Technical Reports Document Library

Surface-water data for the San Antonio area used to calculate annual recharge and discharge of the Edwards aquifer, consist of flow data for streams and discharge data for springs, and quantity data for reservoirs. The data is stored in the National Water Information system, a computerized data base operated by the U. S. Geological Survey.

The average estimated annual groundwater recharge to the Edwards aquifer in the San Antonio area, Texas, from 1934 through 1992 was 682,860 acre-feet. Recharge in 1992 was 2,486,000 acre-feet, which is the largest estimated annual recharge. The lowest annual recharge of 43,700 acre-feet occurred in 1956.

The estimated annual discharge from the Edwards aquifer by wells and springs in 1992 was 1,130,000 acre-feet, which is the largest calculated annual discharge for the period of record which began in 1934. The lowest annual discharge by wells and springs for the same time period was 388,800 acre-feet in 1955.

Water level data for wells during 1992 reflected above average to record volume of groundwater in storage in the Edwards aquifer during most of the year.

Water samples from 61 wells and 3 springs in the Edwards aquifer were analyzed for more than 90 properties or constituents, most of which affect the suitability of the water for domestic use. Concentrations of constituents in water from one well completed in the freshwater zone exceeded the maximum contaminant level for fluoride established for public water systems.

Trace concentrations of volatile organic compounds were detected in samples from three wells. Results of the 1992 water sampling and analysis program illustrate the continued excellent quality of water in the Edwards aquifer.