Consol Energy spokeswoman Lynn Seay said the company was working with federal and state agencies to determine the best way get to the bulldozer at Consol's Robinson Run operation in Harrison County. Crews began dredging the pond Monday to make way for four barges to get into place to aid in the recovery, said U.S. Mine Safety and Health Administration spokeswoman Amy Louviere.

Seay said an investigation into the cause of the collapse of the 200-by-200-foot embankment will begin Tuesday, and further details of the recovery plan are expected to be released on Wednesday.

Over the weekend, the section of the embankment surrounding the holding pond where the collapse occurred was considered unstable and continued to shift, creating difficult conditions for the search. Seay had no update on the status of the embankment Monday.

"Obviously there are safety concerns we need to take into consideration,'' Seay said.

Louviere said the collapse did not pose a threat because the area that failed was inside the impoundment, not outside. Officials could not give an estimated size of the holding pond, or impoundment, which is used to contain both solid refuse and the wastewater product known as slurry.

"We believe there is no public safety threat to the community,'' she said. "The area has been carefully inspected'' by federal and state officials and the company.

In 2000, slurry burst through the bottom of an eastern Kentucky pond and sent goo 6 feet deep into yards and streams, polluting more than 100 miles of waterways.

In the most recent collapse, sonar equipment initially detected an object in the holding pond, which was 12 feet deep. Crews began draining the pond and metal rods were used to confirm the bulldozer's location Saturday. But the slurry's thickness kept divers from going into the holding pond Sunday.

Harrison County emergency services director Paul Bump called the contents of the pond "soupy'' and of "milkshake consistency.''

"It's indeed a scary situation,'' Bump told The State Journal. "It truly was a type of situation that nobody up there has ever experienced before. It certainly wasn't a typical water rescue.''

Dredging began around 1:30 p.m. on Monday to make way for four barges that would install sheet pilings and serve as a staging area for divers. The pilings are expected to segregate the area where the dozer is believed to be located so crews can siphon out the sludge and fill it with water.

The bulldozer operator's name hasn't been released. Two engineers who also tumbled into the holding pond Friday were treated at local hospitals and released.

In 2011, the Robinson Run mine won the state's top award for underground mine safety.

According to MSHA's website, the mine has reported 11 injury-related incidents since June, including a technician who suffered burns to his neck, face and arms when gas at the surface ignited while he was taking measurements.

"This company has been compliant with its requirements, conducting its weekly inspections, filing its reports,'' said state Department of Environmental Protection spokeswoman Kathy Cosco. "Generally speaking, the company's doing satisfactory in its compliance with its permits.''

Seay said full operations at the 605-employee mine are expected to resume Tuesday and "will not interfere with the impending recovery efforts.'' The mine was idle over the weekend and limited activity resumed early Monday.