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.
Intel Facility-Specific Work - 365 E. Middlefield Road
Groundwater extraction at the former Intel Mountain View facility began in 1982 from one extraction located on Lot 3 (365 East Middlefield Road). The well was completed across both the upper A Aquifer and the B1 Aquifer.
Between 1982 and 1984, approximately 27.5 million gallons of groundwater were pumped resulting in an approximately 1,600 pounds of VOCs removed. The extraction well was destroyed in 1984 when Intel conducted a source area removal action.
In 1985, four new groundwater extraction wells were installed. Three of these wells were completed in the A Aquifer and one well was completed in the B1 Aquifer. EPA approved the shut down of extraction well PW-1A in 1996 after an investigation determined that taking the well off-line did not effect the overall capture zone at the facility. Intel manages the operation of the extraction wells and treatment system and shares responsibility with Raytheon for the source control extraction well for Lots 3, 4, and 5, including Well I-1B2.
The Intel groundwater treatment facility consists of two 2,000-pound canisters of GAC operated in series. Between June and August 1998, the treatment system was relocated from along the east side of the existing site building to a location near the southwest corner of the property in preparation for tenant improvements. Although changes were made to influent and effluent piping, no changes were made to the two liquid-phase GAC vessels.
In 1998, a diffused aeration tank or air stripper was installed within the treatment pad enclosure to aerate the extracted groundwater prior to carbon absorption, thus decreasing the potential for exceedances of the NPDES effluent requirements. In April 2003, the use of the diffused aeration tank was discontinued and groundwater treated with GAC was plumbed to discharge to the City of Mountain View sewer. The system has the permitted option of discharging to a storm drain located along the eastern property boundary. The storm drain leads to Stevens Creek.
Over 74 million gallons of groundwater have been treated and 2,000 pounds of VOCs removed since system start-up in 1982.
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.
Current Actions
Intel has begun 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. During the pilot test, the groundwater extraction and treatment system is not operating. See Intel's annual progress report for more information.