Full Opinion

United States Court of Appeals FOR THE DISTRICT OF COLUMBIA CIRCUIT Argued January 20, 2026 Decided August 18, 2026 No. 24-1193 CHAMBER OF COMMERCE OF THE UNITED STATES OF AMERICA, ET AL., PETITIONERS v. ENVIRONMENTAL PROTECTION AGENCY AND LEE M. ZELDIN, IN HIS OFFICIAL CAPACITY AS ADMINISTRATOR, UNITED STATES ENVIRONMENTAL PROTECTION AGENCY, RESPONDENTS CLEAN CAPE FEAR, ET AL., INTERVENORS Consolidated with Nos. 24-1261, 24-1266, 24-1271, 24-1272 On Petitions for Review of a Final Rule of the Environmental Protection Agency Elbert Lin argued the cause for petitioners. With him on the briefs were Andrew R. Varcoe, Stephanie A. Maloney, Paul T. Nyffeler, David M. Parker, Matthew Z. Leopold, Christopher 2 L. Bell, Susan Parker Bodine, Richard S. Moskowitz, and Tyler Kubik. Brittany M. Pemberton entered an appearance. Michael B. Kimberly and Michael A. Tilghman II were on the brief for amici curiae National Association of Manufacturers and Printing United Alliance in support of petitioners. Nicole E. Wittstein entered an appearance. Douglas A. Hastings and Mark Donatiello were on the brief for amicus curiae Superfund Settlements Project in support of petitioners. Erica Spitzig, Aaron M. Herzig, Anne M. McClellan, and David C. Roper were on the brief for amicus curiae Passive Receivers in support of remand. Riley W. Walters, Counsel to the Assistant Attorney General, U.S. Department of Justice, argued the cause for respondents. On the brief were Adam R.F. Gustafson, Principal Deputy Assistant Attorney General, and Jin Hyung Lee, Attorney, and Elizabeth G. Berg and Noel M. Johnson, Attorneys, U.S. Environmental Protection Agency. Jonathan Kalmuss-Katz argued the cause for intervenors Clean Cape Fear, et al. in support of respondents. With him on the brief were Lillian Zhou and Alana R. Reynolds. Letitia James, Attorney General for the State of New York, Barbara D. Underwood, Solicitor General, Judith Vale, Deputy Solicitor General, Joshua N. Cohen, Assistant Solicitor General, Philip M. Bein, Senior Counsel, Kyle Burns, Assistant Attorney General, Mihir Desai, Assistant Attorney General, Kristin K. Mayes, Attorney General for the State of Arizona, Philip J. Weiser, Attorney General for the State of Colorado, William Tong, Attorney General for the State of Connecticut, 3 Brian L. Schwalb, Attorney General for the District of Columbia, Kwame Raoul, Attorney General for the State of Illinois, Anthony G. Brown, Attorney General for the State of Maryland, Andrea J. Campbell, Attorney General for the Commonwealth of Massachusetts, Dana Nessel, Attorney General for the State of Michigan, Keith Ellison, Attorney General for the State of Minnesota, Matthew J. Platkin, Attorney General for the State of New Jersey, Raúl Torrez, Attorney General for the State of New Mexico, Dan Rayfield, Attorney General for the State of Oregon, Nicholas W. Brown, Attorney General for the State of Washington, and Josh Kaul, Attorney General for the State of Wisconsin, were on the brief for amici curiae States of New York, et al. in support of respondents. Before: MILLETT, KATSAS, and RAO, Circuit Judges. Opinion for the Court filed by Circuit Judge MILLETT. MILLETT, Circuit Judge: Perfluorooctanoic Acid (“PFOA”) and Perfluorooctanesulfonic Acid (“PFOS”) are two compounds in a large group of human-made substances commonly referred to as “forever chemicals.” In 2024, the Environmental Protection Agency designated PFOA and PFOS as “hazardous substances” under the Comprehensive Environmental Response, Compensation, and Liability Act of 1980. EPA based its determination on extensive studies that link PFOA and PFOS exposure to serious health conditions in humans, including cancer and developmental delays. Seven interest groups representing industries that use, transport, or discharge PFOA and PFOS petitioned this court to overturn EPA’s decision. We deny those petitions. 4 I A Congress enacted the Comprehensive Environmental Response, Compensation, and Liability Act, Pub. L. No. 96- 510, 94 Stat. 2767, in 1980, and added to that regime in 1986 with the Superfund Amendments and Reauthorization Act of 1986, Pub. L. No. 99-499, 100 Stat. 1613, now codified together at 42 U.S.C. § 9601 et seq. (“CERCLA”). CERCLA governs the cleanup of “hazardous substances” and “pollutants or contaminants” from the environment. 42 U.S.C. §§ 9604, 9606. The Act was Congress’s response to a series of high- profile toxic chemical releases, including the infamous dump of thousands of tons of chemicals in Love Canal, New York that led to birth defects, miscarriages, and a devastated community. See S. REP. NO. 848, 96th Cong., 2d Sess. 4–5, 8– 10 (1980); see also Niagara Mohawk Power Corp. v. Chevron U.S.A., Inc., 596 F.3d 112, 120 & n.5 (2d Cir. 2010). CERCLA classifies as a “hazardous substance” those substances listed in or designated under other environmental laws, like the Clean Water Act. There are currently over 800 such hazardous substances. 42 U.S.C. § 9601(14); 40 C.F.R. § 302.4 table (enumerating those substances). CERCLA also authorizes EPA to designate as additional “hazardous substances” those “elements, compounds, mixtures, solutions, and substances” that, “when released into the environment[,] may present substantial danger to the public health or welfare or the environment[.]” 42 U.S.C. § 9602(a). CERCLA both encourages “timely cleanup” of harmful chemical releases and hazardous waste sites and “ensure[s] that the costs” of cleanups are “borne by those responsible” for the pollution. Atlantic Richfield Co. v. Christian, 140 S. Ct. 1335, 5 1345 (2020) (quoting CTS Corp. v. Waldburger, 573 U.S. 1, 4 (2014)). CERCLA provides for two kinds of cleanups: (1) removal actions and (2) remedial actions. 42 U.S.C. § 9601(23), (24), (25). Removal actions are short-term measures aimed at promptly preventing or mitigating a release of dangerous chemicals. J.A. 447–448. Remedial actions, on the other hand, are longer-term efforts involving “a complex, multi-phase process” aimed at “significantly reduc[ing] serious but not immediately life- threatening risks” from chemical releases. J.A. 447; see 42 U.S.C. § 9601(24). Remedial actions are generally conducted at locations listed on the “National Priorities List,” a statutorily mandated list of sites across the country that present the greatest danger to public health. 42 U.S.C. § 9605(a)(8)(A)– (B); Linemaster Switch Corp. v. EPA, 938 F.2d 1299, 1301 (D.C. Cir. 1991). They are commonly known as “Superfund sites[.]” Atlantic Richfield Co., 140 S. Ct. at 1346. Cleanups can proceed along two statutory pathways. First, “Section 106” cleanups are triggered only by the release of a “hazardous substance[.]” 42 U.S.C. § 9606(a). For these cleanups, EPA may compel responsible parties to undertake the cleanup in the first instance. Id. Second, “Section 104” cleanups can be triggered by the release of either (1) a “hazardous substance” or (2) a “pollutant or contaminant” if it “may present an imminent and substantial danger to the public health or welfare[.]” 42 U.S.C. § 9604(a)(1). A “pollutant or contaminant” is defined as including: 6 [A]ny element, substance, compound, or mixture, including disease-causing agents, which after release into the environment and upon exposure, ingestion, inhalation, or assimilation into any organism, either directly from the environment or indirectly by ingestion through food chains, will or may reasonably be anticipated to cause death, disease, behavioral abnormalities, cancer, genetic mutation, physiological malfunctions (including malfunctions in reproduction) or physical deformations, in such organisms or their offspring[.] 42 U.S.C. § 9601(33). Within Section 104 cleanups, who foots the bill depends on what needs cleaning up. When EPA leads the cleanup of hazardous substances, the responsible polluters can later be made to cover the costs through cost-recovery actions, so long as the cleanups were “not inconsistent with the national contingency plan[.]” 42 U.S.C. § 9607(a); Cooper Indus., Inc. v. Aviall Servs., Inc., 543 U.S. 157, 161 (2004). The National Contingency Plan, in turn, is a series of statutorily required regulations that prescribe the methods and scope of Section 104 cleanups. 42 U.S.C. § 9605; 40 C.F.R. pt. 300. Such refund actions are not possible for releases of pollutants or contaminants, however. See 42 U.S.C. § 9607(a). That means that Section 104 cleanups of pollutants or contaminants are paid for entirely by public funds, either (1) through the Superfund, which Congress set up to pay for major CERCLA cleanup efforts, 42 U.S.C. § 9611(a); Ohio v. Department of the Interior, 880 F.2d 432, 439 (D.C. Cir. 1989), or (2) through appropriations by Congress, see GOVERNMENT ACCOUNTABILITY OFF., GAO-15-812, SUPERFUND: TRENDS IN 7 FEDERAL FUNDING AND CLEANUP OF EPA’S NONFEDERAL NATIONAL PRIORITIES LIST SITES 12 (2015). B Perfluoroalkyl and Polyfluoroalkyl Substances (“PFAS”) is the scientific name for a broad category of human-made chemicals. Designation of Perfluorooctanoic Acid (PFOA) and Perfluorooctanesulfonic Acid (PFOS) as CERCLA Hazardous Substances, 89 Fed. Reg. 39,124, 39,125 (May 8, 2024) (“Designation”). They have been used in the United States since the 1940s to create water- and oil-resistant products like cookware, rain-repellent clothing, and firefighting foam. Id. at 39,126. PFAS take hundreds of years to degrade in the environment and take decades to be eliminated from human bodies, earning them the title “forever chemicals[.]” Designation, 89 Fed. Reg. at 39,126 (quotation marks omitted). PFAS have also been linked to many adverse health effects, including cancer, developmental effects in children, and cardiovascular conditions. See id. at 39,145–39,146. EPA has historically regulated two of the most common PFAS—PFOA and PFOS—as “pollutants or contaminants” under CERCLA. Designation, 89 Fed. Reg. at 39,153. Several years ago, as scientific evidence of the harms posed by PFOA and PFOS accumulated, EPA began considering whether to designate the two chemicals as “hazardous substances” under CERCLA. In studying the issue, EPA published in August 2022 an Economic Assessment delving into a quantitative cost-benefit analysis of the direct impacts of such a designation and a qualitative analysis of the indirect impacts. J.A. 103–111. The Assessment also 8 requested public comment on thirteen discreet issues regarding its initial cost-benefit analyses. J.A. 118. One month later, EPA published a Notice of Proposed Rulemaking suggesting the designation of PFOA and PFOS as “hazardous substances” under CERCLA. See Designation of [PFOA] and [PFOS] as CERCLA Hazardous Substances, 87 Fed. Reg. 54,415, 54,417 (Sept. 6, 2022). In doing so, EPA requested comments specifically on: (1) Whether CERCLA section 102(a) precludes, allows, or requires consideration of cost in designation decisions, and, if so, (2) which costs and benefits of those discussed in the EA [Economic Assessment] should be considered, (3) whether additional benefits and costs not identified in the EA should be considered, (4) if indirect benefits and costs are considered, how they should be assessed in light of the discretion and uncertainties described above, (5) how benefits and costs could be incorporated into the designation decision, and (6) whether designation would be justified if costs were to be considered in the Agency’s designation decision. 87 Fed. Reg. at 54,423. After receiving comments, including from Petitioners, EPA issued its final rule in May 2024. Designation, 89 Fed. Reg. at 39,124; e.g., J.A. 681, 687, 714. EPA used two factors to determine that PFOA and PFOS qualified as “hazardous substances.” First, EPA considered “the potential harm to humans or the environment from exposure to the substance (i.e., hazard),” and second, “how the substance potentially moves, persists, and/or changes when in the environment (i.e., 9 environmental fate and transport).” Designation, 89 Fed. Reg. at 39,141. EPA concluded that both weighed in favor of designation, crediting the significant body of research on adverse health effects as well as the tendency of PFOA and PFOS to remain for many years in the environment and to bioaccumulate in human bodies. See id. at 39,143–39,148. EPA then assumed without deciding that CERCLA required a cost-benefit analysis of that designation. Designation, 89 Fed. Reg. at 39,143. EPA’s evaluation of the costs and benefits contained both “quantitative and qualitative” considerations. Id. at 39,149. EPA published the cost-benefit analysis in a document entitled “Regulatory Impact Analysis[,]” and attached it to the final rule. Id. at 39,149; J.A. 368–659. EPA’s designation of PFOA and PFOS as “hazardous substances” has three direct impacts on regulated parties. First, parties responsible for a release of more than one pound of PFOA or PFOS must report that release to national authorities, 42 U.S.C. §§ 9602(b), 9603; Waterkeeper Alliance v. EPA, 853 F.3d 527, 531 (D.C. Cir. 2017), and, in some cases, to local authorities and the public, 42 U.S.C. §§ 9611(g), 11004; 40 C.F.R. § 355. Second, federal agencies selling land contaminated with PFOA and PFOS generally must provide notice of the presence of hazardous substances. 42 U.S.C. § 9620(h). Third, shippers must identify and mark shipments of PFOA and PFOS weighing more than one pound, pursuant to the Hazardous Materials Transportation Act of 1975, 49 U.S.C. § 5101 et seq., 42 U.S.C. § 9656(a); 49 C.F.R. § 171.1. 10 The Designation leads to indirect impacts as well. In some circumstances, after several more regulatory steps, EPA may compel polluters to abate and clean up releases of PFOA or PFOS. 42 U.S.C. § 9606. In other circumstances, the federal government, States, and adversely affected private parties may pursue enforcement actions to recover cleanup costs from responsible polluters. 42 U.S.C. § 9607; see 40 C.F.R. §§ 300.410, 300.420; 42 U.S.C. § 9606(a). Seven interest groups for various companies that use, transport, or discharge PFOA and PFOS in their manufacturing, transportation, and waste management (“Petitioners”), petitioned this court to vacate the Designation. Petitioners challenge EPA’s (1) interpretation of “hazardous substances” to include PFOA and PFOS as contrary to law, 5 U.S.C. § 706(2)(A); (2) cost-benefit analysis as arbitrary and capricious, id., and in violation of Administrative Procedure Act’s notice requirement, id. § 553; and (3) decision to regulate in the face of uncertainties as arbitrary and capricious, id. § 706(2)(A).1 II We have exclusive jurisdiction over these petitions for review of a “regulation promulgated under” CERCLA. 42 U.S.C. § 9613(a). 1 Petitioners are the Chamber of Commerce of the United States of America (“Chamber of Commerce”), American Chemistry Council, American Fuel & Petrochemical Manufacturers, Associated General Contractors of America, Inc., National Waste & Recycling Association, Institute of Scrap Recycling Industries, d/b/a the Recycled Materials Association, and American Forest & Paper Association. 11 Petitioners have the jurisdictionally required Article III associational standing. See, e.g., Students for Fair Admissions, Inc. v. President & Fellows of Harvard College, 143 S. Ct. 2141, 2157 (2023). Petitioners have identified member companies that use PFOA- and PFOS-containing products and attest that they “are already seeing impacts on their overall project expenses” in complying with the terms of CERCLA. See Decl. of Leah Pilconis ¶¶ 19, 23–24, 27–28; Decl. of Charles Mull ¶¶ 7, 9–12; Decl. of John M. Perkey ¶¶ 18–20; Decl. of Anne Germain ¶ 10. Those increased expenses are concrete injuries in fact assertedly caused by the Designation that could be redressed by court action. In addition, the associations’ interests in protecting companies from CERCLA’s liability regime are germane to their missions of promoting the financial and regulatory interests of private industry. See Decl. of Martin Durbin ¶ 5; Decl. of Anne Germain ¶ 3; Decl. of Leah Pilconis ¶¶ 4–5. Petitioners also have shown that the participation of individual members is not required to seek the equitable relief of vacatur. See Center for Biological Diversity v. EPA, 56 F.4th 55, 67 (D.C. Cir. 2022). In reviewing Petitioners’ contrary to law claims, we must independently determine the “best” reading of CERCLA’s text by “applying all relevant interpretive tools.” Loper Bright Enters. v. Raimondo, 144 S. Ct. 2244, 2266 (2024). Our review of Petitioners’ arbitrary and capricious claims is “deferential” to the agency. FCC v. Prometheus Radio Project, 141 S. Ct. 1150, 1158 (2021) (“A court simply ensures that the agency has acted within a zone of reasonableness and, in particular, has reasonably considered the relevant issues and reasonably explained the decision.”); see also Meritor, Inc. v. EPA, 966 F.3d 864, 869 (D.C. Cir. 2020) (“In conducting this review, we 12 afford the EPA significant deference with respect to the highly technical issues involved.”) (formatting modified). Finally, we must set aside a rule if the agency failed to provide the requisite notice and comment and the petitioner has shown prejudice. 5 U.S.C. § 553(b); Petaluma FX Partners, LLC v. Commissioner, 792 F.3d 72, 81 (D.C. Cir. 2015). III Petitioners advance three challenges to the Designation. They contend that: (1) EPA misinterpreted the term “may present substantial danger” in CERCLA’s definition of a hazardous substance; (2) EPA’s cost-benefit analysis provided insufficient notice to the parties; and (3) EPA’s cost-benefit analysis and decision to regulate in the face of uncertainty were arbitrary and capricious. None of those claims succeeds. The plain language of Section 9602 allows EPA to designate as hazardous substances chemicals like PFOA and PFOS that repeatedly have been linked to adverse health effects in myriad peer-reviewed studies. EPA provided adequate notice of its cost-benefit analysis underlying the ultimate Designation through its earlier Economic Assessment and request for comments on it. Finally, EPA acted reasonably based on the record before it in its calculation of costs and benefits, and in its decision to take this regulatory step of designating PFOA and PFOS to be hazardous substances. A Petitioners argue that, in interpreting the phrase “may present substantial danger” in CERCLA’s definition of a hazardous substance, EPA had to find that substantial danger 13 “will” occur upon release to avoid overinclusion and to comply with the nondelegation and void-for-vagueness doctrines. Pet’rs’ Reply Br. 14; Pet’rs’ Opening Br. at 31–32. Petitioners are wrong as a matter of statutory text and precedent. 1 The plain statutory text refutes Petitioners’ argument. CERCLA provides that EPA “shall” “designat[e] as hazardous substances” those “elements, compounds, mixtures, solutions, and substances which, when released into the environment may present substantial danger to the public health or welfare or the environment[.]” 42 U.S.C. § 9602(a). In making the Designation, EPA determined that “may” means “at a minimum, there is a possibility” that the released substance presents a substantial danger to public health, welfare or the environment, and that “EPA need not have certainty” of that danger. Designation, 89 Fed. Reg. at 39,141. Petitioners challenge EPA’s interpretation of “may[,]” arguing that reading it to mean a “possibility” of substantial harm lacks “fix[ed] boundaries” and is “unreasonably broad.” Pet’rs’ Opening Br. 28–29 (secondly quoting Loper Bright, 144 S. Ct. at 2263). According to Petitioners, “may” in the statute means that whenever a substance is released, the danger “will be actually existing or real.” Pet’rs’ Reply Br. 12–13 (quotation marks omitted). EPA has the best reading of the statute as a matter of text and context. To start, the statute straightforwardly uses “may” to refer to the chance of harm to public health, not its certainty. The primary meaning of “may” is one of contingency both in 14 ordinary usage and in dictionaries at the time of CERCLA’s enactment. See May, BLACK’S LAW DICTIONARY (5th ed. 1979) (“An auxiliary verb qualifying the meaning of another verb by expressing ability, competency, liberty, permission, possibility, probability or contingency.”); May, BALLENTINE’S LAW DICTIONARY 785 (3d. ed. 1969) (“Ordinarily a permissive, rather than a mandatory, term in a statute.”); May, OXFORD AMERICAN DICTIONARY 410 (1980) (“expressing possibility (it may be true)”); May, WEBSTER’S THIRD NEW INTERNATIONAL DICTIONARY 1396 (1981) (“be in some degree likely to” as in “you [may] be right”); May, WEBSTER’S NEW WORLD DICTIONARY 463 (2d Concise ed. 1982) (“possibility or likelihood [it may rain]”); May, THE RANDOM HOUSE DICTIONARY OF THE ENGLISH LANGUAGE 1189 (2d unabr. ed. 1987) (“used to express possibility” as in “[i]t may rain”). Even more to the point, the statute says when that contingency should be assessed, which is at the time— “when”—the substance is “released into the environment[.]” 42 U.S.C. § 9602(a). In that way, the statute directs EPA to forecast the future risk of harm at the time of a release. Petitioners’ insistence that the harm must be certain to occur at the time of release rewrites rather than interprets the statutory text. If Congress wanted to adopt Petitioners’ preferred approach, it would have said: “substances which, when released into the environment may will present substantial danger to the public health or welfare or the environment[.]” Compare Pet’rs’ Reply Br. 12–13 (“[I]f the condition of release is satisfied, the result of substantial danger to the public health or welfare or the environment will be actually existing or real.”) (quotation marks omitted), with 42 U.S.C. § 9602(a) (using simply “may”). 15 Also, the dictionaries on which Petitioners rely refute their argument, providing that the word “may” will not be treated as a word of command or requirement “unless there is something in [the] context” of a statute “to indicate that it was used in such sense.” May, BLACK’S LAW DICTIONARY (5th ed. 1979); see also May, BALLENTINE’S LAW DICTIONARY 785 (3d. ed. 1969) (“Discretionary in its grammatical sense, but subject to construction as mandatory where the sense of the entire context impels such construction[.]”) (emphasis added). Missing from Petitioners’ argument is anything in the context that impels overriding the ordinary meaning of “may[.]” Petitioners also forget that, in CERCLA, Congress wrote a statute that would operate on the basis of scientific knowledge and information about health and environmental risks. Congress presumably knew that “[s]cientists typically speak not of certainty, but of probability; they are trained to act on probabilities that statistically constitute ‘certainties.’” Ethyl Corp. v. EPA, 541 F.2d 1, 25 n.52 (D.C. Cir. 1976) (en banc); see also id. (“Even scientific ‘facts’ are not certain, but only theories with high probabilities of validity.”); cf. Center for Biological Diversity v. EPA, 749 F.3d 1079, 1090 (D.C. Cir. 2014) (“[A statute] may at times require * * * action in the face of uncertainty, lest ‘the precautionary purpose of the statute’ be undermined.”) (quoting Ethyl Corp., 541 F.2d at 28). To require absolute scientific certainty as to what will happen upon every individual release of a dangerous chemical would have been to legislatively paralyze CERCLA. Petitioners worry that such an ordinary and contextual reading of the text would permit EPA to categorize table salt as a hazardous substance. Petitioners’ argument overlooks the required finding that a release may present “substantial danger” to public health, welfare, or the environment. 42 U.S.C. § 9602(a). That criterion has real bite. The risk of harm must 16 be both serious and real, not hypothesized. See Substantial, BLACK’S LAW DICTIONARY (5th ed. 1979) (“actually existing; real; not seeming or imaginary; not illusive; solid; true; veritable”); Substantial, OXFORD AMERICAN DICTIONARY 683 (1980) (“of considerable amount or intensity or validity”); Substantial, WEBSTER’S THIRD NEW INTERNATIONAL DICTIONARY 2280 (1981) (“considerable in amount, value, or worth”); Substantial, XVII THE OXFORD ENGLISH DICTIONARY 66 (2d ed. 1989) (“That is, or exists as, a substance; having a real existence”); Danger, BLACK’S LAW DICTIONARY (5th ed. 1979) (“Jeopardy; exposure to loss or injury; peril.”); Danger, OXFORD AMERICAN DICTIONARY 160 (1980) (“liability or exposure to harm or to death”); Danger, WEBSTER’S THIRD NEW INTERNATIONAL DICTIONARY 573 (1981) (“Harm, Injury, Damage”) (capitalization altered); Danger, IV THE OXFORD ENGLISH DICTIONARY 241 (2d ed. 1989) (“Liability or exposure to harm or injury; the condition of being exposed to the chance of evil; risk, peril.”). More to the point, this case does not require rigidly defining the precise boundaries of the term “substantial danger[.]” That is because, for all their verbal debating, Petitioners tellingly do not dispute that PFOA and PFOS qualify as substances that may pose a substantial risk to public health, welfare, and the environment if released. Nor could they. The Designation cited dozens of studies showing “[c]ollectively” that “each PFOA and PFOS individually pose[s] a human health hazard[.]” Designation, 89 Fed. Reg. at 39,144. The Designation spent three full pages cataloguing just “some” of the health conditions associated with PFOA and PFOS exposure: developmental effects including decreased infant birth weight and effects on fetuses during pregnancy; cardiovascular impacts like increased cholesterol in adolescents; increased liver enzymes, which can impact liver function; immunosuppression in adults and children; impacted 17 thyroid function; and preeclampsia and gestational hypertension in pregnant women. Id. at 39,144–39,146. That is not all. After reviewing toxicity assessments in drinking water, EPA classified PFOA and PFOS as “likely to be carcinogenic to humans[.]” Designation, 89 Fed. Reg. at 39,143 (formatting modified). The PFOA determination was based on “evidence of kidney and testicular cancer in humans and Leydig cell tumors, pancreatic acinar cell tumors, and hepatocellular adenomas in rats.” Id. at 39,144. So too was the PFOS determination based on “evidence of hepatocellular tumors in humans and rats, pancreatic islet cell carcinomas in male rats, and mixed but plausible evidence of bladder, prostate, kidney, and breast cancers in humans[.]” Id. EPA is not alone in these concerns. As the Designation noted, the International Agency for Research on Cancer, a subsidiary of the World Health Organization, has categorized PFOA as “carcinogenic to humans” and PFOS as “possibly carcinogenic to humans[.]” Designation, 89 Fed. Reg. at 39,143. Lastly, Petitioners’ worry overlooks the political accountability issues that would arise from a misguided designation. In addition, Petitioners could voice objections to an unreasonable designation in the ordinary course of notice and comment rulemaking and, if necessary, bring suit to challenge the final designation as contrary to law. For all of these reasons, the phrase “may present a substantial risk of harm” when released into the environment 18 carries its plain meaning of a scientifically possible substantial risk of harm upon release.2 2 Petitioners next argue that the definition of “hazardous substances” must be read more narrowly than “pollutant or contaminant” because “CERCLA confers significantly more authority to address ‘hazardous substances’ than ‘pollutants or contaminants.’” Pet’rs’ Opening Br. 33. Petitioners are mistaken. To start, Petitioners’ insistence that courts must enforce some inflexible hierarchy between these two categories is not supported by anything in the statutory text. Their definitions each require a probability of substantial danger to the public or environmental organisms. Compare 42 U.S.C. § 9601(33) (defining a “pollutant or contaminant” as a substance which “will or may reasonably be anticipated to cause death, disease, behavioral abnormalities, cancer, genetic mutation, physiological malfunctions (including malfunctions in reproduction) or physical deformations” in animals and humans), and id. § 9604(a) (requiring EPA to determine that pollutants or contaminants “may present an imminent and 2 Petitioners urge us not to afford EPA’s interpretation any “respect” in our interpretation of Section 9602 because of (1) a 1983 notice of proposed rulemaking, which never materialized into a final rule, proposing quantitative metrics to operationalize Section 9602, and (2) regulations with more concrete metrics that implement Section 9605, a part of CERCLA that does not use the word “may.” Pet’rs’ Opening Br. 35 & n.12 (citing Loper Bright Enters., 144 S. Ct. at 2258). Contrary to Petitioners’ contention, non-rules and definitions in materially different regulations do not show inconsistency with prior agency positions. More to the point, our decision is made de novo without deference to EPA’s view. 19 substantial danger to the public health or welfare” before initiating cleanup), with id. § 9602(a) (defining “hazardous substances” as those which “may present substantial danger to the public health or welfare or the environment”). So CERCLA does not draw a comparative-harm line between pollutants or contaminants and hazardous substances. Instead, it creates two distinctive cleanup regimes with two different paths for designation. The difference in how hazardous substances and pollutants or contaminants are treated in cleanups turns on (1) the imminence of harm and (2) whether the risk of harm posed is uniform or could vary based on site-specific conditions. Pollutants or contaminants are identified for clean up on a site-by-site basis based both on the risk of harm and— uniquely—the harm’s “imminen[ce.]” 42 U.S.C. § 9604(a)(1); Designation, 89 Fed. Reg. at 39,172. In addition, CERCLA does not require EPA to promulgate any regulations or make formal certifications to designate substances as pollutants or contaminants, presumably because the imminence of harm may not allow for such delays. See 42 U.S.C. § 9604(a)(1). On the other hand, CERCLA mandates that EPA designate hazardous substances in a single rulemaking that then applies to all CERCLA sites. 42 U.S.C. § 9602. While Section 9602 does not explicitly call for notice and comment rulemaking, EPA opted to do so for the PFOA and PFOS Designation, and committed itself to further notice-and-comment rulemaking if it were to update the Designation. Designation, 89 Fed. Reg. at 39,174. To the extent the statutory scheme allows substances, like PFOA and PFOS, to originally qualify as pollutants or contaminants and then later, be designated hazardous 20 substances based on advances in scientific knowledge, that is the “belt and suspenders approach” that CERCLA’s text and context straightforwardly allow. Atlantic Richfield Co., 140 S. Ct. at 1350 n.5. 3 Finally, Petitioners contend that EPA’s reading of Section 9602 runs afoul of the nondelegation and void-for-vagueness doctrines, and that we should reject EPA’s reading to avoid those constitutional questions. Pet’rs’ Opening Br. 31–32. There are no such constitutional concerns in this case. Allowing agencies to make discretionary judgments informed by evidence fully comports with the nondelegation doctrine as long as “Congress has set out an ‘intelligible principle’ to guide what it has given the agency to do.” FCC v. Consumers’ Rsch., 145 S. Ct. 2482, 2497 (2025) (quoting J.W. Hampton, Jr., & Co. v. United States, 276 U.S. 394, 409 (1928)). Under the “intelligible principle” test, courts require Congress to “ma[ke] clear both the general policy that the agency must pursue and the boundaries of its delegated authority.” Id. (formatting modified). Congress has laid out the “general policy” for EPA to pursue—regulating substances that are particularly harmful to humans and the environment by creating a cleanup and cost- allocation scheme that puts the onus on polluters rather than taxpayers. See 42 U.S.C. §§ 9602, 9606, 9607; cf. United States v. E.I. Dupont De Nemours & Co., 432 F.3d 161, 169 (3d Cir. 2005) (“Congress’s decision to hold responsible parties strictly liable for the government’s costs of responding to hazardous waste contamination [in CERCLA] is both a reasonable exercise of legislative authority and different in 21 kind from the unbounded delegation” found in cases that run afoul of the nondelegation doctrine.). Congress also has set fixed “boundaries” for the agency’s authority and “provided sufficient standards” for courts to police agency compliance. Consumers’ Rsch., 145 S. Ct. at 2497. For example, to categorize substances as “hazardous,” EPA must determine that they are harmful enough to risk “substantial danger” to human welfare or the environment. 42 U.S.C. § 9602(a). Tying EPA’s decisions to scientific findings based on a public health standard easily satisfies the requirement that there be an intelligible principle to limit agency action. See, e.g., Consumers’ Rsch., 145 S. Ct. at 2501–2503 (finding an intelligible principle in the Telecommunications Act’s requirement that subsidies paid by telecommunications carriers be enough to “contribute” to “sufficient mechanisms * * * to preserve and advance universal service[,]” 47 U.S.C. § 254(d)); Whitman v. American Trucking Ass’ns, 531 U.S. 457, 465 (2001) (same for Clean Air Act’s delegation to EPA to set ambient air quality standards “‘the attainment and maintenance of which * * * are requisite to protect the public health’ with ‘an adequate margin of safety’”) (quoting 42 U.S.C. § 7409(b)(1)); Touby v. United States, 500 U.S. 160, 163, 165 (1991) (same for Controlled Substances Act’s authorization of the Attorney General to temporarily add a substance to a controlled drug schedule if doing so is “necessary to avoid an imminent hazard to the public safety”) (quoting 21 U.S.C. § 811(h)(1)); see also Sessions v. Dimaya, 584 U.S. 148, 159 (2018) (“Many perfectly constitutional statutes use imprecise terms like ‘serious potential risk’ * * * or ‘substantial risk[.]’”). Section 9602’s plain meaning also fully comports with the Fifth Amendment’s Due Process Clause by affording “the 22 person of ordinary intelligence a reasonable opportunity” to predict whether a substance could be designated hazardous. Grayned v. City of Rockford, 408 U.S. 104, 108–109 (1972). Notice is particularly easy to find here given that PFOA and PFOS previously have been designated under CERCLA as “pollutant[s] or contaminant[s]” that “will or may reasonably be anticipated to cause death, disease, behavioral abnormalities, cancer, genetic mutation, physiological malfunctions (including malfunctions in reproduction) or physical deformations[.]” 42 U.S.C. § 9601(33); Designation, 89 Fed. Reg. at 39,173. That alone provided fair notice that PFOA and PFOS might also qualify as “hazardous substances[.]” Beyond that, Petitioners’ members are seasoned participants in the highly regulated area of chemical substances’ commercial uses. They were provided ample notice and opportunity to be heard through the notice and comment rulemaking process that designated PFOA and PFOS as hazardous substances, followed by judicial review. See Village of Hoffman Ests. v. The Flipside, Hoffman Ests., Inc., 455 U.S. 489, 498 (1982) (“[E]conomic regulation is subject to a less strict vagueness test because * * * the regulated enterprise may have the ability to clarify the meaning of the regulation by its own inquiry, or by resort to an administrative process.”). For all those reasons, affording Section 9602’s “may present substantial danger to the public health or welfare or the environment” language its ordinary meaning comports fully with the nondelegation doctrine and due process. Petitioners’ contrary to law claim fails. 23 B The second chapter in Petitioners’ challenge focuses on EPA’s cost-benefit analysis. Petitioners argue that EPA (1) violated the APA’s notice requirement by failing to disclose its Regulatory Impact Analysis until publication of the final rule, and (2) conducted its cost-benefit analysis in an arbitrary and capricious manner. Pet’rs’ Opening Br. 41–49. Petitioners’ arguments do not hold up. The Regulatory Impact Analysis was a logical outgrowth of the Economic Assessment’s cost-benefit analysis, which was then supplemented with data to address comments made by Petitioners and others. EPA also reasonably explained its quantitative analyses.3 1 First, Petitioners contend that EPA failed to provide adequate notice of its cost-benefit analysis. While they acknowledge that the Economic Assessment provided with the notice of proposed rulemaking contained a cost-benefit analysis, Petitioners argue that the final Regulatory Impact Analysis differed such that they were no longer provided sufficient notice. Pet’rs’ Opening Br. 43. The APA requires that a notice of proposed rulemaking include “either the terms or substance of the proposed rule or a description of the subjects and issues involved,” 5 U.S.C. § 553(b)(3), and “give interested persons an opportunity to 3 Because we reject Petitioners’ challenges to EPA’s cost- benefit analysis, we need not decide whether EPA was required to consider such costs in the first instance. EPA assumed without deciding that it had to do so, 89 Fed. Reg. at 39,143, and we do the same. 24 participate in the rule making through submission of written data, views, or arguments,” id. § 553(c). Notice “ensure[s] that agency regulations are tested via exposure to diverse public comment,” promotes fairness to impacted parties, and gives them “an opportunity to develop evidence in the record to support their objections[.]” International Union, United Mine Workers v. Mine Safety & Health Admin., 626 F.3d 84, 95 (D.C. Cir. 2010) (formatting modified). This notice requirement extends to “critical information” on which the rule is based.