The final round of battles between the people who want to build the Poseidon desalination water plant, and the grass roots environmental groups who oppose it, began Thursday in a crowded city hall chamber in Huntington Beach.

Technically, the hearing before the State Lands Commission — the first of three key regulatory agencies that will consider the Poseidon plant over the next few months — was about the quality of an environmental report and whether or not to use underground pipes that already run between the proposed plant and the ocean.

The three-member commission voted late Thursday to approve the project as long as the operators agree to eliminate or reduce carbon emissions.

That vote paves the way for two more key regulatory hearings. In the spring, the Santa Ana Regional Water Quality Control Board is expected to look at the project. And at some point after that the California Coastal Commission will say yes or no. If approved, construction of Poseidon would take about three years.

But the go-ahead issued Thursday came after a day of public conflict that figures to follow the desalination project through the approval process.

Dozens of people spoke for and against the $1.1 billion plant.

Opponents beat drums and danced outside the meeting, and many expressed dismay that former U.S. Sen. Barbara Boxer and current U.S. Sen. Dianne Feinstein are supporting the project. Some in the audience booed Boxer — a long-time advocate of environmental causes — when she testified.

“I respect everybody’s views, I always have. For my whole career I’ve been an environmentalist,” Boxer said. “Ten years ago, I understood we’d be hit by fires and droughts. I honest to God do not understand how people can stand against a project that will give us mitigation… (against) a project that will give us safe drinkable water.

“People have a right to their opinion,” she added, “But they don’t have a right to the facts.”

Others also spoke in favor of the desalination facility, including representatives from the cities of Orange and Westminster, a Santa Ana school district official and a former Huntington Beach councilwoman.

More than a dozen environmental organizations questioned the need for purified ocean water. Former Huntington Beach Mayor Debbie Cook said Poseidon and officials with the Orange County Water District “cherry picked” numbers that would show a need for water, when none existed.

“Proving there is a need for this project isn’t just a matter of choosing the data” that is favorable, Cook said.

She said officials with the water district that serves 19 Orange County cities haven’t yet decided what to do with the water. “They have tied themselves into a pretzel trying to figure out what to do with this water,” Cook said.

Another group, Oak View Communidad, representing some of the lower income residents in the Oak View area of Huntington Beach, said the $3 to $6 per month cost will affect struggling families.

Victor Valladares said he works at a pizzeria and even a small increase in water prices could strain his budget. “This will definitely have an impact on us.”

Poseidon has a desalination plant operating in San Diego County.

Scott Maloni, a Poseidon vice president who has overseen the project for nine years, told the commission a lack of protected marine life makes Huntington Beach the perfect location for the project.

“There are no areas of special biological significance,” Maloni said, prompting shouts and cackles from opponents in the audience. “There are no kelp beds. In fact, this may be the most ideal spot along the California coast for a desalination facility.”

Union workers voiced supported the project, saying it would create jobs in Orange County and bolster the area’s economy.

“I know you care about this community and I know you care about creating good jobs,” Orange County Labor Federation President Gilbert Davila told commissioners. “That’s why I ask you to vote yes on this project. It will provide all these good jobs for these folks, our members.”

One of the project’s sticking points is money. Poseidon and investors would spend about $859 million to build out the plant, while the Orange County Water District would need to spend about $300 million more on new infrastructure to get the water to residents. Overall, the plant would produce about 12 percent of the county’s water needs.

Meanwhile, based on current costs, water drawn from traditional methods costs about $400 an acre foot, while desalinated water costs about $2,100 an acre foot, though both numbers are likely to change over time.