Central Coast Water Board releases draft permits for Diablo Canyon Nuclear Power Plant

SAN LUIS OBISPO - The Central Coast Regional Water Quality Control Board has released two draft permits for public comment. The permits are necessary to extend operations at Diablo Canyon Nuclear Power Plant, as directed by Senate Bill 846 (2022). The comment period closes on Dec. 8.

Operated by Pacific Gas & Electric Company, the plant located in San Luis Obispo County near Avila Beach is California’s last operable nuclear power plant. The draft permits which require approval by the Central Coast Water Board to become final, contain critical regulatory requirements for PG&E to continue operations following the state mandate to extend the plant’s operational timeline.

The drafts include stricter effluent limits and monitoring requirements to strengthen environmental protection and ensure compliance with the latest state and federal water quality standards. As part of the permit renewal process, regional board staff comprehensively evaluated PG&E’s compliance with the plant’s current discharge requirements and incorporated new regulatory provisions. Among these are requirements to bring the plant in line with the state’s 2010 Once-Through Cooling Policy, which aims to reduce the harmful effects cooling water intakes used at coastal power plants can have on marine life.

The permit renewal process is focused on protecting water quality and ensuring that PG&E operates the plant in compliance with current water quality standards; other aspects of Diablo Canyon’s operations, such as electricity generation, fall outside of the regional board’s mandate and will not be addressed.

“If adopted, the draft permits would improve water quality protection over those issued decades ago, and they would increase monitoring to ensure that the plant’s cooling water and other wastewater discharges are protective of our coastal waters,” said Ryan Lodge, executive officer for the Central Coast Water Board. “Protecting water quality in our coastal waters is a top priority for the regional board.”  

To continue operations, PG&E must obtain an updated National Pollutant Discharge Elimination System (NPDES) permit, which regulates how the plant discharges once-through cooling water, desalination brine and treated wastewater into the ocean. In addition, PG&E is required to secure a Clean Water Act Section 401 water quality certification from the regional board before the federal Nuclear Regulatory Commission can finalize its licenses for the plant’s two reactors.

The regional board is closely coordinating with state and federal agencies and is committed to ensuring a process that allows all interested parties to stay informed and provide meaningful input. On Nov. 12, the regional board will hold a workshop to answer questions and solicit public comments and it expects to consider the draft permits in early 2026.

More information on the permitting process and access to related documents can be found on the regional board’s program page.

The Central Coast Water Board is responsible for protecting and restoring water quality in a 300-mile-long coastal region, from southern San Mateo and Santa Clara counties to the northern part of Ventura County. Protecting beneficial uses in streams, the ocean, and groundwater is essential to ensuring water quality and protecting the health of humans and wildlife.