El Paso is the site of the world's largest inland desalination plant. This plant represents a forward-looking strategy in water supply — not only for a region but also for a world that is increasingly challenged by short supplies of fresh water.

A joint project of El Paso Water Utilities and Ft. Bliss, El Paso's desalination facilities produces 27.5 million gallons of fresh water daily (MGD) making it a critical component of the region's water portfolio. Using a previously unusable brackish groundwater supply, the Kay Bailey Hutchison Desalination Plant is creating a new supply of water - water from water.

In addition to providing a supply of fresh water, the facilities provide other important benefits.

• The facilities serve as a model and center of learning for other inland cities facing diminishing supplies of fresh water.
• The water pumped to the desalination plant protects El Paso's and Ft. Bliss' fresh groundwater supplies from brackish water intrusion by capturing the flow of brackish water toward freshwater wells.
• This desalination process not only removes salts, but also is the most comprehensive water treatment technology available, removing other potential pollutants from the water.
• The facilities augment existing supplies to make sure El Paso and Ft. Bliss have sufficient water for growth and development for 50 years and beyond.

The desalination facilities increase El Paso Water Utilities' fresh water production by approximately 25%, based on current demand, and include a state-of-the-art desalination plant, a learning center, groundwater wells, transmission pipelines, storage and pumping facilities and the disposal of concentrate, the residual that remains after the desalination process.

El Paso's water sources include groundwater from bolsons (aquifers) and surface water from the Rio Grande. Water from the Rio Grande is only available during the spring, summer and early fall months and is further limited in years of drought. The Hueco Bolson, on the east side of the Franklin Mountains, is also the source of water for Ciudad Juárez in México and other communities in the area. Historically, pumping from the bolson has exceeded the recharge rate and water levels in the bolson have declined.

El Paso Water Utilities has long recognized the need to diversify its resources and to reduce reliance on water from the bolsons and has made significant strides in recent years toward that objective.

EPWU's conservation initiatives have been very successful, setting benchmarks for cities across the Western United States. Additionally, EPWU's reclaimed water programs are extensive, with its strategic plan calling for reclaimed water to reach 15% of the annual potable water use by 2012. However, knowing that additional fresh water sources would be needed, El Paso Water Utilities began exploring the idea of desalinating the brackish water in the bolsons in the early 1990s.

The amount of brackish water in the Hueco Bolson exceeds the amount of potable water by approximately 600%. The brackish water contains more salt than is allowed in drinking water, but significantly less than ocean water.

When new technology reduced the cost of the reverse osmosis process, El Paso Water Utilities began to plan the construction of a desalination plant. Because Ft. Bliss was considering a similar facility, a public-public partnership was formed. The two entities recognized the benefits of a partnership in the complex process of building what will become the world's largest inland desalination plant with the capacity to meet the needs of both Ft. Bliss and El Paso Water Utilities. This is the largest public-public project of its kind in the country involving the Defense Department and a local community.

Desalination plants near oceans are becoming more common. They have the benefit of an ample supply of consistent water and can return the concentrate to the ocean.

An inland desalination plant presents significantly more challenges. For the El Paso facility, test wells were needed to find a stable and consistent supply of brackish water. Hydrogeological studies were needed to determine the flow of the brackish water in the Hueco Bolson. Considerable testing, studies and pilot projects were performed to determine the most economically and environmentally sound means of disposing of the concentrate.

The desalination plant uses reverse osmosis to obtain potable water from brackish water drawn from the Hueco Bolson. Raw water from new and existing wells is pumped to the plant and filtered before being sent to reverse osmosis membranes.

Through a pressurized process, raw water will pass through fine membranes that separate salts and other contaminants from the water. Approximately 83% of the water is recovered while the remainder is output as a concentrate.

At the conclusion of the reverse osmosis process, the permeate, or desalted water, is piped to a storage tank and the concentrate is routed to a disposal facility. The permeate will be blended with water from new wells. Following pH adjustment and disinfection, the finished water is sent to the distribution system.

To ensure success of the project, considerable study and research were needed to assure the validity of the design and better understand the environmental effects.

In 1997, EPWU and the Juárez water utility, the Junta Municipal de Aqua y Saneamiento, along with other agencies on both sides of the border, commissioned the U.S. Geological Survey to conduct a detailed analysis of the amount of fresh water remaining in the Hueco Bolson, the amount of brackish water available, plus a determination of the flow patterns. EPWU used data from the model to determine where to locate the desalination plant and source wells and obtained critical information needed to characterize the injection well site. Without these groundwater models and the technology associated with the information, it would have been very difficult to determine where best to locate these facilities.

In 2002, EPWU drilled and monitored nine test wells to characterize a section of the aquifer selected to provide the blend water. EPWU consultants also completed an extensive analysis of existing wells that might be used to supply the desalination facility. A reverse osmosis pilot plant was constructed to test the chemicals, filters, and membranes used in the reverse osmosis process and determine which worked best with local water. In February 2005, U.S. Army consultants completed environmental studies and published the Final Environmental Impact Study.

The most complex studies, however, were directed toward the problem of concentrate disposal. A comprehensive initial study examined six alternatives for disposal. Two methods were determined to be the most feasible: evaporation and deep-well injection. EPWU then tested evaporation methods, including conventional evaporation ponds, evaporation misting equipment and evaporation ponds with concentrators.

Deep-well injection was selected as the preferred method of disposal, and the concentrate is placed in porous, underground rock through wells. The sites would confine the concentrate to prevent migration to fresh water, provide storage volume sufficient for 50 years of operation and meet all the requirements of the Texas Commission on Environmental Quality.

Deep-well injection entailed extensive study of local geological and hydrological conditions as well as the examination of existing data, including seismic analysis and water samples. The University of Texas at El Paso conducted a geophysics study that EPWU used to create a geologic model and the Army drilled four wells to test for geological formation.

The extensive preparation needed to proceed with the construction of the facilities — studies, pilot plants, research, and the state / federal permitting processes — assures the success of the project and will be of great benefit to other communities in developing inland desalination plants.

The availability of fresh water is a serious challenge facing not just the desert Southwest but the world. The demand for a reliable and secure supply of water for a growing region must be met by the carefully selected and economically efficient development of new water. The Kay Bailey Hutchison Desalination Plant is a reflection of these realities.