Mine Mapping and Surveying - Coal Waste Impoundments: Risks, Responses, and Alternatives - page 56

areas. Contours are generated from surveyed control points flagged at the time
of the flight. Maps so determined also show man-made features such as roads,
excavations, and buildings.
Where closed-loop underground mine maps are available (see below), the
accuracy in depicting the surface topography controls the accuracy by which the
coal outcrop is located on a hillside. The committee recommends that
adjacent to existing or proposed refuse impoundments, the coal outcrop
location(s) be determined using aerial topographic measurements.
UNDERGROUND MINE MAPPING
The use of inaccurate or incomplete mine surveys and maps may result in
construction of an impoundment in an area not known to have been mined; if
unknown mine workings are present, the impoundment could suffer unexpected
structural failure (Franklin et al., 1997). In areas where impoundments are
constructed near known or suspected underground mines, vertical and
horizontal barrier distances between the mined area and the impoundment, as
depicted on old maps or surveys, may not be accurate. Regulations promulgated
as a result of the Federal Coal Mine Health and Safety Act (30 C.F.R. §
75.1200-2 (b)), require closed-loop mine surveys. However, surveys for many
older mines were not closed. Furthermore, underground mine surveys may have
been based on a foreman's notes or sketches that lack a reference point or a
recognized coordinate system and therefore cannot be accurately located. These
shortcomings are more common in small mines or room-and-pillar mines where
a number of short panels were driven and extracted. Compounding the problem,
some maps and records of older mines have been lost or destroyed.
The condition and thickness of a barrier, whether composed of coal or
other rock type, between an underground coal mine and a surface impoundment
can be difficult to determine in the steep topography common in Appalachia.
Yet, this information is needed to quantify the potential for breakthrough. The
tools available to determine the extent of mining in an abandoned mine and the
condition and thickness of the outcrop are not highly advanced. Although
extensive drilling can be used, it may miss smaller mined or disturbed areas. In
contrast to invasive drilling, geophysical techniques can obtain useful
information without penetrating the Earth's surface. The objective of
geophysical surveys is to constrain the physical characteristics of some three-
dimensional volume of earth material, including the presence of voids.
Although no geophysical technique