Assessment of managed aquifer recharge in saline confined aquifers for freshwater storage and improved recovery: A 3D tank study under various operational conditions.

Aquifer Storage and Recovery (ASR), a subset of Managed Aquifer Recharge (MAR) techniques, is a promising technique to address water scarcity issues by recharging depleted aquifers. The application of ASR in saline groundwater regions is challenging due to mixing of recharged freshwater with the ambient saline groundwater, decreasing the recoverable amount of freshwater. This paper aimed to investigate the feasibility of ASR techniques for freshwater storage and recovery in saline confined aquifers using a laboratory scale physical model (100 cm length x 30 cm width x 60 cm depth). The study then explored the impact of operational factors (freshwater storage duration, injected freshwater volume, number of injection/extraction cycles etc.) on freshwater recovery from an applied ASR. Firstly, the behaviour of stored freshwater in a saline-confined aquifer was investigated, and in the next step, the impact of ASR operational parameters on the recovery efficiency (RE) was evaluated. Along with the physical model, these effects were studied using a mathematical model (MODFLOW linked with SEAWAT) for the representative aquifer system. The movement and spreading of the stored freshwater were monitored over time. The experimental results presented in this study suggested that several factors significantly influence the efficiency of ASR systems. A negative correlation between ambient groundwater salinity and average recovery efficiency (ARE) was confirmed, with decreasing ARE observed as the salinity level increased. The injection volume of freshwater was found to have a positive influence on ARE, although the relationship was non-linear, a polynomial trend was observed. The longer freshwater was stored in the aquifer, the lower ARE was reported, indicating a negative impact of storage duration on ASR performance. Finally, the number of successive cycles of ASR operation was found to have a positive influence on ARE, but the effect decreased with each subsequent cycle. This research provided valuable insights into the application of ASR techniques for freshwater storage and its enhanced recovery in saline confined aquifers.