The presence of organic residues on soil surface amended with urea increased ammonia volatilization, and was particularly high in sandy compared with clay soils. Application of NBPT reduced ammonia volatilization although its efficiency is reduced in acid soils. Concerning AN fertilization, there were no differences in ammonia volatilization with or without DCD in no-tillage soils.
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.
Recent waste rock pile designs have been proposed to incorporate a fine-grained layer to create a capillary barrier to prevent surface water from draining into the pile interior. This study analyses active fibre optic distributed temperature sensing (FO-DTS) as a tool to measure the effectiveness a capillary barrier system following an infiltration test. A laboratory waste rock column was built with anorthosite waste rock overlain by sand. Volumetric water content is calculated during heat cycles lasting 15 min powered at 15 W/m in the column. A new algorithm is employed to circumvent several requirements for soil specific calibration. The inferred moisture contents were verified by soil moisture probes located adjacent to the cable. The FO-DTS data indicate, at vertical resolutions up to 2 cm, that water is retained in the sand and does not drain into the anorthosite following the infiltration test. The coefficient of determination, R2, between the inferred and measured volumetric water content in the fine cover sand layer is 0.90, while the screened anorthosite maintained an R2 of 0.94 with constant moisture content throughout the test. This study will ultimately help guide future waste rock storage design initiatives incorporating fibre optic sensors, leading to improved environmental mine waste management.
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