BY DAVID J. MITCHELL
River Parishes bureau
September 25, 2012
Regional seismic activity damaged an abandoned Texas Brine Co. salt cavern that has been suspected to be the cause of a 4-acre sinkhole in Assumption Parish, company officials said late Monday.
A tool used to measure the depth of the underground cavern found its floor is 1,300 feet shallower than when it was abandoned in mid 2011, indicating “some type of dense material has fallen to the bottom of the cavern,” Texas Brine officials said in a statement.
The sinkhole was found on Aug. 3 in swampland located between Bayou Corne and Grand Bayou and south La. 70 South and forced the evacuation of residents in 150 households nearby.
Under orders from the Louisiana Department of Natural Resources, Texas Brine hired a contractor to drill an investigatory well for more than a month to peer inside the cavern.
DNR scientists have said they suspected that the cavern failed, leaked its brine contents and caused the sinkhole, which is about 475 feet wide and about 200 feet from the salt cavern.
Texas Brine’s driller punched through the roof of the cavern on Saturday night and testing began Monday after natural gas in the cavern was able to be flared off, Texas Brine officials have said.
Earth tremors and natural gas bubbles in area waterways preceded the formation of the sinkhole by about two months.
But Texas Brine noted Monday that “seismic events began to concentrate around the sinkhole only a few days before it appeared.”
“Texas Brine and the experts who have reviewed the available data believe that the damage to brine cavern No. 3 originated with regional-scale seismic activity,” the statement says.
In a statement late Monday, DNR officials in the Office of Conservation said Texas Brine informed them about the cavern damage.
“This is exactly why the office ordered Texas Brine to drill the investigatory well,” DNR spokesman Patrick Courreges said in a statement.
“The Office of Conservation will hold Texas Brine accountable for this damage and will continue to gather data on the exact conditions in the cavern to determine not only the cause, but what the links may be to the sinkhole/slurry area and natural gas bubbling in the area.”
DNR scientists also have said they suspected that the cavern is the source of the natural gas bubbles.