One of the potential solutions to drought in the Colorado River basin - a major test of desalination - was an environmental and economic success, UA researchers and U.S. officials said this week.

But 20 years after the Yuma desalination plant was built for $250 million in federal tax dollars, it's still not clear if it will ever run permanently, or when a decision might be made.

The plant has been seen by backers in various water agencies as a partial solution to the drought issues plaguing the Colorado River that provides much of Tucson's drinking water. By some environmental groups, it's also been seen as a potentially destructive boondoggle.

A new study led by a University of Arizona researcher found that the plant was able to run for a year in 2010-2011 without disrupting a fragile, marshy ecosystem south of the Mexican border in the Colorado River delta.

The plant also ran below its budgeted cost and ahead of schedule - but for now, there's no money to run it permanently.

THE ENVIRONMENT

During the test, the plant ran at one-third of its capacity, which is enough desalted water to serve nearly 250,000 households annually. The plant is designed to treat salty irrigation runoff water originally from the Colorado River before that water is delivered to Mexico to satisfy U.S.-Mexican treaty obligations.

The new $250,000 study released this week found that the Cienega de Santa Clara, a 15,000-acre, ecologically sensitive Northern Sonora wetland, survived the plant's pilot run from May 2010 through March 2011.

The cienega, lying 30 miles south of the Mexican border, represents 5 to 10 percent of the Colorado River Delta that once flourished before the river's dams cut off most of the water supply.

For years, environmentalists feared that the plant's operation would destroy the cienega by taking away and treating the salty irrigation water that had flowed into the wetland since the 1970s from Yuma-area farmers.

But during the test run, the U.S. and Mexican governments and nonprofit environmental groups combined to furnish as much replacement water to the cienega as was treated.

The area's prized marsh bird populations didn't change significantly during the test, and the cienega survived a major wildfire and a nearby earthquake, said the study led by UA Geosciences Department head Karl Flessa.

THE ECONOMICS

The U.S. Bureau of Reclamation had expected the desal plant's test run to cost $23 million. The final tab was $15.9 million. The test was to last up to 365 days but treatment was finished in 328 days.

Nonetheless, the plant's most immediate obstacle to long-run operations is lack of money. But a significant amount of fact-gathering and discussions must also occur, water officials and environmentalists said.

The current tight federal budget has no money to run the plant at full scale, said Jennifer McCloskey, Yuma-area manager for the Bureau of Reclamation, which runs the plant.

The plant also needs $25 million to $50 million in upgrades, she said.

McCloskey added in an interview that the bureau will keep the plant maintained while discussions continue on its future. Because of the recession, the region's population growth has been less than expected, and "Nobody has said please turn this back on in six months," she said.

The Central Arizona Project and other regional water agencies want the plant open for additional water during droughts - particularly with the Colorado River heading this year toward one of its lowest flows on record. CAP's view is that running the plant is a federal responsibility, and the bureau should figure out the most effective and efficient method of running it, said Chuck Cullom, CAP's Colorado River programs manager.

"The fact that Reclamation doesn't request funding for the plant ... doesn't change what we believe is a pretty clear obligation," Cullom said.

WHAT'S NEXT

• The bureau must replace the plant's pipes and its original treatment membranes, and bring a rail line back into service to deliver chlorine for the treatment. The pipes have leaked and have significant defects due to poor quality of welds during the plant's original construction, said a Bureau of Reclamation report.

• Authorities must determine the cost for treating the water long-term, and who will buy and pay for desalted water, said J.C. Davis, a Southern Nevada Water Authority spokesman. The lower Colorado River serves Nevada and California as well as Arizona and Sonora.

• Officials will spend 24 months evaluating data from a soon-to-be-published technical report on the test run, to lead to the best possible retrofit of the plant for future use, CAP's Cullom said.

• The bureau is researching possible new technologies for the plant, to come up with a design that offers the best cost-benefit ratio. It also must finish a study of 25- to 50-year water supply needs for the Lower Colorado River Basin.

• Many environmental groups want assurances of adequate water for the cienega before the plant runs permanently.

First, an assessment must be done of how much water the cienega needs over the long term, Southern Nevada's Davis said.

That can't happen until there's a U.S.-Mexico agreement on what uses the cienega should be managed for, added Jennifer Pitt of the Environmental Defense Fund.

The environmental monitoring teams

Besides the UA, the environmental monitoring during the desalination plant's test run was conducted by the Sonoran Institute, the Mexican environmental group Pronatura Noreste, a Baja California-based university and the Upper Gulf of California and Colorado River Biosphere Reserve. It was financed by water and environmental agencies on both sides of the border.

Contact reporter Tony Davis at tdavis@azstarnet.com or 806-7746.