The eventual decommissioning of Diablo Canyon nuclear power plant in coastal San Luis Obispo County will have potentially “significant and unavoidable” environmental impacts, according to a new report.
The draft environmental impact report analyzed how decommissioning and dismantling the 2,200-megawatt power plant will affect the ocean and land ecosystems around it. The plant was set to shut down its two nuclear reactors located just north of Avila Beach in 2024 and 2025.
San Luis Obispo County released the draft report on Friday, following more than two years of work at a cost of nearly $2.5 million.
Should the nuclear power plant be decommissioned beginning in 2024, it would take about seven years to plan, decontaminate the facility, demolish most large site structures and begin soil remediation work, according to the report.
Another seven years, from 2032 through 2039, would be spent completing the restoration of the power plant property.
The decontamination and dismantling will likely “destroy or degrade marine habitat;” “harm or disturb” marine invertebrates, fish, reptiles, birds or mammals; release pollutants into Diablo Cove; and impact historical, archaeological and tribal resources, according to the report.
The 14-year decommissioning timeline, however, is contingent on the plant decommissioning as originally planned. That’s no longer the state’s preferred path forward.
Senate Bill 846, signed by California Gov. Gavin Newsom in September, allowed for the allocation of a $1.4 billion forgivable loan to PG&E to help fund continued operations of Diablo Canyon. The Senate bill pushes for the power plant to operate another five years, or through 2030, to help the state meet its renewable energy goals while ensuring grid reliability.
Some decommissioning activities could happen should the plant continue to operate past its originally planned closure dates, the county’s report says. Those include the construction of permanent and temporary buildings on the power plant’s property.
“The county of San Luis Obispo is aware of the significant role Diablo Canyon Power Plant and the land that surrounds it has on our community,” County Supervisor Dawn Ortiz-Legg said in a prepared statement. “Public input is critical as we work together to determine next steps, and we welcome interested residents to review the Draft EIR, provide public comment and attend the upcoming study session.”
Opportunities for public comment on decommissioning impacts
The public has 60 days to review the report and provide input to the county.
The Diablo Canyon Decommissioning Engagement Panel, in conjunction with PG&E, will hold a public meeting on Aug. 9 from 6 to 8 p.m. at the County Government Center at 1055 Monterey St.
Additionally, the county Planning Commission will hold a study session to discuss the report on Sept. 5 beginning at 9 a.m. at the County Government Center.
Once the comment period ends on Sept. 25, the county will review the comments and prepare any edits to the draft environmental impact report. It’s expected the final environmental impact report will be completed in early 2024.
What will decommissioning look like?
During decommissioning, PG&E proposes to dismantle most of the facilities at the power plant property.
This includes the nuclear reactor building, existing offices and the ocean water desalination facilities, according to the report.
The county’s report did not analyze the full removal of the ocean water intake structure for the once-through cooling system, marina breakwater or subsurface structures because those activities would have major impacts on air quality, biological resources, water turbidity and water quality, according to the report.
How will the environment potentially be impacted by decommissioning?
The report separates the environmental impacts from the decommissioning activities into four categories: “potentially significant and unavoidable,” “less than significant with mitigation,” “less than significant” and “no impact.”
The “potentially significant and unavoidable” impacts primarily center on the marine life in Diablo Cove adjacent to the plant.
The cove has been impacted during the entirety of the plant’s life — from construction activities causing harmful pollution, to the plant’s once-through cooling system that sucks in cold ocean water and pumps warm water back out.
Decommissioning the power plant will also impact the cove’s marine ecosystem, which provides habitat to a variety of organisms including kelp, algae, turtles, sea otters, seals, sharks and abalone.
During the removal and restoration of the power plant’s discharge structure — which releases water back into the cove from the once-through cooling system — PG&E has proposed building a cofferdam to isolate the ocean from the work area.
To build the cofferdam, massive circular steel cells would be built in the ocean to form a water-tight barrier. The water on the land side of the structure would then be pumped out, creating a roughly half-acre dry workspace to deconstruct the discharge structure, according to the report.
The impacts from the cofferdam would likely last about 14 months, according to the report. The activity would likely harm the marine life in the cove, the report says.
A large barge with a crane anchored in Diablo Cove would dismantle and remove the discharge structure, according to the report.
The once-through cooling system’s intake structures would also be sealed with concrete during the decommissioning activities.
Additionally, other large barges entering and exiting the marina at the power plant site could disturb or harm marine life, the report says. These barges would be used to transport away refuse, or to bring in gravel or other materials needed to demolish the power plant and restore the property.
Also, to help mitigate the potential marine impacts, PG&E must prepare and implement an eelgrass monitoring plan, a marine safety and anchoring plan, a water quality monitoring plan, a marine habitat restoration and monitoring plan, a marine mammal and sea turtle mitigation and monitoring plan, and an oil spill response plan. The utility must also conduct a preconstruction survey for black abalone and a mooring placement habitat survey, according to the report.
Another “potentially significant and unavoidable” impact from the decommissioning activities would be on historical, archaeological or tribal resources at the property, according to the report.
This would happen while the buildings and their foundations are demolished and removed, the report says.
To mitigate this, PG&E must ensure archaeologists and Chumash tribal experts monitor the work.
“Less than significant” environmental impacts would largely affect land ecosystems during the decommissioning activities, the report says.
The wildlife at the Diablo Canyon property could experience a temporary loss of habitat, disruption of breeding behavior, harm from construction equipment or workers, and exposure to hazardous materials and dust during the decommissioning activities, according to the report.
However, PG&E can mitigate this by training its workers, implementing a habitat restoration and revegetation plan, protecting mature trees and implementing a weed management plan, the report says.
PG&E proposes to build new buildings to facilitate decommissioning
Also during decommissioning, PG&E plans to build several permanent structures and one temporary building.
A 12,000-square-foot building would be built to serve as the new security building for the Independent Spent Fuel Storage Installation and another nuclear waste storage facility.
Another 15,000-square-foot building would provide storage for larger materials, equipment, vehicles and trailers.
To support security-related, long-term operations of the Independent Spent Fuel Storage Installation, PG&E proposes building a 4,800-square-foot security warehouse, the report says.
A 5,400-square-foot warehouse would also be built to house the equipment needed to support the spent nuclear fuel transport, according to the report.
Plus, a 2,880-square-foot temporary decommissioning office building is proposed to be built on the property during the process, the report says.
These buildings would be built on existing disturbed footprints on the power plant property and therefore have less than significant impacts on the environment as long as mitigation measures are in place, the report says.
Alternatives, future uses noted in county report
In a “delayed decommissioning alternative” presented should the power plant remain online past 2024 and 2025, the county noted in the report that these buildings could be constructed before the plant decommissions.
However, any further analysis of the potential environmental impacts of the plant’s potential extended operations was beyond the scope of the draft environmental impact report, according to the report.
Other alternatives mentioned in the report for consideration by the Planning Commission include the possibilities that decommissioning could be delayed to up to 60 years or if the state fails to grant permits to deconstruct the power plant.
The report also mentioned several concepts to potentially reuse the property.
This included a proposal by REACH Central Coast — an economic think tank — alongside Cal Poly, the yak titʸu titʸu yak tiłhini tribe and Land Conservancy of San Luis Obispo to build a “clean tech innovation park.”
Additionally, the power plant property could maintain the desalination plant to help provide San Luis Obispo County with water, the report said.
The power plant property could also be turned into a camping destination, hotel or resort, or be used for various energy projects and research facilities, institutional facilities or cultural and historical preservation, the report says.
