BLM Yuma Desalting Plant

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The Wellton-Mohawk Irrigation and Drainage District (WMIDD) diverts approximately 400,000 acre-feet of Colorado River water annually to irrigate crops. Already salty Colorado River water, combined with the saline soil of WMIDD farmlands, creates a saline groundwater supply. As the underlying groundwater basin fills with water from the irrigated fields, salts are pushed to the surface. To keep the salts below the root zone, pumps remove about 120,000 acre-feet of brackish groundwater annually.

Initially, the saline groundwater pumped from WMID farmlands was blended with Colorado river water and delivered to Mexico. However, a 1973 revision of the US treaty with Mexico on the delivery of water to Mexico, curbed the amount of salts allowed in water deliveries to Mexico. To desalinate the Wellton-Mohawk drainage water before its delivery to Mexico, the Bureau constructed the world's largest reverse osmosis water treatment facility in Yuma, Ariz. At a construction cost of $250 million, the Yuma Desalting Plant is designed to treat up to 96,000 acre-feet of water annually.

During construction of the treatment plant, a $45 million drainage canal was constructed in 1977 to dispose of the brackish WMIDD groundwater until the water could be treated by the plant. The bypass drain transports the salty drainage water 50-miles south into the Cienega de Santa Clara. (This water does not meet international salinity requirements and is not counted towards Mexico's Colorado River apportionment.)

To date, the Yuma Desalting Plant has never been fully online. It operated at one-third capacity for nearly a year, but a flood on the Gila river in 1993 washed out a section of the drainage canal, halting operation. In the meantime, the Yuma Desalting Plant is being kept in "ready reserve" at a cost of $6 million a year. The possibility of operating the plant looms closer as water use on the Colorado continues to grow.
Translation - the $250 million dollar plant may actually be used some day.

However, "There is recognition that operation of the desalting plant will decrease the quantity and increase the salinity of the water traveling to the Cienega," said William Rinne, area manager for the Bureau's Lower Colorado Region, harming the considerable eco system that has developed in the Cienega.
Translation - the $250 million dollar plant will probably never be used.
Meanwhile, we continue to spend $6 million each yr to maintain the plant.
www.sci.sdsu.edu/salton/DecidingAboutCoR%20Delta.html

Also see:
fire.biol.wwu.edu/trent/alles/TheDelta.pdf
pgs 19-23 for info on the plant
"If the desalination plant starts up, the annual 130,000 acre-feet of brackish irrigation wastewater flowing to the marsh would be replaced by 55,000 acre-feet of extremely saline brine. This could mean the destruction of the Cienega De Santa Clara marsh habitat."