Simulated effects of aquifer heterogeneity on ASR system performance

Abstract

All aquifers have some degrees of heterogeneity, which if extreme, can adversely affect the performance of ASR systems. There are many types of aquifer heterogeneity that may be encountered in the field. Two of them are considered here: non-uniform distribution of transmissivity in the storage zone and dual porosity. As indicated by the flowmeter log data, the hydraulic conductivity values may vary by several orders of magnitude within the target storage zone. The heterogeneity introduced by the variable distribution of flow zones may affect the performance of an ASR system. Dual-porosity conditions are often encountered in storage aquifers, which can significantly impact the recovery efficiency of an ASR system. Several cases of heterogeneity and their potential impacts on ASR system recovery efficiency were investigated by simulations of hypothetical ASR systems with reasonable input parameters. Modeling results indicate that aquifer heterogeneity will reduce the performance of ASR systems, compared to systems using a homogeneous aquifer. Existence of dual-porosity conditions has a tendency to lower the recovery efficiency of an ASR system when freshwater is injected into the native brackish water due to mixing and differential solute travel time. Buoyancy effects are more pronounced in the fractured domain than in a homogenous system. This resulted in a wider freshwater plume in the shallower layers within the fractured domain. The simulation results also suggest that recovery efficiency can be improved by setting the extraction point shallower than the injection point.