Aquifer storage recovery: an ASR solution to saltwater intrusion at Hilton Head Island, South Carolina, USA

Achieving high recovery efficiency is a goal for almost all aquifer storage recovery (ASR) wells, whether storing fresh water in brackish aquifers or in fresh aquifers containing native water quality constituents that are not wanted in the recovered water. This goal can be achieved rapidly by initial formation and maintenance of a target storage volume (TSV) that includes the water volume required for recovery plus a buffer zone volume that separates the stored water from the surrounding native groundwater. The buffer zone volume is a one-time addition of water to the well. An ASR demonstration project was constructed and tested at Hilton Head Island, South Carolina, USA, storing drinking water in a brackish limestone, semi-confined, artesian aquifer. Operating performance has confirmed the viability of this TSV approach for development of ASR wells. The stored drinking water was recovered at a flow rate of 8 Ml/D for 126 days, with an ending chloride concentration of 170 mg/l, rapidly achieving 100 % recovery efficiency. The storage aquifer had a chloride concentration of 685 mg/l. Results have since been replicated at two other ASR wells on Hilton Head Island, addressing the expected loss of all remaining fresh public water supply wells on the island due to saltwater intrusion. ASR well cycle testing in which the same volume is stored and recovered, with progressively larger storage volumes in each successive cycle, is appropriate for geochemical and microbial studies but is inappropriate for determination of recovery efficiency since any buffer zone is removed during each cycle.