NGWA Event and Education Recordings Archive

Extended Learning Session: Techniques for Mapping and Characterizing Brackish Aquifers through the Mining of Existing Geophysical Data

Estimated at more than 2.7 billion acre-feet, brackish groundwater constitutes an important desalination water supply option in Texas. One challenging issue - and a potential roadblock to the more widespread development of brackish groundwater - is the lack of detailed information (especially on parameters relevant to desalination). Utilizing the Brackish Resources Aquifer Characterization System (BRACS), the Texas Water Development Board is mapping and characterizing brackish portions (between 1,000 to 10,000 mg/L TDS) of aquifers throughout Texas. The BRACS program received legislative support in 2009 to map and characterize the brackish aquifers of the state in greater detail using existing geophysical well logs and available aquifer data; build replicable numerical groundwater flow models to estimate aquifer productivity; and develop parameter-screening tools to help communities assess the viability of their brackish groundwater supplies. This session will describe the basic components of a BRACS study and provide the results of the a recent Gulf Coast Aquifer study in the Lower Rio Grande Valley, Texas to illustrate the techniques and usage of existing data. A typical study involves evaluating hundreds to thousands of existing water well records, petroleum well geophysical well logs, and geologic reports that have been prepared for the water–bearing formations. The BRACS team has developed a database to store the large amount of information collected from geophysical well logs and water well reports needed to create regional maps of the distribution, volume, and quality of brackish water. A comparison of the geologic structure of water–bearing formations (top, bottom, and lateral extent) between existing datasets and well records is evaluated, and if necessary a new formation structure is compiled. The water–bearing portions of the aquifer are mapped along with estimated salinity from water well records and assessment of geophysical well logs. This information is then used to prepare estimated volumes of brackish groundwater.