Teledyne Semiconductor operated a semiconductor manufacturing facility on a 1-acre site in Mountain View, California starting in 1962. Solvent releases from an underground storage tank contaminated soil and groundwater, and the plume traveled roughly one mile north and northwest, affecting about 50 private domestic wells. The site sits in a densely populated area with around 189,000 people within a 3-mile radius. EPA placed the site on the National Priorities List (NPL) in 1987, and cleanup has been underway for more than 30 years. The site has not yet been deleted from the NPL.
The main contaminants are chlorinated solvents and their breakdown products, including trichloroethene (TCE), tetrachloroethene, 1,1,1-trichloroethane, 1,1-dichloroethane, vinyl chloride, and various dichloroethene compounds. Toluene and chlorobenzenes have also been detected in groundwater. Several of these compounds are present in soil and groundwater, and some have been linked to vapor intrusion, meaning contaminated vapors can move up from the ground and enter buildings. Cleanup is organized into two operable units: one covering soil and groundwater, and one focused specifically on vapor intrusion.
Groundwater extraction and soil vapor extraction ran for decades, removing thousands of pounds of volatile organic compounds (VOCs). In September 2023, EPA issued a Record of Decision Amendment shifting the groundwater approach to anaerobic bioremediation, which injects a substrate into the ground to help naturally occurring microorganisms break down contaminants. That method is combined with soil vapor extraction, monitored natural attenuation, and institutional controls that restrict well use and limit development. A separate 2020 Record of Decision addressed vapor intrusion using sub-slab depressurization, vapor barriers, ventilation enhancements, and indoor air monitoring. Free indoor air testing was conducted in homes and businesses over the contaminated plume.
The September 2024 Five-Year Review found the soil and groundwater remedy is short-term protective. The vapor intrusion remedy will be protective once fully implemented. The review called for additional residential indoor air sampling, long-term monitoring plans, commercial vapor intrusion sampling with HVAC systems off, and assessment of contamination moving through sanitary sewers. The Regional Water Board also directed the responsible party to prepare a sampling plan for PFAS, a class of emerging contaminants, to determine whether they are present in groundwater. Drinking water for Mountain View residents is not affected. The city draws from sources including the Hetch Hetchy Reservoir and tests the supply to meet all state and federal standards. The site building currently supports light industrial and commercial uses, with one business employing 671 people on site as of December 2024.
Community members can contact EPA's Community Involvement Coordinator, David Yogi, with questions or concerns. Site records are available at the San Francisco Bay Water Quality Control Board office in Oakland and at the EPA Superfund Records Center in San Francisco, both open Monday through Friday, 8 a.m. to 5 p.m.
