Laboratory spectral induced polarisation signatures associated with iron and manganese oxide dissolution because of anaerobic degradation

Fernandez, Perrine and Binley, Andrew Mark and French, Helen and Bloem, Esther (2019) Laboratory spectral induced polarisation signatures associated with iron and manganese oxide dissolution because of anaerobic degradation. Journal of Contaminant Hydrology, 221. pp. 1-10. ISSN 0169-7722

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Degradation of organic chemicals in natural soils depends on oxidation-reduction conditions. To protect our groundwater resources we need to understand the degradation processes under anaerobic conditions. Available iron and manganese oxides are used as electron acceptors for anaerobic degradation and are reduced to the dissolved form of metallic cations in pore water. To monitor this process is a challenge, because anaerobic conditions are difficult to sample directly without introducing oxygen. A few studies have shown an impact of iron reduction on spectral induced polarisation (SIP) signature, often associated with bacterial growth. Our objective is to study the impact of iron and manganese oxide dissolution, caused by degradation of an organic compound, with spectral induced polarisation signatures. Twenty-six vertical columns (30cm high, inner diameter 4.6cm) were filled with a sand rich in oxides (manganese and iron) with a static water table in the middle. In half of the columns, a 2cm high contaminated layer was installed just above the water table. As the contaminant degrades, the initial oxygen is consumed and anaerobic conditions form Every three days over a period of one month, spectral induced polarisation (twenty frequencies between 5mHz and 10kHz) data were collected on six columns: three contaminated replicates and three control replicates. Chemical analysis was done on twenty columns assigned for destructive water sampling, ten contaminated columns and ten control. The results show an increase of the real conductivity associated with the degradation processes, independent of frequency. Compared with the pore water electrical conductivity in the saturated zone, the real conductivity measurement revealed the formation of surface conductivity before iron was released in the pore water. In parallel, we also observed an evolution of the imaginary conductivity in both saturated and unsaturated zones at frequencies below 1Hz. Overall, the anaerobic reduction of iron and manganese oxide during the organic degradation increased both the conductive and polarisation component of the complex conductivity.

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Journal Article
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Journal of Contaminant Hydrology
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This is the author’s version of a work that was accepted for publication in Journal of Contaminant Hydrology. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Journal of Contaminant Hydrology, 221, 2019 DOI: 10.1016/j.jconhyd.2018.12.002
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19 Feb 2019 16:20
Last Modified:
16 Sep 2023 01:53