A bioelectrochemical system was developed to facilitate biodegradation of an organic contaminant (propylene glycol) using a sandbox containing an iron bar that crossed the capillary fringe. In the days following the introduction of the organic contaminant, a strong negative electric potential anomaly (on the order of −35 to 50 mV) was observed at the top surface of the sandbox, evidencing the transport of electrons in the metallic bar and the degradation of the organic contaminant. The iron bar served to transmit electrons between the electron donor (i.e., biodegradation of the propylene glycol) and oxygen used as the terminal electron acceptor. Numerical modeling indicates that the source of current associated with the electric potential anomaly is at the position of the iron bar. The monitoring of this anomaly possibly can be used to monitor the amount of electrons passing through the electronic conductor and the radius of influence of the bioelectrochemical cells with respect to biodegradation of the organic contaminant.