GreenLatinos v. Suncor Energy (U.S.A.)

Appellate Case: 25-1243 Document: 40-1 Date Filed: 08/03/2026 Page: 1 FILED United States Court of Appeals Tenth Circuit PUBLISH August 3, 2026 UNITED STATES COURT OF APPEALS Christopher M. Wolpert FOR THE TENTH CIRCUIT Clerk of Court _________________________________ GREENLATINOS; 350 COLORADO; SIERRA CLUB, Plaintiffs - Appellants, v. No. 25-1243 SUNCOR ENERGY (U.S.A.), INC., Defendant - Appellee. _________________________________ Appeal from the United States District Court for the District of Colorado (D.C. No. 1:24-CV-02164-DDD-SBP) _________________________________ Kirti Datla of Earthjustice, Washington, D.C. (Ian Coghill, Rachael Jaffe of Earthjustice, Denver, Colorado, with her on the briefs), for Plaintiffs- Appellants. Hugh Q. Gottschalk of Wheeler Trigg O’Donnell LLP (Eric L. Robertson of Wheeler Trigg O’Donnell LLP; Carlos R. Romo, John H. Bernetich of Williams Weese Pepple & Ferguson PC, with him on the brief), Denver, Colorado, for Defendant-Appellee. _________________________________ Before BACHARACH, KELLY, and FEDERICO, Circuit Judges. _________________________________ FEDERICO, Circuit Judge.  Appellate Case: 25-1243 Document: 40-1 Date Filed: 08/03/2026 Page: 2 Over twenty years ago, the Environmental Protection Agency entered into consent decrees with the Valero Energy Corporation and Conoco Phillips to enforce the Clean Air Act (CAA) with respect to petroleum refineries. Those consent decrees covered refinery plants in Commerce City, Colorado that are now owned and operated by Suncor Energy (U.S.A.), Inc. In spite of this decades-old enforcement initiative by EPA, however, the Commerce City refinery plants continue to emit air pollution. A group of environmental organizations, on behalf of their members affected by the pollution, sued Suncor Energy to enforce the CAA’s mandate. When Congress created a right for citizens to sue for violations of “an emission standard or limitation” under the CAA, 42 U.S.C. § 7604(a), it also created an exception for cases where “the [EPA] Administrator or [a] State has commenced and is diligently prosecuting a civil action in a court of the United States or a State to require compliance with the standard, limitation, or order,” id. at § 7604(b)(1)(B). If the exception applies, then citizen suits for the same enforcement are barred. The district court held that the environmental organizations’ suit fell within this exception, known as the diligent prosecution bar, and granted Suncor Energy’s Rule 12(b)(6) motion to dismiss. The district court’s analysis, 2  Appellate Case: 25-1243 Document: 40-1 Date Filed: 08/03/2026 Page: 3 however, departed from the text enacted by Congress, so exercising our jurisdiction under 28 U.S.C. § 1291, we reverse. I Before we address the merits of this appeal, we will first examine the factual and procedural history of the case. As usual, on review of a Rule 12(b)(6) decision, we take “the bulk” of the relevant facts from the complaint itself. Levorsen v. Octapharma Plasma, Inc., 828 F.3d 1227, 1229 n.2 (10th Cir. 2016). But we also find relevant the statutory and regulatory circumstances that underpin the parties’ dispute, and since these details are judicially noticeable when deciding a Rule 12(b)(6) motion, e.g., United States v. Williams, 442 F.3d 1259, 1261 (10th Cir. 2006), we will attend to these facts as well. We therefore begin our review of the background with an Act of Congress – the CAA. A In 1970, “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,” Congress passed and President Richard Nixon signed the amendments that now encompass the modern CAA. 42 U.S.C. § 7401(b)(1). See generally Brigham Daniels, Andrew P. Follett, & Joshua Davis, The Making of the Clean Air Act, 71 Hastings L.J. 901, 941–43 (2020). The CAA is scaffolded by a complex set of authorities (and acronyms) for EPA to promulgate and enforce emissions limitations. 3  Appellate Case: 25-1243 Document: 40-1 Date Filed: 08/03/2026 Page: 4 At its foundation lie the National Ambient Air Quality Standards (NAAQS), which EPA sets for certain pollutants at a level that is “requisite to protect the public health” and “public welfare.” 42 U.S.C. § 7409(b)(1), (2); Whitman v. American Trucking Associations, 531 U.S. 457, 475–76 (2001). The CAA then authorizes EPA to set New Source Performance Standards (NSPS) that establish technology-based standards of performance to achieve emissions limits. 42 U.S.C. § 7411. It also authorizes states to require regulated entities to employ reasonably available control technology (RACT) for pollution control as part of their state implementation plans. 42 U.S.C. § 7502(c). Separate from the NAAQS, the CAA also regulates certain other, hazardous air pollutants through EPA-set National Emissions Standards for Hazardous Air Pollutants (NESHAPS). 42 U.S.C. § 7412(c)(2). For NESHAPS, EPA establishes technology-based standards for achieving “the maximum degree of reduction,” known as maximum achievable control technology (MACT) standards. 42 U.S.C. § 7412(d)(2); see, e.g., 40 C.F.R. § 63.51. Together with the NAAQS and RACT, this alphabet soup is the principal means by which the CAA accomplishes its purpose. To better understand how these laws operate in practice, consider a regulation found in 40 C.F.R. § 63.670(e), which forms the basis for claim 21 of the organizations’ complaint. That regulation establishes standards for the operation of flares “used as a control device for an emission point.” 40 C.F.R. 4  Appellate Case: 25-1243 Document: 40-1 Date Filed: 08/03/2026 Page: 5 § 63.670. Among other requirements, the flare must be operated “to maintain the net heating value of flare combustion zone gas (NHVcz) at or above the applicable limits,” which vary based on the type of flare technology used, “determined on a 15-minute block period basis when regulated material is routed to the flare for at least 15-minutes.” Id. at § 63.670(e). In other words, to ensure that the flare is actually burning off unhealthy emissions, the flare operator must keep the flare sufficiently hot. This is the MACT requirement described above. See generally Mossville Environmental Action Now v. EPA, 370 F.3d 1232, 1235–36 (D.C. Cir. 2004) (describing MACT standards). At the turn of the century, EPA began a programmatic effort to bring its various authorities to bear on petroleum refineries across the country. See, e.g., Notice of Lodging of Proposed Consent Decree Under Clean Air Act, 77 Fed. Reg. 25750, 25750 (Apr. 30, 2012) (“This is one of numerous national settlements reached as part of the EPA’s Clean Air Act Petroleum Refinery Initiative.”). According to EPA’s website, the petroleum refinery initiative resulted in 37 settlements with companies covering over 95% of the United 5  Appellate Case: 25-1243 Document: 40-1 Date Filed: 08/03/2026 Page: 6 States’ petroleum refining capacity and 112 refineries. 1 This appeal concerns two of those settlements. In 2002, EPA entered into a consent decree with Conoco Inc. as part of the agency’s petroleum refinery initiative. Doc. 29 in United States v. Conoco Inc., No. 4:01-CV-4430 (S.D. Tex. Apr. 29, 2002); see also Notice of Lodging of Consent Decree Under the Clean Air Act, 67 Fed. Reg. 3735 (Jan. 25, 2002). The consent decree required Conoco to take a variety of anti-pollution measures with respect to refineries the company owned and operated across the nation, including one refinery just northwest of Denver in Commerce City. App. VI at 8. Three years later, EPA entered into a similar consent decree with Valero Refining Company, which owned and operated another nearby refinery. Doc. 37 at 10, United States v. Valero Refining Co., No. 5:05-CV-569 (W.D. Tex. Nov. 23, 2005); App. VII at 13; see also Notice of Public Comment Period for Proposed Consent Decree Under the Clean Air Act, 70 Fed. Reg. 36410-01 (June 23, 2005). 1 Petroleum Refinery Nat’l Case Results, EPA, https://perma.cc/TH4Q- P648. “The Court may take judicial notice of the contents of an agency’s website.” Buhendwa v. Regional Transportation District, 82 F. Supp. 3d 1259, 1262 n.1 (D. Colo. 2015) (citing Coleman v. Dretke, 409 F.3d 665, 667 (5th Cir. 2005)); New Mexico ex rel. Richardson v. Bureau of Land Mgmt., 565 F.3d 683, 703 n.22 (10th Cir. 2009). 6  Appellate Case: 25-1243 Document: 40-1 Date Filed: 08/03/2026 Page: 7 In addition to substantive anti-pollution measures, the consent decrees also contained a variety of procedural features for their enforcement. For example, the consent decrees were each entered with respect to a host of state intervenors, so that enforcement responsibilities would be distributed across federal and state environmental agencies. App. VI at 4 (listing Colorado, Louisiana, Oklahoma, and Montana as state intervenors and parties to the consent decree); App. VII at 4 (listing Colorado, Louisiana, New Jersey, Oklahoma, and Texas as state intervenors and parties to the consent decree). The consent decrees also included a variety of reporting requirements, both on a general periodic basis and for specific incidents. See, e.g., App. VI at 57, 71– 72; App. VII at 97, 123–26. And the consent decrees set forth complex schemes of stipulated penalties for violations of the consent decrees’ provisions (in addition to the usual possibility of contempt for violating a court order), and a procedure for federal and state agencies to impose the penalties. App. VI at 83–92; App. VII at 166–77. Finally, each consent decree confirmed the district courts’ continuing jurisdiction over the case after the entry of the consent decree. In the years since the entry of the consent decrees, EPA and the Colorado Department of Public Health and Environment have taken a variety of administrative actions to enforce the anti-pollution objective embodied in the 7  Appellate Case: 25-1243 Document: 40-1 Date Filed: 08/03/2026 Page: 8 consent decrees with respect to the refineries located in Commerce City. 2 For example, in March 2020, Colorado issued a “compliance order on consent” to address violations of state and federal law, including the consent decrees. App. VIII at 4–89. This administrative action imposed stipulated penalties pursuant to the consent decrees. In June 2023, Colorado issued a “compliance advisory” to again address alleged violations of state and federal law, including the consent decrees. App. IX at 88–143. In February 2024, Colorado issued yet another “compliance order on consent.” App. VIII at 91–163. Like the March 2020 compliance order, this one too imposed stipulated penalties pursuant to the consent decrees. Later that year in June, EPA got involved and together with Colorado jointly issued a “notice of violation” alleging violations of state and federal law, including the consent decrees. App. IX at 4–86. The acronym-filled discussion of regulations and administrative jargon in this record should not obscure the material environmental impact that the refineries in Commerce City were having (and presumably continue to have) 2 In 2003, Suncor purchased the refinery operated by Conoco. In 2005, Suncor purchased the refinery operated by Valero. The refinery formerly operated by Conoco is sometimes referred to as Plants 1 and 3 and other times as the West Plant. The refinery formerly operated by Valero is sometimes referred to as Plant 2 and other times as the East Plant. For simplicity’s sake, we will refer to each as the West Plant and the East Plant respectively. After Suncor purchased the West and East Plants, the respective consent decrees were amended to include Suncor as a party bound to them. 8  Appellate Case: 25-1243 Document: 40-1 Date Filed: 08/03/2026 Page: 9 on the health and welfare of Coloradans. According to the complaint, which in turn relied on Suncor’s own filings made pursuant to the consent decrees, the refineries “emitted approximately 25 tons of hazardous air pollutants, 500 tons of CO, 650 of NOx, 125 tons of PM, 450 tons of volatile organic compounds (‘VOCs’), and 230 tons of SO2.” App. I at 26. Unsurprisingly, these emissions have had a deleterious effect on the health of nearby residents, who have some of the highest rates of asthma, cardiovascular disease, and diabetes in the state. The refineries’ neighbors spend less time outdoors, limit the meals they eat outside, and their daily activities are generally affected by the refineries’ belching odors and fumes. On all thirteen metrics that EPA uses to identify disparate environmental effects on vulnerable populations, the area surrounding the Commerce City refineries scored among the highest percentiles in Colorado, ranking among the most heavily polluted regions in the state. B To staunch this flow of emissions in Commerce City, several environmental organizations filed suit in the District of Colorado in August 2024. On October 29 that same year, the environmental organizations filed the first amended and operative complaint. The plaintiffs consisted of three groups: GreenLatinos, “a national nonprofit organization that convenes a broad coalition of Latino leaders committed to addressing environmental, 9  Appellate Case: 25-1243 Document: 40-1 Date Filed: 08/03/2026 Page: 10 natural resources, and conservation issues that significantly affect the health and welfare of the Latino community”; Sierra Club, “a national nonprofit organization” that “works to promote clean energy, safeguard the health of our communities, protect wildlife, and preserve our remaining wild places through grassroots activism, public education, lobbying, and legal action”; and 350 Colorado, “a nonprofit organization and grassroots movement working to build a fossil-free future powered by 100% renewable energy.” App. I at 19–20. We refer to the plaintiff organizations collectively as the “environmental organizations” for the purposes of this opinion. Together, the environmental organizations sought redress on behalf of themselves and their members against Suncor Energy, the company that now owns and operates the Commerce City refineries. They invoked what is known as the “citizen suit” provision of the CAA, which allows “any person” to “commence a civil action. . . against any person . . . who is alleged to have violated (if there is evidence that the alleged violation has been repeated) or to be in violation of [] an emission standard or limitation under” the Act. 42 U.S.C. § 7604(a)(1). The operative complaint made 28 claims for relief, each alleging various violations of the CAA and its implementing regulations. The complaint also alleged violations of the federal consent decrees previously mentioned. To give some texture to the kind of claim that the environmental organizations are making, consider another example. Claim 25 alleged that a 10  Appellate Case: 25-1243 Document: 40-1 Date Filed: 08/03/2026 Page: 11 heater unit known as H-2101 does not comply with the requirements of the West Plant Consent Decree. The West Plant Consent Decree required the refinery operator “to reduce the overall NOx emissions from Controlled Heaters and Boilers at their refineries in an amount greater than or equal to 1,526 tons per year” by, among other things, installing technologies that would “reduce NOx emissions to 0.040 lbs per mmBTU or lower.” App. VI at 21. According to the complaint, however, H-2101 was technologically incapable of meeting this emissions limit. So the complaint alleges that from the moment H-2101 was installed in January 2006, Suncor Energy has been in unbroken violation of the terms of the consent decree. Suncor Energy filed a motion to dismiss under Rule 12(b)(1) for want of jurisdiction and Rule 12(b)(6) for failure to state a claim upon which relief could be granted. Fed. R. Civ. P. 12(b)(1), (6). Suncor argued first that the environmental organizations could not demonstrate an Article III injury-in- fact, so they lacked standing to pursue their claims. Suncor next argued that the environmental organizations’ claims were jurisdictionally barred by 42 U.S.C. § 7604(b)(1)(B), which prevents private parties from suing under the CAA if a government entity is “diligently prosecuting” CAA violations as well. Suncor pointed to the consent decrees filed in the Texas district courts as the basis for applying the diligent-prosecution bar, asserting that “[p]ermitting Plaintiffs to pursue claims alleging the same violations of the Federal Court 11  Appellate Case: 25-1243 Document: 40-1 Date Filed: 08/03/2026 Page: 12 Consent Decrees would undercut the policies” underlying the diligent prosecution bar, and so the bar applied to the environmental organizations’ citizen suit. App. I at 169. The district court granted Suncor’s motion to dismiss, but only on Rule 12(b)(6) grounds. On standing, the district court concluded the environmental organizations had standing to pursue their claims. 3 On diligent prosecution, however, the district court rejected the environmental organizations’ protestations that the bar did not apply. “Taken together,” wrote the district court, “the consent decrees, compliance orders, compliance advisories, and notice of violation serve as ongoing enforcement actions by the EPA and Colorado against Defendant for alleged violations of the Act. As a result, Plaintiffs’ citizen suit, which consists of identical or substantially similar allegations, is barred by statute.” App. X at 295. The district court therefore dismissed the environmental organizations’ operative complaint and entered final judgment for Suncor on May 23, 2025. This timely appeal followed. 3 Suncor does not ask that we revisit the environmental organizations’ standing. Our independent review of the record discloses no basis for disturbing the district court’s conclusion. 12  Appellate Case: 25-1243 Document: 40-1 Date Filed: 08/03/2026 Page: 13 II Before we turn to the substance of this rather technical appeal, we will first describe our standard of review. We will then return to the CAA itself and introduce some basic concepts and the key pieces of the statutory text that frame the parties’ dispute. Finally, we will address the principal issue on appeal: whether the environmental organizations’ complaint is precluded by the diligent prosecution bar. We conclude that the district court incorrectly analyzed the diligent prosecution bar, and its judgment is therefore reversed. A “We review a district court’s grant of a motion to dismiss de novo.” Hennessey v. University of Kansas Hospital Authority, 53 F.4th 516, 527 (10th Cir. 2016). To survive Rule 12(b)(6) and in turn to obtain relief from a dismissal on appeal, a “plaintiff must state a claim that is facially plausible; that is, the plaintiff must ‘plead[ ] factual content that allows the court to draw the reasonable inference that the defendant is liable for the misconduct alleged.’” Messerli v. AW Distributing, Inc., 153 F.4th 1077, 1081 (10th Cir. 2025) (alteration in original, quoting Ashcroft v. Iqbal, 556 U.S. 662, 678 (2009)). Suncor Energy did not move for Rule 12(b)(6) dismissal on diligent- prosecution bar grounds in the district court; instead, it argued that the bar was jurisdictional and so the suit ought to be dismissed on Rule 12(b)(1) grounds. The district court, however, disposed of the diligent prosecution 13  Appellate Case: 25-1243 Document: 40-1 Date Filed: 08/03/2026 Page: 14 bar under Rule 12(b)(6). Although the distinction rarely matters for appellate purposes, Colorado Environmental Coalition v. Wenker, 353 F.3d 1221, 1227 (10th Cir. 2004), had the district court granted Suncor’s Rule 12(b)(1) motion, we would have reviewed the district court’s “findings of jurisdictional fact for clear error.” Stuart v. Colorado Interstate Gas Co., 271 F.3d 1221, 1225 (10th Cir. 2001). The district court did not explain its reasons for analyzing the Rule 12(b)(1) motion under Rule 12(b)(6). Nonetheless, we think the district court was correct to do so: the diligent prosecution bar is not jurisdictional. In the district court, Suncor relied heavily on cases that applied the bar as jurisdictional with little or no reasoning, “exactly the sort of ‘drive-by jurisdictional rulings’ the [Supreme] Court tells us to view with a jaundiced eye.” Hobby Lobby Stores, Inc. v. Sebelius, 723 F.3d 1114, 1159 (10th Cir. 2013) (en banc) (Gorsuch, J., concurring). The latest of those cases, Karr v. Hefner, predated the Supreme Court’s more recent drum-beat that only a clear statement by Congress can suffice to render a requirement jurisdictional. Compare 475 F.3d 1192, 1197–98 (10th Cir. 2007) (omitting any discussion of whether the diligent prosecution bar is jurisdictional), with United States v. Wong, 575 U.S. 402, 409–10 (2015) (noting “procedural rules, including time bars, cabin a court’s power only if Congress has ‘clearly state[d]’ as much” (quoting Sebelius v. Auburn Reg’l Med. Ctr., 568 U.S. 145, 153 (2013)) (alteration in original)). 14  Appellate Case: 25-1243 Document: 40-1 Date Filed: 08/03/2026 Page: 15 And we find little in the text of the diligent prosecution provision to satisfy this “high bar.” Wong, 575 U.S. at 409. The provision does not itself use the term “jurisdiction,” and indeed, another provision in the same statutory section does. Compare 42 U.S.C. § 7604(a), with id. at § 7604(b). Nearly all our sister circuits, so far as we can tell, agree: the diligent prosecution bar is non-jurisdictional. See, e.g., Group Against Smog & Pollution, Inc. (GASP) v. Shenango Inc., 810 F.3d 116, 122–26 (3d Cir. 2016) (holding that the bar is non-jurisdictional even though parties did not raise the issue); Cebollero-Bertran v. Puerto Rico Aqueduct & Sewer Authority, 4 F.4th 63, 70–72 (1st Cir. 2021) (construing similar language in the Clean Water Act, 33 U.S.C. § 1365 (CWA)); South River Watershed Alliance, Inc. v. Dekalb County, 69 F.4th 809, 821–23 (11th Cir. 2023) (CWA); Naturaland Trust v. Dakota Finance LLC, 41 F.4th 342, 346–48 (4th Cir. 2022) (holding prior cases construing CWA’s diligent prosecution bar as jurisdictional were abrogated by “Supreme Court’s current approach to such matters”); Adkins v. VIM Recycling, Inc., 644 F.3d 483, 491–92 (7th Cir. 2011) (construing similar language in the Resource Conservation and Recovery Act, 42 U.S.C. § 6972(b)(1)(B) (RCRA)). 15  Appellate Case: 25-1243 Document: 40-1 Date Filed: 08/03/2026 Page: 16 “The distinction matters. Jurisdictional requirements cannot be waived or forfeited, must be raised by courts sua sponte, and . . . do not allow for equitable exceptions.” Boechler, P.C. v. Commissioner of Internal Revenue, 596 U.S. 199, 203 (2022); see also Adkins, 644 F.3d at 491 (“The distinction is vital.”). With respect to the diligent prosecution bar, the distinction affects which party bears the burden of asserting it and consequently whether a party’s failure to timely invoke the bar can be held to have waived it. With these thoughts, we proceed to apply the standard of review applicable to Rule 12(b)(6) decisions. B We turn now to address the historical background that produced the CAA statutory text. Although the policy debates that animated the CAA era do not alter our legal analysis, they do appropriately contextualize it. Historically, people affected by pollution, like the neighbors of the Commerce City refinery, might have relied on the common law system of torts to deter pollution and obtain redress for pollution-related injuries. Mark Latham, Victor E. Schwartz, & Christopher E. Appel, The Intersection of Tort and Environmental Law: Where the Twains Should Meet and Depart, 80 Fordham L. Rev. 737, 772 (2011). But over time, it became apparent that the individualized and causation-bound nature of tort liability could not fully satisfy the pressing environmental needs of the day. See, e.g., Palma J. Strand, 16  Appellate Case: 25-1243 Document: 40-1 Date Filed: 08/03/2026 Page: 17 Note, The Inapplicability of Traditional Tort Analysis to Environmental Risks: The Example of Toxic Waste Pollution Victim Compensation, 35 Stan. L. Rev. 575, 577–80, 583–84 (1983). In its place arose a robust statutory regime for regulatory enforcement, giving administrative agencies authority to prevent, deter, and remedy environmental harm. Latham, Schwartz, & Appel, The Intersection of Tort and Environmental Law, at 743–45 (identifying “a series of modern federal environmental statutes” as ushering in “the new field of environmental law”). The CAA was one of the first statutes enacted as part of this experiment with public environmental law. Daniels, Follett, & Davis, The Making of the Clean Air Act, at 903–04. Congress did not entirely displace the role of private persons in vindicating its environmental objectives. The CAA provides that “any person may commence a civil action on his own behalf [] against any person . . . who is alleged to have violated (if there is evidence that the alleged violation has been repeated) or to be in violation of (A) an emission standard or limitation under this chapter or (B) an order issued by the Administrator or a State with respect to such a standard or limitation.” 42 U.S.C. § 7604(a)(1). This clause is known as the citizen suit provision. Gwaltney of Smithfield, Ltd. v. Chesapeake Bay Foundation, Inc., 484 U.S. 49, 58–59 (1987) (describing similar provision in CWA). Although compensatory damages are generally understood to not be available under citizen suit provisions, Mulcahey v. Columbia Organic 17  Appellate Case: 25-1243 Document: 40-1 Date Filed: 08/03/2026 Page: 18 Chemicals Co., Inc., 29 F.3d 148, 152 (4th Cir. 1994), plaintiffs can seek equitable relief, Gwaltney, 484 U.S. at 61–62, and extract civil penalties to deter pollution, Friends of the Earth, Inc. v. Laidlaw Environmental Services (TOC), Inc., 528 U.S. 167, 185 (2000). The citizen suit provision has proven structurally vital for the greater statutory scheme. Accord Daniels, Follett, & Davis, The Making of the Clean Air Act, at 930–31. Its most obvious contribution to environmental law has been as a reserve guarantor of congressional objectives if the executive branch is unable or unwilling to advance them. Id.; Environmental Conservation Organization v. City of Dallas, 529 F.3d 519, 526 (5th Cir. 2008); Adkins, 644 F.3d at 499. Relatedly, the specter of citizen suits also serves as a “spur” to government action. Black Warrior Riverkeeper, Inc. v. Cherokee Mining, LLC, 548 F.3d 986, 992 (11th Cir. 2008) (quoting S. Rep. No. 99-50, 28 (1985)). And since Congress also required putative plaintiffs to provide EPA with notice of their anticipated citizen suit 60 days in advance of filing, 42 U.S.C. § 7604(b)(1)(A), the citizen suit provision incentivizes private plaintiffs to investigate CAA violations and then relay that information to EPA – complementing and assisting the government’s investigatory responsibility. So, although in form it bears little resemblance to its tort ancestors, in function the citizen suit builds on a long history of private impulses advancing public goods. 18  Appellate Case: 25-1243 Document: 40-1 Date Filed: 08/03/2026 Page: 19 Congress also acted, however, to preserve the primacy of government agencies in environmental law enforcement. Citizen suits are barred under the CAA “if the [EPA] Administrator or [a] State has commenced and is diligently prosecuting a civil action in a court of the United States or a State to require compliance with the standard, limitation, or order, but in any such action in a court of the United States any person may intervene as a matter of right.” 42 U.S.C. § 7604(b)(1)(B). As already referenced above, this clause is known as the diligent prosecution bar. GASP, 810 F.3d at 121 n.4. “The bar on citizen suits when governmental enforcement action is under way suggests that the citizen suit is meant to supplement rather than to supplant governmental action.” Gwaltney, 484 U.S. at 60. In other words, although private parties can play a “supplementary” and “interstitial” role in the environmental legal universe, administrative agencies retain primacy within that ecosystem. Id. at 60–61. The diligent prosecution bar shares some distinguishing characteristics with other preclusive doctrines of the common law. Just as issue preclusion protects parties “from the expense and vexation attending multiple lawsuits, conserves judicial resources, and fosters reliance on judicial action by minimizing the possibility of inconsistent decisions,” Montana v. United States, 440 U.S. 147, 153–54 (1979), so too does the diligent prosecution bar protect regulated entities from duplicative, expensive, and perhaps inconsistent 19  Appellate Case: 25-1243 Document: 40-1 Date Filed: 08/03/2026 Page: 20 lawsuits. North and South Rivers Watershed Ass’n, Inc. v. Town of Scituate, 949 F.2d 552, 556 (1st Cir. 1991); Friends of Milwaukee’s Rivers v. Milwaukee Metropolitan Sewerage Dist., 382 F.3d 743, 762–63 (7th Cir. 2004) (likening diligent prosecution bar to res judicata). And in doing so, the bar incentivizes regulated entities to cooperate with administrative agencies seeking to enforce the environmental laws. But as with other preclusive doctrines, tension can arise and subsist between the principle of access to justice and the principle of repose. Cf. Montana, 440 U.S. at 164 n.11. This appeal brings the friction between citizen suits and the diligent prosecution bar into sharp focus. On the one hand, the environmental organizations emphasize the care with which Congress balanced the diligent prosecution bar against the citizen suit provision in the statutory text. On their theory of the bar, the text sets forth three steps, none of which are satisfied here, for deciding whether the bar precludes a citizen suit. First, the court must identify a present judicial action, which the environmental organizations argue would not include the Texas consent decrees or any subsequent administrative actions. Second, the court must ensure that the standards and limitations raised in the potentially preclusive judicial action are the same as the ones in the citizen suit, which the environmental organizations also argue would exclude the Texas consent decrees and subsequent administrative actions. Only after these two steps have been satisfied should the district court consider 20  Appellate Case: 25-1243 Document: 40-1 Date Filed: 08/03/2026 Page: 21 whether the judicial action is being diligently prosecuted. See also South River Watershed Alliance, 69 F.4th at 824 (describing these elements as “steps,” and separating diligent prosecution from antecedent questions). On the other hand, Suncor Energy argues that this lawsuit is “a duplicative and unnecessary action to enforce alleged violations of the same emission standards currently being enforced by the federal government and the State of Colorado.” Resp. Br. at 11. Suncor primarily invokes the “clear Congressional intent that citizen suits should not ‘intrude’ on EPA’s and Colorado’s ‘primary enforcement authority.’” Resp. Br. at 28 (quoting Karr, 475 F.3d at 1197). We largely agree with the environmental organizations. “The issues are complicated – so for the details, read on.” Haaland v. Brackeen, 599 U.S. 255, 264 (2023). But in a nutshell, we latch onto the environmental organizations’ text-based theory of the statute over Suncor Energy’s purpose-driven approach. The purpose-driven approach led the district court to apply a diligent prosecution bar that Congress did not enact in the CAA. We therefore reverse the judgment and remand for further proceedings. C We now address the core substance of this appeal – the meaning of the diligent prosecution bar in the CAA. As foreshadowed, we agree with the environmental organizations that the diligent prosecution bar sets forth 21  Appellate Case: 25-1243 Document: 40-1 Date Filed: 08/03/2026 Page: 22 distinct elements (or “steps,” as some courts frame them). South River Watershed Alliance, 69 F.4th at 823–24; Ohio Valley Environmental Coalition, Inc. v. Maple Coal Co., 808 F. Supp. 2d 868, 883 (S.D. W. Va. 2011); Connecticut Fund for Environment v. Contract Plating Co., Inc., 631 F. Supp. 1291, 1293 (D. Conn. 1986). We take each step in turn. 1 The environmental organizations argue first that the diligent prosecution bar can be triggered only by a civil judicial action that is presently being enforced. We agree, but we also reject the environmental organizations’ argument that consent decrees do not satisfy this requirement. The text of the statute would appear to admit of little else. The diligent prosecution bar is triggered when EPA or a state “has commenced and is diligently prosecuting a civil action in a court.” 42 U.S.C. § 7604(b)(1)(B). This court and the Supreme Court have repeatedly stressed that “Congress’ use of a verb tense is significant in construing statutes.” United States v. Wilson, 503 U.S. 329, 333 (1992); see also Carr v. United States, 560 U.S. 438, 448 (2010); United States v. Husted, 545 F.3d 1240, 1243–44 (10th Cir. 2008). Congress’ choice of verb tense here unambiguously refers to something that is current or present, even if it began at some point in the past. The term “has commenced” is phrased in the present perfect tense, see 42 U.S.C. § 7604(b)(1)(B), which usually “conveys to a listener that the event in question continues to be true or 22  Appellate Case: 25-1243 Document: 40-1 Date Filed: 08/03/2026 Page: 23 valid.” Hewitt v. United States, 606 U.S. 419, 429 (2025). And that phrase is followed by the present tense “is.” See 42 U.S.C. § 7604(b)(1)(B). Congress was thus focused on actions that are presently being prosecuted. Indeed, the Supreme Court reached a similar conclusion when construing the Clean Water Act’s citizen suit provision as not reaching wholly past actions. Gwaltney, 484 U.S. at 59 (“One of the most striking indicia of the prospective orientation of the citizen suit is the pervasive use of the present tense throughout § 505.”). Turning from verbs to objects, the phrase “civil action in a court of the United States or a State” is likewise unambiguous. 42 U.S.C. § 7604(b)(1)(B). The term “civil action” refers to “a proceeding in a judicial court, not an administrative” forum. Western Watersheds Project v. U.S. Dept. of the Interior, 677 F.3d 922, 926 (9th Cir. 2012); see also Patham Const. Co. v. Knox County Hospital Ass’n, 326 N.E.2d 844, 854 (Ind. Ct. App. 1975) (“The term ‘action’ in its usual sense, at least its usual legal sense, means a suit brought in court, a formal complaint within the jurisdiction of a court of law.”). The word “court” also usually excludes administrative forums. Baughman v. Bradford Coal Co., Inc., 592 F.2d 215, 217 (3d Cir. 1979) (“Generally, the word ‘court’ in a statute is held to refer only to the tribunals of the judiciary and not to those of an executive agency with quasi-judicial powers.”). Also, the statute expressly provides for otherwise-barred citizen suit plaintiffs to intervene in the pending government-initiated action – a mechanism which does not exist, so far as we 23  Appellate Case: 25-1243 Document: 40-1 Date Filed: 08/03/2026 Page: 24 know, in administrative proceedings. Student Public Interest Research Group of N.J., Inc. v. Fritzche, Dodge & Olcott, Inc., 759 F.2d 1131, 1138–39 (3d Cir. 1985). 4 Putting these phrases together, only one thing can trigger the diligent prosecution bar: an action in a judicial forum that is presently being enforced. Other tools that are related to that judicial action (administrative actions, for example) may well be relevant to determining whether that presently enforced judicial action is being diligently prosecuted. But only the standards and limitations found in that presently enforced judicial action can preclude a citizen suit under the diligent prosecution bar. Our conclusion is buttressed by the fact that other diligent prosecution bars found in other environmental statutes enumerate administrative actions explicitly as a basis for preclusion. 33 U.S.C. § 1319(g)(6) (CWA); 42 U.S.C. § 6972(b)(2)(B)(iv) (RCRA); 42 U.S.C. § 11046(e) (Emergency Planning & 4 Some room for uncertainty can be found on the outer boundaries of the phrase “civil action,” and particularly with respect to state-level bodies. See, e.g., Baughman v. Bradford Coal Co., Inc., 592 F.2d 215 (3d Cir. 1979) (deciding whether Pennsylvania Environmental Hearing Board is a court for the purposes of § 7604(b)(1)(B)). We have no occasion in this case to reach those outer boundaries, however, for no one argues that EPA agency proceedings, or those of the Colorado Department of Public Health and Environment, are court proceedings. 24  Appellate Case: 25-1243 Document: 40-1 Date Filed: 08/03/2026 Page: 25 Community Right-to-Know Act). 5 The omission of similar language in the CAA – arguably the foundational environmental statute – speaks volumes. Applying this judicial-action-only