Additional Information
Applications
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Electromagnetic Methods (EM)
EM instruments are used extensively in environmental and engineering site characterization work and are perhaps the most popular tools for locating unexploded Ordinance (UXO). The family of EM tools are very straight-forward and relatively simple to operate, affording rapid and cost-effective mapping of buried metallic materials. They are also effective for mapping lateral changes in soil conductivity.
Some of the most common applications include:
- mapping buried metallic pipes and utilities
- locating buried drums, underground storage tanks
- mapping landfill boundaries
- locating unexploded ordinance (UXO)
- mapping conductive contaminant plumes
- detecting lateral changes in geology
 The most conventional EM tools - terrain conductivity meters - are highly portable and collect data while “on-the-fly”, allowing for large areas to be surveyed rapidly. Such devices can allow a rapid determination of ground conductivity because they do not require electrical contact with the ground as is required with resistivity techniques. Typically, a two-man team can survey several acres in a single day. Commonly used for engineering and environmental applications, these devices utilize a transmit-receive approach where a transmitter coil produces a primary electromagnetic field which, in turn, produces secondary EM fields (eddy currents) in conductive material in the ground. The eddy currents are measured by a receiver coil and then recorded by the instrument. The amplitude of these secondary currents depends on the conductivity of the material. The depth of survey objective determines which type of instrument is selected for coil separation distance.
Electromagnetic (EM) Mapping
The EM31/EM61 instruments are used to map the location of buried pipelines, or other large buried objects and geologic formations that exhibit higher/lower conductivity than the local native soils. The EM61 is a time- domain electromagnetic instrument (TDEM) that is typically used to detect UST/drums, contaminant plumes and mapping karst geology.
Another, more advanced EM method for conducting surveys requiring very sensitive detection of deeper buried targets is Time Domain Electromagnetic Induction (TDEM). It is a non-invasive, rapid and economical, geophysical tool well-suited for hazardous waste site studies, hydrogeologic studies and numerous other applications.
TDEM is a well proven method for detecting and mapping the location of both ferrous and non-ferrous buried metallic objects of all sizes and to depths greater than that achieved with other EM tools. This method is also effective for mapping conductive soil layers. TDEM generally provides greater vertical depth accuracy and resolution than resistivity soundings, especially for conductive layers. The method is also capable of detecting and mapping contaminant plumes provided there is an adequate, detectable change in soil conductivity/resistivity.
Other applications include:
- mapping lateral and vertical extent of some contaminant plumes
- locating buried metal objects, i.e. drums, UST’s, utilities, pipelines
- lateral and vertical soil conductivity mapping
- periodic landfill perimeter surveys to monitor groundwater quality
- baseline monitoring for proposed landfills
- locating bedrock fractures
- locate voids and solution cavities
- map underground streams and aquifers
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