Electrical monitoring of in situ chemical oxidation by permanganate

An array of electrical monitoring probes was constructed to monitor a concentrated permanganate (MnO(4)(-)) solution injected to treat perchloroethylene (PCE) contamination in a shallow sandy aquifer. The simple probes use pairs of stainless steel wires as electrodes for electrical conductivity (EC) and platinum wires as the working electrodes for oxidation-reduction potential (ORP) measurements. Combined EC/ORP probes were assembled into bundles with multilevel ground water samplers and installed in boreholes around the injection point. Copper/copper sulfate half-cells, inserted to the depth of the water table, acted as ORP reference electrodes. All electrodes were connected to a central data acquisition system, which collected data for a period of 25 d following the injection. Large contrasts in the EC and ORP characteristics of the ground water, compared with the MnO(4)(-) solution, allow the subsurface migration of MnO(4)(-) to be tracked using these relatively simple electrical, measurements. The electrical data were used to track the arrival times of the MnO(4)(-) at discrete positions in the aquifer, to guide the timing and selection of locations for water sampling, and for three-dimensional visualization of the MnO(4)(-) distribution during destruction of PCE.