The Sunnyvale Sun

News

Agencies recommend vapor monitoring for waste sites

By Hugh Biggar

Cleanup efforts are progressing at two toxic waste sites in the North Vallco neighborhood on the Cupertino/Sunnyvale border, but, with the area up for redevelopment, authorities recommend further precautions.

The two sites at 10900 N. Tantau Ave. and 19000 Homestead Road are being treated to remove toxic waste, and have been since the 1980s.

The contaminants, generated by former computer chip manufacturers, are present in a shallow groundwater plume extending from the sites north to Inverness Way in Sunnyvale, slightly west of the sites and just south of Forge Drive.

Cupertino hopes to redevelop the area surrounding the sites. The neighborhood is primarily industrial, and the city is holding talks on redevelopment possibilities, including housing. Apple also plans to build a campus on 50 acres in North Vallco.

While authorities say the contaminants no longer affect drinking water, they also say continued monitoring of vapors--particularly from one of the contaminants, trichloroethlyne, or TCE--is necessary.

"The concentrations could change and is something we monitor every two years," Roger Papler, a geologist for San Francisco Bay Regional Water Quality Control Board, said.

Water board staff said soil samplings now show that concentrations in the shallow ground water do not exceed levels that would require indoor screening for Sunnyvale residences above the plume.

Even so, others suggest proactive screenings for vapors would be a good idea.

"If you are planning to build 100-200 feet horizontally from the plume, then there is an issue," Lenny Siegel, director of the Mountain View-based Center for Public Environmental Oversight, said. "The drinking water is basically protected. The key question is vapor intrusion into the air [from TCE]."

The water board, in its September 2005 report on the Cupertino sites, also said, "Vapor intrusion pathway is an emerging issue, for which the science continues to evolve."

In Cupertino, the affected sites formerly belonged to Intersil and Siemens Components. The companies used TCE, a nonflammable colorless liquid, as a degreaser in manufacturing semi-conductors. The chemical was then stored in underground tanks, which either leaked or spilled.

The Environmental Protection Agency designated both sites as national priorities for cleanup, or Superfund sites, after toxic waste was found in the early 1980s. Since that time, the water board has overseen removal of the contaminants.

Last July, the National Research Council published a report stating TCE is believed more hazardous than previously thought.

For now, Siegel and others stress the importance of ensuring the safety of the sites on the Cupertino/Sunnyvale border ahead of any development.

The next scheduled five-year review of the Cupertino/Sunnyvale Superfund sites is September 2010.