Cross Borehole Electromagnetic Imaging
Cross Borehole Electromagnetic Imaging was designed to characterize waste sites and monitor plume migration. The method is based on radio imaging. This technique measures the strength and timing of a transmitted signal from borehole-to-borehole or borehole-to-surface. In landfills containing metallic waste, the contrasts in electrical properties among contaminants enhance the effectiveness of this method for site characterization and monitoring. For example, it has been used to identify waste trenches and storm-related infiltration.
The imaging system consists of a transmitter and receiver. The transmitter and receiver are placed into separate boreholes and lowered by fiber optic cables, or the transmitter is placed in one borehole and the receiver on the ground surface. The resulting data is similar to medical tomography, which shows a two or three-dimensional image of body structure constructed by computer from a series of flat cross-sectional images made along an axis. The transmitter and receiver are lowered to a station location and a measurement is made. The receiver is moved approximately 2.5 to 5 feet to the next location and another measurement is made. The receiver is again moved, and the measurements are made repeatedly until the ray path fan is completed. The resolution (smallest object imaged) is 1/20 of the distance between the transmitter and the receiver. At Sandia National LaboratoriesŐ Chemical Waste Landfill, the resolution is approximately 1.5 feet.
The advantages of Cross Borehole Electromagnetic Imaging are that it can optimize sampling locations, and that it provides information that fills gaps between sampling locations.
Limitations and Concerns
This technology is not a stand-alone technique for monitoring changes in plume migration.
This is an enhanced characterization technology used at landfills with metallic and radioactive contaminants. This technique is sensitive to changes in moisture content, permeability, and water chemistry. Therefore, it can characterize changes in the landfill system and the zone between the landfill and the water table.
Technology Development Status
Several commercial vendors have used this technology for the Department of Energy remediation projects at Fernald, Rocky Flats, and the Idaho National Engineering Laboratory based on the imaging technologies demonstrated in this project.
Other Resources and Demonstrations
See the description of related Electromagnetic Surveys.