Using Helicopter Tdem Surveys To Identify Flooded Workings In Underground Coal Mines; The First Attempt

The U.S. Department of Energy’s National Energy Technology Laboratory (NETL) has used<br>helicopter-mounted electromagnetic (HEM) surveys to identify mine pools within active and<br>abandoned underground coal mines in the eastern United States. Two types of HEM surveys have<br>been tested: frequency domain electromagnetic (FDEM) and time domain electromagnetic (TDEM).<br>Previous surveys have indicated that FDEM surveys can identify flooded mine workings in areas<br>where overburden is less than 50-m thick. However, most mines are deeper than 50 m. This survey<br>attempted to use helicopter TDEM to locate deep, flooded mine workings at challenging sites in<br>southwestern Virginia, an area containing multiple levels of mining, thin seams, and mine water of<br>relatively low conductivity. The rationale behind this choice of field sites was that if the technology<br>worked in this admittedly difficult region, it could be applied to any coalfield. However, the survey<br>was unsuccessful; mine workings known to be flooded were not detected. This paper discusses<br>problems that were encountered, particularly electromagnetic noise, which rendered 25-50 pct of<br>each flight line unusable.