Location

The West-Cap project area is located on the eastern edge of the Tucson International Airport between Plumer Avenue and S. Tucson Boulevard.  It is just south of the Texas Instruments project area, and southeast of the 162nd Fighter Wing Arizona Air National Guard (AANG) project area.  The address is 2207 E. Elvira Road, in Tucson, Arizona.

Contaminants of Concern

The current contaminants of concern in groundwater include volatile organic compounds (VOCs), mainly trichloroethylene (TCE) ranging from non-detect to about 120 parts per billion (ppb). The federal drinking water standard for TCE is 5 ppb.  Contaminants of concern at the site may change as new data become available.
Health Concerns:  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. If you are drinking water from a private well within the boundaries of the TIAA site, please contact the ADEQ Project Manager.

Site Hydrogeology

In Area B of the TIAA site, which includes the West-Cap project area, the regional aquifer is comprised of two aquifer zones separated by a middle aquitard. The middle aquitard limits the vertical extent of contamination to the upper zone of the regional aquifer. The upper zone of the regional aquifer extends from the water table, located at a depth of about 85 to 100 feet below ground surface (bgs), to the top of the middle aquitard at a depth of about 175 feet bgs.

The upper zone of the regional aquifer can be further subdivided into upper and lower subunits. The lateral continuity of the upper and lower subunits is difficult to estimate due to heterogeneities resulting from meandering streams that deposited these sediments. In some places, the streams deposited relatively coarse-grained sands and gravels, but in other areas fine-grained overbank and floodplain deposits were left behind. In some areas the upper and lower coarse-grained subunit may not exist, and the upper zone of the regional aquifer may be locally composed of almost entirely fine-grained sediments.

The groundwater flow direction in the upper zone of the regional aquifer is generally toward the northwest, but flow within the coarse-grained upper and lower subunits is more toward the west.

More detailed descriptions of the hydrogeology of the West Cap project area can be found in reports and studies available at the TIAA Information Repository.

Action Taken

A pump and treat remediation system operated between 1999 and 2009 that included extraction wells at West-Cap and groundwater treatment at the Texas Instruments project area.  In 2007, ADEQ developed a scope of work for In-Situ Chemical Oxidation as a possible replacement for the pump and treat system, and in 2009 EPA began an ISCO pilot test.  In April 2012, EPA issued the Record of Decision (ROD) Amendment that selected ISCO as the appropriate technology for West-Cap, Texas Instruments, and AANG Project Areas. The ROD Amendment also concluded that monitored natural attenuation would continue for West Plume B.

Status

EPA designed an ISCO remedy to replace the pump and treat remedy at West-Cap with technical input from ADEQ on the remedial design.  Implementation of the ISCO remedy began in 2014 with the drilling of injection wells to inject potassium permanganate into the contaminated groundwater. EPA also installed groundwater monitoring wells downgradient of the West-Cap property in order to monitor the effectiveness of the ISCO remedy. Injection of potassium permanganate was conducted in June 2014. EPA is currently performing periodic groundwater monitoring to determine the effectiveness of the remedial action.