PUBLIC NOTICE | Proposed Leaking UST Case Closure for Case File 0293.09-.10

ADEQ is considering closure of the following leaking underground storage tank (LUST) case:

LUST Case File No.: 0293.09-.10

Facility ID No.: 0-005338
Maricopa County

Facility address: 
Phoenix-Mesa Gateway Airport
5835 S. Sossaman Road
Mesa, AZ 85212


This site was the former Building 760 (ST035) at Williams Air Force Base (WAFB) which covered 4,043 acres.  The majority of the base property has since been converted to the Phoenix-Mesa Gateway Airport, related aviation industrial/commercial facilities, the Arizona State University (ASU) Polytechnic Campus, the Maricopa County Community College Williams Campus, and several other smaller entities since the base was formally closed in 1993.  The Site is near Picacho Hall of ASU.  The UST owner/operator was identified as the United States Air Force.  Bldg. 760 was located in the west-central area of the former WFB, approximately 0.5 miles southeast of the intersection of Williams Field Road and Power Road. Gasoline sales were discontinued in approximately 1986, but lube and oil change services continued until 1993.  The UST system was permanently closed between October 1993 and January 1994.  Investigation of site impacts was conducted during UST system removal, initial site characterization, and supplemental site characterization has been completed by AMEC Foster Wheeler, Environment & Infrastructure, Inc. (AMEC) for the Air Force.  Data collected during these activities indicated that elevated concentrations at the site prior to remediation were relatively isolated to one boring at the former dispenser area (SB-1) and that the contaminant concentrations decreased sharply below 160 feet below ground surface (bgs).  The contamination extended to groundwater.  Numerous groundwater monitoring wells have been installed between March 1997 and November 2012. Volatile Organic Compound (VOC) contamination was found in the groundwater that exceeded applicable regulatory standards.

In 2010, a soil vapor extraction (SVE) system was installed and operated until October 2013. Most of the contaminants in soil and groundwater have decreased as a result of remediation. 1,2-dichloroethane (1,2-DCA) and methyl tert butyl ether (MTBE) concentrations in the source area wells currently exceeded applicable regulatory standards.  The current source area wells are defined as B760-RWD and B760-MW10.  Groundwater sampling results showed significant decrease of contamination as of January 2017. 

Current data provided by the UST owner/operator, and all other available site information has been used by ADEQ to determine whether remaining levels of contaminants at the site are adequately protective of human health and the environment.  A site specific risk assessment and detailed file/information search were also completed.  VOC analytical groundwater results show that 1,2-DCA and MTBE concentrations remain above the applicable Tier 1 Corrective Action Standards. All pertinent groundwater data is available in the LUST file.

Based upon the results of remedial activities and site specific information, the above-referenced LUST site is eligible for alternative LUST closure under Arizona Revised Statutes (A.R.S.) §49-1005(E).  Arizona Administrative Code (A.A.C.) R18-12-263.04 allows case closure of a LUST site with groundwater contamination above the Arizona Aquifer Water Quality Standards (AWQS) or Tier 1 Corrective Action Standards.

Review Document 

Review results of remedial activities and entire public notice | View/Print >

Public Comment Period 

Dates: May 7, 2018  June 7, 2018

Comments may be submitted as follows:
     By Email | Send Email > 
     By Mail (Must be postmarked or received by June 7, 2018):

       Deborah Goodwin
       Waste Programs Division
       1110 W. Washington Street
       Phoenix, AZ  85007 

Documents may also be reviewed in person at the ADEQ Record Center | Learn More >