The Edwards (Balcones Fault Zone) Aquifer is the primary source of public water supply for the City of San Antonio and much of the surrounding region. The San Antonio Water System (SAWS) requires the ability to make complete and efficient use of its permitted withdrawal from the Edwards BFZ Aquifer. The Edwards Aquifer Authority (EAA) is currently preparing to implement a programmed reduction in the permitted withdrawal from the Edwards (BFZ) Aquifer as part of its Habitat Conservation Plan (HCP), thus designed to protect endangered species that rely on springflow at Comal and San Marcos Springs. Proposed withdrawal reductions would limit SAWS service operations during periods of normal precipitation periods and would significantly reduce withdrawals during drought periods. Edwards Aquifer water rights are being leased and purchased to as a method to augment public water supplies in the short-term.

Several other strategies are being implemented or are under study by SAWS to replace the sources of supply no longer available. One of the more innovative strategies involves managing SAWS' Edwards Aquifer withdrawals to achieve full permit utilization while minimizing regional impact on springflow is by the use of Aquifer Storage and Recovery (ASR). During seasonal periods of high spring flow, usually in the winter months, the Edwards aquifer would be produced at a rate exceeding current demands and the excess would be stored in the confined Carrizo Formation of the Carrizo-Wilcox Aquifer in southern Bexar County. The Edwards water would be later recovered to meet peak demand periods (summer months) or augment curtailed supplies during extended drought periods. Benefits of ASR management include a 25-percent reduction in peak summer withdrawals; no evaporative losses or environmental impacts as associated with surface-water impoundment options under consideration; and more complete utilization of the Edwards Aquifer source. The ASR system is a conjunctive use project that will be operated in a production mode until excess capacity (Edwards Aquifer supply) is available for storage.

This discussion provides the details of the ASR system scheduled for startup in February 2004. Initial cycle testing of the ASR system will begin in March 2004. ASR-related facilities under Phase I of construction include a 30-MGD ASR wellfield, treatment plant, high-service pump station, and a 27-mile pipeline to transmit water to and from the SAWS distribution system. Additionally, the Phase II of construction will include 11 additional ASR wells and treatment plant upgrades to expand the system capacity to 66 MGD. Interesting technological features utilized the project include: use of high-technology geophysical logging; pre-packed well screens; reverse-flow well pumps/ piping; and a planned head-to-head comparison of the two popular down-hole control valves. As the manager of the second largest ASR project in the United States, the SAWS is helping to develop new methodologies and technologies in groundwater management.