Flow dynamics in hyper-saline aquifers: hydro-geophysical monitoring and modeling

Abstract

Abstract. Saline-freshwater interaction in porous media is a phenomenon of practical interest particularly for the management of water resources in arid and semi-arid environments, where precious freshwater resources are threatened by seawater intrusion and where storage of freshwater in saline aquifers can be a viable option. Saline-freshwater interactions are controlled by physico-chemical processes that need to be accurately modeled. This in turn requires monitoring of these systems, a non-trivial task for which spatially extensive, high-resolution non-invasive techniques can provide key information. In this paper we present the field monitoring and numerical modeling components of an approach aimed at understanding complex saline-freshwater systems. The approach is applied to a freshwater injection experiment carried out in a hyper-saline aquifer near Cagliari (Sardinia, Italy). The experiment was monitored using time-lapse cross-hole electrical resistivity tomography (ERT). To investigate the flow dynamics, coupled numerical flow and transport modeling of the experiment was carried out using an advanced three-dimensional (3-D) density-driven flow-transport simulator. The simulation results were used to produce synthetic ERT inversion results to be compared against real field ERT results. This exercise demonstrates that the evolution of the freshwater bulb is strongly influenced by the system's (even mild) hydraulic heterogeneities. The example also highlights how the joint use of ERT imaging and gravity-dependent flow and transport modeling give fundamental information for this type of study.

Inversion of Multiconfiguration Complex EMI Data with Minimum Gradient Support Regularization: A Case Study

“…6.6. At this site, [16] investigated the flow dynamics associated with freshwater injection in a hypersaline aquifer through hydrogeophysical monitoring and modeling, using five 20 m deep boreholes ( Fig. 6.6b, c).…”

“…This site appears to be ideal for testing the MGS regularized inversion procedure, as the very high electrical conductivity of the aquifer makes the unsaturated/fully saturated soil interface a sharp electrical conductivity interface. [16]. c Layout and numbering of the boreholes Prior to the freshwater injection experiment, laboratory petrophysical measurements and different surface, in-hole, and cross-hole electrical resistivity surveys were carried out to characterize the background of unsaturated/saturated sedimentary succession dominated by sands.…”

An Integrated Approach Supporting Remediation of an Aquifer Contaminated with Chlorinated Solvents by a Combination of Adsorption and Biodegradation

“…Among the monitoring activities, time-lapse geophysical investigations played a specific role. The use of repeated geophysical measurements to highlight changes in the system is state of the art for several hydrological applications but is used relatively scarcely at contaminated sites, particularly during remediation activities [40,[45][46][47]. An ERT profile during pilot testing was acquired to verify the correct product spread in the first application area.…”

The Issue of Groundwater Salinization in Coastal Areas of the Mediterranean Region: A Review

“…A more complex and data requiring approach is the one that make use of numerical models to deploy new characterization methods, for example, describing the linear and non-linear optimization approaches to manage seawater intrusion via numerical scenarios [144][145][146][147][148][149][150], or determining the long-term effects induced by pumping saline groundwater to feed desalination plants [151]. In addition, the employment of geophysical methods coupled with numerical models to quantify the aquifer salinization extension has been explored only in few studies [152][153][154][155], and only one reported the socio-economic aspects of SWI in the modeling procedure [156]. Finally, two studies have employed complex reactive transport models to quantify biogeochemical reactions induced by SWI [157][158][159].…”