National Semiconductor Corp. ran an electronics manufacturing facility in Santa Clara, California for decades. Underground storage tanks, sumps, and pipes leaked chlorinated solvents into the soil and groundwater below the property. EPA added the site to the National Priorities List (NPL) on July 22, 1987. Texas Instruments acquired National Semiconductor in 2011 and now carries out the cleanup work. The site spans roughly 50 to 60 acres, with one source placing the property at 50 acres and another at 60 acres.
EPA has identified 43 chemical contaminants at the site. The main concern is trichloroethene (TCE), a chlorinated solvent. Other contaminants include tetrachloroethene, benzene, toluene, vinyl chloride, 1,1,1-trichloroethane, various dichloroethane isomers, phenolic compounds, xylenes, ethylbenzene, and chloroform. Most were found in both soil and groundwater. Contaminated groundwater also affects an area shared with the nearby Monolithic Memories Superfund site.
Cleanup started in 1982 with soil removal, tank removal, and the installation of a groundwater pump and treat system. Soil vapor extraction treated 13 of 14 former source areas to cleanup standards. The last area was treated using in-situ chemical oxidation after soil removal. An ozone sparging system ran from 2001 to 2009. The groundwater extraction and treatment system is still running today, and treated water is discharged to Calabasas Creek under a permit. A feasibility study for the remaining operable unit is expected to begin between June and August 2026.
EPA's 2023 Five-Year Review found the remedy currently protects human health and the environment because exposure pathways that could cause unacceptable risks are being controlled. Institutional controls restrict land use and groundwater use as a drinking water source. However, the review also notes that there is insufficient data to confirm all exposure pathways are fully controlled, so vapor intrusion assessments continue in buildings over the contaminated plume. Buildings that showed unacceptable vapor intrusion have had mitigation systems installed. The site has not been deleted from the NPL. The next five-year review is estimated between September and November 2028.
As of December 2024, thirteen businesses operate on the property, employing 1,739 people and generating about 881 million dollars in annual sales. About 15 acres were sold in 2014 for office and commercial use. Community members with questions can contact the EPA Remedial Project Manager. For state-related questions, contact the California Regional Water Quality Control Board, San Francisco Bay Region.
