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Aquifer storage and recovery (ASR) is a potential solution to growing global freshwater insecurity. However, the performance of ASR in saline regions depends on regional hydrogeology and groundwater salinity level. Hydrogeological factors, e.g., hydraulic conductivity, hydraulic gradient, aquifer thickness, aquifer heterogeneity, and hydrodynamic dispersivity, affect freshwater recovery efficiency (RE) prominently along with the groundwater salinity. Therefore, a site feasibility analysis for ASR based on the prevailing hydrogeological conditions is required for its successful operation. This study investigates the influence of these hydrogeological parameters and groundwater salinity level on the performance of ASR. Findings from previous field studies were reviewed, grouped, and analyzed systematically for each hydrogeological factor independently and in combination to understand their influence on RE. The interdependency of the effects caused by each factor is also analyzed. The results show that higher freshwater recovery can be achieved at sites offering moderate hydraulic conductivity, low hydraulic gradient, low hydrodynamic dispersivity, thinner aquifers, and low groundwater salinity. The overall findings of this meta-analysis will help in synthesizing information for site hydrogeological conditions to aid in the decision-making process for ASR application in saline groundwater regions. [ABSTRACT FROM AUTHOR]

Aquifer storage and recovery (ASR) in saline unconfined aquifers is challenging as the injected freshwater makes a thin layer above the groundwater table. For this reason, the efficiency of ASR in unconfined saline aquifers has been reported to be low in the literature. Nevertheless, critical factors like depth of freshwater release, length of storage duration, and rate of injection/extraction control the recovery efficiency (RE) of an ASR and can be adjusted to enhance the performance. This study aims to optimize the ASR technique in unconfined saline aquifers to maximize its recovery efficiency through sand tank experiments and numerical modeling. The tank experiments were conducted using a three-dimensional sand tank setup of dimensions 60 (length)×30 (width)×60 cm (depth) , to examine the interactions between injected freshwater and ambient saline groundwater. Variable density groundwater flow modeling was performed to observe the movement of stored freshwater at varying depths within the aquifer and to examine the influence of storage duration and injection/extraction rates on RE. The results from experimental and numerical studies demonstrated that shallow injection depths, higher injection/extraction rates, and smaller storage durations lead to higher freshwater recovery. Deeper injection allows the freshwater packet to move upward due to buoyancy force, resulting in freshwater losses if the injection and recovery are undertaken at the same depth. The overall findings from the present study can be utilized to enhance freshwater recovery in unconfined saline aquifers through the optimization of influencing factors. [ABSTRACT FROM AUTHOR]

Application of aquifer storage and recovery (ASR) is difficult in highly saline groundwater regions because the recharged freshwater mixes with saline groundwater and makes a thin layer below the capillary fringe. The recovery efficiency (RE) of ASR can be improved by customizing the operational factors and well design of the ASR scheme according to the regional hydrogeology. The RE can be raised in different ways, such as adjusting the operational factors to reduce the mixing or using multiple wells to reduce gravitational segregation. This study developed a variable-density groundwater flow modeling framework for ASR performance estimation in saline groundwater regions, which examined the combined influence of operational factors and well design on RE. The density-driven effect during freshwater injection and its storage within saline groundwater on RE were also investigated. ASR systems with single fully penetrating wells (SFPWs) and multiple partially penetrating wells (MPPWs) were evaluated with respect to operational factors, that is, injection and recovery rates, the volume of injected freshwater, storage duration, and successive number of ASR cycles. The results showed that losses due to mixing are significantly influenced and controlled by successive ASR cycles followed by injection and recovery rates, injection volume, and storage duration. The results also revealed that losses due to gravity could be controlled by using MPPW systems in place of a SFPW system. The model results showed that in three subsequent cycles, no more than 45% of the yearly injected water could be recovered by the SFPW well–type model, which is less than the MPPW case by 11% for the baseline parameters of representative hydrogeology. The results of this study will help in the operational management of ASR schemes to achieve higher RE in the saline groundwater regions. [ABSTRACT FROM AUTHOR]

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. • Investigated influence of operational factors on MAR performance in saline aquifers. • Quantified recovery efficiencies of stored freshwater using controlled experiments. • Confirmed a negative correlation between ambient groundwater salinity and RE. • Established a positive, non-linear relationship between injection volume and RE. • Highlighted the negative impact of increasing storage duration on MAR performance. [ABSTRACT FROM AUTHOR]