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Superfund Site | Former Williams Air Force Base

EPA #: AZ7570028582

Superfund National Priority List (NPL) Placement: Nov. 21, 1989


At approximately 4,043 acres in Mesa, Maricopa County, Arizona, the National Priorities List (NPL) site study area (site) essentially mirrors the former Williams Air Force Base (WAFB) footprint.  The nominal site boundary is Ray Road to the north, Ellsworth Road to the east, Pecos Road to the south, and Power Road to the west.  Impacted areas vary, but with one known exception, are contained within the former WAFB footprint. An impacted groundwater plume extends less than one-quarter mile southerly beyond the former base boundary, but is still part of the NPL clean-up action.

Contaminants of Concern

Groundwater contaminants include light non-aqueous phase liquid (LNAPL) or "free product" related to aviation fuel; volatile organic compounds (VOCs) related to fuels and industrial solvents, and pesticide (dieldrin). Soil contaminants include fuel-related hydrocarbons, VOCs, Poly Chlorinated Biphenyls (PCBs), pesticide (dieldrin), metals, and perfluorinated chemicals (PFCs). 

Debris of concern: Munition debris (generally empty munition casings) have been found in a relatively small, secured area near the south central border.  A few, small, empty chemical agent identification set (CAIS) vials have also been found in the munitions debris area.  The few, small, empty vials appeared to contain mustard gas (liquid-state) samples (chemical warfare agent vials).

Potential contaminants of concern: Perfluorooctanoic Acid and Perfluorooctane Sulfonate (PFOA and PFOS, respectively) assessment was initiated as part of an emerging contaminant study.  The results are not expected until the Department of Defense and the EPA formalize action levels. Note that some reference literature uses the generic terms perfluorinated compounds and also the acronym (PFCs), referring to the chemical family which includes PFOA and PFOS.  The EPA refers to this targeted emerging contaminant chemical family as Per- and Polyfluoroalkyl Substances (PFAS). PFOA and PFOS are found in many products, including aqueous film-forming foam (AFFF) associated with aviation firefighting.

Public Health Concerns

There currently are no known exposures to contaminants of concern (COCs) in excess of applicable health based levels. This includes groundwater, soil (surface and subsurface) and soil vapor studies conducted to date. Drinking water is supplied via City of Mesa off-site sources. Irrigation water is drawn from wells generally upgradient from contaminant impacted areas or from potable water sources. 

Unintended exposure to contaminated soil and groundwater is a potential health hazard. Some sites include soil contaminants left in place.  Land use controls have been placed at those known sites to minimize exposure potential.

Environmental Considerations

Within the WAFB site there are no unique habitats, threatened species or endangered species. Native vegetation is sparse.