On November 26, 2019, EPA issued guidance revising key Clean Air Act definitions in a way that could relax permitting requirements across a number of industries. The guidance narrows EPA's reading the word of "adjacent" in deciding whether different operations run by the same company qualify as a single source significant enough to require a pre-construction permit under the New Source Review (NSR) program. The new guidance instructs EPA to look at "physical proximity" as opposed to "functional interrelatedness," and could allow some operators to avoid the need for an NSR permit where such a permit would have previously been required. The NSR requirement triggers the need for greenhouse gas controls for certain sources.