Geology Reference
In-Depth Information
To develop an extinguishment plan, it was necessary to determine if combustion was occurring near a group of
houses to the south of the reclaimed site. Boreholes were drilled and cased on 30.5m centers in a narrow area
bounded by the houses (south), a water pipeline (west), and a local road (north).
Based on previous experience, the atmosphere in underground mines is assumed to be in a steady state. Although
this baseline condition will vary locally due to combustion, proximity to fresh air, microbial activity, etc., the
composition of air within a given area is generally constant. Applied suction, as in the Bureau
s MFD method, is
usually a temporary perturbation. In the Percy mine, there were significant changes in baseline gas composition
over periods between 1 day and 3 weeks. The lack of a consistent baseline made the interpretation of the diagnostic
results more difficult. However, the results of the diagnostic tests indicated that the primary combustion zone was
located near the road. Combustion signatures were detected at two boreholes at the southern end of the site. An area
of combustion was apparently located beyond the boreholes between the reclaimed area and the houses.
'
Geophysical Methods
D
uring the planning stages of a field test of cryogenic-injection-fire control (section 16.5) at a waste bank in Ohio,
the Bureau of Mines tested several geophysical techniques (magnetometry, terrain conductivity, seismic refraction,
and ground-penetrating radar) to characterize the subsurface conditions.
The burning waste bank was elongated east
west from a remnant strip mine highwall to the concrete foundation for
an old tipple. The bank extended southward to a slope and covered an area of about 5000m
2
(Figure 16.4.7.). The
top of the bank was flat, indicting that it had served as a ramp to the tipple. Drilling 3.0
-
-
10.7 m indicated that the
subsurface consisted of mine waste (coal, shale, local ceramic, and clay material) 0.3
3.7 m thick, and a clay core
up to 7 m thick, with pieces of coal, shale, and ceramic brick and pipe. Weathered sandstone bedrock was detected
at a depth of 4.6
-
-
8.2 m.
A surface grid (Figure 16.4.7.) measuring 65m (east
south) with intersections
at 5m intervals, was used for data points for several temperature and geophysical surveys. Developing a model of the
structure and estimating its physical properties improved the implementation of fire-control procedures.
-
west; lines L1, L2, L3) by 10m (north
-
Magnetometry
It has been suggested that the measurement of small subsurface magnetic anomalies can be used to delineate fire
areas, particularly in coal refuse (Dalverny, 1994). The effect is assumed to be due to the acquisition of remnant
N
Key
× Flag markers
C
60
C
50
C
40
C
30
C
20
C
10
C
0
L
3
L
2
Tipple
L
1
Surface fractures
Ash
Road
Southern slope
Figure 16.4.7. Sketch of the Midvale waste bank with eroded southern slope and fractures in the eastern fire zone.
From Mowrey 1995, p. 100.
