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 Plume B project area.

1998: A remedial investigation (RI) report for the former West-Cap property project area noted that the lateral extent of trichloroethene (TCE) contamination north of Valencia Road was not defined and the report recommended additional investigations to fully characterize West Plume B.

2000: Seismic reflection data was collected and analyzed to help characterize the hydrogeology in the area. ADEQ used this and other site data to develop a computer model of the West Plume B to help estimate the fate and transport of TCE in the plume and to simulate potential remedial strategies.

2002: In May, ADEQ completed an RI report for West Plume B. The report describes the extent and magnitude of groundwater contamination, and it identifies the AANG as the probable source of this contamination. Also in May, EPA completed a feasibility study (FS) report. The FS analyzed remedial alternatives ranging from no action to active pump and treat.  In June, EPA issued a proposed plan for groundwater contamination at West Plume B.

2004: In September, EPA issued an amended ROD for groundwater at this site (and West-Cap). The remedy selected in this amended ROD for the West Plume B area was pump and treat. However, the ROD also specified that if groundwater monitoring data suggested that the plume was attenuating, then EPA would reconsider an MNA remedy.

2006: In the early part of the year, ADEQ recommended implementing MNA at the site. Based on the semi-annual sampling event conducted in February, TCE concentrations detected at the West Plume B area ranged from less than 0.5 parts per billion (ppb) to 12 ppb. TCE concentrations at the site were lower than historical levels, suggesting that the plume was naturally attenuating.

2010: The AANG continues to monitor West Plume B groundwater contamination for the MNA remedy. The TCE plume is stable and/or declining in extent and concentration through time. TCE trends continue to indicate that MNA is an appropriate remedy. ADEQ is providing 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 AANG, West-Cap, West Plume B Project Area, and Texas Instruments Project Areas. In the proposed plan, EPA evaluated several remedial alternatives including ISCO using potassium permanganate. EPA also evaluated the appropriateness of monitored natural attenuation for West Plume B.

2012: In April, EPA issued the ROD Amendment. The ROD Amendment concluded that monitored natural attenuation is the appropriate remedy for West Plume B. The ROD Amendment also selected ISCO to replace the pump and treat remedies at the AANG, West-Cap, and Texas Instruments Project Areas.

2013: ADEQ and EPA continued monitoring the natural attenuation of the groundwater contamination by evaluating the groundwater quality in West Plume B.

2014: ADEQ and EPA are developing methods for more efficient monitoring of groundwater quality in West Plume B. The AANG agreed to continue to sample West Plume B wells in conjunction with their sampling of wells on the AANG property.