Impact significance determination—Basic considerations and a sequenced approach

Abstract

Determination of the significance of anticipated impacts of proposed projects is a key component in the overall environmental impact assessment (EIA) process. Definitions of significance and/or significant impacts are now included in the EIA guidelines or regulations of many countries and international organizations. Where possible in an EIA study, it is desirable to identify and/or establish the significance determination criteria prior to actual study conduction. This paper summarizes some findings of a survey of such definitions resulting from American, European, and other international experiences; both generic definitions and substantive area definitions are highlighted. Traditional perspectives on significance determination have involved institutional (or governmental or regulatory), technical (or professional substantive area), and public interest considerations. A sequenced approach for impact significance determination is described, with this approach organized around ten groups of issues or questions. Examples of such issues include project type/size, project locations in areas with protected or critical resources, and environmental stresses resulting from waste residuals from the project. Examples of significance criteria pertinent to the issues are presented through the paper. Finally, the uses of significance criteria can be noted; included in such uses are: (1) determining if an environmental impact statement (EIS) will be required, or if an environmental assessment/finding of no significant impact (EA/FONSI) will surface; (2) identifying the impacts that should be mitigated; (3) planning a baseline and/or post-EIS environmental monitoring program; and (4) documenting the interpretive rationale used in the conduction of the environmental impact study.