Revised On: Jan. 5, 2023 - 3:10 p.m.

1925: DMAFB began operations at the site. It is a 10,700-acre training facility for tactical aircraft crews, and a primary storage facility for obsolete or excess aircraft.

1940s: LF-01 began operation in the early 1940s. The landfill was used for the disposal of household debris, metals, car and aircraft components, solvents, pesticides and other items.

1976: LF-01 ceased operation.

1982: The installation restoration program (IRP) was initiated. Studies had identified 53 potential areas of concern. (Many of these sites had no confirmed contamination and most of the sites identified for remediation have now been cleaned up.)

1983: Collection of soil and groundwater samples at the LF-01 site began.  The samples were tested for volatile organic compounds (VOCs), metals, pesticides, polychlorinated biphenyls, petroleum hydrocarbons, and other compounds. Analytical results were below regulatory standards.

1985: An automotive gasoline leak was discovered at site ST-36.

1987: Suspected small-arms ammo disposal pits were identified.

1989: A soil investigation was conducted at the ST-35 The investigation, which included 22 soil borings, indicated subsurface soils were contaminated with JP-4 jet fuel to depths of 230 feet. Soil contaminants included petroleum hydrocarbons and benzene, toluene, ethyl benzene and xylene (BTEX).

1994: The LF-01 sampling program was completed. Analytical results were below regulatory standards. Groundwater remediation of the jet fuel at the ST-35 occurred briefly, but was turned off after the water was determined to be free of contamination.

1995: A soil vapor extraction (SVE) system was constructed at the ST-35 following a 1994 study. This system was constructed to remove the BTEX and petroleum hydrocarbon constituents in the soil. (The SVE system continues to operate at the site.)

1999: A landfill cover for LF-01 was designed and installed. A landfill gas collection, control, and treatment system was subsequently installed. Also, benzene was reported at site ST-36 above the Arizona residential soil remediation levels (SRLs) at 43 milligrams per kilogram (mg/kg) at a depth of 60 feet.

2003: While installing a downgradient monitor well at the ST-35 in April, free product was encountered at a depth of 245 feet. Drilling of the well was stopped and a jet fuel investigation commenced. Analysis of the free product revealed the presence of JP-8, which was used at DMAFB starting in the early to mid-1990s. Over a dozen soil borings were drilled and sampled. It was determined that the product was coming from a previously unknown release.

2004: At ST-36, benzene was reported above the Arizona residential SRLs at 23 mg/kg at 50 feet below ground surface (bgs). At ST-35, three new groundwater monitor wells were installed farther away from the ST-35 in the downgradient direction northwest of the site. The monitor wells were installed to address concern about jet fuel penetrating the clay layer above the water table.

2005: A five-year review (FYR) was completed in July at the low level radiation hazardous waste site RW-16. A buried and fenced cement vault containing the hazardous waste is monitored annually. No deficiencies were identified during the FYR and the remedy is to be continued.  An investigation and removal action was completed at the recycling yard areas of concern 50 and 51. Geophysics, trenching and sampling were followed by limited soil and debris removal at the buried disposal area. No contaminants of concern (COCs) above regulatory levels in soils were left in place and a closure letter was issued by ADEQ in July. A FYR was also completed for the automotive gasoline leak at site ST-36, and an SVE system was installed to remediate petroleum hydrocarbons in shallow soils at the former ST-52.

2006: The jet fuel contamination in the subsurface soil at ST-35 was characterized both laterally and vertically. Several of the soil borings were converted to vapor extraction wells. The SVE system removed over 206,000 gallons of petroleum hydrocarbons from the soil and continues to operate.

DMAFB continued maintenance of the cover vegetation and cap at the main base landfill (LF-01). A landfill gas collection, control, and treatment system operated about 20 hours per week to maintain minimum levels of methane beneath the control tower. No COCs were identified above regulatory levels in regional groundwater during the year.

2007: Through the base wide groundwater monitoring program, DMAFB continued to monitor 14 groundwater wells. One of these groundwater wells was abandoned due to damage to the well casing. Prior to abandonment, sample analysis results from this well indicated high concentrations (2700 parts per billion) of toluene. A replacement well was installed.

In November, construction of a new Bank of America was completed at the ST-52 site, and the SVE system installed at ST-52 continued to operate.

Following the FYR, and based on site investigations, the Aerospace Maintenance and Regeneration Center (AMARC) landfill (LF-02) was reclassified from a landfill to disposal pits.

A pilot test of in-situ chemical oxidation (hydrogen peroxide) was conducted at the ST-35. The purpose of the test was to reduce benzene concentrations in the perched water at the site. Since 1995, the SVE system at this site has removed 1.3 million pounds of volatile hydrocarbons.

A Phase I comprehensive site evaluation was completed under the Military Munitions Response Program (MMRP).

2008: In February and March, DMAFB injected hydrogen peroxide into the contaminated perched groundwater at the ST-35.

DMAFB removed debris in the AMARC disposal pits and the ammunition disposal pits (OT-41). OT-41 contained more than 1,000 rounds of inert small-arms ammunition. In October, ADEQ issued a letter of completion for nine IRP sites. A Phase II comprehensive site evaluation under the MMRP was also performed.

2009: In Nov., DMAFB installed four additional wells at LF-01 to further monitor the groundwater beneath the landfill. At ST-52, the soil vapor extraction (SVE) system installed at the ST-52 was taken offline in the first quarter of 2009 while DMAFB and ADEQ evaluated more cost-effective off-gas treatment options. Based on a pilot test performed in June, DMAFB elected to use SVE with GAC to replace the existing thermal oxidation system. The SVE system using GAC was restarted in July. Also in Nov., four additional wells were installed at the ST-52 site to further characterize the groundwater at the former AAFES gas station.

2010: As of June 30, methane was only detected in one gas monitoring probe (GMP), at landfill LF-01, at 2.4 percent during both sampling rounds. Groundwater samples collected from all monitoring wells, including the four new wells installed in 2009, were non-detect for petroleum hydrocarbons and VOCs.

At ST-52, data collected through June 30, document that since start of operation in May 2005, approximately 110,292 pounds of petroleum hydrocarbons have been removed. Groundwater monitoring detected only one compound, 1,2-dichloroethane above its AWQS of 5 micrograms per liter.

The SVE system installed at ST-35, continued to operate. In June, it had removed approximately 1.39 million pounds of petroleum hydrocarbons.

2011 – 2012: Methane has only been detected in one GMP so far at landfill LF-01, at 2.4 percent. Groundwater samples collected from all monitoring wells, including the four new wells installed in 2009, were non-detect for petroleum hydrocarbons and VOCs. At ST-52, data collected through the end of Dec. 2011 indicated that extraction rates of COC had become asymptotic, indicating that a further reduction in soil vapor contamination levels would be unlikely. Since the start of operation of the SVE System in May 2005 through Dec. 2011, approximately 113,000 pounds of petroleum hydrocarbons were removed. The SVE was shut down on Dec. 31, 2011. Results of semi-annual groundwater monitoring, performed in 2011 and 2012, detected only one compound, 1,2-dichloroethane above its AWQS of 5 micrograms per liter.

The SVE system installed at ST-35 ceased to operate in December of 2012 pending evaluation of current subsurface conditions. As of Dec. 2012, approximately 1.41 million pounds of petroleum hydrocarbons have been removed from the subsurface.

2013: A new contractor was hired for the IRP for the Air Force’s new Performance Based Remediation Contract. Ongoing monitoring and remediation of LF-01, ST-35, ST-36 and ST-52 are continuing. Twenty-five additional small sites have been remediated and are in the process of being closed.

2014: The Air Force submitted draft Records of Decision (RODs) for ADEQ review and approval for the following sites: DP-49 [Dump Site]; DP-50 and DP-51 [Disposal Pits]; LF-02 [Old Base Landfill]; OT-29 through OT-34 [Dross Piles]; OT-39 [Dross Piles]; OT-41 [Burial Pits]; SS-09 [CE Storage Yard]; OT-45 [Auto Hobby Shop]; SD-18 [AMARC Flush Farm]; OT-44 [Former Vehicle Maintenance Building 4705]; OT-46 [Chevron Area]; ST-40 [Warrior Park]; ST-53 [J4 Pump house]; and SS-43 [Golf Course Maintenance Building]. ADEQ had previously provided the Air Force with detailed comments regarding each of these draft RODs. In late 2014, ADEQ performed a final evaluation of these RODs.

ADEQ performed field oversight of a subsurface soil gas investigation at Site 36. The Air Force installed soil borings to determine the extent of subsurface contamination in the area of Site 36. After the Air Force evaluates the initial analytical results, additional soil borings may be drilled. Eventually, results of the investigation will be used to refine the remediation options at the site.

ADEQ also continued to coordinate oversight of cleanup activities at RW-16 [low-level radioactive waste] with the Arizona Radiation Regulatory Agency and the Air Force Radioisotope Committee.

2015: RODs were signed for twenty-two sub-sites within the Davis-Monthan AFB property. Twenty-one of these sites were “legacy” sites that required no action or no further action. The additional site was an MMRP site where soil excavation and removal successfully remediated the site.

Release of the Final Preliminary Assessment Report for per and polyfluorinated alkyl substances (PFAS).

2016: Completed the removal and disposal of 4 pipes containing low-level radiation material waste from RW016. Site was backfilled and inspected in October 2016.

2017: Release of the Final Public Involvement Plan Installation Restoration Program in January 2017. Remedial Action Completion /MARSSIM Final Status Survey Report September 2017 Nuclear Regulatory Commission (NRC) Radioactive Materials Permit closed September 2017. Site inspection program for AFFF conducted included installation of three groundwater monitor wells.

2018: RODs signed for ST035 and ST052. Continued monitoring of groundwater and gas collection system along with inspections and maintenance at the landfill site LF001. ADEQ concurrence with closure of ST055.

2019: Final Site Inspection report (ISR) for AFFF published in February 2019. Groundwater monitor wells installed on north side of base to investigate PFAS, the results of which were published in Addendum 01 to SIR in July 2019. Air Force published Draft Final Record of Decision MRS TM553, MRS TM553A, and MRS TM554A in April 2019 where Land Use Controls were selected remedy. In August 2019, a Final Tier 3 Risk Assessment Report for ST-36 was published which concluded that a risk-based closure of ST-36 with no further action will not present an unacceptable risk to human health and the environment. In December 2019, the ADEQ Underground Storage Tank (UST)/Leaking UST Section issued a Case Closure Notice for ST-36.

2020: In April 2020, the USAF published a Final Proposed Plan for ST-36 where No Further Action was presented as the preferred alternative supported by a risk-based evaluation. In August 2020, the USAF published a Relative Risk Site Evaluation (RRSE) for PFAS releases at DM. The RRSE identified the Stormwater Outfall Canal along the north side of the base with an overall site category of High. Five other AFFF release areas had overall site categories of Medium or Low. In 2020, USAF is in the process of preparing a focused RI to investigate PFAS. In March 2020, a Proposed Plan for Site RW016 was provided to the public for review with the recommendation of NFA. In July 2020, a Draft Final ROD was prepared with a selected remedy for RW016 of NFA, based on completion of a Multi-Agency Radiation Survey and Site Investigation Manual (MARSSIM) Site Characterization Investigation and Interim Removal Action.