BAYOU CORNE —Rhett and Donna Pipsair have spent the last 23 years making their home on Sauce Piquante Lane just the way they want it.
The Pipsairs started out in a mobile home and eventually built a two-story house with a manicured lawn, a pond in the backyard and, behind it, a gently curving pier ending at a dock in an endless cypress forest.
While many of the neighbors in Bayou Corne have moved away in the nine months since the Assumption Parish sinkhole formed across La. 70 South from their house, the Pipsairs have remained, in spite of a parish evacuation order issued Aug. 3.
Rhett Pipsair, 50, the father of two adult sons, said he has not evacuated because he has not been afraid of the sinkhole since it formed.
About a month ago, however, gas started bubbling up underneath a deck in one corner of his oblong pond, Pipsair said.
“This is making me think twice now that it’s in my own backyard,” Pipsair said. “I mean I’ve been building this place for 23 years. I can’t just up and leave, you know what I mean.”
Scientists studying the sinkhole say the gases in the bubbles are coming from several sources: Both decomposing organic matter and deep formations likely opened by the events that created the sinkhole, now 15.1 acres at the surface.
Scientists working for the Louisiana Office of Conservation said last week that Pipsair’s pond could be a signal that what they had feared last year — gases collecting underneath people’s houses — may be starting to occur.
The deeper formation of gas may be moving up and pushing shallow swamp gas up before the deeper gas appears in the shallowest layers under the Bayou Corne community.
The shallow gas released from decomposing matter is often called swamp gas, which is common in Louisiana, and is referred by scientists as being “biogenic.”
Known as “thermogenic,” the gas from deep underground, which is the focus of concern, has far older geologic origins.
Scientists have worried since last fall that this deep reservoir of gas could eventually move up closer to the surface, pass through the foundations of homes or accumulate under enclosed crawl spaces in homes, posing an invisible risk for explosions in the community of 350. Methane gas is odorless and colorless.
This fear has been one of the reasons the evacuation order has remained in place since August.
“The deep gas displacing the shallow swamp gas, appears to be occurring,” Gary Hecox, a CB&I hydrogeologist working on the sinkhole for the Louisiana Office of Conservation, told residents in a meeting last week.
A Texas Brine Co. salt dome cavern is suspected of having a sidewall failure that allowed millions of cubic yards of material to fill the hollow subterranean cavern and also unleashed oil and gas from deep underground.
Scientists have said they think about 45 million cubic feet of gas is now under a more than two-square mile area of the Mississippi River Alluvial Aquifer, which ranges from 120 to 600 feet deep.
The thermogenic gas found in the bayou bubble sites were the first warnings last May that something was amiss underground and in vent wells installed since November to burn off the gas.
Hecox said two shallower test wells in the area have since seen this shift from swamp gas toward thermogenic gas. The wells, known as Geoprobes, are about 30 feet deep.
One of those wells is in the Bayou Corne community. Pipsair’s pond may be midway in this process.
“We do have some pretty strong isotopic data now that says at least some of the methane in the community that’s being detected has moved its way up from deep underground andis now coming up into the shallow part of the system,” Hecox said.
But Texas Brine Co. officials have emphasized that testing under the foundations of houses in the community as well as the monitoring of the air inside them has not produced indications of the deep formation gas.
The volume of gas burning from 33 vent wells is going down while tests of the wells appear to show that the layer of gas in the aquifer is decreasing, Bruce Martin, Texas Brine vice president of operations, told residents Wednesday.
In addition, Texas Brine officials said their highly detailed seismic survey of the area shows only one possible source for the deep gas, known as the Big Hum, and it is played out.
“Overall, I feel very good that we’re making progress on getting the gas out of the aquifer as evidence by what we’re seeing on the individual wells,” Martin said.
Sonny Cranch, Texas Brine spokesman, said Friday that the company planned to fly a helicopter with a special probe over the area Saturday to better show were the gas is located in the aquifer for future vent wells.
Don Marlin, the state Office of Conservation’s expert hired to review Texas Brine’s seismic data, has raised the possibility of at least eight sources for the gas based on less detailed seismic data from 2007.
This has raised fears that the gas in the aquifer could be continually fed from several sources.
Patrick Courreges, spokesman for the Department of Natural Resources, said Friday the Blue Ribbon Commission, an expert panel appointed by DNR Secretary Stephen Chustz in late March, will have to work through the data and reach a conclusion. Hecox is one of 13 people on the commission.
Meanwhile, Pipsair said he will entertain a settlement offer from Texas Brine for his home but, speaking from his dock in the cypress forest Friday, he said it will be a hard decision to make.
“It’s real peaceful back here. You don’t hardly hear the traffic from the road. A lot of nature …you name it, we got it back here pretty much,” Pipsair said. “It’s just a shame that we’re going to have to potentially move, I guess.”