Why it matters: An EIR’s reliance on the future review and clearance of a project by a federal agency can be adequate mitigation for potentially significant impacts under CEQA. Facts: Two applicants in Kern County requested a zone change and conditional use permit in order to build and operate a wind farm in the Tehachapi Wind Resource Area. The County prepared and certified an Environmental Impact Report (EIR) for the project in accordance with the California Environmental Quality Act (CEQA) and approved the applications. The EIR indicated that the project’s wind turbine generators (WTGs) might pose a significant safety hazard to aircraft and gliders using a nearby private airport because the application proposed a maximum height of 500 feet. In response to the potentially significant impact identified in the EIR, the project approval required the applicant to obtain a “Determination of No Hazard to Air Navigation” from the Federal Aviation Administration (FAA) for each WTG prior to issuance of building permits. FAA regulations establish standards for determining obstructions in navigable airspace. Citizens Opposing a Dangerous Environment (CODE) challenged the approval by claiming, among other things, that the County’s EIR failed to describe a mitigation measure that could avoid or minimize significant impacts to aviation safety and that the County abdicated its statutory duty under CEQA by deferring to the analysis and determination of another agency. Decision: Key among the arguments raised by CODE was the point that the FAA cannot enforce its own “hazard/no-hazard” determinations because it has no authority to halt construction or require design changes. However, the court quickly noted that the County retained the authority to enforce the mitigation by requiring a “No Hazard” determination before the County would issue building permits for the WTGs. As the County staff explained in a report to the Board, if the FAA determines that the project would result in a potential obstruction unless reduced to a specific height, the project proponents would be required to work with the FAA to resolve any adverse effects on aeronautical operations or abandon the project. CODE also argued that past actions showed the mitigation would not be effective. Presumably, the FAA had issued prior No-Hazard determinations where CODE claimed hazardous aviation impacts still existed. The court responded by clarifying that whether the proposed mitigation measure will really work is not the appropriate question. Instead, the court explained, the proper inquiry is whether the public agency had a sufficient basis in expert opinion and other evidence to conclude that the potential impact of the project had been mitigated to a level of insignificance. In this situation, the court found that it was entirely reasonable for the County to rely on the expertise of the federal agency charged with the entire field of aviation safety. Practice Pointers: When relying on the regulatory approval by another agency to mitigate a potentially significant impact: Make sure the mitigation is an enforceable means to avoid or minimize the impact. If the other agency does not have the authority and responsibility to limit the project, make sure the lead agency will withhold permits unless the effects are appropriately limited. Make sure the record demonstrates the expertise of the other agency.