BATON ROUGE, La. (AP) - State officials said Monday that small amounts of diesel hydrocarbons were found in swamp water where an acre of swampland liquefied over the weekend, while experts try to determine whether the occurrence was natural or manmade.
The sinkhole in Assumption Parish appeared Friday night and grew quickly, toppling cypress trees and bending a 36-inch natural gas pipeline buried 16 feet in the ground as the muck expanded. About 150 homes and several businesses were ordered to evacuate after Gov. Bobby Jindal declared a state of emergency for the parish when the sinkhole appeared to be expanding.
Parish officials said a slight diesel smell was detected as the sinkhole expanded early Friday morning near a plugged well tied to a salt cavern, but it had since dissipated.
John Boudreaux, the head of the parish's Office of Homeland Security and Emergency Preparedness, said he went with an airboat into the slurry hole Saturday to pull samples of the muck water. He said an analysis of a sample he pulled showed there was diesel oil floating on the surface.
Meanwhile about 35 university, government and industry scientists met at Louisiana State University on Monday and came up with a number of possible causes - some natural, some created by people, and some a combination, said John Johnston III, assistant director of the Louisiana Geological Survey.
He said they also drew up a long list of information needed to verify or falsify those theories. It's likely to take at least a couple of weeks to collect that data, he said.
Residents had been reporting gas bubbles and tremors in the area for weeks before Friday and natural gas has been seeping up from Bayou Corne and Grand Bayou, which run below and along the side of the sinkhole. A suspected water well in the area also has been venting natural gas.
Geologists at the Louisiana Department of Natural Resources have said bubbling gas may be connected to a nearby salt dome deep underground, where natural gas is stored in caverns dissolved out of the salt.
The area has a known fault and the salt dome has been mined for brine and used for storage of natural gas and other hydrocarbons.
Adam "Ted" Bourgoyne, a retired Louisiana State University petroleum geology professor, said the diesel might be coming from the solution mining that was done in the salt dome.
"They use it to protect the top part of the cavern so it won't dissolve away, so they can control where the salt dissolves," Bourgoyne said.
"It's hard to say exactly what it means," he said about the traces of diesel found in the slurry samples. "It's an indication that some of the stuff that's in the sinkhole originated in one of those solution caverns."
He said it's also hard to say whether the presence of diesel could cause alarm. He said the sinkhole's location on the edge of the salt dome is a good thing because the gas stored in the caverns are in the middle of the dome, and aren't necessarily at risk if the cave collapses.
Federal, state and parish officials have not been able to pin down the cause of the earthquakes or the source of the natural gas releases in spite of a battery of tests on the oil, gas and brine production infrastructure in the area.
Boudreaux said it was uncertain when people might be able to return home. A shelter was opened up for the evacuees Saturday but he said no one has checked in.
The sinkhole sits on a pocket of private land owned by the Houston-based company Texas Brine Co. LLC facility. Sonny Cranch, a spokesman for the company, said Texas Brine has sent out a company geologist and some other experts to examine the area and collaborate with state officials to get a subsurface image of what's happening below ground.
"The key to all of this is going to be an accurate picture of what's going on down to 5,000 feet below the surface," he said.
Phyllis Darensbourg, a spokeswoman for DNR, said the samples the department is taking will be sent to a lab in Illinois and that it will be at least three weeks before they receive results.
Boudreaux said there have been no changes in the size of the slurry hole since Sunday, after state officials advised there might a risk the area could grow to about 2,000 feet across. The pond of muck now measures about 375 feet across, more than a football field.
Associated Press writer Janet McConnaughey reported from New Orleans.