How many lawyers, regulators, engineers, and contractors does it take to change a light bulb? Lots, if you happen to be changing the light bulb at a "stationary source" of pollution, and the bulb change counts as a "modification" of the source under the Clean Air Act (CAA).¹ According to that statute, any physical or operational change that results in an increase in the source's emission of certain pollutants triggers an exacting and costly set of permitting requirements. Since emissions can increase if a source operates faster or more frequently than it did before, numerous physical or operational changes could potentially trigger an "emissions increase" within the meaning of the statute. Perhaps not changing a light bulb, but replacing old turbine blades, upgrading a computer system, fixing leaky pipes, repairing a broken gauge, or any of a host of other activities might increase total emissions (by causing a source to operate at a higher capacity), and, if these activities count as physical or operational changes, they will all have to undergo the rigors of the CAA's aggressive permitting requirements.

Something seems intuitively wrong with that, even from a committed environmentalist's perspective. Some activities, though technically physical or operational "changes," appear to be so much a part of the routine operation of power plants, incinerators, factories, or other facilities that it seems illogical to subject them to permitting requirements designed to regulate more significant construction or modification programs. And so, the U.S. Environmental Protection Agency (EPA) has quite sensibly chosen to exempt certain types of activities, known as "routine maintenance, repair, and replacement" (RMRR) activities, from the stringent permitting requirements that the CAA would otherwise impose. So, you can change your light bulb or fix your leaky pipe without having to worry, but if you decide to spend a million dollars completely redesigning and renovating your main generator, you'll need to go get your permit.