County desalination feasibility presented; consultants outline five alternatives, large cost and permitting hurdles

Corollo Engineers presented the findings of a yearlong feasibility study on ocean desalination for San Luis Obispo County, telling the Cambria Community Services District board the county has five screened alternatives that range from small local projects to regional facilities producing up to about 7,800 acre‑feet a year.

"Desalination is a drought‑proof supply option," said Anthony Simo, the project engineer with Corollo. "But permitting in the coastal region is difficult, and environmental mitigation and soft costs can drive the budget into the hundreds of millions." Simo said the firm’s planning‑level capital estimates fall roughly between $200 million and $600 million, with wide uncertainty depending on site‑specific ocean infrastructure and pipeline distances.

Simo explained the basic components of ocean desalination—subsurface seawater intake, reverse osmosis treatment, post‑treatment remineralization and an ocean outfall for brine disposal—and said state rules favor subsurface intakes to reduce harm to marine life. He noted that some alternative intake technologies remain unproven and are not included in the five screened options.

The study identifies three alternatives that could include Cambria, with the smallest local options producing several hundred acre‑feet and the largest regional options producing several thousand. The consultant said tradeoffs are familiar: larger projects enjoy economies of scale but require much more pipeline and infrastructure and face larger environmental reviews and permitting burdens.

Board members pressed the consultant on what distinguishes sites that were advanced. "We focused on coastal hydrogeology and areas of relatively low biological sensitivity," Simo said, adding the county used public datasets and a spatial 'pancake' overlay to screen sites. He said Diablo Canyon was not included because of rocky nearshore geology that makes subsurface intakes infeasible.

Vice President Dean asked about marine sanctuaries and confirmed the study seeks to avoid marine protected areas and minimize impacts to national marine sanctuaries. Simo said using existing municipal wastewater outfalls to co‑mix brine with treated effluent — rather than discharging concentrated brine by itself — is a preferred permitting approach when available.

Public speakers did not oppose studying options but urged close attention to environmental impacts. "Ocean desal is problematic in many ways," said resident Ted Sigler, who suggested potable‑reuse investments may be a higher priority for some service areas.

Next steps in the county plan include finalizing a public draft of the study in July, further outreach, governance and finance studies to define possible partner agreements, and more detailed environmental and hydrogeologic studies before any project selection. The board did not take action but directed staff to continue monitoring and public engagement.