County sanitation officials say they have stopped a narrow plume of tainted ground water from moving off the site of the Palos Verdes Landfill, where it was unexpectedly discovered last December. State authorities say they do not know the source of the contamination.
Technicians for the county Sanitation Districts early this year began extracting the contaminated water from an ancient canyon of porous rock beneath the landfill's northwest corner along Hawthorne Boulevard.
They said they are removing 1,000 to 2,000 gallons of polluted water a day from a depth of about 40 feet. Very low levels of contamination were also found in two areas outside the landfill boundaries, but authorities say they do not present a hazard.
Engineers have also completed a 900-foot-long underground barrier to stop the movement of the northbound ground water, which state officials say may be coming from a small natural spring. Because the dam is permanent, the Sanitation District will continue extracting water from the area after the cleanup to prevent a buildup of water pressure.
Not Likely to Occur Again
Although Sanitation District engineers said the contamination is not likely to occur again, they conceded that they are perplexed by the unusually high levels of hazardous chemicals detected beneath the site.
Poisonous solvents including benzene and toluene were found in concentrations of 28,000 parts per billion and 34,000 parts per billion, respectively, according to Patti Kaye, an engineer for the Los Angeles Regional Water Quality Control Board. And vinyl chloride, a cancer-causing chemical, was detected at levels of 2,800 parts per billion, she said.
Under state health laws, benzene is not supposed to be found in drinking water, or in water that eventually finds its way to drinking water, at more than seven-tenths (.7) of a part per billion. The limit on toluene is 100 parts per billion, and the limit on vinyl chloride is 2 parts per billion.
No Threat to Drinking Water
However, Kaye said Tuesday, no drinking water sources are threatened by the chemicals.
"There's not a drinking water well within a mile radius, and the contaminants were detected before they moved off the landfill site," she said.
Kaye said the surprise discovery was the first hint of a major pollution problem beneath the landfill, whose central field was used a hazardous waste dump from 1965 until it closed in 1980.
Municipal trash was dumped on two adjoining sites which were later developed into the South Coast Botanic Gardens and Ernie Howlett Park.
Steve Maguin, an engineer for the district, said it is unlikely that the water was contaminated by leachate--hazardous garbage liquids that percolate through many landfills and are a leading cause of dump-site ground water pollution.
"For one thing, it doesn't have the right chemical attributes to be leachate," Maguin said. "For another, we have never detected leachate at this landfill. This is a relatively dry landfill."
Gas Plant May Be Source
Kaye and Carol Coy, an official of the South Coast Air Quality Management District, said it is possible that at least some of the contamination came from the GSF Energy Inc. plant that operated on the site until last year. The company recovered saleable methane gas from the landfill and disposed of its resulting liquid wastes at the site.
"(The plant's) process could have contributed, but Palos Verdes also took a lot of waste--liquid hazardous waste--before it closed, so it's anybody's guess," Kaye said. "From our standpoint the source does not have to be traced, the problem just has to be cleaned up."
Robert Collins, president of GSF Energy Inc., said his company did not add any new contaminants to the landfill, but only returned chemicals to the site that it had unavoidably removed during its methane recovery operations.
"We stripped out methane and carbon dioxide and put back whatever was left over," he said. Kaye agreed with Collins' assessment, saying the disposal practice may have concentrated landfill chemicals in a small area.
Methane Seepage Possible
The AQMD's Coy said a third remote possibility is that landfill gas--mostly methane--has seeped into the ground water, carrying certain toxic chemicals with it.
However, she said, landfill gas typically carries only tiny amounts of those chemicals, making it "extremely unlikely" that gas seepage caused the high levels found in the ground water.
Geologists have known for several years that ground water beneath the landfill constantly moves north toward the ancient canyon. Maguin said the canyon is the only area beneath the landfill that does not have an impermeable bedrock base.
The contamination was discovered in December when the county began work to construct an underground barrier to seal off the porous canyon, which had always been considered "a weak spot," Maguin said.