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News Releases from Region 09

U.S. EPA reaches settlements to study and mitigate indoor air and groundwater contamination in Sunnyvale, California

Contact Information: 
Soledad Calvino (

SAN FRANCISCO – The U.S. Environmental Protection Agency (EPA) announced two agreements to study indoor air quality, advance cleanup, and take action related to groundwater contamination in Sunnyvale, California.

The first settlement, with Philips Semiconductors Inc. (Philips), requires the company to study indoor air quality in commercial buildings at the Signetics site and evaluate options to speed cleanup of contaminated groundwater. The second settlement adds Advanced Micro Devices (AMD) and Northrop Grumman Systems Corporation (Northrop) as signatory parties—with Philips as the party performing the work— to assess vapor intrusion and implement mitigation measures in residential buildings adjacent to the Signetics site that are located over the groundwater contamination. The work performed under these two settlements is estimated to cost $4 million. 

The Signetics site is part of the “Triple Site,” which includes the adjacent TRW Microwave site and the Advanced Micro Devices 901/902 site. Contamination from the Triple site migrated through groundwater northwards past Highway 101. The Triple Site also includes the residential neighborhood located over this plume of contaminants that is referred to as the Offsite Operable Unit (OOU).  In 1982, volatile organic compounds, including trichloroethene (TCE), were detected in groundwater below the Triple Site.

Once released to soil and groundwater, TCE can evaporate and rise as a vapor, potentially accumulating in buildings above the groundwater plume. Health impacts from TCE exposure can include increased cancer risk from long-term exposure. Other health effects may result from short-term exposure, including liver and kidney damage, as well as heart defects in developing fetuses.

“These actions will help protect public health in this Sunnyvale neighborhood,” said EPA Pacific Southwest Regional Administrator Mike Stoker. “We will expedite the cleanup of the underlying contamination, address vapor risks, and help restore groundwater quality.”

The first agreement with Philips requires the company to study indoor air quality in four commercial buildings at the Signetics site and determine if any protective measures are needed. In addition, the agreement requires Philips to assess options for accelerating the ongoing groundwater cleanup at the Signetics site.

The second agreement with Philips, AMD and Northrop provides for the continuation of residential and school vapor intrusion assessments begun under a settlement with Philips in 2015. For the past 4 years, EPA has overseen Philips’ indoor air sampling efforts in more than 35 school buildings and 220 residences in the OOU and the installation of several school and residential mitigation systems. Under this new settlement, EPA will continue to oversee the design and construction of mitigation systems in affected buildings to prevent unacceptable levels of TCE vapors from accumulating indoors. Philips will continue to perform the work, with AMD and Northrup included as additional responsible parties. This settlement is subject to a 30-day comment period. For more information and to submit comments visit:


In 1991, EPA selected a cleanup strategy for the Triple Site that addressed contaminated soils and soil vapor and expanded the interim system of approximately 45 extraction wells to more than 100 wells that extract and treat contaminated groundwater. More recently, EPA has been overseeing efforts to assess whether vapor intrusion is occurring at the Triple Site. Vapor intrusion is the process in which vapors from contaminated groundwater migrate and accumulate in the indoor air of nearby buildings.

For more information on the Signetics site, please visit:

For more information on the Offsite Operable Unit (OOU), please visit:

For more information on the Advanced Micro Devices site, please visit:

For more information on the TRW Microwave site, please visit:

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