MARIETTA, Ga. -- A giant sinkhole that opened up in a Marietta neighborhood Monday night is finally being filled.

It couldn't happen fast enough for the family whose $300,000 home is just a few feet from slipping into the massive hole.

Marietta City officials released the results Wednesday on tests they took of a massive sinkhole. Officials are still not completely sure, but they said an old mine exploration shaft is likely the cause of the 25 foot deep hole.

The work to fill the hole started just after sunrise Thursday as 8 dump trucks moved in and load by load carried in 180 loads.

The hard part was getting the whole dug out. Now that they have the debris out, they'll have to fill it back in.

CBS Atlanta asked contractor Wayne Marcinkeo how he knew the sinkhole is not going to keep forming?

“Well gosh, I guess there's no way of knowing for sure. There are too many unknowns there,” said Marcinkeo.

On top of all this, the homeowner doesn't know if insurance will cover this.

Her neighbors like Eric Lee, are already calling their agents.

“Sinkholes aren't covered so I'm going to get a rider on my insurance and see if that works,” said Lee.

If insurance doesn’t cover the sinkhole, it's going to be a big bill for the homeowner to pay.

“We’ve got 8 trucks running right now and that adds up and the product you've got to buy,” said Marcinkeo.

One neighbor told CBS Atlanta News he and his brother used to explore mines in the area when they were young.

The mining explanation makes sense to Georgia State University Geo-science Professor Dr. Daniel Deocampo.

“Anytime you’re mining, you’re of course removing material from the ground and that can create a void,” said Deocampo.

Deocampo said a sinkhole in the neighborhood could only be caused by one of two things: an old mine shaft or soil erosion from too much water.

“It’s a different type of rock in Marietta. They’re not limestone like the types of rock water can dissolve. Here we’re probably looking at something that’s a physical mechanism. Either people physically removed it or water [is] physically eroding it,” said Deocampo.

Mike Bulch is just one house away from the sinkhole. He has a sinking feeling his home could be next. There’s a deep ditch in his front lawn leading to the site of the hole he said could be part of a tunnel.

“[The hole] is enormous; it really is, and it occurred so fast; that’s what’s scary about it,” said Bulch. “Lisa Thompson, my neighbor stepped out and actually saw the tree going into the ground when it occurred. “

The Marietta Public Works Department said there is no danger to underground power or water lines.