Opinion: 549 U.S. 561 (2007)
HOLDING: When a statute uses same word in multiple places, courts presume that the word was intended to have the same meaning. But that is not a rigid rule, and the presumption yields when the word is used in a way that reasonably warrants the conclusion that Congress intended for it to have different meanings in different parts of the statute.
Between 1988 and 2000, Duke Energy replaced boiler components at several of its coal-fired power plants in North and South Carolina. The new components allowed the boilers to operate for more hours each day. The federal government and numerous environmental groups sued Duke, alleging that replacing the components without a permit violated the Clean Air Act.
Two separate provisions in the Clean Air Act gave the Environmental Protection Agency authority to regulate modifications to large air polluting facilities, like coal-fired power plants. But the EPA’s regulations used two different methods to determine whether a modification was “major” and therefore required a permit. Under the regulations implementing the older “New Source Performance Standards” provision, an operator only needed a permit if the modification would increase the hourly rate of emissions, while under the regulations implementing the newer “Prevention of Significant Deterioration” provision, a permit was required if the modification would increase the total amount of emissions, regardless of the rate.
The District Court reasoned that because both provisions defined “modification” the same way, the EPA had to use the same metric to assess whether a modification was significant enough to require a permit. The Fourth Circuit affirmed.
The Supreme Court held that even though Congress used the same term, “modification,” with a consistent statutory definition in different parts of the Clean Air Act, there was no indication that Congress intended to limit the EPA’s power to implement different regulatory requirements for different parts of the Act. Because the EPA’s regulations were both reasonable attempts to define a “major” modification, the courts lacked the authority to invalidate them under the Clean Air Act.