At least a dozen salt-dome caverns in Louisiana are as close to the edge of their supporting underground formations as the one that collapsed last year and caused the yawning sinkhole in Assumption Parish.

Data collected by the state in response to the sinkhole also shows those 12 caverns, along with 15 others, would violate proposed rules mandating a buffer zone of sorts for future caverns to help ensure they are structurally sound.

The Texas Brine Co. cavern that caused the sinkhole was mined too close to the outer edge of a salt formation called the Napoleonville Dome, which left a relatively thin wall of salt between the cavity and less stable outer rock.

Scientists believe that salt cavern wall failed, causing a subsurface scrambling of rock that created the sinkhole and freed oil and natural gas from underground deposits.

Marylee Orr, executive director of the Louisiana Environmental Action Network, said the number of caverns within the proposed buffer zone is a concern because a problem with just one of them can be catastrophic. She said the state’s proposed rules need to be even tighter and more protective of the public and the environment.

“I think we need to be cautious because if there is a problem, it is not a small problem, … you know what I mean?” Orr said. “It is very impactful to the community, and, I believe, to their health.”

But state officials say there is no indication elsewhere of problems similar to those that caused Texas Brine’s Oxy Geismar 3 cavern to collapse.

“To date no other cavern facility has been found to demonstrate the type of warning signs that would indicate impending structural failure of the nature experienced by Texas Brine’s Oxy Geismar 3,” said Patrick Courreges, communications director for the state Department of Natural Resources.

Salt-dome caverns are important to industry in Louisiana, either for the brine created by mining them or for the storage capacity they offer when emptied of the brine.

The Texas Brine cavern collapse — which forced the ongoing evacuation of many homes near the sinkhole because of flammable gas bubbling up through aquifers — prompted DNR’s Office of Conservation to rewrite rules.

Courreges said that while there have been no signs of problems with other caverns, the Office of Conservation is playing it safe because of the possible risk.

The changes would apply to caverns used to make brine, such as Texas Brine’s, as well as those used to store gas and other flammable hydrocarbons.

The proposals include a new 300-foot minimum safety distance from what is called the “edge of salt,” along with new requirements for long-term monitoring of some caverns.

After the Texas Brine collapse, the state required salt-dome operators to show how close the 256 caverns in Louisiana are to the edge of the salt formations that, in essence, house them.

In all, 27 caverns are closer than the proposed 300-foot minimum distance for future caverns, according DNR data compiled at The Advocate’s request.

Under the proposed regulations, the six that are 100 feet or closer to the edge of salt would be permanently closed, with long-term monitoring established. Five of the six are already inactive or plugged.

Operators of the remaining 21 caverns between 100 feet and 300 feet from the edge of salt would have a year to demonstrate they can continue to be operated safely.

Many of those are no longer active.

Some worry, some don’t

The 12 caverns within 150 feet of the edge of their salt formations — the estimated distance of the failed Texas Brine cavern — are spread primarily across south Louisiana in eight domes, which are huge underground formations of solid salt. Those domes stretch from Sulphur to Breaux Bridge to the swamps of southeastern Ascension Parish.

Kenneth Carmouche and his wife, Christine,watched the Bayou Corne sinkhole in the news and sometimes talked about the salt dome about a half-mile south of their homein the Anse La Butte community between Breaux Bridge and Lafayette.

The nearby Anse La Butte Dome contains a Cargill mining operation used to produce pharmaceutical and food-grade salt and an Enterprise Products liquefied petroleum gas storage complex.

New industry-submitted data indicate four caverns in the dome are within the proposed 300-foot minimum. One of those, operated by Cargill, is 130 feet from the edge of salt, 20 feet closer than the Texas Brine cavern was thought to be.

Kenneth Carmouche said he worries about companies continuing to remove material from the earth without backfilling the empty space.

“I mean, if you take something out and you don’t put nothing in, something’s going to happen,” he said. “Now, it might not happen tomorrow or the day after. Something’s going to happen. Just, I mean it’s common sense. You take air out of a tire, it’s going to go flat.”

But Pamela Alex, who lives nearby on Salt Mine Highway, is less concerned. Alex, 48, a housekeeper, has lived in the community her whole life and heard the old-timers speaking Creole French that renders Anse La Butte into “Anz La Bit.”

“We’ve always lived here, and there’s never been a problem,” she said.

Rick Rainey, an Enterprise spokesman, said the company is operating within existing rules, adding that its caverns are structurally safe.

Mark Klein, a Cargill spokesman, said none of his company’s three caverns within the buffer zone are currently being used. Two are plugged and stable, and the remaining one, which is closer to the edge of salt than the Texas Brine cavern, is inactive and being monitored. It too is structurally sound, he said.

Two other salt domes in populated areas with caverns close to the edge of salt are the Pine Prairie Dome in Evangeline Parish and the Sulphur Mines Dome in Calcasieu Parish.

Homes in the Easton community are scattered along the east side of the Pine Prairie Dome and are mixed with the infrastructure of an oil and gas field. The new DNR information shows two liquefied petroleum gas storage caverns are within 150 feet of the salt edge. One is active. The other has been out of service since 1996.

Targa Midstream Services, which operates the caverns, did not respond to requests for comment but has told DNR that both caverns have passed safety tests.

Liz Hill, Evangeline Parish director of homeland security and emergency preparedness, said the Targa caverns don’t cause much of a stir in Easton, where many people work in the industry and live near oil and gas wells and pipelines.

“Kids grow up riding their bikes right in front of them,” she said. “People that live in the Easton area usually have grown up with it.”

The Sulphur Mines salt dome, where extraction of oil, gas, brine or sulphur has gone on since the late 1860s, has five caverns within the proposed 300-foot minimum. Some homes dot the area south of the salt dome. The dome contains the cavern that is the closest to the edge of its formation, at 20 feet, according to DNR.

The cavernwas plugged in July 2012. In March, the owner, Axiall Corporation, reported to DNR that the cavern and three others it operates there within the proposed 300-foot minimum are structurally sound.

Other caverns that are closer than 150 feet to the edge of salt include four in the Bayou Choctaw Dome, which lies under swamps in Iberville Parish northwest of Plaquemine.

One cavern there, operated by the nation’s Strategic Petroleum Reserve, is only 60 feet from the boundary of its salt formation.

Concerns about the cavern’s thin salt wall had been raised since the early 1980s. In 2011, before the Bayou Corne sinkhole emerged, the federal agency decided to drain the cavern because of concerns about oil leaking, citing the agency’s own safe minimum distance standard of 300 feet.

Strategic Petroleum Reserve spokesman James Quern said the agency last month finished pumping oil from that cavern into a nearby one. The now-empty cavern, which shows no structural problems, will be continually monitored, he added.

Proposed rules stir debate

Environmentalists, some Bayou Corne residents and others fighting a proposed gas storage cavern expansion at the Jefferson Island Dome under Lake Peigneur in Iberia Parish plan to speak at a public hearing Tuesday on the proposed regulations.

Some find the minimum-safe-distance rules inadequate, while others don’t see enough protections for people affected by failed storage and brine caverns. They also want the state to require environmental impact statements before new caverns are permitted.

Wilma Subra, a LEAN technical advisor, said she would like to see some kind of negotiation on the minimum distance from the edge of salt.

“I still think it needs to be much farther than what they are proposing,” Subra said.

Courreges said the Office of Conservation arrived at the 300-foot minimum by adding a 100-foot safety factor to a U.S. Environmental Protection Agency safety standard calling for a 200-foot separation between salt caverns.

He addedmost new cavern permits include information on environmental impact, and that the new rules would require companies to provide assistance to people evacuated because of sinkholes.

Texas Brine provides assistance to evacuated Bayou Corne residents under the specific terms of its permit.

Some salt-dome cavern operators insist they can safely operate within the proposed 300-foot zone.

Louisiana Offshore Oil Port carved caverns from the onshore Clovelly Dome to hold crude deliveries from big tankers in the Gulf of Mexico. LOOP reported one of its caverns holding oil is 240 feet from the salt edge. Terry Coleman, vice president of engineering and technology for LOOP LLC, said the company continuously monitors cavern conditions.

“We use quite a bit of advanced technology to ensure the integrity of that cavern and all of our caverns,” he said.

Whitney Autin, a geology professor at the State University of New York, College at Brockport, said the development of salt domes is often a question of real estate. Operators want to be in domes that are near pipelines and customers for brine and that have enough sweet spots left inside to mine salt, he said.

Autin, who got his geology doctorate from LSU and has published papers on Louisiana salt domes, said it may be hard to develop a single set of standard regulations that can account for all of the differences in geology and in salt-dome structure to ensure new caverns are safe.

“My analysis would be like there is no one-size-fits-all about the speed limit in a four-lane highway,” he said. “Some places, the speed is 75, and some places, the speed limit on the Interstate is 45 if you’re going through a thick, urban area.”