Evidence that bio-metallic mineral precipitation enhances the complex conductivity response at a hydrocarbon contaminated site |
| |
| Institution: | 1. Oklahoma State University, Stillwater, OK 74078, United States;2. U.S. Environmental Protection Agency, Las Vegas, NV 89119, United States;3. Department of Earth & Environmental Sciences, Rutgers-Newark, NJ 07102, United States;4. Geology Department, Faculty of Science, Assiut University, Assiut 71515, Egypt;5. Department of Geophysics, Colorado School of Mines, Golden, CO 80401, United States;6. ISTerre, CNRS, UMR CNRS 5275, Université de Savoie, 73376 cedex, Le Bourget du Lac, France;1. Leibniz Institute for Applied Geophysics, Hannover, Germany;2. Federal Institute for Geosciences and Resources, Berlin/Hannover, Germany;3. Clausthal University of Technology, Institute of Geophysics, Clausthal-Zellerfeld, Germany;1. Université Grenoble Alpes, USMB, CNRS, EDYTEM, 73000 Chambéry, France;2. Université Grenoble Alpes, USMB, CNRS, IRD, IFSTTAR, ISTerre, 73000 Chambéry, France;3. School of Earth and Environmental Sciences, The University of Queensland, Brisbane, Australia;1. Aalto University, School of Engineering, Department of Civil and Environmental Engineering, P.O. Box 16200, FI-00076 Aalto, Finland;2. Rutgers University Newark, Department of Earth & Environmental Sciences, Newark, NJ, USA;1. Lancaster Environment Centre, Library Avenue, Lancaster University, Lancaster LA1 4YQ, UK;2. Geophysical Tomography Team, British Geological Survey, Nottingham NG12 5GG, UK;3. ETH-Swiss Federal Institute of Technology, Institute of Geophysics, Sonneggstrasse 5, 8092 Zurich, Switzerland;1. Aarhus University, Institute of Geoscience, C.F. Møllers Alle 4, 8000 Aarhus C, Denmark;2. Department of Environmental Engineering, Technical University of Denmark, Bygningstorvet, building 115, 2800 Kgs. Lyngby, Denmark |
| |
| Abstract: | The complex conductivity signatures of a hydrocarbon contaminated site, undergoing biodegradation, near Bemidji, Minnesota were investigated. This site is characterized by a biogeochemical process where iron reduction is coupled with the oxidation of hydrocarbon contaminants. The biogeochemical transformations have resulted in precipitation of different bio-metallic iron mineral precipitates such as magnetite, ferroan calcite, and siderite. Our main objective was to elucidate the major factors controlling the complex conductivity response at the site. We acquired laboratory complex conductivity measurements along four cores retrieved from the site in the frequency range between 0.001 and 1000 Hz. Our results show the following: (1) in general higher imaginary conductivity was observed for samples from contaminated locations compared to samples from the uncontaminated location, (2) the imaginary conductivity for samples contaminated with residual and free phase hydrocarbon (smear zone) was higher compared to samples with dissolved phase hydrocarbon, (3) vadose zone samples located above locations with free phase hydrocarbon show higher imaginary conductivity magnitude compared to vadose zone samples from the dissolved phase and uncontaminated locations, (4) the real conductivity was generally elevated for samples from the contaminated locations, but not as diagnostic to the presence of contamination as the imaginary conductivity; (5) for most of the contaminated samples the imaginary conductivity data show a well-defined peak between 0.001 and 0.01 Hz, and (6) sample locations exhibiting higher imaginary conductivity are concomitant with locations having higher magnetic susceptibility. Controlled experiments indicate that variations in electrolytic conductivity and water content across the site are unlikely to fully account for the higher imaginary conductivity observed within the smear zone of contaminated locations. Instead, using magnetite as an example of the bio-metallic minerals in the contaminated location at the site, we observe a clear increase in the imaginary conductivity response with increasing magnetite content. The presence of bio-metallic mineral phases (e.g., magnetite) within the contaminated location associated with hydrocarbon biodegradation may explain the high imaginary conductivity response. Thus, we postulate that the precipitation of bio-metallic minerals at hydrocarbon contaminated sites impacts their complex conductivity signatures and should be considered in the interpretation of complex conductivity data from oil contaminated sites undergoing intrinsic bioremediation. |
| |
| Keywords: | |
| 本文献已被 ScienceDirect 等数据库收录！ |
|
