EDWARDS AQUIFER

• Current Studies
  • Barton Springs Groundwater Characterization Project
  • Stormwater Runoff
  • Hydrogeology of the Edwards aquifer
  • Evaluation of Seco Creek Basin
  • South-Central Texas (Edwards) NAWQA
  • Hydrogeology of Medina Lake, Medina-Bandera Counties

• Publications
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• Other Resources
  • Levels from San Antonio Water System (SAWS)
  • Level from Edwards Aquifer Authority (EAA)
  • Geologic Discipline Edwards Project Web Site
  • Recharge Summary

QUICK LINKS

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  • Edwards Aquifer WQ & Bio Data Clearinghouse

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USGS IN YOUR STATE

USGS Water Science Centers are located in each state.

Program of the USGS in Texas
Hydrology and flowpaths of the freshwater/saline-water interface of the Edwards aquifer, South-Central, Texas

PROBLEM

Present data regarding movement of saline water into the freshwater zone of the Edwards aquifer is inconclusive. There is little or no understanding of the hydraulics and interconnection of the saline portion of the Edwards aquifer and its relation to the fresh-water portion of the aquifer. This lack of information on the hydrology of the saline zone diminishes the ability of Federal, State, and local agencies to effectively manage the resource and develop a regional water-use management plan.

OBJECTIVE

- To describe the hydrogeologic framework of the freshwater/saline-water interface of the Edwards aquifer.

- To characterize the hydrology of the freshwater/saline-water interface using water level, chemical, geochemical, and hydraulic information.

- To determine the flowpaths and mixing patterns along the interface and in the saline zone of the Edwards aquifer.

APPROACH

Knowledge of the hydrogeologic framework and spatial distribution of the Edwards aquifer hydrogeologic subdivisions is crucial to understanding ground-water flowpaths and the relation between the freshwater and saline-water zones of the Edwards aquifer. Existing hydrogeologic and hydraulic data along with information from newly drilled monitor well transects will be compiled and used to prepare contour maps and cross sections showing the structural framework and configuration of hydrogeologic formations along the interface (objective 1).

The hydrology of the freshwater/saline-water interface will be characterized by collecting and analyzing water-level, chemical, geochemical, and hydraulic property data (objective 2). Selected wells in the monitor transects will be equipped with pressure transducers and data loggers to continuously monitor the water levels in wells along the interface to determine if recharge also affects the patterns of flow along the interface and into the saline zone (objective 1).

At least one water-level synoptic survey will be conducted using available wells completed along the freshwater/saline-water interface and in the saline zone of the aquifer.

Water chemistry and geochemical processes will be used to characterize flow and mixing patterns along the interface and in the saline zone (objective 2). Historical water-quality data along with newly-collected water-quality data will be used in the analysis. Water samples will be collected from newly-drilled monitor wells to characterize the water quality of the interface in the Kyle and Uvalde areas (objective 2). The water samples will be analyzed for major ions, trace elements, and selected environmental isotopes. Continuous water-quality data will be collected from selected wells in the monitor transects as a means of documenting temporal changes in salinity at the interface (objectives 2 and 3). Downhole water-quality monitors will be installed in three freshwater and saline-water wells across the region to collect information on the variation in pH, temperature, and specific conductance. The water-quality monitors will be co-installed with the water-level transducers to determine if changes in the field parameters can be related to head changes in the aquifer.

The ability of an aquifer to transmit and store water can be determined from aquifer tests by computing the properties of transmissivity and storativity (objective 2). To determine if conducting aquifer tests in the interface transect wells is feasible, specific capacity tests will be conducted during FY 2000 at two selected wells in the Kyle and Uvalde transects. Based on the results of the specific capacity tests, additional aquifer tests may be conducted at the Kyle, Cibolo Creek, Uvalde transects, and possibly the San Marcos and New Braunfels transects. These tests may be conducted as either a pumping (withdrawal) test at a constant discharge or stepped-discharge rate or a recovery test.

Ground-water flowpaths and mixing patterns along the interface and in the saline zone will be analyzed using water level and chemical/geochemical data (objectives 2 and 3). Continuous water-level data will be used along with water-level data from the synoptic survey(s) to determine the spatial and temporal distribution of hydraulic head along the interface and in the saline zone. If sufficient water-level measurements are available, a hydraulic conductivity-weighted flow net based on the potentiometric surface of the aquifer will be constructed. General chemistry and environmental isotopes will be used as supporting evidence along with the hydrogeologic and water-level data to confirm regional flowpaths (objective 3).