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Kempton Manshaft AMD
Project - Garrett County
The Kempton Man
Shaft Project is one of several projects sponsored by the
Maryland Department of Natural Resources Power Plant Research
Program, and funded by the U.S. Department of Interior Office of
Surface Mining, to demonstrate the replacement of concrete with
coal combustion products (CCPs) from nearby coal fired power
plants.
The Kempton
Mine complex was an active deep mine during the period
of 1912-1950. The
mine tunnels, varying in depths of 130-420 feet below
grade, lie beneath an area of approximately 12 square
miles spanning portions of West Virginia and Maryland.
Most of the tunnels are flooded by surface water
intrusion of from local aquifers.
The presence of residual coal in the tunnels
acidifies the water and causes environmental damage when
it discharges into nearby Laurel Run, a tributary of the
Potomac River. The Kempton Man Shaft, which
lowered miners to the mine tunnel entrances, is 420 feet
below grade.
Exploratory boreholes drilled around the Kempton
Man Shaft revealed horizontal fractures in
siltstone bedrock at depths between 120-140
feet.
The seepage of ground water into the Kempton Man
Shaft from these fractures is estimated to be
45,000 to 145,000 gallons per day.
Ground water level measurements from
monitoring wells installed in the boreholes
indicated that the Kempton Man Shaft is a direct
conduit for good quality ground water to flow
into the mine pool.
The project objective was to reduce the
amount of ground water lost to the mine pool by
installing a grout curtain to a depth of 160
feet around the shaft using a cementitious grout
prepared from CCPs from nearby power plants.
Because the available coal fly ash was a
Class F ash (low calcium), ash from a fluidized
bed furnace, which mixes the coal with limestone
prior to burning, was added to ensure proper
hardening.
Grout was injected into 28 6-inch holes,
cased to 20 feet and filled to 150-160
feet using tremie line.
For most holes, good
communication between adjacent holes was
observed, indicating the flow of grout
through the fractured siltstone was
occurring.
Since completion of the
grouting, a combination of
potentiometric surface
monitoring and dye tracing
activities is being used to
evaluate the effectiveness of
the grout curtain in limiting
the flow of ground water into
the Kempton Man Shaft.
In addition, core samples
will be taken to evaluate the
bonding integrity of the grout
and rock.
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