Monolithic Memories

Overview

Monolithic Memories is a 20-acre former semiconductor manufacturing facility in Sunnyvale, California. The plant operated from 1970 to 1989, during which underground chemical storage tanks and acid neutralization systems leaked volatile organic compounds into soil and groundwater. EPA added the site to the National Priorities List in July 1987. Advanced Micro Devices, Inc. is the responsible party, and the California Regional Water Quality Control Board leads day-to-day oversight.

Contaminants include 43 chemicals of concern found in soil, groundwater, or both. These include volatile organic compounds such as benzene, toluene, trichloroethene, and tetrachloroethylene (also called perchloroethylene or PCE), along with chlorinated solvents, phenolic compounds, and polycyclic aromatic hydrocarbons. Contamination from this site is believed to have reached a shared groundwater area with the nearby National Semiconductor Superfund site. Chemicals from that upgradient source, including trichloroethylene and cis-1,2-dichloroethylene, have also been detected on site.

Cleanup began in 1984 with excavation of impacted soils. A groundwater extraction and treatment system ran from 1986 to 2005, and soil vapor extraction operated from 1993 to 1997. A separate PCE spill discovered in 2005 on property owned by TWC Storage LLC led to excavation of about 2,000 cubic yards of contaminated soil and installation of additional extraction and treatment systems. Vapor intrusion detected in an on-site building was mitigated, and follow-up sampling confirmed no unacceptable risk remains. A passive sub-slab vapor mitigation system continues to operate at the on-site fitness center.

Physical construction of all cleanup remedies is complete. VOC concentrations in groundwater are at or approaching cleanup levels. The most recent five-year review, completed September 6, 2023, found the remedy protective of human health and the environment. Human exposure and groundwater migration are both under control. Institutional controls restrict groundwater use as a drinking water source. A combined Remedial Investigation and Feasibility Study is estimated to start between June and August 2026, and the next five-year review is expected between September and November 2028.

The site has returned to active use. AMD donated the two main buildings to a local charity in 2005, those buildings were demolished, and a sports club and fitness center opened in 2014. A third building now houses Resource Area for Teaching, a non-profit serving educators. As of December 2024, three on-site businesses employed 38 people. Community members wanting to follow site progress can contact the EPA Remedial Project Manager. For state-related questions, contact the California Regional Water Quality Control Board.