In the Clean Air Act Amendments of 1970, Congress directed EPA to promulgate national ambient air quality standards (NAAQS) for certain pollutants, and assigned each state the primary responsibility to achieve those standards through a State Implementation Plan (SIP) subject to EPA approval. EPA set NAAQS for pollutants including sulfur dioxide and particulate matter in 1971. States then proposed SIPs that, in varying degrees, employed different control approaches to attain the NAAQS by statutory deadlines. Some SIPs included intermittent or supplementary control strategies—such as curtailing operations during adverse meteorological conditions, using taller stacks or dispersion techniques, or other measures not limited to continuous source-specific emission reductions. EPA approved several SIPs and issued guidance reflecting that, provided the statutory criteria were met, states could use such approaches. The Natural Resources Defense Council (NRDC) petitioned for review in the D.C. Circuit, arguing that the Clean Air Act required SIPs to rely on continuous emission limitations at the source and barred intermittent controls. The D.C. Circuit agreed in significant part, vacating EPA approvals to the extent they permitted these strategies. EPA Administrator Russell E. Train sought Supreme Court review.
Under the Clean Air Act, may EPA approve State Implementation Plans that use intermittent or supplementary controls rather than exclusively continuous, source-specific emission limitations to attain and maintain the national ambient air quality standards, or must EPA require states to use a particular form of emission limitation?
Under Clean Air Act § 110, states have primary responsibility to formulate SIPs that will attain and maintain the NAAQS. EPA must approve a SIP if it satisfies the Act's enumerated criteria (including attainment by statutory deadlines, enforceability, adequate monitoring, and compliance with other statutory requirements). The Act does not mandate that SIPs employ any particular form of emission limitation or categorically forbid intermittent or supplementary control strategies, and EPA may not impose additional, non-statutory requirements on states as a condition of SIP approval.
The Supreme Court reversed the D.C. Circuit and held that the Clean Air Act does not require EPA to mandate continuous, source-specific emission limitations or prohibit intermittent or supplementary controls in State Implementation Plans. States retain discretion to choose the mix of control measures, and EPA must approve SIPs that meet the Act's requirements, including timely attainment and enforceability, regardless of the specific techniques selected.
Text and structure: The Court focused on the statutory design separating ends from means. Sections 109 and 110 assign EPA the task of setting NAAQS and reviewing SIPs, while expressly placing the primary responsibility for devising implementation measures on the states. Section 110 directs EPA to approve a SIP if it meets specific, listed criteria; those criteria do not include a requirement that emission limitations be exclusively continuous or technology-based, nor do they categorically bar intermittent or supplementary strategies. By negative implication, EPA may not read in additional prerequisites not grounded in the statute. Federal–state allocation: The Act's policy statement recognizes that air pollution prevention and control at its source is the primary responsibility of states and local governments. The Court emphasized that Congress deliberately chose a cooperative federalism framework: EPA specifies the level of air quality required nationwide, but states have latitude to select control methods tailored to local conditions, provided they will attain and maintain the NAAQS on the statutory timetable and satisfy enforceability and other procedural safeguards. Legislative history and context: The Court found no legislative history indicating an inflexible congressional preference for continuous emission limitations to the exclusion of other methods. To the contrary, Congress contemplated a range of tools—emission limits, scheduling, land-use and transportation controls, and other measures—to achieve ambient standards. While the Act uses the term "emission limitations," the Court interpreted it as one type of permissible control among others, not a command that only continuous limits be used. Limits on state discretion: State discretion is not boundless. EPA remains obligated to disapprove any SIP that will not attain and maintain the NAAQS by the required deadlines, lacks adequate enforcement mechanisms, or otherwise fails to satisfy § 110's criteria. The Court did not license the use of intermittent controls to evade health-based standards or delay attainment; it merely held that the Act left the choice of methods to the states, subject to EPA's review against express statutory benchmarks. Administrative law considerations: Although the case predates modern Chevron doctrine, the Court's analysis reflects respect for statutory boundaries on agency authority. EPA cannot impose requirements beyond what Congress specified, and courts should not rewrite the Act to mandate particular control techniques. Within those limits, EPA's approval decisions are guided by the statutory factors, not by a judicially created preference for one control strategy over another.
Train v. NRDC is a cornerstone of Clean Air Act cooperative federalism. It confirms that states may craft SIPs using a variety of control measures, and that EPA's role is to ensure compliance with statutory criteria rather than to dictate methods. For law students, the case illustrates statutory interpretation anchored in text, structure, and federalism principles; it also shows the limits of agency power to add prerequisites not found in the statute. The decision influenced Congress's subsequent 1977 Amendments, which, among other things, addressed concerns about certain dispersion techniques and added more detailed definitions—underscoring Train's practical impact on environmental legislation and policy design.
Train v. NRDC firmly established that Congress designed the Clean Air Act to separate national environmental ends from state-selected means. EPA sets the ambient air quality goals and ensures that state plans meet the statute's concrete criteria, but it may not dictate the specific control strategies a state must use absent clear statutory direction. By restoring state discretion to choose among lawful tools—while preserving EPA's gatekeeping role—the Court anchored the Act's cooperative federalism framework.