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

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