The optimum current for electrodialytic soil remediation occurs when the limiting current of the anion-exchange membrane is exceeded while that for the cation-exchange membrane is not. At this current, an acidic front will pass through the soil from the anion-exchange membrane towards the cathode, and the polluting heavy metals will be mobilized in the acidic environment. At the same time no production of base will occur from the cation-exchange membrane. A basic environment causes precipitation of hydroxides in the soil next to the cation-exchange membrane, and this will give an increase in voltage drop in the system and furthermore hinder the transport of the heavy metals out of the soil. When the acidic front passes through the soil, the voltage drop will decrease, and the end of the remediation can be predicted by the decrease in voltage to a very low level between the working electrodes.