The Edwards aquifer is one of the most permeable and productive carbonate aquifers in the United States and has been designated a sole source aquifer by the U.S. Environmental Protection Agency. The Edwards aquifer serves the domestic, industrial, and agricultural needs of 2 million people and is the primary source of water for San Antonio, America's 8th largest city. The Trinity aquifer forms the catchment area for the Edwards aquifer in the headwaters of streams that drain south across the Edwards Plateau, and the Trinity intercepts some surface flow above the Edwards recharge zone. General opinion is that the Trinity may also contribute to the Edwards aquifer by subsurface flow across formation boundaries at considerable depths. Dissolution and faulting/fracturing in both aquifers directly affect aquifer geometry and can compartmentalize the aquifer as well as create unique flowpaths.
The Edwards aquifer system contains three areas or zones, the catchment area (also called the contributing area), the recharge zone (formally defined by the Texas Commission on Environmental Quality), and the artesian or confined zone (see below). The geology of the catchment area contains exposed lithologies belonging to the Lower Cretaceous Trinity Group. An example of typical Edwards fault structure, as revealed along cross-section A-B, is expanded on below.
As precipitation falls on the catchment area, it travels down slope as surface water until crossing the Edwards recharge zone. There, it enters the aquifer through fractures and into down-thrown grabens and horsts, eventually reaching the artesian zone (see cross secton below). The normal faults of the recharge zone can either enhance flow by creating linear zones of increased permeability or, they may retard down-gradient flow depending on the fault architecture and the lithologies fractured and juxtaposed by faults.
The overall water budget of the Edwards and Trinity aquifers contains substantial unknowns, including a limited understanding of the system's subsurface geometry and reservoir capacities. Also, Edwards and Trinity flowpaths and flow rates are known to be strongly influenced by geologic structures and understanding the hydrogeologic processes that control the above parameters from the Edwards catchment area (Trinity aquifer) into the recharge area requires mapping of the regional hydrogeologic framework. In this project, digital geologic map and geophysical data provides the foundation for building 3-D geologic models for the recharge and catchment areas with both ground and airborne geophysical surveys providing control on the structures and properties of hydrologic units, magnitude of displacements by faults and degree of karst development. Project results to date demonstrate that geologic field mapping is the cornerstone of geologic research and that mapping is an evolutionary process that directly benefits from geophysical and 3-D subsurface modeling efforts (for more information, see section on Geologic Mapping).
Although the vast majority of project staff are from the Geologic Discipline, all project tasks and their implementation involve close working relationships with Water Resources Discipline staff and their projects.
For FY-02 to FY-06 project study areas, see Completed and Continuing Edward Project Tasks. For new and ongoing research areas, see Planned FY-06 Edwards Project Tasks.
The project is divided into five main areas of research. Click on a topic below for detailed information.
Geologic Mapping
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3-D Modeling
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Ground and Airborne Geophysical Surveys
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Noble Gas Geochemistry
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Geochronology
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Blome, Charles D., Faith, Jason R., Collins, Edwards W., Pedraza, Diane E., and Murray, Kyle E., 2004, Geologic map compilation of the Upper Seco Creek area, Medina and Uvalde Counties, south-central Texas: U.S. Geological Survey Open-file Report 2004-1430.
Blome, Charles D., Faith, Jason R., Pedraza, Diana E., Ozuna, George B., Cole, James C., Clark, Allan K., Small, Ted A., and Morris, Robert R., 2005, Geologic map compilation of the Edwards aquifer recharge zone, south-central Texas: U.S. Geological Survey Scientific Investigations Map 2005-2873.
Blome, Charles D., Miggins, Daniel P., and Smith, David V., 2004, Geophysical and isotopic investigations of the Uvalde intrusive field, south-central Texas: Gulf Coast Association of Geological Societies Transactions, v. 54, p. 61.
Blome, Charles D., Faith, Jason R., Smith, Bruce D., Collins, Edwards W., Clark, Amy R., and Ozuna, George B, 2005, Geologic mapping of the Edwards and Trinity aquifer systems and its synergy with hydrogeologic modeling: National Ground Water Association 2005 Summit, April 17-20, 2005, San Antonio, abstracts with program, p. 223-225.
Cole, James C., and Pantea, Michael P., 2004, Three-dimensional structural modeling of displacements if the Edwards aquifer within the Balcones fault zone in northern Bexar County, Texas: Transactions of the Gulf Coast Association of Geological Societies Transactions, v. 54, p. 121-131.
Faith, Jason R., Blome, Charles D., Clark, Allan K., and Smith, Bruce D., 2005, Structural geology and tectonic analysis of the Balcones fault zone in the upper Seco Creek area, Ecwards aquifer, south-central Texas: Geological Society of America, Abstracts with Programs, v. 37,no. 3, p. 5.
Hunt, A. G., Lambert, R. B., Waugh, J. R., and Landis, Gary P., 2003, Fluid logging and discrete sampling of the fresh-/saline-water interface of the Edwards aquifer, south central Texas: implications for groundwater flow and origin of salinity (part 2-geochemistry): Geological Society of America, Abstracts with Programs, v. 35, no. 6, p. 280.
Lambert, Rebecca B., Hunt, Andy G., Landis, Gary P., and Waugh, John R., 2003, Fluid logging and discrete sampling of the freshwater-saline-water interface of the Edwards aquifer, south-central Texas: Geological Society of America, Abstracts with Programs, v. 35,no. 6, p. 280.
Lambert, Rebecca B., Hunt, Andy G., and Pierce, Herbert A., Directors Approval, Hydrogeology, geochemistry, and flow paths along the freshwater/saline-water interface of the Edwards aquifer. San Antonio area, Texas: U.S. Geological Survey Scientific Investigations Report.
Miggins, Daniel P., Blome, Charles D., and Smith, David V., 2004, Preliminary 40Ar/39Ar geochronology of igneous intrusions from Uvalde County, Texas: Defining a n ore precise history for the southern Balcones volcanic province: U.S. Geological Survey Open-file Report 04-1031, 37 p.
Pantea, Micheal P., and Cole, James C., 2004, Three-Dimensional Geologic Framework Modeling of Faulted Hydrostratigraphic Units within the Edwards Aquifer, Northern Bexar County, Texas: U.S. Geological Survey Scientific Investigations Report 2004-5226.
Paine, Jeffrey G., Smith, Bruce D., Collins, Edwards W., Smith, David V., Blome, Charles D., Pantea, Michael P., and Abraham, Jared D., 2005, Geophysical investigations and geo-hydrologic mapping of the Edwards and Trinity aquifers in the Seco Creek area, Medina and Uvalde counties, Texas: National Ground Water Association 2005 Summit, April 17-20, San Antonio, abstracts with program, p. 226-227.
Pierce, Herbert A., 2002, San Antonio, Texas Audio-magnetotelluric Data: Web site for distribution of data: U.S. Geological Survey Open-file Report 02-118.
Schindel, Geary, and Smith, Bruce D., 2003, The Balcones Fault Zone and Edwards Aquifer of south-central Texas: FastTimes, v. 8. no. 1, p. 17-19.
Smith, Bruce D., Cain, Michael J., Clark, Allan K., Moore, David W., Faith, Jason R., and Hill, Patricia L., 2005, Helicopter electromagnetic and magnetic survey data and maps, northern Bexar County: U.S. Geological Survey Open-file report 2005-1158, 114 p., 1 plate.
Smith, Bruce D., Paine, Jeffery G., Smith, David V., Johnson, Steve, Waugh, John, Abraham, Jared, Blome, Charles D., Ozuna, George B., and Schindel, Geary, 2003, Geophysical characterization of geologic features in the area of the Valdina Farms Sinkhole, Medina County, Texas: Geological Society of America, Abstracts with Programs, v. 35, no. 6., p. 280.
Smith, Bruce D., Smith, David V., Hill, Patricia L., and Labson, Victor F., 2003, Helicopter electromagnetic and magnetic survey data and maps, Seco Creek area, Medina and Uvalde Counties, Texas: U.S. Geological Survey Open-file Report 03-226.
Smith, David V., and Smith, Bruce D., 2002, Aeromagnetic survey of Medina and Uvalde Counties, Texas: U.S. Geological Survey Open-file Report 02-049.
Smith, David V., Smith, Bruce D., Blome, Charles D., Pierce, Herbert A., and Lambert, Rebecca B., 2003, Cretaceous volcanic intrusives in the Edwards aquifer, Texas, as identified from a high-resolution aeromagnetic survey: Geological Society of America, Abstracts with programs, v. 33, no. 6, p. A298.
U.S. Department of the Interior | U.S. Geological Survey
URL: http://esp.cr.usgs.gov/info/edwards/
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