HR: 17:30h
AN: NS44A-04    [Abstracts]
TI: Inverting Residual Self-Potential Data for Redox Potentials of Contaminant Plumes
AU: * Linde, N
EM: linde@aug.ig.erdw.ethz.ch
AF: ETH-Zurich, Institute of Geophysics HPP O2 Schafmattstr. 30, Zurich, 8093, Switzerland
AU: Revil, A
EM: revil@cerege.fr
AF: CNRS-CEREGE, Dépt. Hydrogéophysique & Milieux Poreux BP 80 Cedex 4 FRANCE, Aix-en-Provence, 13545, France
AB: Self-potential (SP) data can be separated into a streaming potential component that is associated with pore water flow and a redox potential component, which is sensitive to differences in the redox potentials of organic-rich contaminant plumes and the surroundings. This work presents the first inversion method that uses residual SP (i.e., corrected for the streaming potential component) to invert for the redox potentials of contaminant plumes. We consider a two-layered electrical conductivity structure, where the boundary corresponds to the water table. We assume that the electrical dipole sources are associated with microbial breakdown of contaminants at the water table. This geobattery model is hypothesized to exist (1) because the water table is associated with a strong redox gradient between highly reducing conditions within the contaminated groundwater (due to biodegradation and oxygen depletion) and the oxidized vadose zone, and (2) because the microbial biofilms and precipitation of metallic particles can provide an electron conductor to complete the circuit required for the geobattery. The inverse method was applied to residual SP estimated from SP measurements collected at the ground surface in the vicinity of the Entressen landfill, South of France. The estimated redox potentials correlate well with in situ measurements (correlation coefficient is 0.93) and the estimated amplitudes of the redox potentials are similar to those measured in situ. A sensitivity analysis reveals that meaningful estimates of the redox potential can be derived even if the electrical conductivity structure is only known within an order of magnitude. These results provide further evidence that the SP method can be useful to monitor the spreading of contaminants around landfills and to evaluate the efficiency of remediation programs.
DE: 0416 Biogeophysics
DE: 0418 Bioremediation
DE: 0478 Pollution: urban, regional and global (0345, 4251)
DE: 0903 Computational methods: potential fields (1214)
DE: 3260 Inverse theory
SC: Near-Surface Geophysics [NS]
MN: 2007 Joint Assembly