The City of Tucson’s Police and Fire Department Headquarters (HQ) buildings are located on the 200 Block of South Stone Avenue (Headquarters Map ). Between these two buildings was a fueling facility used by City vehicles. This fuel island began operation with three underground storage tanks (USTs) (one diesel and two gasoline) in 1972. Two additional USTs (gasoline) were added to the facility in 1975. The fueling facility remained in operation at the subject site until the five USTs and the associated dispensing equipment were removed in November 1993. During the removal of the UST systems, stained soil and a petroleum odor were documented. ADEQ opened a leaking UST case file (LUST File #3208.01) . Approximately 250 cubic yards of soil were removed from the excavation and transported to Los Reales Landfill for disposal. ADEQ closed the case file in November 1999.
In January 2007, gasoline compounds were detected in groundwater samples collected from monitoring wells in the vicinity of the Tucson Convention Center and Police/Fire Department HQ buildings. An investigation of the gasoline took place. The City confirmed a release of petroleum-based fuels from the former fueling facility had historically occurred and ADEQ reopened LUST File #3208.01. The assessment discovered soil impacts above Arizona Soil Remediation Levels (SRLs), dissolved gasoline compounds in the groundwater, and Light Non-aqueous Phase Liquid (LNAPL) floating on the groundwater. The LNAPL consists of old gasoline.
A temporary vapor extraction/groundwater extraction (VEGE) system was installed and began operations in June 2009. The system was located where the UST systems had been removed.
As the efficiency of the VEGE system dropped, an alternate remediation system using pump and treat methodology, with an oil-water separator (OWS) for removal of free product, was completed and installed in January 2010.
The VEGE and OWS systems have extracted and treated 174,798 gallons of groundwater from various groundwater monitoring wells in the vicinity of the former UST systems. The entire volume (after being treated) was discharged to the permitted Pima County sewer discharge location. As of June 2010, a total of 1,044 gallons of gasoline have been removed and destroyed/disposed. Remediation efforts continue, with the following goals:
- Minimize the spread of LNAPL to uncontaminated subsurface areas of the “perched” groundwater
- Recover LNAPL to the maximum extent practicable
- Reduce the concentration of contaminants of concern (COCs) in the soil beneath the former fuel island area and impacted groundwater to the standards specified by ADEQ