Residents living near a sinkhole in a southern Louisiana bayou are not expected to be allowed to return home for at least another month, officials said Friday.

Authorities are investigating the cause of the slurry-filled hole, which is roughly the size of a football field.

Specifically, they are looking into whether a nearby salt cavern could be to blame and have ordered the company that is responsible for that cavern to drill a relief well.

The process is expected to take up to 40 days, said Assumption Parish President Martin Triche. Until the well is drilled, authorities do not anticipate lifting the evacuation order that affects approximately 150 homes.

"We won't feel a level of confidence to lift the evacuation until we have more answers from that well," Triche told reporters.

Roughly half of the residents told to leave heeded the call, he said.

Louisiana officials have reached out to Texas Brine Company, urging it to provide affected residents with some type of assistance while it investigates whether a breach in its cavern might have caused the sinkhole 100 yards away.

The situation is made all the worrisome because the hole is believed to be close to a well containing 1.5 million barrels of liquid butane, a highly volatile liquid that turns into a highly flammable vapor upon release. A breach of that well, Assumption Parish Sheriff Mike Waguespack has said, could be catastrophic.

Texas Brine has until Monday to submit a permit to drill the well or face a $5,000 per day fine, said Stephen Chustz with the Louisiana Department of Natural Resources.

The purpose of the well is to determine the structural status of the cavern as well as the pressure of any gas that might be inside of it, he said, adding that the last mechanical integrity test performed on the cavern was done in late 2010.