U.S. Air Force Plant 44 | Site History
1950s: This site is a federally-owned weapons manufacturing facility operated under contract by the Raytheon Company (formerly Hughes Missile Systems). The facility occupies over two million square feet of buildings. Past waste disposal practices included: industrial wastewater treatment, storage, and disposal; discharge of wastes into unlined surface impoundments; and land disposal of industrial wastewater, spent solvents, and dilute and concentrated acids and alkalines. Waste disposal practices led to widespread soil and groundwater contamination at the site. Resulting groundwater contamination has spread northward beyond the project area boundaries because of the regional groundwater flow gradient.
Groundwater contamination was first noted in the early 1950's when elevated levels of chromium were detected in a municipal water supply well near AFP-44 and when residents near the TIA complained about water quality problems in their private wells.
1976: The State of Arizona closed a well at AFP-44 due to high levels of chromium.
1981: The EPA and the Arizona Department of Health Services identified VOCs in the upper zone of the regional aquifer beneath the TIA. Beginning in 1981, the City of Tucson closed all municipal wells that exceeded the state action level for trichloroethene (TCE), the primary groundwater contaminant, and notified private well users of the potential risks.
1983: The TIAA Superfund site (which includes the APF-44 project area) was added to the NPL on September 8, 1983. Soon thereafter, the USAF began an extensive investigation of groundwater contamination at the AFP-44 site, which revealed high levels of TCE in the groundwater.
1985: The USAF issued a Record of Decision (ROD) for the regional groundwater at AFP-44.
1987: A large-scale pump, treat, and reinjection system was constructed. This system was installed to provide containment and remediation of regional aquifer groundwater contamination.
1991 - 1992: An remedial investigation (RI) of soil contamination at AFP-44 was conducted with supplemental field work being completed in 1993 and 1995.
1993: A risk assessment was performed to identify soil sites that required remediation
1995: Beginning in 1995, nearly 57,000 tons of metals-contaminated soils (cadmium, chromium, and lead) have been excavated and removed from the site.
1994 - 1997: A feasibility study (FS) for soil remediation was completed. From 1994 to 1996, Dual-Phase Extraction (DPE) systems were installed to treat VOC-contaminated soils and groundwater. In 1996, large-scale SVE systems were built to remove VOCs from soils. In 1996 and 1997, the USAF produced a new ROD that specified SVE treatment of VOC contaminated soils at AFP-44.
2000: In September, one source area (Site 1) was closed after vadose zone contamination was reduced to a level where groundwater would not be impacted above the maximum contaminant level (MCL).
2002 - 2004: During the spring and summer of 2002, 1,4-dioxane was discovered at the site in concentrations ranging from 1.0 to 54 parts per billion (ppb). In 2004, an additional monitor well at AFP-44 yielded a 1,4-dioxane concentration of 600 ppb.
At Site 2, post-SVE monitoring was completed. Vadose zone contamination was reduced to a level that will not impact groundwater above the TCE MCL.
2006: The U.S. Geological Survey Arizona Water Science Center and the USAF Aeronautical Systems Command sampled several wells in July to investigate 1,4-dioxane contamination in groundwater west of AFP-44 and to further define the extent of the 1,4-dioxane groundwater plume. In the 34 wells sampled, 1,4-dioxane concentrations ranged from non-detect to 11 ppb.
2007: On July 13th, the EPA issued an order to the USAF and Raytheon to design, build, and operate an advanced oxidation treatment plant at AFP-44 to treat TCE and 1,4-dioxane. This plant would replace the existing treatment plant. EPA issued this order using provisions from the Safe Drinking Water Act. Additionally, in April, EPA issued a draft settlement agreement to the USAF to initiate a focused RI/FS of 1,4-dioxane.
Late in the year, the USAF submitted a revised draft FFA to EPA.
2008: The advanced oxidation treatment system upgrade was delivered to AFP-44 in June, and the USAF proceeded with installation of the system.
Since 1996, the DPE System had pumped and treated shallow groundwater and lowered the water table to expose more of the vadose zone to soil vapor extraction (SVE) treatment. In early 2008, the DPE system was evaluated for operational efficiency and it was determined that it was no longer effective. The DPE system was shut down on November 1, 2008. Together, the DPE and SVE systems removed approximately 107,514 pounds of VOCs from subsurface soils.
The USAF completed the Phase I focused RI of 1,4-dioxane. The Phase I focused RI for 1,4-dioxane included data acquisition and management, review of historical reports and models for the TIAA site, and evaluation of 1,4-dioxane water quality data collected by the USGS. In October, the USAF submitted to the agencies a Shallow Groundwater Zone Remedial Process Optimization (SGZ RPO) Work Plan. The work plan included installation of new monitor wells to further characterize the shallow groundwater zone.
2009: In September 2009, the advanced oxidation treatment system became fully operational. This HiPOx™ (High Pressure Oxidation) treatment system was designed to remove 1,4-dioxane, but also effectively removes VOCs This new system replaced the air-stripping treatment system that was built in 1987.
The USAF submitted to the agencies a work plan for a Phase II focused RI of the 1,4-dioxane. They also submitted a final Shallow Groundwater Zone Remedial Process Optimization work plan that included rotosonic drilling of five boreholes and two or three wells for further characterization of the shallow groundwater zone.
EPA drafted a FFA and requested comments from the USAF and the ADEQ. This agreement would establish a procedural framework and schedule for developing, implementing and monitoring appropriate response actions at the site. The USAF, EPA, and ADEQ reviewed information pertaining to the status of solid waste management units (SWMUs) at AFP-44 as these would also be covered under the proposed FFA.
2010: Several activities of the Phase II focused remedial investigation (FRI) were completed to further define the nature and extent of 1,4-dioxane in the groundwater within Tucson Airport Remediation Project (TARP) and at AFP-44. These activities included: documenting potential sources of 1,4-dioxane; compiling and reviewing existing information related to 1,4-dioxane in groundwater; and identifying data gaps for defining the extent of the 1,4-dioxane contamination in the Regional Aquifer. The USAF also further investigated an area of higher TCE contamination near monitor will EPA-03. As a result, ADEQ, EPA, and the AF agreed upon two locations where monitor well pairs would be installed to help assess the extent and degree of groundwater contamination near EPA-03.
In-situ pilot studies were continued to evaluate the use of potassium permanganate (KMnO4) to degrade VOCs in groundwater beneath site DP-02 (FACO Landfill) and site DP-03 (Inactive Drainage Channel Disposal Pits). Also during this time period, an evaluation was performed of aerobic biodegradation of TCE and 1,4-dioxane in groundwater. Results of this evaluation and additional studies would be presented in the focused FS for 1,4-dioxane.
2011: In September, the AF signed a FFA with EPA and ADEQ to clean up AF-owned property at AFP-44. Under the terms of the agreement, the AF will work with EPA and ADEQ to remediate areas impacted by AFP-44 south of Los Reales Road. The agreement provides for regulatory oversight of the Air Force's Superfund work at AFP-44. This agreement will ensure that EPA and ADEQ will continue to have an active role in the investigation and cleanup performed by the AF. It also provides a framework for the work to be done and a schedule for all the work required at the site.
To help determine the mechanism by which chromium may be attenuating in the subsurface at Building 801 area, the AF collected soil boring and groundwater samples. The data will be validated and a geochemical evaluation of these data will be presented in the upcoming focused FS report.
Several activities of the Phase II 1,4-dioxane FRI were completed to further define the nature and extent of 1,4-dioxane in the groundwater within the TARP and at AFP-44.
2012: The AF entered into a Performance Based Remediation initiative to maximize the effectiveness of remedial actions at AFP-44. As part of this initiative, the AF hired a new contracting team in late summer. The contracting team was tasked with performing expedited field investigations and treatability studies to provide the AF with alternative remedial. The AF also proposed revisions to Appendix F (Site Management Plan) of the FFA.
2013: The AF continued to investigate offsite 1,4-dioxane groundwater contamination north of AFP-44 (North of Los Reales Road). Once the nature and extent of offsite 1,4-dioxane contamination is defined, technologies will be evaluated to address the groundwater contamination. The AF completed work plans to perform expedited field investigations and treatability studies for alternative remedial actions at AFP-44, which were evaluated and approved by ADEQ and EPA.
2014: The Air Force issued a Proposed Plan for No Further Action (NFA) at the 1980s Pistol Range. The original public comment period was 09/17/2014 to 10/16/2014. In response to community concerns, the comment period was extended to 12/4/2014. The Air Force also began treatability studies to determine the effectiveness of hydraulically fracturing and in-situ treatment of groundwater contamination within fine-grained units underlying AFP-44.