Heat as a Proxy to Image Dynamic Processes with 4D Electrical Resistivity Tomography

Abstract

Since salt cannot always be used as a geophysical tracer (because it may pollute the aquifer with the mass that is necessary to induce a geophysical contrast), and since in many contaminated aquifer salts (e.g., chloride) already constitute the main contaminants, another geophysical tracer is needed to force a contrast in the subsurface that can be detected from surface geophysical measurements. In this context, we used heat as a proxy to image and monitor groundwater flow and solute transport in a shallow alluvial aquifer (< 10 m deep) with the help of electrical resistivity tomography (ERT). The goal of our study is to demonstrate the feasibility of such methodology in the context of the validation of the efficiency of a hydraulic barrier that confines a chloride contamination to its source. To do so, we combined a heat tracer push/pull test with time-lapse 3D ERT and classical hydrogeological measurements in wells and piezometers. Our results show that heat can be an excellent salt substitution tracer for geophysical monitoring studies, both qualitatively and semi-quantitatively. Our methodology, based on 3D surface ERT, allows to visually prove that a hydraulic barrier works efficiently and could be used as an assessment of such installations.

Investigations into the First Operational Aquifer Thermal Energy Storage System in Wallonia (Belgium): What Can Potentially Be Expected?

“…Since our simulations started in winter, an artificial temperature offset may have been induced in our model that may have influenced the final results, even if a warm-up ATES heating/cooling cycle was considered. An experimental site implemented in the same hydrogeological unit has been extensively investigated, inter alia, with heat tracer tests [31,32,35,36,84]. It is located in Hermalle-sous-Argenteau, 13 km downstream of the studied site along the Meuse, in a suburban area.…”

“…In Flanders, a decree on deep geothermal use was approved in 2016 and new regulations are expected to be implemented soon [27]. In Wallonia, efforts to develop ATES systems have been made [28,29], with several studies performed on shallow aquifer thermal injection and recovery highlighting some potential ATES target aquifers [30][31][32][33][34][35][36].Reproducing heat transport originating from ATES systems with numerical models has been successfully achieved by various authors [37]. By using the finite element FEFLOW modeling code [38,39], Bridger and Allen [40] simulated 3D seasonal ATES in a heterogeneous unconfined aquifer, highlighting thermal short-circuit issues, which were reported in several other studies [41,42].…”

“…In Flanders, a decree on deep geothermal use was approved in 2016 and new regulations are expected to be implemented soon [27]. In Wallonia, efforts to develop ATES systems have been made [28,29], with several studies performed on shallow aquifer thermal injection and recovery highlighting some potential ATES target aquifers [30][31][32][33][34][35][36].…”

Laboratory Studies Using Electrical Resistivity Tomography and Fiber Optic Techniques to Detect Seepage Zones in River Embankments

“…Long-term monitoring systems should be developed and installed in risky areas to minimize the impacts of such failures. Electrical resistivity tomography (ERT) method is one of the most flexible geophysical techniques that is widely used in a variety of engineering and hydrogeological investigations, e.g., [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. Having the capability of determining anomalous water saturation areas, as well as detecting seepage zones, the ERT method has been increasingly used to monitor the internal conditions of earthen embankments [21][22][23][24][25][26][27][28].…”

Dipole and Convergent Single-Well Thermal Tracer Tests for Characterizing the Effect of Flow Configuration on Thermal Recovery

“…Heat tracer tests appeared also very informative to determine hydrodynamic properties and characterize aquifer heterogeneity [1,2,7,11]. One of the main advantages of the use of heat as a groundwater tracer in the sub-surface is the possibility to image spatially and temporally the spread of a thermal plume thanks to geophysical methods, in an aquifer with Electrical Resistivity Tomography (ERT) [2,12] and at borehole scale, with Fiber Optic-Distributed Temperature Sensing (FO-DTS) [13], with very good spatial and temporal resolutions.…”