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TRANSPORT AND DEGRADATION OF PERCHLORATE IN DEEP VADOSE ZONE: IMPLICATIONS FROM DIRECT OBSERVATIONS DURING BIOREMEDIATION TREATMENT
Dahan, O., I. Katz, L. Avishai, and Z. Ronen.
Hydrology and Earth System Sciences 21:4011-4020(2017)

For a full-scale in situ bioremediation study of a deep vadose zone (~40 m) contaminated with a high concentration of perchlorate (>25,000 mg/L), favorable environmental conditions for biological reduction of perchlorate were sought by infiltrating an electron donor-enriched water solution using drip irrigation beneath an airtight sealing liner. A vadose zone monitoring system 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. Conditions for each infiltration event were adjusted according to insights gained in previous stages. Continuous monitoring of the vadose zone indicated that in the top 13 m of the cross section, perchlorate concentration fell dramatically from thousands of mg/L to near detection limits with a concurrent increase in chloride concentration. In the deeper parts of the vadose zone (17 m and below), however, perchlorate concentration increased, suggesting its downward mobilization 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. https://www.hydrol-earth-syst-sci.net/21/4011/2017/hess-21-4011-2017.pdf



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