Electromagnetic (EM) Conductivity
Electromagnetic (EM) conductivity surveying can be used to map geological variations, including locating gravel and sand deposits, groundwater contaminants, pre-existing or former undocumented landfills or any subsurface features associated with changes in the ground conductivity. This method uses an electromagnetic inductive technique that makes the measurements without electrodes or direct ground contact. With this inductive method, surveys can be carried out under most geological conditions including those of high surface resistivity such as sand, gravel and asphalt. The effective depth of exploration ranges from a few feet to several tens of feet depending on which instrument is utilized, making it ideal for many geotechnical and groundwater contaminant surveys. Important advantages of EM over conventional resistivity methods are the speed with which surveys can be conducted, the precision with which small changes in conductivity can be measured and the continuous readout and data collection while traversing the survey area. Also, EM surveying is particular useful for producing plan view maps, while resistivity methods are typically more advantageous for producing vertical cross sections. The EM method is also especially useful for detecting shallow ore bodies and buried metal hazardous waste.