Raytheon once ran a semiconductor manufacturing facility on a 30-acre property in Mountain View, California. The site is listed on the National Priorities List (NPL), a federal registry of the most serious contaminated locations in the country. It is also part of the larger Middlefield-Ellis-Whisman Superfund Study Area, which covers three other NPL sites nearby. The site was added to the NPL in 1986, and the final cleanup plan was selected in 1989.
The main contaminants are volatile organic compounds (VOCs), which are chemicals that evaporate easily and can move through soil and groundwater. Trichloroethene (TCE) is the primary concern and has been found in groundwater, soil gas, and soil. Other contaminants include tetrachloroethene, chloroform, vinyl chloride, 1,1,1-trichloroethane, and 1,2-dichloroethene. Groundwater also contains metals such as arsenic, cadmium, lead, and antimony. The U.S. Environmental Protection Agency (EPA) has identified 26 contaminants of concern in total across groundwater, soil gas, and soil.
Cleanup has been underway for decades. A slurry wall was built in 1987 to contain contaminated groundwater. A soil vapor extraction system ran from 1996 to 2000 and pulled about 3,000 pounds of VOCs from soil. EPA removed roughly 440 tons of contaminated soil after the facility was demolished. Groundwater extraction and treatment systems ran until 2003, when EPA switched to an oxidation system that can also treat 1,4-dioxane. As of 2023, the groundwater remedy has removed more than 20,000 pounds of VOCs. EPA also selected a vapor intrusion remedy using methods like sub-slab depressurization and indoor air monitoring to reduce TCE exposure inside buildings. Construction of the main cleanup activities finished in August 1999, but the site remains on the NPL.
A Five-Year Review completed in September 2024 found the groundwater and vapor intrusion remedy is protective of human health in the short term. However, the review also found that the current groundwater remedy will take many decades to reach cleanup goals. EPA recommended looking at alternative technologies to speed up TCE reduction, especially in shallow groundwater and soil gas. The review also flagged PFAS (per- and polyfluoroalkyl substances) concentrations above 2024 EPA limits in some groundwater extraction wells and called for more sampling. Groundwater contamination is still migrating, and cleanup goals have not been fully met across the site. Two businesses currently operate on the property, employing 52 people and generating about $8.26 million in annual sales.
Community members can contact EPA directly with questions.
