But the report summary says inspections at the West Virginia impoundments raise questions about whether theory is reality: It says coarse refuse is "primarily low-plasticity silt with rock fragments and some clay," materials that are typically harder to dry out and compress.
That material often arrives at the disposal site wet and in cold weather that makes it impossible to control moisture content, the report says. Bulldozers are then used to compact the material, even though they're designed to work with soil and loose earth.
"Results of the testing tend to indicate that the coarse refuse is not consistently being compacted in accordance with approved specifications," the summary says.
All seven impoundments failed field density tests, the report said. Of 73 total tests, only 16 produced passing results.
In all, there are nearly 600 coal slurry impoundments in 21 states.
West Virginia has the most with 114, but it hasn't had a major failure since 1972, when the earthen dam at Buffalo Creek collapsed after heavy rain. The ensuing flood killed 125 people, injured 1,100 and left 4,000 homeless.
The Brushy Fork impoundment was built in the 1990s by Marfork Coal Co., a Massey subsidiary. Since 2009, Brushy Fork has held 6.5 billion gallons of waste that new owner Alpha says is mostly solid.
But emergency plans show that if the impoundment failed, a 100-foot wave would reach Sherman High School in 17 minutes.