Electrical resistivity survey of groundwater
An electrical resistivity survey produces a graph that allows to determine the salt content of groundwater sources. In most systems, metal probes (electrodes) are inserted into the ground to obtain a reading of the local electrical resistance. A variety of probe configurations are used, most having four probes, often mounted on a rigid frame. In these systems, two of the probes, called current probes, are used to introduce a current (either direct or low-frequency alternating current) into the earth. The other two probes, called voltage or potential probes, are used to measure the voltage, which indicates the local resistivity. In general, greater probe spacings yield greater depth of investigation, but at the cost of sensitivity and spatial resolution. This type of survey was proposed to communities in the Comahue region (Argentina) who depend on digging wells to secure their water supply.