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JAN-13--1994 08-54 FROM TO 12094640138 P 02 <br /> �7ifian,.6ae16pullslaga�l <br /> 9Mu ft rn«Uok SWmxML Vjaw" <br /> Figures 2 and 3 snow the apprcwmate final extent of the excavation, soil sernpling <br /> locations and depths, and TPH as gasoline analytical results. The complete analytical <br /> results are included in Table 1 <br /> Based on the previous boring results, the final excavation depth was approximately 22 <br /> to 25 feet below grade Figure 3 and Table 1 show that all samples analyzed contained <br /> less than 100 parts-per-million (ppm) TPH as gasoline, except sample S-3 at 22 feet <br /> This area was excavated to 25 feet and sample S-11, collected approximately two feet <br /> from S-3, verified removal of the impacted matenal_ Overall, the total of tweive soil <br /> samples oollected and analyzed confirm successful removal of affected sod_ <br /> Analytical results from SS-9 indicated sod from 20 to 31 feet contained TPH as gasoline <br /> concentrations ranging from 180 to 240 ppm. Because of equipment limitations, this soil <br /> could not be removed. However, assuming this sod extends in a 5-foot radius around the <br /> bong location, an estimated 8 6 pounds (or less than 15 gellons) of residual TPH <br /> remains in the sod_ The 54bot radrus assumption is based on the approximate lateral <br /> extent of TPH in the soil around SB-9 at depths of 21 to 22 feet (Figure 3) The <br /> hydrocarbon mass calculation is shown in Attachment 4 No benzene, the most mobile <br /> of the gasoline constituents, was detected in any of the recent soil boring and excavation <br /> samples. However, benzene laboratory detection limits were occasionally elevated <br /> because of interference from TPH concentrations Analytical results from S"indicated <br /> .soil from 26 to 31 feet contains benzene concentrations bekyw detection limits ranging <br /> from 0 005 to 0 05 ppm Assuming a worst case concentration of 0 05 ppm, and sod <br /> extending in a 5-foot radius around the boring location, an estimated 0.0022 pounds of <br /> residual benzene remains in the soil This calculation is a1w shown in Attachment 4 <br /> Based on the data and calculations outilnedl above, remaining hydrocarbons in the soil <br /> do not appear to threaten the relatively deep groundwater Therefore,Aegis recommends <br /> this site for ceMf d closure by San Joaquin County and the California Regional Water <br /> Quality Board, Central Valley Region <br /> ti3-0d6A Rei 3 <br /> • <br />