Coal symposium discusses seismic activity at Crandall mine
A coal symposium was held in Castle Dale on Oct. 24. A variety of topics were covered including the use of booster fans. Professor Mike Nelson from the University of Utah mining engineering department was the first presenter. He said the number of students they have in mining engineering is up to 108 students. The university will soon have a masters degree certification and they are working on that at the current time. Nelson said well controlled booster fans can lead to better ventilation in coal mines. Booster fans are used regularly in the United Kingdom and in Australian mines. Their studies have been working towards developing procedures for risk hazards so NIOSH can go to the Mine Safety and Health Administration and provide data so regulations regarding booster fans can be changed.
Monitoring equipment is installed with the booster fans. If the main fan shuts down then the booster fans would automatically shut down. In Australia they have automatic shutoffs, but in the United Kingdom, they don't rely on an automatic shutoff. They have a person who would control the fan and shut it down. This is done to avoid recirculation of bad gases or to avoid adding air if there was a fire. Nelson said they have been around the world studying these fans throughout the United States, Europe and Australia. The booster fans are smaller than main fans. Booster fans result in saving energy. In the research papers locations are looked at for placing booster fans. Each mine is different. Often a trial and error basis is used for their location. Booster fans work to provide additional air for the long wall.
Tests have been conducted at the University of Utah and at the Missouri experimental mine. All the testing will allow the set-up of procedural guidelines in mine ventilation. Students have also been taken out to mines for field trips to learn about mine ventilation. Nelson thanked the local mine operators that allow the students into their mines so they can learn. They also learned about roof support and soil testing.
Stan Perkes spoke about federal coal cost recovery. He talked about competitive leases and lease modifications. When leases come up there is a fair market value estimate, BLM NEPA review, lease stipulations, bond estimates, fair market value hearings and the notice of sale must be listed in the local newspaper. Procedures for lease modifications are similar. Within the logical mining unit the diligence requirement is mining 1 percent of the reserve each year. There are also rules for lease relinquishments. It must be advertised that they are removing land from their logical mining unit. Perkes asked mining companies that they submit a cost recovery at the same time they ask for lease relinquishment because this can avoid problems at a later date. Lease relinquishments require the tracking of any hazardous materials and an approval to leave any mining equipment within the area.
Professor Nelson presented research done by the University of Utah in mapping out the locations and timing of seismic events before and after the Crandall Canyon mine disaster.
The study has identified hundreds of previously unrecognized small aftershocks that happened after Utah's deadly Crandall Canyon mine collapse in 2007. The aftershocks suggest the collapse was as big, and perhaps bigger, than shown in another study by the university in 2008.
Mapping out the locations of the aftershocks "helps us better delineate the extent of the collapse at Crandall canyon. It's gotten bigger," says Tex Kubacki, a University of Utah master's student in mining engineering.
"We can see now that, prior to the collapse, the seismicity was occurring where the mining was taking place, and that after the collapse, the seismicity migrated to both ends of the collapse zone," including the mine's west end, he adds.
Six coal miners died in the Aug. 6, 2007 mine collapse, and three rescuers died 10 days later. The mine's owner initially blamed the collapse on an earthquake, but the University of Utah Seismograph Stations said it was the collapse itself, not an earthquake, that registered on seismometers.
A 2008 study by University of Utah seismologist Jim Pechmann found the epicenter of the collapse was near where the miners were working, and aftershocks showed the collapse area covered 50 acres, four times larger than originally thought, extending from crosscut 120 on the east to crosscut 143 on the west, where miners worked. A crosscut is a north-south tunnel intersecting the mine's main east-west tunnels.
In the new study, the collapse area "looks like it goes farther west, to the full extent of the western end of the mine, Kubacki says.
Study co-author Michael "Kim" McCarter, a University of Utah professor of mining engineering, says the findings are tentative, but "might extend the collapse farther west." He is puzzled because "some of that is in an area where no mining had occurred."
Kubacki says one theory is that the seismic events at the west end and some of those at the eastern end of the mine may be caused by "faulting forming along a cone of collapse" centered over the mine.
Kubacki and McCarter conducted the new study with seismologists Keith Koper and Kris Pankow of the University of Utah Seismograph Stations. McCarter and Pankow also coauthored the 2008 study.
Before the new study, researchers knew of about 55 seismic events - down to magnitude 1.6 - near the mine before and after the collapse, which measured 3.9 on the local magnitude scale and 4.1 on the "moment" magnitude scale that better reflects energy release, Kubacki says.
The new study analyzed records of seismometers closest to the mine for evidence of tremors down to magnitudes minus-1, which Kubacki says is about one-tenth the energy released by a hand grenade. He found: Strong statistical evidence there were at least 759 seismic events before the mine collapse and 569 aftershocks. Weak evidence there were as many as 1,022 seismic events before the collapse and 1,167 aftershocks.
"We've discovered up to about 2,000 previously unknown events spanning from July 26 to Aug. 30, 2007," Kubacki says, although some of the weak-evidence events may turn out not to be real or to be unrelated to the collapse.
The seismic events found in the new study show tremors clustered in three areas: the east end of the collapse area, the area where miners were working toward the mine's west end, and - new in this study - at the mine's west end, beyond where miners worked.
"We have three clusters to look at and try to come up with an explanation of why there were three," McCarter says. "They are all related to the collapse."
Some of the tremors in the eastern cluster are related to rescue attempts and a second collapse that killed three rescuers, but some remain unexplained, he adds.
Kubacki says most of the seismic activity before the collapse was due to mining, although scientists want to investigate whether any of those small jolts might have been signs of the impending collapse. So far, however, "there is nothing measured that would have said, 'Here's an event [mine collapse] that's ready to happen," McCarter says.
Kubacki came up with the new numbers of seismic events by analyzing the records of seismometers closest to Crandall Canyon (about 12 miles away). "We took the known seismic events already in the catalog and searched for events that looked the same," he adds. "These new events kept popping up. There are tiny events that may show up on one station but not network-wide."
"Any understanding we can get toward learning how and why mine collapses happen is going to be of interest to the mining community," Kubacki says. McCarter adds: "We are looking at the Crandall Canyon event because we have accurate logs and very extensive seismic data, and that provides a way of investigating the data to see if anything could be applied to other mines to improve safety."
Nelson said his graduate students are studying seismic research from Trail Mountain to determine mining's effects on Joe's Valley. One student is also researching with satellite imagery a 2009 large seismic event in Wyoming. Imagery before and after the event are being evaluated. The equipment for detection and recording of events has become highly advanced over the years.
Some mines have seismic monitoring and that can be very useful.
The next presentation was the possibility of using abandoned long wall sections as water storage resources. Those doing the presentation included David Merrell, Ryan Egbert and Dr. Rollin Hotchkiss. They did a study during a four month period. They studied Sufco mine and the possibility of Emery Town using the long wall as a water storage facility. After mining has occurred there is a void space approximately 80 percent. Water can be pumped into the reservoir or you can wait for a natural recharge. With underground storage there is no evaporation issues and no sediment problems and it is low cost without the high costs of constructing an above ground reservoir. The presenters said this method is used at the Alta mine where the water is piped to the town from the mine. The water treatment facility is located within the mine.
The idea needs further research to examine any risks involved.
Dr. Nelson presented a study the University of Utah has done regarding conditions of mine seals and study on any gases that may build up in these areas. Many of these mine seals are on BLM land. In a closed entry area, with 10 people breathing the available air it didn't take long for Co2 to build up. They also looked at wind flow in these areas. The researchers went onsite in the Yellowcat uranium district near Moab and set up the monitoring equipment. They were on site for 36 hours. They would like to be able to leave monitoring equipment out longer, but in that public area someone must stay with the equipment. Another site test was conducted at the Tower Mine where the monitoring equipment was left for a couple of months. Everything was within safe levels. One thing they found out was the wind speed was higher than expected at the mine seal. More study is needed into mine seals and their safety.
Professor Nelson said he is encouraged by the number of students interested in mining engineering. There has been a big increase in students, but no increase in professors so they are working extra hard to educate these students. They are always looking for grants so they can conduct more research to make the mining industry safer.