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Ozone Microsparge System Pilot Test Status Report,Former Unocal Service Station#2859,Stockton,CA June 6,2003 In 1988, two 10,000-gallon gasoline USTs and one 550-gallon waste oil UST were removed Soy] samples collected from the base of the gasoline UST excavation contained TPHg and benzene at maximum concentrations of 13 and 0 29 ppm, respectively Between June 1988 and February 1992, seven monitoring wells (MW-1 through MW-7), three vapor extraction wells (VW-1 through VW-3), and one soil boring were installed by Applied Geosystems and RESNA The highest TPHg and benzene concentrations reported were from an area around the northern product island location,at concentrations up to 17,300 and 28 ppm,respectively A soil vapor extraction test was conducted by RESNA in 1992 The test showed that a wellhead flow rate of 43 cubic feet per minute and an estimated radius of influence of approximately 25 feet could be achieved In July 1994, Pacific Environmental Group, Inc (PEG) installed monitoring wells MW-8 and MW-9 Groundwater samples from the wells were non-detect for benzene,but TPHg were detected in wells MW- 8 and MW-9 at concentrations of 93 and 110 parts per billion(ppb),respectively PEG performed a six-month on-site vapor extraction pilot study in 1996 During that study, approximately 2,745 pounds (450 gallons) of TPHg and 12 pounds (1 6 gallons) of benzene were removed ARCADIS Geraghty& Miller, Inc installed wells MW-10 and NP-1 in January 1999 Soil samples from well NP-1 showed impact beneath the site between 40 and 60 feet below ground surface (bgs) The highest TPHg and benzene concentrations were from a sample at 60 feet bgs at 290 and 5 8 ppm, respectively Discrete grab groundwater samp]es from well boring NP-1 had concentrations of TPHg and benzene in samples collected between 50 and 70 feet bgs The highest concentrations of TPHg and benzene detected were 200,000 (50 feet bgs) and 21,000(60 feet bgs)ppb, respectively In May 2001, GR installed nine groundwater monitoring wells (MW-11 through MW-19) on and downgradient of the site TPHg, benzene, or methyl tert-butyl ether (MtBE) were not detected in soil samples from the well borings MtBE was not detected in groundwater samples from the wells TPHg and benzene were reported in groundwater samples from wells installed on and immediately downgradient of the site at concentrations up to 31,000 and 720 ppb,respectively GR performed a five-day vapor extraction(VE)test at the site from June 18 through 22, 2001 The purpose of the VE test was to evaluate the feasibility of the VE technology and collect needed site specific data for the design of a VE system if necessary A 39 hour VE test was performed using an IC engine and extracted soil vapors from wells VW-1, VW-2, and VW-3 Based on the VE monitoring data, no significant amount of TPHg or benzene were removed during the pilot test GR estimated that less than one pound per day of petroleum hydrocarbons would be extracted and was not a viable remedial technology In March 2002, GR installed two off-site groundwater monitoring wells(MW-20 and MW-21) and eight on site ozone sparge points (SP-lA, SP-113, SP-1C, SP-2A, SP-213, SP-2C, SP-3A and SP-313) TPHg, benzene, or methyl tert-butyl ether (MtBE) were not detected in soil samples from the monitoring well bonngs • 240072 06 2