Abstract

Since creation of the Brackish Resources Aquifer Characterization System (BRACS) in 2009, the Texas Water Development Board (TWDB) has been mapping and quantifying the availability of brackish groundwater in Texas aquifers. As part of this effort, the TWDB has begun a study of the brackish groundwater potential in the Dockum Aquifer. As currently defined by the TWDB, the Dockum Aquifer occurs in 57 counties and underlies approximately 26,000 square miles of Texas. Previous studies have calculated the presence of 136 million acre-feet of brackish groundwater with less than 10,000 milligrams per liter of total dissolved solids. The first phase of this study requires the collection and detailed stratigraphic correlation of over 4,000 geophysical well logs. An early observation from this phase of the study was the presence of a 120 mile long, 10 to 20 mile wide, east to west trending sand body 600 to 800 feet above the base of the Dockum Formation. This sand unit is composed of multiple sandstone beds with a combined thickness of up to 200 feet. Water wells completed in this sand have produced brackish water with total dissolved solids between 5,000 and 6,000 milligrams per liter at rates between 100 and 150 gallons per minute. The character of this sand body and its stratigraphic position, roughly 200 feet above the top of the locally important Santa Rosa sandstone, provide new insights into the depositional history of the Dockum Formation.