he plant, expected to produce 5 million gallons of drinking water per day, enough for some 40,000 people, will serve a small water utility in Orange County, just south of Los Angeles.
It sets precedent as the first desalination that the Coastal Commission has approved since more strict regulations were adopted in 2019.
With environmental protection a concern, experts say smaller can be better.
"It's more nimble. The future is going to be all about modular solutions," said Newsha Ajami, a researcher at Berkeley Lab's Earth & Environmental Sciences Area.
Instead of relying on water pumped from hundreds of miles (km) away, through the State Water Project or the Colorado River, the South Coast Water District would now have its own water supply.
"We're watching what's happening at the Colorado River, and it's not good," said Rick Shintaku, general manager of the South Coast Water District, referring to the extreme drought that may force cutbacks of 15% to 30% for Californians and other Colorado River users. "Desalination could be part of that solution for water reliability for a broad region."
The project still requires other state permits but the Coastal Commission was seen as the most significant regulatory hurdle.
The proposed site is 25 miles (40 km) down the coast from where the Coastal Commission rejected a larger proposal by Poseidon Water, the infrastructure arm of Canada's Brookfield Asset Management.
Environmental groups that led the protests against the Poseidon plant were largely silent this time. Opponents including several Sierra Club activists spoke against the Doheny project at Thursday's hearing, concerned about the impact on marine life and the amount of energy required to pump ocean water through the plant's reverse osmosis filters.
The Coastal Commission staff found that the proposal minimized the harmful impacts and recommended approval.
Poseidon's plant would have sucked in massive amounts of water from above the ocean floor, killing sea life, according to Coastal Commission assessments. The Doheny plant will use a sub-surface intake that creates a barely perceptible current.
At Doheny, the brine that results from desalination will be mingled with the discharge of a neighboring wastewater treatment plant, mitigating the harmful effects of having two diffusers pumping effluent into the sea.
Tom Luster, a senior environmental scientist on the Coastal Commission staff, said the state is studying locations where similar plants might be feasible.
"This could be replicated at a number of places up and down the coast," Luster said. "It's a fairly small-scale facility, but it provides for the local needs and it frees up water for other communities."