Days after work on the Bayou Corne sinkhole halted briefly due to increasing tremors, state regulators ordered Texas Brine Co. to stop production at a second salt dome cavern near the underground cavity that failed two years ago and spawned the sinkhole that has driven hundreds of people from their property.
Louisiana Conservation Commissioner James Welsh ordered Texas Brine on Monday to perform a round of tests to ensure the integrity of the massive underground cavity, known as Oxy Geismar No. 2, and develop a plan if problems are found.
The cavern under the microscope is a little more than the length of football field away from another cavity that Texas Brine mined until a breach in the supporting salt wall set off the underground shifting that eventually led to the sinkhole in August 2012.
The state Office of Conservation issued a statement Wednesday saying the order was triggered by a recent wave of seismic activity that rose and fell over the past few weeks.
Patrick Courreges, a spokesman for the state Department of Natural Resources, which oversees the Office of Conservation, said the order is not an indication that regulators think there is a problem, but said that they want to be sure of the cavern’s integrity and the integrity of surrounding salt.
“So we see a blip and we check it out, but right now that’s all it is. There is nothing indicating there’s a problem. It’s not definitely one thing or another,” he said.
Sonny Cranch, spokesman for Texas Brine, said the company is prepared to comply with the order “as we have with all previous orders.”
The Conservation statement said seismic activity was recorded in what appears to be the eastern salt wall of the failed Oxy Geismar No. 3, as that cavern is called. Scientists believe the cavern was mined too closely to the salt dome’s outer face, which led to the breach and the filling of the cavern with surrounding sediment and rock. That movement of rock sparked the sinkhole.
The cavern drawing new concerns, Oxy Geismar No. 2, is due east of the failed cavern and farther from the small Bayou Corne community that has now been largely displaced. Still, this cavern is near enough to the dome’s outer face to require extra scrutiny under new state rules prompted by the sinkhole.
The Conservation statement noted that the recent tremors are elevated, but less intense than what preceded the cavern failing. They also aren’t as strong as more recent rumblings experienced along with the sinkhole’s signature slough-ins, when it has eaten up trees and land.
In general, officials have been optimistic about the sinkhole recently, saying they are seeing increasing stabilization. But tremors under the sinkhole rose last week, though they subsided by the weekend, parish officials have said.
At 5.8 million cubic yards, the nearly 2,450-foot-long Oxy 2 cavern is a quarter bigger, by volume, than the Mercedes-Benz Superdome and 45 percent bigger than Texas Brine’s Oxy 3.
Oxy 2 and Oxy 3 are 345 feet apart at the nearest point and are roughly at the same depth in the Napoleonville Dome, generally between 3,400 feet and near 6,000 feet underground, Conservation filings say.
The caverns are just two of a group of salt dome caverns under Texas Brine’s operational complex south of La. 70 South. Salt domes, like the Napoleonville Dome that houses these caverns, are giant, columnar deposits of salt squeezed up by the weight of overlying sediments from an ancient layer of salt. The layer is 40,000 feet deep and tens of millions of years old.
Companies like Texas Brine mine these deposits by pumping fresh water into them through a long well, which dissolves the salt and creates a large cavity. The resulting brine is sent to industrial customers.
After the sinkhole emerged in August 2012, concerns were raised about the integrity of other caverns and the salt dome as a whole, so the Office of Conservation ordered Texas Brine to install an array of seismic and pressure monitoring equipment. This equipment picked up the recent seismic activity.
Earlier oversight from the state focused on Oxy Geismar No. 1, which is due north of Oxy 2 on the Texas Brine site. State officials and their contractors actually modeled how large of a sinkhole could be created if Oxy 1 did collapse, but experts have not found indications of instability in that cavern.
On Monday, Welsh ordered Texas Brine to conduct two basic tests the salt dome industry uses to measure the integrity of caverns: a mechanical integrity test and a sonar survey.
The mechanical integrity test is, in effect, a pressure test that checks for leaks. The other test requires workers to drop sonar equipment inside the cavern to create a picture of the internal structure.
The cavern passed a December 2012 mechanical integrity test conducted by a Texas Brine contractor. The last sonar image taken of the cavern was in July 2013, Conservation filings say.
Courreges said Oxy 2 had been in brine production prior to the Monday order.
Texas Brine produces brine under contract for Occidental Chemical Corp., which owns the caverns, and moves the brine by pipeline to the company’s two plants along the Mississippi River.