Mountain View Voice

Opinion - October 18, 2013

Builders should use caution on toxic sites

The Environmental Protection Agency and the city of Mountain View, as well as Navy and NASA officials at Moffett Field, have known about the danger of the toxic chemical TCE (trichloroethylene) since 1981 or before. As far back as the 1960s electronics companies were using TCE-laced solvents in many sectors of the workplace, including sites located between Whisman Road, Middlefield Road and Ellis Street just south of Highway 101, an area now known as the MEW Superfund site.

Earlier this year the Voice published an EPA map showing TCE discovered under Evandale and Devonshire avenues, an area of single- and multi-family homes. Exactly how it got there is still unclear.

The problem is that in these areas and others where TCE has been found, residents and tenants often do not know the extent or toxicity of what is buried in the ground under their homes or workplaces.

And that is the hardest part in dealing with TCE, which moves surreptitiously through the water table 10 to 20 feet below the surface. As these flows migrate, toxic vapors are released that can seep into homes and commercial buildings unless preventive measures are taken. The other problem is that TCE flows below the surface can range from extremely light concentrations to extremely dangerous levels that produce vapors not safe for humans to breathe.

In many locations inside the MEW area and elsewhere, homes and offices have been built over vapor barriers that stop the fumes from entering the buildings. But in numerous cases, the fumes have been measured in buildings at highly toxic levels. In one set of Google buildings at 369 and 379 N. Whisman Road, officials were concerned that pregnant women could have been subjected to vapor concentrations over the legal limit. If the women worked in sections of the building with high concentrations of TCE over a period of time, it could subject their fetuses to birth defects.

Our concern is that the history of this dangerous chemical could be forgotten when officials consider residential development of a 10-acre site at Mora Drive, which is about a mile away from the MEW. Back in the 1960s the electronic component manufacturer Plessey Micro Science left behind a plume of TCE at the site, where Lenar Homes proposes to start construction of up to 250 homes in 2015. Lenar spokesman Douglas Rich says his company has developed homes on military bases and has a lot of "expertise with environmental contamination."

But there are fears that a source of contamination could remain under the commercial buildings on the site, which are now occupied by small business tenants. It appears many of these workers had no idea about the TCE plume under their feet. And although a "soil vapor extraction system that Plessey operated for a number of years was intended to reduce the impact of TCE," the concentrations were recently found to be higher than the limits for plumes under residential buildings, according to reports from the Department of Toxic Substances Control.

Other recent discoveries of TCE outside what had long been thought of as a reasonably firm boundary of the MEW area has shown that perhaps TCE can travel along conduits or sewer lines, and in buildings can come up through wiring or plumbing channels.

So far, the best way to ameliorate the impact of TCE underground has been to place impenetrable barriers in a building's foundation. Ventilation systems also have been successful to some degree. But the discovery of TCE west of the MEW is worrisome. And no one knows for sure how it got there. But regardless of how it traveled, all agencies that oversee housing and commercial construction in these areas should be extremely careful before approving more projects anywhere near a TCE concentration. And for occupants in buildings where TCE has been found, full transparency is essential, so these residents and workers know what risk they are facing. TCE is a well-known carcinogen that can easily be detected with the right equipment. No one should have to breathe toxic TCE fumes in their home or workplace, especially pregnant women.

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