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

Abstract

Core Ideas 3D time‐lapse ERT is used to monitor water infiltration for mining environmental issues. Geoelectrical images provide information where no hydrogeological data is available. Water resistivity must be taken into account to understand bulk resistivity variations. Electrical resistivity of water is used as a tracer to reconstruct water infiltration. Infiltration model integrating both hydrogeological and geophysical data is proposed. Open‐pit mines often generate large quantities of waste rocks that are usually stored in waste rock piles (WRPs). When the waste rocks contain reactive minerals (mainly sulfides), water and air circulation can lead to the generation of contaminated drainage. An experimental WRP was built at the Lac Tio mine (Canada) to validate a new disposal method that aims to limit water infiltration into reactive waste rocks. More specifically, a flow control layer was placed on top of the pile, which represents a typical bench level, to divert water toward the outer edge. Hydrogeological sensors and geophysical electrodes were installed for monitoring moisture distribution in the pile during infiltration events. A three‐dimensional (3D) time‐lapse hydrogeophysical monitoring program was conducted to assess water infiltration and movement. Readings from the 192 circular electrodes buried in the WRP were used to reconstruct the 3D bulk electrical resistivity (ER) variations over time. A significant effort was devoted to assessing the spatiotemporal evolution of water ER because the bulk ER is strongly affected by water quality (and content). The water ER was used as a tracer to monitor the infiltration and flow of resistive and conductive waters. The results indicate that the inclined surface layer efficiently diverts a large part of the added water away from the core of the pile. Local and global models of water infiltration explaining both bulk and water ER variations are proposed. The results shown here are consistent with hydrogeological data and provide additional insights to characterize the behavior of the pile.

Mine Waste Rock: Insights for Sustainable Hydrogeochemical Management

“…Point measurement techniques provide precise measurements of hydrogeological properties but are challenging to extrapolate to larger areas because of the waste-rock heterogeneities. Previous work on the hydrogeological properties of waste-rock piles have used point measurements of water content, for instance using time-domain reflectometry (TDR) sensors [16,279,280], frequency-domain (FDR) sensors [281], and soil water potential sensors [282,283], or by oven-drying discrete waste-rock samples taken at several depths in boreholes [162,163]. Remote sensing techniques offer larger scales of investigation, but often at the expense of lower resolutions that might be inadequate to discriminate the internal fine structure of waste-rock piles.…”

“…Remote sensing techniques offer larger scales of investigation, but often at the expense of lower resolutions that might be inadequate to discriminate the internal fine structure of waste-rock piles. Nevertheless, electrical resistivity techniques (ERT; [275,281]), ground penetrating radar (GPR; [284][285][286]), electromagnetic induction (EMI; [284,287]), fibre optic distributed temperature sensing (FO-DTS; [288]), or oxygen/hydrogen isotopic signatures [162] have all been applied successfully to investigate hydrogeological dynamics in waste-rock piles. In addition, basal lysimeters are often used to record internal mixing and drainage at the bottom of waste-rock piles [115,280,282].…”

Real‐Time Geoelectric Monitoring of Seepage into Sand and Clay Layer

“…However, it is currently difficult to determine water seepage in rock and soil masses in real time, as well as the different levels of seepage in different areas of the rock and soil masses. Therefore, a thorough understanding of water seepage in rock and soil masses is very important for engineering practices (Jiang et al ; Sun et al ; Chambers et al ; Uhlemann et al ; Dimech et al ).…”

“…All of these efforts have proven that geoelectric field signatures are closely related to water flow during infiltration. However, only a small number of hydrological studies have monitored the dynamic changes in groundwater seepage (Pellerin ; Chandra et al ; Sun et al ; Dimech et al ). Moreover, there is the need for long‐term monitoring, and more in‐depth quantitative analyses of groundwater seepage should be carried out.…”

“…The further exploitation of deep underground caves and prevalent use of advance mining have led to the increasing importance of innovative techniques for observing groundwater seepage (Liu et al ), of which technologies for measuring the geoelectric field have been of paramount importance. Among the different technologies, the resistivity method has been very successful (Nowroozi et al ; Petalas and Diamantis ; Nassir et al ; Somay and Gemici ; Gemici et al ; Zhou et al ; Dimech et al ), and the use of SP has also provided very robust results in determining the amount of groundwater seepage (Bogoslovsky and Ogilvy ; Sill ; Birch ; Hashimoto and Tanaka ; Doussan et al ; Revil et al ; Jardani et al ). Zohdy () used the resistivity method in a groundwater exploration program for two locations near El Paso, Texas in the United States and concluded that the static water table was found at a depth of about 91.4 m, while the freshwater interface varied from 91.4 m to about 518.2 m. Nowroozi et al () found that the Schlumberger sounding resistivity method is an efficient means of investigating the interface between salt water and freshwater in the geological setting of the eastern shore of Virginia in the United States.…”