By VICKI SMITHMORGANTOWN, W.Va. (AP) â¿¿ With a driver and his bulldozer missing in a thick, dark lake of coal slurry, a mine safety expert and critic of the coal industry says regulators are ignoring stricter construction standards that could prevent more failures at hundreds of similar dam-like structures around the country. For at least a decade, 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, said Jack Spadaro, an engineering consultant and former director of the National Mine Health and Safety Academy. "They're building on top of the existing slurry, and therein lies the problem," Spadaro said. "It's wet and it has no stability. It's creating hazards for all of us downstream." In all, there are 596 coal slurry impoundments in 21 states. West Virginia has 114, more than any other state, according to the federal Mine Safety and Health Administration. Kentucky has 104, while Illinois is third with 71. 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 like the one at Robinson Run and, less commonly, disposing of it with a costly dry filter-press process. Spadaro's criticisms follow the Nov. 30 failure of a section of embankment at Consol Energy's Robinson Run mine slurry pond near Lumberport in the north-central part of West Virginia. Two workers escaped after pickup trucks slid into the massive pond, but the dozer and driver are missing. "Since we're still in recovery mode and have barely begun the investigation, it would be premature to comment at this time," MSHA spokesman Amy Louviere said. The West Virginia Department of Environmental Protection also declined comment on Spadaro's charges, but Bill Raney, president of the West Virginia Coal Association, said impoundment failures are rare.