EPA #: AZD980737530

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

Location

The Tucson International Airport Area Superfund Site (TIAA) is a Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) site in Tucson, Arizona. The site is on the National Priorities List (NPL), which is periodically updated by the U.S. Environmental Protection Agency (EPA). The TIAA Superfund site contains seven project areas including: Air Force Plant 44 (AFP-44), Tucson Airport Remediation Project (TARP), the Airport Property, the 162nd Fighter Wing Arizona Air National Guard (AANG) facility, Texas Instruments, Inc. (formerly Burr-Brown Corporation), the former West-Cap property, and West Plume B. The site is located in the southern portion of Tucson, south of Ajo Way, north of Hughes Access Road, west of Alvernon Way, and east of Interstate 19. The Tucson International Airport is located within the site.

Contaminants of Concern

The current contaminants of concern in groundwater include trichloroethene (TCE), dichloroethene (DCE), chloroform and chromium. Polychlorinated biphenyls and metals contamination have also been found in some soils at the site. During spring and summer 2002, 1,4-dioxane was discovered at the AFP-44, TARP and the Airport Property project areas. To date, per- and polyfluoroalkyl substances (PFAS) have been detected in groundwater at concentrations above the EPA Health Advisory Level (HAL) of 70 nanograms per liter at the Airport Property, TARP, AANG and West Plume B project areas. Contaminants of concern may change as new data becomes 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 VOCs have been shut down. The municipal water supply in the area now comes from wells outside the site. Some privately owned domestic wells in the area have been impacted, but have either been shut down or converted to irrigation wells. If you are drinking water from a private well within the boundaries of the site, please contact the ADEQ Project Manager.

In February 2015, Pima County DEQ sampled private wells within the TIAA site. Four of these wells were impacted by low levels of 1,4-dioxane. From October-December 2019, ADEQ sampled private wells within the TIAA site for PFAS; three private drinking water wells were impacted with PFAS above the EPA HAL. ADEQ, Tucson Water, and the Air National Guard are working together to ensure that these wells are no longer used for drinking water.

Areas with soil contamination at or very close to the surface have been excavated so that currently there are no known public health impacts resulting from contaminated soils.

Site Hydrogeology

The TIAA site is located within the Tucson Basin, a northwest trending alluvial valley covering an area of about 750 square miles in the Santa Cruz River drainage basin of southeastern Arizona. Site hydrogeology is complex and is detailed within reports and studies available at the TIAA Superfund site information repository.

The Tucson Basin is a broad, down-faulted, sediment-filled depression bounded by mountain ranges composed of crystalline rock. Thousands of feet of alluvial sediment, weathered and eroded from the surrounding mountains, were deposited in the Tucson Basin. Major west-northwest trending drainages intersecting the site include Airport Wash and Hughes Wash, both of which are tributaries of the ephemeral Santa Cruz River.

The regional aquifer (historically targeted for groundwater resource development for public water supply purposes) is composed of three major hydrostratigraphic units: the upper zone of the regional aquifer, the lower zone of the regional aquifer, and the undivided regional aquifer. A middle aquitard divides the regional aquifer into upper and lower zones under most of the site.  In the southern and central portions of the site, groundwater contamination has been found mainly within the upper zone of the regional aquifer as the vertical extent of contamination has been limited by the presence of the middle aquitard.

Depth to groundwater in the regional aquifer varies from 80 to 240 feet below ground surface. The general groundwater flow direction is toward the north-northwest. For more detailed discussion of the site hydrogeology of each of the seven TIAA Superfund site project areas, please refer to their individual web pages.

Action Taken

Remediation systems are operating to remove VOCs at TARP, AANG, the Airport Property (Three Hangars), West-Cap, Texas Instruments, and AFP-44. Preliminary Assessment / Site Investigation (PA/SI) activities have been conducted at AANG and AFP-44 to assess the nature and extent of PFAS in the environment. Existing groundwater wells have been sampled for PFAS within several project areas, including AFP-44, TARP, Airport Property, AANG, and West Plume B. At the TARP treatment facility, Tucson water maintains carbon treatment to remove PFAS in accordance with the City’s strict PFAS operational guidance.

Status

The Air Force finalized investigation of offsite 1,4-dioxane groundwater contamination north of AFP-44 (North of Los Reales Road/TARP) and proposed technologies to address this contamination.  The existing groundwater remediation system at AFP-44 includes an advanced oxidation treatment system to treat 1,4-dioxane, which began continuous operation in 2009, and air strippers to remove TCE. In 2015, the Air Force issued a Record of Decision (ROD) for No Further Action (NFA) at the 1980s Pistol Range at AFP-44. The Air Force also began treatability studies to determine the effectiveness of hydraulically fracturing and in-situ treatment of groundwater contamination within fine-grained units underlying AFP-44. In August 2020, they completed a Record of Decision for groundwater.   The Air Force completed a PFAS Preliminary Assessment in 2018 and a PFAS Site Inspection (SI) is ongoing.

The Tucson Airport Authority operates a shallow groundwater zone (SGZ) remedy to treat TCE that includes pumping, treating, and reinjecting SGZ groundwater and a soil vapor extraction (SVE) system. ADEQ and U.S. EPA have engaged the Settling Defendants for the Airport Property project area in a series of technical meetings to try to better understand the local hydrogeology in this area and determine the effectiveness of the SGZ remedy.  Recently, an additional paleochannel with TCE and 1,4-dioxane contaminated groundwater was discovered and these data are being incorporated into the conceptual site model. Additionally, select monitoring wells within the Airport Property project area were sampled for PFAS in 2019 and PFAS were detected in several wells.

In 2014, the Tucson Water Department constructed an advanced oxidation process (AOP) treatment system that began operating. The purpose of the AOP treatment system is to remove 1,4-dioxane and TCE from the contaminated regional aquifer groundwater. Tucson Water maintains carbon treatment as part of the AOP system which removes PFAS in accordance with the City’s strict PFAS operational guidance.

Following issuance of the April 2012 Record of Decision (ROD) amendment for Area B [AANG, West-Cap, West Plume B, and Texas Instruments], U.S. EPA implemented an In-Situ Chemical Oxidation (ISCO) remedy to replace the pump and treat remedy at West-Cap. Texas Instruments and the National Guard Bureau (NGB)/AANG have also implemented ISCO. Monitored natural attenuation continues for VOCs within West Plume B. PFAS have been detected in groundwater at AANG and West Plume B. AANG completed a PFAS PA in 2016 and an SI in 2018. A Remedial Investigation (RI) is expected to begin in 2021 to further investigate PFAS in this area.

For more detailed discussion of the status of each of the seven TIAA Superfund site project areas, please refer to their individual web pages.

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