EPA #: AZD980737530

Superfund National Priority List (NPL) Status: The EPA listed this site on Sept. 9, 1983

Location

The Airport Property Project Area is located in the central portion of the Tucson International Airport Area (TIAA) Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) site. It is bounded approximately by Los Reales Road to the south and Elvira Road to the north. The Tucson International Airport lies just east of the project area.

Contaminants of Concern

The current contaminants of concern in groundwater include volatile organic compounds (VOCs), mainly trichloroethene (TCE).  The concentration of TCE currently ranges from less than 0.5 parts per billion (ppb) to 1,100 ppb.  The federal drinking water standard for TCE is 5.0 ppb. 1,4-Dioxane has also been found in groundwater at the site, but there is no federal or state drinking water standard for this compound. Contaminants of concern in the soils include polychlorinated biphenyls (PCBs), TCE, 1,1-dichloroethene (DCE), and carbon tetrachloride. Contaminants of concern at the site may change as new data become available.

Public Health Impact

The City of Tucson is the main municipal water provider at this site. All municipal wells in the area that were contaminated with TCE have been shut down and water is now supplied from outside the site. If you are drinking water from a private well within the boundaries of the TIAA site, please contact the ADEQ Project Manager.

Site Hydrogeology

The regional aquifer is composed of two hydrostratigraphic units: the upper zone of the regional aquifer and the lower zone of the regional aquifer. The upper zone of the regional aquifer is composed mainly of gravelly sand with some clayey sand and sandy clay, and it extends to a depth of about 200 feet below ground surface (bgs). The lower zone of the regional aquifer is composed mainly of relatively finer materials including clayey sand with lenses of gravelly sand and sandy clay, and it extends from about 300 feet bgs to an unknown depth. Separating the upper and lower zones of the regional aquifer is a thick clayey sequence termed the middle aquitard. This unit generally prevents contamination in the upper zone from reaching the lower zone.

At the Airport Property project area there is also a shallow groundwater zone (SGZ) that overlies the upper zone of the regional aquifer. The SGZ is composed mainly of fine grained silts and clays. Within the SGZ there are gravel subunits that channel groundwater flow westward and downward into the upper zone of the regional aquifer. The gravel subunits are coarser sediments including fine to coarse-grained sands and gravels.

Depth to groundwater varies from 80 to 240 feet bgs and generally gets deeper in a northward or westward direction. The general groundwater flow direction is toward the north-northwest; however, the gravel subunits within the SGZ channel flow more westward. More detailed descriptions of the hydrogeology of the Airport Property Project Area can be found in reports and studies available at the TIAA Information Repository.

Action Taken

The Settling Defendants, which include General Dynamics Corporation, McDonnell Douglas Corporation, the City of Tucson, and the Tucson Airport Authority (TAA), completed construction of a groundwater and soils remedy in 2007 to address contaminated groundwater and soil-gas in the SGZ.  The purpose of the SGZ remedy is to prevent further impacts to the regional aquifer.  The Settling Defendants also completed a Resource Conservation and Recovery Act (RCRA) Subtitle D landfill cap for the TAA landfill in July 2011, and a polychlorinated biphenyl (PCB) soils remedy in June 2012.  In 2015, a vapor intrusion investigation was completed in the neighborhood immediately west of the Airport Property Three Hangars area because it was thought that this area presented the greatest potential for vapor intrusion.  Results showed that vapor intrusion was not a significant health concern in this area.

Status

As required by an EPA Consent Decree (CD) for the Airport Property, the groundwater and soil vapor extraction (SVE) treatment plant has removed approximately 2,000  pounds of TCE from the groundwater and around 6,400  pounds of VOCs from the soil since Jan. 2008. The groundwater treatment system produced approximately 335 million gallons of treated groundwater from 2008 through June 2017.  This system includes extraction wells pumping groundwater to a treatment facility with an air stripper that removes VOCs from the extracted groundwater. Treated water is injected into the Regional Aquifer and the air stripper off-gas is treated with vapor phase Granular Activated Carbon (GAC).

EPA provided a Certification of Completion for the PCB Soils remedy in July 2017.

ADEQ, EPA, and the Settling Defendants initiated a series of technical meetings to try to resolve remaining questions on the site hydrogeology and the performance of the SGZ remedy.

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