Geology Reference
In-Depth Information
The Large mine fire was typical of problems associated with determining underground fire locations from surface
evidence. The observed venting above the buried outcrop gave no indication of the combustion areas in the interior
portions of the mine. Also, borehole temperature data, when taken alone, would yield misleading results with
regard to the location of the combustion zones.
Renton
The Renton abandoned mine-fire site was a 24 ha region in Allegheny County, southwestern Pennsylvania
(Dalverny and Chaiken, 1991). The mine was located in the Pittsburgh coal seam beneath a hill topped by a
4mL municipal water tank; the overburden ranged between 3 and 30 m. The site was characterized by several large
subsidence holes and venting areas.
The MFD located three noncontiguous combustion zones, totaling ~4 ha near the perimeter of the site. These
coincided with three heated areas of indefinite extent that had been indicated by visual and historical evidence.
Although combustion products had been detected in the central part of the mine, diagnostic tests indicated that
heating was occurring only in areas closer to the buried outcrop.
The diagnostic method was also used to monitor progress during and after the water injection extinguishment effort
of the project. Over a period of 195 days, ~ 27mL of water were injected into the three mine-fire areas. Combustion
activity decreased in one area (Borehole 14), became static in another area (Borehole 57), and increased in the third
area (Borehole 33) (Figure 16.4.6.).
Percy
Approximately 15 years before the MFD project, OSM had attempted to extinguish a fire in the Percy mine by
excavation. The abandoned mine was in the Pittsburgh seam on the flank of the Chestnut Ridge anticline in Fayette
County, Pennsylvania. The approximate depth of excavation was 30.5m and the remaining coal had a 10% dip
away from the excavation boundary. A double line of temperature monitoring boreholes on 7.5 m centers had been
installed around the mine side of the excavated area. Increasing borehole temperatures and the emission of smoke
from surface fractures indicated increased combustion in the unreclaimed portion of the mine.
300
Key
250
— Borehole 14
— Borehole 33
— Borehole 57
200
150
100
50
0
200
400
600
800
1000
Time (days)
Figure 16.4.6. Long-term changes in MFD ratio at the Renton mine-fire site indicating that one area had cooled
(Borehole 14), one area was heated but stable (Borehole 57), and one area continued to heat (Borehole 33). From
Kim and Chaiken 1993, p. 45.
