Landfill Mapping Using Multi-Disciplinary Geophysical Techniques At The U.S. Air Force Academy, Colorado Springs, Co

This paper describes a multi-disciplinary geophysical survey conducted over a<br>landfill on the U.S. Air Force Academy grounds near Colorado Springs, Colorado.<br>The landfill is known to contain waste generated during the construction of the<br>Academy and reportedly contains buried steel drums. The purpose of the<br>geophysical surveys was to determine the subsurface distribution of buried<br>metallic objects within the landfill.<br>Different geophysical techniques were evaluated along a test line to determine<br>their relative effectiveness at this site. The geophysical methods included<br>total magnetic field, vertical magnetic gradient, VLF, horizontal and vertical<br>coplanar electromagnetic, GPR and seismic refraction.<br>Magnetic and coplanar electromagnetic (EM) methods were chosen to survey the<br>entire landfill because they easily detected magnetic and conductive sources and<br>have better anomaly resolution than other methods evaluated, as demonstrated by<br>the test line results. In addition, these methods are rapid and cost effective<br>for surveys involving a large number of measurements.<br>Surveys of the landfill identified numerous magnetic and conductive anomalies<br>indicating the presence of buried metallic objects. The vertical gradient and<br>EM measurements indicate that several of the large total field anomalies are<br>produced by groups of smaller objects rather than by single, large buried<br>sources. Many of the smaller anomalies are associated with the position of a<br>recently dismantled railroad track and result from iron and steel parts buried<br>along the abandoned grade.<br>Two long, narrow conductive anomalies were identified by the electromagnetic<br>surveys. These conductive features have no surface expression and apparently run<br>the length of the landfill. The EM data indicates these conductors are narrow<br>and relatively shallow. One conductor is relatively magnetic, the other<br>conductor has no magnetic signature suggesting a different composition.<br>The geophysical surveys determined that large areas of the landfill are<br>relatively free of buried metal due to the lack of observed magnetic or<br>conductive anomalies. The geophysical data also suggests the landfill may be<br>larger than originally thought. Numerous magnetic and conductive responses were<br>observed beyond the eastern edge of the present landfill in an area thought to<br>be natural terrain.