161st Air National Guard
The 161st Air National Guard (ANG) Base is located on the southwest corner of a 50.7 acre site at the Phoenix Sky Harbor International Airport (PSHIA) in Phoenix, Arizona between the south runway and the Salt River Channel. The facility was relocated in 2001 for the expansion of the runway network at PSHIA.
A Proposed Plan (PP) was developed for the site to include six Installation Reduction Program (IRP) Sites within the ANG Base. The IRP Sites are listed as follows:
The ANG worked in conjunction with ADEQ to develop and review the PP; a public comment period took place from November 29 – December 29, 2013. One comment was received from the City of Phoenix, Aviation – Planning and Environmental department concerning the abandonment of monitoring wells on the site. No other public comments were received for this site.
A Final Record of Decision (ROD) was submitted by the National Guard Bureau in June 2014. ADEQ concurred with the No Further Action (NFA) decision of this ROD.
No community involvement activities are planned at this time.
1951 - 1972: In 1951, the federal government authorized the construction of a new National Guard Base at PSHIA. The land is owned by the City of Phoenix (COP). The 197th Fighter Squadron was the first occupant of the new base. In 1960 the squadron was renamed the 161st Fighter Group. In 1961, the group was designated to the 161st Air Transport Group to fly cargo/passenger missions for the Military Air Transport Command until 1968. From 1968 to 1972, the Phoenix Air Guard was designated as the Aeromedical Airlift Group. The 161st Air Refueling Group has occupied the base since 1972.
Throughout the history of the base, a number of fighter, cargo, and air refueling aircraft have operated from the base. Typical activities at the site included aircraft fueling maintenance, ground equipment maintenance, and other associated activities.
Over the years, waste streams at the site have included fuels and oils, various solvents and paint thinners, and other chemicals. In the earlier years of site operation, many fuels and oils were disposed of through an oil/water separator and then to a storm drain. Some flammable wastes were disposed of at the airport’s Fire Training Pit.
1988: The 161st ANG became a part of the IRP. In July, a preliminary assessment (PA) for the site was completed. The PA identified four areas of potential contamination.
1990: Remediation activities began in December. Activities included a soil gas survey, geophysical testing, monitor well installation, piezometers, and regular groundwater monitoring events.
1992: The National Guard Bureau (NGB) completed a draft final site investigation report. According to the report benzene, ethylbenzene, tetrachloroethene (PCE), trichloroethene (TCE), dichloroethene (DCE), and 1,2-dichloroethane (DCA) were detected in monitor wells at the base. The NGB installed 12 new monitor wells as part of the IRP Site #6 petroleum, oils, and lubricants storage area source characterization. COP installed three monitor wells.
The most significant contamination is associated with petroleum hydrocarbons, specifically benzene, at IRP Site #6. In this area, soil contamination was evident. Groundwater contamination from this area included a plume of benzene that remains within the borders of the facility, and well within the borders of the PSHIA.
1999: In June, a decision document presenting the selected soil remediation action was signed. The selected remedy included an SVE and AS system.
2000: In April, a final action memorandum was prepared by the 161st ANG.
2001: In February, the SVE/AS system was operational.
2003: In January, the AS portion of the treatment system was shut down due to concentrations of benzene below Aquifer Water Quality Standards of five parts per billion (ppb) for the previous four quarters. This was due to the combined result of remedial activities and smearing caused by the historically low groundwater elevations. Semi-annual groundwater monitoring continued during this rebound period.
2005: The SVE/AS systems were restarted in June because of detections of contaminants of concern after rebound, and the effect of rising groundwater levels. During this reporting period, approximately 25 pounds of total non-methane organic carbon (TNMOC) was removed by SVE, and 846 pounds by biological degradation. This reflects only the month of June after the SVE was re-started. Rebound monitoring continued quarterly as agreed upon in the July 2005 meeting between ADEQ and the ANG.
2006: The draft 2006 Sampling and Analysis Plan, which was received September 2005, proposed that after four quarters of monitoring, the data should be assessed as to whether the treatment systems can be shut off again.
2007: An air induction pilot test was completed in January. In July the SVE system was shut down because levels were consistently below soil screening levels for contaminants of concern and because mass removal had been asymptotic for the last two years. The new soil remediation rule revisions, which went into effect in May, eliminated C10-C32 (TNMOC in soil vapor) as a regulated compound, and added other fuel related compounds.
2008: An Explanation of Significant Differences was prepared in November updating the current Applicable or Relevant and Appropriate Requirements to meet the May 5, 2007 revised soil remediation levels.
2009: A Five-Year Review was prepared summarizing the remedial investigation and remedial action conducted at Site No. 6.
2010: A Project Closure report was submitted to ADEQ in early 2010. After comments were addressed ADEQ concurred with the report in July 2010.
2013: Submittal of a Proposed Plan for a request of No Further Action for the IRP sites.
2014: ADEQ approval of the Final ROD for the site.
2016-2017: A PFC (Perfluorinated Chemicals) Investigation began of the site's subsurface soils and groundwater.
Contaminants of concern include: VOCs (including benzene, toluene, ethylbenzene and xylenes [BTEX]), JP-4 (jet propellant fuel), total petroleum hydrocarbons, and various metals. None of the contaminants detected on the site warrant additional subsurface investigation.
ADEQ does not recognize any public health impacts associated with the six IRP sites.
The 161st Air Refueling Group is located within the Basin and Range Physiographic Province. The Basin and Range Province is characterized by broad sloping valleys bounded by steep fault- block mountain ranges.
The site is located in the West Salt River Valley sub-basin of the Phoenix Active Management Area. Valley-filled deposits lie beneath the West Salt River Basin and these deposits are underlain by metamorphic, granitic, and extrusive rocks that form an impermeable hydrologic barrier. The valley-fill deposits are the main sources of groundwater. Based on lithology, the valley-fill deposits can be divided into three water bearing strata. The top layer is the Upper Alluvial Unit. Beneath this layer is the Middle Fine-grained Unit. The bottom layer is the Lower Conglomerate Unit.
The Lower Conglomerate Unit can be divided into two sub units based upon grain size, clast type, and stratigraphy. The lower part of this unit is moderately to well-cemented mudstone or siltstone that may be evaporitic; sand; gravel conglomerate, and massive deposits of gypsum, anhydrite, and halite. Course grains may appear locally in the lower part of the unit, and wells drilled to these areas may yield up to 2,100 gallons per minute. The upper part of the Lower Conglomerate Unit Consists of weakly to moderately cemented clay, silt, mudstone, gypsiferous mudstone, gypsum, sand, and finely grained gravel.
The Middle Fine-grained Unit consists of weakly consolidated silt, sand, gravel and clay and ranges in thickness from 100 to 800 feet throughout the sub-basin. It is made of mostly unconsolidated silt, sand and gravel. The unit ranges from 400 feet thick to less than 200 feet thick.
The primary source of water in the valley-fill deposits is the Upper Alluvial Unit. This unit consists mostly of unconsolidated silt, sand, and gravel. Groundwater is usually unconfined, but semi-confined conditions may occur locally where there is an increase of finer grained materials. Perched conditions are also known to occur. Groundwater flow is usually to the west-northwest direction and occurs from 70 feet to 80 feet below ground surface.
*In Arizona, but outside the Phoenix area, call toll-free at (800) 234-5677.
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.