Quantifying impacts of coupled chemical and physical heterogeneity on water quality evolution during Aquifer Storage and Recovery

Thursday, 18 December 2014
Hailin Deng1, Carlos Descourvieres2, Simone Seibert3, Brett Harris4, Olivier Atteia5, Adam J Siade6,7 and Henning Prommer1,6, (1)CSIRO, Land and Water Flagship, Perth, Australia, (2)Schlumberger Water Services, Perth, Australia, (3)University of Western Australia, School of Earth and Environment, Perth, Australia, (4)Curtin University, Department of Exploration Geophysics, Perth, Australia, (5)Institut Polytechnique de Bordeaux, ENSEGID, Pessac, France, (6)University of Western Australia, School of Earth and Environment, Crawley, WA, Australia, (7)National Center for Groundwater Research and Training, Adelaide, Australia
Aquifer storage and recovery (ASR) is an important water management option in water-scarce regions. During wet periods surplus water is injected into suitable aquifers for storage and later recovery. ASR sites are, however, also ideal natural laboratories that provide opportunities for studying coupled physical and geochemical processes and water quality evolution at field-scale under well-controlled hydrological conditions. In this study, we use reactive transport modelling to assess the impacts of physical and chemical heterogeneities on the water quality evolution during the injection of oxic surface water into the anoxic, pyrite-bearing Leederville aquifer in Perth, Western Australia. Physical heterogeneity was identified from geophysical well logs and time lapse temperature logs. Those data were used to define the spatial, depth-varying alternation of three lithofacies (sandstone, siltstone and clay). Chemical heterogeneity was incorporated through distinct chemical zones, based on data derived from a comprehensive pre-trial geochemical characterization and from dedicated laboratory respirometer experiments. Calibration of flow and conservative transport parameters was constrained by the spatially varying measured chloride breakthrough behavior. Subsequent reactive transport modeling discerned the key geochemical processes that affected the water quality evolution during ASR. Clearly identified processes included oxidation of pyrite, mineralization of sedimentary organic carbon, ion exchange, dissolution of calcite and precipitation of ferrihydrite and siderite. We use the calibrated model to analyze the individual and the combined effects of the physical and chemical heterogeneities on the chemical composition of the recovered water during ASR.