CARLSBAD ---- Separating salt from seawater on the Carlsbad coast would not significantly harm the marine environment, an environmental impact report published by Carlsbad concluded Friday.

The city is working with Connecticut-based Poseidon Resources to build a $270 million desalination plant at the Encina Power Station on the southern edge of the Agua Hedonia Lagoon.

The plant is on the coastal highway and is visible for miles in all directions.

In October, the City Council signed a 30-year agreement with Poseidon to supply the city with desalinated seawater. Carlsbad would use only about 9 percent of the 50 million gallons a day that the plant could produce.

The San Diego County Water Authority is still negotiating with Poseidon on a plan to sell the rest of the water to North County cities and communities.

The report states that using high-pressure filters to produce pure drinking water would not harm marine life or the environment any more than the nearby power plant.

In order to cool its power-producing boilers, Encina sucks an average of 576 million gallons of saltwater from the ocean every day. After it passes through the power plant, the heated saltwater is pumped into the ocean.

The desalination system would piggyback on the power plant's set of cooling pipes. Before the heated water is returned to the ocean, about 100 million gallons would pass through a series of filters, separating salt from water.

Filtering out fresh water would also result in about 50 million gallons of brine, which would then be mixed with the power plant's cooling water and returned to the ocean.

Poseidon Vice President Peter MacLaggan said Friday that his company conducted extensive tests to determine what effect the saltier water would have on marine life. He said Poseidon raised local species of fish, lobster and other marine life in an aquarium filled with enough salt to hit the maximum level that could be produced from the filtration operation.

"After months of study, we found that they all grew and reproduced and ate at the same rate as those that were raised under normal conditions," MacLaggan said.

The report states that elevated salt levels caused by the filtration process should not harm marine life near the plant's outfall. However, the report suggests that salt levels be continually monitored at along the Carlsbad coast to ensure that nearby ocean water is not saltier than expected.

Marco Gonzalez, an attorney for the Surfrider Foundation, said Friday that it is the plant's intake structure, not its salty expellant, that presents an environmental problem.

He noted that the Encina Power Station kills marine life and larvae in the process of using so much ocean water for cooling purposes.

He said that adding a new revenue source to the existing power plant means it may keep operating longer.

"By co-locating these plants, they're effectively trying to extend the life of these dinosaur power plants," Gonzalez said.

Gonzalez said he would like to see the city require Poseidon to accept responsibility for killing marine life if the Encina plant goes the way of the dinosaurs.

"If the power plant shuts down, then they should have to recondition the water intake," Gonzalez said.

MacLaggan said Gonzalez was correct in his assessment.

"If for whatever reason the power plant did shut down, then we would be required to get an intake permit for our facility," he said. "We would have to do whatever mitigation was necessary."

In addition to discussing salt levels and marine creatures, the impact report also recommended replanting all native vegetation that is disturbed when the plant is built.

Also, archaeologists have discovered American Indian artifacts on the land next to the 4-acre filtration plant. To make sure no buried relics are harmed when the plant is built, an archaeologist would have to be present at all times.

The public has 45 days to comment on the environmental impact report, which is posted on Poseidon's Web site at www.carlsbad-desal.com. Call (619) 595-7802 for more information.

Contact staff writer Paul Sisson at (760) 901-4087 or psisson@nctimes.com.