3d Time-Lapse Geoelectrical Monitoring of Moisture Content in an Experimental Waste Rock Pile: Validation Using Hydrogeological Data

Abstract

The hydrogeological behavior of heterogeneous and unsaturated media can be challenging to assess, especially where classical hydrogeological instrumentation cannot be directly installed-such as in the core of waste rock piles. In this paper, the authors present the results of several 3D Electrical Resistivity Tomography surveys carried out in 2017 for time-lapse monitoring of water infiltration events in an experimental waste rock pile. This pile was built according to a recently proposed waste rock disposal method at the Lac Tio mine (RTFT, Québec, CA) that aims at diverting water flow from potentially reactive waste rock, thus limiting metal leaching and contamination of the effluent. The pile has been instrumented with soil moisture sensors and lysimeters to monitor water content over time and collect percolating water. In addition, 192 buried electrodes have been used to carry hourly measurements with an optimized protocol of 1000 configurations uploaded on a Terrameter LS (ABEM) to monitor internal flow of water sprinkled on the top of the pile with a water truck. Time-lapse 3D ERT data were inverted to yield the 3D model of soil electrical resistivity over time before, during and after induced infiltration events in the pile. While resistivity results show consistent variations associated with increased moisture content, conversion of resistivity into volumetric water content is not straightforward. This challenge is related, in part, to changes in the distribution of water resistivity over time in the pile, which in turn strongly affects resistivity within the waste rock. Laboratory column measurements have been conducted to assess the relationship between global (waste rock) resistivity, water resistivity and moisture content for samples from the pile. The images of water content obtained with ERT are then validated with hydrogeological measurements and modeling of the pile. This assessment indicates that geoelectrical monitoring is an efficient tool to monitor water moisture in a complex media.

Three‐Dimensional Time‐Lapse Geoelectrical Monitoring of Water Infiltration in an Experimental Mine Waste Rock Pile

“…The (quasi) static distribution of bulk ER in the experimental WRP obtained by ERT monitoring is consistent with the properties of the materials and geometry of the pile. The results presented above are in good agreement with previous studies on the electrical properties of ilmenite and anorthosite waste rocks for several mines in Québec (Anterrieu et al, 2010; Campos et al, 2003; Chouteau et al, 2010; Dimech et al, 2017; Poisson et al, 2009) and in the laboratory (Dawood et al, 2011; Dimech et al, 2018; Intissar, 2009). Anorthosite waste rocks are typically highly resistive (bulk ER >20000 Ω m), while ilmenite waste rocks usually have a fairly low bulk ER (between 20 and 2000 Ω m) because of their iron content.…”

“…Various applications of the ERT method have been presented over the past two decades for: hydrogeological studies (Clément et al, 2014; Hübner et al, 2017, 2015; Nimmer et al, 2008), agricultural applications (Cassiani et al, 2012; Michot et al, 2003; Uhlemann et al, 2016b), ground water resources (Binley et al, 2002; Kuras et al, 2009), tracer and contaminant plume monitoring (Audebert et al, 2016a, 2016b; Koestel et al, 2009, 2008; Kuras et al, 2016, 2014; Power et al, 2014; Rucker et al, 2011; Wilkinson et al, 2010), geotechnical applications (Chambers et al, 2014, 2015; Uhlemann et al, 2016a, 2017) and mining environmental issues (Anterrieu et al, 2010; Dimech, 2018; Dimech et al, 2018, 2017; Intissar, 2009; Power et al, 2018).…”

“…This issue has been addressed for laboratory studies where one (or several) physical parameters can be controlled and the medium is usually homogeneous (Bechtold et al, 2012; Binley et al, 1996; Garré et al, 2010; Koestel et al, 2008; Kremer et al, 2018; Slater et al, 2000). Large‐scale field studies usually assume that either solute conductivity or volumetric water content is constant over time to provide quantitative hydrogeological results by using empirical or laboratory petrophysical relationships (Clément et al, 2014; Dimech et al, 2018; Dumont et al, 2018; Hübner et al, 2017; Jayawickreme et al, 2008; Kuras et al, 2009; Uhlemann et al, 2017). However, these hypotheses may not be applicable for some media where both water content and quality change during hydrogeological processes, such as for landfills and WRPs.…”

“…Adapted from Aubertin et al (2005) and Aubertin (2013Aubertin ( ). al., 2014Aubertin ( , 2015Uhlemann et al, 2016aUhlemann et al, , 2017 and mining environmental issues (Anterrieu et al, 2010;Dimech, 2018;Dimech et al, 2018Dimech et al, , 2017Intissar, 2009;Power et al, 2018).…”

Investigating the Influence of Structure and Heterogeneity in Waste Rock Piles on Mass Loading Rates—A Reactive Transport Modeling Study

“…Variations in hydraulic conductivity values throughout a pile are expected to affect contaminant residence times and migration pathways (Jung and Navarre-Sitchler, 2018;Vriens et al, 2020a). Porosities throughout WRPs may also be extremely variable (Smith et al, 1995;Lefebvre et al, 2001;Azam et al, 2007;Zhang, 2017;Dimech et al, 2018). In this study, porosity is assumed to have a log-linear relationship with hydraulic conductivity, following the work of Smith et al (1995).…”