Environmental mitigation is the process by which project proponents apply measures to avoid, minimize, or compensate for the adverse effects and environmental impacts resulting from their projects.
The National Environmental Policy Act (NEPA) directs federal agencies, when planning projects or issuing permits, to conduct environmental reviews to consider the potential effects on the environment by their proposed actions. NEPA also established the Council on Environmental Quality (CEQ), which is charged with the administration of NEPA.
The CEQ regulations (40 CFR 1508.20) define mitigation as:
- Avoiding an impact altogether by not taking a certain action or parts of an action
- Minimizing impacts by limiting the degree or magnitude of the action and its implementation
- Rectifying the impact by repairing, rehabilitating, or restoring the affected environment
- Reducing the impact over time by preservation and maintenance operations during the life of the action
- Compensating for the impact by replacing or providing substitute resources or environments
Although it is the policy of the Federal Highway Administration to incorporate measures to mitigate impacts, NEPA does not impose a substantive duty on agencies to mitigate adverse environmental effects. Mitigation is mandated under California Environmental Quality Act (CEQA) Guidelines whenever a project may result in a significant impact to the environment. CEQA Guidelines §15126.4(a) requires lead agencies to consider feasible mitigation measures to avoid or substantially reduce a project’s significant environmental impacts.