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Book Chapter

Geologic structure of the Edwards (Balcones Fault Zone) Aquifer

By
David A. Ferrill
David A. Ferrill
Southwest Research Institute, 6220 Culebra Road, San Antonio, Texas 78238, USA
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;
Alan P. Morris
Alan P. Morris
Southwest Research Institute, 6220 Culebra Road, San Antonio, Texas 78238, USA
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;
Ronald N. McGinnis
Ronald N. McGinnis
Southwest Research Institute, 6220 Culebra Road, San Antonio, Texas 78238, USA
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Publication history
30 January 201923 April 2019

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.

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Contents

GSA Memoirs

The Edwards Aquifer: The Past, Present, and Future of a Vital Water Resource
CONTAINS OPEN ACCESS

Geological Society of America
Volume
215
ISBN electronic:
9780813782157

GeoRef

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