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