david j. mitchell
River Parishes bureau
November 28, 2012
An 8-acre swampland sinkhole between the Grand Bayou and Bayou Corne communities in Assumption Parish burped up vegetation and hydrocarbons from its watery depths Tuesday, parish officials said.
Happening about 11:30 a.m., the “burp” coincided with what is called a long-period earth tremor and caused a few trees along the slurry hole’s southwest corner to fall into the sinkhole, Assumption Parish officials said.
Texas Brine Co. LLC cleanup contractors temporarily were removed from the site following Tuesday’s episode and the Houston company checked the integrity of oil-retardant boom deployed around the sinkhole, parish officials said.
Company spokesman Sonny Cranch said that after the sinkhole quieted, workers resumed cleanup work Tuesday afternoon and were expected to return Wednesday if no other changes occur.
John Boudreaux, director of the parish Office of Homeland Security and Emergency Preparedness, said experts suggest that Tuesday’s burp happened as a result of some movement of the earth under the sinkhole’s surface.
Cranch said the mix of debris, dirt and emulsified oil that surfaced and broke apart Tuesday appeared to have originated from the sinkhole’s bottom.
“The point being, it’s not a belch of just crude oil,” Cranch said.
Boudreaux said before the sinkhole disgorged the material, the water level dropped by about 6 inches and then returned to its original level. The size of the water level change was based on measurements of hydrocarbon rings left on trees.
In a pattern state Department of Natural Resources scientists and Texas Brine officials have predicted, the sinkhole gradually has increased its surface size and continued to swallow forested swampland between Bayou Corne and Grand Bayou south of La. 70 South since the hole was found Aug. 3.
Cranch said the belch Tuesday was part of that process.
“It’s just the natural course of events as this sinkhole follows its natural life,” he said.
Sealed off from the sinkhole’s edges by interior oil-retardant booms designed to guide surface crude oil to cleanup workers, the debris instead appears to be rising up from the center of the sinkhole, Boudreaux said.
The coinciding long-period tremor, which Boudreaux said lasted about four minutes on Tuesday, is of a variety in the Bayou Corne area that researchers at the University of Memphis Center for Earthquake Research and Information previously have attributed to the movement of underground gas or liquids.
Cranch and Boudreaux said that the upwellings of material, such as those seen Tuesday, have happened before, though Boudreaux said the latest instance produced more material than in the past.
Texas Brine reported on its website Nov. 21 that debris had risen from the bottom the sinkhole and was accompanied by “a brief period of water movement.”
Private industry and Louisiana Department of Natural Resources scientists think the failure of a Texas Brine salt cavern in the Napoleonville Dome caused the sinkhole to form in a process also related to methane releases underground and in area waterways.
The failure, which resulted from a caved-in cavern wall deep underground, also is suspected of causing the release of crude oil and natural gas into the Texas Brine cavern and in the sinkhole.
Officials ordered more than 150 residences in the area evacuated Aug. 3 because of concerns for occupants’ safety. The order remains in force.