PUBLIC NOTICE | Proposed Leaking UST Case Closure for Case File 2227.01, .02, .04

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

LUST Case File No.: 2227.01, .02, .04

Facility ID No.: 0-003139
Maricopa County

Facility address: 
Fleet Support Services
310 E. 6th Street
Mesa, AZ 85201

Information

This site is located at 310 E. 6th Street in Mesa.  The City of Mesa owns and uses the property for administrative offices, 911 communications, vehicle fleet maintenance, and automotive re-fueling. The City is the UST owner/operator. The City has conducted corrective actions to mitigate the impact of past fuel releases from three separate USTs systems. The historical UST systems included one dedicated to unleaded gasoline, a second system dedicated to leaded gasoline through part of its service use, and a third system dedicated to diesel fuel.  The City also used four USTs for storage of non-fuel petroleum products. The current UST system is vaulted.

All of the UST systems were removed between 1990 and 1992. Soil contamination was found that exceeded applicable regulatory standards during the UST system removals. The first monitoring well (MW-1) was installed in 1992.  Both soil and groundwater had volatile organic compound (VOC) contamination that exceeded applicable regulatory standards.  Site characterization began in 1993.  Soil borings and several monitoring wells were installed. The monitoring wells were installed on and off site to characterize the groundwater contamination.  ADEQ approved the Site Characterization Report in October 2000. The historic VOCs reported in groundwater with concentrations that exceeded applicable regulatory standards included benzene, toluene, ethylbenzene, toluene, and methyl tert butyl ether (MTBE).

The Corrective Action Plan (CAP) was approved in February 2005 and included active remediation by air sparge (AS) and soil vapor extraction (SVE).  SVE operation started in December 2007 and ended in April 2015 due to low contaminant mass removal rates. Low contaminant removal rates limits the cost-effectiveness of the system. The CAP also identified monitored natural attenuation as the remedial option for the groundwater. The CAP predated the implementation of R18-12-263.04, so groundwater contamination concentrations had to be below applicable Aquifer Water Quality Standards (AWQS) to obtain LUST closure.  

Groundwater data shows that no VOC contamination was ever present in the off-site monitoring wells. All of the off-site monitoring wells were abandoned in June 2014 with the exception of MW-15. The post remediation groundwater data shows that the VOC concentrations have significantly decreased so that only MW-10 shows any VOC (benzene) in concentrations that exceed an applicable regulatory standard.  

A site specific risk assessment and detailed file/information search have been completed. Based upon the results of  remedial activities and site specific information provided by Environmental Technology, Inc. (EN TECH), 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 (A) and (B) allows case closure of a LUST site with groundwater contamination above the Aquifer Water Quality Standard (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 11, 2018  June 11, 2018

Comments may be submitted as follows:
     By Email | Send Email > 
     By Mail (Must be postmarked or received by June 11, 2018):

       ADEQ
       Mark Lucas
       Waste Programs Division
       1110 W. Washington Street
       Phoenix, AZ  85007 

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