Federal Agency Treatment of Uncertainty in Environmental Impact Statements under the CEQ's Amended NEPA Regulation Section 1502.22: Worst Case Analysis or Risk Threshold?

In 1986, the Council on Environmental Quality (CEQ) amended the National Environmental Policy Act (NEPA) regulations requiring worst case analysis in environmental impact statements, where data gaps or uncertainties appeared. After studying judicial interpretations of the 1978 data, the CEQ replaced worst case analysis with a "rule of reason" threshold. Thus, only when it is demonstrated through credible scientific evidence that there is a potential environmental effect is further discussion required. However, some courts, particulary in the Ninth Circuit, still demand worst case analysis, contending that the statutory language and the common law of the National Environmental Policy Act (NEPA) mandate such an analysis. The judicial and administrative handling of uncertainty under the NEPA is acceptable as a proxy for useful, verifiable, good faith agency compliance, providing some evidence that the drafting agency has considered, in the decision-making process, uncertainty of consequences, alternatives, and respective probabilities of occurrence. However, the CEQ's replacement of worst case analysis with a rule-of-reason threshold is endorsed.