Superfund Site | U.S. Air Force Plant 44
EPA #: AZD980737530
Superfund National Priority List (NPL) Status: The EPA listed this site on Sept. 9, 1983
The U.S. Air Force Plant 44 (AFP-44) is located about eight miles south of downtown Tucson, Arizona and is bounded to the north and east by the Tucson International Airport (TIA), to the south by Hughes Access Road and to the west by the Nogales Highway (Route 89).
Contaminants of Concern
The current contaminants of concern in soil and groundwater include metals and volatile organic compounds (VOCs). The principal contaminants of concern are trichloroethene (TCE), 1,1-dichloroethene (1,1-DCE), 1,4-dioxane and chromium. The concentration of TCE in groundwater at the site currently ranges from less than 0.5 parts per billion (ppb) to 1,520 ppb. The federal drinking water standard for TCE is 5.0 ppb. Contaminants of concern at the site may change as new data become available.
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 use wells in the area have been impacted, but these 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. Areas with soil contamination at or very close to the surface have been excavated so that there are no known public health impacts from contaminated soils.
The regional aquifer beneath most of AFP-44 is divided into three main hydrogeologic units including the upper zone, a middle aquitard, and the lower zone. The middle aquitard pinches out several miles north of the site, and the upper and lower zones merge into one regional undivided aquifer. The upper zone (where nearly all of the groundwater contamination is present) is composed of layers of gravelly sand interbedded with clayey sand and sandy clay. A low permeability layer of clay and silt occurs near the potentiometric surface within the upper zone which, due to its hydraulic properties, retains high concentrations of VOCs.
A large-scale pump-treat-reinject system is operating with both advanced oxidation process (AOP) and air-stripping treatment. This system pumps contaminated groundwater from the higher concentration portions of the aquifer and reinjects the treated water at the perimeter of the site to help provide hydraulic containment of the plume.
Beginning in 1995, nearly 57,000 tons of metals contaminated soils (cadmium, chromium, and lead) were excavated and removed from the site. The Air Force also conducted soil excavation at the 1980s Pistol Range to remove lead contaminated soil, and in 2015, issued a Record of Decision (ROD) for No Further Action (NFA).
Dual-phase extraction (DPE) and Soil Vapor Extraction (SVE) systems operated between 1996 and 2008. Together, the DPE and SVE systems removed approximately 107,514 pounds of VOCs from subsurface soils. In-Situ Chemical Oxidation (ISCO) was implanted beginning in 2010 at AFP-44 VOC source areas, and the Air Force is currently conducting hydraulically fracturing and in-situ treatment of groundwater contamination within fine-grained source areas.
The groundwater remediation system is in continuous operation at approximately 5,000 gallons per minute. It has removed approximately 25,082 pounds of VOCs from the Regional Aquifer, and has treated over 32.8 billion gallons of groundwater between April 1987 and May 2017. The groundwater remediation system at AFP-44 includes an AOP treatment system to treat 1,4-dioxane, which began continuous operation in 2009, and air strippers to treat VOCs. Currently, the Air Force is working on a Record of Decision Amendment for groundwater to incorporate the AOP treatment process.
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