DEVELOPMENT OF BRACKISH GROUNDWATER RESOURCES IN THE LOWER RIO GRANDE VALLEY, TEXAS

Facing surface water shortages, rapid population growth, and increasing costs for surface water rights and water treatment, several public water supply providers in the Texas Lower Rio Grande Valley have sought to diversify their water supply with brackish groundwater, a traditionally underutilized water source. Exploration and development of alternative water resources has been a decades-long process that has proven that the production and use of brackish groundwater can be a cost-effective and essentially drought-proof solution that enhances both supply quantity and sustainability.

In 2004, Southmost Regional Water Authority (SRWA) completed a 7.5 MGD (28,400 m³/d) regional brackish groundwater treatment plant that supplies five customers, the largest being the City of Brownsville. The treatment plant has since been expended to treat 15 MGD (56,800 m³/d) of brackish groundwater. North Alamo Water Supply Corporation, has constructed five brackish groundwater treatment plants throughout their service area that treat more than 16 MGD (61,000 m³/d) of brackish groundwater. The City of McAllen has developed 1 MGD (3,800 m³/d) of brackish groundwater which it blends with existing surface water supplies.

While the Lower Rio Grande Valley has a few pockets of fresh groundwater along the Rio Grande, brackish groundwater is abundant throughout Hidalgo, Cameron and portions of Willacy counties. Although the principal water-bearing deposits consist of Quaternary-aged flood plain and deltaic deposits from the ancestral Rio Grande, they are largely indistinguishable from the underlying Beaumont and Lissie formations. The alluvial water-bearing sediments are composed of reworked Tertiary and Cretaceous sediments, as well as igneous and metamorphic rocks originating from the Trans-Pecos region of Texas, Mexico, and New Mexico (BEG, 1976). In addition to the Alluvium/Beaumont/Lissie, the underlying Pliocene Goliad Sand, which crops out in Starr and Hidalgo counties ranges up to 600 feet (about 183 meters) thick and is capable of producing large quantities of brackish groundwater in western and central Hidalgo County.