Imagine a large wooden ship, in service for generations. As its planks decay, they are swapped out for new—but otherwise identical—timbers. Over time, every piece of the ship is replaced in this manner so that eventually not one of its original planks remains. Is it still the same ship? If not, when did it lose its identity? When the first plank was replaced? The last? At some point in between? This ancient brainteaser, commonly known as the Ship of Theseus (after the mythical, Minotaur-slaying king of Athens), illustrates the classic philosophical problem of “Identity Through Time.” How much can an object change before it simply becomes something else? Philosophers have been debating that question for thousands of years. And so, since 1970, have the federal regulators charged with implementing the Clean Air Act. As we explained in Chapter 3, the Clean Air Act authorized the EPA administrator to create performance standards only for “new” stationary sources of pollution. But there was a twist: the statute defined a “new source” as “any stationary source, the construction or modification of which is commenced after the publication of [an applicable New Source Performance Standard].” In other words, the Act included a mechanism—“modification”—by which a source’s identity might change from “existing” to “new.” In theory, treating modified sources as “new” could have served as a de facto limit on the duration of grandfathering, preventing old plants from permanently avoiding compliance with federal performance standards. After all, no plant could keep running forever without requiring at least some upgrades. But what sort of upgrades should qualify as a “modification” within the meaning of the Clean Air Act? For Congress and the EPA, answering this question proved every bit as difficult as determining whether it was the third, thirteenth, or thirtieth replacement plank that transformed the Ship of Theseus into a different vessel. As a result, many of the nation’s power plants have managed to enjoy seemingly indefinite immunity from New Source Performance Standards, even after undertaking comprehensive renovations. Why did Congress decide to treat modified sources differently than other existing sources?
Direct Federal Regulation of Stationary Sources under the Clean Air Act