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2 . 4 . 3 Laboratory Results <br /> Laboratory analyses of the samples collected on March 5, 1993 <br /> showed total petroleum hydrocarbons in MW-1 at levels of 4 ,000 Ag/L <br /> (parts per billion, ppb) TPH-gasoline and 1, 800 ppb TPH-diesel. <br /> Volatile aromatics were detected in monitoring well MW-1 at levels <br /> of 6 . 1 ppb (benzene) , 4 . 1 ppb (toluene) , 29 ppb (ethylbenzene) , and <br /> 450 ppb (xylene) . No hydrocarbon contamination was detected in <br /> monitoring well MW--2 and only toluene (0. 32 ppb) was detected in <br /> monitoring well MW-3 Based on these results, GeoAudit recommended <br /> that an additional monitoring well be installed down-gradient from <br /> MW-1, and that all four wells be sampled during the next quarterly <br /> monitoring event. San Joaquin PHS/EHD concurred with this <br /> recommendation and requested that the next monitoring be completed <br /> during the third quarter of 1993 . PHS/EHD also requested that the <br /> tank cavity be re-excavated to remove the contaminated soil that <br /> had been previously returned to the cavity in early 1990. <br /> E3 . 0 PROCEDURES <br /> 3 . 1 Excavata.on <br /> Using a backhoe and an excavator, Stokely Construction Co. <br /> overexcavated the former tank cavity on August 17 and 18 , 1993 <br /> (Figure 2) . Visual observations were combined with a <br /> photoionization detector (PID) to monitor contamination levels <br /> during excavation and direct the excavator. The excavation was <br /> expanded to approximately 40 feet by 50 feet and extended to a <br /> depth of approximately 14 feet (Figure 3) . Groundwater was <br /> encountered in the excavation at a depth of approximately 12 feet. <br /> Approximately 1, 000 cubic yards of soil were removed from the <br /> excavation. --of the soil removed, 700 cubic yards were placed into <br /> "contaminated" stockpiles and 300 cubic yards were placed into <br /> I "uncontaminated" stockpiles. The contaminated soil was stockpiled <br /> north and west of the building on site, and covered with plastic <br /> sheeting. The uncontaminated material was stockpiled near the pump <br /> islands. <br /> 3 .2 Excavation Sampling <br /> Because of the eventual size of the excavation, the north wall of <br /> the excavation would not be within reach of the backhoe if sampling <br /> were postponed until all excavation was completed. Therefore, three <br /> soil samples were collected from the north wall of the excavation <br /> on August 17 (TP-1 to TP-3 ) . When excavating was completed on <br /> August 18 , four additional samples were collected from the floor <br /> and south, east, and west walls of the excavation (TP-4 to TP-7) . <br /> Sample locations are shown on Figure 3 . <br /> 5 <br />