Previously there had been some speculation that the hot spots discovered late last year — which are not connected to the nearby 1.5-mile long trichloroethylene (TCE) plume left by semiconductor manufacturers — had been caused by "midnight dumping" on the top soil. But there is no evidence of the TCE, used as an industrial solvent, having been dumped on the site: it was all found more than 10 feet underground.
This could prove what longtime toxic cleanup watchdog Lenny Siegel believes to have been the result of dumping by Fairchild Semiconductor and other polluters now responsible for the massive MEW Superfund site roughly bordered by Whisman Road, Ellis Avenue and Middlefield Road. In the late 1970s, local newspapers ran stories about the spills into storm and sewer lines, which were traced to Fairchild, and once killed 100 fish in Stevens Creek.
"It does not appear to be surface release, so it appears to be coming down the sewer," EPA official Alana Lee told over 100 residents in the city's Adobe building on the evening of Nov. 12. "We don't believe there is a continuing release into the sewer lines at this time. No one in this area is currently using TCE."
The EPA has tested over 95 homes in the Leong Drive and Evandale Avenue area for evidence of airborne TCE "vapor intrusion," which can cause cancer, birth defects and other health problems. Six homes have been found with toxic TCE vapors — all on Evandale Avenue, EPA officials said.
Two home have had levels high enough for the EPA to have to special ventilation systems installed to draw the vapors out from under the home and vent them to the roof-line, Lee said. Both homes are located near the Evandale Avenue hot spot a stone's throw from Whisman Road, on the north side of the street. With the ventilation systems installed, they now have clean air samples. The highest level found in the homes was 18 micrograms of TCE vapor per cubic meter of air.
Trace amounts have been found in four other homes below the EPA's indoor cleanup threshold of 1 micro gram per cubic meter of air.
Four hot spots
The largest hotspot of groundwater pollution, on Evandale Avenue, had shockingly high concentrations — 130,000 parts per billion — higher than anything currently found in the area. For context, the EPA's drinking water cleanup goal is 5 parts per billion.
Appearing to follow the trace of storm drains and sewer lines, there are a total of four "hot spots" — a second site on Evandale Avenue with 4,000 parts per billion, one on the city's vacant "Moffett Gateway" site on the western side of Moffett Boulevard, with 440 parts per billion, and one on Leong Drive that was re-sampled in September to find a surprisingly high 110,000 parts per billion of TCE contamination.
Despite the high levels recently found on Leong Drive, the EPA has found only trace amounts of TCE vapors in a hotel above the Leong Drive hot spot.
The responsible parties, including Fairchild descendant Schlumberge Corp., have not taken legal responsibility of the hot spots, but have agreed to clean up the pollution under Evandale Avenue and install special ventilation systems on Evandale Avenue homes that are found with toxic vapors inside.
What level is safe?
Lee said trace amounts of TCE vapors have been found in other homes, below the EPA's indoor cleanup threshold of 1 micro gram per cubic meter of air — not high enough to be a concern, an EPA official said.
"Concern to who?" asked resident Brian David. He said he was one of the residents who had lower levels of TCE vapors in his home. He was concerned about the effects on his health.
"If you are concerned, it is reasonable for you to ask for mitigation if you've got detectable levels," Siegel said. "It is worth requesting it."
EPA toxicologist Gerry Hiatt indicated that the EPA even considers low amounts of TCE vapor a cancer risk, noting that the EPA's 2011 toxicological assessment of TCE lowered cancer risk thresholds from 1.2 micrograms per cubic meter in indoor air of homes to 0.4.
Hiatt said that people generally have a 40 percent chance of getting cancer, and the EPA's action levels were designed to "create exposures" that would have a one in a million chance of causing cancer over decades over exposure, though pregnant women are at risk from only weeks of TCE vapor exposure.
"These numbers are set to protect the most vulnerable people," Siegel said. "Don't panic if you are exposed, but we want you to be protected."
Cleanup of the Evandale Avenue hot spots would begin in February, EPA official Penny Reddy said. A chemical oxidant will be injected into the ground to convert the TCE into carbon dioxide, cleaning up the sites relatively quickly if all of the TCE can be reached.
For more information, or to request indoor air testing on Evandale Avenue or Leong Drive, visit epa.gov/region09/mew or use the contacts below:
EPA Vapor Intrusion Project Manager
EPA Groundwater Project Manager
EPA Community Involvement Coordinator
Center for Public Environmental Oversight