Existing levee sinking, to be repaired and raised near Bayou Corne
Texas Brine Co. says it will build a new protective barrier along the southern side of the Bayou Corne-area sinkhole amid rising concerns about rapid sinking under part of the levee holding back the hole’s briny and oily contents.
In the interim, Texas Brine is moving to repair and raise the existing levee section that sank.
“They started yesterday building back up the existing berm,” said Sonny Cranch, Texas Brine spokesman, on Thursday.
The levee, also known as a containment berm, is to prevent contaminants in the 26-acre, lake-like sinkhole from damaging surrounding freshwater bayous and swamps in Assumption Parish.
The Bayou Corne waterway is just south of the failing levee.
A 200-foot-long section of levee had sunk and cracked previously from micro-earthquakes dating back to late October. Another intense period of tremors between Dec. 23 and Monday caused additional damage, parish officials said.
“It sank a foot in a week,” said John Boudreaux, director of the parish Office of Homeland Security and Emergency Preparedness.
The latest drop left the levee of sand, clay, limestone and protective liner about 4.5 feet lower than its designed height of 6 feet above the surface, he said.
Boudreaux said the sunken section of levee likely would have gone underwater by Friday or Saturday without the interim repairs.
Parish and company officials offered different assessments of what the immediate impact of a levee collapse would have meant for possible contamination.
Cranch and other Texas Brine officials have argued two factors limit the potential for contaminants to spread to the surrounding freshwater bayous and swamps.
Cranch said higher water levels in the swamp would have meant that water would have flowed into the sinkhole, not out, if the levee had subsided farther.
In addition, the sinkhole is naturally drawing water into its depths, a movement company officials suggest keeps deep briny water from easily rising to the surface.
Since November, Texas Brine has had to pump swamp water on occasion into the sinkhole to keep the water level of the hole close to the level in the swamp, balancing pressures on the levee.
Cranch said about 44.5 million gallons were pumped through Dec. 9, enough to fill 69 Olympic swimming pools.
But Boudreaux said failure of the levee could cause significant ecological problems.
He said water levels inside and outside the sinkhole eventually would have reached an equilibrium.
Then, if the sinkhole had one its periodic burps of gas or edge collapses, he said, the salty contents in the hole’s depths could have been stirred up and spread.
Scientists think an underground salt dome cavern had a partial wall collapse, shattering nearby strata and opening up natural deposits of flammable methane gas. They think the wall collapse allowed surrounding rock and sediments to flow into the massive salt cavity and form the sinkhole.
Scientists believe continued filling of the underground cavern is helping drive growth of the sinkhole, which is estimated to reach, at worst, 40 acres before that process stabilizes.
As tremors intensified since October, Texas Brine came under pressure to have contingency plans in case the southern levee was fatally undermined.
In a draft plan submitted earlier this month, the company did not propose replacing the levee immediately but offered triggers to prompt construction of a new levee farther from the sinkhole.
Cranch said those triggers have not been met but state, parish and company officials decided to go ahead and build a new barrier after a meeting Tuesday about recent subsidence.
“It was kind of a group consensus,” he said.
Patrick Courreges, spokesman for the state Department of Natural Resources, said that in the meeting, Texas Brine officials initially proposed ways to maintain the existing levee.
But Courreges said Boudreaux, DNR and other state agency officials objected and argued work on a new barrier needed to start because the existing southern levee would not be viable for the long term.
Though plans are pending, Courreges added, the new approach may involve a different design to lessen the impact on wetlands, possibly using a wall formed by erecting interlocking sheets of metal.