Ground water at landfills in La Puente, Pomona and seven other locations throughout the Los Angeles area is threatened by liquid waste produced when methane is extracted from decomposing garbage, state water officials say.
Samples of the liquid, called gas condensate, taken from the nine landfills all contained unacceptable levels of a variety of hazardous chemicals, according to a study conducted by the state-run Los Angeles Regional Water Quality Control Board.
The study, begun after contamination of ground water was found at several landfills in 1984, was released recently by the regional board.
At a meeting two weeks ago, the board considered ordering all the landfills, including Puente Hills landfill in La Puente and Spadra landfill in Pomona, to stop the condensate disposal within 90 days.
But several landfill operators argued that the state had overestimated the condensate problem and that more tests and more time were needed to solve the problem.
The board delayed any action until April. In the meantime, the landfill operators, including the county and city sanitation departments, have been told to devise plans to eliminate the condensate discharge.
For years, many landfills in the region--including some that no longer accept waste--have had systems in place to extract methane, which is produced when bacteria and other micro-organisms consume buried garbage.
As the waste decomposes, methane, carbon dioxide and other gases are released. If the methane is not collected, it can migrate through the ground, creating an odor and posing a risk of explosion if it collects in enclosed spaces.
Gas-extraction systems are typically a network of perforated pipes sunk into the layers of aging waste, said Steve Maguin, head of Los Angeles County's Solid Waste Management Department, which operates the 416-acre Calabasas landfill and three others on the state's list.
A vacuum pump pulls any gas accumulating in the waste into the pipes. It is then burned in flares or used to power electrical generators.
The condensate is created as a byproduct when the methane, water vapor and other gases--all warmed by chemical reactions that occur when the microbes devour the waste--cool as they are drawn into the pipes. Condensation forms in the pipes in a process similar to the misting of a window as hot air hits cool glass.
In most gas-extraction systems, the condensate trickles down the pipes to traps at low points in the pipe network. In most cases, it has been allowed to drain from the traps directly into the underlying soil.
Officials first realized that gas condensate could carry toxic chemicals into ground water in 1984, after extensive testing at landfills in West Covina, Azusa and Monterey Park disclosed that such pollution had taken place, said Raymond Delacourt, senior waste resource control engineer for the regional board.
The board ordered those landfills to stop discharging gas condensate and instead have it hauled to licensed toxic-waste dumps.
That is also when the board started the broad study of all landfills within its jurisdiction--encompassing most of Los Angeles and Ventura counties--that extracted gas and might have a condensate-disposal problem, Delacourt said.
About 30 Landfills Studied
The 30 or so landfills in the area that have gas-extraction systems were assessed, he said.
The landfills, besides Puente Hills and Spadra, that were tentatively identified as having unacceptable condensate-disposal systems are Sheldon-Arleta landfill in Sun Valley, Watson landfill in Wilmington, Calabasas landfill in Agoura, Mission Canyon landfill in Los Angeles, Santa Clara landfill in Oxnard and two landfills in Scholl Canyon, one operated by the county, the other by the city of Glendale.
The level of risk posed by the disposal of gas condensate at the landfills was determined by weighing several factors, including the amount of liquid discharged, the concentration of pollutants in the liquid and the proximity of each landfill to ground water used for drinking.
One of the most serious potential problems exists at the Sheldon-Arleta landfill, which lies near an important source of Los Angeles drinking water, Delacourt said.
The landfill is next to Los Angeles Department of Water and Power "spreading grounds," where water brought to Los Angeles in aqueducts is released and enters the soil, replenishing San Fernando Valley ground water, according to the state report.
There is evidence of a leak between the DWP facility and the landfill, according to the report, which pointed out: "Therefore, disposal of any liquid at this site may have a detrimental effect on the usable water."
Another factor that put Sheldon-Arleta on the list is the porous, gravelly composition of the soil beneath the landfill, which would allow any pollutants to migrate away from the site. The landfill was built on what was formerly a gravel pit, the report said.