Site Name: Santa Clara 3 Superfund Site

Address: 2880 Northwestern Parkway Santa Clara,

EPA ID: CAT000612184

EPA Region: 9

Media: Ground water

Contaminants: volatile organic compounds (VOCs),
primarily trichloroethene (TCE) and trichlorotrifluoroethane
(Freon 113)

History of Contamination

No source of the ground water contamination has ever been positively identified at the SC3 site. It has been determined that there is no source continuing to contribute pollutants to existing ground water.

Description of Plume

When first delineated, the plume covered an area approximately 350 feet by 250 feet and was limited to the upper water-bearing zone (A-zone), at depths of 28 feet below ground surface or less. By 2015, the plume had been reduced to an area approximately 80 feet by 20 feet (Figure 1). Based on the latest monitoring results, this plume has been fully remediated.

Remedy Selection

Intel Corporation (Intel) conducted extensive source investigations between 1982 and 1988 and no source of the low-level contamination at the site was identified. In 1985, as an effort to remove the contaminants, Intel began extracting and treating ground water at the site.

By the time the EPA Record of Decision (ROD) was issued in 1990, ground water extraction had reduced VOC concentrations by over 90% and the concentrations were leveling off (Figure 2). The selected remedy in the ROD included: (1) a deed restriction to preclude use of the A zone until cleanup standards are achieved; (2) ground water monitoring; (3) pumping, treating, and discharging ground water from three extraction wells; and (4) evaluation of pulsed pumping as a demonstration project at the site. Pulsed pumping is the cycling of extraction wells on and off in an attempt to improve VOC cleanup.

In 1991, Intel implemented the Cyclic Pumping Demonstration Project (the Project). Several pumping scenarios were evaluated during the Project in an effort to optimize the extraction program's efficiency.

Remedial Progress

Trials One through Four of the Project demonstrated that no ground water extraction was just as effective as cyclic and continuous extraction at containing and reducing the VOC concentrations. The final trial of the Project (Trial Five) included monitoring ground water with the pumps at rest for an extended period. In 2006, Intel voluntarily injected an oxidizing product in an attempt to further reduce the residual VOCs at the site.

In 2009 EPA agreed that no additional active remediation is warranted at the site. In September 2010, EPA issued a ROD amendment that officially changed the remedy to "Monitored Natural Attenuation". In attempts to accelerate attainment of cleanup standards, Intel performed targeted groundwater extraction in 2014 and 2015 and injected an activated carbon product in 2016 and 2017. Based on the September 2017 groundwater monitoring results, groundwater concentrations are now below the cleanup standard in all wells. Attainment monitoring will continue into 2018, and EPA approval for closure is expected by 2019.

Site Chronology

  • 1975 – Santa Clara 3 facility is constructed (occupied in 1976).

  • 1977 – Intel discontinues the use of TCE company-wide.

  • July 1982 – TCE and Freon 113 detected in A-zone ground water monitoring well installed for Intel’s voluntary monitoring program.

  • February 1985 – Ground water extraction and GAC treatment begins. Extraction and treatment continues uninterrupted until April 1991.

  • May 1986 – EPA lists the site on the final National Priorities List.

  • September 1990 – EPA issues Record of Decision requiring (1) a demonstration project for cyclic pumping; (2) installation of an extraction well; and (3) adopting California Department of Health Services (DHS) maximum contaminant levels (MCLs) for drinking water as the cleanup standards for site ground water.

  • April 1991 – Cyclic pumping begins.

  • July 1993 – All pumps are shut off.

  • October 1998 – California Regional Water Board approves leaving the extraction system off indefinitely.

  • December 2000 – Second Five-Year Status Report and Effectiveness Evaluation submitted by Intel with recommendations to: (1) leave extraction system off; and (2) reduce monitoring and reporting from bi-annual to annual.

  • 2001 – Regional Water Board and EPA concur with Five-Year Status Report.

  • September 2006 – EPA issues Third Five-year Review indicating NPL deletion may be possible following in-situ chemical oxidation (ISCO) implementation.

  • Late 2006 – Intel injects RegenOX, an ISCO product, to further reduce VOCs.

  • March 2010 - Indoor air evaluation indicates VOC concentrations below levels of concern, even with the facility heating, ventilation and air conditioning (HVAC) system off.

  • September 2010 - EPA issues a ROD amendment to change the site remedy to " Monitored Natural Attenuation" (MNA), thereby acknowledging that no additional active remediation is warranted and that natural processes are expected to restore ground water to drinking water standards within a timeframe that EPA considers reasonable.

  • 2013 – Annual ground water monitoring activities (sampling and level measurement) continue at the Site and VOC concentrations in the ground water remain low (less than 10 ppb).

  • 2014-2015 - Temporary groundwater pumping initiated in August 2014 from monitoring well SC3-3Rep (Figure 1) in attempts to reduce TCE concentrations; however concentrations remain the same so pumping is discontinued in April 2015.

  • 2016-2017 – PlumeStop activated carbon product injected in vicinity of wells SC3-3Rep and SC3-1Rep, reducing groundwater TCE concentrations to below the 5 ppb cleanup standard.

  • For additional information from US EPA, see: http://yosemite.epa.gov