You are visiting the web site of the EPSCI Program at the U.S. Dept. of Energy's Ames Laboratory, Ames, IA
General Description
EOL is based on a technique that uses an electromagnetic source coil, placed at the surface, which sends a low frequency signal into the earth. A receiver coil measures the subsurface effects on the primary field from the source coil at different depths. The data acquired provides the basis for an offset log below the source.
Resistivity measurements of the subsurface reflect the combined effects of the soil matrix and the fluids within the soils. Free-phase hydrocarbons in the vadose zone, on the water table and below the water (DNAPLs) all have very high resistivity values compared to resistivity values for naturally occurring fluids in the shallow subsurface (such as free formation water).
Currently, most site characterization or plume identification techniques available today rely on specific point sampling. That is, the sampling performed provides contaminant analysis information for only that point in space where the sample is obtained. Multiple sampling is required and gross 'averaging' (i.e. iso-concentration lines) is then employed to those areas between the sampling points to effect mapping the affected areas. In order to increase the 'resolution' of the resulting plume definitions, the number of specific sampling points must be increased. In most cases, there is a substantial and direct increase in both time and cost associated with increasing the sampling events.
No technique or system can 'stand alone' in achieving a complete site characterization and EOL is certainly not an exception. However, the potential of EOL is realized when used as the center point of the program and in concert with other available tools such as specific point sampling.
While some extent of confirmatory sampling is necessary, it is minimal compared to the extent of specific point sampling which would be employed in efforts to achieve the same level of information obtained by EOL images. Further, EOL can serve to characterize areas not attainable by conventional methods such as beneath buildings and can serve as a remediation monitoring tool later.
Please e-mail comments to: epsciwebkeeper@ameslab.gov.
Last Modified: 1 January 2002 by dave eckels
Expedited Site Characterization: etd/technologies/projects/esc/technologies/emlogging.html
