Geophysics Helps Characterize and Remediate Polluted Sites

Battelle Geneva operations has been searching for a high-resolution tool to assess polluted sites in industrial areas by identifying small buried structures like drums and pipes, as well as large storage tanks and abandoned dumpsites. The most effective and least intrusive approach to investigating subsoil for buried objects or structures is geophysics. However, this technique can be used only to locate objects that present a measurable physical contrast with the surrounding soil, such as density, resistivity, radiation, or magnetism.

The electromagnetic tool EM61 of Geonics has proven effective at industrial sites, enabling researchers to work close to perturbing structures at a resolution of 20 cm along the line of survey, with little or no disturbance to the signal. (Perturbing structures, including walls, metallic poles, and surface metallic objects, are not buried but may induce an instrumental signal.) The automatic data acquisition system allows thousands of square meters per day to be covered, depending on the access conditions. This technique was applied at several different sites and provided useful information.

To assess the kind of objects detected with a high degree of confidence, it is important to interpret the collected data using a wide range of parameters.

Figure 1 shows significant structures that are deeply buried (defined by red shapes) and well defined with a sensitivity setting of 200 mV, while there is no indication of pipelines (the three yellow lines going across the area). With a sensitivity setting of 10 mV (Figure 2), the pipes are clearly visible while the larger structures have a lesser degree of definition. This example demonstrates why it is necessary to take images at several resolutions to define the various buried objects.

Figure 3 shows an abandoned dumpsite, completely invisible on the surface, but identified by its circular shape and access ramps. A dumpsite is characterized by the presence of a variety of types of buried objects located in the same area, but which generate different responses. It was possible to obtain readings very close to the concrete walls at both the north and south edges of the survey, before the signal was modified by perturbations from the walls. This demonstrates the effectiveness of this method at industrial sites, where other tools generate a signal-to-noise ratio that is far too weak.

For additional information, please contact Marco Pellei at +41-22-8272110, pelleim@battelle.org, or Roland Mage at +41-22-8272244, mager@battelle.org.