Technologies for Locating Mine Workings - Coal Waste Impoundments: Risks, Responses, and Alternatives - page 71

5
Technologies for Locating Mine Workings
Locating underground mine workings in the absence of mine maps is not
impossible, but it can be expensive and time consuming. Drilling enough
vertical holes on a 3-foot grid will locate virtually any mine workings, but, in
addition to the expense, it damages the Earth's surface and creates conduits for
underground fluids, including pollutants that can degrade groundwater. Because
of the time and expense associated with extensive drilling, remote sensing and
geophysical methods have been employed to search for abandoned coal mines
(e.g., Branham and Steeples, 1988; Miller and Steeples, 1991, 1995). The
objective of geophysical surveys is to provide descriptive information about the
physical characteristics of a three-dimensional volume of earth material,
including the presence of voids. Because no geophysical technique is capable of
performing optimally under all geological and topographic conditions, multiple
geophysical techniques may be necessary to reduce the probability for error to
an acceptable level. While these methods have proved successful in some cases,
drilling is still necessary to confirm interpretations of geophysical and remote
sensing data ( Table 5.1 ). In addition, the absence of evidence of a mine is not
evidence of absence of a mine, and there are many opportunities for error in the
modeling and geophysical surveys needed to detect voids.
To give regional context to a local area, geophysical surveys begin with
baseline information. Consequently, the area surveyed with geophysical
methods is commonly several times larger than the planned impoundment,
particularly for the less expensive methods such as magnetic surveys.
Furthermore, during the planning and interpretation stages, geophysical
surveys and data collection should be accompanied by geophysical modeling
using the tools of physics, geology, engineering, and mathematics (NRC,
2000a). Today, modeling software that runs on personal computers is available
for all of the geophysical techniques. Moreover, in-field modeling with a
personal computer can often be of use in making evaluations during