Edwards (Balcones Fault Zone) Aquiferinteractive map | cross-section
Aquifer Facts
- Aquifer type: confined and unconfined
- Area of outcrop: 1,566 square miles
- Area of subsurface: 2,481 square miles
- Proportion of aquifer with groundwater conservation districts: 87 percent
- Number of counties containing the aquifer: 14
Summary
The Edwards (Balcones Fault Zone) Aquifer is a major aquifer in the southcentral part of the state. It consists primarily of partially dissolved limestone that creates a highly permeable aquifer. Aquifer thickness ranges from 200 to 600 feet, and freshwater saturated thickness averages 560 feet in the southern part of the aquifer.
The aquifer feeds several well-known springs, including Comal Springs in Comal County, which is the largest spring in the state, and San Marcos Springs in Hays County, which is the second largest. The Hueco, San Pedro, San Antonio, and Leona springs also discharge from the aquifer. Because of the aquifer's highly permeable nature, water levels and springflows respond quickly to rainfall, drought, and pumping.
Water quality in the aquifer is generally very good. The groundwater is hard but fresh and contains less than 500 milligrams per liter of total dissolved solids. The unconfined area to the north and west of the Balcones Fault Zone has freshwater, and more saline water is in the confined zone to the south and east, largely outside the official aquifer boundary. The rapid recharge and flow through karstic features results in a low residence time for water in the unconfined zone, limiting water-rock interactions that increase total dissolved solids. In the down-dip area the official boundary of the aquifer is largely determined by the extent of freshwater along the so-called “bad water line.” East and south of the “bad water line,” increased residence time and water interaction with evaporite members of the Edwards Formation result in increased groundwater salinity. The Edwards Formation continues laterally beyond the official aquifer boundary to the south and east, becoming highly saline with greater depth. The rapid recharge through the karstic outcrop increases the aquifer’s vulnerability to contamination, making nonpoint source pollution from runoff in urbanized areas a particular concern.
Water from the aquifer is primarily used for municipal, irrigation, and recreational purposes. San Antonio obtains almost all its water supply from the Edwards (Balcones Fault Zone) Aquifer. Although water levels periodically and seasonally decline rapidly in wells throughout the aquifer, they also rebound quickly with adequate rainfall.
Reports
| ID | Date | Type | Description |
|---|---|---|---|
| Texas Aquifers Study | 12/31/2016 | Legislative Report | Texas Aquifers Study: Groundwater Quantity, Quality, Flow, and Contributions to Surface Water |
| LP-214 | 2/1/1995 | Limited publication | Evaluation of Ground-Water Quality in Texas Counties Bordering the Rio Grande |
| B-6212 | 7/1/1962 | Groundwater bulletin | Geology and Ground-Water Resources of Uvalde County, Texas |
| B-5911 | 10/1/1959 | Groundwater bulletin | Ground-Water Geology of Bexar County, Texas |
| R-019 | 3/1/1966 | TWDB numbered report | Ground-Water Resources of Guadalupe County, Texas |
| R-340 | 7/1/1992 | TWDB numbered report | Model Refinement and Applications for the Edwards (Balcones Fault Zone) Aquifer in the San Antonio Region, Texas |
| R-350 | 11/1/1999 | TWDB numbered report | Changes in Groundwater Conditions in the Edwards and Trinity Aquifers, 1987-1997, for Portions of Bastrop, Bell, Burnet, Lee, Milam, Travis, and Williamson Counties, Texas |
| B-5601 | 8/1/1956 | Groundwater bulletin | Geology and Ground-Water Resources of Medina County, Texas |
| B-6216 | 12/1/1962 | Groundwater bulletin | Geology and Ground-Water Resources of Kinney County, Texas |
| B-6004 | 8/1/1960 | Groundwater bulletin | Geology and Ground-Water Resources of Hays County, Texas |
| R-032 | 12/1/1966 | TWDB numbered report | Ground-Water Resources of Atascosa and Frio Counties, Texas |
| R-234 | 6/1/1979 | TWDB numbered report | Geohydrology of Comal, San Marcos, and Hueco Springs |
| R-296 | 11/1/1986 | TWDB numbered report | Carbonate Geology and Hydrology of the Edwards Aquifer in the San Antonio Area, Texas |
| R-239 | 10/1/1979 | TWDB numbered report | Ground-Water Resources and Model Applications for the Edwards (Balcones Fault Zone) Aquifer in the San Antonio Region |
| R-325 | 4/1/1990 | TWDB numbered report | Test Well Drilling Investigation to Delineate the Downdip Limits of Usable-Quality Ground Water in the Edwards Aquifer in the Austin Region, Texas |
| R-276 | 6/1/1983 | TWDB numbered report | Occurrence, Availability, and Quality of Ground Water in Travis County, Texas |
| R-353 | 9/1/2000 | TWDB numbered report | Groundwater Availability of the Trinity Aquifer, Hill Country Area, Texas: Numerical Simulations through 2050 |
| R-358 | 12/1/2003 | TWDB numbered report | Groundwater Availability Modeling: Northern Segment of the Edwards Aquifer, Texas |
| GT10-027_D | 2/9/2011 | GAM task | Predictive simulations for the Edwards (Balcones Fault Zone) and Edwards-Trinity (Plateau) aquifers in Kinney County GCD |
| GR10-015_MP | 6/15/2010 | GAM run - Management Plan | Management plan information for Evergreen UWCD |
| GR10-009_MP | 6/9/2010 | GAM run - Management Plan | Management plan information for Clearwater UWCD |
| GR09-019 | 6/1/2011 | GAM run | Predictive simulations for the Edwards (Balcones Fault Zone) Aquifer in Groundwater Management Area 10 |
| GR08-067_MP | 9/3/2008 | GAM run - Management Plan | Management plan information for the Edwards Aquifer Authority |
| GR08-062_MP | 9/3/2008 | GAM run - Management Plan | Management plan information for Evergreen UWCD |
| GR08-060 | 7/11/2008 | GAM run | Simulation of discharge to springs and streams in the Edwards (Balcones Fault Zone) Aquifer in Groundwater Management Area 8 |
| GR08-059 | 7/11/2008 | GAM run | Simulation of discharge to springs and streams in the Edwards (Balcones Fault Zone) Aquifer in Groundwater Management Area 8 |
| GR08-037_MP | 6/20/2008 | GAM run - Management Plan | Management plan information for Barton Springs/Edwards Aquifer Conservation District |
| GR07-021 | 10/30/2007 | GAM run | Simulation of discharge to springs and streams in the Edwards (Balcones Fault Zone) Aquifer in Groundwater Management Area 8 |
| GR07-015 | 10/30/2007 | GAM run | Simulation of discharge to springs and streams in the Edwards (Balcones Fault Zone) Aquifer in Groundwater Management Area 8 |
| GR07-010 | 3/23/2007 | GAM run | Recharge calculations for the Edwards (Balcones Fault Zone) and Edwards-Trinity (Plateau) aquifers in Kinney County GCD |
| GR06-033 | 2/12/2007 | GAM run | Effects on springflow and river flow of various pumping scenarios in the San Antonio Segment of the Edwards (Balcones Fault Zone) Aquifer |
| GR06-030 | 4/18/2008 | GAM run | Simulation of discharge to the Leona Gravel Aquifer from the Edwards (Balcones Fault Zone) Aquifer |
| GR05-007 | 2/11/2005 | GAM run | Recharge areas in Kinney County's portions of Edwards BFZ Aquifer and Edwards-Trinity (Plateau) Aquifer (Nueces River and Rio Grande basins) |
| R-380 | 7/1/2011 | TWDB numbered report | Aquifers of Texas |
| AA10-40_MAG | 8/20/2012 | Aquifer assessment MAG | Modeled available groundwater for the Edwards Aquifer in Frio County |
| CR-1004831114 | 8/9/2012 | Contract report | Ground Water Recharge Model: Calibration and Validation for Remotely-Sensed Dual Coefficient (RDC) GMA8 ET Estimation |
| GR10-059_MAG_Ver2 | 12/7/2011 | GAM run - MAG | Modeled available groundwater for the Edwards (Balcones Fault Zone) Aquifer in the Northern Subdivision of Groundwater Management Area 10 |
| GR12-014_MP | 2/11/2013 | GAM run - Management Plan | Management plan data for Kinney County GCD |
| GT13-032_TERS | 10/2/2013 | GAM task - Total Estimated Recoverable Storage | Total Estimated Recoverable Storage for aquifers in Groundwater Management Area 9 |
| GT13-033_TERS | 8/20/2013 | GAM task - Total Estimated Recoverable Storage | Total Estimated Recoverable Storage for aquifers in Groundwater Management Area 10 |
| GT13-036_TERS_Ver2 | 7/15/2013 | GAM task - Total Estimated Recoverable Storage | Total Estimated Recoverable Storage for aquifers in Groundwater Management Area 13 |
| GT13-031_TERS | 1/15/2014 | GAM task - Total Estimated Recoverable Storage | Total Estimated Recoverable Storage for aquifers in Groundwater Management Area 8 |
| GR15-009_MP | 3/18/2015 | GAM run - Management Plan | Management Plan data for Edwards Aquifer Authority |
| GR15-004_MP | 6/30/2015 | GAM run - Management Plan | Management Plan data for Evergreen UWCD |
| GR15-003_MP | 11/24/2015 | GAM run - Management Plan | Management Plan data for Clearwater UWCD |
| GR19-027_MP | 12/13/2019 | GAM run - Management Plan | Management plan information for Southwestern Travis County GCD |
| GR20-003_MP | 8/25/2020 | GAM run - Management Plan | Management plan information for Medina County GCD |
| GR20-004_MP | 9/30/2020 | GAM run - Management Plan | Management plan information for Wintergarden GCD |
| GR22-006_MP | 3/28/2022 | GAM run - Management Plan | Management plan information for Barton Springs Edwards Aquifer Conservation District |
| GR22-011_MP | 11/8/2022 | GAM run - Management Plan | Management plan information for Kinney County GCD |
| GR21-015_MAG | 4/12/2023 | GAM run - MAG | Modeled Available Groundwater for the aquifers in Groundwater Management 10 |