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.
Current actions
Intel has been implementing 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