The Edwards Aquifer: The Past, Present, and Future of a Vital Water Resource
CONTAINS OPEN ACCESS
The Edwards aquifer system is one of the great karstic aquifer systems of the world. It supplies water for more than 2 million people and for agricultural, municipal, industrial, and recreational uses. The Edwards (Balcones Fault Zone) Aquifer in the San Antonio, Texas, area was the first to be designated a sole source aquifer by the Environmental Protection Agency in 1975. The Edwards Aquifer also hosts unique groundwater, cave, and spring ecosystems. This 27-chapter memoir reviews the current state of knowledge, current and emerging challenges to wise use of the aquifer system, and some of the technologies that must be adopted to address these challenges.
Geologic structure of the Edwards (Balcones Fault Zone) Aquifer
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Published:September 10, 2019
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CiteCitation
David A. Ferrill, Alan P. Morris, Ronald N. McGinnis, 2019. "Geologic structure of the Edwards (Balcones Fault Zone) Aquifer", The Edwards Aquifer: The Past, Present, and Future of a Vital Water Resource, John M. Sharp, Jr., Ronald T. Green, Geary M. Schindel
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ABSTRACT
The Edwards (Balcones Fault Zone) Aquifer is structurally controlled by the system of normal faults following the Balcones Escarpment, with major domains, including contributing, recharge (unconfined), and artesian (confined) zones, dictated by the large-displacement (50 m to >250 m throw) normal faults and depth of erosion. Faults and extension fractures, in many cases enhanced by dissolution, localize recharge and flow within the Balcones fault zone and into the subsurface of the artesian zone. Juxtaposition of the Edwards with other aquifers provides avenues for interaquifer communication, while juxtaposition against impermeable layers and concentration of clay and mineralization along faults locally produce fault seals for compartmentalization and confinement. Fault block deformation, including small faults and extension fractures, leads to aquifer permeability anisotropy. Faults also locally provide natural pathways for groundwater discharge through springs above the confined (artesian) zone. Although the importance of joints and faults in the Edwards (Balcones Fault Zone) Aquifer system is recognized, there has not been a systematic analysis of the meter-scale structures in the Edwards and associated confining units and their influence on groundwater flow. Here, we review evidence from several key areas showing that an analysis of faults and fractures in the Edwards (Balcones Fault Zone) Aquifer and associated aquifers and confining units is needed to characterize structural fabrics and assess the permeability architecture critical for the next generation of groundwater modeling of the aquifer.