OPINION

ROGERS, Circuit Judge.

This interlocutory appeal concerns whether the federal Clean Air Act preempts common law claims brought against an emitter based on the law of the state in which the emitter operates. The Clean Air Act's text makes clear that the Act does not preempt such claims. This conclusion is further supported by the Act's structure and history, together with relevant Supreme Court precedents.

Diageo Americas Supply, Inc. distills and ages whiskey at its Louisville facilities. The distillation and aging process results in tons of ethanol emissions. Ethanol vapor from the facilities wafts onto nearby real and personal property where the ethanol combines with condensation to propagate whiskey fungus. The whiskey fungus allegedly "creates an unsightly condition [on the property,] requiring abnormal and costly cleaning and maintenance, [and causes] early weathering of surfaces [and] unreasonable and substantial annoyance and unreasonable interference with the use and enjoyment of the property."

Ethanol emissions are regulated under the Clean Air Act. As explained by the Third Circuit in a similar case, the Clean Air Act is:

Bell v. Cheswick Generating Station, 734 F.3d 188, 190-91 (3d Cir. 2013), cert. denied sub nom. GenOn Power Midwest, L.P. v. Bell, ___ U.S. ___, 134 S.Ct. 2696, 189 L.Ed.2d 739 (2014) (some internal citations omitted).

Diageo's Clean Air Act obligations with respect to the Louisville facilities are set out in the terms of a Federally Enforceable District Origin Operating Permit issued and overseen by the Louisville Metro Air Pollution Control District. The permit prescribes detailed requirements for data collection, recordkeeping, and reporting. It also expressly incorporates most of the regulations of the air pollution control district, including Regulation 1.09, which provides:

Finally, the permit sets limits for emissions of various pollutants from the facilities. For purposes of these limits, the permit distinguishes between fugitive and non-fugitive emissions. Fugitive emissions are those emissions that "could not reasonably pass through a stack, chimney, vent, or other functionally equivalent opening," i.e., emissions that cannot reasonably be channeled through some kind of screening mechanism. 40 C.F.R. § 52.21(b)(20). Non-fugitive emissions, by contrast, are those emissions that can reasonably be channeled through a screening mechanism. For volatile organic compounds, including ethanol, the permit caps non-fugitive emissions at 100 tons per year. The permit does not cap fugitive ethanol emissions, i.e., those from Diageo's storage warehouses.

The plaintiffs in this case—owners, lessors, and renters of nearby properties affected by whiskey fungus—complained to the air pollution control district about the proliferation of whiskey fungus on their properties. In response, the district undertook an investigation that resulted in the issuance of a Notice of Violation letter to Diageo on September 7, 2012. In the letter, the district stated that, between June 2011 and May 2012, it received 27 complaints from residents living near the facilities of a "black, sooty substance covering . . . everything exposed to the out-doors." The district found that Diageo had violated District Regulation 1.09 because:

The Notice of Violation letter instructed Diageo to "submit to the District for approval a compliance plan for the abatement and control of emissions from its warehouses that are contributing to a nuisance, in accordance with District Regulation 1.12 by October 5, 2012." Diageo disputed that its operations at the facilities violated any district regulation, but nevertheless committed to vacating two of its whiskey aging warehouses to eliminate the problems of which plaintiffs complain. The record does not show whether Diageo followed through with its commitment and what effect, if any, that had on the growth of whiskey fungus on plaintiffs' properties.

In addition to complaining to the air pollution control district, plaintiffs filed a class action complaint in federal district court, seeking compensatory and punitive damages from Diageo for negligence, nuisance, and trespass, and an injunction requiring Diageo to abate its ethanol emissions by implementing certain control technologies at the facilities. Diageo moved to dismiss the complaint on two grounds. First, Diageo argued that it had no duty to curb ethanol emissions from its Louisville facilities. In support of this contention, Diageo relied on EPA decisions, agency actions from other jurisdictions, and its own permits. Second, in a notice of supplemental authority, Diageo argued that plaintiffs' claims were preempted by the Clean Air Act.

The district court largely rejected Diageo's arguments. Addressing Diageo's preemption argument first, the district court considered the Act's text in connection with decisions by the Supreme Court, this court, and other federal courts of appeals. The district court concluded that "Plaintiffs' state common law tort claims against Diageo are not preempted by the [Clean Air Act]."

The district court then addressed the sufficiency of the three state-law causes of action listed in the complaint, along with the claim for injunctive relief. In doing so, the district court first considered plaintiffs' argument that, because Diageo had offered materials outside the pleadings—concerning its federal and state permits and the feasibility of implementing technologies to control its ethanol emissions—the district court was required to convert Diageo's motion to dismiss into a motion for summary judgment. The district court excluded the documents from its consideration, deciding that the documents "[were] not necessary for the resolution of the issues argued in Diageo's motion to dismiss." Because it had excluded the documents from consideration, the district court concluded, the documents did not obligate it to convert Diageo's motion to dismiss into a motion for summary judgment.

Turning to the substance of plaintiffs' state common law claims, the district court dismissed plaintiffs' negligence claim on the ground that plaintiffs had not pled facts sufficient to establish that Diageo owed them a duty of care, or that Diageo had breached that duty. The court denied Diageo's motion, however, with respect to plaintiffs' remaining causes of action, concluding that plaintiffs had alleged facts sufficient to establish nuisance and trespass, and to entitle them to injunctive relief.

On Diageo's motion, the district court certified its ruling for interlocutory appeal. A panel of this court granted the petition to appeal pursuant to 28 U.S.C. § 1292(b). On appeal, Diageo argues that plaintiffs' state common law claims conflict with the Clean Air Act methods for regulating emissions and, therefore, that allowing such claims to proceed would frustrate the purposes and objectives of the Act.

The states' rights savings clause of the Clean Air Act expressly preserves the state common law standards on which plaintiffs sue. The clause saves from preemption "the right of any State or political subdivision thereof to adopt or enforce (1) any standard or limitation respecting emissions of air pollutants or (2) any requirement respecting control or abatement of air pollution," except that the "State or political subdivision may not adopt or enforce any emission standard or limitation" that is "less stringent" than a standard or limitation under an applicable implementation plan or specified federal statute. 42 U.S.C. § 7416. State courts are arms of the "State," and the common law standards they adopt are "requirement[s] respecting control or abatement of air pollution." Id. Thus, the states' rights savings clause makes clear that states retain the right to "adopt or enforce" common law standards that apply to emissions. A federal statute does not preempt state law if Congress did not intend the statute to do so, and "the best evidence of Congress's intent "is the statutory text adopted by both Houses of Congress and submitted to the President." W. Va. Univ. Hosps., Inc. v. Casey, 499 U.S. 83, 98, 111 S.Ct. 1138, 113 L.Ed.2d 68 (1991).

The phrase "any requirement," as used in the states' rights savings clause, clearly encompasses common law standards. As a four-Justice plurality of the Supreme Court has reasoned with respect to preempting language in a different statute, "[t]he phrase `[n]o requirement or prohibition' sweeps broadly and suggests no distinction between positive enactments and common law; to the contrary, those words easily encompass obligations that take the form of common law rules." Cipollone v. Liggett Grp., Inc., 505 U.S. 504, 521, 112 S.Ct. 2608, 120 L.Ed.2d 407 (1992) (plurality opinion). The phrase "any requirement" is similarly broad in its sweep, suggesting that it, too, encompasses common law rules. An expansive reading of "any requirement" is consistent, moreover, with the Court's historical tendency to treat common law standards as "requirements" for purposes of a variety of statutes. In Bates v. Dow Agrosciences LLC, for instance, the Court determined that the word "requirements" in the Federal Insecticide, Fungicide, and Rodenticide Act "reaches beyond positive enactments, such as statutes and regulations, to embrace common-law duties." 544 U.S. 431, 443, 125 S.Ct. 1788, 161 L.Ed.2d 687 (2005). In Riegel v. Medtronic, Inc., the Court concluded that common law causes of action for negligence and strict liability imposed "requirement[s]" for purposes of the Federal Food, Drug, and Cosmetic Act. 552 U.S. 312, 324, 128 S.Ct. 999, 169 L.Ed.2d 892 (2008). State common law standards therefore qualify as "requirements" for purposes of the Clean Air Act states' rights savings clause.

It is also plain that state courts are parts of the "State" for purposes of the states' rights savings clause. The states' rights savings clause implies that "State" refers to something that can "adopt or enforce . . . requirement[s]." State courts "adopt" state law "requirements" by making and modifying the common law, and state courts are the branch of state government most often tasked with "enforcing" state law "requirements." Indeed, the Supreme Court has interpreted the word "State" in the Clean Water Act states' rights savings clause, 33 U.S.C. § 1370(1)—which is materially indistinguishable from the Clean Air Act states' rights savings clause,1 see Bell, 734 F.3d at 195—to cover state courts and the common law rules they shape. See Int'l Paper Co. v. Ouellette, 479 U.S. 481, 497-98, 107 S.Ct. 805, 93 L.Ed.2d 883 (1987). The Court's interpretation of the word "State" in the Clean Water Act states' rights savings clause strongly indicates that the same word in the Clean Air Act states' rights saving clause, 42 U.S.C. § 7416, includes state courts. State common law standards are thus "requirements" adopted by "States," such that the Clean Air Act states' rights savings clause preserves them against preemption.

Other parts of the text of the Clean Air Act are fully consistent with this conclusion. For instance, Congress set out the Act's purposes and objectives in a section of the Act labeled "Congressional findings and declaration of purpose," which provides in part "that air pollution prevention (that is, the reduction or elimination, through any measures, of the amount of pollutants produced or created at the source) and air pollution control at its source is the primary responsibility of States and local governments." 42 U.S.C. § 7401(a)(3). Allowing states to apply their common law to emissions advances the Act's stated purposes by empowering states to address and curtail air pollution at its source. See id. at § 7401(a)(3), (c). Regulation of emissions under state common law, moreover, is consistent with Congress's declaration that it "is the primary responsibility of States" to prevent and reduce air pollution "through any measures." Id. at § 7401(a)(3) (emphasis added).

The legislative history of the Clean Air Act also indicates that it was not Congress's purpose to preempt state common law claims like those of the plaintiffs. For instance, the Report of the Senate Committee on Public Works explained that the citizen suit provision of the Clean Air Act "would specifically preserve any rights or remedies under any other law. Thus, if damages could be shown, other remedies would remain available. Compliance with standards under this Act would not be a defense to a common law action for pollution damages." S.Rep. No. 91-1196, at 38 (1970).

Supreme Court precedents interpreting and applying the Clean Water Act confirm that the Clean Air Act does not preempt plaintiffs' state common law claims. Clean Water Act precedents are persuasive with respect to the Clean Air Act because many provisions in the Clean Water Act—including the savings clauses—were modeled on the Clean Air Act, so that the two acts are often in pari materia. United States v. Stauffer Chem. Co., 684 F.2d 1174, 1187 (6th Cir.1982). As the Third Circuit has explained:

Bell, 734 F.3d at 196 (internal quotation marks and citation omitted).

The Supreme Court has reasoned that the Clean Water Act preserves source state common law claims, even though it preempts application of source state common law claims to out-of-state sources:

Ouellette, 479 U.S. at 497-98, 107 S.Ct. 805. The Ouellette Court's interpretation of the Clean Water Act states' rights savings clause to preserve claims based on the law of the source state leads directly to the conclusion that the analogous states' rights savings clause in the Clean Air Act similarly preserves claims based on the law of the source state.

This conclusion is directly supported by holdings of the Third Circuit and the Iowa Supreme Court. In cases materially indistinguishable from this one, those courts have held that the Clean Air Act does not preempt claims brought by plaintiffs under the common law of the source state. See Bell, 734 F.3d at 196-98; Freeman v. Grain Processing Corp., 848 N.W.2d 58, 80 (Iowa), cert. denied, ___ U.S. ___, 135 S.Ct. 712, 190 L.Ed.2d 440 (2014). Diageo points to North Carolina, ex rel. Cooper v. TVA, 615 F.3d 291 (4th Cir.2010), in which the Fourth Circuit held that the Clean Air Act preempted a plaintiff's state common law claims. Cooper, however, did not involve claims under the common law of the source state. Rather, Cooper involved claims against Alabama and Tennessee sources brought under North Carolina law. Id. at 297. That difference was dispositive on the preemption issue, for reasons having to do with federalism and the holding in Ouellette:

Id. at 306. The Fourth Circuit in Cooper applied the same framework the Third Circuit applied in Bell and the Iowa Supreme Court applied in Freeman. All three courts distinguished between claims based on the common law of the source state—which are not preempted by the Clean Air Act—and claims based on the common law of a non-source state—which are preempted by the Clean Air Act. Applying that framework here leads to the conclusion that the Clean Air Act does not preempt plaintiffs' claims.

The Supreme Court's decision in American Electric Power Co. v. Connecticut (AEP), ___ U.S. ___, 131 S.Ct. 2527, 180 L.Ed.2d 435 (2011), does not undermine that conclusion. AEP involved a suit against "the five largest emitters of carbon dioxide in the United States." Id. at 2534. The AEP plaintiffs alleged that, by contributing to global warming, "defendants' carbon-dioxide emissions created a `substantial and unreasonable interference with public rights,' in violation of the federal common law of interstate nuisance," and sought injunctive relief through a court-ordered imposition of emissions caps. Id. The Supreme Court, however, held "that the Clean Air Act and the EPA actions it authorizes displace any federal common law right to seek abatement" of such emissions. Id. at 2537. In so holding, the Court emphasized two considerations. First, when it comes to setting federal emissions standards, the Act entrusts expert agencies, not courts, with primary decisionmaking authority. Second, relative to expert agencies, courts are ill suited to the complex balancing required in setting emissions standards. Id. at 2539-40.

Diageo argues that the Supreme Court's reasons for concluding that the Clean Air Act displaces federal common law all militate with equal force in favor of holding that the Act preempts state common law. There are fundamental differences, however, between displacement of federal common law by the Act and preemption of state common law by the Act. For one thing, the Clean Air Act expressly reserves for the states—including state courts—the right to prescribe requirements more stringent than those set under the Clean Air Act. 42 U.S.C. § 7416. The Act does not grant federal courts any similar authority.

In addition, the displacement of federal common law with applicable statutory law is a natural occurrence in a common law legal system where courts with jurisdiction over disputes must come up with legal principles in the absence of statutory rules of decision. See AEP, 131 S.Ct. at 2536. As the Supreme Court explained in AEP:

Id. at 2537 (internal citations omitted).

The question whether state law is preempted demands due "regard for the presuppositions of our embracing federal system." Id. (internal citation omitted). When Congress acts to preempt state law—especially in areas of longstanding state concern—it treads on the states' customary prerogatives in ways that risk upsetting the traditional federal-state balance of authority. See Geib v. Amoco Oil Co., 29 F.3d 1050, 1058 (6th Cir.1994). This is why there is a strong presumption against federal preemption of state law, one that operates with special force in cases "in which Congress has legislated . . . in a field which the States have traditionally occupied." Medtronic, Inc. v. Lohr, 518 U.S. 470, 485, 116 S.Ct. 2240, 135 L.Ed.2d 700 (1996). Environmental regulation is a field that the states have traditionally occupied. See Huron Portland Cement Co. v. City of Detroit, 362 U.S. 440, 442, 80 S.Ct. 813, 4 L.Ed.2d 852 (1960). Accordingly, even if the express language of the states' rights savings clause here did not preserve state common law claims, principles of federalism and respect for states' rights would likely do so in the absence of a clear expression of such preemption.

Finally, the AEP Court itself explicitly stated that its holding was not dispositive of whether the Clean Air Act preempts state common law claims involving emissions.

AEP, 131 S.Ct. at 2540. The distinction the AEP Court drew—between displacement of federal law and preemption of common law—mirrors the distinction the Court drew in the context of the Clean Water Act. In City of Milwaukee v. Illinois & Michigan, 451 U.S. 304, 101 S.Ct. 1784, 68 L.Ed.2d 114 (1981), the Court held that the Clean Water Act displaced federal common law governing water pollution because, by enacting a comprehensive federal water statute, Congress had supplanted federal common law. See id. at 322-25, 101 S.Ct. 1784. The AEP Court's description of the structure and scope of the Clean Air Act closely mirrors the City of Milwaukee Court's description of the structure and scope of the Clean Water Act. Notwithstanding the displacement holding in City of Milwaukee, however, the Supreme Court subsequently held in Ouellette that the Clean Water Act does not preempt claims based on source state common law. See Ouellette, 479 U.S. at 498-99, 107 S.Ct. 805. Given the parallels between the two acts, City of Milwaukee and Ouellette together indicate that AEP's holding concerning displacement of federal common law does not support Clean Air Act preemption of source state common law. Indeed, the citation of Ouellette in AEP suggests the opposite conclusion: that the Clean Air Act does not preempt source state common law. For all of the foregoing reasons, AEP does not support Diageo's preemption arguments.

Many of Diageo's remaining arguments mistake regulatory overlap for regulatory conflict. The bare fact that Kentucky law may impose more stringent requirements than the Clean Air Act does not mean that the Act preempts Kentucky law. "The fact that a state has more stringent regulations than a federal law does not constitute conflict preemption." Patriotic Veterans, Inc. v. Indiana, 736 F.3d 1041, 1049 (7th Cir. 2013). "[S]tates frequently, and without preemption by federal law, create more stringent laws regarding minimum wage, employment discrimination, educational standards, gambling, and highway safety, to name a few." Id. Nor is Kentucky law preempted simply because it is the product of a less sophisticated or expert-driven process than that of the Clean Air Act. The question, for preemption purposes, is whether compliance with the state law defeats the purposes and objectives of the federal law, not whether the two laws impose different standards by different means. There is no evidence that Congress intended that all emissions regulation occur through the Clean Air Act's framework, such that any state law approach to emissions regulation would stand as an obstacle to Congress's objectives.

Diageo suggests that allowing state common law claims would "disrupt the CAA's balance of authority between federal and state law and conflict with the mechanism by which the CAA allows states to impose more stringent standards than the `floor' established by federal law." The Supreme Court disposed of an identical argument in Ouellette, remarking that:

479 U.S. at 498-99, 107 S.Ct. 805. What was true for the Clean Water Act holds true for the Clean Air Act.

We acknowledge the concern that a comprehensive federal scheme imposes substantial costs on industries, and that some suggest it is unduly burdensome for such industries to remain subject, in addition, to the requirements and remedies of state common law. Such a concern must however be directed to Congress. There is no basis in the Clean Air Act on which to hold that the source state common law claims of plaintiffs are preempted.

The order of the district court is affirmed.