The 316(b) assessment process: evolution towards a risk-based approach

Since its inception, the 316(b) assessment process has undergone considerable evolution and refinement. In this paper, the authors review and discuss this evolutionary process focusing on several key scientific findings. Among these are that the potential for adverse environmental impact is relatively low for many ecosystem components (e.g., phytoplankton, microzooplankton); that the survival of entrained organisms is often quite high; that the prediction of adverse environmental impact is hampered by the present inability to effectively quantify compensatory processes; and that subsequent monitoring has revealed that the dire population consequences originally predicted for several aquatic populations have not been borne out. While this evolution has resulted in less divergence in the estimates of cooling water-related losses between the regulatory and regulated communities, accurate determination of the population level consequences of such losses remains elusive. This uncertainty makes final resolution of 316(b)-related issues difficult. To address these difficult issues, we propose an assessment approach based on an ecological risk framework coupled with adaptive resource management. This approach begins with a screening process which helps to focus the assessment on the key resources at risk, followed by a “weight-of-evidence” evaluation of all relevant predictive and retrospective information, and concludes with an evaluation of the relative cost and benefits of intake alternatives and the need for additional monitoring. Such an approach has been successfully employed at several large-scale 316(b) assessments completed in recent years and provides a mechanism for dealing with uncertainties in the assessment process, while at the same time ensuring reasonable protection of the environment.