SPATIAL DISTRIBUTION OF THE QUALITY AND QUANTITY OF BRACKISH GROUNDWATER IN FIVE AQUIFERS IN THE CENTRAL PORTION OF THE UPPER COASTAL PLAINS OF TEXAS

The Texas Water Development Board is a state agency charged with collaborating with 16 regional water planning groups in a comprehensive water planning process that projects demand 50 years into the future. Based on expected population growth and water supply, water shortages have been identified in the 2017 State Water Plan. Characterizing the location, quantity, and quality of brackish groundwater makes this resource more accessible for development.

In “Brackish Groundwater in Aquifers of the Upper Coastal Plains, Central Texas” we used geophysical well logs, submitted driller’s reports, and measured water quality samples, to map the stratigraphy, lithology, and water quality for the Wilcox, Carrizo, Queen City, Sparta, and Yegua aquifers and the Reklaw, Weches, and Cook Mountain aquitards in Central Texas.

To improve upon previous estimates of brackish groundwater available in the study area, we analyzed data from 8,130 wells in all or parts of 14 counties. We used 1,207 of these wells with geophysical well logs to derive 4,652 stratigraphic picks. We used 635 wells with geophysical well logs and 1,834 wells with submitted driller’s reports to make 109,830 lithologic picks. We interpolated this data to generate maps of cumulative sand thickness per aquifer for volume estimates. To map the distribution of water quality in the aquifers, we hand contoured 3,862 measured water quality samples and 5,139 total dissolved solids (TDS) estimates from geophysical well logs using the R_wa Minimum Method. We calculated in-place volumes of groundwater based on aquifer and salinity class. Additionally, we observed complex spatial distribution in groundwater quality related to regional geology. In our study area we estimate that there are more than 660 million acre-feet of in-place groundwater for the five aquifers, 230 of which is brackish.

Results from this study can help water suppliers select areas for well field-scale groundwater desalination evaluation. Prior to this investigation, a detailed regional distribution of groundwater quality and quantity was not available. In addition to the study results, all data (including interpretations and GIS datasets) will be available at http://www.twdb.texas.gov/innovativewater/bracs/index.asp.