Geology Reference
In-Depth Information
MFD testing, utilizing almost 60 cased boreholes indicated an L-shaped combustion zone (Figure 16.4.5.). The
base of the L (150 m) was near the outcrop; the leg of the L extended 180m into the mine, probably along a set of
main entries. Several small isolated combustion zones were located 300
1000 m from the primary combustion
area. Noncontiguous heated areas were detected in the southwest quadrant of the project area.
-
The direction of propagation into the mine appeared to coincide with the location of a set of main entries. Heated
areas were detected to the north and south of this area. Subsurface fires generally move toward a source of air,
which could have been either a portal that old mine maps indicated existed in the valley ~1.6 km from the site or
permeable zones in the outcrop. The heated areas apparently extended beyond the site boundary, and a cold
boundary for the fire area was not located.
Several areas where hydrocarbon concentrations were below 20 ppm CH
4
coincided with areas where water was
observed in the boreholes. Water vapor condensed on the surface of the coal could block desorption of hydro-
carbons. However, if the temperature of the coal is cool enough to allow water condensation, it can be assumed to
be below the combustion point.
Outcrop
line
24
Mine
entry
30
29
950
12
34
33
44
6
32
13
28
45
15
31
33
16
42
47
46
48
7
43
19
21
14
25
36
8
49
59
1050
17
22
37
41
55
2
20
18
50
39
26
27
56
54
38
23
P
52
40
58
57
10
11
53
P
P
51
0
200
Legend
Scale, ft
Estimates of heated zones using BuMines RI ratio/
VENN diagram technique
Gas line
G
Heated zone
P
Power line
Possibly heated zone
Borehole
Cold zone
<20
ppm THC
Outcrop
Contour interval,
10 ft
Mine entry
Figure 16.4.5. Map of the Large, Pennsylvania mine-fire site showing heated and cold zones, topographic
contours, and estimated position of mine entries. From Kim and Dalverny 1994.
