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Symposium on Geotechnical Methods for Mine Mapping lerifications, Charleston, West Virginia October 29 2002 <br />the case of the Inez, Kentucky tailings impoundment failure, the overburden between an <br />abandoned mine and the base of a slurry impoundment was too thin and the slurry broke <br />into the mine. The consequence was that slurry broke out and flooded two separate wa- <br />tersheds with coal refuse. In the case of the Quecreek Mine flood, miners excavated into <br />the flooded workings of the abandoned Saxman Mine, which theythoughtwas hundreds of <br />feet away. <br />Both of the above conditions require that the location of underground workings be pre- <br />cisely defined. This is not an easy task. Detailed mine maps may be unreliable or miss- <br />ing. Conventional exploration (drilling) can easily miss targets as small as a mine entry. <br />Because of these difficulties, the National Resource Council appointed the Committee on <br />Coal Waste Impoundments whose charge included a task to evaluate alternative technolo- <br />gies to locate mine workings, as recently published in the book Coal Waste Impound- <br />ments, Risks, Responses and Alternatives (National Academy of Sciences, 2002). The <br />Governor's Commission on Abandoned Mine Voids and Mine Safety convened in October <br />2002 as a result of the Quecreek inundation is also in the process of compiling information <br />of the various geophysical technologies that could be applied to the mapping of mine work- <br />ings. This paper does not repeat geophysical theory of the different technologies that can <br />be found in the NAS book, but focuses on our experience with the practical application of <br />some of these methods. <br />Potentially Applicable Geophysical Technology <br />The starting point of a geophysical investigation must be basic physics. Geophysics will <br />be effective only if a target of interest has a physical contrast with the surrounding ground. <br />For example, a mine entry containing metal tracks could be an easy target for a magnetic <br />survey, but if the tracks are not present, the magnetic contrast of the entry might be too <br />subtle to measure. Another important consideration is if the geophysical contrast of the <br />target can be distinguished <br />from other features with Physical Prooertv Intact Coal Open Void Flooded Void <br />similar contrasts — what Electrical resistivity high' high" usualy lav"' <br />geophysicists call the signal Seismic velocity low barrier low <br />to noise ratio. A mine entry Density low very low very low <br />might be relatively easy to <br />identifywith a gravitysurvey <br />that can detect a void space <br />as a zone of low density, but <br />if the target is located in an <br />area of rugged topography, <br />the errors associated with <br />the topographic corrections Intact coal normally has ahigh resistivity, but can be of a relatively low resistivity <br />can easily mask the re- ifweathemd or flooded with acidic water. <br />sponse from the mine work- "Open voids are expected to be of a high resistivity, but the authors have <br />s <br />p encountered several examples where voids are marked by resistivity lows, possibly <br />ings. Notwithstanding the because of chemical interactions at the face ofweathered pillars. <br />above difficulties, mine "• Aflooded void could have a high resistivity if the water has a neutral pH. <br />workings can be associated lllustrationofphysical properties associated with rrineopenings <br />with measurable physical <br />2 <br />