One-tenth to one-twentieth of the methane gas estimated to be trapped under the Bayou Corne and Grand Bayou communities in northern Assumption Parish has been burned off so far, according to parish emergency response officials.

Scientists believe the failure of an abandoned underground salt cavern owned by Texas Brine Co. LLC set in motion a series of events that scrambled the substrata thousands of feet deep, creating a 8.5-acre sinkhole at the surface and unleashing oil and gas from nearby natural formations underground.

The cavern, which was never used to store methane, was carved over a 27-year period from the Napoleonville Dome, a large subterranean salt deposit.

This “free gas,” as it is known, presents a risk to the 150 households in Bayou Corne and Grand Bayou areas, scientists have said, because the colorless and odorless gas can accumulate in enclosed spaces in homes and garages and pose a risk of explosion.

The risk is one of the reasons evacuated residents remain out of their homes more than five months since discovery of the swampland sinkhole Aug. 3, parish officials have said.

The pace of installing the wells that will vent the gas has drawn fire from residents and parish officials. Parish Police Jury President Martin “Marty” Triche raised this issue last month during a community meeting in Napoleonville.

As a comparison, he pointed to the reaction of Gulf South Pipeline Co. LP to a natural gas leak in late December 2003 in the Grand Bayou area east of where the sinkhole is now located.

The underground leak resulted from the failure of metal casing in an access well to an underground gas storage cavern on Dow Chemical Co.’s property. The cavern also was carved from the Napoleonville Dome.

The leak led to a 50-day evacuation of 28 residents who lived in Grand Bayou, most of whom were later bought out.

Gulf South, which was in a partnership with Entergy Corp. and Koch Gateway Pipeline at the time and was leasing the cavern from Dow, installed 36 vent wells. Triche said that took only weeks to do.

“I just want to tell that you sit here and you tell us you’ve committed to doing everything you can to resolve the situation and all we can do is take you at face value,” Triche told Bruce Martin, Texas Brine’s vice president of operations, during the meeting amid a broad critique of the company’s response.

“But I can tell you, for those of you that were here, the response to the 2003 incident and what we see today are night and day,” Triche said.

Triche, a lawyer, represented Dow in later litigation over the gas leak.

The 2003 Gulf South leak released an estimated 600 million cubic feet of gas underground in the same water aquifer now affected by the Texas Brine-cavern leak.

Seventeen of the 36 wells drilled collected or burned off gas, removing 375 million cubic feet before officials started closing down the wells in July 2004, according to the Louisiana Office of Conservation and an insurance report filed in connection with litigation over the 2003 leak.

In the latest incident in Bayou Corne, between 50 million and 100 million cubic feet of gas is believed under the area, scientists have estimated. And in the five months since the sinkhole was found, various kinds of wells have drawn off a combined 4.95 million cubic feet of gas through Friday, the new parish estimate says.

At latest count from the state Office of Conservation, three wells are burning off a combined 59,200 cubic feet of gas per day.

But the venting process in Bayou Corne has run into hurdles, affecting the number of wells burning gas and how much gas they burn.

The first batch of four wells installed by the Office of Conservation and its agent, Shaw Environmental and Infrastructure Inc., ran into problems with blockages and water infiltration. Two of their wells are now venting gas.

Two other wells Texas Brine installed on its 40-acre site hit hydrogen sulfide, a potentially lethal gas. That discovery forced the permanent closure of one well and the installation of specialized equipment in another before flaring will be allowed to resume.

Water infiltration ended flaring last month from a converted pressure well, a separate kind of well that measures underground gas, company officials have said.

Texas Brine is looking at two other pressure wells for new flaring options and has one vent well burning off gas.

Texas Brine officials have also pointed out they continue to have trouble with land access around Bayou Corne where there are multiple property owners, including residential owners.

In the Grand Bayou incident in 2003, most of the gas was found over the Napoleonville Dome, east of Bayou Corne and under property owned by industrial users, Texas Brine officials noted.

“I think the circumstances were different,” company spokesman Sonny Cranch said.

The Office of Conservation noted access difficulties Dec. 17 when it did not fine Texas Brine a second time for failing to meet vent well deadlines. The agency had cited that issue in an initial round of fines levied Dec. 1.

But Triche, who reached an agreement with Texas Brine on reimbursement of parish response costs Friday, contends Texas Brine could have started much sooner to find well sites, a delay that is part of a pattern, he says, of not being proactive on its sinkhole response.

Triche said he is glad Texas Brine will pay for its responsibilities, but he remains upset that the company has not done more to mitigate the sinkhole event.

“They still got a lot of work left to do, and it’s long overdue,” he said.