Pacific Southwest, Region 9: Superfund
Serving Arizona, California, Hawaii, Nevada, the Pacific Islands, and Tribal Nations
Middlefield-Ellis-Whisman (MEW) Study Area
EPA #: CAD982463812
County: Santa Clara
City: Mountain View
Congressional District: 12
Other Names: Please also see Site Overviews for Raytheon, Intel Corp - Mtn View, and Fairchild Semiconductor - Mtn View
EPA has developed a Communication Plan for the groundwater cleanup Pilot Test Work in former facility-specific source areas in the MEW Superfund Area.
Click here to read about the plan
On this page
Description and History
NPL Listing History
NPL Status: Part of another site
The Middlefield-Ellis-Whisman (MEW) Superfund Study Area (or MEW Site) is comprised of three National Priorities List (NPL) or Superfund sites: Fairchild Semiconductor Corp. – Mountain View Superfund site; Raytheon Company Superfund site; and Intel Corp. – Mountain View Superfund site; several other facilities; and portions of the former Naval Air Station (NAS) Moffett Field Superfund site. The "MEW Superfund Study Area" itself is not listed on the National Priorities List (NPL).
- The MEW Site was home to several manufacturing and industrial facilities, including semiconductor and other electronics manufacturing facilities and metal finishing facilities. While in operation, these former facilities required the storage, handling, and use of a variety of chemicals, particularly volatile organic compounds (VOCs). The primary chemicals of concern at the MEW Site are trichloroethene (TCE) and its degradation products: cis-1,2-dichloroethene and vinyl chloride. During operations, some of the chemicals leaked or were otherwise released to the ground, impacting soil and groundwater. In 1981 and 1982, investigations in the area of these facilities indicated that significant levels of contaminants had been released to the soil and groundwater.
Contaminants and Risks
The primary contaminants of concern are trichloroethene (TCE) and other volatile organic compounds (VOCs) in groundwater and the potential migration to indoor air (vapor intrusion pathway). The soil has been cleaned up to meet the soil cleanup standards.
Who is Involved
The MEW Site is being addressed through EPA and potentially responsible parties' actions.
Investigation and Cleanup Activities
The contamination addressed in the MEW Record of Decision is both facility-specific and regional. Each individual MEW Company is responsible for investigation, cleanup, and source control for soil and groundwater contamination at their individual facility-specific properties south of U.S. Highway 101. Contaminated groundwater that has bypassed the source control areas and has mixed together with other contaminated groundwater from other source areas is considered part of the regional groundwater contamination plume, or the “regional plume.”
The MEW Regional Groundwater Remediation Program systems south and north of U.S. Highway 101 (South and North of 101) are designed to contain and clean up contaminated groundwater where the contaminated plume has mixed together with other contaminated groundwater and where the source of contamination has not been identified. The Navy and NASA both operate groundwater extraction and treatment systems to contain and clean up contaminated groundwater at their areas of responsibility on Moffett Field, in addition to the MEW regional groundwater system operating North of 101 on Moffett Field.
It is important to note that groundwater currently is not used for drinking water or other potable uses. Groundwater in the area is, however, a potential future source of drinking water and therefore groundwater cleanup standards have been established.
EPA's Soil and Groundwater Remedy - 1989 In June 1989, EPA issued a Record of Decision selecting the soil and groundwater cleanup remedy for the MEW Study Area. The soil remedy includes: excavation, with treatment by aeration; and soil vapor extraction with treatment by vapor-phase granular activated carbon. The groundwater remedy includes: slurry walls (barriers beneath the surface) to contain contaminants; and extraction and treatment systems to contain and clean up groundwater contamination using granular activated carbon and/or air-stripping systems.
Because the groundwater contamination at the MEW Site migrates northward and has mixed with contamination from sources at the NAS Moffett Field Superfund site, the groundwater remedy selected in the MEW Record of Decision also applies to the commingled regional groundwater contamination area on former NAS Moffett Field (the West-Side Aquifers), but not the entire former NAS Moffett Field facility.
Intel, Fairchild, and Raytheon implemented groundwater and soil source control measures in the 1980s, before the soil and groundwater remedy was selected. Based on extensive soil and groundwater investigations and studies at the MEW Site, the MEW Companies implemented soil and groundwater cleanup programs that included soil excavation and treatment, installation of four slurry walls, soil vapor extraction and treatment systems, and groundwater extraction and treatment systems.
In the mid-1990s, Fairchild Semiconductor, Raytheon, Intel, and other MEW Companies (SMI, Vishay/SUMCO, NEC Electronics) implemented the soil remedy by excavation and aeration and soil vapor extraction (SVE). They also began operating or continued to operate the groundwater extraction and treatment systems to control source areas and remove VOCs from the aquifers. The soil cleanup was completed in 2001.
In accordance with the Consent Decree and 106 Order, each of the MEW Companies operates and maintains individual facility-specific groundwater source control measures (i.e., extraction wells, slurry walls, treatment systems, etc.) to contain and clean up contamination source areas in each area for which the MEW Company is responsible.
The MEW Regional Program South of 101 began operation in January 1998; North of 101 began operation in October 1998. The South of 101 and North of 101 are two separate groundwater extraction systems; however, they are designed to operate in unison to remediate and capture the regional plume. The Navy’s West-Side Aquifers Treatment System (WATS) began operation in November 1998, and NASA’s groundwater extraction and treatment system began operation in September 2001.
EPA's First Five-Year Review (2004)
The existing soil and groundwater remedy at the MEW Site does not address risks from long-term exposure through the vapor intrusion pathway. Since the issuance of EPA’s 1989 Record of Decision, new information has been developed regarding the toxicity of TCE and potential vapor intrusion into buildings overlying shallow groundwater contamination. In 2003, as part of EPA’s First Five-Year Review of the MEW Superfund Study Area, EPA began evaluating whether VOCs in shallow groundwater are potentially migrating upward through the soils and cracks in the floors or through plumbing conduits and other preferential pathways, and impacting indoor air.
EPA's First Five-Year Review determined that for the groundwater remedy to remain protective in the long-term, the following actions need to be taken: long-term protectiveness should continue to be verified by monitoring the extent of groundwater contamination along the estimated groundwater contamination plume boundaries. This evaluation should be accomplished through routine annual groundwater sampling events. Current data indicate that the remedy is functioning as required to meet the remedial action objectives; however, EPA recommends optimization of both the regional and facility-specific systems to enhance plume capture, evaluation of applicable technologies to potentially expedite contaminant mass removal and cleanup time, and evaluation of the potential need for institutional controls.
Intel has mplemented an in-situ bioremediation pilot test at its former facility at 365 East Middlefield Road in Mountain View to try to reduce VOC concentrations in the “hot spot” areas in a shorter period of time.
The MEW Companies, Navy and NASA have prepared a work plan to evaluate other alternate groundwater cleanup technologies to address the MEW Site-wide groundwater contamination.
In 2010, after amending the MEW Record of Decision, EPA selected a remedy that addressed potential long-term exposure of TCE, and other VOCs at unacceptable levels, through the vapor intrusion pathway, For more information, please access the 2010 Record of Decision Amendment for the Vapor Intrusion Pathway document either by clicking here or finding it in the Records of Decision subsection of the Documents and Reports section below.
EPA’s Final Third Five-Year Review report for the MEW Site is available to view [Click here].
Cleanup Results to Date
Under EPA’s direction and oversight, the MEW Companies implemented the soil and groundwater cleanup programs that have included soil excavation and treatment, installation of four slurry walls, soil vapor extraction and treatment systems, and groundwater extraction and treatment systems. The soil cleanup by soil vapor extraction and excavation and aeration has been completed at all the former MEW facilities.
- Groundwater cleanup will continue to operate for many decades in order to meet the TCE groundwater cleanup standard of 5 parts per billion. The groundwater remedy has removed over 100,000 pounds of contaminants, and has reduced contaminant concentrations throughout the multiple aquifer zones. The groundwater is not being used as a potable water supply, and there are no direct exposure pathways to the contaminated groundwater while groundwater cleanup continues.
Potentially Responsible Parties
Potentially responsible parties (PRPs) refers to companies that are potentially responsible for generating, transporting, or disposing of the hazardous waste found at the site.
Under EPA's direction and regulatory oversight, the following individual companies are responsible for investigating and cleaning up the soil and groundwater at the MEW Site. These companies are collectively referred to as the MEW Companies:
- Fairchild Semiconductor Corporation
- Intel Corporation
- Raytheon Company
- Schlumberger Technology Corp. (Schlumberger)
- Renesas Electronics America Inc (formerly NEC Electronics America, Inc.)
- SMI Holding LLC (SMI)
- Vishay General Semiconductor (Vishay)
- SUMCO Phoenix Corporation (SUMCO)
- National Semiconductor Corporation
- Tracor X-Ray
- Union Carbide
National Semiconductor Corporation, Tracor X-Ray, and Union Carbide are not involved with the active investigation and cleanup of the MEW Site.
In accordance with a Consent Decree and Unilateral Administrative Order, each of the MEW Companies operates and maintains individual facility-specific groundwater source control measures (i.e., groundwater extraction wells and treatment systems, slurry walls, etc.) to contain and clean up contamination source areas in each area for which the MEW Company is responsible. Additionally, both the Navy and NASA operate individual groundwater extraction and treatment systems. Ongoing groundwater cleanup activities at the MEW Site are performed according to specifications in the individual facility-specific and Regional Program design, construction, operations and maintenance, and monitoring documents.
Documents and Reports
|06/09/89||Record of Decision for MEW Study Area|
|09/01/90||Explanation of Significant Differences|
|04/16/96||Explanation of Significant Differences|
|08/16/10||Record of Decision Amendment for the Vapor Intrusion Pathway|
Public Meetings: For construction status and field monitoring updates on the 277 Fairchild residential development project, please click here to see Warmington Residential’s informational website.
On Saturday, February 11, 2017, EPA conducted a neighborhood meeting at the Middlefield Meadows Community Room at 114 Flynn Ave., Mountain View, CA. The purpose of the meeting was to give an update on recent TCE sampling results on development properties within the MEW Superfund Area.
A community advisory group, the MEW Community Advisory Board, meets regularly to learn about and discuss MEW investigations and cleanup issues.
EPA has awarded a Technical Assistance Grant (TAG) to the Pacific Studies Center. The TAG provides money for activities that help the community understand technical information at the MEW Site. Please contact Lenny Siegel, TAG Administrator, at 650-961-8918 or LSiegel@cpeo.org for more information.
Public Information Repositories
The public information repositories for the site are at the following locations:
Mountain View Public Library,
585 Franklin Street,
Mountain View, CA 94041
Monday-Thursday: 10 am to 9 pm
Friday and Saturday: 10 am to 6 pm
Sunday: 1 pm to 5 pm
EPA Site Manager
Mail Code SFD
75 Hawthorne Street
San Francisco, CA 94105
EPA Community Involvement Coordinator
Mail Code SFD
75 Hawthorne Street
San Francisco, CA 94105
EPA Public Information Center
a Project of the Pacific Studies Center,
278A Hope Street
Mountain View, CA 94041
After Hours (Emergency Response)