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Symposium on Geotechnical Methods for Mine Mapping Verifications Charleston, Nest Virginia October 29, 2002 <br />correspond to rooms and pillars, respectively. An unusual aspect of these results is that <br />the mine is not completely flooded. Typically, there is no more than about two feet of wa- <br />ter in the mine, so it is not obvious why the rooms would be characterized by resistivity <br />lows. We speculate that the reason might be due to oxidation phenomena where the pil- <br />lars are exposed to air and water, or simply due to the trickling of water down the pillars, <br />but this is not certain. <br />The data required to prepare the electrical cross section were acquired in less than two <br />hours. The results identify the mine workings and show where mine voids and barrier coal <br />should be expected to be encountered if additional borings are drilled. Where the base of <br />the coal is approximately 30 feet below ground surface, the DC resistivity method offers <br />the possibilityof rapidly delineating mine workings. <br />Case History No. 2 — Locating Mine Workings at a Mine Tailings Impoundment in <br />Jefferson County, Pennsylvania <br />A DC resistivity survey was conducted at a mine tailings impoundment for the purpose of <br />determining the practicality of mapping mine workings known to be present beneath the <br />pool level of the tailings. This particular facility was designed by D'Appolonia in the 1980s <br />and received tailings through the mid-1990s. The D'Appolonia borings served to provide <br />control on the position of the coal seam and detailed coal maps were available such that <br />the position of known entries could be accurately located in the field. As the known mine <br />entries were known to be approximately 60 feet below ground surface, this survey repre- <br />sented a more difficult situation to be resolved with the DC resistivity technique than was <br />encountered at the Regency Park s ite. <br />The DC resistivity survey was conducted using the pole -dipole technique with the remote <br />electrode placed next to the reservoir water. The results indicate the presence of a pro- <br />nounced resistivity low in the area of the known entries. It is anticipated that the workings <br />of the mine are flooded at this location and that the response is due to the presence of <br />acidic water in the mine. <br />The results serve to demonstrate the usefulness of this type of survey, not only to deline- <br />ate a known entry, but also to indicate where barrier coal can be reasonably assumed to <br />be present, as well as target possible unknown mine workings. Although the anomaly is <br />not as strong, a resistivity low that could also be indicative of mine workings is presentjust <br />above the coal seam at a position of 50 feet along the profile. The relatively minimal effort <br />to obtain the resistivity data (less than a days work) could be useful in providing orienta- <br />tion to a drilling program. <br />Case History No. 3 — Geophysical Characterization of Coal Seams in SW Indiana <br />Geophysical characterization was conducted to supplement existing mine maps and a bor- <br />ing program in assessing the influence of past surface and deep coal mining on the siting <br />of a proposed power plant in southwest Indiana. The property is underlain by two coal <br />seams, the No. 7 seam at an approximate depth of 30 feet and the No. 6 seam at about 90 <br />feet. The shallower of the two seams was partially surface mined and the available mine <br />map indicates the presence of some auger workings extending from the former highwall. <br />The deeper seam was mined underground. <br />A <br />