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Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
doi:10.5194/hess-2016-663
© Author(s) 2017. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
23 Jan 2017
Review status
A revision of this discussion paper is under review for the journal Hydrology and Earth System Sciences (HESS).
Transport and degradation of perchlorate in deep vadose zone: implications from direct observations during bioremediation treatment
Ofer Dahan, Idan Katz, and Zeev Ronen Zuckerberg Institute for Water Research (ZIWR), The Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Israel
Abstract. An in situ bioremediation experiment of a deep vadose zone (~ 40 m) contaminated with a high concentration of perchlorate (> 25,000 mg L−1) was conducted through a full-scale field operation. Favorable environmental conditions for microbiological reduction of perchlorate were sought by infiltrating an electron donor-enriched water solution using drip irrigation underlying an airtight sealing liner. A vadose-zone monitoring system (VMS) was used for real-time tracking of the percolation process, the penetration depth of dissolved organic carbon (DOC), and the variation in perchlorate concentration across the entire soil depth. The experimental conditions for each infiltration event were adjusted according to insight gained from data obtained by the VMS in previous stages. Continuous monitoring of the vadose zone indicated that in the top 13 m of the cross section, perchlorate concentration is dramatically reduced from thousands of milligrams per liter to near-detection limits with a concurrent increase in chloride concentration. Nevertheless, in the deeper parts of the vadose zone (< 17 m), perchlorate concentration increased, suggesting its mobilization down through the cross section. Breakthrough of DOC and bromide at different depths across the unsaturated zone showed limited migration capacity of biologically consumable carbon and energy sources due to their enhanced biodegradation in the upper soil layers. Nevertheless, the increased DOC concentration with concurrent reduction in perchlorate and increase in the chloride-to-perchlorate ratio in the top 13 m indicate partial degradation of perchlorate in this zone. There was no evidence of improved degradation conditions in the deeper parts where the initial concentrations of perchlorate were significantly higher.

Citation: Dahan, O., Katz, I., and Ronen, Z.: Transport and degradation of perchlorate in deep vadose zone: implications from direct observations during bioremediation treatment, Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2016-663, in review, 2017.
Ofer Dahan et al.
Ofer Dahan et al.
Ofer Dahan et al.

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Short summary
In-situ bioremediation of perchlorate contaminated vadose zone was conducted through infiltration of electron donor-enriched water. A vadose-zone monitoring system (VMS) provided real-time tracking of the hydraulic and chemical conditions across the unsaturated zone. Variations in concentration profiles of perchlorate, chloride, DOC and bromide in the vadose zone pore water showed limited migration capacity of biologically consumable carbon and significant mobilization of perchlorate.
In-situ bioremediation of perchlorate contaminated vadose zone was conducted through...
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