119-7 The Edwards -Trinity Connection: What We Believed, What We Know, and What Gaps Remain

Session: Recent Investigations of the Hydrogeology Edwards (Balcones Fault Zone) Aquifer, the Trinity (Hill Country) Aquifer, and Their Interactions, South-Central Texas

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A hydrologic connection between a part of the Trinity Aquifer System and the San Antonio Segment of the Edwards (Balcones Fault Zone) Aquifer was first postulated in 1947. By the 1970s, that connection was tacitly accepted by some hydrogeologists, but they had no direct evidence. In the 1990s, potentiometric and isochemical mapping strongly supported, but lacked one line of evidence to prove that connection. In the 2000s, the first groundwater model connecting the aquifers was developed, followed by dye tracing studies that proved a connection that had been clear to some, but doubted by many, for decades. Over the past 20 years, studies have continued to refine understanding of that connection.

Three important gaps need to be filled in the coming years. First, stop calling it the “Trinity Aquifer.” The name is based on a stratigraphic group, not the hydrologic behavior within its various formations. Clearer understanding will be gained by use of the formation names as names for aquifers, aquitards, and aquicludes, recognition of their hydrogeologic characteristics, and implementation of research appropriate to those characteristics. Second, more research is needed that focuses on defining the conditions of how those Trinity formations connect hydrologically to the Edwards Aquifer. Third, while there has been administrative progress toward managing the Edwards-Trinity as an interconnected aquifer, that groundwater system is not recognized through an agency created for and its funding directed toward total aquifer system study and management.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-10122

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