State water-quality regulators yesterday postponed a decision on a discharge permit for a proposed desalination plant in Carlsbad that would convert seawater into drinking water.

The San Diego Regional Water Quality Control Board's 30-day postponement will allow its staff to make final changes to the plant's proposed discharge permit and provide more time for public review.

The delay also will allow the state agency to decide on the discharge limits for the desalination plant at the same meeting it considers whether to renew a discharge permit for the Encina Power Station.

The desalination plant, which would be built by Poseidon Resources Inc., would operate in tandem with the Encina Power Station, which is owned by NRG Energy Inc.

The permits from the regional board are aimed at minimizing the plants' impacts on marine life and the environment.

A standing-room-only audience of more than 100 people attended the public hearing, which featured more than 20 speakers. Environmentalists lined up to oppose the desalination project, while business and government leaders spoke in favor.

“Growth is going to occur and we have to be prepared for it,” said Carlsbad Mayor Bud Lewis, whose city intends to buy half the water produced by the Poseidon plant.

David Hogan of the Center of Biological Diversity offered a different opinion.

“The purported benefits of the Carlsbad desalination plant have been wildly exaggerated, while very real harm to the environment has been ignored,” Hogan said.

Poseidon Resources wants to build a $270 million desalination plant on about 4 acres within the 95-acre footprint of the Encina Power Station on the southern shore of Agua Hedionda Lagoon and the Pacific Ocean.

To produce 50 million gallons per day of drinking water, the Poseidon plant would siphon 100 million gallons from the 600 million gallons daily already being drawn from the lagoon to cool the power plant's steam-powered turbine system.

At yesterday's public hearing, Peter MacLaggan, Poseidon's senior vice president, said his firm can comply with the state's proposed salinity limit of 40 parts per thousand at the ocean. That's about 20 percent higher than the normal salinity of seawater, which is about 33.5 parts per thousand.

The salinity of the discharge water will be roughly equal to a heaping tablespoon of salt in a quart of water, MacLaggan said.

The company also is willing to monitor salinity levels continuously rather than weekly as originally proposed by the regional board staff, MacLaggan said. To comply with the proposed discharge limit, Poseidon needs to dilute its super-salty wastewater by mixing it with the cooling water used by the Encina power plant.

Scientists hired by Poseidon said the desalination facility will not significantly increase the amount of marine life – from small fish, eggs and larvae to plankton – that is killed as it passes through the power plant.

Environmentalists are leery of the proliferation of coastal desalination plants because they could prolong the life spans of once-through seawater cooling systems used by electric generating plants.

Each day, 21 power plants along California's coast pull in nearly 17 billion gallons of seawater, which is virtually sterilized as it passes though the plants.

The Carlsbad City Council approved the Poseidon project Tuesday. The project requires additional permits from the California Coastal Commission and state Department of Health Services and a lease from the State Lands Commission.