Worker Feared Buried Alive at Garbage Dump : Search: More than 150 rescue workers unsuccessfully search for the man believed to have been accidentally buried under truckloads of garbage.

Using specially trained dogs, sonar devices and their hands, searchers continued an extensive hunt late Thursday for signs of a disposal company worker who was believed to have been accidentally buried in debris at the San Marcos landfill.

U.S. Navy officials with sonar equipment were among the more than 150 searchers at the scene, authorities said.

The worker, part of a two-man team operating a garbage truck, was last seen about 10 a.m. as he stood behind the vehicle while it was being positioned to dump its load, authorities said,

The incident triggered a massive, daylong search of the huge landfill, where scores of law enforcement officers, firefighters, disposal company employees, forestry workers and others painstakingly combed the trash by hand, removing debris bit by bit, alert for any signs of life.

Los Angeles County sheriff’s authorities flew down a special sonar detecting device, and the California Highway Patrol provided a specially trained search dog.

The missing man, Guillermo Ceseno, 25, an immigrant from Mexico, is an employee of Escondido Disposal Inc., said Larry van Dusen, a spokesman for the Sheriff’s Department. His wife was in Ensenada, Mexico, when the accident occurred, Van Dusen said.

Ceseno’s partner, the driver, was identified as Luis Romero, also an employee of Escondido Disposal, the sheriff’s spokesman said.

Ceseno was last seen shortly after 10 a.m., Van Dusen said, when the driver spotted him behind the truck, about 6 feet to one side. Ceseno was helping to guide the truck, then filled with trash, into the disposal zone before dropping its load. Ceseno’s position was customary, Van Dusen said.

It was unclear late Thursday whether Ceseno fell into the huge pile of debris, or whether he was inadvertently inundated by trash from the truck being operated by his partner.

The driver dumped his load of trash at the base of the pile and pulled off to the side, about 100 yards away, where he washed the vehicle for about 25 minutes, Van Dusen said.

After completing the cleanup, the driver became suspicious about Ceseno’s absence and notified authorities, Van Dusen said. Ceseno normally did not participate in washing the truck, so his absence did not at first attract attention, the Sheriff’s Department spokesman noted.

“The driver just assumed he (Ceseno) was off duty,” Van Dusen said. “He assumed he was talking to other workers.”

During that 25 minutes, however, 20 to 30 more vehicles deposited their loads in the same area, which was also regularly driven over by compacting bulldozers, Van Dusen said. Dumping and compacting operations were shut down as soon as it became apparent that Ceseno was missing, Van Dusen said.

During the search, there was considerable uncertainty about whether Ceseno had indeed been covered by the debris. But authorities operated under the assumption that he had become trapped in the mountain of waste.

“He was last seen at the rear of the truck, and there was no indication that he left the area, so we’re reasonably sure he’s here,” Van Dusen said as the search continued.

The area was illuminated by high-powered lights as the search continued. Authorities planned to maintain the effort until at least 10 p.m. Thursday, about 12 hours after Ceseno was last seen.