Em Induction And Magnetic Surveys At Large Landfill Sites Using Gps For Positional Control

Electromagnetic (EM) induction and magnetic surveys were conducted at two large landfill sites, totaling 76<br>acres, using a global positioning system (GPS) as the positional control method. The surveys were conducted at<br>Tinker AFB in Oklahoma, as part of a Phase II Resource Conservation and Recovery Act (RCRA) facility<br>investigation. The objectives of the investigation were to delineate the boundaries of known landfill trenches and<br>determine whether features seen in aerial photographs represented previously unidentified trenches. The GPS<br>method of survey control was chosen rather than the conventional local grid approach because site conditions<br>included extremely rugged surface topography, thick vegetation, and several swampy areas that precluded the<br>establishment of precisely spaced, straight lines. The alternative would have required civil surveying and<br>extensive vegetation removal. The GPS allowed local navigation and reorientation to avoid obstacles and field<br>hazards while continuing to collect valid, accurately located geophysical data.<br>The use of differentially corrected GPS data for this investigation proved to be an excellent way to obtain<br>geophysical survey control at a reduced level of effort; however, it added complexity to the surveys that had to be<br>planned for both in the field and during data processing. Specialized processing techniques were developed to<br>overcome minor satellite signal “dropouts, ” and to allow for proper time-synchroniuttion and merging of the<br>geophysical and GPS data.