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Work Plan to Excavate Gasoline Tank C—vity December 10, 1990 <br /> ARCO Service Station No. 6020, Manteca, California AGS 3'355-2W <br /> relative levels of hydrocarbon vapors, but do not detect the concentration of hydrocarbons <br /> present with the same precision as laboratory analyses. <br /> Our geologist will collect two soil samples within 2 to 4 feet below the base of the former <br /> 10,000-gallon tank and three soil samples within 2 to 4 feet below the base of the two <br /> former 12,000-gallon tanks to evaluate if soil with hydrocarbons remains in place. X'C will <br /> observe additional excavation in the gasoline-tank cavity, only if evidence of hydrocarbons <br /> remains 4 feet below the base of the former tanks. Excavation will continue until (1) the <br /> PID readings are below 50 ppm, (2) the depth of the excavation reaches the safe operating <br /> limits of the equipment or surrounding structures. (3) ground water is encountered or (4, <br /> further excavation would endanger any existing structures. The tank removal contractor will <br /> be responsible for evaluating the safe limits of all excavations, sidewall stability, and safe <br /> "ea <br /> operating limits of the equipment. <br /> After the excavation is terminated, appropriate soil samples will be collected from the <br /> additional excavated area to evaluate if hydrocarbonaceous soil was removed -ertically by <br /> excavation, and one soil sample from each sidewall to evaluate if hydrocarbonaceous soil <br /> was removed laterally by excavation. t <br /> 11 <br />