Opinion of the Court
1
Plaintiffs claim North Carolina breached the Compact in December 1997, when (as it admits) it ceased all efforts toward obtaining a license. At that point, in their view, North Carolina was no longer “tak[ing] appropriate steps to ensure that an application for a license to construct and operate a [low-level radioactive waste storage facility] is filed with and issued by the appropriate authority,” Art. 5(C), 99 Stat. 1877. North Carolina says that once the Commission ceased providing financial assistance on December 1, and once it became clear there was insufficient funding to complete the licensing phase, there were no more “appropriate” steps to take. The Special Master concluded that the phrase “appropriate steps” in Article 5(C) was ambiguous, and that the parties’ course of performance established that North Carolina was not required to take steps toward obtaining a license once it was made to bear the remaining financial burden of the licensing phase. Second Report 10–24, 35–36. Plaintiffs take exception to that conclusion.
Article 5(C) does not require North Carolina to take any and all steps to license a regional-disposal facility; only those that are “appropriate.” Plaintiffs contend that this requires North Carolina to take the steps set forth in the regulations of the Nuclear Regulatory Commission governing the filing and disposition of applications for licenses to operate radioactive waste disposal facilities, 10 CFR pt. 61 (1997). Those regulations set forth some, but certainly not all, of the “steps” the State would have to take to obtain a license. But Article 5(C) does not incorporate the regulations by reference, much less describe them as the appropriate steps.
We could accept Plaintiffs’ contention if “appropriate” meant “necessary” (the steps set forth in the regulation are assuredly necessary to obtaining a license). But it does not. Whether a particular step is “appropriate”—
