EPA #: AZD980737530

Superfund National Priority List (NPL) Status: The EPA listed this site on Sept. 9, 1983

Location

The Texas Instruments site is located at 6730 S. Tucson Boulevard, on the northeast side of the Tucson International Airport. It is bounded by Tucson Boulevard on the east, Aragon Road on the south, Plumer Boulevard on the west and Valencia Road on the north.

Contaminants of Concern

The current contaminants of concern in groundwater include volatile organic compounds (VOCs), mainly trichloroethene (TCE), with smaller amounts of tetrachloroethene (PCE). TCE concentrations currently range from less than 1.0 part per billion (ppb) to about 40 ppb. The federal drinking water standard for TCE is 5.0 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.

Environmental Considerations

In Area B of the TIAA site, which includes the Texas Instruments project area, the regional aquifer is comprised of two aquifer zones separated by a middle aquitard. The middle aquitard limits the contamination to the upper zone of the regional aquifer, which is about 70 to 100 feet thick. The upper zone of the regional aquifer can also 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 places, the streams deposited relatively coarse-grained sands and gravels, but in other areas fine-grained overbank and floodplain deposits were left behind. 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 groundwater flow direction in the upper zone of the regional aquifer is generally toward the north-northwest, but flow within the coarse-grained upper and lower subunits is more toward the northwest or west. More detailed descriptions of the hydrogeology of the Texas Instruments project area can be found in reports and studies available at the TIAA Information Repository.

Action Taken

A pump and treat remediation system operated from 1992 until 2009.  Groundwater from the West-Cap project area was also treated by the Texas Instruments treatment system from 1999 until 2009.  Between 1992 and 2009 the treatment system removed a total of about 16.3 pounds of TCE from approximately 176 million gallons of groundwater.    In the fall of 2009, a pilot test was initiated for In-Situ Chemical Oxidation (ISCO) using potassium permanganate to treat TCE in groundwater.

Status

Following issuance of a Record of Decision (ROD) Amendment in April 2012, EPA and ADEQ entered into discussions with Texas Instruments to negotiate a consent decree (CD) to implement an ISCO remedy at the Texas Instruments project area.  The CD was signed in June 2015, and Texas Instruments initiated the ISCO remedy in February 2016 with baseline groundwater sampling.  Injection of the potassium permanganate into the vadose zone above the TCE contaminated groundwater at the site occurred in July and August 2016.  Currently, the groundwater is being monitored to evaluate the effectiveness of the ISCO remedy and Texas Instruments submits quarterly progress reports to EPA and ADEQ.

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