Clay Used to Smother Underground Fire at Simi Valley Landfill : Emergency: Officials won’t know until Tuesday if smoldering trash has been put out or if flames have spread.

The small, smoldering fire appeared to be no bigger than the size of two tires, but that was big enough to scare up a huge response.

A team of workers at the Simi Valley Landfill off of Madera Road scrambled Thursday and Friday to cover more than an acre of the garbage dump with clay, hoping to smother the underground fire, said Dan Vidal, general manager of the landfill, which is owned and operated by Waste Management Inc., based in Illinois.

Discovered earlier this week when smoke wafted out of an inactive part of the 1,000-acre landfill, the hot spot required a massive response to prevent it from spreading underground.

Company officials said they will not know if their efforts have succeeded until they drill several test holes to determine if the fire has been extinguished or if it has spread.

“We should know for sure by Tuesday,” Vidal said.

If the fire has spread, company officials plan to inject an inert gas into the area to again try to smother it.

Terry Gilday, director of the county’s Environmental Health Division, which is monitoring the blaze, said underground fires such as the one at the landfill can be very difficult to extinguish once they begin to spread.

He said some underground landfill fires have fed for years off of methane gas, which is produced naturally by the decomposition of trash.

Calling this fire “very minor,” Gilday said there did not seem to be a risk of spread, but monitoring tests over the next several days will indicate for sure.

“It’s not a fire in the traditional sense,” Gilday said. “It’s like when you have a fire at the beach, cover it with sand, but it keeps smoldering--the kind where if you step on the area you might get burned.

“This isn’t anything unusual in this business,” he added. A similar fire at the Simi Valley dump happened once before, Gilday said, “but it was probably 10 years ago and the fire was easily put out.”

Officials said the small fire apparently started after surface soil cracked and allowed oxygen to seep underground. Because the sub-surface fill is still in the process of decomposing, it produces heat and methane gas. When mixed with oxygen, the substances can ignite, Vidal said.

“The first thing that we had to do is prevent air intrusion, which is what we’ve done, “ Vidal said. “We hope that will smoother it.”

Officials were concerned at first that the fire might be near methane extraction pumps, which are used to collect the highly combustible gas that eventually is burned off.

But Vidal said Friday that the fire is far away from pumps and any concentrations of gas.