BY David J. Mitchell
River Parishes bureau
August 23, 2012
Salinity estimates based on water samples taken earlier this month from a large sinkhole in northern Assumption Parish suggest the water becomes far saltier, even more than in the waters of the Gulf of Mexico, the deeper the hole gets, state environmental regulators said Monday.
However, Louisiana Department of Environmental Quality officials said test results are pending that may indicate the source of the sinkhole water.
“We should be getting it this week,” said Chris Piehler, DEQ Inspection Division administrator, on Monday.
State Department of Natural Resources scientists have said they believe a nearby 20 million-barrel Texas Brine Co. LLC salt cavern failed, released its salty brine contents and caused the sinkhole between the Bayou Corne and Grand Bayou areas south of La. 70 South. The sinkhole was discovered Aug. 3.
The plugged and abandoned Texas Brine cavern was carved from the 1- by 3-mile Napoleonville Dome, a large solid natural salt deposit, and used for nearly three decades to produce brine for industry.
Under orders from the state Department of Natural Resources, Texas Brine of Houston also is preparing to directionally drill an observational well to get a better idea of what is happening inside the cavern. The sinkhole has variously been called a slurry area or a slurry hole.
In other developments Monday, Texas Brine spokesman Sonny Cranch said a 20-inch diameter casing, a hollow metal pipe, has been driven to 400 feet deep to the caprock that sits atop of the Napoleonville Dome. Crews spent Monday removing dirt inside that casing so drilling into the caprock could start Monday night or sometime Tuesday, Cranch said.
Also on Monday, John Boudreaux, director of the Assumption Parish Office of Homeland Security and Emergency Preparedness, said cleanup work around the sinkhole is not likely to resume this week but possibly next week.
Cleanup of the sinkhole, which has floating vegetation and a sheen of diesel on the surface, was halted Thursday morning after the edge of the hole collapsed, or sloughed off. Two Texas Brine cleanup contractors had to be rescued from their boat before it was pulled under water.
Boudreaux said Texas Brine is waiting on the monitoring equipment to arrive. The monitors will be set up around the sinkhole, he said, and give workers advance warning about further sloughing off.
In the meantime, Boudreaux said, workers will be replacing oil retardant boom that was affected by recent collapses at the edge of the sinkhole.
DNR and Texas Brine officials have said they expect the edges of the sinkhole to gradually fall in, or slough off, making the hole broader in diameter but more shallow.
DEQ’s Piehler said the pending tests on the sinkhole water samples taken Aug. 15 will look at the kind of ions in the water. Those tests may give a clue about whether the water comes from the cavern or naturally salty water in the ground, he said.
Sometimes called “produced water,” this salt water is in the earth and often comes up during oil and gas exploration as waste, Piehler said.
Estimates based on an early round of samples taken Aug. 8 point to increasing salinity as the sinkhole gets deeper, Piehler said. The estimates are based on the assumption that all the chloride ions in the samples are from sodium chloride, or salt, he said.
At 50 feet, samples pointed to a salinity of around 12 parts per thousand. At 100 feet, samples indicated the water had a salinity about 66 parts per thousand. At 150 feet, samples indicated the water had a salinity of 220 parts per thousand.
Fresh water’s salinity is about 0.5 to 1 part per thousand, while the salinity of the open Gulf is about 35 parts per thousand, Piehler has said.
The salinity of brine from the Texas Brine cavern is 312,000 milligrams per liter, Cranch has said. DEQ officials confirmed that figure converts into 312 parts per thousand.
Piehler said it makes sense that the water in the slurry hole gets saltier as it gets deeper because saltier water is heavier than fresh water.
The sinkhole has forced a mandatory evacuation of about 150 homes in the area, briefly threatened nearby natural gas pipelines until they were depressurized and prompted two other cavern operators to take steps to remove or shift hydrocarbons stored in nearby caverns also in the Napoleonville Dome.
Texas Brine officials have offered displaced residents $875 housing assistance checks in the wake of the sinkhole and also agreed to pay for residents’ past expenses going back to the date the evacuation began.
Discovery of the sinkhole on Aug. 3 followed more than two months of tremors and natural gas bubbling from area bayous and water wells. The tremors have ceased, but the bubbles continue and have also showed up in the sinkhole, parish officials have said.