5. In determining the licensing requirements for nuclear reactors, the Nuclear Regulatory Commission (NRC) adopted a zero-release assumption: that the permanent storage of certain nuclear waste would have no significant environmental impact and that potential storage leakages should not be a factor discussed in the appropriate environmental impact statement (EIS) required before permitting construction of a nuclear power plant. This assumption is based on the NRC's belief that technology would be developed to isolate the wastes from the environment, and it was clear from the record that the NRC had \"digested a massive material and disclosed all substantial risks\" and had considered that the zero-release assumption was uncertain. There was a remote possibility of contamination by water leakage into the storage facility. An environmental NCO sued, asserting that the NRC had violated the regulations governing the E15 by arbitrarily and