Pacific Southwest, Region 9: Superfund
Serving Arizona, California, Hawaii, Nevada, the Pacific Islands, and Tribal Nations
EPA #: CAD009205097
County: Santa Clara
City: Mountain View
Congressional District: 14
Other Names: Part of Middlefield-Ellis-Whisman (MEW) Study Area
Aug 2010: EPA announces its selection of the vapor intrusion remedy for the MEW Superfund Study Area in EPA’s Record of Decision Amendment for the Vapor Intrusion Pathway (Click Here). EPA thanks the community for comments received on the Proposed Plan & for participating in the decision making process.
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Description and History
NPL Listing History
NPL Status: Final
Proposed Date: 10/15/84
Final Date: 06/10/86
Raytheon Company. formerly operated as a semiconductor products manufacturer at 350 Ellis Street on this 30-acre property in Mountain View, California. The Raytheon site is one of three Superfund or National Priorities List (NPL) sites that are being cleaned up simultaneously. The other two Superfund sites are the Fairchild Semiconductor Corp - Mountain View site and the Intel - Mountain View site. All three sites are located in the Middlefield-Ellis-Whisman (MEW) Study Area and are being addressed collectively as the MEW SIte. Site investigations at several of these facilities during 1981 and 1982 revealed extensive soil and groundwater contamination, primarily volatile organic compounds (VOCs). The primary causes of the contamination were leaking storage tanks and lines and poor facility management practices.
Contaminants and Risks
- Soil and Sludges
The primary contaminants of concern are trichloroethene (TCE) and other volatile organic compounds (VOCs). The soil has been cleaned up to meet the soil cleanup standards.
Who is Involved
This 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 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 Ames 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 regional 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.
Initial Actions: Initial cleanup activities currently being conducted at the site by the potentially responsible parties include tank removals, well sealing, soil removal and treatment, slurry wall construction around contaminated soil areas, and local groundwater treatment.
In June 1989, EPA issued a Record of Decision selecting the soil and groundwater cleanup remedy for the MEW Site. 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.
350 Ellis Street A soil vapor extraction (SVE) system was installed at the 350 Ellis Street property, and immediately north of the slurry wall. The SVE system began operating in 1996, and included 135 vapor extraction wells and a vapor treatment system consisting of two 8,000-pound vapor-phase GAC units. The SVE system was decommissioned in 2000 after it had removed approximately 3,000 pounds of VOCs from the soils. In 2000, EPA approved the soil cleanup for all SVE remediation areas at the property.
During the demolition of the slab and foundation of the former 350 Ellis Street building in March 2000, TCE-contaminated soil was discovered adjacent to the eastern and southern walls of the former shipping and receiving loading dock. Approximately 440 tons of soil were excavated, characterized, and transported to Forward Landfill (a Class II facility) for disposal.
401/415 East Middlefield Road (Lots 4 and 5)
In 1992, Raytheon conducted a subsurface investigation at Lots 4 and 5 to determine the final source control remedial design. Results of the investigation indicated an SVE system to treat the source area soils should be implemented.
In 1995, it was no longer practical to implement the SVE system designed for Lots 4 and 5 because of the rising groundwater table elevations. Soil samples in the remaining soils above the water table showed that soil concentrations met the cleanup levels. On May 20, 1996, EPA granted confirmation of the soil cleanup at Lots 3, 4, and 5.
Slurry wall construction began at the 350 Ellis Street site in June 1987, and was completed in September 1987. The wall was constructed to a depth of approximately 100 feet bgs around the facility property boundaries, encompassing the original chemical source areas at the facility. Backfill material consisted of a low-permeability soil/bentonite mixture. The slurry wall encompasses the A and B1 Aquifer zones beneath the original facility, and partially penetrates the B2 Aquifer zone.
Groundwater extraction wells were first installed at the site in the A and B1 Aquifers in 1986. Until 2000, extracted groundwater was treated using air stripping with a back-up liquid-phase carbon adsorption system to remove VOCs. The air stripper operated under an air permit from the Bay Area Air Quality Management District, and final discharge of the treated effluent was discharged to Stevens Creek via the storm sewer system.
In 1996, Raytheon added three extraction wells outside the slurry wall (RAY-1A, RAY-1B1, and I-1B2) as part of implementation of its facility-specific remedial design plans. Due to the redevelopment of the property in 2000, the groundwater treatment system was relocated. The relocated treatment system consisted of a low-profile air stripper with one liquid-phase GAC vessel that discharged treated groundwater to a storm sewer inlet onsite. The off-gas from the air stripper was routed through vapor-phase GAC vessels prior to discharging to the atmosphere. Between October 2002 and April 2003, there were four exceedances of 1,4-dioxane in the effluent. An evaluation for treatment a technology that would treat 1,4-dioxane was conducted.
On May 5, 2003, EPA approved Raytheon to shut down the air stripper and the carbon system while a new system was being evaluated. Between May 20 and October 13, 2003, a temporary liquid-phase carbon system consisting of two 5,000-pound and one 2,000-pound vessels operated to treat the extracted groundwater. The treatment compound facility was modified in fall of 2003, and a new oxidation system was installed that could also treat for 1,4-dioxane and meet groundwater effluent discharge criteria. Full operations of the new treatment system began in December 2003.
The groundwater extraction and treatment system has treated an estimated 270 million gallons of groundwater and removed approximately 13,600 pounds of VOCs through December 2006.
401/415 East Middlefield Road (Lots 4 and 5)
During the SVE construction and operation at 350 Ellis Street, Raytheon installed a source control extraction well in the B2 Aquifer (I-1B2) downgradient of 401/415 East Middlefield Road. Extracted groundwater is conveyed into the treatment system at 350 Ellis Street.
Intel manages the operation of the extraction wells and the treatment system at 365 East Middlefield Road. A summary describing the Intel groundwater treatment system is described in the Intel section of EPA's First Five-Year Review Report
EPA First Five-Year Review
EPA's 2004 Five-Year Review for the MEW Study Area 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 implemented 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.
EPA Evaluates Vapor Intrusion Pathway
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 Five-Year Review of the MEW 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.
Based on indoor air sampling of both commercial and residential buildings in the area conducted in 2003 to 2007, EPA has confirmed the presence of the subsurface vapor intrusion pathway into a number of structures overlying the shallow groundwater TCE plume. None of the samples taken to date indicate any immediate or short-term health threat to building occupants from this pathway. EPA’s main concern is whether the chemicals from the Site measured in indoor air pose an unacceptable risk of chronic health effects due to long-term exposure (25 years or more). It is EPA’s policy not to set cleanup levels or take action to reduce levels that are less than ambient background levels.
Some of the sampled buildings indicated indoor air contaminant concentrations that were elevated above background levels and above EPA Region 9’s TCE interim action level in indoor air for long-term exposure. In each of these buildings, the MEW Companies and NASA have taken voluntary interim measures (e.g., sealing cracks/conduits, upgrading/modifying ventilation systems, installing air purifying systems) to reduce the indoor air contaminant concentrations. In addition, many new buildings in the MEW Study Area have taken measures to help prevent or mitigate the vapor intrusion pathway. Although EPA has not yet determined what the long-term mitigation and monitoring strategy should be for all buildings overlying shallow groundwater contamination, the results of these interim measures have generally reduced the indoor air levels thus far and are protective of residents and workers.
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.
In 1985, the EPA issued an Administrative Order on Consent to several potentially responsible parties, including Raytheon Co. The Order required the parties to conduct an investigation into the nature and extent of site contamination and to recommend alternatives for final site cleanup. In 1991, EPA, Raytheon Co. and Intel Corp. signed a Consent Decree Agreement under which Raytheon and Intel agreed to design, construct, and operate the groundwater extraction and treatment systems for the regional groundwater contamination - referred to as the Regional Groundwater Remediation Program.
Cleanup Results to Date
Under EPA’s direction and oversight, Raytheon has implemented the soil and groundwater cleanup program at the former Raytheon facilities. The removal of tanks and soil, the sealing of contaminated wells, and the construction of a slurry wall have reduced the potential of exposure to contaminated materials at the Raytheon site. The soil cleanup by soil vapor extraction and excavation and aeration has been completed at all the former MEW facilities, including the former Raytheon 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 MEW Site groundwater remedy has removed over 100,000 pounds of contaminants, and has reduced contaminant concentrations throughout the multiple aquifer zones. The responsible parties are currently optimizing their pump and treat systems and pilot testing alternative technologies to speed up mass removal. 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, Raytheon Company is responsible for investigating and cleaning up the soil and groundwater at the site-specific Raytheon Superfund Site. In addition, the following individual companies are responsible for investigating and cleaning up the 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 (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.
Documents and Reports
Public Meetings: A community advisory group, the MEW Community Advisory Board, meets to learn about and discuss MEW Superfund Study Area investigation 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)