Testing and treating to reduce city's toxic vapor problem
Health concerns remain for residents in areas affected by TCE vapors
Like toxic vapors coming out of the ground, health concerns about TCE are lingering in northeastern Mountain View.
In a meeting in City Hall for the MEW Superfund site's Community Advisory Board Tuesday evening, Allison Nelson of Sherland Avenue said she had been speaking with her neighbors and noticed that many of them suffer from similar health problems, including cerebral palsy and migraine headaches. She said many of her neighbors eat vegetables grown in their yards, which she is concerned might contaminated by trichloroethylene (TCE).
Nelson lives not far from the former location of numerous silicon chip manufacturing facilities that leaked the solvent from large underground tanks in the 1960s, 70s and 80s, creating the largest toxic site in Silicon Valley. Roughly bordered by Middlefield Road, Ellis Street and Whisman Road, it's known as the "MEW."
Residents' concerns were addressed by local toxic cleanup activists and Environmental Protection Agency officials on Tuesday.
Nelson was cautioned against reading too much into her neighbor's health problems and worrying about vegetables grown in the area.
"You can't infer from disease if there's a connection," said Lenny Siegel, director of the Center for Public Environmental Oversight. He added that what people are exposed to at their workplace is a big factor. "People work in different places. In any area you knock on doors, you are going to find one-third of the population gets cancer."
"TCE is not a chemical that shows up in your vegetables," Siegel said. "One of the reasons it comes up in the air is because it easily volatilizes, so it comes out of the plant, too."
The EPA calls TCE a "carcinogen by all routes of exposure," including drinking contaminated groundwater (the city's water is safe, the EPA says) or breathing its vapors. Inhalation can cause "hepatic, renal, neurological, immunological, reproductive, and developmental effects," the EPA reported in 2011 for its final health assessment of TCE.
In and around the MEW, TCE vapors rise from the contaminated soil and groundwater and enter buildings through cracks in the floor or foundation. Elevated levels of the vapors were recently found inside two homes on Evandale Avenue. EPA officials were recently surprised to find TCE in high concentrations in the groundwater on Evandale Avenue, the only street in the area that hadn't had its groundwater sampled since the plume began to be heavily studied in the mid-1980s.
The EPA found 130,000 parts per billion (ppb) of TCE in one hot spot on the 200 block of Evandale Avenue, and more recently was able to take a sample under private property north of that hot spot, where it found levels as high as high as 7,300 and 1,600 ppb near residences. The EPA's cleanup goal is 5 ppb.
Indoor air testing
The EPA says that homes on Evandale Avenue between Whisman Road and Tyrella Avenue now qualify for free indoor air testing, as do homes along the MEW on North Whisman Road. The testing is voluntary but the EPA requires a landlord's permission.
"I want to hear from anybody who says their landlord doesn't allow their property to test," Siegel said.
He added that landlords may worry that a vapor intrusion problem sounds bad to prospective tenants, but it will sound even worse if the Voice reports that a landlord is unwilling to allow indoor air testing.
Nelson's home doesn't qualify for the free air testing, but she still wants to know.
"What steps or resources do we have to get our air tested at our own expense?" Nelson said. "I need a company that will come and test my house."
The EPA hasn't been able to answer that question, but Siegel recommended a $250 kit that can be mail-ordered, placed in your house for a few days and mailed back to a lab, which sends back a report on your indoor air. He said it is not as accurate as the "Summa" canisters the EPA requires for air samples, but is readily available to the general public and able to flag the presence of several dozen different indoor air contaminants, including TCE.
Siegel said buildings actually suck the vapor inside because the pressure inside a home is lower than outside. The fix is a system that draws the vapor down away from the floor of the home and vents the vapors to the roof line.
Outdoor air safe, says EPA
EPA vapor intrusion manager Alana Lee assured residents that the outdoor air was safe, adding that the average level found from hundreds of samples was .4 micrograms per cubic meter. The EPA's indoor cleanup level is 1.0 micrograms per cubic meter. Siegel said in some places in the United States, the TCE levels are well above that level in the outdoor air. "We actually have very clean air here in Silicon Valley," Lee said.
The EPA has sampled 65 commercial buildings in the MEW and 20 of them are undergoing some kind of modification to fix vapor intrusion, Siegel said. Three were found to have elevated levels late last year that may have been unsafe for short-term exposure for pregnant women, including Google's offices at 369-379 Whisman Road and 480 Ellis Street, home to surgical equipment maker Aesculap and consultant firm Bristlecone.
The Google buildings have since been fixed and tested to show only trace amounts of TCE inside.
"The number one thing that has me concerned is notification of people in the commercial buildings," Siegel said. "I've talked to people whose buildings had been tested but weren't given the results. I talked to a pregnant woman at Google who saw the results and didn't know what the results meant. You shouldn't have to wait for the newspaper to tell you that your building is safe from vapor intrusion."
The EPA is currently putting together a "Focused Feasibility Study" (FFS) for the regional plume, which evaluates the various methods for continuing to clean up the mess. That includes continuing to pump and treat the contaminated groundwater through carbon filters. So far over 100,000 pounds of TCE have been removed this way from 5.25 billion gallons of water, which is then pumped into Stevens Creek. But that method has become less and less effective at removing the last remaining portions of the plume.
The FFS also examines the possibility of turning off the pump and treat systems, allowing the TCE to naturally degrade while being monitored, an option known as "monitored natural attenuation." But "there is a concern about what level will you allow monitored natural attenuation because of vapor intrusion issues in the plume," said EPA groundwater project manager Penny Reddy .
Other methods evaluated include underground permeable barriers that break down the TCE as the groundwater flows moves through. There are also "bioremediation" methods that involve injecting TCE-eating bacteria into the ground to break the chemical down into a harmless gas, ethene. But some of the polluters, also known as "responsible parties" say they are having hard time getting access to their former sites, and buildings stand in the way of injecting clean-up materials.
"Rather than come up with a one-size-fits-all remedy for the entire plume, they are going to evaluate new remedies building by building," Siegel said.
"At one time there was talk about doing bioremediation around the border of the plume," said Jane Horton, whose home on Whisman Road sits on the border and is being mitigated for TCE vapors.
Reddy said the responsible parties — which include Intel, Raytheon and the corporate descendant of Fairchild Semiconductor, Schlumberger Corp. — are "on board" with ways to pull the plume away from residences using "pumping and extraction." She added that "there are plans for two extraction wells on Evandale Avenue that will also reduce the hot spots there.
"Nothing happens overnight, I can tell you," Reddy said. "Reducing what's in interior core will make the most difference."
In the interior core of the plume, where readings were once as high as 1 million ppb, deep trenches were dug in the late 1980s and early 1990s to put in "slurry walls" that keep the core contamination from spreading.
Reddy said that there is concern from some that the slurry walls — which have a 30 year life span — are getting old.
For more information:
EPA Vapor Intrusion Project Manager
EPA Groundwater Project Manager
EPA Community Involvement Coordinator
Center for Public Environmental Oversight
Email Daniel DeBolt at firstname.lastname@example.org