1983: The TIAA site was placed on the NPL on September 8, 1983.

1988: A ROD for the regional groundwater at TIAA was issued by the EPA. This ROD also covered groundwater contamination in Area B which includes the West-Cap project area.

1992: A groundwater pump and treat remediation system for the Burr-Brown facility (now Texas Instruments) became operational. This system apparently captured some West-Cap contamination and spread it northward.

1996: A shallow soil gas survey was conducted by EPA. This survey identified two potential source areas with elevated levels of TCE, PCE, 1,1,1-TCA, and 1,1-dichloroethene (1,1-DCE).

1997 - 1999: The pump and treat system at Burr-Brown (now Texas Instruments) was discontinued from March 1997 through November 1999 while EPA built a groundwater extraction system at the West-Cap project area. The West-Cap extraction system pumped TCE contaminated groundwater northward to the Burr-Brown water treatment plant where it was cleaned and used in their manufacturing processes.

2000: In November, two groundwater monitor wells (WC-8 and WC-9) were installed to determine if TCE was migrating north or west of the West-Cap source area. Information obtained from these new wells indicated that the TCE had migrated westward toward the AANG project area where it is extracted and treated in the AANG treatment plant. Texas Instruments bought Burr-Brown.

2002: In May, a remedial investigation (RI) Addendum and a feasibility study (FS) report were completed.

2004: In May, monitor well WC-10 was installed upgradient of West-Cap to determine if there were any upgradient sources of contamination. In September, EPA issued an amended ROD for groundwater at this site (and West Plume B).

2005: EPA and the Arizona Department of Environmental Quality (ADEQ) began remedial design of additional extraction wells and associated piping to the Texas Instruments treatment plant.

2006: EPA's groundwater removal action at West-Cap removed approximately 3.8 pounds of TCE and PCE from about 105 million gallons of groundwater. The remedial design for additional extraction wells was completed in early 2006. Two new extraction wells and associated piping were installed in September.

In May, ADEQ and EPA agreed to a State Superfund Contract for remedial action at West-Cap. This contract addressed long-term groundwater remediation and funding at the site. As per the CERCLA regulations, the contract specified that EPA would pay for 90% of the remediation costs for the first ten years and ADEQ would pay for 10%. Additionally, in November, EPA and ADEQ signed a Cooperative Agreement whereby EPA provided ADEQ with a grant to cover EPA’s 90% share of the costs for remedial actions at the site.

2007: EPA and ADEQ were informed that Texas Instruments would be moving their manufacturing process out of Tucson in 2009. ADEQ developed a Scope of Work (SOW) for a pilot test and full-scale remedy consisting of ISCO for volatile organic compound (VOC)- contaminated groundwater.

2008: EPA utilized ADEQ’s SOW and developed a draft work plan for the ISCO pilot study.

2009: In March, EPA began conducting an ISCO pilot test at the West-Cap area.

2010: EPA continued to monitor the ISCO treatability study that involved the injection of potassium permanganate into the source zone at former Building A. EPA also prepared the focused FS for the West-Cap project area, which evaluated a number of alternatives for the final groundwater remedy including ISCO and pump and treat. ADEQ provided technical support and oversight on this work.

2011: EPA issued a proposed plan to amend the existing ROD for the clean-up projects associated with Area B. This included the West-Cap, AANG, West Plume B, and Texas Instruments Project Areas. In the proposed plan, EPA evaluated several remedial alternatives including ISCO using potassium permanganate.

2012: In April 2012, EPA issued the ROD Amendment. The ROD Amendment selected ISCO as the appropriate technology for application at the West-Cap, Texas Instruments, and AANG Project Areas. The ROD Amendment also concluded that monitored natural attenuation will continue for West Plume B.

2013: Following issuance of the April 2012 ROD amendment for Area B (AANG, West-Cap, West Plume B, and Texas Instruments), EPA began designing the ISCO remedy to replace the pump and treat remedy at West-Cap. ADEQ provided technical input on the remedy design.

EPA and ADEQ also began discussing ISCO remedy implementation for the AANG and Texas Instruments project areas with representatives of the AANG and Texas Instruments. Monitored natural attenuation continued at West Plume B.

2014: EPA implemented the ISCO remedy by drilling injection wells on the West-Cap property. These wells were used to inject potassium permanganate into the contaminated subsurface units. EPA also drilled groundwater monitoring wells downgradient of the West-Cap property in order to monitor the effectiveness of the ISCO remedy. EPA will be performing periodic groundwater monitoring to determine the successfulness of the remedial action.