Site Name: MicroStorage Corporation (MSC)
Address: 2986 Oakmead Village Court (MSC),
EPA ID: CAD092212497
EPA Region: 9
Media: Ground water
Contaminants: volatile organic compounds (VOCs),
primarily trichloroethene (TCE), 1,1,1-trichloroethane (TCA),
History of Contamination
There were two separate sources of contamination on the MSC/IM site (Figure 1): a chemical storage area on the MSC site was the primary source and an underground storage tank formerly on the IM site was a small, secondary source. Ground water flows from the MSC site across the IM site, thus the two contaminant plumes became commingled.
A 1988 technical report prepared by EPA consultant concluded that the primary source of VOC contamination is at the MSC site, where maximum levels of TCE, 1,1,1-TCA, and Freon were identified. The report also concluded that the IM site was a secondary source of Freon 113 and possibly 1,1,1-TCA. In addition to these sources, another source of TCE appears to be located offsite and upgradient, and is migrating onto, the MSC site.
Description of Plume
VOCs are confined to the upper water-bearing zone (A-zone) which is found from 10 to 20 feet below ground surface (bgs). Ground water flows to the northeast towards the San Francisco Bay. The TCE plume is currently approximately 500 feet long and 400 feet wide
In order to remove the source of contamination on the IM site, Intel removed its underground storage tank and associated soil in 1985. The tank was professionally tested for leaks and none were found, and of the VOCs in ground water, only Freon 113 was detected at a significant concentration (1.7 ppm) in one soil sample, thus confirming that the IM source was minor. In March 1986, Intel began an interim ground water extraction and treatment program at the IM site. By 1988, it had become clear that the primary VOC source was located at the upgradient MSC site and by 1990 the responsibility for ongoing cleanup efforts was shifted to the MSC responsible party (RP).
The EPA Record of Decision (ROD) from 1991 states that the final cleanup plan includes: (1) a deed restriction prohibiting the use of the shallow ground water, (2) ground water monitoring, (3) ground water pumping from the A-zone, and (4) treatment of extracted ground water with granular activated carbon (GAC) and discharge of the treated ground water to the storm drain under a National Pollutant Discharge Elimination System (NPDES) permit.
In 1995 the Regional Water Board approved a request by the Microstorage RP to shut down the ground water extraction and treatment system and see if “monitored natural attenuation” (MNA) could be an effective method of remediation. "Natural attenuation" processes are the biological, chemical and physical processes that reduce VOC mass and/or concentrations in the absence of any human intervention. The extraction system has remained shut down since 1995 based on MNA's effectiveness.
In general, the ground water VOC plume has remained stable since the extraction pumps were turned off. The plume has not expanded downgradient and, in general, the interior of the plume has shown stable or decreasing concentrations of contaminants. There has been a gradual increase in VOC concentrations observed in an upgradient well, indicating the presence of an upgradient VOC source that is migrating onto the MSC/IM site. The Regional Water Board has investigated possible upgradient source locations, but no definitive source has ben identified.
TCA and Freon 113 (the VOCs potentially associated with the Intel source) have been at concentrations below the cleanup standards in all site wells since March 1985 and August 1986, respectively. TCE and some other VOCs associated with the MSC source and the unidentified source upgradient of the MSC site remain above cleanup standards (Figure 1).