Twentymile at a glance
Peabody Energy’s Twentymile Mine, between Oak Creek and Hayden, is one of the largest underground mines in the United States. Coal from Twentymile has a high heating value of 11,350 British thermal units per pound and low sulfur and ash content, which makes it desirable to utility customers. In 2008, the mine shipped 8.6 million tons of coal to customers around the world.
Twentymile is a longwall operation, with one of the fastest, most powerful shearers in the world and longwall panels that are 1,000 feet wide and more than 2 miles long. The operation’s conveyor belt travels more than 5 miles underground and 2 miles on the surface.
Twentymile employed 432 miners as of December.
Steamboat Springs Officials with the federal Mine Safety and Health Administration confirmed Wednesday that it was a March 30 noninjury accident at the underground Twentymile coal mine in West Routt County that closed the longwall mining apparatus for nearly a month.
A Peabody Energy spokesperson said Tuesday that the longwall had been closed March 30 after an “unforeseen geologic condition,” and the company released a news release immediately after the phone interview announcing that Mine Safety and Health Administration had authorized the resumption of longwall mining.
Allyn Davis, administration district manager in Denver, said Wednesday that the accident involved the “compression” of coal pillars that are relied upon to support the ceiling of the underground mine. At the same time the pillars compressed, a roof fall took place, partially blocking the tail end of the longwall, which serves as an exit point for miners.
“There was a significant problem there with the strength of the pillars,” Davis said. “But it sounds worse than it was. It was not a failure of the pillars. There weren’t any workers in that area. Workers don’t work in the area where the problem occurred. They work beneath shields supported by hydraulic jacks.”
Peabody spokeswoman Meg Gallagher said Wednesday that Twentymile’s safety record in 2010 was among the best in the industry.
“Twentymile’s 2010 safety performance reflects a 60 percent year-over-year improvement,” Gallagher said. “We look forward to continuing to work with (the Mine Safety and Health Administration) to improve safety and reach our ultimate goal of zero incidents of any kind.”
She previously said that the mine used alternate equipment to mine coal while the longwall was shut down and that employment levels were unaffected during that time.
The mine accident coincided with a March 29 report of an earthquake in Twentymile Park that prompted state geologist Vince Matthews to contact the mine because of its location and relatively shallow depth. Davis said that although mine-induced seismic activity is a well-known phenomenon, the technology does not exist to positively tie the two events together.
Davis said Twentymile officials promptly reported the accident; however, the mine operators were issued a citation because they did not implement an existing plan to notify workers of the blockage of the tailgate at the nonbusiness end of the 980-foot longwall quickly enough.
“The citation was given for not immediately putting the blocked tailgate plan into place,” Davis said. “It’s a violation of the standard.”
It could have been dangerous for miners to exit the longwall area at the tailgate (opposite the business end of the machinery), but no one entered the affected area, he said.
Records on the Mine Safety and Health Administration website reflect that if a fine is to be imposed on Twentymile in conjunction with the accident, it has not been assessed.
Collaborating on a fix
Davis said upon first assessment of the situation, his agency concluded that it might be necessary to move the longwall to a new area.
The overburden in the ceiling of the mine exerts downward pressure on the coal pillars in the area of the compression, and they were “not large enough to support all that weight,” Davis said.
However, Twentymile officials convinced him there was another option.
“The weight actually compresses a small amount, and that often results in coal material falling off the sides of the pillar,” he said.
“We worked together on a plan that (we think) will address the problem and prevent a future occurrence. We always ask, ‘What are the risks?’ and ‘What is the safest way to proceed?’” Davis said. “They came back to us with a plan we believe has a good chance of moving through” the problem area.
The longwall can extract a meter of coal along its entire length, Davis said. The mine is committed to strengthening the columns with a 600-foot concrete pour before inching the longwall forward for its next meter-deep extraction and then making another concrete pour, and repeating the process for an unspecified number of cycles until Mine Safety and Health Administration inspectors are assured there will not be a repeat of the March 30 pillar compression, Davis said.
He added that it is significant that remote devices will monitor the progress of the mitigation effort at Twentymile.
“It ensures that people won’t be exposed to danger” while confirming the effectiveness of the stabilization work, he said.
— To reach Tom Ross, call 970-871-4205 or email tross@SteamboatToday.com