Brownfield Site Investigation Using Geophysics: A Case History From East Chicago

Brownfields are areas in cities that have been determined to have environmental problems<br>due to industry that once operated at those sites. At present, most of the areas are open tracts of<br>land and they cannot be used or cleaned up until the extent of contamination has been determined.<br>It has been suggested that geophysics be used to conduct non-invasive sit characterization. Urban<br>areas have additional problems associated with then, including power line, rebar in concrete, electrical<br>lines in buildings, and large metal objects near by that often interfere with electromagnetic<br>(EM) and magnetic measurements. All of these aspects must be taken into account in designing an<br>effective geophysical survey in an urban environment. A Brownfield site in East Chicago was used<br>to demonstrate the effectiveness of utilizing geophysics and to develop strategies for applying geophysics<br>to Brownfields. The site contained all of the problems listed above. Ground penetrating<br>radar (GPR), multi-frequency EM measurements, and vertical and horizontal gradient measurements<br>were made. Comparisons of the magnetic and EM measurements proved to make it easier to<br>evaluate the GPR measurements at this site. This is the most extensive study to date of a comparison<br>of geophysical methods in an urban setting. The comparison of methods indicate the following:<br>(1) there needs to be very close (one foot or less) line and station spacing, (2) instruments<br>should be run in orthogonal directions, and (3) multiple methods should be used for the best characterization<br>of the sites.