Why did Consol’s Robinson Run slurry impoundment dam fail? - Beckley, Bluefield & Lewisburg News, Weather, Sports

Why did Consol’s Robinson Run slurry impoundment dam fail?

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Why did the expansion under construction at Consol Energy's Robinson Run coal slurry impoundment dam number nine collapse last Friday, trapping a miner in 30 feet of slurry?

It's a question investigators only just began to get into Tuesday as the search for the missing miner continued.

When a 200-by-200-foot section of dam expansion under construction collapsed, it swept two engineers, two trucks and a bulldozer and its operator down into the slurry.

The engineers were rescued, treated and released, although the company continues to withhold their names.

But the bulldozer and its operator were carried 400 feet out, by one report, and tens of feet down into slurry too thick for diving.

Rescue turned over the weekend to recovery and recovery turned on Monday to a several-days' process of dredging, anchoring barges and constructing a wall around the bulldozer so the slurry can be pumped out.

The work that was going on at Robinson Run, an "upstream pushout" — that is, pushing coarse mine refuse out to pile up on the "upstream," or "inside" side of a dam to, over time, expand its foundation and increase its height — is conducted regularly, mine experts say.

So, why did this one collapse?

The simple, almost self-evident answer: Someone pushed construction too far, too fast.

"You're basically pushing the refuse almost into a swimming pool, so it gets saturated," said Dennis Boyles, regulatory program specialist in the Office of Surface Mining Reclamation and Enforcement's Charleston field office, in an unofficial assessment of the situation. "Apparently they had overextended it."

The process has a relatively narrow range of tolerance for stability, said economic geologist Alan Stagg, president and CEO of Stagg Resource Consultants in Cross Lanes.

"You're on top of it trying to build it up and if you don't watch it you're going to go beyond that threshold," Stagg said. "Somebody just pushed that process too far and got to where the underlying material was saturated and it just yielded."

That's the simple answer. The more complex answer will take months of investigation.

How slurry impoundments work

Coal slurry impoundments hold the waste fluids from washing coal: fine pieces of coal and rock, mainly, suspended in water.

The impoundments are designed for large sizes and long lives. This one has been in use for three decades and its current surface area looks on satellite maps to be around 70 acres. Its maximum design volume is about 10,400 acre-feet, according to its permit — that's more than 5,000 Olympic swimming pools — but its current working volume is around 6,000 acre-feet.

These impoundments are living structures, works in progress that grow as their mines progress. The lowest part is dammed first, Stagg explained. The fine materials cleaned from the mined coal are piped into the impoundment as a suspension in water, the slurry. As the slurry level rises in the impoundment, coarse materials cleaned from the coal are used as structural material to raise the dams — in this case there's more than one dam because the impoundment fills the space between multiple ridges and hilltops — so more slurry can be added.

To raise the dams, the company pushes coarse refuse from washing the coal — "pieces of rock and shale, could be as big as your fingernail or your thumb or in cases as big as your fist," Stagg said —out onto the submerged insides of the existing dams. The idea is that the weight of it will force the fine material out from under it and will settle and, with the addition of more material, get compacted and make a solid, wider foundation for packing more coarse material higher.

The whole huge thing isn't built right from the beginning for reasons that are easy to understand: The higher parts of it aren't needed for decades and, if the company waits to construct those areas until they're needed, the material for constructing them comes for free as a waste product that otherwise would have to be disposed of.

Raising dams safely

"There's some displacement of the fines and once you get firm footing the rest of the embankment is founded on that area," said state Department of Environmental Protection engineer Jim Pierce, who is statewide dam control coordinator and DEP's liaison with the federal Mine Safety and Health Administration. "You have to build it ahead of the slurry, obviously, but you don't want to build it too quickly."

Multiple checks are conducted during design and construction, Pierce said.

Engineers designing a dam expansion sample the coarse refuse and the underlying soil for strength and design with those properties in mind, he said. As construction proceeds, they "field validate" to make sure the design properties match what's being constructed.

Also during construction, piezometers — instruments that measure water pressure inside the dam — are monitored weekly for trends.

"If you saw a weekly increase, going up up up up, you reach a point where you say wait a minute, we're loading this too quickly, so you let it sit," Pierce said. "That's very uncommon."

And before every shift, foremen examine the construction area for "obvious hazard signs such as cracking, displacement ," he said.

What, in general, could cause a slip like this?

"Obviously there was strength lost," Pierce said. "In our investigation we'll be looking at what contributed to that strength loss. Could be the material itself due to saturation, or it could be a foundation failure, or a combination of both."

At another point he said, "Obviously that was not inspected and it should not have happened and in my 30 years of experience, I've never seen anything like that."

Regulatory oversight

The multiplicity of agencies with oversight responsibility would seem to make a dam failure impossible.

Miner safety with regard to impoundments and, to a lesser extent, public safety are the responsibility of, at the state level, the West Virginia Office of Miners' Health, Safety and Training and, at the federal level, MSHA.

Public and environmental safety and, to a lesser extent, miner safety, are the responsibility of the WVDEP and the federal Office of Surface Mining Reclamation and Enforcement.

DEP is required to conduct four complete and eight partial inspections a year of every "inspectable unit" in the state, OSM's Boyles said. That is about 2,100 surface and underground mines and other specific structures, including 136 coal slurry impoundments.

OSM conducts joint inspections with DEP at about 340 sites a year, he said. DEP finished a 35-hour complete inspection of the mine complex on August 27 and has been there for several partial inspections since, most recently on Oct. 16 and Nov. 29. No violations were reported.

As far as The State Journal understands so far, construction of this embankment began some time in the last year and a half.

Slick fines, bad foundation?

This kind of construction, where coarse material is pushed out onto wet fines, shouldn't be happening at all, according to Jack Spadaro — certainly not at the scale it's being done.

Spadaro investigated the 1973 Buffalo Creek disaster that killed 125, which was a similar type of dam failure, although it failed to the outside, not the inside, and drained the impoundment. He helped write the 1979 Office of Surface Mining Reclamation and Enforcement regulations that came in reaction to it. He testifies in federal court as a coal refuse dam safety expert.

The public thinks of a "dam failure" as an incident like Buffalo Creek, where the contents rush downstream, Spadaro said, but he said this type of internal collapse also is a dam failure — it just gets less notice.

He cited as one example a February 2008 incident at a Jim Walter Resources slurry impoundment in Alabama. The collapse created a wave that overturned a dredge operating on the surface; a miner nearly drowned.

When coal fines are wet — when they're in a slurry — they're slick, Spadaro said.

"So you're building a dam on top of slick, wet, fine material," he said. "It is not a sound way of engineering these structures."

Regulations allow for building on fines at a small scale under controlled conditions, he said, adding "it's been very successful, especially through the '70s and '80s."

But, he said, enforcement of the regulations has slipped.

"What I've found is through the '90s, particularly through the administration of George W. Bush, there was a relaxing of vigilance on the part of federal agencies that were supposed to be responsible for these dams and, unfortunately, that has continued into the first four years of the Obama administration.

"We're loading up the tops of these dams now with an enormous amount of material and they're pushing out into these reservoirs farther and farther and they're going higher up," he said. "It could be done on a limited basis very carefully but should not be done on such a large scale."

Large structures like the Robinson Run impoundment should be built complete from the beginning, in Spadaro's mind. Or dams should be expanded not from the inside, but from the outside — a more expensive process, but one that could be conducted dryly and safely.

He charges the state and federal agencies with failure to carry out their responsibilities and asserts that studies have been conducted within OSM and MSHA that confirm that but not have not been released to the public.

"It's not a story just confined to Harrison County; it's a national problem," he said.

Investigation

"There will be a post-accident investigation and there'll be drilling done, strength parameters obtained of the underlying material — a typical forensic analysis of the whole thing," Pierce said.

The coarse refuse and underlying soil will be tested in the laboratory, he said. Federal, state and company inspection logs and other records will be reviewed and employees interviewed.

He did not want to pin a time frame on the investigation, but he pointed to other mine incident investigations that have taken months and longer to conclude.

"There's a lot of that has to be done," he said. "DEP is investigating in coordination with MSHA and West Virginia Miners' Health, Safety and Training, and we will provide a conclusion, a report concluding what we attribute this to."