The impact of storage conditions and aquifer heterogeneity on Aquifer Storage Recharge (ASR) system’s performance

Abstract

Aquifer Storage and Recovery systems (ASR) are an alternative source of fresh water to the increasing demand for water. Its performance varies in terms of flow parameters, aquifer conditions and transport processes. An axisymmetric 50 m thick base model is defined to simulate ASR performance by using Modflow, MT3DMS and Seawat. The heterogeneous setting is defined as an alternation of high-K and low-K layers, where different hydraulic conductivities, contrast ratios and anisotropy factors are simulated for homogeneous and heterogeneous cases. Under the numerical approach the anisotropy factor in the homogeneous cases is the independent variable, while in the geological approach, the heterogeneous layers are the independent variable. The numerical approach makes different scenarios comparable and has a greater impact on the high-K layers’ vertical conductivity KV while the geological approach leads to realistic simulations and has a greater impact on the low-K layers’ KV . Higher values of KV lead to a greater buoyancy effect and tilting of the fresh-naive water interface. Homogeneous cases have a better performance than heterogeneous cases, mainly during the first years of simulation. Peaks on RE after 4 or 6 years of simulation in heterogeneous cases can be explained by the transfer of fresh water to a high-K layer from an underneath low-K or high-K layer due to buoyancy. Homogeneous cases have a better performance than heterogeneous cases. RE is more impacted by KV than horizontal hydraulic conductivity KH, as it controls the amount of buoyancy. In heterogeneous cases, buoyancy in high-K layers is the main responsible for the reduction in RE compared to the homogeneous equivalent cases. Keywords: