Pacific Southwest, Region 9: Superfund
Serving Arizona, California, Hawaii, Nevada, the Pacific Islands, and Tribal Nations
Williams Air Force Base
EPA #: AZ7570028582
Congressional District: 01
On this page
Description and History
NPL Listing History
NPL Status: Final
Proposed Date: 07/14/89
Final Date: 11/21/89
The 4,043 acre Williams Air Force Base (WAFB) site was commissioned as a flight training school in 1941. Contaminants from base activities included organic solvents and paint strippers, petroleum spills, metal plating wastes, hydraulic fluids, pesticides, and radiological wastes. Discharges and disposal at WAFB resulted in soil and groundwater contamination. Thirteen sub-sites were identified as potentially contaminated areas including: two fire training areas, a fuel storage area , two surface storm drainage areas, a hazardous material storage area, a landfill, a pesticide burial pit, a radiological disposal area, and four underground storage tanks. In 1992, several new sub-sites were discovered at the base which were added to the investigation. As of 2017, now most of the identified contaminated sites have been addressed, and the majority of the former base has been transferred for reuse by Phoenix-Mesa Gateway Airport authority and Arizona State University. The most significant remaining areas are include the ST-12 Fuels Spill Site and the LF-004 Landfill Site, Parcel N Debris Area,, SS017 Old Pesticide/Paint Shop, the FT002 Fire Training Area, and ST035 Former Gas Station,
At the ST-12 Fuels Spill Site jet fuel from leaking storage tanks and pipelines has contaminated an aquifer considered by the State of Arizona as a potential drinking water source not currently being used. In October 2008, Air Force initiated a Thermal Enhanced Extraction pilot test utilizing steam injection to extract the most toxic and mobile constituents from the plume. Following successful completion of the pilot, Air Force amended the Record of Decision in September 2013 to select full scale Steam Enhanced Extraction (SEE) followed by enhanced bioremediation as the final remedy for the site. The SEE system was constructed and was in operation from October 2014 to April 2016, removing over 2.5 million pounds of hydrocarbons. However, in the course of operations it was revealed that the area of contamination is larger than the SEE system was designed to treat. EPA and Air Force are currently discussing the next steps.
The final remedy for the LF004 landfill was selected in April of 2014. The original Record of Decision selected a permeable cap of river rock to address direct contact concerns with elevated beryllium in surface soils, and required monitoring of the groundwater. Low levels of industrial solvents Perchloroethylene (PCE) and Trichloroethylene (TCE) were subsequently discovered in the groundwater. The Record of Decision was amended to include soil vapor extraction of shallow sources in the landfill area, In Well Air Stripping (IWAS), and chemical oxidation to treat the ground water. As of 2017 the remedy is operating and approaching attainment of remedial goals.
The Parcel N Debris Area is a vacant lot adjacent to the landfill that was used for military training; a few buried drums and munitions items were discovered on the parcel which has triggered the requirement for further investigation. Air Force and Army Corps of Engineers have completed magnetometer surveys and excavated identified burial pits where a few empty, broken and intact medicine bottle sized Chemical Agent Identification Set (CAIS) mustard (chemical warfare agent) vials used for military training were found. While the AF and ACOE has been doing everything possible to ensure removal of all potentially harmful items on the parcel, It is not possible to exclude the potential for other CAIS bottles remaining on the property as there are no detection methods capable of identifying glass bottles beneath the ground surface.
In 2001 Air Force completed an excavation at the SS017 Old Pesticide / Paint Shop to remove soils contaminated with pesticides, paint thinners, and PCBs to a maximum depth of 12 feet, and backfilled the excavation with clean soil. Subsequently, groundwater monitoring has shown diedrin has consistently been present in the groundwater above human health based risk screening levels, but below the drinking water health advisory. Since 2000 the water table under the site has risen 40 feet into the contaminated deeper soils and dieldrin concentrations in the ground water are increasing. As of March 2017 Air Force, EPA and ADEQ are resolving a formal dispute over the remedy for the SS017 Old Pesticide Paint Shop with a renewed commitment from the AF to finalize the remedy for the site to implement a Declaration of Environmental Use Restriction (DEUR) with the State of Arizona and to continue monitoring the groundwater to ensure the remedy remains protective. AF has also agreed to excavate of lead paint contaminated soils under the water tower under ADEQ's voluntary cleanup program.
The FT002 Fire Training Area consists of two former pits located south of the runways where trash, fuels, and ignitiable liquids were disposed and set on fire for fire fighting exercises. Although the pits were excavated and a bioventing remedy was partially implemented, contamination still remained in deeper soils. Air Force has been operating a soil vapor extraction system since 2014 to complete the removal of contaminants in the subsurface. A recent concern with Perflourooctonic Acid and Perflourooctane Sulfonate (POFA and POFS) found in fire suppressants is an emerging issue at fire training areas at military sites nationwide, and remains to be addressed at this site.
Leaking underground tanks at the Former Gas Station ST035 lead to releases of fuels and gasoline additives MTBE, and 1,2 Dichloroethane iton the groundwater, Soil Vapor Extraction and In Well Air Stripping and ongoing groundwater monitoring have been employed to address these concerns under ADEQ's Underground Storage Tank Program. As of 2017, cleanup objectives have been met and the site is undergoing regulatory closure with the state.
Contaminants and Risks
- Soil and Sludges
- Environmentally Sensitive Area
Groundwater contains Light Non-Aqueous Phase Liquids (LNAPL) or "free product" in the form of floating jet fuel and Volatile Organic Compounds (VOCs) from disposal of industrial solvents.. Soils contained various VOCs, Poly Chlorinated Biphenyls ( PCBs), and pesticides from past disposal practices. Accidental ingestion of contaminated soil and groundwater is a potential health hazard.
Who is Involved
This site is being addressed by the United States Air Force through a Federal Facilities Agreement with the U.S. Environmental Protection Agency, the Arizona Department of Environmental Quality and the Arizona Department of Water Resources. The Air Force community contact for Williams Air Force Base is
Public Affairs Officer
Air Force Real Property Agency Western Region
3411 Olson St.
McClellan CA 95652-1003
(916) 643-6420, ext. 109
Investigation and Cleanup Activities
Williams Air Force Base is participating in the Installation Restoration Program, a specially funded program established by the Department of Defense (DOD) in 1978 to identify, investigate, and control the migration of hazardous contaminants at military and other DOD facilities. This site is being addressed in six operable units employing both short and long-term remedial actions as described below.
Initial Actions: A portion of the Southwest Drainage System was stabilized in 1988 by installing a soil, cement, and concrete cap on the ditch. In 1991, a small pesticide drum burial site was excavated and disposed of off site. Radiological materials were removed from another burial site and disposed of in late 1992. The removal of approximately 20 underground storage tanks at the liquid fuels storage area was conducted during late 1990 and early 1991, eliminating the source of liquid fuel leaks.
Operable Unit 1 (OU-1): Under EPA oversight, the Air Force (AF) completed an investigation of the nature and extent of the contamination at all impacted areas of the base. The 1994 Record of Decision (ROD) selected a remedy that included installation of a permeable river rock cap over the main landfill of the former base, Site LF004 and long term groundwater monitoring. Monitoring of the groundwater at Landfill LF-004 eventually revealed increasing concentrations of TCE and PCE, along with a rising water table. In 1997 groundwater monitoring identified contaminants (TCE and PCE) leaching out of the landfill area and migrating off-site. The Air Force installed additional monitoring wells off site to help delineate the leading edge of contamination. Soil gas investigations have been conducted to identify sources of groundwater contamination within the area of the landfill. Soil gas survey data identified source areas to be remediated. In May 2013, the Air Force solicited public comments on a proposed remedy for soil vapor extraction to treat vadose zone soils and in well air stripping technology to treat the groundwater plume. A Record of Decision Amendment was signed in April 2014. The Soil Vapor Extraction, In Well Air Stripping (IWAS) and Chemical Oxidation remedy has been operating since 2014.
Operable Unit 2 (OU-2): Liquid Fuels Storage Area: In 1990, an investigation into the type and extent of contamination was initiated at the waste liquids storage area. At the conclusion of the investigation in late 1992, a remedy was chosen to pump and treating the groundwater contamination, however the remedy was not feasible. A Focused Feasibility Study (FFS) report was completed and submitted to the regulatory agencies in 1999 which recommended monitored natural attenuation with future studies to evaluate new technologies as they become available. Both the USEPA and the State of Arizona rejected the FFS report. To avoid a formal dispute resolution, the Air Force agreed to add Thermally Enhanced Extraction (TEE) as a component of the groundwater remedy to enhance effectiveness and feasibility of the selected remedy to address LNAPL and dissolved phase contamination. From 2002 to 2005, the Air Force spent over 3 million dollars in the design and construction of this remedy. In a turn-around of events, on February 1, 2005 the Air Force notified EPA that funding to operate the remedy was not approved. Furthermore, the Air Force explained that it unilaterally amended their funding criteria which removed the Liquid Fuel Storage Area from funding eligibility. Following formal dispute resolution, in February 2006, Air Force agreed to fund the operation of the TEE pilot, and if successful, expand it to a scaled up final remedy. The pilot test was completed in 2010 after having successfully removed 118,331 pounds of petroleum hydrocarbons and 3,652 pounds of benzene from the subsurface. The pilot was operated on a calendar schedule due to funding constraints and free product was still being recovered as operations ceased. The intent of the pilot was to demonstrate the removal effectiveness of the technology. In September 2013, the Air Force and the regulatory agencies signed a Record of Decision to complete the Steam Enhanced Extraction (SEE) remedy that had begun under the pilot, followed by enhanced bioremediation to treat residual contamination. The remedy was constructed and the SEE operated from October 2014 to April 2016 removing more than 2.5 million lbs of fuel from the subsurface. However, during the course of operations, it was discovered that the area of contamination was larger than previously thought, and EPA, ADEQ and the Air Force are discussing the next steps. The Air Force has already completed a Finding of Suitability to Transfer the surface property of the ST-12 site.
Operable Unit 3 (OU-3): Site FT002. At this fire training site, all structures, piping, and 117 cubic yards of surface soil were removed and transported to approved off-site disposal areas. In addition, contaminant concentrations in 25,000 cubic feet of contaminated subsurface soil were reduced through bioventing. Bioventing didn't bring the contamination in deeper soil to levels that would allow unrestricted use.
The Air Force submitted a Draft Record of Decision Amendment to EPA with land use controls as part of the remedy. The Air Force then prepared a Proposed Plan for public comment which removed the land use controls from the remedy. The EPA did not concur with the remedy without inclusion of land use controls, and Air Force subsequently formalized their land use control requirements with the State of Arizona. Recent sampling indicates contamination still remains in deep soils above remediation goals. The Air Force installed a Soil Vapor Extraction (SVE) system in June 2014 to complete the remedy, which is nearing achievement of cleanup goals.. Still to be completed are the finalization of the ROD Amendment and transfer of the property.
Operable Unit 4 (OU-4): the Record of Decision for Operable Unit 4 was signed in 1999 to address the former skeet ranges at South Desert Village, and site SS20 along with 8 other facilities. The ROD selected a six inch soil cap for the South Desert village housing area affected by the former skeet range, along with land use restrictions and long term maintenance and monitoring. At the SS- 20 skeet range the ROD specified removal of lead contaminated soils from firing range berm. In addition, institutional controls were specified for sites SS-16, former electroplating and chemical cleaning shop and building 1010 (site SS-24), and no further action was recommended for the other 4 sites.
Operable Unit 5 (OU-5) addressed nine facilities: ST-25 airfield underground storage tanks, WP27 Paint Shop Leach Field, DP-28 Sewage Sludge Trenches, SS-29 Prime Beef Yard, SS-31 Course Maintenance Area, SS-32 Building 1070, SS-34 Munitions Incinerator, LF 26 Concrete Hardfill Drum Removal Area, Area 26 Sewage Sludge Stockpile Area. Removal Actions were completed for these sites in 1995, and the OU-5 ROD was signed recommending no further action for these sites in 1998.
Operable Unit 6 (OU-6) addressed the excavation of Site SS-17 the former Pesticide Paint shop and recommended no further action for the Iinvestigative Waste Facility (IWF) and decontamination pad at building 1069, which managed and stored wastes from investigation and cleanup activities.. The SS-17 Pesticide/Paint Shop was a storage shed located adjacent to the water tower. Pesticides were reportedly disposed to the ground in this area, which also included a leaking PCB transformer. Paint chips were also found in the area. The site was excavated in 2001 to remove dieldrin and PCB contaminated soils to a maximum depth of 12 feet., The excavated contaminated soils from SS-17 were amended and stockpiled at another location on base in an unsuccessful attempt at bioremediation treatment. In November 2007 the bio treatment piles were removed for offsite disposal, as documented in an April 2010 report. In 2011, the Air Force solicited public comments on a final remedy comprising institutional controls and ongoing groundwater monitoring for the remaining contamination in the subsurface at the SS-17 Pesticide Paint Shop site. The Record of Decision was on hold pending formal dispute resolution over the need for institutional controls. AF and the regulatory agencies are finalizing an agreement to continue to implement institutional controls and monitoring; which will be documented in a Final Record of Decision. AF has also agreed to conduct a voluntary cleanup to excavate lead paint contaminated soils beneath the water tower.
Parcel N Debris Area -- a vacant lot near the landfill still remaining to be transferred has been identified as having potential waste disposal and small arms munitions issues. Air Force is investigating this site due to evidence of possible releases and munitions. Excavation of debris pits was halted following the discovery of an intact Chemical Agent Identification Set (CAIS) mustard vial, a chemical warfare agent flask used for training purposes. US Arny Corps of Engineers took over excavation of the pits in 2014 as a possible chemical weapons disposal site. The excavation was completed in 2014; only inert munitions debris and broken or empty CAIS training vials were recovered. The site continues to be investigated for military munitions and CERCLA contaminants.
Cleanup Results to Date
As of November 2014, with the exception of the Parcel N Debris Area and ST12 fuels spill site, all required remedial actions on all parcels of the former Williams Air Force Base have either been undertaken already or have been constructed and are operating,
Potentially Responsible Parties
Potentially responsible parties (PRPs) refers to companies that are potentially responsible for generating, transporting, or disposing of the hazardous waste found at the site.
The Air Force remains responsible for the cleanup of the former base until all the remedies are completed.
Documents and Reports
No documents found
Public Meetings: The Williams Restoration Advisory Board (RAB) meets semi-annually at the Arizona State University Polytechnic Campus, Peralta Hall Room #132, 7171 E. Sonoran Arroyo Mall, Mesa, AZ 85212. For more information about RAB activities contact Scott Johnston at (916) 643-6420 ext 257.
Public Information Repositories
The public information repositories for the site are at the following locations:
Government Records Section (3rd floor)
Arizona State University
300 East Orange Mall
Tempe, AZ 85281
Government Records Reference Desk: (480) 965-3390
EPA Site Manager
75 Hawthorne Street
San Francisco, CA 94105
EPA Community Involvement Coordinator
75 Hawthorne Street
San Francisco, CA 94105
EPA Public Information Center
1110 W. Washington Street
Phoenix, AS 85007
706 Brooks Road,
Rome, New York 13441
Public Affairs Specialist
3411 Olson Street
McClellan CA 95652
After Hours (Emergency Response)