Air Force Plant 44

Science Center Objects

Industrial activity at Air Force Plant 44 (AFP 44), a manufacturing facility located on property owned by the U.S. Air Force and operated by a major defense contractor, resulted in extensive contamination of groundwater with the industrial solvent trichloroethylene (TCE) and other organic compounds. The sole-source regional aquifer underlying AFP 44 provides potable water for municipal, commercial, private, and industrial supplies for the City of Tucson, the municipality of South Tucson, adjacent areas of Pima County, and the Tohono O’odham Nation. Contamination of the aquifer with organic solvents and stabilizers in the area surrounding the Tucson International Airport has been an issue of public concern since being discovered in 1981. 

Map of Air Force Plant 44
Location of Air Force Plant 44 and Tucson International Airport Area Superfund Site, Tucson Basin, southeastern Arizona

The U.S. Environmental Protection Agency identified contaminants in the upper several hundred feet of the regional aquifer underlying areas around the Tucson Airport and identified a number of sources of contamination, including some at AFP 44. The area having contaminated groundwater was designated the Tucson International Airport Area (TIAA) Superfund Site and the U.S. Air Force was given the responsibility for cleanup activities for part of the site. Although large quantities of contaminants have been removed from the subsurface at AFP 44, cleanup activities initiated in 1987 have not yet been successful for complete and permanent aquifer restoration.

OBJECTIVES

The primary objective of this project is to provide technical assistance to the Aeronautical Systems Center (ASC) of the U.S. Air Force for their oversight responsibilities for remediation activities being conducted by contractors at Air Force Plant 44. Additional responsibilities are to provide public information relevant to groundwater contamination at AFP 44 and other areas of the Tucson International Airport Area (TIAA) Superfund Site, remediation activities, and associated geohydrologic and technical issues.

APPROACH

Recent projects by the USGS in the area include an investigation of the extent and trends in 1,4-dioxane contamination in groundwater and an investigation of hexavalent and total chromium in groundwater.

RELEVANCE AND BENEFITS

USGS participation in field activities at AFP 44 enables it to provide appropriate technical assistance to the Air Force and provide accurate information to the public and policy makers. Because water supplies of the Tucson area are a critical concern to the community at large, decisions involving these resources require that the public have access to unbiased technical information.

Results from completed studies:

  • Rebound of Organic Solvent Contamination in Ground Water After Well-Field Shutdown

    Data from 101 wells sampled before and after shutdown of extraction and recharge wells AFP44 were compared. Concentrations of TCE increased in 36 wells, remained the same in 32 wells, and decerased in 33 wells. Increases of concentration of TCE of as much as 1,476 micrograms per liter and decreases of as much as 2,292 micrograms per liter were reported after shutdown. The largest changes in concentrations of TCE occurred in samples collected from wells along the axis of the contaminant plume, in close proximity to previously identified disposal areas. Minimal changes occurred at the perimeter of the plume, suggesting that operation of the reclamation well field has been successful at containing the spread of the plume. New contaminant-source areas were not identified.

    Vertical-profile samples were obtained in five wells. None of the wells showed enough variation of contaminant concentrations with depth to indicate that a major improvement in extraction efficiency could be obtained by pumping selectively from a restricted interval.

    Complete results of this investigation are reported in Graham and others (2001).

     

  • Delineation of Western Plume Boundary of 1,4-Dioxane in Ground Water at the Tucson International Airport Superfund Site

    In the 34 wells sampled, 1,4-dioxane concentrations ranged from non-detect in 10 wells to a high of 11 ppb in 2 wells (Figure 1). Concentrations in 19 wells were greater than the California health advisory level of ≥3 µg/L, with 14 wells above the EPA Region 9 Preliminary Remediation Goal of 6.1 µg/L. Analyses of the two field blanks carried during supply/monitoring well sampling were non-detect for dioxane, indicating no cross-contamination in the transportation of these samples.