Geology Reference
In-Depth Information
4
Mine Mapping and Surveying
A key element of assessment of the potential for breakthrough of coal
slurry materials into underground mine workings is the accurate delineation of
the extent of those workings with respect to the ground surface in the
impoundment's basin area. This chapter deals with several aspects of that
problem. The adequacy of existing mine maps and recommendations for the
storage and preservation of maps make up the first part of the chapter. While
mine maps provide information critical to the characterization of a site, there
are significant limitations to some maps, particularly those for abandoned mines
and mines operating before 1969. In addition, standard practice in mapping and
surveying varies from site to site. When questions concerning the accuracy of
maps remain, additional effort to locate underground workings is warranted.
Chapter 5 reviews geophysical methods that can be applied to locate
underground mines.
SURFACE MAPS
There are two primary sources of surface topographic mapping are the
U.S. Geologic Survey's 7 1/2-minute quadrangle maps and aerial topography.
The U.S. Geological Survey's contour intervals vary according to the steepness
of the terrain. A 40-foot contour interval is common for southern Appalachia.
The generally accepted accuracy in surface elevation using these maps ranges
from 20 to 40 feet. In contrast, mine maps are typically maintained to a tenth or
hundredth of a foot.
However, coal companies commonly use aerial photography to determine
topography for critical construction projects such as refuse impoundments,
preparation plants, and mine portals. The contour intervals for aerial
topographic measurements usually vary in sensitivity relative to the steepness of
the local topography. It is common to have one or two foot contours for
relatively flat terrain and as much as 5 to 10 foot in mountainous
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