Arsenic Flux during Successive Aquifer Storage Recovery Cycle Tests In the Upper Floridan Aquifer System, Central and South Florida

Arsenic mobilization during Aquifer Storage Recovery (ASR) cycle tests represents a significant challenge to feasibility of this water resource management technology. Arsenic concentrations that exceed Florida and Federal regulatory criteria frequently are detected in water that has been stored in, then recovered from, limestone aquifer materials. Further applications of ASR technology in Florida require demonstration that arsenic mobilization can be minimized, or that arsenic concentrations will attenuate during successive cycle tests. Data presented here support arsenic attenuation under certain system operational scenarios.

The magnitude of arsenic mobilized during ASR cycle tests depends on: 1) pyrite composition and occurrence in the storage zone lithology (the source term); 2) redox characteristics of recharge water (reactant solution); 3) geochemical evolution of stored water in the aquifer (reaction environment); and 3) recharge and recovery volumes that define the cycle tests (flux). Generalizations about regional trends and occurrence of arsenic at south Florida ASR systems have been hindered by variability in some or all of these characteristics.

Arsenic flux during two ASR operational scenarios will be presented. The first scenario will show arsenic attenuation during successive cycles in which volumes recharged and recovered are nearly identical during 5 successive cycles. The second scenario will show trends in arsenic concentration during cycles characterized by progressively larger recharge volumes. Percent recovery, expressed as volume recovered having potable water-quality characteristics (less than 250 mg/L chloride, less than 50 or 10 micrograms/L arsenic), will be compared between these representative sites.