Urban Waters Federal Partnership - Edwards Aquifer Recharge in a Developing Landscape

Science Center Objects

San Antonio Texas consistently ranks as one of the fastest growing large cities in the United States. Urban development can affect groundwater quality as trees and open space are replaced by buildings and roads, increasing the amount of urban runoff draining directly into the Edwards aquifer. A network of sophisticated surface water and groundwater monitoring sites is being used to help managers better understand aquifer hydrologic processes and the effects of urban runoff on groundwater quality.  

Encino Rio well

Encino Rio Well Urban Groundwater Monitoring Site

The Edwards aquifer is one of the most productive aquifers in the United States serving as the primary source of drinking water for more than two million people in the San Antonio area, one of the fastest growing large cities in the country. Additionally, the Edwards aquifer supports a thriving agricultural community in south-central Texas. The aquifer is managed to balance municipal and agricultural demands with the water quantity and quality needed to support several endangered species that inhabit the karst caverns and springs. The potential for groundwater contamination is of concern as urbanization continues to expand into the aquifer’s recharge zone. The Edwards aquifer recharge zone is largely unconfined and is characterized by dynamic surface water/groundwater interactions that provide a potential pathway for the rapid introduction of contaminants derived from the land’s surface into the aquifer. 

Encino Rio groundwater monitoring equipment

Interior view of the Encino Rio Well Urban Groundwater Monitoring Site

How much does stormwater runoff from urban areas affect the water quality of the aquifer system? The U.S Geological Survey (USGS) in cooperation with San Antonio Water Systems (SAWS), the City of San Antonio (CoSA), and the San Antonio River Authority (SARA) has established a network of surface water and groundwater sites in areas with various degrees of urbanization to provide long-term monitoring and water-quality data needed to answer this question. Groundwater “super sites” are continuously monitored in real-time for temperature, dissolved oxygen, conductance, pH, water level, and nitrate concentration. In addition, quarterly samples are collected and analyzed for nutrients, pesticides, selected trace ions, nitrate isotopes, strontium isotopes, and hydrogen and oxygen isotopes. The surface-water and groundwater sites are sampled during storm events to see how the stormwater quality compares to the water quality of groundwater sites. 

Goals of this assessment are to assess if water quality in the Edwards aquifer is changing as result of development. Data from this project also could be used to model potential groundwater contamination and provide better understating of the dynamic hydrologic processes involved in controlling water quality, a vital resource for this urban center. 

Satellite view from 1959, 1973, 1995, and 2016

Urban Development of US 281 and 1604 Crossing over the Edwards Aquifer Recharge Zone San Antonio, TX.   (Image Courtesy of Google Earth)

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