Intra-Aquifer Characterization and Potential Management Impacts: Trinity Aquifer, Central Texas

Management of groundwater resources is a critical issue in Texas and groundwater conservation districts have been given this responsibility.  While large databases containing wells and aquifer characteristics are available for use from state agencies, they have not been organized specifically for spatial correlation and analysis.  As a new entity (2007), the Southern Trinity Groundwater Conservation District (STGCD) is faced with developing and analyzing just such data.  An unusual challenge for the STGCD is managing groundwater production among wells completed either solely in the upper aquifer (Hensel member), lower aquifer (Hosston member), or dually completed in both members of the Travis Peak Formation (Trinity Aquifer).  The goals of this project were to to develop a spatially-based well data set that can be used for management decisions.  The current well database has been refined to better reflect aquifer delineations between zones (Hensel and Hosston units).  Specific methods include literature review, driller’s reports, and electric logs.  Screen intervals and trends in water chemistry were also analyzed spatially and chronologically.  Initially, dual-completed wells were excluded from the dataset in order to calibrate the Hensel and Hosston zone characteristics independently.  Once the dataset was calibrated, the transmissivity and storage for each zone was used to assess the production from the dual-completed wells.  Results include a report to the district with a digital database, and isopach and contour maps for different aquifer characteristics such as transmissivity, water levels, storativity, thickness, percent sand, TDS, pH, and temperature.  In addition, the effects of artificial boundary conditions were assessed by first using McLennan County data, then adding adjacent data from surrounding counties and comparing the results.  A recommendation will be made regarding management for the aquifer zones as either independent aquifers or one unit.