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Atlantic Richfield Company 5 Former ARCO#4493 205 North Center Street Stockton,CA August 22 2002 • Other fuel oxygenates were not detected in groundwater samples from the six new monitoring wells above the laboratory detection limit Groundwater analytical data is presented in Table 3 Development/sampling field data sheets are included in Attachment E Certified laboratory analytical results and chain-of-custody documentation are included in Attachment F The newly installed wells were surveyed by Morrow Surveying of West Sacramento, California, a California-licensed surveyor Latitude and longitude coordinates, California state plane coordinates, elevation relative to mean sea level values, and a surveyor's monitoring well exhibit are included in Attachment G Stockpiled Soil Per the City of Stockton encroachment permits (Attachment B), no soil or water was allowed to be stored at the site Drill cuttings and equipment cleaning water was placed in drums and removed from the site by Dillard Environmental Services at the end of each day of drilling Nine drums of soil were generated from the installation of monitoring wells One composite sample (4 parts to 1 sample) was collected from the stockpiled soil, which was analyzed for TPHg, BTEX, and MtBE by the DHSILUFT Method, and total lead by EPA Method 6010B Stockpiled soil was transported by Dillard to Altamont Landfill for disposal Stockpiled soil analytical data is presented in Table 4 and Attachment F SUMMARY OF FINDINGS • Benzene and ethylbenzene were detected in soil samples from the boring for MW-9 at 42 feet bgs at concentrations of 0 0072 mg/kg and 0 024 mg/kg, respectively MtBE was also detected in soil samples from MW-9 at 25 feet bgs (0 020 mg/kg) and 42 feet bgs (0 026 mg/kg) Other fuel oxygenates were not detected in soil samples from the boring of MW-9 above the laboratory detection limit • TPHg was detected in water samples from all six new wells at concentrations ranging from 87 parts per billion (ppb)(MW-10D) to 4,700 ppb (MW-8M) Benzene was detected in water samples from all six new wells at concentrations ranging from 19 ppb (MW-10D) to 70 ppb (MW-8D) MtBE was detected in water samples from all six new wells at concentrations ranging from 3 1 ppb (MW-10D) to 46 ppb (MW-8D) CONCLUSIONS AND RECOMMENDATIONS Based on data collected during this assessment, petroleum hydrocarbons have migrated offsite in soil and groundwater at depths below the shallow monitoring wells installed at 25 feet bgs The lateral and vertical extents of TPHg, BTEX, and MtBE remain undefined SECOR recommends that the groundwater gradient, and hydrocarbon I%ARC0144931Reports\Dua1We11-Rpt doe