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Rf HICX-�-!EBNER ' 2.0 BACKGROUND A 1,000 gallon underground diesel storage tank (UST) served a backup electrical generator for the fire station On 15 March 1989, the (UST) failed tank system integrity testing In response to the test failure, the City of Tracy reported the testing results to San Joaquin County, exposed ' the top of the UST and its piping, and performed a helium test to identify the source of leakage Results of the helium testing revealed the source of leakage to be a vent pipe connection located 36 inches above the top of the UST Since the leaky connection was above the maximum product level of the tank, it was concluded that the quantity of diesel fuel leaked was limited to the 0 206 gallons recorded as lost during the tank integrity testing ' City of Tracy records indicate that the leaky vent pipe connection was repaired and overfill spall protection equipment was installed on 15 May 1989 Soil contaminated by the leaked diesel fuel was reported to have been excavated and remediated using an aeration process During October 1989, the UST and piping were excavated and disposed as a result of the conversion from diesel fuel to propane fuel for the backup generator Tank removal activities were conducted under the supervision of the County which reports that corrosion holes were present at the top of the tank's welded end seam A City of Tracy representative present during ' the tank removal reports that groundwater was present above the bottom level of the UST When the UST was exposed, the City of Tracy representative reports that no visual evidence of leakage was noted in either the exposed soil or the groundwater surface As the UST was tipped when being removed from the ground, it is reported that a quantity of diesel product was spilled from the tank openings into the excavation and the groundwater present within Although the ' sample collection location is not verified by County records, the City of Tracy representative reports that a groundwater sample was collected from within the excavation immediately following the spillage and prior to any cleanup activities Laboratory results for the groundwater sample indicated that diesel was detected at a concentration of 3700 mg/L and xylenes were detected at a concentration of 1600 ug/L Kerosene, motor oil, benzene, toluene, and ethyl benzene were not detected at concentrations greater than their method detection limits of 50 mg/L, 500 mg/L, 250 ug/L, 250 ug/L, and 250 ug/L, respectively No records indicate that a groundwater sample was collected from within the excavation following cleanup of the spilled diesel ' Two soil samples are reported to have been collected from the excavation walls following cleanup of the spilled diesel The soil samples are suspected to have been collected from soil immediately ' above the groundwater surface which, based on the depth of groundwater, is believed to be 7 feet below ground surface The samples were submitted for analysis of total petroleum hydrocarbons as diesel, kerosene, and motor oil using EPA Method 35501GC-FID and benzene, toluene, ' ethylbenzene, and total xylenes using EPA Method 8020 Results of these analyses revealed that none of the compounds were detected in soil at concentrations greater than their method detection ' limit 2