Lots left to do in massive toxic cleanup

EPA seeks comments on five years' of efforts to treat TCE contamination

A watchdog group on Monday evening offered ways to improve the Environmental Protection Agency's efforts to clean up and monitor the toxics left behind by early computer chips makers in northeastern Mountain View.

The EPA has released a draft five-year review of efforts to manage and clean up the portion of the area's 1.5 mile-long underground plume of toxic trichloroethylene (TCE) bordered by Middlefield, Ellis and Whisman roads (a collection of Superfund sites known as the MEW), spurring a meeting at City Hall seeking public comments Monday night.

TCE is a carcinogenic cleaning solvent, once heavily used by early chip makers, that was dumped and/or leaked into the groundwater in large quantities. Over 100,000 pounds of TCE has been removed from the ground in the MEW, once home to plants run by Intel, Fairchild, Raytheon and others.

According to the EPA, "the purpose of the five-year review is to evaluate the performance of the cleanup actions and to determine whether the groundwater and vapor intrusion remedy is protective of human health and the environment."

Of particular concern is the potential for vapor intrusion into buildings, as pregnant women are at risk of having babies with birth defects after only a few weeks' exposure to TCE vapors, and people are at risk of cancer and other health problems from years of exposure, the EPA says.

At the meeting Monday, Peter Strauss and Lenny Siegel of the Center for Public Environmental Oversight said notices should be placed on buildings above the plume to let people know if they could potentially be exposed, as a group of Google employees were for a few weeks in late 2012, when the ventilation systems at 369 and 379 Whisman Road stopped working properly.

"We have been recommending for a long time there be notices at entrances" to buildings, Strauss said, adding that the notice should include a way for people to access more detailed information. "It shouldn't be frightening to people, just put it in a way that people are made aware."

The EPA has tested for vapors in all of the commercial buildings over the MEW area and reports that all of them have clean indoor air. People working in those buildings, including several Google office buildings, rely on special ventilation systems to keep TCE vapors out.

Siegel and Strauss asked the EPA to begin requiring new technology to "move towards continuous monitoring" of indoor TCE vapor levels in buildings over the plume. The current practice is to take air samples over a 24-hour period, a few times a year.

Traditional indoor air sampling "may not catch peaks that may present a risk," Siegel said, pointing to a study done in Utah that showed wide swings in TCE vapor concentrations inside a building. He added that the EPA's monitoring plan "doesn't account for the temporal variability in vapor intrusion, although their new directive says it should account for variability."

"Companies and labs are developing small devices that could be employed like smoke detectors," said Siegel, which could tell whether TCE vapors are exceeding safety limits for women. "We want to catch these peaks when there's exposure to a woman who is pregnant and might not know she is pregnant."

The EPA has sampled over 140 homes in the area for TCE vapors, and so far only three had unsafe levels. Two homes had elevated TCE vapors inside nearby on Evandale Avenue atop two "hot spots" small but highly concentrated deposits of TCE that were unexpectedly found on Evandale Avenue in 2012, just outside the plume boundary on Whisman Road. The EPA is investigating what appears to have been the cause: a leaky sewer line that once carried toxics away from the computer chip factories down Evandale Avenue throughout the 1950s and early 1960s.

The EPA has been hunting for "hot spots" of TCE along sewer lines in the area by sampling air vapors in manhole covers. Over 200 such samples have been taken and so far no new hot spots have been found, said EPA project manager Alana Lee at the Aug. 7 Moffett Field Restoration Advisory Board meeting.

"Manhole vapor sampling only tells us what is currently occurring, it does not tell us what occurred in the past," Lee said.

Lee revealed that the EPA has also found that groundwater contaminated with TCE is finding its way into the area's sewer lines, which did not appear to be major concern, as it would presumably be treated at the waste water plant in Palo Alto where the lines run. The EPA has often permitted some toxic sites to be cleaned up by pumping contaminated groundwater into sewer lines, Lee said.

The EPA is now being called on to investigate sewer lines and storm drains to the south of the Wagon Wheel neighborhood, such as those lines that run by the Silva well on Sherland Avenue where high levels of TCE were once found (and since been cleaned up). No explanation has ever been made for why TCE was found there, says Lenny Siegel, director of Mountain View's Center for Public Environmental Oversight.

"People at the German school wanted me to reassure them they didn't have a hot spot and I couldn't," said Siegel at a meeting for the Moffett Field Restoration Advisory Board on Aug. 8, referring to storm drains and sewer lines that may have once carried toxics from Intel and Raytheon through the area by the German International School of Silicon Valley.

In response, Lee said that one groundwater sample was taken on the north end of the campus of the German International School of Silicon Valley, located on Easy Street, and no TCE was found. The sample was taken in the parking lot of the school.

Another concern is leakage of the "slurry walls" that provide deep underground containment of the TCE within the MEW site. Most of the TCE there has been removed by filtering groundwater in through "pump and treat" systems, which continue to operate, making very slow progress in removing the last small portions of TCE.

"There seems to be some flow out of the slurry walls," Lee said at the RAB meeting. "We're looking for some alternatives to treat that (TCE contamination) rather than rolling along pumping and treating." On Monday EPA officials added that three of the four major MEW slurry walls were leaking, including those along Middlefield Road and Whsiman Road, the plume's boundary with the residential area next door.

"I suspect that it's cracking there's all sort of problems with it," Strauss said of the network of clay and cement slurry walls, which reach 40 to 100 feet deep into the ground to contain the MEW portions of the plume. He suggested replacing some of the walls with a "funneling gate permeable barrier" made of zerovalent iron which passively works to degrade TCE contaminants as it passes through the wall.

Polluters and regulators have been at odds over whether certain areas can be left to "monitored natural attenuation." That means allowing naturally occurring bacteria to break down the TCE and finish the cleanup process. There is also concern about whether enough areas are proposed for new "in-situ" remedies where materials are injected into the ground to help degrade the TCE, as is being done with success to clean up the hot spots on Evandale Avenue.

EPA is seeking comments on the five year review until Aug. 26. It can be found at


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