POTENTIAL OVER-DEVELOPMENT AND AQUIFER CO-MINGLING IN THE HENSELL “MIDDLE TRINITY” AQUIFER; A STUDY WITH BI-PARTISAN MANAGEMENT SUPPORT

The Hensell Formation is often referred to as the “Middle Trinity” aquifer because it is below the Glen Rose Formation and above the more productive Hosston Formation all of which are part of the Trinity aquifer, a major aquifer in the State of Texas. The Hensell Formation was deposited as a fluvial sand then re-worked by shallow marine processes in a regressive sequence. Hensell groundwater is a moderately fresh Na-HCO₃ water while the overlying Glen Rose Formation is a carbonate unit containing brackish Na-SO₄ water.

Increased Hensell groundwater usage spurred by the recent drought and the rapidly growing urban corridor along Interstate Highway 35 appears unsustainable and may exceed “Desired Future Conditions” set by managing entities. Deepening cones of depression and cases of possible aquifer co-mingling threaten both the groundwater quantity and quality in the Hensell Formation. The deepening cones of depression may increase potential for leakage from the overlying Glen Rose brackish water, and the fractured and dissolutioned nature of the Glen Rose Formation causes difficulties with well completions that may result in aquifer co-mingling.

This study provides information regarding the Hensell aquifer that can be used by two adjacent groundwater conservation districts: Clearwater Underground Water Conservation District and the Southern Trinity Groundwater Conservation District. Water level hydrographs, synoptic groundwater chemistry sampling, creative aquifer analysis opportunities, and case studies of potential co-mingling were combined to provide recommendations to the two supportive managing entities.