Tucson Airport Remediation Project (TARP)
The northern operable unit of the Tucson International Airport Area (TIAA) Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) site is the Tucson Airport Remediation Project (TARP). The TIAA site is on the National Priorities List (NPL), which is periodically updated by the U.S. Environmental Protection Agency (EPA). This portion of the main plume extends from Los Reales Road northward just past Irvington Road in Tucson, Arizona. It is bounded on the west by Interstate 19 and the Santa Cruz River, and on the east by S. 6th Avenue and Nogales Highway (Route 89).
TARP is in the operation and maintenance phase of cleanup, and consists of a remediation well-field and a groundwater treatment plant. The remediation well-field includes the South Well Field (SWF) of five extraction wells, and the North Well Field (NWF) of four extraction wells. Piping from these extraction wells goes to the groundwater treatment plant.
The TARP system provides hydraulic control and remediation of Area A of the TIAA Superfund Site Regional Aquifer. The TARP system was started in September 1994 and has pumped and treated over 41,390 billion gallons of groundwater. To date, approximately 5,043 pounds (lbs.) of trichloroethene (TCE) have been removed from the regional aquifer. Clean water from the TARP treatment plant is delivered to the Tucson Water Department (Tucson Water) distribution system.
In early 2013, Tucson Water finalized an engineering design for an Advanced Oxidation Process (AOP) system to remove 1,4-dioxane from the groundwater. The AOP treatment train included such components as ultra-violet reactors, peroxide storage/feed equipment, and a granular activated carbon (GAC) tank for peroxide quenching. The AOP system was constructed in mid-2013 and underwent testing for incorporation into the existing groundwater treatment plant. Tucson Water began full operation in early 2014.
Water level and water quality data were used to evaluate the performance of the existing remediation well fields in achieving capture of the TCE plume, remediating the aquifer, and treating groundwater. Evaluation of water elevation and quality data collected indicated that the TARP remedial system was continuing to meet compliance requirements. The TARP treatment plant continued to show consistent performance in removal of VOCs in treated groundwater.
In 2015, Tucson Water began to plan for replacement of one of the north well field extraction wells (R-009A) due to deterioration of the well since it was installed in 1994.
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 January, April, July, and October. 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.
1950s - 1970: Historic industrial and defense related activities resulted in the release of hazardous wastes into the groundwater leading to extensive contamination of the regional aquifer. The source of contamination for the TARP plume was Air Force Plant 44 (AFP-44) and the Airport Property Project Areas of TIAA.
1983: The TIAA site was placed on the NPL on September 8, 1983.
1985: A remedial investigation (RI), which characterized the extent and concentration of contaminants in the TARP groundwater plume, was completed by the Arizona Department of Health Services.
1994: The TARP groundwater remediation system, including extraction wells, treatment plant, and associated piping, was completed.
2002: During the spring and summer, 1,4-dioxane up to approximately 12 parts per billion (ppb) was discovered in the TARP project area. The 1,4-dioxane was thought to have originated from AFP-44.
2004 - 2005: In 2004, EPA asked Tucson Water and TARP representatives to begin a new RI/FS to evaluate 1,4-dioxane contamination and what remediation technology (if needed) would be applicable. However, in 2005 the U.S. Air Force agreed to conduct the RI/FS with cooperation from Tucson Water, the Tucson Airport Authority, and TARP.
2007: EPA initiated further discussions with the Air Force about conducting a new RI to focus on 1,4-dioxane contamination north of the Air Force Plant #44 boundary. The RI process will help determine if additional groundwater monitor wells are needed to confirm continued TCE plume capture, and to further characterize the 1,4-dioxane plume. Tucson Water uses a groundwater model to evaluate plume capture.
2008: The Air Force completed the Phase I focused RI for 1,4-dioxane contamination north of Los Reales road which includes the TARP area. The Phase I investigation 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 U.S. Geological Survey. The City of Tucson continued to operate the TARP well field to minimize the amount of 1,4-dioxane entering the public water system.
2009: The Air Force submitted to the agencies a Phase II focused RI of 1,4-Dioxane Work Plan which includes the TARP area. The work plan included a summary of existing data, planned field investigations, and a groundwater modeling work plan.
2010: EPA Region 9 revised its toxicity assessment of 1,4-dioxane and lowered the protective risk range in drinking water to between 3.0 ppb and 35 ppb for a lifetime of exposure. Tucson Water conducted pilot testing of ozone-peroxide and UV-peroxide advanced oxidation treatment for 1,4-dioxane. This pilot testing demonstrated that both technologies could effectively treat 1,4-dioxane. In addition, both technologies effectively treated TCE and 1,1-dichloroethene (1,1-DCE).
Several activities, performed as part of the Phase II Focused Remedial Investigation (FRI), were completed by the Air Force. The results of these activities further defined the nature and extent of 1,4-dioxane in the groundwater within 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 in defining the extent of the 1,4-dioxane contamination in the Regional Aquifer throughout both the TARP and AFP-44 areas.
2011: In January, EPA issued a new Drinking Water Health Advisory for 1,4-dioxane that ranged from 35 ppb (excess cancer risk of 100 in one million) to 0.35 ppb (excess cancer risk of 1 in one million). As a result of engineering evaluations and pilot-scale treatability testing, Tucson Water determined that the use of ultraviolet light with hydrogen peroxide injection (UV-peroxide) is the best AOP option for 1,4-dioxane treatment at TARP.
The 1,4-dioxane treatment system was designed to include GAC treatment to quench residual hydrogen peroxide prior to final treatment in the existing packed column aeration system. The system was designed to treat combined flow from both the NWF and SWF.
The United States Air Force (Air Force) is working on Phase II of a 1,4-dioxane FRI. The purpose of the FRI is to further define the nature and extent of 1,4-dioxane in the groundwater within the TIAA Superfund Site Area A.
2012: On July 18th, the City of Tucson sponsored a groundbreaking ceremony for the AOP Water Treatment Facility. This treatment process will remove 1,4-dioxane once it is operational.
2013: In early 2013, Tucson Water finalized an engineering design for the AOP system to remove 1,4-dioxane from the groundwater. The AOP treatment system includes such components as ultra-violet reactors, peroxide storage/feed equipment, and a GAC tank for peroxide quenching. The AOP system was constructed in mid-2013 and underwent testing for incorporation into the existing groundwater treatment plant.
2014: Water level and water quality data were used to evaluate the performance of the existing remediation well fields in achieving capture of the TCE plume, remediating the aquifer, and treating groundwater. Evaluation of water elevation and quality data collected indicated that the TARP remedial system was continuing to meet compliance requirements. The North Well Field (NWF) remediation wells were operated at reduced levels due to startup of the Advanced Oxidation Process (AOP) water treatment facility and rehabilitation of remediation well R-008A. Although the NWF was operated at a reduced level, containment of VOCs in groundwater at the northern extent of the plume was maintained. The TARP treatment plant continued to show consistent performance in removal of VOCs in treated groundwater.
Also in 2014, Tucson Water began to plan for the replacement of north well field well R-009A because of deterioration of the well since it was installed in 1994. Tucson Water has acquired land for the replacement well and started the design process.
The current contaminants of concern in groundwater include VOCs, mainly TCE. TCE concentrations range from non-detect to around 100 ppb. Additionally, in 2002, 1,4-dioxane concentrations of up to approximately 12 ppb were discovered in the TARP project area. Contaminants of concern at the site may change as new data become 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 and 1,4-dioxane 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 Arizona Department of Environmental Quality (ADEQ) Project Manager.
The TARP project area is located in the northwestern portion of the TIAA site. In the southern half of the project area, the regional aquifer is composed of two hydrostratigraphic units: the upper zone of the regional aquifer and the lower zone of the regional aquifer. The regional aquifer in the northern portion of the project area is composed of only one hydrostratigraphic unit called the undivided regional aquifer.
The undivided regional aquifer (in the northern part of the TARP project area) is composed mainly of coarse-grained materials.
Depth to groundwater in the TARP project area varies from 80 to 240 feet bgs and generally gets deeper in a northward direction. The general groundwater flow direction is toward the north-northwest. More detailed descriptions of the hydrogeology of the TARP 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.