Site Name: Former Intel Mountain View Facility
Address: 365 East Middlefield Road Mountain View,
EPA ID: CAD061620217
EPA Region: 9
Media: Ground water
Contaminants: volatile organic compounds (VOCs),
MEW Superfund Site
The former Intel Mountain View facility is one of three Superfund sites within the area defined by Middlefield Road, Ellis Street, and Whisman Road in Mountain View that are part of the Middlefield-Ellis-Whisman (MEW) Superfund study area in Mountain View, CA. The MEW Superfund site also includes portions of former Naval Air Station (NAS) Moffett Field and several other individual companies that formerly operated at the MEW site. These other parties are also responsible for investigating and cleaning up soil and ground water at their respective former facilities at the MEW site. Intel Corporation (Intel) is responsible for clean-up actions at the former Intel Mountain View facility (Lot 3). In addition, Intel and Raytheon Company (Raytheon) are jointly and severally responsible for the remedial actions on Lot 4, immediately east of Lot 3. Intel also shares responsibility with Raytheon and Fairchild Semiconductor Corporation (Fairchild) for the Regional MEW site cleanup.
History of Contamination
Prior to 1965, all the land that is now 365, 401, and 415 East Middlefield Road (Lots 3, 4, and 5, respectively) was used for agricultural purposes. Beginning in 1965, the land was occupied by Union Carbide, which operated facilities at Lots 3 and 5 as a single complex for the manufacture of semiconductor products. As part of the manufacturing process, TCE was used by Union Carbide. To manage some of the waste streams produced in the manufacturing process, Union Carbide constructed an acid neutralization (AN) Vault on Lot 4.
In 1968, Union Carbide’s combined complex was divided into two parcels and operated by two companies. Raytheon occupied Lot 5 and the adjoining vacant Lot 4 and Intel occupied Lot 3. Both companies manufactured semiconductors at their facilities and both used TCE in the process. Beginning in 1968, both companies shared the AN Vault on Lot 4, which was operated by Raytheon.
In late 1972, Intel installed an acid waste neutralization (AWN) system on the southeast side of the building on Lot 3. In early 1973 Intel sealed the line that led from Lot 3 to the AN Vault sump on Lot 4 and began using the AWN system on Lot 3. Raytheon continued to use the Lot 4 AN Vault for another ten years, until 1983. VOCs were first detected in ground water at Lots 3 and 4 in 1981. It is suspected that Lot 3 ground water had been impacted by leaks from the AWN system on Lot 3 and that Lot 4 ground water was impacted by releases from the Lot 4 AN Vault and a chemical storage area on Lot 4.
Description of Plume
The primary VOCs identified in ground water at Lots 3 and 4 are TCE and its biodegradation daughter products, cis-1,2-DCE and vinyl chloride. The daughter products are generated as TCE is reduced by the microorganisms in the subsurface. Biodegradation of TCE requires availability of electron donors. At Lots 3 and 4, the electron donors were likely toluene, ethylbenzene and xylene compounds which were also released at these sites. VOCs are present in the shallowest, A water-bearing zone (from about 18 to 40 feet below ground surface [bgs]) and to a lesser extent in the B1-zone (from about 40 to 80 feet bgs).
Although TCE and its biodegradation daughter products have been and continue to be detected across Lots 3 and 4, the highest concentrations have been detected on Lot 4. The A-zone plume center has progressively moved to the west as a result of ground water extraction on Lot 3, while diminishing in concentration.
Intel began ground water extraction from a well at the AWN source area on Lot 3 in 1982, shortly after the VOCs were first discovered. Between 1982 and 1984, approximately 27.5 million gallons of ground water were pumped from the extraction well and treated, resulting in an estimated mass removal of approximately 1,600 pounds of VOCs.
Extraction of ground water temporarily ceased in 1984 when Intel implemented an extensive source excavation of the AWN vault and over 4,000 cubic yards of associated soil on Lot 3. Confirmation soil sampling indicated that all significant VOC-impacted soil had been removed and EPA declared the Lot 3 soil clean-up complete.
In 1985, ground water extraction and treatment began again, this time from three A-zone and one B1-zone wells. In 1996, one A-zone extraction well was permanently shut down because it was no longer needed for clean-up. Ground water treatment was by granular activated carbon (GAC) and until 2003 discharge was to the storm drain under a National Pollutant Discharge Elimination System (NPDES) permit. In April 2003, the Ground Water Extraction and Treatment System (GWETS) was re-plumbed to discharge to the City of Mountain View sanitary sewer instead of the storm drain. In 2005, EPA approved temporary shutdown of the GWETS while Intel implemented a voluntary "enhanced bioremediation" project on the site.
Intel extracted and treated VOC impacted ground water at Lots 3 and 4 for over 22 years. Although the Ground Water Extraction and Treatment System was designed for hydraulic control and effective VOC mass removal within Lot 3, capture of VOC-impacted ground water on Lot 4, and to a much lesser degree on Lot 5, was later achieved by optimizing the pumping rates of the system. The Ground Water Extraction and Treatment System was successful at containing and reducing the VOC plume on Lot 3. However, the remaining concentrations of VOCs in the ground water, particularly on Lot 4, would require long-term operation of the Ground Water Extraction and Treatment System to reach the established ground water cleanup standards.
Early investigations identified unsaturated soils impacted with VOCs above cleanup level for soils on Lots 4 and 5. Raytheon consequently proposed the implementation of an in-situ soil vapor extraction (SVE) system to treat the source areas on Lot 4 and Lot 5. However, due to the rise of the ground water table these soils became saturated and the proposed soil vapor extraction system was determined to be infeasible. As such, the clean-up of these source areas has been left to the existing Ground Water Extraction and Treatment System operated by Intel.
By 2005 the existing Ground Water Extraction and Treatment System was no longer effective at addressing the VOC mass located on Lot 4. Rather, VOCs on Lot 4 were slowly being pulled onto Lot 3, in effect shifting the future costs and liability of ground water remediation solely on Intel. In order to more aggressively clean-up the ground water at Lot 4, Intel evaluated a range of alternatives. Enhancing the natural reductive dechlorination (bioremediation) at the site was the preferred remedial option, and Intel and Raytheon are working together on the implementation. Currently (2017) four phases of enhanced bioremediation have been implemented, and results have been very positive to date. (Figure 1).
Indoor Air Evaluation and Risk Assessment
In response to the EPA Region 9 request to assess the potential for ground water-to-indoor air vapor intrusion and its associated potential health risks, Intel initially conducted indoor and outdoor air sampling at the site in May, September, and December 2003. The representative indoor air breathing zone sample results indicate there is no unacceptable risk to building occupants from the vapor intrusion pathway. In August 2010, EPA issued a Record of Decision (ROD) Amendment to address the vapor intrusion pathway throughout the MEW site. For both Lot 3 and Lot 4, this led to additional air sampling conducted in 2013 to determine what response actions would be required. All indoor air concentrations, both with and without the buildings' ventilation systems in operation, were below action levels. Therefore, no engineered remedy will be required for vapor intrusion. At the request of EPA, Intel conducted additional investigations in 2014 to assess potential vapor intrusion effects associated with the enhanced bioremediation. The results demonstrated that the bioremediation has no measurable impact on indoor air.