Carrizo Aquifer Water Quality

Science Center Objects

The USGS Texas Water Science Center, in cooperation with the San Antonio Water System, has been collecting data since 2004 to characterize the quality of and ascertain changes in groundwater at and near the water system’s Twin Oaks Aquifer Storage and Recovery (ASR) site, where the water system has been injecting water from the Edwards aquifer into the Carrizo aquifer for storage. Findings are intended to provide a better understanding of possible changes in the quality of groundwater near an active ASR site that might result from the mixing of water from different aquifers. 

Mobilization of trace elements in groundwater as a result of changes in oxidation and pH conditions has been observed at other ASR sites and iron and manganese mobilization is the main concern at the ASR site. As ASR water is injected and withdrawn from the Carrizo aquifer, the influence of ASR activities on ground-water levels and quality in areas surrounding the ASR area is uncertain.  Also, as reliance on the Carrizo aquifer for regional water supplies increases, so does concern for protection of aquifer water-quality.

The Carrizo sands that constitute the outcrop and recharge zone are highly permeable and are possibly subject to contamination from water-quality constituents in runoff that might infiltrate into the aquifer.  Baseline ground-water level and ground-water quality data from the surrounding areas are needed to provide resource-managers with adequate background data to evaluate project impacts on the aquifer.