When are changes to an existing system so extensive that they produce a “new” system? This question is conceptually important in any evolving organization, and can have important regulatory consequences if requirements for “existing” systems are substantially different than those for “new” systems. Emissions regulations under the Clean Air Act (CAA) contain many such situations, and on October 22 the US Environmental Protection Agency (EPA) adopted changes to the “project emissions accounting” it uses to decide whether modifications to an existing major source are so extensive as to trigger preconstruction New Source Review (NSR) requirements. This revision codifies into regulations a policy changed announced in 2018.
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