EPA #: AZD980737530

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

Location

The Tucson Airport Remediation Project area (TARP) is located in the northwestern portion of the TIAA site and is bounded on the west by Interstate 19 and the Santa Cruz River, and on the east by S. 6th Avenue and Nogales Highway (Route 89).  The TARP groundwater plume extends from Los Reales Road at the southern end of the project area northward to just past Irvington Road in Tucson, Arizona.

Contaminants of Concern

The current contaminants of concern in groundwater include volatile organic compounds (VOCs), mainly trichloroethene (TCE) ranging from non-detect to around 88 ppb. The federal drinking water standard for TCE is 5.0 ppb. 1,4-Dioxane concentrations currently range from less than 0.2 ppb up to 7.1 ppb in the TARP project area. There is no federal or state drinking water standard for 1,4-dioxane. Contaminants of concern at the site may change as new data become available.

Health Concerns

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. Most of the domestic wells have either been shut down or converted to irrigation wells. If you are drinking water from a private well within the boundaries of the TIAA site, please contact the ADEQ Project Manager.

Environmental Considerations

In the southern half of the TARP project area, 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 regional aquifer in the northern portion of the project area is composed of only one hydrostratigraphic unit called the undivided 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; 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. The undivided regional aquifer in the northern part of the TARP project area is composed mainly of coarse-grained materials.

Depth to groundwater varies from 80 to 240 feet bgs and generally gets deeper in a northward direction. The general groundwater flow direction is toward the north-northwest. More detailed descriptions of the hydrogeology of the TARP project area can be found in reports and studies available at the TIAA Information Repository.

Action Taken

Groundwater remediation at the TARP project area began in 1994 when Tucson Water began to operate a remediation system consisting of a South Well Field of five extraction wells, a North Well Field of four extraction wells, and a groundwater treatment plant.  The TARP system treats groundwater at a rate of about 4,500 gallons per minute and provides hydraulic control and remediation of main plume of the TIAA Superfund Site regional aquifer. Since September 1994, the TARP system has pumped and treated approximately 47.7 billion gallons of groundwater and removed approximately 5,303 pounds (lbs.) of TCE from the regional aquifer. Clean water from the TARP treatment plant is delivered to the Tucson Water Department (Tucson Water) distribution system.

Status

TARP is in the operation and maintenance phase of cleanup. In 2013, Tucson Water constructed an Advanced Oxidation Process (AOP) system to remove TCE and 1,4-dioxane from the groundwater. The AOP treatment train includes ultra-violet light reactors, peroxide storage/feed equipment, and a granular activated carbon (GAC) tank for peroxide quenching. The AOP system began full operation in early 2014.

Water level and water quality data are used to evaluate the performance of the existing remediation well fields in achieving capture of the groundwater plume, and for remediating TCE and 1,4-dioxane in the aquifer. These data indicate that the TARP remediation system is meeting compliance requirements, and the TARP AOP treatment plant shows consistent performance in removal of VOCs and 1,4-dioxane. Tucson Water has also begun to plan for replacement of the extraction wells due to their deterioration since they were installed in 1994.

EPA plans to issue a Record of Decision (ROD) Amendment for the TARP project area by the end of 2017.  The ROD Amendment will formalize AOP as the treatment method to remove TCE and 1,4-dioxane at the TARP treatment plant.

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