Pacific Southwest, Region 9: Superfund
Serving Arizona, California, Hawaii, Nevada, the Pacific Islands, and Tribal Nations
Hewlett-Packard (620-640 Page Mill Road)
EPA #: CAD980884209
County: Santa Clara
City: Palo Alto
Congressional District: 14
Vapor Intrusion (VI) Study Completed
Between 2011-15 a study to review the potential for VI into overlaying buildings was conducted. Although some underground locations were mitigated for future VI potential, results found no impact from below surface groundwater contaminants in the indoor air.
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Description and History
NPL Listing History
NPL Status: Final
Proposed Date: 06/24/88
Final Date: 02/21/90
The Hewlett-Packard (HP) Site or Site consists of the former Hewlett-Packard (HP) 620 - 640 Page Mill Road, Palo Alto, California manufacturing facility and the associated off-site impacted groundwater plume. Impacted groundwater emanating from the former Varian facility at 601 California Avenue, the former HP facility at 395 Page Mill Road and other release sites in the vicinity comingle with the impacted groundwater plume from the HP Site. The comingled impacted groundwater plume extends generally to the northwest about one-half mile. Land use in the off-site area overlying the impacted groundwater plume is a mix of commercial, residential and recreational.
HP conducted manufacturing operations at the HP Site from October 1962 to December 1986. Redevelopment of the Site was initiated in 1992. Former Site buildings were demolished, and construction of a new multi-story office building with an engineered vapor intrusion barrier and a ventilated underground parking garage was completed in 1994. The office building and surrounding at-grade parking lots encompass the majority of the former HP Site.
Site investigation began in 1981 after a leaking 1000-gallon underground solvent storage tank was discovered at the Site. Since then extensive investigation and cleanup activities have been conducted. Cleanup measures have included excavation of over 10,000 cubic yards of soil, soil vapor extraction and treatment and groundwater extraction and treatment in on- and off-site areas. Ongoing groundwater extraction and treatment has reduced the plume dimensions and plume concentrations.
More recently, investigations (soil vapor and indoor air testing) have been conducted to assess whether vapors may be accumulating in living or work spaces in buildings overlying the groundwater plume (vapor intrusion). The recent vapor intrusion investigation results demonstrated that vapors emanating from the ground are not accumulating at unacceptable levels in the living and work spaces tested.
Contaminants and Risks
- Soil and Sludges
The chemicals that remain in soil and groundwater are chlorinated volatile organic compounds (VOCs), primarily trichloroethene (TCE).
Potential health risks, if sufficient exposure to VOCs occurs, are direct contact with affected soil or groundwater, accidental ingestion of affected soil or groundwater and inhalation of volatilized chemicals. Testing has shown that there are no complete exposure pathways associated with the Site.
Groundwater in the Palo Alto area currently is not used for drinking water. Drinking water in Palo Alto is supplied to homes and businesses from municipal sources including the Hetch Hetchy reservoir in the Sierra Nevada Mountains. For the sake of setting cleanup standards, it is assumed that the groundwater in the area may be a potential future drinking water source. Therefore cleanup standards protective of drinking water have been established.
Recent vapor intrusion testing results have shown elevated levels of TCE vapors in some subgrade structures (elevator shafts, underground parking garages). However, the testing has showed that there are no unacceptable accumulations of vapors in homes or workspaces.
Who is Involved
This site is being addressed through Federal, State, and potentially responsible parties' actions.
Investigation and Cleanup Activities
This site is being addressed in two stages: immediate actions and a long-term remedial phase focusing on cleanup of the entire site.
Extensive investigation and cleanup has been conducted since discovery of a release from a 1,000-gallon underground waste solvent tank in 1981. Interim remedial measures included excavation and off-site disposal between 1987 and 1992 of approximately 10,700 cubic yards of soil, construction and operation (beginning in 1994) of a soil vapor extraction and treatment (SVET) system; and groundwater extraction and treatment beginning in 1987 and continuing.
These interim response actions addressed the principal threats at the former HP Site - soil and groundwater contamination. The final remedy was selected in 1995 and implemented beginning in 1995 and 1996. The final remedy addresses threats that remained after the interim measures.
The major components of the selected remedy included the following:
- Operation of the on-Site soil vapor extraction and treatment (SVET) system. The SVET system was operated regularly until 1996 when shutdown testing was conducted. The SVET system has not operated for any significant time since August 1997 due to saturation of the gravel packs in the lower wells and low VOC concentrations in the other SVE wells.
- Operation of the on-site and off-site groundwater extraction system to capture and treat VOC-impacted groundwater. Groundwater extraction and treatment activities currently consist of extraction from two on-Site and two off-Site extraction wells and treatment of extracted groundwater from those wells at the treatment system at the former HP Site; and operation of a treatment system for the Oregon Expressway Underpass (OEU) dewatering system. The OEU dewatering system was installed beneath the underpass when it was constructed in 1958, and controls natural groundwater inflow and surface runoff.
- Long-term groundwater monitoring. Groundwater monitoring and reporting is conducted annually.
- A deed restriction prohibiting the use of on-site groundwater until final cleanup standards are achieved.
Additional off-Site investigations were conducted in 2011 to further delineate the extent of VOC-impacted groundwater (i.e. plume definition) in support of a subsequent vapor intrusion investigation. Based on the results of the impacted groundwater delineation efforts, work plans for indoor air testing of residential and commercial buildings were developed, received regulatory agency approval, and were implemented during 2012 through mid-2015. Air testing results from the vapor intrusion investigations showed elevated levels of TCE vapors in some subgrade structures (elevator shafts, underground parking garages). However, the testing has showed that there are no unacceptable accumulations of vapors in homes or workspaces.
Cleanup Results to Date
The excavation and disposal of the storage tank and contaminated soil and the continuing treatment of contaminated groundwater have reduced the potential for exposure to hazardous materials.
Vapor Intrusion Study Overview
To find if there are any risks to indoor air from the HP Site, a Vapor Intrusion (VI) study was conducted during 2012 . Through mid-2015 this study has included 34 single-family residences, eight (8) multi-family or mixed use properties (some with multiple buildings) and 13 commercial buildings. All of the single-family residences were offered testing and 12 accepted testing. Seven (7) of eight (8) multi-family or mixed use properties were tested. Testing was also conducted at ten (10) of 13 commercial buildings.
The testing results showed elevated levels of TCE vapors in some subgrade structures (elevator shafts, underground parking garages). However, the testing also showed that there is no unacceptable accumulation of vapors in homes or workspaces.
September 2015 Five-Year Review Findings
In September 2015 EPA and the State of California completed the fourth Five-Year Review for the site. The Five-Year Review concluded that the cleanup remedy for the site currently protects human health and the environment because exposure to the contaminated groundwater is not currently possible and the vapor intrusion study did not find unacceptable vapor levels in currently occupied living or work spaces.
However, to be protective in the long-term, the Five-Year Review recommended that the following two issues be addressed:
Issue #1: Recent vapor intrusion investigations have demonstrated that a complete pathway does exist in subgrade structures. However, there have not been unacceptable exposures or exceedances of the risk range in currently occupied locations.
Recommendation: Evaluate the need for revisions to the current remedy to address potential future unacceptable vapor intrusion.
Issue #2: The California Maximum Contaminant Level (MCL) for 1,2,4-trichlorobenzene has decreased since the signing of the Record of Decision (ROD) and is more stringent than the current ROD cleanup level.
Recommendation: Evaluate whether the cleanup level for 1,2,4-trichlorobenzene should be changed to the new state MCL and include in a decision document modification as necessary.
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.
On-line information about the PRPs for the site is not yet available.
Documents and Reports
Public Information Repositories
The public information repositories for the site are at the following locations:
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
1515 Clay St.
Oakland, CA 94612
After Hours (Emergency Response)