AWWA ACE62979

Like many fast growing regions of the country, rising water demand coupled with increasing pressure on existing water sources is driving the South Central Texas Region (SCTR) to consider desalination of previously untapped water supplies. Simultaneously, regulatory mandates are set to significantly decrease the water available from current fresh groundwater sources. Pursuant to the requirements of Texas Senate Bill 1 (SB1), the SCTR is one of 16 Texas regions that are currently updating their long-term (to the year 2060) water supply plans. The SCTR consists of 21 counties forming a band across Texas from the Mexico border through the City of San Antonio and to the Gulf of Mexico. As part of this planning process, several options to provide a dependable long-term water supply by desalinating seawater or brackish groundwater are being considered. A unique decision framework tool is presented that includes major considerations impacting the cost and feasibility of desalination water supply options. The decision framework tool will be utilized to compare specific desalination water supply options being considered for the SCTR. Major considerations involved in the decision framework include: Water Availability ¿¿¿¿¿¿¿¿ Groundwater available from brackish aquifers, land acquisition/groundwater lease, competing interests and water rights; Treatment Costs ¿¿¿¿¿¿¿¿ Both pretreatment and desalination system capital and O&M costs; Concentrate Disposal ¿¿¿¿¿¿¿¿ Cost and permitting requirements for disposal options including discharge to surface water, deep well injection, and zero liquid discharge; Raw and/or Finished Water Transmission ¿¿¿¿¿¿¿¿ Pumps, pipelines, and tanks required for delivery of finished water and integration into the existing distribution system; and, Finished Water Quality ¿¿¿¿¿¿¿¿ Blending and treatment options to meet compatibility requirements in the distribution system. Specific desalination water supply options being considered for the SCTR include: brackish groundwater from the Wilcox Aquifer in Bexar County; seawater desalination; and, inter-regional seawater desalination. Includes tables, figures.