Mysterious plumes of smoke are rising from the Frank R. Bowerman landfill in Irvine, its operators said Thursday, prompting some nearby residents to call the fire department.

But while there is some danger that the plumes — 15 to 20 so far — could trigger a brush fire, there is so far no threat to the public, said spokeswoman Julie Chay of OC Waste & Recycling.

“We’re monitoring it very carefully, because we don’t want anything above the surface to combust,” Chay said. Firefighters also have been alerted and are ready if fire breaks out.

“It’s normal, and it’s natural, but rare,” Chay said.

The plumes appear to be a combination of smoke from underground combustion along with some water vapor and other gases, she said. But just what is causing it is unknown. An investigator from the U.S. Geological Survey will visit the landfill Tuesday to try to assess the situation, she said.

The smoke comes from “heat vents,”  and similar phenomena have been reported in other natural areas in California in the past, including in the Dick Smith Wilderness northeast of Santa Barbara in 2004.

The vents have opened on a part of the landfill property that remains in a natural state. While it could be used for landfill waste in the future, it remains undisturbed, with native vegetation growing above.

The venting is not related to burning of any landfill trash, or to any landfill operations, Chay said.

Gases detected in the plumes by consultants include hydrogen sulfide, which can be hazardous to workers in the immediate area of the plumes. Protective equipment is needed for those working around the plumes,  Chay said, but the gases dissipate quickly and do not migrate out of the area.

Other gases were similar to those found in the atmosphere, with 78 percent nitrogen and 22 percent oxygen, said Eric Smalstig, a senior engineer at Geosyntec in Huntington Beach.

Temperatures in the plumes have hit at least 1,000 Fahrenheit, he said.

The material burning underground appears to be shale that is part of an old landslide, Smalstig said.

“The heat source is a mineral source, subsurface,” he said. “As a result, water is heating up the shale.” He and other experts are still trying to determine exactly what the mineral heat source is.

Robert Mariner, a hydrologist with the U.S. Geological Survey who will investigate the vents next week, also examined similar vents in the Dick Smith Wilderness in 2004. He said in that case, the source was likely pyrite broken up in a landslide.

The pyrite “oxidizes, and when it does, it heats up,” Mariner said. “It heats up enough to ignite any natural organic material in the slide.”

It was hot enough to ignite a grass fire, quickly put out by the Forest Service, he said.

Pyrite might be the source of the heat beneath the Bowerman site, he said, although that will have to be investigated. 

 The smoke was first noticed weeks ago; see previous Register story.

(Photos of smoking vents courtesy O.C. Waste & Recycling. Register graphic by Brian Moore.)

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