Three Dimensional Self-Potential Inversion For Subsurface Contaminant Detection And Mapping At The Doe Savannah River Site, South Carolina

Abstract

Self-potential (SP) data are collected using a 3D array of non-polarizing electrodes, consisting of a surface grid and four borehole arrays, over an area known to be contaminated with DNAPLs (Dense Non-Aqueous Phase Liquids). The self-potential method is commonly used to measure the electric field produced by electrokinetic, thermoelectric, or electrochemical coupling processes that take place in the subsurface. DNAPLs are known to undergo oxidation-reduction (redox) reactions in the environment, and are proposed as an electrochemical source for this investigation. Electrical currents that exist due to the redox reactions at depth traverse the resistive Earth materials and are manifested as a potential field that is measured at the surface and borehole locations. A 3D inversion algorithm is used to find the electrical current source model that supports the measured data, taking into account the resistivity structure derived from an induced polarization survey at the same field location. The sources and sinks of electrical current are related to the zones of redox activity, and therefore to the areas of contamination. These results are correlated with chemical concentration data obtained from a series of ground-truth well measurements taken at the site.