (noting “storage costs
have declined across most use cases and technologies, particularly
for shorter-duration applications, in part driven by evolving
preferences in the industry”). Nevertheless, the grid’s production
capacity still far exceeds its present storage capacity. Univ. of Mich.
22
constantly be produced, and is almost instantaneously
consumed. See Clean Power Plan, 80 Fed. Reg. at 64,677,
64,692; Grid Experts Amicus Br. 8.

Those unique attributes led to the creation of the American
electrical grid. 2 The grid has been called the “supreme
engineering achievement of the 20th century,” MASS. INST. OF
TECH., THE FUTURE OF THE ELECTRIC GRID 1 (2011)
(formatting modified), and it is an exceptionally complex,
interconnected system. “[A]ny electricity that enters the grid
immediately becomes a part of a vast pool of energy that is
constantly moving[.]” New York v. FERC, 535 U.S. 1, 7
(2002). That means that units of electricity as delivered to the
user are identical, no matter their source. On the grid, there is
no coal-generated electricity or renewable-generated
electricity; there is just electricity. See Clean Power Plan, 80
Fed. Reg. at 64,692; Grid Experts Amicus Br. 7–8. Also,
because storing electricity for any length of time remains
technically challenging and often costly, the components of the
grid must operate as a perfectly calibrated machine to deliver
the amount of electricity that all consumers across the United
States need at the moment they need it. Grid Experts Amicus

Ctr. for Sustainable Sys., U.S. GRID ENERGY STORAGE (Sept. 2020),
http://css.umich.edu/sites/default/files/US%20Grid%20Energy%20
Storage_CSS15-17_e2020.pdf (last visited Jan. 11, 2021) (United
States has 1,100 gigawatts of installed generation capacity and just
23 gigawatts of storage capacity).
2
Technically, “grids.” There are three regional grids in the
contiguous United States: Eastern, Western, and Texas. Grid
Experts Amicus Br. 9; see also United States Dep’t of Energy, North
American Electric Reliability Corporation Interconnections,
https://www.energy.gov/oe/downloads/north-american-electric-
reliability-corporation-interconnections (last visited Jan. 11, 2021).
23
Br. 8, 10–11; see also 80 Fed. Reg. at 64,677. “If [someone]
in Atlanta on the Georgia [leg of the] system turns on a light,
every generator on Florida’s system almost instantly is caused
to produce some quantity of additional electric energy which
serves to maintain the balance in the interconnected system[.]”
Federal Power Comm’n v. Florida Power & Light Co., 404
U.S. 453, 460 (1972) (citation omitted). “Like orchestra
conductors signaling entrances and cut-offs, grid operators use
automated systems to signal particular generators to dispatch
more or less power to the grid as needed over the course of the
day, thus ensuring that power pooled on the grid rises and falls
to meet changing demand.” Grid Experts Amicus Br. 11.

Most generators of electricity on the American grid create
power by burning fossil fuels like coal, oil, and natural gas. See
United States Energy Information Administration (EIA),
Frequently Asked Questions: What Is U.S. Electricity
Generation by Energy Source? (Nov. 2, 2020),
https://www.eia.gov/tools/faqs/faq.php?id=427&t=3 (last
visited Jan. 11, 2021) (fossil fuels represented 62.6 percent of
electricity generation in 2019). Some of those power plants
take a fossil fuel (usually coal) and burn it in a water boiler to
make steam. Other power plants take a different fossil fuel
(usually natural gas), mix it with highly compressed air, and
ignite it to release a combination of super-hot gases. Either
way, that steam or superheated mixture is piped into giant
turbines that catch the gases and rotate at extreme speeds.
Those turbines turn generators, which spin magnets within wire
coils to produce electricity. EIA, Electricity Explained
(Nov. 9, 2020), https://www.eia.gov/energyexplained/
electricity/how-electricity-is-generated.php (last visited Jan
11, 2021).
24
2. Climate Change and the Federal Government

Electrical power has become virtually as indispensable to
modern life as air itself. But electricity generation has come
into conflict with air quality in ways that threaten human health
and well-being when power generated by burning fossil fuels
emits carbon dioxide and other polluting greenhouse gases into
the air.

Since the late 1970s, the federal government has focused
“serious attention” on the effects of carbon dioxide pollution
on the climate. Massachusetts v. EPA, 549 U.S. at 507. In
1978, Congress adopted the National Climate Program Act,
Pub. L. No. 95-367, 92 Stat. 601, which directed the President
to study and devise an appropriate response to “man-induced
climate processes and their implications[,]” id. § 3; see
Massachusetts v. EPA, 549 U.S. at 507–508. In response, the
National Academy of Sciences’ National Research Council
reported “no reason to doubt that climate changes will result”
if “carbon dioxide continues to increase,” and “[a] wait-and-
see policy may mean waiting until it is too late.”
Massachusetts v. EPA, 549 U.S. at 508 (quoting CLIMATE
RESEARCH BOARD , CARBON D IOXIDE & CLIMATE:
A SCIENTIFIC ASSESSMENT, at viii (1979)).

In 1987, Congress passed the Global Climate Protection
Act, which found that “manmade pollution[,]” including “the
release of carbon dioxide, * * * may be producing a long-term
and substantial increase in the average temperature on Earth[.]”
Pub. L. No. 100-204, Title XI, §1102(1), 101 Stat. 1407, 1408
(codified at 15 U.S.C. § 2901 note). The Climate Protection
Act directed the EPA to formulate a “coordinated national
policy on global climate change.” Id. § 1103(b), 101 Stat. at
1408; see Massachusetts v. EPA, 549 U.S. at 508.
25
It was not until the Supreme Court’s 2007 decision in
Massachusetts v. EPA, however, that the Court confirmed that
carbon dioxide and other greenhouse gas emissions constituted
“air pollutant[s]” covered by the Clean Air Act. See 549 U.S.
at 528. The Supreme Court explained that the Clean Air Act’s
“sweeping definition of ‘air pollutant’ includes ‘any air
pollution agent or combination of such agents, including any
physical, chemical . . . substance or matter which is emitted
into or otherwise enters the ambient air[.]’” Id. at 528–529
(quoting 42 U.S.C. § 7602(g)). The Act, the Supreme Court
held, “is unambiguous” in that regard. Id. at 529. “On its face,
the definition embraces all airborne compounds of whatever
stripe, and underscores that intent through the repeated use of
the word ‘any.’” Id. And “[c]arbon dioxide” and other
common greenhouse gases are “without a doubt” chemical
substances that are “emitted into . . . the ambient air.” Id.
(quoting 42 U.S.C. § 7602(g)).

Given that statutory command, the Supreme Court ruled
that the EPA “can avoid taking further action” to regulate such
pollution “only if it determines that greenhouse gases do not
contribute to climate change” or offers some reasonable
explanation for not resolving that question. Massachusetts v.
EPA, 549 U.S. at 533.

Taking up the mantle, the EPA in 2009 found
“compelling[]” evidence that emissions of greenhouse gases
are polluting the atmosphere and are endangering human health
and welfare by causing significant damage to the environment.
2009 Endangerment Finding, 74 Fed. Reg. at 66,497; see id.
(“[T]he Administrator finds that greenhouse gases in the
atmosphere may reasonably be anticipated both to endanger
public health and to endanger public welfare. * * * The
Administrator has determined that the body of scientific
evidence compellingly supports this finding.”); id. at 66,497–
26
66,499. The EPA concluded that “‘compelling’ evidence
supported the ‘attribution of observed climate change to
anthropogenic’ [that is, human-influenced] emissions of
greenhouse gases[.]” AEP, 564 U.S. at 417 (quoting 74 Fed.
Reg. at 66,518). The “[c]onsequent dangers of greenhouse gas
emissions,” the EPA determined, include

increases in heat-related deaths; coastal inundation
and erosion caused by melting icecaps and rising sea
levels; more frequent and intense hurricanes, floods,
and other “extreme weather events” that cause death
and destroy infrastructure; drought due to reductions
in mountain snowpack and shifting precipitation
patterns; destruction of ecosystems supporting
animals and plants; and potentially “significant
disruptions” of food production.

Id. (quoting 74 Fed. Reg. at 66,524–66,535).

Not long thereafter, the Supreme Court ruled that the
significant greenhouse gas pollution caused by fossil-fuel-fired
power plants is subject to regulation under Section 7411 of the
Clean Air Act. AEP, 564 U.S. at 424 (holding that Section
7411 “speaks directly to emissions of carbon dioxide from
[fossil-fuel-fired] plants[]”) (internal quotation marks omitted).
The Court concluded that the EPA’s expertise made it “best
suited to serve as primary regulator of greenhouse gas
emissions.” Id. at 428.

In 2015, with the 2009 carbon dioxide endangerment
finding continuing in effect, the EPA reaffirmed that
greenhouse gases “endanger public health, now and in the
future.” New Source Rule, 80 Fed. Reg. at 64,518. The EPA
explained that, “[b]y raising average temperatures, climate
change increases the likelihood of heat waves, which are
associated with increased deaths and illnesses[,]” particularly
27
among “[c]hildren, the elderly, and the poor[.]” Id. at 64,517.
In addition, the EPA found that “[c]limate change impacts
touch nearly every aspect of public welfare.” Id. Among the
“multiple threats caused by human emissions of [greenhouse
gases],” the EPA pointed to climate changes that “are expected
to place large areas of the country at serious risk of reduced
water supplies, increased water pollution, and increased
occurrence of extreme events such as floods and droughts.” Id.
The EPA “emphasize[d] the urgency of reducing [greenhouse
gas] emissions due to * * * projections that show [greenhouse
gas] concentrations climbing to ever-increasing levels in the
absence of mitigation[,]” citing independent assessments
finding that, “without a reduction in emissions, CO2
concentrations by the end of the century would increase to
levels that the Earth has not experienced for more than 30
million years.” Id. at 64,518.

The federal government’s consistent recognition of the
danger to public health and welfare caused by climate change,
and the signal contribution of greenhouse gas emissions from
power plants to global warming, continues to the present. In
2018, President Trump’s administration concluded that
“Earth’s climate is now changing faster than at any point in the
history of modern civilization, primarily as a result of human
activities.” U.S. GLOBAL CHANGE RESEARCH PROGRAM,
FOURTH NATIONAL CLIMATE A SSESSMENT, VOLUME II:
IMPACTS, RISKS, AND ADAPTATION IN THE UNITED STATES
(REPORT- IN-B RIEF) 24 (2018). The administration added that
“the evidence of human-caused climate change is
overwhelming and continues to strengthen,” and “the impacts
of climate change are intensifying across the country[.]” Id. at
26 (emphasis omitted). “Climate-related changes in weather
patterns and associated changes in air, water, food, and the
environment are affecting the health and well-being of the
American people, causing injuries, illnesses, and death.” Id. at
28
102. The administration’s report concluded that urgent action
is needed to mitigate these dangers because “[f]uture risks from
climate change depend primarily on decisions made today.” Id.
at 13.

In preparing the ACE Rule, the EPA expressly
acknowledged its continued adherence to the 2015
endangerment finding. 84 Fed. Reg. at 32,533 (The 2015 New
Source Rule “continues to provide the requisite predicate for
applicability of [Clean Air Act] section 111(d).”); id. at 32,557
n.250; see also Emission Guidelines for Greenhouse Gas
Emissions from Existing Electric Utility Generating Units;
Revisions to Emission Guideline Implementing Regulations;
Revisions to New Source Review Program: Proposed Rule, 83
Fed. Reg. 44,746, 44,751 (Aug. 31, 2018) (confirming that the
2015 New Source Rule “remains on the books[]”); EPA
Br. 217.

That endangerment finding provided the essential factual
foundation—and triggered a statutory mandate—for the EPA
to regulate greenhouse gas emissions from both new and
existing power plants. See New Source Rule, 80 Fed. Reg. at
64,527, 64,529–64,532; Clean Power Plan, 80 Fed. Reg. at
64,683–64,690; see also 42 U.S.C. §§ 7411(b)(1)(A)–(B) (duty
to regulate new stationary sources that contribute significantly
to dangerous pollution identified in endangerment finding),
7411(d)(1)(A)(ii) (duty to regulate existing stationary sources
that would be regulated under § 7411(b) if they were new
stationary sources). Recall, Section 7411(b)(1)(A) provides
that the EPA Administrator “shall” regulate any category of
sources that, “in his judgment * * * causes, or contributes
significantly to, air pollution which may reasonably be
anticipated to endanger public health or welfare.” The EPA
endangerment findings reflect such well-established risks.
29
C. T HE C LEAN POWER PLAN

In the last decade, the EPA has heavily focused its
regulation of greenhouse gases on the power sector because
“power plants are far and away the largest stationary-category
source of greenhouse gases[,]” and “power plants’
contributions to CO2 pollution * * * dwarf[] other
categories[.]” EPA Br. 169.

In October 2015, the EPA issued greenhouse gas emission
standards for new and modified power plants. See New Source
Rule, 80 Fed. Reg. at 64,510. In so doing, the EPA found that,
“[a]ll told, these fossil fuel-fired [power plants] emit almost
one-third of all U.S. [greenhouse gas] emissions, and are
responsible for almost three times as much as the emissions
from the next ten stationary source categories combined.” Id.
at 64,531. That rule and finding remain in effect and are not
challenged in this litigation.

The EPA then turned to the regulation of existing power
plants. The EPA began, as the Clean Air Act requires, by
determining the best system of emission reduction that has
been adequately demonstrated for existing fossil-fuel-fired
power plants. See 42 U.S.C. § 7411(a)(1); Clean Power Plan,
80 Fed. Reg. at 64,718. In identifying that system, the EPA
chose to build on the established grid system and methods of
operation already adopted by and familiar to the power sector.
See 80 Fed. Reg. at 64,725, 64,727–64,728. The regulations
and standards that the EPA formulated came to be known as
the Clean Power Plan. Id. at 64,663.

In the Clean Power Plan, the EPA determined that a
combination of three existing methods of emission reduction—
which the Plan referred to as building blocks, 80 Fed. Reg. at
64,667—formed the “best system of emission reduction,” 42
U.S.C. § 7411(a)(1).
30
First, the system incorporated heat-rate improvements—
that is, technological measures that improve efficiency at coal-
fired steam power plants and, in that way, reduce the amount
of coal that must be burned to produce each watt of electricity
to the grid. 80 Fed. Reg. at 64,667.

Second, the system added the “substitut[ion of] increased
generation from lower-emitting existing natural gas combined
cycle units for generation from higher-emitting affected steam
generating” power plants, which are mostly coal-fired. 80 Fed.
Reg. at 64,667.

Third, the system prioritized the use of electricity
generated from zero-emitting renewable-energy sources over
electricity from the heavily greenhouse-gas-polluting fossil-
fuel-fired power plants. 80 Fed. Reg. at 64,667.

Those second and third methods of emission control are
often referred to as “generation shifting” because the
reductions occur when the source of power generation shifts
from higher-emission power plants to less-polluting sources of
energy. See Clean Power Plan, 80 Fed. Reg. at 64,728–64,729.
As the EPA observed, such shifts in generation already occur
all the time as a matter of grid mechanics. That is, within the
grid’s “Constrained Least-Cost Dispatch” system, production
from “generators with the lowest variable costs” will be
dispatched “first, as system operational limits allow, until all
demand is satisfied.” Grid Experts Amicus Br. 12.
“[R]enewable energy generators typically receive dispatch
priority because they have lower variable costs than fossil-fuel-
fired generators, which must purchase fuel.” Id. at 13 (citing
80 Fed. Reg. at 64,693). The EPA found that most electricity
is generated by diversified utilities that could achieve most or
all of the shift to lower- or no-emission generation by
31
reassessing the dispatch priority of their own assets. See 80
Fed. Reg. at 64,796, 64,804.

As required by Section 7411(a)(1), the EPA then
quantified the degree of emission reduction achievable under
that three-tier best system for the relevant fossil-fuel-fired
power plants and translated it into state-specific emissions
goals for 2030. Clean Power Plan, 80 Fed. Reg. at 64,824–
64,825. To permit additional flexibility, the Plan actually
provided two alternative types of targets: rate-based goals,
reflecting the rate of emission per certain amount of generation,
and mass-based goals, reflecting the total emission from a
State’s sources. Id. at 64,820, 64,824–64,825 Tables 12, 13.
The alternative metrics were an added source of flexibility for
States in choosing how they would meet the federal limits.

Under the Clean Air Act, States could then propose plans
that set standards of performance for their existing power
plants that would meet those emission goals. Clean Power
Plan, 80 Fed. Reg. at 64,664. In doing so, the States and their
power plants were under no obligation to use the three specific
methods that the EPA had identified in determining the best
system of emission reduction. Rather, consistent with Section
7411(d)’s cooperative federalism approach, States were free to
choose any measures, approaches, or technologies that they
deemed appropriate to meet the federal guidelines. For
example, they could adopt technological controls already in use
by some power plants like carbon capture and sequestration (by
which carbon dioxide is captured from the plant’s flue gas
before it is emitted and then securely stored so it cannot reach
the atmosphere) or co-firing (where fuels that release less
carbon dioxide are burned alongside fuels that release more to
reduce the amount of the latter used). See id. at 64,883. The
EPA also suggested that States might rely on emissions-trading
32
programs (often referred to as cap-and-trade) and other
potential compliance strategies. Id. at 64,887.

The EPA found that its proposed approach was “consistent
with, and in some ways mirrors, the interconnected,
interdependent and highly regulated nature of the utility power
sector[]” and its grid, as well as “the daily operation of affected
[power plants] within this framework, and the critical role of
utilities in providing reliable, affordable electricity at all times
and in all places within this complex, regulated system.” Clean
Power Plan, 80 Fed. Reg. at 64,678.

The Clean Power Plan was challenged in this court. West
Virginia v. EPA, No. 15-1363 (and consolidated cases) (D.C.
Cir. Oct. 23, 2015). After we heard argument en banc, but
before we issued a decision, that litigation was held in
abeyance and ultimately dismissed as the EPA reassessed its
position. No. 15-1363, Docs. 1673071, 1806952.

D. T HE ACE RULE

In 2019, the EPA issued a new rule that repealed and
replaced the Clean Power Plan: The Affordable Clean Energy
(ACE) Rule. See Repeal of the Clean Power Plan; Emission
Guidelines for Greenhouse Gas Emissions from Existing
Electric Utility Generating Units; Revisions to Emission
Guidelines Implementing Regulations, 84 Fed. Reg. 32,520
(July 8, 2019). That Rule is the subject of this litigation.

1. Repeal of the Clean Power Plan

At the outset, the ACE Rule repealed the Clean Power
Plan. The EPA explained that it felt itself statutorily compelled
to do so because, in its view, “the plain meaning” of Section
7411(d) “unambiguously” limits the best system of emission
reduction to only those measures “that can be put into operation
33
at a building, structure, facility, or installation.” ACE Rule, 84
Fed. Reg. at 32,523–32,524. Because the Clean Power Plan’s
best system was determined by using some emission control
measures that the EPA characterized as physically operating
off the site of coal-fired power plants—such as some forms of
generation shifting and emissions trading—the EPA concluded
that it had no choice but to repeal the Plan. Id. The EPA
emphasized “that [its] action is based on the only permissible
reading of the statute and [it] would reach that conclusion even
without consideration of the major question doctrine,” while
adding that application of that latter doctrine “confirms the
unambiguously expressed intent” of Section 7411. Id. at
32,529.

2. Best System of Emission Reduction

Considering its authority under Section 7411 to be
confined to physical changes to the power plants themselves,
the EPA’s ACE Rule determined a new best system of emission
reduction for coal-fired power plants only. The EPA left
unaddressed in this rulemaking (or elsewhere) greenhouse gas
emissions from other types of fossil-fuel-fired power plants,
such as those fired by natural gas or oil. ACE Rule, 84 Fed.
Reg. at 32,533.

The EPA’s proposed system relied solely on heat-rate
improvement technologies and practices that could be applied
at and to existing coal-fired power plants. ACE Rule, 84 Fed.
Reg. at 32,525, 32,537. The EPA selected only seven heat-rate
improvement techniques as components of its best system. Id.
at 32,537. Six of those measures were new-to-the-plant
technologies or “equipment upgrades.” Id. at 32,536–32,537
(naming as part of the best system (1) adding or upgrading
neural networks and intelligent sootblowers; (2) upgrading
boiler feed pumps; (3) replacing or upgrading air heater and
34
duct leakage control devices; (4) adding variable frequency
drives in feed pumps and induced-draft fans; (5) blade path
upgrades; and (6) redesigning or replacing economizers). The
seventh measure was the use of “best operating and
maintenance practices” implementing heat-rate improvement
techniques. Id. at 32,537, 32,540. The EPA limited itself to
techniques that could be “applied broadly” to the Nation’s coal-
fired plants, which primarily amounted to upgrades to existing
equipment. Id. at 32,536.

The EPA explained that only five of the seven listed
techniques directly reduce the heat rate of power plants. See
ACE Rule, 84 Fed. Reg. at 32,538–32,540. The other two
techniques—replacing or upgrading the boiler feed pump and
installing variable frequency drives—serve to reduce the
amount of energy that a power plant must use to run its own
general operations. Id. at 32,538–32,539.3 So those two
techniques do not make a power plant more efficient in turning
coal into power, but instead allow power plants to dispatch
more of the power they produce to the grid rather than using it
internally. Id.

3
The boiler feed pump is a device that is used to pump water
into the boiler. 84 Fed. Reg. at 32,538. It consumes a “large
fraction” of the power used to run the plant. Id. Because the boiler
feed pump requires so much energy, the EPA suggested that
“maintenance on these pumps should be rigorous to ensure both
reliability and high-efficiency operation.” Id. Variable frequency
drives “enable[] very precise and accurate speed control” of both
boiler feed pumps and “induced draft (ID) fans,” which “maintain
proper flue gas flow through downstream air pollutant control
equipment[.]” Id. at 32,539. This precise control would reduce the
excess use of fans and pumps, requiring less energy. See id.
35
The EPA identified two of its other chosen techniques—
blade path and economizer upgrades—as the measures that, of
all the considered technologies, were “expected to offer some
of the largest [heat-rate] improvements.” ACE Rule, 84 Fed.
Reg. at 32,537 (showing table predicting highest heat-rate
improvement range in economizer redesign or replacements
and blade path upgrades).4

But the EPA then stated that it expected some power plants
would not adopt those two technologies because their use could
trigger additional regulation that the companies would find
burdensome. 84 Fed. Reg. at 32,537 (“[B]ased on public
comments * * *, [blade path upgrades and economizer redesign
or replacement] are [heat-rate improvement] technologies that
have the most potential to trigger [New Source Review]
requirements.”). In fact, the EPA did not model those two
techniques in its regulatory impact analysis precisely because
it was unlikely that they would be adopted. J.A. 1656–1657.

Finally, the EPA acknowledged that the proposed
technologies could create a “rebound effect.” ACE Rule, 84
Fed. Reg. at 32,542. A rebound effect means that net carbon
dioxide emissions actually increase as a result of the efficiency
improvements made by power plants. Id. This happens
because, as the efficiency upgrades make coal-based energy
cheaper to produce, coal-fired power plants will have an
incentive to run more often, thereby increasing their overall
emissions. Id. The EPA found that risk of increased emissions
irrelevant because its best system of emission reduction “is
aimed at improving a source’s emissions rate performance at

4
“Blade path upgrades” consist of upgrades to the steam
turbine. Economizers are heat-exchange devices that “capture waste
heat from boiler flue gas” and use that captured heat to help heat the
boiler feedwater. Id. at 32,540.
36
the unit-level,” rather than reducing the overall volume of
emissions by individual sources. Id. at 32,543.

In choosing its seven proposed power-plant-based heat-
rate improvement technologies, the EPA excluded from its best
system several other suggested methods of reducing emissions,
including (1) natural gas co-firing, repowering, and refueling;
(2) biomass co-firing; and (3) carbon capture and storage
technologies. ACE Rule, 84 Fed. Reg. at 32,543–32,547. The
EPA rejected biomass co-firing primarily because “any
potential net reductions in emissions from biomass use occur
outside of the regulated source,” and so do not fall within the
EPA’s reading of Section 7411(d) as confined to emission
limits imposed at and to individual plants. Id. at 32,546. The
EPA excluded natural gas co-firing and carbon capture and
storage from its own best system, citing cost, geographical, and
operational concerns. Id. at 32,544–32,545, 32,547–32,548.
The EPA provided that sources could choose to use natural gas
co-firing or carbon capture—but not biomass co-firing—to
meet state-established standards of performance. Id. at 32,555.

3. Degree of Emission Limitation Achievable

Having determined its best system of emission reduction,
the EPA then purported to prescribe the “degree of emission
limitation achievable,” which States could use to create their
own standards of performance. 42 U.S.C. § 7411(a)(1). What
the EPA produced as its emission guidelines was a chart that
prescribed heat-rate improvement “ranges” for each of the
EPA’s chosen heat-rate improvement technologies, organized
by power plants of differing sizes. ACE Rule, 84 Fed. Reg. at
32,537. The ranges show how much heat-rate improvement
can be “expected” from use of each of the identified
technologies. Id.
37
The EPA was explicit, though, that the “potential” range
of heat-rate reduction was only illustrative and that the actual
reduction for each of the EPA’s chosen technologies would be
“unit-specific” and would “depend upon a range of unit-
specific factors.” ACE Rule, 84 Fed. Reg. at 32,537–32,538.
In that way, the ACE Rule made States responsible for
evaluating “[heat-rate improvement] potential, technical
feasibility, and applicability for each of the [best system of
emission reduction] candidate technologies” on a power-plant–
by–power-plant basis. Id. at 32,538. The ACE Rule expressly
left States free to establish their own standards of performance
for their power plants that “reflect a value of [heat-rate
improvement] that falls outside” the ranges provided in the
EPA’s chart. Id. (emphasis added). In other words, the
minimums listed in the EPA’s emission-reduction chart were
only suggestions.

The EPA explained that its non-mandatory ranges of
efficiency reduction were valid because the applicability of the
heat-rate improvement techniques to different plants and the
effectiveness of each power plant’s existing technology may
vary. See ACE Rule, 84 Fed. Reg. at 32,538 (stating that “not
all” of the technologies would be “applicable or warranted at
the level of a particular facility due to source-specific factors
such as the site-specific operational and maintenance history,
the design and configuration, [or] the expected operating
plans”).

The EPA predicted that its ACE Rule would reduce carbon
dioxide emissions by less than 1% from baseline emission
projections by 2035. J.A. 1651. That calculation did not
reflect emission increases that could result from the rebound
effect.
38
4. Implementing Regulations

The ACE Rule included some new regulations under
Section 7411(d). ACE Rule, 84 Fed. Reg. at 32,575-32,584
(codified at 40 C.F.R. pt. 60, subpart Ba). As relevant here, the
regulations significantly extend the States’ deadlines for the
development and submittal of their plans for emission
reduction from nine months to three years. See 40 C.F.R.
§ 60.23a(a)(1). Similarly, the new regulations extend the
EPA’s deadline to act on those plans from four months to one
year. 40 C.F.R. § 60.27a(b). The new regulations also extend
the EPA’s deadline to substitute its own plan for a non-
compliant State’s plan from six months after the submission
deadline to two years after a finding that the plan was
incomplete, disapproved, or unsubmitted. See 40 C.F.R.
§ 60.27a(c). Finally, the requirement that States demonstrate
compliance progress is now triggered only where a State’s
compliance schedule stretches more than two years from when
its plan was originally due, as opposed to the one-year period
in the prior regulations. See 40 C.F.R. § 60.24a(d).

E. PETITIONS FOR REVIEW

Twelve petitions for review of the ACE Rule were timely
filed in this court and consolidated in this case. Nos. 19‑1140
(lead case), 19‑1165, 19‑1166, 19‑1173, 19‑1175, 19‑1176,
19‑1177, 19‑1179, 19‑1185, 19‑1186, 19‑1187, 19‑1188. The
petitioners fall into three groups.

The first grouping consists of petitioners who seek review
of the ACE Rule’s conclusion that Section 7411 only permits
emission reduction measures that can be implemented at and
applied to the source. Those petitioners include (i) a coalition
of State and municipal governments; (ii) power utilities;
39
(iii) trade associations from the renewable energy industry; and
(iv) several public health and environmental advocacy groups.5

The second grouping is petitioners who challenge the ACE
Rule’s imposition of any emission limits as unlawful because,
in their view, (i) the EPA failed to make a specific
endangerment finding for carbon dioxide emitted from existing
power plants; (ii) the EPA’s regulation of mercury emissions
from coal-fired power plants under Section 7412 precludes the
regulation of greenhouse gas emissions under Section 7411;
and (iii) the EPA should have regulated carbon dioxide from
stationary sources, including power plants, under the NAAQS
program, 42 U.S.C. §§ 7408–7410.

The third petitioner group is the Biogenic CO2 Coalition.
They object only to the ACE Rule’s determination that States
may not count biomass co-firing as a method of complying
with numerical emission limits.

F. JURISDICTION AND STANDARD OF REVIEW

This court has jurisdiction to review these petitions under
the Clean Air Act. 42 U.S.C. § 7607(b)(1); see also Sierra
Club v. EPA, 955 F.3d 56, 61 (D.C. Cir. 2020).

We may set aside the ACE Rule if it is “arbitrary,
capricious, an abuse of discretion, or otherwise not in
accordance with law.” 42 U.S.C. § 7607(d)(1)(C),
(d)(9)(A); see also Maryland v. EPA, 958 F.3d 1185, 1196
(D.C. Cir. 2020) (“[W]e apply the same standard of review
under the Clean Air Act as we do under the Administrative

5
The public health and environmental advocacy groups also
challenge the third prong of the ACE Rule—the new implementing
regulations—as arbitrary and capricious.
40
Procedure Act.”) (quoting Allied Local & Reg’l Mfrs. Caucus
v. EPA, 215 F.3d 61, 68 (D.C. Cir. 2000)).

II. SECTION 7411

A. STATUTORY CONTEXT

In enacting the Clean Air Act, “Congress delegated to EPA
the decision whether and how to regulate carbon-dioxide
emissions from powerplants.” American Elec. Power Co. v.
Connecticut (AEP), 564 U.S. 410, 426 (2011). As the Supreme
Court has observed, 42 U.S.C. § 7411 “speaks directly to” and
outlines the framework for that regulation. Id. at 424 (internal
quotation marks omitted). Specifically, Section 7411 marks
out a pair of distinct regulatory tracks for stationary sources of
air pollutants. See 42 U.S.C. § 7411(a)(2), (6). The first track
applies to new sources, id. § 7411(b), and the second to existing
sources, id. § 7411(d). The statute calls for federal-state
cooperation in regulating existing sources, affording distinct
roles to the federal and state agencies in arriving at what
Section 7411 calls “standards of performance” for the emission
of air pollutants. Id. § 7411(a)(1), (c), (d)(1).

The regulatory regimes for new and existing sources differ
in the process by which such standards are established—and
the roles played by the respective regulatory actors. The Act
assigns the EPA the main regulatory role in specifying the new-
source pollution controls: After the EPA determines that a
particular “category of sources * * * causes, or contributes
significantly to, air pollution which may reasonably be
anticipated to endanger public health or welfare,” it publishes
regulations establishing standards of performance for new
sources in that category. Id. § 7411(b)(1).

The process for regulating existing sources—which raise
distinct concerns about sunk costs and the health and
41
environmental effects of older processes—involves more
actors and steps. Regulation of a given category of existing
sources is triggered by the same EPA air-pollution
determination as for new sources. But for existing sources the
Act adopts a cooperative-federalism approach that leaves the
States discretion in determining how their State and industry
can best meet quantitative emissions guidelines established by
the EPA. See AEP, 564 U.S. at 424. Under Section 7411(d),
the EPA and the States thus have distinct but complementary
roles subject to different procedures and limitations. See 42
U.S.C. § 7411 (a)(1), (d)(1). This case concerns the mechanics
of that cooperative framework for existing sources and,
specifically, restrictions the Agency now claims the statute
imposes on regulation of the air pollutants those sources emit.

Two provisions of Section 7411 shape the existing-source
framework. Subsection (a)(1) defines a standard of
performance, by reference to the “degree of emission
limitation” that the EPA determines is “achievable,” as:

a standard for emissions of air pollutants which
reflects the degree of emission limitation achievable
through the application of the best system of emission
reduction which (taking into account the cost of
achieving such reduction and any nonair quality
health and environmental impact and energy
requirements) the Administrator determines has been
adequately demonstrated.

42 U.S.C. § 7411(a)(1).

Subsection (d)(1), in turn, requires the Secretary to set up
a system by which willing States can submit to the EPA “a plan
which [] establishes standards of performance for any existing
source.” Id. § 7411(d)(1). Only “where [a] State fails to submit
a satisfactory plan” may the EPA step in and directly
42
promulgate standards of performance for existing sources. Id.
§ 7411(d)(2).

Putting these two provisions together results in what are
best understood as three distinct steps involving three sets of
actors, each exercising a degree of leeway in choice of control
measures. See ACE Rule, 84 Fed. Reg. at 32,533, 32,549–
32,550; Clean Power Plan, 80 Fed. Reg. at 64,665–64,666.

First, under subsection (a)(1), the EPA determines the
“best system of emission reduction” that is “adequately
demonstrated,” taking into consideration certain enumerated
statutory criteria: cost, any nonair quality health and
environmental impacts, and energy requirements. 42 U.S.C.
§ 7411(a)(1). The Agency then issues emission guidelines that
quantify the “degree of emission limitation achievable through
the application of the best system” it has identified. Id.; 40
C.F.R. § 60.22a; see AEP, 564 U.S. at 424; EPA Br. 21–22;
ACE Rule, 84 Fed. Reg. at 32,523, 32,551.

Second, under subsection (d)(1), States issue standards of
performance for existing sources that comply with the EPA’s
emission guidelines and “reflect” the achievable degree of
emission limitation set in those guidelines. AEP, 564 U.S. at
424; 42 U.S.C. § 7411(d)(1); 40 C.F.R. § 60.23a; see also
Clean Power Plan, 80 Fed. Reg. at 64,666. That the standards
must “reflect” the emission guidelines does not mean that they
must embody the methods EPA contemplated in identifying the
best system; rather, the States have flexibility in determining
the specifics of the standards they issue so long as they
accomplish the “degree of emission limitation” the EPA
calculated based on its “best system.”

Third, the operators of regulated stationary sources
implement measures to ensure they will in practice comply
with the standards of performance their state agency has
43
established for them. See ACE Rule, 84 Fed. Reg. at 32,555.
States often grant regulated entities some discretion in how
they meet those standards. See, e.g., N.Y. COMP. CODES R. &
REGS. Tit. 6 § 201-6.4(f) (2013) (describing the “operational
flexibility” afforded to Title V facility owners in New York
State to “propose a range of operating conditions that will allow
flexibility [for a facility] to operate under more than one
operating scenario”).

The issue before us arises at the first step—the EPA’s
determination of the best system of emission reduction. In the
Clean Power Plan, the Agency determined that the best system
was one that both improved the heat rate at power plants and
prioritized generation from lower-emitting plants ahead of
high-emitting plants. Clean Power Plan, 80 Fed. Reg. at
64,707. The EPA then calculated specific emission reductions
achievable through application of that best system that it
published as emission guidelines for States. Id. Had the Clean
Power Plan gone into effect, States would then have submitted
to the EPA plans based on the Agency’s guidelines that
established standards of performance for sources in their
jurisdictions, as provided for in subsection (d)(1). The Clean
Power Plan left States flexibility in the measures they included
in their plans, so long as they achieved a reduction in emissions
at least as great as that achieved by EPA-established
quantitative guidelines. See, e.g., id. at 64,665, 64,756–64,757,
64,734–64,737, 64,832–64,837. And it further allowed States,
at their option, to give leeway to sources to select alternate
compliance measures to make the requisite reductions. See id.
at 64,834–64,835.

Based on what it now perceives to be an express and
unambiguous textual limitation in Section 7411 that it says the
Clean Power Plan overlooked, the EPA repealed that Plan and
replaced it with the ACE Rule. The EPA’s new reading of the
44
statute requires the Agency, in modeling its “best system of
emission reduction,” to consider only emission-reduction
measures that “can be applied at and to a stationary source.”
ACE Rule, 84 Fed. Reg. at 32,534; see also id. at 32,526–
32,532.

We address below the EPA’s arguments regarding how the
text and structure of Section 7411 purportedly support this
limitation. That discussion is necessarily somewhat abstract
and technical. So, for starters, it is worth bringing the matter
more concretely into view.

Consider the effect the EPA’s new statutory interpretation
had on its resulting Rule. First, because generation shifting is
not, in the EPA’s view, a measure that can be applied “at and
to” any one individual source, the ACE Rule limits the best
system of emission reduction to heat-rate improvements alone.
84 Fed. Reg. at 32,534–32,535. Then, instead of publishing
emission guidelines quantifying emission reductions
achievable through application of the best system, the ACE
Rule identifies what the Agency has determined are the most
effective heat-rate technologies available and a potential range
of heat-rate improvements achievable through application of
each of those technologies. Id. 32,535–32,537.

As under the Clean Power Plan, the ACE Rule grants
States flexibility in establishing standards of performance for
sources pursuant to the Agency’s emission guidelines. Unlike
the Clean Power Plan, however, the ACE Rule does not require
that the States reach any specified minimum emission
reduction. Instead, States must merely “evaluate the
applicability of each of the candidate technologies” to sources
within their jurisdiction and report their conclusions back to the
Agency. ACE Rule, 84 Fed. Reg. at 32,550, 32,538–32,561.

The Rule recites that regulated entities have “broad
45
discretion” in meeting state-established standards, ACE Rule,
84 Fed. Reg. at 32,555, yet at the same time the Rule deems
impermissible any compliance measure that cannot be applied
at and to the source, id. The ACE Rule thereby disqualifies
compliance by, for example, burning biofuel, id. at 32,557–
32,558, which emits recently captured carbon dioxide, in
contrast to fossil fuels’ release of carbon dioxide stored away
millions of years ago. See generally Center for Biological
Diversity v. EPA, 722 F.3d 401, 405–406 (D.C. Cir. 2013).

The question here is a relatively discrete one. We are not
called upon to decide whether the approach of the ACE Rule is
a permissible reading of the statute as a matter of agency
discretion. Instead, the sole ground on which the EPA defends
its abandonment of the Clean Power Plan in favor of the ACE
Rule is that the text of Section 7411 is clear and unambiguous
in constraining the EPA to use only improvements at and to
existing sources in its best system of emission reduction.

The EPA contends that its current interpretation is “the
only permissible interpretation of the scope of the EPA’s
authority.” ACE Rule, 84 Fed. Reg. at 32,535. Our task is to
assess whether Section 7411 in fact compels the EPA’s new
interpretation. And because “deference to an agency’s
interpretation of a statute is not appropriate when the agency
wrongly believes that interpretation is compelled by
Congress,” Peter Pan Bus Lines, Inc. v. Fed. Motor Carrier
Safety Admin., 471 F.3d 1350, 1354 (D.C. Cir. 2006) (quoting
PDK Labs., Inc. v. DEA, 362 F.3d 786, 798 (D.C. Cir. 2004)
(internal quotation marks omitted)), we may not defer to the
EPA’s reading if it is but one of several permissible
interpretations of the statutory language, see Negusie v. Holder,
555 U.S. 511, 521 (2009). That is, the “regulation must be
declared invalid, even though the agency might be able to adopt
the regulation in the exercise of its discretion, if it ‘was not
46
based on the agency’s own judgment but rather on the
unjustified assumption that it was Congress’ judgment that
such a regulation is desirable” or required. Prill v. NLRB, 755
F.2d 941, 948 (D.C. Cir. 1985) (quoting FCC v. RCA
Commc’ns, 346 U.S. 86, 96 (1953) (formatting modified));
accord Arizona v. Thompson, 281 F.3d 248, 259 (D.C. Cir.
2002) (quoting Prill, 755 F.2d at 948).

For the reasons explained below, Section 7411 does not,
as the EPA claims, constrain the Agency to identifying a best
system of emission reduction consisting only of controls “that
can be applied at and to a stationary source.” ACE Rule, 84
Fed. Reg. at 32,534. The EPA here “failed to rely on its own
judgment and expertise, and instead based its decision on an
erroneous view of the law.” Prill, 755 F.2d at 956. We
accordingly must vacate and remand to the Agency “to
interpret the statutory language anew.” Peter Pan Bus Lines,
471 F.3d at 1354.

1. Text

As just noted, Section 7411 contemplates distinct roles for
the EPA and the States in regulating existing stationary
sources. See 42 U.S.C. § 7411(a)(1) (granting authority to the
EPA to designate the best system and determine achievable
degree of emissions reduction); id. § 7411(d)(1) (outlining the
States’ role in setting standards of performance for their
sources). Nevertheless, the EPA now contends that language
in Section 7411(a)(1) and (d)(1) “unambiguously limits the
[best system of emission reduction] to those systems that can
be put into operation at a building, structure, facility, or
installation.” ACE Rule, 84 Fed. Reg. at 32,524 (emphasis in
original); see id. at 32,528; EPA Br. 70.

In the Agency’s current view, the only pollution-control
methods the Administrator can consider in selecting the “best
47
system of emission reduction” within the meaning of Section
7411(a) are add-ons or retrofits confined to the level of the
individual fossil-fuel-fired power plant. ACE Rule, 84 Fed.
Reg. at 32,524. That is so even though the record before the
EPA shows that generation shifting to prioritize use of the
cleanest sources of power is one of the most cost-effective
means of reducing emissions that plants have already adopted
and that have been demonstrated to work, and that generation
shifting is capable of achieving far more emission reduction
than controls physically confined to the source. See, e.g., Clean
Power Plan, 80 Fed. Reg. at 64,693, 64,728–64,729; 2 J.A. 598;
Grid Experts Amicus Br. 13–16. In other words, the EPA reads
the statute to require the Agency to turn its back on major
elements of the systems that the power sector is actually and
successfully using to efficiently and cost-effectively achieve
the greatest emission reductions. See Grid Experts Amicus Br.
22 (observing that the ACE Rule “imposes greater abatement
costs on industry than other approaches would to achieve the
same effect”).

The Clean Power Plan could not stand, the EPA now
concludes, because its consideration of generation shifting
exceeded the Agency’s narrow authority under Section 7411’s
plain text. ACE Rule, 84 Fed. Reg. at 32,526–32,527. In
promulgating the Clean Power Plan, the EPA read “system of
emission reduction” to mean “a set of measures that work
together to reduce emissions and that are implementable by the
sources themselves.” Clean Power Plan, 80 Fed. Reg. at
64,762. And it concluded that both heat-rate improvements
and generation shifting “are components of a best system of
emission reduction for the affected [electricity generating
units] because they entail actions that the affected [units] may
themselves undertake that have the effect of reducing their
emissions.” Id. at 64,709 (internal quotation marks omitted).
48
All of that is wrong, the EPA has since decided. “[T]he
Agency now recognizes that Congress ‘spoke to the precise
question’ of the scope of [42 U.S.C. § 7411](a)(1) and clearly
precluded the unsupportable reading of that provision asserted
in the [Clean Power Plan].” ACE Rule, 84 Fed. Reg. at 32,527.
The EPA insists that its current reading is mandated by the
statutory text.

It is the EPA’s current position that is wrong. Nothing in
Section 7411(a)(1) itself dictates the “at and to the source”
constraint on permissible ingredients of a “best system” that the
Agency now endorses. For the EPA to prevail, its reading must
be required by the statutory text. Peter Pan Bus Lines, 471
F.3d at 1354. It fails for at least three reasons, any of which is
alone fatal.

First, the plain language of Section 7411(a)(1), the root of
the EPA’s authority to determine the best system, announces
its own limitations. Those limitations simply do not include
the source-specific caveat that the EPA now interposes and
casts as unambiguous.

Second, there is no basis—grammatical, contextual, or
otherwise—for the EPA’s assertion that the source-specific
language of subsection (d)(1) must be read upstream into
subsection (a)(1) to equate the EPA’s “application of the best
system” with the controls States eventually will apply “at and
to” an individual source. As the EPA at times acknowledges,
the two subsections address distinct steps in the regulatory
process, one focused on the EPA’s role and the other focused
on the States’. Any question as to which limitations pertain to
each regulatory actor cannot reasonably be said to have been
resolved by Congress in favor of the unambiguous meaning the
EPA now advocates.

Third, even if subsections (a)(1) and (d)(1) were read
49
together in the way the EPA proposes, they would not confine
the EPA to designating a best system consisting of at-the-
source controls. The EPA’s entire theory hinges on the
Agency’s unexplained replacement of the preposition “for” in
“standards of performance for any existing source” with the
prepositions “at” and “to.” Yet the statutory text calls for
standards of performance “for” existing sources. Emission-
reduction measures “for” sources may readily be understood to
go beyond those that apply physically “at” and “to” the
individual source. Emissions trading, for example, might be a
way “for” a source to meet a standard of performance.

The shortcomings of its statutory interpretation are more
than enough to doom the Agency’s claim that Section 7411
announces an unambiguous limit on the best system of
emission reduction. The issue is not whether the EPA’s
counterarguments to each of these points might show its
interpretation to be permissible as an exercise of discretion.
Again, the EPA has not claimed to be exercising any such
discretion here. It insists instead that the unambiguous terms
of the statute tie its hands.

After reviewing what Section 7411 clearly says about the
nature and limits of the “best system of emission reduction”
that Congress called on the EPA to determine, we take up each
of the EPA’s arguments to show why Section 7411 does not
unambiguously support its at-the-source restriction.

a. Section 7411(a) Defines the Best System

The EPA acknowledges, as it must, that Section 7411(a) is
the source of the EPA’s authority and responsibility to
determine the best system of emission reduction for existing
sources and set corresponding emission guidelines. See, e.g.,
ACE Rule, 84 Fed Reg. at 32,534. Indeed, that is the only
subsection in which the term “best system of emission
50
reduction” appears. But the EPA offers no reading of
subsection (a)(1) itself.

Section 7411(a)(1) expresses Congress’ expectation that
the EPA will study all “adequately demonstrated” means of
emission reduction. And it directs the EPA to draw on
“adequately demonstrated” methods to determine the “best”
system to reduce emissions. Congress imposed no limits on
the types of measures the EPA may consider beyond three
additional criteria: cost, any nonair quality health and
environmental impacts, and energy requirements. 42 U.S.C.
§ 7411(a)(1). Congress largely called on the expert judgment
of the EPA to determine for a particular source category and
pollutant which already-demonstrated methods compose the
“best system.”

Because it did not set out separate definitions for either
“system” or “best,” those words take their ordinary meanings.
See Sandifer v. United States Steel Corp., 571 U.S. 220, 227
(2014). Webster’s Dictionary offers a representative definition
of “system” contemporaneous with the Act’s adoption: “[A]
complex unity formed of many often diverse parts subject to a
common plan or serving a common purpose.” System,
WEBSTER’S THIRD NEW INTERNATIONAL D ICTIONARY OF THE
ENGLISH LANGUAGE UNABRIDGED 2322 (2d ed. 1968). The
superlative “best” as applied to a “system of emission
reduction” plainly places a high priority on efficiently and
effectively reducing emissions. See Best, Merriam-Webster,
https://www.merriam-webster.com/dictionary/best (last visited
Jan. 11, 2021) (“excelling all others,” “offering or producing
the greatest advantage, utility, or satisfaction”).

The ordinary meanings of these terms “reflect[] an
intentional effort to confer the flexibility necessary” for
effective regulation appropriate to the context. Massachusetts
51
v. EPA, 549 U.S. 497, 532 (2007). As the Supreme Court has
acknowledged, “the degree of agency discretion that is
acceptable varies according to the scope of the power
congressionally conferred.” Whitman v. American Trucking
Ass’n, 531 U.S. 457, 475 (2001); see Gaughf Props., L.P. v.
Commissioner, 738 F.3d 415, 424–425 (D.C. Cir. 2013);
Sabre, Inc. v. Department of Transp., 429 F.3d 1113, 1122,
1124–1125 (D.C. Cir. 2005). Congress in Section 7411
deliberately charged the EPA with identifying the best system
of emission reduction to keep pace with escalating threats to air
quality, and, within expressed limits, empowered it to make the
judgments how best to do so.

The Agency simply ignores how the statutory text defines
the “best system of emission reduction,” asserting instead that
definitional language does not confer regulatory authority. See,
e.g., EPA Br. 58–59 (“[I]t is not Section 7411(a) (‘Definitions’)
that grants the agency authority to act.”). Section 7411(a)(1)’s
designation as a definitional provision deprives it of standalone
meaning, the EPA contends. The EPA instead reads it as
“subsidiary” to Section 7411(d), regarding state standards of
performance for existing sources. EPA Br. 58. But Congress
does indeed use definitional provisions to confer regulatory
authority. See, e.g., Weinberger v. Bentex Pharm, Inc., 412
U.S. 645, 652–653 (1973) (holding that the statutory definition
of “new drug” confers authority upon the FDA). That is
precisely what it did in Section 7411(a)(1). See Sierra Club v.
Costle, 657 F.2d 298, 321 (D.C. Cir. 1981) (describing Section
7411(a)(1) as authorizing the EPA to determine the best system
of emission reduction and regulate accordingly); 40 C.F.R.
60.22a.

The EPA offers no support—apart from its own new-
found version of “statutory interpretation 101,” EPA Br. 65—
for ignoring how the Act itself defines and limits the “best
52
system” determination. Nor does it offer any sound
justification for importing language from a different provision
governing States’ “standards of performance.” The EPA’s “at
and to the source” limitation on “best system” finds no footing
in the text of Section 7411(a)(1).

b. Section 7411(d)(1) Does Not Change the Definition

Even taking the EPA’s argument on its own terms does not
work because Section 7411(d)(1)’s text and statutory context
get it no further. To support its narrow reading of the EPA’s
authority to determine the “best system,” the Agency focuses
on the phrase “through the application of” in Section
7411(a)(1). That provision defines a “standard of
performance” as an emission standard that “reflects the degree
of emission limitation achievable through the application of the
best system of emission reduction[.]” The EPA says the
“application” phrase “requires both a direct object and an
indirect object.” ACE Rule, 84 Fed. Reg. at 32,524; accord
EPA Br. 66–68. And, it continues, Congress cannot have
meant to leave its indirect object undefined. The EPA says that,
grammatically speaking, someone must apply something (the
direct object) to something else (the indirect object). EPA Br.
115–116, 118–119. It then picks its preferred, narrow indirect
object from a different statutory subsection and casts that
object as the only statutorily permissible choice. See 84 Fed
Reg. at 32,524.

The EPA locates an indirect object in Section 7411(d).
Unlike subsection (a)(1), subsection (d)—entitled “Standards
of performance for existing sources”—explicates an indirect
object. 42 U.S.C. § 7411(d). Borrowing from subsection (d),
then, the EPA imports into subsection (a)(1) a limitation of the
“best system of emission reduction” to measures that can be
applied “to and at an individual existing source—i.e., any
53
building or facility subject to regulation.” EPA Br. 58
(emphasis added); see also ACE Rule, 84 Fed. Reg. at 32,534.

But the language to which the EPA points supplies the
indirect object only of “standards of performance” adopted by
States pursuant to Section 7411(d)(1), not of the EPA’s “best
system of emission reduction” determined pursuant to Section
7411(a)(1). The latter phrase does not even appear in Section
7411(d)(1). To reach its preferred result, the Agency invokes
surmise rather than statutory text. It insists that the limitations
on States’ standards of performance in Section 7411(d)(1)—
the second step in the regulatory process—must be read
upstream to limit the EPA’s “best system of emission
reduction” in subsection (a)(1). Nothing in the statute so
requires.

In the text, States’ standards of performance need only
“reflect” the emission guidelines (or “degree of emission
limitation achievable”) the EPA calculates based on the “best
system of emission reduction” it determines. As laid out in the
statute and explained above, those state-developed “standards
of performance” follow on but are legally and functionally
distinct from the “best system” that the EPA develops. The
EPA is simply wrong that the statute clearly and
unambiguously requires that the unstated indirect object of
“application of the best system of emission reduction” under
Section 7411(a)(1) must be the same as the indirect object of
States’ standards of performance as stated in Section
7411(d)(1).

Neither does the grammatical rule the EPA invokes to
bridge the gap between these subsections hold up. The crux of
the EPA’s textual argument is that “the verb ‘to apply,’ requires
both a direct object and an indirect object.” ACE Rule, 84 Fed.
Reg. at 32,524; EPA Br. 66–68. The first obvious problem is
54
that, in the relevant passage of Section 7411(a)(1), Congress
did not use the verb “apply,” but rather the noun “application.”
The EPA acknowledges this distinction in passing in the ACE
Rule, but dismisses it without discussion, offering only that
“‘application’ is derived from the verb ‘to apply[.]’” 84 Fed.
Reg. at 32,524. That is, of course, true, as far as it goes. The
phrase “application of the best system of emission reduction”
is what is called a nominalization, a “result of forming a noun
or noun phrase from a clause or a verb.” Nominalization,
Merriam-Webster Dictionary https://www.merriam-
webster.com/dictionary/nominalization (last visited Jan. 11,
2021). Grammar assigns direct or indirect objects only to
verbs—not nouns. No objects are needed to grammatically
complete the actual statutory phrase. So much for the
grammatical imperative.

Even if we were to take the EPA’s leap to the verb “apply”
from the noun “application” that actually appears in the statute,
the Agency comes up short. The EPA is incorrect to insist that
the verb “apply” requires an indirect object. There is nothing
ungrammatical about the sentence “In its effort to reduce
emissions, the EPA applied the best system of emission
reduction.” The verb “apply,” like its nominalization, may
properly be used in a sentence with or without an explicit
indirect object. See Apply, THOMAS HERBST ET AL., A
VALENCY DICTIONARY OF ENGLISH 41–42 (Ian F. Roe et al.
eds., 2004) (listing examples of grammatically correct uses
with and without direct and indirect objects).6

6
Take, for instance, the following sentences: “It appears to
violate GATT regulations, but the rules for applying the regulations
are vague and the Netherlands has so far escaped censure”; “This
information may not apply in Scotland, which has a different legal
system.” Apply, THOMAS HERBST ET AL., A VALENCY DICTIONARY
55
The EPA’s shift from nominalization to verb does not, in
any event, accomplish much. Either way, the lack of an explicit
indirect object in Section 7411(a)(1) does not require that one
be borrowed from Section 7411(d)(1). Equally logical indirect
objects include, for example, the entire category of stationary
sources, or the air pollutant to be limited. In any event, the best
system cannot reasonably be said to be unambiguously
applicable only to the indirect object the EPA suggests.

The EPA faults the Clean Power Plan for reading
“application of” to be functionally equivalent to
“implementation of,” because “implement” “does not require
an indirect object.” EPA Br. 73. But neither does
“application.” So “application” textually supports adoption of
the Clean Power Plan just as well as “implementation.” Again,
so much for grammar mandating the EPA’s result.

The argument fails either way, but the fact is that Congress
used the nominalization “application of” the best system of
emission reduction. A nominalization enables the drafter to
leave certain information unspecified—namely, who is acting
and where their action is directed. See, e.g., George D. Gopen,
Who Done It? Controlling Agency in Legal Writing, Part II,
39 LITIG . 12, 12–13 (Spring 2013) (describing how
nominalizations create ambiguity). Legal writers, including
Congress, employ nominalizations all the time. And they do
so with the full awareness that their use preserves flexibility.

Congress reasonably built in leeway for the EPA to

OF ENGLISH 41–42 (examples from sections D1 and D5). Additional
examples abound. See, e.g., Apply, OXFORD ENGLISH DICTIONARY
(3d ed. 2008) (def. I.9) (“Crest bought the firm[,] and, by applying
its marketing and distribution muscle, has turned it into a $200
million category killer.”).
56
exercise technical expertise in applying Section 7411, given the
variety of pollution problems that it covers and the importance
of allowing States maneuvering room under the cooperative
federalism scheme. Congress may avoid specifying subjects,
objects, or other grammatical information because a degree of
adaptability suits the statutory role and purpose. One way
Congress can denote that it has delegated to an agency’s
judgment the task of filling in the on-the-ground details of a
statutorily defined program is by declining to dictate
grammatically optional information, see Lehrfeld v.
Richardson, 132 F.3d 1463, 1465–1466 (D.C. Cir. 1998);
Appalachian Power Co. v. EPA, 135 F.3d 791, 808–810 (D.C.
Cir. 1998), including an indirect object that the rules of
grammar do not require be explicitly stated, see, e.g., Peter Pan
Bus Lines, 471 F.3d at 1353–1354.

Even if an implicit indirect object can be surmised, there
is more than one plausible candidate here, and the statute does
not unambiguously dictate the object. There certainly is no
rule—grammatical or otherwise—that the specific indirect
object must be the one to which the EPA now points. At the
least, other contextually appropriate indirect objects of the
“best system” include the source category or the emissions.
The EPA has failed to establish that the sole and unambiguous
indirect object must be the individual source. The EPA, of
course, “may fill the gap[s] the Congress left,” and any such
“regulation is entitled to deference.” Gaughf Props., 738 F.3d
at 424; see also Appalachian Power, 135 F.3d at 811–812. But
in the ACE Rule and in its briefing here, the EPA has
assiduously denied the existence of any gap at all. That was
error.

c. EPA’s Reading Itself Falls Short

The third and equally fatal flaw in the EPA’s textual
57
analysis is its unexplained substitution of the prepositions “at”
and “to” where the text it would have us borrow from
subsection (d)(1) actually says “for” in referencing “standards
of performance for any existing source.” See, e.g., ACE Rule,
84 Fed. Reg. at 32,534. As we do with any words enacted by
Congress, we must give effect to the preposition it chose.
Cf. Telecommunications Res. & Action Ctr. v. FCC, 801 F.2d
501, 517–518 (D.C. Cir. 1986) (finding decisive Congress’ use
of the preposition “under” instead of “by”). The word
Congress actually used—“for” the source—lacks the site-
specific connotation on which the EPA’s case depends.

In its brief, the EPA presents the compound construction
it says inexorably follows from reading text from subsection
(a)(1) together with text from subsection (d)(1), and says it is
restricted to determining a “best system of emission reduction
for any building, structure, facility, or installation.” EPA
Br. 56 (formatting modified) (quoting 42 U.S.C. § 7411(a)(1),
(a)(3), (a)(6), (d)(1)). The Agency then asserts that “the natural
reading” of its proffered construction is that “the methods
planned would be ‘for’ and act at the level of the singular,
individual source.” Id. at 62 (emphasis added).

In the preamble to the ACE Rule, the EPA went further,
fully substituting the prepositions “at” and “to” in place of the
preposition “for” that actually appears in the text the Agency
says must be borrowed from subsection (d)(1). ACE Rule, 84
Fed. Reg. at 32,534. It relies on that further substitution to
insist that the best system of emission reduction designated by
the EPA must be limited to controls “that can be applied at and
to,” not “for,” “a stationary source.” Id.; see also id. at 32,524
(“at”); id. at 32,532, 32,534, 32,556 (“at and to”); id. at 32,555,
32,529 (“to and at”); id. at 32,543 (“at or to”); id. at 32,526 n.65
(“to or at”); EPA Br. 4, 58, 74. But nowhere in the ACE Rule
does the EPA explain this swap of one preposition for two
58
meaningfully more restrictive ones. See, e.g., 84 Fed. Reg. at
32,523–32,524, 32,534–32,535.

The EPA rewrites rather than reads the plain statutory text.
Section 7411(a)(1), even if cross-referenced to subsection
(d)(1) in the way the EPA says it must be, calls for the Agency
to determine “the degree of emission limitation achievable
through the application of the best system of emission
reduction for any existing source”—not the application of the
best system “at” and “to” such a source. And the word “for”
lacks the physical on-site connotation that is so critical to the
EPA’s reading of the statutory text. Indeed, a standard of
performance or system of emission reduction “for” a source
just means that the system is “with regard or respect to” or
“concerning” the source. See For, OXFORD ENGLISH
DICTIONARY (2d ed. 1989) (def. 26). In contrast, “at” and “to”
tend to connote direct physical proximity or contact. See At,
OXFORD ENGLISH D ICTIONARY (3d ed. 2008) (def. 1.a)
(“usually determining a point or object with which a thing or
attribute is practically in contact”); To, OXFORD ENGLISH
DICTIONARY (3d. ed 2008) (def. 5.a) (“Into (or in) contact with;
on, against”). A best system “for” a source thus might entail a
broader array of controls that concern but are not immediately
physically proximate to the source—such as, for instance,
generation shifting.

***

In sum, the straitened vision of the EPA’s best system that
the Agency espies in Section 7411 is simply not supported by
the text, let alone plainly and unambiguously required by it.
The Act calls on the EPA to determine the degree of emission
limitation achievable through “application of the best system
of emission reduction” without specifying the system’s indirect
object, and uses the preposition “for” when it calls on the States
59
to develop “standards of performance for existing sources.” 42
U.S.C. § 7411(a), (d). It simply does not unambiguously bar a
system of emission reduction that includes generation shifting.

The EPA’s position depends critically on words that are
not there. It erroneously treats a nominalization of a verb as
requiring an indirect object, collapses two separate functions
and provisions of the Act in order to supply a borrowed indirect
object, does so without any evidence that the borrowed indirect
object was what Congress necessarily intended, and narrowly
focuses the Agency’s authority on that indirect object by using
a different preposition from the one that actually appears in the
borrowed text. Each of those interpretive moves was a misstep.
Read faithfully, Section 7411(a)(1) lacks the straitjacket that
the EPA imposes.

Policy priorities may change from one administration to
the next, but statutory text changes only when it is amended.
The EPA’s tortured series of misreadings of Section 7411
cannot unambiguously foreclose the authority Congress
conferred. The EPA has ample discretion in carrying out its
mandate. But it may not shirk its responsibility by imagining
new limitations that the plain language of the statute does not
clearly require.

2. Statutory History, Structure, and Purpose

Even looking beyond the text does nothing to substantiate
the EPA’s proposed reading of Section 7411. See Kiewit
Power Constructors Co. v. Secretary of Labor, 959 F.3d 381,
395 (D.C. Cir. 2020) (Henderson, J.) (“To discern the
Congress’s intent, we generally examine the statutory text,
structure, purpose and its legislative history.”) (quoting
Lindeen v. SEC, 825 F.3d 646, 653 (D.C. Cir. 2016)). These
other tools of statutory interpretation underscore the flexibility
60
of Section 7411(a)’s text, not the cabined reading the EPA
proposes.

We begin by acknowledging Section 7411’s role within
the Clean Air Act. It is a catch-all, intended to ensure that the
Act achieves comprehensive pollution control by guaranteeing
that there are “no gaps in control activities pertaining to
stationary source emissions that pose any significant danger to
public health or welfare.” S. REP. NO. 91-1196, at 20 (1970).
In other words, Section 7411 is intended to reach pollutants that
do not fit squarely within the ambit of the Act’s other
regulatory provisions. It authorizes regulation of pollutants not
controlled by the other programs under the Act. The EPA does
not contest that greenhouse gases emitted by powerplants fit
that description.

The Agency points to statutory structure and history for
evidence that Congress restricted the “best system of emission
reduction” under Section 7411(a) to physical controls that are
applied “at and to” an existing source. But the history and
structure only confirm what the text shows: Nothing the EPA
has identified suggests that Congress in Section 7411 meant to
so constrict what might be part of a “best system of emission
reduction.”

The Congress that enacted Section 7411 was well aware
that what a “best system” might comprise is necessarily
dynamic and evolving. Congress’ main limitation was that the
“best system” selected by the EPA must be “adequately
demonstrated.” 42 U.S.C. § 7411(a)(1). And it stated three
other key criteria—cost, nonair quality health and
environmental impact, and energy requirements—as factors
the EPA must take into account. See id. With those parameters
in place, Congress largely left the identification of the best
61
system of emission reduction to the Agency’s expert scientific
judgment.

Consider cues from the Clean Air Act as a whole. In
contrast to other systemic benchmarks in the Act,
Section 7411(a)(1)’s prescription of the “best system of
emission reduction” is striking for its paucity of restrictive
language. References to more specific categories of emission-
reduction tools appear elsewhere in the Act. A provision
governing the Nitrogen Oxides Emissions Reduction Program,
for example, directs the Administrator to establish limits based
on the “degree of reduction achievable through the retrofit
application of the best system of continuous emission
reduction, taking into account available technology[.]” 42
U.S.C. § 7651f(b)(2) (emphasis added). The Act’s regional
haze program is likewise specific in its call for use of the “best
available retrofit technology.” Id. § 7491(b)(2)(A), (g)(2). The
specificity of those other provisions highlights the comparative
generality of Section 7411(a)’s reference to the “best system of
emission reduction.”

The sole provision the EPA highlights to shore up its at-
the-source theory only further undermines it. The EPA points
to the Act’s Prevention of Significant Deterioration (PSD)
program, 42 U.S.C. § 7475, and its requirement of controls at
least as stringent as limits set under Section 7411, see
id. § 7479(3), to argue that that “the interrelationship between
the two types of standards”—the best system of emission
reduction and the best available control technology—“is only
intelligible if the standards are in pari materia.” EPA Br. 85.
But the distinct roles of the two provisions make clear that the
limits in Section 7475 have no place in Section 7411(a)(1).

To qualify for a permit under the PSD program before a
source may be built or modified, an applicant must affirm that
62
it will apply to each source the “best available control
technology,” or BACT, to limit its emissions. 42 U.S.C.
§ 7475(a)(4). The statute defines BACT as the degree of
control that the permitting agency “determines is achievable for
such [major emitting] facility through application of
production processes and available methods, systems, and
techniques, including fuel cleaning, clean fuels, or treatment or
innovative fuel combustion techniques[.]” Id. § 7479(3). The
statute further provides that BACT cannot “result in emissions
of any pollutants which will exceed the emissions allowed by
any applicable standard established pursuant to [S]ection 7411
or 7412 of this title.” Id. § 7479(3). The listed BACT options,
EPA observes, are all physically applicable to the source unit.
EPA Br. 85.

But the EPA ignores a critical detail: The BACT
requirement applies only to newly constructed or modified
sources. See Alaska Dep’t of Env’t Conservation v. EPA, 540
U.S. 461, 472 (2004) (describing 42 U.S.C. § 7475). Any
standard established under Section 7411 and also “applicable,”
per the statutory cross-reference, to a facility regulated for
prevention of significant deterioration under Section 7475
would be a standard for new or modified sources established
pursuant to Section 7411(b). The BACT requirement does not
apply to the existing sources covered by the provision at issue
here, Section 7411(d). See New York v. EPA, 413 F.3d 3, 13
(D.C. Cir. 2005). Even if Section 7475 tracks Section 7411(b),
there is simply no conflict between, on one hand, requiring new
source construction to employ the newest and best at-the-
source control technologies and, on the other, empowering the
EPA to look to a wider range of ways to reduce emissions when
it regulates older, existing sources.

The anomaly of looking to Section 7475(a)(4) to confine
Section 7411 is highlighted by the fact that BACT permits are
63
required only in so-called “non-attainment” areas of the
country. See 42 U.S.C. §§ 7407, 7472, 7474. We are
unpersuaded that Congress buried a limit on the EPA’s
Section 7411 authority to address pollution from existing
sources throughout the Nation by making reference to a floor
for certain new facilities in certain parts of the country.

The statutory history of the BACT requirement further
demonstrates that Congress did not intend that it weaken
Section 7411(d). Sections 7475 and 7479 were enacted in the
1977 Clean Air Amendments, Pub. L. No. 95-95, §§ 165, 169,
91 Stat. 685, 735–742 (Aug. 7, 1977). In the very same
legislation, Congress restricted the best system of emission
reduction for new sources to technological methods while
explicitly allowing the best system for existing sources to
include non-technological methods. § 109(c)(1)(A), 91 Stat.
at 700. If Congress wanted to confine Section 7411 to at-the-
source technologies, it would have done so directly rather than
hiding such a substantial limitation in an implicit inference
from a more remote statutory provision.

The Clean Air Act’s legislative history, including the
history of the 1970 enactment of Section 7411 and the 1977
and 1990 amendments, further shows that Congress never
imposed on the “best system of emissions reduction” the
constraints the EPA now advocates. Before Congress settled
on the best-system language it enacted in 1970, the Senate bill
proposed to authorize the EPA to set standards for stationary
sources “reflect[ing] the greatest degree of emission control”
achievable through “the latest available control technology,
processes, operating methods, or other alternatives.” S. 4358,
91st Cong. § 6 (1970). The phrase “other alternatives” was
understood to encompass “[t]he maximum use of available
means of preventing and controlling air pollution”—without
limitation to technological or at-the-source means. S. REP. NO.
64
91-1196, at 16. The Senate believed that was “essential” to
limit emissions from both new and existing sources. Id. The
House, for its part, proposed an initial version of Section 7411
that would have “require[d] new sources to ‘prevent and
control [their] emissions to the fullest extent compatible with
the available technology and economic feasibility,’” H.R.
17255, 91st Cong. § 5 (1970), but included no provision
regarding the regulation of existing sources.

As enacted, Section 7411 simply requires that the EPA
identify as its benchmark for existing sources the “best system
of emission reduction.” 42 U.S.C. § 7411(a)(1). Nothing that
the EPA identifies or that we discern in the relevant history
shows the enacting Congress myopically “focused on steps that
can be taken at and by individual sources to reduce emissions.”
EPA Br. 69. And of course, even if Congress at that time was
only thinking of at-the-source controls, the EPA was well
aware that environmental problems and their solutions rapidly
evolve. At the end of the day, it is the statutory text that
governs. See Bostock v. Clayton County, 140 S. Ct. 1731, 1738
(2020).

Congress has consistently relied on the EPA’s expert
judgment in identifying the “best system” for existing sources.
Its action in making, and then undoing, a limiting amendment
to Section 7411’s “best system of emission reduction” just for
new and modified sources—not existing sources—underscores
the point. First, Congress in 1977 amended the standard for
new sources to require use of “the best technological system of
continuous emission reduction,” but did not make any parallel
change to the standard for existing sources to add those
“technological” and “continuous” limitations. Clean Air
Amendments Act of 1977, Pub. L. No. 95-95, § 109(c)(1)(A),
91 Stat. 685; see also id. at 700 (adding Section 7411(a)(1)(C)).
Then, in 1990, Congress again amended Section 7411, this time
65
to remove those additional limitations, reverting for new
sources to the “best system of emission reduction” that had
applied all along to existing sources. Clean Air Act
Amendments of 1990, Pub. L. No. 101-549, § 403(a), 104 Stat.
2399, 2631 (1990).

The amendment and re-amendment of the new-source
“best system” language emphasizes that Congress consistently
avoided imposing any such technological, at-the-source
limitation on the measures that EPA might include in the “best
system” for reducing emissions from existing-source
categories. And it shows that Congress had always understood
the existing-source “best system” language to go beyond the
technological restrictions that it briefly imposed on the parallel
new source provision.

The ACE Rule is the first EPA rule to read the statute as
so strictly boxing in the Agency. Although agency practice
cannot directly show whether Congress had a specific intent on
the matter in question, it is notable that the regulators closest to
the issue never before saw what the EPA now insists is obvious
on the face of Section 7411.

Over the last half century, no prior Administrator read the
Act to foreclose from consideration in the “best system” all but
at-the-source means of emission control. Rather, the EPA has
exercised latitude to consider any adequately demonstrated
approach to reducing harmful pollutants from existing source
categories that it believed met the cost, grid-reliability and
other statutory criteria. 42 U.S.C. § 7411(a)(1). Where the
characteristics of the source category and the pollutant at issue
point to emissions trading programs or production shifts from
higher- to lower-emitting sources as components of the “best
system,” the EPA has in the past consistently concluded that it
had the authority to consider them.
66
During the administration of President George W. Bush,
for example, the EPA adopted the Clean Air Mercury Rule, 70
Fed. Reg. 28,606 (May 18, 2005), which included a mercury
cap-and-trade program as a component of its best system of
emissions reduction for existing coal-fired power plants, see id.
at 28,619–28,620; id. at 28,617 (“EPA has determined that a
cap-and-trade program based on control technology available
in the relevant timeframe is the best system for reducing
[mercury] emissions from existing coal-fired Utility Units.”). 7

The EPA’s Clinton-era regulation of nitrogen oxide
emissions from municipal solid waste combustors likewise
relied on Section 7411(d), together with the EPA’s waste-
management authority under Section 7429, to authorize States
to include emissions-trading programs in their State Plans. 40
C.F.R. § 60.33b(d)(2). Under state standards of performance
designed to meet guidelines the EPA derived from its “best
system,” regulated entities were permitted to average the
emission rates of multiple units within a single plant as well as
trade emission credits with other plants. Municipal Waste
Combustors Rule, 60 Fed. Reg. 65,387, 65,402 (Dec. 19,
1995).

The EPA’s efforts to distinguish those other
Section 7411(d)(1) programs do not work. The EPA claims
that the Mercury Rule did not primarily rely on a cap-and-trade

7
We vacated the Mercury Rule for unlawfully delisting
mercury-emitting electric utility steam generating units from the
Section 7412 Hazardous Air Pollutants list. See New Jersey v. EPA,
517 F.3d 574, 582–584 (D.C. Cir. 2008). Because we held those
mercury sources must be listed, and because Section 7411 cannot be
used to regulate air pollutants listed under Section 7412, the existing-
source rule the EPA had adopted under Section 7411(d) to control
those same mercury emissions from power plants failed as well.
67
or dispatch shifting program, but rather that the best system
rested on a “combination of a cap-and-trade mechanism
and * * * the technology needed to achieve the chosen cap
level.” EPA Br. 72 n.20 (quoting ACE Rule, 84 Fed. Reg. at
32,526). To be clear, that sort of hybrid best system, involving

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Source: Frix Law Library, https://www.frixlaw.com/law-library/cases/4652158. Public record. Not legal advice.