Delineation of subsurface structures using resistivity, VLF and radiometric measurement around a U-tailings pond and its hydrogeological implication

The hydrogeological characteristics of the uranium mill tailings pond in the vicinity of Jaduguda (Jharkhand, India) were investigated to examine possible contamination and suggest suitable remedial measures, if required. As the hydrogeological characteristics of subsurface geology are closely related to the electrical properties of the subsurface, geophysical measurements using electrical resistivity coupled with Very Low Frequency electromagnetic method and radiation study were used to investigate the geophysical and geological condition of mill tailings in order to characterize the subsurface structures of the tailings pond. The resistivity interpretation depicted the thickness of the soil cover and thickness of tailings in the pond, as well as the depth to the basement. It also suggested the possible flow direction of leachate. It was observed that the resistivity of the top layer decreases in the direction opposite to the dam axis, which in turn, indicated that the groundwater movement occurs in the opposite direction of the dam axis (in the northwest direction). The VLF method depicted the fractures through which groundwater moves, and also showed the current density alignment in the northwest direction at 10 m depth. The radiation measurement showed relatively higher counts in the northwest direction. This correlated well with the resistivity measurement. The current density at a depth of 20 m showed a closed contour suggesting no groundwater movement in the area at this depth, and that high conductivity material was confined to the tailings area only. It was concluded that groundwater moves in opposite direction of the dam axis at shallower depth only. It was found that continuation of fractures do not extend to deeper depths, which suggested that the tailings storage facility at Jaduguda was reasonably safe from any downward contamination.