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The Eaton and Palisades fires had barely broken out when Waste Management offered to accept the inevitable disaster debris at its El Sobrante Landfill near Corona.

But even as the company applied Jan. 8 for an emergency waiver to accept the wildfire rubble, landfill staffers had been struggling for months to control a fiery situation of their own.

In July, El Sobrante managers informed the South Coast Air Quality Management District that a chemical reaction brewing inside the landfill was causing broiling temperatures and producing toxic sulfur pollution, according to air district records.

Waste Management sought approval to increase its tonnage capacity to take in wildfire debris anyway, which Riverside County officials granted the next day.

Riverside County officials are now requesting help from state officials for technical assistance with the situation. They acknowledge they were notified by environmental regulators about the elevated temperatures, but declined to address whether granting the waiver was appropriate.

So far, no fire debris has been taken to El Sobrante Landfill, according to the U.S. Army Corps of Engineers, the federal agency overseeing the debris cleanup. But, as of Thursday morning, the landfill remained on a list of sites that were eligible to accept this material.

Since The Times inquired about the chemical reaction at El Sobrante, state environmental regulators say they have ruled out allowing fire debris to be taken there.

“Debris from this year’s fires has not been sent to the El Sobrante landfill nor is the site under consideration for future use for this purpose,” said Nefretiri Cooley, a spokesperson for the California Environmental Protection Agency. “We are currently investigating this incident and will provide additional details as they are available.”

Waste Management executives say the chemical reaction has not interfered with daily operations at the 1,322-acre landfill. The affected area, they say, is about 3,000 feet from the section of the landfill where they had planned to dump disaster debris.

Environmental advocates, however, were irked that the landfill had even sought permission.

“I’m shocked and appalled that El Sobrante would take ash when it knows that its landfill is on fire,” said Jane Williams, executive director of California Communities Against Toxics. “You greatly increase the public health danger to the communities surrounding when landfills are being operated like this. An out-of-control landfill can emit more [toxic] benzene than an oil refinery.”

The situation at El Sobrante Landfill underscores the checkered compliance history at many Southern California landfills that are poised to receive an estimated 4.5 million tons of potentially hazardous ash, rubble and soil from the federal cleanup efforts. From excessive air pollution to insufficient inspections, state and local environmental regulators have handed down dozens of violations to these waste disposal facilities in the past year alone.

El Sobrante is the second landfill in Southern California, in recent years, to experience this type of scorching-hot chemical reaction — commonly called an underground landfill fire. Since 2022, operators of the since-closed Chiquita Canyon Landfill in Castaic struggled to contain noxious fumes and contaminated runoff caused by an underground garbage fire.

These underground dump fires cannot be easily extinguished and often take years to peter out. Although a cause has not immediately been identified, these incidents have called into question the environmental oversight of California’s landfills.

CalRecycle, the state agency that regulates landfills, declined to provide a comment.

In July, El Sobrante staff told the local air district the landfill had experienced a rise in highly flammable hydrogen gas and lung-aggravating dimethyl sulfide emissions — both telltale signs of abnormal temperatures inside the landfill.

The pollution was emanating from a two-acre “area of concern” where landfill staff had observed temperatures climbing over 200 degrees, according to Waste Management executives. Staff also reported cracks on the landfill’s surface, vapors and liquid waste seeping out. Since then, landfill workers began extracting liquid waste from the reaction area to alleviate the heat and pressure, transporting it to a waste treatment facility, according to air district records.

“South Coast AQMD continues to conduct unannounced on-site inspections at the landfill and responds to all public complaints,” said Nahal Mogharabi, a spokesperson for the air district. “This is an ongoing investigation.”

The conditions at El Sobrante Landfill mirror issues at Chiquita Canyon Landfill, where residents called in thousands of odor complaints to the local air district.

Air district inspectors found white smoke venting from cracks on the landfill’s surface and liquid waste bursting onto the surface in a geyser-like fashion. The Environmental Protection Agency said the reaction posed an “imminent” danger to public health and the environment, citing the toxic chemicals released. L.A. County officials eventually helped organize a temporary relocation program for residents who wanted to escape the stench and toxic fumes.

Waste Connections, the owner of Chiquita Canyon, closed the landfill in December and is focusing on managing the reaction area.

Federal and state environmental regulators suspected the Chiquita Canyon reaction was caused by oxygen intrusion.

Similar to oil drill sites, landfills have an extensive network of underground wells that are used to extract gases produced as buried waste decomposes. But if this system fails or overdraws these gases, these wells can introduce oxygen into the waste, speeding up waste decomposition and producing heat.

In addition to the air pollution, the extreme heat has the potential to damage the protective liner underneath the landfill that prevents liquid waste from seeping into the groundwater beneath and migrating to neighboring areas.

Recently, residents have protested outside of some Southern California landfills to oppose the decision to dispose of fire debris at local landfills, which typically only handle garbage and construction debris. They have expressed concerns about these landfills’ ability to properly dispose of potentially hazardous wildfire ash and rubble — emphasizing long-standing issues with handling municipal solid waste.

In the past year, El Sobrante Landfill has been cited several times for excessive air pollution by the local air district. In that time, Riverside County inspectors also identified violations for elevated levels of flammable methane, improper signage and failure to conduct sufficient truck inspections to ensure hazardous wastes aren’t disposed at the site.