Cavern tied to sinkhole

Dome may be too close to area

PIERRE PART — An underground salt cavern viewed as a possible cause of a large slurry area in northern Assumption Parish may be closer to the outer edge of the Napoleonville Dome than its owners originally thought when the cavern got a permit in 1982, officials said Tuesday.

If the edge of the cavern is too close, it could have been breached and allowed brine inside to seep up along the edge of the salt dome, possibly feeding the sinkhole that emerged last week near the Bayou Corne community, officials said.

The theory describing a possible mechanism or the connection between the sinkhole and the cavern, which may not be directly under the sinkhole, was one of many new details a that emerged Tuesday during a community meeting attended by a few hundred people at St. Joseph the Worker Catholic Church in Pierre Part.

Based on that idea, Madhurendu Kumar, director of the Geological Oil and Gas Division of the Louisiana Department of Natural Resources, presented a worst-case scenario map showing the maximum zone of soil instability to be 1,400 feet in diameter.

The sinkhole, measured at 372 feet in diameter, is in the center of the worst-case scenario area.

Kumar said in a later interview that the worst-case area displayed is a smaller area than the 2,000-foot worst-case scenario that parish and state officials feared Friday was a possibility when a mandatory evacuation was ordered for the Bayou Corne community.

But the uncertainty still present in regard to what may actually be causing the slurry area and other mysterious occurrences in the swamps around Bayou Corne led Parish President Martin “Marty” Triche to announce midway through the meeting that the parish would keep a mandatory evacuation order in place until more definitive information is available.

“There were too many unknowns here,” Triche said.

The slurry area was found Friday morning after a foul diesel smell spread through the area. For two months prior, earth tremors were reported and natural gas bubbled up from Bayou Corne, Grand Bayou and a nearby water well.

Parish officials disclosed on Monday that the sinkhole is filled primarily with salt water with traces of diesel and oil at the surface while the mud and vegetation seen from the air is only floating in the sinkhole.

Frustration from the lack of definitive answers and the pace of scientific inquiry was evident from many of the residents who asked questions and pressed for particular facts or actions by DNR, the Louisiana Department of Environmental Quality or the salt cavern’s owner, Texas Brine Co. LLC of Houston.

One man asked when a relief well would be drilled to relieve natural gas suspected to be in the aquifer. DNR officials acknowledged natural gas was in the aquifer.

Texas Brine President Mark Cartwright said the company is considering drilling a relief well, but added company officials do not know if a well can be effectively located because gas releases from water wells, including one owned by Texas Brine, have been sporadic.

Another man pressed DEQ to test the salinity of water at the bottom of the sinkhole, which has a new measured depth of 422 feet.

Samples have been taken only from the surface as part of the effort to determine the contents of the oil sheen on the sinkhole’s surface, DEQ officials said, but they pledged to take the deeper samples.

Salinity levels may lend further credence to the hypothesis that the salt cavern, which is filled with brine, was a source of the sinkhole.

Vickie Guilbeau, 62, eventually had enough.

“Why can’t all these guys figure out what is going on because we all have homes in Bayou Corne. People do not understand a thing y’all are saying up there, and y’all don’t even know,” Guilbeau said.

“What we want to know is how long are we supposed to stay out of our homes and the risk? You can give us a straight answer for that. That is all we want.”

John Boudreaux, director of Assumption Parish Office of Homeland Security and Emergency Preparedness, addressed the risk, saying an explosion from a natural gas pocket or from a nearby cavern failing and releasing flammable gas is possible.

He said there is still a risk for explosion until scientific findings rule out the possibility.

Guilbeau asked for how long that would take.

Triche responded that until scientists and other officials can tell the parish the risk has been eliminated, all the parish can do is advise residents of the risks with the mandatory order.

“What I’m hearing, ma’am, what I’m hearing, is they don’t know,” Triche said.

Though Cartwright did not have an answer on the relief well or exactly how close the salt cavern is to the edge of the salt dome, he pledged during one point in the meeting that his company will do whatever it takes to find answers.

“We are determined to do everything we can to find the answers. We are very eager to find the answers,” Cartwright said.

Texas Brine is under DNR orders to evaluate the structural integrity of the salt cavern and begin to remediate any problems.

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