Planning Coal Slurry Refuse Impoundments - Coal Waste Impoundments: Risks, Responses, and Alternatives - page 53

• Groundwater Levels—Measured by monitoring wells. In addition, the
groundwater chemistry may also be monitored.
• Surface Water Discharge—Measured by weirs, flumes, or flow meters.
• Subsurface Settlement, Readjustment, and Subsidence—Measured by
borehole extensometers, time domain reflectrometers, accelerometer arrays,
and piezometers to detect changes in hydrostatic pressure. Visual
observations are also used to identify subsidence by propagation of
fractures to the ground's surface.
CLOSURE AND RECLAMATION
The process of changing from an active or inactive impoundment to an
abandoned impoundment is referred to as closure and reclamation (Sweigard,
1992). Three major elements comprise reclamation: surface grading, closure
water management, and long-term stability. Surface grading reconfigures the
final impoundment surface so it sheds runoff and will not erode or form pools
of water. This may require major regrading of solids or selective slurry
discharge during the final stages of operation to create the desired draining
surface. Cover materials such as coarse refuse or soils from surrounding
locations are placed over the consolidated mine refuse mass and graded to the
final closure configuration. The regraded surface is then covered with topsoil or
an approved substitute material and revegetated.
Closely tied with surface regrading is closure water management. This
involves: removal of the residual ponded slurry water (by reuse or evaporation)
before surface regrading; control of adverse geochemical reactions, sometimes
using chemical or other additives, and capping; and management of runoff to
control erosion and sediment before and during establishment of vegetation.
Long-term stability is maintained as the impoundment is transformed from an
operating facility with active observation and monitoring, to a closed facility
with less frequent observation and monitoring. This means that the slope
stability and erosional stability of the closed and reclaimed facilities must not
deteriorate over time. The reclamation surety for slurry impoundments is
typically released in phases. As an operator completes a discrete phase of the
reclamation obligation, such as earthmoving or revegetation, portions of the
surety are released. When the final phase is released, the company has no
further liability for the reclaimed impoundment, unless the regulatory authority
can show that the operator misrepresented submitted material facts (L.Adams,
Kentucky Department of Surface Mining, Reclamation, and Enforcement,
personal communication, 2001).