1941 - 1951: Industrial-type operations started in 1941 and were comparatively small until 1946. After a period of deactivation, the base resumed operations in 1951. During the 1950s, larger quantities of wastes were generated by the expanded maintenance required for the new jet aircraft assigned to the base. At the Waste Treatment Annex (site No. 2), a small quantity of low-level radioactive electron tubes, believed to be encased in concrete, was buried in a pit 12 feet deep in 1956.

1951 - 1973: The Perimeter Road Petroleum, Oil, and Lubricants (POL) Waste Application site (site No. 4) was used during approximately 1951-70. POL wastes were spread on the dirt road around the runway at the western portion of the base. The majority of the wastes consisted of contaminated JP-4 fuel, with some diesel fuel, waste engine oils, and waste solvents. Among the substances that may have been included were methyl ethyl ketone (MEK), trichloroethane (TCA), trichloroethene (TCE), toluene, cresylic acid, o-dichlorobenzene, phenolic paint strippers, acetone, and paint residues and thinners.

The POL Waste Disposal Trench site (site No. 5) was used during about 1970-72. POL wastes were disposed of in numerous trenches approximately 1.5 feet deep and in a shallow lagoon at the northeast corner of the site.

The South Fire Department Training Area (site No. 6) was used during 1941-46, and again during approximately 1951-63.  POL wastes were poured onto old aircraft or simulated aircraft in a cleared, bermed area and then set on fire.

The North Fire Department Training Area (site No. 7) was used during approximately 1963-73. The disposal method was similar to site No. 6.

Thirty-two areas of the base were subject to further investigation: two fire training areas; a waste oil and fuels underground storage tank area; three waste oil disposal trench areas; three surface drainage canals receiving oily wastes; a sewage treatment plant effluent canal; the site of an abandoned Defense Reutilization and Marking Office; thirteen land disposal sites (one of which contains a radiological disposal area); an old incinerator site; a former outside transformer storage site; two leaking underground storage tank sites; an abandoned surface impoundment; an ammunition storage area; a skeet range; and the base production wells.

1983: In November, eight water supply wells on the base were sampled as part of Installation Restoration Program (IRP). Analysis indicated that two of the wells had low levels of 1,2-dichloroethane (1,2-DCA) and trans-1,2-dichloroethene (1,2-DCE). Soil near one of the wells contained 1,2-DCA. An estimated 10,400 people obtain drinking water from base and private wells within three miles of hazardous substances on the base.

1990: The site was placed on the EPA’s NPL on August 30th. The primary use of the site was to provide advanced flight training to fighter pilots. Discharges and waste disposal practices at LAFB resulted in soil contamination. The site participated in the IRP, 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. A Federal Facilities Agreement to conduct the site cleanup plan was signed in Sept. 1990.

1997 - 2002: LAFB conducted a final potential source of contamination inspection in August 1997. Also, EPA and ADEQ conducted a final site inspection in April 2000 and determined that the AF has constructed the remedy in accordance with the requirements in the RODs for the entire site and the remedial action work plans. EPA concurred on the final close-out report for LAFB on April 26, 2001. An institutional control plan dated Dec. 15, 2001 was developed by the AF, and EPA concurred on the plan on January 8, 2002. In 2002, the first LAFB FYR report was completed, and EPA concurred on the review in January. The LAFB was officially deleted from the NPL list on April 22nd; however, there are institutional controls which serve to maintain the current Site conditions and control the risks to human health by prohibiting residential development.

2007: The second FYR was completed in June.

2008: New groundwater monitor wells were installed in April to replace submerged wells. Long-term monitoring of ten IRP sites continued, including the fire training area, bulk fuels storage, wastewater treatment annex landfill, oil/water separator canal and former liquid waste storage facility.

2009: An interim annual groundwater monitoring report summarizing the results of the annual groundwater monitoring activities was conducted at sites ST-18 and SS- 42 as part of the USAF Environmental Restoration Program (ERP). The primary objectives of the groundwater long-term monitoring (LTM) were to document the presence or absence of groundwater contamination in accordance with the Operable Unit (OU)-1 and OU-2 RODs. Groundwater level measurements and groundwater sampling was conducted in May. The results of the annual groundwater monitoring event conducted were consistent with previous years’ annual monitoring data.

The Interim Annual Gamma Radiation Monitoring report (also part of the USAF ERP) summarized the results of the annual gamma radiation monitoring activities that were performed at site RW-02. Gamma radiation measurements were collected from five existing monitor points. The measurements collected during this monitoring event remain consistent with previous years’ monitoring events. The measurements recorded from monitoring points MP-1, MP-2, MP-3, and MP-4 did not exceed the action level of twice the background readings. The measurements were comparable with the measurements collected from a background monitoring point. These results indicate that the containment structure for the buried radiological material remains intact and that the surrounding soil does not appear to have been impacted by this material.

As part of the LAFB LTM Work Plan, an annual inspection at site ST-18 included a detailed visual observation of the concrete cap. The inspection consisted of walking several transects across the concrete cap area and noting visual cracks, joints, former penetrations, and other features of interest (such as previous repairs) that may affect the integrity of the cap. The 2009 annual inspection indicated that the cap has been maintained per the ROD, is still functioning as intended, and remains an effective barrier to surface water infiltration.

2010 - 2011: Annual reports were reviewed by ADEQ and EPA, which included the Potential Source of Contamination (PSC) ST-18 concrete cap inspection report, the annual radiation monitoring report and the annual groundwater monitoring report. Results for the PSC ST-18 concrete cap inspection report concluded that minor repairs to the cap were required in order to maintain its integrity including sealing cracks and gaps. It was recommended that the cap be replaced in the future. Results for the annual radiation monitoring report concluded that the containment structure for the radiological material remains intact and that the surrounding soil does not appear to have been impacted by this material. Results for the annual groundwater monitoring reports for 2010 and 2011 concluded that results were consistent with previous year's annual monitoring data, with a slight increase in groundwater elevation. In 2011, the groundwater elevation of the site was approximately 240 feet below ground surface (bgs).

2012: The third FYR report was finalized in September. It summarized the status of the remedies implemented at ten sites identified in the OU-1 and OU-2 ROD at LAFB which included soil treatment, source capping, groundwater monitoring, gamma radiation monitoring, and institutional controls (ICs).  The third FYR report discusses the following ten sites that required a remedy, as determined from the results of the remedial investigation (RI):

• Drainage Ditch Disposal area (DP-13)
• Eastern portion of North Fire Training area (FT-07E)
• Outboard Runway Landfill (LF-03)
• Old Salvage Yard Burial site (LF-14)
• Northwest Landfill (LF-25)
• Wastewater Treatment Annex Landfill (RW-02)
• Oil/Water Separator at Auto Body Shop (SD-38)
• Bulk Fuels Storage area (SS-42)
• Former Liquid Waste Storage Facility (Facility 993) (ST-18)
• Old Surface Impoundment West of Facility 993 (DP-23)

The assessment conducted as part of this FYR found that the remedies required at the OU-1 and OU-2 sites were implemented in accordance with the requirements of the RODs. All remedies are functioning as designed, continue to be protective of human health and the environment, and control exposure pathways that could result in unacceptable risks. The next FYR will be due January 30, 2017.

2013: In Sept., the performance based remediation contract was awarded. The annual long term monitoring activities were performed. Results for the annual groundwater monitoring reports concluded that results were consistent with previous year’s annual monitoring data.

2014 - 2015: Soil sampling activities were performed at sites FT-07E and ST-18 in the later part of 2014. Results were submitted to ADEQ in 2015. Site SS-42 will continue to undergo annual groundwater monitoring sampling events.