NAPOLEONVILLE — Emotions flared Tuesday during a community meeting on an 8.5-acre sinkhole in northern Assumption Parish as people in the audience realized that attempts by experts to understand the sinkhole’s cause and deal with its long-term aftermath would likely extend into the middle of 2013 or beyond.
More than four months into an evacuation from their homes in the Bayou Corne and Grand Bayou communities and about a week from Christmas, residents and parish Police Jury President Martin “Marty” Triche found fault with the pace of Texas Brine Co. LLC’s response to the sinkhole.
Scientists believe the sidewall of an abandoned Texas Brine salt cavern failed deep underground in the Napoleonville Dome. This failure, scientists say, set in motion a series of events that created the sinkhole and released methane and crude oil, leaving underlying strata in an uncertain and unsettled zone of collapse.
On Tuesday, residents learned from Gary Hecox, a Shaw Environmental and Infrastructure Inc. geologist working on the issue for the Louisiana Office of Conservation, that scientists are monitoring whether the sinkhole and the surrounding collapse zone may affect other salt caverns in the dome.
He said the monitoring would be a long-term effort, likening the issue to how hurricanes are managed for damage risk.
“It’s analogous to a tropical storm off the west coast of Africa, and you’ve got your first notification that it’s out there,” Hecox said.
Earlier in the meeting, one resident shouted at Bruce Martin, Texas Brine vice president of operations — first from afar and then in his face — challenging Martin’s statement that he, Martin, had been in the community since shortly after the sinkhole was found on Aug. 3.
Tapping the shoulders of other residents sitting in the audience, Gary Metrejean, 47, a Bayou Corne evacuee now living in Belle Chasse, asked Martin, one-by-one, if he knew those people.
“If you have been involved since day one, why don’t you know these people? I’m serious. Why you don’t know these people? Does Texas Brine have any compassion for the people that they affect?” Metrejean wanted to know.
Martin assured Metrejean he did know the residents.
“I don’t believe you do. I don’t believe you do. I believe it’s the bottom line. It’s the money,” Metrejean said.
Triche also found fault with the pace of installation of vent wells designed to release methane trapped underground in the vicinity of the 150 houses affected by the evacuation order and urged Martin to consider buyouts for residents who want them.
Confrontations erupted after a detailed presentation in which Martin had described all the activities Texas Brine was undertaking to respond to the sinkhole, as well as telling residents about the importance of agreements to assess and install structures for in-home methane monitors.
Hecox warned residents that not only slab-foundation homes are at risk from methane gas rising from underground sources, but also some homes elevated on piers.
He said a recent review by an indoor toxicology expert Shaw Environmental has hired indicated that residences and mobile homes on piers, in which the crawl spaces beneath the floors are enclosed, may be at more risk than slab-foundation homes from gas accumulation.
Hecox urged residents owning such homes to get in-home monitoring also.
Residents heard from another speaker, the general manger of Itasca, a worldwide firm that specializes in rock mechanics, that the sinkhole is likely to wind up much smaller than worst-case estimates.
The Itasca manager, Will Pettitt, showed an estimate produced with a powerful computer model based on the available data showing that the worst-case scenario diameter of the sinkhole would be about 1,400 feet, slightly less than the 1,500-foot diameter previously disclosed.
But the most likely final diameter, Pettitt said, would be 734 feet. The sinkhole is currently 690 feet across.
Hecox later said that Pettitt’s work has shown that part of the running theory on the formation of the sinkhole is likely incorrect.
Hecox and other scientists had initially theorized that the cavern had a “frack out” of brine that happened almost immediately before the sinkhole’s formation.
He told residents Tuesday that Itasca has persuaded him that the formation of the collapse zone leading to the sinkhole occurred through a slow-moving fracture of the sedimentary rocks along the salt dome during a several-month span.
Hecox said the tremors residents had been feeling in the months before the sinkhole’s emergence were likely part of this process.
But Itasca and other officials will not know better what happened underground until Texas Brine can finish two 6,000-foot wells the state Office of Conservation has ordered the company to drill.
The wells will be used to perform seismic studies of the collapse zone under the sinkhole and inside the western rim of the salt dome.
When asked, Hecox acknowledged it is likely to take six months for the drilling and seismic work to be finished.