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July 27, 1992 . Beacon Station No.492, Manteca, California o Submitting selected soil samples to an Ultramar-approved and State-certified laboratory for analysis for total petroleum hydrocarbons as gasoline and as diesel using Environmental Protection Agency (EPA) Standard Methods 5030 and 8015, benzene, toluene, ethylbenzene, and total xylene isomers using EPA Standard Methods 5030, 602 and 8020, ethylene dlbromide using EPA Standard Methods 8010 and 601, and total lead using EPA Methods 6010 and 7000 o Preparing a report summarizing our findings, conclusions, and recommendations. We will notify Underground Service Alert of our intent to drill at least 48 hours before drilling to identify the location of underground utilities Before drilling, each borehole location will be hand-augered approximately 5 feet as an additional precaution against damage to underground structures. Drill cuttings will be stockpiled on the site on plastic sheeting pending characterization Work will be conducted in accordance with our Work Plan No. 86102-7W, dated December 18, 1991, and our updated Site Safety Plan. The purpose of the confirmation sampling 1s to verify that vapor extraction has effectively • reduced residual hydrocarbon concentrations to levels that will not adversely affect ground- water quality We consider soil remediation by vapor extraction to be complete when hydrocarbon concentrations in the extracted soil vapor show no additional decrease with time If confirmation soil samples contain TPHg concentrations less than 10 ppm, total BTEX concentrations less than 5 ppm, and benzene concentrations less that 10 ppm, we will petition for closure of the environmental investigation at the site. If hydrocarbon concentrations exceed these values, we will apply the Designated Level Methodology to evaluate whether additional work is necessary . 86102-9W 3