Regional Water Board Approves Applications for Diablo Canyon’s Extended Operations

The regional board that protects the Central Coast’s water resources approved applications for the continued operation of Diablo Canyon Power Plant in San Luis Obispo County.

On Thursday (Feb. 26), the Central Coast Regional Water Quality Control Board voted unanimously to approve Diablo Canyon’s applications for:

• A renewed discharge permit under the National Pollution Discharge Elimination System program

• A Federal Clean Water Act Section 401 water quality certification

The board’s approval of the water quality certification is the last step in California’s process to keep Diablo Canyon open through 2030, per Senate Bill 846. A federal process to renew Diablo Canyon’s license for 20 years remains on track.

The approval follows the California Coastal Commission’s approval in December of a Coastal Zone Management Act Consistency Certification and a Coastal Development Permit for Diablo Canyon.

The U.S. Nuclear Regulatory Commission reviewed Diablo Canyon’s license renewal application. The commission found in June 2025 that Diablo Canyon is safe and environmentally sound to operate for another 20 years.

The Nuclear Regulatory Commission is expected to issue its decision on Diablo Canyon’s 20-year license renewal application this spring.

“We appreciate the Regional Water Quality Control Board for its thoughtful consideration of our applications,” said PG&E Senior Vice President and Chief Nuclear Officer Paula Gerfen. “These approvals allow us to continue operating our once-through cooling system as we have throughout our history, remaining respectful and responsible stewards of the surrounding environment.”

Permits protect water quality

The water board’s vote follows a public process that included input from many groups.

The board held public meetings to collect public comments and invited tribal communities to participate in the process.

Board members also considered environmental justice, including how the approvals would affect disadvantaged communities and sources of drinking water.

Following this extensive public process, the water board’s staff report concluded that the approvals would protect water quality and meet all state and federal requirements.

As part of the permitting process, Diablo Canyon will:

·       Augment and update existing water discharge monitoring parameters

·       Perform advanced monitoring and reporting, including ecological monitoring, to ensure discharges continue to meet water quality standards

·       Conduct new studies and prepare technical reports to update prior studies as part of the plant’s culture of continuous improvement

Diablo Canyon key to energy transition 

The board noted that the applications would allow Diablo Canyon to continue providing clean power during California’s energy transition.

Diablo Canyon provides electricity to about 10% of Californians and makes up nearly 20% of California’s clean energy.

In 2016, with state goals to add solar and wind energy and a decline in demand, PG&E agreed with environmental and labor groups to retire Unit 1 in November 2024 and Unit 2 in August 2025.

State regulators approved the agreement in 2018.

But after statewide rotating outages during a heat wave in 2020 and new demand projections in 2022, California lawmakers passed and Gov. Gavin Newsom signed Senate Bill 846, directing Diablo Canyon to run through 2030 for grid reliability and clean energy supply.

In 2023, Diablo Canyon submitted a license renewal application to the U.S. Nuclear Regulatory Commission to renew its license.

On Aug. 27, 2025, Diablo Canyon’s Unit 2 began extended operations — one day after it was set to shut down. Unit 1 began extended operations in November 2024.

Meeting energy demand 

Beyond being the state’s largest source of clean energy, Diablo Canyon runs 24/7. That makes it a steady power source as energy needs increase across the state.

Overall, the California Energy Commission expects peak electricity demand to grow by more than 20 gigawatts by 2045. That is equal to the energy of  nine Diablo Canyons. Big drivers include:

• Electric vehicles, with growth forecasted at 8 gigawatts

• Electrifying home appliances, with growth forecasted at 4 gigawatts

• Data centers, with growth forecasted at 5 gigawatts

The commission’s 2025 Electric Reliability Report also stated that “system reliability is expected to continue to significantly improve due to [several factors that include] the near-term retention of Diablo Canyon Power.”

Benefits for customers 

Diablo Canyon’s extended operations through 2030 provide many benefits to electric customers across California.

For example, 2025 estimates show that Diablo Canyon resulted in wholesale electricity costs savings of $330 million for customers across the PG&E electric system.

There are big societal benefits as well.

Extended operations include cost benefits of $450 million annually due to avoided greenhouse gas emissions.

Diablo Canyon’s extended operations through 2030 are expected to annually reduce greenhouse-gas emissions equivalent to carbon-dioxide emissions from 1.6 million cars.