Edwards Aquifer Recharge Zone Surface-water and Groundwater Interaction

Science Center Objects

The effects of urbanization across the recharge zone in Bexar County and potential impact on the water quality in the Edwards aquifer is a topic of specific concern for the City of San Antonio. The USGS Texas Water Science Center is simultaneously collecting water-quality data from surface-water runoff sites and paired shallow groundwater wells within the recharge zone of the Edwards aquifer to better characterize the water quality connection between surface water and groundwater. 

The San Antonio segment of the Edwards aquifer in south-central Texas is the primary water supply for more than a million people in San Antonio and the surrounding Bexar County area. The aquifer is susceptible to anthropogenic contaminants from urbanization and nutrients and pesticides are commonly detected in the aquifer. 

The objective of this study is to simultaneously collect water-quality data from surface-water runoff sites and paired shallow groundwater wells within the recharge zone of the Edwards aquifer to better characterize the water quality connection between surface water and groundwater. 

Encino Rio well

Encino Rio well, one of the selected groundwater sites.

A water quality sampling network consisting of two pairs of surface water and groundwater sites has been established. One pair of surface water/groundwater sites is located in an area with little urbanization. A second pair of surface water/ groundwater sites is located in the area of highway 1604/281 of northern San Antonio where extensive urbanization has been occurring. 

The two groundwater sites will be monitored continuously for water level, specific conductance, and nitrate.  Additional groundwater quality samples will be collected regularly throughout the year and following storms.  These samples will be analyzed for nutrients, major and trace elements, pesticides, nitrate stable isotopes, and water stable isotopes.

The paired surface water runoff sites only have flow during storm events. During storms, water quality samples will be collected collected and analyzed for the same constituents that are being analyzed for at the groundwater sites.