Desalination of Brackish Ground Water and Deep Well Injection of Concentrate in El Paso, Texas

El Paso has relied on the Hueco Bolson as a major municipal water supply source since 1903.  As a result of high pumping, groundwater levels in the Hueco have declined and brackish groundwater has intruded into areas that historically yielded fresh groundwater.  El Paso Water Utilities (EPWU) began reducing its Hueco pumping in 1989.  This action was made possible by a variety of water management initiatives including increased water conservation, increased surface water diversions, and increased reclaimed water use.  The reduction in pumping has resulted in stabilized groundwater levels in many areas.  However, brackish groundwater intrusion remained an issue. 

 

The most recent component of EPWU’s overall water management strategy is a 27.5 million gallon per day (mgd) desalination plant that was completed in 2007.  Due to the strategic location of the feed wells that supply the plant, brackish groundwater is intercepted before it reaches fresh groundwater wells.  Disposal of the concentrate from this desalination plant is being accomplished via three deep injection wells located about 22 miles from the plant.  The three injection wells were constructed to a depth of between 3,700 to 4,400 feet deep, and can inject over 3 million gallons per day of concentrate into deep Paleozoic formations. 

 

The preliminary work that resulted in constructing the injection wells included test drilling, geophysical surveys, development of a subsurface geologic model of the area, and development of a preliminary numerical model of groundwater flow in the area.  Based on initial testing at startup, and based on the initial year of operation, there appear to be no operational constraints with respect to reservoir boundaries or mineral precipitation of supersaturated minerals.  Currently, the concentrate has total dissolved solids (TDS) of about 6,000 mg/l and the TDS of the native groundwater in the injection zone nearly 9,000 mg/l.