Mine Mapping and Surveying - Coal Waste Impoundments: Risks, Responses, and Alternatives - page 68

in what form, and for how long. Such information might include the presence
of fractures, faults, joints, “hill-seams” (tension cracks), and water inflow from
the roof or floor.
The designation of a coal seam should be regarded as approximate, subject
to verification based upon: seam elevation, seam thickness, and location of
marker beds as obtained from core logs; elevations of seam bottom obtained
from the mine map; or comparison with the elevations of overlying or
underlying mines. Although several resources (e.g., Toothman, 1977; National
Geologic Map Database's Geologic Names Lexicon at http://ngmdb.usgs.gov/
Geolex/geolex_home.html ) exist for designating a particular coal seam, the
correct name is not always identified. For example, a coal seam may be referred
to by several different names depending on geographic location, mine operator,
absence of lateral geologic correlation, or economic value. This point is clearly
illustrated by a few examples: In Pike County, Kentucky, the Pond Creek coal
seam is also known as the Lower Elkhorn seam, which in West Virginia is
synonymous with the No. 2 Gas seam. In Lynch, Kentucky, the geologic cross
section shown on the U.S. Geological Survey 7 1/2-minute geological
quadrangle map describes the first three above-drainage seams as the Harlan,
Kellioka, and Darby. However, on the same property they were referred to as
the A, B, and C by one coal company and the 180, 240, and 260 by a second
company. Upon crossing Black Mountain into Virginia, these seams are known
as the Wilson, B (Marker), and Taggart. The committee concludes that coal
seam names are potentially imprecise. Therefore, the committee recommends
that coal seam names not be the sole basis for determining the vertical
location of an abandoned mine.
SUMMARY
Accurate mine maps are critical to establishing the location of underground
mine workings with respect to existing or proposed coal refuse impoundments.
Mine maps are the primary means by which the thickness of the outcrop barrier
(horizontal separation) or overburden thickness (vertical separation) are
determined. The accuracy of mines operated since the 1970s, in which surveys
were made with modern equipment and closed loops, are likely to be suitable
for use in the design of an impoundment. Maps for older mines may or may not
be suitable. Furthermore, unrecorded final cuts may compromise the accuracy.
In such cases, additional investigation of the locations of abandoned mine
workings in warranted. The next chapter describes geophysical methods for
such investigations.