Adverse environmental impact: 30-year search for a definition

Area of Science:

• Environmental Law
• Ecology
• Aquatic Biology

Background:

• Section 316(b) of the Clean Water Act mandates minimizing adverse environmental impact (AEI) from cooling-water intake structures.
• Defining AEI has been a persistent challenge since the Act's passage in 1972, leading to regulatory and scientific debate.
• A 1995 Consent Decree prompted the Environmental Protection Agency (EPA) to develop new rules, reigniting discussions on AEI.

Purpose of the Study:

• To review and compare eight proposed definitions of adverse environmental impact (AEI).
• To analyze the scientific and policy implications of different AEI definitions.
• To recommend a path forward for defining AEI in the context of Section 316(b).

Main Methods:

• Literature review and comparative analysis of eight proposed AEI definitions.
• Categorization of definitions based on biological organization level (population vs. other).
• Evaluation of stakeholder perspectives and policy integration challenges.

Main Results:

• Six of the eight reviewed AEI definitions focus on population-level or higher biological impacts.
• Two definitions deviate from population-based approaches: a 1% cropping of near-field organisms and the "one fish equals AEI" concept.
• The "one fish equals AEI" definition conflates science-based ecological impacts with policy-based public trust resources, hindering consensus.

Conclusions:

• Population-based definitions of AEI are scientifically robust and facilitate consensus.
• Incorporating population-level AEI definitions into Section 316(b) guidance is recommended.
• State authority to protect public trust resources remains unaffected by adopting population-based AEI definitions.