TWDB maps aquifers to find brackish groundwater and generate new water supplies for Texans Posted on November 20, 2025

Groundwater and desalination are two of the most widely discussed water topics in Texas as the demand for new water supply in communities across the state continues to grow. The TWDB Brackish Resources Aquifers Characterization System (BRACS) program began in 2009 to more thoroughly characterize brackish aquifers in the state to help identify and develop new water supplies. Thanks to the hard work of the BRACS team, the TWDB has designated 31 sites as brackish groundwater production zones to date.

Evan Strickland is a geoscientist licensed by the Texas Board of Professional Geoscientists that works for the TWDB. He has been mapping the brackish portions of the Edwards-Trinity (Plateau) Aquifer as a part of the BRACS program to identify potential brackish groundwater production zones. BRACS map data—which is free and available to the public—helps identify locations of brackish groundwater that can potentially be desalinated and can help identify cost-effective locations for groundwater production.  Ultimately, this work will help Texas communities generate new water supplies by producing desalinated brackish groundwater for general use.

How do you map an aquifer?

Mapping an aquifer typically means identifying the extent of the geologic formations underground that contain sufficient saturated permeable material to yield significant quantities of water. TWDB geoscientists like Strickland primarily rely on existing geophysical logs—mostly from oil and gas wells, but also from water wells—to map aquifers. The measurements in those logs are obtained by dropping sensor-laden probes into wellbore holes to take readings of various characteristics of the surrounding geology. These measurements include radioactivity and resistivity, among others, and they help experts like Strickland understand the types of materials present at various underground levels.

For example, shale and rare earth materials are (relatively) radioactive, while sandstone is not, so radiation measurements in a geophysical log can clearly show the depths of the different layers of material. Meanwhile, resistive sensors use electrical current to measure the resistivity of the material around the wellbore. Low readings indicate the presence of clay and/or salty water, for example, while higher readings indicate solid rock, dry soils, fresh water, or the presence of hydrocarbons. Some sensors, like those for gamma radiation, have very high resolution and can be accurate to within a foot.

For the Edwards-Trinity (Plateau) Aquifer mapping project, Strickland has been working with 4,000 well locations and corresponding logs. “We use water quality measurements where we have them,” says Strickland, “but that’s normally restricted to the shallower portions of the aquifer.” The deeper portions are generally untested because there simply aren’t many wells deep enough—and drilling such wells can cost $1 million or more. In the absence of direct measurements, he makes calculations using existing aquifer information, the data in the geophysical logs, and some informed assumptions.

A new source of mapping data

The BRACS team is always eager to incorporate more data into their work. Because he previously worked in the oil and gas industry, Strickland is familiar with the industry’s use of seismic data to map underground oil reserves. At a rudimentary level, seismic data is obtained by vibrating the ground (through an explosion or specialized equipment) and measuring the reflection of those vibrations as they return—the speed at which vibrational waves travel through different materials varies. The resulting measurements are used to create a time-based picture of the earth’s subsurface structure.

As a test case, Strickland wanted to see if he could leverage existing seismic data—which is useful for mapping faults and identifying other discontinuities in underground formations—to learn more about a portion of the Edwards-Trinity (Plateau) Aquifer in Kinney County with little well data.

How those discontinuities are distributed in the subsurface and how they are connected (or not connected) can illustrate various properties of the aquifer. The parts of aquifers with high porosity (meaning there are many empty spaces to hold water), high permeability (meaning the pores filled with water are connected), and high transmissivity (meaning water can flow freely) combine to make for cost-effective and low-impact groundwater production.

Though the project did not reveal any groundbreaking discoveries about the aquifer in Kinney County, the project served as a proof of concept for the workflow so that others can use this method—which is documented and available in this TWDB report. That report, plus the other aquifer mapping studies produced by the BRACS team, serve as valuable resources for Texas communities.

This article is posted in Aquifers / Water Planning / Technology / Water Supply / Groundwater .