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Potential for updip movement of salinewater in the Edwards Aquifer, San Antonio, Texas

Water-Resources Investigations Report 86-4032

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Abstract

The salinity front, locally known as the ' bad-water ' line, in the Edwards aquifer separates the freshwater from the saline water and occurs where the aquifer is confined. The concentration of dissolved solids of the saline water at the salinity front is 1,000 mg/L. The concentration of dissolved solids in water within the freshwater zone of the aquifer usually ranges from 250 to 350 mg/L. A digital model was used to investigate the potential movement of the salinity front by simulating the transport of saline water into the freshwater zone as a result of pumping from the freshwater zone. The model simulations indicate that a large range in the quantity of solute transported form the saline water zone into the freshwater zone is possible. This uncertainty is caused by the range of estimates of transmissivity, the magnitude of water level decline, and porosity. Simulated transmissivity values for the Edwards aquifer within the saline water zone ranged from 134 to 3,340 sq ft/day and resulted in potential lateral shifts of the salinity front from 16 to 425 feet updip into the freshwater zone at the end of the 10-yr simulation. A simulated decline in water levels from an altitude of 660 to 582 ft above sea level resulted in a potential lateral shift in the salinity front of 133 ft updip into the freshwater zone at the end of the 10-yr simulation. Simulated porosity values from 1% to 20% resulted in lateral shifts of the salinity front from 42 ft to 854 ft updip into the freshwater zone at the end of the 10-yr simulation. An evaluation of the results of the model simulations indicate that contamination created by the movement of saline water into the freshwater zone of the Edwards aquifer will be limited to an area within 0.2 mile of the present salinity front under the tested conditions. (Author 's abstract)

Additional Publication Details

Publication type:
Report
Publication Subtype:
USGS Numbered Series
Title:
Potential for updip movement of salinewater in the Edwards Aquifer, San Antonio, Texas
Series title:
Water-Resources Investigations Report
Series number:
86-4032
Edition:
-
Year Published:
1986
Language:
ENGLISH
Publisher:
U.S. Geological Survey,
Description:
v, 21 p. :ill., maps ;28 cm.