Site assessment at a burning coal waste bank in Midvale, Ohio was conducted by the U.S. Bureau of<br>Mines with five different geophysical techniques. The geophysical study was the first phase of a<br>project to test a control method for subsurface fires. The site characterization was performed using<br>terrain conductivity, magnetometry, ground penetrating radar and seismic surveys, as well as infrared<br>imagery. Results from these five geophysical techniques were integrated to obtain information on<br>the subsurface structure of the bank, the probable location of combustion zones, and the presence of<br>underground water. Magnetometry measured magnetic anomalies due to changes in the magnetic<br>properties of materials exposed to elevated temperatures in combustion zones. Electrical terrain<br>conductivity identified changes in ground conductivity of the waste bank; anomalies were believed<br>to be related to the presence of mineral-bearing water in fracture zones beneath the surface of the<br>bank. Both ground penetrating radar and seismic methods determined waste bank structure and<br>interfaces between dissimilar materials. The ground penetrating radar was effective to a maximum<br>depth of approximately 3 m (10 ft); the seismic technique provided information to a depth of 8.3 m<br>(27 ft). Infrared imagery detected areas of elevated temperature near the surface of the waste bank.<br>These combined results indicated that the bank consisted of a surface layer of coal waste that was<br>underlain by a core of another material. Several high temperature areas were identified on the eastern<br>slope of the bank. Drilling and temperature surveys provide supplemental information and verified<br>the results obtained with geophysical techniques. Site characterization that integrated the data from<br>multiple geophysical techniques resolved uncertainties, with respect to subsurface conditions and the<br>locations of heated zones and water saturated areas, that could not have been adequately explained<br>with any single technique.


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