Water Resources Division, U.S. Geological Survey 1995 Geoelectrical methods have been used since the 1920's to search for metallic ore deposits. During the last decade, traditional mining geophysical techniques have been adapted for environmental site characterization. Geoelectrical geophysics is now a well developed engineering specialty, with different methods to focus both on a range of targets and on depths below the surface. Most methods have also been adapted to borehole measurements. application/pdf 10.3133/fs12195 en U.S. Geological Survey Site characterization techniques reports