Enhanced Performance of Aquifer Storage and Recovery System in Unconfined Saline Aquifer for Different Operational Factors: A Multidimensional Laboratory and Modeling Study

Abstract

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.