Technical Reports Document Library

Note:  This report is included for its historical value; results may have been superseded by more recent studies.

The city of San Antonio and other water users in the San Antonio area have been concerned about the possibility of the encroachment of saline water into the fresh water-bearing part of the aquifer supplying the area. As a result, a program was begun in 1959 to resample wells tapping the zone of transition between water of good quality and saline water in the Edwards and associated limestones, in order to detect changes in quality of the water as the head in the aquifer changed. This program is part of a more extensive hydrologic investigation being carried on by the U.S. Geological Survey in cooperation with the Edwards Underground Water District, the Texas Water Commission, and the City of San Antonio. As part of this program, about 120 wells are resampled twice a year; the water is analyzed in the laboratory of the Geological Survey in Austin, Tex., for specific conductance, pH, chloride, sulfate, bicarbonate, and hardness. A more complete chemical analysis is made for one of the samples from each well in the program. These more complete analyses are on file in the offices of the Geological Survey in Austin and San Antonio.

Chemical analyses of water from 129 wells are shown in the table in this report. The analyses of samples collected before 1959 for many of the wells are shown also. Some of the wells are no longer in use, but chemical analyses of previous samples from these wells are carried in the records, although future sampling may not be possible. Figure 1 shows the location of the resampled wells and an arbitrary boundary line between water of good quality, containing less than 1,000 parts per million (ppm), and saline water, containing more than 1,000 ppm of dissolved solids (Garza, 1962, p. 38 ).