Cumulative impact assessment: A synopsis of guidance and best professional practices
The US Council on Environmental Quality (CEQ) has indicated that there is increasing evidence that the most destructive environmental effects may actually result not from the direct and indirect effects of a given action, but instead from the combination of individual minor effects of numerous actions over time.1 The CEQ’s cumulative effects handbook recognizes the “cumulative effects analysis as an integral part of the National Environmental Policy Act (NEPA) process, not a separate effort.”2 Cumulative impact assessment (CIA) is as necessary and as much of a challenge in environmental assessments (EAs) as it is in environmental impact statements (EISs). In fact, CIA may be an even greater challenge in EAs, which are usually prepared for relatively small actions whose cumulative impacts are not always as evident as they are for the larger projects analyzed in EISs. Moreover, the issue of cumulative impacts has become one of the most widely litigated issues under the NEPA. The high number of challenges over cumulative impacts is likely to continue, if not increase, well into the future.