Investigation of the Fresh/Saline Water Interface in the Edwards Aquifer in New Braunfels and San Marcos, Texas Executive Summary

Author Edwards Underground Water District
Year 1992
Description Attempts to define the freshwater/saline water boundary and its movement in the New Braunfels/San Marcos area from monitoring well data.
Report Number 92-02
Publisher Edwards Underground Water District
Location Edwards Aquifer, Balcones Fault Zone, San Antonio Segment, New Braunfels, San Marcos
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The purpose of this investigation was to develop site-specific information at selected sites along the fresh/saline-water interface and to establish a long term monitoring system. The report discusses the drilling,construction, and testing of a series of monitoring wells located in New Braunfels and San Marcos, Texas. Data collected as a result of this study will continue to provide information needed to determine whether encroachment of poor quality water presents a serious problem to maximum use of the aquifer as natural and man-made stresses on the aquifer system occur….

The conclusions to be drawn from this pump test are not definitive of saline water intrusion because the production well used was a transition well (containing both fresh and saline waters). However, an increase in salinity in the production well could indicate that the interface between the fresh/saline zones moved. This is supported by a low sloping cone of depression during the pump test combined with the ability of water to flow from the saline zone to this transitional well. However, the well must have also drawn fresh water to it, for the salinity values did not increase to the same values observed in the saline zone.  Nevertheless, the data suggests that an element of caution should be considered during periods of increased hydrologic stress on the aquifer system in this area.