Uses of Tiered Significance Levels in NEPA Documents

2014 INTRODUCTION The significance of environmental impacts plays a key role in how agencies of the Federal government implement the National Environmental Policy Act (NEPA). 1 Section 102 of NEPA establishes a requirement that agencies include a detailed statement of the environmental impacts (environmental impact statement, or EIS) of " proposals for legislation and other major Federal actions significantly (emphasis added) affecting the quality of the human environment ". 2 The Council on Environmental Quality (CEQ) has established a process by which agencies can identify categorical exclusions allowing for expedited NEPA documentation for " categories of actions which do not individually or cumulatively have a significant (emphasis added) effect on the human environment… " 3. CEQ also allows agencies to prepare " Findings of No Significant Impact " (FONSIs) in lieu of EISs for actions lacking potentially significant impacts. 4 CEQ has developed limited but useful direction on evaluating the possible significance of environmental impacts calling for an integrated consideration of " context and intensity ". 5 Caselaw has established that agencies must supplement an EIS only if there is new information indicating that a previously evaluated action " will affect the quality of the human environment in a significant (emphasis added) manner or to a significant (emphasis added) extent not already considered. 6 Most agencies distinguish between impacts that are significant and those that are not significant. Few however have attempted to more finely classify impacts on the basis of significance. The tendency has been to identify each environmental impact as either significant or not significant and then focus on those impacts passing this initial significance screen. A more analytical approach would be to recognize impacts as occurring on a spectrum of significance. Somewhere on this spectrum a threshold would theoretically exist above which an impact would be significant; however, it may not always be possible to sharply delineate a meaningful threshold. Impacts may lie above or below the threshold, but those falling closer to the threshold may display intermediate stages of significance that still warrant further consideration. Expressed mathematically, significance could perhaps be better expressed as a smooth curve representing a continuous distribution rather than as a simple two-point discrete distribution. Impacts whose significance is substantially greater than the threshold could warrant greater subsequent focus than impacts only slightly above the threshold; impacts whose significance falls just under the threshold may not warrant being discounted as impacts clearly …