Tremors return by sinkhole

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By David J. Mitchell

River Parishes bureau

September 17, 2012

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GONZALES — The sharp earth tremors that rattled the Bayou Corne community during the summer and presaged the emergence last month of a large sinkhole in Assumption Parish have returned, a University of Memphis scientist said.
The tremors appeared to build in July, reached a crescendo of several hundred per day then stopped at 2 p.m. Aug. 2, hours before the sinkhole was found early Aug. 3 on the property of Texas Brine Co. of Houston, officials said.
Later that same evening, the sinkhole prompted parish officials to call for a mandatory evacuation of 150 households in the Bayou Corne and Grand Bayou areas. It remains in effect.
Steve Horton, research scientist with the University of Memphis Center for Earthquake Research and Information, said Friday that about a week ago, one or two sharp tremors began reoccurring every day or so.
Horton sits on a scientific advisory committee that the Louisiana Department of Natural Resources formed to study the sinkhole, the tremors and natural gas releases that are also occurring in area bayous.
Horton, who is working with the U.S. Geological Survey to study the tremors, said the returning tremors are in the same vicinity as the earlier ones — a shallow area underground on the northwestern edge of the Napoleonville Dome.
The sinkhole and the abandoned Texas Brine salt cavern suspected of causing the sinkhole are also in that area.
The 1-by-3-mile dome is a solid salt deposit pushed up from an ancient seabed and used for decades for brine production, oil and gas exploration and hydrocarbon storage. The cavern was hollowed out of the dome throughout nearly three decades of solution mining to make brine for various industries.
Horton said seismic monitoring has narrowed down the source of the tremors to an area larger than — but containing — the sinkhole and the Texas Brine cavern.
While Horton said there is no cause for concern from the tremors, he said one question is whether they might be occurring in some sort of pattern, given how they built up, stopped and have now restarted.
“We were wondering if there might be a cycle to this and so we may or may not be starting a cycle,” Horton sai.d “We’ll just have to wait and see.”
“That is why we’re monitoring it at this point.”
Other developments surrounding the sinkhole have occurred in recent days, officials said.

• On Thursday, a contract administrator working for Texas Brine issued 153 checks for the weekly $875 payments to evacuated households and 135 checks for retroactive payments for the two-week period before weekly checks began.
• Another Texas Brine contractor continued work Sunday on changing out one drilling rig for another that is better able to handle gas pockets encountered during the drilling of the well, which is aimed at investigating whether the company’s salt cavern is the source of the sinkhole.

John Boudreaux, director of the Assumption Parish Office of Homeland Security and Emergency Preparedness, said some of the returning tremors are being felt.
He said a state trooper was awakened by a tremor about 2:30 a.m. Friday. The trooper was sleeping in cabins near the sinkhole response command post in Bayou Corne along La. 70 South.
Horton said the most recent tremors are probably about a 2 on the Richter scale, which measures the energy of earthquakes.
What might be most vexing about the return of these sharp tremors is that they come in addition to long-period, lower frequency tremors that began Aug. 6. These long-period tremors come from northwest of the sinkhole and not in the salt dome, Horton said.
On a seismometer, the sharp tremors are recorded as having one back-and-forth oscillation in less than a second — multiple oscillations are bunched together like scribble-scratch on a graphical depiction — and the tremors last no more than a minute.
In contrast, on a seismometer, the long-period tremors are recorded as having one back-and-forth oscillation over 20 to 40 seconds — the wave pattern is easily distinguishable on a graph — and the tremors last for three to four minutes.
Horton said he has never seen such a combination of tremors before from the same area at the same time.
“Yes, it does lead to a lot of questions and that’s really where we are,” he said. “We have a lot of questions as to what’s going on and not a lot answers.”
He said the long-period tremors could be related to something connected with natural gas, but he cautioned that was speculation.
“There is something going on with these very long-period signals, and we don’t know what it is … I haven’t figured it out yet,” Horton said.
Recent discoveries of natural gas in a shallow aquifer and in the caprock above the Napoleonville Dome prompted DNR’s Office of Conservation Commissioner James Welsh on Friday to order operators working on the dome to look for gas below their operations. The operators must analyze any gas found and vent or flare it off.

Sinkhole Site, 09/15/12

Louisiana sinkhole alarms reported, seismic activity spikes

 

Alarms heard might link to Bayou Corne sinkhole area seismic activity at Monitor #3 near Hwy. 70 (sample shown in image above) and at Monitor #9.

Credits:

USGS, University of Memphis

Examiner/Lousiana sinkhole area residents reported to Assumption Parish officials hearing alarms over the weekend, but were told by officials that alarms are not going off. The alarm reports coincide with a spike in seismic activity, according to The University of Memphis Center for Earthquake Research and Information (CERI), and also might coincide with resumed drilling into the sinkhole area after Tropical Storm Isaac left it.

Just hearing bells? Alarms heard might link to Bayou Corne sinkhole area seismic activity at Monitors #3 and #9 near Hwy. 70
According to the University of Memphis team's hellicorder charts of two of the six seismic monitors its Louisiana sinkhole team placed in the sinkhole area, monitors # 3 and # 9 at locations near Highway 70 in the Bayou Corne area, have recorded unusually higher seismic activity on September 2.
Those recordings are much higher than on previous days and at other locations that the team of scientists are monitoring in the area, according to the university CERI hellicorder dated graphs.
The University of Memphis, contracted by the US Geological Survey to monitor seismic activity in the Bayou Corne sinkhole area, had recorded thousands of quakes in July and early August, until the sinkhole developed.
After locals reported to officials that they had heard alarms this weekend, officials responded to those reports in their blog post on Sunday:
"It has been brought to our attention that some people are speculating about alarms going off in the Bayou Corne area. Despite the fact that the OEP (Office of Emergency Preparedness) office is closed until Tuesday, calls have been made inquiring about such alarms, and it has been confirmed that alarms are NOT going off in the Bayou Corne area."
Hellicorder charts display each of the six monitors in the Bayou Corne sinkhole area, digitally simulating actual seismograms that are routinely recorded at CERI. The seismograms show a record of how the ground moved at a particular seismograph station in the Southeastern U.S. during a 24-hour period.
Bayou Corne resident and advocate Dennis Landry told the Examiner Monday in a telephone interview, "After reports about hearing alarms in the area were made, a couple of locals went out to listen, but said that they didn't hear anything."
"We don't know who heard and reported those alarms," Landry said.
Drilling and seismic activity
The timing of the alarms reported and the recent seismic spikes might correlate with the resumed drilling of an observation well into the area.
Louisiana Commissioner of Conservation James Welsh stated Friday in a news release that Texas Brine’s rig operator, Riceland Drilling Co. of Lafayette, returned Thursday and resumed drilling shortly before noon Friday.
Before Hurricane Isaac hit the area, "The rig operator laid down the rig derrick, secured site equipment and evacuated the site on Monday, in anticipation of potential winds and flooding," Welsh reported. "Enforcement agents with the Office of Conservation monitored the shutdown of site operations, and continued to make site visits to assess the condition of the site before and after the storm's passage."

On Aug. 17, Assumption Parish officials issued a statement about vibrations that might be felt as drilling began at the sinkhole: "Texas Brine has informed us that the drill operation will start with driving 20 inch casing at the rig site for the next two days. The operations are expected to start between 9:00 p.m. and midnight tonight and will continue until completed. The casing driving may produce noises and vibrations."

At the time operations were suspended before Isaac, the company had drilled to approximately 600 feet and cemented the surface casing from 600 feet back to the surface to maintain well integrity through the Mississippi River Alluvial Aquifer. Blowout preventers and a diverter system had also already been installed.

At a local meeting with officials on Sunday in Bayou Corne, the reported alarms was not discussed, according to Landry.

On Aug. 9, a community explosion monitor alarm sounded in Assumption Parish's Bayou Corne sinkhole area. Officials said they suspected someone tampered with the monitor and that they were investigating the incident. The investigation final report has been unavailable to Deborah Dupré, who requested in an email the week of Aug. 13 that Assumption Parish officials provide her with a copy of that report.

Before the sinkhole rig operators return to the site, "a Conservation agent inspecting the drill pad area noted the storm had caused a minor break in the small containment levee around the project's emergency pit," Jim Welsh reported. "The agent reported that nothing had been released from the pit, and the operator repaired the break Thursday."
"Well, I'm very concerned," a parish official told CBS last month, then referring to Lake Peigneur 80 miles west of the Bayou Corne sinkhole.
Lake Peigneur balances above a salt dome that collapsed in 1980 when a drilling rig punctured a protective layer in the salt mine wall, causing the entire lake, including a drilling rig, several larges barges, and large chunks of surrounding land to be sucked into the cavern.
"When you look at the scenario that happened in Lake Peigneur," the official said on CBS News, "the pronunciation of that I think is Lake Pen-oar, now you have a sink hole on top of a salt dome, with the suction and the pressure going down, I would certainly assume it's possible that it can penetrate the dome and then we definitely have an issue there."
At the time of publishing this article, officials at the Assumption Parish Police Jury and University of Memphis Center for Earthquake Research and Information Center have not returned Dupré's telephone calls and emails she sent to them Monday morning.

Sinkhole In Assumption Parish, La.

I was raised only 20 miles from here. I havent been back in over 21 years but It I still remember this awesome place like it was yesterday! This sink hole is becoming larger and no one knows what it is from. Well it is just from the earth growing and contracting! There is sink holes everywhere!

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For more than two months, officials from federal to local have been unable to pin down the source of a natural gas leak and tremors in assumption parish.
But on Thursday a 200 by 200 foot "slurry area" has appeared in bayou corne in northern assumption parish...
The formation of the slurry area was accompanied by a diesel-like odor that some residents said burned their eyes and noses but dissipated by midmorning Friday...
Assumption parish officials declared an emergency and called for an evacuation of residents living near the nearly 1-acre muddy site.
A potential failure of a cavern operated by Texas brine company may have caused the slurry area, or sinkhole, which swallowed full-grown trees and denuded a formerly forested patch of cypress swamp.
Final determination of a positive link between the failure of the cavern and either the natural gas bubbling or the slurry area has not been made.
In response, gov. bobby jindal declared an emergency Friday.