(This is an updated version of an article published in "The Louisiana Weekly" on Nov. 26, 2012.)
At the eight-acre, Bayou Corne sinkhole in Assumption Parish, owners of slab houses are waiting for methane-gas monitors to be installed in December. The sinkhole deepened in November and coughed up debris and hydrcarbons late in the month. Cypress trees fell into the gap. Residents are watching natural gas being flared from the site and are ventilating homes while bayous around them bubble.
Over 200 people, who were evacuated or voluntarily left 110 homes since August, are staying away. They felt tremors last summer when the sinkhole formed after an underground cavern wall was breached. The hole on the western edge of the Napoleonville Salt Dome, contains salt water and crude oil, and is on swampland leased by Texas Brine in Houston from Occidental Chemical Corp.
Bayou Corne is 35 miles south of Baton Rouge and about 80 miles west of New Orleans.
What are conditions like for the forty households that have stayed? Dennis Landry, a local resident and businessman, said before Thanksgiving "gas remains in the aquifer, and a little crude oil is still coming out of the top of sinkhole. Texas Brine contractors laid boom around the sinkhole to keep any oil or other fuel from escaping." He said "Texas Brine and Shaw Environmental are flaring natural gas off from several wells they drilled. The sinkhole was growing in size but it seems to have stabilized in recent weeks."
But things don't stay still for long at the hole. After Thanksgiving, the hole burped up vegetative debris on Nov. 27, and hydrocarbons rose from beneath the hole, according to the Assumption Parish Police Jury. Trees fell in that day and the next. Boom was repositioned to contain hydrocarbons on the surface.
Texas Brine said sinkhole measurements taken on Nov. 14 and reported on Nov. 27 showed the hole had deepened by 30 feet to 145 feet since Nov. 1.
Wells are flaring natural gas to get rid of it. Sonny Cranch, spokesman for Texas Brine, said after Thanksgiving that his company is operating only one vent well on its site and that's Relief Well #1, which is flaring natural gas from the aquifer. The company's Relief Well #2 will be permanently shut to contain a concentration of hydrogen sulfide gas or H2S, detected because of a rotten egg smell before Thanksgiving.
"Even though only a miniscule amount of H2S was released before detection, H2S is still dangerous in sufficient quantities," Cranch said. "Plugging the well removes any possibility of releasing what is believed to be a significant amount of H2S that remains underground at this drill site. It's an abundance-of-caution issue."
He said H2S, a naturally occurring gas found in geologic formations, often migrates into well water in southern states. That water may smell bad but it's generally safe to drink, he said.
Shaw Environmental, Inc. has four, operating vent wells in the sinkhole area--all of which are flaring gas from the aquifer, Cranch said. Shaw Environmental, a Louisiana Dept. of Natural Resources subcontractor, is based in Baton Rouge.
Before Thangsgiving, Cranch said "we flared a total of 598 thousand cubic feet, or mcf, of natural gas from the cavern between Sept. 24 and Nov. 16 . In addition, we got a lot of natural gas--420 mcf--out of our newly installed, shallow-aquifer vent well in just the last two weeks."
As a point of reference, one mcf or 1,000 cubic feet of natural gas is enough to fuel an average U.S. home for space and water heating and cooking for four days.
Texas Brine has also captured a considerable amount of crude oil at its site. Cranch said "we collected a total of 4,530 barrels, each containing 40 gallons of crude oil, from the cavern from Sept. 24 to Nov. 16, along with 1,500 barrels of crude from the sinkhole's surface since Oct. 8."
Landry said "the hole's still bubbling from natural gas and so is the bayou around us, including the bayou water behind my house. We're told that's because natural gas takes the path of least resistance and comes up though the bayou's soft, sandy bottom. The state Dept. of Environmental Quality says the gas emissions aren't a health hazard. DEQ checks gas emissions twice a day, and it says the levels they've detected so far are not explosive."
In community meetings, however, residents continue to ask whether the area around the sinkhole is unhealthy.
Tim Beckstrom, DEQ spokesman, said on Nov. 20, "as of today, 34 homes at Bayou Corne have had indoor air tests run since last August, with four more homes scheduled. We've found no levels of concern. We've also done some outdoor monitoring in residential areas and found no levels of concern there."
Landry said "Texas Brine will pay for air monitors in homes on slabs because natural gas can accumulate in slab houses. For homes built up off the ground and on piers, gas dissipates more quickly." At a residents' meeting on the sinkhole on Nov. 13, air monitors for slab homes were discussed, he noted.
Cranch said "we're now trying to find the right methane-gas monitors, which are more sophisticated than smoke detectors and aren't something you typically find in a hardware store. The ones we choose will have to send signals to a monitoring station." He said the company hopes to have monitors installed in slab homes sometime in December.
Landry's house is on a slab, and he opens his garage and storage room doors each morning for ventilation.
As for tremors, Landry said "I haven't felt them, but other people have. U.S. Geological Survey experts tell us the Aug. 3 collapse of the cavern knocked off large chunks of salt, causing tremors. USGS says the tremors are internal or localized and were not caused by broader seismic activity."
On Nov. 23, the Assumption Parsh Police Jury said "Dr. Will Pettitt, principal geophysicist at Itasca Consulting Group, reviewed seismic data recorded overnight on Nov. 20 to 21. Long-period seismic tremors and micro-earthquakes have been observed." Itasca Consulting, based in Minneapolis, was hired by Shaw to examine the collapsed rock zone under the sinkhole. The area's long-period, seismic tremors are belived to hav been caused by gas or fluid movements through the collapsed zone below the hole on the edge of the salt dome.
"Micro-earthquakes of this nature are typically associated with small-scale rock movements, and are believed to be occurring in the collapse zone," according to the Assumption Parish Police Jury.
Prior to that, Texas Brine on Oct. 1 was ordered by the state to do a geologic survey and collect relevant data. Cranch said "we submitted a subsurface survey plan to the state's Dept. of Natural Resources and are waiting to hear back about it."
Since caverns mined for brine in the area are also used to store natural gas, propane and butane, and because of the presence of crude oil in the hole, residents worry about possible explosions. Natural gas pipelines cross the region.
Meanwhile, fish and wildlife appear to be unaffected by the sinkhole, Landry said. "A modest fish kill in the area in late August was caused by Hurricane Isaac. If there were oil slicks or other noticeable pollution in the bayou, we would have seen it by now since many of us are out in the water in our boats."
The sinkhole's impact on businesses has been mixed."I've lost thousands of dollars in cancellations at my Cajun Cabins since last August," Landry said. "I own three cabins on Bayou Corne. But at the same time, I'm renting my cabins and recreational-vehicle spaces to responding state agencies and to Shaw Environmental."
Landry said "boaters don't stop as often at my Bayou Corne landing, where they launch boats for a fee, because they see the response activity and think we're closed." He also said "highway traffic is down in this area but stores, restaurants and other businesses that lost customers are now frequented by responders."
Texas Brine is helping people stay afloat. Landry said "every household in the 1.5 mile-long, evacuation zone has received $875 a week from Texas Brine since August, whether they've evacuated or not. People who had to leave are staying in their camps or house boats, or with relatives or in rentals. Most local kids are still attending the same schools."
Landry said "this is a beautiful, bayou community that's not exactly in the sticks because we're a half hour drive or less to Baton Rouge, Gonzalez, Morgan City and Thibodaux. But our homes have declined 50 to 100 percent in value because of the sinkhole. We're hoping Texas Brine will give us lump-sum payments for what we've lost."
On the north side of Highway 70, about 75 percent of the houses at Bayou Corne were evacuated. Those homes are 2,000 to 2,500 feet from the hole, Landry said. No homes have been swallowed by the hole. However, "many residents on the north side of the highway felt tremors," he said. "Many of them don't want to return but they can't sell their houses right now."
On the south side of Highway 70, 27 homes are located in a subdivision that Landry has been developing for the past eighteen years. "They're substantial brick homes on concrete slabs on the bayou. Twenty of the homes are occupied right now. I'm staying there now, and those of us on my street, Sportsman's Drive, don't want to move." But he said "most of us on the south side haven't felt tremors."
Evacuees don't know when they'll be able to return. "We're waiting for air monitors, waiting to see more flaring of gas," Landry said. "We expect to attend another community meeting in the first or second week of December."
He continued "I feel the authorities and Texas Brine are telling us most of what we need to know, and people in the community are staying on top of that information. But we're frustrated because there are still so many unknowns. Florida and other states have sinkholes but the dynamics are fairly unique here in that oil and gas are involved. And from what I can tell, this shouldn't even be called a sinkhole. Geologically, what we had was a collapse." end