Mountain View Voice

Opinion - May 27, 2011

Living with toxic TCE vapors

Despite working and living over a huge underground stream that contains large concentrations of the dangerous chemical TCE, many Mountain View companies and a small number of residents have learned to live with the danger that has been present for more than 30 years.

The contaminated groundwater was left behind by several of the city's earliest high-tech companies and continues to percolate through the soil under the northeastern section of the city known as the MEW, which is bordered by Middlefield Road, Ellis Street and Whisman Road.

The TCE was unleashed when underground tanks at Fairchild Semiconducter, Raytheon and Intel leaked solvent into the ground and since 1981 has been tracked by the Environmental Protection Agency. The chemical migrated north of the MEW area to parts of Moffett Field and is now a mile and a half long and 2,000 feet wide.

But despite the presence of TCE and the EPA's conclusion that very high concentrations of Volatile Organic Compounds (VOCs) are present, Google announced last week that it was leasing the Ellis Street office complex known as "The Quad," the site of the Fairchild buildings where the TCE leak was first discovered. The Fairchild Superfund site is said to contain the largest concentration of toxic chemicals in the plume but the vapors given off have to be kept out of the buildings with the careful use of HVAC systems.

Over the years, efforts to reduce the impact of TCE have proved modestly successful, but experts say it could take much more time to clear the substance from the underground aquifers where it is entrenched. The United States Navy, as well as Fairchild, Raytheon and Intel, have used "pump and treat" systems to clean up a majority of the toxics, but are seeing those methods losing effectiveness — they are not expected to reduce contamination levels much in the next 10 years.

The EPA, however, is continuing to study new methods of reducing TCE from the aquifer. In a recent report to the Moffett Field Restoration Advisory Board, EPA official Penny Ready said the ideas include injecting microbes into the ground that change TCE into gases that will not harm the atmosphere.

Lenny Siegel, the city's expert on Superfund sites and director of the Center for Public Environmental Oversight, supports the EPA's pursuit of alternatives ways to clean up TCE. He called it "a national model of how you go back to a site where 'pump and treat' has lost its effectiveness."

Another EPA decision will allow MEW-area property owners to retrofit buildings with what are called sub-slab depressurization systems, which will save owners the cost of operating HVAC systems at all hours, Siegel said. Although expensive — an estimated $200,000 for a 20,000 square foot building — sub-slabs could help reduce the impact of the toxic plume.

A test using microbes conducted near the Moffett Field Museum shows that when microbes were injected into the upper plume, TCE within a four-foot radius was eliminated. Siegel called the test a positive result, but said such a method would be difficult in a larger area.

These tests and others that are sure to come are encouraging and show that there are ways to live safely over a large TCE plume, even if the chemical cannot be eliminated. Google's willingness to lease space at the site of the original TCE spill is proof that tenants today are confident that they and their employees can live and work safely in the area despite the presence of TCE vapors escaping from the ground below.

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