MORGANTOWN, W.Va. (AP) -- Federal regulators have approved Alpha Natural Resources' plan to expand one of the nation's biggest coal slurry impoundments to a height taller than the Hoover Dam.
The plan will also increase the volume of waste it holds to 8.5 billion gallons.
The Mine Safety and Health Administration confirmed the approval this week and provided The Associated Press a copy of a letter giving Virginia-based Alpha permission to expand the Brushy Fork impoundment near Whitesville in southern West Virginia.
Alpha calls MSHA's approval an incremental development in what has long been part of the construction plan. The impoundment was built in the 1990s by Marfork Coal Co., which was a subsidiary of Massey Energy Co. before Alpha bought Massey in 2011.
Since 2009, Brushy Fork has held 6.5 billion gallons of coal waste that Alpha says is mostly solid, not liquid.
Though the coal slurry impoundment has never failed, some citizen-activists question whether it was properly built. Retired miner Joe Stanley doubts the years-old waste inside has ever properly compacted and dried, meaning Alpha could be building on an unstable base.
"What about the additional weight placed on top of that?" he said. "I don't think this is going to fail. I truly believe it will fail. It's just a matter of time."
If it does, emergency plans suggest a 100-foot wave of sludge would reach Sherman High School in 17 minutes.
"This thing could go all the way to Charleston," Stanley said, "depending on what it takes out and which way it goes."
But Alpha says past state and federal reviews found no deficiencies and that the company is "committed to designing, building and operating facilities safely."
"We make the safety of our impoundments among the highest priorities in our company because we recognize the responsibility that comes with impoundment ownership," said Alpha spokeswoman Samantha Davidson. "If safety is ever in doubt, we won't hesitate to stop working and shut down a mining operation."
In central Appalachia, coal companies use impoundments to dispose of both "coarse refuse," or larger pieces of rock separated from coal during the cleaning process, and "fine refuse," or clay, silt and sand-size particles. Fine refuse is pumped in from the processing plant to the reservoir behind the coarse refuse. Over time, the "fines" are supposed to settle to the bottom, compressing and solidifying.
At Brushy Fork, the water that remains is pumped out.
When fully expanded, the impoundment will stretch 910 feet from the toe of the embankment to the crest, but Alpha says the vertical dimension from the natural surface to the top of the dam is 740 feet.