Investigating Groundwater Flow between the Upper and Middle Trinity Aquifers in Central Texas

The purpose of this study is to investigate the degree of vertical inter-aquifer flow occurring between hydrogeological units of the Upper and Middle Trinity Aquifers in northern Hays County under normal and stressed aquifer conditions. This study also evaluates water quality data to identify all major aqueous geochemical contributors to the natural groundwater of the Middle and Upper Trinity Aquifers within Central Texas. The methods of data collection involve taking measurements of hydraulic head and major ion concentrations in three multiport monitor wells owned by the Barton Springs Edwards Aquifer Conservation District and in various monitor wells throughout the Central Texas region owned by local residents. Methods of data processing include t-tests, water level data, piper diagrams, boxplots, ANOVA tests, and relationships among major cations and anions. The results indicate that vertical flow between hydrogeological units of the Upper and Middle Trinity Aquifer does not occur under normal aquifer conditions at a regional scale. However, heavy pumping of Cow Creek unit of the Middle Trinity Aquifer does induce vertical flow from overlying units of the Middle and Upper Trinity Aquifers. The geochemical data indicates that natural dissolved ions in Trinity groundwater come from the dissolution of limestone, dolomite, gypsum, and anhydrite rather than mixing with the deep saline water. This study aims to provide evidence to guide water usage towards environmentally sound management practices.