Advocate staff photo by HEATHER MCCLELLAND — Gary Hecox, a geologist with Shaw Environmental and Infrastructure, urges Pierre Part-area residents to get their homes checked for possible natural gas migration, and added that homes on slabs are the most at risk. He spoke Tuesday night at a community meeting on the status of the Assumption Parish sinkhole emergency that was held in the St. Joseph the Worker Catholic Church hall.
BY DAVID MITCHELL
River Parishes bureau
November 14, 2012
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PIERRE PART — A Shaw geologist working on the response to the Bayou Corne-area sinkhole urged evacuees Tuesday to get in-home testing of the air in their residences.
He told the people ordered to leave their homes when the sinkhole emerged Aug. 3 that installing methane monitors and ventilation improvements likely would be the only way they could get back into their homes.
Gary Hecox explained to about 150 people at St. Joseph the Worker Catholic Church hall that this shallow gas, methane, is at low pressures and it is virtually impossible to tell where it may come up on dry ground, unlike more well-known bubble sites in area bayous.
Hecox also presented a map depicting the estimated geographical extent of the shallow gas zone, which lies 20 to 40 feet underground, based on the locations of bubble sites in area bayous, the fact that shallow wells called Geoprobes have detected gas pressure and deeper vent wells have hit gas and other data.
The map showed an area extending from the Grand Bayou community west to a point past Bayou Corne that included the sinkhole area south of La. 70 and extended farther south into swamps to the southwest of the sinkhole to the east of Pierre Part.
Hecox warned the gas can pass through concrete slabs and accumulate in enclosed spaces.
He said he hopes there is no gas accumulation problem, but right now there is no way to tell.
“I hope that more than anybody in this room does, but right now I cannot make that assumption,” Hecox said.
The Louisiana Office of Conservation announced Nov. 7 that it was reviving an in-home air testing program in cooperation with the Louisiana Department of Environmental Quality.
A DEQ official who heads the inspection division told residents a prior round of in-home air inspections and more recent testing, including seven or eight houses on Tuesday, have not detected any levels of concern.
Hecox added that due to the changing conditions around the sinkhole, in-home testing that does not detect gas one day does not mean residents are clear to return home.
“I am sorry, that’s the way it is. That just means your home is safe today,” he said.
He said the methane detectors and ventilation of enclosed spaces that the Office of Conservation ordered Monday for Texas Brine Co. LLC to install in affected homes would provide the only options available for residents wishing to return home.
That prompted an angry outburst from residents listening to Hecox, one of whom said officials had “lost their damned minds” if they thought residents were going back to their homes. Another man dismissed the Bayou Corne community as no longer fit for human habitation.
Hecox responded that he had lived in Colorado with his children and had to install similar kinds of ventilation and detectors for radon gas.
“I am telling you as straight as I can (that) to get back in your houses, these are the only ways it can be done. Whether it is safe for you is a personal decision,” he said.
Scientists believe a Texas Brine salt cavern inside but near the western edge of the Napoleonville Dome had a wall breach that caused the sinkhole and released naturally occurring crude oil and natural gas along the edge of the dome. The oil land gas then worked toward the surface.
Discovery of the sinkhole in early August led to a mandatory evacuation of 150 homes in the area that remains in place.
Hecox showed data that appears to indicate the cavern is stabilizing, but said officials still do not know about the underground collapse zone that is next to the failed cavern and is believed to have provided a key escape route for the migrating oil and gas.
He said Shaw has hired experts in rock mechanics, Itasca Consulting Group Inc., of Minneapolis, Minn., to study the collapse zone and check the current theory explaining the connection between the sinkhole and failed cavern.