EPA to host meeting on MV's largest toxic plume


On Monday evening, Aug. 11, the Environmental Protection Agency will host a meeting at City Hall about ongoing efforts to clean up the toxics left behind by early computer chips makers in northeastern Mountain View.

The purpose of the meeting is to allow public comment on a five-year review of efforts to cleanup the large underground plume of trichloroethene (TCE) in the area bordered by Middlefield, Ellis and Whisman roads (known as the MEW).

TCE is a carcinogenic solvent 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 with 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.

The EPA has tested for vapors in all of the buildings over the MEW area and reports that all of them have clean indoor air. Some had to be mitigated with special ventilation systems to remove TCE vapors, including several Google office buildings and two homes nearby on Evandale Avenue atop two "hot spots" -– small but highly concentrated deposits of TCE, which were unexpectedly found on Evandale Avenue in 2012, just outside the plume boundary on Whisman Road.

The EPA has since sampled over 140 homes in the area for TCE vapors. 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 August 7 Moffett Field Restoration Advisory Board meeting.

"Manhole vapor sampling only tells us what is currently occurring, it does tell us what occurred in the past," Lee said.

Lee revealed Tuesday that the EPA has also found that ground water 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, referring to storm drains and sewer lines that may have once carried toxics from Intel and Raytheon through the area, at a meeting for the Moffett Field Restoration Advisory Board on Aug. 8.

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

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. "We're looking for some alternatives to treat that (TCE contamination) rather than rolling along pumping and treating."

The meeting will be held from 7 p.m. to 9 p.m. in the Plaza conference room in the second floor of City Hall at 500 Castro St. EPA is seeking comments on the five year review until Aug. 26.


Like this comment
Posted by Did anyone attend?
a resident of The Crossings
on Aug 12, 2014 at 8:47 am

I saw this story too late to attend the meeting. What new information came out?

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