Unraveling the partial failure of a permeable reactive barrier using a multi-tracer experiment and Cr isotope measurements |
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| Institution: | 1. Institute of Geological Sciences, University of Bern, Baltzerstr. 1-3, CH-3012 Bern, Switzerland;2. Institute of Mineralogy, Leibniz University of Hannover, Callinstr. 3, Hannover D-30167, Germany;1. Department of Cardiology, Ghent University Hospital, Ghent, Belgium;2. Department of Public Health, Ghent University, Ghent, Belgium;3. Department of Cardiology, AZ Maria-Middelares Hospital, Ghent, Belgium;4. Department of Cardiology, UZ Brussel, Brussels, Belgium;5. Department of Internal Medicine Ghent University, Ghent, Belgium;1. Institute of Applied Geosciences, Graz University of Technology, Rechbauerstr. 12, A-8010 Graz, Austria;2. Géosciences Environnement Toulouse (GET), CNRS, UMR5563, 14 Avenue Edouard Belin, 31400 Toulouse, France;3. Institute of Geological Sciences, Baltzerstr. 3, University of Bern, CH-3012 Bern, Switzerland;1. Unité Matériaux et Transformations, Université Lille 1, CNRS UMR 8207, 59655 Villeneuve d’Ascq, France;2. Origins Laboratory, Department of the Geophysical Sciences and Enrico Fermi Institute, The University of Chicago, 5734 South Ellis Avenue, Chicago, IL 60637, USA;3. Advanced Photon Source, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 13 60439, USA;1. School of Earth Sciences, Yunnan University, Kunming, Yunnan 650500, China;2. CAS Key Laboratory of Crust-Mantle Materials and Environments, School of Earth and Space Sciences, University of Science and Technology of China, Hefei, Anhui 230026, China;3. CAS Center for Excellence in Comparative Planetology, University of Science and Technology of China, Hefei, Anhui 230026, China;4. College of Natural Resources and Environment, South China Agricultural University, Guangzhou, Guangdong 510642, China;1. Department of Environmental Engineering Sciences, University of Florida, P.O. Box 116450, Gainesville, FL 32611, USA;2. Innovative Waste Consulting Services, LLC, 6628 NW 9th Blvd., Suite 3, Gainesville, FL 32605, USA |
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| Abstract: | At a Cr(VI) contaminated site in Thun, Switzerland, a permeable reactive barrier (PRB) was installed in 2008. Downstream Cr(VI) concentrations did not indicate any sign of its successful operation more than 2 years after PRB installation. The cause for this potential PRB failure was investigated by performing Cr isotope measurements and a multi-tracer experiment. The combination of reactive (Cr isotopes) and non-reactive tracers allowed characterizing the groundwater flow regime in the vicinity of the PRB in detail. In particular, it could be confirmed that most of the Cr(VI) load is currently bypassing the barrier, whereas only a minor Cr(VI) load is flowing through the PRB. Fitting of observed breakthrough curves using a conventional advection dispersion model resulted in average linear flow velocities of 13–15 m/day for the bypassing Cr(VI) load and 4–5 m/day for the Cr(VI) flowing through the barrier. Using a Rayleigh fractionation model a Cr(VI) reduction efficiency of 77–98% was estimated for the Cr(VI) load that is flowing through the barrier. In contrast, a value of 0–23% was estimated for the current overall PRB reduction efficiency. It is concluded that the PRB bypass and the low overall Cr(VI) reduction efficiency are caused by a limited PRB permeability inherited from skin effects that occurred during PRB emplacement. |
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