Sinkhole swallows more trees

About 25 trees fell into the Assumption Parish sinkhole and a new crack formed Monday night in a earthen well pad south of the lake-like slurry hole, state regulators said.

Experts working for the state Office of Conservation believe the collapse and cracked well pad are linked to now-calmed seismic events from late last week, officials said in a statement Tuesday.

Because of that connection, agency officials said the discovery did not halt work around the sinkhole and the area remains in emergency officials’ lowest “alert” status.

Parish officials also estimated Tuesday that the edge collapse, or slough-in, probably bit off a quarter-acre from the formerly 13-acre sinkhole’s southeastern edge. More firm measurements are pending.

The sinkhole is located in swamps between the Bayou Corne and Grand Bayou communities and has required the continued evacuation of more than 350 people in those areas.

A failed Texas Brine Co. LLC cavern in the Napoleonville Dome is suspected of causing the sinkhole and related consequences. The cracked surface pad had been used for the original access well to the failed cavern, Oxy Geismar No. 3.

John Boudreaux, director of the parish Office of Homeland Security and Emergency Preparedness, updated other activities in the sinkhole response Tuesday:

Data gathering for a critical three-dimensional seismic survey of the subsurface under the sinkhole ended Sunday and equipment is being collected. Results are due April 21.

Crews moved in a specialized drilling rig, called a snubbing unit, on Tuesday that can handle high pressures so they can begin clearing out blockages in a key access well to the failed Texas Brine cavern.

Early on Friday, experts detected an uptick in “very long period” tremors, a type of stretched-out seismic event, that have been linked to fluid and gas movement underground.

The tremors were detected under the sinkhole and around the failed Texas Brine cavern.

Past increases in tremors sometimes have preceded slough-ins and burps by the growing sinkhole.

The state Office of Conservation statement was listed Tuesday on an Assumption Parish government blog about the sinkhole.

The edge collapse happened roughly opposite from a nearly 1-acre slough-in on the western edge of the sinkhole that followed other tremors earlier this month.

That earlier slough-in, combined with other measurement changes, had boosted the sinkhole’s area to 13 acres.

The new crack is in an out-of-use ramp connecting the well pad to the sinkhole. The crack is parallel to the sinkhole’s southern edge.

Boudreaux said the crack in the well pad ramp seem to be providing “real signs” that the ramp is likely to fall into the sinkhole soon.

At one time, the ramp, which is on the northwestern side of the well pad, had been used as an access point for operations on the sinkhole, but earlier tremors this year cracked the pad and led to fencing off that area.

Boudreaux said crews more recently have accessed the sinkhole from a spot on the east side of the pad.

Conservation officials said they were continuing to monitor the situation.