PG&E – Diablo Canyon

The Central Coast Regional Water Quality Control Board is preparing to issue two permits required for Pacific Gas and Electric Company's continued operations of Diablo Canyon Nuclear Power Plant near Avila Beach in San Luis Obispo County. The permits include a five-year renewal of the National Pollutant Discharge Elimination System (NPDES) permit, which regulates discharges such as cooling water and treated process water, and issuance of a Clean Water Act section 401 water quality certification. These regulatory actions follow federal and state decisions to extend Diablo Canyon's operations to 2030.

At the same time as the Central Coast Water Board is considering the two draft permits for Diablo Canyon, the federal Nuclear Regulatory Commission is considering PG&E’s request for 20-year license renewals for each of the two Diablo Canyon reactors. The NRC has released a safety evaluation report and an environmental impact statement in response to PG&E’s application. As explained below, renewals of the Diablo Canyon NRC licenses are dependent upon permitting by the Central Coast Water Board.

Central Coast Water Board Permits

California legislation passed in 2022 requires the California Public Utilities Commission to extend Diablo Canyon’s operations to October 31, 2030. To allow continued operation of the power plant, the Central Coast Water Board will consider two actions: renewing the National Pollutant Discharge Elimination System (NPDES) permit and issuing a Clean Water Act section 401 water quality certification.

NPDES Permit

The Central Coast Water Board regulates waste discharges from the power plant via the NPDES permit. These waste discharges include cooling water, treated process water, desalination brine, stormwater, and treated domestic wastewater discharged into Diablo Cove.

Clean Water Act Section 401 Water Quality Certification

Before the NRC’s license renewals can take effect, the Central Coast Water Board must certify that discharges to ocean waters resulting from the license renewals will comply with California’s water quality standards. Among other things, the Clean Water Act section 401 water quality certification will rely on the NPDES permit requirements, which include effluent limitations to control the waste discharges described above, to confirm water quality standard compliance.

Permit and CWA Section 401 Certification Renewal Process

The NPDES permit renewal process includes a comprehensive evaluation of PG&E’s compliance with current discharge requirements and the incorporation of any new regulatory provisions. These may include updated standards for the once-through cooling system. Updated permit conditions will reflect the latest state and federal water quality standards and include monitoring to ensure compliance and environmental protection. The water quality certification will reflect the revised NPDES permit requirements.

The NPDES permit renewal and water quality certification may be considered for adoption by the Central Coast Water Board in February 2026. If adopted, the new permit and water quality certification will be in effect for five years.

Prior to the potential February 2026 hearing, the permitting process will involve the following actions:

1. Review of technical data and monitoring reports
2. Coordination with state and federal agencies
3. Release of draft permits for a public review and comment period
4. A public workshop to solicit public comments on the draft permits prior to adoption

Participate and Stay Informed

There are a variety of ways for agencies, interested persons, and the public to participate in and stay informed on the permitting process.

1. Sign up for our email subscription service.
2. Public comment period – a public comment period will begin following the release of the draft permits in late October 2025.
3. Public workshop – a hybrid public workshop will be held on November 12, 2025, to present the draft permits, answer questions, and receive comments.

Documents

• Permitting Actions for Diablo Canyon Nuclear Power Plant Information Sheet (English | Spanish)
• Press releases and media advisories related to Diablo Canyon Power Plant