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TARP | Site History

1950 - 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.

1988: A feasibility study (FS) was completed and the EPA issued a site-wide Record of Decision  for volatile organic compounds (VOCs) contaminated groundwater.

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 mainly 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, 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.