APPROACHES TO MONITORING AND REGULATION OF AN AQUIFER STORAGE AND RECOVERY SYSTEM IN THE EDWARDS AQUIFER, SOUTH-CENTRAL TEXAS, USA Jennifer R. Adkins Schudrowitz, Alyssa B. Balzen , F. Paul Bertetti AbstractThe Edwards (Balcones Fault Zone) Aquifer (Edwards BFZA) is a major karstic limestone aquifer in south-central Texas, USA. The aquifer serves as the primary water supply for approximately 2.5 million people and is integral to the ecosystems of major springs that are home to several threatened and endangered species. The region served by the aquifer continues to experience significant population growth; however, the quantity of permitted withdrawals from the Edwards Aquifer is capped by law. In response, many water suppliers and utilities are exploring alternate supply sources as part of their long-term water management strategies. New Braunfels Utilities (NBU) is evaluating an Aquifer Storage and Recovery (ASR) system in the brackish zone of the Edwards BFZA. The Edwards Aquifer Authority (EAA) regulates the withdrawal permitting process including storage and recovery of water from the brackish zone of the aquifer. The EAA and NBU have entered into a cooperative contract authorizing NBU to recharge, store, and recover water from the ASR pending results from a phased investigation that demonstrates (i) the continued feasibility of the project and (ii) no unacceptable impacts to Comal Springs flow or Edwards BFZA freshwater quality. The contract also defines roles of the operator (NBU) and regulator (EAA) with respect to monitoring for and mitigation of any potential adverse effects. The complexities of karst aquifer systems represent challenges to effective operation and monitoring of the ASR. The EAA and NBU have addressed some of these challenges through (i) development of detailed sampling and monitoring plans, (ii) incorporation of hydraulic modeling to estimate system responses, (iii) development of a robust monitoring network capable of functioning at extreme depths and chemically aggressive conditions, and (iv) compilation and analysis of data focusing on sensitive parameters with known temporal stability in both freshwater and brackish water.