Limiting Potential Failures - Coal Waste Impoundments: Risks, Responses, and Alternatives - page 106

SIDEBAR 6.1 MITIGATION MEASURES AT LONE MOUNTAIN
AND BUCHANAN, VIRGINIA
In August 1996, at the Lone Mountain, Virginia, slurry breached the
impoundment and went into abandoned mine workings that were much
closer to the pool than was shown on mine maps. The area was
excavated to expose underlying bedrock. The exposed workings were
sealed by backfilling with competent rock. This was covered with a geo-
textile and further backfilled with compacted earthen materials. Backfill
was placed over the seal to an additional depth of 20 feet and compacted.
To protect the area further, along the western wall of the impoundment
pool, a barrier of compacted earthen materials was constructed. In
October 1996, two large sinkholes developed at a different location.
Excavation revealed a fracture in the roof of old workings that had allowed
slurry to enter the mine. The loose rock was removed, and the void was
sealed with polyurethane grout. The exposed rock face was covered with
a geo-textile and backfilled with compacted earthen materials (K.Mohn,
Lone Mountain Processing, Inc., personal communication, 2001).
In November 1996, the impoundment at Buchanan, Virginia, failed
and slurry entered old workings created by a different mining company.
The area was excavated, exposing filled auger holes. Mine workings were
backfilled; a filter fabric was placed along the entire perimeter of the coal
seam; cohesive soil fill was compacted in lifts to create a barrier, and
coarse refuse was then used to backfill the remaining excavation; and
French drains were installed around the entire perimeter of the facility to
drain the coarse refuse perimeter embankment (B.Thacker, Geo/
Environmental Associates, personal communication, 2001).
water-sensitive, clay-bearing strata. The size, integrity, and strength of the
surrounding coal pillars, roof, and floor are critical to successful sealing.
Generally, seals constructed for ventilation cannot withstand the anticipated
water pressures.
IMPOUNDMENT MANAGEMENT
Risk reduction cannot be achieved by design and regulation alone, but
requires adopting the best available construction and operating practices. The
annual inspection review provides one check in this system, but it may not
identify all construction and operation problems. Experience with tailings dam
failures suggests that all concerned with safe impoundment management must
pay additional attention. The International Committee on Large Dams (ICOLD,
2001) recently summarized lessons learned from tailings dam