Unusual Geological Event / Louisiana

Assumption Parish emergency officials have asked to meet with an expert from the U.S. Geological Survey and for portable seismic equipment to get a better understanding of new tremors reported in the Bayou Corne and Grand Bayou areas, officials said Friday. The earth tremors are being reported by residents in a swampy area of northern Assumption Parish where venting streams of natural gas have been roiling the surface of waterways for about a month. The source of the natural gas remains uncertain and is not an explosive risk but detailed tests to fingerprint the source of the leaking gas are pending, said John Boudreaux, director of the parish Office of Homeland Security and Emergency Preparedness.

He said company reports posted on the parish’s website are from earlier tests that mainly established that natural gas had been bubbling up through the waterways. Boudreaux said residents reported tremors last month and again on Tuesday and Wednesday, about 7:30 a.m. each day. State and parish officials have not made a connection between the tremors and the natural gas releases and are focusing on the oil and gas infrastructure in the area to pinpoint the source of the leaking gas. One of those lines of inquiry has been the Napoleonville Dome, a 3-by-1-mile salt dome containing 51 caverns used to produce brine and for hydrocarbon storage.

The Bayou Corne and Grand Bayou areas are on one of the dome’s flanks. Two of the caverns store natural gas.Boudreaux said the cavern holding natural gas nearest to the two communities has undergone a scientific test to assess its integrity. He said the Louisiana Department of Natural Resources is evaluating a report on the test and is expected to provide the results next week. The cavern is ultimately owned by Chevron Pipeline. The other cavern, which is about a mile north of the Chevron cavern and is owned by Acadian Gas Pipeline of Houston, Texas, has been shut in for the past five days as a precaution and is being monitored, Boudreaux said. Parish officials have also said they monitoring the air for natural gas levels and what is called the lower explosive limit, or LEL, around the waterborne bubble locations and in populated areas. LEL indicates a risk of explosion.

The LEL has been zero in almost all reports. In a news release Friday, parish officials said that in the Sportsman’s Drive area of Bayou Corne, a stationary air monitor hit 25.2 percent of the LEL on Thursday but officials say the reading is suspicious. Sheriff Mike Waguespack warned the public Friday not to tamper with the monitoring equipment. He said anyone caught tampering or trying to feed the monitors some type of foreign source “will be handled accordingly and will be arrested.”

Concerns would occur at 60 percent of LEL, and 100 percent would reflect an ignition risk. Boudreaux said he also heard community concerns about daily air monitoring reports on the parish website. The reports reflect passes by a boat near the bubbling locations and recently installed neighborhood air monitoring equipment, Boudreaux said. He said monitoring tests for chemicals in addition to LEL, including, in some cases, hydrogen sulfide, or H2S. Hydrogen sulfide is regularly tested in connection with oil and gas exploration. He said concerns would begin at levels of 35 parts per million and can be toxic at 100 ppm. The latest reports Friday show less than 1 ppm for hydrogen sulfide