162nd Fighter Wing Arizona Air National Guard (AANG) Project Area
The Arizona Air National Guard (AANG) site is located in Area B of the Tucson International Airport Area (TIAA) Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) site. The site is on the National Priorities List (NPL), which is periodically updated by the U.S. Environmental Protection Agency (EPA). The United States Air Force is the lead agency at the AANG site, with the Arizona Department of Environmental Quality (ADEQ) and EPA providing regulatory and technical oversight of remedial response actions. The property is located on the north-central side of the Tucson International Airport and is bounded on the north by Valencia Road, and on the west, south, and east by the Tucson International Airport in Tucson, Arizona.
The Groundwater Extraction, Treatment, and Recharge System (GWETRS) was a pump and treat remediation system installed at the AANG project area in May 1997. The GWETRS was installed to capture and treat groundwater contaminated with volatile organic compounds (VOCs) and to prevent offsite migration by maintaining hydraulic control of the trichloroethene (TCE) groundwater plume.
Between May 1997 and May 2012, a total of approximately 820 million gallons of groundwater were treated at the GWETRS, and approximately 39 pounds of TCE were removed from the upper regional aquifer. The GWETRS was shut down in May 2012 and a quarterly groundwater monitoring rebound program began.
Following issuance of the Record of Decision (ROD) Amendment in April 2012, EPA and ADEQ entered into discussions with the National Guard Bureau (NGB) and the AANG to implement the In-Situ Chemical Oxidation (ISCO) remedy for the AANG site.
In late 2014, the NGB/AANG began Remedial Design activities to implement the requirements identified in the ROD Amendment. In the spring of 2015 the AANG conducted baseline groundwater sampling of approximately 100 monitoring wells within the AANG and West Plume B project areas. These data will be used to determine the final design of the ISCO remedy.
To provide community members with an opportunity to learn about the cleanup process and to obtain local perspective for decisions concerning the cleanup, a Unified Community Advisory Board (UCAB) was formed in 1995. The UCAB meets the third Wednesdays of Jan., April, July, and Oct.. These meetings, which are open to the public, begin at 5:45 p.m. located at the El Pueblo Activity Center located at 101 W. Irvington Rd. in Tucson.
1956: The base became operational in training functions for various tactical fighter aircraft. The AANG 162nd Tactical Fighter Group Base has been used to train fighter pilots from the United States and other countries. Operations also include aircraft and vehicle maintenance and fueling. These activities resulted in the release of hazardous substances to the soil and groundwater.
1983: The TIAA site was placed on the NPL on September 8, 1983.
1995 - 1997: In June 1995, a remedial investigation (RI) was completed. The RI characterized the extent of contamination in the soil and groundwater at the AANG project area. Eight sites were investigated on the AANG property, but only site 5 required active remediation of soil and groundwater. Site 5 included a wash rack area that was used for the engine shop and aircraft maintenance shops from 1959 to 1985.
In November 1995, a feasibility study (FS) for site 5 soils was completed. In February 1996, the Remedial Design for groundwater remediation was completed. In August 1996, a ROD was completed that specified that soil vapor extraction (SVE) would be used to remediate TCE- contaminated soil at site 5.
The site 5 SVE system operated from April 1996 to November 1997. During this time, the system removed approximately 64 pounds of volatile organic compounds (VOCs) and reduced the concentration of VOCs in the soil gas to below the cleanup goal of less than 200 micrograms per liter (mg/l). At this level, groundwater would no longer be impacted.
Pursuant to the EPA's 1988 regional groundwater ROD, a groundwater pump and treat system for site 5 was built in 1997. This remediation system extracts contaminated groundwater and removes contaminants using air stripping technology before re-injecting the treated water into shallow vadose zone wells.
2002: In May, EPA and ADEQ completed an RI report that identified the AANG as a source for groundwater contamination at West Plume B.
2003: The AANG completed a Five Year Review (FYR) of their groundwater remediation system to determine if any modifications or improvements were needed. One of the main conclusions of the FYR was that the AANG cannot completely clean up the groundwater at their site until EPA achieves full capture of the upgradient West-Cap plume.
2004: An amended ROD for groundwater at West-Cap and West Plume B was completed in September.
2005: EPA began remedial design of additional extraction wells at West-Cap.
2006: The AANG installed three new monitor wells on the south end of West Plume B. Groundwater sample results indicated that these well locations would be useful for possible monitored natural attenuation monitoring at West Plume B.
2007: To address a data gap, between July and August, the AANG installed six new monitor wells west of the AANG property boundary. The August groundwater sample analysis results for these wells ranged from non-detect to 7.2 ppb for TCE.
The U.S. Air Force conducted a Remedial Process Optimization (RPO) at the AANG project area in October. The purpose of the Air Force's RPO process is to evaluate the status and optimize remediation at sites across the United States. The last RPO for the AANG project area occurred in 2002. The RPO occurs in three phases with Phase I focusing on data collection and review, Phase II directed at intensive evaluation of system optimization and applicability of new technologies, and Phase III focused on implementation of recommendations developed from the first two phases. The Air Force conducted Phase I and most of Phase II during a site visit in October.
2008: The AANG began well drilling related to an in-situ pilot study of potassium permanganate at the base.
2009: The groundwater remediation system at the AANG site 5 continued to operate.
2010: In September , the 162nd FW-AANG submitted a report on the results of the ISCO pilot study. The ISCO pilot test evaluated the effectiveness of potassium permanganate (KMnO4) in oxidizing TCE in groundwater. Results of the ISCO pilot test suggested that TCE was effectively oxidized by the KMnO4.
The AANG reported that the TCE groundwater plume in both the upper and lower subunits at the AANG project area appeared to be steadily decreasing. The reduction of the TCE groundwater plume may be attributed to the combination of remedial actions [ISCO and the GWETRS] in operation at the project area.
2011: EPA issued a proposed plan to amend the existing ROD for the clean-up projects associated with the Area B. This included the AANG, West-Cap, West Plume B, and the Texas Instruments Project Areas. In the proposed plan, EPA evaluated several remedial alternatives including ISCO using potassium permanganate.
2012: In April, EPA issued a ROD Amendment. The ROD Amendment selected ISCO using potassium permanganate to replace the pump and treat remedy at the AANG, West-Cap, and Texas Instruments Project Areas. The ROD Amendment also concluded that monitored natural attenuation will continue for West Plume B. The GWETRS was shut down in May and a quarterly groundwater monitoring rebound program began.
2013: The National Guard Bureau (NGB) and the AANG began discussions with ADEQ and EPA for implementation of the final ISCO phase at the AANG property.
2014: IIn late 2014, the NGB/AANG began Remedial Design activities to implement the requirements identified in the ROD Amendment. EPA and ADEQ continued to will work closely with the NGB/AANG to ensure that the activities are implemented in accordance with the ROD Amendment.
The current contaminants of concern in groundwater include VOCs; mainly TCE. On-site historical TCE concentrations have ranged from non-detect to 46 ppb. Contaminants of concern at the site may change as new data becomes available.
The City of Tucson is the main municipal water provider at this site. All municipal wells in the area that were contaminated with TCE have been shut down. Most of the domestic wells have either been shut down or converted to irrigation wells. However, a few residents with domestic wells with low levels of TCE have chosen to continue using their wells. If you are drinking water from a private well within the boundaries of the TIAA site, please contact the ADEQ Project Manager.
The vadose zone at the AANG project area extends from the surface to a depth of approximately 88 feet below ground surface (bgs) and is composed of silty sands, caliche deposits, and gravelly sands.
The upper zone of the regional aquifer in the AANG project area consists of two subunits and a middle aquitard. All of the known groundwater contamination at the AANG project area is found in these subunits. The upper subunit consists of well-graded, gravelly, course sand and is found at a depth of approximately 88 to 103 feet bgs.
The middle aquitard separates the upper and lower subunits and is composed of tight sandy silt with scattered pebbles. At site 5, the middle aquitard lies at a depth of about 103 to 128 feet bgs.
At site 5, the lower subunit is found at a depth of approximately 128 to 138 feet bgs and is composed primarily of course-grained sand. There is also a northwest-southeast trending sand channel in the lower subunit along the south-central portion of the AANG base.
The groundwater flow direction in the upper and lower subunits is toward the northwest, and the depth to groundwater is approximately 90 feet bgs. More detailed descriptions of the hydrogeology of the AANG project area can be found in reports and studies available at the TIAA Information Repository.
*In Arizona, but outside the Tucson area, call toll-free at (888) 271-9302.
Interested parties can review select site documents at the TCE Superfund Information Library located at 202 W. Valencia Road, Tucson, AZ 85706, at the Valencia Branch Public Library in Tucson, (520) 594-5390. The complete official site file can be reviewed at the EPA Region IX, Records Center, Mail Stop SFD-7C, 95 Hawthorne Street, Room 403, San Francisco, CA 94105, (415) 536-2000.
Interested parties can review site information here on this page and at the ADEQ Record Center located at 1110 W. Washington Street, Phoenix, Arizona. Please contact (602) 771-4380 or (800) 234-5677 ext. 6027714380 for hours of operation and to schedule an appointment.