Sinkhole showing signs of stabilizing, expert says

The Bayou Corne-area sinkhole that emerged in an Assumption Parish swamp 18 months ago, and later dramatically swallowed trees and earth, has shown signs of stabilizing, a leading scientist studying the hole said Tuesday.

But removal of the methane gas also unleashed from the sinkhole’s formation in August 2012 remains a yearslong task and appears to involve more gas than once estimated, the scientists and other officials said.

A CB&I hydrogeologist working for the Louisiana Department of Natural Resources on the sinkhole, Gary Hecox, told about 40 residents and officials at a community meeting in Napoleonville that a variety of scientific measurements show the sinkhole is trending toward stability and tracking with past models for its ultimate size.

Those models would mean the hole would not reach La. 70 to the north, Bayou Corne to the south or the Bayou Corne community to the west. Hecox said the hole is still growing, but the rate of growth has slowed.

Newly released surveys show the hole has grown from about 25 acres in November to 29 acres in February and is continuing southwest beyond the southern arm of a containment levee surrounding the sinkhole and toward the Bayou Corne waterway.

Hecox cautioned that the hole bears more monitoring.

“This is Bayou Corne. Every time you think you’ve got a tight handle on this, she rears up and does something …but right now, a lot of data is trending towards a much more stable condition,” Hecox said.

Scientists believe an underground salt dome cavern owned by Occidental Chemical Corp. and operated by Texas Brine Co. had some sort of collapse or breach of its outer supporting sidewall of salt.

This failure deep underground allowed rock to flow into the massive hollow cavern carved from the salt, scrambled the rock surrounding the salt dome and led to the sinkhole.

The sinkhole and gas fears have forced an evacuation of the 350 residents in the area, though a few people still live in Bayou Corne.

Hecox’s latest assessment follows a burst of underground seismic activity in October and December that led state regulators and Texas Brine officials to agree on construction of a new containment levee wing farther south from the hole.

State regulators had required construction of the levee early on to prevent the sinkhole’s then oily and briney contents from damaging the surrounding cypress swamp.

The original southern wing of the ring levee suffered a series of cracks and sinking following the tremors last year.

Texas Brine contractors began building the new wing in early January and officials said Tuesday in a statement that they expect to have it finished in mid-April.

The first layer of sand has been in place since mid-February, cutting a new path through the scenic swamp between the sinkhole and the Bayou Corne waterway to the south.

Chris Foreman, a contractor who oversees safety at the site for Texas Brine, said during a visit earlier on Tuesday that the levee needs to be raised another 3 feet with layers of clay and special fabric.

Meanwhile, on the gas front, Hecox told residents later at the community meeting that early estimates of 45 million cubic feet of gas being underground are wrong.

He said the series of wells drilled into the aquifer now believed to hold the escaped gas, as well as the sinkhole and the 100 bubble sites discovered around it, have already released 45 million cubic feet of gas with more still underground.