Performance Evaluation of Aquifer Storage and Recovery (ASR) System in Saline Groundwater Regions: Impact of Operational Factors and Well Design

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.