2015 – 2024: The site is in Long-term Monitoring which consists of operation and maintenance requirements for the landfill. Annual landfill cap inspections and maintenance are performed on an annual basis, in-well air stripping and soil vapor extraction (SVE) system sampling and maintenance activities were performed on quarterly basis up to 2019, and periodic oxidant injections continue to address residual contaminants in groundwater and semi-annual groundwater monitoring. Notably, in 2019 the SVE and air stripping was stopped.

2014: Final Record of Decision (ROD) Amendment initiating a site remedy consisting of SVE, in-well air stripping and chemical oxidation; landfill cover inspections, maintenance and annual reports; groundwater monitoring and reporting. In addition, the site initiated the Remedial Design and Remedial Action Work Plan for OU1 Groundwater and Soil Gas Remedies; Pre-Design Oxidant Test Work Plan; and Technical Memorandum on Groundwater Monitoring Program Optimization.

2013: Amended Proposed Plan (PP); Focused Feasibility Study (FFS); and groundwater monitoring and reporting.

2012: Installed five off-base groundwater monitoring wells south of LF004 to monitor for possible off-site migration of contamination; completed a Five Year Review (FYR).

2011: Groundwater monitoring and reporting; operation and maintenance of remedial systems and reporting.

2010: Supplemental Remedial Investigation (RI) report that included a draft FFS.

2009: Groundwater monitoring and reporting; operation and maintenance of remedial systems and reporting; Installed 31 new groundwater monitoring wells; prepared a Groundwater Monitoring Work Plan; conducted a bench scale ozone sparging test.

2008: Supplemental RI investigation was extended; soil vapor investigation fieldwork completed; four new monitor wells were installed at the site.

2007: Supplemental RI began and further investigated through 2009.

1994 – 2000: The ROD was signed in 1994. The remedy specified a permeable cap (soil) and monitoring wells. At the time of the ROD, only low levels of contaminants were present in the wells. In 1997, higher levels of contamination were discovered in the landfill monitor wells and a Supplemental RI was conducted in mid 2000. Concentrations of contaminants in some of the monitor wells installed during the Supplemental RI were the highest seen since monitoring began at the site and indicated that contamination was migrating off of the former base.

2023 – 2024: US Army Corps of Engineers rubble removal work plan in progress; work to be conducted for property transfer to the Bureau of Indian Affairs; performed archeological monitoring of work area;  investigation for potential munitions debris, material potentially presenting an explosive hazard, munitions and explosives of concern (MEC), and empty (or pieces of) K941 chemical agent identification set glass.

2021 – 2022: United States Air Force (USAF) awarded a contract for the Site Inspection (SI) field activities and reporting; ongoing development of the SI work plan.

2015 – 2020: Continue evaluation for steps forward; SI Addendum Letter Report, Chemical Warfare Materiel , and MEC, Munitions Response Sites XU403a and XU403b.

2014: Excavation, investigation and removal of unexploded ordnance, discarded military munitions; munitions constituents; empty chemical weapons (mustard gas oil) training sample vials. 

2011 – 2012: Performed and reported on the final SI and MEC clearance (Phase 3).

2010: Investigation searching for munitions constituents as well as sampling and testing at selected locations for contaminants. Performed and reported on the final SI and MEC investigation (Phase 2).  

2009: Published the Parcel N Debris Area preliminary assessment/site inspection (PA/SI) work plan and initiated work on it; completed installation of a fence around Parcel N; published a final Interim Parcel N PA report.

2023 – 2024: Continued groundwater sampling and SVE system maintenance and operation, containment monitoring of the area and reporting; perimeter groundwater monitoring wells completed in March 2023 to fill data gap and plume characterization. 

2021 – 2022: Continued groundwater sampling and SVE system maintenance and operation, containment monitoring of the area and reporting; field activities for additional investigation of the plume boundary; and investigation and reporting on Vapor Intrusion at the U.S. Army Reserve Center west of the site.

2019 – 2020: Continued groundwater sampling and SVE system maintenance and operation, containment monitoring of the area and reporting. 

2018: Continued groundwater sampling and SVE system maintenance and operation, containment monitoring of the area and reporting; and Pilot Study Implementation Work Plan for OU2, Revised Groundwater Remedy. Sulfate injection began in November 2018.  

2017: Continued groundwater sampling and SVE system maintenance and operation, containment monitoring of the area and reporting; submission of Final Field Variance Memorandum #5A – Extraction and Treatment System Construction.

2016: Continued SEE and SVE Systems operation, maintenance and reporting; submission of Final Field Variance Memorandum #4 – Extraction and Treatment System Construction; groundwater monitoring and reporting. SEE remedy was shut down on April 29, 2016.

2015: Continued SEE and SVE Systems operation, maintenance and reporting; Construction Completion/Start up Report for OU2 Revised Groundwater Remedy; Revision No. 2 to SVE Operations Maintenance and Monitoring Manual, Post SEE Installation.

2014: Installed and initiated an SEE system Remedial Design and RA Work Plan for OU2 Revised Groundwater Remedy; SVE and groundwater monitoring, operation, maintenance and reporting; Containment System Status and Shutdown Reports; Declaration of Environmental Use Restriction (DEUR).

2013: Amended PP identified the preferred alternative of SEE and Enhanced Bioremediation for groundwater;  draft ROD Amendment 2 for OU2 groundwater; began the Remedial Design and Remedial Action Work Plan; SVE and groundwater monitoring, operation, maintenance and reporting.

2012: The FFS was completed that evaluated remedial alternatives for ST012.

2011: Finalized the site ST012 containment study work plan.

2010: A report evaluating the pilot test of the Thermal Enhanced Extraction (TEE) system at ST012 was submitted.

2009: Performed Steps 2 through 5 of the TEE Work Plan; produced a site ST012 Groundwater Monitoring Work Plan; groundwater monitoring and reporting.

2008: SVE was conducted to remove jet fuel (JP-4) from the vadose zone; the TEE pilot project was designed to remove fuel and fuel components from the groundwater and begin operation; six new groundwater monitor wells were installed at the site; DEUR completed to facilitate dispersal of the property to the Gateway Airport.

2007: SVE continued to remove jet fuel (JP-4) from the vadose zone at ST012; construction continued on the TEE pilot project.

2004 – 2005: Completed design of the groundwater and vadose zone remedies,  which consisted of a full-scale SVE system. The SVE system began operation in April 2005. The groundwater remedy consisted of a process called TEE. 

1995 – 1996: ROD Amendment 1 to deep soils document in the OU2 PP Amendment and Feasibility Study identified the preferred remedial alternative as SVE, bioventing, and natural attenuation.   

1991 – 1993: Results of the RI at ST012 confirmed that the primary contaminants were jet fuel (JP-4) and aviation gas. The ROD for OU2 was signed in December 1992 identifying groundwater extraction, treatment, and injection plus SVE with in situ bioremediation as the selected remedy. 

2024: A DEUR was finalized in 2024 and annual reporting is conducted as part of long-term monitoring. 

2023: Finding of Suitability to Transfer (FOST)- Supplemental Environmental Baseline Survey finalized.

2022: USAF, EPA, and ADEQ  agreed on an Explanation of Significant Difference to the ROD.  

2020: An SI was conducted for Aqueous Film Forming Foam (AFFF), see Basewide section below. 

2019 – 2020: The Remedial Action Completion Report (RACR) was completed, the report title was revised and a Remedial Action Report was issued. The results concluded that soil, soil gas and groundwater investigation is protective for unlimited use/unlimited exposure (UU/UE); however, there were some detections above screening levels and to account for this uncertainty land-use restrictions were retained. 

2015 – 2016: Two excavations were conducted to remove contaminated soil and confirmation soil gas and soil samples were collected. 

2014 – 2015: Installed and re-initiated an SVE system. Remediation Construction Complete and Start Up Report; continued SVE system operation, maintenance and reporting. The SVE system was shut down in June 2015 and rebound testing was implemented.  

2012 – 2013: Soil gas sampling was conducted to evaluate subsurface conditions. 

2008: A DEUR was executed that prohibits residential use and restricts excavations greater than five feet below ground surface at the site and was completed to facilitate dispersal of the property to the Gateway Airport. A draft ROD Amendment was prepared but not finalized. 

2006: Institutional controls were decided necessary for the site to protect human health and the environment until clean up levels can achieve UU/UE. 

1997 – 2004: SVE pilot study was conducted showing low levels of contamination concluding SVE would be inefficient and not cost effective. A site receptor evaluation was performed in 1998 and under both non-residential risk evaluation and groundwater protection modeling resulted in no threat to human health or the environment under non-residential use. However, ADEQ did not concur with the risk assessment finding based on the evaluation may not have been sufficient for all contaminants and was only for the upper five feet of soil. 

1996: The ROD for OU3 addressing FT002, was signed. The selected remedy was in situ treatment via bioventing. 

2023: In August, ADEQ sends communications to Arizona State University (ASU) to transmit the lead protective cap plan for the 85 residence demolition project of the South Desert Village Protective Cap at the ASU Polytechnic Campus.

2001: Site was transferred to ASU, including deed restriction and the voluntary environmental mitigation and use restriction (VEMUR). Semi-annual protective cap inspections and reporting is performed.  

2000: ROD was completed for the site. 

1999: Operation and Maintenance Manual was finalized outlining the requirements for the owner. 

1998: SDV currently serving as student housing for Arizona State University East. Beneath SDV is a former six-station skeet range which was demolished and graded in 1950, prior to construction of SDV. Contamination in the form of lead pellets in soil associated with the former skeet range underlies 85 housing units in SDV.  Since complete removal of contaminated soil would have required demolition of this valuable housing, a compromise solution involved removal of the top six inches of contaminated soil and installation of six inches of clean soil. The replacement soil is considered a protective cap over the remaining contamination, and will be subject to repair and maintenance, as well as land use restrictions in the form of a VEMUR. The VEMUR defines the affected area as non-residential, and places deed restrictions to bind occupants to maintain the protective cap.

2023 – 2024: Continued groundwater monitoring and summary reporting. 

2022: Continued groundwater monitoring and summary reporting; and a FOST for the property was signed. The Air Force transferred the property to ASU who then as the new landowner formally applied for a DEUR at the Site.

2021: Continued groundwater monitoring and summary reporting; a request for a DEUR was initiated by the USAF.

2020: Continued groundwater monitoring and summary reporting; a Final Field Variance Memorandum #2 – Groundwater Monitoring was submitted.

2016 – 2019: Continued groundwater monitoring and summary reporting in accordance with the ROD; a Field Variance Memorandum #1 (2018) was submitted.

2018: OU6 ROD was finalized, including the site with the conclusion that residual deieldrin in deeper soils greater than feet meter could have future impacts to groundwater. The selected remedy is groundwater monitoring, establishing Institutional Controls in the form of deed restrictions, and placement of a DEUR for management of soil deeper than four meters. 

2014: Continued groundwater monitoring and summary reporting; and a final supplemental risk assessment was completed relating to the soil removal action.

2013: A RACR was finalized on the time critical removal action (TCRA) concluding no further action and protection of human health to a depth of four meters and dieldrin exceeding the Arizona soil remediation levels at depths greater than four meters below ground surface remains a contaminant of concern. Continued groundwater monitoring and summary reports; draft supplemental risk assessment for soil removal action.

2009: Produced a site SS017 Groundwater Monitoring Work Plan; continued groundwater monitoring and summary reporting. 

2007: Dieldrin-contaminated soil from the Old Pesticide/Paint Shop (SS017) was removed following an unsuccessful attempt at bioremediation. A total of approximately 6,000 cubic yards of contaminated soil and amendments were removed from the site and disposed of under an approved work plan. Following removal of the contaminated soil and amendments, confirmation sampling of the underlying soil indicated five “hot spots” where additional soil removal is required.

2004: Groundwater monitoring frequency was reduced from quarterly to annually. 

2001: USAF performed a TCRA of contaminated soil to mitigate potential exposure to the soil and migration to groundwater. A removal action consisting of dieldrin contaminated soil was removed and backfilled with clean soil following verification of clean up goals. The dieldrin contaminated soil was transported to a temporary treatment facility constructed near the former base landfill to undergo bioremediation. The TCRA was conducted in accordance with the Final Action Memorandum. 

1993 – 1999: The site was investigated for the presence of dieldrin under OU4 and OU6. 

2018: ADEQ provided a Leaking Underground Storage Tank (LUST) Case Closure Notice of Decision letter on June 11, 2018 to the Department of the Air Force closing the LUST case file for releases 0263.01-.03 (former building 760). 

2015-2017: Continued groundwater monitoring and reporting; Corrective Action Completion Report (2017).

2014: Continued groundwater monitoring and reporting; SVE system operation and result reports.

2013: Continued groundwater monitoring and reporting;  SVE system operation and result reports. One groundwater monitoring well (MW-21) installation.  

2012: Completed the final in-well air stripping and monitor well installation work plan for site ST035 and installed one remediation well and two groundwater monitor wells.

2010: Groundwater monitoring and reporting; produced a site ST035 Groundwater Monitoring Work Plan; installed five new groundwater monitor wells; completed installation of an SVE system, and operations began in October.

1994 – 2009: Site characterization and delineation was conducted at the site. 

1993 – 1994: Underground Storage Tanks, ancillary piping, and dispensers were removed from the site. 

2024: RI for polyfluorinated chemicals (PFAS) continues. 

2023: Fifth FYR finalized in September. RI for per- and polyfluoroalkyl substances (PFAS) in progress. 

2018 – 2024: A sitewide groundwater potentiometric surface map is conducted. 

2020: USAF submitted a Final PFAS SI for AFFF areas. The purpose of the SI was to determine the presence or absence of PFAS in the environment, as related to historic USAF use of AFFF.

2018: OU6 ROD finalized and the Basewide Specific Uniform Federal Policy Quality Assurance Project Plan (QAPP) Addendum was submitted. The USAF adjourned the Restoration Advisory Board (RAB) community forum. 

2017: Basewide QAPP submittal and Fourth FYR was finalized.

2016: Perfluorinated compounds (PFC) Preliminary Assessment finalized. 

2013 – 2014: The USAF initiated a program to systematically sample its active and closed bases for PFCs at fire training areas as the unregulated chemicals gained increasing regulatory attention for their potential risks to human health and the environment. The OU1 ROD Amendment was finalized in 2014 and OU2 Amendment 2 was finalized in 2013. 

2012: Completed a new Basewide QAPP with standard operating procedures, and the Third FYR was finalized.

2009: Basewide activities included publishing an update to the Basewide Sampling and Analysis Plan and a Basewide Waste Management Plan.

2006: Second FYR was finalized.

2000: OU4 ROD was finalized. 

2001: FYR was finalized.

1998: OU6 was established. Phoenix-Mesa Gateway Airport acquired ownership of the airport facilities. 

1997: OU5 ROD was finalized. 

1996: OU2 Amendment was finalized and OU3 ROD was finalized.

1995: OU5 final action memorandum was finalized. 

1994: OU1 ROD was finalized. Williams Gateway Airport opens. 

1991 – 1993: WAFB formally was closed in September 1993. After the announcement of closure in 1991, the community immediately began work to redevelop the base. Upon closing, WAFB was transferred to the Air Force Base Conversion Agency (AFBCA), and now the successor agency for environmental oversight is the Air Force Civil Engineer Center . AFBCA assumed responsibilities for the restoration and reuse of the base and worked with the RAB and Williams Redevelopment Partnership to maximize reuse of the land.

For cleanup purposes, the former base was divided into five operable units (OUs), OU1 through OU5, with OU6 added in 1998. Each OU consists of many sites of potential concern.

OU5 was set up to address nine soil sites which were closed out through expedited removal fill actions. No groundwater contamination is known to exist at any of the OU5 sites. 

1989: WAFB was placed on the EPA's National Priority List in November. RIs initiated under the Comprehensive Environmental Response Compensation and Liability Act discovered several new areas of contamination that were added to the existing list of sites.

1983: Site investigations initiated in 1983 under the auspices of the Department of Defense installation restoration program identified thirteen 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.

1941: WAFB was constructed in 1941 and served primarily as a pilot training facility, primarily flight training school. At the time the base was constructed, the site was surrounded by irrigated farmland and desert. Industrial activities at WAFB included heavy maintenance of aircraft and ground equipment in support of pilot training.