4.7 Article

Imaging acidic contaminants in a confined aquifer using electromagnetic geophysical method constrained by hydrochemical data

Journal

JOURNAL OF HYDROLOGY
Volume 609, Issue -, Pages -

Publisher

ELSEVIER
DOI: 10.1016/j.jhydrol.2022.127704

Keywords

Uranium mining; In-situ leaching; Groundwater contaminant; CSAMT; Electrical resistivity structure

Funding

  1. National Natural Science Foundation of China [42004060, 41630317]
  2. National Key Research and Development Project of China [2019YFC0604901]
  3. Chinese Academy of Sciences [2020-DX03-B-007]

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Acid in-situ uranium leach mining is an effective technique for uranium extraction, but it leads to high concentrations of acidic contaminants in aquifers. This study used CSAMT to investigate a uranium mining area in northwest China and successfully identified the scale and position of acid contaminant plumes. The study also showed that low-permeability sandstone restricts the migration of contaminants.
Acid in-situ uranium leach mining is an effective, popular technology for extracting uranium without large uranium mill tailings. However, acid in-situ leaching causes extremely high concentrations of acidic contaminants in aquifers. To represent the migration and range of acidic contaminant pollutants in confined aquifers, this study applied the controlled source audio-frequency magnetotellurics (CSAMT) method to a uranium mining area located in the Yili Basin, Xinjiang, northwest China. We collected ten CSAMT profiles from 364 sites with an average site interval of 20 m. The electrical resistivity model of the uranium mining area was obtained via twodimensional inversion using CSAMT data, with 23 frequencies, ranging from 8192 Hz to 4 Hz. Combined with geological, geochemical, and well log data, this resistivity model was successfully used to identify the scale and position of acid contaminant plumes beneath the uranium mining area, which appear as electrically well-defined features that closely coincide with the distribution of sulfate and uranium ions in groundwater. With uranium mining activities ceasing, the scale of acid contaminant plumes has been reduced, owing to the natural attenuation of the aquifer or the contaminants well confined in the mining site. The low-permeability sandstone surrounding the aquifer was imaged as a resistive feature, which confines the contaminant plumes to the uranium mining area and slows the downstream migration of contaminants. According to the modified Archie's law, the porosity of the sandstone bearing uranium beneath the injection well zone increases, owing to acidification, while the porosity of the sandstone beneath the production well zone decreases, owing to pore plugging.

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