Sinkhole to be seen in 3-D | HoumaToday.com
January 20, 2013
An aerial view of the sinkhole in Assumption Parish taken earlier this week. Flooding from heavy rains mix the swamp with the 9-acre hole.
Published: Saturday, January 19, 2013 at 6:01 a.m.
Last Modified: Saturday, January 19, 2013 at 12:42 a.m.
Scientists are starting to map out a three-dimensional look of the ground below the Assumption Parish sinkhole as nearby residents approach the sixth month of being evacuated.
The sinkhole was discovered on Aug. 3, (2012) prompting an evacuation of about 150 homes in the nearby Bayou Corne community.
In the time since, state and local officials have been able to determine the cause of the now 9-acre hole but have not been confident enough with the situation to lift the evacuation order.
“There are many things that are still a mystery,” said John Boudreaux, Assumption Parish Office of Emergency Preparedness director.
The hole is about 660 feet wide and has grown largely because of sloughing off on the edges, Boudreaux said.
“The evacuation order is still necessary because there are three benchmarks we are still looking for answers to,” Boudreaux said.
Last year, scientists determined the hole was caused when a subterranean cavern owned by Texas Brine LLC collapsed.
The cavern sits thousands of feet below the surface in the Napoleonville Salt Dome. Salt domes are naturally occurring deposits of salt. Private companies commonly carve out deposits in these domes to store volatile gases or waste.
Texas Brine was using the failed cavern to extract brine, which is used in various industrial and oilfield applications.
Boudreaux said officials want to determine how much of the earth between the sinkhole and failed cavern has settled.
“There is the possibility that there are other void spaces in the ground,” Boudreaux said.
These void spaces could eventually lead to the sinkhole growing or another hole as the failed cavern fills completely in.
“We don’t know for sure yet, that is the issue,” Boudreaux said.
Following a brief conflict over what solution would work best, the state Department of Natural Resource and Texas Brine agreed that 3-D imaging of the subsurface would give researchers an exact picture of how the earth might shift in the future, said DNR spokesman Patrick Courreges.
Courreges said the goal is to have the imaging complete by April(2013).
Boudreaux said there also needs to be an effort to get the gasses trapped below the community down to safe levels.
Texas Brine and the Department of Natural Resources have underground wells venting off the gas.
Boudreaux said they’ve vented about 5 percent of the gas estimated to have accumulated near the surface. Nobody knows how much gas is below the area, he said.
Texas Brine is in the process of drilling more vent wells, Courreges said.
Texas Brine has been fined twice for not following a state directive to install gas monitors in local homes, Courreges said. The fines total $250,000 and were also assessed for failing to property contain oil and gas in the sinkhole.
The first of the in-home monitors were installed Thursday while the rest should go in within a few days, Boudreaux said.
Another concern is the stability of the rest of the salt dome. Boudreaux noted there are other caverns inside the dome and some house oil and gas.
“The concern is this cavern would have a domino effect on other caverns because this one is failing,” Boudreaux said. “It could cause a bigger problem.”
Boudreaux said there isn’t a time frame for lifting the evacuation order because there are still these unknowns.
“There is no book to tell us what will happen over time,” Boudreaux said.
Parish Police Jury President Martin Triche said the residents of about half of the 150 homes under evacuation have heeded the order.
“I’ve always said the pace is going too slow,” Triche said. “My impression is that if Texas Brine had been more aggressive early along, we could have had this settled by now.”
Aside from the residents’ safety there is also concerns about property values plummeting, Triche said. He said he asked Texas Brine to consider offering buyouts to those who don’t feel the area is fit to live in anymore.
“Many of the residents don’t want to move away,” Triche said. “We hope to restore things back to their normal environment.”
It’s unclear how long that might take, but in the meantime, Boudreaux said there are two public meetings scheduled in the coming weeks. The first will take place on Jan. 30 (2013) and feature scientists from Texas Brine. The next will be on Feb. 6 and feature state scientists and scientists from the Shaw Group.
Both meetings are scheduled for 6 p.m. at the Assumption Parish Community Center.