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e - <br /> Pui <br /> a <br /> iY i <br /> .w. <br /> Work Plan to Excavate Gasoline Tank Cavity December 10, 1990 <br /> ARCO Service Station No. 6020, Manteca, California AGS 30055-2W <br /> We will conduct the following tasks: <br /> o Observe excavation of soil in and around the gasoline-lank cavity. <br /> o Collect appropriate soil samples within 2 to 4 feet below the base of the <br /> former tanks to evaluate if hydrocarbonaceous soil remains in place. <br /> o Observe additional excavation in the gasoline-tank cavity, if soil containing <br /> less than 10 ppm of TPHg and less than IA ppm benzene remains 4 feet <br /> below the base of the former tanks. Excavation will continue until (1) <br /> photoionization detector readings are below 50 ppm, (2) subjective evidence <br /> such as obvious product odor and discoloration are removed,(3)ground water <br /> is encountered, or(4) the excavation reaches the safe operating limits of the <br /> equipment of surrounding structures. Appropriate soi! samples will be <br /> collected from the base and sidewalls of the excavated area to evaluate if <br /> hydrocarbonaceous soil has been re.noved vertically and laterally. <br /> o Observe excavation of soil in and around the proposed gasoline-tai,k cavity <br /> to approximately 12 feet below grade. <br /> o Collect appropriate soil samples from the base of the proposed tank cavity to <br /> evaluate if hydrocarbons in soil were removed by excavation. If evidecue <br /> indicates concentrations greater than 10 ppm of TP Hg and greater than 1.0 <br /> ppm benzene remain in place, we will observe further excavation of the <br /> proposed tank cavity using the above criteria for excavating the existing tank <br /> cavity. <br /> o Collect one soil sample every 20 linear feet below the former product lines. <br /> o Collect soil samples from the stockpiled soil to evaluate disposal options for <br /> the soil. <br /> o Submit soil samples to a State-certified laboratory for analysis of'rPHg,and <br /> BTEX. Soil samples collected from under the former leaded gasoline tank <br /> will be submitted for total and organic lead. <br /> o Prepare a report summarizing tank removal operations and our findings, <br /> conclusions, and recommendations. <br /> 9 <br /> APplr`eor Geosystems <br />