$180 million desalination plant to be built in stages

The Rio Grande Valley has moved a step closer toward turning seawater into an abundant drinking-water source. But an originally planned, $180 million desalination plant will have to wait.

In a recently released report from the Texas Water Development Board, officials confirmed that the Brownsville Public Utility Board has completed an 18-month pilot study on seawater desalination, and now is planning to build a larger "demonstration project" at the Port of Brownsville.

However, the full-scale plant officials initially planned to build is just too expensive to construct all at once, and so the utility is planning to build it in phases, engineers said.

"We believe we can save funds on a full-sized project by doing the demonstration facility first," said Bill Norris, principal engineer at NRS Consulting Engineers, which oversaw the Brownsville pilot project. "And it would be a demonstration not only for the Valley, but for the rest of the state."

After years of studying the feasibility of tapping seawater as a new water source, BPUB and the Texas Water Development Board opened a pilot desalination plant from February 2007 to July 2008. The plant was a miniature of a large-scale plant, treating only about 100,000 gallons of salty water a day. The water was not used, but instead reconstituted and returned to the shipping channel.

Although the region and state now have numerous desalination plants that treat groundwater, Brownsville's pilot plant was the first seawater-desalination facility in Texas, and one of only a handful in the country.

Investigating the possibility of using seawater is important in a region that depends heavily on the overtaxed Rio Grande, said Jake White, director of technical services for NRS Consulting Engineers.

State environmental officials have said that every drop of the Rio Grande's water is appropriated - to a city, a water utility, an irrigator or a landowner. Meanwhile, Mexico doesn't always promptly deliver the water it owes to the United States under a binational treaty, leaving the Valley's water reserves perilously low during a drought, engineers said.

Currently, U.S. water reservoirs are nearly full after heavy rainfall in 2008, but that won't always be the case, they said.

"Right now, when we're not in the position of saying ‘we have to have water now,' is the time to pursue (desalination)," White said.

Texas also needs all the new water supplies it can get, according to TWDB. The state will need 3.7 million acre feet of new water by 2010 and nearly 9 million acre feet by 2060, the agency reports.

An acre-foot is the amount of water it takes to cover an acre, one foot deep, and provides enough water for two households for a year.
For that reason, seawater desalination is a needed strategy for the state, said Jorge Arroyo, director of TWDB's Innovative Water Technologies program.

"It's being practiced in many other parts of the world," Arroyo said.

‘Paving the way'
Soon, Brownsville will have the first seawater-desalination plant in Texas that will actually contribute to the water supply.

BPUB's demonstration facility, projected to be completed in 2012, would treat 2.5 million gallons of seawater per day and eventually provide 9 percent of the drinking water in BPUB's service area, according to officials.

The price tag for this plant will be $67 million, which will include much of the infrastructure for a large-scale facility, said Genoveva Gomez,
director of water and wastewater for BPUB.

BPUB is proposing paying for the plant's construction partly through a loan from the Texas Water Development Board and partly through a state grant.

Ultimately, city officials and engineers hope to expand that capacity to 25 million gallons per day.

"When we are ready to build the larger plant, a lot of the infrastructure will already be in place," Gomez said.

Engineers learned many lessons from the pilot plant that they will apply to the larger demonstration plant, including how best to remove sediment and contaminants from shipping channel water, Norris said. Those lessons caused the projected cost of a full-scale, 25-million-gallon plant to increase from $150 million to more than $180 million.

"Before, it was all an on-paper evaluation," Norris said.

A smaller-scale demonstration project would allow officials to collect more data and further refine the desalination process, likely cutting down on future costs, the engineers said.

Treating seawater is more costly in general than treating salty groundwater or river water. The region's largest groundwater-desalination plant, for example, only cost $30 million to build. But seawater would be a more abundant and reliable source than groundwater, officials said.

South Padre Island also is exploring seawater desalination. The Laguna Madre Water District has opened its own pilot plant, which cost $500,000, said Gavino Sotelo, general manager of the water district. The pilot plant will remain operational until April 2009, he said.

Ultimately, the district, with assistance from the state, hopes to build a plant that would treat 1 million gallons per day of seawater.
"We'll be the first plant in the state pulling water directly from the ocean," Sotelo said.

With these two projects, the Valley region is really "paving the way" for the rest of Texas to begin using seawater, Arroyo said. "(Valley officials) have demonstrated a lot of foresight in developing this water-supply source," he said.