Cumulative impacts are not properly addressed in environmental assessments

Environmental assessments (EAs) refer to preliminary studies conducted within the environmental impact assessment (EIA) process in the United States; such studies are used to determine the significance of anticipated impacts of proposed actions. If significant impacts are identified, detailed studies leading to the preparation of environmental impact statements (EISs) are necessary. If no significant impacts are expected, findings of no significant impacts (FONSIs) are prepared and the EIA process is completed. Cumulative impacts (CIs) should be considered, along with direct and indirect impacts, in the significance determination documented within an EA. However, CIs may not receive detailed attention due to either the absence of specific requirements or uncertainty as to what to address. This study included a systematic review of CI considerations in 30 EAs prepared on a variety of project types in the United States. In general, it was determined that CIs are neither normally mentioned nor thoroughly addressed; in fact, only 14 EAs even mentioned the term. When CIs were mentioned, they were typically addressed in a qualitative manner without clear delineations of spatial and temporal study boundaries and utilized guidelines or methodologies. Therefore, if EAs are to continue to be decision documents for determining if EISs need to be prepared, significance determinations for CIs must be more systematically addressed and documented. Such documentation could refer to the consideration of CIs and the determination that they are not significant; in contrast; for some EAs the topic of CIs may be the determining issue in decisions to prepare EISs.