West Plume B Project Area
The West Plume B project area is located in Area B of the Tucson International Airport Area (TIAA) Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) site. The site is on the National Priorities List (NPL), which is periodically updated by the U.S. Environmental Protection Agency (EPA). West Plume B is an EPA-funded site, meaning that no existing or financially viable responsible party has been identified. It is a narrow northwest trending plume located between Valencia and Drexel Roads, and east of the main TIAA plume in Tucson, Arizona.
With technical support from the Arizona Department of Environmental Quality (ADEQ), EPA has installed numerous groundwater monitor wells to investigate the extent and magnitude of the groundwater contamination in West Plume B.
In April 2012, EPA issued a Record of Decision (ROD) amendment. The ROD amendment concluded that monitored natural attenuation is the appropriate remedy for West Plume B. ADEQ and EPA continue to monitor and review the groundwater quality in West Plume B. The Arizona Air National Guard (AANG) continues to conduct groundwater sampling of West Plume B wells to evaluate the monitored natural attenuation (MNA) remedy.
A Unified Community Advisory Board (UCAB) was formed in 1995 to provide community members with an opportunity to learn about the cleanup process and to obtain local perspective for decisions concerning the cleanup. The UCAB meets the third Wednesdays of Jan., April, July, and Oct. These meetings, which are open to the public, begin at 5:45 p.m. located at the El Pueblo Activity Center located at 101 W. Irvington Rd. in Tucson, AZ 85714.
Further information may be found in the Jan. 2012 TIAA Superfund site fact sheet published by EPA.
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.
The current contaminants of concern in groundwater include volatile organic compounds; mainly TCE. TCE concentrations range from less than 0.5 ppb to about 6 ppb. Contaminants of concern at the site may change as new data become available.
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. However, a few residents with domestic wells with low levels of TCE have chosen to continue using their wells. If you are drinking water from a private well within the boundaries of the site, please contact the ADEQ Project Manager.
In Area B of the TIAA site, which includes the West Plume B 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 75 to 90 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 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 the meandering streams that deposited these sediments. In places, the streams deposited relatively course-grained sands and gravels, but in other areas fine-grained overbank and floodplain deposits were left behind. The coarse-grained upper subunit at West Plume B appears to correlate with the upper subunit at the AANG project area, and is only five to ten feet thick. Seismic reflection data suggest that the coarse-grained upper subunit at West Plume B may actually be multiple units that dip slightly toward the south. The upper subunit is the first course-grained water bearing unit. Groundwater contamination is thought to be confined to the upper subunit in the West Plume B project area.
*In Arizona, but outside the Tucson area, call toll-free at (888) 271-9302.
Interested parties can review select site documents at the TCE Superfund Information Library located at 202 W. Valencia Road, Tucson, AZ 85706, at the Valencia Branch Public Library in Tucson, (520) 594-5390. The complete official site file can be reviewed at the EPA Region IX, Records Center, Mail Stop SFD-7C, 95 Hawthorne Street, Room 403, San Francisco, CA 94105, (415) 536-2000.
Interested parties can review site information here on this page and at the ADEQ Record Center located at 1110 W. Washington Street, Phoenix, Arizona. Please contact (602) 771-4380 or (800) 234-5677 ext. 6027714380 for hours of operation and to schedule an appointment.