Calhoun said his agency reviewed 15 sites for the latest report, and it's planning similar reviews of impoundments in six other states â¿¿ Kentucky, Maryland, Ohio, Pennsylvania, Tennessee, and Virginia. Completing that will take about three years.

Critics of the coal industry have long complained that operators and regulators are ignoring stricter construction standards that could prevent future impoundment failures. For at least a decade, they say, state and federal regulators have allowed coal companies to build or expand the massive ponds of gray liquid and silt atop loose and wet coal waste â¿¿ an unstable base that creates hazards for people and the environment downstream.

The industry, however, argues impoundments are the best-engineered, most-scrutinized earthen structures in the world.

The West Virginia Coal Association said it has cooperated with regulators "to improve the technical analysis" of impoundments. But Vice President Jason Bostic said Thursday it's disappointed with the current OSM review, "which has been conducted largely behind closed doors with little or no outreach or communication" with operators.

"The agency never requested any information from the industry that may have satisfied their concerns, nor did they contact the industry to make them aware of the pending release of these reports," Bostic complained. "Sensationalism has never advanced meaningful dialogue and progress with respect to developing a path forward."

In all, there are nearly 600 coal slurry impoundments in 21 states, including 104 in Kentucky.

Slurry is a byproduct of washing coal to help it burn more cleanly. Companies have disposed of the dirty water and solids in various ways over the years, injecting it into abandoned mines, damming it in huge ponds and, less commonly, disposing of it with a costly dry filter-press process.

OSM laid out several continuing concerns about West Virginia's regulatory system, including the practice of allowing smaller ponds or "slurry cells" to be built on top of larger ponds once they're capped with solid material. The contents under the cap could still be loose or liquid, and the increasing pressure from the smaller cells could increase the likelihood of a breakthrough, it said.

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